source: draft-ietf-httpbis/latest/p1-messaging.xml @ 2530

Last change on this file since 2530 was 2530, checked in by julian.reschke@…, 7 years ago

update acks after directorate and IESG reviews (see #219)

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 235.9 KB
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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='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "January">
16  <!ENTITY ID-YEAR "2014">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY Note "<x:h xmlns:x='http://purl.org/net/xml2rfc/ext'>Note:</x:h>">
19  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#response.cacheability' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY payload                "<xref target='Part2' x:rel='#payload' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY media-type            "<xref target='Part2' x:rel='#media.type' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY content-codings        "<xref target='Part2' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY content.negotiation    "<xref target='Part2' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY diff-mime              "<xref target='Part2' x:rel='#differences.between.http.and.mime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY representation         "<xref target='Part2' x:rel='#representations' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY HEAD                   "<xref target='Part2' x:rel='#HEAD' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-allow           "<xref target='Part2' x:rel='#header.allow' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-content-encoding    "<xref target='Part2' x:rel='#header.content-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY header-content-location    "<xref target='Part2' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY header-content-range   "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY header-content-type    "<xref target='Part2' x:rel='#header.content-type' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY header-date            "<xref target='Part2' x:rel='#header.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY header-etag            "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY header-expires         "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY header-last-modified   "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY header-mime-version    "<xref target='Part2' x:rel='#mime-version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY header-server          "<xref target='Part2' x:rel='#header.server' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY safe-methods           "<xref target='Part2' x:rel='#safe.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY methods                "<xref target='Part2' x:rel='#methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY OPTIONS                "<xref target='Part2' x:rel='#OPTIONS' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY qvalue                 "<xref target='Part2' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY resource               "<xref target='Part2' x:rel='#resources' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56  <!ENTITY status-304             "<xref target='Part4' x:rel='#status.304' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
57  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
58  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
59  <!ENTITY iana-header-registry   "<xref target='Part2' x:rel='#header.field.registry' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
60]>
61<?rfc toc="yes" ?>
62<?rfc symrefs="yes" ?>
63<?rfc sortrefs="yes" ?>
64<?rfc compact="yes"?>
65<?rfc subcompact="no" ?>
66<?rfc linkmailto="no" ?>
67<?rfc editing="no" ?>
68<?rfc comments="yes"?>
69<?rfc inline="yes"?>
70<?rfc rfcedstyle="yes"?>
71<?rfc-ext allow-markup-in-artwork="yes" ?>
72<?rfc-ext include-references-in-index="yes" ?>
73<rfc obsoletes="2145,2616" updates="2817,2818" category="std" x:maturity-level="proposed"
74     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
75     xmlns:x='http://purl.org/net/xml2rfc/ext'>
76<x:link rel="next" basename="p2-semantics"/>
77<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
78<front>
79
80  <title abbrev="HTTP/1.1 Message Syntax and Routing">Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing</title>
81
82  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
83    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
84    <address>
85      <postal>
86        <street>345 Park Ave</street>
87        <city>San Jose</city>
88        <region>CA</region>
89        <code>95110</code>
90        <country>USA</country>
91      </postal>
92      <email>fielding@gbiv.com</email>
93      <uri>http://roy.gbiv.com/</uri>
94    </address>
95  </author>
96
97  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
98    <organization abbrev="greenbytes">greenbytes GmbH</organization>
99    <address>
100      <postal>
101        <street>Hafenweg 16</street>
102        <city>Muenster</city><region>NW</region><code>48155</code>
103        <country>Germany</country>
104      </postal>
105      <email>julian.reschke@greenbytes.de</email>
106      <uri>http://greenbytes.de/tech/webdav/</uri>
107    </address>
108  </author>
109
110  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
111  <workgroup>HTTPbis Working Group</workgroup>
112
113<abstract>
114<t>
115   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
116   distributed, collaborative, hypertext information systems. HTTP has been in
117   use by the World Wide Web global information initiative since 1990.
118   This document provides an overview of HTTP architecture and its associated
119   terminology, defines the "http" and "https" Uniform Resource Identifier
120   (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements,
121   and describes general security concerns for implementations.
122</t>   
123</abstract>
124
125<note title="Editorial Note (To be removed by RFC Editor)">
126  <t>
127    Discussion of this draft takes place on the HTTPBIS working group
128    mailing list (ietf-http-wg@w3.org), which is archived at
129    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
130  </t>
131  <t>
132    The current issues list is at
133    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
134    documents (including fancy diffs) can be found at
135    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
136  </t>
137  <t>
138    The changes in this draft are summarized in <xref target="changes.since.25"/>.
139  </t>
140</note>
141</front>
142<middle>
143<section title="Introduction" anchor="introduction">
144<t>
145   The Hypertext Transfer Protocol (HTTP) is an application-level
146   request/response protocol that uses extensible semantics and self-descriptive
147   message payloads for flexible interaction with network-based hypertext
148   information systems. This document is the first in a series of documents
149   that collectively form the HTTP/1.1 specification:
150   <list style="empty">
151    <t>RFC xxx1: Message Syntax and Routing</t>
152    <t><xref target="Part2" x:fmt="none">RFC xxx2</xref>: Semantics and Content</t>
153    <t><xref target="Part4" x:fmt="none">RFC xxx3</xref>: Conditional Requests</t>
154    <t><xref target="Part5" x:fmt="none">RFC xxx4</xref>: Range Requests</t>
155    <t><xref target="Part6" x:fmt="none">RFC xxx5</xref>: Caching</t>
156    <t><xref target="Part7" x:fmt="none">RFC xxx6</xref>: Authentication</t>
157   </list>
158</t>
159<t>
160   This HTTP/1.1 specification obsoletes
161   <xref target="RFC2616" x:fmt="none">RFC 2616</xref> and
162   <xref target="RFC2145" x:fmt="none">RFC 2145</xref> (on HTTP versioning).
163   This specification also updates the use of CONNECT to establish a tunnel,
164   previously defined in <xref target="RFC2817" x:fmt="none">RFC 2817</xref>,
165   and defines the "https" URI scheme that was described informally in
166   <xref target="RFC2818" x:fmt="none">RFC 2818</xref>.
167</t>
168<t>
169   HTTP is a generic interface protocol for information systems. It is
170   designed to hide the details of how a service is implemented by presenting
171   a uniform interface to clients that is independent of the types of
172   resources provided. Likewise, servers do not need to be aware of each
173   client's purpose: an HTTP request can be considered in isolation rather
174   than being associated with a specific type of client or a predetermined
175   sequence of application steps. The result is a protocol that can be used
176   effectively in many different contexts and for which implementations can
177   evolve independently over time.
178</t>
179<t>
180   HTTP is also designed for use as an intermediation protocol for translating
181   communication to and from non-HTTP information systems.
182   HTTP proxies and gateways can provide access to alternative information
183   services by translating their diverse protocols into a hypertext
184   format that can be viewed and manipulated by clients in the same way
185   as HTTP services.
186</t>
187<t>
188   One consequence of this flexibility is that the protocol cannot be
189   defined in terms of what occurs behind the interface. Instead, we
190   are limited to defining the syntax of communication, the intent
191   of received communication, and the expected behavior of recipients.
192   If the communication is considered in isolation, then successful
193   actions ought to be reflected in corresponding changes to the
194   observable interface provided by servers. However, since multiple
195   clients might act in parallel and perhaps at cross-purposes, we
196   cannot require that such changes be observable beyond the scope
197   of a single response.
198</t>
199<t>
200   This document describes the architectural elements that are used or
201   referred to in HTTP, defines the "http" and "https" URI schemes,
202   describes overall network operation and connection management,
203   and defines HTTP message framing and forwarding requirements.
204   Our goal is to define all of the mechanisms necessary for HTTP message
205   handling that are independent of message semantics, thereby defining the
206   complete set of requirements for message parsers and
207   message-forwarding intermediaries.
208</t>
209
210
211<section title="Requirement Notation" anchor="intro.requirements">
212<t>
213   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
214   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
215   document are to be interpreted as described in <xref target="RFC2119"/>.
216</t>
217<t>
218   Conformance criteria and considerations regarding error handling
219   are defined in <xref target="conformance"/>.
220</t>
221</section>
222
223<section title="Syntax Notation" anchor="notation">
224<iref primary="true" item="Grammar" subitem="ALPHA"/>
225<iref primary="true" item="Grammar" subitem="CR"/>
226<iref primary="true" item="Grammar" subitem="CRLF"/>
227<iref primary="true" item="Grammar" subitem="CTL"/>
228<iref primary="true" item="Grammar" subitem="DIGIT"/>
229<iref primary="true" item="Grammar" subitem="DQUOTE"/>
230<iref primary="true" item="Grammar" subitem="HEXDIG"/>
231<iref primary="true" item="Grammar" subitem="HTAB"/>
232<iref primary="true" item="Grammar" subitem="LF"/>
233<iref primary="true" item="Grammar" subitem="OCTET"/>
234<iref primary="true" item="Grammar" subitem="SP"/>
235<iref primary="true" item="Grammar" subitem="VCHAR"/>
236<t>
237   This specification uses the Augmented Backus-Naur Form (ABNF) notation of
238   <xref target="RFC5234"/> with an extension defined in
239   <xref target="abnf.extension"/> that adds compact support for
240   comma-separated lists with the addition of a '#' operator, similar to the '*'
241   operator.
242   <xref target="collected.abnf"/> shows the collected ABNF with the rules using
243   the list operator expanded to standard ABNF notation.
244</t>
245<t anchor="core.rules">
246  <x:anchor-alias value="ALPHA"/>
247  <x:anchor-alias value="CTL"/>
248  <x:anchor-alias value="CR"/>
249  <x:anchor-alias value="CRLF"/>
250  <x:anchor-alias value="DIGIT"/>
251  <x:anchor-alias value="DQUOTE"/>
252  <x:anchor-alias value="HEXDIG"/>
253  <x:anchor-alias value="HTAB"/>
254  <x:anchor-alias value="LF"/>
255  <x:anchor-alias value="OCTET"/>
256  <x:anchor-alias value="SP"/>
257  <x:anchor-alias value="VCHAR"/>
258   The following core rules are included by
259   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
260   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
261   DIGIT (decimal 0-9), DQUOTE (double quote),
262   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
263   OCTET (any 8-bit sequence of data), SP (space), and
264   VCHAR (any visible <xref target="USASCII"/> character).
265</t>
266<t>
267   As a convention, ABNF rule names prefixed with "obs-" denote
268   "obsolete" grammar rules that appear for historical reasons.
269</t>
270</section>
271</section>
272
273<section title="Architecture" anchor="architecture">
274<t>
275   HTTP was created for the World Wide Web architecture
276   and has evolved over time to support the scalability needs of a worldwide
277   hypertext system. Much of that architecture is reflected in the terminology
278   and syntax productions used to define HTTP.
279</t>
280
281<section title="Client/Server Messaging" anchor="operation">
282<iref primary="true" item="client"/>
283<iref primary="true" item="server"/>
284<iref primary="true" item="connection"/>
285<t>
286   HTTP is a stateless request/response protocol that operates by exchanging
287   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
288   transport or session-layer
289   "<x:dfn>connection</x:dfn>" (<xref target="connection.management"/>).
290   An HTTP "<x:dfn>client</x:dfn>" is a program that establishes a connection
291   to a server for the purpose of sending one or more HTTP requests.
292   An HTTP "<x:dfn>server</x:dfn>" is a program that accepts connections
293   in order to service HTTP requests by sending HTTP responses.
294</t>
295<iref primary="true" item="user agent"/>
296<iref primary="true" item="origin server"/>
297<iref primary="true" item="browser"/>
298<iref primary="true" item="spider"/>
299<iref primary="true" item="sender"/>
300<iref primary="true" item="recipient"/>
301<t>
302   The terms client and server refer only to the roles that
303   these programs perform for a particular connection.  The same program
304   might act as a client on some connections and a server on others.
305   We use the term "<x:dfn>user agent</x:dfn>" to refer to any of the various
306   client programs that initiate a request, including (but not limited to)
307   browsers, spiders (web-based robots), command-line tools, native
308   applications, and mobile apps.  The term "<x:dfn>origin server</x:dfn>" is
309   used to refer to the program that can originate authoritative responses to
310   a request. For general requirements, we use the terms
311   "<x:dfn>sender</x:dfn>" and "<x:dfn>recipient</x:dfn>" to refer to any
312   component that sends or receives, respectively, a given message.
313</t>
314<t>
315   HTTP relies upon the Uniform Resource Identifier (URI)
316   standard <xref target="RFC3986"/> to indicate the target resource
317   (<xref target="target-resource"/>) and relationships between resources.
318   Messages are passed in a format similar to that used by Internet mail
319   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
320   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
321   between HTTP and MIME messages).
322</t>
323<t>
324   Most HTTP communication consists of a retrieval request (GET) for
325   a representation of some resource identified by a URI.  In the
326   simplest case, this might be accomplished via a single bidirectional
327   connection (===) between the user agent (UA) and the origin server (O).
328</t>
329<figure><artwork type="drawing">
330         request   &gt;
331    <x:highlight>UA</x:highlight> ======================================= <x:highlight>O</x:highlight>
332                                &lt;   response
333</artwork></figure>
334<iref primary="true" item="message"/>
335<iref primary="true" item="request"/>
336<iref primary="true" item="response"/>
337<t>
338   A client sends an HTTP request to a server in the form of a <x:dfn>request</x:dfn>
339   message, beginning with a request-line that includes a method, URI, and
340   protocol version (<xref target="request.line"/>),
341   followed by header fields containing
342   request modifiers, client information, and representation metadata
343   (<xref target="header.fields"/>),
344   an empty line to indicate the end of the header section, and finally
345   a message body containing the payload body (if any,
346   <xref target="message.body"/>).
347</t>
348<t>
349   A server responds to a client's request by sending one or more HTTP
350   <x:dfn>response</x:dfn>
351   messages, each beginning with a status line that
352   includes the protocol version, a success or error code, and textual
353   reason phrase (<xref target="status.line"/>),
354   possibly followed by header fields containing server
355   information, resource metadata, and representation metadata
356   (<xref target="header.fields"/>),
357   an empty line to indicate the end of the header section, and finally
358   a message body containing the payload body (if any,
359   <xref target="message.body"/>).
360</t>
361<t>
362   A connection might be used for multiple request/response exchanges,
363   as defined in <xref target="persistent.connections"/>.
364</t>
365<t>
366   The following example illustrates a typical message exchange for a
367   GET request on the URI "http://www.example.com/hello.txt":
368</t>
369<figure><preamble>
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
374Host: www.example.com
375Accept-Language: en, mi
376
377</artwork></figure>
378<figure><preamble>
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
390
391<x:span anchor="exbody">Hello World! My payload includes a trailing CRLF.
392</x:span></artwork>
393</figure>
394</section>
395
396<section title="Implementation Diversity" anchor="implementation-diversity">
397<t>
398   When considering the design of HTTP, it is easy to fall into a trap of
399   thinking that all user agents are general-purpose browsers and all origin
400   servers are large public websites. That is not the case in practice.
401   Common HTTP user agents include household appliances, stereos, scales,
402   firmware update scripts, command-line programs, mobile apps,
403   and communication devices in a multitude of shapes and sizes.  Likewise,
404   common HTTP origin servers include home automation units, configurable
405   networking components, office machines, autonomous robots, news feeds,
406   traffic cameras, ad selectors, and video delivery platforms.
407</t>
408<t>
409   The term "user agent" does not imply that there is a human user directly
410   interacting with the software agent at the time of a request. In many
411   cases, a user agent is installed or configured to run in the background
412   and save its results for later inspection (or save only a subset of those
413   results that might be interesting or erroneous). Spiders, for example, are
414   typically given a start URI and configured to follow certain behavior while
415   crawling the Web as a hypertext graph.
416</t>
417<t>
418   The implementation diversity of HTTP means that we cannot assume the
419   user agent can make interactive suggestions to a user or provide adequate
420   warning for security or privacy options.  In the few cases where this
421   specification requires reporting of errors to the user, it is acceptable
422   for such reporting to only be observable in an error console or log file.
423   Likewise, requirements that an automated action be confirmed by the user
424   before proceeding might be met via advance configuration choices,
425   run-time options, or simple avoidance of the unsafe action; confirmation
426   does not imply any specific user interface or interruption of normal
427   processing if the user has already made that choice.
428</t>
429</section>
430
431<section title="Intermediaries" anchor="intermediaries">
432<iref primary="true" item="intermediary"/>
433<t>
434   HTTP enables the use of intermediaries to satisfy requests through
435   a chain of connections.  There are three common forms of HTTP
436   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
437   a single intermediary might act as an origin server, proxy, gateway,
438   or tunnel, switching behavior based on the nature of each request.
439</t>
440<figure><artwork type="drawing">
441         &gt;             &gt;             &gt;             &gt;
442    <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>
443               &lt;             &lt;             &lt;             &lt;
444</artwork></figure>
445<t>
446   The figure above shows three intermediaries (A, B, and C) between the
447   user agent and origin server. A request or response message that
448   travels the whole chain will pass through four separate connections.
449   Some HTTP communication options
450   might apply only to the connection with the nearest, non-tunnel
451   neighbor, only to the end-points of the chain, or to all connections
452   along the chain. Although the diagram is linear, each participant might
453   be engaged in multiple, simultaneous communications. For example, B
454   might be receiving requests from many clients other than A, and/or
455   forwarding requests to servers other than C, at the same time that it
456   is handling A's request. Likewise, later requests might be sent through a
457   different path of connections, often based on dynamic configuration for
458   load balancing.   
459</t>
460<t>
461<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
462<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
463   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
464   to describe various requirements in relation to the directional flow of a
465   message: all messages flow from upstream to downstream.
466   Likewise, we use the terms inbound and outbound to refer to
467   directions in relation to the request path:
468   "<x:dfn>inbound</x:dfn>" means toward the origin server and
469   "<x:dfn>outbound</x:dfn>" means toward the user agent.
470</t>
471<t><iref primary="true" item="proxy"/>
472   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
473   client, usually via local configuration rules, to receive requests
474   for some type(s) of absolute URI and attempt to satisfy those
475   requests via translation through the HTTP interface.  Some translations
476   are minimal, such as for proxy requests for "http" URIs, whereas
477   other requests might require translation to and from entirely different
478   application-level protocols. Proxies are often used to group an
479   organization's HTTP requests through a common intermediary for the
480   sake of security, annotation services, or shared caching.
481</t>
482<t>
483<iref primary="true" item="transforming proxy"/>
484<iref primary="true" item="non-transforming proxy"/>
485   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
486   or configured to modify request or response messages in a semantically
487   meaningful way (i.e., modifications, beyond those required by normal
488   HTTP processing, that change the message in a way that would be
489   significant to the original sender or potentially significant to
490   downstream recipients).  For example, a transforming proxy might be
491   acting as a shared annotation server (modifying responses to include
492   references to a local annotation database), a malware filter, a
493   format transcoder, or an intranet-to-Internet privacy filter.  Such
494   transformations are presumed to be desired by the client (or client
495   organization) that selected the proxy and are beyond the scope of
496   this specification.  However, when a proxy is not intended to transform
497   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
498   requirements that preserve HTTP message semantics. See &status-203; and
499   &header-warning; for status and warning codes related to transformations.
500</t>
501<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
502<iref primary="true" item="accelerator"/>
503   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>") is an
504   intermediary that acts as an origin server for the outbound connection, but
505   translates received requests and forwards them inbound to another server or
506   servers. Gateways are often used to encapsulate legacy or untrusted
507   information services, to improve server performance through
508   "<x:dfn>accelerator</x:dfn>" caching, and to enable partitioning or load
509   balancing of HTTP services across multiple machines.
510</t>
511<t>
512   All HTTP requirements applicable to an origin server
513   also apply to the outbound communication of a gateway.
514   A gateway communicates with inbound servers using any protocol that
515   it desires, including private extensions to HTTP that are outside
516   the scope of this specification.  However, an HTTP-to-HTTP gateway
517   that wishes to interoperate with third-party HTTP servers ought to conform
518   to user agent requirements on the gateway's inbound connection.
519</t>
520<t><iref primary="true" item="tunnel"/>
521   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
522   without changing the messages. Once active, a tunnel is not
523   considered a party to the HTTP communication, though the tunnel might
524   have been initiated by an HTTP request. A tunnel ceases to exist when
525   both ends of the relayed connection are closed. Tunnels are used to
526   extend a virtual connection through an intermediary, such as when
527   Transport Layer Security (TLS, <xref target="RFC5246"/>) is used to
528   establish confidential communication through a shared firewall proxy.
529</t>
530<t><iref primary="true" item="interception proxy"/>
531<iref primary="true" item="transparent proxy"/>
532<iref primary="true" item="captive portal"/>
533   The above categories for intermediary only consider those acting as
534   participants in the HTTP communication.  There are also intermediaries
535   that can act on lower layers of the network protocol stack, filtering or
536   redirecting HTTP traffic without the knowledge or permission of message
537   senders. Network intermediaries often introduce security flaws or
538   interoperability problems by violating HTTP semantics.  For example, an
539   "<x:dfn>interception proxy</x:dfn>" <xref target="RFC3040"/> (also commonly
540   known as a "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/> or
541   "<x:dfn>captive portal</x:dfn>")
542   differs from an HTTP proxy because it is not selected by the client.
543   Instead, an interception proxy filters or redirects outgoing TCP port 80
544   packets (and occasionally other common port traffic).
545   Interception proxies are commonly found on public network access points,
546   as a means of enforcing account subscription prior to allowing use of
547   non-local Internet services, and within corporate firewalls to enforce
548   network usage policies.
549   They are indistinguishable from a man-in-the-middle attack.
550</t>
551<t>
552   HTTP is defined as a stateless protocol, meaning that each request message
553   can be understood in isolation.  Many implementations depend on HTTP's
554   stateless design in order to reuse proxied connections or dynamically
555   load-balance requests across multiple servers.  Hence, a server &MUST-NOT;
556   assume that two requests on the same connection are from the same user
557   agent unless the connection is secured and specific to that agent.
558   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
559   been known to violate this requirement, resulting in security and
560   interoperability problems.
561</t>
562</section>
563
564<section title="Caches" anchor="caches">
565<iref primary="true" item="cache"/>
566<t>
567   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
568   subsystem that controls its message storage, retrieval, and deletion.
569   A cache stores cacheable responses in order to reduce the response
570   time and network bandwidth consumption on future, equivalent
571   requests. Any client or server &MAY; employ a cache, though a cache
572   cannot be used by a server while it is acting as a tunnel.
573</t>
574<t>
575   The effect of a cache is that the request/response chain is shortened
576   if one of the participants along the chain has a cached response
577   applicable to that request. The following illustrates the resulting
578   chain if B has a cached copy of an earlier response from O (via C)
579   for a request that has not been cached by UA or A.
580</t>
581<figure><artwork type="drawing">
582            &gt;             &gt;
583       <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>
584                  &lt;             &lt;
585</artwork></figure>
586<t><iref primary="true" item="cacheable"/>
587   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
588   the response message for use in answering subsequent requests.
589   Even when a response is cacheable, there might be additional
590   constraints placed by the client or by the origin server on when
591   that cached response can be used for a particular request. HTTP
592   requirements for cache behavior and cacheable responses are
593   defined in &caching-overview;. 
594</t>
595<t>
596   There are a wide variety of architectures and configurations
597   of caches deployed across the World Wide Web and
598   inside large organizations. These include national hierarchies
599   of proxy caches to save transoceanic bandwidth, collaborative systems that
600   broadcast or multicast cache entries, archives of pre-fetched cache
601   entries for use in off-line or high-latency environments, and so on.
602</t>
603</section>
604
605<section title="Conformance and Error Handling" anchor="conformance">
606<t>
607   This specification targets conformance criteria according to the role of
608   a participant in HTTP communication.  Hence, HTTP requirements are placed
609   on senders, recipients, clients, servers, user agents, intermediaries,
610   origin servers, proxies, gateways, or caches, depending on what behavior
611   is being constrained by the requirement. Additional (social) requirements
612   are placed on implementations, resource owners, and protocol element
613   registrations when they apply beyond the scope of a single communication.
614</t>
615<t>
616   The verb "generate" is used instead of "send" where a requirement
617   differentiates between creating a protocol element and merely forwarding a
618   received element downstream.
619</t>
620<t>
621   An implementation is considered conformant if it complies with all of the
622   requirements associated with the roles it partakes in HTTP.
623</t>
624<t>
625   Conformance includes both the syntax and semantics of protocol
626   elements. A sender &MUST-NOT; generate protocol elements that convey a
627   meaning that is known by that sender to be false. A sender &MUST-NOT;
628   generate protocol elements that do not match the grammar defined by the
629   corresponding ABNF rules. Within a given message, a sender &MUST-NOT;
630   generate protocol elements or syntax alternatives that are only allowed to
631   be generated by participants in other roles (i.e., a role that the sender
632   does not have for that message).
633</t>
634<t>
635   When a received protocol element is parsed, the recipient &MUST; be able to
636   parse any value of reasonable length that is applicable to the recipient's
637   role and matches the grammar defined by the corresponding ABNF rules.
638   Note, however, that some received protocol elements might not be parsed.
639   For example, an intermediary forwarding a message might parse a
640   header-field into generic field-name and field-value components, but then
641   forward the header field without further parsing inside the field-value.
642</t>
643<t>
644   HTTP does not have specific length limitations for many of its protocol
645   elements because the lengths that might be appropriate will vary widely,
646   depending on the deployment context and purpose of the implementation.
647   Hence, interoperability between senders and recipients depends on shared
648   expectations regarding what is a reasonable length for each protocol
649   element. Furthermore, what is commonly understood to be a reasonable length
650   for some protocol elements has changed over the course of the past two
651   decades of HTTP use, and is expected to continue changing in the future.
652</t>
653<t>
654   At a minimum, a recipient &MUST; be able to parse and process protocol
655   element lengths that are at least as long as the values that it generates
656   for those same protocol elements in other messages. For example, an origin
657   server that publishes very long URI references to its own resources needs
658   to be able to parse and process those same references when received as a
659   request target.
660</t>
661<t>
662   A recipient &MUST; interpret a received protocol element according to the
663   semantics defined for it by this specification, including extensions to
664   this specification, unless the recipient has determined (through experience
665   or configuration) that the sender incorrectly implements what is implied by
666   those semantics.
667   For example, an origin server might disregard the contents of a received
668   <x:ref>Accept-Encoding</x:ref> header field if inspection of the
669   <x:ref>User-Agent</x:ref> header field indicates a specific implementation
670   version that is known to fail on receipt of certain content codings.
671</t>
672<t>
673   Unless noted otherwise, a recipient &MAY; attempt to recover a usable
674   protocol element from an invalid construct.  HTTP does not define
675   specific error handling mechanisms except when they have a direct impact
676   on security, since different applications of the protocol require
677   different error handling strategies.  For example, a Web browser might
678   wish to transparently recover from a response where the
679   <x:ref>Location</x:ref> header field doesn't parse according to the ABNF,
680   whereas a systems control client might consider any form of error recovery
681   to be dangerous.
682</t>
683</section>
684
685<section title="Protocol Versioning" anchor="http.version">
686  <x:anchor-alias value="HTTP-version"/>
687  <x:anchor-alias value="HTTP-name"/>
688<t>
689   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
690   versions of the protocol. This specification defines version "1.1".
691   The protocol version as a whole indicates the sender's conformance
692   with the set of requirements laid out in that version's corresponding
693   specification of HTTP.
694</t>
695<t>
696   The version of an HTTP message is indicated by an HTTP-version field
697   in the first line of the message. HTTP-version is case-sensitive.
698</t>
699<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/>
700  <x:ref>HTTP-version</x:ref>  = <x:ref>HTTP-name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
701  <x:ref>HTTP-name</x:ref>     = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
702</artwork></figure>
703<t>
704   The HTTP version number consists of two decimal digits separated by a "."
705   (period or decimal point).  The first digit ("major version") indicates the
706   HTTP messaging syntax, whereas the second digit ("minor version") indicates
707   the highest minor version within that major version to which the sender is
708   conformant and able to understand for future communication.  The minor
709   version advertises the sender's communication capabilities even when the
710   sender is only using a backwards-compatible subset of the protocol,
711   thereby letting the recipient know that more advanced features can
712   be used in response (by servers) or in future requests (by clients).
713</t>
714<t>
715   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
716   <xref target="RFC1945"/> or a recipient whose version is unknown,
717   the HTTP/1.1 message is constructed such that it can be interpreted
718   as a valid HTTP/1.0 message if all of the newer features are ignored.
719   This specification places recipient-version requirements on some
720   new features so that a conformant sender will only use compatible
721   features until it has determined, through configuration or the
722   receipt of a message, that the recipient supports HTTP/1.1.
723</t>
724<t>
725   The interpretation of a header field does not change between minor
726   versions of the same major HTTP version, though the default
727   behavior of a recipient in the absence of such a field can change.
728   Unless specified otherwise, header fields defined in HTTP/1.1 are
729   defined for all versions of HTTP/1.x.  In particular, the <x:ref>Host</x:ref>
730   and <x:ref>Connection</x:ref> header fields ought to be implemented by all
731   HTTP/1.x implementations whether or not they advertise conformance with
732   HTTP/1.1.
733</t>
734<t>
735   New header fields can be introduced without changing the protocol version
736   if their defined semantics allow them to be safely ignored by recipients
737   that do not recognize them. Header field extensibility is discussed in
738   <xref target="field.extensibility"/>.
739</t>
740<t>
741   Intermediaries that process HTTP messages (i.e., all intermediaries
742   other than those acting as tunnels) &MUST; send their own HTTP-version
743   in forwarded messages.  In other words, they are not allowed to blindly
744   forward the first line of an HTTP message without ensuring that the
745   protocol version in that message matches a version to which that
746   intermediary is conformant for both the receiving and
747   sending of messages.  Forwarding an HTTP message without rewriting
748   the HTTP-version might result in communication errors when downstream
749   recipients use the message sender's version to determine what features
750   are safe to use for later communication with that sender.
751</t>
752<t>
753   A client &SHOULD; send a request version equal to the highest
754   version to which the client is conformant and
755   whose major version is no higher than the highest version supported
756   by the server, if this is known.  A client &MUST-NOT; send a
757   version to which it is not conformant.
758</t>
759<t>
760   A client &MAY; send a lower request version if it is known that
761   the server incorrectly implements the HTTP specification, but only
762   after the client has attempted at least one normal request and determined
763   from the response status code or header fields (e.g., <x:ref>Server</x:ref>) that
764   the server improperly handles higher request versions.
765</t>
766<t>
767   A server &SHOULD; send a response version equal to the highest version to
768   which the server is conformant that has a major version less than or equal
769   to the one received in the request.
770   A server &MUST-NOT; send a version to which it is not conformant.
771   A server can send a <x:ref>505 (HTTP Version Not Supported)</x:ref>
772   response if it wishes, for any reason, to refuse service of the client's
773   major protocol version.
774</t>
775<t>
776   A server &MAY; send an HTTP/1.0 response to a request
777   if it is known or suspected that the client incorrectly implements the
778   HTTP specification and is incapable of correctly processing later
779   version responses, such as when a client fails to parse the version
780   number correctly or when an intermediary is known to blindly forward
781   the HTTP-version even when it doesn't conform to the given minor
782   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
783   performed unless triggered by specific client attributes, such as when
784   one or more of the request header fields (e.g., <x:ref>User-Agent</x:ref>)
785   uniquely match the values sent by a client known to be in error.
786</t>
787<t>
788   The intention of HTTP's versioning design is that the major number
789   will only be incremented if an incompatible message syntax is
790   introduced, and that the minor number will only be incremented when
791   changes made to the protocol have the effect of adding to the message
792   semantics or implying additional capabilities of the sender.  However,
793   the minor version was not incremented for the changes introduced between
794   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
795   has specifically avoided any such changes to the protocol.
796</t>
797<t>
798   When an HTTP message is received with a major version number that the
799   recipient implements, but a higher minor version number than what the
800   recipient implements, the recipient &SHOULD; process the message as if it
801   were in the highest minor version within that major version to which the
802   recipient is conformant. A recipient can assume that a message with a
803   higher minor version, when sent to a recipient that has not yet indicated
804   support for that higher version, is sufficiently backwards-compatible to be
805   safely processed by any implementation of the same major version.
806</t>
807</section>
808
809<section title="Uniform Resource Identifiers" anchor="uri">
810<iref primary="true" item="resource"/>
811<t>
812   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
813   throughout HTTP as the means for identifying resources (&resource;).
814   URI references are used to target requests, indicate redirects, and define
815   relationships.
816</t>
817  <x:anchor-alias value="URI-reference"/>
818  <x:anchor-alias value="absolute-URI"/>
819  <x:anchor-alias value="relative-part"/>
820  <x:anchor-alias value="authority"/>
821  <x:anchor-alias value="uri-host"/>
822  <x:anchor-alias value="port"/>
823  <x:anchor-alias value="path-abempty"/>
824  <x:anchor-alias value="segment"/>
825  <x:anchor-alias value="query"/>
826  <x:anchor-alias value="fragment"/>
827  <x:anchor-alias value="absolute-path"/>
828  <x:anchor-alias value="partial-URI"/>
829<t>
830   This specification adopts the definitions of "URI-reference",
831   "absolute-URI", "relative-part", "authority", "port", "host",
832   "path-abempty", "segment", "query", and "fragment" from the
833   URI generic syntax.
834   In addition, we define an "absolute-path" rule (that differs from
835   RFC 3986's "path-absolute" in that it allows a leading "//")
836   and a "partial-URI" rule for protocol elements
837   that allow a relative URI but not a fragment.
838</t>
839<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="absolute-path"/><iref primary="true" item="Grammar" subitem="port"/><iref primary="true" item="Grammar" subitem="query"/><iref primary="true" item="Grammar" subitem="fragment"/><iref primary="true" item="Grammar" subitem="segment"/><iref primary="true" item="Grammar" subitem="uri-host"/><iref primary="true" item="Grammar" subitem="partial-URI"><!--exported production--></iref>
840  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
841  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
842  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
843  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
844  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
845  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
846  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
847  <x:ref>segment</x:ref>       = &lt;segment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
848  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
849  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>&gt;
850 
851  <x:ref>absolute-path</x:ref> = 1*( "/" segment )
852  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
853</artwork></figure>
854<t>
855   Each protocol element in HTTP that allows a URI reference will indicate
856   in its ABNF production whether the element allows any form of reference
857   (URI-reference), only a URI in absolute form (absolute-URI), only the
858   path and optional query components, or some combination of the above.
859   Unless otherwise indicated, URI references are parsed
860   relative to the effective request URI
861   (<xref target="effective.request.uri"/>).
862</t>
863
864<section title="http URI scheme" anchor="http.uri">
865  <x:anchor-alias value="http-URI"/>
866  <iref item="http URI scheme" primary="true"/>
867  <iref item="URI scheme" subitem="http" primary="true"/>
868<t>
869   The "http" URI scheme is hereby defined for the purpose of minting
870   identifiers according to their association with the hierarchical
871   namespace governed by a potential HTTP origin server listening for
872   TCP (<xref target="RFC0793"/>) connections on a given port.
873</t>
874<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"><!--terminal production--></iref>
875  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
876             [ "#" <x:ref>fragment</x:ref> ]
877</artwork></figure>
878<t>
879   The HTTP origin server is identified by the generic syntax's
880   <x:ref>authority</x:ref> component, which includes a host identifier
881   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
882   The remainder of the URI, consisting of both the hierarchical path
883   component and optional query component, serves as an identifier for
884   a potential resource within that origin server's name space.
885</t>
886<t>
887   A sender &MUST-NOT; generate an "http" URI with an empty host identifier.
888   A recipient that processes such a URI reference &MUST; reject it as invalid.
889</t>
890<t>
891   If the host identifier is provided as an IP address,
892   then the origin server is any listener on the indicated TCP port at
893   that IP address. If host is a registered name, then that name is
894   considered an indirect identifier and the recipient might use a name
895   resolution service, such as DNS, to find the address of a listener
896   for that host.
897   If the port subcomponent is empty or not given, then TCP port 80 is
898   assumed (the default reserved port for WWW services).
899</t>
900<t>
901   Regardless of the form of host identifier, access to that host is not
902   implied by the mere presence of its name or address. The host might or might
903   not exist and, even when it does exist, might or might not be running an
904   HTTP server or listening to the indicated port. The "http" URI scheme
905   makes use of the delegated nature of Internet names and addresses to
906   establish a naming authority (whatever entity has the ability to place
907   an HTTP server at that Internet name or address) and allows that
908   authority to determine which names are valid and how they might be used.
909</t>
910<t>
911   When an "http" URI is used within a context that calls for access to the
912   indicated resource, a client &MAY; attempt access by resolving
913   the host to an IP address, establishing a TCP connection to that address
914   on the indicated port, and sending an HTTP request message
915   (<xref target="http.message"/>) containing the URI's identifying data
916   (<xref target="message.routing"/>) to the server.
917   If the server responds to that request with a non-interim HTTP response
918   message, as described in &status-codes;, then that response
919   is considered an authoritative answer to the client's request.
920</t>
921<t>
922   Although HTTP is independent of the transport protocol, the "http"
923   scheme is specific to TCP-based services because the name delegation
924   process depends on TCP for establishing authority.
925   An HTTP service based on some other underlying connection protocol
926   would presumably be identified using a different URI scheme, just as
927   the "https" scheme (below) is used for resources that require an
928   end-to-end secured connection. Other protocols might also be used to
929   provide access to "http" identified resources &mdash; it is only the
930   authoritative interface that is specific to TCP.
931</t>
932<t>
933   The URI generic syntax for authority also includes a deprecated
934   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
935   for including user authentication information in the URI.  Some
936   implementations make use of the userinfo component for internal
937   configuration of authentication information, such as within command
938   invocation options, configuration files, or bookmark lists, even
939   though such usage might expose a user identifier or password.
940   A sender &MUST-NOT; generate the userinfo subcomponent (and its "@"
941   delimiter) when an "http" URI reference is generated within a message as a
942   request target or header field value.
943   Before making use of an "http" URI reference received from an untrusted
944   source, a recipient ought to parse for userinfo and treat its presence as
945   an error; it is likely being used to obscure the authority for the sake of
946   phishing attacks.
947</t>
948</section>
949
950<section title="https URI scheme" anchor="https.uri">
951   <x:anchor-alias value="https-URI"/>
952   <iref item="https URI scheme"/>
953   <iref item="URI scheme" subitem="https"/>
954<t>
955   The "https" URI scheme is hereby defined for the purpose of minting
956   identifiers according to their association with the hierarchical
957   namespace governed by a potential HTTP origin server listening to a
958   given TCP port for TLS-secured connections
959   (<xref target="RFC0793"/>, <xref target="RFC5246"/>).
960</t>
961<t>
962   All of the requirements listed above for the "http" scheme are also
963   requirements for the "https" scheme, except that a default TCP port
964   of 443 is assumed if the port subcomponent is empty or not given,
965   and the user agent &MUST; ensure that its connection to the origin
966   server is secured through the use of strong encryption, end-to-end,
967   prior to sending the first HTTP request.
968</t>
969<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"><!--terminal production--></iref>
970  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
971              [ "#" <x:ref>fragment</x:ref> ]
972</artwork></figure>
973<t>
974   Note that the "https" URI scheme depends on both TLS and TCP for
975   establishing authority.
976   Resources made available via the "https" scheme have no shared
977   identity with the "http" scheme even if their resource identifiers
978   indicate the same authority (the same host listening to the same
979   TCP port).  They are distinct name spaces and are considered to be
980   distinct origin servers.  However, an extension to HTTP that is
981   defined to apply to entire host domains, such as the Cookie protocol
982   <xref target="RFC6265"/>, can allow information
983   set by one service to impact communication with other services
984   within a matching group of host domains.
985</t>
986<t>
987   The process for authoritative access to an "https" identified
988   resource is defined in <xref target="RFC2818"/>.
989</t>
990</section>
991
992<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
993<t>
994   Since the "http" and "https" schemes conform to the URI generic syntax,
995   such URIs are normalized and compared according to the algorithm defined
996   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
997   described above for each scheme.
998</t>
999<t>
1000   If the port is equal to the default port for a scheme, the normal form is
1001   to omit the port subcomponent. When not being used in absolute form as the
1002   request target of an OPTIONS request, an empty path component is equivalent
1003   to an absolute path of "/", so the normal form is to provide a path of "/"
1004   instead. The scheme and host are case-insensitive and normally provided in
1005   lowercase; all other components are compared in a case-sensitive manner.
1006   Characters other than those in the "reserved" set are equivalent to their
1007   percent-encoded octets (see <xref target="RFC3986" x:fmt=","
1008   x:sec="2.1"/>): the normal form is to not encode them.
1009</t>
1010<t>
1011   For example, the following three URIs are equivalent:
1012</t>
1013<figure><artwork type="example">
1014   http://example.com:80/~smith/home.html
1015   http://EXAMPLE.com/%7Esmith/home.html
1016   http://EXAMPLE.com:/%7esmith/home.html
1017</artwork></figure>
1018</section>
1019</section>
1020</section>
1021
1022<section title="Message Format" anchor="http.message">
1023<x:anchor-alias value="generic-message"/>
1024<x:anchor-alias value="message.types"/>
1025<x:anchor-alias value="HTTP-message"/>
1026<x:anchor-alias value="start-line"/>
1027<iref item="header section"/>
1028<iref item="headers"/>
1029<iref item="header field"/>
1030<t>
1031   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1032   octets in a format similar to the Internet Message Format
1033   <xref target="RFC5322"/>: zero or more header fields (collectively
1034   referred to as the "headers" or the "header section"), an empty line
1035   indicating the end of the header section, and an optional message body.
1036</t>
1037<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"><!--terminal production--></iref>
1038  <x:ref>HTTP-message</x:ref>   = <x:ref>start-line</x:ref>
1039                   *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1040                   <x:ref>CRLF</x:ref>
1041                   [ <x:ref>message-body</x:ref> ]
1042</artwork></figure>
1043<t>
1044   The normal procedure for parsing an HTTP message is to read the
1045   start-line into a structure, read each header field into a hash
1046   table by field name until the empty line, and then use the parsed
1047   data to determine if a message body is expected.  If a message body
1048   has been indicated, then it is read as a stream until an amount
1049   of octets equal to the message body length is read or the connection
1050   is closed.
1051</t>
1052<t>
1053   A recipient &MUST; parse an HTTP message as a sequence of octets in an
1054   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1055   Parsing an HTTP message as a stream of Unicode characters, without regard
1056   for the specific encoding, creates security vulnerabilities due to the
1057   varying ways that string processing libraries handle invalid multibyte
1058   character sequences that contain the octet LF (%x0A).  String-based
1059   parsers can only be safely used within protocol elements after the element
1060   has been extracted from the message, such as within a header field-value
1061   after message parsing has delineated the individual fields.
1062</t>
1063<t>
1064   An HTTP message can be parsed as a stream for incremental processing or
1065   forwarding downstream.  However, recipients cannot rely on incremental
1066   delivery of partial messages, since some implementations will buffer or
1067   delay message forwarding for the sake of network efficiency, security
1068   checks, or payload transformations.
1069</t>
1070<t>
1071   A sender &MUST-NOT; send whitespace between the start-line and
1072   the first header field.
1073   A recipient that receives whitespace between the start-line and
1074   the first header field &MUST; either reject the message as invalid or
1075   consume each whitespace-preceded line without further processing of it
1076   (i.e., ignore the entire line, along with any subsequent lines preceded
1077   by whitespace, until a properly formed header field is received or the
1078   header section is terminated).
1079</t>
1080<t>
1081   The presence of such whitespace in a request
1082   might be an attempt to trick a server into ignoring that field or
1083   processing the line after it as a new request, either of which might
1084   result in a security vulnerability if other implementations within
1085   the request chain interpret the same message differently.
1086   Likewise, the presence of such whitespace in a response might be
1087   ignored by some clients or cause others to cease parsing.
1088</t>
1089
1090<section title="Start Line" anchor="start.line">
1091  <x:anchor-alias value="Start-Line"/>
1092<t>
1093   An HTTP message can either be a request from client to server or a
1094   response from server to client.  Syntactically, the two types of message
1095   differ only in the start-line, which is either a request-line (for requests)
1096   or a status-line (for responses), and in the algorithm for determining
1097   the length of the message body (<xref target="message.body"/>).
1098</t>
1099<t>
1100   In theory, a client could receive requests and a server could receive
1101   responses, distinguishing them by their different start-line formats,
1102   but in practice servers are implemented to only expect a request
1103   (a response is interpreted as an unknown or invalid request method)
1104   and clients are implemented to only expect a response.
1105</t>
1106<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1107  <x:ref>start-line</x:ref>     = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1108</artwork></figure>
1109
1110<section title="Request Line" anchor="request.line">
1111  <x:anchor-alias value="Request"/>
1112  <x:anchor-alias value="request-line"/>
1113<t>
1114   A request-line begins with a method token, followed by a single
1115   space (SP), the request-target, another single space (SP), the
1116   protocol version, and ending with CRLF.
1117</t>
1118<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1119  <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>
1120</artwork></figure>
1121<iref primary="true" item="method"/>
1122<t anchor="method">
1123   The method token indicates the request method to be performed on the
1124   target resource. The request method is case-sensitive.
1125</t>
1126<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1127  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1128</artwork></figure>
1129<t>
1130   The request methods defined by this specification can be found in
1131   &methods;, along with information regarding the HTTP method registry
1132   and considerations for defining new methods.
1133</t>
1134<iref item="request-target"/>
1135<t>
1136   The request-target identifies the target resource upon which to apply
1137   the request, as defined in <xref target="request-target"/>.
1138</t>
1139<t>
1140   Recipients typically parse the request-line into its component parts by
1141   splitting on whitespace (see <xref target="message.robustness"/>), since
1142   no whitespace is allowed in the three components.
1143   Unfortunately, some user agents fail to properly encode or exclude
1144   whitespace found in hypertext references, resulting in those disallowed
1145   characters being sent in a request-target.
1146</t>
1147<t>
1148   Recipients of an invalid request-line &SHOULD; respond with either a
1149   <x:ref>400 (Bad Request)</x:ref> error or a <x:ref>301 (Moved Permanently)</x:ref>
1150   redirect with the request-target properly encoded.  A recipient &SHOULD-NOT;
1151   attempt to autocorrect and then process the request without a redirect,
1152   since the invalid request-line might be deliberately crafted to bypass
1153   security filters along the request chain.
1154</t>
1155<t>
1156   HTTP does not place a pre-defined limit on the length of a request-line.
1157   A server that receives a method longer than any that it implements
1158   &SHOULD; respond with a <x:ref>501 (Not Implemented)</x:ref> status code.
1159   A server ought to be prepared to receive URIs of unbounded length, as
1160   described in <xref target="conformance"/>, and &MUST; respond with a
1161   <x:ref>414 (URI Too Long)</x:ref> status code if the received
1162   request-target is longer than the server wishes to parse (see &status-414;).
1163</t>
1164<t>
1165   Various ad-hoc limitations on request-line length are found in practice.
1166   It is &RECOMMENDED; that all HTTP senders and recipients support, at a
1167   minimum, request-line lengths of 8000 octets.
1168</t>
1169</section>
1170
1171<section title="Status Line" anchor="status.line">
1172  <x:anchor-alias value="response"/>
1173  <x:anchor-alias value="status-line"/>
1174  <x:anchor-alias value="status-code"/>
1175  <x:anchor-alias value="reason-phrase"/>
1176<t>
1177   The first line of a response message is the status-line, consisting
1178   of the protocol version, a space (SP), the status code, another space,
1179   a possibly-empty textual phrase describing the status code, and
1180   ending with CRLF.
1181</t>
1182<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1183  <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>
1184</artwork></figure>
1185<t>
1186   The status-code element is a 3-digit integer code describing the
1187   result of the server's attempt to understand and satisfy the client's
1188   corresponding request. The rest of the response message is to be
1189   interpreted in light of the semantics defined for that status code.
1190   See &status-codes; for information about the semantics of status codes,
1191   including the classes of status code (indicated by the first digit),
1192   the status codes defined by this specification, considerations for the
1193   definition of new status codes, and the IANA registry.
1194</t>
1195<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1196  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1197</artwork></figure>
1198<t>  
1199   The reason-phrase element exists for the sole purpose of providing a
1200   textual description associated with the numeric status code, mostly
1201   out of deference to earlier Internet application protocols that were more
1202   frequently used with interactive text clients. A client &SHOULD; ignore
1203   the reason-phrase content.
1204</t>
1205<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1206  <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> )
1207</artwork></figure>
1208</section>
1209</section>
1210
1211<section title="Header Fields" anchor="header.fields">
1212  <x:anchor-alias value="header-field"/>
1213  <x:anchor-alias value="field-content"/>
1214  <x:anchor-alias value="field-name"/>
1215  <x:anchor-alias value="field-value"/>
1216  <x:anchor-alias value="obs-fold"/>
1217<t>
1218   Each HTTP header field consists of a case-insensitive field name
1219   followed by a colon (":"), optional leading whitespace, the field value,
1220   and optional trailing whitespace.
1221</t>
1222<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"/>
1223  <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>OWS</x:ref>
1224  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1225  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1226  <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> )
1227  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1228                 ; obsolete line folding
1229                 ; see <xref target="field.parsing"/>
1230</artwork></figure>
1231<t>
1232   The field-name token labels the corresponding field-value as having the
1233   semantics defined by that header field.  For example, the <x:ref>Date</x:ref>
1234   header field is defined in &header-date; as containing the origination
1235   timestamp for the message in which it appears.
1236</t>
1237<t>
1238   Extraction of field-name/field-value pairs from a message is generic and
1239   thus independent of the actual field name. Consequently, the ABNF specified
1240   for each header field only defines the syntax of the field-value (not the
1241   whole header-field, as it was the case in previous revisions of this
1242   specification).
1243</t>
1244
1245<section title="Field Extensibility" anchor="field.extensibility">
1246<t>
1247   Header fields are fully extensible: there is no limit on the
1248   introduction of new field names, each presumably defining new semantics,
1249   nor on the number of header fields used in a given message.  Existing
1250   fields are defined in each part of this specification and in many other
1251   specifications outside the core standard.
1252</t>
1253<t>
1254   New header fields can be defined such that, when they are understood by a
1255   recipient, they might override or enhance the interpretation of previously
1256   defined header fields, define preconditions on request evaluation, or
1257   refine the meaning of responses.
1258</t>
1259<t>
1260   A proxy &MUST; forward unrecognized header fields unless the
1261   field-name is listed in the <x:ref>Connection</x:ref> header field
1262   (<xref target="header.connection"/>) or the proxy is specifically
1263   configured to block, or otherwise transform, such fields.
1264   Other recipients &SHOULD; ignore unrecognized header fields.
1265   These requirements allow HTTP's functionality to be enhanced without
1266   requiring prior update of deployed intermediaries.
1267</t>
1268<t>
1269   All defined header fields ought to be registered with IANA in the
1270   Message Header Field Registry, as described in &iana-header-registry;.
1271</t>
1272</section>
1273
1274<section title="Field Order" anchor="field.order">
1275<t>
1276   The order in which header fields with differing field names are
1277   received is not significant. However, it is "good practice" to send
1278   header fields that contain control data first, such as <x:ref>Host</x:ref>
1279   on requests and <x:ref>Date</x:ref> on responses, so that implementations
1280   can decide when not to handle a message as early as possible.  A server
1281   &MUST; wait until the entire header section is received before interpreting
1282   a request message, since later header fields might include conditionals,
1283   authentication credentials, or deliberately misleading duplicate
1284   header fields that would impact request processing.
1285</t>
1286<t>
1287   A sender &MUST-NOT; generate multiple header fields with the same field
1288   name in a message unless either the entire field value for that
1289   header field is defined as a comma-separated list [i.e., #(values)]
1290   or the header field is a well-known exception (as noted below).
1291</t>
1292<t>
1293   A recipient &MAY; combine multiple header fields with the same field name
1294   into one "field-name: field-value" pair, without changing the semantics of
1295   the message, by appending each subsequent field value to the combined
1296   field value in order, separated by a comma. The order in which
1297   header fields with the same field name are received is therefore
1298   significant to the interpretation of the combined field value;
1299   a proxy &MUST-NOT; change the order of these field values when
1300   forwarding a message.
1301</t>
1302<x:note>
1303  <t>
1304   &Note; In practice, the "Set-Cookie" header field (<xref target="RFC6265"/>)
1305   often appears multiple times in a response message and does not use the
1306   list syntax, violating the above requirements on multiple header fields
1307   with the same name. Since it cannot be combined into a single field-value,
1308   recipients ought to handle "Set-Cookie" as a special case while processing
1309   header fields. (See Appendix A.2.3 of <xref target="Kri2001"/> for details.)
1310  </t>
1311</x:note>
1312</section>
1313
1314<section title="Whitespace" anchor="whitespace">
1315<t anchor="rule.LWS">
1316   This specification uses three rules to denote the use of linear
1317   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1318   BWS ("bad" whitespace).
1319</t>
1320<t anchor="rule.OWS">
1321   The OWS rule is used where zero or more linear whitespace octets might
1322   appear. For protocol elements where optional whitespace is preferred to
1323   improve readability, a sender &SHOULD; generate the optional whitespace
1324   as a single SP; otherwise, a sender &SHOULD-NOT; generate optional
1325   whitespace except as needed to white-out invalid or unwanted protocol
1326   elements during in-place message filtering.
1327</t>
1328<t anchor="rule.RWS">
1329   The RWS rule is used when at least one linear whitespace octet is required
1330   to separate field tokens. A sender &SHOULD; generate RWS as a single SP.
1331</t>
1332<t anchor="rule.BWS">
1333   The BWS rule is used where the grammar allows optional whitespace only for
1334   historical reasons. A sender &MUST-NOT; generate BWS in messages.
1335   A recipient &MUST; parse for such bad whitespace and remove it before
1336   interpreting the protocol element.
1337</t>
1338<t anchor="rule.whitespace">
1339  <x:anchor-alias value="BWS"/>
1340  <x:anchor-alias value="OWS"/>
1341  <x:anchor-alias value="RWS"/>
1342</t>
1343<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"/>
1344  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1345                 ; optional whitespace
1346  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1347                 ; required whitespace
1348  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1349                 ; "bad" whitespace
1350</artwork></figure>
1351</section>
1352
1353<section title="Field Parsing" anchor="field.parsing">
1354<t>
1355   No whitespace is allowed between the header field-name and colon.
1356   In the past, differences in the handling of such whitespace have led to
1357   security vulnerabilities in request routing and response handling.
1358   A server &MUST; reject any received request message that contains
1359   whitespace between a header field-name and colon with a response code of
1360   <x:ref>400 (Bad Request)</x:ref>. A proxy &MUST; remove any such whitespace
1361   from a response message before forwarding the message downstream.
1362</t>
1363<t>
1364   A field value is preceded by optional whitespace (OWS); a single SP is
1365   preferred. The field value does not include any leading or trailing white
1366   space: OWS occurring before the first non-whitespace octet of the field
1367   value or after the last non-whitespace octet of the field value ought to be
1368   excluded by parsers when extracting the field value from a header field.
1369</t>
1370<t>
1371   A recipient of field-content containing multiple sequential octets of
1372   optional (OWS) or required (RWS) whitespace &SHOULD; either replace the
1373   sequence with a single SP or transform any non-SP octets in the sequence to
1374   SP octets before interpreting the field value or forwarding the message
1375   downstream.
1376</t>
1377<t>
1378   Historically, HTTP header field values could be extended over multiple
1379   lines by preceding each extra line with at least one space or horizontal
1380   tab (obs-fold). This specification deprecates such line folding except
1381   within the message/http media type
1382   (<xref target="internet.media.type.message.http"/>).
1383   A sender &MUST-NOT; generate a message that includes line folding
1384   (i.e., that has any field-value that contains a match to the
1385   <x:ref>obs-fold</x:ref> rule) unless the message is intended for packaging
1386   within the message/http media type.
1387</t>
1388<t>
1389   A server that receives an <x:ref>obs-fold</x:ref> in a request message that
1390   is not within a message/http container &MUST; either reject the message by
1391   sending a <x:ref>400 (Bad Request)</x:ref>, preferably with a
1392   representation explaining that obsolete line folding is unacceptable, or
1393   replace each received <x:ref>obs-fold</x:ref> with one or more
1394   <x:ref>SP</x:ref> octets prior to interpreting the field value or
1395   forwarding the message downstream.
1396</t>
1397<t>
1398   A proxy or gateway that receives an <x:ref>obs-fold</x:ref> in a response
1399   message that is not within a message/http container &MUST; either discard
1400   the message and replace it with a <x:ref>502 (Bad Gateway)</x:ref>
1401   response, preferably with a representation explaining that unacceptable
1402   line folding was received, or replace each received <x:ref>obs-fold</x:ref>
1403   with one or more <x:ref>SP</x:ref> octets prior to interpreting the field
1404   value or forwarding the message downstream.
1405</t>
1406<t>
1407   A user agent that receives an <x:ref>obs-fold</x:ref> in a response message
1408   that is not within a message/http container &MUST; replace each received
1409   <x:ref>obs-fold</x:ref> with one or more <x:ref>SP</x:ref> octets prior to
1410   interpreting the field value.
1411</t>
1412<t>
1413   Historically, HTTP has allowed field content with text in the ISO-8859-1
1414   <xref target="ISO-8859-1"/> charset, supporting other charsets only
1415   through use of <xref target="RFC2047"/> encoding.
1416   In practice, most HTTP header field values use only a subset of the
1417   US-ASCII charset <xref target="USASCII"/>. Newly defined
1418   header fields &SHOULD; limit their field values to US-ASCII octets.
1419   A recipient &SHOULD; treat other octets in field content (obs-text) as
1420   opaque data.
1421</t>
1422</section>
1423
1424<section title="Field Limits" anchor="field.limits">
1425<t>
1426   HTTP does not place a pre-defined limit on the length of each header field
1427   or on the length of the header section as a whole, as described in
1428   <xref target="conformance"/>. Various ad-hoc limitations on individual
1429   header field length are found in practice, often depending on the specific
1430   field semantics.
1431</t>
1432<t>
1433   A server ought to be prepared to receive request header fields of unbounded
1434   length and &MUST; respond with an appropriate
1435   <x:ref>4xx (Client Error)</x:ref> status code if the received header
1436   field(s) are larger than the server wishes to process.
1437</t>
1438<t>
1439   A client ought to be prepared to receive response header fields of
1440   unbounded length.
1441   A client &MAY; discard or truncate received header fields that are larger
1442   than the client wishes to process if the field semantics are such that the
1443   dropped value(s) can be safely ignored without changing the
1444   message framing or response semantics.
1445</t>
1446</section>
1447
1448<section title="Field value components" anchor="field.components">
1449<t anchor="rule.token.separators">
1450  <x:anchor-alias value="tchar"/>
1451  <x:anchor-alias value="token"/>
1452  <x:anchor-alias value="special"/>
1453   Most HTTP header field values are defined using common syntax components
1454   (token, quoted-string, and comment) separated by whitespace or specific
1455   delimiting characters. Delimiters are chosen from the set of US-ASCII
1456   visual characters not allowed in a token ({VCHAR - tchar}).
1457</t>
1458<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/>
1459  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1460<!--
1461  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1462 -->
1463  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1464                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1465                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1466                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1467
1468  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1469                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1470                 / "]" / "?" / "=" / "{" / "}"
1471</artwork></figure>
1472<t anchor="rule.quoted-string">
1473  <x:anchor-alias value="quoted-string"/>
1474  <x:anchor-alias value="qdtext"/>
1475  <x:anchor-alias value="obs-text"/>
1476   A string of text is parsed as a single value if it is quoted using
1477   double-quote marks.
1478</t>
1479<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"/>
1480  <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>
1481  <x:ref>qdtext</x:ref>         = <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> /%x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1482  <x:ref>obs-text</x:ref>       = %x80-FF
1483</artwork></figure>
1484<t anchor="rule.comment">
1485  <x:anchor-alias value="comment"/>
1486  <x:anchor-alias value="ctext"/>
1487   Comments can be included in some HTTP header fields by surrounding
1488   the comment text with parentheses. Comments are only allowed in
1489   fields containing "comment" as part of their field value definition.
1490</t>
1491<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1492  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1493  <x:ref>ctext</x:ref>          = <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1494</artwork></figure>
1495<t anchor="rule.quoted-pair">
1496  <x:anchor-alias value="quoted-pair"/>
1497   The backslash octet ("\") can be used as a single-octet
1498   quoting mechanism within quoted-string and comment constructs.
1499   Recipients that process the value of a quoted-string &MUST; handle a
1500   quoted-pair as if it were replaced by the octet following the backslash.
1501</t>
1502<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1503  <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> )
1504</artwork></figure>
1505<t>
1506   A sender &SHOULD-NOT; generate a quoted-pair in a quoted-string except
1507   where necessary to quote DQUOTE and backslash octets occurring within that
1508   string.
1509   A sender &SHOULD-NOT; generate a quoted-pair in a comment except
1510   where necessary to quote parentheses ["(" and ")"] and backslash octets
1511   occurring within that comment.
1512</t>
1513</section>
1514
1515</section>
1516
1517<section title="Message Body" anchor="message.body">
1518  <x:anchor-alias value="message-body"/>
1519<t>
1520   The message body (if any) of an HTTP message is used to carry the
1521   payload body of that request or response.  The message body is
1522   identical to the payload body unless a transfer coding has been
1523   applied, as described in <xref target="header.transfer-encoding"/>.
1524</t>
1525<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1526  <x:ref>message-body</x:ref> = *OCTET
1527</artwork></figure>
1528<t>
1529   The rules for when a message body is allowed in a message differ for
1530   requests and responses.
1531</t>
1532<t>
1533   The presence of a message body in a request is signaled by a
1534   <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1535   field. Request message framing is independent of method semantics,
1536   even if the method does not define any use for a message body.
1537</t>
1538<t>
1539   The presence of a message body in a response depends on both
1540   the request method to which it is responding and the response
1541   status code (<xref target="status.line"/>).
1542   Responses to the HEAD request method never include a message body
1543   because the associated response header fields (e.g.,
1544   <x:ref>Transfer-Encoding</x:ref>, <x:ref>Content-Length</x:ref>, etc.),
1545   if present, indicate only what their values would have been if the request
1546   method had been GET (&HEAD;).
1547   <x:ref>2xx (Successful)</x:ref> responses to CONNECT switch to tunnel
1548   mode instead of having a message body (&CONNECT;).
1549   All <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, and
1550   <x:ref>304 (Not Modified)</x:ref> responses do not include a message body.
1551   All other responses do include a message body, although the body
1552   might be of zero length.
1553</t>
1554
1555<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1556  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1557  <iref item="chunked (Coding Format)"/>
1558  <x:anchor-alias value="Transfer-Encoding"/>
1559<t>
1560   The Transfer-Encoding header field lists the transfer coding names
1561   corresponding to the sequence of transfer codings that have been
1562   (or will be) applied to the payload body in order to form the message body.
1563   Transfer codings are defined in <xref target="transfer.codings"/>.
1564</t>
1565<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1566  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1567</artwork></figure>
1568<t>
1569   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1570   MIME, which was designed to enable safe transport of binary data over a
1571   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1572   However, safe transport has a different focus for an 8bit-clean transfer
1573   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1574   accurately delimit a dynamically generated payload and to distinguish
1575   payload encodings that are only applied for transport efficiency or
1576   security from those that are characteristics of the selected resource.
1577</t>
1578<t>
1579   A recipient &MUST; be able to parse the chunked transfer coding
1580   (<xref target="chunked.encoding"/>) because it plays a crucial role in
1581   framing messages when the payload body size is not known in advance.
1582   A sender &MUST-NOT; apply chunked more than once to a message body
1583   (i.e., chunking an already chunked message is not allowed).
1584   If any transfer coding other than chunked is applied to a request payload
1585   body, the sender &MUST; apply chunked as the final transfer coding to
1586   ensure that the message is properly framed.
1587   If any transfer coding other than chunked is applied to a response payload
1588   body, the sender &MUST; either apply chunked as the final transfer coding
1589   or terminate the message by closing the connection.
1590</t>
1591<figure><preamble>
1592   For example,
1593</preamble><artwork type="example">
1594  Transfer-Encoding: gzip, chunked
1595</artwork><postamble>
1596   indicates that the payload body has been compressed using the gzip
1597   coding and then chunked using the chunked coding while forming the
1598   message body.
1599</postamble></figure>
1600<t>
1601   Unlike <x:ref>Content-Encoding</x:ref> (&content-codings;),
1602   Transfer-Encoding is a property of the message, not of the representation, and
1603   any recipient along the request/response chain &MAY; decode the received
1604   transfer coding(s) or apply additional transfer coding(s) to the message
1605   body, assuming that corresponding changes are made to the Transfer-Encoding
1606   field-value. Additional information about the encoding parameters &MAY; be
1607   provided by other header fields not defined by this specification.
1608</t>
1609<t>
1610   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1611   <x:ref>304 (Not Modified)</x:ref> response (&status-304;) to a GET request,
1612   neither of which includes a message body,
1613   to indicate that the origin server would have applied a transfer coding
1614   to the message body if the request had been an unconditional GET.
1615   This indication is not required, however, because any recipient on
1616   the response chain (including the origin server) can remove transfer
1617   codings when they are not needed.
1618</t>
1619<t>
1620   A server &MUST-NOT; send a Transfer-Encoding header field in any response
1621   with a status code of
1622   <x:ref>1xx (Informational)</x:ref> or <x:ref>204 (No Content)</x:ref>.
1623   A server &MUST-NOT; send a Transfer-Encoding header field in any
1624   <x:ref>2xx (Successful)</x:ref> response to a CONNECT request (&CONNECT;).
1625</t>
1626<t>
1627   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1628   implementations advertising only HTTP/1.0 support will not understand
1629   how to process a transfer-encoded payload.
1630   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1631   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1632   might be in the form of specific user configuration or by remembering the
1633   version of a prior received response.
1634   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1635   the corresponding request indicates HTTP/1.1 (or later).
1636</t>
1637<t>
1638   A server that receives a request message with a transfer coding it does
1639   not understand &SHOULD; respond with <x:ref>501 (Not Implemented)</x:ref>.
1640</t>
1641</section>
1642
1643<section title="Content-Length" anchor="header.content-length">
1644  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1645  <x:anchor-alias value="Content-Length"/>
1646<t>
1647   When a message does not have a <x:ref>Transfer-Encoding</x:ref> header
1648   field, a Content-Length header field can provide the anticipated size,
1649   as a decimal number of octets, for a potential payload body.
1650   For messages that do include a payload body, the Content-Length field-value
1651   provides the framing information necessary for determining where the body
1652   (and message) ends.  For messages that do not include a payload body, the
1653   Content-Length indicates the size of the selected representation
1654   (&representation;).
1655</t>
1656<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1657  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1658</artwork></figure>
1659<t>
1660   An example is
1661</t>
1662<figure><artwork type="example">
1663  Content-Length: 3495
1664</artwork></figure>
1665<t>
1666   A sender &MUST-NOT; send a Content-Length header field in any message that
1667   contains a <x:ref>Transfer-Encoding</x:ref> header field.
1668</t>
1669<t>
1670   A user agent &SHOULD; send a Content-Length in a request message when no
1671   <x:ref>Transfer-Encoding</x:ref> is sent and the request method defines
1672   a meaning for an enclosed payload body. For example, a Content-Length
1673   header field is normally sent in a POST request even when the value is
1674   0 (indicating an empty payload body).  A user agent &SHOULD-NOT; send a
1675   Content-Length header field when the request message does not contain a
1676   payload body and the method semantics do not anticipate such a body.
1677</t>
1678<t>
1679   A server &MAY; send a Content-Length header field in a response to a HEAD
1680   request (&HEAD;); a server &MUST-NOT; send Content-Length in such a
1681   response unless its field-value equals the decimal number of octets that
1682   would have been sent in the payload body of a response if the same
1683   request had used the GET method.
1684</t>
1685<t>
1686   A server &MAY; send a Content-Length header field in a
1687   <x:ref>304 (Not Modified)</x:ref> response to a conditional GET request
1688   (&status-304;); a server &MUST-NOT; send Content-Length in such a
1689   response unless its field-value equals the decimal number of octets that
1690   would have been sent in the payload body of a <x:ref>200 (OK)</x:ref>
1691   response to the same request.
1692</t>
1693<t>
1694   A server &MUST-NOT; send a Content-Length header field in any response
1695   with a status code of
1696   <x:ref>1xx (Informational)</x:ref> or <x:ref>204 (No Content)</x:ref>.
1697   A server &MUST-NOT; send a Content-Length header field in any
1698   <x:ref>2xx (Successful)</x:ref> response to a CONNECT request (&CONNECT;).
1699</t>
1700<t>
1701   Aside from the cases defined above, in the absence of Transfer-Encoding,
1702   an origin server &SHOULD; send a Content-Length header field when the
1703   payload body size is known prior to sending the complete header section.
1704   This will allow downstream recipients to measure transfer progress,
1705   know when a received message is complete, and potentially reuse the
1706   connection for additional requests.
1707</t>
1708<t>
1709   Any Content-Length field value greater than or equal to zero is valid.
1710   Since there is no predefined limit to the length of a payload, a
1711   recipient &MUST; anticipate potentially large decimal numerals and
1712   prevent parsing errors due to integer conversion overflows
1713   (<xref target="attack.protocol.element.size.overflows"/>).
1714</t>
1715<t>
1716   If a message is received that has multiple Content-Length header fields
1717   with field-values consisting of the same decimal value, or a single
1718   Content-Length header field with a field value containing a list of
1719   identical decimal values (e.g., "Content-Length: 42, 42"), indicating that
1720   duplicate Content-Length header fields have been generated or combined by an
1721   upstream message processor, then the recipient &MUST; either reject the
1722   message as invalid or replace the duplicated field-values with a single
1723   valid Content-Length field containing that decimal value prior to
1724   determining the message body length or forwarding the message.
1725</t>
1726<x:note>
1727  <t>
1728   &Note; HTTP's use of Content-Length for message framing differs
1729   significantly from the same field's use in MIME, where it is an optional
1730   field used only within the "message/external-body" media-type.
1731  </t>
1732</x:note>
1733</section>
1734
1735<section title="Message Body Length" anchor="message.body.length">
1736  <iref item="chunked (Coding Format)"/>
1737<t>
1738   The length of a message body is determined by one of the following
1739   (in order of precedence):
1740</t>
1741<t>
1742  <list style="numbers">
1743    <x:lt><t>
1744     Any response to a HEAD request and any response with a
1745     <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, or
1746     <x:ref>304 (Not Modified)</x:ref> status code is always
1747     terminated by the first empty line after the header fields, regardless of
1748     the header fields present in the message, and thus cannot contain a
1749     message body.
1750    </t></x:lt>
1751    <x:lt><t>
1752     Any <x:ref>2xx (Successful)</x:ref> response to a CONNECT request implies that the
1753     connection will become a tunnel immediately after the empty line that
1754     concludes the header fields.  A client &MUST; ignore any
1755     <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1756     fields received in such a message.
1757    </t></x:lt>
1758    <x:lt><t>
1759     If a <x:ref>Transfer-Encoding</x:ref> header field is present
1760     and the chunked transfer coding (<xref target="chunked.encoding"/>)
1761     is the final encoding, the message body length is determined by reading
1762     and decoding the chunked data until the transfer coding indicates the
1763     data is complete.
1764    </t>
1765    <t>
1766     If a <x:ref>Transfer-Encoding</x:ref> header field is present in a
1767     response and the chunked transfer coding is not the final encoding, the
1768     message body length is determined by reading the connection until it is
1769     closed by the server.
1770     If a <x:ref>Transfer-Encoding</x:ref> header field is present in a request and the
1771     chunked transfer coding is not the final encoding, the message body
1772     length cannot be determined reliably; the server &MUST; respond with
1773     the <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1774    </t>
1775    <t>
1776     If a message is received with both a <x:ref>Transfer-Encoding</x:ref>
1777     and a <x:ref>Content-Length</x:ref> header field, the Transfer-Encoding
1778     overrides the Content-Length. Such a message might indicate an attempt
1779     to perform request or response smuggling (bypass of security-related
1780     checks on message routing or content) and thus ought to be handled as
1781     an error.  A sender &MUST; remove the received Content-Length field
1782     prior to forwarding such a message downstream.
1783    </t></x:lt>
1784    <x:lt><t>
1785     If a message is received without <x:ref>Transfer-Encoding</x:ref> and with
1786     either multiple <x:ref>Content-Length</x:ref> header fields having
1787     differing field-values or a single Content-Length header field having an
1788     invalid value, then the message framing is invalid and
1789     the recipient &MUST; treat it as an unrecoverable error to prevent
1790     request or response smuggling.
1791     If this is a request message, the server &MUST; respond with
1792     a <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1793     If this is a response message received by a proxy,
1794     the proxy &MUST; close the connection to the server, discard the received
1795     response, and send a <x:ref>502 (Bad Gateway)</x:ref> response to the
1796     client.
1797     If this is a response message received by a user agent,
1798     the user agent &MUST; close the connection to the server and discard the
1799     received response.
1800    </t></x:lt>
1801    <x:lt><t>
1802     If a valid <x:ref>Content-Length</x:ref> header field is present without
1803     <x:ref>Transfer-Encoding</x:ref>, its decimal value defines the
1804     expected message body length in octets.
1805     If the sender closes the connection or the recipient times out before the
1806     indicated number of octets are received, the recipient &MUST; consider
1807     the message to be incomplete and close the connection.
1808    </t></x:lt>
1809    <x:lt><t>
1810     If this is a request message and none of the above are true, then the
1811     message body length is zero (no message body is present).
1812    </t></x:lt>
1813    <x:lt><t>
1814     Otherwise, this is a response message without a declared message body
1815     length, so the message body length is determined by the number of octets
1816     received prior to the server closing the connection.
1817    </t></x:lt>
1818  </list>
1819</t>
1820<t>
1821   Since there is no way to distinguish a successfully completed,
1822   close-delimited message from a partially-received message interrupted
1823   by network failure, a server &SHOULD; generate encoding or
1824   length-delimited messages whenever possible.  The close-delimiting
1825   feature exists primarily for backwards compatibility with HTTP/1.0.
1826</t>
1827<t>
1828   A server &MAY; reject a request that contains a message body but
1829   not a <x:ref>Content-Length</x:ref> by responding with
1830   <x:ref>411 (Length Required)</x:ref>.
1831</t>
1832<t>
1833   Unless a transfer coding other than chunked has been applied,
1834   a client that sends a request containing a message body &SHOULD;
1835   use a valid <x:ref>Content-Length</x:ref> header field if the message body
1836   length is known in advance, rather than the chunked transfer coding, since some
1837   existing services respond to chunked with a <x:ref>411 (Length Required)</x:ref>
1838   status code even though they understand the chunked transfer coding.  This
1839   is typically because such services are implemented via a gateway that
1840   requires a content-length in advance of being called and the server
1841   is unable or unwilling to buffer the entire request before processing.
1842</t>
1843<t>
1844   A user agent that sends a request containing a message body &MUST; send a
1845   valid <x:ref>Content-Length</x:ref> header field if it does not know the
1846   server will handle HTTP/1.1 (or later) requests; such knowledge can be in
1847   the form of specific user configuration or by remembering the version of a
1848   prior received response.
1849</t>
1850<t>
1851   If the final response to the last request on a connection has been
1852   completely received and there remains additional data to read, a user agent
1853   &MAY; discard the remaining data or attempt to determine if that data
1854   belongs as part of the prior response body, which might be the case if the
1855   prior message's Content-Length value is incorrect. A client &MUST-NOT;
1856   process, cache, or forward such extra data as a separate response, since
1857   such behavior would be vulnerable to cache poisoning.
1858</t>
1859</section>
1860</section>
1861
1862<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1863<t>
1864   A server that receives an incomplete request message, usually due to a
1865   canceled request or a triggered time-out exception, &MAY; send an error
1866   response prior to closing the connection.
1867</t>
1868<t>
1869   A client that receives an incomplete response message, which can occur
1870   when a connection is closed prematurely or when decoding a supposedly
1871   chunked transfer coding fails, &MUST; record the message as incomplete.
1872   Cache requirements for incomplete responses are defined in
1873   &cache-incomplete;.
1874</t>
1875<t>
1876   If a response terminates in the middle of the header section (before the
1877   empty line is received) and the status code might rely on header fields to
1878   convey the full meaning of the response, then the client cannot assume
1879   that meaning has been conveyed; the client might need to repeat the
1880   request in order to determine what action to take next.
1881</t>
1882<t>
1883   A message body that uses the chunked transfer coding is
1884   incomplete if the zero-sized chunk that terminates the encoding has not
1885   been received.  A message that uses a valid <x:ref>Content-Length</x:ref> is
1886   incomplete if the size of the message body received (in octets) is less than
1887   the value given by Content-Length.  A response that has neither chunked
1888   transfer coding nor Content-Length is terminated by closure of the
1889   connection, and thus is considered complete regardless of the number of
1890   message body octets received, provided that the header section was received
1891   intact.
1892</t>
1893</section>
1894
1895<section title="Message Parsing Robustness" anchor="message.robustness">
1896<t>
1897   Older HTTP/1.0 user agent implementations might send an extra CRLF
1898   after a POST request as a workaround for some early server
1899   applications that failed to read message body content that was
1900   not terminated by a line-ending. An HTTP/1.1 user agent &MUST-NOT;
1901   preface or follow a request with an extra CRLF.  If terminating
1902   the request message body with a line-ending is desired, then the
1903   user agent &MUST; count the terminating CRLF octets as part of the
1904   message body length.
1905</t>
1906<t>
1907   In the interest of robustness, a server that is expecting to receive and
1908   parse a request-line &SHOULD; ignore at least one empty line (CRLF)
1909   received prior to the request-line.
1910</t>
1911<t>
1912   Although the line terminator for the start-line and header
1913   fields is the sequence CRLF, a recipient &MAY; recognize a
1914   single LF as a line terminator and ignore any preceding CR.
1915</t>
1916<t>
1917   Although the request-line and status-line grammar rules require that each
1918   of the component elements be separated by a single SP octet, recipients
1919   &MAY; instead parse on whitespace-delimited word boundaries and, aside
1920   from the CRLF terminator, treat any form of whitespace as the SP separator
1921   while ignoring preceding or trailing whitespace;
1922   such whitespace includes one or more of the following octets:
1923   SP, HTAB, VT (%x0B), FF (%x0C), or bare CR.
1924</t>
1925<t>
1926   When a server listening only for HTTP request messages, or processing
1927   what appears from the start-line to be an HTTP request message,
1928   receives a sequence of octets that does not match the HTTP-message
1929   grammar aside from the robustness exceptions listed above, the
1930   server &SHOULD; respond with a <x:ref>400 (Bad Request)</x:ref> response. 
1931</t>
1932</section>
1933</section>
1934
1935<section title="Transfer Codings" anchor="transfer.codings">
1936  <x:anchor-alias value="transfer-coding"/>
1937  <x:anchor-alias value="transfer-extension"/>
1938<t>
1939   Transfer coding names are used to indicate an encoding
1940   transformation that has been, can be, or might need to be applied to a
1941   payload body in order to ensure "safe transport" through the network.
1942   This differs from a content coding in that the transfer coding is a
1943   property of the message rather than a property of the representation
1944   that is being transferred.
1945</t>
1946<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1947  <x:ref>transfer-coding</x:ref>    = "chunked" ; <xref target="chunked.encoding"/>
1948                     / "compress" ; <xref target="compress.coding"/>
1949                     / "deflate" ; <xref target="deflate.coding"/>
1950                     / "gzip" ; <xref target="gzip.coding"/>
1951                     / <x:ref>transfer-extension</x:ref>
1952  <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> )
1953</artwork></figure>
1954<t anchor="rule.parameter">
1955  <x:anchor-alias value="transfer-parameter"/>
1956   Parameters are in the form of a name or name=value pair.
1957</t>
1958<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-parameter"/>
1959  <x:ref>transfer-parameter</x:ref> = <x:ref>token</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
1960</artwork></figure>
1961<t>
1962   All transfer-coding names are case-insensitive and ought to be registered
1963   within the HTTP Transfer Coding registry, as defined in
1964   <xref target="transfer.coding.registry"/>.
1965   They are used in the <x:ref>TE</x:ref> (<xref target="header.te"/>) and
1966   <x:ref>Transfer-Encoding</x:ref> (<xref target="header.transfer-encoding"/>)
1967   header fields.
1968</t>
1969
1970<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1971  <iref primary="true" item="chunked (Coding Format)"/>
1972  <x:anchor-alias value="chunk"/>
1973  <x:anchor-alias value="chunked-body"/>
1974  <x:anchor-alias value="chunk-data"/>
1975  <x:anchor-alias value="chunk-size"/>
1976  <x:anchor-alias value="last-chunk"/>
1977<t>
1978   The chunked transfer coding wraps the payload body in order to transfer it
1979   as a series of chunks, each with its own size indicator, followed by an
1980   &OPTIONAL; trailer containing header fields. Chunked enables content
1981   streams of unknown size to be transferred as a sequence of length-delimited
1982   buffers, which enables the sender to retain connection persistence and the
1983   recipient to know when it has received the entire message.
1984</t>
1985<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="false" item="Grammar" subitem="trailer-part"/>
1986  <x:ref>chunked-body</x:ref>   = *<x:ref>chunk</x:ref>
1987                   <x:ref>last-chunk</x:ref>
1988                   <x:ref>trailer-part</x:ref>
1989                   <x:ref>CRLF</x:ref>
1990 
1991  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1992                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1993  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1994  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1995 
1996  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1997</artwork></figure>
1998<t>
1999   The chunk-size field is a string of hex digits indicating the size of
2000   the chunk-data in octets. The chunked transfer coding is complete when a
2001   chunk with a chunk-size of zero is received, possibly followed by a
2002   trailer, and finally terminated by an empty line.
2003</t>
2004<t>
2005   A recipient &MUST; be able to parse and decode the chunked transfer coding.
2006</t>
2007
2008<section title="Chunk Extensions" anchor="chunked.extension">
2009  <x:anchor-alias value="chunk-ext"/>
2010  <x:anchor-alias value="chunk-ext-name"/>
2011  <x:anchor-alias value="chunk-ext-val"/>
2012<t>
2013   The chunked encoding allows each chunk to include zero or more chunk
2014   extensions, immediately following the <x:ref>chunk-size</x:ref>, for the
2015   sake of supplying per-chunk metadata (such as a signature or hash),
2016   mid-message control information, or randomization of message body size.
2017</t>
2018<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="false" item="Grammar" subitem="trailer-part"/><iref primary="true" item="Grammar" subitem="quoted-str-nf"/><iref primary="true" item="Grammar" subitem="qdtext-nf"/>
2019  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
2020
2021  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2022  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
2023</artwork></figure>
2024<t>
2025   The chunked encoding is specific to each connection and is likely to be
2026   removed or recoded by each recipient (including intermediaries) before any
2027   higher-level application would have a chance to inspect the extensions.
2028   Hence, use of chunk extensions is generally limited to specialized HTTP
2029   services such as "long polling" (where client and server can have shared
2030   expectations regarding the use of chunk extensions) or for padding within
2031   an end-to-end secured connection.
2032</t>
2033<t>
2034   A recipient &MUST; ignore unrecognized chunk extensions.
2035   A server ought to limit the total length of chunk extensions received in a
2036   request to an amount reasonable for the services provided, in the same way
2037   that it applies length limitations and timeouts for other parts of a
2038   message, and generate an appropriate <x:ref>4xx (Client Error)</x:ref>
2039   response if that amount is exceeded.
2040</t>
2041</section>
2042
2043<section title="Chunked Trailer Part" anchor="chunked.trailer.part">
2044  <x:anchor-alias value="trailer-part"/>
2045<t>
2046   A trailer allows the sender to include additional fields at the end of a
2047   chunked message in order to supply metadata that might be dynamically
2048   generated while the message body is sent, such as a message integrity
2049   check, digital signature, or post-processing status. The trailer fields are
2050   identical to header fields, except they are sent in a chunked trailer
2051   instead of the message's header section.
2052</t>
2053<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="trailer-part"/>
2054  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2055</artwork></figure>
2056<t>
2057   A sender &MUST-NOT; generate a trailer that contains a field which needs to
2058   be known by the recipient before it can begin processing the message body.
2059   For example, most recipients need to know the values of
2060   <x:ref>Content-Encoding</x:ref> and <x:ref>Content-Type</x:ref> in order to
2061   select a content handler, so placing those fields in a trailer would force
2062   the recipient to buffer the entire body before it could begin, greatly
2063   increasing user-perceived latency and defeating one of the main advantages
2064   of using chunked to send data streams of unknown length.
2065   A sender &MUST-NOT; generate a trailer containing a
2066   <x:ref>Transfer-Encoding</x:ref>,
2067   <x:ref>Content-Length</x:ref>, or
2068   <x:ref>Trailer</x:ref> field.
2069</t>
2070<t>
2071   A server &MUST; generate an empty trailer with the chunked transfer coding
2072   unless at least one of the following is true:
2073  <list style="numbers">
2074    <t>the request included a <x:ref>TE</x:ref> header field that indicates
2075    "trailers" is acceptable in the transfer coding of the response, as
2076    described in <xref target="header.te"/>; or,</t>
2077     
2078    <t>the trailer fields consist entirely of optional metadata and the
2079    recipient could use the message (in a manner acceptable to the generating
2080    server) without receiving that metadata. In other words, the generating
2081    server is willing to accept the possibility that the trailer fields might
2082    be silently discarded along the path to the client.</t>
2083  </list>
2084</t>
2085<t>
2086   The above requirement prevents the need for an infinite buffer when a
2087   message is being received by an HTTP/1.1 (or later) proxy and forwarded to
2088   an HTTP/1.0 recipient.
2089</t>
2090</section>
2091
2092<section title="Decoding Chunked" anchor="decoding.chunked">
2093<t>
2094   A process for decoding the chunked transfer coding
2095   can be represented in pseudo-code as:
2096</t>
2097<figure><artwork type="code">
2098  length := 0
2099  read chunk-size, chunk-ext (if any), and CRLF
2100  while (chunk-size &gt; 0) {
2101     read chunk-data and CRLF
2102     append chunk-data to decoded-body
2103     length := length + chunk-size
2104     read chunk-size, chunk-ext (if any), and CRLF
2105  }
2106  read header-field
2107  while (header-field not empty) {
2108     append header-field to existing header fields
2109     read header-field
2110  }
2111  Content-Length := length
2112  Remove "chunked" from Transfer-Encoding
2113  Remove Trailer from existing header fields
2114</artwork></figure>
2115</section>
2116</section>
2117
2118<section title="Compression Codings" anchor="compression.codings">
2119<t>
2120   The codings defined below can be used to compress the payload of a
2121   message.
2122</t>
2123
2124<section title="Compress Coding" anchor="compress.coding">
2125<iref item="compress (Coding Format)"/>
2126<t>
2127   The "compress" coding is an adaptive Lempel-Ziv-Welch (LZW) coding
2128   <xref target="Welch"/> that is commonly produced by the UNIX file
2129   compression program "compress".
2130   A recipient &SHOULD; consider "x-compress" to be equivalent to "compress".
2131</t>
2132</section>
2133
2134<section title="Deflate Coding" anchor="deflate.coding">
2135<iref item="deflate (Coding Format)"/>
2136<t>
2137   The "deflate" coding is a "zlib" data format <xref target="RFC1950"/>
2138   containing a "deflate" compressed data stream <xref target="RFC1951"/>
2139   that uses a combination of the Lempel-Ziv (LZ77) compression algorithm and
2140   Huffman coding.
2141</t>
2142<x:note>
2143  <t>
2144    &Note; Some incorrect implementations send the "deflate"
2145    compressed data without the zlib wrapper.
2146   </t>
2147</x:note>
2148</section>
2149
2150<section title="Gzip Coding" anchor="gzip.coding">
2151<iref item="gzip (Coding Format)"/>
2152<t>
2153   The "gzip" coding is an LZ77 coding with a 32 bit CRC that is commonly
2154   produced by the gzip file compression program <xref target="RFC1952"/>.
2155   A recipient &SHOULD; consider "x-gzip" to be equivalent to "gzip".
2156</t>
2157</section>
2158
2159</section>
2160
2161<section title="TE" anchor="header.te">
2162  <iref primary="true" item="TE header field" x:for-anchor=""/>
2163  <x:anchor-alias value="TE"/>
2164  <x:anchor-alias value="t-codings"/>
2165  <x:anchor-alias value="t-ranking"/>
2166  <x:anchor-alias value="rank"/>
2167<t>
2168   The "TE" header field in a request indicates what transfer codings,
2169   besides chunked, the client is willing to accept in response, and
2170   whether or not the client is willing to accept trailer fields in a
2171   chunked transfer coding.
2172</t>
2173<t>
2174   The TE field-value consists of a comma-separated list of transfer coding
2175   names, each allowing for optional parameters (as described in
2176   <xref target="transfer.codings"/>), and/or the keyword "trailers".
2177   A client &MUST-NOT; send the chunked transfer coding name in TE;
2178   chunked is always acceptable for HTTP/1.1 recipients.
2179</t>
2180<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="t-ranking"/><iref primary="true" item="Grammar" subitem="rank"/>
2181  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2182  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-coding</x:ref> [ <x:ref>t-ranking</x:ref> ] )
2183  <x:ref>t-ranking</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>rank</x:ref>
2184  <x:ref>rank</x:ref>      = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2185             / ( "1" [ "." 0*3("0") ] )
2186</artwork></figure>
2187<t>
2188   Three examples of TE use are below.
2189</t>
2190<figure><artwork type="example">
2191  TE: deflate
2192  TE:
2193  TE: trailers, deflate;q=0.5
2194</artwork></figure>
2195<t>
2196   The presence of the keyword "trailers" indicates that the client is willing
2197   to accept trailer fields in a chunked transfer coding, as defined in
2198   <xref target="chunked.trailer.part"/>, on behalf of itself and any downstream
2199   clients. For requests from an intermediary, this implies that either:
2200   (a) all downstream clients are willing to accept trailer fields in the
2201   forwarded response; or,
2202   (b) the intermediary will attempt to buffer the response on behalf of
2203   downstream recipients.
2204   Note that HTTP/1.1 does not define any means to limit the size of a
2205   chunked response such that an intermediary can be assured of buffering the
2206   entire response.
2207</t>
2208<t>
2209   When multiple transfer codings are acceptable, the client &MAY; rank the
2210   codings by preference using a case-insensitive "q" parameter (similar to
2211   the qvalues used in content negotiation fields, &qvalue;). The rank value
2212   is a real number in the range 0 through 1, where 0.001 is the least
2213   preferred and 1 is the most preferred; a value of 0 means "not acceptable".
2214</t>
2215<t>
2216   If the TE field-value is empty or if no TE field is present, the only
2217   acceptable transfer coding is chunked. A message with no transfer coding
2218   is always acceptable.
2219</t>
2220<t>
2221   Since the TE header field only applies to the immediate connection,
2222   a sender of TE &MUST; also send a "TE" connection option within the
2223   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
2224   in order to prevent the TE field from being forwarded by intermediaries
2225   that do not support its semantics.
2226</t>
2227</section>
2228
2229<section title="Trailer" anchor="header.trailer">
2230  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
2231  <x:anchor-alias value="Trailer"/>
2232<t>
2233   When a message includes a message body encoded with the chunked
2234   transfer coding and the sender desires to send metadata in the form of
2235   trailer fields at the end of the message, the sender &SHOULD; generate a
2236   <x:ref>Trailer</x:ref> header field before the message body to indicate
2237   which fields will be present in the trailers. This allows the recipient
2238   to prepare for receipt of that metadata before it starts processing the body,
2239   which is useful if the message is being streamed and the recipient wishes
2240   to confirm an integrity check on the fly.
2241</t>
2242<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2243  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
2244</artwork></figure>
2245</section>
2246</section>
2247
2248<section title="Message Routing" anchor="message.routing">
2249<t>
2250   HTTP request message routing is determined by each client based on the
2251   target resource, the client's proxy configuration, and
2252   establishment or reuse of an inbound connection.  The corresponding
2253   response routing follows the same connection chain back to the client.
2254</t>
2255
2256<section title="Identifying a Target Resource" anchor="target-resource">
2257  <iref primary="true" item="target resource"/>
2258  <iref primary="true" item="target URI"/>
2259  <x:anchor-alias value="target resource"/>
2260  <x:anchor-alias value="target URI"/>
2261<t>
2262   HTTP is used in a wide variety of applications, ranging from
2263   general-purpose computers to home appliances.  In some cases,
2264   communication options are hard-coded in a client's configuration.
2265   However, most HTTP clients rely on the same resource identification
2266   mechanism and configuration techniques as general-purpose Web browsers.
2267</t>
2268<t>
2269   HTTP communication is initiated by a user agent for some purpose.
2270   The purpose is a combination of request semantics, which are defined in
2271   <xref target="Part2"/>, and a target resource upon which to apply those
2272   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2273   an identifier for the "<x:dfn>target resource</x:dfn>", which a user agent
2274   would resolve to its absolute form in order to obtain the
2275   "<x:dfn>target URI</x:dfn>".  The target URI
2276   excludes the reference's fragment component, if any,
2277   since fragment identifiers are reserved for client-side processing
2278   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2279</t>
2280</section>
2281
2282<section title="Connecting Inbound" anchor="connecting.inbound">
2283<t>
2284   Once the target URI is determined, a client needs to decide whether
2285   a network request is necessary to accomplish the desired semantics and,
2286   if so, where that request is to be directed.
2287</t>
2288<t>
2289   If the client has a cache <xref target="Part6"/> and the request can be
2290   satisfied by it, then the request is
2291   usually directed there first.
2292</t>
2293<t>
2294   If the request is not satisfied by a cache, then a typical client will
2295   check its configuration to determine whether a proxy is to be used to
2296   satisfy the request.  Proxy configuration is implementation-dependent,
2297   but is often based on URI prefix matching, selective authority matching,
2298   or both, and the proxy itself is usually identified by an "http" or
2299   "https" URI.  If a proxy is applicable, the client connects inbound by
2300   establishing (or reusing) a connection to that proxy.
2301</t>
2302<t>
2303   If no proxy is applicable, a typical client will invoke a handler routine,
2304   usually specific to the target URI's scheme, to connect directly
2305   to an authority for the target resource.  How that is accomplished is
2306   dependent on the target URI scheme and defined by its associated
2307   specification, similar to how this specification defines origin server
2308   access for resolution of the "http" (<xref target="http.uri"/>) and
2309   "https" (<xref target="https.uri"/>) schemes.
2310</t>
2311<t>
2312   HTTP requirements regarding connection management are defined in
2313   <xref target="connection.management"/>.
2314</t>
2315</section>
2316
2317<section title="Request Target" anchor="request-target">
2318<t>
2319   Once an inbound connection is obtained,
2320   the client sends an HTTP request message (<xref target="http.message"/>)
2321   with a request-target derived from the target URI.
2322   There are four distinct formats for the request-target, depending on both
2323   the method being requested and whether the request is to a proxy.
2324</t>   
2325<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"/>
2326  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2327                 / <x:ref>absolute-form</x:ref>
2328                 / <x:ref>authority-form</x:ref>
2329                 / <x:ref>asterisk-form</x:ref>
2330
2331  <x:ref>origin-form</x:ref>    = <x:ref>absolute-path</x:ref> [ "?" <x:ref>query</x:ref> ]
2332  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2333  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2334  <x:ref>asterisk-form</x:ref>  = "*"
2335</artwork></figure>
2336<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2337  <x:h>origin-form</x:h>
2338</t>
2339<t>
2340   The most common form of request-target is the <x:dfn>origin-form</x:dfn>.
2341   When making a request directly to an origin server, other than a CONNECT
2342   or server-wide OPTIONS request (as detailed below),
2343   a client &MUST; send only the absolute path and query components of
2344   the target URI as the request-target.
2345   If the target URI's path component is empty, then the client &MUST; send
2346   "/" as the path within the origin-form of request-target.
2347   A <x:ref>Host</x:ref> header field is also sent, as defined in
2348   <xref target="header.host"/>.
2349</t>
2350<t>
2351   For example, a client wishing to retrieve a representation of the resource
2352   identified as
2353</t>
2354<figure><artwork x:indent-with="  " type="example">
2355http://www.example.org/where?q=now
2356</artwork></figure>
2357<t>
2358   directly from the origin server would open (or reuse) a TCP connection
2359   to port 80 of the host "www.example.org" and send the lines:
2360</t>
2361<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2362GET /where?q=now HTTP/1.1
2363Host: www.example.org
2364</artwork></figure>
2365<t>
2366   followed by the remainder of the request message.
2367</t>
2368<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2369  <x:h>absolute-form</x:h>
2370</t>
2371<t>
2372   When making a request to a proxy, other than a CONNECT or server-wide
2373   OPTIONS request (as detailed below), a client &MUST; send the target URI
2374   in <x:dfn>absolute-form</x:dfn> as the request-target.
2375   The proxy is requested to either service that request from a valid cache,
2376   if possible, or make the same request on the client's behalf to either
2377   the next inbound proxy server or directly to the origin server indicated
2378   by the request-target.  Requirements on such "forwarding" of messages are
2379   defined in <xref target="message.forwarding"/>.
2380</t>
2381<t>
2382   An example absolute-form of request-line would be:
2383</t>
2384<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2385GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
2386</artwork></figure>
2387<t>
2388   To allow for transition to the absolute-form for all requests in some
2389   future version of HTTP, a server &MUST; accept the absolute-form
2390   in requests, even though HTTP/1.1 clients will only send them in requests
2391   to proxies.
2392</t>
2393<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2394  <x:h>authority-form</x:h>
2395</t>
2396<t>
2397   The <x:dfn>authority-form</x:dfn> of request-target is only used for
2398   CONNECT requests (&CONNECT;). When making a CONNECT request to establish a
2399   tunnel through one or more proxies, a client &MUST; send only the target
2400   URI's authority component (excluding any userinfo and its "@" delimiter) as
2401   the request-target. For example,
2402</t>
2403<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2404CONNECT www.example.com:80 HTTP/1.1
2405</artwork></figure>
2406<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2407  <x:h>asterisk-form</x:h>
2408</t>
2409<t>
2410   The <x:dfn>asterisk-form</x:dfn> of request-target is only used for a server-wide
2411   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2412   for the server as a whole, as opposed to a specific named resource of
2413   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2414   For example,
2415</t>
2416<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2417OPTIONS * HTTP/1.1
2418</artwork></figure>
2419<t>
2420   If a proxy receives an OPTIONS request with an absolute-form of
2421   request-target in which the URI has an empty path and no query component,
2422   then the last proxy on the request chain &MUST; send a request-target
2423   of "*" when it forwards the request to the indicated origin server.
2424</t>
2425<figure><preamble>  
2426   For example, the request
2427</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2428OPTIONS http://www.example.org:8001 HTTP/1.1
2429</artwork></figure>
2430<figure><preamble>  
2431  would be forwarded by the final proxy as
2432</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2433OPTIONS * HTTP/1.1
2434Host: www.example.org:8001
2435</artwork>
2436<postamble>
2437   after connecting to port 8001 of host "www.example.org".
2438</postamble>
2439</figure>
2440</section>
2441
2442<section title="Host" anchor="header.host">
2443  <iref primary="true" item="Host header field" x:for-anchor=""/>
2444  <x:anchor-alias value="Host"/>
2445<t>
2446   The "Host" header field in a request provides the host and port
2447   information from the target URI, enabling the origin
2448   server to distinguish among resources while servicing requests
2449   for multiple host names on a single IP address.
2450</t>
2451<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2452  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2453</artwork></figure>
2454<t>
2455   A client &MUST; send a Host header field in all HTTP/1.1 request messages.
2456   If the target URI includes an authority component, then a client &MUST;
2457   send a field-value for Host that is identical to that authority
2458   component, excluding any userinfo subcomponent and its "@" delimiter
2459   (<xref target="http.uri"/>).
2460   If the authority component is missing or undefined for the target URI,
2461   then a client &MUST; send a Host header field with an empty field-value.
2462</t>
2463<t>
2464   Since the Host field-value is critical information for handling a request,
2465   a user agent &SHOULD; generate Host as the first header field following the
2466   request-line.
2467</t>
2468<t>
2469   For example, a GET request to the origin server for
2470   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
2471</t>
2472<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2473GET /pub/WWW/ HTTP/1.1
2474Host: www.example.org
2475</artwork></figure>
2476<t>
2477   A client &MUST; send a Host header field in an HTTP/1.1 request even
2478   if the request-target is in the absolute-form, since this
2479   allows the Host information to be forwarded through ancient HTTP/1.0
2480   proxies that might not have implemented Host.
2481</t>
2482<t>
2483   When a proxy receives a request with an absolute-form of
2484   request-target, the proxy &MUST; ignore the received
2485   Host header field (if any) and instead replace it with the host
2486   information of the request-target.  A proxy that forwards such a request
2487   &MUST; generate a new Host field-value based on the received
2488   request-target rather than forward the received Host field-value.
2489</t>
2490<t>
2491   Since the Host header field acts as an application-level routing
2492   mechanism, it is a frequent target for malware seeking to poison
2493   a shared cache or redirect a request to an unintended server.
2494   An interception proxy is particularly vulnerable if it relies on
2495   the Host field-value for redirecting requests to internal
2496   servers, or for use as a cache key in a shared cache, without
2497   first verifying that the intercepted connection is targeting a
2498   valid IP address for that host.
2499</t>
2500<t>
2501   A server &MUST; respond with a <x:ref>400 (Bad Request)</x:ref> status code
2502   to any HTTP/1.1 request message that lacks a Host header field and
2503   to any request message that contains more than one Host header field
2504   or a Host header field with an invalid field-value.
2505</t>
2506</section>
2507
2508<section title="Effective Request URI" anchor="effective.request.uri">
2509  <iref primary="true" item="effective request URI"/>
2510  <x:anchor-alias value="effective request URI"/>
2511<t>
2512   A server that receives an HTTP request message &MUST; reconstruct
2513   the user agent's original target URI, based on the pieces of information
2514   learned from the request-target, <x:ref>Host</x:ref> header field, and
2515   connection context, in order to identify the intended target resource and
2516   properly service the request. The URI derived from this reconstruction
2517   process is referred to as the "<x:dfn>effective request URI</x:dfn>".
2518</t>
2519<t>
2520   For a user agent, the effective request URI is the target URI.
2521</t>
2522<t>
2523   If the request-target is in absolute-form, then the effective request URI
2524   is the same as the request-target.  Otherwise, the effective request URI
2525   is constructed as follows.
2526</t>
2527<t>
2528   If the request is received over a TLS-secured TCP connection,
2529   then the effective request URI's scheme is "https"; otherwise, the
2530   scheme is "http".
2531</t>
2532<t>
2533   If the request-target is in authority-form, then the effective
2534   request URI's authority component is the same as the request-target.
2535   Otherwise, if a <x:ref>Host</x:ref> header field is supplied with a
2536   non-empty field-value, then the authority component is the same as the
2537   Host field-value. Otherwise, the authority component is the concatenation of
2538   the default host name configured for the server, a colon (":"), and the
2539   connection's incoming TCP port number in decimal form.
2540</t>
2541<t>
2542   If the request-target is in authority-form or asterisk-form, then the
2543   effective request URI's combined path and query component is empty.
2544   Otherwise, the combined path and query component is the same as the
2545   request-target.
2546</t>
2547<t>
2548   The components of the effective request URI, once determined as above,
2549   can be combined into absolute-URI form by concatenating the scheme,
2550   "://", authority, and combined path and query component.
2551</t>
2552<figure>
2553<preamble>
2554   Example 1: the following message received over an insecure TCP connection
2555</preamble>
2556<artwork type="example" x:indent-with="  ">
2557GET /pub/WWW/TheProject.html HTTP/1.1
2558Host: www.example.org:8080
2559</artwork>
2560</figure>
2561<figure>
2562<preamble>
2563  has an effective request URI of
2564</preamble>
2565<artwork type="example" x:indent-with="  ">
2566http://www.example.org:8080/pub/WWW/TheProject.html
2567</artwork>
2568</figure>
2569<figure>
2570<preamble>
2571   Example 2: the following message received over a TLS-secured TCP connection
2572</preamble>
2573<artwork type="example" x:indent-with="  ">
2574OPTIONS * HTTP/1.1
2575Host: www.example.org
2576</artwork>
2577</figure>
2578<figure>
2579<preamble>
2580  has an effective request URI of
2581</preamble>
2582<artwork type="example" x:indent-with="  ">
2583https://www.example.org
2584</artwork>
2585</figure>
2586<t>
2587   An origin server that does not allow resources to differ by requested
2588   host &MAY; ignore the <x:ref>Host</x:ref> field-value and instead replace it
2589   with a configured server name when constructing the effective request URI.
2590</t>
2591<t>
2592   Recipients of an HTTP/1.0 request that lacks a <x:ref>Host</x:ref> header
2593   field &MAY; attempt to use heuristics (e.g., examination of the URI path for
2594   something unique to a particular host) in order to guess the
2595   effective request URI's authority component.
2596</t>
2597</section>
2598
2599<section title="Associating a Response to a Request" anchor="associating.response.to.request">
2600<t>
2601   HTTP does not include a request identifier for associating a given
2602   request message with its corresponding one or more response messages.
2603   Hence, it relies on the order of response arrival to correspond exactly
2604   to the order in which requests are made on the same connection.
2605   More than one response message per request only occurs when one or more
2606   informational responses (<x:ref>1xx</x:ref>, see &status-1xx;) precede a
2607   final response to the same request.
2608</t>
2609<t>
2610   A client that has more than one outstanding request on a connection &MUST;
2611   maintain a list of outstanding requests in the order sent and &MUST;
2612   associate each received response message on that connection to the highest
2613   ordered request that has not yet received a final (non-<x:ref>1xx</x:ref>)
2614   response.
2615</t>
2616</section>
2617
2618<section title="Message Forwarding" anchor="message.forwarding">
2619<t>
2620   As described in <xref target="intermediaries"/>, intermediaries can serve
2621   a variety of roles in the processing of HTTP requests and responses.
2622   Some intermediaries are used to improve performance or availability.
2623   Others are used for access control or to filter content.
2624   Since an HTTP stream has characteristics similar to a pipe-and-filter
2625   architecture, there are no inherent limits to the extent an intermediary
2626   can enhance (or interfere) with either direction of the stream.
2627</t>
2628<t>
2629   An intermediary not acting as a tunnel &MUST; implement the
2630   <x:ref>Connection</x:ref> header field, as specified in
2631   <xref target="header.connection"/>, and exclude fields from being forwarded
2632   that are only intended for the incoming connection.
2633</t>
2634<t>
2635   An intermediary &MUST-NOT; forward a message to itself unless it is
2636   protected from an infinite request loop. In general, an intermediary ought
2637   to recognize its own server names, including any aliases, local variations,
2638   or literal IP addresses, and respond to such requests directly.
2639</t>
2640
2641<section title="Via" anchor="header.via">
2642  <iref primary="true" item="Via header field" x:for-anchor=""/>
2643  <x:anchor-alias value="pseudonym"/>
2644  <x:anchor-alias value="received-by"/>
2645  <x:anchor-alias value="received-protocol"/>
2646  <x:anchor-alias value="Via"/>
2647<t>
2648   The "Via" header field indicates the presence of intermediate protocols and
2649   recipients between the user agent and the server (on requests) or between
2650   the origin server and the client (on responses), similar to the
2651   "Received" header field in email
2652   (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>).
2653   Via can be used for tracking message forwards,
2654   avoiding request loops, and identifying the protocol capabilities of
2655   senders along the request/response chain.
2656</t>
2657<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"/>
2658  <x:ref>Via</x:ref> = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref> [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2659
2660  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2661                      ; see <xref target="header.upgrade"/>
2662  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2663  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2664</artwork></figure>
2665<t>
2666   Multiple Via field values represent each proxy or gateway that has
2667   forwarded the message. Each intermediary appends its own information
2668   about how the message was received, such that the end result is ordered
2669   according to the sequence of forwarding recipients.
2670</t>
2671<t>
2672   A proxy &MUST; send an appropriate Via header field, as described below, in
2673   each message that it forwards.
2674   An HTTP-to-HTTP gateway &MUST; send an appropriate Via header field in
2675   each inbound request message and &MAY; send a Via header field in
2676   forwarded response messages.
2677</t>
2678<t>
2679   For each intermediary, the received-protocol indicates the protocol and
2680   protocol version used by the upstream sender of the message. Hence, the
2681   Via field value records the advertised protocol capabilities of the
2682   request/response chain such that they remain visible to downstream
2683   recipients; this can be useful for determining what backwards-incompatible
2684   features might be safe to use in response, or within a later request, as
2685   described in <xref target="http.version"/>. For brevity, the protocol-name
2686   is omitted when the received protocol is HTTP.
2687</t>
2688<t>
2689   The received-by field is normally the host and optional port number of a
2690   recipient server or client that subsequently forwarded the message.
2691   However, if the real host is considered to be sensitive information, a
2692   sender &MAY; replace it with a pseudonym. If a port is not provided,
2693   a recipient &MAY; interpret that as meaning it was received on the default
2694   TCP port, if any, for the received-protocol.
2695</t>
2696<t>
2697   A sender &MAY; generate comments in the Via header field to identify the
2698   software of each recipient, analogous to the <x:ref>User-Agent</x:ref> and
2699   <x:ref>Server</x:ref> header fields. However, all comments in the Via field
2700   are optional and a recipient &MAY; remove them prior to forwarding the
2701   message.
2702</t>
2703<t>
2704   For example, a request message could be sent from an HTTP/1.0 user
2705   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2706   forward the request to a public proxy at p.example.net, which completes
2707   the request by forwarding it to the origin server at www.example.com.
2708   The request received by www.example.com would then have the following
2709   Via header field:
2710</t>
2711<figure><artwork type="example">
2712  Via: 1.0 fred, 1.1 p.example.net
2713</artwork></figure>
2714<t>
2715   An intermediary used as a portal through a network firewall
2716   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2717   region unless it is explicitly enabled to do so. If not enabled, such an
2718   intermediary &SHOULD; replace each received-by host of any host behind the
2719   firewall by an appropriate pseudonym for that host.
2720</t>
2721<t>
2722   An intermediary &MAY; combine an ordered subsequence of Via header
2723   field entries into a single such entry if the entries have identical
2724   received-protocol values. For example,
2725</t>
2726<figure><artwork type="example">
2727  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2728</artwork></figure>
2729<t>
2730  could be collapsed to
2731</t>
2732<figure><artwork type="example">
2733  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2734</artwork></figure>
2735<t>
2736   A sender &SHOULD-NOT; combine multiple entries unless they are all
2737   under the same organizational control and the hosts have already been
2738   replaced by pseudonyms. A sender &MUST-NOT; combine entries that
2739   have different received-protocol values.
2740</t>
2741</section>
2742
2743<section title="Transformations" anchor="message.transformations">
2744<t>
2745   Some intermediaries include features for transforming messages and their
2746   payloads.  A transforming proxy might, for example, convert between image
2747   formats in order to save cache space or to reduce the amount of traffic on
2748   a slow link. However, operational problems might occur when these
2749   transformations are applied to payloads intended for critical applications,
2750   such as medical imaging or scientific data analysis, particularly when
2751   integrity checks or digital signatures are used to ensure that the payload
2752   received is identical to the original.
2753</t>
2754<t>
2755   If a proxy receives a request-target with a host name that is not a
2756   fully qualified domain name, it &MAY; add its own domain to the host name
2757   it received when forwarding the request.  A proxy &MUST-NOT; change the
2758   host name if it is a fully qualified domain name.
2759</t>
2760<t>
2761   A proxy &MUST-NOT; modify the "absolute-path" and "query" parts of the
2762   received request-target when forwarding it to the next inbound server,
2763   except as noted above to replace an empty path with "/" or "*".
2764</t>
2765<t>
2766   A proxy &MUST-NOT; modify header fields that provide information about the
2767   end points of the communication chain, the resource state, or the selected
2768   representation. A proxy &MAY; change the message body through application
2769   or removal of a transfer coding (<xref target="transfer.codings"/>).
2770</t>
2771<t>
2772   A non-transforming proxy &MUST-NOT; modify the message payload (&payload;).
2773   A transforming proxy &MUST-NOT; modify the payload of a message that
2774   contains the no-transform cache-control directive.
2775</t>
2776<t>
2777   A transforming proxy &MAY; transform the payload of a message
2778   that does not contain the no-transform cache-control directive;
2779   if the payload is transformed, the transforming proxy &MUST; add a
2780   Warning header field with the warn-code of 214 ("Transformation Applied")
2781   if one does not already appear in the message (see &header-warning;).
2782   If the payload of a <x:ref>200 (OK)</x:ref> response is transformed, the
2783   transforming proxy can also inform downstream recipients that a
2784   transformation has been applied by changing the response status code to
2785   <x:ref>203 (Non-Authoritative Information)</x:ref> (&status-203;).
2786</t>
2787</section>
2788</section>
2789</section>
2790
2791<section title="Connection Management" anchor="connection.management">
2792<t>
2793   HTTP messaging is independent of the underlying transport or
2794   session-layer connection protocol(s).  HTTP only presumes a reliable
2795   transport with in-order delivery of requests and the corresponding
2796   in-order delivery of responses.  The mapping of HTTP request and
2797   response structures onto the data units of an underlying transport
2798   protocol is outside the scope of this specification.
2799</t>
2800<t>
2801   As described in <xref target="connecting.inbound"/>, the specific
2802   connection protocols to be used for an HTTP interaction are determined by
2803   client configuration and the <x:ref>target URI</x:ref>.
2804   For example, the "http" URI scheme
2805   (<xref target="http.uri"/>) indicates a default connection of TCP
2806   over IP, with a default TCP port of 80, but the client might be
2807   configured to use a proxy via some other connection, port, or protocol.
2808</t>
2809<t>
2810   HTTP implementations are expected to engage in connection management,
2811   which includes maintaining the state of current connections,
2812   establishing a new connection or reusing an existing connection,
2813   processing messages received on a connection, detecting connection
2814   failures, and closing each connection.
2815   Most clients maintain multiple connections in parallel, including
2816   more than one connection per server endpoint.
2817   Most servers are designed to maintain thousands of concurrent connections,
2818   while controlling request queues to enable fair use and detect
2819   denial of service attacks.
2820</t>
2821
2822<section title="Connection" anchor="header.connection">
2823  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2824  <iref primary="true" item="close" x:for-anchor=""/>
2825  <x:anchor-alias value="Connection"/>
2826  <x:anchor-alias value="connection-option"/>
2827  <x:anchor-alias value="close"/>
2828<t>
2829   The "Connection" header field allows the sender to indicate desired
2830   control options for the current connection.  In order to avoid confusing
2831   downstream recipients, a proxy or gateway &MUST; remove or replace any
2832   received connection options before forwarding the message.
2833</t>
2834<t>
2835   When a header field aside from Connection is used to supply control
2836   information for or about the current connection, the sender &MUST; list
2837   the corresponding field-name within the "Connection" header field.
2838   A proxy or gateway &MUST; parse a received Connection
2839   header field before a message is forwarded and, for each
2840   connection-option in this field, remove any header field(s) from
2841   the message with the same name as the connection-option, and then
2842   remove the Connection header field itself (or replace it with the
2843   intermediary's own connection options for the forwarded message).
2844</t>
2845<t>
2846   Hence, the Connection header field provides a declarative way of
2847   distinguishing header fields that are only intended for the
2848   immediate recipient ("hop-by-hop") from those fields that are
2849   intended for all recipients on the chain ("end-to-end"), enabling the
2850   message to be self-descriptive and allowing future connection-specific
2851   extensions to be deployed without fear that they will be blindly
2852   forwarded by older intermediaries.
2853</t>
2854<t>
2855   The Connection header field's value has the following grammar:
2856</t>
2857<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-option"/>
2858  <x:ref>Connection</x:ref>        = 1#<x:ref>connection-option</x:ref>
2859  <x:ref>connection-option</x:ref> = <x:ref>token</x:ref>
2860</artwork></figure>
2861<t>
2862   Connection options are case-insensitive.
2863</t>
2864<t>
2865   A sender &MUST-NOT; send a connection option corresponding to a header
2866   field that is intended for all recipients of the payload.
2867   For example, <x:ref>Cache-Control</x:ref> is never appropriate as a
2868   connection option (&header-cache-control;).
2869</t>
2870<t>
2871   The connection options do not always correspond to a header field
2872   present in the message, since a connection-specific header field
2873   might not be needed if there are no parameters associated with a
2874   connection option. In contrast, a connection-specific header field that
2875   is received without a corresponding connection option usually indicates
2876   that the field has been improperly forwarded by an intermediary and
2877   ought to be ignored by the recipient.
2878</t>
2879<t>
2880   When defining new connection options, specification authors ought to survey
2881   existing header field names and ensure that the new connection option does
2882   not share the same name as an already deployed header field.
2883   Defining a new connection option essentially reserves that potential
2884   field-name for carrying additional information related to the
2885   connection option, since it would be unwise for senders to use
2886   that field-name for anything else.
2887</t>
2888<t>
2889   The "<x:dfn>close</x:dfn>" connection option is defined for a
2890   sender to signal that this connection will be closed after completion of
2891   the response. For example,
2892</t>
2893<figure><artwork type="example">
2894  Connection: close
2895</artwork></figure>
2896<t>
2897   in either the request or the response header fields indicates that the
2898   sender is going to close the connection after the current request/response
2899   is complete (<xref target="persistent.tear-down"/>).
2900</t>
2901<t>
2902   A client that does not support <x:ref>persistent connections</x:ref> &MUST;
2903   send the "close" connection option in every request message.
2904</t>
2905<t>
2906   A server that does not support <x:ref>persistent connections</x:ref> &MUST;
2907   send the "close" connection option in every response message that
2908   does not have a <x:ref>1xx (Informational)</x:ref> status code.
2909</t>
2910</section>
2911
2912<section title="Establishment" anchor="persistent.establishment">
2913<t>
2914   It is beyond the scope of this specification to describe how connections
2915   are established via various transport or session-layer protocols.
2916   Each connection applies to only one transport link.
2917</t>
2918</section>
2919
2920<section title="Persistence" anchor="persistent.connections">
2921   <x:anchor-alias value="persistent connections"/>
2922<t>
2923   HTTP/1.1 defaults to the use of "<x:dfn>persistent connections</x:dfn>",
2924   allowing multiple requests and responses to be carried over a single
2925   connection. The "<x:ref>close</x:ref>" connection-option is used to signal
2926   that a connection will not persist after the current request/response.
2927   HTTP implementations &SHOULD; support persistent connections.
2928</t>
2929<t>
2930   A recipient determines whether a connection is persistent or not based on
2931   the most recently received message's protocol version and
2932   <x:ref>Connection</x:ref> header field (if any):
2933   <list style="symbols">
2934     <t>If the <x:ref>close</x:ref> connection option is present, the
2935        connection will not persist after the current response; else,</t>
2936     <t>If the received protocol is HTTP/1.1 (or later), the connection will
2937        persist after the current response; else,</t>
2938     <t>If the received protocol is HTTP/1.0, the "keep-alive"
2939        connection option is present, the recipient is not a proxy, and
2940        the recipient wishes to honor the HTTP/1.0 "keep-alive" mechanism,
2941        the connection will persist after the current response; otherwise,</t>
2942     <t>The connection will close after the current response.</t>
2943   </list>
2944</t>
2945<t>
2946   A server &MAY; assume that an HTTP/1.1 client intends to maintain a
2947   persistent connection until a <x:ref>close</x:ref> connection option
2948   is received in a request.
2949</t>
2950<t>
2951   A client &MAY; reuse a persistent connection until it sends or receives
2952   a <x:ref>close</x:ref> connection option or receives an HTTP/1.0 response
2953   without a "keep-alive" connection option.
2954</t>
2955<t>
2956   In order to remain persistent, all messages on a connection need to
2957   have a self-defined message length (i.e., one not defined by closure
2958   of the connection), as described in <xref target="message.body"/>.
2959   A server &MUST; read the entire request message body or close
2960   the connection after sending its response, since otherwise the
2961   remaining data on a persistent connection would be misinterpreted
2962   as the next request.  Likewise,
2963   a client &MUST; read the entire response message body if it intends
2964   to reuse the same connection for a subsequent request.
2965</t>
2966<t>
2967   A proxy server &MUST-NOT; maintain a persistent connection with an
2968   HTTP/1.0 client (see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/> for
2969   information and discussion of the problems with the Keep-Alive header field
2970   implemented by many HTTP/1.0 clients).
2971</t>
2972<t>
2973   Clients and servers &SHOULD-NOT; assume that a persistent connection is
2974   maintained for HTTP versions less than 1.1 unless it is explicitly
2975   signaled.
2976   See <xref target="compatibility.with.http.1.0.persistent.connections"/>
2977   for more information on backward compatibility with HTTP/1.0 clients.
2978</t>
2979
2980<section title="Retrying Requests" anchor="persistent.retrying.requests">
2981<t>
2982   Connections can be closed at any time, with or without intention.
2983   Implementations ought to anticipate the need to recover
2984   from asynchronous close events.
2985</t>
2986<t>
2987   When an inbound connection is closed prematurely, a client &MAY; open a new
2988   connection and automatically retransmit an aborted sequence of requests if
2989   all of those requests have idempotent methods (&idempotent-methods;).
2990   A proxy &MUST-NOT; automatically retry non-idempotent requests.
2991</t>
2992<t>
2993   A user agent &MUST-NOT; automatically retry a request with a non-idempotent
2994   method unless it has some means to know that the request semantics are
2995   actually idempotent, regardless of the method, or some means to detect that
2996   the original request was never applied. For example, a user agent that
2997   knows (through design or configuration) that a POST request to a given
2998   resource is safe can repeat that request automatically.
2999   Likewise, a user agent designed specifically to operate on a version
3000   control repository might be able to recover from partial failure conditions
3001   by checking the target resource revision(s) after a failed connection,
3002   reverting or fixing any changes that were partially applied, and then
3003   automatically retrying the requests that failed.
3004</t>
3005<t>
3006   A client &SHOULD-NOT; automatically retry a failed automatic retry.
3007</t>
3008</section>
3009
3010<section title="Pipelining" anchor="pipelining">
3011   <x:anchor-alias value="pipeline"/>
3012<t>
3013   A client that supports persistent connections &MAY; "<x:dfn>pipeline</x:dfn>"
3014   its requests (i.e., send multiple requests without waiting for each
3015   response). A server &MAY; process a sequence of pipelined requests in
3016   parallel if they all have safe methods (&safe-methods;), but &MUST; send
3017   the corresponding responses in the same order that the requests were
3018   received.
3019</t>
3020<t>
3021   A client that pipelines requests &SHOULD; retry unanswered requests if the
3022   connection closes before it receives all of the corresponding responses.
3023   When retrying pipelined requests after a failed connection (a connection
3024   not explicitly closed by the server in its last complete response), a
3025   client &MUST-NOT; pipeline immediately after connection establishment,
3026   since the first remaining request in the prior pipeline might have caused
3027   an error response that can be lost again if multiple requests are sent on a
3028   prematurely closed connection (see the TCP reset problem described in
3029   <xref target="persistent.tear-down"/>).
3030</t>
3031<t>
3032   Idempotent methods (&idempotent-methods;) are significant to pipelining
3033   because they can be automatically retried after a connection failure.
3034   A user agent &SHOULD-NOT; pipeline requests after a non-idempotent method,
3035   until the final response status code for that method has been received,
3036   unless the user agent has a means to detect and recover from partial
3037   failure conditions involving the pipelined sequence.
3038</t>
3039<t>
3040   An intermediary that receives pipelined requests &MAY; pipeline those
3041   requests when forwarding them inbound, since it can rely on the outbound
3042   user agent(s) to determine what requests can be safely pipelined. If the
3043   inbound connection fails before receiving a response, the pipelining
3044   intermediary &MAY; attempt to retry a sequence of requests that have yet
3045   to receive a response if the requests all have idempotent methods;
3046   otherwise, the pipelining intermediary &SHOULD; forward any received
3047   responses and then close the corresponding outbound connection(s) so that
3048   the outbound user agent(s) can recover accordingly.
3049</t>
3050</section>
3051</section>
3052   
3053<section title="Concurrency" anchor="persistent.concurrency">
3054<t>
3055   A client &SHOULD; limit the number of simultaneous open
3056   connections that it maintains to a given server.
3057</t>
3058<t>
3059   Previous revisions of HTTP gave a specific number of connections as a
3060   ceiling, but this was found to be impractical for many applications. As a
3061   result, this specification does not mandate a particular maximum number of
3062   connections, but instead encourages clients to be conservative when opening
3063   multiple connections.
3064</t>
3065<t>
3066   Multiple connections are typically used to avoid the "head-of-line
3067   blocking" problem, wherein a request that takes significant server-side
3068   processing and/or has a large payload blocks subsequent requests on the
3069   same connection. However, each connection consumes server resources.
3070   Furthermore, using multiple connections can cause undesirable side effects
3071   in congested networks.
3072</t>
3073<t>
3074   Note that servers might reject traffic that they deem abusive, including an
3075   excessive number of connections from a client.
3076</t>
3077</section>
3078
3079<section title="Failures and Time-outs" anchor="persistent.failures">
3080<t>
3081   Servers will usually have some time-out value beyond which they will
3082   no longer maintain an inactive connection. Proxy servers might make
3083   this a higher value since it is likely that the client will be making
3084   more connections through the same proxy server. The use of persistent
3085   connections places no requirements on the length (or existence) of
3086   this time-out for either the client or the server.
3087</t>
3088<t>
3089   A client or server that wishes to time-out &SHOULD; issue a graceful close
3090   on the connection. Implementations &SHOULD; constantly monitor open
3091   connections for a received closure signal and respond to it as appropriate,
3092   since prompt closure of both sides of a connection enables allocated system
3093   resources to be reclaimed.
3094</t>
3095<t>
3096   A client, server, or proxy &MAY; close the transport connection at any
3097   time. For example, a client might have started to send a new request
3098   at the same time that the server has decided to close the "idle"
3099   connection. From the server's point of view, the connection is being
3100   closed while it was idle, but from the client's point of view, a
3101   request is in progress.
3102</t>
3103<t>
3104   A server &SHOULD; sustain persistent connections, when possible, and allow
3105   the underlying
3106   transport's flow control mechanisms to resolve temporary overloads, rather
3107   than terminate connections with the expectation that clients will retry.
3108   The latter technique can exacerbate network congestion.
3109</t>
3110<t>
3111   A client sending a message body &SHOULD; monitor
3112   the network connection for an error response while it is transmitting
3113   the request. If the client sees a response that indicates the server does
3114   not wish to receive the message body and is closing the connection, the
3115   client &SHOULD; immediately cease transmitting the body and close its side
3116   of the connection.
3117</t>
3118</section>
3119   
3120<section title="Tear-down" anchor="persistent.tear-down">
3121  <iref primary="false" item="Connection header field" x:for-anchor=""/>
3122  <iref primary="false" item="close" x:for-anchor=""/>
3123<t>
3124   The <x:ref>Connection</x:ref> header field
3125   (<xref target="header.connection"/>) provides a "<x:ref>close</x:ref>"
3126   connection option that a sender &SHOULD; send when it wishes to close
3127   the connection after the current request/response pair.
3128</t>
3129<t>
3130   A client that sends a <x:ref>close</x:ref> connection option &MUST-NOT;
3131   send further requests on that connection (after the one containing
3132   <x:ref>close</x:ref>) and &MUST; close the connection after reading the
3133   final response message corresponding to this request.
3134</t>
3135<t>
3136   A server that receives a <x:ref>close</x:ref> connection option &MUST;
3137   initiate a close of the connection (see below) after it sends the
3138   final response to the request that contained <x:ref>close</x:ref>.
3139   The server &SHOULD; send a <x:ref>close</x:ref> connection option
3140   in its final response on that connection. The server &MUST-NOT; process
3141   any further requests received on that connection.
3142</t>
3143<t>
3144   A server that sends a <x:ref>close</x:ref> connection option &MUST;
3145   initiate a close of the connection (see below) after it sends the
3146   response containing <x:ref>close</x:ref>. The server &MUST-NOT; process
3147   any further requests received on that connection.
3148</t>
3149<t>
3150   A client that receives a <x:ref>close</x:ref> connection option &MUST;
3151   cease sending requests on that connection and close the connection
3152   after reading the response message containing the close; if additional
3153   pipelined requests had been sent on the connection, the client &SHOULD-NOT;
3154   assume that they will be processed by the server.
3155</t>
3156<t>
3157   If a server performs an immediate close of a TCP connection, there is a
3158   significant risk that the client will not be able to read the last HTTP
3159   response.  If the server receives additional data from the client on a
3160   fully-closed connection, such as another request that was sent by the
3161   client before receiving the server's response, the server's TCP stack will
3162   send a reset packet to the client; unfortunately, the reset packet might
3163   erase the client's unacknowledged input buffers before they can be read
3164   and interpreted by the client's HTTP parser.
3165</t>
3166<t>
3167   To avoid the TCP reset problem, servers typically close a connection in
3168   stages. First, the server performs a half-close by closing only the write
3169   side of the read/write connection. The server then continues to read from
3170   the connection until it receives a corresponding close by the client, or
3171   until the server is reasonably certain that its own TCP stack has received
3172   the client's acknowledgement of the packet(s) containing the server's last
3173   response. Finally, the server fully closes the connection.
3174</t>
3175<t>
3176   It is unknown whether the reset problem is exclusive to TCP or might also
3177   be found in other transport connection protocols.
3178</t>
3179</section>
3180
3181<section title="Upgrade" anchor="header.upgrade">
3182  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3183  <x:anchor-alias value="Upgrade"/>
3184  <x:anchor-alias value="protocol"/>
3185  <x:anchor-alias value="protocol-name"/>
3186  <x:anchor-alias value="protocol-version"/>
3187<t>
3188   The "Upgrade" header field is intended to provide a simple mechanism
3189   for transitioning from HTTP/1.1 to some other protocol on the same
3190   connection.  A client &MAY; send a list of protocols in the Upgrade
3191   header field of a request to invite the server to switch to one or
3192   more of those protocols, in order of descending preference, before sending
3193   the final response. A server &MAY; ignore a received Upgrade header field
3194   if it wishes to continue using the current protocol on that connection.
3195</t>
3196<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3197  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3198
3199  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3200  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3201  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3202</artwork></figure>
3203<t>
3204   A server that sends a <x:ref>101 (Switching Protocols)</x:ref> response
3205   &MUST; send an Upgrade header field to indicate the new protocol(s) to
3206   which the connection is being switched; if multiple protocol layers are
3207   being switched, the sender &MUST; list the protocols in layer-ascending
3208   order. A server &MUST-NOT; switch to a protocol that was not indicated by
3209   the client in the corresponding request's Upgrade header field.
3210   A server &MAY; choose to ignore the order of preference indicated by the
3211   client and select the new protocol(s) based on other factors, such as the
3212   nature of the request or the current load on the server.
3213</t>
3214<t>
3215   A server that sends a <x:ref>426 (Upgrade Required)</x:ref> response
3216   &MUST; send an Upgrade header field to indicate the acceptable protocols,
3217   in order of descending preference.
3218</t>
3219<t>
3220   A server &MAY; send an Upgrade header field in any other response to
3221   advertise that it implements support for upgrading to the listed protocols,
3222   in order of descending preference, when appropriate for a future request.
3223</t>
3224<figure><preamble>
3225   The following is a hypothetical example sent by a client:
3226</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3227GET /hello.txt HTTP/1.1
3228Host: www.example.com
3229Connection: upgrade
3230Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3231
3232</artwork></figure>
3233<t>
3234   Upgrade cannot be used to insist on a protocol change; its acceptance and
3235   use by the server is optional. The capabilities and nature of the
3236   application-level communication after the protocol change is entirely
3237   dependent upon the new protocol(s) chosen. However, immediately after
3238   sending the 101 response, the server is expected to continue responding to
3239   the original request as if it had received its equivalent within the new
3240   protocol (i.e., the server still has an outstanding request to satisfy
3241   after the protocol has been changed, and is expected to do so without
3242   requiring the request to be repeated).
3243</t>
3244<t>
3245   For example, if the Upgrade header field is received in a GET request
3246   and the server decides to switch protocols, it first responds
3247   with a <x:ref>101 (Switching Protocols)</x:ref> message in HTTP/1.1 and
3248   then immediately follows that with the new protocol's equivalent of a
3249   response to a GET on the target resource.  This allows a connection to be
3250   upgraded to protocols with the same semantics as HTTP without the
3251   latency cost of an additional round-trip.  A server &MUST-NOT; switch
3252   protocols unless the received message semantics can be honored by the new
3253   protocol; an OPTIONS request can be honored by any protocol.
3254</t>
3255<figure><preamble>
3256   The following is an example response to the above hypothetical request:
3257</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
3258HTTP/1.1 101 Switching Protocols
3259Connection: upgrade
3260Upgrade: HTTP/2.0
3261
3262[... data stream switches to HTTP/2.0 with an appropriate response
3263(as defined by new protocol) to the "GET /hello.txt" request ...]
3264</artwork></figure>
3265<t>
3266   When Upgrade is sent, the sender &MUST; also send a
3267   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
3268   that contains an "upgrade" connection option, in order to prevent Upgrade
3269   from being accidentally forwarded by intermediaries that might not implement
3270   the listed protocols.  A server &MUST; ignore an Upgrade header field that
3271   is received in an HTTP/1.0 request.
3272</t>
3273<t>
3274   A client cannot begin using an upgraded protocol on the connection until
3275   it has completely sent the request message (i.e., the client can't change
3276   the protocol it is sending in the middle of a message).
3277   If a server receives both Upgrade and an <x:ref>Expect</x:ref> header field
3278   with the "100-continue" expectation (&header-expect;), the
3279   server &MUST; send a <x:ref>100 (Continue)</x:ref> response before sending
3280   a <x:ref>101 (Switching Protocols)</x:ref> response.
3281</t>
3282<t>
3283   The Upgrade header field only applies to switching protocols on top of the
3284   existing connection; it cannot be used to switch the underlying connection
3285   (transport) protocol, nor to switch the existing communication to a
3286   different connection. For those purposes, it is more appropriate to use a
3287   <x:ref>3xx (Redirection)</x:ref> response (&status-3xx;).
3288</t>
3289<t>
3290   This specification only defines the protocol name "HTTP" for use by
3291   the family of Hypertext Transfer Protocols, as defined by the HTTP
3292   version rules of <xref target="http.version"/> and future updates to this
3293   specification. Additional tokens ought to be registered with IANA using the
3294   registration procedure defined in <xref target="upgrade.token.registry"/>.
3295</t>
3296</section>
3297</section>
3298
3299<section title="ABNF list extension: #rule" anchor="abnf.extension">
3300<t>
3301  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
3302  improve readability in the definitions of some header field values.
3303</t>
3304<t>
3305  A construct "#" is defined, similar to "*", for defining comma-delimited
3306  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
3307  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
3308  comma (",") and optional whitespace (OWS).   
3309</t>
3310<figure><preamble>
3311  Thus, a sender &MUST; expand the list construct as follows:
3312</preamble><artwork type="example">
3313  1#element =&gt; element *( OWS "," OWS element )
3314</artwork></figure>
3315<figure><preamble>
3316  and:
3317</preamble><artwork type="example">
3318  #element =&gt; [ 1#element ]
3319</artwork></figure>
3320<figure><preamble>
3321  and for n &gt;= 1 and m &gt; 1:
3322</preamble><artwork type="example">
3323  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
3324</artwork></figure>
3325<t>
3326  For compatibility with legacy list rules, a recipient &MUST; parse and ignore
3327  a reasonable number of empty list elements: enough to handle common mistakes
3328  by senders that merge values, but not so much that they could be used as a
3329  denial of service mechanism. In other words, a recipient &MUST; expand the
3330  list construct as follows:
3331</t>
3332<figure><artwork type="example">
3333  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
3334 
3335  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
3336</artwork></figure>
3337<t>
3338  Empty elements do not contribute to the count of elements present.
3339  For example, given these ABNF productions:
3340</t>
3341<figure><artwork type="example">
3342  example-list      = 1#example-list-elmt
3343  example-list-elmt = token ; see <xref target="field.components"/>
3344</artwork></figure>
3345<t>
3346  Then the following are valid values for example-list (not including the
3347  double quotes, which are present for delimitation only):
3348</t>
3349<figure><artwork type="example">
3350  "foo,bar"
3351  "foo ,bar,"
3352  "foo , ,bar,charlie   "
3353</artwork></figure>
3354<t>
3355  In contrast, the following values would be invalid, since at least one
3356  non-empty element is required by the example-list production:
3357</t>
3358<figure><artwork type="example">
3359  ""
3360  ","
3361  ",   ,"
3362</artwork></figure>
3363<t>
3364  <xref target="collected.abnf"/> shows the collected ABNF after the list
3365  constructs have been expanded, as described above, for recipients.
3366</t>
3367</section>
3368
3369<section title="IANA Considerations" anchor="IANA.considerations">
3370
3371<section title="Header Field Registration" anchor="header.field.registration">
3372<t>
3373   HTTP header fields are registered within the Message Header Field Registry
3374   maintained at
3375   <eref target="http://www.iana.org/assignments/message-headers/"/>.
3376</t>
3377<t>
3378   This document defines the following HTTP header fields, so their
3379   associated registry entries shall be updated according to the permanent
3380   registrations below (see <xref target="BCP90"/>):
3381</t>
3382<?BEGININC p1-messaging.iana-headers ?>
3383<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3384<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3385   <ttcol>Header Field Name</ttcol>
3386   <ttcol>Protocol</ttcol>
3387   <ttcol>Status</ttcol>
3388   <ttcol>Reference</ttcol>
3389
3390   <c>Connection</c>
3391   <c>http</c>
3392   <c>standard</c>
3393   <c>
3394      <xref target="header.connection"/>
3395   </c>
3396   <c>Content-Length</c>
3397   <c>http</c>
3398   <c>standard</c>
3399   <c>
3400      <xref target="header.content-length"/>
3401   </c>
3402   <c>Host</c>
3403   <c>http</c>
3404   <c>standard</c>
3405   <c>
3406      <xref target="header.host"/>
3407   </c>
3408   <c>TE</c>
3409   <c>http</c>
3410   <c>standard</c>
3411   <c>
3412      <xref target="header.te"/>
3413   </c>
3414   <c>Trailer</c>
3415   <c>http</c>
3416   <c>standard</c>
3417   <c>
3418      <xref target="header.trailer"/>
3419   </c>
3420   <c>Transfer-Encoding</c>
3421   <c>http</c>
3422   <c>standard</c>
3423   <c>
3424      <xref target="header.transfer-encoding"/>
3425   </c>
3426   <c>Upgrade</c>
3427   <c>http</c>
3428   <c>standard</c>
3429   <c>
3430      <xref target="header.upgrade"/>
3431   </c>
3432   <c>Via</c>
3433   <c>http</c>
3434   <c>standard</c>
3435   <c>
3436      <xref target="header.via"/>
3437   </c>
3438</texttable>
3439<!--(END)-->
3440<?ENDINC p1-messaging.iana-headers ?>
3441<t>
3442   Furthermore, the header field-name "Close" shall be registered as
3443   "reserved", since using that name as an HTTP header field might
3444   conflict with the "close" connection option of the "<x:ref>Connection</x:ref>"
3445   header field (<xref target="header.connection"/>).
3446</t>
3447<texttable align="left" suppress-title="true">
3448   <ttcol>Header Field Name</ttcol>
3449   <ttcol>Protocol</ttcol>
3450   <ttcol>Status</ttcol>
3451   <ttcol>Reference</ttcol>
3452
3453   <c>Close</c>
3454   <c>http</c>
3455   <c>reserved</c>
3456   <c>
3457      <xref target="header.field.registration"/>
3458   </c>
3459</texttable>
3460<t>
3461   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3462</t>
3463</section>
3464
3465<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3466<t>
3467   IANA maintains the registry of URI Schemes <xref target="BCP115"/> at
3468   <eref target="http://www.iana.org/assignments/uri-schemes/"/>.
3469</t>
3470<t>
3471   This document defines the following URI schemes, so their
3472   associated registry entries shall be updated according to the permanent
3473   registrations below:
3474</t>
3475<texttable align="left" suppress-title="true">
3476   <ttcol>URI Scheme</ttcol>
3477   <ttcol>Description</ttcol>
3478   <ttcol>Reference</ttcol>
3479
3480   <c>http</c>
3481   <c>Hypertext Transfer Protocol</c>
3482   <c><xref target="http.uri"/></c>
3483
3484   <c>https</c>
3485   <c>Hypertext Transfer Protocol Secure</c>
3486   <c><xref target="https.uri"/></c>
3487</texttable>
3488</section>
3489
3490<section title="Internet Media Type Registration" anchor="internet.media.type.http">
3491<t>
3492   IANA maintains the registry of Internet media types <xref target="BCP13"/> at
3493   <eref target="http://www.iana.org/assignments/media-types"/>.
3494</t>
3495<t>
3496   This document serves as the specification for the Internet media types
3497   "message/http" and "application/http". The following is to be registered with
3498   IANA.
3499</t>
3500<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3501<iref item="Media Type" subitem="message/http" primary="true"/>
3502<iref item="message/http Media Type" primary="true"/>
3503<t>
3504   The message/http type can be used to enclose a single HTTP request or
3505   response message, provided that it obeys the MIME restrictions for all
3506   "message" types regarding line length and encodings.
3507</t>
3508<t>
3509  <list style="hanging" x:indent="12em">
3510    <t hangText="Type name:">
3511      message
3512    </t>
3513    <t hangText="Subtype name:">
3514      http
3515    </t>
3516    <t hangText="Required parameters:">
3517      N/A
3518    </t>
3519    <t hangText="Optional parameters:">
3520      version, msgtype
3521      <list style="hanging">
3522        <t hangText="version:">
3523          The HTTP-version number of the enclosed message
3524          (e.g., "1.1"). If not present, the version can be
3525          determined from the first line of the body.
3526        </t>
3527        <t hangText="msgtype:">
3528          The message type &mdash; "request" or "response". If not
3529          present, the type can be determined from the first
3530          line of the body.
3531        </t>
3532      </list>
3533    </t>
3534    <t hangText="Encoding considerations:">
3535      only "7bit", "8bit", or "binary" are permitted
3536    </t>
3537    <t hangText="Security considerations:">
3538      see <xref target="security.considerations"/>
3539    </t>
3540    <t hangText="Interoperability considerations:">
3541      N/A
3542    </t>
3543    <t hangText="Published specification:">
3544      This specification (see <xref target="internet.media.type.message.http"/>).
3545    </t>
3546    <t hangText="Applications that use this media type:">
3547      N/A
3548    </t>
3549    <t hangText="Fragment identifier considerations:">
3550      N/A
3551    </t>
3552    <t hangText="Additional information:">
3553      <list style="hanging">
3554        <t hangText="Magic number(s):">N/A</t>
3555        <t hangText="Deprecated alias names for this type:">N/A</t>
3556        <t hangText="File extension(s):">N/A</t>
3557        <t hangText="Macintosh file type code(s):">N/A</t>
3558      </list>
3559    </t>
3560    <t hangText="Person and email address to contact for further information:">
3561      See Authors Section.
3562    </t>
3563    <t hangText="Intended usage:">
3564      COMMON
3565    </t>
3566    <t hangText="Restrictions on usage:">
3567      N/A
3568    </t>
3569    <t hangText="Author:">
3570      See Authors Section.
3571    </t>
3572    <t hangText="Change controller:">
3573      IESG
3574    </t>
3575  </list>
3576</t>
3577</section>
3578<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3579<iref item="Media Type" subitem="application/http" primary="true"/>
3580<iref item="application/http Media Type" primary="true"/>
3581<t>
3582   The application/http type can be used to enclose a pipeline of one or more
3583   HTTP request or response messages (not intermixed).
3584</t>
3585<t>
3586  <list style="hanging" x:indent="12em">
3587    <t hangText="Type name:">
3588      application
3589    </t>
3590    <t hangText="Subtype name:">
3591      http
3592    </t>
3593    <t hangText="Required parameters:">
3594      N/A
3595    </t>
3596    <t hangText="Optional parameters:">
3597      version, msgtype
3598      <list style="hanging">
3599        <t hangText="version:">
3600          The HTTP-version number of the enclosed messages
3601          (e.g., "1.1"). If not present, the version can be
3602          determined from the first line of the body.
3603        </t>
3604        <t hangText="msgtype:">
3605          The message type &mdash; "request" or "response". If not
3606          present, the type can be determined from the first
3607          line of the body.
3608        </t>
3609      </list>
3610    </t>
3611    <t hangText="Encoding considerations:">
3612      HTTP messages enclosed by this type
3613      are in "binary" format; use of an appropriate
3614      Content-Transfer-Encoding is required when
3615      transmitted via E-mail.
3616    </t>
3617    <t hangText="Security considerations:">
3618      see <xref target="security.considerations"/>
3619    </t>
3620    <t hangText="Interoperability considerations:">
3621      N/A
3622    </t>
3623    <t hangText="Published specification:">
3624      This specification (see <xref target="internet.media.type.application.http"/>).
3625    </t>
3626    <t hangText="Applications that use this media type:">
3627      N/A
3628    </t>
3629    <t hangText="Fragment identifier considerations:">
3630      N/A
3631    </t>
3632    <t hangText="Additional information:">
3633      <list style="hanging">
3634        <t hangText="Deprecated alias names for this type:">N/A</t>
3635        <t hangText="Magic number(s):">N/A</t>
3636        <t hangText="File extension(s):">N/A</t>
3637        <t hangText="Macintosh file type code(s):">N/A</t>
3638      </list>
3639    </t>
3640    <t hangText="Person and email address to contact for further information:">
3641      See Authors Section.
3642    </t>
3643    <t hangText="Intended usage:">
3644      COMMON
3645    </t>
3646    <t hangText="Restrictions on usage:">
3647      N/A
3648    </t>
3649    <t hangText="Author:">
3650      See Authors Section.
3651    </t>
3652    <t hangText="Change controller:">
3653      IESG
3654    </t>
3655  </list>
3656</t>
3657</section>
3658</section>
3659
3660<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3661<t>
3662   The HTTP Transfer Coding Registry defines the name space for transfer
3663   coding names. It is maintained at <eref target="http://www.iana.org/assignments/http-parameters"/>.
3664</t>
3665
3666<section title="Procedure" anchor="transfer.coding.registry.procedure">
3667<t>
3668   Registrations &MUST; include the following fields:
3669   <list style="symbols">
3670     <t>Name</t>
3671     <t>Description</t>
3672     <t>Pointer to specification text</t>
3673   </list>
3674</t>
3675<t>
3676   Names of transfer codings &MUST-NOT; overlap with names of content codings
3677   (&content-codings;) unless the encoding transformation is identical, as
3678   is the case for the compression codings defined in
3679   <xref target="compression.codings"/>.
3680</t>
3681<t>
3682   Values to be added to this name space require IETF Review (see
3683   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3684   conform to the purpose of transfer coding defined in this specification.
3685</t>
3686<t>
3687   Use of program names for the identification of encoding formats
3688   is not desirable and is discouraged for future encodings.
3689</t>
3690</section>
3691
3692<section title="Registration" anchor="transfer.coding.registration">
3693<t>
3694   The HTTP Transfer Coding Registry shall be updated with the registrations
3695   below:
3696</t>
3697<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3698   <ttcol>Name</ttcol>
3699   <ttcol>Description</ttcol>
3700   <ttcol>Reference</ttcol>
3701   <c>chunked</c>
3702   <c>Transfer in a series of chunks</c>
3703   <c>
3704      <xref target="chunked.encoding"/>
3705   </c>
3706   <c>compress</c>
3707   <c>UNIX "compress" data format <xref target="Welch"/></c>
3708   <c>
3709      <xref target="compress.coding"/>
3710   </c>
3711   <c>deflate</c>
3712   <c>"deflate" compressed data (<xref target="RFC1951"/>) inside
3713   the "zlib" data format (<xref target="RFC1950"/>)
3714   </c>
3715   <c>
3716      <xref target="deflate.coding"/>
3717   </c>
3718   <c>gzip</c>
3719   <c>GZIP file format <xref target="RFC1952"/></c>
3720   <c>
3721      <xref target="gzip.coding"/>
3722   </c>
3723   <c>x-compress</c>
3724   <c>Deprecated (alias for compress)</c>
3725   <c>
3726      <xref target="compress.coding"/>
3727   </c>
3728   <c>x-gzip</c>
3729   <c>Deprecated (alias for gzip)</c>
3730   <c>
3731      <xref target="gzip.coding"/>
3732   </c>
3733</texttable>
3734</section>
3735</section>
3736
3737<section title="Content Coding Registration" anchor="content.coding.registration">
3738<t>
3739   IANA maintains the registry of HTTP Content Codings at
3740   <eref target="http://www.iana.org/assignments/http-parameters"/>.
3741</t>
3742<t>
3743   The HTTP Content Codings Registry shall be updated with the registrations
3744   below:
3745</t>
3746<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
3747   <ttcol>Name</ttcol>
3748   <ttcol>Description</ttcol>
3749   <ttcol>Reference</ttcol>
3750   <c>compress</c>
3751   <c>UNIX "compress" data format <xref target="Welch"/></c>
3752   <c>
3753      <xref target="compress.coding"/>
3754   </c>
3755   <c>deflate</c>
3756   <c>"deflate" compressed data (<xref target="RFC1951"/>) inside
3757   the "zlib" data format (<xref target="RFC1950"/>)</c>
3758   <c>
3759      <xref target="deflate.coding"/>
3760   </c>
3761   <c>gzip</c>
3762   <c>GZIP file format <xref target="RFC1952"/></c>
3763   <c>
3764      <xref target="gzip.coding"/>
3765   </c>
3766   <c>x-compress</c>
3767   <c>Deprecated (alias for compress)</c>
3768   <c>
3769      <xref target="compress.coding"/>
3770   </c>
3771   <c>x-gzip</c>
3772   <c>Deprecated (alias for gzip)</c>
3773   <c>
3774      <xref target="gzip.coding"/>
3775   </c>
3776</texttable>
3777</section>
3778
3779<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3780<t>
3781   The HTTP Upgrade Token Registry defines the name space for protocol-name
3782   tokens used to identify protocols in the <x:ref>Upgrade</x:ref> header
3783   field. The registry is maintained at <eref target="http://www.iana.org/assignments/http-upgrade-tokens"/>.
3784</t>
3785
3786<section title="Procedure" anchor="upgrade.token.registry.procedure">  
3787<t>
3788   Each registered protocol name is associated with contact information
3789   and an optional set of specifications that details how the connection
3790   will be processed after it has been upgraded.
3791</t>
3792<t>
3793   Registrations happen on a "First Come First Served" basis (see
3794   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3795   following rules:
3796  <list style="numbers">
3797    <t>A protocol-name token, once registered, stays registered forever.</t>
3798    <t>The registration &MUST; name a responsible party for the
3799       registration.</t>
3800    <t>The registration &MUST; name a point of contact.</t>
3801    <t>The registration &MAY; name a set of specifications associated with
3802       that token. Such specifications need not be publicly available.</t>
3803    <t>The registration &SHOULD; name a set of expected "protocol-version"
3804       tokens associated with that token at the time of registration.</t>
3805    <t>The responsible party &MAY; change the registration at any time.
3806       The IANA will keep a record of all such changes, and make them
3807       available upon request.</t>
3808    <t>The IESG &MAY; reassign responsibility for a protocol token.
3809       This will normally only be used in the case when a
3810       responsible party cannot be contacted.</t>
3811  </list>
3812</t>
3813<t>
3814   This registration procedure for HTTP Upgrade Tokens replaces that
3815   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3816</t>
3817</section>
3818
3819<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3820<t>
3821   The "HTTP" entry in the HTTP Upgrade Token Registry shall be updated with
3822   the registration below:
3823</t>
3824<texttable align="left" suppress-title="true">
3825   <ttcol>Value</ttcol>
3826   <ttcol>Description</ttcol>
3827   <ttcol>Expected Version Tokens</ttcol>
3828   <ttcol>Reference</ttcol>
3829
3830   <c>HTTP</c>
3831   <c>Hypertext Transfer Protocol</c>
3832   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3833   <c><xref target="http.version"/></c>
3834</texttable>
3835<t>
3836   The responsible party is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3837</t>
3838</section>
3839</section>
3840
3841</section>
3842
3843<section title="Security Considerations" anchor="security.considerations">
3844<t>
3845   This section is meant to inform developers, information providers, and
3846   users of known security concerns relevant to HTTP/1.1 message syntax,
3847   parsing, and routing.
3848</t>
3849
3850<section title="DNS-related Attacks" anchor="dns.related.attacks">
3851<t>
3852   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3853   generally prone to security attacks based on the deliberate misassociation
3854   of IP addresses and DNS names not protected by DNSSEC. Clients need to be
3855   cautious in assuming the validity of an IP number/DNS name association unless
3856   the response is protected by DNSSEC (<xref target="RFC4033"/>).
3857</t>
3858</section>
3859
3860<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3861<t>
3862   By their very nature, HTTP intermediaries are men-in-the-middle, and
3863   represent an opportunity for man-in-the-middle attacks. Compromise of
3864   the systems on which the intermediaries run can result in serious security
3865   and privacy problems. Intermediaries have access to security-related
3866   information, personal information about individual users and
3867   organizations, and proprietary information belonging to users and
3868   content providers. A compromised intermediary, or an intermediary
3869   implemented or configured without regard to security and privacy
3870   considerations, might be used in the commission of a wide range of
3871   potential attacks.
3872</t>
3873<t>
3874   Intermediaries that contain a shared cache are especially vulnerable
3875   to cache poisoning attacks.
3876</t>
3877<t>
3878   Implementers need to consider the privacy and security
3879   implications of their design and coding decisions, and of the
3880   configuration options they provide to operators (especially the
3881   default configuration).
3882</t>
3883<t>
3884   Users need to be aware that intermediaries are no more trustworthy than
3885   the people who run them; HTTP itself cannot solve this problem.
3886</t>
3887</section>
3888
3889<section title="Buffer Overflows" anchor="attack.protocol.element.size.overflows">
3890<t>
3891   Because HTTP uses mostly textual, character-delimited fields, attackers can
3892   overflow buffers in implementations, and/or perform a Denial of Service
3893   against implementations that accept fields with unlimited lengths.
3894</t>
3895<t>
3896   To promote interoperability, this specification makes specific
3897   recommendations for minimum size limits on request-line
3898   (<xref target="request.line"/>)
3899   and header fields (<xref target="header.fields"/>). These are
3900   minimum recommendations, chosen to be supportable even by implementations
3901   with limited resources; it is expected that most implementations will
3902   choose substantially higher limits.
3903</t>
3904<t>
3905   This specification also provides a way for servers to reject messages that
3906   have request-targets that are too long (&status-414;) or request entities
3907   that are too large (&status-4xx;). Additional status codes related to
3908   capacity limits have been defined by extensions to HTTP
3909   <xref target="RFC6585"/>.
3910</t>
3911<t>
3912   Recipients ought to carefully limit the extent to which they read other
3913   fields, including (but not limited to) request methods, response status
3914   phrases, header field-names, and body chunks, so as to avoid denial of
3915   service attacks without impeding interoperability.
3916</t>
3917</section>
3918
3919<section title="Message Integrity" anchor="message.integrity">
3920<t>
3921   HTTP does not define a specific mechanism for ensuring message integrity,
3922   instead relying on the error-detection ability of underlying transport
3923   protocols and the use of length or chunk-delimited framing to detect
3924   completeness. Additional integrity mechanisms, such as hash functions or
3925   digital signatures applied to the content, can be selectively added to
3926   messages via extensible metadata header fields. Historically, the lack of
3927   a single integrity mechanism has been justified by the informal nature of
3928   most HTTP communication.  However, the prevalence of HTTP as an information
3929   access mechanism has resulted in its increasing use within environments
3930   where verification of message integrity is crucial.
3931</t>
3932<t>
3933   User agents are encouraged to implement configurable means for detecting
3934   and reporting failures of message integrity such that those means can be
3935   enabled within environments for which integrity is necessary. For example,
3936   a browser being used to view medical history or drug interaction
3937   information needs to indicate to the user when such information is detected
3938   by the protocol to be incomplete, expired, or corrupted during transfer.
3939   Such mechanisms might be selectively enabled via user agent extensions or
3940   the presence of message integrity metadata in a response.
3941   At a minimum, user agents ought to provide some indication that allows a
3942   user to distinguish between a complete and incomplete response message
3943   (<xref target="incomplete.messages"/>) when such verification is desired.
3944</t>
3945</section>
3946
3947<section title="Server Log Information" anchor="abuse.of.server.log.information">
3948<t>
3949   A server is in the position to save personal data about a user's requests
3950   over time, which might identify their reading patterns or subjects of
3951   interest.  In particular, log information gathered at an intermediary
3952   often contains a history of user agent interaction, across a multitude
3953   of sites, that can be traced to individual users.
3954</t>
3955<t>
3956   HTTP log information is confidential in nature; its handling is often
3957   constrained by laws and regulations.  Log information needs to be securely
3958   stored and appropriate guidelines followed for its analysis.
3959   Anonymization of personal information within individual entries helps,
3960   but is generally not sufficient to prevent real log traces from being
3961   re-identified based on correlation with other access characteristics.
3962   As such, access traces that are keyed to a specific client are unsafe to
3963   publish even if the key is pseudonymous.
3964</t>
3965<t>
3966   To minimize the risk of theft or accidental publication, log information
3967   ought to be purged of personally identifiable information, including
3968   user identifiers, IP addresses, and user-provided query parameters,
3969   as soon as that information is no longer necessary to support operational
3970   needs for security, auditing, or fraud control.
3971</t>
3972</section>
3973</section>
3974
3975<section title="Acknowledgments" anchor="acks">
3976<t>
3977   This edition of HTTP/1.1 builds on the many contributions that went into
3978   <xref target="RFC1945" format="none">RFC 1945</xref>,
3979   <xref target="RFC2068" format="none">RFC 2068</xref>,
3980   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3981   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3982   substantial contributions made by the previous authors, editors, and
3983   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3984   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3985   and Paul J. Leach. Mark Nottingham oversaw this effort as working group chair.
3986</t>
3987<t>
3988   Since 1999, the following contributors have helped improve the HTTP
3989   specification by reporting bugs, asking smart questions, drafting or
3990   reviewing text, and evaluating open issues:
3991</t>
3992<?BEGININC acks ?>
3993<t>Adam Barth,
3994Adam Roach,
3995Addison Phillips,
3996Adrian Chadd,
3997Adrien W. de Croy,
3998Alan Ford,
3999Alan Ruttenberg,
4000Albert Lunde,
4001Alek Storm,
4002Alex Rousskov,
4003Alexandre Morgaut,
4004Alexey Melnikov,
4005Alisha Smith,
4006Amichai Rothman,
4007Amit Klein,
4008Amos Jeffries,
4009Andreas Maier,
4010Andreas Petersson,
4011Andrei Popov,
4012Anil Sharma,
4013Anne van Kesteren,
4014Anthony Bryan,
4015Asbjorn Ulsberg,
4016Ashok Kumar,
4017Balachander Krishnamurthy,
4018Barry Leiba,
4019Ben Laurie,
4020Benjamin Carlyle,
4021Benjamin Niven-Jenkins,
4022Benoit Claise,
4023Bil Corry,
4024Bill Burke,
4025Bjoern Hoehrmann,
4026Bob Scheifler,
4027Boris Zbarsky,
4028Brett Slatkin,
4029Brian Kell,
4030Brian McBarron,
4031Brian Pane,
4032Brian Raymor,
4033Brian Smith,
4034Bruce Perens,
4035Bryce Nesbitt,
4036Cameron Heavon-Jones,
4037Carl Kugler,
4038Carsten Bormann,
4039Charles Fry,
4040Chris Burdess,
4041Chris Newman,
4042Christian Huitema,
4043Cyrus Daboo,
4044Dale Robert Anderson,
4045Dan Wing,
4046Dan Winship,
4047Daniel Stenberg,
4048Darrel Miller,
4049Dave Cridland,
4050Dave Crocker,
4051Dave Kristol,
4052Dave Thaler,
4053David Booth,
4054David Singer,
4055David W. Morris,
4056Diwakar Shetty,
4057Dmitry Kurochkin,
4058Drummond Reed,
4059Duane Wessels,
4060Edward Lee,
4061Eitan Adler,
4062Eliot Lear,
4063Emile Stephan,
4064Eran Hammer-Lahav,
4065Eric D. Williams,
4066Eric J. Bowman,
4067Eric Lawrence,
4068Eric Rescorla,
4069Erik Aronesty,
4070EungJun Yi,
4071Evan Prodromou,
4072Felix Geisendoerfer,
4073Florian Weimer,
4074Frank Ellermann,
4075Fred Akalin,
4076Fred Bohle,
4077Frederic Kayser,
4078Gabor Molnar,
4079Gabriel Montenegro,
4080Geoffrey Sneddon,
4081Gervase Markham,
4082Gili Tzabari,
4083Grahame Grieve,
4084Greg Slepak,
4085Greg Wilkins,
4086Grzegorz Calkowski,
4087Harald Tveit Alvestrand,
4088Harry Halpin,
4089Helge Hess,
4090Henrik Nordstrom,
4091Henry S. Thompson,
4092Henry Story,
4093Herbert van de Sompel,
4094Herve Ruellan,
4095Howard Melman,
4096Hugo Haas,
4097Ian Fette,
4098Ian Hickson,
4099Ido Safruti,
4100Ilari Liusvaara,
4101Ilya Grigorik,
4102Ingo Struck,
4103J. Ross Nicoll,
4104James Cloos,
4105James H. Manger,
4106James Lacey,
4107James M. Snell,
4108Jamie Lokier,
4109Jan Algermissen,
4110Jari Arkko,
4111Jeff Hodges (who came up with the term 'effective Request-URI'),
4112Jeff Pinner,
4113Jeff Walden,
4114Jim Luther,
4115Jitu Padhye,
4116Joe D. Williams,
4117Joe Gregorio,
4118Joe Orton,
4119Joel Jaeggli,
4120John C. Klensin,
4121John C. Mallery,
4122John Cowan,
4123John Kemp,
4124John Panzer,
4125John Schneider,
4126John Stracke,
4127John Sullivan,
4128Jonas Sicking,
4129Jonathan A. Rees,
4130Jonathan Billington,
4131Jonathan Moore,
4132Jonathan Silvera,
4133Jordi Ros,
4134Joris Dobbelsteen,
4135Josh Cohen,
4136Julien Pierre,
4137Jungshik Shin,
4138Justin Chapweske,
4139Justin Erenkrantz,
4140Justin James,
4141Kalvinder Singh,
4142Karl Dubost,
4143Kathleen Moriarty,
4144Keith Hoffman,
4145Keith Moore,
4146Ken Murchison,
4147Koen Holtman,
4148Konstantin Voronkov,
4149Kris Zyp,
4150Leif Hedstrom,
4151Lionel Morand,
4152Lisa Dusseault,
4153Maciej Stachowiak,
4154Manu Sporny,
4155Marc Schneider,
4156Marc Slemko,
4157Mark Baker,
4158Mark Pauley,
4159Mark Watson,
4160Markus Isomaki,
4161Markus Lanthaler,
4162Martin J. Duerst,
4163Martin Musatov,
4164Martin Nilsson,
4165Martin Thomson,
4166Matt Lynch,
4167Matthew Cox,
4168Matthew Kerwin,
4169Max Clark,
4170Menachem Dodge,
4171Meral Shirazipour,
4172Michael Burrows,
4173Michael Hausenblas,
4174Michael Scharf,
4175Michael Sweet,
4176Michael Tuexen,
4177Michael Welzl,
4178Mike Amundsen,
4179Mike Belshe,
4180Mike Bishop,
4181Mike Kelly,
4182Mike Schinkel,
4183Miles Sabin,
4184Murray S. Kucherawy,
4185Mykyta Yevstifeyev,
4186Nathan Rixham,
4187Nicholas Shanks,
4188Nico Williams,
4189Nicolas Alvarez,
4190Nicolas Mailhot,
4191Noah Slater,
4192Osama Mazahir,
4193Pablo Castro,
4194Pat Hayes,
4195Patrick R. McManus,
4196Paul E. Jones,
4197Paul Hoffman,
4198Paul Marquess,
4199Pete Resnick,
4200Peter Lepeska,
4201Peter Occil,
4202Peter Saint-Andre,
4203Peter Watkins,
4204Phil Archer,
4205Philippe Mougin,
4206Phillip Hallam-Baker,
4207Piotr Dobrogost,
4208Poul-Henning Kamp,
4209Preethi Natarajan,
4210Rajeev Bector,
4211Ray Polk,
4212Reto Bachmann-Gmuer,
4213Richard Barnes,
4214Richard Cyganiak,
4215Robby Simpson,
4216Robert Brewer,
4217Robert Collins,
4218Robert Mattson,
4219Robert O'Callahan,
4220Robert Olofsson,
4221Robert Sayre,
4222Robert Siemer,
4223Robert de Wilde,
4224Roberto Javier Godoy,
4225Roberto Peon,
4226Roland Zink,
4227Ronny Widjaja,
4228Ryan Hamilton,
4229S. Mike Dierken,
4230Salvatore Loreto,
4231Sam Johnston,
4232Sam Pullara,
4233Sam Ruby,
4234Saurabh Kulkarni,
4235Scott Lawrence (who maintained the original issues list),
4236Sean B. Palmer,
4237Sean Turner,
4238Sebastien Barnoud,
4239Shane McCarron,
4240Shigeki Ohtsu,
4241Simon Yarde,
4242Stefan Eissing,
4243Stefan Tilkov,
4244Stefanos Harhalakis,
4245Stephane Bortzmeyer,
4246Stephen Farrell,
4247Stephen Kent,
4248Stephen Ludin,
4249Stuart Williams,
4250Subbu Allamaraju,
4251Subramanian Moonesamy,
4252Susan Hares,
4253Sylvain Hellegouarch,
4254Tapan Divekar,
4255Tatsuhiro Tsujikawa,
4256Tatsuya Hayashi,
4257Ted Hardie,
4258Ted Lemon,
4259Thomas Broyer,
4260Thomas Fossati,
4261Thomas Maslen,
4262Thomas Nadeau,
4263Thomas Nordin,
4264Thomas Roessler,
4265Tim Bray,
4266Tim Morgan,
4267Tim Olsen,
4268Tom Zhou,
4269Travis Snoozy,
4270Tyler Close,
4271Vincent Murphy,
4272Wenbo Zhu,
4273Werner Baumann,
4274Wilbur Streett,
4275Wilfredo Sanchez Vega,
4276William A. Rowe Jr.,
4277William Chan,
4278Willy Tarreau,
4279Xiaoshu Wang,
4280Yaron Goland,
4281Yngve Nysaeter Pettersen,
4282Yoav Nir,
4283Yogesh Bang,
4284Yuchung Cheng,
4285Yutaka Oiwa,
4286Yves Lafon (long-time member of the editor team),
4287Zed A. Shaw, and
4288Zhong Yu.
4289</t>
4290<?ENDINC acks ?>
4291<t>
4292   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
4293   acknowledgements from prior revisions.
4294</t>
4295</section>
4296
4297</middle>
4298<back>
4299
4300<references title="Normative References">
4301
4302<reference anchor="Part2">
4303  <front>
4304    <title>Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</title>
4305    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4306      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4307      <address><email>fielding@gbiv.com</email></address>
4308    </author>
4309    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4310      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4311      <address><email>julian.reschke@greenbytes.de</email></address>
4312    </author>
4313    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4314  </front>
4315  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4316  <x:source href="p2-semantics.xml" basename="p2-semantics">
4317    <x:defines>1xx (Informational)</x:defines>
4318    <x:defines>1xx</x:defines>
4319    <x:defines>100 (Continue)</x:defines>
4320    <x:defines>101 (Switching Protocols)</x:defines>
4321    <x:defines>2xx (Successful)</x:defines>
4322    <x:defines>2xx</x:defines>
4323    <x:defines>200 (OK)</x:defines>
4324    <x:defines>203 (Non-Authoritative Information)</x:defines>
4325    <x:defines>204 (No Content)</x:defines>
4326    <x:defines>3xx (Redirection)</x:defines>
4327    <x:defines>3xx</x:defines>
4328    <x:defines>301 (Moved Permanently)</x:defines>
4329    <x:defines>4xx (Client Error)</x:defines>
4330    <x:defines>4xx</x:defines>
4331    <x:defines>400 (Bad Request)</x:defines>
4332    <x:defines>411 (Length Required)</x:defines>
4333    <x:defines>414 (URI Too Long)</x:defines>
4334    <x:defines>417 (Expectation Failed)</x:defines>
4335    <x:defines>426 (Upgrade Required)</x:defines>
4336    <x:defines>501 (Not Implemented)</x:defines>
4337    <x:defines>502 (Bad Gateway)</x:defines>
4338    <x:defines>505 (HTTP Version Not Supported)</x:defines>
4339    <x:defines>Accept-Encoding</x:defines>
4340    <x:defines>Allow</x:defines>
4341    <x:defines>Content-Encoding</x:defines>
4342    <x:defines>Content-Location</x:defines>
4343    <x:defines>Content-Type</x:defines>
4344    <x:defines>Date</x:defines>
4345    <x:defines>Expect</x:defines>
4346    <x:defines>Location</x:defines>
4347    <x:defines>Server</x:defines>
4348    <x:defines>User-Agent</x:defines>
4349  </x:source>
4350</reference>
4351
4352<reference anchor="Part4">
4353  <front>
4354    <title>Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests</title>
4355    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
4356      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4357      <address><email>fielding@gbiv.com</email></address>
4358    </author>
4359    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
4360      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4361      <address><email>julian.reschke@greenbytes.de</email></address>
4362    </author>
4363    <date month="&ID-MONTH;" year="&ID-YEAR;" />
4364  </front>
4365  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;" />
4366  <x:source basename="p4-conditional" href="p4-conditional.xml">
4367    <x:defines>304 (Not Modified)</x:defines>
4368    <x:defines>ETag</x:defines>
4369    <x:defines>Last-Modified</x:defines>
4370  </x:source>
4371</reference>
4372
4373<reference anchor="Part5">
4374  <front>
4375    <title>Hypertext Transfer Protocol (HTTP/1.1): Range Requests</title>
4376    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4377      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4378      <address><email>fielding@gbiv.com</email></address>
4379    </author>
4380    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4381      <organization abbrev="W3C">World Wide Web Consortium</organization>
4382      <address><email>ylafon@w3.org</email></address>
4383    </author>
4384    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4385      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4386      <address><email>julian.reschke@greenbytes.de</email></address>
4387    </author>
4388    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4389  </front>
4390  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
4391  <x:source href="p5-range.xml" basename="p5-range">
4392    <x:defines>Content-Range</x:defines>
4393  </x:source>
4394</reference>
4395
4396<reference anchor="Part6">
4397  <front>
4398    <title>Hypertext Transfer Protocol (HTTP/1.1): Caching</title>
4399    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4400      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4401      <address><email>fielding@gbiv.com</email></address>
4402    </author>
4403    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4404      <organization>Akamai</organization>
4405      <address><email>mnot@mnot.net</email></address>
4406    </author>
4407    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4408      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4409      <address><email>julian.reschke@greenbytes.de</email></address>
4410    </author>
4411    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4412  </front>
4413  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4414  <x:source href="p6-cache.xml" basename="p6-cache">
4415    <x:defines>Cache-Control</x:defines>
4416    <x:defines>Expires</x:defines>
4417  </x:source>
4418</reference>
4419
4420<reference anchor="Part7">
4421  <front>
4422    <title>Hypertext Transfer Protocol (HTTP/1.1): Authentication</title>
4423    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4424      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4425      <address><email>fielding@gbiv.com</email></address>
4426    </author>
4427    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4428      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4429      <address><email>julian.reschke@greenbytes.de</email></address>
4430    </author>
4431    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4432  </front>
4433  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
4434  <x:source href="p7-auth.xml" basename="p7-auth">
4435    <x:defines>Proxy-Authenticate</x:defines>
4436    <x:defines>Proxy-Authorization</x:defines>
4437  </x:source>
4438</reference>
4439
4440<reference anchor="RFC5234">
4441  <front>
4442    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4443    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4444      <organization>Brandenburg InternetWorking</organization>
4445      <address>
4446        <email>dcrocker@bbiw.net</email>
4447      </address> 
4448    </author>
4449    <author initials="P." surname="Overell" fullname="Paul Overell">
4450      <organization>THUS plc.</organization>
4451      <address>
4452        <email>paul.overell@thus.net</email>
4453      </address>
4454    </author>
4455    <date month="January" year="2008"/>
4456  </front>
4457  <seriesInfo name="STD" value="68"/>
4458  <seriesInfo name="RFC" value="5234"/>
4459</reference>
4460
4461<reference anchor="RFC2119">
4462  <front>
4463    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4464    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4465      <organization>Harvard University</organization>
4466      <address><email>sob@harvard.edu</email></address>
4467    </author>
4468    <date month="March" year="1997"/>
4469  </front>
4470  <seriesInfo name="BCP" value="14"/>
4471  <seriesInfo name="RFC" value="2119"/>
4472</reference>
4473
4474<reference anchor="RFC3986">
4475 <front>
4476  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4477  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4478    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4479    <address>
4480       <email>timbl@w3.org</email>
4481       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4482    </address>
4483  </author>
4484  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4485    <organization abbrev="Day Software">Day Software</organization>
4486    <address>
4487      <email>fielding@gbiv.com</email>
4488      <uri>http://roy.gbiv.com/</uri>
4489    </address>
4490  </author>
4491  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4492    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4493    <address>
4494      <email>LMM@acm.org</email>
4495      <uri>http://larry.masinter.net/</uri>
4496    </address>
4497  </author>
4498  <date month='January' year='2005'></date>
4499 </front>
4500 <seriesInfo name="STD" value="66"/>
4501 <seriesInfo name="RFC" value="3986"/>
4502</reference>
4503
4504<reference anchor="RFC0793">
4505  <front>
4506    <title>Transmission Control Protocol</title>
4507    <author initials='J.' surname='Postel' fullname='Jon Postel'>
4508      <organization>University of Southern California (USC)/Information Sciences Institute</organization>
4509    </author>
4510    <date year='1981' month='September' />
4511  </front>
4512  <seriesInfo name='STD' value='7' />
4513  <seriesInfo name='RFC' value='793' />
4514</reference>
4515
4516<reference anchor="USASCII">
4517  <front>
4518    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4519    <author>
4520      <organization>American National Standards Institute</organization>
4521    </author>
4522    <date year="1986"/>
4523  </front>
4524  <seriesInfo name="ANSI" value="X3.4"/>
4525</reference>
4526
4527<reference anchor="RFC1950">
4528  <front>
4529    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4530    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4531      <organization>Aladdin Enterprises</organization>
4532      <address><email>ghost@aladdin.com</email></address>
4533    </author>
4534    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4535    <date month="May" year="1996"/>
4536  </front>
4537  <seriesInfo name="RFC" value="1950"/>
4538  <!--<annotation>
4539    RFC 1950 is an Informational RFC, thus it might be less stable than
4540    this specification. On the other hand, this downward reference was
4541    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4542    therefore it is unlikely to cause problems in practice. See also
4543    <xref target="BCP97"/>.
4544  </annotation>-->
4545</reference>
4546
4547<reference anchor="RFC1951">
4548  <front>
4549    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4550    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4551      <organization>Aladdin Enterprises</organization>
4552      <address><email>ghost@aladdin.com</email></address>
4553    </author>
4554    <date month="May" year="1996"/>
4555  </front>
4556  <seriesInfo name="RFC" value="1951"/>
4557  <!--<annotation>
4558    RFC 1951 is an Informational RFC, thus it might be less stable than
4559    this specification. On the other hand, this downward reference was
4560    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4561    therefore it is unlikely to cause problems in practice. See also
4562    <xref target="BCP97"/>.
4563  </annotation>-->
4564</reference>
4565
4566<reference anchor="RFC1952">
4567  <front>
4568    <title>GZIP file format specification version 4.3</title>
4569    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4570      <organization>Aladdin Enterprises</organization>
4571      <address><email>ghost@aladdin.com</email></address>
4572    </author>
4573    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4574      <address><email>gzip@prep.ai.mit.edu</email></address>
4575    </author>
4576    <author initials="M." surname="Adler" fullname="Mark Adler">
4577      <address><email>madler@alumni.caltech.edu</email></address>
4578    </author>
4579    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4580      <address><email>ghost@aladdin.com</email></address>
4581    </author>
4582    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4583      <address><email>randeg@alumni.rpi.edu</email></address>
4584    </author>
4585    <date month="May" year="1996"/>
4586  </front>
4587  <seriesInfo name="RFC" value="1952"/>
4588  <!--<annotation>
4589    RFC 1952 is an Informational RFC, thus it might be less stable than
4590    this specification. On the other hand, this downward reference was
4591    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4592    therefore it is unlikely to cause problems in practice. See also
4593    <xref target="BCP97"/>.
4594  </annotation>-->
4595</reference>
4596
4597<reference anchor="Welch">
4598  <front>
4599    <title>A Technique for High Performance Data Compression</title>
4600    <author initials="T.A." surname="Welch" fullname="Terry A. Welch"/>
4601    <date month="June" year="1984"/>
4602  </front>
4603  <seriesInfo name="IEEE Computer" value="17(6)"/>
4604</reference>
4605
4606</references>
4607
4608<references title="Informative References">
4609
4610<reference anchor="ISO-8859-1">
4611  <front>
4612    <title>
4613     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4614    </title>
4615    <author>
4616      <organization>International Organization for Standardization</organization>
4617    </author>
4618    <date year="1998"/>
4619  </front>
4620  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4621</reference>
4622
4623<reference anchor='RFC1919'>
4624  <front>
4625    <title>Classical versus Transparent IP Proxies</title>
4626    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4627      <address><email>mchatel@pax.eunet.ch</email></address>
4628    </author>
4629    <date year='1996' month='March' />
4630  </front>
4631  <seriesInfo name='RFC' value='1919' />
4632</reference>
4633
4634<reference anchor="RFC1945">
4635  <front>
4636    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4637    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4638      <organization>MIT, Laboratory for Computer Science</organization>
4639      <address><email>timbl@w3.org</email></address>
4640    </author>
4641    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4642      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4643      <address><email>fielding@ics.uci.edu</email></address>
4644    </author>
4645    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4646      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4647      <address><email>frystyk@w3.org</email></address>
4648    </author>
4649    <date month="May" year="1996"/>
4650  </front>
4651  <seriesInfo name="RFC" value="1945"/>
4652</reference>
4653
4654<reference anchor="RFC2045">
4655  <front>
4656    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4657    <author initials="N." surname="Freed" fullname="Ned Freed">
4658      <organization>Innosoft International, Inc.</organization>
4659      <address><email>ned@innosoft.com</email></address>
4660    </author>
4661    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4662      <organization>First Virtual Holdings</organization>
4663      <address><email>nsb@nsb.fv.com</email></address>
4664    </author>
4665    <date month="November" year="1996"/>
4666  </front>
4667  <seriesInfo name="RFC" value="2045"/>
4668</reference>
4669
4670<reference anchor="RFC2047">
4671  <front>
4672    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4673    <author initials="K." surname="Moore" fullname="Keith Moore">
4674      <organization>University of Tennessee</organization>
4675      <address><email>moore@cs.utk.edu</email></address>
4676    </author>
4677    <date month="November" year="1996"/>
4678  </front>
4679  <seriesInfo name="RFC" value="2047"/>
4680</reference>
4681
4682<reference anchor="RFC2068">
4683  <front>
4684    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4685    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4686      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4687      <address><email>fielding@ics.uci.edu</email></address>
4688    </author>
4689    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4690      <organization>MIT Laboratory for Computer Science</organization>
4691      <address><email>jg@w3.org</email></address>
4692    </author>
4693    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4694      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4695      <address><email>mogul@wrl.dec.com</email></address>
4696    </author>
4697    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4698      <organization>MIT Laboratory for Computer Science</organization>
4699      <address><email>frystyk@w3.org</email></address>
4700    </author>
4701    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4702      <organization>MIT Laboratory for Computer Science</organization>
4703      <address><email>timbl@w3.org</email></address>
4704    </author>
4705    <date month="January" year="1997"/>
4706  </front>
4707  <seriesInfo name="RFC" value="2068"/>
4708</reference>
4709
4710<reference anchor="RFC2145">
4711  <front>
4712    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4713    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4714      <organization>Western Research Laboratory</organization>
4715      <address><email>mogul@wrl.dec.com</email></address>
4716    </author>
4717    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4718      <organization>Department of Information and Computer Science</organization>
4719      <address><email>fielding@ics.uci.edu</email></address>
4720    </author>
4721    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4722      <organization>MIT Laboratory for Computer Science</organization>
4723      <address><email>jg@w3.org</email></address>
4724    </author>
4725    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4726      <organization>W3 Consortium</organization>
4727      <address><email>frystyk@w3.org</email></address>
4728    </author>
4729    <date month="May" year="1997"/>
4730  </front>
4731  <seriesInfo name="RFC" value="2145"/>
4732</reference>
4733
4734<reference anchor="RFC2616">
4735  <front>
4736    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4737    <author initials="R." surname="Fielding" fullname="R. Fielding">
4738      <organization>University of California, Irvine</organization>
4739      <address><email>fielding@ics.uci.edu</email></address>
4740    </author>
4741    <author initials="J." surname="Gettys" fullname="J. Gettys">
4742      <organization>W3C</organization>
4743      <address><email>jg@w3.org</email></address>
4744    </author>
4745    <author initials="J." surname="Mogul" fullname="J. Mogul">
4746      <organization>Compaq Computer Corporation</organization>
4747      <address><email>mogul@wrl.dec.com</email></address>
4748    </author>
4749    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4750      <organization>MIT Laboratory for Computer Science</organization>
4751      <address><email>frystyk@w3.org</email></address>
4752    </author>
4753    <author initials="L." surname="Masinter" fullname="L. Masinter">
4754      <organization>Xerox Corporation</organization>
4755      <address><email>masinter@parc.xerox.com</email></address>
4756    </author>
4757    <author initials="P." surname="Leach" fullname="P. Leach">
4758      <organization>Microsoft Corporation</organization>
4759      <address><email>paulle@microsoft.com</email></address>
4760    </author>
4761    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4762      <organization>W3C</organization>
4763      <address><email>timbl@w3.org</email></address>
4764    </author>
4765    <date month="June" year="1999"/>
4766  </front>
4767  <seriesInfo name="RFC" value="2616"/>
4768</reference>
4769
4770<reference anchor='RFC2817'>
4771  <front>
4772    <title>Upgrading to TLS Within HTTP/1.1</title>
4773    <author initials='R.' surname='Khare' fullname='R. Khare'>
4774      <organization>4K Associates / UC Irvine</organization>
4775      <address><email>rohit@4K-associates.com</email></address>
4776    </author>
4777    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4778      <organization>Agranat Systems, Inc.</organization>
4779      <address><email>lawrence@agranat.com</email></address>
4780    </author>
4781    <date year='2000' month='May' />
4782  </front>
4783  <seriesInfo name='RFC' value='2817' />
4784</reference>
4785
4786<reference anchor='RFC2818'>
4787  <front>
4788    <title>HTTP Over TLS</title>
4789    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4790      <organization>RTFM, Inc.</organization>
4791      <address><email>ekr@rtfm.com</email></address>
4792    </author>
4793    <date year='2000' month='May' />
4794  </front>
4795  <seriesInfo name='RFC' value='2818' />
4796</reference>
4797
4798<reference anchor='RFC3040'>
4799  <front>
4800    <title>Internet Web Replication and Caching Taxonomy</title>
4801    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4802      <organization>Equinix, Inc.</organization>
4803    </author>
4804    <author initials='I.' surname='Melve' fullname='I. Melve'>
4805      <organization>UNINETT</organization>
4806    </author>
4807    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4808      <organization>CacheFlow Inc.</organization>
4809    </author>
4810    <date year='2001' month='January' />
4811  </front>
4812  <seriesInfo name='RFC' value='3040' />
4813</reference>
4814
4815<reference anchor='BCP90'>
4816  <front>
4817    <title>Registration Procedures for Message Header Fields</title>
4818    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4819      <organization>Nine by Nine</organization>
4820      <address><email>GK-IETF@ninebynine.org</email></address>
4821    </author>
4822    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4823      <organization>BEA Systems</organization>
4824      <address><email>mnot@pobox.com</email></address>
4825    </author>
4826    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4827      <organization>HP Labs</organization>
4828      <address><email>JeffMogul@acm.org</email></address>
4829    </author>
4830    <date year='2004' month='September' />
4831  </front>
4832  <seriesInfo name='BCP' value='90' />
4833  <seriesInfo name='RFC' value='3864' />
4834</reference>
4835
4836<reference anchor='RFC4033'>
4837  <front>
4838    <title>DNS Security Introduction and Requirements</title>
4839    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4840    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4841    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4842    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4843    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4844    <date year='2005' month='March' />
4845  </front>
4846  <seriesInfo name='RFC' value='4033' />
4847</reference>
4848
4849<reference anchor="BCP13">
4850  <front>
4851    <title>Media Type Specifications and Registration Procedures</title>
4852    <author initials="N." surname="Freed" fullname="Ned Freed">
4853      <organization>Oracle</organization>
4854      <address>
4855        <email>ned+ietf@mrochek.com</email>
4856      </address>
4857    </author>
4858    <author initials="J." surname="Klensin" fullname="John C. Klensin">
4859      <address>
4860        <email>john+ietf@jck.com</email>
4861      </address>
4862    </author>
4863    <author initials="T." surname="Hansen" fullname="Tony Hansen">
4864      <organization>AT&amp;T Laboratories</organization>
4865      <address>
4866        <email>tony+mtsuffix@maillennium.att.com</email>
4867      </address>
4868    </author>
4869    <date year="2013" month="January"/>
4870  </front>
4871  <seriesInfo name="BCP" value="13"/>
4872  <seriesInfo name="RFC" value="6838"/>
4873</reference>
4874
4875<reference anchor='BCP115'>
4876  <front>
4877    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4878    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4879      <organization>AT&amp;T Laboratories</organization>
4880      <address>
4881        <email>tony+urireg@maillennium.att.com</email>
4882      </address>
4883    </author>
4884    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4885      <organization>Qualcomm, Inc.</organization>
4886      <address>
4887        <email>hardie@qualcomm.com</email>
4888      </address>
4889    </author>
4890    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4891      <organization>Adobe Systems</organization>
4892      <address>
4893        <email>LMM@acm.org</email>
4894      </address>
4895    </author>
4896    <date year='2006' month='February' />
4897  </front>
4898  <seriesInfo name='BCP' value='115' />
4899  <seriesInfo name='RFC' value='4395' />
4900</reference>
4901
4902<reference anchor='RFC4559'>
4903  <front>
4904    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4905    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4906    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4907    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4908    <date year='2006' month='June' />
4909  </front>
4910  <seriesInfo name='RFC' value='4559' />
4911</reference>
4912
4913<reference anchor='RFC5226'>
4914  <front>
4915    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4916    <author initials='T.' surname='Narten' fullname='T. Narten'>
4917      <organization>IBM</organization>
4918      <address><email>narten@us.ibm.com</email></address>
4919    </author>
4920    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4921      <organization>Google</organization>
4922      <address><email>Harald@Alvestrand.no</email></address>
4923    </author>
4924    <date year='2008' month='May' />
4925  </front>
4926  <seriesInfo name='BCP' value='26' />
4927  <seriesInfo name='RFC' value='5226' />
4928</reference>
4929
4930<reference anchor='RFC5246'>
4931   <front>
4932      <title>The Transport Layer Security (TLS) Protocol Version 1.2</title>
4933      <author initials='T.' surname='Dierks' fullname='T. Dierks'>
4934         <organization />
4935      </author>
4936      <author initials='E.' surname='Rescorla' fullname='E. Rescorla'>
4937         <organization>RTFM, Inc.</organization>
4938      </author>
4939      <date year='2008' month='August' />
4940   </front>
4941   <seriesInfo name='RFC' value='5246' />
4942</reference>
4943
4944<reference anchor="RFC5322">
4945  <front>
4946    <title>Internet Message Format</title>
4947    <author initials="P." surname="Resnick" fullname="P. Resnick">
4948      <organization>Qualcomm Incorporated</organization>
4949    </author>
4950    <date year="2008" month="October"/>
4951  </front>
4952  <seriesInfo name="RFC" value="5322"/>
4953</reference>
4954
4955<reference anchor="RFC6265">
4956  <front>
4957    <title>HTTP State Management Mechanism</title>
4958    <author initials="A." surname="Barth" fullname="Adam Barth">
4959      <organization abbrev="U.C. Berkeley">
4960        University of California, Berkeley
4961      </organization>
4962      <address><email>abarth@eecs.berkeley.edu</email></address>
4963    </author>
4964    <date year="2011" month="April" />
4965  </front>
4966  <seriesInfo name="RFC" value="6265"/>
4967</reference>
4968
4969<reference anchor='RFC6585'>
4970  <front>
4971    <title>Additional HTTP Status Codes</title>
4972    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4973      <organization>Rackspace</organization>
4974    </author>
4975    <author initials='R.' surname='Fielding' fullname='R. Fielding'>
4976      <organization>Adobe</organization>
4977    </author>
4978    <date year='2012' month='April' />
4979   </front>
4980   <seriesInfo name='RFC' value='6585' />
4981</reference>
4982
4983<!--<reference anchor='BCP97'>
4984  <front>
4985    <title>Handling Normative References to Standards-Track Documents</title>
4986    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4987      <address>
4988        <email>klensin+ietf@jck.com</email>
4989      </address>
4990    </author>
4991    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4992      <organization>MIT</organization>
4993      <address>
4994        <email>hartmans-ietf@mit.edu</email>
4995      </address>
4996    </author>
4997    <date year='2007' month='June' />
4998  </front>
4999  <seriesInfo name='BCP' value='97' />
5000  <seriesInfo name='RFC' value='4897' />
5001</reference>-->
5002
5003<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
5004  <front>
5005    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
5006    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
5007    <date year="2001" month="November"/>
5008  </front>
5009  <seriesInfo name="ACM Transactions on Internet Technology" value="1(2)"/>
5010</reference>
5011
5012</references>
5013
5014
5015<section title="HTTP Version History" anchor="compatibility">
5016<t>
5017   HTTP has been in use by the World-Wide Web global information initiative
5018   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
5019   was a simple protocol for hypertext data transfer across the Internet
5020   with only a single request method (GET) and no metadata.
5021   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
5022   methods and MIME-like messaging that could include metadata about the data
5023   transferred and modifiers on the request/response semantics. However,
5024   HTTP/1.0 did not sufficiently take into consideration the effects of
5025   hierarchical proxies, caching, the need for persistent connections, or
5026   name-based virtual hosts. The proliferation of incompletely-implemented
5027   applications calling themselves "HTTP/1.0" further necessitated a
5028   protocol version change in order for two communicating applications
5029   to determine each other's true capabilities.
5030</t>
5031<t>
5032   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
5033   requirements that enable reliable implementations, adding only
5034   those new features that will either be safely ignored by an HTTP/1.0
5035   recipient or only sent when communicating with a party advertising
5036   conformance with HTTP/1.1.
5037</t>
5038<t>
5039   It is beyond the scope of a protocol specification to mandate
5040   conformance with previous versions. HTTP/1.1 was deliberately
5041   designed, however, to make supporting previous versions easy.
5042   We would expect a general-purpose HTTP/1.1 server to understand
5043   any valid request in the format of HTTP/1.0 and respond appropriately
5044   with an HTTP/1.1 message that only uses features understood (or
5045   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
5046   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
5047</t>
5048<t>
5049   Since HTTP/0.9 did not support header fields in a request,
5050   there is no mechanism for it to support name-based virtual
5051   hosts (selection of resource by inspection of the <x:ref>Host</x:ref> header
5052   field).  Any server that implements name-based virtual hosts
5053   ought to disable support for HTTP/0.9.  Most requests that
5054   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
5055   requests wherein a buggy client failed to properly encode
5056   linear whitespace found in a URI reference and placed in
5057   the request-target.
5058</t>
5059
5060<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
5061<t>
5062   This section summarizes major differences between versions HTTP/1.0
5063   and HTTP/1.1.
5064</t>
5065
5066<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
5067<t>
5068   The requirements that clients and servers support the <x:ref>Host</x:ref>
5069   header field (<xref target="header.host"/>), report an error if it is
5070   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
5071   are among the most important changes defined by HTTP/1.1.
5072</t>
5073<t>
5074   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
5075   addresses and servers; there was no other established mechanism for
5076   distinguishing the intended server of a request than the IP address
5077   to which that request was directed. The <x:ref>Host</x:ref> header field was
5078   introduced during the development of HTTP/1.1 and, though it was
5079   quickly implemented by most HTTP/1.0 browsers, additional requirements
5080   were placed on all HTTP/1.1 requests in order to ensure complete
5081   adoption.  At the time of this writing, most HTTP-based services
5082   are dependent upon the Host header field for targeting requests.
5083</t>
5084</section>
5085
5086<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
5087<t>
5088   In HTTP/1.0, each connection is established by the client prior to the
5089   request and closed by the server after sending the response. However, some
5090   implementations implement the explicitly negotiated ("Keep-Alive") version
5091   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
5092   target="RFC2068"/>.
5093</t>
5094<t>
5095   Some clients and servers might wish to be compatible with these previous
5096   approaches to persistent connections, by explicitly negotiating for them
5097   with a "Connection: keep-alive" request header field. However, some
5098   experimental implementations of HTTP/1.0 persistent connections are faulty;
5099   for example, if an HTTP/1.0 proxy server doesn't understand
5100   <x:ref>Connection</x:ref>, it will erroneously forward that header field
5101   to the next inbound server, which would result in a hung connection.
5102</t>
5103<t>
5104   One attempted solution was the introduction of a Proxy-Connection header
5105   field, targeted specifically at proxies. In practice, this was also
5106   unworkable, because proxies are often deployed in multiple layers, bringing
5107   about the same problem discussed above.
5108</t>
5109<t>
5110   As a result, clients are encouraged not to send the Proxy-Connection header
5111   field in any requests.
5112</t>
5113<t>
5114   Clients are also encouraged to consider the use of Connection: keep-alive
5115   in requests carefully; while they can enable persistent connections with
5116   HTTP/1.0 servers, clients using them will need to monitor the
5117   connection for "hung" requests (which indicate that the client ought stop
5118   sending the header field), and this mechanism ought not be used by clients
5119   at all when a proxy is being used.
5120</t>
5121</section>
5122
5123<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
5124<t>
5125   HTTP/1.1 introduces the <x:ref>Transfer-Encoding</x:ref> header field
5126   (<xref target="header.transfer-encoding"/>).
5127   Transfer codings need to be decoded prior to forwarding an HTTP message
5128   over a MIME-compliant protocol.
5129</t>
5130</section>
5131
5132</section>
5133
5134<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
5135<t>
5136  HTTP's approach to error handling has been explained.
5137  (<xref target="conformance" />)
5138</t>
5139<t>
5140  The HTTP-version ABNF production has been clarified to be case-sensitive.
5141  Additionally, version numbers has been restricted to single digits, due
5142  to the fact that implementations are known to handle multi-digit version
5143  numbers incorrectly.
5144  (<xref target="http.version"/>)
5145</t>
5146<t>
5147  Userinfo (i.e., username and password) are now disallowed in HTTP and
5148  HTTPS URIs, because of security issues related to their transmission on the
5149  wire.
5150  (<xref target="http.uri" />)
5151</t>
5152<t>
5153  The HTTPS URI scheme is now defined by this specification; previously,
5154  it was done in  <xref target="RFC2818" x:fmt="of" x:sec="2.4"/>.
5155  Furthermore, it implies end-to-end security.
5156  (<xref target="https.uri"/>)
5157</t>
5158<t>
5159  HTTP messages can be (and often are) buffered by implementations; despite
5160  it sometimes being available as a stream, HTTP is fundamentally a
5161  message-oriented protocol.
5162  Minimum supported sizes for various protocol elements have been
5163  suggested, to improve interoperability.
5164  (<xref target="http.message" />)
5165</t>
5166<t>
5167  Invalid whitespace around field-names is now required to be rejected,
5168  because accepting it represents a security vulnerability.
5169  The ABNF productions defining header fields now only list the field value.
5170  (<xref target="header.fields"/>)
5171</t>
5172<t>
5173  Rules about implicit linear whitespace between certain grammar productions
5174  have been removed; now whitespace is only allowed where specifically
5175  defined in the ABNF.
5176  (<xref target="whitespace"/>)
5177</t>
5178<t>
5179  Header fields that span multiple lines ("line folding") are deprecated.
5180  (<xref target="field.parsing" />)
5181</t>
5182<t> 
5183  The NUL octet is no longer allowed in comment and quoted-string text, and
5184  handling of backslash-escaping in them has been clarified.
5185  The quoted-pair rule no longer allows escaping control characters other than
5186  HTAB.
5187  Non-ASCII content in header fields and the reason phrase has been obsoleted
5188  and made opaque (the TEXT rule was removed).
5189  (<xref target="field.components"/>)
5190</t> 
5191<t>
5192  Bogus "<x:ref>Content-Length</x:ref>" header fields are now required to be
5193  handled as errors by recipients.
5194  (<xref target="header.content-length"/>)
5195</t>
5196<t>
5197  The algorithm for determining the message body length has been clarified
5198  to indicate all of the special cases (e.g., driven by methods or status
5199  codes) that affect it, and that new protocol elements cannot define such
5200  special cases.
5201  CONNECT is a new, special case in determining message body length.
5202  "multipart/byteranges" is no longer a way of determining message body length
5203  detection.
5204  (<xref target="message.body.length"/>)
5205</t>
5206<t>
5207  The "identity" transfer coding token has been removed.
5208  (Sections <xref format="counter" target="message.body"/> and
5209  <xref format="counter" target="transfer.codings"/>)
5210</t>
5211<t>
5212  Chunk length does not include the count of the octets in the
5213  chunk header and trailer.
5214  Line folding in chunk extensions is  disallowed.
5215  (<xref target="chunked.encoding"/>)
5216</t>
5217<t>
5218  The meaning of the "deflate" content coding has been clarified.
5219  (<xref target="deflate.coding" />)
5220</t>
5221<t>
5222  The segment + query components of RFC 3986 have been used to define the
5223  request-target, instead of abs_path from RFC 1808.
5224  The asterisk-form of the request-target is only allowed with the OPTIONS
5225  method.
5226  (<xref target="request-target"/>)
5227</t>
5228<t>
5229  The term "Effective Request URI" has been introduced.
5230  (<xref target="effective.request.uri" />)
5231</t>
5232<t>
5233  Gateways do not need to generate <x:ref>Via</x:ref> header fields anymore.
5234  (<xref target="header.via"/>)
5235</t>
5236<t>
5237  Exactly when "close" connection options have to be sent has been clarified.
5238  Also, "hop-by-hop" header fields are required to appear in the Connection header
5239  field; just because they're defined as hop-by-hop in this specification
5240  doesn't exempt them.
5241  (<xref target="header.connection"/>)
5242</t>
5243<t>
5244  The limit of two connections per server has been removed.
5245  An idempotent sequence of requests is no longer required to be retried.
5246  The requirement to retry requests under certain circumstances when the
5247  server prematurely closes the connection has been removed.
5248  Also, some extraneous requirements about when servers are allowed to close
5249  connections prematurely have been removed.
5250  (<xref target="persistent.connections"/>)
5251</t>
5252<t>
5253  The semantics of the <x:ref>Upgrade</x:ref> header field is now defined in
5254  responses other than 101 (this was incorporated from <xref
5255  target="RFC2817"/>). Furthermore, the ordering in the field value is now
5256  significant.
5257  (<xref target="header.upgrade"/>)
5258</t>
5259<t>
5260  Empty list elements in list productions (e.g., a list header field containing
5261  ", ,") have been deprecated.
5262  (<xref target="abnf.extension"/>)
5263</t>
5264<t>
5265  Registration of Transfer Codings now requires IETF Review
5266  (<xref target="transfer.coding.registry"/>)
5267</t>
5268<t>
5269  This specification now defines the Upgrade Token Registry, previously
5270  defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
5271  (<xref target="upgrade.token.registry"/>)
5272</t>
5273<t>
5274  The expectation to support HTTP/0.9 requests has been removed.
5275  (<xref target="compatibility"/>)
5276</t>
5277<t>
5278  Issues with the Keep-Alive and Proxy-Connection header fields in requests
5279  are pointed out, with use of the latter being discouraged altogether.
5280  (<xref target="compatibility.with.http.1.0.persistent.connections" />)
5281</t>
5282</section>
5283</section>
5284
5285<?BEGININC p1-messaging.abnf-appendix ?>
5286<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
5287<figure>
5288<artwork type="abnf" name="p1-messaging.parsed-abnf">
5289<x:ref>BWS</x:ref> = OWS
5290
5291<x:ref>Connection</x:ref> = *( "," OWS ) connection-option *( OWS "," [ OWS
5292 connection-option ] )
5293<x:ref>Content-Length</x:ref> = 1*DIGIT
5294
5295<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5296 ]
5297<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
5298<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
5299<x:ref>Host</x:ref> = uri-host [ ":" port ]
5300
5301<x:ref>OWS</x:ref> = *( SP / HTAB )
5302
5303<x:ref>RWS</x:ref> = 1*( SP / HTAB )
5304
5305<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5306<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5307<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5308 transfer-coding ] )
5309
5310<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5311<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
5312
5313<x:ref>Via</x:ref> = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment
5314 ] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS
5315 comment ] ) ] )
5316
5317<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5318<x:ref>absolute-form</x:ref> = absolute-URI
5319<x:ref>absolute-path</x:ref> = 1*( "/" segment )
5320<x:ref>asterisk-form</x:ref> = "*"
5321<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5322<x:ref>authority-form</x:ref> = authority
5323
5324<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5325<x:ref>chunk-data</x:ref> = 1*OCTET
5326<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5327<x:ref>chunk-ext-name</x:ref> = token
5328<x:ref>chunk-ext-val</x:ref> = token / quoted-string
5329<x:ref>chunk-size</x:ref> = 1*HEXDIG
5330<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
5331<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
5332<x:ref>connection-option</x:ref> = token
5333<x:ref>ctext</x:ref> = HTAB / SP / %x21-27 ; '!'-'''
5334 / %x2A-5B ; '*'-'['
5335 / %x5D-7E ; ']'-'~'
5336 / obs-text
5337
5338<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5339<x:ref>field-name</x:ref> = token
5340<x:ref>field-value</x:ref> = *( field-content / obs-fold )
5341<x:ref>fragment</x:ref> = &lt;fragment, defined in [RFC3986], Section 3.5&gt;
5342
5343<x:ref>header-field</x:ref> = field-name ":" OWS field-value OWS
5344<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ] [ "#"
5345 fragment ]
5346<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ] [ "#"
5347 fragment ]
5348
5349<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
5350
5351<x:ref>message-body</x:ref> = *OCTET
5352<x:ref>method</x:ref> = token
5353
5354<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
5355<x:ref>obs-text</x:ref> = %x80-FF
5356<x:ref>origin-form</x:ref> = absolute-path [ "?" query ]
5357
5358<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5359<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5360<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5361<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
5362<x:ref>protocol-name</x:ref> = token
5363<x:ref>protocol-version</x:ref> = token
5364<x:ref>pseudonym</x:ref> = token
5365
5366<x:ref>qdtext</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
5367 / %x5D-7E ; ']'-'~'
5368 / obs-text
5369<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5370<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5371<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5372
5373<x:ref>rank</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5374<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5375<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5376<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5377<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5378<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
5379<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
5380 asterisk-form
5381
5382<x:ref>segment</x:ref> = &lt;segment, defined in [RFC3986], Section 3.3&gt;
5383<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5384 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5385<x:ref>start-line</x:ref> = request-line / status-line
5386<x:ref>status-code</x:ref> = 3DIGIT
5387<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
5388
5389<x:ref>t-codings</x:ref> = "trailers" / ( transfer-coding [ t-ranking ] )
5390<x:ref>t-ranking</x:ref> = OWS ";" OWS "q=" rank
5391<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5392 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5393<x:ref>token</x:ref> = 1*tchar
5394<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5395<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5396 transfer-extension
5397<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5398<x:ref>transfer-parameter</x:ref> = token BWS "=" BWS ( token / quoted-string )
5399
5400<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5401</artwork>
5402</figure>
5403</section>
5404<?ENDINC p1-messaging.abnf-appendix ?>
5405
5406<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5407
5408<section title="Since RFC 2616">
5409<t>
5410  Changes up to the IETF Last Call draft are summarized
5411  in <eref target="http://trac.tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-24#appendix-C"/>.
5412</t>
5413</section>
5414
5415<section title="Since draft-ietf-httpbis-p1-messaging-24" anchor="changes.since.24">
5416<t>
5417  Closed issues:
5418  <list style="symbols">
5419    <t>
5420      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/502"/>:
5421      "APPSDIR review of draft-ietf-httpbis-p1-messaging-24"
5422    </t>
5423    <t>
5424      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/507"/>:
5425      "integer value parsing"
5426    </t>
5427    <t>
5428      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/517"/>:
5429      "move IANA registrations to correct draft"
5430    </t>
5431  </list>
5432</t>
5433</section>
5434
5435<section title="Since draft-ietf-httpbis-p1-messaging-25" anchor="changes.since.25">
5436<t>
5437  Closed issues:
5438  <list style="symbols">
5439    <t>
5440      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/526"/>:
5441      "check media type registration templates"
5442    </t>
5443    <t>
5444      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/528"/>:
5445      "Redundant rule quoted-str-nf"
5446    </t>
5447    <t>
5448      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/540"/>:
5449      "clarify ABNF layering"
5450    </t>
5451    <t>
5452      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/541"/>:
5453      "use of 'word' ABNF production"
5454    </t>
5455    <t>
5456      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/542"/>:
5457      "improve introduction of list rule"
5458    </t>
5459    <t>
5460      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/544"/>:
5461      "moving 2616/2068/2145 to historic"
5462    </t>
5463  </list>
5464</t>
5465</section>
5466</section>
5467
5468</back>
5469</rfc>
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