source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1837

Last change on this file since 1837 was 1837, checked in by fielding@…, 8 years ago

start the plow through connection management

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  • Property svn:mime-type set to text/xml
File size: 245.9 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "August">
16  <!ENTITY ID-YEAR "2012">
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' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY media-types            "<xref target='Part2' x:rel='#media.types' 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='#representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-allow           "<xref target='Part2' x:rel='#header.allow' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-content-encoding    "<xref target='Part2' x:rel='#header.content-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-content-location    "<xref target='Part2' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY header-content-range   "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY header-content-type    "<xref target='Part2' x:rel='#header.content-type' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY header-date            "<xref target='Part2' x:rel='#header.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY header-etag            "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY header-expires         "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY header-last-modified   "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY header-mime-version    "<xref target='Part2' x:rel='#mime-version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY header-server          "<xref target='Part2' x:rel='#header.server' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY methods                "<xref target='Part2' x:rel='#methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY OPTIONS                "<xref target='Part2' x:rel='#OPTIONS' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY qvalue                 "<xref target='Part2' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY status-304             "<xref target='Part4' x:rel='#status.304' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
57  <!ENTITY cons-new-header-fields "<xref target='Part2' x:rel='#considerations.for.creating.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
58]>
59<?rfc toc="yes" ?>
60<?rfc symrefs="yes" ?>
61<?rfc sortrefs="yes" ?>
62<?rfc compact="yes"?>
63<?rfc subcompact="no" ?>
64<?rfc linkmailto="no" ?>
65<?rfc editing="no" ?>
66<?rfc comments="yes"?>
67<?rfc inline="yes"?>
68<?rfc rfcedstyle="yes"?>
69<?rfc-ext allow-markup-in-artwork="yes" ?>
70<?rfc-ext include-references-in-index="yes" ?>
71<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="proposed"
72     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
73     xmlns:x='http://purl.org/net/xml2rfc/ext'>
74<x:link rel="next" basename="p2-semantics"/>
75<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
76<front>
77
78  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: Message Routing and Syntax"</title>
79
80  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
81    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
82    <address>
83      <postal>
84        <street>345 Park Ave</street>
85        <city>San Jose</city>
86        <region>CA</region>
87        <code>95110</code>
88        <country>USA</country>
89      </postal>
90      <email>fielding@gbiv.com</email>
91      <uri>http://roy.gbiv.com/</uri>
92    </address>
93  </author>
94
95  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
96    <organization abbrev="W3C">World Wide Web Consortium</organization>
97    <address>
98      <postal>
99        <street>W3C / ERCIM</street>
100        <street>2004, rte des Lucioles</street>
101        <city>Sophia-Antipolis</city>
102        <region>AM</region>
103        <code>06902</code>
104        <country>France</country>
105      </postal>
106      <email>ylafon@w3.org</email>
107      <uri>http://www.raubacapeu.net/people/yves/</uri>
108    </address>
109  </author>
110
111  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
112    <organization abbrev="greenbytes">greenbytes GmbH</organization>
113    <address>
114      <postal>
115        <street>Hafenweg 16</street>
116        <city>Muenster</city><region>NW</region><code>48155</code>
117        <country>Germany</country>
118      </postal>
119      <email>julian.reschke@greenbytes.de</email>
120      <uri>http://greenbytes.de/tech/webdav/</uri>
121    </address>
122  </author>
123
124  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
125  <workgroup>HTTPbis Working Group</workgroup>
126
127<abstract>
128<t>
129   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
130   distributed, collaborative, hypertext information systems. HTTP has been in
131   use by the World Wide Web global information initiative since 1990.
132   This document provides an overview of HTTP architecture and its associated
133   terminology, defines the "http" and "https" Uniform Resource Identifier
134   (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements,
135   and describes general security concerns for implementations.
136</t>   
137</abstract>
138
139<note title="Editorial Note (To be removed by RFC Editor)">
140  <t>
141    Discussion of this draft takes place on the HTTPBIS working group
142    mailing list (ietf-http-wg@w3.org), which is archived at
143    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
144  </t>
145  <t>
146    The current issues list is at
147    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
148    documents (including fancy diffs) can be found at
149    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
150  </t>
151  <t>
152    The changes in this draft are summarized in <xref target="changes.since.20"/>.
153  </t>
154</note>
155</front>
156<middle>
157<section title="Introduction" anchor="introduction">
158<t>
159   The Hypertext Transfer Protocol (HTTP) is an application-level
160   request/response protocol that uses extensible semantics and MIME-like
161   message payloads for flexible interaction with network-based hypertext
162   information systems. This document is the first in a series of documents
163   that collectively form the HTTP/1.1 specification:
164   <list style="empty">
165    <t>RFC xxx1: Message Routing and Syntax</t>
166    <t><xref target="Part2" x:fmt="none">RFC xxx2</xref>: Semantics and Payloads</t>
167    <t><xref target="Part4" x:fmt="none">RFC xxx3</xref>: Conditional Requests</t>
168    <t><xref target="Part5" x:fmt="none">RFC xxx4</xref>: Range Requests</t>
169    <t><xref target="Part6" x:fmt="none">RFC xxx5</xref>: Caching</t>
170    <t><xref target="Part7" x:fmt="none">RFC xxx6</xref>: Authentication</t>
171   </list>
172</t>
173<t>
174   This HTTP/1.1 specification obsoletes and moves to historic status
175   <xref target="RFC2616" x:fmt="none">RFC 2616</xref>, its predecessor
176   <xref target="RFC2068" x:fmt="none">RFC 2068</xref>,
177   <xref target="RFC2145" x:fmt="none">RFC 2145</xref> (on HTTP versioning),
178   and <xref target="RFC2817" x:fmt="none">RFC 2817</xref> (on using CONNECT
179   for TLS upgrades).
180</t>
181<t>
182   HTTP is a generic interface protocol for information systems. It is
183   designed to hide the details of how a service is implemented by presenting
184   a uniform interface to clients that is independent of the types of
185   resources provided. Likewise, servers do not need to be aware of each
186   client's purpose: an HTTP request can be considered in isolation rather
187   than being associated with a specific type of client or a predetermined
188   sequence of application steps. The result is a protocol that can be used
189   effectively in many different contexts and for which implementations can
190   evolve independently over time.
191</t>
192<t>
193   HTTP is also designed for use as an intermediation protocol for translating
194   communication to and from non-HTTP information systems.
195   HTTP proxies and gateways can provide access to alternative information
196   services by translating their diverse protocols into a hypertext
197   format that can be viewed and manipulated by clients in the same way
198   as HTTP services.
199</t>
200<t>
201   One consequence of HTTP flexibility is that the protocol cannot be
202   defined in terms of what occurs behind the interface. Instead, we
203   are limited to defining the syntax of communication, the intent
204   of received communication, and the expected behavior of recipients.
205   If the communication is considered in isolation, then successful
206   actions ought to be reflected in corresponding changes to the
207   observable interface provided by servers. However, since multiple
208   clients might act in parallel and perhaps at cross-purposes, we
209   cannot require that such changes be observable beyond the scope
210   of a single response.
211</t>
212<t>
213   This document describes the architectural elements that are used or
214   referred to in HTTP, defines the "http" and "https" URI schemes,
215   describes overall network operation and connection management,
216   and defines HTTP message framing and forwarding requirements.
217   Our goal is to define all of the mechanisms necessary for HTTP message
218   handling that are independent of message semantics, thereby defining the
219   complete set of requirements for message parsers and
220   message-forwarding intermediaries.
221</t>
222
223
224<section title="Requirement Notation" anchor="intro.requirements">
225<t>
226   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
227   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
228   document are to be interpreted as described in <xref target="RFC2119"/>.
229</t>
230</section>
231
232<section title="Syntax Notation" anchor="notation">
233<iref primary="true" item="Grammar" subitem="ALPHA"/>
234<iref primary="true" item="Grammar" subitem="CR"/>
235<iref primary="true" item="Grammar" subitem="CRLF"/>
236<iref primary="true" item="Grammar" subitem="CTL"/>
237<iref primary="true" item="Grammar" subitem="DIGIT"/>
238<iref primary="true" item="Grammar" subitem="DQUOTE"/>
239<iref primary="true" item="Grammar" subitem="HEXDIG"/>
240<iref primary="true" item="Grammar" subitem="HTAB"/>
241<iref primary="true" item="Grammar" subitem="LF"/>
242<iref primary="true" item="Grammar" subitem="OCTET"/>
243<iref primary="true" item="Grammar" subitem="SP"/>
244<iref primary="true" item="Grammar" subitem="VCHAR"/>
245<t>
246   This specification uses the Augmented Backus-Naur Form (ABNF) notation
247   of <xref target="RFC5234"/> with the list rule extension defined in
248   <xref target="abnf.extension"/>.  <xref target="collected.abnf"/> shows
249   the collected ABNF with the list rule expanded.
250</t>
251<t anchor="core.rules">
252  <x:anchor-alias value="ALPHA"/>
253  <x:anchor-alias value="CTL"/>
254  <x:anchor-alias value="CR"/>
255  <x:anchor-alias value="CRLF"/>
256  <x:anchor-alias value="DIGIT"/>
257  <x:anchor-alias value="DQUOTE"/>
258  <x:anchor-alias value="HEXDIG"/>
259  <x:anchor-alias value="HTAB"/>
260  <x:anchor-alias value="LF"/>
261  <x:anchor-alias value="OCTET"/>
262  <x:anchor-alias value="SP"/>
263  <x:anchor-alias value="VCHAR"/>
264   The following core rules are included by
265   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
266   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
267   DIGIT (decimal 0-9), DQUOTE (double quote),
268   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
269   OCTET (any 8-bit sequence of data), SP (space), and
270   VCHAR (any visible <xref target="USASCII"/> character).
271</t>
272<t>
273   As a convention, ABNF rule names prefixed with "obs-" denote
274   "obsolete" grammar rules that appear for historical reasons.
275</t>
276</section>
277</section>
278
279<section title="Architecture" anchor="architecture">
280<t>
281   HTTP was created for the World Wide Web architecture
282   and has evolved over time to support the scalability needs of a worldwide
283   hypertext system. Much of that architecture is reflected in the terminology
284   and syntax productions used to define HTTP.
285</t>
286
287<section title="Client/Server Messaging" anchor="operation">
288<iref primary="true" item="client"/>
289<iref primary="true" item="server"/>
290<iref primary="true" item="connection"/>
291<t>
292   HTTP is a stateless request/response protocol that operates by exchanging
293   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
294   transport or session-layer
295   "<x:dfn>connection</x:dfn>" (<xref target="connection.management"/>).
296   An HTTP "<x:dfn>client</x:dfn>" is a program that establishes a connection
297   to a server for the purpose of sending one or more HTTP requests.
298   An HTTP "<x:dfn>server</x:dfn>" is a program that accepts connections
299   in order to service HTTP requests by sending HTTP responses.
300</t>
301<iref primary="true" item="user agent"/>
302<iref primary="true" item="origin server"/>
303<iref primary="true" item="browser"/>
304<iref primary="true" item="spider"/>
305<iref primary="true" item="sender"/>
306<iref primary="true" item="recipient"/>
307<t>
308   The terms client and server refer only to the roles that
309   these programs perform for a particular connection.  The same program
310   might act as a client on some connections and a server on others.  We use
311   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
312   such as a WWW browser, editor, or spider (web-traversing robot), and
313   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
314   authoritative responses to a request.  For general requirements, we use
315   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
316   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
317   message.
318</t>
319<t>
320   HTTP relies upon the Uniform Resource Identifier (URI)
321   standard <xref target="RFC3986"/> to indicate the target resource
322   (<xref target="target-resource"/>) and relationships between resources.
323   Messages are passed in a format similar to that used by Internet mail
324   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
325   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
326   between HTTP and MIME messages).
327</t>
328<t>
329   Most HTTP communication consists of a retrieval request (GET) for
330   a representation of some resource identified by a URI.  In the
331   simplest case, this might be accomplished via a single bidirectional
332   connection (===) between the user agent (UA) and the origin server (O).
333</t>
334<figure><artwork type="drawing">
335         request   &gt;
336    <x:highlight>UA</x:highlight> ======================================= <x:highlight>O</x:highlight>
337                                &lt;   response
338</artwork></figure>
339<iref primary="true" item="message"/>
340<iref primary="true" item="request"/>
341<iref primary="true" item="response"/>
342<t>
343   A client sends an HTTP request to a server in the form of a <x:dfn>request</x:dfn>
344   message, beginning with a request-line that includes a method, URI, and
345   protocol version (<xref target="request.line"/>),
346   followed by header fields containing
347   request modifiers, client information, and representation metadata
348   (<xref target="header.fields"/>),
349   an empty line to indicate the end of the header section, and finally
350   a message body containing the payload body (if any,
351   <xref target="message.body"/>).
352</t>
353<t>
354   A server responds to a client's request by sending one or more HTTP
355   <x:dfn>response</x:dfn>
356   messages, each beginning with a status line that
357   includes the protocol version, a success or error code, and textual
358   reason phrase (<xref target="status.line"/>),
359   possibly followed by header fields containing server
360   information, resource metadata, and representation metadata
361   (<xref target="header.fields"/>),
362   an empty line to indicate the end of the header section, and finally
363   a message body containing the payload body (if any,
364   <xref target="message.body"/>).
365</t>
366<t>
367   A connection might be used for multiple request/response exchanges,
368   as defined in <xref target="persistent.connections"/>.
369</t>
370<t>
371   The following example illustrates a typical message exchange for a
372   GET request on the URI "http://www.example.com/hello.txt":
373</t>
374<figure><preamble>
375client request:
376</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
377GET /hello.txt HTTP/1.1
378User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
379Host: www.example.com
380Accept-Language: en, mi
381
382</artwork></figure>
383<figure><preamble>
384server response:
385</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
386HTTP/1.1 200 OK
387Date: Mon, 27 Jul 2009 12:28:53 GMT
388Server: Apache
389Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
390ETag: "34aa387-d-1568eb00"
391Accept-Ranges: bytes
392Content-Length: <x:length-of target="exbody"/>
393Vary: Accept-Encoding
394Content-Type: text/plain
395
396<x:span anchor="exbody">Hello World!
397</x:span></artwork></figure>
398</section>
399
400<section title="Implementation Diversity" anchor="implementation-diversity">
401<t>
402   When considering the design of HTTP, it is easy to fall into a trap of
403   thinking that all user agents are general-purpose browsers and all origin
404   servers are large public websites. That is not the case in practice.
405   Common HTTP user agents include household appliances, stereos, scales,
406   firmware update scripts, command-line programs, mobile apps,
407   and communication devices in a multitude of shapes and sizes.  Likewise,
408   common HTTP origin servers include home automation units, configurable
409   networking components, office machines, autonomous robots, news feeds,
410   traffic cameras, ad selectors, and video delivery platforms.
411</t>
412<t>
413   The term "user agent" does not imply that there is a human user directly
414   interacting with the software agent at the time of a request. In many
415   cases, a user agent is installed or configured to run in the background
416   and save its results for later inspection (or save only a subset of those
417   results that might be interesting or erroneous). Spiders, for example, are
418   typically given a start URI and configured to follow certain behavior while
419   crawling the Web as a hypertext graph.
420</t>
421<t>
422   The implementation diversity of HTTP means that we cannot assume the
423   user agent can make interactive suggestions to a user or provide adequate
424   warning for security or privacy options.  In the few cases where this
425   specification requires reporting of errors to the user, it is acceptable
426   for such reporting to only be observable in an error console or log file.
427   Likewise, requirements that an automated action be confirmed by the user
428   before proceeding can me met via advance configuration choices,
429   run-time options, or simply not proceeding with the unsafe action.
430</t>
431</section>
432
433<section title="Intermediaries" anchor="intermediaries">
434<iref primary="true" item="intermediary"/>
435<t>
436   HTTP enables the use of intermediaries to satisfy requests through
437   a chain of connections.  There are three common forms of HTTP
438   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
439   a single intermediary might act as an origin server, proxy, gateway,
440   or tunnel, switching behavior based on the nature of each request.
441</t>
442<figure><artwork type="drawing">
443         &gt;             &gt;             &gt;             &gt;
444    <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>
445               &lt;             &lt;             &lt;             &lt;
446</artwork></figure>
447<t>
448   The figure above shows three intermediaries (A, B, and C) between the
449   user agent and origin server. A request or response message that
450   travels the whole chain will pass through four separate connections.
451   Some HTTP communication options
452   might apply only to the connection with the nearest, non-tunnel
453   neighbor, only to the end-points of the chain, or to all connections
454   along the chain. Although the diagram is linear, each participant might
455   be engaged in multiple, simultaneous communications. For example, B
456   might be receiving requests from many clients other than A, and/or
457   forwarding requests to servers other than C, at the same time that it
458   is handling A's request.
459</t>
460<t>
461<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
462<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
463   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
464   to describe various requirements in relation to the directional flow of a
465   message: all messages flow from upstream to downstream.
466   Likewise, we use the terms inbound and outbound to refer to
467   directions in relation to the request path:
468   "<x:dfn>inbound</x:dfn>" means toward the origin server and
469   "<x:dfn>outbound</x:dfn>" means toward the user agent.
470</t>
471<t><iref primary="true" item="proxy"/>
472   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
473   client, usually via local configuration rules, to receive requests
474   for some type(s) of absolute URI and attempt to satisfy those
475   requests via translation through the HTTP interface.  Some translations
476   are minimal, such as for proxy requests for "http" URIs, whereas
477   other requests might require translation to and from entirely different
478   application-layer protocols. Proxies are often used to group an
479   organization's HTTP requests through a common intermediary for the
480   sake of security, annotation services, or shared caching.
481</t>
482<t>
483<iref primary="true" item="transforming proxy"/>
484<iref primary="true" item="non-transforming proxy"/>
485   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
486   or configured to modify request or response messages in a semantically
487   meaningful way (i.e., modifications, beyond those required by normal
488   HTTP processing, that change the message in a way that would be
489   significant to the original sender or potentially significant to
490   downstream recipients).  For example, a transforming proxy might be
491   acting as a shared annotation server (modifying responses to include
492   references to a local annotation database), a malware filter, a
493   format transcoder, or an intranet-to-Internet privacy filter.  Such
494   transformations are presumed to be desired by the client (or client
495   organization) that selected the proxy and are beyond the scope of
496   this specification.  However, when a proxy is not intended to transform
497   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
498   requirements that preserve HTTP message semantics. See &status-203; and
499   &header-warning; for status and warning codes related to transformations.
500</t>
501<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
502<iref primary="true" item="accelerator"/>
503   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
504   is a receiving agent that acts
505   as a layer above some other server(s) and translates the received
506   requests to the underlying server's protocol.  Gateways are often
507   used to encapsulate legacy or untrusted information services, to
508   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
509   enable partitioning or load-balancing of HTTP services across
510   multiple machines.
511</t>
512<t>
513   A gateway behaves as an origin server on its outbound connection and
514   as a user agent on its inbound connection.
515   All HTTP requirements applicable to an origin server
516   also apply to the outbound communication of a gateway.
517   A gateway communicates with inbound servers using any protocol that
518   it desires, including private extensions to HTTP that are outside
519   the scope of this specification.  However, an HTTP-to-HTTP gateway
520   that wishes to interoperate with third-party HTTP servers &MUST;
521   conform to HTTP user agent requirements on the gateway's inbound
522   connection and &MUST; implement the <x:ref>Connection</x:ref>
523   (<xref target="header.connection"/>) and <x:ref>Via</x:ref>
524   (<xref target="header.via"/>) header fields for both connections.
525</t>
526<t><iref primary="true" item="tunnel"/>
527   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
528   without changing the messages. Once active, a tunnel is not
529   considered a party to the HTTP communication, though the tunnel might
530   have been initiated by an HTTP request. A tunnel ceases to exist when
531   both ends of the relayed connection are closed. Tunnels are used to
532   extend a virtual connection through an intermediary, such as when
533   transport-layer security is used to establish confidential communication
534   through a shared firewall proxy.
535</t>
536<t><iref primary="true" item="interception proxy"/>
537<iref primary="true" item="transparent proxy"/>
538<iref primary="true" item="captive portal"/>
539   The above categories for intermediary only consider those acting as
540   participants in the HTTP communication.  There are also intermediaries
541   that can act on lower layers of the network protocol stack, filtering or
542   redirecting HTTP traffic without the knowledge or permission of message
543   senders. Network intermediaries often introduce security flaws or
544   interoperability problems by violating HTTP semantics.  For example, an
545   "<x:dfn>interception proxy</x:dfn>" <xref target="RFC3040"/> (also commonly
546   known as a "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/> or
547   "<x:dfn>captive portal</x:dfn>")
548   differs from an HTTP proxy because it is not selected by the client.
549   Instead, an interception proxy filters or redirects outgoing TCP port 80
550   packets (and occasionally other common port traffic).
551   Interception proxies are commonly found on public network access points,
552   as a means of enforcing account subscription prior to allowing use of
553   non-local Internet services, and within corporate firewalls to enforce
554   network usage policies.
555   They are indistinguishable from a man-in-the-middle attack.
556</t>
557<t>
558   HTTP is defined as a stateless protocol, meaning that each request message
559   can be understood in isolation.  Many implementations depend on HTTP's
560   stateless design in order to reuse proxied connections or dynamically
561   load balance requests across multiple servers.  Hence, servers &MUST-NOT;
562   assume that two requests on the same connection are from the same user
563   agent unless the connection is secured and specific to that agent.
564   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
565   been known to violate this requirement, resulting in security and
566   interoperability problems.
567</t>
568</section>
569
570<section title="Caches" anchor="caches">
571<iref primary="true" item="cache"/>
572<t>
573   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
574   subsystem that controls its message storage, retrieval, and deletion.
575   A cache stores cacheable responses in order to reduce the response
576   time and network bandwidth consumption on future, equivalent
577   requests. Any client or server &MAY; employ a cache, though a cache
578   cannot be used by a server while it is acting as a tunnel.
579</t>
580<t>
581   The effect of a cache is that the request/response chain is shortened
582   if one of the participants along the chain has a cached response
583   applicable to that request. The following illustrates the resulting
584   chain if B has a cached copy of an earlier response from O (via C)
585   for a request which has not been cached by UA or A.
586</t>
587<figure><artwork type="drawing">
588            &gt;             &gt;
589       <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>
590                  &lt;             &lt;
591</artwork></figure>
592<t><iref primary="true" item="cacheable"/>
593   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
594   the response message for use in answering subsequent requests.
595   Even when a response is cacheable, there might be additional
596   constraints placed by the client or by the origin server on when
597   that cached response can be used for a particular request. HTTP
598   requirements for cache behavior and cacheable responses are
599   defined in &caching-overview;. 
600</t>
601<t>
602   There are a wide variety of architectures and configurations
603   of caches and proxies deployed across the World Wide Web and
604   inside large organizations. These systems include national hierarchies
605   of proxy caches to save transoceanic bandwidth, systems that
606   broadcast or multicast cache entries, organizations that distribute
607   subsets of cached data via optical media, and so on.
608</t>
609</section>
610
611<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
612<t>
613   This specification targets conformance criteria according to the role of
614   a participant in HTTP communication.  Hence, HTTP requirements are placed
615   on senders, recipients, clients, servers, user agents, intermediaries,
616   origin servers, proxies, gateways, or caches, depending on what behavior
617   is being constrained by the requirement.
618</t>
619<t>
620   The verb "generate" is used instead of "send" where a requirement
621   differentiates between creating a protocol element and merely forwarding a
622   received element downstream.
623</t>
624<t>
625   An implementation is considered conformant if it complies with all of the
626   requirements associated with the roles it partakes in HTTP. Note that
627   SHOULD-level requirements are relevant here, unless one of the documented
628   exceptions is applicable.
629</t>
630<t>
631   In addition to the prose requirements placed upon them, senders &MUST-NOT;
632   generate protocol elements that do not match the grammar defined by the
633   ABNF rules for those protocol elements that are applicable to the sender's
634   role. If a received protocol element is processed, the recipient &MUST; be
635   able to parse any value that would match the ABNF rules for that protocol
636   element, excluding only those rules not applicable to the recipient's role.
637</t>
638<t>
639   Unless noted otherwise, a recipient &MAY; attempt to recover a usable
640   protocol element from an invalid construct.  HTTP does not define
641   specific error handling mechanisms except when they have a direct impact
642   on security, since different applications of the protocol require
643   different error handling strategies.  For example, a Web browser might
644   wish to transparently recover from a response where the
645   <x:ref>Location</x:ref> header field doesn't parse according to the ABNF,
646   whereas a systems control client might consider any form of error recovery
647   to be dangerous.
648</t>
649</section>
650
651<section title="Protocol Versioning" anchor="http.version">
652  <x:anchor-alias value="HTTP-version"/>
653  <x:anchor-alias value="HTTP-name"/>
654<t>
655   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
656   versions of the protocol. This specification defines version "1.1".
657   The protocol version as a whole indicates the sender's conformance
658   with the set of requirements laid out in that version's corresponding
659   specification of HTTP.
660</t>
661<t>
662   The version of an HTTP message is indicated by an HTTP-version field
663   in the first line of the message. HTTP-version is case-sensitive.
664</t>
665<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/>
666  <x:ref>HTTP-version</x:ref>  = <x:ref>HTTP-name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
667  <x:ref>HTTP-name</x:ref>     = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
668</artwork></figure>
669<t>
670   The HTTP version number consists of two decimal digits separated by a "."
671   (period or decimal point).  The first digit ("major version") indicates the
672   HTTP messaging syntax, whereas the second digit ("minor version") indicates
673   the highest minor version to which the sender is
674   conformant and able to understand for future communication.  The minor
675   version advertises the sender's communication capabilities even when the
676   sender is only using a backwards-compatible subset of the protocol,
677   thereby letting the recipient know that more advanced features can
678   be used in response (by servers) or in future requests (by clients).
679</t>
680<t>
681   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
682   <xref target="RFC1945"/> or a recipient whose version is unknown,
683   the HTTP/1.1 message is constructed such that it can be interpreted
684   as a valid HTTP/1.0 message if all of the newer features are ignored.
685   This specification places recipient-version requirements on some
686   new features so that a conformant sender will only use compatible
687   features until it has determined, through configuration or the
688   receipt of a message, that the recipient supports HTTP/1.1.
689</t>
690<t>
691   The interpretation of a header field does not change between minor
692   versions of the same major HTTP version, though the default
693   behavior of a recipient in the absence of such a field can change.
694   Unless specified otherwise, header fields defined in HTTP/1.1 are
695   defined for all versions of HTTP/1.x.  In particular, the <x:ref>Host</x:ref>
696   and <x:ref>Connection</x:ref> header fields ought to be implemented by all
697   HTTP/1.x implementations whether or not they advertise conformance with
698   HTTP/1.1.
699</t>
700<t>
701   New header fields can be defined such that, when they are
702   understood by a recipient, they might override or enhance the
703   interpretation of previously defined header fields.  When an
704   implementation receives an unrecognized header field, the recipient
705   &MUST; ignore that header field for local processing regardless of
706   the message's HTTP version.  An unrecognized header field received
707   by a proxy &MUST; be forwarded downstream unless the header field's
708   field-name is listed in the message's <x:ref>Connection</x:ref> header field
709   (see <xref target="header.connection"/>).
710   These requirements allow HTTP's functionality to be enhanced without
711   requiring prior update of deployed intermediaries.
712</t>
713<t>
714   Intermediaries that process HTTP messages (i.e., all intermediaries
715   other than those acting as tunnels) &MUST; send their own HTTP-version
716   in forwarded messages.  In other words, they &MUST-NOT; blindly
717   forward the first line of an HTTP message without ensuring that the
718   protocol version in that message matches a version to which that
719   intermediary is conformant for both the receiving and
720   sending of messages.  Forwarding an HTTP message without rewriting
721   the HTTP-version might result in communication errors when downstream
722   recipients use the message sender's version to determine what features
723   are safe to use for later communication with that sender.
724</t>
725<t>
726   An HTTP client &SHOULD; send a request version equal to the highest
727   version to which the client is conformant and
728   whose major version is no higher than the highest version supported
729   by the server, if this is known.  An HTTP client &MUST-NOT; send a
730   version to which it is not conformant.
731</t>
732<t>
733   An HTTP client &MAY; send a lower request version if it is known that
734   the server incorrectly implements the HTTP specification, but only
735   after the client has attempted at least one normal request and determined
736   from the response status or header fields (e.g., <x:ref>Server</x:ref>) that
737   the server improperly handles higher request versions.
738</t>
739<t>
740   An HTTP server &SHOULD; send a response version equal to the highest
741   version to which the server is conformant and
742   whose major version is less than or equal to the one received in the
743   request.  An HTTP server &MUST-NOT; send a version to which it is not
744   conformant.  A server &MAY; send a <x:ref>505 (HTTP Version Not
745   Supported)</x:ref> response if it cannot send a response using the
746   major version used in the client's request.
747</t>
748<t>
749   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
750   if it is known or suspected that the client incorrectly implements the
751   HTTP specification and is incapable of correctly processing later
752   version responses, such as when a client fails to parse the version
753   number correctly or when an intermediary is known to blindly forward
754   the HTTP-version even when it doesn't conform to the given minor
755   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
756   performed unless triggered by specific client attributes, such as when
757   one or more of the request header fields (e.g., <x:ref>User-Agent</x:ref>)
758   uniquely match the values sent by a client known to be in error.
759</t>
760<t>
761   The intention of HTTP's versioning design is that the major number
762   will only be incremented if an incompatible message syntax is
763   introduced, and that the minor number will only be incremented when
764   changes made to the protocol have the effect of adding to the message
765   semantics or implying additional capabilities of the sender.  However,
766   the minor version was not incremented for the changes introduced between
767   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
768   is specifically avoiding any such changes to the protocol.
769</t>
770</section>
771
772<section title="Uniform Resource Identifiers" anchor="uri">
773<iref primary="true" item="resource"/>
774<t>
775   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
776   throughout HTTP as the means for identifying resources. URI references
777   are used to target requests, indicate redirects, and define relationships.
778   HTTP does not limit what a resource might be; it merely defines an interface
779   that can be used to interact with a resource via HTTP. More information on
780   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
781</t>
782  <x:anchor-alias value="URI-reference"/>
783  <x:anchor-alias value="absolute-URI"/>
784  <x:anchor-alias value="relative-part"/>
785  <x:anchor-alias value="authority"/>
786  <x:anchor-alias value="path-abempty"/>
787  <x:anchor-alias value="path-absolute"/>
788  <x:anchor-alias value="port"/>
789  <x:anchor-alias value="query"/>
790  <x:anchor-alias value="uri-host"/>
791  <x:anchor-alias value="partial-URI"/>
792<t>
793   This specification adopts the definitions of "URI-reference",
794   "absolute-URI", "relative-part", "port", "host",
795   "path-abempty", "path-absolute", "query", and "authority" from the
796   URI generic syntax <xref target="RFC3986"/>.
797   In addition, we define a partial-URI rule for protocol elements
798   that allow a relative URI but not a fragment.
799</t>
800<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="URI-reference"><!--exported production--></iref><iref primary="true" item="Grammar" subitem="absolute-URI"/><iref primary="true" item="Grammar" subitem="authority"/><iref primary="true" item="Grammar" subitem="path-absolute"/><iref primary="true" item="Grammar" subitem="port"/><iref primary="true" item="Grammar" subitem="query"/><iref primary="true" item="Grammar" subitem="uri-host"/><iref primary="true" item="Grammar" subitem="partial-URI"><!--exported production--></iref>
801  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
802  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
803  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
804  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
805  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
806  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
807  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
808  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
809  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
810 
811  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
812</artwork></figure>
813<t>
814   Each protocol element in HTTP that allows a URI reference will indicate
815   in its ABNF production whether the element allows any form of reference
816   (URI-reference), only a URI in absolute form (absolute-URI), only the
817   path and optional query components, or some combination of the above.
818   Unless otherwise indicated, URI references are parsed
819   relative to the effective request URI
820   (<xref target="effective.request.uri"/>).
821</t>
822
823<section title="http URI scheme" anchor="http.uri">
824  <x:anchor-alias value="http-URI"/>
825  <iref item="http URI scheme" primary="true"/>
826  <iref item="URI scheme" subitem="http" primary="true"/>
827<t>
828   The "http" URI scheme is hereby defined for the purpose of minting
829   identifiers according to their association with the hierarchical
830   namespace governed by a potential HTTP origin server listening for
831   TCP connections on a given port.
832</t>
833<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"><!--terminal production--></iref>
834  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
835</artwork></figure>
836<t>
837   The HTTP origin server is identified by the generic syntax's
838   <x:ref>authority</x:ref> component, which includes a host identifier
839   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
840   The remainder of the URI, consisting of both the hierarchical path
841   component and optional query component, serves as an identifier for
842   a potential resource within that origin server's name space.
843</t>
844<t>
845   If the host identifier is provided as an IP literal or IPv4 address,
846   then the origin server is any listener on the indicated TCP port at
847   that IP address. If host is a registered name, then that name is
848   considered an indirect identifier and the recipient might use a name
849   resolution service, such as DNS, to find the address of a listener
850   for that host.
851   The host &MUST-NOT; be empty; if an "http" URI is received with an
852   empty host, then it &MUST; be rejected as invalid.
853   If the port subcomponent is empty or not given, then TCP port 80 is
854   assumed (the default reserved port for WWW services).
855</t>
856<t>
857   Regardless of the form of host identifier, access to that host is not
858   implied by the mere presence of its name or address. The host might or might
859   not exist and, even when it does exist, might or might not be running an
860   HTTP server or listening to the indicated port. The "http" URI scheme
861   makes use of the delegated nature of Internet names and addresses to
862   establish a naming authority (whatever entity has the ability to place
863   an HTTP server at that Internet name or address) and allows that
864   authority to determine which names are valid and how they might be used.
865</t>
866<t>
867   When an "http" URI is used within a context that calls for access to the
868   indicated resource, a client &MAY; attempt access by resolving
869   the host to an IP address, establishing a TCP connection to that address
870   on the indicated port, and sending an HTTP request message
871   (<xref target="http.message"/>) containing the URI's identifying data
872   (<xref target="message.routing"/>) to the server.
873   If the server responds to that request with a non-interim HTTP response
874   message, as described in &status-codes;, then that response
875   is considered an authoritative answer to the client's request.
876</t>
877<t>
878   Although HTTP is independent of the transport protocol, the "http"
879   scheme is specific to TCP-based services because the name delegation
880   process depends on TCP for establishing authority.
881   An HTTP service based on some other underlying connection protocol
882   would presumably be identified using a different URI scheme, just as
883   the "https" scheme (below) is used for servers that require an SSL/TLS
884   transport layer on a connection. Other protocols might also be used to
885   provide access to "http" identified resources &mdash; it is only the
886   authoritative interface used for mapping the namespace that is
887   specific to TCP.
888</t>
889<t>
890   The URI generic syntax for authority also includes a deprecated
891   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
892   for including user authentication information in the URI.  Some
893   implementations make use of the userinfo component for internal
894   configuration of authentication information, such as within command
895   invocation options, configuration files, or bookmark lists, even
896   though such usage might expose a user identifier or password.
897   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
898   delimiter) when transmitting an "http" URI in a message.  Recipients
899   of HTTP messages that contain a URI reference &SHOULD; parse for the
900   existence of userinfo and treat its presence as an error, likely
901   indicating that the deprecated subcomponent is being used to obscure
902   the authority for the sake of phishing attacks.
903</t>
904</section>
905
906<section title="https URI scheme" anchor="https.uri">
907   <x:anchor-alias value="https-URI"/>
908   <iref item="https URI scheme"/>
909   <iref item="URI scheme" subitem="https"/>
910<t>
911   The "https" URI scheme is hereby defined for the purpose of minting
912   identifiers according to their association with the hierarchical
913   namespace governed by a potential HTTP origin server listening for
914   SSL/TLS-secured connections on a given TCP port.
915</t>
916<t>
917   All of the requirements listed above for the "http" scheme are also
918   requirements for the "https" scheme, except that a default TCP port
919   of 443 is assumed if the port subcomponent is empty or not given,
920   and the TCP connection &MUST; be secured through the
921   use of strong encryption prior to sending the first HTTP request.
922</t>
923<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"><!--terminal production--></iref>
924  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
925</artwork></figure>
926<t>
927   Unlike the "http" scheme, responses to "https" identified requests
928   are never "public" and thus &MUST-NOT; be reused for shared caching.
929   They can, however, be reused in a private cache if the message is
930   cacheable by default in HTTP or specifically indicated as such by
931   the Cache-Control header field (&header-cache-control;).
932</t>
933<t>
934   Resources made available via the "https" scheme have no shared
935   identity with the "http" scheme even if their resource identifiers
936   indicate the same authority (the same host listening to the same
937   TCP port).  They are distinct name spaces and are considered to be
938   distinct origin servers.  However, an extension to HTTP that is
939   defined to apply to entire host domains, such as the Cookie protocol
940   <xref target="RFC6265"/>, can allow information
941   set by one service to impact communication with other services
942   within a matching group of host domains.
943</t>
944<t>
945   The process for authoritative access to an "https" identified
946   resource is defined in <xref target="RFC2818"/>.
947</t>
948</section>
949
950<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
951<t>
952   Since the "http" and "https" schemes conform to the URI generic syntax,
953   such URIs are normalized and compared according to the algorithm defined
954   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
955   described above for each scheme.
956</t>
957<t>
958   If the port is equal to the default port for a scheme, the normal
959   form is to elide the port subcomponent. Likewise, an empty path
960   component is equivalent to an absolute path of "/", so the normal
961   form is to provide a path of "/" instead. The scheme and host
962   are case-insensitive and normally provided in lowercase; all
963   other components are compared in a case-sensitive manner.
964   Characters other than those in the "reserved" set are equivalent
965   to their percent-encoded octets (see <xref target="RFC3986"
966   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
967</t>
968<t>
969   For example, the following three URIs are equivalent:
970</t>
971<figure><artwork type="example">
972   http://example.com:80/~smith/home.html
973   http://EXAMPLE.com/%7Esmith/home.html
974   http://EXAMPLE.com:/%7esmith/home.html
975</artwork></figure>
976</section>
977</section>
978</section>
979
980<section title="Message Format" anchor="http.message">
981<x:anchor-alias value="generic-message"/>
982<x:anchor-alias value="message.types"/>
983<x:anchor-alias value="HTTP-message"/>
984<x:anchor-alias value="start-line"/>
985<iref item="header section"/>
986<iref item="headers"/>
987<iref item="header field"/>
988<t>
989   All HTTP/1.1 messages consist of a start-line followed by a sequence of
990   octets in a format similar to the Internet Message Format
991   <xref target="RFC5322"/>: zero or more header fields (collectively
992   referred to as the "headers" or the "header section"), an empty line
993   indicating the end of the header section, and an optional message body.
994</t>
995<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"><!--terminal production--></iref>
996  <x:ref>HTTP-message</x:ref>   = <x:ref>start-line</x:ref>
997                   *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
998                   <x:ref>CRLF</x:ref>
999                   [ <x:ref>message-body</x:ref> ]
1000</artwork></figure>
1001<t>
1002   The normal procedure for parsing an HTTP message is to read the
1003   start-line into a structure, read each header field into a hash
1004   table by field name until the empty line, and then use the parsed
1005   data to determine if a message body is expected.  If a message body
1006   has been indicated, then it is read as a stream until an amount
1007   of octets equal to the message body length is read or the connection
1008   is closed.
1009</t>
1010<t>
1011   Recipients &MUST; parse an HTTP message as a sequence of octets in an
1012   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1013   Parsing an HTTP message as a stream of Unicode characters, without regard
1014   for the specific encoding, creates security vulnerabilities due to the
1015   varying ways that string processing libraries handle invalid multibyte
1016   character sequences that contain the octet LF (%x0A).  String-based
1017   parsers can only be safely used within protocol elements after the element
1018   has been extracted from the message, such as within a header field-value
1019   after message parsing has delineated the individual fields.
1020</t>
1021<t>
1022   An HTTP message can be parsed as a stream for incremental processing or
1023   forwarding downstream.  However, recipients cannot rely on incremental
1024   delivery of partial messages, since some implementations will buffer or
1025   delay message forwarding for the sake of network efficiency, security
1026   checks, or payload transformations.
1027</t>
1028
1029<section title="Start Line" anchor="start.line">
1030  <x:anchor-alias value="Start-Line"/>
1031<t>
1032   An HTTP message can either be a request from client to server or a
1033   response from server to client.  Syntactically, the two types of message
1034   differ only in the start-line, which is either a request-line (for requests)
1035   or a status-line (for responses), and in the algorithm for determining
1036   the length of the message body (<xref target="message.body"/>).
1037   In theory, a client could receive requests and a server could receive
1038   responses, distinguishing them by their different start-line formats,
1039   but in practice servers are implemented to only expect a request
1040   (a response is interpreted as an unknown or invalid request method)
1041   and clients are implemented to only expect a response.
1042</t>
1043<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1044  <x:ref>start-line</x:ref>     = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1045</artwork></figure>
1046<t>
1047   Implementations &MUST-NOT; send whitespace between the start-line and
1048   the first header field. The presence of such whitespace in a request
1049   might be an attempt to trick a server into ignoring that field or
1050   processing the line after it as a new request, either of which might
1051   result in a security vulnerability if other implementations within
1052   the request chain interpret the same message differently.
1053   Likewise, the presence of such whitespace in a response might be
1054   ignored by some clients or cause others to cease parsing.
1055</t>
1056
1057<section title="Request Line" anchor="request.line">
1058  <x:anchor-alias value="Request"/>
1059  <x:anchor-alias value="request-line"/>
1060<t>
1061   A request-line begins with a method token, followed by a single
1062   space (SP), the request-target, another single space (SP), the
1063   protocol version, and ending with CRLF.
1064</t>
1065<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1066  <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>
1067</artwork></figure>
1068<t>
1069   A server &MUST; be able to parse any received message that begins
1070   with a request-line and matches the ABNF rule for HTTP-message.
1071</t>
1072<iref primary="true" item="method"/>
1073<t anchor="method">
1074   The method token indicates the request method to be performed on the
1075   target resource. The request method is case-sensitive.
1076</t>
1077<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1078  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1079</artwork></figure>
1080<t>
1081   The methods defined by this specification can be found in
1082   &methods;, along with information regarding the HTTP method registry
1083   and considerations for defining new methods.
1084</t>
1085<iref item="request-target"/>
1086<t>
1087   The request-target identifies the target resource upon which to apply
1088   the request, as defined in <xref target="request-target"/>.
1089</t>
1090<t>
1091   No whitespace is allowed inside the method, request-target, and
1092   protocol version.  Hence, recipients typically parse the request-line
1093   into its component parts by splitting on the SP characters.
1094</t>
1095<t>
1096   Unfortunately, some user agents fail to properly encode hypertext
1097   references that have embedded whitespace, sending the characters
1098   directly instead of properly percent-encoding the disallowed characters.
1099   Recipients of an invalid request-line &SHOULD; respond with either a
1100   <x:ref>400 (Bad Request)</x:ref> error or a <x:ref>301 (Moved Permanently)</x:ref>
1101   redirect with the request-target properly encoded.  Recipients &SHOULD-NOT;
1102   attempt to autocorrect and then process the request without a redirect,
1103   since the invalid request-line might be deliberately crafted to bypass
1104   security filters along the request chain.
1105</t>
1106<t>
1107   HTTP does not place a pre-defined limit on the length of a request-line.
1108   A server that receives a method longer than any that it implements
1109   &SHOULD; respond with either a <x:ref>405 (Method Not Allowed)</x:ref>, if it is an origin
1110   server, or a <x:ref>501 (Not Implemented)</x:ref> status code.
1111   A server &MUST; be prepared to receive URIs of unbounded length and
1112   respond with the <x:ref>414 (URI Too Long)</x:ref> status code if the received
1113   request-target would be longer than the server wishes to handle
1114   (see &status-414;).
1115</t>
1116<t>
1117   Various ad-hoc limitations on request-line length are found in practice.
1118   It is &RECOMMENDED; that all HTTP senders and recipients support, at a
1119   minimum, request-line lengths of up to 8000 octets.
1120</t>
1121</section>
1122
1123<section title="Status Line" anchor="status.line">
1124  <x:anchor-alias value="response"/>
1125  <x:anchor-alias value="status-line"/>
1126  <x:anchor-alias value="status-code"/>
1127  <x:anchor-alias value="reason-phrase"/>
1128<t>
1129   The first line of a response message is the status-line, consisting
1130   of the protocol version, a space (SP), the status code, another space,
1131   a possibly-empty textual phrase describing the status code, and
1132   ending with CRLF.
1133</t>
1134<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1135  <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>
1136</artwork></figure>
1137<t>
1138   A client &MUST; be able to parse any received message that begins
1139   with a status-line and matches the ABNF rule for HTTP-message.
1140</t>
1141<t>
1142   The status-code element is a 3-digit integer code describing the
1143   result of the server's attempt to understand and satisfy the client's
1144   corresponding request. The rest of the response message is to be
1145   interpreted in light of the semantics defined for that status code.
1146   See &status-codes; for information about the semantics of status codes,
1147   including the classes of status code (indicated by the first digit),
1148   the status codes defined by this specification, considerations for the
1149   definition of new status codes, and the IANA registry.
1150</t>
1151<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1152  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1153</artwork></figure>
1154<t>  
1155   The reason-phrase element exists for the sole purpose of providing a
1156   textual description associated with the numeric status code, mostly
1157   out of deference to earlier Internet application protocols that were more
1158   frequently used with interactive text clients. A client &SHOULD; ignore
1159   the reason-phrase content.
1160</t>
1161<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1162  <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> )
1163</artwork></figure>
1164</section>
1165</section>
1166
1167<section title="Header Fields" anchor="header.fields">
1168  <x:anchor-alias value="header-field"/>
1169  <x:anchor-alias value="field-content"/>
1170  <x:anchor-alias value="field-name"/>
1171  <x:anchor-alias value="field-value"/>
1172  <x:anchor-alias value="obs-fold"/>
1173<t>
1174   Each HTTP header field consists of a case-insensitive field name
1175   followed by a colon (":"), optional whitespace, and the field value.
1176</t>
1177<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"/>
1178  <x:ref>header-field</x:ref>   = <x:ref>field-name</x:ref> ":" <x:ref>OWS</x:ref> <x:ref>field-value</x:ref> <x:ref>BWS</x:ref>
1179  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1180  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1181  <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> )
1182  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1183                 ; obsolete line folding
1184                 ; see <xref target="field.parsing"/>
1185</artwork></figure>
1186<t>
1187   The field-name token labels the corresponding field-value as having the
1188   semantics defined by that header field.  For example, the <x:ref>Date</x:ref>
1189   header field is defined in &header-date; as containing the origination
1190   timestamp for the message in which it appears.
1191</t>
1192<t>
1193   HTTP header fields are fully extensible: there is no limit on the
1194   introduction of new field names, each presumably defining new semantics,
1195   or on the number of header fields used in a given message.  Existing
1196   fields are defined in each part of this specification and in many other
1197   specifications outside the standards process.
1198   New header fields can be introduced without changing the protocol version
1199   if their defined semantics allow them to be safely ignored by recipients
1200   that do not recognize them.
1201</t>
1202<t>
1203   New HTTP header fields &SHOULD; be registered with IANA according
1204   to the procedures in &cons-new-header-fields;.
1205   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1206   field-name is listed in the <x:ref>Connection</x:ref> header field
1207   (<xref target="header.connection"/>) or the proxy is specifically
1208   configured to block or otherwise transform such fields.
1209   Unrecognized header fields &SHOULD; be ignored by other recipients.
1210</t>
1211<t>
1212   The order in which header fields with differing field names are
1213   received is not significant. However, it is "good practice" to send
1214   header fields that contain control data first, such as <x:ref>Host</x:ref>
1215   on requests and <x:ref>Date</x:ref> on responses, so that implementations
1216   can decide when not to handle a message as early as possible.  A server
1217   &MUST; wait until the entire header section is received before interpreting
1218   a request message, since later header fields might include conditionals,
1219   authentication credentials, or deliberately misleading duplicate
1220   header fields that would impact request processing.
1221</t>
1222<t>
1223   Multiple header fields with the same field name &MUST-NOT; be
1224   sent in a message unless the entire field value for that
1225   header field is defined as a comma-separated list [i.e., #(values)].
1226   Multiple header fields with the same field name can be combined into
1227   one "field-name: field-value" pair, without changing the semantics of the
1228   message, by appending each subsequent field value to the combined
1229   field value in order, separated by a comma. The order in which
1230   header fields with the same field name are received is therefore
1231   significant to the interpretation of the combined field value;
1232   a proxy &MUST-NOT; change the order of these field values when
1233   forwarding a message.
1234</t>
1235<x:note>
1236  <t>
1237   &Note; The "Set-Cookie" header field as implemented in
1238   practice can occur multiple times, but does not use the list syntax, and
1239   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1240   for details.) Also note that the Set-Cookie2 header field specified in
1241   <xref target="RFC2965"/> does not share this problem.
1242  </t>
1243</x:note>
1244
1245<section title="Whitespace" anchor="whitespace">
1246<t anchor="rule.LWS">
1247   This specification uses three rules to denote the use of linear
1248   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1249   BWS ("bad" whitespace).
1250</t>
1251<t anchor="rule.OWS">
1252   The OWS rule is used where zero or more linear whitespace octets might
1253   appear. OWS &SHOULD; either not be produced or be produced as a single
1254   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1255   be replaced with a single SP or transformed to all SP octets (each
1256   octet other than SP replaced with SP) before interpreting the field value
1257   or forwarding the message downstream.
1258</t>
1259<t anchor="rule.RWS">
1260   RWS is used when at least one linear whitespace octet is required to
1261   separate field tokens. RWS &SHOULD; be produced as a single SP.
1262   Multiple RWS octets that occur within field-content &SHOULD; either
1263   be replaced with a single SP or transformed to all SP octets before
1264   interpreting the field value or forwarding the message downstream.
1265</t>
1266<t anchor="rule.BWS">
1267   BWS is used where the grammar allows optional whitespace for historical
1268   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
1269   recipients &MUST; accept such bad optional whitespace and remove it before
1270   interpreting the field value or forwarding the message downstream.
1271</t>
1272<t anchor="rule.whitespace">
1273  <x:anchor-alias value="BWS"/>
1274  <x:anchor-alias value="OWS"/>
1275  <x:anchor-alias value="RWS"/>
1276</t>
1277<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"/>
1278  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1279                 ; "optional" whitespace
1280  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1281                 ; "required" whitespace
1282  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1283                 ; "bad" whitespace
1284</artwork></figure>
1285</section>
1286
1287<section title="Field Parsing" anchor="field.parsing">
1288<t>
1289   No whitespace is allowed between the header field-name and colon.
1290   In the past, differences in the handling of such whitespace have led to
1291   security vulnerabilities in request routing and response handling.
1292   Any received request message that contains whitespace between a header
1293   field-name and colon &MUST; be rejected with a response code of 400
1294   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1295   message before forwarding the message downstream.
1296</t>
1297<t>
1298   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1299   preferred. The field value does not include any leading or trailing white
1300   space: OWS occurring before the first non-whitespace octet of the
1301   field value or after the last non-whitespace octet of the field value
1302   is ignored and &SHOULD; be removed before further processing (as this does
1303   not change the meaning of the header field).
1304</t>
1305<t>
1306   Historically, HTTP header field values could be extended over multiple
1307   lines by preceding each extra line with at least one space or horizontal
1308   tab (obs-fold). This specification deprecates such line
1309   folding except within the message/http media type
1310   (<xref target="internet.media.type.message.http"/>).
1311   HTTP senders &MUST-NOT; produce messages that include line folding
1312   (i.e., that contain any field-value that matches the obs-fold rule) unless
1313   the message is intended for packaging within the message/http media type.
1314   HTTP recipients &SHOULD; accept line folding and replace any embedded
1315   obs-fold whitespace with either a single SP or a matching number of SP
1316   octets (to avoid buffer copying) prior to interpreting the field value or
1317   forwarding the message downstream.
1318</t>
1319<t>
1320   Historically, HTTP has allowed field content with text in the ISO-8859-1
1321   <xref target="ISO-8859-1"/> character encoding and supported other
1322   character sets only through use of <xref target="RFC2047"/> encoding.
1323   In practice, most HTTP header field values use only a subset of the
1324   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1325   header fields &SHOULD; limit their field values to US-ASCII octets.
1326   Recipients &SHOULD; treat other (obs-text) octets in field content as
1327   opaque data.
1328</t>
1329</section>
1330
1331<section title="Field Length" anchor="field.length">
1332<t>
1333   HTTP does not place a pre-defined limit on the length of header fields,
1334   either in isolation or as a set. A server &MUST; be prepared to receive
1335   request header fields of unbounded length and respond with a <x:ref>4xx
1336   (Client Error)</x:ref> status code if the received header field(s) would be
1337   longer than the server wishes to handle.
1338</t>
1339<t>
1340   A client that receives response header fields that are longer than it wishes
1341   to handle can only treat it as a server error.
1342</t>
1343<t>
1344   Various ad-hoc limitations on header field length are found in practice. It
1345   is &RECOMMENDED; that all HTTP senders and recipients support messages whose
1346   combined header fields have 4000 or more octets.
1347</t>
1348</section>
1349
1350<section title="Field value components" anchor="field.components">
1351<t anchor="rule.token.separators">
1352  <x:anchor-alias value="tchar"/>
1353  <x:anchor-alias value="token"/>
1354  <x:anchor-alias value="special"/>
1355  <x:anchor-alias value="word"/>
1356   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1357   separated by whitespace or special characters. These special characters
1358   &MUST; be in a quoted string to be used within a parameter value (as defined
1359   in <xref target="transfer.codings"/>).
1360</t>
1361<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="word"/><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"><!--unused production--></iref>
1362  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1363
1364  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1365<!--
1366  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1367 -->
1368  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1369                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1370                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1371                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1372
1373  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1374                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1375                 / "]" / "?" / "=" / "{" / "}"
1376</artwork></figure>
1377<t anchor="rule.quoted-string">
1378  <x:anchor-alias value="quoted-string"/>
1379  <x:anchor-alias value="qdtext"/>
1380  <x:anchor-alias value="obs-text"/>
1381   A string of text is parsed as a single word if it is quoted using
1382   double-quote marks.
1383</t>
1384<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"/>
1385  <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>
1386  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1387  <x:ref>obs-text</x:ref>       = %x80-FF
1388</artwork></figure>
1389<t anchor="rule.quoted-pair">
1390  <x:anchor-alias value="quoted-pair"/>
1391   The backslash octet ("\") can be used as a single-octet
1392   quoting mechanism within quoted-string constructs:
1393</t>
1394<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1395  <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> )
1396</artwork></figure>
1397<t>
1398   Recipients that process the value of the quoted-string &MUST; handle a
1399   quoted-pair as if it were replaced by the octet following the backslash.
1400</t>
1401<t>
1402   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1403   escaping (i.e., other than DQUOTE and the backslash octet).
1404</t>
1405<t anchor="rule.comment">
1406  <x:anchor-alias value="comment"/>
1407  <x:anchor-alias value="ctext"/>
1408   Comments can be included in some HTTP header fields by surrounding
1409   the comment text with parentheses. Comments are only allowed in
1410   fields containing "comment" as part of their field value definition.
1411</t>
1412<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1413  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1414  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1415</artwork></figure>
1416<t anchor="rule.quoted-cpair">
1417  <x:anchor-alias value="quoted-cpair"/>
1418   The backslash octet ("\") can be used as a single-octet
1419   quoting mechanism within comment constructs:
1420</t>
1421<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1422  <x:ref>quoted-cpair</x:ref>   = "\" ( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1423</artwork></figure>
1424<t>
1425   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1426   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1427</t>
1428</section>
1429
1430</section>
1431
1432<section title="Message Body" anchor="message.body">
1433  <x:anchor-alias value="message-body"/>
1434<t>
1435   The message body (if any) of an HTTP message is used to carry the
1436   payload body of that request or response.  The message body is
1437   identical to the payload body unless a transfer coding has been
1438   applied, as described in <xref target="header.transfer-encoding"/>.
1439</t>
1440<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1441  <x:ref>message-body</x:ref> = *OCTET
1442</artwork></figure>
1443<t>
1444   The rules for when a message body is allowed in a message differ for
1445   requests and responses.
1446</t>
1447<t>
1448   The presence of a message body in a request is signaled by a
1449   a <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1450   field. Request message framing is independent of method semantics,
1451   even if the method does not define any use for a message body.
1452</t>
1453<t>
1454   The presence of a message body in a response depends on both
1455   the request method to which it is responding and the response
1456   status code (<xref target="status.line"/>).
1457   Responses to the HEAD request method never include a message body
1458   because the associated response header fields (e.g.,
1459   <x:ref>Transfer-Encoding</x:ref>, <x:ref>Content-Length</x:ref>, etc.) only
1460   indicate what their values would have been if the request method had been
1461   GET. <x:ref>2xx (Successful)</x:ref> responses to CONNECT switch to tunnel
1462   mode instead of having a message body.
1463   All <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, and
1464   <x:ref>304 (Not Modified)</x:ref> responses &MUST-NOT; include a message body.
1465   All other responses do include a message body, although the body
1466   &MAY; be of zero length.
1467</t>
1468
1469<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1470  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1471  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
1472  <x:anchor-alias value="Transfer-Encoding"/>
1473<t>
1474   When one or more transfer codings are applied to a payload body in order
1475   to form the message body, a Transfer-Encoding header field &MUST; be sent
1476   in the message and &MUST; contain the list of corresponding
1477   transfer-coding names in the same order that they were applied.
1478   Transfer codings are defined in <xref target="transfer.codings"/>.
1479</t>
1480<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1481  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1482</artwork></figure>
1483<t>
1484   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1485   MIME, which was designed to enable safe transport of binary data over a
1486   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1487   However, safe transport has a different focus for an 8bit-clean transfer
1488   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1489   accurately delimit a dynamically generated payload and to distinguish
1490   payload encodings that are only applied for transport efficiency or
1491   security from those that are characteristics of the target resource.
1492</t>
1493<t>
1494   The "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1495   &MUST; be implemented by all HTTP/1.1 recipients because it plays a
1496   crucial role in delimiting messages when the payload body size is not
1497   known in advance.
1498   When the "chunked" transfer-coding is used, it &MUST; be the last
1499   transfer-coding applied to form the message body and &MUST-NOT;
1500   be applied more than once in a message body.
1501   If any transfer-coding is applied to a request payload body,
1502   the final transfer-coding applied &MUST; be "chunked".
1503   If any transfer-coding is applied to a response payload body, then either
1504   the final transfer-coding applied &MUST; be "chunked" or
1505   the message &MUST; be terminated by closing the connection.
1506</t>
1507<figure><preamble>
1508   For example,
1509</preamble><artwork type="example">
1510  Transfer-Encoding: gzip, chunked
1511</artwork><postamble>
1512   indicates that the payload body has been compressed using the gzip
1513   coding and then chunked using the chunked coding while forming the
1514   message body.
1515</postamble></figure>
1516<t>
1517   If more than one Transfer-Encoding header field is present in a message,
1518   the multiple field-values &MUST; be combined into one field-value,
1519   according to the algorithm defined in <xref target="header.fields"/>,
1520   before determining the message body length.
1521</t>
1522<t>
1523   Unlike <x:ref>Content-Encoding</x:ref> (&content-codings;),
1524   Transfer-Encoding is a property of the message, not of the payload, and thus
1525   &MAY; be added or removed by any implementation along the request/response
1526   chain. Additional information about the encoding parameters &MAY; be
1527   provided by other header fields not defined by this specification.
1528</t>
1529<t>
1530   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1531   <x:ref>304 (Not Modified)</x:ref> response (&status-304;) to a GET request,
1532   neither of which includes a message body,
1533   to indicate that the origin server would have applied a transfer coding
1534   to the message body if the request had been an unconditional GET.
1535   This indication is not required, however, because any recipient on
1536   the response chain (including the origin server) can remove transfer
1537   codings when they are not needed.
1538</t>
1539<t>
1540   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1541   implementations advertising only HTTP/1.0 support will not understand
1542   how to process a transfer-encoded payload.
1543   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1544   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1545   might be in the form of specific user configuration or by remembering the
1546   version of a prior received response.
1547   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1548   the corresponding request indicates HTTP/1.1 (or later).
1549</t>
1550<t>
1551   A server that receives a request message with a transfer-coding it does
1552   not understand &SHOULD; respond with <x:ref>501 (Not Implemented)</x:ref> and then
1553   close the connection.
1554</t>
1555</section>
1556
1557<section title="Content-Length" anchor="header.content-length">
1558  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1559  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
1560  <x:anchor-alias value="Content-Length"/>
1561<t>
1562   When a message does not have a <x:ref>Transfer-Encoding</x:ref> header field
1563   and the payload body length can be determined prior to being transferred, a
1564   Content-Length header field &SHOULD; be sent to indicate the length of the
1565   payload body that is either present as the message body, for requests
1566   and non-HEAD responses other than <x:ref>304 (Not Modified)</x:ref>, or
1567   would have been present had the request been an unconditional GET.  The
1568   length is expressed as a decimal number of octets.
1569</t>
1570<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1571  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1572</artwork></figure>
1573<t>
1574   An example is
1575</t>
1576<figure><artwork type="example">
1577  Content-Length: 3495
1578</artwork></figure>
1579<t>
1580   In the case of a response to a HEAD request, Content-Length indicates
1581   the size of the payload body (without any potential transfer-coding)
1582   that would have been sent had the request been a GET.
1583   In the case of a <x:ref>304 (Not Modified)</x:ref> response (&status-304;)
1584   to a GET request, Content-Length indicates the size of the payload body (without
1585   any potential transfer-coding) that would have been sent in a <x:ref>200 (OK)</x:ref>
1586   response.
1587</t>
1588<t>
1589   Any Content-Length field value greater than or equal to zero is valid.
1590   Since there is no predefined limit to the length of an HTTP payload,
1591   recipients &SHOULD; anticipate potentially large decimal numerals and
1592   prevent parsing errors due to integer conversion overflows
1593   (<xref target="attack.protocol.element.size.overflows"/>).
1594</t>
1595<t>
1596   If a message is received that has multiple Content-Length header fields
1597   with field-values consisting of the same decimal value, or a single
1598   Content-Length header field with a field value containing a list of
1599   identical decimal values (e.g., "Content-Length: 42, 42"), indicating that
1600   duplicate Content-Length header fields have been generated or combined by an
1601   upstream message processor, then the recipient &MUST; either reject the
1602   message as invalid or replace the duplicated field-values with a single
1603   valid Content-Length field containing that decimal value prior to
1604   determining the message body length.
1605</t>
1606<x:note>
1607  <t>
1608   &Note; HTTP's use of Content-Length for message framing differs
1609   significantly from the same field's use in MIME, where it is an optional
1610   field used only within the "message/external-body" media-type.
1611  </t>
1612</x:note>
1613</section>
1614
1615<section title="Message Body Length" anchor="message.body.length">
1616<t>
1617   The length of a message body is determined by one of the following
1618   (in order of precedence):
1619</t>
1620<t>
1621  <list style="numbers">
1622    <x:lt><t>
1623     Any response to a HEAD request and any response with a
1624     <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, or
1625     <x:ref>304 (Not Modified)</x:ref> status code is always
1626     terminated by the first empty line after the header fields, regardless of
1627     the header fields present in the message, and thus cannot contain a
1628     message body.
1629    </t></x:lt>
1630    <x:lt><t>
1631     Any <x:ref>2xx (Successful)</x:ref> response to a CONNECT request implies that the
1632     connection will become a tunnel immediately after the empty line that
1633     concludes the header fields.  A client &MUST; ignore any
1634     <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1635     fields received in such a message.
1636    </t></x:lt>
1637    <x:lt><t>
1638     If a <x:ref>Transfer-Encoding</x:ref> header field is present
1639     and the "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1640     is the final encoding, the message body length is determined by reading
1641     and decoding the chunked data until the transfer-coding indicates the
1642     data is complete.
1643    </t>
1644    <t>
1645     If a <x:ref>Transfer-Encoding</x:ref> header field is present in a
1646     response and the "chunked" transfer-coding is not the final encoding, the
1647     message body length is determined by reading the connection until it is
1648     closed by the server.
1649     If a Transfer-Encoding header field is present in a request and the
1650     "chunked" transfer-coding is not the final encoding, the message body
1651     length cannot be determined reliably; the server &MUST; respond with
1652     the <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1653    </t>
1654    <t>
1655     If a message is received with both a <x:ref>Transfer-Encoding</x:ref>
1656     and a <x:ref>Content-Length</x:ref> header field, the
1657     Transfer-Encoding overrides the Content-Length.
1658     Such a message might indicate an attempt to perform request or response
1659     smuggling (bypass of security-related checks on message routing or content)
1660     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1661     be removed, prior to forwarding the message downstream, or replaced with
1662     the real message body length after the transfer-coding is decoded.
1663    </t></x:lt>
1664    <x:lt><t>
1665     If a message is received without <x:ref>Transfer-Encoding</x:ref> and with
1666     either multiple <x:ref>Content-Length</x:ref> header fields having
1667     differing field-values or a single Content-Length header field having an
1668     invalid value, then the message framing is invalid and &MUST; be treated
1669     as an error to prevent request or response smuggling.
1670     If this is a request message, the server &MUST; respond with
1671     a <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1672     If this is a response message received by a proxy, the proxy
1673     &MUST; discard the received response, send a <x:ref>502 (Bad Gateway)</x:ref>
1674     status code as its downstream response, and then close the connection.
1675     If this is a response message received by a user-agent, it &MUST; be
1676     treated as an error by discarding the message and closing the connection.
1677    </t></x:lt>
1678    <x:lt><t>
1679     If a valid <x:ref>Content-Length</x:ref> header field is present without
1680     <x:ref>Transfer-Encoding</x:ref>, its decimal value defines the
1681     message body length in octets.  If the actual number of octets sent in
1682     the message is less than the indicated Content-Length, the recipient
1683     &MUST; consider the message to be incomplete and treat the connection
1684     as no longer usable.
1685     If the actual number of octets sent in the message is more than the indicated
1686     Content-Length, the recipient &MUST; only process the message body up to the
1687     field value's number of octets; the remainder of the message &MUST; either
1688     be discarded or treated as the next message in a pipeline.  For the sake of
1689     robustness, a user-agent &MAY; attempt to detect and correct such an error
1690     in message framing if it is parsing the response to the last request on
1691     a connection and the connection has been closed by the server.
1692    </t></x:lt>
1693    <x:lt><t>
1694     If this is a request message and none of the above are true, then the
1695     message body length is zero (no message body is present).
1696    </t></x:lt>
1697    <x:lt><t>
1698     Otherwise, this is a response message without a declared message body
1699     length, so the message body length is determined by the number of octets
1700     received prior to the server closing the connection.
1701    </t></x:lt>
1702  </list>
1703</t>
1704<t>
1705   Since there is no way to distinguish a successfully completed,
1706   close-delimited message from a partially-received message interrupted
1707   by network failure, implementations &SHOULD; use encoding or
1708   length-delimited messages whenever possible.  The close-delimiting
1709   feature exists primarily for backwards compatibility with HTTP/1.0.
1710</t>
1711<t>
1712   A server &MAY; reject a request that contains a message body but
1713   not a <x:ref>Content-Length</x:ref> by responding with
1714   <x:ref>411 (Length Required)</x:ref>.
1715</t>
1716<t>
1717   Unless a transfer-coding other than "chunked" has been applied,
1718   a client that sends a request containing a message body &SHOULD;
1719   use a valid <x:ref>Content-Length</x:ref> header field if the message body
1720   length is known in advance, rather than the "chunked" encoding, since some
1721   existing services respond to "chunked" with a <x:ref>411 (Length Required)</x:ref>
1722   status code even though they understand the chunked encoding.  This
1723   is typically because such services are implemented via a gateway that
1724   requires a content-length in advance of being called and the server
1725   is unable or unwilling to buffer the entire request before processing.
1726</t>
1727<t>
1728   A client that sends a request containing a message body &MUST; include a
1729   valid <x:ref>Content-Length</x:ref> header field if it does not know the
1730   server will handle HTTP/1.1 (or later) requests; such knowledge can be in
1731   the form of specific user configuration or by remembering the version of a
1732   prior received response.
1733</t>
1734</section>
1735</section>
1736
1737<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1738<t>
1739   Request messages that are prematurely terminated, possibly due to a
1740   canceled connection or a server-imposed time-out exception, &MUST;
1741   result in closure of the connection; sending an HTTP/1.1 error response
1742   prior to closing the connection is &OPTIONAL;.
1743</t>
1744<t>
1745   Response messages that are prematurely terminated, usually by closure
1746   of the connection prior to receiving the expected number of octets or by
1747   failure to decode a transfer-encoded message body, &MUST; be recorded
1748   as incomplete.  A response that terminates in the middle of the header
1749   block (before the empty line is received) cannot be assumed to convey the
1750   full semantics of the response and &MUST; be treated as an error.
1751</t>
1752<t>
1753   A message body that uses the chunked transfer encoding is
1754   incomplete if the zero-sized chunk that terminates the encoding has not
1755   been received.  A message that uses a valid <x:ref>Content-Length</x:ref> is
1756   incomplete if the size of the message body received (in octets) is less than
1757   the value given by Content-Length.  A response that has neither chunked
1758   transfer encoding nor Content-Length is terminated by closure of the
1759   connection, and thus is considered complete regardless of the number of
1760   message body octets received, provided that the header block was received
1761   intact.
1762</t>
1763<t>
1764   A user agent &MUST-NOT; render an incomplete response message body as if
1765   it were complete (i.e., some indication needs to be given to the user that an
1766   error occurred).  Cache requirements for incomplete responses are defined
1767   in &cache-incomplete;.
1768</t>
1769<t>
1770   A server &MUST; read the entire request message body or close
1771   the connection after sending its response, since otherwise the
1772   remaining data on a persistent connection would be misinterpreted
1773   as the next request.  Likewise,
1774   a client &MUST; read the entire response message body if it intends
1775   to reuse the same connection for a subsequent request.  Pipelining
1776   multiple requests on a connection is described in <xref target="pipelining"/>.
1777</t>
1778</section>
1779
1780<section title="Message Parsing Robustness" anchor="message.robustness">
1781<t>
1782   Older HTTP/1.0 client implementations might send an extra CRLF
1783   after a POST request as a lame workaround for some early server
1784   applications that failed to read message body content that was
1785   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1786   preface or follow a request with an extra CRLF.  If terminating
1787   the request message body with a line-ending is desired, then the
1788   client &MUST; include the terminating CRLF octets as part of the
1789   message body length.
1790</t>
1791<t>
1792   In the interest of robustness, servers &SHOULD; ignore at least one
1793   empty line received where a request-line is expected. In other words, if
1794   the server is reading the protocol stream at the beginning of a
1795   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1796   Likewise, although the line terminator for the start-line and header
1797   fields is the sequence CRLF, we recommend that recipients recognize a
1798   single LF as a line terminator and ignore any CR.
1799</t>
1800<t>
1801   When a server listening only for HTTP request messages, or processing
1802   what appears from the start-line to be an HTTP request message,
1803   receives a sequence of octets that does not match the HTTP-message
1804   grammar aside from the robustness exceptions listed above, the
1805   server &MUST; respond with an HTTP/1.1 <x:ref>400 (Bad Request)</x:ref> response. 
1806</t>
1807</section>
1808</section>
1809
1810<section title="Transfer Codings" anchor="transfer.codings">
1811  <x:anchor-alias value="transfer-coding"/>
1812  <x:anchor-alias value="transfer-extension"/>
1813<t>
1814   Transfer-coding values are used to indicate an encoding
1815   transformation that has been, can be, or might need to be applied to a
1816   payload body in order to ensure "safe transport" through the network.
1817   This differs from a content coding in that the transfer-coding is a
1818   property of the message rather than a property of the representation
1819   that is being transferred.
1820</t>
1821<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1822  <x:ref>transfer-coding</x:ref>    = "chunked" ; <xref target="chunked.encoding"/>
1823                     / "compress" ; <xref target="compress.coding"/>
1824                     / "deflate" ; <xref target="deflate.coding"/>
1825                     / "gzip" ; <xref target="gzip.coding"/>
1826                     / <x:ref>transfer-extension</x:ref>
1827  <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> )
1828</artwork></figure>
1829<t anchor="rule.parameter">
1830  <x:anchor-alias value="attribute"/>
1831  <x:anchor-alias value="transfer-parameter"/>
1832  <x:anchor-alias value="value"/>
1833   Parameters are in the form of attribute/value pairs.
1834</t>
1835<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/>
1836  <x:ref>transfer-parameter</x:ref> = <x:ref>attribute</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>value</x:ref>
1837  <x:ref>attribute</x:ref>          = <x:ref>token</x:ref>
1838  <x:ref>value</x:ref>              = <x:ref>word</x:ref>
1839</artwork></figure>
1840<t>
1841   All transfer-coding values are case-insensitive.
1842   The HTTP Transfer Coding registry is defined in
1843   <xref target="transfer.coding.registry"/>.
1844   HTTP/1.1 uses transfer-coding values in the <x:ref>TE</x:ref> header field
1845   (<xref target="header.te"/>) and in the <x:ref>Transfer-Encoding</x:ref>
1846   header field (<xref target="header.transfer-encoding"/>).
1847</t>
1848
1849<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1850  <iref item="chunked (Coding Format)"/>
1851  <iref item="Coding Format" subitem="chunked"/>
1852  <x:anchor-alias value="chunk"/>
1853  <x:anchor-alias value="chunked-body"/>
1854  <x:anchor-alias value="chunk-data"/>
1855  <x:anchor-alias value="chunk-ext"/>
1856  <x:anchor-alias value="chunk-ext-name"/>
1857  <x:anchor-alias value="chunk-ext-val"/>
1858  <x:anchor-alias value="chunk-size"/>
1859  <x:anchor-alias value="last-chunk"/>
1860  <x:anchor-alias value="trailer-part"/>
1861  <x:anchor-alias value="quoted-str-nf"/>
1862  <x:anchor-alias value="qdtext-nf"/>
1863<t>
1864   The chunked encoding modifies the body of a message in order to
1865   transfer it as a series of chunks, each with its own size indicator,
1866   followed by an &OPTIONAL; trailer containing header fields. This
1867   allows dynamically produced content to be transferred along with the
1868   information necessary for the recipient to verify that it has
1869   received the full message.
1870</t>
1871<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="chunked-body"><!--terminal production--></iref><iref primary="true" item="Grammar" subitem="chunk"/><iref primary="true" item="Grammar" subitem="chunk-size"/><iref primary="true" item="Grammar" subitem="last-chunk"/><iref primary="true" item="Grammar" subitem="chunk-ext"/><iref primary="true" item="Grammar" subitem="chunk-ext-name"/><iref primary="true" item="Grammar" subitem="chunk-ext-val"/><iref primary="true" item="Grammar" subitem="chunk-data"/><iref primary="true" item="Grammar" subitem="trailer-part"/><iref primary="true" item="Grammar" subitem="quoted-str-nf"/><iref primary="true" item="Grammar" subitem="qdtext-nf"/>
1872  <x:ref>chunked-body</x:ref>   = *<x:ref>chunk</x:ref>
1873                   <x:ref>last-chunk</x:ref>
1874                   <x:ref>trailer-part</x:ref>
1875                   <x:ref>CRLF</x:ref>
1876 
1877  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1878                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1879  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1880  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1881 
1882  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1883  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1884  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1885  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1886  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1887 
1888  <x:ref>quoted-str-nf</x:ref>  = <x:ref>DQUOTE</x:ref> *( <x:ref>qdtext-nf</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref>
1889                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1890  <x:ref>qdtext-nf</x:ref>      = <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1891</artwork></figure>
1892<t>
1893   Chunk extensions within the chucked encoding are deprecated.
1894   Senders &SHOULD-NOT; send chunk-ext.
1895   Definition of new chunk extensions is discouraged.
1896</t>
1897<t>
1898   The chunk-size field is a string of hex digits indicating the size of
1899   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1900   zero, followed by the trailer, which is terminated by an empty line.
1901</t>
1902
1903<section title="Trailer" anchor="header.trailer">
1904  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
1905  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
1906  <x:anchor-alias value="Trailer"/>
1907<t>
1908   A trailer allows the sender to include additional fields at the end of a
1909   chunked message in order to supply metadata that might be dynamically
1910   generated while the message body is sent, such as a message integrity
1911   check, digital signature, or post-processing status.
1912   The trailer &MUST-NOT; contain fields that need to be known before a
1913   recipient processes the body, such as <x:ref>Transfer-Encoding</x:ref>,
1914   <x:ref>Content-Length</x:ref>, and <x:ref>Trailer</x:ref>.
1915</t>
1916<t>
1917   When a message includes a message body encoded with the chunked
1918   transfer-coding and the sender desires to send metadata in the form of
1919   trailer fields at the end of the message, the sender &SHOULD; send a
1920   <x:ref>Trailer</x:ref> header field before the message body to indicate
1921   which fields will be present in the trailers. This allows the recipient
1922   to prepare for receipt of that metadata before it starts processing the body,
1923   which is useful if the message is being streamed and the recipient wishes
1924   to confirm an integrity check on the fly.
1925</t>
1926<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
1927  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
1928</artwork></figure>
1929<t>
1930   If no <x:ref>Trailer</x:ref> header field is present, the sender of a
1931   chunked message body &SHOULD; send an empty trailer.
1932</t>
1933<t>
1934   A server &MUST; send an empty trailer with the chunked transfer-coding
1935   unless at least one of the following is true:
1936  <list style="numbers">
1937    <t>the request included a <x:ref>TE</x:ref> header field that indicates
1938    "trailers" is acceptable in the transfer-coding of the response, as
1939    described in <xref target="header.te"/>; or,</t>
1940     
1941    <t>the trailer fields consist entirely of optional metadata and the
1942    recipient could use the message (in a manner acceptable to the server where
1943    the field originated) without receiving that metadata. In other words,
1944    the server that generated the header field is willing to accept the
1945    possibility that the trailer fields might be silently discarded along
1946    the path to the client.</t>
1947  </list>
1948</t>
1949<t>
1950   The above requirement prevents the need for an infinite buffer when a
1951   message is being received by an HTTP/1.1 (or later) proxy and forwarded to
1952   an HTTP/1.0 recipient.
1953</t>
1954</section>
1955
1956<section title="Decoding chunked" anchor="decoding.chunked">
1957<t>
1958   A process for decoding the "chunked" transfer-coding
1959   can be represented in pseudo-code as:
1960</t>
1961<figure><artwork type="code">
1962  length := 0
1963  read chunk-size, chunk-ext (if any) and CRLF
1964  while (chunk-size &gt; 0) {
1965     read chunk-data and CRLF
1966     append chunk-data to decoded-body
1967     length := length + chunk-size
1968     read chunk-size and CRLF
1969  }
1970  read header-field
1971  while (header-field not empty) {
1972     append header-field to existing header fields
1973     read header-field
1974  }
1975  Content-Length := length
1976  Remove "chunked" from Transfer-Encoding
1977  Remove Trailer from existing header fields
1978</artwork></figure>
1979<t>
1980   All HTTP/1.1 applications &MUST; be able to receive and decode the
1981   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
1982   they do not understand.
1983</t>
1984</section>
1985</section>
1986
1987<section title="Compression Codings" anchor="compression.codings">
1988<t>
1989   The codings defined below can be used to compress the payload of a
1990   message.
1991</t>
1992
1993<section title="Compress Coding" anchor="compress.coding">
1994<iref item="compress (Coding Format)"/>
1995<iref item="Coding Format" subitem="compress"/>
1996<t>
1997   The "compress" format is produced by the common UNIX file compression
1998   program "compress". This format is an adaptive Lempel-Ziv-Welch
1999   coding (LZW). Recipients &SHOULD; consider "x-compress" to be
2000   equivalent to "compress".
2001</t>
2002</section>
2003
2004<section title="Deflate Coding" anchor="deflate.coding">
2005<iref item="deflate (Coding Format)"/>
2006<iref item="Coding Format" subitem="deflate"/>
2007<t>
2008   The "deflate" format is defined as the "deflate" compression mechanism
2009   (described in <xref target="RFC1951"/>) used inside the "zlib"
2010   data format (<xref target="RFC1950"/>).
2011</t>
2012<x:note>
2013  <t>
2014    &Note; Some incorrect implementations send the "deflate"
2015    compressed data without the zlib wrapper.
2016   </t>
2017</x:note>
2018</section>
2019
2020<section title="Gzip Coding" anchor="gzip.coding">
2021<iref item="gzip (Coding Format)"/>
2022<iref item="Coding Format" subitem="gzip"/>
2023<t>
2024   The "gzip" format is produced by the file compression program
2025   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2026   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2027   Recipients &SHOULD; consider "x-gzip" to be equivalent to "gzip".
2028</t>
2029</section>
2030
2031</section>
2032
2033<section title="TE" anchor="header.te">
2034  <iref primary="true" item="TE header field" x:for-anchor=""/>
2035  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
2036  <x:anchor-alias value="TE"/>
2037  <x:anchor-alias value="t-codings"/>
2038  <x:anchor-alias value="t-ranking"/>
2039  <x:anchor-alias value="rank"/>
2040<t>
2041   The "TE" header field in a request indicates what transfer-codings,
2042   besides "chunked", the client is willing to accept in response, and
2043   whether or not the client is willing to accept trailer fields in a
2044   chunked transfer-coding.
2045</t>
2046<t>
2047   The TE field-value consists of a comma-separated list of transfer-coding
2048   names, each allowing for optional parameters (as described in
2049   <xref target="transfer.codings"/>), and/or the keyword "trailers".
2050   Clients &MUST-NOT; send the chunked transfer-coding name in TE;
2051   chunked is always acceptable for HTTP/1.1 recipients.
2052</t>
2053<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"/>
2054  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2055  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-coding</x:ref> [ <x:ref>t-ranking</x:ref> ] )
2056  <x:ref>t-ranking</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>rank</x:ref>
2057  <x:ref>rank</x:ref>      = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2058             / ( "1" [ "." 0*3("0") ] )
2059</artwork></figure>
2060<t>
2061   Three examples of TE use are below.
2062</t>
2063<figure><artwork type="example">
2064  TE: deflate
2065  TE:
2066  TE: trailers, deflate;q=0.5
2067</artwork></figure>
2068<t>
2069   The presence of the keyword "trailers" indicates that the client is
2070   willing to accept trailer fields in a chunked transfer-coding,
2071   as defined in <xref target="chunked.encoding"/>, on behalf of itself and
2072   any downstream clients. For chained requests, this implies that either:
2073   (a) all downstream clients are willing to accept trailer fields in the
2074   forwarded response; or,
2075   (b) the client will attempt to buffer the response on behalf of downstream
2076   recipients.
2077   Note that HTTP/1.1 does not define any means to limit the size of a
2078   chunked response such that a client can be assured of buffering the
2079   entire response.
2080</t>
2081<t>
2082   When multiple transfer-codings are acceptable, the client &MAY; rank the
2083   codings by preference using a "q" parameter (similar to the qvalues
2084   used in content negotiation fields, &qvalue;). The rank value is a real
2085   number in the range 0 through 1, where 0.001 is the least preferred and
2086   1 is the most preferred; a value of 0 means "not acceptable".
2087</t>
2088<t>
2089   If the TE field-value is empty or if no TE field is present, the only
2090   acceptable transfer-coding is "chunked". A message with no transfer-coding
2091   is always acceptable.
2092</t>
2093<t>
2094   Since the TE header field only applies to the immediate connection,
2095   a sender of TE &MUST; also send a "TE" connection option within the
2096   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
2097   in order to prevent the TE field from being forwarded by intermediaries
2098   that do not support its semantics.
2099</t>
2100</section>
2101</section>
2102
2103<section title="Message Routing" anchor="message.routing">
2104<t>
2105   HTTP request message routing is determined by each client based on the
2106   target resource, the client's proxy configuration, and
2107   establishment or reuse of an inbound connection.  The corresponding
2108   response routing follows the same connection chain back to the client.
2109</t>
2110
2111<section title="Identifying a Target Resource" anchor="target-resource">
2112  <iref primary="true" item="target resource"/>
2113  <iref primary="true" item="target URI"/>
2114  <x:anchor-alias value="target resource"/>
2115  <x:anchor-alias value="target URI"/>
2116<t>
2117   HTTP is used in a wide variety of applications, ranging from
2118   general-purpose computers to home appliances.  In some cases,
2119   communication options are hard-coded in a client's configuration.
2120   However, most HTTP clients rely on the same resource identification
2121   mechanism and configuration techniques as general-purpose Web browsers.
2122</t>
2123<t>
2124   HTTP communication is initiated by a user agent for some purpose.
2125   The purpose is a combination of request semantics, which are defined in
2126   <xref target="Part2"/>, and a target resource upon which to apply those
2127   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2128   an identifier for the "<x:dfn>target resource</x:dfn>", which a user agent
2129   would resolve to its absolute form in order to obtain the
2130   "<x:dfn>target URI</x:dfn>".  The target URI
2131   excludes the reference's fragment identifier component, if any,
2132   since fragment identifiers are reserved for client-side processing
2133   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2134</t>
2135<t>
2136   HTTP intermediaries obtain the request semantics and target URI
2137   from the request-line of an incoming request message.
2138</t>
2139</section>
2140
2141<section title="Connecting Inbound" anchor="connecting.inbound">
2142<t>
2143   Once the target URI is determined, a client needs to decide whether
2144   a network request is necessary to accomplish the desired semantics and,
2145   if so, where that request is to be directed.
2146</t>
2147<t>
2148   If the client has a response cache and the request semantics can be
2149   satisfied by a cache (<xref target="Part6"/>), then the request is
2150   usually directed to the cache first.
2151</t>
2152<t>
2153   If the request is not satisfied by a cache, then a typical client will
2154   check its configuration to determine whether a proxy is to be used to
2155   satisfy the request.  Proxy configuration is implementation-dependent,
2156   but is often based on URI prefix matching, selective authority matching,
2157   or both, and the proxy itself is usually identified by an "http" or
2158   "https" URI.  If a proxy is applicable, the client connects inbound by
2159   establishing (or reusing) a connection to that proxy.
2160</t>
2161<t>
2162   If no proxy is applicable, a typical client will invoke a handler routine,
2163   usually specific to the target URI's scheme, to connect directly
2164   to an authority for the target resource.  How that is accomplished is
2165   dependent on the target URI scheme and defined by its associated
2166   specification, similar to how this specification defines origin server
2167   access for resolution of the "http" (<xref target="http.uri"/>) and
2168   "https" (<xref target="https.uri"/>) schemes.
2169</t>
2170<t>
2171   HTTP requirements regarding connection management are defined in
2172   <xref target="connection.management"/>.
2173</t>
2174</section>
2175
2176<section title="Request Target" anchor="request-target">
2177<t>
2178   Once an inbound connection is obtained,
2179   the client sends an HTTP request message (<xref target="http.message"/>)
2180   with a request-target derived from the target URI.
2181   There are four distinct formats for the request-target, depending on both
2182   the method being requested and whether the request is to a proxy.
2183</t>   
2184<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"/>
2185  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2186                 / <x:ref>absolute-form</x:ref>
2187                 / <x:ref>authority-form</x:ref>
2188                 / <x:ref>asterisk-form</x:ref>
2189
2190  <x:ref>origin-form</x:ref>    = <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]
2191  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2192  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2193  <x:ref>asterisk-form</x:ref>  = "*"
2194</artwork></figure>
2195<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2196   The most common form of request-target is the origin-form.
2197   When making a request directly to an origin server, other than a CONNECT
2198   or server-wide OPTIONS request (as detailed below),
2199   a client &MUST; send only the absolute path and query components of
2200   the target URI as the request-target.
2201   If the target URI's path component is empty, then the client &MUST; send
2202   "/" as the path within the origin-form of request-target.
2203   A <x:ref>Host</x:ref> header field is also sent, as defined in
2204   <xref target="header.host"/>, containing the target URI's
2205   authority component (excluding any userinfo).
2206</t>
2207<t>
2208   For example, a client wishing to retrieve a representation of the resource
2209   identified as
2210</t>
2211<figure><artwork x:indent-with="  " type="example">
2212http://www.example.org/where?q=now
2213</artwork></figure>
2214<t>
2215   directly from the origin server would open (or reuse) a TCP connection
2216   to port 80 of the host "www.example.org" and send the lines:
2217</t>
2218<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2219GET /where?q=now HTTP/1.1
2220Host: www.example.org
2221</artwork></figure>
2222<t>
2223   followed by the remainder of the request message.
2224</t>
2225<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2226   When making a request to a proxy, other than a CONNECT or server-wide
2227   OPTIONS request (as detailed below), a client &MUST; send the target URI
2228   in absolute-form as the request-target.
2229   The proxy is requested to either service that request from a valid cache,
2230   if possible, or make the same request on the client's behalf to either
2231   the next inbound proxy server or directly to the origin server indicated
2232   by the request-target.  Requirements on such "forwarding" of messages are
2233   defined in <xref target="message.forwarding"/>.
2234</t>
2235<t>
2236   An example absolute-form of request-line would be:
2237</t>
2238<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2239GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
2240</artwork></figure>
2241<t>
2242   To allow for transition to the absolute-form for all requests in some
2243   future version of HTTP, HTTP/1.1 servers &MUST; accept the absolute-form
2244   in requests, even though HTTP/1.1 clients will only send them in requests
2245   to proxies.
2246</t>
2247<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2248   The authority-form of request-target is only used for CONNECT requests
2249   (&CONNECT;).  When making a CONNECT request to establish a tunnel through
2250   one or more proxies, a client &MUST; send only the target URI's
2251   authority component (excluding any userinfo) as the request-target.
2252   For example,
2253</t>
2254<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2255CONNECT www.example.com:80 HTTP/1.1
2256</artwork></figure>
2257<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2258   The asterisk-form of request-target is only used for a server-wide
2259   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2260   for the server as a whole, as opposed to a specific named resource of
2261   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2262   For example,
2263</t>
2264<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2265OPTIONS * HTTP/1.1
2266</artwork></figure>
2267<t>
2268   If a proxy receives an OPTIONS request with an absolute-form of
2269   request-target in which the URI has an empty path and no query component,
2270   then the last proxy on the request chain &MUST; send a request-target
2271   of "*" when it forwards the request to the indicated origin server.
2272</t>
2273<figure><preamble>  
2274   For example, the request
2275</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2276OPTIONS http://www.example.org:8001 HTTP/1.1
2277</artwork></figure>
2278<figure><preamble>  
2279  would be forwarded by the final proxy as
2280</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2281OPTIONS * HTTP/1.1
2282Host: www.example.org:8001
2283</artwork>
2284<postamble>
2285   after connecting to port 8001 of host "www.example.org".
2286</postamble>
2287</figure>
2288</section>
2289
2290<section title="Host" anchor="header.host">
2291  <iref primary="true" item="Host header field" x:for-anchor=""/>
2292  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
2293  <x:anchor-alias value="Host"/>
2294<t>
2295   The "Host" header field in a request provides the host and port
2296   information from the target URI, enabling the origin
2297   server to distinguish among resources while servicing requests
2298   for multiple host names on a single IP address.  Since the Host
2299   field-value is critical information for handling a request, it
2300   &SHOULD; be sent as the first header field following the request-line.
2301</t>
2302<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2303  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2304</artwork></figure>
2305<t>
2306   A client &MUST; send a Host header field in all HTTP/1.1 request
2307   messages.  If the target URI includes an authority component, then
2308   the Host field-value &MUST; be identical to that authority component
2309   after excluding any userinfo (<xref target="http.uri"/>).
2310   If the authority component is missing or undefined for the target URI,
2311   then the Host header field &MUST; be sent with an empty field-value.
2312</t>
2313<t>
2314   For example, a GET request to the origin server for
2315   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
2316</t>
2317<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2318GET /pub/WWW/ HTTP/1.1
2319Host: www.example.org
2320</artwork></figure>
2321<t>
2322   The Host header field &MUST; be sent in an HTTP/1.1 request even
2323   if the request-target is in the absolute-form, since this
2324   allows the Host information to be forwarded through ancient HTTP/1.0
2325   proxies that might not have implemented Host.
2326</t>
2327<t>
2328   When an HTTP/1.1 proxy receives a request with an absolute-form of
2329   request-target, the proxy &MUST; ignore the received
2330   Host header field (if any) and instead replace it with the host
2331   information of the request-target.  If the proxy forwards the request,
2332   it &MUST; generate a new Host field-value based on the received
2333   request-target rather than forward the received Host field-value.
2334</t>
2335<t>
2336   Since the Host header field acts as an application-level routing
2337   mechanism, it is a frequent target for malware seeking to poison
2338   a shared cache or redirect a request to an unintended server.
2339   An interception proxy is particularly vulnerable if it relies on
2340   the Host field-value for redirecting requests to internal
2341   servers, or for use as a cache key in a shared cache, without
2342   first verifying that the intercepted connection is targeting a
2343   valid IP address for that host.
2344</t>
2345<t>
2346   A server &MUST; respond with a <x:ref>400 (Bad Request)</x:ref> status code
2347   to any HTTP/1.1 request message that lacks a Host header field and
2348   to any request message that contains more than one Host header field
2349   or a Host header field with an invalid field-value.
2350</t>
2351</section>
2352
2353<section title="Effective Request URI" anchor="effective.request.uri">
2354  <iref primary="true" item="effective request URI"/>
2355<t>
2356   A server that receives an HTTP request message &MUST; reconstruct
2357   the user agent's original target URI, based on the pieces of information
2358   learned from the request-target, <x:ref>Host</x:ref> header field, and
2359   connection context, in order to identify the intended target resource and
2360   properly service the request. The URI derived from this reconstruction
2361   process is referred to as the "<x:dfn>effective request URI</x:dfn>".
2362</t>
2363<t>
2364   For a user agent, the effective request URI is the target URI.
2365</t>
2366<t>
2367   If the request-target is in absolute-form, then the effective request URI
2368   is the same as the request-target.  Otherwise, the effective request URI
2369   is constructed as follows.
2370</t>
2371<t>
2372   If the request is received over an SSL/TLS-secured TCP connection,
2373   then the effective request URI's scheme is "https"; otherwise, the
2374   scheme is "http".
2375</t>
2376<t>
2377   If the request-target is in authority-form, then the effective
2378   request URI's authority component is the same as the request-target.
2379   Otherwise, if a <x:ref>Host</x:ref> header field is supplied with a
2380   non-empty field-value, then the authority component is the same as the
2381   Host field-value. Otherwise, the authority component is the concatenation of
2382   the default host name configured for the server, a colon (":"), and the
2383   connection's incoming TCP port number in decimal form.
2384</t>
2385<t>
2386   If the request-target is in authority-form or asterisk-form, then the
2387   effective request URI's combined path and query component is empty.
2388   Otherwise, the combined path and query component is the same as the
2389   request-target.
2390</t>
2391<t>
2392   The components of the effective request URI, once determined as above,
2393   can be combined into absolute-URI form by concatenating the scheme,
2394   "://", authority, and combined path and query component.
2395</t>
2396<figure>
2397<preamble>
2398   Example 1: the following message received over an insecure TCP connection
2399</preamble>
2400<artwork type="example" x:indent-with="  ">
2401GET /pub/WWW/TheProject.html HTTP/1.1
2402Host: www.example.org:8080
2403</artwork>
2404</figure>
2405<figure>
2406<preamble>
2407  has an effective request URI of
2408</preamble>
2409<artwork type="example" x:indent-with="  ">
2410http://www.example.org:8080/pub/WWW/TheProject.html
2411</artwork>
2412</figure>
2413<figure>
2414<preamble>
2415   Example 2: the following message received over an SSL/TLS-secured TCP
2416   connection
2417</preamble>
2418<artwork type="example" x:indent-with="  ">
2419OPTIONS * HTTP/1.1
2420Host: www.example.org
2421</artwork>
2422</figure>
2423<figure>
2424<preamble>
2425  has an effective request URI of
2426</preamble>
2427<artwork type="example" x:indent-with="  ">
2428https://www.example.org
2429</artwork>
2430</figure>
2431<t>
2432   An origin server that does not allow resources to differ by requested
2433   host &MAY; ignore the <x:ref>Host</x:ref> field-value and instead replace it
2434   with a configured server name when constructing the effective request URI.
2435</t>
2436<t>
2437   Recipients of an HTTP/1.0 request that lacks a <x:ref>Host</x:ref> header
2438   field &MAY; attempt to use heuristics (e.g., examination of the URI path for
2439   something unique to a particular host) in order to guess the
2440   effective request URI's authority component.
2441</t>
2442</section>
2443
2444<section title="Message Forwarding" anchor="message.forwarding">
2445<t>
2446   As described in <xref target="intermediaries"/>, intermediaries can serve
2447   a variety of roles in the processing of HTTP requests and responses.
2448   Some intermediaries are used to improve performance or availability.
2449   Others are used for access control or to filter content.
2450   Since an HTTP stream has characteristics similar to a pipe-and-filter
2451   architecture, there are no inherent limits to the extent an intermediary
2452   can enhance (or interfere) with either direction of the stream.
2453</t>
2454<t>
2455   Intermediaries that forward a message &MUST; implement the
2456   <x:ref>Connection</x:ref> header field, as specified in
2457   <xref target="header.connection"/>, to exclude fields that are only
2458   intended for the incoming connection.
2459</t>
2460<t>
2461   In order to avoid request loops, a proxy that forwards requests to other
2462   proxies &MUST; be able to recognize and exclude all of its own server
2463   names, including any aliases, local variations, or literal IP addresses.
2464</t>
2465</section>
2466
2467<section title="Via" anchor="header.via">
2468  <iref primary="true" item="Via header field" x:for-anchor=""/>
2469  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
2470  <x:anchor-alias value="pseudonym"/>
2471  <x:anchor-alias value="received-by"/>
2472  <x:anchor-alias value="received-protocol"/>
2473  <x:anchor-alias value="Via"/>
2474<t>
2475   The "Via" header field &MUST; be sent by a proxy or gateway
2476   in forwarded messages to
2477   indicate the intermediate protocols and recipients between the user
2478   agent and the server on requests, and between the origin server and
2479   the client on responses. It is analogous to the "Received" field
2480   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>).
2481   Via is used in HTTP for tracking message forwards,
2482   avoiding request loops, and identifying the protocol capabilities of
2483   all senders along the request/response chain.
2484</t>
2485<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"/>
2486  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2487                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2488  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2489  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2490  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2491</artwork></figure>
2492<t>
2493   The received-protocol indicates the protocol version of the message
2494   received by the server or client along each segment of the
2495   request/response chain. The received-protocol version is appended to
2496   the Via field value when the message is forwarded so that information
2497   about the protocol capabilities of upstream applications remains
2498   visible to all recipients.
2499</t>
2500<t>
2501   The protocol-name is excluded if and only if it would be "HTTP". The
2502   received-by field is normally the host and optional port number of a
2503   recipient server or client that subsequently forwarded the message.
2504   However, if the real host is considered to be sensitive information,
2505   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2506   be assumed to be the default port of the received-protocol.
2507</t>
2508<t>
2509   Multiple Via field values represent each proxy or gateway that has
2510   forwarded the message. Each recipient &MUST; append its information
2511   such that the end result is ordered according to the sequence of
2512   forwarding applications.
2513</t>
2514<t>
2515   Comments &MAY; be used in the Via header field to identify the software
2516   of each recipient, analogous to the <x:ref>User-Agent</x:ref> and
2517   <x:ref>Server</x:ref> header fields. However, all comments in the Via field
2518   are optional and &MAY; be removed by any recipient prior to forwarding the
2519   message.
2520</t>
2521<t>
2522   For example, a request message could be sent from an HTTP/1.0 user
2523   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2524   forward the request to a public proxy at p.example.net, which completes
2525   the request by forwarding it to the origin server at www.example.com.
2526   The request received by www.example.com would then have the following
2527   Via header field:
2528</t>
2529<figure><artwork type="example">
2530  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2531</artwork></figure>
2532<t>
2533   A proxy or gateway used as a portal through a network firewall
2534   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2535   region unless it is explicitly enabled to do so. If not enabled, the
2536   received-by host of any host behind the firewall &SHOULD; be replaced
2537   by an appropriate pseudonym for that host.
2538</t>
2539<t>
2540   A proxy or gateway &MAY; combine an ordered subsequence of Via header
2541   field entries into a single such entry if the entries have identical
2542   received-protocol values. For example,
2543</t>
2544<figure><artwork type="example">
2545  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2546</artwork></figure>
2547<t>
2548  could be collapsed to
2549</t>
2550<figure><artwork type="example">
2551  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2552</artwork></figure>
2553<t>
2554   Senders &SHOULD-NOT; combine multiple entries unless they are all
2555   under the same organizational control and the hosts have already been
2556   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
2557   have different received-protocol values.
2558</t>
2559</section>
2560
2561<section title="Message Transforming" anchor="message.transforming">
2562<t>
2563   If a proxy receives a request-target with a host name that is not a
2564   fully qualified domain name, it &MAY; add its own domain to the host name
2565   it received when forwarding the request.  A proxy &MUST-NOT; change the
2566   host name if it is a fully qualified domain name.
2567</t>
2568<t>
2569   A non-transforming proxy &MUST-NOT; modify the "path-absolute" and "query"
2570   parts of the received request-target when forwarding it to the next inbound
2571   server, except as noted above to replace an empty path with "/" or "*".
2572</t>
2573<t>
2574   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2575   though it &MAY; change the message body through application or removal
2576   of a transfer-coding (<xref target="transfer.codings"/>).
2577</t>
2578<t>
2579   A non-transforming proxy &SHOULD-NOT; modify header fields that provide
2580   information about the end points of the communication chain, the resource
2581   state, or the selected representation.
2582</t>
2583<t>
2584   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2585   request or response, and it &MUST-NOT; add any of these fields if not
2586   already present:
2587  <list style="symbols">
2588    <t><x:ref>Allow</x:ref> (&header-allow;)</t>
2589    <t><x:ref>Content-Location</x:ref> (&header-content-location;)</t>
2590    <t>Content-MD5 (<xref target="RFC2616" x:fmt="of" x:sec="14.15"/>)</t>
2591    <t><x:ref>ETag</x:ref> (&header-etag;)</t>
2592    <t><x:ref>Last-Modified</x:ref> (&header-last-modified;)</t>
2593    <t><x:ref>Server</x:ref> (&header-server;)</t>
2594  </list>
2595</t>
2596<t>
2597   A non-transforming proxy &MUST-NOT; modify an <x:ref>Expires</x:ref>
2598   header field (&header-expires;) if already present in a response, but
2599   it &MAY; add an <x:ref>Expires</x:ref> header field with a field-value
2600   identical to that of the <x:ref>Date</x:ref> header field.
2601</t>
2602<t>
2603   A proxy &MUST-NOT; modify or add any of the following fields in a
2604   message that contains the no-transform cache-control directive:
2605  <list style="symbols">
2606    <t><x:ref>Content-Encoding</x:ref> (&header-content-encoding;)</t>
2607    <t><x:ref>Content-Range</x:ref> (&header-content-range;)</t>
2608    <t><x:ref>Content-Type</x:ref> (&header-content-type;)</t>
2609  </list>
2610</t>
2611<t>
2612   A transforming proxy &MAY; modify or add these fields to a message
2613   that does not include no-transform, but if it does so, it &MUST; add a
2614   Warning 214 (Transformation applied) if one does not already appear
2615   in the message (see &header-warning;).
2616</t>
2617<x:note>
2618  <t>
2619    <x:h>Warning:</x:h> Unnecessary modification of header fields might
2620    cause authentication failures if stronger authentication
2621    mechanisms are introduced in later versions of HTTP. Such
2622    authentication mechanisms &MAY; rely on the values of header fields
2623    not listed here.
2624  </t>
2625</x:note>
2626</section>
2627
2628<section title="Associating a Response to a Request" anchor="associating.response.to.request">
2629<t>
2630   HTTP does not include a request identifier for associating a given
2631   request message with its corresponding one or more response messages.
2632   Hence, it relies on the order of response arrival to correspond exactly
2633   to the order in which requests are made on the same connection.
2634   More than one response message per request only occurs when one or more
2635   informational responses (<x:ref>1xx</x:ref>, see &status-1xx;) precede a final response
2636   to the same request.
2637</t>
2638<t>
2639   A client that uses persistent connections and sends more than one request
2640   per connection &MUST; maintain a list of outstanding requests in the
2641   order sent on that connection and &MUST; associate each received response
2642   message to the highest ordered request that has not yet received a final
2643   (non-<x:ref>1xx</x:ref>) response.
2644</t>
2645</section>
2646</section>
2647
2648<section title="Connection Management" anchor="connection.management">
2649<t>
2650   HTTP messaging is independent of the underlying transport or
2651   session-layer connection protocol(s).  HTTP only presumes a reliable
2652   transport with in-order delivery of requests and the corresponding
2653   in-order delivery of responses.  The mapping of HTTP request and
2654   response structures onto the data units of an underlying transport
2655   protocol is outside the scope of this specification.
2656</t>
2657<t>
2658   As described in <xref target="connecting.inbound"/>, the specific
2659   connection protocols to be used for an HTTP interaction are determined by
2660   client configuration and the <x:ref>target URI</x:ref>.
2661   For example, the "http" URI scheme
2662   (<xref target="http.uri"/>) indicates a default connection of TCP
2663   over IP, with a default TCP port of 80, but the client might be
2664   configured to use a proxy via some other connection, port, or protocol.
2665</t>
2666<t>
2667   HTTP implementations are expected to engage in connection management,
2668   which includes maintaining the state of current connections,
2669   establishing a new connection or reusing an existing connection,
2670   processing messages received on a connection, detecting connection
2671   failures, and closing each connection.
2672   Most clients maintain multiple connections in parallel, including
2673   more than one connection per server endpoint.
2674   Most servers are designed to maintain thousands of concurrent connections,
2675   while controlling request queues to enable fair use and detect
2676   denial of service attacks.
2677</t>
2678
2679<section title="Connection" anchor="header.connection">
2680  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2681  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2682  <x:anchor-alias value="Connection"/>
2683  <x:anchor-alias value="connection-option"/>
2684<t>
2685   The "Connection" header field allows the sender to indicate desired
2686   control options for the current connection.  In order to avoid confusing
2687   downstream recipients, a proxy or gateway &MUST; remove or replace any
2688   received connection options before forwarding the message.
2689</t>
2690<t>
2691   When a header field is used to supply control information for or about
2692   the current connection, the sender &SHOULD; list the corresponding
2693   field-name within the "Connection" header field.
2694   A proxy or gateway &MUST; parse a received Connection
2695   header field before a message is forwarded and, for each
2696   connection-option in this field, remove any header field(s) from
2697   the message with the same name as the connection-option, and then
2698   remove the Connection header field itself (or replace it with the
2699   intermediary's own connection options for the forwarded message).
2700</t>
2701<t>
2702   Hence, the Connection header field provides a declarative way of
2703   distinguishing header fields that are only intended for the
2704   immediate recipient ("hop-by-hop") from those fields that are
2705   intended for all recipients on the chain ("end-to-end"), enabling the
2706   message to be self-descriptive and allowing future connection-specific
2707   extensions to be deployed without fear that they will be blindly
2708   forwarded by older intermediaries.
2709</t>
2710<t>
2711   The Connection header field's value has the following grammar:
2712</t>
2713<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-option"/>
2714  <x:ref>Connection</x:ref>        = 1#<x:ref>connection-option</x:ref>
2715  <x:ref>connection-option</x:ref> = <x:ref>token</x:ref>
2716</artwork></figure>
2717<t>
2718   Connection options are compared case-insensitively.
2719</t>
2720<t>
2721   A sender &MUST-NOT; include field-names in the Connection header
2722   field-value for fields that are defined as expressing constraints
2723   for all recipients in the request or response chain, such as the
2724   Cache-Control header field (&header-cache-control;).
2725</t>
2726<t>
2727   The connection options do not have to correspond to a header field
2728   present in the message, since a connection-specific header field
2729   might not be needed if there are no parameters associated with that
2730   connection option.  Recipients that trigger certain connection
2731   behavior based on the presence of connection options &MUST; do so
2732   based on the presence of the connection-option rather than only the
2733   presence of the optional header field.  In other words, if the
2734   connection option is received as a header field but not indicated
2735   within the Connection field-value, then the recipient &MUST; ignore
2736   the connection-specific header field because it has likely been
2737   forwarded by an intermediary that is only partially conformant.
2738</t>
2739<t>
2740   When defining new connection options, specifications ought to
2741   carefully consider existing deployed header fields and ensure
2742   that the new connection option does not share the same name as
2743   an unrelated header field that might already be deployed.
2744   Defining a new connection option essentially reserves that potential
2745   field-name for carrying additional information related to the
2746   connection option, since it would be unwise for senders to use
2747   that field-name for anything else.
2748</t>
2749<t>
2750   HTTP/1.1 defines the "close" connection option for the sender to
2751   signal that the connection will be closed after completion of the
2752   response. For example,
2753</t>
2754<figure><artwork type="example">
2755  Connection: close
2756</artwork></figure>
2757<t>
2758   in either the request or the response header fields indicates that
2759   the connection &SHOULD; be closed after the current request/response
2760   is complete (<xref target="persistent.connections"/>).
2761</t>
2762<t>
2763   An HTTP/1.1 client that does not support persistent connections &MUST;
2764   include the "close" connection option in every request message.
2765</t>
2766<t>
2767   An HTTP/1.1 server that does not support persistent connections &MUST;
2768   include the "close" connection option in every response message that
2769   does not have a <x:ref>1xx (Informational)</x:ref> status code.
2770</t>
2771</section>
2772
2773<section title="Persistent Connections" anchor="persistent.connections">
2774  <x:anchor-alias value="persistent connections"/>
2775<t>
2776   HTTP was originally designed to use a separate connection for each
2777   request/response pair. As the Web evolved and embedded requests became
2778   common for inline images, the connection establishment overhead was
2779   a significant drain on performance and a concern for Internet congestion.
2780   Message framing (via <x:ref>Content-Length</x:ref>) and optional
2781   long-lived connections (via Keep-Alive) were added to HTTP/1.0 in order
2782   to improve performance for some requests. However, these extensions were
2783   insufficient for dynamically generated responses and difficult to use
2784   with intermediaries.
2785</t>
2786<t>
2787   HTTP/1.1 defaults to the use of "<x:ref>persistent connections</x:ref>",
2788   which allow multiple requests and responses to be carried over a single
2789   connection.
2790   Persistent connections have a number of advantages:
2791  <list style="symbols">
2792      <t>
2793        By opening and closing fewer connections, CPU time is saved
2794        in routers and hosts (clients, servers, proxies, gateways,
2795        tunnels, or caches), and memory used for protocol control
2796        blocks can be saved in hosts.
2797      </t>
2798      <t>
2799        Most requests and responses can be pipelined on a connection.
2800        Pipelining allows a client to make multiple requests without
2801        waiting for each response, allowing a single connection to
2802        be used much more efficiently and with less overall latency.
2803      </t>
2804      <t>
2805        Network congestion is reduced by reducing the number of packets
2806        caused by connection establishment and tear-down, and by allowing
2807        sufficient time for send/receive windows to adjust to the
2808        available network bandwidth.
2809      </t>
2810      <t>
2811        Latency on subsequent requests is reduced since there is no time
2812        spent in the connection opening handshake.
2813      </t>
2814      <t>
2815        HTTP can evolve more gracefully, since most errors can be reported
2816        without the penalty of closing the connection. Clients using
2817        future versions of HTTP might optimistically try a new feature,
2818        but if communicating with an older server, retry with old
2819        semantics after an error is reported.
2820      </t>
2821    </list>
2822</t>
2823<t>
2824   HTTP implementations &SHOULD; implement persistent connections.
2825</t>
2826
2827<section title="Overall Operation" anchor="persistent.overall">
2828<t>
2829   A significant difference between HTTP/1.1 and earlier versions of
2830   HTTP is that persistent connections are the default behavior of any
2831   HTTP connection. That is, unless otherwise indicated, the client
2832   &SHOULD; assume that the server will maintain a persistent connection,
2833   even after error responses from the server.
2834</t>
2835<t>
2836   Persistent connections provide a mechanism by which a client and a
2837   server can signal the close of a TCP connection. This signaling takes
2838   place using the <x:ref>Connection</x:ref> header field
2839   (<xref target="header.connection"/>). Once a close has been signaled, the
2840   client &MUST-NOT; send any more requests on that
2841   connection.
2842</t>
2843
2844<section title="Negotiation" anchor="persistent.negotiation">
2845<t>
2846   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2847   maintain a persistent connection unless a <x:ref>Connection</x:ref> header
2848   field including the connection option "close" was sent in the request. If
2849   the server chooses to close the connection immediately after sending the
2850   response, it &SHOULD; send a Connection header field including the
2851   connection option "close".
2852</t>
2853<t>
2854   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2855   decide to keep it open based on whether the response from a server
2856   contains a <x:ref>Connection</x:ref> header field with the connection option
2857   "close". In case the client does not want to maintain a connection for more
2858   than that request, it &SHOULD; send a Connection header field including the
2859   connection option "close".
2860</t>
2861<t>
2862   If either the client or the server sends the "close" option in the
2863   <x:ref>Connection</x:ref> header field, that request becomes the last one
2864   for the connection.
2865</t>
2866<t>
2867   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2868   maintained for HTTP versions less than 1.1 unless it is explicitly
2869   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2870   compatibility with HTTP/1.0 clients.
2871</t>
2872<t>
2873   Each persistent connection applies to only one transport link.
2874</t>
2875<t>
2876   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2877   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2878   for information and discussion of the problems with the Keep-Alive header field
2879   implemented by many HTTP/1.0 clients).
2880</t>
2881<t>
2882   In order to remain persistent, all messages on the connection &MUST;
2883   have a self-defined message length (i.e., one not defined by closure
2884   of the connection), as described in <xref target="message.body"/>.
2885</t>
2886</section>
2887
2888<section title="Pipelining" anchor="pipelining">
2889<t>
2890   A client that supports persistent connections &MAY; "pipeline" its
2891   requests (i.e., send multiple requests without waiting for each
2892   response). A server &MUST; send its responses to those requests in the
2893   same order that the requests were received.
2894</t>
2895<t>
2896   Clients which assume persistent connections and pipeline immediately
2897   after connection establishment &SHOULD; be prepared to retry their
2898   connection if the first pipelined attempt fails. If a client does
2899   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2900   persistent. Clients &MUST; also be prepared to resend their requests if
2901   the server closes the connection before sending all of the
2902   corresponding responses.
2903</t>
2904<t>
2905   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2906   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2907   premature termination of the transport connection could lead to
2908   indeterminate results. A client wishing to send a non-idempotent
2909   request &SHOULD; wait to send that request until it has received the
2910   response status line for the previous request.
2911</t>
2912</section>
2913</section>
2914
2915<section title="Practical Considerations" anchor="persistent.practical">
2916<t>
2917   Servers will usually have some time-out value beyond which they will
2918   no longer maintain an inactive connection. Proxy servers might make
2919   this a higher value since it is likely that the client will be making
2920   more connections through the same server. The use of persistent
2921   connections places no requirements on the length (or existence) of
2922   this time-out for either the client or the server.
2923</t>
2924<t>
2925   When a client or server wishes to time-out it &SHOULD; issue a graceful
2926   close on the transport connection. Clients and servers &SHOULD; both
2927   constantly watch for the other side of the transport close, and
2928   respond to it as appropriate. If a client or server does not detect
2929   the other side's close promptly it could cause unnecessary resource
2930   drain on the network.
2931</t>
2932<t>
2933   A client, server, or proxy &MAY; close the transport connection at any
2934   time. For example, a client might have started to send a new request
2935   at the same time that the server has decided to close the "idle"
2936   connection. From the server's point of view, the connection is being
2937   closed while it was idle, but from the client's point of view, a
2938   request is in progress.
2939</t>
2940<t>
2941   Clients (including proxies) &SHOULD; limit the number of simultaneous
2942   connections that they maintain to a given server (including proxies).
2943</t>
2944<t>
2945   Previous revisions of HTTP gave a specific number of connections as a
2946   ceiling, but this was found to be impractical for many applications. As a
2947   result, this specification does not mandate a particular maximum number of
2948   connections, but instead encourages clients to be conservative when opening
2949   multiple connections.
2950</t>
2951<t>
2952   In particular, while using multiple connections avoids the "head-of-line
2953   blocking" problem (whereby a request that takes significant server-side
2954   processing and/or has a large payload can block subsequent requests on the
2955   same connection), each connection used consumes server resources (sometimes
2956   significantly), and furthermore using multiple connections can cause
2957   undesirable side effects in congested networks.
2958</t>
2959<t>
2960   Note that servers might reject traffic that they deem abusive, including an
2961   excessive number of connections from a client.
2962</t>
2963</section>
2964
2965<section title="Retrying Requests" anchor="persistent.retrying.requests">
2966<t>
2967   Senders can close the transport connection at any time. Therefore,
2968   clients, servers, and proxies &MUST; be able to recover
2969   from asynchronous close events. Client software &MAY; reopen the
2970   transport connection and retransmit the aborted sequence of requests
2971   without user interaction so long as the request sequence is
2972   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2973   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2974   human operator the choice of retrying the request(s). Confirmation by
2975   user-agent software with semantic understanding of the application
2976   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2977   be repeated if the second sequence of requests fails.
2978</t>
2979</section>
2980</section>
2981
2982<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2983
2984<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2985<t>
2986   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2987   flow control mechanisms to resolve temporary overloads, rather than
2988   terminating connections with the expectation that clients will retry.
2989   The latter technique can exacerbate network congestion.
2990</t>
2991</section>
2992
2993<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2994<t>
2995   An HTTP/1.1 (or later) client sending a message body &SHOULD; monitor
2996   the network connection for an error status code while it is transmitting
2997   the request. If the client sees an error status code, it &SHOULD;
2998   immediately cease transmitting the body. If the body is being sent
2999   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
3000   empty trailer &MAY; be used to prematurely mark the end of the message.
3001   If the body was preceded by a Content-Length header field, the client &MUST;
3002   close the connection.
3003</t>
3004</section>
3005
3006<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
3007<t>
3008   The purpose of the <x:ref>100 (Continue)</x:ref> status code (see &status-100;)
3009   is to allow a client that is sending a request message with a request body
3010   to determine if the origin server is willing to accept the request
3011   (based on the request header fields) before the client sends the request
3012   body. In some cases, it might either be inappropriate or highly
3013   inefficient for the client to send the body if the server will reject
3014   the message without looking at the body.
3015</t>
3016<t>
3017   Requirements for HTTP/1.1 clients:
3018  <list style="symbols">
3019    <t>
3020        If a client will wait for a <x:ref>100 (Continue)</x:ref> response before
3021        sending the request body, it &MUST; send an <x:ref>Expect</x:ref> header
3022        field (&header-expect;) with the "100-continue" expectation.
3023    </t>
3024    <t>
3025        A client &MUST-NOT; send an <x:ref>Expect</x:ref> header field with
3026        the "100-continue" expectation if it does not intend to send a request
3027        body.
3028    </t>
3029  </list>
3030</t>
3031<t>
3032   Because of the presence of older implementations, the protocol allows
3033   ambiguous situations in which a client might send "Expect: 100-continue"
3034   without receiving either a <x:ref>417 (Expectation Failed)</x:ref>
3035   or a <x:ref>100 (Continue)</x:ref> status code. Therefore, when a client sends this
3036   header field to an origin server (possibly via a proxy) from which it
3037   has never seen a <x:ref>100 (Continue)</x:ref> status code, the client &SHOULD-NOT; 
3038   wait for an indefinite period before sending the request body.
3039</t>
3040<t>
3041   Requirements for HTTP/1.1 origin servers:
3042  <list style="symbols">
3043    <t> Upon receiving a request which includes an <x:ref>Expect</x:ref> header
3044        field with the "100-continue" expectation, an origin server &MUST;
3045        either respond with <x:ref>100 (Continue)</x:ref> status code and continue to read
3046        from the input stream, or respond with a final status code. The
3047        origin server &MUST-NOT; wait for the request body before sending
3048        the <x:ref>100 (Continue)</x:ref> response. If it responds with a final status
3049        code, it &MAY; close the transport connection or it &MAY; continue
3050        to read and discard the rest of the request.  It &MUST-NOT;
3051        perform the request method if it returns a final status code.
3052    </t>
3053    <t> An origin server &SHOULD-NOT;  send a <x:ref>100 (Continue)</x:ref> response if
3054        the request message does not include an <x:ref>Expect</x:ref> header
3055        field with the "100-continue" expectation, and &MUST-NOT; send a
3056        <x:ref>100 (Continue)</x:ref> response if such a request comes from an HTTP/1.0
3057        (or earlier) client. There is an exception to this rule: for
3058        compatibility with <xref target="RFC2068"/>, a server &MAY; send a <x:ref>100 (Continue)</x:ref>
3059        status code in response to an HTTP/1.1 PUT or POST request that does
3060        not include an Expect header field with the "100-continue"
3061        expectation. This exception, the purpose of which is
3062        to minimize any client processing delays associated with an
3063        undeclared wait for <x:ref>100 (Continue)</x:ref> status code, applies only to
3064        HTTP/1.1 requests, and not to requests with any other HTTP-version
3065        value.
3066    </t>
3067    <t> An origin server &MAY; omit a <x:ref>100 (Continue)</x:ref> response if it has
3068        already received some or all of the request body for the
3069        corresponding request.
3070    </t>
3071    <t> An origin server that sends a <x:ref>100 (Continue)</x:ref> response &MUST;
3072        ultimately send a final status code, once the request body is
3073        received and processed, unless it terminates the transport
3074        connection prematurely.
3075    </t>
3076    <t> If an origin server receives a request that does not include an
3077        <x:ref>Expect</x:ref> header field with the "100-continue" expectation,
3078        the request includes a request body, and the server responds
3079        with a final status code before reading the entire request body
3080        from the transport connection, then the server &SHOULD-NOT;  close
3081        the transport connection until it has read the entire request,
3082        or until the client closes the connection. Otherwise, the client
3083        might not reliably receive the response message. However, this
3084        requirement ought not be construed as preventing a server from
3085        defending itself against denial-of-service attacks, or from
3086        badly broken client implementations.
3087      </t>
3088    </list>
3089</t>
3090<t>
3091   Requirements for HTTP/1.1 proxies:
3092  <list style="symbols">
3093    <t> If a proxy receives a request that includes an <x:ref>Expect</x:ref>
3094        header field with the "100-continue" expectation, and the proxy
3095        either knows that the next-hop server complies with HTTP/1.1 or
3096        higher, or does not know the HTTP version of the next-hop
3097        server, it &MUST; forward the request, including the Expect header
3098        field.
3099    </t>
3100    <t> If the proxy knows that the version of the next-hop server is
3101        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
3102        respond with a <x:ref>417 (Expectation Failed)</x:ref> status code.
3103    </t>
3104    <t> Proxies &SHOULD; maintain a record of the HTTP version
3105        numbers received from recently-referenced next-hop servers.
3106    </t>
3107    <t> A proxy &MUST-NOT; forward a <x:ref>100 (Continue)</x:ref> response if the
3108        request message was received from an HTTP/1.0 (or earlier)
3109        client and did not include an <x:ref>Expect</x:ref> header field with
3110        the "100-continue" expectation. This requirement overrides the
3111        general rule for forwarding of <x:ref>1xx</x:ref> responses (see &status-1xx;).
3112    </t>
3113  </list>
3114</t>
3115</section>
3116
3117<section title="Closing Connections on Error" anchor="closing.connections.on.error">
3118<t>
3119   If the client is sending data, a server implementation using TCP
3120   &SHOULD; be careful to ensure that the client acknowledges receipt of
3121   the packet(s) containing the response, before the server closes the
3122   input connection. If the client continues sending data to the server
3123   after the close, the server's TCP stack will send a reset packet to
3124   the client, which might erase the client's unacknowledged input buffers
3125   before they can be read and interpreted by the HTTP application.
3126</t>
3127</section>
3128
3129</section>
3130
3131<section title="Upgrade" anchor="header.upgrade">
3132  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3133  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3134  <x:anchor-alias value="Upgrade"/>
3135  <x:anchor-alias value="protocol"/>
3136  <x:anchor-alias value="protocol-name"/>
3137  <x:anchor-alias value="protocol-version"/>
3138<t>
3139   The "Upgrade" header field allows the client to specify what
3140   additional communication protocols it would like to use, if the server
3141   chooses to switch protocols. Servers can use it to indicate what protocols
3142   they are willing to switch to.
3143</t>
3144<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3145  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3146
3147  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3148  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3149  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3150</artwork></figure>
3151<t>
3152   For example,
3153</t>
3154<figure><artwork type="example">
3155  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3156</artwork></figure>
3157<t>
3158   The Upgrade header field is intended to provide a simple mechanism
3159   for transitioning from HTTP/1.1 to some other, incompatible protocol. It
3160   does so by allowing the client to advertise its desire to use another
3161   protocol, such as a later version of HTTP with a higher major version
3162   number, even though the current request has been made using HTTP/1.1.
3163   This eases the difficult transition between incompatible protocols by
3164   allowing the client to initiate a request in the more commonly
3165   supported protocol while indicating to the server that it would like
3166   to use a "better" protocol if available (where "better" is determined
3167   by the server, possibly according to the nature of the request method
3168   or target resource).
3169</t>
3170<t>
3171   The Upgrade header field only applies to switching application-layer
3172   protocols upon the existing transport-layer connection. Upgrade
3173   cannot be used to insist on a protocol change; its acceptance and use
3174   by the server is optional. The capabilities and nature of the
3175   application-layer communication after the protocol change is entirely
3176   dependent upon the new protocol chosen, although the first action
3177   after changing the protocol &MUST; be a response to the initial HTTP
3178   request containing the Upgrade header field.
3179</t>
3180<t>
3181   The Upgrade header field only applies to the immediate connection.
3182   Therefore, the upgrade keyword &MUST; be supplied within a
3183   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
3184   whenever Upgrade is present in an HTTP/1.1 message.
3185</t>
3186<t>
3187   The Upgrade header field cannot be used to indicate a switch to a
3188   protocol on a different connection. For that purpose, it is more
3189   appropriate to use a <x:ref>3xx (Redirection)</x:ref> response (&status-3xx;).
3190</t>
3191<t>
3192   Servers &MUST; include the "Upgrade" header field in <x:ref>101 (Switching
3193   Protocols)</x:ref> responses to indicate which protocol(s) are being switched to,
3194   and &MUST; include it in <x:ref>426 (Upgrade Required)</x:ref> responses to indicate
3195   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3196   response to indicate that they are willing to upgrade to one of the
3197   specified protocols.
3198</t>
3199<t>
3200   This specification only defines the protocol name "HTTP" for use by
3201   the family of Hypertext Transfer Protocols, as defined by the HTTP
3202   version rules of <xref target="http.version"/> and future updates to this
3203   specification. Additional tokens can be registered with IANA using the
3204   registration procedure defined in <xref target="upgrade.token.registry"/>.
3205</t>
3206</section>
3207
3208</section>
3209
3210<section title="IANA Considerations" anchor="IANA.considerations">
3211
3212<section title="Header Field Registration" anchor="header.field.registration">
3213<t>
3214   HTTP header fields are registered within the Message Header Field Registry
3215   <xref target="RFC3864"/> maintained by IANA at
3216   <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/>.
3217</t>
3218<t>
3219   This document defines the following HTTP header fields, so their
3220   associated registry entries shall be updated according to the permanent
3221   registrations below:
3222</t>
3223<?BEGININC p1-messaging.iana-headers ?>
3224<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3225<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3226   <ttcol>Header Field Name</ttcol>
3227   <ttcol>Protocol</ttcol>
3228   <ttcol>Status</ttcol>
3229   <ttcol>Reference</ttcol>
3230
3231   <c>Connection</c>
3232   <c>http</c>
3233   <c>standard</c>
3234   <c>
3235      <xref target="header.connection"/>
3236   </c>
3237   <c>Content-Length</c>
3238   <c>http</c>
3239   <c>standard</c>
3240   <c>
3241      <xref target="header.content-length"/>
3242   </c>
3243   <c>Host</c>
3244   <c>http</c>
3245   <c>standard</c>
3246   <c>
3247      <xref target="header.host"/>
3248   </c>
3249   <c>TE</c>
3250   <c>http</c>
3251   <c>standard</c>
3252   <c>
3253      <xref target="header.te"/>
3254   </c>
3255   <c>Trailer</c>
3256   <c>http</c>
3257   <c>standard</c>
3258   <c>
3259      <xref target="header.trailer"/>
3260   </c>
3261   <c>Transfer-Encoding</c>
3262   <c>http</c>
3263   <c>standard</c>
3264   <c>
3265      <xref target="header.transfer-encoding"/>
3266   </c>
3267   <c>Upgrade</c>
3268   <c>http</c>
3269   <c>standard</c>
3270   <c>
3271      <xref target="header.upgrade"/>
3272   </c>
3273   <c>Via</c>
3274   <c>http</c>
3275   <c>standard</c>
3276   <c>
3277      <xref target="header.via"/>
3278   </c>
3279</texttable>
3280<!--(END)-->
3281<?ENDINC p1-messaging.iana-headers ?>
3282<t>
3283   Furthermore, the header field-name "Close" shall be registered as
3284   "reserved", since using that name as an HTTP header field might
3285   conflict with the "close" connection option of the "<x:ref>Connection</x:ref>"
3286   header field (<xref target="header.connection"/>).
3287</t>
3288<texttable align="left" suppress-title="true">
3289   <ttcol>Header Field Name</ttcol>
3290   <ttcol>Protocol</ttcol>
3291   <ttcol>Status</ttcol>
3292   <ttcol>Reference</ttcol>
3293
3294   <c>Close</c>
3295   <c>http</c>
3296   <c>reserved</c>
3297   <c>
3298      <xref target="header.field.registration"/>
3299   </c>
3300</texttable>
3301<t>
3302   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3303</t>
3304</section>
3305
3306<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3307<t>
3308   IANA maintains the registry of URI Schemes <xref target="RFC4395"/> at
3309   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>.
3310</t>
3311<t>
3312   This document defines the following URI schemes, so their
3313   associated registry entries shall be updated according to the permanent
3314   registrations below:
3315</t>
3316<texttable align="left" suppress-title="true">
3317   <ttcol>URI Scheme</ttcol>
3318   <ttcol>Description</ttcol>
3319   <ttcol>Reference</ttcol>
3320
3321   <c>http</c>
3322   <c>Hypertext Transfer Protocol</c>
3323   <c><xref target="http.uri"/></c>
3324
3325   <c>https</c>
3326   <c>Hypertext Transfer Protocol Secure</c>
3327   <c><xref target="https.uri"/></c>
3328</texttable>
3329</section>
3330
3331<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3332<t>
3333   This document serves as the specification for the Internet media types
3334   "message/http" and "application/http". The following is to be registered with
3335   IANA (see <xref target="RFC4288"/>).
3336</t>
3337<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3338<iref item="Media Type" subitem="message/http" primary="true"/>
3339<iref item="message/http Media Type" primary="true"/>
3340<t>
3341   The message/http type can be used to enclose a single HTTP request or
3342   response message, provided that it obeys the MIME restrictions for all
3343   "message" types regarding line length and encodings.
3344</t>
3345<t>
3346  <list style="hanging" x:indent="12em">
3347    <t hangText="Type name:">
3348      message
3349    </t>
3350    <t hangText="Subtype name:">
3351      http
3352    </t>
3353    <t hangText="Required parameters:">
3354      none
3355    </t>
3356    <t hangText="Optional parameters:">
3357      version, msgtype
3358      <list style="hanging">
3359        <t hangText="version:">
3360          The HTTP-version number of the enclosed message
3361          (e.g., "1.1"). If not present, the version can be
3362          determined from the first line of the body.
3363        </t>
3364        <t hangText="msgtype:">
3365          The message type &mdash; "request" or "response". If not
3366          present, the type can be determined from the first
3367          line of the body.
3368        </t>
3369      </list>
3370    </t>
3371    <t hangText="Encoding considerations:">
3372      only "7bit", "8bit", or "binary" are permitted
3373    </t>
3374    <t hangText="Security considerations:">
3375      none
3376    </t>
3377    <t hangText="Interoperability considerations:">
3378      none
3379    </t>
3380    <t hangText="Published specification:">
3381      This specification (see <xref target="internet.media.type.message.http"/>).
3382    </t>
3383    <t hangText="Applications that use this media type:">
3384    </t>
3385    <t hangText="Additional information:">
3386      <list style="hanging">
3387        <t hangText="Magic number(s):">none</t>
3388        <t hangText="File extension(s):">none</t>
3389        <t hangText="Macintosh file type code(s):">none</t>
3390      </list>
3391    </t>
3392    <t hangText="Person and email address to contact for further information:">
3393      See Authors Section.
3394    </t>
3395    <t hangText="Intended usage:">
3396      COMMON
3397    </t>
3398    <t hangText="Restrictions on usage:">
3399      none
3400    </t>
3401    <t hangText="Author/Change controller:">
3402      IESG
3403    </t>
3404  </list>
3405</t>
3406</section>
3407<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3408<iref item="Media Type" subitem="application/http" primary="true"/>
3409<iref item="application/http Media Type" primary="true"/>
3410<t>
3411   The application/http type can be used to enclose a pipeline of one or more
3412   HTTP request or response messages (not intermixed).
3413</t>
3414<t>
3415  <list style="hanging" x:indent="12em">
3416    <t hangText="Type name:">
3417      application
3418    </t>
3419    <t hangText="Subtype name:">
3420      http
3421    </t>
3422    <t hangText="Required parameters:">
3423      none
3424    </t>
3425    <t hangText="Optional parameters:">
3426      version, msgtype
3427      <list style="hanging">
3428        <t hangText="version:">
3429          The HTTP-version number of the enclosed messages
3430          (e.g., "1.1"). If not present, the version can be
3431          determined from the first line of the body.
3432        </t>
3433        <t hangText="msgtype:">
3434          The message type &mdash; "request" or "response". If not
3435          present, the type can be determined from the first
3436          line of the body.
3437        </t>
3438      </list>
3439    </t>
3440    <t hangText="Encoding considerations:">
3441      HTTP messages enclosed by this type
3442      are in "binary" format; use of an appropriate
3443      Content-Transfer-Encoding is required when
3444      transmitted via E-mail.
3445    </t>
3446    <t hangText="Security considerations:">
3447      none
3448    </t>
3449    <t hangText="Interoperability considerations:">
3450      none
3451    </t>
3452    <t hangText="Published specification:">
3453      This specification (see <xref target="internet.media.type.application.http"/>).
3454    </t>
3455    <t hangText="Applications that use this media type:">
3456    </t>
3457    <t hangText="Additional information:">
3458      <list style="hanging">
3459        <t hangText="Magic number(s):">none</t>
3460        <t hangText="File extension(s):">none</t>
3461        <t hangText="Macintosh file type code(s):">none</t>
3462      </list>
3463    </t>
3464    <t hangText="Person and email address to contact for further information:">
3465      See Authors Section.
3466    </t>
3467    <t hangText="Intended usage:">
3468      COMMON
3469    </t>
3470    <t hangText="Restrictions on usage:">
3471      none
3472    </t>
3473    <t hangText="Author/Change controller:">
3474      IESG
3475    </t>
3476  </list>
3477</t>
3478</section>
3479</section>
3480
3481<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3482<t>
3483   The HTTP Transfer Coding Registry defines the name space for transfer
3484   coding names.
3485</t>
3486<t>
3487   Registrations &MUST; include the following fields:
3488   <list style="symbols">
3489     <t>Name</t>
3490     <t>Description</t>
3491     <t>Pointer to specification text</t>
3492   </list>
3493</t>
3494<t>
3495   Names of transfer codings &MUST-NOT; overlap with names of content codings
3496   (&content-codings;) unless the encoding transformation is identical, as
3497   is the case for the compression codings defined in
3498   <xref target="compression.codings"/>.
3499</t>
3500<t>
3501   Values to be added to this name space require IETF Review (see
3502   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3503   conform to the purpose of transfer coding defined in this section.
3504   Use of program names for the identification of encoding formats
3505   is not desirable and is discouraged for future encodings.
3506</t>
3507<t>
3508   The registry itself is maintained at
3509   <eref target="http://www.iana.org/assignments/http-parameters"/>.
3510</t>
3511</section>
3512
3513<section title="Transfer Coding Registrations" anchor="transfer.coding.registration">
3514<t>
3515   The HTTP Transfer Coding Registry shall be updated with the registrations
3516   below:
3517</t>
3518<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3519   <ttcol>Name</ttcol>
3520   <ttcol>Description</ttcol>
3521   <ttcol>Reference</ttcol>
3522   <c>chunked</c>
3523   <c>Transfer in a series of chunks</c>
3524   <c>
3525      <xref target="chunked.encoding"/>
3526   </c>
3527   <c>compress</c>
3528   <c>UNIX "compress" program method</c>
3529   <c>
3530      <xref target="compress.coding"/>
3531   </c>
3532   <c>deflate</c>
3533   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3534   the "zlib" data format (<xref target="RFC1950"/>)
3535   </c>
3536   <c>
3537      <xref target="deflate.coding"/>
3538   </c>
3539   <c>gzip</c>
3540   <c>Same as GNU zip <xref target="RFC1952"/></c>
3541   <c>
3542      <xref target="gzip.coding"/>
3543   </c>
3544</texttable>
3545</section>
3546
3547<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3548<t>
3549   The HTTP Upgrade Token Registry defines the name space for protocol-name
3550   tokens used to identify protocols in the <x:ref>Upgrade</x:ref> header
3551   field. Each registered protocol name is associated with contact information
3552   and an optional set of specifications that details how the connection
3553   will be processed after it has been upgraded.
3554</t>
3555<t>
3556   Registrations happen on a "First Come First Served" basis (see
3557   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3558   following rules:
3559  <list style="numbers">
3560    <t>A protocol-name token, once registered, stays registered forever.</t>
3561    <t>The registration &MUST; name a responsible party for the
3562       registration.</t>
3563    <t>The registration &MUST; name a point of contact.</t>
3564    <t>The registration &MAY; name a set of specifications associated with
3565       that token. Such specifications need not be publicly available.</t>
3566    <t>The registration &SHOULD; name a set of expected "protocol-version"
3567       tokens associated with that token at the time of registration.</t>
3568    <t>The responsible party &MAY; change the registration at any time.
3569       The IANA will keep a record of all such changes, and make them
3570       available upon request.</t>
3571    <t>The IESG &MAY; reassign responsibility for a protocol token.
3572       This will normally only be used in the case when a
3573       responsible party cannot be contacted.</t>
3574  </list>
3575</t>
3576<t>
3577   This registration procedure for HTTP Upgrade Tokens replaces that
3578   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3579</t>
3580</section>
3581
3582<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3583<t>
3584   The HTTP Upgrade Token Registry shall be updated with the registration
3585   below:
3586</t>
3587<texttable align="left" suppress-title="true">
3588   <ttcol>Value</ttcol>
3589   <ttcol>Description</ttcol>
3590   <ttcol>Expected Version Tokens</ttcol>
3591   <ttcol>Reference</ttcol>
3592
3593   <c>HTTP</c>
3594   <c>Hypertext Transfer Protocol</c>
3595   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3596   <c><xref target="http.version"/></c>
3597</texttable>
3598<t>
3599   The responsible party is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3600</t>
3601</section>
3602
3603</section>
3604
3605<section title="Security Considerations" anchor="security.considerations">
3606<t>
3607   This section is meant to inform application developers, information
3608   providers, and users of the security limitations in HTTP/1.1 as
3609   described by this document. The discussion does not include
3610   definitive solutions to the problems revealed, though it does make
3611   some suggestions for reducing security risks.
3612</t>
3613
3614<section title="Personal Information" anchor="personal.information">
3615<t>
3616   HTTP clients are often privy to large amounts of personal information,
3617   including both information provided by the user to interact with resources
3618   (e.g., the user's name, location, mail address, passwords, encryption
3619   keys, etc.) and information about the user's browsing activity over
3620   time (e.g., history, bookmarks, etc.). HTTP implementations need to
3621   prevent unintentional leakage of this information.
3622</t>
3623</section>
3624
3625<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3626<t>
3627   A server is in the position to save personal data about a user's
3628   requests which might identify their reading patterns or subjects of
3629   interest.  In particular, log information gathered at an intermediary
3630   often contains a history of user agent interaction, across a multitude
3631   of sites, that can be traced to individual users.
3632</t>
3633<t>
3634   HTTP log information is confidential in nature; its handling is often
3635   constrained by laws and regulations.  Log information needs to be securely
3636   stored and appropriate guidelines followed for its analysis.
3637   Anonymization of personal information within individual entries helps,
3638   but is generally not sufficient to prevent real log traces from being
3639   re-identified based on correlation with other access characteristics.
3640   As such, access traces that are keyed to a specific client should not
3641   be published even if the key is pseudonymous.
3642</t>
3643<t>
3644   To minimize the risk of theft or accidental publication, log information
3645   should be purged of personally identifiable information, including
3646   user identifiers, IP addresses, and user-provided query parameters,
3647   as soon as that information is no longer necessary to support operational
3648   needs for security, auditing, or fraud control.
3649</t>
3650</section>
3651
3652<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3653<t>
3654   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3655   the documents returned by HTTP requests to be only those that were
3656   intended by the server administrators. If an HTTP server translates
3657   HTTP URIs directly into file system calls, the server &MUST; take
3658   special care not to serve files that were not intended to be
3659   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3660   other operating systems use ".." as a path component to indicate a
3661   directory level above the current one. On such a system, an HTTP
3662   server &MUST; disallow any such construct in the request-target if it
3663   would otherwise allow access to a resource outside those intended to
3664   be accessible via the HTTP server. Similarly, files intended for
3665   reference only internally to the server (such as access control
3666   files, configuration files, and script code) &MUST; be protected from
3667   inappropriate retrieval, since they might contain sensitive
3668   information. Experience has shown that minor bugs in such HTTP server
3669   implementations have turned into security risks.
3670</t>
3671</section>
3672
3673<section title="DNS-related Attacks" anchor="dns.related.attacks">
3674<t>
3675   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3676   generally prone to security attacks based on the deliberate misassociation
3677   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3678   cautious in assuming the validity of an IP number/DNS name association unless
3679   the response is protected by DNSSec (<xref target="RFC4033"/>).
3680</t>
3681</section>
3682
3683<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3684<t>
3685   By their very nature, HTTP intermediaries are men-in-the-middle, and
3686   represent an opportunity for man-in-the-middle attacks. Compromise of
3687   the systems on which the intermediaries run can result in serious security
3688   and privacy problems. Intermediaries have access to security-related
3689   information, personal information about individual users and
3690   organizations, and proprietary information belonging to users and
3691   content providers. A compromised intermediary, or an intermediary
3692   implemented or configured without regard to security and privacy
3693   considerations, might be used in the commission of a wide range of
3694   potential attacks.
3695</t>
3696<t>
3697   Intermediaries that contain a shared cache are especially vulnerable
3698   to cache poisoning attacks.
3699</t>
3700<t>
3701   Implementers need to consider the privacy and security
3702   implications of their design and coding decisions, and of the
3703   configuration options they provide to operators (especially the
3704   default configuration).
3705</t>
3706<t>
3707   Users need to be aware that intermediaries are no more trustworthy than
3708   the people who run them; HTTP itself cannot solve this problem.
3709</t>
3710</section>
3711
3712<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3713<t>
3714   Because HTTP uses mostly textual, character-delimited fields, attackers can
3715   overflow buffers in implementations, and/or perform a Denial of Service
3716   against implementations that accept fields with unlimited lengths.
3717</t>
3718<t>
3719   To promote interoperability, this specification makes specific
3720   recommendations for minimum size limits on request-line
3721   (<xref target="request.line"/>)
3722   and blocks of header fields (<xref target="header.fields"/>). These are
3723   minimum recommendations, chosen to be supportable even by implementations
3724   with limited resources; it is expected that most implementations will
3725   choose substantially higher limits.
3726</t>
3727<t>
3728   This specification also provides a way for servers to reject messages that
3729   have request-targets that are too long (&status-414;) or request entities
3730   that are too large (&status-4xx;).
3731</t>
3732<t>
3733   Other fields (including but not limited to request methods, response status
3734   phrases, header field-names, and body chunks) &SHOULD; be limited by
3735   implementations carefully, so as to not impede interoperability.
3736</t>
3737</section>
3738</section>
3739
3740<section title="Acknowledgments" anchor="acks">
3741<t>
3742   This edition of HTTP builds on the many contributions that went into
3743   <xref target="RFC1945" format="none">RFC 1945</xref>,
3744   <xref target="RFC2068" format="none">RFC 2068</xref>,
3745   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3746   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3747   substantial contributions made by the previous authors, editors, and
3748   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3749   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3750   Paul J. Leach, and Mark Nottingham.
3751   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
3752   acknowledgements from prior revisions.
3753</t>
3754<t>
3755   Since 1999, the following contributors have helped improve the HTTP
3756   specification by reporting bugs, asking smart questions, drafting or
3757   reviewing text, and evaluating open issues:
3758</t>
3759<?BEGININC acks ?>
3760<t>Adam Barth,
3761Adam Roach,
3762Addison Phillips,
3763Adrian Chadd,
3764Adrien W. de Croy,
3765Alan Ford,
3766Alan Ruttenberg,
3767Albert Lunde,
3768Alek Storm,
3769Alex Rousskov,
3770Alexandre Morgaut,
3771Alexey Melnikov,
3772Alisha Smith,
3773Amichai Rothman,
3774Amit Klein,
3775Amos Jeffries,
3776Andreas Maier,
3777Andreas Petersson,
3778Anil Sharma,
3779Anne van Kesteren,
3780Anthony Bryan,
3781Asbjorn Ulsberg,
3782Balachander Krishnamurthy,
3783Barry Leiba,
3784Ben Laurie,
3785Benjamin Niven-Jenkins,
3786Bil Corry,
3787Bill Burke,
3788Bjoern Hoehrmann,
3789Bob Scheifler,
3790Boris Zbarsky,
3791Brett Slatkin,
3792Brian Kell,
3793Brian McBarron,
3794Brian Pane,
3795Brian Smith,
3796Bryce Nesbitt,
3797Cameron Heavon-Jones,
3798Carl Kugler,
3799Carsten Bormann,
3800Charles Fry,
3801Chris Newman,
3802Cyrus Daboo,
3803Dale Robert Anderson,
3804Dan Wing,
3805Dan Winship,
3806Daniel Stenberg,
3807Dave Cridland,
3808Dave Crocker,
3809Dave Kristol,
3810David Booth,
3811David Singer,
3812David W. Morris,
3813Diwakar Shetty,
3814Dmitry Kurochkin,
3815Drummond Reed,
3816Duane Wessels,
3817Edward Lee,
3818Eliot Lear,
3819Eran Hammer-Lahav,
3820Eric D. Williams,
3821Eric J. Bowman,
3822Eric Lawrence,
3823Eric Rescorla,
3824Erik Aronesty,
3825Florian Weimer,
3826Frank Ellermann,
3827Fred Bohle,
3828Gabriel Montenegro,
3829Geoffrey Sneddon,
3830Gervase Markham,
3831Grahame Grieve,
3832Greg Wilkins,
3833Harald Tveit Alvestrand,
3834Harry Halpin,
3835Helge Hess,
3836Henrik Nordstrom,
3837Henry S. Thompson,
3838Henry Story,
3839Herbert van de Sompel,
3840Howard Melman,
3841Hugo Haas,
3842Ian Fette,
3843Ian Hickson,
3844Ido Safruti,
3845Ingo Struck,
3846J. Ross Nicoll,
3847James H. Manger,
3848James Lacey,
3849James M. Snell,
3850Jamie Lokier,
3851Jan Algermissen,
3852Jeff Hodges (who came up with the term 'effective Request-URI'),
3853Jeff Walden,
3854Jim Luther,
3855Joe D. Williams,
3856Joe Gregorio,
3857Joe Orton,
3858John C. Klensin,
3859John C. Mallery,
3860John Cowan,
3861John Kemp,
3862John Panzer,
3863John Schneider,
3864John Stracke,
3865John Sullivan,
3866Jonas Sicking,
3867Jonathan Billington,
3868Jonathan Moore,
3869Jonathan Rees,
3870Jonathan Silvera,
3871Jordi Ros,
3872Joris Dobbelsteen,
3873Josh Cohen,
3874Julien Pierre,
3875Jungshik Shin,
3876Justin Chapweske,
3877Justin Erenkrantz,
3878Justin James,
3879Kalvinder Singh,
3880Karl Dubost,
3881Keith Hoffman,
3882Keith Moore,
3883Koen Holtman,
3884Konstantin Voronkov,
3885Kris Zyp,
3886Lisa Dusseault,
3887Maciej Stachowiak,
3888Marc Schneider,
3889Marc Slemko,
3890Mark Baker,
3891Mark Pauley,
3892Mark Watson,
3893Markus Isomaki,
3894Markus Lanthaler,
3895Martin J. Duerst,
3896Martin Musatov,
3897Martin Nilsson,
3898Martin Thomson,
3899Matt Lynch,
3900Matthew Cox,
3901Max Clark,
3902Michael Burrows,
3903Michael Hausenblas,
3904Mike Amundsen,
3905Mike Belshe,
3906Mike Kelly,
3907Mike Schinkel,
3908Miles Sabin,
3909Murray S. Kucherawy,
3910Mykyta Yevstifeyev,
3911Nathan Rixham,
3912Nicholas Shanks,
3913Nico Williams,
3914Nicolas Alvarez,
3915Nicolas Mailhot,
3916Noah Slater,
3917Pablo Castro,
3918Pat Hayes,
3919Patrick R. McManus,
3920Paul E. Jones,
3921Paul Hoffman,
3922Paul Marquess,
3923Peter Lepeska,
3924Peter Saint-Andre,
3925Peter Watkins,
3926Phil Archer,
3927Philippe Mougin,
3928Phillip Hallam-Baker,
3929Poul-Henning Kamp,
3930Preethi Natarajan,
3931Rajeev Bector,
3932Ray Polk,
3933Reto Bachmann-Gmuer,
3934Richard Cyganiak,
3935Robert Brewer,
3936Robert Collins,
3937Robert O'Callahan,
3938Robert Olofsson,
3939Robert Sayre,
3940Robert Siemer,
3941Robert de Wilde,
3942Roberto Javier Godoy,
3943Roberto Peon,
3944Ronny Widjaja,
3945S. Mike Dierken,
3946Salvatore Loreto,
3947Sam Johnston,
3948Sam Ruby,
3949Scott Lawrence (who maintained the original issues list),
3950Sean B. Palmer,
3951Shane McCarron,
3952Stefan Eissing,
3953Stefan Tilkov,
3954Stefanos Harhalakis,
3955Stephane Bortzmeyer,
3956Stephen Farrell,
3957Stephen Ludin,
3958Stuart Williams,
3959Subbu Allamaraju,
3960Sylvain Hellegouarch,
3961Tapan Divekar,
3962Tatsuya Hayashi,
3963Ted Hardie,
3964Thomas Broyer,
3965Thomas Nordin,
3966Thomas Roessler,
3967Tim Bray,
3968Tim Morgan,
3969Tim Olsen,
3970Tom Zhou,
3971Travis Snoozy,
3972Tyler Close,
3973Vincent Murphy,
3974Wenbo Zhu,
3975Werner Baumann,
3976Wilbur Streett,
3977Wilfredo Sanchez Vega,
3978William A. Rowe Jr.,
3979William Chan,
3980Willy Tarreau,
3981Xiaoshu Wang,
3982Yaron Goland,
3983Yngve Nysaeter Pettersen,
3984Yoav Nir,
3985Yogesh Bang,
3986Yutaka Oiwa,
3987Zed A. Shaw, and
3988Zhong Yu.
3989</t>
3990<?ENDINC acks ?>
3991</section>
3992
3993</middle>
3994<back>
3995
3996<references title="Normative References">
3997
3998<reference anchor="Part2">
3999  <front>
4000    <title>HTTP/1.1, part 2: Semantics and Payloads</title>
4001    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4002      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4003      <address><email>fielding@gbiv.com</email></address>
4004    </author>
4005    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4006      <organization abbrev="W3C">World Wide Web Consortium</organization>
4007      <address><email>ylafon@w3.org</email></address>
4008    </author>
4009    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4010      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4011      <address><email>julian.reschke@greenbytes.de</email></address>
4012    </author>
4013    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4014  </front>
4015  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4016  <x:source href="p2-semantics.xml" basename="p2-semantics">
4017    <x:defines>1xx (Informational)</x:defines>
4018    <x:defines>1xx</x:defines>
4019    <x:defines>100 (Continue)</x:defines>
4020    <x:defines>101 (Switching Protocols)</x:defines>
4021    <x:defines>2xx (Successful)</x:defines>
4022    <x:defines>2xx</x:defines>
4023    <x:defines>200 (OK)</x:defines>
4024    <x:defines>204 (No Content)</x:defines>
4025    <x:defines>3xx (Redirection)</x:defines>
4026    <x:defines>3xx</x:defines>
4027    <x:defines>301 (Moved Permanently)</x:defines>
4028    <x:defines>4xx (Client Error)</x:defines>
4029    <x:defines>4xx</x:defines>
4030    <x:defines>400 (Bad Request)</x:defines>
4031    <x:defines>405 (Method Not Allowed)</x:defines>
4032    <x:defines>411 (Length Required)</x:defines>
4033    <x:defines>414 (URI Too Long)</x:defines>
4034    <x:defines>417 (Expectation Failed)</x:defines>
4035    <x:defines>426 (Upgrade Required)</x:defines>
4036    <x:defines>501 (Not Implemented)</x:defines>
4037    <x:defines>502 (Bad Gateway)</x:defines>
4038    <x:defines>505 (HTTP Version Not Supported)</x:defines>
4039    <x:defines>Allow</x:defines>
4040    <x:defines>Content-Encoding</x:defines>
4041    <x:defines>Content-Location</x:defines>
4042    <x:defines>Content-Type</x:defines>
4043    <x:defines>Date</x:defines>
4044    <x:defines>Expect</x:defines>
4045    <x:defines>Location</x:defines>
4046    <x:defines>Server</x:defines>
4047    <x:defines>User-Agent</x:defines>
4048  </x:source>
4049</reference>
4050
4051<reference anchor="Part4">
4052  <front>
4053    <title>HTTP/1.1, part 4: Conditional Requests</title>
4054    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
4055      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4056      <address><email>fielding@gbiv.com</email></address>
4057    </author>
4058    <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
4059      <organization abbrev="W3C">World Wide Web Consortium</organization>
4060      <address><email>ylafon@w3.org</email></address>
4061    </author>
4062    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
4063      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4064      <address><email>julian.reschke@greenbytes.de</email></address>
4065    </author>
4066    <date month="&ID-MONTH;" year="&ID-YEAR;" />
4067  </front>
4068  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;" />
4069  <x:source basename="p4-conditional" href="p4-conditional.xml">
4070    <x:defines>304 (Not Modified)</x:defines>
4071    <x:defines>ETag</x:defines>
4072    <x:defines>Last-Modified</x:defines>
4073  </x:source>
4074</reference>
4075
4076<reference anchor="Part5">
4077  <front>
4078    <title>HTTP/1.1, part 5: Range Requests</title>
4079    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4080      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4081      <address><email>fielding@gbiv.com</email></address>
4082    </author>
4083    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4084      <organization abbrev="W3C">World Wide Web Consortium</organization>
4085      <address><email>ylafon@w3.org</email></address>
4086    </author>
4087    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4088      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4089      <address><email>julian.reschke@greenbytes.de</email></address>
4090    </author>
4091    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4092  </front>
4093  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
4094  <x:source href="p5-range.xml" basename="p5-range">
4095    <x:defines>Content-Range</x:defines>
4096  </x:source>
4097</reference>
4098
4099<reference anchor="Part6">
4100  <front>
4101    <title>HTTP/1.1, part 6: Caching</title>
4102    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4103      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4104      <address><email>fielding@gbiv.com</email></address>
4105    </author>
4106    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4107      <organization abbrev="W3C">World Wide Web Consortium</organization>
4108      <address><email>ylafon@w3.org</email></address>
4109    </author>
4110    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4111      <organization>Rackspace</organization>
4112      <address><email>mnot@mnot.net</email></address>
4113    </author>
4114    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4115      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4116      <address><email>julian.reschke@greenbytes.de</email></address>
4117    </author>
4118    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4119  </front>
4120  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4121  <x:source href="p6-cache.xml" basename="p6-cache">
4122    <x:defines>Expires</x:defines>
4123  </x:source>
4124</reference>
4125
4126<reference anchor="Part7">
4127  <front>
4128    <title>HTTP/1.1, part 7: Authentication</title>
4129    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4130      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4131      <address><email>fielding@gbiv.com</email></address>
4132    </author>
4133    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4134      <organization abbrev="W3C">World Wide Web Consortium</organization>
4135      <address><email>ylafon@w3.org</email></address>
4136    </author>
4137    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4138      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4139      <address><email>julian.reschke@greenbytes.de</email></address>
4140    </author>
4141    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4142  </front>
4143  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
4144  <x:source href="p7-auth.xml" basename="p7-auth">
4145    <x:defines>Proxy-Authenticate</x:defines>
4146    <x:defines>Proxy-Authorization</x:defines>
4147  </x:source>
4148</reference>
4149
4150<reference anchor="RFC5234">
4151  <front>
4152    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4153    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4154      <organization>Brandenburg InternetWorking</organization>
4155      <address>
4156        <email>dcrocker@bbiw.net</email>
4157      </address> 
4158    </author>
4159    <author initials="P." surname="Overell" fullname="Paul Overell">
4160      <organization>THUS plc.</organization>
4161      <address>
4162        <email>paul.overell@thus.net</email>
4163      </address>
4164    </author>
4165    <date month="January" year="2008"/>
4166  </front>
4167  <seriesInfo name="STD" value="68"/>
4168  <seriesInfo name="RFC" value="5234"/>
4169</reference>
4170
4171<reference anchor="RFC2119">
4172  <front>
4173    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4174    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4175      <organization>Harvard University</organization>
4176      <address><email>sob@harvard.edu</email></address>
4177    </author>
4178    <date month="March" year="1997"/>
4179  </front>
4180  <seriesInfo name="BCP" value="14"/>
4181  <seriesInfo name="RFC" value="2119"/>
4182</reference>
4183
4184<reference anchor="RFC3986">
4185 <front>
4186  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4187  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4188    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4189    <address>
4190       <email>timbl@w3.org</email>
4191       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4192    </address>
4193  </author>
4194  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4195    <organization abbrev="Day Software">Day Software</organization>
4196    <address>
4197      <email>fielding@gbiv.com</email>
4198      <uri>http://roy.gbiv.com/</uri>
4199    </address>
4200  </author>
4201  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4202    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4203    <address>
4204      <email>LMM@acm.org</email>
4205      <uri>http://larry.masinter.net/</uri>
4206    </address>
4207  </author>
4208  <date month='January' year='2005'></date>
4209 </front>
4210 <seriesInfo name="STD" value="66"/>
4211 <seriesInfo name="RFC" value="3986"/>
4212</reference>
4213
4214<reference anchor="USASCII">
4215  <front>
4216    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4217    <author>
4218      <organization>American National Standards Institute</organization>
4219    </author>
4220    <date year="1986"/>
4221  </front>
4222  <seriesInfo name="ANSI" value="X3.4"/>
4223</reference>
4224
4225<reference anchor="RFC1950">
4226  <front>
4227    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4228    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4229      <organization>Aladdin Enterprises</organization>
4230      <address><email>ghost@aladdin.com</email></address>
4231    </author>
4232    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4233    <date month="May" year="1996"/>
4234  </front>
4235  <seriesInfo name="RFC" value="1950"/>
4236  <!--<annotation>
4237    RFC 1950 is an Informational RFC, thus it might be less stable than
4238    this specification. On the other hand, this downward reference was
4239    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4240    therefore it is unlikely to cause problems in practice. See also
4241    <xref target="BCP97"/>.
4242  </annotation>-->
4243</reference>
4244
4245<reference anchor="RFC1951">
4246  <front>
4247    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4248    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4249      <organization>Aladdin Enterprises</organization>
4250      <address><email>ghost@aladdin.com</email></address>
4251    </author>
4252    <date month="May" year="1996"/>
4253  </front>
4254  <seriesInfo name="RFC" value="1951"/>
4255  <!--<annotation>
4256    RFC 1951 is an Informational RFC, thus it might be less stable than
4257    this specification. On the other hand, this downward reference was
4258    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4259    therefore it is unlikely to cause problems in practice. See also
4260    <xref target="BCP97"/>.
4261  </annotation>-->
4262</reference>
4263
4264<reference anchor="RFC1952">
4265  <front>
4266    <title>GZIP file format specification version 4.3</title>
4267    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4268      <organization>Aladdin Enterprises</organization>
4269      <address><email>ghost@aladdin.com</email></address>
4270    </author>
4271    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4272      <address><email>gzip@prep.ai.mit.edu</email></address>
4273    </author>
4274    <author initials="M." surname="Adler" fullname="Mark Adler">
4275      <address><email>madler@alumni.caltech.edu</email></address>
4276    </author>
4277    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4278      <address><email>ghost@aladdin.com</email></address>
4279    </author>
4280    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4281      <address><email>randeg@alumni.rpi.edu</email></address>
4282    </author>
4283    <date month="May" year="1996"/>
4284  </front>
4285  <seriesInfo name="RFC" value="1952"/>
4286  <!--<annotation>
4287    RFC 1952 is an Informational RFC, thus it might be less stable than
4288    this specification. On the other hand, this downward reference was
4289    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4290    therefore it is unlikely to cause problems in practice. See also
4291    <xref target="BCP97"/>.
4292  </annotation>-->
4293</reference>
4294
4295</references>
4296
4297<references title="Informative References">
4298
4299<reference anchor="ISO-8859-1">
4300  <front>
4301    <title>
4302     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4303    </title>
4304    <author>
4305      <organization>International Organization for Standardization</organization>
4306    </author>
4307    <date year="1998"/>
4308  </front>
4309  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4310</reference>
4311
4312<reference anchor='RFC1919'>
4313  <front>
4314    <title>Classical versus Transparent IP Proxies</title>
4315    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4316      <address><email>mchatel@pax.eunet.ch</email></address>
4317    </author>
4318    <date year='1996' month='March' />
4319  </front>
4320  <seriesInfo name='RFC' value='1919' />
4321</reference>
4322
4323<reference anchor="RFC1945">
4324  <front>
4325    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4326    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4327      <organization>MIT, Laboratory for Computer Science</organization>
4328      <address><email>timbl@w3.org</email></address>
4329    </author>
4330    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4331      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4332      <address><email>fielding@ics.uci.edu</email></address>
4333    </author>
4334    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4335      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4336      <address><email>frystyk@w3.org</email></address>
4337    </author>
4338    <date month="May" year="1996"/>
4339  </front>
4340  <seriesInfo name="RFC" value="1945"/>
4341</reference>
4342
4343<reference anchor="RFC2045">
4344  <front>
4345    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4346    <author initials="N." surname="Freed" fullname="Ned Freed">
4347      <organization>Innosoft International, Inc.</organization>
4348      <address><email>ned@innosoft.com</email></address>
4349    </author>
4350    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4351      <organization>First Virtual Holdings</organization>
4352      <address><email>nsb@nsb.fv.com</email></address>
4353    </author>
4354    <date month="November" year="1996"/>
4355  </front>
4356  <seriesInfo name="RFC" value="2045"/>
4357</reference>
4358
4359<reference anchor="RFC2047">
4360  <front>
4361    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4362    <author initials="K." surname="Moore" fullname="Keith Moore">
4363      <organization>University of Tennessee</organization>
4364      <address><email>moore@cs.utk.edu</email></address>
4365    </author>
4366    <date month="November" year="1996"/>
4367  </front>
4368  <seriesInfo name="RFC" value="2047"/>
4369</reference>
4370
4371<reference anchor="RFC2068">
4372  <front>
4373    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4374    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4375      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4376      <address><email>fielding@ics.uci.edu</email></address>
4377    </author>
4378    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4379      <organization>MIT Laboratory for Computer Science</organization>
4380      <address><email>jg@w3.org</email></address>
4381    </author>
4382    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4383      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4384      <address><email>mogul@wrl.dec.com</email></address>
4385    </author>
4386    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4387      <organization>MIT Laboratory for Computer Science</organization>
4388      <address><email>frystyk@w3.org</email></address>
4389    </author>
4390    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4391      <organization>MIT Laboratory for Computer Science</organization>
4392      <address><email>timbl@w3.org</email></address>
4393    </author>
4394    <date month="January" year="1997"/>
4395  </front>
4396  <seriesInfo name="RFC" value="2068"/>
4397</reference>
4398
4399<reference anchor="RFC2145">
4400  <front>
4401    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4402    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4403      <organization>Western Research Laboratory</organization>
4404      <address><email>mogul@wrl.dec.com</email></address>
4405    </author>
4406    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4407      <organization>Department of Information and Computer Science</organization>
4408      <address><email>fielding@ics.uci.edu</email></address>
4409    </author>
4410    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4411      <organization>MIT Laboratory for Computer Science</organization>
4412      <address><email>jg@w3.org</email></address>
4413    </author>
4414    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4415      <organization>W3 Consortium</organization>
4416      <address><email>frystyk@w3.org</email></address>
4417    </author>
4418    <date month="May" year="1997"/>
4419  </front>
4420  <seriesInfo name="RFC" value="2145"/>
4421</reference>
4422
4423<reference anchor="RFC2616">
4424  <front>
4425    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4426    <author initials="R." surname="Fielding" fullname="R. Fielding">
4427      <organization>University of California, Irvine</organization>
4428      <address><email>fielding@ics.uci.edu</email></address>
4429    </author>
4430    <author initials="J." surname="Gettys" fullname="J. Gettys">
4431      <organization>W3C</organization>
4432      <address><email>jg@w3.org</email></address>
4433    </author>
4434    <author initials="J." surname="Mogul" fullname="J. Mogul">
4435      <organization>Compaq Computer Corporation</organization>
4436      <address><email>mogul@wrl.dec.com</email></address>
4437    </author>
4438    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4439      <organization>MIT Laboratory for Computer Science</organization>
4440      <address><email>frystyk@w3.org</email></address>
4441    </author>
4442    <author initials="L." surname="Masinter" fullname="L. Masinter">
4443      <organization>Xerox Corporation</organization>
4444      <address><email>masinter@parc.xerox.com</email></address>
4445    </author>
4446    <author initials="P." surname="Leach" fullname="P. Leach">
4447      <organization>Microsoft Corporation</organization>
4448      <address><email>paulle@microsoft.com</email></address>
4449    </author>
4450    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4451      <organization>W3C</organization>
4452      <address><email>timbl@w3.org</email></address>
4453    </author>
4454    <date month="June" year="1999"/>
4455  </front>
4456  <seriesInfo name="RFC" value="2616"/>
4457</reference>
4458
4459<reference anchor='RFC2817'>
4460  <front>
4461    <title>Upgrading to TLS Within HTTP/1.1</title>
4462    <author initials='R.' surname='Khare' fullname='R. Khare'>
4463      <organization>4K Associates / UC Irvine</organization>
4464      <address><email>rohit@4K-associates.com</email></address>
4465    </author>
4466    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4467      <organization>Agranat Systems, Inc.</organization>
4468      <address><email>lawrence@agranat.com</email></address>
4469    </author>
4470    <date year='2000' month='May' />
4471  </front>
4472  <seriesInfo name='RFC' value='2817' />
4473</reference>
4474
4475<reference anchor='RFC2818'>
4476  <front>
4477    <title>HTTP Over TLS</title>
4478    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4479      <organization>RTFM, Inc.</organization>
4480      <address><email>ekr@rtfm.com</email></address>
4481    </author>
4482    <date year='2000' month='May' />
4483  </front>
4484  <seriesInfo name='RFC' value='2818' />
4485</reference>
4486
4487<reference anchor='RFC2965'>
4488  <front>
4489    <title>HTTP State Management Mechanism</title>
4490    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4491      <organization>Bell Laboratories, Lucent Technologies</organization>
4492      <address><email>dmk@bell-labs.com</email></address>
4493    </author>
4494    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4495      <organization>Epinions.com, Inc.</organization>
4496      <address><email>lou@montulli.org</email></address>
4497    </author>
4498    <date year='2000' month='October' />
4499  </front>
4500  <seriesInfo name='RFC' value='2965' />
4501</reference>
4502
4503<reference anchor='RFC3040'>
4504  <front>
4505    <title>Internet Web Replication and Caching Taxonomy</title>
4506    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4507      <organization>Equinix, Inc.</organization>
4508    </author>
4509    <author initials='I.' surname='Melve' fullname='I. Melve'>
4510      <organization>UNINETT</organization>
4511    </author>
4512    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4513      <organization>CacheFlow Inc.</organization>
4514    </author>
4515    <date year='2001' month='January' />
4516  </front>
4517  <seriesInfo name='RFC' value='3040' />
4518</reference>
4519
4520<reference anchor='RFC3864'>
4521  <front>
4522    <title>Registration Procedures for Message Header Fields</title>
4523    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4524      <organization>Nine by Nine</organization>
4525      <address><email>GK-IETF@ninebynine.org</email></address>
4526    </author>
4527    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4528      <organization>BEA Systems</organization>
4529      <address><email>mnot@pobox.com</email></address>
4530    </author>
4531    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4532      <organization>HP Labs</organization>
4533      <address><email>JeffMogul@acm.org</email></address>
4534    </author>
4535    <date year='2004' month='September' />
4536  </front>
4537  <seriesInfo name='BCP' value='90' />
4538  <seriesInfo name='RFC' value='3864' />
4539</reference>
4540
4541<reference anchor='RFC4033'>
4542  <front>
4543    <title>DNS Security Introduction and Requirements</title>
4544    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4545    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4546    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4547    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4548    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4549    <date year='2005' month='March' />
4550  </front>
4551  <seriesInfo name='RFC' value='4033' />
4552</reference>
4553
4554<reference anchor="RFC4288">
4555  <front>
4556    <title>Media Type Specifications and Registration Procedures</title>
4557    <author initials="N." surname="Freed" fullname="N. Freed">
4558      <organization>Sun Microsystems</organization>
4559      <address>
4560        <email>ned.freed@mrochek.com</email>
4561      </address>
4562    </author>
4563    <author initials="J." surname="Klensin" fullname="J. Klensin">
4564      <address>
4565        <email>klensin+ietf@jck.com</email>
4566      </address>
4567    </author>
4568    <date year="2005" month="December"/>
4569  </front>
4570  <seriesInfo name="BCP" value="13"/>
4571  <seriesInfo name="RFC" value="4288"/>
4572</reference>
4573
4574<reference anchor='RFC4395'>
4575  <front>
4576    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4577    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4578      <organization>AT&amp;T Laboratories</organization>
4579      <address>
4580        <email>tony+urireg@maillennium.att.com</email>
4581      </address>
4582    </author>
4583    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4584      <organization>Qualcomm, Inc.</organization>
4585      <address>
4586        <email>hardie@qualcomm.com</email>
4587      </address>
4588    </author>
4589    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4590      <organization>Adobe Systems</organization>
4591      <address>
4592        <email>LMM@acm.org</email>
4593      </address>
4594    </author>
4595    <date year='2006' month='February' />
4596  </front>
4597  <seriesInfo name='BCP' value='115' />
4598  <seriesInfo name='RFC' value='4395' />
4599</reference>
4600
4601<reference anchor='RFC4559'>
4602  <front>
4603    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4604    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4605    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4606    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4607    <date year='2006' month='June' />
4608  </front>
4609  <seriesInfo name='RFC' value='4559' />
4610</reference>
4611
4612<reference anchor='RFC5226'>
4613  <front>
4614    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4615    <author initials='T.' surname='Narten' fullname='T. Narten'>
4616      <organization>IBM</organization>
4617      <address><email>narten@us.ibm.com</email></address>
4618    </author>
4619    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4620      <organization>Google</organization>
4621      <address><email>Harald@Alvestrand.no</email></address>
4622    </author>
4623    <date year='2008' month='May' />
4624  </front>
4625  <seriesInfo name='BCP' value='26' />
4626  <seriesInfo name='RFC' value='5226' />
4627</reference>
4628
4629<reference anchor="RFC5322">
4630  <front>
4631    <title>Internet Message Format</title>
4632    <author initials="P." surname="Resnick" fullname="P. Resnick">
4633      <organization>Qualcomm Incorporated</organization>
4634    </author>
4635    <date year="2008" month="October"/>
4636  </front>
4637  <seriesInfo name="RFC" value="5322"/>
4638</reference>
4639
4640<reference anchor="RFC6265">
4641  <front>
4642    <title>HTTP State Management Mechanism</title>
4643    <author initials="A." surname="Barth" fullname="Adam Barth">
4644      <organization abbrev="U.C. Berkeley">
4645        University of California, Berkeley
4646      </organization>
4647      <address><email>abarth@eecs.berkeley.edu</email></address>
4648    </author>
4649    <date year="2011" month="April" />
4650  </front>
4651  <seriesInfo name="RFC" value="6265"/>
4652</reference>
4653
4654<!--<reference anchor='BCP97'>
4655  <front>
4656    <title>Handling Normative References to Standards-Track Documents</title>
4657    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4658      <address>
4659        <email>klensin+ietf@jck.com</email>
4660      </address>
4661    </author>
4662    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4663      <organization>MIT</organization>
4664      <address>
4665        <email>hartmans-ietf@mit.edu</email>
4666      </address>
4667    </author>
4668    <date year='2007' month='June' />
4669  </front>
4670  <seriesInfo name='BCP' value='97' />
4671  <seriesInfo name='RFC' value='4897' />
4672</reference>-->
4673
4674<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4675  <front>
4676    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4677    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4678    <date year="2001" month="November"/>
4679  </front>
4680  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4681</reference>
4682
4683</references>
4684
4685
4686<section title="HTTP Version History" anchor="compatibility">
4687<t>
4688   HTTP has been in use by the World-Wide Web global information initiative
4689   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4690   was a simple protocol for hypertext data transfer across the Internet
4691   with only a single request method (GET) and no metadata.
4692   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4693   methods and MIME-like messaging that could include metadata about the data
4694   transferred and modifiers on the request/response semantics. However,
4695   HTTP/1.0 did not sufficiently take into consideration the effects of
4696   hierarchical proxies, caching, the need for persistent connections, or
4697   name-based virtual hosts. The proliferation of incompletely-implemented
4698   applications calling themselves "HTTP/1.0" further necessitated a
4699   protocol version change in order for two communicating applications
4700   to determine each other's true capabilities.
4701</t>
4702<t>
4703   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4704   requirements that enable reliable implementations, adding only
4705   those new features that will either be safely ignored by an HTTP/1.0
4706   recipient or only sent when communicating with a party advertising
4707   conformance with HTTP/1.1.
4708</t>
4709<t>
4710   It is beyond the scope of a protocol specification to mandate
4711   conformance with previous versions. HTTP/1.1 was deliberately
4712   designed, however, to make supporting previous versions easy.
4713   We would expect a general-purpose HTTP/1.1 server to understand
4714   any valid request in the format of HTTP/1.0 and respond appropriately
4715   with an HTTP/1.1 message that only uses features understood (or
4716   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4717   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4718</t>
4719<t>
4720   Since HTTP/0.9 did not support header fields in a request,
4721   there is no mechanism for it to support name-based virtual
4722   hosts (selection of resource by inspection of the <x:ref>Host</x:ref> header
4723   field).  Any server that implements name-based virtual hosts
4724   ought to disable support for HTTP/0.9.  Most requests that
4725   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4726   requests wherein a buggy client failed to properly encode
4727   linear whitespace found in a URI reference and placed in
4728   the request-target.
4729</t>
4730
4731<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4732<t>
4733   This section summarizes major differences between versions HTTP/1.0
4734   and HTTP/1.1.
4735</t>
4736
4737<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4738<t>
4739   The requirements that clients and servers support the <x:ref>Host</x:ref>
4740   header field (<xref target="header.host"/>), report an error if it is
4741   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4742   are among the most important changes defined by HTTP/1.1.
4743</t>
4744<t>
4745   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4746   addresses and servers; there was no other established mechanism for
4747   distinguishing the intended server of a request than the IP address
4748   to which that request was directed. The <x:ref>Host</x:ref> header field was
4749   introduced during the development of HTTP/1.1 and, though it was
4750   quickly implemented by most HTTP/1.0 browsers, additional requirements
4751   were placed on all HTTP/1.1 requests in order to ensure complete
4752   adoption.  At the time of this writing, most HTTP-based services
4753   are dependent upon the Host header field for targeting requests.
4754</t>
4755</section>
4756
4757<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4758<t>
4759   In HTTP/1.0, each connection is established by the client prior to the
4760   request and closed by the server after sending the response. However, some
4761   implementations implement the explicitly negotiated ("Keep-Alive") version
4762   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4763   target="RFC2068"/>.
4764</t>
4765<t>
4766   Some clients and servers might wish to be compatible with these previous
4767   approaches to persistent connections, by explicitly negotiating for them
4768   with a "Connection: keep-alive" request header field. However, some
4769   experimental implementations of HTTP/1.0 persistent connections are faulty;
4770   for example, if a HTTP/1.0 proxy server doesn't understand
4771   <x:ref>Connection</x:ref>, it will erroneously forward that header field
4772   to the next inbound server, which would result in a hung connection.
4773</t>
4774<t>
4775   One attempted solution was the introduction of a Proxy-Connection header
4776   field, targeted specifically at proxies. In practice, this was also
4777   unworkable, because proxies are often deployed in multiple layers, bringing
4778   about the same problem discussed above.
4779</t>
4780<t>
4781   As a result, clients are encouraged not to send the Proxy-Connection header
4782   field in any requests.
4783</t>
4784<t>
4785   Clients are also encouraged to consider the use of Connection: keep-alive
4786   in requests carefully; while they can enable persistent connections with
4787   HTTP/1.0 servers, clients using them need will need to monitor the
4788   connection for "hung" requests (which indicate that the client ought stop
4789   sending the header field), and this mechanism ought not be used by clients
4790   at all when a proxy is being used.
4791</t>
4792</section>
4793
4794<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
4795<t>
4796   HTTP/1.1 introduces the <x:ref>Transfer-Encoding</x:ref> header field
4797   (<xref target="header.transfer-encoding"/>). Proxies/gateways &MUST; remove
4798   any transfer-coding prior to forwarding a message via a MIME-compliant
4799   protocol.
4800</t>
4801</section>
4802
4803</section>
4804
4805<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4806<t>
4807  Clarify that the string "HTTP" in the HTTP-version ABNF production is case
4808  sensitive. Restrict the version numbers to be single digits due to the fact
4809  that implementations are known to handle multi-digit version numbers
4810  incorrectly.
4811  (<xref target="http.version"/>)
4812</t>
4813<t>
4814  Update use of abs_path production from RFC 1808 to the path-absolute + query
4815  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4816  request method only.
4817  (<xref target="request-target"/>)
4818</t>
4819<t>
4820  Require that invalid whitespace around field-names be rejected.
4821  (<xref target="header.fields"/>)
4822</t>
4823<t>
4824  Rules about implicit linear whitespace between certain grammar productions
4825  have been removed; now whitespace is only allowed where specifically
4826  defined in the ABNF.
4827  (<xref target="whitespace"/>)
4828</t>
4829<t> 
4830  The NUL octet is no longer allowed in comment and quoted-string
4831  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4832  Non-ASCII content in header fields and reason phrase has been obsoleted and
4833  made opaque (the TEXT rule was removed).
4834  (<xref target="field.components"/>)
4835</t>
4836<t>
4837  Empty list elements in list productions have been deprecated.
4838  (<xref target="abnf.extension"/>)
4839</t>
4840<t>
4841  Require recipients to handle bogus <x:ref>Content-Length</x:ref> header
4842  fields as errors.
4843  (<xref target="message.body"/>)
4844</t>
4845<t>
4846  Remove reference to non-existent identity transfer-coding value tokens.
4847  (Sections <xref format="counter" target="message.body"/> and
4848  <xref format="counter" target="transfer.codings"/>)
4849</t>
4850<t>
4851  Clarification that the chunk length does not include the count of the octets
4852  in the chunk header and trailer. Furthermore disallowed line folding
4853  in chunk extensions, and deprecate their use.
4854  (<xref target="chunked.encoding"/>)
4855</t>
4856<t>
4857  Registration of Transfer Codings now requires IETF Review
4858  (<xref target="transfer.coding.registry"/>)
4859</t>
4860<t>
4861  Remove hard limit of two connections per server.
4862  Remove requirement to retry a sequence of requests as long it was idempotent.
4863  Remove requirements about when servers are allowed to close connections
4864  prematurely.
4865  (<xref target="persistent.practical"/>)
4866</t>
4867<t>
4868  Remove requirement to retry requests under certain circumstances when the
4869  server prematurely closes the connection.
4870  (<xref target="message.transmission.requirements"/>)
4871</t>
4872<t>
4873  Change ABNF productions for header fields to only define the field value.
4874</t>
4875<t>
4876  Clarify exactly when "close" connection options have to be sent.
4877  (<xref target="header.connection"/>)
4878</t>
4879<t>
4880  Define the semantics of the <x:ref>Upgrade</x:ref> header field in responses
4881  other than 101 (this was incorporated from <xref target="RFC2817"/>).
4882  (<xref target="header.upgrade"/>)
4883</t>
4884<t>
4885  Take over the Upgrade Token Registry, previously defined in
4886  <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
4887  (<xref target="upgrade.token.registry"/>)
4888</t>
4889</section>
4890</section>
4891
4892<section title="ABNF list extension: #rule" anchor="abnf.extension">
4893<t>
4894  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
4895  improve readability in the definitions of some header field values.
4896</t>
4897<t>
4898  A construct "#" is defined, similar to "*", for defining comma-delimited
4899  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
4900  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
4901  comma (",") and optional whitespace (OWS).   
4902</t>
4903<figure><preamble>
4904  Thus,
4905</preamble><artwork type="example">
4906  1#element =&gt; element *( OWS "," OWS element )
4907</artwork></figure>
4908<figure><preamble>
4909  and:
4910</preamble><artwork type="example">
4911  #element =&gt; [ 1#element ]
4912</artwork></figure>
4913<figure><preamble>
4914  and for n &gt;= 1 and m &gt; 1:
4915</preamble><artwork type="example">
4916  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
4917</artwork></figure>
4918<t>
4919  For compatibility with legacy list rules, recipients &SHOULD; accept empty
4920  list elements. In other words, consumers would follow the list productions:
4921</t>
4922<figure><artwork type="example">
4923  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
4924 
4925  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
4926</artwork></figure>
4927<t>
4928  Note that empty elements do not contribute to the count of elements present,
4929  though.
4930</t>
4931<t>
4932  For example, given these ABNF productions:
4933</t>
4934<figure><artwork type="example">
4935  example-list      = 1#example-list-elmt
4936  example-list-elmt = token ; see <xref target="field.components"/>
4937</artwork></figure>
4938<t>
4939  Then these are valid values for example-list (not including the double
4940  quotes, which are present for delimitation only):
4941</t>
4942<figure><artwork type="example">
4943  "foo,bar"
4944  "foo ,bar,"
4945  "foo , ,bar,charlie   "
4946</artwork></figure>
4947<t>
4948  But these values would be invalid, as at least one non-empty element is
4949  required:
4950</t>
4951<figure><artwork type="example">
4952  ""
4953  ","
4954  ",   ,"
4955</artwork></figure>
4956<t>
4957  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
4958  expanded as explained above.
4959</t>
4960</section>
4961
4962<?BEGININC p1-messaging.abnf-appendix ?>
4963<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4964<figure>
4965<artwork type="abnf" name="p1-messaging.parsed-abnf">
4966<x:ref>BWS</x:ref> = OWS
4967
4968<x:ref>Connection</x:ref> = *( "," OWS ) connection-option *( OWS "," [ OWS
4969 connection-option ] )
4970<x:ref>Content-Length</x:ref> = 1*DIGIT
4971
4972<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4973 ]
4974<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
4975<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
4976<x:ref>Host</x:ref> = uri-host [ ":" port ]
4977
4978<x:ref>OWS</x:ref> = *( SP / HTAB )
4979
4980<x:ref>RWS</x:ref> = 1*( SP / HTAB )
4981
4982<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4983<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4984<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4985 transfer-coding ] )
4986
4987<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4988<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
4989
4990<x:ref>Via</x:ref> = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment
4991 ] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS
4992 comment ] ) ] )
4993
4994<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4995<x:ref>absolute-form</x:ref> = absolute-URI
4996<x:ref>asterisk-form</x:ref> = "*"
4997<x:ref>attribute</x:ref> = token
4998<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4999<x:ref>authority-form</x:ref> = authority
5000
5001<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5002<x:ref>chunk-data</x:ref> = 1*OCTET
5003<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5004<x:ref>chunk-ext-name</x:ref> = token
5005<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5006<x:ref>chunk-size</x:ref> = 1*HEXDIG
5007<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
5008<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5009<x:ref>connection-option</x:ref> = token
5010<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5011 / %x2A-5B ; '*'-'['
5012 / %x5D-7E ; ']'-'~'
5013 / obs-text
5014
5015<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5016<x:ref>field-name</x:ref> = token
5017<x:ref>field-value</x:ref> = *( field-content / obs-fold )
5018
5019<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
5020<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5021<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5022
5023<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
5024
5025<x:ref>message-body</x:ref> = *OCTET
5026<x:ref>method</x:ref> = token
5027
5028<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
5029<x:ref>obs-text</x:ref> = %x80-FF
5030<x:ref>origin-form</x:ref> = path-absolute [ "?" query ]
5031
5032<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5033<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5034<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5035<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5036<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
5037<x:ref>protocol-name</x:ref> = token
5038<x:ref>protocol-version</x:ref> = token
5039<x:ref>pseudonym</x:ref> = token
5040
5041<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5042 / %x5D-7E ; ']'-'~'
5043 / obs-text
5044<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
5045 / %x5D-7E ; ']'-'~'
5046 / obs-text
5047<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5048<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5049<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5050<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5051<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5052
5053<x:ref>rank</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5054<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5055<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5056<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5057<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5058<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
5059<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
5060 asterisk-form
5061
5062<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5063 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5064<x:ref>start-line</x:ref> = request-line / status-line
5065<x:ref>status-code</x:ref> = 3DIGIT
5066<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
5067
5068<x:ref>t-codings</x:ref> = "trailers" / ( transfer-coding [ t-ranking ] )
5069<x:ref>t-ranking</x:ref> = OWS ";" OWS "q=" rank
5070<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5071 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5072<x:ref>token</x:ref> = 1*tchar
5073<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5074<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5075 transfer-extension
5076<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5077<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5078
5079<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5080
5081<x:ref>value</x:ref> = word
5082
5083<x:ref>word</x:ref> = token / quoted-string
5084</artwork>
5085</figure>
5086</section>
5087<?ENDINC p1-messaging.abnf-appendix ?>
5088
5089<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5090
5091<section title="Since RFC 2616">
5092<t>
5093  Extracted relevant partitions from <xref target="RFC2616"/>.
5094</t>
5095</section>
5096
5097<section title="Since draft-ietf-httpbis-p1-messaging-00">
5098<t>
5099  Closed issues:
5100  <list style="symbols">
5101    <t>
5102      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5103      "HTTP Version should be case sensitive"
5104      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5105    </t>
5106    <t>
5107      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5108      "'unsafe' characters"
5109      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5110    </t>
5111    <t>
5112      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5113      "Chunk Size Definition"
5114      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5115    </t>
5116    <t>
5117      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5118      "Message Length"
5119      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5120    </t>
5121    <t>
5122      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5123      "Media Type Registrations"
5124      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5125    </t>
5126    <t>
5127      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5128      "URI includes query"
5129      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5130    </t>
5131    <t>
5132      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5133      "No close on 1xx responses"
5134      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5135    </t>
5136    <t>
5137      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5138      "Remove 'identity' token references"
5139      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5140    </t>
5141    <t>
5142      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5143      "Import query BNF"
5144    </t>
5145    <t>
5146      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5147      "qdtext BNF"
5148    </t>
5149    <t>
5150      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5151      "Normative and Informative references"
5152    </t>
5153    <t>
5154      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5155      "RFC2606 Compliance"
5156    </t>
5157    <t>
5158      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5159      "RFC977 reference"
5160    </t>
5161    <t>
5162      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5163      "RFC1700 references"
5164    </t>
5165    <t>
5166      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5167      "inconsistency in date format explanation"
5168    </t>
5169    <t>
5170      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5171      "Date reference typo"
5172    </t>
5173    <t>
5174      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5175      "Informative references"
5176    </t>
5177    <t>
5178      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5179      "ISO-8859-1 Reference"
5180    </t>
5181    <t>
5182      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5183      "Normative up-to-date references"
5184    </t>
5185  </list>
5186</t>
5187<t>
5188  Other changes:
5189  <list style="symbols">
5190    <t>
5191      Update media type registrations to use RFC4288 template.
5192    </t>
5193    <t>
5194      Use names of RFC4234 core rules DQUOTE and HTAB,
5195      fix broken ABNF for chunk-data
5196      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5197    </t>
5198  </list>
5199</t>
5200</section>
5201
5202<section title="Since draft-ietf-httpbis-p1-messaging-01">
5203<t>
5204  Closed issues:
5205  <list style="symbols">
5206    <t>
5207      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5208      "Bodies on GET (and other) requests"
5209    </t>
5210    <t>
5211      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5212      "Updating to RFC4288"
5213    </t>
5214    <t>
5215      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5216      "Status Code and Reason Phrase"
5217    </t>
5218    <t>
5219      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5220      "rel_path not used"
5221    </t>
5222  </list>
5223</t>
5224<t>
5225  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5226  <list style="symbols">
5227    <t>
5228      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5229      "trailer-part").
5230    </t>
5231    <t>
5232      Avoid underscore character in rule names ("http_URL" ->
5233      "http-URL", "abs_path" -> "path-absolute").
5234    </t>
5235    <t>
5236      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5237      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5238      have to be updated when switching over to RFC3986.
5239    </t>
5240    <t>
5241      Synchronize core rules with RFC5234.
5242    </t>
5243    <t>
5244      Get rid of prose rules that span multiple lines.
5245    </t>
5246    <t>
5247      Get rid of unused rules LOALPHA and UPALPHA.
5248    </t>
5249    <t>
5250      Move "Product Tokens" section (back) into Part 1, as "token" is used
5251      in the definition of the Upgrade header field.
5252    </t>
5253    <t>
5254      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5255    </t>
5256    <t>
5257      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5258    </t>
5259  </list>
5260</t>
5261</section>
5262
5263<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5264<t>
5265  Closed issues:
5266  <list style="symbols">
5267    <t>
5268      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5269      "HTTP-date vs. rfc1123-date"
5270    </t>
5271    <t>
5272      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5273      "WS in quoted-pair"
5274    </t>
5275  </list>
5276</t>
5277<t>
5278  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5279  <list style="symbols">
5280    <t>
5281      Reference RFC 3984, and update header field registrations for header
5282      fields defined in this document.
5283    </t>
5284  </list>
5285</t>
5286<t>
5287  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5288  <list style="symbols">
5289    <t>
5290      Replace string literals when the string really is case-sensitive (HTTP-version).
5291    </t>
5292  </list>
5293</t>
5294</section>
5295
5296<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5297<t>
5298  Closed issues:
5299  <list style="symbols">
5300    <t>
5301      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5302      "Connection closing"
5303    </t>
5304    <t>
5305      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5306      "Move registrations and registry information to IANA Considerations"
5307    </t>
5308    <t>
5309      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5310      "need new URL for PAD1995 reference"
5311    </t>
5312    <t>
5313      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5314      "IANA Considerations: update HTTP URI scheme registration"
5315    </t>
5316    <t>
5317      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5318      "Cite HTTPS URI scheme definition"
5319    </t>
5320    <t>
5321      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5322      "List-type header fields vs Set-Cookie"
5323    </t>
5324  </list>
5325</t>
5326<t>
5327  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5328  <list style="symbols">
5329    <t>
5330      Replace string literals when the string really is case-sensitive (HTTP-Date).
5331    </t>
5332    <t>
5333      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5334    </t>
5335  </list>
5336</t>
5337</section>
5338
5339<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5340<t>
5341  Closed issues:
5342  <list style="symbols">
5343    <t>
5344      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5345      "Out-of-date reference for URIs"
5346    </t>
5347    <t>
5348      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5349      "RFC 2822 is updated by RFC 5322"
5350    </t>
5351  </list>
5352</t>
5353<t>
5354  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5355  <list style="symbols">
5356    <t>
5357      Use "/" instead of "|" for alternatives.
5358    </t>
5359    <t>
5360      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5361    </t>
5362    <t>
5363      Only reference RFC 5234's core rules.
5364    </t>
5365    <t>
5366      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5367      whitespace ("OWS") and required whitespace ("RWS").
5368    </t>
5369    <t>
5370      Rewrite ABNFs to spell out whitespace rules, factor out
5371      header field value format definitions.
5372    </t>
5373  </list>
5374</t>
5375</section>
5376
5377<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5378<t>
5379  Closed issues:
5380  <list style="symbols">
5381    <t>
5382      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5383      "Header LWS"
5384    </t>
5385    <t>
5386      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5387      "Sort 1.3 Terminology"
5388    </t>
5389    <t>
5390      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5391      "RFC2047 encoded words"
5392    </t>
5393    <t>
5394      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5395      "Character Encodings in TEXT"
5396    </t>
5397    <t>
5398      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5399      "Line Folding"
5400    </t>
5401    <t>
5402      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5403      "OPTIONS * and proxies"
5404    </t>
5405    <t>
5406      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5407      "reason-phrase BNF"
5408    </t>
5409    <t>
5410      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5411      "Use of TEXT"
5412    </t>
5413    <t>
5414      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5415      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5416    </t>
5417    <t>
5418      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5419      "RFC822 reference left in discussion of date formats"
5420    </t>
5421  </list>
5422</t>
5423<t>
5424  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5425  <list style="symbols">
5426    <t>
5427      Rewrite definition of list rules, deprecate empty list elements.
5428    </t>
5429    <t>
5430      Add appendix containing collected and expanded ABNF.
5431    </t>
5432  </list>
5433</t>
5434<t>
5435  Other changes:
5436  <list style="symbols">
5437    <t>
5438      Rewrite introduction; add mostly new Architecture Section.
5439    </t>
5440    <t>
5441      Move definition of quality values from Part 3 into Part 1;
5442      make TE request header field grammar independent of accept-params (defined in Part 3).
5443    </t>
5444  </list>
5445</t>
5446</section>
5447
5448<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5449<t>
5450  Closed issues:
5451  <list style="symbols">
5452    <t>
5453      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5454      "base for numeric protocol elements"
5455    </t>
5456    <t>
5457      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5458      "comment ABNF"
5459    </t>
5460  </list>
5461</t>
5462<t>
5463  Partly resolved issues:
5464  <list style="symbols">
5465    <t>
5466      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5467      "205 Bodies" (took out language that implied that there might be
5468      methods for which a request body MUST NOT be included)
5469    </t>
5470    <t>
5471      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5472      "editorial improvements around HTTP-date"
5473    </t>
5474  </list>
5475</t>
5476</section>
5477
5478<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5479<t>
5480  Closed issues:
5481  <list style="symbols">
5482    <t>
5483      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5484      "Repeating single-value header fields"
5485    </t>
5486    <t>
5487      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5488      "increase connection limit"
5489    </t>
5490    <t>
5491      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5492      "IP addresses in URLs"
5493    </t>
5494    <t>
5495      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5496      "take over HTTP Upgrade Token Registry"
5497    </t>
5498    <t>
5499      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5500      "CR and LF in chunk extension values"
5501    </t>
5502    <t>
5503      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5504      "HTTP/0.9 support"
5505    </t>
5506    <t>
5507      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5508      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5509    </t>
5510    <t>
5511      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5512      "move definitions of gzip/deflate/compress to part 1"
5513    </t>
5514    <t>
5515      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5516      "disallow control characters in quoted-pair"
5517    </t>
5518  </list>
5519</t>
5520<t>
5521  Partly resolved issues:
5522  <list style="symbols">
5523    <t>
5524      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5525      "update IANA requirements wrt Transfer-Coding values" (add the
5526      IANA Considerations subsection)
5527    </t>
5528  </list>
5529</t>
5530</section>
5531
5532<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5533<t>
5534  Closed issues:
5535  <list style="symbols">
5536    <t>
5537      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5538      "header parsing, treatment of leading and trailing OWS"
5539    </t>
5540  </list>
5541</t>
5542<t>
5543  Partly resolved issues:
5544  <list style="symbols">
5545    <t>
5546      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5547      "Placement of 13.5.1 and 13.5.2"
5548    </t>
5549    <t>
5550      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5551      "use of term "word" when talking about header field structure"
5552    </t>
5553  </list>
5554</t>
5555</section>
5556
5557<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5558<t>
5559  Closed issues:
5560  <list style="symbols">
5561    <t>
5562      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5563      "Clarification of the term 'deflate'"
5564    </t>
5565    <t>
5566      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5567      "OPTIONS * and proxies"
5568    </t>
5569    <t>
5570      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5571      "MIME-Version not listed in P1, general header fields"
5572    </t>
5573    <t>
5574      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5575      "IANA registry for content/transfer encodings"
5576    </t>
5577    <t>
5578      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5579      "Case-sensitivity of HTTP-date"
5580    </t>
5581    <t>
5582      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5583      "use of term "word" when talking about header field structure"
5584    </t>
5585  </list>
5586</t>
5587<t>
5588  Partly resolved issues:
5589  <list style="symbols">
5590    <t>
5591      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5592      "Term for the requested resource's URI"
5593    </t>
5594  </list>
5595</t>
5596</section>
5597
5598<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5599<t>
5600  Closed issues:
5601  <list style="symbols">
5602    <t>
5603      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5604      "Connection Closing"
5605    </t>
5606    <t>
5607      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5608      "Delimiting messages with multipart/byteranges"
5609    </t>
5610    <t>
5611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5612      "Handling multiple Content-Length header fields"
5613    </t>
5614    <t>
5615      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5616      "Clarify entity / representation / variant terminology"
5617    </t>
5618    <t>
5619      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5620      "consider removing the 'changes from 2068' sections"
5621    </t>
5622  </list>
5623</t>
5624<t>
5625  Partly resolved issues:
5626  <list style="symbols">
5627    <t>
5628      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5629      "HTTP(s) URI scheme definitions"
5630    </t>
5631  </list>
5632</t>
5633</section>
5634
5635<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5636<t>
5637  Closed issues:
5638  <list style="symbols">
5639    <t>
5640      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5641      "Trailer requirements"
5642    </t>
5643    <t>
5644      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5645      "Text about clock requirement for caches belongs in p6"
5646    </t>
5647    <t>
5648      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5649      "effective request URI: handling of missing host in HTTP/1.0"
5650    </t>
5651    <t>
5652      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5653      "confusing Date requirements for clients"
5654    </t>
5655  </list>
5656</t>
5657<t>
5658  Partly resolved issues:
5659  <list style="symbols">
5660    <t>
5661      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5662      "Handling multiple Content-Length header fields"
5663    </t>
5664  </list>
5665</t>
5666</section>
5667
5668<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5669<t>
5670  Closed issues:
5671  <list style="symbols">
5672    <t>
5673      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5674      "RFC2145 Normative"
5675    </t>
5676    <t>
5677      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5678      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5679    </t>
5680    <t>
5681      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5682      "define 'transparent' proxy"
5683    </t>
5684    <t>
5685      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5686      "Header Field Classification"
5687    </t>
5688    <t>
5689      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5690      "Is * usable as a request-uri for new methods?"
5691    </t>
5692    <t>
5693      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5694      "Migrate Upgrade details from RFC2817"
5695    </t>
5696    <t>
5697      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5698      "untangle ABNFs for header fields"
5699    </t>
5700    <t>
5701      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5702      "update RFC 2109 reference"
5703    </t>
5704  </list>
5705</t>
5706</section>
5707
5708<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5709<t>
5710  Closed issues:
5711  <list style="symbols">
5712    <t>
5713      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5714      "Allow is not in 13.5.2"
5715    </t>
5716    <t>
5717      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5718      "Handling multiple Content-Length header fields"
5719    </t>
5720    <t>
5721      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5722      "untangle ABNFs for header fields"
5723    </t>
5724    <t>
5725      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5726      "Content-Length ABNF broken"
5727    </t>
5728  </list>
5729</t>
5730</section>
5731
5732<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5733<t>
5734  Closed issues:
5735  <list style="symbols">
5736    <t>
5737      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5738      "HTTP-version should be redefined as fixed length pair of DIGIT . DIGIT"
5739    </t>
5740    <t>
5741      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5742      "Recommend minimum sizes for protocol elements"
5743    </t>
5744    <t>
5745      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5746      "Set expectations around buffering"
5747    </t>
5748    <t>
5749      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5750      "Considering messages in isolation"
5751    </t>
5752  </list>
5753</t>
5754</section>
5755
5756<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5757<t>
5758  Closed issues:
5759  <list style="symbols">
5760    <t>
5761      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5762      "DNS Spoofing / DNS Binding advice"
5763    </t>
5764    <t>
5765      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5766      "move RFCs 2145, 2616, 2817 to Historic status"
5767    </t>
5768    <t>
5769      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5770      "\-escaping in quoted strings"
5771    </t>
5772    <t>
5773      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5774      "'Close' should be reserved in the HTTP header field registry"
5775    </t>
5776  </list>
5777</t>
5778</section>
5779
5780<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5781<t>
5782  Closed issues:
5783  <list style="symbols">
5784    <t>
5785      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5786      "Document HTTP's error-handling philosophy"
5787    </t>
5788    <t>
5789      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5790      "Explain header field registration"
5791    </t>
5792    <t>
5793      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5794      "Revise Acknowledgements Sections"
5795    </t>
5796    <t>
5797      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5798      "Retrying Requests"
5799    </t>
5800    <t>
5801      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5802      "Closing the connection on server error"
5803    </t>
5804  </list>
5805</t>
5806</section>
5807
5808<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5809<t>
5810  Closed issues:
5811  <list style="symbols">
5812    <t>
5813      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/158"/>:
5814      "Proxy-Connection and Keep-Alive"
5815    </t>
5816    <t>
5817      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/166"/>:
5818      "Clarify 'User Agent'"
5819    </t>
5820    <t>
5821      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/300"/>:
5822      "Define non-final responses"
5823    </t>
5824    <t>
5825      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
5826      "intended maturity level vs normative references"
5827    </t>
5828    <t>
5829      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/324"/>:
5830      "Intermediary rewriting of queries"
5831    </t>
5832  </list>
5833</t>
5834</section>
5835
5836<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5837<t>
5838  Closed issues:
5839  <list style="symbols">
5840    <t>
5841      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
5842      "message-body in CONNECT response"
5843    </t>
5844    <t>
5845      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
5846      "Misplaced text on connection handling in p2"
5847    </t>
5848    <t>
5849      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/335"/>:
5850      "wording of line folding rule"
5851    </t>
5852    <t>
5853      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/343"/>:
5854      "chunk-extensions"
5855    </t>
5856    <t>
5857      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5858      "make IANA policy definitions consistent"
5859    </t>
5860  </list>
5861</t>
5862</section>
5863
5864<section title="Since draft-ietf-httpbis-p1-messaging-19" anchor="changes.since.19">
5865<t>
5866  Closed issues:
5867  <list style="symbols">
5868    <t>
5869      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5870      "make IANA policy definitions consistent"
5871    </t>
5872    <t>
5873      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/359"/>:
5874      "clarify connection header field values are case-insensitive"
5875    </t>
5876    <t>
5877      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/361"/>:
5878      "ABNF requirements for recipients"
5879    </t>
5880    <t>
5881      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/368"/>:
5882      "note introduction of new IANA registries as normative changes"
5883    </t>
5884    <t>
5885      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/374"/>:
5886      "Reference to ISO-8859-1 is informative"
5887    </t>
5888  </list>
5889</t>
5890</section>
5891
5892<section title="Since draft-ietf-httpbis-p1-messaging-20" anchor="changes.since.20">
5893<t>
5894  None yet.
5895</t>
5896</section>
5897
5898</section>
5899
5900</back>
5901</rfc>
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