source: draft-ietf-httpbis/20/p1-messaging.xml @ 1807

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Prepare release of -20 drafts

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
15  <!ENTITY ID-MONTH "July">
16  <!ENTITY ID-YEAR "2012">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY Note "<x:h xmlns:x=''>Note:</x:h>">
19  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x=''/>">
20  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#response.cacheability' xmlns:x=''/>">
21  <!ENTITY payload                "<xref target='Part2' xmlns:x=''/>">
22  <!ENTITY media-types            "<xref target='Part2' x:rel='#media.types' xmlns:x=''/>">
23  <!ENTITY content-codings        "<xref target='Part2' x:rel='#content.codings' xmlns:x=''/>">
24  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x=''/>">
25  <!ENTITY content.negotiation    "<xref target='Part2' x:rel='#content.negotiation' xmlns:x=''/>">
26  <!ENTITY diff-mime              "<xref target='Part2' x:rel='#differences.between.http.and.mime' xmlns:x=''/>">
27  <!ENTITY representation         "<xref target='Part2' x:rel='#representation' xmlns:x=''/>">
28  <!ENTITY header-allow           "<xref target='Part2' x:rel='#header.allow' xmlns:x=''/>">
29  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
30  <!ENTITY header-content-encoding    "<xref target='Part2' x:rel='#header.content-encoding' xmlns:x=''/>">
31  <!ENTITY header-content-location    "<xref target='Part2' x:rel='#header.content-location' xmlns:x=''/>">
32  <!ENTITY header-content-range   "<xref target='Part5' x:rel='#header.content-range' xmlns:x=''/>">
33  <!ENTITY header-content-type    "<xref target='Part2' x:rel='#header.content-type' xmlns:x=''/>">
34  <!ENTITY header-date            "<xref target='Part2' x:rel='' xmlns:x=''/>">
35  <!ENTITY header-etag            "<xref target='Part4' x:rel='#header.etag' xmlns:x=''/>">
36  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x=''/>">
37  <!ENTITY header-expires         "<xref target='Part6' x:rel='#header.expires' xmlns:x=''/>">
38  <!ENTITY header-last-modified   "<xref target='Part4' x:rel='#header.last-modified' xmlns:x=''/>">
39  <!ENTITY header-mime-version    "<xref target='Part2' x:rel='#mime-version' xmlns:x=''/>">
40  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
41  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x=''/>">
42  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x=''/>">
43  <!ENTITY header-server          "<xref target='Part2' x:rel='#header.server' xmlns:x=''/>">
44  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
45  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x=''/>">
46  <!ENTITY methods                "<xref target='Part2' x:rel='#methods' xmlns:x=''/>">
47  <!ENTITY OPTIONS                "<xref target='Part2' x:rel='#OPTIONS' xmlns:x=''/>">
48  <!ENTITY status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
49  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
50  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
51  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x=''/>">
52  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x=''/>">
53  <!ENTITY status-304             "<xref target='Part4' x:rel='#status.304' xmlns:x=''/>">
54  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x=''/>">
55  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
56  <!ENTITY cons-new-header-fields "<xref target='Part2' x:rel='#considerations.for.creating.header.fields' xmlns:x=''/>">
58<?rfc toc="yes" ?>
59<?rfc symrefs="yes" ?>
60<?rfc sortrefs="yes" ?>
61<?rfc compact="yes"?>
62<?rfc subcompact="no" ?>
63<?rfc linkmailto="no" ?>
64<?rfc editing="no" ?>
65<?rfc comments="yes"?>
66<?rfc inline="yes"?>
67<?rfc rfcedstyle="yes"?>
68<?rfc-ext allow-markup-in-artwork="yes" ?>
69<?rfc-ext include-references-in-index="yes" ?>
70<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="proposed"
71     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
72     xmlns:x=''>
73<x:link rel="next" basename="p2-semantics"/>
74<x:feedback template="{docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
77  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: Message Routing and Syntax"</title>
79  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
80    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
81    <address>
82      <postal>
83        <street>345 Park Ave</street>
84        <city>San Jose</city>
85        <region>CA</region>
86        <code>95110</code>
87        <country>USA</country>
88      </postal>
89      <email></email>
90      <uri></uri>
91    </address>
92  </author>
94  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
95    <organization abbrev="W3C">World Wide Web Consortium</organization>
96    <address>
97      <postal>
98        <street>W3C / ERCIM</street>
99        <street>2004, rte des Lucioles</street>
100        <city>Sophia-Antipolis</city>
101        <region>AM</region>
102        <code>06902</code>
103        <country>France</country>
104      </postal>
105      <email></email>
106      <uri></uri>
107    </address>
108  </author>
110  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
111    <organization abbrev="greenbytes">greenbytes GmbH</organization>
112    <address>
113      <postal>
114        <street>Hafenweg 16</street>
115        <city>Muenster</city><region>NW</region><code>48155</code>
116        <country>Germany</country>
117      </postal>
118      <email></email>
119      <uri></uri>
120    </address>
121  </author>
123  <date month="&ID-MONTH;" year="&ID-YEAR;" day="16"/>
124  <workgroup>HTTPbis Working Group</workgroup>
128   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
129   distributed, collaborative, hypertext information systems. HTTP has been in
130   use by the World Wide Web global information initiative since 1990.
131   This document provides an overview of HTTP architecture and its associated
132   terminology, defines the "http" and "https" Uniform Resource Identifier
133   (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements,
134   and describes general security concerns for implementations.
138<note title="Editorial Note (To be removed by RFC Editor)">
139  <t>
140    Discussion of this draft takes place on the HTTPBIS working group
141    mailing list (, which is archived at
142    <eref target=""/>.
143  </t>
144  <t>
145    The current issues list is at
146    <eref target=""/> and related
147    documents (including fancy diffs) can be found at
148    <eref target=""/>.
149  </t>
150  <t>
151    The changes in this draft are summarized in <xref target="changes.since.19"/>.
152  </t>
156<section title="Introduction" anchor="introduction">
158   The Hypertext Transfer Protocol (HTTP) is an application-level
159   request/response protocol that uses extensible semantics and MIME-like
160   message payloads for flexible interaction with network-based hypertext
161   information systems. This document is the first in a series of documents
162   that collectively form the HTTP/1.1 specification:
163   <list style="empty">
164    <t>RFC xxx1: Message Routing and Syntax</t>
165    <t><xref target="Part2" x:fmt="none">RFC xxx2</xref>: Semantics and Payloads</t>
166    <t><xref target="Part4" x:fmt="none">RFC xxx3</xref>: Conditional Requests</t>
167    <t><xref target="Part5" x:fmt="none">RFC xxx4</xref>: Range Requests</t>
168    <t><xref target="Part6" x:fmt="none">RFC xxx5</xref>: Caching</t>
169    <t><xref target="Part7" x:fmt="none">RFC xxx6</xref>: Authentication</t>
170   </list>
173   This HTTP/1.1 specification obsoletes and moves to historic status
174   <xref target="RFC2616" x:fmt="none">RFC 2616</xref>, its predecessor
175   <xref target="RFC2068" x:fmt="none">RFC 2068</xref>,
176   <xref target="RFC2145" x:fmt="none">RFC 2145</xref> (on HTTP versioning),
177   and <xref target="RFC2817" x:fmt="none">RFC 2817</xref> (on using CONNECT
178   for TLS upgrades).
181   HTTP is a generic interface protocol for information systems. It is
182   designed to hide the details of how a service is implemented by presenting
183   a uniform interface to clients that is independent of the types of
184   resources provided. Likewise, servers do not need to be aware of each
185   client's purpose: an HTTP request can be considered in isolation rather
186   than being associated with a specific type of client or a predetermined
187   sequence of application steps. The result is a protocol that can be used
188   effectively in many different contexts and for which implementations can
189   evolve independently over time.
192   HTTP is also designed for use as an intermediation protocol for translating
193   communication to and from non-HTTP information systems.
194   HTTP proxies and gateways can provide access to alternative information
195   services by translating their diverse protocols into a hypertext
196   format that can be viewed and manipulated by clients in the same way
197   as HTTP services.
200   One consequence of HTTP flexibility is that the protocol cannot be
201   defined in terms of what occurs behind the interface. Instead, we
202   are limited to defining the syntax of communication, the intent
203   of received communication, and the expected behavior of recipients.
204   If the communication is considered in isolation, then successful
205   actions ought to be reflected in corresponding changes to the
206   observable interface provided by servers. However, since multiple
207   clients might act in parallel and perhaps at cross-purposes, we
208   cannot require that such changes be observable beyond the scope
209   of a single response.
212   This document describes the architectural elements that are used or
213   referred to in HTTP, defines the "http" and "https" URI schemes,
214   describes overall network operation and connection management,
215   and defines HTTP message framing and forwarding requirements.
216   Our goal is to define all of the mechanisms necessary for HTTP message
217   handling that are independent of message semantics, thereby defining the
218   complete set of requirements for message parsers and
219   message-forwarding intermediaries.
223<section title="Requirement Notation" anchor="intro.requirements">
225   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
226   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
227   document are to be interpreted as described in <xref target="RFC2119"/>.
231<section title="Syntax Notation" anchor="notation">
232<iref primary="true" item="Grammar" subitem="ALPHA"/>
233<iref primary="true" item="Grammar" subitem="CR"/>
234<iref primary="true" item="Grammar" subitem="CRLF"/>
235<iref primary="true" item="Grammar" subitem="CTL"/>
236<iref primary="true" item="Grammar" subitem="DIGIT"/>
237<iref primary="true" item="Grammar" subitem="DQUOTE"/>
238<iref primary="true" item="Grammar" subitem="HEXDIG"/>
239<iref primary="true" item="Grammar" subitem="HTAB"/>
240<iref primary="true" item="Grammar" subitem="LF"/>
241<iref primary="true" item="Grammar" subitem="OCTET"/>
242<iref primary="true" item="Grammar" subitem="SP"/>
243<iref primary="true" item="Grammar" subitem="VCHAR"/>
245   This specification uses the Augmented Backus-Naur Form (ABNF) notation
246   of <xref target="RFC5234"/> with the list rule extension defined in
247   <xref target="abnf.extension"/>.  <xref target="collected.abnf"/> shows
248   the collected ABNF with the list rule expanded.
250<t anchor="core.rules">
251  <x:anchor-alias value="ALPHA"/>
252  <x:anchor-alias value="CTL"/>
253  <x:anchor-alias value="CR"/>
254  <x:anchor-alias value="CRLF"/>
255  <x:anchor-alias value="DIGIT"/>
256  <x:anchor-alias value="DQUOTE"/>
257  <x:anchor-alias value="HEXDIG"/>
258  <x:anchor-alias value="HTAB"/>
259  <x:anchor-alias value="LF"/>
260  <x:anchor-alias value="OCTET"/>
261  <x:anchor-alias value="SP"/>
262  <x:anchor-alias value="VCHAR"/>
263   The following core rules are included by
264   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
265   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
266   DIGIT (decimal 0-9), DQUOTE (double quote),
267   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
268   OCTET (any 8-bit sequence of data), SP (space), and
269   VCHAR (any visible <xref target="USASCII"/> character).
272   As a convention, ABNF rule names prefixed with "obs-" denote
273   "obsolete" grammar rules that appear for historical reasons.
278<section title="Architecture" anchor="architecture">
280   HTTP was created for the World Wide Web architecture
281   and has evolved over time to support the scalability needs of a worldwide
282   hypertext system. Much of that architecture is reflected in the terminology
283   and syntax productions used to define HTTP.
286<section title="Client/Server Messaging" anchor="operation">
287<iref primary="true" item="client"/>
288<iref primary="true" item="server"/>
289<iref primary="true" item="connection"/>
291   HTTP is a stateless request/response protocol that operates by exchanging
292   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
293   transport or session-layer
294   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
295   program that establishes a connection to a server for the purpose of
296   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
297   program that accepts connections in order to service HTTP requests by
298   sending HTTP responses.
300<iref primary="true" item="user agent"/>
301<iref primary="true" item="origin server"/>
302<iref primary="true" item="browser"/>
303<iref primary="true" item="spider"/>
304<iref primary="true" item="sender"/>
305<iref primary="true" item="recipient"/>
307   The terms client and server refer only to the roles that
308   these programs perform for a particular connection.  The same program
309   might act as a client on some connections and a server on others.  We use
310   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
311   such as a WWW browser, editor, or spider (web-traversing robot), and
312   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
313   authoritative responses to a request.  For general requirements, we use
314   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
315   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
316   message.
319   HTTP relies upon the Uniform Resource Identifier (URI)
320   standard <xref target="RFC3986"/> to indicate the target resource
321   (<xref target="target-resource"/>) and relationships between resources.
322   Messages are passed in a format similar to that used by Internet mail
323   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
324   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
325   between HTTP and MIME messages).
328   Most HTTP communication consists of a retrieval request (GET) for
329   a representation of some resource identified by a URI.  In the
330   simplest case, this might be accomplished via a single bidirectional
331   connection (===) between the user agent (UA) and the origin server (O).
333<figure><artwork type="drawing">
334         request   &gt;
335    <x:highlight>UA</x:highlight> ======================================= <x:highlight>O</x:highlight>
336                                &lt;   response
338<iref primary="true" item="message"/>
339<iref primary="true" item="request"/>
340<iref primary="true" item="response"/>
342   A client sends an HTTP request to a server in the form of a <x:dfn>request</x:dfn>
343   message, beginning with a request-line that includes a method, URI, and
344   protocol version (<xref target="request.line"/>),
345   followed by header fields containing
346   request modifiers, client information, and representation metadata
347   (<xref target="header.fields"/>),
348   an empty line to indicate the end of the header section, and finally
349   a message body containing the payload body (if any,
350   <xref target="message.body"/>).
353   A server responds to a client's request by sending one or more HTTP
354   <x:dfn>response</x:dfn>
355   messages, each beginning with a status line that
356   includes the protocol version, a success or error code, and textual
357   reason phrase (<xref target="status.line"/>),
358   possibly followed by header fields containing server
359   information, resource metadata, and representation metadata
360   (<xref target="header.fields"/>),
361   an empty line to indicate the end of the header section, and finally
362   a message body containing the payload body (if any,
363   <xref target="message.body"/>).
366   The following example illustrates a typical message exchange for a
367   GET request on the URI "":
370client request:
371</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
372GET /hello.txt HTTP/1.1
373User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
375Accept-Language: en, mi
379server response:
380</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
381HTTP/1.1 200 OK
382Date: Mon, 27 Jul 2009 12:28:53 GMT
383Server: Apache
384Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
385ETag: "34aa387-d-1568eb00"
386Accept-Ranges: bytes
387Content-Length: <x:length-of target="exbody"/>
388Vary: Accept-Encoding
389Content-Type: text/plain
391<x:span anchor="exbody">Hello World!
395<section title="Implementation Diversity" anchor="implementation-diversity">
397   When considering the design of HTTP, it is easy to fall into a trap of
398   thinking that all user agents are general-purpose browsers and all origin
399   servers are large public websites. That is not the case in practice.
400   Common HTTP user agents include household appliances, stereos, scales,
401   software/firmware updaters, command-line programs, mobile apps,
402   and communication devices in a multitude of shapes and sizes.  Likewise,
403   common HTTP origin servers include home automation units, configurable
404   networking components, office machines, autonomous robots, news feeds,
405   traffic cameras, ad selectors, and video delivery platforms.
408   The term "user agent" does not imply that there is a human user directly
409   interacting with the software agent at the time of a request. In many
410   cases, a user agent is installed or configured to run in the background
411   and save its results for later inspection (or save only a subset of those
412   results that might be interesting or erroneous). Spiders, for example, are
413   typically given a start URI and configured to follow certain behavior while
414   crawling the Web as a hypertext graph.
417   The implementation diversity of HTTP means that we cannot assume the
418   user agent can make interactive suggestions to a user or provide adequate
419   warning for security or privacy options.  In the few cases where this
420   specification requires reporting of errors to the user, it is acceptable
421   for such reporting to only be visible in an error console or log file.
422   Likewise, requirements that an automated action be confirmed by the user
423   before proceeding can me met via advance configuration choices,
424   run-time options, or simply not proceeding with the unsafe action.
428<section title="Connections and Transport Independence" anchor="transport-independence">
430   HTTP messaging is independent of the underlying transport or
431   session-layer connection protocol(s).  HTTP only presumes a reliable
432   transport with in-order delivery of requests and the corresponding
433   in-order delivery of responses.  The mapping of HTTP request and
434   response structures onto the data units of the underlying transport
435   protocol is outside the scope of this specification.
438   The specific connection protocols to be used for an interaction
439   are determined by client configuration and the target URI
440   (<xref target="target-resource"/>).
441   For example, the "http" URI scheme
442   (<xref target="http.uri"/>) indicates a default connection of TCP
443   over IP, with a default TCP port of 80, but the client might be
444   configured to use a proxy via some other connection port or protocol
445   instead of using the defaults.
448   A connection might be used for multiple HTTP request/response exchanges,
449   as defined in <xref target="persistent.connections"/>.
453<section title="Intermediaries" anchor="intermediaries">
454<iref primary="true" item="intermediary"/>
456   HTTP enables the use of intermediaries to satisfy requests through
457   a chain of connections.  There are three common forms of HTTP
458   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
459   a single intermediary might act as an origin server, proxy, gateway,
460   or tunnel, switching behavior based on the nature of each request.
462<figure><artwork type="drawing">
463         &gt;             &gt;             &gt;             &gt;
464    <x:highlight>UA</x:highlight> =========== <x:highlight>A</x:highlight> =========== <x:highlight>B</x:highlight> =========== <x:highlight>C</x:highlight> =========== <x:highlight>O</x:highlight>
465               &lt;             &lt;             &lt;             &lt;
468   The figure above shows three intermediaries (A, B, and C) between the
469   user agent and origin server. A request or response message that
470   travels the whole chain will pass through four separate connections.
471   Some HTTP communication options
472   might apply only to the connection with the nearest, non-tunnel
473   neighbor, only to the end-points of the chain, or to all connections
474   along the chain. Although the diagram is linear, each participant might
475   be engaged in multiple, simultaneous communications. For example, B
476   might be receiving requests from many clients other than A, and/or
477   forwarding requests to servers other than C, at the same time that it
478   is handling A's request.
481<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
482<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
483   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
484   to describe various requirements in relation to the directional flow of a
485   message: all messages flow from upstream to downstream.
486   Likewise, we use the terms inbound and outbound to refer to
487   directions in relation to the request path:
488   "<x:dfn>inbound</x:dfn>" means toward the origin server and
489   "<x:dfn>outbound</x:dfn>" means toward the user agent.
491<t><iref primary="true" item="proxy"/>
492   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
493   client, usually via local configuration rules, to receive requests
494   for some type(s) of absolute URI and attempt to satisfy those
495   requests via translation through the HTTP interface.  Some translations
496   are minimal, such as for proxy requests for "http" URIs, whereas
497   other requests might require translation to and from entirely different
498   application-layer protocols. Proxies are often used to group an
499   organization's HTTP requests through a common intermediary for the
500   sake of security, annotation services, or shared caching.
503<iref primary="true" item="transforming proxy"/>
504<iref primary="true" item="non-transforming proxy"/>
505   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
506   or configured to modify request or response messages in a semantically
507   meaningful way (i.e., modifications, beyond those required by normal
508   HTTP processing, that change the message in a way that would be
509   significant to the original sender or potentially significant to
510   downstream recipients).  For example, a transforming proxy might be
511   acting as a shared annotation server (modifying responses to include
512   references to a local annotation database), a malware filter, a
513   format transcoder, or an intranet-to-Internet privacy filter.  Such
514   transformations are presumed to be desired by the client (or client
515   organization) that selected the proxy and are beyond the scope of
516   this specification.  However, when a proxy is not intended to transform
517   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
518   requirements that preserve HTTP message semantics. See &status-203; and
519   &header-warning; for status and warning codes related to transformations.
521<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
522<iref primary="true" item="accelerator"/>
523   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
524   is a receiving agent that acts
525   as a layer above some other server(s) and translates the received
526   requests to the underlying server's protocol.  Gateways are often
527   used to encapsulate legacy or untrusted information services, to
528   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
529   enable partitioning or load-balancing of HTTP services across
530   multiple machines.
533   A gateway behaves as an origin server on its outbound connection and
534   as a user agent on its inbound connection.
535   All HTTP requirements applicable to an origin server
536   also apply to the outbound communication of a gateway.
537   A gateway communicates with inbound servers using any protocol that
538   it desires, including private extensions to HTTP that are outside
539   the scope of this specification.  However, an HTTP-to-HTTP gateway
540   that wishes to interoperate with third-party HTTP servers &MUST;
541   conform to HTTP user agent requirements on the gateway's inbound
542   connection and &MUST; implement the <x:ref>Connection</x:ref>
543   (<xref target="header.connection"/>) and <x:ref>Via</x:ref>
544   (<xref target="header.via"/>) header fields for both connections.
546<t><iref primary="true" item="tunnel"/>
547   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
548   without changing the messages. Once active, a tunnel is not
549   considered a party to the HTTP communication, though the tunnel might
550   have been initiated by an HTTP request. A tunnel ceases to exist when
551   both ends of the relayed connection are closed. Tunnels are used to
552   extend a virtual connection through an intermediary, such as when
553   transport-layer security is used to establish private communication
554   through a shared firewall proxy.
556<t><iref primary="true" item="interception proxy"/>
557<iref primary="true" item="transparent proxy"/>
558<iref primary="true" item="captive portal"/>
559   The above categories for intermediary only consider those acting as
560   participants in the HTTP communication.  There are also intermediaries
561   that can act on lower layers of the network protocol stack, filtering or
562   redirecting HTTP traffic without the knowledge or permission of message
563   senders. Network intermediaries often introduce security flaws or
564   interoperability problems by violating HTTP semantics.  For example, an
565   "<x:dfn>interception proxy</x:dfn>" <xref target="RFC3040"/> (also commonly
566   known as a "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/> or
567   "<x:dfn>captive portal</x:dfn>")
568   differs from an HTTP proxy because it is not selected by the client.
569   Instead, an interception proxy filters or redirects outgoing TCP port 80
570   packets (and occasionally other common port traffic).
571   Interception proxies are commonly found on public network access points,
572   as a means of enforcing account subscription prior to allowing use of
573   non-local Internet services, and within corporate firewalls to enforce
574   network usage policies.
575   They are indistinguishable from a man-in-the-middle attack.
578   HTTP is defined as a stateless protocol, meaning that each request message
579   can be understood in isolation.  Many implementations depend on HTTP's
580   stateless design in order to reuse proxied connections or dynamically
581   load balance requests across multiple servers.  Hence, servers &MUST-NOT;
582   assume that two requests on the same connection are from the same user
583   agent unless the connection is secured and specific to that agent.
584   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
585   been known to violate this requirement, resulting in security and
586   interoperability problems.
590<section title="Caches" anchor="caches">
591<iref primary="true" item="cache"/>
593   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
594   subsystem that controls its message storage, retrieval, and deletion.
595   A cache stores cacheable responses in order to reduce the response
596   time and network bandwidth consumption on future, equivalent
597   requests. Any client or server &MAY; employ a cache, though a cache
598   cannot be used by a server while it is acting as a tunnel.
601   The effect of a cache is that the request/response chain is shortened
602   if one of the participants along the chain has a cached response
603   applicable to that request. The following illustrates the resulting
604   chain if B has a cached copy of an earlier response from O (via C)
605   for a request which has not been cached by UA or A.
607<figure><artwork type="drawing">
608            &gt;             &gt;
609       <x:highlight>UA</x:highlight> =========== <x:highlight>A</x:highlight> =========== <x:highlight>B</x:highlight> - - - - - - <x:highlight>C</x:highlight> - - - - - - <x:highlight>O</x:highlight>
610                  &lt;             &lt;
612<t><iref primary="true" item="cacheable"/>
613   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
614   the response message for use in answering subsequent requests.
615   Even when a response is cacheable, there might be additional
616   constraints placed by the client or by the origin server on when
617   that cached response can be used for a particular request. HTTP
618   requirements for cache behavior and cacheable responses are
619   defined in &caching-overview;. 
622   There are a wide variety of architectures and configurations
623   of caches and proxies deployed across the World Wide Web and
624   inside large organizations. These systems include national hierarchies
625   of proxy caches to save transoceanic bandwidth, systems that
626   broadcast or multicast cache entries, organizations that distribute
627   subsets of cached data via optical media, and so on.
631<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
633   This specification targets conformance criteria according to the role of
634   a participant in HTTP communication.  Hence, HTTP requirements are placed
635   on senders, recipients, clients, servers, user agents, intermediaries,
636   origin servers, proxies, gateways, or caches, depending on what behavior
637   is being constrained by the requirement.
640   The verb "generate" is used instead of "send" where a requirement
641   differentiates between creating a protocol element and merely forwarding a
642   received element downstream.
645   An implementation is considered conformant if it complies with all of the
646   requirements associated with the roles it partakes in HTTP. Note that
647   SHOULD-level requirements are relevant here, unless one of the documented
648   exceptions is applicable.
651   In addition to the prose requirements placed upon them, senders &MUST-NOT;
652   generate protocol elements that do not match the grammar defined by the
653   ABNF rules for those protocol elements that are applicable to the sender's
654   role. If a received protocol element is processed, the recipient &MUST; be
655   able to parse any value that would match the ABNF rules for that protocol
656   element, excluding only those rules not applicable to the recipient's role.
659   Unless noted otherwise, a recipient &MAY; attempt to recover a usable
660   protocol element from an invalid construct.  HTTP does not define
661   specific error handling mechanisms except when they have a direct impact
662   on security, since different applications of the protocol require
663   different error handling strategies.  For example, a Web browser might
664   wish to transparently recover from a response where the
665   <x:ref>Location</x:ref> header field doesn't parse according to the ABNF,
666   whereas a systems control client might consider any form of error recovery
667   to be dangerous.
671<section title="Protocol Versioning" anchor="http.version">
672  <x:anchor-alias value="HTTP-version"/>
673  <x:anchor-alias value="HTTP-name"/>
675   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
676   versions of the protocol. This specification defines version "1.1".
677   The protocol version as a whole indicates the sender's conformance
678   with the set of requirements laid out in that version's corresponding
679   specification of HTTP.
682   The version of an HTTP message is indicated by an HTTP-version field
683   in the first line of the message. HTTP-version is case-sensitive.
685<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/>
686  <x:ref>HTTP-version</x:ref>  = <x:ref>HTTP-name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
687  <x:ref>HTTP-name</x:ref>     = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
690   The HTTP version number consists of two decimal digits separated by a "."
691   (period or decimal point).  The first digit ("major version") indicates the
692   HTTP messaging syntax, whereas the second digit ("minor version") indicates
693   the highest minor version to which the sender is
694   conformant and able to understand for future communication.  The minor
695   version advertises the sender's communication capabilities even when the
696   sender is only using a backwards-compatible subset of the protocol,
697   thereby letting the recipient know that more advanced features can
698   be used in response (by servers) or in future requests (by clients).
701   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
702   <xref target="RFC1945"/> or a recipient whose version is unknown,
703   the HTTP/1.1 message is constructed such that it can be interpreted
704   as a valid HTTP/1.0 message if all of the newer features are ignored.
705   This specification places recipient-version requirements on some
706   new features so that a conformant sender will only use compatible
707   features until it has determined, through configuration or the
708   receipt of a message, that the recipient supports HTTP/1.1.
711   The interpretation of a header field does not change between minor
712   versions of the same major HTTP version, though the default
713   behavior of a recipient in the absence of such a field can change.
714   Unless specified otherwise, header fields defined in HTTP/1.1 are
715   defined for all versions of HTTP/1.x.  In particular, the <x:ref>Host</x:ref>
716   and <x:ref>Connection</x:ref> header fields ought to be implemented by all
717   HTTP/1.x implementations whether or not they advertise conformance with
718   HTTP/1.1.
721   New header fields can be defined such that, when they are
722   understood by a recipient, they might override or enhance the
723   interpretation of previously defined header fields.  When an
724   implementation receives an unrecognized header field, the recipient
725   &MUST; ignore that header field for local processing regardless of
726   the message's HTTP version.  An unrecognized header field received
727   by a proxy &MUST; be forwarded downstream unless the header field's
728   field-name is listed in the message's <x:ref>Connection</x:ref> header field
729   (see <xref target="header.connection"/>).
730   These requirements allow HTTP's functionality to be enhanced without
731   requiring prior update of deployed intermediaries.
734   Intermediaries that process HTTP messages (i.e., all intermediaries
735   other than those acting as tunnels) &MUST; send their own HTTP-version
736   in forwarded messages.  In other words, they &MUST-NOT; blindly
737   forward the first line of an HTTP message without ensuring that the
738   protocol version in that message matches a version to which that
739   intermediary is conformant for both the receiving and
740   sending of messages.  Forwarding an HTTP message without rewriting
741   the HTTP-version might result in communication errors when downstream
742   recipients use the message sender's version to determine what features
743   are safe to use for later communication with that sender.
746   An HTTP client &SHOULD; send a request version equal to the highest
747   version to which the client is conformant and
748   whose major version is no higher than the highest version supported
749   by the server, if this is known.  An HTTP client &MUST-NOT; send a
750   version to which it is not conformant.
753   An HTTP client &MAY; send a lower request version if it is known that
754   the server incorrectly implements the HTTP specification, but only
755   after the client has attempted at least one normal request and determined
756   from the response status or header fields (e.g., <x:ref>Server</x:ref>) that
757   the server improperly handles higher request versions.
760   An HTTP server &SHOULD; send a response version equal to the highest
761   version to which the server is conformant and
762   whose major version is less than or equal to the one received in the
763   request.  An HTTP server &MUST-NOT; send a version to which it is not
764   conformant.  A server &MAY; send a <x:ref>505 (HTTP Version Not
765   Supported)</x:ref> response if it cannot send a response using the
766   major version used in the client's request.
769   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
770   if it is known or suspected that the client incorrectly implements the
771   HTTP specification and is incapable of correctly processing later
772   version responses, such as when a client fails to parse the version
773   number correctly or when an intermediary is known to blindly forward
774   the HTTP-version even when it doesn't conform to the given minor
775   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
776   performed unless triggered by specific client attributes, such as when
777   one or more of the request header fields (e.g., <x:ref>User-Agent</x:ref>)
778   uniquely match the values sent by a client known to be in error.
781   The intention of HTTP's versioning design is that the major number
782   will only be incremented if an incompatible message syntax is
783   introduced, and that the minor number will only be incremented when
784   changes made to the protocol have the effect of adding to the message
785   semantics or implying additional capabilities of the sender.  However,
786   the minor version was not incremented for the changes introduced between
787   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
788   is specifically avoiding any such changes to the protocol.
792<section title="Uniform Resource Identifiers" anchor="uri">
793<iref primary="true" item="resource"/>
795   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
796   throughout HTTP as the means for identifying resources. URI references
797   are used to target requests, indicate redirects, and define relationships.
798   HTTP does not limit what a resource might be; it merely defines an interface
799   that can be used to interact with a resource via HTTP. More information on
800   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
802  <x:anchor-alias value="URI-reference"/>
803  <x:anchor-alias value="absolute-URI"/>
804  <x:anchor-alias value="relative-part"/>
805  <x:anchor-alias value="authority"/>
806  <x:anchor-alias value="path-abempty"/>
807  <x:anchor-alias value="path-absolute"/>
808  <x:anchor-alias value="port"/>
809  <x:anchor-alias value="query"/>
810  <x:anchor-alias value="uri-host"/>
811  <x:anchor-alias value="partial-URI"/>
813   This specification adopts the definitions of "URI-reference",
814   "absolute-URI", "relative-part", "port", "host",
815   "path-abempty", "path-absolute", "query", and "authority" from the
816   URI generic syntax <xref target="RFC3986"/>.
817   In addition, we define a partial-URI rule for protocol elements
818   that allow a relative URI but not a fragment.
820<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="URI-reference"><!--exported production--></iref><iref primary="true" item="Grammar" subitem="absolute-URI"/><iref primary="true" item="Grammar" subitem="authority"/><iref primary="true" item="Grammar" subitem="path-absolute"/><iref primary="true" item="Grammar" subitem="port"/><iref primary="true" item="Grammar" subitem="query"/><iref primary="true" item="Grammar" subitem="uri-host"/><iref primary="true" item="Grammar" subitem="partial-URI"><!--exported production--></iref>
821  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
822  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
823  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
824  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
825  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
826  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
827  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
828  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
829  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
831  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
834   Each protocol element in HTTP that allows a URI reference will indicate
835   in its ABNF production whether the element allows any form of reference
836   (URI-reference), only a URI in absolute form (absolute-URI), only the
837   path and optional query components, or some combination of the above.
838   Unless otherwise indicated, URI references are parsed
839   relative to the effective request URI
840   (<xref target="effective.request.uri"/>).
843<section title="http URI scheme" anchor="http.uri">
844  <x:anchor-alias value="http-URI"/>
845  <iref item="http URI scheme" primary="true"/>
846  <iref item="URI scheme" subitem="http" primary="true"/>
848   The "http" URI scheme is hereby defined for the purpose of minting
849   identifiers according to their association with the hierarchical
850   namespace governed by a potential HTTP origin server listening for
851   TCP connections on a given port.
853<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"><!--terminal production--></iref>
854  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
857   The HTTP origin server is identified by the generic syntax's
858   <x:ref>authority</x:ref> component, which includes a host identifier
859   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
860   The remainder of the URI, consisting of both the hierarchical path
861   component and optional query component, serves as an identifier for
862   a potential resource within that origin server's name space.
865   If the host identifier is provided as an IP literal or IPv4 address,
866   then the origin server is any listener on the indicated TCP port at
867   that IP address. If host is a registered name, then that name is
868   considered an indirect identifier and the recipient might use a name
869   resolution service, such as DNS, to find the address of a listener
870   for that host.
871   The host &MUST-NOT; be empty; if an "http" URI is received with an
872   empty host, then it &MUST; be rejected as invalid.
873   If the port subcomponent is empty or not given, then TCP port 80 is
874   assumed (the default reserved port for WWW services).
877   Regardless of the form of host identifier, access to that host is not
878   implied by the mere presence of its name or address. The host might or might
879   not exist and, even when it does exist, might or might not be running an
880   HTTP server or listening to the indicated port. The "http" URI scheme
881   makes use of the delegated nature of Internet names and addresses to
882   establish a naming authority (whatever entity has the ability to place
883   an HTTP server at that Internet name or address) and allows that
884   authority to determine which names are valid and how they might be used.
887   When an "http" URI is used within a context that calls for access to the
888   indicated resource, a client &MAY; attempt access by resolving
889   the host to an IP address, establishing a TCP connection to that address
890   on the indicated port, and sending an HTTP request message
891   (<xref target="http.message"/>) containing the URI's identifying data
892   (<xref target="message.routing"/>) to the server.
893   If the server responds to that request with a non-interim HTTP response
894   message, as described in &status-codes;, then that response
895   is considered an authoritative answer to the client's request.
898   Although HTTP is independent of the transport protocol, the "http"
899   scheme is specific to TCP-based services because the name delegation
900   process depends on TCP for establishing authority.
901   An HTTP service based on some other underlying connection protocol
902   would presumably be identified using a different URI scheme, just as
903   the "https" scheme (below) is used for servers that require an SSL/TLS
904   transport layer on a connection. Other protocols might also be used to
905   provide access to "http" identified resources &mdash; it is only the
906   authoritative interface used for mapping the namespace that is
907   specific to TCP.
910   The URI generic syntax for authority also includes a deprecated
911   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
912   for including user authentication information in the URI.  Some
913   implementations make use of the userinfo component for internal
914   configuration of authentication information, such as within command
915   invocation options, configuration files, or bookmark lists, even
916   though such usage might expose a user identifier or password.
917   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
918   delimiter) when transmitting an "http" URI in a message.  Recipients
919   of HTTP messages that contain a URI reference &SHOULD; parse for the
920   existence of userinfo and treat its presence as an error, likely
921   indicating that the deprecated subcomponent is being used to obscure
922   the authority for the sake of phishing attacks.
926<section title="https URI scheme" anchor="https.uri">
927   <x:anchor-alias value="https-URI"/>
928   <iref item="https URI scheme"/>
929   <iref item="URI scheme" subitem="https"/>
931   The "https" URI scheme is hereby defined for the purpose of minting
932   identifiers according to their association with the hierarchical
933   namespace governed by a potential HTTP origin server listening for
934   SSL/TLS-secured connections on a given TCP port.
937   All of the requirements listed above for the "http" scheme are also
938   requirements for the "https" scheme, except that a default TCP port
939   of 443 is assumed if the port subcomponent is empty or not given,
940   and the TCP connection &MUST; be secured for privacy through the
941   use of strong encryption prior to sending the first HTTP request.
943<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"><!--terminal production--></iref>
944  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
947   Unlike the "http" scheme, responses to "https" identified requests
948   are never "public" and thus &MUST-NOT; be reused for shared caching.
949   They can, however, be reused in a private cache if the message is
950   cacheable by default in HTTP or specifically indicated as such by
951   the Cache-Control header field (&header-cache-control;).
954   Resources made available via the "https" scheme have no shared
955   identity with the "http" scheme even if their resource identifiers
956   indicate the same authority (the same host listening to the same
957   TCP port).  They are distinct name spaces and are considered to be
958   distinct origin servers.  However, an extension to HTTP that is
959   defined to apply to entire host domains, such as the Cookie protocol
960   <xref target="RFC6265"/>, can allow information
961   set by one service to impact communication with other services
962   within a matching group of host domains.
965   The process for authoritative access to an "https" identified
966   resource is defined in <xref target="RFC2818"/>.
970<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
972   Since the "http" and "https" schemes conform to the URI generic syntax,
973   such URIs are normalized and compared according to the algorithm defined
974   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
975   described above for each scheme.
978   If the port is equal to the default port for a scheme, the normal
979   form is to elide the port subcomponent. Likewise, an empty path
980   component is equivalent to an absolute path of "/", so the normal
981   form is to provide a path of "/" instead. The scheme and host
982   are case-insensitive and normally provided in lowercase; all
983   other components are compared in a case-sensitive manner.
984   Characters other than those in the "reserved" set are equivalent
985   to their percent-encoded octets (see <xref target="RFC3986"
986   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
989   For example, the following three URIs are equivalent:
991<figure><artwork type="example">
1000<section title="Message Format" anchor="http.message">
1001<x:anchor-alias value="generic-message"/>
1002<x:anchor-alias value="message.types"/>
1003<x:anchor-alias value="HTTP-message"/>
1004<x:anchor-alias value="start-line"/>
1005<iref item="header section"/>
1006<iref item="headers"/>
1007<iref item="header field"/>
1009   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1010   octets in a format similar to the Internet Message Format
1011   <xref target="RFC5322"/>: zero or more header fields (collectively
1012   referred to as the "headers" or the "header section"), an empty line
1013   indicating the end of the header section, and an optional message body.
1015<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"><!--terminal production--></iref>
1016  <x:ref>HTTP-message</x:ref>   = <x:ref>start-line</x:ref>
1017                   *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1018                   <x:ref>CRLF</x:ref>
1019                   [ <x:ref>message-body</x:ref> ]
1022   The normal procedure for parsing an HTTP message is to read the
1023   start-line into a structure, read each header field into a hash
1024   table by field name until the empty line, and then use the parsed
1025   data to determine if a message body is expected.  If a message body
1026   has been indicated, then it is read as a stream until an amount
1027   of octets equal to the message body length is read or the connection
1028   is closed.
1031   Recipients &MUST; parse an HTTP message as a sequence of octets in an
1032   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1033   Parsing an HTTP message as a stream of Unicode characters, without regard
1034   for the specific encoding, creates security vulnerabilities due to the
1035   varying ways that string processing libraries handle invalid multibyte
1036   character sequences that contain the octet LF (%x0A).  String-based
1037   parsers can only be safely used within protocol elements after the element
1038   has been extracted from the message, such as within a header field-value
1039   after message parsing has delineated the individual fields.
1042   An HTTP message can be parsed as a stream for incremental processing or
1043   forwarding downstream.  However, recipients cannot rely on incremental
1044   delivery of partial messages, since some implementations will buffer or
1045   delay message forwarding for the sake of network efficiency, security
1046   checks, or payload transformations.
1049<section title="Start Line" anchor="start.line">
1050  <x:anchor-alias value="Start-Line"/>
1052   An HTTP message can either be a request from client to server or a
1053   response from server to client.  Syntactically, the two types of message
1054   differ only in the start-line, which is either a request-line (for requests)
1055   or a status-line (for responses), and in the algorithm for determining
1056   the length of the message body (<xref target="message.body"/>).
1057   In theory, a client could receive requests and a server could receive
1058   responses, distinguishing them by their different start-line formats,
1059   but in practice servers are implemented to only expect a request
1060   (a response is interpreted as an unknown or invalid request method)
1061   and clients are implemented to only expect a response.
1063<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1064  <x:ref>start-line</x:ref>     = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1067   Implementations &MUST-NOT; send whitespace between the start-line and
1068   the first header field. The presence of such whitespace in a request
1069   might be an attempt to trick a server into ignoring that field or
1070   processing the line after it as a new request, either of which might
1071   result in a security vulnerability if other implementations within
1072   the request chain interpret the same message differently.
1073   Likewise, the presence of such whitespace in a response might be
1074   ignored by some clients or cause others to cease parsing.
1077<section title="Request Line" anchor="request.line">
1078  <x:anchor-alias value="Request"/>
1079  <x:anchor-alias value="request-line"/>
1081   A request-line begins with a method token, followed by a single
1082   space (SP), the request-target, another single space (SP), the
1083   protocol version, and ending with CRLF.
1085<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1086  <x:ref>request-line</x:ref>   = <x:ref>method</x:ref> <x:ref>SP</x:ref> <x:ref>request-target</x:ref> <x:ref>SP</x:ref> <x:ref>HTTP-version</x:ref> <x:ref>CRLF</x:ref>
1089   A server &MUST; be able to parse any received message that begins
1090   with a request-line and matches the ABNF rule for HTTP-message.
1092<iref primary="true" item="method"/>
1093<t anchor="method">
1094   The method token indicates the request method to be performed on the
1095   target resource. The request method is case-sensitive.
1097<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1098  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1101   The methods defined by this specification can be found in
1102   &methods;, along with information regarding the HTTP method registry
1103   and considerations for defining new methods.
1105<iref item="request-target"/>
1107   The request-target identifies the target resource upon which to apply
1108   the request, as defined in <xref target="request-target"/>.
1111   No whitespace is allowed inside the method, request-target, and
1112   protocol version.  Hence, recipients typically parse the request-line
1113   into its component parts by splitting on the SP characters.
1116   Unfortunately, some user agents fail to properly encode hypertext
1117   references that have embedded whitespace, sending the characters
1118   directly instead of properly percent-encoding the disallowed characters.
1119   Recipients of an invalid request-line &SHOULD; respond with either a
1120   <x:ref>400 (Bad Request)</x:ref> error or a <x:ref>301 (Moved Permanently)</x:ref>
1121   redirect with the request-target properly encoded.  Recipients &SHOULD-NOT;
1122   attempt to autocorrect and then process the request without a redirect,
1123   since the invalid request-line might be deliberately crafted to bypass
1124   security filters along the request chain.
1127   HTTP does not place a pre-defined limit on the length of a request-line.
1128   A server that receives a method longer than any that it implements
1129   &SHOULD; respond with either a <x:ref>405 (Method Not Allowed)</x:ref>, if it is an origin
1130   server, or a <x:ref>501 (Not Implemented)</x:ref> status code.
1131   A server &MUST; be prepared to receive URIs of unbounded length and
1132   respond with the <x:ref>414 (URI Too Long)</x:ref> status code if the received
1133   request-target would be longer than the server wishes to handle
1134   (see &status-414;).
1137   Various ad-hoc limitations on request-line length are found in practice.
1138   It is &RECOMMENDED; that all HTTP senders and recipients support, at a
1139   minimum, request-line lengths of up to 8000 octets.
1143<section title="Status Line" anchor="status.line">
1144  <x:anchor-alias value="response"/>
1145  <x:anchor-alias value="status-line"/>
1146  <x:anchor-alias value="status-code"/>
1147  <x:anchor-alias value="reason-phrase"/>
1149   The first line of a response message is the status-line, consisting
1150   of the protocol version, a space (SP), the status code, another space,
1151   a possibly-empty textual phrase describing the status code, and
1152   ending with CRLF.
1154<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1155  <x:ref>status-line</x:ref> = <x:ref>HTTP-version</x:ref> <x:ref>SP</x:ref> <x:ref>status-code</x:ref> <x:ref>SP</x:ref> <x:ref>reason-phrase</x:ref> <x:ref>CRLF</x:ref>
1158   A client &MUST; be able to parse any received message that begins
1159   with a status-line and matches the ABNF rule for HTTP-message.
1162   The status-code element is a 3-digit integer code describing the
1163   result of the server's attempt to understand and satisfy the client's
1164   corresponding request. The rest of the response message is to be
1165   interpreted in light of the semantics defined for that status code.
1166   See &status-codes; for information about the semantics of status codes,
1167   including the classes of status code (indicated by the first digit),
1168   the status codes defined by this specification, considerations for the
1169   definition of new status codes, and the IANA registry.
1171<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1172  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1175   The reason-phrase element exists for the sole purpose of providing a
1176   textual description associated with the numeric status code, mostly
1177   out of deference to earlier Internet application protocols that were more
1178   frequently used with interactive text clients. A client &SHOULD; ignore
1179   the reason-phrase content.
1181<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1182  <x:ref>reason-phrase</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1187<section title="Header Fields" anchor="header.fields">
1188  <x:anchor-alias value="header-field"/>
1189  <x:anchor-alias value="field-content"/>
1190  <x:anchor-alias value="field-name"/>
1191  <x:anchor-alias value="field-value"/>
1192  <x:anchor-alias value="obs-fold"/>
1194   Each HTTP header field consists of a case-insensitive field name
1195   followed by a colon (":"), optional whitespace, and the field value.
1197<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="header-field"/><iref primary="true" item="Grammar" subitem="field-name"/><iref primary="true" item="Grammar" subitem="field-value"/><iref primary="true" item="Grammar" subitem="field-content"/><iref primary="true" item="Grammar" subitem="obs-fold"/>
1198  <x:ref>header-field</x:ref>   = <x:ref>field-name</x:ref> ":" <x:ref>OWS</x:ref> <x:ref>field-value</x:ref> <x:ref>BWS</x:ref>
1199  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1200  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1201  <x:ref>field-content</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1202  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1203                 ; obsolete line folding
1204                 ; see <xref target="field.parsing"/>
1207   The field-name token labels the corresponding field-value as having the
1208   semantics defined by that header field.  For example, the <x:ref>Date</x:ref>
1209   header field is defined in &header-date; as containing the origination
1210   timestamp for the message in which it appears.
1213   HTTP header fields are fully extensible: there is no limit on the
1214   introduction of new field names, each presumably defining new semantics,
1215   or on the number of header fields used in a given message.  Existing
1216   fields are defined in each part of this specification and in many other
1217   specifications outside the standards process.
1218   New header fields can be introduced without changing the protocol version
1219   if their defined semantics allow them to be safely ignored by recipients
1220   that do not recognize them.
1223   New HTTP header fields &SHOULD; be registered with IANA according
1224   to the procedures in &cons-new-header-fields;.
1225   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1226   field-name is listed in the <x:ref>Connection</x:ref> header field
1227   (<xref target="header.connection"/>) or the proxy is specifically
1228   configured to block or otherwise transform such fields.
1229   Unrecognized header fields &SHOULD; be ignored by other recipients.
1232   The order in which header fields with differing field names are
1233   received is not significant. However, it is "good practice" to send
1234   header fields that contain control data first, such as <x:ref>Host</x:ref>
1235   on requests and <x:ref>Date</x:ref> on responses, so that implementations
1236   can decide when not to handle a message as early as possible.  A server
1237   &MUST; wait until the entire header section is received before interpreting
1238   a request message, since later header fields might include conditionals,
1239   authentication credentials, or deliberately misleading duplicate
1240   header fields that would impact request processing.
1243   Multiple header fields with the same field name &MUST-NOT; be
1244   sent in a message unless the entire field value for that
1245   header field is defined as a comma-separated list [i.e., #(values)].
1246   Multiple header fields with the same field name can be combined into
1247   one "field-name: field-value" pair, without changing the semantics of the
1248   message, by appending each subsequent field value to the combined
1249   field value in order, separated by a comma. The order in which
1250   header fields with the same field name are received is therefore
1251   significant to the interpretation of the combined field value;
1252   a proxy &MUST-NOT; change the order of these field values when
1253   forwarding a message.
1256  <t>
1257   &Note; The "Set-Cookie" header field as implemented in
1258   practice can occur multiple times, but does not use the list syntax, and
1259   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1260   for details.) Also note that the Set-Cookie2 header field specified in
1261   <xref target="RFC2965"/> does not share this problem.
1262  </t>
1265<section title="Whitespace" anchor="whitespace">
1266<t anchor="rule.LWS">
1267   This specification uses three rules to denote the use of linear
1268   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1269   BWS ("bad" whitespace).
1271<t anchor="rule.OWS">
1272   The OWS rule is used where zero or more linear whitespace octets might
1273   appear. OWS &SHOULD; either not be produced or be produced as a single
1274   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1275   be replaced with a single SP or transformed to all SP octets (each
1276   octet other than SP replaced with SP) before interpreting the field value
1277   or forwarding the message downstream.
1279<t anchor="rule.RWS">
1280   RWS is used when at least one linear whitespace octet is required to
1281   separate field tokens. RWS &SHOULD; be produced as a single SP.
1282   Multiple RWS octets that occur within field-content &SHOULD; either
1283   be replaced with a single SP or transformed to all SP octets before
1284   interpreting the field value or forwarding the message downstream.
1286<t anchor="rule.BWS">
1287   BWS is used where the grammar allows optional whitespace for historical
1288   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
1289   recipients &MUST; accept such bad optional whitespace and remove it before
1290   interpreting the field value or forwarding the message downstream.
1292<t anchor="rule.whitespace">
1293  <x:anchor-alias value="BWS"/>
1294  <x:anchor-alias value="OWS"/>
1295  <x:anchor-alias value="RWS"/>
1297<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/>
1298  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1299                 ; "optional" whitespace
1300  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1301                 ; "required" whitespace
1302  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1303                 ; "bad" whitespace
1307<section title="Field Parsing" anchor="field.parsing">
1309   No whitespace is allowed between the header field-name and colon.
1310   In the past, differences in the handling of such whitespace have led to
1311   security vulnerabilities in request routing and response handling.
1312   Any received request message that contains whitespace between a header
1313   field-name and colon &MUST; be rejected with a response code of 400
1314   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1315   message before forwarding the message downstream.
1318   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1319   preferred. The field value does not include any leading or trailing white
1320   space: OWS occurring before the first non-whitespace octet of the
1321   field value or after the last non-whitespace octet of the field value
1322   is ignored and &SHOULD; be removed before further processing (as this does
1323   not change the meaning of the header field).
1326   Historically, HTTP header field values could be extended over multiple
1327   lines by preceding each extra line with at least one space or horizontal
1328   tab (obs-fold). This specification deprecates such line
1329   folding except within the message/http media type
1330   (<xref target=""/>).
1331   HTTP senders &MUST-NOT; produce messages that include line folding
1332   (i.e., that contain any field-value that matches the obs-fold rule) unless
1333   the message is intended for packaging within the message/http media type.
1334   HTTP recipients &SHOULD; accept line folding and replace any embedded
1335   obs-fold whitespace with either a single SP or a matching number of SP
1336   octets (to avoid buffer copying) prior to interpreting the field value or
1337   forwarding the message downstream.
1340   Historically, HTTP has allowed field content with text in the ISO-8859-1
1341   <xref target="ISO-8859-1"/> character encoding and supported other
1342   character sets only through use of <xref target="RFC2047"/> encoding.
1343   In practice, most HTTP header field values use only a subset of the
1344   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1345   header fields &SHOULD; limit their field values to US-ASCII octets.
1346   Recipients &SHOULD; treat other (obs-text) octets in field content as
1347   opaque data.
1351<section title="Field Length" anchor="field.length">
1353   HTTP does not place a pre-defined limit on the length of header fields,
1354   either in isolation or as a set. A server &MUST; be prepared to receive
1355   request header fields of unbounded length and respond with a <x:ref>4xx
1356   (Client Error)</x:ref> status code if the received header field(s) would be
1357   longer than the server wishes to handle.
1360   A client that receives response header fields that are longer than it wishes
1361   to handle can only treat it as a server error.
1364   Various ad-hoc limitations on header field length are found in practice. It
1365   is &RECOMMENDED; that all HTTP senders and recipients support messages whose
1366   combined header fields have 4000 or more octets.
1370<section title="Field value components" anchor="field.components">
1371<t anchor="rule.token.separators">
1372  <x:anchor-alias value="tchar"/>
1373  <x:anchor-alias value="token"/>
1374  <x:anchor-alias value="special"/>
1375  <x:anchor-alias value="word"/>
1376   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1377   separated by whitespace or special characters. These special characters
1378   &MUST; be in a quoted string to be used within a parameter value (as defined
1379   in <xref target="transfer.codings"/>).
1381<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="word"/><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"><!--unused production--></iref>
1382  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1384  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1386  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1387 -->
1388  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1389                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1390                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1391                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1393  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1394                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1395                 / "]" / "?" / "=" / "{" / "}"
1397<t anchor="rule.quoted-string">
1398  <x:anchor-alias value="quoted-string"/>
1399  <x:anchor-alias value="qdtext"/>
1400  <x:anchor-alias value="obs-text"/>
1401   A string of text is parsed as a single word if it is quoted using
1402   double-quote marks.
1404<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/><iref primary="true" item="Grammar" subitem="obs-text"/>
1405  <x:ref>quoted-string</x:ref>  = <x:ref>DQUOTE</x:ref> *( <x:ref>qdtext</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref>
1406  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1407  <x:ref>obs-text</x:ref>       = %x80-FF
1409<t anchor="rule.quoted-pair">
1410  <x:anchor-alias value="quoted-pair"/>
1411   The backslash octet ("\") can be used as a single-octet
1412   quoting mechanism within quoted-string constructs:
1414<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1415  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1418   Recipients that process the value of the quoted-string &MUST; handle a
1419   quoted-pair as if it were replaced by the octet following the backslash.
1422   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1423   escaping (i.e., other than DQUOTE and the backslash octet).
1425<t anchor="rule.comment">
1426  <x:anchor-alias value="comment"/>
1427  <x:anchor-alias value="ctext"/>
1428   Comments can be included in some HTTP header fields by surrounding
1429   the comment text with parentheses. Comments are only allowed in
1430   fields containing "comment" as part of their field value definition.
1432<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1433  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1434  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1436<t anchor="rule.quoted-cpair">
1437  <x:anchor-alias value="quoted-cpair"/>
1438   The backslash octet ("\") can be used as a single-octet
1439   quoting mechanism within comment constructs:
1441<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1442  <x:ref>quoted-cpair</x:ref>   = "\" ( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1445   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1446   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1452<section title="Message Body" anchor="message.body">
1453  <x:anchor-alias value="message-body"/>
1455   The message body (if any) of an HTTP message is used to carry the
1456   payload body of that request or response.  The message body is
1457   identical to the payload body unless a transfer coding has been
1458   applied, as described in <xref target="header.transfer-encoding"/>.
1460<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1461  <x:ref>message-body</x:ref> = *OCTET
1464   The rules for when a message body is allowed in a message differ for
1465   requests and responses.
1468   The presence of a message body in a request is signaled by a
1469   a <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1470   field. Request message framing is independent of method semantics,
1471   even if the method does not define any use for a message body.
1474   The presence of a message body in a response depends on both
1475   the request method to which it is responding and the response
1476   status code (<xref target="status.line"/>).
1477   Responses to the HEAD request method never include a message body
1478   because the associated response header fields (e.g.,
1479   <x:ref>Transfer-Encoding</x:ref>, <x:ref>Content-Length</x:ref>, etc.) only
1480   indicate what their values would have been if the request method had been
1481   GET. <x:ref>2xx (Successful)</x:ref> responses to CONNECT switch to tunnel
1482   mode instead of having a message body.
1483   All <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, and
1484   <x:ref>304 (Not Modified)</x:ref> responses &MUST-NOT; include a message body.
1485   All other responses do include a message body, although the body
1486   &MAY; be of zero length.
1489<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1490  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1491  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
1492  <x:anchor-alias value="Transfer-Encoding"/>
1494   When one or more transfer codings are applied to a payload body in order
1495   to form the message body, a Transfer-Encoding header field &MUST; be sent
1496   in the message and &MUST; contain the list of corresponding
1497   transfer-coding names in the same order that they were applied.
1498   Transfer codings are defined in <xref target="transfer.codings"/>.
1500<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1501  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1504   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1505   MIME, which was designed to enable safe transport of binary data over a
1506   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1507   However, safe transport has a different focus for an 8bit-clean transfer
1508   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1509   accurately delimit a dynamically generated payload and to distinguish
1510   payload encodings that are only applied for transport efficiency or
1511   security from those that are characteristics of the target resource.
1514   The "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1515   &MUST; be implemented by all HTTP/1.1 recipients because it plays a
1516   crucial role in delimiting messages when the payload body size is not
1517   known in advance.
1518   When the "chunked" transfer-coding is used, it &MUST; be the last
1519   transfer-coding applied to form the message body and &MUST-NOT;
1520   be applied more than once in a message body.
1521   If any transfer-coding is applied to a request payload body,
1522   the final transfer-coding applied &MUST; be "chunked".
1523   If any transfer-coding is applied to a response payload body, then either
1524   the final transfer-coding applied &MUST; be "chunked" or
1525   the message &MUST; be terminated by closing the connection.
1528   For example,
1529</preamble><artwork type="example">
1530  Transfer-Encoding: gzip, chunked
1532   indicates that the payload body has been compressed using the gzip
1533   coding and then chunked using the chunked coding while forming the
1534   message body.
1537   If more than one Transfer-Encoding header field is present in a message,
1538   the multiple field-values &MUST; be combined into one field-value,
1539   according to the algorithm defined in <xref target="header.fields"/>,
1540   before determining the message body length.
1543   Unlike <x:ref>Content-Encoding</x:ref> (&content-codings;),
1544   Transfer-Encoding is a property of the message, not of the payload, and thus
1545   &MAY; be added or removed by any implementation along the request/response
1546   chain. Additional information about the encoding parameters &MAY; be
1547   provided by other header fields not defined by this specification.
1550   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1551   <x:ref>304 (Not Modified)</x:ref> response (&status-304;) to a GET request,
1552   neither of which includes a message body,
1553   to indicate that the origin server would have applied a transfer coding
1554   to the message body if the request had been an unconditional GET.
1555   This indication is not required, however, because any recipient on
1556   the response chain (including the origin server) can remove transfer
1557   codings when they are not needed.
1560   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1561   implementations advertising only HTTP/1.0 support will not understand
1562   how to process a transfer-encoded payload.
1563   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1564   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1565   might be in the form of specific user configuration or by remembering the
1566   version of a prior received response.
1567   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1568   the corresponding request indicates HTTP/1.1 (or later).
1571   A server that receives a request message with a transfer-coding it does
1572   not understand &SHOULD; respond with <x:ref>501 (Not Implemented)</x:ref> and then
1573   close the connection.
1577<section title="Content-Length" anchor="header.content-length">
1578  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1579  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
1580  <x:anchor-alias value="Content-Length"/>
1582   When a message does not have a <x:ref>Transfer-Encoding</x:ref> header field
1583   and the payload body length can be determined prior to being transferred, a
1584   Content-Length header field &SHOULD; be sent to indicate the length of the
1585   payload body that is either present as the message body, for requests
1586   and non-HEAD responses other than <x:ref>304 (Not Modified)</x:ref>, or
1587   would have been present had the request been an unconditional GET.  The
1588   length is expressed as a decimal number of octets.
1590<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1591  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1594   An example is
1596<figure><artwork type="example">
1597  Content-Length: 3495
1600   In the case of a response to a HEAD request, Content-Length indicates
1601   the size of the payload body (without any potential transfer-coding)
1602   that would have been sent had the request been a GET.
1603   In the case of a <x:ref>304 (Not Modified)</x:ref> response (&status-304;)
1604   to a GET request, Content-Length indicates the size of the payload body (without
1605   any potential transfer-coding) that would have been sent in a <x:ref>200 (OK)</x:ref>
1606   response.
1609   Any Content-Length field value greater than or equal to zero is valid.
1610   Since there is no predefined limit to the length of an HTTP payload,
1611   recipients &SHOULD; anticipate potentially large decimal numerals and
1612   prevent parsing errors due to integer conversion overflows
1613   (<xref target="attack.protocol.element.size.overflows"/>).
1616   If a message is received that has multiple Content-Length header fields
1617   with field-values consisting of the same decimal value, or a single
1618   Content-Length header field with a field value containing a list of
1619   identical decimal values (e.g., "Content-Length: 42, 42"), indicating that
1620   duplicate Content-Length header fields have been generated or combined by an
1621   upstream message processor, then the recipient &MUST; either reject the
1622   message as invalid or replace the duplicated field-values with a single
1623   valid Content-Length field containing that decimal value prior to
1624   determining the message body length.
1627  <t>
1628   &Note; HTTP's use of Content-Length for message framing differs
1629   significantly from the same field's use in MIME, where it is an optional
1630   field used only within the "message/external-body" media-type.
1631  </t>
1635<section title="Message Body Length" anchor="message.body.length">
1637   The length of a message body is determined by one of the following
1638   (in order of precedence):
1641  <list style="numbers">
1642    <x:lt><t>
1643     Any response to a HEAD request and any response with a
1644     <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, or
1645     <x:ref>304 (Not Modified)</x:ref> status code is always
1646     terminated by the first empty line after the header fields, regardless of
1647     the header fields present in the message, and thus cannot contain a
1648     message body.
1649    </t></x:lt>
1650    <x:lt><t>
1651     Any <x:ref>2xx (Successful)</x:ref> response to a CONNECT request implies that the
1652     connection will become a tunnel immediately after the empty line that
1653     concludes the header fields.  A client &MUST; ignore any
1654     <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1655     fields received in such a message.
1656    </t></x:lt>
1657    <x:lt><t>
1658     If a <x:ref>Transfer-Encoding</x:ref> header field is present
1659     and the "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1660     is the final encoding, the message body length is determined by reading
1661     and decoding the chunked data until the transfer-coding indicates the
1662     data is complete.
1663    </t>
1664    <t>
1665     If a <x:ref>Transfer-Encoding</x:ref> header field is present in a
1666     response and the "chunked" transfer-coding is not the final encoding, the
1667     message body length is determined by reading the connection until it is
1668     closed by the server.
1669     If a Transfer-Encoding header field is present in a request and the
1670     "chunked" transfer-coding is not the final encoding, the message body
1671     length cannot be determined reliably; the server &MUST; respond with
1672     the <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1673    </t>
1674    <t>
1675     If a message is received with both a <x:ref>Transfer-Encoding</x:ref>
1676     and a <x:ref>Content-Length</x:ref> header field, the
1677     Transfer-Encoding overrides the Content-Length.
1678     Such a message might indicate an attempt to perform request or response
1679     smuggling (bypass of security-related checks on message routing or content)
1680     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1681     be removed, prior to forwarding the message downstream, or replaced with
1682     the real message body length after the transfer-coding is decoded.
1683    </t></x:lt>
1684    <x:lt><t>
1685     If a message is received without <x:ref>Transfer-Encoding</x:ref> and with
1686     either multiple <x:ref>Content-Length</x:ref> header fields having
1687     differing field-values or a single Content-Length header field having an
1688     invalid value, then the message framing is invalid and &MUST; be treated
1689     as an error to prevent request or response smuggling.
1690     If this is a request message, the server &MUST; respond with
1691     a <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1692     If this is a response message received by a proxy, the proxy
1693     &MUST; discard the received response, send a <x:ref>502 (Bad Gateway)</x:ref>
1694     status code as its downstream response, and then close the connection.
1695     If this is a response message received by a user-agent, it &MUST; be
1696     treated as an error by discarding the message and closing the connection.
1697    </t></x:lt>
1698    <x:lt><t>
1699     If a valid <x:ref>Content-Length</x:ref> header field is present without
1700     <x:ref>Transfer-Encoding</x:ref>, its decimal value defines the
1701     message body length in octets.  If the actual number of octets sent in
1702     the message is less than the indicated Content-Length, the recipient
1703     &MUST; consider the message to be incomplete and treat the connection
1704     as no longer usable.
1705     If the actual number of octets sent in the message is more than the indicated
1706     Content-Length, the recipient &MUST; only process the message body up to the
1707     field value's number of octets; the remainder of the message &MUST; either
1708     be discarded or treated as the next message in a pipeline.  For the sake of
1709     robustness, a user-agent &MAY; attempt to detect and correct such an error
1710     in message framing if it is parsing the response to the last request on
1711     a connection and the connection has been closed by the server.
1712    </t></x:lt>
1713    <x:lt><t>
1714     If this is a request message and none of the above are true, then the
1715     message body length is zero (no message body is present).
1716    </t></x:lt>
1717    <x:lt><t>
1718     Otherwise, this is a response message without a declared message body
1719     length, so the message body length is determined by the number of octets
1720     received prior to the server closing the connection.
1721    </t></x:lt>
1722  </list>
1725   Since there is no way to distinguish a successfully completed,
1726   close-delimited message from a partially-received message interrupted
1727   by network failure, implementations &SHOULD; use encoding or
1728   length-delimited messages whenever possible.  The close-delimiting
1729   feature exists primarily for backwards compatibility with HTTP/1.0.
1732   A server &MAY; reject a request that contains a message body but
1733   not a <x:ref>Content-Length</x:ref> by responding with
1734   <x:ref>411 (Length Required)</x:ref>.
1737   Unless a transfer-coding other than "chunked" has been applied,
1738   a client that sends a request containing a message body &SHOULD;
1739   use a valid <x:ref>Content-Length</x:ref> header field if the message body
1740   length is known in advance, rather than the "chunked" encoding, since some
1741   existing services respond to "chunked" with a <x:ref>411 (Length Required)</x:ref>
1742   status code even though they understand the chunked encoding.  This
1743   is typically because such services are implemented via a gateway that
1744   requires a content-length in advance of being called and the server
1745   is unable or unwilling to buffer the entire request before processing.
1748   A client that sends a request containing a message body &MUST; include a
1749   valid <x:ref>Content-Length</x:ref> header field if it does not know the
1750   server will handle HTTP/1.1 (or later) requests; such knowledge can be in
1751   the form of specific user configuration or by remembering the version of a
1752   prior received response.
1757<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1759   Request messages that are prematurely terminated, possibly due to a
1760   canceled connection or a server-imposed time-out exception, &MUST;
1761   result in closure of the connection; sending an HTTP/1.1 error response
1762   prior to closing the connection is &OPTIONAL;.
1765   Response messages that are prematurely terminated, usually by closure
1766   of the connection prior to receiving the expected number of octets or by
1767   failure to decode a transfer-encoded message body, &MUST; be recorded
1768   as incomplete.  A response that terminates in the middle of the header
1769   block (before the empty line is received) cannot be assumed to convey the
1770   full semantics of the response and &MUST; be treated as an error.
1773   A message body that uses the chunked transfer encoding is
1774   incomplete if the zero-sized chunk that terminates the encoding has not
1775   been received.  A message that uses a valid <x:ref>Content-Length</x:ref> is
1776   incomplete if the size of the message body received (in octets) is less than
1777   the value given by Content-Length.  A response that has neither chunked
1778   transfer encoding nor Content-Length is terminated by closure of the
1779   connection, and thus is considered complete regardless of the number of
1780   message body octets received, provided that the header block was received
1781   intact.
1784   A user agent &MUST-NOT; render an incomplete response message body as if
1785   it were complete (i.e., some indication needs to be given to the user that an
1786   error occurred).  Cache requirements for incomplete responses are defined
1787   in &cache-incomplete;.
1790   A server &MUST; read the entire request message body or close
1791   the connection after sending its response, since otherwise the
1792   remaining data on a persistent connection would be misinterpreted
1793   as the next request.  Likewise,
1794   a client &MUST; read the entire response message body if it intends
1795   to reuse the same connection for a subsequent request.  Pipelining
1796   multiple requests on a connection is described in <xref target="pipelining"/>.
1800<section title="Message Parsing Robustness" anchor="message.robustness">
1802   Older HTTP/1.0 client implementations might send an extra CRLF
1803   after a POST request as a lame workaround for some early server
1804   applications that failed to read message body content that was
1805   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1806   preface or follow a request with an extra CRLF.  If terminating
1807   the request message body with a line-ending is desired, then the
1808   client &MUST; include the terminating CRLF octets as part of the
1809   message body length.
1812   In the interest of robustness, servers &SHOULD; ignore at least one
1813   empty line received where a request-line is expected. In other words, if
1814   the server is reading the protocol stream at the beginning of a
1815   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1816   Likewise, although the line terminator for the start-line and header
1817   fields is the sequence CRLF, we recommend that recipients recognize a
1818   single LF as a line terminator and ignore any CR.
1821   When a server listening only for HTTP request messages, or processing
1822   what appears from the start-line to be an HTTP request message,
1823   receives a sequence of octets that does not match the HTTP-message
1824   grammar aside from the robustness exceptions listed above, the
1825   server &MUST; respond with an HTTP/1.1 <x:ref>400 (Bad Request)</x:ref> response. 
1830<section title="Transfer Codings" anchor="transfer.codings">
1831  <x:anchor-alias value="transfer-coding"/>
1832  <x:anchor-alias value="transfer-extension"/>
1834   Transfer-coding values are used to indicate an encoding
1835   transformation that has been, can be, or might need to be applied to a
1836   payload body in order to ensure "safe transport" through the network.
1837   This differs from a content coding in that the transfer-coding is a
1838   property of the message rather than a property of the representation
1839   that is being transferred.
1841<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1842  <x:ref>transfer-coding</x:ref>    = "chunked" ; <xref target="chunked.encoding"/>
1843                     / "compress" ; <xref target="compress.coding"/>
1844                     / "deflate" ; <xref target="deflate.coding"/>
1845                     / "gzip" ; <xref target="gzip.coding"/>
1846                     / <x:ref>transfer-extension</x:ref>
1847  <x:ref>transfer-extension</x:ref> = <x:ref>token</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>transfer-parameter</x:ref> )
1849<t anchor="rule.parameter">
1850  <x:anchor-alias value="attribute"/>
1851  <x:anchor-alias value="transfer-parameter"/>
1852  <x:anchor-alias value="value"/>
1853   Parameters are in the form of attribute/value pairs.
1855<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/>
1856  <x:ref>transfer-parameter</x:ref> = <x:ref>attribute</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>value</x:ref>
1857  <x:ref>attribute</x:ref>          = <x:ref>token</x:ref>
1858  <x:ref>value</x:ref>              = <x:ref>word</x:ref>
1861   All transfer-coding values are case-insensitive.
1862   The HTTP Transfer Coding registry is defined in
1863   <xref target="transfer.coding.registry"/>.
1864   HTTP/1.1 uses transfer-coding values in the <x:ref>TE</x:ref> header field
1865   (<xref target="header.te"/>) and in the <x:ref>Transfer-Encoding</x:ref>
1866   header field (<xref target="header.transfer-encoding"/>).
1869<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1870  <iref item="chunked (Coding Format)"/>
1871  <iref item="Coding Format" subitem="chunked"/>
1872  <x:anchor-alias value="chunk"/>
1873  <x:anchor-alias value="chunked-body"/>
1874  <x:anchor-alias value="chunk-data"/>
1875  <x:anchor-alias value="chunk-ext"/>
1876  <x:anchor-alias value="chunk-ext-name"/>
1877  <x:anchor-alias value="chunk-ext-val"/>
1878  <x:anchor-alias value="chunk-size"/>
1879  <x:anchor-alias value="last-chunk"/>
1880  <x:anchor-alias value="trailer-part"/>
1881  <x:anchor-alias value="quoted-str-nf"/>
1882  <x:anchor-alias value="qdtext-nf"/>
1884   The chunked encoding modifies the body of a message in order to
1885   transfer it as a series of chunks, each with its own size indicator,
1886   followed by an &OPTIONAL; trailer containing header fields. This
1887   allows dynamically produced content to be transferred along with the
1888   information necessary for the recipient to verify that it has
1889   received the full message.
1891<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="chunked-body"><!--terminal production--></iref><iref primary="true" item="Grammar" subitem="chunk"/><iref primary="true" item="Grammar" subitem="chunk-size"/><iref primary="true" item="Grammar" subitem="last-chunk"/><iref primary="true" item="Grammar" subitem="chunk-ext"/><iref primary="true" item="Grammar" subitem="chunk-ext-name"/><iref primary="true" item="Grammar" subitem="chunk-ext-val"/><iref primary="true" item="Grammar" subitem="chunk-data"/><iref primary="true" item="Grammar" subitem="trailer-part"/><iref primary="true" item="Grammar" subitem="quoted-str-nf"/><iref primary="true" item="Grammar" subitem="qdtext-nf"/>
1892  <x:ref>chunked-body</x:ref>   = *<x:ref>chunk</x:ref>
1893                   <x:ref>last-chunk</x:ref>
1894                   <x:ref>trailer-part</x:ref>
1895                   <x:ref>CRLF</x:ref>
1897  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1898                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1899  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1900  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1902  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1903  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1904  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1905  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1906  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1908  <x:ref>quoted-str-nf</x:ref>  = <x:ref>DQUOTE</x:ref> *( <x:ref>qdtext-nf</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref>
1909                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1910  <x:ref>qdtext-nf</x:ref>      = <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1913   The chunk-size field is a string of hex digits indicating the size of
1914   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1915   zero, followed by the trailer, which is terminated by an empty line.
1918   The trailer allows the sender to include additional HTTP header
1919   fields at the end of the message. The <x:ref>Trailer</x:ref> header field
1920   can be used to indicate which header fields are included in a trailer (see
1921   <xref target="header.trailer"/>).
1924   A server using chunked transfer-coding in a response &MUST-NOT; use the
1925   trailer for any header fields unless at least one of the following is
1926   true:
1927  <list style="numbers">
1928    <t>the request included a <x:ref>TE</x:ref> header field that indicates
1929    "trailers" is acceptable in the transfer-coding of the response, as
1930    described in <xref target="header.te"/>; or,</t>
1932    <t>the trailer fields consist entirely of optional metadata, and the
1933    recipient could use the message (in a manner acceptable to the server where
1934    the field originated) without receiving it. In other words, the server that
1935    generated the header field (often but not always the origin server) is
1936    willing to accept the possibility that the trailer fields might be silently
1937    discarded along the path to the client.</t>
1938  </list>
1941   This requirement prevents an interoperability failure when the
1942   message is being received by an HTTP/1.1 (or later) proxy and
1943   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1944   conformance with the protocol would have necessitated a possibly
1945   infinite buffer on the proxy.
1948   A process for decoding the "chunked" transfer-coding
1949   can be represented in pseudo-code as:
1951<figure><artwork type="code">
1952  length := 0
1953  read chunk-size, chunk-ext (if any) and CRLF
1954  while (chunk-size &gt; 0) {
1955     read chunk-data and CRLF
1956     append chunk-data to decoded-body
1957     length := length + chunk-size
1958     read chunk-size and CRLF
1959  }
1960  read header-field
1961  while (header-field not empty) {
1962     append header-field to existing header fields
1963     read header-field
1964  }
1965  Content-Length := length
1966  Remove "chunked" from Transfer-Encoding
1969   All HTTP/1.1 applications &MUST; be able to receive and decode the
1970   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
1971   they do not understand.
1974   Use of chunk-ext extensions by senders is deprecated; they &SHOULD-NOT; be
1975   sent and definition of new chunk-extensions is discouraged.
1979<section title="Compression Codings" anchor="compression.codings">
1981   The codings defined below can be used to compress the payload of a
1982   message.
1985   &Note; Use of program names for the identification of encoding formats
1986   is not desirable and is discouraged for future encodings. Their
1987   use here is representative of historical practice, not good
1988   design.
1991   &Note; For compatibility with previous implementations of HTTP,
1992   applications &SHOULD; consider "x-gzip" and "x-compress" to be
1993   equivalent to "gzip" and "compress" respectively.
1996<section title="Compress Coding" anchor="compress.coding">
1997<iref item="compress (Coding Format)"/>
1998<iref item="Coding Format" subitem="compress"/>
2000   The "compress" format is produced by the common UNIX file compression
2001   program "compress". This format is an adaptive Lempel-Ziv-Welch
2002   coding (LZW).
2006<section title="Deflate Coding" anchor="deflate.coding">
2007<iref item="deflate (Coding Format)"/>
2008<iref item="Coding Format" subitem="deflate"/>
2010   The "deflate" format is defined as the "deflate" compression mechanism
2011   (described in <xref target="RFC1951"/>) used inside the "zlib"
2012   data format (<xref target="RFC1950"/>).
2015  <t>
2016    &Note; Some incorrect implementations send the "deflate"
2017    compressed data without the zlib wrapper.
2018   </t>
2022<section title="Gzip Coding" anchor="gzip.coding">
2023<iref item="gzip (Coding Format)"/>
2024<iref item="Coding Format" subitem="gzip"/>
2026   The "gzip" format is produced by the file compression program
2027   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2028   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2034<section title="TE" anchor="header.te">
2035  <iref primary="true" item="TE header field" x:for-anchor=""/>
2036  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
2037  <x:anchor-alias value="TE"/>
2038  <x:anchor-alias value="t-codings"/>
2039  <x:anchor-alias value="te-params"/>
2040  <x:anchor-alias value="te-ext"/>
2042   The "TE" header field indicates what extension transfer-codings
2043   the client is willing to accept in the response, and whether or not it is
2044   willing to accept trailer fields in a chunked transfer-coding.
2047   Its value consists of the keyword "trailers" and/or a comma-separated
2048   list of extension transfer-coding names with optional accept
2049   parameters (as described in <xref target="transfer.codings"/>).
2051<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
2052  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2053  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2054  <x:ref>te-params</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>te-ext</x:ref> )
2055  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
2058   The presence of the keyword "trailers" indicates that the client is
2059   willing to accept trailer fields in a chunked transfer-coding, as
2060   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
2061   transfer-coding values even though it does not itself represent a
2062   transfer-coding.
2065   Examples of its use are:
2067<figure><artwork type="example">
2068  TE: deflate
2069  TE:
2070  TE: trailers, deflate;q=0.5
2073   The TE header field only applies to the immediate connection.
2074   Therefore, the keyword &MUST; be supplied within a <x:ref>Connection</x:ref>
2075   header field (<xref target="header.connection"/>) whenever TE is present in
2076   an HTTP/1.1 message.
2079   A server tests whether a transfer-coding is acceptable, according to
2080   a TE field, using these rules:
2081  <list style="numbers">
2082    <x:lt>
2083      <t>The "chunked" transfer-coding is always acceptable. If the
2084         keyword "trailers" is listed, the client indicates that it is
2085         willing to accept trailer fields in the chunked response on
2086         behalf of itself and any downstream clients. The implication is
2087         that, if given, the client is stating that either all
2088         downstream clients are willing to accept trailer fields in the
2089         forwarded response, or that it will attempt to buffer the
2090         response on behalf of downstream recipients.
2091      </t><t>
2092         &Note; HTTP/1.1 does not define any means to limit the size of a
2093         chunked response such that a client can be assured of buffering
2094         the entire response.</t>
2095    </x:lt>
2096    <x:lt>
2097      <t>If the transfer-coding being tested is one of the transfer-codings
2098         listed in the TE field, then it is acceptable unless it
2099         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2100         qvalue of 0 means "not acceptable".)</t>
2101    </x:lt>
2102    <x:lt>
2103      <t>If multiple transfer-codings are acceptable, then the
2104         acceptable transfer-coding with the highest non-zero qvalue is
2105         preferred.  The "chunked" transfer-coding always has a qvalue
2106         of 1.</t>
2107    </x:lt>
2108  </list>
2111   If the TE field-value is empty or if no TE field is present, the only
2112   acceptable transfer-coding is "chunked". A message with no transfer-coding is
2113   always acceptable.
2116<section title="Quality Values" anchor="quality.values">
2117  <x:anchor-alias value="qvalue"/>
2119   Both transfer codings (<x:ref>TE</x:ref> request header field,
2120   <xref target="header.te"/>) and content negotiation (&content.negotiation;)
2121   use short "floating point" numbers to indicate the relative importance
2122   ("weight") of various negotiable parameters.  A weight is normalized to a
2123   real number in the range 0 through 1, where 0 is the minimum and 1 the
2124   maximum value. If a parameter has a quality value of 0, then content with
2125   this parameter is "not acceptable" for the client. HTTP/1.1
2126   applications &MUST-NOT; generate more than three digits after the
2127   decimal point. User configuration of these values &SHOULD; also be
2128   limited in this fashion.
2130<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2131  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2132                 / ( "1" [ "." 0*3("0") ] )
2135  <t>
2136     &Note; "Quality values" is a misnomer, since these values merely represent
2137     relative degradation in desired quality.
2138  </t>
2143<section title="Trailer" anchor="header.trailer">
2144  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
2145  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
2146  <x:anchor-alias value="Trailer"/>
2148   The "Trailer" header field indicates that the given set of
2149   header fields is present in the trailer of a message encoded with
2150   chunked transfer-coding.
2152<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2153  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
2156   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2157   message using chunked transfer-coding with a non-empty trailer. Doing
2158   so allows the recipient to know which header fields to expect in the
2159   trailer.
2162   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2163   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
2164   trailer fields in a "chunked" transfer-coding.
2167   Message header fields listed in the Trailer header field &MUST-NOT;
2168   include the following header fields:
2169  <list style="symbols">
2170    <t><x:ref>Transfer-Encoding</x:ref></t>
2171    <t><x:ref>Content-Length</x:ref></t>
2172    <t><x:ref>Trailer</x:ref></t>
2173  </list>
2178<section title="Message Routing" anchor="message.routing">
2180   HTTP request message routing is determined by each client based on the
2181   target resource, the client's proxy configuration, and
2182   establishment or reuse of an inbound connection.  The corresponding
2183   response routing follows the same connection chain back to the client.
2186<section title="Identifying a Target Resource" anchor="target-resource">
2187  <iref primary="true" item="target resource"/>
2188  <iref primary="true" item="target URI"/>
2190   HTTP is used in a wide variety of applications, ranging from
2191   general-purpose computers to home appliances.  In some cases,
2192   communication options are hard-coded in a client's configuration.
2193   However, most HTTP clients rely on the same resource identification
2194   mechanism and configuration techniques as general-purpose Web browsers.
2197   HTTP communication is initiated by a user agent for some purpose.
2198   The purpose is a combination of request semantics, which are defined in
2199   <xref target="Part2"/>, and a target resource upon which to apply those
2200   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2201   an identifier for the "target resource", which a user agent would resolve
2202   to its absolute form in order to obtain the "target URI".  The target URI
2203   excludes the reference's fragment identifier component, if any,
2204   since fragment identifiers are reserved for client-side processing
2205   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2208   HTTP intermediaries obtain the request semantics and target URI
2209   from the request-line of an incoming request message.
2213<section title="Connecting Inbound" anchor="connecting.inbound">
2215   Once the target URI is determined, a client needs to decide whether
2216   a network request is necessary to accomplish the desired semantics and,
2217   if so, where that request is to be directed.
2220   If the client has a response cache and the request semantics can be
2221   satisfied by a cache (<xref target="Part6"/>), then the request is
2222   usually directed to the cache first.
2225   If the request is not satisfied by a cache, then a typical client will
2226   check its configuration to determine whether a proxy is to be used to
2227   satisfy the request.  Proxy configuration is implementation-dependent,
2228   but is often based on URI prefix matching, selective authority matching,
2229   or both, and the proxy itself is usually identified by an "http" or
2230   "https" URI.  If a proxy is applicable, the client connects inbound by
2231   establishing (or reusing) a connection to that proxy.
2234   If no proxy is applicable, a typical client will invoke a handler routine,
2235   usually specific to the target URI's scheme, to connect directly
2236   to an authority for the target resource.  How that is accomplished is
2237   dependent on the target URI scheme and defined by its associated
2238   specification, similar to how this specification defines origin server
2239   access for resolution of the "http" (<xref target="http.uri"/>) and
2240   "https" (<xref target="https.uri"/>) schemes.
2244<section title="Request Target" anchor="request-target">
2246   Once an inbound connection is obtained
2247   (<xref target=""/>),
2248   the client sends an HTTP request message (<xref target="http.message"/>)
2249   with a request-target derived from the target URI.
2250   There are four distinct formats for the request-target, depending on both
2251   the method being requested and whether the request is to a proxy.
2253<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/><iref primary="true" item="Grammar" subitem="origin-form"/><iref primary="true" item="Grammar" subitem="absolute-form"/><iref primary="true" item="Grammar" subitem="authority-form"/><iref primary="true" item="Grammar" subitem="asterisk-form"/>
2254  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2255                 / <x:ref>absolute-form</x:ref>
2256                 / <x:ref>authority-form</x:ref>
2257                 / <x:ref>asterisk-form</x:ref>
2259  <x:ref>origin-form</x:ref>    = <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]
2260  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2261  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2262  <x:ref>asterisk-form</x:ref>  = "*"
2264<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2265   The most common form of request-target is the origin-form.
2266   When making a request directly to an origin server, other than a CONNECT
2267   or server-wide OPTIONS request (as detailed below),
2268   a client &MUST; send only the absolute path and query components of
2269   the target URI as the request-target.
2270   If the target URI's path component is empty, then the client &MUST; send
2271   "/" as the path within the origin-form of request-target.
2272   A <x:ref>Host</x:ref> header field is also sent, as defined in
2273   <xref target=""/>, containing the target URI's
2274   authority component (excluding any userinfo).
2277   For example, a client wishing to retrieve a representation of the resource
2278   identified as
2280<figure><artwork x:indent-with="  " type="example">
2284   directly from the origin server would open (or reuse) a TCP connection
2285   to port 80 of the host "" and send the lines:
2287<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2288GET /where?q=now HTTP/1.1
2292   followed by the remainder of the request message.
2294<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2295   When making a request to a proxy, other than a CONNECT or server-wide
2296   OPTIONS request (as detailed below), a client &MUST; send the target URI
2297   in absolute-form as the request-target.
2298   The proxy is requested to either service that request from a valid cache,
2299   if possible, or make the same request on the client's behalf to either
2300   the next inbound proxy server or directly to the origin server indicated
2301   by the request-target.  Requirements on such "forwarding" of messages are
2302   defined in <xref target="intermediary.forwarding"/>.
2305   An example absolute-form of request-line would be:
2307<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2308GET HTTP/1.1
2311   To allow for transition to the absolute-form for all requests in some
2312   future version of HTTP, HTTP/1.1 servers &MUST; accept the absolute-form
2313   in requests, even though HTTP/1.1 clients will only send them in requests
2314   to proxies.
2316<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2317   The authority-form of request-target is only used for CONNECT requests
2318   (&CONNECT;).  When making a CONNECT request to establish a tunnel through
2319   one or more proxies, a client &MUST; send only the target URI's
2320   authority component (excluding any userinfo) as the request-target.
2321   For example,
2323<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2326<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2327   The asterisk-form of request-target is only used for a server-wide
2328   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2329   for the server as a whole, as opposed to a specific named resource of
2330   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2331   For example,
2333<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2334OPTIONS * HTTP/1.1
2337   If a proxy receives an OPTIONS request with an absolute-form of
2338   request-target in which the URI has an empty path and no query component,
2339   then the last proxy on the request chain &MUST; send a request-target
2340   of "*" when it forwards the request to the indicated origin server.
2343   For example, the request
2344</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2348  would be forwarded by the final proxy as
2349</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2350OPTIONS * HTTP/1.1
2354   after connecting to port 8001 of host "".
2359<section title="Host" anchor="">
2360  <iref primary="true" item="Host header field" x:for-anchor=""/>
2361  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
2362  <x:anchor-alias value="Host"/>
2364   The "Host" header field in a request provides the host and port
2365   information from the target URI, enabling the origin
2366   server to distinguish among resources while servicing requests
2367   for multiple host names on a single IP address.  Since the Host
2368   field-value is critical information for handling a request, it
2369   &SHOULD; be sent as the first header field following the request-line.
2371<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2372  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2375   A client &MUST; send a Host header field in all HTTP/1.1 request
2376   messages.  If the target URI includes an authority component, then
2377   the Host field-value &MUST; be identical to that authority component
2378   after excluding any userinfo (<xref target="http.uri"/>).
2379   If the authority component is missing or undefined for the target URI,
2380   then the Host header field &MUST; be sent with an empty field-value.
2383   For example, a GET request to the origin server for
2384   &lt;; would begin with:
2386<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2387GET /pub/WWW/ HTTP/1.1
2391   The Host header field &MUST; be sent in an HTTP/1.1 request even
2392   if the request-target is in the absolute-form, since this
2393   allows the Host information to be forwarded through ancient HTTP/1.0
2394   proxies that might not have implemented Host.
2397   When an HTTP/1.1 proxy receives a request with an absolute-form of
2398   request-target, the proxy &MUST; ignore the received
2399   Host header field (if any) and instead replace it with the host
2400   information of the request-target.  If the proxy forwards the request,
2401   it &MUST; generate a new Host field-value based on the received
2402   request-target rather than forward the received Host field-value.
2405   Since the Host header field acts as an application-level routing
2406   mechanism, it is a frequent target for malware seeking to poison
2407   a shared cache or redirect a request to an unintended server.
2408   An interception proxy is particularly vulnerable if it relies on
2409   the Host field-value for redirecting requests to internal
2410   servers, or for use as a cache key in a shared cache, without
2411   first verifying that the intercepted connection is targeting a
2412   valid IP address for that host.
2415   A server &MUST; respond with a <x:ref>400 (Bad Request)</x:ref> status code
2416   to any HTTP/1.1 request message that lacks a Host header field and
2417   to any request message that contains more than one Host header field
2418   or a Host header field with an invalid field-value.
2422<section title="Effective Request URI" anchor="effective.request.uri">
2423  <iref primary="true" item="effective request URI"/>
2425   A server that receives an HTTP request message &MUST; reconstruct
2426   the user agent's original target URI, based on the pieces of information
2427   learned from the request-target, <x:ref>Host</x:ref> header field, and
2428   connection context, in order to identify the intended target resource and
2429   properly service the request. The URI derived from this reconstruction
2430   process is referred to as the "effective request URI".
2433   For a user agent, the effective request URI is the target URI.
2436   If the request-target is in absolute-form, then the effective request URI
2437   is the same as the request-target.  Otherwise, the effective request URI
2438   is constructed as follows.
2441   If the request is received over an SSL/TLS-secured TCP connection,
2442   then the effective request URI's scheme is "https"; otherwise, the
2443   scheme is "http".
2446   If the request-target is in authority-form, then the effective
2447   request URI's authority component is the same as the request-target.
2448   Otherwise, if a <x:ref>Host</x:ref> header field is supplied with a
2449   non-empty field-value, then the authority component is the same as the
2450   Host field-value. Otherwise, the authority component is the concatenation of
2451   the default host name configured for the server, a colon (":"), and the
2452   connection's incoming TCP port number in decimal form.
2455   If the request-target is in authority-form or asterisk-form, then the
2456   effective request URI's combined path and query component is empty.
2457   Otherwise, the combined path and query component is the same as the
2458   request-target.
2461   The components of the effective request URI, once determined as above,
2462   can be combined into absolute-URI form by concatenating the scheme,
2463   "://", authority, and combined path and query component.
2467   Example 1: the following message received over an insecure TCP connection
2469<artwork type="example" x:indent-with="  ">
2470GET /pub/WWW/TheProject.html HTTP/1.1
2476  has an effective request URI of
2478<artwork type="example" x:indent-with="  ">
2484   Example 2: the following message received over an SSL/TLS-secured TCP
2485   connection
2487<artwork type="example" x:indent-with="  ">
2488OPTIONS * HTTP/1.1
2494  has an effective request URI of
2496<artwork type="example" x:indent-with="  ">
2501   An origin server that does not allow resources to differ by requested
2502   host &MAY; ignore the <x:ref>Host</x:ref> field-value and instead replace it
2503   with a configured server name when constructing the effective request URI.
2506   Recipients of an HTTP/1.0 request that lacks a <x:ref>Host</x:ref> header
2507   field &MAY; attempt to use heuristics (e.g., examination of the URI path for
2508   something unique to a particular host) in order to guess the
2509   effective request URI's authority component.
2513<section title="Intermediary Forwarding" anchor="intermediary.forwarding">
2515   As described in <xref target="intermediaries"/>, intermediaries can serve
2516   a variety of roles in the processing of HTTP requests and responses.
2517   Some intermediaries are used to improve performance or availability.
2518   Others are used for access control or to filter content.
2519   Since an HTTP stream has characteristics similar to a pipe-and-filter
2520   architecture, there are no inherent limits to the extent an intermediary
2521   can enhance (or interfere) with either direction of the stream.
2524   In order to avoid request loops, a proxy that forwards requests to other
2525   proxies &MUST; be able to recognize and exclude all of its own server
2526   names, including any aliases, local variations, or literal IP addresses.
2529   If a proxy receives a request-target with a host name that is not a
2530   fully qualified domain name, it &MAY; add its domain to the host name
2531   it received when forwarding the request.  A proxy &MUST-NOT; change the
2532   host name if it is a fully qualified domain name.
2535   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" and "query"
2536   parts of the received request-target when forwarding it to the next inbound
2537   server, except as noted above to replace an empty path with "/" or "*".
2540   Intermediaries that forward a message &MUST; implement the
2541   <x:ref>Connection</x:ref> header field as specified in
2542   <xref target="header.connection"/>.
2545<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2547  <cref anchor="TODO-end-to-end" source="jre">
2548    Restored from <eref target=""/>.
2549    See also <eref target=""/>.
2550  </cref>
2553   For the purpose of defining the behavior of caches and non-caching
2554   proxies, we divide HTTP header fields into two categories:
2555  <list style="symbols">
2556      <t>End-to-end header fields, which are  transmitted to the ultimate
2557        recipient of a request or response. End-to-end header fields in
2558        responses &MUST; be stored as part of a cache entry and &MUST; be
2559        transmitted in any response formed from a cache entry.</t>
2561      <t>Hop-by-hop header fields, which are meaningful only for a single
2562        transport-level connection, and are not stored by caches or
2563        forwarded by proxies.</t>
2564  </list>
2567   The following HTTP/1.1 header fields are hop-by-hop header fields:
2568  <list style="symbols">
2569      <t><x:ref>Connection</x:ref></t>
2570      <t>Keep-Alive (<xref target="RFC2068" x:fmt="of" x:sec=""/>)</t>
2571      <t><x:ref>Proxy-Authenticate</x:ref> (&header-proxy-authenticate;)</t>
2572      <t><x:ref>Proxy-Authorization</x:ref> (&header-proxy-authorization;)</t>
2573      <t><x:ref>TE</x:ref></t>
2574      <t><x:ref>Trailer</x:ref></t>
2575      <t><x:ref>Transfer-Encoding</x:ref></t>
2576      <t><x:ref>Upgrade</x:ref></t>
2577  </list>
2580   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2583   Other hop-by-hop header fields &MUST; be listed in a
2584   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>).
2588<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2590  <cref anchor="TODO-non-mod-headers" source="jre">
2591    Restored from <eref target=""/>.
2592    See also <eref target=""/>.
2593  </cref>
2596   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2597   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2598   modify an end-to-end header field unless the definition of that header field requires
2599   or specifically allows that.
2602   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2603   request or response, and it &MUST-NOT; add any of these fields if not
2604   already present:
2605  <list style="symbols">
2606    <t><x:ref>Allow</x:ref> (&header-allow;)</t>
2607    <t><x:ref>Content-Location</x:ref> (&header-content-location;)</t>
2608    <t>Content-MD5 (<xref target="RFC2616" x:fmt="of" x:sec="14.15"/>)</t>
2609    <t><x:ref>ETag</x:ref> (&header-etag;)</t>
2610    <t><x:ref>Last-Modified</x:ref> (&header-last-modified;)</t>
2611    <t><x:ref>Server</x:ref> (&header-server;)</t>
2612  </list>
2615   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2616   response:
2617  <list style="symbols">
2618    <t><x:ref>Expires</x:ref> (&header-expires;)</t>
2619  </list>
2622   but it &MAY; add any of these fields if not already present. If an
2623   <x:ref>Expires</x:ref> header field is added, it &MUST; be given a
2624   field value identical to that of the <x:ref>Date</x:ref> header field in
2625   that response.
2628   A proxy &MUST-NOT; modify or add any of the following fields in a
2629   message that contains the no-transform cache-control directive, or in
2630   any request:
2631  <list style="symbols">
2632    <t><x:ref>Content-Encoding</x:ref> (&header-content-encoding;)</t>
2633    <t><x:ref>Content-Range</x:ref> (&header-content-range;)</t>
2634    <t><x:ref>Content-Type</x:ref> (&header-content-type;)</t>
2635  </list>
2638   A transforming proxy &MAY; modify or add these fields to a message
2639   that does not include no-transform, but if it does so, it &MUST; add a
2640   Warning 214 (Transformation applied) if one does not already appear
2641   in the message (see &header-warning;).
2644  <t>
2645    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2646    cause authentication failures if stronger authentication
2647    mechanisms are introduced in later versions of HTTP. Such
2648    authentication mechanisms &MAY; rely on the values of header fields
2649    not listed here.
2650  </t>
2653   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2654   though it &MAY; change the message body through application or removal
2655   of a transfer-coding (<xref target="transfer.codings"/>).
2661<section title="Associating a Response to a Request" anchor="">
2663   HTTP does not include a request identifier for associating a given
2664   request message with its corresponding one or more response messages.
2665   Hence, it relies on the order of response arrival to correspond exactly
2666   to the order in which requests are made on the same connection.
2667   More than one response message per request only occurs when one or more
2668   informational responses (<x:ref>1xx</x:ref>, see &status-1xx;) precede a final response
2669   to the same request.
2672   A client that uses persistent connections and sends more than one request
2673   per connection &MUST; maintain a list of outstanding requests in the
2674   order sent on that connection and &MUST; associate each received response
2675   message to the highest ordered request that has not yet received a final
2676   (non-<x:ref>1xx</x:ref>) response.
2681<section title="Connection Management" anchor="">
2683<section title="Connection" anchor="header.connection">
2684  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2685  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2686  <x:anchor-alias value="Connection"/>
2687  <x:anchor-alias value="connection-option"/>
2689   The "Connection" header field allows the sender to specify
2690   options that are desired only for that particular connection.
2691   Such connection options &MUST; be removed or replaced before the
2692   message can be forwarded downstream by a proxy or gateway.
2693   This mechanism also allows the sender to indicate which HTTP
2694   header fields used in the message are only intended for the
2695   immediate recipient ("hop-by-hop"), as opposed to all recipients
2696   on the chain ("end-to-end"), enabling the message to be
2697   self-descriptive and allowing future connection-specific extensions
2698   to be deployed in HTTP without fear that they will be blindly
2699   forwarded by previously deployed intermediaries.
2702   The Connection header field's value has the following grammar:
2704<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-option"/>
2705  <x:ref>Connection</x:ref>        = 1#<x:ref>connection-option</x:ref>
2706  <x:ref>connection-option</x:ref> = <x:ref>token</x:ref>
2709   Connection options are compared case-insensitively.
2712   A proxy or gateway &MUST; parse a received Connection
2713   header field before a message is forwarded and, for each
2714   connection-option in this field, remove any header field(s) from
2715   the message with the same name as the connection-option, and then
2716   remove the Connection header field itself or replace it with the
2717   sender's own connection options for the forwarded message.
2720   A sender &MUST-NOT; include field-names in the Connection header
2721   field-value for fields that are defined as expressing constraints
2722   for all recipients in the request or response chain, such as the
2723   Cache-Control header field (&header-cache-control;).
2726   The connection options do not have to correspond to a header field
2727   present in the message, since a connection-specific header field
2728   might not be needed if there are no parameters associated with that
2729   connection option.  Recipients that trigger certain connection
2730   behavior based on the presence of connection options &MUST; do so
2731   based on the presence of the connection-option rather than only the
2732   presence of the optional header field.  In other words, if the
2733   connection option is received as a header field but not indicated
2734   within the Connection field-value, then the recipient &MUST; ignore
2735   the connection-specific header field because it has likely been
2736   forwarded by an intermediary that is only partially conformant.
2739   When defining new connection options, specifications ought to
2740   carefully consider existing deployed header fields and ensure
2741   that the new connection option does not share the same name as
2742   an unrelated header field that might already be deployed.
2743   Defining a new connection option essentially reserves that potential
2744   field-name for carrying additional information related to the
2745   connection option, since it would be unwise for senders to use
2746   that field-name for anything else.
2749   HTTP/1.1 defines the "close" connection option for the sender to
2750   signal that the connection will be closed after completion of the
2751   response. For example,
2753<figure><artwork type="example">
2754  Connection: close
2757   in either the request or the response header fields indicates that
2758   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2759   after the current request/response is complete.
2762   An HTTP/1.1 client that does not support persistent connections &MUST;
2763   include the "close" connection option in every request message.
2766   An HTTP/1.1 server that does not support persistent connections &MUST;
2767   include the "close" connection option in every response message that
2768   does not have a <x:ref>1xx (Informational)</x:ref> status code.
2772<section title="Via" anchor="header.via">
2773  <iref primary="true" item="Via header field" x:for-anchor=""/>
2774  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
2775  <x:anchor-alias value="pseudonym"/>
2776  <x:anchor-alias value="received-by"/>
2777  <x:anchor-alias value="received-protocol"/>
2778  <x:anchor-alias value="Via"/>
2780   The "Via" header field &MUST; be sent by a proxy or gateway to
2781   indicate the intermediate protocols and recipients between the user
2782   agent and the server on requests, and between the origin server and
2783   the client on responses. It is analogous to the "Received" field
2784   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
2785   and is intended to be used for tracking message forwards,
2786   avoiding request loops, and identifying the protocol capabilities of
2787   all senders along the request/response chain.
2789<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/>
2790  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2791                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2792  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2793  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2794  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2797   The received-protocol indicates the protocol version of the message
2798   received by the server or client along each segment of the
2799   request/response chain. The received-protocol version is appended to
2800   the Via field value when the message is forwarded so that information
2801   about the protocol capabilities of upstream applications remains
2802   visible to all recipients.
2805   The protocol-name is excluded if and only if it would be "HTTP". The
2806   received-by field is normally the host and optional port number of a
2807   recipient server or client that subsequently forwarded the message.
2808   However, if the real host is considered to be sensitive information,
2809   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2810   be assumed to be the default port of the received-protocol.
2813   Multiple Via field values represent each proxy or gateway that has
2814   forwarded the message. Each recipient &MUST; append its information
2815   such that the end result is ordered according to the sequence of
2816   forwarding applications.
2819   Comments &MAY; be used in the Via header field to identify the software
2820   of each recipient, analogous to the <x:ref>User-Agent</x:ref> and
2821   <x:ref>Server</x:ref> header fields. However, all comments in the Via field
2822   are optional and &MAY; be removed by any recipient prior to forwarding the
2823   message.
2826   For example, a request message could be sent from an HTTP/1.0 user
2827   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2828   forward the request to a public proxy at, which completes
2829   the request by forwarding it to the origin server at
2830   The request received by would then have the following
2831   Via header field:
2833<figure><artwork type="example">
2834  Via: 1.0 fred, 1.1 (Apache/1.1)
2837   A proxy or gateway used as a portal through a network firewall
2838   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2839   region unless it is explicitly enabled to do so. If not enabled, the
2840   received-by host of any host behind the firewall &SHOULD; be replaced
2841   by an appropriate pseudonym for that host.
2844   For organizations that have strong privacy requirements for hiding
2845   internal structures, a proxy or gateway &MAY; combine an ordered
2846   subsequence of Via header field entries with identical received-protocol
2847   values into a single such entry. For example,
2849<figure><artwork type="example">
2850  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2853  could be collapsed to
2855<figure><artwork type="example">
2856  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2859   Senders &SHOULD-NOT; combine multiple entries unless they are all
2860   under the same organizational control and the hosts have already been
2861   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
2862   have different received-protocol values.
2866<section title="Persistent Connections" anchor="persistent.connections">
2868<section title="Purpose" anchor="persistent.purpose">
2870   Prior to persistent connections, a separate TCP connection was
2871   established for each request, increasing the load on HTTP servers
2872   and causing congestion on the Internet. The use of inline images and
2873   other associated data often requires a client to make multiple
2874   requests of the same server in a short amount of time. Analysis of
2875   these performance problems and results from a prototype
2876   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2877   measurements of actual HTTP/1.1 implementations show good
2878   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2879   T/TCP <xref target="Tou1998"/>.
2882   Persistent HTTP connections have a number of advantages:
2883  <list style="symbols">
2884      <t>
2885        By opening and closing fewer TCP connections, CPU time is saved
2886        in routers and hosts (clients, servers, proxies, gateways,
2887        tunnels, or caches), and memory used for TCP protocol control
2888        blocks can be saved in hosts.
2889      </t>
2890      <t>
2891        HTTP requests and responses can be pipelined on a connection.
2892        Pipelining allows a client to make multiple requests without
2893        waiting for each response, allowing a single TCP connection to
2894        be used much more efficiently, with much lower elapsed time.
2895      </t>
2896      <t>
2897        Network congestion is reduced by reducing the number of packets
2898        caused by TCP opens, and by allowing TCP sufficient time to
2899        determine the congestion state of the network.
2900      </t>
2901      <t>
2902        Latency on subsequent requests is reduced since there is no time
2903        spent in TCP's connection opening handshake.
2904      </t>
2905      <t>
2906        HTTP can evolve more gracefully, since errors can be reported
2907        without the penalty of closing the TCP connection. Clients using
2908        future versions of HTTP might optimistically try a new feature,
2909        but if communicating with an older server, retry with old
2910        semantics after an error is reported.
2911      </t>
2912    </list>
2915   HTTP implementations &SHOULD; implement persistent connections.
2919<section title="Overall Operation" anchor="persistent.overall">
2921   A significant difference between HTTP/1.1 and earlier versions of
2922   HTTP is that persistent connections are the default behavior of any
2923   HTTP connection. That is, unless otherwise indicated, the client
2924   &SHOULD; assume that the server will maintain a persistent connection,
2925   even after error responses from the server.
2928   Persistent connections provide a mechanism by which a client and a
2929   server can signal the close of a TCP connection. This signaling takes
2930   place using the <x:ref>Connection</x:ref> header field
2931   (<xref target="header.connection"/>). Once a close has been signaled, the
2932   client &MUST-NOT; send any more requests on that
2933   connection.
2936<section title="Negotiation" anchor="persistent.negotiation">
2938   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2939   maintain a persistent connection unless a <x:ref>Connection</x:ref> header
2940   field including the connection option "close" was sent in the request. If
2941   the server chooses to close the connection immediately after sending the
2942   response, it &SHOULD; send a Connection header field including the
2943   connection option "close".
2946   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2947   decide to keep it open based on whether the response from a server
2948   contains a <x:ref>Connection</x:ref> header field with the connection option
2949   "close". In case the client does not want to maintain a connection for more
2950   than that request, it &SHOULD; send a Connection header field including the
2951   connection option "close".
2954   If either the client or the server sends the "close" option in the
2955   <x:ref>Connection</x:ref> header field, that request becomes the last one
2956   for the connection.
2959   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2960   maintained for HTTP versions less than 1.1 unless it is explicitly
2961   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2962   compatibility with HTTP/1.0 clients.
2965   Each persistent connection applies to only one transport link.
2968   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2969   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2970   for information and discussion of the problems with the Keep-Alive header field
2971   implemented by many HTTP/1.0 clients).
2974   In order to remain persistent, all messages on the connection &MUST;
2975   have a self-defined message length (i.e., one not defined by closure
2976   of the connection), as described in <xref target="message.body"/>.
2980<section title="Pipelining" anchor="pipelining">
2982   A client that supports persistent connections &MAY; "pipeline" its
2983   requests (i.e., send multiple requests without waiting for each
2984   response). A server &MUST; send its responses to those requests in the
2985   same order that the requests were received.
2988   Clients which assume persistent connections and pipeline immediately
2989   after connection establishment &SHOULD; be prepared to retry their
2990   connection if the first pipelined attempt fails. If a client does
2991   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2992   persistent. Clients &MUST; also be prepared to resend their requests if
2993   the server closes the connection before sending all of the
2994   corresponding responses.
2997   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2998   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2999   premature termination of the transport connection could lead to
3000   indeterminate results. A client wishing to send a non-idempotent
3001   request &SHOULD; wait to send that request until it has received the
3002   response status line for the previous request.
3007<section title="Practical Considerations" anchor="persistent.practical">
3009   Servers will usually have some time-out value beyond which they will
3010   no longer maintain an inactive connection. Proxy servers might make
3011   this a higher value since it is likely that the client will be making
3012   more connections through the same server. The use of persistent
3013   connections places no requirements on the length (or existence) of
3014   this time-out for either the client or the server.
3017   When a client or server wishes to time-out it &SHOULD; issue a graceful
3018   close on the transport connection. Clients and servers &SHOULD; both
3019   constantly watch for the other side of the transport close, and
3020   respond to it as appropriate. If a client or server does not detect
3021   the other side's close promptly it could cause unnecessary resource
3022   drain on the network.
3025   A client, server, or proxy &MAY; close the transport connection at any
3026   time. For example, a client might have started to send a new request
3027   at the same time that the server has decided to close the "idle"
3028   connection. From the server's point of view, the connection is being
3029   closed while it was idle, but from the client's point of view, a
3030   request is in progress.
3033   Clients (including proxies) &SHOULD; limit the number of simultaneous
3034   connections that they maintain to a given server (including proxies).
3037   Previous revisions of HTTP gave a specific number of connections as a
3038   ceiling, but this was found to be impractical for many applications. As a
3039   result, this specification does not mandate a particular maximum number of
3040   connections, but instead encourages clients to be conservative when opening
3041   multiple connections.
3044   In particular, while using multiple connections avoids the "head-of-line
3045   blocking" problem (whereby a request that takes significant server-side
3046   processing and/or has a large payload can block subsequent requests on the
3047   same connection), each connection used consumes server resources (sometimes
3048   significantly), and furthermore using multiple connections can cause
3049   undesirable side effects in congested networks.
3052   Note that servers might reject traffic that they deem abusive, including an
3053   excessive number of connections from a client.
3057<section title="Retrying Requests" anchor="persistent.retrying.requests">
3059   Senders can close the transport connection at any time. Therefore,
3060   clients, servers, and proxies &MUST; be able to recover
3061   from asynchronous close events. Client software &MAY; reopen the
3062   transport connection and retransmit the aborted sequence of requests
3063   without user interaction so long as the request sequence is
3064   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
3065   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
3066   human operator the choice of retrying the request(s). Confirmation by
3067   user-agent software with semantic understanding of the application
3068   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
3069   be repeated if the second sequence of requests fails.
3074<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
3076<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
3078   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
3079   flow control mechanisms to resolve temporary overloads, rather than
3080   terminating connections with the expectation that clients will retry.
3081   The latter technique can exacerbate network congestion.
3085<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
3087   An HTTP/1.1 (or later) client sending a message body &SHOULD; monitor
3088   the network connection for an error status code while it is transmitting
3089   the request. If the client sees an error status code, it &SHOULD;
3090   immediately cease transmitting the body. If the body is being sent
3091   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
3092   empty trailer &MAY; be used to prematurely mark the end of the message.
3093   If the body was preceded by a Content-Length header field, the client &MUST;
3094   close the connection.
3098<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
3100   The purpose of the <x:ref>100 (Continue)</x:ref> status code (see &status-100;)
3101   is to allow a client that is sending a request message with a request body
3102   to determine if the origin server is willing to accept the request
3103   (based on the request header fields) before the client sends the request
3104   body. In some cases, it might either be inappropriate or highly
3105   inefficient for the client to send the body if the server will reject
3106   the message without looking at the body.
3109   Requirements for HTTP/1.1 clients:
3110  <list style="symbols">
3111    <t>
3112        If a client will wait for a <x:ref>100 (Continue)</x:ref> response before
3113        sending the request body, it &MUST; send an <x:ref>Expect</x:ref> header
3114        field (&header-expect;) with the "100-continue" expectation.
3115    </t>
3116    <t>
3117        A client &MUST-NOT; send an <x:ref>Expect</x:ref> header field with
3118        the "100-continue" expectation if it does not intend to send a request
3119        body.
3120    </t>
3121  </list>
3124   Because of the presence of older implementations, the protocol allows
3125   ambiguous situations in which a client might send "Expect: 100-continue"
3126   without receiving either a <x:ref>417 (Expectation Failed)</x:ref>
3127   or a <x:ref>100 (Continue)</x:ref> status code. Therefore, when a client sends this
3128   header field to an origin server (possibly via a proxy) from which it
3129   has never seen a <x:ref>100 (Continue)</x:ref> status code, the client &SHOULD-NOT; 
3130   wait for an indefinite period before sending the request body.
3133   Requirements for HTTP/1.1 origin servers:
3134  <list style="symbols">
3135    <t> Upon receiving a request which includes an <x:ref>Expect</x:ref> header
3136        field with the "100-continue" expectation, an origin server &MUST;
3137        either respond with <x:ref>100 (Continue)</x:ref> status code and continue to read
3138        from the input stream, or respond with a final status code. The
3139        origin server &MUST-NOT; wait for the request body before sending
3140        the <x:ref>100 (Continue)</x:ref> response. If it responds with a final status
3141        code, it &MAY; close the transport connection or it &MAY; continue
3142        to read and discard the rest of the request.  It &MUST-NOT;
3143        perform the request method if it returns a final status code.
3144    </t>
3145    <t> An origin server &SHOULD-NOT;  send a <x:ref>100 (Continue)</x:ref> response if
3146        the request message does not include an <x:ref>Expect</x:ref> header
3147        field with the "100-continue" expectation, and &MUST-NOT; send a
3148        <x:ref>100 (Continue)</x:ref> response if such a request comes from an HTTP/1.0
3149        (or earlier) client. There is an exception to this rule: for
3150        compatibility with <xref target="RFC2068"/>, a server &MAY; send a <x:ref>100 (Continue)</x:ref>
3151        status code in response to an HTTP/1.1 PUT or POST request that does
3152        not include an Expect header field with the "100-continue"
3153        expectation. This exception, the purpose of which is
3154        to minimize any client processing delays associated with an
3155        undeclared wait for <x:ref>100 (Continue)</x:ref> status code, applies only to
3156        HTTP/1.1 requests, and not to requests with any other HTTP-version
3157        value.
3158    </t>
3159    <t> An origin server &MAY; omit a <x:ref>100 (Continue)</x:ref> response if it has
3160        already received some or all of the request body for the
3161        corresponding request.
3162    </t>
3163    <t> An origin server that sends a <x:ref>100 (Continue)</x:ref> response &MUST;
3164        ultimately send a final status code, once the request body is
3165        received and processed, unless it terminates the transport
3166        connection prematurely.
3167    </t>
3168    <t> If an origin server receives a request that does not include an
3169        <x:ref>Expect</x:ref> header field with the "100-continue" expectation,
3170        the request includes a request body, and the server responds
3171        with a final status code before reading the entire request body
3172        from the transport connection, then the server &SHOULD-NOT;  close
3173        the transport connection until it has read the entire request,
3174        or until the client closes the connection. Otherwise, the client
3175        might not reliably receive the response message. However, this
3176        requirement ought not be construed as preventing a server from
3177        defending itself against denial-of-service attacks, or from
3178        badly broken client implementations.
3179      </t>
3180    </list>
3183   Requirements for HTTP/1.1 proxies:
3184  <list style="symbols">
3185    <t> If a proxy receives a request that includes an <x:ref>Expect</x:ref>
3186        header field with the "100-continue" expectation, and the proxy
3187        either knows that the next-hop server complies with HTTP/1.1 or
3188        higher, or does not know the HTTP version of the next-hop
3189        server, it &MUST; forward the request, including the Expect header
3190        field.
3191    </t>
3192    <t> If the proxy knows that the version of the next-hop server is
3193        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
3194        respond with a <x:ref>417 (Expectation Failed)</x:ref> status code.
3195    </t>
3196    <t> Proxies &SHOULD; maintain a record of the HTTP version
3197        numbers received from recently-referenced next-hop servers.
3198    </t>
3199    <t> A proxy &MUST-NOT; forward a <x:ref>100 (Continue)</x:ref> response if the
3200        request message was received from an HTTP/1.0 (or earlier)
3201        client and did not include an <x:ref>Expect</x:ref> header field with
3202        the "100-continue" expectation. This requirement overrides the
3203        general rule for forwarding of <x:ref>1xx</x:ref> responses (see &status-1xx;).
3204    </t>
3205  </list>
3209<section title="Closing Connections on Error" anchor="closing.connections.on.error">
3211   If the client is sending data, a server implementation using TCP
3212   &SHOULD; be careful to ensure that the client acknowledges receipt of
3213   the packet(s) containing the response, before the server closes the
3214   input connection. If the client continues sending data to the server
3215   after the close, the server's TCP stack will send a reset packet to
3216   the client, which might erase the client's unacknowledged input buffers
3217   before they can be read and interpreted by the HTTP application.
3223<section title="Upgrade" anchor="header.upgrade">
3224  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3225  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3226  <x:anchor-alias value="Upgrade"/>
3227  <x:anchor-alias value="protocol"/>
3228  <x:anchor-alias value="protocol-name"/>
3229  <x:anchor-alias value="protocol-version"/>
3231   The "Upgrade" header field allows the client to specify what
3232   additional communication protocols it would like to use, if the server
3233   chooses to switch protocols. Servers can use it to indicate what protocols
3234   they are willing to switch to.
3236<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3237  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3239  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3240  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3241  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3244   For example,
3246<figure><artwork type="example">
3247  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3250   The Upgrade header field is intended to provide a simple mechanism
3251   for transitioning from HTTP/1.1 to some other, incompatible protocol. It
3252   does so by allowing the client to advertise its desire to use another
3253   protocol, such as a later version of HTTP with a higher major version
3254   number, even though the current request has been made using HTTP/1.1.
3255   This eases the difficult transition between incompatible protocols by
3256   allowing the client to initiate a request in the more commonly
3257   supported protocol while indicating to the server that it would like
3258   to use a "better" protocol if available (where "better" is determined
3259   by the server, possibly according to the nature of the request method
3260   or target resource).
3263   The Upgrade header field only applies to switching application-layer
3264   protocols upon the existing transport-layer connection. Upgrade
3265   cannot be used to insist on a protocol change; its acceptance and use
3266   by the server is optional. The capabilities and nature of the
3267   application-layer communication after the protocol change is entirely
3268   dependent upon the new protocol chosen, although the first action
3269   after changing the protocol &MUST; be a response to the initial HTTP
3270   request containing the Upgrade header field.
3273   The Upgrade header field only applies to the immediate connection.
3274   Therefore, the upgrade keyword &MUST; be supplied within a
3275   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
3276   whenever Upgrade is present in an HTTP/1.1 message.
3279   The Upgrade header field cannot be used to indicate a switch to a
3280   protocol on a different connection. For that purpose, it is more
3281   appropriate to use a <x:ref>3xx (Redirection)</x:ref> response (&status-3xx;).
3284   Servers &MUST; include the "Upgrade" header field in <x:ref>101 (Switching
3285   Protocols)</x:ref> responses to indicate which protocol(s) are being switched to,
3286   and &MUST; include it in <x:ref>426 (Upgrade Required)</x:ref> responses to indicate
3287   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3288   response to indicate that they are willing to upgrade to one of the
3289   specified protocols.
3292   This specification only defines the protocol name "HTTP" for use by
3293   the family of Hypertext Transfer Protocols, as defined by the HTTP
3294   version rules of <xref target="http.version"/> and future updates to this
3295   specification. Additional tokens can be registered with IANA using the
3296   registration procedure defined in <xref target="upgrade.token.registry"/>.
3302<section title="IANA Considerations" anchor="IANA.considerations">
3304<section title="Header Field Registration" anchor="header.field.registration">
3306   HTTP header fields are registered within the Message Header Field Registry
3307   <xref target="RFC3864"/> maintained by IANA at
3308   <eref target=""/>.
3311   This document defines the following HTTP header fields, so their
3312   associated registry entries shall be updated according to the permanent
3313   registrations below:
3315<?BEGININC p1-messaging.iana-headers ?>
3316<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3317<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3318   <ttcol>Header Field Name</ttcol>
3319   <ttcol>Protocol</ttcol>
3320   <ttcol>Status</ttcol>
3321   <ttcol>Reference</ttcol>
3323   <c>Connection</c>
3324   <c>http</c>
3325   <c>standard</c>
3326   <c>
3327      <xref target="header.connection"/>
3328   </c>
3329   <c>Content-Length</c>
3330   <c>http</c>
3331   <c>standard</c>
3332   <c>
3333      <xref target="header.content-length"/>
3334   </c>
3335   <c>Host</c>
3336   <c>http</c>
3337   <c>standard</c>
3338   <c>
3339      <xref target=""/>
3340   </c>
3341   <c>TE</c>
3342   <c>http</c>
3343   <c>standard</c>
3344   <c>
3345      <xref target="header.te"/>
3346   </c>
3347   <c>Trailer</c>
3348   <c>http</c>
3349   <c>standard</c>
3350   <c>
3351      <xref target="header.trailer"/>
3352   </c>
3353   <c>Transfer-Encoding</c>
3354   <c>http</c>
3355   <c>standard</c>
3356   <c>
3357      <xref target="header.transfer-encoding"/>
3358   </c>
3359   <c>Upgrade</c>
3360   <c>http</c>
3361   <c>standard</c>
3362   <c>
3363      <xref target="header.upgrade"/>
3364   </c>
3365   <c>Via</c>
3366   <c>http</c>
3367   <c>standard</c>
3368   <c>
3369      <xref target="header.via"/>
3370   </c>
3373<?ENDINC p1-messaging.iana-headers ?>
3375   Furthermore, the header field-name "Close" shall be registered as
3376   "reserved", since using that name as an HTTP header field might
3377   conflict with the "close" connection option of the "<x:ref>Connection</x:ref>"
3378   header field (<xref target="header.connection"/>).
3380<texttable align="left" suppress-title="true">
3381   <ttcol>Header Field Name</ttcol>
3382   <ttcol>Protocol</ttcol>
3383   <ttcol>Status</ttcol>
3384   <ttcol>Reference</ttcol>
3386   <c>Close</c>
3387   <c>http</c>
3388   <c>reserved</c>
3389   <c>
3390      <xref target="header.field.registration"/>
3391   </c>
3394   The change controller is: "IETF ( - Internet Engineering Task Force".
3398<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3400   IANA maintains the registry of URI Schemes <xref target="RFC4395"/> at
3401   <eref target=""/>.
3404   This document defines the following URI schemes, so their
3405   associated registry entries shall be updated according to the permanent
3406   registrations below:
3408<texttable align="left" suppress-title="true">
3409   <ttcol>URI Scheme</ttcol>
3410   <ttcol>Description</ttcol>
3411   <ttcol>Reference</ttcol>
3413   <c>http</c>
3414   <c>Hypertext Transfer Protocol</c>
3415   <c><xref target="http.uri"/></c>
3417   <c>https</c>
3418   <c>Hypertext Transfer Protocol Secure</c>
3419   <c><xref target="https.uri"/></c>
3423<section title="Internet Media Type Registrations" anchor="">
3425   This document serves as the specification for the Internet media types
3426   "message/http" and "application/http". The following is to be registered with
3427   IANA (see <xref target="RFC4288"/>).
3429<section title="Internet Media Type message/http" anchor="">
3430<iref item="Media Type" subitem="message/http" primary="true"/>
3431<iref item="message/http Media Type" primary="true"/>
3433   The message/http type can be used to enclose a single HTTP request or
3434   response message, provided that it obeys the MIME restrictions for all
3435   "message" types regarding line length and encodings.
3438  <list style="hanging" x:indent="12em">
3439    <t hangText="Type name:">
3440      message
3441    </t>
3442    <t hangText="Subtype name:">
3443      http
3444    </t>
3445    <t hangText="Required parameters:">
3446      none
3447    </t>
3448    <t hangText="Optional parameters:">
3449      version, msgtype
3450      <list style="hanging">
3451        <t hangText="version:">
3452          The HTTP-version number of the enclosed message
3453          (e.g., "1.1"). If not present, the version can be
3454          determined from the first line of the body.
3455        </t>
3456        <t hangText="msgtype:">
3457          The message type &mdash; "request" or "response". If not
3458          present, the type can be determined from the first
3459          line of the body.
3460        </t>
3461      </list>
3462    </t>
3463    <t hangText="Encoding considerations:">
3464      only "7bit", "8bit", or "binary" are permitted
3465    </t>
3466    <t hangText="Security considerations:">
3467      none
3468    </t>
3469    <t hangText="Interoperability considerations:">
3470      none
3471    </t>
3472    <t hangText="Published specification:">
3473      This specification (see <xref target=""/>).
3474    </t>
3475    <t hangText="Applications that use this media type:">
3476    </t>
3477    <t hangText="Additional information:">
3478      <list style="hanging">
3479        <t hangText="Magic number(s):">none</t>
3480        <t hangText="File extension(s):">none</t>
3481        <t hangText="Macintosh file type code(s):">none</t>
3482      </list>
3483    </t>
3484    <t hangText="Person and email address to contact for further information:">
3485      See Authors Section.
3486    </t>
3487    <t hangText="Intended usage:">
3488      COMMON
3489    </t>
3490    <t hangText="Restrictions on usage:">
3491      none
3492    </t>
3493    <t hangText="Author/Change controller:">
3494      IESG
3495    </t>
3496  </list>
3499<section title="Internet Media Type application/http" anchor="">
3500<iref item="Media Type" subitem="application/http" primary="true"/>
3501<iref item="application/http Media Type" primary="true"/>
3503   The application/http type can be used to enclose a pipeline of one or more
3504   HTTP request or response messages (not intermixed).
3507  <list style="hanging" x:indent="12em">
3508    <t hangText="Type name:">
3509      application
3510    </t>
3511    <t hangText="Subtype name:">
3512      http
3513    </t>
3514    <t hangText="Required parameters:">
3515      none
3516    </t>
3517    <t hangText="Optional parameters:">
3518      version, msgtype
3519      <list style="hanging">
3520        <t hangText="version:">
3521          The HTTP-version number of the enclosed messages
3522          (e.g., "1.1"). If not present, the version can be
3523          determined from the first line of the body.
3524        </t>
3525        <t hangText="msgtype:">
3526          The message type &mdash; "request" or "response". If not
3527          present, the type can be determined from the first
3528          line of the body.
3529        </t>
3530      </list>
3531    </t>
3532    <t hangText="Encoding considerations:">
3533      HTTP messages enclosed by this type
3534      are in "binary" format; use of an appropriate
3535      Content-Transfer-Encoding is required when
3536      transmitted via E-mail.
3537    </t>
3538    <t hangText="Security considerations:">
3539      none
3540    </t>
3541    <t hangText="Interoperability considerations:">
3542      none
3543    </t>
3544    <t hangText="Published specification:">
3545      This specification (see <xref target=""/>).
3546    </t>
3547    <t hangText="Applications that use this media type:">
3548    </t>
3549    <t hangText="Additional information:">
3550      <list style="hanging">
3551        <t hangText="Magic number(s):">none</t>
3552        <t hangText="File extension(s):">none</t>
3553        <t hangText="Macintosh file type code(s):">none</t>
3554      </list>
3555    </t>
3556    <t hangText="Person and email address to contact for further information:">
3557      See Authors Section.
3558    </t>
3559    <t hangText="Intended usage:">
3560      COMMON
3561    </t>
3562    <t hangText="Restrictions on usage:">
3563      none
3564    </t>
3565    <t hangText="Author/Change controller:">
3566      IESG
3567    </t>
3568  </list>
3573<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3575   The HTTP Transfer Coding Registry defines the name space for transfer
3576   coding names.
3579   Registrations &MUST; include the following fields:
3580   <list style="symbols">
3581     <t>Name</t>
3582     <t>Description</t>
3583     <t>Pointer to specification text</t>
3584   </list>
3587   Names of transfer codings &MUST-NOT; overlap with names of content codings
3588   (&content-codings;) unless the encoding transformation is identical, as it
3589   is the case for the compression codings defined in
3590   <xref target="compression.codings"/>.
3593   Values to be added to this name space require IETF Review (see
3594   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3595   conform to the purpose of transfer coding defined in this section.
3598   The registry itself is maintained at
3599   <eref target=""/>.
3603<section title="Transfer Coding Registrations" anchor="transfer.coding.registration">
3605   The HTTP Transfer Coding Registry shall be updated with the registrations
3606   below:
3608<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3609   <ttcol>Name</ttcol>
3610   <ttcol>Description</ttcol>
3611   <ttcol>Reference</ttcol>
3612   <c>chunked</c>
3613   <c>Transfer in a series of chunks</c>
3614   <c>
3615      <xref target="chunked.encoding"/>
3616   </c>
3617   <c>compress</c>
3618   <c>UNIX "compress" program method</c>
3619   <c>
3620      <xref target="compress.coding"/>
3621   </c>
3622   <c>deflate</c>
3623   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3624   the "zlib" data format (<xref target="RFC1950"/>)
3625   </c>
3626   <c>
3627      <xref target="deflate.coding"/>
3628   </c>
3629   <c>gzip</c>
3630   <c>Same as GNU zip <xref target="RFC1952"/></c>
3631   <c>
3632      <xref target="gzip.coding"/>
3633   </c>
3637<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3639   The HTTP Upgrade Token Registry defines the name space for protocol-name
3640   tokens used to identify protocols in the <x:ref>Upgrade</x:ref> header
3641   field. Each registered protocol name is associated with contact information
3642   and an optional set of specifications that details how the connection
3643   will be processed after it has been upgraded.
3646   Registrations happen on a "First Come First Served" basis (see
3647   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3648   following rules:
3649  <list style="numbers">
3650    <t>A protocol-name token, once registered, stays registered forever.</t>
3651    <t>The registration &MUST; name a responsible party for the
3652       registration.</t>
3653    <t>The registration &MUST; name a point of contact.</t>
3654    <t>The registration &MAY; name a set of specifications associated with
3655       that token. Such specifications need not be publicly available.</t>
3656    <t>The registration &SHOULD; name a set of expected "protocol-version"
3657       tokens associated with that token at the time of registration.</t>
3658    <t>The responsible party &MAY; change the registration at any time.
3659       The IANA will keep a record of all such changes, and make them
3660       available upon request.</t>
3661    <t>The IESG &MAY; reassign responsibility for a protocol token.
3662       This will normally only be used in the case when a
3663       responsible party cannot be contacted.</t>
3664  </list>
3667   This registration procedure for HTTP Upgrade Tokens replaces that
3668   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3672<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3674   The HTTP Upgrade Token Registry shall be updated with the registration
3675   below:
3677<texttable align="left" suppress-title="true">
3678   <ttcol>Value</ttcol>
3679   <ttcol>Description</ttcol>
3680   <ttcol>Expected Version Tokens</ttcol>
3681   <ttcol>Reference</ttcol>
3683   <c>HTTP</c>
3684   <c>Hypertext Transfer Protocol</c>
3685   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3686   <c><xref target="http.version"/></c>
3689   The responsible party is: "IETF ( - Internet Engineering Task Force".
3695<section title="Security Considerations" anchor="security.considerations">
3697   This section is meant to inform application developers, information
3698   providers, and users of the security limitations in HTTP/1.1 as
3699   described by this document. The discussion does not include
3700   definitive solutions to the problems revealed, though it does make
3701   some suggestions for reducing security risks.
3704<section title="Personal Information" anchor="personal.information">
3706   HTTP clients are often privy to large amounts of personal information
3707   (e.g., the user's name, location, mail address, passwords, encryption
3708   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3709   leakage of this information.
3710   We very strongly recommend that a convenient interface be provided
3711   for the user to control dissemination of such information, and that
3712   designers and implementers be particularly careful in this area.
3713   History shows that errors in this area often create serious security
3714   and/or privacy problems and generate highly adverse publicity for the
3715   implementer's company.
3719<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3721   A server is in the position to save personal data about a user's
3722   requests which might identify their reading patterns or subjects of
3723   interest.  In particular, log information gathered at an intermediary
3724   often contains a history of user agent interaction, across a multitude
3725   of sites, that can be traced to individual users.
3728   HTTP log information is confidential in nature; its handling is often
3729   constrained by laws and regulations.  Log information needs to be securely
3730   stored and appropriate guidelines followed for its analysis.
3731   Anonymization of personal information within individual entries helps,
3732   but is generally not sufficient to prevent real log traces from being
3733   re-identified based on correlation with other access characteristics.
3734   As such, access traces that are keyed to a specific client should not
3735   be published even if the key is pseudonymous.
3738   To minimize the risk of theft or accidental publication, log information
3739   should be purged of personally identifiable information, including
3740   user identifiers, IP addresses, and user-provided query parameters,
3741   as soon as that information is no longer necessary to support operational
3742   needs for security, auditing, or fraud control.
3746<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3748   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3749   the documents returned by HTTP requests to be only those that were
3750   intended by the server administrators. If an HTTP server translates
3751   HTTP URIs directly into file system calls, the server &MUST; take
3752   special care not to serve files that were not intended to be
3753   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3754   other operating systems use ".." as a path component to indicate a
3755   directory level above the current one. On such a system, an HTTP
3756   server &MUST; disallow any such construct in the request-target if it
3757   would otherwise allow access to a resource outside those intended to
3758   be accessible via the HTTP server. Similarly, files intended for
3759   reference only internally to the server (such as access control
3760   files, configuration files, and script code) &MUST; be protected from
3761   inappropriate retrieval, since they might contain sensitive
3762   information. Experience has shown that minor bugs in such HTTP server
3763   implementations have turned into security risks.
3767<section title="DNS-related Attacks" anchor="dns.related.attacks">
3769   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3770   generally prone to security attacks based on the deliberate misassociation
3771   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3772   cautious in assuming the validity of an IP number/DNS name association unless
3773   the response is protected by DNSSec (<xref target="RFC4033"/>).
3777<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3779   By their very nature, HTTP intermediaries are men-in-the-middle, and
3780   represent an opportunity for man-in-the-middle attacks. Compromise of
3781   the systems on which the intermediaries run can result in serious security
3782   and privacy problems. Intermediaries have access to security-related
3783   information, personal information about individual users and
3784   organizations, and proprietary information belonging to users and
3785   content providers. A compromised intermediary, or an intermediary
3786   implemented or configured without regard to security and privacy
3787   considerations, might be used in the commission of a wide range of
3788   potential attacks.
3791   Intermediaries that contain a shared cache are especially vulnerable
3792   to cache poisoning attacks.
3795   Implementers need to consider the privacy and security
3796   implications of their design and coding decisions, and of the
3797   configuration options they provide to operators (especially the
3798   default configuration).
3801   Users need to be aware that intermediaries are no more trustworthy than
3802   the people who run them; HTTP itself cannot solve this problem.
3805   The judicious use of cryptography, when appropriate, might suffice to
3806   protect against a broad range of security and privacy attacks. Such
3807   cryptography is beyond the scope of the HTTP/1.1 specification.
3811<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3813   Because HTTP uses mostly textual, character-delimited fields, attackers can
3814   overflow buffers in implementations, and/or perform a Denial of Service
3815   against implementations that accept fields with unlimited lengths.
3818   To promote interoperability, this specification makes specific
3819   recommendations for minimum size limits on request-line
3820   (<xref target="request.line"/>)
3821   and blocks of header fields (<xref target="header.fields"/>). These are
3822   minimum recommendations, chosen to be supportable even by implementations
3823   with limited resources; it is expected that most implementations will
3824   choose substantially higher limits.
3827   This specification also provides a way for servers to reject messages that
3828   have request-targets that are too long (&status-414;) or request entities
3829   that are too large (&status-4xx;).
3832   Other fields (including but not limited to request methods, response status
3833   phrases, header field-names, and body chunks) &SHOULD; be limited by
3834   implementations carefully, so as to not impede interoperability.
3839<section title="Acknowledgments" anchor="acks">
3841   This edition of HTTP builds on the many contributions that went into
3842   <xref target="RFC1945" format="none">RFC 1945</xref>,
3843   <xref target="RFC2068" format="none">RFC 2068</xref>,
3844   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3845   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3846   substantial contributions made by the previous authors, editors, and
3847   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3848   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3849   Paul J. Leach, and Mark Nottingham.
3850   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
3851   acknowledgements from prior revisions.
3854   Since 1999, the following contributors have helped improve the HTTP
3855   specification by reporting bugs, asking smart questions, drafting or
3856   reviewing text, and evaluating open issues:
3858<?BEGININC acks ?>
3859<t>Adam Barth,
3860Adam Roach,
3861Addison Phillips,
3862Adrian Chadd,
3863Adrien W. de Croy,
3864Alan Ford,
3865Alan Ruttenberg,
3866Albert Lunde,
3867Alek Storm,
3868Alex Rousskov,
3869Alexandre Morgaut,
3870Alexey Melnikov,
3871Alisha Smith,
3872Amichai Rothman,
3873Amit Klein,
3874Amos Jeffries,
3875Andreas Maier,
3876Andreas Petersson,
3877Anne van Kesteren,
3878Anthony Bryan,
3879Asbjorn Ulsberg,
3880Balachander Krishnamurthy,
3881Barry Leiba,
3882Ben Laurie,
3883Benjamin Niven-Jenkins,
3884Bil Corry,
3885Bill Burke,
3886Bjoern Hoehrmann,
3887Bob Scheifler,
3888Boris Zbarsky,
3889Brett Slatkin,
3890Brian Kell,
3891Brian McBarron,
3892Brian Pane,
3893Brian Smith,
3894Bryce Nesbitt,
3895Cameron Heavon-Jones,
3896Carl Kugler,
3897Carsten Bormann,
3898Charles Fry,
3899Chris Newman,
3900Cyrus Daboo,
3901Dale Robert Anderson,
3902Dan Winship,
3903Daniel Stenberg,
3904Dave Cridland,
3905Dave Crocker,
3906Dave Kristol,
3907David Booth,
3908David Singer,
3909David W. Morris,
3910Diwakar Shetty,
3911Dmitry Kurochkin,
3912Drummond Reed,
3913Duane Wessels,
3914Edward Lee,
3915Eliot Lear,
3916Eran Hammer-Lahav,
3917Eric D. Williams,
3918Eric J. Bowman,
3919Eric Lawrence,
3920Eric Rescorla,
3921Erik Aronesty,
3922Florian Weimer,
3923Frank Ellermann,
3924Fred Bohle,
3925Geoffrey Sneddon,
3926Gervase Markham,
3927Greg Wilkins,
3928Harald Tveit Alvestrand,
3929Harry Halpin,
3930Helge Hess,
3931Henrik Nordstrom,
3932Henry S. Thompson,
3933Henry Story,
3934Herbert van de Sompel,
3935Howard Melman,
3936Hugo Haas,
3937Ian Hickson,
3938Ingo Struck,
3939J. Ross Nicoll,
3940James H. Manger,
3941James Lacey,
3942James M. Snell,
3943Jamie Lokier,
3944Jan Algermissen,
3945Jeff Hodges (who came up with the term 'effective Request-URI'),
3946Jeff Walden,
3947Jim Luther,
3948Joe D. Williams,
3949Joe Gregorio,
3950Joe Orton,
3951John C. Klensin,
3952John C. Mallery,
3953John Cowan,
3954John Kemp,
3955John Panzer,
3956John Schneider,
3957John Stracke,
3958John Sullivan,
3959Jonas Sicking,
3960Jonathan Billington,
3961Jonathan Moore,
3962Jonathan Rees,
3963Jonathan Silvera,
3964Jordi Ros,
3965Joris Dobbelsteen,
3966Josh Cohen,
3967Julien Pierre,
3968Jungshik Shin,
3969Justin Chapweske,
3970Justin Erenkrantz,
3971Justin James,
3972Kalvinder Singh,
3973Karl Dubost,
3974Keith Hoffman,
3975Keith Moore,
3976Koen Holtman,
3977Konstantin Voronkov,
3978Kris Zyp,
3979Lisa Dusseault,
3980Maciej Stachowiak,
3981Marc Schneider,
3982Marc Slemko,
3983Mark Baker,
3984Mark Pauley,
3985Mark Watson,
3986Markus Isomaki,
3987Markus Lanthaler,
3988Martin J. Duerst,
3989Martin Musatov,
3990Martin Nilsson,
3991Martin Thomson,
3992Matt Lynch,
3993Matthew Cox,
3994Max Clark,
3995Michael Burrows,
3996Michael Hausenblas,
3997Mike Amundsen,
3998Mike Belshe,
3999Mike Kelly,
4000Mike Schinkel,
4001Miles Sabin,
4002Murray S. Kucherawy,
4003Mykyta Yevstifeyev,
4004Nathan Rixham,
4005Nicholas Shanks,
4006Nico Williams,
4007Nicolas Alvarez,
4008Nicolas Mailhot,
4009Noah Slater,
4010Pablo Castro,
4011Pat Hayes,
4012Patrick R. McManus,
4013Paul E. Jones,
4014Paul Hoffman,
4015Paul Marquess,
4016Peter Lepeska,
4017Peter Saint-Andre,
4018Peter Watkins,
4019Phil Archer,
4020Phillip Hallam-Baker,
4021Poul-Henning Kamp,
4022Preethi Natarajan,
4023Ray Polk,
4024Reto Bachmann-Gmuer,
4025Richard Cyganiak,
4026Robert Brewer,
4027Robert Collins,
4028Robert O'Callahan,
4029Robert Olofsson,
4030Robert Sayre,
4031Robert Siemer,
4032Robert de Wilde,
4033Roberto Javier Godoy,
4034Roberto Peon,
4035Ronny Widjaja,
4036S. Mike Dierken,
4037Salvatore Loreto,
4038Sam Johnston,
4039Sam Ruby,
4040Scott Lawrence (who maintained the original issues list),
4041Sean B. Palmer,
4042Shane McCarron,
4043Stefan Eissing,
4044Stefan Tilkov,
4045Stefanos Harhalakis,
4046Stephane Bortzmeyer,
4047Stephen Farrell,
4048Stephen Ludin,
4049Stuart Williams,
4050Subbu Allamaraju,
4051Sylvain Hellegouarch,
4052Tapan Divekar,
4053Tatsuya Hayashi,
4054Ted Hardie,
4055Thomas Broyer,
4056Thomas Nordin,
4057Thomas Roessler,
4058Tim Bray,
4059Tim Morgan,
4060Tim Olsen,
4061Tom Zhou,
4062Travis Snoozy,
4063Tyler Close,
4064Vincent Murphy,
4065Wenbo Zhu,
4066Werner Baumann,
4067Wilbur Streett,
4068Wilfredo Sanchez Vega,
4069William A. Rowe Jr.,
4070William Chan,
4071Willy Tarreau,
4072Xiaoshu Wang,
4073Yaron Goland,
4074Yngve Nysaeter Pettersen,
4075Yoav Nir,
4076Yogesh Bang,
4077Yutaka Oiwa,
4078Zed A. Shaw, and
4079Zhong Yu.
4081<?ENDINC acks ?>
4087<references title="Normative References">
4089<reference anchor="Part2">
4090  <front>
4091    <title>HTTP/1.1, part 2: Semantics and Payloads</title>
4092    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4093      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4094      <address><email></email></address>
4095    </author>
4096    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4097      <organization abbrev="W3C">World Wide Web Consortium</organization>
4098      <address><email></email></address>
4099    </author>
4100    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4101      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4102      <address><email></email></address>
4103    </author>
4104    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4105  </front>
4106  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4107  <x:source href="p2-semantics.xml" basename="p2-semantics">
4108    <x:defines>1xx (Informational)</x:defines>
4109    <x:defines>1xx</x:defines>
4110    <x:defines>100 (Continue)</x:defines>
4111    <x:defines>101 (Switching Protocols)</x:defines>
4112    <x:defines>2xx (Successful)</x:defines>
4113    <x:defines>2xx</x:defines>
4114    <x:defines>200 (OK)</x:defines>
4115    <x:defines>204 (No Content)</x:defines>
4116    <x:defines>3xx (Redirection)</x:defines>
4117    <x:defines>3xx</x:defines>
4118    <x:defines>301 (Moved Permanently)</x:defines>
4119    <x:defines>4xx (Client Error)</x:defines>
4120    <x:defines>4xx</x:defines>
4121    <x:defines>400 (Bad Request)</x:defines>
4122    <x:defines>405 (Method Not Allowed)</x:defines>
4123    <x:defines>411 (Length Required)</x:defines>
4124    <x:defines>414 (URI Too Long)</x:defines>
4125    <x:defines>417 (Expectation Failed)</x:defines>
4126    <x:defines>426 (Upgrade Required)</x:defines>
4127    <x:defines>501 (Not Implemented)</x:defines>
4128    <x:defines>502 (Bad Gateway)</x:defines>
4129    <x:defines>505 (HTTP Version Not Supported)</x:defines>
4130    <x:defines>Allow</x:defines>
4131    <x:defines>Content-Encoding</x:defines>
4132    <x:defines>Content-Location</x:defines>
4133    <x:defines>Content-Type</x:defines>
4134    <x:defines>Date</x:defines>
4135    <x:defines>Expect</x:defines>
4136    <x:defines>Location</x:defines>
4137    <x:defines>Server</x:defines>
4138    <x:defines>User-Agent</x:defines>
4139  </x:source>
4142<reference anchor="Part4">
4143  <front>
4144    <title>HTTP/1.1, part 4: Conditional Requests</title>
4145    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
4146      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4147      <address><email></email></address>
4148    </author>
4149    <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
4150      <organization abbrev="W3C">World Wide Web Consortium</organization>
4151      <address><email></email></address>
4152    </author>
4153    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
4154      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4155      <address><email></email></address>
4156    </author>
4157    <date month="&ID-MONTH;" year="&ID-YEAR;" />
4158  </front>
4159  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;" />
4160  <x:source basename="p4-conditional" href="p4-conditional.xml">
4161    <x:defines>304 (Not Modified)</x:defines>
4162    <x:defines>ETag</x:defines>
4163    <x:defines>Last-Modified</x:defines>
4164  </x:source>
4167<reference anchor="Part5">
4168  <front>
4169    <title>HTTP/1.1, part 5: Range Requests</title>
4170    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4171      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4172      <address><email></email></address>
4173    </author>
4174    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4175      <organization abbrev="W3C">World Wide Web Consortium</organization>
4176      <address><email></email></address>
4177    </author>
4178    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4179      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4180      <address><email></email></address>
4181    </author>
4182    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4183  </front>
4184  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
4185  <x:source href="p5-range.xml" basename="p5-range">
4186    <x:defines>Content-Range</x:defines>
4187  </x:source>
4190<reference anchor="Part6">
4191  <front>
4192    <title>HTTP/1.1, part 6: Caching</title>
4193    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4194      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4195      <address><email></email></address>
4196    </author>
4197    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4198      <organization abbrev="W3C">World Wide Web Consortium</organization>
4199      <address><email></email></address>
4200    </author>
4201    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4202      <organization>Rackspace</organization>
4203      <address><email></email></address>
4204    </author>
4205    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4206      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4207      <address><email></email></address>
4208    </author>
4209    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4210  </front>
4211  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4212  <x:source href="p6-cache.xml" basename="p6-cache">
4213    <x:defines>Expires</x:defines>
4214  </x:source>
4217<reference anchor="Part7">
4218  <front>
4219    <title>HTTP/1.1, part 7: Authentication</title>
4220    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4221      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4222      <address><email></email></address>
4223    </author>
4224    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4225      <organization abbrev="W3C">World Wide Web Consortium</organization>
4226      <address><email></email></address>
4227    </author>
4228    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4229      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4230      <address><email></email></address>
4231    </author>
4232    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4233  </front>
4234  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
4235  <x:source href="p7-auth.xml" basename="p7-auth">
4236    <x:defines>Proxy-Authenticate</x:defines>
4237    <x:defines>Proxy-Authorization</x:defines>
4238  </x:source>
4241<reference anchor="RFC5234">
4242  <front>
4243    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4244    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4245      <organization>Brandenburg InternetWorking</organization>
4246      <address>
4247        <email></email>
4248      </address> 
4249    </author>
4250    <author initials="P." surname="Overell" fullname="Paul Overell">
4251      <organization>THUS plc.</organization>
4252      <address>
4253        <email></email>
4254      </address>
4255    </author>
4256    <date month="January" year="2008"/>
4257  </front>
4258  <seriesInfo name="STD" value="68"/>
4259  <seriesInfo name="RFC" value="5234"/>
4262<reference anchor="RFC2119">
4263  <front>
4264    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4265    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4266      <organization>Harvard University</organization>
4267      <address><email></email></address>
4268    </author>
4269    <date month="March" year="1997"/>
4270  </front>
4271  <seriesInfo name="BCP" value="14"/>
4272  <seriesInfo name="RFC" value="2119"/>
4275<reference anchor="RFC3986">
4276 <front>
4277  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4278  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4279    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4280    <address>
4281       <email></email>
4282       <uri></uri>
4283    </address>
4284  </author>
4285  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4286    <organization abbrev="Day Software">Day Software</organization>
4287    <address>
4288      <email></email>
4289      <uri></uri>
4290    </address>
4291  </author>
4292  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4293    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4294    <address>
4295      <email></email>
4296      <uri></uri>
4297    </address>
4298  </author>
4299  <date month='January' year='2005'></date>
4300 </front>
4301 <seriesInfo name="STD" value="66"/>
4302 <seriesInfo name="RFC" value="3986"/>
4305<reference anchor="USASCII">
4306  <front>
4307    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4308    <author>
4309      <organization>American National Standards Institute</organization>
4310    </author>
4311    <date year="1986"/>
4312  </front>
4313  <seriesInfo name="ANSI" value="X3.4"/>
4316<reference anchor="RFC1950">
4317  <front>
4318    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4319    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4320      <organization>Aladdin Enterprises</organization>
4321      <address><email></email></address>
4322    </author>
4323    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4324    <date month="May" year="1996"/>
4325  </front>
4326  <seriesInfo name="RFC" value="1950"/>
4327  <!--<annotation>
4328    RFC 1950 is an Informational RFC, thus it might be less stable than
4329    this specification. On the other hand, this downward reference was
4330    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4331    therefore it is unlikely to cause problems in practice. See also
4332    <xref target="BCP97"/>.
4333  </annotation>-->
4336<reference anchor="RFC1951">
4337  <front>
4338    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4339    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4340      <organization>Aladdin Enterprises</organization>
4341      <address><email></email></address>
4342    </author>
4343    <date month="May" year="1996"/>
4344  </front>
4345  <seriesInfo name="RFC" value="1951"/>
4346  <!--<annotation>
4347    RFC 1951 is an Informational RFC, thus it might be less stable than
4348    this specification. On the other hand, this downward reference was
4349    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4350    therefore it is unlikely to cause problems in practice. See also
4351    <xref target="BCP97"/>.
4352  </annotation>-->
4355<reference anchor="RFC1952">
4356  <front>
4357    <title>GZIP file format specification version 4.3</title>
4358    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4359      <organization>Aladdin Enterprises</organization>
4360      <address><email></email></address>
4361    </author>
4362    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4363      <address><email></email></address>
4364    </author>
4365    <author initials="M." surname="Adler" fullname="Mark Adler">
4366      <address><email></email></address>
4367    </author>
4368    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4369      <address><email></email></address>
4370    </author>
4371    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4372      <address><email></email></address>
4373    </author>
4374    <date month="May" year="1996"/>
4375  </front>
4376  <seriesInfo name="RFC" value="1952"/>
4377  <!--<annotation>
4378    RFC 1952 is an Informational RFC, thus it might be less stable than
4379    this specification. On the other hand, this downward reference was
4380    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4381    therefore it is unlikely to cause problems in practice. See also
4382    <xref target="BCP97"/>.
4383  </annotation>-->
4388<references title="Informative References">
4390<reference anchor="ISO-8859-1">
4391  <front>
4392    <title>
4393     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4394    </title>
4395    <author>
4396      <organization>International Organization for Standardization</organization>
4397    </author>
4398    <date year="1998"/>
4399  </front>
4400  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4403<reference anchor="Nie1997" target="">
4404  <front>
4405    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4406    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4407    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4408    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4409    <author initials="H." surname="Lie" fullname="H. Lie"/>
4410    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4411    <date year="1997" month="September"/>
4412  </front>
4413  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4416<reference anchor="Pad1995" target="">
4417  <front>
4418    <title>Improving HTTP Latency</title>
4419    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4420    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4421    <date year="1995" month="December"/>
4422  </front>
4423  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4426<reference anchor='RFC1919'>
4427  <front>
4428    <title>Classical versus Transparent IP Proxies</title>
4429    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4430      <address><email></email></address>
4431    </author>
4432    <date year='1996' month='March' />
4433  </front>
4434  <seriesInfo name='RFC' value='1919' />
4437<reference anchor="RFC1945">
4438  <front>
4439    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4440    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4441      <organization>MIT, Laboratory for Computer Science</organization>
4442      <address><email></email></address>
4443    </author>
4444    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4445      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4446      <address><email></email></address>
4447    </author>
4448    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4449      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4450      <address><email></email></address>
4451    </author>
4452    <date month="May" year="1996"/>
4453  </front>
4454  <seriesInfo name="RFC" value="1945"/>
4457<reference anchor="RFC2045">
4458  <front>
4459    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4460    <author initials="N." surname="Freed" fullname="Ned Freed">
4461      <organization>Innosoft International, Inc.</organization>
4462      <address><email></email></address>
4463    </author>
4464    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4465      <organization>First Virtual Holdings</organization>
4466      <address><email></email></address>
4467    </author>
4468    <date month="November" year="1996"/>
4469  </front>
4470  <seriesInfo name="RFC" value="2045"/>
4473<reference anchor="RFC2047">
4474  <front>
4475    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4476    <author initials="K." surname="Moore" fullname="Keith Moore">
4477      <organization>University of Tennessee</organization>
4478      <address><email></email></address>
4479    </author>
4480    <date month="November" year="1996"/>
4481  </front>
4482  <seriesInfo name="RFC" value="2047"/>
4485<reference anchor="RFC2068">
4486  <front>
4487    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4488    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4489      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4490      <address><email></email></address>
4491    </author>
4492    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4493      <organization>MIT Laboratory for Computer Science</organization>
4494      <address><email></email></address>
4495    </author>
4496    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4497      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4498      <address><email></email></address>
4499    </author>
4500    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4501      <organization>MIT Laboratory for Computer Science</organization>
4502      <address><email></email></address>
4503    </author>
4504    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4505      <organization>MIT Laboratory for Computer Science</organization>
4506      <address><email></email></address>
4507    </author>
4508    <date month="January" year="1997"/>
4509  </front>
4510  <seriesInfo name="RFC" value="2068"/>
4513<reference anchor="RFC2145">
4514  <front>
4515    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4516    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4517      <organization>Western Research Laboratory</organization>
4518      <address><email></email></address>
4519    </author>
4520    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4521      <organization>Department of Information and Computer Science</organization>
4522      <address><email></email></address>
4523    </author>
4524    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4525      <organization>MIT Laboratory for Computer Science</organization>
4526      <address><email></email></address>
4527    </author>
4528    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4529      <organization>W3 Consortium</organization>
4530      <address><email></email></address>
4531    </author>
4532    <date month="May" year="1997"/>
4533  </front>
4534  <seriesInfo name="RFC" value="2145"/>
4537<reference anchor="RFC2616">
4538  <front>
4539    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4540    <author initials="R." surname="Fielding" fullname="R. Fielding">
4541      <organization>University of California, Irvine</organization>
4542      <address><email></email></address>
4543    </author>
4544    <author initials="J." surname="Gettys" fullname="J. Gettys">
4545      <organization>W3C</organization>
4546      <address><email></email></address>
4547    </author>
4548    <author initials="J." surname="Mogul" fullname="J. Mogul">
4549      <organization>Compaq Computer Corporation</organization>
4550      <address><email></email></address>
4551    </author>
4552    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4553      <organization>MIT Laboratory for Computer Science</organization>
4554      <address><email></email></address>
4555    </author>
4556    <author initials="L." surname="Masinter" fullname="L. Masinter">
4557      <organization>Xerox Corporation</organization>
4558      <address><email></email></address>
4559    </author>
4560    <author initials="P." surname="Leach" fullname="P. Leach">
4561      <organization>Microsoft Corporation</organization>
4562      <address><email></email></address>
4563    </author>
4564    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4565      <organization>W3C</organization>
4566      <address><email></email></address>
4567    </author>
4568    <date month="June" year="1999"/>
4569  </front>
4570  <seriesInfo name="RFC" value="2616"/>
4573<reference anchor='RFC2817'>
4574  <front>
4575    <title>Upgrading to TLS Within HTTP/1.1</title>
4576    <author initials='R.' surname='Khare' fullname='R. Khare'>
4577      <organization>4K Associates / UC Irvine</organization>
4578      <address><email></email></address>
4579    </author>
4580    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4581      <organization>Agranat Systems, Inc.</organization>
4582      <address><email></email></address>
4583    </author>
4584    <date year='2000' month='May' />
4585  </front>
4586  <seriesInfo name='RFC' value='2817' />
4589<reference anchor='RFC2818'>
4590  <front>
4591    <title>HTTP Over TLS</title>
4592    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4593      <organization>RTFM, Inc.</organization>
4594      <address><email></email></address>
4595    </author>
4596    <date year='2000' month='May' />
4597  </front>
4598  <seriesInfo name='RFC' value='2818' />
4601<reference anchor='RFC2965'>
4602  <front>
4603    <title>HTTP State Management Mechanism</title>
4604    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4605      <organization>Bell Laboratories, Lucent Technologies</organization>
4606      <address><email></email></address>
4607    </author>
4608    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4609      <organization>, Inc.</organization>
4610      <address><email></email></address>
4611    </author>
4612    <date year='2000' month='October' />
4613  </front>
4614  <seriesInfo name='RFC' value='2965' />
4617<reference anchor='RFC3040'>
4618  <front>
4619    <title>Internet Web Replication and Caching Taxonomy</title>
4620    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4621      <organization>Equinix, Inc.</organization>
4622    </author>
4623    <author initials='I.' surname='Melve' fullname='I. Melve'>
4624      <organization>UNINETT</organization>
4625    </author>
4626    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4627      <organization>CacheFlow Inc.</organization>
4628    </author>
4629    <date year='2001' month='January' />
4630  </front>
4631  <seriesInfo name='RFC' value='3040' />
4634<reference anchor='RFC3864'>
4635  <front>
4636    <title>Registration Procedures for Message Header Fields</title>
4637    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4638      <organization>Nine by Nine</organization>
4639      <address><email></email></address>
4640    </author>
4641    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4642      <organization>BEA Systems</organization>
4643      <address><email></email></address>
4644    </author>
4645    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4646      <organization>HP Labs</organization>
4647      <address><email></email></address>
4648    </author>
4649    <date year='2004' month='September' />
4650  </front>
4651  <seriesInfo name='BCP' value='90' />
4652  <seriesInfo name='RFC' value='3864' />
4655<reference anchor='RFC4033'>
4656  <front>
4657    <title>DNS Security Introduction and Requirements</title>
4658    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4659    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4660    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4661    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4662    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4663    <date year='2005' month='March' />
4664  </front>
4665  <seriesInfo name='RFC' value='4033' />
4668<reference anchor="RFC4288">
4669  <front>
4670    <title>Media Type Specifications and Registration Procedures</title>
4671    <author initials="N." surname="Freed" fullname="N. Freed">
4672      <organization>Sun Microsystems</organization>
4673      <address>
4674        <email></email>
4675      </address>
4676    </author>
4677    <author initials="J." surname="Klensin" fullname="J. Klensin">
4678      <address>
4679        <email></email>
4680      </address>
4681    </author>
4682    <date year="2005" month="December"/>
4683  </front>
4684  <seriesInfo name="BCP" value="13"/>
4685  <seriesInfo name="RFC" value="4288"/>
4688<reference anchor='RFC4395'>
4689  <front>
4690    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4691    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4692      <organization>AT&amp;T Laboratories</organization>
4693      <address>
4694        <email></email>
4695      </address>
4696    </author>
4697    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4698      <organization>Qualcomm, Inc.</organization>
4699      <address>
4700        <email></email>
4701      </address>
4702    </author>
4703    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4704      <organization>Adobe Systems</organization>
4705      <address>
4706        <email></email>
4707      </address>
4708    </author>
4709    <date year='2006' month='February' />
4710  </front>
4711  <seriesInfo name='BCP' value='115' />
4712  <seriesInfo name='RFC' value='4395' />
4715<reference anchor='RFC4559'>
4716  <front>
4717    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4718    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4719    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4720    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4721    <date year='2006' month='June' />
4722  </front>
4723  <seriesInfo name='RFC' value='4559' />
4726<reference anchor='RFC5226'>
4727  <front>
4728    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4729    <author initials='T.' surname='Narten' fullname='T. Narten'>
4730      <organization>IBM</organization>
4731      <address><email></email></address>
4732    </author>
4733    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4734      <organization>Google</organization>
4735      <address><email></email></address>
4736    </author>
4737    <date year='2008' month='May' />
4738  </front>
4739  <seriesInfo name='BCP' value='26' />
4740  <seriesInfo name='RFC' value='5226' />
4743<reference anchor="RFC5322">
4744  <front>
4745    <title>Internet Message Format</title>
4746    <author initials="P." surname="Resnick" fullname="P. Resnick">
4747      <organization>Qualcomm Incorporated</organization>
4748    </author>
4749    <date year="2008" month="October"/>
4750  </front>
4751  <seriesInfo name="RFC" value="5322"/>
4754<reference anchor="RFC6265">
4755  <front>
4756    <title>HTTP State Management Mechanism</title>
4757    <author initials="A." surname="Barth" fullname="Adam Barth">
4758      <organization abbrev="U.C. Berkeley">
4759        University of California, Berkeley
4760      </organization>
4761      <address><email></email></address>
4762    </author>
4763    <date year="2011" month="April" />
4764  </front>
4765  <seriesInfo name="RFC" value="6265"/>
4768<!--<reference anchor='BCP97'>
4769  <front>
4770    <title>Handling Normative References to Standards-Track Documents</title>
4771    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4772      <address>
4773        <email></email>
4774      </address>
4775    </author>
4776    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4777      <organization>MIT</organization>
4778      <address>
4779        <email></email>
4780      </address>
4781    </author>
4782    <date year='2007' month='June' />
4783  </front>
4784  <seriesInfo name='BCP' value='97' />
4785  <seriesInfo name='RFC' value='4897' />
4788<reference anchor="Kri2001" target="">
4789  <front>
4790    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4791    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4792    <date year="2001" month="November"/>
4793  </front>
4794  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4797<reference anchor="Spe" target="">
4798  <front>
4799    <title>Analysis of HTTP Performance Problems</title>
4800    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4801    <date/>
4802  </front>
4805<reference anchor="Tou1998" target="">
4806  <front>
4807  <title>Analysis of HTTP Performance</title>
4808  <author initials="J." surname="Touch" fullname="Joe Touch">
4809    <organization>USC/Information Sciences Institute</organization>
4810    <address><email></email></address>
4811  </author>
4812  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4813    <organization>USC/Information Sciences Institute</organization>
4814    <address><email></email></address>
4815  </author>
4816  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4817    <organization>USC/Information Sciences Institute</organization>
4818    <address><email></email></address>
4819  </author>
4820  <date year="1998" month="Aug"/>
4821  </front>
4822  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4823  <annotation>(original report dated Aug. 1996)</annotation>
4829<section title="HTTP Version History" anchor="compatibility">
4831   HTTP has been in use by the World-Wide Web global information initiative
4832   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4833   was a simple protocol for hypertext data transfer across the Internet
4834   with only a single request method (GET) and no metadata.
4835   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4836   methods and MIME-like messaging that could include metadata about the data
4837   transferred and modifiers on the request/response semantics. However,
4838   HTTP/1.0 did not sufficiently take into consideration the effects of
4839   hierarchical proxies, caching, the need for persistent connections, or
4840   name-based virtual hosts. The proliferation of incompletely-implemented
4841   applications calling themselves "HTTP/1.0" further necessitated a
4842   protocol version change in order for two communicating applications
4843   to determine each other's true capabilities.
4846   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4847   requirements that enable reliable implementations, adding only
4848   those new features that will either be safely ignored by an HTTP/1.0
4849   recipient or only sent when communicating with a party advertising
4850   conformance with HTTP/1.1.
4853   It is beyond the scope of a protocol specification to mandate
4854   conformance with previous versions. HTTP/1.1 was deliberately
4855   designed, however, to make supporting previous versions easy.
4856   We would expect a general-purpose HTTP/1.1 server to understand
4857   any valid request in the format of HTTP/1.0 and respond appropriately
4858   with an HTTP/1.1 message that only uses features understood (or
4859   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4860   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4863   Since HTTP/0.9 did not support header fields in a request,
4864   there is no mechanism for it to support name-based virtual
4865   hosts (selection of resource by inspection of the <x:ref>Host</x:ref> header
4866   field).  Any server that implements name-based virtual hosts
4867   ought to disable support for HTTP/0.9.  Most requests that
4868   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4869   requests wherein a buggy client failed to properly encode
4870   linear whitespace found in a URI reference and placed in
4871   the request-target.
4874<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4876   This section summarizes major differences between versions HTTP/1.0
4877   and HTTP/1.1.
4880<section title="Multi-homed Web Servers" anchor="">
4882   The requirements that clients and servers support the <x:ref>Host</x:ref>
4883   header field (<xref target=""/>), report an error if it is
4884   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4885   are among the most important changes defined by HTTP/1.1.
4888   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4889   addresses and servers; there was no other established mechanism for
4890   distinguishing the intended server of a request than the IP address
4891   to which that request was directed. The <x:ref>Host</x:ref> header field was
4892   introduced during the development of HTTP/1.1 and, though it was
4893   quickly implemented by most HTTP/1.0 browsers, additional requirements
4894   were placed on all HTTP/1.1 requests in order to ensure complete
4895   adoption.  At the time of this writing, most HTTP-based services
4896   are dependent upon the Host header field for targeting requests.
4900<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4902   In HTTP/1.0, each connection is established by the client prior to the
4903   request and closed by the server after sending the response. However, some
4904   implementations implement the explicitly negotiated ("Keep-Alive") version
4905   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4906   target="RFC2068"/>.
4909   Some clients and servers might wish to be compatible with these previous
4910   approaches to persistent connections, by explicitly negotiating for them
4911   with a "Connection: keep-alive" request header field. However, some
4912   experimental implementations of HTTP/1.0 persistent connections are faulty;
4913   for example, if a HTTP/1.0 proxy server doesn't understand
4914   <x:ref>Connection</x:ref>, it will erroneously forward that header field
4915   to the next inbound server, which would result in a hung connection.
4918   One attempted solution was the introduction of a Proxy-Connection header
4919   field, targeted specifically at proxies. In practice, this was also
4920   unworkable, because proxies are often deployed in multiple layers, bringing
4921   about the same problem discussed above.
4924   As a result, clients are encouraged not to send the Proxy-Connection header
4925   field in any requests.
4928   Clients are also encouraged to consider the use of Connection: keep-alive
4929   in requests carefully; while they can enable persistent connections with
4930   HTTP/1.0 servers, clients using them need will need to monitor the
4931   connection for "hung" requests (which indicate that the client ought stop
4932   sending the header field), and this mechanism ought not be used by clients
4933   at all when a proxy is being used.
4937<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
4939   HTTP/1.1 introduces the <x:ref>Transfer-Encoding</x:ref> header field
4940   (<xref target="header.transfer-encoding"/>). Proxies/gateways &MUST; remove
4941   any transfer-coding prior to forwarding a message via a MIME-compliant
4942   protocol.
4948<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4950  Clarify that the string "HTTP" in the HTTP-version ABNF production is case
4951  sensitive. Restrict the version numbers to be single digits due to the fact
4952  that implementations are known to handle multi-digit version numbers
4953  incorrectly.
4954  (<xref target="http.version"/>)
4957  Update use of abs_path production from RFC 1808 to the path-absolute + query
4958  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4959  request method only.
4960  (<xref target="request-target"/>)
4963  Require that invalid whitespace around field-names be rejected.
4964  (<xref target="header.fields"/>)
4967  Rules about implicit linear whitespace between certain grammar productions
4968  have been removed; now whitespace is only allowed where specifically
4969  defined in the ABNF.
4970  (<xref target="whitespace"/>)
4973  The NUL octet is no longer allowed in comment and quoted-string
4974  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4975  Non-ASCII content in header fields and reason phrase has been obsoleted and
4976  made opaque (the TEXT rule was removed).
4977  (<xref target="field.components"/>)
4980  Empty list elements in list productions have been deprecated.
4981  (<xref target="abnf.extension"/>)
4984  Require recipients to handle bogus <x:ref>Content-Length</x:ref> header
4985  fields as errors.
4986  (<xref target="message.body"/>)
4989  Remove reference to non-existent identity transfer-coding value tokens.
4990  (Sections <xref format="counter" target="message.body"/> and
4991  <xref format="counter" target="transfer.codings"/>)
4994  Clarification that the chunk length does not include the count of the octets
4995  in the chunk header and trailer. Furthermore disallowed line folding
4996  in chunk extensions, and deprecate their use.
4997  (<xref target="chunked.encoding"/>)
5000  Registration of Transfer Codings now requires IETF Review
5001  (<xref target="transfer.coding.registry"/>)
5004  Remove hard limit of two connections per server.
5005  Remove requirement to retry a sequence of requests as long it was idempotent.
5006  Remove requirements about when servers are allowed to close connections
5007  prematurely.
5008  (<xref target="persistent.practical"/>)
5011  Remove requirement to retry requests under certain circumstances when the
5012  server prematurely closes the connection.
5013  (<xref target="message.transmission.requirements"/>)
5016  Change ABNF productions for header fields to only define the field value.
5019  Clarify exactly when "close" connection options have to be sent.
5020  (<xref target="header.connection"/>)
5023  Define the semantics of the <x:ref>Upgrade</x:ref> header field in responses
5024  other than 101 (this was incorporated from <xref target="RFC2817"/>).
5025  (<xref target="header.upgrade"/>)
5028  Take over the Upgrade Token Registry, previously defined in
5029  <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
5030  (<xref target="upgrade.token.registry"/>)
5035<section title="ABNF list extension: #rule" anchor="abnf.extension">
5037  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
5038  improve readability in the definitions of some header field values.
5041  A construct "#" is defined, similar to "*", for defining comma-delimited
5042  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
5043  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
5044  comma (",") and optional whitespace (OWS).   
5047  Thus,
5048</preamble><artwork type="example">
5049  1#element =&gt; element *( OWS "," OWS element )
5052  and:
5053</preamble><artwork type="example">
5054  #element =&gt; [ 1#element ]
5057  and for n &gt;= 1 and m &gt; 1:
5058</preamble><artwork type="example">
5059  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
5062  For compatibility with legacy list rules, recipients &SHOULD; accept empty
5063  list elements. In other words, consumers would follow the list productions:
5065<figure><artwork type="example">
5066  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
5068  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
5071  Note that empty elements do not contribute to the count of elements present,
5072  though.
5075  For example, given these ABNF productions:
5077<figure><artwork type="example">
5078  example-list      = 1#example-list-elmt
5079  example-list-elmt = token ; see <xref target="field.components"/>
5082  Then these are valid values for example-list (not including the double
5083  quotes, which are present for delimitation only):
5085<figure><artwork type="example">
5086  "foo,bar"
5087  "foo ,bar,"
5088  "foo , ,bar,charlie   "
5091  But these values would be invalid, as at least one non-empty element is
5092  required:
5094<figure><artwork type="example">
5095  ""
5096  ","
5097  ",   ,"
5100  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
5101  expanded as explained above.
5105<?BEGININC p1-messaging.abnf-appendix ?>
5106<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5108<artwork type="abnf" name="p1-messaging.parsed-abnf">
5109<x:ref>BWS</x:ref> = OWS
5111<x:ref>Connection</x:ref> = *( "," OWS ) connection-option *( OWS "," [ OWS
5112 connection-option ] )
5113<x:ref>Content-Length</x:ref> = 1*DIGIT
5115<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5116 ]
5117<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
5118<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
5119<x:ref>Host</x:ref> = uri-host [ ":" port ]
5121<x:ref>OWS</x:ref> = *( SP / HTAB )
5123<x:ref>RWS</x:ref> = 1*( SP / HTAB )
5125<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5126<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5127<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5128 transfer-coding ] )
5130<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5131<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
5133<x:ref>Via</x:ref> = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment
5134 ] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS
5135 comment ] ) ] )
5137<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5138<x:ref>absolute-form</x:ref> = absolute-URI
5139<x:ref>asterisk-form</x:ref> = "*"
5140<x:ref>attribute</x:ref> = token
5141<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5142<x:ref>authority-form</x:ref> = authority
5144<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5145<x:ref>chunk-data</x:ref> = 1*OCTET
5146<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5147<x:ref>chunk-ext-name</x:ref> = token
5148<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5149<x:ref>chunk-size</x:ref> = 1*HEXDIG
5150<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
5151<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5152<x:ref>connection-option</x:ref> = token
5153<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5154 / %x2A-5B ; '*'-'['
5155 / %x5D-7E ; ']'-'~'
5156 / obs-text
5158<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5159<x:ref>field-name</x:ref> = token
5160<x:ref>field-value</x:ref> = *( field-content / obs-fold )
5162<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
5163<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5164<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5166<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
5168<x:ref>message-body</x:ref> = *OCTET
5169<x:ref>method</x:ref> = token
5171<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
5172<x:ref>obs-text</x:ref> = %x80-FF
5173<x:ref>origin-form</x:ref> = path-absolute [ "?" query ]
5175<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5176<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5177<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5178<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5179<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
5180<x:ref>protocol-name</x:ref> = token
5181<x:ref>protocol-version</x:ref> = token
5182<x:ref>pseudonym</x:ref> = token
5184<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5185 / %x5D-7E ; ']'-'~'
5186 / obs-text
5187<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
5188 / %x5D-7E ; ']'-'~'
5189 / obs-text
5190<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5191<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5192<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5193<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5194<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5195<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5197<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5198<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5199<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5200<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5201<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
5202<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
5203 asterisk-form
5205<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5206 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5207<x:ref>start-line</x:ref> = request-line / status-line
5208<x:ref>status-code</x:ref> = 3DIGIT
5209<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
5211<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5212<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5213 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5214<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5215<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5216<x:ref>token</x:ref> = 1*tchar
5217<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5218<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5219 transfer-extension
5220<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5221<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5223<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5225<x:ref>value</x:ref> = word
5227<x:ref>word</x:ref> = token / quoted-string
5231<?ENDINC p1-messaging.abnf-appendix ?>
5233<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5235<section title="Since RFC 2616">
5237  Extracted relevant partitions from <xref target="RFC2616"/>.
5241<section title="Since draft-ietf-httpbis-p1-messaging-00">
5243  Closed issues:
5244  <list style="symbols">
5245    <t>
5246      <eref target=""/>:
5247      "HTTP Version should be case sensitive"
5248      (<eref target=""/>)
5249    </t>
5250    <t>
5251      <eref target=""/>:
5252      "'unsafe' characters"
5253      (<eref target=""/>)
5254    </t>
5255    <t>
5256      <eref target=""/>:
5257      "Chunk Size Definition"
5258      (<eref target=""/>)
5259    </t>
5260    <t>
5261      <eref target=""/>:
5262      "Message Length"
5263      (<eref target=""/>)
5264    </t>
5265    <t>
5266      <eref target=""/>:
5267      "Media Type Registrations"
5268      (<eref target=""/>)
5269    </t>
5270    <t>
5271      <eref target=""/>:
5272      "URI includes query"
5273      (<eref target=""/>)
5274    </t>
5275    <t>
5276      <eref target=""/>:
5277      "No close on 1xx responses"
5278      (<eref target=""/>)
5279    </t>
5280    <t>
5281      <eref target=""/>:
5282      "Remove 'identity' token references"
5283      (<eref target=""/>)
5284    </t>
5285    <t>
5286      <eref target=""/>:
5287      "Import query BNF"
5288    </t>
5289    <t>
5290      <eref target=""/>:
5291      "qdtext BNF"
5292    </t>
5293    <t>
5294      <eref target=""/>:
5295      "Normative and Informative references"
5296    </t>
5297    <t>
5298      <eref target=""/>:
5299      "RFC2606 Compliance"
5300    </t>
5301    <t>
5302      <eref target=""/>:
5303      "RFC977 reference"
5304    </t>
5305    <t>
5306      <eref target=""/>:
5307      "RFC1700 references"
5308    </t>
5309    <t>
5310      <eref target=""/>:
5311      "inconsistency in date format explanation"
5312    </t>
5313    <t>
5314      <eref target=""/>:
5315      "Date reference typo"
5316    </t>
5317    <t>
5318      <eref target=""/>:
5319      "Informative references"
5320    </t>
5321    <t>
5322      <eref target=""/>:
5323      "ISO-8859-1 Reference"
5324    </t>
5325    <t>
5326      <eref target=""/>:
5327      "Normative up-to-date references"
5328    </t>
5329  </list>
5332  Other changes:
5333  <list style="symbols">
5334    <t>
5335      Update media type registrations to use RFC4288 template.
5336    </t>
5337    <t>
5338      Use names of RFC4234 core rules DQUOTE and HTAB,
5339      fix broken ABNF for chunk-data
5340      (work in progress on <eref target=""/>)
5341    </t>
5342  </list>
5346<section title="Since draft-ietf-httpbis-p1-messaging-01">
5348  Closed issues:
5349  <list style="symbols">
5350    <t>
5351      <eref target=""/>:
5352      "Bodies on GET (and other) requests"
5353    </t>
5354    <t>
5355      <eref target=""/>:
5356      "Updating to RFC4288"
5357    </t>
5358    <t>
5359      <eref target=""/>:
5360      "Status Code and Reason Phrase"
5361    </t>
5362    <t>
5363      <eref target=""/>:
5364      "rel_path not used"
5365    </t>
5366  </list>
5369  Ongoing work on ABNF conversion (<eref target=""/>):
5370  <list style="symbols">
5371    <t>
5372      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5373      "trailer-part").
5374    </t>
5375    <t>
5376      Avoid underscore character in rule names ("http_URL" ->
5377      "http-URL", "abs_path" -> "path-absolute").
5378    </t>
5379    <t>
5380      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5381      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5382      have to be updated when switching over to RFC3986.
5383    </t>
5384    <t>
5385      Synchronize core rules with RFC5234.
5386    </t>
5387    <t>
5388      Get rid of prose rules that span multiple lines.
5389    </t>
5390    <t>
5391      Get rid of unused rules LOALPHA and UPALPHA.
5392    </t>
5393    <t>
5394      Move "Product Tokens" section (back) into Part 1, as "token" is used
5395      in the definition of the Upgrade header field.
5396    </t>
5397    <t>
5398      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5399    </t>
5400    <t>
5401      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5402    </t>
5403  </list>
5407<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5409  Closed issues:
5410  <list style="symbols">
5411    <t>
5412      <eref target=""/>:
5413      "HTTP-date vs. rfc1123-date"
5414    </t>
5415    <t>
5416      <eref target=""/>:
5417      "WS in quoted-pair"
5418    </t>
5419  </list>
5422  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5423  <list style="symbols">
5424    <t>
5425      Reference RFC 3984, and update header field registrations for header
5426      fields defined in this document.
5427    </t>
5428  </list>
5431  Ongoing work on ABNF conversion (<eref target=""/>):
5432  <list style="symbols">
5433    <t>
5434      Replace string literals when the string really is case-sensitive (HTTP-version).
5435    </t>
5436  </list>
5440<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5442  Closed issues:
5443  <list style="symbols">
5444    <t>
5445      <eref target=""/>:
5446      "Connection closing"
5447    </t>
5448    <t>
5449      <eref target=""/>:
5450      "Move registrations and registry information to IANA Considerations"
5451    </t>
5452    <t>
5453      <eref target=""/>:
5454      "need new URL for PAD1995 reference"
5455    </t>
5456    <t>
5457      <eref target=""/>:
5458      "IANA Considerations: update HTTP URI scheme registration"
5459    </t>
5460    <t>
5461      <eref target=""/>:
5462      "Cite HTTPS URI scheme definition"
5463    </t>
5464    <t>
5465      <eref target=""/>:
5466      "List-type header fields vs Set-Cookie"
5467    </t>
5468  </list>
5471  Ongoing work on ABNF conversion (<eref target=""/>):
5472  <list style="symbols">
5473    <t>
5474      Replace string literals when the string really is case-sensitive (HTTP-Date).
5475    </t>
5476    <t>
5477      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5478    </t>
5479  </list>
5483<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5485  Closed issues:
5486  <list style="symbols">
5487    <t>
5488      <eref target=""/>:
5489      "Out-of-date reference for URIs"
5490    </t>
5491    <t>
5492      <eref target=""/>:
5493      "RFC 2822 is updated by RFC 5322"
5494    </t>
5495  </list>
5498  Ongoing work on ABNF conversion (<eref target=""/>):
5499  <list style="symbols">
5500    <t>
5501      Use "/" instead of "|" for alternatives.
5502    </t>
5503    <t>
5504      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5505    </t>
5506    <t>
5507      Only reference RFC 5234's core rules.
5508    </t>
5509    <t>
5510      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5511      whitespace ("OWS") and required whitespace ("RWS").
5512    </t>
5513    <t>
5514      Rewrite ABNFs to spell out whitespace rules, factor out
5515      header field value format definitions.
5516    </t>
5517  </list>
5521<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5523  Closed issues:
5524  <list style="symbols">
5525    <t>
5526      <eref target=""/>:
5527      "Header LWS"
5528    </t>
5529    <t>
5530      <eref target=""/>:
5531      "Sort 1.3 Terminology"
5532    </t>
5533    <t>
5534      <eref target=""/>:
5535      "RFC2047 encoded words"
5536    </t>
5537    <t>
5538      <eref target=""/>:
5539      "Character Encodings in TEXT"
5540    </t>
5541    <t>
5542      <eref target=""/>:
5543      "Line Folding"
5544    </t>
5545    <t>
5546      <eref target=""/>:
5547      "OPTIONS * and proxies"
5548    </t>
5549    <t>
5550      <eref target=""/>:
5551      "reason-phrase BNF"
5552    </t>
5553    <t>
5554      <eref target=""/>:
5555      "Use of TEXT"
5556    </t>
5557    <t>
5558      <eref target=""/>:
5559      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5560    </t>
5561    <t>
5562      <eref target=""/>:
5563      "RFC822 reference left in discussion of date formats"
5564    </t>
5565  </list>
5568  Final work on ABNF conversion (<eref target=""/>):
5569  <list style="symbols">
5570    <t>
5571      Rewrite definition of list rules, deprecate empty list elements.
5572    </t>
5573    <t>
5574      Add appendix containing collected and expanded ABNF.
5575    </t>
5576  </list>
5579  Other changes:
5580  <list style="symbols">
5581    <t>
5582      Rewrite introduction; add mostly new Architecture Section.
5583    </t>
5584    <t>
5585      Move definition of quality values from Part 3 into Part 1;
5586      make TE request header field grammar independent of accept-params (defined in Part 3).
5587    </t>
5588  </list>
5592<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5594  Closed issues:
5595  <list style="symbols">
5596    <t>
5597      <eref target=""/>:
5598      "base for numeric protocol elements"
5599    </t>
5600    <t>
5601      <eref target=""/>:
5602      "comment ABNF"
5603    </t>
5604  </list>
5607  Partly resolved issues:
5608  <list style="symbols">
5609    <t>
5610      <eref target=""/>:
5611      "205 Bodies" (took out language that implied that there might be
5612      methods for which a request body MUST NOT be included)
5613    </t>
5614    <t>
5615      <eref target=""/>:
5616      "editorial improvements around HTTP-date"
5617    </t>
5618  </list>
5622<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5624  Closed issues:
5625  <list style="symbols">
5626    <t>
5627      <eref target=""/>:
5628      "Repeating single-value header fields"
5629    </t>
5630    <t>
5631      <eref target=""/>:
5632      "increase connection limit"
5633    </t>
5634    <t>
5635      <eref target=""/>:
5636      "IP addresses in URLs"
5637    </t>
5638    <t>
5639      <eref target=""/>:
5640      "take over HTTP Upgrade Token Registry"
5641    </t>
5642    <t>
5643      <eref target=""/>:
5644      "CR and LF in chunk extension values"
5645    </t>
5646    <t>
5647      <eref target=""/>:
5648      "HTTP/0.9 support"
5649    </t>
5650    <t>
5651      <eref target=""/>:
5652      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5653    </t>
5654    <t>
5655      <eref target=""/>:
5656      "move definitions of gzip/deflate/compress to part 1"
5657    </t>
5658    <t>
5659      <eref target=""/>:
5660      "disallow control characters in quoted-pair"
5661    </t>
5662  </list>
5665  Partly resolved issues:
5666  <list style="symbols">
5667    <t>
5668      <eref target=""/>:
5669      "update IANA requirements wrt Transfer-Coding values" (add the
5670      IANA Considerations subsection)
5671    </t>
5672  </list>
5676<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5678  Closed issues:
5679  <list style="symbols">
5680    <t>
5681      <eref target=""/>:
5682      "header parsing, treatment of leading and trailing OWS"
5683    </t>
5684  </list>
5687  Partly resolved issues:
5688  <list style="symbols">
5689    <t>
5690      <eref target=""/>:
5691      "Placement of 13.5.1 and 13.5.2"
5692    </t>
5693    <t>
5694      <eref target=""/>:
5695      "use of term "word" when talking about header field structure"
5696    </t>
5697  </list>
5701<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5703  Closed issues:
5704  <list style="symbols">
5705    <t>
5706      <eref target=""/>:
5707      "Clarification of the term 'deflate'"
5708    </t>
5709    <t>
5710      <eref target=""/>:
5711      "OPTIONS * and proxies"
5712    </t>
5713    <t>
5714      <eref target=""/>:
5715      "MIME-Version not listed in P1, general header fields"
5716    </t>
5717    <t>
5718      <eref target=""/>:
5719      "IANA registry for content/transfer encodings"
5720    </t>
5721    <t>
5722      <eref target=""/>:
5723      "Case-sensitivity of HTTP-date"
5724    </t>
5725    <t>
5726      <eref target=""/>:
5727      "use of term "word" when talking about header field structure"
5728    </t>
5729  </list>
5732  Partly resolved issues:
5733  <list style="symbols">
5734    <t>
5735      <eref target=""/>:
5736      "Term for the requested resource's URI"
5737    </t>
5738  </list>
5742<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5744  Closed issues:
5745  <list style="symbols">
5746    <t>
5747      <eref target=""/>:
5748      "Connection Closing"
5749    </t>
5750    <t>
5751      <eref target=""/>:
5752      "Delimiting messages with multipart/byteranges"
5753    </t>
5754    <t>
5755      <eref target=""/>:
5756      "Handling multiple Content-Length header fields"
5757    </t>
5758    <t>
5759      <eref target=""/>:
5760      "Clarify entity / representation / variant terminology"
5761    </t>
5762    <t>
5763      <eref target=""/>:
5764      "consider removing the 'changes from 2068' sections"
5765    </t>
5766  </list>
5769  Partly resolved issues:
5770  <list style="symbols">
5771    <t>
5772      <eref target=""/>:
5773      "HTTP(s) URI scheme definitions"
5774    </t>
5775  </list>
5779<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5781  Closed issues:
5782  <list style="symbols">
5783    <t>
5784      <eref target=""/>:
5785      "Trailer requirements"
5786    </t>
5787    <t>
5788      <eref target=""/>:
5789      "Text about clock requirement for caches belongs in p6"
5790    </t>
5791    <t>
5792      <eref target=""/>:
5793      "effective request URI: handling of missing host in HTTP/1.0"
5794    </t>
5795    <t>
5796      <eref target=""/>:
5797      "confusing Date requirements for clients"
5798    </t>
5799  </list>
5802  Partly resolved issues:
5803  <list style="symbols">
5804    <t>
5805      <eref target=""/>:
5806      "Handling multiple Content-Length header fields"
5807    </t>
5808  </list>
5812<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5814  Closed issues:
5815  <list style="symbols">
5816    <t>
5817      <eref target=""/>:
5818      "RFC2145 Normative"
5819    </t>
5820    <t>
5821      <eref target=""/>:
5822      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5823    </t>
5824    <t>
5825      <eref target=""/>:
5826      "define 'transparent' proxy"
5827    </t>
5828    <t>
5829      <eref target=""/>:
5830      "Header Field Classification"
5831    </t>
5832    <t>
5833      <eref target=""/>:
5834      "Is * usable as a request-uri for new methods?"
5835    </t>
5836    <t>
5837      <eref target=""/>:
5838      "Migrate Upgrade details from RFC2817"
5839    </t>
5840    <t>
5841      <eref target=""/>:
5842      "untangle ABNFs for header fields"
5843    </t>
5844    <t>
5845      <eref target=""/>:
5846      "update RFC 2109 reference"
5847    </t>
5848  </list>
5852<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5854  Closed issues:
5855  <list style="symbols">
5856    <t>
5857      <eref target=""/>:
5858      "Allow is not in 13.5.2"
5859    </t>
5860    <t>
5861      <eref target=""/>:
5862      "Handling multiple Content-Length header fields"
5863    </t>
5864    <t>
5865      <eref target=""/>:
5866      "untangle ABNFs for header fields"
5867    </t>
5868    <t>
5869      <eref target=""/>:
5870      "Content-Length ABNF broken"
5871    </t>
5872  </list>
5876<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5878  Closed issues:
5879  <list style="symbols">
5880    <t>
5881      <eref target=""/>:
5882      "HTTP-version should be redefined as fixed length pair of DIGIT . DIGIT"
5883    </t>
5884    <t>
5885      <eref target=""/>:
5886      "Recommend minimum sizes for protocol elements"
5887    </t>
5888    <t>
5889      <eref target=""/>:
5890      "Set expectations around buffering"
5891    </t>
5892    <t>
5893      <eref target=""/>:
5894      "Considering messages in isolation"
5895    </t>
5896  </list>
5900<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5902  Closed issues:
5903  <list style="symbols">
5904    <t>
5905      <eref target=""/>:
5906      "DNS Spoofing / DNS Binding advice"
5907    </t>
5908    <t>
5909      <eref target=""/>:
5910      "move RFCs 2145, 2616, 2817 to Historic status"
5911    </t>
5912    <t>
5913      <eref target=""/>:
5914      "\-escaping in quoted strings"
5915    </t>
5916    <t>
5917      <eref target=""/>:
5918      "'Close' should be reserved in the HTTP header field registry"
5919    </t>
5920  </list>
5924<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5926  Closed issues:
5927  <list style="symbols">
5928    <t>
5929      <eref target=""/>:
5930      "Document HTTP's error-handling philosophy"
5931    </t>
5932    <t>
5933      <eref target=""/>:
5934      "Explain header field registration"
5935    </t>
5936    <t>
5937      <eref target=""/>:
5938      "Revise Acknowledgements Sections"
5939    </t>
5940    <t>
5941      <eref target=""/>:
5942      "Retrying Requests"
5943    </t>
5944    <t>
5945      <eref target=""/>:
5946      "Closing the connection on server error"
5947    </t>
5948  </list>
5952<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5954  Closed issues:
5955  <list style="symbols">
5956    <t>
5957      <eref target=""/>:
5958      "Proxy-Connection and Keep-Alive"
5959    </t>
5960    <t>
5961      <eref target=""/>:
5962      "Clarify 'User Agent'"
5963    </t>
5964    <t>
5965      <eref target=""/>:
5966      "Define non-final responses"
5967    </t>
5968    <t>
5969      <eref target=""/>:
5970      "intended maturity level vs normative references"
5971    </t>
5972    <t>
5973      <eref target=""/>:
5974      "Intermediary rewriting of queries"
5975    </t>
5976  </list>
5980<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5982  Closed issues:
5983  <list style="symbols">
5984    <t>
5985      <eref target=""/>:
5986      "message-body in CONNECT response"
5987    </t>
5988    <t>
5989      <eref target=""/>:
5990      "Misplaced text on connection handling in p2"
5991    </t>
5992    <t>
5993      <eref target=""/>:
5994      "wording of line folding rule"
5995    </t>
5996    <t>
5997      <eref target=""/>:
5998      "chunk-extensions"
5999    </t>
6000    <t>
6001      <eref target=""/>:
6002      "make IANA policy definitions consistent"
6003    </t>
6004  </list>
6008<section title="Since draft-ietf-httpbis-p1-messaging-19" anchor="changes.since.19">
6010  Closed issues:
6011  <list style="symbols">
6012    <t>
6013      <eref target=""/>:
6014      "make IANA policy definitions consistent"
6015    </t>
6016    <t>
6017      <eref target=""/>:
6018      "clarify connection header field values are case-insensitive"
6019    </t>
6020    <t>
6021      <eref target=""/>:
6022      "ABNF requirements for recipients"
6023    </t>
6024    <t>
6025      <eref target=""/>:
6026      "note introduction of new IANA registries as normative changes"
6027    </t>
6028    <t>
6029      <eref target=""/>:
6030      "Reference to ISO-8859-1 is informative"
6031    </t>
6032  </list>
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