Changeset 2734 for specs


Ignore:
Timestamp:
17/12/14 14:46:09 (5 years ago)
Author:
julian.reschke@…
Message:

update XSLTs, switch to Saxon 9.6 HE in Makefile, regen specs

Location:
specs
Files:
9 edited

Legend:

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  • specs/rfc7230.html

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    511 </style><link rel="Contents" href="#rfc.toc"><link rel="Author" href="#rfc.authors"><link rel="Copyright" href="#rfc.copyrightnotice"><link rel="Index" href="#rfc.index"><link rel="Chapter" title="1 Introduction" href="#rfc.section.1"><link rel="Chapter" title="2 Architecture" href="#rfc.section.2"><link rel="Chapter" title="3 Message Format" href="#rfc.section.3"><link rel="Chapter" title="4 Transfer Codings" href="#rfc.section.4"><link rel="Chapter" title="5 Message Routing" href="#rfc.section.5"><link rel="Chapter" title="6 Connection Management" href="#rfc.section.6"><link rel="Chapter" title="7 ABNF List Extension: #rule" href="#rfc.section.7"><link rel="Chapter" title="8 IANA Considerations" href="#rfc.section.8"><link rel="Chapter" title="9 Security Considerations" href="#rfc.section.9"><link rel="Chapter" title="10 Acknowledgments" href="#rfc.section.10"><link rel="Chapter" href="#rfc.section.11" title="11 References"><link rel="Appendix" title="A HTTP Version History" href="#rfc.section.A"><link rel="Appendix" title="B Collected ABNF" href="#rfc.section.B"><link href="rfc7231.html" rel="next"><link rel="Alternate" title="Authorative ASCII Version" href="http://www.ietf.org/rfc/rfc7230.txt"><link rel="Help" title="RFC-Editor's Status Page" href="http://www.rfc-editor.org/info/rfc7230"><link rel="Help" title="Additional Information on tools.ietf.org" href="http://tools.ietf.org/html/rfc7230"><meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.669, 2014/09/04 09:19:16, XSLT vendor: SAXON 6.5.5 from Michael Kay http://saxon.sf.net/"><meta name="keywords" content="Hypertext Transfer Protocol, HTTP, HTTP message format"><link rel="schema.dct" href="http://purl.org/dc/terms/"><meta name="dct.creator" content="Fielding, R."><meta name="dct.creator" content="Reschke, J. F."><meta name="dct.identifier" content="urn:ietf:rfc:7230"><meta name="dct.issued" scheme="ISO8601" content="2014-06"><meta name="dct.replaces" content="urn:ietf:rfc:2145"><meta name="dct.replaces" content="urn:ietf:rfc:2616"><meta name="dct.abstract" content="The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document provides an overview of HTTP architecture and its associated terminology, defines the &#34;http&#34; and &#34;https&#34; Uniform Resource Identifier (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements, and describes related security concerns for implementations."><meta name="dct.isPartOf" content="urn:issn:2070-1721"><meta name="description" content="The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document provides an overview of HTTP architecture and its associated terminology, defines the &#34;http&#34; and &#34;https&#34; Uniform Resource Identifier (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements, and describes related security concerns for implementations."></head><body onload="getMeta(7230,&#34;rfc.meta&#34;);"><table class="header" id="rfc.headerblock"><tbody><tr><td class="left">Internet Engineering Task Force (IETF)</td><td class="right">R. Fielding, Editor</td></tr><tr><td class="left">Request for Comments: 7230</td><td class="right">Adobe</td></tr><tr><td class="left">Obsoletes: <a href="https://tools.ietf.org/html/rfc2145">2145</a>, <a href="https://tools.ietf.org/html/rfc2616">2616</a></td><td class="right">J. Reschke, Editor</td></tr><tr><td class="left">Updates: <a href="https://tools.ietf.org/html/rfc2817">2817</a>, <a href="https://tools.ietf.org/html/rfc2818">2818</a></td><td class="right">greenbytes</td></tr><tr><td class="left">Category: Standards Track</td><td class="right">June 2014</td></tr><tr><td class="left">ISSN: 2070-1721</td><td class="right"></td></tr></tbody></table><p class="title" id="rfc.title">Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing</p><h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1><p>The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document provides an overview of HTTP architecture and its associated terminology, defines the "http" and "https" Uniform Resource Identifier (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements, and describes related security concerns for implementations.</p><div id="rfc.meta" style="float: right; border: 1px solid black; margin: 2em; padding: 1em; display: none;"></div><div id="rfc.status"><h1><a href="#rfc.status">Status of This Memo</a></h1><p>This is an Internet Standards Track document.</p><p>This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.</p><p>Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at <a href="http://www.rfc-editor.org/info/rfc7230">http://www.rfc-editor.org/info/rfc7230</a>.</p></div><div id="rfc.copyrightnotice"><h1><a href="#rfc.copyrightnotice">Copyright Notice</a></h1><p>Copyright &copy; 2014 IETF Trust and the persons identified as the document authors. All rights reserved.</p><p>This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.</p><p>This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English.</p></div><hr class="noprint"><div id="rfc.toc"><h1 class="np"><a href="#rfc.toc">Table of Contents</a></h1><ul class="toc"><li><a href="#rfc.section.1">1.</a>&nbsp;&nbsp;&nbsp;<a href="#introduction">Introduction</a><ul><li><a href="#rfc.section.1.1">1.1</a>&nbsp;&nbsp;&nbsp;<a href="#intro.requirements">Requirements Notation</a></li><li><a href="#rfc.section.1.2">1.2</a>&nbsp;&nbsp;&nbsp;<a href="#notation">Syntax Notation</a></li></ul></li><li><a href="#rfc.section.2">2.</a>&nbsp;&nbsp;&nbsp;<a href="#architecture">Architecture</a><ul><li><a href="#rfc.section.2.1">2.1</a>&nbsp;&nbsp;&nbsp;<a href="#operation">Client/Server Messaging</a></li><li><a href="#rfc.section.2.2">2.2</a>&nbsp;&nbsp;&nbsp;<a href="#implementation-diversity">Implementation Diversity</a></li><li><a href="#rfc.section.2.3">2.3</a>&nbsp;&nbsp;&nbsp;<a href="#intermediaries">Intermediaries</a></li><li><a href="#rfc.section.2.4">2.4</a>&nbsp;&nbsp;&nbsp;<a href="#caches">Caches</a></li><li><a href="#rfc.section.2.5">2.5</a>&nbsp;&nbsp;&nbsp;<a href="#conformance">Conformance and Error Handling</a></li><li><a href="#rfc.section.2.6">2.6</a>&nbsp;&nbsp;&nbsp;<a href="#http.version">Protocol Versioning</a></li><li><a href="#rfc.section.2.7">2.7</a>&nbsp;&nbsp;&nbsp;<a href="#uri">Uniform Resource Identifiers</a><ul><li><a href="#rfc.section.2.7.1">2.7.1</a>&nbsp;&nbsp;&nbsp;<a href="#http.uri">http URI Scheme</a></li><li><a href="#rfc.section.2.7.2">2.7.2</a>&nbsp;&nbsp;&nbsp;<a href="#https.uri">https URI Scheme</a></li><li><a href="#rfc.section.2.7.3">2.7.3</a>&nbsp;&nbsp;&nbsp;<a href="#uri.comparison">http and https URI Normalization and Comparison</a></li></ul></li></ul></li><li><a href="#rfc.section.3">3.</a>&nbsp;&nbsp;&nbsp;<a href="#http.message">Message Format</a><ul><li><a href="#rfc.section.3.1">3.1</a>&nbsp;&nbsp;&nbsp;<a href="#start.line">Start Line</a><ul><li><a href="#rfc.section.3.1.1">3.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#request.line">Request Line</a></li><li><a href="#rfc.section.3.1.2">3.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.line">Status Line</a></li></ul></li><li><a href="#rfc.section.3.2">3.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.fields">Header Fields</a><ul><li><a href="#rfc.section.3.2.1">3.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#field.extensibility">Field Extensibility</a></li><li><a href="#rfc.section.3.2.2">3.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#field.order">Field Order</a></li><li><a href="#rfc.section.3.2.3">3.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#whitespace">Whitespace</a></li><li><a href="#rfc.section.3.2.4">3.2.4</a>&nbsp;&nbsp;&nbsp;<a href="#field.parsing">Field Parsing</a></li><li><a href="#rfc.section.3.2.5">3.2.5</a>&nbsp;&nbsp;&nbsp;<a href="#field.limits">Field Limits</a></li><li><a href="#rfc.section.3.2.6">3.2.6</a>&nbsp;&nbsp;&nbsp;<a href="#field.components">Field Value Components</a></li></ul></li><li><a href="#rfc.section.3.3">3.3</a>&nbsp;&nbsp;&nbsp;<a href="#message.body">Message Body</a><ul><li><a href="#rfc.section.3.3.1">3.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.transfer-encoding">Transfer-Encoding</a></li><li><a href="#rfc.section.3.3.2">3.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.content-length">Content-Length</a></li><li><a href="#rfc.section.3.3.3">3.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#message.body.length">Message Body Length</a></li></ul></li><li><a href="#rfc.section.3.4">3.4</a>&nbsp;&nbsp;&nbsp;<a href="#incomplete.messages">Handling Incomplete Messages</a></li><li><a href="#rfc.section.3.5">3.5</a>&nbsp;&nbsp;&nbsp;<a href="#message.robustness">Message Parsing Robustness</a></li></ul></li><li><a href="#rfc.section.4">4.</a>&nbsp;&nbsp;&nbsp;<a href="#transfer.codings">Transfer Codings</a><ul><li><a href="#rfc.section.4.1">4.1</a>&nbsp;&nbsp;&nbsp;<a href="#chunked.encoding">Chunked Transfer Coding</a><ul><li><a href="#rfc.section.4.1.1">4.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#chunked.extension">Chunk Extensions</a></li><li><a href="#rfc.section.4.1.2">4.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#chunked.trailer.part">Chunked Trailer Part</a></li><li><a href="#rfc.section.4.1.3">4.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#decoding.chunked">Decoding Chunked</a></li></ul></li><li><a href="#rfc.section.4.2">4.2</a>&nbsp;&nbsp;&nbsp;<a href="#compression.codings">Compression Codings</a><ul><li><a href="#rfc.section.4.2.1">4.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#compress.coding">Compress Coding</a></li><li><a href="#rfc.section.4.2.2">4.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#deflate.coding">Deflate Coding</a></li><li><a href="#rfc.section.4.2.3">4.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#gzip.coding">Gzip Coding</a></li></ul></li><li><a href="#rfc.section.4.3">4.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.te">TE</a></li><li><a href="#rfc.section.4.4">4.4</a>&nbsp;&nbsp;&nbsp;<a href="#header.trailer">Trailer</a></li></ul></li><li><a href="#rfc.section.5">5.</a>&nbsp;&nbsp;&nbsp;<a href="#message.routing">Message Routing</a><ul><li><a href="#rfc.section.5.1">5.1</a>&nbsp;&nbsp;&nbsp;<a href="#target-resource">Identifying a Target Resource</a></li><li><a href="#rfc.section.5.2">5.2</a>&nbsp;&nbsp;&nbsp;<a href="#connecting.inbound">Connecting Inbound</a></li><li><a href="#rfc.section.5.3">5.3</a>&nbsp;&nbsp;&nbsp;<a href="#request-target">Request Target</a><ul><li><a href="#rfc.section.5.3.1">5.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#origin-form">origin-form</a></li><li><a href="#rfc.section.5.3.2">5.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#absolute-form">absolute-form</a></li><li><a href="#rfc.section.5.3.3">5.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#authority-form">authority-form</a></li><li><a href="#rfc.section.5.3.4">5.3.4</a>&nbsp;&nbsp;&nbsp;<a href="#asterisk-form">asterisk-form</a></li></ul></li><li><a href="#rfc.section.5.4">5.4</a>&nbsp;&nbsp;&nbsp;<a href="#header.host">Host</a></li><li><a href="#rfc.section.5.5">5.5</a>&nbsp;&nbsp;&nbsp;<a href="#effective.request.uri">Effective Request URI</a></li><li><a href="#rfc.section.5.6">5.6</a>&nbsp;&nbsp;&nbsp;<a href="#associating.response.to.request">Associating a Response to a Request</a></li><li><a href="#rfc.section.5.7">5.7</a>&nbsp;&nbsp;&nbsp;<a href="#message.forwarding">Message Forwarding</a><ul><li><a href="#rfc.section.5.7.1">5.7.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.via">Via</a></li><li><a href="#rfc.section.5.7.2">5.7.2</a>&nbsp;&nbsp;&nbsp;<a href="#message.transformations">Transformations</a></li></ul></li></ul></li><li><a href="#rfc.section.6">6.</a>&nbsp;&nbsp;&nbsp;<a href="#connection.management">Connection Management</a><ul><li><a href="#rfc.section.6.1">6.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.connection">Connection</a></li><li><a href="#rfc.section.6.2">6.2</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.establishment">Establishment</a></li><li><a href="#rfc.section.6.3">6.3</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.connections">Persistence</a><ul><li><a href="#rfc.section.6.3.1">6.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.retrying.requests">Retrying Requests</a></li><li><a href="#rfc.section.6.3.2">6.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#pipelining">Pipelining</a></li></ul></li><li><a href="#rfc.section.6.4">6.4</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.concurrency">Concurrency</a></li><li><a href="#rfc.section.6.5">6.5</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.failures">Failures and Timeouts</a></li><li><a href="#rfc.section.6.6">6.6</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.tear-down">Tear-down</a></li><li><a href="#rfc.section.6.7">6.7</a>&nbsp;&nbsp;&nbsp;<a href="#header.upgrade">Upgrade</a></li></ul></li><li><a href="#rfc.section.7">7.</a>&nbsp;&nbsp;&nbsp;<a href="#abnf.extension">ABNF List Extension: #rule</a></li><li><a href="#rfc.section.8">8.</a>&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a><ul><li><a href="#rfc.section.8.1">8.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.field.registration">Header Field Registration</a></li><li><a href="#rfc.section.8.2">8.2</a>&nbsp;&nbsp;&nbsp;<a href="#uri.scheme.registration">URI Scheme Registration</a></li><li><a href="#rfc.section.8.3">8.3</a>&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.http">Internet Media Type Registration</a><ul><li><a href="#rfc.section.8.3.1">8.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.message.http">Internet Media Type message/http</a></li><li><a href="#rfc.section.8.3.2">8.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.application.http">Internet Media Type application/http</a></li></ul></li><li><a href="#rfc.section.8.4">8.4</a>&nbsp;&nbsp;&nbsp;<a href="#transfer.coding.registry">Transfer Coding Registry</a><ul><li><a href="#rfc.section.8.4.1">8.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#transfer.coding.registry.procedure">Procedure</a></li><li><a href="#rfc.section.8.4.2">8.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#transfer.coding.registration">Registration</a></li></ul></li><li><a href="#rfc.section.8.5">8.5</a>&nbsp;&nbsp;&nbsp;<a href="#content.coding.registration">Content Coding Registration</a></li><li><a href="#rfc.section.8.6">8.6</a>&nbsp;&nbsp;&nbsp;<a href="#upgrade.token.registry">Upgrade Token Registry</a><ul><li><a href="#rfc.section.8.6.1">8.6.1</a>&nbsp;&nbsp;&nbsp;<a href="#upgrade.token.registry.procedure">Procedure</a></li><li><a href="#rfc.section.8.6.2">8.6.2</a>&nbsp;&nbsp;&nbsp;<a href="#upgrade.token.registration">Upgrade Token Registration</a></li></ul></li></ul></li><li><a href="#rfc.section.9">9.</a>&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a><ul><li><a href="#rfc.section.9.1">9.1</a>&nbsp;&nbsp;&nbsp;<a href="#establishing.authority">Establishing Authority</a></li><li><a href="#rfc.section.9.2">9.2</a>&nbsp;&nbsp;&nbsp;<a href="#risks.intermediaries">Risks of Intermediaries</a></li><li><a href="#rfc.section.9.3">9.3</a>&nbsp;&nbsp;&nbsp;<a href="#attack.protocol.element.length">Attacks via Protocol Element Length</a></li><li><a href="#rfc.section.9.4">9.4</a>&nbsp;&nbsp;&nbsp;<a href="#response.splitting">Response Splitting</a></li><li><a href="#rfc.section.9.5">9.5</a>&nbsp;&nbsp;&nbsp;<a href="#request.smuggling">Request Smuggling</a></li><li><a href="#rfc.section.9.6">9.6</a>&nbsp;&nbsp;&nbsp;<a href="#message.integrity">Message Integrity</a></li><li><a href="#rfc.section.9.7">9.7</a>&nbsp;&nbsp;&nbsp;<a href="#message.confidentiality">Message Confidentiality</a></li><li><a href="#rfc.section.9.8">9.8</a>&nbsp;&nbsp;&nbsp;<a href="#privacy.of.server.log.information">Privacy of Server Log Information</a></li></ul></li><li><a href="#rfc.section.10">10.</a>&nbsp;&nbsp;&nbsp;<a href="#acks">Acknowledgments</a></li><li><a href="#rfc.section.11">11.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul><li><a href="#rfc.section.11.1">11.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li><li><a href="#rfc.section.11.2">11.2</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li></ul></li><li><a href="#rfc.section.A">A.</a>&nbsp;&nbsp;&nbsp;<a href="#compatibility">HTTP Version History</a><ul><li><a href="#rfc.section.A.1">A.1</a>&nbsp;&nbsp;&nbsp;<a href="#changes.from.1.0">Changes from HTTP/1.0</a><ul><li><a href="#rfc.section.A.1.1">A.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#changes.to.simplify.multihomed.web.servers.and.conserve.ip.addresses">Multihomed Web Servers</a></li><li><a href="#rfc.section.A.1.2">A.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#compatibility.with.http.1.0.persistent.connections">Keep-Alive Connections</a></li><li><a href="#rfc.section.A.1.3">A.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#introduction.of.transfer-encoding">Introduction of Transfer-Encoding</a></li></ul></li><li><a href="#rfc.section.A.2">A.2</a>&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li></ul></li><li><a href="#rfc.section.B">B.</a>&nbsp;&nbsp;&nbsp;<a href="#collected.abnf">Collected ABNF</a></li><li><a href="#rfc.index">Index</a></li><li><a href="#rfc.authors">Authors' Addresses</a></li></ul></div><div id="introduction"><h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;<a href="#introduction">Introduction</a></h1><div id="rfc.section.1.p.1"><p>The Hypertext Transfer Protocol (HTTP) is a stateless application-level request/response protocol that uses extensible semantics and self-descriptive message payloads for flexible interaction with network-based hypertext information systems. This document is the first in a series of documents that collectively form the HTTP/1.1 specification: <a class="self" href="#rfc.section.1.p.1">&para;</a></p><ol><li>"Message Syntax and Routing" (this document)</li><li>"Semantics and Content" <a href="#RFC7231" id="rfc.xref.RFC7231.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a></li><li>"Conditional Requests" <a href="#RFC7232" id="rfc.xref.RFC7232.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a></li><li>"Range Requests" <a href="#RFC7233" id="rfc.xref.RFC7233.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a></li><li>"Caching" <a href="#RFC7234" id="rfc.xref.RFC7234.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a></li><li>"Authentication" <a href="#RFC7235" id="rfc.xref.RFC7235.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a></li></ol></div><div id="rfc.section.1.p.2"><p>This HTTP/1.1 specification obsoletes <cite title="Hypertext Transfer Protocol -- HTTP/1.1" id="rfc.xref.RFC2616.1">RFC 2616</cite> and <cite title="Use and Interpretation of HTTP Version Numbers" id="rfc.xref.RFC2145.1">RFC 2145</cite> (on HTTP versioning). This specification also updates the use of CONNECT to establish a tunnel, previously defined in <cite title="Upgrading to TLS Within HTTP/1.1" id="rfc.xref.RFC2817.1">RFC 2817</cite>, and defines the "https" URI scheme that was described informally in <cite title="HTTP Over TLS" id="rfc.xref.RFC2818.1">RFC 2818</cite>.<a class="self" href="#rfc.section.1.p.2">&para;</a></p></div><div id="rfc.section.1.p.3"><p>HTTP is a generic interface protocol for information systems. It is designed to hide the details of how a service is implemented by presenting a uniform interface to clients that is independent of the types of resources provided. Likewise, servers do not need to be aware of each client's purpose: an HTTP request can be considered in isolation rather than being associated with a specific type of client or a predetermined sequence of application steps. The result is a protocol that can be used effectively in many different contexts and for which implementations can evolve independently over time.<a class="self" href="#rfc.section.1.p.3">&para;</a></p></div><div id="rfc.section.1.p.4"><p>HTTP is also designed for use as an intermediation protocol for translating communication to and from non-HTTP information systems. HTTP proxies and gateways can provide access to alternative information services by translating their diverse protocols into a hypertext format that can be viewed and manipulated by clients in the same way as HTTP services.<a class="self" href="#rfc.section.1.p.4">&para;</a></p></div><div id="rfc.section.1.p.5"><p>One consequence of this flexibility is that the protocol cannot be defined in terms of what occurs behind the interface. Instead, we are limited to defining the syntax of communication, the intent of received communication, and the expected behavior of recipients. If the communication is considered in isolation, then successful actions ought to be reflected in corresponding changes to the observable interface provided by servers. However, since multiple clients might act in parallel and perhaps at cross-purposes, we cannot require that such changes be observable beyond the scope of a single response.<a class="self" href="#rfc.section.1.p.5">&para;</a></p></div><div id="rfc.section.1.p.6"><p>This document describes the architectural elements that are used or referred to in HTTP, defines the "http" and "https" URI schemes, describes overall network operation and connection management, and defines HTTP message framing and forwarding requirements. Our goal is to define all of the mechanisms necessary for HTTP message handling that are independent of message semantics, thereby defining the complete set of requirements for message parsers and message-forwarding intermediaries.<a class="self" href="#rfc.section.1.p.6">&para;</a></p></div><div id="intro.requirements"><h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a>&nbsp;<a href="#intro.requirements">Requirements Notation</a></h2><div id="rfc.section.1.1.p.1"><p>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in <a href="#RFC2119" id="rfc.xref.RFC2119.1"><cite title="Key words for use in RFCs to Indicate Requirement Levels">[RFC2119]</cite></a>.<a class="self" href="#rfc.section.1.1.p.1">&para;</a></p></div><div id="rfc.section.1.1.p.2"><p>Conformance criteria and considerations regarding error handling are defined in <a href="#conformance" title="Conformance and Error Handling">Section&nbsp;2.5</a>.<a class="self" href="#rfc.section.1.1.p.2">&para;</a></p></div></div><div id="notation"><h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a>&nbsp;<a href="#notation">Syntax Notation</a></h2><div id="rfc.section.1.2.p.1"><p>This specification uses the Augmented Backus-Naur Form (ABNF) notation of <a href="#RFC5234" id="rfc.xref.RFC5234.1"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a> with a list extension, defined in <a href="#abnf.extension" title="ABNF List Extension: #rule">Section&nbsp;7</a>, that allows for compact definition of comma-separated lists using a '#' operator (similar to how the '*' operator indicates repetition). <a href="#collected.abnf" title="Collected ABNF">Appendix&nbsp;B</a> shows the collected grammar with all list operators expanded to standard ABNF notation.<a class="self" href="#rfc.section.1.2.p.1">&para;</a></p></div><div id="core.rules"><div id="rfc.section.1.2.p.2"><p>            The following core rules are included by reference, as defined in <a href="#RFC5234" id="rfc.xref.RFC5234.2"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>, <a href="https://tools.ietf.org/html/rfc5234#appendix-B.1">Appendix B.1</a>: ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote), HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed), OCTET (any 8-bit sequence of data), SP (space), and VCHAR (any visible <a href="#USASCII" id="rfc.xref.USASCII.1"><cite title="Coded Character Set -- 7-bit American Standard Code for Information Interchange">[USASCII]</cite></a> character).<a class="self" href="#rfc.section.1.2.p.2">&para;</a></p></div></div><div id="rfc.section.1.2.p.3"><p>As a convention, ABNF rule names prefixed with "obs-" denote "obsolete" grammar rules that appear for historical reasons.<a class="self" href="#rfc.section.1.2.p.3">&para;</a></p></div></div></div><div id="architecture"><h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a href="#architecture">Architecture</a></h1><div id="rfc.section.2.p.1"><p>HTTP was created for the World Wide Web (WWW) architecture and has evolved over time to support the scalability needs of a worldwide hypertext system. Much of that architecture is reflected in the terminology and syntax productions used to define HTTP.<a class="self" href="#rfc.section.2.p.1">&para;</a></p></div><div id="operation"><h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a href="#operation">Client/Server Messaging</a></h2><div id="rfc.section.2.1.p.1"><p>HTTP is a stateless request/response protocol that operates by exchanging <dfn>messages</dfn> (<a href="#http.message" title="Message Format">Section&nbsp;3</a>) across a reliable transport- or session-layer "<dfn>connection</dfn>" (<a href="#connection.management" title="Connection Management">Section&nbsp;6</a>). An HTTP "<dfn>client</dfn>" is a program that establishes a connection to a server for the purpose of sending one or more HTTP requests. An HTTP "<dfn>server</dfn>" is a program that accepts connections in order to service HTTP requests by sending HTTP responses.<a class="self" href="#rfc.section.2.1.p.1">&para;</a></p></div><div id="rfc.iref.u.1"></div><div id="rfc.iref.o.1"></div><div id="rfc.iref.b.1"></div><div id="rfc.iref.s.1"></div><div id="rfc.iref.s.2"></div><div id="rfc.iref.r.1"></div><div id="rfc.section.2.1.p.2"><p>The terms "client" and "server" refer only to the roles that these programs perform for a particular connection. The same program might act as a client on some connections and a server on others. The term "<dfn>user agent</dfn>" refers to any of the various client programs that initiate a request, including (but not limited to) browsers, spiders (web-based robots), command-line tools, custom applications, and mobile apps. The term "<dfn>origin server</dfn>" refers to the program that can originate authoritative responses for a given target resource. The terms "<dfn>sender</dfn>" and "<dfn>recipient</dfn>" refer to any implementation that sends or receives a given message, respectively.<a class="self" href="#rfc.section.2.1.p.2">&para;</a></p></div><div id="rfc.section.2.1.p.3"><p>HTTP relies upon the Uniform Resource Identifier (URI) standard <a href="#RFC3986" id="rfc.xref.RFC3986.1"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a> to indicate the target resource (<a href="#target-resource" title="Identifying a Target Resource">Section&nbsp;5.1</a>) and relationships between resources. Messages are passed in a format similar to that used by Internet mail <a href="#RFC5322" id="rfc.xref.RFC5322.1"><cite title="Internet Message Format">[RFC5322]</cite></a> and the Multipurpose Internet Mail Extensions (MIME) <a href="#RFC2045" id="rfc.xref.RFC2045.1"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a> (see <a href="rfc7231.html#differences.between.http.and.mime" title="Differences between HTTP and MIME">Appendix A</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a> for the differences between HTTP and MIME messages).<a class="self" href="#rfc.section.2.1.p.3">&para;</a></p></div><div id="rfc.section.2.1.p.4"><p>Most HTTP communication consists of a retrieval request (GET) for a representation of some resource identified by a URI. In the simplest case, this might be accomplished via a single bidirectional connection (===) between the user agent (UA) and the origin server (O).<a class="self" href="#rfc.section.2.1.p.4">&para;</a></p></div><div id="rfc.figure.u.1"><pre class="drawing">         request   &gt;
     527</style><link rel="Contents" href="#rfc.toc"><link rel="Author" href="#rfc.authors"><link rel="Copyright" href="#rfc.copyrightnotice"><link rel="Index" href="#rfc.index"><link rel="Chapter" title="1 Introduction" href="#rfc.section.1"><link rel="Chapter" title="2 Architecture" href="#rfc.section.2"><link rel="Chapter" title="3 Message Format" href="#rfc.section.3"><link rel="Chapter" title="4 Transfer Codings" href="#rfc.section.4"><link rel="Chapter" title="5 Message Routing" href="#rfc.section.5"><link rel="Chapter" title="6 Connection Management" href="#rfc.section.6"><link rel="Chapter" title="7 ABNF List Extension: #rule" href="#rfc.section.7"><link rel="Chapter" title="8 IANA Considerations" href="#rfc.section.8"><link rel="Chapter" title="9 Security Considerations" href="#rfc.section.9"><link rel="Chapter" title="10 Acknowledgments" href="#rfc.section.10"><link rel="Chapter" href="#rfc.section.11" title="11 References"><link rel="Appendix" title="A HTTP Version History" href="#rfc.section.A"><link rel="Appendix" title="B Collected ABNF" href="#rfc.section.B"><link href="rfc7231.html" rel="next"><link rel="Alternate" title="Authorative ASCII Version" href="http://www.ietf.org/rfc/rfc7230.txt"><link rel="Help" title="RFC-Editor's Status Page" href="http://www.rfc-editor.org/info/rfc7230"><link rel="Help" title="Additional Information on tools.ietf.org" href="http://tools.ietf.org/html/rfc7230"><meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.710, 2014/12/09 13:12:18, XSLT vendor: SAXON 6.5.5 from Michael Kay http://saxon.sf.net/"><meta name="keywords" content="Hypertext Transfer Protocol, HTTP, HTTP message format"><link rel="schema.dct" href="http://purl.org/dc/terms/"><meta name="dct.creator" content="Fielding, R."><meta name="dct.creator" content="Reschke, J. F."><meta name="dct.identifier" content="urn:ietf:rfc:7230"><meta name="dct.issued" scheme="ISO8601" content="2014-06"><meta name="dct.replaces" content="urn:ietf:rfc:2145"><meta name="dct.replaces" content="urn:ietf:rfc:2616"><meta name="dct.abstract" content="The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document provides an overview of HTTP architecture and its associated terminology, defines the &#34;http&#34; and &#34;https&#34; Uniform Resource Identifier (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements, and describes related security concerns for implementations."><meta name="dct.isPartOf" content="urn:issn:2070-1721"><meta name="description" content="The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document provides an overview of HTTP architecture and its associated terminology, defines the &#34;http&#34; and &#34;https&#34; Uniform Resource Identifier (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements, and describes related security concerns for implementations."></head><body onload="getMeta(7230,&#34;rfc.meta&#34;);"><table class="header" id="rfc.headerblock"><tbody><tr><td class="left">Internet Engineering Task Force (IETF)</td><td class="right">R. Fielding, Editor</td></tr><tr><td class="left">Request for Comments: 7230</td><td class="right">Adobe</td></tr><tr><td class="left">Obsoletes: <a href="https://tools.ietf.org/html/rfc2145">2145</a>, <a href="https://tools.ietf.org/html/rfc2616">2616</a></td><td class="right">J. Reschke, Editor</td></tr><tr><td class="left">Updates: <a href="https://tools.ietf.org/html/rfc2817">2817</a>, <a href="https://tools.ietf.org/html/rfc2818">2818</a></td><td class="right">greenbytes</td></tr><tr><td class="left">Category: Standards Track</td><td class="right">June 2014</td></tr><tr><td class="left">ISSN: 2070-1721</td><td class="right"></td></tr></tbody></table><p class="title" id="rfc.title">Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing</p><h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1><p>The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document provides an overview of HTTP architecture and its associated terminology, defines the "http" and "https" Uniform Resource Identifier (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements, and describes related security concerns for implementations.</p><div id="rfc.meta" style="float: right; border: 1px solid black; margin: 2em; padding: 1em; display: none;"></div><div id="rfc.status"><h1><a href="#rfc.status">Status of This Memo</a></h1><p>This is an Internet Standards Track document.</p><p>This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.</p><p>Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at <a href="http://www.rfc-editor.org/info/rfc7230">http://www.rfc-editor.org/info/rfc7230</a>.</p></div><div id="rfc.copyrightnotice"><h1><a href="#rfc.copyrightnotice">Copyright Notice</a></h1><p>Copyright &copy; 2014 IETF Trust and the persons identified as the document authors. All rights reserved.</p><p>This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.</p><p>This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English.</p></div><hr class="noprint"><div id="rfc.toc"><h1 class="np"><a href="#rfc.toc">Table of Contents</a></h1><ul class="toc"><li><a href="#rfc.section.1">1.</a>&nbsp;&nbsp;&nbsp;<a href="#introduction">Introduction</a><ul><li><a href="#rfc.section.1.1">1.1</a>&nbsp;&nbsp;&nbsp;<a href="#intro.requirements">Requirements Notation</a></li><li><a href="#rfc.section.1.2">1.2</a>&nbsp;&nbsp;&nbsp;<a href="#notation">Syntax Notation</a></li></ul></li><li><a href="#rfc.section.2">2.</a>&nbsp;&nbsp;&nbsp;<a href="#architecture">Architecture</a><ul><li><a href="#rfc.section.2.1">2.1</a>&nbsp;&nbsp;&nbsp;<a href="#operation">Client/Server Messaging</a></li><li><a href="#rfc.section.2.2">2.2</a>&nbsp;&nbsp;&nbsp;<a href="#implementation-diversity">Implementation Diversity</a></li><li><a href="#rfc.section.2.3">2.3</a>&nbsp;&nbsp;&nbsp;<a href="#intermediaries">Intermediaries</a></li><li><a href="#rfc.section.2.4">2.4</a>&nbsp;&nbsp;&nbsp;<a href="#caches">Caches</a></li><li><a href="#rfc.section.2.5">2.5</a>&nbsp;&nbsp;&nbsp;<a href="#conformance">Conformance and Error Handling</a></li><li><a href="#rfc.section.2.6">2.6</a>&nbsp;&nbsp;&nbsp;<a href="#http.version">Protocol Versioning</a></li><li><a href="#rfc.section.2.7">2.7</a>&nbsp;&nbsp;&nbsp;<a href="#uri">Uniform Resource Identifiers</a><ul><li><a href="#rfc.section.2.7.1">2.7.1</a>&nbsp;&nbsp;&nbsp;<a href="#http.uri">http URI Scheme</a></li><li><a href="#rfc.section.2.7.2">2.7.2</a>&nbsp;&nbsp;&nbsp;<a href="#https.uri">https URI Scheme</a></li><li><a href="#rfc.section.2.7.3">2.7.3</a>&nbsp;&nbsp;&nbsp;<a href="#uri.comparison">http and https URI Normalization and Comparison</a></li></ul></li></ul></li><li><a href="#rfc.section.3">3.</a>&nbsp;&nbsp;&nbsp;<a href="#http.message">Message Format</a><ul><li><a href="#rfc.section.3.1">3.1</a>&nbsp;&nbsp;&nbsp;<a href="#start.line">Start Line</a><ul><li><a href="#rfc.section.3.1.1">3.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#request.line">Request Line</a></li><li><a href="#rfc.section.3.1.2">3.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.line">Status Line</a></li></ul></li><li><a href="#rfc.section.3.2">3.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.fields">Header Fields</a><ul><li><a href="#rfc.section.3.2.1">3.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#field.extensibility">Field Extensibility</a></li><li><a href="#rfc.section.3.2.2">3.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#field.order">Field Order</a></li><li><a href="#rfc.section.3.2.3">3.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#whitespace">Whitespace</a></li><li><a href="#rfc.section.3.2.4">3.2.4</a>&nbsp;&nbsp;&nbsp;<a href="#field.parsing">Field Parsing</a></li><li><a href="#rfc.section.3.2.5">3.2.5</a>&nbsp;&nbsp;&nbsp;<a href="#field.limits">Field Limits</a></li><li><a href="#rfc.section.3.2.6">3.2.6</a>&nbsp;&nbsp;&nbsp;<a href="#field.components">Field Value Components</a></li></ul></li><li><a href="#rfc.section.3.3">3.3</a>&nbsp;&nbsp;&nbsp;<a href="#message.body">Message Body</a><ul><li><a href="#rfc.section.3.3.1">3.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.transfer-encoding">Transfer-Encoding</a></li><li><a href="#rfc.section.3.3.2">3.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.content-length">Content-Length</a></li><li><a href="#rfc.section.3.3.3">3.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#message.body.length">Message Body Length</a></li></ul></li><li><a href="#rfc.section.3.4">3.4</a>&nbsp;&nbsp;&nbsp;<a href="#incomplete.messages">Handling Incomplete Messages</a></li><li><a href="#rfc.section.3.5">3.5</a>&nbsp;&nbsp;&nbsp;<a href="#message.robustness">Message Parsing Robustness</a></li></ul></li><li><a href="#rfc.section.4">4.</a>&nbsp;&nbsp;&nbsp;<a href="#transfer.codings">Transfer Codings</a><ul><li><a href="#rfc.section.4.1">4.1</a>&nbsp;&nbsp;&nbsp;<a href="#chunked.encoding">Chunked Transfer Coding</a><ul><li><a href="#rfc.section.4.1.1">4.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#chunked.extension">Chunk Extensions</a></li><li><a href="#rfc.section.4.1.2">4.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#chunked.trailer.part">Chunked Trailer Part</a></li><li><a href="#rfc.section.4.1.3">4.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#decoding.chunked">Decoding Chunked</a></li></ul></li><li><a href="#rfc.section.4.2">4.2</a>&nbsp;&nbsp;&nbsp;<a href="#compression.codings">Compression Codings</a><ul><li><a href="#rfc.section.4.2.1">4.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#compress.coding">Compress Coding</a></li><li><a href="#rfc.section.4.2.2">4.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#deflate.coding">Deflate Coding</a></li><li><a href="#rfc.section.4.2.3">4.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#gzip.coding">Gzip Coding</a></li></ul></li><li><a href="#rfc.section.4.3">4.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.te">TE</a></li><li><a href="#rfc.section.4.4">4.4</a>&nbsp;&nbsp;&nbsp;<a href="#header.trailer">Trailer</a></li></ul></li><li><a href="#rfc.section.5">5.</a>&nbsp;&nbsp;&nbsp;<a href="#message.routing">Message Routing</a><ul><li><a href="#rfc.section.5.1">5.1</a>&nbsp;&nbsp;&nbsp;<a href="#target-resource">Identifying a Target Resource</a></li><li><a href="#rfc.section.5.2">5.2</a>&nbsp;&nbsp;&nbsp;<a href="#connecting.inbound">Connecting Inbound</a></li><li><a href="#rfc.section.5.3">5.3</a>&nbsp;&nbsp;&nbsp;<a href="#request-target">Request Target</a><ul><li><a href="#rfc.section.5.3.1">5.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#origin-form">origin-form</a></li><li><a href="#rfc.section.5.3.2">5.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#absolute-form">absolute-form</a></li><li><a href="#rfc.section.5.3.3">5.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#authority-form">authority-form</a></li><li><a href="#rfc.section.5.3.4">5.3.4</a>&nbsp;&nbsp;&nbsp;<a href="#asterisk-form">asterisk-form</a></li></ul></li><li><a href="#rfc.section.5.4">5.4</a>&nbsp;&nbsp;&nbsp;<a href="#header.host">Host</a></li><li><a href="#rfc.section.5.5">5.5</a>&nbsp;&nbsp;&nbsp;<a href="#effective.request.uri">Effective Request URI</a></li><li><a href="#rfc.section.5.6">5.6</a>&nbsp;&nbsp;&nbsp;<a href="#associating.response.to.request">Associating a Response to a Request</a></li><li><a href="#rfc.section.5.7">5.7</a>&nbsp;&nbsp;&nbsp;<a href="#message.forwarding">Message Forwarding</a><ul><li><a href="#rfc.section.5.7.1">5.7.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.via">Via</a></li><li><a href="#rfc.section.5.7.2">5.7.2</a>&nbsp;&nbsp;&nbsp;<a href="#message.transformations">Transformations</a></li></ul></li></ul></li><li><a href="#rfc.section.6">6.</a>&nbsp;&nbsp;&nbsp;<a href="#connection.management">Connection Management</a><ul><li><a href="#rfc.section.6.1">6.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.connection">Connection</a></li><li><a href="#rfc.section.6.2">6.2</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.establishment">Establishment</a></li><li><a href="#rfc.section.6.3">6.3</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.connections">Persistence</a><ul><li><a href="#rfc.section.6.3.1">6.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.retrying.requests">Retrying Requests</a></li><li><a href="#rfc.section.6.3.2">6.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#pipelining">Pipelining</a></li></ul></li><li><a href="#rfc.section.6.4">6.4</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.concurrency">Concurrency</a></li><li><a href="#rfc.section.6.5">6.5</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.failures">Failures and Timeouts</a></li><li><a href="#rfc.section.6.6">6.6</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.tear-down">Tear-down</a></li><li><a href="#rfc.section.6.7">6.7</a>&nbsp;&nbsp;&nbsp;<a href="#header.upgrade">Upgrade</a></li></ul></li><li><a href="#rfc.section.7">7.</a>&nbsp;&nbsp;&nbsp;<a href="#abnf.extension">ABNF List Extension: #rule</a></li><li><a href="#rfc.section.8">8.</a>&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a><ul><li><a href="#rfc.section.8.1">8.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.field.registration">Header Field Registration</a></li><li><a href="#rfc.section.8.2">8.2</a>&nbsp;&nbsp;&nbsp;<a href="#uri.scheme.registration">URI Scheme Registration</a></li><li><a href="#rfc.section.8.3">8.3</a>&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.http">Internet Media Type Registration</a><ul><li><a href="#rfc.section.8.3.1">8.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.message.http">Internet Media Type message/http</a></li><li><a href="#rfc.section.8.3.2">8.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.application.http">Internet Media Type application/http</a></li></ul></li><li><a href="#rfc.section.8.4">8.4</a>&nbsp;&nbsp;&nbsp;<a href="#transfer.coding.registry">Transfer Coding Registry</a><ul><li><a href="#rfc.section.8.4.1">8.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#transfer.coding.registry.procedure">Procedure</a></li><li><a href="#rfc.section.8.4.2">8.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#transfer.coding.registration">Registration</a></li></ul></li><li><a href="#rfc.section.8.5">8.5</a>&nbsp;&nbsp;&nbsp;<a href="#content.coding.registration">Content Coding Registration</a></li><li><a href="#rfc.section.8.6">8.6</a>&nbsp;&nbsp;&nbsp;<a href="#upgrade.token.registry">Upgrade Token Registry</a><ul><li><a href="#rfc.section.8.6.1">8.6.1</a>&nbsp;&nbsp;&nbsp;<a href="#upgrade.token.registry.procedure">Procedure</a></li><li><a href="#rfc.section.8.6.2">8.6.2</a>&nbsp;&nbsp;&nbsp;<a href="#upgrade.token.registration">Upgrade Token Registration</a></li></ul></li></ul></li><li><a href="#rfc.section.9">9.</a>&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a><ul><li><a href="#rfc.section.9.1">9.1</a>&nbsp;&nbsp;&nbsp;<a href="#establishing.authority">Establishing Authority</a></li><li><a href="#rfc.section.9.2">9.2</a>&nbsp;&nbsp;&nbsp;<a href="#risks.intermediaries">Risks of Intermediaries</a></li><li><a href="#rfc.section.9.3">9.3</a>&nbsp;&nbsp;&nbsp;<a href="#attack.protocol.element.length">Attacks via Protocol Element Length</a></li><li><a href="#rfc.section.9.4">9.4</a>&nbsp;&nbsp;&nbsp;<a href="#response.splitting">Response Splitting</a></li><li><a href="#rfc.section.9.5">9.5</a>&nbsp;&nbsp;&nbsp;<a href="#request.smuggling">Request Smuggling</a></li><li><a href="#rfc.section.9.6">9.6</a>&nbsp;&nbsp;&nbsp;<a href="#message.integrity">Message Integrity</a></li><li><a href="#rfc.section.9.7">9.7</a>&nbsp;&nbsp;&nbsp;<a href="#message.confidentiality">Message Confidentiality</a></li><li><a href="#rfc.section.9.8">9.8</a>&nbsp;&nbsp;&nbsp;<a href="#privacy.of.server.log.information">Privacy of Server Log Information</a></li></ul></li><li><a href="#rfc.section.10">10.</a>&nbsp;&nbsp;&nbsp;<a href="#acks">Acknowledgments</a></li><li><a href="#rfc.section.11">11.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul><li><a href="#rfc.section.11.1">11.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li><li><a href="#rfc.section.11.2">11.2</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li></ul></li><li><a href="#rfc.section.A">A.</a>&nbsp;&nbsp;&nbsp;<a href="#compatibility">HTTP Version History</a><ul><li><a href="#rfc.section.A.1">A.1</a>&nbsp;&nbsp;&nbsp;<a href="#changes.from.1.0">Changes from HTTP/1.0</a><ul><li><a href="#rfc.section.A.1.1">A.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#changes.to.simplify.multihomed.web.servers.and.conserve.ip.addresses">Multihomed Web Servers</a></li><li><a href="#rfc.section.A.1.2">A.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#compatibility.with.http.1.0.persistent.connections">Keep-Alive Connections</a></li><li><a href="#rfc.section.A.1.3">A.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#introduction.of.transfer-encoding">Introduction of Transfer-Encoding</a></li></ul></li><li><a href="#rfc.section.A.2">A.2</a>&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li></ul></li><li><a href="#rfc.section.B">B.</a>&nbsp;&nbsp;&nbsp;<a href="#collected.abnf">Collected ABNF</a></li><li><a href="#rfc.index">Index</a></li><li><a href="#rfc.authors">Authors' Addresses</a></li></ul></div><div id="introduction"><h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;<a href="#introduction">Introduction</a></h1><div id="rfc.section.1.p.1"><p>The Hypertext Transfer Protocol (HTTP) is a stateless application-level request/response protocol that uses extensible semantics and self-descriptive message payloads for flexible interaction with network-based hypertext information systems. This document is the first in a series of documents that collectively form the HTTP/1.1 specification: <a class="self" href="#rfc.section.1.p.1">&para;</a></p><ol><li>"Message Syntax and Routing" (this document)</li><li>"Semantics and Content" <a href="#RFC7231" id="rfc.xref.RFC7231.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a></li><li>"Conditional Requests" <a href="#RFC7232" id="rfc.xref.RFC7232.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a></li><li>"Range Requests" <a href="#RFC7233" id="rfc.xref.RFC7233.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a></li><li>"Caching" <a href="#RFC7234" id="rfc.xref.RFC7234.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a></li><li>"Authentication" <a href="#RFC7235" id="rfc.xref.RFC7235.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a></li></ol></div><div id="rfc.section.1.p.2"><p>This HTTP/1.1 specification obsoletes <cite title="Hypertext Transfer Protocol -- HTTP/1.1" id="rfc.xref.RFC2616.1">RFC 2616</cite> and <cite title="Use and Interpretation of HTTP Version Numbers" id="rfc.xref.RFC2145.1">RFC 2145</cite> (on HTTP versioning). This specification also updates the use of CONNECT to establish a tunnel, previously defined in <cite title="Upgrading to TLS Within HTTP/1.1" id="rfc.xref.RFC2817.1">RFC 2817</cite>, and defines the "https" URI scheme that was described informally in <cite title="HTTP Over TLS" id="rfc.xref.RFC2818.1">RFC 2818</cite>.<a class="self" href="#rfc.section.1.p.2">&para;</a></p></div><div id="rfc.section.1.p.3"><p>HTTP is a generic interface protocol for information systems. It is designed to hide the details of how a service is implemented by presenting a uniform interface to clients that is independent of the types of resources provided. Likewise, servers do not need to be aware of each client's purpose: an HTTP request can be considered in isolation rather than being associated with a specific type of client or a predetermined sequence of application steps. The result is a protocol that can be used effectively in many different contexts and for which implementations can evolve independently over time.<a class="self" href="#rfc.section.1.p.3">&para;</a></p></div><div id="rfc.section.1.p.4"><p>HTTP is also designed for use as an intermediation protocol for translating communication to and from non-HTTP information systems. HTTP proxies and gateways can provide access to alternative information services by translating their diverse protocols into a hypertext format that can be viewed and manipulated by clients in the same way as HTTP services.<a class="self" href="#rfc.section.1.p.4">&para;</a></p></div><div id="rfc.section.1.p.5"><p>One consequence of this flexibility is that the protocol cannot be defined in terms of what occurs behind the interface. Instead, we are limited to defining the syntax of communication, the intent of received communication, and the expected behavior of recipients. If the communication is considered in isolation, then successful actions ought to be reflected in corresponding changes to the observable interface provided by servers. However, since multiple clients might act in parallel and perhaps at cross-purposes, we cannot require that such changes be observable beyond the scope of a single response.<a class="self" href="#rfc.section.1.p.5">&para;</a></p></div><div id="rfc.section.1.p.6"><p>This document describes the architectural elements that are used or referred to in HTTP, defines the "http" and "https" URI schemes, describes overall network operation and connection management, and defines HTTP message framing and forwarding requirements. Our goal is to define all of the mechanisms necessary for HTTP message handling that are independent of message semantics, thereby defining the complete set of requirements for message parsers and message-forwarding intermediaries.<a class="self" href="#rfc.section.1.p.6">&para;</a></p></div><div id="intro.requirements"><h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a>&nbsp;<a href="#intro.requirements">Requirements Notation</a></h2><div id="rfc.section.1.1.p.1"><p>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in <a href="#RFC2119" id="rfc.xref.RFC2119.1"><cite title="Key words for use in RFCs to Indicate Requirement Levels">[RFC2119]</cite></a>.<a class="self" href="#rfc.section.1.1.p.1">&para;</a></p></div><div id="rfc.section.1.1.p.2"><p>Conformance criteria and considerations regarding error handling are defined in <a href="#conformance" title="Conformance and Error Handling">Section&nbsp;2.5</a>.<a class="self" href="#rfc.section.1.1.p.2">&para;</a></p></div></div><div id="notation"><h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a>&nbsp;<a href="#notation">Syntax Notation</a></h2><div id="rfc.section.1.2.p.1"><p>This specification uses the Augmented Backus-Naur Form (ABNF) notation of <a href="#RFC5234" id="rfc.xref.RFC5234.1"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a> with a list extension, defined in <a href="#abnf.extension" title="ABNF List Extension: #rule">Section&nbsp;7</a>, that allows for compact definition of comma-separated lists using a '#' operator (similar to how the '*' operator indicates repetition). <a href="#collected.abnf" title="Collected ABNF">Appendix&nbsp;B</a> shows the collected grammar with all list operators expanded to standard ABNF notation.<a class="self" href="#rfc.section.1.2.p.1">&para;</a></p></div><div id="core.rules"><div id="rfc.section.1.2.p.2"><p>            The following core rules are included by reference, as defined in <a href="#RFC5234" id="rfc.xref.RFC5234.2"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>, <a href="https://tools.ietf.org/html/rfc5234#appendix-B.1">Appendix B.1</a>: ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote), HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed), OCTET (any 8-bit sequence of data), SP (space), and VCHAR (any visible <a href="#USASCII" id="rfc.xref.USASCII.1"><cite title="Coded Character Set -- 7-bit American Standard Code for Information Interchange">[USASCII]</cite></a> character).<a class="self" href="#rfc.section.1.2.p.2">&para;</a></p></div></div><div id="rfc.section.1.2.p.3"><p>As a convention, ABNF rule names prefixed with "obs-" denote "obsolete" grammar rules that appear for historical reasons.<a class="self" href="#rfc.section.1.2.p.3">&para;</a></p></div></div></div><div id="architecture"><h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a href="#architecture">Architecture</a></h1><div id="rfc.section.2.p.1"><p>HTTP was created for the World Wide Web (WWW) architecture and has evolved over time to support the scalability needs of a worldwide hypertext system. Much of that architecture is reflected in the terminology and syntax productions used to define HTTP.<a class="self" href="#rfc.section.2.p.1">&para;</a></p></div><div id="operation"><h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a href="#operation">Client/Server Messaging</a></h2><div id="rfc.section.2.1.p.1"><p>HTTP is a stateless request/response protocol that operates by exchanging <dfn>messages</dfn> (<a href="#http.message" title="Message Format">Section&nbsp;3</a>) across a reliable transport- or session-layer "<dfn>connection</dfn>" (<a href="#connection.management" title="Connection Management">Section&nbsp;6</a>). An HTTP "<dfn>client</dfn>" is a program that establishes a connection to a server for the purpose of sending one or more HTTP requests. An HTTP "<dfn>server</dfn>" is a program that accepts connections in order to service HTTP requests by sending HTTP responses.<a class="self" href="#rfc.section.2.1.p.1">&para;</a></p></div><div id="rfc.iref.u.1"></div><div id="rfc.iref.o.1"></div><div id="rfc.iref.b.1"></div><div id="rfc.iref.s.1"></div><div id="rfc.iref.s.2"></div><div id="rfc.iref.r.1"></div><div id="rfc.section.2.1.p.2"><p>The terms "client" and "server" refer only to the roles that these programs perform for a particular connection. The same program might act as a client on some connections and a server on others. The term "<dfn>user agent</dfn>" refers to any of the various client programs that initiate a request, including (but not limited to) browsers, spiders (web-based robots), command-line tools, custom applications, and mobile apps. The term "<dfn>origin server</dfn>" refers to the program that can originate authoritative responses for a given target resource. The terms "<dfn>sender</dfn>" and "<dfn>recipient</dfn>" refer to any implementation that sends or receives a given message, respectively.<a class="self" href="#rfc.section.2.1.p.2">&para;</a></p></div><div id="rfc.section.2.1.p.3"><p>HTTP relies upon the Uniform Resource Identifier (URI) standard <a href="#RFC3986" id="rfc.xref.RFC3986.1"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a> to indicate the target resource (<a href="#target-resource" title="Identifying a Target Resource">Section&nbsp;5.1</a>) and relationships between resources. Messages are passed in a format similar to that used by Internet mail <a href="#RFC5322" id="rfc.xref.RFC5322.1"><cite title="Internet Message Format">[RFC5322]</cite></a> and the Multipurpose Internet Mail Extensions (MIME) <a href="#RFC2045" id="rfc.xref.RFC2045.1"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a> (see <a href="rfc7231.html#differences.between.http.and.mime" title="Differences between HTTP and MIME">Appendix A</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a> for the differences between HTTP and MIME messages).<a class="self" href="#rfc.section.2.1.p.3">&para;</a></p></div><div id="rfc.section.2.1.p.4"><p>Most HTTP communication consists of a retrieval request (GET) for a representation of some resource identified by a URI. In the simplest case, this might be accomplished via a single bidirectional connection (===) between the user agent (UA) and the origin server (O).<a class="self" href="#rfc.section.2.1.p.4">&para;</a></p></div><div id="rfc.figure.u.1"><pre class="drawing">         request   &gt;
    512528    <b>UA</b> ======================================= <b>O</b>
    513529                                &lt;   response
     
    577593                 ; obsolete line folding
    578594                 ; see <a href="#field.parsing" title="Field Parsing">Section&nbsp;3.2.4</a>
    579 </pre></div><div id="rfc.section.3.2.p.2"><p>The field-name token labels the corresponding field-value as having the semantics defined by that header field. For example, the <a href="rfc7231.html#header.date" class="smpl">Date</a> header field is defined in <a href="rfc7231.html#header.date" title="Date">Section 7.1.1.2</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.9"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a> as containing the origination timestamp for the message in which it appears.<a class="self" href="#rfc.section.3.2.p.2">&para;</a></p></div><div id="field.extensibility"><h3 id="rfc.section.3.2.1"><a href="#rfc.section.3.2.1">3.2.1</a>&nbsp;<a href="#field.extensibility">Field Extensibility</a></h3><div id="rfc.section.3.2.1.p.1"><p>Header fields are fully extensible: there is no limit on the introduction of new field names, each presumably defining new semantics, nor on the number of header fields used in a given message. Existing fields are defined in each part of this specification and in many other specifications outside this document set.<a class="self" href="#rfc.section.3.2.1.p.1">&para;</a></p></div><div id="rfc.section.3.2.1.p.2"><p>New header fields can be defined such that, when they are understood by a recipient, they might override or enhance the interpretation of previously defined header fields, define preconditions on request evaluation, or refine the meaning of responses.<a class="self" href="#rfc.section.3.2.1.p.2">&para;</a></p></div><div id="rfc.section.3.2.1.p.3"><p>A proxy <em class="bcp14">MUST</em> forward unrecognized header fields unless the field-name is listed in the <a href="#header.connection" class="smpl">Connection</a> header field (<a href="#header.connection" id="rfc.xref.header.connection.1" title="Connection">Section&nbsp;6.1</a>) or the proxy is specifically configured to block, or otherwise transform, such fields. Other recipients <em class="bcp14">SHOULD</em> ignore unrecognized header fields. These requirements allow HTTP's functionality to be enhanced without requiring prior update of deployed intermediaries.<a class="self" href="#rfc.section.3.2.1.p.3">&para;</a></p></div><div id="rfc.section.3.2.1.p.4"><p>All defined header fields ought to be registered with IANA in the "Message Headers" registry, as described in <a href="rfc7231.html#header.field.registry" title="Header Field Registry">Section 8.3</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.10"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a>.<a class="self" href="#rfc.section.3.2.1.p.4">&para;</a></p></div></div><div id="field.order"><h3 id="rfc.section.3.2.2"><a href="#rfc.section.3.2.2">3.2.2</a>&nbsp;<a href="#field.order">Field Order</a></h3><div id="rfc.section.3.2.2.p.1"><p>The order in which header fields with differing field names are received is not significant. However, it is good practice to send header fields that contain control data first, such as <a href="#header.host" class="smpl">Host</a> on requests and <a href="rfc7231.html#header.date" class="smpl">Date</a> on responses, so that implementations can decide when not to handle a message as early as possible. A server <em class="bcp14">MUST NOT</em> apply a request to the target resource until the entire request header section is received, since later header fields might include conditionals, authentication credentials, or deliberately misleading duplicate header fields that would impact request processing.<a class="self" href="#rfc.section.3.2.2.p.1">&para;</a></p></div><div id="rfc.section.3.2.2.p.2"><p>A sender <em class="bcp14">MUST NOT</em> generate multiple header fields with the same field name in a message unless either the entire field value for that header field is defined as a comma-separated list [i.e., #(values)] or the header field is a well-known exception (as noted below).<a class="self" href="#rfc.section.3.2.2.p.2">&para;</a></p></div><div id="rfc.section.3.2.2.p.3"><p>A recipient <em class="bcp14">MAY</em> combine multiple header fields with the same field name into one "field-name: field-value" pair, without changing the semantics of the message, by appending each subsequent field value to the combined field value in order, separated by a comma. The order in which header fields with the same field name are received is therefore significant to the interpretation of the combined field value; a proxy <em class="bcp14">MUST NOT</em> change the order of these field values when forwarding a message.<a class="self" href="#rfc.section.3.2.2.p.3">&para;</a></p></div><div class="note" id="rfc.section.3.2.2.p.4"><p><b>Note:</b> In practice, the "Set-Cookie" header field (<a href="#RFC6265" id="rfc.xref.RFC6265.2"><cite title="HTTP State Management Mechanism">[RFC6265]</cite></a>) often appears multiple times in a response message and does not use the list syntax, violating the above requirements on multiple header fields with the same name. Since it cannot be combined into a single field-value, recipients ought to handle "Set-Cookie" as a special case while processing header fields. (See Appendix A.2.3 of <a href="#Kri2001" id="rfc.xref.Kri2001.1"><cite title="HTTP Cookies: Standards, Privacy, and Politics">[Kri2001]</cite></a> for details.)<a class="self" href="#rfc.section.3.2.2.p.4">&para;</a></p></div></div><div id="whitespace"><h3 id="rfc.section.3.2.3"><a href="#rfc.section.3.2.3">3.2.3</a>&nbsp;<a href="#whitespace">Whitespace</a></h3><div id="rule.LWS"><div id="rfc.section.3.2.3.p.1"><p>This specification uses three rules to denote the use of linear whitespace: OWS (optional whitespace), RWS (required whitespace), and BWS ("bad" whitespace).<a class="self" href="#rfc.section.3.2.3.p.1">&para;</a></p></div></div><div id="rule.OWS"><div id="rfc.section.3.2.3.p.2"><p>The OWS rule is used where zero or more linear whitespace octets might appear. For protocol elements where optional whitespace is preferred to improve readability, a sender <em class="bcp14">SHOULD</em> generate the optional whitespace as a single SP; otherwise, a sender <em class="bcp14">SHOULD NOT</em> generate optional whitespace except as needed to white out invalid or unwanted protocol elements during in-place message filtering.<a class="self" href="#rfc.section.3.2.3.p.2">&para;</a></p></div></div><div id="rule.RWS"><div id="rfc.section.3.2.3.p.3"><p>The RWS rule is used when at least one linear whitespace octet is required to separate field tokens. A sender <em class="bcp14">SHOULD</em> generate RWS as a single SP.<a class="self" href="#rfc.section.3.2.3.p.3">&para;</a></p></div></div><div id="rule.BWS"><div id="rfc.section.3.2.3.p.4"><p>The BWS rule is used where the grammar allows optional whitespace only for historical reasons. A sender <em class="bcp14">MUST NOT</em> generate BWS in messages. A recipient <em class="bcp14">MUST</em> parse for such bad whitespace and remove it before interpreting the protocol element.<a class="self" href="#rfc.section.3.2.3.p.4">&para;</a></p></div></div><div id="rule.whitespace"><div id="rfc.section.3.2.3.p.5"></div></div><div id="rfc.figure.u.19"><pre class="inline"><span id="rfc.iref.g.30"></span><span id="rfc.iref.g.31"></span><span id="rfc.iref.g.32"></span>  <a href="#rule.whitespace" class="smpl">OWS</a>            = *( <a href="#core.rules" class="smpl">SP</a> / <a href="#core.rules" class="smpl">HTAB</a> )
     595</pre></div><div id="rfc.section.3.2.p.2"><p>The field-name token labels the corresponding field-value as having the semantics defined by that header field. For example, the <a href="rfc7231.html#header.date" class="smpl">Date</a> header field is defined in <a href="rfc7231.html#header.date" title="Date">Section 7.1.1.2</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.9"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a> as containing the origination timestamp for the message in which it appears.<a class="self" href="#rfc.section.3.2.p.2">&para;</a></p></div><div id="field.extensibility"><h3 id="rfc.section.3.2.1"><a href="#rfc.section.3.2.1">3.2.1</a>&nbsp;<a href="#field.extensibility">Field Extensibility</a></h3><div id="rfc.section.3.2.1.p.1"><p>Header fields are fully extensible: there is no limit on the introduction of new field names, each presumably defining new semantics, nor on the number of header fields used in a given message. Existing fields are defined in each part of this specification and in many other specifications outside this document set.<a class="self" href="#rfc.section.3.2.1.p.1">&para;</a></p></div><div id="rfc.section.3.2.1.p.2"><p>New header fields can be defined such that, when they are understood by a recipient, they might override or enhance the interpretation of previously defined header fields, define preconditions on request evaluation, or refine the meaning of responses.<a class="self" href="#rfc.section.3.2.1.p.2">&para;</a></p></div><div id="rfc.section.3.2.1.p.3"><p>A proxy <em class="bcp14">MUST</em> forward unrecognized header fields unless the field-name is listed in the <a href="#header.connection" class="smpl">Connection</a> header field (<a href="#header.connection" id="rfc.xref.header.connection.1" title="Connection">Section&nbsp;6.1</a>) or the proxy is specifically configured to block, or otherwise transform, such fields. Other recipients <em class="bcp14">SHOULD</em> ignore unrecognized header fields. These requirements allow HTTP's functionality to be enhanced without requiring prior update of deployed intermediaries.<a class="self" href="#rfc.section.3.2.1.p.3">&para;</a></p></div><div id="rfc.section.3.2.1.p.4"><p>All defined header fields ought to be registered with IANA in the "Message Headers" registry, as described in <a href="rfc7231.html#header.field.registry" title="Header Field Registry">Section 8.3</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.10"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a>.<a class="self" href="#rfc.section.3.2.1.p.4">&para;</a></p></div></div><div id="field.order"><h3 id="rfc.section.3.2.2"><a href="#rfc.section.3.2.2">3.2.2</a>&nbsp;<a href="#field.order">Field Order</a></h3><div id="rfc.section.3.2.2.p.1"><p>The order in which header fields with differing field names are received is not significant. However, it is good practice to send header fields that contain control data first, such as <a href="#header.host" class="smpl">Host</a> on requests and <a href="rfc7231.html#header.date" class="smpl">Date</a> on responses, so that implementations can decide when not to handle a message as early as possible. A server <em class="bcp14">MUST NOT</em> apply a request to the target resource until the entire request header section is received, since later header fields might include conditionals, authentication credentials, or deliberately misleading duplicate header fields that would impact request processing.<a class="self" href="#rfc.section.3.2.2.p.1">&para;</a></p></div><div id="rfc.section.3.2.2.p.2"><p>A sender <em class="bcp14">MUST NOT</em> generate multiple header fields with the same field name in a message unless either the entire field value for that header field is defined as a comma-separated list [i.e., #(values)] or the header field is a well-known exception (as noted below).<a class="self" href="#rfc.section.3.2.2.p.2">&para;</a></p></div><div id="rfc.section.3.2.2.p.3"><p>A recipient <em class="bcp14">MAY</em> combine multiple header fields with the same field name into one "field-name: field-value" pair, without changing the semantics of the message, by appending each subsequent field value to the combined field value in order, separated by a comma. The order in which header fields with the same field name are received is therefore significant to the interpretation of the combined field value; a proxy <em class="bcp14">MUST NOT</em> change the order of these field values when forwarding a message.<a class="self" href="#rfc.section.3.2.2.p.3">&para;</a></p></div><div class="note"><div id="rfc.section.3.2.2.p.4"><p><b>Note:</b> In practice, the "Set-Cookie" header field (<a href="#RFC6265" id="rfc.xref.RFC6265.2"><cite title="HTTP State Management Mechanism">[RFC6265]</cite></a>) often appears multiple times in a response message and does not use the list syntax, violating the above requirements on multiple header fields with the same name. Since it cannot be combined into a single field-value, recipients ought to handle "Set-Cookie" as a special case while processing header fields. (See Appendix A.2.3 of <a href="#Kri2001" id="rfc.xref.Kri2001.1"><cite title="HTTP Cookies: Standards, Privacy, and Politics">[Kri2001]</cite></a> for details.)<a class="self" href="#rfc.section.3.2.2.p.4">&para;</a></p></div></div></div><div id="whitespace"><h3 id="rfc.section.3.2.3"><a href="#rfc.section.3.2.3">3.2.3</a>&nbsp;<a href="#whitespace">Whitespace</a></h3><div id="rule.LWS"><div id="rfc.section.3.2.3.p.1"><p>This specification uses three rules to denote the use of linear whitespace: OWS (optional whitespace), RWS (required whitespace), and BWS ("bad" whitespace).<a class="self" href="#rfc.section.3.2.3.p.1">&para;</a></p></div></div><div id="rule.OWS"><div id="rfc.section.3.2.3.p.2"><p>The OWS rule is used where zero or more linear whitespace octets might appear. For protocol elements where optional whitespace is preferred to improve readability, a sender <em class="bcp14">SHOULD</em> generate the optional whitespace as a single SP; otherwise, a sender <em class="bcp14">SHOULD NOT</em> generate optional whitespace except as needed to white out invalid or unwanted protocol elements during in-place message filtering.<a class="self" href="#rfc.section.3.2.3.p.2">&para;</a></p></div></div><div id="rule.RWS"><div id="rfc.section.3.2.3.p.3"><p>The RWS rule is used when at least one linear whitespace octet is required to separate field tokens. A sender <em class="bcp14">SHOULD</em> generate RWS as a single SP.<a class="self" href="#rfc.section.3.2.3.p.3">&para;</a></p></div></div><div id="rule.BWS"><div id="rfc.section.3.2.3.p.4"><p>The BWS rule is used where the grammar allows optional whitespace only for historical reasons. A sender <em class="bcp14">MUST NOT</em> generate BWS in messages. A recipient <em class="bcp14">MUST</em> parse for such bad whitespace and remove it before interpreting the protocol element.<a class="self" href="#rfc.section.3.2.3.p.4">&para;</a></p></div></div><div id="rule.whitespace"><div id="rfc.section.3.2.3.p.5"></div></div><div id="rfc.figure.u.19"><pre class="inline"><span id="rfc.iref.g.30"></span><span id="rfc.iref.g.31"></span><span id="rfc.iref.g.32"></span>  <a href="#rule.whitespace" class="smpl">OWS</a>            = *( <a href="#core.rules" class="smpl">SP</a> / <a href="#core.rules" class="smpl">HTAB</a> )
    580596                 ; optional whitespace
    581597  <a href="#rule.whitespace" class="smpl">RWS</a>            = 1*( <a href="#core.rules" class="smpl">SP</a> / <a href="#core.rules" class="smpl">HTAB</a> )
     
    600616</pre><p>indicates that the payload body has been compressed using the gzip coding and then chunked using the chunked coding while forming the message body.</p></div><div id="rfc.section.3.3.1.p.4"><p>Unlike <a href="rfc7231.html#header.content-encoding" class="smpl">Content-Encoding</a> (<a href="rfc7231.html#content.codings" title="Content Codings">Section 3.1.2.1</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.14"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a>), Transfer-Encoding is a property of the message, not of the representation, and any recipient along the request/response chain <em class="bcp14">MAY</em> decode the received transfer coding(s) or apply additional transfer coding(s) to the message body, assuming that corresponding changes are made to the Transfer-Encoding field-value. Additional information about the encoding parameters can be provided by other header fields not defined by this specification.<a class="self" href="#rfc.section.3.3.1.p.4">&para;</a></p></div><div id="rfc.section.3.3.1.p.5"><p>Transfer-Encoding <em class="bcp14">MAY</em> be sent in a response to a HEAD request or in a <a href="rfc7232.html#status.304" class="smpl">304 (Not Modified)</a> response (<a href="rfc7232.html#status.304" title="304 Not Modified">Section 4.1</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a>) to a GET request, neither of which includes a message body, to indicate that the origin server would have applied a transfer coding to the message body if the request had been an unconditional GET. This indication is not required, however, because any recipient on the response chain (including the origin server) can remove transfer codings when they are not needed.<a class="self" href="#rfc.section.3.3.1.p.5">&para;</a></p></div><div id="rfc.section.3.3.1.p.6"><p>A server <em class="bcp14">MUST NOT</em> send a Transfer-Encoding header field in any response with a status code of <a href="rfc7231.html#status.1xx" class="smpl">1xx (Informational)</a> or <a href="rfc7231.html#status.204" class="smpl">204 (No Content)</a>. A server <em class="bcp14">MUST NOT</em> send a Transfer-Encoding header field in any <a href="rfc7231.html#status.2xx" class="smpl">2xx (Successful)</a> response to a CONNECT request (<a href="rfc7231.html#CONNECT" title="CONNECT">Section 4.3.6</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.15"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a>).<a class="self" href="#rfc.section.3.3.1.p.6">&para;</a></p></div><div id="rfc.section.3.3.1.p.7"><p>Transfer-Encoding was added in HTTP/1.1. It is generally assumed that implementations advertising only HTTP/1.0 support will not understand how to process a transfer-encoded payload. A client <em class="bcp14">MUST NOT</em> send a request containing Transfer-Encoding unless it knows the server will handle HTTP/1.1 (or later) requests; such knowledge might be in the form of specific user configuration or by remembering the version of a prior received response. A server <em class="bcp14">MUST NOT</em> send a response containing Transfer-Encoding unless the corresponding request indicates HTTP/1.1 (or later).<a class="self" href="#rfc.section.3.3.1.p.7">&para;</a></p></div><div id="rfc.section.3.3.1.p.8"><p>A server that receives a request message with a transfer coding it does not understand <em class="bcp14">SHOULD</em> respond with <a href="rfc7231.html#status.501" class="smpl">501 (Not Implemented)</a>.<a class="self" href="#rfc.section.3.3.1.p.8">&para;</a></p></div></div><div id="header.content-length"><h3 id="rfc.section.3.3.2"><a href="#rfc.section.3.3.2">3.3.2</a>&nbsp;<a href="#header.content-length">Content-Length</a></h3><div id="rfc.section.3.3.2.p.1"><p>When a message does not have a <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> header field, a Content-Length header field can provide the anticipated size, as a decimal number of octets, for a potential payload body. For messages that do include a payload body, the Content-Length field-value provides the framing information necessary for determining where the body (and message) ends. For messages that do not include a payload body, the Content-Length indicates the size of the selected representation (<a href="rfc7231.html#representations" title="Representations">Section 3</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.16"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a>).<a class="self" href="#rfc.section.3.3.2.p.1">&para;</a></p></div><div id="rfc.figure.u.27"><pre class="inline"><span id="rfc.iref.g.43"></span>  <a href="#header.content-length" class="smpl">Content-Length</a> = 1*<a href="#core.rules" class="smpl">DIGIT</a>
    601617</pre></div><div id="rfc.section.3.3.2.p.2"><p>An example is<a class="self" href="#rfc.section.3.3.2.p.2">&para;</a></p></div><div id="rfc.figure.u.28"><pre class="text">  Content-Length: 3495
    602 </pre></div><div id="rfc.section.3.3.2.p.3"><p>A sender <em class="bcp14">MUST NOT</em> send a Content-Length header field in any message that contains a <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> header field.<a class="self" href="#rfc.section.3.3.2.p.3">&para;</a></p></div><div id="rfc.section.3.3.2.p.4"><p>A user agent <em class="bcp14">SHOULD</em> send a Content-Length in a request message when no <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> is sent and the request method defines a meaning for an enclosed payload body. For example, a Content-Length header field is normally sent in a POST request even when the value is 0 (indicating an empty payload body). A user agent <em class="bcp14">SHOULD NOT</em> send a Content-Length header field when the request message does not contain a payload body and the method semantics do not anticipate such a body.<a class="self" href="#rfc.section.3.3.2.p.4">&para;</a></p></div><div id="rfc.section.3.3.2.p.5"><p>A server <em class="bcp14">MAY</em> send a Content-Length header field in a response to a HEAD request (<a href="rfc7231.html#HEAD" title="HEAD">Section 4.3.2</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.17"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a>); a server <em class="bcp14">MUST NOT</em> send Content-Length in such a response unless its field-value equals the decimal number of octets that would have been sent in the payload body of a response if the same request had used the GET method.<a class="self" href="#rfc.section.3.3.2.p.5">&para;</a></p></div><div id="rfc.section.3.3.2.p.6"><p>A server <em class="bcp14">MAY</em> send a Content-Length header field in a <a href="rfc7232.html#status.304" class="smpl">304 (Not Modified)</a> response to a conditional GET request (<a href="rfc7232.html#status.304" title="304 Not Modified">Section 4.1</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a>); a server <em class="bcp14">MUST NOT</em> send Content-Length in such a response unless its field-value equals the decimal number of octets that would have been sent in the payload body of a <a href="rfc7231.html#status.200" class="smpl">200 (OK)</a> response to the same request.<a class="self" href="#rfc.section.3.3.2.p.6">&para;</a></p></div><div id="rfc.section.3.3.2.p.7"><p>A server <em class="bcp14">MUST NOT</em> send a Content-Length header field in any response with a status code of <a href="rfc7231.html#status.1xx" class="smpl">1xx (Informational)</a> or <a href="rfc7231.html#status.204" class="smpl">204 (No Content)</a>. A server <em class="bcp14">MUST NOT</em> send a Content-Length header field in any <a href="rfc7231.html#status.2xx" class="smpl">2xx (Successful)</a> response to a CONNECT request (<a href="rfc7231.html#CONNECT" title="CONNECT">Section 4.3.6</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.18"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a>).<a class="self" href="#rfc.section.3.3.2.p.7">&para;</a></p></div><div id="rfc.section.3.3.2.p.8"><p>Aside from the cases defined above, in the absence of Transfer-Encoding, an origin server <em class="bcp14">SHOULD</em> send a Content-Length header field when the payload body size is known prior to sending the complete header section. This will allow downstream recipients to measure transfer progress, know when a received message is complete, and potentially reuse the connection for additional requests.<a class="self" href="#rfc.section.3.3.2.p.8">&para;</a></p></div><div id="rfc.section.3.3.2.p.9"><p>Any Content-Length field value greater than or equal to zero is valid. Since there is no predefined limit to the length of a payload, a recipient <em class="bcp14">MUST</em> anticipate potentially large decimal numerals and prevent parsing errors due to integer conversion overflows (<a href="#attack.protocol.element.length" title="Attacks via Protocol Element Length">Section&nbsp;9.3</a>).<a class="self" href="#rfc.section.3.3.2.p.9">&para;</a></p></div><div id="rfc.section.3.3.2.p.10"><p>If a message is received that has multiple Content-Length header fields with field-values consisting of the same decimal value, or a single Content-Length header field with a field value containing a list of identical decimal values (e.g., "Content-Length: 42, 42"), indicating that duplicate Content-Length header fields have been generated or combined by an upstream message processor, then the recipient <em class="bcp14">MUST</em> either reject the message as invalid or replace the duplicated field-values with a single valid Content-Length field containing that decimal value prior to determining the message body length or forwarding the message.<a class="self" href="#rfc.section.3.3.2.p.10">&para;</a></p></div><div class="note" id="rfc.section.3.3.2.p.11"><p><b>Note:</b> HTTP's use of Content-Length for message framing differs significantly from the same field's use in MIME, where it is an optional field used only within the "message/external-body" media-type.<a class="self" href="#rfc.section.3.3.2.p.11">&para;</a></p></div></div><div id="message.body.length"><h3 id="rfc.section.3.3.3"><a href="#rfc.section.3.3.3">3.3.3</a>&nbsp;<a href="#message.body.length">Message Body Length</a></h3><div id="rfc.section.3.3.3.p.1"><p>The length of a message body is determined by one of the following (in order of precedence):<a class="self" href="#rfc.section.3.3.3.p.1">&para;</a></p></div><div id="rfc.section.3.3.3.p.2"><ol><li><p>Any response to a HEAD request and any response with a <a href="rfc7231.html#status.1xx" class="smpl">1xx (Informational)</a>, <a href="rfc7231.html#status.204" class="smpl">204 (No Content)</a>, or <a href="rfc7232.html#status.304" class="smpl">304 (Not Modified)</a> status code is always terminated by the first empty line after the header fields, regardless of the header fields present in the message, and thus cannot contain a message body.</p></li><li><p>Any <a href="rfc7231.html#status.2xx" class="smpl">2xx (Successful)</a> response to a CONNECT request implies that the connection will become a tunnel immediately after the empty line that concludes the header fields. A client <em class="bcp14">MUST</em> ignore any <a href="#header.content-length" class="smpl">Content-Length</a> or <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> header fields received in such a message.</p></li><li><p>If a <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> header field is present and the chunked transfer coding (<a href="#chunked.encoding" title="Chunked Transfer Coding">Section&nbsp;4.1</a>) is the final encoding, the message body length is determined by reading and decoding the chunked data until the transfer coding indicates the data is complete.</p><p>If a <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> header field is present in a response and the chunked transfer coding is not the final encoding, the message body length is determined by reading the connection until it is closed by the server. If a <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> header field is present in a request and the chunked transfer coding is not the final encoding, the message body length cannot be determined reliably; the server <em class="bcp14">MUST</em> respond with the <a href="rfc7231.html#status.400" class="smpl">400 (Bad Request)</a> status code and then close the connection.</p><p>If a message is received with both a <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> and a <a href="#header.content-length" class="smpl">Content-Length</a> header field, the Transfer-Encoding overrides the Content-Length. Such a message might indicate an attempt to perform request smuggling (<a href="#request.smuggling" title="Request Smuggling">Section&nbsp;9.5</a>) or response splitting (<a href="#response.splitting" title="Response Splitting">Section&nbsp;9.4</a>) and ought to be handled as an error. A sender <em class="bcp14">MUST</em> remove the received Content-Length field prior to forwarding such a message downstream.</p></li><li><p>If a message is received without <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> and with either multiple <a href="#header.content-length" class="smpl">Content-Length</a> header fields having differing field-values or a single Content-Length header field having an invalid value, then the message framing is invalid and the recipient <em class="bcp14">MUST</em> treat it as an unrecoverable error. If this is a request message, the server <em class="bcp14">MUST</em> respond with a <a href="rfc7231.html#status.400" class="smpl">400 (Bad Request)</a> status code and then close the connection. If this is a response message received by a proxy, the proxy <em class="bcp14">MUST</em> close the connection to the server, discard the received response, and send a <a href="rfc7231.html#status.502" class="smpl">502 (Bad Gateway)</a> response to the client. If this is a response message received by a user agent, the user agent <em class="bcp14">MUST</em> close the connection to the server and discard the received response.</p></li><li><p>If a valid <a href="#header.content-length" class="smpl">Content-Length</a> header field is present without <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a>, its decimal value defines the expected message body length in octets. If the sender closes the connection or the recipient times out before the indicated number of octets are received, the recipient <em class="bcp14">MUST</em> consider the message to be incomplete and close the connection.</p></li><li><p>If this is a request message and none of the above are true, then the message body length is zero (no message body is present).</p></li><li><p>Otherwise, this is a response message without a declared message body length, so the message body length is determined by the number of octets received prior to the server closing the connection.</p></li></ol></div><div id="rfc.section.3.3.3.p.3"><p>Since there is no way to distinguish a successfully completed, close-delimited message from a partially received message interrupted by network failure, a server <em class="bcp14">SHOULD</em> generate encoding or length-delimited messages whenever possible. The close-delimiting feature exists primarily for backwards compatibility with HTTP/1.0.<a class="self" href="#rfc.section.3.3.3.p.3">&para;</a></p></div><div id="rfc.section.3.3.3.p.4"><p>A server <em class="bcp14">MAY</em> reject a request that contains a message body but not a <a href="#header.content-length" class="smpl">Content-Length</a> by responding with <a href="rfc7231.html#status.411" class="smpl">411 (Length Required)</a>.<a class="self" href="#rfc.section.3.3.3.p.4">&para;</a></p></div><div id="rfc.section.3.3.3.p.5"><p>Unless a transfer coding other than chunked has been applied, a client that sends a request containing a message body <em class="bcp14">SHOULD</em> use a valid <a href="#header.content-length" class="smpl">Content-Length</a> header field if the message body length is known in advance, rather than the chunked transfer coding, since some existing services respond to chunked with a <a href="rfc7231.html#status.411" class="smpl">411 (Length Required)</a> status code even though they understand the chunked transfer coding. This is typically because such services are implemented via a gateway that requires a content-length in advance of being called and the server is unable or unwilling to buffer the entire request before processing.<a class="self" href="#rfc.section.3.3.3.p.5">&para;</a></p></div><div id="rfc.section.3.3.3.p.6"><p>A user agent that sends a request containing a message body <em class="bcp14">MUST</em> send a valid <a href="#header.content-length" class="smpl">Content-Length</a> header field if it does not know the server will handle HTTP/1.1 (or later) requests; such knowledge can be in the form of specific user configuration or by remembering the version of a prior received response.<a class="self" href="#rfc.section.3.3.3.p.6">&para;</a></p></div><div id="rfc.section.3.3.3.p.7"><p>If the final response to the last request on a connection has been completely received and there remains additional data to read, a user agent <em class="bcp14">MAY</em> discard the remaining data or attempt to determine if that data belongs as part of the prior response body, which might be the case if the prior message's Content-Length value is incorrect. A client <em class="bcp14">MUST NOT</em> process, cache, or forward such extra data as a separate response, since such behavior would be vulnerable to cache poisoning.<a class="self" href="#rfc.section.3.3.3.p.7">&para;</a></p></div></div></div><div id="incomplete.messages"><h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a>&nbsp;<a href="#incomplete.messages">Handling Incomplete Messages</a></h2><div id="rfc.section.3.4.p.1"><p>A server that receives an incomplete request message, usually due to a canceled request or a triggered timeout exception, <em class="bcp14">MAY</em> send an error response prior to closing the connection.<a class="self" href="#rfc.section.3.4.p.1">&para;</a></p></div><div id="rfc.section.3.4.p.2"><p>A client that receives an incomplete response message, which can occur when a connection is closed prematurely or when decoding a supposedly chunked transfer coding fails, <em class="bcp14">MUST</em> record the message as incomplete. Cache requirements for incomplete responses are defined in <a href="rfc7234.html#response.cacheability" title="Storing Responses in Caches">Section 3</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>.<a class="self" href="#rfc.section.3.4.p.2">&para;</a></p></div><div id="rfc.section.3.4.p.3"><p>If a response terminates in the middle of the header section (before the empty line is received) and the status code might rely on header fields to convey the full meaning of the response, then the client cannot assume that meaning has been conveyed; the client might need to repeat the request in order to determine what action to take next.<a class="self" href="#rfc.section.3.4.p.3">&para;</a></p></div><div id="rfc.section.3.4.p.4"><p>A message body that uses the chunked transfer coding is incomplete if the zero-sized chunk that terminates the encoding has not been received. A message that uses a valid <a href="#header.content-length" class="smpl">Content-Length</a> is incomplete if the size of the message body received (in octets) is less than the value given by Content-Length. A response that has neither chunked transfer coding nor Content-Length is terminated by closure of the connection and, thus, is considered complete regardless of the number of message body octets received, provided that the header section was received intact.<a class="self" href="#rfc.section.3.4.p.4">&para;</a></p></div></div><div id="message.robustness"><h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a>&nbsp;<a href="#message.robustness">Message Parsing Robustness</a></h2><div id="rfc.section.3.5.p.1"><p>Older HTTP/1.0 user agent implementations might send an extra CRLF after a POST request as a workaround for some early server applications that failed to read message body content that was not terminated by a line-ending. An HTTP/1.1 user agent <em class="bcp14">MUST NOT</em> preface or follow a request with an extra CRLF. If terminating the request message body with a line-ending is desired, then the user agent <em class="bcp14">MUST</em> count the terminating CRLF octets as part of the message body length.<a class="self" href="#rfc.section.3.5.p.1">&para;</a></p></div><div id="rfc.section.3.5.p.2"><p>In the interest of robustness, a server that is expecting to receive and parse a request-line <em class="bcp14">SHOULD</em> ignore at least one empty line (CRLF) received prior to the request-line.<a class="self" href="#rfc.section.3.5.p.2">&para;</a></p></div><div id="rfc.section.3.5.p.3"><p>Although the line terminator for the start-line and header fields is the sequence CRLF, a recipient <em class="bcp14">MAY</em> recognize a single LF as a line terminator and ignore any preceding CR.<a class="self" href="#rfc.section.3.5.p.3">&para;</a></p></div><div id="rfc.section.3.5.p.4"><p>Although the request-line and status-line grammar rules require that each of the component elements be separated by a single SP octet, recipients <em class="bcp14">MAY</em> instead parse on whitespace-delimited word boundaries and, aside from the CRLF terminator, treat any form of whitespace as the SP separator while ignoring preceding or trailing whitespace; such whitespace includes one or more of the following octets: SP, HTAB, VT (%x0B), FF (%x0C), or bare CR. However, lenient parsing can result in security vulnerabilities if there are multiple recipients of the message and each has its own unique interpretation of robustness (see <a href="#request.smuggling" title="Request Smuggling">Section&nbsp;9.5</a>).<a class="self" href="#rfc.section.3.5.p.4">&para;</a></p></div><div id="rfc.section.3.5.p.5"><p>When a server listening only for HTTP request messages, or processing what appears from the start-line to be an HTTP request message, receives a sequence of octets that does not match the HTTP-message grammar aside from the robustness exceptions listed above, the server <em class="bcp14">SHOULD</em> respond with a <a href="rfc7231.html#status.400" class="smpl">400 (Bad Request)</a> response.<a class="self" href="#rfc.section.3.5.p.5">&para;</a></p></div></div></div><div id="transfer.codings"><h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a>&nbsp;<a href="#transfer.codings">Transfer Codings</a></h1><div id="rfc.section.4.p.1"><p>Transfer coding names are used to indicate an encoding transformation that has been, can be, or might need to be applied to a payload body in order to ensure "safe transport" through the network. This differs from a content coding in that the transfer coding is a property of the message rather than a property of the representation that is being transferred.<a class="self" href="#rfc.section.4.p.1">&para;</a></p></div><div id="rfc.figure.u.29"><pre class="inline"><span id="rfc.iref.g.44"></span><span id="rfc.iref.g.45"></span>  <a href="#transfer.codings" class="smpl">transfer-coding</a>    = "chunked" ; <a href="#chunked.encoding" title="Chunked Transfer Coding">Section&nbsp;4.1</a>
     618</pre></div><div id="rfc.section.3.3.2.p.3"><p>A sender <em class="bcp14">MUST NOT</em> send a Content-Length header field in any message that contains a <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> header field.<a class="self" href="#rfc.section.3.3.2.p.3">&para;</a></p></div><div id="rfc.section.3.3.2.p.4"><p>A user agent <em class="bcp14">SHOULD</em> send a Content-Length in a request message when no <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> is sent and the request method defines a meaning for an enclosed payload body. For example, a Content-Length header field is normally sent in a POST request even when the value is 0 (indicating an empty payload body). A user agent <em class="bcp14">SHOULD NOT</em> send a Content-Length header field when the request message does not contain a payload body and the method semantics do not anticipate such a body.<a class="self" href="#rfc.section.3.3.2.p.4">&para;</a></p></div><div id="rfc.section.3.3.2.p.5"><p>A server <em class="bcp14">MAY</em> send a Content-Length header field in a response to a HEAD request (<a href="rfc7231.html#HEAD" title="HEAD">Section 4.3.2</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.17"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a>); a server <em class="bcp14">MUST NOT</em> send Content-Length in such a response unless its field-value equals the decimal number of octets that would have been sent in the payload body of a response if the same request had used the GET method.<a class="self" href="#rfc.section.3.3.2.p.5">&para;</a></p></div><div id="rfc.section.3.3.2.p.6"><p>A server <em class="bcp14">MAY</em> send a Content-Length header field in a <a href="rfc7232.html#status.304" class="smpl">304 (Not Modified)</a> response to a conditional GET request (<a href="rfc7232.html#status.304" title="304 Not Modified">Section 4.1</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a>); a server <em class="bcp14">MUST NOT</em> send Content-Length in such a response unless its field-value equals the decimal number of octets that would have been sent in the payload body of a <a href="rfc7231.html#status.200" class="smpl">200 (OK)</a> response to the same request.<a class="self" href="#rfc.section.3.3.2.p.6">&para;</a></p></div><div id="rfc.section.3.3.2.p.7"><p>A server <em class="bcp14">MUST NOT</em> send a Content-Length header field in any response with a status code of <a href="rfc7231.html#status.1xx" class="smpl">1xx (Informational)</a> or <a href="rfc7231.html#status.204" class="smpl">204 (No Content)</a>. A server <em class="bcp14">MUST NOT</em> send a Content-Length header field in any <a href="rfc7231.html#status.2xx" class="smpl">2xx (Successful)</a> response to a CONNECT request (<a href="rfc7231.html#CONNECT" title="CONNECT">Section 4.3.6</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.18"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a>).<a class="self" href="#rfc.section.3.3.2.p.7">&para;</a></p></div><div id="rfc.section.3.3.2.p.8"><p>Aside from the cases defined above, in the absence of Transfer-Encoding, an origin server <em class="bcp14">SHOULD</em> send a Content-Length header field when the payload body size is known prior to sending the complete header section. This will allow downstream recipients to measure transfer progress, know when a received message is complete, and potentially reuse the connection for additional requests.<a class="self" href="#rfc.section.3.3.2.p.8">&para;</a></p></div><div id="rfc.section.3.3.2.p.9"><p>Any Content-Length field value greater than or equal to zero is valid. Since there is no predefined limit to the length of a payload, a recipient <em class="bcp14">MUST</em> anticipate potentially large decimal numerals and prevent parsing errors due to integer conversion overflows (<a href="#attack.protocol.element.length" title="Attacks via Protocol Element Length">Section&nbsp;9.3</a>).<a class="self" href="#rfc.section.3.3.2.p.9">&para;</a></p></div><div id="rfc.section.3.3.2.p.10"><p>If a message is received that has multiple Content-Length header fields with field-values consisting of the same decimal value, or a single Content-Length header field with a field value containing a list of identical decimal values (e.g., "Content-Length: 42, 42"), indicating that duplicate Content-Length header fields have been generated or combined by an upstream message processor, then the recipient <em class="bcp14">MUST</em> either reject the message as invalid or replace the duplicated field-values with a single valid Content-Length field containing that decimal value prior to determining the message body length or forwarding the message.<a class="self" href="#rfc.section.3.3.2.p.10">&para;</a></p></div><div class="note"><div id="rfc.section.3.3.2.p.11"><p><b>Note:</b> HTTP's use of Content-Length for message framing differs significantly from the same field's use in MIME, where it is an optional field used only within the "message/external-body" media-type.<a class="self" href="#rfc.section.3.3.2.p.11">&para;</a></p></div></div></div><div id="message.body.length"><h3 id="rfc.section.3.3.3"><a href="#rfc.section.3.3.3">3.3.3</a>&nbsp;<a href="#message.body.length">Message Body Length</a></h3><div id="rfc.section.3.3.3.p.1"><p>The length of a message body is determined by one of the following (in order of precedence):<a class="self" href="#rfc.section.3.3.3.p.1">&para;</a></p></div><div id="rfc.section.3.3.3.p.2"><ol><li><p>Any response to a HEAD request and any response with a <a href="rfc7231.html#status.1xx" class="smpl">1xx (Informational)</a>, <a href="rfc7231.html#status.204" class="smpl">204 (No Content)</a>, or <a href="rfc7232.html#status.304" class="smpl">304 (Not Modified)</a> status code is always terminated by the first empty line after the header fields, regardless of the header fields present in the message, and thus cannot contain a message body.</p></li><li><p>Any <a href="rfc7231.html#status.2xx" class="smpl">2xx (Successful)</a> response to a CONNECT request implies that the connection will become a tunnel immediately after the empty line that concludes the header fields. A client <em class="bcp14">MUST</em> ignore any <a href="#header.content-length" class="smpl">Content-Length</a> or <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> header fields received in such a message.</p></li><li><p>If a <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> header field is present and the chunked transfer coding (<a href="#chunked.encoding" title="Chunked Transfer Coding">Section&nbsp;4.1</a>) is the final encoding, the message body length is determined by reading and decoding the chunked data until the transfer coding indicates the data is complete.</p><p>If a <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> header field is present in a response and the chunked transfer coding is not the final encoding, the message body length is determined by reading the connection until it is closed by the server. If a <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> header field is present in a request and the chunked transfer coding is not the final encoding, the message body length cannot be determined reliably; the server <em class="bcp14">MUST</em> respond with the <a href="rfc7231.html#status.400" class="smpl">400 (Bad Request)</a> status code and then close the connection.</p><p>If a message is received with both a <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> and a <a href="#header.content-length" class="smpl">Content-Length</a> header field, the Transfer-Encoding overrides the Content-Length. Such a message might indicate an attempt to perform request smuggling (<a href="#request.smuggling" title="Request Smuggling">Section&nbsp;9.5</a>) or response splitting (<a href="#response.splitting" title="Response Splitting">Section&nbsp;9.4</a>) and ought to be handled as an error. A sender <em class="bcp14">MUST</em> remove the received Content-Length field prior to forwarding such a message downstream.</p></li><li><p>If a message is received without <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> and with either multiple <a href="#header.content-length" class="smpl">Content-Length</a> header fields having differing field-values or a single Content-Length header field having an invalid value, then the message framing is invalid and the recipient <em class="bcp14">MUST</em> treat it as an unrecoverable error. If this is a request message, the server <em class="bcp14">MUST</em> respond with a <a href="rfc7231.html#status.400" class="smpl">400 (Bad Request)</a> status code and then close the connection. If this is a response message received by a proxy, the proxy <em class="bcp14">MUST</em> close the connection to the server, discard the received response, and send a <a href="rfc7231.html#status.502" class="smpl">502 (Bad Gateway)</a> response to the client. If this is a response message received by a user agent, the user agent <em class="bcp14">MUST</em> close the connection to the server and discard the received response.</p></li><li><p>If a valid <a href="#header.content-length" class="smpl">Content-Length</a> header field is present without <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a>, its decimal value defines the expected message body length in octets. If the sender closes the connection or the recipient times out before the indicated number of octets are received, the recipient <em class="bcp14">MUST</em> consider the message to be incomplete and close the connection.</p></li><li><p>If this is a request message and none of the above are true, then the message body length is zero (no message body is present).</p></li><li><p>Otherwise, this is a response message without a declared message body length, so the message body length is determined by the number of octets received prior to the server closing the connection.</p></li></ol></div><div id="rfc.section.3.3.3.p.3"><p>Since there is no way to distinguish a successfully completed, close-delimited message from a partially received message interrupted by network failure, a server <em class="bcp14">SHOULD</em> generate encoding or length-delimited messages whenever possible. The close-delimiting feature exists primarily for backwards compatibility with HTTP/1.0.<a class="self" href="#rfc.section.3.3.3.p.3">&para;</a></p></div><div id="rfc.section.3.3.3.p.4"><p>A server <em class="bcp14">MAY</em> reject a request that contains a message body but not a <a href="#header.content-length" class="smpl">Content-Length</a> by responding with <a href="rfc7231.html#status.411" class="smpl">411 (Length Required)</a>.<a class="self" href="#rfc.section.3.3.3.p.4">&para;</a></p></div><div id="rfc.section.3.3.3.p.5"><p>Unless a transfer coding other than chunked has been applied, a client that sends a request containing a message body <em class="bcp14">SHOULD</em> use a valid <a href="#header.content-length" class="smpl">Content-Length</a> header field if the message body length is known in advance, rather than the chunked transfer coding, since some existing services respond to chunked with a <a href="rfc7231.html#status.411" class="smpl">411 (Length Required)</a> status code even though they understand the chunked transfer coding. This is typically because such services are implemented via a gateway that requires a content-length in advance of being called and the server is unable or unwilling to buffer the entire request before processing.<a class="self" href="#rfc.section.3.3.3.p.5">&para;</a></p></div><div id="rfc.section.3.3.3.p.6"><p>A user agent that sends a request containing a message body <em class="bcp14">MUST</em> send a valid <a href="#header.content-length" class="smpl">Content-Length</a> header field if it does not know the server will handle HTTP/1.1 (or later) requests; such knowledge can be in the form of specific user configuration or by remembering the version of a prior received response.<a class="self" href="#rfc.section.3.3.3.p.6">&para;</a></p></div><div id="rfc.section.3.3.3.p.7"><p>If the final response to the last request on a connection has been completely received and there remains additional data to read, a user agent <em class="bcp14">MAY</em> discard the remaining data or attempt to determine if that data belongs as part of the prior response body, which might be the case if the prior message's Content-Length value is incorrect. A client <em class="bcp14">MUST NOT</em> process, cache, or forward such extra data as a separate response, since such behavior would be vulnerable to cache poisoning.<a class="self" href="#rfc.section.3.3.3.p.7">&para;</a></p></div></div></div><div id="incomplete.messages"><h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a>&nbsp;<a href="#incomplete.messages">Handling Incomplete Messages</a></h2><div id="rfc.section.3.4.p.1"><p>A server that receives an incomplete request message, usually due to a canceled request or a triggered timeout exception, <em class="bcp14">MAY</em> send an error response prior to closing the connection.<a class="self" href="#rfc.section.3.4.p.1">&para;</a></p></div><div id="rfc.section.3.4.p.2"><p>A client that receives an incomplete response message, which can occur when a connection is closed prematurely or when decoding a supposedly chunked transfer coding fails, <em class="bcp14">MUST</em> record the message as incomplete. Cache requirements for incomplete responses are defined in <a href="rfc7234.html#response.cacheability" title="Storing Responses in Caches">Section 3</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>.<a class="self" href="#rfc.section.3.4.p.2">&para;</a></p></div><div id="rfc.section.3.4.p.3"><p>If a response terminates in the middle of the header section (before the empty line is received) and the status code might rely on header fields to convey the full meaning of the response, then the client cannot assume that meaning has been conveyed; the client might need to repeat the request in order to determine what action to take next.<a class="self" href="#rfc.section.3.4.p.3">&para;</a></p></div><div id="rfc.section.3.4.p.4"><p>A message body that uses the chunked transfer coding is incomplete if the zero-sized chunk that terminates the encoding has not been received. A message that uses a valid <a href="#header.content-length" class="smpl">Content-Length</a> is incomplete if the size of the message body received (in octets) is less than the value given by Content-Length. A response that has neither chunked transfer coding nor Content-Length is terminated by closure of the connection and, thus, is considered complete regardless of the number of message body octets received, provided that the header section was received intact.<a class="self" href="#rfc.section.3.4.p.4">&para;</a></p></div></div><div id="message.robustness"><h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a>&nbsp;<a href="#message.robustness">Message Parsing Robustness</a></h2><div id="rfc.section.3.5.p.1"><p>Older HTTP/1.0 user agent implementations might send an extra CRLF after a POST request as a workaround for some early server applications that failed to read message body content that was not terminated by a line-ending. An HTTP/1.1 user agent <em class="bcp14">MUST NOT</em> preface or follow a request with an extra CRLF. If terminating the request message body with a line-ending is desired, then the user agent <em class="bcp14">MUST</em> count the terminating CRLF octets as part of the message body length.<a class="self" href="#rfc.section.3.5.p.1">&para;</a></p></div><div id="rfc.section.3.5.p.2"><p>In the interest of robustness, a server that is expecting to receive and parse a request-line <em class="bcp14">SHOULD</em> ignore at least one empty line (CRLF) received prior to the request-line.<a class="self" href="#rfc.section.3.5.p.2">&para;</a></p></div><div id="rfc.section.3.5.p.3"><p>Although the line terminator for the start-line and header fields is the sequence CRLF, a recipient <em class="bcp14">MAY</em> recognize a single LF as a line terminator and ignore any preceding CR.<a class="self" href="#rfc.section.3.5.p.3">&para;</a></p></div><div id="rfc.section.3.5.p.4"><p>Although the request-line and status-line grammar rules require that each of the component elements be separated by a single SP octet, recipients <em class="bcp14">MAY</em> instead parse on whitespace-delimited word boundaries and, aside from the CRLF terminator, treat any form of whitespace as the SP separator while ignoring preceding or trailing whitespace; such whitespace includes one or more of the following octets: SP, HTAB, VT (%x0B), FF (%x0C), or bare CR. However, lenient parsing can result in security vulnerabilities if there are multiple recipients of the message and each has its own unique interpretation of robustness (see <a href="#request.smuggling" title="Request Smuggling">Section&nbsp;9.5</a>).<a class="self" href="#rfc.section.3.5.p.4">&para;</a></p></div><div id="rfc.section.3.5.p.5"><p>When a server listening only for HTTP request messages, or processing what appears from the start-line to be an HTTP request message, receives a sequence of octets that does not match the HTTP-message grammar aside from the robustness exceptions listed above, the server <em class="bcp14">SHOULD</em> respond with a <a href="rfc7231.html#status.400" class="smpl">400 (Bad Request)</a> response.<a class="self" href="#rfc.section.3.5.p.5">&para;</a></p></div></div></div><div id="transfer.codings"><h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a>&nbsp;<a href="#transfer.codings">Transfer Codings</a></h1><div id="rfc.section.4.p.1"><p>Transfer coding names are used to indicate an encoding transformation that has been, can be, or might need to be applied to a payload body in order to ensure "safe transport" through the network. This differs from a content coding in that the transfer coding is a property of the message rather than a property of the representation that is being transferred.<a class="self" href="#rfc.section.4.p.1">&para;</a></p></div><div id="rfc.figure.u.29"><pre class="inline"><span id="rfc.iref.g.44"></span><span id="rfc.iref.g.45"></span>  <a href="#transfer.codings" class="smpl">transfer-coding</a>    = "chunked" ; <a href="#chunked.encoding" title="Chunked Transfer Coding">Section&nbsp;4.1</a>
    603619                     / "compress" ; <a href="#compress.coding" title="Compress Coding">Section&nbsp;4.2.1</a>
    604620                     / "deflate" ; <a href="#deflate.coding" title="Deflate Coding">Section&nbsp;4.2.2</a>
     
    641657  Remove "chunked" from Transfer-Encoding
    642658  Remove Trailer from existing header fields
    643 </pre></div></div></div><div id="compression.codings"><h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a>&nbsp;<a href="#compression.codings">Compression Codings</a></h2><div id="rfc.section.4.2.p.1"><p>The codings defined below can be used to compress the payload of a message.<a class="self" href="#rfc.section.4.2.p.1">&para;</a></p></div><div id="compress.coding"><h3 id="rfc.section.4.2.1"><a href="#rfc.section.4.2.1">4.2.1</a>&nbsp;<a href="#compress.coding">Compress Coding</a></h3><div id="rfc.section.4.2.1.p.1"><p>The "compress" coding is an adaptive Lempel-Ziv-Welch (LZW) coding <a href="#Welch" id="rfc.xref.Welch.1"><cite title="A Technique for High-Performance Data Compression">[Welch]</cite></a> that is commonly produced by the UNIX file compression program "compress". A recipient <em class="bcp14">SHOULD</em> consider "x-compress" to be equivalent to "compress".<a class="self" href="#rfc.section.4.2.1.p.1">&para;</a></p></div></div><div id="deflate.coding"><h3 id="rfc.section.4.2.2"><a href="#rfc.section.4.2.2">4.2.2</a>&nbsp;<a href="#deflate.coding">Deflate Coding</a></h3><div id="rfc.section.4.2.2.p.1"><p>The "deflate" coding is a "zlib" data format <a href="#RFC1950" id="rfc.xref.RFC1950.1"><cite title="ZLIB Compressed Data Format Specification version 3.3">[RFC1950]</cite></a> containing a "deflate" compressed data stream <a href="#RFC1951" id="rfc.xref.RFC1951.1"><cite title="DEFLATE Compressed Data Format Specification version 1.3">[RFC1951]</cite></a> that uses a combination of the Lempel-Ziv (LZ77) compression algorithm and Huffman coding.<a class="self" href="#rfc.section.4.2.2.p.1">&para;</a></p></div><div class="note" id="rfc.section.4.2.2.p.2"><p><b>Note:</b> Some non-conformant implementations send the "deflate" compressed data without the zlib wrapper.<a class="self" href="#rfc.section.4.2.2.p.2">&para;</a></p></div></div><div id="gzip.coding"><h3 id="rfc.section.4.2.3"><a href="#rfc.section.4.2.3">4.2.3</a>&nbsp;<a href="#gzip.coding">Gzip Coding</a></h3><div id="rfc.section.4.2.3.p.1"><p>The "gzip" coding is an LZ77 coding with a 32-bit Cyclic Redundancy Check (CRC) that is commonly produced by the gzip file compression program <a href="#RFC1952" id="rfc.xref.RFC1952.1"><cite title="GZIP file format specification version 4.3">[RFC1952]</cite></a>. A recipient <em class="bcp14">SHOULD</em> consider "x-gzip" to be equivalent to "gzip".<a class="self" href="#rfc.section.4.2.3.p.1">&para;</a></p></div></div></div><div id="header.te"><h2 id="rfc.section.4.3"><a href="#rfc.section.4.3">4.3</a>&nbsp;<a href="#header.te">TE</a></h2><div id="rfc.section.4.3.p.1"><p>The "TE" header field in a request indicates what transfer codings, besides chunked, the client is willing to accept in response, and whether or not the client is willing to accept trailer fields in a chunked transfer coding.<a class="self" href="#rfc.section.4.3.p.1">&para;</a></p></div><div id="rfc.section.4.3.p.2"><p>The TE field-value consists of a comma-separated list of transfer coding names, each allowing for optional parameters (as described in <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;4</a>), and/or the keyword "trailers". A client <em class="bcp14">MUST NOT</em> send the chunked transfer coding name in TE; chunked is always acceptable for HTTP/1.1 recipients.<a class="self" href="#rfc.section.4.3.p.2">&para;</a></p></div><div id="rfc.figure.u.35"><pre class="inline"><span id="rfc.iref.g.60"></span><span id="rfc.iref.g.61"></span><span id="rfc.iref.g.62"></span><span id="rfc.iref.g.63"></span>  <a href="#header.te" class="smpl">TE</a>        = #<a href="#header.te" class="smpl">t-codings</a>
     659</pre></div></div></div><div id="compression.codings"><h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a>&nbsp;<a href="#compression.codings">Compression Codings</a></h2><div id="rfc.section.4.2.p.1"><p>The codings defined below can be used to compress the payload of a message.<a class="self" href="#rfc.section.4.2.p.1">&para;</a></p></div><div id="compress.coding"><h3 id="rfc.section.4.2.1"><a href="#rfc.section.4.2.1">4.2.1</a>&nbsp;<a href="#compress.coding">Compress Coding</a></h3><div id="rfc.section.4.2.1.p.1"><p>The "compress" coding is an adaptive Lempel-Ziv-Welch (LZW) coding <a href="#Welch" id="rfc.xref.Welch.1"><cite title="A Technique for High-Performance Data Compression">[Welch]</cite></a> that is commonly produced by the UNIX file compression program "compress". A recipient <em class="bcp14">SHOULD</em> consider "x-compress" to be equivalent to "compress".<a class="self" href="#rfc.section.4.2.1.p.1">&para;</a></p></div></div><div id="deflate.coding"><h3 id="rfc.section.4.2.2"><a href="#rfc.section.4.2.2">4.2.2</a>&nbsp;<a href="#deflate.coding">Deflate Coding</a></h3><div id="rfc.section.4.2.2.p.1"><p>The "deflate" coding is a "zlib" data format <a href="#RFC1950" id="rfc.xref.RFC1950.1"><cite title="ZLIB Compressed Data Format Specification version 3.3">[RFC1950]</cite></a> containing a "deflate" compressed data stream <a href="#RFC1951" id="rfc.xref.RFC1951.1"><cite title="DEFLATE Compressed Data Format Specification version 1.3">[RFC1951]</cite></a> that uses a combination of the Lempel-Ziv (LZ77) compression algorithm and Huffman coding.<a class="self" href="#rfc.section.4.2.2.p.1">&para;</a></p></div><div class="note"><div id="rfc.section.4.2.2.p.2"><p><b>Note:</b> Some non-conformant implementations send the "deflate" compressed data without the zlib wrapper.<a class="self" href="#rfc.section.4.2.2.p.2">&para;</a></p></div></div></div><div id="gzip.coding"><h3 id="rfc.section.4.2.3"><a href="#rfc.section.4.2.3">4.2.3</a>&nbsp;<a href="#gzip.coding">Gzip Coding</a></h3><div id="rfc.section.4.2.3.p.1"><p>The "gzip" coding is an LZ77 coding with a 32-bit Cyclic Redundancy Check (CRC) that is commonly produced by the gzip file compression program <a href="#RFC1952" id="rfc.xref.RFC1952.1"><cite title="GZIP file format specification version 4.3">[RFC1952]</cite></a>. A recipient <em class="bcp14">SHOULD</em> consider "x-gzip" to be equivalent to "gzip".<a class="self" href="#rfc.section.4.2.3.p.1">&para;</a></p></div></div></div><div id="header.te"><h2 id="rfc.section.4.3"><a href="#rfc.section.4.3">4.3</a>&nbsp;<a href="#header.te">TE</a></h2><div id="rfc.section.4.3.p.1"><p>The "TE" header field in a request indicates what transfer codings, besides chunked, the client is willing to accept in response, and whether or not the client is willing to accept trailer fields in a chunked transfer coding.<a class="self" href="#rfc.section.4.3.p.1">&para;</a></p></div><div id="rfc.section.4.3.p.2"><p>The TE field-value consists of a comma-separated list of transfer coding names, each allowing for optional parameters (as described in <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;4</a>), and/or the keyword "trailers". A client <em class="bcp14">MUST NOT</em> send the chunked transfer coding name in TE; chunked is always acceptable for HTTP/1.1 recipients.<a class="self" href="#rfc.section.4.3.p.2">&para;</a></p></div><div id="rfc.figure.u.35"><pre class="inline"><span id="rfc.iref.g.60"></span><span id="rfc.iref.g.61"></span><span id="rfc.iref.g.62"></span><span id="rfc.iref.g.63"></span>  <a href="#header.te" class="smpl">TE</a>        = #<a href="#header.te" class="smpl">t-codings</a>
    644660  <a href="#header.te" class="smpl">t-codings</a> = "trailers" / ( <a href="#transfer.codings" class="smpl">transfer-coding</a> [ <a href="#header.te" class="smpl">t-ranking</a> ] )
    645661  <a href="#header.te" class="smpl">t-ranking</a> = <a href="#rule.whitespace" class="smpl">OWS</a> ";" <a href="#rule.whitespace" class="smpl">OWS</a> "q=" <a href="#header.te" class="smpl">rank</a>
     
    718734  ","
    719735  ",   ,"
    720 </pre></div><div id="rfc.section.7.p.7"><p><a href="#collected.abnf" title="Collected ABNF">Appendix&nbsp;B</a> shows the collected ABNF for recipients after the list constructs have been expanded.<a class="self" href="#rfc.section.7.p.7">&para;</a></p></div></div><div id="IANA.considerations"><h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a href="#IANA.considerations">IANA Considerations</a></h1><div id="header.field.registration"><h2 id="rfc.section.8.1"><a href="#rfc.section.8.1">8.1</a>&nbsp;<a href="#header.field.registration">Header Field Registration</a></h2><div id="rfc.section.8.1.p.1"><p>HTTP header fields are registered within the "Message Headers" registry maintained at &lt;<a href="http://www.iana.org/assignments/message-headers/">http://www.iana.org/assignments/message-headers/</a>&gt;.<a class="self" href="#rfc.section.8.1.p.1">&para;</a></p></div><div id="rfc.section.8.1.p.2"><p>This document defines the following HTTP header fields, so the "Permanent Message Header Field Names" registry has been updated accordingly (see <a href="#BCP90" id="rfc.xref.BCP90.1"><cite title="Registration Procedures for Message Header Fields">[BCP90]</cite></a>).<a class="self" href="#rfc.section.8.1.p.2">&para;</a></p></div><div id="rfc.table.1"><div id="iana.header.registration.table"></div><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Header Field Name</th><th>Protocol</th><th>Status</th><th>Reference</th></tr></thead><tbody><tr><td class="left">Connection</td><td class="left">http</td><td class="left">standard</td><td class="left"><a href="#header.connection" id="rfc.xref.header.connection.6" title="Connection">Section&nbsp;6.1</a> </td></tr><tr><td class="left">Content-Length</td><td class="left">http</td><td class="left">standard</td><td class="left"><a href="#header.content-length" id="rfc.xref.header.content-length.1" title="Content-Length">Section&nbsp;3.3.2</a> </td></tr><tr><td class="left">Host</td><td class="left">http</td><td class="left">standard</td><td class="left"><a href="#header.host" id="rfc.xref.header.host.2" title="Host">Section&nbsp;5.4</a> </td></tr><tr><td class="left">TE</td><td class="left">http</td><td class="left">standard</td><td class="left"><a href="#header.te" id="rfc.xref.header.te.3" title="TE">Section&nbsp;4.3</a> </td></tr><tr><td class="left">Trailer</td><td class="left">http</td><td class="left">standard</td><td class="left"><a href="#header.trailer" id="rfc.xref.header.trailer.1" title="Trailer">Section&nbsp;4.4</a> </td></tr><tr><td class="left">Transfer-Encoding</td><td class="left">http</td><td class="left">standard</td><td class="left"><a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.3" title="Transfer-Encoding">Section&nbsp;3.3.1</a> </td></tr><tr><td class="left">Upgrade</td><td class="left">http</td><td class="left">standard</td><td class="left"><a href="#header.upgrade" id="rfc.xref.header.upgrade.2" title="Upgrade">Section&nbsp;6.7</a> </td></tr><tr><td class="left">Via</td><td class="left">http</td><td class="left">standard</td><td class="left"><a href="#header.via" id="rfc.xref.header.via.1" title="Via">Section&nbsp;5.7.1</a> </td></tr></tbody></table></div><div id="rfc.section.8.1.p.3"><p>Furthermore, the header field-name "Close" has been registered as "reserved", since using that name as an HTTP header field might conflict with the "close" connection option of the <a href="#header.connection" class="smpl">Connection</a> header field (<a href="#header.connection" id="rfc.xref.header.connection.7" title="Connection">Section&nbsp;6.1</a>).<a class="self" href="#rfc.section.8.1.p.3">&para;</a></p></div><div id="rfc.table.u.1"><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Header Field Name</th><th>Protocol</th><th>Status</th><th>Reference</th></tr></thead><tbody><tr><td class="left">Close</td><td class="left">http</td><td class="left">reserved</td><td class="left"><a href="#header.field.registration" title="Header Field Registration">Section&nbsp;8.1</a> </td></tr></tbody></table></div><div id="rfc.section.8.1.p.4"><p>The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".<a class="self" href="#rfc.section.8.1.p.4">&para;</a></p></div></div><div id="uri.scheme.registration"><h2 id="rfc.section.8.2"><a href="#rfc.section.8.2">8.2</a>&nbsp;<a href="#uri.scheme.registration">URI Scheme Registration</a></h2><div id="rfc.section.8.2.p.1"><p>IANA maintains the registry of URI Schemes <a href="#BCP115" id="rfc.xref.BCP115.1"><cite title="Guidelines and Registration Procedures for New URI Schemes">[BCP115]</cite></a> at &lt;<a href="http://www.iana.org/assignments/uri-schemes/">http://www.iana.org/assignments/uri-schemes/</a>&gt;.<a class="self" href="#rfc.section.8.2.p.1">&para;</a></p></div><div id="rfc.section.8.2.p.2"><p>This document defines the following URI schemes, so the "Permanent URI Schemes" registry has been updated accordingly.<a class="self" href="#rfc.section.8.2.p.2">&para;</a></p></div><div id="rfc.table.u.2"><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>URI Scheme</th><th>Description</th><th>Reference</th></tr></thead><tbody><tr><td class="left">http</td><td class="left">Hypertext Transfer Protocol</td><td class="left"><a href="#http.uri" title="http URI Scheme">Section&nbsp;2.7.1</a></td></tr><tr><td class="left">https</td><td class="left">Hypertext Transfer Protocol Secure</td><td class="left"><a href="#https.uri" title="https URI Scheme">Section&nbsp;2.7.2</a></td></tr></tbody></table></div></div><div id="internet.media.type.http"><h2 id="rfc.section.8.3"><a href="#rfc.section.8.3">8.3</a>&nbsp;<a href="#internet.media.type.http">Internet Media Type Registration</a></h2><div id="rfc.section.8.3.p.1"><p>IANA maintains the registry of Internet media types <a href="#BCP13" id="rfc.xref.BCP13.1"><cite title="Media Type Specifications and Registration Procedures">[BCP13]</cite></a> at &lt;<a href="http://www.iana.org/assignments/media-types">http://www.iana.org/assignments/media-types</a>&gt;.<a class="self" href="#rfc.section.8.3.p.1">&para;</a></p></div><div id="rfc.section.8.3.p.2"><p>This document serves as the specification for the Internet media types "message/http" and "application/http". The following has been registered with IANA.<a class="self" href="#rfc.section.8.3.p.2">&para;</a></p></div><div id="internet.media.type.message.http"><h3 id="rfc.section.8.3.1"><a href="#rfc.section.8.3.1">8.3.1</a>&nbsp;<a href="#internet.media.type.message.http">Internet Media Type message/http</a></h3><div id="rfc.section.8.3.1.p.1"><p>The message/http type can be used to enclose a single HTTP request or response message, provided that it obeys the MIME restrictions for all "message" types regarding line length and encodings.<a class="self" href="#rfc.section.8.3.1.p.1">&para;</a></p></div><div id="rfc.section.8.3.1.p.2"><dl><dt>Type name:</dt><dd>message</dd><dt>Subtype name:</dt><dd>http</dd><dt>Required parameters:</dt><dd>N/A</dd><dt>Optional parameters:</dt><dd>version, msgtype <dl><dt>version:</dt><dd>The HTTP-version number of the enclosed message (e.g., "1.1"). If not present, the version can be determined from the first line of the body.</dd><dt>msgtype:</dt><dd>The message type &#8212; "request" or "response". If not present, the type can be determined from the first line of the body.</dd></dl> </dd><dt>Encoding considerations:</dt><dd>only "7bit", "8bit", or "binary" are permitted</dd><dt>Security considerations:</dt><dd>see <a href="#security.considerations" title="Security Considerations">Section&nbsp;9</a> </dd><dt>Interoperability considerations:</dt><dd>N/A</dd><dt>Published specification:</dt><dd>This specification (see <a href="#internet.media.type.message.http" title="Internet Media Type message/http">Section&nbsp;8.3.1</a>).</dd><dt>Applications that use this media type:</dt><dd>N/A</dd><dt>Fragment identifier considerations:</dt><dd>N/A</dd><dt>Additional information:</dt><dd><dl><dt>Magic number(s):</dt><dd>N/A</dd><dt>Deprecated alias names for this type:</dt><dd>N/A</dd><dt>File extension(s):</dt><dd>N/A</dd><dt>Macintosh file type code(s):</dt><dd>N/A</dd></dl> </dd><dt>Person and email address to contact for further information:</dt><dd>See&nbsp;Authors'&nbsp;Addresses section.</dd><dt>Intended usage:</dt><dd>COMMON</dd><dt>Restrictions on usage:</dt><dd>N/A</dd><dt>Author:</dt><dd>See Authors' Addresses section.</dd><dt>Change controller:</dt><dd>IESG</dd></dl></div></div><div id="internet.media.type.application.http"><h3 id="rfc.section.8.3.2"><a href="#rfc.section.8.3.2">8.3.2</a>&nbsp;<a href="#internet.media.type.application.http">Internet Media Type application/http</a></h3><div id="rfc.section.8.3.2.p.1"><p>The application/http type can be used to enclose a pipeline of one or more HTTP request or response messages (not intermixed).<a class="self" href="#rfc.section.8.3.2.p.1">&para;</a></p></div><div id="rfc.section.8.3.2.p.2"><dl><dt>Type name:</dt><dd>application</dd><dt>Subtype name:</dt><dd>http</dd><dt>Required parameters:</dt><dd>N/A</dd><dt>Optional parameters:</dt><dd>version, msgtype <dl><dt>version:</dt><dd>The HTTP-version number of the enclosed messages (e.g., "1.1"). If not present, the version can be determined from the first line of the body.</dd><dt>msgtype:</dt><dd>The message type &#8212; "request" or "response". If not present, the type can be determined from the first line of the body.</dd></dl> </dd><dt>Encoding considerations:</dt><dd>HTTP messages enclosed by this type are in "binary" format; use of an appropriate Content-Transfer-Encoding is required when transmitted via email.</dd><dt>Security considerations:</dt><dd>see <a href="#security.considerations" title="Security Considerations">Section&nbsp;9</a> </dd><dt>Interoperability considerations:</dt><dd>N/A</dd><dt>Published specification:</dt><dd>This specification (see <a href="#internet.media.type.application.http" title="Internet Media Type application/http">Section&nbsp;8.3.2</a>).</dd><dt>Applications that use this media type:</dt><dd>N/A</dd><dt>Fragment identifier considerations:</dt><dd>N/A</dd><dt>Additional information:</dt><dd><dl><dt>Deprecated alias names for this type:</dt><dd>N/A</dd><dt>Magic number(s):</dt><dd>N/A</dd><dt>File extension(s):</dt><dd>N/A</dd><dt>Macintosh file type code(s):</dt><dd>N/A</dd></dl> </dd><dt>Person and email address to contact for further information:</dt><dd>See&nbsp;Authors'&nbsp;Addresses section.</dd><dt>Intended usage:</dt><dd>COMMON</dd><dt>Restrictions on usage:</dt><dd>N/A</dd><dt>Author:</dt><dd>See Authors' Addresses section.</dd><dt>Change controller:</dt><dd>IESG</dd></dl></div></div></div><div id="transfer.coding.registry"><h2 id="rfc.section.8.4"><a href="#rfc.section.8.4">8.4</a>&nbsp;<a href="#transfer.coding.registry">Transfer Coding Registry</a></h2><div id="rfc.section.8.4.p.1"><p>The "HTTP Transfer Coding Registry" defines the namespace for transfer coding names. It is maintained at &lt;<a href="http://www.iana.org/assignments/http-parameters">http://www.iana.org/assignments/http-parameters</a>&gt;.<a class="self" href="#rfc.section.8.4.p.1">&para;</a></p></div><div id="transfer.coding.registry.procedure"><h3 id="rfc.section.8.4.1"><a href="#rfc.section.8.4.1">8.4.1</a>&nbsp;<a href="#transfer.coding.registry.procedure">Procedure</a></h3><div id="rfc.section.8.4.1.p.1"><p>Registrations <em class="bcp14">MUST</em> include the following fields: <a class="self" href="#rfc.section.8.4.1.p.1">&para;</a></p><ul><li>Name</li><li>Description</li><li>Pointer to specification text</li></ul></div><div id="rfc.section.8.4.1.p.2"><p>Names of transfer codings <em class="bcp14">MUST NOT</em> overlap with names of content codings (<a href="rfc7231.html#content.codings" title="Content Codings">Section 3.1.2.1</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.33"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a>) unless the encoding transformation is identical, as is the case for the compression codings defined in <a href="#compression.codings" title="Compression Codings">Section&nbsp;4.2</a>.<a class="self" href="#rfc.section.8.4.1.p.2">&para;</a></p></div><div id="rfc.section.8.4.1.p.3"><p>Values to be added to this namespace require IETF Review (see <a href="https://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a> of <a href="#RFC5226" id="rfc.xref.RFC5226.1"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>), and <em class="bcp14">MUST</em> conform to the purpose of transfer coding defined in this specification.<a class="self" href="#rfc.section.8.4.1.p.3">&para;</a></p></div><div id="rfc.section.8.4.1.p.4"><p>Use of program names for the identification of encoding formats is not desirable and is discouraged for future encodings.<a class="self" href="#rfc.section.8.4.1.p.4">&para;</a></p></div></div><div id="transfer.coding.registration"><h3 id="rfc.section.8.4.2"><a href="#rfc.section.8.4.2">8.4.2</a>&nbsp;<a href="#transfer.coding.registration">Registration</a></h3><div id="rfc.section.8.4.2.p.1"><p>The "HTTP Transfer Coding Registry" has been updated with the registrations below:<a class="self" href="#rfc.section.8.4.2.p.1">&para;</a></p></div><div id="rfc.table.2"><div id="iana.transfer.coding.registration.table"></div><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Name</th><th>Description</th><th>Reference</th></tr></thead><tbody><tr><td class="left">chunked</td><td class="left">Transfer in a series of chunks</td><td class="left"><a href="#chunked.encoding" title="Chunked Transfer Coding">Section&nbsp;4.1</a> </td></tr><tr><td class="left">compress</td><td class="left">UNIX "compress" data format <a href="#Welch" id="rfc.xref.Welch.2"><cite title="A Technique for High-Performance Data Compression">[Welch]</cite></a></td><td class="left"><a href="#compress.coding" title="Compress Coding">Section&nbsp;4.2.1</a> </td></tr><tr><td class="left">deflate</td><td class="left">"deflate" compressed data (<a href="#RFC1951" id="rfc.xref.RFC1951.2"><cite title="DEFLATE Compressed Data Format Specification version 1.3">[RFC1951]</cite></a>) inside the "zlib" data format (<a href="#RFC1950" id="rfc.xref.RFC1950.2"><cite title="ZLIB Compressed Data Format Specification version 3.3">[RFC1950]</cite></a>)</td><td class="left"><a href="#deflate.coding" title="Deflate Coding">Section&nbsp;4.2.2</a> </td></tr><tr><td class="left">gzip</td><td class="left">GZIP file format <a href="#RFC1952" id="rfc.xref.RFC1952.2"><cite title="GZIP file format specification version 4.3">[RFC1952]</cite></a></td><td class="left"><a href="#gzip.coding" title="Gzip Coding">Section&nbsp;4.2.3</a> </td></tr><tr><td class="left">x-compress</td><td class="left">Deprecated (alias for compress)</td><td class="left"><a href="#compress.coding" title="Compress Coding">Section&nbsp;4.2.1</a> </td></tr><tr><td class="left">x-gzip</td><td class="left">Deprecated (alias for gzip)</td><td class="left"><a href="#gzip.coding" title="Gzip Coding">Section&nbsp;4.2.3</a> </td></tr></tbody></table></div></div></div><div id="content.coding.registration"><h2 id="rfc.section.8.5"><a href="#rfc.section.8.5">8.5</a>&nbsp;<a href="#content.coding.registration">Content Coding Registration</a></h2><div id="rfc.section.8.5.p.1"><p>IANA maintains the "HTTP Content Coding Registry" at &lt;<a href="http://www.iana.org/assignments/http-parameters">http://www.iana.org/assignments/http-parameters</a>&gt;.<a class="self" href="#rfc.section.8.5.p.1">&para;</a></p></div><div id="rfc.section.8.5.p.2"><p>The "HTTP Content Coding Registry" has been updated with the registrations below:<a class="self" href="#rfc.section.8.5.p.2">&para;</a></p></div><div id="rfc.table.3"><div id="iana.content.coding.registration.table"></div><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Name</th><th>Description</th><th>Reference</th></tr></thead><tbody><tr><td class="left">compress</td><td class="left">UNIX "compress" data format <a href="#Welch" id="rfc.xref.Welch.3"><cite title="A Technique for High-Performance Data Compression">[Welch]</cite></a></td><td class="left"><a href="#compress.coding" title="Compress Coding">Section&nbsp;4.2.1</a> </td></tr><tr><td class="left">deflate</td><td class="left">"deflate" compressed data (<a href="#RFC1951" id="rfc.xref.RFC1951.3"><cite title="DEFLATE Compressed Data Format Specification version 1.3">[RFC1951]</cite></a>) inside the "zlib" data format (<a href="#RFC1950" id="rfc.xref.RFC1950.3"><cite title="ZLIB Compressed Data Format Specification version 3.3">[RFC1950]</cite></a>)</td><td class="left"><a href="#deflate.coding" title="Deflate Coding">Section&nbsp;4.2.2</a> </td></tr><tr><td class="left">gzip</td><td class="left">GZIP file format <a href="#RFC1952" id="rfc.xref.RFC1952.3"><cite title="GZIP file format specification version 4.3">[RFC1952]</cite></a></td><td class="left"><a href="#gzip.coding" title="Gzip Coding">Section&nbsp;4.2.3</a> </td></tr><tr><td class="left">x-compress</td><td class="left">Deprecated (alias for compress)</td><td class="left"><a href="#compress.coding" title="Compress Coding">Section&nbsp;4.2.1</a> </td></tr><tr><td class="left">x-gzip</td><td class="left">Deprecated (alias for gzip)</td><td class="left"><a href="#gzip.coding" title="Gzip Coding">Section&nbsp;4.2.3</a> </td></tr></tbody></table></div></div><div id="upgrade.token.registry"><h2 id="rfc.section.8.6"><a href="#rfc.section.8.6">8.6</a>&nbsp;<a href="#upgrade.token.registry">Upgrade Token Registry</a></h2><div id="rfc.section.8.6.p.1"><p>The "Hypertext Transfer Protocol (HTTP) Upgrade Token Registry" defines the namespace for protocol-name tokens used to identify protocols in the <a href="#header.upgrade" class="smpl">Upgrade</a> header field. The registry is maintained at &lt;<a href="http://www.iana.org/assignments/http-upgrade-tokens">http://www.iana.org/assignments/http-upgrade-tokens</a>&gt;.<a class="self" href="#rfc.section.8.6.p.1">&para;</a></p></div><div id="upgrade.token.registry.procedure"><h3 id="rfc.section.8.6.1"><a href="#rfc.section.8.6.1">8.6.1</a>&nbsp;<a href="#upgrade.token.registry.procedure">Procedure</a></h3><div id="rfc.section.8.6.1.p.1"><p>Each registered protocol name is associated with contact information and an optional set of specifications that details how the connection will be processed after it has been upgraded.<a class="self" href="#rfc.section.8.6.1.p.1">&para;</a></p></div><div id="rfc.section.8.6.1.p.2"><p>Registrations happen on a "First Come First Served" basis (see <a href="https://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a> of <a href="#RFC5226" id="rfc.xref.RFC5226.2"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>) and are subject to the following rules: <a class="self" href="#rfc.section.8.6.1.p.2">&para;</a></p><ol><li>A protocol-name token, once registered, stays registered forever.</li><li>The registration <em class="bcp14">MUST</em> name a responsible party for the registration.</li><li>The registration <em class="bcp14">MUST</em> name a point of contact.</li><li>The registration <em class="bcp14">MAY</em> name a set of specifications associated with that token. Such specifications need not be publicly available.</li><li>The registration <em class="bcp14">SHOULD</em> name a set of expected "protocol-version" tokens associated with that token at the time of registration.</li><li>The responsible party <em class="bcp14">MAY</em> change the registration at any time. The IANA will keep a record of all such changes, and make them available upon request.</li><li>The IESG <em class="bcp14">MAY</em> reassign responsibility for a protocol token. This will normally only be used in the case when a responsible party cannot be contacted.</li></ol></div><div id="rfc.section.8.6.1.p.3"><p>This registration procedure for HTTP Upgrade Tokens replaces that previously defined in <a href="https://tools.ietf.org/html/rfc2817#section-7.2">Section 7.2</a> of <a href="#RFC2817" id="rfc.xref.RFC2817.2"><cite title="Upgrading to TLS Within HTTP/1.1">[RFC2817]</cite></a>.<a class="self" href="#rfc.section.8.6.1.p.3">&para;</a></p></div></div><div id="upgrade.token.registration"><h3 id="rfc.section.8.6.2"><a href="#rfc.section.8.6.2">8.6.2</a>&nbsp;<a href="#upgrade.token.registration">Upgrade Token Registration</a></h3><div id="rfc.section.8.6.2.p.1"><p>The "HTTP" entry in the upgrade token registry has been updated with the registration below:<a class="self" href="#rfc.section.8.6.2.p.1">&para;</a></p></div><div id="rfc.table.u.3"><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Value</th><th>Description</th><th>Expected Version Tokens</th><th>Reference</th></tr></thead><tbody><tr><td class="left">HTTP</td><td class="left">Hypertext Transfer Protocol</td><td class="left">any DIGIT.DIGIT (e.g, "2.0")</td><td class="left"><a href="#http.version" title="Protocol Versioning">Section&nbsp;2.6</a></td></tr></tbody></table></div><div id="rfc.section.8.6.2.p.2"><p>The responsible party is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".<a class="self" href="#rfc.section.8.6.2.p.2">&para;</a></p></div></div></div></div><div id="security.considerations"><h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a>&nbsp;<a href="#security.considerations">Security Considerations</a></h1><div id="rfc.section.9.p.1"><p>This section is meant to inform developers, information providers, and users of known security considerations relevant to HTTP message syntax, parsing, and routing. Security considerations about HTTP semantics and payloads are addressed in <a href="#RFC7231" id="rfc.xref.RFC7231.34"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a>.<a class="self" href="#rfc.section.9.p.1">&para;</a></p></div><div id="establishing.authority"><h2 id="rfc.section.9.1"><a href="#rfc.section.9.1">9.1</a>&nbsp;<a href="#establishing.authority">Establishing Authority</a></h2><div id="rfc.section.9.1.p.1"><p>HTTP relies on the notion of an <dfn>authoritative response</dfn>: a response that has been determined by (or at the direction of) the authority identified within the target URI to be the most appropriate response for that request given the state of the target resource at the time of response message origination. Providing a response from a non-authoritative source, such as a shared cache, is often useful to improve performance and availability, but only to the extent that the source can be trusted or the distrusted response can be safely used.<a class="self" href="#rfc.section.9.1.p.1">&para;</a></p></div><div id="rfc.section.9.1.p.2"><p>Unfortunately, establishing authority can be difficult. For example, <dfn>phishing</dfn> is an attack on the user's perception of authority, where that perception can be misled by presenting similar branding in hypertext, possibly aided by userinfo obfuscating the authority component (see <a href="#http.uri" title="http URI Scheme">Section&nbsp;2.7.1</a>). User agents can reduce the impact of phishing attacks by enabling users to easily inspect a target URI prior to making an action, by prominently distinguishing (or rejecting) userinfo when present, and by not sending stored credentials and cookies when the referring document is from an unknown or untrusted source.<a class="self" href="#rfc.section.9.1.p.2">&para;</a></p></div><div id="rfc.section.9.1.p.3"><p>When a registered name is used in the authority component, the "http" URI scheme (<a href="#http.uri" title="http URI Scheme">Section&nbsp;2.7.1</a>) relies on the user's local name resolution service to determine where it can find authoritative responses. This means that any attack on a user's network host table, cached names, or name resolution libraries becomes an avenue for attack on establishing authority. Likewise, the user's choice of server for Domain Name Service (DNS), and the hierarchy of servers from which it obtains resolution results, could impact the authenticity of address mappings; DNS Security Extensions (DNSSEC, <a href="#RFC4033" id="rfc.xref.RFC4033.1"><cite title="DNS Security Introduction and Requirements">[RFC4033]</cite></a>) are one way to improve authenticity.<a class="self" href="#rfc.section.9.1.p.3">&para;</a></p></div><div id="rfc.section.9.1.p.4"><p>Furthermore, after an IP address is obtained, establishing authority for an "http" URI is vulnerable to attacks on Internet Protocol routing.<a class="self" href="#rfc.section.9.1.p.4">&para;</a></p></div><div id="rfc.section.9.1.p.5"><p>The "https" scheme (<a href="#https.uri" title="https URI Scheme">Section&nbsp;2.7.2</a>) is intended to prevent (or at least reveal) many of these potential attacks on establishing authority, provided that the negotiated TLS connection is secured and the client properly verifies that the communicating server's identity matches the target URI's authority component (see <a href="#RFC2818" id="rfc.xref.RFC2818.3"><cite title="HTTP Over TLS">[RFC2818]</cite></a>). Correctly implementing such verification can be difficult (see <a href="#Georgiev" id="rfc.xref.Georgiev.1"><cite title="The Most Dangerous Code in the World: Validating SSL Certificates in Non-browser Software">[Georgiev]</cite></a>).<a class="self" href="#rfc.section.9.1.p.5">&para;</a></p></div></div><div id="risks.intermediaries"><h2 id="rfc.section.9.2"><a href="#rfc.section.9.2">9.2</a>&nbsp;<a href="#risks.intermediaries">Risks of Intermediaries</a></h2><div id="rfc.section.9.2.p.1"><p>By their very nature, HTTP intermediaries are men-in-the-middle and, thus, represent an opportunity for man-in-the-middle attacks. Compromise of the systems on which the intermediaries run can result in serious security and privacy problems. Intermediaries might have access to security-related information, personal information about individual users and organizations, and proprietary information belonging to users and content providers. A compromised intermediary, or an intermediary implemented or configured without regard to security and privacy considerations, might be used in the commission of a wide range of potential attacks.<a class="self" href="#rfc.section.9.2.p.1">&para;</a></p></div><div id="rfc.section.9.2.p.2"><p>Intermediaries that contain a shared cache are especially vulnerable to cache poisoning attacks, as described in <a href="rfc7234.html#security.considerations" title="Security Considerations">Section 8</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.8"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>.<a class="self" href="#rfc.section.9.2.p.2">&para;</a></p></div><div id="rfc.section.9.2.p.3"><p>Implementers need to consider the privacy and security implications of their design and coding decisions, and of the configuration options they provide to operators (especially the default configuration).<a class="self" href="#rfc.section.9.2.p.3">&para;</a></p></div><div id="rfc.section.9.2.p.4"><p>Users need to be aware that intermediaries are no more trustworthy than the people who run them; HTTP itself cannot solve this problem.<a class="self" href="#rfc.section.9.2.p.4">&para;</a></p></div></div><div id="attack.protocol.element.length"><h2 id="rfc.section.9.3"><a href="#rfc.section.9.3">9.3</a>&nbsp;<a href="#attack.protocol.element.length">Attacks via Protocol Element Length</a></h2><div id="rfc.section.9.3.p.1"><p>Because HTTP uses mostly textual, character-delimited fields, parsers are often vulnerable to attacks based on sending very long (or very slow) streams of data, particularly where an implementation is expecting a protocol element with no predefined length.<a class="self" href="#rfc.section.9.3.p.1">&para;</a></p></div><div id="rfc.section.9.3.p.2"><p>To promote interoperability, specific recommendations are made for minimum size limits on request-line (<a href="#request.line" title="Request Line">Section&nbsp;3.1.1</a>) and header fields (<a href="#header.fields" title="Header Fields">Section&nbsp;3.2</a>). These are minimum recommendations, chosen to be supportable even by implementations with limited resources; it is expected that most implementations will choose substantially higher limits.<a class="self" href="#rfc.section.9.3.p.2">&para;</a></p></div><div id="rfc.section.9.3.p.3"><p>A server can reject a message that has a request-target that is too long (<a href="rfc7231.html#status.414" title="414 URI Too Long">Section 6.5.12</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.35"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a>) or a request payload that is too large (<a href="rfc7231.html#status.413" title="413 Payload Too Large">Section 6.5.11</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.36"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a>). Additional status codes related to capacity limits have been defined by extensions to HTTP <a href="#RFC6585" id="rfc.xref.RFC6585.1"><cite title="Additional HTTP Status Codes">[RFC6585]</cite></a>.<a class="self" href="#rfc.section.9.3.p.3">&para;</a></p></div><div id="rfc.section.9.3.p.4"><p>Recipients ought to carefully limit the extent to which they process other protocol elements, including (but not limited to) request methods, response status phrases, header field-names, numeric values, and body chunks. Failure to limit such processing can result in buffer overflows, arithmetic overflows, or increased vulnerability to denial-of-service attacks.<a class="self" href="#rfc.section.9.3.p.4">&para;</a></p></div></div><div id="response.splitting"><h2 id="rfc.section.9.4"><a href="#rfc.section.9.4">9.4</a>&nbsp;<a href="#response.splitting">Response Splitting</a></h2><div id="rfc.section.9.4.p.1"><p>Response splitting (a.k.a, CRLF injection) is a common technique, used in various attacks on Web usage, that exploits the line-based nature of HTTP message framing and the ordered association of requests to responses on persistent connections <a href="#Klein" id="rfc.xref.Klein.1"><cite title="Divide and Conquer - HTTP Response Splitting, Web Cache Poisoning Attacks, and Related Topics">[Klein]</cite></a>. This technique can be particularly damaging when the requests pass through a shared cache.<a class="self" href="#rfc.section.9.4.p.1">&para;</a></p></div><div id="rfc.section.9.4.p.2"><p>Response splitting exploits a vulnerability in servers (usually within an application server) where an attacker can send encoded data within some parameter of the request that is later decoded and echoed within any of the response header fields of the response. If the decoded data is crafted to look like the response has ended and a subsequent response has begun, the response has been split and the content within the apparent second response is controlled by the attacker. The attacker can then make any other request on the same persistent connection and trick the recipients (including intermediaries) into believing that the second half of the split is an authoritative answer to the second request.<a class="self" href="#rfc.section.9.4.p.2">&para;</a></p></div><div id="rfc.section.9.4.p.3"><p>For example, a parameter within the request-target might be read by an application server and reused within a redirect, resulting in the same parameter being echoed in the <a href="rfc7231.html#header.location" class="smpl">Location</a> header field of the response. If the parameter is decoded by the application and not properly encoded when placed in the response field, the attacker can send encoded CRLF octets and other content that will make the application's single response look like two or more responses.<a class="self" href="#rfc.section.9.4.p.3">&para;</a></p></div><div id="rfc.section.9.4.p.4"><p>A common defense against response splitting is to filter requests for data that looks like encoded CR and LF (e.g., "%0D" and "%0A"). However, that assumes the application server is only performing URI decoding, rather than more obscure data transformations like charset transcoding, XML entity translation, base64 decoding, sprintf reformatting, etc. A more effective mitigation is to prevent anything other than the server's core protocol libraries from sending a CR or LF within the header section, which means restricting the output of header fields to APIs that filter for bad octets and not allowing application servers to write directly to the protocol stream.<a class="self" href="#rfc.section.9.4.p.4">&para;</a></p></div></div><div id="request.smuggling"><h2 id="rfc.section.9.5"><a href="#rfc.section.9.5">9.5</a>&nbsp;<a href="#request.smuggling">Request Smuggling</a></h2><div id="rfc.section.9.5.p.1"><p>Request smuggling (<a href="#Linhart" id="rfc.xref.Linhart.1"><cite title="HTTP Request Smuggling">[Linhart]</cite></a>) is a technique that exploits differences in protocol parsing among various recipients to hide additional requests (which might otherwise be blocked or disabled by policy) within an apparently harmless request. Like response splitting, request smuggling can lead to a variety of attacks on HTTP usage.<a class="self" href="#rfc.section.9.5.p.1">&para;</a></p></div><div id="rfc.section.9.5.p.2"><p>This specification has introduced new requirements on request parsing, particularly with regard to message framing in <a href="#message.body.length" title="Message Body Length">Section&nbsp;3.3.3</a>, to reduce the effectiveness of request smuggling.<a class="self" href="#rfc.section.9.5.p.2">&para;</a></p></div></div><div id="message.integrity"><h2 id="rfc.section.9.6"><a href="#rfc.section.9.6">9.6</a>&nbsp;<a href="#message.integrity">Message Integrity</a></h2><div id="rfc.section.9.6.p.1"><p>HTTP does not define a specific mechanism for ensuring message integrity, instead relying on the error-detection ability of underlying transport protocols and the use of length or chunk-delimited framing to detect completeness. Additional integrity mechanisms, such as hash functions or digital signatures applied to the content, can be selectively added to messages via extensible metadata header fields. Historically, the lack of a single integrity mechanism has been justified by the informal nature of most HTTP communication. However, the prevalence of HTTP as an information access mechanism has resulted in its increasing use within environments where verification of message integrity is crucial.<a class="self" href="#rfc.section.9.6.p.1">&para;</a></p></div><div id="rfc.section.9.6.p.2"><p>User agents are encouraged to implement configurable means for detecting and reporting failures of message integrity such that those means can be enabled within environments for which integrity is necessary. For example, a browser being used to view medical history or drug interaction information needs to indicate to the user when such information is detected by the protocol to be incomplete, expired, or corrupted during transfer. Such mechanisms might be selectively enabled via user agent extensions or the presence of message integrity metadata in a response. At a minimum, user agents ought to provide some indication that allows a user to distinguish between a complete and incomplete response message (<a href="#incomplete.messages" title="Handling Incomplete Messages">Section&nbsp;3.4</a>) when such verification is desired.<a class="self" href="#rfc.section.9.6.p.2">&para;</a></p></div></div><div id="message.confidentiality"><h2 id="rfc.section.9.7"><a href="#rfc.section.9.7">9.7</a>&nbsp;<a href="#message.confidentiality">Message Confidentiality</a></h2><div id="rfc.section.9.7.p.1"><p>HTTP relies on underlying transport protocols to provide message confidentiality when that is desired. HTTP has been specifically designed to be independent of the transport protocol, such that it can be used over many different forms of encrypted connection, with the selection of such transports being identified by the choice of URI scheme or within user agent configuration.<a class="self" href="#rfc.section.9.7.p.1">&para;</a></p></div><div id="rfc.section.9.7.p.2"><p>The "https" scheme can be used to identify resources that require a confidential connection, as described in <a href="#https.uri" title="https URI Scheme">Section&nbsp;2.7.2</a>.<a class="self" href="#rfc.section.9.7.p.2">&para;</a></p></div></div><div id="privacy.of.server.log.information"><h2 id="rfc.section.9.8"><a href="#rfc.section.9.8">9.8</a>&nbsp;<a href="#privacy.of.server.log.information">Privacy of Server Log Information</a></h2><div id="rfc.section.9.8.p.1"><p>A server is in the position to save personal data about a user's requests over time, which might identify their reading patterns or subjects of interest. In particular, log information gathered at an intermediary often contains a history of user agent interaction, across a multitude of sites, that can be traced to individual users.<a class="self" href="#rfc.section.9.8.p.1">&para;</a></p></div><div id="rfc.section.9.8.p.2"><p>HTTP log information is confidential in nature; its handling is often constrained by laws and regulations. Log information needs to be securely stored and appropriate guidelines followed for its analysis. Anonymization of personal information within individual entries helps, but it is generally not sufficient to prevent real log traces from being re-identified based on correlation with other access characteristics. As such, access traces that are keyed to a specific client are unsafe to publish even if the key is pseudonymous.<a class="self" href="#rfc.section.9.8.p.2">&para;</a></p></div><div id="rfc.section.9.8.p.3"><p>To minimize the risk of theft or accidental publication, log information ought to be purged of personally identifiable information, including user identifiers, IP addresses, and user-provided query parameters, as soon as that information is no longer necessary to support operational needs for security, auditing, or fraud control.<a class="self" href="#rfc.section.9.8.p.3">&para;</a></p></div></div></div><div id="acks"><h1 id="rfc.section.10"><a href="#rfc.section.10">10.</a>&nbsp;<a href="#acks">Acknowledgments</a></h1><div id="rfc.section.10.p.1"><p>This edition of HTTP/1.1 builds on the many contributions that went into <a href="#RFC1945" id="rfc.xref.RFC1945.2">RFC 1945</a>, <a href="#RFC2068" id="rfc.xref.RFC2068.3">RFC 2068</a>, <a href="#RFC2145" id="rfc.xref.RFC2145.2">RFC 2145</a>, and <a href="#RFC2616" id="rfc.xref.RFC2616.3">RFC 2616</a>, including substantial contributions made by the previous authors, editors, and Working Group Chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding, Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter, and Paul J. Leach. Mark Nottingham oversaw this effort as Working Group Chair.<a class="self" href="#rfc.section.10.p.1">&para;</a></p></div><div id="rfc.section.10.p.2"><p>Since 1999, the following contributors have helped improve the HTTP specification by reporting bugs, asking smart questions, drafting or reviewing text, and evaluating open issues:<a class="self" href="#rfc.section.10.p.2">&para;</a></p></div><div id="rfc.section.10.p.3"><p>Adam Barth, Adam Roach, Addison Phillips, Adrian Chadd, Adrian Cole, Adrien W. de Croy, Alan Ford, Alan Ruttenberg, Albert Lunde, Alek Storm, Alex Rousskov, Alexandre Morgaut, Alexey Melnikov, Alisha Smith, Amichai Rothman, Amit Klein, Amos Jeffries, Andreas Maier, Andreas Petersson, Andrei Popov, Anil Sharma, Anne van Kesteren, Anthony Bryan, Asbjorn Ulsberg, Ashok Kumar, Balachander Krishnamurthy, Barry Leiba, Ben Laurie, Benjamin Carlyle, Benjamin Niven-Jenkins, Benoit Claise, Bil Corry, Bill Burke, Bjoern Hoehrmann, Bob Scheifler, Boris Zbarsky, Brett Slatkin, Brian Kell, Brian McBarron, Brian Pane, Brian Raymor, Brian Smith, Bruce Perens, Bryce Nesbitt, Cameron Heavon-Jones, Carl Kugler, Carsten Bormann, Charles Fry, Chris Burdess, Chris Newman, Christian Huitema, Cyrus Daboo, Dale Robert Anderson, Dan Wing, Dan Winship, Daniel Stenberg, Darrel Miller, Dave Cridland, Dave Crocker, Dave Kristol, Dave Thaler, David Booth, David Singer, David W. Morris, Diwakar Shetty, Dmitry Kurochkin, Drummond Reed, Duane Wessels, Edward Lee, Eitan Adler, Eliot Lear, Emile Stephan, Eran Hammer-Lahav, Eric D. Williams, Eric J. Bowman, Eric Lawrence, Eric Rescorla, Erik Aronesty, EungJun Yi, Evan Prodromou, Felix Geisendoerfer, Florian Weimer, Frank Ellermann, Fred Akalin, Fred Bohle, Frederic Kayser, Gabor Molnar, Gabriel Montenegro, Geoffrey Sneddon, Gervase Markham, Gili Tzabari, Grahame Grieve, Greg Slepak, Greg Wilkins, Grzegorz Calkowski, Harald Tveit Alvestrand, Harry Halpin, Helge Hess, Henrik Nordstrom, Henry S. Thompson, Henry Story, Herbert van de Sompel, Herve Ruellan, Howard Melman, Hugo Haas, Ian Fette, Ian Hickson, Ido Safruti, Ilari Liusvaara, Ilya Grigorik, Ingo Struck, J. Ross Nicoll, James Cloos, James H. Manger, James Lacey, James M. Snell, Jamie Lokier, Jan Algermissen, Jari Arkko, Jeff Hodges (who came up with the term 'effective Request-URI'), Jeff Pinner, Jeff Walden, Jim Luther, Jitu Padhye, Joe D. Williams, Joe Gregorio, Joe Orton, Joel Jaeggli, John C. Klensin, John C. Mallery, John Cowan, John Kemp, John Panzer, John Schneider, John Stracke, John Sullivan, Jonas Sicking, Jonathan A. Rees, Jonathan Billington, Jonathan Moore, Jonathan Silvera, Jordi Ros, Joris Dobbelsteen, Josh Cohen, Julien Pierre, Jungshik Shin, Justin Chapweske, Justin Erenkrantz, Justin James, Kalvinder Singh, Karl Dubost, Kathleen Moriarty, Keith Hoffman, Keith Moore, Ken Murchison, Koen Holtman, Konstantin Voronkov, Kris Zyp, Leif Hedstrom, Lionel Morand, Lisa Dusseault, Maciej Stachowiak, Manu Sporny, Marc Schneider, Marc Slemko, Mark Baker, Mark Pauley, Mark Watson, Markus Isomaki, Markus Lanthaler, Martin J. Duerst, Martin Musatov, Martin Nilsson, Martin Thomson, Matt Lynch, Matthew Cox, Matthew Kerwin, Max Clark, Menachem Dodge, Meral Shirazipour, Michael Burrows, Michael Hausenblas, Michael Scharf, Michael Sweet, Michael Tuexen, Michael Welzl, Mike Amundsen, Mike Belshe, Mike Bishop, Mike Kelly, Mike Schinkel, Miles Sabin, Murray S. Kucherawy, Mykyta Yevstifeyev, Nathan Rixham, Nicholas Shanks, Nico Williams, Nicolas Alvarez, Nicolas Mailhot, Noah Slater, Osama Mazahir, Pablo Castro, Pat Hayes, Patrick R. McManus, Paul E. Jones, Paul Hoffman, Paul Marquess, Pete Resnick, Peter Lepeska, Peter Occil, Peter Saint-Andre, Peter Watkins, Phil Archer, Phil Hunt, Philippe Mougin, Phillip Hallam-Baker, Piotr Dobrogost, Poul-Henning Kamp, Preethi Natarajan, Rajeev Bector, Ray Polk, Reto Bachmann-Gmuer, Richard Barnes, Richard Cyganiak, Rob Trace, Robby Simpson, Robert Brewer, Robert Collins, Robert Mattson, Robert O'Callahan, Robert Olofsson, Robert Sayre, Robert Siemer, Robert de Wilde, Roberto Javier Godoy, Roberto Peon, Roland Zink, Ronny Widjaja, Ryan Hamilton, S. Mike Dierken, Salvatore Loreto, Sam Johnston, Sam Pullara, Sam Ruby, Saurabh Kulkarni, Scott Lawrence (who maintained the original issues list), Sean B. Palmer, Sean Turner, Sebastien Barnoud, Shane McCarron, Shigeki Ohtsu, Simon Yarde, Stefan Eissing, Stefan Tilkov, Stefanos Harhalakis, Stephane Bortzmeyer, Stephen Farrell, Stephen Kent, Stephen Ludin, Stuart Williams, Subbu Allamaraju, Subramanian Moonesamy, Susan Hares, Sylvain Hellegouarch, Tapan Divekar, Tatsuhiro Tsujikawa, Tatsuya Hayashi, Ted Hardie, Ted Lemon, Thomas Broyer, Thomas Fossati, Thomas Maslen, Thomas Nadeau, Thomas Nordin, Thomas Roessler, Tim Bray, Tim Morgan, Tim Olsen, Tom Zhou, Travis Snoozy, Tyler Close, Vincent Murphy, Wenbo Zhu, Werner Baumann, Wilbur Streett, Wilfredo Sanchez Vega, William A. Rowe Jr., William Chan, Willy Tarreau, Xiaoshu Wang, Yaron Goland, Yngve Nysaeter Pettersen, Yoav Nir, Yogesh Bang, Yuchung Cheng, Yutaka Oiwa, Yves Lafon (long-time member of the editor team), Zed A. Shaw, and Zhong Yu.<a class="self" href="#rfc.section.10.p.3">&para;</a></p></div><div id="rfc.section.10.p.4"><p>See <a href="https://tools.ietf.org/html/rfc2616#section-16">Section 16</a> of <a href="#RFC2616" id="rfc.xref.RFC2616.4"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a> for additional acknowledgements from prior revisions.<a class="self" href="#rfc.section.10.p.4">&para;</a></p></div></div><h1 id="rfc.references"><a id="rfc.section.11" href="#rfc.section.11">11.</a> References</h1><h2 id="rfc.references.1"><a href="#rfc.section.11.1" id="rfc.section.11.1">11.1</a> Normative References</h2><table><tr><td class="reference"><b id="RFC0793">[RFC0793]</b></td><td class="top">Postel, J., &#8220;<a href="https://tools.ietf.org/html/rfc793">Transmission Control Protocol</a>&#8221;, STD&nbsp;7, RFC&nbsp;793, September&nbsp;1981.</td></tr><tr><td class="reference"><b id="RFC1950">[RFC1950]</b></td><td class="top">Deutsch, L. and J-L. Gailly, &#8220;<a href="https://tools.ietf.org/html/rfc1950">ZLIB Compressed Data Format Specification version 3.3</a>&#8221;, RFC&nbsp;1950, May&nbsp;1996.</td></tr><tr><td class="reference"><b id="RFC1951">[RFC1951]</b></td><td class="top">Deutsch, P., &#8220;<a href="https://tools.ietf.org/html/rfc1951">DEFLATE Compressed Data Format Specification version 1.3</a>&#8221;, RFC&nbsp;1951, May&nbsp;1996.</td></tr><tr><td class="reference"><b id="RFC1952">[RFC1952]</b></td><td class="top">Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and G. Randers-Pehrson, &#8220;<a href="https://tools.ietf.org/html/rfc1952">GZIP file format specification version 4.3</a>&#8221;, RFC&nbsp;1952, May&nbsp;1996.</td></tr><tr><td class="reference"><b id="RFC2119">[RFC2119]</b></td><td class="top">Bradner, S., &#8220;<a href="https://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>&#8221;, BCP&nbsp;14, RFC&nbsp;2119, March&nbsp;1997.</td></tr><tr><td class="reference"><b id="RFC3986">[RFC3986]</b></td><td class="top">Berners-Lee, T., Fielding, R., and L. Masinter, &#8220;<a href="https://tools.ietf.org/html/rfc3986">Uniform Resource Identifier (URI): Generic Syntax</a>&#8221;, STD&nbsp;66, RFC&nbsp;3986, January&nbsp;2005.</td></tr><tr><td class="reference"><b id="RFC5234">[RFC5234]</b></td><td class="top">Crocker, D., Ed. and P. Overell, &#8220;<a href="https://tools.ietf.org/html/rfc5234">Augmented BNF for Syntax Specifications: ABNF</a>&#8221;, STD&nbsp;68, RFC&nbsp;5234, January&nbsp;2008.</td></tr><tr><td class="reference"><b id="RFC7231">[RFC7231]</b></td><td class="top">Fielding, R., Ed. and J. Reschke, Ed., &#8220;<a href="https://tools.ietf.org/html/rfc7231">Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</a>&#8221;, RFC&nbsp;7231, June&nbsp;2014.</td></tr><tr><td class="reference"><b id="RFC7232">[RFC7232]</b></td><td class="top">Fielding, R., Ed. and J. Reschke, Ed., &#8220;<a href="https://tools.ietf.org/html/rfc7232">Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests</a>&#8221;, RFC&nbsp;7232, June&nbsp;2014.</td></tr><tr><td class="reference"><b id="RFC7233">[RFC7233]</b></td><td class="top">Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed., &#8220;<a href="https://tools.ietf.org/html/rfc7233">Hypertext Transfer Protocol (HTTP/1.1): Range Requests</a>&#8221;, RFC&nbsp;7233, June&nbsp;2014.</td></tr><tr><td class="reference"><b id="RFC7234">[RFC7234]</b></td><td class="top">Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., &#8220;<a href="https://tools.ietf.org/html/rfc7234">Hypertext Transfer Protocol (HTTP/1.1): Caching</a>&#8221;, RFC&nbsp;7234, June&nbsp;2014.</td></tr><tr><td class="reference"><b id="RFC7235">[RFC7235]</b></td><td class="top">Fielding, R., Ed. and J. Reschke, Ed., &#8220;<a href="https://tools.ietf.org/html/rfc7235">Hypertext Transfer Protocol (HTTP/1.1): Authentication</a>&#8221;, RFC&nbsp;7235, June&nbsp;2014.</td></tr><tr><td class="reference"><b id="USASCII">[USASCII]</b></td><td class="top">American National Standards Institute, &#8220;Coded Character Set -- 7-bit American Standard Code for Information Interchange&#8221;, ANSI&nbsp;X3.4, 1986.</td></tr><tr><td class="reference"><b id="Welch">[Welch]</b></td><td class="top">Welch, T., &#8220;A Technique for High-Performance Data Compression&#8221;, IEEE Computer&nbsp;17(6), June&nbsp;1984.</td></tr></table><h2 id="rfc.references.2"><a href="#rfc.section.11.2" id="rfc.section.11.2">11.2</a> Informative References</h2><table><tr><td class="reference"><b id="BCP115">[BCP115]</b></td><td class="top">Hansen, T., Hardie, T., and L. Masinter, &#8220;<a href="https://tools.ietf.org/html/rfc4395">Guidelines and Registration Procedures for New URI Schemes</a>&#8221;, BCP&nbsp;115, RFC&nbsp;4395, February&nbsp;2006.</td></tr><tr><td class="reference"><b id="BCP13">[BCP13]</b></td><td class="top">Freed, N., Klensin, J., and T. Hansen, &#8220;<a href="https://tools.ietf.org/html/rfc6838">Media Type Specifications and Registration Procedures</a>&#8221;, BCP&nbsp;13, RFC&nbsp;6838, January&nbsp;2013.</td></tr><tr><td class="reference"><b id="BCP90">[BCP90]</b></td><td class="top">Klyne, G., Nottingham, M., and J. Mogul, &#8220;<a href="https://tools.ietf.org/html/rfc3864">Registration Procedures for Message Header Fields</a>&#8221;, BCP&nbsp;90, RFC&nbsp;3864, September&nbsp;2004.</td></tr><tr><td class="reference"><b id="Georgiev">[Georgiev]</b></td><td class="top">Georgiev, M., Iyengar, S., Jana, S., Anubhai, R., Boneh, D., and V. Shmatikov, &#8220;<a href="http://doi.acm.org/10.1145/2382196.2382204">The Most Dangerous Code in the World: Validating SSL Certificates in Non-browser Software</a>&#8221;, In Proceedings of the 2012 ACM Conference on Computer and Communications Security (CCS '12), pp. 38-49, October&nbsp;2012, &lt;<a href="http://doi.acm.org/10.1145/2382196.2382204">http://doi.acm.org/10.1145/2382196.2382204</a>&gt;.</td></tr><tr><td class="reference"><b id="ISO-8859-1">[ISO-8859-1]</b></td><td class="top">International Organization for Standardization, &#8220;Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1&#8221;, ISO/IEC&nbsp;8859-1:1998, 1998.</td></tr><tr><td class="reference"><b id="Klein">[Klein]</b></td><td class="top">Klein, A., &#8220;<a href="http://packetstormsecurity.com/papers/general/whitepaper_httpresponse.pdf">Divide and Conquer - HTTP Response Splitting, Web Cache Poisoning Attacks, and Related Topics</a>&#8221;, March&nbsp;2004, &lt;<a href="http://packetstormsecurity.com/papers/general/whitepaper_httpresponse.pdf">http://packetstormsecurity.com/papers/general/whitepaper_httpresponse.pdf</a>&gt;.</td></tr><tr><td class="reference"><b id="Kri2001">[Kri2001]</b></td><td class="top">Kristol, D., &#8220;<a href="http://arxiv.org/abs/cs.SE/0105018">HTTP Cookies: Standards, Privacy, and Politics</a>&#8221;, ACM Transactions on Internet Technology&nbsp;1(2), November&nbsp;2001, &lt;<a href="http://arxiv.org/abs/cs.SE/0105018">http://arxiv.org/abs/cs.SE/0105018</a>&gt;.</td></tr><tr><td class="reference"><b id="Linhart">[Linhart]</b></td><td class="top">Linhart, C., Klein, A., Heled, R., and S. Orrin, &#8220;<a href="http://www.watchfire.com/news/whitepapers.aspx">HTTP Request Smuggling</a>&#8221;, June&nbsp;2005, &lt;<a href="http://www.watchfire.com/news/whitepapers.aspx">http://www.watchfire.com/news/whitepapers.aspx</a>&gt;.</td></tr><tr><td class="reference"><b id="RFC1919">[RFC1919]</b></td><td class="top">Chatel, M., &#8220;<a href="https://tools.ietf.org/html/rfc1919">Classical versus Transparent IP Proxies</a>&#8221;, RFC&nbsp;1919, March&nbsp;1996.</td></tr><tr><td class="reference"><b id="RFC1945">[RFC1945]</b></td><td class="top">Berners-Lee, T., Fielding, R., and H. Nielsen, &#8220;<a href="https://tools.ietf.org/html/rfc1945">Hypertext Transfer Protocol -- HTTP/1.0</a>&#8221;, RFC&nbsp;1945, May&nbsp;1996.</td></tr><tr><td class="reference"><b id="RFC2045">[RFC2045]</b></td><td class="top">Freed, N. and N. Borenstein, &#8220;<a href="https://tools.ietf.org/html/rfc2045">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</a>&#8221;, RFC&nbsp;2045, November&nbsp;1996.</td></tr><tr><td class="reference"><b id="RFC2047">[RFC2047]</b></td><td class="top">Moore, K., &#8220;<a href="https://tools.ietf.org/html/rfc2047">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</a>&#8221;, RFC&nbsp;2047, November&nbsp;1996.</td></tr><tr><td class="reference"><b id="RFC2068">[RFC2068]</b></td><td class="top">Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T. Berners-Lee, &#8220;<a href="https://tools.ietf.org/html/rfc2068">Hypertext Transfer Protocol -- HTTP/1.1</a>&#8221;, RFC&nbsp;2068, January&nbsp;1997.</td></tr><tr><td class="reference"><b id="RFC2145">[RFC2145]</b></td><td class="top">Mogul, J., Fielding, R., Gettys, J., and H. Nielsen, &#8220;<a href="https://tools.ietf.org/html/rfc2145">Use and Interpretation of HTTP Version Numbers</a>&#8221;, RFC&nbsp;2145, May&nbsp;1997.</td></tr><tr><td class="reference"><b id="RFC2616">[RFC2616]</b></td><td class="top">Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, &#8220;<a href="https://tools.ietf.org/html/rfc2616">Hypertext Transfer Protocol -- HTTP/1.1</a>&#8221;, RFC&nbsp;2616, June&nbsp;1999.</td></tr><tr><td class="reference"><b id="RFC2817">[RFC2817]</b></td><td class="top">Khare, R. and S. Lawrence, &#8220;<a href="https://tools.ietf.org/html/rfc2817">Upgrading to TLS Within HTTP/1.1</a>&#8221;, RFC&nbsp;2817, May&nbsp;2000.</td></tr><tr><td class="reference"><b id="RFC2818">[RFC2818]</b></td><td class="top">Rescorla, E., &#8220;<a href="https://tools.ietf.org/html/rfc2818">HTTP Over TLS</a>&#8221;, RFC&nbsp;2818, May&nbsp;2000.</td></tr><tr><td class="reference"><b id="RFC3040">[RFC3040]</b></td><td class="top">Cooper, I., Melve, I., and G. Tomlinson, &#8220;<a href="https://tools.ietf.org/html/rfc3040">Internet Web Replication and Caching Taxonomy</a>&#8221;, RFC&nbsp;3040, January&nbsp;2001.</td></tr><tr><td class="reference"><b id="RFC4033">[RFC4033]</b></td><td class="top">Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, &#8220;<a href="https://tools.ietf.org/html/rfc4033">DNS Security Introduction and Requirements</a>&#8221;, RFC&nbsp;4033, March&nbsp;2005.</td></tr><tr><td class="reference"><b id="RFC4559">[RFC4559]</b></td><td class="top">Jaganathan, K., Zhu, L., and J. Brezak, &#8220;<a href="https://tools.ietf.org/html/rfc4559">SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</a>&#8221;, RFC&nbsp;4559, June&nbsp;2006.</td></tr><tr><td class="reference"><b id="RFC5226">[RFC5226]</b></td><td class="top">Narten, T. and H. Alvestrand, &#8220;<a href="https://tools.ietf.org/html/rfc5226">Guidelines for Writing an IANA Considerations Section in RFCs</a>&#8221;, BCP&nbsp;26, RFC&nbsp;5226, May&nbsp;2008.</td></tr><tr><td class="reference"><b id="RFC5246">[RFC5246]</b></td><td class="top">Dierks, T. and E. Rescorla, &#8220;<a href="https://tools.ietf.org/html/rfc5246">The Transport Layer Security (TLS) Protocol Version 1.2</a>&#8221;, RFC&nbsp;5246, August&nbsp;2008.</td></tr><tr><td class="reference"><b id="RFC5322">[RFC5322]</b></td><td class="top">Resnick, P., &#8220;<a href="https://tools.ietf.org/html/rfc5322">Internet Message Format</a>&#8221;, RFC&nbsp;5322, October&nbsp;2008.</td></tr><tr><td class="reference"><b id="RFC6265">[RFC6265]</b></td><td class="top">Barth, A., &#8220;<a href="https://tools.ietf.org/html/rfc6265">HTTP State Management Mechanism</a>&#8221;, RFC&nbsp;6265, April&nbsp;2011.</td></tr><tr><td class="reference"><b id="RFC6585">[RFC6585]</b></td><td class="top">Nottingham, M. and R. Fielding, &#8220;<a href="https://tools.ietf.org/html/rfc6585">Additional HTTP Status Codes</a>&#8221;, RFC&nbsp;6585, April&nbsp;2012.</td></tr></table><div id="compatibility"><h1 id="rfc.section.A" class="np"><a href="#rfc.section.A">A.</a>&nbsp;<a href="#compatibility">HTTP Version History</a></h1><div id="rfc.section.A.p.1"><p>HTTP has been in use since 1990. The first version, later referred to as HTTP/0.9, was a simple protocol for hypertext data transfer across the Internet, using only a single request method (GET) and no metadata. HTTP/1.0, as defined by <a href="#RFC1945" id="rfc.xref.RFC1945.3"><cite title="Hypertext Transfer Protocol -- HTTP/1.0">[RFC1945]</cite></a>, added a range of request methods and MIME-like messaging, allowing for metadata to be transferred and modifiers placed on the request/response semantics. However, HTTP/1.0 did not sufficiently take into consideration the effects of hierarchical proxies, caching, the need for persistent connections, or name-based virtual hosts. The proliferation of incompletely implemented applications calling themselves "HTTP/1.0" further necessitated a protocol version change in order for two communicating applications to determine each other's true capabilities.<a class="self" href="#rfc.section.A.p.1">&para;</a></p></div><div id="rfc.section.A.p.2"><p>HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent requirements that enable reliable implementations, adding only those features that can either be safely ignored by an HTTP/1.0 recipient or only be sent when communicating with a party advertising conformance with HTTP/1.1.<a class="self" href="#rfc.section.A.p.2">&para;</a></p></div><div id="rfc.section.A.p.3"><p>HTTP/1.1 has been designed to make supporting previous versions easy. A general-purpose HTTP/1.1 server ought to be able to understand any valid request in the format of HTTP/1.0, responding appropriately with an HTTP/1.1 message that only uses features understood (or safely ignored) by HTTP/1.0 clients. Likewise, an HTTP/1.1 client can be expected to understand any valid HTTP/1.0 response.<a class="self" href="#rfc.section.A.p.3">&para;</a></p></div><div id="rfc.section.A.p.4"><p>Since HTTP/0.9 did not support header fields in a request, there is no mechanism for it to support name-based virtual hosts (selection of resource by inspection of the <a href="#header.host" class="smpl">Host</a> header field). Any server that implements name-based virtual hosts ought to disable support for HTTP/0.9. Most requests that appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x requests caused by a client failing to properly encode the request-target.<a class="self" href="#rfc.section.A.p.4">&para;</a></p></div><div id="changes.from.1.0"><h2 id="rfc.section.A.1"><a href="#rfc.section.A.1">A.1</a>&nbsp;<a href="#changes.from.1.0">Changes from HTTP/1.0</a></h2><div id="rfc.section.A.1.p.1"><p>This section summarizes major differences between versions HTTP/1.0 and HTTP/1.1.<a class="self" href="#rfc.section.A.1.p.1">&para;</a></p></div><div id="changes.to.simplify.multihomed.web.servers.and.conserve.ip.addresses"><h3 id="rfc.section.A.1.1"><a href="#rfc.section.A.1.1">A.1.1</a>&nbsp;<a href="#changes.to.simplify.multihomed.web.servers.and.conserve.ip.addresses">Multihomed Web Servers</a></h3><div id="rfc.section.A.1.1.p.1"><p>The requirements that clients and servers support the <a href="#header.host" class="smpl">Host</a> header field (<a href="#header.host" id="rfc.xref.header.host.3" title="Host">Section&nbsp;5.4</a>), report an error if it is missing from an HTTP/1.1 request, and accept absolute URIs (<a href="#request-target" title="Request Target">Section&nbsp;5.3</a>) are among the most important changes defined by HTTP/1.1.<a class="self" href="#rfc.section.A.1.1.p.1">&para;</a></p></div><div id="rfc.section.A.1.1.p.2"><p>Older HTTP/1.0 clients assumed a one-to-one relationship of IP addresses and servers; there was no other established mechanism for distinguishing the intended server of a request than the IP address to which that request was directed. The <a href="#header.host" class="smpl">Host</a> header field was introduced during the development of HTTP/1.1 and, though it was quickly implemented by most HTTP/1.0 browsers, additional requirements were placed on all HTTP/1.1 requests in order to ensure complete adoption. At the time of this writing, most HTTP-based services are dependent upon the Host header field for targeting requests.<a class="self" href="#rfc.section.A.1.1.p.2">&para;</a></p></div></div><div id="compatibility.with.http.1.0.persistent.connections"><h3 id="rfc.section.A.1.2"><a href="#rfc.section.A.1.2">A.1.2</a>&nbsp;<a href="#compatibility.with.http.1.0.persistent.connections">Keep-Alive Connections</a></h3><div id="rfc.section.A.1.2.p.1"><p>In HTTP/1.0, each connection is established by the client prior to the request and closed by the server after sending the response. However, some implementations implement the explicitly negotiated ("Keep-Alive") version of persistent connections described in <a href="https://tools.ietf.org/html/rfc2068#section-19.7.1">Section 19.7.1</a> of <a href="#RFC2068" id="rfc.xref.RFC2068.4"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>.<a class="self" href="#rfc.section.A.1.2.p.1">&para;</a></p></div><div id="rfc.section.A.1.2.p.2"><p>Some clients and servers might wish to be compatible with these previous approaches to persistent connections, by explicitly negotiating for them with a "Connection: keep-alive" request header field. However, some experimental implementations of HTTP/1.0 persistent connections are faulty; for example, if an HTTP/1.0 proxy server doesn't understand <a href="#header.connection" class="smpl">Connection</a>, it will erroneously forward that header field to the next inbound server, which would result in a hung connection.<a class="self" href="#rfc.section.A.1.2.p.2">&para;</a></p></div><div id="rfc.section.A.1.2.p.3"><p>One attempted solution was the introduction of a Proxy-Connection header field, targeted specifically at proxies. In practice, this was also unworkable, because proxies are often deployed in multiple layers, bringing about the same problem discussed above.<a class="self" href="#rfc.section.A.1.2.p.3">&para;</a></p></div><div id="rfc.section.A.1.2.p.4"><p>As a result, clients are encouraged not to send the Proxy-Connection header field in any requests.<a class="self" href="#rfc.section.A.1.2.p.4">&para;</a></p></div><div id="rfc.section.A.1.2.p.5"><p>Clients are also encouraged to consider the use of Connection: keep-alive in requests carefully; while they can enable persistent connections with HTTP/1.0 servers, clients using them will need to monitor the connection for "hung" requests (which indicate that the client ought stop sending the header field), and this mechanism ought not be used by clients at all when a proxy is being used.<a class="self" href="#rfc.section.A.1.2.p.5">&para;</a></p></div></div><div id="introduction.of.transfer-encoding"><h3 id="rfc.section.A.1.3"><a href="#rfc.section.A.1.3">A.1.3</a>&nbsp;<a href="#introduction.of.transfer-encoding">Introduction of Transfer-Encoding</a></h3><div id="rfc.section.A.1.3.p.1"><p>HTTP/1.1 introduces the <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.4" title="Transfer-Encoding">Section&nbsp;3.3.1</a>). Transfer codings need to be decoded prior to forwarding an HTTP message over a MIME-compliant protocol.<a class="self" href="#rfc.section.A.1.3.p.1">&para;</a></p></div></div></div><div id="changes.from.rfc.2616"><h2 id="rfc.section.A.2"><a href="#rfc.section.A.2">A.2</a>&nbsp;<a href="#changes.from.rfc.2616">Changes from RFC 2616</a></h2><div id="rfc.section.A.2.p.1"><p>HTTP's approach to error handling has been explained. (<a href="#conformance" title="Conformance and Error Handling">Section&nbsp;2.5</a>)<a class="self" href="#rfc.section.A.2.p.1">&para;</a></p></div><div id="rfc.section.A.2.p.2"><p>The HTTP-version ABNF production has been clarified to be case-sensitive. Additionally, version numbers have been restricted to single digits, due to the fact that implementations are known to handle multi-digit version numbers incorrectly. (<a href="#http.version" title="Protocol Versioning">Section&nbsp;2.6</a>)<a class="self" href="#rfc.section.A.2.p.2">&para;</a></p></div><div id="rfc.section.A.2.p.3"><p>Userinfo (i.e., username and password) are now disallowed in HTTP and HTTPS URIs, because of security issues related to their transmission on the wire. (<a href="#http.uri" title="http URI Scheme">Section&nbsp;2.7.1</a>)<a class="self" href="#rfc.section.A.2.p.3">&para;</a></p></div><div id="rfc.section.A.2.p.4"><p>The HTTPS URI scheme is now defined by this specification; previously, it was done in <a href="https://tools.ietf.org/html/rfc2818#section-2.4">Section 2.4</a> of <a href="#RFC2818" id="rfc.xref.RFC2818.4"><cite title="HTTP Over TLS">[RFC2818]</cite></a>. Furthermore, it implies end-to-end security. (<a href="#https.uri" title="https URI Scheme">Section&nbsp;2.7.2</a>)<a class="self" href="#rfc.section.A.2.p.4">&para;</a></p></div><div id="rfc.section.A.2.p.5"><p>HTTP messages can be (and often are) buffered by implementations; despite it sometimes being available as a stream, HTTP is fundamentally a message-oriented protocol. Minimum supported sizes for various protocol elements have been suggested, to improve interoperability. (<a href="#http.message" title="Message Format">Section&nbsp;3</a>)<a class="self" href="#rfc.section.A.2.p.5">&para;</a></p></div><div id="rfc.section.A.2.p.6"><p>Invalid whitespace around field-names is now required to be rejected, because accepting it represents a security vulnerability. The ABNF productions defining header fields now only list the field value. (<a href="#header.fields" title="Header Fields">Section&nbsp;3.2</a>)<a class="self" href="#rfc.section.A.2.p.6">&para;</a></p></div><div id="rfc.section.A.2.p.7"><p>Rules about implicit linear whitespace between certain grammar productions have been removed; now whitespace is only allowed where specifically defined in the ABNF. (<a href="#whitespace" title="Whitespace">Section&nbsp;3.2.3</a>)<a class="self" href="#rfc.section.A.2.p.7">&para;</a></p></div><div id="rfc.section.A.2.p.8"><p>Header fields that span multiple lines ("line folding") are deprecated. (<a href="#field.parsing" title="Field Parsing">Section&nbsp;3.2.4</a>)<a class="self" href="#rfc.section.A.2.p.8">&para;</a></p></div><div id="rfc.section.A.2.p.9"><p>The NUL octet is no longer allowed in comment and quoted-string text, and handling of backslash-escaping in them has been clarified. The quoted-pair rule no longer allows escaping control characters other than HTAB. Non-US-ASCII content in header fields and the reason phrase has been obsoleted and made opaque (the TEXT rule was removed). (<a href="#field.components" title="Field Value Components">Section&nbsp;3.2.6</a>)<a class="self" href="#rfc.section.A.2.p.9">&para;</a></p></div><div id="rfc.section.A.2.p.10"><p>Bogus <a href="#header.content-length" class="smpl">Content-Length</a> header fields are now required to be handled as errors by recipients. (<a href="#header.content-length" id="rfc.xref.header.content-length.2" title="Content-Length">Section&nbsp;3.3.2</a>)<a class="self" href="#rfc.section.A.2.p.10">&para;</a></p></div><div id="rfc.section.A.2.p.11"><p>The algorithm for determining the message body length has been clarified to indicate all of the special cases (e.g., driven by methods or status codes) that affect it, and that new protocol elements cannot define such special cases. CONNECT is a new, special case in determining message body length. "multipart/byteranges" is no longer a way of determining message body length detection. (<a href="#message.body.length" title="Message Body Length">Section&nbsp;3.3.3</a>)<a class="self" href="#rfc.section.A.2.p.11">&para;</a></p></div><div id="rfc.section.A.2.p.12"><p>The "identity" transfer coding token has been removed. (Sections <a href="#message.body" title="Message Body">3.3</a> and <a href="#transfer.codings" title="Transfer Codings">4</a>)<a class="self" href="#rfc.section.A.2.p.12">&para;</a></p></div><div id="rfc.section.A.2.p.13"><p>Chunk length does not include the count of the octets in the chunk header and trailer. Line folding in chunk extensions is disallowed. (<a href="#chunked.encoding" title="Chunked Transfer Coding">Section&nbsp;4.1</a>)<a class="self" href="#rfc.section.A.2.p.13">&para;</a></p></div><div id="rfc.section.A.2.p.14"><p>The meaning of the "deflate" content coding has been clarified. (<a href="#deflate.coding" title="Deflate Coding">Section&nbsp;4.2.2</a>)<a class="self" href="#rfc.section.A.2.p.14">&para;</a></p></div><div id="rfc.section.A.2.p.15"><p>The segment + query components of RFC 3986 have been used to define the request-target, instead of abs_path from RFC 1808. The asterisk-form of the request-target is only allowed with the OPTIONS method. (<a href="#request-target" title="Request Target">Section&nbsp;5.3</a>)<a class="self" href="#rfc.section.A.2.p.15">&para;</a></p></div><div id="rfc.section.A.2.p.16"><p>The term "Effective Request URI" has been introduced. (<a href="#effective.request.uri" title="Effective Request URI">Section&nbsp;5.5</a>)<a class="self" href="#rfc.section.A.2.p.16">&para;</a></p></div><div id="rfc.section.A.2.p.17"><p>Gateways do not need to generate <a href="#header.via" class="smpl">Via</a> header fields anymore. (<a href="#header.via" id="rfc.xref.header.via.2" title="Via">Section&nbsp;5.7.1</a>)<a class="self" href="#rfc.section.A.2.p.17">&para;</a></p></div><div id="rfc.section.A.2.p.18"><p>Exactly when "close" connection options have to be sent has been clarified. Also, "hop-by-hop" header fields are required to appear in the Connection header field; just because they're defined as hop-by-hop in this specification doesn't exempt them. (<a href="#header.connection" id="rfc.xref.header.connection.8" title="Connection">Section&nbsp;6.1</a>)<a class="self" href="#rfc.section.A.2.p.18">&para;</a></p></div><div id="rfc.section.A.2.p.19"><p>The limit of two connections per server has been removed. An idempotent sequence of requests is no longer required to be retried. The requirement to retry requests under certain circumstances when the server prematurely closes the connection has been removed. Also, some extraneous requirements about when servers are allowed to close connections prematurely have been removed. (<a href="#persistent.connections" title="Persistence">Section&nbsp;6.3</a>)<a class="self" href="#rfc.section.A.2.p.19">&para;</a></p></div><div id="rfc.section.A.2.p.20"><p>The semantics of the <a href="#header.upgrade" class="smpl">Upgrade</a> header field is now defined in responses other than 101 (this was incorporated from <a href="#RFC2817" id="rfc.xref.RFC2817.3"><cite title="Upgrading to TLS Within HTTP/1.1">[RFC2817]</cite></a>). Furthermore, the ordering in the field value is now significant. (<a href="#header.upgrade" id="rfc.xref.header.upgrade.3" title="Upgrade">Section&nbsp;6.7</a>)<a class="self" href="#rfc.section.A.2.p.20">&para;</a></p></div><div id="rfc.section.A.2.p.21"><p>Empty list elements in list productions (e.g., a list header field containing ", ,") have been deprecated. (<a href="#abnf.extension" title="ABNF List Extension: #rule">Section&nbsp;7</a>)<a class="self" href="#rfc.section.A.2.p.21">&para;</a></p></div><div id="rfc.section.A.2.p.22"><p>Registration of Transfer Codings now requires IETF Review (<a href="#transfer.coding.registry" title="Transfer Coding Registry">Section&nbsp;8.4</a>)<a class="self" href="#rfc.section.A.2.p.22">&para;</a></p></div><div id="rfc.section.A.2.p.23"><p>This specification now defines the Upgrade Token Registry, previously defined in <a href="https://tools.ietf.org/html/rfc2817#section-7.2">Section 7.2</a> of <a href="#RFC2817" id="rfc.xref.RFC2817.4"><cite title="Upgrading to TLS Within HTTP/1.1">[RFC2817]</cite></a>. (<a href="#upgrade.token.registry" title="Upgrade Token Registry">Section&nbsp;8.6</a>)<a class="self" href="#rfc.section.A.2.p.23">&para;</a></p></div><div id="rfc.section.A.2.p.24"><p>The expectation to support HTTP/0.9 requests has been removed. (<a href="#compatibility" title="HTTP Version History">Appendix&nbsp;A</a>)<a class="self" href="#rfc.section.A.2.p.24">&para;</a></p></div><div id="rfc.section.A.2.p.25"><p>Issues with the Keep-Alive and Proxy-Connection header fields in requests are pointed out, with use of the latter being discouraged altogether. (<a href="#compatibility.with.http.1.0.persistent.connections" title="Keep-Alive Connections">Appendix&nbsp;A.1.2</a>)<a class="self" href="#rfc.section.A.2.p.25">&para;</a></p></div></div></div><div id="collected.abnf"><h1 id="rfc.section.B"><a href="#rfc.section.B">B.</a>&nbsp;<a href="#collected.abnf">Collected ABNF</a></h1><div id="rfc.figure.u.72"><pre class="inline"><a href="#rule.whitespace" class="smpl">BWS</a> = OWS
     736</pre></div><div id="rfc.section.7.p.7"><p><a href="#collected.abnf" title="Collected ABNF">Appendix&nbsp;B</a> shows the collected ABNF for recipients after the list constructs have been expanded.<a class="self" href="#rfc.section.7.p.7">&para;</a></p></div></div><div id="IANA.considerations"><h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a href="#IANA.considerations">IANA Considerations</a></h1><div id="header.field.registration"><h2 id="rfc.section.8.1"><a href="#rfc.section.8.1">8.1</a>&nbsp;<a href="#header.field.registration">Header Field Registration</a></h2><div id="rfc.section.8.1.p.1"><p>HTTP header fields are registered within the "Message Headers" registry maintained at &lt;<a href="http://www.iana.org/assignments/message-headers/">http://www.iana.org/assignments/message-headers/</a>&gt;.<a class="self" href="#rfc.section.8.1.p.1">&para;</a></p></div><div id="rfc.section.8.1.p.2"><p>This document defines the following HTTP header fields, so the "Permanent Message Header Field Names" registry has been updated accordingly (see <a href="#BCP90" id="rfc.xref.BCP90.1"><cite title="Registration Procedures for Message Header Fields">[BCP90]</cite></a>).<a class="self" href="#rfc.section.8.1.p.2">&para;</a></p></div><div id="rfc.table.1"><div id="iana.header.registration.table"></div><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Header Field Name</th><th>Protocol</th><th>Status</th><th>Reference</th></tr></thead><tbody><tr><td class="left">Connection</td><td class="left">http</td><td class="left">standard</td><td class="left"><a href="#header.connection" id="rfc.xref.header.connection.6" title="Connection">Section&nbsp;6.1</a> </td></tr><tr><td class="left">Content-Length</td><td class="left">http</td><td class="left">standard</td><td class="left"><a href="#header.content-length" id="rfc.xref.header.content-length.1" title="Content-Length">Section&nbsp;3.3.2</a> </td></tr><tr><td class="left">Host</td><td class="left">http</td><td class="left">standard</td><td class="left"><a href="#header.host" id="rfc.xref.header.host.2" title="Host">Section&nbsp;5.4</a> </td></tr><tr><td class="left">TE</td><td class="left">http</td><td class="left">standard</td><td class="left"><a href="#header.te" id="rfc.xref.header.te.3" title="TE">Section&nbsp;4.3</a> </td></tr><tr><td class="left">Trailer</td><td class="left">http</td><td class="left">standard</td><td class="left"><a href="#header.trailer" id="rfc.xref.header.trailer.1" title="Trailer">Section&nbsp;4.4</a> </td></tr><tr><td class="left">Transfer-Encoding</td><td class="left">http</td><td class="left">standard</td><td class="left"><a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.3" title="Transfer-Encoding">Section&nbsp;3.3.1</a> </td></tr><tr><td class="left">Upgrade</td><td class="left">http</td><td class="left">standard</td><td class="left"><a href="#header.upgrade" id="rfc.xref.header.upgrade.2" title="Upgrade">Section&nbsp;6.7</a> </td></tr><tr><td class="left">Via</td><td class="left">http</td><td class="left">standard</td><td class="left"><a href="#header.via" id="rfc.xref.header.via.1" title="Via">Section&nbsp;5.7.1</a> </td></tr></tbody></table></div><div id="rfc.section.8.1.p.3"><p>Furthermore, the header field-name "Close" has been registered as "reserved", since using that name as an HTTP header field might conflict with the "close" connection option of the <a href="#header.connection" class="smpl">Connection</a> header field (<a href="#header.connection" id="rfc.xref.header.connection.7" title="Connection">Section&nbsp;6.1</a>).<a class="self" href="#rfc.section.8.1.p.3">&para;</a></p></div><div id="rfc.table.u.1"><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Header Field Name</th><th>Protocol</th><th>Status</th><th>Reference</th></tr></thead><tbody><tr><td class="left">Close</td><td class="left">http</td><td class="left">reserved</td><td class="left"><a href="#header.field.registration" title="Header Field Registration">Section&nbsp;8.1</a> </td></tr></tbody></table></div><div id="rfc.section.8.1.p.4"><p>The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".<a class="self" href="#rfc.section.8.1.p.4">&para;</a></p></div></div><div id="uri.scheme.registration"><h2 id="rfc.section.8.2"><a href="#rfc.section.8.2">8.2</a>&nbsp;<a href="#uri.scheme.registration">URI Scheme Registration</a></h2><div id="rfc.section.8.2.p.1"><p>IANA maintains the registry of URI Schemes <a href="#BCP115" id="rfc.xref.BCP115.1"><cite title="Guidelines and Registration Procedures for New URI Schemes">[BCP115]</cite></a> at &lt;<a href="http://www.iana.org/assignments/uri-schemes/">http://www.iana.org/assignments/uri-schemes/</a>&gt;.<a class="self" href="#rfc.section.8.2.p.1">&para;</a></p></div><div id="rfc.section.8.2.p.2"><p>This document defines the following URI schemes, so the "Permanent URI Schemes" registry has been updated accordingly.<a class="self" href="#rfc.section.8.2.p.2">&para;</a></p></div><div id="rfc.table.u.2"><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>URI Scheme</th><th>Description</th><th>Reference</th></tr></thead><tbody><tr><td class="left">http</td><td class="left">Hypertext Transfer Protocol</td><td class="left"><a href="#http.uri" title="http URI Scheme">Section&nbsp;2.7.1</a></td></tr><tr><td class="left">https</td><td class="left">Hypertext Transfer Protocol Secure</td><td class="left"><a href="#https.uri" title="https URI Scheme">Section&nbsp;2.7.2</a></td></tr></tbody></table></div></div><div id="internet.media.type.http"><h2 id="rfc.section.8.3"><a href="#rfc.section.8.3">8.3</a>&nbsp;<a href="#internet.media.type.http">Internet Media Type Registration</a></h2><div id="rfc.section.8.3.p.1"><p>IANA maintains the registry of Internet media types <a href="#BCP13" id="rfc.xref.BCP13.1"><cite title="Media Type Specifications and Registration Procedures">[BCP13]</cite></a> at &lt;<a href="http://www.iana.org/assignments/media-types">http://www.iana.org/assignments/media-types</a>&gt;.<a class="self" href="#rfc.section.8.3.p.1">&para;</a></p></div><div id="rfc.section.8.3.p.2"><p>This document serves as the specification for the Internet media types "message/http" and "application/http". The following has been registered with IANA.<a class="self" href="#rfc.section.8.3.p.2">&para;</a></p></div><div id="internet.media.type.message.http"><h3 id="rfc.section.8.3.1"><a href="#rfc.section.8.3.1">8.3.1</a>&nbsp;<a href="#internet.media.type.message.http">Internet Media Type message/http</a></h3><div id="rfc.section.8.3.1.p.1"><p>The message/http type can be used to enclose a single HTTP request or response message, provided that it obeys the MIME restrictions for all "message" types regarding line length and encodings.<a class="self" href="#rfc.section.8.3.1.p.1">&para;</a></p></div><div id="rfc.section.8.3.1.p.2"><dl><dt>Type name:</dt><dd>message</dd><dt>Subtype name:</dt><dd>http</dd><dt>Required parameters:</dt><dd>N/A</dd><dt>Optional parameters:</dt><dd>version, msgtype <dl><dt>version:</dt><dd>The HTTP-version number of the enclosed message (e.g., "1.1"). If not present, the version can be determined from the first line of the body.</dd><dt>msgtype:</dt><dd>The message type &#8212; "request" or "response". If not present, the type can be determined from the first line of the body.</dd></dl> </dd><dt>Encoding considerations:</dt><dd>only "7bit", "8bit", or "binary" are permitted</dd><dt>Security considerations:</dt><dd>see <a href="#security.considerations" title="Security Considerations">Section&nbsp;9</a> </dd><dt>Interoperability considerations:</dt><dd>N/A</dd><dt>Published specification:</dt><dd>This specification (see <a href="#internet.media.type.message.http" title="Internet Media Type message/http">Section&nbsp;8.3.1</a>).</dd><dt>Applications that use this media type:</dt><dd>N/A</dd><dt>Fragment identifier considerations:</dt><dd>N/A</dd><dt>Additional information:</dt><dd>&nbsp;<dl><dt>Magic number(s):</dt><dd>N/A</dd><dt>Deprecated alias names for this type:</dt><dd>N/A</dd><dt>File extension(s):</dt><dd>N/A</dd><dt>Macintosh file type code(s):</dt><dd>N/A</dd></dl> </dd><dt>Person and email address to contact for further information:</dt><dd>See&nbsp;Authors'&nbsp;Addresses section.</dd><dt>Intended usage:</dt><dd>COMMON</dd><dt>Restrictions on usage:</dt><dd>N/A</dd><dt>Author:</dt><dd>See Authors' Addresses section.</dd><dt>Change controller:</dt><dd>IESG</dd></dl></div></div><div id="internet.media.type.application.http"><h3 id="rfc.section.8.3.2"><a href="#rfc.section.8.3.2">8.3.2</a>&nbsp;<a href="#internet.media.type.application.http">Internet Media Type application/http</a></h3><div id="rfc.section.8.3.2.p.1"><p>The application/http type can be used to enclose a pipeline of one or more HTTP request or response messages (not intermixed).<a class="self" href="#rfc.section.8.3.2.p.1">&para;</a></p></div><div id="rfc.section.8.3.2.p.2"><dl><dt>Type name:</dt><dd>application</dd><dt>Subtype name:</dt><dd>http</dd><dt>Required parameters:</dt><dd>N/A</dd><dt>Optional parameters:</dt><dd>version, msgtype <dl><dt>version:</dt><dd>The HTTP-version number of the enclosed messages (e.g., "1.1"). If not present, the version can be determined from the first line of the body.</dd><dt>msgtype:</dt><dd>The message type &#8212; "request" or "response". If not present, the type can be determined from the first line of the body.</dd></dl> </dd><dt>Encoding considerations:</dt><dd>HTTP messages enclosed by this type are in "binary" format; use of an appropriate Content-Transfer-Encoding is required when transmitted via email.</dd><dt>Security considerations:</dt><dd>see <a href="#security.considerations" title="Security Considerations">Section&nbsp;9</a> </dd><dt>Interoperability considerations:</dt><dd>N/A</dd><dt>Published specification:</dt><dd>This specification (see <a href="#internet.media.type.application.http" title="Internet Media Type application/http">Section&nbsp;8.3.2</a>).</dd><dt>Applications that use this media type:</dt><dd>N/A</dd><dt>Fragment identifier considerations:</dt><dd>N/A</dd><dt>Additional information:</dt><dd>&nbsp;<dl><dt>Deprecated alias names for this type:</dt><dd>N/A</dd><dt>Magic number(s):</dt><dd>N/A</dd><dt>File extension(s):</dt><dd>N/A</dd><dt>Macintosh file type code(s):</dt><dd>N/A</dd></dl> </dd><dt>Person and email address to contact for further information:</dt><dd>See&nbsp;Authors'&nbsp;Addresses section.</dd><dt>Intended usage:</dt><dd>COMMON</dd><dt>Restrictions on usage:</dt><dd>N/A</dd><dt>Author:</dt><dd>See Authors' Addresses section.</dd><dt>Change controller:</dt><dd>IESG</dd></dl></div></div></div><div id="transfer.coding.registry"><h2 id="rfc.section.8.4"><a href="#rfc.section.8.4">8.4</a>&nbsp;<a href="#transfer.coding.registry">Transfer Coding Registry</a></h2><div id="rfc.section.8.4.p.1"><p>The "HTTP Transfer Coding Registry" defines the namespace for transfer coding names. It is maintained at &lt;<a href="http://www.iana.org/assignments/http-parameters">http://www.iana.org/assignments/http-parameters</a>&gt;.<a class="self" href="#rfc.section.8.4.p.1">&para;</a></p></div><div id="transfer.coding.registry.procedure"><h3 id="rfc.section.8.4.1"><a href="#rfc.section.8.4.1">8.4.1</a>&nbsp;<a href="#transfer.coding.registry.procedure">Procedure</a></h3><div id="rfc.section.8.4.1.p.1"><p>Registrations <em class="bcp14">MUST</em> include the following fields: <a class="self" href="#rfc.section.8.4.1.p.1">&para;</a></p><ul><li>Name</li><li>Description</li><li>Pointer to specification text</li></ul></div><div id="rfc.section.8.4.1.p.2"><p>Names of transfer codings <em class="bcp14">MUST NOT</em> overlap with names of content codings (<a href="rfc7231.html#content.codings" title="Content Codings">Section 3.1.2.1</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.33"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a>) unless the encoding transformation is identical, as is the case for the compression codings defined in <a href="#compression.codings" title="Compression Codings">Section&nbsp;4.2</a>.<a class="self" href="#rfc.section.8.4.1.p.2">&para;</a></p></div><div id="rfc.section.8.4.1.p.3"><p>Values to be added to this namespace require IETF Review (see <a href="https://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a> of <a href="#RFC5226" id="rfc.xref.RFC5226.1"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>), and <em class="bcp14">MUST</em> conform to the purpose of transfer coding defined in this specification.<a class="self" href="#rfc.section.8.4.1.p.3">&para;</a></p></div><div id="rfc.section.8.4.1.p.4"><p>Use of program names for the identification of encoding formats is not desirable and is discouraged for future encodings.<a class="self" href="#rfc.section.8.4.1.p.4">&para;</a></p></div></div><div id="transfer.coding.registration"><h3 id="rfc.section.8.4.2"><a href="#rfc.section.8.4.2">8.4.2</a>&nbsp;<a href="#transfer.coding.registration">Registration</a></h3><div id="rfc.section.8.4.2.p.1"><p>The "HTTP Transfer Coding Registry" has been updated with the registrations below:<a class="self" href="#rfc.section.8.4.2.p.1">&para;</a></p></div><div id="rfc.table.2"><div id="iana.transfer.coding.registration.table"></div><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Name</th><th>Description</th><th>Reference</th></tr></thead><tbody><tr><td class="left">chunked</td><td class="left">Transfer in a series of chunks</td><td class="left"><a href="#chunked.encoding" title="Chunked Transfer Coding">Section&nbsp;4.1</a> </td></tr><tr><td class="left">compress</td><td class="left">UNIX "compress" data format <a href="#Welch" id="rfc.xref.Welch.2"><cite title="A Technique for High-Performance Data Compression">[Welch]</cite></a></td><td class="left"><a href="#compress.coding" title="Compress Coding">Section&nbsp;4.2.1</a> </td></tr><tr><td class="left">deflate</td><td class="left">"deflate" compressed data (<a href="#RFC1951" id="rfc.xref.RFC1951.2"><cite title="DEFLATE Compressed Data Format Specification version 1.3">[RFC1951]</cite></a>) inside the "zlib" data format (<a href="#RFC1950" id="rfc.xref.RFC1950.2"><cite title="ZLIB Compressed Data Format Specification version 3.3">[RFC1950]</cite></a>)</td><td class="left"><a href="#deflate.coding" title="Deflate Coding">Section&nbsp;4.2.2</a> </td></tr><tr><td class="left">gzip</td><td class="left">GZIP file format <a href="#RFC1952" id="rfc.xref.RFC1952.2"><cite title="GZIP file format specification version 4.3">[RFC1952]</cite></a></td><td class="left"><a href="#gzip.coding" title="Gzip Coding">Section&nbsp;4.2.3</a> </td></tr><tr><td class="left">x-compress</td><td class="left">Deprecated (alias for compress)</td><td class="left"><a href="#compress.coding" title="Compress Coding">Section&nbsp;4.2.1</a> </td></tr><tr><td class="left">x-gzip</td><td class="left">Deprecated (alias for gzip)</td><td class="left"><a href="#gzip.coding" title="Gzip Coding">Section&nbsp;4.2.3</a> </td></tr></tbody></table></div></div></div><div id="content.coding.registration"><h2 id="rfc.section.8.5"><a href="#rfc.section.8.5">8.5</a>&nbsp;<a href="#content.coding.registration">Content Coding Registration</a></h2><div id="rfc.section.8.5.p.1"><p>IANA maintains the "HTTP Content Coding Registry" at &lt;<a href="http://www.iana.org/assignments/http-parameters">http://www.iana.org/assignments/http-parameters</a>&gt;.<a class="self" href="#rfc.section.8.5.p.1">&para;</a></p></div><div id="rfc.section.8.5.p.2"><p>The "HTTP Content Coding Registry" has been updated with the registrations below:<a class="self" href="#rfc.section.8.5.p.2">&para;</a></p></div><div id="rfc.table.3"><div id="iana.content.coding.registration.table"></div><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Name</th><th>Description</th><th>Reference</th></tr></thead><tbody><tr><td class="left">compress</td><td class="left">UNIX "compress" data format <a href="#Welch" id="rfc.xref.Welch.3"><cite title="A Technique for High-Performance Data Compression">[Welch]</cite></a></td><td class="left"><a href="#compress.coding" title="Compress Coding">Section&nbsp;4.2.1</a> </td></tr><tr><td class="left">deflate</td><td class="left">"deflate" compressed data (<a href="#RFC1951" id="rfc.xref.RFC1951.3"><cite title="DEFLATE Compressed Data Format Specification version 1.3">[RFC1951]</cite></a>) inside the "zlib" data format (<a href="#RFC1950" id="rfc.xref.RFC1950.3"><cite title="ZLIB Compressed Data Format Specification version 3.3">[RFC1950]</cite></a>)</td><td class="left"><a href="#deflate.coding" title="Deflate Coding">Section&nbsp;4.2.2</a> </td></tr><tr><td class="left">gzip</td><td class="left">GZIP file format <a href="#RFC1952" id="rfc.xref.RFC1952.3"><cite title="GZIP file format specification version 4.3">[RFC1952]</cite></a></td><td class="left"><a href="#gzip.coding" title="Gzip Coding">Section&nbsp;4.2.3</a> </td></tr><tr><td class="left">x-compress</td><td class="left">Deprecated (alias for compress)</td><td class="left"><a href="#compress.coding" title="Compress Coding">Section&nbsp;4.2.1</a> </td></tr><tr><td class="left">x-gzip</td><td class="left">Deprecated (alias for gzip)</td><td class="left"><a href="#gzip.coding" title="Gzip Coding">Section&nbsp;4.2.3</a> </td></tr></tbody></table></div></div><div id="upgrade.token.registry"><h2 id="rfc.section.8.6"><a href="#rfc.section.8.6">8.6</a>&nbsp;<a href="#upgrade.token.registry">Upgrade Token Registry</a></h2><div id="rfc.section.8.6.p.1"><p>The "Hypertext Transfer Protocol (HTTP) Upgrade Token Registry" defines the namespace for protocol-name tokens used to identify protocols in the <a href="#header.upgrade" class="smpl">Upgrade</a> header field. The registry is maintained at &lt;<a href="http://www.iana.org/assignments/http-upgrade-tokens">http://www.iana.org/assignments/http-upgrade-tokens</a>&gt;.<a class="self" href="#rfc.section.8.6.p.1">&para;</a></p></div><div id="upgrade.token.registry.procedure"><h3 id="rfc.section.8.6.1"><a href="#rfc.section.8.6.1">8.6.1</a>&nbsp;<a href="#upgrade.token.registry.procedure">Procedure</a></h3><div id="rfc.section.8.6.1.p.1"><p>Each registered protocol name is associated with contact information and an optional set of specifications that details how the connection will be processed after it has been upgraded.<a class="self" href="#rfc.section.8.6.1.p.1">&para;</a></p></div><div id="rfc.section.8.6.1.p.2"><p>Registrations happen on a "First Come First Served" basis (see <a href="https://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a> of <a href="#RFC5226" id="rfc.xref.RFC5226.2"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>) and are subject to the following rules: <a class="self" href="#rfc.section.8.6.1.p.2">&para;</a></p><ol><li>A protocol-name token, once registered, stays registered forever.</li><li>The registration <em class="bcp14">MUST</em> name a responsible party for the registration.</li><li>The registration <em class="bcp14">MUST</em> name a point of contact.</li><li>The registration <em class="bcp14">MAY</em> name a set of specifications associated with that token. Such specifications need not be publicly available.</li><li>The registration <em class="bcp14">SHOULD</em> name a set of expected "protocol-version" tokens associated with that token at the time of registration.</li><li>The responsible party <em class="bcp14">MAY</em> change the registration at any time. The IANA will keep a record of all such changes, and make them available upon request.</li><li>The IESG <em class="bcp14">MAY</em> reassign responsibility for a protocol token. This will normally only be used in the case when a responsible party cannot be contacted.</li></ol></div><div id="rfc.section.8.6.1.p.3"><p>This registration procedure for HTTP Upgrade Tokens replaces that previously defined in <a href="https://tools.ietf.org/html/rfc2817#section-7.2">Section 7.2</a> of <a href="#RFC2817" id="rfc.xref.RFC2817.2"><cite title="Upgrading to TLS Within HTTP/1.1">[RFC2817]</cite></a>.<a class="self" href="#rfc.section.8.6.1.p.3">&para;</a></p></div></div><div id="upgrade.token.registration"><h3 id="rfc.section.8.6.2"><a href="#rfc.section.8.6.2">8.6.2</a>&nbsp;<a href="#upgrade.token.registration">Upgrade Token Registration</a></h3><div id="rfc.section.8.6.2.p.1"><p>The "HTTP" entry in the upgrade token registry has been updated with the registration below:<a class="self" href="#rfc.section.8.6.2.p.1">&para;</a></p></div><div id="rfc.table.u.3"><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Value</th><th>Description</th><th>Expected Version Tokens</th><th>Reference</th></tr></thead><tbody><tr><td class="left">HTTP</td><td class="left">Hypertext Transfer Protocol</td><td class="left">any DIGIT.DIGIT (e.g, "2.0")</td><td class="left"><a href="#http.version" title="Protocol Versioning">Section&nbsp;2.6</a></td></tr></tbody></table></div><div id="rfc.section.8.6.2.p.2"><p>The responsible party is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".<a class="self" href="#rfc.section.8.6.2.p.2">&para;</a></p></div></div></div></div><div id="security.considerations"><h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a>&nbsp;<a href="#security.considerations">Security Considerations</a></h1><div id="rfc.section.9.p.1"><p>This section is meant to inform developers, information providers, and users of known security considerations relevant to HTTP message syntax, parsing, and routing. Security considerations about HTTP semantics and payloads are addressed in <a href="#RFC7231" id="rfc.xref.RFC7231.34"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a>.<a class="self" href="#rfc.section.9.p.1">&para;</a></p></div><div id="establishing.authority"><h2 id="rfc.section.9.1"><a href="#rfc.section.9.1">9.1</a>&nbsp;<a href="#establishing.authority">Establishing Authority</a></h2><div id="rfc.section.9.1.p.1"><p>HTTP relies on the notion of an <dfn>authoritative response</dfn>: a response that has been determined by (or at the direction of) the authority identified within the target URI to be the most appropriate response for that request given the state of the target resource at the time of response message origination. Providing a response from a non-authoritative source, such as a shared cache, is often useful to improve performance and availability, but only to the extent that the source can be trusted or the distrusted response can be safely used.<a class="self" href="#rfc.section.9.1.p.1">&para;</a></p></div><div id="rfc.section.9.1.p.2"><p>Unfortunately, establishing authority can be difficult. For example, <dfn>phishing</dfn> is an attack on the user's perception of authority, where that perception can be misled by presenting similar branding in hypertext, possibly aided by userinfo obfuscating the authority component (see <a href="#http.uri" title="http URI Scheme">Section&nbsp;2.7.1</a>). User agents can reduce the impact of phishing attacks by enabling users to easily inspect a target URI prior to making an action, by prominently distinguishing (or rejecting) userinfo when present, and by not sending stored credentials and cookies when the referring document is from an unknown or untrusted source.<a class="self" href="#rfc.section.9.1.p.2">&para;</a></p></div><div id="rfc.section.9.1.p.3"><p>When a registered name is used in the authority component, the "http" URI scheme (<a href="#http.uri" title="http URI Scheme">Section&nbsp;2.7.1</a>) relies on the user's local name resolution service to determine where it can find authoritative responses. This means that any attack on a user's network host table, cached names, or name resolution libraries becomes an avenue for attack on establishing authority. Likewise, the user's choice of server for Domain Name Service (DNS), and the hierarchy of servers from which it obtains resolution results, could impact the authenticity of address mappings; DNS Security Extensions (DNSSEC, <a href="#RFC4033" id="rfc.xref.RFC4033.1"><cite title="DNS Security Introduction and Requirements">[RFC4033]</cite></a>) are one way to improve authenticity.<a class="self" href="#rfc.section.9.1.p.3">&para;</a></p></div><div id="rfc.section.9.1.p.4"><p>Furthermore, after an IP address is obtained, establishing authority for an "http" URI is vulnerable to attacks on Internet Protocol routing.<a class="self" href="#rfc.section.9.1.p.4">&para;</a></p></div><div id="rfc.section.9.1.p.5"><p>The "https" scheme (<a href="#https.uri" title="https URI Scheme">Section&nbsp;2.7.2</a>) is intended to prevent (or at least reveal) many of these potential attacks on establishing authority, provided that the negotiated TLS connection is secured and the client properly verifies that the communicating server's identity matches the target URI's authority component (see <a href="#RFC2818" id="rfc.xref.RFC2818.3"><cite title="HTTP Over TLS">[RFC2818]</cite></a>). Correctly implementing such verification can be difficult (see <a href="#Georgiev" id="rfc.xref.Georgiev.1"><cite title="The Most Dangerous Code in the World: Validating SSL Certificates in Non-browser Software">[Georgiev]</cite></a>).<a class="self" href="#rfc.section.9.1.p.5">&para;</a></p></div></div><div id="risks.intermediaries"><h2 id="rfc.section.9.2"><a href="#rfc.section.9.2">9.2</a>&nbsp;<a href="#risks.intermediaries">Risks of Intermediaries</a></h2><div id="rfc.section.9.2.p.1"><p>By their very nature, HTTP intermediaries are men-in-the-middle and, thus, represent an opportunity for man-in-the-middle attacks. Compromise of the systems on which the intermediaries run can result in serious security and privacy problems. Intermediaries might have access to security-related information, personal information about individual users and organizations, and proprietary information belonging to users and content providers. A compromised intermediary, or an intermediary implemented or configured without regard to security and privacy considerations, might be used in the commission of a wide range of potential attacks.<a class="self" href="#rfc.section.9.2.p.1">&para;</a></p></div><div id="rfc.section.9.2.p.2"><p>Intermediaries that contain a shared cache are especially vulnerable to cache poisoning attacks, as described in <a href="rfc7234.html#security.considerations" title="Security Considerations">Section 8</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.8"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>.<a class="self" href="#rfc.section.9.2.p.2">&para;</a></p></div><div id="rfc.section.9.2.p.3"><p>Implementers need to consider the privacy and security implications of their design and coding decisions, and of the configuration options they provide to operators (especially the default configuration).<a class="self" href="#rfc.section.9.2.p.3">&para;</a></p></div><div id="rfc.section.9.2.p.4"><p>Users need to be aware that intermediaries are no more trustworthy than the people who run them; HTTP itself cannot solve this problem.<a class="self" href="#rfc.section.9.2.p.4">&para;</a></p></div></div><div id="attack.protocol.element.length"><h2 id="rfc.section.9.3"><a href="#rfc.section.9.3">9.3</a>&nbsp;<a href="#attack.protocol.element.length">Attacks via Protocol Element Length</a></h2><div id="rfc.section.9.3.p.1"><p>Because HTTP uses mostly textual, character-delimited fields, parsers are often vulnerable to attacks based on sending very long (or very slow) streams of data, particularly where an implementation is expecting a protocol element with no predefined length.<a class="self" href="#rfc.section.9.3.p.1">&para;</a></p></div><div id="rfc.section.9.3.p.2"><p>To promote interoperability, specific recommendations are made for minimum size limits on request-line (<a href="#request.line" title="Request Line">Section&nbsp;3.1.1</a>) and header fields (<a href="#header.fields" title="Header Fields">Section&nbsp;3.2</a>). These are minimum recommendations, chosen to be supportable even by implementations with limited resources; it is expected that most implementations will choose substantially higher limits.<a class="self" href="#rfc.section.9.3.p.2">&para;</a></p></div><div id="rfc.section.9.3.p.3"><p>A server can reject a message that has a request-target that is too long (<a href="rfc7231.html#status.414" title="414 URI Too Long">Section 6.5.12</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.35"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a>) or a request payload that is too large (<a href="rfc7231.html#status.413" title="413 Payload Too Large">Section 6.5.11</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.36"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a>). Additional status codes related to capacity limits have been defined by extensions to HTTP <a href="#RFC6585" id="rfc.xref.RFC6585.1"><cite title="Additional HTTP Status Codes">[RFC6585]</cite></a>.<a class="self" href="#rfc.section.9.3.p.3">&para;</a></p></div><div id="rfc.section.9.3.p.4"><p>Recipients ought to carefully limit the extent to which they process other protocol elements, including (but not limited to) request methods, response status phrases, header field-names, numeric values, and body chunks. Failure to limit such processing can result in buffer overflows, arithmetic overflows, or increased vulnerability to denial-of-service attacks.<a class="self" href="#rfc.section.9.3.p.4">&para;</a></p></div></div><div id="response.splitting"><h2 id="rfc.section.9.4"><a href="#rfc.section.9.4">9.4</a>&nbsp;<a href="#response.splitting">Response Splitting</a></h2><div id="rfc.section.9.4.p.1"><p>Response splitting (a.k.a, CRLF injection) is a common technique, used in various attacks on Web usage, that exploits the line-based nature of HTTP message framing and the ordered association of requests to responses on persistent connections <a href="#Klein" id="rfc.xref.Klein.1"><cite title="Divide and Conquer - HTTP Response Splitting, Web Cache Poisoning Attacks, and Related Topics">[Klein]</cite></a>. This technique can be particularly damaging when the requests pass through a shared cache.<a class="self" href="#rfc.section.9.4.p.1">&para;</a></p></div><div id="rfc.section.9.4.p.2"><p>Response splitting exploits a vulnerability in servers (usually within an application server) where an attacker can send encoded data within some parameter of the request that is later decoded and echoed within any of the response header fields of the response. If the decoded data is crafted to look like the response has ended and a subsequent response has begun, the response has been split and the content within the apparent second response is controlled by the attacker. The attacker can then make any other request on the same persistent connection and trick the recipients (including intermediaries) into believing that the second half of the split is an authoritative answer to the second request.<a class="self" href="#rfc.section.9.4.p.2">&para;</a></p></div><div id="rfc.section.9.4.p.3"><p>For example, a parameter within the request-target might be read by an application server and reused within a redirect, resulting in the same parameter being echoed in the <a href="rfc7231.html#header.location" class="smpl">Location</a> header field of the response. If the parameter is decoded by the application and not properly encoded when placed in the response field, the attacker can send encoded CRLF octets and other content that will make the application's single response look like two or more responses.<a class="self" href="#rfc.section.9.4.p.3">&para;</a></p></div><div id="rfc.section.9.4.p.4"><p>A common defense against response splitting is to filter requests for data that looks like encoded CR and LF (e.g., "%0D" and "%0A"). However, that assumes the application server is only performing URI decoding, rather than more obscure data transformations like charset transcoding, XML entity translation, base64 decoding, sprintf reformatting, etc. A more effective mitigation is to prevent anything other than the server's core protocol libraries from sending a CR or LF within the header section, which means restricting the output of header fields to APIs that filter for bad octets and not allowing application servers to write directly to the protocol stream.<a class="self" href="#rfc.section.9.4.p.4">&para;</a></p></div></div><div id="request.smuggling"><h2 id="rfc.section.9.5"><a href="#rfc.section.9.5">9.5</a>&nbsp;<a href="#request.smuggling">Request Smuggling</a></h2><div id="rfc.section.9.5.p.1"><p>Request smuggling (<a href="#Linhart" id="rfc.xref.Linhart.1"><cite title="HTTP Request Smuggling">[Linhart]</cite></a>) is a technique that exploits differences in protocol parsing among various recipients to hide additional requests (which might otherwise be blocked or disabled by policy) within an apparently harmless request. Like response splitting, request smuggling can lead to a variety of attacks on HTTP usage.<a class="self" href="#rfc.section.9.5.p.1">&para;</a></p></div><div id="rfc.section.9.5.p.2"><p>This specification has introduced new requirements on request parsing, particularly with regard to message framing in <a href="#message.body.length" title="Message Body Length">Section&nbsp;3.3.3</a>, to reduce the effectiveness of request smuggling.<a class="self" href="#rfc.section.9.5.p.2">&para;</a></p></div></div><div id="message.integrity"><h2 id="rfc.section.9.6"><a href="#rfc.section.9.6">9.6</a>&nbsp;<a href="#message.integrity">Message Integrity</a></h2><div id="rfc.section.9.6.p.1"><p>HTTP does not define a specific mechanism for ensuring message integrity, instead relying on the error-detection ability of underlying transport protocols and the use of length or chunk-delimited framing to detect completeness. Additional integrity mechanisms, such as hash functions or digital signatures applied to the content, can be selectively added to messages via extensible metadata header fields. Historically, the lack of a single integrity mechanism has been justified by the informal nature of most HTTP communication. However, the prevalence of HTTP as an information access mechanism has resulted in its increasing use within environments where verification of message integrity is crucial.<a class="self" href="#rfc.section.9.6.p.1">&para;</a></p></div><div id="rfc.section.9.6.p.2"><p>User agents are encouraged to implement configurable means for detecting and reporting failures of message integrity such that those means can be enabled within environments for which integrity is necessary. For example, a browser being used to view medical history or drug interaction information needs to indicate to the user when such information is detected by the protocol to be incomplete, expired, or corrupted during transfer. Such mechanisms might be selectively enabled via user agent extensions or the presence of message integrity metadata in a response. At a minimum, user agents ought to provide some indication that allows a user to distinguish between a complete and incomplete response message (<a href="#incomplete.messages" title="Handling Incomplete Messages">Section&nbsp;3.4</a>) when such verification is desired.<a class="self" href="#rfc.section.9.6.p.2">&para;</a></p></div></div><div id="message.confidentiality"><h2 id="rfc.section.9.7"><a href="#rfc.section.9.7">9.7</a>&nbsp;<a href="#message.confidentiality">Message Confidentiality</a></h2><div id="rfc.section.9.7.p.1"><p>HTTP relies on underlying transport protocols to provide message confidentiality when that is desired. HTTP has been specifically designed to be independent of the transport protocol, such that it can be used over many different forms of encrypted connection, with the selection of such transports being identified by the choice of URI scheme or within user agent configuration.<a class="self" href="#rfc.section.9.7.p.1">&para;</a></p></div><div id="rfc.section.9.7.p.2"><p>The "https" scheme can be used to identify resources that require a confidential connection, as described in <a href="#https.uri" title="https URI Scheme">Section&nbsp;2.7.2</a>.<a class="self" href="#rfc.section.9.7.p.2">&para;</a></p></div></div><div id="privacy.of.server.log.information"><h2 id="rfc.section.9.8"><a href="#rfc.section.9.8">9.8</a>&nbsp;<a href="#privacy.of.server.log.information">Privacy of Server Log Information</a></h2><div id="rfc.section.9.8.p.1"><p>A server is in the position to save personal data about a user's requests over time, which might identify their reading patterns or subjects of interest. In particular, log information gathered at an intermediary often contains a history of user agent interaction, across a multitude of sites, that can be traced to individual users.<a class="self" href="#rfc.section.9.8.p.1">&para;</a></p></div><div id="rfc.section.9.8.p.2"><p>HTTP log information is confidential in nature; its handling is often constrained by laws and regulations. Log information needs to be securely stored and appropriate guidelines followed for its analysis. Anonymization of personal information within individual entries helps, but it is generally not sufficient to prevent real log traces from being re-identified based on correlation with other access characteristics. As such, access traces that are keyed to a specific client are unsafe to publish even if the key is pseudonymous.<a class="self" href="#rfc.section.9.8.p.2">&para;</a></p></div><div id="rfc.section.9.8.p.3"><p>To minimize the risk of theft or accidental publication, log information ought to be purged of personally identifiable information, including user identifiers, IP addresses, and user-provided query parameters, as soon as that information is no longer necessary to support operational needs for security, auditing, or fraud control.<a class="self" href="#rfc.section.9.8.p.3">&para;</a></p></div></div></div><div id="acks"><h1 id="rfc.section.10"><a href="#rfc.section.10">10.</a>&nbsp;<a href="#acks">Acknowledgments</a></h1><div id="rfc.section.10.p.1"><p>This edition of HTTP/1.1 builds on the many contributions that went into <a href="#RFC1945" id="rfc.xref.RFC1945.2">RFC 1945</a>, <a href="#RFC2068" id="rfc.xref.RFC2068.3">RFC 2068</a>, <a href="#RFC2145" id="rfc.xref.RFC2145.2">RFC 2145</a>, and <a href="#RFC2616" id="rfc.xref.RFC2616.3">RFC 2616</a>, including substantial contributions made by the previous authors, editors, and Working Group Chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding, Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter, and Paul J. Leach. Mark Nottingham oversaw this effort as Working Group Chair.<a class="self" href="#rfc.section.10.p.1">&para;</a></p></div><div id="rfc.section.10.p.2"><p>Since 1999, the following contributors have helped improve the HTTP specification by reporting bugs, asking smart questions, drafting or reviewing text, and evaluating open issues:<a class="self" href="#rfc.section.10.p.2">&para;</a></p></div><div id="rfc.section.10.p.3"><p>Adam Barth, Adam Roach, Addison Phillips, Adrian Chadd, Adrian Cole, Adrien W. de Croy, Alan Ford, Alan Ruttenberg, Albert Lunde, Alek Storm, Alex Rousskov, Alexandre Morgaut, Alexey Melnikov, Alisha Smith, Amichai Rothman, Amit Klein, Amos Jeffries, Andreas Maier, Andreas Petersson, Andrei Popov, Anil Sharma, Anne van Kesteren, Anthony Bryan, Asbjorn Ulsberg, Ashok Kumar, Balachander Krishnamurthy, Barry Leiba, Ben Laurie, Benjamin Carlyle, Benjamin Niven-Jenkins, Benoit Claise, Bil Corry, Bill Burke, Bjoern Hoehrmann, Bob Scheifler, Boris Zbarsky, Brett Slatkin, Brian Kell, Brian McBarron, Brian Pane, Brian Raymor, Brian Smith, Bruce Perens, Bryce Nesbitt, Cameron Heavon-Jones, Carl Kugler, Carsten Bormann, Charles Fry, Chris Burdess, Chris Newman, Christian Huitema, Cyrus Daboo, Dale Robert Anderson, Dan Wing, Dan Winship, Daniel Stenberg, Darrel Miller, Dave Cridland, Dave Crocker, Dave Kristol, Dave Thaler, David Booth, David Singer, David W. Morris, Diwakar Shetty, Dmitry Kurochkin, Drummond Reed, Duane Wessels, Edward Lee, Eitan Adler, Eliot Lear, Emile Stephan, Eran Hammer-Lahav, Eric D. Williams, Eric J. Bowman, Eric Lawrence, Eric Rescorla, Erik Aronesty, EungJun Yi, Evan Prodromou, Felix Geisendoerfer, Florian Weimer, Frank Ellermann, Fred Akalin, Fred Bohle, Frederic Kayser, Gabor Molnar, Gabriel Montenegro, Geoffrey Sneddon, Gervase Markham, Gili Tzabari, Grahame Grieve, Greg Slepak, Greg Wilkins, Grzegorz Calkowski, Harald Tveit Alvestrand, Harry Halpin, Helge Hess, Henrik Nordstrom, Henry S. Thompson, Henry Story, Herbert van de Sompel, Herve Ruellan, Howard Melman, Hugo Haas, Ian Fette, Ian Hickson, Ido Safruti, Ilari Liusvaara, Ilya Grigorik, Ingo Struck, J. Ross Nicoll, James Cloos, James H. Manger, James Lacey, James M. Snell, Jamie Lokier, Jan Algermissen, Jari Arkko, Jeff Hodges (who came up with the term 'effective Request-URI'), Jeff Pinner, Jeff Walden, Jim Luther, Jitu Padhye, Joe D. Williams, Joe Gregorio, Joe Orton, Joel Jaeggli, John C. Klensin, John C. Mallery, John Cowan, John Kemp, John Panzer, John Schneider, John Stracke, John Sullivan, Jonas Sicking, Jonathan A. Rees, Jonathan Billington, Jonathan Moore, Jonathan Silvera, Jordi Ros, Joris Dobbelsteen, Josh Cohen, Julien Pierre, Jungshik Shin, Justin Chapweske, Justin Erenkrantz, Justin James, Kalvinder Singh, Karl Dubost, Kathleen Moriarty, Keith Hoffman, Keith Moore, Ken Murchison, Koen Holtman, Konstantin Voronkov, Kris Zyp, Leif Hedstrom, Lionel Morand, Lisa Dusseault, Maciej Stachowiak, Manu Sporny, Marc Schneider, Marc Slemko, Mark Baker, Mark Pauley, Mark Watson, Markus Isomaki, Markus Lanthaler, Martin J. Duerst, Martin Musatov, Martin Nilsson, Martin Thomson, Matt Lynch, Matthew Cox, Matthew Kerwin, Max Clark, Menachem Dodge, Meral Shirazipour, Michael Burrows, Michael Hausenblas, Michael Scharf, Michael Sweet, Michael Tuexen, Michael Welzl, Mike Amundsen, Mike Belshe, Mike Bishop, Mike Kelly, Mike Schinkel, Miles Sabin, Murray S. Kucherawy, Mykyta Yevstifeyev, Nathan Rixham, Nicholas Shanks, Nico Williams, Nicolas Alvarez, Nicolas Mailhot, Noah Slater, Osama Mazahir, Pablo Castro, Pat Hayes, Patrick R. McManus, Paul E. Jones, Paul Hoffman, Paul Marquess, Pete Resnick, Peter Lepeska, Peter Occil, Peter Saint-Andre, Peter Watkins, Phil Archer, Phil Hunt, Philippe Mougin, Phillip Hallam-Baker, Piotr Dobrogost, Poul-Henning Kamp, Preethi Natarajan, Rajeev Bector, Ray Polk, Reto Bachmann-Gmuer, Richard Barnes, Richard Cyganiak, Rob Trace, Robby Simpson, Robert Brewer, Robert Collins, Robert Mattson, Robert O'Callahan, Robert Olofsson, Robert Sayre, Robert Siemer, Robert de Wilde, Roberto Javier Godoy, Roberto Peon, Roland Zink, Ronny Widjaja, Ryan Hamilton, S. Mike Dierken, Salvatore Loreto, Sam Johnston, Sam Pullara, Sam Ruby, Saurabh Kulkarni, Scott Lawrence (who maintained the original issues list), Sean B. Palmer, Sean Turner, Sebastien Barnoud, Shane McCarron, Shigeki Ohtsu, Simon Yarde, Stefan Eissing, Stefan Tilkov, Stefanos Harhalakis, Stephane Bortzmeyer, Stephen Farrell, Stephen Kent, Stephen Ludin, Stuart Williams, Subbu Allamaraju, Subramanian Moonesamy, Susan Hares, Sylvain Hellegouarch, Tapan Divekar, Tatsuhiro Tsujikawa, Tatsuya Hayashi, Ted Hardie, Ted Lemon, Thomas Broyer, Thomas Fossati, Thomas Maslen, Thomas Nadeau, Thomas Nordin, Thomas Roessler, Tim Bray, Tim Morgan, Tim Olsen, Tom Zhou, Travis Snoozy, Tyler Close, Vincent Murphy, Wenbo Zhu, Werner Baumann, Wilbur Streett, Wilfredo Sanchez Vega, William A. Rowe Jr., William Chan, Willy Tarreau, Xiaoshu Wang, Yaron Goland, Yngve Nysaeter Pettersen, Yoav Nir, Yogesh Bang, Yuchung Cheng, Yutaka Oiwa, Yves Lafon (long-time member of the editor team), Zed A. Shaw, and Zhong Yu.<a class="self" href="#rfc.section.10.p.3">&para;</a></p></div><div id="rfc.section.10.p.4"><p>See <a href="https://tools.ietf.org/html/rfc2616#section-16">Section 16</a> of <a href="#RFC2616" id="rfc.xref.RFC2616.4"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a> for additional acknowledgements from prior revisions.<a class="self" href="#rfc.section.10.p.4">&para;</a></p></div></div><h1 id="rfc.references"><a id="rfc.section.11" href="#rfc.section.11">11.</a> References</h1><h2 id="rfc.references.1"><a href="#rfc.section.11.1" id="rfc.section.11.1">11.1</a> Normative References</h2><table><tr><td class="reference"><b id="RFC0793">[RFC0793]</b></td><td class="top">Postel, J., &#8220;<a href="https://tools.ietf.org/html/rfc793">Transmission Control Protocol</a>&#8221;, STD&nbsp;7, RFC&nbsp;793, September&nbsp;1981.</td></tr><tr><td class="reference"><b id="RFC1950">[RFC1950]</b></td><td class="top">Deutsch, L. and J-L. Gailly, &#8220;<a href="https://tools.ietf.org/html/rfc1950">ZLIB Compressed Data Format Specification version 3.3</a>&#8221;, RFC&nbsp;1950, May&nbsp;1996.</td></tr><tr><td class="reference"><b id="RFC1951">[RFC1951]</b></td><td class="top">Deutsch, P., &#8220;<a href="https://tools.ietf.org/html/rfc1951">DEFLATE Compressed Data Format Specification version 1.3</a>&#8221;, RFC&nbsp;1951, May&nbsp;1996.</td></tr><tr><td class="reference"><b id="RFC1952">[RFC1952]</b></td><td class="top">Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and G. Randers-Pehrson, &#8220;<a href="https://tools.ietf.org/html/rfc1952">GZIP file format specification version 4.3</a>&#8221;, RFC&nbsp;1952, May&nbsp;1996.</td></tr><tr><td class="reference"><b id="RFC2119">[RFC2119]</b></td><td class="top">Bradner, S., &#8220;<a href="https://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>&#8221;, BCP&nbsp;14, RFC&nbsp;2119, March&nbsp;1997.</td></tr><tr><td class="reference"><b id="RFC3986">[RFC3986]</b></td><td class="top">Berners-Lee, T., Fielding, R., and L. Masinter, &#8220;<a href="https://tools.ietf.org/html/rfc3986">Uniform Resource Identifier (URI): Generic Syntax</a>&#8221;, STD&nbsp;66, RFC&nbsp;3986, January&nbsp;2005.</td></tr><tr><td class="reference"><b id="RFC5234">[RFC5234]</b></td><td class="top">Crocker, D., Ed. and P. Overell, &#8220;<a href="https://tools.ietf.org/html/rfc5234">Augmented BNF for Syntax Specifications: ABNF</a>&#8221;, STD&nbsp;68, RFC&nbsp;5234, January&nbsp;2008.</td></tr><tr><td class="reference"><b id="RFC7231">[RFC7231]</b></td><td class="top">Fielding, R., Ed. and J. Reschke, Ed., &#8220;<a href="https://tools.ietf.org/html/rfc7231">Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</a>&#8221;, RFC&nbsp;7231, June&nbsp;2014.</td></tr><tr><td class="reference"><b id="RFC7232">[RFC7232]</b></td><td class="top">Fielding, R., Ed. and J. Reschke, Ed., &#8220;<a href="https://tools.ietf.org/html/rfc7232">Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests</a>&#8221;, RFC&nbsp;7232, June&nbsp;2014.</td></tr><tr><td class="reference"><b id="RFC7233">[RFC7233]</b></td><td class="top">Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed., &#8220;<a href="https://tools.ietf.org/html/rfc7233">Hypertext Transfer Protocol (HTTP/1.1): Range Requests</a>&#8221;, RFC&nbsp;7233, June&nbsp;2014.</td></tr><tr><td class="reference"><b id="RFC7234">[RFC7234]</b></td><td class="top">Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., &#8220;<a href="https://tools.ietf.org/html/rfc7234">Hypertext Transfer Protocol (HTTP/1.1): Caching</a>&#8221;, RFC&nbsp;7234, June&nbsp;2014.</td></tr><tr><td class="reference"><b id="RFC7235">[RFC7235]</b></td><td class="top">Fielding, R., Ed. and J. Reschke, Ed., &#8220;<a href="https://tools.ietf.org/html/rfc7235">Hypertext Transfer Protocol (HTTP/1.1): Authentication</a>&#8221;, RFC&nbsp;7235, June&nbsp;2014.</td></tr><tr><td class="reference"><b id="USASCII">[USASCII]</b></td><td class="top">American National Standards Institute, &#8220;Coded Character Set -- 7-bit American Standard Code for Information Interchange&#8221;, ANSI&nbsp;X3.4, 1986.</td></tr><tr><td class="reference"><b id="Welch">[Welch]</b></td><td class="top">Welch, T., &#8220;A Technique for High-Performance Data Compression&#8221;, IEEE Computer&nbsp;17(6), June&nbsp;1984.</td></tr></table><h2 id="rfc.references.2"><a href="#rfc.section.11.2" id="rfc.section.11.2">11.2</a> Informative References</h2><table><tr><td class="reference"><b id="BCP115">[BCP115]</b></td><td class="top">Hansen, T., Hardie, T., and L. Masinter, &#8220;<a href="https://tools.ietf.org/html/rfc4395">Guidelines and Registration Procedures for New URI Schemes</a>&#8221;, BCP&nbsp;115, RFC&nbsp;4395, February&nbsp;2006.</td></tr><tr><td class="reference"><b id="BCP13">[BCP13]</b></td><td class="top">Freed, N., Klensin, J., and T. Hansen, &#8220;<a href="https://tools.ietf.org/html/rfc6838">Media Type Specifications and Registration Procedures</a>&#8221;, BCP&nbsp;13, RFC&nbsp;6838, January&nbsp;2013.</td></tr><tr><td class="reference"><b id="BCP90">[BCP90]</b></td><td class="top">Klyne, G., Nottingham, M., and J. Mogul, &#8220;<a href="https://tools.ietf.org/html/rfc3864">Registration Procedures for Message Header Fields</a>&#8221;, BCP&nbsp;90, RFC&nbsp;3864, September&nbsp;2004.</td></tr><tr><td class="reference"><b id="Georgiev">[Georgiev]</b></td><td class="top">Georgiev, M., Iyengar, S., Jana, S., Anubhai, R., Boneh, D., and V. Shmatikov, &#8220;<a href="http://doi.acm.org/10.1145/2382196.2382204">The Most Dangerous Code in the World: Validating SSL Certificates in Non-browser Software</a>&#8221;, In Proceedings of the 2012 ACM Conference on Computer and Communications Security (CCS '12), pp. 38-49, October&nbsp;2012, &lt;<a href="http://doi.acm.org/10.1145/2382196.2382204">http://doi.acm.org/10.1145/2382196.2382204</a>&gt;.</td></tr><tr><td class="reference"><b id="ISO-8859-1">[ISO-8859-1]</b></td><td class="top">International Organization for Standardization, &#8220;Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1&#8221;, ISO/IEC&nbsp;8859-1:1998, 1998.</td></tr><tr><td class="reference"><b id="Klein">[Klein]</b></td><td class="top">Klein, A., &#8220;<a href="http://packetstormsecurity.com/papers/general/whitepaper_httpresponse.pdf">Divide and Conquer - HTTP Response Splitting, Web Cache Poisoning Attacks, and Related Topics</a>&#8221;, March&nbsp;2004, &lt;<a href="http://packetstormsecurity.com/papers/general/whitepaper_httpresponse.pdf">http://packetstormsecurity.com/papers/general/whitepaper_httpresponse.pdf</a>&gt;.</td></tr><tr><td class="reference"><b id="Kri2001">[Kri2001]</b></td><td class="top">Kristol, D., &#8220;<a href="http://arxiv.org/abs/cs.SE/0105018">HTTP Cookies: Standards, Privacy, and Politics</a>&#8221;, ACM Transactions on Internet Technology&nbsp;1(2), November&nbsp;2001, &lt;<a href="http://arxiv.org/abs/cs.SE/0105018">http://arxiv.org/abs/cs.SE/0105018</a>&gt;.</td></tr><tr><td class="reference"><b id="Linhart">[Linhart]</b></td><td class="top">Linhart, C., Klein, A., Heled, R., and S. Orrin, &#8220;<a href="http://www.watchfire.com/news/whitepapers.aspx">HTTP Request Smuggling</a>&#8221;, June&nbsp;2005, &lt;<a href="http://www.watchfire.com/news/whitepapers.aspx">http://www.watchfire.com/news/whitepapers.aspx</a>&gt;.</td></tr><tr><td class="reference"><b id="RFC1919">[RFC1919]</b></td><td class="top">Chatel, M., &#8220;<a href="https://tools.ietf.org/html/rfc1919">Classical versus Transparent IP Proxies</a>&#8221;, RFC&nbsp;1919, March&nbsp;1996.</td></tr><tr><td class="reference"><b id="RFC1945">[RFC1945]</b></td><td class="top">Berners-Lee, T., Fielding, R., and H. Nielsen, &#8220;<a href="https://tools.ietf.org/html/rfc1945">Hypertext Transfer Protocol -- HTTP/1.0</a>&#8221;, RFC&nbsp;1945, May&nbsp;1996.</td></tr><tr><td class="reference"><b id="RFC2045">[RFC2045]</b></td><td class="top">Freed, N. and N. Borenstein, &#8220;<a href="https://tools.ietf.org/html/rfc2045">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</a>&#8221;, RFC&nbsp;2045, November&nbsp;1996.</td></tr><tr><td class="reference"><b id="RFC2047">[RFC2047]</b></td><td class="top">Moore, K., &#8220;<a href="https://tools.ietf.org/html/rfc2047">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</a>&#8221;, RFC&nbsp;2047, November&nbsp;1996.</td></tr><tr><td class="reference"><b id="RFC2068">[RFC2068]</b></td><td class="top">Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T. Berners-Lee, &#8220;<a href="https://tools.ietf.org/html/rfc2068">Hypertext Transfer Protocol -- HTTP/1.1</a>&#8221;, RFC&nbsp;2068, January&nbsp;1997.</td></tr><tr><td class="reference"><b id="RFC2145">[RFC2145]</b></td><td class="top">Mogul, J., Fielding, R., Gettys, J., and H. Nielsen, &#8220;<a href="https://tools.ietf.org/html/rfc2145">Use and Interpretation of HTTP Version Numbers</a>&#8221;, RFC&nbsp;2145, May&nbsp;1997.</td></tr><tr><td class="reference"><b id="RFC2616">[RFC2616]</b></td><td class="top">Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, &#8220;<a href="https://tools.ietf.org/html/rfc2616">Hypertext Transfer Protocol -- HTTP/1.1</a>&#8221;, RFC&nbsp;2616, June&nbsp;1999.</td></tr><tr><td class="reference"><b id="RFC2817">[RFC2817]</b></td><td class="top">Khare, R. and S. Lawrence, &#8220;<a href="https://tools.ietf.org/html/rfc2817">Upgrading to TLS Within HTTP/1.1</a>&#8221;, RFC&nbsp;2817, May&nbsp;2000.</td></tr><tr><td class="reference"><b id="RFC2818">[RFC2818]</b></td><td class="top">Rescorla, E., &#8220;<a href="https://tools.ietf.org/html/rfc2818">HTTP Over TLS</a>&#8221;, RFC&nbsp;2818, May&nbsp;2000.</td></tr><tr><td class="reference"><b id="RFC3040">[RFC3040]</b></td><td class="top">Cooper, I., Melve, I., and G. Tomlinson, &#8220;<a href="https://tools.ietf.org/html/rfc3040">Internet Web Replication and Caching Taxonomy</a>&#8221;, RFC&nbsp;3040, January&nbsp;2001.</td></tr><tr><td class="reference"><b id="RFC4033">[RFC4033]</b></td><td class="top">Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, &#8220;<a href="https://tools.ietf.org/html/rfc4033">DNS Security Introduction and Requirements</a>&#8221;, RFC&nbsp;4033, March&nbsp;2005.</td></tr><tr><td class="reference"><b id="RFC4559">[RFC4559]</b></td><td class="top">Jaganathan, K., Zhu, L., and J. Brezak, &#8220;<a href="https://tools.ietf.org/html/rfc4559">SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</a>&#8221;, RFC&nbsp;4559, June&nbsp;2006.</td></tr><tr><td class="reference"><b id="RFC5226">[RFC5226]</b></td><td class="top">Narten, T. and H. Alvestrand, &#8220;<a href="https://tools.ietf.org/html/rfc5226">Guidelines for Writing an IANA Considerations Section in RFCs</a>&#8221;, BCP&nbsp;26, RFC&nbsp;5226, May&nbsp;2008.</td></tr><tr><td class="reference"><b id="RFC5246">[RFC5246]</b></td><td class="top">Dierks, T. and E. Rescorla, &#8220;<a href="https://tools.ietf.org/html/rfc5246">The Transport Layer Security (TLS) Protocol Version 1.2</a>&#8221;, RFC&nbsp;5246, August&nbsp;2008.</td></tr><tr><td class="reference"><b id="RFC5322">[RFC5322]</b></td><td class="top">Resnick, P., &#8220;<a href="https://tools.ietf.org/html/rfc5322">Internet Message Format</a>&#8221;, RFC&nbsp;5322, October&nbsp;2008.</td></tr><tr><td class="reference"><b id="RFC6265">[RFC6265]</b></td><td class="top">Barth, A., &#8220;<a href="https://tools.ietf.org/html/rfc6265">HTTP State Management Mechanism</a>&#8221;, RFC&nbsp;6265, April&nbsp;2011.</td></tr><tr><td class="reference"><b id="RFC6585">[RFC6585]</b></td><td class="top">Nottingham, M. and R. Fielding, &#8220;<a href="https://tools.ietf.org/html/rfc6585">Additional HTTP Status Codes</a>&#8221;, RFC&nbsp;6585, April&nbsp;2012.</td></tr></table><div id="compatibility"><h1 id="rfc.section.A" class="np"><a href="#rfc.section.A">A.</a>&nbsp;<a href="#compatibility">HTTP Version History</a></h1><div id="rfc.section.A.p.1"><p>HTTP has been in use since 1990. The first version, later referred to as HTTP/0.9, was a simple protocol for hypertext data transfer across the Internet, using only a single request method (GET) and no metadata. HTTP/1.0, as defined by <a href="#RFC1945" id="rfc.xref.RFC1945.3"><cite title="Hypertext Transfer Protocol -- HTTP/1.0">[RFC1945]</cite></a>, added a range of request methods and MIME-like messaging, allowing for metadata to be transferred and modifiers placed on the request/response semantics. However, HTTP/1.0 did not sufficiently take into consideration the effects of hierarchical proxies, caching, the need for persistent connections, or name-based virtual hosts. The proliferation of incompletely implemented applications calling themselves "HTTP/1.0" further necessitated a protocol version change in order for two communicating applications to determine each other's true capabilities.<a class="self" href="#rfc.section.A.p.1">&para;</a></p></div><div id="rfc.section.A.p.2"><p>HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent requirements that enable reliable implementations, adding only those features that can either be safely ignored by an HTTP/1.0 recipient or only be sent when communicating with a party advertising conformance with HTTP/1.1.<a class="self" href="#rfc.section.A.p.2">&para;</a></p></div><div id="rfc.section.A.p.3"><p>HTTP/1.1 has been designed to make supporting previous versions easy. A general-purpose HTTP/1.1 server ought to be able to understand any valid request in the format of HTTP/1.0, responding appropriately with an HTTP/1.1 message that only uses features understood (or safely ignored) by HTTP/1.0 clients. Likewise, an HTTP/1.1 client can be expected to understand any valid HTTP/1.0 response.<a class="self" href="#rfc.section.A.p.3">&para;</a></p></div><div id="rfc.section.A.p.4"><p>Since HTTP/0.9 did not support header fields in a request, there is no mechanism for it to support name-based virtual hosts (selection of resource by inspection of the <a href="#header.host" class="smpl">Host</a> header field). Any server that implements name-based virtual hosts ought to disable support for HTTP/0.9. Most requests that appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x requests caused by a client failing to properly encode the request-target.<a class="self" href="#rfc.section.A.p.4">&para;</a></p></div><div id="changes.from.1.0"><h2 id="rfc.section.A.1"><a href="#rfc.section.A.1">A.1</a>&nbsp;<a href="#changes.from.1.0">Changes from HTTP/1.0</a></h2><div id="rfc.section.A.1.p.1"><p>This section summarizes major differences between versions HTTP/1.0 and HTTP/1.1.<a class="self" href="#rfc.section.A.1.p.1">&para;</a></p></div><div id="changes.to.simplify.multihomed.web.servers.and.conserve.ip.addresses"><h3 id="rfc.section.A.1.1"><a href="#rfc.section.A.1.1">A.1.1</a>&nbsp;<a href="#changes.to.simplify.multihomed.web.servers.and.conserve.ip.addresses">Multihomed Web Servers</a></h3><div id="rfc.section.A.1.1.p.1"><p>The requirements that clients and servers support the <a href="#header.host" class="smpl">Host</a> header field (<a href="#header.host" id="rfc.xref.header.host.3" title="Host">Section&nbsp;5.4</a>), report an error if it is missing from an HTTP/1.1 request, and accept absolute URIs (<a href="#request-target" title="Request Target">Section&nbsp;5.3</a>) are among the most important changes defined by HTTP/1.1.<a class="self" href="#rfc.section.A.1.1.p.1">&para;</a></p></div><div id="rfc.section.A.1.1.p.2"><p>Older HTTP/1.0 clients assumed a one-to-one relationship of IP addresses and servers; there was no other established mechanism for distinguishing the intended server of a request than the IP address to which that request was directed. The <a href="#header.host" class="smpl">Host</a> header field was introduced during the development of HTTP/1.1 and, though it was quickly implemented by most HTTP/1.0 browsers, additional requirements were placed on all HTTP/1.1 requests in order to ensure complete adoption. At the time of this writing, most HTTP-based services are dependent upon the Host header field for targeting requests.<a class="self" href="#rfc.section.A.1.1.p.2">&para;</a></p></div></div><div id="compatibility.with.http.1.0.persistent.connections"><h3 id="rfc.section.A.1.2"><a href="#rfc.section.A.1.2">A.1.2</a>&nbsp;<a href="#compatibility.with.http.1.0.persistent.connections">Keep-Alive Connections</a></h3><div id="rfc.section.A.1.2.p.1"><p>In HTTP/1.0, each connection is established by the client prior to the request and closed by the server after sending the response. However, some implementations implement the explicitly negotiated ("Keep-Alive") version of persistent connections described in <a href="https://tools.ietf.org/html/rfc2068#section-19.7.1">Section 19.7.1</a> of <a href="#RFC2068" id="rfc.xref.RFC2068.4"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>.<a class="self" href="#rfc.section.A.1.2.p.1">&para;</a></p></div><div id="rfc.section.A.1.2.p.2"><p>Some clients and servers might wish to be compatible with these previous approaches to persistent connections, by explicitly negotiating for them with a "Connection: keep-alive" request header field. However, some experimental implementations of HTTP/1.0 persistent connections are faulty; for example, if an HTTP/1.0 proxy server doesn't understand <a href="#header.connection" class="smpl">Connection</a>, it will erroneously forward that header field to the next inbound server, which would result in a hung connection.<a class="self" href="#rfc.section.A.1.2.p.2">&para;</a></p></div><div id="rfc.section.A.1.2.p.3"><p>One attempted solution was the introduction of a Proxy-Connection header field, targeted specifically at proxies. In practice, this was also unworkable, because proxies are often deployed in multiple layers, bringing about the same problem discussed above.<a class="self" href="#rfc.section.A.1.2.p.3">&para;</a></p></div><div id="rfc.section.A.1.2.p.4"><p>As a result, clients are encouraged not to send the Proxy-Connection header field in any requests.<a class="self" href="#rfc.section.A.1.2.p.4">&para;</a></p></div><div id="rfc.section.A.1.2.p.5"><p>Clients are also encouraged to consider the use of Connection: keep-alive in requests carefully; while they can enable persistent connections with HTTP/1.0 servers, clients using them will need to monitor the connection for "hung" requests (which indicate that the client ought stop sending the header field), and this mechanism ought not be used by clients at all when a proxy is being used.<a class="self" href="#rfc.section.A.1.2.p.5">&para;</a></p></div></div><div id="introduction.of.transfer-encoding"><h3 id="rfc.section.A.1.3"><a href="#rfc.section.A.1.3">A.1.3</a>&nbsp;<a href="#introduction.of.transfer-encoding">Introduction of Transfer-Encoding</a></h3><div id="rfc.section.A.1.3.p.1"><p>HTTP/1.1 introduces the <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.4" title="Transfer-Encoding">Section&nbsp;3.3.1</a>). Transfer codings need to be decoded prior to forwarding an HTTP message over a MIME-compliant protocol.<a class="self" href="#rfc.section.A.1.3.p.1">&para;</a></p></div></div></div><div id="changes.from.rfc.2616"><h2 id="rfc.section.A.2"><a href="#rfc.section.A.2">A.2</a>&nbsp;<a href="#changes.from.rfc.2616">Changes from RFC 2616</a></h2><div id="rfc.section.A.2.p.1"><p>HTTP's approach to error handling has been explained. (<a href="#conformance" title="Conformance and Error Handling">Section&nbsp;2.5</a>)<a class="self" href="#rfc.section.A.2.p.1">&para;</a></p></div><div id="rfc.section.A.2.p.2"><p>The HTTP-version ABNF production has been clarified to be case-sensitive. Additionally, version numbers have been restricted to single digits, due to the fact that implementations are known to handle multi-digit version numbers incorrectly. (<a href="#http.version" title="Protocol Versioning">Section&nbsp;2.6</a>)<a class="self" href="#rfc.section.A.2.p.2">&para;</a></p></div><div id="rfc.section.A.2.p.3"><p>Userinfo (i.e., username and password) are now disallowed in HTTP and HTTPS URIs, because of security issues related to their transmission on the wire. (<a href="#http.uri" title="http URI Scheme">Section&nbsp;2.7.1</a>)<a class="self" href="#rfc.section.A.2.p.3">&para;</a></p></div><div id="rfc.section.A.2.p.4"><p>The HTTPS URI scheme is now defined by this specification; previously, it was done in <a href="https://tools.ietf.org/html/rfc2818#section-2.4">Section 2.4</a> of <a href="#RFC2818" id="rfc.xref.RFC2818.4"><cite title="HTTP Over TLS">[RFC2818]</cite></a>. Furthermore, it implies end-to-end security. (<a href="#https.uri" title="https URI Scheme">Section&nbsp;2.7.2</a>)<a class="self" href="#rfc.section.A.2.p.4">&para;</a></p></div><div id="rfc.section.A.2.p.5"><p>HTTP messages can be (and often are) buffered by implementations; despite it sometimes being available as a stream, HTTP is fundamentally a message-oriented protocol. Minimum supported sizes for various protocol elements have been suggested, to improve interoperability. (<a href="#http.message" title="Message Format">Section&nbsp;3</a>)<a class="self" href="#rfc.section.A.2.p.5">&para;</a></p></div><div id="rfc.section.A.2.p.6"><p>Invalid whitespace around field-names is now required to be rejected, because accepting it represents a security vulnerability. The ABNF productions defining header fields now only list the field value. (<a href="#header.fields" title="Header Fields">Section&nbsp;3.2</a>)<a class="self" href="#rfc.section.A.2.p.6">&para;</a></p></div><div id="rfc.section.A.2.p.7"><p>Rules about implicit linear whitespace between certain grammar productions have been removed; now whitespace is only allowed where specifically defined in the ABNF. (<a href="#whitespace" title="Whitespace">Section&nbsp;3.2.3</a>)<a class="self" href="#rfc.section.A.2.p.7">&para;</a></p></div><div id="rfc.section.A.2.p.8"><p>Header fields that span multiple lines ("line folding") are deprecated. (<a href="#field.parsing" title="Field Parsing">Section&nbsp;3.2.4</a>)<a class="self" href="#rfc.section.A.2.p.8">&para;</a></p></div><div id="rfc.section.A.2.p.9"><p>The NUL octet is no longer allowed in comment and quoted-string text, and handling of backslash-escaping in them has been clarified. The quoted-pair rule no longer allows escaping control characters other than HTAB. Non-US-ASCII content in header fields and the reason phrase has been obsoleted and made opaque (the TEXT rule was removed). (<a href="#field.components" title="Field Value Components">Section&nbsp;3.2.6</a>)<a class="self" href="#rfc.section.A.2.p.9">&para;</a></p></div><div id="rfc.section.A.2.p.10"><p>Bogus <a href="#header.content-length" class="smpl">Content-Length</a> header fields are now required to be handled as errors by recipients. (<a href="#header.content-length" id="rfc.xref.header.content-length.2" title="Content-Length">Section&nbsp;3.3.2</a>)<a class="self" href="#rfc.section.A.2.p.10">&para;</a></p></div><div id="rfc.section.A.2.p.11"><p>The algorithm for determining the message body length has been clarified to indicate all of the special cases (e.g., driven by methods or status codes) that affect it, and that new protocol elements cannot define such special cases. CONNECT is a new, special case in determining message body length. "multipart/byteranges" is no longer a way of determining message body length detection. (<a href="#message.body.length" title="Message Body Length">Section&nbsp;3.3.3</a>)<a class="self" href="#rfc.section.A.2.p.11">&para;</a></p></div><div id="rfc.section.A.2.p.12"><p>The "identity" transfer coding token has been removed. (Sections <a href="#message.body" title="Message Body">3.3</a> and <a href="#transfer.codings" title="Transfer Codings">4</a>)<a class="self" href="#rfc.section.A.2.p.12">&para;</a></p></div><div id="rfc.section.A.2.p.13"><p>Chunk length does not include the count of the octets in the chunk header and trailer. Line folding in chunk extensions is disallowed. (<a href="#chunked.encoding" title="Chunked Transfer Coding">Section&nbsp;4.1</a>)<a class="self" href="#rfc.section.A.2.p.13">&para;</a></p></div><div id="rfc.section.A.2.p.14"><p>The meaning of the "deflate" content coding has been clarified. (<a href="#deflate.coding" title="Deflate Coding">Section&nbsp;4.2.2</a>)<a class="self" href="#rfc.section.A.2.p.14">&para;</a></p></div><div id="rfc.section.A.2.p.15"><p>The segment + query components of RFC 3986 have been used to define the request-target, instead of abs_path from RFC 1808. The asterisk-form of the request-target is only allowed with the OPTIONS method. (<a href="#request-target" title="Request Target">Section&nbsp;5.3</a>)<a class="self" href="#rfc.section.A.2.p.15">&para;</a></p></div><div id="rfc.section.A.2.p.16"><p>The term "Effective Request URI" has been introduced. (<a href="#effective.request.uri" title="Effective Request URI">Section&nbsp;5.5</a>)<a class="self" href="#rfc.section.A.2.p.16">&para;</a></p></div><div id="rfc.section.A.2.p.17"><p>Gateways do not need to generate <a href="#header.via" class="smpl">Via</a> header fields anymore. (<a href="#header.via" id="rfc.xref.header.via.2" title="Via">Section&nbsp;5.7.1</a>)<a class="self" href="#rfc.section.A.2.p.17">&para;</a></p></div><div id="rfc.section.A.2.p.18"><p>Exactly when "close" connection options have to be sent has been clarified. Also, "hop-by-hop" header fields are required to appear in the Connection header field; just because they're defined as hop-by-hop in this specification doesn't exempt them. (<a href="#header.connection" id="rfc.xref.header.connection.8" title="Connection">Section&nbsp;6.1</a>)<a class="self" href="#rfc.section.A.2.p.18">&para;</a></p></div><div id="rfc.section.A.2.p.19"><p>The limit of two connections per server has been removed. An idempotent sequence of requests is no longer required to be retried. The requirement to retry requests under certain circumstances when the server prematurely closes the connection has been removed. Also, some extraneous requirements about when servers are allowed to close connections prematurely have been removed. (<a href="#persistent.connections" title="Persistence">Section&nbsp;6.3</a>)<a class="self" href="#rfc.section.A.2.p.19">&para;</a></p></div><div id="rfc.section.A.2.p.20"><p>The semantics of the <a href="#header.upgrade" class="smpl">Upgrade</a> header field is now defined in responses other than 101 (this was incorporated from <a href="#RFC2817" id="rfc.xref.RFC2817.3"><cite title="Upgrading to TLS Within HTTP/1.1">[RFC2817]</cite></a>). Furthermore, the ordering in the field value is now significant. (<a href="#header.upgrade" id="rfc.xref.header.upgrade.3" title="Upgrade">Section&nbsp;6.7</a>)<a class="self" href="#rfc.section.A.2.p.20">&para;</a></p></div><div id="rfc.section.A.2.p.21"><p>Empty list elements in list productions (e.g., a list header field containing ", ,") have been deprecated. (<a href="#abnf.extension" title="ABNF List Extension: #rule">Section&nbsp;7</a>)<a class="self" href="#rfc.section.A.2.p.21">&para;</a></p></div><div id="rfc.section.A.2.p.22"><p>Registration of Transfer Codings now requires IETF Review (<a href="#transfer.coding.registry" title="Transfer Coding Registry">Section&nbsp;8.4</a>)<a class="self" href="#rfc.section.A.2.p.22">&para;</a></p></div><div id="rfc.section.A.2.p.23"><p>This specification now defines the Upgrade Token Registry, previously defined in <a href="https://tools.ietf.org/html/rfc2817#section-7.2">Section 7.2</a> of <a href="#RFC2817" id="rfc.xref.RFC2817.4"><cite title="Upgrading to TLS Within HTTP/1.1">[RFC2817]</cite></a>. (<a href="#upgrade.token.registry" title="Upgrade Token Registry">Section&nbsp;8.6</a>)<a class="self" href="#rfc.section.A.2.p.23">&para;</a></p></div><div id="rfc.section.A.2.p.24"><p>The expectation to support HTTP/0.9 requests has been removed. (<a href="#compatibility" title="HTTP Version History">Appendix&nbsp;A</a>)<a class="self" href="#rfc.section.A.2.p.24">&para;</a></p></div><div id="rfc.section.A.2.p.25"><p>Issues with the Keep-Alive and Proxy-Connection header fields in requests are pointed out, with use of the latter being discouraged altogether. (<a href="#compatibility.with.http.1.0.persistent.connections" title="Keep-Alive Connections">Appendix&nbsp;A.1.2</a>)<a class="self" href="#rfc.section.A.2.p.25">&para;</a></p></div></div></div><div id="collected.abnf"><h1 id="rfc.section.B"><a href="#rfc.section.B">B.</a>&nbsp;<a href="#collected.abnf">Collected ABNF</a></h1><div id="rfc.figure.u.72"><pre class="inline"><a href="#rule.whitespace" class="smpl">BWS</a> = OWS
    721737
    722738<a href="#header.connection" class="smpl">Connection</a> = *( "," OWS ) connection-option *( OWS "," [ OWS
     
    830846
    831847<a href="#uri" class="smpl">uri-host</a> = &lt;host, see [RFC3986], Section 3.2.2&gt;
    832 </pre></div></div><h1 id="rfc.index"><a href="#rfc.index">Index</a></h1><p class="noprint"><a href="#rfc.index.A">A</a> <a href="#rfc.index.B">B</a> <a href="#rfc.index.C">C</a> <a href="#rfc.index.D">D</a> <a href="#rfc.index.E">E</a> <a href="#rfc.index.G">G</a> <a href="#rfc.index.H">H</a> <a href="#rfc.index.I">I</a> <a href="#rfc.index.K">K</a> <a href="#rfc.index.L">L</a> <a href="#rfc.index.M">M</a> <a href="#rfc.index.N">N</a> <a href="#rfc.index.O">O</a> <a href="#rfc.index.P">P</a> <a href="#rfc.index.R">R</a> <a href="#rfc.index.S">S</a> <a href="#rfc.index.T">T</a> <a href="#rfc.index.U">U</a> <a href="#rfc.index.V">V</a> <a href="#rfc.index.W">W</a> </p><div class="print2col"><ul class="ind"><li><a id="rfc.index.A" href="#rfc.index.A"><b>A</b></a><ul><li>absolute-form (of request-target)&nbsp;&nbsp;<a href="#rfc.section.5.3.2">5.3.2</a></li><li>accelerator&nbsp;&nbsp;<a href="#rfc.iref.a.1"><b>2.3</b></a></li><li>application/http Media Type&nbsp;&nbsp;<a href="#rfc.section.8.3.2"><b>8.3.2</b></a></li><li>asterisk-form (of request-target)&nbsp;&nbsp;<a href="#rfc.section.5.3.4">5.3.4</a></li><li>authoritative response&nbsp;&nbsp;<a href="#rfc.section.9.1"><b>9.1</b></a></li><li>authority-form (of request-target)&nbsp;&nbsp;<a href="#rfc.section.5.3.3">5.3.3</a></li></ul></li><li><a id="rfc.index.B" href="#rfc.index.B"><b>B</b></a><ul><li><em>BCP115</em>&nbsp;&nbsp;<a href="#rfc.xref.BCP115.1">8.2</a>, <a href="#BCP115"><b>11.2</b></a></li><li><em>BCP13</em>&nbsp;&nbsp;<a href="#rfc.xref.BCP13.1">8.3</a>, <a href="#BCP13"><b>11.2</b></a></li><li><em>BCP90</em>&nbsp;&nbsp;<a href="#rfc.xref.BCP90.1">8.1</a>, <a href="#BCP90"><b>11.2</b></a></li><li>browser&nbsp;&nbsp;<a href="#rfc.iref.b.1"><b>2.1</b></a></li></ul></li><li><a id="rfc.index.C" href="#rfc.index.C"><b>C</b></a><ul><li>cache&nbsp;&nbsp;<a href="#rfc.section.2.4"><b>2.4</b></a></li><li>cacheable&nbsp;&nbsp;<a href="#rfc.iref.c.2"><b>2.4</b></a></li><li>captive portal&nbsp;&nbsp;<a href="#rfc.iref.c.1"><b>2.3</b></a></li><li>chunked (Coding Format)&nbsp;&nbsp;<a href="#rfc.section.3.3.1">3.3.1</a>, <a href="#rfc.section.3.3.3">3.3.3</a>, <a href="#rfc.section.4.1"><b>4.1</b></a></li><li>client&nbsp;&nbsp;<a href="#rfc.section.2.1"><b>2.1</b></a></li><li>close&nbsp;&nbsp;<a href="#rfc.xref.header.connection.1">3.2.1</a>, <a href="#rfc.xref.header.connection.2">4.3</a>, <a href="#rfc.xref.header.connection.3">5.7</a>, <a href="#rfc.section.6.1"><b>6.1</b></a>, <a href="#rfc.xref.persistent.tear-down.1">6.1</a>, <a href="#rfc.xref.persistent.tear-down.2">6.3.2</a>, <a href="#rfc.section.6.6">6.6</a>, <a href="#rfc.xref.header.connection.4">6.6</a>, <a href="#rfc.xref.header.connection.5">6.7</a>, <a href="#rfc.xref.header.connection.6">8.1</a>, <a href="#rfc.xref.header.connection.7">8.1</a>, <a href="#rfc.xref.header.connection.8">A.2</a></li><li>compress (Coding Format)&nbsp;&nbsp;<a href="#rfc.section.4.2.1">4.2.1</a></li><li>connection&nbsp;&nbsp;<a href="#rfc.section.2.1"><b>2.1</b></a></li><li>Connection header field&nbsp;&nbsp;<a href="#rfc.xref.header.connection.1">3.2.1</a>, <a href="#rfc.xref.header.connection.2">4.3</a>, <a href="#rfc.xref.header.connection.3">5.7</a>, <a href="#rfc.section.6.1"><b>6.1</b></a>, <a href="#rfc.xref.persistent.tear-down.1">6.1</a>, <a href="#rfc.xref.persistent.tear-down.2">6.3.2</a>, <a href="#rfc.section.6.6">6.6</a>, <a href="#rfc.xref.header.connection.4">6.6</a>, <a href="#rfc.xref.header.connection.5">6.7</a>, <a href="#rfc.xref.header.connection.6">8.1</a>, <a href="#rfc.xref.header.connection.7">8.1</a>, <a href="#rfc.xref.header.connection.8">A.2</a></li><li>Content-Length header field&nbsp;&nbsp;<a href="#rfc.section.3.3.2"><b>3.3.2</b></a>, <a href="#rfc.xref.header.content-length.1">8.1</a>, <a href="#rfc.xref.header.content-length.2">A.2</a></li></ul></li><li><a id="rfc.index.D" href="#rfc.index.D"><b>D</b></a><ul><li>deflate (Coding Format)&nbsp;&nbsp;<a href="#rfc.section.4.2.2">4.2.2</a></li><li>Delimiters&nbsp;&nbsp;<a href="#rfc.iref.d.2">3.2.6</a></li><li>downstream&nbsp;&nbsp;<a href="#rfc.iref.d.1"><b>2.3</b></a></li></ul></li><li><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul><li>effective request URI&nbsp;&nbsp;<a href="#rfc.section.5.5"><b>5.5</b></a></li></ul></li><li><a id="rfc.index.G" href="#rfc.index.G"><b>G</b></a><ul><li>gateway&nbsp;&nbsp;<a href="#rfc.iref.g.1"><b>2.3</b></a></li><li><em>Georgiev</em>&nbsp;&nbsp;<a href="#rfc.xref.Georgiev.1">9.1</a>, <a href="#Georgiev"><b>11.2</b></a></li><li><tt>Grammar</tt>&nbsp;&nbsp;<ul><li><tt>absolute-form</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.68">5.3</a>, <a href="#rfc.iref.g.72"><b>5.3.2</b></a></li><li><tt>absolute-path</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.8"><b>2.7</b></a></li><li><tt>absolute-URI</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.5"><b>2.7</b></a></li><li>ALPHA&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li><tt>asterisk-form</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.70">5.3</a>, <a href="#rfc.iref.g.74"><b>5.3.4</b></a></li><li><tt>authority</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.7"><b>2.7</b></a></li><li><tt>authority-form</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.69">5.3</a>, <a href="#rfc.iref.g.73"><b>5.3.3</b></a></li><li><tt>BWS</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.32"><b>3.2.3</b></a></li><li><tt>chunk</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.48"><b>4.1</b></a></li><li><tt>chunk-data</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.53"><b>4.1</b></a></li><li><tt>chunk-ext</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.52">4.1</a>, <a href="#rfc.iref.g.55"><b>4.1.1</b></a></li><li><tt>chunk-ext-name</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.56"><b>4.1.1</b></a></li><li><tt>chunk-ext-val</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.57"><b>4.1.1</b></a></li><li><tt>chunk-size</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.49"><b>4.1</b></a></li><li><tt>chunked-body</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.47"><b>4.1</b></a>, <a href="#rfc.iref.g.54"><b>4.1.1</b></a></li><li><tt>comment</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.38"><b>3.2.6</b></a></li><li><tt>Connection</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.82"><b>6.1</b></a></li><li><tt>connection-option</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.83"><b>6.1</b></a></li><li><tt>Content-Length</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.43"><b>3.3.2</b></a></li><li>CR&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li>CRLF&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li><tt>ctext</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.39"><b>3.2.6</b></a></li><li>CTL&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li>DIGIT&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li>DQUOTE&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li><tt>field-content</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.28"><b>3.2</b></a></li><li><tt>field-name</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.25"><b>3.2</b></a>, <a href="#rfc.iref.g.65">4.4</a></li><li><tt>field-value</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.26"><b>3.2</b></a></li><li><tt>field-vchar</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.27"><b>3.2</b></a></li><li><tt>fragment</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.11"><b>2.7</b></a></li><li><tt>header-field</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.24"><b>3.2</b></a>, <a href="#rfc.iref.g.59">4.1.2</a></li><li>HEXDIG&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li><tt>Host</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.75"><b>5.4</b></a></li><li>HTAB&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li><tt>HTTP-message</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.17"><b>3</b></a></li><li><tt>HTTP-name</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.3"><b>2.6</b></a></li><li><tt>http-URI</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.15"><b>2.7.1</b></a></li><li><tt>HTTP-version</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.2"><b>2.6</b></a></li><li><tt>https-URI</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.16"><b>2.7.2</b></a></li><li><tt>last-chunk</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.50"><b>4.1</b></a></li><li>LF&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li><tt>message-body</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.41"><b>3.3</b></a></li><li><tt>method</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.20"><b>3.1.1</b></a></li><li><tt>obs-fold</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.29"><b>3.2</b></a></li><li><tt>obs-text</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.37"><b>3.2.6</b></a></li><li>OCTET&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li><tt>origin-form</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.67">5.3</a>, <a href="#rfc.iref.g.71"><b>5.3.1</b></a></li><li><tt>OWS</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.30"><b>3.2.3</b></a></li><li><tt>partial-URI</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.14"><b>2.7</b></a></li><li><tt>port</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.9"><b>2.7</b></a></li><li><tt>protocol-name</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.78"><b>5.7.1</b></a></li><li><tt>protocol-version</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.79"><b>5.7.1</b></a></li><li><tt>pseudonym</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.81"><b>5.7.1</b></a></li><li><tt>qdtext</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.36"><b>3.2.6</b></a></li><li><tt>query</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.10"><b>2.7</b></a></li><li><tt>quoted-pair</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.40"><b>3.2.6</b></a></li><li><tt>quoted-string</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.35"><b>3.2.6</b></a></li><li><tt>rank</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.63"><b>4.3</b></a></li><li><tt>reason-phrase</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.23"><b>3.1.2</b></a></li><li><tt>received-by</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.80"><b>5.7.1</b></a></li><li><tt>received-protocol</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.77"><b>5.7.1</b></a></li><li><tt>request-line</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.19"><b>3.1.1</b></a></li><li><tt>request-target</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.66"><b>5.3</b></a></li><li><tt>RWS</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.31"><b>3.2.3</b></a></li><li><tt>scheme</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.6"><b>2.7</b></a></li><li><tt>segment</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.12"><b>2.7</b></a></li><li>SP&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li><tt>start-line</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.18"><b>3.1</b></a></li><li><tt>status-code</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.22"><b>3.1.2</b></a></li><li><tt>status-line</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.21"><b>3.1.2</b></a></li><li><tt>t-codings</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.61"><b>4.3</b></a></li><li><tt>t-ranking</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.62"><b>4.3</b></a></li><li><tt>tchar</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.34"><b>3.2.6</b></a></li><li><tt>TE</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.60"><b>4.3</b></a></li><li><tt>token</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.33"><b>3.2.6</b></a></li><li><tt>Trailer</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.64"><b>4.4</b></a></li><li><tt>trailer-part</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.51">4.1</a>, <a href="#rfc.iref.g.58"><b>4.1.2</b></a></li><li><tt>transfer-coding</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.44"><b>4</b></a></li><li><tt>Transfer-Encoding</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.42"><b>3.3.1</b></a></li><li><tt>transfer-extension</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.45"><b>4</b></a></li><li><tt>transfer-parameter</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.46"><b>4</b></a></li><li><tt>Upgrade</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.84"><b>6.7</b></a></li><li><tt>uri-host</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.13"><b>2.7</b></a></li><li><tt>URI-reference</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.4"><b>2.7</b></a></li><li>VCHAR&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li><tt>Via</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.76"><b>5.7.1</b></a></li></ul></li><li>gzip (Coding Format)&nbsp;&nbsp;<a href="#rfc.section.4.2.3">4.2.3</a></li></ul></li><li><a id="rfc.index.H" href="#rfc.index.H"><b>H</b></a><ul><li>header field&nbsp;&nbsp;<a href="#rfc.section.3">3</a></li><li>header section&nbsp;&nbsp;<a href="#rfc.section.3">3</a></li><li>headers&nbsp;&nbsp;<a href="#rfc.section.3">3</a></li><li>Host header field&nbsp;&nbsp;<a href="#rfc.xref.header.host.1">5.3.1</a>, <a href="#rfc.section.5.4"><b>5.4</b></a>, <a href="#rfc.xref.header.host.2">8.1</a>, <a href="#rfc.xref.header.host.3">A.1.1</a></li><li>http URI scheme&nbsp;&nbsp;<a href="#rfc.section.2.7.1"><b>2.7.1</b></a></li><li>https URI scheme&nbsp;&nbsp;<a href="#rfc.section.2.7.2">2.7.2</a></li></ul></li><li><a id="rfc.index.I" href="#rfc.index.I"><b>I</b></a><ul><li>inbound&nbsp;&nbsp;<a href="#rfc.iref.i.1"><b>2.3</b></a></li><li>interception proxy&nbsp;&nbsp;<a href="#rfc.iref.i.2"><b>2.3</b></a></li><li>intermediary&nbsp;&nbsp;<a href="#rfc.section.2.3"><b>2.3</b></a></li><li><em>ISO-8859-1</em>&nbsp;&nbsp;<a href="#rfc.xref.ISO-8859-1.1">3.2.4</a>, <a href="#ISO-8859-1"><b>11.2</b></a></li></ul></li><li><a id="rfc.index.K" href="#rfc.index.K"><b>K</b></a><ul><li><em>Klein</em>&nbsp;&nbsp;<a href="#rfc.xref.Klein.1">9.4</a>, <a href="#Klein"><b>11.2</b></a></li><li><em>Kri2001</em>&nbsp;&nbsp;<a href="#rfc.xref.Kri2001.1">3.2.2</a>, <a href="#Kri2001"><b>11.2</b></a></li></ul></li><li><a id="rfc.index.L" href="#rfc.index.L"><b>L</b></a><ul><li><em>Linhart</em>&nbsp;&nbsp;<a href="#rfc.xref.Linhart.1">9.5</a>, <a href="#Linhart"><b>11.2</b></a></li></ul></li><li><a id="rfc.index.M" href="#rfc.index.M"><b>M</b></a><ul><li>Media Type&nbsp;&nbsp;<ul><li>application/http&nbsp;&nbsp;<a href="#rfc.section.8.3.2"><b>8.3.2</b></a></li><li>message/http&nbsp;&nbsp;<a href="#rfc.section.8.3.1"><b>8.3.1</b></a></li></ul></li><li>message&nbsp;&nbsp;<a href="#rfc.iref.m.1"><b>2.1</b></a></li><li>message/http Media Type&nbsp;&nbsp;<a href="#rfc.section.8.3.1"><b>8.3.1</b></a></li><li>method&nbsp;&nbsp;<a href="#rfc.iref.m.2"><b>3.1.1</b></a></li></ul></li><li><a id="rfc.index.N" href="#rfc.index.N"><b>N</b></a><ul><li>non-transforming proxy&nbsp;&nbsp;<a href="#rfc.section.5.7.2"><b>5.7.2</b></a></li></ul></li><li><a id="rfc.index.O" href="#rfc.index.O"><b>O</b></a><ul><li>origin server&nbsp;&nbsp;<a href="#rfc.iref.o.1"><b>2.1</b></a></li><li>origin-form (of request-target)&nbsp;&nbsp;<a href="#rfc.section.5.3.1">5.3.1</a></li><li>outbound&nbsp;&nbsp;<a href="#rfc.iref.o.2"><b>2.3</b></a></li></ul></li><li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul><li>phishing&nbsp;&nbsp;<a href="#rfc.section.9.1"><b>9.1</b></a></li><li>proxy&nbsp;&nbsp;<a href="#rfc.iref.p.1"><b>2.3</b></a></li></ul></li><li><a id="rfc.index.R" href="#rfc.index.R"><b>R</b></a><ul><li>recipient&nbsp;&nbsp;<a href="#rfc.iref.r.1"><b>2.1</b></a></li><li>request&nbsp;&nbsp;<a href="#rfc.iref.r.2"><b>2.1</b></a></li><li>request-target&nbsp;&nbsp;<a href="#rfc.iref.r.5">3.1.1</a></li><li>resource&nbsp;&nbsp;<a href="#rfc.section.2.7"><b>2.7</b></a></li><li>response&nbsp;&nbsp;<a href="#rfc.iref.r.3"><b>2.1</b></a></li><li>reverse proxy&nbsp;&nbsp;<a href="#rfc.iref.r.4"><b>2.3</b></a></li><li><em>RFC0793</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC0793.1">2.7.1</a>, <a href="#RFC0793"><b>11.1</b></a></li><li><em>RFC1919</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1919.1">2.3</a>, <a href="#RFC1919"><b>11.2</b></a></li><li><em>RFC1945</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1945.1">2.6</a>, <a href="#rfc.xref.RFC1945.2">10</a>, <a href="#RFC1945"><b>11.2</b></a>, <a href="#rfc.xref.RFC1945.3">A</a></li><li><em>RFC1950</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1950.1">4.2.2</a>, <a href="#rfc.xref.RFC1950.2">8.4.2</a>, <a href="#rfc.xref.RFC1950.3">8.5</a>, <a href="#RFC1950"><b>11.1</b></a></li><li><em>RFC1951</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1951.1">4.2.2</a>, <a href="#rfc.xref.RFC1951.2">8.4.2</a>, <a href="#rfc.xref.RFC1951.3">8.5</a>, <a href="#RFC1951"><b>11.1</b></a></li><li><em>RFC1952</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1952.1">4.2.3</a>, <a href="#rfc.xref.RFC1952.2">8.4.2</a>, <a href="#rfc.xref.RFC1952.3">8.5</a>, <a href="#RFC1952"><b>11.1</b></a></li><li><em>RFC2045</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2045.1">2.1</a>, <a href="#rfc.xref.RFC2045.2">3.3.1</a>, <a href="#RFC2045"><b>11.2</b></a><ul><li><em>Section 6</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2045.2">3.3.1</a></li></ul></li><li><em>RFC2047</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2047.1">3.2.4</a>, <a href="#RFC2047"><b>11.2</b></a></li><li><em>RFC2068</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2068.1">2.6</a>, <a href="#rfc.xref.RFC2068.2">6.3</a>, <a href="#rfc.xref.RFC2068.3">10</a>, <a href="#RFC2068"><b>11.2</b></a>, <a href="#rfc.xref.RFC2068.4">A.1.2</a><ul><li><em>Section 19.7.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2068.2">6.3</a>, <a href="#rfc.xref.RFC2068.4">A.1.2</a></li></ul></li><li><em>RFC2119</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2119.1">1.1</a>, <a href="#RFC2119"><b>11.1</b></a></li><li><em>RFC2145</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2145.1">1</a>, <a href="#rfc.xref.RFC2145.2">10</a>, <a href="#RFC2145"><b>11.2</b></a></li><li><em>RFC2616</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2616.1">1</a>, <a href="#rfc.xref.RFC2616.2">2.6</a>, <a href="#rfc.xref.RFC2616.3">10</a>, <a href="#rfc.xref.RFC2616.4">10</a>, <a href="#RFC2616"><b>11.2</b></a><ul><li><em>Section 16</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2616.4">10</a></li></ul></li><li><em>RFC2817</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2817.1">1</a>, <a href="#rfc.xref.RFC2817.2">8.6.1</a>, <a href="#RFC2817"><b>11.2</b></a>, <a href="#rfc.xref.RFC2817.3">A.2</a>, <a href="#rfc.xref.RFC2817.4">A.2</a><ul><li><em>Section 7.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2817.2">8.6.1</a>, <a href="#rfc.xref.RFC2817.4">A.2</a></li></ul></li><li><em>RFC2818</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2818.1">1</a>, <a href="#rfc.xref.RFC2818.2">2.7.2</a>, <a href="#rfc.xref.RFC2818.3">9.1</a>, <a href="#RFC2818"><b>11.2</b></a>, <a href="#rfc.xref.RFC2818.4">A.2</a><ul><li><em>Section 2.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2818.4">A.2</a></li></ul></li><li><em>RFC3040</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3040.1">2.3</a>, <a href="#RFC3040"><b>11.2</b></a></li><li><em>RFC3986</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.1">2.1</a>, <a href="#rfc.xref.RFC3986.2">2.7</a>, <a href="#rfc.xref.RFC3986.3">2.7</a>, <a href="#rfc.xref.RFC3986.4">2.7</a>, <a href="#rfc.xref.RFC3986.5">2.7</a>, <a href="#rfc.xref.RFC3986.6">2.7</a>, <a href="#rfc.xref.RFC3986.7">2.7</a>, <a href="#rfc.xref.RFC3986.8">2.7</a>, <a href="#rfc.xref.RFC3986.9">2.7</a>, <a href="#rfc.xref.RFC3986.10">2.7</a>, <a href="#rfc.xref.RFC3986.11">2.7</a>, <a href="#rfc.xref.RFC3986.12">2.7</a>, <a href="#rfc.xref.RFC3986.13">2.7</a>, <a href="#rfc.xref.RFC3986.14">2.7.1</a>, <a href="#rfc.xref.RFC3986.15">2.7.1</a>, <a href="#rfc.xref.RFC3986.16">2.7.1</a>, <a href="#rfc.xref.RFC3986.17">2.7.3</a>, <a href="#rfc.xref.RFC3986.18">2.7.3</a>, <a href="#rfc.xref.RFC3986.19">2.7.3</a>, <a href="#rfc.xref.RFC3986.20">2.7.3</a>, <a href="#rfc.xref.RFC3986.21">5.1</a>, <a href="#RFC3986"><b>11.1</b></a><ul><li><em>Section 2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.18">2.7.3</a></li><li><em>Section 2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.19">2.7.3</a></li><li><em>Section 3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.6">2.7</a></li><li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.7">2.7</a></li><li><em>Section 3.2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.16">2.7.1</a></li><li><em>Section 3.2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.8">2.7</a>, <a href="#rfc.xref.RFC3986.14">2.7.1</a></li><li><em>Section 3.2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.9">2.7</a></li><li><em>Section 3.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.10">2.7</a>, <a href="#rfc.xref.RFC3986.11">2.7</a></li><li><em>Section 3.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.12">2.7</a></li><li><em>Section 3.5</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.13">2.7</a>, <a href="#rfc.xref.RFC3986.15">2.7.1</a>, <a href="#rfc.xref.RFC3986.21">5.1</a></li><li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.3">2.7</a></li><li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.5">2.7</a></li><li><em>Section 4.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.4">2.7</a></li><li><em>Section 6</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.17">2.7.3</a></li></ul></li><li><em>RFC4033</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4033.1">9.1</a>, <a href="#RFC4033"><b>11.2</b></a></li><li><em>RFC4559</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4559.1">2.3</a>, <a href="#RFC4559"><b>11.2</b></a></li><li><em>RFC5226</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5226.1">8.4.1</a>, <a href="#rfc.xref.RFC5226.2">8.6.1</a>, <a href="#RFC5226"><b>11.2</b></a><ul><li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5226.1">8.4.1</a>, <a href="#rfc.xref.RFC5226.2">8.6.1</a></li></ul></li><li><em>RFC5234</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5234.1">1.2</a>, <a href="#rfc.xref.RFC5234.2">1.2</a>, <a href="#rfc.xref.RFC5234.3">7</a>, <a href="#RFC5234"><b>11.1</b></a><ul><li><em>Appendix B.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5234.2">1.2</a></li></ul></li><li><em>RFC5246</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5246.1">2.3</a>, <a href="#rfc.xref.RFC5246.2">2.7.2</a>, <a href="#RFC5246"><b>11.2</b></a></li><li><em>RFC5322</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5322.1">2.1</a>, <a href="#rfc.xref.RFC5322.2">3</a>, <a href="#rfc.xref.RFC5322.3">5.7.1</a>, <a href="#RFC5322"><b>11.2</b></a><ul><li><em>Section 3.6.7</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5322.3">5.7.1</a></li></ul></li><li><em>RFC6265</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC6265.1">2.7.2</a>, <a href="#rfc.xref.RFC6265.2">3.2.2</a>, <a href="#rfc.xref.RFC6265.3">4.1.2</a>, <a href="#RFC6265"><b>11.2</b></a></li><li><em>RFC6585</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC6585.1">9.3</a>, <a href="#RFC6585"><b>11.2</b></a></li><li><em>RFC7231</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.1">1</a>, <a href="#rfc.xref.RFC7231.2">2.1</a>, <a href="#rfc.xref.RFC7231.3">2.1</a>, <a href="#rfc.xref.RFC7231.4">2.7</a>, <a href="#rfc.xref.RFC7231.5">2.7.1</a>, <a href="#rfc.xref.RFC7231.6">3.1.1</a>, <a href="#rfc.xref.RFC7231.7">3.1.1</a>, <a href="#rfc.xref.RFC7231.8">3.1.2</a>, <a href="#rfc.xref.RFC7231.9">3.2</a>, <a href="#rfc.xref.RFC7231.10">3.2.1</a>, <a href="#rfc.xref.RFC7231.11">3.3</a>, <a href="#rfc.xref.RFC7231.12">3.3</a>, <a href="#rfc.xref.RFC7231.13">3.3</a>, <a href="#rfc.xref.RFC7231.14">3.3.1</a>, <a href="#rfc.xref.RFC7231.15">3.3.1</a>, <a href="#rfc.xref.RFC7231.16">3.3.2</a>, <a href="#rfc.xref.RFC7231.17">3.3.2</a>, <a href="#rfc.xref.RFC7231.18">3.3.2</a>, <a href="#rfc.xref.RFC7231.19">4.1.2</a>, <a href="#rfc.xref.RFC7231.20">4.1.2</a>, <a href="#rfc.xref.RFC7231.21">4.3</a>, <a href="#rfc.xref.RFC7231.22">5.1</a>, <a href="#rfc.xref.RFC7231.23">5.3.3</a>, <a href="#rfc.xref.RFC7231.24">5.3.4</a>, <a href="#rfc.xref.RFC7231.25">5.6</a>, <a href="#rfc.xref.RFC7231.26">5.7.2</a>, <a href="#rfc.xref.RFC7231.27">5.7.2</a>, <a href="#rfc.xref.RFC7231.28">6.3.1</a>, <a href="#rfc.xref.RFC7231.29">6.3.2</a>, <a href="#rfc.xref.RFC7231.30">6.3.2</a>, <a href="#rfc.xref.RFC7231.31">6.7</a>, <a href="#rfc.xref.RFC7231.32">6.7</a>, <a href="#rfc.xref.RFC7231.33">8.4.1</a>, <a href="#rfc.xref.RFC7231.34">9</a>, <a href="#rfc.xref.RFC7231.35">9.3</a>, <a href="#rfc.xref.RFC7231.36">9.3</a>, <a href="#RFC7231"><b>11.1</b></a><ul><li><em>Section 2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.4">2.7</a></li><li><em>Section 3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.16">3.3.2</a></li><li><em>Section 3.1.2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.14">3.3.1</a>, <a href="#rfc.xref.RFC7231.33">8.4.1</a></li><li><em>Section 3.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.26">5.7.2</a></li><li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.6">3.1.1</a></li><li><em>Section 4.2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.29">6.3.2</a></li><li><em>Section 4.2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.28">6.3.1</a>, <a href="#rfc.xref.RFC7231.30">6.3.2</a></li><li><em>Section 4.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.3">2.1</a>, <a href="#rfc.xref.RFC7231.12">3.3</a></li><li><em>Section 4.3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.11">3.3</a>, <a href="#rfc.xref.RFC7231.17">3.3.2</a></li><li><em>Section 4.3.6</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.13">3.3</a>, <a href="#rfc.xref.RFC7231.15">3.3.1</a>, <a href="#rfc.xref.RFC7231.18">3.3.2</a>, <a href="#rfc.xref.RFC7231.23">5.3.3</a></li><li><em>Section 4.3.7</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.24">5.3.4</a></li><li><em>Section 5</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.19">4.1.2</a></li><li><em>Section 5.1.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.31">6.7</a></li><li><em>Section 5.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.21">4.3</a></li><li><em>Section 6</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.5">2.7.1</a>, <a href="#rfc.xref.RFC7231.8">3.1.2</a></li><li><em>Section 6.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.25">5.6</a></li><li><em>Section 6.3.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.27">5.7.2</a></li><li><em>Section 6.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.32">6.7</a></li><li><em>Section 6.5.11</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.36">9.3</a></li><li><em>Section 6.5.12</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.7">3.1.1</a>, <a href="#rfc.xref.RFC7231.35">9.3</a></li><li><em>Section 7.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.20">4.1.2</a></li><li><em>Section 7.1.1.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.9">3.2</a></li><li><em>Section 8.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.10">3.2.1</a></li><li><em>Appendix A</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.2">2.1</a></li></ul></li><li><em>RFC7232</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.1">1</a>, <a href="#rfc.xref.RFC7232.2">3.3.1</a>, <a href="#rfc.xref.RFC7232.3">3.3.2</a>, <a href="#RFC7232"><b>11.1</b></a><ul><li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.2">3.3.1</a>, <a href="#rfc.xref.RFC7232.3">3.3.2</a></li></ul></li><li><em>RFC7233</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.1">1</a>, <a href="#RFC7233"><b>11.1</b></a></li><li><em>RFC7234</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.1">1</a>, <a href="#rfc.xref.RFC7234.2">2.4</a>, <a href="#rfc.xref.RFC7234.3">3.4</a>, <a href="#rfc.xref.RFC7234.4">5.2</a>, <a href="#rfc.xref.RFC7234.5">5.7.2</a>, <a href="#rfc.xref.RFC7234.6">5.7.2</a>, <a href="#rfc.xref.RFC7234.7">6.1</a>, <a href="#rfc.xref.RFC7234.8">9.2</a>, <a href="#RFC7234"><b>11.1</b></a><ul><li><em>Section 2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.2">2.4</a></li><li><em>Section 3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.3">3.4</a></li><li><em>Section 5.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.5">5.7.2</a>, <a href="#rfc.xref.RFC7234.7">6.1</a></li><li><em>Section 5.5</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.6">5.7.2</a></li><li><em>Section 8</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.8">9.2</a></li></ul></li><li><em>RFC7235</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7235.1">1</a>, <a href="#rfc.xref.RFC7235.2">4.1.2</a>, <a href="#RFC7235"><b>11.1</b></a></li></ul></li><li><a id="rfc.index.S" href="#rfc.index.S"><b>S</b></a><ul><li>sender&nbsp;&nbsp;<a href="#rfc.iref.s.2"><b>2.1</b></a></li><li>server&nbsp;&nbsp;<a href="#rfc.section.2.1"><b>2.1</b></a></li><li>spider&nbsp;&nbsp;<a href="#rfc.iref.s.1"><b>2.1</b></a></li></ul></li><li><a id="rfc.index.T" href="#rfc.index.T"><b>T</b></a><ul><li>target resource&nbsp;&nbsp;<a href="#rfc.section.5.1"><b>5.1</b></a></li><li>target URI&nbsp;&nbsp;<a href="#rfc.section.5.1"><b>5.1</b></a></li><li>TE header field&nbsp;&nbsp;<a href="#rfc.xref.header.te.1">4</a>, <a href="#rfc.xref.header.te.2">4.1.2</a>, <a href="#rfc.section.4.3"><b>4.3</b></a>, <a href="#rfc.xref.header.te.3">8.1</a></li><li>Trailer header field&nbsp;&nbsp;<a href="#rfc.section.4.4"><b>4.4</b></a>, <a href="#rfc.xref.header.trailer.1">8.1</a></li><li>Transfer-Encoding header field&nbsp;&nbsp;<a href="#rfc.xref.header.transfer-encoding.1">3.3</a>, <a href="#rfc.section.3.3.1"><b>3.3.1</b></a>, <a href="#rfc.xref.header.transfer-encoding.2">4</a>, <a href="#rfc.xref.header.transfer-encoding.3">8.1</a>, <a href="#rfc.xref.header.transfer-encoding.4">A.1.3</a></li><li>transforming proxy&nbsp;&nbsp;<a href="#rfc.section.5.7.2"><b>5.7.2</b></a></li><li>transparent proxy&nbsp;&nbsp;<a href="#rfc.iref.t.2"><b>2.3</b></a></li><li>tunnel&nbsp;&nbsp;<a href="#rfc.iref.t.1"><b>2.3</b></a></li></ul></li><li><a id="rfc.index.U" href="#rfc.index.U"><b>U</b></a><ul><li>Upgrade header field&nbsp;&nbsp;<a href="#rfc.xref.header.upgrade.1">5.7.1</a>, <a href="#rfc.section.6.7"><b>6.7</b></a>, <a href="#rfc.xref.header.upgrade.2">8.1</a>, <a href="#rfc.xref.header.upgrade.3">A.2</a></li><li>upstream&nbsp;&nbsp;<a href="#rfc.iref.u.2"><b>2.3</b></a></li><li>URI scheme&nbsp;&nbsp;<ul><li>http&nbsp;&nbsp;<a href="#rfc.section.2.7.1"><b>2.7.1</b></a></li><li>https&nbsp;&nbsp;<a href="#rfc.section.2.7.2">2.7.2</a></li></ul></li><li><em>USASCII</em>&nbsp;&nbsp;<a href="#rfc.xref.USASCII.1">1.2</a>, <a href="#rfc.xref.USASCII.2">3</a>, <a href="#rfc.xref.USASCII.3">3.2.4</a>, <a href="#USASCII"><b>11.1</b></a></li><li>user agent&nbsp;&nbsp;<a href="#rfc.iref.u.1"><b>2.1</b></a></li></ul></li><li><a id="rfc.index.V" href="#rfc.index.V"><b>V</b></a><ul><li>Via header field&nbsp;&nbsp;<a href="#rfc.section.5.7.1"><b>5.7.1</b></a>, <a href="#rfc.xref.header.via.1">8.1</a>, <a href="#rfc.xref.header.via.2">A.2</a></li></ul></li><li><a id="rfc.index.W" href="#rfc.index.W"><b>W</b></a><ul><li><em>Welch</em>&nbsp;&nbsp;<a href="#rfc.xref.Welch.1">4.2.1</a>, <a href="#rfc.xref.Welch.2">8.4.2</a>, <a href="#rfc.xref.Welch.3">8.5</a>, <a href="#Welch"><b>11.1</b></a></li></ul></li></ul></div><div class="avoidbreak"><h1 id="rfc.authors"><a href="#rfc.authors">Authors' Addresses</a></h1><p><b>Roy T. Fielding</b>
     848</pre></div></div><h1 id="rfc.index"><a href="#rfc.index">Index</a></h1><p class="noprint"><a href="#rfc.index.A">A</a> <a href="#rfc.index.B">B</a> <a href="#rfc.index.C">C</a> <a href="#rfc.index.D">D</a> <a href="#rfc.index.E">E</a> <a href="#rfc.index.G">G</a> <a href="#rfc.index.H">H</a> <a href="#rfc.index.I">I</a> <a href="#rfc.index.K">K</a> <a href="#rfc.index.L">L</a> <a href="#rfc.index.M">M</a> <a href="#rfc.index.N">N</a> <a href="#rfc.index.O">O</a> <a href="#rfc.index.P">P</a> <a href="#rfc.index.R">R</a> <a href="#rfc.index.S">S</a> <a href="#rfc.index.T">T</a> <a href="#rfc.index.U">U</a> <a href="#rfc.index.V">V</a> <a href="#rfc.index.W">W</a> </p><div class="print2col"><ul class="ind"><li><a id="rfc.index.A" href="#rfc.index.A"><b>A</b></a><ul><li>absolute-form (of request-target)&nbsp;&nbsp;<a href="#rfc.section.5.3.2">5.3.2</a></li><li>accelerator&nbsp;&nbsp;<a href="#rfc.iref.a.1"><b>2.3</b></a></li><li>application/http Media Type&nbsp;&nbsp;<a href="#rfc.section.8.3.2"><b>8.3.2</b></a></li><li>asterisk-form (of request-target)&nbsp;&nbsp;<a href="#rfc.section.5.3.4">5.3.4</a></li><li>authoritative response&nbsp;&nbsp;<a href="#rfc.section.9.1"><b>9.1</b></a></li><li>authority-form (of request-target)&nbsp;&nbsp;<a href="#rfc.section.5.3.3">5.3.3</a></li></ul></li><li><a id="rfc.index.B" href="#rfc.index.B"><b>B</b></a><ul><li><em>BCP115</em>&nbsp;&nbsp;<a href="#rfc.xref.BCP115.1">8.2</a>, <a href="#BCP115"><b>11.2</b></a></li><li><em>BCP13</em>&nbsp;&nbsp;<a href="#rfc.xref.BCP13.1">8.3</a>, <a href="#BCP13"><b>11.2</b></a></li><li><em>BCP90</em>&nbsp;&nbsp;<a href="#rfc.xref.BCP90.1">8.1</a>, <a href="#BCP90"><b>11.2</b></a></li><li>browser&nbsp;&nbsp;<a href="#rfc.iref.b.1"><b>2.1</b></a></li></ul></li><li><a id="rfc.index.C" href="#rfc.index.C"><b>C</b></a><ul><li>cache&nbsp;&nbsp;<a href="#rfc.section.2.4"><b>2.4</b></a></li><li>cacheable&nbsp;&nbsp;<a href="#rfc.iref.c.2"><b>2.4</b></a></li><li>captive portal&nbsp;&nbsp;<a href="#rfc.iref.c.1"><b>2.3</b></a></li><li>chunked (Coding Format)&nbsp;&nbsp;<a href="#rfc.section.3.3.1">3.3.1</a>, <a href="#rfc.section.3.3.3">3.3.3</a>, <a href="#rfc.section.4.1"><b>4.1</b></a></li><li>client&nbsp;&nbsp;<a href="#rfc.section.2.1"><b>2.1</b></a></li><li>close&nbsp;&nbsp;<a href="#rfc.xref.header.connection.1">3.2.1</a>, <a href="#rfc.xref.header.connection.2">4.3</a>, <a href="#rfc.xref.header.connection.3">5.7</a>, <a href="#rfc.section.6.1"><b>6.1</b></a>, <a href="#rfc.xref.persistent.tear-down.1">6.1</a>, <a href="#rfc.xref.persistent.tear-down.2">6.3.2</a>, <a href="#rfc.section.6.6">6.6</a>, <a href="#rfc.xref.header.connection.4">6.6</a>, <a href="#rfc.xref.header.connection.5">6.7</a>, <a href="#rfc.xref.header.connection.6">8.1</a>, <a href="#rfc.xref.header.connection.7">8.1</a>, <a href="#rfc.xref.header.connection.8">A.2</a></li><li>compress (Coding Format)&nbsp;&nbsp;<a href="#rfc.section.4.2.1">4.2.1</a></li><li>connection&nbsp;&nbsp;<a href="#rfc.section.2.1"><b>2.1</b></a></li><li>Connection header field&nbsp;&nbsp;<a href="#rfc.xref.header.connection.1">3.2.1</a>, <a href="#rfc.xref.header.connection.2">4.3</a>, <a href="#rfc.xref.header.connection.3">5.7</a>, <a href="#rfc.section.6.1"><b>6.1</b></a>, <a href="#rfc.xref.persistent.tear-down.1">6.1</a>, <a href="#rfc.xref.persistent.tear-down.2">6.3.2</a>, <a href="#rfc.section.6.6">6.6</a>, <a href="#rfc.xref.header.connection.4">6.6</a>, <a href="#rfc.xref.header.connection.5">6.7</a>, <a href="#rfc.xref.header.connection.6">8.1</a>, <a href="#rfc.xref.header.connection.7">8.1</a>, <a href="#rfc.xref.header.connection.8">A.2</a></li><li>Content-Length header field&nbsp;&nbsp;<a href="#rfc.section.3.3.2"><b>3.3.2</b></a>, <a href="#rfc.xref.header.content-length.1">8.1</a>, <a href="#rfc.xref.header.content-length.2">A.2</a></li></ul></li><li><a id="rfc.index.D" href="#rfc.index.D"><b>D</b></a><ul><li>deflate (Coding Format)&nbsp;&nbsp;<a href="#rfc.section.4.2.2">4.2.2</a></li><li>Delimiters&nbsp;&nbsp;<a href="#rfc.iref.d.2">3.2.6</a></li><li>downstream&nbsp;&nbsp;<a href="#rfc.iref.d.1"><b>2.3</b></a></li></ul></li><li><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul><li>effective request URI&nbsp;&nbsp;<a href="#rfc.section.5.5"><b>5.5</b></a></li></ul></li><li><a id="rfc.index.G" href="#rfc.index.G"><b>G</b></a><ul><li>gateway&nbsp;&nbsp;<a href="#rfc.iref.g.1"><b>2.3</b></a></li><li><em>Georgiev</em>&nbsp;&nbsp;<a href="#rfc.xref.Georgiev.1">9.1</a>, <a href="#Georgiev"><b>11.2</b></a></li><li><tt>Grammar</tt>&nbsp;&nbsp;<ul><li><tt>absolute-form</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.68">5.3</a>, <a href="#rfc.iref.g.72"><b>5.3.2</b></a></li><li><tt>absolute-path</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.8"><b>2.7</b></a></li><li><tt>absolute-URI</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.5"><b>2.7</b></a></li><li>ALPHA&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li><tt>asterisk-form</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.70">5.3</a>, <a href="#rfc.iref.g.74"><b>5.3.4</b></a></li><li><tt>authority</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.7"><b>2.7</b></a></li><li><tt>authority-form</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.69">5.3</a>, <a href="#rfc.iref.g.73"><b>5.3.3</b></a></li><li><tt>BWS</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.32"><b>3.2.3</b></a></li><li><tt>chunk</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.48"><b>4.1</b></a></li><li><tt>chunk-data</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.53"><b>4.1</b></a></li><li><tt>chunk-ext</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.52">4.1</a>, <a href="#rfc.iref.g.55"><b>4.1.1</b></a></li><li><tt>chunk-ext-name</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.56"><b>4.1.1</b></a></li><li><tt>chunk-ext-val</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.57"><b>4.1.1</b></a></li><li><tt>chunk-size</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.49"><b>4.1</b></a></li><li><tt>chunked-body</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.47"><b>4.1</b></a>, <a href="#rfc.iref.g.54"><b>4.1.1</b></a></li><li><tt>comment</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.38"><b>3.2.6</b></a></li><li><tt>Connection</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.82"><b>6.1</b></a></li><li><tt>connection-option</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.83"><b>6.1</b></a></li><li><tt>Content-Length</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.43"><b>3.3.2</b></a></li><li>CR&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li>CRLF&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li><tt>ctext</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.39"><b>3.2.6</b></a></li><li>CTL&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li>DIGIT&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li>DQUOTE&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li><tt>field-content</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.28"><b>3.2</b></a></li><li><tt>field-name</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.25"><b>3.2</b></a>, <a href="#rfc.iref.g.65">4.4</a></li><li><tt>field-value</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.26"><b>3.2</b></a></li><li><tt>field-vchar</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.27"><b>3.2</b></a></li><li><tt>fragment</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.11"><b>2.7</b></a></li><li><tt>header-field</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.24"><b>3.2</b></a>, <a href="#rfc.iref.g.59">4.1.2</a></li><li>HEXDIG&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li><tt>Host</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.75"><b>5.4</b></a></li><li>HTAB&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li><tt>HTTP-message</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.17"><b>3</b></a></li><li><tt>HTTP-name</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.3"><b>2.6</b></a></li><li><tt>http-URI</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.15"><b>2.7.1</b></a></li><li><tt>HTTP-version</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.2"><b>2.6</b></a></li><li><tt>https-URI</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.16"><b>2.7.2</b></a></li><li><tt>last-chunk</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.50"><b>4.1</b></a></li><li>LF&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li><tt>message-body</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.41"><b>3.3</b></a></li><li><tt>method</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.20"><b>3.1.1</b></a></li><li><tt>obs-fold</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.29"><b>3.2</b></a></li><li><tt>obs-text</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.37"><b>3.2.6</b></a></li><li>OCTET&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li><tt>origin-form</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.67">5.3</a>, <a href="#rfc.iref.g.71"><b>5.3.1</b></a></li><li><tt>OWS</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.30"><b>3.2.3</b></a></li><li><tt>partial-URI</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.14"><b>2.7</b></a></li><li><tt>port</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.9"><b>2.7</b></a></li><li><tt>protocol-name</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.78"><b>5.7.1</b></a></li><li><tt>protocol-version</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.79"><b>5.7.1</b></a></li><li><tt>pseudonym</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.81"><b>5.7.1</b></a></li><li><tt>qdtext</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.36"><b>3.2.6</b></a></li><li><tt>query</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.10"><b>2.7</b></a></li><li><tt>quoted-pair</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.40"><b>3.2.6</b></a></li><li><tt>quoted-string</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.35"><b>3.2.6</b></a></li><li><tt>rank</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.63"><b>4.3</b></a></li><li><tt>reason-phrase</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.23"><b>3.1.2</b></a></li><li><tt>received-by</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.80"><b>5.7.1</b></a></li><li><tt>received-protocol</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.77"><b>5.7.1</b></a></li><li><tt>request-line</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.19"><b>3.1.1</b></a></li><li><tt>request-target</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.66"><b>5.3</b></a></li><li><tt>RWS</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.31"><b>3.2.3</b></a></li><li><tt>scheme</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.6"><b>2.7</b></a></li><li><tt>segment</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.12"><b>2.7</b></a></li><li>SP&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li><tt>start-line</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.18"><b>3.1</b></a></li><li><tt>status-code</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.22"><b>3.1.2</b></a></li><li><tt>status-line</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.21"><b>3.1.2</b></a></li><li><tt>t-codings</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.61"><b>4.3</b></a></li><li><tt>t-ranking</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.62"><b>4.3</b></a></li><li><tt>tchar</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.34"><b>3.2.6</b></a></li><li><tt>TE</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.60"><b>4.3</b></a></li><li><tt>token</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.33"><b>3.2.6</b></a></li><li><tt>Trailer</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.64"><b>4.4</b></a></li><li><tt>trailer-part</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.51">4.1</a>, <a href="#rfc.iref.g.58"><b>4.1.2</b></a></li><li><tt>transfer-coding</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.44"><b>4</b></a></li><li><tt>Transfer-Encoding</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.42"><b>3.3.1</b></a></li><li><tt>transfer-extension</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.45"><b>4</b></a></li><li><tt>transfer-parameter</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.46"><b>4</b></a></li><li><tt>Upgrade</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.84"><b>6.7</b></a></li><li><tt>uri-host</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.13"><b>2.7</b></a></li><li><tt>URI-reference</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.4"><b>2.7</b></a></li><li>VCHAR&nbsp;&nbsp;<a href="#rfc.section.1.2"><b>1.2</b></a></li><li><tt>Via</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.76"><b>5.7.1</b></a></li></ul></li><li>gzip (Coding Format)&nbsp;&nbsp;<a href="#rfc.section.4.2.3">4.2.3</a></li></ul></li><li><a id="rfc.index.H" href="#rfc.index.H"><b>H</b></a><ul><li>header field&nbsp;&nbsp;<a href="#rfc.section.3">3</a></li><li>header section&nbsp;&nbsp;<a href="#rfc.section.3">3</a></li><li>headers&nbsp;&nbsp;<a href="#rfc.section.3">3</a></li><li>Host header field&nbsp;&nbsp;<a href="#rfc.xref.header.host.1">5.3.1</a>, <a href="#rfc.section.5.4"><b>5.4</b></a>, <a href="#rfc.xref.header.host.2">8.1</a>, <a href="#rfc.xref.header.host.3">A.1.1</a></li><li>http URI scheme&nbsp;&nbsp;<a href="#rfc.section.2.7.1"><b>2.7.1</b></a></li><li>https URI scheme&nbsp;&nbsp;<a href="#rfc.section.2.7.2">2.7.2</a></li></ul></li><li><a id="rfc.index.I" href="#rfc.index.I"><b>I</b></a><ul><li>inbound&nbsp;&nbsp;<a href="#rfc.iref.i.1"><b>2.3</b></a></li><li>interception proxy&nbsp;&nbsp;<a href="#rfc.iref.i.2"><b>2.3</b></a></li><li>intermediary&nbsp;&nbsp;<a href="#rfc.section.2.3"><b>2.3</b></a></li><li><em>ISO-8859-1</em>&nbsp;&nbsp;<a href="#rfc.xref.ISO-8859-1.1">3.2.4</a>, <a href="#ISO-8859-1"><b>11.2</b></a></li></ul></li><li><a id="rfc.index.K" href="#rfc.index.K"><b>K</b></a><ul><li><em>Klein</em>&nbsp;&nbsp;<a href="#rfc.xref.Klein.1">9.4</a>, <a href="#Klein"><b>11.2</b></a></li><li><em>Kri2001</em>&nbsp;&nbsp;<a href="#rfc.xref.Kri2001.1">3.2.2</a>, <a href="#Kri2001"><b>11.2</b></a></li></ul></li><li><a id="rfc.index.L" href="#rfc.index.L"><b>L</b></a><ul><li><em>Linhart</em>&nbsp;&nbsp;<a href="#rfc.xref.Linhart.1">9.5</a>, <a href="#Linhart"><b>11.2</b></a></li></ul></li><li><a id="rfc.index.M" href="#rfc.index.M"><b>M</b></a><ul><li>Media Type&nbsp;&nbsp;<ul><li>application/http&nbsp;&nbsp;<a href="#rfc.section.8.3.2"><b>8.3.2</b></a></li><li>message/http&nbsp;&nbsp;<a href="#rfc.section.8.3.1"><b>8.3.1</b></a></li></ul></li><li>message&nbsp;&nbsp;<a href="#rfc.iref.m.1"><b>2.1</b></a></li><li>message/http Media Type&nbsp;&nbsp;<a href="#rfc.section.8.3.1"><b>8.3.1</b></a></li><li>method&nbsp;&nbsp;<a href="#rfc.iref.m.2"><b>3.1.1</b></a></li></ul></li><li><a id="rfc.index.N" href="#rfc.index.N"><b>N</b></a><ul><li>non-transforming proxy&nbsp;&nbsp;<a href="#rfc.section.5.7.2"><b>5.7.2</b></a></li></ul></li><li><a id="rfc.index.O" href="#rfc.index.O"><b>O</b></a><ul><li>origin server&nbsp;&nbsp;<a href="#rfc.iref.o.1"><b>2.1</b></a></li><li>origin-form (of request-target)&nbsp;&nbsp;<a href="#rfc.section.5.3.1">5.3.1</a></li><li>outbound&nbsp;&nbsp;<a href="#rfc.iref.o.2"><b>2.3</b></a></li></ul></li><li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul><li>phishing&nbsp;&nbsp;<a href="#rfc.section.9.1"><b>9.1</b></a></li><li>proxy&nbsp;&nbsp;<a href="#rfc.iref.p.1"><b>2.3</b></a></li></ul></li><li><a id="rfc.index.R" href="#rfc.index.R"><b>R</b></a><ul><li>recipient&nbsp;&nbsp;<a href="#rfc.iref.r.1"><b>2.1</b></a></li><li>request&nbsp;&nbsp;<a href="#rfc.iref.r.2"><b>2.1</b></a></li><li>request-target&nbsp;&nbsp;<a href="#rfc.iref.r.5">3.1.1</a></li><li>resource&nbsp;&nbsp;<a href="#rfc.section.2.7"><b>2.7</b></a></li><li>response&nbsp;&nbsp;<a href="#rfc.iref.r.3"><b>2.1</b></a></li><li>reverse proxy&nbsp;&nbsp;<a href="#rfc.iref.r.4"><b>2.3</b></a></li><li><em>RFC0793</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC0793.1">2.7.1</a>, <a href="#RFC0793"><b>11.1</b></a></li><li><em>RFC1919</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1919.1">2.3</a>, <a href="#RFC1919"><b>11.2</b></a></li><li><em>RFC1945</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1945.1">2.6</a>, <a href="#rfc.xref.RFC1945.2">10</a>, <a href="#RFC1945"><b>11.2</b></a>, <a href="#rfc.xref.RFC1945.3">A</a></li><li><em>RFC1950</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1950.1">4.2.2</a>, <a href="#rfc.xref.RFC1950.2">8.4.2</a>, <a href="#rfc.xref.RFC1950.3">8.5</a>, <a href="#RFC1950"><b>11.1</b></a></li><li><em>RFC1951</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1951.1">4.2.2</a>, <a href="#rfc.xref.RFC1951.2">8.4.2</a>, <a href="#rfc.xref.RFC1951.3">8.5</a>, <a href="#RFC1951"><b>11.1</b></a></li><li><em>RFC1952</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1952.1">4.2.3</a>, <a href="#rfc.xref.RFC1952.2">8.4.2</a>, <a href="#rfc.xref.RFC1952.3">8.5</a>, <a href="#RFC1952"><b>11.1</b></a></li><li><em>RFC2045</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2045.1">2.1</a>, <a href="#rfc.xref.RFC2045.2">3.3.1</a>, <a href="#RFC2045"><b>11.2</b></a><ul><li><em>Section 6</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2045.2">3.3.1</a></li></ul></li><li><em>RFC2047</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2047.1">3.2.4</a>, <a href="#RFC2047"><b>11.2</b></a></li><li><em>RFC2068</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2068.1">2.6</a>, <a href="#rfc.xref.RFC2068.2">6.3</a>, <a href="#rfc.xref.RFC2068.3">10</a>, <a href="#RFC2068"><b>11.2</b></a>, <a href="#rfc.xref.RFC2068.4">A.1.2</a><ul><li><em>Section 19.7.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2068.2">6.3</a>, <a href="#rfc.xref.RFC2068.4">A.1.2</a></li></ul></li><li><em>RFC2119</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2119.1">1.1</a>, <a href="#RFC2119"><b>11.1</b></a></li><li><em>RFC2145</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2145.1">1</a>, <a href="#rfc.xref.RFC2145.2">10</a>, <a href="#RFC2145"><b>11.2</b></a></li><li><em>RFC2616</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2616.1">1</a>, <a href="#rfc.xref.RFC2616.2">2.6</a>, <a href="#rfc.xref.RFC2616.3">10</a>, <a href="#rfc.xref.RFC2616.4">10</a>, <a href="#RFC2616"><b>11.2</b></a><ul><li><em>Section 16</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2616.4">10</a></li></ul></li><li><em>RFC2817</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2817.1">1</a>, <a href="#rfc.xref.RFC2817.2">8.6.1</a>, <a href="#RFC2817"><b>11.2</b></a>, <a href="#rfc.xref.RFC2817.3">A.2</a>, <a href="#rfc.xref.RFC2817.4">A.2</a><ul><li><em>Section 7.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2817.2">8.6.1</a>, <a href="#rfc.xref.RFC2817.4">A.2</a></li></ul></li><li><em>RFC2818</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2818.1">1</a>, <a href="#rfc.xref.RFC2818.2">2.7.2</a>, <a href="#rfc.xref.RFC2818.3">9.1</a>, <a href="#RFC2818"><b>11.2</b></a>, <a href="#rfc.xref.RFC2818.4">A.2</a><ul><li><em>Section 2.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2818.4">A.2</a></li></ul></li><li><em>RFC3040</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3040.1">2.3</a>, <a href="#RFC3040"><b>11.2</b></a></li><li><em>RFC3986</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.1">2.1</a>, <a href="#rfc.xref.RFC3986.2">2.7</a>, <a href="#rfc.xref.RFC3986.3">2.7</a>, <a href="#rfc.xref.RFC3986.4">2.7</a>, <a href="#rfc.xref.RFC3986.5">2.7</a>, <a href="#rfc.xref.RFC3986.6">2.7</a>, <a href="#rfc.xref.RFC3986.7">2.7</a>, <a href="#rfc.xref.RFC3986.8">2.7</a>, <a href="#rfc.xref.RFC3986.9">2.7</a>, <a href="#rfc.xref.RFC3986.10">2.7</a>, <a href="#rfc.xref.RFC3986.11">2.7</a>, <a href="#rfc.xref.RFC3986.12">2.7</a>, <a href="#rfc.xref.RFC3986.13">2.7</a>, <a href="#rfc.xref.RFC3986.14">2.7.1</a>, <a href="#rfc.xref.RFC3986.15">2.7.1</a>, <a href="#rfc.xref.RFC3986.16">2.7.1</a>, <a href="#rfc.xref.RFC3986.17">2.7.3</a>, <a href="#rfc.xref.RFC3986.18">2.7.3</a>, <a href="#rfc.xref.RFC3986.19">2.7.3</a>, <a href="#rfc.xref.RFC3986.20">2.7.3</a>, <a href="#rfc.xref.RFC3986.21">5.1</a>, <a href="#RFC3986"><b>11.1</b></a><ul><li><em>Section 2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.18">2.7.3</a></li><li><em>Section 2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.19">2.7.3</a></li><li><em>Section 3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.6">2.7</a></li><li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.7">2.7</a></li><li><em>Section 3.2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.16">2.7.1</a></li><li><em>Section 3.2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.8">2.7</a>, <a href="#rfc.xref.RFC3986.14">2.7.1</a></li><li><em>Section 3.2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.9">2.7</a></li><li><em>Section 3.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.10">2.7</a>, <a href="#rfc.xref.RFC3986.11">2.7</a></li><li><em>Section 3.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.12">2.7</a></li><li><em>Section 3.5</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.13">2.7</a>, <a href="#rfc.xref.RFC3986.15">2.7.1</a>, <a href="#rfc.xref.RFC3986.21">5.1</a></li><li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.3">2.7</a></li><li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.5">2.7</a></li><li><em>Section 4.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.4">2.7</a></li><li><em>Section 6</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.17">2.7.3</a></li></ul></li><li><em>RFC4033</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4033.1">9.1</a>, <a href="#RFC4033"><b>11.2</b></a></li><li><em>RFC4559</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4559.1">2.3</a>, <a href="#RFC4559"><b>11.2</b></a></li><li><em>RFC5226</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5226.1">8.4.1</a>, <a href="#rfc.xref.RFC5226.2">8.6.1</a>, <a href="#RFC5226"><b>11.2</b></a><ul><li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5226.1">8.4.1</a>, <a href="#rfc.xref.RFC5226.2">8.6.1</a></li></ul></li><li><em>RFC5234</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5234.1">1.2</a>, <a href="#rfc.xref.RFC5234.2">1.2</a>, <a href="#rfc.xref.RFC5234.3">7</a>, <a href="#RFC5234"><b>11.1</b></a><ul><li><em>Appendix B.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5234.2">1.2</a></li></ul></li><li><em>RFC5246</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5246.1">2.3</a>, <a href="#rfc.xref.RFC5246.2">2.7.2</a>, <a href="#RFC5246"><b>11.2</b></a></li><li><em>RFC5322</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5322.1">2.1</a>, <a href="#rfc.xref.RFC5322.2">3</a>, <a href="#rfc.xref.RFC5322.3">5.7.1</a>, <a href="#RFC5322"><b>11.2</b></a><ul><li><em>Section 3.6.7</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5322.3">5.7.1</a></li></ul></li><li><em>RFC6265</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC6265.1">2.7.2</a>, <a href="#rfc.xref.RFC6265.2">3.2.2</a>, <a href="#rfc.xref.RFC6265.3">4.1.2</a>, <a href="#RFC6265"><b>11.2</b></a></li><li><em>RFC6585</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC6585.1">9.3</a>, <a href="#RFC6585"><b>11.2</b></a></li><li><em>RFC7231</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.1">1</a>, <a href="#rfc.xref.RFC7231.2">2.1</a>, <a href="#rfc.xref.RFC7231.3">2.1</a>, <a href="#rfc.xref.RFC7231.4">2.7</a>, <a href="#rfc.xref.RFC7231.5">2.7.1</a>, <a href="#rfc.xref.RFC7231.6">3.1.1</a>, <a href="#rfc.xref.RFC7231.7">3.1.1</a>, <a href="#rfc.xref.RFC7231.8">3.1.2</a>, <a href="#rfc.xref.RFC7231.9">3.2</a>, <a href="#rfc.xref.RFC7231.10">3.2.1</a>, <a href="#rfc.xref.RFC7231.11">3.3</a>, <a href="#rfc.xref.RFC7231.12">3.3</a>, <a href="#rfc.xref.RFC7231.13">3.3</a>, <a href="#rfc.xref.RFC7231.14">3.3.1</a>, <a href="#rfc.xref.RFC7231.15">3.3.1</a>, <a href="#rfc.xref.RFC7231.16">3.3.2</a>, <a href="#rfc.xref.RFC7231.17">3.3.2</a>, <a href="#rfc.xref.RFC7231.18">3.3.2</a>, <a href="#rfc.xref.RFC7231.19">4.1.2</a>, <a href="#rfc.xref.RFC7231.20">4.1.2</a>, <a href="#rfc.xref.RFC7231.21">4.3</a>, <a href="#rfc.xref.RFC7231.22">5.1</a>, <a href="#rfc.xref.RFC7231.23">5.3.3</a>, <a href="#rfc.xref.RFC7231.24">5.3.4</a>, <a href="#rfc.xref.RFC7231.25">5.6</a>, <a href="#rfc.xref.RFC7231.26">5.7.2</a>, <a href="#rfc.xref.RFC7231.27">5.7.2</a>, <a href="#rfc.xref.RFC7231.28">6.3.1</a>, <a href="#rfc.xref.RFC7231.29">6.3.2</a>, <a href="#rfc.xref.RFC7231.30">6.3.2</a>, <a href="#rfc.xref.RFC7231.31">6.7</a>, <a href="#rfc.xref.RFC7231.32">6.7</a>, <a href="#rfc.xref.RFC7231.33">8.4.1</a>, <a href="#rfc.xref.RFC7231.34">9</a>, <a href="#rfc.xref.RFC7231.35">9.3</a>, <a href="#rfc.xref.RFC7231.36">9.3</a>, <a href="#RFC7231"><b>11.1</b></a><ul><li><em>Section 2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.4">2.7</a></li><li><em>Section 3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.16">3.3.2</a></li><li><em>Section 3.1.2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.14">3.3.1</a>, <a href="#rfc.xref.RFC7231.33">8.4.1</a></li><li><em>Section 3.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.26">5.7.2</a></li><li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.6">3.1.1</a></li><li><em>Section 4.2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.29">6.3.2</a></li><li><em>Section 4.2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.28">6.3.1</a>, <a href="#rfc.xref.RFC7231.30">6.3.2</a></li><li><em>Section 4.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.3">2.1</a>, <a href="#rfc.xref.RFC7231.12">3.3</a></li><li><em>Section 4.3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.11">3.3</a>, <a href="#rfc.xref.RFC7231.17">3.3.2</a></li><li><em>Section 4.3.6</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.13">3.3</a>, <a href="#rfc.xref.RFC7231.15">3.3.1</a>, <a href="#rfc.xref.RFC7231.18">3.3.2</a>, <a href="#rfc.xref.RFC7231.23">5.3.3</a></li><li><em>Section 4.3.7</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.24">5.3.4</a></li><li><em>Section 5</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.19">4.1.2</a></li><li><em>Section 5.1.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.31">6.7</a></li><li><em>Section 5.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.21">4.3</a></li><li><em>Section 6</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.5">2.7.1</a>, <a href="#rfc.xref.RFC7231.8">3.1.2</a></li><li><em>Section 6.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.25">5.6</a></li><li><em>Section 6.3.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.27">5.7.2</a></li><li><em>Section 6.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.32">6.7</a></li><li><em>Section 6.5.11</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.36">9.3</a></li><li><em>Section 6.5.12</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.7">3.1.1</a>, <a href="#rfc.xref.RFC7231.35">9.3</a></li><li><em>Section 7.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.20">4.1.2</a></li><li><em>Section 7.1.1.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.9">3.2</a></li><li><em>Section 8.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.10">3.2.1</a></li><li><em>Appendix A</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7231.2">2.1</a></li></ul></li><li><em>RFC7232</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.1">1</a>, <a href="#rfc.xref.RFC7232.2">3.3.1</a>, <a href="#rfc.xref.RFC7232.3">3.3.2</a>, <a href="#RFC7232"><b>11.1</b></a><ul><li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.2">3.3.1</a>, <a href="#rfc.xref.RFC7232.3">3.3.2</a></li></ul></li><li><em>RFC7233</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.1">1</a>, <a href="#RFC7233"><b>11.1</b></a></li><li><em>RFC7234</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.1">1</a>, <a href="#rfc.xref.RFC7234.2">2.4</a>, <a href="#rfc.xref.RFC7234.3">3.4</a>, <a href="#rfc.xref.RFC7234.4">5.2</a>, <a href="#rfc.xref.RFC7234.5">5.7.2</a>, <a href="#rfc.xref.RFC7234.6">5.7.2</a>, <a href="#rfc.xref.RFC7234.7">6.1</a>, <a href="#rfc.xref.RFC7234.8">9.2</a>, <a href="#RFC7234"><b>11.1</b></a><ul><li><em>Section 2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.2">2.4</a></li><li><em>Section 3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.3">3.4</a></li><li><em>Section 5.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.5">5.7.2</a>, <a href="#rfc.xref.RFC7234.7">6.1</a></li><li><em>Section 5.5</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.6">5.7.2</a></li><li><em>Section 8</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.8">9.2</a></li></ul></li><li><em>RFC7235</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7235.1">1</a>, <a href="#rfc.xref.RFC7235.2">4.1.2</a>, <a href="#RFC7235"><b>11.1</b></a></li></ul></li><li><a id="rfc.index.S" href="#rfc.index.S"><b>S</b></a><ul><li>sender&nbsp;&nbsp;<a href="#rfc.iref.s.2"><b>2.1</b></a></li><li>server&nbsp;&nbsp;<a href="#rfc.section.2.1"><b>2.1</b></a></li><li>spider&nbsp;&nbsp;<a href="#rfc.iref.s.1"><b>2.1</b></a></li></ul></li><li><a id="rfc.index.T" href="#rfc.index.T"><b>T</b></a><ul><li>target resource&nbsp;&nbsp;<a href="#rfc.section.5.1"><b>5.1</b></a></li><li>target URI&nbsp;&nbsp;<a href="#rfc.section.5.1"><b>5.1</b></a></li><li>TE header field&nbsp;&nbsp;<a href="#rfc.xref.header.te.1">4</a>, <a href="#rfc.xref.header.te.2">4.1.2</a>, <a href="#rfc.section.4.3"><b>4.3</b></a>, <a href="#rfc.xref.header.te.3">8.1</a></li><li>Trailer header field&nbsp;&nbsp;<a href="#rfc.section.4.4"><b>4.4</b></a>, <a href="#rfc.xref.header.trailer.1">8.1</a></li><li>Transfer-Encoding header field&nbsp;&nbsp;<a href="#rfc.xref.header.transfer-encoding.1">3.3</a>, <a href="#rfc.section.3.3.1"><b>3.3.1</b></a>, <a href="#rfc.xref.header.transfer-encoding.2">4</a>, <a href="#rfc.xref.header.transfer-encoding.3">8.1</a>, <a href="#rfc.xref.header.transfer-encoding.4">A.1.3</a></li><li>transforming proxy&nbsp;&nbsp;<a href="#rfc.section.5.7.2"><b>5.7.2</b></a></li><li>transparent proxy&nbsp;&nbsp;<a href="#rfc.iref.t.2"><b>2.3</b></a></li><li>tunnel&nbsp;&nbsp;<a href="#rfc.iref.t.1"><b>2.3</b></a></li></ul></li><li><a id="rfc.index.U" href="#rfc.index.U"><b>U</b></a><ul><li>Upgrade header field&nbsp;&nbsp;<a href="#rfc.xref.header.upgrade.1">5.7.1</a>, <a href="#rfc.section.6.7"><b>6.7</b></a>, <a href="#rfc.xref.header.upgrade.2">8.1</a>, <a href="#rfc.xref.header.upgrade.3">A.2</a></li><li>upstream&nbsp;&nbsp;<a href="#rfc.iref.u.2"><b>2.3</b></a></li><li>URI scheme&nbsp;&nbsp;<ul><li>http&nbsp;&nbsp;<a href="#rfc.section.2.7.1"><b>2.7.1</b></a></li><li>https&nbsp;&nbsp;<a href="#rfc.section.2.7.2">2.7.2</a></li></ul></li><li><em>USASCII</em>&nbsp;&nbsp;<a href="#rfc.xref.USASCII.1">1.2</a>, <a href="#rfc.xref.USASCII.2">3</a>, <a href="#rfc.xref.USASCII.3">3.2.4</a>, <a href="#USASCII"><b>11.1</b></a></li><li>user agent&nbsp;&nbsp;<a href="#rfc.iref.u.1"><b>2.1</b></a></li></ul></li><li><a id="rfc.index.V" href="#rfc.index.V"><b>V</b></a><ul><li>Via header field&nbsp;&nbsp;<a href="#rfc.section.5.7.1"><b>5.7.1</b></a>, <a href="#rfc.xref.header.via.1">8.1</a>, <a href="#rfc.xref.header.via.2">A.2</a></li></ul></li><li><a id="rfc.index.W" href="#rfc.index.W"><b>W</b></a><ul><li><em>Welch</em>&nbsp;&nbsp;<a href="#rfc.xref.Welch.1">4.2.1</a>, <a href="#rfc.xref.Welch.2">8.4.2</a>, <a href="#rfc.xref.Welch.3">8.5</a>, <a href="#Welch"><b>11.1</b></a></li></ul></li></ul></div><div class="avoidbreakinside"><h1 id="rfc.authors"><a href="#rfc.authors">Authors' Addresses</a></h1><p><b>Roy T. Fielding</b>
    833849      (editor)
    834850    <br>Adobe Systems Incorporated<br>345 Park Ave<br>San Jose, CA&nbsp;95110<br>USA<br>Email: fielding@gbiv.com<br>URI: <a href="http://roy.gbiv.com/">http://roy.gbiv.com/</a></p><p><b>Julian F. Reschke</b>
  • specs/rfc7231.html

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    511 </style><link rel="Contents" href="#rfc.toc"><link rel="Author" href="#rfc.authors"><link rel="Copyright" href="#rfc.copyrightnotice"><link rel="Index" href="#rfc.index"><link rel="Chapter" title="1 Introduction" href="#rfc.section.1"><link rel="Chapter" title="2 Resources" href="#rfc.section.2"><link rel="Chapter" title="3 Representations" href="#rfc.section.3"><link rel="Chapter" title="4 Request Methods" href="#rfc.section.4"><link rel="Chapter" title="5 Request Header Fields" href="#rfc.section.5"><link rel="Chapter" title="6 Response Status Codes" href="#rfc.section.6"><link rel="Chapter" title="7 Response Header Fields" href="#rfc.section.7"><link rel="Chapter" title="8 IANA Considerations" href="#rfc.section.8"><link rel="Chapter" title="9 Security Considerations" href="#rfc.section.9"><link rel="Chapter" title="10 Acknowledgments" href="#rfc.section.10"><link rel="Chapter" href="#rfc.section.11" title="11 References"><link rel="Appendix" title="A Differences between HTTP and MIME" href="#rfc.section.A"><link rel="Appendix" title="B Changes from RFC 2616" href="#rfc.section.B"><link rel="Appendix" title="C Imported ABNF" href="#rfc.section.C"><link rel="Appendix" title="D Collected ABNF" href="#rfc.section.D"><link href="rfc7230.html" rel="prev"><link href="rfc7232.html" rel="next"><link rel="Alternate" title="Authorative ASCII Version" href="http://www.ietf.org/rfc/rfc7231.txt"><link rel="Help" title="RFC-Editor's Status Page" href="http://www.rfc-editor.org/info/rfc7231"><link rel="Help" title="Additional Information on tools.ietf.org" href="http://tools.ietf.org/html/rfc7231"><meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.669, 2014/09/04 09:19:16, XSLT vendor: SAXON 6.5.5 from Michael Kay http://saxon.sf.net/"><meta name="keywords" content="Hypertext Transfer Protocol, HTTP, HTTP semantics, HTTP payload, HTTP content, HTTP method, HTTP status code"><link rel="schema.dct" href="http://purl.org/dc/terms/"><meta name="dct.creator" content="Fielding, R."><meta name="dct.creator" content="Reschke, J. F."><meta name="dct.identifier" content="urn:ietf:rfc:7231"><meta name="dct.issued" scheme="ISO8601" content="2014-06"><meta name="dct.replaces" content="urn:ietf:rfc:2616"><meta name="dct.abstract" content="The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines the semantics of HTTP/1.1 messages, as expressed by request methods, request header fields, response status codes, and response header fields, along with the payload of messages (metadata and body content) and mechanisms for content negotiation."><meta name="dct.isPartOf" content="urn:issn:2070-1721"><meta name="description" content="The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines the semantics of HTTP/1.1 messages, as expressed by request methods, request header fields, response status codes, and response header fields, along with the payload of messages (metadata and body content) and mechanisms for content negotiation."></head><body onload="getMeta(7231,&#34;rfc.meta&#34;);"><table class="header" id="rfc.headerblock"><tbody><tr><td class="left">Internet Engineering Task Force (IETF)</td><td class="right">R. Fielding, Editor</td></tr><tr><td class="left">Request for Comments: 7231</td><td class="right">Adobe</td></tr><tr><td class="left">Obsoletes: <a href="https://tools.ietf.org/html/rfc2616">2616</a></td><td class="right">J. Reschke, Editor</td></tr><tr><td class="left">Updates: <a href="https://tools.ietf.org/html/rfc2817">2817</a></td><td class="right">greenbytes</td></tr><tr><td class="left">Category: Standards Track</td><td class="right">June 2014</td></tr><tr><td class="left">ISSN: 2070-1721</td><td class="right"></td></tr></tbody></table><p class="title" id="rfc.title">Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</p><h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1><p>The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines the semantics of HTTP/1.1 messages, as expressed by request methods, request header fields, response status codes, and response header fields, along with the payload of messages (metadata and body content) and mechanisms for content negotiation.</p><div id="rfc.meta" style="float: right; border: 1px solid black; margin: 2em; padding: 1em; display: none;"></div><div id="rfc.status"><h1><a href="#rfc.status">Status of This Memo</a></h1><p>This is an Internet Standards Track document.</p><p>This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.</p><p>Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at <a href="http://www.rfc-editor.org/info/rfc7231">http://www.rfc-editor.org/info/rfc7231</a>.</p></div><div id="rfc.copyrightnotice"><h1><a href="#rfc.copyrightnotice">Copyright Notice</a></h1><p>Copyright &copy; 2014 IETF Trust and the persons identified as the document authors. All rights reserved.</p><p>This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.</p><p>This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English.</p></div><hr class="noprint"><div id="rfc.toc"><h1 class="np"><a href="#rfc.toc">Table of Contents</a></h1><ul class="toc"><li><a href="#rfc.section.1">1.</a>&nbsp;&nbsp;&nbsp;<a href="#introduction">Introduction</a><ul><li><a href="#rfc.section.1.1">1.1</a>&nbsp;&nbsp;&nbsp;<a href="#conformance">Conformance and Error Handling</a></li><li><a href="#rfc.section.1.2">1.2</a>&nbsp;&nbsp;&nbsp;<a href="#notation">Syntax Notation</a></li></ul></li><li><a href="#rfc.section.2">2.</a>&nbsp;&nbsp;&nbsp;<a href="#resources">Resources</a></li><li><a href="#rfc.section.3">3.</a>&nbsp;&nbsp;&nbsp;<a href="#representations">Representations</a><ul><li><a href="#rfc.section.3.1">3.1</a>&nbsp;&nbsp;&nbsp;<a href="#representation.metadata">Representation Metadata</a><ul><li><a href="#rfc.section.3.1.1">3.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#data.type">Processing Representation Data</a></li><li><a href="#rfc.section.3.1.2">3.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#data.encoding">Encoding for Compression or Integrity</a></li><li><a href="#rfc.section.3.1.3">3.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#audience.language">Audience Language</a></li><li><a href="#rfc.section.3.1.4">3.1.4</a>&nbsp;&nbsp;&nbsp;<a href="#identification">Identification</a></li></ul></li><li><a href="#rfc.section.3.2">3.2</a>&nbsp;&nbsp;&nbsp;<a href="#representation.data">Representation Data</a></li><li><a href="#rfc.section.3.3">3.3</a>&nbsp;&nbsp;&nbsp;<a href="#payload">Payload Semantics</a></li><li><a href="#rfc.section.3.4">3.4</a>&nbsp;&nbsp;&nbsp;<a href="#content.negotiation">Content Negotiation</a><ul><li><a href="#rfc.section.3.4.1">3.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#proactive.negotiation">Proactive Negotiation</a></li><li><a href="#rfc.section.3.4.2">3.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#reactive.negotiation">Reactive Negotiation</a></li></ul></li></ul></li><li><a href="#rfc.section.4">4.</a>&nbsp;&nbsp;&nbsp;<a href="#methods">Request Methods</a><ul><li><a href="#rfc.section.4.1">4.1</a>&nbsp;&nbsp;&nbsp;<a href="#method.overview">Overview</a></li><li><a href="#rfc.section.4.2">4.2</a>&nbsp;&nbsp;&nbsp;<a href="#method.properties">Common Method Properties</a><ul><li><a href="#rfc.section.4.2.1">4.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#safe.methods">Safe Methods</a></li><li><a href="#rfc.section.4.2.2">4.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#idempotent.methods">Idempotent Methods</a></li><li><a href="#rfc.section.4.2.3">4.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#cacheable.methods">Cacheable Methods</a></li></ul></li><li><a href="#rfc.section.4.3">4.3</a>&nbsp;&nbsp;&nbsp;<a href="#method.definitions">Method Definitions</a><ul><li><a href="#rfc.section.4.3.1">4.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#GET">GET</a></li><li><a href="#rfc.section.4.3.2">4.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#HEAD">HEAD</a></li><li><a href="#rfc.section.4.3.3">4.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#POST">POST</a></li><li><a href="#rfc.section.4.3.4">4.3.4</a>&nbsp;&nbsp;&nbsp;<a href="#PUT">PUT</a></li><li><a href="#rfc.section.4.3.5">4.3.5</a>&nbsp;&nbsp;&nbsp;<a href="#DELETE">DELETE</a></li><li><a href="#rfc.section.4.3.6">4.3.6</a>&nbsp;&nbsp;&nbsp;<a href="#CONNECT">CONNECT</a></li><li><a href="#rfc.section.4.3.7">4.3.7</a>&nbsp;&nbsp;&nbsp;<a href="#OPTIONS">OPTIONS</a></li><li><a href="#rfc.section.4.3.8">4.3.8</a>&nbsp;&nbsp;&nbsp;<a href="#TRACE">TRACE</a></li></ul></li></ul></li><li><a href="#rfc.section.5">5.</a>&nbsp;&nbsp;&nbsp;<a href="#request.header.fields">Request Header Fields</a><ul><li><a href="#rfc.section.5.1">5.1</a>&nbsp;&nbsp;&nbsp;<a href="#request.controls">Controls</a><ul><li><a href="#rfc.section.5.1.1">5.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.expect">Expect</a></li><li><a href="#rfc.section.5.1.2">5.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.max-forwards">Max-Forwards</a></li></ul></li><li><a href="#rfc.section.5.2">5.2</a>&nbsp;&nbsp;&nbsp;<a href="#request.conditionals">Conditionals</a></li><li><a href="#rfc.section.5.3">5.3</a>&nbsp;&nbsp;&nbsp;<a href="#request.conneg">Content Negotiation</a><ul><li><a href="#rfc.section.5.3.1">5.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#quality.values">Quality Values</a></li><li><a href="#rfc.section.5.3.2">5.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept">Accept</a></li><li><a href="#rfc.section.5.3.3">5.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept-charset">Accept-Charset</a></li><li><a href="#rfc.section.5.3.4">5.3.4</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept-encoding">Accept-Encoding</a></li><li><a href="#rfc.section.5.3.5">5.3.5</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept-language">Accept-Language</a></li></ul></li><li><a href="#rfc.section.5.4">5.4</a>&nbsp;&nbsp;&nbsp;<a href="#request.auth">Authentication Credentials</a></li><li><a href="#rfc.section.5.5">5.5</a>&nbsp;&nbsp;&nbsp;<a href="#request.context">Request Context</a><ul><li><a href="#rfc.section.5.5.1">5.5.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.from">From</a></li><li><a href="#rfc.section.5.5.2">5.5.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.referer">Referer</a></li><li><a href="#rfc.section.5.5.3">5.5.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.user-agent">User-Agent</a></li></ul></li></ul></li><li><a href="#rfc.section.6">6.</a>&nbsp;&nbsp;&nbsp;<a href="#status.codes">Response Status Codes</a><ul><li><a href="#rfc.section.6.1">6.1</a>&nbsp;&nbsp;&nbsp;<a href="#overview.of.status.codes">Overview of Status Codes</a></li><li><a href="#rfc.section.6.2">6.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.1xx">Informational 1xx</a><ul><li><a href="#rfc.section.6.2.1">6.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.100">100 Continue</a></li><li><a href="#rfc.section.6.2.2">6.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.101">101 Switching Protocols</a></li></ul></li><li><a href="#rfc.section.6.3">6.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.2xx">Successful 2xx</a><ul><li><a href="#rfc.section.6.3.1">6.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.200">200 OK</a></li><li><a href="#rfc.section.6.3.2">6.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.201">201 Created</a></li><li><a href="#rfc.section.6.3.3">6.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.202">202 Accepted</a></li><li><a href="#rfc.section.6.3.4">6.3.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.203">203 Non-Authoritative Information</a></li><li><a href="#rfc.section.6.3.5">6.3.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.204">204 No Content</a></li><li><a href="#rfc.section.6.3.6">6.3.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.205">205 Reset Content</a></li></ul></li><li><a href="#rfc.section.6.4">6.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.3xx">Redirection 3xx</a><ul><li><a href="#rfc.section.6.4.1">6.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.300">300 Multiple Choices</a></li><li><a href="#rfc.section.6.4.2">6.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.301">301 Moved Permanently</a></li><li><a href="#rfc.section.6.4.3">6.4.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.302">302 Found</a></li><li><a href="#rfc.section.6.4.4">6.4.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.303">303 See Other</a></li><li><a href="#rfc.section.6.4.5">6.4.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.305">305 Use Proxy</a></li><li><a href="#rfc.section.6.4.6">6.4.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.306">306 (Unused)</a></li><li><a href="#rfc.section.6.4.7">6.4.7</a>&nbsp;&nbsp;&nbsp;<a href="#status.307">307 Temporary Redirect</a></li></ul></li><li><a href="#rfc.section.6.5">6.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.4xx">Client Error 4xx</a><ul><li><a href="#rfc.section.6.5.1">6.5.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.400">400 Bad Request</a></li><li><a href="#rfc.section.6.5.2">6.5.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.402">402 Payment Required</a></li><li><a href="#rfc.section.6.5.3">6.5.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.403">403 Forbidden</a></li><li><a href="#rfc.section.6.5.4">6.5.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.404">404 Not Found</a></li><li><a href="#rfc.section.6.5.5">6.5.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.405">405 Method Not Allowed</a></li><li><a href="#rfc.section.6.5.6">6.5.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.406">406 Not Acceptable</a></li><li><a href="#rfc.section.6.5.7">6.5.7</a>&nbsp;&nbsp;&nbsp;<a href="#status.408">408 Request Timeout</a></li><li><a href="#rfc.section.6.5.8">6.5.8</a>&nbsp;&nbsp;&nbsp;<a href="#status.409">409 Conflict</a></li><li><a href="#rfc.section.6.5.9">6.5.9</a>&nbsp;&nbsp;&nbsp;<a href="#status.410">410 Gone</a></li><li><a href="#rfc.section.6.5.10">6.5.10</a>&nbsp;&nbsp;&nbsp;<a href="#status.411">411 Length Required</a></li><li><a href="#rfc.section.6.5.11">6.5.11</a>&nbsp;&nbsp;&nbsp;<a href="#status.413">413 Payload Too Large</a></li><li><a href="#rfc.section.6.5.12">6.5.12</a>&nbsp;&nbsp;&nbsp;<a href="#status.414">414 URI Too Long</a></li><li><a href="#rfc.section.6.5.13">6.5.13</a>&nbsp;&nbsp;&nbsp;<a href="#status.415">415 Unsupported Media Type</a></li><li><a href="#rfc.section.6.5.14">6.5.14</a>&nbsp;&nbsp;&nbsp;<a href="#status.417">417 Expectation Failed</a></li><li><a href="#rfc.section.6.5.15">6.5.15</a>&nbsp;&nbsp;&nbsp;<a href="#status.426">426 Upgrade Required</a></li></ul></li><li><a href="#rfc.section.6.6">6.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.5xx">Server Error 5xx</a><ul><li><a href="#rfc.section.6.6.1">6.6.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.500">500 Internal Server Error</a></li><li><a href="#rfc.section.6.6.2">6.6.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.501">501 Not Implemented</a></li><li><a href="#rfc.section.6.6.3">6.6.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.502">502 Bad Gateway</a></li><li><a href="#rfc.section.6.6.4">6.6.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.503">503 Service Unavailable</a></li><li><a href="#rfc.section.6.6.5">6.6.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.504">504 Gateway Timeout</a></li><li><a href="#rfc.section.6.6.6">6.6.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.505">505 HTTP Version Not Supported</a></li></ul></li></ul></li><li><a href="#rfc.section.7">7.</a>&nbsp;&nbsp;&nbsp;<a href="#response.header.fields">Response Header Fields</a><ul><li><a href="#rfc.section.7.1">7.1</a>&nbsp;&nbsp;&nbsp;<a href="#response.control.data">Control Data</a><ul><li><a href="#rfc.section.7.1.1">7.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#origination.date">Origination Date</a></li><li><a href="#rfc.section.7.1.2">7.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.location">Location</a></li><li><a href="#rfc.section.7.1.3">7.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.retry-after">Retry-After</a></li><li><a href="#rfc.section.7.1.4">7.1.4</a>&nbsp;&nbsp;&nbsp;<a href="#header.vary">Vary</a></li></ul></li><li><a href="#rfc.section.7.2">7.2</a>&nbsp;&nbsp;&nbsp;<a href="#response.validator">Validator Header Fields</a></li><li><a href="#rfc.section.7.3">7.3</a>&nbsp;&nbsp;&nbsp;<a href="#response.auth">Authentication Challenges</a></li><li><a href="#rfc.section.7.4">7.4</a>&nbsp;&nbsp;&nbsp;<a href="#response.context">Response Context</a><ul><li><a href="#rfc.section.7.4.1">7.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.allow">Allow</a></li><li><a href="#rfc.section.7.4.2">7.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.server">Server</a></li></ul></li></ul></li><li><a href="#rfc.section.8">8.</a>&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a><ul><li><a href="#rfc.section.8.1">8.1</a>&nbsp;&nbsp;&nbsp;<a href="#method.registry">Method Registry</a><ul><li><a href="#rfc.section.8.1.1">8.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#method.registry.procedure">Procedure</a></li><li><a href="#rfc.section.8.1.2">8.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#considerations.for.new.methods">Considerations for New Methods</a></li><li><a href="#rfc.section.8.1.3">8.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#method.registration">Registrations</a></li></ul></li><li><a href="#rfc.section.8.2">8.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.code.registry">Status Code Registry</a><ul><li><a href="#rfc.section.8.2.1">8.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.code.registry.procedure">Procedure</a></li><li><a href="#rfc.section.8.2.2">8.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#considerations.for.new.status.codes">Considerations for New Status Codes</a></li><li><a href="#rfc.section.8.2.3">8.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.code.registration">Registrations</a></li></ul></li><li><a href="#rfc.section.8.3">8.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.field.registry">Header Field Registry</a><ul><li><a href="#rfc.section.8.3.1">8.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#considerations.for.new.header.fields">Considerations for New Header Fields</a></li><li><a href="#rfc.section.8.3.2">8.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.field.registration">Registrations</a></li></ul></li><li><a href="#rfc.section.8.4">8.4</a>&nbsp;&nbsp;&nbsp;<a href="#content.coding.registry">Content Coding Registry</a><ul><li><a href="#rfc.section.8.4.1">8.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#content.coding.procedure">Procedure</a></li><li><a href="#rfc.section.8.4.2">8.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#content.coding.registration">Registrations</a></li></ul></li></ul></li><li><a href="#rfc.section.9">9.</a>&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a><ul><li><a href="#rfc.section.9.1">9.1</a>&nbsp;&nbsp;&nbsp;<a href="#attack.pathname">Attacks Based on File and Path Names</a></li><li><a href="#rfc.section.9.2">9.2</a>&nbsp;&nbsp;&nbsp;<a href="#attack.injection">Attacks Based on Command, Code, or Query Injection</a></li><li><a href="#rfc.section.9.3">9.3</a>&nbsp;&nbsp;&nbsp;<a href="#personal.information">Disclosure of Personal Information</a></li><li><a href="#rfc.section.9.4">9.4</a>&nbsp;&nbsp;&nbsp;<a href="#sensitive.information.in.uris">Disclosure of Sensitive Information in URIs</a></li><li><a href="#rfc.section.9.5">9.5</a>&nbsp;&nbsp;&nbsp;<a href="#fragment.disclosure">Disclosure of Fragment after Redirects</a></li><li><a href="#rfc.section.9.6">9.6</a>&nbsp;&nbsp;&nbsp;<a href="#disclosure.product.information">Disclosure of Product Information</a></li><li><a href="#rfc.section.9.7">9.7</a>&nbsp;&nbsp;&nbsp;<a href="#fingerprinting">Browser Fingerprinting</a></li></ul></li><li><a href="#rfc.section.10">10.</a>&nbsp;&nbsp;&nbsp;<a href="#acks">Acknowledgments</a></li><li><a href="#rfc.section.11">11.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul><li><a href="#rfc.section.11.1">11.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li><li><a href="#rfc.section.11.2">11.2</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li></ul></li><li><a href="#rfc.section.A">A.</a>&nbsp;&nbsp;&nbsp;<a href="#differences.between.http.and.mime">Differences between HTTP and MIME</a><ul><li><a href="#rfc.section.A.1">A.1</a>&nbsp;&nbsp;&nbsp;<a href="#mime-version">MIME-Version</a></li><li><a href="#rfc.section.A.2">A.2</a>&nbsp;&nbsp;&nbsp;<a href="#conversion.to.canonical.form">Conversion to Canonical Form</a></li><li><a href="#rfc.section.A.3">A.3</a>&nbsp;&nbsp;&nbsp;<a href="#conversion.of.date.formats">Conversion of Date Formats</a></li><li><a href="#rfc.section.A.4">A.4</a>&nbsp;&nbsp;&nbsp;<a href="#conversion.content-encoding">Conversion of Content-Encoding</a></li><li><a href="#rfc.section.A.5">A.5</a>&nbsp;&nbsp;&nbsp;<a href="#conversion.content-transfer-encoding">Conversion of Content-Transfer-Encoding</a></li><li><a href="#rfc.section.A.6">A.6</a>&nbsp;&nbsp;&nbsp;<a href="#mhtml.line.length">MHTML and Line Length Limitations</a></li></ul></li><li><a href="#rfc.section.B">B.</a>&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li><li><a href="#rfc.section.C">C.</a>&nbsp;&nbsp;&nbsp;<a href="#imported.abnf">Imported ABNF</a></li><li><a href="#rfc.section.D">D.</a>&nbsp;&nbsp;&nbsp;<a href="#collected.abnf">Collected ABNF</a></li><li><a href="#rfc.index">Index</a></li><li><a href="#rfc.authors">Authors' Addresses</a></li></ul></div><div id="introduction"><h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;<a href="#introduction">Introduction</a></h1><div id="rfc.section.1.p.1"><p>Each Hypertext Transfer Protocol (HTTP) message is either a request or a response. A server listens on a connection for a request, parses each message received, interprets the message semantics in relation to the identified request target, and responds to that request with one or more response messages. A client constructs request messages to communicate specific intentions, examines received responses to see if the intentions were carried out, and determines how to interpret the results. This document defines HTTP/1.1 request and response semantics in terms of the architecture defined in <a href="#RFC7230" id="rfc.xref.RFC7230.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>.<a class="self" href="#rfc.section.1.p.1">&para;</a></p></div><div id="rfc.section.1.p.2"><p>HTTP provides a uniform interface for interacting with a resource (<a href="#resources" title="Resources">Section&nbsp;2</a>), regardless of its type, nature, or implementation, via the manipulation and transfer of representations (<a href="#representations" title="Representations">Section&nbsp;3</a>).<a class="self" href="#rfc.section.1.p.2">&para;</a></p></div><div id="rfc.section.1.p.3"><p>HTTP semantics include the intentions defined by each request method (<a href="#methods" title="Request Methods">Section&nbsp;4</a>), extensions to those semantics that might be described in request header fields (<a href="#request.header.fields" title="Request Header Fields">Section&nbsp;5</a>), the meaning of status codes to indicate a machine-readable response (<a href="#status.codes" title="Response Status Codes">Section&nbsp;6</a>), and the meaning of other control data and resource metadata that might be given in response header fields (<a href="#response.header.fields" title="Response Header Fields">Section&nbsp;7</a>).<a class="self" href="#rfc.section.1.p.3">&para;</a></p></div><div id="rfc.section.1.p.4"><p><span id="rfc.iref.c.1"></span> This document also defines representation metadata that describe how a payload is intended to be interpreted by a recipient, the request header fields that might influence content selection, and the various selection algorithms that are collectively referred to as "<dfn>content negotiation</dfn>" (<a href="#content.negotiation" title="Content Negotiation">Section&nbsp;3.4</a>).<a class="self" href="#rfc.section.1.p.4">&para;</a></p></div><div id="conformance"><h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a>&nbsp;<a href="#conformance">Conformance and Error Handling</a></h2><div id="rfc.section.1.1.p.1"><p>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in <a href="#RFC2119" id="rfc.xref.RFC2119.1"><cite title="Key words for use in RFCs to Indicate Requirement Levels">[RFC2119]</cite></a>.<a class="self" href="#rfc.section.1.1.p.1">&para;</a></p></div><div id="rfc.section.1.1.p.2"><p>Conformance criteria and considerations regarding error handling are defined in <a href="rfc7230.html#conformance" title="Conformance and Error Handling">Section 2.5</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>.<a class="self" href="#rfc.section.1.1.p.2">&para;</a></p></div></div><div id="notation"><h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a>&nbsp;<a href="#notation">Syntax Notation</a></h2><div id="rfc.section.1.2.p.1"><p>This specification uses the Augmented Backus-Naur Form (ABNF) notation of <a href="#RFC5234" id="rfc.xref.RFC5234.1"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a> with a list extension, defined in <a href="rfc7230.html#abnf.extension" title="ABNF List Extension: #rule">Section 7</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>, that allows for compact definition of comma-separated lists using a '#' operator (similar to how the '*' operator indicates repetition). <a href="#imported.abnf" title="Imported ABNF">Appendix&nbsp;C</a> describes rules imported from other documents. <a href="#collected.abnf" title="Collected ABNF">Appendix&nbsp;D</a> shows the collected grammar with all list operators expanded to standard ABNF notation.<a class="self" href="#rfc.section.1.2.p.1">&para;</a></p></div><div id="rfc.section.1.2.p.2"><p>This specification uses the terms "character", "character encoding scheme", "charset", and "protocol element" as they are defined in <a href="#RFC6365" id="rfc.xref.RFC6365.1"><cite title="Terminology Used in Internationalization in the IETF">[RFC6365]</cite></a>.<a class="self" href="#rfc.section.1.2.p.2">&para;</a></p></div></div></div><div id="resources"><h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a href="#resources">Resources</a></h1><div id="rfc.section.2.p.1"><p>The target of an HTTP request is called a "<dfn>resource</dfn>". HTTP does not limit the nature of a resource; it merely defines an interface that might be used to interact with resources. Each resource is identified by a Uniform Resource Identifier (URI), as described in <a href="rfc7230.html#uri" title="Uniform Resource Identifiers">Section 2.7</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.4"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>.<a class="self" href="#rfc.section.2.p.1">&para;</a></p></div><div id="rfc.section.2.p.2"><p>When a client constructs an HTTP/1.1 request message, it sends the <a href="rfc7230.html#target-resource" class="smpl">target URI</a> in one of various forms, as defined in (<a href="rfc7230.html#request-target" title="Request Target">Section 5.3</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.5"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>). When a request is received, the server reconstructs an <a href="rfc7230.html#effective.request.uri" class="smpl">effective request URI</a> for the target resource (<a href="rfc7230.html#effective.request.uri" title="Effective Request URI">Section 5.5</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.6"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>).<a class="self" href="#rfc.section.2.p.2">&para;</a></p></div><div id="rfc.section.2.p.3"><p>One design goal of HTTP is to separate resource identification from request semantics, which is made possible by vesting the request semantics in the request method (<a href="#methods" title="Request Methods">Section&nbsp;4</a>) and a few request-modifying header fields (<a href="#request.header.fields" title="Request Header Fields">Section&nbsp;5</a>). If there is a conflict between the method semantics and any semantic implied by the URI itself, as described in <a href="#safe.methods" title="Safe Methods">Section&nbsp;4.2.1</a>, the method semantics take precedence.<a class="self" href="#rfc.section.2.p.3">&para;</a></p></div></div><div id="representations"><h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;<a href="#representations">Representations</a></h1><div id="rfc.section.3.p.1"><p>Considering that a resource could be anything, and that the uniform interface provided by HTTP is similar to a window through which one can observe and act upon such a thing only through the communication of messages to some independent actor on the other side, an abstraction is needed to represent ("take the place of") the current or desired state of that thing in our communications. That abstraction is called a representation <a href="#REST" id="rfc.xref.REST.1"><cite title="Architectural Styles and the Design of Network-based Software Architectures">[REST]</cite></a>.<a class="self" href="#rfc.section.3.p.1">&para;</a></p></div><div id="rfc.section.3.p.2"><p>For the purposes of HTTP, a "<dfn>representation</dfn>" is information that is intended to reflect a past, current, or desired state of a given resource, in a format that can be readily communicated via the protocol, and that consists of a set of representation metadata and a potentially unbounded stream of representation data.<a class="self" href="#rfc.section.3.p.2">&para;</a></p></div><div id="rfc.section.3.p.3"><p>An origin server might be provided with, or be capable of generating, multiple representations that are each intended to reflect the current state of a <a href="#resources" class="smpl">target resource</a>. In such cases, some algorithm is used by the origin server to select one of those representations as most applicable to a given request, usually based on <a href="#content.negotiation" class="smpl">content negotiation</a>. This "<dfn>selected representation</dfn>" is used to provide the data and metadata for evaluating conditional requests <a href="#RFC7232" id="rfc.xref.RFC7232.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a> and constructing the payload for <a href="#status.200" class="smpl">200 (OK)</a> and <a href="rfc7232.html#status.304" class="smpl">304 (Not Modified)</a> responses to GET (<a href="#GET" id="rfc.xref.GET.1" title="GET">Section&nbsp;4.3.1</a>).<a class="self" href="#rfc.section.3.p.3">&para;</a></p></div><div id="representation.metadata"><h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a>&nbsp;<a href="#representation.metadata">Representation Metadata</a></h2><div id="rfc.section.3.1.p.1"><p>Representation header fields provide metadata about the representation. When a message includes a payload body, the representation header fields describe how to interpret the representation data enclosed in the payload body. In a response to a HEAD request, the representation header fields describe the representation data that would have been enclosed in the payload body if the same request had been a GET.<a class="self" href="#rfc.section.3.1.p.1">&para;</a></p></div><div id="rfc.section.3.1.p.2"><p>The following header fields convey representation metadata:<a class="self" href="#rfc.section.3.1.p.2">&para;</a></p></div><div id="rfc.table.u.1"><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Header Field Name</th><th>Defined in...</th></tr></thead><tbody><tr><td class="left">Content-Type</td><td class="left"><a href="#header.content-type" id="rfc.xref.header.content-type.1" title="Content-Type">Section&nbsp;3.1.1.5</a></td></tr><tr><td class="left">Content-Encoding</td><td class="left"><a href="#header.content-encoding" id="rfc.xref.header.content-encoding.1" title="Content-Encoding">Section&nbsp;3.1.2.2</a></td></tr><tr><td class="left">Content-Language</td><td class="left"><a href="#header.content-language" id="rfc.xref.header.content-language.1" title="Content-Language">Section&nbsp;3.1.3.2</a></td></tr><tr><td class="left">Content-Location</td><td class="left"><a href="#header.content-location" id="rfc.xref.header.content-location.1" title="Content-Location">Section&nbsp;3.1.4.2</a></td></tr></tbody></table></div><div id="data.type"><h3 id="rfc.section.3.1.1"><a href="#rfc.section.3.1.1">3.1.1</a>&nbsp;<a href="#data.type">Processing Representation Data</a></h3><div id="media.type"><h4 id="rfc.section.3.1.1.1"><a href="#rfc.section.3.1.1.1">3.1.1.1</a>&nbsp;<a href="#media.type">Media Type</a></h4><div id="rfc.section.3.1.1.1.p.1"><p>HTTP uses Internet media types <a href="#RFC2046" id="rfc.xref.RFC2046.1"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types">[RFC2046]</cite></a> in the <a href="#header.content-type" class="smpl">Content-Type</a> (<a href="#header.content-type" id="rfc.xref.header.content-type.2" title="Content-Type">Section&nbsp;3.1.1.5</a>) and <a href="#header.accept" class="smpl">Accept</a> (<a href="#header.accept" id="rfc.xref.header.accept.1" title="Accept">Section&nbsp;5.3.2</a>) header fields in order to provide open and extensible data typing and type negotiation. Media types define both a data format and various processing models: how to process that data in accordance with each context in which it is received.<a class="self" href="#rfc.section.3.1.1.1.p.1">&para;</a></p></div><div id="rfc.figure.u.1"><pre class="inline"><span id="rfc.iref.g.1"></span><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span>  <a href="#media.type" class="smpl">media-type</a> = <a href="#media.type" class="smpl">type</a> "/" <a href="#media.type" class="smpl">subtype</a> *( <a href="#imported.abnf" class="smpl">OWS</a> ";" <a href="#imported.abnf" class="smpl">OWS</a> <a href="#rule.parameter" class="smpl">parameter</a> )
     527</style><link rel="Contents" href="#rfc.toc"><link rel="Author" href="#rfc.authors"><link rel="Copyright" href="#rfc.copyrightnotice"><link rel="Index" href="#rfc.index"><link rel="Chapter" title="1 Introduction" href="#rfc.section.1"><link rel="Chapter" title="2 Resources" href="#rfc.section.2"><link rel="Chapter" title="3 Representations" href="#rfc.section.3"><link rel="Chapter" title="4 Request Methods" href="#rfc.section.4"><link rel="Chapter" title="5 Request Header Fields" href="#rfc.section.5"><link rel="Chapter" title="6 Response Status Codes" href="#rfc.section.6"><link rel="Chapter" title="7 Response Header Fields" href="#rfc.section.7"><link rel="Chapter" title="8 IANA Considerations" href="#rfc.section.8"><link rel="Chapter" title="9 Security Considerations" href="#rfc.section.9"><link rel="Chapter" title="10 Acknowledgments" href="#rfc.section.10"><link rel="Chapter" href="#rfc.section.11" title="11 References"><link rel="Appendix" title="A Differences between HTTP and MIME" href="#rfc.section.A"><link rel="Appendix" title="B Changes from RFC 2616" href="#rfc.section.B"><link rel="Appendix" title="C Imported ABNF" href="#rfc.section.C"><link rel="Appendix" title="D Collected ABNF" href="#rfc.section.D"><link href="rfc7230.html" rel="prev"><link href="rfc7232.html" rel="next"><link rel="Alternate" title="Authorative ASCII Version" href="http://www.ietf.org/rfc/rfc7231.txt"><link rel="Help" title="RFC-Editor's Status Page" href="http://www.rfc-editor.org/info/rfc7231"><link rel="Help" title="Additional Information on tools.ietf.org" href="http://tools.ietf.org/html/rfc7231"><meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.710, 2014/12/09 13:12:18, XSLT vendor: SAXON 6.5.5 from Michael Kay http://saxon.sf.net/"><meta name="keywords" content="Hypertext Transfer Protocol, HTTP, HTTP semantics, HTTP payload, HTTP content, HTTP method, HTTP status code"><link rel="schema.dct" href="http://purl.org/dc/terms/"><meta name="dct.creator" content="Fielding, R."><meta name="dct.creator" content="Reschke, J. F."><meta name="dct.identifier" content="urn:ietf:rfc:7231"><meta name="dct.issued" scheme="ISO8601" content="2014-06"><meta name="dct.replaces" content="urn:ietf:rfc:2616"><meta name="dct.abstract" content="The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines the semantics of HTTP/1.1 messages, as expressed by request methods, request header fields, response status codes, and response header fields, along with the payload of messages (metadata and body content) and mechanisms for content negotiation."><meta name="dct.isPartOf" content="urn:issn:2070-1721"><meta name="description" content="The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines the semantics of HTTP/1.1 messages, as expressed by request methods, request header fields, response status codes, and response header fields, along with the payload of messages (metadata and body content) and mechanisms for content negotiation."></head><body onload="getMeta(7231,&#34;rfc.meta&#34;);"><table class="header" id="rfc.headerblock"><tbody><tr><td class="left">Internet Engineering Task Force (IETF)</td><td class="right">R. Fielding, Editor</td></tr><tr><td class="left">Request for Comments: 7231</td><td class="right">Adobe</td></tr><tr><td class="left">Obsoletes: <a href="https://tools.ietf.org/html/rfc2616">2616</a></td><td class="right">J. Reschke, Editor</td></tr><tr><td class="left">Updates: <a href="https://tools.ietf.org/html/rfc2817">2817</a></td><td class="right">greenbytes</td></tr><tr><td class="left">Category: Standards Track</td><td class="right">June 2014</td></tr><tr><td class="left">ISSN: 2070-1721</td><td class="right"></td></tr></tbody></table><p class="title" id="rfc.title">Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</p><h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1><p>The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines the semantics of HTTP/1.1 messages, as expressed by request methods, request header fields, response status codes, and response header fields, along with the payload of messages (metadata and body content) and mechanisms for content negotiation.</p><div id="rfc.meta" style="float: right; border: 1px solid black; margin: 2em; padding: 1em; display: none;"></div><div id="rfc.status"><h1><a href="#rfc.status">Status of This Memo</a></h1><p>This is an Internet Standards Track document.</p><p>This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.</p><p>Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at <a href="http://www.rfc-editor.org/info/rfc7231">http://www.rfc-editor.org/info/rfc7231</a>.</p></div><div id="rfc.copyrightnotice"><h1><a href="#rfc.copyrightnotice">Copyright Notice</a></h1><p>Copyright &copy; 2014 IETF Trust and the persons identified as the document authors. All rights reserved.</p><p>This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.</p><p>This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English.</p></div><hr class="noprint"><div id="rfc.toc"><h1 class="np"><a href="#rfc.toc">Table of Contents</a></h1><ul class="toc"><li><a href="#rfc.section.1">1.</a>&nbsp;&nbsp;&nbsp;<a href="#introduction">Introduction</a><ul><li><a href="#rfc.section.1.1">1.1</a>&nbsp;&nbsp;&nbsp;<a href="#conformance">Conformance and Error Handling</a></li><li><a href="#rfc.section.1.2">1.2</a>&nbsp;&nbsp;&nbsp;<a href="#notation">Syntax Notation</a></li></ul></li><li><a href="#rfc.section.2">2.</a>&nbsp;&nbsp;&nbsp;<a href="#resources">Resources</a></li><li><a href="#rfc.section.3">3.</a>&nbsp;&nbsp;&nbsp;<a href="#representations">Representations</a><ul><li><a href="#rfc.section.3.1">3.1</a>&nbsp;&nbsp;&nbsp;<a href="#representation.metadata">Representation Metadata</a><ul><li><a href="#rfc.section.3.1.1">3.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#data.type">Processing Representation Data</a></li><li><a href="#rfc.section.3.1.2">3.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#data.encoding">Encoding for Compression or Integrity</a></li><li><a href="#rfc.section.3.1.3">3.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#audience.language">Audience Language</a></li><li><a href="#rfc.section.3.1.4">3.1.4</a>&nbsp;&nbsp;&nbsp;<a href="#identification">Identification</a></li></ul></li><li><a href="#rfc.section.3.2">3.2</a>&nbsp;&nbsp;&nbsp;<a href="#representation.data">Representation Data</a></li><li><a href="#rfc.section.3.3">3.3</a>&nbsp;&nbsp;&nbsp;<a href="#payload">Payload Semantics</a></li><li><a href="#rfc.section.3.4">3.4</a>&nbsp;&nbsp;&nbsp;<a href="#content.negotiation">Content Negotiation</a><ul><li><a href="#rfc.section.3.4.1">3.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#proactive.negotiation">Proactive Negotiation</a></li><li><a href="#rfc.section.3.4.2">3.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#reactive.negotiation">Reactive Negotiation</a></li></ul></li></ul></li><li><a href="#rfc.section.4">4.</a>&nbsp;&nbsp;&nbsp;<a href="#methods">Request Methods</a><ul><li><a href="#rfc.section.4.1">4.1</a>&nbsp;&nbsp;&nbsp;<a href="#method.overview">Overview</a></li><li><a href="#rfc.section.4.2">4.2</a>&nbsp;&nbsp;&nbsp;<a href="#method.properties">Common Method Properties</a><ul><li><a href="#rfc.section.4.2.1">4.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#safe.methods">Safe Methods</a></li><li><a href="#rfc.section.4.2.2">4.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#idempotent.methods">Idempotent Methods</a></li><li><a href="#rfc.section.4.2.3">4.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#cacheable.methods">Cacheable Methods</a></li></ul></li><li><a href="#rfc.section.4.3">4.3</a>&nbsp;&nbsp;&nbsp;<a href="#method.definitions">Method Definitions</a><ul><li><a href="#rfc.section.4.3.1">4.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#GET">GET</a></li><li><a href="#rfc.section.4.3.2">4.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#HEAD">HEAD</a></li><li><a href="#rfc.section.4.3.3">4.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#POST">POST</a></li><li><a href="#rfc.section.4.3.4">4.3.4</a>&nbsp;&nbsp;&nbsp;<a href="#PUT">PUT</a></li><li><a href="#rfc.section.4.3.5">4.3.5</a>&nbsp;&nbsp;&nbsp;<a href="#DELETE">DELETE</a></li><li><a href="#rfc.section.4.3.6">4.3.6</a>&nbsp;&nbsp;&nbsp;<a href="#CONNECT">CONNECT</a></li><li><a href="#rfc.section.4.3.7">4.3.7</a>&nbsp;&nbsp;&nbsp;<a href="#OPTIONS">OPTIONS</a></li><li><a href="#rfc.section.4.3.8">4.3.8</a>&nbsp;&nbsp;&nbsp;<a href="#TRACE">TRACE</a></li></ul></li></ul></li><li><a href="#rfc.section.5">5.</a>&nbsp;&nbsp;&nbsp;<a href="#request.header.fields">Request Header Fields</a><ul><li><a href="#rfc.section.5.1">5.1</a>&nbsp;&nbsp;&nbsp;<a href="#request.controls">Controls</a><ul><li><a href="#rfc.section.5.1.1">5.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.expect">Expect</a></li><li><a href="#rfc.section.5.1.2">5.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.max-forwards">Max-Forwards</a></li></ul></li><li><a href="#rfc.section.5.2">5.2</a>&nbsp;&nbsp;&nbsp;<a href="#request.conditionals">Conditionals</a></li><li><a href="#rfc.section.5.3">5.3</a>&nbsp;&nbsp;&nbsp;<a href="#request.conneg">Content Negotiation</a><ul><li><a href="#rfc.section.5.3.1">5.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#quality.values">Quality Values</a></li><li><a href="#rfc.section.5.3.2">5.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept">Accept</a></li><li><a href="#rfc.section.5.3.3">5.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept-charset">Accept-Charset</a></li><li><a href="#rfc.section.5.3.4">5.3.4</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept-encoding">Accept-Encoding</a></li><li><a href="#rfc.section.5.3.5">5.3.5</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept-language">Accept-Language</a></li></ul></li><li><a href="#rfc.section.5.4">5.4</a>&nbsp;&nbsp;&nbsp;<a href="#request.auth">Authentication Credentials</a></li><li><a href="#rfc.section.5.5">5.5</a>&nbsp;&nbsp;&nbsp;<a href="#request.context">Request Context</a><ul><li><a href="#rfc.section.5.5.1">5.5.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.from">From</a></li><li><a href="#rfc.section.5.5.2">5.5.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.referer">Referer</a></li><li><a href="#rfc.section.5.5.3">5.5.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.user-agent">User-Agent</a></li></ul></li></ul></li><li><a href="#rfc.section.6">6.</a>&nbsp;&nbsp;&nbsp;<a href="#status.codes">Response Status Codes</a><ul><li><a href="#rfc.section.6.1">6.1</a>&nbsp;&nbsp;&nbsp;<a href="#overview.of.status.codes">Overview of Status Codes</a></li><li><a href="#rfc.section.6.2">6.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.1xx">Informational 1xx</a><ul><li><a href="#rfc.section.6.2.1">6.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.100">100 Continue</a></li><li><a href="#rfc.section.6.2.2">6.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.101">101 Switching Protocols</a></li></ul></li><li><a href="#rfc.section.6.3">6.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.2xx">Successful 2xx</a><ul><li><a href="#rfc.section.6.3.1">6.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.200">200 OK</a></li><li><a href="#rfc.section.6.3.2">6.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.201">201 Created</a></li><li><a href="#rfc.section.6.3.3">6.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.202">202 Accepted</a></li><li><a href="#rfc.section.6.3.4">6.3.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.203">203 Non-Authoritative Information</a></li><li><a href="#rfc.section.6.3.5">6.3.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.204">204 No Content</a></li><li><a href="#rfc.section.6.3.6">6.3.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.205">205 Reset Content</a></li></ul></li><li><a href="#rfc.section.6.4">6.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.3xx">Redirection 3xx</a><ul><li><a href="#rfc.section.6.4.1">6.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.300">300 Multiple Choices</a></li><li><a href="#rfc.section.6.4.2">6.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.301">301 Moved Permanently</a></li><li><a href="#rfc.section.6.4.3">6.4.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.302">302 Found</a></li><li><a href="#rfc.section.6.4.4">6.4.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.303">303 See Other</a></li><li><a href="#rfc.section.6.4.5">6.4.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.305">305 Use Proxy</a></li><li><a href="#rfc.section.6.4.6">6.4.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.306">306 (Unused)</a></li><li><a href="#rfc.section.6.4.7">6.4.7</a>&nbsp;&nbsp;&nbsp;<a href="#status.307">307 Temporary Redirect</a></li></ul></li><li><a href="#rfc.section.6.5">6.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.4xx">Client Error 4xx</a><ul><li><a href="#rfc.section.6.5.1">6.5.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.400">400 Bad Request</a></li><li><a href="#rfc.section.6.5.2">6.5.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.402">402 Payment Required</a></li><li><a href="#rfc.section.6.5.3">6.5.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.403">403 Forbidden</a></li><li><a href="#rfc.section.6.5.4">6.5.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.404">404 Not Found</a></li><li><a href="#rfc.section.6.5.5">6.5.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.405">405 Method Not Allowed</a></li><li><a href="#rfc.section.6.5.6">6.5.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.406">406 Not Acceptable</a></li><li><a href="#rfc.section.6.5.7">6.5.7</a>&nbsp;&nbsp;&nbsp;<a href="#status.408">408 Request Timeout</a></li><li><a href="#rfc.section.6.5.8">6.5.8</a>&nbsp;&nbsp;&nbsp;<a href="#status.409">409 Conflict</a></li><li><a href="#rfc.section.6.5.9">6.5.9</a>&nbsp;&nbsp;&nbsp;<a href="#status.410">410 Gone</a></li><li><a href="#rfc.section.6.5.10">6.5.10</a>&nbsp;&nbsp;&nbsp;<a href="#status.411">411 Length Required</a></li><li><a href="#rfc.section.6.5.11">6.5.11</a>&nbsp;&nbsp;&nbsp;<a href="#status.413">413 Payload Too Large</a></li><li><a href="#rfc.section.6.5.12">6.5.12</a>&nbsp;&nbsp;&nbsp;<a href="#status.414">414 URI Too Long</a></li><li><a href="#rfc.section.6.5.13">6.5.13</a>&nbsp;&nbsp;&nbsp;<a href="#status.415">415 Unsupported Media Type</a></li><li><a href="#rfc.section.6.5.14">6.5.14</a>&nbsp;&nbsp;&nbsp;<a href="#status.417">417 Expectation Failed</a></li><li><a href="#rfc.section.6.5.15">6.5.15</a>&nbsp;&nbsp;&nbsp;<a href="#status.426">426 Upgrade Required</a></li></ul></li><li><a href="#rfc.section.6.6">6.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.5xx">Server Error 5xx</a><ul><li><a href="#rfc.section.6.6.1">6.6.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.500">500 Internal Server Error</a></li><li><a href="#rfc.section.6.6.2">6.6.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.501">501 Not Implemented</a></li><li><a href="#rfc.section.6.6.3">6.6.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.502">502 Bad Gateway</a></li><li><a href="#rfc.section.6.6.4">6.6.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.503">503 Service Unavailable</a></li><li><a href="#rfc.section.6.6.5">6.6.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.504">504 Gateway Timeout</a></li><li><a href="#rfc.section.6.6.6">6.6.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.505">505 HTTP Version Not Supported</a></li></ul></li></ul></li><li><a href="#rfc.section.7">7.</a>&nbsp;&nbsp;&nbsp;<a href="#response.header.fields">Response Header Fields</a><ul><li><a href="#rfc.section.7.1">7.1</a>&nbsp;&nbsp;&nbsp;<a href="#response.control.data">Control Data</a><ul><li><a href="#rfc.section.7.1.1">7.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#origination.date">Origination Date</a></li><li><a href="#rfc.section.7.1.2">7.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.location">Location</a></li><li><a href="#rfc.section.7.1.3">7.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.retry-after">Retry-After</a></li><li><a href="#rfc.section.7.1.4">7.1.4</a>&nbsp;&nbsp;&nbsp;<a href="#header.vary">Vary</a></li></ul></li><li><a href="#rfc.section.7.2">7.2</a>&nbsp;&nbsp;&nbsp;<a href="#response.validator">Validator Header Fields</a></li><li><a href="#rfc.section.7.3">7.3</a>&nbsp;&nbsp;&nbsp;<a href="#response.auth">Authentication Challenges</a></li><li><a href="#rfc.section.7.4">7.4</a>&nbsp;&nbsp;&nbsp;<a href="#response.context">Response Context</a><ul><li><a href="#rfc.section.7.4.1">7.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.allow">Allow</a></li><li><a href="#rfc.section.7.4.2">7.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.server">Server</a></li></ul></li></ul></li><li><a href="#rfc.section.8">8.</a>&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a><ul><li><a href="#rfc.section.8.1">8.1</a>&nbsp;&nbsp;&nbsp;<a href="#method.registry">Method Registry</a><ul><li><a href="#rfc.section.8.1.1">8.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#method.registry.procedure">Procedure</a></li><li><a href="#rfc.section.8.1.2">8.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#considerations.for.new.methods">Considerations for New Methods</a></li><li><a href="#rfc.section.8.1.3">8.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#method.registration">Registrations</a></li></ul></li><li><a href="#rfc.section.8.2">8.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.code.registry">Status Code Registry</a><ul><li><a href="#rfc.section.8.2.1">8.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.code.registry.procedure">Procedure</a></li><li><a href="#rfc.section.8.2.2">8.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#considerations.for.new.status.codes">Considerations for New Status Codes</a></li><li><a href="#rfc.section.8.2.3">8.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.code.registration">Registrations</a></li></ul></li><li><a href="#rfc.section.8.3">8.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.field.registry">Header Field Registry</a><ul><li><a href="#rfc.section.8.3.1">8.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#considerations.for.new.header.fields">Considerations for New Header Fields</a></li><li><a href="#rfc.section.8.3.2">8.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.field.registration">Registrations</a></li></ul></li><li><a href="#rfc.section.8.4">8.4</a>&nbsp;&nbsp;&nbsp;<a href="#content.coding.registry">Content Coding Registry</a><ul><li><a href="#rfc.section.8.4.1">8.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#content.coding.procedure">Procedure</a></li><li><a href="#rfc.section.8.4.2">8.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#content.coding.registration">Registrations</a></li></ul></li></ul></li><li><a href="#rfc.section.9">9.</a>&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a><ul><li><a href="#rfc.section.9.1">9.1</a>&nbsp;&nbsp;&nbsp;<a href="#attack.pathname">Attacks Based on File and Path Names</a></li><li><a href="#rfc.section.9.2">9.2</a>&nbsp;&nbsp;&nbsp;<a href="#attack.injection">Attacks Based on Command, Code, or Query Injection</a></li><li><a href="#rfc.section.9.3">9.3</a>&nbsp;&nbsp;&nbsp;<a href="#personal.information">Disclosure of Personal Information</a></li><li><a href="#rfc.section.9.4">9.4</a>&nbsp;&nbsp;&nbsp;<a href="#sensitive.information.in.uris">Disclosure of Sensitive Information in URIs</a></li><li><a href="#rfc.section.9.5">9.5</a>&nbsp;&nbsp;&nbsp;<a href="#fragment.disclosure">Disclosure of Fragment after Redirects</a></li><li><a href="#rfc.section.9.6">9.6</a>&nbsp;&nbsp;&nbsp;<a href="#disclosure.product.information">Disclosure of Product Information</a></li><li><a href="#rfc.section.9.7">9.7</a>&nbsp;&nbsp;&nbsp;<a href="#fingerprinting">Browser Fingerprinting</a></li></ul></li><li><a href="#rfc.section.10">10.</a>&nbsp;&nbsp;&nbsp;<a href="#acks">Acknowledgments</a></li><li><a href="#rfc.section.11">11.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul><li><a href="#rfc.section.11.1">11.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li><li><a href="#rfc.section.11.2">11.2</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li></ul></li><li><a href="#rfc.section.A">A.</a>&nbsp;&nbsp;&nbsp;<a href="#differences.between.http.and.mime">Differences between HTTP and MIME</a><ul><li><a href="#rfc.section.A.1">A.1</a>&nbsp;&nbsp;&nbsp;<a href="#mime-version">MIME-Version</a></li><li><a href="#rfc.section.A.2">A.2</a>&nbsp;&nbsp;&nbsp;<a href="#conversion.to.canonical.form">Conversion to Canonical Form</a></li><li><a href="#rfc.section.A.3">A.3</a>&nbsp;&nbsp;&nbsp;<a href="#conversion.of.date.formats">Conversion of Date Formats</a></li><li><a href="#rfc.section.A.4">A.4</a>&nbsp;&nbsp;&nbsp;<a href="#conversion.content-encoding">Conversion of Content-Encoding</a></li><li><a href="#rfc.section.A.5">A.5</a>&nbsp;&nbsp;&nbsp;<a href="#conversion.content-transfer-encoding">Conversion of Content-Transfer-Encoding</a></li><li><a href="#rfc.section.A.6">A.6</a>&nbsp;&nbsp;&nbsp;<a href="#mhtml.line.length">MHTML and Line Length Limitations</a></li></ul></li><li><a href="#rfc.section.B">B.</a>&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li><li><a href="#rfc.section.C">C.</a>&nbsp;&nbsp;&nbsp;<a href="#imported.abnf">Imported ABNF</a></li><li><a href="#rfc.section.D">D.</a>&nbsp;&nbsp;&nbsp;<a href="#collected.abnf">Collected ABNF</a></li><li><a href="#rfc.index">Index</a></li><li><a href="#rfc.authors">Authors' Addresses</a></li></ul></div><div id="introduction"><h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;<a href="#introduction">Introduction</a></h1><div id="rfc.section.1.p.1"><p>Each Hypertext Transfer Protocol (HTTP) message is either a request or a response. A server listens on a connection for a request, parses each message received, interprets the message semantics in relation to the identified request target, and responds to that request with one or more response messages. A client constructs request messages to communicate specific intentions, examines received responses to see if the intentions were carried out, and determines how to interpret the results. This document defines HTTP/1.1 request and response semantics in terms of the architecture defined in <a href="#RFC7230" id="rfc.xref.RFC7230.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>.<a class="self" href="#rfc.section.1.p.1">&para;</a></p></div><div id="rfc.section.1.p.2"><p>HTTP provides a uniform interface for interacting with a resource (<a href="#resources" title="Resources">Section&nbsp;2</a>), regardless of its type, nature, or implementation, via the manipulation and transfer of representations (<a href="#representations" title="Representations">Section&nbsp;3</a>).<a class="self" href="#rfc.section.1.p.2">&para;</a></p></div><div id="rfc.section.1.p.3"><p>HTTP semantics include the intentions defined by each request method (<a href="#methods" title="Request Methods">Section&nbsp;4</a>), extensions to those semantics that might be described in request header fields (<a href="#request.header.fields" title="Request Header Fields">Section&nbsp;5</a>), the meaning of status codes to indicate a machine-readable response (<a href="#status.codes" title="Response Status Codes">Section&nbsp;6</a>), and the meaning of other control data and resource metadata that might be given in response header fields (<a href="#response.header.fields" title="Response Header Fields">Section&nbsp;7</a>).<a class="self" href="#rfc.section.1.p.3">&para;</a></p></div><div id="rfc.section.1.p.4"><p><span id="rfc.iref.c.1"></span> This document also defines representation metadata that describe how a payload is intended to be interpreted by a recipient, the request header fields that might influence content selection, and the various selection algorithms that are collectively referred to as "<dfn>content negotiation</dfn>" (<a href="#content.negotiation" title="Content Negotiation">Section&nbsp;3.4</a>).<a class="self" href="#rfc.section.1.p.4">&para;</a></p></div><div id="conformance"><h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a>&nbsp;<a href="#conformance">Conformance and Error Handling</a></h2><div id="rfc.section.1.1.p.1"><p>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in <a href="#RFC2119" id="rfc.xref.RFC2119.1"><cite title="Key words for use in RFCs to Indicate Requirement Levels">[RFC2119]</cite></a>.<a class="self" href="#rfc.section.1.1.p.1">&para;</a></p></div><div id="rfc.section.1.1.p.2"><p>Conformance criteria and considerations regarding error handling are defined in <a href="rfc7230.html#conformance" title="Conformance and Error Handling">Section 2.5</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>.<a class="self" href="#rfc.section.1.1.p.2">&para;</a></p></div></div><div id="notation"><h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a>&nbsp;<a href="#notation">Syntax Notation</a></h2><div id="rfc.section.1.2.p.1"><p>This specification uses the Augmented Backus-Naur Form (ABNF) notation of <a href="#RFC5234" id="rfc.xref.RFC5234.1"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a> with a list extension, defined in <a href="rfc7230.html#abnf.extension" title="ABNF List Extension: #rule">Section 7</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>, that allows for compact definition of comma-separated lists using a '#' operator (similar to how the '*' operator indicates repetition). <a href="#imported.abnf" title="Imported ABNF">Appendix&nbsp;C</a> describes rules imported from other documents. <a href="#collected.abnf" title="Collected ABNF">Appendix&nbsp;D</a> shows the collected grammar with all list operators expanded to standard ABNF notation.<a class="self" href="#rfc.section.1.2.p.1">&para;</a></p></div><div id="rfc.section.1.2.p.2"><p>This specification uses the terms "character", "character encoding scheme", "charset", and "protocol element" as they are defined in <a href="#RFC6365" id="rfc.xref.RFC6365.1"><cite title="Terminology Used in Internationalization in the IETF">[RFC6365]</cite></a>.<a class="self" href="#rfc.section.1.2.p.2">&para;</a></p></div></div></div><div id="resources"><h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a href="#resources">Resources</a></h1><div id="rfc.section.2.p.1"><p>The target of an HTTP request is called a "<dfn>resource</dfn>". HTTP does not limit the nature of a resource; it merely defines an interface that might be used to interact with resources. Each resource is identified by a Uniform Resource Identifier (URI), as described in <a href="rfc7230.html#uri" title="Uniform Resource Identifiers">Section 2.7</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.4"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>.<a class="self" href="#rfc.section.2.p.1">&para;</a></p></div><div id="rfc.section.2.p.2"><p>When a client constructs an HTTP/1.1 request message, it sends the <a href="rfc7230.html#target-resource" class="smpl">target URI</a> in one of various forms, as defined in (<a href="rfc7230.html#request-target" title="Request Target">Section 5.3</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.5"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>). When a request is received, the server reconstructs an <a href="rfc7230.html#effective.request.uri" class="smpl">effective request URI</a> for the target resource (<a href="rfc7230.html#effective.request.uri" title="Effective Request URI">Section 5.5</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.6"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>).<a class="self" href="#rfc.section.2.p.2">&para;</a></p></div><div id="rfc.section.2.p.3"><p>One design goal of HTTP is to separate resource identification from request semantics, which is made possible by vesting the request semantics in the request method (<a href="#methods" title="Request Methods">Section&nbsp;4</a>) and a few request-modifying header fields (<a href="#request.header.fields" title="Request Header Fields">Section&nbsp;5</a>). If there is a conflict between the method semantics and any semantic implied by the URI itself, as described in <a href="#safe.methods" title="Safe Methods">Section&nbsp;4.2.1</a>, the method semantics take precedence.<a class="self" href="#rfc.section.2.p.3">&para;</a></p></div></div><div id="representations"><h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;<a href="#representations">Representations</a></h1><div id="rfc.section.3.p.1"><p>Considering that a resource could be anything, and that the uniform interface provided by HTTP is similar to a window through which one can observe and act upon such a thing only through the communication of messages to some independent actor on the other side, an abstraction is needed to represent ("take the place of") the current or desired state of that thing in our communications. That abstraction is called a representation <a href="#REST" id="rfc.xref.REST.1"><cite title="Architectural Styles and the Design of Network-based Software Architectures">[REST]</cite></a>.<a class="self" href="#rfc.section.3.p.1">&para;</a></p></div><div id="rfc.section.3.p.2"><p>For the purposes of HTTP, a "<dfn>representation</dfn>" is information that is intended to reflect a past, current, or desired state of a given resource, in a format that can be readily communicated via the protocol, and that consists of a set of representation metadata and a potentially unbounded stream of representation data.<a class="self" href="#rfc.section.3.p.2">&para;</a></p></div><div id="rfc.section.3.p.3"><p>An origin server might be provided with, or be capable of generating, multiple representations that are each intended to reflect the current state of a <a href="#resources" class="smpl">target resource</a>. In such cases, some algorithm is used by the origin server to select one of those representations as most applicable to a given request, usually based on <a href="#content.negotiation" class="smpl">content negotiation</a>. This "<dfn>selected representation</dfn>" is used to provide the data and metadata for evaluating conditional requests <a href="#RFC7232" id="rfc.xref.RFC7232.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a> and constructing the payload for <a href="#status.200" class="smpl">200 (OK)</a> and <a href="rfc7232.html#status.304" class="smpl">304 (Not Modified)</a> responses to GET (<a href="#GET" id="rfc.xref.GET.1" title="GET">Section&nbsp;4.3.1</a>).<a class="self" href="#rfc.section.3.p.3">&para;</a></p></div><div id="representation.metadata"><h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a>&nbsp;<a href="#representation.metadata">Representation Metadata</a></h2><div id="rfc.section.3.1.p.1"><p>Representation header fields provide metadata about the representation. When a message includes a payload body, the representation header fields describe how to interpret the representation data enclosed in the payload body. In a response to a HEAD request, the representation header fields describe the representation data that would have been enclosed in the payload body if the same request had been a GET.<a class="self" href="#rfc.section.3.1.p.1">&para;</a></p></div><div id="rfc.section.3.1.p.2"><p>The following header fields convey representation metadata:<a class="self" href="#rfc.section.3.1.p.2">&para;</a></p></div><div id="rfc.table.u.1"><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Header Field Name</th><th>Defined in...</th></tr></thead><tbody><tr><td class="left">Content-Type</td><td class="left"><a href="#header.content-type" id="rfc.xref.header.content-type.1" title="Content-Type">Section&nbsp;3.1.1.5</a></td></tr><tr><td class="left">Content-Encoding</td><td class="left"><a href="#header.content-encoding" id="rfc.xref.header.content-encoding.1" title="Content-Encoding">Section&nbsp;3.1.2.2</a></td></tr><tr><td class="left">Content-Language</td><td class="left"><a href="#header.content-language" id="rfc.xref.header.content-language.1" title="Content-Language">Section&nbsp;3.1.3.2</a></td></tr><tr><td class="left">Content-Location</td><td class="left"><a href="#header.content-location" id="rfc.xref.header.content-location.1" title="Content-Location">Section&nbsp;3.1.4.2</a></td></tr></tbody></table></div><div id="data.type"><h3 id="rfc.section.3.1.1"><a href="#rfc.section.3.1.1">3.1.1</a>&nbsp;<a href="#data.type">Processing Representation Data</a></h3><div id="media.type"><h4 id="rfc.section.3.1.1.1"><a href="#rfc.section.3.1.1.1">3.1.1.1</a>&nbsp;<a href="#media.type">Media Type</a></h4><div id="rfc.section.3.1.1.1.p.1"><p>HTTP uses Internet media types <a href="#RFC2046" id="rfc.xref.RFC2046.1"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types">[RFC2046]</cite></a> in the <a href="#header.content-type" class="smpl">Content-Type</a> (<a href="#header.content-type" id="rfc.xref.header.content-type.2" title="Content-Type">Section&nbsp;3.1.1.5</a>) and <a href="#header.accept" class="smpl">Accept</a> (<a href="#header.accept" id="rfc.xref.header.accept.1" title="Accept">Section&nbsp;5.3.2</a>) header fields in order to provide open and extensible data typing and type negotiation. Media types define both a data format and various processing models: how to process that data in accordance with each context in which it is received.<a class="self" href="#rfc.section.3.1.1.1.p.1">&para;</a></p></div><div id="rfc.figure.u.1"><pre class="inline"><span id="rfc.iref.g.1"></span><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span>  <a href="#media.type" class="smpl">media-type</a> = <a href="#media.type" class="smpl">type</a> "/" <a href="#media.type" class="smpl">subtype</a> *( <a href="#imported.abnf" class="smpl">OWS</a> ";" <a href="#imported.abnf" class="smpl">OWS</a> <a href="#rule.parameter" class="smpl">parameter</a> )
    512528  <a href="#media.type" class="smpl">type</a>       = <a href="#imported.abnf" class="smpl">token</a>
    513529  <a href="#media.type" class="smpl">subtype</a>    = <a href="#imported.abnf" class="smpl">token</a>
     
    517533  Text/HTML;Charset="utf-8"
    518534  text/html; charset="utf-8"
    519 </pre></div><div id="rfc.section.3.1.1.1.p.5"><p>Internet media types ought to be registered with IANA according to the procedures defined in <a href="#BCP13" id="rfc.xref.BCP13.1"><cite title="Media Type Specifications and Registration Procedures">[BCP13]</cite></a>.<a class="self" href="#rfc.section.3.1.1.1.p.5">&para;</a></p></div><div class="note" id="rfc.section.3.1.1.1.p.6"><p><b>Note:</b> Unlike some similar constructs in other header fields, media type parameters do not allow whitespace (even "bad" whitespace) around the "=" character.<a class="self" href="#rfc.section.3.1.1.1.p.6">&para;</a></p></div></div><div id="charset"><h4 id="rfc.section.3.1.1.2"><a href="#rfc.section.3.1.1.2">3.1.1.2</a>&nbsp;<a href="#charset">Charset</a></h4><div id="rfc.section.3.1.1.2.p.1"><p>HTTP uses <dfn>charset</dfn> names to indicate or negotiate the character encoding scheme of a textual representation <a href="#RFC6365" id="rfc.xref.RFC6365.2"><cite title="Terminology Used in Internationalization in the IETF">[RFC6365]</cite></a>. A charset is identified by a case-insensitive token.<a class="self" href="#rfc.section.3.1.1.2.p.1">&para;</a></p></div><div id="rfc.figure.u.4"><pre class="inline"><span id="rfc.iref.g.5"></span>  <a href="#charset" class="smpl">charset</a> = <a href="#imported.abnf" class="smpl">token</a>
     535</pre></div><div id="rfc.section.3.1.1.1.p.5"><p>Internet media types ought to be registered with IANA according to the procedures defined in <a href="#BCP13" id="rfc.xref.BCP13.1"><cite title="Media Type Specifications and Registration Procedures">[BCP13]</cite></a>.<a class="self" href="#rfc.section.3.1.1.1.p.5">&para;</a></p></div><div class="note"><div id="rfc.section.3.1.1.1.p.6"><p><b>Note:</b> Unlike some similar constructs in other header fields, media type parameters do not allow whitespace (even "bad" whitespace) around the "=" character.<a class="self" href="#rfc.section.3.1.1.1.p.6">&para;</a></p></div></div></div><div id="charset"><h4 id="rfc.section.3.1.1.2"><a href="#rfc.section.3.1.1.2">3.1.1.2</a>&nbsp;<a href="#charset">Charset</a></h4><div id="rfc.section.3.1.1.2.p.1"><p>HTTP uses <dfn>charset</dfn> names to indicate or negotiate the character encoding scheme of a textual representation <a href="#RFC6365" id="rfc.xref.RFC6365.2"><cite title="Terminology Used in Internationalization in the IETF">[RFC6365]</cite></a>. A charset is identified by a case-insensitive token.<a class="self" href="#rfc.section.3.1.1.2.p.1">&para;</a></p></div><div id="rfc.figure.u.4"><pre class="inline"><span id="rfc.iref.g.5"></span>  <a href="#charset" class="smpl">charset</a> = <a href="#imported.abnf" class="smpl">token</a>
    520536</pre></div><div id="rfc.section.3.1.1.2.p.2"><p>Charset names ought to be registered in the IANA "Character Sets" registry (&lt;<a href="http://www.iana.org/assignments/character-sets">http://www.iana.org/assignments/character-sets</a>&gt;) according to the procedures defined in <a href="#RFC2978" id="rfc.xref.RFC2978.1"><cite title="IANA Charset Registration Procedures">[RFC2978]</cite></a>.<a class="self" href="#rfc.section.3.1.1.2.p.2">&para;</a></p></div></div><div id="canonicalization.and.text.defaults"><h4 id="rfc.section.3.1.1.3"><a href="#rfc.section.3.1.1.3">3.1.1.3</a>&nbsp;<a href="#canonicalization.and.text.defaults">Canonicalization and Text Defaults</a></h4><div id="rfc.section.3.1.1.3.p.1"><p>Internet media types are registered with a canonical form in order to be interoperable among systems with varying native encoding formats. Representations selected or transferred via HTTP ought to be in canonical form, for many of the same reasons described by the Multipurpose Internet Mail Extensions (MIME) <a href="#RFC2045" id="rfc.xref.RFC2045.1"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a>. However, the performance characteristics of email deployments (i.e., store and forward messages to peers) are significantly different from those common to HTTP and the Web (server-based information services). Furthermore, MIME's constraints for the sake of compatibility with older mail transfer protocols do not apply to HTTP (see <a href="#differences.between.http.and.mime" title="Differences between HTTP and MIME">Appendix&nbsp;A</a>).<a class="self" href="#rfc.section.3.1.1.3.p.1">&para;</a></p></div><div id="rfc.section.3.1.1.3.p.2"><p>MIME's canonical form requires that media subtypes of the "text" type use CRLF as the text line break. HTTP allows the transfer of text media with plain CR or LF alone representing a line break, when such line breaks are consistent for an entire representation. An HTTP sender <em class="bcp14">MAY</em> generate, and a recipient <em class="bcp14">MUST</em> be able to parse, line breaks in text media that consist of CRLF, bare CR, or bare LF. In addition, text media in HTTP is not limited to charsets that use octets 13 and 10 for CR and LF, respectively. This flexibility regarding line breaks applies only to text within a representation that has been assigned a "text" media type; it does not apply to "multipart" types or HTTP elements outside the payload body (e.g., header fields).<a class="self" href="#rfc.section.3.1.1.3.p.2">&para;</a></p></div><div id="rfc.section.3.1.1.3.p.3"><p>If a representation is encoded with a content-coding, the underlying data ought to be in a form defined above prior to being encoded.<a class="self" href="#rfc.section.3.1.1.3.p.3">&para;</a></p></div></div><div id="multipart.types"><h4 id="rfc.section.3.1.1.4"><a href="#rfc.section.3.1.1.4">3.1.1.4</a>&nbsp;<a href="#multipart.types">Multipart Types</a></h4><div id="rfc.section.3.1.1.4.p.1"><p>MIME provides for a number of "multipart" types &#8212; encapsulations of one or more representations within a single message body. All multipart types share a common syntax, as defined in <a href="https://tools.ietf.org/html/rfc2046#section-5.1.1">Section 5.1.1</a> of <a href="#RFC2046" id="rfc.xref.RFC2046.2"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types">[RFC2046]</cite></a>, and include a boundary parameter as part of the media type value. The message body is itself a protocol element; a sender <em class="bcp14">MUST</em> generate only CRLF to represent line breaks between body parts.<a class="self" href="#rfc.section.3.1.1.4.p.1">&para;</a></p></div><div id="rfc.section.3.1.1.4.p.2"><p>HTTP message framing does not use the multipart boundary as an indicator of message body length, though it might be used by implementations that generate or process the payload. For example, the "multipart/form-data" type is often used for carrying form data in a request, as described in <a href="#RFC2388" id="rfc.xref.RFC2388.1"><cite title="Returning Values from Forms: multipart/form-data">[RFC2388]</cite></a>, and the "multipart/byteranges" type is defined by this specification for use in some <a href="rfc7233.html#status.206" class="smpl">206 (Partial Content)</a> responses <a href="#RFC7233" id="rfc.xref.RFC7233.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a>.<a class="self" href="#rfc.section.3.1.1.4.p.2">&para;</a></p></div></div><div id="header.content-type"><h4 id="rfc.section.3.1.1.5"><a href="#rfc.section.3.1.1.5">3.1.1.5</a>&nbsp;<a href="#header.content-type">Content-Type</a></h4><div id="rfc.section.3.1.1.5.p.1"><p>The "Content-Type" header field indicates the media type of the associated representation: either the representation enclosed in the message payload or the <a href="#representations" class="smpl">selected representation</a>, as determined by the message semantics. The indicated media type defines both the data format and how that data is intended to be processed by a recipient, within the scope of the received message semantics, after any content codings indicated by <a href="#header.content-encoding" class="smpl">Content-Encoding</a> are decoded.<a class="self" href="#rfc.section.3.1.1.5.p.1">&para;</a></p></div><div id="rfc.figure.u.5"><pre class="inline"><span id="rfc.iref.g.6"></span>  <a href="#header.content-type" class="smpl">Content-Type</a> = <a href="#media.type" class="smpl">media-type</a>
    521537</pre></div><div id="rfc.section.3.1.1.5.p.2"><p>Media types are defined in <a href="#media.type" title="Media Type">Section&nbsp;3.1.1.1</a>. An example of the field is<a class="self" href="#rfc.section.3.1.1.5.p.2">&para;</a></p></div><div id="rfc.figure.u.6"><pre class="text">  Content-Type: text/html; charset=ISO-8859-4
     
    545561Expect: 100-continue
    546562
    547 </pre></div><div id="rfc.section.5.1.1.p.6"><p>allows the origin server to immediately respond with an error message, such as <a href="rfc7235.html#status.401" class="smpl">401 (Unauthorized)</a> or <a href="#status.405" class="smpl">405 (Method Not Allowed)</a>, before the client starts filling the pipes with an unnecessary data transfer.<a class="self" href="#rfc.section.5.1.1.p.6">&para;</a></p></div><div id="rfc.section.5.1.1.p.7"><p>Requirements for clients: <a class="self" href="#rfc.section.5.1.1.p.7">&para;</a></p><ul><li>A client <em class="bcp14">MUST NOT</em> generate a 100-continue expectation in a request that does not include a message body.</li><li>A client that will wait for a <a href="#status.100" class="smpl">100 (Continue)</a> response before sending the request message body <em class="bcp14">MUST</em> send an <a href="#header.expect" class="smpl">Expect</a> header field containing a 100-continue expectation.</li><li>A client that sends a 100-continue expectation is not required to wait for any specific length of time; such a client <em class="bcp14">MAY</em> proceed to send the message body even if it has not yet received a response. Furthermore, since <a href="#status.100" class="smpl">100 (Continue)</a> responses cannot be sent through an HTTP/1.0 intermediary, such a client <em class="bcp14">SHOULD NOT</em> wait for an indefinite period before sending the message body.</li><li>A client that receives a <a href="#status.417" class="smpl">417 (Expectation Failed)</a> status code in response to a request containing a 100-continue expectation <em class="bcp14">SHOULD</em> repeat that request without a 100-continue expectation, since the 417 response merely indicates that the response chain does not support expectations (e.g., it passes through an HTTP/1.0 server).</li></ul></div><div id="rfc.section.5.1.1.p.8"><p>Requirements for servers: <a class="self" href="#rfc.section.5.1.1.p.8">&para;</a></p><ul><li>A server that receives a 100-continue expectation in an HTTP/1.0 request <em class="bcp14">MUST</em> ignore that expectation.</li><li>A server <em class="bcp14">MAY</em> omit sending a <a href="#status.100" class="smpl">100 (Continue)</a> response if it has already received some or all of the message body for the corresponding request, or if the framing indicates that there is no message body.</li><li>A server that sends a <a href="#status.100" class="smpl">100 (Continue)</a> response <em class="bcp14">MUST</em> ultimately send a final status code, once the message body is received and processed, unless the connection is closed prematurely.</li><li>A server that responds with a final status code before reading the entire message body <em class="bcp14">SHOULD</em> indicate in that response whether it intends to close the connection or continue reading and discarding the request message (see <a href="rfc7230.html#persistent.tear-down" title="Tear-down">Section 6.6</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.22"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>).</li></ul></div><div id="rfc.section.5.1.1.p.9"><p>An origin server <em class="bcp14">MUST</em>, upon receiving an HTTP/1.1 (or later) request-line and a complete header section that contains a 100-continue expectation and indicates a request message body will follow, either send an immediate response with a final status code, if that status can be determined by examining just the request-line and header fields, or send an immediate <a href="#status.100" class="smpl">100 (Continue)</a> response to encourage the client to send the request's message body. The origin server <em class="bcp14">MUST NOT</em> wait for the message body before sending the <a href="#status.100" class="smpl">100 (Continue)</a> response.<a class="self" href="#rfc.section.5.1.1.p.9">&para;</a></p></div><div id="rfc.section.5.1.1.p.10"><p>A proxy <em class="bcp14">MUST</em>, upon receiving an HTTP/1.1 (or later) request-line and a complete header section that contains a 100-continue expectation and indicates a request message body will follow, either send an immediate response with a final status code, if that status can be determined by examining just the request-line and header fields, or begin forwarding the request toward the origin server by sending a corresponding request-line and header section to the next inbound server. If the proxy believes (from configuration or past interaction) that the next inbound server only supports HTTP/1.0, the proxy <em class="bcp14">MAY</em> generate an immediate <a href="#status.100" class="smpl">100 (Continue)</a> response to encourage the client to begin sending the message body.<a class="self" href="#rfc.section.5.1.1.p.10">&para;</a></p></div><div class="note" id="rfc.section.5.1.1.p.11"><p><b>Note:</b> The Expect header field was added after the original publication of HTTP/1.1 <a href="#RFC2068" id="rfc.xref.RFC2068.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a> as both the means to request an interim <a href="#status.100" class="smpl">100 (Continue)</a> response and the general mechanism for indicating must-understand extensions. However, the extension mechanism has not been used by clients and the must-understand requirements have not been implemented by many servers, rendering the extension mechanism useless. This specification has removed the extension mechanism in order to simplify the definition and processing of 100-continue.<a class="self" href="#rfc.section.5.1.1.p.11">&para;</a></p></div></div><div id="header.max-forwards"><h3 id="rfc.section.5.1.2"><a href="#rfc.section.5.1.2">5.1.2</a>&nbsp;<a href="#header.max-forwards">Max-Forwards</a></h3><div id="rfc.section.5.1.2.p.1"><p>The "Max-Forwards" header field provides a mechanism with the TRACE (<a href="#TRACE" id="rfc.xref.TRACE.2" title="TRACE">Section&nbsp;4.3.8</a>) and OPTIONS (<a href="#OPTIONS" id="rfc.xref.OPTIONS.2" title="OPTIONS">Section&nbsp;4.3.7</a>) request methods to limit the number of times that the request is forwarded by proxies. This can be useful when the client is attempting to trace a request that appears to be failing or looping mid-chain.<a class="self" href="#rfc.section.5.1.2.p.1">&para;</a></p></div><div id="rfc.figure.u.22"><pre class="inline"><span id="rfc.iref.g.15"></span>  <a href="#header.max-forwards" class="smpl">Max-Forwards</a> = 1*<a href="#imported.abnf" class="smpl">DIGIT</a>
     563</pre></div><div id="rfc.section.5.1.1.p.6"><p>allows the origin server to immediately respond with an error message, such as <a href="rfc7235.html#status.401" class="smpl">401 (Unauthorized)</a> or <a href="#status.405" class="smpl">405 (Method Not Allowed)</a>, before the client starts filling the pipes with an unnecessary data transfer.<a class="self" href="#rfc.section.5.1.1.p.6">&para;</a></p></div><div id="rfc.section.5.1.1.p.7"><p>Requirements for clients: <a class="self" href="#rfc.section.5.1.1.p.7">&para;</a></p><ul><li>A client <em class="bcp14">MUST NOT</em> generate a 100-continue expectation in a request that does not include a message body.</li><li>A client that will wait for a <a href="#status.100" class="smpl">100 (Continue)</a> response before sending the request message body <em class="bcp14">MUST</em> send an <a href="#header.expect" class="smpl">Expect</a> header field containing a 100-continue expectation.</li><li>A client that sends a 100-continue expectation is not required to wait for any specific length of time; such a client <em class="bcp14">MAY</em> proceed to send the message body even if it has not yet received a response. Furthermore, since <a href="#status.100" class="smpl">100 (Continue)</a> responses cannot be sent through an HTTP/1.0 intermediary, such a client <em class="bcp14">SHOULD NOT</em> wait for an indefinite period before sending the message body.</li><li>A client that receives a <a href="#status.417" class="smpl">417 (Expectation Failed)</a> status code in response to a request containing a 100-continue expectation <em class="bcp14">SHOULD</em> repeat that request without a 100-continue expectation, since the 417 response merely indicates that the response chain does not support expectations (e.g., it passes through an HTTP/1.0 server).</li></ul></div><div id="rfc.section.5.1.1.p.8"><p>Requirements for servers: <a class="self" href="#rfc.section.5.1.1.p.8">&para;</a></p><ul><li>A server that receives a 100-continue expectation in an HTTP/1.0 request <em class="bcp14">MUST</em> ignore that expectation.</li><li>A server <em class="bcp14">MAY</em> omit sending a <a href="#status.100" class="smpl">100 (Continue)</a> response if it has already received some or all of the message body for the corresponding request, or if the framing indicates that there is no message body.</li><li>A server that sends a <a href="#status.100" class="smpl">100 (Continue)</a> response <em class="bcp14">MUST</em> ultimately send a final status code, once the message body is received and processed, unless the connection is closed prematurely.</li><li>A server that responds with a final status code before reading the entire message body <em class="bcp14">SHOULD</em> indicate in that response whether it intends to close the connection or continue reading and discarding the request message (see <a href="rfc7230.html#persistent.tear-down" title="Tear-down">Section 6.6</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.22"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>).</li></ul></div><div id="rfc.section.5.1.1.p.9"><p>An origin server <em class="bcp14">MUST</em>, upon receiving an HTTP/1.1 (or later) request-line and a complete header section that contains a 100-continue expectation and indicates a request message body will follow, either send an immediate response with a final status code, if that status can be determined by examining just the request-line and header fields, or send an immediate <a href="#status.100" class="smpl">100 (Continue)</a> response to encourage the client to send the request's message body. The origin server <em class="bcp14">MUST NOT</em> wait for the message body before sending the <a href="#status.100" class="smpl">100 (Continue)</a> response.<a class="self" href="#rfc.section.5.1.1.p.9">&para;</a></p></div><div id="rfc.section.5.1.1.p.10"><p>A proxy <em class="bcp14">MUST</em>, upon receiving an HTTP/1.1 (or later) request-line and a complete header section that contains a 100-continue expectation and indicates a request message body will follow, either send an immediate response with a final status code, if that status can be determined by examining just the request-line and header fields, or begin forwarding the request toward the origin server by sending a corresponding request-line and header section to the next inbound server. If the proxy believes (from configuration or past interaction) that the next inbound server only supports HTTP/1.0, the proxy <em class="bcp14">MAY</em> generate an immediate <a href="#status.100" class="smpl">100 (Continue)</a> response to encourage the client to begin sending the message body.<a class="self" href="#rfc.section.5.1.1.p.10">&para;</a></p></div><div class="note"><div id="rfc.section.5.1.1.p.11"><p><b>Note:</b> The Expect header field was added after the original publication of HTTP/1.1 <a href="#RFC2068" id="rfc.xref.RFC2068.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a> as both the means to request an interim <a href="#status.100" class="smpl">100 (Continue)</a> response and the general mechanism for indicating must-understand extensions. However, the extension mechanism has not been used by clients and the must-understand requirements have not been implemented by many servers, rendering the extension mechanism useless. This specification has removed the extension mechanism in order to simplify the definition and processing of 100-continue.<a class="self" href="#rfc.section.5.1.1.p.11">&para;</a></p></div></div></div><div id="header.max-forwards"><h3 id="rfc.section.5.1.2"><a href="#rfc.section.5.1.2">5.1.2</a>&nbsp;<a href="#header.max-forwards">Max-Forwards</a></h3><div id="rfc.section.5.1.2.p.1"><p>The "Max-Forwards" header field provides a mechanism with the TRACE (<a href="#TRACE" id="rfc.xref.TRACE.2" title="TRACE">Section&nbsp;4.3.8</a>) and OPTIONS (<a href="#OPTIONS" id="rfc.xref.OPTIONS.2" title="OPTIONS">Section&nbsp;4.3.7</a>) request methods to limit the number of times that the request is forwarded by proxies. This can be useful when the client is attempting to trace a request that appears to be failing or looping mid-chain.<a class="self" href="#rfc.section.5.1.2.p.1">&para;</a></p></div><div id="rfc.figure.u.22"><pre class="inline"><span id="rfc.iref.g.15"></span>  <a href="#header.max-forwards" class="smpl">Max-Forwards</a> = 1*<a href="#imported.abnf" class="smpl">DIGIT</a>
    548564</pre></div><div id="rfc.section.5.1.2.p.2"><p>The Max-Forwards value is a decimal integer indicating the remaining number of times this request message can be forwarded.<a class="self" href="#rfc.section.5.1.2.p.2">&para;</a></p></div><div id="rfc.section.5.1.2.p.3"><p>Each intermediary that receives a TRACE or OPTIONS request containing a Max-Forwards header field <em class="bcp14">MUST</em> check and update its value prior to forwarding the request. If the received value is zero (0), the intermediary <em class="bcp14">MUST NOT</em> forward the request; instead, the intermediary <em class="bcp14">MUST</em> respond as the final recipient. If the received Max-Forwards value is greater than zero, the intermediary <em class="bcp14">MUST</em> generate an updated Max-Forwards field in the forwarded message with a field-value that is the lesser of a) the received value decremented by one (1) or b) the recipient's maximum supported value for Max-Forwards.<a class="self" href="#rfc.section.5.1.2.p.3">&para;</a></p></div><div id="rfc.section.5.1.2.p.4"><p>A recipient <em class="bcp14">MAY</em> ignore a Max-Forwards header field received with any other request methods.<a class="self" href="#rfc.section.5.1.2.p.4">&para;</a></p></div></div></div><div id="request.conditionals"><h2 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2</a>&nbsp;<a href="#request.conditionals">Conditionals</a></h2><div id="rfc.section.5.2.p.1"><p>The HTTP conditional request header fields <a href="#RFC7232" id="rfc.xref.RFC7232.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a> allow a client to place a precondition on the state of the target resource, so that the action corresponding to the method semantics will not be applied if the precondition evaluates to false. Each precondition defined by this specification consists of a comparison between a set of validators obtained from prior representations of the target resource to the current state of validators for the <a href="#representations" class="smpl">selected representation</a> (<a href="#response.validator" title="Validator Header Fields">Section&nbsp;7.2</a>). Hence, these preconditions evaluate whether the state of the target resource has changed since a given state known by the client. The effect of such an evaluation depends on the method semantics and choice of conditional, as defined in <a href="rfc7232.html#evaluation" title="Evaluation">Section 5</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.4"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a>.<a class="self" href="#rfc.section.5.2.p.1">&para;</a></p></div><div id="rfc.table.u.4"><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Header Field Name</th><th>Defined in...</th></tr></thead><tbody><tr><td class="left">If-Match</td><td class="left"><a href="rfc7232.html#header.if-match" title="If-Match">Section 3.1</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.5"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a></td></tr><tr><td class="left">If-None-Match</td><td class="left"><a href="rfc7232.html#header.if-none-match" title="If-None-Match">Section 3.2</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.6"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a></td></tr><tr><td class="left">If-Modified-Since</td><td class="left"><a href="rfc7232.html#header.if-modified-since" title="If-Modified-Since">Section 3.3</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.7"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a></td></tr><tr><td class="left">If-Unmodified-Since</td><td class="left"><a href="rfc7232.html#header.if-unmodified-since" title="If-Unmodified-Since">Section 3.4</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.8"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a></td></tr><tr><td class="left">If-Range</td><td class="left"><a href="rfc7233.html#header.if-range" title="If-Range">Section 3.2</a> of <a href="#RFC7233" id="rfc.xref.RFC7233.6"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a></td></tr></tbody></table></div></div><div id="request.conneg"><h2 id="rfc.section.5.3"><a href="#rfc.section.5.3">5.3</a>&nbsp;<a href="#request.conneg">Content Negotiation</a></h2><div id="rfc.section.5.3.p.1"><p>The following request header fields are sent by a user agent to engage in <a href="#proactive.negotiation" class="smpl">proactive negotiation</a> of the response content, as defined in <a href="#proactive.negotiation" title="Proactive Negotiation">Section&nbsp;3.4.1</a>. The preferences sent in these fields apply to any content in the response, including representations of the target resource, representations of error or processing status, and potentially even the miscellaneous text strings that might appear within the protocol.<a class="self" href="#rfc.section.5.3.p.1">&para;</a></p></div><div id="rfc.table.u.5"><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Header Field Name</th><th>Defined in...</th></tr></thead><tbody><tr><td class="left">Accept</td><td class="left"><a href="#header.accept" id="rfc.xref.header.accept.2" title="Accept">Section&nbsp;5.3.2</a></td></tr><tr><td class="left">Accept-Charset</td><td class="left"><a href="#header.accept-charset" id="rfc.xref.header.accept-charset.1" title="Accept-Charset">Section&nbsp;5.3.3</a></td></tr><tr><td class="left">Accept-Encoding</td><td class="left"><a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.2" title="Accept-Encoding">Section&nbsp;5.3.4</a></td></tr><tr><td class="left">Accept-Language</td><td class="left"><a href="#header.accept-language" id="rfc.xref.header.accept-language.2" title="Accept-Language">Section&nbsp;5.3.5</a></td></tr></tbody></table></div><div id="quality.values"><h3 id="rfc.section.5.3.1"><a href="#rfc.section.5.3.1">5.3.1</a>&nbsp;<a href="#quality.values">Quality Values</a></h3><div id="rfc.section.5.3.1.p.1"><p>Many of the request header fields for <a href="#proactive.negotiation" class="smpl">proactive negotiation</a> use a common parameter, named "q" (case-insensitive), to assign a relative "weight" to the preference for that associated kind of content. This weight is referred to as a "quality value" (or "qvalue") because the same parameter name is often used within server configurations to assign a weight to the relative quality of the various representations that can be selected for a resource.<a class="self" href="#rfc.section.5.3.1.p.1">&para;</a></p></div><div id="rfc.section.5.3.1.p.2"><p>The weight is normalized to a real number in the range 0 through 1, where 0.001 is the least preferred and 1 is the most preferred; a value of 0 means "not acceptable". If no "q" parameter is present, the default weight is 1.<a class="self" href="#rfc.section.5.3.1.p.2">&para;</a></p></div><div id="rfc.figure.u.23"><pre class="inline"><span id="rfc.iref.g.16"></span><span id="rfc.iref.g.17"></span>  <a href="#quality.values" class="smpl">weight</a> = <a href="#imported.abnf" class="smpl">OWS</a> ";" <a href="#imported.abnf" class="smpl">OWS</a> "q=" <a href="#quality.values" class="smpl">qvalue</a>
    549565  <a href="#quality.values" class="smpl">qvalue</a> = ( "0" [ "." 0*3<a href="#imported.abnf" class="smpl">DIGIT</a> ] )
     
    557573  <a href="#header.accept" class="smpl">accept-params</a>  = <a href="#quality.values" class="smpl">weight</a> *( <a href="#header.accept" class="smpl">accept-ext</a> )
    558574  <a href="#header.accept" class="smpl">accept-ext</a> = <a href="#imported.abnf" class="smpl">OWS</a> ";" <a href="#imported.abnf" class="smpl">OWS</a> <a href="#imported.abnf" class="smpl">token</a> [ "=" ( <a href="#imported.abnf" class="smpl">token</a> / <a href="#imported.abnf" class="smpl">quoted-string</a> ) ]
    559 </pre></div><div id="rfc.section.5.3.2.p.2"><p>The asterisk "*" character is used to group media types into ranges, with "*/*" indicating all media types and "type/*" indicating all subtypes of that type. The media-range can include media type parameters that are applicable to that range.<a class="self" href="#rfc.section.5.3.2.p.2">&para;</a></p></div><div id="rfc.section.5.3.2.p.3"><p>Each media-range might be followed by zero or more applicable media type parameters (e.g., <a href="#charset" class="smpl">charset</a>), an optional "q" parameter for indicating a relative weight (<a href="#quality.values" title="Quality Values">Section&nbsp;5.3.1</a>), and then zero or more extension parameters. The "q" parameter is necessary if any extensions (accept-ext) are present, since it acts as a separator between the two parameter sets.<a class="self" href="#rfc.section.5.3.2.p.3">&para;</a></p></div><div class="note" id="rfc.section.5.3.2.p.4"><p><b>Note:</b> Use of the "q" parameter name to separate media type parameters from Accept extension parameters is due to historical practice. Although this prevents any media type parameter named "q" from being used with a media range, such an event is believed to be unlikely given the lack of any "q" parameters in the IANA media type registry and the rare usage of any media type parameters in Accept. Future media types are discouraged from registering any parameter named "q".<a class="self" href="#rfc.section.5.3.2.p.4">&para;</a></p></div><div id="rfc.section.5.3.2.p.5"><p>The example<a class="self" href="#rfc.section.5.3.2.p.5">&para;</a></p></div><div id="rfc.figure.u.25"><pre class="text">  Accept: audio/*; q=0.2, audio/basic
     575</pre></div><div id="rfc.section.5.3.2.p.2"><p>The asterisk "*" character is used to group media types into ranges, with "*/*" indicating all media types and "type/*" indicating all subtypes of that type. The media-range can include media type parameters that are applicable to that range.<a class="self" href="#rfc.section.5.3.2.p.2">&para;</a></p></div><div id="rfc.section.5.3.2.p.3"><p>Each media-range might be followed by zero or more applicable media type parameters (e.g., <a href="#charset" class="smpl">charset</a>), an optional "q" parameter for indicating a relative weight (<a href="#quality.values" title="Quality Values">Section&nbsp;5.3.1</a>), and then zero or more extension parameters. The "q" parameter is necessary if any extensions (accept-ext) are present, since it acts as a separator between the two parameter sets.<a class="self" href="#rfc.section.5.3.2.p.3">&para;</a></p></div><div class="note"><div id="rfc.section.5.3.2.p.4"><p><b>Note:</b> Use of the "q" parameter name to separate media type parameters from Accept extension parameters is due to historical practice. Although this prevents any media type parameter named "q" from being used with a media range, such an event is believed to be unlikely given the lack of any "q" parameters in the IANA media type registry and the rare usage of any media type parameters in Accept. Future media types are discouraged from registering any parameter named "q".<a class="self" href="#rfc.section.5.3.2.p.4">&para;</a></p></div></div><div id="rfc.section.5.3.2.p.5"><p>The example<a class="self" href="#rfc.section.5.3.2.p.5">&para;</a></p></div><div id="rfc.figure.u.25"><pre class="text">  Accept: audio/*; q=0.2, audio/basic
    560576</pre></div><div id="rfc.section.5.3.2.p.6"><p>is interpreted as "I prefer audio/basic, but send me any audio type if it is the best available after an 80% markdown in quality".<a class="self" href="#rfc.section.5.3.2.p.6">&para;</a></p></div><div id="rfc.section.5.3.2.p.7"><p>A request without any Accept header field implies that the user agent will accept any media type in response. If the header field is present in a request and none of the available representations for the response have a media type that is listed as acceptable, the origin server can either honor the header field by sending a <a href="#status.406" class="smpl">406 (Not Acceptable)</a> response or disregard the header field by treating the response as if it is not subject to content negotiation.<a class="self" href="#rfc.section.5.3.2.p.7">&para;</a></p></div><div id="rfc.section.5.3.2.p.8"><p>A more elaborate example is<a class="self" href="#rfc.section.5.3.2.p.8">&para;</a></p></div><div id="rfc.figure.u.26"><pre class="text">  Accept: text/plain; q=0.5, text/html,
    561577          text/x-dvi; q=0.8, text/x-c
     
    572588  Accept-Encoding: compress;q=0.5, gzip;q=1.0
    573589  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
    574 </pre></div><div id="rfc.section.5.3.4.p.4"><p>A request without an Accept-Encoding header field implies that the user agent has no preferences regarding content-codings. Although this allows the server to use any content-coding in a response, it does not imply that the user agent will be able to correctly process all encodings.<a class="self" href="#rfc.section.5.3.4.p.4">&para;</a></p></div><div id="rfc.section.5.3.4.p.5"><p>A server tests whether a content-coding for a given representation is acceptable using these rules: <a class="self" href="#rfc.section.5.3.4.p.5">&para;</a></p><ol><li>If no Accept-Encoding field is in the request, any content-coding is considered acceptable by the user agent.</li><li>If the representation has no content-coding, then it is acceptable by default unless specifically excluded by the Accept-Encoding field stating either "identity;q=0" or "*;q=0" without a more specific entry for "identity".</li><li>If the representation's content-coding is one of the content-codings listed in the Accept-Encoding field, then it is acceptable unless it is accompanied by a qvalue of 0. (As defined in <a href="#quality.values" title="Quality Values">Section&nbsp;5.3.1</a>, a qvalue of 0 means "not acceptable".)</li><li>If multiple content-codings are acceptable, then the acceptable content-coding with the highest non-zero qvalue is preferred.</li></ol></div><div id="rfc.section.5.3.4.p.6"><p>An Accept-Encoding header field with a combined field-value that is empty implies that the user agent does not want any content-coding in response. If an Accept-Encoding header field is present in a request and none of the available representations for the response have a content-coding that is listed as acceptable, the origin server <em class="bcp14">SHOULD</em> send a response without any content-coding.<a class="self" href="#rfc.section.5.3.4.p.6">&para;</a></p></div><div class="note" id="rfc.section.5.3.4.p.7"><p><b>Note:</b> Most HTTP/1.0 applications do not recognize or obey qvalues associated with content-codings. This means that qvalues might not work and are not permitted with x-gzip or x-compress.<a class="self" href="#rfc.section.5.3.4.p.7">&para;</a></p></div></div><div id="header.accept-language"><h3 id="rfc.section.5.3.5"><a href="#rfc.section.5.3.5">5.3.5</a>&nbsp;<a href="#header.accept-language">Accept-Language</a></h3><div id="rfc.section.5.3.5.p.1"><p>The "Accept-Language" header field can be used by user agents to indicate the set of natural languages that are preferred in the response. Language tags are defined in <a href="#language.tags" title="Language Tags">Section&nbsp;3.1.3.1</a>.<a class="self" href="#rfc.section.5.3.5.p.1">&para;</a></p></div><div id="rfc.figure.u.33"><pre class="inline"><span id="rfc.iref.g.25"></span><span id="rfc.iref.g.26"></span>  <a href="#header.accept-language" class="smpl">Accept-Language</a> = 1#( <a href="#header.accept-language" class="smpl">language-range</a> [ <a href="#quality.values" class="smpl">weight</a> ] )
     590</pre></div><div id="rfc.section.5.3.4.p.4"><p>A request without an Accept-Encoding header field implies that the user agent has no preferences regarding content-codings. Although this allows the server to use any content-coding in a response, it does not imply that the user agent will be able to correctly process all encodings.<a class="self" href="#rfc.section.5.3.4.p.4">&para;</a></p></div><div id="rfc.section.5.3.4.p.5"><p>A server tests whether a content-coding for a given representation is acceptable using these rules: <a class="self" href="#rfc.section.5.3.4.p.5">&para;</a></p><ol><li>If no Accept-Encoding field is in the request, any content-coding is considered acceptable by the user agent.</li><li>If the representation has no content-coding, then it is acceptable by default unless specifically excluded by the Accept-Encoding field stating either "identity;q=0" or "*;q=0" without a more specific entry for "identity".</li><li>If the representation's content-coding is one of the content-codings listed in the Accept-Encoding field, then it is acceptable unless it is accompanied by a qvalue of 0. (As defined in <a href="#quality.values" title="Quality Values">Section&nbsp;5.3.1</a>, a qvalue of 0 means "not acceptable".)</li><li>If multiple content-codings are acceptable, then the acceptable content-coding with the highest non-zero qvalue is preferred.</li></ol></div><div id="rfc.section.5.3.4.p.6"><p>An Accept-Encoding header field with a combined field-value that is empty implies that the user agent does not want any content-coding in response. If an Accept-Encoding header field is present in a request and none of the available representations for the response have a content-coding that is listed as acceptable, the origin server <em class="bcp14">SHOULD</em> send a response without any content-coding.<a class="self" href="#rfc.section.5.3.4.p.6">&para;</a></p></div><div class="note"><div id="rfc.section.5.3.4.p.7"><p><b>Note:</b> Most HTTP/1.0 applications do not recognize or obey qvalues associated with content-codings. This means that qvalues might not work and are not permitted with x-gzip or x-compress.<a class="self" href="#rfc.section.5.3.4.p.7">&para;</a></p></div></div></div><div id="header.accept-language"><h3 id="rfc.section.5.3.5"><a href="#rfc.section.5.3.5">5.3.5</a>&nbsp;<a href="#header.accept-language">Accept-Language</a></h3><div id="rfc.section.5.3.5.p.1"><p>The "Accept-Language" header field can be used by user agents to indicate the set of natural languages that are preferred in the response. Language tags are defined in <a href="#language.tags" title="Language Tags">Section&nbsp;3.1.3.1</a>.<a class="self" href="#rfc.section.5.3.5.p.1">&para;</a></p></div><div id="rfc.figure.u.33"><pre class="inline"><span id="rfc.iref.g.25"></span><span id="rfc.iref.g.26"></span>  <a href="#header.accept-language" class="smpl">Accept-Language</a> = 1#( <a href="#header.accept-language" class="smpl">language-range</a> [ <a href="#quality.values" class="smpl">weight</a> ] )
    575591  <a href="#header.accept-language" class="smpl">language-range</a>  =
    576592            &lt;language-range, see <a href="#RFC4647" id="rfc.xref.RFC4647.1"><cite title="Matching of Language Tags">[RFC4647]</cite></a>, <a href="https://tools.ietf.org/html/rfc4647#section-2.1">Section 2.1</a>&gt;
    577593</pre></div><div id="rfc.section.5.3.5.p.2"><p>Each language-range can be given an associated quality value representing an estimate of the user's preference for the languages specified by that range, as defined in <a href="#quality.values" title="Quality Values">Section&nbsp;5.3.1</a>. For example,<a class="self" href="#rfc.section.5.3.5.p.2">&para;</a></p></div><div id="rfc.figure.u.34"><pre class="text">  Accept-Language: da, en-gb;q=0.8, en;q=0.7
    578 </pre></div><div id="rfc.section.5.3.5.p.3"><p>would mean: "I prefer Danish, but will accept British English and other types of English".<a class="self" href="#rfc.section.5.3.5.p.3">&para;</a></p></div><div id="rfc.section.5.3.5.p.4"><p>A request without any Accept-Language header field implies that the user agent will accept any language in response. If the header field is present in a request and none of the available representations for the response have a matching language tag, the origin server can either disregard the header field by treating the response as if it is not subject to content negotiation or honor the header field by sending a <a href="#status.406" class="smpl">406 (Not Acceptable)</a> response. However, the latter is not encouraged, as doing so can prevent users from accessing content that they might be able to use (with translation software, for example).<a class="self" href="#rfc.section.5.3.5.p.4">&para;</a></p></div><div id="rfc.section.5.3.5.p.5"><p>Note that some recipients treat the order in which language tags are listed as an indication of descending priority, particularly for tags that are assigned equal quality values (no value is the same as q=1). However, this behavior cannot be relied upon. For consistency and to maximize interoperability, many user agents assign each language tag a unique quality value while also listing them in order of decreasing quality. Additional discussion of language priority lists can be found in <a href="https://tools.ietf.org/html/rfc4647#section-2.3">Section 2.3</a> of <a href="#RFC4647" id="rfc.xref.RFC4647.2"><cite title="Matching of Language Tags">[RFC4647]</cite></a>.<a class="self" href="#rfc.section.5.3.5.p.5">&para;</a></p></div><div id="rfc.section.5.3.5.p.6"><p>For matching, <a href="https://tools.ietf.org/html/rfc4647#section-3">Section 3</a> of <a href="#RFC4647" id="rfc.xref.RFC4647.3"><cite title="Matching of Language Tags">[RFC4647]</cite></a> defines several matching schemes. Implementations can offer the most appropriate matching scheme for their requirements. The "Basic Filtering" scheme (<a href="#RFC4647" id="rfc.xref.RFC4647.4"><cite title="Matching of Language Tags">[RFC4647]</cite></a>, <a href="https://tools.ietf.org/html/rfc4647#section-3.3.1">Section 3.3.1</a>) is identical to the matching scheme that was previously defined for HTTP in <a href="https://tools.ietf.org/html/rfc2616#section-14.4">Section 14.4</a> of <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>.<a class="self" href="#rfc.section.5.3.5.p.6">&para;</a></p></div><div id="rfc.section.5.3.5.p.7"><p>It might be contrary to the privacy expectations of the user to send an Accept-Language header field with the complete linguistic preferences of the user in every request (<a href="#fingerprinting" title="Browser Fingerprinting">Section&nbsp;9.7</a>).<a class="self" href="#rfc.section.5.3.5.p.7">&para;</a></p></div><div id="rfc.section.5.3.5.p.8"><p>Since intelligibility is highly dependent on the individual user, user agents need to allow user control over the linguistic preference (either through configuration of the user agent itself or by defaulting to a user controllable system setting). A user agent that does not provide such control to the user <em class="bcp14">MUST NOT</em> send an Accept-Language header field.<a class="self" href="#rfc.section.5.3.5.p.8">&para;</a></p></div><div class="note" id="rfc.section.5.3.5.p.9"><p><b>Note:</b> User agents ought to provide guidance to users when setting a preference, since users are rarely familiar with the details of language matching as described above. For example, users might assume that on selecting "en-gb", they will be served any kind of English document if British English is not available. A user agent might suggest, in such a case, to add "en" to the list for better matching behavior.<a class="self" href="#rfc.section.5.3.5.p.9">&para;</a></p></div></div></div><div id="request.auth"><h2 id="rfc.section.5.4"><a href="#rfc.section.5.4">5.4</a>&nbsp;<a href="#request.auth">Authentication Credentials</a></h2><div id="rfc.section.5.4.p.1"><p>Two header fields are used for carrying authentication credentials, as defined in <a href="#RFC7235" id="rfc.xref.RFC7235.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a>. Note that various custom mechanisms for user authentication use the Cookie header field for this purpose, as defined in <a href="#RFC6265" id="rfc.xref.RFC6265.2"><cite title="HTTP State Management Mechanism">[RFC6265]</cite></a>.<a class="self" href="#rfc.section.5.4.p.1">&para;</a></p></div><div id="rfc.table.u.7"><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Header Field Name</th><th>Defined in...</th></tr></thead><tbody><tr><td class="left">Authorization</td><td class="left"><a href="rfc7235.html#header.authorization" title="Authorization">Section 4.2</a> of <a href="#RFC7235" id="rfc.xref.RFC7235.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a></td></tr><tr><td class="left">Proxy-Authorization</td><td class="left"><a href="rfc7235.html#header.proxy-authorization" title="Proxy-Authorization">Section 4.4</a> of <a href="#RFC7235" id="rfc.xref.RFC7235.4"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a></td></tr></tbody></table></div></div><div id="request.context"><h2 id="rfc.section.5.5"><a href="#rfc.section.5.5">5.5</a>&nbsp;<a href="#request.context">Request Context</a></h2><div id="rfc.section.5.5.p.1"><p>The following request header fields provide additional information about the request context, including information about the user, user agent, and resource behind the request.<a class="self" href="#rfc.section.5.5.p.1">&para;</a></p></div><div id="rfc.table.u.8"><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Header Field Name</th><th>Defined in...</th></tr></thead><tbody><tr><td class="left">From</td><td class="left"><a href="#header.from" id="rfc.xref.header.from.1" title="From">Section&nbsp;5.5.1</a></td></tr><tr><td class="left">Referer</td><td class="left"><a href="#header.referer" id="rfc.xref.header.referer.1" title="Referer">Section&nbsp;5.5.2</a></td></tr><tr><td class="left">User-Agent</td><td class="left"><a href="#header.user-agent" id="rfc.xref.header.user-agent.1" title="User-Agent">Section&nbsp;5.5.3</a></td></tr></tbody></table></div><div id="header.from"><h3 id="rfc.section.5.5.1"><a href="#rfc.section.5.5.1">5.5.1</a>&nbsp;<a href="#header.from">From</a></h3><div id="rfc.section.5.5.1.p.1"><p>The "From" header field contains an Internet email address for a human user who controls the requesting user agent. The address ought to be machine-usable, as defined by "mailbox" in <a href="https://tools.ietf.org/html/rfc5322#section-3.4">Section 3.4</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.1"><cite title="Internet Message Format">[RFC5322]</cite></a>:<a class="self" href="#rfc.section.5.5.1.p.1">&para;</a></p></div><div id="rfc.figure.u.35"><pre class="inline"><span id="rfc.iref.g.27"></span>  <a href="#header.from" class="smpl">From</a>    = <a href="#header.from" class="smpl">mailbox</a>
     594</pre></div><div id="rfc.section.5.3.5.p.3"><p>would mean: "I prefer Danish, but will accept British English and other types of English".<a class="self" href="#rfc.section.5.3.5.p.3">&para;</a></p></div><div id="rfc.section.5.3.5.p.4"><p>A request without any Accept-Language header field implies that the user agent will accept any language in response. If the header field is present in a request and none of the available representations for the response have a matching language tag, the origin server can either disregard the header field by treating the response as if it is not subject to content negotiation or honor the header field by sending a <a href="#status.406" class="smpl">406 (Not Acceptable)</a> response. However, the latter is not encouraged, as doing so can prevent users from accessing content that they might be able to use (with translation software, for example).<a class="self" href="#rfc.section.5.3.5.p.4">&para;</a></p></div><div id="rfc.section.5.3.5.p.5"><p>Note that some recipients treat the order in which language tags are listed as an indication of descending priority, particularly for tags that are assigned equal quality values (no value is the same as q=1). However, this behavior cannot be relied upon. For consistency and to maximize interoperability, many user agents assign each language tag a unique quality value while also listing them in order of decreasing quality. Additional discussion of language priority lists can be found in <a href="https://tools.ietf.org/html/rfc4647#section-2.3">Section 2.3</a> of <a href="#RFC4647" id="rfc.xref.RFC4647.2"><cite title="Matching of Language Tags">[RFC4647]</cite></a>.<a class="self" href="#rfc.section.5.3.5.p.5">&para;</a></p></div><div id="rfc.section.5.3.5.p.6"><p>For matching, <a href="https://tools.ietf.org/html/rfc4647#section-3">Section 3</a> of <a href="#RFC4647" id="rfc.xref.RFC4647.3"><cite title="Matching of Language Tags">[RFC4647]</cite></a> defines several matching schemes. Implementations can offer the most appropriate matching scheme for their requirements. The "Basic Filtering" scheme (<a href="#RFC4647" id="rfc.xref.RFC4647.4"><cite title="Matching of Language Tags">[RFC4647]</cite></a>, <a href="https://tools.ietf.org/html/rfc4647#section-3.3.1">Section 3.3.1</a>) is identical to the matching scheme that was previously defined for HTTP in <a href="https://tools.ietf.org/html/rfc2616#section-14.4">Section 14.4</a> of <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>.<a class="self" href="#rfc.section.5.3.5.p.6">&para;</a></p></div><div id="rfc.section.5.3.5.p.7"><p>It might be contrary to the privacy expectations of the user to send an Accept-Language header field with the complete linguistic preferences of the user in every request (<a href="#fingerprinting" title="Browser Fingerprinting">Section&nbsp;9.7</a>).<a class="self" href="#rfc.section.5.3.5.p.7">&para;</a></p></div><div id="rfc.section.5.3.5.p.8"><p>Since intelligibility is highly dependent on the individual user, user agents need to allow user control over the linguistic preference (either through configuration of the user agent itself or by defaulting to a user controllable system setting). A user agent that does not provide such control to the user <em class="bcp14">MUST NOT</em> send an Accept-Language header field.<a class="self" href="#rfc.section.5.3.5.p.8">&para;</a></p></div><div class="note"><div id="rfc.section.5.3.5.p.9"><p><b>Note:</b> User agents ought to provide guidance to users when setting a preference, since users are rarely familiar with the details of language matching as described above. For example, users might assume that on selecting "en-gb", they will be served any kind of English document if British English is not available. A user agent might suggest, in such a case, to add "en" to the list for better matching behavior.<a class="self" href="#rfc.section.5.3.5.p.9">&para;</a></p></div></div></div></div><div id="request.auth"><h2 id="rfc.section.5.4"><a href="#rfc.section.5.4">5.4</a>&nbsp;<a href="#request.auth">Authentication Credentials</a></h2><div id="rfc.section.5.4.p.1"><p>Two header fields are used for carrying authentication credentials, as defined in <a href="#RFC7235" id="rfc.xref.RFC7235.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a>. Note that various custom mechanisms for user authentication use the Cookie header field for this purpose, as defined in <a href="#RFC6265" id="rfc.xref.RFC6265.2"><cite title="HTTP State Management Mechanism">[RFC6265]</cite></a>.<a class="self" href="#rfc.section.5.4.p.1">&para;</a></p></div><div id="rfc.table.u.7"><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Header Field Name</th><th>Defined in...</th></tr></thead><tbody><tr><td class="left">Authorization</td><td class="left"><a href="rfc7235.html#header.authorization" title="Authorization">Section 4.2</a> of <a href="#RFC7235" id="rfc.xref.RFC7235.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a></td></tr><tr><td class="left">Proxy-Authorization</td><td class="left"><a href="rfc7235.html#header.proxy-authorization" title="Proxy-Authorization">Section 4.4</a> of <a href="#RFC7235" id="rfc.xref.RFC7235.4"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a></td></tr></tbody></table></div></div><div id="request.context"><h2 id="rfc.section.5.5"><a href="#rfc.section.5.5">5.5</a>&nbsp;<a href="#request.context">Request Context</a></h2><div id="rfc.section.5.5.p.1"><p>The following request header fields provide additional information about the request context, including information about the user, user agent, and resource behind the request.<a class="self" href="#rfc.section.5.5.p.1">&para;</a></p></div><div id="rfc.table.u.8"><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Header Field Name</th><th>Defined in...</th></tr></thead><tbody><tr><td class="left">From</td><td class="left"><a href="#header.from" id="rfc.xref.header.from.1" title="From">Section&nbsp;5.5.1</a></td></tr><tr><td class="left">Referer</td><td class="left"><a href="#header.referer" id="rfc.xref.header.referer.1" title="Referer">Section&nbsp;5.5.2</a></td></tr><tr><td class="left">User-Agent</td><td class="left"><a href="#header.user-agent" id="rfc.xref.header.user-agent.1" title="User-Agent">Section&nbsp;5.5.3</a></td></tr></tbody></table></div><div id="header.from"><h3 id="rfc.section.5.5.1"><a href="#rfc.section.5.5.1">5.5.1</a>&nbsp;<a href="#header.from">From</a></h3><div id="rfc.section.5.5.1.p.1"><p>The "From" header field contains an Internet email address for a human user who controls the requesting user agent. The address ought to be machine-usable, as defined by "mailbox" in <a href="https://tools.ietf.org/html/rfc5322#section-3.4">Section 3.4</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.1"><cite title="Internet Message Format">[RFC5322]</cite></a>:<a class="self" href="#rfc.section.5.5.1.p.1">&para;</a></p></div><div id="rfc.figure.u.35"><pre class="inline"><span id="rfc.iref.g.27"></span>  <a href="#header.from" class="smpl">From</a>    = <a href="#header.from" class="smpl">mailbox</a>
    579595 
    580596  <a href="#header.from" class="smpl">mailbox</a> = &lt;mailbox, see <a href="#RFC5322" id="rfc.xref.RFC5322.2"><cite title="Internet Message Format">[RFC5322]</cite></a>, <a href="https://tools.ietf.org/html/rfc5322#section-3.4">Section 3.4</a>&gt;
     
    586602  <a href="#header.user-agent" class="smpl">product-version</a> = <a href="#imported.abnf" class="smpl">token</a>
    587603</pre></div><div id="rfc.section.5.5.3.p.3"><p>A sender <em class="bcp14">SHOULD</em> limit generated product identifiers to what is necessary to identify the product; a sender <em class="bcp14">MUST NOT</em> generate advertising or other nonessential information within the product identifier. A sender <em class="bcp14">SHOULD NOT</em> generate information in <a href="#header.user-agent" class="smpl">product-version</a> that is not a version identifier (i.e., successive versions of the same product name ought to differ only in the product-version portion of the product identifier).<a class="self" href="#rfc.section.5.5.3.p.3">&para;</a></p></div><div id="rfc.section.5.5.3.p.4"><p>Example:<a class="self" href="#rfc.section.5.5.3.p.4">&para;</a></p></div><div id="rfc.figure.u.41"><pre class="text">  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
    588 </pre></div><div id="rfc.section.5.5.3.p.5"><p>A user agent <em class="bcp14">SHOULD NOT</em> generate a User-Agent field containing needlessly fine-grained detail and <em class="bcp14">SHOULD</em> limit the addition of subproducts by third parties. Overly long and detailed User-Agent field values increase request latency and the risk of a user being identified against their wishes ("fingerprinting").<a class="self" href="#rfc.section.5.5.3.p.5">&para;</a></p></div><div id="rfc.section.5.5.3.p.6"><p>Likewise, implementations are encouraged not to use the product tokens of other implementations in order to declare compatibility with them, as this circumvents the purpose of the field. If a user agent masquerades as a different user agent, recipients can assume that the user intentionally desires to see responses tailored for that identified user agent, even if they might not work as well for the actual user agent being used.<a class="self" href="#rfc.section.5.5.3.p.6">&para;</a></p></div></div></div></div><div id="status.codes"><h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a>&nbsp;<a href="#status.codes">Response Status Codes</a></h1><div id="rfc.section.6.p.1"><p>The status-code element is a three-digit integer code giving the result of the attempt to understand and satisfy the request.<a class="self" href="#rfc.section.6.p.1">&para;</a></p></div><div id="rfc.section.6.p.2"><p>HTTP status codes are extensible. HTTP clients are not required to understand the meaning of all registered status codes, though such understanding is obviously desirable. However, a client <em class="bcp14">MUST</em> understand the class of any status code, as indicated by the first digit, and treat an unrecognized status code as being equivalent to the x00 status code of that class, with the exception that a recipient <em class="bcp14">MUST NOT</em> cache a response with an unrecognized status code.<a class="self" href="#rfc.section.6.p.2">&para;</a></p></div><div id="rfc.section.6.p.3"><p>For example, if an unrecognized status code of 471 is received by a client, the client can assume that there was something wrong with its request and treat the response as if it had received a <a href="#status.400" class="smpl">400 (Bad Request)</a> status code. The response message will usually contain a representation that explains the status.<a class="self" href="#rfc.section.6.p.3">&para;</a></p></div><div id="rfc.section.6.p.4"><p>The first digit of the status-code defines the class of response. The last two digits do not have any categorization role. There are five values for the first digit: <a class="self" href="#rfc.section.6.p.4">&para;</a></p><ul><li><a href="#status.1xx" class="smpl">1xx (Informational)</a>: The request was received, continuing process</li><li><a href="#status.2xx" class="smpl">2xx (Successful)</a>: The request was successfully received, understood, and accepted</li><li><a href="#status.3xx" class="smpl">3xx (Redirection)</a>: Further action needs to be taken in order to complete the request</li><li><a href="#status.4xx" class="smpl">4xx (Client Error)</a>: The request contains bad syntax or cannot be fulfilled</li><li><a href="#status.5xx" class="smpl">5xx (Server Error)</a>: The server failed to fulfill an apparently valid request</li></ul></div><div id="overview.of.status.codes"><h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a>&nbsp;<a href="#overview.of.status.codes">Overview of Status Codes</a></h2><div id="rfc.section.6.1.p.1"><p>The status codes listed below are defined in this specification, <a href="rfc7232.html#status.code.definitions" title="Status Code Definitions">Section 4</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.9"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a>, <a href="rfc7233.html#range.response" title="Responses to a Range Request">Section 4</a> of <a href="#RFC7233" id="rfc.xref.RFC7233.7"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a>, and <a href="rfc7235.html#status.code.definitions" title="Status Code Definitions">Section 3</a> of <a href="#RFC7235" id="rfc.xref.RFC7235.5"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a>. The reason phrases listed here are only recommendations &#8212; they can be replaced by local equivalents without affecting the protocol.<a class="self" href="#rfc.section.6.1.p.1">&para;</a></p></div><div id="rfc.section.6.1.p.2"><p>Responses with status codes that are defined as cacheable by default (e.g., 200, 203, 204, 206, 300, 301, 404, 405, 410, 414, and 501 in this specification) can be reused by a cache with heuristic expiration unless otherwise indicated by the method definition or explicit cache controls <a href="#RFC7234" id="rfc.xref.RFC7234.10"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>; all other status codes are not cacheable by default.<a class="self" href="#rfc.section.6.1.p.2">&para;</a></p></div><div id="rfc.table.u.9"><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Code</th><th>Reason-Phrase</th><th>Defined in...</th></tr></thead><tbody><tr><td class="left">100</td><td class="left">Continue</td><td class="left"><a href="#status.100" id="rfc.xref.status.100.1" title="100 Continue">Section&nbsp;6.2.1</a></td></tr><tr><td class="left">101</td><td class="left">Switching Protocols</td><td class="left"><a href="#status.101" id="rfc.xref.status.101.1" title="101 Switching Protocols">Section&nbsp;6.2.2</a></td></tr><tr><td class="left">200</td><td class="left">OK</td><td class="left"><a href="#status.200" id="rfc.xref.status.200.1" title="200 OK">Section&nbsp;6.3.1</a></td></tr><tr><td class="left">201</td><td class="left">Created</td><td class="left"><a href="#status.201" id="rfc.xref.status.201.1" title="201 Created">Section&nbsp;6.3.2</a></td></tr><tr><td class="left">202</td><td class="left">Accepted</td><td class="left"><a href="#status.202" id="rfc.xref.status.202.1" title="202 Accepted">Section&nbsp;6.3.3</a></td></tr><tr><td class="left">203</td><td class="left">Non-Authoritative Information</td><td class="left"><a href="#status.203" id="rfc.xref.status.203.1" title="203 Non-Authoritative Information">Section&nbsp;6.3.4</a></td></tr><tr><td class="left">204</td><td class="left">No Content</td><td class="left"><a href="#status.204" id="rfc.xref.status.204.1" title="204 No Content">Section&nbsp;6.3.5</a></td></tr><tr><td class="left">205</td><td class="left">Reset Content</td><td class="left"><a href="#status.205" id="rfc.xref.status.205.1" title="205 Reset Content">Section&nbsp;6.3.6</a></td></tr><tr><td class="left">206</td><td class="left">Partial Content</td><td id="status.206" class="left"><a href="rfc7233.html#status.206" title="206 Partial Content">Section 4.1</a> of <a href="#RFC7233" id="rfc.xref.RFC7233.8"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a></td></tr><tr><td class="left">300</td><td class="left">Multiple Choices</td><td class="left"><a href="#status.300" id="rfc.xref.status.300.1" title="300 Multiple Choices">Section&nbsp;6.4.1</a></td></tr><tr><td class="left">301</td><td class="left">Moved Permanently</td><td class="left"><a href="#status.301" id="rfc.xref.status.301.1" title="301 Moved Permanently">Section&nbsp;6.4.2</a></td></tr><tr><td class="left">302</td><td class="left">Found</td><td class="left"><a href="#status.302" id="rfc.xref.status.302.1" title="302 Found">Section&nbsp;6.4.3</a></td></tr><tr><td class="left">303</td><td class="left">See Other</td><td class="left"><a href="#status.303" id="rfc.xref.status.303.1" title="303 See Other">Section&nbsp;6.4.4</a></td></tr><tr><td class="left">304</td><td class="left">Not Modified</td><td id="status.304" class="left"><a href="rfc7232.html#status.304" title="304 Not Modified">Section 4.1</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.10"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a></td></tr><tr><td class="left">305</td><td class="left">Use Proxy</td><td class="left"><a href="#status.305" id="rfc.xref.status.305.1" title="305 Use Proxy">Section&nbsp;6.4.5</a></td></tr><tr><td class="left">307</td><td class="left">Temporary Redirect</td><td class="left"><a href="#status.307" id="rfc.xref.status.307.1" title="307 Temporary Redirect">Section&nbsp;6.4.7</a></td></tr><tr><td class="left">400</td><td class="left">Bad Request</td><td class="left"><a href="#status.400" id="rfc.xref.status.400.1" title="400 Bad Request">Section&nbsp;6.5.1</a></td></tr><tr><td class="left">401</td><td class="left">Unauthorized</td><td id="status.401" class="left"><a href="rfc7235.html#status.401" title="401 Unauthorized">Section 3.1</a> of <a href="#RFC7235" id="rfc.xref.RFC7235.6"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a></td></tr><tr><td class="left">402</td><td class="left">Payment Required</td><td class="left"><a href="#status.402" id="rfc.xref.status.402.1" title="402 Payment Required">Section&nbsp;6.5.2</a></td></tr><tr><td class="left">403</td><td class="left">Forbidden</td><td class="left"><a href="#status.403" id="rfc.xref.status.403.1" title="403 Forbidden">Section&nbsp;6.5.3</a></td></tr><tr><td class="left">404</td><td class="left">Not Found</td><td class="left"><a href="#status.404" id="rfc.xref.status.404.1" title="404 Not Found">Section&nbsp;6.5.4</a></td></tr><tr><td class="left">405</td><td class="left">Method Not Allowed</td><td class="left"><a href="#status.405" id="rfc.xref.status.405.1" title="405 Method Not Allowed">Section&nbsp;6.5.5</a></td></tr><tr><td class="left">406</td><td class="left">Not Acceptable</td><td class="left"><a href="#status.406" id="rfc.xref.status.406.1" title="406 Not Acceptable">Section&nbsp;6.5.6</a></td></tr><tr><td class="left">407</td><td class="left">Proxy Authentication Required</td><td id="status.407" class="left"><a href="rfc7235.html#status.407" title="407 Proxy Authentication Required">Section 3.2</a> of <a href="#RFC7235" id="rfc.xref.RFC7235.7"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a></td></tr><tr><td class="left">408</td><td class="left">Request Timeout</td><td class="left"><a href="#status.408" id="rfc.xref.status.408.1" title="408 Request Timeout">Section&nbsp;6.5.7</a></td></tr><tr><td class="left">409</td><td class="left">Conflict</td><td class="left"><a href="#status.409" id="rfc.xref.status.409.1" title="409 Conflict">Section&nbsp;6.5.8</a></td></tr><tr><td class="left">410</td><td class="left">Gone</td><td class="left"><a href="#status.410" id="rfc.xref.status.410.1" title="410 Gone">Section&nbsp;6.5.9</a></td></tr><tr><td class="left">411</td><td class="left">Length Required</td><td class="left"><a href="#status.411" id="rfc.xref.status.411.1" title="411 Length Required">Section&nbsp;6.5.10</a></td></tr><tr><td class="left">412</td><td class="left">Precondition Failed</td><td id="status.412" class="left"><a href="rfc7232.html#status.412" title="412 Precondition Failed">Section 4.2</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.11"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a></td></tr><tr><td class="left">413</td><td class="left">Payload Too Large</td><td class="left"><a href="#status.413" id="rfc.xref.status.413.1" title="413 Payload Too Large">Section&nbsp;6.5.11</a></td></tr><tr><td class="left">414</td><td class="left">URI Too Long</td><td class="left"><a href="#status.414" id="rfc.xref.status.414.1" title="414 URI Too Long">Section&nbsp;6.5.12</a></td></tr><tr><td class="left">415</td><td class="left">Unsupported Media Type</td><td class="left"><a href="#status.415" id="rfc.xref.status.415.1" title="415 Unsupported Media Type">Section&nbsp;6.5.13</a></td></tr><tr><td class="left">416</td><td class="left">Range Not Satisfiable</td><td id="status.416" class="left"><a href="rfc7233.html#status.416" title="416 Range Not Satisfiable">Section 4.4</a> of <a href="#RFC7233" id="rfc.xref.RFC7233.9"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a></td></tr><tr><td class="left">417</td><td class="left">Expectation Failed</td><td class="left"><a href="#status.417" id="rfc.xref.status.417.1" title="417 Expectation Failed">Section&nbsp;6.5.14</a></td></tr><tr><td class="left">426</td><td class="left">Upgrade Required</td><td class="left"><a href="#status.426" id="rfc.xref.status.426.1" title="426 Upgrade Required">Section&nbsp;6.5.15</a></td></tr><tr><td class="left">500</td><td class="left">Internal Server Error</td><td class="left"><a href="#status.500" id="rfc.xref.status.500.1" title="500 Internal Server Error">Section&nbsp;6.6.1</a></td></tr><tr><td class="left">501</td><td class="left">Not Implemented</td><td class="left"><a href="#status.501" id="rfc.xref.status.501.1" title="501 Not Implemented">Section&nbsp;6.6.2</a></td></tr><tr><td class="left">502</td><td class="left">Bad Gateway</td><td class="left"><a href="#status.502" id="rfc.xref.status.502.1" title="502 Bad Gateway">Section&nbsp;6.6.3</a></td></tr><tr><td class="left">503</td><td class="left">Service Unavailable</td><td class="left"><a href="#status.503" id="rfc.xref.status.503.1" title="503 Service Unavailable">Section&nbsp;6.6.4</a></td></tr><tr><td class="left">504</td><td class="left">Gateway Timeout</td><td class="left"><a href="#status.504" id="rfc.xref.status.504.1" title="504 Gateway Timeout">Section&nbsp;6.6.5</a></td></tr><tr><td class="left">505</td><td class="left">HTTP Version Not Supported</td><td class="left"><a href="#status.505" id="rfc.xref.status.505.1" title="505 HTTP Version Not Supported">Section&nbsp;6.6.6</a></td></tr></tbody></table></div><div id="rfc.section.6.1.p.3"><p>Note that this list is not exhaustive &#8212; it does not include extension status codes defined in other specifications. The complete list of status codes is maintained by IANA. See <a href="#status.code.registry" title="Status Code Registry">Section&nbsp;8.2</a> for details.<a class="self" href="#rfc.section.6.1.p.3">&para;</a></p></div></div><div id="status.1xx"><h2 id="rfc.section.6.2"><a href="#rfc.section.6.2">6.2</a>&nbsp;<a href="#status.1xx">Informational 1xx</a></h2><div id="rfc.section.6.2.p.1"><p>The <dfn>1xx (Informational)</dfn> class of status code indicates an interim response for communicating connection status or request progress prior to completing the requested action and sending a final response. 1xx responses are terminated by the first empty line after the status-line (the empty line signaling the end of the header section). Since HTTP/1.0 did not define any 1xx status codes, a server <em class="bcp14">MUST NOT</em> send a 1xx response to an HTTP/1.0 client.<a class="self" href="#rfc.section.6.2.p.1">&para;</a></p></div><div id="rfc.section.6.2.p.2"><p>A client <em class="bcp14">MUST</em> be able to parse one or more 1xx responses received prior to a final response, even if the client does not expect one. A user agent <em class="bcp14">MAY</em> ignore unexpected 1xx responses.<a class="self" href="#rfc.section.6.2.p.2">&para;</a></p></div><div id="rfc.section.6.2.p.3"><p>A proxy <em class="bcp14">MUST</em> forward 1xx responses unless the proxy itself requested the generation of the 1xx response. For example, if a proxy adds an "Expect: 100-continue" field when it forwards a request, then it need not forward the corresponding <a href="#status.100" class="smpl">100 (Continue)</a> response(s).<a class="self" href="#rfc.section.6.2.p.3">&para;</a></p></div><div id="status.100"><h3 id="rfc.section.6.2.1"><a href="#rfc.section.6.2.1">6.2.1</a>&nbsp;<a href="#status.100">100 Continue</a></h3><div id="rfc.section.6.2.1.p.1"><p>The <dfn>100 (Continue)</dfn> status code indicates that the initial part of a request has been received and has not yet been rejected by the server. The server intends to send a final response after the request has been fully received and acted upon.<a class="self" href="#rfc.section.6.2.1.p.1">&para;</a></p></div><div id="rfc.section.6.2.1.p.2"><p>When the request contains an <a href="#header.expect" class="smpl">Expect</a> header field that includes a <a href="#header.expect" class="smpl">100-continue</a> expectation, the 100 response indicates that the server wishes to receive the request payload body, as described in <a href="#header.expect" id="rfc.xref.header.expect.2" title="Expect">Section&nbsp;5.1.1</a>. The client ought to continue sending the request and discard the 100 response.<a class="self" href="#rfc.section.6.2.1.p.2">&para;</a></p></div><div id="rfc.section.6.2.1.p.3"><p>If the request did not contain an <a href="#header.expect" class="smpl">Expect</a> header field containing the <a href="#header.expect" class="smpl">100-continue</a> expectation, the client can simply discard this interim response.<a class="self" href="#rfc.section.6.2.1.p.3">&para;</a></p></div></div><div id="status.101"><h3 id="rfc.section.6.2.2"><a href="#rfc.section.6.2.2">6.2.2</a>&nbsp;<a href="#status.101">101 Switching Protocols</a></h3><div id="rfc.section.6.2.2.p.1"><p>The <dfn>101 (Switching Protocols)</dfn> status code indicates that the server understands and is willing to comply with the client's request, via the <a href="rfc7230.html#header.upgrade" class="smpl">Upgrade</a> header field (<a href="rfc7230.html#header.upgrade" title="Upgrade">Section 6.7</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.24"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>), for a change in the application protocol being used on this connection. The server <em class="bcp14">MUST</em> generate an Upgrade header field in the response that indicates which protocol(s) will be switched to immediately after the empty line that terminates the 101 response.<a class="self" href="#rfc.section.6.2.2.p.1">&para;</a></p></div><div id="rfc.section.6.2.2.p.2"><p>It is assumed that the server will only agree to switch protocols when it is advantageous to do so. For example, switching to a newer version of HTTP might be advantageous over older versions, and switching to a real-time, synchronous protocol might be advantageous when delivering resources that use such features.<a class="self" href="#rfc.section.6.2.2.p.2">&para;</a></p></div></div></div><div id="status.2xx"><h2 id="rfc.section.6.3"><a href="#rfc.section.6.3">6.3</a>&nbsp;<a href="#status.2xx">Successful 2xx</a></h2><div id="rfc.section.6.3.p.1"><p>The <dfn>2xx (Successful)</dfn> class of status code indicates that the client's request was successfully received, understood, and accepted.<a class="self" href="#rfc.section.6.3.p.1">&para;</a></p></div><div id="status.200"><h3 id="rfc.section.6.3.1"><a href="#rfc.section.6.3.1">6.3.1</a>&nbsp;<a href="#status.200">200 OK</a></h3><div id="rfc.section.6.3.1.p.1"><p>The <dfn>200 (OK)</dfn> status code indicates that the request has succeeded. The payload sent in a 200 response depends on the request method. For the methods defined by this specification, the intended meaning of the payload can be summarized as: <a class="self" href="#rfc.section.6.3.1.p.1">&para;</a></p><dl><dt>GET</dt><dd>a representation of the <a href="#resources" class="smpl">target resource</a>;</dd><dt>HEAD</dt><dd>the same representation as GET, but without the representation data;</dd><dt>POST</dt><dd>a representation of the status of, or results obtained from, the action;</dd><dt>PUT, DELETE</dt><dd>a representation of the status of the action;</dd><dt>OPTIONS</dt><dd>a representation of the communications options;</dd><dt>TRACE</dt><dd>a representation of the request message as received by the end server.</dd></dl></div><div id="rfc.section.6.3.1.p.2"><p>Aside from responses to CONNECT, a 200 response always has a payload, though an origin server <em class="bcp14">MAY</em> generate a payload body of zero length. If no payload is desired, an origin server ought to send <dfn>204 (No Content)</dfn> instead. For CONNECT, no payload is allowed because the successful result is a tunnel, which begins immediately after the 200 response header section.<a class="self" href="#rfc.section.6.3.1.p.2">&para;</a></p></div><div id="rfc.section.6.3.1.p.3"><p>A 200 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.11"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.3.1.p.3">&para;</a></p></div></div><div id="status.201"><h3 id="rfc.section.6.3.2"><a href="#rfc.section.6.3.2">6.3.2</a>&nbsp;<a href="#status.201">201 Created</a></h3><div id="rfc.section.6.3.2.p.1"><p>The <dfn>201 (Created)</dfn> status code indicates that the request has been fulfilled and has resulted in one or more new resources being created. The primary resource created by the request is identified by either a <a href="#header.location" class="smpl">Location</a> header field in the response or, if no <a href="#header.location" class="smpl">Location</a> field is received, by the effective request URI.<a class="self" href="#rfc.section.6.3.2.p.1">&para;</a></p></div><div id="rfc.section.6.3.2.p.2"><p>The 201 response payload typically describes and links to the resource(s) created. See <a href="#response.validator" title="Validator Header Fields">Section&nbsp;7.2</a> for a discussion of the meaning and purpose of validator header fields, such as <a href="rfc7232.html#header.etag" class="smpl">ETag</a> and <a href="rfc7232.html#header.last-modified" class="smpl">Last-Modified</a>, in a 201 response.<a class="self" href="#rfc.section.6.3.2.p.2">&para;</a></p></div></div><div id="status.202"><h3 id="rfc.section.6.3.3"><a href="#rfc.section.6.3.3">6.3.3</a>&nbsp;<a href="#status.202">202 Accepted</a></h3><div id="rfc.section.6.3.3.p.1"><p>The <dfn>202 (Accepted)</dfn> status code indicates that the request has been accepted for processing, but the processing has not been completed. The request might or might not eventually be acted upon, as it might be disallowed when processing actually takes place. There is no facility in HTTP for re-sending a status code from an asynchronous operation.<a class="self" href="#rfc.section.6.3.3.p.1">&para;</a></p></div><div id="rfc.section.6.3.3.p.2"><p>The 202 response is intentionally noncommittal. Its purpose is to allow a server to accept a request for some other process (perhaps a batch-oriented process that is only run once per day) without requiring that the user agent's connection to the server persist until the process is completed. The representation sent with this response ought to describe the request's current status and point to (or embed) a status monitor that can provide the user with an estimate of when the request will be fulfilled.<a class="self" href="#rfc.section.6.3.3.p.2">&para;</a></p></div></div><div id="status.203"><h3 id="rfc.section.6.3.4"><a href="#rfc.section.6.3.4">6.3.4</a>&nbsp;<a href="#status.203">203 Non-Authoritative Information</a></h3><div id="rfc.section.6.3.4.p.1"><p>The <dfn>203 (Non-Authoritative Information)</dfn> status code indicates that the request was successful but the enclosed payload has been modified from that of the origin server's <a href="#status.200" class="smpl">200 (OK)</a> response by a transforming proxy (<a href="rfc7230.html#message.transformations" title="Transformations">Section 5.7.2</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.25"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>). This status code allows the proxy to notify recipients when a transformation has been applied, since that knowledge might impact later decisions regarding the content. For example, future cache validation requests for the content might only be applicable along the same request path (through the same proxies).<a class="self" href="#rfc.section.6.3.4.p.1">&para;</a></p></div><div id="rfc.section.6.3.4.p.2"><p>The 203 response is similar to the Warning code of 214 Transformation Applied (<a href="rfc7234.html#header.warning" title="Warning">Section 5.5</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.12"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>), which has the advantage of being applicable to responses with any status code.<a class="self" href="#rfc.section.6.3.4.p.2">&para;</a></p></div><div id="rfc.section.6.3.4.p.3"><p>A 203 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.13"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.3.4.p.3">&para;</a></p></div></div><div id="status.204"><h3 id="rfc.section.6.3.5"><a href="#rfc.section.6.3.5">6.3.5</a>&nbsp;<a href="#status.204">204 No Content</a></h3><div id="rfc.section.6.3.5.p.1"><p>The <dfn>204 (No Content)</dfn> status code indicates that the server has successfully fulfilled the request and that there is no additional content to send in the response payload body. Metadata in the response header fields refer to the <a href="#resources" class="smpl">target resource</a> and its <a href="#representations" class="smpl">selected representation</a> after the requested action was applied.<a class="self" href="#rfc.section.6.3.5.p.1">&para;</a></p></div><div id="rfc.section.6.3.5.p.2"><p>For example, if a 204 status code is received in response to a PUT request and the response contains an <a href="rfc7232.html#header.etag" class="smpl">ETag</a> header field, then the PUT was successful and the ETag field-value contains the entity-tag for the new representation of that target resource.<a class="self" href="#rfc.section.6.3.5.p.2">&para;</a></p></div><div id="rfc.section.6.3.5.p.3"><p>The 204 response allows a server to indicate that the action has been successfully applied to the target resource, while implying that the user agent does not need to traverse away from its current "document view" (if any). The server assumes that the user agent will provide some indication of the success to its user, in accord with its own interface, and apply any new or updated metadata in the response to its active representation.<a class="self" href="#rfc.section.6.3.5.p.3">&para;</a></p></div><div id="rfc.section.6.3.5.p.4"><p>For example, a 204 status code is commonly used with document editing interfaces corresponding to a "save" action, such that the document being saved remains available to the user for editing. It is also frequently used with interfaces that expect automated data transfers to be prevalent, such as within distributed version control systems.<a class="self" href="#rfc.section.6.3.5.p.4">&para;</a></p></div><div id="rfc.section.6.3.5.p.5"><p>A 204 response is terminated by the first empty line after the header fields because it cannot contain a message body.<a class="self" href="#rfc.section.6.3.5.p.5">&para;</a></p></div><div id="rfc.section.6.3.5.p.6"><p>A 204 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.14"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.3.5.p.6">&para;</a></p></div></div><div id="status.205"><h3 id="rfc.section.6.3.6"><a href="#rfc.section.6.3.6">6.3.6</a>&nbsp;<a href="#status.205">205 Reset Content</a></h3><div id="rfc.section.6.3.6.p.1"><p>The <dfn>205 (Reset Content)</dfn> status code indicates that the server has fulfilled the request and desires that the user agent reset the "document view", which caused the request to be sent, to its original state as received from the origin server.<a class="self" href="#rfc.section.6.3.6.p.1">&para;</a></p></div><div id="rfc.section.6.3.6.p.2"><p>This response is intended to support a common data entry use case where the user receives content that supports data entry (a form, notepad, canvas, etc.), enters or manipulates data in that space, causes the entered data to be submitted in a request, and then the data entry mechanism is reset for the next entry so that the user can easily initiate another input action.<a class="self" href="#rfc.section.6.3.6.p.2">&para;</a></p></div><div id="rfc.section.6.3.6.p.3"><p>Since the 205 status code implies that no additional content will be provided, a server <em class="bcp14">MUST NOT</em> generate a payload in a 205 response. In other words, a server <em class="bcp14">MUST</em> do one of the following for a 205 response: a) indicate a zero-length body for the response by including a <a href="rfc7230.html#header.content-length" class="smpl">Content-Length</a> header field with a value of 0; b) indicate a zero-length payload for the response by including a <a href="rfc7230.html#header.transfer-encoding" class="smpl">Transfer-Encoding</a> header field with a value of chunked and a message body consisting of a single chunk of zero-length; or, c) close the connection immediately after sending the blank line terminating the header section.<a class="self" href="#rfc.section.6.3.6.p.3">&para;</a></p></div></div></div><div id="status.3xx"><h2 id="rfc.section.6.4"><a href="#rfc.section.6.4">6.4</a>&nbsp;<a href="#status.3xx">Redirection 3xx</a></h2><div id="rfc.section.6.4.p.1"><p>The <dfn>3xx (Redirection)</dfn> class of status code indicates that further action needs to be taken by the user agent in order to fulfill the request. If a <a href="#header.location" class="smpl">Location</a> header field (<a href="#header.location" id="rfc.xref.header.location.2" title="Location">Section&nbsp;7.1.2</a>) is provided, the user agent <em class="bcp14">MAY</em> automatically redirect its request to the URI referenced by the Location field value, even if the specific status code is not understood. Automatic redirection needs to done with care for methods not known to be <a href="#safe.methods" class="smpl">safe</a>, as defined in <a href="#safe.methods" title="Safe Methods">Section&nbsp;4.2.1</a>, since the user might not wish to redirect an unsafe request.<a class="self" href="#rfc.section.6.4.p.1">&para;</a></p></div><div id="rfc.section.6.4.p.2"><p>There are several types of redirects: <a class="self" href="#rfc.section.6.4.p.2">&para;</a></p><ol><li><p>Redirects that indicate the resource might be available at a different URI, as provided by the <a href="#header.location" class="smpl">Location</a> field, as in the status codes <a href="#status.301" class="smpl">301 (Moved Permanently)</a>, <a href="#status.302" class="smpl">302 (Found)</a>, and <a href="#status.307" class="smpl">307 (Temporary Redirect)</a>.</p></li><li><p>Redirection that offers a choice of matching resources, each capable of representing the original request target, as in the <a href="#status.300" class="smpl">300 (Multiple Choices)</a> status code.</p></li><li><p>Redirection to a different resource, identified by the <a href="#header.location" class="smpl">Location</a> field, that can represent an indirect response to the request, as in the <a href="#status.303" class="smpl">303 (See Other)</a> status code.</p></li><li><p>Redirection to a previously cached result, as in the <a href="rfc7232.html#status.304" class="smpl">304 (Not Modified)</a> status code.</p></li></ol></div><div class="note" id="rfc.section.6.4.p.3"><p><b>Note:</b> In HTTP/1.0, the status codes <a href="#status.301" class="smpl">301 (Moved Permanently)</a> and <a href="#status.302" class="smpl">302 (Found)</a> were defined for the first type of redirect (<a href="#RFC1945" id="rfc.xref.RFC1945.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.0">[RFC1945]</cite></a>, <a href="https://tools.ietf.org/html/rfc1945#section-9.3">Section 9.3</a>). Early user agents split on whether the method applied to the redirect target would be the same as the original request or would be rewritten as GET. Although HTTP originally defined the former semantics for <a href="#status.301" class="smpl">301</a> and <a href="#status.302" class="smpl">302</a> (to match its original implementation at CERN), and defined <a href="#status.303" class="smpl">303 (See Other)</a> to match the latter semantics, prevailing practice gradually converged on the latter semantics for <a href="#status.301" class="smpl">301</a> and <a href="#status.302" class="smpl">302</a> as well. The first revision of HTTP/1.1 added <a href="#status.307" class="smpl">307 (Temporary Redirect)</a> to indicate the former semantics without being impacted by divergent practice. Over 10 years later, most user agents still do method rewriting for <a href="#status.301" class="smpl">301</a> and <a href="#status.302" class="smpl">302</a>; therefore, this specification makes that behavior conformant when the original request is POST.<a class="self" href="#rfc.section.6.4.p.3">&para;</a></p></div><div id="rfc.section.6.4.p.4"><p>A client <em class="bcp14">SHOULD</em> detect and intervene in cyclical redirections (i.e., "infinite" redirection loops).<a class="self" href="#rfc.section.6.4.p.4">&para;</a></p></div><div class="note" id="rfc.section.6.4.p.5"><p><b>Note:</b> An earlier version of this specification recommended a maximum of five redirections (<a href="#RFC2068" id="rfc.xref.RFC2068.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, <a href="https://tools.ietf.org/html/rfc2068#section-10.3">Section 10.3</a>). Content developers need to be aware that some clients might implement such a fixed limitation.<a class="self" href="#rfc.section.6.4.p.5">&para;</a></p></div><div id="status.300"><h3 id="rfc.section.6.4.1"><a href="#rfc.section.6.4.1">6.4.1</a>&nbsp;<a href="#status.300">300 Multiple Choices</a></h3><div id="rfc.section.6.4.1.p.1"><p>The <dfn>300 (Multiple Choices)</dfn> status code indicates that the <a href="#resources" class="smpl">target resource</a> has more than one representation, each with its own more specific identifier, and information about the alternatives is being provided so that the user (or user agent) can select a preferred representation by redirecting its request to one or more of those identifiers. In other words, the server desires that the user agent engage in reactive negotiation to select the most appropriate representation(s) for its needs (<a href="#content.negotiation" title="Content Negotiation">Section&nbsp;3.4</a>).<a class="self" href="#rfc.section.6.4.1.p.1">&para;</a></p></div><div id="rfc.section.6.4.1.p.2"><p>If the server has a preferred choice, the server <em class="bcp14">SHOULD</em> generate a <a href="#header.location" class="smpl">Location</a> header field containing a preferred choice's URI reference. The user agent <em class="bcp14">MAY</em> use the Location field value for automatic redirection.<a class="self" href="#rfc.section.6.4.1.p.2">&para;</a></p></div><div id="rfc.section.6.4.1.p.3"><p>For request methods other than HEAD, the server <em class="bcp14">SHOULD</em> generate a payload in the 300 response containing a list of representation metadata and URI reference(s) from which the user or user agent can choose the one most preferred. The user agent <em class="bcp14">MAY</em> make a selection from that list automatically if it understands the provided media type. A specific format for automatic selection is not defined by this specification because HTTP tries to remain orthogonal to the definition of its payloads. In practice, the representation is provided in some easily parsed format believed to be acceptable to the user agent, as determined by shared design or content negotiation, or in some commonly accepted hypertext format.<a class="self" href="#rfc.section.6.4.1.p.3">&para;</a></p></div><div id="rfc.section.6.4.1.p.4"><p>A 300 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.15"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.4.1.p.4">&para;</a></p></div><div class="note" id="rfc.section.6.4.1.p.5"><p><b>Note:</b> The original proposal for the 300 status code defined the URI header field as providing a list of alternative representations, such that it would be usable for 200, 300, and 406 responses and be transferred in responses to the HEAD method. However, lack of deployment and disagreement over syntax led to both URI and Alternates (a subsequent proposal) being dropped from this specification. It is possible to communicate the list using a set of Link header fields <a href="#RFC5988" id="rfc.xref.RFC5988.1"><cite title="Web Linking">[RFC5988]</cite></a>, each with a relationship of "alternate", though deployment is a chicken-and-egg problem.<a class="self" href="#rfc.section.6.4.1.p.5">&para;</a></p></div></div><div id="status.301"><h3 id="rfc.section.6.4.2"><a href="#rfc.section.6.4.2">6.4.2</a>&nbsp;<a href="#status.301">301 Moved Permanently</a></h3><div id="rfc.section.6.4.2.p.1"><p>The <dfn>301 (Moved Permanently)</dfn> status code indicates that the <a href="#resources" class="smpl">target resource</a> has been assigned a new permanent URI and any future references to this resource ought to use one of the enclosed URIs. Clients with link-editing capabilities ought to automatically re-link references to the effective request URI to one or more of the new references sent by the server, where possible.<a class="self" href="#rfc.section.6.4.2.p.1">&para;</a></p></div><div id="rfc.section.6.4.2.p.2"><p>The server <em class="bcp14">SHOULD</em> generate a <a href="#header.location" class="smpl">Location</a> header field in the response containing a preferred URI reference for the new permanent URI. The user agent <em class="bcp14">MAY</em> use the Location field value for automatic redirection. The server's response payload usually contains a short hypertext note with a hyperlink to the new URI(s).<a class="self" href="#rfc.section.6.4.2.p.2">&para;</a></p></div><div class="note" id="rfc.section.6.4.2.p.3"><p><b>Note:</b> For historical reasons, a user agent <em class="bcp14">MAY</em> change the request method from POST to GET for the subsequent request. If this behavior is undesired, the <a href="#status.307" class="smpl">307 (Temporary Redirect)</a> status code can be used instead.<a class="self" href="#rfc.section.6.4.2.p.3">&para;</a></p></div><div id="rfc.section.6.4.2.p.4"><p>A 301 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.16"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.4.2.p.4">&para;</a></p></div></div><div id="status.302"><h3 id="rfc.section.6.4.3"><a href="#rfc.section.6.4.3">6.4.3</a>&nbsp;<a href="#status.302">302 Found</a></h3><div id="rfc.section.6.4.3.p.1"><p>The <dfn>302 (Found)</dfn> status code indicates that the target resource resides temporarily under a different URI. Since the redirection might be altered on occasion, the client ought to continue to use the effective request URI for future requests.<a class="self" href="#rfc.section.6.4.3.p.1">&para;</a></p></div><div id="rfc.section.6.4.3.p.2"><p>The server <em class="bcp14">SHOULD</em> generate a <a href="#header.location" class="smpl">Location</a> header field in the response containing a URI reference for the different URI. The user agent <em class="bcp14">MAY</em> use the Location field value for automatic redirection. The server's response payload usually contains a short hypertext note with a hyperlink to the different URI(s).<a class="self" href="#rfc.section.6.4.3.p.2">&para;</a></p></div><div class="note" id="rfc.section.6.4.3.p.3"><p><b>Note:</b> For historical reasons, a user agent <em class="bcp14">MAY</em> change the request method from POST to GET for the subsequent request. If this behavior is undesired, the <a href="#status.307" class="smpl">307 (Temporary Redirect)</a> status code can be used instead.<a class="self" href="#rfc.section.6.4.3.p.3">&para;</a></p></div></div><div id="status.303"><h3 id="rfc.section.6.4.4"><a href="#rfc.section.6.4.4">6.4.4</a>&nbsp;<a href="#status.303">303 See Other</a></h3><div id="rfc.section.6.4.4.p.1"><p>The <dfn>303 (See Other)</dfn> status code indicates that the server is redirecting the user agent to a different resource, as indicated by a URI in the <a href="#header.location" class="smpl">Location</a> header field, which is intended to provide an indirect response to the original request. A user agent can perform a retrieval request targeting that URI (a GET or HEAD request if using HTTP), which might also be redirected, and present the eventual result as an answer to the original request. Note that the new URI in the Location header field is not considered equivalent to the effective request URI.<a class="self" href="#rfc.section.6.4.4.p.1">&para;</a></p></div><div id="rfc.section.6.4.4.p.2"><p>This status code is applicable to any HTTP method. It is primarily used to allow the output of a POST action to redirect the user agent to a selected resource, since doing so provides the information corresponding to the POST response in a form that can be separately identified, bookmarked, and cached, independent of the original request.<a class="self" href="#rfc.section.6.4.4.p.2">&para;</a></p></div><div id="rfc.section.6.4.4.p.3"><p>A 303 response to a GET request indicates that the origin server does not have a representation of the <a href="#resources" class="smpl">target resource</a> that can be transferred by the server over HTTP. However, the <a href="#header.location" class="smpl">Location</a> field value refers to a resource that is descriptive of the target resource, such that making a retrieval request on that other resource might result in a representation that is useful to recipients without implying that it represents the original target resource. Note that answers to the questions of what can be represented, what representations are adequate, and what might be a useful description are outside the scope of HTTP.<a class="self" href="#rfc.section.6.4.4.p.3">&para;</a></p></div><div id="rfc.section.6.4.4.p.4"><p>Except for responses to a HEAD request, the representation of a 303 response ought to contain a short hypertext note with a hyperlink to the same URI reference provided in the <a href="#header.location" class="smpl">Location</a> header field.<a class="self" href="#rfc.section.6.4.4.p.4">&para;</a></p></div></div><div id="status.305"><h3 id="rfc.section.6.4.5"><a href="#rfc.section.6.4.5">6.4.5</a>&nbsp;<a href="#status.305">305 Use Proxy</a></h3><div id="rfc.section.6.4.5.p.1"><p>The <dfn>305 (Use Proxy)</dfn> status code was defined in a previous version of this specification and is now deprecated (<a href="#changes.from.rfc.2616" title="Changes from RFC 2616">Appendix&nbsp;B</a>).<a class="self" href="#rfc.section.6.4.5.p.1">&para;</a></p></div></div><div id="status.306"><h3 id="rfc.section.6.4.6"><a href="#rfc.section.6.4.6">6.4.6</a>&nbsp;<a href="#status.306">306 (Unused)</a></h3><div id="rfc.section.6.4.6.p.1"><p>The 306 status code was defined in a previous version of this specification, is no longer used, and the code is reserved.<a class="self" href="#rfc.section.6.4.6.p.1">&para;</a></p></div></div><div id="status.307"><h3 id="rfc.section.6.4.7"><a href="#rfc.section.6.4.7">6.4.7</a>&nbsp;<a href="#status.307">307 Temporary Redirect</a></h3><div id="rfc.section.6.4.7.p.1"><p>The <dfn>307 (Temporary Redirect)</dfn> status code indicates that the <a href="#resources" class="smpl">target resource</a> resides temporarily under a different URI and the user agent <em class="bcp14">MUST NOT</em> change the request method if it performs an automatic redirection to that URI. Since the redirection can change over time, the client ought to continue using the original effective request URI for future requests.<a class="self" href="#rfc.section.6.4.7.p.1">&para;</a></p></div><div id="rfc.section.6.4.7.p.2"><p>The server <em class="bcp14">SHOULD</em> generate a <a href="#header.location" class="smpl">Location</a> header field in the response containing a URI reference for the different URI. The user agent <em class="bcp14">MAY</em> use the Location field value for automatic redirection. The server's response payload usually contains a short hypertext note with a hyperlink to the different URI(s).<a class="self" href="#rfc.section.6.4.7.p.2">&para;</a></p></div><div class="note" id="rfc.section.6.4.7.p.3"><p><b>Note:</b> This status code is similar to <a href="#status.302" class="smpl">302 (Found)</a>, except that it does not allow changing the request method from POST to GET. This specification defines no equivalent counterpart for <a href="#status.301" class="smpl">301 (Moved
    589     Permanently)</a> (<a href="#RFC7238" id="rfc.xref.RFC7238.1"><cite title="The Hypertext Transfer Protocol (HTTP) Status Code 308 (Permanent Redirect)">[RFC7238]</cite></a>, however, defines the status code 308 (Permanent Redirect) for this purpose).<a class="self" href="#rfc.section.6.4.7.p.3">&para;</a></p></div></div></div><div id="status.4xx"><h2 id="rfc.section.6.5"><a href="#rfc.section.6.5">6.5</a>&nbsp;<a href="#status.4xx">Client Error 4xx</a></h2><div id="rfc.section.6.5.p.1"><p>The <dfn>4xx (Client Error)</dfn> class of status code indicates that the client seems to have erred. Except when responding to a HEAD request, the server <em class="bcp14">SHOULD</em> send a representation containing an explanation of the error situation, and whether it is a temporary or permanent condition. These status codes are applicable to any request method. User agents <em class="bcp14">SHOULD</em> display any included representation to the user.<a class="self" href="#rfc.section.6.5.p.1">&para;</a></p></div><div id="status.400"><h3 id="rfc.section.6.5.1"><a href="#rfc.section.6.5.1">6.5.1</a>&nbsp;<a href="#status.400">400 Bad Request</a></h3><div id="rfc.section.6.5.1.p.1"><p>The <dfn>400 (Bad Request)</dfn> status code indicates that the server cannot or will not process the request due to something that is perceived to be a client error (e.g., malformed request syntax, invalid request message framing, or deceptive request routing).<a class="self" href="#rfc.section.6.5.1.p.1">&para;</a></p></div></div><div id="status.402"><h3 id="rfc.section.6.5.2"><a href="#rfc.section.6.5.2">6.5.2</a>&nbsp;<a href="#status.402">402 Payment Required</a></h3><div id="rfc.section.6.5.2.p.1"><p>The <dfn>402 (Payment Required)</dfn> status code is reserved for future use.<a class="self" href="#rfc.section.6.5.2.p.1">&para;</a></p></div></div><div id="status.403"><h3 id="rfc.section.6.5.3"><a href="#rfc.section.6.5.3">6.5.3</a>&nbsp;<a href="#status.403">403 Forbidden</a></h3><div id="rfc.section.6.5.3.p.1"><p>The <dfn>403 (Forbidden)</dfn> status code indicates that the server understood the request but refuses to authorize it. A server that wishes to make public why the request has been forbidden can describe that reason in the response payload (if any).<a class="self" href="#rfc.section.6.5.3.p.1">&para;</a></p></div><div id="rfc.section.6.5.3.p.2"><p>If authentication credentials were provided in the request, the server considers them insufficient to grant access. The client <em class="bcp14">SHOULD NOT</em> automatically repeat the request with the same credentials. The client <em class="bcp14">MAY</em> repeat the request with new or different credentials. However, a request might be forbidden for reasons unrelated to the credentials.<a class="self" href="#rfc.section.6.5.3.p.2">&para;</a></p></div><div id="rfc.section.6.5.3.p.3"><p>An origin server that wishes to "hide" the current existence of a forbidden <a href="#resources" class="smpl">target resource</a> <em class="bcp14">MAY</em> instead respond with a status code of <a href="#status.404" class="smpl">404 (Not Found)</a>.<a class="self" href="#rfc.section.6.5.3.p.3">&para;</a></p></div></div><div id="status.404"><h3 id="rfc.section.6.5.4"><a href="#rfc.section.6.5.4">6.5.4</a>&nbsp;<a href="#status.404">404 Not Found</a></h3><div id="rfc.section.6.5.4.p.1"><p>The <dfn>404 (Not Found)</dfn> status code indicates that the origin server did not find a current representation for the <a href="#resources" class="smpl">target resource</a> or is not willing to disclose that one exists. A 404 status code does not indicate whether this lack of representation is temporary or permanent; the <a href="#status.410" class="smpl">410 (Gone)</a> status code is preferred over 404 if the origin server knows, presumably through some configurable means, that the condition is likely to be permanent.<a class="self" href="#rfc.section.6.5.4.p.1">&para;</a></p></div><div id="rfc.section.6.5.4.p.2"><p>A 404 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.17"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.5.4.p.2">&para;</a></p></div></div><div id="status.405"><h3 id="rfc.section.6.5.5"><a href="#rfc.section.6.5.5">6.5.5</a>&nbsp;<a href="#status.405">405 Method Not Allowed</a></h3><div id="rfc.section.6.5.5.p.1"><p>The <dfn>405 (Method Not Allowed)</dfn> status code indicates that the method received in the request-line is known by the origin server but not supported by the <a href="#resources" class="smpl">target resource</a>. The origin server <em class="bcp14">MUST</em> generate an <a href="#header.allow" class="smpl">Allow</a> header field in a 405 response containing a list of the target resource's currently supported methods.<a class="self" href="#rfc.section.6.5.5.p.1">&para;</a></p></div><div id="rfc.section.6.5.5.p.2"><p>A 405 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.18"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.5.5.p.2">&para;</a></p></div></div><div id="status.406"><h3 id="rfc.section.6.5.6"><a href="#rfc.section.6.5.6">6.5.6</a>&nbsp;<a href="#status.406">406 Not Acceptable</a></h3><div id="rfc.section.6.5.6.p.1"><p>The <dfn>406 (Not Acceptable)</dfn> status code indicates that the <a href="#resources" class="smpl">target resource</a> does not have a current representation that would be acceptable to the user agent, according to the <a href="#proactive.negotiation" class="smpl">proactive negotiation</a> header fields received in the request (<a href="#request.conneg" title="Content Negotiation">Section&nbsp;5.3</a>), and the server is unwilling to supply a default representation.<a class="self" href="#rfc.section.6.5.6.p.1">&para;</a></p></div><div id="rfc.section.6.5.6.p.2"><p>The server <em class="bcp14">SHOULD</em> generate a payload containing a list of available representation characteristics and corresponding resource identifiers from which the user or user agent can choose the one most appropriate. A user agent <em class="bcp14">MAY</em> automatically select the most appropriate choice from that list. However, this specification does not define any standard for such automatic selection, as described in <a href="#status.300" id="rfc.xref.status.300.2" title="300 Multiple Choices">Section&nbsp;6.4.1</a>.<a class="self" href="#rfc.section.6.5.6.p.2">&para;</a></p></div></div><div id="status.408"><h3 id="rfc.section.6.5.7"><a href="#rfc.section.6.5.7">6.5.7</a>&nbsp;<a href="#status.408">408 Request Timeout</a></h3><div id="rfc.section.6.5.7.p.1"><p>The <dfn>408 (Request Timeout)</dfn> status code indicates that the server did not receive a complete request message within the time that it was prepared to wait. A server <em class="bcp14">SHOULD</em> send the "<a href="rfc7230.html#header.connection" class="smpl">close</a>" connection option (<a href="rfc7230.html#header.connection" title="Connection">Section 6.1</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.26"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>) in the response, since 408 implies that the server has decided to close the connection rather than continue waiting. If the client has an outstanding request in transit, the client <em class="bcp14">MAY</em> repeat that request on a new connection.<a class="self" href="#rfc.section.6.5.7.p.1">&para;</a></p></div></div><div id="status.409"><h3 id="rfc.section.6.5.8"><a href="#rfc.section.6.5.8">6.5.8</a>&nbsp;<a href="#status.409">409 Conflict</a></h3><div id="rfc.section.6.5.8.p.1"><p>The <dfn>409 (Conflict)</dfn> status code indicates that the request could not be completed due to a conflict with the current state of the target resource. This code is used in situations where the user might be able to resolve the conflict and resubmit the request. The server <em class="bcp14">SHOULD</em> generate a payload that includes enough information for a user to recognize the source of the conflict.<a class="self" href="#rfc.section.6.5.8.p.1">&para;</a></p></div><div id="rfc.section.6.5.8.p.2"><p>Conflicts are most likely to occur in response to a PUT request. For example, if versioning were being used and the representation being PUT included changes to a resource that conflict with those made by an earlier (third-party) request, the origin server might use a 409 response to indicate that it can't complete the request. In this case, the response representation would likely contain information useful for merging the differences based on the revision history.<a class="self" href="#rfc.section.6.5.8.p.2">&para;</a></p></div></div><div id="status.410"><h3 id="rfc.section.6.5.9"><a href="#rfc.section.6.5.9">6.5.9</a>&nbsp;<a href="#status.410">410 Gone</a></h3><div id="rfc.section.6.5.9.p.1"><p>The <dfn>410 (Gone)</dfn> status code indicates that access to the <a href="#resources" class="smpl">target resource</a> is no longer available at the origin server and that this condition is likely to be permanent. If the origin server does not know, or has no facility to determine, whether or not the condition is permanent, the status code <a href="#status.404" class="smpl">404 (Not Found)</a> ought to be used instead.<a class="self" href="#rfc.section.6.5.9.p.1">&para;</a></p></div><div id="rfc.section.6.5.9.p.2"><p>The 410 response is primarily intended to assist the task of web maintenance by notifying the recipient that the resource is intentionally unavailable and that the server owners desire that remote links to that resource be removed. Such an event is common for limited-time, promotional services and for resources belonging to individuals no longer associated with the origin server's site. It is not necessary to mark all permanently unavailable resources as "gone" or to keep the mark for any length of time &#8212; that is left to the discretion of the server owner.<a class="self" href="#rfc.section.6.5.9.p.2">&para;</a></p></div><div id="rfc.section.6.5.9.p.3"><p>A 410 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.19"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.5.9.p.3">&para;</a></p></div></div><div id="status.411"><h3 id="rfc.section.6.5.10"><a href="#rfc.section.6.5.10">6.5.10</a>&nbsp;<a href="#status.411">411 Length Required</a></h3><div id="rfc.section.6.5.10.p.1"><p>The <dfn>411 (Length Required)</dfn> status code indicates that the server refuses to accept the request without a defined <a href="rfc7230.html#header.content-length" class="smpl">Content-Length</a> (<a href="rfc7230.html#header.content-length" title="Content-Length">Section 3.3.2</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.27"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>). The client <em class="bcp14">MAY</em> repeat the request if it adds a valid Content-Length header field containing the length of the message body in the request message.<a class="self" href="#rfc.section.6.5.10.p.1">&para;</a></p></div></div><div id="status.413"><h3 id="rfc.section.6.5.11"><a href="#rfc.section.6.5.11">6.5.11</a>&nbsp;<a href="#status.413">413 Payload Too Large</a></h3><div id="rfc.section.6.5.11.p.1"><p>The <dfn>413 (Payload Too Large)</dfn> status code indicates that the server is refusing to process a request because the request payload is larger than the server is willing or able to process. The server <em class="bcp14">MAY</em> close the connection to prevent the client from continuing the request.<a class="self" href="#rfc.section.6.5.11.p.1">&para;</a></p></div><div id="rfc.section.6.5.11.p.2"><p>If the condition is temporary, the server <em class="bcp14">SHOULD</em> generate a <a href="#header.retry-after" class="smpl">Retry-After</a> header field to indicate that it is temporary and after what time the client <em class="bcp14">MAY</em> try again.<a class="self" href="#rfc.section.6.5.11.p.2">&para;</a></p></div></div><div id="status.414"><h3 id="rfc.section.6.5.12"><a href="#rfc.section.6.5.12">6.5.12</a>&nbsp;<a href="#status.414">414 URI Too Long</a></h3><div id="rfc.section.6.5.12.p.1"><p>The <dfn>414 (URI Too Long)</dfn> status code indicates that the server is refusing to service the request because the request-target (<a href="rfc7230.html#request-target" title="Request Target">Section 5.3</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.28"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>) is longer than the server is willing to interpret. This rare condition is only likely to occur when a client has improperly converted a POST request to a GET request with long query information, when the client has descended into a "black hole" of redirection (e.g., a redirected URI prefix that points to a suffix of itself) or when the server is under attack by a client attempting to exploit potential security holes.<a class="self" href="#rfc.section.6.5.12.p.1">&para;</a></p></div><div id="rfc.section.6.5.12.p.2"><p>A 414 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.20"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.5.12.p.2">&para;</a></p></div></div><div id="status.415"><h3 id="rfc.section.6.5.13"><a href="#rfc.section.6.5.13">6.5.13</a>&nbsp;<a href="#status.415">415 Unsupported Media Type</a></h3><div id="rfc.section.6.5.13.p.1"><p>The <dfn>415 (Unsupported Media Type)</dfn> status code indicates that the origin server is refusing to service the request because the payload is in a format not supported by this method on the <a href="#resources" class="smpl">target resource</a>. The format problem might be due to the request's indicated <a href="#header.content-type" class="smpl">Content-Type</a> or <a href="#header.content-encoding" class="smpl">Content-Encoding</a>, or as a result of inspecting the data directly.<a class="self" href="#rfc.section.6.5.13.p.1">&para;</a></p></div></div><div id="status.417"><h3 id="rfc.section.6.5.14"><a href="#rfc.section.6.5.14">6.5.14</a>&nbsp;<a href="#status.417">417 Expectation Failed</a></h3><div id="rfc.section.6.5.14.p.1"><p>The <dfn>417 (Expectation Failed)</dfn> status code indicates that the expectation given in the request's <a href="#header.expect" class="smpl">Expect</a> header field (<a href="#header.expect" id="rfc.xref.header.expect.3" title="Expect">Section&nbsp;5.1.1</a>) could not be met by at least one of the inbound servers.<a class="self" href="#rfc.section.6.5.14.p.1">&para;</a></p></div></div><div id="status.426"><h3 id="rfc.section.6.5.15"><a href="#rfc.section.6.5.15">6.5.15</a>&nbsp;<a href="#status.426">426 Upgrade Required</a></h3><div id="rfc.section.6.5.15.p.1"><p>The <dfn>426 (Upgrade Required)</dfn> status code indicates that the server refuses to perform the request using the current protocol but might be willing to do so after the client upgrades to a different protocol. The server <em class="bcp14">MUST</em> send an <a href="rfc7230.html#header.upgrade" class="smpl">Upgrade</a> header field in a 426 response to indicate the required protocol(s) (<a href="rfc7230.html#header.upgrade" title="Upgrade">Section 6.7</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.29"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>).<a class="self" href="#rfc.section.6.5.15.p.1">&para;</a></p></div><div id="rfc.figure.u.42"><p>Example:</p><pre class="text">HTTP/1.1 426 Upgrade Required
     604</pre></div><div id="rfc.section.5.5.3.p.5"><p>A user agent <em class="bcp14">SHOULD NOT</em> generate a User-Agent field containing needlessly fine-grained detail and <em class="bcp14">SHOULD</em> limit the addition of subproducts by third parties. Overly long and detailed User-Agent field values increase request latency and the risk of a user being identified against their wishes ("fingerprinting").<a class="self" href="#rfc.section.5.5.3.p.5">&para;</a></p></div><div id="rfc.section.5.5.3.p.6"><p>Likewise, implementations are encouraged not to use the product tokens of other implementations in order to declare compatibility with them, as this circumvents the purpose of the field. If a user agent masquerades as a different user agent, recipients can assume that the user intentionally desires to see responses tailored for that identified user agent, even if they might not work as well for the actual user agent being used.<a class="self" href="#rfc.section.5.5.3.p.6">&para;</a></p></div></div></div></div><div id="status.codes"><h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a>&nbsp;<a href="#status.codes">Response Status Codes</a></h1><div id="rfc.section.6.p.1"><p>The status-code element is a three-digit integer code giving the result of the attempt to understand and satisfy the request.<a class="self" href="#rfc.section.6.p.1">&para;</a></p></div><div id="rfc.section.6.p.2"><p>HTTP status codes are extensible. HTTP clients are not required to understand the meaning of all registered status codes, though such understanding is obviously desirable. However, a client <em class="bcp14">MUST</em> understand the class of any status code, as indicated by the first digit, and treat an unrecognized status code as being equivalent to the x00 status code of that class, with the exception that a recipient <em class="bcp14">MUST NOT</em> cache a response with an unrecognized status code.<a class="self" href="#rfc.section.6.p.2">&para;</a></p></div><div id="rfc.section.6.p.3"><p>For example, if an unrecognized status code of 471 is received by a client, the client can assume that there was something wrong with its request and treat the response as if it had received a <a href="#status.400" class="smpl">400 (Bad Request)</a> status code. The response message will usually contain a representation that explains the status.<a class="self" href="#rfc.section.6.p.3">&para;</a></p></div><div id="rfc.section.6.p.4"><p>The first digit of the status-code defines the class of response. The last two digits do not have any categorization role. There are five values for the first digit: <a class="self" href="#rfc.section.6.p.4">&para;</a></p><ul><li><a href="#status.1xx" class="smpl">1xx (Informational)</a>: The request was received, continuing process</li><li><a href="#status.2xx" class="smpl">2xx (Successful)</a>: The request was successfully received, understood, and accepted</li><li><a href="#status.3xx" class="smpl">3xx (Redirection)</a>: Further action needs to be taken in order to complete the request</li><li><a href="#status.4xx" class="smpl">4xx (Client Error)</a>: The request contains bad syntax or cannot be fulfilled</li><li><a href="#status.5xx" class="smpl">5xx (Server Error)</a>: The server failed to fulfill an apparently valid request</li></ul></div><div id="overview.of.status.codes"><h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a>&nbsp;<a href="#overview.of.status.codes">Overview of Status Codes</a></h2><div id="rfc.section.6.1.p.1"><p>The status codes listed below are defined in this specification, <a href="rfc7232.html#status.code.definitions" title="Status Code Definitions">Section 4</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.9"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a>, <a href="rfc7233.html#range.response" title="Responses to a Range Request">Section 4</a> of <a href="#RFC7233" id="rfc.xref.RFC7233.7"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a>, and <a href="rfc7235.html#status.code.definitions" title="Status Code Definitions">Section 3</a> of <a href="#RFC7235" id="rfc.xref.RFC7235.5"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a>. The reason phrases listed here are only recommendations &#8212; they can be replaced by local equivalents without affecting the protocol.<a class="self" href="#rfc.section.6.1.p.1">&para;</a></p></div><div id="rfc.section.6.1.p.2"><p>Responses with status codes that are defined as cacheable by default (e.g., 200, 203, 204, 206, 300, 301, 404, 405, 410, 414, and 501 in this specification) can be reused by a cache with heuristic expiration unless otherwise indicated by the method definition or explicit cache controls <a href="#RFC7234" id="rfc.xref.RFC7234.10"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>; all other status codes are not cacheable by default.<a class="self" href="#rfc.section.6.1.p.2">&para;</a></p></div><div id="rfc.table.u.9"><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Code</th><th>Reason-Phrase</th><th>Defined in...</th></tr></thead><tbody><tr><td class="left">100</td><td class="left">Continue</td><td class="left"><a href="#status.100" id="rfc.xref.status.100.1" title="100 Continue">Section&nbsp;6.2.1</a></td></tr><tr><td class="left">101</td><td class="left">Switching Protocols</td><td class="left"><a href="#status.101" id="rfc.xref.status.101.1" title="101 Switching Protocols">Section&nbsp;6.2.2</a></td></tr><tr><td class="left">200</td><td class="left">OK</td><td class="left"><a href="#status.200" id="rfc.xref.status.200.1" title="200 OK">Section&nbsp;6.3.1</a></td></tr><tr><td class="left">201</td><td class="left">Created</td><td class="left"><a href="#status.201" id="rfc.xref.status.201.1" title="201 Created">Section&nbsp;6.3.2</a></td></tr><tr><td class="left">202</td><td class="left">Accepted</td><td class="left"><a href="#status.202" id="rfc.xref.status.202.1" title="202 Accepted">Section&nbsp;6.3.3</a></td></tr><tr><td class="left">203</td><td class="left">Non-Authoritative Information</td><td class="left"><a href="#status.203" id="rfc.xref.status.203.1" title="203 Non-Authoritative Information">Section&nbsp;6.3.4</a></td></tr><tr><td class="left">204</td><td class="left">No Content</td><td class="left"><a href="#status.204" id="rfc.xref.status.204.1" title="204 No Content">Section&nbsp;6.3.5</a></td></tr><tr><td class="left">205</td><td class="left">Reset Content</td><td class="left"><a href="#status.205" id="rfc.xref.status.205.1" title="205 Reset Content">Section&nbsp;6.3.6</a></td></tr><tr><td class="left">206</td><td class="left">Partial Content</td><td id="status.206" class="left"><a href="rfc7233.html#status.206" title="206 Partial Content">Section 4.1</a> of <a href="#RFC7233" id="rfc.xref.RFC7233.8"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a></td></tr><tr><td class="left">300</td><td class="left">Multiple Choices</td><td class="left"><a href="#status.300" id="rfc.xref.status.300.1" title="300 Multiple Choices">Section&nbsp;6.4.1</a></td></tr><tr><td class="left">301</td><td class="left">Moved Permanently</td><td class="left"><a href="#status.301" id="rfc.xref.status.301.1" title="301 Moved Permanently">Section&nbsp;6.4.2</a></td></tr><tr><td class="left">302</td><td class="left">Found</td><td class="left"><a href="#status.302" id="rfc.xref.status.302.1" title="302 Found">Section&nbsp;6.4.3</a></td></tr><tr><td class="left">303</td><td class="left">See Other</td><td class="left"><a href="#status.303" id="rfc.xref.status.303.1" title="303 See Other">Section&nbsp;6.4.4</a></td></tr><tr><td class="left">304</td><td class="left">Not Modified</td><td id="status.304" class="left"><a href="rfc7232.html#status.304" title="304 Not Modified">Section 4.1</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.10"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a></td></tr><tr><td class="left">305</td><td class="left">Use Proxy</td><td class="left"><a href="#status.305" id="rfc.xref.status.305.1" title="305 Use Proxy">Section&nbsp;6.4.5</a></td></tr><tr><td class="left">307</td><td class="left">Temporary Redirect</td><td class="left"><a href="#status.307" id="rfc.xref.status.307.1" title="307 Temporary Redirect">Section&nbsp;6.4.7</a></td></tr><tr><td class="left">400</td><td class="left">Bad Request</td><td class="left"><a href="#status.400" id="rfc.xref.status.400.1" title="400 Bad Request">Section&nbsp;6.5.1</a></td></tr><tr><td class="left">401</td><td class="left">Unauthorized</td><td id="status.401" class="left"><a href="rfc7235.html#status.401" title="401 Unauthorized">Section 3.1</a> of <a href="#RFC7235" id="rfc.xref.RFC7235.6"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a></td></tr><tr><td class="left">402</td><td class="left">Payment Required</td><td class="left"><a href="#status.402" id="rfc.xref.status.402.1" title="402 Payment Required">Section&nbsp;6.5.2</a></td></tr><tr><td class="left">403</td><td class="left">Forbidden</td><td class="left"><a href="#status.403" id="rfc.xref.status.403.1" title="403 Forbidden">Section&nbsp;6.5.3</a></td></tr><tr><td class="left">404</td><td class="left">Not Found</td><td class="left"><a href="#status.404" id="rfc.xref.status.404.1" title="404 Not Found">Section&nbsp;6.5.4</a></td></tr><tr><td class="left">405</td><td class="left">Method Not Allowed</td><td class="left"><a href="#status.405" id="rfc.xref.status.405.1" title="405 Method Not Allowed">Section&nbsp;6.5.5</a></td></tr><tr><td class="left">406</td><td class="left">Not Acceptable</td><td class="left"><a href="#status.406" id="rfc.xref.status.406.1" title="406 Not Acceptable">Section&nbsp;6.5.6</a></td></tr><tr><td class="left">407</td><td class="left">Proxy Authentication Required</td><td id="status.407" class="left"><a href="rfc7235.html#status.407" title="407 Proxy Authentication Required">Section 3.2</a> of <a href="#RFC7235" id="rfc.xref.RFC7235.7"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[RFC7235]</cite></a></td></tr><tr><td class="left">408</td><td class="left">Request Timeout</td><td class="left"><a href="#status.408" id="rfc.xref.status.408.1" title="408 Request Timeout">Section&nbsp;6.5.7</a></td></tr><tr><td class="left">409</td><td class="left">Conflict</td><td class="left"><a href="#status.409" id="rfc.xref.status.409.1" title="409 Conflict">Section&nbsp;6.5.8</a></td></tr><tr><td class="left">410</td><td class="left">Gone</td><td class="left"><a href="#status.410" id="rfc.xref.status.410.1" title="410 Gone">Section&nbsp;6.5.9</a></td></tr><tr><td class="left">411</td><td class="left">Length Required</td><td class="left"><a href="#status.411" id="rfc.xref.status.411.1" title="411 Length Required">Section&nbsp;6.5.10</a></td></tr><tr><td class="left">412</td><td class="left">Precondition Failed</td><td id="status.412" class="left"><a href="rfc7232.html#status.412" title="412 Precondition Failed">Section 4.2</a> of <a href="#RFC7232" id="rfc.xref.RFC7232.11"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests">[RFC7232]</cite></a></td></tr><tr><td class="left">413</td><td class="left">Payload Too Large</td><td class="left"><a href="#status.413" id="rfc.xref.status.413.1" title="413 Payload Too Large">Section&nbsp;6.5.11</a></td></tr><tr><td class="left">414</td><td class="left">URI Too Long</td><td class="left"><a href="#status.414" id="rfc.xref.status.414.1" title="414 URI Too Long">Section&nbsp;6.5.12</a></td></tr><tr><td class="left">415</td><td class="left">Unsupported Media Type</td><td class="left"><a href="#status.415" id="rfc.xref.status.415.1" title="415 Unsupported Media Type">Section&nbsp;6.5.13</a></td></tr><tr><td class="left">416</td><td class="left">Range Not Satisfiable</td><td id="status.416" class="left"><a href="rfc7233.html#status.416" title="416 Range Not Satisfiable">Section 4.4</a> of <a href="#RFC7233" id="rfc.xref.RFC7233.9"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a></td></tr><tr><td class="left">417</td><td class="left">Expectation Failed</td><td class="left"><a href="#status.417" id="rfc.xref.status.417.1" title="417 Expectation Failed">Section&nbsp;6.5.14</a></td></tr><tr><td class="left">426</td><td class="left">Upgrade Required</td><td class="left"><a href="#status.426" id="rfc.xref.status.426.1" title="426 Upgrade Required">Section&nbsp;6.5.15</a></td></tr><tr><td class="left">500</td><td class="left">Internal Server Error</td><td class="left"><a href="#status.500" id="rfc.xref.status.500.1" title="500 Internal Server Error">Section&nbsp;6.6.1</a></td></tr><tr><td class="left">501</td><td class="left">Not Implemented</td><td class="left"><a href="#status.501" id="rfc.xref.status.501.1" title="501 Not Implemented">Section&nbsp;6.6.2</a></td></tr><tr><td class="left">502</td><td class="left">Bad Gateway</td><td class="left"><a href="#status.502" id="rfc.xref.status.502.1" title="502 Bad Gateway">Section&nbsp;6.6.3</a></td></tr><tr><td class="left">503</td><td class="left">Service Unavailable</td><td class="left"><a href="#status.503" id="rfc.xref.status.503.1" title="503 Service Unavailable">Section&nbsp;6.6.4</a></td></tr><tr><td class="left">504</td><td class="left">Gateway Timeout</td><td class="left"><a href="#status.504" id="rfc.xref.status.504.1" title="504 Gateway Timeout">Section&nbsp;6.6.5</a></td></tr><tr><td class="left">505</td><td class="left">HTTP Version Not Supported</td><td class="left"><a href="#status.505" id="rfc.xref.status.505.1" title="505 HTTP Version Not Supported">Section&nbsp;6.6.6</a></td></tr></tbody></table></div><div id="rfc.section.6.1.p.3"><p>Note that this list is not exhaustive &#8212; it does not include extension status codes defined in other specifications. The complete list of status codes is maintained by IANA. See <a href="#status.code.registry" title="Status Code Registry">Section&nbsp;8.2</a> for details.<a class="self" href="#rfc.section.6.1.p.3">&para;</a></p></div></div><div id="status.1xx"><h2 id="rfc.section.6.2"><a href="#rfc.section.6.2">6.2</a>&nbsp;<a href="#status.1xx">Informational 1xx</a></h2><div id="rfc.section.6.2.p.1"><p>The <dfn>1xx (Informational)</dfn> class of status code indicates an interim response for communicating connection status or request progress prior to completing the requested action and sending a final response. 1xx responses are terminated by the first empty line after the status-line (the empty line signaling the end of the header section). Since HTTP/1.0 did not define any 1xx status codes, a server <em class="bcp14">MUST NOT</em> send a 1xx response to an HTTP/1.0 client.<a class="self" href="#rfc.section.6.2.p.1">&para;</a></p></div><div id="rfc.section.6.2.p.2"><p>A client <em class="bcp14">MUST</em> be able to parse one or more 1xx responses received prior to a final response, even if the client does not expect one. A user agent <em class="bcp14">MAY</em> ignore unexpected 1xx responses.<a class="self" href="#rfc.section.6.2.p.2">&para;</a></p></div><div id="rfc.section.6.2.p.3"><p>A proxy <em class="bcp14">MUST</em> forward 1xx responses unless the proxy itself requested the generation of the 1xx response. For example, if a proxy adds an "Expect: 100-continue" field when it forwards a request, then it need not forward the corresponding <a href="#status.100" class="smpl">100 (Continue)</a> response(s).<a class="self" href="#rfc.section.6.2.p.3">&para;</a></p></div><div id="status.100"><h3 id="rfc.section.6.2.1"><a href="#rfc.section.6.2.1">6.2.1</a>&nbsp;<a href="#status.100">100 Continue</a></h3><div id="rfc.section.6.2.1.p.1"><p>The <dfn>100 (Continue)</dfn> status code indicates that the initial part of a request has been received and has not yet been rejected by the server. The server intends to send a final response after the request has been fully received and acted upon.<a class="self" href="#rfc.section.6.2.1.p.1">&para;</a></p></div><div id="rfc.section.6.2.1.p.2"><p>When the request contains an <a href="#header.expect" class="smpl">Expect</a> header field that includes a <a href="#header.expect" class="smpl">100-continue</a> expectation, the 100 response indicates that the server wishes to receive the request payload body, as described in <a href="#header.expect" id="rfc.xref.header.expect.2" title="Expect">Section&nbsp;5.1.1</a>. The client ought to continue sending the request and discard the 100 response.<a class="self" href="#rfc.section.6.2.1.p.2">&para;</a></p></div><div id="rfc.section.6.2.1.p.3"><p>If the request did not contain an <a href="#header.expect" class="smpl">Expect</a> header field containing the <a href="#header.expect" class="smpl">100-continue</a> expectation, the client can simply discard this interim response.<a class="self" href="#rfc.section.6.2.1.p.3">&para;</a></p></div></div><div id="status.101"><h3 id="rfc.section.6.2.2"><a href="#rfc.section.6.2.2">6.2.2</a>&nbsp;<a href="#status.101">101 Switching Protocols</a></h3><div id="rfc.section.6.2.2.p.1"><p>The <dfn>101 (Switching Protocols)</dfn> status code indicates that the server understands and is willing to comply with the client's request, via the <a href="rfc7230.html#header.upgrade" class="smpl">Upgrade</a> header field (<a href="rfc7230.html#header.upgrade" title="Upgrade">Section 6.7</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.24"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>), for a change in the application protocol being used on this connection. The server <em class="bcp14">MUST</em> generate an Upgrade header field in the response that indicates which protocol(s) will be switched to immediately after the empty line that terminates the 101 response.<a class="self" href="#rfc.section.6.2.2.p.1">&para;</a></p></div><div id="rfc.section.6.2.2.p.2"><p>It is assumed that the server will only agree to switch protocols when it is advantageous to do so. For example, switching to a newer version of HTTP might be advantageous over older versions, and switching to a real-time, synchronous protocol might be advantageous when delivering resources that use such features.<a class="self" href="#rfc.section.6.2.2.p.2">&para;</a></p></div></div></div><div id="status.2xx"><h2 id="rfc.section.6.3"><a href="#rfc.section.6.3">6.3</a>&nbsp;<a href="#status.2xx">Successful 2xx</a></h2><div id="rfc.section.6.3.p.1"><p>The <dfn>2xx (Successful)</dfn> class of status code indicates that the client's request was successfully received, understood, and accepted.<a class="self" href="#rfc.section.6.3.p.1">&para;</a></p></div><div id="status.200"><h3 id="rfc.section.6.3.1"><a href="#rfc.section.6.3.1">6.3.1</a>&nbsp;<a href="#status.200">200 OK</a></h3><div id="rfc.section.6.3.1.p.1"><p>The <dfn>200 (OK)</dfn> status code indicates that the request has succeeded. The payload sent in a 200 response depends on the request method. For the methods defined by this specification, the intended meaning of the payload can be summarized as: <a class="self" href="#rfc.section.6.3.1.p.1">&para;</a></p><dl><dt>GET</dt><dd>a representation of the <a href="#resources" class="smpl">target resource</a>;</dd><dt>HEAD</dt><dd>the same representation as GET, but without the representation data;</dd><dt>POST</dt><dd>a representation of the status of, or results obtained from, the action;</dd><dt>PUT, DELETE</dt><dd>a representation of the status of the action;</dd><dt>OPTIONS</dt><dd>a representation of the communications options;</dd><dt>TRACE</dt><dd>a representation of the request message as received by the end server.</dd></dl></div><div id="rfc.section.6.3.1.p.2"><p>Aside from responses to CONNECT, a 200 response always has a payload, though an origin server <em class="bcp14">MAY</em> generate a payload body of zero length. If no payload is desired, an origin server ought to send <dfn>204 (No Content)</dfn> instead. For CONNECT, no payload is allowed because the successful result is a tunnel, which begins immediately after the 200 response header section.<a class="self" href="#rfc.section.6.3.1.p.2">&para;</a></p></div><div id="rfc.section.6.3.1.p.3"><p>A 200 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.11"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.3.1.p.3">&para;</a></p></div></div><div id="status.201"><h3 id="rfc.section.6.3.2"><a href="#rfc.section.6.3.2">6.3.2</a>&nbsp;<a href="#status.201">201 Created</a></h3><div id="rfc.section.6.3.2.p.1"><p>The <dfn>201 (Created)</dfn> status code indicates that the request has been fulfilled and has resulted in one or more new resources being created. The primary resource created by the request is identified by either a <a href="#header.location" class="smpl">Location</a> header field in the response or, if no <a href="#header.location" class="smpl">Location</a> field is received, by the effective request URI.<a class="self" href="#rfc.section.6.3.2.p.1">&para;</a></p></div><div id="rfc.section.6.3.2.p.2"><p>The 201 response payload typically describes and links to the resource(s) created. See <a href="#response.validator" title="Validator Header Fields">Section&nbsp;7.2</a> for a discussion of the meaning and purpose of validator header fields, such as <a href="rfc7232.html#header.etag" class="smpl">ETag</a> and <a href="rfc7232.html#header.last-modified" class="smpl">Last-Modified</a>, in a 201 response.<a class="self" href="#rfc.section.6.3.2.p.2">&para;</a></p></div></div><div id="status.202"><h3 id="rfc.section.6.3.3"><a href="#rfc.section.6.3.3">6.3.3</a>&nbsp;<a href="#status.202">202 Accepted</a></h3><div id="rfc.section.6.3.3.p.1"><p>The <dfn>202 (Accepted)</dfn> status code indicates that the request has been accepted for processing, but the processing has not been completed. The request might or might not eventually be acted upon, as it might be disallowed when processing actually takes place. There is no facility in HTTP for re-sending a status code from an asynchronous operation.<a class="self" href="#rfc.section.6.3.3.p.1">&para;</a></p></div><div id="rfc.section.6.3.3.p.2"><p>The 202 response is intentionally noncommittal. Its purpose is to allow a server to accept a request for some other process (perhaps a batch-oriented process that is only run once per day) without requiring that the user agent's connection to the server persist until the process is completed. The representation sent with this response ought to describe the request's current status and point to (or embed) a status monitor that can provide the user with an estimate of when the request will be fulfilled.<a class="self" href="#rfc.section.6.3.3.p.2">&para;</a></p></div></div><div id="status.203"><h3 id="rfc.section.6.3.4"><a href="#rfc.section.6.3.4">6.3.4</a>&nbsp;<a href="#status.203">203 Non-Authoritative Information</a></h3><div id="rfc.section.6.3.4.p.1"><p>The <dfn>203 (Non-Authoritative Information)</dfn> status code indicates that the request was successful but the enclosed payload has been modified from that of the origin server's <a href="#status.200" class="smpl">200 (OK)</a> response by a transforming proxy (<a href="rfc7230.html#message.transformations" title="Transformations">Section 5.7.2</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.25"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>). This status code allows the proxy to notify recipients when a transformation has been applied, since that knowledge might impact later decisions regarding the content. For example, future cache validation requests for the content might only be applicable along the same request path (through the same proxies).<a class="self" href="#rfc.section.6.3.4.p.1">&para;</a></p></div><div id="rfc.section.6.3.4.p.2"><p>The 203 response is similar to the Warning code of 214 Transformation Applied (<a href="rfc7234.html#header.warning" title="Warning">Section 5.5</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.12"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>), which has the advantage of being applicable to responses with any status code.<a class="self" href="#rfc.section.6.3.4.p.2">&para;</a></p></div><div id="rfc.section.6.3.4.p.3"><p>A 203 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.13"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.3.4.p.3">&para;</a></p></div></div><div id="status.204"><h3 id="rfc.section.6.3.5"><a href="#rfc.section.6.3.5">6.3.5</a>&nbsp;<a href="#status.204">204 No Content</a></h3><div id="rfc.section.6.3.5.p.1"><p>The <dfn>204 (No Content)</dfn> status code indicates that the server has successfully fulfilled the request and that there is no additional content to send in the response payload body. Metadata in the response header fields refer to the <a href="#resources" class="smpl">target resource</a> and its <a href="#representations" class="smpl">selected representation</a> after the requested action was applied.<a class="self" href="#rfc.section.6.3.5.p.1">&para;</a></p></div><div id="rfc.section.6.3.5.p.2"><p>For example, if a 204 status code is received in response to a PUT request and the response contains an <a href="rfc7232.html#header.etag" class="smpl">ETag</a> header field, then the PUT was successful and the ETag field-value contains the entity-tag for the new representation of that target resource.<a class="self" href="#rfc.section.6.3.5.p.2">&para;</a></p></div><div id="rfc.section.6.3.5.p.3"><p>The 204 response allows a server to indicate that the action has been successfully applied to the target resource, while implying that the user agent does not need to traverse away from its current "document view" (if any). The server assumes that the user agent will provide some indication of the success to its user, in accord with its own interface, and apply any new or updated metadata in the response to its active representation.<a class="self" href="#rfc.section.6.3.5.p.3">&para;</a></p></div><div id="rfc.section.6.3.5.p.4"><p>For example, a 204 status code is commonly used with document editing interfaces corresponding to a "save" action, such that the document being saved remains available to the user for editing. It is also frequently used with interfaces that expect automated data transfers to be prevalent, such as within distributed version control systems.<a class="self" href="#rfc.section.6.3.5.p.4">&para;</a></p></div><div id="rfc.section.6.3.5.p.5"><p>A 204 response is terminated by the first empty line after the header fields because it cannot contain a message body.<a class="self" href="#rfc.section.6.3.5.p.5">&para;</a></p></div><div id="rfc.section.6.3.5.p.6"><p>A 204 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.14"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.3.5.p.6">&para;</a></p></div></div><div id="status.205"><h3 id="rfc.section.6.3.6"><a href="#rfc.section.6.3.6">6.3.6</a>&nbsp;<a href="#status.205">205 Reset Content</a></h3><div id="rfc.section.6.3.6.p.1"><p>The <dfn>205 (Reset Content)</dfn> status code indicates that the server has fulfilled the request and desires that the user agent reset the "document view", which caused the request to be sent, to its original state as received from the origin server.<a class="self" href="#rfc.section.6.3.6.p.1">&para;</a></p></div><div id="rfc.section.6.3.6.p.2"><p>This response is intended to support a common data entry use case where the user receives content that supports data entry (a form, notepad, canvas, etc.), enters or manipulates data in that space, causes the entered data to be submitted in a request, and then the data entry mechanism is reset for the next entry so that the user can easily initiate another input action.<a class="self" href="#rfc.section.6.3.6.p.2">&para;</a></p></div><div id="rfc.section.6.3.6.p.3"><p>Since the 205 status code implies that no additional content will be provided, a server <em class="bcp14">MUST NOT</em> generate a payload in a 205 response. In other words, a server <em class="bcp14">MUST</em> do one of the following for a 205 response: a) indicate a zero-length body for the response by including a <a href="rfc7230.html#header.content-length" class="smpl">Content-Length</a> header field with a value of 0; b) indicate a zero-length payload for the response by including a <a href="rfc7230.html#header.transfer-encoding" class="smpl">Transfer-Encoding</a> header field with a value of chunked and a message body consisting of a single chunk of zero-length; or, c) close the connection immediately after sending the blank line terminating the header section.<a class="self" href="#rfc.section.6.3.6.p.3">&para;</a></p></div></div></div><div id="status.3xx"><h2 id="rfc.section.6.4"><a href="#rfc.section.6.4">6.4</a>&nbsp;<a href="#status.3xx">Redirection 3xx</a></h2><div id="rfc.section.6.4.p.1"><p>The <dfn>3xx (Redirection)</dfn> class of status code indicates that further action needs to be taken by the user agent in order to fulfill the request. If a <a href="#header.location" class="smpl">Location</a> header field (<a href="#header.location" id="rfc.xref.header.location.2" title="Location">Section&nbsp;7.1.2</a>) is provided, the user agent <em class="bcp14">MAY</em> automatically redirect its request to the URI referenced by the Location field value, even if the specific status code is not understood. Automatic redirection needs to done with care for methods not known to be <a href="#safe.methods" class="smpl">safe</a>, as defined in <a href="#safe.methods" title="Safe Methods">Section&nbsp;4.2.1</a>, since the user might not wish to redirect an unsafe request.<a class="self" href="#rfc.section.6.4.p.1">&para;</a></p></div><div id="rfc.section.6.4.p.2"><p>There are several types of redirects: <a class="self" href="#rfc.section.6.4.p.2">&para;</a></p><ol><li><p>Redirects that indicate the resource might be available at a different URI, as provided by the <a href="#header.location" class="smpl">Location</a> field, as in the status codes <a href="#status.301" class="smpl">301 (Moved Permanently)</a>, <a href="#status.302" class="smpl">302 (Found)</a>, and <a href="#status.307" class="smpl">307 (Temporary Redirect)</a>.</p></li><li><p>Redirection that offers a choice of matching resources, each capable of representing the original request target, as in the <a href="#status.300" class="smpl">300 (Multiple Choices)</a> status code.</p></li><li><p>Redirection to a different resource, identified by the <a href="#header.location" class="smpl">Location</a> field, that can represent an indirect response to the request, as in the <a href="#status.303" class="smpl">303 (See Other)</a> status code.</p></li><li><p>Redirection to a previously cached result, as in the <a href="rfc7232.html#status.304" class="smpl">304 (Not Modified)</a> status code.</p></li></ol></div><div class="note"><div id="rfc.section.6.4.p.3"><p><b>Note:</b> In HTTP/1.0, the status codes <a href="#status.301" class="smpl">301 (Moved Permanently)</a> and <a href="#status.302" class="smpl">302 (Found)</a> were defined for the first type of redirect (<a href="#RFC1945" id="rfc.xref.RFC1945.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.0">[RFC1945]</cite></a>, <a href="https://tools.ietf.org/html/rfc1945#section-9.3">Section 9.3</a>). Early user agents split on whether the method applied to the redirect target would be the same as the original request or would be rewritten as GET. Although HTTP originally defined the former semantics for <a href="#status.301" class="smpl">301</a> and <a href="#status.302" class="smpl">302</a> (to match its original implementation at CERN), and defined <a href="#status.303" class="smpl">303 (See Other)</a> to match the latter semantics, prevailing practice gradually converged on the latter semantics for <a href="#status.301" class="smpl">301</a> and <a href="#status.302" class="smpl">302</a> as well. The first revision of HTTP/1.1 added <a href="#status.307" class="smpl">307 (Temporary Redirect)</a> to indicate the former semantics without being impacted by divergent practice. Over 10 years later, most user agents still do method rewriting for <a href="#status.301" class="smpl">301</a> and <a href="#status.302" class="smpl">302</a>; therefore, this specification makes that behavior conformant when the original request is POST.<a class="self" href="#rfc.section.6.4.p.3">&para;</a></p></div></div><div id="rfc.section.6.4.p.4"><p>A client <em class="bcp14">SHOULD</em> detect and intervene in cyclical redirections (i.e., "infinite" redirection loops).<a class="self" href="#rfc.section.6.4.p.4">&para;</a></p></div><div class="note"><div id="rfc.section.6.4.p.5"><p><b>Note:</b> An earlier version of this specification recommended a maximum of five redirections (<a href="#RFC2068" id="rfc.xref.RFC2068.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, <a href="https://tools.ietf.org/html/rfc2068#section-10.3">Section 10.3</a>). Content developers need to be aware that some clients might implement such a fixed limitation.<a class="self" href="#rfc.section.6.4.p.5">&para;</a></p></div></div><div id="status.300"><h3 id="rfc.section.6.4.1"><a href="#rfc.section.6.4.1">6.4.1</a>&nbsp;<a href="#status.300">300 Multiple Choices</a></h3><div id="rfc.section.6.4.1.p.1"><p>The <dfn>300 (Multiple Choices)</dfn> status code indicates that the <a href="#resources" class="smpl">target resource</a> has more than one representation, each with its own more specific identifier, and information about the alternatives is being provided so that the user (or user agent) can select a preferred representation by redirecting its request to one or more of those identifiers. In other words, the server desires that the user agent engage in reactive negotiation to select the most appropriate representation(s) for its needs (<a href="#content.negotiation" title="Content Negotiation">Section&nbsp;3.4</a>).<a class="self" href="#rfc.section.6.4.1.p.1">&para;</a></p></div><div id="rfc.section.6.4.1.p.2"><p>If the server has a preferred choice, the server <em class="bcp14">SHOULD</em> generate a <a href="#header.location" class="smpl">Location</a> header field containing a preferred choice's URI reference. The user agent <em class="bcp14">MAY</em> use the Location field value for automatic redirection.<a class="self" href="#rfc.section.6.4.1.p.2">&para;</a></p></div><div id="rfc.section.6.4.1.p.3"><p>For request methods other than HEAD, the server <em class="bcp14">SHOULD</em> generate a payload in the 300 response containing a list of representation metadata and URI reference(s) from which the user or user agent can choose the one most preferred. The user agent <em class="bcp14">MAY</em> make a selection from that list automatically if it understands the provided media type. A specific format for automatic selection is not defined by this specification because HTTP tries to remain orthogonal to the definition of its payloads. In practice, the representation is provided in some easily parsed format believed to be acceptable to the user agent, as determined by shared design or content negotiation, or in some commonly accepted hypertext format.<a class="self" href="#rfc.section.6.4.1.p.3">&para;</a></p></div><div id="rfc.section.6.4.1.p.4"><p>A 300 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.15"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.4.1.p.4">&para;</a></p></div><div class="note"><div id="rfc.section.6.4.1.p.5"><p><b>Note:</b> The original proposal for the 300 status code defined the URI header field as providing a list of alternative representations, such that it would be usable for 200, 300, and 406 responses and be transferred in responses to the HEAD method. However, lack of deployment and disagreement over syntax led to both URI and Alternates (a subsequent proposal) being dropped from this specification. It is possible to communicate the list using a set of Link header fields <a href="#RFC5988" id="rfc.xref.RFC5988.1"><cite title="Web Linking">[RFC5988]</cite></a>, each with a relationship of "alternate", though deployment is a chicken-and-egg problem.<a class="self" href="#rfc.section.6.4.1.p.5">&para;</a></p></div></div></div><div id="status.301"><h3 id="rfc.section.6.4.2"><a href="#rfc.section.6.4.2">6.4.2</a>&nbsp;<a href="#status.301">301 Moved Permanently</a></h3><div id="rfc.section.6.4.2.p.1"><p>The <dfn>301 (Moved Permanently)</dfn> status code indicates that the <a href="#resources" class="smpl">target resource</a> has been assigned a new permanent URI and any future references to this resource ought to use one of the enclosed URIs. Clients with link-editing capabilities ought to automatically re-link references to the effective request URI to one or more of the new references sent by the server, where possible.<a class="self" href="#rfc.section.6.4.2.p.1">&para;</a></p></div><div id="rfc.section.6.4.2.p.2"><p>The server <em class="bcp14">SHOULD</em> generate a <a href="#header.location" class="smpl">Location</a> header field in the response containing a preferred URI reference for the new permanent URI. The user agent <em class="bcp14">MAY</em> use the Location field value for automatic redirection. The server's response payload usually contains a short hypertext note with a hyperlink to the new URI(s).<a class="self" href="#rfc.section.6.4.2.p.2">&para;</a></p></div><div class="note"><div id="rfc.section.6.4.2.p.3"><p><b>Note:</b> For historical reasons, a user agent <em class="bcp14">MAY</em> change the request method from POST to GET for the subsequent request. If this behavior is undesired, the <a href="#status.307" class="smpl">307 (Temporary Redirect)</a> status code can be used instead.<a class="self" href="#rfc.section.6.4.2.p.3">&para;</a></p></div></div><div id="rfc.section.6.4.2.p.4"><p>A 301 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.16"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.4.2.p.4">&para;</a></p></div></div><div id="status.302"><h3 id="rfc.section.6.4.3"><a href="#rfc.section.6.4.3">6.4.3</a>&nbsp;<a href="#status.302">302 Found</a></h3><div id="rfc.section.6.4.3.p.1"><p>The <dfn>302 (Found)</dfn> status code indicates that the target resource resides temporarily under a different URI. Since the redirection might be altered on occasion, the client ought to continue to use the effective request URI for future requests.<a class="self" href="#rfc.section.6.4.3.p.1">&para;</a></p></div><div id="rfc.section.6.4.3.p.2"><p>The server <em class="bcp14">SHOULD</em> generate a <a href="#header.location" class="smpl">Location</a> header field in the response containing a URI reference for the different URI. The user agent <em class="bcp14">MAY</em> use the Location field value for automatic redirection. The server's response payload usually contains a short hypertext note with a hyperlink to the different URI(s).<a class="self" href="#rfc.section.6.4.3.p.2">&para;</a></p></div><div class="note"><div id="rfc.section.6.4.3.p.3"><p><b>Note:</b> For historical reasons, a user agent <em class="bcp14">MAY</em> change the request method from POST to GET for the subsequent request. If this behavior is undesired, the <a href="#status.307" class="smpl">307 (Temporary Redirect)</a> status code can be used instead.<a class="self" href="#rfc.section.6.4.3.p.3">&para;</a></p></div></div></div><div id="status.303"><h3 id="rfc.section.6.4.4"><a href="#rfc.section.6.4.4">6.4.4</a>&nbsp;<a href="#status.303">303 See Other</a></h3><div id="rfc.section.6.4.4.p.1"><p>The <dfn>303 (See Other)</dfn> status code indicates that the server is redirecting the user agent to a different resource, as indicated by a URI in the <a href="#header.location" class="smpl">Location</a> header field, which is intended to provide an indirect response to the original request. A user agent can perform a retrieval request targeting that URI (a GET or HEAD request if using HTTP), which might also be redirected, and present the eventual result as an answer to the original request. Note that the new URI in the Location header field is not considered equivalent to the effective request URI.<a class="self" href="#rfc.section.6.4.4.p.1">&para;</a></p></div><div id="rfc.section.6.4.4.p.2"><p>This status code is applicable to any HTTP method. It is primarily used to allow the output of a POST action to redirect the user agent to a selected resource, since doing so provides the information corresponding to the POST response in a form that can be separately identified, bookmarked, and cached, independent of the original request.<a class="self" href="#rfc.section.6.4.4.p.2">&para;</a></p></div><div id="rfc.section.6.4.4.p.3"><p>A 303 response to a GET request indicates that the origin server does not have a representation of the <a href="#resources" class="smpl">target resource</a> that can be transferred by the server over HTTP. However, the <a href="#header.location" class="smpl">Location</a> field value refers to a resource that is descriptive of the target resource, such that making a retrieval request on that other resource might result in a representation that is useful to recipients without implying that it represents the original target resource. Note that answers to the questions of what can be represented, what representations are adequate, and what might be a useful description are outside the scope of HTTP.<a class="self" href="#rfc.section.6.4.4.p.3">&para;</a></p></div><div id="rfc.section.6.4.4.p.4"><p>Except for responses to a HEAD request, the representation of a 303 response ought to contain a short hypertext note with a hyperlink to the same URI reference provided in the <a href="#header.location" class="smpl">Location</a> header field.<a class="self" href="#rfc.section.6.4.4.p.4">&para;</a></p></div></div><div id="status.305"><h3 id="rfc.section.6.4.5"><a href="#rfc.section.6.4.5">6.4.5</a>&nbsp;<a href="#status.305">305 Use Proxy</a></h3><div id="rfc.section.6.4.5.p.1"><p>The <dfn>305 (Use Proxy)</dfn> status code was defined in a previous version of this specification and is now deprecated (<a href="#changes.from.rfc.2616" title="Changes from RFC 2616">Appendix&nbsp;B</a>).<a class="self" href="#rfc.section.6.4.5.p.1">&para;</a></p></div></div><div id="status.306"><h3 id="rfc.section.6.4.6"><a href="#rfc.section.6.4.6">6.4.6</a>&nbsp;<a href="#status.306">306 (Unused)</a></h3><div id="rfc.section.6.4.6.p.1"><p>The 306 status code was defined in a previous version of this specification, is no longer used, and the code is reserved.<a class="self" href="#rfc.section.6.4.6.p.1">&para;</a></p></div></div><div id="status.307"><h3 id="rfc.section.6.4.7"><a href="#rfc.section.6.4.7">6.4.7</a>&nbsp;<a href="#status.307">307 Temporary Redirect</a></h3><div id="rfc.section.6.4.7.p.1"><p>The <dfn>307 (Temporary Redirect)</dfn> status code indicates that the <a href="#resources" class="smpl">target resource</a> resides temporarily under a different URI and the user agent <em class="bcp14">MUST NOT</em> change the request method if it performs an automatic redirection to that URI. Since the redirection can change over time, the client ought to continue using the original effective request URI for future requests.<a class="self" href="#rfc.section.6.4.7.p.1">&para;</a></p></div><div id="rfc.section.6.4.7.p.2"><p>The server <em class="bcp14">SHOULD</em> generate a <a href="#header.location" class="smpl">Location</a> header field in the response containing a URI reference for the different URI. The user agent <em class="bcp14">MAY</em> use the Location field value for automatic redirection. The server's response payload usually contains a short hypertext note with a hyperlink to the different URI(s).<a class="self" href="#rfc.section.6.4.7.p.2">&para;</a></p></div><div class="note"><div id="rfc.section.6.4.7.p.3"><p><b>Note:</b> This status code is similar to <a href="#status.302" class="smpl">302 (Found)</a>, except that it does not allow changing the request method from POST to GET. This specification defines no equivalent counterpart for <a href="#status.301" class="smpl">301 (Moved
     605    Permanently)</a> (<a href="#RFC7238" id="rfc.xref.RFC7238.1"><cite title="The Hypertext Transfer Protocol (HTTP) Status Code 308 (Permanent Redirect)">[RFC7238]</cite></a>, however, defines the status code 308 (Permanent Redirect) for this purpose).<a class="self" href="#rfc.section.6.4.7.p.3">&para;</a></p></div></div></div></div><div id="status.4xx"><h2 id="rfc.section.6.5"><a href="#rfc.section.6.5">6.5</a>&nbsp;<a href="#status.4xx">Client Error 4xx</a></h2><div id="rfc.section.6.5.p.1"><p>The <dfn>4xx (Client Error)</dfn> class of status code indicates that the client seems to have erred. Except when responding to a HEAD request, the server <em class="bcp14">SHOULD</em> send a representation containing an explanation of the error situation, and whether it is a temporary or permanent condition. These status codes are applicable to any request method. User agents <em class="bcp14">SHOULD</em> display any included representation to the user.<a class="self" href="#rfc.section.6.5.p.1">&para;</a></p></div><div id="status.400"><h3 id="rfc.section.6.5.1"><a href="#rfc.section.6.5.1">6.5.1</a>&nbsp;<a href="#status.400">400 Bad Request</a></h3><div id="rfc.section.6.5.1.p.1"><p>The <dfn>400 (Bad Request)</dfn> status code indicates that the server cannot or will not process the request due to something that is perceived to be a client error (e.g., malformed request syntax, invalid request message framing, or deceptive request routing).<a class="self" href="#rfc.section.6.5.1.p.1">&para;</a></p></div></div><div id="status.402"><h3 id="rfc.section.6.5.2"><a href="#rfc.section.6.5.2">6.5.2</a>&nbsp;<a href="#status.402">402 Payment Required</a></h3><div id="rfc.section.6.5.2.p.1"><p>The <dfn>402 (Payment Required)</dfn> status code is reserved for future use.<a class="self" href="#rfc.section.6.5.2.p.1">&para;</a></p></div></div><div id="status.403"><h3 id="rfc.section.6.5.3"><a href="#rfc.section.6.5.3">6.5.3</a>&nbsp;<a href="#status.403">403 Forbidden</a></h3><div id="rfc.section.6.5.3.p.1"><p>The <dfn>403 (Forbidden)</dfn> status code indicates that the server understood the request but refuses to authorize it. A server that wishes to make public why the request has been forbidden can describe that reason in the response payload (if any).<a class="self" href="#rfc.section.6.5.3.p.1">&para;</a></p></div><div id="rfc.section.6.5.3.p.2"><p>If authentication credentials were provided in the request, the server considers them insufficient to grant access. The client <em class="bcp14">SHOULD NOT</em> automatically repeat the request with the same credentials. The client <em class="bcp14">MAY</em> repeat the request with new or different credentials. However, a request might be forbidden for reasons unrelated to the credentials.<a class="self" href="#rfc.section.6.5.3.p.2">&para;</a></p></div><div id="rfc.section.6.5.3.p.3"><p>An origin server that wishes to "hide" the current existence of a forbidden <a href="#resources" class="smpl">target resource</a> <em class="bcp14">MAY</em> instead respond with a status code of <a href="#status.404" class="smpl">404 (Not Found)</a>.<a class="self" href="#rfc.section.6.5.3.p.3">&para;</a></p></div></div><div id="status.404"><h3 id="rfc.section.6.5.4"><a href="#rfc.section.6.5.4">6.5.4</a>&nbsp;<a href="#status.404">404 Not Found</a></h3><div id="rfc.section.6.5.4.p.1"><p>The <dfn>404 (Not Found)</dfn> status code indicates that the origin server did not find a current representation for the <a href="#resources" class="smpl">target resource</a> or is not willing to disclose that one exists. A 404 status code does not indicate whether this lack of representation is temporary or permanent; the <a href="#status.410" class="smpl">410 (Gone)</a> status code is preferred over 404 if the origin server knows, presumably through some configurable means, that the condition is likely to be permanent.<a class="self" href="#rfc.section.6.5.4.p.1">&para;</a></p></div><div id="rfc.section.6.5.4.p.2"><p>A 404 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.17"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.5.4.p.2">&para;</a></p></div></div><div id="status.405"><h3 id="rfc.section.6.5.5"><a href="#rfc.section.6.5.5">6.5.5</a>&nbsp;<a href="#status.405">405 Method Not Allowed</a></h3><div id="rfc.section.6.5.5.p.1"><p>The <dfn>405 (Method Not Allowed)</dfn> status code indicates that the method received in the request-line is known by the origin server but not supported by the <a href="#resources" class="smpl">target resource</a>. The origin server <em class="bcp14">MUST</em> generate an <a href="#header.allow" class="smpl">Allow</a> header field in a 405 response containing a list of the target resource's currently supported methods.<a class="self" href="#rfc.section.6.5.5.p.1">&para;</a></p></div><div id="rfc.section.6.5.5.p.2"><p>A 405 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.18"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.5.5.p.2">&para;</a></p></div></div><div id="status.406"><h3 id="rfc.section.6.5.6"><a href="#rfc.section.6.5.6">6.5.6</a>&nbsp;<a href="#status.406">406 Not Acceptable</a></h3><div id="rfc.section.6.5.6.p.1"><p>The <dfn>406 (Not Acceptable)</dfn> status code indicates that the <a href="#resources" class="smpl">target resource</a> does not have a current representation that would be acceptable to the user agent, according to the <a href="#proactive.negotiation" class="smpl">proactive negotiation</a> header fields received in the request (<a href="#request.conneg" title="Content Negotiation">Section&nbsp;5.3</a>), and the server is unwilling to supply a default representation.<a class="self" href="#rfc.section.6.5.6.p.1">&para;</a></p></div><div id="rfc.section.6.5.6.p.2"><p>The server <em class="bcp14">SHOULD</em> generate a payload containing a list of available representation characteristics and corresponding resource identifiers from which the user or user agent can choose the one most appropriate. A user agent <em class="bcp14">MAY</em> automatically select the most appropriate choice from that list. However, this specification does not define any standard for such automatic selection, as described in <a href="#status.300" id="rfc.xref.status.300.2" title="300 Multiple Choices">Section&nbsp;6.4.1</a>.<a class="self" href="#rfc.section.6.5.6.p.2">&para;</a></p></div></div><div id="status.408"><h3 id="rfc.section.6.5.7"><a href="#rfc.section.6.5.7">6.5.7</a>&nbsp;<a href="#status.408">408 Request Timeout</a></h3><div id="rfc.section.6.5.7.p.1"><p>The <dfn>408 (Request Timeout)</dfn> status code indicates that the server did not receive a complete request message within the time that it was prepared to wait. A server <em class="bcp14">SHOULD</em> send the "<a href="rfc7230.html#header.connection" class="smpl">close</a>" connection option (<a href="rfc7230.html#header.connection" title="Connection">Section 6.1</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.26"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>) in the response, since 408 implies that the server has decided to close the connection rather than continue waiting. If the client has an outstanding request in transit, the client <em class="bcp14">MAY</em> repeat that request on a new connection.<a class="self" href="#rfc.section.6.5.7.p.1">&para;</a></p></div></div><div id="status.409"><h3 id="rfc.section.6.5.8"><a href="#rfc.section.6.5.8">6.5.8</a>&nbsp;<a href="#status.409">409 Conflict</a></h3><div id="rfc.section.6.5.8.p.1"><p>The <dfn>409 (Conflict)</dfn> status code indicates that the request could not be completed due to a conflict with the current state of the target resource. This code is used in situations where the user might be able to resolve the conflict and resubmit the request. The server <em class="bcp14">SHOULD</em> generate a payload that includes enough information for a user to recognize the source of the conflict.<a class="self" href="#rfc.section.6.5.8.p.1">&para;</a></p></div><div id="rfc.section.6.5.8.p.2"><p>Conflicts are most likely to occur in response to a PUT request. For example, if versioning were being used and the representation being PUT included changes to a resource that conflict with those made by an earlier (third-party) request, the origin server might use a 409 response to indicate that it can't complete the request. In this case, the response representation would likely contain information useful for merging the differences based on the revision history.<a class="self" href="#rfc.section.6.5.8.p.2">&para;</a></p></div></div><div id="status.410"><h3 id="rfc.section.6.5.9"><a href="#rfc.section.6.5.9">6.5.9</a>&nbsp;<a href="#status.410">410 Gone</a></h3><div id="rfc.section.6.5.9.p.1"><p>The <dfn>410 (Gone)</dfn> status code indicates that access to the <a href="#resources" class="smpl">target resource</a> is no longer available at the origin server and that this condition is likely to be permanent. If the origin server does not know, or has no facility to determine, whether or not the condition is permanent, the status code <a href="#status.404" class="smpl">404 (Not Found)</a> ought to be used instead.<a class="self" href="#rfc.section.6.5.9.p.1">&para;</a></p></div><div id="rfc.section.6.5.9.p.2"><p>The 410 response is primarily intended to assist the task of web maintenance by notifying the recipient that the resource is intentionally unavailable and that the server owners desire that remote links to that resource be removed. Such an event is common for limited-time, promotional services and for resources belonging to individuals no longer associated with the origin server's site. It is not necessary to mark all permanently unavailable resources as "gone" or to keep the mark for any length of time &#8212; that is left to the discretion of the server owner.<a class="self" href="#rfc.section.6.5.9.p.2">&para;</a></p></div><div id="rfc.section.6.5.9.p.3"><p>A 410 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.19"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.5.9.p.3">&para;</a></p></div></div><div id="status.411"><h3 id="rfc.section.6.5.10"><a href="#rfc.section.6.5.10">6.5.10</a>&nbsp;<a href="#status.411">411 Length Required</a></h3><div id="rfc.section.6.5.10.p.1"><p>The <dfn>411 (Length Required)</dfn> status code indicates that the server refuses to accept the request without a defined <a href="rfc7230.html#header.content-length" class="smpl">Content-Length</a> (<a href="rfc7230.html#header.content-length" title="Content-Length">Section 3.3.2</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.27"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>). The client <em class="bcp14">MAY</em> repeat the request if it adds a valid Content-Length header field containing the length of the message body in the request message.<a class="self" href="#rfc.section.6.5.10.p.1">&para;</a></p></div></div><div id="status.413"><h3 id="rfc.section.6.5.11"><a href="#rfc.section.6.5.11">6.5.11</a>&nbsp;<a href="#status.413">413 Payload Too Large</a></h3><div id="rfc.section.6.5.11.p.1"><p>The <dfn>413 (Payload Too Large)</dfn> status code indicates that the server is refusing to process a request because the request payload is larger than the server is willing or able to process. The server <em class="bcp14">MAY</em> close the connection to prevent the client from continuing the request.<a class="self" href="#rfc.section.6.5.11.p.1">&para;</a></p></div><div id="rfc.section.6.5.11.p.2"><p>If the condition is temporary, the server <em class="bcp14">SHOULD</em> generate a <a href="#header.retry-after" class="smpl">Retry-After</a> header field to indicate that it is temporary and after what time the client <em class="bcp14">MAY</em> try again.<a class="self" href="#rfc.section.6.5.11.p.2">&para;</a></p></div></div><div id="status.414"><h3 id="rfc.section.6.5.12"><a href="#rfc.section.6.5.12">6.5.12</a>&nbsp;<a href="#status.414">414 URI Too Long</a></h3><div id="rfc.section.6.5.12.p.1"><p>The <dfn>414 (URI Too Long)</dfn> status code indicates that the server is refusing to service the request because the request-target (<a href="rfc7230.html#request-target" title="Request Target">Section 5.3</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.28"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>) is longer than the server is willing to interpret. This rare condition is only likely to occur when a client has improperly converted a POST request to a GET request with long query information, when the client has descended into a "black hole" of redirection (e.g., a redirected URI prefix that points to a suffix of itself) or when the server is under attack by a client attempting to exploit potential security holes.<a class="self" href="#rfc.section.6.5.12.p.1">&para;</a></p></div><div id="rfc.section.6.5.12.p.2"><p>A 414 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.20"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.5.12.p.2">&para;</a></p></div></div><div id="status.415"><h3 id="rfc.section.6.5.13"><a href="#rfc.section.6.5.13">6.5.13</a>&nbsp;<a href="#status.415">415 Unsupported Media Type</a></h3><div id="rfc.section.6.5.13.p.1"><p>The <dfn>415 (Unsupported Media Type)</dfn> status code indicates that the origin server is refusing to service the request because the payload is in a format not supported by this method on the <a href="#resources" class="smpl">target resource</a>. The format problem might be due to the request's indicated <a href="#header.content-type" class="smpl">Content-Type</a> or <a href="#header.content-encoding" class="smpl">Content-Encoding</a>, or as a result of inspecting the data directly.<a class="self" href="#rfc.section.6.5.13.p.1">&para;</a></p></div></div><div id="status.417"><h3 id="rfc.section.6.5.14"><a href="#rfc.section.6.5.14">6.5.14</a>&nbsp;<a href="#status.417">417 Expectation Failed</a></h3><div id="rfc.section.6.5.14.p.1"><p>The <dfn>417 (Expectation Failed)</dfn> status code indicates that the expectation given in the request's <a href="#header.expect" class="smpl">Expect</a> header field (<a href="#header.expect" id="rfc.xref.header.expect.3" title="Expect">Section&nbsp;5.1.1</a>) could not be met by at least one of the inbound servers.<a class="self" href="#rfc.section.6.5.14.p.1">&para;</a></p></div></div><div id="status.426"><h3 id="rfc.section.6.5.15"><a href="#rfc.section.6.5.15">6.5.15</a>&nbsp;<a href="#status.426">426 Upgrade Required</a></h3><div id="rfc.section.6.5.15.p.1"><p>The <dfn>426 (Upgrade Required)</dfn> status code indicates that the server refuses to perform the request using the current protocol but might be willing to do so after the client upgrades to a different protocol. The server <em class="bcp14">MUST</em> send an <a href="rfc7230.html#header.upgrade" class="smpl">Upgrade</a> header field in a 426 response to indicate the required protocol(s) (<a href="rfc7230.html#header.upgrade" title="Upgrade">Section 6.7</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.29"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>).<a class="self" href="#rfc.section.6.5.15.p.1">&para;</a></p></div><div id="rfc.figure.u.42"><p>Example:</p><pre class="text">HTTP/1.1 426 Upgrade Required
    590606Upgrade: HTTP/3.0
    591607Connection: Upgrade
     
    594610
    595611<span id="s426body">This service requires use of the HTTP/3.0 protocol.
    596 </span></pre></div></div></div><div id="status.5xx"><h2 id="rfc.section.6.6"><a href="#rfc.section.6.6">6.6</a>&nbsp;<a href="#status.5xx">Server Error 5xx</a></h2><div id="rfc.section.6.6.p.1"><p>The <dfn>5xx (Server Error)</dfn> class of status code indicates that the server is aware that it has erred or is incapable of performing the requested method. Except when responding to a HEAD request, the server <em class="bcp14">SHOULD</em> send a representation containing an explanation of the error situation, and whether it is a temporary or permanent condition. A user agent <em class="bcp14">SHOULD</em> display any included representation to the user. These response codes are applicable to any request method.<a class="self" href="#rfc.section.6.6.p.1">&para;</a></p></div><div id="status.500"><h3 id="rfc.section.6.6.1"><a href="#rfc.section.6.6.1">6.6.1</a>&nbsp;<a href="#status.500">500 Internal Server Error</a></h3><div id="rfc.section.6.6.1.p.1"><p>The <dfn>500 (Internal Server Error)</dfn> status code indicates that the server encountered an unexpected condition that prevented it from fulfilling the request.<a class="self" href="#rfc.section.6.6.1.p.1">&para;</a></p></div></div><div id="status.501"><h3 id="rfc.section.6.6.2"><a href="#rfc.section.6.6.2">6.6.2</a>&nbsp;<a href="#status.501">501 Not Implemented</a></h3><div id="rfc.section.6.6.2.p.1"><p>The <dfn>501 (Not Implemented)</dfn> status code indicates that the server does not support the functionality required to fulfill the request. This is the appropriate response when the server does not recognize the request method and is not capable of supporting it for any resource.<a class="self" href="#rfc.section.6.6.2.p.1">&para;</a></p></div><div id="rfc.section.6.6.2.p.2"><p>A 501 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.21"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.6.2.p.2">&para;</a></p></div></div><div id="status.502"><h3 id="rfc.section.6.6.3"><a href="#rfc.section.6.6.3">6.6.3</a>&nbsp;<a href="#status.502">502 Bad Gateway</a></h3><div id="rfc.section.6.6.3.p.1"><p>The <dfn>502 (Bad Gateway)</dfn> status code indicates that the server, while acting as a gateway or proxy, received an invalid response from an inbound server it accessed while attempting to fulfill the request.<a class="self" href="#rfc.section.6.6.3.p.1">&para;</a></p></div></div><div id="status.503"><h3 id="rfc.section.6.6.4"><a href="#rfc.section.6.6.4">6.6.4</a>&nbsp;<a href="#status.503">503 Service Unavailable</a></h3><div id="rfc.section.6.6.4.p.1"><p>The <dfn>503 (Service Unavailable)</dfn> status code indicates that the server is currently unable to handle the request due to a temporary overload or scheduled maintenance, which will likely be alleviated after some delay. The server <em class="bcp14">MAY</em> send a <a href="#header.retry-after" class="smpl">Retry-After</a> header field (<a href="#header.retry-after" id="rfc.xref.header.retry-after.1" title="Retry-After">Section&nbsp;7.1.3</a>) to suggest an appropriate amount of time for the client to wait before retrying the request.<a class="self" href="#rfc.section.6.6.4.p.1">&para;</a></p></div><div class="note" id="rfc.section.6.6.4.p.2"><p><b>Note:</b> The existence of the 503 status code does not imply that a server has to use it when becoming overloaded. Some servers might simply refuse the connection.<a class="self" href="#rfc.section.6.6.4.p.2">&para;</a></p></div></div><div id="status.504"><h3 id="rfc.section.6.6.5"><a href="#rfc.section.6.6.5">6.6.5</a>&nbsp;<a href="#status.504">504 Gateway Timeout</a></h3><div id="rfc.section.6.6.5.p.1"><p>The <dfn>504 (Gateway Timeout)</dfn> status code indicates that the server, while acting as a gateway or proxy, did not receive a timely response from an upstream server it needed to access in order to complete the request.<a class="self" href="#rfc.section.6.6.5.p.1">&para;</a></p></div></div><div id="status.505"><h3 id="rfc.section.6.6.6"><a href="#rfc.section.6.6.6">6.6.6</a>&nbsp;<a href="#status.505">505 HTTP Version Not Supported</a></h3><div id="rfc.section.6.6.6.p.1"><p>The <dfn>505 (HTTP Version Not Supported)</dfn> status code indicates that the server does not support, or refuses to support, the major version of HTTP that was used in the request message. The server is indicating that it is unable or unwilling to complete the request using the same major version as the client, as described in <a href="rfc7230.html#http.version" title="Protocol Versioning">Section 2.6</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.30"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>, other than with this error message. The server <em class="bcp14">SHOULD</em> generate a representation for the 505 response that describes why that version is not supported and what other protocols are supported by that server.<a class="self" href="#rfc.section.6.6.6.p.1">&para;</a></p></div></div></div></div><div id="response.header.fields"><h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a href="#response.header.fields">Response Header Fields</a></h1><div id="rfc.section.7.p.1"><p>The response header fields allow the server to pass additional information about the response beyond what is placed in the status-line. These header fields give information about the server, about further access to the <a href="#resources" class="smpl">target resource</a>, or about related resources.<a class="self" href="#rfc.section.7.p.1">&para;</a></p></div><div id="rfc.section.7.p.2"><p>Although each response header field has a defined meaning, in general, the precise semantics might be further refined by the semantics of the request method and/or response status code.<a class="self" href="#rfc.section.7.p.2">&para;</a></p></div><div id="response.control.data"><h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a>&nbsp;<a href="#response.control.data">Control Data</a></h2><div id="rfc.section.7.1.p.1"><p>Response header fields can supply control data that supplements the status code, directs caching, or instructs the client where to go next.<a class="self" href="#rfc.section.7.1.p.1">&para;</a></p></div><div id="rfc.table.u.10"><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Header Field Name</th><th>Defined in...</th></tr></thead><tbody><tr><td class="left">Age</td><td class="left"><a href="rfc7234.html#header.age" title="Age">Section 5.1</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.22"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a></td></tr><tr><td class="left">Cache-Control</td><td class="left"><a href="rfc7234.html#header.cache-control" title="Cache-Control">Section 5.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.23"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a></td></tr><tr><td class="left">Expires</td><td class="left"><a href="rfc7234.html#header.expires" title="Expires">Section 5.3</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.24"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a></td></tr><tr><td class="left">Date</td><td class="left"><a href="#header.date" id="rfc.xref.header.date.2" title="Date">Section&nbsp;7.1.1.2</a></td></tr><tr><td class="left">Location</td><td class="left"><a href="#header.location" id="rfc.xref.header.location.3" title="Location">Section&nbsp;7.1.2</a></td></tr><tr><td class="left">Retry-After</td><td class="left"><a href="#header.retry-after" id="rfc.xref.header.retry-after.2" title="Retry-After">Section&nbsp;7.1.3</a></td></tr><tr><td class="left">Vary</td><td class="left"><a href="#header.vary" id="rfc.xref.header.vary.2" title="Vary">Section&nbsp;7.1.4</a></td></tr><tr><td class="left">Warning</td><td class="left"><a href="rfc7234.html#header.warning" title="Warning">Section 5.5</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.25"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a></td></tr></tbody></table></div><div id="origination.date"><h3 id="rfc.section.7.1.1"><a href="#rfc.section.7.1.1">7.1.1</a>&nbsp;<a href="#origination.date">Origination Date</a></h3><div id="http.date"><h4 id="rfc.section.7.1.1.1"><a href="#rfc.section.7.1.1.1">7.1.1.1</a>&nbsp;<a href="#http.date">Date/Time Formats</a></h4><div id="rfc.section.7.1.1.1.p.1"><p>Prior to 1995, there were three different formats commonly used by servers to communicate timestamps. For compatibility with old implementations, all three are defined here. The preferred format is a fixed-length and single-zone subset of the date and time specification used by the Internet Message Format <a href="#RFC5322" id="rfc.xref.RFC5322.3"><cite title="Internet Message Format">[RFC5322]</cite></a>.<a class="self" href="#rfc.section.7.1.1.1.p.1">&para;</a></p></div><div id="rfc.figure.u.43"><pre class="inline"><span id="rfc.iref.g.32"></span>  <a href="#http.date" class="smpl">HTTP-date</a>    = <a href="#preferred.date.format" class="smpl">IMF-fixdate</a> / <a href="#obsolete.date.formats" class="smpl">obs-date</a>
     612</span></pre></div></div></div><div id="status.5xx"><h2 id="rfc.section.6.6"><a href="#rfc.section.6.6">6.6</a>&nbsp;<a href="#status.5xx">Server Error 5xx</a></h2><div id="rfc.section.6.6.p.1"><p>The <dfn>5xx (Server Error)</dfn> class of status code indicates that the server is aware that it has erred or is incapable of performing the requested method. Except when responding to a HEAD request, the server <em class="bcp14">SHOULD</em> send a representation containing an explanation of the error situation, and whether it is a temporary or permanent condition. A user agent <em class="bcp14">SHOULD</em> display any included representation to the user. These response codes are applicable to any request method.<a class="self" href="#rfc.section.6.6.p.1">&para;</a></p></div><div id="status.500"><h3 id="rfc.section.6.6.1"><a href="#rfc.section.6.6.1">6.6.1</a>&nbsp;<a href="#status.500">500 Internal Server Error</a></h3><div id="rfc.section.6.6.1.p.1"><p>The <dfn>500 (Internal Server Error)</dfn> status code indicates that the server encountered an unexpected condition that prevented it from fulfilling the request.<a class="self" href="#rfc.section.6.6.1.p.1">&para;</a></p></div></div><div id="status.501"><h3 id="rfc.section.6.6.2"><a href="#rfc.section.6.6.2">6.6.2</a>&nbsp;<a href="#status.501">501 Not Implemented</a></h3><div id="rfc.section.6.6.2.p.1"><p>The <dfn>501 (Not Implemented)</dfn> status code indicates that the server does not support the functionality required to fulfill the request. This is the appropriate response when the server does not recognize the request method and is not capable of supporting it for any resource.<a class="self" href="#rfc.section.6.6.2.p.1">&para;</a></p></div><div id="rfc.section.6.6.2.p.2"><p>A 501 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see <a href="rfc7234.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.2.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.21"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>).<a class="self" href="#rfc.section.6.6.2.p.2">&para;</a></p></div></div><div id="status.502"><h3 id="rfc.section.6.6.3"><a href="#rfc.section.6.6.3">6.6.3</a>&nbsp;<a href="#status.502">502 Bad Gateway</a></h3><div id="rfc.section.6.6.3.p.1"><p>The <dfn>502 (Bad Gateway)</dfn> status code indicates that the server, while acting as a gateway or proxy, received an invalid response from an inbound server it accessed while attempting to fulfill the request.<a class="self" href="#rfc.section.6.6.3.p.1">&para;</a></p></div></div><div id="status.503"><h3 id="rfc.section.6.6.4"><a href="#rfc.section.6.6.4">6.6.4</a>&nbsp;<a href="#status.503">503 Service Unavailable</a></h3><div id="rfc.section.6.6.4.p.1"><p>The <dfn>503 (Service Unavailable)</dfn> status code indicates that the server is currently unable to handle the request due to a temporary overload or scheduled maintenance, which will likely be alleviated after some delay. The server <em class="bcp14">MAY</em> send a <a href="#header.retry-after" class="smpl">Retry-After</a> header field (<a href="#header.retry-after" id="rfc.xref.header.retry-after.1" title="Retry-After">Section&nbsp;7.1.3</a>) to suggest an appropriate amount of time for the client to wait before retrying the request.<a class="self" href="#rfc.section.6.6.4.p.1">&para;</a></p></div><div class="note"><div id="rfc.section.6.6.4.p.2"><p><b>Note:</b> The existence of the 503 status code does not imply that a server has to use it when becoming overloaded. Some servers might simply refuse the connection.<a class="self" href="#rfc.section.6.6.4.p.2">&para;</a></p></div></div></div><div id="status.504"><h3 id="rfc.section.6.6.5"><a href="#rfc.section.6.6.5">6.6.5</a>&nbsp;<a href="#status.504">504 Gateway Timeout</a></h3><div id="rfc.section.6.6.5.p.1"><p>The <dfn>504 (Gateway Timeout)</dfn> status code indicates that the server, while acting as a gateway or proxy, did not receive a timely response from an upstream server it needed to access in order to complete the request.<a class="self" href="#rfc.section.6.6.5.p.1">&para;</a></p></div></div><div id="status.505"><h3 id="rfc.section.6.6.6"><a href="#rfc.section.6.6.6">6.6.6</a>&nbsp;<a href="#status.505">505 HTTP Version Not Supported</a></h3><div id="rfc.section.6.6.6.p.1"><p>The <dfn>505 (HTTP Version Not Supported)</dfn> status code indicates that the server does not support, or refuses to support, the major version of HTTP that was used in the request message. The server is indicating that it is unable or unwilling to complete the request using the same major version as the client, as described in <a href="rfc7230.html#http.version" title="Protocol Versioning">Section 2.6</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.30"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>, other than with this error message. The server <em class="bcp14">SHOULD</em> generate a representation for the 505 response that describes why that version is not supported and what other protocols are supported by that server.<a class="self" href="#rfc.section.6.6.6.p.1">&para;</a></p></div></div></div></div><div id="response.header.fields"><h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a href="#response.header.fields">Response Header Fields</a></h1><div id="rfc.section.7.p.1"><p>The response header fields allow the server to pass additional information about the response beyond what is placed in the status-line. These header fields give information about the server, about further access to the <a href="#resources" class="smpl">target resource</a>, or about related resources.<a class="self" href="#rfc.section.7.p.1">&para;</a></p></div><div id="rfc.section.7.p.2"><p>Although each response header field has a defined meaning, in general, the precise semantics might be further refined by the semantics of the request method and/or response status code.<a class="self" href="#rfc.section.7.p.2">&para;</a></p></div><div id="response.control.data"><h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a>&nbsp;<a href="#response.control.data">Control Data</a></h2><div id="rfc.section.7.1.p.1"><p>Response header fields can supply control data that supplements the status code, directs caching, or instructs the client where to go next.<a class="self" href="#rfc.section.7.1.p.1">&para;</a></p></div><div id="rfc.table.u.10"><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Header Field Name</th><th>Defined in...</th></tr></thead><tbody><tr><td class="left">Age</td><td class="left"><a href="rfc7234.html#header.age" title="Age">Section 5.1</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.22"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a></td></tr><tr><td class="left">Cache-Control</td><td class="left"><a href="rfc7234.html#header.cache-control" title="Cache-Control">Section 5.2</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.23"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a></td></tr><tr><td class="left">Expires</td><td class="left"><a href="rfc7234.html#header.expires" title="Expires">Section 5.3</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.24"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a></td></tr><tr><td class="left">Date</td><td class="left"><a href="#header.date" id="rfc.xref.header.date.2" title="Date">Section&nbsp;7.1.1.2</a></td></tr><tr><td class="left">Location</td><td class="left"><a href="#header.location" id="rfc.xref.header.location.3" title="Location">Section&nbsp;7.1.2</a></td></tr><tr><td class="left">Retry-After</td><td class="left"><a href="#header.retry-after" id="rfc.xref.header.retry-after.2" title="Retry-After">Section&nbsp;7.1.3</a></td></tr><tr><td class="left">Vary</td><td class="left"><a href="#header.vary" id="rfc.xref.header.vary.2" title="Vary">Section&nbsp;7.1.4</a></td></tr><tr><td class="left">Warning</td><td class="left"><a href="rfc7234.html#header.warning" title="Warning">Section 5.5</a> of <a href="#RFC7234" id="rfc.xref.RFC7234.25"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a></td></tr></tbody></table></div><div id="origination.date"><h3 id="rfc.section.7.1.1"><a href="#rfc.section.7.1.1">7.1.1</a>&nbsp;<a href="#origination.date">Origination Date</a></h3><div id="http.date"><h4 id="rfc.section.7.1.1.1"><a href="#rfc.section.7.1.1.1">7.1.1.1</a>&nbsp;<a href="#http.date">Date/Time Formats</a></h4><div id="rfc.section.7.1.1.1.p.1"><p>Prior to 1995, there were three different formats commonly used by servers to communicate timestamps. For compatibility with old implementations, all three are defined here. The preferred format is a fixed-length and single-zone subset of the date and time specification used by the Internet Message Format <a href="#RFC5322" id="rfc.xref.RFC5322.3"><cite title="Internet Message Format">[RFC5322]</cite></a>.<a class="self" href="#rfc.section.7.1.1.1.p.1">&para;</a></p></div><div id="rfc.figure.u.43"><pre class="inline"><span id="rfc.iref.g.32"></span>  <a href="#http.date" class="smpl">HTTP-date</a>    = <a href="#preferred.date.format" class="smpl">IMF-fixdate</a> / <a href="#obsolete.date.formats" class="smpl">obs-date</a>
    597613</pre></div><div id="rfc.figure.u.44"><p>An example of the preferred format is</p><pre class="text">Sun, 06 Nov 1994 08:49:37 GMT    ; IMF-fixdate
    598614</pre></div><div id="rfc.figure.u.45"><p>Examples of the two obsolete formats are</p><pre class="text">Sunday, 06-Nov-94 08:49:37 GMT   ; obsolete RFC 850 format
    599615Sun Nov  6 08:49:37 1994         ; ANSI C's asctime() format
    600 </pre></div><div id="rfc.section.7.1.1.1.p.2"><p>A recipient that parses a timestamp value in an HTTP header field <em class="bcp14">MUST</em> accept all three HTTP-date formats. When a sender generates a header field that contains one or more timestamps defined as HTTP-date, the sender <em class="bcp14">MUST</em> generate those timestamps in the IMF-fixdate format.<a class="self" href="#rfc.section.7.1.1.1.p.2">&para;</a></p></div><div id="rfc.section.7.1.1.1.p.3"><p>An HTTP-date value represents time as an instance of Coordinated Universal Time (UTC). The first two formats indicate UTC by the three-letter abbreviation for Greenwich Mean Time, "GMT", a predecessor of the UTC name; values in the asctime format are assumed to be in UTC. A sender that generates HTTP-date values from a local clock ought to use NTP (<a href="#RFC5905" id="rfc.xref.RFC5905.1"><cite title="Network Time Protocol Version 4: Protocol and Algorithms Specification">[RFC5905]</cite></a>) or some similar protocol to synchronize its clock to UTC.<a class="self" href="#rfc.section.7.1.1.1.p.3">&para;</a></p></div><div id="preferred.date.format"><div id="rfc.section.7.1.1.1.p.4"><p>          Preferred format:<a class="self" href="#rfc.section.7.1.1.1.p.4">&para;</a></p></div></div><div id="rfc.figure.u.46"><pre class="inline"><span id="rfc.iref.g.33"></span><span id="rfc.iref.g.34"></span><span id="rfc.iref.g.35"></span><span id="rfc.iref.g.36"></span><span id="rfc.iref.g.37"></span><span id="rfc.iref.g.38"></span><span id="rfc.iref.g.39"></span><span id="rfc.iref.g.40"></span><span id="rfc.iref.g.41"></span><span id="rfc.iref.g.42"></span><span id="rfc.iref.g.43"></span><span id="rfc.iref.g.44"></span>  <a href="#preferred.date.format" class="smpl">IMF-fixdate</a>  = <a href="#preferred.date.format" class="smpl">day-name</a> "," <a href="#imported.abnf" class="smpl">SP</a> date1 <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">time-of-day</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">GMT</a>
     616</pre></div><div id="rfc.section.7.1.1.1.p.2"><p>A recipient that parses a timestamp value in an HTTP header field <em class="bcp14">MUST</em> accept all three HTTP-date formats. When a sender generates a header field that contains one or more timestamps defined as HTTP-date, the sender <em class="bcp14">MUST</em> generate those timestamps in the IMF-fixdate format.<a class="self" href="#rfc.section.7.1.1.1.p.2">&para;</a></p></div><div id="rfc.section.7.1.1.1.p.3"><p>An HTTP-date value represents time as an instance of Coordinated Universal Time (UTC). The first two formats indicate UTC by the three-letter abbreviation for Greenwich Mean Time, "GMT", a predecessor of the UTC name; values in the asctime format are assumed to be in UTC. A sender that generates HTTP-date values from a local clock ought to use NTP (<a href="#RFC5905" id="rfc.xref.RFC5905.1"><cite title="Network Time Protocol Version 4: Protocol and Algorithms Specification">[RFC5905]</cite></a>) or some similar protocol to synchronize its clock to UTC.<a class="self" href="#rfc.section.7.1.1.1.p.3">&para;</a></p></div><div id="preferred.date.format" class="avoidbreakafter"><div id="rfc.section.7.1.1.1.p.4"><p>          Preferred format:<a class="self" href="#rfc.section.7.1.1.1.p.4">&para;</a></p></div></div><div id="rfc.figure.u.46"><pre class="inline"><span id="rfc.iref.g.33"></span><span id="rfc.iref.g.34"></span><span id="rfc.iref.g.35"></span><span id="rfc.iref.g.36"></span><span id="rfc.iref.g.37"></span><span id="rfc.iref.g.38"></span><span id="rfc.iref.g.39"></span><span id="rfc.iref.g.40"></span><span id="rfc.iref.g.41"></span><span id="rfc.iref.g.42"></span><span id="rfc.iref.g.43"></span><span id="rfc.iref.g.44"></span>  <a href="#preferred.date.format" class="smpl">IMF-fixdate</a>  = <a href="#preferred.date.format" class="smpl">day-name</a> "," <a href="#imported.abnf" class="smpl">SP</a> date1 <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">time-of-day</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">GMT</a>
    601617  ; fixed length/zone/capitalization subset of the format
    602618  ; see <a href="https://tools.ietf.org/html/rfc5322#section-3.3">Section 3.3</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.4"><cite title="Internet Message Format">[RFC5322]</cite></a>
     
    636652  <a href="#preferred.date.format" class="smpl">minute</a>       = 2<a href="#imported.abnf" class="smpl">DIGIT</a>               
    637653  <a href="#preferred.date.format" class="smpl">second</a>       = 2<a href="#imported.abnf" class="smpl">DIGIT</a>               
    638 </pre></div><div id="obsolete.date.formats"><div id="rfc.section.7.1.1.1.p.5"><p>       Obsolete formats:<a class="self" href="#rfc.section.7.1.1.1.p.5">&para;</a></p></div></div><div id="rfc.figure.u.47"><pre class="inline"><span id="rfc.iref.g.45"></span>  <a href="#obsolete.date.formats" class="smpl">obs-date</a>     = <a href="#obsolete.date.formats" class="smpl">rfc850-date</a> / <a href="#obsolete.date.formats" class="smpl">asctime-date</a>
     654</pre></div><div id="obsolete.date.formats" class="avoidbreakafter"><div id="rfc.section.7.1.1.1.p.5"><p>       Obsolete formats:<a class="self" href="#rfc.section.7.1.1.1.p.5">&para;</a></p></div></div><div id="rfc.figure.u.47"><pre class="inline"><span id="rfc.iref.g.45"></span>  <a href="#obsolete.date.formats" class="smpl">obs-date</a>     = <a href="#obsolete.date.formats" class="smpl">rfc850-date</a> / <a href="#obsolete.date.formats" class="smpl">asctime-date</a>
    639655</pre></div><div id="rfc.figure.u.48"><pre class="inline"><span id="rfc.iref.g.46"></span>  <a href="#obsolete.date.formats" class="smpl">rfc850-date</a>  = <a href="#obsolete.date.formats" class="smpl">day-name-l</a> "," <a href="#imported.abnf" class="smpl">SP</a> <a href="#obsolete.date.formats" class="smpl">date2</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">time-of-day</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">GMT</a>
    640656  <a href="#obsolete.date.formats" class="smpl">date2</a>        = <a href="#preferred.date.format" class="smpl">day</a> "-" <a href="#preferred.date.format" class="smpl">month</a> "-" 2<a href="#imported.abnf" class="smpl">DIGIT</a>
     
    651667  <a href="#obsolete.date.formats" class="smpl">date3</a>        = <a href="#preferred.date.format" class="smpl">month</a> <a href="#imported.abnf" class="smpl">SP</a> ( 2<a href="#imported.abnf" class="smpl">DIGIT</a> / ( <a href="#imported.abnf" class="smpl">SP</a> 1<a href="#imported.abnf" class="smpl">DIGIT</a> ))
    652668               ; e.g., Jun  2
    653 </pre></div><div id="rfc.section.7.1.1.1.p.6"><p>HTTP-date is case sensitive. A sender <em class="bcp14">MUST NOT</em> generate additional whitespace in an HTTP-date beyond that specifically included as SP in the grammar. The semantics of <a href="#preferred.date.format" class="smpl">day-name</a>, <a href="#preferred.date.format" class="smpl">day</a>, <a href="#preferred.date.format" class="smpl">month</a>, <a href="#preferred.date.format" class="smpl">year</a>, and <a href="#preferred.date.format" class="smpl">time-of-day</a> are the same as those defined for the Internet Message Format constructs with the corresponding name (<a href="#RFC5322" id="rfc.xref.RFC5322.5"><cite title="Internet Message Format">[RFC5322]</cite></a>, <a href="https://tools.ietf.org/html/rfc5322#section-3.3">Section 3.3</a>).<a class="self" href="#rfc.section.7.1.1.1.p.6">&para;</a></p></div><div id="rfc.section.7.1.1.1.p.7"><p>Recipients of a timestamp value in rfc850-date format, which uses a two-digit year, <em class="bcp14">MUST</em> interpret a timestamp that appears to be more than 50 years in the future as representing the most recent year in the past that had the same last two digits.<a class="self" href="#rfc.section.7.1.1.1.p.7">&para;</a></p></div><div id="rfc.section.7.1.1.1.p.8"><p>Recipients of timestamp values are encouraged to be robust in parsing timestamps unless otherwise restricted by the field definition. For example, messages are occasionally forwarded over HTTP from a non-HTTP source that might generate any of the date and time specifications defined by the Internet Message Format.<a class="self" href="#rfc.section.7.1.1.1.p.8">&para;</a></p></div><div class="note" id="rfc.section.7.1.1.1.p.9"><p><b>Note:</b> HTTP requirements for the date/time stamp format apply only to their usage within the protocol stream. Implementations are not required to use these formats for user presentation, request logging, etc.<a class="self" href="#rfc.section.7.1.1.1.p.9">&para;</a></p></div></div><div id="header.date"><h4 id="rfc.section.7.1.1.2"><a href="#rfc.section.7.1.1.2">7.1.1.2</a>&nbsp;<a href="#header.date">Date</a></h4><div id="rfc.section.7.1.1.2.p.1"><p>The "Date" header field represents the date and time at which the message was originated, having the same semantics as the Origination Date Field (orig-date) defined in <a href="https://tools.ietf.org/html/rfc5322#section-3.6.1">Section 3.6.1</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.6"><cite title="Internet Message Format">[RFC5322]</cite></a>. The field value is an HTTP-date, as defined in <a href="#http.date" title="Date/Time Formats">Section&nbsp;7.1.1.1</a>.<a class="self" href="#rfc.section.7.1.1.2.p.1">&para;</a></p></div><div id="rfc.figure.u.50"><pre class="inline"><span id="rfc.iref.g.48"></span>  <a href="#header.date" class="smpl">Date</a> = <a href="#http.date" class="smpl">HTTP-date</a>
     669</pre></div><div id="rfc.section.7.1.1.1.p.6"><p>HTTP-date is case sensitive. A sender <em class="bcp14">MUST NOT</em> generate additional whitespace in an HTTP-date beyond that specifically included as SP in the grammar. The semantics of <a href="#preferred.date.format" class="smpl">day-name</a>, <a href="#preferred.date.format" class="smpl">day</a>, <a href="#preferred.date.format" class="smpl">month</a>, <a href="#preferred.date.format" class="smpl">year</a>, and <a href="#preferred.date.format" class="smpl">time-of-day</a> are the same as those defined for the Internet Message Format constructs with the corresponding name (<a href="#RFC5322" id="rfc.xref.RFC5322.5"><cite title="Internet Message Format">[RFC5322]</cite></a>, <a href="https://tools.ietf.org/html/rfc5322#section-3.3">Section 3.3</a>).<a class="self" href="#rfc.section.7.1.1.1.p.6">&para;</a></p></div><div id="rfc.section.7.1.1.1.p.7"><p>Recipients of a timestamp value in rfc850-date format, which uses a two-digit year, <em class="bcp14">MUST</em> interpret a timestamp that appears to be more than 50 years in the future as representing the most recent year in the past that had the same last two digits.<a class="self" href="#rfc.section.7.1.1.1.p.7">&para;</a></p></div><div id="rfc.section.7.1.1.1.p.8"><p>Recipients of timestamp values are encouraged to be robust in parsing timestamps unless otherwise restricted by the field definition. For example, messages are occasionally forwarded over HTTP from a non-HTTP source that might generate any of the date and time specifications defined by the Internet Message Format.<a class="self" href="#rfc.section.7.1.1.1.p.8">&para;</a></p></div><div class="note"><div id="rfc.section.7.1.1.1.p.9"><p><b>Note:</b> HTTP requirements for the date/time stamp format apply only to their usage within the protocol stream. Implementations are not required to use these formats for user presentation, request logging, etc.<a class="self" href="#rfc.section.7.1.1.1.p.9">&para;</a></p></div></div></div><div id="header.date"><h4 id="rfc.section.7.1.1.2"><a href="#rfc.section.7.1.1.2">7.1.1.2</a>&nbsp;<a href="#header.date">Date</a></h4><div id="rfc.section.7.1.1.2.p.1"><p>The "Date" header field represents the date and time at which the message was originated, having the same semantics as the Origination Date Field (orig-date) defined in <a href="https://tools.ietf.org/html/rfc5322#section-3.6.1">Section 3.6.1</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.6"><cite title="Internet Message Format">[RFC5322]</cite></a>. The field value is an HTTP-date, as defined in <a href="#http.date" title="Date/Time Formats">Section&nbsp;7.1.1.1</a>.<a class="self" href="#rfc.section.7.1.1.2.p.1">&para;</a></p></div><div id="rfc.figure.u.50"><pre class="inline"><span id="rfc.iref.g.48"></span>  <a href="#header.date" class="smpl">Date</a> = <a href="#http.date" class="smpl">HTTP-date</a>
    654670</pre></div><div id="rfc.section.7.1.1.2.p.2"><p>An example is<a class="self" href="#rfc.section.7.1.1.2.p.2">&para;</a></p></div><div id="rfc.figure.u.51"><pre class="text">  Date: Tue, 15 Nov 1994 08:12:31 GMT
    655671</pre></div><div id="rfc.section.7.1.1.2.p.3"><p>When a Date header field is generated, the sender <em class="bcp14">SHOULD</em> generate its field value as the best available approximation of the date and time of message generation. In theory, the date ought to represent the moment just before the payload is generated. In practice, the date can be generated at any time during message origination.<a class="self" href="#rfc.section.7.1.1.2.p.3">&para;</a></p></div><div id="rfc.section.7.1.1.2.p.4"><p>An origin server <em class="bcp14">MUST NOT</em> send a Date header field if it does not have a clock capable of providing a reasonable approximation of the current instance in Coordinated Universal Time. An origin server <em class="bcp14">MAY</em> send a Date header field if the response is in the <a href="#status.1xx" class="smpl">1xx (Informational)</a> or <a href="#status.5xx" class="smpl">5xx (Server Error)</a> class of status codes. An origin server <em class="bcp14">MUST</em> send a Date header field in all other cases.<a class="self" href="#rfc.section.7.1.1.2.p.4">&para;</a></p></div><div id="rfc.section.7.1.1.2.p.5"><p>A recipient with a clock that receives a response message without a Date header field <em class="bcp14">MUST</em> record the time it was received and append a corresponding Date header field to the message's header section if it is cached or forwarded downstream.<a class="self" href="#rfc.section.7.1.1.2.p.5">&para;</a></p></div><div id="rfc.section.7.1.1.2.p.6"><p>A user agent <em class="bcp14">MAY</em> send a Date header field in a request, though generally will not do so unless it is believed to convey useful information to the server. For example, custom applications of HTTP might convey a Date if the server is expected to adjust its interpretation of the user's request based on differences between the user agent and server clocks.<a class="self" href="#rfc.section.7.1.1.2.p.6">&para;</a></p></div></div></div><div id="header.location"><h3 id="rfc.section.7.1.2"><a href="#rfc.section.7.1.2">7.1.2</a>&nbsp;<a href="#header.location">Location</a></h3><div id="rfc.section.7.1.2.p.1"><p>The "Location" header field is used in some responses to refer to a specific resource in relation to the response. The type of relationship is defined by the combination of request method and status code semantics.<a class="self" href="#rfc.section.7.1.2.p.1">&para;</a></p></div><div id="rfc.figure.u.52"><pre class="inline"><span id="rfc.iref.g.49"></span>  <a href="#header.location" class="smpl">Location</a> = <a href="#imported.abnf" class="smpl">URI-reference</a>
    656672</pre></div><div id="rfc.section.7.1.2.p.2"><p>The field value consists of a single URI-reference. When it has the form of a relative reference (<a href="#RFC3986" id="rfc.xref.RFC3986.2"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-4.2">Section 4.2</a>), the final value is computed by resolving it against the effective request URI (<a href="#RFC3986" id="rfc.xref.RFC3986.3"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-5">Section 5</a>).<a class="self" href="#rfc.section.7.1.2.p.2">&para;</a></p></div><div id="rfc.section.7.1.2.p.3"><p>For <a href="#status.201" class="smpl">201 (Created)</a> responses, the Location value refers to the primary resource created by the request. For <a href="#status.3xx" class="smpl">3xx (Redirection)</a> responses, the Location value refers to the preferred target resource for automatically redirecting the request.<a class="self" href="#rfc.section.7.1.2.p.3">&para;</a></p></div><div id="rfc.section.7.1.2.p.4"><p>If the Location value provided in a <a href="#status.3xx" class="smpl">3xx (Redirection)</a> response does not have a fragment component, a user agent <em class="bcp14">MUST</em> process the redirection as if the value inherits the fragment component of the URI reference used to generate the request target (i.e., the redirection inherits the original reference's fragment, if any).<a class="self" href="#rfc.section.7.1.2.p.4">&para;</a></p></div><div id="rfc.figure.u.53"><p>For example, a GET request generated for the URI reference "http://www.example.org/~tim" might result in a <a href="#status.303" class="smpl">303 (See Other)</a> response containing the header field:</p><pre class="text">  Location: /People.html#tim
    657673</pre><p>which suggests that the user agent redirect to "http://www.example.org/People.html#tim"</p></div><div id="rfc.figure.u.54"><p>Likewise, a GET request generated for the URI reference "http://www.example.org/index.html#larry" might result in a <a href="#status.301" class="smpl">301 (Moved Permanently)</a> response containing the header field:</p><pre class="text">  Location: http://www.example.net/index.html
    658 </pre><p>which suggests that the user agent redirect to "http://www.example.net/index.html#larry", preserving the original fragment identifier.</p></div><div id="rfc.section.7.1.2.p.5"><p>There are circumstances in which a fragment identifier in a Location value would not be appropriate. For example, the Location header field in a <a href="#status.201" class="smpl">201 (Created)</a> response is supposed to provide a URI that is specific to the created resource.<a class="self" href="#rfc.section.7.1.2.p.5">&para;</a></p></div><div class="note" id="rfc.section.7.1.2.p.6"><p><b>Note:</b> Some recipients attempt to recover from Location fields that are not valid URI references. This specification does not mandate or define such processing, but does allow it for the sake of robustness.<a class="self" href="#rfc.section.7.1.2.p.6">&para;</a></p></div><div class="note" id="rfc.section.7.1.2.p.7"><p><b>Note:</b> The <a href="#header.content-location" class="smpl">Content-Location</a> header field (<a href="#header.content-location" id="rfc.xref.header.content-location.3" title="Content-Location">Section&nbsp;3.1.4.2</a>) differs from Location in that the Content-Location refers to the most specific resource corresponding to the enclosed representation. It is therefore possible for a response to contain both the Location and Content-Location header fields.<a class="self" href="#rfc.section.7.1.2.p.7">&para;</a></p></div></div><div id="header.retry-after"><h3 id="rfc.section.7.1.3"><a href="#rfc.section.7.1.3">7.1.3</a>&nbsp;<a href="#header.retry-after">Retry-After</a></h3><div id="rfc.section.7.1.3.p.1"><p>Servers send the "Retry-After" header field to indicate how long the user agent ought to wait before making a follow-up request. When sent with a <a href="#status.503" class="smpl">503 (Service Unavailable)</a> response, Retry-After indicates how long the service is expected to be unavailable to the client. When sent with any <a href="#status.3xx" class="smpl">3xx (Redirection)</a> response, Retry-After indicates the minimum time that the user agent is asked to wait before issuing the redirected request.<a class="self" href="#rfc.section.7.1.3.p.1">&para;</a></p></div><div id="rfc.section.7.1.3.p.2"><p>The value of this field can be either an HTTP-date or a number of seconds to delay after the response is received.<a class="self" href="#rfc.section.7.1.3.p.2">&para;</a></p></div><div id="rfc.figure.u.55"><pre class="inline"><span id="rfc.iref.g.50"></span>  <a href="#header.retry-after" class="smpl">Retry-After</a> = <a href="#http.date" class="smpl">HTTP-date</a> / <a href="#rule.delay-seconds" class="smpl">delay-seconds</a>
     674</pre><p>which suggests that the user agent redirect to "http://www.example.net/index.html#larry", preserving the original fragment identifier.</p></div><div id="rfc.section.7.1.2.p.5"><p>There are circumstances in which a fragment identifier in a Location value would not be appropriate. For example, the Location header field in a <a href="#status.201" class="smpl">201 (Created)</a> response is supposed to provide a URI that is specific to the created resource.<a class="self" href="#rfc.section.7.1.2.p.5">&para;</a></p></div><div class="note"><div id="rfc.section.7.1.2.p.6"><p><b>Note:</b> Some recipients attempt to recover from Location fields that are not valid URI references. This specification does not mandate or define such processing, but does allow it for the sake of robustness.<a class="self" href="#rfc.section.7.1.2.p.6">&para;</a></p></div></div><div class="note"><div id="rfc.section.7.1.2.p.7"><p><b>Note:</b> The <a href="#header.content-location" class="smpl">Content-Location</a> header field (<a href="#header.content-location" id="rfc.xref.header.content-location.3" title="Content-Location">Section&nbsp;3.1.4.2</a>) differs from Location in that the Content-Location refers to the most specific resource corresponding to the enclosed representation. It is therefore possible for a response to contain both the Location and Content-Location header fields.<a class="self" href="#rfc.section.7.1.2.p.7">&para;</a></p></div></div></div><div id="header.retry-after"><h3 id="rfc.section.7.1.3"><a href="#rfc.section.7.1.3">7.1.3</a>&nbsp;<a href="#header.retry-after">Retry-After</a></h3><div id="rfc.section.7.1.3.p.1"><p>Servers send the "Retry-After" header field to indicate how long the user agent ought to wait before making a follow-up request. When sent with a <a href="#status.503" class="smpl">503 (Service Unavailable)</a> response, Retry-After indicates how long the service is expected to be unavailable to the client. When sent with any <a href="#status.3xx" class="smpl">3xx (Redirection)</a> response, Retry-After indicates the minimum time that the user agent is asked to wait before issuing the redirected request.<a class="self" href="#rfc.section.7.1.3.p.1">&para;</a></p></div><div id="rfc.section.7.1.3.p.2"><p>The value of this field can be either an HTTP-date or a number of seconds to delay after the response is received.<a class="self" href="#rfc.section.7.1.3.p.2">&para;</a></p></div><div id="rfc.figure.u.55"><pre class="inline"><span id="rfc.iref.g.50"></span>  <a href="#header.retry-after" class="smpl">Retry-After</a> = <a href="#http.date" class="smpl">HTTP-date</a> / <a href="#rule.delay-seconds" class="smpl">delay-seconds</a>
    659675</pre></div><div id="rule.delay-seconds"><div id="rfc.section.7.1.3.p.3"><p> A delay-seconds value is a non-negative decimal integer, representing time in seconds.<a class="self" href="#rfc.section.7.1.3.p.3">&para;</a></p></div></div><div id="rfc.figure.u.56"><pre class="inline"><span id="rfc.iref.g.51"></span>  <a href="#rule.delay-seconds" class="smpl">delay-seconds</a>  = 1*<a href="#imported.abnf" class="smpl">DIGIT</a>
    660676</pre></div><div id="rfc.section.7.1.3.p.4"><p>Two examples of its use are<a class="self" href="#rfc.section.7.1.3.p.4">&para;</a></p></div><div id="rfc.figure.u.57"><pre class="text">  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
     
    666682</pre></div><div id="rfc.section.7.4.1.p.3"><p>The actual set of allowed methods is defined by the origin server at the time of each request. An origin server <em class="bcp14">MUST</em> generate an Allow field in a <a href="#status.405" class="smpl">405 (Method Not Allowed)</a> response and <em class="bcp14">MAY</em> do so in any other response. An empty Allow field value indicates that the resource allows no methods, which might occur in a 405 response if the resource has been temporarily disabled by configuration.<a class="self" href="#rfc.section.7.4.1.p.3">&para;</a></p></div><div id="rfc.section.7.4.1.p.4"><p>A proxy <em class="bcp14">MUST NOT</em> modify the Allow header field &#8212; it does not need to understand all of the indicated methods in order to handle them according to the generic message handling rules.<a class="self" href="#rfc.section.7.4.1.p.4">&para;</a></p></div></div><div id="header.server"><h3 id="rfc.section.7.4.2"><a href="#rfc.section.7.4.2">7.4.2</a>&nbsp;<a href="#header.server">Server</a></h3><div id="rfc.section.7.4.2.p.1"><p>The "Server" header field contains information about the software used by the origin server to handle the request, which is often used by clients to help identify the scope of reported interoperability problems, to work around or tailor requests to avoid particular server limitations, and for analytics regarding server or operating system use. An origin server <em class="bcp14">MAY</em> generate a Server field in its responses.<a class="self" href="#rfc.section.7.4.2.p.1">&para;</a></p></div><div id="rfc.figure.u.62"><pre class="inline"><span id="rfc.iref.g.54"></span>  <a href="#header.server" class="smpl">Server</a> = <a href="#header.user-agent" class="smpl">product</a> *( <a href="#imported.abnf" class="smpl">RWS</a> ( <a href="#header.user-agent" class="smpl">product</a> / <a href="#imported.abnf" class="smpl">comment</a> ) )
    667683</pre></div><div id="rfc.section.7.4.2.p.2"><p>The Server field-value consists of one or more product identifiers, each followed by zero or more comments (<a href="rfc7230.html#header.fields" title="Header Fields">Section 3.2</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.31"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>), which together identify the origin server software and its significant subproducts. By convention, the product identifiers are listed in decreasing order of their significance for identifying the origin server software. Each product identifier consists of a name and optional version, as defined in <a href="#header.user-agent" id="rfc.xref.header.user-agent.2" title="User-Agent">Section&nbsp;5.5.3</a>.<a class="self" href="#rfc.section.7.4.2.p.2">&para;</a></p></div><div id="rfc.section.7.4.2.p.3"><p>Example:<a class="self" href="#rfc.section.7.4.2.p.3">&para;</a></p></div><div id="rfc.figure.u.63"><pre class="text">  Server: CERN/3.0 libwww/2.17
    668 </pre></div><div id="rfc.section.7.4.2.p.4"><p>An origin server <em class="bcp14">SHOULD NOT</em> generate a Server field containing needlessly fine-grained detail and <em class="bcp14">SHOULD</em> limit the addition of subproducts by third parties. Overly long and detailed Server field values increase response latency and potentially reveal internal implementation details that might make it (slightly) easier for attackers to find and exploit known security holes.<a class="self" href="#rfc.section.7.4.2.p.4">&para;</a></p></div></div></div></div><div id="IANA.considerations"><h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a href="#IANA.considerations">IANA Considerations</a></h1><div id="method.registry"><h2 id="rfc.section.8.1"><a href="#rfc.section.8.1">8.1</a>&nbsp;<a href="#method.registry">Method Registry</a></h2><div id="rfc.section.8.1.p.1"><p>The "Hypertext Transfer Protocol (HTTP) Method Registry" defines the namespace for the request method token (<a href="#methods" title="Request Methods">Section&nbsp;4</a>). The method registry has been created and is now maintained at &lt;<a href="http://www.iana.org/assignments/http-methods">http://www.iana.org/assignments/http-methods</a>&gt;.<a class="self" href="#rfc.section.8.1.p.1">&para;</a></p></div><div id="method.registry.procedure"><h3 id="rfc.section.8.1.1"><a href="#rfc.section.8.1.1">8.1.1</a>&nbsp;<a href="#method.registry.procedure">Procedure</a></h3><div id="rfc.section.8.1.1.p.1"><p>HTTP method registrations <em class="bcp14">MUST</em> include the following fields: <a class="self" href="#rfc.section.8.1.1.p.1">&para;</a></p><ul><li>Method Name (see <a href="#methods" title="Request Methods">Section&nbsp;4</a>)</li><li>Safe ("yes" or "no", see <a href="#safe.methods" title="Safe Methods">Section&nbsp;4.2.1</a>)</li><li>Idempotent ("yes" or "no", see <a href="#idempotent.methods" title="Idempotent Methods">Section&nbsp;4.2.2</a>)</li><li>Pointer to specification text</li></ul></div><div id="rfc.section.8.1.1.p.2"><p>Values to be added to this namespace require IETF Review (see <a href="#RFC5226" id="rfc.xref.RFC5226.1"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>, <a href="https://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a>).<a class="self" href="#rfc.section.8.1.1.p.2">&para;</a></p></div></div><div id="considerations.for.new.methods"><h3 id="rfc.section.8.1.2"><a href="#rfc.section.8.1.2">8.1.2</a>&nbsp;<a href="#considerations.for.new.methods">Considerations for New Methods</a></h3><div id="rfc.section.8.1.2.p.1"><p>Standardized methods are generic; that is, they are potentially applicable to any resource, not just one particular media type, kind of resource, or application. As such, it is preferred that new methods be registered in a document that isn't specific to a single application or data format, since orthogonal technologies deserve orthogonal specification.<a class="self" href="#rfc.section.8.1.2.p.1">&para;</a></p></div><div id="rfc.section.8.1.2.p.2"><p>Since message parsing (<a href="rfc7230.html#message.body" title="Message Body">Section 3.3</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.32"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>) needs to be independent of method semantics (aside from responses to HEAD), definitions of new methods cannot change the parsing algorithm or prohibit the presence of a message body on either the request or the response message. Definitions of new methods can specify that only a zero-length message body is allowed by requiring a Content-Length header field with a value of "0".<a class="self" href="#rfc.section.8.1.2.p.2">&para;</a></p></div><div id="rfc.section.8.1.2.p.3"><p>A new method definition needs to indicate whether it is safe (<a href="#safe.methods" title="Safe Methods">Section&nbsp;4.2.1</a>), idempotent (<a href="#idempotent.methods" title="Idempotent Methods">Section&nbsp;4.2.2</a>), cacheable (<a href="#cacheable.methods" title="Cacheable Methods">Section&nbsp;4.2.3</a>), what semantics are to be associated with the payload body if any is present in the request and what refinements the method makes to header field or status code semantics. If the new method is cacheable, its definition ought to describe how, and under what conditions, a cache can store a response and use it to satisfy a subsequent request. The new method ought to describe whether it can be made conditional (<a href="#request.conditionals" title="Conditionals">Section&nbsp;5.2</a>) and, if so, how a server responds when the condition is false. Likewise, if the new method might have some use for partial response semantics (<a href="#RFC7233" id="rfc.xref.RFC7233.11"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a>), it ought to document this, too.<a class="self" href="#rfc.section.8.1.2.p.3">&para;</a></p></div><div class="note" id="rfc.section.8.1.2.p.4"><p><b>Note:</b> Avoid defining a method name that starts with "M-", since that prefix might be misinterpreted as having the semantics assigned to it by <a href="#RFC2774" id="rfc.xref.RFC2774.1"><cite title="An HTTP Extension Framework">[RFC2774]</cite></a>.<a class="self" href="#rfc.section.8.1.2.p.4">&para;</a></p></div></div><div id="method.registration"><h3 id="rfc.section.8.1.3"><a href="#rfc.section.8.1.3">8.1.3</a>&nbsp;<a href="#method.registration">Registrations</a></h3><div id="rfc.section.8.1.3.p.1"><p>The "Hypertext Transfer Protocol (HTTP) Method Registry" has been populated with the registrations below:<a class="self" href="#rfc.section.8.1.3.p.1">&para;</a></p></div><div id="rfc.table.2"><div id="iana.method.registration.table"></div><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Method</th><th>Safe</th><th>Idempotent</th><th>Reference</th></tr></thead><tbody><tr><td class="left">CONNECT</td><td class="left">no</td><td class="left">no</td><td class="left"><a href="#CONNECT" id="rfc.xref.CONNECT.2" title="CONNECT">Section&nbsp;4.3.6</a> </td></tr><tr><td class="left">DELETE</td><td class="left">no</td><td class="left">yes</td><td class="left"><a href="#DELETE" id="rfc.xref.DELETE.2" title="DELETE">Section&nbsp;4.3.5</a> </td></tr><tr><td class="left">GET</td><td class="left">yes</td><td class="left">yes</td><td class="left"><a href="#GET" id="rfc.xref.GET.5" title="GET">Section&nbsp;4.3.1</a> </td></tr><tr><td class="left">HEAD</td><td class="left">yes</td><td class="left">yes</td><td class="left"><a href="#HEAD" id="rfc.xref.HEAD.3" title="HEAD">Section&nbsp;4.3.2</a> </td></tr><tr><td class="left">OPTIONS</td><td class="left">yes</td><td class="left">yes</td><td class="left"><a href="#OPTIONS" id="rfc.xref.OPTIONS.3" title="OPTIONS">Section&nbsp;4.3.7</a> </td></tr><tr><td class="left">POST</td><td class="left">no</td><td class="left">no</td><td class="left"><a href="#POST" id="rfc.xref.POST.4" title="POST">Section&nbsp;4.3.3</a> </td></tr><tr><td class="left">PUT</td><td class="left">no</td><td class="left">yes</td><td class="left"><a href="#PUT" id="rfc.xref.PUT.4" title="PUT">Section&nbsp;4.3.4</a> </td></tr><tr><td class="left">TRACE</td><td class="left">yes</td><td class="left">yes</td><td class="left"><a href="#TRACE" id="rfc.xref.TRACE.3" title="TRACE">Section&nbsp;4.3.8</a> </td></tr></tbody></table></div></div></div><div id="status.code.registry"><h2 id="rfc.section.8.2"><a href="#rfc.section.8.2">8.2</a>&nbsp;<a href="#status.code.registry">Status Code Registry</a></h2><div id="rfc.section.8.2.p.1"><p>The "Hypertext Transfer Protocol (HTTP) Status Code Registry" defines the namespace for the response status-code token (<a href="#status.codes" title="Response Status Codes">Section&nbsp;6</a>). The status code registry is maintained at &lt;<a href="http://www.iana.org/assignments/http-status-codes">http://www.iana.org/assignments/http-status-codes</a>&gt;.<a class="self" href="#rfc.section.8.2.p.1">&para;</a></p></div><div id="rfc.section.8.2.p.2"><p>This section replaces the registration procedure for HTTP Status Codes previously defined in <a href="https://tools.ietf.org/html/rfc2817#section-7.1">Section 7.1</a> of <a href="#RFC2817" id="rfc.xref.RFC2817.1"><cite title="Upgrading to TLS Within HTTP/1.1">[RFC2817]</cite></a>.<a class="self" href="#rfc.section.8.2.p.2">&para;</a></p></div><div id="status.code.registry.procedure"><h3 id="rfc.section.8.2.1"><a href="#rfc.section.8.2.1">8.2.1</a>&nbsp;<a href="#status.code.registry.procedure">Procedure</a></h3><div id="rfc.section.8.2.1.p.1"><p>A registration <em class="bcp14">MUST</em> include the following fields: <a class="self" href="#rfc.section.8.2.1.p.1">&para;</a></p><ul><li>Status Code (3 digits)</li><li>Short Description</li><li>Pointer to specification text</li></ul></div><div id="rfc.section.8.2.1.p.2"><p>Values to be added to the HTTP status code namespace require IETF Review (see <a href="#RFC5226" id="rfc.xref.RFC5226.2"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>, <a href="https://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a>).<a class="self" href="#rfc.section.8.2.1.p.2">&para;</a></p></div></div><div id="considerations.for.new.status.codes"><h3 id="rfc.section.8.2.2"><a href="#rfc.section.8.2.2">8.2.2</a>&nbsp;<a href="#considerations.for.new.status.codes">Considerations for New Status Codes</a></h3><div id="rfc.section.8.2.2.p.1"><p>When it is necessary to express semantics for a response that are not defined by current status codes, a new status code can be registered. Status codes are generic; they are potentially applicable to any resource, not just one particular media type, kind of resource, or application of HTTP. As such, it is preferred that new status codes be registered in a document that isn't specific to a single application.<a class="self" href="#rfc.section.8.2.2.p.1">&para;</a></p></div><div id="rfc.section.8.2.2.p.2"><p>New status codes are required to fall under one of the categories defined in <a href="#status.codes" title="Response Status Codes">Section&nbsp;6</a>. To allow existing parsers to process the response message, new status codes cannot disallow a payload, although they can mandate a zero-length payload body.<a class="self" href="#rfc.section.8.2.2.p.2">&para;</a></p></div><div id="rfc.section.8.2.2.p.3"><p>Proposals for new status codes that are not yet widely deployed ought to avoid allocating a specific number for the code until there is clear consensus that it will be registered; instead, early drafts can use a notation such as "4NN", or "3N0" .. "3N9", to indicate the class of the proposed status code(s) without consuming a number prematurely.<a class="self" href="#rfc.section.8.2.2.p.3">&para;</a></p></div><div id="rfc.section.8.2.2.p.4"><p>The definition of a new status code ought to explain the request conditions that would cause a response containing that status code (e.g., combinations of request header fields and/or method(s)) along with any dependencies on response header fields (e.g., what fields are required, what fields can modify the semantics, and what header field semantics are further refined when used with the new status code).<a class="self" href="#rfc.section.8.2.2.p.4">&para;</a></p></div><div id="rfc.section.8.2.2.p.5"><p>The definition of a new status code ought to specify whether or not it is cacheable. Note that all status codes can be cached if the response they occur in has explicit freshness information; however, status codes that are defined as being cacheable are allowed to be cached without explicit freshness information. Likewise, the definition of a status code can place constraints upon cache behavior. See <a href="#RFC7234" id="rfc.xref.RFC7234.28"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a> for more information.<a class="self" href="#rfc.section.8.2.2.p.5">&para;</a></p></div><div id="rfc.section.8.2.2.p.6"><p>Finally, the definition of a new status code ought to indicate whether the payload has any implied association with an identified resource (<a href="#identifying.payload" title="Identifying a Representation">Section&nbsp;3.1.4.1</a>).<a class="self" href="#rfc.section.8.2.2.p.6">&para;</a></p></div></div><div id="status.code.registration"><h3 id="rfc.section.8.2.3"><a href="#rfc.section.8.2.3">8.2.3</a>&nbsp;<a href="#status.code.registration">Registrations</a></h3><div id="rfc.section.8.2.3.p.1"><p>The status code registry has been updated with the registrations below:<a class="self" href="#rfc.section.8.2.3.p.1">&para;</a></p></div><div id="rfc.table.3"><div id="iana.status.code.registration.table"></div><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Value</th><th>Description</th><th>Reference</th></tr></thead><tbody><tr><td class="left">100</td><td class="left">Continue</td><td class="left"><a href="#status.100" id="rfc.xref.status.100.2" title="100 Continue">Section&nbsp;6.2.1</a> </td></tr><tr><td class="left">101</td><td class="left">Switching Protocols</td><td class="left"><a href="#status.101" id="rfc.xref.status.101.2" title="101 Switching Protocols">Section&nbsp;6.2.2</a> </td></tr><tr><td class="left">200</td><td class="left">OK</td><td class="left"><a href="#status.200" id="rfc.xref.status.200.2" title="200 OK">Section&nbsp;6.3.1</a> </td></tr><tr><td class="left">201</td><td class="left">Created</td><td class="left"><a href="#status.201" id="rfc.xref.status.201.2" title="201 Created">Section&nbsp;6.3.2</a> </td></tr><tr><td class="left">202</td><td class="left">Accepted</td><td class="left"><a href="#status.202" id="rfc.xref.status.202.2" title="202 Accepted">Section&nbsp;6.3.3</a> </td></tr><tr><td class="left">203</td><td class="left">Non-Authoritative Information</td><td class="left"><a href="#status.203" id="rfc.xref.status.203.2" title="203 Non-Authoritative Information">Section&nbsp;6.3.4</a> </td></tr><tr><td class="left">204</td><td class="left">No Content</td><td class="left"><a href="#status.204" id="rfc.xref.status.204.2" title="204 No Content">Section&nbsp;6.3.5</a> </td></tr><tr><td class="left">205</td><td class="left">Reset Content</td><td class="left"><a href="#status.205" id="rfc.xref.status.205.2" title="205 Reset Content">Section&nbsp;6.3.6</a> </td></tr><tr><td class="left">300</td><td class="left">Multiple Choices</td><td class="left"><a href="#status.300" id="rfc.xref.status.300.3" title="300 Multiple Choices">Section&nbsp;6.4.1</a> </td></tr><tr><td class="left">301</td><td class="left">Moved Permanently</td><td class="left"><a href="#status.301" id="rfc.xref.status.301.2" title="301 Moved Permanently">Section&nbsp;6.4.2</a> </td></tr><tr><td class="left">302</td><td class="left">Found</td><td class="left"><a href="#status.302" id="rfc.xref.status.302.2" title="302 Found">Section&nbsp;6.4.3</a> </td></tr><tr><td class="left">303</td><td class="left">See Other</td><td class="left"><a href="#status.303" id="rfc.xref.status.303.2" title="303 See Other">Section&nbsp;6.4.4</a> </td></tr><tr><td class="left">305</td><td class="left">Use Proxy</td><td class="left"><a href="#status.305" id="rfc.xref.status.305.2" title="305 Use Proxy">Section&nbsp;6.4.5</a> </td></tr><tr><td class="left">306</td><td class="left">(Unused)</td><td class="left"><a href="#status.306" id="rfc.xref.status.306.1" title="306 (Unused)">Section&nbsp;6.4.6</a> </td></tr><tr><td class="left">307</td><td class="left">Temporary Redirect</td><td class="left"><a href="#status.307" id="rfc.xref.status.307.2" title="307 Temporary Redirect">Section&nbsp;6.4.7</a> </td></tr><tr><td class="left">400</td><td class="left">Bad Request</td><td class="left"><a href="#status.400" id="rfc.xref.status.400.2" title="400 Bad Request">Section&nbsp;6.5.1</a> </td></tr><tr><td class="left">402</td><td class="left">Payment Required</td><td class="left"><a href="#status.402" id="rfc.xref.status.402.2" title="402 Payment Required">Section&nbsp;6.5.2</a> </td></tr><tr><td class="left">403</td><td class="left">Forbidden</td><td class="left"><a href="#status.403" id="rfc.xref.status.403.2" title="403 Forbidden">Section&nbsp;6.5.3</a> </td></tr><tr><td class="left">404</td><td class="left">Not Found</td><td class="left"><a href="#status.404" id="rfc.xref.status.404.2" title="404 Not Found">Section&nbsp;6.5.4</a> </td></tr><tr><td class="left">405</td><td class="left">Method Not Allowed</td><td class="left"><a href="#status.405" id="rfc.xref.status.405.2" title="405 Method Not Allowed">Section&nbsp;6.5.5</a> </td></tr><tr><td class="left">406</td><td class="left">Not Acceptable</td><td class="left"><a href="#status.406" id="rfc.xref.status.406.2" title="406 Not Acceptable">Section&nbsp;6.5.6</a> </td></tr><tr><td class="left">408</td><td class="left">Request Timeout</td><td class="left"><a href="#status.408" id="rfc.xref.status.408.2" title="408 Request Timeout">Section&nbsp;6.5.7</a> </td></tr><tr><td class="left">409</td><td class="left">Conflict</td><td class="left"><a href="#status.409" id="rfc.xref.status.409.2" title="409 Conflict">Section&nbsp;6.5.8</a> </td></tr><tr><td class="left">410</td><td class="left">Gone</td><td class="left"><a href="#status.410" id="rfc.xref.status.410.2" title="410 Gone">Section&nbsp;6.5.9</a> </td></tr><tr><td class="left">411</td><td class="left">Length Required</td><td class="left"><a href="#status.411" id="rfc.xref.status.411.2" title="411 Length Required">Section&nbsp;6.5.10</a> </td></tr><tr><td class="left">413</td><td class="left">Payload Too Large</td><td class="left"><a href="#status.413" id="rfc.xref.status.413.2" title="413 Payload Too Large">Section&nbsp;6.5.11</a> </td></tr><tr><td class="left">414</td><td class="left">URI Too Long</td><td class="left"><a href="#status.414" id="rfc.xref.status.414.2" title="414 URI Too Long">Section&nbsp;6.5.12</a> </td></tr><tr><td class="left">415</td><td class="left">Unsupported Media Type</td><td class="left"><a href="#status.415" id="rfc.xref.status.415.2" title="415 Unsupported Media Type">Section&nbsp;6.5.13</a> </td></tr><tr><td class="left">417</td><td class="left">Expectation Failed</td><td class="left"><a href="#status.417" id="rfc.xref.status.417.2" title="417 Expectation Failed">Section&nbsp;6.5.14</a> </td></tr><tr><td class="left">426</td><td class="left">Upgrade Required</td><td class="left"><a href="#status.426" id="rfc.xref.status.426.2" title="426 Upgrade Required">Section&nbsp;6.5.15</a> </td></tr><tr><td class="left">500</td><td class="left">Internal Server Error</td><td class="left"><a href="#status.500" id="rfc.xref.status.500.2" title="500 Internal Server Error">Section&nbsp;6.6.1</a> </td></tr><tr><td class="left">501</td><td class="left">Not Implemented</td><td class="left"><a href="#status.501" id="rfc.xref.status.501.2" title="501 Not Implemented">Section&nbsp;6.6.2</a> </td></tr><tr><td class="left">502</td><td class="left">Bad Gateway</td><td class="left"><a href="#status.502" id="rfc.xref.status.502.2" title="502 Bad Gateway">Section&nbsp;6.6.3</a> </td></tr><tr><td class="left">503</td><td class="left">Service Unavailable</td><td class="left"><a href="#status.503" id="rfc.xref.status.503.2" title="503 Service Unavailable">Section&nbsp;6.6.4</a> </td></tr><tr><td class="left">504</td><td class="left">Gateway Timeout</td><td class="left"><a href="#status.504" id="rfc.xref.status.504.2" title="504 Gateway Timeout">Section&nbsp;6.6.5</a> </td></tr><tr><td class="left">505</td><td class="left">HTTP Version Not Supported</td><td class="left"><a href="#status.505" id="rfc.xref.status.505.2" title="505 HTTP Version Not Supported">Section&nbsp;6.6.6</a> </td></tr></tbody></table></div></div></div><div id="header.field.registry"><h2 id="rfc.section.8.3"><a href="#rfc.section.8.3">8.3</a>&nbsp;<a href="#header.field.registry">Header Field Registry</a></h2><div id="rfc.section.8.3.p.1"><p>HTTP header fields are registered within the "Message Headers" registry located at &lt;<a href="http://www.iana.org/assignments/message-headers">http://www.iana.org/assignments/message-headers</a>&gt;, as defined by <a href="#BCP90" id="rfc.xref.BCP90.1"><cite title="Registration Procedures for Message Header Fields">[BCP90]</cite></a>.<a class="self" href="#rfc.section.8.3.p.1">&para;</a></p></div><div id="considerations.for.new.header.fields"><h3 id="rfc.section.8.3.1"><a href="#rfc.section.8.3.1">8.3.1</a>&nbsp;<a href="#considerations.for.new.header.fields">Considerations for New Header Fields</a></h3><div id="rfc.section.8.3.1.p.1"><p>Header fields are key:value pairs that can be used to communicate data about the message, its payload, the target resource, or the connection (i.e., control data). See <a href="rfc7230.html#header.fields" title="Header Fields">Section 3.2</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.33"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a> for a general definition of header field syntax in HTTP messages.<a class="self" href="#rfc.section.8.3.1.p.1">&para;</a></p></div><div id="rfc.section.8.3.1.p.2"><p>The requirements for header field names are defined in <a href="#BCP90" id="rfc.xref.BCP90.2"><cite title="Registration Procedures for Message Header Fields">[BCP90]</cite></a>.<a class="self" href="#rfc.section.8.3.1.p.2">&para;</a></p></div><div id="rfc.section.8.3.1.p.3"><p>Authors of specifications defining new fields are advised to keep the name as short as practical and not to prefix the name with "X-" unless the header field will never be used on the Internet. (The "X-" prefix idiom has been extensively misused in practice; it was intended to only be used as a mechanism for avoiding name collisions inside proprietary software or intranet processing, since the prefix would ensure that private names never collide with a newly registered Internet name; see <a href="#BCP178" id="rfc.xref.BCP178.1"><cite title="Deprecating the &#34;X-&#34; Prefix and Similar Constructs in Application Protocols">[BCP178]</cite></a> for further information).<a class="self" href="#rfc.section.8.3.1.p.3">&para;</a></p></div><div id="rfc.section.8.3.1.p.4"><p>New header field values typically have their syntax defined using ABNF (<a href="#RFC5234" id="rfc.xref.RFC5234.2"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>), using the extension defined in <a href="rfc7230.html#abnf.extension" title="ABNF List Extension: #rule">Section 7</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.34"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a> as necessary, and are usually constrained to the range of US-ASCII characters. Header fields needing a greater range of characters can use an encoding such as the one defined in <a href="#RFC5987" id="rfc.xref.RFC5987.1"><cite title="Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters">[RFC5987]</cite></a>.<a class="self" href="#rfc.section.8.3.1.p.4">&para;</a></p></div><div id="rfc.section.8.3.1.p.5"><p>Leading and trailing whitespace in raw field values is removed upon field parsing (<a href="rfc7230.html#field.parsing" title="Field Parsing">Section 3.2.4</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.35"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>). Field definitions where leading or trailing whitespace in values is significant will have to use a container syntax such as quoted-string (<a href="rfc7230.html#field.components" title="Field Value Components">Section 3.2.6</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.36"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>).<a class="self" href="#rfc.section.8.3.1.p.5">&para;</a></p></div><div id="rfc.section.8.3.1.p.6"><p>Because commas (",") are used as a generic delimiter between field-values, they need to be treated with care if they are allowed in the field-value. Typically, components that might contain a comma are protected with double-quotes using the quoted-string ABNF production.<a class="self" href="#rfc.section.8.3.1.p.6">&para;</a></p></div><div id="rfc.section.8.3.1.p.7"><p>For example, a textual date and a URI (either of which might contain a comma) could be safely carried in field-values like these:<a class="self" href="#rfc.section.8.3.1.p.7">&para;</a></p></div><div id="rfc.figure.u.64"><pre class="text">  Example-URI-Field: "http://example.com/a.html,foo",
     684</pre></div><div id="rfc.section.7.4.2.p.4"><p>An origin server <em class="bcp14">SHOULD NOT</em> generate a Server field containing needlessly fine-grained detail and <em class="bcp14">SHOULD</em> limit the addition of subproducts by third parties. Overly long and detailed Server field values increase response latency and potentially reveal internal implementation details that might make it (slightly) easier for attackers to find and exploit known security holes.<a class="self" href="#rfc.section.7.4.2.p.4">&para;</a></p></div></div></div></div><div id="IANA.considerations"><h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a href="#IANA.considerations">IANA Considerations</a></h1><div id="method.registry"><h2 id="rfc.section.8.1"><a href="#rfc.section.8.1">8.1</a>&nbsp;<a href="#method.registry">Method Registry</a></h2><div id="rfc.section.8.1.p.1"><p>The "Hypertext Transfer Protocol (HTTP) Method Registry" defines the namespace for the request method token (<a href="#methods" title="Request Methods">Section&nbsp;4</a>). The method registry has been created and is now maintained at &lt;<a href="http://www.iana.org/assignments/http-methods">http://www.iana.org/assignments/http-methods</a>&gt;.<a class="self" href="#rfc.section.8.1.p.1">&para;</a></p></div><div id="method.registry.procedure"><h3 id="rfc.section.8.1.1"><a href="#rfc.section.8.1.1">8.1.1</a>&nbsp;<a href="#method.registry.procedure">Procedure</a></h3><div id="rfc.section.8.1.1.p.1"><p>HTTP method registrations <em class="bcp14">MUST</em> include the following fields: <a class="self" href="#rfc.section.8.1.1.p.1">&para;</a></p><ul><li>Method Name (see <a href="#methods" title="Request Methods">Section&nbsp;4</a>)</li><li>Safe ("yes" or "no", see <a href="#safe.methods" title="Safe Methods">Section&nbsp;4.2.1</a>)</li><li>Idempotent ("yes" or "no", see <a href="#idempotent.methods" title="Idempotent Methods">Section&nbsp;4.2.2</a>)</li><li>Pointer to specification text</li></ul></div><div id="rfc.section.8.1.1.p.2"><p>Values to be added to this namespace require IETF Review (see <a href="#RFC5226" id="rfc.xref.RFC5226.1"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>, <a href="https://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a>).<a class="self" href="#rfc.section.8.1.1.p.2">&para;</a></p></div></div><div id="considerations.for.new.methods"><h3 id="rfc.section.8.1.2"><a href="#rfc.section.8.1.2">8.1.2</a>&nbsp;<a href="#considerations.for.new.methods">Considerations for New Methods</a></h3><div id="rfc.section.8.1.2.p.1"><p>Standardized methods are generic; that is, they are potentially applicable to any resource, not just one particular media type, kind of resource, or application. As such, it is preferred that new methods be registered in a document that isn't specific to a single application or data format, since orthogonal technologies deserve orthogonal specification.<a class="self" href="#rfc.section.8.1.2.p.1">&para;</a></p></div><div id="rfc.section.8.1.2.p.2"><p>Since message parsing (<a href="rfc7230.html#message.body" title="Message Body">Section 3.3</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.32"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>) needs to be independent of method semantics (aside from responses to HEAD), definitions of new methods cannot change the parsing algorithm or prohibit the presence of a message body on either the request or the response message. Definitions of new methods can specify that only a zero-length message body is allowed by requiring a Content-Length header field with a value of "0".<a class="self" href="#rfc.section.8.1.2.p.2">&para;</a></p></div><div id="rfc.section.8.1.2.p.3"><p>A new method definition needs to indicate whether it is safe (<a href="#safe.methods" title="Safe Methods">Section&nbsp;4.2.1</a>), idempotent (<a href="#idempotent.methods" title="Idempotent Methods">Section&nbsp;4.2.2</a>), cacheable (<a href="#cacheable.methods" title="Cacheable Methods">Section&nbsp;4.2.3</a>), what semantics are to be associated with the payload body if any is present in the request and what refinements the method makes to header field or status code semantics. If the new method is cacheable, its definition ought to describe how, and under what conditions, a cache can store a response and use it to satisfy a subsequent request. The new method ought to describe whether it can be made conditional (<a href="#request.conditionals" title="Conditionals">Section&nbsp;5.2</a>) and, if so, how a server responds when the condition is false. Likewise, if the new method might have some use for partial response semantics (<a href="#RFC7233" id="rfc.xref.RFC7233.11"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Range Requests">[RFC7233]</cite></a>), it ought to document this, too.<a class="self" href="#rfc.section.8.1.2.p.3">&para;</a></p></div><div class="note"><div id="rfc.section.8.1.2.p.4"><p><b>Note:</b> Avoid defining a method name that starts with "M-", since that prefix might be misinterpreted as having the semantics assigned to it by <a href="#RFC2774" id="rfc.xref.RFC2774.1"><cite title="An HTTP Extension Framework">[RFC2774]</cite></a>.<a class="self" href="#rfc.section.8.1.2.p.4">&para;</a></p></div></div></div><div id="method.registration"><h3 id="rfc.section.8.1.3"><a href="#rfc.section.8.1.3">8.1.3</a>&nbsp;<a href="#method.registration">Registrations</a></h3><div id="rfc.section.8.1.3.p.1"><p>The "Hypertext Transfer Protocol (HTTP) Method Registry" has been populated with the registrations below:<a class="self" href="#rfc.section.8.1.3.p.1">&para;</a></p></div><div id="rfc.table.2"><div id="iana.method.registration.table"></div><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Method</th><th>Safe</th><th>Idempotent</th><th>Reference</th></tr></thead><tbody><tr><td class="left">CONNECT</td><td class="left">no</td><td class="left">no</td><td class="left"><a href="#CONNECT" id="rfc.xref.CONNECT.2" title="CONNECT">Section&nbsp;4.3.6</a> </td></tr><tr><td class="left">DELETE</td><td class="left">no</td><td class="left">yes</td><td class="left"><a href="#DELETE" id="rfc.xref.DELETE.2" title="DELETE">Section&nbsp;4.3.5</a> </td></tr><tr><td class="left">GET</td><td class="left">yes</td><td class="left">yes</td><td class="left"><a href="#GET" id="rfc.xref.GET.5" title="GET">Section&nbsp;4.3.1</a> </td></tr><tr><td class="left">HEAD</td><td class="left">yes</td><td class="left">yes</td><td class="left"><a href="#HEAD" id="rfc.xref.HEAD.3" title="HEAD">Section&nbsp;4.3.2</a> </td></tr><tr><td class="left">OPTIONS</td><td class="left">yes</td><td class="left">yes</td><td class="left"><a href="#OPTIONS" id="rfc.xref.OPTIONS.3" title="OPTIONS">Section&nbsp;4.3.7</a> </td></tr><tr><td class="left">POST</td><td class="left">no</td><td class="left">no</td><td class="left"><a href="#POST" id="rfc.xref.POST.4" title="POST">Section&nbsp;4.3.3</a> </td></tr><tr><td class="left">PUT</td><td class="left">no</td><td class="left">yes</td><td class="left"><a href="#PUT" id="rfc.xref.PUT.4" title="PUT">Section&nbsp;4.3.4</a> </td></tr><tr><td class="left">TRACE</td><td class="left">yes</td><td class="left">yes</td><td class="left"><a href="#TRACE" id="rfc.xref.TRACE.3" title="TRACE">Section&nbsp;4.3.8</a> </td></tr></tbody></table></div></div></div><div id="status.code.registry"><h2 id="rfc.section.8.2"><a href="#rfc.section.8.2">8.2</a>&nbsp;<a href="#status.code.registry">Status Code Registry</a></h2><div id="rfc.section.8.2.p.1"><p>The "Hypertext Transfer Protocol (HTTP) Status Code Registry" defines the namespace for the response status-code token (<a href="#status.codes" title="Response Status Codes">Section&nbsp;6</a>). The status code registry is maintained at &lt;<a href="http://www.iana.org/assignments/http-status-codes">http://www.iana.org/assignments/http-status-codes</a>&gt;.<a class="self" href="#rfc.section.8.2.p.1">&para;</a></p></div><div id="rfc.section.8.2.p.2"><p>This section replaces the registration procedure for HTTP Status Codes previously defined in <a href="https://tools.ietf.org/html/rfc2817#section-7.1">Section 7.1</a> of <a href="#RFC2817" id="rfc.xref.RFC2817.1"><cite title="Upgrading to TLS Within HTTP/1.1">[RFC2817]</cite></a>.<a class="self" href="#rfc.section.8.2.p.2">&para;</a></p></div><div id="status.code.registry.procedure"><h3 id="rfc.section.8.2.1"><a href="#rfc.section.8.2.1">8.2.1</a>&nbsp;<a href="#status.code.registry.procedure">Procedure</a></h3><div id="rfc.section.8.2.1.p.1"><p>A registration <em class="bcp14">MUST</em> include the following fields: <a class="self" href="#rfc.section.8.2.1.p.1">&para;</a></p><ul><li>Status Code (3 digits)</li><li>Short Description</li><li>Pointer to specification text</li></ul></div><div id="rfc.section.8.2.1.p.2"><p>Values to be added to the HTTP status code namespace require IETF Review (see <a href="#RFC5226" id="rfc.xref.RFC5226.2"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>, <a href="https://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a>).<a class="self" href="#rfc.section.8.2.1.p.2">&para;</a></p></div></div><div id="considerations.for.new.status.codes"><h3 id="rfc.section.8.2.2"><a href="#rfc.section.8.2.2">8.2.2</a>&nbsp;<a href="#considerations.for.new.status.codes">Considerations for New Status Codes</a></h3><div id="rfc.section.8.2.2.p.1"><p>When it is necessary to express semantics for a response that are not defined by current status codes, a new status code can be registered. Status codes are generic; they are potentially applicable to any resource, not just one particular media type, kind of resource, or application of HTTP. As such, it is preferred that new status codes be registered in a document that isn't specific to a single application.<a class="self" href="#rfc.section.8.2.2.p.1">&para;</a></p></div><div id="rfc.section.8.2.2.p.2"><p>New status codes are required to fall under one of the categories defined in <a href="#status.codes" title="Response Status Codes">Section&nbsp;6</a>. To allow existing parsers to process the response message, new status codes cannot disallow a payload, although they can mandate a zero-length payload body.<a class="self" href="#rfc.section.8.2.2.p.2">&para;</a></p></div><div id="rfc.section.8.2.2.p.3"><p>Proposals for new status codes that are not yet widely deployed ought to avoid allocating a specific number for the code until there is clear consensus that it will be registered; instead, early drafts can use a notation such as "4NN", or "3N0" .. "3N9", to indicate the class of the proposed status code(s) without consuming a number prematurely.<a class="self" href="#rfc.section.8.2.2.p.3">&para;</a></p></div><div id="rfc.section.8.2.2.p.4"><p>The definition of a new status code ought to explain the request conditions that would cause a response containing that status code (e.g., combinations of request header fields and/or method(s)) along with any dependencies on response header fields (e.g., what fields are required, what fields can modify the semantics, and what header field semantics are further refined when used with the new status code).<a class="self" href="#rfc.section.8.2.2.p.4">&para;</a></p></div><div id="rfc.section.8.2.2.p.5"><p>The definition of a new status code ought to specify whether or not it is cacheable. Note that all status codes can be cached if the response they occur in has explicit freshness information; however, status codes that are defined as being cacheable are allowed to be cached without explicit freshness information. Likewise, the definition of a status code can place constraints upon cache behavior. See <a href="#RFC7234" id="rfc.xref.RFC7234.28"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a> for more information.<a class="self" href="#rfc.section.8.2.2.p.5">&para;</a></p></div><div id="rfc.section.8.2.2.p.6"><p>Finally, the definition of a new status code ought to indicate whether the payload has any implied association with an identified resource (<a href="#identifying.payload" title="Identifying a Representation">Section&nbsp;3.1.4.1</a>).<a class="self" href="#rfc.section.8.2.2.p.6">&para;</a></p></div></div><div id="status.code.registration"><h3 id="rfc.section.8.2.3"><a href="#rfc.section.8.2.3">8.2.3</a>&nbsp;<a href="#status.code.registration">Registrations</a></h3><div id="rfc.section.8.2.3.p.1"><p>The status code registry has been updated with the registrations below:<a class="self" href="#rfc.section.8.2.3.p.1">&para;</a></p></div><div id="rfc.table.3"><div id="iana.status.code.registration.table"></div><table class="tt full left" cellpadding="3" cellspacing="0"><thead><tr><th>Value</th><th>Description</th><th>Reference</th></tr></thead><tbody><tr><td class="left">100</td><td class="left">Continue</td><td class="left"><a href="#status.100" id="rfc.xref.status.100.2" title="100 Continue">Section&nbsp;6.2.1</a> </td></tr><tr><td class="left">101</td><td class="left">Switching Protocols</td><td class="left"><a href="#status.101" id="rfc.xref.status.101.2" title="101 Switching Protocols">Section&nbsp;6.2.2</a> </td></tr><tr><td class="left">200</td><td class="left">OK</td><td class="left"><a href="#status.200" id="rfc.xref.status.200.2" title="200 OK">Section&nbsp;6.3.1</a> </td></tr><tr><td class="left">201</td><td class="left">Created</td><td class="left"><a href="#status.201" id="rfc.xref.status.201.2" title="201 Created">Section&nbsp;6.3.2</a> </td></tr><tr><td class="left">202</td><td class="left">Accepted</td><td class="left"><a href="#status.202" id="rfc.xref.status.202.2" title="202 Accepted">Section&nbsp;6.3.3</a> </td></tr><tr><td class="left">203</td><td class="left">Non-Authoritative Information</td><td class="left"><a href="#status.203" id="rfc.xref.status.203.2" title="203 Non-Authoritative Information">Section&nbsp;6.3.4</a> </td></tr><tr><td class="left">204</td><td class="left">No Content</td><td class="left"><a href="#status.204" id="rfc.xref.status.204.2" title="204 No Content">Section&nbsp;6.3.5</a> </td></tr><tr><td class="left">205</td><td class="left">Reset Content</td><td class="left"><a href="#status.205" id="rfc.xref.status.205.2" title="205 Reset Content">Section&nbsp;6.3.6</a> </td></tr><tr><td class="left">300</td><td class="left">Multiple Choices</td><td class="left"><a href="#status.300" id="rfc.xref.status.300.3" title="300 Multiple Choices">Section&nbsp;6.4.1</a> </td></tr><tr><td class="left">301</td><td class="left">Moved Permanently</td><td class="left"><a href="#status.301" id="rfc.xref.status.301.2" title="301 Moved Permanently">Section&nbsp;6.4.2</a> </td></tr><tr><td class="left">302</td><td class="left">Found</td><td class="left"><a href="#status.302" id="rfc.xref.status.302.2" title="302 Found">Section&nbsp;6.4.3</a> </td></tr><tr><td class="left">303</td><td class="left">See Other</td><td class="left"><a href="#status.303" id="rfc.xref.status.303.2" title="303 See Other">Section&nbsp;6.4.4</a> </td></tr><tr><td class="left">305</td><td class="left">Use Proxy</td><td class="left"><a href="#status.305" id="rfc.xref.status.305.2" title="305 Use Proxy">Section&nbsp;6.4.5</a> </td></tr><tr><td class="left">306</td><td class="left">(Unused)</td><td class="left"><a href="#status.306" id="rfc.xref.status.306.1" title="306 (Unused)">Section&nbsp;6.4.6</a> </td></tr><tr><td class="left">307</td><td class="left">Temporary Redirect</td><td class="left"><a href="#status.307" id="rfc.xref.status.307.2" title="307 Temporary Redirect">Section&nbsp;6.4.7</a> </td></tr><tr><td class="left">400</td><td class="left">Bad Request</td><td class="left"><a href="#status.400" id="rfc.xref.status.400.2" title="400 Bad Request">Section&nbsp;6.5.1</a> </td></tr><tr><td class="left">402</td><td class="left">Payment Required</td><td class="left"><a href="#status.402" id="rfc.xref.status.402.2" title="402 Payment Required">Section&nbsp;6.5.2</a> </td></tr><tr><td class="left">403</td><td class="left">Forbidden</td><td class="left"><a href="#status.403" id="rfc.xref.status.403.2" title="403 Forbidden">Section&nbsp;6.5.3</a> </td></tr><tr><td class="left">404</td><td class="left">Not Found</td><td class="left"><a href="#status.404" id="rfc.xref.status.404.2" title="404 Not Found">Section&nbsp;6.5.4</a> </td></tr><tr><td class="left">405</td><td class="left">Method Not Allowed</td><td class="left"><a href="#status.405" id="rfc.xref.status.405.2" title="405 Method Not Allowed">Section&nbsp;6.5.5</a> </td></tr><tr><td class="left">406</td><td class="left">Not Acceptable</td><td class="left"><a href="#status.406" id="rfc.xref.status.406.2" title="406 Not Acceptable">Section&nbsp;6.5.6</a> </td></tr><tr><td class="left">408</td><td class="left">Request Timeout</td><td class="left"><a href="#status.408" id="rfc.xref.status.408.2" title="408 Request Timeout">Section&nbsp;6.5.7</a> </td></tr><tr><td class="left">409</td><td class="left">Conflict</td><td class="left"><a href="#status.409" id="rfc.xref.status.409.2" title="409 Conflict">Section&nbsp;6.5.8</a> </td></tr><tr><td class="left">410</td><td class="left">Gone</td><td class="left"><a href="#status.410" id="rfc.xref.status.410.2" title="410 Gone">Section&nbsp;6.5.9</a> </td></tr><tr><td class="left">411</td><td class="left">Length Required</td><td class="left"><a href="#status.411" id="rfc.xref.status.411.2" title="411 Length Required">Section&nbsp;6.5.10</a> </td></tr><tr><td class="left">413</td><td class="left">Payload Too Large</td><td class="left"><a href="#status.413" id="rfc.xref.status.413.2" title="413 Payload Too Large">Section&nbsp;6.5.11</a> </td></tr><tr><td class="left">414</td><td class="left">URI Too Long</td><td class="left"><a href="#status.414" id="rfc.xref.status.414.2" title="414 URI Too Long">Section&nbsp;6.5.12</a> </td></tr><tr><td class="left">415</td><td class="left">Unsupported Media Type</td><td class="left"><a href="#status.415" id="rfc.xref.status.415.2" title="415 Unsupported Media Type">Section&nbsp;6.5.13</a> </td></tr><tr><td class="left">417</td><td class="left">Expectation Failed</td><td class="left"><a href="#status.417" id="rfc.xref.status.417.2" title="417 Expectation Failed">Section&nbsp;6.5.14</a> </td></tr><tr><td class="left">426</td><td class="left">Upgrade Required</td><td class="left"><a href="#status.426" id="rfc.xref.status.426.2" title="426 Upgrade Required">Section&nbsp;6.5.15</a> </td></tr><tr><td class="left">500</td><td class="left">Internal Server Error</td><td class="left"><a href="#status.500" id="rfc.xref.status.500.2" title="500 Internal Server Error">Section&nbsp;6.6.1</a> </td></tr><tr><td class="left">501</td><td class="left">Not Implemented</td><td class="left"><a href="#status.501" id="rfc.xref.status.501.2" title="501 Not Implemented">Section&nbsp;6.6.2</a> </td></tr><tr><td class="left">502</td><td class="left">Bad Gateway</td><td class="left"><a href="#status.502" id="rfc.xref.status.502.2" title="502 Bad Gateway">Section&nbsp;6.6.3</a> </td></tr><tr><td class="left">503</td><td class="left">Service Unavailable</td><td class="left"><a href="#status.503" id="rfc.xref.status.503.2" title="503 Service Unavailable">Section&nbsp;6.6.4</a> </td></tr><tr><td class="left">504</td><td class="left">Gateway Timeout</td><td class="left"><a href="#status.504" id="rfc.xref.status.504.2" title="504 Gateway Timeout">Section&nbsp;6.6.5</a> </td></tr><tr><td class="left">505</td><td class="left">HTTP Version Not Supported</td><td class="left"><a href="#status.505" id="rfc.xref.status.505.2" title="505 HTTP Version Not Supported">Section&nbsp;6.6.6</a> </td></tr></tbody></table></div></div></div><div id="header.field.registry"><h2 id="rfc.section.8.3"><a href="#rfc.section.8.3">8.3</a>&nbsp;<a href="#header.field.registry">Header Field Registry</a></h2><div id="rfc.section.8.3.p.1"><p>HTTP header fields are registered within the "Message Headers" registry located at &lt;<a href="http://www.iana.org/assignments/message-headers">http://www.iana.org/assignments/message-headers</a>&gt;, as defined by <a href="#BCP90" id="rfc.xref.BCP90.1"><cite title="Registration Procedures for Message Header Fields">[BCP90]</cite></a>.<a class="self" href="#rfc.section.8.3.p.1">&para;</a></p></div><div id="considerations.for.new.header.fields"><h3 id="rfc.section.8.3.1"><a href="#rfc.section.8.3.1">8.3.1</a>&nbsp;<a href="#considerations.for.new.header.fields">Considerations for New Header Fields</a></h3><div id="rfc.section.8.3.1.p.1"><p>Header fields are key:value pairs that can be used to communicate data about the message, its payload, the target resource, or the connection (i.e., control data). See <a href="rfc7230.html#header.fields" title="Header Fields">Section 3.2</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.33"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a> for a general definition of header field syntax in HTTP messages.<a class="self" href="#rfc.section.8.3.1.p.1">&para;</a></p></div><div id="rfc.section.8.3.1.p.2"><p>The requirements for header field names are defined in <a href="#BCP90" id="rfc.xref.BCP90.2"><cite title="Registration Procedures for Message Header Fields">[BCP90]</cite></a>.<a class="self" href="#rfc.section.8.3.1.p.2">&para;</a></p></div><div id="rfc.section.8.3.1.p.3"><p>Authors of specifications defining new fields are advised to keep the name as short as practical and not to prefix the name with "X-" unless the header field will never be used on the Internet. (The "X-" prefix idiom has been extensively misused in practice; it was intended to only be used as a mechanism for avoiding name collisions inside proprietary software or intranet processing, since the prefix would ensure that private names never collide with a newly registered Internet name; see <a href="#BCP178" id="rfc.xref.BCP178.1"><cite title="Deprecating the &#34;X-&#34; Prefix and Similar Constructs in Application Protocols">[BCP178]</cite></a> for further information).<a class="self" href="#rfc.section.8.3.1.p.3">&para;</a></p></div><div id="rfc.section.8.3.1.p.4"><p>New header field values typically have their syntax defined using ABNF (<a href="#RFC5234" id="rfc.xref.RFC5234.2"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>), using the extension defined in <a href="rfc7230.html#abnf.extension" title="ABNF List Extension: #rule">Section 7</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.34"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a> as necessary, and are usually constrained to the range of US-ASCII characters. Header fields needing a greater range of characters can use an encoding such as the one defined in <a href="#RFC5987" id="rfc.xref.RFC5987.1"><cite title="Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters">[RFC5987]</cite></a>.<a class="self" href="#rfc.section.8.3.1.p.4">&para;</a></p></div><div id="rfc.section.8.3.1.p.5"><p>Leading and trailing whitespace in raw field values is removed upon field parsing (<a href="rfc7230.html#field.parsing" title="Field Parsing">Section 3.2.4</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.35"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>). Field definitions where leading or trailing whitespace in values is significant will have to use a container syntax such as quoted-string (<a href="rfc7230.html#field.components" title="Field Value Components">Section 3.2.6</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.36"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>).<a class="self" href="#rfc.section.8.3.1.p.5">&para;</a></p></div><div id="rfc.section.8.3.1.p.6"><p>Because commas (",") are used as a generic delimiter between field-values, they need to be treated with care if they are allowed in the field-value. Typically, components that might contain a comma are protected with double-quotes using the quoted-string ABNF production.<a class="self" href="#rfc.section.8.3.1.p.6">&para;</a></p></div><div id="rfc.section.8.3.1.p.7"><p>For example, a textual date and a URI (either of which might contain a comma) could be safely carried in field-values like these:<a class="self" href="#rfc.section.8.3.1.p.7">&para;</a></p></div><div id="rfc.figure.u.64"><pre class="text">  Example-URI-Field: "http://example.com/a.html,foo",
    669685                     "http://without-a-comma.example.com/"
    670686  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
     
    806822
    807823<a href="#preferred.date.format" class="smpl">year</a> = 4DIGIT
    808 </pre></div></div><h1 id="rfc.index"><a href="#rfc.index">Index</a></h1><p class="noprint"><a href="#rfc.index.1">1</a> <a href="#rfc.index.2">2</a> <a href="#rfc.index.3">3</a> <a href="#rfc.index.4">4</a> <a href="#rfc.index.5">5</a> <a href="#rfc.index.A">A</a> <a href="#rfc.index.B">B</a> <a href="#rfc.index.C">C</a> <a href="#rfc.index.D">D</a> <a href="#rfc.index.E">E</a> <a href="#rfc.index.F">F</a> <a href="#rfc.index.G">G</a> <a href="#rfc.index.H">H</a> <a href="#rfc.index.I">I</a> <a href="#rfc.index.L">L</a> <a href="#rfc.index.M">M</a> <a href="#rfc.index.O">O</a> <a href="#rfc.index.P">P</a> <a href="#rfc.index.R">R</a> <a href="#rfc.index.S">S</a> <a href="#rfc.index.T">T</a> <a href="#rfc.index.U">U</a> <a href="#rfc.index.V">V</a> <a href="#rfc.index.X">X</a> </p><div class="print2col"><ul class="ind"><li><a id="rfc.index.1" href="#rfc.index.1"><b>1</b></a><ul><li>100 Continue (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.100.1">6.1</a>, <a href="#rfc.section.6.2.1"><b>6.2.1</b></a>, <a href="#rfc.xref.status.100.2">8.2.3</a></li><li>100-continue (expect value)&nbsp;&nbsp;<a href="#rfc.section.5.1.1"><b>5.1.1</b></a></li><li>101 Switching Protocols (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.101.1">6.1</a>, <a href="#rfc.section.6.2.2"><b>6.2.2</b></a>, <a href="#rfc.xref.status.101.2">8.2.3</a></li><li>1xx Informational (status code class)&nbsp;&nbsp;<a href="#rfc.section.6.2"><b>6.2</b></a></li></ul></li><li><a id="rfc.index.2" href="#rfc.index.2"><b>2</b></a><ul><li>200 OK (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.200.1">6.1</a>, <a href="#rfc.section.6.3.1"><b>6.3.1</b></a>, <a href="#rfc.xref.status.200.2">8.2.3</a></li><li>201 Created (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.201.1">6.1</a>, <a href="#rfc.section.6.3.2"><b>6.3.2</b></a>, <a href="#rfc.xref.status.201.2">8.2.3</a>, <a href="#rfc.xref.status.201.3">B</a></li><li>202 Accepted (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.202.1">6.1</a>, <a href="#rfc.section.6.3.3"><b>6.3.3</b></a>, <a href="#rfc.xref.status.202.2">8.2.3</a></li><li>203 Non-Authoritative Information (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.203.1">6.1</a>, <a href="#rfc.section.6.3.4"><b>6.3.4</b></a>, <a href="#rfc.xref.status.203.2">8.2.3</a>, <a href="#rfc.xref.status.203.3">B</a></li><li>204 No Content (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.204.1">6.1</a>, <a href="#rfc.section.6.3.5"><b>6.3.5</b></a>, <a href="#rfc.xref.status.204.2">8.2.3</a></li><li>205 Reset Content (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.205.1">6.1</a>, <a href="#rfc.section.6.3.6"><b>6.3.6</b></a>, <a href="#rfc.xref.status.205.2">8.2.3</a></li><li>2xx Successful (status code class)&nbsp;&nbsp;<a href="#rfc.section.6.3"><b>6.3</b></a></li></ul></li><li><a id="rfc.index.3" href="#rfc.index.3"><b>3</b></a><ul><li>300 Multiple Choices (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.300.1">6.1</a>, <a href="#rfc.section.6.4.1"><b>6.4.1</b></a>, <a href="#rfc.xref.status.300.2">6.5.6</a>, <a href="#rfc.xref.status.300.3">8.2.3</a></li><li>301 Moved Permanently (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.301.1">6.1</a>, <a href="#rfc.section.6.4.2"><b>6.4.2</b></a>, <a href="#rfc.xref.status.301.2">8.2.3</a>, <a href="#rfc.xref.status.301.3">B</a></li><li>302 Found (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.302.1">6.1</a>, <a href="#rfc.section.6.4.3"><b>6.4.3</b></a>, <a href="#rfc.xref.status.302.2">8.2.3</a>, <a href="#rfc.xref.status.302.3">B</a></li><li>303 See Other (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.303.1">6.1</a>, <a href="#rfc.section.6.4.4"><b>6.4.4</b></a>, <a href="#rfc.xref.status.303.2">8.2.3</a>, <a href="#rfc.xref.status.303.3">B</a></li><li>305 Use Proxy (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.305.1">6.1</a>, <a href="#rfc.section.6.4.5"><b>6.4.5</b></a>, <a href="#rfc.xref.status.305.2">8.2.3</a>, <a href="#rfc.xref.status.305.3">B</a></li><li>306 (Unused) (status code)&nbsp;&nbsp;<a href="#rfc.section.6.4.6"><b>6.4.6</b></a>, <a href="#rfc.xref.status.306.1">8.2.3</a></li><li>307 Temporary Redirect (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.307.1">6.1</a>, <a href="#rfc.section.6.4.7"><b>6.4.7</b></a>, <a href="#rfc.xref.status.307.2">8.2.3</a></li><li>3xx Redirection (status code class)&nbsp;&nbsp;<a href="#rfc.section.6.4"><b>6.4</b></a>, <a href="#rfc.xref.status.3xx.1">B</a></li></ul></li><li><a id="rfc.index.4" href="#rfc.index.4"><b>4</b></a><ul><li>400 Bad Request (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.400.1">6.1</a>, <a href="#rfc.section.6.5.1"><b>6.5.1</b></a>, <a href="#rfc.xref.status.400.2">8.2.3</a>, <a href="#rfc.xref.status.400.3">B</a></li><li>402 Payment Required (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.402.1">6.1</a>, <a href="#rfc.section.6.5.2"><b>6.5.2</b></a>, <a href="#rfc.xref.status.402.2">8.2.3</a></li><li>403 Forbidden (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.403.1">6.1</a>, <a href="#rfc.section.6.5.3"><b>6.5.3</b></a>, <a href="#rfc.xref.status.403.2">8.2.3</a></li><li>404 Not Found (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.404.1">6.1</a>, <a href="#rfc.section.6.5.4"><b>6.5.4</b></a>, <a href="#rfc.xref.status.404.2">8.2.3</a></li><li>405 Method Not Allowed (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.405.1">6.1</a>, <a href="#rfc.section.6.5.5"><b>6.5.5</b></a>, <a href="#rfc.xref.status.405.2">8.2.3</a></li><li>406 Not Acceptable (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.406.1">6.1</a>, <a href="#rfc.section.6.5.6"><b>6.5.6</b></a>, <a href="#rfc.xref.status.406.2">8.2.3</a></li><li>408 Request Timeout (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.408.1">6.1</a>, <a href="#rfc.section.6.5.7"><b>6.5.7</b></a>, <a href="#rfc.xref.status.408.2">8.2.3</a></li><li>409 Conflict (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.409.1">6.1</a>, <a href="#rfc.section.6.5.8"><b>6.5.8</b></a>, <a href="#rfc.xref.status.409.2">8.2.3</a></li><li>410 Gone (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.410.1">6.1</a>, <a href="#rfc.section.6.5.9"><b>6.5.9</b></a>, <a href="#rfc.xref.status.410.2">8.2.3</a></li><li>411 Length Required (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.411.1">6.1</a>, <a href="#rfc.section.6.5.10"><b>6.5.10</b></a>, <a href="#rfc.xref.status.411.2">8.2.3</a></li><li>413 Payload Too Large (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.413.1">6.1</a>, <a href="#rfc.section.6.5.11"><b>6.5.11</b></a>, <a href="#rfc.xref.status.413.2">8.2.3</a></li><li>414 URI Too Long (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.414.1">6.1</a>, <a href="#rfc.section.6.5.12"><b>6.5.12</b></a>, <a href="#rfc.xref.status.414.2">8.2.3</a></li><li>415 Unsupported Media Type (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.415.1">6.1</a>, <a href="#rfc.section.6.5.13"><b>6.5.13</b></a>, <a href="#rfc.xref.status.415.2">8.2.3</a></li><li>417 Expectation Failed (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.417.1">6.1</a>, <a href="#rfc.section.6.5.14"><b>6.5.14</b></a>, <a href="#rfc.xref.status.417.2">8.2.3</a></li><li>426 Upgrade Required (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.426.1">6.1</a>, <a href="#rfc.section.6.5.15"><b>6.5.15</b></a>, <a href="#rfc.xref.status.426.2">8.2.3</a>, <a href="#rfc.xref.status.426.3">B</a></li><li>4xx Client Error (status code class)&nbsp;&nbsp;<a href="#rfc.section.6.5"><b>6.5</b></a></li></ul></li><li><a id="rfc.index.5" href="#rfc.index.5"><b>5</b></a><ul><li>500 Internal Server Error (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.500.1">6.1</a>, <a href="#rfc.section.6.6.1"><b>6.6.1</b></a>, <a href="#rfc.xref.status.500.2">8.2.3</a></li><li>501 Not Implemented (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.501.1">6.1</a>, <a href="#rfc.section.6.6.2"><b>6.6.2</b></a>, <a href="#rfc.xref.status.501.2">8.2.3</a></li><li>502 Bad Gateway (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.502.1">6.1</a>, <a href="#rfc.section.6.6.3"><b>6.6.3</b></a>, <a href="#rfc.xref.status.502.2">8.2.3</a></li><li>503 Service Unavailable (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.503.1">6.1</a>, <a href="#rfc.section.6.6.4"><b>6.6.4</b></a>, <a href="#rfc.xref.status.503.2">8.2.3</a></li><li>504 Gateway Timeout (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.504.1">6.1</a>, <a href="#rfc.section.6.6.5"><b>6.6.5</b></a>, <a href="#rfc.xref.status.504.2">8.2.3</a></li><li>505 HTTP Version Not Supported (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.505.1">6.1</a>, <a href="#rfc.section.6.6.6"><b>6.6.6</b></a>, <a href="#rfc.xref.status.505.2">8.2.3</a></li><li>5xx Server Error (status code class)&nbsp;&nbsp;<a href="#rfc.section.6.6"><b>6.6</b></a></li></ul></li><li><a id="rfc.index.A" href="#rfc.index.A"><b>A</b></a><ul><li>Accept header field&nbsp;&nbsp;<a href="#rfc.xref.header.accept.1">3.1.1.1</a>, <a href="#rfc.xref.header.accept.2">5.3</a>, <a href="#rfc.section.5.3.2"><b>5.3.2</b></a>, <a href="#rfc.xref.header.accept.3">8.3.2</a></li><li>Accept-Charset header field&nbsp;&nbsp;<a href="#rfc.xref.header.accept-charset.1">5.3</a>, <a href="#rfc.section.5.3.3"><b>5.3.3</b></a>, <a href="#rfc.xref.header.accept-charset.2">8.3.2</a>, <a href="#rfc.xref.header.accept-charset.3">B</a></li><li>Accept-Encoding header field&nbsp;&nbsp;<a href="#rfc.xref.header.accept-encoding.1">3.1.2.1</a>, <a href="#rfc.xref.header.accept-encoding.2">5.3</a>, <a href="#rfc.section.5.3.4"><b>5.3.4</b></a>, <a href="#rfc.xref.header.accept-encoding.3">8.3.2</a>, <a href="#rfc.xref.header.accept-encoding.4">8.4.2</a></li><li>Accept-Language header field&nbsp;&nbsp;<a href="#rfc.xref.header.accept-language.1">3.1.3.1</a>, <a href="#rfc.xref.header.accept-language.2">5.3</a>, <a href="#rfc.section.5.3.5"><b>5.3.5</b></a>, <a href="#rfc.xref.header.accept-language.3">8.3.2</a></li><li>Allow header field&nbsp;&nbsp;<a href="#rfc.xref.header.allow.1">4.1</a>, <a href="#rfc.xref.header.allow.2">7.4</a>, <a href="#rfc.section.7.4.1"><b>7.4.1</b></a>, <a href="#rfc.xref.header.allow.3">8.3.2</a>, <a href="#rfc.xref.header.allow.4">B</a></li></ul></li><li><a id="rfc.index.B" href="#rfc.index.B"><b>B</b></a><ul><li><em>BCP13</em>&nbsp;&nbsp;<a href="#rfc.xref.BCP13.1">3.1.1.1</a>, <a href="#BCP13"><b>11.2</b></a></li><li><em>BCP178</em>&nbsp;&nbsp;<a href="#rfc.xref.BCP178.1">8.3.1</a>, <a href="#BCP178"><b>11.2</b></a></li><li><em>BCP90</em>&nbsp;&nbsp;<a href="#rfc.xref.BCP90.1">8.3</a>, <a href="#rfc.xref.BCP90.2">8.3.1</a>, <a href="#BCP90"><b>11.2</b></a></li></ul></li><li><a id="rfc.index.C" href="#rfc.index.C"><b>C</b></a><ul><li>cacheable&nbsp;&nbsp;<a href="#rfc.section.4.2.3"><b>4.2.3</b></a></li><li>compress (content coding)&nbsp;&nbsp;<a href="#rfc.section.3.1.2.1"><b>3.1.2.1</b></a></li><li>conditional request&nbsp;&nbsp;<a href="#rfc.section.5.2"><b>5.2</b></a></li><li>CONNECT method&nbsp;&nbsp;<a href="#rfc.xref.CONNECT.1">4.1</a>, <a href="#rfc.section.4.3.6"><b>4.3.6</b></a>, <a href="#rfc.xref.CONNECT.2">8.1.3</a>, <a href="#rfc.xref.CONNECT.3">B</a></li><li>content coding&nbsp;&nbsp;<a href="#rfc.section.3.1.2.1"><b>3.1.2.1</b></a></li><li>content negotiation&nbsp;&nbsp;<a href="#rfc.iref.c.1">1</a></li><li>Content-Encoding header field&nbsp;&nbsp;<a href="#rfc.xref.header.content-encoding.1">3.1</a>, <a href="#rfc.xref.header.content-encoding.2">3.1.2.1</a>, <a href="#rfc.section.3.1.2.2"><b>3.1.2.2</b></a>, <a href="#rfc.xref.header.content-encoding.3">8.3.2</a></li><li>Content-Language header field&nbsp;&nbsp;<a href="#rfc.xref.header.content-language.1">3.1</a>, <a href="#rfc.section.3.1.3.2"><b>3.1.3.2</b></a>, <a href="#rfc.xref.header.content-language.2">8.3.2</a></li><li>Content-Location header field&nbsp;&nbsp;<a href="#rfc.xref.header.content-location.1">3.1</a>, <a href="#rfc.section.3.1.4.2"><b>3.1.4.2</b></a>, <a href="#rfc.xref.header.content-location.2">4.3.3</a>, <a href="#rfc.xref.header.content-location.3">7.1.2</a>, <a href="#rfc.xref.header.content-location.4">8.3.2</a>, <a href="#rfc.xref.header.content-location.5">B</a></li><li>Content-Transfer-Encoding header field&nbsp;&nbsp;<a href="#rfc.section.A.5">A.5</a></li><li>Content-Type header field&nbsp;&nbsp;<a href="#rfc.xref.header.content-type.1">3.1</a>, <a href="#rfc.xref.header.content-type.2">3.1.1.1</a>, <a href="#rfc.section.3.1.1.5"><b>3.1.1.5</b></a>, <a href="#rfc.xref.header.content-type.3">8.3.1</a>, <a href="#rfc.xref.header.content-type.4">8.3.2</a></li></ul></li><li><a id="rfc.index.D" href="#rfc.index.D"><b>D</b></a><ul><li>Date header field&nbsp;&nbsp;<a href="#rfc.xref.header.date.1">3.3</a>, <a href="#rfc.xref.header.date.2">7.1</a>, <a href="#rfc.section.7.1.1.2"><b>7.1.1.2</b></a>, <a href="#rfc.xref.header.date.3">8.3.2</a></li><li>deflate (content coding)&nbsp;&nbsp;<a href="#rfc.section.3.1.2.1"><b>3.1.2.1</b></a></li><li>DELETE method&nbsp;&nbsp;<a href="#rfc.xref.DELETE.1">4.1</a>, <a href="#rfc.iref.d.1"><b>4.3.5</b></a>, <a href="#rfc.xref.DELETE.2">8.1.3</a></li></ul></li><li><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul><li>Expect header field&nbsp;&nbsp;<a href="#rfc.xref.header.expect.1">5.1</a>, <a href="#rfc.section.5.1.1"><b>5.1.1</b></a>, <a href="#rfc.xref.header.expect.2">6.2.1</a>, <a href="#rfc.xref.header.expect.3">6.5.14</a>, <a href="#rfc.xref.header.expect.4">8.3.2</a>, <a href="#rfc.xref.header.expect.5">B</a></li></ul></li><li><a id="rfc.index.F" href="#rfc.index.F"><b>F</b></a><ul><li>From header field&nbsp;&nbsp;<a href="#rfc.xref.header.from.1">5.5</a>, <a href="#rfc.section.5.5.1"><b>5.5.1</b></a>, <a href="#rfc.xref.header.from.2">8.3.2</a></li></ul></li><li><a id="rfc.index.G" href="#rfc.index.G"><b>G</b></a><ul><li>GET method&nbsp;&nbsp;<a href="#rfc.xref.GET.1">3</a>, <a href="#rfc.xref.GET.2">3.1.4.2</a>, <a href="#rfc.xref.GET.3">3.3</a>, <a href="#rfc.xref.GET.4">4.1</a>, <a href="#rfc.iref.g.13"><b>4.3.1</b></a>, <a href="#rfc.xref.GET.5">8.1.3</a>, <a href="#rfc.xref.GET.6">B</a></li><li><tt>Grammar</tt>&nbsp;&nbsp;<ul><li><tt>Accept</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.18"><b>5.3.2</b></a></li><li><tt>Accept-Charset</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.22"><b>5.3.3</b></a></li><li><tt>Accept-Encoding</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.23"><b>5.3.4</b></a></li><li><tt>accept-ext</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.21"><b>5.3.2</b></a></li><li><tt>Accept-Language</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.25"><b>5.3.5</b></a></li><li><tt>accept-params</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.20"><b>5.3.2</b></a></li><li><tt>Allow</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.53"><b>7.4.1</b></a></li><li><tt>asctime-date</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.47"><b>7.1.1.1</b></a></li><li><tt>charset</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.5"><b>3.1.1.2</b></a></li><li><tt>codings</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.24"><b>5.3.4</b></a></li><li><tt>content-coding</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.7"><b>3.1.2.1</b></a></li><li><tt>Content-Encoding</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.8"><b>3.1.2.2</b></a></li><li><tt>Content-Language</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.10"><b>3.1.3.2</b></a></li><li><tt>Content-Location</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.11"><b>3.1.4.2</b></a></li><li><tt>Content-Type</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.6"><b>3.1.1.5</b></a></li><li><tt>Date</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.48"><b>7.1.1.2</b></a></li><li><tt>date1</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.34"><b>7.1.1.1</b></a></li><li><tt>day</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.41"><b>7.1.1.1</b></a></li><li><tt>day-name</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.39"><b>7.1.1.1</b></a></li><li><tt>day-name-l</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.40"><b>7.1.1.1</b></a></li><li><tt>delay-seconds</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.51"><b>7.1.3</b></a></li><li><tt>Expect</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.14"><b>5.1.1</b></a></li><li><tt>From</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.27"><b>5.5.1</b></a></li><li><tt>GMT</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.44"><b>7.1.1.1</b></a></li><li><tt>hour</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.36"><b>7.1.1.1</b></a></li><li><tt>HTTP-date</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.32"><b>7.1.1.1</b></a></li><li><tt>IMF-fixdate</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.33"><b>7.1.1.1</b></a></li><li><tt>language-range</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.26"><b>5.3.5</b></a></li><li><tt>language-tag</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.9"><b>3.1.3.1</b></a></li><li><tt>Location</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.49"><b>7.1.2</b></a></li><li><tt>Max-Forwards</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.15"><b>5.1.2</b></a></li><li><tt>media-range</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.19"><b>5.3.2</b></a></li><li><tt>media-type</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.1"><b>3.1.1.1</b></a></li><li><tt>method</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.12"><b>4.1</b></a></li><li><tt>minute</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.37"><b>7.1.1.1</b></a></li><li><tt>month</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.42"><b>7.1.1.1</b></a></li><li><tt>obs-date</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.45"><b>7.1.1.1</b></a></li><li><tt>parameter</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.4"><b>3.1.1.1</b></a></li><li><tt>product</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.30"><b>5.5.3</b></a></li><li><tt>product-version</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.31"><b>5.5.3</b></a></li><li><tt>qvalue</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.17"><b>5.3.1</b></a></li><li><tt>Referer</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.28"><b>5.5.2</b></a></li><li><tt>Retry-After</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.50"><b>7.1.3</b></a></li><li><tt>rfc850-date</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.46"><b>7.1.1.1</b></a></li><li><tt>second</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.38"><b>7.1.1.1</b></a></li><li><tt>Server</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.54"><b>7.4.2</b></a></li><li><tt>subtype</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.3"><b>3.1.1.1</b></a></li><li><tt>time-of-day</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.35"><b>7.1.1.1</b></a></li><li><tt>type</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.2"><b>3.1.1.1</b></a></li><li><tt>User-Agent</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.29"><b>5.5.3</b></a></li><li><tt>Vary</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.52"><b>7.1.4</b></a></li><li><tt>weight</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.16"><b>5.3.1</b></a></li><li><tt>year</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.43"><b>7.1.1.1</b></a></li></ul></li><li>gzip (content coding)&nbsp;&nbsp;<a href="#rfc.section.3.1.2.1"><b>3.1.2.1</b></a></li></ul></li><li><a id="rfc.index.H" href="#rfc.index.H"><b>H</b></a><ul><li>HEAD method&nbsp;&nbsp;<a href="#rfc.xref.HEAD.1">3.1.4.2</a>, <a href="#rfc.xref.HEAD.2">4.1</a>, <a href="#rfc.iref.h.1"><b>4.3.2</b></a>, <a href="#rfc.xref.HEAD.3">8.1.3</a></li></ul></li><li><a id="rfc.index.I" href="#rfc.index.I"><b>I</b></a><ul><li>idempotent&nbsp;&nbsp;<a href="#rfc.section.4.2.2"><b>4.2.2</b></a></li></ul></li><li><a id="rfc.index.L" href="#rfc.index.L"><b>L</b></a><ul><li>Location header field&nbsp;&nbsp;<a href="#rfc.xref.header.location.1">4.3.3</a>, <a href="#rfc.xref.header.location.2">6.4</a>, <a href="#rfc.xref.header.location.3">7.1</a>, <a href="#rfc.section.7.1.2"><b>7.1.2</b></a>, <a href="#rfc.xref.header.location.4">8.3.2</a>, <a href="#rfc.xref.header.location.5">9.5</a>, <a href="#rfc.xref.header.location.6">B</a></li></ul></li><li><a id="rfc.index.M" href="#rfc.index.M"><b>M</b></a><ul><li>Max-Forwards header field&nbsp;&nbsp;<a href="#rfc.xref.header.max-forwards.1">4.3.7</a>, <a href="#rfc.xref.header.max-forwards.2">4.3.8</a>, <a href="#rfc.xref.header.max-forwards.3">5.1</a>, <a href="#rfc.section.5.1.2"><b>5.1.2</b></a>, <a href="#rfc.xref.header.max-forwards.4">8.3.2</a>, <a href="#rfc.xref.header.max-forwards.5">B</a></li><li>MIME-Version header field&nbsp;&nbsp;<a href="#rfc.xref.mime-version.1">8.3.2</a>, <a href="#rfc.section.A.1"><b>A.1</b></a></li></ul></li><li><a id="rfc.index.O" href="#rfc.index.O"><b>O</b></a><ul><li>OPTIONS method&nbsp;&nbsp;<a href="#rfc.xref.OPTIONS.1">4.1</a>, <a href="#rfc.iref.o.1"><b>4.3.7</b></a>, <a href="#rfc.xref.OPTIONS.2">5.1.2</a>, <a href="#rfc.xref.OPTIONS.3">8.1.3</a>, <a href="#rfc.extref.o.11">B</a>, <a href="#rfc.xref.OPTIONS.4">B</a>, <a href="#rfc.extref.o.12">B</a></li><li><em>OWASP</em>&nbsp;&nbsp;<a href="#rfc.xref.OWASP.1">9</a>, <a href="#OWASP"><b>11.2</b></a></li></ul></li><li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul><li>payload&nbsp;&nbsp;<a href="#rfc.section.3.3">3.3</a></li><li>POST method&nbsp;&nbsp;<a href="#rfc.xref.POST.1">3.1.4.2</a>, <a href="#rfc.xref.POST.2">3.3</a>, <a href="#rfc.xref.POST.3">4.1</a>, <a href="#rfc.section.4.3.3"><b>4.3.3</b></a>, <a href="#rfc.xref.POST.4">8.1.3</a></li><li>PUT method&nbsp;&nbsp;<a href="#rfc.xref.PUT.1">3.1.4.2</a>, <a href="#rfc.xref.PUT.2">3.3</a>, <a href="#rfc.xref.PUT.3">4.1</a>, <a href="#rfc.iref.p.1"><b>4.3.4</b></a>, <a href="#rfc.xref.PUT.4">8.1.3</a>, <a href="#rfc.xref.PUT.5">B</a></li></ul></li><li><a id="rfc.index.R" href="#rfc.index.R"><b>R</b></a><ul><li>Referer header field&nbsp;&nbsp;<a href="#rfc.xref.header.referer.1">5.5</a>, <a href="#rfc.section.5.5.2"><b>5.5.2</b></a>, <a href="#rfc.xref.header.referer.2">8.3.2</a>, <a href="#rfc.xref.header.referer.3">9.4</a>, <a href="#rfc.xref.header.referer.4">B</a></li><li>representation&nbsp;&nbsp;<a href="#rfc.section.3"><b>3</b></a></li><li><em>REST</em>&nbsp;&nbsp;<a href="#rfc.xref.REST.1">3</a>, <a href="#rfc.xref.REST.2">4.1</a>, <a href="#REST"><b>11.2</b></a></li><li>Retry-After header field&nbsp;&nbsp;<a href="#rfc.xref.header.retry-after.1">6.6.4</a>, <a href="#rfc.xref.header.retry-after.2">7.1</a>, <a href="#rfc.section.7.1.3"><b>7.1.3</b></a>, <a href="#rfc.xref.header.retry-after.3">8.3.2</a></li><li><em>RFC1945</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1945.1">6.4</a>, <a href="#RFC1945"><b>11.2</b></a><ul><li><em>Section 9.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1945.1">6.4</a></li></ul></li><li><em>RFC2045</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2045.1">3.1.1.3</a>, <a href="#RFC2045"><b>11.1</b></a>, <a href="#rfc.xref.RFC2045.2">A</a>, <a href="#rfc.xref.RFC2045.3">A.1</a></li><li><em>RFC2046</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2046.1">3.1.1.1</a>, <a href="#rfc.xref.RFC2046.2">3.1.1.4</a>, <a href="#rfc.xref.RFC2046.3">3.1.1.5</a>, <a href="#RFC2046"><b>11.1</b></a>, <a href="#rfc.xref.RFC2046.4">A.2</a><ul><li><em>Section 4.5.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2046.3">3.1.1.5</a></li><li><em>Section 5.1.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2046.2">3.1.1.4</a></li></ul></li><li><em>RFC2049</em>&nbsp;&nbsp;<a href="#RFC2049"><b>11.2</b></a>, <a href="#rfc.xref.RFC2049.1">A.2</a><ul><li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2049.1">A.2</a></li></ul></li><li><em>RFC2068</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2068.1">5.1.1</a>, <a href="#rfc.xref.RFC2068.2">6.4</a>, <a href="#RFC2068"><b>11.2</b></a><ul><li><em>Section 10.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2068.2">6.4</a></li></ul></li><li><em>RFC2119</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2119.1">1.1</a>, <a href="#RFC2119"><b>11.1</b></a></li><li><em>RFC2295</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2295.1">3.4</a>, <a href="#RFC2295"><b>11.2</b></a></li><li><em>RFC2388</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2388.1">3.1.1.4</a>, <a href="#RFC2388"><b>11.2</b></a></li><li><em>RFC2557</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2557.1">3.1.4.2</a>, <a href="#RFC2557"><b>11.2</b></a>, <a href="#rfc.xref.RFC2557.2">A.6</a><ul><li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2557.1">3.1.4.2</a></li></ul></li><li><em>RFC2616</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2616.1">5.3.5</a>, <a href="#RFC2616"><b>11.2</b></a><ul><li><em>Section 14.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2616.1">5.3.5</a></li></ul></li><li><em>RFC2774</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2774.1">8.1.2</a>, <a href="#RFC2774"><b>11.2</b></a></li><li><em>RFC2817</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2817.1">8.2</a>, <a href="#RFC2817"><b>11.2</b></a>, <a href="#rfc.xref.RFC2817.2">B</a>, <a href="#rfc.xref.RFC2817.3">B</a>, <a href="#rfc.xref.RFC2817.4">B</a><ul><li><em>Section 7.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2817.1">8.2</a>, <a href="#rfc.xref.RFC2817.4">B</a></li></ul></li><li><em>RFC2978</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2978.1">3.1.1.2</a>, <a href="#RFC2978"><b>11.2</b></a></li><li><em>RFC3986</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.1">5.5.2</a>, <a href="#rfc.xref.RFC3986.2">7.1.2</a>, <a href="#rfc.xref.RFC3986.3">7.1.2</a>, <a href="#RFC3986"><b>11.1</b></a><ul><li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.2">7.1.2</a></li><li><em>Section 5</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.3">7.1.2</a></li></ul></li><li><em>RFC4647</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4647.1">5.3.5</a>, <a href="#rfc.xref.RFC4647.2">5.3.5</a>, <a href="#rfc.xref.RFC4647.3">5.3.5</a>, <a href="#rfc.xref.RFC4647.4">5.3.5</a>, <a href="#RFC4647"><b>11.1</b></a><ul><li><em>Section 2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4647.1">5.3.5</a></li><li><em>Section 2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4647.2">5.3.5</a></li><li><em>Section 3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4647.3">5.3.5</a></li><li><em>Section 3.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4647.4">5.3.5</a></li></ul></li><li><em>RFC5226</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5226.1">8.1.1</a>, <a href="#rfc.xref.RFC5226.2">8.2.1</a>, <a href="#rfc.xref.RFC5226.3">8.4.1</a>, <a href="#RFC5226"><b>11.2</b></a><ul><li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5226.1">8.1.1</a>, <a href="#rfc.xref.RFC5226.2">8.2.1</a>, <a href="#rfc.xref.RFC5226.3">8.4.1</a></li></ul></li><li><em>RFC5234</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5234.1">1.2</a>, <a href="#rfc.xref.RFC5234.2">8.3.1</a>, <a href="#RFC5234"><b>11.1</b></a>, <a href="#rfc.xref.RFC5234.3">C</a><ul><li><em>Appendix B.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5234.3">C</a></li></ul></li><li><em>RFC5246</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5246.1">4.3.6</a>, <a href="#RFC5246"><b>11.2</b></a></li><li><em>RFC5322</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5322.1">5.5.1</a>, <a href="#rfc.xref.RFC5322.2">5.5.1</a>, <a href="#rfc.xref.RFC5322.3">7.1.1.1</a>, <a href="#rfc.xref.RFC5322.4">7.1.1.1</a>, <a href="#rfc.xref.RFC5322.5">7.1.1.1</a>, <a href="#rfc.xref.RFC5322.6">7.1.1.2</a>, <a href="#RFC5322"><b>11.2</b></a>, <a href="#rfc.xref.RFC5322.7">A</a><ul><li><em>Section 3.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5322.4">7.1.1.1</a>, <a href="#rfc.xref.RFC5322.5">7.1.1.1</a></li><li><em>Section 3.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5322.1">5.5.1</a>, <a href="#rfc.xref.RFC5322.2">5.5.1</a></li><li><em>Section 3.6.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5322.6">7.1.1.2</a></li></ul></li><li><em>RFC5646</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5646.1">3.1.3.1</a>, <a href="#rfc.xref.RFC5646.2">3.1.3.1</a>, <a href="#rfc.xref.RFC5646.3">3.1.3.1</a>, <a href="#RFC5646"><b>11.1</b></a><ul><li><em>Section 2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5646.2">3.1.3.1</a></li></ul></li><li><em>RFC5789</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5789.1">4.3.4</a>, <a href="#RFC5789"><b>11.2</b></a></li><li><em>RFC5905</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5905.1">7.1.1.1</a>, <a href="#RFC5905"><b>11.2</b></a></li><li><em>RFC5987</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5987.1">8.3.1</a>, <a href="#RFC5987"><b>11.2</b></a></li><li><em>RFC5988</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5988.1">6.4.1</a>, <a href="#RFC5988"><b>11.2</b></a></li><li><em>RFC6265</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC6265.1">4.3.8</a>, <a href="#rfc.xref.RFC6265.2">5.4</a>, <a href="#RFC6265"><b>11.2</b></a></li><li><em>RFC6266</em>&nbsp;&nbsp;<a href="#RFC6266"><b>11.2</b></a>, <a href="#rfc.xref.RFC6266.1">B</a></li><li><em>RFC6365</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC6365.1">1.2</a>, <a href="#rfc.xref.RFC6365.2">3.1.1.2</a>, <a href="#RFC6365"><b>11.1</b></a></li><li><em>RFC7230</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.1">1</a>, <a href="#rfc.xref.RFC7230.2">1.1</a>, <a href="#rfc.xref.RFC7230.3">1.2</a>, <a href="#rfc.xref.RFC7230.4">2</a>, <a href="#rfc.xref.RFC7230.5">2</a>, <a href="#rfc.xref.RFC7230.6">2</a>, <a href="#rfc.xref.RFC7230.7">3.1.2.1</a>, <a href="#rfc.xref.RFC7230.8">3.1.2.1</a>, <a href="#rfc.xref.RFC7230.9">3.1.2.1</a>, <a href="#rfc.xref.RFC7230.10">3.1.2.2</a>, <a href="#rfc.xref.RFC7230.11">3.1.4.1</a>, <a href="#rfc.xref.RFC7230.12">3.1.4.2</a>, <a href="#rfc.xref.RFC7230.13">3.3</a>, <a href="#rfc.xref.RFC7230.14">3.3</a>, <a href="#rfc.xref.RFC7230.15">3.3</a>, <a href="#rfc.xref.RFC7230.16">4.3.6</a>, <a href="#rfc.xref.RFC7230.17">4.3.7</a>, <a href="#rfc.xref.RFC7230.18">4.3.8</a>, <a href="#rfc.xref.RFC7230.19">4.3.8</a>, <a href="#rfc.xref.RFC7230.20">5.1</a>, <a href="#rfc.xref.RFC7230.21">5.1</a>, <a href="#rfc.xref.RFC7230.22">5.1.1</a>, <a href="#rfc.xref.RFC7230.23">5.5.3</a>, <a href="#rfc.xref.RFC7230.24">6.2.2</a>, <a href="#rfc.xref.RFC7230.25">6.3.4</a>, <a href="#rfc.xref.RFC7230.26">6.5.7</a>, <a href="#rfc.xref.RFC7230.27">6.5.10</a>, <a href="#rfc.xref.RFC7230.28">6.5.12</a>, <a href="#rfc.xref.RFC7230.29">6.5.15</a>, <a href="#rfc.xref.RFC7230.30">6.6.6</a>, <a href="#rfc.xref.RFC7230.31">7.4.2</a>, <a href="#rfc.xref.RFC7230.32">8.1.2</a>, <a href="#rfc.xref.RFC7230.33">8.3.1</a>, <a href="#rfc.xref.RFC7230.34">8.3.1</a>, <a href="#rfc.xref.RFC7230.35">8.3.1</a>, <a href="#rfc.xref.RFC7230.36">8.3.1</a>, <a href="#rfc.xref.RFC7230.37">8.3.1</a>, <a href="#rfc.xref.RFC7230.38">8.3.1</a>, <a href="#rfc.xref.RFC7230.39">8.3.1</a>, <a href="#rfc.xref.RFC7230.40">8.4</a>, <a href="#rfc.xref.RFC7230.41">8.4.1</a>, <a href="#rfc.xref.RFC7230.42">8.4.1</a>, <a href="#rfc.xref.RFC7230.43">9</a>, <a href="#rfc.xref.RFC7230.44">9.6</a>, <a href="#rfc.xref.RFC7230.45">10</a>, <a href="#RFC7230"><b>11.1</b></a>, <a href="#rfc.xref.RFC7230.46">B</a>, <a href="#rfc.xref.RFC7230.47">C</a>, <a href="#rfc.xref.RFC7230.48">C</a>, <a href="#rfc.xref.RFC7230.49">C</a>, <a href="#rfc.xref.RFC7230.50">C</a>, <a href="#rfc.xref.RFC7230.51">C</a>, <a href="#rfc.xref.RFC7230.52">C</a>, <a href="#rfc.xref.RFC7230.53">C</a>, <a href="#rfc.xref.RFC7230.54">C</a>, <a href="#rfc.xref.RFC7230.55">C</a>, <a href="#rfc.xref.RFC7230.56">C</a>, <a href="#rfc.xref.RFC7230.57">C</a>, <a href="#rfc.xref.RFC7230.58">D</a><ul><li><em>Section 1.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.58">D</a></li><li><em>Section 2.5</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.2">1.1</a></li><li><em>Section 2.6</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.30">6.6.6</a></li><li><em>Section 2.7</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.4">2</a>, <a href="#rfc.xref.RFC7230.51">C</a>, <a href="#rfc.xref.RFC7230.52">C</a>, <a href="#rfc.xref.RFC7230.55">C</a></li><li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.23">5.5.3</a>, <a href="#rfc.xref.RFC7230.31">7.4.2</a>, <a href="#rfc.xref.RFC7230.33">8.3.1</a>, <a href="#rfc.xref.RFC7230.37">8.3.1</a>, <a href="#rfc.xref.RFC7230.54">C</a></li><li><em>Section 3.2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.48">C</a>, <a href="#rfc.xref.RFC7230.49">C</a>, <a href="#rfc.xref.RFC7230.50">C</a></li><li><em>Section 3.2.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.35">8.3.1</a></li><li><em>Section 3.2.6</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.36">8.3.1</a>, <a href="#rfc.xref.RFC7230.53">C</a>, <a href="#rfc.xref.RFC7230.56">C</a>, <a href="#rfc.xref.RFC7230.57">C</a></li><li><em>Section 3.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.10">3.1.2.2</a>, <a href="#rfc.xref.RFC7230.15">3.3</a></li><li><em>Section 3.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.32">8.1.2</a></li><li><em>Section 3.3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.13">3.3</a>, <a href="#rfc.xref.RFC7230.27">6.5.10</a></li><li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.41">8.4.1</a></li><li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.39">8.3.1</a></li><li><em>Section 4.2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.7">3.1.2.1</a></li><li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.40">8.4</a>, <a href="#rfc.xref.RFC7230.42">8.4.1</a></li><li><em>Section 4.2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.8">3.1.2.1</a></li><li><em>Section 4.2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.9">3.1.2.1</a></li><li><em>Section 4.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.21">5.1</a></li><li><em>Section 4.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.14">3.3</a></li><li><em>Section 5.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.5">2</a>, <a href="#rfc.xref.RFC7230.16">4.3.6</a>, <a href="#rfc.xref.RFC7230.17">4.3.7</a>, <a href="#rfc.xref.RFC7230.28">6.5.12</a></li><li><em>Section 5.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.20">5.1</a></li><li><em>Section 5.5</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.6">2</a>, <a href="#rfc.xref.RFC7230.11">3.1.4.1</a>, <a href="#rfc.xref.RFC7230.12">3.1.4.2</a></li><li><em>Section 5.7.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.19">4.3.8</a>, <a href="#rfc.xref.RFC7230.44">9.6</a></li><li><em>Section 5.7.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.25">6.3.4</a></li><li><em>Section 6.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.26">6.5.7</a>, <a href="#rfc.xref.RFC7230.38">8.3.1</a></li><li><em>Section 6.6</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.22">5.1.1</a></li><li><em>Section 6.7</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.24">6.2.2</a>, <a href="#rfc.xref.RFC7230.29">6.5.15</a></li><li><em>Section 7</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.3">1.2</a>, <a href="#rfc.xref.RFC7230.34">8.3.1</a></li><li><em>Section 8.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.18">4.3.8</a></li><li><em>Section 9</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.43">9</a></li><li><em>Section 10</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.45">10</a></li></ul></li><li><em>RFC7232</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.1">3</a>, <a href="#rfc.xref.RFC7232.2">4.1</a>, <a href="#rfc.xref.RFC7232.3">5.2</a>, <a href="#rfc.xref.RFC7232.4">5.2</a>, <a href="#rfc.xref.RFC7232.5">5.2</a>, <a href="#rfc.xref.RFC7232.6">5.2</a>, <a href="#rfc.xref.RFC7232.7">5.2</a>, <a href="#rfc.xref.RFC7232.8">5.2</a>, <a href="#rfc.xref.RFC7232.9">6.1</a>, <a href="#rfc.xref.RFC7232.10">6.1</a>, <a href="#rfc.xref.RFC7232.11">6.1</a>, <a href="#rfc.xref.RFC7232.12">7.2</a>, <a href="#rfc.xref.RFC7232.13">7.2</a>, <a href="#rfc.xref.RFC7232.14">7.2</a>, <a href="#RFC7232"><b>11.1</b></a><ul><li><em>Section 2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.14">7.2</a></li><li><em>Section 2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.13">7.2</a></li><li><em>Section 3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.5">5.2</a></li><li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.6">5.2</a></li><li><em>Section 3.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.7">5.2</a></li><li><em>Section 3.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.8">5.2</a></li><li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.9">6.1</a></li><li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.10">6.1</a></li><li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.11">6.1</a></li><li><em>Section 5</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.4">5.2</a></li></ul></li><li><em>RFC7233</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.1">3.1.1.4</a>, <a href="#rfc.xref.RFC7233.2">3.3</a>, <a href="#rfc.xref.RFC7233.3">4.3.1</a>, <a href="#rfc.xref.RFC7233.4">4.3.4</a>, <a href="#rfc.xref.RFC7233.5">5.1</a>, <a href="#rfc.xref.RFC7233.6">5.2</a>, <a href="#rfc.xref.RFC7233.7">6.1</a>, <a href="#rfc.xref.RFC7233.8">6.1</a>, <a href="#rfc.xref.RFC7233.9">6.1</a>, <a href="#rfc.xref.RFC7233.10">7.4</a>, <a href="#rfc.xref.RFC7233.11">8.1.2</a>, <a href="#RFC7233"><b>11.1</b></a>, <a href="#rfc.xref.RFC7233.12">A.6</a><ul><li><em>Section 2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.10">7.4</a></li><li><em>Section 3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.5">5.1</a></li><li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.6">5.2</a></li><li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.7">6.1</a></li><li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.8">6.1</a></li><li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.2">3.3</a>, <a href="#rfc.xref.RFC7233.4">4.3.4</a></li><li><em>Section 4.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.9">6.1</a></li><li><em>Appendix A</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.12">A.6</a></li></ul></li><li><em>RFC7234</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.1">4.2.3</a>, <a href="#rfc.xref.RFC7234.2">4.3.1</a>, <a href="#rfc.xref.RFC7234.3">4.3.2</a>, <a href="#rfc.xref.RFC7234.4">4.3.2</a>, <a href="#rfc.xref.RFC7234.5">4.3.3</a>, <a href="#rfc.xref.RFC7234.6">4.3.4</a>, <a href="#rfc.xref.RFC7234.7">4.3.5</a>, <a href="#rfc.xref.RFC7234.8">5.1</a>, <a href="#rfc.xref.RFC7234.9">5.1</a>, <a href="#rfc.xref.RFC7234.10">6.1</a>, <a href="#rfc.xref.RFC7234.11">6.3.1</a>, <a href="#rfc.xref.RFC7234.12">6.3.4</a>, <a href="#rfc.xref.RFC7234.13">6.3.4</a>, <a href="#rfc.xref.RFC7234.14">6.3.5</a>, <a href="#rfc.xref.RFC7234.15">6.4.1</a>, <a href="#rfc.xref.RFC7234.16">6.4.2</a>, <a href="#rfc.xref.RFC7234.17">6.5.4</a>, <a href="#rfc.xref.RFC7234.18">6.5.5</a>, <a href="#rfc.xref.RFC7234.19">6.5.9</a>, <a href="#rfc.xref.RFC7234.20">6.5.12</a>, <a href="#rfc.xref.RFC7234.21">6.6.2</a>, <a href="#rfc.xref.RFC7234.22">7.1</a>, <a href="#rfc.xref.RFC7234.23">7.1</a>, <a href="#rfc.xref.RFC7234.24">7.1</a>, <a href="#rfc.xref.RFC7234.25">7.1</a>, <a href="#rfc.xref.RFC7234.26">7.1.4</a>, <a href="#rfc.xref.RFC7234.27">7.1.4</a>, <a href="#rfc.xref.RFC7234.28">8.2.2</a>, <a href="#RFC7234"><b>11.1</b></a><ul><li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.26">7.1.4</a></li><li><em>Section 4.2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.5">4.3.3</a></li><li><em>Section 4.2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.11">6.3.1</a>, <a href="#rfc.xref.RFC7234.13">6.3.4</a>, <a href="#rfc.xref.RFC7234.14">6.3.5</a>, <a href="#rfc.xref.RFC7234.15">6.4.1</a>, <a href="#rfc.xref.RFC7234.16">6.4.2</a>, <a href="#rfc.xref.RFC7234.17">6.5.4</a>, <a href="#rfc.xref.RFC7234.18">6.5.5</a>, <a href="#rfc.xref.RFC7234.19">6.5.9</a>, <a href="#rfc.xref.RFC7234.20">6.5.12</a>, <a href="#rfc.xref.RFC7234.21">6.6.2</a></li><li><em>Section 4.3.5</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.4">4.3.2</a></li><li><em>Section 4.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.6">4.3.4</a>, <a href="#rfc.xref.RFC7234.7">4.3.5</a></li><li><em>Section 5.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.22">7.1</a></li><li><em>Section 5.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.2">4.3.1</a>, <a href="#rfc.xref.RFC7234.3">4.3.2</a>, <a href="#rfc.xref.RFC7234.8">5.1</a>, <a href="#rfc.xref.RFC7234.23">7.1</a>, <a href="#rfc.xref.RFC7234.27">7.1.4</a></li><li><em>Section 5.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.24">7.1</a></li><li><em>Section 5.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.9">5.1</a></li><li><em>Section 5.5</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.12">6.3.4</a>, <a href="#rfc.xref.RFC7234.25">7.1</a></li></ul></li><li><em>RFC7235</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7235.1">4.3.8</a>, <a href="#rfc.xref.RFC7235.2">5.4</a>, <a href="#rfc.xref.RFC7235.3">5.4</a>, <a href="#rfc.xref.RFC7235.4">5.4</a>, <a href="#rfc.xref.RFC7235.5">6.1</a>, <a href="#rfc.xref.RFC7235.6">6.1</a>, <a href="#rfc.xref.RFC7235.7">6.1</a>, <a href="#rfc.xref.RFC7235.8">7.1.4</a>, <a href="#rfc.xref.RFC7235.9">7.3</a>, <a href="#rfc.xref.RFC7235.10">7.3</a>, <a href="#RFC7235"><b>11.1</b></a><ul><li><em>Section 3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7235.5">6.1</a></li><li><em>Section 3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7235.6">6.1</a></li><li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7235.7">6.1</a></li><li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7235.9">7.3</a></li><li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7235.3">5.4</a>, <a href="#rfc.xref.RFC7235.8">7.1.4</a></li><li><em>Section 4.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7235.10">7.3</a></li><li><em>Section 4.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7235.4">5.4</a></li></ul></li><li><em>RFC7238</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7238.1">6.4.7</a>, <a href="#RFC7238"><b>11.2</b></a></li></ul></li><li><a id="rfc.index.S" href="#rfc.index.S"><b>S</b></a><ul><li>safe&nbsp;&nbsp;<a href="#rfc.section.4.2.1"><b>4.2.1</b></a></li><li>selected representation&nbsp;&nbsp;<a href="#rfc.section.3"><b>3</b></a>, <a href="#rfc.section.7.2">7.2</a></li><li>Server header field&nbsp;&nbsp;<a href="#rfc.xref.header.server.1">7.4</a>, <a href="#rfc.section.7.4.2"><b>7.4.2</b></a>, <a href="#rfc.xref.header.server.2">8.3.2</a>, <a href="#rfc.xref.header.server.3">9.6</a></li><li>Status Codes Classes&nbsp;&nbsp;<ul><li>1xx Informational&nbsp;&nbsp;<a href="#rfc.section.6.2"><b>6.2</b></a></li><li>2xx Successful&nbsp;&nbsp;<a href="#rfc.section.6.3"><b>6.3</b></a></li><li>3xx Redirection&nbsp;&nbsp;<a href="#rfc.section.6.4"><b>6.4</b></a>, <a href="#rfc.xref.status.3xx.1">B</a></li><li>4xx Client Error&nbsp;&nbsp;<a href="#rfc.section.6.5"><b>6.5</b></a></li><li>5xx Server Error&nbsp;&nbsp;<a href="#rfc.section.6.6"><b>6.6</b></a></li></ul></li></ul></li><li><a id="rfc.index.T" href="#rfc.index.T"><b>T</b></a><ul><li>TRACE method&nbsp;&nbsp;<a href="#rfc.xref.TRACE.1">4.1</a>, <a href="#rfc.iref.t.1"><b>4.3.8</b></a>, <a href="#rfc.xref.TRACE.2">5.1.2</a>, <a href="#rfc.xref.TRACE.3">8.1.3</a>, <a href="#rfc.extref.t.50">B</a>, <a href="#rfc.xref.TRACE.4">B</a>, <a href="#rfc.extref.t.51">B</a></li></ul></li><li><a id="rfc.index.U" href="#rfc.index.U"><b>U</b></a><ul><li>User-Agent header field&nbsp;&nbsp;<a href="#rfc.xref.header.user-agent.1">5.5</a>, <a href="#rfc.section.5.5.3"><b>5.5.3</b></a>, <a href="#rfc.xref.header.user-agent.2">7.4.2</a>, <a href="#rfc.xref.header.user-agent.3">8.3.2</a>, <a href="#rfc.xref.header.user-agent.4">9.6</a></li></ul></li><li><a id="rfc.index.V" href="#rfc.index.V"><b>V</b></a><ul><li>Vary header field&nbsp;&nbsp;<a href="#rfc.xref.header.vary.1">3.4.1</a>, <a href="#rfc.xref.header.vary.2">7.1</a>, <a href="#rfc.section.7.1.4"><b>7.1.4</b></a>, <a href="#rfc.xref.header.vary.3">8.3.1</a>, <a href="#rfc.xref.header.vary.4">8.3.2</a></li></ul></li><li><a id="rfc.index.X" href="#rfc.index.X"><b>X</b></a><ul><li>x-compress (content coding)&nbsp;&nbsp;<a href="#rfc.section.3.1.2.1"><b>3.1.2.1</b></a></li><li>x-gzip (content coding)&nbsp;&nbsp;<a href="#rfc.section.3.1.2.1"><b>3.1.2.1</b></a></li></ul></li></ul></div><div class="avoidbreak"><h1 id="rfc.authors"><a href="#rfc.authors">Authors' Addresses</a></h1><p><b>Roy T. Fielding</b>
     824</pre></div></div><h1 id="rfc.index"><a href="#rfc.index">Index</a></h1><p class="noprint"><a href="#rfc.index.1">1</a> <a href="#rfc.index.2">2</a> <a href="#rfc.index.3">3</a> <a href="#rfc.index.4">4</a> <a href="#rfc.index.5">5</a> <a href="#rfc.index.A">A</a> <a href="#rfc.index.B">B</a> <a href="#rfc.index.C">C</a> <a href="#rfc.index.D">D</a> <a href="#rfc.index.E">E</a> <a href="#rfc.index.F">F</a> <a href="#rfc.index.G">G</a> <a href="#rfc.index.H">H</a> <a href="#rfc.index.I">I</a> <a href="#rfc.index.L">L</a> <a href="#rfc.index.M">M</a> <a href="#rfc.index.O">O</a> <a href="#rfc.index.P">P</a> <a href="#rfc.index.R">R</a> <a href="#rfc.index.S">S</a> <a href="#rfc.index.T">T</a> <a href="#rfc.index.U">U</a> <a href="#rfc.index.V">V</a> <a href="#rfc.index.X">X</a> </p><div class="print2col"><ul class="ind"><li><a id="rfc.index.1" href="#rfc.index.1"><b>1</b></a><ul><li>100 Continue (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.100.1">6.1</a>, <a href="#rfc.section.6.2.1"><b>6.2.1</b></a>, <a href="#rfc.xref.status.100.2">8.2.3</a></li><li>100-continue (expect value)&nbsp;&nbsp;<a href="#rfc.section.5.1.1"><b>5.1.1</b></a></li><li>101 Switching Protocols (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.101.1">6.1</a>, <a href="#rfc.section.6.2.2"><b>6.2.2</b></a>, <a href="#rfc.xref.status.101.2">8.2.3</a></li><li>1xx Informational (status code class)&nbsp;&nbsp;<a href="#rfc.section.6.2"><b>6.2</b></a></li></ul></li><li><a id="rfc.index.2" href="#rfc.index.2"><b>2</b></a><ul><li>200 OK (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.200.1">6.1</a>, <a href="#rfc.section.6.3.1"><b>6.3.1</b></a>, <a href="#rfc.xref.status.200.2">8.2.3</a></li><li>201 Created (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.201.1">6.1</a>, <a href="#rfc.section.6.3.2"><b>6.3.2</b></a>, <a href="#rfc.xref.status.201.2">8.2.3</a>, <a href="#rfc.xref.status.201.3">B</a></li><li>202 Accepted (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.202.1">6.1</a>, <a href="#rfc.section.6.3.3"><b>6.3.3</b></a>, <a href="#rfc.xref.status.202.2">8.2.3</a></li><li>203 Non-Authoritative Information (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.203.1">6.1</a>, <a href="#rfc.section.6.3.4"><b>6.3.4</b></a>, <a href="#rfc.xref.status.203.2">8.2.3</a>, <a href="#rfc.xref.status.203.3">B</a></li><li>204 No Content (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.204.1">6.1</a>, <a href="#rfc.section.6.3.5"><b>6.3.5</b></a>, <a href="#rfc.xref.status.204.2">8.2.3</a></li><li>205 Reset Content (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.205.1">6.1</a>, <a href="#rfc.section.6.3.6"><b>6.3.6</b></a>, <a href="#rfc.xref.status.205.2">8.2.3</a></li><li>2xx Successful (status code class)&nbsp;&nbsp;<a href="#rfc.section.6.3"><b>6.3</b></a></li></ul></li><li><a id="rfc.index.3" href="#rfc.index.3"><b>3</b></a><ul><li>300 Multiple Choices (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.300.1">6.1</a>, <a href="#rfc.section.6.4.1"><b>6.4.1</b></a>, <a href="#rfc.xref.status.300.2">6.5.6</a>, <a href="#rfc.xref.status.300.3">8.2.3</a></li><li>301 Moved Permanently (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.301.1">6.1</a>, <a href="#rfc.section.6.4.2"><b>6.4.2</b></a>, <a href="#rfc.xref.status.301.2">8.2.3</a>, <a href="#rfc.xref.status.301.3">B</a></li><li>302 Found (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.302.1">6.1</a>, <a href="#rfc.section.6.4.3"><b>6.4.3</b></a>, <a href="#rfc.xref.status.302.2">8.2.3</a>, <a href="#rfc.xref.status.302.3">B</a></li><li>303 See Other (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.303.1">6.1</a>, <a href="#rfc.section.6.4.4"><b>6.4.4</b></a>, <a href="#rfc.xref.status.303.2">8.2.3</a>, <a href="#rfc.xref.status.303.3">B</a></li><li>305 Use Proxy (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.305.1">6.1</a>, <a href="#rfc.section.6.4.5"><b>6.4.5</b></a>, <a href="#rfc.xref.status.305.2">8.2.3</a>, <a href="#rfc.xref.status.305.3">B</a></li><li>306 (Unused) (status code)&nbsp;&nbsp;<a href="#rfc.section.6.4.6"><b>6.4.6</b></a>, <a href="#rfc.xref.status.306.1">8.2.3</a></li><li>307 Temporary Redirect (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.307.1">6.1</a>, <a href="#rfc.section.6.4.7"><b>6.4.7</b></a>, <a href="#rfc.xref.status.307.2">8.2.3</a></li><li>3xx Redirection (status code class)&nbsp;&nbsp;<a href="#rfc.section.6.4"><b>6.4</b></a>, <a href="#rfc.xref.status.3xx.1">B</a></li></ul></li><li><a id="rfc.index.4" href="#rfc.index.4"><b>4</b></a><ul><li>400 Bad Request (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.400.1">6.1</a>, <a href="#rfc.section.6.5.1"><b>6.5.1</b></a>, <a href="#rfc.xref.status.400.2">8.2.3</a>, <a href="#rfc.xref.status.400.3">B</a></li><li>402 Payment Required (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.402.1">6.1</a>, <a href="#rfc.section.6.5.2"><b>6.5.2</b></a>, <a href="#rfc.xref.status.402.2">8.2.3</a></li><li>403 Forbidden (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.403.1">6.1</a>, <a href="#rfc.section.6.5.3"><b>6.5.3</b></a>, <a href="#rfc.xref.status.403.2">8.2.3</a></li><li>404 Not Found (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.404.1">6.1</a>, <a href="#rfc.section.6.5.4"><b>6.5.4</b></a>, <a href="#rfc.xref.status.404.2">8.2.3</a></li><li>405 Method Not Allowed (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.405.1">6.1</a>, <a href="#rfc.section.6.5.5"><b>6.5.5</b></a>, <a href="#rfc.xref.status.405.2">8.2.3</a></li><li>406 Not Acceptable (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.406.1">6.1</a>, <a href="#rfc.section.6.5.6"><b>6.5.6</b></a>, <a href="#rfc.xref.status.406.2">8.2.3</a></li><li>408 Request Timeout (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.408.1">6.1</a>, <a href="#rfc.section.6.5.7"><b>6.5.7</b></a>, <a href="#rfc.xref.status.408.2">8.2.3</a></li><li>409 Conflict (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.409.1">6.1</a>, <a href="#rfc.section.6.5.8"><b>6.5.8</b></a>, <a href="#rfc.xref.status.409.2">8.2.3</a></li><li>410 Gone (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.410.1">6.1</a>, <a href="#rfc.section.6.5.9"><b>6.5.9</b></a>, <a href="#rfc.xref.status.410.2">8.2.3</a></li><li>411 Length Required (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.411.1">6.1</a>, <a href="#rfc.section.6.5.10"><b>6.5.10</b></a>, <a href="#rfc.xref.status.411.2">8.2.3</a></li><li>413 Payload Too Large (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.413.1">6.1</a>, <a href="#rfc.section.6.5.11"><b>6.5.11</b></a>, <a href="#rfc.xref.status.413.2">8.2.3</a></li><li>414 URI Too Long (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.414.1">6.1</a>, <a href="#rfc.section.6.5.12"><b>6.5.12</b></a>, <a href="#rfc.xref.status.414.2">8.2.3</a></li><li>415 Unsupported Media Type (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.415.1">6.1</a>, <a href="#rfc.section.6.5.13"><b>6.5.13</b></a>, <a href="#rfc.xref.status.415.2">8.2.3</a></li><li>417 Expectation Failed (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.417.1">6.1</a>, <a href="#rfc.section.6.5.14"><b>6.5.14</b></a>, <a href="#rfc.xref.status.417.2">8.2.3</a></li><li>426 Upgrade Required (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.426.1">6.1</a>, <a href="#rfc.section.6.5.15"><b>6.5.15</b></a>, <a href="#rfc.xref.status.426.2">8.2.3</a>, <a href="#rfc.xref.status.426.3">B</a></li><li>4xx Client Error (status code class)&nbsp;&nbsp;<a href="#rfc.section.6.5"><b>6.5</b></a></li></ul></li><li><a id="rfc.index.5" href="#rfc.index.5"><b>5</b></a><ul><li>500 Internal Server Error (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.500.1">6.1</a>, <a href="#rfc.section.6.6.1"><b>6.6.1</b></a>, <a href="#rfc.xref.status.500.2">8.2.3</a></li><li>501 Not Implemented (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.501.1">6.1</a>, <a href="#rfc.section.6.6.2"><b>6.6.2</b></a>, <a href="#rfc.xref.status.501.2">8.2.3</a></li><li>502 Bad Gateway (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.502.1">6.1</a>, <a href="#rfc.section.6.6.3"><b>6.6.3</b></a>, <a href="#rfc.xref.status.502.2">8.2.3</a></li><li>503 Service Unavailable (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.503.1">6.1</a>, <a href="#rfc.section.6.6.4"><b>6.6.4</b></a>, <a href="#rfc.xref.status.503.2">8.2.3</a></li><li>504 Gateway Timeout (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.504.1">6.1</a>, <a href="#rfc.section.6.6.5"><b>6.6.5</b></a>, <a href="#rfc.xref.status.504.2">8.2.3</a></li><li>505 HTTP Version Not Supported (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.505.1">6.1</a>, <a href="#rfc.section.6.6.6"><b>6.6.6</b></a>, <a href="#rfc.xref.status.505.2">8.2.3</a></li><li>5xx Server Error (status code class)&nbsp;&nbsp;<a href="#rfc.section.6.6"><b>6.6</b></a></li></ul></li><li><a id="rfc.index.A" href="#rfc.index.A"><b>A</b></a><ul><li>Accept header field&nbsp;&nbsp;<a href="#rfc.xref.header.accept.1">3.1.1.1</a>, <a href="#rfc.xref.header.accept.2">5.3</a>, <a href="#rfc.section.5.3.2"><b>5.3.2</b></a>, <a href="#rfc.xref.header.accept.3">8.3.2</a></li><li>Accept-Charset header field&nbsp;&nbsp;<a href="#rfc.xref.header.accept-charset.1">5.3</a>, <a href="#rfc.section.5.3.3"><b>5.3.3</b></a>, <a href="#rfc.xref.header.accept-charset.2">8.3.2</a>, <a href="#rfc.xref.header.accept-charset.3">B</a></li><li>Accept-Encoding header field&nbsp;&nbsp;<a href="#rfc.xref.header.accept-encoding.1">3.1.2.1</a>, <a href="#rfc.xref.header.accept-encoding.2">5.3</a>, <a href="#rfc.section.5.3.4"><b>5.3.4</b></a>, <a href="#rfc.xref.header.accept-encoding.3">8.3.2</a>, <a href="#rfc.xref.header.accept-encoding.4">8.4.2</a></li><li>Accept-Language header field&nbsp;&nbsp;<a href="#rfc.xref.header.accept-language.1">3.1.3.1</a>, <a href="#rfc.xref.header.accept-language.2">5.3</a>, <a href="#rfc.section.5.3.5"><b>5.3.5</b></a>, <a href="#rfc.xref.header.accept-language.3">8.3.2</a></li><li>Allow header field&nbsp;&nbsp;<a href="#rfc.xref.header.allow.1">4.1</a>, <a href="#rfc.xref.header.allow.2">7.4</a>, <a href="#rfc.section.7.4.1"><b>7.4.1</b></a>, <a href="#rfc.xref.header.allow.3">8.3.2</a>, <a href="#rfc.xref.header.allow.4">B</a></li></ul></li><li><a id="rfc.index.B" href="#rfc.index.B"><b>B</b></a><ul><li><em>BCP13</em>&nbsp;&nbsp;<a href="#rfc.xref.BCP13.1">3.1.1.1</a>, <a href="#BCP13"><b>11.2</b></a></li><li><em>BCP178</em>&nbsp;&nbsp;<a href="#rfc.xref.BCP178.1">8.3.1</a>, <a href="#BCP178"><b>11.2</b></a></li><li><em>BCP90</em>&nbsp;&nbsp;<a href="#rfc.xref.BCP90.1">8.3</a>, <a href="#rfc.xref.BCP90.2">8.3.1</a>, <a href="#BCP90"><b>11.2</b></a></li></ul></li><li><a id="rfc.index.C" href="#rfc.index.C"><b>C</b></a><ul><li>cacheable&nbsp;&nbsp;<a href="#rfc.section.4.2.3"><b>4.2.3</b></a></li><li>compress (content coding)&nbsp;&nbsp;<a href="#rfc.section.3.1.2.1"><b>3.1.2.1</b></a></li><li>conditional request&nbsp;&nbsp;<a href="#rfc.section.5.2"><b>5.2</b></a></li><li>CONNECT method&nbsp;&nbsp;<a href="#rfc.xref.CONNECT.1">4.1</a>, <a href="#rfc.section.4.3.6"><b>4.3.6</b></a>, <a href="#rfc.xref.CONNECT.2">8.1.3</a>, <a href="#rfc.xref.CONNECT.3">B</a></li><li>content coding&nbsp;&nbsp;<a href="#rfc.section.3.1.2.1"><b>3.1.2.1</b></a></li><li>content negotiation&nbsp;&nbsp;<a href="#rfc.iref.c.1">1</a></li><li>Content-Encoding header field&nbsp;&nbsp;<a href="#rfc.xref.header.content-encoding.1">3.1</a>, <a href="#rfc.xref.header.content-encoding.2">3.1.2.1</a>, <a href="#rfc.section.3.1.2.2"><b>3.1.2.2</b></a>, <a href="#rfc.xref.header.content-encoding.3">8.3.2</a></li><li>Content-Language header field&nbsp;&nbsp;<a href="#rfc.xref.header.content-language.1">3.1</a>, <a href="#rfc.section.3.1.3.2"><b>3.1.3.2</b></a>, <a href="#rfc.xref.header.content-language.2">8.3.2</a></li><li>Content-Location header field&nbsp;&nbsp;<a href="#rfc.xref.header.content-location.1">3.1</a>, <a href="#rfc.section.3.1.4.2"><b>3.1.4.2</b></a>, <a href="#rfc.xref.header.content-location.2">4.3.3</a>, <a href="#rfc.xref.header.content-location.3">7.1.2</a>, <a href="#rfc.xref.header.content-location.4">8.3.2</a>, <a href="#rfc.xref.header.content-location.5">B</a></li><li>Content-Transfer-Encoding header field&nbsp;&nbsp;<a href="#rfc.section.A.5">A.5</a></li><li>Content-Type header field&nbsp;&nbsp;<a href="#rfc.xref.header.content-type.1">3.1</a>, <a href="#rfc.xref.header.content-type.2">3.1.1.1</a>, <a href="#rfc.section.3.1.1.5"><b>3.1.1.5</b></a>, <a href="#rfc.xref.header.content-type.3">8.3.1</a>, <a href="#rfc.xref.header.content-type.4">8.3.2</a></li></ul></li><li><a id="rfc.index.D" href="#rfc.index.D"><b>D</b></a><ul><li>Date header field&nbsp;&nbsp;<a href="#rfc.xref.header.date.1">3.3</a>, <a href="#rfc.xref.header.date.2">7.1</a>, <a href="#rfc.section.7.1.1.2"><b>7.1.1.2</b></a>, <a href="#rfc.xref.header.date.3">8.3.2</a></li><li>deflate (content coding)&nbsp;&nbsp;<a href="#rfc.section.3.1.2.1"><b>3.1.2.1</b></a></li><li>DELETE method&nbsp;&nbsp;<a href="#rfc.xref.DELETE.1">4.1</a>, <a href="#rfc.iref.d.1"><b>4.3.5</b></a>, <a href="#rfc.xref.DELETE.2">8.1.3</a></li></ul></li><li><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul><li>Expect header field&nbsp;&nbsp;<a href="#rfc.xref.header.expect.1">5.1</a>, <a href="#rfc.section.5.1.1"><b>5.1.1</b></a>, <a href="#rfc.xref.header.expect.2">6.2.1</a>, <a href="#rfc.xref.header.expect.3">6.5.14</a>, <a href="#rfc.xref.header.expect.4">8.3.2</a>, <a href="#rfc.xref.header.expect.5">B</a></li></ul></li><li><a id="rfc.index.F" href="#rfc.index.F"><b>F</b></a><ul><li>From header field&nbsp;&nbsp;<a href="#rfc.xref.header.from.1">5.5</a>, <a href="#rfc.section.5.5.1"><b>5.5.1</b></a>, <a href="#rfc.xref.header.from.2">8.3.2</a></li></ul></li><li><a id="rfc.index.G" href="#rfc.index.G"><b>G</b></a><ul><li>GET method&nbsp;&nbsp;<a href="#rfc.xref.GET.1">3</a>, <a href="#rfc.xref.GET.2">3.1.4.2</a>, <a href="#rfc.xref.GET.3">3.3</a>, <a href="#rfc.xref.GET.4">4.1</a>, <a href="#rfc.iref.g.13"><b>4.3.1</b></a>, <a href="#rfc.xref.GET.5">8.1.3</a>, <a href="#rfc.xref.GET.6">B</a></li><li><tt>Grammar</tt>&nbsp;&nbsp;<ul><li><tt>Accept</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.18"><b>5.3.2</b></a></li><li><tt>Accept-Charset</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.22"><b>5.3.3</b></a></li><li><tt>Accept-Encoding</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.23"><b>5.3.4</b></a></li><li><tt>accept-ext</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.21"><b>5.3.2</b></a></li><li><tt>Accept-Language</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.25"><b>5.3.5</b></a></li><li><tt>accept-params</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.20"><b>5.3.2</b></a></li><li><tt>Allow</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.53"><b>7.4.1</b></a></li><li><tt>asctime-date</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.47"><b>7.1.1.1</b></a></li><li><tt>charset</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.5"><b>3.1.1.2</b></a></li><li><tt>codings</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.24"><b>5.3.4</b></a></li><li><tt>content-coding</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.7"><b>3.1.2.1</b></a></li><li><tt>Content-Encoding</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.8"><b>3.1.2.2</b></a></li><li><tt>Content-Language</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.10"><b>3.1.3.2</b></a></li><li><tt>Content-Location</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.11"><b>3.1.4.2</b></a></li><li><tt>Content-Type</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.6"><b>3.1.1.5</b></a></li><li><tt>Date</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.48"><b>7.1.1.2</b></a></li><li><tt>date1</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.34"><b>7.1.1.1</b></a></li><li><tt>day</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.41"><b>7.1.1.1</b></a></li><li><tt>day-name</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.39"><b>7.1.1.1</b></a></li><li><tt>day-name-l</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.40"><b>7.1.1.1</b></a></li><li><tt>delay-seconds</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.51"><b>7.1.3</b></a></li><li><tt>Expect</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.14"><b>5.1.1</b></a></li><li><tt>From</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.27"><b>5.5.1</b></a></li><li><tt>GMT</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.44"><b>7.1.1.1</b></a></li><li><tt>hour</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.36"><b>7.1.1.1</b></a></li><li><tt>HTTP-date</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.32"><b>7.1.1.1</b></a></li><li><tt>IMF-fixdate</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.33"><b>7.1.1.1</b></a></li><li><tt>language-range</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.26"><b>5.3.5</b></a></li><li><tt>language-tag</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.9"><b>3.1.3.1</b></a></li><li><tt>Location</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.49"><b>7.1.2</b></a></li><li><tt>Max-Forwards</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.15"><b>5.1.2</b></a></li><li><tt>media-range</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.19"><b>5.3.2</b></a></li><li><tt>media-type</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.1"><b>3.1.1.1</b></a></li><li><tt>method</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.12"><b>4.1</b></a></li><li><tt>minute</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.37"><b>7.1.1.1</b></a></li><li><tt>month</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.42"><b>7.1.1.1</b></a></li><li><tt>obs-date</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.45"><b>7.1.1.1</b></a></li><li><tt>parameter</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.4"><b>3.1.1.1</b></a></li><li><tt>product</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.30"><b>5.5.3</b></a></li><li><tt>product-version</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.31"><b>5.5.3</b></a></li><li><tt>qvalue</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.17"><b>5.3.1</b></a></li><li><tt>Referer</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.28"><b>5.5.2</b></a></li><li><tt>Retry-After</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.50"><b>7.1.3</b></a></li><li><tt>rfc850-date</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.46"><b>7.1.1.1</b></a></li><li><tt>second</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.38"><b>7.1.1.1</b></a></li><li><tt>Server</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.54"><b>7.4.2</b></a></li><li><tt>subtype</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.3"><b>3.1.1.1</b></a></li><li><tt>time-of-day</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.35"><b>7.1.1.1</b></a></li><li><tt>type</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.2"><b>3.1.1.1</b></a></li><li><tt>User-Agent</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.29"><b>5.5.3</b></a></li><li><tt>Vary</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.52"><b>7.1.4</b></a></li><li><tt>weight</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.16"><b>5.3.1</b></a></li><li><tt>year</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.43"><b>7.1.1.1</b></a></li></ul></li><li>gzip (content coding)&nbsp;&nbsp;<a href="#rfc.section.3.1.2.1"><b>3.1.2.1</b></a></li></ul></li><li><a id="rfc.index.H" href="#rfc.index.H"><b>H</b></a><ul><li>HEAD method&nbsp;&nbsp;<a href="#rfc.xref.HEAD.1">3.1.4.2</a>, <a href="#rfc.xref.HEAD.2">4.1</a>, <a href="#rfc.iref.h.1"><b>4.3.2</b></a>, <a href="#rfc.xref.HEAD.3">8.1.3</a></li></ul></li><li><a id="rfc.index.I" href="#rfc.index.I"><b>I</b></a><ul><li>idempotent&nbsp;&nbsp;<a href="#rfc.section.4.2.2"><b>4.2.2</b></a></li></ul></li><li><a id="rfc.index.L" href="#rfc.index.L"><b>L</b></a><ul><li>Location header field&nbsp;&nbsp;<a href="#rfc.xref.header.location.1">4.3.3</a>, <a href="#rfc.xref.header.location.2">6.4</a>, <a href="#rfc.xref.header.location.3">7.1</a>, <a href="#rfc.section.7.1.2"><b>7.1.2</b></a>, <a href="#rfc.xref.header.location.4">8.3.2</a>, <a href="#rfc.xref.header.location.5">9.5</a>, <a href="#rfc.xref.header.location.6">B</a></li></ul></li><li><a id="rfc.index.M" href="#rfc.index.M"><b>M</b></a><ul><li>Max-Forwards header field&nbsp;&nbsp;<a href="#rfc.xref.header.max-forwards.1">4.3.7</a>, <a href="#rfc.xref.header.max-forwards.2">4.3.8</a>, <a href="#rfc.xref.header.max-forwards.3">5.1</a>, <a href="#rfc.section.5.1.2"><b>5.1.2</b></a>, <a href="#rfc.xref.header.max-forwards.4">8.3.2</a>, <a href="#rfc.xref.header.max-forwards.5">B</a></li><li>MIME-Version header field&nbsp;&nbsp;<a href="#rfc.xref.mime-version.1">8.3.2</a>, <a href="#rfc.section.A.1"><b>A.1</b></a></li></ul></li><li><a id="rfc.index.O" href="#rfc.index.O"><b>O</b></a><ul><li>OPTIONS method&nbsp;&nbsp;<a href="#rfc.xref.OPTIONS.1">4.1</a>, <a href="#rfc.iref.o.1"><b>4.3.7</b></a>, <a href="#rfc.xref.OPTIONS.2">5.1.2</a>, <a href="#rfc.xref.OPTIONS.3">8.1.3</a>, <a href="#rfc.extref.o.11">B</a>, <a href="#rfc.xref.OPTIONS.4">B</a>, <a href="#rfc.extref.o.12">B</a></li><li><em>OWASP</em>&nbsp;&nbsp;<a href="#rfc.xref.OWASP.1">9</a>, <a href="#OWASP"><b>11.2</b></a></li></ul></li><li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul><li>payload&nbsp;&nbsp;<a href="#rfc.section.3.3">3.3</a></li><li>POST method&nbsp;&nbsp;<a href="#rfc.xref.POST.1">3.1.4.2</a>, <a href="#rfc.xref.POST.2">3.3</a>, <a href="#rfc.xref.POST.3">4.1</a>, <a href="#rfc.section.4.3.3"><b>4.3.3</b></a>, <a href="#rfc.xref.POST.4">8.1.3</a></li><li>PUT method&nbsp;&nbsp;<a href="#rfc.xref.PUT.1">3.1.4.2</a>, <a href="#rfc.xref.PUT.2">3.3</a>, <a href="#rfc.xref.PUT.3">4.1</a>, <a href="#rfc.iref.p.1"><b>4.3.4</b></a>, <a href="#rfc.xref.PUT.4">8.1.3</a>, <a href="#rfc.xref.PUT.5">B</a></li></ul></li><li><a id="rfc.index.R" href="#rfc.index.R"><b>R</b></a><ul><li>Referer header field&nbsp;&nbsp;<a href="#rfc.xref.header.referer.1">5.5</a>, <a href="#rfc.section.5.5.2"><b>5.5.2</b></a>, <a href="#rfc.xref.header.referer.2">8.3.2</a>, <a href="#rfc.xref.header.referer.3">9.4</a>, <a href="#rfc.xref.header.referer.4">B</a></li><li>representation&nbsp;&nbsp;<a href="#rfc.section.3"><b>3</b></a></li><li><em>REST</em>&nbsp;&nbsp;<a href="#rfc.xref.REST.1">3</a>, <a href="#rfc.xref.REST.2">4.1</a>, <a href="#REST"><b>11.2</b></a></li><li>Retry-After header field&nbsp;&nbsp;<a href="#rfc.xref.header.retry-after.1">6.6.4</a>, <a href="#rfc.xref.header.retry-after.2">7.1</a>, <a href="#rfc.section.7.1.3"><b>7.1.3</b></a>, <a href="#rfc.xref.header.retry-after.3">8.3.2</a></li><li><em>RFC1945</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1945.1">6.4</a>, <a href="#RFC1945"><b>11.2</b></a><ul><li><em>Section 9.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1945.1">6.4</a></li></ul></li><li><em>RFC2045</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2045.1">3.1.1.3</a>, <a href="#RFC2045"><b>11.1</b></a>, <a href="#rfc.xref.RFC2045.2">A</a>, <a href="#rfc.xref.RFC2045.3">A.1</a></li><li><em>RFC2046</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2046.1">3.1.1.1</a>, <a href="#rfc.xref.RFC2046.2">3.1.1.4</a>, <a href="#rfc.xref.RFC2046.3">3.1.1.5</a>, <a href="#RFC2046"><b>11.1</b></a>, <a href="#rfc.xref.RFC2046.4">A.2</a><ul><li><em>Section 4.5.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2046.3">3.1.1.5</a></li><li><em>Section 5.1.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2046.2">3.1.1.4</a></li></ul></li><li><em>RFC2049</em>&nbsp;&nbsp;<a href="#RFC2049"><b>11.2</b></a>, <a href="#rfc.xref.RFC2049.1">A.2</a><ul><li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2049.1">A.2</a></li></ul></li><li><em>RFC2068</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2068.1">5.1.1</a>, <a href="#rfc.xref.RFC2068.2">6.4</a>, <a href="#RFC2068"><b>11.2</b></a><ul><li><em>Section 10.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2068.2">6.4</a></li></ul></li><li><em>RFC2119</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2119.1">1.1</a>, <a href="#RFC2119"><b>11.1</b></a></li><li><em>RFC2295</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2295.1">3.4</a>, <a href="#RFC2295"><b>11.2</b></a></li><li><em>RFC2388</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2388.1">3.1.1.4</a>, <a href="#RFC2388"><b>11.2</b></a></li><li><em>RFC2557</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2557.1">3.1.4.2</a>, <a href="#RFC2557"><b>11.2</b></a>, <a href="#rfc.xref.RFC2557.2">A.6</a><ul><li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2557.1">3.1.4.2</a></li></ul></li><li><em>RFC2616</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2616.1">5.3.5</a>, <a href="#RFC2616"><b>11.2</b></a><ul><li><em>Section 14.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2616.1">5.3.5</a></li></ul></li><li><em>RFC2774</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2774.1">8.1.2</a>, <a href="#RFC2774"><b>11.2</b></a></li><li><em>RFC2817</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2817.1">8.2</a>, <a href="#RFC2817"><b>11.2</b></a>, <a href="#rfc.xref.RFC2817.2">B</a>, <a href="#rfc.xref.RFC2817.3">B</a>, <a href="#rfc.xref.RFC2817.4">B</a><ul><li><em>Section 7.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2817.1">8.2</a>, <a href="#rfc.xref.RFC2817.4">B</a></li></ul></li><li><em>RFC2978</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2978.1">3.1.1.2</a>, <a href="#RFC2978"><b>11.2</b></a></li><li><em>RFC3986</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.1">5.5.2</a>, <a href="#rfc.xref.RFC3986.2">7.1.2</a>, <a href="#rfc.xref.RFC3986.3">7.1.2</a>, <a href="#RFC3986"><b>11.1</b></a><ul><li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.2">7.1.2</a></li><li><em>Section 5</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC3986.3">7.1.2</a></li></ul></li><li><em>RFC4647</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4647.1">5.3.5</a>, <a href="#rfc.xref.RFC4647.2">5.3.5</a>, <a href="#rfc.xref.RFC4647.3">5.3.5</a>, <a href="#rfc.xref.RFC4647.4">5.3.5</a>, <a href="#RFC4647"><b>11.1</b></a><ul><li><em>Section 2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4647.1">5.3.5</a></li><li><em>Section 2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4647.2">5.3.5</a></li><li><em>Section 3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4647.3">5.3.5</a></li><li><em>Section 3.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC4647.4">5.3.5</a></li></ul></li><li><em>RFC5226</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5226.1">8.1.1</a>, <a href="#rfc.xref.RFC5226.2">8.2.1</a>, <a href="#rfc.xref.RFC5226.3">8.4.1</a>, <a href="#RFC5226"><b>11.2</b></a><ul><li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5226.1">8.1.1</a>, <a href="#rfc.xref.RFC5226.2">8.2.1</a>, <a href="#rfc.xref.RFC5226.3">8.4.1</a></li></ul></li><li><em>RFC5234</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5234.1">1.2</a>, <a href="#rfc.xref.RFC5234.2">8.3.1</a>, <a href="#RFC5234"><b>11.1</b></a>, <a href="#rfc.xref.RFC5234.3">C</a><ul><li><em>Appendix B.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5234.3">C</a></li></ul></li><li><em>RFC5246</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5246.1">4.3.6</a>, <a href="#RFC5246"><b>11.2</b></a></li><li><em>RFC5322</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5322.1">5.5.1</a>, <a href="#rfc.xref.RFC5322.2">5.5.1</a>, <a href="#rfc.xref.RFC5322.3">7.1.1.1</a>, <a href="#rfc.xref.RFC5322.4">7.1.1.1</a>, <a href="#rfc.xref.RFC5322.5">7.1.1.1</a>, <a href="#rfc.xref.RFC5322.6">7.1.1.2</a>, <a href="#RFC5322"><b>11.2</b></a>, <a href="#rfc.xref.RFC5322.7">A</a><ul><li><em>Section 3.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5322.4">7.1.1.1</a>, <a href="#rfc.xref.RFC5322.5">7.1.1.1</a></li><li><em>Section 3.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5322.1">5.5.1</a>, <a href="#rfc.xref.RFC5322.2">5.5.1</a></li><li><em>Section 3.6.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5322.6">7.1.1.2</a></li></ul></li><li><em>RFC5646</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5646.1">3.1.3.1</a>, <a href="#rfc.xref.RFC5646.2">3.1.3.1</a>, <a href="#rfc.xref.RFC5646.3">3.1.3.1</a>, <a href="#RFC5646"><b>11.1</b></a><ul><li><em>Section 2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5646.2">3.1.3.1</a></li></ul></li><li><em>RFC5789</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5789.1">4.3.4</a>, <a href="#RFC5789"><b>11.2</b></a></li><li><em>RFC5905</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5905.1">7.1.1.1</a>, <a href="#RFC5905"><b>11.2</b></a></li><li><em>RFC5987</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5987.1">8.3.1</a>, <a href="#RFC5987"><b>11.2</b></a></li><li><em>RFC5988</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC5988.1">6.4.1</a>, <a href="#RFC5988"><b>11.2</b></a></li><li><em>RFC6265</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC6265.1">4.3.8</a>, <a href="#rfc.xref.RFC6265.2">5.4</a>, <a href="#RFC6265"><b>11.2</b></a></li><li><em>RFC6266</em>&nbsp;&nbsp;<a href="#RFC6266"><b>11.2</b></a>, <a href="#rfc.xref.RFC6266.1">B</a></li><li><em>RFC6365</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC6365.1">1.2</a>, <a href="#rfc.xref.RFC6365.2">3.1.1.2</a>, <a href="#RFC6365"><b>11.1</b></a></li><li><em>RFC7230</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.1">1</a>, <a href="#rfc.xref.RFC7230.2">1.1</a>, <a href="#rfc.xref.RFC7230.3">1.2</a>, <a href="#rfc.xref.RFC7230.4">2</a>, <a href="#rfc.xref.RFC7230.5">2</a>, <a href="#rfc.xref.RFC7230.6">2</a>, <a href="#rfc.xref.RFC7230.7">3.1.2.1</a>, <a href="#rfc.xref.RFC7230.8">3.1.2.1</a>, <a href="#rfc.xref.RFC7230.9">3.1.2.1</a>, <a href="#rfc.xref.RFC7230.10">3.1.2.2</a>, <a href="#rfc.xref.RFC7230.11">3.1.4.1</a>, <a href="#rfc.xref.RFC7230.12">3.1.4.2</a>, <a href="#rfc.xref.RFC7230.13">3.3</a>, <a href="#rfc.xref.RFC7230.14">3.3</a>, <a href="#rfc.xref.RFC7230.15">3.3</a>, <a href="#rfc.xref.RFC7230.16">4.3.6</a>, <a href="#rfc.xref.RFC7230.17">4.3.7</a>, <a href="#rfc.xref.RFC7230.18">4.3.8</a>, <a href="#rfc.xref.RFC7230.19">4.3.8</a>, <a href="#rfc.xref.RFC7230.20">5.1</a>, <a href="#rfc.xref.RFC7230.21">5.1</a>, <a href="#rfc.xref.RFC7230.22">5.1.1</a>, <a href="#rfc.xref.RFC7230.23">5.5.3</a>, <a href="#rfc.xref.RFC7230.24">6.2.2</a>, <a href="#rfc.xref.RFC7230.25">6.3.4</a>, <a href="#rfc.xref.RFC7230.26">6.5.7</a>, <a href="#rfc.xref.RFC7230.27">6.5.10</a>, <a href="#rfc.xref.RFC7230.28">6.5.12</a>, <a href="#rfc.xref.RFC7230.29">6.5.15</a>, <a href="#rfc.xref.RFC7230.30">6.6.6</a>, <a href="#rfc.xref.RFC7230.31">7.4.2</a>, <a href="#rfc.xref.RFC7230.32">8.1.2</a>, <a href="#rfc.xref.RFC7230.33">8.3.1</a>, <a href="#rfc.xref.RFC7230.34">8.3.1</a>, <a href="#rfc.xref.RFC7230.35">8.3.1</a>, <a href="#rfc.xref.RFC7230.36">8.3.1</a>, <a href="#rfc.xref.RFC7230.37">8.3.1</a>, <a href="#rfc.xref.RFC7230.38">8.3.1</a>, <a href="#rfc.xref.RFC7230.39">8.3.1</a>, <a href="#rfc.xref.RFC7230.40">8.4</a>, <a href="#rfc.xref.RFC7230.41">8.4.1</a>, <a href="#rfc.xref.RFC7230.42">8.4.1</a>, <a href="#rfc.xref.RFC7230.43">9</a>, <a href="#rfc.xref.RFC7230.44">9.6</a>, <a href="#rfc.xref.RFC7230.45">10</a>, <a href="#RFC7230"><b>11.1</b></a>, <a href="#rfc.xref.RFC7230.46">B</a>, <a href="#rfc.xref.RFC7230.47">C</a>, <a href="#rfc.xref.RFC7230.48">C</a>, <a href="#rfc.xref.RFC7230.49">C</a>, <a href="#rfc.xref.RFC7230.50">C</a>, <a href="#rfc.xref.RFC7230.51">C</a>, <a href="#rfc.xref.RFC7230.52">C</a>, <a href="#rfc.xref.RFC7230.53">C</a>, <a href="#rfc.xref.RFC7230.54">C</a>, <a href="#rfc.xref.RFC7230.55">C</a>, <a href="#rfc.xref.RFC7230.56">C</a>, <a href="#rfc.xref.RFC7230.57">C</a>, <a href="#rfc.xref.RFC7230.58">D</a><ul><li><em>Section 1.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.58">D</a></li><li><em>Section 2.5</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.2">1.1</a></li><li><em>Section 2.6</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.30">6.6.6</a></li><li><em>Section 2.7</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.4">2</a>, <a href="#rfc.xref.RFC7230.51">C</a>, <a href="#rfc.xref.RFC7230.52">C</a>, <a href="#rfc.xref.RFC7230.55">C</a></li><li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.23">5.5.3</a>, <a href="#rfc.xref.RFC7230.31">7.4.2</a>, <a href="#rfc.xref.RFC7230.33">8.3.1</a>, <a href="#rfc.xref.RFC7230.37">8.3.1</a>, <a href="#rfc.xref.RFC7230.54">C</a></li><li><em>Section 3.2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.48">C</a>, <a href="#rfc.xref.RFC7230.49">C</a>, <a href="#rfc.xref.RFC7230.50">C</a></li><li><em>Section 3.2.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.35">8.3.1</a></li><li><em>Section 3.2.6</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.36">8.3.1</a>, <a href="#rfc.xref.RFC7230.53">C</a>, <a href="#rfc.xref.RFC7230.56">C</a>, <a href="#rfc.xref.RFC7230.57">C</a></li><li><em>Section 3.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.10">3.1.2.2</a>, <a href="#rfc.xref.RFC7230.15">3.3</a></li><li><em>Section 3.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.32">8.1.2</a></li><li><em>Section 3.3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.13">3.3</a>, <a href="#rfc.xref.RFC7230.27">6.5.10</a></li><li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.41">8.4.1</a></li><li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.39">8.3.1</a></li><li><em>Section 4.2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.7">3.1.2.1</a></li><li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.40">8.4</a>, <a href="#rfc.xref.RFC7230.42">8.4.1</a></li><li><em>Section 4.2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.8">3.1.2.1</a></li><li><em>Section 4.2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.9">3.1.2.1</a></li><li><em>Section 4.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.21">5.1</a></li><li><em>Section 4.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.14">3.3</a></li><li><em>Section 5.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.5">2</a>, <a href="#rfc.xref.RFC7230.16">4.3.6</a>, <a href="#rfc.xref.RFC7230.17">4.3.7</a>, <a href="#rfc.xref.RFC7230.28">6.5.12</a></li><li><em>Section 5.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.20">5.1</a></li><li><em>Section 5.5</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.6">2</a>, <a href="#rfc.xref.RFC7230.11">3.1.4.1</a>, <a href="#rfc.xref.RFC7230.12">3.1.4.2</a></li><li><em>Section 5.7.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.19">4.3.8</a>, <a href="#rfc.xref.RFC7230.44">9.6</a></li><li><em>Section 5.7.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.25">6.3.4</a></li><li><em>Section 6.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.26">6.5.7</a>, <a href="#rfc.xref.RFC7230.38">8.3.1</a></li><li><em>Section 6.6</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.22">5.1.1</a></li><li><em>Section 6.7</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.24">6.2.2</a>, <a href="#rfc.xref.RFC7230.29">6.5.15</a></li><li><em>Section 7</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.3">1.2</a>, <a href="#rfc.xref.RFC7230.34">8.3.1</a></li><li><em>Section 8.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.18">4.3.8</a></li><li><em>Section 9</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.43">9</a></li><li><em>Section 10</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7230.45">10</a></li></ul></li><li><em>RFC7232</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.1">3</a>, <a href="#rfc.xref.RFC7232.2">4.1</a>, <a href="#rfc.xref.RFC7232.3">5.2</a>, <a href="#rfc.xref.RFC7232.4">5.2</a>, <a href="#rfc.xref.RFC7232.5">5.2</a>, <a href="#rfc.xref.RFC7232.6">5.2</a>, <a href="#rfc.xref.RFC7232.7">5.2</a>, <a href="#rfc.xref.RFC7232.8">5.2</a>, <a href="#rfc.xref.RFC7232.9">6.1</a>, <a href="#rfc.xref.RFC7232.10">6.1</a>, <a href="#rfc.xref.RFC7232.11">6.1</a>, <a href="#rfc.xref.RFC7232.12">7.2</a>, <a href="#rfc.xref.RFC7232.13">7.2</a>, <a href="#rfc.xref.RFC7232.14">7.2</a>, <a href="#RFC7232"><b>11.1</b></a><ul><li><em>Section 2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.14">7.2</a></li><li><em>Section 2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.13">7.2</a></li><li><em>Section 3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.5">5.2</a></li><li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.6">5.2</a></li><li><em>Section 3.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.7">5.2</a></li><li><em>Section 3.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.8">5.2</a></li><li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.9">6.1</a></li><li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.10">6.1</a></li><li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.11">6.1</a></li><li><em>Section 5</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7232.4">5.2</a></li></ul></li><li><em>RFC7233</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.1">3.1.1.4</a>, <a href="#rfc.xref.RFC7233.2">3.3</a>, <a href="#rfc.xref.RFC7233.3">4.3.1</a>, <a href="#rfc.xref.RFC7233.4">4.3.4</a>, <a href="#rfc.xref.RFC7233.5">5.1</a>, <a href="#rfc.xref.RFC7233.6">5.2</a>, <a href="#rfc.xref.RFC7233.7">6.1</a>, <a href="#rfc.xref.RFC7233.8">6.1</a>, <a href="#rfc.xref.RFC7233.9">6.1</a>, <a href="#rfc.xref.RFC7233.10">7.4</a>, <a href="#rfc.xref.RFC7233.11">8.1.2</a>, <a href="#RFC7233"><b>11.1</b></a>, <a href="#rfc.xref.RFC7233.12">A.6</a><ul><li><em>Section 2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.10">7.4</a></li><li><em>Section 3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.5">5.1</a></li><li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.6">5.2</a></li><li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.7">6.1</a></li><li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.8">6.1</a></li><li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.2">3.3</a>, <a href="#rfc.xref.RFC7233.4">4.3.4</a></li><li><em>Section 4.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.9">6.1</a></li><li><em>Appendix A</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7233.12">A.6</a></li></ul></li><li><em>RFC7234</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.1">4.2.3</a>, <a href="#rfc.xref.RFC7234.2">4.3.1</a>, <a href="#rfc.xref.RFC7234.3">4.3.2</a>, <a href="#rfc.xref.RFC7234.4">4.3.2</a>, <a href="#rfc.xref.RFC7234.5">4.3.3</a>, <a href="#rfc.xref.RFC7234.6">4.3.4</a>, <a href="#rfc.xref.RFC7234.7">4.3.5</a>, <a href="#rfc.xref.RFC7234.8">5.1</a>, <a href="#rfc.xref.RFC7234.9">5.1</a>, <a href="#rfc.xref.RFC7234.10">6.1</a>, <a href="#rfc.xref.RFC7234.11">6.3.1</a>, <a href="#rfc.xref.RFC7234.12">6.3.4</a>, <a href="#rfc.xref.RFC7234.13">6.3.4</a>, <a href="#rfc.xref.RFC7234.14">6.3.5</a>, <a href="#rfc.xref.RFC7234.15">6.4.1</a>, <a href="#rfc.xref.RFC7234.16">6.4.2</a>, <a href="#rfc.xref.RFC7234.17">6.5.4</a>, <a href="#rfc.xref.RFC7234.18">6.5.5</a>, <a href="#rfc.xref.RFC7234.19">6.5.9</a>, <a href="#rfc.xref.RFC7234.20">6.5.12</a>, <a href="#rfc.xref.RFC7234.21">6.6.2</a>, <a href="#rfc.xref.RFC7234.22">7.1</a>, <a href="#rfc.xref.RFC7234.23">7.1</a>, <a href="#rfc.xref.RFC7234.24">7.1</a>, <a href="#rfc.xref.RFC7234.25">7.1</a>, <a href="#rfc.xref.RFC7234.26">7.1.4</a>, <a href="#rfc.xref.RFC7234.27">7.1.4</a>, <a href="#rfc.xref.RFC7234.28">8.2.2</a>, <a href="#RFC7234"><b>11.1</b></a><ul><li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.26">7.1.4</a></li><li><em>Section 4.2.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.5">4.3.3</a></li><li><em>Section 4.2.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.11">6.3.1</a>, <a href="#rfc.xref.RFC7234.13">6.3.4</a>, <a href="#rfc.xref.RFC7234.14">6.3.5</a>, <a href="#rfc.xref.RFC7234.15">6.4.1</a>, <a href="#rfc.xref.RFC7234.16">6.4.2</a>, <a href="#rfc.xref.RFC7234.17">6.5.4</a>, <a href="#rfc.xref.RFC7234.18">6.5.5</a>, <a href="#rfc.xref.RFC7234.19">6.5.9</a>, <a href="#rfc.xref.RFC7234.20">6.5.12</a>, <a href="#rfc.xref.RFC7234.21">6.6.2</a></li><li><em>Section 4.3.5</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.4">4.3.2</a></li><li><em>Section 4.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.6">4.3.4</a>, <a href="#rfc.xref.RFC7234.7">4.3.5</a></li><li><em>Section 5.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.22">7.1</a></li><li><em>Section 5.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.2">4.3.1</a>, <a href="#rfc.xref.RFC7234.3">4.3.2</a>, <a href="#rfc.xref.RFC7234.8">5.1</a>, <a href="#rfc.xref.RFC7234.23">7.1</a>, <a href="#rfc.xref.RFC7234.27">7.1.4</a></li><li><em>Section 5.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.24">7.1</a></li><li><em>Section 5.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.9">5.1</a></li><li><em>Section 5.5</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7234.12">6.3.4</a>, <a href="#rfc.xref.RFC7234.25">7.1</a></li></ul></li><li><em>RFC7235</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7235.1">4.3.8</a>, <a href="#rfc.xref.RFC7235.2">5.4</a>, <a href="#rfc.xref.RFC7235.3">5.4</a>, <a href="#rfc.xref.RFC7235.4">5.4</a>, <a href="#rfc.xref.RFC7235.5">6.1</a>, <a href="#rfc.xref.RFC7235.6">6.1</a>, <a href="#rfc.xref.RFC7235.7">6.1</a>, <a href="#rfc.xref.RFC7235.8">7.1.4</a>, <a href="#rfc.xref.RFC7235.9">7.3</a>, <a href="#rfc.xref.RFC7235.10">7.3</a>, <a href="#RFC7235"><b>11.1</b></a><ul><li><em>Section 3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7235.5">6.1</a></li><li><em>Section 3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7235.6">6.1</a></li><li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7235.7">6.1</a></li><li><em>Section 4.1</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7235.9">7.3</a></li><li><em>Section 4.2</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7235.3">5.4</a>, <a href="#rfc.xref.RFC7235.8">7.1.4</a></li><li><em>Section 4.3</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7235.10">7.3</a></li><li><em>Section 4.4</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7235.4">5.4</a></li></ul></li><li><em>RFC7238</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC7238.1">6.4.7</a>, <a href="#RFC7238"><b>11.2</b></a></li></ul></li><li><a id="rfc.index.S" href="#rfc.index.S"><b>S</b></a><ul><li>safe&nbsp;&nbsp;<a href="#rfc.section.4.2.1"><b>4.2.1</b></a></li><li>selected representation&nbsp;&nbsp;<a href="#rfc.section.3"><b>3</b></a>, <a href="#rfc.section.7.2">7.2</a></li><li>Server header field&nbsp;&nbsp;<a href="#rfc.xref.header.server.1">7.4</a>, <a href="#rfc.section.7.4.2"><b>7.4.2</b></a>, <a href="#rfc.xref.header.server.2">8.3.2</a>, <a href="#rfc.xref.header.server.3">9.6</a></li><li>Status Codes Classes&nbsp;&nbsp;<ul><li>1xx Informational&nbsp;&nbsp;<a href="#rfc.section.6.2"><b>6.2</b></a></li><li>2xx Successful&nbsp;&nbsp;<a href="#rfc.section.6.3"><b>6.3</b></a></li><li>3xx Redirection&nbsp;&nbsp;<a href="#rfc.section.6.4"><b>6.4</b></a>, <a href="#rfc.xref.status.3xx.1">B</a></li><li>4xx Client Error&nbsp;&nbsp;<a href="#rfc.section.6.5"><b>6.5</b></a></li><li>5xx Server Error&nbsp;&nbsp;<a href="#rfc.section.6.6"><b>6.6</b></a></li></ul></li></ul></li><li><a id="rfc.index.T" href="#rfc.index.T"><b>T</b></a><ul><li>TRACE method&nbsp;&nbsp;<a href="#rfc.xref.TRACE.1">4.1</a>, <a href="#rfc.iref.t.1"><b>4.3.8</b></a>, <a href="#rfc.xref.TRACE.2">5.1.2</a>, <a href="#rfc.xref.TRACE.3">8.1.3</a>, <a href="#rfc.extref.t.50">B</a>, <a href="#rfc.xref.TRACE.4">B</a>, <a href="#rfc.extref.t.51">B</a></li></ul></li><li><a id="rfc.index.U" href="#rfc.index.U"><b>U</b></a><ul><li>User-Agent header field&nbsp;&nbsp;<a href="#rfc.xref.header.user-agent.1">5.5</a>, <a href="#rfc.section.5.5.3"><b>5.5.3</b></a>, <a href="#rfc.xref.header.user-agent.2">7.4.2</a>, <a href="#rfc.xref.header.user-agent.3">8.3.2</a>, <a href="#rfc.xref.header.user-agent.4">9.6</a></li></ul></li><li><a id="rfc.index.V" href="#rfc.index.V"><b>V</b></a><ul><li>Vary header field&nbsp;&nbsp;<a href="#rfc.xref.header.vary.1">3.4.1</a>, <a href="#rfc.xref.header.vary.2">7.1</a>, <a href="#rfc.section.7.1.4"><b>7.1.4</b></a>, <a href="#rfc.xref.header.vary.3">8.3.1</a>, <a href="#rfc.xref.header.vary.4">8.3.2</a></li></ul></li><li><a id="rfc.index.X" href="#rfc.index.X"><b>X</b></a><ul><li>x-compress (content coding)&nbsp;&nbsp;<a href="#rfc.section.3.1.2.1"><b>3.1.2.1</b></a></li><li>x-gzip (content coding)&nbsp;&nbsp;<a href="#rfc.section.3.1.2.1"><b>3.1.2.1</b></a></li></ul></li></ul></div><div class="avoidbreakinside"><h1 id="rfc.authors"><a href="#rfc.authors">Authors' Addresses</a></h1><p><b>Roy T. Fielding</b>
    809825      (editor)
    810826    <br>Adobe Systems Incorporated<br>345 Park Ave<br>San Jose, CA&nbsp;95110<br>USA<br>Email: fielding@gbiv.com<br>URI: <a href="http://roy.gbiv.com/">http://roy.gbiv.com/</a></p><p><b>Julian F. Reschke</b>
  • specs/rfc7232.html

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    511 </style><link rel="Contents" href="#rfc.toc"><link rel="Author" href="#rfc.authors"><link rel="Copyright" href="#rfc.copyrightnotice"><link rel="Index" href="#rfc.index"><link rel="Chapter" title="1 Introduction" href="#rfc.section.1"><link rel="Chapter" title="2 Validators" href="#rfc.section.2"><link rel="Chapter" title="3 Precondition Header Fields" href="#rfc.section.3"><link rel="Chapter" title="4 Status Code Definitions" href="#rfc.section.4"><link rel="Chapter" title="5 Evaluation" href="#rfc.section.5"><link rel="Chapter" title="6 Precedence" href="#rfc.section.6"><link rel="Chapter" title="7 IANA Considerations" href="#rfc.section.7"><link rel="Chapter" title="8 Security Considerations" href="#rfc.section.8"><link rel="Chapter" title="9 Acknowledgments" href="#rfc.section.9"><link rel="Chapter" href="#rfc.section.10" title="10 References"><link rel="Appendix" title="A Changes from RFC 2616" href="#rfc.section.A"><link rel="Appendix" title="B Imported ABNF" href="#rfc.section.B"><link rel="Appendix" title="C Collected ABNF" href="#rfc.section.C"><link href="rfc7231.html" rel="prev"><link href="rfc7233.html" rel="next"><link rel="Alternate" title="Authorative ASCII Version" href="http://www.ietf.org/rfc/rfc7232.txt"><link rel="Help" title="RFC-Editor's Status Page" href="http://www.rfc-editor.org/info/rfc7232"><link rel="Help" title="Additional Information on tools.ietf.org" href="http://tools.ietf.org/html/rfc7232"><meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.669, 2014/09/04 09:19:16, XSLT vendor: SAXON 6.5.5 from Michael Kay http://saxon.sf.net/"><meta name="keywords" content="Hypertext Transfer Protocol, HTTP, HTTP conditional requests"><link rel="schema.dct" href="http://purl.org/dc/terms/"><meta name="dct.creator" content="Fielding, R."><meta name="dct.creator" content="Reschke, J. F."><meta name="dct.identifier" content="urn:ietf:rfc:7232"><meta name="dct.issued" scheme="ISO8601" content="2014-06"><meta name="dct.replaces" content="urn:ietf:rfc:2616"><meta name="dct.abstract" content="The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines HTTP/1.1 conditional requests, including metadata header fields for indicating state changes, request header fields for making preconditions on such state, and rules for constructing the responses to a conditional request when one or more preconditions evaluate to false."><meta name="dct.isPartOf" content="urn:issn:2070-1721"><meta name="description" content="The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines HTTP/1.1 conditional requests, including metadata header fields for indicating state changes, request header fields for making preconditions on such state, and rules for constructing the responses to a conditional request when one or more preconditions evaluate to false."></head><body onload="getMeta(7232,&#34;rfc.meta&#34;);"><table class="header" id="rfc.headerblock"><tbody><tr><td class="left">Internet Engineering Task Force (IETF)</td><td class="right">R. Fielding, Editor</td></tr><tr><td class="left">Request for Comments: 7232</td><td class="right">Adobe</td></tr><tr><td class="left">Obsoletes: <a href="https://tools.ietf.org/html/rfc2616">2616</a></td><td class="right">J. Reschke, Editor</td></tr><tr><td class="left">Category: Standards Track</td><td class="right">greenbytes</td></tr><tr><td class="left">ISSN: 2070-1721</td><td class="right">June 2014</td></tr></tbody></table><p class="title" id="rfc.title">Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests</p><h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1><p>The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines HTTP/1.1 conditional requests, including metadata header fields for indicating state changes, request header fields for making preconditions on such state, and rules for constructing the responses to a conditional request when one or more preconditions evaluate to false.</p><div id="rfc.meta" style="float: right; border: 1px solid black; margin: 2em; padding: 1em; display: none;"></div><div id="rfc.status"><h1><a href="#rfc.status">Status of This Memo</a></h1><p>This is an Internet Standards Track document.</p><p>This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.</p><p>Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at <a href="http://www.rfc-editor.org/info/rfc7232">http://www.rfc-editor.org/info/rfc7232</a>.</p></div><div id="rfc.copyrightnotice"><h1><a href="#rfc.copyrightnotice">Copyright Notice</a></h1><p>Copyright &copy; 2014 IETF Trust and the persons identified as the document authors. All rights reserved.</p><p>This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.</p><p>This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English.</p></div><hr class="noprint"><div id="rfc.toc"><h1 class="np"><a href="#rfc.toc">Table of Contents</a></h1><ul class="toc"><li><a href="#rfc.section.1">1.</a>&nbsp;&nbsp;&nbsp;<a href="#introduction">Introduction</a><ul><li><a href="#rfc.section.1.1">1.1</a>&nbsp;&nbsp;&nbsp;<a href="#conformance">Conformance and Error Handling</a></li><li><a href="#rfc.section.1.2">1.2</a>&nbsp;&nbsp;&nbsp;<a href="#notation">Syntax Notation</a></li></ul></li><li><a href="#rfc.section.2">2.</a>&nbsp;&nbsp;&nbsp;<a href="#validators">Validators</a><ul><li><a href="#rfc.section.2.1">2.1</a>&nbsp;&nbsp;&nbsp;<a href="#weak.and.strong.validators">Weak versus Strong</a></li><li><a href="#rfc.section.2.2">2.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.last-modified">Last-Modified</a><ul><li><a href="#rfc.section.2.2.1">2.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#lastmod.generation">Generation</a></li><li><a href="#rfc.section.2.2.2">2.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#lastmod.comparison">Comparison</a></li></ul></li><li><a href="#rfc.section.2.3">2.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.etag">ETag</a><ul><li><a href="#rfc.section.2.3.1">2.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#entity.tag.generation">Generation</a></li><li><a href="#rfc.section.2.3.2">2.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#entity.tag.comparison">Comparison</a></li><li><a href="#rfc.section.2.3.3">2.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#example.entity.tag.vs.conneg">Example: Entity-Tags Varying on Content-Negotiated Resources</a></li></ul></li><li><a href="#rfc.section.2.4">2.4</a>&nbsp;&nbsp;&nbsp;<a href="#when.to.use.entity.tags.and.last-modified.dates">When to Use Entity-Tags and Last-Modified Dates</a></li></ul></li><li><a href="#rfc.section.3">3.</a>&nbsp;&nbsp;&nbsp;<a href="#preconditions">Precondition Header Fields</a><ul><li><a href="#rfc.section.3.1">3.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.if-match">If-Match</a></li><li><a href="#rfc.section.3.2">3.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.if-none-match">If-None-Match</a></li><li><a href="#rfc.section.3.3">3.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.if-modified-since">If-Modified-Since</a></li><li><a href="#rfc.section.3.4">3.4</a>&nbsp;&nbsp;&nbsp;<a href="#header.if-unmodified-since">If-Unmodified-Since</a></li><li><a href="#rfc.section.3.5">3.5</a>&nbsp;&nbsp;&nbsp;<a href="#header.if-range">If-Range</a></li></ul></li><li><a href="#rfc.section.4">4.</a>&nbsp;&nbsp;&nbsp;<a href="#status.code.definitions">Status Code Definitions</a><ul><li><a href="#rfc.section.4.1">4.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.304">304 Not Modified</a></li><li><a href="#rfc.section.4.2">4.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.412">412 Precondition Failed</a></li></ul></li><li><a href="#rfc.section.5">5.</a>&nbsp;&nbsp;&nbsp;<a href="#evaluation">Evaluation</a></li><li><a href="#rfc.section.6">6.</a>&nbsp;&nbsp;&nbsp;<a href="#precedence">Precedence</a></li><li><a href="#rfc.section.7">7.</a>&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a><ul><li><a href="#rfc.section.7.1">7.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.code.registration">Status Code Registration</a></li><li><a href="#rfc.section.7.2">7.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.field.registration">Header Field Registration</a></li></ul></li><li><a href="#rfc.section.8">8.</a>&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a></li><li><a href="#rfc.section.9">9.</a>&nbsp;&nbsp;&nbsp;<a href="#acks">Acknowledgments</a></li><li><a href="#rfc.section.10">10.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul><li><a href="#rfc.section.10.1">10.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li><li><a href="#rfc.section.10.2">10.2</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li></ul></li><li><a href="#rfc.section.A">A.</a>&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li><li><a href="#rfc.section.B">B.</a>&nbsp;&nbsp;&nbsp;<a href="#imported.abnf">Imported ABNF</a></li><li><a href="#rfc.section.C">C.</a>&nbsp;&nbsp;&nbsp;<a href="#collected.abnf">Collected ABNF</a></li><li><a href="#rfc.index">Index</a></li><li><a href="#rfc.authors">Authors' Addresses</a></li></ul></div><div id="introduction"><h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;<a href="#introduction">Introduction</a></h1><div id="rfc.section.1.p.1"><p>Conditional requests are HTTP requests <a href="#RFC7231" id="rfc.xref.RFC7231.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a> that include one or more header fields indicating a precondition to be tested before applying the method semantics to the target resource. This document defines the HTTP/1.1 conditional request mechanisms in terms of the architecture, syntax notation, and conformance criteria defined in <a href="#RFC7230" id="rfc.xref.RFC7230.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>.<a class="self" href="#rfc.section.1.p.1">&para;</a></p></div><div id="rfc.section.1.p.2"><p>Conditional GET requests are the most efficient mechanism for HTTP cache updates <a href="#RFC7234" id="rfc.xref.RFC7234.1"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[RFC7234]</cite></a>. Conditionals can also be applied to state-changing methods, such as PUT and DELETE, to prevent the "lost update" problem: one client accidentally overwriting the work of another client that has been acting in parallel.<a class="self" href="#rfc.section.1.p.2">&para;</a></p></div><div id="rfc.section.1.p.3"><p><span id="rfc.iref.s.1"></span> Conditional request preconditions are based on the state of the target resource as a whole (its current value set) or the state as observed in a previously obtained representation (one value in that set). A resource might have multiple current representations, each with its own observable state. The conditional request mechanisms assume that the mapping of requests to a "selected representation" (<a href="rfc7231.html#representations" title="Representations">Section 3</a> of <a href="#RFC7231" id="rfc.xref.RFC7231.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content">[RFC7231]</cite></a>) will be consistent over time if the server intends to take advantage of conditionals. Regardless, if the mapping is inconsistent and the server is unable to select the appropriate representation, then no harm will result when the precondition evaluates to false.<a class="self" href="#rfc.section.1.p.3">&para;</a></p></div><div id="rfc.section.1.p.4"><p>The conditional request preconditions defined by this specification (<a href="#preconditions" title="Precondition Header Fields">Section&nbsp;3</a>) are evaluated when applicable to the recipient (<a href="#evaluation" title="Evaluation">Section&nbsp;5</a>) according to their order of precedence (<a href="#precedence" title="Precedence">Section&nbsp;6</a>).<a class="self" href="#rfc.section.1.p.4">&para;</a></p></div><div id="conformance"><h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a>&nbsp;<a href="#conformance">Conformance and Error Handling</a></h2><div id="rfc.section.1.1.p.1"><p>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in <a href="#RFC2119" id="rfc.xref.RFC2119.1"><cite title="Key words for use in RFCs to Indicate Requirement Levels">[RFC2119]</cite></a>.<a class="self" href="#rfc.section.1.1.p.1">&para;</a></p></div><div id="rfc.section.1.1.p.2"><p>Conformance criteria and considerations regarding error handling are defined in <a href="rfc7230.html#conformance" title="Conformance and Error Handling">Section 2.5</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.2"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>.<a class="self" href="#rfc.section.1.1.p.2">&para;</a></p></div></div><div id="notation"><h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a>&nbsp;<a href="#notation">Syntax Notation</a></h2><div id="rfc.section.1.2.p.1"><p>This specification uses the Augmented Backus-Naur Form (ABNF) notation of <a href="#RFC5234" id="rfc.xref.RFC5234.1"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a> with a list extension, defined in <a href="rfc7230.html#abnf.extension" title="ABNF List Extension: #rule">Section 7</a> of <a href="#RFC7230" id="rfc.xref.RFC7230.3"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing">[RFC7230]</cite></a>, that allows for compact definition of comma-separated lists using a '#' operator (similar to how the '*' operator indicates repetition). <a href="#imported.abnf" title="Imported ABNF">Appendix&nbsp;B</a> describes rules imported from other documents. <a href="#collected.abnf" title="Collected ABNF">Appendix&nbsp;C</a> shows the collected grammar with all list operators expanded to standard ABNF notation.<a class="self" href="#rfc.section.1.2.p.1">&para;</a></p></div></div></div><div id="validators"><h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a href="#validators">Validators</a></h1><div id="rfc.section.2.p.1"><p>This specification defines two forms of metadata that are commonly used to observe resource state and test for preconditions: modification dates (<a href="#header.last-modified" id="rfc.xref.header.last-modified.1" title="Last-Modified">Section&nbsp;2.2</a>) and opaque entity tags (<a href="#header.etag" id="rfc.xref.header.etag.1" title="ETag">Section&nbsp;2.3</a>). Additional metadata that reflects resource state has been defined by various extensions of HTTP, such as Web Distributed Authoring and Versioning (WebDAV, <a href="#RFC4918" id="rfc.xref.RFC4918.1"><cite title="HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)">[RFC4918]</cite></a>), that are beyond the scope of this specification. A resource metadata value is referred to as a "<dfn>validator</dfn>" when it is used within a precondition.<a class="self" href="#rfc.section.2.p.1">&para;</a></p></div><div id="weak.and.strong.validators"><h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a href="#weak.and.strong.validators">Weak versus Strong</a></h2><div id="rfc.section.2.1.p.1"><p>Validators come in two flavors: strong or weak. Weak validators are easy to generate but are far less useful for comparisons. Strong validators are ideal for comparisons but can be very difficult (and occasionally impossible) to generate efficiently. Rather than impose that all forms of resource adhere to the same strength of validator, HTTP exposes the type of validator in use and imposes restrictions on when weak validators can be used as preconditions.<a class="self" href="#rfc.section.2.1.p.1">&para;</a></p></div><div id="rfc.section.2.1.p.2"><p>A "strong validator" is representation metadata that changes value whenever a change occurs to the representation data that would be observable in the payload body of a <a href="rfc7231.html#status.200" class="smpl">200 (OK)</a> response to GET.<a class="self" href="#rfc.section.2.1.p.2">&para;</a></p></div><div id="rfc.section.2.1.p.3"><p>A strong validator might change for reasons other than a change to the representation data, such as when a semantically significant part of the representation metadata is changed (e.g., <a href="rfc7231.html#header.content-type" class="smpl">Content-Type</a>), but it is in the best interests of the origin server to only change the value when it is necessary to invalidate the stored responses held by remote caches and authoring tools.<a class="self" href="#rfc.section.2.1.p.3">&para;</a></p></div><div id="rfc.section.2.1.p.4"><p>Cache entries might persist for arbitrarily long periods, regardless of expiration times. Thus, a cache might attempt to validate an entry using a validator that it obtained in the distant past. A strong validator is unique across all versions of all representations associated with a particular resource over time. However, there is no implication of uniqueness across representations of different resources (i.e., the same strong validator might be in use for representations of multiple resources at the same time and does not imply that those representations are equivalent).<a class="self" href="#rfc.section.2.1.p.4">&para;</a></p></div><div id="rfc.section.2.1.p.5"><p>There are a variety of strong validators used in practice. The best are based on strict revision control, wherein each change to a representation always results in a unique node name and revision identifier being assigned before the representation is made accessible to GET. A collision-resistant hash function applied to the representation data is also sufficient if the data is available prior to the response header fields being sent and the digest does not need to be recalculated every time a validation request is received. However, if a resource has distinct representations that differ only in their metadata, such as might occur with content negotiation over media types that happen to share the same data format, then the origin server needs to incorporate additional information in the validator to distinguish those representations.<a class="self" href="#rfc.section.2.1.p.5">&para;</a></p></div><div id="rfc.section.2.1.p.6"><p>In contrast, a "weak validator" is representation metadata that might not change for every change to the representation data. This weakness might be due to limitations in how the value is calculated, such as clock resolution, an inability to ensure uniqueness for all possible representations of the resource, or a desire of the resource owner to group representations by some self-determined set of equivalency rather than unique sequences of data. An origin server <em class="bcp14">SHOULD</em> change a weak entity-tag whenever it considers prior representations to be unacceptable as a substitute for the current representation. In other words, a weak entity-tag ought to change whenever the origin server wants caches to invalidate old responses.<a class="self" href="#rfc.section.2.1.p.6">&para;</a></p></div><div id="rfc.section.2.1.p.7"><p>For example, the representation of a weather report that changes in content every second, based on dynamic measurements, might be grouped into sets of equivalent representations (from the origin server's perspective) with the same weak validator in order to allow cached representations to be valid for a reasonable period of time (perhaps adjusted dynamically based on server load or weather quality). Likewise, a representation's modification time, if defined with only one-second resolution, might be a weak validator if it is possible for the representation to be modified twice during a single second and retrieved between those modifications.<a class="self" href="#rfc.section.2.1.p.7">&para;</a></p></div><div id="rfc.section.2.1.p.8"><p>Likewise, a validator is weak if it is shared by two or more representations of a given resource at the same time, unless those representations have identical representation data. For example, if the origin server sends the same validator for a representation with a gzip content coding applied as it does for a representation with no content coding, then that validator is weak. However, two simultaneous representations might share the same strong validator if they differ only in the representation metadata, such as when two different media types are available for the same representation data.<a class="self" href="#rfc.section.2.1.p.8">&para;</a></p></div><div id="rfc.section.2.1.p.9"><p>Strong validators are usable for all conditional requests, including cache validation, partial content ranges, and "lost update" avoidance. Weak validators are only usable when the client does not require exact equality with previously obtained representation data, such as when validating a cache entry or limiting a web traversal to recent changes.<a class="self" href="#rfc.section.2.1.p.9">&para;</a></p></div></div><div id="header.last-modified"><h2 id="rfc.section.2.2"><a href="