source: draft-ietf-httpbis/latest/p1-messaging.xml @ 2527

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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 and moves to historic status
161   <xref target="RFC2616" x:fmt="none">RFC 2616</xref>, its predecessor
162   <xref target="RFC2068" x:fmt="none">RFC 2068</xref>, and
163   <xref target="RFC2145" x:fmt="none">RFC 2145</xref> (on HTTP versioning).
164   This specification also updates the use of CONNECT to establish a tunnel,
165   previously defined in <xref target="RFC2817" x:fmt="none">RFC 2817</xref>,
166   and defines the "https" URI scheme that was described informally in
167   <xref target="RFC2818" x:fmt="none">RFC 2818</xref>.
168</t>
169<t>
170   HTTP is a generic interface protocol for information systems. It is
171   designed to hide the details of how a service is implemented by presenting
172   a uniform interface to clients that is independent of the types of
173   resources provided. Likewise, servers do not need to be aware of each
174   client's purpose: an HTTP request can be considered in isolation rather
175   than being associated with a specific type of client or a predetermined
176   sequence of application steps. The result is a protocol that can be used
177   effectively in many different contexts and for which implementations can
178   evolve independently over time.
179</t>
180<t>
181   HTTP is also designed for use as an intermediation protocol for translating
182   communication to and from non-HTTP information systems.
183   HTTP proxies and gateways can provide access to alternative information
184   services by translating their diverse protocols into a hypertext
185   format that can be viewed and manipulated by clients in the same way
186   as HTTP services.
187</t>
188<t>
189   One consequence of this flexibility is that the protocol cannot be
190   defined in terms of what occurs behind the interface. Instead, we
191   are limited to defining the syntax of communication, the intent
192   of received communication, and the expected behavior of recipients.
193   If the communication is considered in isolation, then successful
194   actions ought to be reflected in corresponding changes to the
195   observable interface provided by servers. However, since multiple
196   clients might act in parallel and perhaps at cross-purposes, we
197   cannot require that such changes be observable beyond the scope
198   of a single response.
199</t>
200<t>
201   This document describes the architectural elements that are used or
202   referred to in HTTP, defines the "http" and "https" URI schemes,
203   describes overall network operation and connection management,
204   and defines HTTP message framing and forwarding requirements.
205   Our goal is to define all of the mechanisms necessary for HTTP message
206   handling that are independent of message semantics, thereby defining the
207   complete set of requirements for message parsers and
208   message-forwarding intermediaries.
209</t>
210
211
212<section title="Requirement Notation" anchor="intro.requirements">
213<t>
214   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
215   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
216   document are to be interpreted as described in <xref target="RFC2119"/>.
217</t>
218<t>
219   Conformance criteria and considerations regarding error handling
220   are defined in <xref target="conformance"/>.
221</t>
222</section>
223
224<section title="Syntax Notation" anchor="notation">
225<iref primary="true" item="Grammar" subitem="ALPHA"/>
226<iref primary="true" item="Grammar" subitem="CR"/>
227<iref primary="true" item="Grammar" subitem="CRLF"/>
228<iref primary="true" item="Grammar" subitem="CTL"/>
229<iref primary="true" item="Grammar" subitem="DIGIT"/>
230<iref primary="true" item="Grammar" subitem="DQUOTE"/>
231<iref primary="true" item="Grammar" subitem="HEXDIG"/>
232<iref primary="true" item="Grammar" subitem="HTAB"/>
233<iref primary="true" item="Grammar" subitem="LF"/>
234<iref primary="true" item="Grammar" subitem="OCTET"/>
235<iref primary="true" item="Grammar" subitem="SP"/>
236<iref primary="true" item="Grammar" subitem="VCHAR"/>
237<t>
238   This specification uses the Augmented Backus-Naur Form (ABNF) notation of
239   <xref target="RFC5234"/> with an extension defined in
240   <xref target="abnf.extension"/> that adds compact support for
241   comma-separated lists with the addition of a '#' operator, similar to the '*'
242   operator.
243   <xref target="collected.abnf"/> shows the collected ABNF with the rules using
244   the list operator expanded to standard ABNF notation.
245</t>
246<t anchor="core.rules">
247  <x:anchor-alias value="ALPHA"/>
248  <x:anchor-alias value="CTL"/>
249  <x:anchor-alias value="CR"/>
250  <x:anchor-alias value="CRLF"/>
251  <x:anchor-alias value="DIGIT"/>
252  <x:anchor-alias value="DQUOTE"/>
253  <x:anchor-alias value="HEXDIG"/>
254  <x:anchor-alias value="HTAB"/>
255  <x:anchor-alias value="LF"/>
256  <x:anchor-alias value="OCTET"/>
257  <x:anchor-alias value="SP"/>
258  <x:anchor-alias value="VCHAR"/>
259   The following core rules are included by
260   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
261   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
262   DIGIT (decimal 0-9), DQUOTE (double quote),
263   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
264   OCTET (any 8-bit sequence of data), SP (space), and
265   VCHAR (any visible <xref target="USASCII"/> character).
266</t>
267<t>
268   As a convention, ABNF rule names prefixed with "obs-" denote
269   "obsolete" grammar rules that appear for historical reasons.
270</t>
271</section>
272</section>
273
274<section title="Architecture" anchor="architecture">
275<t>
276   HTTP was created for the World Wide Web architecture
277   and has evolved over time to support the scalability needs of a worldwide
278   hypertext system. Much of that architecture is reflected in the terminology
279   and syntax productions used to define HTTP.
280</t>
281
282<section title="Client/Server Messaging" anchor="operation">
283<iref primary="true" item="client"/>
284<iref primary="true" item="server"/>
285<iref primary="true" item="connection"/>
286<t>
287   HTTP is a stateless request/response protocol that operates by exchanging
288   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
289   transport or session-layer
290   "<x:dfn>connection</x:dfn>" (<xref target="connection.management"/>).
291   An HTTP "<x:dfn>client</x:dfn>" is a program that establishes a connection
292   to a server for the purpose of sending one or more HTTP requests.
293   An HTTP "<x:dfn>server</x:dfn>" is a program that accepts connections
294   in order to service HTTP requests by sending HTTP responses.
295</t>
296<iref primary="true" item="user agent"/>
297<iref primary="true" item="origin server"/>
298<iref primary="true" item="browser"/>
299<iref primary="true" item="spider"/>
300<iref primary="true" item="sender"/>
301<iref primary="true" item="recipient"/>
302<t>
303   The terms client and server refer only to the roles that
304   these programs perform for a particular connection.  The same program
305   might act as a client on some connections and a server on others.
306   We use the term "<x:dfn>user agent</x:dfn>" to refer to any of the various
307   client programs that initiate a request, including (but not limited to)
308   browsers, spiders (web-based robots), command-line tools, native
309   applications, and mobile apps.  The term "<x:dfn>origin server</x:dfn>" is
310   used to refer to the program that can originate authoritative responses to
311   a request. For general requirements, we use the terms
312   "<x:dfn>sender</x:dfn>" and "<x:dfn>recipient</x:dfn>" to refer to any
313   component that sends or receives, respectively, a given message.
314</t>
315<t>
316   HTTP relies upon the Uniform Resource Identifier (URI)
317   standard <xref target="RFC3986"/> to indicate the target resource
318   (<xref target="target-resource"/>) and relationships between resources.
319   Messages are passed in a format similar to that used by Internet mail
320   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
321   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
322   between HTTP and MIME messages).
323</t>
324<t>
325   Most HTTP communication consists of a retrieval request (GET) for
326   a representation of some resource identified by a URI.  In the
327   simplest case, this might be accomplished via a single bidirectional
328   connection (===) between the user agent (UA) and the origin server (O).
329</t>
330<figure><artwork type="drawing">
331         request   &gt;
332    <x:highlight>UA</x:highlight> ======================================= <x:highlight>O</x:highlight>
333                                &lt;   response
334</artwork></figure>
335<iref primary="true" item="message"/>
336<iref primary="true" item="request"/>
337<iref primary="true" item="response"/>
338<t>
339   A client sends an HTTP request to a server in the form of a <x:dfn>request</x:dfn>
340   message, beginning with a request-line that includes a method, URI, and
341   protocol version (<xref target="request.line"/>),
342   followed by header fields containing
343   request modifiers, client information, and representation metadata
344   (<xref target="header.fields"/>),
345   an empty line to indicate the end of the header section, and finally
346   a message body containing the payload body (if any,
347   <xref target="message.body"/>).
348</t>
349<t>
350   A server responds to a client's request by sending one or more HTTP
351   <x:dfn>response</x:dfn>
352   messages, each beginning with a status line that
353   includes the protocol version, a success or error code, and textual
354   reason phrase (<xref target="status.line"/>),
355   possibly followed by header fields containing server
356   information, resource metadata, and representation metadata
357   (<xref target="header.fields"/>),
358   an empty line to indicate the end of the header section, and finally
359   a message body containing the payload body (if any,
360   <xref target="message.body"/>).
361</t>
362<t>
363   A connection might be used for multiple request/response exchanges,
364   as defined in <xref target="persistent.connections"/>.
365</t>
366<t>
367   The following example illustrates a typical message exchange for a
368   GET request on the URI "http://www.example.com/hello.txt":
369</t>
370<figure><preamble>
371Client request:
372</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
373GET /hello.txt HTTP/1.1
374User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
375Host: www.example.com
376Accept-Language: en, mi
377
378</artwork></figure>
379<figure><preamble>
380Server response:
381</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
382HTTP/1.1 200 OK
383Date: Mon, 27 Jul 2009 12:28:53 GMT
384Server: Apache
385Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
386ETag: "34aa387-d-1568eb00"
387Accept-Ranges: bytes
388Content-Length: <x:length-of target="exbody"/>
389Vary: Accept-Encoding
390Content-Type: text/plain
391
392<x:span anchor="exbody">Hello World! My payload includes a trailing CRLF.
393</x:span></artwork>
394</figure>
395</section>
396
397<section title="Implementation Diversity" anchor="implementation-diversity">
398<t>
399   When considering the design of HTTP, it is easy to fall into a trap of
400   thinking that all user agents are general-purpose browsers and all origin
401   servers are large public websites. That is not the case in practice.
402   Common HTTP user agents include household appliances, stereos, scales,
403   firmware update scripts, command-line programs, mobile apps,
404   and communication devices in a multitude of shapes and sizes.  Likewise,
405   common HTTP origin servers include home automation units, configurable
406   networking components, office machines, autonomous robots, news feeds,
407   traffic cameras, ad selectors, and video delivery platforms.
408</t>
409<t>
410   The term "user agent" does not imply that there is a human user directly
411   interacting with the software agent at the time of a request. In many
412   cases, a user agent is installed or configured to run in the background
413   and save its results for later inspection (or save only a subset of those
414   results that might be interesting or erroneous). Spiders, for example, are
415   typically given a start URI and configured to follow certain behavior while
416   crawling the Web as a hypertext graph.
417</t>
418<t>
419   The implementation diversity of HTTP means that we cannot assume the
420   user agent can make interactive suggestions to a user or provide adequate
421   warning for security or privacy options.  In the few cases where this
422   specification requires reporting of errors to the user, it is acceptable
423   for such reporting to only be observable in an error console or log file.
424   Likewise, requirements that an automated action be confirmed by the user
425   before proceeding might be met via advance configuration choices,
426   run-time options, or simple avoidance of the unsafe action; confirmation
427   does not imply any specific user interface or interruption of normal
428   processing if the user has already made that choice.
429</t>
430</section>
431
432<section title="Intermediaries" anchor="intermediaries">
433<iref primary="true" item="intermediary"/>
434<t>
435   HTTP enables the use of intermediaries to satisfy requests through
436   a chain of connections.  There are three common forms of HTTP
437   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
438   a single intermediary might act as an origin server, proxy, gateway,
439   or tunnel, switching behavior based on the nature of each request.
440</t>
441<figure><artwork type="drawing">
442         &gt;             &gt;             &gt;             &gt;
443    <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>
444               &lt;             &lt;             &lt;             &lt;
445</artwork></figure>
446<t>
447   The figure above shows three intermediaries (A, B, and C) between the
448   user agent and origin server. A request or response message that
449   travels the whole chain will pass through four separate connections.
450   Some HTTP communication options
451   might apply only to the connection with the nearest, non-tunnel
452   neighbor, only to the end-points of the chain, or to all connections
453   along the chain. Although the diagram is linear, each participant might
454   be engaged in multiple, simultaneous communications. For example, B
455   might be receiving requests from many clients other than A, and/or
456   forwarding requests to servers other than C, at the same time that it
457   is handling A's request. Likewise, later requests might be sent through a
458   different path of connections, often based on dynamic configuration for
459   load balancing.   
460</t>
461<t>
462<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
463<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
464   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
465   to describe various requirements in relation to the directional flow of a
466   message: all messages flow from upstream to downstream.
467   Likewise, we use the terms inbound and outbound to refer to
468   directions in relation to the request path:
469   "<x:dfn>inbound</x:dfn>" means toward the origin server and
470   "<x:dfn>outbound</x:dfn>" means toward the user agent.
471</t>
472<t><iref primary="true" item="proxy"/>
473   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
474   client, usually via local configuration rules, to receive requests
475   for some type(s) of absolute URI and attempt to satisfy those
476   requests via translation through the HTTP interface.  Some translations
477   are minimal, such as for proxy requests for "http" URIs, whereas
478   other requests might require translation to and from entirely different
479   application-level protocols. Proxies are often used to group an
480   organization's HTTP requests through a common intermediary for the
481   sake of security, annotation services, or shared caching.
482</t>
483<t>
484<iref primary="true" item="transforming proxy"/>
485<iref primary="true" item="non-transforming proxy"/>
486   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
487   or configured to modify request or response messages in a semantically
488   meaningful way (i.e., modifications, beyond those required by normal
489   HTTP processing, that change the message in a way that would be
490   significant to the original sender or potentially significant to
491   downstream recipients).  For example, a transforming proxy might be
492   acting as a shared annotation server (modifying responses to include
493   references to a local annotation database), a malware filter, a
494   format transcoder, or an intranet-to-Internet privacy filter.  Such
495   transformations are presumed to be desired by the client (or client
496   organization) that selected the proxy and are beyond the scope of
497   this specification.  However, when a proxy is not intended to transform
498   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
499   requirements that preserve HTTP message semantics. See &status-203; and
500   &header-warning; for status and warning codes related to transformations.
501</t>
502<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
503<iref primary="true" item="accelerator"/>
504   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>") is an
505   intermediary that acts as an origin server for the outbound connection, but
506   translates received requests and forwards them inbound to another server or
507   servers. Gateways are often used to encapsulate legacy or untrusted
508   information services, to improve server performance through
509   "<x:dfn>accelerator</x:dfn>" caching, and to enable partitioning or load
510   balancing of HTTP services across multiple machines.
511</t>
512<t>
513   All HTTP requirements applicable to an origin server
514   also apply to the outbound communication of a gateway.
515   A gateway communicates with inbound servers using any protocol that
516   it desires, including private extensions to HTTP that are outside
517   the scope of this specification.  However, an HTTP-to-HTTP gateway
518   that wishes to interoperate with third-party HTTP servers ought to conform
519   to user agent requirements on the gateway's inbound connection.
520</t>
521<t><iref primary="true" item="tunnel"/>
522   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
523   without changing the messages. Once active, a tunnel is not
524   considered a party to the HTTP communication, though the tunnel might
525   have been initiated by an HTTP request. A tunnel ceases to exist when
526   both ends of the relayed connection are closed. Tunnels are used to
527   extend a virtual connection through an intermediary, such as when
528   Transport Layer Security (TLS, <xref target="RFC5246"/>) is used to
529   establish confidential communication through a shared firewall proxy.
530</t>
531<t><iref primary="true" item="interception proxy"/>
532<iref primary="true" item="transparent proxy"/>
533<iref primary="true" item="captive portal"/>
534   The above categories for intermediary only consider those acting as
535   participants in the HTTP communication.  There are also intermediaries
536   that can act on lower layers of the network protocol stack, filtering or
537   redirecting HTTP traffic without the knowledge or permission of message
538   senders. Network intermediaries often introduce security flaws or
539   interoperability problems by violating HTTP semantics.  For example, an
540   "<x:dfn>interception proxy</x:dfn>" <xref target="RFC3040"/> (also commonly
541   known as a "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/> or
542   "<x:dfn>captive portal</x:dfn>")
543   differs from an HTTP proxy because it is not selected by the client.
544   Instead, an interception proxy filters or redirects outgoing TCP port 80
545   packets (and occasionally other common port traffic).
546   Interception proxies are commonly found on public network access points,
547   as a means of enforcing account subscription prior to allowing use of
548   non-local Internet services, and within corporate firewalls to enforce
549   network usage policies.
550   They are indistinguishable from a man-in-the-middle attack.
551</t>
552<t>
553   HTTP is defined as a stateless protocol, meaning that each request message
554   can be understood in isolation.  Many implementations depend on HTTP's
555   stateless design in order to reuse proxied connections or dynamically
556   load-balance requests across multiple servers.  Hence, a server &MUST-NOT;
557   assume that two requests on the same connection are from the same user
558   agent unless the connection is secured and specific to that agent.
559   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
560   been known to violate this requirement, resulting in security and
561   interoperability problems.
562</t>
563</section>
564
565<section title="Caches" anchor="caches">
566<iref primary="true" item="cache"/>
567<t>
568   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
569   subsystem that controls its message storage, retrieval, and deletion.
570   A cache stores cacheable responses in order to reduce the response
571   time and network bandwidth consumption on future, equivalent
572   requests. Any client or server &MAY; employ a cache, though a cache
573   cannot be used by a server while it is acting as a tunnel.
574</t>
575<t>
576   The effect of a cache is that the request/response chain is shortened
577   if one of the participants along the chain has a cached response
578   applicable to that request. The following illustrates the resulting
579   chain if B has a cached copy of an earlier response from O (via C)
580   for a request that has not been cached by UA or A.
581</t>
582<figure><artwork type="drawing">
583            &gt;             &gt;
584       <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>
585                  &lt;             &lt;
586</artwork></figure>
587<t><iref primary="true" item="cacheable"/>
588   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
589   the response message for use in answering subsequent requests.
590   Even when a response is cacheable, there might be additional
591   constraints placed by the client or by the origin server on when
592   that cached response can be used for a particular request. HTTP
593   requirements for cache behavior and cacheable responses are
594   defined in &caching-overview;. 
595</t>
596<t>
597   There are a wide variety of architectures and configurations
598   of caches deployed across the World Wide Web and
599   inside large organizations. These include national hierarchies
600   of proxy caches to save transoceanic bandwidth, collaborative systems that
601   broadcast or multicast cache entries, archives of pre-fetched cache
602   entries for use in off-line or high-latency environments, and so on.
603</t>
604</section>
605
606<section title="Conformance and Error Handling" anchor="conformance">
607<t>
608   This specification targets conformance criteria according to the role of
609   a participant in HTTP communication.  Hence, HTTP requirements are placed
610   on senders, recipients, clients, servers, user agents, intermediaries,
611   origin servers, proxies, gateways, or caches, depending on what behavior
612   is being constrained by the requirement. Additional (social) requirements
613   are placed on implementations, resource owners, and protocol element
614   registrations when they apply beyond the scope of a single communication.
615</t>
616<t>
617   The verb "generate" is used instead of "send" where a requirement
618   differentiates between creating a protocol element and merely forwarding a
619   received element downstream.
620</t>
621<t>
622   An implementation is considered conformant if it complies with all of the
623   requirements associated with the roles it partakes in HTTP.
624</t>
625<t>
626   Conformance includes both the syntax and semantics of protocol
627   elements. A sender &MUST-NOT; generate protocol elements that convey a
628   meaning that is known by that sender to be false. A sender &MUST-NOT;
629   generate protocol elements that do not match the grammar defined by the
630   corresponding ABNF rules. Within a given message, a sender &MUST-NOT;
631   generate protocol elements or syntax alternatives that are only allowed to
632   be generated by participants in other roles (i.e., a role that the sender
633   does not have for that message).
634</t>
635<t>
636   When a received protocol element is parsed, the recipient &MUST; be able to
637   parse any value of reasonable length that is applicable to the recipient's
638   role and matches the grammar defined by the corresponding ABNF rules.
639   Note, however, that some received protocol elements might not be parsed.
640   For example, an intermediary forwarding a message might parse a
641   header-field into generic field-name and field-value components, but then
642   forward the header field without further parsing inside the field-value.
643</t>
644<t>
645   HTTP does not have specific length limitations for many of its protocol
646   elements because the lengths that might be appropriate will vary widely,
647   depending on the deployment context and purpose of the implementation.
648   Hence, interoperability between senders and recipients depends on shared
649   expectations regarding what is a reasonable length for each protocol
650   element. Furthermore, what is commonly understood to be a reasonable length
651   for some protocol elements has changed over the course of the past two
652   decades of HTTP use, and is expected to continue changing in the future.
653</t>
654<t>
655   At a minimum, a recipient &MUST; be able to parse and process protocol
656   element lengths that are at least as long as the values that it generates
657   for those same protocol elements in other messages. For example, an origin
658   server that publishes very long URI references to its own resources needs
659   to be able to parse and process those same references when received as a
660   request target.
661</t>
662<t>
663   A recipient &MUST; interpret a received protocol element according to the
664   semantics defined for it by this specification, including extensions to
665   this specification, unless the recipient has determined (through experience
666   or configuration) that the sender incorrectly implements what is implied by
667   those semantics.
668   For example, an origin server might disregard the contents of a received
669   <x:ref>Accept-Encoding</x:ref> header field if inspection of the
670   <x:ref>User-Agent</x:ref> header field indicates a specific implementation
671   version that is known to fail on receipt of certain content codings.
672</t>
673<t>
674   Unless noted otherwise, a recipient &MAY; attempt to recover a usable
675   protocol element from an invalid construct.  HTTP does not define
676   specific error handling mechanisms except when they have a direct impact
677   on security, since different applications of the protocol require
678   different error handling strategies.  For example, a Web browser might
679   wish to transparently recover from a response where the
680   <x:ref>Location</x:ref> header field doesn't parse according to the ABNF,
681   whereas a systems control client might consider any form of error recovery
682   to be dangerous.
683</t>
684</section>
685
686<section title="Protocol Versioning" anchor="http.version">
687  <x:anchor-alias value="HTTP-version"/>
688  <x:anchor-alias value="HTTP-name"/>
689<t>
690   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
691   versions of the protocol. This specification defines version "1.1".
692   The protocol version as a whole indicates the sender's conformance
693   with the set of requirements laid out in that version's corresponding
694   specification of HTTP.
695</t>
696<t>
697   The version of an HTTP message is indicated by an HTTP-version field
698   in the first line of the message. HTTP-version is case-sensitive.
699</t>
700<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/>
701  <x:ref>HTTP-version</x:ref>  = <x:ref>HTTP-name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
702  <x:ref>HTTP-name</x:ref>     = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
703</artwork></figure>
704<t>
705   The HTTP version number consists of two decimal digits separated by a "."
706   (period or decimal point).  The first digit ("major version") indicates the
707   HTTP messaging syntax, whereas the second digit ("minor version") indicates
708   the highest minor version within that major version to which the sender is
709   conformant and able to understand for future communication.  The minor
710   version advertises the sender's communication capabilities even when the
711   sender is only using a backwards-compatible subset of the protocol,
712   thereby letting the recipient know that more advanced features can
713   be used in response (by servers) or in future requests (by clients).
714</t>
715<t>
716   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
717   <xref target="RFC1945"/> or a recipient whose version is unknown,
718   the HTTP/1.1 message is constructed such that it can be interpreted
719   as a valid HTTP/1.0 message if all of the newer features are ignored.
720   This specification places recipient-version requirements on some
721   new features so that a conformant sender will only use compatible
722   features until it has determined, through configuration or the
723   receipt of a message, that the recipient supports HTTP/1.1.
724</t>
725<t>
726   The interpretation of a header field does not change between minor
727   versions of the same major HTTP version, though the default
728   behavior of a recipient in the absence of such a field can change.
729   Unless specified otherwise, header fields defined in HTTP/1.1 are
730   defined for all versions of HTTP/1.x.  In particular, the <x:ref>Host</x:ref>
731   and <x:ref>Connection</x:ref> header fields ought to be implemented by all
732   HTTP/1.x implementations whether or not they advertise conformance with
733   HTTP/1.1.
734</t>
735<t>
736   New header fields can be introduced without changing the protocol version
737   if their defined semantics allow them to be safely ignored by recipients
738   that do not recognize them. Header field extensibility is discussed in
739   <xref target="field.extensibility"/>.
740</t>
741<t>
742   Intermediaries that process HTTP messages (i.e., all intermediaries
743   other than those acting as tunnels) &MUST; send their own HTTP-version
744   in forwarded messages.  In other words, they are not allowed to blindly
745   forward the first line of an HTTP message without ensuring that the
746   protocol version in that message matches a version to which that
747   intermediary is conformant for both the receiving and
748   sending of messages.  Forwarding an HTTP message without rewriting
749   the HTTP-version might result in communication errors when downstream
750   recipients use the message sender's version to determine what features
751   are safe to use for later communication with that sender.
752</t>
753<t>
754   A client &SHOULD; send a request version equal to the highest
755   version to which the client is conformant and
756   whose major version is no higher than the highest version supported
757   by the server, if this is known.  A client &MUST-NOT; send a
758   version to which it is not conformant.
759</t>
760<t>
761   A client &MAY; send a lower request version if it is known that
762   the server incorrectly implements the HTTP specification, but only
763   after the client has attempted at least one normal request and determined
764   from the response status code or header fields (e.g., <x:ref>Server</x:ref>) that
765   the server improperly handles higher request versions.
766</t>
767<t>
768   A server &SHOULD; send a response version equal to the highest version to
769   which the server is conformant that has a major version less than or equal
770   to the one received in the request.
771   A server &MUST-NOT; send a version to which it is not conformant.
772   A server can send a <x:ref>505 (HTTP Version Not Supported)</x:ref>
773   response if it wishes, for any reason, to refuse service of the client's
774   major protocol version.
775</t>
776<t>
777   A server &MAY; send an HTTP/1.0 response to a request
778   if it is known or suspected that the client incorrectly implements the
779   HTTP specification and is incapable of correctly processing later
780   version responses, such as when a client fails to parse the version
781   number correctly or when an intermediary is known to blindly forward
782   the HTTP-version even when it doesn't conform to the given minor
783   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
784   performed unless triggered by specific client attributes, such as when
785   one or more of the request header fields (e.g., <x:ref>User-Agent</x:ref>)
786   uniquely match the values sent by a client known to be in error.
787</t>
788<t>
789   The intention of HTTP's versioning design is that the major number
790   will only be incremented if an incompatible message syntax is
791   introduced, and that the minor number will only be incremented when
792   changes made to the protocol have the effect of adding to the message
793   semantics or implying additional capabilities of the sender.  However,
794   the minor version was not incremented for the changes introduced between
795   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
796   has specifically avoided any such changes to the protocol.
797</t>
798<t>
799   When an HTTP message is received with a major version number that the
800   recipient implements, but a higher minor version number than what the
801   recipient implements, the recipient &SHOULD; process the message as if it
802   were in the highest minor version within that major version to which the
803   recipient is conformant. A recipient can assume that a message with a
804   higher minor version, when sent to a recipient that has not yet indicated
805   support for that higher version, is sufficiently backwards-compatible to be
806   safely processed by any implementation of the same major version.
807</t>
808</section>
809
810<section title="Uniform Resource Identifiers" anchor="uri">
811<iref primary="true" item="resource"/>
812<t>
813   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
814   throughout HTTP as the means for identifying resources (&resource;).
815   URI references are used to target requests, indicate redirects, and define
816   relationships.
817</t>
818  <x:anchor-alias value="URI-reference"/>
819  <x:anchor-alias value="absolute-URI"/>
820  <x:anchor-alias value="relative-part"/>
821  <x:anchor-alias value="authority"/>
822  <x:anchor-alias value="uri-host"/>
823  <x:anchor-alias value="port"/>
824  <x:anchor-alias value="path-abempty"/>
825  <x:anchor-alias value="segment"/>
826  <x:anchor-alias value="query"/>
827  <x:anchor-alias value="fragment"/>
828  <x:anchor-alias value="absolute-path"/>
829  <x:anchor-alias value="partial-URI"/>
830<t>
831   This specification adopts the definitions of "URI-reference",
832   "absolute-URI", "relative-part", "authority", "port", "host",
833   "path-abempty", "segment", "query", and "fragment" from the
834   URI generic syntax.
835   In addition, we define an "absolute-path" rule (that differs from
836   RFC 3986's "path-absolute" in that it allows a leading "//")
837   and a "partial-URI" rule for protocol elements
838   that allow a relative URI but not a fragment.
839</t>
840<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>
841  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
842  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
843  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
844  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
845  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
846  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
847  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
848  <x:ref>segment</x:ref>       = &lt;segment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
849  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
850  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>&gt;
851 
852  <x:ref>absolute-path</x:ref> = 1*( "/" segment )
853  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
854</artwork></figure>
855<t>
856   Each protocol element in HTTP that allows a URI reference will indicate
857   in its ABNF production whether the element allows any form of reference
858   (URI-reference), only a URI in absolute form (absolute-URI), only the
859   path and optional query components, or some combination of the above.
860   Unless otherwise indicated, URI references are parsed
861   relative to the effective request URI
862   (<xref target="effective.request.uri"/>).
863</t>
864
865<section title="http URI scheme" anchor="http.uri">
866  <x:anchor-alias value="http-URI"/>
867  <iref item="http URI scheme" primary="true"/>
868  <iref item="URI scheme" subitem="http" primary="true"/>
869<t>
870   The "http" URI scheme is hereby defined for the purpose of minting
871   identifiers according to their association with the hierarchical
872   namespace governed by a potential HTTP origin server listening for
873   TCP (<xref target="RFC0793"/>) connections on a given port.
874</t>
875<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"><!--terminal production--></iref>
876  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
877             [ "#" <x:ref>fragment</x:ref> ]
878</artwork></figure>
879<t>
880   The HTTP origin server is identified by the generic syntax's
881   <x:ref>authority</x:ref> component, which includes a host identifier
882   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
883   The remainder of the URI, consisting of both the hierarchical path
884   component and optional query component, serves as an identifier for
885   a potential resource within that origin server's name space.
886</t>
887<t>
888   A sender &MUST-NOT; generate an "http" URI with an empty host identifier.
889   A recipient that processes such a URI reference &MUST; reject it as invalid.
890</t>
891<t>
892   If the host identifier is provided as an IP address,
893   then the origin server is any listener on the indicated TCP port at
894   that IP address. If host is a registered name, then that name is
895   considered an indirect identifier and the recipient might use a name
896   resolution service, such as DNS, to find the address of a listener
897   for that host.
898   If the port subcomponent is empty or not given, then TCP port 80 is
899   assumed (the default reserved port for WWW services).
900</t>
901<t>
902   Regardless of the form of host identifier, access to that host is not
903   implied by the mere presence of its name or address. The host might or might
904   not exist and, even when it does exist, might or might not be running an
905   HTTP server or listening to the indicated port. The "http" URI scheme
906   makes use of the delegated nature of Internet names and addresses to
907   establish a naming authority (whatever entity has the ability to place
908   an HTTP server at that Internet name or address) and allows that
909   authority to determine which names are valid and how they might be used.
910</t>
911<t>
912   When an "http" URI is used within a context that calls for access to the
913   indicated resource, a client &MAY; attempt access by resolving
914   the host to an IP address, establishing a TCP connection to that address
915   on the indicated port, and sending an HTTP request message
916   (<xref target="http.message"/>) containing the URI's identifying data
917   (<xref target="message.routing"/>) to the server.
918   If the server responds to that request with a non-interim HTTP response
919   message, as described in &status-codes;, then that response
920   is considered an authoritative answer to the client's request.
921</t>
922<t>
923   Although HTTP is independent of the transport protocol, the "http"
924   scheme is specific to TCP-based services because the name delegation
925   process depends on TCP for establishing authority.
926   An HTTP service based on some other underlying connection protocol
927   would presumably be identified using a different URI scheme, just as
928   the "https" scheme (below) is used for resources that require an
929   end-to-end secured connection. Other protocols might also be used to
930   provide access to "http" identified resources &mdash; it is only the
931   authoritative interface that is specific to TCP.
932</t>
933<t>
934   The URI generic syntax for authority also includes a deprecated
935   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
936   for including user authentication information in the URI.  Some
937   implementations make use of the userinfo component for internal
938   configuration of authentication information, such as within command
939   invocation options, configuration files, or bookmark lists, even
940   though such usage might expose a user identifier or password.
941   A sender &MUST-NOT; generate the userinfo subcomponent (and its "@"
942   delimiter) when an "http" URI reference is generated within a message as a
943   request target or header field value.
944   Before making use of an "http" URI reference received from an untrusted
945   source, a recipient ought to parse for userinfo and treat its presence as
946   an error; it is likely being used to obscure the authority for the sake of
947   phishing attacks.
948</t>
949</section>
950
951<section title="https URI scheme" anchor="https.uri">
952   <x:anchor-alias value="https-URI"/>
953   <iref item="https URI scheme"/>
954   <iref item="URI scheme" subitem="https"/>
955<t>
956   The "https" URI scheme is hereby defined for the purpose of minting
957   identifiers according to their association with the hierarchical
958   namespace governed by a potential HTTP origin server listening to a
959   given TCP port for TLS-secured connections
960   (<xref target="RFC0793"/>, <xref target="RFC5246"/>).
961</t>
962<t>
963   All of the requirements listed above for the "http" scheme are also
964   requirements for the "https" scheme, except that a default TCP port
965   of 443 is assumed if the port subcomponent is empty or not given,
966   and the user agent &MUST; ensure that its connection to the origin
967   server is secured through the use of strong encryption, end-to-end,
968   prior to sending the first HTTP request.
969</t>
970<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"><!--terminal production--></iref>
971  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
972              [ "#" <x:ref>fragment</x:ref> ]
973</artwork></figure>
974<t>
975   Note that the "https" URI scheme depends on both TLS and TCP for
976   establishing authority.
977   Resources made available via the "https" scheme have no shared
978   identity with the "http" scheme even if their resource identifiers
979   indicate the same authority (the same host listening to the same
980   TCP port).  They are distinct name spaces and are considered to be
981   distinct origin servers.  However, an extension to HTTP that is
982   defined to apply to entire host domains, such as the Cookie protocol
983   <xref target="RFC6265"/>, can allow information
984   set by one service to impact communication with other services
985   within a matching group of host domains.
986</t>
987<t>
988   The process for authoritative access to an "https" identified
989   resource is defined in <xref target="RFC2818"/>.
990</t>
991</section>
992
993<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
994<t>
995   Since the "http" and "https" schemes conform to the URI generic syntax,
996   such URIs are normalized and compared according to the algorithm defined
997   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
998   described above for each scheme.
999</t>
1000<t>
1001   If the port is equal to the default port for a scheme, the normal form is
1002   to omit the port subcomponent. When not being used in absolute form as the
1003   request target of an OPTIONS request, an empty path component is equivalent
1004   to an absolute path of "/", so the normal form is to provide a path of "/"
1005   instead. The scheme and host are case-insensitive and normally provided in
1006   lowercase; all other components are compared in a case-sensitive manner.
1007   Characters other than those in the "reserved" set are equivalent to their
1008   percent-encoded octets (see <xref target="RFC3986" x:fmt=","
1009   x:sec="2.1"/>): the normal form is to not encode them.
1010</t>
1011<t>
1012   For example, the following three URIs are equivalent:
1013</t>
1014<figure><artwork type="example">
1015   http://example.com:80/~smith/home.html
1016   http://EXAMPLE.com/%7Esmith/home.html
1017   http://EXAMPLE.com:/%7esmith/home.html
1018</artwork></figure>
1019</section>
1020</section>
1021</section>
1022
1023<section title="Message Format" anchor="http.message">
1024<x:anchor-alias value="generic-message"/>
1025<x:anchor-alias value="message.types"/>
1026<x:anchor-alias value="HTTP-message"/>
1027<x:anchor-alias value="start-line"/>
1028<iref item="header section"/>
1029<iref item="headers"/>
1030<iref item="header field"/>
1031<t>
1032   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1033   octets in a format similar to the Internet Message Format
1034   <xref target="RFC5322"/>: zero or more header fields (collectively
1035   referred to as the "headers" or the "header section"), an empty line
1036   indicating the end of the header section, and an optional message body.
1037</t>
1038<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"><!--terminal production--></iref>
1039  <x:ref>HTTP-message</x:ref>   = <x:ref>start-line</x:ref>
1040                   *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1041                   <x:ref>CRLF</x:ref>
1042                   [ <x:ref>message-body</x:ref> ]
1043</artwork></figure>
1044<t>
1045   The normal procedure for parsing an HTTP message is to read the
1046   start-line into a structure, read each header field into a hash
1047   table by field name until the empty line, and then use the parsed
1048   data to determine if a message body is expected.  If a message body
1049   has been indicated, then it is read as a stream until an amount
1050   of octets equal to the message body length is read or the connection
1051   is closed.
1052</t>
1053<t>
1054   A recipient &MUST; parse an HTTP message as a sequence of octets in an
1055   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1056   Parsing an HTTP message as a stream of Unicode characters, without regard
1057   for the specific encoding, creates security vulnerabilities due to the
1058   varying ways that string processing libraries handle invalid multibyte
1059   character sequences that contain the octet LF (%x0A).  String-based
1060   parsers can only be safely used within protocol elements after the element
1061   has been extracted from the message, such as within a header field-value
1062   after message parsing has delineated the individual fields.
1063</t>
1064<t>
1065   An HTTP message can be parsed as a stream for incremental processing or
1066   forwarding downstream.  However, recipients cannot rely on incremental
1067   delivery of partial messages, since some implementations will buffer or
1068   delay message forwarding for the sake of network efficiency, security
1069   checks, or payload transformations.
1070</t>
1071<t>
1072   A sender &MUST-NOT; send whitespace between the start-line and
1073   the first header field.
1074   A recipient that receives whitespace between the start-line and
1075   the first header field &MUST; either reject the message as invalid or
1076   consume each whitespace-preceded line without further processing of it
1077   (i.e., ignore the entire line, along with any subsequent lines preceded
1078   by whitespace, until a properly formed header field is received or the
1079   header section is terminated).
1080</t>
1081<t>
1082   The presence of such whitespace in a request
1083   might be an attempt to trick a server into ignoring that field or
1084   processing the line after it as a new request, either of which might
1085   result in a security vulnerability if other implementations within
1086   the request chain interpret the same message differently.
1087   Likewise, the presence of such whitespace in a response might be
1088   ignored by some clients or cause others to cease parsing.
1089</t>
1090
1091<section title="Start Line" anchor="start.line">
1092  <x:anchor-alias value="Start-Line"/>
1093<t>
1094   An HTTP message can either be a request from client to server or a
1095   response from server to client.  Syntactically, the two types of message
1096   differ only in the start-line, which is either a request-line (for requests)
1097   or a status-line (for responses), and in the algorithm for determining
1098   the length of the message body (<xref target="message.body"/>).
1099</t>
1100<t>
1101   In theory, a client could receive requests and a server could receive
1102   responses, distinguishing them by their different start-line formats,
1103   but in practice servers are implemented to only expect a request
1104   (a response is interpreted as an unknown or invalid request method)
1105   and clients are implemented to only expect a response.
1106</t>
1107<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1108  <x:ref>start-line</x:ref>     = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1109</artwork></figure>
1110
1111<section title="Request Line" anchor="request.line">
1112  <x:anchor-alias value="Request"/>
1113  <x:anchor-alias value="request-line"/>
1114<t>
1115   A request-line begins with a method token, followed by a single
1116   space (SP), the request-target, another single space (SP), the
1117   protocol version, and ending with CRLF.
1118</t>
1119<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1120  <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>
1121</artwork></figure>
1122<iref primary="true" item="method"/>
1123<t anchor="method">
1124   The method token indicates the request method to be performed on the
1125   target resource. The request method is case-sensitive.
1126</t>
1127<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1128  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1129</artwork></figure>
1130<t>
1131   The request methods defined by this specification can be found in
1132   &methods;, along with information regarding the HTTP method registry
1133   and considerations for defining new methods.
1134</t>
1135<iref item="request-target"/>
1136<t>
1137   The request-target identifies the target resource upon which to apply
1138   the request, as defined in <xref target="request-target"/>.
1139</t>
1140<t>
1141   Recipients typically parse the request-line into its component parts by
1142   splitting on whitespace (see <xref target="message.robustness"/>), since
1143   no whitespace is allowed in the three components.
1144   Unfortunately, some user agents fail to properly encode or exclude
1145   whitespace found in hypertext references, resulting in those disallowed
1146   characters being sent in a request-target.
1147</t>
1148<t>
1149   Recipients of an invalid request-line &SHOULD; respond with either a
1150   <x:ref>400 (Bad Request)</x:ref> error or a <x:ref>301 (Moved Permanently)</x:ref>
1151   redirect with the request-target properly encoded.  A recipient &SHOULD-NOT;
1152   attempt to autocorrect and then process the request without a redirect,
1153   since the invalid request-line might be deliberately crafted to bypass
1154   security filters along the request chain.
1155</t>
1156<t>
1157   HTTP does not place a pre-defined limit on the length of a request-line.
1158   A server that receives a method longer than any that it implements
1159   &SHOULD; respond with a <x:ref>501 (Not Implemented)</x:ref> status code.
1160   A server ought to be prepared to receive URIs of unbounded length, as
1161   described in <xref target="conformance"/>, and &MUST; respond with a
1162   <x:ref>414 (URI Too Long)</x:ref> status code if the received
1163   request-target is longer than the server wishes to parse (see &status-414;).
1164</t>
1165<t>
1166   Various ad-hoc limitations on request-line length are found in practice.
1167   It is &RECOMMENDED; that all HTTP senders and recipients support, at a
1168   minimum, request-line lengths of 8000 octets.
1169</t>
1170</section>
1171
1172<section title="Status Line" anchor="status.line">
1173  <x:anchor-alias value="response"/>
1174  <x:anchor-alias value="status-line"/>
1175  <x:anchor-alias value="status-code"/>
1176  <x:anchor-alias value="reason-phrase"/>
1177<t>
1178   The first line of a response message is the status-line, consisting
1179   of the protocol version, a space (SP), the status code, another space,
1180   a possibly-empty textual phrase describing the status code, and
1181   ending with CRLF.
1182</t>
1183<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1184  <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>
1185</artwork></figure>
1186<t>
1187   The status-code element is a 3-digit integer code describing the
1188   result of the server's attempt to understand and satisfy the client's
1189   corresponding request. The rest of the response message is to be
1190   interpreted in light of the semantics defined for that status code.
1191   See &status-codes; for information about the semantics of status codes,
1192   including the classes of status code (indicated by the first digit),
1193   the status codes defined by this specification, considerations for the
1194   definition of new status codes, and the IANA registry.
1195</t>
1196<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1197  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1198</artwork></figure>
1199<t>  
1200   The reason-phrase element exists for the sole purpose of providing a
1201   textual description associated with the numeric status code, mostly
1202   out of deference to earlier Internet application protocols that were more
1203   frequently used with interactive text clients. A client &SHOULD; ignore
1204   the reason-phrase content.
1205</t>
1206<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1207  <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> )
1208</artwork></figure>
1209</section>
1210</section>
1211
1212<section title="Header Fields" anchor="header.fields">
1213  <x:anchor-alias value="header-field"/>
1214  <x:anchor-alias value="field-content"/>
1215  <x:anchor-alias value="field-name"/>
1216  <x:anchor-alias value="field-value"/>
1217  <x:anchor-alias value="obs-fold"/>
1218<t>
1219   Each HTTP header field consists of a case-insensitive field name
1220   followed by a colon (":"), optional leading whitespace, the field value,
1221   and optional trailing whitespace.
1222</t>
1223<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"/>
1224  <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>
1225  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1226  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1227  <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> )
1228  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1229                 ; obsolete line folding
1230                 ; see <xref target="field.parsing"/>
1231</artwork></figure>
1232<t>
1233   The field-name token labels the corresponding field-value as having the
1234   semantics defined by that header field.  For example, the <x:ref>Date</x:ref>
1235   header field is defined in &header-date; as containing the origination
1236   timestamp for the message in which it appears.
1237</t>
1238
1239<section title="Field Extensibility" anchor="field.extensibility">
1240<t>
1241   Header fields are fully extensible: there is no limit on the
1242   introduction of new field names, each presumably defining new semantics,
1243   nor on the number of header fields used in a given message.  Existing
1244   fields are defined in each part of this specification and in many other
1245   specifications outside the core standard.
1246</t>
1247<t>
1248   New header fields can be defined such that, when they are understood by a
1249   recipient, they might override or enhance the interpretation of previously
1250   defined header fields, define preconditions on request evaluation, or
1251   refine the meaning of responses.
1252</t>
1253<t>
1254   A proxy &MUST; forward unrecognized header fields unless the
1255   field-name is listed in the <x:ref>Connection</x:ref> header field
1256   (<xref target="header.connection"/>) or the proxy is specifically
1257   configured to block, or otherwise transform, such fields.
1258   Other recipients &SHOULD; ignore unrecognized header fields.
1259   These requirements allow HTTP's functionality to be enhanced without
1260   requiring prior update of deployed intermediaries.
1261</t>
1262<t>
1263   All defined header fields ought to be registered with IANA in the
1264   Message Header Field Registry, as described in &iana-header-registry;.
1265</t>
1266</section>
1267
1268<section title="Field Order" anchor="field.order">
1269<t>
1270   The order in which header fields with differing field names are
1271   received is not significant. However, it is "good practice" to send
1272   header fields that contain control data first, such as <x:ref>Host</x:ref>
1273   on requests and <x:ref>Date</x:ref> on responses, so that implementations
1274   can decide when not to handle a message as early as possible.  A server
1275   &MUST; wait until the entire header section is received before interpreting
1276   a request message, since later header fields might include conditionals,
1277   authentication credentials, or deliberately misleading duplicate
1278   header fields that would impact request processing.
1279</t>
1280<t>
1281   A sender &MUST-NOT; generate multiple header fields with the same field
1282   name in a message unless either the entire field value for that
1283   header field is defined as a comma-separated list [i.e., #(values)]
1284   or the header field is a well-known exception (as noted below).
1285</t>
1286<t>
1287   A recipient &MAY; combine multiple header fields with the same field name
1288   into one "field-name: field-value" pair, without changing the semantics of
1289   the message, by appending each subsequent field value to the combined
1290   field value in order, separated by a comma. The order in which
1291   header fields with the same field name are received is therefore
1292   significant to the interpretation of the combined field value;
1293   a proxy &MUST-NOT; change the order of these field values when
1294   forwarding a message.
1295</t>
1296<x:note>
1297  <t>
1298   &Note; In practice, the "Set-Cookie" header field (<xref target="RFC6265"/>)
1299   often appears multiple times in a response message and does not use the
1300   list syntax, violating the above requirements on multiple header fields
1301   with the same name. Since it cannot be combined into a single field-value,
1302   recipients ought to handle "Set-Cookie" as a special case while processing
1303   header fields. (See Appendix A.2.3 of <xref target="Kri2001"/> for details.)
1304  </t>
1305</x:note>
1306</section>
1307
1308<section title="Whitespace" anchor="whitespace">
1309<t anchor="rule.LWS">
1310   This specification uses three rules to denote the use of linear
1311   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1312   BWS ("bad" whitespace).
1313</t>
1314<t anchor="rule.OWS">
1315   The OWS rule is used where zero or more linear whitespace octets might
1316   appear. For protocol elements where optional whitespace is preferred to
1317   improve readability, a sender &SHOULD; generate the optional whitespace
1318   as a single SP; otherwise, a sender &SHOULD-NOT; generate optional
1319   whitespace except as needed to white-out invalid or unwanted protocol
1320   elements during in-place message filtering.
1321</t>
1322<t anchor="rule.RWS">
1323   The RWS rule is used when at least one linear whitespace octet is required
1324   to separate field tokens. A sender &SHOULD; generate RWS as a single SP.
1325</t>
1326<t anchor="rule.BWS">
1327   The BWS rule is used where the grammar allows optional whitespace only for
1328   historical reasons. A sender &MUST-NOT; generate BWS in messages.
1329   A recipient &MUST; parse for such bad whitespace and remove it before
1330   interpreting the protocol element.
1331</t>
1332<t anchor="rule.whitespace">
1333  <x:anchor-alias value="BWS"/>
1334  <x:anchor-alias value="OWS"/>
1335  <x:anchor-alias value="RWS"/>
1336</t>
1337<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"/>
1338  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1339                 ; optional whitespace
1340  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1341                 ; required whitespace
1342  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1343                 ; "bad" whitespace
1344</artwork></figure>
1345</section>
1346
1347<section title="Field Parsing" anchor="field.parsing">
1348<t>
1349   No whitespace is allowed between the header field-name and colon.
1350   In the past, differences in the handling of such whitespace have led to
1351   security vulnerabilities in request routing and response handling.
1352   A server &MUST; reject any received request message that contains
1353   whitespace between a header field-name and colon with a response code of
1354   <x:ref>400 (Bad Request)</x:ref>. A proxy &MUST; remove any such whitespace
1355   from a response message before forwarding the message downstream.
1356</t>
1357<t>
1358   A field value is preceded by optional whitespace (OWS); a single SP is
1359   preferred. The field value does not include any leading or trailing white
1360   space: OWS occurring before the first non-whitespace octet of the field
1361   value or after the last non-whitespace octet of the field value ought to be
1362   excluded by parsers when extracting the field value from a header field.
1363</t>
1364<t>
1365   A recipient of field-content containing multiple sequential octets of
1366   optional (OWS) or required (RWS) whitespace &SHOULD; either replace the
1367   sequence with a single SP or transform any non-SP octets in the sequence to
1368   SP octets before interpreting the field value or forwarding the message
1369   downstream.
1370</t>
1371<t>
1372   Historically, HTTP header field values could be extended over multiple
1373   lines by preceding each extra line with at least one space or horizontal
1374   tab (obs-fold). This specification deprecates such line folding except
1375   within the message/http media type
1376   (<xref target="internet.media.type.message.http"/>).
1377   A sender &MUST-NOT; generate a message that includes line folding
1378   (i.e., that has any field-value that contains a match to the
1379   <x:ref>obs-fold</x:ref> rule) unless the message is intended for packaging
1380   within the message/http media type.
1381</t>
1382<t>
1383   A server that receives an <x:ref>obs-fold</x:ref> in a request message that
1384   is not within a message/http container &MUST; either reject the message by
1385   sending a <x:ref>400 (Bad Request)</x:ref>, preferably with a
1386   representation explaining that obsolete line folding is unacceptable, or
1387   replace each received <x:ref>obs-fold</x:ref> with one or more
1388   <x:ref>SP</x:ref> octets prior to interpreting the field value or
1389   forwarding the message downstream.
1390</t>
1391<t>
1392   A proxy or gateway that receives an <x:ref>obs-fold</x:ref> in a response
1393   message that is not within a message/http container &MUST; either discard
1394   the message and replace it with a <x:ref>502 (Bad Gateway)</x:ref>
1395   response, preferably with a representation explaining that unacceptable
1396   line folding was received, or replace each received <x:ref>obs-fold</x:ref>
1397   with one or more <x:ref>SP</x:ref> octets prior to interpreting the field
1398   value or forwarding the message downstream.
1399</t>
1400<t>
1401   A user agent that receives an <x:ref>obs-fold</x:ref> in a response message
1402   that is not within a message/http container &MUST; replace each received
1403   <x:ref>obs-fold</x:ref> with one or more <x:ref>SP</x:ref> octets prior to
1404   interpreting the field value.
1405</t>
1406<t>
1407   Historically, HTTP has allowed field content with text in the ISO-8859-1
1408   <xref target="ISO-8859-1"/> charset, supporting other charsets only
1409   through use of <xref target="RFC2047"/> encoding.
1410   In practice, most HTTP header field values use only a subset of the
1411   US-ASCII charset <xref target="USASCII"/>. Newly defined
1412   header fields &SHOULD; limit their field values to US-ASCII octets.
1413   A recipient &SHOULD; treat other octets in field content (obs-text) as
1414   opaque data.
1415</t>
1416</section>
1417
1418<section title="Field Limits" anchor="field.limits">
1419<t>
1420   HTTP does not place a pre-defined limit on the length of each header field
1421   or on the length of the header section as a whole, as described in
1422   <xref target="conformance"/>. Various ad-hoc limitations on individual
1423   header field length are found in practice, often depending on the specific
1424   field semantics.
1425</t>
1426<t>
1427   A server ought to be prepared to receive request header fields of unbounded
1428   length and &MUST; respond with an appropriate
1429   <x:ref>4xx (Client Error)</x:ref> status code if the received header
1430   field(s) are larger than the server wishes to process.
1431</t>
1432<t>
1433   A client ought to be prepared to receive response header fields of
1434   unbounded length.
1435   A client &MAY; discard or truncate received header fields that are larger
1436   than the client wishes to process if the field semantics are such that the
1437   dropped value(s) can be safely ignored without changing the
1438   message framing or response semantics.
1439</t>
1440</section>
1441
1442<section title="Field value components" anchor="field.components">
1443<t anchor="rule.token.separators">
1444  <x:anchor-alias value="tchar"/>
1445  <x:anchor-alias value="token"/>
1446  <x:anchor-alias value="special"/>
1447   Most HTTP header field values are defined using common syntax components
1448   (token, quoted-string, and comment) separated by whitespace or specific
1449   delimiting characters. Delimiters are chosen from the set of US-ASCII
1450   visual characters not allowed in a token ({VCHAR - tchar}).
1451</t>
1452<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/>
1453  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1454<!--
1455  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1456 -->
1457  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1458                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1459                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1460                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1461
1462  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1463                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1464                 / "]" / "?" / "=" / "{" / "}"
1465</artwork></figure>
1466<t anchor="rule.quoted-string">
1467  <x:anchor-alias value="quoted-string"/>
1468  <x:anchor-alias value="qdtext"/>
1469  <x:anchor-alias value="obs-text"/>
1470   A string of text is parsed as a single value if it is quoted using
1471   double-quote marks.
1472</t>
1473<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"/>
1474  <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>
1475  <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>
1476  <x:ref>obs-text</x:ref>       = %x80-FF
1477</artwork></figure>
1478<t anchor="rule.comment">
1479  <x:anchor-alias value="comment"/>
1480  <x:anchor-alias value="ctext"/>
1481   Comments can be included in some HTTP header fields by surrounding
1482   the comment text with parentheses. Comments are only allowed in
1483   fields containing "comment" as part of their field value definition.
1484</t>
1485<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1486  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1487  <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>
1488</artwork></figure>
1489<t anchor="rule.quoted-pair">
1490  <x:anchor-alias value="quoted-pair"/>
1491   The backslash octet ("\") can be used as a single-octet
1492   quoting mechanism within quoted-string and comment constructs.
1493   Recipients that process the value of a quoted-string &MUST; handle a
1494   quoted-pair as if it were replaced by the octet following the backslash.
1495</t>
1496<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1497  <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> )
1498</artwork></figure>
1499<t>
1500   A sender &SHOULD-NOT; generate a quoted-pair in a quoted-string except
1501   where necessary to quote DQUOTE and backslash octets occurring within that
1502   string.
1503   A sender &SHOULD-NOT; generate a quoted-pair in a comment except
1504   where necessary to quote parentheses ["(" and ")"] and backslash octets
1505   occurring within that comment.
1506</t>
1507</section>
1508
1509</section>
1510
1511<section title="Message Body" anchor="message.body">
1512  <x:anchor-alias value="message-body"/>
1513<t>
1514   The message body (if any) of an HTTP message is used to carry the
1515   payload body of that request or response.  The message body is
1516   identical to the payload body unless a transfer coding has been
1517   applied, as described in <xref target="header.transfer-encoding"/>.
1518</t>
1519<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1520  <x:ref>message-body</x:ref> = *OCTET
1521</artwork></figure>
1522<t>
1523   The rules for when a message body is allowed in a message differ for
1524   requests and responses.
1525</t>
1526<t>
1527   The presence of a message body in a request is signaled by a
1528   <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1529   field. Request message framing is independent of method semantics,
1530   even if the method does not define any use for a message body.
1531</t>
1532<t>
1533   The presence of a message body in a response depends on both
1534   the request method to which it is responding and the response
1535   status code (<xref target="status.line"/>).
1536   Responses to the HEAD request method never include a message body
1537   because the associated response header fields (e.g.,
1538   <x:ref>Transfer-Encoding</x:ref>, <x:ref>Content-Length</x:ref>, etc.),
1539   if present, indicate only what their values would have been if the request
1540   method had been GET (&HEAD;).
1541   <x:ref>2xx (Successful)</x:ref> responses to CONNECT switch to tunnel
1542   mode instead of having a message body (&CONNECT;).
1543   All <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, and
1544   <x:ref>304 (Not Modified)</x:ref> responses do not include a message body.
1545   All other responses do include a message body, although the body
1546   might be of zero length.
1547</t>
1548
1549<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1550  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1551  <iref item="chunked (Coding Format)"/>
1552  <x:anchor-alias value="Transfer-Encoding"/>
1553<t>
1554   The Transfer-Encoding header field lists the transfer coding names
1555   corresponding to the sequence of transfer codings that have been
1556   (or will be) applied to the payload body in order to form the message body.
1557   Transfer codings are defined in <xref target="transfer.codings"/>.
1558</t>
1559<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1560  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1561</artwork></figure>
1562<t>
1563   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1564   MIME, which was designed to enable safe transport of binary data over a
1565   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1566   However, safe transport has a different focus for an 8bit-clean transfer
1567   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1568   accurately delimit a dynamically generated payload and to distinguish
1569   payload encodings that are only applied for transport efficiency or
1570   security from those that are characteristics of the selected resource.
1571</t>
1572<t>
1573   A recipient &MUST; be able to parse the chunked transfer coding
1574   (<xref target="chunked.encoding"/>) because it plays a crucial role in
1575   framing messages when the payload body size is not known in advance.
1576   A sender &MUST-NOT; apply chunked more than once to a message body
1577   (i.e., chunking an already chunked message is not allowed).
1578   If any transfer coding other than chunked is applied to a request payload
1579   body, the sender &MUST; apply chunked as the final transfer coding to
1580   ensure that the message is properly framed.
1581   If any transfer coding other than chunked is applied to a response payload
1582   body, the sender &MUST; either apply chunked as the final transfer coding
1583   or terminate the message by closing the connection.
1584</t>
1585<figure><preamble>
1586   For example,
1587</preamble><artwork type="example">
1588  Transfer-Encoding: gzip, chunked
1589</artwork><postamble>
1590   indicates that the payload body has been compressed using the gzip
1591   coding and then chunked using the chunked coding while forming the
1592   message body.
1593</postamble></figure>
1594<t>
1595   Unlike <x:ref>Content-Encoding</x:ref> (&content-codings;),
1596   Transfer-Encoding is a property of the message, not of the representation, and
1597   any recipient along the request/response chain &MAY; decode the received
1598   transfer coding(s) or apply additional transfer coding(s) to the message
1599   body, assuming that corresponding changes are made to the Transfer-Encoding
1600   field-value. Additional information about the encoding parameters &MAY; be
1601   provided by other header fields not defined by this specification.
1602</t>
1603<t>
1604   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1605   <x:ref>304 (Not Modified)</x:ref> response (&status-304;) to a GET request,
1606   neither of which includes a message body,
1607   to indicate that the origin server would have applied a transfer coding
1608   to the message body if the request had been an unconditional GET.
1609   This indication is not required, however, because any recipient on
1610   the response chain (including the origin server) can remove transfer
1611   codings when they are not needed.
1612</t>
1613<t>
1614   A server &MUST-NOT; send a Transfer-Encoding header field in any response
1615   with a status code of
1616   <x:ref>1xx (Informational)</x:ref> or <x:ref>204 (No Content)</x:ref>.
1617   A server &MUST-NOT; send a Transfer-Encoding header field in any
1618   <x:ref>2xx (Successful)</x:ref> response to a CONNECT request (&CONNECT;).
1619</t>
1620<t>
1621   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1622   implementations advertising only HTTP/1.0 support will not understand
1623   how to process a transfer-encoded payload.
1624   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1625   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1626   might be in the form of specific user configuration or by remembering the
1627   version of a prior received response.
1628   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1629   the corresponding request indicates HTTP/1.1 (or later).
1630</t>
1631<t>
1632   A server that receives a request message with a transfer coding it does
1633   not understand &SHOULD; respond with <x:ref>501 (Not Implemented)</x:ref>.
1634</t>
1635</section>
1636
1637<section title="Content-Length" anchor="header.content-length">
1638  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1639  <x:anchor-alias value="Content-Length"/>
1640<t>
1641   When a message does not have a <x:ref>Transfer-Encoding</x:ref> header
1642   field, a Content-Length header field can provide the anticipated size,
1643   as a decimal number of octets, for a potential payload body.
1644   For messages that do include a payload body, the Content-Length field-value
1645   provides the framing information necessary for determining where the body
1646   (and message) ends.  For messages that do not include a payload body, the
1647   Content-Length indicates the size of the selected representation
1648   (&representation;).
1649</t>
1650<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1651  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1652</artwork></figure>
1653<t>
1654   An example is
1655</t>
1656<figure><artwork type="example">
1657  Content-Length: 3495
1658</artwork></figure>
1659<t>
1660   A sender &MUST-NOT; send a Content-Length header field in any message that
1661   contains a <x:ref>Transfer-Encoding</x:ref> header field.
1662</t>
1663<t>
1664   A user agent &SHOULD; send a Content-Length in a request message when no
1665   <x:ref>Transfer-Encoding</x:ref> is sent and the request method defines
1666   a meaning for an enclosed payload body. For example, a Content-Length
1667   header field is normally sent in a POST request even when the value is
1668   0 (indicating an empty payload body).  A user agent &SHOULD-NOT; send a
1669   Content-Length header field when the request message does not contain a
1670   payload body and the method semantics do not anticipate such a body.
1671</t>
1672<t>
1673   A server &MAY; send a Content-Length header field in a response to a HEAD
1674   request (&HEAD;); a server &MUST-NOT; send Content-Length in such a
1675   response unless its field-value equals the decimal number of octets that
1676   would have been sent in the payload body of a response if the same
1677   request had used the GET method.
1678</t>
1679<t>
1680   A server &MAY; send a Content-Length header field in a
1681   <x:ref>304 (Not Modified)</x:ref> response to a conditional GET request
1682   (&status-304;); 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 <x:ref>200 (OK)</x:ref>
1685   response to the same request.
1686</t>
1687<t>
1688   A server &MUST-NOT; send a Content-Length header field in any response
1689   with a status code of
1690   <x:ref>1xx (Informational)</x:ref> or <x:ref>204 (No Content)</x:ref>.
1691   A server &MUST-NOT; send a Content-Length header field in any
1692   <x:ref>2xx (Successful)</x:ref> response to a CONNECT request (&CONNECT;).
1693</t>
1694<t>
1695   Aside from the cases defined above, in the absence of Transfer-Encoding,
1696   an origin server &SHOULD; send a Content-Length header field when the
1697   payload body size is known prior to sending the complete header section.
1698   This will allow downstream recipients to measure transfer progress,
1699   know when a received message is complete, and potentially reuse the
1700   connection for additional requests.
1701</t>
1702<t>
1703   Any Content-Length field value greater than or equal to zero is valid.
1704   Since there is no predefined limit to the length of a payload, a
1705   recipient &MUST; anticipate potentially large decimal numerals and
1706   prevent parsing errors due to integer conversion overflows
1707   (<xref target="attack.protocol.element.size.overflows"/>).
1708</t>
1709<t>
1710   If a message is received that has multiple Content-Length header fields
1711   with field-values consisting of the same decimal value, or a single
1712   Content-Length header field with a field value containing a list of
1713   identical decimal values (e.g., "Content-Length: 42, 42"), indicating that
1714   duplicate Content-Length header fields have been generated or combined by an
1715   upstream message processor, then the recipient &MUST; either reject the
1716   message as invalid or replace the duplicated field-values with a single
1717   valid Content-Length field containing that decimal value prior to
1718   determining the message body length or forwarding the message.
1719</t>
1720<x:note>
1721  <t>
1722   &Note; HTTP's use of Content-Length for message framing differs
1723   significantly from the same field's use in MIME, where it is an optional
1724   field used only within the "message/external-body" media-type.
1725  </t>
1726</x:note>
1727</section>
1728
1729<section title="Message Body Length" anchor="message.body.length">
1730  <iref item="chunked (Coding Format)"/>
1731<t>
1732   The length of a message body is determined by one of the following
1733   (in order of precedence):
1734</t>
1735<t>
1736  <list style="numbers">
1737    <x:lt><t>
1738     Any response to a HEAD request and any response with a
1739     <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, or
1740     <x:ref>304 (Not Modified)</x:ref> status code is always
1741     terminated by the first empty line after the header fields, regardless of
1742     the header fields present in the message, and thus cannot contain a
1743     message body.
1744    </t></x:lt>
1745    <x:lt><t>
1746     Any <x:ref>2xx (Successful)</x:ref> response to a CONNECT request implies that the
1747     connection will become a tunnel immediately after the empty line that
1748     concludes the header fields.  A client &MUST; ignore any
1749     <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1750     fields received in such a message.
1751    </t></x:lt>
1752    <x:lt><t>
1753     If a <x:ref>Transfer-Encoding</x:ref> header field is present
1754     and the chunked transfer coding (<xref target="chunked.encoding"/>)
1755     is the final encoding, the message body length is determined by reading
1756     and decoding the chunked data until the transfer coding indicates the
1757     data is complete.
1758    </t>
1759    <t>
1760     If a <x:ref>Transfer-Encoding</x:ref> header field is present in a
1761     response and the chunked transfer coding is not the final encoding, the
1762     message body length is determined by reading the connection until it is
1763     closed by the server.
1764     If a <x:ref>Transfer-Encoding</x:ref> header field is present in a request and the
1765     chunked transfer coding is not the final encoding, the message body
1766     length cannot be determined reliably; the server &MUST; respond with
1767     the <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1768    </t>
1769    <t>
1770     If a message is received with both a <x:ref>Transfer-Encoding</x:ref>
1771     and a <x:ref>Content-Length</x:ref> header field, the Transfer-Encoding
1772     overrides the Content-Length. Such a message might indicate an attempt
1773     to perform request or response smuggling (bypass of security-related
1774     checks on message routing or content) and thus ought to be handled as
1775     an error.  A sender &MUST; remove the received Content-Length field
1776     prior to forwarding such a message downstream.
1777    </t></x:lt>
1778    <x:lt><t>
1779     If a message is received without <x:ref>Transfer-Encoding</x:ref> and with
1780     either multiple <x:ref>Content-Length</x:ref> header fields having
1781     differing field-values or a single Content-Length header field having an
1782     invalid value, then the message framing is invalid and
1783     the recipient &MUST; treat it as an unrecoverable error to prevent
1784     request or response smuggling.
1785     If this is a request message, the server &MUST; respond with
1786     a <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1787     If this is a response message received by a proxy,
1788     the proxy &MUST; close the connection to the server, discard the received
1789     response, and send a <x:ref>502 (Bad Gateway)</x:ref> response to the
1790     client.
1791     If this is a response message received by a user agent,
1792     the user agent &MUST; close the connection to the server and discard the
1793     received response.
1794    </t></x:lt>
1795    <x:lt><t>
1796     If a valid <x:ref>Content-Length</x:ref> header field is present without
1797     <x:ref>Transfer-Encoding</x:ref>, its decimal value defines the
1798     expected message body length in octets.
1799     If the sender closes the connection or the recipient times out before the
1800     indicated number of octets are received, the recipient &MUST; consider
1801     the message to be incomplete and close the connection.
1802    </t></x:lt>
1803    <x:lt><t>
1804     If this is a request message and none of the above are true, then the
1805     message body length is zero (no message body is present).
1806    </t></x:lt>
1807    <x:lt><t>
1808     Otherwise, this is a response message without a declared message body
1809     length, so the message body length is determined by the number of octets
1810     received prior to the server closing the connection.
1811    </t></x:lt>
1812  </list>
1813</t>
1814<t>
1815   Since there is no way to distinguish a successfully completed,
1816   close-delimited message from a partially-received message interrupted
1817   by network failure, a server &SHOULD; generate encoding or
1818   length-delimited messages whenever possible.  The close-delimiting
1819   feature exists primarily for backwards compatibility with HTTP/1.0.
1820</t>
1821<t>
1822   A server &MAY; reject a request that contains a message body but
1823   not a <x:ref>Content-Length</x:ref> by responding with
1824   <x:ref>411 (Length Required)</x:ref>.
1825</t>
1826<t>
1827   Unless a transfer coding other than chunked has been applied,
1828   a client that sends a request containing a message body &SHOULD;
1829   use a valid <x:ref>Content-Length</x:ref> header field if the message body
1830   length is known in advance, rather than the chunked transfer coding, since some
1831   existing services respond to chunked with a <x:ref>411 (Length Required)</x:ref>
1832   status code even though they understand the chunked transfer coding.  This
1833   is typically because such services are implemented via a gateway that
1834   requires a content-length in advance of being called and the server
1835   is unable or unwilling to buffer the entire request before processing.
1836</t>
1837<t>
1838   A user agent that sends a request containing a message body &MUST; send a
1839   valid <x:ref>Content-Length</x:ref> header field if it does not know the
1840   server will handle HTTP/1.1 (or later) requests; such knowledge can be in
1841   the form of specific user configuration or by remembering the version of a
1842   prior received response.
1843</t>
1844<t>
1845   If the final response to the last request on a connection has been
1846   completely received and there remains additional data to read, a user agent
1847   &MAY; discard the remaining data or attempt to determine if that data
1848   belongs as part of the prior response body, which might be the case if the
1849   prior message's Content-Length value is incorrect. A client &MUST-NOT;
1850   process, cache, or forward such extra data as a separate response, since
1851   such behavior would be vulnerable to cache poisoning.
1852</t>
1853</section>
1854</section>
1855
1856<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1857<t>
1858   A server that receives an incomplete request message, usually due to a
1859   canceled request or a triggered time-out exception, &MAY; send an error
1860   response prior to closing the connection.
1861</t>
1862<t>
1863   A client that receives an incomplete response message, which can occur
1864   when a connection is closed prematurely or when decoding a supposedly
1865   chunked transfer coding fails, &MUST; record the message as incomplete.
1866   Cache requirements for incomplete responses are defined in
1867   &cache-incomplete;.
1868</t>
1869<t>
1870   If a response terminates in the middle of the header section (before the
1871   empty line is received) and the status code might rely on header fields to
1872   convey the full meaning of the response, then the client cannot assume
1873   that meaning has been conveyed; the client might need to repeat the
1874   request in order to determine what action to take next.
1875</t>
1876<t>
1877   A message body that uses the chunked transfer coding is
1878   incomplete if the zero-sized chunk that terminates the encoding has not
1879   been received.  A message that uses a valid <x:ref>Content-Length</x:ref> is
1880   incomplete if the size of the message body received (in octets) is less than
1881   the value given by Content-Length.  A response that has neither chunked
1882   transfer coding nor Content-Length is terminated by closure of the
1883   connection, and thus is considered complete regardless of the number of
1884   message body octets received, provided that the header section was received
1885   intact.
1886</t>
1887</section>
1888
1889<section title="Message Parsing Robustness" anchor="message.robustness">
1890<t>
1891   Older HTTP/1.0 user agent implementations might send an extra CRLF
1892   after a POST request as a workaround for some early server
1893   applications that failed to read message body content that was
1894   not terminated by a line-ending. An HTTP/1.1 user agent &MUST-NOT;
1895   preface or follow a request with an extra CRLF.  If terminating
1896   the request message body with a line-ending is desired, then the
1897   user agent &MUST; count the terminating CRLF octets as part of the
1898   message body length.
1899</t>
1900<t>
1901   In the interest of robustness, a server that is expecting to receive and
1902   parse a request-line &SHOULD; ignore at least one empty line (CRLF)
1903   received prior to the request-line.
1904</t>
1905<t>
1906   Although the line terminator for the start-line and header
1907   fields is the sequence CRLF, a recipient &MAY; recognize a
1908   single LF as a line terminator and ignore any preceding CR.
1909</t>
1910<t>
1911   Although the request-line and status-line grammar rules require that each
1912   of the component elements be separated by a single SP octet, recipients
1913   &MAY; instead parse on whitespace-delimited word boundaries and, aside
1914   from the CRLF terminator, treat any form of whitespace as the SP separator
1915   while ignoring preceding or trailing whitespace;
1916   such whitespace includes one or more of the following octets:
1917   SP, HTAB, VT (%x0B), FF (%x0C), or bare CR.
1918</t>
1919<t>
1920   When a server listening only for HTTP request messages, or processing
1921   what appears from the start-line to be an HTTP request message,
1922   receives a sequence of octets that does not match the HTTP-message
1923   grammar aside from the robustness exceptions listed above, the
1924   server &SHOULD; respond with a <x:ref>400 (Bad Request)</x:ref> response. 
1925</t>
1926</section>
1927</section>
1928
1929<section title="Transfer Codings" anchor="transfer.codings">
1930  <x:anchor-alias value="transfer-coding"/>
1931  <x:anchor-alias value="transfer-extension"/>
1932<t>
1933   Transfer coding names are used to indicate an encoding
1934   transformation that has been, can be, or might need to be applied to a
1935   payload body in order to ensure "safe transport" through the network.
1936   This differs from a content coding in that the transfer coding is a
1937   property of the message rather than a property of the representation
1938   that is being transferred.
1939</t>
1940<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1941  <x:ref>transfer-coding</x:ref>    = "chunked" ; <xref target="chunked.encoding"/>
1942                     / "compress" ; <xref target="compress.coding"/>
1943                     / "deflate" ; <xref target="deflate.coding"/>
1944                     / "gzip" ; <xref target="gzip.coding"/>
1945                     / <x:ref>transfer-extension</x:ref>
1946  <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> )
1947</artwork></figure>
1948<t anchor="rule.parameter">
1949  <x:anchor-alias value="transfer-parameter"/>
1950   Parameters are in the form of a name or name=value pair.
1951</t>
1952<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-parameter"/>
1953  <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> )
1954</artwork></figure>
1955<t>
1956   All transfer-coding names are case-insensitive and ought to be registered
1957   within the HTTP Transfer Coding registry, as defined in
1958   <xref target="transfer.coding.registry"/>.
1959   They are used in the <x:ref>TE</x:ref> (<xref target="header.te"/>) and
1960   <x:ref>Transfer-Encoding</x:ref> (<xref target="header.transfer-encoding"/>)
1961   header fields.
1962</t>
1963
1964<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1965  <iref primary="true" item="chunked (Coding Format)"/>
1966  <x:anchor-alias value="chunk"/>
1967  <x:anchor-alias value="chunked-body"/>
1968  <x:anchor-alias value="chunk-data"/>
1969  <x:anchor-alias value="chunk-size"/>
1970  <x:anchor-alias value="last-chunk"/>
1971<t>
1972   The chunked transfer coding wraps the payload body in order to transfer it
1973   as a series of chunks, each with its own size indicator, followed by an
1974   &OPTIONAL; trailer containing header fields. Chunked enables content
1975   streams of unknown size to be transferred as a sequence of length-delimited
1976   buffers, which enables the sender to retain connection persistence and the
1977   recipient to know when it has received the entire message.
1978</t>
1979<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"/>
1980  <x:ref>chunked-body</x:ref>   = *<x:ref>chunk</x:ref>
1981                   <x:ref>last-chunk</x:ref>
1982                   <x:ref>trailer-part</x:ref>
1983                   <x:ref>CRLF</x:ref>
1984 
1985  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1986                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1987  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1988  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1989 
1990  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1991</artwork></figure>
1992<t>
1993   The chunk-size field is a string of hex digits indicating the size of
1994   the chunk-data in octets. The chunked transfer coding is complete when a
1995   chunk with a chunk-size of zero is received, possibly followed by a
1996   trailer, and finally terminated by an empty line.
1997</t>
1998<t>
1999   A recipient &MUST; be able to parse and decode the chunked transfer coding.
2000</t>
2001
2002<section title="Chunk Extensions" anchor="chunked.extension">
2003  <x:anchor-alias value="chunk-ext"/>
2004  <x:anchor-alias value="chunk-ext-name"/>
2005  <x:anchor-alias value="chunk-ext-val"/>
2006<t>
2007   The chunked encoding allows each chunk to include zero or more chunk
2008   extensions, immediately following the <x:ref>chunk-size</x:ref>, for the
2009   sake of supplying per-chunk metadata (such as a signature or hash),
2010   mid-message control information, or randomization of message body size.
2011</t>
2012<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"/>
2013  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
2014
2015  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2016  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
2017</artwork></figure>
2018<t>
2019   The chunked encoding is specific to each connection and is likely to be
2020   removed or recoded by each recipient (including intermediaries) before any
2021   higher-level application would have a chance to inspect the extensions.
2022   Hence, use of chunk extensions is generally limited to specialized HTTP
2023   services such as "long polling" (where client and server can have shared
2024   expectations regarding the use of chunk extensions) or for padding within
2025   an end-to-end secured connection.
2026</t>
2027<t>
2028   A recipient &MUST; ignore unrecognized chunk extensions.
2029   A server ought to limit the total length of chunk extensions received in a
2030   request to an amount reasonable for the services provided, in the same way
2031   that it applies length limitations and timeouts for other parts of a
2032   message, and generate an appropriate <x:ref>4xx (Client Error)</x:ref>
2033   response if that amount is exceeded.
2034</t>
2035</section>
2036
2037<section title="Chunked Trailer Part" anchor="chunked.trailer.part">
2038  <x:anchor-alias value="trailer-part"/>
2039<t>
2040   A trailer allows the sender to include additional fields at the end of a
2041   chunked message in order to supply metadata that might be dynamically
2042   generated while the message body is sent, such as a message integrity
2043   check, digital signature, or post-processing status. The trailer fields are
2044   identical to header fields, except they are sent in a chunked trailer
2045   instead of the message's header section.
2046</t>
2047<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="trailer-part"/>
2048  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2049</artwork></figure>
2050<t>
2051   A sender &MUST-NOT; generate a trailer that contains a field which needs to
2052   be known by the recipient before it can begin processing the message body.
2053   For example, most recipients need to know the values of
2054   <x:ref>Content-Encoding</x:ref> and <x:ref>Content-Type</x:ref> in order to
2055   select a content handler, so placing those fields in a trailer would force
2056   the recipient to buffer the entire body before it could begin, greatly
2057   increasing user-perceived latency and defeating one of the main advantages
2058   of using chunked to send data streams of unknown length.
2059   A sender &MUST-NOT; generate a trailer containing a
2060   <x:ref>Transfer-Encoding</x:ref>,
2061   <x:ref>Content-Length</x:ref>, or
2062   <x:ref>Trailer</x:ref> field.
2063</t>
2064<t>
2065   A server &MUST; generate an empty trailer with the chunked transfer coding
2066   unless at least one of the following is true:
2067  <list style="numbers">
2068    <t>the request included a <x:ref>TE</x:ref> header field that indicates
2069    "trailers" is acceptable in the transfer coding of the response, as
2070    described in <xref target="header.te"/>; or,</t>
2071     
2072    <t>the trailer fields consist entirely of optional metadata and the
2073    recipient could use the message (in a manner acceptable to the generating
2074    server) without receiving that metadata. In other words, the generating
2075    server is willing to accept the possibility that the trailer fields might
2076    be silently discarded along the path to the client.</t>
2077  </list>
2078</t>
2079<t>
2080   The above requirement prevents the need for an infinite buffer when a
2081   message is being received by an HTTP/1.1 (or later) proxy and forwarded to
2082   an HTTP/1.0 recipient.
2083</t>
2084</section>
2085
2086<section title="Decoding Chunked" anchor="decoding.chunked">
2087<t>
2088   A process for decoding the chunked transfer coding
2089   can be represented in pseudo-code as:
2090</t>
2091<figure><artwork type="code">
2092  length := 0
2093  read chunk-size, chunk-ext (if any), and CRLF
2094  while (chunk-size &gt; 0) {
2095     read chunk-data and CRLF
2096     append chunk-data to decoded-body
2097     length := length + chunk-size
2098     read chunk-size, chunk-ext (if any), and CRLF
2099  }
2100  read header-field
2101  while (header-field not empty) {
2102     append header-field to existing header fields
2103     read header-field
2104  }
2105  Content-Length := length
2106  Remove "chunked" from Transfer-Encoding
2107  Remove Trailer from existing header fields
2108</artwork></figure>
2109</section>
2110</section>
2111
2112<section title="Compression Codings" anchor="compression.codings">
2113<t>
2114   The codings defined below can be used to compress the payload of a
2115   message.
2116</t>
2117
2118<section title="Compress Coding" anchor="compress.coding">
2119<iref item="compress (Coding Format)"/>
2120<t>
2121   The "compress" coding is an adaptive Lempel-Ziv-Welch (LZW) coding
2122   <xref target="Welch"/> that is commonly produced by the UNIX file
2123   compression program "compress".
2124   A recipient &SHOULD; consider "x-compress" to be equivalent to "compress".
2125</t>
2126</section>
2127
2128<section title="Deflate Coding" anchor="deflate.coding">
2129<iref item="deflate (Coding Format)"/>
2130<t>
2131   The "deflate" coding is a "zlib" data format <xref target="RFC1950"/>
2132   containing a "deflate" compressed data stream <xref target="RFC1951"/>
2133   that uses a combination of the Lempel-Ziv (LZ77) compression algorithm and
2134   Huffman coding.
2135</t>
2136<x:note>
2137  <t>
2138    &Note; Some incorrect implementations send the "deflate"
2139    compressed data without the zlib wrapper.
2140   </t>
2141</x:note>
2142</section>
2143
2144<section title="Gzip Coding" anchor="gzip.coding">
2145<iref item="gzip (Coding Format)"/>
2146<t>
2147   The "gzip" coding is an LZ77 coding with a 32 bit CRC that is commonly
2148   produced by the gzip file compression program <xref target="RFC1952"/>.
2149   A recipient &SHOULD; consider "x-gzip" to be equivalent to "gzip".
2150</t>
2151</section>
2152
2153</section>
2154
2155<section title="TE" anchor="header.te">
2156  <iref primary="true" item="TE header field" x:for-anchor=""/>
2157  <x:anchor-alias value="TE"/>
2158  <x:anchor-alias value="t-codings"/>
2159  <x:anchor-alias value="t-ranking"/>
2160  <x:anchor-alias value="rank"/>
2161<t>
2162   The "TE" header field in a request indicates what transfer codings,
2163   besides chunked, the client is willing to accept in response, and
2164   whether or not the client is willing to accept trailer fields in a
2165   chunked transfer coding.
2166</t>
2167<t>
2168   The TE field-value consists of a comma-separated list of transfer coding
2169   names, each allowing for optional parameters (as described in
2170   <xref target="transfer.codings"/>), and/or the keyword "trailers".
2171   A client &MUST-NOT; send the chunked transfer coding name in TE;
2172   chunked is always acceptable for HTTP/1.1 recipients.
2173</t>
2174<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"/>
2175  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2176  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-coding</x:ref> [ <x:ref>t-ranking</x:ref> ] )
2177  <x:ref>t-ranking</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>rank</x:ref>
2178  <x:ref>rank</x:ref>      = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2179             / ( "1" [ "." 0*3("0") ] )
2180</artwork></figure>
2181<t>
2182   Three examples of TE use are below.
2183</t>
2184<figure><artwork type="example">
2185  TE: deflate
2186  TE:
2187  TE: trailers, deflate;q=0.5
2188</artwork></figure>
2189<t>
2190   The presence of the keyword "trailers" indicates that the client is willing
2191   to accept trailer fields in a chunked transfer coding, as defined in
2192   <xref target="chunked.trailer.part"/>, on behalf of itself and any downstream
2193   clients. For requests from an intermediary, this implies that either:
2194   (a) all downstream clients are willing to accept trailer fields in the
2195   forwarded response; or,
2196   (b) the intermediary will attempt to buffer the response on behalf of
2197   downstream recipients.
2198   Note that HTTP/1.1 does not define any means to limit the size of a
2199   chunked response such that an intermediary can be assured of buffering the
2200   entire response.
2201</t>
2202<t>
2203   When multiple transfer codings are acceptable, the client &MAY; rank the
2204   codings by preference using a case-insensitive "q" parameter (similar to
2205   the qvalues used in content negotiation fields, &qvalue;). The rank value
2206   is a real number in the range 0 through 1, where 0.001 is the least
2207   preferred and 1 is the most preferred; a value of 0 means "not acceptable".
2208</t>
2209<t>
2210   If the TE field-value is empty or if no TE field is present, the only
2211   acceptable transfer coding is chunked. A message with no transfer coding
2212   is always acceptable.
2213</t>
2214<t>
2215   Since the TE header field only applies to the immediate connection,
2216   a sender of TE &MUST; also send a "TE" connection option within the
2217   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
2218   in order to prevent the TE field from being forwarded by intermediaries
2219   that do not support its semantics.
2220</t>
2221</section>
2222
2223<section title="Trailer" anchor="header.trailer">
2224  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
2225  <x:anchor-alias value="Trailer"/>
2226<t>
2227   When a message includes a message body encoded with the chunked
2228   transfer coding and the sender desires to send metadata in the form of
2229   trailer fields at the end of the message, the sender &SHOULD; generate a
2230   <x:ref>Trailer</x:ref> header field before the message body to indicate
2231   which fields will be present in the trailers. This allows the recipient
2232   to prepare for receipt of that metadata before it starts processing the body,
2233   which is useful if the message is being streamed and the recipient wishes
2234   to confirm an integrity check on the fly.
2235</t>
2236<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2237  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
2238</artwork></figure>
2239</section>
2240</section>
2241
2242<section title="Message Routing" anchor="message.routing">
2243<t>
2244   HTTP request message routing is determined by each client based on the
2245   target resource, the client's proxy configuration, and
2246   establishment or reuse of an inbound connection.  The corresponding
2247   response routing follows the same connection chain back to the client.
2248</t>
2249
2250<section title="Identifying a Target Resource" anchor="target-resource">
2251  <iref primary="true" item="target resource"/>
2252  <iref primary="true" item="target URI"/>
2253  <x:anchor-alias value="target resource"/>
2254  <x:anchor-alias value="target URI"/>
2255<t>
2256   HTTP is used in a wide variety of applications, ranging from
2257   general-purpose computers to home appliances.  In some cases,
2258   communication options are hard-coded in a client's configuration.
2259   However, most HTTP clients rely on the same resource identification
2260   mechanism and configuration techniques as general-purpose Web browsers.
2261</t>
2262<t>
2263   HTTP communication is initiated by a user agent for some purpose.
2264   The purpose is a combination of request semantics, which are defined in
2265   <xref target="Part2"/>, and a target resource upon which to apply those
2266   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2267   an identifier for the "<x:dfn>target resource</x:dfn>", which a user agent
2268   would resolve to its absolute form in order to obtain the
2269   "<x:dfn>target URI</x:dfn>".  The target URI
2270   excludes the reference's fragment component, if any,
2271   since fragment identifiers are reserved for client-side processing
2272   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2273</t>
2274</section>
2275
2276<section title="Connecting Inbound" anchor="connecting.inbound">
2277<t>
2278   Once the target URI is determined, a client needs to decide whether
2279   a network request is necessary to accomplish the desired semantics and,
2280   if so, where that request is to be directed.
2281</t>
2282<t>
2283   If the client has a cache <xref target="Part6"/> and the request can be
2284   satisfied by it, then the request is
2285   usually directed there first.
2286</t>
2287<t>
2288   If the request is not satisfied by a cache, then a typical client will
2289   check its configuration to determine whether a proxy is to be used to
2290   satisfy the request.  Proxy configuration is implementation-dependent,
2291   but is often based on URI prefix matching, selective authority matching,
2292   or both, and the proxy itself is usually identified by an "http" or
2293   "https" URI.  If a proxy is applicable, the client connects inbound by
2294   establishing (or reusing) a connection to that proxy.
2295</t>
2296<t>
2297   If no proxy is applicable, a typical client will invoke a handler routine,
2298   usually specific to the target URI's scheme, to connect directly
2299   to an authority for the target resource.  How that is accomplished is
2300   dependent on the target URI scheme and defined by its associated
2301   specification, similar to how this specification defines origin server
2302   access for resolution of the "http" (<xref target="http.uri"/>) and
2303   "https" (<xref target="https.uri"/>) schemes.
2304</t>
2305<t>
2306   HTTP requirements regarding connection management are defined in
2307   <xref target="connection.management"/>.
2308</t>
2309</section>
2310
2311<section title="Request Target" anchor="request-target">
2312<t>
2313   Once an inbound connection is obtained,
2314   the client sends an HTTP request message (<xref target="http.message"/>)
2315   with a request-target derived from the target URI.
2316   There are four distinct formats for the request-target, depending on both
2317   the method being requested and whether the request is to a proxy.
2318</t>   
2319<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"/>
2320  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2321                 / <x:ref>absolute-form</x:ref>
2322                 / <x:ref>authority-form</x:ref>
2323                 / <x:ref>asterisk-form</x:ref>
2324
2325  <x:ref>origin-form</x:ref>    = <x:ref>absolute-path</x:ref> [ "?" <x:ref>query</x:ref> ]
2326  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2327  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2328  <x:ref>asterisk-form</x:ref>  = "*"
2329</artwork></figure>
2330<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2331  <x:h>origin-form</x:h>
2332</t>
2333<t>
2334   The most common form of request-target is the <x:dfn>origin-form</x:dfn>.
2335   When making a request directly to an origin server, other than a CONNECT
2336   or server-wide OPTIONS request (as detailed below),
2337   a client &MUST; send only the absolute path and query components of
2338   the target URI as the request-target.
2339   If the target URI's path component is empty, then the client &MUST; send
2340   "/" as the path within the origin-form of request-target.
2341   A <x:ref>Host</x:ref> header field is also sent, as defined in
2342   <xref target="header.host"/>.
2343</t>
2344<t>
2345   For example, a client wishing to retrieve a representation of the resource
2346   identified as
2347</t>
2348<figure><artwork x:indent-with="  " type="example">
2349http://www.example.org/where?q=now
2350</artwork></figure>
2351<t>
2352   directly from the origin server would open (or reuse) a TCP connection
2353   to port 80 of the host "www.example.org" and send the lines:
2354</t>
2355<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2356GET /where?q=now HTTP/1.1
2357Host: www.example.org
2358</artwork></figure>
2359<t>
2360   followed by the remainder of the request message.
2361</t>
2362<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2363  <x:h>absolute-form</x:h>
2364</t>
2365<t>
2366   When making a request to a proxy, other than a CONNECT or server-wide
2367   OPTIONS request (as detailed below), a client &MUST; send the target URI
2368   in <x:dfn>absolute-form</x:dfn> as the request-target.
2369   The proxy is requested to either service that request from a valid cache,
2370   if possible, or make the same request on the client's behalf to either
2371   the next inbound proxy server or directly to the origin server indicated
2372   by the request-target.  Requirements on such "forwarding" of messages are
2373   defined in <xref target="message.forwarding"/>.
2374</t>
2375<t>
2376   An example absolute-form of request-line would be:
2377</t>
2378<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2379GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
2380</artwork></figure>
2381<t>
2382   To allow for transition to the absolute-form for all requests in some
2383   future version of HTTP, a server &MUST; accept the absolute-form
2384   in requests, even though HTTP/1.1 clients will only send them in requests
2385   to proxies.
2386</t>
2387<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2388  <x:h>authority-form</x:h>
2389</t>
2390<t>
2391   The <x:dfn>authority-form</x:dfn> of request-target is only used for
2392   CONNECT requests (&CONNECT;). When making a CONNECT request to establish a
2393   tunnel through one or more proxies, a client &MUST; send only the target
2394   URI's authority component (excluding any userinfo and its "@" delimiter) as
2395   the request-target. For example,
2396</t>
2397<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2398CONNECT www.example.com:80 HTTP/1.1
2399</artwork></figure>
2400<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2401  <x:h>asterisk-form</x:h>
2402</t>
2403<t>
2404   The <x:dfn>asterisk-form</x:dfn> of request-target is only used for a server-wide
2405   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2406   for the server as a whole, as opposed to a specific named resource of
2407   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2408   For example,
2409</t>
2410<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2411OPTIONS * HTTP/1.1
2412</artwork></figure>
2413<t>
2414   If a proxy receives an OPTIONS request with an absolute-form of
2415   request-target in which the URI has an empty path and no query component,
2416   then the last proxy on the request chain &MUST; send a request-target
2417   of "*" when it forwards the request to the indicated origin server.
2418</t>
2419<figure><preamble>  
2420   For example, the request
2421</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2422OPTIONS http://www.example.org:8001 HTTP/1.1
2423</artwork></figure>
2424<figure><preamble>  
2425  would be forwarded by the final proxy as
2426</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2427OPTIONS * HTTP/1.1
2428Host: www.example.org:8001
2429</artwork>
2430<postamble>
2431   after connecting to port 8001 of host "www.example.org".
2432</postamble>
2433</figure>
2434</section>
2435
2436<section title="Host" anchor="header.host">
2437  <iref primary="true" item="Host header field" x:for-anchor=""/>
2438  <x:anchor-alias value="Host"/>
2439<t>
2440   The "Host" header field in a request provides the host and port
2441   information from the target URI, enabling the origin
2442   server to distinguish among resources while servicing requests
2443   for multiple host names on a single IP address.
2444</t>
2445<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2446  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2447</artwork></figure>
2448<t>
2449   A client &MUST; send a Host header field in all HTTP/1.1 request messages.
2450   If the target URI includes an authority component, then a client &MUST;
2451   send a field-value for Host that is identical to that authority
2452   component, excluding any userinfo subcomponent and its "@" delimiter
2453   (<xref target="http.uri"/>).
2454   If the authority component is missing or undefined for the target URI,
2455   then a client &MUST; send a Host header field with an empty field-value.
2456</t>
2457<t>
2458   Since the Host field-value is critical information for handling a request,
2459   a user agent &SHOULD; generate Host as the first header field following the
2460   request-line.
2461</t>
2462<t>
2463   For example, a GET request to the origin server for
2464   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
2465</t>
2466<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2467GET /pub/WWW/ HTTP/1.1
2468Host: www.example.org
2469</artwork></figure>
2470<t>
2471   A client &MUST; send a Host header field in an HTTP/1.1 request even
2472   if the request-target is in the absolute-form, since this
2473   allows the Host information to be forwarded through ancient HTTP/1.0
2474   proxies that might not have implemented Host.
2475</t>
2476<t>
2477   When a proxy receives a request with an absolute-form of
2478   request-target, the proxy &MUST; ignore the received
2479   Host header field (if any) and instead replace it with the host
2480   information of the request-target.  A proxy that forwards such a request
2481   &MUST; generate a new Host field-value based on the received
2482   request-target rather than forward the received Host field-value.
2483</t>
2484<t>
2485   Since the Host header field acts as an application-level routing
2486   mechanism, it is a frequent target for malware seeking to poison
2487   a shared cache or redirect a request to an unintended server.
2488   An interception proxy is particularly vulnerable if it relies on
2489   the Host field-value for redirecting requests to internal
2490   servers, or for use as a cache key in a shared cache, without
2491   first verifying that the intercepted connection is targeting a
2492   valid IP address for that host.
2493</t>
2494<t>
2495   A server &MUST; respond with a <x:ref>400 (Bad Request)</x:ref> status code
2496   to any HTTP/1.1 request message that lacks a Host header field and
2497   to any request message that contains more than one Host header field
2498   or a Host header field with an invalid field-value.
2499</t>
2500</section>
2501
2502<section title="Effective Request URI" anchor="effective.request.uri">
2503  <iref primary="true" item="effective request URI"/>
2504  <x:anchor-alias value="effective request URI"/>
2505<t>
2506   A server that receives an HTTP request message &MUST; reconstruct
2507   the user agent's original target URI, based on the pieces of information
2508   learned from the request-target, <x:ref>Host</x:ref> header field, and
2509   connection context, in order to identify the intended target resource and
2510   properly service the request. The URI derived from this reconstruction
2511   process is referred to as the "<x:dfn>effective request URI</x:dfn>".
2512</t>
2513<t>
2514   For a user agent, the effective request URI is the target URI.
2515</t>
2516<t>
2517   If the request-target is in absolute-form, then the effective request URI
2518   is the same as the request-target.  Otherwise, the effective request URI
2519   is constructed as follows.
2520</t>
2521<t>
2522   If the request is received over a TLS-secured TCP connection,
2523   then the effective request URI's scheme is "https"; otherwise, the
2524   scheme is "http".
2525</t>
2526<t>
2527   If the request-target is in authority-form, then the effective
2528   request URI's authority component is the same as the request-target.
2529   Otherwise, if a <x:ref>Host</x:ref> header field is supplied with a
2530   non-empty field-value, then the authority component is the same as the
2531   Host field-value. Otherwise, the authority component is the concatenation of
2532   the default host name configured for the server, a colon (":"), and the
2533   connection's incoming TCP port number in decimal form.
2534</t>
2535<t>
2536   If the request-target is in authority-form or asterisk-form, then the
2537   effective request URI's combined path and query component is empty.
2538   Otherwise, the combined path and query component is the same as the
2539   request-target.
2540</t>
2541<t>
2542   The components of the effective request URI, once determined as above,
2543   can be combined into absolute-URI form by concatenating the scheme,
2544   "://", authority, and combined path and query component.
2545</t>
2546<figure>
2547<preamble>
2548   Example 1: the following message received over an insecure TCP connection
2549</preamble>
2550<artwork type="example" x:indent-with="  ">
2551GET /pub/WWW/TheProject.html HTTP/1.1
2552Host: www.example.org:8080
2553</artwork>
2554</figure>
2555<figure>
2556<preamble>
2557  has an effective request URI of
2558</preamble>
2559<artwork type="example" x:indent-with="  ">
2560http://www.example.org:8080/pub/WWW/TheProject.html
2561</artwork>
2562</figure>
2563<figure>
2564<preamble>
2565   Example 2: the following message received over a TLS-secured TCP connection
2566</preamble>
2567<artwork type="example" x:indent-with="  ">
2568OPTIONS * HTTP/1.1
2569Host: www.example.org
2570</artwork>
2571</figure>
2572<figure>
2573<preamble>
2574  has an effective request URI of
2575</preamble>
2576<artwork type="example" x:indent-with="  ">
2577https://www.example.org
2578</artwork>
2579</figure>
2580<t>
2581   An origin server that does not allow resources to differ by requested
2582   host &MAY; ignore the <x:ref>Host</x:ref> field-value and instead replace it
2583   with a configured server name when constructing the effective request URI.
2584</t>
2585<t>
2586   Recipients of an HTTP/1.0 request that lacks a <x:ref>Host</x:ref> header
2587   field &MAY; attempt to use heuristics (e.g., examination of the URI path for
2588   something unique to a particular host) in order to guess the
2589   effective request URI's authority component.
2590</t>
2591</section>
2592
2593<section title="Associating a Response to a Request" anchor="associating.response.to.request">
2594<t>
2595   HTTP does not include a request identifier for associating a given
2596   request message with its corresponding one or more response messages.
2597   Hence, it relies on the order of response arrival to correspond exactly
2598   to the order in which requests are made on the same connection.
2599   More than one response message per request only occurs when one or more
2600   informational responses (<x:ref>1xx</x:ref>, see &status-1xx;) precede a
2601   final response to the same request.
2602</t>
2603<t>
2604   A client that has more than one outstanding request on a connection &MUST;
2605   maintain a list of outstanding requests in the order sent and &MUST;
2606   associate each received response message on that connection to the highest
2607   ordered request that has not yet received a final (non-<x:ref>1xx</x:ref>)
2608   response.
2609</t>
2610</section>
2611
2612<section title="Message Forwarding" anchor="message.forwarding">
2613<t>
2614   As described in <xref target="intermediaries"/>, intermediaries can serve
2615   a variety of roles in the processing of HTTP requests and responses.
2616   Some intermediaries are used to improve performance or availability.
2617   Others are used for access control or to filter content.
2618   Since an HTTP stream has characteristics similar to a pipe-and-filter
2619   architecture, there are no inherent limits to the extent an intermediary
2620   can enhance (or interfere) with either direction of the stream.
2621</t>
2622<t>
2623   An intermediary not acting as a tunnel &MUST; implement the
2624   <x:ref>Connection</x:ref> header field, as specified in
2625   <xref target="header.connection"/>, and exclude fields from being forwarded
2626   that are only intended for the incoming connection.
2627</t>
2628<t>
2629   An intermediary &MUST-NOT; forward a message to itself unless it is
2630   protected from an infinite request loop. In general, an intermediary ought
2631   to recognize its own server names, including any aliases, local variations,
2632   or literal IP addresses, and respond to such requests directly.
2633</t>
2634
2635<section title="Via" anchor="header.via">
2636  <iref primary="true" item="Via header field" x:for-anchor=""/>
2637  <x:anchor-alias value="pseudonym"/>
2638  <x:anchor-alias value="received-by"/>
2639  <x:anchor-alias value="received-protocol"/>
2640  <x:anchor-alias value="Via"/>
2641<t>
2642   The "Via" header field indicates the presence of intermediate protocols and
2643   recipients between the user agent and the server (on requests) or between
2644   the origin server and the client (on responses), similar to the
2645   "Received" header field in email
2646   (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>).
2647   Via can be used for tracking message forwards,
2648   avoiding request loops, and identifying the protocol capabilities of
2649   senders along the request/response chain.
2650</t>
2651<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"/>
2652  <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> ] )
2653
2654  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2655                      ; see <xref target="header.upgrade"/>
2656  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2657  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2658</artwork></figure>
2659<t>
2660   Multiple Via field values represent each proxy or gateway that has
2661   forwarded the message. Each intermediary appends its own information
2662   about how the message was received, such that the end result is ordered
2663   according to the sequence of forwarding recipients.
2664</t>
2665<t>
2666   A proxy &MUST; send an appropriate Via header field, as described below, in
2667   each message that it forwards.
2668   An HTTP-to-HTTP gateway &MUST; send an appropriate Via header field in
2669   each inbound request message and &MAY; send a Via header field in
2670   forwarded response messages.
2671</t>
2672<t>
2673   For each intermediary, the received-protocol indicates the protocol and
2674   protocol version used by the upstream sender of the message. Hence, the
2675   Via field value records the advertised protocol capabilities of the
2676   request/response chain such that they remain visible to downstream
2677   recipients; this can be useful for determining what backwards-incompatible
2678   features might be safe to use in response, or within a later request, as
2679   described in <xref target="http.version"/>. For brevity, the protocol-name
2680   is omitted when the received protocol is HTTP.
2681</t>
2682<t>
2683   The received-by field is normally the host and optional port number of a
2684   recipient server or client that subsequently forwarded the message.
2685   However, if the real host is considered to be sensitive information, a
2686   sender &MAY; replace it with a pseudonym. If a port is not provided,
2687   a recipient &MAY; interpret that as meaning it was received on the default
2688   TCP port, if any, for the received-protocol.
2689</t>
2690<t>
2691   A sender &MAY; generate comments in the Via header field to identify the
2692   software of each recipient, analogous to the <x:ref>User-Agent</x:ref> and
2693   <x:ref>Server</x:ref> header fields. However, all comments in the Via field
2694   are optional and a recipient &MAY; remove them prior to forwarding the
2695   message.
2696</t>
2697<t>
2698   For example, a request message could be sent from an HTTP/1.0 user
2699   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2700   forward the request to a public proxy at p.example.net, which completes
2701   the request by forwarding it to the origin server at www.example.com.
2702   The request received by www.example.com would then have the following
2703   Via header field:
2704</t>
2705<figure><artwork type="example">
2706  Via: 1.0 fred, 1.1 p.example.net
2707</artwork></figure>
2708<t>
2709   An intermediary used as a portal through a network firewall
2710   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2711   region unless it is explicitly enabled to do so. If not enabled, such an
2712   intermediary &SHOULD; replace each received-by host of any host behind the
2713   firewall by an appropriate pseudonym for that host.
2714</t>
2715<t>
2716   An intermediary &MAY; combine an ordered subsequence of Via header
2717   field entries into a single such entry if the entries have identical
2718   received-protocol values. For example,
2719</t>
2720<figure><artwork type="example">
2721  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2722</artwork></figure>
2723<t>
2724  could be collapsed to
2725</t>
2726<figure><artwork type="example">
2727  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2728</artwork></figure>
2729<t>
2730   A sender &SHOULD-NOT; combine multiple entries unless they are all
2731   under the same organizational control and the hosts have already been
2732   replaced by pseudonyms. A sender &MUST-NOT; combine entries that
2733   have different received-protocol values.
2734</t>
2735</section>
2736
2737<section title="Transformations" anchor="message.transformations">
2738<t>
2739   Some intermediaries include features for transforming messages and their
2740   payloads.  A transforming proxy might, for example, convert between image
2741   formats in order to save cache space or to reduce the amount of traffic on
2742   a slow link. However, operational problems might occur when these
2743   transformations are applied to payloads intended for critical applications,
2744   such as medical imaging or scientific data analysis, particularly when
2745   integrity checks or digital signatures are used to ensure that the payload
2746   received is identical to the original.
2747</t>
2748<t>
2749   If a proxy receives a request-target with a host name that is not a
2750   fully qualified domain name, it &MAY; add its own domain to the host name
2751   it received when forwarding the request.  A proxy &MUST-NOT; change the
2752   host name if it is a fully qualified domain name.
2753</t>
2754<t>
2755   A proxy &MUST-NOT; modify the "absolute-path" and "query" parts of the
2756   received request-target when forwarding it to the next inbound server,
2757   except as noted above to replace an empty path with "/" or "*".
2758</t>
2759<t>
2760   A proxy &MUST-NOT; modify header fields that provide information about the
2761   end points of the communication chain, the resource state, or the selected
2762   representation. A proxy &MAY; change the message body through application
2763   or removal of a transfer coding (<xref target="transfer.codings"/>).
2764</t>
2765<t>
2766   A non-transforming proxy &MUST-NOT; modify the message payload (&payload;).
2767   A transforming proxy &MUST-NOT; modify the payload of a message that
2768   contains the no-transform cache-control directive.
2769</t>
2770<t>
2771   A transforming proxy &MAY; transform the payload of a message
2772   that does not contain the no-transform cache-control directive;
2773   if the payload is transformed, the transforming proxy &MUST; add a
2774   Warning header field with the warn-code of 214 ("Transformation Applied")
2775   if one does not already appear in the message (see &header-warning;).
2776   If the payload of a <x:ref>200 (OK)</x:ref> response is transformed, the
2777   transforming proxy can also inform downstream recipients that a
2778   transformation has been applied by changing the response status code to
2779   <x:ref>203 (Non-Authoritative Information)</x:ref> (&status-203;).
2780</t>
2781</section>
2782</section>
2783</section>
2784
2785<section title="Connection Management" anchor="connection.management">
2786<t>
2787   HTTP messaging is independent of the underlying transport or
2788   session-layer connection protocol(s).  HTTP only presumes a reliable
2789   transport with in-order delivery of requests and the corresponding
2790   in-order delivery of responses.  The mapping of HTTP request and
2791   response structures onto the data units of an underlying transport
2792   protocol is outside the scope of this specification.
2793</t>
2794<t>
2795   As described in <xref target="connecting.inbound"/>, the specific
2796   connection protocols to be used for an HTTP interaction are determined by
2797   client configuration and the <x:ref>target URI</x:ref>.
2798   For example, the "http" URI scheme
2799   (<xref target="http.uri"/>) indicates a default connection of TCP
2800   over IP, with a default TCP port of 80, but the client might be
2801   configured to use a proxy via some other connection, port, or protocol.
2802</t>
2803<t>
2804   HTTP implementations are expected to engage in connection management,
2805   which includes maintaining the state of current connections,
2806   establishing a new connection or reusing an existing connection,
2807   processing messages received on a connection, detecting connection
2808   failures, and closing each connection.
2809   Most clients maintain multiple connections in parallel, including
2810   more than one connection per server endpoint.
2811   Most servers are designed to maintain thousands of concurrent connections,
2812   while controlling request queues to enable fair use and detect
2813   denial of service attacks.
2814</t>
2815
2816<section title="Connection" anchor="header.connection">
2817  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2818  <iref primary="true" item="close" x:for-anchor=""/>
2819  <x:anchor-alias value="Connection"/>
2820  <x:anchor-alias value="connection-option"/>
2821  <x:anchor-alias value="close"/>
2822<t>
2823   The "Connection" header field allows the sender to indicate desired
2824   control options for the current connection.  In order to avoid confusing
2825   downstream recipients, a proxy or gateway &MUST; remove or replace any
2826   received connection options before forwarding the message.
2827</t>
2828<t>
2829   When a header field aside from Connection is used to supply control
2830   information for or about the current connection, the sender &MUST; list
2831   the corresponding field-name within the "Connection" header field.
2832   A proxy or gateway &MUST; parse a received Connection
2833   header field before a message is forwarded and, for each
2834   connection-option in this field, remove any header field(s) from
2835   the message with the same name as the connection-option, and then
2836   remove the Connection header field itself (or replace it with the
2837   intermediary's own connection options for the forwarded message).
2838</t>
2839<t>
2840   Hence, the Connection header field provides a declarative way of
2841   distinguishing header fields that are only intended for the
2842   immediate recipient ("hop-by-hop") from those fields that are
2843   intended for all recipients on the chain ("end-to-end"), enabling the
2844   message to be self-descriptive and allowing future connection-specific
2845   extensions to be deployed without fear that they will be blindly
2846   forwarded by older intermediaries.
2847</t>
2848<t>
2849   The Connection header field's value has the following grammar:
2850</t>
2851<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-option"/>
2852  <x:ref>Connection</x:ref>        = 1#<x:ref>connection-option</x:ref>
2853  <x:ref>connection-option</x:ref> = <x:ref>token</x:ref>
2854</artwork></figure>
2855<t>
2856   Connection options are case-insensitive.
2857</t>
2858<t>
2859   A sender &MUST-NOT; send a connection option corresponding to a header
2860   field that is intended for all recipients of the payload.
2861   For example, <x:ref>Cache-Control</x:ref> is never appropriate as a
2862   connection option (&header-cache-control;).
2863</t>
2864<t>
2865   The connection options do not always correspond to a header field
2866   present in the message, since a connection-specific header field
2867   might not be needed if there are no parameters associated with a
2868   connection option. In contrast, a connection-specific header field that
2869   is received without a corresponding connection option usually indicates
2870   that the field has been improperly forwarded by an intermediary and
2871   ought to be ignored by the recipient.
2872</t>
2873<t>
2874   When defining new connection options, specification authors ought to survey
2875   existing header field names and ensure that the new connection option does
2876   not share the same name as an already deployed header field.
2877   Defining a new connection option essentially reserves that potential
2878   field-name for carrying additional information related to the
2879   connection option, since it would be unwise for senders to use
2880   that field-name for anything else.
2881</t>
2882<t>
2883   The "<x:dfn>close</x:dfn>" connection option is defined for a
2884   sender to signal that this connection will be closed after completion of
2885   the response. For example,
2886</t>
2887<figure><artwork type="example">
2888  Connection: close
2889</artwork></figure>
2890<t>
2891   in either the request or the response header fields indicates that the
2892   sender is going to close the connection after the current request/response
2893   is complete (<xref target="persistent.tear-down"/>).
2894</t>
2895<t>
2896   A client that does not support <x:ref>persistent connections</x:ref> &MUST;
2897   send the "close" connection option in every request message.
2898</t>
2899<t>
2900   A server that does not support <x:ref>persistent connections</x:ref> &MUST;
2901   send the "close" connection option in every response message that
2902   does not have a <x:ref>1xx (Informational)</x:ref> status code.
2903</t>
2904</section>
2905
2906<section title="Establishment" anchor="persistent.establishment">
2907<t>
2908   It is beyond the scope of this specification to describe how connections
2909   are established via various transport or session-layer protocols.
2910   Each connection applies to only one transport link.
2911</t>
2912</section>
2913
2914<section title="Persistence" anchor="persistent.connections">
2915   <x:anchor-alias value="persistent connections"/>
2916<t>
2917   HTTP/1.1 defaults to the use of "<x:dfn>persistent connections</x:dfn>",
2918   allowing multiple requests and responses to be carried over a single
2919   connection. The "<x:ref>close</x:ref>" connection-option is used to signal
2920   that a connection will not persist after the current request/response.
2921   HTTP implementations &SHOULD; support persistent connections.
2922</t>
2923<t>
2924   A recipient determines whether a connection is persistent or not based on
2925   the most recently received message's protocol version and
2926   <x:ref>Connection</x:ref> header field (if any):
2927   <list style="symbols">
2928     <t>If the <x:ref>close</x:ref> connection option is present, the
2929        connection will not persist after the current response; else,</t>
2930     <t>If the received protocol is HTTP/1.1 (or later), the connection will
2931        persist after the current response; else,</t>
2932     <t>If the received protocol is HTTP/1.0, the "keep-alive"
2933        connection option is present, the recipient is not a proxy, and
2934        the recipient wishes to honor the HTTP/1.0 "keep-alive" mechanism,
2935        the connection will persist after the current response; otherwise,</t>
2936     <t>The connection will close after the current response.</t>
2937   </list>
2938</t>
2939<t>
2940   A server &MAY; assume that an HTTP/1.1 client intends to maintain a
2941   persistent connection until a <x:ref>close</x:ref> connection option
2942   is received in a request.
2943</t>
2944<t>
2945   A client &MAY; reuse a persistent connection until it sends or receives
2946   a <x:ref>close</x:ref> connection option or receives an HTTP/1.0 response
2947   without a "keep-alive" connection option.
2948</t>
2949<t>
2950   In order to remain persistent, all messages on a connection need to
2951   have a self-defined message length (i.e., one not defined by closure
2952   of the connection), as described in <xref target="message.body"/>.
2953   A server &MUST; read the entire request message body or close
2954   the connection after sending its response, since otherwise the
2955   remaining data on a persistent connection would be misinterpreted
2956   as the next request.  Likewise,
2957   a client &MUST; read the entire response message body if it intends
2958   to reuse the same connection for a subsequent request.
2959</t>
2960<t>
2961   A proxy server &MUST-NOT; maintain a persistent connection with an
2962   HTTP/1.0 client (see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/> for
2963   information and discussion of the problems with the Keep-Alive header field
2964   implemented by many HTTP/1.0 clients).
2965</t>
2966<t>
2967   Clients and servers &SHOULD-NOT; assume that a persistent connection is
2968   maintained for HTTP versions less than 1.1 unless it is explicitly
2969   signaled.
2970   See <xref target="compatibility.with.http.1.0.persistent.connections"/>
2971   for more information on backward compatibility with HTTP/1.0 clients.
2972</t>
2973
2974<section title="Retrying Requests" anchor="persistent.retrying.requests">
2975<t>
2976   Connections can be closed at any time, with or without intention.
2977   Implementations ought to anticipate the need to recover
2978   from asynchronous close events.
2979</t>
2980<t>
2981   When an inbound connection is closed prematurely, a client &MAY; open a new
2982   connection and automatically retransmit an aborted sequence of requests if
2983   all of those requests have idempotent methods (&idempotent-methods;).
2984   A proxy &MUST-NOT; automatically retry non-idempotent requests.
2985</t>
2986<t>
2987   A user agent &MUST-NOT; automatically retry a request with a non-idempotent
2988   method unless it has some means to know that the request semantics are
2989   actually idempotent, regardless of the method, or some means to detect that
2990   the original request was never applied. For example, a user agent that
2991   knows (through design or configuration) that a POST request to a given
2992   resource is safe can repeat that request automatically.
2993   Likewise, a user agent designed specifically to operate on a version
2994   control repository might be able to recover from partial failure conditions
2995   by checking the target resource revision(s) after a failed connection,
2996   reverting or fixing any changes that were partially applied, and then
2997   automatically retrying the requests that failed.
2998</t>
2999<t>
3000   A client &SHOULD-NOT; automatically retry a failed automatic retry.
3001</t>
3002</section>
3003
3004<section title="Pipelining" anchor="pipelining">
3005   <x:anchor-alias value="pipeline"/>
3006<t>
3007   A client that supports persistent connections &MAY; "<x:dfn>pipeline</x:dfn>"
3008   its requests (i.e., send multiple requests without waiting for each
3009   response). A server &MAY; process a sequence of pipelined requests in
3010   parallel if they all have safe methods (&safe-methods;), but &MUST; send
3011   the corresponding responses in the same order that the requests were
3012   received.
3013</t>
3014<t>
3015   A client that pipelines requests &SHOULD; retry unanswered requests if the
3016   connection closes before it receives all of the corresponding responses.
3017   When retrying pipelined requests after a failed connection (a connection
3018   not explicitly closed by the server in its last complete response), a
3019   client &MUST-NOT; pipeline immediately after connection establishment,
3020   since the first remaining request in the prior pipeline might have caused
3021   an error response that can be lost again if multiple requests are sent on a
3022   prematurely closed connection (see the TCP reset problem described in
3023   <xref target="persistent.tear-down"/>).
3024</t>
3025<t>
3026   Idempotent methods (&idempotent-methods;) are significant to pipelining
3027   because they can be automatically retried after a connection failure.
3028   A user agent &SHOULD-NOT; pipeline requests after a non-idempotent method,
3029   until the final response status code for that method has been received,
3030   unless the user agent has a means to detect and recover from partial
3031   failure conditions involving the pipelined sequence.
3032</t>
3033<t>
3034   An intermediary that receives pipelined requests &MAY; pipeline those
3035   requests when forwarding them inbound, since it can rely on the outbound
3036   user agent(s) to determine what requests can be safely pipelined. If the
3037   inbound connection fails before receiving a response, the pipelining
3038   intermediary &MAY; attempt to retry a sequence of requests that have yet
3039   to receive a response if the requests all have idempotent methods;
3040   otherwise, the pipelining intermediary &SHOULD; forward any received
3041   responses and then close the corresponding outbound connection(s) so that
3042   the outbound user agent(s) can recover accordingly.
3043</t>
3044</section>
3045</section>
3046   
3047<section title="Concurrency" anchor="persistent.concurrency">
3048<t>
3049   A client &SHOULD; limit the number of simultaneous open
3050   connections that it maintains to a given server.
3051</t>
3052<t>
3053   Previous revisions of HTTP gave a specific number of connections as a
3054   ceiling, but this was found to be impractical for many applications. As a
3055   result, this specification does not mandate a particular maximum number of
3056   connections, but instead encourages clients to be conservative when opening
3057   multiple connections.
3058</t>
3059<t>
3060   Multiple connections are typically used to avoid the "head-of-line
3061   blocking" problem, wherein a request that takes significant server-side
3062   processing and/or has a large payload blocks subsequent requests on the
3063   same connection. However, each connection consumes server resources.
3064   Furthermore, using multiple connections can cause undesirable side effects
3065   in congested networks.
3066</t>
3067<t>
3068   Note that servers might reject traffic that they deem abusive, including an
3069   excessive number of connections from a client.
3070</t>
3071</section>
3072
3073<section title="Failures and Time-outs" anchor="persistent.failures">
3074<t>
3075   Servers will usually have some time-out value beyond which they will
3076   no longer maintain an inactive connection. Proxy servers might make
3077   this a higher value since it is likely that the client will be making
3078   more connections through the same proxy server. The use of persistent
3079   connections places no requirements on the length (or existence) of
3080   this time-out for either the client or the server.
3081</t>
3082<t>
3083   A client or server that wishes to time-out &SHOULD; issue a graceful close
3084   on the connection. Implementations &SHOULD; constantly monitor open
3085   connections for a received closure signal and respond to it as appropriate,
3086   since prompt closure of both sides of a connection enables allocated system
3087   resources to be reclaimed.
3088</t>
3089<t>
3090   A client, server, or proxy &MAY; close the transport connection at any
3091   time. For example, a client might have started to send a new request
3092   at the same time that the server has decided to close the "idle"
3093   connection. From the server's point of view, the connection is being
3094   closed while it was idle, but from the client's point of view, a
3095   request is in progress.
3096</t>
3097<t>
3098   A server &SHOULD; sustain persistent connections, when possible, and allow
3099   the underlying
3100   transport's flow control mechanisms to resolve temporary overloads, rather
3101   than terminate connections with the expectation that clients will retry.
3102   The latter technique can exacerbate network congestion.
3103</t>
3104<t>
3105   A client sending a message body &SHOULD; monitor
3106   the network connection for an error response while it is transmitting
3107   the request. If the client sees a response that indicates the server does
3108   not wish to receive the message body and is closing the connection, the
3109   client &SHOULD; immediately cease transmitting the body and close its side
3110   of the connection.
3111</t>
3112</section>
3113   
3114<section title="Tear-down" anchor="persistent.tear-down">
3115  <iref primary="false" item="Connection header field" x:for-anchor=""/>
3116  <iref primary="false" item="close" x:for-anchor=""/>
3117<t>
3118   The <x:ref>Connection</x:ref> header field
3119   (<xref target="header.connection"/>) provides a "<x:ref>close</x:ref>"
3120   connection option that a sender &SHOULD; send when it wishes to close
3121   the connection after the current request/response pair.
3122</t>
3123<t>
3124   A client that sends a <x:ref>close</x:ref> connection option &MUST-NOT;
3125   send further requests on that connection (after the one containing
3126   <x:ref>close</x:ref>) and &MUST; close the connection after reading the
3127   final response message corresponding to this request.
3128</t>
3129<t>
3130   A server that receives a <x:ref>close</x:ref> connection option &MUST;
3131   initiate a close of the connection (see below) after it sends the
3132   final response to the request that contained <x:ref>close</x:ref>.
3133   The server &SHOULD; send a <x:ref>close</x:ref> connection option
3134   in its final response on that connection. The server &MUST-NOT; process
3135   any further requests received on that connection.
3136</t>
3137<t>
3138   A server that sends a <x:ref>close</x:ref> connection option &MUST;
3139   initiate a close of the connection (see below) after it sends the
3140   response containing <x:ref>close</x:ref>. The server &MUST-NOT; process
3141   any further requests received on that connection.
3142</t>
3143<t>
3144   A client that receives a <x:ref>close</x:ref> connection option &MUST;
3145   cease sending requests on that connection and close the connection
3146   after reading the response message containing the close; if additional
3147   pipelined requests had been sent on the connection, the client &SHOULD-NOT;
3148   assume that they will be processed by the server.
3149</t>
3150<t>
3151   If a server performs an immediate close of a TCP connection, there is a
3152   significant risk that the client will not be able to read the last HTTP
3153   response.  If the server receives additional data from the client on a
3154   fully-closed connection, such as another request that was sent by the
3155   client before receiving the server's response, the server's TCP stack will
3156   send a reset packet to the client; unfortunately, the reset packet might
3157   erase the client's unacknowledged input buffers before they can be read
3158   and interpreted by the client's HTTP parser.
3159</t>
3160<t>
3161   To avoid the TCP reset problem, servers typically close a connection in
3162   stages. First, the server performs a half-close by closing only the write
3163   side of the read/write connection. The server then continues to read from
3164   the connection until it receives a corresponding close by the client, or
3165   until the server is reasonably certain that its own TCP stack has received
3166   the client's acknowledgement of the packet(s) containing the server's last
3167   response. Finally, the server fully closes the connection.
3168</t>
3169<t>
3170   It is unknown whether the reset problem is exclusive to TCP or might also
3171   be found in other transport connection protocols.
3172</t>
3173</section>
3174
3175<section title="Upgrade" anchor="header.upgrade">
3176  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3177  <x:anchor-alias value="Upgrade"/>
3178  <x:anchor-alias value="protocol"/>
3179  <x:anchor-alias value="protocol-name"/>
3180  <x:anchor-alias value="protocol-version"/>
3181<t>
3182   The "Upgrade" header field is intended to provide a simple mechanism
3183   for transitioning from HTTP/1.1 to some other protocol on the same
3184   connection.  A client &MAY; send a list of protocols in the Upgrade
3185   header field of a request to invite the server to switch to one or
3186   more of those protocols, in order of descending preference, before sending
3187   the final response. A server &MAY; ignore a received Upgrade header field
3188   if it wishes to continue using the current protocol on that connection.
3189</t>
3190<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3191  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3192
3193  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3194  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3195  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3196</artwork></figure>
3197<t>
3198   A server that sends a <x:ref>101 (Switching Protocols)</x:ref> response
3199   &MUST; send an Upgrade header field to indicate the new protocol(s) to
3200   which the connection is being switched; if multiple protocol layers are
3201   being switched, the sender &MUST; list the protocols in layer-ascending
3202   order. A server &MUST-NOT; switch to a protocol that was not indicated by
3203   the client in the corresponding request's Upgrade header field.
3204   A server &MAY; choose to ignore the order of preference indicated by the
3205   client and select the new protocol(s) based on other factors, such as the
3206   nature of the request or the current load on the server.
3207</t>
3208<t>
3209   A server that sends a <x:ref>426 (Upgrade Required)</x:ref> response
3210   &MUST; send an Upgrade header field to indicate the acceptable protocols,
3211   in order of descending preference.
3212</t>
3213<t>
3214   A server &MAY; send an Upgrade header field in any other response to
3215   advertise that it implements support for upgrading to the listed protocols,
3216   in order of descending preference, when appropriate for a future request.
3217</t>
3218<figure><preamble>
3219   The following is a hypothetical example sent by a client:
3220</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3221GET /hello.txt HTTP/1.1
3222Host: www.example.com
3223Connection: upgrade
3224Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3225
3226</artwork></figure>
3227<t>
3228   Upgrade cannot be used to insist on a protocol change; its acceptance and
3229   use by the server is optional. The capabilities and nature of the
3230   application-level communication after the protocol change is entirely
3231   dependent upon the new protocol(s) chosen. However, immediately after
3232   sending the 101 response, the server is expected to continue responding to
3233   the original request as if it had received its equivalent within the new
3234   protocol (i.e., the server still has an outstanding request to satisfy
3235   after the protocol has been changed, and is expected to do so without
3236   requiring the request to be repeated).
3237</t>
3238<t>
3239   For example, if the Upgrade header field is received in a GET request
3240   and the server decides to switch protocols, it first responds
3241   with a <x:ref>101 (Switching Protocols)</x:ref> message in HTTP/1.1 and
3242   then immediately follows that with the new protocol's equivalent of a
3243   response to a GET on the target resource.  This allows a connection to be
3244   upgraded to protocols with the same semantics as HTTP without the
3245   latency cost of an additional round-trip.  A server &MUST-NOT; switch
3246   protocols unless the received message semantics can be honored by the new
3247   protocol; an OPTIONS request can be honored by any protocol.
3248</t>
3249<figure><preamble>
3250   The following is an example response to the above hypothetical request:
3251</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
3252HTTP/1.1 101 Switching Protocols
3253Connection: upgrade
3254Upgrade: HTTP/2.0
3255
3256[... data stream switches to HTTP/2.0 with an appropriate response
3257(as defined by new protocol) to the "GET /hello.txt" request ...]
3258</artwork></figure>
3259<t>
3260   When Upgrade is sent, the sender &MUST; also send a
3261   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
3262   that contains an "upgrade" connection option, in order to prevent Upgrade
3263   from being accidentally forwarded by intermediaries that might not implement
3264   the listed protocols.  A server &MUST; ignore an Upgrade header field that
3265   is received in an HTTP/1.0 request.
3266</t>
3267<t>
3268   A client cannot begin using an upgraded protocol on the connection until
3269   it has completely sent the request message (i.e., the client can't change
3270   the protocol it is sending in the middle of a message).
3271   If a server receives both Upgrade and an <x:ref>Expect</x:ref> header field
3272   with the "100-continue" expectation (&header-expect;), the
3273   server &MUST; send a <x:ref>100 (Continue)</x:ref> response before sending
3274   a <x:ref>101 (Switching Protocols)</x:ref> response.
3275</t>
3276<t>
3277   The Upgrade header field only applies to switching protocols on top of the
3278   existing connection; it cannot be used to switch the underlying connection
3279   (transport) protocol, nor to switch the existing communication to a
3280   different connection. For those purposes, it is more appropriate to use a
3281   <x:ref>3xx (Redirection)</x:ref> response (&status-3xx;).
3282</t>
3283<t>
3284   This specification only defines the protocol name "HTTP" for use by
3285   the family of Hypertext Transfer Protocols, as defined by the HTTP
3286   version rules of <xref target="http.version"/> and future updates to this
3287   specification. Additional tokens ought to be registered with IANA using the
3288   registration procedure defined in <xref target="upgrade.token.registry"/>.
3289</t>
3290</section>
3291</section>
3292
3293<section title="ABNF list extension: #rule" anchor="abnf.extension">
3294<t>
3295  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
3296  improve readability in the definitions of some header field values.
3297</t>
3298<t>
3299  A construct "#" is defined, similar to "*", for defining comma-delimited
3300  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
3301  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
3302  comma (",") and optional whitespace (OWS).   
3303</t>
3304<figure><preamble>
3305  Thus, a sender &MUST; expand the list construct as follows:
3306</preamble><artwork type="example">
3307  1#element =&gt; element *( OWS "," OWS element )
3308</artwork></figure>
3309<figure><preamble>
3310  and:
3311</preamble><artwork type="example">
3312  #element =&gt; [ 1#element ]
3313</artwork></figure>
3314<figure><preamble>
3315  and for n &gt;= 1 and m &gt; 1:
3316</preamble><artwork type="example">
3317  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
3318</artwork></figure>
3319<t>
3320  For compatibility with legacy list rules, a recipient &MUST; parse and ignore
3321  a reasonable number of empty list elements: enough to handle common mistakes
3322  by senders that merge values, but not so much that they could be used as a
3323  denial of service mechanism. In other words, a recipient &MUST; expand the
3324  list construct as follows:
3325</t>
3326<figure><artwork type="example">
3327  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
3328 
3329  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
3330</artwork></figure>
3331<t>
3332  Empty elements do not contribute to the count of elements present.
3333  For example, given these ABNF productions:
3334</t>
3335<figure><artwork type="example">
3336  example-list      = 1#example-list-elmt
3337  example-list-elmt = token ; see <xref target="field.components"/>
3338</artwork></figure>
3339<t>
3340  Then the following are valid values for example-list (not including the
3341  double quotes, which are present for delimitation only):
3342</t>
3343<figure><artwork type="example">
3344  "foo,bar"
3345  "foo ,bar,"
3346  "foo , ,bar,charlie   "
3347</artwork></figure>
3348<t>
3349  In contrast, the following values would be invalid, since at least one
3350  non-empty element is required by the example-list production:
3351</t>
3352<figure><artwork type="example">
3353  ""
3354  ","
3355  ",   ,"
3356</artwork></figure>
3357<t>
3358  <xref target="collected.abnf"/> shows the collected ABNF after the list
3359  constructs have been expanded, as described above, for recipients.
3360</t>
3361</section>
3362
3363<section title="IANA Considerations" anchor="IANA.considerations">
3364
3365<section title="Header Field Registration" anchor="header.field.registration">
3366<t>
3367   HTTP header fields are registered within the Message Header Field Registry
3368   maintained at
3369   <eref target="http://www.iana.org/assignments/message-headers/"/>.
3370</t>
3371<t>
3372   This document defines the following HTTP header fields, so their
3373   associated registry entries shall be updated according to the permanent
3374   registrations below (see <xref target="BCP90"/>):
3375</t>
3376<?BEGININC p1-messaging.iana-headers ?>
3377<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3378<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3379   <ttcol>Header Field Name</ttcol>
3380   <ttcol>Protocol</ttcol>
3381   <ttcol>Status</ttcol>
3382   <ttcol>Reference</ttcol>
3383
3384   <c>Connection</c>
3385   <c>http</c>
3386   <c>standard</c>
3387   <c>
3388      <xref target="header.connection"/>
3389   </c>
3390   <c>Content-Length</c>
3391   <c>http</c>
3392   <c>standard</c>
3393   <c>
3394      <xref target="header.content-length"/>
3395   </c>
3396   <c>Host</c>
3397   <c>http</c>
3398   <c>standard</c>
3399   <c>
3400      <xref target="header.host"/>
3401   </c>
3402   <c>TE</c>
3403   <c>http</c>
3404   <c>standard</c>
3405   <c>
3406      <xref target="header.te"/>
3407   </c>
3408   <c>Trailer</c>
3409   <c>http</c>
3410   <c>standard</c>
3411   <c>
3412      <xref target="header.trailer"/>
3413   </c>
3414   <c>Transfer-Encoding</c>
3415   <c>http</c>
3416   <c>standard</c>
3417   <c>
3418      <xref target="header.transfer-encoding"/>
3419   </c>
3420   <c>Upgrade</c>
3421   <c>http</c>
3422   <c>standard</c>
3423   <c>
3424      <xref target="header.upgrade"/>
3425   </c>
3426   <c>Via</c>
3427   <c>http</c>
3428   <c>standard</c>
3429   <c>
3430      <xref target="header.via"/>
3431   </c>
3432</texttable>
3433<!--(END)-->
3434<?ENDINC p1-messaging.iana-headers ?>
3435<t>
3436   Furthermore, the header field-name "Close" shall be registered as
3437   "reserved", since using that name as an HTTP header field might
3438   conflict with the "close" connection option of the "<x:ref>Connection</x:ref>"
3439   header field (<xref target="header.connection"/>).
3440</t>
3441<texttable align="left" suppress-title="true">
3442   <ttcol>Header Field Name</ttcol>
3443   <ttcol>Protocol</ttcol>
3444   <ttcol>Status</ttcol>
3445   <ttcol>Reference</ttcol>
3446
3447   <c>Close</c>
3448   <c>http</c>
3449   <c>reserved</c>
3450   <c>
3451      <xref target="header.field.registration"/>
3452   </c>
3453</texttable>
3454<t>
3455   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3456</t>
3457</section>
3458
3459<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3460<t>
3461   IANA maintains the registry of URI Schemes <xref target="BCP115"/> at
3462   <eref target="http://www.iana.org/assignments/uri-schemes/"/>.
3463</t>
3464<t>
3465   This document defines the following URI schemes, so their
3466   associated registry entries shall be updated according to the permanent
3467   registrations below:
3468</t>
3469<texttable align="left" suppress-title="true">
3470   <ttcol>URI Scheme</ttcol>
3471   <ttcol>Description</ttcol>
3472   <ttcol>Reference</ttcol>
3473
3474   <c>http</c>
3475   <c>Hypertext Transfer Protocol</c>
3476   <c><xref target="http.uri"/></c>
3477
3478   <c>https</c>
3479   <c>Hypertext Transfer Protocol Secure</c>
3480   <c><xref target="https.uri"/></c>
3481</texttable>
3482</section>
3483
3484<section title="Internet Media Type Registration" anchor="internet.media.type.http">
3485<t>
3486   IANA maintains the registry of Internet media types <xref target="BCP13"/> at
3487   <eref target="http://www.iana.org/assignments/media-types"/>.
3488</t>
3489<t>
3490   This document serves as the specification for the Internet media types
3491   "message/http" and "application/http". The following is to be registered with
3492   IANA.
3493</t>
3494<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3495<iref item="Media Type" subitem="message/http" primary="true"/>
3496<iref item="message/http Media Type" primary="true"/>
3497<t>
3498   The message/http type can be used to enclose a single HTTP request or
3499   response message, provided that it obeys the MIME restrictions for all
3500   "message" types regarding line length and encodings.
3501</t>
3502<t>
3503  <list style="hanging" x:indent="12em">
3504    <t hangText="Type name:">
3505      message
3506    </t>
3507    <t hangText="Subtype name:">
3508      http
3509    </t>
3510    <t hangText="Required parameters:">
3511      N/A
3512    </t>
3513    <t hangText="Optional parameters:">
3514      version, msgtype
3515      <list style="hanging">
3516        <t hangText="version:">
3517          The HTTP-version number of the enclosed message
3518          (e.g., "1.1"). If not present, the version can be
3519          determined from the first line of the body.
3520        </t>
3521        <t hangText="msgtype:">
3522          The message type &mdash; "request" or "response". If not
3523          present, the type can be determined from the first
3524          line of the body.
3525        </t>
3526      </list>
3527    </t>
3528    <t hangText="Encoding considerations:">
3529      only "7bit", "8bit", or "binary" are permitted
3530    </t>
3531    <t hangText="Security considerations:">
3532      see <xref target="security.considerations"/>
3533    </t>
3534    <t hangText="Interoperability considerations:">
3535      N/A
3536    </t>
3537    <t hangText="Published specification:">
3538      This specification (see <xref target="internet.media.type.message.http"/>).
3539    </t>
3540    <t hangText="Applications that use this media type:">
3541      N/A
3542    </t>
3543    <t hangText="Fragment identifier considerations:">
3544      N/A
3545    </t>
3546    <t hangText="Additional information:">
3547      <list style="hanging">
3548        <t hangText="Magic number(s):">N/A</t>
3549        <t hangText="Deprecated alias names for this type:">N/A</t>
3550        <t hangText="File extension(s):">N/A</t>
3551        <t hangText="Macintosh file type code(s):">N/A</t>
3552      </list>
3553    </t>
3554    <t hangText="Person and email address to contact for further information:">
3555      See Authors Section.
3556    </t>
3557    <t hangText="Intended usage:">
3558      COMMON
3559    </t>
3560    <t hangText="Restrictions on usage:">
3561      N/A
3562    </t>
3563    <t hangText="Author:">
3564      See Authors Section.
3565    </t>
3566    <t hangText="Change controller:">
3567      IESG
3568    </t>
3569  </list>
3570</t>
3571</section>
3572<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3573<iref item="Media Type" subitem="application/http" primary="true"/>
3574<iref item="application/http Media Type" primary="true"/>
3575<t>
3576   The application/http type can be used to enclose a pipeline of one or more
3577   HTTP request or response messages (not intermixed).
3578</t>
3579<t>
3580  <list style="hanging" x:indent="12em">
3581    <t hangText="Type name:">
3582      application
3583    </t>
3584    <t hangText="Subtype name:">
3585      http
3586    </t>
3587    <t hangText="Required parameters:">
3588      N/A
3589    </t>
3590    <t hangText="Optional parameters:">
3591      version, msgtype
3592      <list style="hanging">
3593        <t hangText="version:">
3594          The HTTP-version number of the enclosed messages
3595          (e.g., "1.1"). If not present, the version can be
3596          determined from the first line of the body.
3597        </t>
3598        <t hangText="msgtype:">
3599          The message type &mdash; "request" or "response". If not
3600          present, the type can be determined from the first
3601          line of the body.
3602        </t>
3603      </list>
3604    </t>
3605    <t hangText="Encoding considerations:">
3606      HTTP messages enclosed by this type
3607      are in "binary" format; use of an appropriate
3608      Content-Transfer-Encoding is required when
3609      transmitted via E-mail.
3610    </t>
3611    <t hangText="Security considerations:">
3612      see <xref target="security.considerations"/>
3613    </t>
3614    <t hangText="Interoperability considerations:">
3615      N/A
3616    </t>
3617    <t hangText="Published specification:">
3618      This specification (see <xref target="internet.media.type.application.http"/>).
3619    </t>
3620    <t hangText="Applications that use this media type:">
3621      N/A
3622    </t>
3623    <t hangText="Fragment identifier considerations:">
3624      N/A
3625    </t>
3626    <t hangText="Additional information:">
3627      <list style="hanging">
3628        <t hangText="Deprecated alias names for this type:">N/A</t>
3629        <t hangText="Magic number(s):">N/A</t>
3630        <t hangText="File extension(s):">N/A</t>
3631        <t hangText="Macintosh file type code(s):">N/A</t>
3632      </list>
3633    </t>
3634    <t hangText="Person and email address to contact for further information:">
3635      See Authors Section.
3636    </t>
3637    <t hangText="Intended usage:">
3638      COMMON
3639    </t>
3640    <t hangText="Restrictions on usage:">
3641      N/A
3642    </t>
3643    <t hangText="Author:">
3644      See Authors Section.
3645    </t>
3646    <t hangText="Change controller:">
3647      IESG
3648    </t>
3649  </list>
3650</t>
3651</section>
3652</section>
3653
3654<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3655<t>
3656   The HTTP Transfer Coding Registry defines the name space for transfer
3657   coding names. It is maintained at <eref target="http://www.iana.org/assignments/http-parameters"/>.
3658</t>
3659
3660<section title="Procedure" anchor="transfer.coding.registry.procedure">
3661<t>
3662   Registrations &MUST; include the following fields:
3663   <list style="symbols">
3664     <t>Name</t>
3665     <t>Description</t>
3666     <t>Pointer to specification text</t>
3667   </list>
3668</t>
3669<t>
3670   Names of transfer codings &MUST-NOT; overlap with names of content codings
3671   (&content-codings;) unless the encoding transformation is identical, as
3672   is the case for the compression codings defined in
3673   <xref target="compression.codings"/>.
3674</t>
3675<t>
3676   Values to be added to this name space require IETF Review (see
3677   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3678   conform to the purpose of transfer coding defined in this specification.
3679</t>
3680<t>
3681   Use of program names for the identification of encoding formats
3682   is not desirable and is discouraged for future encodings.
3683</t>
3684</section>
3685
3686<section title="Registration" anchor="transfer.coding.registration">
3687<t>
3688   The HTTP Transfer Coding Registry shall be updated with the registrations
3689   below:
3690</t>
3691<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3692   <ttcol>Name</ttcol>
3693   <ttcol>Description</ttcol>
3694   <ttcol>Reference</ttcol>
3695   <c>chunked</c>
3696   <c>Transfer in a series of chunks</c>
3697   <c>
3698      <xref target="chunked.encoding"/>
3699   </c>
3700   <c>compress</c>
3701   <c>UNIX "compress" data format <xref target="Welch"/></c>
3702   <c>
3703      <xref target="compress.coding"/>
3704   </c>
3705   <c>deflate</c>
3706   <c>"deflate" compressed data (<xref target="RFC1951"/>) inside
3707   the "zlib" data format (<xref target="RFC1950"/>)
3708   </c>
3709   <c>
3710      <xref target="deflate.coding"/>
3711   </c>
3712   <c>gzip</c>
3713   <c>GZIP file format <xref target="RFC1952"/></c>
3714   <c>
3715      <xref target="gzip.coding"/>
3716   </c>
3717   <c>x-compress</c>
3718   <c>Deprecated (alias for compress)</c>
3719   <c>
3720      <xref target="compress.coding"/>
3721   </c>
3722   <c>x-gzip</c>
3723   <c>Deprecated (alias for gzip)</c>
3724   <c>
3725      <xref target="gzip.coding"/>
3726   </c>
3727</texttable>
3728</section>
3729</section>
3730
3731<section title="Content Coding Registration" anchor="content.coding.registration">
3732<t>
3733   IANA maintains the registry of HTTP Content Codings at
3734   <eref target="http://www.iana.org/assignments/http-parameters"/>.
3735</t>
3736<t>
3737   The HTTP Content Codings Registry shall be updated with the registrations
3738   below:
3739</t>
3740<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
3741   <ttcol>Name</ttcol>
3742   <ttcol>Description</ttcol>
3743   <ttcol>Reference</ttcol>
3744   <c>compress</c>
3745   <c>UNIX "compress" data format <xref target="Welch"/></c>
3746   <c>
3747      <xref target="compress.coding"/>
3748   </c>
3749   <c>deflate</c>
3750   <c>"deflate" compressed data (<xref target="RFC1951"/>) inside
3751   the "zlib" data format (<xref target="RFC1950"/>)</c>
3752   <c>
3753      <xref target="deflate.coding"/>
3754   </c>
3755   <c>gzip</c>
3756   <c>GZIP file format <xref target="RFC1952"/></c>
3757   <c>
3758      <xref target="gzip.coding"/>
3759   </c>
3760   <c>x-compress</c>
3761   <c>Deprecated (alias for compress)</c>
3762   <c>
3763      <xref target="compress.coding"/>
3764   </c>
3765   <c>x-gzip</c>
3766   <c>Deprecated (alias for gzip)</c>
3767   <c>
3768      <xref target="gzip.coding"/>
3769   </c>
3770</texttable>
3771</section>
3772
3773<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3774<t>
3775   The HTTP Upgrade Token Registry defines the name space for protocol-name
3776   tokens used to identify protocols in the <x:ref>Upgrade</x:ref> header
3777   field. The registry is maintained at <eref target="http://www.iana.org/assignments/http-upgrade-tokens"/>.
3778</t>
3779
3780<section title="Procedure" anchor="upgrade.token.registry.procedure">  
3781<t>
3782   Each registered protocol name is associated with contact information
3783   and an optional set of specifications that details how the connection
3784   will be processed after it has been upgraded.
3785</t>
3786<t>
3787   Registrations happen on a "First Come First Served" basis (see
3788   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3789   following rules:
3790  <list style="numbers">
3791    <t>A protocol-name token, once registered, stays registered forever.</t>
3792    <t>The registration &MUST; name a responsible party for the
3793       registration.</t>
3794    <t>The registration &MUST; name a point of contact.</t>
3795    <t>The registration &MAY; name a set of specifications associated with
3796       that token. Such specifications need not be publicly available.</t>
3797    <t>The registration &SHOULD; name a set of expected "protocol-version"
3798       tokens associated with that token at the time of registration.</t>
3799    <t>The responsible party &MAY; change the registration at any time.
3800       The IANA will keep a record of all such changes, and make them
3801       available upon request.</t>
3802    <t>The IESG &MAY; reassign responsibility for a protocol token.
3803       This will normally only be used in the case when a
3804       responsible party cannot be contacted.</t>
3805  </list>
3806</t>
3807<t>
3808   This registration procedure for HTTP Upgrade Tokens replaces that
3809   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3810</t>
3811</section>
3812
3813<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3814<t>
3815   The "HTTP" entry in the HTTP Upgrade Token Registry shall be updated with
3816   the registration below:
3817</t>
3818<texttable align="left" suppress-title="true">
3819   <ttcol>Value</ttcol>
3820   <ttcol>Description</ttcol>
3821   <ttcol>Expected Version Tokens</ttcol>
3822   <ttcol>Reference</ttcol>
3823
3824   <c>HTTP</c>
3825   <c>Hypertext Transfer Protocol</c>
3826   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3827   <c><xref target="http.version"/></c>
3828</texttable>
3829<t>
3830   The responsible party is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3831</t>
3832</section>
3833</section>
3834
3835</section>
3836
3837<section title="Security Considerations" anchor="security.considerations">
3838<t>
3839   This section is meant to inform developers, information providers, and
3840   users of known security concerns relevant to HTTP/1.1 message syntax,
3841   parsing, and routing.
3842</t>
3843
3844<section title="DNS-related Attacks" anchor="dns.related.attacks">
3845<t>
3846   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3847   generally prone to security attacks based on the deliberate misassociation
3848   of IP addresses and DNS names not protected by DNSSEC. Clients need to be
3849   cautious in assuming the validity of an IP number/DNS name association unless
3850   the response is protected by DNSSEC (<xref target="RFC4033"/>).
3851</t>
3852</section>
3853
3854<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3855<t>
3856   By their very nature, HTTP intermediaries are men-in-the-middle, and
3857   represent an opportunity for man-in-the-middle attacks. Compromise of
3858   the systems on which the intermediaries run can result in serious security
3859   and privacy problems. Intermediaries have access to security-related
3860   information, personal information about individual users and
3861   organizations, and proprietary information belonging to users and
3862   content providers. A compromised intermediary, or an intermediary
3863   implemented or configured without regard to security and privacy
3864   considerations, might be used in the commission of a wide range of
3865   potential attacks.
3866</t>
3867<t>
3868   Intermediaries that contain a shared cache are especially vulnerable
3869   to cache poisoning attacks.
3870</t>
3871<t>
3872   Implementers need to consider the privacy and security
3873   implications of their design and coding decisions, and of the
3874   configuration options they provide to operators (especially the
3875   default configuration).
3876</t>
3877<t>
3878   Users need to be aware that intermediaries are no more trustworthy than
3879   the people who run them; HTTP itself cannot solve this problem.
3880</t>
3881</section>
3882
3883<section title="Buffer Overflows" anchor="attack.protocol.element.size.overflows">
3884<t>
3885   Because HTTP uses mostly textual, character-delimited fields, attackers can
3886   overflow buffers in implementations, and/or perform a Denial of Service
3887   against implementations that accept fields with unlimited lengths.
3888</t>
3889<t>
3890   To promote interoperability, this specification makes specific
3891   recommendations for minimum size limits on request-line
3892   (<xref target="request.line"/>)
3893   and header fields (<xref target="header.fields"/>). These are
3894   minimum recommendations, chosen to be supportable even by implementations
3895   with limited resources; it is expected that most implementations will
3896   choose substantially higher limits.
3897</t>
3898<t>
3899   This specification also provides a way for servers to reject messages that
3900   have request-targets that are too long (&status-414;) or request entities
3901   that are too large (&status-4xx;). Additional status codes related to
3902   capacity limits have been defined by extensions to HTTP
3903   <xref target="RFC6585"/>.
3904</t>
3905<t>
3906   Recipients ought to carefully limit the extent to which they read other
3907   fields, including (but not limited to) request methods, response status
3908   phrases, header field-names, and body chunks, so as to avoid denial of
3909   service attacks without impeding interoperability.
3910</t>
3911</section>
3912
3913<section title="Message Integrity" anchor="message.integrity">
3914<t>
3915   HTTP does not define a specific mechanism for ensuring message integrity,
3916   instead relying on the error-detection ability of underlying transport
3917   protocols and the use of length or chunk-delimited framing to detect
3918   completeness. Additional integrity mechanisms, such as hash functions or
3919   digital signatures applied to the content, can be selectively added to
3920   messages via extensible metadata header fields. Historically, the lack of
3921   a single integrity mechanism has been justified by the informal nature of
3922   most HTTP communication.  However, the prevalence of HTTP as an information
3923   access mechanism has resulted in its increasing use within environments
3924   where verification of message integrity is crucial.
3925</t>
3926<t>
3927   User agents are encouraged to implement configurable means for detecting
3928   and reporting failures of message integrity such that those means can be
3929   enabled within environments for which integrity is necessary. For example,
3930   a browser being used to view medical history or drug interaction
3931   information needs to indicate to the user when such information is detected
3932   by the protocol to be incomplete, expired, or corrupted during transfer.
3933   Such mechanisms might be selectively enabled via user agent extensions or
3934   the presence of message integrity metadata in a response.
3935   At a minimum, user agents ought to provide some indication that allows a
3936   user to distinguish between a complete and incomplete response message
3937   (<xref target="incomplete.messages"/>) when such verification is desired.
3938</t>
3939</section>
3940
3941<section title="Server Log Information" anchor="abuse.of.server.log.information">
3942<t>
3943   A server is in the position to save personal data about a user's requests
3944   over time, which might identify their reading patterns or subjects of
3945   interest.  In particular, log information gathered at an intermediary
3946   often contains a history of user agent interaction, across a multitude
3947   of sites, that can be traced to individual users.
3948</t>
3949<t>
3950   HTTP log information is confidential in nature; its handling is often
3951   constrained by laws and regulations.  Log information needs to be securely
3952   stored and appropriate guidelines followed for its analysis.
3953   Anonymization of personal information within individual entries helps,
3954   but is generally not sufficient to prevent real log traces from being
3955   re-identified based on correlation with other access characteristics.
3956   As such, access traces that are keyed to a specific client are unsafe to
3957   publish even if the key is pseudonymous.
3958</t>
3959<t>
3960   To minimize the risk of theft or accidental publication, log information
3961   ought to be purged of personally identifiable information, including
3962   user identifiers, IP addresses, and user-provided query parameters,
3963   as soon as that information is no longer necessary to support operational
3964   needs for security, auditing, or fraud control.
3965</t>
3966</section>
3967</section>
3968
3969<section title="Acknowledgments" anchor="acks">
3970<t>
3971   This edition of HTTP/1.1 builds on the many contributions that went into
3972   <xref target="RFC1945" format="none">RFC 1945</xref>,
3973   <xref target="RFC2068" format="none">RFC 2068</xref>,
3974   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3975   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3976   substantial contributions made by the previous authors, editors, and
3977   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3978   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3979   and Paul J. Leach. Mark Nottingham oversaw this effort as working group chair.
3980</t>
3981<t>
3982   Since 1999, the following contributors have helped improve the HTTP
3983   specification by reporting bugs, asking smart questions, drafting or
3984   reviewing text, and evaluating open issues:
3985</t>
3986<?BEGININC acks ?>
3987<t>Adam Barth,
3988Adam Roach,
3989Addison Phillips,
3990Adrian Chadd,
3991Adrien W. de Croy,
3992Alan Ford,
3993Alan Ruttenberg,
3994Albert Lunde,
3995Alek Storm,
3996Alex Rousskov,
3997Alexandre Morgaut,
3998Alexey Melnikov,
3999Alisha Smith,
4000Amichai Rothman,
4001Amit Klein,
4002Amos Jeffries,
4003Andreas Maier,
4004Andreas Petersson,
4005Andrei Popov,
4006Anil Sharma,
4007Anne van Kesteren,
4008Anthony Bryan,
4009Asbjorn Ulsberg,
4010Ashok Kumar,
4011Balachander Krishnamurthy,
4012Barry Leiba,
4013Ben Laurie,
4014Benjamin Carlyle,
4015Benjamin Niven-Jenkins,
4016Bil Corry,
4017Bill Burke,
4018Bjoern Hoehrmann,
4019Bob Scheifler,
4020Boris Zbarsky,
4021Brett Slatkin,
4022Brian Kell,
4023Brian McBarron,
4024Brian Pane,
4025Brian Raymor,
4026Brian Smith,
4027Bruce Perens,
4028Bryce Nesbitt,
4029Cameron Heavon-Jones,
4030Carl Kugler,
4031Carsten Bormann,
4032Charles Fry,
4033Chris Burdess,
4034Chris Newman,
4035Cyrus Daboo,
4036Dale Robert Anderson,
4037Dan Wing,
4038Dan Winship,
4039Daniel Stenberg,
4040Darrel Miller,
4041Dave Cridland,
4042Dave Crocker,
4043Dave Kristol,
4044Dave Thaler,
4045David Booth,
4046David Singer,
4047David W. Morris,
4048Diwakar Shetty,
4049Dmitry Kurochkin,
4050Drummond Reed,
4051Duane Wessels,
4052Edward Lee,
4053Eitan Adler,
4054Eliot Lear,
4055Emile Stephan,
4056Eran Hammer-Lahav,
4057Eric D. Williams,
4058Eric J. Bowman,
4059Eric Lawrence,
4060Eric Rescorla,
4061Erik Aronesty,
4062EungJun Yi,
4063Evan Prodromou,
4064Felix Geisendoerfer,
4065Florian Weimer,
4066Frank Ellermann,
4067Fred Akalin,
4068Fred Bohle,
4069Frederic Kayser,
4070Gabor Molnar,
4071Gabriel Montenegro,
4072Geoffrey Sneddon,
4073Gervase Markham,
4074Gili Tzabari,
4075Grahame Grieve,
4076Greg Slepak,
4077Greg Wilkins,
4078Grzegorz Calkowski,
4079Harald Tveit Alvestrand,
4080Harry Halpin,
4081Helge Hess,
4082Henrik Nordstrom,
4083Henry S. Thompson,
4084Henry Story,
4085Herbert van de Sompel,
4086Herve Ruellan,
4087Howard Melman,
4088Hugo Haas,
4089Ian Fette,
4090Ian Hickson,
4091Ido Safruti,
4092Ilari Liusvaara,
4093Ilya Grigorik,
4094Ingo Struck,
4095J. Ross Nicoll,
4096James Cloos,
4097James H. Manger,
4098James Lacey,
4099James M. Snell,
4100Jamie Lokier,
4101Jan Algermissen,
4102Jeff Hodges (who came up with the term 'effective Request-URI'),
4103Jeff Pinner,
4104Jeff Walden,
4105Jim Luther,
4106Jitu Padhye,
4107Joe D. Williams,
4108Joe Gregorio,
4109Joe Orton,
4110John C. Klensin,
4111John C. Mallery,
4112John Cowan,
4113John Kemp,
4114John Panzer,
4115John Schneider,
4116John Stracke,
4117John Sullivan,
4118Jonas Sicking,
4119Jonathan A. Rees,
4120Jonathan Billington,
4121Jonathan Moore,
4122Jonathan Silvera,
4123Jordi Ros,
4124Joris Dobbelsteen,
4125Josh Cohen,
4126Julien Pierre,
4127Jungshik Shin,
4128Justin Chapweske,
4129Justin Erenkrantz,
4130Justin James,
4131Kalvinder Singh,
4132Karl Dubost,
4133Keith Hoffman,
4134Keith Moore,
4135Ken Murchison,
4136Koen Holtman,
4137Konstantin Voronkov,
4138Kris Zyp,
4139Leif Hedstrom,
4140Lisa Dusseault,
4141Maciej Stachowiak,
4142Manu Sporny,
4143Marc Schneider,
4144Marc Slemko,
4145Mark Baker,
4146Mark Pauley,
4147Mark Watson,
4148Markus Isomaki,
4149Markus Lanthaler,
4150Martin J. Duerst,
4151Martin Musatov,
4152Martin Nilsson,
4153Martin Thomson,
4154Matt Lynch,
4155Matthew Cox,
4156Matthew Kerwin,
4157Max Clark,
4158Michael Burrows,
4159Michael Hausenblas,
4160Michael Scharf,
4161Michael Sweet,
4162Michael Tuexen,
4163Michael Welzl,
4164Mike Amundsen,
4165Mike Belshe,
4166Mike Bishop,
4167Mike Kelly,
4168Mike Schinkel,
4169Miles Sabin,
4170Murray S. Kucherawy,
4171Mykyta Yevstifeyev,
4172Nathan Rixham,
4173Nicholas Shanks,
4174Nico Williams,
4175Nicolas Alvarez,
4176Nicolas Mailhot,
4177Noah Slater,
4178Osama Mazahir,
4179Pablo Castro,
4180Pat Hayes,
4181Patrick R. McManus,
4182Paul E. Jones,
4183Paul Hoffman,
4184Paul Marquess,
4185Peter Lepeska,
4186Peter Occil,
4187Peter Saint-Andre,
4188Peter Watkins,
4189Phil Archer,
4190Philippe Mougin,
4191Phillip Hallam-Baker,
4192Piotr Dobrogost,
4193Poul-Henning Kamp,
4194Preethi Natarajan,
4195Rajeev Bector,
4196Ray Polk,
4197Reto Bachmann-Gmuer,
4198Richard Cyganiak,
4199Robby Simpson,
4200Robert Brewer,
4201Robert Collins,
4202Robert Mattson,
4203Robert O'Callahan,
4204Robert Olofsson,
4205Robert Sayre,
4206Robert Siemer,
4207Robert de Wilde,
4208Roberto Javier Godoy,
4209Roberto Peon,
4210Roland Zink,
4211Ronny Widjaja,
4212Ryan Hamilton,
4213S. Mike Dierken,
4214Salvatore Loreto,
4215Sam Johnston,
4216Sam Pullara,
4217Sam Ruby,
4218Saurabh Kulkarni,
4219Scott Lawrence (who maintained the original issues list),
4220Sean B. Palmer,
4221Sebastien Barnoud,
4222Shane McCarron,
4223Shigeki Ohtsu,
4224Simon Yarde,
4225Stefan Eissing,
4226Stefan Tilkov,
4227Stefanos Harhalakis,
4228Stephane Bortzmeyer,
4229Stephen Farrell,
4230Stephen Ludin,
4231Stuart Williams,
4232Subbu Allamaraju,
4233Subramanian Moonesamy,
4234Sylvain Hellegouarch,
4235Tapan Divekar,
4236Tatsuhiro Tsujikawa,
4237Tatsuya Hayashi,
4238Ted Hardie,
4239Thomas Broyer,
4240Thomas Fossati,
4241Thomas Maslen,
4242Thomas Nordin,
4243Thomas Roessler,
4244Tim Bray,
4245Tim Morgan,
4246Tim Olsen,
4247Tom Zhou,
4248Travis Snoozy,
4249Tyler Close,
4250Vincent Murphy,
4251Wenbo Zhu,
4252Werner Baumann,
4253Wilbur Streett,
4254Wilfredo Sanchez Vega,
4255William A. Rowe Jr.,
4256William Chan,
4257Willy Tarreau,
4258Xiaoshu Wang,
4259Yaron Goland,
4260Yngve Nysaeter Pettersen,
4261Yoav Nir,
4262Yogesh Bang,
4263Yuchung Cheng,
4264Yutaka Oiwa,
4265Yves Lafon (long-time member of the editor team),
4266Zed A. Shaw, and
4267Zhong Yu.
4268</t>
4269<?ENDINC acks ?>
4270<t>
4271   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
4272   acknowledgements from prior revisions.
4273</t>
4274</section>
4275
4276</middle>
4277<back>
4278
4279<references title="Normative References">
4280
4281<reference anchor="Part2">
4282  <front>
4283    <title>Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</title>
4284    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4285      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4286      <address><email>fielding@gbiv.com</email></address>
4287    </author>
4288    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4289      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4290      <address><email>julian.reschke@greenbytes.de</email></address>
4291    </author>
4292    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4293  </front>
4294  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4295  <x:source href="p2-semantics.xml" basename="p2-semantics">
4296    <x:defines>1xx (Informational)</x:defines>
4297    <x:defines>1xx</x:defines>
4298    <x:defines>100 (Continue)</x:defines>
4299    <x:defines>101 (Switching Protocols)</x:defines>
4300    <x:defines>2xx (Successful)</x:defines>
4301    <x:defines>2xx</x:defines>
4302    <x:defines>200 (OK)</x:defines>
4303    <x:defines>203 (Non-Authoritative Information)</x:defines>
4304    <x:defines>204 (No Content)</x:defines>
4305    <x:defines>3xx (Redirection)</x:defines>
4306    <x:defines>3xx</x:defines>
4307    <x:defines>301 (Moved Permanently)</x:defines>
4308    <x:defines>4xx (Client Error)</x:defines>
4309    <x:defines>4xx</x:defines>
4310    <x:defines>400 (Bad Request)</x:defines>
4311    <x:defines>411 (Length Required)</x:defines>
4312    <x:defines>414 (URI Too Long)</x:defines>
4313    <x:defines>417 (Expectation Failed)</x:defines>
4314    <x:defines>426 (Upgrade Required)</x:defines>
4315    <x:defines>501 (Not Implemented)</x:defines>
4316    <x:defines>502 (Bad Gateway)</x:defines>
4317    <x:defines>505 (HTTP Version Not Supported)</x:defines>
4318    <x:defines>Accept-Encoding</x:defines>
4319    <x:defines>Allow</x:defines>
4320    <x:defines>Content-Encoding</x:defines>
4321    <x:defines>Content-Location</x:defines>
4322    <x:defines>Content-Type</x:defines>
4323    <x:defines>Date</x:defines>
4324    <x:defines>Expect</x:defines>
4325    <x:defines>Location</x:defines>
4326    <x:defines>Server</x:defines>
4327    <x:defines>User-Agent</x:defines>
4328  </x:source>
4329</reference>
4330
4331<reference anchor="Part4">
4332  <front>
4333    <title>Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests</title>
4334    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
4335      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4336      <address><email>fielding@gbiv.com</email></address>
4337    </author>
4338    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
4339      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4340      <address><email>julian.reschke@greenbytes.de</email></address>
4341    </author>
4342    <date month="&ID-MONTH;" year="&ID-YEAR;" />
4343  </front>
4344  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;" />
4345  <x:source basename="p4-conditional" href="p4-conditional.xml">
4346    <x:defines>304 (Not Modified)</x:defines>
4347    <x:defines>ETag</x:defines>
4348    <x:defines>Last-Modified</x:defines>
4349  </x:source>
4350</reference>
4351
4352<reference anchor="Part5">
4353  <front>
4354    <title>Hypertext Transfer Protocol (HTTP/1.1): Range Requests</title>
4355    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4356      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4357      <address><email>fielding@gbiv.com</email></address>
4358    </author>
4359    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4360      <organization abbrev="W3C">World Wide Web Consortium</organization>
4361      <address><email>ylafon@w3.org</email></address>
4362    </author>
4363    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4364      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4365      <address><email>julian.reschke@greenbytes.de</email></address>
4366    </author>
4367    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4368  </front>
4369  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
4370  <x:source href="p5-range.xml" basename="p5-range">
4371    <x:defines>Content-Range</x:defines>
4372  </x:source>
4373</reference>
4374
4375<reference anchor="Part6">
4376  <front>
4377    <title>Hypertext Transfer Protocol (HTTP/1.1): Caching</title>
4378    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4379      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4380      <address><email>fielding@gbiv.com</email></address>
4381    </author>
4382    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4383      <organization>Akamai</organization>
4384      <address><email>mnot@mnot.net</email></address>
4385    </author>
4386    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4387      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4388      <address><email>julian.reschke@greenbytes.de</email></address>
4389    </author>
4390    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4391  </front>
4392  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4393  <x:source href="p6-cache.xml" basename="p6-cache">
4394    <x:defines>Cache-Control</x:defines>
4395    <x:defines>Expires</x:defines>
4396  </x:source>
4397</reference>
4398
4399<reference anchor="Part7">
4400  <front>
4401    <title>Hypertext Transfer Protocol (HTTP/1.1): Authentication</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="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4407      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4408      <address><email>julian.reschke@greenbytes.de</email></address>
4409    </author>
4410    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4411  </front>
4412  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
4413  <x:source href="p7-auth.xml" basename="p7-auth">
4414    <x:defines>Proxy-Authenticate</x:defines>
4415    <x:defines>Proxy-Authorization</x:defines>
4416  </x:source>
4417</reference>
4418
4419<reference anchor="RFC5234">
4420  <front>
4421    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4422    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4423      <organization>Brandenburg InternetWorking</organization>
4424      <address>
4425        <email>dcrocker@bbiw.net</email>
4426      </address> 
4427    </author>
4428    <author initials="P." surname="Overell" fullname="Paul Overell">
4429      <organization>THUS plc.</organization>
4430      <address>
4431        <email>paul.overell@thus.net</email>
4432      </address>
4433    </author>
4434    <date month="January" year="2008"/>
4435  </front>
4436  <seriesInfo name="STD" value="68"/>
4437  <seriesInfo name="RFC" value="5234"/>
4438</reference>
4439
4440<reference anchor="RFC2119">
4441  <front>
4442    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4443    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4444      <organization>Harvard University</organization>
4445      <address><email>sob@harvard.edu</email></address>
4446    </author>
4447    <date month="March" year="1997"/>
4448  </front>
4449  <seriesInfo name="BCP" value="14"/>
4450  <seriesInfo name="RFC" value="2119"/>
4451</reference>
4452
4453<reference anchor="RFC3986">
4454 <front>
4455  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4456  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4457    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4458    <address>
4459       <email>timbl@w3.org</email>
4460       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4461    </address>
4462  </author>
4463  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4464    <organization abbrev="Day Software">Day Software</organization>
4465    <address>
4466      <email>fielding@gbiv.com</email>
4467      <uri>http://roy.gbiv.com/</uri>
4468    </address>
4469  </author>
4470  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4471    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4472    <address>
4473      <email>LMM@acm.org</email>
4474      <uri>http://larry.masinter.net/</uri>
4475    </address>
4476  </author>
4477  <date month='January' year='2005'></date>
4478 </front>
4479 <seriesInfo name="STD" value="66"/>
4480 <seriesInfo name="RFC" value="3986"/>
4481</reference>
4482
4483<reference anchor="RFC0793">
4484  <front>
4485    <title>Transmission Control Protocol</title>
4486    <author initials='J.' surname='Postel' fullname='Jon Postel'>
4487      <organization>University of Southern California (USC)/Information Sciences Institute</organization>
4488    </author>
4489    <date year='1981' month='September' />
4490  </front>
4491  <seriesInfo name='STD' value='7' />
4492  <seriesInfo name='RFC' value='793' />
4493</reference>
4494
4495<reference anchor="USASCII">
4496  <front>
4497    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4498    <author>
4499      <organization>American National Standards Institute</organization>
4500    </author>
4501    <date year="1986"/>
4502  </front>
4503  <seriesInfo name="ANSI" value="X3.4"/>
4504</reference>
4505
4506<reference anchor="RFC1950">
4507  <front>
4508    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4509    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4510      <organization>Aladdin Enterprises</organization>
4511      <address><email>ghost@aladdin.com</email></address>
4512    </author>
4513    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4514    <date month="May" year="1996"/>
4515  </front>
4516  <seriesInfo name="RFC" value="1950"/>
4517  <!--<annotation>
4518    RFC 1950 is an Informational RFC, thus it might be less stable than
4519    this specification. On the other hand, this downward reference was
4520    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4521    therefore it is unlikely to cause problems in practice. See also
4522    <xref target="BCP97"/>.
4523  </annotation>-->
4524</reference>
4525
4526<reference anchor="RFC1951">
4527  <front>
4528    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4529    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4530      <organization>Aladdin Enterprises</organization>
4531      <address><email>ghost@aladdin.com</email></address>
4532    </author>
4533    <date month="May" year="1996"/>
4534  </front>
4535  <seriesInfo name="RFC" value="1951"/>
4536  <!--<annotation>
4537    RFC 1951 is an Informational RFC, thus it might be less stable than
4538    this specification. On the other hand, this downward reference was
4539    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4540    therefore it is unlikely to cause problems in practice. See also
4541    <xref target="BCP97"/>.
4542  </annotation>-->
4543</reference>
4544
4545<reference anchor="RFC1952">
4546  <front>
4547    <title>GZIP file format specification version 4.3</title>
4548    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4549      <organization>Aladdin Enterprises</organization>
4550      <address><email>ghost@aladdin.com</email></address>
4551    </author>
4552    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4553      <address><email>gzip@prep.ai.mit.edu</email></address>
4554    </author>
4555    <author initials="M." surname="Adler" fullname="Mark Adler">
4556      <address><email>madler@alumni.caltech.edu</email></address>
4557    </author>
4558    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4559      <address><email>ghost@aladdin.com</email></address>
4560    </author>
4561    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4562      <address><email>randeg@alumni.rpi.edu</email></address>
4563    </author>
4564    <date month="May" year="1996"/>
4565  </front>
4566  <seriesInfo name="RFC" value="1952"/>
4567  <!--<annotation>
4568    RFC 1952 is an Informational RFC, thus it might be less stable than
4569    this specification. On the other hand, this downward reference was
4570    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4571    therefore it is unlikely to cause problems in practice. See also
4572    <xref target="BCP97"/>.
4573  </annotation>-->
4574</reference>
4575
4576<reference anchor="Welch">
4577  <front>
4578    <title>A Technique for High Performance Data Compression</title>
4579    <author initials="T.A." surname="Welch" fullname="Terry A. Welch"/>
4580    <date month="June" year="1984"/>
4581  </front>
4582  <seriesInfo name="IEEE Computer" value="17(6)"/>
4583</reference>
4584
4585</references>
4586
4587<references title="Informative References">
4588
4589<reference anchor="ISO-8859-1">
4590  <front>
4591    <title>
4592     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4593    </title>
4594    <author>
4595      <organization>International Organization for Standardization</organization>
4596    </author>
4597    <date year="1998"/>
4598  </front>
4599  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4600</reference>
4601
4602<reference anchor='RFC1919'>
4603  <front>
4604    <title>Classical versus Transparent IP Proxies</title>
4605    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4606      <address><email>mchatel@pax.eunet.ch</email></address>
4607    </author>
4608    <date year='1996' month='March' />
4609  </front>
4610  <seriesInfo name='RFC' value='1919' />
4611</reference>
4612
4613<reference anchor="RFC1945">
4614  <front>
4615    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4616    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4617      <organization>MIT, Laboratory for Computer Science</organization>
4618      <address><email>timbl@w3.org</email></address>
4619    </author>
4620    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4621      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4622      <address><email>fielding@ics.uci.edu</email></address>
4623    </author>
4624    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4625      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4626      <address><email>frystyk@w3.org</email></address>
4627    </author>
4628    <date month="May" year="1996"/>
4629  </front>
4630  <seriesInfo name="RFC" value="1945"/>
4631</reference>
4632
4633<reference anchor="RFC2045">
4634  <front>
4635    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4636    <author initials="N." surname="Freed" fullname="Ned Freed">
4637      <organization>Innosoft International, Inc.</organization>
4638      <address><email>ned@innosoft.com</email></address>
4639    </author>
4640    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4641      <organization>First Virtual Holdings</organization>
4642      <address><email>nsb@nsb.fv.com</email></address>
4643    </author>
4644    <date month="November" year="1996"/>
4645  </front>
4646  <seriesInfo name="RFC" value="2045"/>
4647</reference>
4648
4649<reference anchor="RFC2047">
4650  <front>
4651    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4652    <author initials="K." surname="Moore" fullname="Keith Moore">
4653      <organization>University of Tennessee</organization>
4654      <address><email>moore@cs.utk.edu</email></address>
4655    </author>
4656    <date month="November" year="1996"/>
4657  </front>
4658  <seriesInfo name="RFC" value="2047"/>
4659</reference>
4660
4661<reference anchor="RFC2068">
4662  <front>
4663    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4664    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4665      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4666      <address><email>fielding@ics.uci.edu</email></address>
4667    </author>
4668    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4669      <organization>MIT Laboratory for Computer Science</organization>
4670      <address><email>jg@w3.org</email></address>
4671    </author>
4672    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4673      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4674      <address><email>mogul@wrl.dec.com</email></address>
4675    </author>
4676    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4677      <organization>MIT Laboratory for Computer Science</organization>
4678      <address><email>frystyk@w3.org</email></address>
4679    </author>
4680    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4681      <organization>MIT Laboratory for Computer Science</organization>
4682      <address><email>timbl@w3.org</email></address>
4683    </author>
4684    <date month="January" year="1997"/>
4685  </front>
4686  <seriesInfo name="RFC" value="2068"/>
4687</reference>
4688
4689<reference anchor="RFC2145">
4690  <front>
4691    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4692    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4693      <organization>Western Research Laboratory</organization>
4694      <address><email>mogul@wrl.dec.com</email></address>
4695    </author>
4696    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4697      <organization>Department of Information and Computer Science</organization>
4698      <address><email>fielding@ics.uci.edu</email></address>
4699    </author>
4700    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4701      <organization>MIT Laboratory for Computer Science</organization>
4702      <address><email>jg@w3.org</email></address>
4703    </author>
4704    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4705      <organization>W3 Consortium</organization>
4706      <address><email>frystyk@w3.org</email></address>
4707    </author>
4708    <date month="May" year="1997"/>
4709  </front>
4710  <seriesInfo name="RFC" value="2145"/>
4711</reference>
4712
4713<reference anchor="RFC2616">
4714  <front>
4715    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4716    <author initials="R." surname="Fielding" fullname="R. Fielding">
4717      <organization>University of California, Irvine</organization>
4718      <address><email>fielding@ics.uci.edu</email></address>
4719    </author>
4720    <author initials="J." surname="Gettys" fullname="J. Gettys">
4721      <organization>W3C</organization>
4722      <address><email>jg@w3.org</email></address>
4723    </author>
4724    <author initials="J." surname="Mogul" fullname="J. Mogul">
4725      <organization>Compaq Computer Corporation</organization>
4726      <address><email>mogul@wrl.dec.com</email></address>
4727    </author>
4728    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4729      <organization>MIT Laboratory for Computer Science</organization>
4730      <address><email>frystyk@w3.org</email></address>
4731    </author>
4732    <author initials="L." surname="Masinter" fullname="L. Masinter">
4733      <organization>Xerox Corporation</organization>
4734      <address><email>masinter@parc.xerox.com</email></address>
4735    </author>
4736    <author initials="P." surname="Leach" fullname="P. Leach">
4737      <organization>Microsoft Corporation</organization>
4738      <address><email>paulle@microsoft.com</email></address>
4739    </author>
4740    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4741      <organization>W3C</organization>
4742      <address><email>timbl@w3.org</email></address>
4743    </author>
4744    <date month="June" year="1999"/>
4745  </front>
4746  <seriesInfo name="RFC" value="2616"/>
4747</reference>
4748
4749<reference anchor='RFC2817'>
4750  <front>
4751    <title>Upgrading to TLS Within HTTP/1.1</title>
4752    <author initials='R.' surname='Khare' fullname='R. Khare'>
4753      <organization>4K Associates / UC Irvine</organization>
4754      <address><email>rohit@4K-associates.com</email></address>
4755    </author>
4756    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4757      <organization>Agranat Systems, Inc.</organization>
4758      <address><email>lawrence@agranat.com</email></address>
4759    </author>
4760    <date year='2000' month='May' />
4761  </front>
4762  <seriesInfo name='RFC' value='2817' />
4763</reference>
4764
4765<reference anchor='RFC2818'>
4766  <front>
4767    <title>HTTP Over TLS</title>
4768    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4769      <organization>RTFM, Inc.</organization>
4770      <address><email>ekr@rtfm.com</email></address>
4771    </author>
4772    <date year='2000' month='May' />
4773  </front>
4774  <seriesInfo name='RFC' value='2818' />
4775</reference>
4776
4777<reference anchor='RFC3040'>
4778  <front>
4779    <title>Internet Web Replication and Caching Taxonomy</title>
4780    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4781      <organization>Equinix, Inc.</organization>
4782    </author>
4783    <author initials='I.' surname='Melve' fullname='I. Melve'>
4784      <organization>UNINETT</organization>
4785    </author>
4786    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4787      <organization>CacheFlow Inc.</organization>
4788    </author>
4789    <date year='2001' month='January' />
4790  </front>
4791  <seriesInfo name='RFC' value='3040' />
4792</reference>
4793
4794<reference anchor='BCP90'>
4795  <front>
4796    <title>Registration Procedures for Message Header Fields</title>
4797    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4798      <organization>Nine by Nine</organization>
4799      <address><email>GK-IETF@ninebynine.org</email></address>
4800    </author>
4801    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4802      <organization>BEA Systems</organization>
4803      <address><email>mnot@pobox.com</email></address>
4804    </author>
4805    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4806      <organization>HP Labs</organization>
4807      <address><email>JeffMogul@acm.org</email></address>
4808    </author>
4809    <date year='2004' month='September' />
4810  </front>
4811  <seriesInfo name='BCP' value='90' />
4812  <seriesInfo name='RFC' value='3864' />
4813</reference>
4814
4815<reference anchor='RFC4033'>
4816  <front>
4817    <title>DNS Security Introduction and Requirements</title>
4818    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4819    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4820    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4821    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4822    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4823    <date year='2005' month='March' />
4824  </front>
4825  <seriesInfo name='RFC' value='4033' />
4826</reference>
4827
4828<reference anchor="BCP13">
4829  <front>
4830    <title>Media Type Specifications and Registration Procedures</title>
4831    <author initials="N." surname="Freed" fullname="Ned Freed">
4832      <organization>Oracle</organization>
4833      <address>
4834        <email>ned+ietf@mrochek.com</email>
4835      </address>
4836    </author>
4837    <author initials="J." surname="Klensin" fullname="John C. Klensin">
4838      <address>
4839        <email>john+ietf@jck.com</email>
4840      </address>
4841    </author>
4842    <author initials="T." surname="Hansen" fullname="Tony Hansen">
4843      <organization>AT&amp;T Laboratories</organization>
4844      <address>
4845        <email>tony+mtsuffix@maillennium.att.com</email>
4846      </address>
4847    </author>
4848    <date year="2013" month="January"/>
4849  </front>
4850  <seriesInfo name="BCP" value="13"/>
4851  <seriesInfo name="RFC" value="6838"/>
4852</reference>
4853
4854<reference anchor='BCP115'>
4855  <front>
4856    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4857    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4858      <organization>AT&amp;T Laboratories</organization>
4859      <address>
4860        <email>tony+urireg@maillennium.att.com</email>
4861      </address>
4862    </author>
4863    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4864      <organization>Qualcomm, Inc.</organization>
4865      <address>
4866        <email>hardie@qualcomm.com</email>
4867      </address>
4868    </author>
4869    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4870      <organization>Adobe Systems</organization>
4871      <address>
4872        <email>LMM@acm.org</email>
4873      </address>
4874    </author>
4875    <date year='2006' month='February' />
4876  </front>
4877  <seriesInfo name='BCP' value='115' />
4878  <seriesInfo name='RFC' value='4395' />
4879</reference>
4880
4881<reference anchor='RFC4559'>
4882  <front>
4883    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4884    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4885    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4886    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4887    <date year='2006' month='June' />
4888  </front>
4889  <seriesInfo name='RFC' value='4559' />
4890</reference>
4891
4892<reference anchor='RFC5226'>
4893  <front>
4894    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4895    <author initials='T.' surname='Narten' fullname='T. Narten'>
4896      <organization>IBM</organization>
4897      <address><email>narten@us.ibm.com</email></address>
4898    </author>
4899    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4900      <organization>Google</organization>
4901      <address><email>Harald@Alvestrand.no</email></address>
4902    </author>
4903    <date year='2008' month='May' />
4904  </front>
4905  <seriesInfo name='BCP' value='26' />
4906  <seriesInfo name='RFC' value='5226' />
4907</reference>
4908
4909<reference anchor='RFC5246'>
4910   <front>
4911      <title>The Transport Layer Security (TLS) Protocol Version 1.2</title>
4912      <author initials='T.' surname='Dierks' fullname='T. Dierks'>
4913         <organization />
4914      </author>
4915      <author initials='E.' surname='Rescorla' fullname='E. Rescorla'>
4916         <organization>RTFM, Inc.</organization>
4917      </author>
4918      <date year='2008' month='August' />
4919   </front>
4920   <seriesInfo name='RFC' value='5246' />
4921</reference>
4922
4923<reference anchor="RFC5322">
4924  <front>
4925    <title>Internet Message Format</title>
4926    <author initials="P." surname="Resnick" fullname="P. Resnick">
4927      <organization>Qualcomm Incorporated</organization>
4928    </author>
4929    <date year="2008" month="October"/>
4930  </front>
4931  <seriesInfo name="RFC" value="5322"/>
4932</reference>
4933
4934<reference anchor="RFC6265">
4935  <front>
4936    <title>HTTP State Management Mechanism</title>
4937    <author initials="A." surname="Barth" fullname="Adam Barth">
4938      <organization abbrev="U.C. Berkeley">
4939        University of California, Berkeley
4940      </organization>
4941      <address><email>abarth@eecs.berkeley.edu</email></address>
4942    </author>
4943    <date year="2011" month="April" />
4944  </front>
4945  <seriesInfo name="RFC" value="6265"/>
4946</reference>
4947
4948<reference anchor='RFC6585'>
4949  <front>
4950    <title>Additional HTTP Status Codes</title>
4951    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4952      <organization>Rackspace</organization>
4953    </author>
4954    <author initials='R.' surname='Fielding' fullname='R. Fielding'>
4955      <organization>Adobe</organization>
4956    </author>
4957    <date year='2012' month='April' />
4958   </front>
4959   <seriesInfo name='RFC' value='6585' />
4960</reference>
4961
4962<!--<reference anchor='BCP97'>
4963  <front>
4964    <title>Handling Normative References to Standards-Track Documents</title>
4965    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4966      <address>
4967        <email>klensin+ietf@jck.com</email>
4968      </address>
4969    </author>
4970    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4971      <organization>MIT</organization>
4972      <address>
4973        <email>hartmans-ietf@mit.edu</email>
4974      </address>
4975    </author>
4976    <date year='2007' month='June' />
4977  </front>
4978  <seriesInfo name='BCP' value='97' />
4979  <seriesInfo name='RFC' value='4897' />
4980</reference>-->
4981
4982<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4983  <front>
4984    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4985    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4986    <date year="2001" month="November"/>
4987  </front>
4988  <seriesInfo name="ACM Transactions on Internet Technology" value="1(2)"/>
4989</reference>
4990
4991</references>
4992
4993
4994<section title="HTTP Version History" anchor="compatibility">
4995<t>
4996   HTTP has been in use by the World-Wide Web global information initiative
4997   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4998   was a simple protocol for hypertext data transfer across the Internet
4999   with only a single request method (GET) and no metadata.
5000   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
5001   methods and MIME-like messaging that could include metadata about the data
5002   transferred and modifiers on the request/response semantics. However,
5003   HTTP/1.0 did not sufficiently take into consideration the effects of
5004   hierarchical proxies, caching, the need for persistent connections, or
5005   name-based virtual hosts. The proliferation of incompletely-implemented
5006   applications calling themselves "HTTP/1.0" further necessitated a
5007   protocol version change in order for two communicating applications
5008   to determine each other's true capabilities.
5009</t>
5010<t>
5011   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
5012   requirements that enable reliable implementations, adding only
5013   those new features that will either be safely ignored by an HTTP/1.0
5014   recipient or only sent when communicating with a party advertising
5015   conformance with HTTP/1.1.
5016</t>
5017<t>
5018   It is beyond the scope of a protocol specification to mandate
5019   conformance with previous versions. HTTP/1.1 was deliberately
5020   designed, however, to make supporting previous versions easy.
5021   We would expect a general-purpose HTTP/1.1 server to understand
5022   any valid request in the format of HTTP/1.0 and respond appropriately
5023   with an HTTP/1.1 message that only uses features understood (or
5024   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
5025   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
5026</t>
5027<t>
5028   Since HTTP/0.9 did not support header fields in a request,
5029   there is no mechanism for it to support name-based virtual
5030   hosts (selection of resource by inspection of the <x:ref>Host</x:ref> header
5031   field).  Any server that implements name-based virtual hosts
5032   ought to disable support for HTTP/0.9.  Most requests that
5033   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
5034   requests wherein a buggy client failed to properly encode
5035   linear whitespace found in a URI reference and placed in
5036   the request-target.
5037</t>
5038
5039<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
5040<t>
5041   This section summarizes major differences between versions HTTP/1.0
5042   and HTTP/1.1.
5043</t>
5044
5045<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
5046<t>
5047   The requirements that clients and servers support the <x:ref>Host</x:ref>
5048   header field (<xref target="header.host"/>), report an error if it is
5049   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
5050   are among the most important changes defined by HTTP/1.1.
5051</t>
5052<t>
5053   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
5054   addresses and servers; there was no other established mechanism for
5055   distinguishing the intended server of a request than the IP address
5056   to which that request was directed. The <x:ref>Host</x:ref> header field was
5057   introduced during the development of HTTP/1.1 and, though it was
5058   quickly implemented by most HTTP/1.0 browsers, additional requirements
5059   were placed on all HTTP/1.1 requests in order to ensure complete
5060   adoption.  At the time of this writing, most HTTP-based services
5061   are dependent upon the Host header field for targeting requests.
5062</t>
5063</section>
5064
5065<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
5066<t>
5067   In HTTP/1.0, each connection is established by the client prior to the
5068   request and closed by the server after sending the response. However, some
5069   implementations implement the explicitly negotiated ("Keep-Alive") version
5070   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
5071   target="RFC2068"/>.
5072</t>
5073<t>
5074   Some clients and servers might wish to be compatible with these previous
5075   approaches to persistent connections, by explicitly negotiating for them
5076   with a "Connection: keep-alive" request header field. However, some
5077   experimental implementations of HTTP/1.0 persistent connections are faulty;
5078   for example, if an HTTP/1.0 proxy server doesn't understand
5079   <x:ref>Connection</x:ref>, it will erroneously forward that header field
5080   to the next inbound server, which would result in a hung connection.
5081</t>
5082<t>
5083   One attempted solution was the introduction of a Proxy-Connection header
5084   field, targeted specifically at proxies. In practice, this was also
5085   unworkable, because proxies are often deployed in multiple layers, bringing
5086   about the same problem discussed above.
5087</t>
5088<t>
5089   As a result, clients are encouraged not to send the Proxy-Connection header
5090   field in any requests.
5091</t>
5092<t>
5093   Clients are also encouraged to consider the use of Connection: keep-alive
5094   in requests carefully; while they can enable persistent connections with
5095   HTTP/1.0 servers, clients using them will need to monitor the
5096   connection for "hung" requests (which indicate that the client ought stop
5097   sending the header field), and this mechanism ought not be used by clients
5098   at all when a proxy is being used.
5099</t>
5100</section>
5101
5102<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
5103<t>
5104   HTTP/1.1 introduces the <x:ref>Transfer-Encoding</x:ref> header field
5105   (<xref target="header.transfer-encoding"/>).
5106   Transfer codings need to be decoded prior to forwarding an HTTP message
5107   over a MIME-compliant protocol.
5108</t>
5109</section>
5110
5111</section>
5112
5113<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
5114<t>
5115  HTTP's approach to error handling has been explained.
5116  (<xref target="conformance" />)
5117</t>
5118<t>
5119  The HTTP-version ABNF production has been clarified to be case-sensitive.
5120  Additionally, version numbers has been restricted to single digits, due
5121  to the fact that implementations are known to handle multi-digit version
5122  numbers incorrectly.
5123  (<xref target="http.version"/>)
5124</t>
5125<t>
5126  Userinfo (i.e., username and password) are now disallowed in HTTP and
5127  HTTPS URIs, because of security issues related to their transmission on the
5128  wire.
5129  (<xref target="http.uri" />)
5130</t>
5131<t>
5132  The HTTPS URI scheme is now defined by this specification; previously,
5133  it was done in  <xref target="RFC2818" x:fmt="of" x:sec="2.4"/>.
5134  Furthermore, it implies end-to-end security.
5135  (<xref target="https.uri"/>)
5136</t>
5137<t>
5138  HTTP messages can be (and often are) buffered by implementations; despite
5139  it sometimes being available as a stream, HTTP is fundamentally a
5140  message-oriented protocol.
5141  Minimum supported sizes for various protocol elements have been
5142  suggested, to improve interoperability.
5143  (<xref target="http.message" />)
5144</t>
5145<t>
5146  Invalid whitespace around field-names is now required to be rejected,
5147  because accepting it represents a security vulnerability.
5148  The ABNF productions defining header fields now only list the field value.
5149  (<xref target="header.fields"/>)
5150</t>
5151<t>
5152  Rules about implicit linear whitespace between certain grammar productions
5153  have been removed; now whitespace is only allowed where specifically
5154  defined in the ABNF.
5155  (<xref target="whitespace"/>)
5156</t>
5157<t>
5158  Header fields that span multiple lines ("line folding") are deprecated.
5159  (<xref target="field.parsing" />)
5160</t>
5161<t> 
5162  The NUL octet is no longer allowed in comment and quoted-string text, and
5163  handling of backslash-escaping in them has been clarified.
5164  The quoted-pair rule no longer allows escaping control characters other than
5165  HTAB.
5166  Non-ASCII content in header fields and the reason phrase has been obsoleted
5167  and made opaque (the TEXT rule was removed).
5168  (<xref target="field.components"/>)
5169</t> 
5170<t>
5171  Bogus "<x:ref>Content-Length</x:ref>" header fields are now required to be
5172  handled as errors by recipients.
5173  (<xref target="header.content-length"/>)
5174</t>
5175<t>
5176  The algorithm for determining the message body length has been clarified
5177  to indicate all of the special cases (e.g., driven by methods or status
5178  codes) that affect it, and that new protocol elements cannot define such
5179  special cases.
5180  CONNECT is a new, special case in determining message body length.
5181  "multipart/byteranges" is no longer a way of determining message body length
5182  detection.
5183  (<xref target="message.body.length"/>)
5184</t>
5185<t>
5186  The "identity" transfer coding token has been removed.
5187  (Sections <xref format="counter" target="message.body"/> and
5188  <xref format="counter" target="transfer.codings"/>)
5189</t>
5190<t>
5191  Chunk length does not include the count of the octets in the
5192  chunk header and trailer.
5193  Line folding in chunk extensions is  disallowed.
5194  (<xref target="chunked.encoding"/>)
5195</t>
5196<t>
5197  The meaning of the "deflate" content coding has been clarified.
5198  (<xref target="deflate.coding" />)
5199</t>
5200<t>
5201  The segment + query components of RFC 3986 have been used to define the
5202  request-target, instead of abs_path from RFC 1808.
5203  The asterisk-form of the request-target is only allowed with the OPTIONS
5204  method.
5205  (<xref target="request-target"/>)
5206</t>
5207<t>
5208  The term "Effective Request URI" has been introduced.
5209  (<xref target="effective.request.uri" />)
5210</t>
5211<t>
5212  Gateways do not need to generate <x:ref>Via</x:ref> header fields anymore.
5213  (<xref target="header.via"/>)
5214</t>
5215<t>
5216  Exactly when "close" connection options have to be sent has been clarified.
5217  Also, "hop-by-hop" header fields are required to appear in the Connection header
5218  field; just because they're defined as hop-by-hop in this specification
5219  doesn't exempt them.
5220  (<xref target="header.connection"/>)
5221</t>
5222<t>
5223  The limit of two connections per server has been removed.
5224  An idempotent sequence of requests is no longer required to be retried.
5225  The requirement to retry requests under certain circumstances when the
5226  server prematurely closes the connection has been removed.
5227  Also, some extraneous requirements about when servers are allowed to close
5228  connections prematurely have been removed.
5229  (<xref target="persistent.connections"/>)
5230</t>
5231<t>
5232  The semantics of the <x:ref>Upgrade</x:ref> header field is now defined in
5233  responses other than 101 (this was incorporated from <xref
5234  target="RFC2817"/>). Furthermore, the ordering in the field value is now
5235  significant.
5236  (<xref target="header.upgrade"/>)
5237</t>
5238<t>
5239  Empty list elements in list productions (e.g., a list header field containing
5240  ", ,") have been deprecated.
5241  (<xref target="abnf.extension"/>)
5242</t>
5243<t>
5244  Registration of Transfer Codings now requires IETF Review
5245  (<xref target="transfer.coding.registry"/>)
5246</t>
5247<t>
5248  This specification now defines the Upgrade Token Registry, previously
5249  defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
5250  (<xref target="upgrade.token.registry"/>)
5251</t>
5252<t>
5253  The expectation to support HTTP/0.9 requests has been removed.
5254  (<xref target="compatibility"/>)
5255</t>
5256<t>
5257  Issues with the Keep-Alive and Proxy-Connection header fields in requests
5258  are pointed out, with use of the latter being discouraged altogether.
5259  (<xref target="compatibility.with.http.1.0.persistent.connections" />)
5260</t>
5261</section>
5262</section>
5263
5264<?BEGININC p1-messaging.abnf-appendix ?>
5265<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
5266<figure>
5267<artwork type="abnf" name="p1-messaging.parsed-abnf">
5268<x:ref>BWS</x:ref> = OWS
5269
5270<x:ref>Connection</x:ref> = *( "," OWS ) connection-option *( OWS "," [ OWS
5271 connection-option ] )
5272<x:ref>Content-Length</x:ref> = 1*DIGIT
5273
5274<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5275 ]
5276<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
5277<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
5278<x:ref>Host</x:ref> = uri-host [ ":" port ]
5279
5280<x:ref>OWS</x:ref> = *( SP / HTAB )
5281
5282<x:ref>RWS</x:ref> = 1*( SP / HTAB )
5283
5284<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5285<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5286<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5287 transfer-coding ] )
5288
5289<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5290<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
5291
5292<x:ref>Via</x:ref> = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment
5293 ] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS
5294 comment ] ) ] )
5295
5296<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5297<x:ref>absolute-form</x:ref> = absolute-URI
5298<x:ref>absolute-path</x:ref> = 1*( "/" segment )
5299<x:ref>asterisk-form</x:ref> = "*"
5300<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5301<x:ref>authority-form</x:ref> = authority
5302
5303<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5304<x:ref>chunk-data</x:ref> = 1*OCTET
5305<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5306<x:ref>chunk-ext-name</x:ref> = token
5307<x:ref>chunk-ext-val</x:ref> = token / quoted-string
5308<x:ref>chunk-size</x:ref> = 1*HEXDIG
5309<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
5310<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
5311<x:ref>connection-option</x:ref> = token
5312<x:ref>ctext</x:ref> = HTAB / SP / %x21-27 ; '!'-'''
5313 / %x2A-5B ; '*'-'['
5314 / %x5D-7E ; ']'-'~'
5315 / obs-text
5316
5317<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5318<x:ref>field-name</x:ref> = token
5319<x:ref>field-value</x:ref> = *( field-content / obs-fold )
5320<x:ref>fragment</x:ref> = &lt;fragment, defined in [RFC3986], Section 3.5&gt;
5321
5322<x:ref>header-field</x:ref> = field-name ":" OWS field-value OWS
5323<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ] [ "#"
5324 fragment ]
5325<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ] [ "#"
5326 fragment ]
5327
5328<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
5329
5330<x:ref>message-body</x:ref> = *OCTET
5331<x:ref>method</x:ref> = token
5332
5333<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
5334<x:ref>obs-text</x:ref> = %x80-FF
5335<x:ref>origin-form</x:ref> = absolute-path [ "?" query ]
5336
5337<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5338<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5339<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5340<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
5341<x:ref>protocol-name</x:ref> = token
5342<x:ref>protocol-version</x:ref> = token
5343<x:ref>pseudonym</x:ref> = token
5344
5345<x:ref>qdtext</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
5346 / %x5D-7E ; ']'-'~'
5347 / obs-text
5348<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5349<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5350<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5351
5352<x:ref>rank</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5353<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5354<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5355<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5356<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5357<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
5358<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
5359 asterisk-form
5360
5361<x:ref>segment</x:ref> = &lt;segment, defined in [RFC3986], Section 3.3&gt;
5362<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5363 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5364<x:ref>start-line</x:ref> = request-line / status-line
5365<x:ref>status-code</x:ref> = 3DIGIT
5366<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
5367
5368<x:ref>t-codings</x:ref> = "trailers" / ( transfer-coding [ t-ranking ] )
5369<x:ref>t-ranking</x:ref> = OWS ";" OWS "q=" rank
5370<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5371 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5372<x:ref>token</x:ref> = 1*tchar
5373<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5374<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5375 transfer-extension
5376<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5377<x:ref>transfer-parameter</x:ref> = token BWS "=" BWS ( token / quoted-string )
5378
5379<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5380</artwork>
5381</figure>
5382</section>
5383<?ENDINC p1-messaging.abnf-appendix ?>
5384
5385<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5386
5387<section title="Since RFC 2616">
5388<t>
5389  Changes up to the IETF Last Call draft are summarized
5390  in <eref target="http://trac.tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-24#appendix-C"/>.
5391</t>
5392</section>
5393
5394<section title="Since draft-ietf-httpbis-p1-messaging-24" anchor="changes.since.24">
5395<t>
5396  Closed issues:
5397  <list style="symbols">
5398    <t>
5399      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/502"/>:
5400      "APPSDIR review of draft-ietf-httpbis-p1-messaging-24"
5401    </t>
5402    <t>
5403      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/507"/>:
5404      "integer value parsing"
5405    </t>
5406    <t>
5407      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/517"/>:
5408      "move IANA registrations to correct draft"
5409    </t>
5410  </list>
5411</t>
5412</section>
5413
5414<section title="Since draft-ietf-httpbis-p1-messaging-25" anchor="changes.since.25">
5415<t>
5416  Closed issues:
5417  <list style="symbols">
5418    <t>
5419      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/526"/>:
5420      "check media type registration templates"
5421    </t>
5422    <t>
5423      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/528"/>:
5424      "Redundant rule quoted-str-nf"
5425    </t>
5426    <t>
5427      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/541"/>:
5428      "use of 'word' ABNF production"
5429    </t>
5430    <t>
5431      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/542"/>:
5432      "improve introduction of list rule"
5433    </t>
5434  </list>
5435</t>
5436</section>
5437</section>
5438
5439</back>
5440</rfc>
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