Changeset 2726 for draft-ietf-httpbis/11


Ignore:
Timestamp:
Jun 14, 2014, 4:20:37 AM (5 years ago)
Author:
julian.reschke@…
Message:

update to latest version of rfc2629.xslt, regen all HTML

Location:
draft-ietf-httpbis/11
Files:
7 edited

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  • draft-ietf-httpbis/11/p1-messaging.html

    r1099 r2726  
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    346        content: "August 2010"; 
    347   } 
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    392401      <link rel="Appendix" title="C Collected ABNF" href="#rfc.section.C">
    393402      <link rel="Appendix" title="D Change Log (to be removed by RFC Editor before publication)" href="#rfc.section.D">
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    395404      <link rel="schema.dct" href="http://purl.org/dc/terms/">
    396405      <meta name="dct.creator" content="Fielding, R.">
     
    421430            </tr>
    422431            <tr>
    423                <td class="left">Obsoletes: <a href="http://tools.ietf.org/html/rfc2616">2616</a> (if approved)
     432               <td class="left">Obsoletes: <a href="https://tools.ietf.org/html/rfc2616">2616</a> (if approved)
    424433               </td>
    425434               <td class="right">J. Gettys</td>
    426435            </tr>
    427436            <tr>
    428                <td class="left">Updates: <a href="http://tools.ietf.org/html/rfc2817">2817</a> (if approved)
     437               <td class="left">Updates: <a href="https://tools.ietf.org/html/rfc2817">2817</a> (if approved)
    429438               </td>
    430439               <td class="right">Alcatel-Lucent</td>
     
    493502      </table>
    494503      <p class="title">HTTP/1.1, part 1: URIs, Connections, and Message Parsing<br><span class="filename">draft-ietf-httpbis-p1-messaging-11</span></p>
    495       <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1> 
     504      <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1>
    496505      <p>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypertext information
    497506         systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 1 of the
     
    500509         (URI) schemes, defines the generic message syntax and parsing requirements for HTTP message frames, and describes general
    501510         security concerns for implementations.
    502       </p> 
    503       <h1 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note (To be removed by RFC Editor)</a></h1> 
     511      </p>
     512      <h1 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note (To be removed by RFC Editor)</a></h1>
    504513      <p>Discussion of this draft should take place on the HTTPBIS working group mailing list (ietf-http-wg@w3.org). The current issues
    505514         list is at &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/report/3">http://tools.ietf.org/wg/httpbis/trac/report/3</a>&gt; and related documents (including fancy diffs) can be found at &lt;<a href="http://tools.ietf.org/wg/httpbis/">http://tools.ietf.org/wg/httpbis/</a>&gt;.
    506       </p> 
     515      </p>
    507516      <p>The changes in this draft are summarized in <a href="#changes.since.10" title="Since draft-ietf-httpbis-p1-messaging-10">Appendix&nbsp;D.12</a>.
    508       </p>
    509       <h1><a id="rfc.status" href="#rfc.status">Status of This Memo</a></h1>
    510       <p>This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.</p>
    511       <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute
    512          working documents as Internet-Drafts. The list of current Internet-Drafts is at <a href="http://datatracker.ietf.org/drafts/current/">http://datatracker.ietf.org/drafts/current/</a>.
    513517      </p>
    514       <p>Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other
    515          documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work
    516          in progress”.
    517       </p>
    518       <p>This Internet-Draft will expire on February 5, 2011.</p>
    519       <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1>
    520       <p>Copyright © 2010 IETF Trust and the persons identified as the document authors. All rights reserved.</p>
    521       <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
    522          and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License
    523          text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified
    524          BSD License.
    525       </p>
    526       <p>This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November
    527          10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to
    528          allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s)
    529          controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative
    530          works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate
    531          it into languages other than English.
    532       </p>
     518      <div id="rfc.status">
     519         <h1><a href="#rfc.status">Status of This Memo</a></h1>
     520         <p>This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.</p>
     521         <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute
     522            working documents as Internet-Drafts. The list of current Internet-Drafts is at <a href="http://datatracker.ietf.org/drafts/current/">http://datatracker.ietf.org/drafts/current/</a>.
     523         </p>
     524         <p>Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other
     525            documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work
     526            in progress”.
     527         </p>
     528         <p>This Internet-Draft will expire on February 5, 2011.</p>
     529      </div>
     530      <div id="rfc.copyrightnotice">
     531         <h1><a href="#rfc.copyrightnotice">Copyright Notice</a></h1>
     532         <p>Copyright © 2010 IETF Trust and the persons identified as the document authors. All rights reserved.</p>
     533         <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
     534            and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License
     535            text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified
     536            BSD License.
     537         </p>
     538         <p>This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November
     539            10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to
     540            allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s)
     541            controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative
     542            works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate
     543            it into languages other than English.
     544         </p>
     545      </div>
    533546      <hr class="noprint">
    534547      <h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1>
    535548      <ul class="toc">
    536          <li>1.&nbsp;&nbsp;&nbsp;<a href="#introduction">Introduction</a><ul>
    537                <li>1.1&nbsp;&nbsp;&nbsp;<a href="#intro.requirements">Requirements</a></li>
    538                <li>1.2&nbsp;&nbsp;&nbsp;<a href="#notation">Syntax Notation</a><ul>
    539                      <li>1.2.1&nbsp;&nbsp;&nbsp;<a href="#notation.abnf">ABNF Extension: #rule</a></li>
    540                      <li>1.2.2&nbsp;&nbsp;&nbsp;<a href="#basic.rules">Basic Rules</a></li>
    541                      <li>1.2.3&nbsp;&nbsp;&nbsp;<a href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></li>
     549         <li><a href="#rfc.section.1">1.</a>&nbsp;&nbsp;&nbsp;<a href="#introduction">Introduction</a><ul>
     550               <li><a href="#rfc.section.1.1">1.1</a>&nbsp;&nbsp;&nbsp;<a href="#intro.requirements">Requirements</a></li>
     551               <li><a href="#rfc.section.1.2">1.2</a>&nbsp;&nbsp;&nbsp;<a href="#notation">Syntax Notation</a><ul>
     552                     <li><a href="#rfc.section.1.2.1">1.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#notation.abnf">ABNF Extension: #rule</a></li>
     553                     <li><a href="#rfc.section.1.2.2">1.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#basic.rules">Basic Rules</a></li>
     554                     <li><a href="#rfc.section.1.2.3">1.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></li>
    542555                  </ul>
    543556               </li>
    544557            </ul>
    545558         </li>
    546          <li>2.&nbsp;&nbsp;&nbsp;<a href="#architecture">HTTP-related architecture</a><ul>
    547                <li>2.1&nbsp;&nbsp;&nbsp;<a href="#operation">Client/Server Messaging</a></li>
    548                <li>2.2&nbsp;&nbsp;&nbsp;<a href="#intermediaries">Intermediaries</a></li>
    549                <li>2.3&nbsp;&nbsp;&nbsp;<a href="#caches">Caches</a></li>
    550                <li>2.4&nbsp;&nbsp;&nbsp;<a href="#transport-independence">Transport Independence</a></li>
    551                <li>2.5&nbsp;&nbsp;&nbsp;<a href="#http.version">HTTP Version</a></li>
    552                <li>2.6&nbsp;&nbsp;&nbsp;<a href="#uri">Uniform Resource Identifiers</a><ul>
    553                      <li>2.6.1&nbsp;&nbsp;&nbsp;<a href="#http.uri">http URI scheme</a></li>
    554                      <li>2.6.2&nbsp;&nbsp;&nbsp;<a href="#https.uri">https URI scheme</a></li>
    555                      <li>2.6.3&nbsp;&nbsp;&nbsp;<a href="#uri.comparison">http and https URI Normalization and Comparison</a></li>
     559         <li><a href="#rfc.section.2">2.</a>&nbsp;&nbsp;&nbsp;<a href="#architecture">HTTP-related architecture</a><ul>
     560               <li><a href="#rfc.section.2.1">2.1</a>&nbsp;&nbsp;&nbsp;<a href="#operation">Client/Server Messaging</a></li>
     561               <li><a href="#rfc.section.2.2">2.2</a>&nbsp;&nbsp;&nbsp;<a href="#intermediaries">Intermediaries</a></li>
     562               <li><a href="#rfc.section.2.3">2.3</a>&nbsp;&nbsp;&nbsp;<a href="#caches">Caches</a></li>
     563               <li><a href="#rfc.section.2.4">2.4</a>&nbsp;&nbsp;&nbsp;<a href="#transport-independence">Transport Independence</a></li>
     564               <li><a href="#rfc.section.2.5">2.5</a>&nbsp;&nbsp;&nbsp;<a href="#http.version">HTTP Version</a></li>
     565               <li><a href="#rfc.section.2.6">2.6</a>&nbsp;&nbsp;&nbsp;<a href="#uri">Uniform Resource Identifiers</a><ul>
     566                     <li><a href="#rfc.section.2.6.1">2.6.1</a>&nbsp;&nbsp;&nbsp;<a href="#http.uri">http URI scheme</a></li>
     567                     <li><a href="#rfc.section.2.6.2">2.6.2</a>&nbsp;&nbsp;&nbsp;<a href="#https.uri">https URI scheme</a></li>
     568                     <li><a href="#rfc.section.2.6.3">2.6.3</a>&nbsp;&nbsp;&nbsp;<a href="#uri.comparison">http and https URI Normalization and Comparison</a></li>
    556569                  </ul>
    557570               </li>
    558571            </ul>
    559572         </li>
    560          <li>3.&nbsp;&nbsp;&nbsp;<a href="#http.message">HTTP Message</a><ul>
    561                <li>3.1&nbsp;&nbsp;&nbsp;<a href="#message.robustness">Message Parsing Robustness</a></li>
    562                <li>3.2&nbsp;&nbsp;&nbsp;<a href="#header.fields">Header Fields</a></li>
    563                <li>3.3&nbsp;&nbsp;&nbsp;<a href="#message.body">Message Body</a></li>
    564                <li>3.4&nbsp;&nbsp;&nbsp;<a href="#general.header.fields">General Header Fields</a></li>
     573         <li><a href="#rfc.section.3">3.</a>&nbsp;&nbsp;&nbsp;<a href="#http.message">HTTP Message</a><ul>
     574               <li><a href="#rfc.section.3.1">3.1</a>&nbsp;&nbsp;&nbsp;<a href="#message.robustness">Message Parsing Robustness</a></li>
     575               <li><a href="#rfc.section.3.2">3.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.fields">Header Fields</a></li>
     576               <li><a href="#rfc.section.3.3">3.3</a>&nbsp;&nbsp;&nbsp;<a href="#message.body">Message Body</a></li>
     577               <li><a href="#rfc.section.3.4">3.4</a>&nbsp;&nbsp;&nbsp;<a href="#general.header.fields">General Header Fields</a></li>
    565578            </ul>
    566579         </li>
    567          <li>4.&nbsp;&nbsp;&nbsp;<a href="#request">Request</a><ul>
    568                <li>4.1&nbsp;&nbsp;&nbsp;<a href="#request-line">Request-Line</a><ul>
    569                      <li>4.1.1&nbsp;&nbsp;&nbsp;<a href="#method">Method</a></li>
    570                      <li>4.1.2&nbsp;&nbsp;&nbsp;<a href="#request-target">request-target</a></li>
     580         <li><a href="#rfc.section.4">4.</a>&nbsp;&nbsp;&nbsp;<a href="#request">Request</a><ul>
     581               <li><a href="#rfc.section.4.1">4.1</a>&nbsp;&nbsp;&nbsp;<a href="#request-line">Request-Line</a><ul>
     582                     <li><a href="#rfc.section.4.1.1">4.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#method">Method</a></li>
     583                     <li><a href="#rfc.section.4.1.2">4.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#request-target">request-target</a></li>
    571584                  </ul>
    572585               </li>
    573                <li>4.2&nbsp;&nbsp;&nbsp;<a href="#the.resource.identified.by.a.request">The Resource Identified by a Request</a></li>
    574                <li>4.3&nbsp;&nbsp;&nbsp;<a href="#effective.request.uri">Effective Request URI</a></li>
     586               <li><a href="#rfc.section.4.2">4.2</a>&nbsp;&nbsp;&nbsp;<a href="#the.resource.identified.by.a.request">The Resource Identified by a Request</a></li>
     587               <li><a href="#rfc.section.4.3">4.3</a>&nbsp;&nbsp;&nbsp;<a href="#effective.request.uri">Effective Request URI</a></li>
    575588            </ul>
    576589         </li>
    577          <li>5.&nbsp;&nbsp;&nbsp;<a href="#response">Response</a><ul>
    578                <li>5.1&nbsp;&nbsp;&nbsp;<a href="#status-line">Status-Line</a><ul>
    579                      <li>5.1.1&nbsp;&nbsp;&nbsp;<a href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></li>
     590         <li><a href="#rfc.section.5">5.</a>&nbsp;&nbsp;&nbsp;<a href="#response">Response</a><ul>
     591               <li><a href="#rfc.section.5.1">5.1</a>&nbsp;&nbsp;&nbsp;<a href="#status-line">Status-Line</a><ul>
     592                     <li><a href="#rfc.section.5.1.1">5.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></li>
    580593                  </ul>
    581594               </li>
    582595            </ul>
    583596         </li>
    584          <li>6.&nbsp;&nbsp;&nbsp;<a href="#protocol.parameters">Protocol Parameters</a><ul>
    585                <li>6.1&nbsp;&nbsp;&nbsp;<a href="#date.time.formats.full.date">Date/Time Formats: Full Date</a></li>
    586                <li>6.2&nbsp;&nbsp;&nbsp;<a href="#transfer.codings">Transfer Codings</a><ul>
    587                      <li>6.2.1&nbsp;&nbsp;&nbsp;<a href="#chunked.encoding">Chunked Transfer Coding</a></li>
    588                      <li>6.2.2&nbsp;&nbsp;&nbsp;<a href="#compression.codings">Compression Codings</a><ul>
    589                            <li>6.2.2.1&nbsp;&nbsp;&nbsp;<a href="#compress.coding">Compress Coding</a></li>
    590                            <li>6.2.2.2&nbsp;&nbsp;&nbsp;<a href="#deflate.coding">Deflate Coding</a></li>
    591                            <li>6.2.2.3&nbsp;&nbsp;&nbsp;<a href="#gzip.coding">Gzip Coding</a></li>
    592                         </ul>
    593                      </li>
    594                      <li>6.2.3&nbsp;&nbsp;&nbsp;<a href="#transfer.coding.registry">Transfer Coding Registry</a></li>
     597         <li><a href="#rfc.section.6">6.</a>&nbsp;&nbsp;&nbsp;<a href="#protocol.parameters">Protocol Parameters</a><ul>
     598               <li><a href="#rfc.section.6.1">6.1</a>&nbsp;&nbsp;&nbsp;<a href="#date.time.formats.full.date">Date/Time Formats: Full Date</a></li>
     599               <li><a href="#rfc.section.6.2">6.2</a>&nbsp;&nbsp;&nbsp;<a href="#transfer.codings">Transfer Codings</a><ul>
     600                     <li><a href="#rfc.section.6.2.1">6.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#chunked.encoding">Chunked Transfer Coding</a></li>
     601                     <li><a href="#rfc.section.6.2.2">6.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#compression.codings">Compression Codings</a></li>
     602                     <li><a href="#rfc.section.6.2.3">6.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#transfer.coding.registry">Transfer Coding Registry</a></li>
    595603                  </ul>
    596604               </li>
    597                <li>6.3&nbsp;&nbsp;&nbsp;<a href="#product.tokens">Product Tokens</a></li>
    598                <li>6.4&nbsp;&nbsp;&nbsp;<a href="#quality.values">Quality Values</a></li>
     605               <li><a href="#rfc.section.6.3">6.3</a>&nbsp;&nbsp;&nbsp;<a href="#product.tokens">Product Tokens</a></li>
     606               <li><a href="#rfc.section.6.4">6.4</a>&nbsp;&nbsp;&nbsp;<a href="#quality.values">Quality Values</a></li>
    599607            </ul>
    600608         </li>
    601          <li>7.&nbsp;&nbsp;&nbsp;<a href="#connections">Connections</a><ul>
    602                <li>7.1&nbsp;&nbsp;&nbsp;<a href="#persistent.connections">Persistent Connections</a><ul>
    603                      <li>7.1.1&nbsp;&nbsp;&nbsp;<a href="#persistent.purpose">Purpose</a></li>
    604                      <li>7.1.2&nbsp;&nbsp;&nbsp;<a href="#persistent.overall">Overall Operation</a><ul>
    605                            <li>7.1.2.1&nbsp;&nbsp;&nbsp;<a href="#persistent.negotiation">Negotiation</a></li>
    606                            <li>7.1.2.2&nbsp;&nbsp;&nbsp;<a href="#pipelining">Pipelining</a></li>
    607                         </ul>
    608                      </li>
    609                      <li>7.1.3&nbsp;&nbsp;&nbsp;<a href="#persistent.proxy">Proxy Servers</a><ul>
    610                            <li>7.1.3.1&nbsp;&nbsp;&nbsp;<a href="#end-to-end.and.hop-by-hop.headers">End-to-end and Hop-by-hop Headers</a></li>
    611                            <li>7.1.3.2&nbsp;&nbsp;&nbsp;<a href="#non-modifiable.headers">Non-modifiable Headers</a></li>
    612                         </ul>
    613                      </li>
    614                      <li>7.1.4&nbsp;&nbsp;&nbsp;<a href="#persistent.practical">Practical Considerations</a></li>
     609         <li><a href="#rfc.section.7">7.</a>&nbsp;&nbsp;&nbsp;<a href="#connections">Connections</a><ul>
     610               <li><a href="#rfc.section.7.1">7.1</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.connections">Persistent Connections</a><ul>
     611                     <li><a href="#rfc.section.7.1.1">7.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.purpose">Purpose</a></li>
     612                     <li><a href="#rfc.section.7.1.2">7.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.overall">Overall Operation</a></li>
     613                     <li><a href="#rfc.section.7.1.3">7.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.proxy">Proxy Servers</a></li>
     614                     <li><a href="#rfc.section.7.1.4">7.1.4</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.practical">Practical Considerations</a></li>
    615615                  </ul>
    616616               </li>
    617                <li>7.2&nbsp;&nbsp;&nbsp;<a href="#message.transmission.requirements">Message Transmission Requirements</a><ul>
    618                      <li>7.2.1&nbsp;&nbsp;&nbsp;<a href="#persistent.flow">Persistent Connections and Flow Control</a></li>
    619                      <li>7.2.2&nbsp;&nbsp;&nbsp;<a href="#persistent.monitor">Monitoring Connections for Error Status Messages</a></li>
    620                      <li>7.2.3&nbsp;&nbsp;&nbsp;<a href="#use.of.the.100.status">Use of the 100 (Continue) Status</a></li>
    621                      <li>7.2.4&nbsp;&nbsp;&nbsp;<a href="#connection.premature">Client Behavior if Server Prematurely Closes Connection</a></li>
     617               <li><a href="#rfc.section.7.2">7.2</a>&nbsp;&nbsp;&nbsp;<a href="#message.transmission.requirements">Message Transmission Requirements</a><ul>
     618                     <li><a href="#rfc.section.7.2.1">7.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.flow">Persistent Connections and Flow Control</a></li>
     619                     <li><a href="#rfc.section.7.2.2">7.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.monitor">Monitoring Connections for Error Status Messages</a></li>
     620                     <li><a href="#rfc.section.7.2.3">7.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#use.of.the.100.status">Use of the 100 (Continue) Status</a></li>
     621                     <li><a href="#rfc.section.7.2.4">7.2.4</a>&nbsp;&nbsp;&nbsp;<a href="#connection.premature">Client Behavior if Server Prematurely Closes Connection</a></li>
    622622                  </ul>
    623623               </li>
    624624            </ul>
    625625         </li>
    626          <li>8.&nbsp;&nbsp;&nbsp;<a href="#misc">Miscellaneous notes that might disappear</a><ul>
    627                <li>8.1&nbsp;&nbsp;&nbsp;<a href="#scheme.aliases">Scheme aliases considered harmful</a></li>
    628                <li>8.2&nbsp;&nbsp;&nbsp;<a href="#http.proxy">Use of HTTP for proxy communication</a></li>
    629                <li>8.3&nbsp;&nbsp;&nbsp;<a href="#http.intercept">Interception of HTTP for access control</a></li>
    630                <li>8.4&nbsp;&nbsp;&nbsp;<a href="#http.others">Use of HTTP by other protocols</a></li>
    631                <li>8.5&nbsp;&nbsp;&nbsp;<a href="#http.media">Use of HTTP by media type specification</a></li>
     626         <li><a href="#rfc.section.8">8.</a>&nbsp;&nbsp;&nbsp;<a href="#misc">Miscellaneous notes that might disappear</a><ul>
     627               <li><a href="#rfc.section.8.1">8.1</a>&nbsp;&nbsp;&nbsp;<a href="#scheme.aliases">Scheme aliases considered harmful</a></li>
     628               <li><a href="#rfc.section.8.2">8.2</a>&nbsp;&nbsp;&nbsp;<a href="#http.proxy">Use of HTTP for proxy communication</a></li>
     629               <li><a href="#rfc.section.8.3">8.3</a>&nbsp;&nbsp;&nbsp;<a href="#http.intercept">Interception of HTTP for access control</a></li>
     630               <li><a href="#rfc.section.8.4">8.4</a>&nbsp;&nbsp;&nbsp;<a href="#http.others">Use of HTTP by other protocols</a></li>
     631               <li><a href="#rfc.section.8.5">8.5</a>&nbsp;&nbsp;&nbsp;<a href="#http.media">Use of HTTP by media type specification</a></li>
    632632            </ul>
    633633         </li>
    634          <li>9.&nbsp;&nbsp;&nbsp;<a href="#header.field.definitions">Header Field Definitions</a><ul>
    635                <li>9.1&nbsp;&nbsp;&nbsp;<a href="#header.connection">Connection</a></li>
    636                <li>9.2&nbsp;&nbsp;&nbsp;<a href="#header.content-length">Content-Length</a></li>
    637                <li>9.3&nbsp;&nbsp;&nbsp;<a href="#header.date">Date</a><ul>
    638                      <li>9.3.1&nbsp;&nbsp;&nbsp;<a href="#clockless.origin.server.operation">Clockless Origin Server Operation</a></li>
     634         <li><a href="#rfc.section.9">9.</a>&nbsp;&nbsp;&nbsp;<a href="#header.field.definitions">Header Field Definitions</a><ul>
     635               <li><a href="#rfc.section.9.1">9.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.connection">Connection</a></li>
     636               <li><a href="#rfc.section.9.2">9.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.content-length">Content-Length</a></li>
     637               <li><a href="#rfc.section.9.3">9.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.date">Date</a><ul>
     638                     <li><a href="#rfc.section.9.3.1">9.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#clockless.origin.server.operation">Clockless Origin Server Operation</a></li>
    639639                  </ul>
    640640               </li>
    641                <li>9.4&nbsp;&nbsp;&nbsp;<a href="#header.host">Host</a></li>
    642                <li>9.5&nbsp;&nbsp;&nbsp;<a href="#header.te">TE</a></li>
    643                <li>9.6&nbsp;&nbsp;&nbsp;<a href="#header.trailer">Trailer</a></li>
    644                <li>9.7&nbsp;&nbsp;&nbsp;<a href="#header.transfer-encoding">Transfer-Encoding</a></li>
    645                <li>9.8&nbsp;&nbsp;&nbsp;<a href="#header.upgrade">Upgrade</a><ul>
    646                      <li>9.8.1&nbsp;&nbsp;&nbsp;<a href="#upgrade.token.registry">Upgrade Token Registry</a></li>
     641               <li><a href="#rfc.section.9.4">9.4</a>&nbsp;&nbsp;&nbsp;<a href="#header.host">Host</a></li>
     642               <li><a href="#rfc.section.9.5">9.5</a>&nbsp;&nbsp;&nbsp;<a href="#header.te">TE</a></li>
     643               <li><a href="#rfc.section.9.6">9.6</a>&nbsp;&nbsp;&nbsp;<a href="#header.trailer">Trailer</a></li>
     644               <li><a href="#rfc.section.9.7">9.7</a>&nbsp;&nbsp;&nbsp;<a href="#header.transfer-encoding">Transfer-Encoding</a></li>
     645               <li><a href="#rfc.section.9.8">9.8</a>&nbsp;&nbsp;&nbsp;<a href="#header.upgrade">Upgrade</a><ul>
     646                     <li><a href="#rfc.section.9.8.1">9.8.1</a>&nbsp;&nbsp;&nbsp;<a href="#upgrade.token.registry">Upgrade Token Registry</a></li>
    647647                  </ul>
    648648               </li>
    649                <li>9.9&nbsp;&nbsp;&nbsp;<a href="#header.via">Via</a></li>
     649               <li><a href="#rfc.section.9.9">9.9</a>&nbsp;&nbsp;&nbsp;<a href="#header.via">Via</a></li>
    650650            </ul>
    651651         </li>
    652          <li>10.&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a><ul>
    653                <li>10.1&nbsp;&nbsp;&nbsp;<a href="#header.field.registration">Header Field Registration</a></li>
    654                <li>10.2&nbsp;&nbsp;&nbsp;<a href="#uri.scheme.registration">URI Scheme Registration</a></li>
    655                <li>10.3&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.http">Internet Media Type Registrations</a><ul>
    656                      <li>10.3.1&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.message.http">Internet Media Type message/http</a></li>
    657                      <li>10.3.2&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.application.http">Internet Media Type application/http</a></li>
     652         <li><a href="#rfc.section.10">10.</a>&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a><ul>
     653               <li><a href="#rfc.section.10.1">10.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.field.registration">Header Field Registration</a></li>
     654               <li><a href="#rfc.section.10.2">10.2</a>&nbsp;&nbsp;&nbsp;<a href="#uri.scheme.registration">URI Scheme Registration</a></li>
     655               <li><a href="#rfc.section.10.3">10.3</a>&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.http">Internet Media Type Registrations</a><ul>
     656                     <li><a href="#rfc.section.10.3.1">10.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.message.http">Internet Media Type message/http</a></li>
     657                     <li><a href="#rfc.section.10.3.2">10.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.application.http">Internet Media Type application/http</a></li>
    658658                  </ul>
    659659               </li>
    660                <li>10.4&nbsp;&nbsp;&nbsp;<a href="#transfer.coding.registration">Transfer Coding Registry</a></li>
    661                <li>10.5&nbsp;&nbsp;&nbsp;<a href="#upgrade.token.registration">Upgrade Token Registration</a></li>
     660               <li><a href="#rfc.section.10.4">10.4</a>&nbsp;&nbsp;&nbsp;<a href="#transfer.coding.registration">Transfer Coding Registry</a></li>
     661               <li><a href="#rfc.section.10.5">10.5</a>&nbsp;&nbsp;&nbsp;<a href="#upgrade.token.registration">Upgrade Token Registration</a></li>
    662662            </ul>
    663663         </li>
    664          <li>11.&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a><ul>
    665                <li>11.1&nbsp;&nbsp;&nbsp;<a href="#personal.information">Personal Information</a></li>
    666                <li>11.2&nbsp;&nbsp;&nbsp;<a href="#abuse.of.server.log.information">Abuse of Server Log Information</a></li>
    667                <li>11.3&nbsp;&nbsp;&nbsp;<a href="#attack.pathname">Attacks Based On File and Path Names</a></li>
    668                <li>11.4&nbsp;&nbsp;&nbsp;<a href="#dns.spoofing">DNS Spoofing</a></li>
    669                <li>11.5&nbsp;&nbsp;&nbsp;<a href="#attack.proxies">Proxies and Caching</a></li>
    670                <li>11.6&nbsp;&nbsp;&nbsp;<a href="#attack.DoS">Denial of Service Attacks on Proxies</a></li>
     664         <li><a href="#rfc.section.11">11.</a>&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a><ul>
     665               <li><a href="#rfc.section.11.1">11.1</a>&nbsp;&nbsp;&nbsp;<a href="#personal.information">Personal Information</a></li>
     666               <li><a href="#rfc.section.11.2">11.2</a>&nbsp;&nbsp;&nbsp;<a href="#abuse.of.server.log.information">Abuse of Server Log Information</a></li>
     667               <li><a href="#rfc.section.11.3">11.3</a>&nbsp;&nbsp;&nbsp;<a href="#attack.pathname">Attacks Based On File and Path Names</a></li>
     668               <li><a href="#rfc.section.11.4">11.4</a>&nbsp;&nbsp;&nbsp;<a href="#dns.spoofing">DNS Spoofing</a></li>
     669               <li><a href="#rfc.section.11.5">11.5</a>&nbsp;&nbsp;&nbsp;<a href="#attack.proxies">Proxies and Caching</a></li>
     670               <li><a href="#rfc.section.11.6">11.6</a>&nbsp;&nbsp;&nbsp;<a href="#attack.DoS">Denial of Service Attacks on Proxies</a></li>
    671671            </ul>
    672672         </li>
    673          <li>12.&nbsp;&nbsp;&nbsp;<a href="#ack">Acknowledgments</a></li>
    674          <li>13.&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul>
    675                <li>13.1&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li>
    676                <li>13.2&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li>
     673         <li><a href="#rfc.section.12">12.</a>&nbsp;&nbsp;&nbsp;<a href="#ack">Acknowledgments</a></li>
     674         <li><a href="#rfc.section.13">13.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul>
     675               <li><a href="#rfc.section.13.1">13.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li>
     676               <li><a href="#rfc.section.13.2">13.2</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li>
    677677            </ul>
    678678         </li>
    679          <li><a href="#rfc.authors">Authors' Addresses</a></li>
    680          <li>A.&nbsp;&nbsp;&nbsp;<a href="#tolerant.applications">Tolerant Applications</a></li>
    681          <li>B.&nbsp;&nbsp;&nbsp;<a href="#compatibility">Compatibility with Previous Versions</a><ul>
    682                <li>B.1&nbsp;&nbsp;&nbsp;<a href="#changes.from.1.0">Changes from HTTP/1.0</a><ul>
    683                      <li>B.1.1&nbsp;&nbsp;&nbsp;<a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses</a></li>
     679         <li><a href="#rfc.section.A">A.</a>&nbsp;&nbsp;&nbsp;<a href="#tolerant.applications">Tolerant Applications</a></li>
     680         <li><a href="#rfc.section.B">B.</a>&nbsp;&nbsp;&nbsp;<a href="#compatibility">Compatibility with Previous Versions</a><ul>
     681               <li><a href="#rfc.section.B.1">B.1</a>&nbsp;&nbsp;&nbsp;<a href="#changes.from.1.0">Changes from HTTP/1.0</a><ul>
     682                     <li><a href="#rfc.section.B.1.1">B.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses</a></li>
    684683                  </ul>
    685684               </li>
    686                <li>B.2&nbsp;&nbsp;&nbsp;<a href="#compatibility.with.http.1.0.persistent.connections">Compatibility with HTTP/1.0 Persistent Connections</a></li>
    687                <li>B.3&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li>
     685               <li><a href="#rfc.section.B.2">B.2</a>&nbsp;&nbsp;&nbsp;<a href="#compatibility.with.http.1.0.persistent.connections">Compatibility with HTTP/1.0 Persistent Connections</a></li>
     686               <li><a href="#rfc.section.B.3">B.3</a>&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li>
    688687            </ul>
    689688         </li>
    690          <li>C.&nbsp;&nbsp;&nbsp;<a href="#collected.abnf">Collected ABNF</a></li>
    691          <li>D.&nbsp;&nbsp;&nbsp;<a href="#change.log">Change Log (to be removed by RFC Editor before publication)</a><ul>
    692                <li>D.1&nbsp;&nbsp;&nbsp;<a href="#rfc.section.D.1">Since RFC2616</a></li>
    693                <li>D.2&nbsp;&nbsp;&nbsp;<a href="#rfc.section.D.2">Since draft-ietf-httpbis-p1-messaging-00</a></li>
    694                <li>D.3&nbsp;&nbsp;&nbsp;<a href="#rfc.section.D.3">Since draft-ietf-httpbis-p1-messaging-01</a></li>
    695                <li>D.4&nbsp;&nbsp;&nbsp;<a href="#changes.since.02">Since draft-ietf-httpbis-p1-messaging-02</a></li>
    696                <li>D.5&nbsp;&nbsp;&nbsp;<a href="#changes.since.03">Since draft-ietf-httpbis-p1-messaging-03</a></li>
    697                <li>D.6&nbsp;&nbsp;&nbsp;<a href="#changes.since.04">Since draft-ietf-httpbis-p1-messaging-04</a></li>
    698                <li>D.7&nbsp;&nbsp;&nbsp;<a href="#changes.since.05">Since draft-ietf-httpbis-p1-messaging-05</a></li>
    699                <li>D.8&nbsp;&nbsp;&nbsp;<a href="#changes.since.06">Since draft-ietf-httpbis-p1-messaging-06</a></li>
    700                <li>D.9&nbsp;&nbsp;&nbsp;<a href="#changes.since.07">Since draft-ietf-httpbis-p1-messaging-07</a></li>
    701                <li>D.10&nbsp;&nbsp;&nbsp;<a href="#changes.since.08">Since draft-ietf-httpbis-p1-messaging-08</a></li>
    702                <li>D.11&nbsp;&nbsp;&nbsp;<a href="#changes.since.09">Since draft-ietf-httpbis-p1-messaging-09</a></li>
    703                <li>D.12&nbsp;&nbsp;&nbsp;<a href="#changes.since.10">Since draft-ietf-httpbis-p1-messaging-10</a></li>
     689         <li><a href="#rfc.section.C">C.</a>&nbsp;&nbsp;&nbsp;<a href="#collected.abnf">Collected ABNF</a></li>
     690         <li><a href="#rfc.section.D">D.</a>&nbsp;&nbsp;&nbsp;<a href="#change.log">Change Log (to be removed by RFC Editor before publication)</a><ul>
     691               <li><a href="#rfc.section.D.1">D.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.D.1">Since RFC2616</a></li>
     692               <li><a href="#rfc.section.D.2">D.2</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.D.2">Since draft-ietf-httpbis-p1-messaging-00</a></li>
     693               <li><a href="#rfc.section.D.3">D.3</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.D.3">Since draft-ietf-httpbis-p1-messaging-01</a></li>
     694               <li><a href="#rfc.section.D.4">D.4</a>&nbsp;&nbsp;&nbsp;<a href="#changes.since.02">Since draft-ietf-httpbis-p1-messaging-02</a></li>
     695               <li><a href="#rfc.section.D.5">D.5</a>&nbsp;&nbsp;&nbsp;<a href="#changes.since.03">Since draft-ietf-httpbis-p1-messaging-03</a></li>
     696               <li><a href="#rfc.section.D.6">D.6</a>&nbsp;&nbsp;&nbsp;<a href="#changes.since.04">Since draft-ietf-httpbis-p1-messaging-04</a></li>
     697               <li><a href="#rfc.section.D.7">D.7</a>&nbsp;&nbsp;&nbsp;<a href="#changes.since.05">Since draft-ietf-httpbis-p1-messaging-05</a></li>
     698               <li><a href="#rfc.section.D.8">D.8</a>&nbsp;&nbsp;&nbsp;<a href="#changes.since.06">Since draft-ietf-httpbis-p1-messaging-06</a></li>
     699               <li><a href="#rfc.section.D.9">D.9</a>&nbsp;&nbsp;&nbsp;<a href="#changes.since.07">Since draft-ietf-httpbis-p1-messaging-07</a></li>
     700               <li><a href="#rfc.section.D.10">D.10</a>&nbsp;&nbsp;&nbsp;<a href="#changes.since.08">Since draft-ietf-httpbis-p1-messaging-08</a></li>
     701               <li><a href="#rfc.section.D.11">D.11</a>&nbsp;&nbsp;&nbsp;<a href="#changes.since.09">Since draft-ietf-httpbis-p1-messaging-09</a></li>
     702               <li><a href="#rfc.section.D.12">D.12</a>&nbsp;&nbsp;&nbsp;<a href="#changes.since.10">Since draft-ietf-httpbis-p1-messaging-10</a></li>
    704703            </ul>
    705704         </li>
    706705         <li><a href="#rfc.index">Index</a></li>
     706         <li><a href="#rfc.authors">Authors' Addresses</a></li>
    707707      </ul>
    708       <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;<a id="introduction" href="#introduction">Introduction</a></h1>
    709       <p id="rfc.section.1.p.1">The Hypertext Transfer Protocol (HTTP) is an application-level request/response protocol that uses extensible semantics and
    710          MIME-like message payloads for flexible interaction with network-based hypertext information systems. HTTP relies upon the
    711          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 request targets and relationships between resources. Messages are passed in a format similar to that used by Internet
    712          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="p3-payload.html#differences.between.http.and.mime" title="Differences between HTTP and MIME">Appendix A</a> of <a href="#Part3" id="rfc.xref.Part3.1"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a> for the differences between HTTP and MIME messages).
    713       </p>
    714       <p id="rfc.section.1.p.2">HTTP is a generic interface protocol for information systems. It is designed to hide the details of how a service is implemented
    715          by presenting a uniform interface to clients that is independent of the types of resources provided. Likewise, servers do
    716          not need to be aware of each client's purpose: an HTTP request can be considered in isolation rather than being associated
    717          with a specific type of client or a predetermined sequence of application steps. The result is a protocol that can be used
    718          effectively in many different contexts and for which implementations can evolve independently over time.
    719       </p>
    720       <p id="rfc.section.1.p.3">HTTP is also designed for use as an intermediation protocol for translating communication to and from non-HTTP information
    721          systems. HTTP proxies and gateways can provide access to alternative information services by translating their diverse protocols
    722          into a hypertext format that can be viewed and manipulated by clients in the same way as HTTP services.
    723       </p>
    724       <p id="rfc.section.1.p.4">One consequence of HTTP flexibility is that the protocol cannot be defined in terms of what occurs behind the interface. Instead,
    725          we are limited to defining the syntax of communication, the intent of received communication, and the expected behavior of
    726          recipients. If the communication is considered in isolation, then successful actions ought to be reflected in corresponding
    727          changes to the observable interface provided by servers. However, since multiple clients might act in parallel and perhaps
    728          at cross-purposes, we cannot require that such changes be observable beyond the scope of a single response.
    729       </p>
    730       <p id="rfc.section.1.p.5">This document is Part 1 of the seven-part specification of HTTP, defining the protocol referred to as "HTTP/1.1" and obsoleting <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>. Part 1 describes the architectural elements that are used or referred to in HTTP, defines the "http" and "https" URI schemes,
    731          describes overall network operation and connection management, and defines HTTP message framing and forwarding requirements.
    732          Our goal is to define all of the mechanisms necessary for HTTP message handling that are independent of message semantics,
    733          thereby defining the complete set of requirements for message parsers and message-forwarding intermediaries.
    734       </p>
    735       <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a>&nbsp;<a id="intro.requirements" href="#intro.requirements">Requirements</a></h2>
    736       <p id="rfc.section.1.1.p.1">The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL"
    737          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>.
    738       </p>
    739       <p id="rfc.section.1.1.p.2">An implementation is not compliant if it fails to satisfy one or more of the "MUST" or "REQUIRED" level requirements for the
    740          protocols it implements. An implementation that satisfies all the "MUST" or "REQUIRED" level and all the "SHOULD" level requirements
    741          for its protocols is said to be "unconditionally compliant"; one that satisfies all the "MUST" level requirements but not
    742          all the "SHOULD" level requirements for its protocols is said to be "conditionally compliant".
    743       </p>
    744       <div id="rfc.iref.g.1"></div>
    745       <div id="rfc.iref.g.2"></div>
    746       <div id="rfc.iref.g.3"></div>
    747       <div id="rfc.iref.g.4"></div>
    748       <div id="rfc.iref.g.5"></div>
    749       <div id="rfc.iref.g.6"></div>
    750       <div id="rfc.iref.g.7"></div>
    751       <div id="rfc.iref.g.8"></div>
    752       <div id="rfc.iref.g.9"></div>
    753       <div id="rfc.iref.g.10"></div>
    754       <div id="rfc.iref.g.11"></div>
    755       <div id="rfc.iref.g.12"></div>
    756       <h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a>&nbsp;<a id="notation" href="#notation">Syntax Notation</a></h2>
    757       <p id="rfc.section.1.2.p.1">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>.
    758       </p>
    759       <div id="core.rules">
    760          <p id="rfc.section.1.2.p.2">                        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="http://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
    761             (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit sequence of data), SP (space), 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), and WSP (whitespace).
     708      <div id="introduction">
     709         <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;<a href="#introduction">Introduction</a></h1>
     710         <p id="rfc.section.1.p.1">The Hypertext Transfer Protocol (HTTP) is an application-level request/response protocol that uses extensible semantics and
     711            MIME-like message payloads for flexible interaction with network-based hypertext information systems. HTTP relies upon the
     712            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 request targets and relationships between resources. Messages are passed in a format similar to that used by Internet
     713            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="p3-payload.html#differences.between.http.and.mime" title="Differences between HTTP and MIME">Appendix A</a> of <a href="#Part3" id="rfc.xref.Part3.1"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a> for the differences between HTTP and MIME messages).
    762714         </p>
    763       </div>
    764       <p id="rfc.section.1.2.p.3">As a syntactic convention, ABNF rule names prefixed with "obs-" denote "obsolete" grammar rules that appear for historical
    765          reasons.
    766       </p>
    767       <h3 id="rfc.section.1.2.1"><a href="#rfc.section.1.2.1">1.2.1</a>&nbsp;<a id="notation.abnf" href="#notation.abnf">ABNF Extension: #rule</a></h3>
    768       <p id="rfc.section.1.2.1.p.1">The #rule extension to the ABNF rules of <a href="#RFC5234" id="rfc.xref.RFC5234.3"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a> is used to improve readability.
    769       </p>
    770       <p id="rfc.section.1.2.1.p.2">A construct "#" is defined, similar to "*", for defining comma-delimited lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element"
    771          indicating at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single comma (",") and optional whitespace (OWS, <a href="#basic.rules" title="Basic Rules">Section&nbsp;1.2.2</a>).
    772       </p>
    773       <div id="rfc.figure.u.1"></div>
    774       <p>Thus,</p><pre class="text">  1#element =&gt; element *( OWS "," OWS element )
     715         <p id="rfc.section.1.p.2">HTTP is a generic interface protocol for information systems. It is designed to hide the details of how a service is implemented
     716            by presenting a uniform interface to clients that is independent of the types of resources provided. Likewise, servers do
     717            not need to be aware of each client's purpose: an HTTP request can be considered in isolation rather than being associated
     718            with a specific type of client or a predetermined sequence of application steps. The result is a protocol that can be used
     719            effectively in many different contexts and for which implementations can evolve independently over time.
     720         </p>
     721         <p id="rfc.section.1.p.3">HTTP is also designed for use as an intermediation protocol for translating communication to and from non-HTTP information
     722            systems. HTTP proxies and gateways can provide access to alternative information services by translating their diverse protocols
     723            into a hypertext format that can be viewed and manipulated by clients in the same way as HTTP services.
     724         </p>
     725         <p id="rfc.section.1.p.4">One consequence of HTTP flexibility is that the protocol cannot be defined in terms of what occurs behind the interface. Instead,
     726            we are limited to defining the syntax of communication, the intent of received communication, and the expected behavior of
     727            recipients. If the communication is considered in isolation, then successful actions ought to be reflected in corresponding
     728            changes to the observable interface provided by servers. However, since multiple clients might act in parallel and perhaps
     729            at cross-purposes, we cannot require that such changes be observable beyond the scope of a single response.
     730         </p>
     731         <p id="rfc.section.1.p.5">This document is Part 1 of the seven-part specification of HTTP, defining the protocol referred to as "HTTP/1.1" and obsoleting <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>. Part 1 describes the architectural elements that are used or referred to in HTTP, defines the "http" and "https" URI schemes,
     732            describes overall network operation and connection management, and defines HTTP message framing and forwarding requirements.
     733            Our goal is to define all of the mechanisms necessary for HTTP message handling that are independent of message semantics,
     734            thereby defining the complete set of requirements for message parsers and message-forwarding intermediaries.
     735         </p>
     736         <div id="intro.requirements">
     737            <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a>&nbsp;<a href="#intro.requirements">Requirements</a></h2>
     738            <p id="rfc.section.1.1.p.1">The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL"
     739               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>.
     740            </p>
     741            <p id="rfc.section.1.1.p.2">An implementation is not compliant if it fails to satisfy one or more of the "MUST" or "REQUIRED" level requirements for the
     742               protocols it implements. An implementation that satisfies all the "MUST" or "REQUIRED" level and all the "SHOULD" level requirements
     743               for its protocols is said to be "unconditionally compliant"; one that satisfies all the "MUST" level requirements but not
     744               all the "SHOULD" level requirements for its protocols is said to be "conditionally compliant".
     745            </p>
     746         </div>
     747         <div id="notation">
     748            <div id="rfc.iref.g.1"></div>
     749            <div id="rfc.iref.g.2"></div>
     750            <div id="rfc.iref.g.3"></div>
     751            <div id="rfc.iref.g.4"></div>
     752            <div id="rfc.iref.g.5"></div>
     753            <div id="rfc.iref.g.6"></div>
     754            <div id="rfc.iref.g.7"></div>
     755            <div id="rfc.iref.g.8"></div>
     756            <div id="rfc.iref.g.9"></div>
     757            <div id="rfc.iref.g.10"></div>
     758            <div id="rfc.iref.g.11"></div>
     759            <div id="rfc.iref.g.12"></div>
     760            <h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a>&nbsp;<a href="#notation">Syntax Notation</a></h2>
     761            <p id="rfc.section.1.2.p.1">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>.
     762            </p>
     763            <div id="core.rules">
     764               <p id="rfc.section.1.2.p.2">            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
     765                  (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit sequence of data), SP (space), 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), and WSP (whitespace).
     766               </p>
     767            </div>
     768            <p id="rfc.section.1.2.p.3">As a syntactic convention, ABNF rule names prefixed with "obs-" denote "obsolete" grammar rules that appear for historical
     769               reasons.
     770            </p>
     771            <div id="notation.abnf">
     772               <h3 id="rfc.section.1.2.1"><a href="#rfc.section.1.2.1">1.2.1</a>&nbsp;<a href="#notation.abnf">ABNF Extension: #rule</a></h3>
     773               <p id="rfc.section.1.2.1.p.1">The #rule extension to the ABNF rules of <a href="#RFC5234" id="rfc.xref.RFC5234.3"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a> is used to improve readability.
     774               </p>
     775               <p id="rfc.section.1.2.1.p.2">A construct "#" is defined, similar to "*", for defining comma-delimited lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element"
     776                  indicating at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single comma (",") and optional whitespace (OWS, <a href="#basic.rules" title="Basic Rules">Section&nbsp;1.2.2</a>).
     777               </p>
     778               <div id="rfc.figure.u.1"></div>
     779               <p>Thus,</p><pre class="text">  1#element =&gt; element *( OWS "," OWS element )
    775780</pre><div id="rfc.figure.u.2"></div>
    776       <p>and:</p><pre class="text">  #element =&gt; [ 1#element ]
     781               <p>and:</p><pre class="text">  #element =&gt; [ 1#element ]
    777782</pre><div id="rfc.figure.u.3"></div>
    778       <p>and for n &gt;= 1 and m &gt; 1:</p><pre class="text">  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
     783               <p>and for n &gt;= 1 and m &gt; 1:</p><pre class="text">  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
    779784</pre><p id="rfc.section.1.2.1.p.6">For compatibility with legacy list rules, recipients <em class="bcp14">SHOULD</em> accept empty list elements. In other words, consumers would follow the list productions:
    780       </p>
    781       <div id="rfc.figure.u.4"></div><pre class="text">  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
     785               </p>
     786               <div id="rfc.figure.u.4"></div><pre class="text">  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
    782787 
    783788  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
    784789</pre><p id="rfc.section.1.2.1.p.8">Note that empty elements do not contribute to the count of elements present, though.</p>
    785       <p id="rfc.section.1.2.1.p.9">For example, given these ABNF productions:</p>
    786       <div id="rfc.figure.u.5"></div><pre class="text">  example-list      = 1#example-list-elmt
     790               <p id="rfc.section.1.2.1.p.9">For example, given these ABNF productions:</p>
     791               <div id="rfc.figure.u.5"></div><pre class="text">  example-list      = 1#example-list-elmt
    787792  example-list-elmt = token ; see <a href="#basic.rules" title="Basic Rules">Section&nbsp;1.2.2</a>
    788793</pre><p id="rfc.section.1.2.1.p.11">Then these are valid values for example-list (not including the double quotes, which are present for delimitation only):</p>
    789       <div id="rfc.figure.u.6"></div><pre class="text">  "foo,bar"
     794               <div id="rfc.figure.u.6"></div><pre class="text">  "foo,bar"
    790795  " foo ,bar,"
    791796  "  foo , ,bar,charlie   "
    792797  "foo ,bar,   charlie "
    793798</pre><p id="rfc.section.1.2.1.p.13">But these values would be invalid, as at least one non-empty element is required:</p>
    794       <div id="rfc.figure.u.7"></div><pre class="text">  ""
     799               <div id="rfc.figure.u.7"></div><pre class="text">  ""
    795800  ","
    796801  ",   ,"
    797 </pre><p id="rfc.section.1.2.1.p.15"> <a href="#collected.abnf" title="Collected ABNF">Appendix&nbsp;C</a> shows the collected ABNF, with the list rules expanded as explained above.
    798       </p>
    799       <h3 id="rfc.section.1.2.2"><a href="#rfc.section.1.2.2">1.2.2</a>&nbsp;<a id="basic.rules" href="#basic.rules">Basic Rules</a></h3>
    800       <div id="rule.CRLF">
    801          <p id="rfc.section.1.2.2.p.1">  HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all protocol elements other than the message-body (see <a href="#tolerant.applications" title="Tolerant Applications">Appendix&nbsp;A</a> for tolerant applications).
    802          </p>
    803       </div>
    804       <div id="rule.LWS">
    805          <p id="rfc.section.1.2.2.p.2">This specification uses three rules to denote the use of linear whitespace: OWS (optional whitespace), RWS (required whitespace),
    806             and BWS ("bad" whitespace).
    807          </p>
    808       </div>
    809       <p id="rfc.section.1.2.2.p.3">The OWS rule is used where zero or more linear whitespace characters might appear. OWS <em class="bcp14">SHOULD</em> either not be produced or be produced as a single SP character. Multiple OWS characters that occur within field-content <em class="bcp14">SHOULD</em> be replaced with a single SP before interpreting the field value or forwarding the message downstream.
    810       </p>
    811       <p id="rfc.section.1.2.2.p.4">RWS is used when at least one linear whitespace character is required to separate field tokens. RWS <em class="bcp14">SHOULD</em> be produced as a single SP character. Multiple RWS characters that occur within field-content <em class="bcp14">SHOULD</em> be replaced with a single SP before interpreting the field value or forwarding the message downstream.
    812       </p>
    813       <p id="rfc.section.1.2.2.p.5">BWS is used where the grammar allows optional whitespace for historical reasons but senders <em class="bcp14">SHOULD NOT</em> produce it in messages. HTTP/1.1 recipients <em class="bcp14">MUST</em> accept such bad optional whitespace and remove it before interpreting the field value or forwarding the message downstream.
    814       </p>
    815       <div id="rule.whitespace">
    816          <p id="rfc.section.1.2.2.p.6">        </p>
    817       </div>
    818       <div id="rfc.figure.u.8"></div><pre class="inline"><span id="rfc.iref.g.13"></span><span id="rfc.iref.g.14"></span><span id="rfc.iref.g.15"></span>  <a href="#rule.whitespace" class="smpl">OWS</a>            = *( [ obs-fold ] <a href="#core.rules" class="smpl">WSP</a> )
     802</pre><p id="rfc.section.1.2.1.p.15"><a href="#collected.abnf" title="Collected ABNF">Appendix&nbsp;C</a> shows the collected ABNF, with the list rules expanded as explained above.
     803               </p>
     804            </div>
     805            <div id="basic.rules">
     806               <h3 id="rfc.section.1.2.2"><a href="#rfc.section.1.2.2">1.2.2</a>&nbsp;<a href="#basic.rules">Basic Rules</a></h3>
     807               <div id="rule.CRLF">
     808                  <p id="rfc.section.1.2.2.p.1"> HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all protocol elements other than the message-body (see <a href="#tolerant.applications" title="Tolerant Applications">Appendix&nbsp;A</a> for tolerant applications).
     809                  </p>
     810               </div>
     811               <div id="rule.LWS">
     812                  <p id="rfc.section.1.2.2.p.2">This specification uses three rules to denote the use of linear whitespace: OWS (optional whitespace), RWS (required whitespace),
     813                     and BWS ("bad" whitespace).
     814                  </p>
     815               </div>
     816               <p id="rfc.section.1.2.2.p.3">The OWS rule is used where zero or more linear whitespace characters might appear. OWS <em class="bcp14">SHOULD</em> either not be produced or be produced as a single SP character. Multiple OWS characters that occur within field-content <em class="bcp14">SHOULD</em> be replaced with a single SP before interpreting the field value or forwarding the message downstream.
     817               </p>
     818               <p id="rfc.section.1.2.2.p.4">RWS is used when at least one linear whitespace character is required to separate field tokens. RWS <em class="bcp14">SHOULD</em> be produced as a single SP character. Multiple RWS characters that occur within field-content <em class="bcp14">SHOULD</em> be replaced with a single SP before interpreting the field value or forwarding the message downstream.
     819               </p>
     820               <p id="rfc.section.1.2.2.p.5">BWS is used where the grammar allows optional whitespace for historical reasons but senders <em class="bcp14">SHOULD NOT</em> produce it in messages. HTTP/1.1 recipients <em class="bcp14">MUST</em> accept such bad optional whitespace and remove it before interpreting the field value or forwarding the message downstream.
     821               </p>
     822               <div id="rule.whitespace">
     823                  <p id="rfc.section.1.2.2.p.6">    </p>
     824               </div>
     825               <div id="rfc.figure.u.8"></div><pre class="inline"><span id="rfc.iref.g.13"></span><span id="rfc.iref.g.14"></span><span id="rfc.iref.g.15"></span>  <a href="#rule.whitespace" class="smpl">OWS</a>            = *( [ obs-fold ] <a href="#core.rules" class="smpl">WSP</a> )
    819826                 ; "optional" whitespace
    820827  <a href="#rule.whitespace" class="smpl">RWS</a>            = 1*( [ obs-fold ] <a href="#core.rules" class="smpl">WSP</a> )
     
    825832                 ; see <a href="#header.fields" title="Header Fields">Section&nbsp;3.2</a>
    826833</pre><div id="rule.token.separators">
    827          <p id="rfc.section.1.2.2.p.8">        Many HTTP/1.1 header field values consist of words (token or quoted-string) separated by whitespace or special characters.
    828             These special characters <em class="bcp14">MUST</em> be in a quoted string to be used within a parameter value (as defined in <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;6.2</a>).
    829          </p>
    830       </div>
    831       <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.16"></span><span id="rfc.iref.g.17"></span><span id="rfc.iref.g.18"></span><span id="rfc.iref.g.19"></span>  <a href="#rule.token.separators" class="smpl">word</a>           = <a href="#rule.token.separators" class="smpl">token</a> / <a href="#rule.quoted-string" class="smpl">quoted-string</a>
     834                  <p id="rfc.section.1.2.2.p.8">    Many HTTP/1.1 header field values consist of words (token or quoted-string) separated by whitespace or special characters.
     835                     These special characters <em class="bcp14">MUST</em> be in a quoted string to be used within a parameter value (as defined in <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;6.2</a>).
     836                  </p>
     837               </div>
     838               <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.16"></span><span id="rfc.iref.g.17"></span><span id="rfc.iref.g.18"></span><span id="rfc.iref.g.19"></span>  <a href="#rule.token.separators" class="smpl">word</a>           = <a href="#rule.token.separators" class="smpl">token</a> / <a href="#rule.quoted-string" class="smpl">quoted-string</a>
    832839
    833840  <a href="#rule.token.separators" class="smpl">token</a>          = 1*<a href="#rule.token.separators" class="smpl">tchar</a>
     
    842849                 / "]" / "?" / "=" / "{" / "}"
    843850</pre><div id="rule.quoted-string">
    844          <p id="rfc.section.1.2.2.p.10">      A string of text is parsed as a single word if it is quoted using double-quote marks.</p>
    845       </div>
    846       <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.20"></span><span id="rfc.iref.g.21"></span><span id="rfc.iref.g.22"></span>  <a href="#rule.quoted-string" class="smpl">quoted-string</a>  = <a href="#core.rules" class="smpl">DQUOTE</a> *( <a href="#rule.quoted-string" class="smpl">qdtext</a> / <a href="#rule.quoted-pair" class="smpl">quoted-pair</a> ) <a href="#core.rules" class="smpl">DQUOTE</a>
     851                  <p id="rfc.section.1.2.2.p.10">   A string of text is parsed as a single word if it is quoted using double-quote marks.</p>
     852               </div>
     853               <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.20"></span><span id="rfc.iref.g.21"></span><span id="rfc.iref.g.22"></span>  <a href="#rule.quoted-string" class="smpl">quoted-string</a>  = <a href="#core.rules" class="smpl">DQUOTE</a> *( <a href="#rule.quoted-string" class="smpl">qdtext</a> / <a href="#rule.quoted-pair" class="smpl">quoted-pair</a> ) <a href="#core.rules" class="smpl">DQUOTE</a>
    847854  <a href="#rule.quoted-string" class="smpl">qdtext</a>         = <a href="#rule.whitespace" class="smpl">OWS</a> / %x21 / %x23-5B / %x5D-7E / <a href="#rule.quoted-string" class="smpl">obs-text</a>
    848855                 ; <a href="#rule.whitespace" class="smpl">OWS</a> / &lt;<a href="#core.rules" class="smpl">VCHAR</a> except <a href="#core.rules" class="smpl">DQUOTE</a> and "\"&gt; / <a href="#rule.quoted-string" class="smpl">obs-text</a>
    849856  <a href="#rule.quoted-string" class="smpl">obs-text</a>       = %x80-FF
    850857</pre><div id="rule.quoted-pair">
    851          <p id="rfc.section.1.2.2.p.12"> The backslash character ("\") can be used as a single-character quoting mechanism within quoted-string constructs:</p>
    852       </div>
    853       <div id="rfc.figure.u.11"></div><pre class="inline"><span id="rfc.iref.g.23"></span>  <a href="#rule.quoted-pair" class="smpl">quoted-pair</a>    = "\" ( <a href="#core.rules" class="smpl">WSP</a> / <a href="#core.rules" class="smpl">VCHAR</a> / <a href="#rule.quoted-string" class="smpl">obs-text</a> )
     858                  <p id="rfc.section.1.2.2.p.12"> The backslash character ("\") can be used as a single-character quoting mechanism within quoted-string constructs:</p>
     859               </div>
     860               <div id="rfc.figure.u.11"></div><pre class="inline"><span id="rfc.iref.g.23"></span>  <a href="#rule.quoted-pair" class="smpl">quoted-pair</a>    = "\" ( <a href="#core.rules" class="smpl">WSP</a> / <a href="#core.rules" class="smpl">VCHAR</a> / <a href="#rule.quoted-string" class="smpl">obs-text</a> )
    854861</pre><p id="rfc.section.1.2.2.p.14">Producers <em class="bcp14">SHOULD NOT</em> escape characters that do not require escaping (i.e., other than DQUOTE and the backslash character).
    855       </p>
    856       <h3 id="rfc.section.1.2.3"><a href="#rfc.section.1.2.3">1.2.3</a>&nbsp;<a id="abnf.dependencies" href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></h3>
    857       <p id="rfc.section.1.2.3.p.1">The ABNF rules below are defined in other parts:</p>
    858       <div id="rfc.figure.u.12"></div><pre class="inline">  <a href="#abnf.dependencies" class="smpl">request-header</a>  = &lt;request-header, defined in <a href="#Part2" id="rfc.xref.Part2.1"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>, <a href="p2-semantics.html#request.header.fields" title="Request Header Fields">Section 3</a>&gt;
     862               </p>
     863            </div>
     864            <div id="abnf.dependencies">
     865               <h3 id="rfc.section.1.2.3"><a href="#rfc.section.1.2.3">1.2.3</a>&nbsp;<a href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></h3>
     866               <p id="rfc.section.1.2.3.p.1">The ABNF rules below are defined in other parts:</p>
     867               <div id="rfc.figure.u.12"></div><pre class="inline">  <a href="#abnf.dependencies" class="smpl">request-header</a>  = &lt;request-header, defined in <a href="#Part2" id="rfc.xref.Part2.1"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>, <a href="p2-semantics.html#request.header.fields" title="Request Header Fields">Section 3</a>&gt;
    859868  <a href="#abnf.dependencies" class="smpl">response-header</a> = &lt;response-header, defined in <a href="#Part2" id="rfc.xref.Part2.2"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>, <a href="p2-semantics.html#response.header.fields" title="Response Header Fields">Section 5</a>&gt;
    860869</pre><div id="rfc.figure.u.13"></div><pre class="inline">  <a href="#abnf.dependencies" class="smpl">MIME-Version</a>    = &lt;MIME-Version, defined in <a href="#Part3" id="rfc.xref.Part3.2"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>, <a href="p3-payload.html#mime-version" title="MIME-Version">Appendix A.1</a>&gt;
     
    862871  <a href="#abnf.dependencies" class="smpl">Pragma</a>          = &lt;Pragma, defined in <a href="#Part6" id="rfc.xref.Part6.2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>, <a href="p6-cache.html#header.pragma" title="Pragma">Section 3.4</a>&gt;
    863872  <a href="#abnf.dependencies" class="smpl">Warning</a>         = &lt;Warning, defined in <a href="#Part6" id="rfc.xref.Part6.3"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>, <a href="p6-cache.html#header.warning" title="Warning">Section 3.6</a>&gt;
    864 </pre><h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a id="architecture" href="#architecture">HTTP-related architecture</a></h1>
    865       <p id="rfc.section.2.p.1">HTTP was created for the World Wide Web architecture and has evolved over time to support the scalability needs of a worldwide
    866          hypertext system. Much of that architecture is reflected in the terminology and syntax productions used to define HTTP.
    867       </p>
    868       <div id="rfc.iref.c.1"></div>
    869       <div id="rfc.iref.s.1"></div>
    870       <div id="rfc.iref.c.2"></div>
    871       <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a id="operation" href="#operation">Client/Server Messaging</a></h2>
    872       <p id="rfc.section.2.1.p.1">HTTP is a stateless request/response protocol that operates by exchanging messages across a reliable transport or session-layer
    873          connection. An HTTP "client" is a program that establishes a connection to a server for the purpose of sending one or more
    874          HTTP requests. An HTTP "server" is a program that accepts connections in order to service HTTP requests by sending HTTP responses.
    875       </p>
    876       <div id="rfc.iref.u.1"></div>
    877       <div id="rfc.iref.o.1"></div>
    878       <div id="rfc.iref.b.1"></div>
    879       <div id="rfc.iref.s.2"></div>
    880       <p id="rfc.section.2.1.p.2">Note that the terms client and server refer only to the roles that these programs perform for a particular connection. The
    881          same program might act as a client on some connections and a server on others. We use the term "user agent" to refer to the
    882          program that initiates a request, such as a WWW browser, editor, or spider (web-traversing robot), and the term "origin server"
    883          to refer to the program that can originate authoritative responses to a request. For general requirements, we use the term
    884          "sender" to refer to whichever component sent a given message and the term "recipient" to refer to any component that receives
    885          the message.
    886       </p>
    887       <p id="rfc.section.2.1.p.3">Most HTTP communication consists of a retrieval request (GET) for a representation of some resource identified by a URI. In
    888          the simplest case, this might be accomplished via a single bidirectional connection (===) between the user agent (UA) and
    889          the origin server (O).
    890       </p>
    891       <div id="rfc.figure.u.15"></div><pre class="drawing">         request   &gt;
     873</pre></div>
     874         </div>
     875      </div>
     876      <div id="architecture">
     877         <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a href="#architecture">HTTP-related architecture</a></h1>
     878         <p id="rfc.section.2.p.1">HTTP was created for the World Wide Web architecture and has evolved over time to support the scalability needs of a worldwide
     879            hypertext system. Much of that architecture is reflected in the terminology and syntax productions used to define HTTP.
     880         </p>
     881         <div id="operation">
     882            <div id="rfc.iref.c.1"></div>
     883            <div id="rfc.iref.s.1"></div>
     884            <div id="rfc.iref.c.2"></div>
     885            <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a href="#operation">Client/Server Messaging</a></h2>
     886            <p id="rfc.section.2.1.p.1">HTTP is a stateless request/response protocol that operates by exchanging messages across a reliable transport or session-layer
     887               connection. An HTTP "client" is a program that establishes a connection to a server for the purpose of sending one or more
     888               HTTP requests. An HTTP "server" is a program that accepts connections in order to service HTTP requests by sending HTTP responses.
     889            </p>
     890            <div id="rfc.iref.u.1"></div>
     891            <div id="rfc.iref.o.1"></div>
     892            <div id="rfc.iref.b.1"></div>
     893            <div id="rfc.iref.s.2"></div>
     894            <p id="rfc.section.2.1.p.2">Note that the terms client and server refer only to the roles that these programs perform for a particular connection. The
     895               same program might act as a client on some connections and a server on others. We use the term "user agent" to refer to the
     896               program that initiates a request, such as a WWW browser, editor, or spider (web-traversing robot), and the term "origin server"
     897               to refer to the program that can originate authoritative responses to a request. For general requirements, we use the term
     898               "sender" to refer to whichever component sent a given message and the term "recipient" to refer to any component that receives
     899               the message.
     900            </p>
     901            <p id="rfc.section.2.1.p.3">Most HTTP communication consists of a retrieval request (GET) for a representation of some resource identified by a URI. In
     902               the simplest case, this might be accomplished via a single bidirectional connection (===) between the user agent (UA) and
     903               the origin server (O).
     904            </p>
     905            <div id="rfc.figure.u.15"></div><pre class="drawing">         request   &gt;
    892906    UA ======================================= O
    893907                                &lt;   response
    894908</pre><div id="rfc.iref.m.1"></div>
    895       <div id="rfc.iref.r.1"></div>
    896       <div id="rfc.iref.r.2"></div>
    897       <p id="rfc.section.2.1.p.5">A client sends an HTTP request to the server in the form of a request message (<a href="#request" title="Request">Section&nbsp;4</a>), beginning with a method, URI, and protocol version, followed by MIME-like header fields containing request modifiers, client
    898          information, and payload metadata, an empty line to indicate the end of the header section, and finally the payload body (if
    899          any).
    900       </p>
    901       <p id="rfc.section.2.1.p.6">A server responds to the client's request by sending an HTTP response message (<a href="#response" title="Response">Section&nbsp;5</a>), beginning with a status line that includes the protocol version, a success or error code, and textual reason phrase, followed
    902          by MIME-like header fields containing server information, resource metadata, and payload metadata, an empty line to indicate
    903          the end of the header section, and finally the payload body (if any).
    904       </p>
    905       <p id="rfc.section.2.1.p.7">The following example illustrates a typical message exchange for a GET request on the URI "http://www.example.com/hello.txt":</p>
    906       <div id="rfc.figure.u.16"></div>
    907       <p>client request:</p><pre class="text2">GET /hello.txt HTTP/1.1
     909            <div id="rfc.iref.r.1"></div>
     910            <div id="rfc.iref.r.2"></div>
     911            <p id="rfc.section.2.1.p.5">A client sends an HTTP request to the server in the form of a request message (<a href="#request" title="Request">Section&nbsp;4</a>), beginning with a method, URI, and protocol version, followed by MIME-like header fields containing request modifiers, client
     912               information, and payload metadata, an empty line to indicate the end of the header section, and finally the payload body (if
     913               any).
     914            </p>
     915            <p id="rfc.section.2.1.p.6">A server responds to the client's request by sending an HTTP response message (<a href="#response" title="Response">Section&nbsp;5</a>), beginning with a status line that includes the protocol version, a success or error code, and textual reason phrase, followed
     916               by MIME-like header fields containing server information, resource metadata, and payload metadata, an empty line to indicate
     917               the end of the header section, and finally the payload body (if any).
     918            </p>
     919            <p id="rfc.section.2.1.p.7">The following example illustrates a typical message exchange for a GET request on the URI "http://www.example.com/hello.txt":</p>
     920            <div id="rfc.figure.u.16"></div>
     921            <p>client request:</p><pre class="text2">GET /hello.txt HTTP/1.1
    908922User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
    909923Host: www.example.com
     
    911925
    912926</pre><div id="rfc.figure.u.17"></div>
    913       <p>server response:</p><pre class="text">HTTP/1.1 200 OK
     927            <p>server response:</p><pre class="text">HTTP/1.1 200 OK
    914928Date: Mon, 27 Jul 2009 12:28:53 GMT
    915929Server: Apache
     
    922936
    923937<span id="exbody">Hello World!
    924 </span></pre><div id="rfc.iref.i.1"></div>
    925       <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a>&nbsp;<a id="intermediaries" href="#intermediaries">Intermediaries</a></h2>
    926       <p id="rfc.section.2.2.p.1">A more complicated situation occurs when one or more intermediaries are present in the request/response chain. There are three
    927          common forms of intermediary: proxy, gateway, and tunnel. In some cases, a single intermediary might act as an origin server,
    928          proxy, gateway, or tunnel, switching behavior based on the nature of each request.
    929       </p>
    930       <div id="rfc.figure.u.18"></div><pre class="drawing">         &gt;             &gt;             &gt;             &gt;
     938</span></pre></div>
     939         <div id="intermediaries">
     940            <div id="rfc.iref.i.1"></div>
     941            <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a>&nbsp;<a href="#intermediaries">Intermediaries</a></h2>
     942            <p id="rfc.section.2.2.p.1">A more complicated situation occurs when one or more intermediaries are present in the request/response chain. There are three
     943               common forms of intermediary: proxy, gateway, and tunnel. In some cases, a single intermediary might act as an origin server,
     944               proxy, gateway, or tunnel, switching behavior based on the nature of each request.
     945            </p>
     946            <div id="rfc.figure.u.18"></div><pre class="drawing">         &gt;             &gt;             &gt;             &gt;
    931947    UA =========== A =========== B =========== C =========== O
    932948               &lt;             &lt;             &lt;             &lt;
    933949</pre><p id="rfc.section.2.2.p.3">The figure above shows three intermediaries (A, B, and C) between the user agent and origin server. A request or response
    934          message that travels the whole chain will pass through four separate connections. Some HTTP communication options might apply
    935          only to the connection with the nearest, non-tunnel neighbor, only to the end-points of the chain, or to all connections along
    936          the chain. Although the diagram is linear, each participant might be engaged in multiple, simultaneous communications. For
    937          example, B might be receiving requests from many clients other than A, and/or forwarding requests to servers other than C,
    938          at the same time that it is handling A's request.
    939       </p>
    940       <p id="rfc.section.2.2.p.4"> <span id="rfc.iref.u.2"></span><span id="rfc.iref.d.1"></span>  <span id="rfc.iref.i.2"></span><span id="rfc.iref.o.2"></span> We use the terms "upstream" and "downstream" to describe various requirements in relation to the directional flow of a message:
    941          all messages flow from upstream to downstream. Likewise, we use the terms "inbound" and "outbound" to refer to directions
    942          in relation to the request path: "inbound" means toward the origin server and "outbound" means toward the user agent.
    943       </p>
    944       <p id="rfc.section.2.2.p.5"><span id="rfc.iref.p.1"></span> A "proxy" is a message forwarding agent that is selected by the client, usually via local configuration rules, to receive
    945          requests for some type(s) of absolute URI and attempt to satisfy those requests via translation through the HTTP interface.
    946          Some translations are minimal, such as for proxy requests for "http" URIs, whereas other requests might require translation
    947          to and from entirely different application-layer protocols. Proxies are often used to group an organization's HTTP requests
    948          through a common intermediary for the sake of security, annotation services, or shared caching.
    949       </p>
    950       <p id="rfc.section.2.2.p.6"><span id="rfc.iref.g.24"></span><span id="rfc.iref.r.3"></span> A "gateway" (a.k.a., "reverse proxy") is a receiving agent that acts as a layer above some other server(s) and translates
    951          the received requests to the underlying server's protocol. Gateways are often used for load balancing or partitioning HTTP
    952          services across multiple machines. Unlike a proxy, a gateway receives requests as if it were the origin server for the target
    953          resource; the requesting client will not be aware that it is communicating with a gateway. A gateway communicates with the
    954          client as if the gateway is the origin server and thus is subject to all of the requirements on origin servers for that connection.
    955          A gateway communicates with inbound servers using any protocol it desires, including private extensions to HTTP that are outside
    956          the scope of this specification.
    957       </p>
    958       <p id="rfc.section.2.2.p.7"><span id="rfc.iref.t.1"></span> A "tunnel" acts as a blind relay between two connections without changing the messages. Once active, a tunnel is not considered
    959          a party to the HTTP communication, though the tunnel might have been initiated by an HTTP request. A tunnel ceases to exist
    960          when both ends of the relayed connection are closed. Tunnels are used to extend a virtual connection through an intermediary,
    961          such as when transport-layer security is used to establish private communication through a shared firewall proxy.
    962       </p>
    963       <div id="rfc.iref.c.3"></div>
    964       <h2 id="rfc.section.2.3"><a href="#rfc.section.2.3">2.3</a>&nbsp;<a id="caches" href="#caches">Caches</a></h2>
    965       <p id="rfc.section.2.3.p.1">A "cache" is a local store of previous response messages and the subsystem that controls its message storage, retrieval, and
    966          deletion. A cache stores cacheable responses in order to reduce the response time and network bandwidth consumption on future,
    967          equivalent requests. Any client or server <em class="bcp14">MAY</em> employ a cache, though a cache cannot be used by a server while it is acting as a tunnel.
    968       </p>
    969       <p id="rfc.section.2.3.p.2">The effect of a cache is that the request/response chain is shortened if one of the participants along the chain has a cached
    970          response applicable to that request. The following illustrates the resulting chain if B has a cached copy of an earlier response
    971          from O (via C) for a request which has not been cached by UA or A.
    972       </p>
    973       <div id="rfc.figure.u.19"></div><pre class="drawing">            &gt;             &gt;
     950               message that travels the whole chain will pass through four separate connections. Some HTTP communication options might apply
     951               only to the connection with the nearest, non-tunnel neighbor, only to the end-points of the chain, or to all connections along
     952               the chain. Although the diagram is linear, each participant might be engaged in multiple, simultaneous communications. For
     953               example, B might be receiving requests from many clients other than A, and/or forwarding requests to servers other than C,
     954               at the same time that it is handling A's request.
     955            </p>
     956            <p id="rfc.section.2.2.p.4"><span id="rfc.iref.u.2"></span><span id="rfc.iref.d.1"></span> <span id="rfc.iref.i.2"></span><span id="rfc.iref.o.2"></span> We use the terms "upstream" and "downstream" to describe various requirements in relation to the directional flow of a message:
     957               all messages flow from upstream to downstream. Likewise, we use the terms "inbound" and "outbound" to refer to directions
     958               in relation to the request path: "inbound" means toward the origin server and "outbound" means toward the user agent.
     959            </p>
     960            <p id="rfc.section.2.2.p.5"><span id="rfc.iref.p.1"></span> A "proxy" is a message forwarding agent that is selected by the client, usually via local configuration rules, to receive
     961               requests for some type(s) of absolute URI and attempt to satisfy those requests via translation through the HTTP interface.
     962               Some translations are minimal, such as for proxy requests for "http" URIs, whereas other requests might require translation
     963               to and from entirely different application-layer protocols. Proxies are often used to group an organization's HTTP requests
     964               through a common intermediary for the sake of security, annotation services, or shared caching.
     965            </p>
     966            <p id="rfc.section.2.2.p.6"><span id="rfc.iref.g.24"></span><span id="rfc.iref.r.3"></span> A "gateway" (a.k.a., "reverse proxy") is a receiving agent that acts as a layer above some other server(s) and translates
     967               the received requests to the underlying server's protocol. Gateways are often used for load balancing or partitioning HTTP
     968               services across multiple machines. Unlike a proxy, a gateway receives requests as if it were the origin server for the target
     969               resource; the requesting client will not be aware that it is communicating with a gateway. A gateway communicates with the
     970               client as if the gateway is the origin server and thus is subject to all of the requirements on origin servers for that connection.
     971               A gateway communicates with inbound servers using any protocol it desires, including private extensions to HTTP that are outside
     972               the scope of this specification.
     973            </p>
     974            <p id="rfc.section.2.2.p.7"><span id="rfc.iref.t.1"></span> A "tunnel" acts as a blind relay between two connections without changing the messages. Once active, a tunnel is not considered
     975               a party to the HTTP communication, though the tunnel might have been initiated by an HTTP request. A tunnel ceases to exist
     976               when both ends of the relayed connection are closed. Tunnels are used to extend a virtual connection through an intermediary,
     977               such as when transport-layer security is used to establish private communication through a shared firewall proxy.
     978            </p>
     979         </div>
     980         <div id="caches">
     981            <div id="rfc.iref.c.3"></div>
     982            <h2 id="rfc.section.2.3"><a href="#rfc.section.2.3">2.3</a>&nbsp;<a href="#caches">Caches</a></h2>
     983            <p id="rfc.section.2.3.p.1">A "cache" is a local store of previous response messages and the subsystem that controls its message storage, retrieval, and
     984               deletion. A cache stores cacheable responses in order to reduce the response time and network bandwidth consumption on future,
     985               equivalent requests. Any client or server <em class="bcp14">MAY</em> employ a cache, though a cache cannot be used by a server while it is acting as a tunnel.
     986            </p>
     987            <p id="rfc.section.2.3.p.2">The effect of a cache is that the request/response chain is shortened if one of the participants along the chain has a cached
     988               response applicable to that request. The following illustrates the resulting chain if B has a cached copy of an earlier response
     989               from O (via C) for a request which has not been cached by UA or A.
     990            </p>
     991            <div id="rfc.figure.u.19"></div><pre class="drawing">            &gt;             &gt;
    974992       UA =========== A =========== B - - - - - - C - - - - - - O
    975993                  &lt;             &lt;
    976994</pre><p id="rfc.section.2.3.p.4"><span id="rfc.iref.c.4"></span> A response is "cacheable" if a cache is allowed to store a copy of the response message for use in answering subsequent requests.
    977          Even when a response is cacheable, there might be additional constraints placed by the client or by the origin server on when
    978          that cached response can be used for a particular request. HTTP requirements for cache behavior and cacheable responses are
    979          defined in <a href="p6-cache.html#caching.overview" title="Cache Operation">Section 2</a> of <a href="#Part6" id="rfc.xref.Part6.4"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>.
    980       </p>
    981       <p id="rfc.section.2.3.p.5">There are a wide variety of architectures and configurations of caches and proxies deployed across the World Wide Web and
    982          inside large organizations. These systems include national hierarchies of proxy caches to save transoceanic bandwidth, systems
    983          that broadcast or multicast cache entries, organizations that distribute subsets of cached data via optical media, and so
    984          on.
    985       </p>
    986       <h2 id="rfc.section.2.4"><a href="#rfc.section.2.4">2.4</a>&nbsp;<a id="transport-independence" href="#transport-independence">Transport Independence</a></h2>
    987       <p id="rfc.section.2.4.p.1">HTTP systems are used in a wide variety of environments, from corporate intranets with high-bandwidth links to long-distance
    988          communication over low-power radio links and intermittent connectivity.
    989       </p>
    990       <p id="rfc.section.2.4.p.2">HTTP communication usually takes place over TCP/IP connections. The default port is TCP 80 (&lt;<a href="http://www.iana.org/assignments/port-numbers">http://www.iana.org/assignments/port-numbers</a>&gt;), but other ports can be used. This does not preclude HTTP from being implemented on top of any other protocol on the Internet,
    991          or on other networks. HTTP only presumes a reliable transport; any protocol that provides such guarantees can be used; the
    992          mapping of the HTTP/1.1 request and response structures onto the transport data units of the protocol in question is outside
    993          the scope of this specification.
    994       </p>
    995       <p id="rfc.section.2.4.p.3">In HTTP/1.0, most implementations used a new connection for each request/response exchange. In HTTP/1.1, a connection might
    996          be used for one or more request/response exchanges, although connections might be closed for a variety of reasons (see <a href="#persistent.connections" title="Persistent Connections">Section&nbsp;7.1</a>).
    997       </p>
    998       <h2 id="rfc.section.2.5"><a href="#rfc.section.2.5">2.5</a>&nbsp;<a id="http.version" href="#http.version">HTTP Version</a></h2>
    999       <p id="rfc.section.2.5.p.1">HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions of the protocol. The protocol versioning policy is intended
    1000          to allow the sender to indicate the format of a message and its capacity for understanding further HTTP communication, rather
    1001          than the features obtained via that communication. No change is made to the version number for the addition of message components
    1002          which do not affect communication behavior or which only add to extensible field values. The &lt;minor&gt; number is incremented
    1003          when the changes made to the protocol add features which do not change the general message parsing algorithm, but which might
    1004          add to the message semantics and imply additional capabilities of the sender. The &lt;major&gt; number is incremented when the format
    1005          of a message within the protocol is changed. See <a href="#RFC2145" id="rfc.xref.RFC2145.1"><cite title="Use and Interpretation of HTTP Version Numbers">[RFC2145]</cite></a> for a fuller explanation.
    1006       </p>
    1007       <p id="rfc.section.2.5.p.2">The version of an HTTP message is indicated by an HTTP-Version field in the first line of the message. HTTP-Version is case-sensitive.</p>
    1008       <div id="rfc.figure.u.20"></div><pre class="inline"><span id="rfc.iref.g.25"></span><span id="rfc.iref.g.26"></span>  <a href="#http.version" class="smpl">HTTP-Version</a>   = <a href="#http.version" class="smpl">HTTP-Prot-Name</a> "/" 1*<a href="#core.rules" class="smpl">DIGIT</a> "." 1*<a href="#core.rules" class="smpl">DIGIT</a>
     995               Even when a response is cacheable, there might be additional constraints placed by the client or by the origin server on when
     996               that cached response can be used for a particular request. HTTP requirements for cache behavior and cacheable responses are
     997               defined in <a href="p6-cache.html#caching.overview" title="Cache Operation">Section 2</a> of <a href="#Part6" id="rfc.xref.Part6.4"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>.
     998            </p>
     999            <p id="rfc.section.2.3.p.5">There are a wide variety of architectures and configurations of caches and proxies deployed across the World Wide Web and
     1000               inside large organizations. These systems include national hierarchies of proxy caches to save transoceanic bandwidth, systems
     1001               that broadcast or multicast cache entries, organizations that distribute subsets of cached data via optical media, and so
     1002               on.
     1003            </p>
     1004         </div>
     1005         <div id="transport-independence">
     1006            <h2 id="rfc.section.2.4"><a href="#rfc.section.2.4">2.4</a>&nbsp;<a href="#transport-independence">Transport Independence</a></h2>
     1007            <p id="rfc.section.2.4.p.1">HTTP systems are used in a wide variety of environments, from corporate intranets with high-bandwidth links to long-distance
     1008               communication over low-power radio links and intermittent connectivity.
     1009            </p>
     1010            <p id="rfc.section.2.4.p.2">HTTP communication usually takes place over TCP/IP connections. The default port is TCP 80 (&lt;<a href="http://www.iana.org/assignments/port-numbers">http://www.iana.org/assignments/port-numbers</a>&gt;), but other ports can be used. This does not preclude HTTP from being implemented on top of any other protocol on the Internet,
     1011               or on other networks. HTTP only presumes a reliable transport; any protocol that provides such guarantees can be used; the
     1012               mapping of the HTTP/1.1 request and response structures onto the transport data units of the protocol in question is outside
     1013               the scope of this specification.
     1014            </p>
     1015            <p id="rfc.section.2.4.p.3">In HTTP/1.0, most implementations used a new connection for each request/response exchange. In HTTP/1.1, a connection might
     1016               be used for one or more request/response exchanges, although connections might be closed for a variety of reasons (see <a href="#persistent.connections" title="Persistent Connections">Section&nbsp;7.1</a>).
     1017            </p>
     1018         </div>
     1019         <div id="http.version">
     1020            <h2 id="rfc.section.2.5"><a href="#rfc.section.2.5">2.5</a>&nbsp;<a href="#http.version">HTTP Version</a></h2>
     1021            <p id="rfc.section.2.5.p.1">HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions of the protocol. The protocol versioning policy is intended
     1022               to allow the sender to indicate the format of a message and its capacity for understanding further HTTP communication, rather
     1023               than the features obtained via that communication. No change is made to the version number for the addition of message components
     1024               which do not affect communication behavior or which only add to extensible field values. The &lt;minor&gt; number is incremented
     1025               when the changes made to the protocol add features which do not change the general message parsing algorithm, but which might
     1026               add to the message semantics and imply additional capabilities of the sender. The &lt;major&gt; number is incremented when the format
     1027               of a message within the protocol is changed. See <a href="#RFC2145" id="rfc.xref.RFC2145.1"><cite title="Use and Interpretation of HTTP Version Numbers">[RFC2145]</cite></a> for a fuller explanation.
     1028            </p>
     1029            <p id="rfc.section.2.5.p.2">The version of an HTTP message is indicated by an HTTP-Version field in the first line of the message. HTTP-Version is case-sensitive.</p>
     1030            <div id="rfc.figure.u.20"></div><pre class="inline"><span id="rfc.iref.g.25"></span><span id="rfc.iref.g.26"></span>  <a href="#http.version" class="smpl">HTTP-Version</a>   = <a href="#http.version" class="smpl">HTTP-Prot-Name</a> "/" 1*<a href="#core.rules" class="smpl">DIGIT</a> "." 1*<a href="#core.rules" class="smpl">DIGIT</a>
    10091031  <a href="#http.version" class="smpl">HTTP-Prot-Name</a> = %x48.54.54.50 ; "HTTP", case-sensitive
    10101032</pre><p id="rfc.section.2.5.p.4">Note that the major and minor numbers <em class="bcp14">MUST</em> be treated as separate integers and that each <em class="bcp14">MAY</em> be incremented higher than a single digit. Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is lower than HTTP/12.3.
    1011          Leading zeros <em class="bcp14">MUST</em> be ignored by recipients and <em class="bcp14">MUST NOT</em> be sent.
    1012       </p>
    1013       <p id="rfc.section.2.5.p.5">An application that sends a request or response message that includes HTTP-Version of "HTTP/1.1" <em class="bcp14">MUST</em> be at least conditionally compliant with this specification. Applications that are at least conditionally compliant with this
    1014          specification <em class="bcp14">SHOULD</em> use an HTTP-Version of "HTTP/1.1" in their messages, and <em class="bcp14">MUST</em> do so for any message that is not compatible with HTTP/1.0. For more details on when to send specific HTTP-Version values,
    1015          see <a href="#RFC2145" id="rfc.xref.RFC2145.2"><cite title="Use and Interpretation of HTTP Version Numbers">[RFC2145]</cite></a>.
    1016       </p>
    1017       <p id="rfc.section.2.5.p.6">The HTTP version of an application is the highest HTTP version for which the application is at least conditionally compliant.</p>
    1018       <p id="rfc.section.2.5.p.7">Proxy and gateway applications need to be careful when forwarding messages in protocol versions different from that of the
    1019          application. Since the protocol version indicates the protocol capability of the sender, a proxy/gateway <em class="bcp14">MUST NOT</em> send a message with a version indicator which is greater than its actual version. If a higher version request is received,
    1020          the proxy/gateway <em class="bcp14">MUST</em> either downgrade the request version, or respond with an error, or switch to tunnel behavior.
    1021       </p>
    1022       <p id="rfc.section.2.5.p.8">Due to interoperability problems with HTTP/1.0 proxies discovered since the publication of <a href="#RFC2068" id="rfc.xref.RFC2068.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, caching proxies <em class="bcp14">MUST</em>, gateways <em class="bcp14">MAY</em>, and tunnels <em class="bcp14">MUST NOT</em> upgrade the request to the highest version they support. The proxy/gateway's response to that request <em class="bcp14">MUST</em> be in the same major version as the request.
    1023       </p>
    1024       <div class="note" id="rfc.section.2.5.p.9">
    1025          <p> <b>Note:</b> Converting between versions of HTTP might involve modification of header fields required or forbidden by the versions involved.
    1026          </p>
    1027       </div>
    1028       <div id="rfc.iref.r.4"></div>
    1029       <h2 id="rfc.section.2.6"><a href="#rfc.section.2.6">2.6</a>&nbsp;<a id="uri" href="#uri">Uniform Resource Identifiers</a></h2>
    1030       <p id="rfc.section.2.6.p.1">Uniform Resource Identifiers (URIs) <a href="#RFC3986" id="rfc.xref.RFC3986.2"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a> are used throughout HTTP as the means for identifying resources. URI references are used to target requests, indicate redirects,
    1031          and define relationships. HTTP does not limit what a resource might be; it merely defines an interface that can be used to
    1032          interact with a resource via HTTP. More information on the scope of URIs and resources can be found in <a href="#RFC3986" id="rfc.xref.RFC3986.3"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>.
    1033       </p>
    1034       <p id="rfc.section.2.6.p.2">This specification adopts the definitions of "URI-reference", "absolute-URI", "relative-part", "port", "host", "path-abempty",
    1035          "path-absolute", "query", and "authority" from <a href="#RFC3986" id="rfc.xref.RFC3986.4"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>. In addition, we define a partial-URI rule for protocol elements that allow a relative URI without a fragment.
    1036       </p>
    1037       <div id="rfc.figure.u.21"></div><pre class="inline"><span id="rfc.iref.g.27"></span><span id="rfc.iref.g.28"></span><span id="rfc.iref.g.29"></span><span id="rfc.iref.g.30"></span><span id="rfc.iref.g.31"></span><span id="rfc.iref.g.32"></span><span id="rfc.iref.g.33"></span>  <a href="#uri" class="smpl">URI-reference</a> = &lt;URI-reference, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.5"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-4.1">Section 4.1</a>&gt;
    1038   <a href="#uri" class="smpl">absolute-URI</a>  = &lt;absolute-URI, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.6"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-4.3">Section 4.3</a>&gt;
    1039   <a href="#uri" class="smpl">relative-part</a> = &lt;relative-part, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.7"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-4.2">Section 4.2</a>&gt;
    1040   <a href="#uri" class="smpl">authority</a>     = &lt;authority, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.8"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-3.2">Section 3.2</a>&gt;
    1041   <a href="#uri" class="smpl">path-abempty</a>  = &lt;path-abempty, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.9"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-3.3">Section 3.3</a>&gt;
    1042   <a href="#uri" class="smpl">path-absolute</a> = &lt;path-absolute, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.10"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-3.3">Section 3.3</a>&gt;
    1043   <a href="#uri" class="smpl">port</a>          = &lt;port, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.11"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-3.2.3">Section 3.2.3</a>&gt;
    1044   <a href="#uri" class="smpl">query</a>         = &lt;query, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.12"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-3.4">Section 3.4</a>&gt;
    1045   <a href="#uri" class="smpl">uri-host</a>      = &lt;host, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.13"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-3.2.2">Section 3.2.2</a>&gt;
     1033               Leading zeros <em class="bcp14">MUST</em> be ignored by recipients and <em class="bcp14">MUST NOT</em> be sent.
     1034            </p>
     1035            <p id="rfc.section.2.5.p.5">An application that sends a request or response message that includes HTTP-Version of "HTTP/1.1" <em class="bcp14">MUST</em> be at least conditionally compliant with this specification. Applications that are at least conditionally compliant with this
     1036               specification <em class="bcp14">SHOULD</em> use an HTTP-Version of "HTTP/1.1" in their messages, and <em class="bcp14">MUST</em> do so for any message that is not compatible with HTTP/1.0. For more details on when to send specific HTTP-Version values,
     1037               see <a href="#RFC2145" id="rfc.xref.RFC2145.2"><cite title="Use and Interpretation of HTTP Version Numbers">[RFC2145]</cite></a>.
     1038            </p>
     1039            <p id="rfc.section.2.5.p.6">The HTTP version of an application is the highest HTTP version for which the application is at least conditionally compliant.</p>
     1040            <p id="rfc.section.2.5.p.7">Proxy and gateway applications need to be careful when forwarding messages in protocol versions different from that of the
     1041               application. Since the protocol version indicates the protocol capability of the sender, a proxy/gateway <em class="bcp14">MUST NOT</em> send a message with a version indicator which is greater than its actual version. If a higher version request is received,
     1042               the proxy/gateway <em class="bcp14">MUST</em> either downgrade the request version, or respond with an error, or switch to tunnel behavior.
     1043            </p>
     1044            <p id="rfc.section.2.5.p.8">Due to interoperability problems with HTTP/1.0 proxies discovered since the publication of <a href="#RFC2068" id="rfc.xref.RFC2068.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, caching proxies <em class="bcp14">MUST</em>, gateways <em class="bcp14">MAY</em>, and tunnels <em class="bcp14">MUST NOT</em> upgrade the request to the highest version they support. The proxy/gateway's response to that request <em class="bcp14">MUST</em> be in the same major version as the request.
     1045            </p>
     1046            <div class="note" id="rfc.section.2.5.p.9">
     1047               <p><b>Note:</b> Converting between versions of HTTP might involve modification of header fields required or forbidden by the versions involved.
     1048               </p>
     1049            </div>
     1050         </div>
     1051         <div id="uri">
     1052            <div id="rfc.iref.r.4"></div>
     1053            <h2 id="rfc.section.2.6"><a href="#rfc.section.2.6">2.6</a>&nbsp;<a href="#uri">Uniform Resource Identifiers</a></h2>
     1054            <p id="rfc.section.2.6.p.1">Uniform Resource Identifiers (URIs) <a href="#RFC3986" id="rfc.xref.RFC3986.2"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a> are used throughout HTTP as the means for identifying resources. URI references are used to target requests, indicate redirects,
     1055               and define relationships. HTTP does not limit what a resource might be; it merely defines an interface that can be used to
     1056               interact with a resource via HTTP. More information on the scope of URIs and resources can be found in <a href="#RFC3986" id="rfc.xref.RFC3986.3"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>.
     1057            </p>
     1058            <p id="rfc.section.2.6.p.2">This specification adopts the definitions of "URI-reference", "absolute-URI", "relative-part", "port", "host", "path-abempty",
     1059               "path-absolute", "query", and "authority" from <a href="#RFC3986" id="rfc.xref.RFC3986.4"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>. In addition, we define a partial-URI rule for protocol elements that allow a relative URI without a fragment.
     1060            </p>
     1061            <div id="rfc.figure.u.21"></div><pre class="inline"><span id="rfc.iref.g.27"></span><span id="rfc.iref.g.28"></span><span id="rfc.iref.g.29"></span><span id="rfc.iref.g.30"></span><span id="rfc.iref.g.31"></span><span id="rfc.iref.g.32"></span><span id="rfc.iref.g.33"></span>  <a href="#uri" class="smpl">URI-reference</a> = &lt;URI-reference, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.5"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-4.1">Section 4.1</a>&gt;
     1062  <a href="#uri" class="smpl">absolute-URI</a>  = &lt;absolute-URI, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.6"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-4.3">Section 4.3</a>&gt;
     1063  <a href="#uri" class="smpl">relative-part</a> = &lt;relative-part, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.7"><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>&gt;
     1064  <a href="#uri" class="smpl">authority</a>     = &lt;authority, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.8"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-3.2">Section 3.2</a>&gt;
     1065  <a href="#uri" class="smpl">path-abempty</a>  = &lt;path-abempty, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.9"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-3.3">Section 3.3</a>&gt;
     1066  <a href="#uri" class="smpl">path-absolute</a> = &lt;path-absolute, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.10"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-3.3">Section 3.3</a>&gt;
     1067  <a href="#uri" class="smpl">port</a>          = &lt;port, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.11"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-3.2.3">Section 3.2.3</a>&gt;
     1068  <a href="#uri" class="smpl">query</a>         = &lt;query, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.12"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-3.4">Section 3.4</a>&gt;
     1069  <a href="#uri" class="smpl">uri-host</a>      = &lt;host, defined in <a href="#RFC3986" id="rfc.xref.RFC3986.13"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-3.2.2">Section 3.2.2</a>&gt;
    10461070 
    10471071  <a href="#uri" class="smpl">partial-URI</a>   = relative-part [ "?" query ]
    10481072</pre><p id="rfc.section.2.6.p.4">Each protocol element in HTTP that allows a URI reference will indicate in its ABNF production whether the element allows
    1049          only a URI in absolute form (absolute-URI), any relative reference (relative-ref), or some other subset of the URI-reference
    1050          grammar. Unless otherwise indicated, URI references are parsed relative to the request target (the default base URI for both
    1051          the request and its corresponding response).
    1052       </p>
    1053       <h3 id="rfc.section.2.6.1"><a href="#rfc.section.2.6.1">2.6.1</a>&nbsp;<a id="http.uri" href="#http.uri">http URI scheme</a></h3>
    1054       <div id="rfc.iref.h.1"></div>
    1055       <div id="rfc.iref.u.3"></div>
    1056       <p id="rfc.section.2.6.1.p.1">The "http" URI scheme is hereby defined for the purpose of minting identifiers according to their association with the hierarchical
    1057          namespace governed by a potential HTTP origin server listening for TCP connections on a given port. The HTTP server is identified
    1058          via the generic syntax's <a href="#uri" class="smpl">authority</a> component, which includes a host identifier and optional TCP port, and the remainder of the URI is considered to be identifying
    1059          data corresponding to a resource for which that server might provide an HTTP interface.
    1060       </p>
    1061       <div id="rfc.figure.u.22"></div><pre class="inline"><span id="rfc.iref.g.34"></span>  <a href="#http.uri" class="smpl">http-URI</a> = "http:" "//" <a href="#uri" class="smpl">authority</a> <a href="#uri" class="smpl">path-abempty</a> [ "?" <a href="#uri" class="smpl">query</a> ]
    1062 </pre><p id="rfc.section.2.6.1.p.3">The host identifier within an <a href="#uri" class="smpl">authority</a> component is defined in <a href="#RFC3986" id="rfc.xref.RFC3986.14"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-3.2.2">Section 3.2.2</a>. If host is provided as an IP literal or IPv4 address, then the HTTP server is any listener on the indicated TCP port at
    1063          that IP address. If host is a registered name, then that name is considered an indirect identifier and the recipient might
    1064          use a name resolution service, such as DNS, to find the address of a listener for that host. The host <em class="bcp14">MUST NOT</em> be empty; if an "http" URI is received with an empty host, then it <em class="bcp14">MUST</em> be rejected as invalid. If the port subcomponent is empty or not given, then TCP port 80 is assumed (the default reserved
    1065          port for WWW services).
    1066       </p>
    1067       <p id="rfc.section.2.6.1.p.4">Regardless of the form of host identifier, access to that host is not implied by the mere presence of its name or address.
    1068          The host might or might not exist and, even when it does exist, might or might not be running an HTTP server or listening
    1069          to the indicated port. The "http" URI scheme makes use of the delegated nature of Internet names and addresses to establish
    1070          a naming authority (whatever entity has the ability to place an HTTP server at that Internet name or address) and allows that
    1071          authority to determine which names are valid and how they might be used.
    1072       </p>
    1073       <p id="rfc.section.2.6.1.p.5">When an "http" URI is used within a context that calls for access to the indicated resource, a client <em class="bcp14">MAY</em> attempt access by resolving the host to an IP address, establishing a TCP connection to that address on the indicated port,
    1074          and sending an HTTP request message to the server containing the URI's identifying data as described in <a href="#request" title="Request">Section&nbsp;4</a>. If the server responds to that request with a non-interim HTTP response message, as described in <a href="#response" title="Response">Section&nbsp;5</a>, then that response is considered an authoritative answer to the client's request.
    1075       </p>
    1076       <p id="rfc.section.2.6.1.p.6">Although HTTP is independent of the transport protocol, the "http" scheme is specific to TCP-based services because the name
    1077          delegation process depends on TCP for establishing authority. An HTTP service based on some other underlying connection protocol
    1078          would presumably be identified using a different URI scheme, just as the "https" scheme (below) is used for servers that require
    1079          an SSL/TLS transport layer on a connection. Other protocols might also be used to provide access to "http" identified resources
    1080          --- it is only the authoritative interface used for mapping the namespace that is specific to TCP.
    1081       </p>
    1082       <p id="rfc.section.2.6.1.p.7">The URI generic syntax for authority also includes a deprecated userinfo subcomponent (<a href="#RFC3986" id="rfc.xref.RFC3986.15"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-3.2.1">Section 3.2.1</a>) for including user authentication information in the URI. The userinfo subcomponent (and its "@" delimiter) <em class="bcp14">MUST NOT</em> be used in an "http" URI. URI reference recipients <em class="bcp14">SHOULD</em> parse for the existence of userinfo and treat its presence as an error, likely indicating that the deprecated subcomponent
    1083          is being used to obscure the authority for the sake of phishing attacks.
    1084       </p>
    1085       <h3 id="rfc.section.2.6.2"><a href="#rfc.section.2.6.2">2.6.2</a>&nbsp;<a id="https.uri" href="#https.uri">https URI scheme</a></h3>
    1086       <div id="rfc.iref.h.2"></div>
    1087       <div id="rfc.iref.u.4"></div>
    1088       <p id="rfc.section.2.6.2.p.1">The "https" URI scheme is hereby defined for the purpose of minting identifiers according to their association with the hierarchical
    1089          namespace governed by a potential HTTP origin server listening for SSL/TLS-secured connections on a given TCP port.
    1090       </p>
    1091       <p id="rfc.section.2.6.2.p.2">All of the requirements listed above for the "http" scheme are also requirements for the "https" scheme, except that a default
    1092          TCP port of 443 is assumed if the port subcomponent is empty or not given, and the TCP connection <em class="bcp14">MUST</em> be secured for privacy through the use of strong encryption prior to sending the first HTTP request.
    1093       </p>
    1094       <div id="rfc.figure.u.23"></div><pre class="inline"><span id="rfc.iref.g.35"></span>  <a href="#https.uri" class="smpl">https-URI</a> = "https:" "//" <a href="#uri" class="smpl">authority</a> <a href="#uri" class="smpl">path-abempty</a> [ "?" <a href="#uri" class="smpl">query</a> ]
     1073               only a URI in absolute form (absolute-URI), any relative reference (relative-ref), or some other subset of the URI-reference
     1074               grammar. Unless otherwise indicated, URI references are parsed relative to the request target (the default base URI for both
     1075               the request and its corresponding response).
     1076            </p>
     1077            <div id="http.uri">
     1078               <h3 id="rfc.section.2.6.1"><a href="#rfc.section.2.6.1">2.6.1</a>&nbsp;<a href="#http.uri">http URI scheme</a></h3>
     1079               <div id="rfc.iref.h.1"></div>
     1080               <div id="rfc.iref.u.3"></div>
     1081               <p id="rfc.section.2.6.1.p.1">The "http" URI scheme is hereby defined for the purpose of minting identifiers according to their association with the hierarchical
     1082                  namespace governed by a potential HTTP origin server listening for TCP connections on a given port. The HTTP server is identified
     1083                  via the generic syntax's <a href="#uri" class="smpl">authority</a> component, which includes a host identifier and optional TCP port, and the remainder of the URI is considered to be identifying
     1084                  data corresponding to a resource for which that server might provide an HTTP interface.
     1085               </p>
     1086               <div id="rfc.figure.u.22"></div><pre class="inline"><span id="rfc.iref.g.34"></span>  <a href="#http.uri" class="smpl">http-URI</a> = "http:" "//" <a href="#uri" class="smpl">authority</a> <a href="#uri" class="smpl">path-abempty</a> [ "?" <a href="#uri" class="smpl">query</a> ]
     1087</pre><p id="rfc.section.2.6.1.p.3">The host identifier within an <a href="#uri" class="smpl">authority</a> component is defined in <a href="#RFC3986" id="rfc.xref.RFC3986.14"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-3.2.2">Section 3.2.2</a>. If host is provided as an IP literal or IPv4 address, then the HTTP server is any listener on the indicated TCP port at
     1088                  that IP address. If host is a registered name, then that name is considered an indirect identifier and the recipient might
     1089                  use a name resolution service, such as DNS, to find the address of a listener for that host. The host <em class="bcp14">MUST NOT</em> be empty; if an "http" URI is received with an empty host, then it <em class="bcp14">MUST</em> be rejected as invalid. If the port subcomponent is empty or not given, then TCP port 80 is assumed (the default reserved
     1090                  port for WWW services).
     1091               </p>
     1092               <p id="rfc.section.2.6.1.p.4">Regardless of the form of host identifier, access to that host is not implied by the mere presence of its name or address.
     1093                  The host might or might not exist and, even when it does exist, might or might not be running an HTTP server or listening
     1094                  to the indicated port. The "http" URI scheme makes use of the delegated nature of Internet names and addresses to establish
     1095                  a naming authority (whatever entity has the ability to place an HTTP server at that Internet name or address) and allows that
     1096                  authority to determine which names are valid and how they might be used.
     1097               </p>
     1098               <p id="rfc.section.2.6.1.p.5">When an "http" URI is used within a context that calls for access to the indicated resource, a client <em class="bcp14">MAY</em> attempt access by resolving the host to an IP address, establishing a TCP connection to that address on the indicated port,
     1099                  and sending an HTTP request message to the server containing the URI's identifying data as described in <a href="#request" title="Request">Section&nbsp;4</a>. If the server responds to that request with a non-interim HTTP response message, as described in <a href="#response" title="Response">Section&nbsp;5</a>, then that response is considered an authoritative answer to the client's request.
     1100               </p>
     1101               <p id="rfc.section.2.6.1.p.6">Although HTTP is independent of the transport protocol, the "http" scheme is specific to TCP-based services because the name
     1102                  delegation process depends on TCP for establishing authority. An HTTP service based on some other underlying connection protocol
     1103                  would presumably be identified using a different URI scheme, just as the "https" scheme (below) is used for servers that require
     1104                  an SSL/TLS transport layer on a connection. Other protocols might also be used to provide access to "http" identified resources
     1105                  --- it is only the authoritative interface used for mapping the namespace that is specific to TCP.
     1106               </p>
     1107               <p id="rfc.section.2.6.1.p.7">The URI generic syntax for authority also includes a deprecated userinfo subcomponent (<a href="#RFC3986" id="rfc.xref.RFC3986.15"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-3.2.1">Section 3.2.1</a>) for including user authentication information in the URI. The userinfo subcomponent (and its "@" delimiter) <em class="bcp14">MUST NOT</em> be used in an "http" URI. URI reference recipients <em class="bcp14">SHOULD</em> parse for the existence of userinfo and treat its presence as an error, likely indicating that the deprecated subcomponent
     1108                  is being used to obscure the authority for the sake of phishing attacks.
     1109               </p>
     1110            </div>
     1111            <div id="https.uri">
     1112               <h3 id="rfc.section.2.6.2"><a href="#rfc.section.2.6.2">2.6.2</a>&nbsp;<a href="#https.uri">https URI scheme</a></h3>
     1113               <div id="rfc.iref.h.2"></div>
     1114               <div id="rfc.iref.u.4"></div>
     1115               <p id="rfc.section.2.6.2.p.1">The "https" URI scheme is hereby defined for the purpose of minting identifiers according to their association with the hierarchical
     1116                  namespace governed by a potential HTTP origin server listening for SSL/TLS-secured connections on a given TCP port.
     1117               </p>
     1118               <p id="rfc.section.2.6.2.p.2">All of the requirements listed above for the "http" scheme are also requirements for the "https" scheme, except that a default
     1119                  TCP port of 443 is assumed if the port subcomponent is empty or not given, and the TCP connection <em class="bcp14">MUST</em> be secured for privacy through the use of strong encryption prior to sending the first HTTP request.
     1120               </p>
     1121               <div id="rfc.figure.u.23"></div><pre class="inline"><span id="rfc.iref.g.35"></span>  <a href="#https.uri" class="smpl">https-URI</a> = "https:" "//" <a href="#uri" class="smpl">authority</a> <a href="#uri" class="smpl">path-abempty</a> [ "?" <a href="#uri" class="smpl">query</a> ]
    10951122</pre><p id="rfc.section.2.6.2.p.4">Unlike the "http" scheme, responses to "https" identified requests are never "public" and thus are ineligible for shared caching.
    1096          Their default is "private" and might be further constrained via use of the Cache-Control header field.
    1097       </p>
    1098       <p id="rfc.section.2.6.2.p.5">Resources made available via the "https" scheme have no shared identity with the "http" scheme even if their resource identifiers
    1099          only differ by the single "s" in the scheme name. They are different services governed by different authorities. However,
    1100          some extensions to HTTP that apply to entire host domains, such as the Cookie protocol, do allow one service to effect communication
    1101          with the other services based on host domain matching.
    1102       </p>
    1103       <p id="rfc.section.2.6.2.p.6">The process for authoritative access to an "https" identified resource is defined in <a href="#RFC2818" id="rfc.xref.RFC2818.1"><cite title="HTTP Over TLS">[RFC2818]</cite></a>.
    1104       </p>
    1105       <h3 id="rfc.section.2.6.3"><a href="#rfc.section.2.6.3">2.6.3</a>&nbsp;<a id="uri.comparison" href="#uri.comparison">http and https URI Normalization and Comparison</a></h3>
    1106       <p id="rfc.section.2.6.3.p.1">Since the "http" and "https" schemes conform to the URI generic syntax, such URIs are normalized and compared according to
    1107          the algorithm defined in <a href="#RFC3986" id="rfc.xref.RFC3986.16"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-6">Section 6</a>, using the defaults described above for each scheme.
    1108       </p>
    1109       <p id="rfc.section.2.6.3.p.2">If the port is equal to the default port for a scheme, the normal form is to elide the port subcomponent. Likewise, an empty
    1110          path component is equivalent to an absolute path of "/", so the normal form is to provide a path of "/" instead. The scheme
    1111          and host are case-insensitive and normally provided in lowercase; all other components are compared in a case-sensitive manner.
    1112          Characters other than those in the "reserved" set are equivalent to their percent-encoded octets (see <a href="#RFC3986" id="rfc.xref.RFC3986.17"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-2.1">Section 2.1</a>): the normal form is to not encode them.
    1113       </p>
    1114       <p id="rfc.section.2.6.3.p.3">For example, the following three URIs are equivalent:</p>
    1115       <div id="rfc.figure.u.24"></div><pre class="text">   http://example.com:80/~smith/home.html
     1123                  Their default is "private" and might be further constrained via use of the Cache-Control header field.
     1124               </p>
     1125               <p id="rfc.section.2.6.2.p.5">Resources made available via the "https" scheme have no shared identity with the "http" scheme even if their resource identifiers
     1126                  only differ by the single "s" in the scheme name. They are different services governed by different authorities. However,
     1127                  some extensions to HTTP that apply to entire host domains, such as the Cookie protocol, do allow one service to effect communication
     1128                  with the other services based on host domain matching.
     1129               </p>
     1130               <p id="rfc.section.2.6.2.p.6">The process for authoritative access to an "https" identified resource is defined in <a href="#RFC2818" id="rfc.xref.RFC2818.1"><cite title="HTTP Over TLS">[RFC2818]</cite></a>.
     1131               </p>
     1132            </div>
     1133            <div id="uri.comparison">
     1134               <h3 id="rfc.section.2.6.3"><a href="#rfc.section.2.6.3">2.6.3</a>&nbsp;<a href="#uri.comparison">http and https URI Normalization and Comparison</a></h3>
     1135               <p id="rfc.section.2.6.3.p.1">Since the "http" and "https" schemes conform to the URI generic syntax, such URIs are normalized and compared according to
     1136                  the algorithm defined in <a href="#RFC3986" id="rfc.xref.RFC3986.16"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-6">Section 6</a>, using the defaults described above for each scheme.
     1137               </p>
     1138               <p id="rfc.section.2.6.3.p.2">If the port is equal to the default port for a scheme, the normal form is to elide the port subcomponent. Likewise, an empty
     1139                  path component is equivalent to an absolute path of "/", so the normal form is to provide a path of "/" instead. The scheme
     1140                  and host are case-insensitive and normally provided in lowercase; all other components are compared in a case-sensitive manner.
     1141                  Characters other than those in the "reserved" set are equivalent to their percent-encoded octets (see <a href="#RFC3986" id="rfc.xref.RFC3986.17"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-2.1">Section 2.1</a>): the normal form is to not encode them.
     1142               </p>
     1143               <p id="rfc.section.2.6.3.p.3">For example, the following three URIs are equivalent:</p>
     1144               <div id="rfc.figure.u.24"></div><pre class="text">   http://example.com:80/~smith/home.html
    11161145   http://EXAMPLE.com/%7Esmith/home.html
    11171146   http://EXAMPLE.com:/%7esmith/home.html
    1118 </pre><p id="rfc.section.2.6.3.p.5"> <span class="comment" id="TODO-not-here">[<a href="#TODO-not-here" class="smpl">TODO-not-here</a>: This paragraph does not belong here. --roy]</span> If path-abempty is the empty string (i.e., there is no slash "/" path separator following the authority), then the "http"
    1119          URI <em class="bcp14">MUST</em> be given as "/" when used as a request-target (<a href="#request-target" title="request-target">Section&nbsp;4.1.2</a>). If a proxy receives a host name which is not a fully qualified domain name, it <em class="bcp14">MAY</em> add its domain to the host name it received. If a proxy receives a fully qualified domain name, the proxy <em class="bcp14">MUST NOT</em> change the host name.
    1120       </p>
    1121       <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;<a id="http.message" href="#http.message">HTTP Message</a></h1>
    1122       <div id="rfc.iref.h.3"></div>
    1123       <div id="rfc.iref.h.4"></div>
    1124       <div id="rfc.iref.h.5"></div>
    1125       <p id="rfc.section.3.p.1">All HTTP/1.1 messages consist of a start-line followed by a sequence of characters in a format similar to the Internet Message
    1126          Format <a href="#RFC5322" id="rfc.xref.RFC5322.2"><cite title="Internet Message Format">[RFC5322]</cite></a>: zero or more header fields (collectively referred to as the "headers" or the "header section"), an empty line indicating
    1127          the end of the header section, and an optional message-body.
    1128       </p>
    1129       <p id="rfc.section.3.p.2">An HTTP message can either be a request from client to server or a response from server to client. Syntactically, the two
    1130          types of message differ only in the start-line, which is either a Request-Line (for requests) or a Status-Line (for responses),
    1131          and in the algorithm for determining the length of the message-body (<a href="#message.body" title="Message Body">Section&nbsp;3.3</a>). In theory, a client could receive requests and a server could receive responses, distinguishing them by their different
    1132          start-line formats, but in practice servers are implemented to only expect a request (a response is interpreted as an unknown
    1133          or invalid request method) and clients are implemented to only expect a response.
    1134       </p>
    1135       <div id="rfc.figure.u.25"></div><pre class="inline"><span id="rfc.iref.g.36"></span>  <a href="#http.message" class="smpl">HTTP-message</a>    = <a href="#http.message" class="smpl">start-line</a>
     1147</pre><p id="rfc.section.2.6.3.p.5"><span class="comment" id="TODO-not-here">[<a href="#TODO-not-here" class="smpl">TODO-not-here</a>: This paragraph does not belong here. --roy]</span> If path-abempty is the empty string (i.e., there is no slash "/" path separator following the authority), then the "http"
     1148                  URI <em class="bcp14">MUST</em> be given as "/" when used as a request-target (<a href="#request-target" title="request-target">Section&nbsp;4.1.2</a>). If a proxy receives a host name which is not a fully qualified domain name, it <em class="bcp14">MAY</em> add its domain to the host name it received. If a proxy receives a fully qualified domain name, the proxy <em class="bcp14">MUST NOT</em> change the host name.
     1149               </p>
     1150            </div>
     1151         </div>
     1152      </div>
     1153      <div id="http.message">
     1154         <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;<a href="#http.message">HTTP Message</a></h1>
     1155         <div id="rfc.iref.h.3"></div>
     1156         <div id="rfc.iref.h.4"></div>
     1157         <div id="rfc.iref.h.5"></div>
     1158         <p id="rfc.section.3.p.1">All HTTP/1.1 messages consist of a start-line followed by a sequence of characters in a format similar to the Internet Message
     1159            Format <a href="#RFC5322" id="rfc.xref.RFC5322.2"><cite title="Internet Message Format">[RFC5322]</cite></a>: zero or more header fields (collectively referred to as the "headers" or the "header section"), an empty line indicating
     1160            the end of the header section, and an optional message-body.
     1161         </p>
     1162         <p id="rfc.section.3.p.2">An HTTP message can either be a request from client to server or a response from server to client. Syntactically, the two
     1163            types of message differ only in the start-line, which is either a Request-Line (for requests) or a Status-Line (for responses),
     1164            and in the algorithm for determining the length of the message-body (<a href="#message.body" title="Message Body">Section&nbsp;3.3</a>). In theory, a client could receive requests and a server could receive responses, distinguishing them by their different
     1165            start-line formats, but in practice servers are implemented to only expect a request (a response is interpreted as an unknown
     1166            or invalid request method) and clients are implemented to only expect a response.
     1167         </p>
     1168         <div id="rfc.figure.u.25"></div><pre class="inline"><span id="rfc.iref.g.36"></span>  <a href="#http.message" class="smpl">HTTP-message</a>    = <a href="#http.message" class="smpl">start-line</a>
    11361169                    *( <a href="#header.fields" class="smpl">header-field</a> <a href="#core.rules" class="smpl">CRLF</a> )
    11371170                    <a href="#core.rules" class="smpl">CRLF</a>
     
    11391172  <a href="#http.message" class="smpl">start-line</a>      = <a href="#request-line" class="smpl">Request-Line</a> / <a href="#status-line" class="smpl">Status-Line</a>
    11401173</pre><p id="rfc.section.3.p.4">Whitespace (WSP) <em class="bcp14">MUST NOT</em> be sent between the start-line and the first header field. The presence of whitespace might be an attempt to trick a noncompliant
    1141          implementation of HTTP into ignoring that field or processing the next line as a new request, either of which might result
    1142          in security issues when implementations within the request chain interpret the same message differently. HTTP/1.1 servers <em class="bcp14">MUST</em> reject such a message with a 400 (Bad Request) response.
    1143       </p>
    1144       <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a>&nbsp;<a id="message.robustness" href="#message.robustness">Message Parsing Robustness</a></h2>
    1145       <p id="rfc.section.3.1.p.1">In the interest of robustness, servers <em class="bcp14">SHOULD</em> ignore at least one empty line received where a Request-Line is expected. In other words, if the server is reading the protocol
    1146          stream at the beginning of a message and receives a CRLF first, it <em class="bcp14">SHOULD</em> ignore the CRLF.
    1147       </p>
    1148       <p id="rfc.section.3.1.p.2">Some old HTTP/1.0 client implementations generate an extra CRLF after a POST request as a lame workaround for some early server
    1149          applications that failed to read message-body content that was not terminated by a line-ending. An HTTP/1.1 client <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
    1150          the client <em class="bcp14">MUST</em> include the terminating CRLF octets as part of the message-body length.
    1151       </p>
    1152       <p id="rfc.section.3.1.p.3">The normal procedure for parsing an HTTP message is to read the start-line into a structure, read each header field into a
    1153          hash table by field name until the empty line, and then use the parsed data to determine if a message-body is expected. If
    1154          a message-body has been indicated, then it is read as a stream until an amount of octets equal to the message-body length
    1155          is read or the connection is closed. Care must be taken to parse an HTTP message as a sequence of octets in an encoding that
    1156          is a superset of US-ASCII. Attempting to parse HTTP as a stream of Unicode characters in a character encoding like UTF-16
    1157          might introduce security flaws due to the differing ways that such parsers interpret invalid characters.
    1158       </p>
    1159       <p id="rfc.section.3.1.p.4">HTTP allows the set of defined header fields to be extended without changing the protocol version (see <a href="#header.field.registration" title="Header Field Registration">Section&nbsp;10.1</a>). However, such fields might not be recognized by a downstream recipient and might be stripped by non-transparent intermediaries.
    1160          Unrecognized header fields <em class="bcp14">MUST</em> be forwarded by transparent proxies and <em class="bcp14">SHOULD</em> be ignored by a recipient.
    1161       </p>
    1162       <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a>&nbsp;<a id="header.fields" href="#header.fields">Header Fields</a></h2>
    1163       <p id="rfc.section.3.2.p.1">Each HTTP header field consists of a case-insensitive field name followed by a colon (":"), optional whitespace, and the field
    1164          value.
    1165       </p>
    1166       <div id="rfc.figure.u.26"></div><pre class="inline"><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>  <a href="#header.fields" class="smpl">header-field</a>   = <a href="#header.fields" class="smpl">field-name</a> ":" <a href="#rule.whitespace" class="smpl">OWS</a> [ <a href="#header.fields" class="smpl">field-value</a> ] <a href="#rule.whitespace" class="smpl">OWS</a>
     1174            implementation of HTTP into ignoring that field or processing the next line as a new request, either of which might result
     1175            in security issues when implementations within the request chain interpret the same message differently. HTTP/1.1 servers <em class="bcp14">MUST</em> reject such a message with a 400 (Bad Request) response.
     1176         </p>
     1177         <div id="message.robustness">
     1178            <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a>&nbsp;<a href="#message.robustness">Message Parsing Robustness</a></h2>
     1179            <p id="rfc.section.3.1.p.1">In the interest of robustness, servers <em class="bcp14">SHOULD</em> ignore at least one empty line received where a Request-Line is expected. In other words, if the server is reading the protocol
     1180               stream at the beginning of a message and receives a CRLF first, it <em class="bcp14">SHOULD</em> ignore the CRLF.
     1181            </p>
     1182            <p id="rfc.section.3.1.p.2">Some old HTTP/1.0 client implementations generate an extra CRLF after a POST request as a lame workaround for some early server
     1183               applications that failed to read message-body content that was not terminated by a line-ending. An HTTP/1.1 client <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
     1184               the client <em class="bcp14">MUST</em> include the terminating CRLF octets as part of the message-body length.
     1185            </p>
     1186            <p id="rfc.section.3.1.p.3">The normal procedure for parsing an HTTP message is to read the start-line into a structure, read each header field into a
     1187               hash table by field name until the empty line, and then use the parsed data to determine if a message-body is expected. If
     1188               a message-body has been indicated, then it is read as a stream until an amount of octets equal to the message-body length
     1189               is read or the connection is closed. Care must be taken to parse an HTTP message as a sequence of octets in an encoding that
     1190               is a superset of US-ASCII. Attempting to parse HTTP as a stream of Unicode characters in a character encoding like UTF-16
     1191               might introduce security flaws due to the differing ways that such parsers interpret invalid characters.
     1192            </p>
     1193            <p id="rfc.section.3.1.p.4">HTTP allows the set of defined header fields to be extended without changing the protocol version (see <a href="#header.field.registration" title="Header Field Registration">Section&nbsp;10.1</a>). However, such fields might not be recognized by a downstream recipient and might be stripped by non-transparent intermediaries.
     1194               Unrecognized header fields <em class="bcp14">MUST</em> be forwarded by transparent proxies and <em class="bcp14">SHOULD</em> be ignored by a recipient.
     1195            </p>
     1196         </div>
     1197         <div id="header.fields">
     1198            <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a>&nbsp;<a href="#header.fields">Header Fields</a></h2>
     1199            <p id="rfc.section.3.2.p.1">Each HTTP header field consists of a case-insensitive field name followed by a colon (":"), optional whitespace, and the field
     1200               value.
     1201            </p>
     1202            <div id="rfc.figure.u.26"></div><pre class="inline"><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>  <a href="#header.fields" class="smpl">header-field</a>   = <a href="#header.fields" class="smpl">field-name</a> ":" <a href="#rule.whitespace" class="smpl">OWS</a> [ <a href="#header.fields" class="smpl">field-value</a> ] <a href="#rule.whitespace" class="smpl">OWS</a>
    11671203  <a href="#header.fields" class="smpl">field-name</a>     = <a href="#rule.token.separators" class="smpl">token</a>
    11681204  <a href="#header.fields" class="smpl">field-value</a>    = *( <a href="#header.fields" class="smpl">field-content</a> / <a href="#rule.whitespace" class="smpl">OWS</a> )
    11691205  <a href="#header.fields" class="smpl">field-content</a>  = *( <a href="#core.rules" class="smpl">WSP</a> / <a href="#core.rules" class="smpl">VCHAR</a> / <a href="#rule.quoted-string" class="smpl">obs-text</a> )
    11701206</pre><p id="rfc.section.3.2.p.3">No whitespace is allowed between the header field name and colon. For security reasons, any request message received containing
    1171          such whitespace <em class="bcp14">MUST</em> be rejected with a response code of 400 (Bad Request). A proxy <em class="bcp14">MUST</em> remove any such whitespace from a response message before forwarding the message downstream.
    1172       </p>
    1173       <p id="rfc.section.3.2.p.4">A field value <em class="bcp14">MAY</em> be preceded by optional whitespace (OWS); a single SP is preferred. The field value does not include any leading or trailing
    1174          white space: OWS occurring before the first non-whitespace character of the field value or after the last non-whitespace character
    1175          of the field value is ignored and <em class="bcp14">SHOULD</em> be removed before further processing (as this does not change the meaning of the header field).
    1176       </p>
    1177       <p id="rfc.section.3.2.p.5">The order in which header fields with differing field names are received is not significant. However, it is "good practice"
    1178          to send header fields that contain control data first, such as Host on requests and Date on responses, so that implementations
    1179          can decide when not to handle a message as early as possible. A server <em class="bcp14">MUST</em> wait until the entire header section is received before interpreting a request message, since later header fields might include
    1180          conditionals, authentication credentials, or deliberately misleading duplicate header fields that would impact request processing.
    1181       </p>
    1182       <p id="rfc.section.3.2.p.6">Multiple header fields with the same field name <em class="bcp14">MUST NOT</em> be sent in a message unless the entire field value for that header field is defined as a comma-separated list [i.e., #(values)].
    1183          Multiple header fields with the same field name can be combined into one "field-name: field-value" pair, without changing
    1184          the semantics of the message, by appending each subsequent field value to the combined field value in order, separated by
    1185          a comma. The order in which header fields with the same field name are received is therefore significant to the interpretation
    1186          of the combined field value; a proxy <em class="bcp14">MUST NOT</em> change the order of these field values when forwarding a message.
    1187       </p>
    1188       <div class="note" id="rfc.section.3.2.p.7">
    1189          <p> <b>Note:</b> The "Set-Cookie" header as implemented in practice (as opposed to how it is specified in <a href="#RFC2109" id="rfc.xref.RFC2109.1"><cite title="HTTP State Management Mechanism">[RFC2109]</cite></a>) can occur multiple times, but does not use the list syntax, and thus cannot be combined into a single line. (See Appendix
    1190             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.) Also note that the Set-Cookie2 header specified in <a href="#RFC2965" id="rfc.xref.RFC2965.1"><cite title="HTTP State Management Mechanism">[RFC2965]</cite></a> does not share this problem.
    1191          </p>
    1192       </div>
    1193       <p id="rfc.section.3.2.p.8">Historically, HTTP header field values could be extended over multiple lines by preceding each extra line with at least one
    1194          space or horizontal tab character (line folding). This specification deprecates such line folding except within the message/http
    1195          media type (<a href="#internet.media.type.message.http" title="Internet Media Type message/http">Section&nbsp;10.3.1</a>). HTTP/1.1 senders <em class="bcp14">MUST NOT</em> produce messages that include line folding (i.e., that contain any field-content that matches the obs-fold rule) unless the
    1196          message is intended for packaging within the message/http media type. HTTP/1.1 recipients <em class="bcp14">SHOULD</em> accept line folding and replace any embedded obs-fold whitespace with a single SP prior to interpreting the field value or
    1197          forwarding the message downstream.
    1198       </p>
    1199       <p id="rfc.section.3.2.p.9">Historically, HTTP has allowed field content with text in the ISO-8859-1 <a href="#ISO-8859-1" id="rfc.xref.ISO-8859-1.1"><cite title="Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1">[ISO-8859-1]</cite></a> character encoding and supported other character sets only through use of <a href="#RFC2047" id="rfc.xref.RFC2047.1"><cite title="MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text">[RFC2047]</cite></a> encoding. In practice, most HTTP header field values use only a subset of the US-ASCII character encoding <a href="#USASCII" id="rfc.xref.USASCII.2"><cite title="Coded Character Set -- 7-bit American Standard Code for Information Interchange">[USASCII]</cite></a>. Newly defined header fields <em class="bcp14">SHOULD</em> limit their field values to US-ASCII characters. Recipients <em class="bcp14">SHOULD</em> treat other (obs-text) octets in field content as opaque data.
    1200       </p>
    1201       <div id="rule.comment">
    1202          <p id="rfc.section.3.2.p.10">    Comments can be included in some HTTP header fields by surrounding the comment text with parentheses. Comments are only allowed
    1203             in fields containing "comment" as part of their field value definition.
    1204          </p>
    1205       </div>
    1206       <div id="rfc.figure.u.27"></div><pre class="inline"><span id="rfc.iref.g.41"></span><span id="rfc.iref.g.42"></span>  <a href="#rule.comment" class="smpl">comment</a>        = "(" *( <a href="#rule.comment" class="smpl">ctext</a> / <a href="#rule.quoted-cpair" class="smpl">quoted-cpair</a> / <a href="#rule.comment" class="smpl">comment</a> ) ")"
     1207               such whitespace <em class="bcp14">MUST</em> be rejected with a response code of 400 (Bad Request). A proxy <em class="bcp14">MUST</em> remove any such whitespace from a response message before forwarding the message downstream.
     1208            </p>
     1209            <p id="rfc.section.3.2.p.4">A field value <em class="bcp14">MAY</em> be preceded by optional whitespace (OWS); a single SP is preferred. The field value does not include any leading or trailing
     1210               white space: OWS occurring before the first non-whitespace character of the field value or after the last non-whitespace character
     1211               of the field value is ignored and <em class="bcp14">SHOULD</em> be removed before further processing (as this does not change the meaning of the header field).
     1212            </p>
     1213            <p id="rfc.section.3.2.p.5">The order in which header fields with differing field names are received is not significant. However, it is "good practice"
     1214               to send header fields that contain control data first, such as Host on requests and Date on responses, so that implementations
     1215               can decide when not to handle a message as early as possible. A server <em class="bcp14">MUST</em> wait until the entire header section is received before interpreting a request message, since later header fields might include
     1216               conditionals, authentication credentials, or deliberately misleading duplicate header fields that would impact request processing.
     1217            </p>
     1218            <p id="rfc.section.3.2.p.6">Multiple header fields with the same field name <em class="bcp14">MUST NOT</em> be sent in a message unless the entire field value for that header field is defined as a comma-separated list [i.e., #(values)].
     1219               Multiple header fields with the same field name can be combined into one "field-name: field-value" pair, without changing
     1220               the semantics of the message, by appending each subsequent field value to the combined field value in order, separated by
     1221               a comma. The order in which header fields with the same field name are received is therefore significant to the interpretation
     1222               of the combined field value; a proxy <em class="bcp14">MUST NOT</em> change the order of these field values when forwarding a message.
     1223            </p>
     1224            <div class="note" id="rfc.section.3.2.p.7">
     1225               <p><b>Note:</b> The "Set-Cookie" header as implemented in practice (as opposed to how it is specified in <a href="#RFC2109" id="rfc.xref.RFC2109.1"><cite title="HTTP State Management Mechanism">[RFC2109]</cite></a>) can occur multiple times, but does not use the list syntax, and thus cannot be combined into a single line. (See Appendix
     1226                  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.) Also note that the Set-Cookie2 header specified in <a href="#RFC2965" id="rfc.xref.RFC2965.1"><cite title="HTTP State Management Mechanism">[RFC2965]</cite></a> does not share this problem.
     1227               </p>
     1228            </div>
     1229            <p id="rfc.section.3.2.p.8">Historically, HTTP header field values could be extended over multiple lines by preceding each extra line with at least one
     1230               space or horizontal tab character (line folding). This specification deprecates such line folding except within the message/http
     1231               media type (<a href="#internet.media.type.message.http" title="Internet Media Type message/http">Section&nbsp;10.3.1</a>). HTTP/1.1 senders <em class="bcp14">MUST NOT</em> produce messages that include line folding (i.e., that contain any field-content that matches the obs-fold rule) unless the
     1232               message is intended for packaging within the message/http media type. HTTP/1.1 recipients <em class="bcp14">SHOULD</em> accept line folding and replace any embedded obs-fold whitespace with a single SP prior to interpreting the field value or
     1233               forwarding the message downstream.
     1234            </p>
     1235            <p id="rfc.section.3.2.p.9">Historically, HTTP has allowed field content with text in the ISO-8859-1 <a href="#ISO-8859-1" id="rfc.xref.ISO-8859-1.1"><cite title="Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1">[ISO-8859-1]</cite></a> character encoding and supported other character sets only through use of <a href="#RFC2047" id="rfc.xref.RFC2047.1"><cite title="MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text">[RFC2047]</cite></a> encoding. In practice, most HTTP header field values use only a subset of the US-ASCII character encoding <a href="#USASCII" id="rfc.xref.USASCII.2"><cite title="Coded Character Set -- 7-bit American Standard Code for Information Interchange">[USASCII]</cite></a>. Newly defined header fields <em class="bcp14">SHOULD</em> limit their field values to US-ASCII characters. Recipients <em class="bcp14">SHOULD</em> treat other (obs-text) octets in field content as opaque data.
     1236            </p>
     1237            <div id="rule.comment">
     1238               <p id="rfc.section.3.2.p.10">  Comments can be included in some HTTP header fields by surrounding the comment text with parentheses. Comments are only allowed
     1239                  in fields containing "comment" as part of their field value definition.
     1240               </p>
     1241            </div>
     1242            <div id="rfc.figure.u.27"></div><pre class="inline"><span id="rfc.iref.g.41"></span><span id="rfc.iref.g.42"></span>  <a href="#rule.comment" class="smpl">comment</a>        = "(" *( <a href="#rule.comment" class="smpl">ctext</a> / <a href="#rule.quoted-cpair" class="smpl">quoted-cpair</a> / <a href="#rule.comment" class="smpl">comment</a> ) ")"
    12071243  <a href="#rule.comment" class="smpl">ctext</a>          = <a href="#rule.whitespace" class="smpl">OWS</a> / %x21-27 / %x2A-5B / %x5D-7E / <a href="#rule.quoted-string" class="smpl">obs-text</a>
    12081244                 ; <a href="#rule.whitespace" class="smpl">OWS</a> / &lt;<a href="#core.rules" class="smpl">VCHAR</a> except "(", ")", and "\"&gt; / <a href="#rule.quoted-string" class="smpl">obs-text</a>
    12091245</pre><div id="rule.quoted-cpair">
    1210          <p id="rfc.section.3.2.p.12"> The backslash character ("\") can be used as a single-character quoting mechanism within comment constructs:</p>
    1211       </div>
    1212       <div id="rfc.figure.u.28"></div><pre class="inline"><span id="rfc.iref.g.43"></span>  <a href="#rule.quoted-cpair" class="smpl">quoted-cpair</a>    = "\" ( <a href="#core.rules" class="smpl">WSP</a> / <a href="#core.rules" class="smpl">VCHAR</a> / <a href="#rule.quoted-string" class="smpl">obs-text</a> )
     1246               <p id="rfc.section.3.2.p.12"> The backslash character ("\") can be used as a single-character quoting mechanism within comment constructs:</p>
     1247            </div>
     1248            <div id="rfc.figure.u.28"></div><pre class="inline"><span id="rfc.iref.g.43"></span>  <a href="#rule.quoted-cpair" class="smpl">quoted-cpair</a>    = "\" ( <a href="#core.rules" class="smpl">WSP</a> / <a href="#core.rules" class="smpl">VCHAR</a> / <a href="#rule.quoted-string" class="smpl">obs-text</a> )
    12131249</pre><p id="rfc.section.3.2.p.14">Producers <em class="bcp14">SHOULD NOT</em> escape characters that do not require escaping (i.e., other than the backslash character "\" and the parentheses "(" and ")").
    1214       </p>
    1215       <h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3</a>&nbsp;<a id="message.body" href="#message.body">Message Body</a></h2>
    1216       <p id="rfc.section.3.3.p.1">The message-body (if any) of an HTTP message is used to carry the payload body associated with the request or response.</p>
    1217       <div id="rfc.figure.u.29"></div><pre class="inline"><span id="rfc.iref.g.44"></span>  <a href="#message.body" class="smpl">message-body</a> = *OCTET
     1250            </p>
     1251         </div>
     1252         <div id="message.body">
     1253            <h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3</a>&nbsp;<a href="#message.body">Message Body</a></h2>
     1254            <p id="rfc.section.3.3.p.1">The message-body (if any) of an HTTP message is used to carry the payload body associated with the request or response.</p>
     1255            <div id="rfc.figure.u.29"></div><pre class="inline"><span id="rfc.iref.g.44"></span>  <a href="#message.body" class="smpl">message-body</a> = *OCTET
    12181256</pre><p id="rfc.section.3.3.p.3">The message-body differs from the payload body only when a transfer-coding has been applied, as indicated by the Transfer-Encoding
    1219          header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.1" title="Transfer-Encoding">Section&nbsp;9.7</a>). When one or more transfer-codings are applied to a payload in order to form the message-body, the Transfer-Encoding header
    1220          field <em class="bcp14">MUST</em> contain the list of transfer-codings applied. Transfer-Encoding is a property of the message, not of the payload, and thus <em class="bcp14">MAY</em> be added or removed by any implementation along the request/response chain under the constraints found in <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;6.2</a>.
    1221       </p>
    1222       <p id="rfc.section.3.3.p.4">The rules for when a message-body is allowed in a message differ for requests and responses.</p>
    1223       <p id="rfc.section.3.3.p.5">The presence of a message-body in a request is signaled by the inclusion of a Content-Length or Transfer-Encoding header field
    1224          in the request's header fields, even if the request method does not define any use for a message-body. This allows the request
    1225          message framing algorithm to be independent of method semantics.
    1226       </p>
    1227       <p id="rfc.section.3.3.p.6">For response messages, whether or not a message-body is included with a message is dependent on both the request method and
    1228          the response status code (<a href="#status.code.and.reason.phrase" title="Status Code and Reason Phrase">Section&nbsp;5.1.1</a>). Responses to the HEAD request method never include a message-body because the associated response header fields (e.g.,
    1229          Transfer-Encoding, Content-Length, etc.) only indicate what their values would have been if the method had been GET. All 1xx
    1230          (Informational), 204 (No Content), and 304 (Not Modified) responses <em class="bcp14">MUST NOT</em> include a message-body. All other responses do include a message-body, although the body <em class="bcp14">MAY</em> be of zero length.
    1231       </p>
    1232       <p id="rfc.section.3.3.p.7">The length of the message-body is determined by one of the following (in order of precedence):</p>
    1233       <p id="rfc.section.3.3.p.8"> </p>
    1234       <ol>
    1235          <li>
    1236             <p>Any response to a HEAD request and any response with a status code of 100-199, 204, or 304 is always terminated by the first
    1237                empty line after the header fields, regardless of the header fields present in the message, and thus cannot contain a message-body.
    1238             </p>
    1239          </li>
    1240          <li>
    1241             <p>If a Transfer-Encoding header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.2" title="Transfer-Encoding">Section&nbsp;9.7</a>) is present and the "chunked" transfer-coding (<a href="#transfer.codings" title="Transfer Codings">Section&nbsp;6.2</a>) is the final encoding, the message-body length is determined by reading and decoding the chunked data until the transfer-coding
    1242                indicates the data is complete.
    1243             </p>
    1244             <p>If a Transfer-Encoding header field is present in a response and the "chunked" transfer-coding is not the final encoding,
    1245                the message-body length is determined by reading the connection until it is closed by the server. If a Transfer-Encoding header
    1246                field is present in a request and the "chunked" transfer-coding is not the final encoding, the message-body length cannot
    1247                be determined reliably; the server <em class="bcp14">MUST</em> respond with the 400 (Bad Request) status code and then close the connection.
    1248             </p>
    1249             <p>If a message is received with both a Transfer-Encoding header field and a Content-Length header field, the Transfer-Encoding
    1250                overrides the Content-Length. Such a message might indicate an attempt to perform request or response smuggling (bypass of
    1251                security-related checks on message routing or content) and thus ought to be handled as an error. The provided Content-Length <em class="bcp14">MUST</em> be removed, prior to forwarding the message downstream, or replaced with the real message-body length after the transfer-coding
    1252                is decoded.
    1253             </p>
    1254          </li>
    1255          <li>
    1256             <p>If a message is received without Transfer-Encoding and with either multiple Content-Length header fields or a single Content-Length
    1257                header field with an invalid value, then the message framing is invalid and <em class="bcp14">MUST</em> be treated as an error to prevent request or response smuggling. If this is a request message, the server <em class="bcp14">MUST</em> respond with a 400 (Bad Request) status code and then close the connection. If this is a response message received by a proxy
    1258                or gateway, the proxy or gateway <em class="bcp14">MUST</em> discard the received response, send a 502 (Bad Gateway) status code as its downstream response, and then close the connection.
    1259                If this is a response message received by a user-agent, the message-body length is determined by reading the connection until
    1260                it is closed; an error <em class="bcp14">SHOULD</em> be indicated to the user.
    1261             </p>
    1262          </li>
    1263          <li>
    1264             <p>If a valid Content-Length header field (<a href="#header.content-length" id="rfc.xref.header.content-length.1" title="Content-Length">Section&nbsp;9.2</a>) is present without Transfer-Encoding, its decimal value defines the message-body length in octets. If the actual number
    1265                of octets sent in the message is less than the indicated Content-Length, the recipient <em class="bcp14">MUST</em> consider the message to be incomplete and treat the connection as no longer usable. If the actual number of octets sent in
    1266                the message is more than the indicated Content-Length, the recipient <em class="bcp14">MUST</em> only process the message-body up to the field value's number of octets; the remainder of the message <em class="bcp14">MUST</em> either be discarded or treated as the next message in a pipeline. For the sake of robustness, a user-agent <em class="bcp14">MAY</em> attempt to detect and correct such an error in message framing if it is parsing the response to the last request on on a connection
    1267                and the connection has been closed by the server.
    1268             </p>
    1269          </li>
    1270          <li>
    1271             <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>
    1272          </li>
    1273          <li>
    1274             <p>Otherwise, this is a response message without a declared message-body length, so the message-body length is determined by
    1275                the number of octets received prior to the server closing the connection.
    1276             </p>
    1277          </li>
    1278       </ol>
    1279       <p id="rfc.section.3.3.p.9">Since there is no way to distinguish a successfully completed, close-delimited message from a partially-received message interrupted
    1280          by network failure, implementations <em class="bcp14">SHOULD</em> use encoding or length-delimited messages whenever possible. The close-delimiting feature exists primarily for backwards compatibility
    1281          with HTTP/1.0.
    1282       </p>
    1283       <p id="rfc.section.3.3.p.10">A server <em class="bcp14">MAY</em> reject a request that contains a message-body but not a Content-Length by responding with 411 (Length Required).
    1284       </p>
    1285       <p id="rfc.section.3.3.p.11">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 Content-Length header field if the message-body length is known in advance, rather than the "chunked" encoding,
    1286          since some existing services respond to "chunked" with a 411 (Length Required) status code even though they understand the
    1287          chunked encoding. This is typically because such services are implemented via a gateway that requires a content-length in
    1288          advance of being called and the server is unable or unwilling to buffer the entire request before processing.
    1289       </p>
    1290       <p id="rfc.section.3.3.p.12">A client that sends a request containing a message-body <em class="bcp14">MUST</em> include a valid Content-Length header field if it does not know the server will handle HTTP/1.1 (or later) requests; such
    1291          knowledge can be in the form of specific user configuration or by remembering the version of a prior received response.
    1292       </p>
    1293       <p id="rfc.section.3.3.p.13">Request messages that are prematurely terminated, possibly due to a cancelled connection or a server-imposed time-out exception, <em class="bcp14">MUST</em> result in closure of the connection; sending an HTTP/1.1 error response prior to closing the connection is <em class="bcp14">OPTIONAL</em>. Response messages that are prematurely terminated, usually by closure of the connection prior to receiving the expected
    1294          number of octets or by failure to decode a transfer-encoded message-body, <em class="bcp14">MUST</em> be recorded as incomplete. A user agent <em class="bcp14">MUST NOT</em> render an incomplete response message-body as if it were complete (i.e., some indication must be given to the user that an
    1295          error occurred). Cache requirements for incomplete responses are defined in <a href="p6-cache.html#errors.or.incomplete.response.cache.behavior" title="Storing Partial and Incomplete Responses">Section 2.1.1</a> of <a href="#Part6" id="rfc.xref.Part6.5"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>.
    1296       </p>
    1297       <p id="rfc.section.3.3.p.14">A server <em class="bcp14">MUST</em> read the entire request message-body or close the connection after sending its response, since otherwise the remaining data
    1298          on a persistent connection would be misinterpreted as the next request. Likewise, a client <em class="bcp14">MUST</em> read the entire response message-body if it intends to reuse the same connection for a subsequent request. Pipelining multiple
    1299          requests on a connection is described in <a href="#pipelining" title="Pipelining">Section&nbsp;7.1.2.2</a>.
    1300       </p>
    1301       <h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a>&nbsp;<a id="general.header.fields" href="#general.header.fields">General Header Fields</a></h2>
    1302       <p id="rfc.section.3.4.p.1">There are a few header fields which have general applicability for both request and response messages, but which do not apply
    1303          to the payload being transferred. These header fields apply only to the message being transmitted.
    1304       </p>
    1305       <div id="rfc.figure.u.30"></div><pre class="inline"><span id="rfc.iref.g.45"></span>  <a href="#general.header.fields" class="smpl">general-header</a> = <a href="#abnf.dependencies" class="smpl">Cache-Control</a>            ; <a href="#Part6" id="rfc.xref.Part6.6"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>, <a href="p6-cache.html#header.cache-control" title="Cache-Control">Section 3.2</a>
     1257               header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.1" title="Transfer-Encoding">Section&nbsp;9.7</a>). When one or more transfer-codings are applied to a payload in order to form the message-body, the Transfer-Encoding header
     1258               field <em class="bcp14">MUST</em> contain the list of transfer-codings applied. Transfer-Encoding is a property of the message, not of the payload, and thus <em class="bcp14">MAY</em> be added or removed by any implementation along the request/response chain under the constraints found in <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;6.2</a>.
     1259            </p>
     1260            <p id="rfc.section.3.3.p.4">The rules for when a message-body is allowed in a message differ for requests and responses.</p>
     1261            <p id="rfc.section.3.3.p.5">The presence of a message-body in a request is signaled by the inclusion of a Content-Length or Transfer-Encoding header field
     1262               in the request's header fields, even if the request method does not define any use for a message-body. This allows the request
     1263               message framing algorithm to be independent of method semantics.
     1264            </p>
     1265            <p id="rfc.section.3.3.p.6">For response messages, whether or not a message-body is included with a message is dependent on both the request method and
     1266               the response status code (<a href="#status.code.and.reason.phrase" title="Status Code and Reason Phrase">Section&nbsp;5.1.1</a>). Responses to the HEAD request method never include a message-body because the associated response header fields (e.g.,
     1267               Transfer-Encoding, Content-Length, etc.) only indicate what their values would have been if the method had been GET. All 1xx
     1268               (Informational), 204 (No Content), and 304 (Not Modified) responses <em class="bcp14">MUST NOT</em> include a message-body. All other responses do include a message-body, although the body <em class="bcp14">MAY</em> be of zero length.
     1269            </p>
     1270            <p id="rfc.section.3.3.p.7">The length of the message-body is determined by one of the following (in order of precedence):</p>
     1271            <p id="rfc.section.3.3.p.8"></p>
     1272            <ol>
     1273               <li>
     1274                  <p>Any response to a HEAD request and any response with a status code of 100-199, 204, or 304 is always terminated by the first
     1275                     empty line after the header fields, regardless of the header fields present in the message, and thus cannot contain a message-body.
     1276                  </p>
     1277               </li>
     1278               <li>
     1279                  <p>If a Transfer-Encoding header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.2" title="Transfer-Encoding">Section&nbsp;9.7</a>) is present and the "chunked" transfer-coding (<a href="#transfer.codings" title="Transfer Codings">Section&nbsp;6.2</a>) is the final encoding, the message-body length is determined by reading and decoding the chunked data until the transfer-coding
     1280                     indicates the data is complete.
     1281                  </p>
     1282                  <p>If a Transfer-Encoding header field is present in a response and the "chunked" transfer-coding is not the final encoding,
     1283                     the message-body length is determined by reading the connection until it is closed by the server. If a Transfer-Encoding header
     1284                     field is present in a request and the "chunked" transfer-coding is not the final encoding, the message-body length cannot
     1285                     be determined reliably; the server <em class="bcp14">MUST</em> respond with the 400 (Bad Request) status code and then close the connection.
     1286                  </p>
     1287                  <p>If a message is received with both a Transfer-Encoding header field and a Content-Length header field, the Transfer-Encoding
     1288                     overrides the Content-Length. Such a message might indicate an attempt to perform request or response smuggling (bypass of
     1289                     security-related checks on message routing or content) and thus ought to be handled as an error. The provided Content-Length <em class="bcp14">MUST</em> be removed, prior to forwarding the message downstream, or replaced with the real message-body length after the transfer-coding
     1290                     is decoded.
     1291                  </p>
     1292               </li>
     1293               <li>
     1294                  <p>If a message is received without Transfer-Encoding and with either multiple Content-Length header fields or a single Content-Length
     1295                     header field with an invalid value, then the message framing is invalid and <em class="bcp14">MUST</em> be treated as an error to prevent request or response smuggling. If this is a request message, the server <em class="bcp14">MUST</em> respond with a 400 (Bad Request) status code and then close the connection. If this is a response message received by a proxy
     1296                     or gateway, the proxy or gateway <em class="bcp14">MUST</em> discard the received response, send a 502 (Bad Gateway) status code as its downstream response, and then close the connection.
     1297                     If this is a response message received by a user-agent, the message-body length is determined by reading the connection until
     1298                     it is closed; an error <em class="bcp14">SHOULD</em> be indicated to the user.
     1299                  </p>
     1300               </li>
     1301               <li>
     1302                  <p>If a valid Content-Length header field (<a href="#header.content-length" id="rfc.xref.header.content-length.1" title="Content-Length">Section&nbsp;9.2</a>) is present without Transfer-Encoding, its decimal value defines the message-body length in octets. If the actual number
     1303                     of octets sent in the message is less than the indicated Content-Length, the recipient <em class="bcp14">MUST</em> consider the message to be incomplete and treat the connection as no longer usable. If the actual number of octets sent in
     1304                     the message is more than the indicated Content-Length, the recipient <em class="bcp14">MUST</em> only process the message-body up to the field value's number of octets; the remainder of the message <em class="bcp14">MUST</em> either be discarded or treated as the next message in a pipeline. For the sake of robustness, a user-agent <em class="bcp14">MAY</em> attempt to detect and correct such an error in message framing if it is parsing the response to the last request on on a connection
     1305                     and the connection has been closed by the server.
     1306                  </p>
     1307               </li>
     1308               <li>
     1309                  <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>
     1310               </li>
     1311               <li>
     1312                  <p>Otherwise, this is a response message without a declared message-body length, so the message-body length is determined by
     1313                     the number of octets received prior to the server closing the connection.
     1314                  </p>
     1315               </li>
     1316            </ol>
     1317            <p id="rfc.section.3.3.p.9">Since there is no way to distinguish a successfully completed, close-delimited message from a partially-received message interrupted
     1318               by network failure, implementations <em class="bcp14">SHOULD</em> use encoding or length-delimited messages whenever possible. The close-delimiting feature exists primarily for backwards compatibility
     1319               with HTTP/1.0.
     1320            </p>
     1321            <p id="rfc.section.3.3.p.10">A server <em class="bcp14">MAY</em> reject a request that contains a message-body but not a Content-Length by responding with 411 (Length Required).
     1322            </p>
     1323            <p id="rfc.section.3.3.p.11">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 Content-Length header field if the message-body length is known in advance, rather than the "chunked" encoding,
     1324               since some existing services respond to "chunked" with a 411 (Length Required) status code even though they understand the
     1325               chunked encoding. This is typically because such services are implemented via a gateway that requires a content-length in
     1326               advance of being called and the server is unable or unwilling to buffer the entire request before processing.
     1327            </p>
     1328            <p id="rfc.section.3.3.p.12">A client that sends a request containing a message-body <em class="bcp14">MUST</em> include a valid Content-Length header field if it does not know the server will handle HTTP/1.1 (or later) requests; such
     1329               knowledge can be in the form of specific user configuration or by remembering the version of a prior received response.
     1330            </p>
     1331            <p id="rfc.section.3.3.p.13">Request messages that are prematurely terminated, possibly due to a cancelled connection or a server-imposed time-out exception, <em class="bcp14">MUST</em> result in closure of the connection; sending an HTTP/1.1 error response prior to closing the connection is <em class="bcp14">OPTIONAL</em>. Response messages that are prematurely terminated, usually by closure of the connection prior to receiving the expected
     1332               number of octets or by failure to decode a transfer-encoded message-body, <em class="bcp14">MUST</em> be recorded as incomplete. A user agent <em class="bcp14">MUST NOT</em> render an incomplete response message-body as if it were complete (i.e., some indication must be given to the user that an
     1333               error occurred). Cache requirements for incomplete responses are defined in <a href="p6-cache.html#errors.or.incomplete.response.cache.behavior" title="Storing Partial and Incomplete Responses">Section 2.1.1</a> of <a href="#Part6" id="rfc.xref.Part6.5"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>.
     1334            </p>
     1335            <p id="rfc.section.3.3.p.14">A server <em class="bcp14">MUST</em> read the entire request message-body or close the connection after sending its response, since otherwise the remaining data
     1336               on a persistent connection would be misinterpreted as the next request. Likewise, a client <em class="bcp14">MUST</em> read the entire response message-body if it intends to reuse the same connection for a subsequent request. Pipelining multiple
     1337               requests on a connection is described in <a href="#pipelining" title="Pipelining">Section&nbsp;7.1.2.2</a>.
     1338            </p>
     1339         </div>
     1340         <div id="general.header.fields">
     1341            <h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a>&nbsp;<a href="#general.header.fields">General Header Fields</a></h2>
     1342            <p id="rfc.section.3.4.p.1">There are a few header fields which have general applicability for both request and response messages, but which do not apply
     1343               to the payload being transferred. These header fields apply only to the message being transmitted.
     1344            </p>
     1345            <div id="rfc.figure.u.30"></div><pre class="inline"><span id="rfc.iref.g.45"></span>  <a href="#general.header.fields" class="smpl">general-header</a> = <a href="#abnf.dependencies" class="smpl">Cache-Control</a>            ; <a href="#Part6" id="rfc.xref.Part6.6"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>, <a href="p6-cache.html#header.cache-control" title="Cache-Control">Section 3.2</a>
    13061346                 / <a href="#header.connection" class="smpl">Connection</a>               ; <a href="#header.connection" id="rfc.xref.header.connection.1" title="Connection">Section&nbsp;9.1</a>
    13071347                 / <a href="#header.date" class="smpl">Date</a>                     ; <a href="#header.date" id="rfc.xref.header.date.1" title="Date">Section&nbsp;9.3</a>
     
    13141354                 / <a href="#abnf.dependencies" class="smpl">MIME-Version</a>             ; <a href="#Part3" id="rfc.xref.Part3.3"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>, <a href="p3-payload.html#mime-version" title="MIME-Version">Appendix A.1</a>
    13151355</pre><p id="rfc.section.3.4.p.3">General-header field names can be extended reliably only in combination with a change in the protocol version. However, new
    1316          or experimental header fields might be given the semantics of general header fields if all parties in the communication recognize
    1317          them to be general-header fields.
    1318       </p>
    1319       <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a>&nbsp;<a id="request" href="#request">Request</a></h1>
    1320       <p id="rfc.section.4.p.1">A request message from a client to a server includes, within the first line of that message, the method to be applied to the
    1321          resource, the identifier of the resource, and the protocol version in use.
    1322       </p>
    1323       <div id="rfc.figure.u.31"></div><pre class="inline"><span id="rfc.iref.g.46"></span>  <a href="#request" class="smpl">Request</a>       = <a href="#request-line" class="smpl">Request-Line</a>              ; <a href="#request-line" title="Request-Line">Section&nbsp;4.1</a>
     1356               or experimental header fields might be given the semantics of general header fields if all parties in the communication recognize
     1357               them to be general-header fields.
     1358            </p>
     1359         </div>
     1360      </div>
     1361      <div id="request">
     1362         <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a>&nbsp;<a href="#request">Request</a></h1>
     1363         <p id="rfc.section.4.p.1">A request message from a client to a server includes, within the first line of that message, the method to be applied to the
     1364            resource, the identifier of the resource, and the protocol version in use.
     1365         </p>
     1366         <div id="rfc.figure.u.31"></div><pre class="inline"><span id="rfc.iref.g.46"></span>  <a href="#request" class="smpl">Request</a>       = <a href="#request-line" class="smpl">Request-Line</a>              ; <a href="#request-line" title="Request-Line">Section&nbsp;4.1</a>
    13241367                  *( <a href="#header.fields" class="smpl">header-field</a> <a href="#core.rules" class="smpl">CRLF</a> )    ; <a href="#header.fields" title="Header Fields">Section&nbsp;3.2</a>
    13251368                  <a href="#core.rules" class="smpl">CRLF</a>
    13261369                  [ <a href="#message.body" class="smpl">message-body</a> ]          ; <a href="#message.body" title="Message Body">Section&nbsp;3.3</a>
    1327 </pre><h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a>&nbsp;<a id="request-line" href="#request-line">Request-Line</a></h2>
    1328       <p id="rfc.section.4.1.p.1">The Request-Line begins with a method token, followed by the request-target and the protocol version, and ending with CRLF.
    1329          The elements are separated by SP characters. No CR or LF is allowed except in the final CRLF sequence.
    1330       </p>
    1331       <div id="rfc.figure.u.32"></div><pre class="inline"><span id="rfc.iref.g.47"></span>  <a href="#request-line" class="smpl">Request-Line</a>   = <a href="#method" class="smpl">Method</a> <a href="#core.rules" class="smpl">SP</a> <a href="#request-target" class="smpl">request-target</a> <a href="#core.rules" class="smpl">SP</a> <a href="#http.version" class="smpl">HTTP-Version</a> <a href="#core.rules" class="smpl">CRLF</a>
    1332 </pre><h3 id="rfc.section.4.1.1"><a href="#rfc.section.4.1.1">4.1.1</a>&nbsp;<a id="method" href="#method">Method</a></h3>
    1333       <p id="rfc.section.4.1.1.p.1">The Method token indicates the method to be performed on the resource identified by the request-target. The method is case-sensitive.</p>
    1334       <div id="rfc.figure.u.33"></div><pre class="inline"><span id="rfc.iref.g.48"></span><span id="rfc.iref.g.49"></span>  <a href="#method" class="smpl">Method</a>         = <a href="#rule.token.separators" class="smpl">token</a>
    1335 </pre><h3 id="rfc.section.4.1.2"><a href="#rfc.section.4.1.2">4.1.2</a>&nbsp;<a id="request-target" href="#request-target">request-target</a></h3>
    1336       <p id="rfc.section.4.1.2.p.1">The request-target identifies the resource upon which to apply the request.</p>
    1337       <div id="rfc.figure.u.34"></div><pre class="inline"><span id="rfc.iref.g.50"></span>  <a href="#request-target" class="smpl">request-target</a> = "*"
     1370</pre><div id="request-line">
     1371            <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a>&nbsp;<a href="#request-line">Request-Line</a></h2>
     1372            <p id="rfc.section.4.1.p.1">The Request-Line begins with a method token, followed by the request-target and the protocol version, and ending with CRLF.
     1373               The elements are separated by SP characters. No CR or LF is allowed except in the final CRLF sequence.
     1374            </p>
     1375            <div id="rfc.figure.u.32"></div><pre class="inline"><span id="rfc.iref.g.47"></span>  <a href="#request-line" class="smpl">Request-Line</a>   = <a href="#method" class="smpl">Method</a> <a href="#core.rules" class="smpl">SP</a> <a href="#request-target" class="smpl">request-target</a> <a href="#core.rules" class="smpl">SP</a> <a href="#http.version" class="smpl">HTTP-Version</a> <a href="#core.rules" class="smpl">CRLF</a>
     1376</pre><div id="method">
     1377               <h3 id="rfc.section.4.1.1"><a href="#rfc.section.4.1.1">4.1.1</a>&nbsp;<a href="#method">Method</a></h3>
     1378               <p id="rfc.section.4.1.1.p.1">The Method token indicates the method to be performed on the resource identified by the request-target. The method is case-sensitive.</p>
     1379               <div id="rfc.figure.u.33"></div><pre class="inline"><span id="rfc.iref.g.48"></span><span id="rfc.iref.g.49"></span>  <a href="#method" class="smpl">Method</a>         = <a href="#rule.token.separators" class="smpl">token</a>
     1380</pre></div>
     1381            <div id="request-target">
     1382               <h3 id="rfc.section.4.1.2"><a href="#rfc.section.4.1.2">4.1.2</a>&nbsp;<a href="#request-target">request-target</a></h3>
     1383               <p id="rfc.section.4.1.2.p.1">The request-target identifies the resource upon which to apply the request.</p>
     1384               <div id="rfc.figure.u.34"></div><pre class="inline"><span id="rfc.iref.g.50"></span>  <a href="#request-target" class="smpl">request-target</a> = "*"
    13381385                 / <a href="#uri" class="smpl">absolute-URI</a>
    13391386                 / ( <a href="#uri" class="smpl">path-absolute</a> [ "?" <a href="#uri" class="smpl">query</a> ] )
    13401387                 / <a href="#uri" class="smpl">authority</a>
    13411388</pre><p id="rfc.section.4.1.2.p.3">The four options for request-target are dependent on the nature of the request.</p>
    1342       <p id="rfc.section.4.1.2.p.4">The asterisk "*" means that the request does not apply to a particular resource, but to the server itself, and is only allowed
    1343          when the method used does not necessarily apply to a resource. One example would be
    1344       </p>
    1345       <div id="rfc.figure.u.35"></div><pre class="text2">OPTIONS * HTTP/1.1
     1389               <p id="rfc.section.4.1.2.p.4">The asterisk "*" means that the request does not apply to a particular resource, but to the server itself, and is only allowed
     1390                  when the method used does not necessarily apply to a resource. One example would be
     1391               </p>
     1392               <div id="rfc.figure.u.35"></div><pre class="text2">OPTIONS * HTTP/1.1
    13461393</pre><p id="rfc.section.4.1.2.p.6">The absolute-URI form is <em class="bcp14">REQUIRED</em> when the request is being made to a proxy. The proxy is requested to forward the request or service it from a valid cache,
    1347          and return the response. Note that the proxy <em class="bcp14">MAY</em> forward the request on to another proxy or directly to the server specified by the absolute-URI. In order to avoid request
    1348          loops, a proxy <em class="bcp14">MUST</em> be able to recognize all of its server names, including any aliases, local variations, and the numeric IP address. An example
    1349          Request-Line would be:
    1350       </p>
    1351       <div id="rfc.figure.u.36"></div><pre class="text2">GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
     1394                  and return the response. Note that the proxy <em class="bcp14">MAY</em> forward the request on to another proxy or directly to the server specified by the absolute-URI. In order to avoid request
     1395                  loops, a proxy <em class="bcp14">MUST</em> be able to recognize all of its server names, including any aliases, local variations, and the numeric IP address. An example
     1396                  Request-Line would be:
     1397               </p>
     1398               <div id="rfc.figure.u.36"></div><pre class="text2">GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
    13521399</pre><p id="rfc.section.4.1.2.p.8">To allow for transition to absolute-URIs in all requests in future versions of HTTP, all HTTP/1.1 servers <em class="bcp14">MUST</em> accept the absolute-URI form in requests, even though HTTP/1.1 clients will only generate them in requests to proxies.
    1353       </p>
    1354       <p id="rfc.section.4.1.2.p.9">The authority form is only used by the CONNECT method (<a href="p2-semantics.html#CONNECT" title="CONNECT">Section 7.9</a> of <a href="#Part2" id="rfc.xref.Part2.3"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>).
    1355       </p>
    1356       <p id="rfc.section.4.1.2.p.10">The most common form of request-target is that used to identify a resource on an origin server or gateway. In this case the
    1357          absolute path of the URI <em class="bcp14">MUST</em> be transmitted (see <a href="#http.uri" title="http URI scheme">Section&nbsp;2.6.1</a>, path-absolute) as the request-target, and the network location of the URI (authority) <em class="bcp14">MUST</em> be transmitted in a Host header field. For example, a client wishing to retrieve the resource above directly from the origin
    1358          server would create a TCP connection to port 80 of the host "www.example.org" and send the lines:
    1359       </p>
    1360       <div id="rfc.figure.u.37"></div><pre class="text2">GET /pub/WWW/TheProject.html HTTP/1.1
     1400               </p>
     1401               <p id="rfc.section.4.1.2.p.9">The authority form is only used by the CONNECT method (<a href="p2-semantics.html#CONNECT" title="CONNECT">Section 7.9</a> of <a href="#Part2" id="rfc.xref.Part2.3"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>).
     1402               </p>
     1403               <p id="rfc.section.4.1.2.p.10">The most common form of request-target is that used to identify a resource on an origin server or gateway. In this case the
     1404                  absolute path of the URI <em class="bcp14">MUST</em> be transmitted (see <a href="#http.uri" title="http URI scheme">Section&nbsp;2.6.1</a>, path-absolute) as the request-target, and the network location of the URI (authority) <em class="bcp14">MUST</em> be transmitted in a Host header field. For example, a client wishing to retrieve the resource above directly from the origin
     1405                  server would create a TCP connection to port 80 of the host "www.example.org" and send the lines:
     1406               </p>
     1407               <div id="rfc.figure.u.37"></div><pre class="text2">GET /pub/WWW/TheProject.html HTTP/1.1
    13611408Host: www.example.org
    13621409</pre><p id="rfc.section.4.1.2.p.12">followed by the remainder of the Request. Note that the absolute path cannot be empty; if none is present in the original
    1363          URI, it <em class="bcp14">MUST</em> be given as "/" (the server root).
    1364       </p>
    1365       <p id="rfc.section.4.1.2.p.13">If a proxy receives a request without any path in the request-target and the method specified is capable of supporting the
    1366          asterisk form of request-target, then the last proxy on the request chain <em class="bcp14">MUST</em> forward the request with "*" as the final request-target.
    1367       </p>
    1368       <div id="rfc.figure.u.38"></div>
    1369       <p>For example, the request</p><pre class="text2">OPTIONS http://www.example.org:8001 HTTP/1.1
     1410                  URI, it <em class="bcp14">MUST</em> be given as "/" (the server root).
     1411               </p>
     1412               <p id="rfc.section.4.1.2.p.13">If a proxy receives a request without any path in the request-target and the method specified is capable of supporting the
     1413                  asterisk form of request-target, then the last proxy on the request chain <em class="bcp14">MUST</em> forward the request with "*" as the final request-target.
     1414               </p>
     1415               <div id="rfc.figure.u.38"></div>
     1416               <p>For example, the request</p><pre class="text2">OPTIONS http://www.example.org:8001 HTTP/1.1
    13701417</pre><div id="rfc.figure.u.39"></div>
    1371       <p>would be forwarded by the proxy as</p><pre class="text2">OPTIONS * HTTP/1.1
     1418               <p>would be forwarded by the proxy as</p><pre class="text2">OPTIONS * HTTP/1.1
    13721419Host: www.example.org:8001
    1373 </pre>  <p>after connecting to port 8001 of host "www.example.org".</p>
    1374       <p id="rfc.section.4.1.2.p.16">The request-target is transmitted in the format specified in <a href="#http.uri" title="http URI scheme">Section&nbsp;2.6.1</a>. If the request-target is percent-encoded (<a href="#RFC3986" id="rfc.xref.RFC3986.18"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-2.1">Section 2.1</a>), the origin server <em class="bcp14">MUST</em> decode the request-target in order to properly interpret the request. Servers <em class="bcp14">SHOULD</em> respond to invalid request-targets with an appropriate status code.
    1375       </p>
    1376       <p id="rfc.section.4.1.2.p.17">A transparent proxy <em class="bcp14">MUST NOT</em> rewrite the "path-absolute" part of the received request-target when forwarding it to the next inbound server, except as noted
    1377          above to replace a null path-absolute with "/" or "*".
    1378       </p>
    1379       <div class="note" id="rfc.section.4.1.2.p.18">
    1380          <p> <b>Note:</b> The "no rewrite" rule prevents the proxy from changing the meaning of the request when the origin server is improperly using
    1381             a non-reserved URI character for a reserved purpose. Implementors need to be aware that some pre-HTTP/1.1 proxies have been
    1382             known to rewrite the request-target.
    1383          </p>
     1420</pre><p>after connecting to port 8001 of host "www.example.org".</p>
     1421               <p id="rfc.section.4.1.2.p.16">The request-target is transmitted in the format specified in <a href="#http.uri" title="http URI scheme">Section&nbsp;2.6.1</a>. If the request-target is percent-encoded (<a href="#RFC3986" id="rfc.xref.RFC3986.18"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-2.1">Section 2.1</a>), the origin server <em class="bcp14">MUST</em> decode the request-target in order to properly interpret the request. Servers <em class="bcp14">SHOULD</em> respond to invalid request-targets with an appropriate status code.
     1422               </p>
     1423               <p id="rfc.section.4.1.2.p.17">A transparent proxy <em class="bcp14">MUST NOT</em> rewrite the "path-absolute" part of the received request-target when forwarding it to the next inbound server, except as noted
     1424                  above to replace a null path-absolute with "/" or "*".
     1425               </p>
     1426               <div class="note" id="rfc.section.4.1.2.p.18">
     1427                  <p><b>Note:</b> The "no rewrite" rule prevents the proxy from changing the meaning of the request when the origin server is improperly using
     1428                     a non-reserved URI character for a reserved purpose. Implementors need to be aware that some pre-HTTP/1.1 proxies have been
     1429                     known to rewrite the request-target.
     1430                  </p>
     1431               </div>
     1432               <p id="rfc.section.4.1.2.p.19">HTTP does not place a pre-defined limit on the length of a request-target. A server <em class="bcp14">MUST</em> be prepared to receive URIs of unbounded length and respond with the 414 (URI Too Long) status code if the received request-target
     1433                  would be longer than the server wishes to handle (see <a href="p2-semantics.html#status.414" title="414 URI Too Long">Section 8.4.15</a> of <a href="#Part2" id="rfc.xref.Part2.4"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>).
     1434               </p>
     1435               <p id="rfc.section.4.1.2.p.20">Various ad-hoc limitations on request-target length are found in practice. It is <em class="bcp14">RECOMMENDED</em> that all HTTP senders and recipients support request-target lengths of 8000 or more octets.
     1436               </p>
     1437               <div class="note" id="rfc.section.4.1.2.p.21">
     1438                  <p><b>Note:</b> Fragments (<a href="#RFC3986" id="rfc.xref.RFC3986.19"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-3.5">Section 3.5</a>) are not part of the request-target and thus will not be transmitted in an HTTP request.
     1439                  </p>
     1440               </div>
     1441            </div>
     1442         </div>
     1443         <div id="the.resource.identified.by.a.request">
     1444            <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a>&nbsp;<a href="#the.resource.identified.by.a.request">The Resource Identified by a Request</a></h2>
     1445            <p id="rfc.section.4.2.p.1">The exact resource identified by an Internet request is determined by examining both the request-target and the Host header
     1446               field.
     1447            </p>
     1448            <p id="rfc.section.4.2.p.2">An origin server that does not allow resources to differ by the requested host <em class="bcp14">MAY</em> ignore the Host header field value when determining the resource identified by an HTTP/1.1 request. (But see <a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses">Appendix&nbsp;B.1.1</a> for other requirements on Host support in HTTP/1.1.)
     1449            </p>
     1450            <p id="rfc.section.4.2.p.3">An origin server that does differentiate resources based on the host requested (sometimes referred to as virtual hosts or
     1451               vanity host names) <em class="bcp14">MUST</em> use the following rules for determining the requested resource on an HTTP/1.1 request:
     1452            </p>
     1453            <ol>
     1454               <li>If request-target is an absolute-URI, the host is part of the request-target. Any Host header field value in the request <em class="bcp14">MUST</em> be ignored.
     1455               </li>
     1456               <li>If the request-target is not an absolute-URI, and the request includes a Host header field, the host is determined by the
     1457                  Host header field value.
     1458               </li>
     1459               <li>If the host as determined by rule 1 or 2 is not a valid host on the server, the response <em class="bcp14">MUST</em> be a 400 (Bad Request) error message.
     1460               </li>
     1461            </ol>
     1462            <p id="rfc.section.4.2.p.4">Recipients of an HTTP/1.0 request that lacks a Host header field <em class="bcp14">MAY</em> attempt to use heuristics (e.g., examination of the URI path for something unique to a particular host) in order to determine
     1463               what exact resource is being requested.
     1464            </p>
     1465         </div>
     1466         <div id="effective.request.uri">
     1467            <div id="rfc.iref.e.1"></div>
     1468            <div id="rfc.iref.t.2"></div>
     1469            <h2 id="rfc.section.4.3"><a href="#rfc.section.4.3">4.3</a>&nbsp;<a href="#effective.request.uri">Effective Request URI</a></h2>
     1470            <p id="rfc.section.4.3.p.1">HTTP requests often do not carry the absolute URI (<a href="#RFC3986" id="rfc.xref.RFC3986.20"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="https://tools.ietf.org/html/rfc3986#section-4.3">Section 4.3</a>) for the target resource; instead, the URI needs to be inferred from the request-target, Host header field, and connection
     1471               context. The result of this process is called the "effective request URI". The "target resource" is the resource identified
     1472               by the effective request URI.
     1473            </p>
     1474            <p id="rfc.section.4.3.p.2">If the request-target is an absolute-URI, then the effective request URI is the request-target.</p>
     1475            <p id="rfc.section.4.3.p.3">If the request-target uses the path-absolute (plus optional query) syntax or if it is just the asterisk "*", then the effective
     1476               request URI is constructed by concatenating
     1477            </p>
     1478            <p id="rfc.section.4.3.p.4"></p>
     1479            <ul>
     1480               <li>the scheme name: "http" if the request was received over an insecure TCP connection, or "https" when received over a SSL/TLS-secured
     1481                  TCP connection,
     1482               </li>
     1483               <li>the character sequence "://",</li>
     1484               <li>the authority component, as specified in the Host header (<a href="#header.host" id="rfc.xref.header.host.1" title="Host">Section&nbsp;9.4</a>) and determined by the rules in <a href="#the.resource.identified.by.a.request" title="The Resource Identified by a Request">Section&nbsp;4.2</a>, <span class="comment" id="effrequri-nohost">[<a href="#effrequri-nohost" class="smpl">effrequri-nohost</a>: Do we need to include the handling of missing hosts in HTTP/1.0 messages, as described in <a href="#the.resource.identified.by.a.request" title="The Resource Identified by a Request">Section&nbsp;4.2</a>? -- See &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/221">http://tools.ietf.org/wg/httpbis/trac/ticket/221</a>&gt; --jre]</span> and
     1485               </li>
     1486               <li>the request-target obtained from the Request-Line, unless the request-target is just the asterisk "*".</li>
     1487            </ul>
     1488            <p id="rfc.section.4.3.p.5">Otherwise, when request-target uses the authority form, the effective Request URI is undefined.</p>
     1489            <div id="rfc.figure.u.40"></div>
     1490            <p>Example 1: the effective request URI for the message</p><pre class="text">GET /pub/WWW/TheProject.html HTTP/1.1
     1491Host: www.example.org:8080
     1492</pre><p>(received over an insecure TCP connection) is "http", plus "://", plus the authority component "www.example.org:8080", plus
     1493               the request-target "/pub/WWW/TheProject.html", thus "http://www.example.org:8080/pub/WWW/TheProject.html".
     1494            </p>
     1495            <div id="rfc.figure.u.41"></div>
     1496            <p>Example 2: the effective request URI for the message</p><pre class="text">GET * HTTP/1.1
     1497Host: www.example.org
     1498</pre><p>(received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the authority component "www.example.org",
     1499               thus "https://www.example.org".
     1500            </p>
     1501            <p id="rfc.section.4.3.p.8">Effective request URIs are compared using the rules described in <a href="#uri.comparison" title="http and https URI Normalization and Comparison">Section&nbsp;2.6.3</a>, except that empty path components <em class="bcp14">MUST NOT</em> be treated as equivalent to an absolute path of "/".
     1502            </p>
     1503         </div>
    13841504      </div>
    1385       <p id="rfc.section.4.1.2.p.19">HTTP does not place a pre-defined limit on the length of a request-target. A server <em class="bcp14">MUST</em> be prepared to receive URIs of unbounded length and respond with the 414 (URI Too Long) status code if the received request-target
    1386          would be longer than the server wishes to handle (see <a href="p2-semantics.html#status.414" title="414 URI Too Long">Section 8.4.15</a> of <a href="#Part2" id="rfc.xref.Part2.4"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>).
    1387       </p>
    1388       <p id="rfc.section.4.1.2.p.20">Various ad-hoc limitations on request-target length are found in practice. It is <em class="bcp14">RECOMMENDED</em> that all HTTP senders and recipients support request-target lengths of 8000 or more octets.
    1389       </p>
    1390       <div class="note" id="rfc.section.4.1.2.p.21">
    1391          <p> <b>Note:</b> Fragments (<a href="#RFC3986" id="rfc.xref.RFC3986.19"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-3.5">Section 3.5</a>) are not part of the request-target and thus will not be transmitted in an HTTP request.
    1392          </p>
    1393       </div>
    1394       <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a>&nbsp;<a id="the.resource.identified.by.a.request" href="#the.resource.identified.by.a.request">The Resource Identified by a Request</a></h2>
    1395       <p id="rfc.section.4.2.p.1">The exact resource identified by an Internet request is determined by examining both the request-target and the Host header
    1396          field.
    1397       </p>
    1398       <p id="rfc.section.4.2.p.2">An origin server that does not allow resources to differ by the requested host <em class="bcp14">MAY</em> ignore the Host header field value when determining the resource identified by an HTTP/1.1 request. (But see <a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses">Appendix&nbsp;B.1.1</a> for other requirements on Host support in HTTP/1.1.)
    1399       </p>
    1400       <p id="rfc.section.4.2.p.3">An origin server that does differentiate resources based on the host requested (sometimes referred to as virtual hosts or
    1401          vanity host names) <em class="bcp14">MUST</em> use the following rules for determining the requested resource on an HTTP/1.1 request:
    1402       </p>
    1403       <ol>
    1404          <li>If request-target is an absolute-URI, the host is part of the request-target. Any Host header field value in the request <em class="bcp14">MUST</em> be ignored.
    1405          </li>
    1406          <li>If the request-target is not an absolute-URI, and the request includes a Host header field, the host is determined by the
    1407             Host header field value.
    1408          </li>
    1409          <li>If the host as determined by rule 1 or 2 is not a valid host on the server, the response <em class="bcp14">MUST</em> be a 400 (Bad Request) error message.
    1410          </li>
    1411       </ol>
    1412       <p id="rfc.section.4.2.p.4">Recipients of an HTTP/1.0 request that lacks a Host header field <em class="bcp14">MAY</em> attempt to use heuristics (e.g., examination of the URI path for something unique to a particular host) in order to determine
    1413          what exact resource is being requested.
    1414       </p>
    1415       <div id="rfc.iref.e.1"></div>
    1416       <div id="rfc.iref.t.2"></div>
    1417       <h2 id="rfc.section.4.3"><a href="#rfc.section.4.3">4.3</a>&nbsp;<a id="effective.request.uri" href="#effective.request.uri">Effective Request URI</a></h2>
    1418       <p id="rfc.section.4.3.p.1">HTTP requests often do not carry the absolute URI (<a href="#RFC3986" id="rfc.xref.RFC3986.20"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-4.3">Section 4.3</a>) for the target resource; instead, the URI needs to be inferred from the request-target, Host header field, and connection
    1419          context. The result of this process is called the "effective request URI". The "target resource" is the resource identified
    1420          by the effective request URI.
    1421       </p>
    1422       <p id="rfc.section.4.3.p.2">If the request-target is an absolute-URI, then the effective request URI is the request-target.</p>
    1423       <p id="rfc.section.4.3.p.3">If the request-target uses the path-absolute (plus optional query) syntax or if it is just the asterisk "*", then the effective
    1424          request URI is constructed by concatenating
    1425       </p>
    1426       <p id="rfc.section.4.3.p.4"> </p>
    1427       <ul>
    1428          <li>the scheme name: "http" if the request was received over an insecure TCP connection, or "https" when received over a SSL/TLS-secured
    1429             TCP connection,
    1430          </li>
    1431          <li>the character sequence "://",</li>
    1432          <li>the authority component, as specified in the Host header (<a href="#header.host" id="rfc.xref.header.host.1" title="Host">Section&nbsp;9.4</a>) and determined by the rules in <a href="#the.resource.identified.by.a.request" title="The Resource Identified by a Request">Section&nbsp;4.2</a>, <span class="comment" id="effrequri-nohost">[<a href="#effrequri-nohost" class="smpl">effrequri-nohost</a>: Do we need to include the handling of missing hosts in HTTP/1.0 messages, as described in <a href="#the.resource.identified.by.a.request" title="The Resource Identified by a Request">Section&nbsp;4.2</a>? -- See &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/221">http://tools.ietf.org/wg/httpbis/trac/ticket/221</a>&gt; --jre]</span> and
    1433          </li>
    1434          <li>the request-target obtained from the Request-Line, unless the request-target is just the asterisk "*".</li>
    1435       </ul>
    1436       <p id="rfc.section.4.3.p.5">Otherwise, when request-target uses the authority form, the effective Request URI is undefined.</p>
    1437       <div id="rfc.figure.u.40"></div>
    1438       <p>Example 1: the effective request URI for the message</p>  <pre class="text">GET /pub/WWW/TheProject.html HTTP/1.1
    1439 Host: www.example.org:8080
    1440 </pre>  <p>(received over an insecure TCP connection) is "http", plus "://", plus the authority component "www.example.org:8080", plus
    1441          the request-target "/pub/WWW/TheProject.html", thus "http://www.example.org:8080/pub/WWW/TheProject.html".
    1442       </p>
    1443       <div id="rfc.figure.u.41"></div>
    1444       <p>Example 2: the effective request URI for the message</p>  <pre class="text">GET * HTTP/1.1
    1445 Host: www.example.org
    1446 </pre>  <p>(received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the authority component "www.example.org",
    1447          thus "https://www.example.org".
    1448       </p>
    1449       <p id="rfc.section.4.3.p.8">Effective request URIs are compared using the rules described in <a href="#uri.comparison" title="http and https URI Normalization and Comparison">Section&nbsp;2.6.3</a>, except that empty path components <em class="bcp14">MUST NOT</em> be treated as equivalent to an absolute path of "/".
    1450       </p>
    1451       <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a>&nbsp;<a id="response" href="#response">Response</a></h1>
    1452       <p id="rfc.section.5.p.1">After receiving and interpreting a request message, a server responds with an HTTP response message.</p>
    1453       <div id="rfc.figure.u.42"></div><pre class="inline"><span id="rfc.iref.g.51"></span>  <a href="#response" class="smpl">Response</a>      = <a href="#status-line" class="smpl">Status-Line</a>               ; <a href="#status-line" title="Status-Line">Section&nbsp;5.1</a>
     1505      <div id="response">
     1506         <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a>&nbsp;<a href="#response">Response</a></h1>
     1507         <p id="rfc.section.5.p.1">After receiving and interpreting a request message, a server responds with an HTTP response message.</p>
     1508         <div id="rfc.figure.u.42"></div><pre class="inline"><span id="rfc.iref.g.51"></span>  <a href="#response" class="smpl">Response</a>      = <a href="#status-line" class="smpl">Status-Line</a>               ; <a href="#status-line" title="Status-Line">Section&nbsp;5.1</a>
    14541509                  *( <a href="#header.fields" class="smpl">header-field</a> <a href="#core.rules" class="smpl">CRLF</a> )    ; <a href="#header.fields" title="Header Fields">Section&nbsp;3.2</a>
    14551510                  <a href="#core.rules" class="smpl">CRLF</a>
    14561511                  [ <a href="#message.body" class="smpl">message-body</a> ]          ; <a href="#message.body" title="Message Body">Section&nbsp;3.3</a>
    1457 </pre><h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a>&nbsp;<a id="status-line" href="#status-line">Status-Line</a></h2>
    1458       <p id="rfc.section.5.1.p.1">The first line of a Response message is the Status-Line, consisting of the protocol version followed by a numeric status code
    1459          and its associated textual phrase, with each element separated by SP characters. No CR or LF is allowed except in the final
    1460          CRLF sequence.
    1461       </p>
    1462       <div id="rfc.figure.u.43"></div><pre class="inline"><span id="rfc.iref.g.52"></span>  <a href="#status-line" class="smpl">Status-Line</a> = <a href="#http.version" class="smpl">HTTP-Version</a> <a href="#core.rules" class="smpl">SP</a> <a href="#status.code.and.reason.phrase" class="smpl">Status-Code</a> <a href="#core.rules" class="smpl">SP</a> <a href="#status.code.and.reason.phrase" class="smpl">Reason-Phrase</a> <a href="#core.rules" class="smpl">CRLF</a>
    1463 </pre><h3 id="rfc.section.5.1.1"><a href="#rfc.section.5.1.1">5.1.1</a>&nbsp;<a id="status.code.and.reason.phrase" href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></h3>
    1464       <p id="rfc.section.5.1.1.p.1">The Status-Code element is a 3-digit integer result code of the attempt to understand and satisfy the request. These codes
    1465          are fully defined in <a href="p2-semantics.html#status.codes" title="Status Code Definitions">Section 8</a> of <a href="#Part2" id="rfc.xref.Part2.5"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>. The Reason Phrase exists for the sole purpose of providing a textual description associated with the numeric status code,
    1466          out of deference to earlier Internet application protocols that were more frequently used with interactive text clients. A
    1467          client <em class="bcp14">SHOULD</em> ignore the content of the Reason Phrase.
    1468       </p>
    1469       <p id="rfc.section.5.1.1.p.2">The first digit of the Status-Code defines the class of response. The last two digits do not have any categorization role.
    1470          There are 5 values for the first digit:
    1471       </p>
    1472       <ul>
    1473          <li>1xx: Informational - Request received, continuing process</li>
    1474          <li>2xx: Success - The action was successfully received, understood, and accepted</li>
    1475          <li>3xx: Redirection - Further action must be taken in order to complete the request</li>
    1476          <li>4xx: Client Error - The request contains bad syntax or cannot be fulfilled</li>
    1477          <li>5xx: Server Error - The server failed to fulfill an apparently valid request</li>
    1478       </ul>
    1479       <div id="rfc.figure.u.44"></div><pre class="inline"><span id="rfc.iref.g.53"></span><span id="rfc.iref.g.54"></span><span id="rfc.iref.g.55"></span>  <a href="#status.code.and.reason.phrase" class="smpl">Status-Code</a>    = 3<a href="#core.rules" class="smpl">DIGIT</a>
     1512</pre><div id="status-line">
     1513            <h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a>&nbsp;<a href="#status-line">Status-Line</a></h2>
     1514            <p id="rfc.section.5.1.p.1">The first line of a Response message is the Status-Line, consisting of the protocol version followed by a numeric status code
     1515               and its associated textual phrase, with each element separated by SP characters. No CR or LF is allowed except in the final
     1516               CRLF sequence.
     1517            </p>
     1518            <div id="rfc.figure.u.43"></div><pre class="inline"><span id="rfc.iref.g.52"></span>  <a href="#status-line" class="smpl">Status-Line</a> = <a href="#http.version" class="smpl">HTTP-Version</a> <a href="#core.rules" class="smpl">SP</a> <a href="#status.code.and.reason.phrase" class="smpl">Status-Code</a> <a href="#core.rules" class="smpl">SP</a> <a href="#status.code.and.reason.phrase" class="smpl">Reason-Phrase</a> <a href="#core.rules" class="smpl">CRLF</a>
     1519</pre><div id="status.code.and.reason.phrase">
     1520               <h3 id="rfc.section.5.1.1"><a href="#rfc.section.5.1.1">5.1.1</a>&nbsp;<a href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></h3>
     1521               <p id="rfc.section.5.1.1.p.1">The Status-Code element is a 3-digit integer result code of the attempt to understand and satisfy the request. These codes
     1522                  are fully defined in <a href="p2-semantics.html#status.codes" title="Status Code Definitions">Section 8</a> of <a href="#Part2" id="rfc.xref.Part2.5"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>. The Reason Phrase exists for the sole purpose of providing a textual description associated with the numeric status code,
     1523                  out of deference to earlier Internet application protocols that were more frequently used with interactive text clients. A
     1524                  client <em class="bcp14">SHOULD</em> ignore the content of the Reason Phrase.
     1525               </p>
     1526               <p id="rfc.section.5.1.1.p.2">The first digit of the Status-Code defines the class of response. The last two digits do not have any categorization role.
     1527                  There are 5 values for the first digit:
     1528               </p>
     1529               <ul>
     1530                  <li>1xx: Informational - Request received, continuing process</li>
     1531                  <li>2xx: Success - The action was successfully received, understood, and accepted</li>
     1532                  <li>3xx: Redirection - Further action must be taken in order to complete the request</li>
     1533                  <li>4xx: Client Error - The request contains bad syntax or cannot be fulfilled</li>
     1534                  <li>5xx: Server Error - The server failed to fulfill an apparently valid request</li>
     1535               </ul>
     1536               <div id="rfc.figure.u.44"></div><pre class="inline"><span id="rfc.iref.g.53"></span><span id="rfc.iref.g.54"></span><span id="rfc.iref.g.55"></span>  <a href="#status.code.and.reason.phrase" class="smpl">Status-Code</a>    = 3<a href="#core.rules" class="smpl">DIGIT</a>
    14801537  <a href="#status.code.and.reason.phrase" class="smpl">Reason-Phrase</a>  = *( <a href="#core.rules" class="smpl">WSP</a> / <a href="#core.rules" class="smpl">VCHAR</a> / <a href="#rule.quoted-string" class="smpl">obs-text</a> )
    1481 </pre><h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a>&nbsp;<a id="protocol.parameters" href="#protocol.parameters">Protocol Parameters</a></h1>
    1482       <h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a>&nbsp;<a id="date.time.formats.full.date" href="#date.time.formats.full.date">Date/Time Formats: Full Date</a></h2>
    1483       <p id="rfc.section.6.1.p.1">HTTP applications have historically allowed three different formats for date/time stamps. However, the preferred format is
    1484          a fixed-length subset of that defined by <a href="#RFC1123" id="rfc.xref.RFC1123.1"><cite title="Requirements for Internet Hosts - Application and Support">[RFC1123]</cite></a>:
    1485       </p>
    1486       <div id="rfc.figure.u.45"></div><pre class="text">Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
     1538</pre></div>
     1539         </div>
     1540      </div>
     1541      <div id="protocol.parameters">
     1542         <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a>&nbsp;<a href="#protocol.parameters">Protocol Parameters</a></h1>
     1543         <div id="date.time.formats.full.date">
     1544            <h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a>&nbsp;<a href="#date.time.formats.full.date">Date/Time Formats: Full Date</a></h2>
     1545            <p id="rfc.section.6.1.p.1">HTTP applications have historically allowed three different formats for date/time stamps. However, the preferred format is
     1546               a fixed-length subset of that defined by <a href="#RFC1123" id="rfc.xref.RFC1123.1"><cite title="Requirements for Internet Hosts - Application and Support">[RFC1123]</cite></a>:
     1547            </p>
     1548            <div id="rfc.figure.u.45"></div><pre class="text">Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
    14871549</pre><p id="rfc.section.6.1.p.3">The other formats are described here only for compatibility with obsolete implementations.</p>
    1488       <div id="rfc.figure.u.46"></div><pre class="text">Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
     1550            <div id="rfc.figure.u.46"></div><pre class="text">Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
    14891551Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
    14901552</pre><p id="rfc.section.6.1.p.5">HTTP/1.1 clients and servers that parse a date value <em class="bcp14">MUST</em> accept all three formats (for compatibility with HTTP/1.0), though they <em class="bcp14">MUST</em> only generate the RFC 1123 format for representing HTTP-date values in header fields. See <a href="#tolerant.applications" title="Tolerant Applications">Appendix&nbsp;A</a> for further information.
    1491       </p>
    1492       <p id="rfc.section.6.1.p.6">All HTTP date/time stamps <em class="bcp14">MUST</em> be represented in Greenwich Mean Time (GMT), without exception. For the purposes of HTTP, GMT is exactly equal to UTC (Coordinated
    1493          Universal Time). This is indicated in the first two formats by the inclusion of "GMT" as the three-letter abbreviation for
    1494          time zone, and <em class="bcp14">MUST</em> be assumed when reading the asctime format. HTTP-date is case sensitive and <em class="bcp14">MUST NOT</em> include additional whitespace beyond that specifically included as SP in the grammar.
    1495       </p>
    1496       <div id="rfc.figure.u.47"></div><pre class="inline"><span id="rfc.iref.g.56"></span>  <a href="#date.time.formats.full.date" class="smpl">HTTP-date</a>    = <a href="#preferred.date.format" class="smpl">rfc1123-date</a> / <a href="#obsolete.date.formats" class="smpl">obs-date</a>
     1553            </p>
     1554            <p id="rfc.section.6.1.p.6">All HTTP date/time stamps <em class="bcp14">MUST</em> be represented in Greenwich Mean Time (GMT), without exception. For the purposes of HTTP, GMT is exactly equal to UTC (Coordinated
     1555               Universal Time). This is indicated in the first two formats by the inclusion of "GMT" as the three-letter abbreviation for
     1556               time zone, and <em class="bcp14">MUST</em> be assumed when reading the asctime format. HTTP-date is case sensitive and <em class="bcp14">MUST NOT</em> include additional whitespace beyond that specifically included as SP in the grammar.
     1557            </p>
     1558            <div id="rfc.figure.u.47"></div><pre class="inline"><span id="rfc.iref.g.56"></span>  <a href="#date.time.formats.full.date" class="smpl">HTTP-date</a>    = <a href="#preferred.date.format" class="smpl">rfc1123-date</a> / <a href="#obsolete.date.formats" class="smpl">obs-date</a>
    14971559</pre><div id="preferred.date.format">
    1498          <p id="rfc.section.6.1.p.8">                    Preferred format:</p>
    1499       </div>
    1500       <div id="rfc.figure.u.48"></div><pre class="inline"><span id="rfc.iref.g.57"></span><span id="rfc.iref.g.58"></span><span id="rfc.iref.g.59"></span><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><span id="rfc.iref.g.64"></span><span id="rfc.iref.g.65"></span><span id="rfc.iref.g.66"></span><span id="rfc.iref.g.67"></span><span id="rfc.iref.g.68"></span>  <a href="#preferred.date.format" class="smpl">rfc1123-date</a> = <a href="#preferred.date.format" class="smpl">day-name</a> "," <a href="#core.rules" class="smpl">SP</a> date1 <a href="#core.rules" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">time-of-day</a> <a href="#core.rules" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">GMT</a>
     1560               <p id="rfc.section.6.1.p.8">          Preferred format:</p>
     1561            </div>
     1562            <div id="rfc.figure.u.48"></div><pre class="inline"><span id="rfc.iref.g.57"></span><span id="rfc.iref.g.58"></span><span id="rfc.iref.g.59"></span><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><span id="rfc.iref.g.64"></span><span id="rfc.iref.g.65"></span><span id="rfc.iref.g.66"></span><span id="rfc.iref.g.67"></span><span id="rfc.iref.g.68"></span>  <a href="#preferred.date.format" class="smpl">rfc1123-date</a> = <a href="#preferred.date.format" class="smpl">day-name</a> "," <a href="#core.rules" class="smpl">SP</a> date1 <a href="#core.rules" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">time-of-day</a> <a href="#core.rules" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">GMT</a>
    15011563
    15021564  <a href="#preferred.date.format" class="smpl">day-name</a>     = %x4D.6F.6E ; "Mon", case-sensitive
     
    15341596  <a href="#preferred.date.format" class="smpl">minute</a>       = 2<a href="#core.rules" class="smpl">DIGIT</a>               
    15351597  <a href="#preferred.date.format" class="smpl">second</a>       = 2<a href="#core.rules" class="smpl">DIGIT</a>               
    1536 </pre><p id="rfc.section.6.1.p.10">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 RFC 5322 constructs with the corresponding name (<a href="#RFC5322" id="rfc.xref.RFC5322.3"><cite title="Internet Message Format">[RFC5322]</cite></a>, <a href="http://tools.ietf.org/html/rfc5322#section-3.3">Section 3.3</a>).
    1537       </p>
    1538       <div id="obsolete.date.formats">
    1539          <p id="rfc.section.6.1.p.11">                Obsolete formats:</p>
    1540       </div>
    1541       <div id="rfc.figure.u.49"></div><pre class="inline"><span id="rfc.iref.g.69"></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>
     1598</pre><p id="rfc.section.6.1.p.10">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 RFC 5322 constructs with the corresponding name (<a href="#RFC5322" id="rfc.xref.RFC5322.3"><cite title="Internet Message Format">[RFC5322]</cite></a>, <a href="https://tools.ietf.org/html/rfc5322#section-3.3">Section 3.3</a>).
     1599            </p>
     1600            <div id="obsolete.date.formats">
     1601               <p id="rfc.section.6.1.p.11">        Obsolete formats:</p>
     1602            </div>
     1603            <div id="rfc.figure.u.49"></div><pre class="inline"><span id="rfc.iref.g.69"></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>
    15421604</pre><div id="rfc.figure.u.50"></div><pre class="inline"><span id="rfc.iref.g.70"></span>  <a href="#obsolete.date.formats" class="smpl">rfc850-date</a>  = <a href="#obsolete.date.formats" class="smpl">day-name-l</a> "," <a href="#core.rules" class="smpl">SP</a> <a href="#obsolete.date.formats" class="smpl">date2</a> <a href="#core.rules" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">time-of-day</a> <a href="#core.rules" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">GMT</a>
    15431605  <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="#core.rules" class="smpl">DIGIT</a>
     
    15541616  <a href="#obsolete.date.formats" class="smpl">date3</a>        = <a href="#preferred.date.format" class="smpl">month</a> <a href="#core.rules" class="smpl">SP</a> ( 2<a href="#core.rules" class="smpl">DIGIT</a> / ( <a href="#core.rules" class="smpl">SP</a> 1<a href="#core.rules" class="smpl">DIGIT</a> ))
    15551617                 ; month day (e.g., Jun  2)
    1556 </pre><div class="note" id="rfc.section.6.1.p.15">
    1557          <p> <b>Note:</b> Recipients of date values are encouraged to be robust in accepting date values that might have been sent by non-HTTP applications,
    1558             as is sometimes the case when retrieving or posting messages via proxies/gateways to SMTP or NNTP.
    1559          </p>
    1560       </div>
    1561       <div class="note" id="rfc.section.6.1.p.16">
    1562          <p> <b>Note:</b> HTTP requirements for the date/time stamp format apply only to their usage within the protocol stream. Clients and servers
    1563             are not required to use these formats for user presentation, request logging, etc.
    1564          </p>
    1565       </div>
    1566       <h2 id="rfc.section.6.2"><a href="#rfc.section.6.2">6.2</a>&nbsp;<a id="transfer.codings" href="#transfer.codings">Transfer Codings</a></h2>
    1567       <p id="rfc.section.6.2.p.1">Transfer-coding values are used to indicate an encoding transformation that has been, can be, or might need to be applied
    1568          to a payload body in order to ensure "safe transport" through the network. This differs from a content coding in that the
    1569          transfer-coding is a property of the message rather than a property of the representation that is being transferred.
    1570       </p>
    1571       <div id="rfc.figure.u.52"></div><pre class="inline"><span id="rfc.iref.g.72"></span><span id="rfc.iref.g.73"></span>  <a href="#transfer.codings" class="smpl">transfer-coding</a>         = "chunked" ; <a href="#chunked.encoding" title="Chunked Transfer Coding">Section&nbsp;6.2.1</a>
     1618</pre><div class="note" id="rfc.section.6.1.p.15">
     1619               <p><b>Note:</b> Recipients of date values are encouraged to be robust in accepting date values that might have been sent by non-HTTP applications,
     1620                  as is sometimes the case when retrieving or posting messages via proxies/gateways to SMTP or NNTP.
     1621               </p>
     1622            </div>
     1623            <div class="note" id="rfc.section.6.1.p.16">
     1624               <p><b>Note:</b> HTTP requirements for the date/time stamp format apply only to their usage within the protocol stream. Clients and servers
     1625                  are not required to use these formats for user presentation, request logging, etc.
     1626               </p>
     1627            </div>
     1628         </div>
     1629         <div id="transfer.codings">
     1630            <h2 id="rfc.section.6.2"><a href="#rfc.section.6.2">6.2</a>&nbsp;<a href="#transfer.codings">Transfer Codings</a></h2>
     1631            <p id="rfc.section.6.2.p.1">Transfer-coding values are used to indicate an encoding transformation that has been, can be, or might need to be applied
     1632               to a payload body in order to ensure "safe transport" through the network. This differs from a content coding in that the
     1633               transfer-coding is a property of the message rather than a property of the representation that is being transferred.
     1634            </p>
     1635            <div id="rfc.figure.u.52"></div><pre class="inline"><span id="rfc.iref.g.72"></span><span id="rfc.iref.g.73"></span>  <a href="#transfer.codings" class="smpl">transfer-coding</a>         = "chunked" ; <a href="#chunked.encoding" title="Chunked Transfer Coding">Section&nbsp;6.2.1</a>
    15721636                          / "compress" ; <a href="#compress.coding" title="Compress Coding">Section&nbsp;6.2.2.1</a>
    15731637                          / "deflate" ; <a href="#deflate.coding" title="Deflate Coding">Section&nbsp;6.2.2.2</a>
     
    15761640  <a href="#transfer.codings" class="smpl">transfer-extension</a>      = <a href="#rule.token.separators" class="smpl">token</a> *( <a href="#rule.whitespace" class="smpl">OWS</a> ";" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#rule.parameter" class="smpl">transfer-parameter</a> )
    15771641</pre><div id="rule.parameter">
    1578          <p id="rfc.section.6.2.p.3">      Parameters are in the form of attribute/value pairs.</p>
    1579       </div>
    1580       <div id="rfc.figure.u.53"></div><pre class="inline"><span id="rfc.iref.g.74"></span><span id="rfc.iref.g.75"></span><span id="rfc.iref.g.76"></span><span id="rfc.iref.g.77"></span><span id="rfc.iref.g.78"></span>  <a href="#rule.parameter" class="smpl">transfer-parameter</a>      = <a href="#rule.parameter" class="smpl">attribute</a> <a href="#rule.whitespace" class="smpl">BWS</a> "=" <a href="#rule.whitespace" class="smpl">BWS</a> <a href="#rule.parameter" class="smpl">value</a>
     1642               <p id="rfc.section.6.2.p.3">   Parameters are in the form of attribute/value pairs.</p>
     1643            </div>
     1644            <div id="rfc.figure.u.53"></div><pre class="inline"><span id="rfc.iref.g.74"></span><span id="rfc.iref.g.75"></span><span id="rfc.iref.g.76"></span><span id="rfc.iref.g.77"></span><span id="rfc.iref.g.78"></span>  <a href="#rule.parameter" class="smpl">transfer-parameter</a>      = <a href="#rule.parameter" class="smpl">attribute</a> <a href="#rule.whitespace" class="smpl">BWS</a> "=" <a href="#rule.whitespace" class="smpl">BWS</a> <a href="#rule.parameter" class="smpl">value</a>
    15811645  <a href="#rule.parameter" class="smpl">attribute</a>               = <a href="#rule.token.separators" class="smpl">token</a>
    15821646  <a href="#rule.parameter" class="smpl">value</a>                   = <a href="#rule.token.separators" class="smpl">word</a>
    15831647</pre><p id="rfc.section.6.2.p.5">All transfer-coding values are case-insensitive. HTTP/1.1 uses transfer-coding values in the TE header field (<a href="#header.te" id="rfc.xref.header.te.1" title="TE">Section&nbsp;9.5</a>) and in the Transfer-Encoding header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.4" title="Transfer-Encoding">Section&nbsp;9.7</a>).
    1584       </p>
    1585       <p id="rfc.section.6.2.p.6">Transfer-codings are analogous to the Content-Transfer-Encoding values of MIME, which were designed to enable safe transport
    1586          of binary data over a 7-bit transport service (<a href="#RFC2045" id="rfc.xref.RFC2045.2"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a>, <a href="http://tools.ietf.org/html/rfc2045#section-6">Section 6</a>). However, safe transport has a different focus for an 8bit-clean transfer protocol. In HTTP, the only unsafe characteristic
    1587          of message-bodies is the difficulty in determining the exact message body length (<a href="#message.body" title="Message Body">Section&nbsp;3.3</a>), or the desire to encrypt data over a shared transport.
    1588       </p>
    1589       <p id="rfc.section.6.2.p.7">A server that receives a request message with a transfer-coding it does not understand <em class="bcp14">SHOULD</em> respond with 501 (Not Implemented) and then close the connection. A server <em class="bcp14">MUST NOT</em> send transfer-codings to an HTTP/1.0 client.
    1590       </p>
    1591       <div id="rfc.iref.c.5"></div>
    1592       <div id="rfc.iref.c.6"></div>
    1593       <h3 id="rfc.section.6.2.1"><a href="#rfc.section.6.2.1">6.2.1</a>&nbsp;<a id="chunked.encoding" href="#chunked.encoding">Chunked Transfer Coding</a></h3>
    1594       <p id="rfc.section.6.2.1.p.1">The chunked encoding modifies the body of a message in order to transfer it as a series of chunks, each with its own size
    1595          indicator, followed by an <em class="bcp14">OPTIONAL</em> trailer containing header fields. This allows dynamically produced content to be transferred along with the information necessary
    1596          for the recipient to verify that it has received the full message.
    1597       </p>
    1598       <div id="rfc.figure.u.54"></div><pre class="inline"><span id="rfc.iref.g.79"></span><span id="rfc.iref.g.80"></span><span id="rfc.iref.g.81"></span><span id="rfc.iref.g.82"></span><span id="rfc.iref.g.83"></span><span id="rfc.iref.g.84"></span><span id="rfc.iref.g.85"></span><span id="rfc.iref.g.86"></span><span id="rfc.iref.g.87"></span><span id="rfc.iref.g.88"></span><span id="rfc.iref.g.89"></span>  <a href="#chunked.encoding" class="smpl">Chunked-Body</a>   = *<a href="#chunked.encoding" class="smpl">chunk</a>
     1648            </p>
     1649            <p id="rfc.section.6.2.p.6">Transfer-codings are analogous to the Content-Transfer-Encoding values of MIME, which were designed to enable safe transport
     1650               of binary data over a 7-bit transport service (<a href="#RFC2045" id="rfc.xref.RFC2045.2"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a>, <a href="https://tools.ietf.org/html/rfc2045#section-6">Section 6</a>). However, safe transport has a different focus for an 8bit-clean transfer protocol. In HTTP, the only unsafe characteristic
     1651               of message-bodies is the difficulty in determining the exact message body length (<a href="#message.body" title="Message Body">Section&nbsp;3.3</a>), or the desire to encrypt data over a shared transport.
     1652            </p>
     1653            <p id="rfc.section.6.2.p.7">A server that receives a request message with a transfer-coding it does not understand <em class="bcp14">SHOULD</em> respond with 501 (Not Implemented) and then close the connection. A server <em class="bcp14">MUST NOT</em> send transfer-codings to an HTTP/1.0 client.
     1654            </p>
     1655            <div id="chunked.encoding">
     1656               <div id="rfc.iref.c.5"></div>
     1657               <div id="rfc.iref.c.6"></div>
     1658               <h3 id="rfc.section.6.2.1"><a href="#rfc.section.6.2.1">6.2.1</a>&nbsp;<a href="#chunked.encoding">Chunked Transfer Coding</a></h3>
     1659               <p id="rfc.section.6.2.1.p.1">The chunked encoding modifies the body of a message in order to transfer it as a series of chunks, each with its own size
     1660                  indicator, followed by an <em class="bcp14">OPTIONAL</em> trailer containing header fields. This allows dynamically produced content to be transferred along with the information necessary
     1661                  for the recipient to verify that it has received the full message.
     1662               </p>
     1663               <div id="rfc.figure.u.54"></div><pre class="inline"><span id="rfc.iref.g.79"></span><span id="rfc.iref.g.80"></span><span id="rfc.iref.g.81"></span><span id="rfc.iref.g.82"></span><span id="rfc.iref.g.83"></span><span id="rfc.iref.g.84"></span><span id="rfc.iref.g.85"></span><span id="rfc.iref.g.86"></span><span id="rfc.iref.g.87"></span><span id="rfc.iref.g.88"></span><span id="rfc.iref.g.89"></span>  <a href="#chunked.encoding" class="smpl">Chunked-Body</a>   = *<a href="#chunked.encoding" class="smpl">chunk</a>
    15991664                   <a href="#chunked.encoding" class="smpl">last-chunk</a>
    16001665                   <a href="#chunked.encoding" class="smpl">trailer-part</a>
     
    16181683                 ; <a href="#core.rules" class="smpl">WSP</a> / &lt;<a href="#core.rules" class="smpl">VCHAR</a> except <a href="#core.rules" class="smpl">DQUOTE</a> and "\"&gt; / <a href="#rule.quoted-string" class="smpl">obs-text</a>
    16191684</pre><p id="rfc.section.6.2.1.p.3">The chunk-size field is a string of hex digits indicating the size of the chunk-data in octets. The chunked encoding is ended
    1620          by any chunk whose size is zero, followed by the trailer, which is terminated by an empty line.
    1621       </p>
    1622       <p id="rfc.section.6.2.1.p.4">The trailer allows the sender to include additional HTTP header fields at the end of the message. The Trailer header field
    1623          can be used to indicate which header fields are included in a trailer (see <a href="#header.trailer" id="rfc.xref.header.trailer.2" title="Trailer">Section&nbsp;9.6</a>).
    1624       </p>
    1625       <p id="rfc.section.6.2.1.p.5">A server using chunked transfer-coding in a response <em class="bcp14">MUST NOT</em> use the trailer for any header fields unless at least one of the following is true:
    1626       </p>
    1627       <ol>
    1628          <li>the request included a TE header field that indicates "trailers" is acceptable in the transfer-coding of the response, as
    1629             described in <a href="#header.te" id="rfc.xref.header.te.2" title="TE">Section&nbsp;9.5</a>; or,
    1630          </li>
    1631          <li>the server is the origin server for the response, the trailer fields consist entirely of optional metadata, and the recipient
    1632             could use the message (in a manner acceptable to the origin server) without receiving this metadata. In other words, the origin
    1633             server is willing to accept the possibility that the trailer fields might be silently discarded along the path to the client.
    1634          </li>
    1635       </ol>
    1636       <p id="rfc.section.6.2.1.p.6">This requirement prevents an interoperability failure when the message is being received by an HTTP/1.1 (or later) proxy and
    1637          forwarded to an HTTP/1.0 recipient. It avoids a situation where compliance with the protocol would have necessitated a possibly
    1638          infinite buffer on the proxy.
    1639       </p>
    1640       <p id="rfc.section.6.2.1.p.7">A process for decoding the "chunked" transfer-coding can be represented in pseudo-code as:</p>
    1641       <div id="rfc.figure.u.55"></div><pre class="text">  length := 0
     1685                  by any chunk whose size is zero, followed by the trailer, which is terminated by an empty line.
     1686               </p>
     1687               <p id="rfc.section.6.2.1.p.4">The trailer allows the sender to include additional HTTP header fields at the end of the message. The Trailer header field
     1688                  can be used to indicate which header fields are included in a trailer (see <a href="#header.trailer" id="rfc.xref.header.trailer.2" title="Trailer">Section&nbsp;9.6</a>).
     1689               </p>
     1690               <p id="rfc.section.6.2.1.p.5">A server using chunked transfer-coding in a response <em class="bcp14">MUST NOT</em> use the trailer for any header fields unless at least one of the following is true:
     1691               </p>
     1692               <ol>
     1693                  <li>the request included a TE header field that indicates "trailers" is acceptable in the transfer-coding of the response, as
     1694                     described in <a href="#header.te" id="rfc.xref.header.te.2" title="TE">Section&nbsp;9.5</a>; or,
     1695                  </li>
     1696                  <li>the server is the origin server for the response, the trailer fields consist entirely of optional metadata, and the recipient
     1697                     could use the message (in a manner acceptable to the origin server) without receiving this metadata. In other words, the origin
     1698                     server is willing to accept the possibility that the trailer fields might be silently discarded along the path to the client.
     1699                  </li>
     1700               </ol>
     1701               <p id="rfc.section.6.2.1.p.6">This requirement prevents an interoperability failure when the message is being received by an HTTP/1.1 (or later) proxy and
     1702                  forwarded to an HTTP/1.0 recipient. It avoids a situation where compliance with the protocol would have necessitated a possibly
     1703                  infinite buffer on the proxy.
     1704               </p>
     1705               <p id="rfc.section.6.2.1.p.7">A process for decoding the "chunked" transfer-coding can be represented in pseudo-code as:</p>
     1706               <div id="rfc.figure.u.55"></div><pre class="text">  length := 0
    16421707  read chunk-size, chunk-ext (if any) and CRLF
    16431708  while (chunk-size &gt; 0) {
     
    16551720  Remove "chunked" from Transfer-Encoding
    16561721</pre><p id="rfc.section.6.2.1.p.9">All HTTP/1.1 applications <em class="bcp14">MUST</em> be able to receive and decode the "chunked" transfer-coding and <em class="bcp14">MUST</em> ignore chunk-ext extensions they do not understand.
    1657       </p>
    1658       <p id="rfc.section.6.2.1.p.10">Since "chunked" is the only transfer-coding required to be understood by HTTP/1.1 recipients, it plays a crucial role in delimiting
    1659          messages on a persistent connection. Whenever a transfer-coding is applied to a payload body in a request, the final transfer-coding
    1660          applied <em class="bcp14">MUST</em> be "chunked". If a transfer-coding is applied to a response payload body, then either the final transfer-coding applied <em class="bcp14">MUST</em> be "chunked" or the message <em class="bcp14">MUST</em> be terminated by closing the connection. When the "chunked" transfer-coding is used, it <em class="bcp14">MUST</em> be the last transfer-coding applied to form the message-body. The "chunked" transfer-coding <em class="bcp14">MUST NOT</em> be applied more than once in a message-body.
    1661       </p>
    1662       <h3 id="rfc.section.6.2.2"><a href="#rfc.section.6.2.2">6.2.2</a>&nbsp;<a id="compression.codings" href="#compression.codings">Compression Codings</a></h3>
    1663       <p id="rfc.section.6.2.2.p.1">The codings defined below can be used to compress the payload of a message.</p>
    1664       <div class="note" id="rfc.section.6.2.2.p.2">
    1665          <p> <b>Note:</b> Use of program names for the identification of encoding formats is not desirable and is discouraged for future encodings.
    1666             Their use here is representative of historical practice, not good design.
    1667          </p>
    1668       </div>
    1669       <div class="note" id="rfc.section.6.2.2.p.3">
    1670          <p> <b>Note:</b> For compatibility with previous implementations of HTTP, applications <em class="bcp14">SHOULD</em> consider "x-gzip" and "x-compress" to be equivalent to "gzip" and "compress" respectively.
    1671          </p>
    1672       </div>
    1673       <div id="rfc.iref.c.7"></div>
    1674       <div id="rfc.iref.c.8"></div>
    1675       <h4 id="rfc.section.6.2.2.1"><a href="#rfc.section.6.2.2.1">6.2.2.1</a>&nbsp;<a id="compress.coding" href="#compress.coding">Compress Coding</a></h4>
    1676       <p id="rfc.section.6.2.2.1.p.1">The "compress" format is produced by the common UNIX file compression program "compress". This format is an adaptive Lempel-Ziv-Welch
    1677          coding (LZW).
    1678       </p>
    1679       <div id="rfc.iref.d.2"></div>
    1680       <div id="rfc.iref.c.9"></div>
    1681       <h4 id="rfc.section.6.2.2.2"><a href="#rfc.section.6.2.2.2">6.2.2.2</a>&nbsp;<a id="deflate.coding" href="#deflate.coding">Deflate Coding</a></h4>
    1682       <p id="rfc.section.6.2.2.2.p.1">The "deflate" format is defined as the "deflate" compression mechanism (described in <a href="#RFC1951" id="rfc.xref.RFC1951.1"><cite title="DEFLATE Compressed Data Format Specification version 1.3">[RFC1951]</cite></a>) used inside the "zlib" data format (<a href="#RFC1950" id="rfc.xref.RFC1950.1"><cite title="ZLIB Compressed Data Format Specification version 3.3">[RFC1950]</cite></a>).
    1683       </p>
    1684       <div class="note" id="rfc.section.6.2.2.2.p.2">
    1685          <p> <b>Note:</b> Some incorrect implementations send the "deflate" compressed data without the zlib wrapper.
    1686          </p>
    1687       </div>
    1688       <div id="rfc.iref.g.90"></div>
    1689       <div id="rfc.iref.c.10"></div>
    1690       <h4 id="rfc.section.6.2.2.3"><a href="#rfc.section.6.2.2.3">6.2.2.3</a>&nbsp;<a id="gzip.coding" href="#gzip.coding">Gzip Coding</a></h4>
    1691       <p id="rfc.section.6.2.2.3.p.1">The "gzip" format is produced by the file compression program "gzip" (GNU zip), as described in <a href="#RFC1952" id="rfc.xref.RFC1952.1"><cite title="GZIP file format specification version 4.3">[RFC1952]</cite></a>. This format is a Lempel-Ziv coding (LZ77) with a 32 bit CRC.
    1692       </p>
    1693       <h3 id="rfc.section.6.2.3"><a href="#rfc.section.6.2.3">6.2.3</a>&nbsp;<a id="transfer.coding.registry" href="#transfer.coding.registry">Transfer Coding Registry</a></h3>
    1694       <p id="rfc.section.6.2.3.p.1">The HTTP Transfer Coding Registry defines the name space for the transfer coding names.</p>
    1695       <p id="rfc.section.6.2.3.p.2">Registrations <em class="bcp14">MUST</em> include the following fields:
    1696       </p>
    1697       <ul>
    1698          <li>Name</li>
    1699          <li>Description</li>
    1700          <li>Pointer to specification text</li>
    1701       </ul>
    1702       <p id="rfc.section.6.2.3.p.3">Names of transfer codings <em class="bcp14">MUST NOT</em> overlap with names of content codings (<a href="p3-payload.html#content.codings" title="Content Codings">Section 2.2</a> of <a href="#Part3" id="rfc.xref.Part3.4"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>), unless the encoding transformation is identical (as it is the case for the compression codings defined in <a href="#compression.codings" title="Compression Codings">Section&nbsp;6.2.2</a>).
    1703       </p>
    1704       <p id="rfc.section.6.2.3.p.4">Values to be added to this name space require a specification (see "Specification Required" in <a href="http://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 section.
    1705       </p>
    1706       <p id="rfc.section.6.2.3.p.5">The registry itself is maintained at &lt;<a href="http://www.iana.org/assignments/http-parameters">http://www.iana.org/assignments/http-parameters</a>&gt;.
    1707       </p>
    1708       <h2 id="rfc.section.6.3"><a href="#rfc.section.6.3">6.3</a>&nbsp;<a id="product.tokens" href="#product.tokens">Product Tokens</a></h2>
    1709       <p id="rfc.section.6.3.p.1">Product tokens are used to allow communicating applications to identify themselves by software name and version. Most fields
    1710          using product tokens also allow sub-products which form a significant part of the application to be listed, separated by whitespace.
    1711          By convention, the products are listed in order of their significance for identifying the application.
    1712       </p>
    1713       <div id="rfc.figure.u.56"></div><pre class="inline"><span id="rfc.iref.g.91"></span><span id="rfc.iref.g.92"></span>  <a href="#product.tokens" class="smpl">product</a>         = <a href="#rule.token.separators" class="smpl">token</a> ["/" <a href="#product.tokens" class="smpl">product-version</a>]
     1722               </p>
     1723               <p id="rfc.section.6.2.1.p.10">Since "chunked" is the only transfer-coding required to be understood by HTTP/1.1 recipients, it plays a crucial role in delimiting
     1724                  messages on a persistent connection. Whenever a transfer-coding is applied to a payload body in a request, the final transfer-coding
     1725                  applied <em class="bcp14">MUST</em> be "chunked". If a transfer-coding is applied to a response payload body, then either the final transfer-coding applied <em class="bcp14">MUST</em> be "chunked" or the message <em class="bcp14">MUST</em> be terminated by closing the connection. When the "chunked" transfer-coding is used, it <em class="bcp14">MUST</em> be the last transfer-coding applied to form the message-body. The "chunked" transfer-coding <em class="bcp14">MUST NOT</em> be applied more than once in a message-body.
     1726               </p>
     1727            </div>
     1728            <div id="compression.codings">
     1729               <h3 id="rfc.section.6.2.2"><a href="#rfc.section.6.2.2">6.2.2</a>&nbsp;<a href="#compression.codings">Compression Codings</a></h3>
     1730               <p id="rfc.section.6.2.2.p.1">The codings defined below can be used to compress the payload of a message.</p>
     1731               <div class="note" id="rfc.section.6.2.2.p.2">
     1732                  <p><b>Note:</b> Use of program names for the identification of encoding formats is not desirable and is discouraged for future encodings.
     1733                     Their use here is representative of historical practice, not good design.
     1734                  </p>
     1735               </div>
     1736               <div class="note" id="rfc.section.6.2.2.p.3">
     1737                  <p><b>Note:</b> For compatibility with previous implementations of HTTP, applications <em class="bcp14">SHOULD</em> consider "x-gzip" and "x-compress" to be equivalent to "gzip" and "compress" respectively.
     1738                  </p>
     1739               </div>
     1740               <div id="compress.coding">
     1741                  <div id="rfc.iref.c.7"></div>
     1742                  <div id="rfc.iref.c.8"></div>
     1743                  <h4 id="rfc.section.6.2.2.1"><a href="#rfc.section.6.2.2.1">6.2.2.1</a>&nbsp;<a href="#compress.coding">Compress Coding</a></h4>
     1744                  <p id="rfc.section.6.2.2.1.p.1">The "compress" format is produced by the common UNIX file compression program "compress". This format is an adaptive Lempel-Ziv-Welch
     1745                     coding (LZW).
     1746                  </p>
     1747               </div>
     1748               <div id="deflate.coding">
     1749                  <div id="rfc.iref.d.2"></div>
     1750                  <div id="rfc.iref.c.9"></div>
     1751                  <h4 id="rfc.section.6.2.2.2"><a href="#rfc.section.6.2.2.2">6.2.2.2</a>&nbsp;<a href="#deflate.coding">Deflate Coding</a></h4>
     1752                  <p id="rfc.section.6.2.2.2.p.1">The "deflate" format is defined as the "deflate" compression mechanism (described in <a href="#RFC1951" id="rfc.xref.RFC1951.1"><cite title="DEFLATE Compressed Data Format Specification version 1.3">[RFC1951]</cite></a>) used inside the "zlib" data format (<a href="#RFC1950" id="rfc.xref.RFC1950.1"><cite title="ZLIB Compressed Data Format Specification version 3.3">[RFC1950]</cite></a>).
     1753                  </p>
     1754                  <div class="note" id="rfc.section.6.2.2.2.p.2">
     1755                     <p><b>Note:</b> Some incorrect implementations send the "deflate" compressed data without the zlib wrapper.
     1756                     </p>
     1757                  </div>
     1758               </div>
     1759               <div id="gzip.coding">
     1760                  <div id="rfc.iref.g.90"></div>
     1761                  <div id="rfc.iref.c.10"></div>
     1762                  <h4 id="rfc.section.6.2.2.3"><a href="#rfc.section.6.2.2.3">6.2.2.3</a>&nbsp;<a href="#gzip.coding">Gzip Coding</a></h4>
     1763                  <p id="rfc.section.6.2.2.3.p.1">The "gzip" format is produced by the file compression program "gzip" (GNU zip), as described in <a href="#RFC1952" id="rfc.xref.RFC1952.1"><cite title="GZIP file format specification version 4.3">[RFC1952]</cite></a>. This format is a Lempel-Ziv coding (LZ77) with a 32 bit CRC.
     1764                  </p>
     1765               </div>
     1766            </div>
     1767            <div id="transfer.coding.registry">
     1768               <h3 id="rfc.section.6.2.3"><a href="#rfc.section.6.2.3">6.2.3</a>&nbsp;<a href="#transfer.coding.registry">Transfer Coding Registry</a></h3>
     1769               <p id="rfc.section.6.2.3.p.1">The HTTP Transfer Coding Registry defines the name space for the transfer coding names.</p>
     1770               <p id="rfc.section.6.2.3.p.2">Registrations <em class="bcp14">MUST</em> include the following fields:
     1771               </p>
     1772               <ul>
     1773                  <li>Name</li>
     1774                  <li>Description</li>
     1775                  <li>Pointer to specification text</li>
     1776               </ul>
     1777               <p id="rfc.section.6.2.3.p.3">Names of transfer codings <em class="bcp14">MUST NOT</em> overlap with names of content codings (<a href="p3-payload.html#content.codings" title="Content Codings">Section 2.2</a> of <a href="#Part3" id="rfc.xref.Part3.4"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>), unless the encoding transformation is identical (as it is the case for the compression codings defined in <a href="#compression.codings" title="Compression Codings">Section&nbsp;6.2.2</a>).
     1778               </p>
     1779               <p id="rfc.section.6.2.3.p.4">Values to be added to this name space require a specification (see "Specification Required" in <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 section.
     1780               </p>
     1781               <p id="rfc.section.6.2.3.p.5">The registry itself is maintained at &lt;<a href="http://www.iana.org/assignments/http-parameters">http://www.iana.org/assignments/http-parameters</a>&gt;.
     1782               </p>
     1783            </div>
     1784         </div>
     1785         <div id="product.tokens">
     1786            <h2 id="rfc.section.6.3"><a href="#rfc.section.6.3">6.3</a>&nbsp;<a href="#product.tokens">Product Tokens</a></h2>
     1787            <p id="rfc.section.6.3.p.1">Product tokens are used to allow communicating applications to identify themselves by software name and version. Most fields
     1788               using product tokens also allow sub-products which form a significant part of the application to be listed, separated by whitespace.
     1789               By convention, the products are listed in order of their significance for identifying the application.
     1790            </p>
     1791            <div id="rfc.figure.u.56"></div><pre class="inline"><span id="rfc.iref.g.91"></span><span id="rfc.iref.g.92"></span>  <a href="#product.tokens" class="smpl">product</a>         = <a href="#rule.token.separators" class="smpl">token</a> ["/" <a href="#product.tokens" class="smpl">product-version</a>]
    17141792  <a href="#product.tokens" class="smpl">product-version</a> = <a href="#rule.token.separators" class="smpl">token</a>
    17151793</pre><p id="rfc.section.6.3.p.3">Examples:</p>
    1716       <div id="rfc.figure.u.57"></div><pre class="text">  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
     1794            <div id="rfc.figure.u.57"></div><pre class="text">  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
    17171795  Server: Apache/0.8.4
    17181796</pre><p id="rfc.section.6.3.p.5">Product tokens <em class="bcp14">SHOULD</em> be short and to the point. They <em class="bcp14">MUST NOT</em> be used for advertising or other non-essential information. Although any token character <em class="bcp14">MAY</em> appear in a product-version, this token <em class="bcp14">SHOULD</em> only be used for a version identifier (i.e., successive versions of the same product <em class="bcp14">SHOULD</em> only differ in the product-version portion of the product value).
    1719       </p>
    1720       <h2 id="rfc.section.6.4"><a href="#rfc.section.6.4">6.4</a>&nbsp;<a id="quality.values" href="#quality.values">Quality Values</a></h2>
    1721       <p id="rfc.section.6.4.p.1">Both transfer codings (TE request header, <a href="#header.te" id="rfc.xref.header.te.3" title="TE">Section&nbsp;9.5</a>) and content negotiation (<a href="p3-payload.html#content.negotiation" title="Content Negotiation">Section 5</a> of <a href="#Part3" id="rfc.xref.Part3.5"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>) use short "floating point" numbers to indicate the relative importance ("weight") of various negotiable parameters. A weight
    1722          is normalized to a real number in the range 0 through 1, where 0 is the minimum and 1 the maximum value. If a parameter has
    1723          a quality value of 0, then content with this parameter is "not acceptable" for the client. HTTP/1.1 applications <em class="bcp14">MUST NOT</em> generate more than three digits after the decimal point. User configuration of these values <em class="bcp14">SHOULD</em> also be limited in this fashion.
    1724       </p>
    1725       <div id="rfc.figure.u.58"></div><pre class="inline"><span id="rfc.iref.g.93"></span>  <a href="#quality.values" class="smpl">qvalue</a>         = ( "0" [ "." 0*3<a href="#core.rules" class="smpl">DIGIT</a> ] )
     1797            </p>
     1798         </div>
     1799         <div id="quality.values">
     1800            <h2 id="rfc.section.6.4"><a href="#rfc.section.6.4">6.4</a>&nbsp;<a href="#quality.values">Quality Values</a></h2>
     1801            <p id="rfc.section.6.4.p.1">Both transfer codings (TE request header, <a href="#header.te" id="rfc.xref.header.te.3" title="TE">Section&nbsp;9.5</a>) and content negotiation (<a href="p3-payload.html#content.negotiation" title="Content Negotiation">Section 5</a> of <a href="#Part3" id="rfc.xref.Part3.5"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>) use short "floating point" numbers to indicate the relative importance ("weight") of various negotiable parameters. A weight
     1802               is normalized to a real number in the range 0 through 1, where 0 is the minimum and 1 the maximum value. If a parameter has
     1803               a quality value of 0, then content with this parameter is "not acceptable" for the client. HTTP/1.1 applications <em class="bcp14">MUST NOT</em> generate more than three digits after the decimal point. User configuration of these values <em class="bcp14">SHOULD</em> also be limited in this fashion.
     1804            </p>
     1805            <div id="rfc.figure.u.58"></div><pre class="inline"><span id="rfc.iref.g.93"></span>  <a href="#quality.values" class="smpl">qvalue</a>         = ( "0" [ "." 0*3<a href="#core.rules" class="smpl">DIGIT</a> ] )
    17261806                 / ( "1" [ "." 0*3("0") ] )
    1727 </pre><div class="note" id="rfc.section.6.4.p.3">
    1728          <p> <b>Note:</b> "Quality values" is a misnomer, since these values merely represent relative degradation in desired quality.
    1729          </p>
     1807</pre><div class="note" id="rfc.section.6.4.p.3">
     1808               <p><b>Note:</b> "Quality values" is a misnomer, since these values merely represent relative degradation in desired quality.
     1809               </p>
     1810            </div>
     1811         </div>
    17301812      </div>
    1731       <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a id="connections" href="#connections">Connections</a></h1>
    1732       <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a>&nbsp;<a id="persistent.connections" href="#persistent.connections">Persistent Connections</a></h2>
    1733       <h3 id="rfc.section.7.1.1"><a href="#rfc.section.7.1.1">7.1.1</a>&nbsp;<a id="persistent.purpose" href="#persistent.purpose">Purpose</a></h3>
    1734       <p id="rfc.section.7.1.1.p.1">Prior to persistent connections, a separate TCP connection was established to fetch each URL, increasing the load on HTTP
    1735          servers and causing congestion on the Internet. The use of inline images and other associated data often requires a client
    1736          to make multiple requests of the same server in a short amount of time. Analysis of these performance problems and results
    1737          from a prototype implementation are available <a href="#Pad1995" id="rfc.xref.Pad1995.1"><cite title="Improving HTTP Latency">[Pad1995]</cite></a>  <a href="#Spe" id="rfc.xref.Spe.1"><cite title="Analysis of HTTP Performance Problems">[Spe]</cite></a>. Implementation experience and measurements of actual HTTP/1.1 implementations show good results <a href="#Nie1997" id="rfc.xref.Nie1997.1"><cite title="Network Performance Effects of HTTP/1.1, CSS1, and PNG">[Nie1997]</cite></a>. Alternatives have also been explored, for example, T/TCP <a href="#Tou1998" id="rfc.xref.Tou1998.1"><cite title="Analysis of HTTP Performance">[Tou1998]</cite></a>.
    1738       </p>
    1739       <p id="rfc.section.7.1.1.p.2">Persistent HTTP connections have a number of advantages: </p>
    1740       <ul>
    1741          <li>By opening and closing fewer TCP connections, CPU time is saved in routers and hosts (clients, servers, proxies, gateways,
    1742             tunnels, or caches), and memory used for TCP protocol control blocks can be saved in hosts.
    1743          </li>
    1744          <li>HTTP requests and responses can be pipelined on a connection. Pipelining allows a client to make multiple requests without
    1745             waiting for each response, allowing a single TCP connection to be used much more efficiently, with much lower elapsed time.
    1746          </li>
    1747          <li>Network congestion is reduced by reducing the number of packets caused by TCP opens, and by allowing TCP sufficient time to
    1748             determine the congestion state of the network.
    1749          </li>
    1750          <li>Latency on subsequent requests is reduced since there is no time spent in TCP's connection opening handshake.</li>
    1751          <li>HTTP can evolve more gracefully, since errors can be reported without the penalty of closing the TCP connection. Clients using
    1752             future versions of HTTP might optimistically try a new feature, but if communicating with an older server, retry with old
    1753             semantics after an error is reported.
    1754          </li>
    1755       </ul>
    1756       <p id="rfc.section.7.1.1.p.3">HTTP implementations <em class="bcp14">SHOULD</em> implement persistent connections.
    1757       </p>
    1758       <h3 id="rfc.section.7.1.2"><a href="#rfc.section.7.1.2">7.1.2</a>&nbsp;<a id="persistent.overall" href="#persistent.overall">Overall Operation</a></h3>
    1759       <p id="rfc.section.7.1.2.p.1">A significant difference between HTTP/1.1 and earlier versions of HTTP is that persistent connections are the default behavior
    1760          of any HTTP connection. That is, unless otherwise indicated, the client <em class="bcp14">SHOULD</em> assume that the server will maintain a persistent connection, even after error responses from the server.
    1761       </p>
    1762       <p id="rfc.section.7.1.2.p.2">Persistent connections provide a mechanism by which a client and a server can signal the close of a TCP connection. This signaling
    1763          takes place using the Connection header field (<a href="#header.connection" id="rfc.xref.header.connection.2" title="Connection">Section&nbsp;9.1</a>). Once a close has been signaled, the client <em class="bcp14">MUST NOT</em> send any more requests on that connection.
    1764       </p>
    1765       <h4 id="rfc.section.7.1.2.1"><a href="#rfc.section.7.1.2.1">7.1.2.1</a>&nbsp;<a id="persistent.negotiation" href="#persistent.negotiation">Negotiation</a></h4>
    1766       <p id="rfc.section.7.1.2.1.p.1">An HTTP/1.1 server <em class="bcp14">MAY</em> assume that a HTTP/1.1 client intends to maintain a persistent connection unless a Connection header including the connection-token
    1767          "close" was sent in the request. If the server chooses to close the connection immediately after sending the response, it <em class="bcp14">SHOULD</em> send a Connection header including the connection-token "close".
    1768       </p>
    1769       <p id="rfc.section.7.1.2.1.p.2">An HTTP/1.1 client <em class="bcp14">MAY</em> expect a connection to remain open, but would decide to keep it open based on whether the response from a server contains
    1770          a Connection header with the connection-token close. In case the client does not want to maintain a connection for more than
    1771          that request, it <em class="bcp14">SHOULD</em> send a Connection header including the connection-token close.
    1772       </p>
    1773       <p id="rfc.section.7.1.2.1.p.3">If either the client or the server sends the close token in the Connection header, that request becomes the last one for the
    1774          connection.
    1775       </p>
    1776       <p id="rfc.section.7.1.2.1.p.4">Clients and servers <em class="bcp14">SHOULD NOT</em> assume that a persistent connection is maintained for HTTP versions less than 1.1 unless it is explicitly signaled. See <a href="#compatibility.with.http.1.0.persistent.connections" title="Compatibility with HTTP/1.0 Persistent Connections">Appendix&nbsp;B.2</a> for more information on backward compatibility with HTTP/1.0 clients.
    1777       </p>
    1778       <p id="rfc.section.7.1.2.1.p.5">In order to remain persistent, all messages on the connection <em class="bcp14">MUST</em> have a self-defined message length (i.e., one not defined by closure of the connection), as described in <a href="#message.body" title="Message Body">Section&nbsp;3.3</a>.
    1779       </p>
    1780       <h4 id="rfc.section.7.1.2.2"><a href="#rfc.section.7.1.2.2">7.1.2.2</a>&nbsp;<a id="pipelining" href="#pipelining">Pipelining</a></h4>
    1781       <p id="rfc.section.7.1.2.2.p.1">A client that supports persistent connections <em class="bcp14">MAY</em> "pipeline" its requests (i.e., send multiple requests without waiting for each response). A server <em class="bcp14">MUST</em> send its responses to those requests in the same order that the requests were received.
    1782       </p>
    1783       <p id="rfc.section.7.1.2.2.p.2">Clients which assume persistent connections and pipeline immediately after connection establishment <em class="bcp14">SHOULD</em> be prepared to retry their connection if the first pipelined attempt fails. If a client does such a retry, it <em class="bcp14">MUST NOT</em> pipeline before it knows the connection is persistent. Clients <em class="bcp14">MUST</em> also be prepared to resend their requests if the server closes the connection before sending all of the corresponding responses.
    1784       </p>
    1785       <p id="rfc.section.7.1.2.2.p.3">Clients <em class="bcp14">SHOULD NOT</em> pipeline requests using non-idempotent methods or non-idempotent sequences of methods (see <a href="p2-semantics.html#idempotent.methods" title="Idempotent Methods">Section 7.1.2</a> of <a href="#Part2" id="rfc.xref.Part2.6"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>). Otherwise, a premature termination of the transport connection could lead to indeterminate results. A client wishing to
    1786          send a non-idempotent request <em class="bcp14">SHOULD</em> wait to send that request until it has received the response status line for the previous request.
    1787       </p>
    1788       <h3 id="rfc.section.7.1.3"><a href="#rfc.section.7.1.3">7.1.3</a>&nbsp;<a id="persistent.proxy" href="#persistent.proxy">Proxy Servers</a></h3>
    1789       <p id="rfc.section.7.1.3.p.1">It is especially important that proxies correctly implement the properties of the Connection header field as specified in <a href="#header.connection" id="rfc.xref.header.connection.3" title="Connection">Section&nbsp;9.1</a>.
    1790       </p>
    1791       <p id="rfc.section.7.1.3.p.2">The proxy server <em class="bcp14">MUST</em> signal persistent connections separately with its clients and the origin servers (or other proxy servers) that it connects
    1792          to. Each persistent connection applies to only one transport link.
    1793       </p>
    1794       <p id="rfc.section.7.1.3.p.3">A proxy server <em class="bcp14">MUST NOT</em> establish a HTTP/1.1 persistent connection with an HTTP/1.0 client (but see <a href="http://tools.ietf.org/html/rfc2068#section-19.7.1">Section 19.7.1</a> of <a href="#RFC2068" id="rfc.xref.RFC2068.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a> for information and discussion of the problems with the Keep-Alive header implemented by many HTTP/1.0 clients).
    1795       </p>
    1796       <h4 id="rfc.section.7.1.3.1"><a href="#rfc.section.7.1.3.1">7.1.3.1</a>&nbsp;<a id="end-to-end.and.hop-by-hop.headers" href="#end-to-end.and.hop-by-hop.headers">End-to-end and Hop-by-hop Headers</a></h4>
    1797       <p id="rfc.section.7.1.3.1.p.1">For the purpose of defining the behavior of caches and non-caching proxies, we divide HTTP headers into two categories: </p>
    1798       <ul>
    1799          <li>End-to-end headers, which are transmitted to the ultimate recipient of a request or response. End-to-end headers in responses
    1800             MUST be stored as part of a cache entry and <em class="bcp14">MUST</em> be transmitted in any response formed from a cache entry.
    1801          </li>
    1802          <li>Hop-by-hop headers, which are meaningful only for a single transport-level connection, and are not stored by caches or forwarded
    1803             by proxies.
    1804          </li>
    1805       </ul>
    1806       <p id="rfc.section.7.1.3.1.p.2">The following HTTP/1.1 headers are hop-by-hop headers: </p>
    1807       <ul>
    1808          <li>Connection</li>
    1809          <li>Keep-Alive</li>
    1810          <li>Proxy-Authenticate</li>
    1811          <li>Proxy-Authorization</li>
    1812          <li>TE</li>
    1813          <li>Trailer</li>
    1814          <li>Transfer-Encoding</li>
    1815          <li>Upgrade</li>
    1816       </ul>
    1817       <p id="rfc.section.7.1.3.1.p.3">All other headers defined by HTTP/1.1 are end-to-end headers.</p>
    1818       <p id="rfc.section.7.1.3.1.p.4">Other hop-by-hop headers <em class="bcp14">MUST</em> be listed in a Connection header (<a href="#header.connection" id="rfc.xref.header.connection.4" title="Connection">Section&nbsp;9.1</a>).
    1819       </p>
    1820       <h4 id="rfc.section.7.1.3.2"><a href="#rfc.section.7.1.3.2">7.1.3.2</a>&nbsp;<a id="non-modifiable.headers" href="#non-modifiable.headers">Non-modifiable Headers</a></h4>
    1821       <p id="rfc.section.7.1.3.2.p.1">Some features of HTTP/1.1, such as Digest Authentication, depend on the value of certain end-to-end headers. A transparent
    1822          proxy <em class="bcp14">SHOULD NOT</em> modify an end-to-end header unless the definition of that header requires or specifically allows that.
    1823       </p>
    1824       <p id="rfc.section.7.1.3.2.p.2">A transparent proxy <em class="bcp14">MUST NOT</em> modify any of the following fields in a request or response, and it <em class="bcp14">MUST NOT</em> add any of these fields if not already present:
    1825       </p>
    1826       <ul>
    1827          <li>Content-Location</li>
    1828          <li>Content-MD5</li>
    1829          <li>ETag</li>
    1830          <li>Last-Modified</li>
    1831       </ul>
    1832       <p id="rfc.section.7.1.3.2.p.3">A transparent proxy <em class="bcp14">MUST NOT</em> modify any of the following fields in a response:
    1833       </p>
    1834       <ul>
    1835          <li>Expires</li>
    1836       </ul>
    1837       <p id="rfc.section.7.1.3.2.p.4">but it <em class="bcp14">MAY</em> add any of these fields if not already present. If an Expires header is added, it <em class="bcp14">MUST</em> be given a field-value identical to that of the Date header in that response.
    1838       </p>
    1839       <p id="rfc.section.7.1.3.2.p.5">A proxy <em class="bcp14">MUST NOT</em> modify or add any of the following fields in a message that contains the no-transform cache-control directive, or in any request:
    1840       </p>
    1841       <ul>
    1842          <li>Content-Encoding</li>
    1843          <li>Content-Range</li>
    1844          <li>Content-Type</li>
    1845       </ul>
    1846       <p id="rfc.section.7.1.3.2.p.6">A non-transparent proxy <em class="bcp14">MAY</em> modify or add these fields to a message that does not include no-transform, but if it does so, it <em class="bcp14">MUST</em> add a Warning 214 (Transformation applied) if one does not already appear in the message (see <a href="p6-cache.html#header.warning" title="Warning">Section 3.6</a> of <a href="#Part6" id="rfc.xref.Part6.9"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>).
    1847       </p>
    1848       <div class="note" id="rfc.section.7.1.3.2.p.7">
    1849          <p> <b>Warning:</b> Unnecessary modification of end-to-end headers might cause authentication failures if stronger authentication mechanisms are
    1850             introduced in later versions of HTTP. Such authentication mechanisms <em class="bcp14">MAY</em> rely on the values of header fields not listed here.
    1851          </p>
     1813      <div id="connections">
     1814         <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a href="#connections">Connections</a></h1>
     1815         <div id="persistent.connections">
     1816            <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a>&nbsp;<a href="#persistent.connections">Persistent Connections</a></h2>
     1817            <div id="persistent.purpose">
     1818               <h3 id="rfc.section.7.1.1"><a href="#rfc.section.7.1.1">7.1.1</a>&nbsp;<a href="#persistent.purpose">Purpose</a></h3>
     1819               <p id="rfc.section.7.1.1.p.1">Prior to persistent connections, a separate TCP connection was established to fetch each URL, increasing the load on HTTP
     1820                  servers and causing congestion on the Internet. The use of inline images and other associated data often requires a client
     1821                  to make multiple requests of the same server in a short amount of time. Analysis of these performance problems and results
     1822                  from a prototype implementation are available <a href="#Pad1995" id="rfc.xref.Pad1995.1"><cite title="Improving HTTP Latency">[Pad1995]</cite></a> <a href="#Spe" id="rfc.xref.Spe.1"><cite title="Analysis of HTTP Performance Problems">[Spe]</cite></a>. Implementation experience and measurements of actual HTTP/1.1 implementations show good results <a href="#Nie1997" id="rfc.xref.Nie1997.1"><cite title="Network Performance Effects of HTTP/1.1, CSS1, and PNG">[Nie1997]</cite></a>. Alternatives have also been explored, for example, T/TCP <a href="#Tou1998" id="rfc.xref.Tou1998.1"><cite title="Analysis of HTTP Performance">[Tou1998]</cite></a>.
     1823               </p>
     1824               <p id="rfc.section.7.1.1.p.2">Persistent HTTP connections have a number of advantages: </p>
     1825               <ul>
     1826                  <li>By opening and closing fewer TCP connections, CPU time is saved in routers and hosts (clients, servers, proxies, gateways,
     1827                     tunnels, or caches), and memory used for TCP protocol control blocks can be saved in hosts.
     1828                  </li>
     1829                  <li>HTTP requests and responses can be pipelined on a connection. Pipelining allows a client to make multiple requests without
     1830                     waiting for each response, allowing a single TCP connection to be used much more efficiently, with much lower elapsed time.
     1831                  </li>
     1832                  <li>Network congestion is reduced by reducing the number of packets caused by TCP opens, and by allowing TCP sufficient time to
     1833                     determine the congestion state of the network.
     1834                  </li>
     1835                  <li>Latency on subsequent requests is reduced since there is no time spent in TCP's connection opening handshake.</li>
     1836                  <li>HTTP can evolve more gracefully, since errors can be reported without the penalty of closing the TCP connection. Clients using
     1837                     future versions of HTTP might optimistically try a new feature, but if communicating with an older server, retry with old
     1838                     semantics after an error is reported.
     1839                  </li>
     1840               </ul>
     1841               <p id="rfc.section.7.1.1.p.3">HTTP implementations <em class="bcp14">SHOULD</em> implement persistent connections.
     1842               </p>
     1843            </div>
     1844            <div id="persistent.overall">
     1845               <h3 id="rfc.section.7.1.2"><a href="#rfc.section.7.1.2">7.1.2</a>&nbsp;<a href="#persistent.overall">Overall Operation</a></h3>
     1846               <p id="rfc.section.7.1.2.p.1">A significant difference between HTTP/1.1 and earlier versions of HTTP is that persistent connections are the default behavior
     1847                  of any HTTP connection. That is, unless otherwise indicated, the client <em class="bcp14">SHOULD</em> assume that the server will maintain a persistent connection, even after error responses from the server.
     1848               </p>
     1849               <p id="rfc.section.7.1.2.p.2">Persistent connections provide a mechanism by which a client and a server can signal the close of a TCP connection. This signaling
     1850                  takes place using the Connection header field (<a href="#header.connection" id="rfc.xref.header.connection.2" title="Connection">Section&nbsp;9.1</a>). Once a close has been signaled, the client <em class="bcp14">MUST NOT</em> send any more requests on that connection.
     1851               </p>
     1852               <div id="persistent.negotiation">
     1853                  <h4 id="rfc.section.7.1.2.1"><a href="#rfc.section.7.1.2.1">7.1.2.1</a>&nbsp;<a href="#persistent.negotiation">Negotiation</a></h4>
     1854                  <p id="rfc.section.7.1.2.1.p.1">An HTTP/1.1 server <em class="bcp14">MAY</em> assume that a HTTP/1.1 client intends to maintain a persistent connection unless a Connection header including the connection-token
     1855                     "close" was sent in the request. If the server chooses to close the connection immediately after sending the response, it <em class="bcp14">SHOULD</em> send a Connection header including the connection-token "close".
     1856                  </p>
     1857                  <p id="rfc.section.7.1.2.1.p.2">An HTTP/1.1 client <em class="bcp14">MAY</em> expect a connection to remain open, but would decide to keep it open based on whether the response from a server contains
     1858                     a Connection header with the connection-token close. In case the client does not want to maintain a connection for more than
     1859                     that request, it <em class="bcp14">SHOULD</em> send a Connection header including the connection-token close.
     1860                  </p>
     1861                  <p id="rfc.section.7.1.2.1.p.3">If either the client or the server sends the close token in the Connection header, that request becomes the last one for the
     1862                     connection.
     1863                  </p>
     1864                  <p id="rfc.section.7.1.2.1.p.4">Clients and servers <em class="bcp14">SHOULD NOT</em> assume that a persistent connection is maintained for HTTP versions less than 1.1 unless it is explicitly signaled. See <a href="#compatibility.with.http.1.0.persistent.connections" title="Compatibility with HTTP/1.0 Persistent Connections">Appendix&nbsp;B.2</a> for more information on backward compatibility with HTTP/1.0 clients.
     1865                  </p>
     1866                  <p id="rfc.section.7.1.2.1.p.5">In order to remain persistent, all messages on the connection <em class="bcp14">MUST</em> have a self-defined message length (i.e., one not defined by closure of the connection), as described in <a href="#message.body" title="Message Body">Section&nbsp;3.3</a>.
     1867                  </p>
     1868               </div>
     1869               <div id="pipelining">
     1870                  <h4 id="rfc.section.7.1.2.2"><a href="#rfc.section.7.1.2.2">7.1.2.2</a>&nbsp;<a href="#pipelining">Pipelining</a></h4>
     1871                  <p id="rfc.section.7.1.2.2.p.1">A client that supports persistent connections <em class="bcp14">MAY</em> "pipeline" its requests (i.e., send multiple requests without waiting for each response). A server <em class="bcp14">MUST</em> send its responses to those requests in the same order that the requests were received.
     1872                  </p>
     1873                  <p id="rfc.section.7.1.2.2.p.2">Clients which assume persistent connections and pipeline immediately after connection establishment <em class="bcp14">SHOULD</em> be prepared to retry their connection if the first pipelined attempt fails. If a client does such a retry, it <em class="bcp14">MUST NOT</em> pipeline before it knows the connection is persistent. Clients <em class="bcp14">MUST</em> also be prepared to resend their requests if the server closes the connection before sending all of the corresponding responses.
     1874                  </p>
     1875                  <p id="rfc.section.7.1.2.2.p.3">Clients <em class="bcp14">SHOULD NOT</em> pipeline requests using non-idempotent methods or non-idempotent sequences of methods (see <a href="p2-semantics.html#idempotent.methods" title="Idempotent Methods">Section 7.1.2</a> of <a href="#Part2" id="rfc.xref.Part2.6"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>). Otherwise, a premature termination of the transport connection could lead to indeterminate results. A client wishing to
     1876                     send a non-idempotent request <em class="bcp14">SHOULD</em> wait to send that request until it has received the response status line for the previous request.
     1877                  </p>
     1878               </div>
     1879            </div>
     1880            <div id="persistent.proxy">
     1881               <h3 id="rfc.section.7.1.3"><a href="#rfc.section.7.1.3">7.1.3</a>&nbsp;<a href="#persistent.proxy">Proxy Servers</a></h3>
     1882               <p id="rfc.section.7.1.3.p.1">It is especially important that proxies correctly implement the properties of the Connection header field as specified in <a href="#header.connection" id="rfc.xref.header.connection.3" title="Connection">Section&nbsp;9.1</a>.
     1883               </p>
     1884               <p id="rfc.section.7.1.3.p.2">The proxy server <em class="bcp14">MUST</em> signal persistent connections separately with its clients and the origin servers (or other proxy servers) that it connects
     1885                  to. Each persistent connection applies to only one transport link.
     1886               </p>
     1887               <p id="rfc.section.7.1.3.p.3">A proxy server <em class="bcp14">MUST NOT</em> establish a HTTP/1.1 persistent connection with an HTTP/1.0 client (but see <a href="https://tools.ietf.org/html/rfc2068#section-19.7.1">Section 19.7.1</a> of <a href="#RFC2068" id="rfc.xref.RFC2068.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a> for information and discussion of the problems with the Keep-Alive header implemented by many HTTP/1.0 clients).
     1888               </p>
     1889               <div id="end-to-end.and.hop-by-hop.headers">
     1890                  <h4 id="rfc.section.7.1.3.1"><a href="#rfc.section.7.1.3.1">7.1.3.1</a>&nbsp;<a href="#end-to-end.and.hop-by-hop.headers">End-to-end and Hop-by-hop Headers</a></h4>
     1891                  <p id="rfc.section.7.1.3.1.p.1">For the purpose of defining the behavior of caches and non-caching proxies, we divide HTTP headers into two categories: </p>
     1892                  <ul>
     1893                     <li>End-to-end headers, which are transmitted to the ultimate recipient of a request or response. End-to-end headers in responses
     1894                        MUST be stored as part of a cache entry and <em class="bcp14">MUST</em> be transmitted in any response formed from a cache entry.
     1895                     </li>
     1896                     <li>Hop-by-hop headers, which are meaningful only for a single transport-level connection, and are not stored by caches or forwarded
     1897                        by proxies.
     1898                     </li>
     1899                  </ul>
     1900                  <p id="rfc.section.7.1.3.1.p.2">The following HTTP/1.1 headers are hop-by-hop headers: </p>
     1901                  <ul>
     1902                     <li>Connection</li>
     1903                     <li>Keep-Alive</li>
     1904                     <li>Proxy-Authenticate</li>
     1905                     <li>Proxy-Authorization</li>
     1906                     <li>TE</li>
     1907                     <li>Trailer</li>
     1908                     <li>Transfer-Encoding</li>
     1909                     <li>Upgrade</li>
     1910                  </ul>
     1911                  <p id="rfc.section.7.1.3.1.p.3">All other headers defined by HTTP/1.1 are end-to-end headers.</p>
     1912                  <p id="rfc.section.7.1.3.1.p.4">Other hop-by-hop headers <em class="bcp14">MUST</em> be listed in a Connection header (<a href="#header.connection" id="rfc.xref.header.connection.4" title="Connection">Section&nbsp;9.1</a>).
     1913                  </p>
     1914               </div>
     1915               <div id="non-modifiable.headers">
     1916                  <h4 id="rfc.section.7.1.3.2"><a href="#rfc.section.7.1.3.2">7.1.3.2</a>&nbsp;<a href="#non-modifiable.headers">Non-modifiable Headers</a></h4>
     1917                  <p id="rfc.section.7.1.3.2.p.1">Some features of HTTP/1.1, such as Digest Authentication, depend on the value of certain end-to-end headers. A transparent
     1918                     proxy <em class="bcp14">SHOULD NOT</em> modify an end-to-end header unless the definition of that header requires or specifically allows that.
     1919                  </p>
     1920                  <p id="rfc.section.7.1.3.2.p.2">A transparent proxy <em class="bcp14">MUST NOT</em> modify any of the following fields in a request or response, and it <em class="bcp14">MUST NOT</em> add any of these fields if not already present:
     1921                  </p>
     1922                  <ul>
     1923                     <li>Content-Location</li>
     1924                     <li>Content-MD5</li>
     1925                     <li>ETag</li>
     1926                     <li>Last-Modified</li>
     1927                  </ul>
     1928                  <p id="rfc.section.7.1.3.2.p.3">A transparent proxy <em class="bcp14">MUST NOT</em> modify any of the following fields in a response:
     1929                  </p>
     1930                  <ul>
     1931                     <li>Expires</li>
     1932                  </ul>
     1933                  <p id="rfc.section.7.1.3.2.p.4">but it <em class="bcp14">MAY</em> add any of these fields if not already present. If an Expires header is added, it <em class="bcp14">MUST</em> be given a field-value identical to that of the Date header in that response.
     1934                  </p>
     1935                  <p id="rfc.section.7.1.3.2.p.5">A proxy <em class="bcp14">MUST NOT</em> modify or add any of the following fields in a message that contains the no-transform cache-control directive, or in any request:
     1936                  </p>
     1937                  <ul>
     1938                     <li>Content-Encoding</li>
     1939                     <li>Content-Range</li>
     1940                     <li>Content-Type</li>
     1941                  </ul>
     1942                  <p id="rfc.section.7.1.3.2.p.6">A non-transparent proxy <em class="bcp14">MAY</em> modify or add these fields to a message that does not include no-transform, but if it does so, it <em class="bcp14">MUST</em> add a Warning 214 (Transformation applied) if one does not already appear in the message (see <a href="p6-cache.html#header.warning" title="Warning">Section 3.6</a> of <a href="#Part6" id="rfc.xref.Part6.9"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>).
     1943                  </p>
     1944                  <div class="note" id="rfc.section.7.1.3.2.p.7">
     1945                     <p><b>Warning:</b> Unnecessary modification of end-to-end headers might cause authentication failures if stronger authentication mechanisms are
     1946                        introduced in later versions of HTTP. Such authentication mechanisms <em class="bcp14">MAY</em> rely on the values of header fields not listed here.
     1947                     </p>
     1948                  </div>
     1949                  <p id="rfc.section.7.1.3.2.p.8">A transparent proxy <em class="bcp14">MUST</em> preserve the message payload (<a href="#Part3" id="rfc.xref.Part3.6"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>), though it <em class="bcp14">MAY</em> change the message-body through application or removal of a transfer-coding (<a href="#transfer.codings" title="Transfer Codings">Section&nbsp;6.2</a>).
     1950                  </p>
     1951               </div>
     1952            </div>
     1953            <div id="persistent.practical">
     1954               <h3 id="rfc.section.7.1.4"><a href="#rfc.section.7.1.4">7.1.4</a>&nbsp;<a href="#persistent.practical">Practical Considerations</a></h3>
     1955               <p id="rfc.section.7.1.4.p.1">Servers will usually have some time-out value beyond which they will no longer maintain an inactive connection. Proxy servers
     1956                  might make this a higher value since it is likely that the client will be making more connections through the same server.
     1957                  The use of persistent connections places no requirements on the length (or existence) of this time-out for either the client
     1958                  or the server.
     1959               </p>
     1960               <p id="rfc.section.7.1.4.p.2">When a client or server wishes to time-out it <em class="bcp14">SHOULD</em> issue a graceful close on the transport connection. Clients and servers <em class="bcp14">SHOULD</em> both constantly watch for the other side of the transport close, and respond to it as appropriate. If a client or server does
     1961                  not detect the other side's close promptly it could cause unnecessary resource drain on the network.
     1962               </p>
     1963               <p id="rfc.section.7.1.4.p.3">A client, server, or proxy <em class="bcp14">MAY</em> close the transport connection at any time. For example, a client might have started to send a new request at the same time
     1964                  that the server has decided to close the "idle" connection. From the server's point of view, the connection is being closed
     1965                  while it was idle, but from the client's point of view, a request is in progress.
     1966               </p>
     1967               <p id="rfc.section.7.1.4.p.4">This means that clients, servers, and proxies <em class="bcp14">MUST</em> be able to recover from asynchronous close events. Client software <em class="bcp14">SHOULD</em> reopen the transport connection and retransmit the aborted sequence of requests without user interaction so long as the request
     1968                  sequence is idempotent (see <a href="p2-semantics.html#idempotent.methods" title="Idempotent Methods">Section 7.1.2</a> of <a href="#Part2" id="rfc.xref.Part2.7"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>). Non-idempotent methods or sequences <em class="bcp14">MUST NOT</em> be automatically retried, although user agents <em class="bcp14">MAY</em> offer a human operator the choice of retrying the request(s). Confirmation by user-agent software with semantic understanding
     1969                  of the application <em class="bcp14">MAY</em> substitute for user confirmation. The automatic retry <em class="bcp14">SHOULD NOT</em> be repeated if the second sequence of requests fails.
     1970               </p>
     1971               <p id="rfc.section.7.1.4.p.5">Servers <em class="bcp14">SHOULD</em> always respond to at least one request per connection, if at all possible. Servers <em class="bcp14">SHOULD NOT</em> close a connection in the middle of transmitting a response, unless a network or client failure is suspected.
     1972               </p>
     1973               <p id="rfc.section.7.1.4.p.6">Clients (including proxies) <em class="bcp14">SHOULD</em> limit the number of simultaneous connections that they maintain to a given server (including proxies).
     1974               </p>
     1975               <p id="rfc.section.7.1.4.p.7">Previous revisions of HTTP gave a specific number of connections as a ceiling, but this was found to be impractical for many
     1976                  applications. As a result, this specification does not mandate a particular maximum number of connections, but instead encourages
     1977                  clients to be conservative when opening multiple connections.
     1978               </p>
     1979               <p id="rfc.section.7.1.4.p.8">In particular, while using multiple connections avoids the "head-of-line blocking" problem (whereby a request that takes significant
     1980                  server-side processing and/or has a large payload can block subsequent requests on the same connection), each connection used
     1981                  consumes server resources (sometimes significantly), and furthermore using multiple connections can cause undesirable side
     1982                  effects in congested networks.
     1983               </p>
     1984               <p id="rfc.section.7.1.4.p.9">Note that servers might reject traffic that they deem abusive, including an excessive number of connections from a client.</p>
     1985            </div>
     1986         </div>
     1987         <div id="message.transmission.requirements">
     1988            <h2 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2</a>&nbsp;<a href="#message.transmission.requirements">Message Transmission Requirements</a></h2>
     1989            <div id="persistent.flow">
     1990               <h3 id="rfc.section.7.2.1"><a href="#rfc.section.7.2.1">7.2.1</a>&nbsp;<a href="#persistent.flow">Persistent Connections and Flow Control</a></h3>
     1991               <p id="rfc.section.7.2.1.p.1">HTTP/1.1 servers <em class="bcp14">SHOULD</em> maintain persistent connections and use TCP's flow control mechanisms to resolve temporary overloads, rather than terminating
     1992                  connections with the expectation that clients will retry. The latter technique can exacerbate network congestion.
     1993               </p>
     1994            </div>
     1995            <div id="persistent.monitor">
     1996               <h3 id="rfc.section.7.2.2"><a href="#rfc.section.7.2.2">7.2.2</a>&nbsp;<a href="#persistent.monitor">Monitoring Connections for Error Status Messages</a></h3>
     1997               <p id="rfc.section.7.2.2.p.1">An HTTP/1.1 (or later) client sending a message-body <em class="bcp14">SHOULD</em> monitor the network connection for an error status code while it is transmitting the request. If the client sees an error
     1998                  status code, it <em class="bcp14">SHOULD</em> immediately cease transmitting the body. If the body is being sent using a "chunked" encoding (<a href="#transfer.codings" title="Transfer Codings">Section&nbsp;6.2</a>), a zero length chunk and empty trailer <em class="bcp14">MAY</em> be used to prematurely mark the end of the message. If the body was preceded by a Content-Length header, the client <em class="bcp14">MUST</em> close the connection.
     1999               </p>
     2000            </div>
     2001            <div id="use.of.the.100.status">
     2002               <h3 id="rfc.section.7.2.3"><a href="#rfc.section.7.2.3">7.2.3</a>&nbsp;<a href="#use.of.the.100.status">Use of the 100 (Continue) Status</a></h3>
     2003               <p id="rfc.section.7.2.3.p.1">The purpose of the 100 (Continue) status code (see <a href="p2-semantics.html#status.100" title="100 Continue">Section 8.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.8"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) is to allow a client that is sending a request message with a request body to determine if the origin server is willing
     2004                  to accept the request (based on the request headers) before the client sends the request body. In some cases, it might either
     2005                  be inappropriate or highly inefficient for the client to send the body if the server will reject the message without looking
     2006                  at the body.
     2007               </p>
     2008               <p id="rfc.section.7.2.3.p.2">Requirements for HTTP/1.1 clients: </p>
     2009               <ul>
     2010                  <li>If a client will wait for a 100 (Continue) response before sending the request body, it <em class="bcp14">MUST</em> send an Expect request-header field (<a href="p2-semantics.html#header.expect" title="Expect">Section 9.2</a> of <a href="#Part2" id="rfc.xref.Part2.9"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) with the "100-continue" expectation.
     2011                  </li>
     2012                  <li>A client <em class="bcp14">MUST NOT</em> send an Expect request-header field (<a href="p2-semantics.html#header.expect" title="Expect">Section 9.2</a> of <a href="#Part2" id="rfc.xref.Part2.10"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) with the "100-continue" expectation if it does not intend to send a request body.
     2013                  </li>
     2014               </ul>
     2015               <p id="rfc.section.7.2.3.p.3">Because of the presence of older implementations, the protocol allows ambiguous situations in which a client might send "Expect:
     2016                  100-continue" without receiving either a 417 (Expectation Failed) or a 100 (Continue) status code. Therefore, when a client
     2017                  sends this header field to an origin server (possibly via a proxy) from which it has never seen a 100 (Continue) status code,
     2018                  the client <em class="bcp14">SHOULD NOT</em> wait for an indefinite period before sending the request body.
     2019               </p>
     2020               <p id="rfc.section.7.2.3.p.4">Requirements for HTTP/1.1 origin servers: </p>
     2021               <ul>
     2022                  <li>Upon receiving a request which includes an Expect request-header field with the "100-continue" expectation, an origin server <em class="bcp14">MUST</em> either respond with 100 (Continue) status code and continue to read from the input stream, or respond with a final status
     2023                     code. The origin server <em class="bcp14">MUST NOT</em> wait for the request body before sending the 100 (Continue) response. If it responds with a final status code, it <em class="bcp14">MAY</em> close the transport connection or it <em class="bcp14">MAY</em> continue to read and discard the rest of the request. It <em class="bcp14">MUST NOT</em> perform the requested method if it returns a final status code.
     2024                  </li>
     2025                  <li>An origin server <em class="bcp14">SHOULD NOT</em> send a 100 (Continue) response if the request message does not include an Expect request-header field with the "100-continue"
     2026                     expectation, and <em class="bcp14">MUST NOT</em> send a 100 (Continue) response if such a request comes from an HTTP/1.0 (or earlier) client. There is an exception to this
     2027                     rule: for compatibility with <a href="#RFC2068" id="rfc.xref.RFC2068.3"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, a server <em class="bcp14">MAY</em> send a 100 (Continue) status code in response to an HTTP/1.1 PUT or POST request that does not include an Expect request-header
     2028                     field with the "100-continue" expectation. This exception, the purpose of which is to minimize any client processing delays
     2029                     associated with an undeclared wait for 100 (Continue) status code, applies only to HTTP/1.1 requests, and not to requests
     2030                     with any other HTTP-version value.
     2031                  </li>
     2032                  <li>An origin server <em class="bcp14">MAY</em> omit a 100 (Continue) response if it has already received some or all of the request body for the corresponding request.
     2033                  </li>
     2034                  <li>An origin server that sends a 100 (Continue) response <em class="bcp14">MUST</em> ultimately send a final status code, once the request body is received and processed, unless it terminates the transport connection
     2035                     prematurely.
     2036                  </li>
     2037                  <li>If an origin server receives a request that does not include an Expect request-header field with the "100-continue" expectation,
     2038                     the request includes a request body, and the server responds with a final status code before reading the entire request body
     2039                     from the transport connection, then the server <em class="bcp14">SHOULD NOT</em> close the transport connection until it has read the entire request, or until the client closes the connection. Otherwise,
     2040                     the client might not reliably receive the response message. However, this requirement is not be construed as preventing a
     2041                     server from defending itself against denial-of-service attacks, or from badly broken client implementations.
     2042                  </li>
     2043               </ul>
     2044               <p id="rfc.section.7.2.3.p.5">Requirements for HTTP/1.1 proxies: </p>
     2045               <ul>
     2046                  <li>If a proxy receives a request that includes an Expect request-header field with the "100-continue" expectation, and the proxy
     2047                     either knows that the next-hop server complies with HTTP/1.1 or higher, or does not know the HTTP version of the next-hop
     2048                     server, it <em class="bcp14">MUST</em> forward the request, including the Expect header field.
     2049                  </li>
     2050                  <li>If the proxy knows that the version of the next-hop server is HTTP/1.0 or lower, it <em class="bcp14">MUST NOT</em> forward the request, and it <em class="bcp14">MUST</em> respond with a 417 (Expectation Failed) status code.
     2051                  </li>
     2052                  <li>Proxies <em class="bcp14">SHOULD</em> maintain a cache recording the HTTP version numbers received from recently-referenced next-hop servers.
     2053                  </li>
     2054                  <li>A proxy <em class="bcp14">MUST NOT</em> forward a 100 (Continue) response if the request message was received from an HTTP/1.0 (or earlier) client and did not include
     2055                     an Expect request-header field with the "100-continue" expectation. This requirement overrides the general rule for forwarding
     2056                     of 1xx responses (see <a href="p2-semantics.html#status.1xx" title="Informational 1xx">Section 8.1</a> of <a href="#Part2" id="rfc.xref.Part2.11"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>).
     2057                  </li>
     2058               </ul>
     2059            </div>
     2060            <div id="connection.premature">
     2061               <h3 id="rfc.section.7.2.4"><a href="#rfc.section.7.2.4">7.2.4</a>&nbsp;<a href="#connection.premature">Client Behavior if Server Prematurely Closes Connection</a></h3>
     2062               <p id="rfc.section.7.2.4.p.1">If an HTTP/1.1 client sends a request which includes a request body, but which does not include an Expect request-header field
     2063                  with the "100-continue" expectation, and if the client is not directly connected to an HTTP/1.1 origin server, and if the
     2064                  client sees the connection close before receiving a status line from the server, the client <em class="bcp14">SHOULD</em> retry the request. If the client does retry this request, it <em class="bcp14">MAY</em> use the following "binary exponential backoff" algorithm to be assured of obtaining a reliable response:
     2065               </p>
     2066               <ol>
     2067                  <li>Initiate a new connection to the server</li>
     2068                  <li>Transmit the request-headers</li>
     2069                  <li>Initialize a variable R to the estimated round-trip time to the server (e.g., based on the time it took to establish the connection),
     2070                     or to a constant value of 5 seconds if the round-trip time is not available.
     2071                  </li>
     2072                  <li>Compute T = R * (2**N), where N is the number of previous retries of this request.</li>
     2073                  <li>Wait either for an error response from the server, or for T seconds (whichever comes first)</li>
     2074                  <li>If no error response is received, after T seconds transmit the body of the request.</li>
     2075                  <li>If client sees that the connection is closed prematurely, repeat from step 1 until the request is accepted, an error response
     2076                     is received, or the user becomes impatient and terminates the retry process.
     2077                  </li>
     2078               </ol>
     2079               <p id="rfc.section.7.2.4.p.2">If at any point an error status code is received, the client </p>
     2080               <ul>
     2081                  <li><em class="bcp14">SHOULD NOT</em> continue and
     2082                  </li>
     2083                  <li><em class="bcp14">SHOULD</em> close the connection if it has not completed sending the request message.
     2084                  </li>
     2085               </ul>
     2086            </div>
     2087         </div>
    18522088      </div>
    1853       <p id="rfc.section.7.1.3.2.p.8">A transparent proxy <em class="bcp14">MUST</em> preserve the message payload (<a href="#Part3" id="rfc.xref.Part3.6"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>), though it <em class="bcp14">MAY</em> change the message-body through application or removal of a transfer-coding (<a href="#transfer.codings" title="Transfer Codings">Section&nbsp;6.2</a>).
    1854       </p>
    1855       <h3 id="rfc.section.7.1.4"><a href="#rfc.section.7.1.4">7.1.4</a>&nbsp;<a id="persistent.practical" href="#persistent.practical">Practical Considerations</a></h3>
    1856       <p id="rfc.section.7.1.4.p.1">Servers will usually have some time-out value beyond which they will no longer maintain an inactive connection. Proxy servers
    1857          might make this a higher value since it is likely that the client will be making more connections through the same server.
    1858          The use of persistent connections places no requirements on the length (or existence) of this time-out for either the client
    1859          or the server.
    1860       </p>
    1861       <p id="rfc.section.7.1.4.p.2">When a client or server wishes to time-out it <em class="bcp14">SHOULD</em> issue a graceful close on the transport connection. Clients and servers <em class="bcp14">SHOULD</em> both constantly watch for the other side of the transport close, and respond to it as appropriate. If a client or server does
    1862          not detect the other side's close promptly it could cause unnecessary resource drain on the network.
    1863       </p>
    1864       <p id="rfc.section.7.1.4.p.3">A client, server, or proxy <em class="bcp14">MAY</em> close the transport connection at any time. For example, a client might have started to send a new request at the same time
    1865          that the server has decided to close the "idle" connection. From the server's point of view, the connection is being closed
    1866          while it was idle, but from the client's point of view, a request is in progress.
    1867       </p>
    1868       <p id="rfc.section.7.1.4.p.4">This means that clients, servers, and proxies <em class="bcp14">MUST</em> be able to recover from asynchronous close events. Client software <em class="bcp14">SHOULD</em> reopen the transport connection and retransmit the aborted sequence of requests without user interaction so long as the request
    1869          sequence is idempotent (see <a href="p2-semantics.html#idempotent.methods" title="Idempotent Methods">Section 7.1.2</a> of <a href="#Part2" id="rfc.xref.Part2.7"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>). Non-idempotent methods or sequences <em class="bcp14">MUST NOT</em> be automatically retried, although user agents <em class="bcp14">MAY</em> offer a human operator the choice of retrying the request(s). Confirmation by user-agent software with semantic understanding
    1870          of the application <em class="bcp14">MAY</em> substitute for user confirmation. The automatic retry <em class="bcp14">SHOULD NOT</em> be repeated if the second sequence of requests fails.
    1871       </p>
    1872       <p id="rfc.section.7.1.4.p.5">Servers <em class="bcp14">SHOULD</em> always respond to at least one request per connection, if at all possible. Servers <em class="bcp14">SHOULD NOT</em> close a connection in the middle of transmitting a response, unless a network or client failure is suspected.
    1873       </p>
    1874       <p id="rfc.section.7.1.4.p.6">Clients (including proxies) <em class="bcp14">SHOULD</em> limit the number of simultaneous connections that they maintain to a given server (including proxies).
    1875       </p>
    1876       <p id="rfc.section.7.1.4.p.7">Previous revisions of HTTP gave a specific number of connections as a ceiling, but this was found to be impractical for many
    1877          applications. As a result, this specification does not mandate a particular maximum number of connections, but instead encourages
    1878          clients to be conservative when opening multiple connections.
    1879       </p>
    1880       <p id="rfc.section.7.1.4.p.8">In particular, while using multiple connections avoids the "head-of-line blocking" problem (whereby a request that takes significant
    1881          server-side processing and/or has a large payload can block subsequent requests on the same connection), each connection used
    1882          consumes server resources (sometimes significantly), and furthermore using multiple connections can cause undesirable side
    1883          effects in congested networks.
    1884       </p>
    1885       <p id="rfc.section.7.1.4.p.9">Note that servers might reject traffic that they deem abusive, including an excessive number of connections from a client.</p>
    1886       <h2 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2</a>&nbsp;<a id="message.transmission.requirements" href="#message.transmission.requirements">Message Transmission Requirements</a></h2>
    1887       <h3 id="rfc.section.7.2.1"><a href="#rfc.section.7.2.1">7.2.1</a>&nbsp;<a id="persistent.flow" href="#persistent.flow">Persistent Connections and Flow Control</a></h3>
    1888       <p id="rfc.section.7.2.1.p.1">HTTP/1.1 servers <em class="bcp14">SHOULD</em> maintain persistent connections and use TCP's flow control mechanisms to resolve temporary overloads, rather than terminating
    1889          connections with the expectation that clients will retry. The latter technique can exacerbate network congestion.
    1890       </p>
    1891       <h3 id="rfc.section.7.2.2"><a href="#rfc.section.7.2.2">7.2.2</a>&nbsp;<a id="persistent.monitor" href="#persistent.monitor">Monitoring Connections for Error Status Messages</a></h3>
    1892       <p id="rfc.section.7.2.2.p.1">An HTTP/1.1 (or later) client sending a message-body <em class="bcp14">SHOULD</em> monitor the network connection for an error status code while it is transmitting the request. If the client sees an error
    1893          status code, it <em class="bcp14">SHOULD</em> immediately cease transmitting the body. If the body is being sent using a "chunked" encoding (<a href="#transfer.codings" title="Transfer Codings">Section&nbsp;6.2</a>), a zero length chunk and empty trailer <em class="bcp14">MAY</em> be used to prematurely mark the end of the message. If the body was preceded by a Content-Length header, the client <em class="bcp14">MUST</em> close the connection.
    1894       </p>
    1895       <h3 id="rfc.section.7.2.3"><a href="#rfc.section.7.2.3">7.2.3</a>&nbsp;<a id="use.of.the.100.status" href="#use.of.the.100.status">Use of the 100 (Continue) Status</a></h3>
    1896       <p id="rfc.section.7.2.3.p.1">The purpose of the 100 (Continue) status code (see <a href="p2-semantics.html#status.100" title="100 Continue">Section 8.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.8"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) is to allow a client that is sending a request message with a request body to determine if the origin server is willing
    1897          to accept the request (based on the request headers) before the client sends the request body. In some cases, it might either
    1898          be inappropriate or highly inefficient for the client to send the body if the server will reject the message without looking
    1899          at the body.
    1900       </p>
    1901       <p id="rfc.section.7.2.3.p.2">Requirements for HTTP/1.1 clients: </p>
    1902       <ul>
    1903          <li>If a client will wait for a 100 (Continue) response before sending the request body, it <em class="bcp14">MUST</em> send an Expect request-header field (<a href="p2-semantics.html#header.expect" title="Expect">Section 9.2</a> of <a href="#Part2" id="rfc.xref.Part2.9"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) with the "100-continue" expectation.
    1904          </li>
    1905          <li>A client <em class="bcp14">MUST NOT</em> send an Expect request-header field (<a href="p2-semantics.html#header.expect" title="Expect">Section 9.2</a> of <a href="#Part2" id="rfc.xref.Part2.10"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) with the "100-continue" expectation if it does not intend to send a request body.
    1906          </li>
    1907       </ul>
    1908       <p id="rfc.section.7.2.3.p.3">Because of the presence of older implementations, the protocol allows ambiguous situations in which a client might send "Expect:
    1909          100-continue" without receiving either a 417 (Expectation Failed) or a 100 (Continue) status code. Therefore, when a client
    1910          sends this header field to an origin server (possibly via a proxy) from which it has never seen a 100 (Continue) status code,
    1911          the client <em class="bcp14">SHOULD NOT</em> wait for an indefinite period before sending the request body.
    1912       </p>
    1913       <p id="rfc.section.7.2.3.p.4">Requirements for HTTP/1.1 origin servers: </p>
    1914       <ul>
    1915          <li>Upon receiving a request which includes an Expect request-header field with the "100-continue" expectation, an origin server <em class="bcp14">MUST</em> either respond with 100 (Continue) status code and continue to read from the input stream, or respond with a final status
    1916             code. The origin server <em class="bcp14">MUST NOT</em> wait for the request body before sending the 100 (Continue) response. If it responds with a final status code, it <em class="bcp14">MAY</em> close the transport connection or it <em class="bcp14">MAY</em> continue to read and discard the rest of the request. It <em class="bcp14">MUST NOT</em> perform the requested method if it returns a final status code.
    1917          </li>
    1918          <li>An origin server <em class="bcp14">SHOULD NOT</em> send a 100 (Continue) response if the request message does not include an Expect request-header field with the "100-continue"
    1919             expectation, and <em class="bcp14">MUST NOT</em> send a 100 (Continue) response if such a request comes from an HTTP/1.0 (or earlier) client. There is an exception to this
    1920             rule: for compatibility with <a href="#RFC2068" id="rfc.xref.RFC2068.3"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, a server <em class="bcp14">MAY</em> send a 100 (Continue) status code in response to an HTTP/1.1 PUT or POST request that does not include an Expect request-header
    1921             field with the "100-continue" expectation. This exception, the purpose of which is to minimize any client processing delays
    1922             associated with an undeclared wait for 100 (Continue) status code, applies only to HTTP/1.1 requests, and not to requests
    1923             with any other HTTP-version value.
    1924          </li>
    1925          <li>An origin server <em class="bcp14">MAY</em> omit a 100 (Continue) response if it has already received some or all of the request body for the corresponding request.
    1926          </li>
    1927          <li>An origin server that sends a 100 (Continue) response <em class="bcp14">MUST</em> ultimately send a final status code, once the request body is received and processed, unless it terminates the transport connection
    1928             prematurely.
    1929          </li>
    1930          <li>If an origin server receives a request that does not include an Expect request-header field with the "100-continue" expectation,
    1931             the request includes a request body, and the server responds with a final status code before reading the entire request body
    1932             from the transport connection, then the server <em class="bcp14">SHOULD NOT</em> close the transport connection until it has read the entire request, or until the client closes the connection. Otherwise,
    1933             the client might not reliably receive the response message. However, this requirement is not be construed as preventing a
    1934             server from defending itself against denial-of-service attacks, or from badly broken client implementations.
    1935          </li>
    1936       </ul>
    1937       <p id="rfc.section.7.2.3.p.5">Requirements for HTTP/1.1 proxies: </p>
    1938       <ul>
    1939          <li>If a proxy receives a request that includes an Expect request-header field with the "100-continue" expectation, and the proxy
    1940             either knows that the next-hop server complies with HTTP/1.1 or higher, or does not know the HTTP version of the next-hop
    1941             server, it <em class="bcp14">MUST</em> forward the request, including the Expect header field.
    1942          </li>
    1943          <li>If the proxy knows that the version of the next-hop server is HTTP/1.0 or lower, it <em class="bcp14">MUST NOT</em> forward the request, and it <em class="bcp14">MUST</em> respond with a 417 (Expectation Failed) status code.
    1944          </li>
    1945          <li>Proxies <em class="bcp14">SHOULD</em> maintain a cache recording the HTTP version numbers received from recently-referenced next-hop servers.
    1946          </li>
    1947          <li>A proxy <em class="bcp14">MUST NOT</em> forward a 100 (Continue) response if the request message was received from an HTTP/1.0 (or earlier) client and did not include
    1948             an Expect request-header field with the "100-continue" expectation. This requirement overrides the general rule for forwarding
    1949             of 1xx responses (see <a href="p2-semantics.html#status.1xx" title="Informational 1xx">Section 8.1</a> of <a href="#Part2" id="rfc.xref.Part2.11"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>).
    1950          </li>
    1951       </ul>
    1952       <h3 id="rfc.section.7.2.4"><a href="#rfc.section.7.2.4">7.2.4</a>&nbsp;<a id="connection.premature" href="#connection.premature">Client Behavior if Server Prematurely Closes Connection</a></h3>
    1953       <p id="rfc.section.7.2.4.p.1">If an HTTP/1.1 client sends a request which includes a request body, but which does not include an Expect request-header field
    1954          with the "100-continue" expectation, and if the client is not directly connected to an HTTP/1.1 origin server, and if the
    1955          client sees the connection close before receiving a status line from the server, the client <em class="bcp14">SHOULD</em> retry the request. If the client does retry this request, it <em class="bcp14">MAY</em> use the following "binary exponential backoff" algorithm to be assured of obtaining a reliable response:
    1956       </p>
    1957       <ol>
    1958          <li>Initiate a new connection to the server</li>
    1959          <li>Transmit the request-headers</li>
    1960          <li>Initialize a variable R to the estimated round-trip time to the server (e.g., based on the time it took to establish the connection),
    1961             or to a constant value of 5 seconds if the round-trip time is not available.
    1962          </li>
    1963          <li>Compute T = R * (2**N), where N is the number of previous retries of this request.</li>
    1964          <li>Wait either for an error response from the server, or for T seconds (whichever comes first)</li>
    1965          <li>If no error response is received, after T seconds transmit the body of the request.</li>
    1966          <li>If client sees that the connection is closed prematurely, repeat from step 1 until the request is accepted, an error response
    1967             is received, or the user becomes impatient and terminates the retry process.
    1968          </li>
    1969       </ol>
    1970       <p id="rfc.section.7.2.4.p.2">If at any point an error status code is received, the client </p>
    1971       <ul>
    1972          <li><em class="bcp14">SHOULD NOT</em> continue and
    1973          </li>
    1974          <li><em class="bcp14">SHOULD</em> close the connection if it has not completed sending the request message.
    1975          </li>
    1976       </ul>
    1977       <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a id="misc" href="#misc">Miscellaneous notes that might disappear</a></h1>
    1978       <h2 id="rfc.section.8.1"><a href="#rfc.section.8.1">8.1</a>&nbsp;<a id="scheme.aliases" href="#scheme.aliases">Scheme aliases considered harmful</a></h2>
    1979       <p id="rfc.section.8.1.p.1"> <span class="comment" id="TBD-aliases-harmful">[<a href="#TBD-aliases-harmful" class="smpl">TBD-aliases-harmful</a>: describe why aliases like webcal are harmful.]</span>
    1980       </p>
    1981       <h2 id="rfc.section.8.2"><a href="#rfc.section.8.2">8.2</a>&nbsp;<a id="http.proxy" href="#http.proxy">Use of HTTP for proxy communication</a></h2>
    1982       <p id="rfc.section.8.2.p.1"> <span class="comment" id="TBD-proxy-other">[<a href="#TBD-proxy-other" class="smpl">TBD-proxy-other</a>: Configured to use HTTP to proxy HTTP or other protocols.]</span>
    1983       </p>
    1984       <h2 id="rfc.section.8.3"><a href="#rfc.section.8.3">8.3</a>&nbsp;<a id="http.intercept" href="#http.intercept">Interception of HTTP for access control</a></h2>
    1985       <p id="rfc.section.8.3.p.1"> <span class="comment" id="TBD-intercept">[<a href="#TBD-intercept" class="smpl">TBD-intercept</a>: Interception of HTTP traffic for initiating access control.]</span>
    1986       </p>
    1987       <h2 id="rfc.section.8.4"><a href="#rfc.section.8.4">8.4</a>&nbsp;<a id="http.others" href="#http.others">Use of HTTP by other protocols</a></h2>
    1988       <p id="rfc.section.8.4.p.1"> <span class="comment" id="TBD-profiles">[<a href="#TBD-profiles" class="smpl">TBD-profiles</a>: Profiles of HTTP defined by other protocol. Extensions of HTTP like WebDAV.]</span>
    1989       </p>
    1990       <h2 id="rfc.section.8.5"><a href="#rfc.section.8.5">8.5</a>&nbsp;<a id="http.media" href="#http.media">Use of HTTP by media type specification</a></h2>
    1991       <p id="rfc.section.8.5.p.1"> <span class="comment" id="TBD-hypertext">[<a href="#TBD-hypertext" class="smpl">TBD-hypertext</a>: Instructions on composing HTTP requests via hypertext formats.]</span>
    1992       </p>
    1993       <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a>&nbsp;<a id="header.field.definitions" href="#header.field.definitions">Header Field Definitions</a></h1>
    1994       <p id="rfc.section.9.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to message framing and transport protocols.</p>
    1995       <div id="rfc.iref.c.11"></div>
    1996       <div id="rfc.iref.h.6"></div>
    1997       <h2 id="rfc.section.9.1"><a href="#rfc.section.9.1">9.1</a>&nbsp;<a id="header.connection" href="#header.connection">Connection</a></h2>
    1998       <p id="rfc.section.9.1.p.1">The "Connection" general-header field allows the sender to specify options that are desired for that particular connection
    1999          and <em class="bcp14">MUST NOT</em> be communicated by proxies over further connections.
    2000       </p>
    2001       <p id="rfc.section.9.1.p.2">The Connection header's value has the following grammar:</p>
    2002       <div id="rfc.figure.u.59"></div><pre class="inline"><span id="rfc.iref.g.94"></span><span id="rfc.iref.g.95"></span><span id="rfc.iref.g.96"></span>  <a href="#header.connection" class="smpl">Connection</a>       = "Connection" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.connection" class="smpl">Connection-v</a>
     2089      <div id="misc">
     2090         <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a href="#misc">Miscellaneous notes that might disappear</a></h1>
     2091         <div id="scheme.aliases">
     2092            <h2 id="rfc.section.8.1"><a href="#rfc.section.8.1">8.1</a>&nbsp;<a href="#scheme.aliases">Scheme aliases considered harmful</a></h2>
     2093            <p id="rfc.section.8.1.p.1"><span class="comment" id="TBD-aliases-harmful">[<a href="#TBD-aliases-harmful" class="smpl">TBD-aliases-harmful</a>: describe why aliases like webcal are harmful.]</span>
     2094            </p>
     2095         </div>
     2096         <div id="http.proxy">
     2097            <h2 id="rfc.section.8.2"><a href="#rfc.section.8.2">8.2</a>&nbsp;<a href="#http.proxy">Use of HTTP for proxy communication</a></h2>
     2098            <p id="rfc.section.8.2.p.1"><span class="comment" id="TBD-proxy-other">[<a href="#TBD-proxy-other" class="smpl">TBD-proxy-other</a>: Configured to use HTTP to proxy HTTP or other protocols.]</span>
     2099            </p>
     2100         </div>
     2101         <div id="http.intercept">
     2102            <h2 id="rfc.section.8.3"><a href="#rfc.section.8.3">8.3</a>&nbsp;<a href="#http.intercept">Interception of HTTP for access control</a></h2>
     2103            <p id="rfc.section.8.3.p.1"><span class="comment" id="TBD-intercept">[<a href="#TBD-intercept" class="smpl">TBD-intercept</a>: Interception of HTTP traffic for initiating access control.]</span>
     2104            </p>
     2105         </div>
     2106         <div id="http.others">
     2107            <h2 id="rfc.section.8.4"><a href="#rfc.section.8.4">8.4</a>&nbsp;<a href="#http.others">Use of HTTP by other protocols</a></h2>
     2108            <p id="rfc.section.8.4.p.1"><span class="comment" id="TBD-profiles">[<a href="#TBD-profiles" class="smpl">TBD-profiles</a>: Profiles of HTTP defined by other protocol. Extensions of HTTP like WebDAV.]</span>
     2109            </p>
     2110         </div>
     2111         <div id="http.media">
     2112            <h2 id="rfc.section.8.5"><a href="#rfc.section.8.5">8.5</a>&nbsp;<a href="#http.media">Use of HTTP by media type specification</a></h2>
     2113            <p id="rfc.section.8.5.p.1"><span class="comment" id="TBD-hypertext">[<a href="#TBD-hypertext" class="smpl">TBD-hypertext</a>: Instructions on composing HTTP requests via hypertext formats.]</span>
     2114            </p>
     2115         </div>
     2116      </div>
     2117      <div id="header.field.definitions">
     2118         <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a>&nbsp;<a href="#header.field.definitions">Header Field Definitions</a></h1>
     2119         <p id="rfc.section.9.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to message framing and transport protocols.</p>
     2120         <div id="header.connection">
     2121            <div id="rfc.iref.c.11"></div>
     2122            <div id="rfc.iref.h.6"></div>
     2123            <h2 id="rfc.section.9.1"><a href="#rfc.section.9.1">9.1</a>&nbsp;<a href="#header.connection">Connection</a></h2>
     2124            <p id="rfc.section.9.1.p.1">The "Connection" general-header field allows the sender to specify options that are desired for that particular connection
     2125               and <em class="bcp14">MUST NOT</em> be communicated by proxies over further connections.
     2126            </p>
     2127            <p id="rfc.section.9.1.p.2">The Connection header's value has the following grammar:</p>
     2128            <div id="rfc.figure.u.59"></div><pre class="inline"><span id="rfc.iref.g.94"></span><span id="rfc.iref.g.95"></span><span id="rfc.iref.g.96"></span>  <a href="#header.connection" class="smpl">Connection</a>       = "Connection" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.connection" class="smpl">Connection-v</a>
    20032129  <a href="#header.connection" class="smpl">Connection-v</a>     = 1#<a href="#header.connection" class="smpl">connection-token</a>
    20042130  <a href="#header.connection" class="smpl">connection-token</a> = <a href="#rule.token.separators" class="smpl">token</a>
    20052131</pre><p id="rfc.section.9.1.p.4">HTTP/1.1 proxies <em class="bcp14">MUST</em> parse the Connection header field before a message is forwarded and, for each connection-token in this field, remove any header
    2006          field(s) from the message with the same name as the connection-token. Connection options are signaled by the presence of a
    2007          connection-token in the Connection header field, not by any corresponding additional header field(s), since the additional
    2008          header field might not be sent if there are no parameters associated with that connection option.
    2009       </p>
    2010       <p id="rfc.section.9.1.p.5">Message headers listed in the Connection header <em class="bcp14">MUST NOT</em> include end-to-end headers, such as Cache-Control.
    2011       </p>
    2012       <p id="rfc.section.9.1.p.6">HTTP/1.1 defines the "close" connection option for the sender to signal that the connection will be closed after completion
    2013          of the response. For example,
    2014       </p>
    2015       <div id="rfc.figure.u.60"></div><pre class="text">  Connection: close
     2132               field(s) from the message with the same name as the connection-token. Connection options are signaled by the presence of a
     2133               connection-token in the Connection header field, not by any corresponding additional header field(s), since the additional
     2134               header field might not be sent if there are no parameters associated with that connection option.
     2135            </p>
     2136            <p id="rfc.section.9.1.p.5">Message headers listed in the Connection header <em class="bcp14">MUST NOT</em> include end-to-end headers, such as Cache-Control.
     2137            </p>
     2138            <p id="rfc.section.9.1.p.6">HTTP/1.1 defines the "close" connection option for the sender to signal that the connection will be closed after completion
     2139               of the response. For example,
     2140            </p>
     2141            <div id="rfc.figure.u.60"></div><pre class="text">  Connection: close
    20162142</pre><p id="rfc.section.9.1.p.8">in either the request or the response header fields indicates that the connection <em class="bcp14">SHOULD NOT</em> be considered "persistent" (<a href="#persistent.connections" title="Persistent Connections">Section&nbsp;7.1</a>) after the current request/response is complete.
    2017       </p>
    2018       <p id="rfc.section.9.1.p.9">An HTTP/1.1 client that does not support persistent connections <em class="bcp14">MUST</em> include the "close" connection option in every request message.
    2019       </p>
    2020       <p id="rfc.section.9.1.p.10">An HTTP/1.1 server that does not support persistent connections <em class="bcp14">MUST</em> include the "close" connection option in every response message that does not have a 1xx (Informational) status code.
    2021       </p>
    2022       <p id="rfc.section.9.1.p.11">A system receiving an HTTP/1.0 (or lower-version) message that includes a Connection header <em class="bcp14">MUST</em>, for each connection-token in this field, remove and ignore any header field(s) from the message with the same name as the
    2023          connection-token. This protects against mistaken forwarding of such header fields by pre-HTTP/1.1 proxies. See <a href="#compatibility.with.http.1.0.persistent.connections" title="Compatibility with HTTP/1.0 Persistent Connections">Appendix&nbsp;B.2</a>.
    2024       </p>
    2025       <div id="rfc.iref.c.12"></div>
    2026       <div id="rfc.iref.h.7"></div>
    2027       <h2 id="rfc.section.9.2"><a href="#rfc.section.9.2">9.2</a>&nbsp;<a id="header.content-length" href="#header.content-length">Content-Length</a></h2>
    2028       <p id="rfc.section.9.2.p.1">The "Content-Length" header field indicates the size of the message-body, in decimal number of octets, for any message other
    2029          than a response to the HEAD method or a response with a status code of 304. In the case of responses to the HEAD method, it
    2030          indicates the size of the payload body (not including any potential transfer-coding) that would have been sent had the request
    2031          been a GET. In the case of the 304 (Not Modified) response, it indicates the size of the payload body (not including any potential
    2032          transfer-coding) that would have been sent in a 200 (OK) response.
    2033       </p>
    2034       <div id="rfc.figure.u.61"></div><pre class="inline"><span id="rfc.iref.g.97"></span><span id="rfc.iref.g.98"></span>  <a href="#header.content-length" class="smpl">Content-Length</a>   = "Content-Length" ":" <a href="#rule.whitespace" class="smpl">OWS</a> 1*<a href="#header.content-length" class="smpl">Content-Length-v</a>
     2143            </p>
     2144            <p id="rfc.section.9.1.p.9">An HTTP/1.1 client that does not support persistent connections <em class="bcp14">MUST</em> include the "close" connection option in every request message.
     2145            </p>
     2146            <p id="rfc.section.9.1.p.10">An HTTP/1.1 server that does not support persistent connections <em class="bcp14">MUST</em> include the "close" connection option in every response message that does not have a 1xx (Informational) status code.
     2147            </p>
     2148            <p id="rfc.section.9.1.p.11">A system receiving an HTTP/1.0 (or lower-version) message that includes a Connection header <em class="bcp14">MUST</em>, for each connection-token in this field, remove and ignore any header field(s) from the message with the same name as the
     2149               connection-token. This protects against mistaken forwarding of such header fields by pre-HTTP/1.1 proxies. See <a href="#compatibility.with.http.1.0.persistent.connections" title="Compatibility with HTTP/1.0 Persistent Connections">Appendix&nbsp;B.2</a>.
     2150            </p>
     2151         </div>
     2152         <div id="header.content-length">
     2153            <div id="rfc.iref.c.12"></div>
     2154            <div id="rfc.iref.h.7"></div>
     2155            <h2 id="rfc.section.9.2"><a href="#rfc.section.9.2">9.2</a>&nbsp;<a href="#header.content-length">Content-Length</a></h2>
     2156            <p id="rfc.section.9.2.p.1">The "Content-Length" header field indicates the size of the message-body, in decimal number of octets, for any message other
     2157               than a response to the HEAD method or a response with a status code of 304. In the case of responses to the HEAD method, it
     2158               indicates the size of the payload body (not including any potential transfer-coding) that would have been sent had the request
     2159               been a GET. In the case of the 304 (Not Modified) response, it indicates the size of the payload body (not including any potential
     2160               transfer-coding) that would have been sent in a 200 (OK) response.
     2161            </p>
     2162            <div id="rfc.figure.u.61"></div><pre class="inline"><span id="rfc.iref.g.97"></span><span id="rfc.iref.g.98"></span>  <a href="#header.content-length" class="smpl">Content-Length</a>   = "Content-Length" ":" <a href="#rule.whitespace" class="smpl">OWS</a> 1*<a href="#header.content-length" class="smpl">Content-Length-v</a>
    20352163  <a href="#header.content-length" class="smpl">Content-Length-v</a> = 1*<a href="#core.rules" class="smpl">DIGIT</a>
    20362164</pre><p id="rfc.section.9.2.p.3">An example is</p>
    2037       <div id="rfc.figure.u.62"></div><pre class="text">  Content-Length: 3495
     2165            <div id="rfc.figure.u.62"></div><pre class="text">  Content-Length: 3495
    20382166</pre><p id="rfc.section.9.2.p.5">Implementations <em class="bcp14">SHOULD</em> use this field to indicate the message-body length when no transfer-coding is being applied and the payload's body length
    2039          can be determined prior to being transferred. <a href="#message.body" title="Message Body">Section&nbsp;3.3</a> describes how recipients determine the length of a message-body.
    2040       </p>
    2041       <p id="rfc.section.9.2.p.6">Any Content-Length greater than or equal to zero is a valid value.</p>
    2042       <p id="rfc.section.9.2.p.7">Note that the use of this field in HTTP is significantly different from the corresponding definition in MIME, where it is
    2043          an optional field used within the "message/external-body" content-type.
    2044       </p>
    2045       <div id="rfc.iref.d.3"></div>
    2046       <div id="rfc.iref.h.8"></div>
    2047       <h2 id="rfc.section.9.3"><a href="#rfc.section.9.3">9.3</a>&nbsp;<a id="header.date" href="#header.date">Date</a></h2>
    2048       <p id="rfc.section.9.3.p.1">The "Date" general-header field represents the date and time at which the message was originated, having the same semantics
    2049          as the Origination Date Field (orig-date) defined in <a href="http://tools.ietf.org/html/rfc5322#section-3.6.1">Section 3.6.1</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.4"><cite title="Internet Message Format">[RFC5322]</cite></a>. The field value is an HTTP-date, as described in <a href="#date.time.formats.full.date" title="Date/Time Formats: Full Date">Section&nbsp;6.1</a>; it <em class="bcp14">MUST</em> be sent in rfc1123-date format.
    2050       </p>
    2051       <div id="rfc.figure.u.63"></div><pre class="inline"><span id="rfc.iref.g.99"></span><span id="rfc.iref.g.100"></span>  <a href="#header.date" class="smpl">Date</a>   = "Date" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.date" class="smpl">Date-v</a>
     2167               can be determined prior to being transferred. <a href="#message.body" title="Message Body">Section&nbsp;3.3</a> describes how recipients determine the length of a message-body.
     2168            </p>
     2169            <p id="rfc.section.9.2.p.6">Any Content-Length greater than or equal to zero is a valid value.</p>
     2170            <p id="rfc.section.9.2.p.7">Note that the use of this field in HTTP is significantly different from the corresponding definition in MIME, where it is
     2171               an optional field used within the "message/external-body" content-type.
     2172            </p>
     2173         </div>
     2174         <div id="header.date">
     2175            <div id="rfc.iref.d.3"></div>
     2176            <div id="rfc.iref.h.8"></div>
     2177            <h2 id="rfc.section.9.3"><a href="#rfc.section.9.3">9.3</a>&nbsp;<a href="#header.date">Date</a></h2>
     2178            <p id="rfc.section.9.3.p.1">The "Date" general-header field represents the date and time at which the message was originated, having the same semantics
     2179               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.RFC5322.4"><cite title="Internet Message Format">[RFC5322]</cite></a>. The field value is an HTTP-date, as described in <a href="#date.time.formats.full.date" title="Date/Time Formats: Full Date">Section&nbsp;6.1</a>; it <em class="bcp14">MUST</em> be sent in rfc1123-date format.
     2180            </p>
     2181            <div id="rfc.figure.u.63"></div><pre class="inline"><span id="rfc.iref.g.99"></span><span id="rfc.iref.g.100"></span>  <a href="#header.date" class="smpl">Date</a>   = "Date" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.date" class="smpl">Date-v</a>
    20522182  <a href="#header.date" class="smpl">Date-v</a> = <a href="#date.time.formats.full.date" class="smpl">HTTP-date</a>
    20532183</pre><p id="rfc.section.9.3.p.3">An example is</p>
    2054       <div id="rfc.figure.u.64"></div><pre class="text">  Date: Tue, 15 Nov 1994 08:12:31 GMT
     2184            <div id="rfc.figure.u.64"></div><pre class="text">  Date: Tue, 15 Nov 1994 08:12:31 GMT
    20552185</pre><p id="rfc.section.9.3.p.5">Origin servers <em class="bcp14">MUST</em> include a Date header field in all responses, except in these cases:
    2056       </p>
    2057       <ol>
    2058          <li>If the response status code is 100 (Continue) or 101 (Switching Protocols), the response <em class="bcp14">MAY</em> include a Date header field, at the server's option.
    2059          </li>
    2060          <li>If the response status code conveys a server error, e.g., 500 (Internal Server Error) or 503 (Service Unavailable), and it
    2061             is inconvenient or impossible to generate a valid Date.
    2062          </li>
    2063          <li>If the server does not have a clock that can provide a reasonable approximation of the current time, its responses <em class="bcp14">MUST NOT</em> include a Date header field. In this case, the rules in <a href="#clockless.origin.server.operation" title="Clockless Origin Server Operation">Section&nbsp;9.3.1</a>  <em class="bcp14">MUST</em> be followed.
    2064          </li>
    2065       </ol>
    2066       <p id="rfc.section.9.3.p.6">A received message that does not have a Date header field <em class="bcp14">MUST</em> be assigned one by the recipient if the message will be cached by that recipient or gatewayed via a protocol which requires
    2067          a Date. An HTTP implementation without a clock <em class="bcp14">MUST NOT</em> cache responses without revalidating them on every use. An HTTP cache, especially a shared cache, <em class="bcp14">SHOULD</em> use a mechanism, such as NTP <a href="#RFC1305" id="rfc.xref.RFC1305.1"><cite title="Network Time Protocol (Version 3) Specification, Implementation">[RFC1305]</cite></a>, to synchronize its clock with a reliable external standard.
    2068       </p>
    2069       <p id="rfc.section.9.3.p.7">Clients <em class="bcp14">SHOULD</em> only send a Date header field in messages that include a payload, as is usually the case for PUT and POST requests, and even
    2070          then it is optional. A client without a clock <em class="bcp14">MUST NOT</em> send a Date header field in a request.
    2071       </p>
    2072       <p id="rfc.section.9.3.p.8">The HTTP-date sent in a Date header <em class="bcp14">SHOULD NOT</em> represent a date and time subsequent to the generation of the message. It <em class="bcp14">SHOULD</em> represent the best available approximation of the date and time of message generation, unless the implementation has no means
    2073          of generating a reasonably accurate date and time. In theory, the date ought to represent the moment just before the payload
    2074          is generated. In practice, the date can be generated at any time during the message origination without affecting its semantic
    2075          value.
    2076       </p>
    2077       <h3 id="rfc.section.9.3.1"><a href="#rfc.section.9.3.1">9.3.1</a>&nbsp;<a id="clockless.origin.server.operation" href="#clockless.origin.server.operation">Clockless Origin Server Operation</a></h3>
    2078       <p id="rfc.section.9.3.1.p.1">Some origin server implementations might not have a clock available. An origin server without a clock <em class="bcp14">MUST NOT</em> assign Expires or Last-Modified values to a response, unless these values were associated with the resource by a system or
    2079          user with a reliable clock. It <em class="bcp14">MAY</em> assign an Expires value that is known, at or before server configuration time, to be in the past (this allows "pre-expiration"
    2080          of responses without storing separate Expires values for each resource).
    2081       </p>
    2082       <div id="rfc.iref.h.9"></div>
    2083       <div id="rfc.iref.h.10"></div>
    2084       <h2 id="rfc.section.9.4"><a href="#rfc.section.9.4">9.4</a>&nbsp;<a id="header.host" href="#header.host">Host</a></h2>
    2085       <p id="rfc.section.9.4.p.1">The "Host" request-header field specifies the Internet host and port number of the resource being requested, allowing the
    2086          origin server or gateway to differentiate between internally-ambiguous URLs, such as the root "/" URL of a server for multiple
    2087          host names on a single IP address.
    2088       </p>
    2089       <p id="rfc.section.9.4.p.2">The Host field value <em class="bcp14">MUST</em> represent the naming authority of the origin server or gateway given by the original URL obtained from the user or referring
    2090          resource (generally an http URI, as described in <a href="#http.uri" title="http URI scheme">Section&nbsp;2.6.1</a>).
    2091       </p>
    2092       <div id="rfc.figure.u.65"></div><pre class="inline"><span id="rfc.iref.g.101"></span><span id="rfc.iref.g.102"></span>  <a href="#header.host" class="smpl">Host</a>   = "Host" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.host" class="smpl">Host-v</a>
     2186            </p>
     2187            <ol>
     2188               <li>If the response status code is 100 (Continue) or 101 (Switching Protocols), the response <em class="bcp14">MAY</em> include a Date header field, at the server's option.
     2189               </li>
     2190               <li>If the response status code conveys a server error, e.g., 500 (Internal Server Error) or 503 (Service Unavailable), and it
     2191                  is inconvenient or impossible to generate a valid Date.
     2192               </li>
     2193               <li>If the server does not have a clock that can provide a reasonable approximation of the current time, its responses <em class="bcp14">MUST NOT</em> include a Date header field. In this case, the rules in <a href="#clockless.origin.server.operation" title="Clockless Origin Server Operation">Section&nbsp;9.3.1</a> <em class="bcp14">MUST</em> be followed.
     2194               </li>
     2195            </ol>
     2196            <p id="rfc.section.9.3.p.6">A received message that does not have a Date header field <em class="bcp14">MUST</em> be assigned one by the recipient if the message will be cached by that recipient or gatewayed via a protocol which requires
     2197               a Date. An HTTP implementation without a clock <em class="bcp14">MUST NOT</em> cache responses without revalidating them on every use. An HTTP cache, especially a shared cache, <em class="bcp14">SHOULD</em> use a mechanism, such as NTP <a href="#RFC1305" id="rfc.xref.RFC1305.1"><cite title="Network Time Protocol (Version 3) Specification, Implementation">[RFC1305]</cite></a>, to synchronize its clock with a reliable external standard.
     2198            </p>
     2199            <p id="rfc.section.9.3.p.7">Clients <em class="bcp14">SHOULD</em> only send a Date header field in messages that include a payload, as is usually the case for PUT and POST requests, and even
     2200               then it is optional. A client without a clock <em class="bcp14">MUST NOT</em> send a Date header field in a request.
     2201            </p>
     2202            <p id="rfc.section.9.3.p.8">The HTTP-date sent in a Date header <em class="bcp14">SHOULD NOT</em> represent a date and time subsequent to the generation of the message. It <em class="bcp14">SHOULD</em> represent the best available approximation of the date and time of message generation, unless the implementation has no means
     2203               of generating a reasonably accurate date and time. In theory, the date ought to represent the moment just before the payload
     2204               is generated. In practice, the date can be generated at any time during the message origination without affecting its semantic
     2205               value.
     2206            </p>
     2207            <div id="clockless.origin.server.operation">
     2208               <h3 id="rfc.section.9.3.1"><a href="#rfc.section.9.3.1">9.3.1</a>&nbsp;<a href="#clockless.origin.server.operation">Clockless Origin Server Operation</a></h3>
     2209               <p id="rfc.section.9.3.1.p.1">Some origin server implementations might not have a clock available. An origin server without a clock <em class="bcp14">MUST NOT</em> assign Expires or Last-Modified values to a response, unless these values were associated with the resource by a system or
     2210                  user with a reliable clock. It <em class="bcp14">MAY</em> assign an Expires value that is known, at or before server configuration time, to be in the past (this allows "pre-expiration"
     2211                  of responses without storing separate Expires values for each resource).
     2212               </p>
     2213            </div>
     2214         </div>
     2215         <div id="header.host">
     2216            <div id="rfc.iref.h.9"></div>
     2217            <div id="rfc.iref.h.10"></div>
     2218            <h2 id="rfc.section.9.4"><a href="#rfc.section.9.4">9.4</a>&nbsp;<a href="#header.host">Host</a></h2>
     2219            <p id="rfc.section.9.4.p.1">The "Host" request-header field specifies the Internet host and port number of the resource being requested, allowing the
     2220               origin server or gateway to differentiate between internally-ambiguous URLs, such as the root "/" URL of a server for multiple
     2221               host names on a single IP address.
     2222            </p>
     2223            <p id="rfc.section.9.4.p.2">The Host field value <em class="bcp14">MUST</em> represent the naming authority of the origin server or gateway given by the original URL obtained from the user or referring
     2224               resource (generally an http URI, as described in <a href="#http.uri" title="http URI scheme">Section&nbsp;2.6.1</a>).
     2225            </p>
     2226            <div id="rfc.figure.u.65"></div><pre class="inline"><span id="rfc.iref.g.101"></span><span id="rfc.iref.g.102"></span>  <a href="#header.host" class="smpl">Host</a>   = "Host" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.host" class="smpl">Host-v</a>
    20932227  <a href="#header.host" class="smpl">Host-v</a> = <a href="#uri" class="smpl">uri-host</a> [ ":" <a href="#uri" class="smpl">port</a> ] ; <a href="#http.uri" title="http URI scheme">Section&nbsp;2.6.1</a>
    20942228</pre><p id="rfc.section.9.4.p.4">A "host" without any trailing port information implies the default port for the service requested (e.g., "80" for an HTTP
    2095          URL). For example, a request on the origin server for &lt;http://www.example.org/pub/WWW/&gt; would properly include:
    2096       </p>
    2097       <div id="rfc.figure.u.66"></div><pre class="text2">GET /pub/WWW/ HTTP/1.1
     2229               URL). For example, a request on the origin server for &lt;http://www.example.org/pub/WWW/&gt; would properly include:
     2230            </p>
     2231            <div id="rfc.figure.u.66"></div><pre class="text2">GET /pub/WWW/ HTTP/1.1
    20982232Host: www.example.org
    20992233</pre><p id="rfc.section.9.4.p.6">A client <em class="bcp14">MUST</em> include a Host header field in all HTTP/1.1 request messages. If the requested URI does not include an Internet host name
    2100          for the service being requested, then the Host header field <em class="bcp14">MUST</em> be given with an empty value. An HTTP/1.1 proxy <em class="bcp14">MUST</em> ensure that any request message it forwards does contain an appropriate Host header field that identifies the service being
    2101          requested by the proxy. All Internet-based HTTP/1.1 servers <em class="bcp14">MUST</em> respond with a 400 (Bad Request) status code to any HTTP/1.1 request message which lacks a Host header field.
    2102       </p>
    2103       <p id="rfc.section.9.4.p.7">See Sections <a href="#the.resource.identified.by.a.request" title="The Resource Identified by a Request">4.2</a> and <a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses">B.1.1</a> for other requirements relating to Host.
    2104       </p>
    2105       <div id="rfc.iref.t.3"></div>
    2106       <div id="rfc.iref.h.11"></div>
    2107       <h2 id="rfc.section.9.5"><a href="#rfc.section.9.5">9.5</a>&nbsp;<a id="header.te" href="#header.te">TE</a></h2>
    2108       <p id="rfc.section.9.5.p.1">The "TE" request-header field indicates what extension transfer-codings it is willing to accept in the response, and whether
    2109          or not it is willing to accept trailer fields in a chunked transfer-coding.
    2110       </p>
    2111       <p id="rfc.section.9.5.p.2">Its value consists of the keyword "trailers" and/or a comma-separated list of extension transfer-coding names with optional
    2112          accept parameters (as described in <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;6.2</a>).
    2113       </p>
    2114       <div id="rfc.figure.u.67"></div><pre class="inline"><span id="rfc.iref.g.103"></span><span id="rfc.iref.g.104"></span><span id="rfc.iref.g.105"></span><span id="rfc.iref.g.106"></span><span id="rfc.iref.g.107"></span>  <a href="#header.te" class="smpl">TE</a>        = "TE" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.te" class="smpl">TE-v</a>
     2234               for the service being requested, then the Host header field <em class="bcp14">MUST</em> be given with an empty value. An HTTP/1.1 proxy <em class="bcp14">MUST</em> ensure that any request message it forwards does contain an appropriate Host header field that identifies the service being
     2235               requested by the proxy. All Internet-based HTTP/1.1 servers <em class="bcp14">MUST</em> respond with a 400 (Bad Request) status code to any HTTP/1.1 request message which lacks a Host header field.
     2236            </p>
     2237            <p id="rfc.section.9.4.p.7">See Sections <a href="#the.resource.identified.by.a.request" title="The Resource Identified by a Request">4.2</a> and <a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses">B.1.1</a> for other requirements relating to Host.
     2238            </p>
     2239         </div>
     2240         <div id="header.te">
     2241            <div id="rfc.iref.t.3"></div>
     2242            <div id="rfc.iref.h.11"></div>
     2243            <h2 id="rfc.section.9.5"><a href="#rfc.section.9.5">9.5</a>&nbsp;<a href="#header.te">TE</a></h2>
     2244            <p id="rfc.section.9.5.p.1">The "TE" request-header field indicates what extension transfer-codings it is willing to accept in the response, and whether
     2245               or not it is willing to accept trailer fields in a chunked transfer-coding.
     2246            </p>
     2247            <p id="rfc.section.9.5.p.2">Its value consists of the keyword "trailers" and/or a comma-separated list of extension transfer-coding names with optional
     2248               accept parameters (as described in <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;6.2</a>).
     2249            </p>
     2250            <div id="rfc.figure.u.67"></div><pre class="inline"><span id="rfc.iref.g.103"></span><span id="rfc.iref.g.104"></span><span id="rfc.iref.g.105"></span><span id="rfc.iref.g.106"></span><span id="rfc.iref.g.107"></span>  <a href="#header.te" class="smpl">TE</a>        = "TE" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.te" class="smpl">TE-v</a>
    21152251  <a href="#header.te" class="smpl">TE-v</a>      = #<a href="#header.te" class="smpl">t-codings</a>
    21162252  <a href="#header.te" class="smpl">t-codings</a> = "trailers" / ( <a href="#transfer.codings" class="smpl">transfer-extension</a> [ <a href="#header.te" class="smpl">te-params</a> ] )
     
    21182254  <a href="#header.te" class="smpl">te-ext</a>    = <a href="#rule.whitespace" class="smpl">OWS</a> ";" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#rule.token.separators" class="smpl">token</a> [ "=" <a href="#rule.token.separators" class="smpl">word</a> ]
    21192255</pre><p id="rfc.section.9.5.p.4">The presence of the keyword "trailers" indicates that the client is willing to accept trailer fields in a chunked transfer-coding,
    2120          as defined in <a href="#chunked.encoding" title="Chunked Transfer Coding">Section&nbsp;6.2.1</a>. This keyword is reserved for use with transfer-coding values even though it does not itself represent a transfer-coding.
    2121       </p>
    2122       <p id="rfc.section.9.5.p.5">Examples of its use are:</p>
    2123       <div id="rfc.figure.u.68"></div><pre class="text">  TE: deflate
     2256               as defined in <a href="#chunked.encoding" title="Chunked Transfer Coding">Section&nbsp;6.2.1</a>. This keyword is reserved for use with transfer-coding values even though it does not itself represent a transfer-coding.
     2257            </p>
     2258            <p id="rfc.section.9.5.p.5">Examples of its use are:</p>
     2259            <div id="rfc.figure.u.68"></div><pre class="text">  TE: deflate
    21242260  TE:
    21252261  TE: trailers, deflate;q=0.5
    21262262</pre><p id="rfc.section.9.5.p.7">The TE header field only applies to the immediate connection. Therefore, the keyword <em class="bcp14">MUST</em> be supplied within a Connection header field (<a href="#header.connection" id="rfc.xref.header.connection.5" title="Connection">Section&nbsp;9.1</a>) whenever TE is present in an HTTP/1.1 message.
    2127       </p>
    2128       <p id="rfc.section.9.5.p.8">A server tests whether a transfer-coding is acceptable, according to a TE field, using these rules: </p>
    2129       <ol>
    2130          <li>
    2131             <p>The "chunked" transfer-coding is always acceptable. If the keyword "trailers" is listed, the client indicates that it is willing
    2132                to accept trailer fields in the chunked response on behalf of itself and any downstream clients. The implication is that,
    2133                if given, the client is stating that either all downstream clients are willing to accept trailer fields in the forwarded response,
    2134                or that it will attempt to buffer the response on behalf of downstream recipients.
    2135             </p>
    2136             <p> <b>Note:</b> HTTP/1.1 does not define any means to limit the size of a chunked response such that a client can be assured of buffering
    2137                the entire response.
    2138             </p>
    2139          </li>
    2140          <li>
    2141             <p>If the transfer-coding being tested is one of the transfer-codings listed in the TE field, then it is acceptable unless it
    2142                is accompanied by a qvalue of 0. (As defined in <a href="#quality.values" title="Quality Values">Section&nbsp;6.4</a>, a qvalue of 0 means "not acceptable".)
    2143             </p>
    2144          </li>
    2145          <li>
    2146             <p>If multiple transfer-codings are acceptable, then the acceptable transfer-coding with the highest non-zero qvalue is preferred.
    2147                The "chunked" transfer-coding always has a qvalue of 1.
    2148             </p>
    2149          </li>
    2150       </ol>
    2151       <p id="rfc.section.9.5.p.9">If the TE field-value is empty or if no TE field is present, the only transfer-coding is "chunked". A message with no transfer-coding
    2152          is always acceptable.
    2153       </p>
    2154       <div id="rfc.iref.t.4"></div>
    2155       <div id="rfc.iref.h.12"></div>
    2156       <h2 id="rfc.section.9.6"><a href="#rfc.section.9.6">9.6</a>&nbsp;<a id="header.trailer" href="#header.trailer">Trailer</a></h2>
    2157       <p id="rfc.section.9.6.p.1">The "Trailer" general-header field indicates that the given set of header fields is present in the trailer of a message encoded
    2158          with chunked transfer-coding.
    2159       </p>
    2160       <div id="rfc.figure.u.69"></div><pre class="inline"><span id="rfc.iref.g.108"></span><span id="rfc.iref.g.109"></span>  <a href="#header.trailer" class="smpl">Trailer</a>   = "Trailer" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.trailer" class="smpl">Trailer-v</a>
     2263            </p>
     2264            <p id="rfc.section.9.5.p.8">A server tests whether a transfer-coding is acceptable, according to a TE field, using these rules: </p>
     2265            <ol>
     2266               <li>
     2267                  <p>The "chunked" transfer-coding is always acceptable. If the keyword "trailers" is listed, the client indicates that it is willing
     2268                     to accept trailer fields in the chunked response on behalf of itself and any downstream clients. The implication is that,
     2269                     if given, the client is stating that either all downstream clients are willing to accept trailer fields in the forwarded response,
     2270                     or that it will attempt to buffer the response on behalf of downstream recipients.
     2271                  </p>
     2272                  <p><b>Note:</b> HTTP/1.1 does not define any means to limit the size of a chunked response such that a client can be assured of buffering
     2273                     the entire response.
     2274                  </p>
     2275               </li>
     2276               <li>
     2277                  <p>If the transfer-coding being tested is one of the transfer-codings listed in the TE field, then it is acceptable unless it
     2278                     is accompanied by a qvalue of 0. (As defined in <a href="#quality.values" title="Quality Values">Section&nbsp;6.4</a>, a qvalue of 0 means "not acceptable".)
     2279                  </p>
     2280               </li>
     2281               <li>
     2282                  <p>If multiple transfer-codings are acceptable, then the acceptable transfer-coding with the highest non-zero qvalue is preferred.
     2283                     The "chunked" transfer-coding always has a qvalue of 1.
     2284                  </p>
     2285               </li>
     2286            </ol>
     2287            <p id="rfc.section.9.5.p.9">If the TE field-value is empty or if no TE field is present, the only transfer-coding is "chunked". A message with no transfer-coding
     2288               is always acceptable.
     2289            </p>
     2290         </div>
     2291         <div id="header.trailer">
     2292            <div id="rfc.iref.t.4"></div>
     2293            <div id="rfc.iref.h.12"></div>
     2294            <h2 id="rfc.section.9.6"><a href="#rfc.section.9.6">9.6</a>&nbsp;<a href="#header.trailer">Trailer</a></h2>
     2295            <p id="rfc.section.9.6.p.1">The "Trailer" general-header field indicates that the given set of header fields is present in the trailer of a message encoded
     2296               with chunked transfer-coding.
     2297            </p>
     2298            <div id="rfc.figure.u.69"></div><pre class="inline"><span id="rfc.iref.g.108"></span><span id="rfc.iref.g.109"></span>  <a href="#header.trailer" class="smpl">Trailer</a>   = "Trailer" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.trailer" class="smpl">Trailer-v</a>
    21612299  <a href="#header.trailer" class="smpl">Trailer-v</a> = 1#<a href="#header.fields" class="smpl">field-name</a>
    21622300</pre><p id="rfc.section.9.6.p.3">An HTTP/1.1 message <em class="bcp14">SHOULD</em> include a Trailer header field in a message using chunked transfer-coding with a non-empty trailer. Doing so allows the recipient
    2163          to know which header fields to expect in the trailer.
    2164       </p>
    2165       <p id="rfc.section.9.6.p.4">If no Trailer header field is present, the trailer <em class="bcp14">SHOULD NOT</em> include any header fields. See <a href="#chunked.encoding" title="Chunked Transfer Coding">Section&nbsp;6.2.1</a> for restrictions on the use of trailer fields in a "chunked" transfer-coding.
    2166       </p>
    2167       <p id="rfc.section.9.6.p.5">Message header fields listed in the Trailer header field <em class="bcp14">MUST NOT</em> include the following header fields:
    2168       </p>
    2169       <ul>
    2170          <li>Transfer-Encoding</li>
    2171          <li>Content-Length</li>
    2172          <li>Trailer</li>
    2173       </ul>
    2174       <div id="rfc.iref.t.5"></div>
    2175       <div id="rfc.iref.h.13"></div>
    2176       <h2 id="rfc.section.9.7"><a href="#rfc.section.9.7">9.7</a>&nbsp;<a id="header.transfer-encoding" href="#header.transfer-encoding">Transfer-Encoding</a></h2>
    2177       <p id="rfc.section.9.7.p.1">The "Transfer-Encoding" general-header field indicates what transfer-codings (if any) have been applied to the message body.
    2178          It differs from Content-Encoding (<a href="p3-payload.html#content.codings" title="Content Codings">Section 2.2</a> of <a href="#Part3" id="rfc.xref.Part3.7"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>) in that transfer-codings are a property of the message (and therefore are removed by intermediaries), whereas content-codings
    2179          are not.
    2180       </p>
    2181       <div id="rfc.figure.u.70"></div><pre class="inline"><span id="rfc.iref.g.110"></span><span id="rfc.iref.g.111"></span>  <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a>   = "Transfer-Encoding" ":" <a href="#rule.whitespace" class="smpl">OWS</a>
     2301               to know which header fields to expect in the trailer.
     2302            </p>
     2303            <p id="rfc.section.9.6.p.4">If no Trailer header field is present, the trailer <em class="bcp14">SHOULD NOT</em> include any header fields. See <a href="#chunked.encoding" title="Chunked Transfer Coding">Section&nbsp;6.2.1</a> for restrictions on the use of trailer fields in a "chunked" transfer-coding.
     2304            </p>
     2305            <p id="rfc.section.9.6.p.5">Message header fields listed in the Trailer header field <em class="bcp14">MUST NOT</em> include the following header fields:
     2306            </p>
     2307            <ul>
     2308               <li>Transfer-Encoding</li>
     2309               <li>Content-Length</li>
     2310               <li>Trailer</li>
     2311            </ul>
     2312         </div>
     2313         <div id="header.transfer-encoding">
     2314            <div id="rfc.iref.t.5"></div>
     2315            <div id="rfc.iref.h.13"></div>
     2316            <h2 id="rfc.section.9.7"><a href="#rfc.section.9.7">9.7</a>&nbsp;<a href="#header.transfer-encoding">Transfer-Encoding</a></h2>
     2317            <p id="rfc.section.9.7.p.1">The "Transfer-Encoding" general-header field indicates what transfer-codings (if any) have been applied to the message body.
     2318               It differs from Content-Encoding (<a href="p3-payload.html#content.codings" title="Content Codings">Section 2.2</a> of <a href="#Part3" id="rfc.xref.Part3.7"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>) in that transfer-codings are a property of the message (and therefore are removed by intermediaries), whereas content-codings
     2319               are not.
     2320            </p>
     2321            <div id="rfc.figure.u.70"></div><pre class="inline"><span id="rfc.iref.g.110"></span><span id="rfc.iref.g.111"></span>  <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a>   = "Transfer-Encoding" ":" <a href="#rule.whitespace" class="smpl">OWS</a>
    21822322                        <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding-v</a>
    21832323  <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding-v</a> = 1#<a href="#transfer.codings" class="smpl">transfer-coding</a>
    21842324</pre><p id="rfc.section.9.7.p.3">Transfer-codings are defined in <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;6.2</a>. An example is:
    2185       </p>
    2186       <div id="rfc.figure.u.71"></div><pre class="text">  Transfer-Encoding: chunked
     2325            </p>
     2326            <div id="rfc.figure.u.71"></div><pre class="text">  Transfer-Encoding: chunked
    21872327</pre><p id="rfc.section.9.7.p.5">If multiple encodings have been applied to a representation, the transfer-codings <em class="bcp14">MUST</em> be listed in the order in which they were applied. Additional information about the encoding parameters <em class="bcp14">MAY</em> be provided by other header fields not defined by this specification.
    2188       </p>
    2189       <p id="rfc.section.9.7.p.6">Many older HTTP/1.0 applications do not understand the Transfer-Encoding header.</p>
    2190       <div id="rfc.iref.u.5"></div>
    2191       <div id="rfc.iref.h.14"></div>
    2192       <h2 id="rfc.section.9.8"><a href="#rfc.section.9.8">9.8</a>&nbsp;<a id="header.upgrade" href="#header.upgrade">Upgrade</a></h2>
    2193       <p id="rfc.section.9.8.p.1">The "Upgrade" general-header field allows the client to specify what additional communication protocols it would like to use,
    2194          if the server chooses to switch protocols. Additionally, the server <em class="bcp14">MUST</em> use the Upgrade header field within a 101 (Switching Protocols) response to indicate which protocol(s) are being switched
    2195          to.
    2196       </p>
    2197       <div id="rfc.figure.u.72"></div><pre class="inline"><span id="rfc.iref.g.112"></span><span id="rfc.iref.g.113"></span>  <a href="#header.upgrade" class="smpl">Upgrade</a>   = "Upgrade" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.upgrade" class="smpl">Upgrade-v</a>
     2328            </p>
     2329            <p id="rfc.section.9.7.p.6">Many older HTTP/1.0 applications do not understand the Transfer-Encoding header.</p>
     2330         </div>
     2331         <div id="header.upgrade">
     2332            <div id="rfc.iref.u.5"></div>
     2333            <div id="rfc.iref.h.14"></div>
     2334            <h2 id="rfc.section.9.8"><a href="#rfc.section.9.8">9.8</a>&nbsp;<a href="#header.upgrade">Upgrade</a></h2>
     2335            <p id="rfc.section.9.8.p.1">The "Upgrade" general-header field allows the client to specify what additional communication protocols it would like to use,
     2336               if the server chooses to switch protocols. Additionally, the server <em class="bcp14">MUST</em> use the Upgrade header field within a 101 (Switching Protocols) response to indicate which protocol(s) are being switched
     2337               to.
     2338            </p>
     2339            <div id="rfc.figure.u.72"></div><pre class="inline"><span id="rfc.iref.g.112"></span><span id="rfc.iref.g.113"></span>  <a href="#header.upgrade" class="smpl">Upgrade</a>   = "Upgrade" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.upgrade" class="smpl">Upgrade-v</a>
    21982340  <a href="#header.upgrade" class="smpl">Upgrade-v</a> = 1#<a href="#product.tokens" class="smpl">product</a>
    21992341</pre><p id="rfc.section.9.8.p.3">For example,</p>
    2200       <div id="rfc.figure.u.73"></div><pre class="text">  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
     2342            <div id="rfc.figure.u.73"></div><pre class="text">  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
    22012343</pre><p id="rfc.section.9.8.p.5">The Upgrade header field is intended to provide a simple mechanism for transition from HTTP/1.1 to some other, incompatible
    2202          protocol. It does so by allowing the client to advertise its desire to use another protocol, such as a later version of HTTP
    2203          with a higher major version number, even though the current request has been made using HTTP/1.1. This eases the difficult
    2204          transition between incompatible protocols by allowing the client to initiate a request in the more commonly supported protocol
    2205          while indicating to the server that it would like to use a "better" protocol if available (where "better" is determined by
    2206          the server, possibly according to the nature of the method and/or resource being requested).
    2207       </p>
    2208       <p id="rfc.section.9.8.p.6">The Upgrade header field only applies to switching application-layer protocols upon the existing transport-layer connection.
    2209          Upgrade cannot be used to insist on a protocol change; its acceptance and use by the server is optional. The capabilities
    2210          and nature of the application-layer communication after the protocol change is entirely dependent upon the new protocol chosen,
    2211          although the first action after changing the protocol <em class="bcp14">MUST</em> be a response to the initial HTTP request containing the Upgrade header field.
    2212       </p>
    2213       <p id="rfc.section.9.8.p.7">The Upgrade header field only applies to the immediate connection. Therefore, the upgrade keyword <em class="bcp14">MUST</em> be supplied within a Connection header field (<a href="#header.connection" id="rfc.xref.header.connection.6" title="Connection">Section&nbsp;9.1</a>) whenever Upgrade is present in an HTTP/1.1 message.
    2214       </p>
    2215       <p id="rfc.section.9.8.p.8">The Upgrade header field cannot be used to indicate a switch to a protocol on a different connection. For that purpose, it
    2216          is more appropriate to use a 301, 302, 303, or 305 redirection response.
    2217       </p>
    2218       <p id="rfc.section.9.8.p.9">This specification only defines the protocol name "HTTP" for use by the family of Hypertext Transfer Protocols, as defined
    2219          by the HTTP version rules of <a href="#http.version" title="HTTP Version">Section&nbsp;2.5</a> and future updates to this specification. Additional tokens can be registered with IANA using the registration procedure defined
    2220          below.
    2221       </p>
    2222       <h3 id="rfc.section.9.8.1"><a href="#rfc.section.9.8.1">9.8.1</a>&nbsp;<a id="upgrade.token.registry" href="#upgrade.token.registry">Upgrade Token Registry</a></h3>
    2223       <p id="rfc.section.9.8.1.p.1">The HTTP Upgrade Token Registry defines the name space for product tokens used to identify protocols in the Upgrade header
    2224          field. Each registered token is associated with contact information and an optional set of specifications that details how
    2225          the connection will be processed after it has been upgraded.
    2226       </p>
    2227       <p id="rfc.section.9.8.1.p.2">Registrations are allowed on a First Come First Served basis as described in <a href="http://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>. The specifications need not be IETF documents or be subject to IESG review. Registrations are subject to the following rules:
    2228       </p>
    2229       <ol>
    2230          <li>A token, once registered, stays registered forever.</li>
    2231          <li>The registration <em class="bcp14">MUST</em> name a responsible party for the registration.
    2232          </li>
    2233          <li>The registration <em class="bcp14">MUST</em> name a point of contact.
    2234          </li>
    2235          <li>The registration <em class="bcp14">MAY</em> name a set of specifications associated with that token. Such specifications need not be publicly available.
    2236          </li>
    2237          <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.
    2238          </li>
    2239          <li>The responsible party for the first registration of a "product" token <em class="bcp14">MUST</em> approve later registrations of a "version" token together with that "product" token before they can be registered.
    2240          </li>
    2241          <li>If absolutely required, the IESG <em class="bcp14">MAY</em> reassign the responsibility for a token. This will normally only be used in the case when a responsible party cannot be contacted.
    2242          </li>
    2243       </ol>
    2244       <div id="rfc.iref.v.1"></div>
    2245       <div id="rfc.iref.h.15"></div>
    2246       <h2 id="rfc.section.9.9"><a href="#rfc.section.9.9">9.9</a>&nbsp;<a id="header.via" href="#header.via">Via</a></h2>
    2247       <p id="rfc.section.9.9.p.1">The "Via" general-header field <em class="bcp14">MUST</em> be used by gateways and proxies to indicate the intermediate protocols and recipients between the user agent and the server
    2248          on requests, and between the origin server and the client on responses. It is analogous to the "Received" field defined in <a href="http://tools.ietf.org/html/rfc5322#section-3.6.7">Section 3.6.7</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.5"><cite title="Internet Message Format">[RFC5322]</cite></a> and is intended to be used for tracking message forwards, avoiding request loops, and identifying the protocol capabilities
    2249          of all senders along the request/response chain.
    2250       </p>
    2251       <div id="rfc.figure.u.74"></div><pre class="inline"><span id="rfc.iref.g.114"></span><span id="rfc.iref.g.115"></span><span id="rfc.iref.g.116"></span><span id="rfc.iref.g.117"></span><span id="rfc.iref.g.118"></span><span id="rfc.iref.g.119"></span><span id="rfc.iref.g.120"></span>  <a href="#header.via" class="smpl">Via</a>               = "Via" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.via" class="smpl">Via-v</a>
     2344               protocol. It does so by allowing the client to advertise its desire to use another protocol, such as a later version of HTTP
     2345               with a higher major version number, even though the current request has been made using HTTP/1.1. This eases the difficult
     2346               transition between incompatible protocols by allowing the client to initiate a request in the more commonly supported protocol
     2347               while indicating to the server that it would like to use a "better" protocol if available (where "better" is determined by
     2348               the server, possibly according to the nature of the method and/or resource being requested).
     2349            </p>
     2350            <p id="rfc.section.9.8.p.6">The Upgrade header field only applies to switching application-layer protocols upon the existing transport-layer connection.
     2351               Upgrade cannot be used to insist on a protocol change; its acceptance and use by the server is optional. The capabilities
     2352               and nature of the application-layer communication after the protocol change is entirely dependent upon the new protocol chosen,
     2353               although the first action after changing the protocol <em class="bcp14">MUST</em> be a response to the initial HTTP request containing the Upgrade header field.
     2354            </p>
     2355            <p id="rfc.section.9.8.p.7">The Upgrade header field only applies to the immediate connection. Therefore, the upgrade keyword <em class="bcp14">MUST</em> be supplied within a Connection header field (<a href="#header.connection" id="rfc.xref.header.connection.6" title="Connection">Section&nbsp;9.1</a>) whenever Upgrade is present in an HTTP/1.1 message.
     2356            </p>
     2357            <p id="rfc.section.9.8.p.8">The Upgrade header field cannot be used to indicate a switch to a protocol on a different connection. For that purpose, it
     2358               is more appropriate to use a 301, 302, 303, or 305 redirection response.
     2359            </p>
     2360            <p id="rfc.section.9.8.p.9">This specification only defines the protocol name "HTTP" for use by the family of Hypertext Transfer Protocols, as defined
     2361               by the HTTP version rules of <a href="#http.version" title="HTTP Version">Section&nbsp;2.5</a> and future updates to this specification. Additional tokens can be registered with IANA using the registration procedure defined
     2362               below.
     2363            </p>
     2364            <div id="upgrade.token.registry">
     2365               <h3 id="rfc.section.9.8.1"><a href="#rfc.section.9.8.1">9.8.1</a>&nbsp;<a href="#upgrade.token.registry">Upgrade Token Registry</a></h3>
     2366               <p id="rfc.section.9.8.1.p.1">The HTTP Upgrade Token Registry defines the name space for product tokens used to identify protocols in the Upgrade header
     2367                  field. Each registered token is associated with contact information and an optional set of specifications that details how
     2368                  the connection will be processed after it has been upgraded.
     2369               </p>
     2370               <p id="rfc.section.9.8.1.p.2">Registrations are allowed on a First Come First Served basis as described in <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>. The specifications need not be IETF documents or be subject to IESG review. Registrations are subject to the following rules:
     2371               </p>
     2372               <ol>
     2373                  <li>A token, once registered, stays registered forever.</li>
     2374                  <li>The registration <em class="bcp14">MUST</em> name a responsible party for the registration.
     2375                  </li>
     2376                  <li>The registration <em class="bcp14">MUST</em> name a point of contact.
     2377                  </li>
     2378                  <li>The registration <em class="bcp14">MAY</em> name a set of specifications associated with that token. Such specifications need not be publicly available.
     2379                  </li>
     2380                  <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.
     2381                  </li>
     2382                  <li>The responsible party for the first registration of a "product" token <em class="bcp14">MUST</em> approve later registrations of a "version" token together with that "product" token before they can be registered.
     2383                  </li>
     2384                  <li>If absolutely required, the IESG <em class="bcp14">MAY</em> reassign the responsibility for a token. This will normally only be used in the case when a responsible party cannot be contacted.
     2385                  </li>
     2386               </ol>
     2387            </div>
     2388         </div>
     2389         <div id="header.via">
     2390            <div id="rfc.iref.v.1"></div>
     2391            <div id="rfc.iref.h.15"></div>
     2392            <h2 id="rfc.section.9.9"><a href="#rfc.section.9.9">9.9</a>&nbsp;<a href="#header.via">Via</a></h2>
     2393            <p id="rfc.section.9.9.p.1">The "Via" general-header field <em class="bcp14">MUST</em> be used by gateways and proxies to indicate the intermediate protocols and recipients between the user agent and the server
     2394               on requests, and between the origin server and the client on responses. It is analogous to the "Received" field defined in <a href="https://tools.ietf.org/html/rfc5322#section-3.6.7">Section 3.6.7</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.5"><cite title="Internet Message Format">[RFC5322]</cite></a> and is intended to be used for tracking message forwards, avoiding request loops, and identifying the protocol capabilities
     2395               of all senders along the request/response chain.
     2396            </p>
     2397            <div id="rfc.figure.u.74"></div><pre class="inline"><span id="rfc.iref.g.114"></span><span id="rfc.iref.g.115"></span><span id="rfc.iref.g.116"></span><span id="rfc.iref.g.117"></span><span id="rfc.iref.g.118"></span><span id="rfc.iref.g.119"></span><span id="rfc.iref.g.120"></span>  <a href="#header.via" class="smpl">Via</a>               = "Via" ":" <a href="#rule.whitespace" class="smpl">OWS</a> <a href="#header.via" class="smpl">Via-v</a>
    22522398  <a href="#header.via" class="smpl">Via-v</a>             = 1#( <a href="#header.via" class="smpl">received-protocol</a> <a href="#rule.whitespace" class="smpl">RWS</a> <a href="#header.via" class="smpl">received-by</a>
    22532399                          [ <a href="#rule.whitespace" class="smpl">RWS</a> <a href="#rule.comment" class="smpl">comment</a> ] )
     
    22582404  <a href="#header.via" class="smpl">pseudonym</a>         = <a href="#rule.token.separators" class="smpl">token</a>
    22592405</pre><p id="rfc.section.9.9.p.3">The received-protocol indicates the protocol version of the message received by the server or client along each segment of
    2260          the request/response chain. The received-protocol version is appended to the Via field value when the message is forwarded
    2261          so that information about the protocol capabilities of upstream applications remains visible to all recipients.
    2262       </p>
    2263       <p id="rfc.section.9.9.p.4">The protocol-name is optional if and only if it would be "HTTP". The received-by field is normally the host and optional port
    2264          number of a recipient server or client that subsequently forwarded the message. However, if the real host is considered to
    2265          be sensitive information, it <em class="bcp14">MAY</em> be replaced by a pseudonym. If the port is not given, it <em class="bcp14">MAY</em> be assumed to be the default port of the received-protocol.
    2266       </p>
    2267       <p id="rfc.section.9.9.p.5">Multiple Via field values represent each proxy or gateway that has forwarded the message. Each recipient <em class="bcp14">MUST</em> append its information such that the end result is ordered according to the sequence of forwarding applications.
    2268       </p>
    2269       <p id="rfc.section.9.9.p.6">Comments <em class="bcp14">MAY</em> be used in the Via header field to identify the software of the recipient proxy or gateway, analogous to the User-Agent and
    2270          Server header fields. However, all comments in the Via field are optional and <em class="bcp14">MAY</em> be removed by any recipient prior to forwarding the message.
    2271       </p>
    2272       <p id="rfc.section.9.9.p.7">For example, a request message could be sent from an HTTP/1.0 user agent to an internal proxy code-named "fred", which uses
    2273          HTTP/1.1 to forward the request to a public proxy at p.example.net, which completes the request by forwarding it to the origin
    2274          server at www.example.com. The request received by www.example.com would then have the following Via header field:
    2275       </p>
    2276       <div id="rfc.figure.u.75"></div><pre class="text">  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
     2406               the request/response chain. The received-protocol version is appended to the Via field value when the message is forwarded
     2407               so that information about the protocol capabilities of upstream applications remains visible to all recipients.
     2408            </p>
     2409            <p id="rfc.section.9.9.p.4">The protocol-name is optional if and only if it would be "HTTP". The received-by field is normally the host and optional port
     2410               number of a recipient server or client that subsequently forwarded the message. However, if the real host is considered to
     2411               be sensitive information, it <em class="bcp14">MAY</em> be replaced by a pseudonym. If the port is not given, it <em class="bcp14">MAY</em> be assumed to be the default port of the received-protocol.
     2412            </p>
     2413            <p id="rfc.section.9.9.p.5">Multiple Via field values represent each proxy or gateway that has forwarded the message. Each recipient <em class="bcp14">MUST</em> append its information such that the end result is ordered according to the sequence of forwarding applications.
     2414            </p>
     2415            <p id="rfc.section.9.9.p.6">Comments <em class="bcp14">MAY</em> be used in the Via header field to identify the software of the recipient proxy or gateway, analogous to the User-Agent and
     2416               Server header fields. However, all comments in the Via field are optional and <em class="bcp14">MAY</em> be removed by any recipient prior to forwarding the message.
     2417            </p>
     2418            <p id="rfc.section.9.9.p.7">For example, a request message could be sent from an HTTP/1.0 user agent to an internal proxy code-named "fred", which uses
     2419               HTTP/1.1 to forward the request to a public proxy at p.example.net, which completes the request by forwarding it to the origin
     2420               server at www.example.com. The request received by www.example.com would then have the following Via header field:
     2421            </p>
     2422            <div id="rfc.figure.u.75"></div><pre class="text">  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
    22772423</pre><p id="rfc.section.9.9.p.9">Proxies and gateways used as a portal through a network firewall <em class="bcp14">SHOULD NOT</em>, by default, forward the names and ports of hosts within the firewall region. This information <em class="bcp14">SHOULD</em> only be propagated if explicitly enabled. If not enabled, the received-by host of any host behind the firewall <em class="bcp14">SHOULD</em> be replaced by an appropriate pseudonym for that host.
    2278       </p>
    2279       <p id="rfc.section.9.9.p.10">For organizations that have strong privacy requirements for hiding internal structures, a proxy <em class="bcp14">MAY</em> combine an ordered subsequence of Via header field entries with identical received-protocol values into a single such entry.
    2280          For example,
    2281       </p>
    2282       <div id="rfc.figure.u.76"></div><pre class="text">  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
     2424            </p>
     2425            <p id="rfc.section.9.9.p.10">For organizations that have strong privacy requirements for hiding internal structures, a proxy <em class="bcp14">MAY</em> combine an ordered subsequence of Via header field entries with identical received-protocol values into a single such entry.
     2426               For example,
     2427            </p>
     2428            <div id="rfc.figure.u.76"></div><pre class="text">  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
    22832429</pre><p id="rfc.section.9.9.p.12">could be collapsed to</p>
    2284       <div id="rfc.figure.u.77"></div><pre class="text">  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
     2430            <div id="rfc.figure.u.77"></div><pre class="text">  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
    22852431</pre><p id="rfc.section.9.9.p.14">Applications <em class="bcp14">SHOULD NOT</em> combine multiple entries unless they are all under the same organizational control and the hosts have already been replaced
    2286          by pseudonyms. Applications <em class="bcp14">MUST NOT</em> combine entries which have different received-protocol values.
    2287       </p>
    2288       <h1 id="rfc.section.10"><a href="#rfc.section.10">10.</a>&nbsp;<a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1>
    2289       <h2 id="rfc.section.10.1"><a href="#rfc.section.10.1">10.1</a>&nbsp;<a id="header.field.registration" href="#header.field.registration">Header Field Registration</a></h2>
    2290       <p id="rfc.section.10.1.p.1">The Message Header Field Registry located at &lt;<a href="http://www.iana.org/assignments/message-headers/message-header-index.html">http://www.iana.org/assignments/message-headers/message-header-index.html</a>&gt; shall be updated with the permanent registrations below (see <a href="#RFC3864" id="rfc.xref.RFC3864.1"><cite title="Registration Procedures for Message Header Fields">[RFC3864]</cite></a>):
    2291       </p>
    2292       <div id="rfc.table.1">
    2293          <div id="iana.header.registration.table"></div>
    2294          <table class="tt full left" cellpadding="3" cellspacing="0">
    2295             <thead>
    2296                <tr>
    2297                   <th>Header Field Name</th>
    2298                   <th>Protocol</th>
    2299                   <th>Status</th>
    2300                   <th>Reference</th>
    2301                </tr>
    2302             </thead>
    2303             <tbody>
    2304                <tr>
    2305                   <td class="left">Connection</td>
    2306                   <td class="left">http</td>
    2307                   <td class="left">standard</td>
    2308                   <td class="left"> <a href="#header.connection" id="rfc.xref.header.connection.7" title="Connection">Section&nbsp;9.1</a>
    2309                   </td>
    2310                </tr>
    2311                <tr>
    2312                   <td class="left">Content-Length</td>
    2313                   <td class="left">http</td>
    2314                   <td class="left">standard</td>
    2315                   <td class="left"> <a href="#header.content-length" id="rfc.xref.header.content-length.2" title="Content-Length">Section&nbsp;9.2</a>
    2316                   </td>
    2317                </tr>
    2318                <tr>
    2319                   <td class="left">Date</td>
    2320                   <td class="left">http</td>
    2321                   <td class="left">standard</td>
    2322                   <td class="left"> <a href="#header.date" id="rfc.xref.header.date.2" title="Date">Section&nbsp;9.3</a>
    2323                   </td>
    2324                </tr>
    2325                <tr>
    2326                   <td class="left">Host</td>
    2327                   <td class="left">http</td>
    2328                   <td class="left">standard</td>
    2329                   <td class="left"> <a href="#header.host" id="rfc.xref.header.host.2" title="Host">Section&nbsp;9.4</a>
    2330                   </td>
    2331                </tr>
    2332                <tr>
    2333                   <td class="left">TE</td>
    2334                   <td class="left">http</td>
    2335                   <td class="left">standard</td>
    2336                   <td class="left"> <a href="#header.te" id="rfc.xref.header.te.4" title="TE">Section&nbsp;9.5</a>
    2337                   </td>
    2338                </tr>
    2339                <tr>
    2340                   <td class="left">Trailer</td>
    2341                   <td class="left">http</td>
    2342                   <td class="left">standard</td>
    2343                   <td class="left"> <a href="#header.trailer" id="rfc.xref.header.trailer.3" title="Trailer">Section&nbsp;9.6</a>
    2344                   </td>
    2345                </tr>
    2346                <tr>
    2347                   <td class="left">Transfer-Encoding</td>
    2348                   <td class="left">http</td>
    2349                   <td class="left">standard</td>
    2350                   <td class="left"> <a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.5" title="Transfer-Encoding">Section&nbsp;9.7</a>
    2351                   </td>
    2352                </tr>
    2353                <tr>
    2354                   <td class="left">Upgrade</td>
    2355                   <td class="left">http</td>
    2356                   <td class="left">standard</td>
    2357                   <td class="left"> <a href="#header.upgrade" id="rfc.xref.header.upgrade.2" title="Upgrade">Section&nbsp;9.8</a>
    2358                   </td>
    2359                </tr>
    2360                <tr>
    2361                   <td class="left">Via</td>
    2362                   <td class="left">http</td>
    2363                   <td class="left">standard</td>
    2364                   <td class="left"> <a href="#header.via" id="rfc.xref.header.via.2" title="Via">Section&nbsp;9.9</a>
    2365                   </td>
    2366                </tr>
    2367             </tbody>
    2368          </table>
     2432               by pseudonyms. Applications <em class="bcp14">MUST NOT</em> combine entries which have different received-protocol values.
     2433            </p>
     2434         </div>
    23692435      </div>
    2370       <p id="rfc.section.10.1.p.2">The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".</p>
    2371       <h2 id="rfc.section.10.2"><a href="#rfc.section.10.2">10.2</a>&nbsp;<a id="uri.scheme.registration" href="#uri.scheme.registration">URI Scheme Registration</a></h2>
    2372       <p id="rfc.section.10.2.p.1">The entries for the "http" and "https" URI Schemes in the registry located at &lt;<a href="http://www.iana.org/assignments/uri-schemes.html">http://www.iana.org/assignments/uri-schemes.html</a>&gt; shall be updated to point to Sections <a href="#http.uri" title="http URI scheme">2.6.1</a> and <a href="#https.uri" title="https URI scheme">2.6.2</a> of this document (see <a href="#RFC4395" id="rfc.xref.RFC4395.1"><cite title="Guidelines and Registration Procedures for New URI Schemes">[RFC4395]</cite></a>).
    2373       </p>
    2374       <h2 id="rfc.section.10.3"><a href="#rfc.section.10.3">10.3</a>&nbsp;<a id="internet.media.type.http" href="#internet.media.type.http">Internet Media Type Registrations</a></h2>
    2375       <p id="rfc.section.10.3.p.1">This document serves as the specification for the Internet media types "message/http" and "application/http". The following
    2376          is to be registered with IANA (see <a href="#RFC4288" id="rfc.xref.RFC4288.1"><cite title="Media Type Specifications and Registration Procedures">[RFC4288]</cite></a>).
    2377       </p>
    2378       <div id="rfc.iref.m.2"></div>
    2379       <div id="rfc.iref.m.3"></div>
    2380       <h3 id="rfc.section.10.3.1"><a href="#rfc.section.10.3.1">10.3.1</a>&nbsp;<a id="internet.media.type.message.http" href="#internet.media.type.message.http">Internet Media Type message/http</a></h3>
    2381       <p id="rfc.section.10.3.1.p.1">The message/http type can be used to enclose a single HTTP request or response message, provided that it obeys the MIME restrictions
    2382          for all "message" types regarding line length and encodings.
    2383       </p>
    2384       <p id="rfc.section.10.3.1.p.2"> </p>
    2385       <dl>
    2386          <dt>Type name:</dt>
    2387          <dd>message</dd>
    2388          <dt>Subtype name:</dt>
    2389          <dd>http</dd>
    2390          <dt>Required parameters:</dt>
    2391          <dd>none</dd>
    2392          <dt>Optional parameters:</dt>
    2393          <dd>version, msgtype
    2394             <dl>
    2395                <dt>version:</dt>
    2396                <dd>The HTTP-Version number of the enclosed message (e.g., "1.1"). If not present, the version can be determined from the first
    2397                   line of the body.
    2398                </dd>
    2399                <dt>msgtype:</dt>
    2400                <dd>The message type -- "request" or "response". If not present, the type can be determined from the first line of the body.</dd>
    2401             </dl>
    2402          </dd>
    2403          <dt>Encoding considerations:</dt>
    2404          <dd>only "7bit", "8bit", or "binary" are permitted</dd>
    2405          <dt>Security considerations:</dt>
    2406          <dd>none</dd>
    2407          <dt>Interoperability considerations:</dt>
    2408          <dd>none</dd>
    2409          <dt>Published specification:</dt>
    2410          <dd>This specification (see <a href="#internet.media.type.message.http" title="Internet Media Type message/http">Section&nbsp;10.3.1</a>).
    2411          </dd>
    2412          <dt>Applications that use this media type:</dt>
    2413          <dt>Additional information:</dt>
    2414          <dd>
    2415             <dl>
    2416                <dt>Magic number(s):</dt>
    2417                <dd>none</dd>
    2418                <dt>File extension(s):</dt>
    2419                <dd>none</dd>
    2420                <dt>Macintosh file type code(s):</dt>
    2421                <dd>none</dd>
    2422             </dl>
    2423          </dd>
    2424          <dt>Person and email address to contact for further information:</dt>
    2425          <dd>See Authors Section.</dd>
    2426          <dt>Intended usage:</dt>
    2427          <dd>COMMON</dd>
    2428          <dt>Restrictions on usage:</dt>
    2429          <dd>none</dd>
    2430          <dt>Author/Change controller:</dt>
    2431          <dd>IESG</dd>
    2432       </dl>
    2433       <div id="rfc.iref.m.4"></div>
    2434       <div id="rfc.iref.a.1"></div>
    2435       <h3 id="rfc.section.10.3.2"><a href="#rfc.section.10.3.2">10.3.2</a>&nbsp;<a id="internet.media.type.application.http" href="#internet.media.type.application.http">Internet Media Type application/http</a></h3>
    2436       <p id="rfc.section.10.3.2.p.1">The application/http type can be used to enclose a pipeline of one or more HTTP request or response messages (not intermixed).</p>
    2437       <p id="rfc.section.10.3.2.p.2"> </p>
    2438       <dl>
    2439          <dt>Type name:</dt>
    2440          <dd>application</dd>
    2441          <dt>Subtype name:</dt>
    2442          <dd>http</dd>
    2443          <dt>Required parameters:</dt>
    2444          <dd>none</dd>
    2445          <dt>Optional parameters:</dt>
    2446          <dd>version, msgtype
    2447             <dl>
    2448                <dt>version:</dt>
    2449                <dd>The HTTP-Version number of the enclosed messages (e.g., "1.1"). If not present, the version can be determined from the first
    2450                   line of the body.
    2451                </dd>
    2452                <dt>msgtype:</dt>
    2453                <dd>The message type -- "request" or "response". If not present, the type can be determined from the first line of the body.</dd>
    2454             </dl>
    2455          </dd>
    2456          <dt>Encoding considerations:</dt>
    2457          <dd>HTTP messages enclosed by this type are in "binary" format; use of an appropriate Content-Transfer-Encoding is required when
    2458             transmitted via E-mail.
    2459          </dd>
    2460          <dt>Security considerations:</dt>
    2461          <dd>none</dd>
    2462          <dt>Interoperability considerations:</dt>
    2463          <dd>none</dd>
    2464          <dt>Published specification:</dt>
    2465          <dd>This specification (see <a href="#internet.media.type.application.http" title="Internet Media Type application/http">Section&nbsp;10.3.2</a>).
    2466          </dd>
    2467          <dt>Applications that use this media type:</dt>
    2468          <dt>Additional information:</dt>
    2469          <dd>
    2470             <dl>
    2471                <dt>Magic number(s):</dt>
    2472                <dd>none</dd>
    2473       &nb