source: draft-ietf-httpbis/latest/p1-messaging.xml @ 2545

Last change on this file since 2545 was 2545, checked in by julian.reschke@…, 6 years ago

update acks (#219)

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
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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 a list extension, defined in
239   <xref target="abnf.extension"/>, that allows for compact definition of
240   comma-separated lists using a '#' operator (similar to how the '*' operator
241   indicates repetition).
242   <xref target="collected.abnf"/> shows the collected grammar with all list
243   operators 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="of" 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 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
1238<section title="Field Extensibility" anchor="field.extensibility">
1239<t>
1240   Header fields are fully extensible: there is no limit on the
1241   introduction of new field names, each presumably defining new semantics,
1242   nor on the number of header fields used in a given message.  Existing
1243   fields are defined in each part of this specification and in many other
1244   specifications outside the core standard.
1245</t>
1246<t>
1247   New header fields can be defined such that, when they are understood by a
1248   recipient, they might override or enhance the interpretation of previously
1249   defined header fields, define preconditions on request evaluation, or
1250   refine the meaning of responses.
1251</t>
1252<t>
1253   A proxy &MUST; forward unrecognized header fields unless the
1254   field-name is listed in the <x:ref>Connection</x:ref> header field
1255   (<xref target="header.connection"/>) or the proxy is specifically
1256   configured to block, or otherwise transform, such fields.
1257   Other recipients &SHOULD; ignore unrecognized header fields.
1258   These requirements allow HTTP's functionality to be enhanced without
1259   requiring prior update of deployed intermediaries.
1260</t>
1261<t>
1262   All defined header fields ought to be registered with IANA in the
1263   Message Header Field Registry, as described in &iana-header-registry;.
1264</t>
1265</section>
1266
1267<section title="Field Order" anchor="field.order">
1268<t>
1269   The order in which header fields with differing field names are
1270   received is not significant. However, it is "good practice" to send
1271   header fields that contain control data first, such as <x:ref>Host</x:ref>
1272   on requests and <x:ref>Date</x:ref> on responses, so that implementations
1273   can decide when not to handle a message as early as possible.  A server
1274   &MUST; wait until the entire header section is received before interpreting
1275   a request message, since later header fields might include conditionals,
1276   authentication credentials, or deliberately misleading duplicate
1277   header fields that would impact request processing.
1278</t>
1279<t>
1280   A sender &MUST-NOT; generate multiple header fields with the same field
1281   name in a message unless either the entire field value for that
1282   header field is defined as a comma-separated list [i.e., #(values)]
1283   or the header field is a well-known exception (as noted below).
1284</t>
1285<t>
1286   A recipient &MAY; combine multiple header fields with the same field name
1287   into one "field-name: field-value" pair, without changing the semantics of
1288   the message, by appending each subsequent field value to the combined
1289   field value in order, separated by a comma. The order in which
1290   header fields with the same field name are received is therefore
1291   significant to the interpretation of the combined field value;
1292   a proxy &MUST-NOT; change the order of these field values when
1293   forwarding a message.
1294</t>
1295<x:note>
1296  <t>
1297   &Note; In practice, the "Set-Cookie" header field (<xref target="RFC6265"/>)
1298   often appears multiple times in a response message and does not use the
1299   list syntax, violating the above requirements on multiple header fields
1300   with the same name. Since it cannot be combined into a single field-value,
1301   recipients ought to handle "Set-Cookie" as a special case while processing
1302   header fields. (See Appendix A.2.3 of <xref target="Kri2001"/> for details.)
1303  </t>
1304</x:note>
1305</section>
1306
1307<section title="Whitespace" anchor="whitespace">
1308<t anchor="rule.LWS">
1309   This specification uses three rules to denote the use of linear
1310   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1311   BWS ("bad" whitespace).
1312</t>
1313<t anchor="rule.OWS">
1314   The OWS rule is used where zero or more linear whitespace octets might
1315   appear. For protocol elements where optional whitespace is preferred to
1316   improve readability, a sender &SHOULD; generate the optional whitespace
1317   as a single SP; otherwise, a sender &SHOULD-NOT; generate optional
1318   whitespace except as needed to white-out invalid or unwanted protocol
1319   elements during in-place message filtering.
1320</t>
1321<t anchor="rule.RWS">
1322   The RWS rule is used when at least one linear whitespace octet is required
1323   to separate field tokens. A sender &SHOULD; generate RWS as a single SP.
1324</t>
1325<t anchor="rule.BWS">
1326   The BWS rule is used where the grammar allows optional whitespace only for
1327   historical reasons. A sender &MUST-NOT; generate BWS in messages.
1328   A recipient &MUST; parse for such bad whitespace and remove it before
1329   interpreting the protocol element.
1330</t>
1331<t anchor="rule.whitespace">
1332  <x:anchor-alias value="BWS"/>
1333  <x:anchor-alias value="OWS"/>
1334  <x:anchor-alias value="RWS"/>
1335</t>
1336<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"/>
1337  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1338                 ; optional whitespace
1339  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1340                 ; required whitespace
1341  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1342                 ; "bad" whitespace
1343</artwork></figure>
1344</section>
1345
1346<section title="Field Parsing" anchor="field.parsing">
1347<t>
1348   Messages are parsed using a generic algorithm, independent of the
1349   individual header field names. The contents within a given field value are
1350   not parsed until a later stage of message interpretation (usually after the
1351   message's entire header section has been processed).
1352   Consequently, this specification does not use ABNF rules to define each
1353   "Field-Name: Field Value" pair, as was done in previous editions.
1354   Instead, this specification uses ABNF rules which are named according to
1355   each registered field name, wherein the rule defines the valid grammar for
1356   that field's corresponding field values (i.e., after the field-value
1357   has been extracted from the header section by a generic field parser).
1358</t>
1359<t>
1360   No whitespace is allowed between the header field-name and colon.
1361   In the past, differences in the handling of such whitespace have led to
1362   security vulnerabilities in request routing and response handling.
1363   A server &MUST; reject any received request message that contains
1364   whitespace between a header field-name and colon with a response code of
1365   <x:ref>400 (Bad Request)</x:ref>. A proxy &MUST; remove any such whitespace
1366   from a response message before forwarding the message downstream.
1367</t>
1368<t>
1369   A field value is preceded by optional whitespace (OWS); a single SP is
1370   preferred. The field value does not include any leading or trailing white
1371   space: OWS occurring before the first non-whitespace octet of the field
1372   value or after the last non-whitespace octet of the field value ought to be
1373   excluded by parsers when extracting the field value from a header field.
1374</t>
1375<t>
1376   A recipient of field-content containing multiple sequential octets of
1377   optional (OWS) or required (RWS) whitespace &SHOULD; either replace the
1378   sequence with a single SP or transform any non-SP octets in the sequence to
1379   SP octets before interpreting the field value or forwarding the message
1380   downstream.
1381</t>
1382<t>
1383   Historically, HTTP header field values could be extended over multiple
1384   lines by preceding each extra line with at least one space or horizontal
1385   tab (obs-fold). This specification deprecates such line folding except
1386   within the message/http media type
1387   (<xref target="internet.media.type.message.http"/>).
1388   A sender &MUST-NOT; generate a message that includes line folding
1389   (i.e., that has any field-value that contains a match to the
1390   <x:ref>obs-fold</x:ref> rule) unless the message is intended for packaging
1391   within the message/http media type.
1392</t>
1393<t>
1394   A server that receives an <x:ref>obs-fold</x:ref> in a request message that
1395   is not within a message/http container &MUST; either reject the message by
1396   sending a <x:ref>400 (Bad Request)</x:ref>, preferably with a
1397   representation explaining that obsolete line folding is unacceptable, or
1398   replace each received <x:ref>obs-fold</x:ref> with one or more
1399   <x:ref>SP</x:ref> octets prior to interpreting the field value or
1400   forwarding the message downstream.
1401</t>
1402<t>
1403   A proxy or gateway that receives an <x:ref>obs-fold</x:ref> in a response
1404   message that is not within a message/http container &MUST; either discard
1405   the message and replace it with a <x:ref>502 (Bad Gateway)</x:ref>
1406   response, preferably with a representation explaining that unacceptable
1407   line folding was received, or replace each received <x:ref>obs-fold</x:ref>
1408   with one or more <x:ref>SP</x:ref> octets prior to interpreting the field
1409   value or forwarding the message downstream.
1410</t>
1411<t>
1412   A user agent that receives an <x:ref>obs-fold</x:ref> in a response message
1413   that is not within a message/http container &MUST; replace each received
1414   <x:ref>obs-fold</x:ref> with one or more <x:ref>SP</x:ref> octets prior to
1415   interpreting the field value.
1416</t>
1417<t>
1418   Historically, HTTP has allowed field content with text in the ISO-8859-1
1419   <xref target="ISO-8859-1"/> charset, supporting other charsets only
1420   through use of <xref target="RFC2047"/> encoding.
1421   In practice, most HTTP header field values use only a subset of the
1422   US-ASCII charset <xref target="USASCII"/>. Newly defined
1423   header fields &SHOULD; limit their field values to US-ASCII octets.
1424   A recipient &SHOULD; treat other octets in field content (obs-text) as
1425   opaque data.
1426</t>
1427</section>
1428
1429<section title="Field Limits" anchor="field.limits">
1430<t>
1431   HTTP does not place a pre-defined limit on the length of each header field
1432   or on the length of the header section as a whole, as described in
1433   <xref target="conformance"/>. Various ad-hoc limitations on individual
1434   header field length are found in practice, often depending on the specific
1435   field semantics.
1436</t>
1437<t>
1438   A server ought to be prepared to receive request header fields of unbounded
1439   length and &MUST; respond with an appropriate
1440   <x:ref>4xx (Client Error)</x:ref> status code if the received header
1441   field(s) are larger than the server wishes to process.
1442</t>
1443<t>
1444   A client ought to be prepared to receive response header fields of
1445   unbounded length.
1446   A client &MAY; discard or truncate received header fields that are larger
1447   than the client wishes to process if the field semantics are such that the
1448   dropped value(s) can be safely ignored without changing the
1449   message framing or response semantics.
1450</t>
1451</section>
1452
1453<section title="Field value components" anchor="field.components">
1454<t anchor="rule.token.separators">
1455  <x:anchor-alias value="tchar"/>
1456  <x:anchor-alias value="token"/>
1457  <iref item="Delimiters"/>
1458   Most HTTP header field values are defined using common syntax components
1459   (token, quoted-string, and comment) separated by whitespace or specific
1460   delimiting characters. Delimiters are chosen from the set of US-ASCII
1461   visual characters not allowed in a <x:ref>token</x:ref>
1462   (DQUOTE and "(),/:;&lt;=>?@[\]{}").
1463</t>
1464<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/>
1465  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1466<!--
1467  NOTE: the definition of tchar and the prose above about special characters need to match!
1468 -->
1469  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1470                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1471                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1472                 ; any <x:ref>VCHAR</x:ref>, except delimiters
1473</artwork></figure>
1474<t anchor="rule.quoted-string">
1475  <x:anchor-alias value="quoted-string"/>
1476  <x:anchor-alias value="qdtext"/>
1477  <x:anchor-alias value="obs-text"/>
1478   A string of text is parsed as a single value if it is quoted using
1479   double-quote marks.
1480</t>
1481<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"/>
1482  <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>
1483  <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>
1484  <x:ref>obs-text</x:ref>       = %x80-FF
1485</artwork></figure>
1486<t anchor="rule.comment">
1487  <x:anchor-alias value="comment"/>
1488  <x:anchor-alias value="ctext"/>
1489   Comments can be included in some HTTP header fields by surrounding
1490   the comment text with parentheses. Comments are only allowed in
1491   fields containing "comment" as part of their field value definition.
1492</t>
1493<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1494  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1495  <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>
1496</artwork></figure>
1497<t anchor="rule.quoted-pair">
1498  <x:anchor-alias value="quoted-pair"/>
1499   The backslash octet ("\") can be used as a single-octet
1500   quoting mechanism within quoted-string and comment constructs.
1501   Recipients that process the value of a quoted-string &MUST; handle a
1502   quoted-pair as if it were replaced by the octet following the backslash.
1503</t>
1504<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1505  <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> )
1506</artwork></figure>
1507<t>
1508   A sender &SHOULD-NOT; generate a quoted-pair in a quoted-string except
1509   where necessary to quote DQUOTE and backslash octets occurring within that
1510   string.
1511   A sender &SHOULD-NOT; generate a quoted-pair in a comment except
1512   where necessary to quote parentheses ["(" and ")"] and backslash octets
1513   occurring within that comment.
1514</t>
1515</section>
1516
1517</section>
1518
1519<section title="Message Body" anchor="message.body">
1520  <x:anchor-alias value="message-body"/>
1521<t>
1522   The message body (if any) of an HTTP message is used to carry the
1523   payload body of that request or response.  The message body is
1524   identical to the payload body unless a transfer coding has been
1525   applied, as described in <xref target="header.transfer-encoding"/>.
1526</t>
1527<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1528  <x:ref>message-body</x:ref> = *OCTET
1529</artwork></figure>
1530<t>
1531   The rules for when a message body is allowed in a message differ for
1532   requests and responses.
1533</t>
1534<t>
1535   The presence of a message body in a request is signaled by a
1536   <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1537   field. Request message framing is independent of method semantics,
1538   even if the method does not define any use for a message body.
1539</t>
1540<t>
1541   The presence of a message body in a response depends on both
1542   the request method to which it is responding and the response
1543   status code (<xref target="status.line"/>).
1544   Responses to the HEAD request method never include a message body
1545   because the associated response header fields (e.g.,
1546   <x:ref>Transfer-Encoding</x:ref>, <x:ref>Content-Length</x:ref>, etc.),
1547   if present, indicate only what their values would have been if the request
1548   method had been GET (&HEAD;).
1549   <x:ref>2xx (Successful)</x:ref> responses to CONNECT switch to tunnel
1550   mode instead of having a message body (&CONNECT;).
1551   All <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, and
1552   <x:ref>304 (Not Modified)</x:ref> responses do not include a message body.
1553   All other responses do include a message body, although the body
1554   might be of zero length.
1555</t>
1556
1557<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1558  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1559  <iref item="chunked (Coding Format)"/>
1560  <x:anchor-alias value="Transfer-Encoding"/>
1561<t>
1562   The Transfer-Encoding header field lists the transfer coding names
1563   corresponding to the sequence of transfer codings that have been
1564   (or will be) applied to the payload body in order to form the message body.
1565   Transfer codings are defined in <xref target="transfer.codings"/>.
1566</t>
1567<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1568  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1569</artwork></figure>
1570<t>
1571   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1572   MIME, which was designed to enable safe transport of binary data over a
1573   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1574   However, safe transport has a different focus for an 8bit-clean transfer
1575   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1576   accurately delimit a dynamically generated payload and to distinguish
1577   payload encodings that are only applied for transport efficiency or
1578   security from those that are characteristics of the selected resource.
1579</t>
1580<t>
1581   A recipient &MUST; be able to parse the chunked transfer coding
1582   (<xref target="chunked.encoding"/>) because it plays a crucial role in
1583   framing messages when the payload body size is not known in advance.
1584   A sender &MUST-NOT; apply chunked more than once to a message body
1585   (i.e., chunking an already chunked message is not allowed).
1586   If any transfer coding other than chunked is applied to a request payload
1587   body, the sender &MUST; apply chunked as the final transfer coding to
1588   ensure that the message is properly framed.
1589   If any transfer coding other than chunked is applied to a response payload
1590   body, the sender &MUST; either apply chunked as the final transfer coding
1591   or terminate the message by closing the connection.
1592</t>
1593<figure><preamble>
1594   For example,
1595</preamble><artwork type="example">
1596  Transfer-Encoding: gzip, chunked
1597</artwork><postamble>
1598   indicates that the payload body has been compressed using the gzip
1599   coding and then chunked using the chunked coding while forming the
1600   message body.
1601</postamble></figure>
1602<t>
1603   Unlike <x:ref>Content-Encoding</x:ref> (&content-codings;),
1604   Transfer-Encoding is a property of the message, not of the representation, and
1605   any recipient along the request/response chain &MAY; decode the received
1606   transfer coding(s) or apply additional transfer coding(s) to the message
1607   body, assuming that corresponding changes are made to the Transfer-Encoding
1608   field-value. Additional information about the encoding parameters &MAY; be
1609   provided by other header fields not defined by this specification.
1610</t>
1611<t>
1612   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1613   <x:ref>304 (Not Modified)</x:ref> response (&status-304;) to a GET request,
1614   neither of which includes a message body,
1615   to indicate that the origin server would have applied a transfer coding
1616   to the message body if the request had been an unconditional GET.
1617   This indication is not required, however, because any recipient on
1618   the response chain (including the origin server) can remove transfer
1619   codings when they are not needed.
1620</t>
1621<t>
1622   A server &MUST-NOT; send a Transfer-Encoding header field in any response
1623   with a status code of
1624   <x:ref>1xx (Informational)</x:ref> or <x:ref>204 (No Content)</x:ref>.
1625   A server &MUST-NOT; send a Transfer-Encoding header field in any
1626   <x:ref>2xx (Successful)</x:ref> response to a CONNECT request (&CONNECT;).
1627</t>
1628<t>
1629   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1630   implementations advertising only HTTP/1.0 support will not understand
1631   how to process a transfer-encoded payload.
1632   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1633   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1634   might be in the form of specific user configuration or by remembering the
1635   version of a prior received response.
1636   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1637   the corresponding request indicates HTTP/1.1 (or later).
1638</t>
1639<t>
1640   A server that receives a request message with a transfer coding it does
1641   not understand &SHOULD; respond with <x:ref>501 (Not Implemented)</x:ref>.
1642</t>
1643</section>
1644
1645<section title="Content-Length" anchor="header.content-length">
1646  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1647  <x:anchor-alias value="Content-Length"/>
1648<t>
1649   When a message does not have a <x:ref>Transfer-Encoding</x:ref> header
1650   field, a Content-Length header field can provide the anticipated size,
1651   as a decimal number of octets, for a potential payload body.
1652   For messages that do include a payload body, the Content-Length field-value
1653   provides the framing information necessary for determining where the body
1654   (and message) ends.  For messages that do not include a payload body, the
1655   Content-Length indicates the size of the selected representation
1656   (&representation;).
1657</t>
1658<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1659  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1660</artwork></figure>
1661<t>
1662   An example is
1663</t>
1664<figure><artwork type="example">
1665  Content-Length: 3495
1666</artwork></figure>
1667<t>
1668   A sender &MUST-NOT; send a Content-Length header field in any message that
1669   contains a <x:ref>Transfer-Encoding</x:ref> header field.
1670</t>
1671<t>
1672   A user agent &SHOULD; send a Content-Length in a request message when no
1673   <x:ref>Transfer-Encoding</x:ref> is sent and the request method defines
1674   a meaning for an enclosed payload body. For example, a Content-Length
1675   header field is normally sent in a POST request even when the value is
1676   0 (indicating an empty payload body).  A user agent &SHOULD-NOT; send a
1677   Content-Length header field when the request message does not contain a
1678   payload body and the method semantics do not anticipate such a body.
1679</t>
1680<t>
1681   A server &MAY; send a Content-Length header field in a response to a HEAD
1682   request (&HEAD;); a server &MUST-NOT; send Content-Length in such a
1683   response unless its field-value equals the decimal number of octets that
1684   would have been sent in the payload body of a response if the same
1685   request had used the GET method.
1686</t>
1687<t>
1688   A server &MAY; send a Content-Length header field in a
1689   <x:ref>304 (Not Modified)</x:ref> response to a conditional GET request
1690   (&status-304;); a server &MUST-NOT; send Content-Length in such a
1691   response unless its field-value equals the decimal number of octets that
1692   would have been sent in the payload body of a <x:ref>200 (OK)</x:ref>
1693   response to the same request.
1694</t>
1695<t>
1696   A server &MUST-NOT; send a Content-Length header field in any response
1697   with a status code of
1698   <x:ref>1xx (Informational)</x:ref> or <x:ref>204 (No Content)</x:ref>.
1699   A server &MUST-NOT; send a Content-Length header field in any
1700   <x:ref>2xx (Successful)</x:ref> response to a CONNECT request (&CONNECT;).
1701</t>
1702<t>
1703   Aside from the cases defined above, in the absence of Transfer-Encoding,
1704   an origin server &SHOULD; send a Content-Length header field when the
1705   payload body size is known prior to sending the complete header section.
1706   This will allow downstream recipients to measure transfer progress,
1707   know when a received message is complete, and potentially reuse the
1708   connection for additional requests.
1709</t>
1710<t>
1711   Any Content-Length field value greater than or equal to zero is valid.
1712   Since there is no predefined limit to the length of a payload, a
1713   recipient &MUST; anticipate potentially large decimal numerals and
1714   prevent parsing errors due to integer conversion overflows
1715   (<xref target="attack.protocol.element.size.overflows"/>).
1716</t>
1717<t>
1718   If a message is received that has multiple Content-Length header fields
1719   with field-values consisting of the same decimal value, or a single
1720   Content-Length header field with a field value containing a list of
1721   identical decimal values (e.g., "Content-Length: 42, 42"), indicating that
1722   duplicate Content-Length header fields have been generated or combined by an
1723   upstream message processor, then the recipient &MUST; either reject the
1724   message as invalid or replace the duplicated field-values with a single
1725   valid Content-Length field containing that decimal value prior to
1726   determining the message body length or forwarding the message.
1727</t>
1728<x:note>
1729  <t>
1730   &Note; HTTP's use of Content-Length for message framing differs
1731   significantly from the same field's use in MIME, where it is an optional
1732   field used only within the "message/external-body" media-type.
1733  </t>
1734</x:note>
1735</section>
1736
1737<section title="Message Body Length" anchor="message.body.length">
1738  <iref item="chunked (Coding Format)"/>
1739<t>
1740   The length of a message body is determined by one of the following
1741   (in order of precedence):
1742</t>
1743<t>
1744  <list style="numbers">
1745    <x:lt><t>
1746     Any response to a HEAD request and any response with a
1747     <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, or
1748     <x:ref>304 (Not Modified)</x:ref> status code is always
1749     terminated by the first empty line after the header fields, regardless of
1750     the header fields present in the message, and thus cannot contain a
1751     message body.
1752    </t></x:lt>
1753    <x:lt><t>
1754     Any <x:ref>2xx (Successful)</x:ref> response to a CONNECT request implies that the
1755     connection will become a tunnel immediately after the empty line that
1756     concludes the header fields.  A client &MUST; ignore any
1757     <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1758     fields received in such a message.
1759    </t></x:lt>
1760    <x:lt><t>
1761     If a <x:ref>Transfer-Encoding</x:ref> header field is present
1762     and the chunked transfer coding (<xref target="chunked.encoding"/>)
1763     is the final encoding, the message body length is determined by reading
1764     and decoding the chunked data until the transfer coding indicates the
1765     data is complete.
1766    </t>
1767    <t>
1768     If a <x:ref>Transfer-Encoding</x:ref> header field is present in a
1769     response and the chunked transfer coding is not the final encoding, the
1770     message body length is determined by reading the connection until it is
1771     closed by the server.
1772     If a <x:ref>Transfer-Encoding</x:ref> header field is present in a request and the
1773     chunked transfer coding is not the final encoding, the message body
1774     length cannot be determined reliably; the server &MUST; respond with
1775     the <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1776    </t>
1777    <t>
1778     If a message is received with both a <x:ref>Transfer-Encoding</x:ref>
1779     and a <x:ref>Content-Length</x:ref> header field, the Transfer-Encoding
1780     overrides the Content-Length. Such a message might indicate an attempt
1781     to perform request or response smuggling (bypass of security-related
1782     checks on message routing or content) and thus ought to be handled as
1783     an error.  A sender &MUST; remove the received Content-Length field
1784     prior to forwarding such a message downstream.
1785    </t></x:lt>
1786    <x:lt><t>
1787     If a message is received without <x:ref>Transfer-Encoding</x:ref> and with
1788     either multiple <x:ref>Content-Length</x:ref> header fields having
1789     differing field-values or a single Content-Length header field having an
1790     invalid value, then the message framing is invalid and
1791     the recipient &MUST; treat it as an unrecoverable error to prevent
1792     request or response smuggling.
1793     If this is a request message, the server &MUST; respond with
1794     a <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1795     If this is a response message received by a proxy,
1796     the proxy &MUST; close the connection to the server, discard the received
1797     response, and send a <x:ref>502 (Bad Gateway)</x:ref> response to the
1798     client.
1799     If this is a response message received by a user agent,
1800     the user agent &MUST; close the connection to the server and discard the
1801     received response.
1802    </t></x:lt>
1803    <x:lt><t>
1804     If a valid <x:ref>Content-Length</x:ref> header field is present without
1805     <x:ref>Transfer-Encoding</x:ref>, its decimal value defines the
1806     expected message body length in octets.
1807     If the sender closes the connection or the recipient times out before the
1808     indicated number of octets are received, the recipient &MUST; consider
1809     the message to be incomplete and close the connection.
1810    </t></x:lt>
1811    <x:lt><t>
1812     If this is a request message and none of the above are true, then the
1813     message body length is zero (no message body is present).
1814    </t></x:lt>
1815    <x:lt><t>
1816     Otherwise, this is a response message without a declared message body
1817     length, so the message body length is determined by the number of octets
1818     received prior to the server closing the connection.
1819    </t></x:lt>
1820  </list>
1821</t>
1822<t>
1823   Since there is no way to distinguish a successfully completed,
1824   close-delimited message from a partially-received message interrupted
1825   by network failure, a server &SHOULD; generate encoding or
1826   length-delimited messages whenever possible.  The close-delimiting
1827   feature exists primarily for backwards compatibility with HTTP/1.0.
1828</t>
1829<t>
1830   A server &MAY; reject a request that contains a message body but
1831   not a <x:ref>Content-Length</x:ref> by responding with
1832   <x:ref>411 (Length Required)</x:ref>.
1833</t>
1834<t>
1835   Unless a transfer coding other than chunked has been applied,
1836   a client that sends a request containing a message body &SHOULD;
1837   use a valid <x:ref>Content-Length</x:ref> header field if the message body
1838   length is known in advance, rather than the chunked transfer coding, since some
1839   existing services respond to chunked with a <x:ref>411 (Length Required)</x:ref>
1840   status code even though they understand the chunked transfer coding.  This
1841   is typically because such services are implemented via a gateway that
1842   requires a content-length in advance of being called and the server
1843   is unable or unwilling to buffer the entire request before processing.
1844</t>
1845<t>
1846   A user agent that sends a request containing a message body &MUST; send a
1847   valid <x:ref>Content-Length</x:ref> header field if it does not know the
1848   server will handle HTTP/1.1 (or later) requests; such knowledge can be in
1849   the form of specific user configuration or by remembering the version of a
1850   prior received response.
1851</t>
1852<t>
1853   If the final response to the last request on a connection has been
1854   completely received and there remains additional data to read, a user agent
1855   &MAY; discard the remaining data or attempt to determine if that data
1856   belongs as part of the prior response body, which might be the case if the
1857   prior message's Content-Length value is incorrect. A client &MUST-NOT;
1858   process, cache, or forward such extra data as a separate response, since
1859   such behavior would be vulnerable to cache poisoning.
1860</t>
1861</section>
1862</section>
1863
1864<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1865<t>
1866   A server that receives an incomplete request message, usually due to a
1867   canceled request or a triggered time-out exception, &MAY; send an error
1868   response prior to closing the connection.
1869</t>
1870<t>
1871   A client that receives an incomplete response message, which can occur
1872   when a connection is closed prematurely or when decoding a supposedly
1873   chunked transfer coding fails, &MUST; record the message as incomplete.
1874   Cache requirements for incomplete responses are defined in
1875   &cache-incomplete;.
1876</t>
1877<t>
1878   If a response terminates in the middle of the header section (before the
1879   empty line is received) and the status code might rely on header fields to
1880   convey the full meaning of the response, then the client cannot assume
1881   that meaning has been conveyed; the client might need to repeat the
1882   request in order to determine what action to take next.
1883</t>
1884<t>
1885   A message body that uses the chunked transfer coding is
1886   incomplete if the zero-sized chunk that terminates the encoding has not
1887   been received.  A message that uses a valid <x:ref>Content-Length</x:ref> is
1888   incomplete if the size of the message body received (in octets) is less than
1889   the value given by Content-Length.  A response that has neither chunked
1890   transfer coding nor Content-Length is terminated by closure of the
1891   connection, and thus is considered complete regardless of the number of
1892   message body octets received, provided that the header section was received
1893   intact.
1894</t>
1895</section>
1896
1897<section title="Message Parsing Robustness" anchor="message.robustness">
1898<t>
1899   Older HTTP/1.0 user agent implementations might send an extra CRLF
1900   after a POST request as a workaround for some early server
1901   applications that failed to read message body content that was
1902   not terminated by a line-ending. An HTTP/1.1 user agent &MUST-NOT;
1903   preface or follow a request with an extra CRLF.  If terminating
1904   the request message body with a line-ending is desired, then the
1905   user agent &MUST; count the terminating CRLF octets as part of the
1906   message body length.
1907</t>
1908<t>
1909   In the interest of robustness, a server that is expecting to receive and
1910   parse a request-line &SHOULD; ignore at least one empty line (CRLF)
1911   received prior to the request-line.
1912</t>
1913<t>
1914   Although the line terminator for the start-line and header
1915   fields is the sequence CRLF, a recipient &MAY; recognize a
1916   single LF as a line terminator and ignore any preceding CR.
1917</t>
1918<t>
1919   Although the request-line and status-line grammar rules require that each
1920   of the component elements be separated by a single SP octet, recipients
1921   &MAY; instead parse on whitespace-delimited word boundaries and, aside
1922   from the CRLF terminator, treat any form of whitespace as the SP separator
1923   while ignoring preceding or trailing whitespace;
1924   such whitespace includes one or more of the following octets:
1925   SP, HTAB, VT (%x0B), FF (%x0C), or bare CR.
1926</t>
1927<t>
1928   When a server listening only for HTTP request messages, or processing
1929   what appears from the start-line to be an HTTP request message,
1930   receives a sequence of octets that does not match the HTTP-message
1931   grammar aside from the robustness exceptions listed above, the
1932   server &SHOULD; respond with a <x:ref>400 (Bad Request)</x:ref> response. 
1933</t>
1934</section>
1935</section>
1936
1937<section title="Transfer Codings" anchor="transfer.codings">
1938  <x:anchor-alias value="transfer-coding"/>
1939  <x:anchor-alias value="transfer-extension"/>
1940<t>
1941   Transfer coding names are used to indicate an encoding
1942   transformation that has been, can be, or might need to be applied to a
1943   payload body in order to ensure "safe transport" through the network.
1944   This differs from a content coding in that the transfer coding is a
1945   property of the message rather than a property of the representation
1946   that is being transferred.
1947</t>
1948<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1949  <x:ref>transfer-coding</x:ref>    = "chunked" ; <xref target="chunked.encoding"/>
1950                     / "compress" ; <xref target="compress.coding"/>
1951                     / "deflate" ; <xref target="deflate.coding"/>
1952                     / "gzip" ; <xref target="gzip.coding"/>
1953                     / <x:ref>transfer-extension</x:ref>
1954  <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> )
1955</artwork></figure>
1956<t anchor="rule.parameter">
1957  <x:anchor-alias value="transfer-parameter"/>
1958   Parameters are in the form of a name or name=value pair.
1959</t>
1960<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-parameter"/>
1961  <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> )
1962</artwork></figure>
1963<t>
1964   All transfer-coding names are case-insensitive and ought to be registered
1965   within the HTTP Transfer Coding registry, as defined in
1966   <xref target="transfer.coding.registry"/>.
1967   They are used in the <x:ref>TE</x:ref> (<xref target="header.te"/>) and
1968   <x:ref>Transfer-Encoding</x:ref> (<xref target="header.transfer-encoding"/>)
1969   header fields.
1970</t>
1971
1972<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1973  <iref primary="true" item="chunked (Coding Format)"/>
1974  <x:anchor-alias value="chunk"/>
1975  <x:anchor-alias value="chunked-body"/>
1976  <x:anchor-alias value="chunk-data"/>
1977  <x:anchor-alias value="chunk-size"/>
1978  <x:anchor-alias value="last-chunk"/>
1979<t>
1980   The chunked transfer coding wraps the payload body in order to transfer it
1981   as a series of chunks, each with its own size indicator, followed by an
1982   &OPTIONAL; trailer containing header fields. Chunked enables content
1983   streams of unknown size to be transferred as a sequence of length-delimited
1984   buffers, which enables the sender to retain connection persistence and the
1985   recipient to know when it has received the entire message.
1986</t>
1987<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"/>
1988  <x:ref>chunked-body</x:ref>   = *<x:ref>chunk</x:ref>
1989                   <x:ref>last-chunk</x:ref>
1990                   <x:ref>trailer-part</x:ref>
1991                   <x:ref>CRLF</x:ref>
1992 
1993  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1994                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1995  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1996  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1997 
1998  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1999</artwork></figure>
2000<t>
2001   The chunk-size field is a string of hex digits indicating the size of
2002   the chunk-data in octets. The chunked transfer coding is complete when a
2003   chunk with a chunk-size of zero is received, possibly followed by a
2004   trailer, and finally terminated by an empty line.
2005</t>
2006<t>
2007   A recipient &MUST; be able to parse and decode the chunked transfer coding.
2008</t>
2009
2010<section title="Chunk Extensions" anchor="chunked.extension">
2011  <x:anchor-alias value="chunk-ext"/>
2012  <x:anchor-alias value="chunk-ext-name"/>
2013  <x:anchor-alias value="chunk-ext-val"/>
2014<t>
2015   The chunked encoding allows each chunk to include zero or more chunk
2016   extensions, immediately following the <x:ref>chunk-size</x:ref>, for the
2017   sake of supplying per-chunk metadata (such as a signature or hash),
2018   mid-message control information, or randomization of message body size.
2019</t>
2020<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"/>
2021  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
2022
2023  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2024  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
2025</artwork></figure>
2026<t>
2027   The chunked encoding is specific to each connection and is likely to be
2028   removed or recoded by each recipient (including intermediaries) before any
2029   higher-level application would have a chance to inspect the extensions.
2030   Hence, use of chunk extensions is generally limited to specialized HTTP
2031   services such as "long polling" (where client and server can have shared
2032   expectations regarding the use of chunk extensions) or for padding within
2033   an end-to-end secured connection.
2034</t>
2035<t>
2036   A recipient &MUST; ignore unrecognized chunk extensions.
2037   A server ought to limit the total length of chunk extensions received in a
2038   request to an amount reasonable for the services provided, in the same way
2039   that it applies length limitations and timeouts for other parts of a
2040   message, and generate an appropriate <x:ref>4xx (Client Error)</x:ref>
2041   response if that amount is exceeded.
2042</t>
2043</section>
2044
2045<section title="Chunked Trailer Part" anchor="chunked.trailer.part">
2046  <x:anchor-alias value="trailer-part"/>
2047<t>
2048   A trailer allows the sender to include additional fields at the end of a
2049   chunked message in order to supply metadata that might be dynamically
2050   generated while the message body is sent, such as a message integrity
2051   check, digital signature, or post-processing status. The trailer fields are
2052   identical to header fields, except they are sent in a chunked trailer
2053   instead of the message's header section.
2054</t>
2055<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="trailer-part"/>
2056  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2057</artwork></figure>
2058<t>
2059   A sender &MUST-NOT; generate a trailer that contains a field which needs to
2060   be known by the recipient before it can begin processing the message body.
2061   For example, most recipients need to know the values of
2062   <x:ref>Content-Encoding</x:ref> and <x:ref>Content-Type</x:ref> in order to
2063   select a content handler, so placing those fields in a trailer would force
2064   the recipient to buffer the entire body before it could begin, greatly
2065   increasing user-perceived latency and defeating one of the main advantages
2066   of using chunked to send data streams of unknown length.
2067   A sender &MUST-NOT; generate a trailer containing a
2068   <x:ref>Transfer-Encoding</x:ref>,
2069   <x:ref>Content-Length</x:ref>, or
2070   <x:ref>Trailer</x:ref> field.
2071</t>
2072<t>
2073   A server &MUST; generate an empty trailer with the chunked transfer coding
2074   unless at least one of the following is true:
2075  <list style="numbers">
2076    <t>the request included a <x:ref>TE</x:ref> header field that indicates
2077    "trailers" is acceptable in the transfer coding of the response, as
2078    described in <xref target="header.te"/>; or,</t>
2079     
2080    <t>the trailer fields consist entirely of optional metadata and the
2081    recipient could use the message (in a manner acceptable to the generating
2082    server) without receiving that metadata. In other words, the generating
2083    server is willing to accept the possibility that the trailer fields might
2084    be silently discarded along the path to the client.</t>
2085  </list>
2086</t>
2087<t>
2088   The above requirement prevents the need for an infinite buffer when a
2089   message is being received by an HTTP/1.1 (or later) proxy and forwarded to
2090   an HTTP/1.0 recipient.
2091</t>
2092</section>
2093
2094<section title="Decoding Chunked" anchor="decoding.chunked">
2095<t>
2096   A process for decoding the chunked transfer coding
2097   can be represented in pseudo-code as:
2098</t>
2099<figure><artwork type="code">
2100  length := 0
2101  read chunk-size, chunk-ext (if any), and CRLF
2102  while (chunk-size &gt; 0) {
2103     read chunk-data and CRLF
2104     append chunk-data to decoded-body
2105     length := length + chunk-size
2106     read chunk-size, chunk-ext (if any), and CRLF
2107  }
2108  read header-field
2109  while (header-field not empty) {
2110     append header-field to existing header fields
2111     read header-field
2112  }
2113  Content-Length := length
2114  Remove "chunked" from Transfer-Encoding
2115  Remove Trailer from existing header fields
2116</artwork></figure>
2117</section>
2118</section>
2119
2120<section title="Compression Codings" anchor="compression.codings">
2121<t>
2122   The codings defined below can be used to compress the payload of a
2123   message.
2124</t>
2125
2126<section title="Compress Coding" anchor="compress.coding">
2127<iref item="compress (Coding Format)"/>
2128<t>
2129   The "compress" coding is an adaptive Lempel-Ziv-Welch (LZW) coding
2130   <xref target="Welch"/> that is commonly produced by the UNIX file
2131   compression program "compress".
2132   A recipient &SHOULD; consider "x-compress" to be equivalent to "compress".
2133</t>
2134</section>
2135
2136<section title="Deflate Coding" anchor="deflate.coding">
2137<iref item="deflate (Coding Format)"/>
2138<t>
2139   The "deflate" coding is a "zlib" data format <xref target="RFC1950"/>
2140   containing a "deflate" compressed data stream <xref target="RFC1951"/>
2141   that uses a combination of the Lempel-Ziv (LZ77) compression algorithm and
2142   Huffman coding.
2143</t>
2144<x:note>
2145  <t>
2146    &Note; Some incorrect implementations send the "deflate"
2147    compressed data without the zlib wrapper.
2148   </t>
2149</x:note>
2150</section>
2151
2152<section title="Gzip Coding" anchor="gzip.coding">
2153<iref item="gzip (Coding Format)"/>
2154<t>
2155   The "gzip" coding is an LZ77 coding with a 32 bit CRC that is commonly
2156   produced by the gzip file compression program <xref target="RFC1952"/>.
2157   A recipient &SHOULD; consider "x-gzip" to be equivalent to "gzip".
2158</t>
2159</section>
2160
2161</section>
2162
2163<section title="TE" anchor="header.te">
2164  <iref primary="true" item="TE header field" x:for-anchor=""/>
2165  <x:anchor-alias value="TE"/>
2166  <x:anchor-alias value="t-codings"/>
2167  <x:anchor-alias value="t-ranking"/>
2168  <x:anchor-alias value="rank"/>
2169<t>
2170   The "TE" header field in a request indicates what transfer codings,
2171   besides chunked, the client is willing to accept in response, and
2172   whether or not the client is willing to accept trailer fields in a
2173   chunked transfer coding.
2174</t>
2175<t>
2176   The TE field-value consists of a comma-separated list of transfer coding
2177   names, each allowing for optional parameters (as described in
2178   <xref target="transfer.codings"/>), and/or the keyword "trailers".
2179   A client &MUST-NOT; send the chunked transfer coding name in TE;
2180   chunked is always acceptable for HTTP/1.1 recipients.
2181</t>
2182<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"/>
2183  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2184  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-coding</x:ref> [ <x:ref>t-ranking</x:ref> ] )
2185  <x:ref>t-ranking</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>rank</x:ref>
2186  <x:ref>rank</x:ref>      = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2187             / ( "1" [ "." 0*3("0") ] )
2188</artwork></figure>
2189<t>
2190   Three examples of TE use are below.
2191</t>
2192<figure><artwork type="example">
2193  TE: deflate
2194  TE:
2195  TE: trailers, deflate;q=0.5
2196</artwork></figure>
2197<t>
2198   The presence of the keyword "trailers" indicates that the client is willing
2199   to accept trailer fields in a chunked transfer coding, as defined in
2200   <xref target="chunked.trailer.part"/>, on behalf of itself and any downstream
2201   clients. For requests from an intermediary, this implies that either:
2202   (a) all downstream clients are willing to accept trailer fields in the
2203   forwarded response; or,
2204   (b) the intermediary will attempt to buffer the response on behalf of
2205   downstream recipients.
2206   Note that HTTP/1.1 does not define any means to limit the size of a
2207   chunked response such that an intermediary can be assured of buffering the
2208   entire response.
2209</t>
2210<t>
2211   When multiple transfer codings are acceptable, the client &MAY; rank the
2212   codings by preference using a case-insensitive "q" parameter (similar to
2213   the qvalues used in content negotiation fields, &qvalue;). The rank value
2214   is a real number in the range 0 through 1, where 0.001 is the least
2215   preferred and 1 is the most preferred; a value of 0 means "not acceptable".
2216</t>
2217<t>
2218   If the TE field-value is empty or if no TE field is present, the only
2219   acceptable transfer coding is chunked. A message with no transfer coding
2220   is always acceptable.
2221</t>
2222<t>
2223   Since the TE header field only applies to the immediate connection,
2224   a sender of TE &MUST; also send a "TE" connection option within the
2225   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
2226   in order to prevent the TE field from being forwarded by intermediaries
2227   that do not support its semantics.
2228</t>
2229</section>
2230
2231<section title="Trailer" anchor="header.trailer">
2232  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
2233  <x:anchor-alias value="Trailer"/>
2234<t>
2235   When a message includes a message body encoded with the chunked
2236   transfer coding and the sender desires to send metadata in the form of
2237   trailer fields at the end of the message, the sender &SHOULD; generate a
2238   <x:ref>Trailer</x:ref> header field before the message body to indicate
2239   which fields will be present in the trailers. This allows the recipient
2240   to prepare for receipt of that metadata before it starts processing the body,
2241   which is useful if the message is being streamed and the recipient wishes
2242   to confirm an integrity check on the fly.
2243</t>
2244<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2245  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
2246</artwork></figure>
2247</section>
2248</section>
2249
2250<section title="Message Routing" anchor="message.routing">
2251<t>
2252   HTTP request message routing is determined by each client based on the
2253   target resource, the client's proxy configuration, and
2254   establishment or reuse of an inbound connection.  The corresponding
2255   response routing follows the same connection chain back to the client.
2256</t>
2257
2258<section title="Identifying a Target Resource" anchor="target-resource">
2259  <iref primary="true" item="target resource"/>
2260  <iref primary="true" item="target URI"/>
2261  <x:anchor-alias value="target resource"/>
2262  <x:anchor-alias value="target URI"/>
2263<t>
2264   HTTP is used in a wide variety of applications, ranging from
2265   general-purpose computers to home appliances.  In some cases,
2266   communication options are hard-coded in a client's configuration.
2267   However, most HTTP clients rely on the same resource identification
2268   mechanism and configuration techniques as general-purpose Web browsers.
2269</t>
2270<t>
2271   HTTP communication is initiated by a user agent for some purpose.
2272   The purpose is a combination of request semantics, which are defined in
2273   <xref target="Part2"/>, and a target resource upon which to apply those
2274   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2275   an identifier for the "<x:dfn>target resource</x:dfn>", which a user agent
2276   would resolve to its absolute form in order to obtain the
2277   "<x:dfn>target URI</x:dfn>".  The target URI
2278   excludes the reference's fragment component, if any,
2279   since fragment identifiers are reserved for client-side processing
2280   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2281</t>
2282</section>
2283
2284<section title="Connecting Inbound" anchor="connecting.inbound">
2285<t>
2286   Once the target URI is determined, a client needs to decide whether
2287   a network request is necessary to accomplish the desired semantics and,
2288   if so, where that request is to be directed.
2289</t>
2290<t>
2291   If the client has a cache <xref target="Part6"/> and the request can be
2292   satisfied by it, then the request is
2293   usually directed there first.
2294</t>
2295<t>
2296   If the request is not satisfied by a cache, then a typical client will
2297   check its configuration to determine whether a proxy is to be used to
2298   satisfy the request.  Proxy configuration is implementation-dependent,
2299   but is often based on URI prefix matching, selective authority matching,
2300   or both, and the proxy itself is usually identified by an "http" or
2301   "https" URI.  If a proxy is applicable, the client connects inbound by
2302   establishing (or reusing) a connection to that proxy.
2303</t>
2304<t>
2305   If no proxy is applicable, a typical client will invoke a handler routine,
2306   usually specific to the target URI's scheme, to connect directly
2307   to an authority for the target resource.  How that is accomplished is
2308   dependent on the target URI scheme and defined by its associated
2309   specification, similar to how this specification defines origin server
2310   access for resolution of the "http" (<xref target="http.uri"/>) and
2311   "https" (<xref target="https.uri"/>) schemes.
2312</t>
2313<t>
2314   HTTP requirements regarding connection management are defined in
2315   <xref target="connection.management"/>.
2316</t>
2317</section>
2318
2319<section title="Request Target" anchor="request-target">
2320<t>
2321   Once an inbound connection is obtained,
2322   the client sends an HTTP request message (<xref target="http.message"/>)
2323   with a request-target derived from the target URI.
2324   There are four distinct formats for the request-target, depending on both
2325   the method being requested and whether the request is to a proxy.
2326</t>   
2327<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"/>
2328  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2329                 / <x:ref>absolute-form</x:ref>
2330                 / <x:ref>authority-form</x:ref>
2331                 / <x:ref>asterisk-form</x:ref>
2332
2333  <x:ref>origin-form</x:ref>    = <x:ref>absolute-path</x:ref> [ "?" <x:ref>query</x:ref> ]
2334  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2335  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2336  <x:ref>asterisk-form</x:ref>  = "*"
2337</artwork></figure>
2338<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2339  <x:h>origin-form</x:h>
2340</t>
2341<t>
2342   The most common form of request-target is the <x:dfn>origin-form</x:dfn>.
2343   When making a request directly to an origin server, other than a CONNECT
2344   or server-wide OPTIONS request (as detailed below),
2345   a client &MUST; send only the absolute path and query components of
2346   the target URI as the request-target.
2347   If the target URI's path component is empty, then the client &MUST; send
2348   "/" as the path within the origin-form of request-target.
2349   A <x:ref>Host</x:ref> header field is also sent, as defined in
2350   <xref target="header.host"/>.
2351</t>
2352<t>
2353   For example, a client wishing to retrieve a representation of the resource
2354   identified as
2355</t>
2356<figure><artwork x:indent-with="  " type="example">
2357http://www.example.org/where?q=now
2358</artwork></figure>
2359<t>
2360   directly from the origin server would open (or reuse) a TCP connection
2361   to port 80 of the host "www.example.org" and send the lines:
2362</t>
2363<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2364GET /where?q=now HTTP/1.1
2365Host: www.example.org
2366</artwork></figure>
2367<t>
2368   followed by the remainder of the request message.
2369</t>
2370<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2371  <x:h>absolute-form</x:h>
2372</t>
2373<t>
2374   When making a request to a proxy, other than a CONNECT or server-wide
2375   OPTIONS request (as detailed below), a client &MUST; send the target URI
2376   in <x:dfn>absolute-form</x:dfn> as the request-target.
2377   The proxy is requested to either service that request from a valid cache,
2378   if possible, or make the same request on the client's behalf to either
2379   the next inbound proxy server or directly to the origin server indicated
2380   by the request-target.  Requirements on such "forwarding" of messages are
2381   defined in <xref target="message.forwarding"/>.
2382</t>
2383<t>
2384   An example absolute-form of request-line would be:
2385</t>
2386<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2387GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
2388</artwork></figure>
2389<t>
2390   To allow for transition to the absolute-form for all requests in some
2391   future version of HTTP, a server &MUST; accept the absolute-form
2392   in requests, even though HTTP/1.1 clients will only send them in requests
2393   to proxies.
2394</t>
2395<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2396  <x:h>authority-form</x:h>
2397</t>
2398<t>
2399   The <x:dfn>authority-form</x:dfn> of request-target is only used for
2400   CONNECT requests (&CONNECT;). When making a CONNECT request to establish a
2401   tunnel through one or more proxies, a client &MUST; send only the target
2402   URI's authority component (excluding any userinfo and its "@" delimiter) as
2403   the request-target. For example,
2404</t>
2405<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2406CONNECT www.example.com:80 HTTP/1.1
2407</artwork></figure>
2408<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2409  <x:h>asterisk-form</x:h>
2410</t>
2411<t>
2412   The <x:dfn>asterisk-form</x:dfn> of request-target is only used for a server-wide
2413   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2414   for the server as a whole, as opposed to a specific named resource of
2415   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2416   For example,
2417</t>
2418<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2419OPTIONS * HTTP/1.1
2420</artwork></figure>
2421<t>
2422   If a proxy receives an OPTIONS request with an absolute-form of
2423   request-target in which the URI has an empty path and no query component,
2424   then the last proxy on the request chain &MUST; send a request-target
2425   of "*" when it forwards the request to the indicated origin server.
2426</t>
2427<figure><preamble>  
2428   For example, the request
2429</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2430OPTIONS http://www.example.org:8001 HTTP/1.1
2431</artwork></figure>
2432<figure><preamble>  
2433  would be forwarded by the final proxy as
2434</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2435OPTIONS * HTTP/1.1
2436Host: www.example.org:8001
2437</artwork>
2438<postamble>
2439   after connecting to port 8001 of host "www.example.org".
2440</postamble>
2441</figure>
2442</section>
2443
2444<section title="Host" anchor="header.host">
2445  <iref primary="true" item="Host header field" x:for-anchor=""/>
2446  <x:anchor-alias value="Host"/>
2447<t>
2448   The "Host" header field in a request provides the host and port
2449   information from the target URI, enabling the origin
2450   server to distinguish among resources while servicing requests
2451   for multiple host names on a single IP address.
2452</t>
2453<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2454  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2455</artwork></figure>
2456<t>
2457   A client &MUST; send a Host header field in all HTTP/1.1 request messages.
2458   If the target URI includes an authority component, then a client &MUST;
2459   send a field-value for Host that is identical to that authority
2460   component, excluding any userinfo subcomponent and its "@" delimiter
2461   (<xref target="http.uri"/>).
2462   If the authority component is missing or undefined for the target URI,
2463   then a client &MUST; send a Host header field with an empty field-value.
2464</t>
2465<t>
2466   Since the Host field-value is critical information for handling a request,
2467   a user agent &SHOULD; generate Host as the first header field following the
2468   request-line.
2469</t>
2470<t>
2471   For example, a GET request to the origin server for
2472   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
2473</t>
2474<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2475GET /pub/WWW/ HTTP/1.1
2476Host: www.example.org
2477</artwork></figure>
2478<t>
2479   A client &MUST; send a Host header field in an HTTP/1.1 request even
2480   if the request-target is in the absolute-form, since this
2481   allows the Host information to be forwarded through ancient HTTP/1.0
2482   proxies that might not have implemented Host.
2483</t>
2484<t>
2485   When a proxy receives a request with an absolute-form of
2486   request-target, the proxy &MUST; ignore the received
2487   Host header field (if any) and instead replace it with the host
2488   information of the request-target.  A proxy that forwards such a request
2489   &MUST; generate a new Host field-value based on the received
2490   request-target rather than forward the received Host field-value.
2491</t>
2492<t>
2493   Since the Host header field acts as an application-level routing
2494   mechanism, it is a frequent target for malware seeking to poison
2495   a shared cache or redirect a request to an unintended server.
2496   An interception proxy is particularly vulnerable if it relies on
2497   the Host field-value for redirecting requests to internal
2498   servers, or for use as a cache key in a shared cache, without
2499   first verifying that the intercepted connection is targeting a
2500   valid IP address for that host.
2501</t>
2502<t>
2503   A server &MUST; respond with a <x:ref>400 (Bad Request)</x:ref> status code
2504   to any HTTP/1.1 request message that lacks a Host header field and
2505   to any request message that contains more than one Host header field
2506   or a Host header field with an invalid field-value.
2507</t>
2508</section>
2509
2510<section title="Effective Request URI" anchor="effective.request.uri">
2511  <iref primary="true" item="effective request URI"/>
2512  <x:anchor-alias value="effective request URI"/>
2513<t>
2514   A server that receives an HTTP request message &MUST; reconstruct
2515   the user agent's original target URI, based on the pieces of information
2516   learned from the request-target, <x:ref>Host</x:ref> header field, and
2517   connection context, in order to identify the intended target resource and
2518   properly service the request. The URI derived from this reconstruction
2519   process is referred to as the "<x:dfn>effective request URI</x:dfn>".
2520</t>
2521<t>
2522   For a user agent, the effective request URI is the target URI.
2523</t>
2524<t>
2525   If the request-target is in absolute-form, then the effective request URI
2526   is the same as the request-target.  Otherwise, the effective request URI
2527   is constructed as follows.
2528</t>
2529<t>
2530   If the request is received over a TLS-secured TCP connection,
2531   then the effective request URI's scheme is "https"; otherwise, the
2532   scheme is "http".
2533</t>
2534<t>
2535   If the request-target is in authority-form, then the effective
2536   request URI's authority component is the same as the request-target.
2537   Otherwise, if a <x:ref>Host</x:ref> header field is supplied with a
2538   non-empty field-value, then the authority component is the same as the
2539   Host field-value. Otherwise, the authority component is the concatenation of
2540   the default host name configured for the server, a colon (":"), and the
2541   connection's incoming TCP port number in decimal form.
2542</t>
2543<t>
2544   If the request-target is in authority-form or asterisk-form, then the
2545   effective request URI's combined path and query component is empty.
2546   Otherwise, the combined path and query component is the same as the
2547   request-target.
2548</t>
2549<t>
2550   The components of the effective request URI, once determined as above,
2551   can be combined into absolute-URI form by concatenating the scheme,
2552   "://", authority, and combined path and query component.
2553</t>
2554<figure>
2555<preamble>
2556   Example 1: the following message received over an insecure TCP connection
2557</preamble>
2558<artwork type="example" x:indent-with="  ">
2559GET /pub/WWW/TheProject.html HTTP/1.1
2560Host: www.example.org:8080
2561</artwork>
2562</figure>
2563<figure>
2564<preamble>
2565  has an effective request URI of
2566</preamble>
2567<artwork type="example" x:indent-with="  ">
2568http://www.example.org:8080/pub/WWW/TheProject.html
2569</artwork>
2570</figure>
2571<figure>
2572<preamble>
2573   Example 2: the following message received over a TLS-secured TCP connection
2574</preamble>
2575<artwork type="example" x:indent-with="  ">
2576OPTIONS * HTTP/1.1
2577Host: www.example.org
2578</artwork>
2579</figure>
2580<figure>
2581<preamble>
2582  has an effective request URI of
2583</preamble>
2584<artwork type="example" x:indent-with="  ">
2585https://www.example.org
2586</artwork>
2587</figure>
2588<t>
2589   An origin server that does not allow resources to differ by requested
2590   host &MAY; ignore the <x:ref>Host</x:ref> field-value and instead replace it
2591   with a configured server name when constructing the effective request URI.
2592</t>
2593<t>
2594   Recipients of an HTTP/1.0 request that lacks a <x:ref>Host</x:ref> header
2595   field &MAY; attempt to use heuristics (e.g., examination of the URI path for
2596   something unique to a particular host) in order to guess the
2597   effective request URI's authority component.
2598</t>
2599</section>
2600
2601<section title="Associating a Response to a Request" anchor="associating.response.to.request">
2602<t>
2603   HTTP does not include a request identifier for associating a given
2604   request message with its corresponding one or more response messages.
2605   Hence, it relies on the order of response arrival to correspond exactly
2606   to the order in which requests are made on the same connection.
2607   More than one response message per request only occurs when one or more
2608   informational responses (<x:ref>1xx</x:ref>, see &status-1xx;) precede a
2609   final response to the same request.
2610</t>
2611<t>
2612   A client that has more than one outstanding request on a connection &MUST;
2613   maintain a list of outstanding requests in the order sent and &MUST;
2614   associate each received response message on that connection to the highest
2615   ordered request that has not yet received a final (non-<x:ref>1xx</x:ref>)
2616   response.
2617</t>
2618</section>
2619
2620<section title="Message Forwarding" anchor="message.forwarding">
2621<t>
2622   As described in <xref target="intermediaries"/>, intermediaries can serve
2623   a variety of roles in the processing of HTTP requests and responses.
2624   Some intermediaries are used to improve performance or availability.
2625   Others are used for access control or to filter content.
2626   Since an HTTP stream has characteristics similar to a pipe-and-filter
2627   architecture, there are no inherent limits to the extent an intermediary
2628   can enhance (or interfere) with either direction of the stream.
2629</t>
2630<t>
2631   An intermediary not acting as a tunnel &MUST; implement the
2632   <x:ref>Connection</x:ref> header field, as specified in
2633   <xref target="header.connection"/>, and exclude fields from being forwarded
2634   that are only intended for the incoming connection.
2635</t>
2636<t>
2637   An intermediary &MUST-NOT; forward a message to itself unless it is
2638   protected from an infinite request loop. In general, an intermediary ought
2639   to recognize its own server names, including any aliases, local variations,
2640   or literal IP addresses, and respond to such requests directly.
2641</t>
2642
2643<section title="Via" anchor="header.via">
2644  <iref primary="true" item="Via header field" x:for-anchor=""/>
2645  <x:anchor-alias value="pseudonym"/>
2646  <x:anchor-alias value="received-by"/>
2647  <x:anchor-alias value="received-protocol"/>
2648  <x:anchor-alias value="Via"/>
2649<t>
2650   The "Via" header field indicates the presence of intermediate protocols and
2651   recipients between the user agent and the server (on requests) or between
2652   the origin server and the client (on responses), similar to the
2653   "Received" header field in email
2654   (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>).
2655   Via can be used for tracking message forwards,
2656   avoiding request loops, and identifying the protocol capabilities of
2657   senders along the request/response chain.
2658</t>
2659<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"/>
2660  <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> ] )
2661
2662  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2663                      ; see <xref target="header.upgrade"/>
2664  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2665  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2666</artwork></figure>
2667<t>
2668   Multiple Via field values represent each proxy or gateway that has
2669   forwarded the message. Each intermediary appends its own information
2670   about how the message was received, such that the end result is ordered
2671   according to the sequence of forwarding recipients.
2672</t>
2673<t>
2674   A proxy &MUST; send an appropriate Via header field, as described below, in
2675   each message that it forwards.
2676   An HTTP-to-HTTP gateway &MUST; send an appropriate Via header field in
2677   each inbound request message and &MAY; send a Via header field in
2678   forwarded response messages.
2679</t>
2680<t>
2681   For each intermediary, the received-protocol indicates the protocol and
2682   protocol version used by the upstream sender of the message. Hence, the
2683   Via field value records the advertised protocol capabilities of the
2684   request/response chain such that they remain visible to downstream
2685   recipients; this can be useful for determining what backwards-incompatible
2686   features might be safe to use in response, or within a later request, as
2687   described in <xref target="http.version"/>. For brevity, the protocol-name
2688   is omitted when the received protocol is HTTP.
2689</t>
2690<t>
2691   The received-by field is normally the host and optional port number of a
2692   recipient server or client that subsequently forwarded the message.
2693   However, if the real host is considered to be sensitive information, a
2694   sender &MAY; replace it with a pseudonym. If a port is not provided,
2695   a recipient &MAY; interpret that as meaning it was received on the default
2696   TCP port, if any, for the received-protocol.
2697</t>
2698<t>
2699   A sender &MAY; generate comments in the Via header field to identify the
2700   software of each recipient, analogous to the <x:ref>User-Agent</x:ref> and
2701   <x:ref>Server</x:ref> header fields. However, all comments in the Via field
2702   are optional and a recipient &MAY; remove them prior to forwarding the
2703   message.
2704</t>
2705<t>
2706   For example, a request message could be sent from an HTTP/1.0 user
2707   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2708   forward the request to a public proxy at p.example.net, which completes
2709   the request by forwarding it to the origin server at www.example.com.
2710   The request received by www.example.com would then have the following
2711   Via header field:
2712</t>
2713<figure><artwork type="example">
2714  Via: 1.0 fred, 1.1 p.example.net
2715</artwork></figure>
2716<t>
2717   An intermediary used as a portal through a network firewall
2718   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2719   region unless it is explicitly enabled to do so. If not enabled, such an
2720   intermediary &SHOULD; replace each received-by host of any host behind the
2721   firewall by an appropriate pseudonym for that host.
2722</t>
2723<t>
2724   An intermediary &MAY; combine an ordered subsequence of Via header
2725   field entries into a single such entry if the entries have identical
2726   received-protocol values. For example,
2727</t>
2728<figure><artwork type="example">
2729  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2730</artwork></figure>
2731<t>
2732  could be collapsed to
2733</t>
2734<figure><artwork type="example">
2735  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2736</artwork></figure>
2737<t>
2738   A sender &SHOULD-NOT; combine multiple entries unless they are all
2739   under the same organizational control and the hosts have already been
2740   replaced by pseudonyms. A sender &MUST-NOT; combine entries that
2741   have different received-protocol values.
2742</t>
2743</section>
2744
2745<section title="Transformations" anchor="message.transformations">
2746<t>
2747   Some intermediaries include features for transforming messages and their
2748   payloads.  A transforming proxy might, for example, convert between image
2749   formats in order to save cache space or to reduce the amount of traffic on
2750   a slow link. However, operational problems might occur when these
2751   transformations are applied to payloads intended for critical applications,
2752   such as medical imaging or scientific data analysis, particularly when
2753   integrity checks or digital signatures are used to ensure that the payload
2754   received is identical to the original.
2755</t>
2756<t>
2757   If a proxy receives a request-target with a host name that is not a
2758   fully qualified domain name, it &MAY; add its own domain to the host name
2759   it received when forwarding the request.  A proxy &MUST-NOT; change the
2760   host name if it is a fully qualified domain name.
2761</t>
2762<t>
2763   A proxy &MUST-NOT; modify the "absolute-path" and "query" parts of the
2764   received request-target when forwarding it to the next inbound server,
2765   except as noted above to replace an empty path with "/" or "*".
2766</t>
2767<t>
2768   A proxy &MUST-NOT; modify header fields that provide information about the
2769   end points of the communication chain, the resource state, or the selected
2770   representation. A proxy &MAY; change the message body through application
2771   or removal of a transfer coding (<xref target="transfer.codings"/>).
2772</t>
2773<t>
2774   A non-transforming proxy &MUST-NOT; modify the message payload (&payload;).
2775   A transforming proxy &MUST-NOT; modify the payload of a message that
2776   contains the no-transform cache-control directive.
2777</t>
2778<t>
2779   A transforming proxy &MAY; transform the payload of a message
2780   that does not contain the no-transform cache-control directive;
2781   if the payload is transformed, the transforming proxy &MUST; add a
2782   Warning header field with the warn-code of 214 ("Transformation Applied")
2783   if one does not already appear in the message (see &header-warning;).
2784   If the payload of a <x:ref>200 (OK)</x:ref> response is transformed, the
2785   transforming proxy can also inform downstream recipients that a
2786   transformation has been applied by changing the response status code to
2787   <x:ref>203 (Non-Authoritative Information)</x:ref> (&status-203;).
2788</t>
2789</section>
2790</section>
2791</section>
2792
2793<section title="Connection Management" anchor="connection.management">
2794<t>
2795   HTTP messaging is independent of the underlying transport or
2796   session-layer connection protocol(s).  HTTP only presumes a reliable
2797   transport with in-order delivery of requests and the corresponding
2798   in-order delivery of responses.  The mapping of HTTP request and
2799   response structures onto the data units of an underlying transport
2800   protocol is outside the scope of this specification.
2801</t>
2802<t>
2803   As described in <xref target="connecting.inbound"/>, the specific
2804   connection protocols to be used for an HTTP interaction are determined by
2805   client configuration and the <x:ref>target URI</x:ref>.
2806   For example, the "http" URI scheme
2807   (<xref target="http.uri"/>) indicates a default connection of TCP
2808   over IP, with a default TCP port of 80, but the client might be
2809   configured to use a proxy via some other connection, port, or protocol.
2810</t>
2811<t>
2812   HTTP implementations are expected to engage in connection management,
2813   which includes maintaining the state of current connections,
2814   establishing a new connection or reusing an existing connection,
2815   processing messages received on a connection, detecting connection
2816   failures, and closing each connection.
2817   Most clients maintain multiple connections in parallel, including
2818   more than one connection per server endpoint.
2819   Most servers are designed to maintain thousands of concurrent connections,
2820   while controlling request queues to enable fair use and detect
2821   denial of service attacks.
2822</t>
2823
2824<section title="Connection" anchor="header.connection">
2825  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2826  <iref primary="true" item="close" x:for-anchor=""/>
2827  <x:anchor-alias value="Connection"/>
2828  <x:anchor-alias value="connection-option"/>
2829  <x:anchor-alias value="close"/>
2830<t>
2831   The "Connection" header field allows the sender to indicate desired
2832   control options for the current connection.  In order to avoid confusing
2833   downstream recipients, a proxy or gateway &MUST; remove or replace any
2834   received connection options before forwarding the message.
2835</t>
2836<t>
2837   When a header field aside from Connection is used to supply control
2838   information for or about the current connection, the sender &MUST; list
2839   the corresponding field-name within the "Connection" header field.
2840   A proxy or gateway &MUST; parse a received Connection
2841   header field before a message is forwarded and, for each
2842   connection-option in this field, remove any header field(s) from
2843   the message with the same name as the connection-option, and then
2844   remove the Connection header field itself (or replace it with the
2845   intermediary's own connection options for the forwarded message).
2846</t>
2847<t>
2848   Hence, the Connection header field provides a declarative way of
2849   distinguishing header fields that are only intended for the
2850   immediate recipient ("hop-by-hop") from those fields that are
2851   intended for all recipients on the chain ("end-to-end"), enabling the
2852   message to be self-descriptive and allowing future connection-specific
2853   extensions to be deployed without fear that they will be blindly
2854   forwarded by older intermediaries.
2855</t>
2856<t>
2857   The Connection header field's value has the following grammar:
2858</t>
2859<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-option"/>
2860  <x:ref>Connection</x:ref>        = 1#<x:ref>connection-option</x:ref>
2861  <x:ref>connection-option</x:ref> = <x:ref>token</x:ref>
2862</artwork></figure>
2863<t>
2864   Connection options are case-insensitive.
2865</t>
2866<t>
2867   A sender &MUST-NOT; send a connection option corresponding to a header
2868   field that is intended for all recipients of the payload.
2869   For example, <x:ref>Cache-Control</x:ref> is never appropriate as a
2870   connection option (&header-cache-control;).
2871</t>
2872<t>
2873   The connection options do not always correspond to a header field
2874   present in the message, since a connection-specific header field
2875   might not be needed if there are no parameters associated with a
2876   connection option. In contrast, a connection-specific header field that
2877   is received without a corresponding connection option usually indicates
2878   that the field has been improperly forwarded by an intermediary and
2879   ought to be ignored by the recipient.
2880</t>
2881<t>
2882   When defining new connection options, specification authors ought to survey
2883   existing header field names and ensure that the new connection option does
2884   not share the same name as an already deployed header field.
2885   Defining a new connection option essentially reserves that potential
2886   field-name for carrying additional information related to the
2887   connection option, since it would be unwise for senders to use
2888   that field-name for anything else.
2889</t>
2890<t>
2891   The "<x:dfn>close</x:dfn>" connection option is defined for a
2892   sender to signal that this connection will be closed after completion of
2893   the response. For example,
2894</t>
2895<figure><artwork type="example">
2896  Connection: close
2897</artwork></figure>
2898<t>
2899   in either the request or the response header fields indicates that the
2900   sender is going to close the connection after the current request/response
2901   is complete (<xref target="persistent.tear-down"/>).
2902</t>
2903<t>
2904   A client that does not support <x:ref>persistent connections</x:ref> &MUST;
2905   send the "close" connection option in every request message.
2906</t>
2907<t>
2908   A server that does not support <x:ref>persistent connections</x:ref> &MUST;
2909   send the "close" connection option in every response message that
2910   does not have a <x:ref>1xx (Informational)</x:ref> status code.
2911</t>
2912</section>
2913
2914<section title="Establishment" anchor="persistent.establishment">
2915<t>
2916   It is beyond the scope of this specification to describe how connections
2917   are established via various transport or session-layer protocols.
2918   Each connection applies to only one transport link.
2919</t>
2920</section>
2921
2922<section title="Persistence" anchor="persistent.connections">
2923   <x:anchor-alias value="persistent connections"/>
2924<t>
2925   HTTP/1.1 defaults to the use of "<x:dfn>persistent connections</x:dfn>",
2926   allowing multiple requests and responses to be carried over a single
2927   connection. The "<x:ref>close</x:ref>" connection-option is used to signal
2928   that a connection will not persist after the current request/response.
2929   HTTP implementations &SHOULD; support persistent connections.
2930</t>
2931<t>
2932   A recipient determines whether a connection is persistent or not based on
2933   the most recently received message's protocol version and
2934   <x:ref>Connection</x:ref> header field (if any):
2935   <list style="symbols">
2936     <t>If the <x:ref>close</x:ref> connection option is present, the
2937        connection will not persist after the current response; else,</t>
2938     <t>If the received protocol is HTTP/1.1 (or later), the connection will
2939        persist after the current response; else,</t>
2940     <t>If the received protocol is HTTP/1.0, the "keep-alive"
2941        connection option is present, the recipient is not a proxy, and
2942        the recipient wishes to honor the HTTP/1.0 "keep-alive" mechanism,
2943        the connection will persist after the current response; otherwise,</t>
2944     <t>The connection will close after the current response.</t>
2945   </list>
2946</t>
2947<t>
2948   A server &MAY; assume that an HTTP/1.1 client intends to maintain a
2949   persistent connection until a <x:ref>close</x:ref> connection option
2950   is received in a request.
2951</t>
2952<t>
2953   A client &MAY; reuse a persistent connection until it sends or receives
2954   a <x:ref>close</x:ref> connection option or receives an HTTP/1.0 response
2955   without a "keep-alive" connection option.
2956</t>
2957<t>
2958   In order to remain persistent, all messages on a connection need to
2959   have a self-defined message length (i.e., one not defined by closure
2960   of the connection), as described in <xref target="message.body"/>.
2961   A server &MUST; read the entire request message body or close
2962   the connection after sending its response, since otherwise the
2963   remaining data on a persistent connection would be misinterpreted
2964   as the next request.  Likewise,
2965   a client &MUST; read the entire response message body if it intends
2966   to reuse the same connection for a subsequent request.
2967</t>
2968<t>
2969   A proxy server &MUST-NOT; maintain a persistent connection with an
2970   HTTP/1.0 client (see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/> for
2971   information and discussion of the problems with the Keep-Alive header field
2972   implemented by many HTTP/1.0 clients).
2973</t>
2974<t>
2975   Clients and servers &SHOULD-NOT; assume that a persistent connection is
2976   maintained for HTTP versions less than 1.1 unless it is explicitly
2977   signaled.
2978   See <xref target="compatibility.with.http.1.0.persistent.connections"/>
2979   for more information on backward compatibility with HTTP/1.0 clients.
2980</t>
2981
2982<section title="Retrying Requests" anchor="persistent.retrying.requests">
2983<t>
2984   Connections can be closed at any time, with or without intention.
2985   Implementations ought to anticipate the need to recover
2986   from asynchronous close events.
2987</t>
2988<t>
2989   When an inbound connection is closed prematurely, a client &MAY; open a new
2990   connection and automatically retransmit an aborted sequence of requests if
2991   all of those requests have idempotent methods (&idempotent-methods;).
2992   A proxy &MUST-NOT; automatically retry non-idempotent requests.
2993</t>
2994<t>
2995   A user agent &MUST-NOT; automatically retry a request with a non-idempotent
2996   method unless it has some means to know that the request semantics are
2997   actually idempotent, regardless of the method, or some means to detect that
2998   the original request was never applied. For example, a user agent that
2999   knows (through design or configuration) that a POST request to a given
3000   resource is safe can repeat that request automatically.
3001   Likewise, a user agent designed specifically to operate on a version
3002   control repository might be able to recover from partial failure conditions
3003   by checking the target resource revision(s) after a failed connection,
3004   reverting or fixing any changes that were partially applied, and then
3005   automatically retrying the requests that failed.
3006</t>
3007<t>
3008   A client &SHOULD-NOT; automatically retry a failed automatic retry.
3009</t>
3010</section>
3011
3012<section title="Pipelining" anchor="pipelining">
3013   <x:anchor-alias value="pipeline"/>
3014<t>
3015   A client that supports persistent connections &MAY; "<x:dfn>pipeline</x:dfn>"
3016   its requests (i.e., send multiple requests without waiting for each
3017   response). A server &MAY; process a sequence of pipelined requests in
3018   parallel if they all have safe methods (&safe-methods;), but &MUST; send
3019   the corresponding responses in the same order that the requests were
3020   received.
3021</t>
3022<t>
3023   A client that pipelines requests &SHOULD; retry unanswered requests if the
3024   connection closes before it receives all of the corresponding responses.
3025   When retrying pipelined requests after a failed connection (a connection
3026   not explicitly closed by the server in its last complete response), a
3027   client &MUST-NOT; pipeline immediately after connection establishment,
3028   since the first remaining request in the prior pipeline might have caused
3029   an error response that can be lost again if multiple requests are sent on a
3030   prematurely closed connection (see the TCP reset problem described in
3031   <xref target="persistent.tear-down"/>).
3032</t>
3033<t>
3034   Idempotent methods (&idempotent-methods;) are significant to pipelining
3035   because they can be automatically retried after a connection failure.
3036   A user agent &SHOULD-NOT; pipeline requests after a non-idempotent method,
3037   until the final response status code for that method has been received,
3038   unless the user agent has a means to detect and recover from partial
3039   failure conditions involving the pipelined sequence.
3040</t>
3041<t>
3042   An intermediary that receives pipelined requests &MAY; pipeline those
3043   requests when forwarding them inbound, since it can rely on the outbound
3044   user agent(s) to determine what requests can be safely pipelined. If the
3045   inbound connection fails before receiving a response, the pipelining
3046   intermediary &MAY; attempt to retry a sequence of requests that have yet
3047   to receive a response if the requests all have idempotent methods;
3048   otherwise, the pipelining intermediary &SHOULD; forward any received
3049   responses and then close the corresponding outbound connection(s) so that
3050   the outbound user agent(s) can recover accordingly.
3051</t>
3052</section>
3053</section>
3054   
3055<section title="Concurrency" anchor="persistent.concurrency">
3056<t>
3057   A client &SHOULD; limit the number of simultaneous open
3058   connections that it maintains to a given server.
3059</t>
3060<t>
3061   Previous revisions of HTTP gave a specific number of connections as a
3062   ceiling, but this was found to be impractical for many applications. As a
3063   result, this specification does not mandate a particular maximum number of
3064   connections, but instead encourages clients to be conservative when opening
3065   multiple connections.
3066</t>
3067<t>
3068   Multiple connections are typically used to avoid the "head-of-line
3069   blocking" problem, wherein a request that takes significant server-side
3070   processing and/or has a large payload blocks subsequent requests on the
3071   same connection. However, each connection consumes server resources.
3072   Furthermore, using multiple connections can cause undesirable side effects
3073   in congested networks.
3074</t>
3075<t>
3076   Note that servers might reject traffic that they deem abusive, including an
3077   excessive number of connections from a client.
3078</t>
3079</section>
3080
3081<section title="Failures and Time-outs" anchor="persistent.failures">
3082<t>
3083   Servers will usually have some time-out value beyond which they will
3084   no longer maintain an inactive connection. Proxy servers might make
3085   this a higher value since it is likely that the client will be making
3086   more connections through the same proxy server. The use of persistent
3087   connections places no requirements on the length (or existence) of
3088   this time-out for either the client or the server.
3089</t>
3090<t>
3091   A client or server that wishes to time-out &SHOULD; issue a graceful close
3092   on the connection. Implementations &SHOULD; constantly monitor open
3093   connections for a received closure signal and respond to it as appropriate,
3094   since prompt closure of both sides of a connection enables allocated system
3095   resources to be reclaimed.
3096</t>
3097<t>
3098   A client, server, or proxy &MAY; close the transport connection at any
3099   time. For example, a client might have started to send a new request
3100   at the same time that the server has decided to close the "idle"
3101   connection. From the server's point of view, the connection is being
3102   closed while it was idle, but from the client's point of view, a
3103   request is in progress.
3104</t>
3105<t>
3106   A server &SHOULD; sustain persistent connections, when possible, and allow
3107   the underlying
3108   transport's flow control mechanisms to resolve temporary overloads, rather
3109   than terminate connections with the expectation that clients will retry.
3110   The latter technique can exacerbate network congestion.
3111</t>
3112<t>
3113   A client sending a message body &SHOULD; monitor
3114   the network connection for an error response while it is transmitting
3115   the request. If the client sees a response that indicates the server does
3116   not wish to receive the message body and is closing the connection, the
3117   client &SHOULD; immediately cease transmitting the body and close its side
3118   of the connection.
3119</t>
3120</section>
3121   
3122<section title="Tear-down" anchor="persistent.tear-down">
3123  <iref primary="false" item="Connection header field" x:for-anchor=""/>
3124  <iref primary="false" item="close" x:for-anchor=""/>
3125<t>
3126   The <x:ref>Connection</x:ref> header field
3127   (<xref target="header.connection"/>) provides a "<x:ref>close</x:ref>"
3128   connection option that a sender &SHOULD; send when it wishes to close
3129   the connection after the current request/response pair.
3130</t>
3131<t>
3132   A client that sends a <x:ref>close</x:ref> connection option &MUST-NOT;
3133   send further requests on that connection (after the one containing
3134   <x:ref>close</x:ref>) and &MUST; close the connection after reading the
3135   final response message corresponding to this request.
3136</t>
3137<t>
3138   A server that receives a <x:ref>close</x:ref> connection option &MUST;
3139   initiate a close of the connection (see below) after it sends the
3140   final response to the request that contained <x:ref>close</x:ref>.
3141   The server &SHOULD; send a <x:ref>close</x:ref> connection option
3142   in its final response on that connection. The server &MUST-NOT; process
3143   any further requests received on that connection.
3144</t>
3145<t>
3146   A server that sends a <x:ref>close</x:ref> connection option &MUST;
3147   initiate a close of the connection (see below) after it sends the
3148   response containing <x:ref>close</x:ref>. The server &MUST-NOT; process
3149   any further requests received on that connection.
3150</t>
3151<t>
3152   A client that receives a <x:ref>close</x:ref> connection option &MUST;
3153   cease sending requests on that connection and close the connection
3154   after reading the response message containing the close; if additional
3155   pipelined requests had been sent on the connection, the client &SHOULD-NOT;
3156   assume that they will be processed by the server.
3157</t>
3158<t>
3159   If a server performs an immediate close of a TCP connection, there is a
3160   significant risk that the client will not be able to read the last HTTP
3161   response.  If the server receives additional data from the client on a
3162   fully-closed connection, such as another request that was sent by the
3163   client before receiving the server's response, the server's TCP stack will
3164   send a reset packet to the client; unfortunately, the reset packet might
3165   erase the client's unacknowledged input buffers before they can be read
3166   and interpreted by the client's HTTP parser.
3167</t>
3168<t>
3169   To avoid the TCP reset problem, servers typically close a connection in
3170   stages. First, the server performs a half-close by closing only the write
3171   side of the read/write connection. The server then continues to read from
3172   the connection until it receives a corresponding close by the client, or
3173   until the server is reasonably certain that its own TCP stack has received
3174   the client's acknowledgement of the packet(s) containing the server's last
3175   response. Finally, the server fully closes the connection.
3176</t>
3177<t>
3178   It is unknown whether the reset problem is exclusive to TCP or might also
3179   be found in other transport connection protocols.
3180</t>
3181</section>
3182
3183<section title="Upgrade" anchor="header.upgrade">
3184  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3185  <x:anchor-alias value="Upgrade"/>
3186  <x:anchor-alias value="protocol"/>
3187  <x:anchor-alias value="protocol-name"/>
3188  <x:anchor-alias value="protocol-version"/>
3189<t>
3190   The "Upgrade" header field is intended to provide a simple mechanism
3191   for transitioning from HTTP/1.1 to some other protocol on the same
3192   connection.  A client &MAY; send a list of protocols in the Upgrade
3193   header field of a request to invite the server to switch to one or
3194   more of those protocols, in order of descending preference, before sending
3195   the final response. A server &MAY; ignore a received Upgrade header field
3196   if it wishes to continue using the current protocol on that connection.
3197</t>
3198<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3199  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3200
3201  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3202  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3203  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3204</artwork></figure>
3205<t>
3206   A server that sends a <x:ref>101 (Switching Protocols)</x:ref> response
3207   &MUST; send an Upgrade header field to indicate the new protocol(s) to
3208   which the connection is being switched; if multiple protocol layers are
3209   being switched, the sender &MUST; list the protocols in layer-ascending
3210   order. A server &MUST-NOT; switch to a protocol that was not indicated by
3211   the client in the corresponding request's Upgrade header field.
3212   A server &MAY; choose to ignore the order of preference indicated by the
3213   client and select the new protocol(s) based on other factors, such as the
3214   nature of the request or the current load on the server.
3215</t>
3216<t>
3217   A server that sends a <x:ref>426 (Upgrade Required)</x:ref> response
3218   &MUST; send an Upgrade header field to indicate the acceptable protocols,
3219   in order of descending preference.
3220</t>
3221<t>
3222   A server &MAY; send an Upgrade header field in any other response to
3223   advertise that it implements support for upgrading to the listed protocols,
3224   in order of descending preference, when appropriate for a future request.
3225</t>
3226<figure><preamble>
3227   The following is a hypothetical example sent by a client:
3228</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3229GET /hello.txt HTTP/1.1
3230Host: www.example.com
3231Connection: upgrade
3232Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3233
3234</artwork></figure>
3235<t>
3236   Upgrade cannot be used to insist on a protocol change; its acceptance and
3237   use by the server is optional. The capabilities and nature of the
3238   application-level communication after the protocol change is entirely
3239   dependent upon the new protocol(s) chosen. However, immediately after
3240   sending the 101 response, the server is expected to continue responding to
3241   the original request as if it had received its equivalent within the new
3242   protocol (i.e., the server still has an outstanding request to satisfy
3243   after the protocol has been changed, and is expected to do so without
3244   requiring the request to be repeated).
3245</t>
3246<t>
3247   For example, if the Upgrade header field is received in a GET request
3248   and the server decides to switch protocols, it first responds
3249   with a <x:ref>101 (Switching Protocols)</x:ref> message in HTTP/1.1 and
3250   then immediately follows that with the new protocol's equivalent of a
3251   response to a GET on the target resource.  This allows a connection to be
3252   upgraded to protocols with the same semantics as HTTP without the
3253   latency cost of an additional round-trip.  A server &MUST-NOT; switch
3254   protocols unless the received message semantics can be honored by the new
3255   protocol; an OPTIONS request can be honored by any protocol.
3256</t>
3257<figure><preamble>
3258   The following is an example response to the above hypothetical request:
3259</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
3260HTTP/1.1 101 Switching Protocols
3261Connection: upgrade
3262Upgrade: HTTP/2.0
3263
3264[... data stream switches to HTTP/2.0 with an appropriate response
3265(as defined by new protocol) to the "GET /hello.txt" request ...]
3266</artwork></figure>
3267<t>
3268   When Upgrade is sent, the sender &MUST; also send a
3269   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
3270   that contains an "upgrade" connection option, in order to prevent Upgrade
3271   from being accidentally forwarded by intermediaries that might not implement
3272   the listed protocols.  A server &MUST; ignore an Upgrade header field that
3273   is received in an HTTP/1.0 request.
3274</t>
3275<t>
3276   A client cannot begin using an upgraded protocol on the connection until
3277   it has completely sent the request message (i.e., the client can't change
3278   the protocol it is sending in the middle of a message).
3279   If a server receives both Upgrade and an <x:ref>Expect</x:ref> header field
3280   with the "100-continue" expectation (&header-expect;), the
3281   server &MUST; send a <x:ref>100 (Continue)</x:ref> response before sending
3282   a <x:ref>101 (Switching Protocols)</x:ref> response.
3283</t>
3284<t>
3285   The Upgrade header field only applies to switching protocols on top of the
3286   existing connection; it cannot be used to switch the underlying connection
3287   (transport) protocol, nor to switch the existing communication to a
3288   different connection. For those purposes, it is more appropriate to use a
3289   <x:ref>3xx (Redirection)</x:ref> response (&status-3xx;).
3290</t>
3291<t>
3292   This specification only defines the protocol name "HTTP" for use by
3293   the family of Hypertext Transfer Protocols, as defined by the HTTP
3294   version rules of <xref target="http.version"/> and future updates to this
3295   specification. Additional tokens ought to be registered with IANA using the
3296   registration procedure defined in <xref target="upgrade.token.registry"/>.
3297</t>
3298</section>
3299</section>
3300
3301<section title="ABNF list extension: #rule" anchor="abnf.extension">
3302<t>
3303  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
3304  improve readability in the definitions of some header field values.
3305</t>
3306<t>
3307  A construct "#" is defined, similar to "*", for defining comma-delimited
3308  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
3309  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
3310  comma (",") and optional whitespace (OWS).   
3311</t>
3312<figure><preamble>
3313  Thus, a sender &MUST; expand the list construct as follows:
3314</preamble><artwork type="example">
3315  1#element =&gt; element *( OWS "," OWS element )
3316</artwork></figure>
3317<figure><preamble>
3318  and:
3319</preamble><artwork type="example">
3320  #element =&gt; [ 1#element ]
3321</artwork></figure>
3322<figure><preamble>
3323  and for n &gt;= 1 and m &gt; 1:
3324</preamble><artwork type="example">
3325  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
3326</artwork></figure>
3327<t>
3328  For compatibility with legacy list rules, a recipient &MUST; parse and ignore
3329  a reasonable number of empty list elements: enough to handle common mistakes
3330  by senders that merge values, but not so much that they could be used as a
3331  denial of service mechanism. In other words, a recipient &MUST; expand the
3332  list construct as follows:
3333</t>
3334<figure><artwork type="example">
3335  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
3336 
3337  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
3338</artwork></figure>
3339<t>
3340  Empty elements do not contribute to the count of elements present.
3341  For example, given these ABNF productions:
3342</t>
3343<figure><artwork type="example">
3344  example-list      = 1#example-list-elmt
3345  example-list-elmt = token ; see <xref target="field.components"/>
3346</artwork></figure>
3347<t>
3348  Then the following are valid values for example-list (not including the
3349  double quotes, which are present for delimitation only):
3350</t>
3351<figure><artwork type="example">
3352  "foo,bar"
3353  "foo ,bar,"
3354  "foo , ,bar,charlie   "
3355</artwork></figure>
3356<t>
3357  In contrast, the following values would be invalid, since at least one
3358  non-empty element is required by the example-list production:
3359</t>
3360<figure><artwork type="example">
3361  ""
3362  ","
3363  ",   ,"
3364</artwork></figure>
3365<t>
3366  <xref target="collected.abnf"/> shows the collected ABNF after the list
3367  constructs have been expanded, as described above, for recipients.
3368</t>
3369</section>
3370
3371<section title="IANA Considerations" anchor="IANA.considerations">
3372
3373<section title="Header Field Registration" anchor="header.field.registration">
3374<t>
3375   HTTP header fields are registered within the Message Header Field Registry
3376   maintained at
3377   <eref target="http://www.iana.org/assignments/message-headers/"/>.
3378</t>
3379<t>
3380   This document defines the following HTTP header fields, so their
3381   associated registry entries shall be updated according to the permanent
3382   registrations below (see <xref target="BCP90"/>):
3383</t>
3384<?BEGININC p1-messaging.iana-headers ?>
3385<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3386<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3387   <ttcol>Header Field Name</ttcol>
3388   <ttcol>Protocol</ttcol>
3389   <ttcol>Status</ttcol>
3390   <ttcol>Reference</ttcol>
3391
3392   <c>Connection</c>
3393   <c>http</c>
3394   <c>standard</c>
3395   <c>
3396      <xref target="header.connection"/>
3397   </c>
3398   <c>Content-Length</c>
3399   <c>http</c>
3400   <c>standard</c>
3401   <c>
3402      <xref target="header.content-length"/>
3403   </c>
3404   <c>Host</c>
3405   <c>http</c>
3406   <c>standard</c>
3407   <c>
3408      <xref target="header.host"/>
3409   </c>
3410   <c>TE</c>
3411   <c>http</c>
3412   <c>standard</c>
3413   <c>
3414      <xref target="header.te"/>
3415   </c>
3416   <c>Trailer</c>
3417   <c>http</c>
3418   <c>standard</c>
3419   <c>
3420      <xref target="header.trailer"/>
3421   </c>
3422   <c>Transfer-Encoding</c>
3423   <c>http</c>
3424   <c>standard</c>
3425   <c>
3426      <xref target="header.transfer-encoding"/>
3427   </c>
3428   <c>Upgrade</c>
3429   <c>http</c>
3430   <c>standard</c>
3431   <c>
3432      <xref target="header.upgrade"/>
3433   </c>
3434   <c>Via</c>
3435   <c>http</c>
3436   <c>standard</c>
3437   <c>
3438      <xref target="header.via"/>
3439   </c>
3440</texttable>
3441<!--(END)-->
3442<?ENDINC p1-messaging.iana-headers ?>
3443<t>
3444   Furthermore, the header field-name "Close" shall be registered as
3445   "reserved", since using that name as an HTTP header field might
3446   conflict with the "close" connection option of the "<x:ref>Connection</x:ref>"
3447   header field (<xref target="header.connection"/>).
3448</t>
3449<texttable align="left" suppress-title="true">
3450   <ttcol>Header Field Name</ttcol>
3451   <ttcol>Protocol</ttcol>
3452   <ttcol>Status</ttcol>
3453   <ttcol>Reference</ttcol>
3454
3455   <c>Close</c>
3456   <c>http</c>
3457   <c>reserved</c>
3458   <c>
3459      <xref target="header.field.registration"/>
3460   </c>
3461</texttable>
3462<t>
3463   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3464</t>
3465</section>
3466
3467<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3468<t>
3469   IANA maintains the registry of URI Schemes <xref target="BCP115"/> at
3470   <eref target="http://www.iana.org/assignments/uri-schemes/"/>.
3471</t>
3472<t>
3473   This document defines the following URI schemes, so their
3474   associated registry entries shall be updated according to the permanent
3475   registrations below:
3476</t>
3477<texttable align="left" suppress-title="true">
3478   <ttcol>URI Scheme</ttcol>
3479   <ttcol>Description</ttcol>
3480   <ttcol>Reference</ttcol>
3481
3482   <c>http</c>
3483   <c>Hypertext Transfer Protocol</c>
3484   <c><xref target="http.uri"/></c>
3485
3486   <c>https</c>
3487   <c>Hypertext Transfer Protocol Secure</c>
3488   <c><xref target="https.uri"/></c>
3489</texttable>
3490</section>
3491
3492<section title="Internet Media Type Registration" anchor="internet.media.type.http">
3493<t>
3494   IANA maintains the registry of Internet media types <xref target="BCP13"/> at
3495   <eref target="http://www.iana.org/assignments/media-types"/>.
3496</t>
3497<t>
3498   This document serves as the specification for the Internet media types
3499   "message/http" and "application/http". The following is to be registered with
3500   IANA.
3501</t>
3502<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3503<iref item="Media Type" subitem="message/http" primary="true"/>
3504<iref item="message/http Media Type" primary="true"/>
3505<t>
3506   The message/http type can be used to enclose a single HTTP request or
3507   response message, provided that it obeys the MIME restrictions for all
3508   "message" types regarding line length and encodings.
3509</t>
3510<t>
3511  <list style="hanging" x:indent="12em">
3512    <t hangText="Type name:">
3513      message
3514    </t>
3515    <t hangText="Subtype name:">
3516      http
3517    </t>
3518    <t hangText="Required parameters:">
3519      N/A
3520    </t>
3521    <t hangText="Optional parameters:">
3522      version, msgtype
3523      <list style="hanging">
3524        <t hangText="version:">
3525          The HTTP-version number of the enclosed message
3526          (e.g., "1.1"). If not present, the version can be
3527          determined from the first line of the body.
3528        </t>
3529        <t hangText="msgtype:">
3530          The message type &mdash; "request" or "response". If not
3531          present, the type can be determined from the first
3532          line of the body.
3533        </t>
3534      </list>
3535    </t>
3536    <t hangText="Encoding considerations:">
3537      only "7bit", "8bit", or "binary" are permitted
3538    </t>
3539    <t hangText="Security considerations:">
3540      see <xref target="security.considerations"/>
3541    </t>
3542    <t hangText="Interoperability considerations:">
3543      N/A
3544    </t>
3545    <t hangText="Published specification:">
3546      This specification (see <xref target="internet.media.type.message.http"/>).
3547    </t>
3548    <t hangText="Applications that use this media type:">
3549      N/A
3550    </t>
3551    <t hangText="Fragment identifier considerations:">
3552      N/A
3553    </t>
3554    <t hangText="Additional information:">
3555      <list style="hanging">
3556        <t hangText="Magic number(s):">N/A</t>
3557        <t hangText="Deprecated alias names for this type:">N/A</t>
3558        <t hangText="File extension(s):">N/A</t>
3559        <t hangText="Macintosh file type code(s):">N/A</t>
3560      </list>
3561    </t>
3562    <t hangText="Person and email address to contact for further information:">
3563      See Authors Section.
3564    </t>
3565    <t hangText="Intended usage:">
3566      COMMON
3567    </t>
3568    <t hangText="Restrictions on usage:">
3569      N/A
3570    </t>
3571    <t hangText="Author:">
3572      See Authors Section.
3573    </t>
3574    <t hangText="Change controller:">
3575      IESG
3576    </t>
3577  </list>
3578</t>
3579</section>
3580<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3581<iref item="Media Type" subitem="application/http" primary="true"/>
3582<iref item="application/http Media Type" primary="true"/>
3583<t>
3584   The application/http type can be used to enclose a pipeline of one or more
3585   HTTP request or response messages (not intermixed).
3586</t>
3587<t>
3588  <list style="hanging" x:indent="12em">
3589    <t hangText="Type name:">
3590      application
3591    </t>
3592    <t hangText="Subtype name:">
3593      http
3594    </t>
3595    <t hangText="Required parameters:">
3596      N/A
3597    </t>
3598    <t hangText="Optional parameters:">
3599      version, msgtype
3600      <list style="hanging">
3601        <t hangText="version:">
3602          The HTTP-version number of the enclosed messages
3603          (e.g., "1.1"). If not present, the version can be
3604          determined from the first line of the body.
3605        </t>
3606        <t hangText="msgtype:">
3607          The message type &mdash; "request" or "response". If not
3608          present, the type can be determined from the first
3609          line of the body.
3610        </t>
3611      </list>
3612    </t>
3613    <t hangText="Encoding considerations:">
3614      HTTP messages enclosed by this type
3615      are in "binary" format; use of an appropriate
3616      Content-Transfer-Encoding is required when
3617      transmitted via E-mail.
3618    </t>
3619    <t hangText="Security considerations:">
3620      see <xref target="security.considerations"/>
3621    </t>
3622    <t hangText="Interoperability considerations:">
3623      N/A
3624    </t>
3625    <t hangText="Published specification:">
3626      This specification (see <xref target="internet.media.type.application.http"/>).
3627    </t>
3628    <t hangText="Applications that use this media type:">
3629      N/A
3630    </t>
3631    <t hangText="Fragment identifier considerations:">
3632      N/A
3633    </t>
3634    <t hangText="Additional information:">
3635      <list style="hanging">
3636        <t hangText="Deprecated alias names for this type:">N/A</t>
3637        <t hangText="Magic number(s):">N/A</t>
3638        <t hangText="File extension(s):">N/A</t>
3639        <t hangText="Macintosh file type code(s):">N/A</t>
3640      </list>
3641    </t>
3642    <t hangText="Person and email address to contact for further information:">
3643      See Authors Section.
3644    </t>
3645    <t hangText="Intended usage:">
3646      COMMON
3647    </t>
3648    <t hangText="Restrictions on usage:">
3649      N/A
3650    </t>
3651    <t hangText="Author:">
3652      See Authors Section.
3653    </t>
3654    <t hangText="Change controller:">
3655      IESG
3656    </t>
3657  </list>
3658</t>
3659</section>
3660</section>
3661
3662<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3663<t>
3664   The HTTP Transfer Coding Registry defines the name space for transfer
3665   coding names. It is maintained at <eref target="http://www.iana.org/assignments/http-parameters"/>.
3666</t>
3667
3668<section title="Procedure" anchor="transfer.coding.registry.procedure">
3669<t>
3670   Registrations &MUST; include the following fields:
3671   <list style="symbols">
3672     <t>Name</t>
3673     <t>Description</t>
3674     <t>Pointer to specification text</t>
3675   </list>
3676</t>
3677<t>
3678   Names of transfer codings &MUST-NOT; overlap with names of content codings
3679   (&content-codings;) unless the encoding transformation is identical, as
3680   is the case for the compression codings defined in
3681   <xref target="compression.codings"/>.
3682</t>
3683<t>
3684   Values to be added to this name space require IETF Review (see
3685   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3686   conform to the purpose of transfer coding defined in this specification.
3687</t>
3688<t>
3689   Use of program names for the identification of encoding formats
3690   is not desirable and is discouraged for future encodings.
3691</t>
3692</section>
3693
3694<section title="Registration" anchor="transfer.coding.registration">
3695<t>
3696   The HTTP Transfer Coding Registry shall be updated with the registrations
3697   below:
3698</t>
3699<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3700   <ttcol>Name</ttcol>
3701   <ttcol>Description</ttcol>
3702   <ttcol>Reference</ttcol>
3703   <c>chunked</c>
3704   <c>Transfer in a series of chunks</c>
3705   <c>
3706      <xref target="chunked.encoding"/>
3707   </c>
3708   <c>compress</c>
3709   <c>UNIX "compress" data format <xref target="Welch"/></c>
3710   <c>
3711      <xref target="compress.coding"/>
3712   </c>
3713   <c>deflate</c>
3714   <c>"deflate" compressed data (<xref target="RFC1951"/>) inside
3715   the "zlib" data format (<xref target="RFC1950"/>)
3716   </c>
3717   <c>
3718      <xref target="deflate.coding"/>
3719   </c>
3720   <c>gzip</c>
3721   <c>GZIP file format <xref target="RFC1952"/></c>
3722   <c>
3723      <xref target="gzip.coding"/>
3724   </c>
3725   <c>x-compress</c>
3726   <c>Deprecated (alias for compress)</c>
3727   <c>
3728      <xref target="compress.coding"/>
3729   </c>
3730   <c>x-gzip</c>
3731   <c>Deprecated (alias for gzip)</c>
3732   <c>
3733      <xref target="gzip.coding"/>
3734   </c>
3735</texttable>
3736</section>
3737</section>
3738
3739<section title="Content Coding Registration" anchor="content.coding.registration">
3740<t>
3741   IANA maintains the registry of HTTP Content Codings at
3742   <eref target="http://www.iana.org/assignments/http-parameters"/>.
3743</t>
3744<t>
3745   The HTTP Content Codings Registry shall be updated with the registrations
3746   below:
3747</t>
3748<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
3749   <ttcol>Name</ttcol>
3750   <ttcol>Description</ttcol>
3751   <ttcol>Reference</ttcol>
3752   <c>compress</c>
3753   <c>UNIX "compress" data format <xref target="Welch"/></c>
3754   <c>
3755      <xref target="compress.coding"/>
3756   </c>
3757   <c>deflate</c>
3758   <c>"deflate" compressed data (<xref target="RFC1951"/>) inside
3759   the "zlib" data format (<xref target="RFC1950"/>)</c>
3760   <c>
3761      <xref target="deflate.coding"/>
3762   </c>
3763   <c>gzip</c>
3764   <c>GZIP file format <xref target="RFC1952"/></c>
3765   <c>
3766      <xref target="gzip.coding"/>
3767   </c>
3768   <c>x-compress</c>
3769   <c>Deprecated (alias for compress)</c>
3770   <c>
3771      <xref target="compress.coding"/>
3772   </c>
3773   <c>x-gzip</c>
3774   <c>Deprecated (alias for gzip)</c>
3775   <c>
3776      <xref target="gzip.coding"/>
3777   </c>
3778</texttable>
3779</section>
3780
3781<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3782<t>
3783   The HTTP Upgrade Token Registry defines the name space for protocol-name
3784   tokens used to identify protocols in the <x:ref>Upgrade</x:ref> header
3785   field. The registry is maintained at <eref target="http://www.iana.org/assignments/http-upgrade-tokens"/>.
3786</t>
3787
3788<section title="Procedure" anchor="upgrade.token.registry.procedure">  
3789<t>
3790   Each registered protocol name is associated with contact information
3791   and an optional set of specifications that details how the connection
3792   will be processed after it has been upgraded.
3793</t>
3794<t>
3795   Registrations happen on a "First Come First Served" basis (see
3796   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3797   following rules:
3798  <list style="numbers">
3799    <t>A protocol-name token, once registered, stays registered forever.</t>
3800    <t>The registration &MUST; name a responsible party for the
3801       registration.</t>
3802    <t>The registration &MUST; name a point of contact.</t>
3803    <t>The registration &MAY; name a set of specifications associated with
3804       that token. Such specifications need not be publicly available.</t>
3805    <t>The registration &SHOULD; name a set of expected "protocol-version"
3806       tokens associated with that token at the time of registration.</t>
3807    <t>The responsible party &MAY; change the registration at any time.
3808       The IANA will keep a record of all such changes, and make them
3809       available upon request.</t>
3810    <t>The IESG &MAY; reassign responsibility for a protocol token.
3811       This will normally only be used in the case when a
3812       responsible party cannot be contacted.</t>
3813  </list>
3814</t>
3815<t>
3816   This registration procedure for HTTP Upgrade Tokens replaces that
3817   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3818</t>
3819</section>
3820
3821<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3822<t>
3823   The "HTTP" entry in the HTTP Upgrade Token Registry shall be updated with
3824   the registration below:
3825</t>
3826<texttable align="left" suppress-title="true">
3827   <ttcol>Value</ttcol>
3828   <ttcol>Description</ttcol>
3829   <ttcol>Expected Version Tokens</ttcol>
3830   <ttcol>Reference</ttcol>
3831
3832   <c>HTTP</c>
3833   <c>Hypertext Transfer Protocol</c>
3834   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3835   <c><xref target="http.version"/></c>
3836</texttable>
3837<t>
3838   The responsible party is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3839</t>
3840</section>
3841</section>
3842
3843</section>
3844
3845<section title="Security Considerations" anchor="security.considerations">
3846<t>
3847   This section is meant to inform developers, information providers, and
3848   users of known security concerns relevant to HTTP/1.1 message syntax,
3849   parsing, and routing.
3850</t>
3851
3852<section title="DNS-related Attacks" anchor="dns.related.attacks">
3853<t>
3854   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3855   generally prone to security attacks based on the deliberate misassociation
3856   of IP addresses and DNS names not protected by DNSSEC. Clients need to be
3857   cautious in assuming the validity of an IP number/DNS name association unless
3858   the response is protected by DNSSEC (<xref target="RFC4033"/>).
3859</t>
3860</section>
3861
3862<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3863<t>
3864   By their very nature, HTTP intermediaries are men-in-the-middle, and
3865   represent an opportunity for man-in-the-middle attacks. Compromise of
3866   the systems on which the intermediaries run can result in serious security
3867   and privacy problems. Intermediaries have access to security-related
3868   information, personal information about individual users and
3869   organizations, and proprietary information belonging to users and
3870   content providers. A compromised intermediary, or an intermediary
3871   implemented or configured without regard to security and privacy
3872   considerations, might be used in the commission of a wide range of
3873   potential attacks.
3874</t>
3875<t>
3876   Intermediaries that contain a shared cache are especially vulnerable
3877   to cache poisoning attacks.
3878</t>
3879<t>
3880   Implementers need to consider the privacy and security
3881   implications of their design and coding decisions, and of the
3882   configuration options they provide to operators (especially the
3883   default configuration).
3884</t>
3885<t>
3886   Users need to be aware that intermediaries are no more trustworthy than
3887   the people who run them; HTTP itself cannot solve this problem.
3888</t>
3889</section>
3890
3891<section title="Buffer Overflows" anchor="attack.protocol.element.size.overflows">
3892<t>
3893   Because HTTP uses mostly textual, character-delimited fields, attackers can
3894   overflow buffers in implementations, and/or perform a Denial of Service
3895   against implementations that accept fields with unlimited lengths.
3896</t>
3897<t>
3898   To promote interoperability, this specification makes specific
3899   recommendations for minimum size limits on request-line
3900   (<xref target="request.line"/>)
3901   and header fields (<xref target="header.fields"/>). These are
3902   minimum recommendations, chosen to be supportable even by implementations
3903   with limited resources; it is expected that most implementations will
3904   choose substantially higher limits.
3905</t>
3906<t>
3907   This specification also provides a way for servers to reject messages that
3908   have request-targets that are too long (&status-414;) or request entities
3909   that are too large (&status-4xx;). Additional status codes related to
3910   capacity limits have been defined by extensions to HTTP
3911   <xref target="RFC6585"/>.
3912</t>
3913<t>
3914   Recipients ought to carefully limit the extent to which they read other
3915   fields, including (but not limited to) request methods, response status
3916   phrases, header field-names, and body chunks, so as to avoid denial of
3917   service attacks without impeding interoperability.
3918</t>
3919</section>
3920
3921<section title="Message Integrity" anchor="message.integrity">
3922<t>
3923   HTTP does not define a specific mechanism for ensuring message integrity,
3924   instead relying on the error-detection ability of underlying transport
3925   protocols and the use of length or chunk-delimited framing to detect
3926   completeness. Additional integrity mechanisms, such as hash functions or
3927   digital signatures applied to the content, can be selectively added to
3928   messages via extensible metadata header fields. Historically, the lack of
3929   a single integrity mechanism has been justified by the informal nature of
3930   most HTTP communication.  However, the prevalence of HTTP as an information
3931   access mechanism has resulted in its increasing use within environments
3932   where verification of message integrity is crucial.
3933</t>
3934<t>
3935   User agents are encouraged to implement configurable means for detecting
3936   and reporting failures of message integrity such that those means can be
3937   enabled within environments for which integrity is necessary. For example,
3938   a browser being used to view medical history or drug interaction
3939   information needs to indicate to the user when such information is detected
3940   by the protocol to be incomplete, expired, or corrupted during transfer.
3941   Such mechanisms might be selectively enabled via user agent extensions or
3942   the presence of message integrity metadata in a response.
3943   At a minimum, user agents ought to provide some indication that allows a
3944   user to distinguish between a complete and incomplete response message
3945   (<xref target="incomplete.messages"/>) when such verification is desired.
3946</t>
3947</section>
3948
3949<section title="Server Log Information" anchor="abuse.of.server.log.information">
3950<t>
3951   A server is in the position to save personal data about a user's requests
3952   over time, which might identify their reading patterns or subjects of
3953   interest.  In particular, log information gathered at an intermediary
3954   often contains a history of user agent interaction, across a multitude
3955   of sites, that can be traced to individual users.
3956</t>
3957<t>
3958   HTTP log information is confidential in nature; its handling is often
3959   constrained by laws and regulations.  Log information needs to be securely
3960   stored and appropriate guidelines followed for its analysis.
3961   Anonymization of personal information within individual entries helps,
3962   but is generally not sufficient to prevent real log traces from being
3963   re-identified based on correlation with other access characteristics.
3964   As such, access traces that are keyed to a specific client are unsafe to
3965   publish even if the key is pseudonymous.
3966</t>
3967<t>
3968   To minimize the risk of theft or accidental publication, log information
3969   ought to be purged of personally identifiable information, including
3970   user identifiers, IP addresses, and user-provided query parameters,
3971   as soon as that information is no longer necessary to support operational
3972   needs for security, auditing, or fraud control.
3973</t>
3974</section>
3975</section>
3976
3977<section title="Acknowledgments" anchor="acks">
3978<t>
3979   This edition of HTTP/1.1 builds on the many contributions that went into
3980   <xref target="RFC1945" format="none">RFC 1945</xref>,
3981   <xref target="RFC2068" format="none">RFC 2068</xref>,
3982   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3983   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3984   substantial contributions made by the previous authors, editors, and
3985   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3986   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3987   and Paul J. Leach. Mark Nottingham oversaw this effort as working group chair.
3988</t>
3989<t>
3990   Since 1999, the following contributors have helped improve the HTTP
3991   specification by reporting bugs, asking smart questions, drafting or
3992   reviewing text, and evaluating open issues:
3993</t>
3994<?BEGININC acks ?>
3995<t>Adam Barth,
3996Adam Roach,
3997Addison Phillips,
3998Adrian Chadd,
3999Adrien W. de Croy,
4000Alan Ford,
4001Alan Ruttenberg,
4002Albert Lunde,
4003Alek Storm,
4004Alex Rousskov,
4005Alexandre Morgaut,
4006Alexey Melnikov,
4007Alisha Smith,
4008Amichai Rothman,
4009Amit Klein,
4010Amos Jeffries,
4011Andreas Maier,
4012Andreas Petersson,
4013Andrei Popov,
4014Anil Sharma,
4015Anne van Kesteren,
4016Anthony Bryan,
4017Asbjorn Ulsberg,
4018Ashok Kumar,
4019Balachander Krishnamurthy,
4020Barry Leiba,
4021Ben Laurie,
4022Benjamin Carlyle,
4023Benjamin Niven-Jenkins,
4024Benoit Claise,
4025Bil Corry,
4026Bill Burke,
4027Bjoern Hoehrmann,
4028Bob Scheifler,
4029Boris Zbarsky,
4030Brett Slatkin,
4031Brian Kell,
4032Brian McBarron,
4033Brian Pane,
4034Brian Raymor,
4035Brian Smith,
4036Bruce Perens,
4037Bryce Nesbitt,
4038Cameron Heavon-Jones,
4039Carl Kugler,
4040Carsten Bormann,
4041Charles Fry,
4042Chris Burdess,
4043Chris Newman,
4044Christian Huitema,
4045Cyrus Daboo,
4046Dale Robert Anderson,
4047Dan Wing,
4048Dan Winship,
4049Daniel Stenberg,
4050Darrel Miller,
4051Dave Cridland,
4052Dave Crocker,
4053Dave Kristol,
4054Dave Thaler,
4055David Booth,
4056David Singer,
4057David W. Morris,
4058Diwakar Shetty,
4059Dmitry Kurochkin,
4060Drummond Reed,
4061Duane Wessels,
4062Edward Lee,
4063Eitan Adler,
4064Eliot Lear,
4065Emile Stephan,
4066Eran Hammer-Lahav,
4067Eric D. Williams,
4068Eric J. Bowman,
4069Eric Lawrence,
4070Eric Rescorla,
4071Erik Aronesty,
4072EungJun Yi,
4073Evan Prodromou,
4074Felix Geisendoerfer,
4075Florian Weimer,
4076Frank Ellermann,
4077Fred Akalin,
4078Fred Bohle,
4079Frederic Kayser,
4080Gabor Molnar,
4081Gabriel Montenegro,
4082Geoffrey Sneddon,
4083Gervase Markham,
4084Gili Tzabari,
4085Grahame Grieve,
4086Greg Slepak,
4087Greg Wilkins,
4088Grzegorz Calkowski,
4089Harald Tveit Alvestrand,
4090Harry Halpin,
4091Helge Hess,
4092Henrik Nordstrom,
4093Henry S. Thompson,
4094Henry Story,
4095Herbert van de Sompel,
4096Herve Ruellan,
4097Howard Melman,
4098Hugo Haas,
4099Ian Fette,
4100Ian Hickson,
4101Ido Safruti,
4102Ilari Liusvaara,
4103Ilya Grigorik,
4104Ingo Struck,
4105J. Ross Nicoll,
4106James Cloos,
4107James H. Manger,
4108James Lacey,
4109James M. Snell,
4110Jamie Lokier,
4111Jan Algermissen,
4112Jari Arkko,
4113Jeff Hodges (who came up with the term 'effective Request-URI'),
4114Jeff Pinner,
4115Jeff Walden,
4116Jim Luther,
4117Jitu Padhye,
4118Joe D. Williams,
4119Joe Gregorio,
4120Joe Orton,
4121Joel Jaeggli,
4122John C. Klensin,
4123John C. Mallery,
4124John Cowan,
4125John Kemp,
4126John Panzer,
4127John Schneider,
4128John Stracke,
4129John Sullivan,
4130Jonas Sicking,
4131Jonathan A. Rees,
4132Jonathan Billington,
4133Jonathan Moore,
4134Jonathan Silvera,
4135Jordi Ros,
4136Joris Dobbelsteen,
4137Josh Cohen,
4138Julien Pierre,
4139Jungshik Shin,
4140Justin Chapweske,
4141Justin Erenkrantz,
4142Justin James,
4143Kalvinder Singh,
4144Karl Dubost,
4145Kathleen Moriarty,
4146Keith Hoffman,
4147Keith Moore,
4148Ken Murchison,
4149Koen Holtman,
4150Konstantin Voronkov,
4151Kris Zyp,
4152Leif Hedstrom,
4153Lionel Morand,
4154Lisa Dusseault,
4155Maciej Stachowiak,
4156Manu Sporny,
4157Marc Schneider,
4158Marc Slemko,
4159Mark Baker,
4160Mark Pauley,
4161Mark Watson,
4162Markus Isomaki,
4163Markus Lanthaler,
4164Martin J. Duerst,
4165Martin Musatov,
4166Martin Nilsson,
4167Martin Thomson,
4168Matt Lynch,
4169Matthew Cox,
4170Matthew Kerwin,
4171Max Clark,
4172Menachem Dodge,
4173Meral Shirazipour,
4174Michael Burrows,
4175Michael Hausenblas,
4176Michael Scharf,
4177Michael Sweet,
4178Michael Tuexen,
4179Michael Welzl,
4180Mike Amundsen,
4181Mike Belshe,
4182Mike Bishop,
4183Mike Kelly,
4184Mike Schinkel,
4185Miles Sabin,
4186Murray S. Kucherawy,
4187Mykyta Yevstifeyev,
4188Nathan Rixham,
4189Nicholas Shanks,
4190Nico Williams,
4191Nicolas Alvarez,
4192Nicolas Mailhot,
4193Noah Slater,
4194Osama Mazahir,
4195Pablo Castro,
4196Pat Hayes,
4197Patrick R. McManus,
4198Paul E. Jones,
4199Paul Hoffman,
4200Paul Marquess,
4201Pete Resnick,
4202Peter Lepeska,
4203Peter Occil,
4204Peter Saint-Andre,
4205Peter Watkins,
4206Phil Archer,
4207Philippe Mougin,
4208Phillip Hallam-Baker,
4209Piotr Dobrogost,
4210Poul-Henning Kamp,
4211Preethi Natarajan,
4212Rajeev Bector,
4213Ray Polk,
4214Reto Bachmann-Gmuer,
4215Richard Barnes,
4216Richard Cyganiak,
4217Rob Trace,
4218Robby Simpson,
4219Robert Brewer,
4220Robert Collins,
4221Robert Mattson,
4222Robert O'Callahan,
4223Robert Olofsson,
4224Robert Sayre,
4225Robert Siemer,
4226Robert de Wilde,
4227Roberto Javier Godoy,
4228Roberto Peon,
4229Roland Zink,
4230Ronny Widjaja,
4231Ryan Hamilton,
4232S. Mike Dierken,
4233Salvatore Loreto,
4234Sam Johnston,
4235Sam Pullara,
4236Sam Ruby,
4237Saurabh Kulkarni,
4238Scott Lawrence (who maintained the original issues list),
4239Sean B. Palmer,
4240Sean Turner,
4241Sebastien Barnoud,
4242Shane McCarron,
4243Shigeki Ohtsu,
4244Simon Yarde,
4245Stefan Eissing,
4246Stefan Tilkov,
4247Stefanos Harhalakis,
4248Stephane Bortzmeyer,
4249Stephen Farrell,
4250Stephen Kent,
4251Stephen Ludin,
4252Stuart Williams,
4253Subbu Allamaraju,
4254Subramanian Moonesamy,
4255Susan Hares,
4256Sylvain Hellegouarch,
4257Tapan Divekar,
4258Tatsuhiro Tsujikawa,
4259Tatsuya Hayashi,
4260Ted Hardie,
4261Ted Lemon,
4262Thomas Broyer,
4263Thomas Fossati,
4264Thomas Maslen,
4265Thomas Nadeau,
4266Thomas Nordin,
4267Thomas Roessler,
4268Tim Bray,
4269Tim Morgan,
4270Tim Olsen,
4271Tom Zhou,
4272Travis Snoozy,
4273Tyler Close,
4274Vincent Murphy,
4275Wenbo Zhu,
4276Werner Baumann,
4277Wilbur Streett,
4278Wilfredo Sanchez Vega,
4279William A. Rowe Jr.,
4280William Chan,
4281Willy Tarreau,
4282Xiaoshu Wang,
4283Yaron Goland,
4284Yngve Nysaeter Pettersen,
4285Yoav Nir,
4286Yogesh Bang,
4287Yuchung Cheng,
4288Yutaka Oiwa,
4289Yves Lafon (long-time member of the editor team),
4290Zed A. Shaw, and
4291Zhong Yu.
4292</t>
4293<?ENDINC acks ?>
4294<t>
4295   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
4296   acknowledgements from prior revisions.
4297</t>
4298</section>
4299
4300</middle>
4301<back>
4302
4303<references title="Normative References">
4304
4305<reference anchor="Part2">
4306  <front>
4307    <title>Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</title>
4308    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4309      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4310      <address><email>fielding@gbiv.com</email></address>
4311    </author>
4312    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4313      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4314      <address><email>julian.reschke@greenbytes.de</email></address>
4315    </author>
4316    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4317  </front>
4318  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4319  <x:source href="p2-semantics.xml" basename="p2-semantics">
4320    <x:defines>1xx (Informational)</x:defines>
4321    <x:defines>1xx</x:defines>
4322    <x:defines>100 (Continue)</x:defines>
4323    <x:defines>101 (Switching Protocols)</x:defines>
4324    <x:defines>2xx (Successful)</x:defines>
4325    <x:defines>2xx</x:defines>
4326    <x:defines>200 (OK)</x:defines>
4327    <x:defines>203 (Non-Authoritative Information)</x:defines>
4328    <x:defines>204 (No Content)</x:defines>
4329    <x:defines>3xx (Redirection)</x:defines>
4330    <x:defines>3xx</x:defines>
4331    <x:defines>301 (Moved Permanently)</x:defines>
4332    <x:defines>4xx (Client Error)</x:defines>
4333    <x:defines>4xx</x:defines>
4334    <x:defines>400 (Bad Request)</x:defines>
4335    <x:defines>411 (Length Required)</x:defines>
4336    <x:defines>414 (URI Too Long)</x:defines>
4337    <x:defines>417 (Expectation Failed)</x:defines>
4338    <x:defines>426 (Upgrade Required)</x:defines>
4339    <x:defines>501 (Not Implemented)</x:defines>
4340    <x:defines>502 (Bad Gateway)</x:defines>
4341    <x:defines>505 (HTTP Version Not Supported)</x:defines>
4342    <x:defines>Accept-Encoding</x:defines>
4343    <x:defines>Allow</x:defines>
4344    <x:defines>Content-Encoding</x:defines>
4345    <x:defines>Content-Location</x:defines>
4346    <x:defines>Content-Type</x:defines>
4347    <x:defines>Date</x:defines>
4348    <x:defines>Expect</x:defines>
4349    <x:defines>Location</x:defines>
4350    <x:defines>Server</x:defines>
4351    <x:defines>User-Agent</x:defines>
4352  </x:source>
4353</reference>
4354
4355<reference anchor="Part4">
4356  <front>
4357    <title>Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests</title>
4358    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
4359      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4360      <address><email>fielding@gbiv.com</email></address>
4361    </author>
4362    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
4363      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4364      <address><email>julian.reschke@greenbytes.de</email></address>
4365    </author>
4366    <date month="&ID-MONTH;" year="&ID-YEAR;" />
4367  </front>
4368  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;" />
4369  <x:source basename="p4-conditional" href="p4-conditional.xml">
4370    <x:defines>304 (Not Modified)</x:defines>
4371    <x:defines>ETag</x:defines>
4372    <x:defines>Last-Modified</x:defines>
4373  </x:source>
4374</reference>
4375
4376<reference anchor="Part5">
4377  <front>
4378    <title>Hypertext Transfer Protocol (HTTP/1.1): Range Requests</title>
4379    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4380      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4381      <address><email>fielding@gbiv.com</email></address>
4382    </author>
4383    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4384      <organization abbrev="W3C">World Wide Web Consortium</organization>
4385      <address><email>ylafon@w3.org</email></address>
4386    </author>
4387    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4388      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4389      <address><email>julian.reschke@greenbytes.de</email></address>
4390    </author>
4391    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4392  </front>
4393  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
4394  <x:source href="p5-range.xml" basename="p5-range">
4395    <x:defines>Content-Range</x:defines>
4396  </x:source>
4397</reference>
4398
4399<reference anchor="Part6">
4400  <front>
4401    <title>Hypertext Transfer Protocol (HTTP/1.1): Caching</title>
4402    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4403      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4404      <address><email>fielding@gbiv.com</email></address>
4405    </author>
4406    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4407      <organization>Akamai</organization>
4408      <address><email>mnot@mnot.net</email></address>
4409    </author>
4410    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4411      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4412      <address><email>julian.reschke@greenbytes.de</email></address>
4413    </author>
4414    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4415  </front>
4416  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4417  <x:source href="p6-cache.xml" basename="p6-cache">
4418    <x:defines>Cache-Control</x:defines>
4419    <x:defines>Expires</x:defines>
4420  </x:source>
4421</reference>
4422
4423<reference anchor="Part7">
4424  <front>
4425    <title>Hypertext Transfer Protocol (HTTP/1.1): Authentication</title>
4426    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4427      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4428      <address><email>fielding@gbiv.com</email></address>
4429    </author>
4430    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4431      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4432      <address><email>julian.reschke@greenbytes.de</email></address>
4433    </author>
4434    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4435  </front>
4436  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
4437  <x:source href="p7-auth.xml" basename="p7-auth">
4438    <x:defines>Proxy-Authenticate</x:defines>
4439    <x:defines>Proxy-Authorization</x:defines>
4440  </x:source>
4441</reference>
4442
4443<reference anchor="RFC5234">
4444  <front>
4445    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4446    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4447      <organization>Brandenburg InternetWorking</organization>
4448      <address>
4449        <email>dcrocker@bbiw.net</email>
4450      </address> 
4451    </author>
4452    <author initials="P." surname="Overell" fullname="Paul Overell">
4453      <organization>THUS plc.</organization>
4454      <address>
4455        <email>paul.overell@thus.net</email>
4456      </address>
4457    </author>
4458    <date month="January" year="2008"/>
4459  </front>
4460  <seriesInfo name="STD" value="68"/>
4461  <seriesInfo name="RFC" value="5234"/>
4462</reference>
4463
4464<reference anchor="RFC2119">
4465  <front>
4466    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4467    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4468      <organization>Harvard University</organization>
4469      <address><email>sob@harvard.edu</email></address>
4470    </author>
4471    <date month="March" year="1997"/>
4472  </front>
4473  <seriesInfo name="BCP" value="14"/>
4474  <seriesInfo name="RFC" value="2119"/>
4475</reference>
4476
4477<reference anchor="RFC3986">
4478 <front>
4479  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4480  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4481    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4482    <address>
4483       <email>timbl@w3.org</email>
4484       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4485    </address>
4486  </author>
4487  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4488    <organization abbrev="Day Software">Day Software</organization>
4489    <address>
4490      <email>fielding@gbiv.com</email>
4491      <uri>http://roy.gbiv.com/</uri>
4492    </address>
4493  </author>
4494  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4495    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4496    <address>
4497      <email>LMM@acm.org</email>
4498      <uri>http://larry.masinter.net/</uri>
4499    </address>
4500  </author>
4501  <date month='January' year='2005'></date>
4502 </front>
4503 <seriesInfo name="STD" value="66"/>
4504 <seriesInfo name="RFC" value="3986"/>
4505</reference>
4506
4507<reference anchor="RFC0793">
4508  <front>
4509    <title>Transmission Control Protocol</title>
4510    <author initials='J.' surname='Postel' fullname='Jon Postel'>
4511      <organization>University of Southern California (USC)/Information Sciences Institute</organization>
4512    </author>
4513    <date year='1981' month='September' />
4514  </front>
4515  <seriesInfo name='STD' value='7' />
4516  <seriesInfo name='RFC' value='793' />
4517</reference>
4518
4519<reference anchor="USASCII">
4520  <front>
4521    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4522    <author>
4523      <organization>American National Standards Institute</organization>
4524    </author>
4525    <date year="1986"/>
4526  </front>
4527  <seriesInfo name="ANSI" value="X3.4"/>
4528</reference>
4529
4530<reference anchor="RFC1950">
4531  <front>
4532    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4533    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4534      <organization>Aladdin Enterprises</organization>
4535      <address><email>ghost@aladdin.com</email></address>
4536    </author>
4537    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4538    <date month="May" year="1996"/>
4539  </front>
4540  <seriesInfo name="RFC" value="1950"/>
4541  <!--<annotation>
4542    RFC 1950 is an Informational RFC, thus it might be less stable than
4543    this specification. On the other hand, this downward reference was
4544    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4545    therefore it is unlikely to cause problems in practice. See also
4546    <xref target="BCP97"/>.
4547  </annotation>-->
4548</reference>
4549
4550<reference anchor="RFC1951">
4551  <front>
4552    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4553    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4554      <organization>Aladdin Enterprises</organization>
4555      <address><email>ghost@aladdin.com</email></address>
4556    </author>
4557    <date month="May" year="1996"/>
4558  </front>
4559  <seriesInfo name="RFC" value="1951"/>
4560  <!--<annotation>
4561    RFC 1951 is an Informational RFC, thus it might be less stable than
4562    this specification. On the other hand, this downward reference was
4563    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4564    therefore it is unlikely to cause problems in practice. See also
4565    <xref target="BCP97"/>.
4566  </annotation>-->
4567</reference>
4568
4569<reference anchor="RFC1952">
4570  <front>
4571    <title>GZIP file format specification version 4.3</title>
4572    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4573      <organization>Aladdin Enterprises</organization>
4574      <address><email>ghost@aladdin.com</email></address>
4575    </author>
4576    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4577      <address><email>gzip@prep.ai.mit.edu</email></address>
4578    </author>
4579    <author initials="M." surname="Adler" fullname="Mark Adler">
4580      <address><email>madler@alumni.caltech.edu</email></address>
4581    </author>
4582    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4583      <address><email>ghost@aladdin.com</email></address>
4584    </author>
4585    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4586      <address><email>randeg@alumni.rpi.edu</email></address>
4587    </author>
4588    <date month="May" year="1996"/>
4589  </front>
4590  <seriesInfo name="RFC" value="1952"/>
4591  <!--<annotation>
4592    RFC 1952 is an Informational RFC, thus it might be less stable than
4593    this specification. On the other hand, this downward reference was
4594    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4595    therefore it is unlikely to cause problems in practice. See also
4596    <xref target="BCP97"/>.
4597  </annotation>-->
4598</reference>
4599
4600<reference anchor="Welch">
4601  <front>
4602    <title>A Technique for High Performance Data Compression</title>
4603    <author initials="T.A." surname="Welch" fullname="Terry A. Welch"/>
4604    <date month="June" year="1984"/>
4605  </front>
4606  <seriesInfo name="IEEE Computer" value="17(6)"/>
4607</reference>
4608
4609</references>
4610
4611<references title="Informative References">
4612
4613<reference anchor="ISO-8859-1">
4614  <front>
4615    <title>
4616     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4617    </title>
4618    <author>
4619      <organization>International Organization for Standardization</organization>
4620    </author>
4621    <date year="1998"/>
4622  </front>
4623  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4624</reference>
4625
4626<reference anchor='RFC1919'>
4627  <front>
4628    <title>Classical versus Transparent IP Proxies</title>
4629    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4630      <address><email>mchatel@pax.eunet.ch</email></address>
4631    </author>
4632    <date year='1996' month='March' />
4633  </front>
4634  <seriesInfo name='RFC' value='1919' />
4635</reference>
4636
4637<reference anchor="RFC1945">
4638  <front>
4639    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4640    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4641      <organization>MIT, Laboratory for Computer Science</organization>
4642      <address><email>timbl@w3.org</email></address>
4643    </author>
4644    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4645      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4646      <address><email>fielding@ics.uci.edu</email></address>
4647    </author>
4648    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4649      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4650      <address><email>frystyk@w3.org</email></address>
4651    </author>
4652    <date month="May" year="1996"/>
4653  </front>
4654  <seriesInfo name="RFC" value="1945"/>
4655</reference>
4656
4657<reference anchor="RFC2045">
4658  <front>
4659    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4660    <author initials="N." surname="Freed" fullname="Ned Freed">
4661      <organization>Innosoft International, Inc.</organization>
4662      <address><email>ned@innosoft.com</email></address>
4663    </author>
4664    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4665      <organization>First Virtual Holdings</organization>
4666      <address><email>nsb@nsb.fv.com</email></address>
4667    </author>
4668    <date month="November" year="1996"/>
4669  </front>
4670  <seriesInfo name="RFC" value="2045"/>
4671</reference>
4672
4673<reference anchor="RFC2047">
4674  <front>
4675    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4676    <author initials="K." surname="Moore" fullname="Keith Moore">
4677      <organization>University of Tennessee</organization>
4678      <address><email>moore@cs.utk.edu</email></address>
4679    </author>
4680    <date month="November" year="1996"/>
4681  </front>
4682  <seriesInfo name="RFC" value="2047"/>
4683</reference>
4684
4685<reference anchor="RFC2068">
4686  <front>
4687    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4688    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4689      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4690      <address><email>fielding@ics.uci.edu</email></address>
4691    </author>
4692    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4693      <organization>MIT Laboratory for Computer Science</organization>
4694      <address><email>jg@w3.org</email></address>
4695    </author>
4696    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4697      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4698      <address><email>mogul@wrl.dec.com</email></address>
4699    </author>
4700    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4701      <organization>MIT Laboratory for Computer Science</organization>
4702      <address><email>frystyk@w3.org</email></address>
4703    </author>
4704    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4705      <organization>MIT Laboratory for Computer Science</organization>
4706      <address><email>timbl@w3.org</email></address>
4707    </author>
4708    <date month="January" year="1997"/>
4709  </front>
4710  <seriesInfo name="RFC" value="2068"/>
4711</reference>
4712
4713<reference anchor="RFC2145">
4714  <front>
4715    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4716    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4717      <organization>Western Research Laboratory</organization>
4718      <address><email>mogul@wrl.dec.com</email></address>
4719    </author>
4720    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4721      <organization>Department of Information and Computer Science</organization>
4722      <address><email>fielding@ics.uci.edu</email></address>
4723    </author>
4724    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4725      <organization>MIT Laboratory for Computer Science</organization>
4726      <address><email>jg@w3.org</email></address>
4727    </author>
4728    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4729      <organization>W3 Consortium</organization>
4730      <address><email>frystyk@w3.org</email></address>
4731    </author>
4732    <date month="May" year="1997"/>
4733  </front>
4734  <seriesInfo name="RFC" value="2145"/>
4735</reference>
4736
4737<reference anchor="RFC2616">
4738  <front>
4739    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4740    <author initials="R." surname="Fielding" fullname="R. Fielding">
4741      <organization>University of California, Irvine</organization>
4742      <address><email>fielding@ics.uci.edu</email></address>
4743    </author>
4744    <author initials="J." surname="Gettys" fullname="J. Gettys">
4745      <organization>W3C</organization>
4746      <address><email>jg@w3.org</email></address>
4747    </author>
4748    <author initials="J." surname="Mogul" fullname="J. Mogul">
4749      <organization>Compaq Computer Corporation</organization>
4750      <address><email>mogul@wrl.dec.com</email></address>
4751    </author>
4752    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4753      <organization>MIT Laboratory for Computer Science</organization>
4754      <address><email>frystyk@w3.org</email></address>
4755    </author>
4756    <author initials="L." surname="Masinter" fullname="L. Masinter">
4757      <organization>Xerox Corporation</organization>
4758      <address><email>masinter@parc.xerox.com</email></address>
4759    </author>
4760    <author initials="P." surname="Leach" fullname="P. Leach">
4761      <organization>Microsoft Corporation</organization>
4762      <address><email>paulle@microsoft.com</email></address>
4763    </author>
4764    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4765      <organization>W3C</organization>
4766      <address><email>timbl@w3.org</email></address>
4767    </author>
4768    <date month="June" year="1999"/>
4769  </front>
4770  <seriesInfo name="RFC" value="2616"/>
4771</reference>
4772
4773<reference anchor='RFC2817'>
4774  <front>
4775    <title>Upgrading to TLS Within HTTP/1.1</title>
4776    <author initials='R.' surname='Khare' fullname='R. Khare'>
4777      <organization>4K Associates / UC Irvine</organization>
4778      <address><email>rohit@4K-associates.com</email></address>
4779    </author>
4780    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4781      <organization>Agranat Systems, Inc.</organization>
4782      <address><email>lawrence@agranat.com</email></address>
4783    </author>
4784    <date year='2000' month='May' />
4785  </front>
4786  <seriesInfo name='RFC' value='2817' />
4787</reference>
4788
4789<reference anchor='RFC2818'>
4790  <front>
4791    <title>HTTP Over TLS</title>
4792    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4793      <organization>RTFM, Inc.</organization>
4794      <address><email>ekr@rtfm.com</email></address>
4795    </author>
4796    <date year='2000' month='May' />
4797  </front>
4798  <seriesInfo name='RFC' value='2818' />
4799</reference>
4800
4801<reference anchor='RFC3040'>
4802  <front>
4803    <title>Internet Web Replication and Caching Taxonomy</title>
4804    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4805      <organization>Equinix, Inc.</organization>
4806    </author>
4807    <author initials='I.' surname='Melve' fullname='I. Melve'>
4808      <organization>UNINETT</organization>
4809    </author>
4810    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4811      <organization>CacheFlow Inc.</organization>
4812    </author>
4813    <date year='2001' month='January' />
4814  </front>
4815  <seriesInfo name='RFC' value='3040' />
4816</reference>
4817
4818<reference anchor='BCP90'>
4819  <front>
4820    <title>Registration Procedures for Message Header Fields</title>
4821    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4822      <organization>Nine by Nine</organization>
4823      <address><email>GK-IETF@ninebynine.org</email></address>
4824    </author>
4825    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4826      <organization>BEA Systems</organization>
4827      <address><email>mnot@pobox.com</email></address>
4828    </author>
4829    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4830      <organization>HP Labs</organization>
4831      <address><email>JeffMogul@acm.org</email></address>
4832    </author>
4833    <date year='2004' month='September' />
4834  </front>
4835  <seriesInfo name='BCP' value='90' />
4836  <seriesInfo name='RFC' value='3864' />
4837</reference>
4838
4839<reference anchor='RFC4033'>
4840  <front>
4841    <title>DNS Security Introduction and Requirements</title>
4842    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4843    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4844    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4845    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4846    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4847    <date year='2005' month='March' />
4848  </front>
4849  <seriesInfo name='RFC' value='4033' />
4850</reference>
4851
4852<reference anchor="BCP13">
4853  <front>
4854    <title>Media Type Specifications and Registration Procedures</title>
4855    <author initials="N." surname="Freed" fullname="Ned Freed">
4856      <organization>Oracle</organization>
4857      <address>
4858        <email>ned+ietf@mrochek.com</email>
4859      </address>
4860    </author>
4861    <author initials="J." surname="Klensin" fullname="John C. Klensin">
4862      <address>
4863        <email>john+ietf@jck.com</email>
4864      </address>
4865    </author>
4866    <author initials="T." surname="Hansen" fullname="Tony Hansen">
4867      <organization>AT&amp;T Laboratories</organization>
4868      <address>
4869        <email>tony+mtsuffix@maillennium.att.com</email>
4870      </address>
4871    </author>
4872    <date year="2013" month="January"/>
4873  </front>
4874  <seriesInfo name="BCP" value="13"/>
4875  <seriesInfo name="RFC" value="6838"/>
4876</reference>
4877
4878<reference anchor='BCP115'>
4879  <front>
4880    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4881    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4882      <organization>AT&amp;T Laboratories</organization>
4883      <address>
4884        <email>tony+urireg@maillennium.att.com</email>
4885      </address>
4886    </author>
4887    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4888      <organization>Qualcomm, Inc.</organization>
4889      <address>
4890        <email>hardie@qualcomm.com</email>
4891      </address>
4892    </author>
4893    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4894      <organization>Adobe Systems</organization>
4895      <address>
4896        <email>LMM@acm.org</email>
4897      </address>
4898    </author>
4899    <date year='2006' month='February' />
4900  </front>
4901  <seriesInfo name='BCP' value='115' />
4902  <seriesInfo name='RFC' value='4395' />
4903</reference>
4904
4905<reference anchor='RFC4559'>
4906  <front>
4907    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4908    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4909    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4910    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4911    <date year='2006' month='June' />
4912  </front>
4913  <seriesInfo name='RFC' value='4559' />
4914</reference>
4915
4916<reference anchor='RFC5226'>
4917  <front>
4918    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4919    <author initials='T.' surname='Narten' fullname='T. Narten'>
4920      <organization>IBM</organization>
4921      <address><email>narten@us.ibm.com</email></address>
4922    </author>
4923    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4924      <organization>Google</organization>
4925      <address><email>Harald@Alvestrand.no</email></address>
4926    </author>
4927    <date year='2008' month='May' />
4928  </front>
4929  <seriesInfo name='BCP' value='26' />
4930  <seriesInfo name='RFC' value='5226' />
4931</reference>
4932
4933<reference anchor='RFC5246'>
4934   <front>
4935      <title>The Transport Layer Security (TLS) Protocol Version 1.2</title>
4936      <author initials='T.' surname='Dierks' fullname='T. Dierks'>
4937         <organization />
4938      </author>
4939      <author initials='E.' surname='Rescorla' fullname='E. Rescorla'>
4940         <organization>RTFM, Inc.</organization>
4941      </author>
4942      <date year='2008' month='August' />
4943   </front>
4944   <seriesInfo name='RFC' value='5246' />
4945</reference>
4946
4947<reference anchor="RFC5322">
4948  <front>
4949    <title>Internet Message Format</title>
4950    <author initials="P." surname="Resnick" fullname="P. Resnick">
4951      <organization>Qualcomm Incorporated</organization>
4952    </author>
4953    <date year="2008" month="October"/>
4954  </front>
4955  <seriesInfo name="RFC" value="5322"/>
4956</reference>
4957
4958<reference anchor="RFC6265">
4959  <front>
4960    <title>HTTP State Management Mechanism</title>
4961    <author initials="A." surname="Barth" fullname="Adam Barth">
4962      <organization abbrev="U.C. Berkeley">
4963        University of California, Berkeley
4964      </organization>
4965      <address><email>abarth@eecs.berkeley.edu</email></address>
4966    </author>
4967    <date year="2011" month="April" />
4968  </front>
4969  <seriesInfo name="RFC" value="6265"/>
4970</reference>
4971
4972<reference anchor='RFC6585'>
4973  <front>
4974    <title>Additional HTTP Status Codes</title>
4975    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4976      <organization>Rackspace</organization>
4977    </author>
4978    <author initials='R.' surname='Fielding' fullname='R. Fielding'>
4979      <organization>Adobe</organization>
4980    </author>
4981    <date year='2012' month='April' />
4982   </front>
4983   <seriesInfo name='RFC' value='6585' />
4984</reference>
4985
4986<!--<reference anchor='BCP97'>
4987  <front>
4988    <title>Handling Normative References to Standards-Track Documents</title>
4989    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4990      <address>
4991        <email>klensin+ietf@jck.com</email>
4992      </address>
4993    </author>
4994    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4995      <organization>MIT</organization>
4996      <address>
4997        <email>hartmans-ietf@mit.edu</email>
4998      </address>
4999    </author>
5000    <date year='2007' month='June' />
5001  </front>
5002  <seriesInfo name='BCP' value='97' />
5003  <seriesInfo name='RFC' value='4897' />
5004</reference>-->
5005
5006<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
5007  <front>
5008    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
5009    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
5010    <date year="2001" month="November"/>
5011  </front>
5012  <seriesInfo name="ACM Transactions on Internet Technology" value="1(2)"/>
5013</reference>
5014
5015</references>
5016
5017
5018<section title="HTTP Version History" anchor="compatibility">
5019<t>
5020   HTTP has been in use by the World-Wide Web global information initiative
5021   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
5022   was a simple protocol for hypertext data transfer across the Internet
5023   with only a single request method (GET) and no metadata.
5024   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
5025   methods and MIME-like messaging that could include metadata about the data
5026   transferred and modifiers on the request/response semantics. However,
5027   HTTP/1.0 did not sufficiently take into consideration the effects of
5028   hierarchical proxies, caching, the need for persistent connections, or
5029   name-based virtual hosts. The proliferation of incompletely-implemented
5030   applications calling themselves "HTTP/1.0" further necessitated a
5031   protocol version change in order for two communicating applications
5032   to determine each other's true capabilities.
5033</t>
5034<t>
5035   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
5036   requirements that enable reliable implementations, adding only
5037   those new features that will either be safely ignored by an HTTP/1.0
5038   recipient or only sent when communicating with a party advertising
5039   conformance with HTTP/1.1.
5040</t>
5041<t>
5042   It is beyond the scope of a protocol specification to mandate
5043   conformance with previous versions. HTTP/1.1 was deliberately
5044   designed, however, to make supporting previous versions easy.
5045   We would expect a general-purpose HTTP/1.1 server to understand
5046   any valid request in the format of HTTP/1.0 and respond appropriately
5047   with an HTTP/1.1 message that only uses features understood (or
5048   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
5049   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
5050</t>
5051<t>
5052   Since HTTP/0.9 did not support header fields in a request,
5053   there is no mechanism for it to support name-based virtual
5054   hosts (selection of resource by inspection of the <x:ref>Host</x:ref> header
5055   field).  Any server that implements name-based virtual hosts
5056   ought to disable support for HTTP/0.9.  Most requests that
5057   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
5058   requests wherein a buggy client failed to properly encode
5059   linear whitespace found in a URI reference and placed in
5060   the request-target.
5061</t>
5062
5063<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
5064<t>
5065   This section summarizes major differences between versions HTTP/1.0
5066   and HTTP/1.1.
5067</t>
5068
5069<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
5070<t>
5071   The requirements that clients and servers support the <x:ref>Host</x:ref>
5072   header field (<xref target="header.host"/>), report an error if it is
5073   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
5074   are among the most important changes defined by HTTP/1.1.
5075</t>
5076<t>
5077   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
5078   addresses and servers; there was no other established mechanism for
5079   distinguishing the intended server of a request than the IP address
5080   to which that request was directed. The <x:ref>Host</x:ref> header field was
5081   introduced during the development of HTTP/1.1 and, though it was
5082   quickly implemented by most HTTP/1.0 browsers, additional requirements
5083   were placed on all HTTP/1.1 requests in order to ensure complete
5084   adoption.  At the time of this writing, most HTTP-based services
5085   are dependent upon the Host header field for targeting requests.
5086</t>
5087</section>
5088
5089<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
5090<t>
5091   In HTTP/1.0, each connection is established by the client prior to the
5092   request and closed by the server after sending the response. However, some
5093   implementations implement the explicitly negotiated ("Keep-Alive") version
5094   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
5095   target="RFC2068"/>.
5096</t>
5097<t>
5098   Some clients and servers might wish to be compatible with these previous
5099   approaches to persistent connections, by explicitly negotiating for them
5100   with a "Connection: keep-alive" request header field. However, some
5101   experimental implementations of HTTP/1.0 persistent connections are faulty;
5102   for example, if an HTTP/1.0 proxy server doesn't understand
5103   <x:ref>Connection</x:ref>, it will erroneously forward that header field
5104   to the next inbound server, which would result in a hung connection.
5105</t>
5106<t>
5107   One attempted solution was the introduction of a Proxy-Connection header
5108   field, targeted specifically at proxies. In practice, this was also
5109   unworkable, because proxies are often deployed in multiple layers, bringing
5110   about the same problem discussed above.
5111</t>
5112<t>
5113   As a result, clients are encouraged not to send the Proxy-Connection header
5114   field in any requests.
5115</t>
5116<t>
5117   Clients are also encouraged to consider the use of Connection: keep-alive
5118   in requests carefully; while they can enable persistent connections with
5119   HTTP/1.0 servers, clients using them will need to monitor the
5120   connection for "hung" requests (which indicate that the client ought stop
5121   sending the header field), and this mechanism ought not be used by clients
5122   at all when a proxy is being used.
5123</t>
5124</section>
5125
5126<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
5127<t>
5128   HTTP/1.1 introduces the <x:ref>Transfer-Encoding</x:ref> header field
5129   (<xref target="header.transfer-encoding"/>).
5130   Transfer codings need to be decoded prior to forwarding an HTTP message
5131   over a MIME-compliant protocol.
5132</t>
5133</section>
5134
5135</section>
5136
5137<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
5138<t>
5139  HTTP's approach to error handling has been explained.
5140  (<xref target="conformance" />)
5141</t>
5142<t>
5143  The HTTP-version ABNF production has been clarified to be case-sensitive.
5144  Additionally, version numbers has been restricted to single digits, due
5145  to the fact that implementations are known to handle multi-digit version
5146  numbers incorrectly.
5147  (<xref target="http.version"/>)
5148</t>
5149<t>
5150  Userinfo (i.e., username and password) are now disallowed in HTTP and
5151  HTTPS URIs, because of security issues related to their transmission on the
5152  wire.
5153  (<xref target="http.uri" />)
5154</t>
5155<t>
5156  The HTTPS URI scheme is now defined by this specification; previously,
5157  it was done in  <xref target="RFC2818" x:fmt="of" x:sec="2.4"/>.
5158  Furthermore, it implies end-to-end security.
5159  (<xref target="https.uri"/>)
5160</t>
5161<t>
5162  HTTP messages can be (and often are) buffered by implementations; despite
5163  it sometimes being available as a stream, HTTP is fundamentally a
5164  message-oriented protocol.
5165  Minimum supported sizes for various protocol elements have been
5166  suggested, to improve interoperability.
5167  (<xref target="http.message" />)
5168</t>
5169<t>
5170  Invalid whitespace around field-names is now required to be rejected,
5171  because accepting it represents a security vulnerability.
5172  The ABNF productions defining header fields now only list the field value.
5173  (<xref target="header.fields"/>)
5174</t>
5175<t>
5176  Rules about implicit linear whitespace between certain grammar productions
5177  have been removed; now whitespace is only allowed where specifically
5178  defined in the ABNF.
5179  (<xref target="whitespace"/>)
5180</t>
5181<t>
5182  Header fields that span multiple lines ("line folding") are deprecated.
5183  (<xref target="field.parsing" />)
5184</t>
5185<t> 
5186  The NUL octet is no longer allowed in comment and quoted-string text, and
5187  handling of backslash-escaping in them has been clarified.
5188  The quoted-pair rule no longer allows escaping control characters other than
5189  HTAB.
5190  Non-ASCII content in header fields and the reason phrase has been obsoleted
5191  and made opaque (the TEXT rule was removed).
5192  (<xref target="field.components"/>)
5193</t> 
5194<t>
5195  Bogus "<x:ref>Content-Length</x:ref>" header fields are now required to be
5196  handled as errors by recipients.
5197  (<xref target="header.content-length"/>)
5198</t>
5199<t>
5200  The algorithm for determining the message body length has been clarified
5201  to indicate all of the special cases (e.g., driven by methods or status
5202  codes) that affect it, and that new protocol elements cannot define such
5203  special cases.
5204  CONNECT is a new, special case in determining message body length.
5205  "multipart/byteranges" is no longer a way of determining message body length
5206  detection.
5207  (<xref target="message.body.length"/>)
5208</t>
5209<t>
5210  The "identity" transfer coding token has been removed.
5211  (Sections <xref format="counter" target="message.body"/> and
5212  <xref format="counter" target="transfer.codings"/>)
5213</t>
5214<t>
5215  Chunk length does not include the count of the octets in the
5216  chunk header and trailer.
5217  Line folding in chunk extensions is  disallowed.
5218  (<xref target="chunked.encoding"/>)
5219</t>
5220<t>
5221  The meaning of the "deflate" content coding has been clarified.
5222  (<xref target="deflate.coding" />)
5223</t>
5224<t>
5225  The segment + query components of RFC 3986 have been used to define the
5226  request-target, instead of abs_path from RFC 1808.
5227  The asterisk-form of the request-target is only allowed with the OPTIONS
5228  method.
5229  (<xref target="request-target"/>)
5230</t>
5231<t>
5232  The term "Effective Request URI" has been introduced.
5233  (<xref target="effective.request.uri" />)
5234</t>
5235<t>
5236  Gateways do not need to generate <x:ref>Via</x:ref> header fields anymore.
5237  (<xref target="header.via"/>)
5238</t>
5239<t>
5240  Exactly when "close" connection options have to be sent has been clarified.
5241  Also, "hop-by-hop" header fields are required to appear in the Connection header
5242  field; just because they're defined as hop-by-hop in this specification
5243  doesn't exempt them.
5244  (<xref target="header.connection"/>)
5245</t>
5246<t>
5247  The limit of two connections per server has been removed.
5248  An idempotent sequence of requests is no longer required to be retried.
5249  The requirement to retry requests under certain circumstances when the
5250  server prematurely closes the connection has been removed.
5251  Also, some extraneous requirements about when servers are allowed to close
5252  connections prematurely have been removed.
5253  (<xref target="persistent.connections"/>)
5254</t>
5255<t>
5256  The semantics of the <x:ref>Upgrade</x:ref> header field is now defined in
5257  responses other than 101 (this was incorporated from <xref
5258  target="RFC2817"/>). Furthermore, the ordering in the field value is now
5259  significant.
5260  (<xref target="header.upgrade"/>)
5261</t>
5262<t>
5263  Empty list elements in list productions (e.g., a list header field containing
5264  ", ,") have been deprecated.
5265  (<xref target="abnf.extension"/>)
5266</t>
5267<t>
5268  Registration of Transfer Codings now requires IETF Review
5269  (<xref target="transfer.coding.registry"/>)
5270</t>
5271<t>
5272  This specification now defines the Upgrade Token Registry, previously
5273  defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
5274  (<xref target="upgrade.token.registry"/>)
5275</t>
5276<t>
5277  The expectation to support HTTP/0.9 requests has been removed.
5278  (<xref target="compatibility"/>)
5279</t>
5280<t>
5281  Issues with the Keep-Alive and Proxy-Connection header fields in requests
5282  are pointed out, with use of the latter being discouraged altogether.
5283  (<xref target="compatibility.with.http.1.0.persistent.connections" />)
5284</t>
5285</section>
5286</section>
5287
5288<?BEGININC p1-messaging.abnf-appendix ?>
5289<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
5290<figure>
5291<artwork type="abnf" name="p1-messaging.parsed-abnf">
5292<x:ref>BWS</x:ref> = OWS
5293
5294<x:ref>Connection</x:ref> = *( "," OWS ) connection-option *( OWS "," [ OWS
5295 connection-option ] )
5296<x:ref>Content-Length</x:ref> = 1*DIGIT
5297
5298<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5299 ]
5300<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
5301<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
5302<x:ref>Host</x:ref> = uri-host [ ":" port ]
5303
5304<x:ref>OWS</x:ref> = *( SP / HTAB )
5305
5306<x:ref>RWS</x:ref> = 1*( SP / HTAB )
5307
5308<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5309<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5310<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5311 transfer-coding ] )
5312
5313<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5314<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
5315
5316<x:ref>Via</x:ref> = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment
5317 ] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS
5318 comment ] ) ] )
5319
5320<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5321<x:ref>absolute-form</x:ref> = absolute-URI
5322<x:ref>absolute-path</x:ref> = 1*( "/" segment )
5323<x:ref>asterisk-form</x:ref> = "*"
5324<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5325<x:ref>authority-form</x:ref> = authority
5326
5327<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5328<x:ref>chunk-data</x:ref> = 1*OCTET
5329<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5330<x:ref>chunk-ext-name</x:ref> = token
5331<x:ref>chunk-ext-val</x:ref> = token / quoted-string
5332<x:ref>chunk-size</x:ref> = 1*HEXDIG
5333<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
5334<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
5335<x:ref>connection-option</x:ref> = token
5336<x:ref>ctext</x:ref> = HTAB / SP / %x21-27 ; '!'-'''
5337 / %x2A-5B ; '*'-'['
5338 / %x5D-7E ; ']'-'~'
5339 / obs-text
5340
5341<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5342<x:ref>field-name</x:ref> = token
5343<x:ref>field-value</x:ref> = *( field-content / obs-fold )
5344<x:ref>fragment</x:ref> = &lt;fragment, defined in [RFC3986], Section 3.5&gt;
5345
5346<x:ref>header-field</x:ref> = field-name ":" OWS field-value OWS
5347<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ] [ "#"
5348 fragment ]
5349<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ] [ "#"
5350 fragment ]
5351
5352<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
5353
5354<x:ref>message-body</x:ref> = *OCTET
5355<x:ref>method</x:ref> = token
5356
5357<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
5358<x:ref>obs-text</x:ref> = %x80-FF
5359<x:ref>origin-form</x:ref> = absolute-path [ "?" query ]
5360
5361<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5362<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5363<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5364<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
5365<x:ref>protocol-name</x:ref> = token
5366<x:ref>protocol-version</x:ref> = token
5367<x:ref>pseudonym</x:ref> = token
5368
5369<x:ref>qdtext</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
5370 / %x5D-7E ; ']'-'~'
5371 / obs-text
5372<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5373<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5374<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5375
5376<x:ref>rank</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5377<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5378<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5379<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5380<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5381<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
5382<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
5383 asterisk-form
5384
5385<x:ref>segment</x:ref> = &lt;segment, defined in [RFC3986], Section 3.3&gt;
5386<x:ref>start-line</x:ref> = request-line / status-line
5387<x:ref>status-code</x:ref> = 3DIGIT
5388<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
5389
5390<x:ref>t-codings</x:ref> = "trailers" / ( transfer-coding [ t-ranking ] )
5391<x:ref>t-ranking</x:ref> = OWS ";" OWS "q=" rank
5392<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5393 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5394<x:ref>token</x:ref> = 1*tchar
5395<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5396<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5397 transfer-extension
5398<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5399<x:ref>transfer-parameter</x:ref> = token BWS "=" BWS ( token / quoted-string )
5400
5401<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5402</artwork>
5403</figure>
5404</section>
5405<?ENDINC p1-messaging.abnf-appendix ?>
5406
5407<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5408
5409<section title="Since RFC 2616">
5410<t>
5411  Changes up to the IETF Last Call draft are summarized
5412  in <eref target="http://trac.tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-24#appendix-C"/>.
5413</t>
5414</section>
5415
5416<section title="Since draft-ietf-httpbis-p1-messaging-24" anchor="changes.since.24">
5417<t>
5418  Closed issues:
5419  <list style="symbols">
5420    <t>
5421      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/502"/>:
5422      "APPSDIR review of draft-ietf-httpbis-p1-messaging-24"
5423    </t>
5424    <t>
5425      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/507"/>:
5426      "integer value parsing"
5427    </t>
5428    <t>
5429      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/517"/>:
5430      "move IANA registrations to correct draft"
5431    </t>
5432  </list>
5433</t>
5434</section>
5435
5436<section title="Since draft-ietf-httpbis-p1-messaging-25" anchor="changes.since.25">
5437<t>
5438  Closed issues:
5439  <list style="symbols">
5440    <t>
5441      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/526"/>:
5442      "check media type registration templates"
5443    </t>
5444    <t>
5445      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/528"/>:
5446      "Redundant rule quoted-str-nf"
5447    </t>
5448    <t>
5449      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/540"/>:
5450      "clarify ABNF layering"
5451    </t>
5452    <t>
5453      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/541"/>:
5454      "use of 'word' ABNF production"
5455    </t>
5456    <t>
5457      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/542"/>:
5458      "improve introduction of list rule"
5459    </t>
5460    <t>
5461      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/544"/>:
5462      "moving 2616/2068/2145 to historic"
5463    </t>
5464  </list>
5465</t>
5466</section>
5467</section>
5468
5469</back>
5470</rfc>
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