source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1558

Last change on this file since 1558 was 1558, checked in by fielding@…, 8 years ago

(editorial) missed a spot

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 243.2 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 "March">
16  <!ENTITY ID-YEAR "2012">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#response.cacheability' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY diff-mime              "<xref target='Part3' x:rel='#differences.between.http.and.mime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY representation         "<xref target='Part3' x:rel='#representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-date            "<xref target='Part2' x:rel='#header.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-mime-version    "<xref target='Part3' x:rel='#mime-version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY status-code-reasonphr  "<xref target='Part2' x:rel='#status.code.and.reason.phrase' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY cons-new-header-fields "<xref target='Part2' x:rel='#considerations.for.creating.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44]>
45<?rfc toc="yes" ?>
46<?rfc symrefs="yes" ?>
47<?rfc sortrefs="yes" ?>
48<?rfc compact="yes"?>
49<?rfc subcompact="no" ?>
50<?rfc linkmailto="no" ?>
51<?rfc editing="no" ?>
52<?rfc comments="yes"?>
53<?rfc inline="yes"?>
54<?rfc rfcedstyle="yes"?>
55<?rfc-ext allow-markup-in-artwork="yes" ?>
56<?rfc-ext include-references-in-index="yes" ?>
57<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="proposed"
58     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
59     xmlns:x='http://purl.org/net/xml2rfc/ext'>
60<x:link rel="next" basename="p2-semantics"/>
61<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
62<front>
63
64  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
65
66  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
67    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
68    <address>
69      <postal>
70        <street>345 Park Ave</street>
71        <city>San Jose</city>
72        <region>CA</region>
73        <code>95110</code>
74        <country>USA</country>
75      </postal>
76      <email>fielding@gbiv.com</email>
77      <uri>http://roy.gbiv.com/</uri>
78    </address>
79  </author>
80
81  <author initials="J." surname="Gettys" fullname="Jim Gettys">
82    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
83    <address>
84      <postal>
85        <street>21 Oak Knoll Road</street>
86        <city>Carlisle</city>
87        <region>MA</region>
88        <code>01741</code>
89        <country>USA</country>
90      </postal>
91      <email>jg@freedesktop.org</email>
92      <uri>http://gettys.wordpress.com/</uri>
93    </address>
94  </author>
95 
96  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
97    <organization abbrev="HP">Hewlett-Packard Company</organization>
98    <address>
99      <postal>
100        <street>HP Labs, Large Scale Systems Group</street>
101        <street>1501 Page Mill Road, MS 1177</street>
102        <city>Palo Alto</city>
103        <region>CA</region>
104        <code>94304</code>
105        <country>USA</country>
106      </postal>
107      <email>JeffMogul@acm.org</email>
108    </address>
109  </author>
110
111  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
112    <organization abbrev="Microsoft">Microsoft Corporation</organization>
113    <address>
114      <postal>
115        <street>1 Microsoft Way</street>
116        <city>Redmond</city>
117        <region>WA</region>
118        <code>98052</code>
119        <country>USA</country>
120      </postal>
121      <email>henrikn@microsoft.com</email>
122    </address>
123  </author>
124
125  <author initials="L." surname="Masinter" fullname="Larry Masinter">
126    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
127    <address>
128      <postal>
129        <street>345 Park Ave</street>
130        <city>San Jose</city>
131        <region>CA</region>
132        <code>95110</code>
133        <country>USA</country>
134      </postal>
135      <email>LMM@acm.org</email>
136      <uri>http://larry.masinter.net/</uri>
137    </address>
138  </author>
139 
140  <author initials="P." surname="Leach" fullname="Paul J. Leach">
141    <organization abbrev="Microsoft">Microsoft Corporation</organization>
142    <address>
143      <postal>
144        <street>1 Microsoft Way</street>
145        <city>Redmond</city>
146        <region>WA</region>
147        <code>98052</code>
148      </postal>
149      <email>paulle@microsoft.com</email>
150    </address>
151  </author>
152   
153  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
154    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
155    <address>
156      <postal>
157        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
158        <street>The Stata Center, Building 32</street>
159        <street>32 Vassar Street</street>
160        <city>Cambridge</city>
161        <region>MA</region>
162        <code>02139</code>
163        <country>USA</country>
164      </postal>
165      <email>timbl@w3.org</email>
166      <uri>http://www.w3.org/People/Berners-Lee/</uri>
167    </address>
168  </author>
169
170  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
171    <organization abbrev="W3C">World Wide Web Consortium</organization>
172    <address>
173      <postal>
174        <street>W3C / ERCIM</street>
175        <street>2004, rte des Lucioles</street>
176        <city>Sophia-Antipolis</city>
177        <region>AM</region>
178        <code>06902</code>
179        <country>France</country>
180      </postal>
181      <email>ylafon@w3.org</email>
182      <uri>http://www.raubacapeu.net/people/yves/</uri>
183    </address>
184  </author>
185
186  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
187    <organization abbrev="greenbytes">greenbytes GmbH</organization>
188    <address>
189      <postal>
190        <street>Hafenweg 16</street>
191        <city>Muenster</city><region>NW</region><code>48155</code>
192        <country>Germany</country>
193      </postal>
194      <phone>+49 251 2807760</phone>
195      <facsimile>+49 251 2807761</facsimile>
196      <email>julian.reschke@greenbytes.de</email>
197      <uri>http://greenbytes.de/tech/webdav/</uri>
198    </address>
199  </author>
200
201  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
202  <workgroup>HTTPbis Working Group</workgroup>
203
204<abstract>
205<t>
206   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
207   distributed, collaborative, hypertext information systems. HTTP has been in
208   use by the World Wide Web global information initiative since 1990. This
209   document is Part 1 of the seven-part specification that defines the protocol
210   referred to as "HTTP/1.1" and, taken together, obsoletes
211   <xref target="RFC2616" x:fmt="none">RFC 2616</xref> and moves it to historic
212   status, along with its predecessor <xref target="RFC2068" x:fmt="none">RFC
213   2068</xref>.
214</t>
215<t>
216   Part 1 provides an overview of HTTP and its associated terminology, defines
217   the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
218   the generic message syntax and parsing requirements for HTTP message frames,
219   and describes general security concerns for implementations.
220</t>
221<t>
222   This part also obsoletes RFCs <xref target="RFC2145" x:fmt="none">2145</xref>
223   (on HTTP version numbers) and <xref target="RFC2817" x:fmt="none">2817</xref>
224   (on using CONNECT for TLS upgrades) and moves them to historic status.
225</t>
226</abstract>
227
228<note title="Editorial Note (To be removed by RFC Editor)">
229  <t>
230    Discussion of this draft should take place on the HTTPBIS working group
231    mailing list (ietf-http-wg@w3.org), which is archived at
232    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
233  </t>
234  <t>
235    The current issues list is at
236    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
237    documents (including fancy diffs) can be found at
238    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
239  </t>
240  <t>
241    The changes in this draft are summarized in <xref target="changes.since.18"/>.
242  </t>
243</note>
244</front>
245<middle>
246<section title="Introduction" anchor="introduction">
247<t>
248   The Hypertext Transfer Protocol (HTTP) is an application-level
249   request/response protocol that uses extensible semantics and MIME-like
250   message payloads for flexible interaction with network-based hypertext
251   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
252   standard <xref target="RFC3986"/> to indicate the target resource and
253   relationships between resources.
254   Messages are passed in a format similar to that used by Internet mail
255   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
256   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
257   between HTTP and MIME messages).
258</t>
259<t>
260   HTTP is a generic interface protocol for information systems. It is
261   designed to hide the details of how a service is implemented by presenting
262   a uniform interface to clients that is independent of the types of
263   resources provided. Likewise, servers do not need to be aware of each
264   client's purpose: an HTTP request can be considered in isolation rather
265   than being associated with a specific type of client or a predetermined
266   sequence of application steps. The result is a protocol that can be used
267   effectively in many different contexts and for which implementations can
268   evolve independently over time.
269</t>
270<t>
271   HTTP is also designed for use as an intermediation protocol for translating
272   communication to and from non-HTTP information systems.
273   HTTP proxies and gateways can provide access to alternative information
274   services by translating their diverse protocols into a hypertext
275   format that can be viewed and manipulated by clients in the same way
276   as HTTP services.
277</t>
278<t>
279   One consequence of HTTP flexibility is that the protocol cannot be
280   defined in terms of what occurs behind the interface. Instead, we
281   are limited to defining the syntax of communication, the intent
282   of received communication, and the expected behavior of recipients.
283   If the communication is considered in isolation, then successful
284   actions ought to be reflected in corresponding changes to the
285   observable interface provided by servers. However, since multiple
286   clients might act in parallel and perhaps at cross-purposes, we
287   cannot require that such changes be observable beyond the scope
288   of a single response.
289</t>
290<t>
291   This document is Part 1 of the seven-part specification of HTTP,
292   defining the protocol referred to as "HTTP/1.1", obsoleting
293   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
294   Part 1 describes the architectural elements that are used or
295   referred to in HTTP, defines the "http" and "https" URI schemes,
296   describes overall network operation and connection management,
297   and defines HTTP message framing and forwarding requirements.
298   Our goal is to define all of the mechanisms necessary for HTTP message
299   handling that are independent of message semantics, thereby defining the
300   complete set of requirements for message parsers and
301   message-forwarding intermediaries.
302</t>
303
304<section title="Requirement Notation" anchor="intro.requirements">
305<t>
306   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
307   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
308   document are to be interpreted as described in <xref target="RFC2119"/>.
309</t>
310</section>
311
312<section title="Syntax Notation" anchor="notation">
313<iref primary="true" item="Grammar" subitem="ALPHA"/>
314<iref primary="true" item="Grammar" subitem="CR"/>
315<iref primary="true" item="Grammar" subitem="CRLF"/>
316<iref primary="true" item="Grammar" subitem="CTL"/>
317<iref primary="true" item="Grammar" subitem="DIGIT"/>
318<iref primary="true" item="Grammar" subitem="DQUOTE"/>
319<iref primary="true" item="Grammar" subitem="HEXDIG"/>
320<iref primary="true" item="Grammar" subitem="HTAB"/>
321<iref primary="true" item="Grammar" subitem="LF"/>
322<iref primary="true" item="Grammar" subitem="OCTET"/>
323<iref primary="true" item="Grammar" subitem="SP"/>
324<iref primary="true" item="Grammar" subitem="VCHAR"/>
325<t>
326   This specification uses the Augmented Backus-Naur Form (ABNF) notation
327   of <xref target="RFC5234"/> with the list rule extension defined in
328   <xref target="abnf.extension"/><xref target="collected.abnf"/> shows
329   the collected ABNF with the list rule expanded.
330</t>
331<t anchor="core.rules">
332  <x:anchor-alias value="ALPHA"/>
333  <x:anchor-alias value="CTL"/>
334  <x:anchor-alias value="CR"/>
335  <x:anchor-alias value="CRLF"/>
336  <x:anchor-alias value="DIGIT"/>
337  <x:anchor-alias value="DQUOTE"/>
338  <x:anchor-alias value="HEXDIG"/>
339  <x:anchor-alias value="HTAB"/>
340  <x:anchor-alias value="LF"/>
341  <x:anchor-alias value="OCTET"/>
342  <x:anchor-alias value="SP"/>
343  <x:anchor-alias value="VCHAR"/>
344   The following core rules are included by
345   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
346   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
347   DIGIT (decimal 0-9), DQUOTE (double quote),
348   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
349   OCTET (any 8-bit sequence of data), SP (space), and
350   VCHAR (any visible <xref target="USASCII"/> character).
351</t>
352<t>
353   As a convention, ABNF rule names prefixed with "obs-" denote
354   "obsolete" grammar rules that appear for historical reasons.
355</t>
356</section>
357</section>
358
359<section title="Architecture" anchor="architecture">
360<t>
361   HTTP was created for the World Wide Web architecture
362   and has evolved over time to support the scalability needs of a worldwide
363   hypertext system. Much of that architecture is reflected in the terminology
364   and syntax productions used to define HTTP.
365</t>
366
367<section title="Client/Server Messaging" anchor="operation">
368<iref primary="true" item="client"/>
369<iref primary="true" item="server"/>
370<iref primary="true" item="connection"/>
371<t>
372   HTTP is a stateless request/response protocol that operates by exchanging
373   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
374   transport or session-layer
375   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
376   program that establishes a connection to a server for the purpose of
377   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
378   program that accepts connections in order to service HTTP requests by
379   sending HTTP responses.
380</t>
381<iref primary="true" item="user agent"/>
382<iref primary="true" item="origin server"/>
383<iref primary="true" item="browser"/>
384<iref primary="true" item="spider"/>
385<iref primary="true" item="sender"/>
386<iref primary="true" item="recipient"/>
387<t>
388   Note that the terms client and server refer only to the roles that
389   these programs perform for a particular connection.  The same program
390   might act as a client on some connections and a server on others.  We use
391   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
392   such as a WWW browser, editor, or spider (web-traversing robot), and
393   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
394   authoritative responses to a request.  For general requirements, we use
395   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
396   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
397   message.
398</t>
399<x:note>
400  <t>
401    <x:h>Note:</x:h> The term 'user agent' covers both those situations where
402    there is a user (human) interacting with the software agent (and for which
403    user interface or interactive suggestions might be made, e.g., warning the
404    user or given the user an option in the case of security or privacy
405    options) and also those where the software agent may act autonomously.
406  </t>
407</x:note>
408<t>
409   Most HTTP communication consists of a retrieval request (GET) for
410   a representation of some resource identified by a URI.  In the
411   simplest case, this might be accomplished via a single bidirectional
412   connection (===) between the user agent (UA) and the origin server (O).
413</t>
414<figure><artwork type="drawing">
415         request   &gt;
416    UA ======================================= O
417                                &lt;   response
418</artwork></figure>
419<iref primary="true" item="message"/>
420<iref primary="true" item="request"/>
421<iref primary="true" item="response"/>
422<t>
423   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
424   message, beginning with a request-line that includes a method, URI, and
425   protocol version (<xref target="request.line"/>),
426   followed by MIME-like header fields containing
427   request modifiers, client information, and payload metadata
428   (<xref target="header.fields"/>),
429   an empty line to indicate the end of the header section, and finally
430   a message body containing the payload body (if any,
431   <xref target="message.body"/>).
432</t>
433<t>
434   A server responds to the client's request by sending one or more HTTP
435   <x:dfn>response</x:dfn>
436   messages, each beginning with a status line that
437   includes the protocol version, a success or error code, and textual
438   reason phrase (<xref target="status.line"/>),
439   possibly followed by MIME-like header fields containing server
440   information, resource metadata, and payload metadata
441   (<xref target="header.fields"/>),
442   an empty line to indicate the end of the header section, and finally
443   a message body containing the payload body (if any,
444   <xref target="message.body"/>).
445</t>
446<t>
447   The following example illustrates a typical message exchange for a
448   GET request on the URI "http://www.example.com/hello.txt":
449</t>
450<figure><preamble>
451client request:
452</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
453GET /hello.txt HTTP/1.1
454User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
455Host: www.example.com
456Accept: */*
457
458</artwork></figure>
459<figure><preamble>
460server response:
461</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
462HTTP/1.1 200 OK
463Date: Mon, 27 Jul 2009 12:28:53 GMT
464Server: Apache
465Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
466ETag: "34aa387-d-1568eb00"
467Accept-Ranges: bytes
468Content-Length: <x:length-of target="exbody"/>
469Vary: Accept-Encoding
470Content-Type: text/plain
471
472<x:span anchor="exbody">Hello World!
473</x:span></artwork></figure>
474</section>
475
476<section title="Connections and Transport Independence" anchor="transport-independence">
477<t>
478   HTTP messaging is independent of the underlying transport or
479   session-layer connection protocol(s).  HTTP only presumes a reliable
480   transport with in-order delivery of requests and the corresponding
481   in-order delivery of responses.  The mapping of HTTP request and
482   response structures onto the data units of the underlying transport
483   protocol is outside the scope of this specification.
484</t>
485<t>
486   The specific connection protocols to be used for an interaction
487   are determined by client configuration and the target resource's URI.
488   For example, the "http" URI scheme
489   (<xref target="http.uri"/>) indicates a default connection of TCP
490   over IP, with a default TCP port of 80, but the client might be
491   configured to use a proxy via some other connection port or protocol
492   instead of using the defaults.
493</t>
494<t>
495   A connection might be used for multiple HTTP request/response exchanges,
496   as defined in <xref target="persistent.connections"/>.
497</t>
498</section>
499
500<section title="Intermediaries" anchor="intermediaries">
501<iref primary="true" item="intermediary"/>
502<t>
503   HTTP enables the use of intermediaries to satisfy requests through
504   a chain of connections.  There are three common forms of HTTP
505   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
506   a single intermediary might act as an origin server, proxy, gateway,
507   or tunnel, switching behavior based on the nature of each request.
508</t>
509<figure><artwork type="drawing">
510         &gt;             &gt;             &gt;             &gt;
511    <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>
512               &lt;             &lt;             &lt;             &lt;
513</artwork></figure>
514<t>
515   The figure above shows three intermediaries (A, B, and C) between the
516   user agent and origin server. A request or response message that
517   travels the whole chain will pass through four separate connections.
518   Some HTTP communication options
519   might apply only to the connection with the nearest, non-tunnel
520   neighbor, only to the end-points of the chain, or to all connections
521   along the chain. Although the diagram is linear, each participant might
522   be engaged in multiple, simultaneous communications. For example, B
523   might be receiving requests from many clients other than A, and/or
524   forwarding requests to servers other than C, at the same time that it
525   is handling A's request.
526</t>
527<t>
528<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
529<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
530   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
531   to describe various requirements in relation to the directional flow of a
532   message: all messages flow from upstream to downstream.
533   Likewise, we use the terms inbound and outbound to refer to
534   directions in relation to the request path:
535   "<x:dfn>inbound</x:dfn>" means toward the origin server and
536   "<x:dfn>outbound</x:dfn>" means toward the user agent.
537</t>
538<t><iref primary="true" item="proxy"/>
539   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
540   client, usually via local configuration rules, to receive requests
541   for some type(s) of absolute URI and attempt to satisfy those
542   requests via translation through the HTTP interface.  Some translations
543   are minimal, such as for proxy requests for "http" URIs, whereas
544   other requests might require translation to and from entirely different
545   application-layer protocols. Proxies are often used to group an
546   organization's HTTP requests through a common intermediary for the
547   sake of security, annotation services, or shared caching.
548</t>
549<t>
550<iref primary="true" item="transforming proxy"/>
551<iref primary="true" item="non-transforming proxy"/>
552   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
553   or configured to modify request or response messages in a semantically
554   meaningful way (i.e., modifications, beyond those required by normal
555   HTTP processing, that change the message in a way that would be
556   significant to the original sender or potentially significant to
557   downstream recipients).  For example, a transforming proxy might be
558   acting as a shared annotation server (modifying responses to include
559   references to a local annotation database), a malware filter, a
560   format transcoder, or an intranet-to-Internet privacy filter.  Such
561   transformations are presumed to be desired by the client (or client
562   organization) that selected the proxy and are beyond the scope of
563   this specification.  However, when a proxy is not intended to transform
564   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
565   requirements that preserve HTTP message semantics. See &status-203; and
566   &header-warning; for status and warning codes related to transformations.
567</t>
568<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
569<iref primary="true" item="accelerator"/>
570   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
571   is a receiving agent that acts
572   as a layer above some other server(s) and translates the received
573   requests to the underlying server's protocol.  Gateways are often
574   used to encapsulate legacy or untrusted information services, to
575   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
576   enable partitioning or load-balancing of HTTP services across
577   multiple machines.
578</t>
579<t>
580   A gateway behaves as an origin server on its outbound connection and
581   as a user agent on its inbound connection.
582   All HTTP requirements applicable to an origin server
583   also apply to the outbound communication of a gateway.
584   A gateway communicates with inbound servers using any protocol that
585   it desires, including private extensions to HTTP that are outside
586   the scope of this specification.  However, an HTTP-to-HTTP gateway
587   that wishes to interoperate with third-party HTTP servers &MUST;
588   conform to HTTP user agent requirements on the gateway's inbound
589   connection and &MUST; implement the Connection
590   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
591   header fields for both connections.
592</t>
593<t><iref primary="true" item="tunnel"/>
594   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
595   without changing the messages. Once active, a tunnel is not
596   considered a party to the HTTP communication, though the tunnel might
597   have been initiated by an HTTP request. A tunnel ceases to exist when
598   both ends of the relayed connection are closed. Tunnels are used to
599   extend a virtual connection through an intermediary, such as when
600   transport-layer security is used to establish private communication
601   through a shared firewall proxy.
602</t>
603<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
604<iref primary="true" item="captive portal"/>
605   In addition, there may exist network intermediaries that are not
606   considered part of the HTTP communication but nevertheless act as
607   filters or redirecting agents (usually violating HTTP semantics,
608   causing security problems, and otherwise making a mess of things).
609   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
610   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
611   or "<x:dfn>captive portal</x:dfn>",
612   differs from an HTTP proxy because it has not been selected by the client.
613   Instead, the network intermediary redirects outgoing TCP port 80 packets
614   (and occasionally other common port traffic) to an internal HTTP server.
615   Interception proxies are commonly found on public network access points,
616   as a means of enforcing account subscription prior to allowing use of
617   non-local Internet services, and within corporate firewalls to enforce
618   network usage policies.
619   They are indistinguishable from a man-in-the-middle attack.
620</t>
621<t>
622   HTTP is defined as a stateless protocol, meaning that each request message
623   can be understood in isolation.  Many implementations depend on HTTP's
624   stateless design in order to reuse proxied connections or dynamically
625   load balance requests across multiple servers.  Hence, servers &MUST-NOT;
626   assume that two requests on the same connection are from the same user
627   agent unless the connection is secured and specific to that agent.
628   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
629   been known to violate this requirement, resulting in security and
630   interoperability problems.
631</t>
632</section>
633
634<section title="Caches" anchor="caches">
635<iref primary="true" item="cache"/>
636<t>
637   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
638   subsystem that controls its message storage, retrieval, and deletion.
639   A cache stores cacheable responses in order to reduce the response
640   time and network bandwidth consumption on future, equivalent
641   requests. Any client or server &MAY; employ a cache, though a cache
642   cannot be used by a server while it is acting as a tunnel.
643</t>
644<t>
645   The effect of a cache is that the request/response chain is shortened
646   if one of the participants along the chain has a cached response
647   applicable to that request. The following illustrates the resulting
648   chain if B has a cached copy of an earlier response from O (via C)
649   for a request which has not been cached by UA or A.
650</t>
651<figure><artwork type="drawing">
652            &gt;             &gt;
653       UA =========== A =========== B - - - - - - C - - - - - - O
654                  &lt;             &lt;
655</artwork></figure>
656<t><iref primary="true" item="cacheable"/>
657   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
658   the response message for use in answering subsequent requests.
659   Even when a response is cacheable, there might be additional
660   constraints placed by the client or by the origin server on when
661   that cached response can be used for a particular request. HTTP
662   requirements for cache behavior and cacheable responses are
663   defined in &caching-overview;
664</t>
665<t>
666   There are a wide variety of architectures and configurations
667   of caches and proxies deployed across the World Wide Web and
668   inside large organizations. These systems include national hierarchies
669   of proxy caches to save transoceanic bandwidth, systems that
670   broadcast or multicast cache entries, organizations that distribute
671   subsets of cached data via optical media, and so on.
672</t>
673</section>
674
675<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
676<t>
677   This specification targets conformance criteria according to the role of
678   a participant in HTTP communication.  Hence, HTTP requirements are placed
679   on senders, recipients, clients, servers, user agents, intermediaries,
680   origin servers, proxies, gateways, or caches, depending on what behavior
681   is being constrained by the requirement.
682</t>
683<t>
684   An implementation is considered conformant if it complies with all of the
685   requirements associated with the roles it partakes in HTTP.
686</t>
687<t>
688   Senders &MUST-NOT; generate protocol elements that do not match the grammar
689   defined by the ABNF rules for those protocol elements.
690</t>
691<t>
692   Unless otherwise noted, recipients &MAY; attempt to recover a usable
693   protocol element from an invalid construct.  HTTP does not define
694   specific error handling mechanisms except when they have a direct impact
695   on security, since different applications of the protocol require
696   different error handling strategies.  For example, a Web browser might
697   wish to transparently recover from a response where the Location header
698   field doesn't parse according to the ABNF, whereas a systems control
699   client might consider any form of error recovery to be dangerous.
700</t>
701</section>
702
703<section title="Protocol Versioning" anchor="http.version">
704  <x:anchor-alias value="HTTP-version"/>
705  <x:anchor-alias value="HTTP-name"/>
706<t>
707   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
708   versions of the protocol. This specification defines version "1.1".
709   The protocol version as a whole indicates the sender's conformance
710   with the set of requirements laid out in that version's corresponding
711   specification of HTTP.
712</t>
713<t>
714   The version of an HTTP message is indicated by an HTTP-version field
715   in the first line of the message. HTTP-version is case-sensitive.
716</t>
717<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/>
718  <x:ref>HTTP-version</x:ref>   = <x:ref>HTTP-name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
719  <x:ref>HTTP-name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
720</artwork></figure>
721<t>
722   The HTTP version number consists of two decimal digits separated by a "."
723   (period or decimal point).  The first digit ("major version") indicates the
724   HTTP messaging syntax, whereas the second digit ("minor version") indicates
725   the highest minor version to which the sender is
726   conformant and able to understand for future communication.  The minor
727   version advertises the sender's communication capabilities even when the
728   sender is only using a backwards-compatible subset of the protocol,
729   thereby letting the recipient know that more advanced features can
730   be used in response (by servers) or in future requests (by clients).
731</t>
732<t>
733   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
734   <xref target="RFC1945"/> or a recipient whose version is unknown,
735   the HTTP/1.1 message is constructed such that it can be interpreted
736   as a valid HTTP/1.0 message if all of the newer features are ignored.
737   This specification places recipient-version requirements on some
738   new features so that a conformant sender will only use compatible
739   features until it has determined, through configuration or the
740   receipt of a message, that the recipient supports HTTP/1.1.
741</t>
742<t>
743   The interpretation of a header field does not change between minor
744   versions of the same major HTTP version, though the default
745   behavior of a recipient in the absence of such a field can change.
746   Unless specified otherwise, header fields defined in HTTP/1.1 are
747   defined for all versions of HTTP/1.x.  In particular, the Host and
748   Connection header fields ought to be implemented by all HTTP/1.x
749   implementations whether or not they advertise conformance with HTTP/1.1.
750</t>
751<t>
752   New header fields can be defined such that, when they are
753   understood by a recipient, they might override or enhance the
754   interpretation of previously defined header fields.  When an
755   implementation receives an unrecognized header field, the recipient
756   &MUST; ignore that header field for local processing regardless of
757   the message's HTTP version.  An unrecognized header field received
758   by a proxy &MUST; be forwarded downstream unless the header field's
759   field-name is listed in the message's Connection header-field
760   (see <xref target="header.connection"/>).
761   These requirements allow HTTP's functionality to be enhanced without
762   requiring prior update of deployed intermediaries.
763</t>
764<t>
765   Intermediaries that process HTTP messages (i.e., all intermediaries
766   other than those acting as tunnels) &MUST; send their own HTTP-version
767   in forwarded messages.  In other words, they &MUST-NOT; blindly
768   forward the first line of an HTTP message without ensuring that the
769   protocol version in that message matches a version to which that
770   intermediary is conformant for both the receiving and
771   sending of messages.  Forwarding an HTTP message without rewriting
772   the HTTP-version might result in communication errors when downstream
773   recipients use the message sender's version to determine what features
774   are safe to use for later communication with that sender.
775</t>
776<t>
777   An HTTP client &SHOULD; send a request version equal to the highest
778   version to which the client is conformant and
779   whose major version is no higher than the highest version supported
780   by the server, if this is known.  An HTTP client &MUST-NOT; send a
781   version to which it is not conformant.
782</t>
783<t>
784   An HTTP client &MAY; send a lower request version if it is known that
785   the server incorrectly implements the HTTP specification, but only
786   after the client has attempted at least one normal request and determined
787   from the response status or header fields (e.g., Server) that the
788   server improperly handles higher request versions.
789</t>
790<t>
791   An HTTP server &SHOULD; send a response version equal to the highest
792   version to which the server is conformant and
793   whose major version is less than or equal to the one received in the
794   request.  An HTTP server &MUST-NOT; send a version to which it is not
795   conformant.  A server &MAY; send a 505 (HTTP
796   Version Not Supported) response if it cannot send a response using the
797   major version used in the client's request.
798</t>
799<t>
800   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
801   if it is known or suspected that the client incorrectly implements the
802   HTTP specification and is incapable of correctly processing later
803   version responses, such as when a client fails to parse the version
804   number correctly or when an intermediary is known to blindly forward
805   the HTTP-version even when it doesn't conform to the given minor
806   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
807   performed unless triggered by specific client attributes, such as when
808   one or more of the request header fields (e.g., User-Agent) uniquely
809   match the values sent by a client known to be in error.
810</t>
811<t>
812   The intention of HTTP's versioning design is that the major number
813   will only be incremented if an incompatible message syntax is
814   introduced, and that the minor number will only be incremented when
815   changes made to the protocol have the effect of adding to the message
816   semantics or implying additional capabilities of the sender.  However,
817   the minor version was not incremented for the changes introduced between
818   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
819   is specifically avoiding any such changes to the protocol.
820</t>
821</section>
822
823<section title="Uniform Resource Identifiers" anchor="uri">
824<iref primary="true" item="resource"/>
825<t>
826   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
827   throughout HTTP as the means for identifying resources. URI references
828   are used to target requests, indicate redirects, and define relationships.
829   HTTP does not limit what a resource might be; it merely defines an interface
830   that can be used to interact with a resource via HTTP. More information on
831   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
832</t>
833  <x:anchor-alias value="URI-reference"/>
834  <x:anchor-alias value="absolute-URI"/>
835  <x:anchor-alias value="relative-part"/>
836  <x:anchor-alias value="authority"/>
837  <x:anchor-alias value="path-abempty"/>
838  <x:anchor-alias value="path-absolute"/>
839  <x:anchor-alias value="port"/>
840  <x:anchor-alias value="query"/>
841  <x:anchor-alias value="uri-host"/>
842  <x:anchor-alias value="partial-URI"/>
843<t>
844   This specification adopts the definitions of "URI-reference",
845   "absolute-URI", "relative-part", "port", "host",
846   "path-abempty", "path-absolute", "query", and "authority" from the
847   URI generic syntax <xref target="RFC3986"/>.
848   In addition, we define a partial-URI rule for protocol elements
849   that allow a relative URI but not a fragment.
850</t>
851<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="URI-reference"/><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"/>
852  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
853  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
854  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
855  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
856  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
857  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
858  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
859  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
860  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
861 
862  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
863</artwork></figure>
864<t>
865   Each protocol element in HTTP that allows a URI reference will indicate
866   in its ABNF production whether the element allows any form of reference
867   (URI-reference), only a URI in absolute form (absolute-URI), only the
868   path and optional query components, or some combination of the above.
869   Unless otherwise indicated, URI references are parsed relative to the
870   effective request URI, which defines the default base URI for references
871   in both the request and its corresponding response.
872</t>
873
874<section title="http URI scheme" anchor="http.uri">
875  <x:anchor-alias value="http-URI"/>
876  <iref item="http URI scheme" primary="true"/>
877  <iref item="URI scheme" subitem="http" primary="true"/>
878<t>
879   The "http" URI scheme is hereby defined for the purpose of minting
880   identifiers according to their association with the hierarchical
881   namespace governed by a potential HTTP origin server listening for
882   TCP connections on a given port.
883</t>
884<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
885  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
886</artwork></figure>
887<t>
888   The HTTP origin server is identified by the generic syntax's
889   <x:ref>authority</x:ref> component, which includes a host identifier
890   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
891   The remainder of the URI, consisting of both the hierarchical path
892   component and optional query component, serves as an identifier for
893   a potential resource within that origin server's name space.
894</t>
895<t>
896   If the host identifier is provided as an IP literal or IPv4 address,
897   then the origin server is any listener on the indicated TCP port at
898   that IP address. If host is a registered name, then that name is
899   considered an indirect identifier and the recipient might use a name
900   resolution service, such as DNS, to find the address of a listener
901   for that host.
902   The host &MUST-NOT; be empty; if an "http" URI is received with an
903   empty host, then it &MUST; be rejected as invalid.
904   If the port subcomponent is empty or not given, then TCP port 80 is
905   assumed (the default reserved port for WWW services).
906</t>
907<t>
908   Regardless of the form of host identifier, access to that host is not
909   implied by the mere presence of its name or address. The host might or might
910   not exist and, even when it does exist, might or might not be running an
911   HTTP server or listening to the indicated port. The "http" URI scheme
912   makes use of the delegated nature of Internet names and addresses to
913   establish a naming authority (whatever entity has the ability to place
914   an HTTP server at that Internet name or address) and allows that
915   authority to determine which names are valid and how they might be used.
916</t>
917<t>
918   When an "http" URI is used within a context that calls for access to the
919   indicated resource, a client &MAY; attempt access by resolving
920   the host to an IP address, establishing a TCP connection to that address
921   on the indicated port, and sending an HTTP request message
922   (<xref target="http.message"/>) containing the URI's identifying data
923   (<xref target="message.routing"/>) to the server.
924   If the server responds to that request with a non-interim HTTP response
925   message, as described in &status-code-reasonphr;, then that response
926   is considered an authoritative answer to the client's request.
927</t>
928<t>
929   Although HTTP is independent of the transport protocol, the "http"
930   scheme is specific to TCP-based services because the name delegation
931   process depends on TCP for establishing authority.
932   An HTTP service based on some other underlying connection protocol
933   would presumably be identified using a different URI scheme, just as
934   the "https" scheme (below) is used for servers that require an SSL/TLS
935   transport layer on a connection. Other protocols might also be used to
936   provide access to "http" identified resources &mdash; it is only the
937   authoritative interface used for mapping the namespace that is
938   specific to TCP.
939</t>
940<t>
941   The URI generic syntax for authority also includes a deprecated
942   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
943   for including user authentication information in the URI.  Some
944   implementations make use of the userinfo component for internal
945   configuration of authentication information, such as within command
946   invocation options, configuration files, or bookmark lists, even
947   though such usage might expose a user identifier or password.
948   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
949   delimiter) when transmitting an "http" URI in a message.  Recipients
950   of HTTP messages that contain a URI reference &SHOULD; parse for the
951   existence of userinfo and treat its presence as an error, likely
952   indicating that the deprecated subcomponent is being used to obscure
953   the authority for the sake of phishing attacks.
954</t>
955</section>
956
957<section title="https URI scheme" anchor="https.uri">
958   <x:anchor-alias value="https-URI"/>
959   <iref item="https URI scheme"/>
960   <iref item="URI scheme" subitem="https"/>
961<t>
962   The "https" URI scheme is hereby defined for the purpose of minting
963   identifiers according to their association with the hierarchical
964   namespace governed by a potential HTTP origin server listening for
965   SSL/TLS-secured connections on a given TCP port.
966</t>
967<t>
968   All of the requirements listed above for the "http" scheme are also
969   requirements for the "https" scheme, except that a default TCP port
970   of 443 is assumed if the port subcomponent is empty or not given,
971   and the TCP connection &MUST; be secured for privacy through the
972   use of strong encryption prior to sending the first HTTP request.
973</t>
974<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
975  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
976</artwork></figure>
977<t>
978   Unlike the "http" scheme, responses to "https" identified requests
979   are never "public" and thus &MUST-NOT; be reused for shared caching.
980   They can, however, be reused in a private cache if the message is
981   cacheable by default in HTTP or specifically indicated as such by
982   the Cache-Control header field (&header-cache-control;).
983</t>
984<t>
985   Resources made available via the "https" scheme have no shared
986   identity with the "http" scheme even if their resource identifiers
987   indicate the same authority (the same host listening to the same
988   TCP port).  They are distinct name spaces and are considered to be
989   distinct origin servers.  However, an extension to HTTP that is
990   defined to apply to entire host domains, such as the Cookie protocol
991   <xref target="RFC6265"/>, can allow information
992   set by one service to impact communication with other services
993   within a matching group of host domains.
994</t>
995<t>
996   The process for authoritative access to an "https" identified
997   resource is defined in <xref target="RFC2818"/>.
998</t>
999</section>
1000
1001<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1002<t>
1003   Since the "http" and "https" schemes conform to the URI generic syntax,
1004   such URIs are normalized and compared according to the algorithm defined
1005   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1006   described above for each scheme.
1007</t>
1008<t>
1009   If the port is equal to the default port for a scheme, the normal
1010   form is to elide the port subcomponent. Likewise, an empty path
1011   component is equivalent to an absolute path of "/", so the normal
1012   form is to provide a path of "/" instead. The scheme and host
1013   are case-insensitive and normally provided in lowercase; all
1014   other components are compared in a case-sensitive manner.
1015   Characters other than those in the "reserved" set are equivalent
1016   to their percent-encoded octets (see <xref target="RFC3986"
1017   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1018</t>
1019<t>
1020   For example, the following three URIs are equivalent:
1021</t>
1022<figure><artwork type="example">
1023   http://example.com:80/~smith/home.html
1024   http://EXAMPLE.com/%7Esmith/home.html
1025   http://EXAMPLE.com:/%7esmith/home.html
1026</artwork></figure>
1027</section>
1028</section>
1029</section>
1030
1031<section title="Message Format" anchor="http.message">
1032<x:anchor-alias value="generic-message"/>
1033<x:anchor-alias value="message.types"/>
1034<x:anchor-alias value="HTTP-message"/>
1035<x:anchor-alias value="start-line"/>
1036<iref item="header section"/>
1037<iref item="headers"/>
1038<iref item="header field"/>
1039<t>
1040   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1041   octets in a format similar to the Internet Message Format
1042   <xref target="RFC5322"/>: zero or more header fields (collectively
1043   referred to as the "headers" or the "header section"), an empty line
1044   indicating the end of the header section, and an optional message body.
1045</t>
1046<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1047  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1048                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1049                    <x:ref>CRLF</x:ref>
1050                    [ <x:ref>message-body</x:ref> ]
1051</artwork></figure>
1052<t>
1053   The normal procedure for parsing an HTTP message is to read the
1054   start-line into a structure, read each header field into a hash
1055   table by field name until the empty line, and then use the parsed
1056   data to determine if a message body is expected.  If a message body
1057   has been indicated, then it is read as a stream until an amount
1058   of octets equal to the message body length is read or the connection
1059   is closed.
1060</t>
1061<t>
1062   Recipients &MUST; parse an HTTP message as a sequence of octets in an
1063   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1064   Parsing an HTTP message as a stream of Unicode characters, without regard
1065   for the specific encoding, creates security vulnerabilities due to the
1066   varying ways that string processing libraries handle invalid multibyte
1067   character sequences that contain the octet LF (%x0A).  String-based
1068   parsers can only be safely used within protocol elements after the element
1069   has been extracted from the message, such as within a header field-value
1070   after message parsing has delineated the individual fields.
1071</t>
1072<t>
1073   An HTTP message can be parsed as a stream for incremental processing or
1074   forwarding downstream.  However, recipients cannot rely on incremental
1075   delivery of partial messages, since some implementations will buffer or
1076   delay message forwarding for the sake of network efficiency, security
1077   checks, or payload transformations.
1078</t>
1079
1080<section title="Start Line" anchor="start.line">
1081  <x:anchor-alias value="Start-Line"/>
1082<t>
1083   An HTTP message can either be a request from client to server or a
1084   response from server to client.  Syntactically, the two types of message
1085   differ only in the start-line, which is either a request-line (for requests)
1086   or a status-line (for responses), and in the algorithm for determining
1087   the length of the message body (<xref target="message.body"/>).
1088   In theory, a client could receive requests and a server could receive
1089   responses, distinguishing them by their different start-line formats,
1090   but in practice servers are implemented to only expect a request
1091   (a response is interpreted as an unknown or invalid request method)
1092   and clients are implemented to only expect a response.
1093</t>
1094<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1095  <x:ref>start-line</x:ref>      = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1096</artwork></figure>
1097<t>
1098</t>
1099<t>
1100   Implementations &MUST-NOT; send whitespace between the start-line and
1101   the first header field. The presence of such whitespace in a request
1102   might be an attempt to trick a server into ignoring that field or
1103   processing the line after it as a new request, either of which might
1104   result in a security vulnerability if other implementations within
1105   the request chain interpret the same message differently.
1106   Likewise, the presence of such whitespace in a response might be
1107   ignored by some clients or cause others to cease parsing.
1108</t>
1109
1110<section title="Request Line" anchor="request.line">
1111  <x:anchor-alias value="Request"/>
1112  <x:anchor-alias value="request-line"/>
1113<t>
1114   A request-line begins with a method token, followed by a single
1115   space (SP), the request-target, another single space (SP), the
1116   protocol version, and ending with CRLF.
1117</t>
1118<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1119  <x:ref>request-line</x:ref>   = <x:ref>method</x:ref> <x:ref>SP</x:ref> <x:ref>request-target</x:ref> <x:ref>SP</x:ref> <x:ref>HTTP-version</x:ref> <x:ref>CRLF</x:ref>
1120</artwork></figure>
1121
1122<section title="Method" anchor="method">
1123  <x:anchor-alias value="method"/>
1124<t>
1125   The method token indicates the request method to be performed on the
1126   target resource. The request method is case-sensitive.
1127</t>
1128<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1129  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1130</artwork></figure>
1131<t>
1132   The methods defined by this specification can be found in
1133   &method;, along with information regarding the HTTP method registry
1134   and considerations for defining new methods.
1135</t>
1136</section>
1137
1138<section title="request-target" anchor="request-target">
1139  <x:anchor-alias value="request-target"/>
1140<t>
1141   The request-target identifies the target resource upon which to apply
1142   the request.  The four options for request-target are described in
1143   <xref target="request-target-types"/>.
1144</t>
1145<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1146  <x:ref>request-target</x:ref> = "*"
1147                 / <x:ref>absolute-URI</x:ref>
1148                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1149                 / <x:ref>authority</x:ref>
1150</artwork></figure>
1151<t>
1152   HTTP does not place a pre-defined limit on the length of a request-target.
1153   A server &MUST; be prepared to receive URIs of unbounded length and
1154   respond with the 414 (URI Too Long) status code if the received
1155   request-target would be longer than the server wishes to handle
1156   (see &status-414;).
1157</t>
1158<t>
1159   Various ad-hoc limitations on request-target length are found in practice.
1160   It is &RECOMMENDED; that all HTTP senders and recipients support
1161   request-target lengths of 8000 or more octets.
1162</t>
1163<x:note>
1164  <t>
1165    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1166    are not part of the request-target and thus will not be transmitted
1167    in an HTTP request.
1168  </t>
1169</x:note>
1170</section>
1171</section>
1172
1173<section title="Response Status Line" anchor="status.line">
1174  <x:anchor-alias value="response"/>
1175  <x:anchor-alias value="status-line"/>
1176<t>
1177   The first line of a response message is the status-line, consisting
1178   of the protocol version, a space (SP), the status code, another space,
1179   a possibly-empty textual phrase describing the status code, and
1180   ending with CRLF.
1181</t>
1182<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1183  <x:ref>status-line</x:ref> = <x:ref>HTTP-version</x:ref> <x:ref>SP</x:ref> <x:ref>status-code</x:ref> <x:ref>SP</x:ref> <x:ref>reason-phrase</x:ref> <x:ref>CRLF</x:ref>
1184</artwork></figure>
1185
1186<section title="Status Code" anchor="status.code">
1187  <x:anchor-alias value="status-code"/>
1188<t>
1189   The status-code element is a 3-digit integer result code of the attempt to
1190   understand and satisfy the request. See &status-code-reasonphr; for
1191   further information, such as the list of status codes defined by this
1192   specification, the IANA registry, and considerations for new status codes.
1193</t>
1194<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1195  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1196</artwork></figure>
1197</section>
1198
1199<section title="Reason Phrase" anchor="reason.phrase">
1200  <x:anchor-alias value="reason-phrase"/>
1201<t>   
1202   The reason-phrase element exists for the sole purpose of providing a
1203   textual description associated with the numeric status code, mostly
1204   out of deference to earlier Internet application protocols that were more
1205   frequently used with interactive text clients. A client &SHOULD; ignore
1206   the reason-phrase content.
1207</t>
1208<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1209  <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> )
1210</artwork></figure>
1211</section>
1212</section>
1213</section>
1214
1215<section title="Header Fields" anchor="header.fields">
1216  <x:anchor-alias value="header-field"/>
1217  <x:anchor-alias value="field-content"/>
1218  <x:anchor-alias value="field-name"/>
1219  <x:anchor-alias value="field-value"/>
1220  <x:anchor-alias value="obs-fold"/>
1221<t>
1222   Each HTTP header field consists of a case-insensitive field name
1223   followed by a colon (":"), optional whitespace, and the field value.
1224</t>
1225<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"/>
1226  <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>
1227  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1228  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1229  <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> )
1230  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1231                 ; obsolete line folding
1232                 ; see <xref target="field.parsing"/>
1233</artwork></figure>
1234<t>
1235   The field-name token labels the corresponding field-value as having the
1236   semantics defined by that header field.  For example, the Date header field
1237   is defined in &header-date; as containing the origination
1238   timestamp for the message in which it appears.
1239</t>
1240<t>
1241   HTTP header fields are fully extensible: there is no limit on the
1242   introduction of new field names, each presumably defining new semantics,
1243   or on the number of header fields used in a given message.  Existing
1244   fields are defined in each part of this specification and in many other
1245   specifications outside the standards process.
1246   New header fields can be introduced without changing the protocol version
1247   if their defined semantics allow them to be safely ignored by recipients
1248   that do not recognize them.
1249</t>
1250<t>
1251   New HTTP header fields &SHOULD; be registered with IANA according
1252   to the procedures in &cons-new-header-fields;.
1253   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1254   field-name is listed in the Connection header field
1255   (<xref target="header.connection"/>) or the proxy is specifically
1256   configured to block or otherwise transform such fields.
1257   Unrecognized header fields &SHOULD; be ignored by other recipients.
1258</t>
1259<t>
1260   The order in which header fields with differing field names are
1261   received is not significant. However, it is "good practice" to send
1262   header fields that contain control data first, such as Host on
1263   requests and Date on responses, so that implementations can decide
1264   when not to handle a message as early as possible.  A server &MUST;
1265   wait until the entire header section is received before interpreting
1266   a request message, since later header fields might include conditionals,
1267   authentication credentials, or deliberately misleading duplicate
1268   header fields that would impact request processing.
1269</t>
1270<t>
1271   Multiple header fields with the same field name &MUST-NOT; be
1272   sent in a message unless the entire field value for that
1273   header field is defined as a comma-separated list [i.e., #(values)].
1274   Multiple header fields with the same field name can be combined into
1275   one "field-name: field-value" pair, without changing the semantics of the
1276   message, by appending each subsequent field value to the combined
1277   field value in order, separated by a comma. The order in which
1278   header fields with the same field name are received is therefore
1279   significant to the interpretation of the combined field value;
1280   a proxy &MUST-NOT; change the order of these field values when
1281   forwarding a message.
1282</t>
1283<x:note>
1284  <t>
1285   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1286   practice can occur multiple times, but does not use the list syntax, and
1287   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1288   for details.) Also note that the Set-Cookie2 header field specified in
1289   <xref target="RFC2965"/> does not share this problem.
1290  </t>
1291</x:note>
1292
1293<section title="Whitespace" anchor="whitespace">
1294<t anchor="rule.LWS">
1295   This specification uses three rules to denote the use of linear
1296   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1297   BWS ("bad" whitespace).
1298</t>
1299<t anchor="rule.OWS">
1300   The OWS rule is used where zero or more linear whitespace octets might
1301   appear. OWS &SHOULD; either not be produced or be produced as a single
1302   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1303   be replaced with a single SP or transformed to all SP octets (each
1304   octet other than SP replaced with SP) before interpreting the field value
1305   or forwarding the message downstream.
1306</t>
1307<t anchor="rule.RWS">
1308   RWS is used when at least one linear whitespace octet is required to
1309   separate field tokens. RWS &SHOULD; be produced as a single SP.
1310   Multiple RWS octets that occur within field-content &SHOULD; either
1311   be replaced with a single SP or transformed to all SP octets before
1312   interpreting the field value or forwarding the message downstream.
1313</t>
1314<t anchor="rule.BWS">
1315   BWS is used where the grammar allows optional whitespace for historical
1316   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
1317   recipients &MUST; accept such bad optional whitespace and remove it before
1318   interpreting the field value or forwarding the message downstream.
1319</t>
1320<t anchor="rule.whitespace">
1321  <x:anchor-alias value="BWS"/>
1322  <x:anchor-alias value="OWS"/>
1323  <x:anchor-alias value="RWS"/>
1324</t>
1325<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"/>
1326  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1327                 ; "optional" whitespace
1328  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1329                 ; "required" whitespace
1330  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1331                 ; "bad" whitespace
1332</artwork></figure>
1333</section>
1334
1335<section title="Field Parsing" anchor="field.parsing">
1336<t>
1337   No whitespace is allowed between the header field-name and colon.
1338   In the past, differences in the handling of such whitespace have led to
1339   security vulnerabilities in request routing and response handling.
1340   Any received request message that contains whitespace between a header
1341   field-name and colon &MUST; be rejected with a response code of 400
1342   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1343   message before forwarding the message downstream.
1344</t>
1345<t>
1346   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1347   preferred. The field value does not include any leading or trailing white
1348   space: OWS occurring before the first non-whitespace octet of the
1349   field value or after the last non-whitespace octet of the field value
1350   is ignored and &SHOULD; be removed before further processing (as this does
1351   not change the meaning of the header field).
1352</t>
1353<t>
1354   Historically, HTTP header field values could be extended over multiple
1355   lines by preceding each extra line with at least one space or horizontal
1356   tab (obs-fold). This specification deprecates such line
1357   folding except within the message/http media type
1358   (<xref target="internet.media.type.message.http"/>).
1359   HTTP senders &MUST-NOT; produce messages that include line folding
1360   (i.e., that contain any field-value that matches the obs-fold rule) unless
1361   the message is intended for packaging within the message/http media type.
1362   HTTP recipients &SHOULD; accept line folding and replace any embedded
1363   obs-fold whitespace with either a single SP or a matching number of SP
1364   octets (to avoid buffer copying) prior to interpreting the field value or
1365   forwarding the message downstream.
1366</t>
1367<t>
1368   Historically, HTTP has allowed field content with text in the ISO-8859-1
1369   <xref target="ISO-8859-1"/> character encoding and supported other
1370   character sets only through use of <xref target="RFC2047"/> encoding.
1371   In practice, most HTTP header field values use only a subset of the
1372   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1373   header fields &SHOULD; limit their field values to US-ASCII octets.
1374   Recipients &SHOULD; treat other (obs-text) octets in field content as
1375   opaque data.
1376</t>
1377</section>
1378
1379<section title="Field Length" anchor="field.length">
1380<t>
1381   HTTP does not place a pre-defined limit on the length of header fields,
1382   either in isolation or as a set. A server &MUST; be prepared to receive
1383   request header fields of unbounded length and respond with a 4xx status
1384   code if the received header field(s) would be longer than the server wishes
1385   to handle.
1386</t>
1387<t>
1388   A client that receives response headers that are longer than it wishes to
1389   handle can only treat it as a server error.
1390</t>
1391<t>
1392   Various ad-hoc limitations on header length are found in practice. It is
1393   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1394   combined header fields have 4000 or more octets.
1395</t>
1396</section>
1397
1398<section title="Field value components" anchor="field.components">
1399<t anchor="rule.token.separators">
1400  <x:anchor-alias value="tchar"/>
1401  <x:anchor-alias value="token"/>
1402  <x:anchor-alias value="special"/>
1403  <x:anchor-alias value="word"/>
1404   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1405   separated by whitespace or special characters. These special characters
1406   &MUST; be in a quoted string to be used within a parameter value (as defined
1407   in <xref target="transfer.codings"/>).
1408</t>
1409<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"/>
1410  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1411
1412  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1413<!--
1414  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1415 -->
1416  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1417                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1418                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1419                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1420
1421  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1422                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1423                 / "]" / "?" / "=" / "{" / "}"
1424</artwork></figure>
1425<t anchor="rule.quoted-string">
1426  <x:anchor-alias value="quoted-string"/>
1427  <x:anchor-alias value="qdtext"/>
1428  <x:anchor-alias value="obs-text"/>
1429   A string of text is parsed as a single word if it is quoted using
1430   double-quote marks.
1431</t>
1432<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"/>
1433  <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>
1434  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1435  <x:ref>obs-text</x:ref>       = %x80-FF
1436</artwork></figure>
1437<t anchor="rule.quoted-pair">
1438  <x:anchor-alias value="quoted-pair"/>
1439   The backslash octet ("\") can be used as a single-octet
1440   quoting mechanism within quoted-string constructs:
1441</t>
1442<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1443  <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> )
1444</artwork></figure>
1445<t>
1446   Recipients that process the value of the quoted-string &MUST; handle a
1447   quoted-pair as if it were replaced by the octet following the backslash.
1448</t>
1449<t>
1450   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1451   escaping (i.e., other than DQUOTE and the backslash octet).
1452</t>
1453<t anchor="rule.comment">
1454  <x:anchor-alias value="comment"/>
1455  <x:anchor-alias value="ctext"/>
1456   Comments can be included in some HTTP header fields by surrounding
1457   the comment text with parentheses. Comments are only allowed in
1458   fields containing "comment" as part of their field value definition.
1459</t>
1460<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1461  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1462  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1463</artwork></figure>
1464<t anchor="rule.quoted-cpair">
1465  <x:anchor-alias value="quoted-cpair"/>
1466   The backslash octet ("\") can be used as a single-octet
1467   quoting mechanism within comment constructs:
1468</t>
1469<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1470  <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> )
1471</artwork></figure>
1472<t>
1473   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1474   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1475</t>
1476</section>
1477
1478<section title="ABNF list extension: #rule" anchor="abnf.extension">
1479<t>
1480  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
1481  improve readability in the definitions of some header field values.
1482</t>
1483<t>
1484  A construct "#" is defined, similar to "*", for defining comma-delimited
1485  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
1486  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
1487  comma (",") and optional whitespace (OWS).   
1488</t>
1489<figure><preamble>
1490  Thus,
1491</preamble><artwork type="example">
1492  1#element =&gt; element *( OWS "," OWS element )
1493</artwork></figure>
1494<figure><preamble>
1495  and:
1496</preamble><artwork type="example">
1497  #element =&gt; [ 1#element ]
1498</artwork></figure>
1499<figure><preamble>
1500  and for n &gt;= 1 and m &gt; 1:
1501</preamble><artwork type="example">
1502  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
1503</artwork></figure>
1504<t>
1505  For compatibility with legacy list rules, recipients &SHOULD; accept empty
1506  list elements. In other words, consumers would follow the list productions:
1507</t>
1508<figure><artwork type="example">
1509  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
1510 
1511  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
1512</artwork></figure>
1513<t>
1514  Note that empty elements do not contribute to the count of elements present,
1515  though.
1516</t>
1517<t>
1518  For example, given these ABNF productions:
1519</t>
1520<figure><artwork type="example">
1521  example-list      = 1#example-list-elmt
1522  example-list-elmt = token ; see <xref target="field.components"/> 
1523</artwork></figure>
1524<t>
1525  Then these are valid values for example-list (not including the double
1526  quotes, which are present for delimitation only):
1527</t>
1528<figure><artwork type="example">
1529  "foo,bar"
1530  "foo ,bar,"
1531  "foo , ,bar,charlie   "
1532</artwork></figure>
1533<t>
1534  But these values would be invalid, as at least one non-empty element is
1535  required:
1536</t>
1537<figure><artwork type="example">
1538  ""
1539  ","
1540  ",   ,"
1541</artwork></figure>
1542<t>
1543  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
1544  expanded as explained above.
1545</t>
1546</section>
1547</section>
1548
1549<section title="Message Body" anchor="message.body">
1550  <x:anchor-alias value="message-body"/>
1551<t>
1552   The message body (if any) of an HTTP message is used to carry the
1553   payload body of that request or response.  The message body is
1554   identical to the payload body unless a transfer coding has been
1555   applied, as described in <xref target="header.transfer-encoding"/>.
1556</t>
1557<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1558  <x:ref>message-body</x:ref> = *OCTET
1559</artwork></figure>
1560<t>
1561   The rules for when a message body is allowed in a message differ for
1562   requests and responses.
1563</t>
1564<t>
1565   The presence of a message body in a request is signaled by a
1566   a Content-Length or Transfer-Encoding header field.
1567   Request message framing is independent of method semantics,
1568   even if the method does not define any use for a message body.
1569</t>
1570<t>
1571   The presence of a message body in a response depends on both
1572   the request method to which it is responding and the response
1573   status code (<xref target="status.code"/>).
1574   Responses to the HEAD request method never include a message body
1575   because the associated response header fields (e.g., Transfer-Encoding,
1576   Content-Length, etc.) only indicate what their values would have been
1577   if the request method had been GET.
1578   All 1xx (Informational), 204 (No Content), and 304 (Not Modified)
1579   responses &MUST-NOT; include a message body.
1580   All other responses do include a message body, although the body
1581   &MAY; be of zero length.
1582</t>
1583
1584<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1585  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1586  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
1587  <x:anchor-alias value="Transfer-Encoding"/>
1588<t>
1589   When one or more transfer codings are applied to a payload body in order
1590   to form the message body, a Transfer-Encoding header field &MUST; be sent
1591   in the message and &MUST; contain the list of corresponding
1592   transfer-coding names in the same order that they were applied.
1593   Transfer codings are defined in <xref target="transfer.codings"/>.
1594</t>
1595<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1596  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1597</artwork></figure>
1598<t>
1599   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1600   MIME, which was designed to enable safe transport of binary data over a
1601   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1602   However, safe transport has a different focus for an 8bit-clean transfer
1603   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1604   accurately delimit a dynamically generated payload and to distinguish
1605   payload encodings that are only applied for transport efficiency or
1606   security from those that are characteristics of the target resource.
1607</t>
1608<t>
1609   The "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1610   &MUST; be implemented by all HTTP/1.1 recipients because it plays a
1611   crucial role in delimiting messages when the payload body size is not
1612   known in advance.
1613   When the "chunked" transfer-coding is used, it &MUST; be the last
1614   transfer-coding applied to form the message body and &MUST-NOT;
1615   be applied more than once in a message body.
1616   If any transfer-coding is applied to a request payload body,
1617   the final transfer-coding applied &MUST; be "chunked".
1618   If any transfer-coding is applied to a response payload body, then either
1619   the final transfer-coding applied &MUST; be "chunked" or
1620   the message &MUST; be terminated by closing the connection.
1621</t>
1622<figure><preamble>
1623   For example,
1624</preamble><artwork type="example">
1625  Transfer-Encoding: gzip, chunked
1626</artwork><postamble>
1627   indicates that the payload body has been compressed using the gzip
1628   coding and then chunked using the chunked coding while forming the
1629   message body.
1630</postamble></figure>
1631<t>
1632   If more than one Transfer-Encoding header field is present in a message,
1633   the multiple field-values &MUST; be combined into one field-value,
1634   according to the algorithm defined in <xref target="header.fields"/>,
1635   before determining the message body length.
1636</t>
1637<t>
1638   Unlike Content-Encoding (&content-codings;), Transfer-Encoding is a
1639   property of the message, not of the payload, and thus &MAY; be added or
1640   removed by any implementation along the request/response chain.
1641   Additional information about the encoding parameters &MAY; be provided
1642   by other header fields not defined by this specification.
1643</t>
1644<t>
1645   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1646   304 response to a GET request, neither of which includes a message body,
1647   to indicate that the origin server would have applied a transfer coding
1648   to the message body if the request had been an unconditional GET.
1649   This indication is not required, however, because any recipient on
1650   the response chain (including the origin server) can remove transfer
1651   codings when they are not needed.
1652</t>
1653<t>
1654   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1655   implementations advertising only HTTP/1.0 support will not understand
1656   how to process a transfer-encoded payload.
1657   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1658   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1659   might be in the form of specific user configuration or by remembering the
1660   version of a prior received response.
1661   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1662   the corresponding request indicates HTTP/1.1 (or later).
1663</t>
1664<t>
1665   A server that receives a request message with a transfer-coding it does
1666   not understand &SHOULD; respond with 501 (Not Implemented) and then
1667   close the connection.
1668</t>
1669</section>
1670
1671<section title="Content-Length" anchor="header.content-length">
1672  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1673  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
1674  <x:anchor-alias value="Content-Length"/>
1675<t>
1676   When a message does not have a Transfer-Encoding header field and the
1677   payload body length can be determined prior to being transferred, a
1678   Content-Length header field &SHOULD; be sent to indicate the length of the
1679   payload body that is either present as the message body, for requests
1680   and non-HEAD responses other than 304, or would have been present had
1681   the request been an unconditional GET.  The length is expressed as a
1682   decimal number of octets.
1683</t>
1684<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1685  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1686</artwork></figure>
1687<t>
1688   An example is
1689</t>
1690<figure><artwork type="example">
1691  Content-Length: 3495
1692</artwork></figure>
1693<t>
1694   In the case of a response to a HEAD request, Content-Length indicates
1695   the size of the payload body (not including any potential transfer-coding)
1696   that would have been sent had the request been a GET.
1697   In the case of a 304 (Not Modified) response to a GET request,
1698   Content-Length indicates the size of the payload body (not including
1699   any potential transfer-coding) that would have been sent in a 200 (OK)
1700   response.
1701</t>
1702<t>
1703   Any Content-Length field value greater than or equal to zero is valid.
1704   Since there is no predefined limit to the length of an HTTP payload,
1705   recipients &SHOULD; anticipate potentially large decimal numerals and
1706   prevent parsing errors due to integer conversion overflows
1707   (<xref target="attack.protocol.element.size.overflows"/>).
1708</t>
1709<t>
1710   If a message is received that has multiple Content-Length header fields
1711   (<xref target="header.content-length"/>) with field-values consisting
1712   of the same decimal value, or a single Content-Length header field with
1713   a field value containing a list of identical decimal values (e.g.,
1714   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1715   header fields have been generated or combined by an upstream message
1716   processor, then the recipient &MUST; either reject the message as invalid
1717   or replace the duplicated field-values with a single valid Content-Length
1718   field containing that decimal value prior to determining the message body
1719   length.
1720</t>
1721<t>
1722   HTTP's use of Content-Length is significantly different from how it is
1723   used in MIME, where it is an optional field used only within the
1724   "message/external-body" media-type.
1725</t>
1726</section>
1727
1728<section title="Message Body Length" anchor="message.body.length">
1729<t>
1730   The length of a message body is determined by one of the following
1731   (in order of precedence):
1732</t>
1733<t>
1734  <list style="numbers">
1735    <x:lt><t>
1736     Any response to a HEAD request and any response with a status
1737     code of 100-199, 204, or 304 is always terminated by the first
1738     empty line after the header fields, regardless of the header
1739     fields present in the message, and thus cannot contain a message body.
1740    </t></x:lt>
1741    <x:lt><t>
1742     If a Transfer-Encoding header field is present
1743     and the "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1744     is the final encoding, the message body length is determined by reading
1745     and decoding the chunked data until the transfer-coding indicates the
1746     data is complete.
1747    </t>
1748    <t>
1749     If a Transfer-Encoding header field is present in a response and the
1750     "chunked" transfer-coding is not the final encoding, the message body
1751     length is determined by reading the connection until it is closed by
1752     the server.
1753     If a Transfer-Encoding header field is present in a request and the
1754     "chunked" transfer-coding is not the final encoding, the message body
1755     length cannot be determined reliably; the server &MUST; respond with
1756     the 400 (Bad Request) status code and then close the connection.
1757    </t>
1758    <t>
1759     If a message is received with both a Transfer-Encoding header field
1760     and a Content-Length header field, the Transfer-Encoding overrides
1761     the Content-Length.
1762     Such a message might indicate an attempt to perform request or response
1763     smuggling (bypass of security-related checks on message routing or content)
1764     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1765     be removed, prior to forwarding the message downstream, or replaced with
1766     the real message body length after the transfer-coding is decoded.
1767    </t></x:lt>
1768    <x:lt><t>
1769     If a message is received without Transfer-Encoding and with either
1770     multiple Content-Length header fields having differing field-values or
1771     a single Content-Length header field having an invalid value, then the
1772     message framing is invalid and &MUST; be treated as an error to
1773     prevent request or response smuggling.
1774     If this is a request message, the server &MUST; respond with
1775     a 400 (Bad Request) status code and then close the connection.
1776     If this is a response message received by a proxy, the proxy
1777     &MUST; discard the received response, send a 502 (Bad Gateway)
1778     status code as its downstream response, and then close the connection.
1779     If this is a response message received by a user-agent, it &MUST; be
1780     treated as an error by discarding the message and closing the connection.
1781    </t></x:lt>
1782    <x:lt><t>
1783     If a valid Content-Length header field
1784     is present without Transfer-Encoding, its decimal value defines the
1785     message body length in octets.  If the actual number of octets sent in
1786     the message is less than the indicated Content-Length, the recipient
1787     &MUST; consider the message to be incomplete and treat the connection
1788     as no longer usable.
1789     If the actual number of octets sent in the message is more than the indicated
1790     Content-Length, the recipient &MUST; only process the message body up to the
1791     field value's number of octets; the remainder of the message &MUST; either
1792     be discarded or treated as the next message in a pipeline.  For the sake of
1793     robustness, a user-agent &MAY; attempt to detect and correct such an error
1794     in message framing if it is parsing the response to the last request on
1795     a connection and the connection has been closed by the server.
1796    </t></x:lt>
1797    <x:lt><t>
1798     If this is a request message and none of the above are true, then the
1799     message body length is zero (no message body is present).
1800    </t></x:lt>
1801    <x:lt><t>
1802     Otherwise, this is a response message without a declared message body
1803     length, so the message body length is determined by the number of octets
1804     received prior to the server closing the connection.
1805    </t></x:lt>
1806  </list>
1807</t>
1808<t>
1809   Since there is no way to distinguish a successfully completed,
1810   close-delimited message from a partially-received message interrupted
1811   by network failure, implementations &SHOULD; use encoding or
1812   length-delimited messages whenever possible.  The close-delimiting
1813   feature exists primarily for backwards compatibility with HTTP/1.0.
1814</t>
1815<t>
1816   A server &MAY; reject a request that contains a message body but
1817   not a Content-Length by responding with 411 (Length Required).
1818</t>
1819<t>
1820   Unless a transfer-coding other than "chunked" has been applied,
1821   a client that sends a request containing a message body &SHOULD;
1822   use a valid Content-Length header field if the message body length
1823   is known in advance, rather than the "chunked" encoding, since some
1824   existing services respond to "chunked" with a 411 (Length Required)
1825   status code even though they understand the chunked encoding.  This
1826   is typically because such services are implemented via a gateway that
1827   requires a content-length in advance of being called and the server
1828   is unable or unwilling to buffer the entire request before processing.
1829</t>
1830<t>
1831   A client that sends a request containing a message body &MUST; include a
1832   valid Content-Length header field if it does not know the server will
1833   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1834   of specific user configuration or by remembering the version of a prior
1835   received response.
1836</t>
1837</section>
1838</section>
1839
1840<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1841<t>
1842   Request messages that are prematurely terminated, possibly due to a
1843   cancelled connection or a server-imposed time-out exception, &MUST;
1844   result in closure of the connection; sending an HTTP/1.1 error response
1845   prior to closing the connection is &OPTIONAL;.
1846</t>
1847<t>
1848   Response messages that are prematurely terminated, usually by closure
1849   of the connection prior to receiving the expected number of octets or by
1850   failure to decode a transfer-encoded message body, &MUST; be recorded
1851   as incomplete.  A response that terminates in the middle of the header
1852   block (before the empty line is received) cannot be assumed to convey the
1853   full semantics of the response and &MUST; be treated as an error.
1854</t>
1855<t>
1856   A message body that uses the chunked transfer encoding is
1857   incomplete if the zero-sized chunk that terminates the encoding has not
1858   been received.  A message that uses a valid Content-Length is incomplete
1859   if the size of the message body received (in octets) is less than the
1860   value given by Content-Length.  A response that has neither chunked
1861   transfer encoding nor Content-Length is terminated by closure of the
1862   connection, and thus is considered complete regardless of the number of
1863   message body octets received, provided that the header block was received
1864   intact.
1865</t>
1866<t>
1867   A user agent &MUST-NOT; render an incomplete response message body as if
1868   it were complete (i.e., some indication must be given to the user that an
1869   error occurred).  Cache requirements for incomplete responses are defined
1870   in &cache-incomplete;.
1871</t>
1872<t>
1873   A server &MUST; read the entire request message body or close
1874   the connection after sending its response, since otherwise the
1875   remaining data on a persistent connection would be misinterpreted
1876   as the next request.  Likewise,
1877   a client &MUST; read the entire response message body if it intends
1878   to reuse the same connection for a subsequent request.  Pipelining
1879   multiple requests on a connection is described in <xref target="pipelining"/>.
1880</t>
1881</section>
1882
1883<section title="Message Parsing Robustness" anchor="message.robustness">
1884<t>
1885   Older HTTP/1.0 client implementations might send an extra CRLF
1886   after a POST request as a lame workaround for some early server
1887   applications that failed to read message body content that was
1888   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1889   preface or follow a request with an extra CRLF.  If terminating
1890   the request message body with a line-ending is desired, then the
1891   client &MUST; include the terminating CRLF octets as part of the
1892   message body length.
1893</t>
1894<t>
1895   In the interest of robustness, servers &SHOULD; ignore at least one
1896   empty line received where a request-line is expected. In other words, if
1897   the server is reading the protocol stream at the beginning of a
1898   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1899   Likewise, although the line terminator for the start-line and header
1900   fields is the sequence CRLF, we recommend that recipients recognize a
1901   single LF as a line terminator and ignore any CR.
1902</t>
1903<t>
1904   When a server listening only for HTTP request messages, or processing
1905   what appears from the start-line to be an HTTP request message,
1906   receives a sequence of octets that does not match the HTTP-message
1907   grammar aside from the robustness exceptions listed above, the
1908   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1909</t>
1910</section>
1911</section>
1912
1913<section title="Message Routing" anchor="message.routing">
1914<t>
1915   In most cases, the user agent is provided a URI reference
1916   from which it determines an absolute URI for identifying the target
1917   resource.  When a request to the resource is initiated, all or part
1918   of that URI is used to construct the HTTP request-target.
1919</t>
1920
1921<section title="Types of Request Target" anchor="request-target-types">
1922<t>
1923   The proper format choice of the four options available to request-target
1924   depends on the method being requested and if the request is being made to
1925   a proxy.
1926</t>   
1927<t anchor="origin-form"><iref item="origin form (of request-target)"/>
1928   The most common form of request-target is that used when making
1929   a request to an origin server ("origin form") to access a resource
1930   identified by an "http" (<xref target="http.uri"/>) or
1931   "https" (<xref target="https.uri"/>) URI.
1932   In this case, the absolute path and query components of the URI
1933   &MUST; be transmitted as the request-target and the authority component
1934   (excluding any userinfo) &MUST; be transmitted in a Host header field.
1935   For example, a client wishing to retrieve a representation of the resource
1936   identified as
1937</t>
1938<figure><artwork x:indent-with="  ">
1939http://www.example.org/where?q=now
1940</artwork></figure>
1941<t>
1942   directly from the origin server would open (or reuse) a TCP connection
1943   to port 80 of the host "www.example.org" and send the lines:
1944</t>
1945<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1946GET /where?q=now HTTP/1.1
1947Host: www.example.org
1948</artwork></figure>
1949<t>
1950   followed by the remainder of the request. Note that the origin form
1951   of request-target always starts with an absolute path. If the target
1952   resource's URI path is empty, then an absolute path of "/" &MUST; be
1953   provided in the request-target.
1954</t>
1955<t>
1956   If the request-target is percent-encoded
1957   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1958   &MUST; decode the request-target in order to
1959   properly interpret the request. Servers &SHOULD; respond to invalid
1960   request-targets with an appropriate status code.
1961</t>
1962<t anchor="absolute-URI-form"><iref item="absolute-URI form (of request-target)"/>
1963   The "absolute-URI" form of request-target is &REQUIRED; when the request
1964   is being made to a proxy.  The proxy is requested to either forward the
1965   request or service it from a valid cache, and then return the response.
1966   Note that the proxy &MAY; forward the request on to another proxy or
1967   directly to the server specified by the absolute-URI.
1968   In order to avoid request loops, a proxy that forwards requests to other
1969   proxies &MUST; be able to recognize and exclude all of its own server
1970   names, including any aliases, local variations, or literal IP addresses.
1971   An example request-line would be:
1972</t>
1973<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1974GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1975</artwork></figure>
1976<t>
1977   To allow for transition to absolute-URIs in all requests in future
1978   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1979   form in requests, even though HTTP/1.1 clients will only generate
1980   them in requests to proxies.
1981</t>
1982<t>
1983   If a proxy receives a host name that is not a fully qualified domain
1984   name, it &MAY; add its domain to the host name it received. If a proxy
1985   receives a fully qualified domain name, the proxy &MUST-NOT; change
1986   the host name.
1987</t>
1988<t anchor="authority-form"><iref item="authority form (of request-target)"/>
1989   The "authority form" of request-target, which &MUST-NOT; be used
1990   with any request method other than CONNECT, is used to establish a
1991   tunnel through one or more proxies (&CONNECT;).  For example,
1992</t>
1993<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1994CONNECT www.example.com:80 HTTP/1.1
1995</artwork></figure>
1996<t anchor="asterix-form"><iref item="asterisk form (of request-target)"/>
1997   The asterisk ("*") form of request-target, which &MUST-NOT; be used
1998   with any request method other than OPTIONS, means that the request
1999   applies to the server as a whole (the listening process) rather than
2000   to a specific named resource at that server.  For example,
2001</t>
2002<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2003OPTIONS * HTTP/1.1
2004</artwork></figure>
2005<t>
2006   If a proxy receives an OPTIONS request with an absolute-URI form of
2007   request-target in which the URI has an empty path and no query component,
2008   then the last proxy on the request chain &MUST; use a request-target
2009   of "*" when it forwards the request to the indicated origin server.
2010</t>
2011<figure><preamble>   
2012   For example, the request
2013</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2014OPTIONS http://www.example.org:8001 HTTP/1.1
2015</artwork></figure>
2016<figure><preamble>   
2017  would be forwarded by the final proxy as
2018</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2019OPTIONS * HTTP/1.1
2020Host: www.example.org:8001
2021</artwork>
2022<postamble>
2023   after connecting to port 8001 of host "www.example.org".
2024</postamble>
2025</figure>
2026<t>
2027   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" and "query"
2028   parts of the received request-target when forwarding it to the next inbound
2029   server, except as noted above to replace a null path-absolute with "/" or
2030   "*".
2031</t>
2032</section>
2033
2034<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
2035<t>
2036   The exact resource identified by an Internet request is determined by
2037   examining both the request-target and the Host header field.
2038</t>
2039<t>
2040   An origin server that does not allow resources to differ by the
2041   requested host &MAY; ignore the Host header field value when
2042   determining the resource identified by an HTTP/1.1 request. (But see
2043   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
2044   for other requirements on Host support in HTTP/1.1.)
2045</t>
2046<t>
2047   An origin server that does differentiate resources based on the host
2048   requested (sometimes referred to as virtual hosts or vanity host
2049   names) &MUST; use the following rules for determining the requested
2050   resource on an HTTP/1.1 request:
2051  <list style="numbers">
2052    <t>If request-target is an absolute-URI, the host is part of the
2053     request-target. Any Host header field value in the request &MUST; be
2054     ignored.</t>
2055    <t>If the request-target is not an absolute-URI, and the request includes
2056     a Host header field, the host is determined by the Host header
2057     field value.</t>
2058    <t>If the host as determined by rule 1 or 2 is not a valid host on
2059     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
2060  </list>
2061</t>
2062<t>
2063   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
2064   attempt to use heuristics (e.g., examination of the URI path for
2065   something unique to a particular host) in order to determine what
2066   exact resource is being requested.
2067</t>
2068</section>
2069
2070<section title="Effective Request URI" anchor="effective.request.uri">
2071  <iref primary="true" item="effective request URI"/>
2072  <iref primary="true" item="target resource"/>
2073<t>
2074   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
2075   for the target resource; instead, the URI needs to be inferred from the
2076   request-target, Host header field, and connection context. The result of
2077   this process is called the "effective request URI".  The "target resource"
2078   is the resource identified by the effective request URI.
2079</t>
2080<t>
2081   If the request-target is an absolute-URI, then the effective request URI is
2082   the request-target.
2083</t>
2084<t>
2085   If the request-target uses the origin form or the asterisk form,
2086   and the Host header field is present, then the effective request URI is
2087   constructed by concatenating
2088</t>
2089<t>
2090  <list style="symbols">
2091    <t>
2092      the scheme name: "http" if the request was received over an insecure
2093      TCP connection, or "https" when received over a SSL/TLS-secured TCP
2094      connection,
2095    </t>
2096    <t>
2097      the octet sequence "://",
2098    </t>
2099    <t>
2100      the authority component, as specified in the Host header field
2101      (<xref target="header.host"/>), and
2102    </t>
2103    <t>
2104      the request-target obtained from the request-line, unless the
2105      request-target is just the asterisk "*".
2106    </t>
2107  </list>
2108</t>
2109<t>
2110   If the request-target uses the origin form or the asterisk form,
2111   and the Host header field is not present, then the effective request URI is
2112   undefined.
2113</t>
2114<t>
2115   Otherwise, when request-target uses the authority form, the effective
2116   request URI is undefined.
2117</t>
2118<figure>
2119<preamble>
2120   Example 1: the effective request URI for the message
2121</preamble> 
2122<artwork type="example" x:indent-with="  ">
2123GET /pub/WWW/TheProject.html HTTP/1.1
2124Host: www.example.org:8080
2125</artwork>
2126<postamble>
2127  (received over an insecure TCP connection) is "http", plus "://", plus the
2128  authority component "www.example.org:8080", plus the request-target
2129  "/pub/WWW/TheProject.html", thus
2130  "http://www.example.org:8080/pub/WWW/TheProject.html".
2131</postamble>
2132</figure>
2133<figure>
2134<preamble>
2135   Example 2: the effective request URI for the message
2136</preamble> 
2137<artwork type="example" x:indent-with="  ">
2138OPTIONS * HTTP/1.1
2139Host: www.example.org
2140</artwork>
2141<postamble>
2142  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
2143  authority component "www.example.org", thus "https://www.example.org".
2144</postamble>
2145</figure>
2146<t>
2147   Effective request URIs are compared using the rules described in
2148   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
2149   be treated as equivalent to an absolute path of "/".
2150</t> 
2151</section>
2152
2153<section title="Associating a Response to a Request" anchor="associating.response.to.request">
2154<t>
2155   HTTP does not include a request identifier for associating a given
2156   request message with its corresponding one or more response messages.
2157   Hence, it relies on the order of response arrival to correspond exactly
2158   to the order in which requests are made on the same connection.
2159   More than one response message per request only occurs when one or more
2160   informational responses (1xx, see &status-1xx;) precede a final response
2161   to the same request.
2162</t>
2163<t>
2164   A client that uses persistent connections and sends more than one request
2165   per connection &MUST; maintain a list of outstanding requests in the
2166   order sent on that connection and &MUST; associate each received response
2167   message to the highest ordered request that has not yet received a final
2168   (non-1xx) response.
2169</t>
2170</section>
2171</section>
2172
2173<section title="Transfer Codings" anchor="transfer.codings">
2174  <x:anchor-alias value="transfer-coding"/>
2175  <x:anchor-alias value="transfer-extension"/>
2176<t>
2177   Transfer-coding values are used to indicate an encoding
2178   transformation that has been, can be, or might need to be applied to a
2179   payload body in order to ensure "safe transport" through the network.
2180   This differs from a content coding in that the transfer-coding is a
2181   property of the message rather than a property of the representation
2182   that is being transferred.
2183</t>
2184<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2185  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2186                          / "compress" ; <xref target="compress.coding"/>
2187                          / "deflate" ; <xref target="deflate.coding"/>
2188                          / "gzip" ; <xref target="gzip.coding"/>
2189                          / <x:ref>transfer-extension</x:ref>
2190  <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> )
2191</artwork></figure>
2192<t anchor="rule.parameter">
2193  <x:anchor-alias value="attribute"/>
2194  <x:anchor-alias value="transfer-parameter"/>
2195  <x:anchor-alias value="value"/>
2196   Parameters are in the form of attribute/value pairs.
2197</t>
2198<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"/>
2199  <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>
2200  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2201  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2202</artwork></figure>
2203<t>
2204   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2205   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2206   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2207</t>
2208
2209<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2210  <iref item="chunked (Coding Format)"/>
2211  <iref item="Coding Format" subitem="chunked"/>
2212  <x:anchor-alias value="chunk"/>
2213  <x:anchor-alias value="chunked-body"/>
2214  <x:anchor-alias value="chunk-data"/>
2215  <x:anchor-alias value="chunk-ext"/>
2216  <x:anchor-alias value="chunk-ext-name"/>
2217  <x:anchor-alias value="chunk-ext-val"/>
2218  <x:anchor-alias value="chunk-size"/>
2219  <x:anchor-alias value="last-chunk"/>
2220  <x:anchor-alias value="trailer-part"/>
2221  <x:anchor-alias value="quoted-str-nf"/>
2222  <x:anchor-alias value="qdtext-nf"/>
2223<t>
2224   The chunked encoding modifies the body of a message in order to
2225   transfer it as a series of chunks, each with its own size indicator,
2226   followed by an &OPTIONAL; trailer containing header fields. This
2227   allows dynamically produced content to be transferred along with the
2228   information necessary for the recipient to verify that it has
2229   received the full message.
2230</t>
2231<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="chunked-body"/><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"/>
2232  <x:ref>chunked-body</x:ref>   = *<x:ref>chunk</x:ref>
2233                   <x:ref>last-chunk</x:ref>
2234                   <x:ref>trailer-part</x:ref>
2235                   <x:ref>CRLF</x:ref>
2236 
2237  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2238                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2239  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2240  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2241 
2242  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref>
2243                      [ "=" <x:ref>chunk-ext-val</x:ref> ] )
2244  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2245  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2246  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2247  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2248 
2249  <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>
2250                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2251  <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>
2252</artwork></figure>
2253<t>
2254   The chunk-size field is a string of hex digits indicating the size of
2255   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2256   zero, followed by the trailer, which is terminated by an empty line.
2257</t>
2258<t>
2259   The trailer allows the sender to include additional HTTP header
2260   fields at the end of the message. The Trailer header field can be
2261   used to indicate which header fields are included in a trailer (see
2262   <xref target="header.trailer"/>).
2263</t>
2264<t>
2265   A server using chunked transfer-coding in a response &MUST-NOT; use the
2266   trailer for any header fields unless at least one of the following is
2267   true:
2268  <list style="numbers">
2269    <t>the request included a TE header field that indicates "trailers" is
2270     acceptable in the transfer-coding of the  response, as described in
2271     <xref target="header.te"/>; or,</t>
2272     
2273    <t>the trailer fields consist entirely of optional metadata, and the
2274    recipient could use the message (in a manner acceptable to the server where
2275    the field originated) without receiving it. In other words, the server that
2276    generated the header (often but not always the origin server) is willing to
2277    accept the possibility that the trailer fields might be silently discarded
2278    along the path to the client.</t>
2279  </list>
2280</t>
2281<t>
2282   This requirement prevents an interoperability failure when the
2283   message is being received by an HTTP/1.1 (or later) proxy and
2284   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2285   conformance with the protocol would have necessitated a possibly
2286   infinite buffer on the proxy.
2287</t>
2288<t>
2289   A process for decoding the "chunked" transfer-coding
2290   can be represented in pseudo-code as:
2291</t>
2292<figure><artwork type="code">
2293  length := 0
2294  read chunk-size, chunk-ext (if any) and CRLF
2295  while (chunk-size &gt; 0) {
2296     read chunk-data and CRLF
2297     append chunk-data to decoded-body
2298     length := length + chunk-size
2299     read chunk-size and CRLF
2300  }
2301  read header-field
2302  while (header-field not empty) {
2303     append header-field to existing header fields
2304     read header-field
2305  }
2306  Content-Length := length
2307  Remove "chunked" from Transfer-Encoding
2308</artwork></figure>
2309<t>
2310   All HTTP/1.1 applications &MUST; be able to receive and decode the
2311   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2312   they do not understand.
2313</t>
2314<t>
2315   Use of chunk-ext extensions by senders is deprecated; they &SHOULD-NOT; be
2316   sent and definition of new chunk-extensions is discouraged.
2317</t>
2318</section>
2319
2320<section title="Compression Codings" anchor="compression.codings">
2321<t>
2322   The codings defined below can be used to compress the payload of a
2323   message.
2324</t>
2325<x:note><t>
2326   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2327   is not desirable and is discouraged for future encodings. Their
2328   use here is representative of historical practice, not good
2329   design.
2330</t></x:note>
2331<x:note><t>
2332   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2333   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2334   equivalent to "gzip" and "compress" respectively.
2335</t></x:note>
2336
2337<section title="Compress Coding" anchor="compress.coding">
2338<iref item="compress (Coding Format)"/>
2339<iref item="Coding Format" subitem="compress"/>
2340<t>
2341   The "compress" format is produced by the common UNIX file compression
2342   program "compress". This format is an adaptive Lempel-Ziv-Welch
2343   coding (LZW).
2344</t>
2345</section>
2346
2347<section title="Deflate Coding" anchor="deflate.coding">
2348<iref item="deflate (Coding Format)"/>
2349<iref item="Coding Format" subitem="deflate"/>
2350<t>
2351   The "deflate" format is defined as the "deflate" compression mechanism
2352   (described in <xref target="RFC1951"/>) used inside the "zlib"
2353   data format (<xref target="RFC1950"/>).
2354</t>
2355<x:note>
2356  <t>
2357    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2358    compressed data without the zlib wrapper.
2359   </t>
2360</x:note>
2361</section>
2362
2363<section title="Gzip Coding" anchor="gzip.coding">
2364<iref item="gzip (Coding Format)"/>
2365<iref item="Coding Format" subitem="gzip"/>
2366<t>
2367   The "gzip" format is produced by the file compression program
2368   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2369   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2370</t>
2371</section>
2372
2373</section>
2374
2375<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2376<t>
2377   The HTTP Transfer Coding Registry defines the name space for the transfer
2378   coding names.
2379</t>
2380<t>
2381   Registrations &MUST; include the following fields:
2382   <list style="symbols">
2383     <t>Name</t>
2384     <t>Description</t>
2385     <t>Pointer to specification text</t>
2386   </list>
2387</t>
2388<t>
2389   Names of transfer codings &MUST-NOT; overlap with names of content codings
2390   (&content-codings;), unless the encoding transformation is identical (as it
2391   is the case for the compression codings defined in
2392   <xref target="compression.codings"/>).
2393</t>
2394<t>
2395   Values to be added to this name space require a specification
2396   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2397   conform to the purpose of transfer coding defined in this section.
2398</t>
2399<t>
2400   The registry itself is maintained at
2401   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2402</t>
2403</section>
2404
2405<section title="TE" anchor="header.te">
2406  <iref primary="true" item="TE header field" x:for-anchor=""/>
2407  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
2408  <x:anchor-alias value="TE"/>
2409  <x:anchor-alias value="t-codings"/>
2410  <x:anchor-alias value="te-params"/>
2411  <x:anchor-alias value="te-ext"/>
2412<t>
2413   The "TE" header field indicates what extension transfer-codings
2414   the client is willing to accept in the response, and whether or not it is
2415   willing to accept trailer fields in a chunked transfer-coding.
2416</t>
2417<t>
2418   Its value consists of the keyword "trailers" and/or a comma-separated
2419   list of extension transfer-coding names with optional accept
2420   parameters (as described in <xref target="transfer.codings"/>).
2421</t>
2422<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
2423  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2424  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2425  <x:ref>te-params</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>te-ext</x:ref> )
2426  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
2427</artwork></figure>
2428<t>
2429   The presence of the keyword "trailers" indicates that the client is
2430   willing to accept trailer fields in a chunked transfer-coding, as
2431   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
2432   transfer-coding values even though it does not itself represent a
2433   transfer-coding.
2434</t>
2435<t>
2436   Examples of its use are:
2437</t>
2438<figure><artwork type="example">
2439  TE: deflate
2440  TE:
2441  TE: trailers, deflate;q=0.5
2442</artwork></figure>
2443<t>
2444   The TE header field only applies to the immediate connection.
2445   Therefore, the keyword &MUST; be supplied within a Connection header
2446   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2447</t>
2448<t>
2449   A server tests whether a transfer-coding is acceptable, according to
2450   a TE field, using these rules:
2451  <list style="numbers">
2452    <x:lt>
2453      <t>The "chunked" transfer-coding is always acceptable. If the
2454         keyword "trailers" is listed, the client indicates that it is
2455         willing to accept trailer fields in the chunked response on
2456         behalf of itself and any downstream clients. The implication is
2457         that, if given, the client is stating that either all
2458         downstream clients are willing to accept trailer fields in the
2459         forwarded response, or that it will attempt to buffer the
2460         response on behalf of downstream recipients.
2461      </t><t>
2462         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2463         chunked response such that a client can be assured of buffering
2464         the entire response.</t>
2465    </x:lt>
2466    <x:lt>
2467      <t>If the transfer-coding being tested is one of the transfer-codings
2468         listed in the TE field, then it is acceptable unless it
2469         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2470         qvalue of 0 means "not acceptable".)</t>
2471    </x:lt>
2472    <x:lt>
2473      <t>If multiple transfer-codings are acceptable, then the
2474         acceptable transfer-coding with the highest non-zero qvalue is
2475         preferred.  The "chunked" transfer-coding always has a qvalue
2476         of 1.</t>
2477    </x:lt>
2478  </list>
2479</t>
2480<t>
2481   If the TE field-value is empty or if no TE field is present, the only
2482   acceptable transfer-coding is "chunked". A message with no transfer-coding is
2483   always acceptable.
2484</t>
2485
2486<section title="Quality Values" anchor="quality.values">
2487  <x:anchor-alias value="qvalue"/>
2488<t>
2489   Both transfer codings (TE request header field, <xref target="header.te"/>)
2490   and content negotiation (&content.negotiation;) use short "floating point"
2491   numbers to indicate the relative importance ("weight") of various
2492   negotiable parameters.  A weight is normalized to a real number in
2493   the range 0 through 1, where 0 is the minimum and 1 the maximum
2494   value. If a parameter has a quality value of 0, then content with
2495   this parameter is "not acceptable" for the client. HTTP/1.1
2496   applications &MUST-NOT; generate more than three digits after the
2497   decimal point. User configuration of these values &SHOULD; also be
2498   limited in this fashion.
2499</t>
2500<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2501  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2502                 / ( "1" [ "." 0*3("0") ] )
2503</artwork></figure>
2504<x:note>
2505  <t>
2506     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2507     relative degradation in desired quality.
2508  </t>
2509</x:note>
2510</section>
2511</section>
2512
2513<section title="Trailer" anchor="header.trailer">
2514  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
2515  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
2516  <x:anchor-alias value="Trailer"/>
2517<t>
2518   The "Trailer" header field indicates that the given set of
2519   header fields is present in the trailer of a message encoded with
2520   chunked transfer-coding.
2521</t>
2522<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2523  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
2524</artwork></figure>
2525<t>
2526   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2527   message using chunked transfer-coding with a non-empty trailer. Doing
2528   so allows the recipient to know which header fields to expect in the
2529   trailer.
2530</t>
2531<t>
2532   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2533   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
2534   trailer fields in a "chunked" transfer-coding.
2535</t>
2536<t>
2537   Message header fields listed in the Trailer header field &MUST-NOT;
2538   include the following header fields:
2539  <list style="symbols">
2540    <t>Transfer-Encoding</t>
2541    <t>Content-Length</t>
2542    <t>Trailer</t>
2543  </list>
2544</t>
2545</section>
2546</section>
2547
2548<section title="Connections" anchor="connections">
2549
2550<section title="Persistent Connections" anchor="persistent.connections">
2551
2552<section title="Purpose" anchor="persistent.purpose">
2553<t>
2554   Prior to persistent connections, a separate TCP connection was
2555   established for each request, increasing the load on HTTP servers
2556   and causing congestion on the Internet. The use of inline images and
2557   other associated data often requires a client to make multiple
2558   requests of the same server in a short amount of time. Analysis of
2559   these performance problems and results from a prototype
2560   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2561   measurements of actual HTTP/1.1 implementations show good
2562   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2563   T/TCP <xref target="Tou1998"/>.
2564</t>
2565<t>
2566   Persistent HTTP connections have a number of advantages:
2567  <list style="symbols">
2568      <t>
2569        By opening and closing fewer TCP connections, CPU time is saved
2570        in routers and hosts (clients, servers, proxies, gateways,
2571        tunnels, or caches), and memory used for TCP protocol control
2572        blocks can be saved in hosts.
2573      </t>
2574      <t>
2575        HTTP requests and responses can be pipelined on a connection.
2576        Pipelining allows a client to make multiple requests without
2577        waiting for each response, allowing a single TCP connection to
2578        be used much more efficiently, with much lower elapsed time.
2579      </t>
2580      <t>
2581        Network congestion is reduced by reducing the number of packets
2582        caused by TCP opens, and by allowing TCP sufficient time to
2583        determine the congestion state of the network.
2584      </t>
2585      <t>
2586        Latency on subsequent requests is reduced since there is no time
2587        spent in TCP's connection opening handshake.
2588      </t>
2589      <t>
2590        HTTP can evolve more gracefully, since errors can be reported
2591        without the penalty of closing the TCP connection. Clients using
2592        future versions of HTTP might optimistically try a new feature,
2593        but if communicating with an older server, retry with old
2594        semantics after an error is reported.
2595      </t>
2596    </list>
2597</t>
2598<t>
2599   HTTP implementations &SHOULD; implement persistent connections.
2600</t>
2601</section>
2602
2603<section title="Overall Operation" anchor="persistent.overall">
2604<t>
2605   A significant difference between HTTP/1.1 and earlier versions of
2606   HTTP is that persistent connections are the default behavior of any
2607   HTTP connection. That is, unless otherwise indicated, the client
2608   &SHOULD; assume that the server will maintain a persistent connection,
2609   even after error responses from the server.
2610</t>
2611<t>
2612   Persistent connections provide a mechanism by which a client and a
2613   server can signal the close of a TCP connection. This signaling takes
2614   place using the Connection header field (<xref target="header.connection"/>). Once a close
2615   has been signaled, the client &MUST-NOT; send any more requests on that
2616   connection.
2617</t>
2618
2619<section title="Negotiation" anchor="persistent.negotiation">
2620<t>
2621   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2622   maintain a persistent connection unless a Connection header field including
2623   the connection-token "close" was sent in the request. If the server
2624   chooses to close the connection immediately after sending the
2625   response, it &SHOULD; send a Connection header field including the
2626   connection-token "close".
2627</t>
2628<t>
2629   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2630   decide to keep it open based on whether the response from a server
2631   contains a Connection header field with the connection-token close. In case
2632   the client does not want to maintain a connection for more than that
2633   request, it &SHOULD; send a Connection header field including the
2634   connection-token close.
2635</t>
2636<t>
2637   If either the client or the server sends the close token in the
2638   Connection header field, that request becomes the last one for the
2639   connection.
2640</t>
2641<t>
2642   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2643   maintained for HTTP versions less than 1.1 unless it is explicitly
2644   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2645   compatibility with HTTP/1.0 clients.
2646</t>
2647<t>
2648   In order to remain persistent, all messages on the connection &MUST;
2649   have a self-defined message length (i.e., one not defined by closure
2650   of the connection), as described in <xref target="message.body"/>.
2651</t>
2652</section>
2653
2654<section title="Pipelining" anchor="pipelining">
2655<t>
2656   A client that supports persistent connections &MAY; "pipeline" its
2657   requests (i.e., send multiple requests without waiting for each
2658   response). A server &MUST; send its responses to those requests in the
2659   same order that the requests were received.
2660</t>
2661<t>
2662   Clients which assume persistent connections and pipeline immediately
2663   after connection establishment &SHOULD; be prepared to retry their
2664   connection if the first pipelined attempt fails. If a client does
2665   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2666   persistent. Clients &MUST; also be prepared to resend their requests if
2667   the server closes the connection before sending all of the
2668   corresponding responses.
2669</t>
2670<t>
2671   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2672   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2673   premature termination of the transport connection could lead to
2674   indeterminate results. A client wishing to send a non-idempotent
2675   request &SHOULD; wait to send that request until it has received the
2676   response status line for the previous request.
2677</t>
2678</section>
2679</section>
2680
2681<section title="Proxy Servers" anchor="persistent.proxy">
2682<t>
2683   It is especially important that proxies correctly implement the
2684   properties of the Connection header field as specified in <xref target="header.connection"/>.
2685</t>
2686<t>
2687   The proxy server &MUST; signal persistent connections separately with
2688   its clients and the origin servers (or other proxy servers) that it
2689   connects to. Each persistent connection applies to only one transport
2690   link.
2691</t>
2692<t>
2693   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2694   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2695   for information and discussion of the problems with the Keep-Alive header field
2696   implemented by many HTTP/1.0 clients).
2697</t>
2698
2699<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2700<!--<t>
2701  <cref anchor="TODO-end-to-end" source="jre">
2702    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2703    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2704  </cref>
2705</t>-->
2706<t>
2707   For the purpose of defining the behavior of caches and non-caching
2708   proxies, we divide HTTP header fields into two categories:
2709  <list style="symbols">
2710      <t>End-to-end header fields, which are  transmitted to the ultimate
2711        recipient of a request or response. End-to-end header fields in
2712        responses &MUST; be stored as part of a cache entry and &MUST; be
2713        transmitted in any response formed from a cache entry.</t>
2714
2715      <t>Hop-by-hop header fields, which are meaningful only for a single
2716        transport-level connection, and are not stored by caches or
2717        forwarded by proxies.</t>
2718  </list>
2719</t>
2720<t>
2721   The following HTTP/1.1 header fields are hop-by-hop header fields:
2722  <list style="symbols">
2723      <t>Connection</t>
2724      <t>Keep-Alive</t>
2725      <t>Proxy-Authenticate</t>
2726      <t>Proxy-Authorization</t>
2727      <t>TE</t>
2728      <t>Trailer</t>
2729      <t>Transfer-Encoding</t>
2730      <t>Upgrade</t>
2731  </list>
2732</t>
2733<t>
2734   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2735</t>
2736<t>
2737   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2738   (<xref target="header.connection"/>).
2739</t>
2740</section>
2741
2742<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2743<!--<t>
2744  <cref anchor="TODO-non-mod-headers" source="jre">
2745    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2746    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2747  </cref>
2748</t>-->
2749<t>
2750   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2751   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2752   modify an end-to-end header field unless the definition of that header field requires
2753   or specifically allows that.
2754</t>
2755<t>
2756   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2757   request or response, and it &MUST-NOT; add any of these fields if not
2758   already present:
2759  <list style="symbols">
2760    <t>Allow</t>
2761    <t>Content-Location</t>
2762    <t>Content-MD5</t>
2763    <t>ETag</t>
2764    <t>Last-Modified</t>
2765    <t>Server</t>
2766  </list>
2767</t>
2768<t>
2769   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2770   response:
2771  <list style="symbols">
2772    <t>Expires</t>
2773  </list>
2774</t>
2775<t>
2776   but it &MAY; add any of these fields if not already present. If an
2777   Expires header field is added, it &MUST; be given a field-value identical to
2778   that of the Date header field in that response.
2779</t>
2780<t>
2781   A proxy &MUST-NOT; modify or add any of the following fields in a
2782   message that contains the no-transform cache-control directive, or in
2783   any request:
2784  <list style="symbols">
2785    <t>Content-Encoding</t>
2786    <t>Content-Range</t>
2787    <t>Content-Type</t>
2788  </list>
2789</t>
2790<t>
2791   A transforming proxy &MAY; modify or add these fields to a message
2792   that does not include no-transform, but if it does so, it &MUST; add a
2793   Warning 214 (Transformation applied) if one does not already appear
2794   in the message (see &header-warning;).
2795</t>
2796<x:note>
2797  <t>
2798    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2799    cause authentication failures if stronger authentication
2800    mechanisms are introduced in later versions of HTTP. Such
2801    authentication mechanisms &MAY; rely on the values of header fields
2802    not listed here.
2803  </t>
2804</x:note>
2805<t>
2806   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2807   though it &MAY; change the message body through application or removal
2808   of a transfer-coding (<xref target="transfer.codings"/>).
2809</t>
2810</section>
2811
2812</section>
2813
2814<section title="Practical Considerations" anchor="persistent.practical">
2815<t>
2816   Servers will usually have some time-out value beyond which they will
2817   no longer maintain an inactive connection. Proxy servers might make
2818   this a higher value since it is likely that the client will be making
2819   more connections through the same server. The use of persistent
2820   connections places no requirements on the length (or existence) of
2821   this time-out for either the client or the server.
2822</t>
2823<t>
2824   When a client or server wishes to time-out it &SHOULD; issue a graceful
2825   close on the transport connection. Clients and servers &SHOULD; both
2826   constantly watch for the other side of the transport close, and
2827   respond to it as appropriate. If a client or server does not detect
2828   the other side's close promptly it could cause unnecessary resource
2829   drain on the network.
2830</t>
2831<t>
2832   A client, server, or proxy &MAY; close the transport connection at any
2833   time. For example, a client might have started to send a new request
2834   at the same time that the server has decided to close the "idle"
2835   connection. From the server's point of view, the connection is being
2836   closed while it was idle, but from the client's point of view, a
2837   request is in progress.
2838</t>
2839<t>
2840   Clients (including proxies) &SHOULD; limit the number of simultaneous
2841   connections that they maintain to a given server (including proxies).
2842</t>
2843<t>
2844   Previous revisions of HTTP gave a specific number of connections as a
2845   ceiling, but this was found to be impractical for many applications. As a
2846   result, this specification does not mandate a particular maximum number of
2847   connections, but instead encourages clients to be conservative when opening
2848   multiple connections.
2849</t>
2850<t>
2851   In particular, while using multiple connections avoids the "head-of-line
2852   blocking" problem (whereby a request that takes significant server-side
2853   processing and/or has a large payload can block subsequent requests on the
2854   same connection), each connection used consumes server resources (sometimes
2855   significantly), and furthermore using multiple connections can cause
2856   undesirable side effects in congested networks.
2857</t>
2858<t>
2859   Note that servers might reject traffic that they deem abusive, including an
2860   excessive number of connections from a client.
2861</t>
2862</section>
2863
2864<section title="Retrying Requests" anchor="persistent.retrying.requests">
2865<t>
2866   Senders can close the transport connection at any time. Therefore,
2867   clients, servers, and proxies &MUST; be able to recover
2868   from asynchronous close events. Client software &MAY; reopen the
2869   transport connection and retransmit the aborted sequence of requests
2870   without user interaction so long as the request sequence is
2871   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2872   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2873   human operator the choice of retrying the request(s). Confirmation by
2874   user-agent software with semantic understanding of the application
2875   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2876   be repeated if the second sequence of requests fails.
2877</t>
2878</section>
2879
2880</section>
2881
2882<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2883
2884<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2885<t>
2886   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2887   flow control mechanisms to resolve temporary overloads, rather than
2888   terminating connections with the expectation that clients will retry.
2889   The latter technique can exacerbate network congestion.
2890</t>
2891</section>
2892
2893<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2894<t>
2895   An HTTP/1.1 (or later) client sending a message body &SHOULD; monitor
2896   the network connection for an error status code while it is transmitting
2897   the request. If the client sees an error status code, it &SHOULD;
2898   immediately cease transmitting the body. If the body is being sent
2899   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2900   empty trailer &MAY; be used to prematurely mark the end of the message.
2901   If the body was preceded by a Content-Length header field, the client &MUST;
2902   close the connection.
2903</t>
2904</section>
2905
2906<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2907<t>
2908   The purpose of the 100 (Continue) status code (see &status-100;) is to
2909   allow a client that is sending a request message with a request body
2910   to determine if the origin server is willing to accept the request
2911   (based on the request header fields) before the client sends the request
2912   body. In some cases, it might either be inappropriate or highly
2913   inefficient for the client to send the body if the server will reject
2914   the message without looking at the body.
2915</t>
2916<t>
2917   Requirements for HTTP/1.1 clients:
2918  <list style="symbols">
2919    <t>
2920        If a client will wait for a 100 (Continue) response before
2921        sending the request body, it &MUST; send an Expect header
2922        field (&header-expect;) with the "100-continue" expectation.
2923    </t>
2924    <t>
2925        A client &MUST-NOT; send an Expect header field (&header-expect;)
2926        with the "100-continue" expectation if it does not intend
2927        to send a request body.
2928    </t>
2929  </list>
2930</t>
2931<t>
2932   Because of the presence of older implementations, the protocol allows
2933   ambiguous situations in which a client might send "Expect: 100-continue"
2934   without receiving either a 417 (Expectation Failed)
2935   or a 100 (Continue) status code. Therefore, when a client sends this
2936   header field to an origin server (possibly via a proxy) from which it
2937   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2938   wait for an indefinite period before sending the request body.
2939</t>
2940<t>
2941   Requirements for HTTP/1.1 origin servers:
2942  <list style="symbols">
2943    <t> Upon receiving a request which includes an Expect header
2944        field with the "100-continue" expectation, an origin server &MUST;
2945        either respond with 100 (Continue) status code and continue to read
2946        from the input stream, or respond with a final status code. The
2947        origin server &MUST-NOT; wait for the request body before sending
2948        the 100 (Continue) response. If it responds with a final status
2949        code, it &MAY; close the transport connection or it &MAY; continue
2950        to read and discard the rest of the request.  It &MUST-NOT;
2951        perform the request method if it returns a final status code.
2952    </t>
2953    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2954        the request message does not include an Expect header
2955        field with the "100-continue" expectation, and &MUST-NOT; send a
2956        100 (Continue) response if such a request comes from an HTTP/1.0
2957        (or earlier) client. There is an exception to this rule: for
2958        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2959        status code in response to an HTTP/1.1 PUT or POST request that does
2960        not include an Expect header field with the "100-continue"
2961        expectation. This exception, the purpose of which is
2962        to minimize any client processing delays associated with an
2963        undeclared wait for 100 (Continue) status code, applies only to
2964        HTTP/1.1 requests, and not to requests with any other HTTP-version
2965        value.
2966    </t>
2967    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2968        already received some or all of the request body for the
2969        corresponding request.
2970    </t>
2971    <t> An origin server that sends a 100 (Continue) response &MUST;
2972        ultimately send a final status code, once the request body is
2973        received and processed, unless it terminates the transport
2974        connection prematurely.
2975    </t>
2976    <t> If an origin server receives a request that does not include an
2977        Expect header field with the "100-continue" expectation,
2978        the request includes a request body, and the server responds
2979        with a final status code before reading the entire request body
2980        from the transport connection, then the server &SHOULD-NOT;  close
2981        the transport connection until it has read the entire request,
2982        or until the client closes the connection. Otherwise, the client
2983        might not reliably receive the response message. However, this
2984        requirement ought not be construed as preventing a server from
2985        defending itself against denial-of-service attacks, or from
2986        badly broken client implementations.
2987      </t>
2988    </list>
2989</t>
2990<t>
2991   Requirements for HTTP/1.1 proxies:
2992  <list style="symbols">
2993    <t> If a proxy receives a request that includes an Expect header
2994        field with the "100-continue" expectation, and the proxy
2995        either knows that the next-hop server complies with HTTP/1.1 or
2996        higher, or does not know the HTTP version of the next-hop
2997        server, it &MUST; forward the request, including the Expect header
2998        field.
2999    </t>
3000    <t> If the proxy knows that the version of the next-hop server is
3001        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
3002        respond with a 417 (Expectation Failed) status code.
3003    </t>
3004    <t> Proxies &SHOULD; maintain a record of the HTTP version
3005        numbers received from recently-referenced next-hop servers.
3006    </t>
3007    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
3008        request message was received from an HTTP/1.0 (or earlier)
3009        client and did not include an Expect header field with
3010        the "100-continue" expectation. This requirement overrides the
3011        general rule for forwarding of 1xx responses (see &status-1xx;).
3012    </t>
3013  </list>
3014</t>
3015</section>
3016
3017<section title="Closing Connections on Error" anchor="closing.connections.on.error">
3018<t>
3019   If the client is sending data, a server implementation using TCP
3020   &SHOULD; be careful to ensure that the client acknowledges receipt of
3021   the packet(s) containing the response, before the server closes the
3022   input connection. If the client continues sending data to the server
3023   after the close, the server's TCP stack will send a reset packet to
3024   the client, which might erase the client's unacknowledged input buffers
3025   before they can be read and interpreted by the HTTP application.
3026</t>
3027</section>
3028
3029</section>
3030</section>
3031
3032
3033<section title="Miscellaneous notes that might disappear" anchor="misc">
3034<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
3035<t>
3036   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
3037</t>
3038</section>
3039
3040<section title="Use of HTTP for proxy communication" anchor="http.proxy">
3041<t>
3042   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
3043</t>
3044</section>
3045
3046<section title="Interception of HTTP for access control" anchor="http.intercept">
3047<t>
3048   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
3049</t>
3050</section>
3051
3052<section title="Use of HTTP by other protocols" anchor="http.others">
3053<t>
3054   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
3055   Extensions of HTTP like WebDAV.</cref>
3056</t>
3057
3058</section>
3059<section title="Use of HTTP by media type specification" anchor="http.media">
3060<t>
3061   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
3062</t>
3063</section>
3064</section>
3065
3066<section title="Header Field Definitions" anchor="header.field.definitions">
3067<t>
3068   This section defines the syntax and semantics of HTTP header fields
3069   related to message origination, framing, and routing.
3070</t>
3071<texttable align="left">
3072  <ttcol>Header Field Name</ttcol>
3073  <ttcol>Defined in...</ttcol>
3074 
3075  <c>Connection</c> <c><xref target="header.connection"/></c>
3076  <c>Content-Length</c> <c><xref target="header.content-length"/></c>
3077  <c>Host</c> <c><xref target="header.host"/></c>
3078  <c>TE</c> <c><xref target="header.te"/></c>
3079  <c>Trailer</c> <c><xref target="header.trailer"/></c>
3080  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
3081  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
3082  <c>Via</c> <c><xref target="header.via"/></c>
3083</texttable>
3084
3085<section title="Connection" anchor="header.connection">
3086  <iref primary="true" item="Connection header field" x:for-anchor=""/>
3087  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
3088  <x:anchor-alias value="Connection"/>
3089  <x:anchor-alias value="connection-token"/>
3090<t>
3091   The "Connection" header field allows the sender to specify
3092   options that are desired only for that particular connection.
3093   Such connection options &MUST; be removed or replaced before the
3094   message can be forwarded downstream by a proxy or gateway.
3095   This mechanism also allows the sender to indicate which HTTP
3096   header fields used in the message are only intended for the
3097   immediate recipient ("hop-by-hop"), as opposed to all recipients
3098   on the chain ("end-to-end"), enabling the message to be
3099   self-descriptive and allowing future connection-specific extensions
3100   to be deployed in HTTP without fear that they will be blindly
3101   forwarded by previously deployed intermediaries.
3102</t>
3103<t>
3104   The Connection header field's value has the following grammar:
3105</t>
3106<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
3107  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
3108  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
3109</artwork></figure>
3110<t>
3111   A proxy or gateway &MUST; parse a received Connection
3112   header field before a message is forwarded and, for each
3113   connection-token in this field, remove any header field(s) from
3114   the message with the same name as the connection-token, and then
3115   remove the Connection header field itself or replace it with the
3116   sender's own connection options for the forwarded message.
3117</t>
3118<t>
3119   A sender &MUST-NOT; include field-names in the Connection header
3120   field-value for fields that are defined as expressing constraints
3121   for all recipients in the request or response chain, such as the
3122   Cache-Control header field (&header-cache-control;).
3123</t>
3124<t>
3125   The connection options do not have to correspond to a header field
3126   present in the message, since a connection-specific header field
3127   might not be needed if there are no parameters associated with that
3128   connection option.  Recipients that trigger certain connection
3129   behavior based on the presence of connection options &MUST; do so
3130   based on the presence of the connection-token rather than only the
3131   presence of the optional header field.  In other words, if the
3132   connection option is received as a header field but not indicated
3133   within the Connection field-value, then the recipient &MUST; ignore
3134   the connection-specific header field because it has likely been
3135   forwarded by an intermediary that is only partially conformant.
3136</t>
3137<t>
3138   When defining new connection options, specifications ought to
3139   carefully consider existing deployed header fields and ensure
3140   that the new connection-token does not share the same name as
3141   an unrelated header field that might already be deployed.
3142   Defining a new connection-token essentially reserves that potential
3143   field-name for carrying additional information related to the
3144   connection option, since it would be unwise for senders to use
3145   that field-name for anything else.
3146</t>
3147<t>
3148   HTTP/1.1 defines the "close" connection option for the sender to
3149   signal that the connection will be closed after completion of the
3150   response. For example,
3151</t>
3152<figure><artwork type="example">
3153  Connection: close
3154</artwork></figure>
3155<t>
3156   in either the request or the response header fields indicates that
3157   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
3158   after the current request/response is complete.
3159</t>
3160<t>
3161   An HTTP/1.1 client that does not support persistent connections &MUST;
3162   include the "close" connection option in every request message.
3163</t>
3164<t>
3165   An HTTP/1.1 server that does not support persistent connections &MUST;
3166   include the "close" connection option in every response message that
3167   does not have a 1xx (Informational) status code.
3168</t>
3169</section>
3170
3171<section title="Host" anchor="header.host">
3172  <iref primary="true" item="Host header field" x:for-anchor=""/>
3173  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3174  <x:anchor-alias value="Host"/>
3175<t>
3176   The "Host" header field in a request provides the host and port
3177   information from the target resource's URI, enabling the origin
3178   server to distinguish between resources while servicing requests
3179   for multiple host names on a single IP address.  Since the Host
3180   field-value is critical information for handling a request, it
3181   &SHOULD; be sent as the first header field following the request-line.
3182</t>
3183<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
3184  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3185</artwork></figure>
3186<t>
3187   A client &MUST; send a Host header field in all HTTP/1.1 request
3188   messages.  If the target resource's URI includes an authority
3189   component, then the Host field-value &MUST; be identical to that
3190   authority component after excluding any userinfo (<xref target="http.uri"/>).
3191   If the authority component is missing or undefined for the target
3192   resource's URI, then the Host header field &MUST; be sent with an
3193   empty field-value.
3194</t>
3195<t>
3196   For example, a GET request to the origin server for
3197   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
3198</t>
3199<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3200GET /pub/WWW/ HTTP/1.1
3201Host: www.example.org
3202</artwork></figure>
3203<t>
3204   The Host header field &MUST; be sent in an HTTP/1.1 request even
3205   if the request-target is in the form of an absolute-URI, since this
3206   allows the Host information to be forwarded through ancient HTTP/1.0
3207   proxies that might not have implemented Host.
3208</t>
3209<t>
3210   When an HTTP/1.1 proxy receives a request with a request-target in
3211   the form of an absolute-URI, the proxy &MUST; ignore the received
3212   Host header field (if any) and instead replace it with the host
3213   information of the request-target.  When a proxy forwards a request,
3214   it &MUST; generate the Host header field based on the received
3215   absolute-URI rather than the received Host.
3216</t>
3217<t>
3218   Since the Host header field acts as an application-level routing
3219   mechanism, it is a frequent target for malware seeking to poison
3220   a shared cache or redirect a request to an unintended server.
3221   An interception proxy is particularly vulnerable if it relies on
3222   the Host header field value for redirecting requests to internal
3223   servers, or for use as a cache key in a shared cache, without
3224   first verifying that the intercepted connection is targeting a
3225   valid IP address for that host.
3226</t>
3227<t>
3228   A server &MUST; respond with a 400 (Bad Request) status code to
3229   any HTTP/1.1 request message that lacks a Host header field and
3230   to any request message that contains more than one Host header field
3231   or a Host header field with an invalid field-value.
3232</t>
3233<t>
3234   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3235   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3236   for other requirements relating to Host.
3237</t>
3238</section>
3239
3240<section title="Upgrade" anchor="header.upgrade">
3241  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3242  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3243  <x:anchor-alias value="Upgrade"/>
3244  <x:anchor-alias value="protocol"/>
3245  <x:anchor-alias value="protocol-name"/>
3246  <x:anchor-alias value="protocol-version"/>
3247<t>
3248   The "Upgrade" header field allows the client to specify what
3249   additional communication protocols it would like to use, if the server
3250   chooses to switch protocols. Servers can use it to indicate what protocols
3251   they are willing to switch to.
3252</t>
3253<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3254  <x:ref>Upgrade</x:ref>  = 1#<x:ref>protocol</x:ref>
3255
3256  <x:ref>protocol</x:ref> = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3257  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3258  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3259</artwork></figure>
3260<t>
3261   For example,
3262</t>
3263<figure><artwork type="example">
3264  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3265</artwork></figure>
3266<t>
3267   The Upgrade header field is intended to provide a simple mechanism
3268   for transitioning from HTTP/1.1 to some other, incompatible protocol. It
3269   does so by allowing the client to advertise its desire to use another
3270   protocol, such as a later version of HTTP with a higher major version
3271   number, even though the current request has been made using HTTP/1.1.
3272   This eases the difficult transition between incompatible protocols by
3273   allowing the client to initiate a request in the more commonly
3274   supported protocol while indicating to the server that it would like
3275   to use a "better" protocol if available (where "better" is determined
3276   by the server, possibly according to the nature of the request method
3277   or target resource).
3278</t>
3279<t>
3280   The Upgrade header field only applies to switching application-layer
3281   protocols upon the existing transport-layer connection. Upgrade
3282   cannot be used to insist on a protocol change; its acceptance and use
3283   by the server is optional. The capabilities and nature of the
3284   application-layer communication after the protocol change is entirely
3285   dependent upon the new protocol chosen, although the first action
3286   after changing the protocol &MUST; be a response to the initial HTTP
3287   request containing the Upgrade header field.
3288</t>
3289<t>
3290   The Upgrade header field only applies to the immediate connection.
3291   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3292   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3293   HTTP/1.1 message.
3294</t>
3295<t>
3296   The Upgrade header field cannot be used to indicate a switch to a
3297   protocol on a different connection. For that purpose, it is more
3298   appropriate to use a 3xx redirection response (&status-3xx;).
3299</t>
3300<t>
3301   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3302   Protocols) responses to indicate which protocol(s) are being switched to,
3303   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3304   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3305   response to indicate that they are willing to upgrade to one of the
3306   specified protocols.
3307</t>
3308<t>
3309   This specification only defines the protocol name "HTTP" for use by
3310   the family of Hypertext Transfer Protocols, as defined by the HTTP
3311   version rules of <xref target="http.version"/> and future updates to this
3312   specification. Additional tokens can be registered with IANA using the
3313   registration procedure defined below. 
3314</t>
3315
3316<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3317<t>
3318   The HTTP Upgrade Token Registry defines the name space for protocol-name
3319   tokens used to identify protocols in the Upgrade header field.
3320   Each registered protocol-name is associated with contact information and
3321   an optional set of specifications that details how the connection
3322   will be processed after it has been upgraded.
3323</t>
3324<t>
3325   Registrations are allowed on a First Come First Served basis as
3326   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3327   specifications need not be IETF documents or be subject to IESG review.
3328   Registrations are subject to the following rules:
3329  <list style="numbers">
3330    <t>A protocol-name token, once registered, stays registered forever.</t>
3331    <t>The registration &MUST; name a responsible party for the
3332       registration.</t>
3333    <t>The registration &MUST; name a point of contact.</t>
3334    <t>The registration &MAY; name a set of specifications associated with
3335       that token. Such specifications need not be publicly available.</t>
3336    <t>The registration &SHOULD; name a set of expected "protocol-version"
3337       tokens associated with that token at the time of registration.</t>
3338    <t>The responsible party &MAY; change the registration at any time.
3339       The IANA will keep a record of all such changes, and make them
3340       available upon request.</t>
3341    <t>The IESG &MAY; reassign responsibility for a protocol token.
3342       This will normally only be used in the case when a
3343       responsible party cannot be contacted.</t>
3344  </list>
3345</t>
3346</section>
3347
3348
3349</section>
3350
3351<section title="Via" anchor="header.via">
3352  <iref primary="true" item="Via header field" x:for-anchor=""/>
3353  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3354  <x:anchor-alias value="pseudonym"/>
3355  <x:anchor-alias value="received-by"/>
3356  <x:anchor-alias value="received-protocol"/>
3357  <x:anchor-alias value="Via"/>
3358<t>
3359   The "Via" header field &MUST; be sent by a proxy or gateway to
3360   indicate the intermediate protocols and recipients between the user
3361   agent and the server on requests, and between the origin server and
3362   the client on responses. It is analogous to the "Received" field
3363   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3364   and is intended to be used for tracking message forwards,
3365   avoiding request loops, and identifying the protocol capabilities of
3366   all senders along the request/response chain.
3367</t>
3368<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"/>
3369  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3370                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3371  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3372  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3373  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3374</artwork></figure>
3375<t>
3376   The received-protocol indicates the protocol version of the message
3377   received by the server or client along each segment of the
3378   request/response chain. The received-protocol version is appended to
3379   the Via field value when the message is forwarded so that information
3380   about the protocol capabilities of upstream applications remains
3381   visible to all recipients.
3382</t>
3383<t>
3384   The protocol-name is excluded if and only if it would be "HTTP". The
3385   received-by field is normally the host and optional port number of a
3386   recipient server or client that subsequently forwarded the message.
3387   However, if the real host is considered to be sensitive information,
3388   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3389   be assumed to be the default port of the received-protocol.
3390</t>
3391<t>
3392   Multiple Via field values represent each proxy or gateway that has
3393   forwarded the message. Each recipient &MUST; append its information
3394   such that the end result is ordered according to the sequence of
3395   forwarding applications.
3396</t>
3397<t>
3398   Comments &MAY; be used in the Via header field to identify the software
3399   of each recipient, analogous to the User-Agent and Server header fields.
3400   However, all comments in the Via field are optional and &MAY; be removed
3401   by any recipient prior to forwarding the message.
3402</t>
3403<t>
3404   For example, a request message could be sent from an HTTP/1.0 user
3405   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3406   forward the request to a public proxy at p.example.net, which completes
3407   the request by forwarding it to the origin server at www.example.com.
3408   The request received by www.example.com would then have the following
3409   Via header field:
3410</t>
3411<figure><artwork type="example">
3412  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3413</artwork></figure>
3414<t>
3415   A proxy or gateway used as a portal through a network firewall
3416   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3417   region unless it is explicitly enabled to do so. If not enabled, the
3418   received-by host of any host behind the firewall &SHOULD; be replaced
3419   by an appropriate pseudonym for that host.
3420</t>
3421<t>
3422   For organizations that have strong privacy requirements for hiding
3423   internal structures, a proxy or gateway &MAY; combine an ordered
3424   subsequence of Via header field entries with identical received-protocol
3425   values into a single such entry. For example,
3426</t>
3427<figure><artwork type="example">
3428  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3429</artwork></figure>
3430<t>
3431  could be collapsed to
3432</t>
3433<figure><artwork type="example">
3434  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3435</artwork></figure>
3436<t>
3437   Senders &SHOULD-NOT; combine multiple entries unless they are all
3438   under the same organizational control and the hosts have already been
3439   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3440   have different received-protocol values.
3441</t>
3442</section>
3443
3444</section>
3445
3446<section title="IANA Considerations" anchor="IANA.considerations">
3447
3448<section title="Header Field Registration" anchor="header.field.registration">
3449<t>
3450   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3451   with the permanent registrations below (see <xref target="RFC3864"/>):
3452</t>
3453<?BEGININC p1-messaging.iana-headers ?>
3454<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3455<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3456   <ttcol>Header Field Name</ttcol>
3457   <ttcol>Protocol</ttcol>
3458   <ttcol>Status</ttcol>
3459   <ttcol>Reference</ttcol>
3460
3461   <c>Connection</c>
3462   <c>http</c>
3463   <c>standard</c>
3464   <c>
3465      <xref target="header.connection"/>
3466   </c>
3467   <c>Content-Length</c>
3468   <c>http</c>
3469   <c>standard</c>
3470   <c>
3471      <xref target="header.content-length"/>
3472   </c>
3473   <c>Host</c>
3474   <c>http</c>
3475   <c>standard</c>
3476   <c>
3477      <xref target="header.host"/>
3478   </c>
3479   <c>TE</c>
3480   <c>http</c>
3481   <c>standard</c>
3482   <c>
3483      <xref target="header.te"/>
3484   </c>
3485   <c>Trailer</c>
3486   <c>http</c>
3487   <c>standard</c>
3488   <c>
3489      <xref target="header.trailer"/>
3490   </c>
3491   <c>Transfer-Encoding</c>
3492   <c>http</c>
3493   <c>standard</c>
3494   <c>
3495      <xref target="header.transfer-encoding"/>
3496   </c>
3497   <c>Upgrade</c>
3498   <c>http</c>
3499   <c>standard</c>
3500   <c>
3501      <xref target="header.upgrade"/>
3502   </c>
3503   <c>Via</c>
3504   <c>http</c>
3505   <c>standard</c>
3506   <c>
3507      <xref target="header.via"/>
3508   </c>
3509</texttable>
3510<!--(END)-->
3511<?ENDINC p1-messaging.iana-headers ?>
3512<t>
3513   Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
3514   HTTP header field would be in conflict with the use of the "close" connection
3515   option for the "Connection" header field (<xref target="header.connection"/>).
3516</t>
3517<texttable align="left" suppress-title="true">
3518   <ttcol>Header Field Name</ttcol>
3519   <ttcol>Protocol</ttcol>
3520   <ttcol>Status</ttcol>
3521   <ttcol>Reference</ttcol>
3522
3523   <c>Close</c>
3524   <c>http</c>
3525   <c>reserved</c>
3526   <c>
3527      <xref target="header.field.registration"/>
3528   </c>
3529</texttable>
3530<t>
3531   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3532</t>
3533</section>
3534
3535<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3536<t>
3537   The entries for the "http" and "https" URI Schemes in the registry located at
3538   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3539   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3540   and <xref target="https.uri" format="counter"/> of this document
3541   (see <xref target="RFC4395"/>).
3542</t>
3543</section>
3544
3545<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3546<t>
3547   This document serves as the specification for the Internet media types
3548   "message/http" and "application/http". The following is to be registered with
3549   IANA (see <xref target="RFC4288"/>).
3550</t>
3551<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3552<iref item="Media Type" subitem="message/http" primary="true"/>
3553<iref item="message/http Media Type" primary="true"/>
3554<t>
3555   The message/http type can be used to enclose a single HTTP request or
3556   response message, provided that it obeys the MIME restrictions for all
3557   "message" types regarding line length and encodings.
3558</t>
3559<t>
3560  <list style="hanging" x:indent="12em">
3561    <t hangText="Type name:">
3562      message
3563    </t>
3564    <t hangText="Subtype name:">
3565      http
3566    </t>
3567    <t hangText="Required parameters:">
3568      none
3569    </t>
3570    <t hangText="Optional parameters:">
3571      version, msgtype
3572      <list style="hanging">
3573        <t hangText="version:">
3574          The HTTP-version number of the enclosed message
3575          (e.g., "1.1"). If not present, the version can be
3576          determined from the first line of the body.
3577        </t>
3578        <t hangText="msgtype:">
3579          The message type &mdash; "request" or "response". If not
3580          present, the type can be determined from the first
3581          line of the body.
3582        </t>
3583      </list>
3584    </t>
3585    <t hangText="Encoding considerations:">
3586      only "7bit", "8bit", or "binary" are permitted
3587    </t>
3588    <t hangText="Security considerations:">
3589      none
3590    </t>
3591    <t hangText="Interoperability considerations:">
3592      none
3593    </t>
3594    <t hangText="Published specification:">
3595      This specification (see <xref target="internet.media.type.message.http"/>).
3596    </t>
3597    <t hangText="Applications that use this media type:">
3598    </t>
3599    <t hangText="Additional information:">
3600      <list style="hanging">
3601        <t hangText="Magic number(s):">none</t>
3602        <t hangText="File extension(s):">none</t>
3603        <t hangText="Macintosh file type code(s):">none</t>
3604      </list>
3605    </t>
3606    <t hangText="Person and email address to contact for further information:">
3607      See Authors Section.
3608    </t>
3609    <t hangText="Intended usage:">
3610      COMMON
3611    </t>
3612    <t hangText="Restrictions on usage:">
3613      none
3614    </t>
3615    <t hangText="Author/Change controller:">
3616      IESG
3617    </t>
3618  </list>
3619</t>
3620</section>
3621<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3622<iref item="Media Type" subitem="application/http" primary="true"/>
3623<iref item="application/http Media Type" primary="true"/>
3624<t>
3625   The application/http type can be used to enclose a pipeline of one or more
3626   HTTP request or response messages (not intermixed).
3627</t>
3628<t>
3629  <list style="hanging" x:indent="12em">
3630    <t hangText="Type name:">
3631      application
3632    </t>
3633    <t hangText="Subtype name:">
3634      http
3635    </t>
3636    <t hangText="Required parameters:">
3637      none
3638    </t>
3639    <t hangText="Optional parameters:">
3640      version, msgtype
3641      <list style="hanging">
3642        <t hangText="version:">
3643          The HTTP-version number of the enclosed messages
3644          (e.g., "1.1"). If not present, the version can be
3645          determined from the first line of the body.
3646        </t>
3647        <t hangText="msgtype:">
3648          The message type &mdash; "request" or "response". If not
3649          present, the type can be determined from the first
3650          line of the body.
3651        </t>
3652      </list>
3653    </t>
3654    <t hangText="Encoding considerations:">
3655      HTTP messages enclosed by this type
3656      are in "binary" format; use of an appropriate
3657      Content-Transfer-Encoding is required when
3658      transmitted via E-mail.
3659    </t>
3660    <t hangText="Security considerations:">
3661      none
3662    </t>
3663    <t hangText="Interoperability considerations:">
3664      none
3665    </t>
3666    <t hangText="Published specification:">
3667      This specification (see <xref target="internet.media.type.application.http"/>).
3668    </t>
3669    <t hangText="Applications that use this media type:">
3670    </t>
3671    <t hangText="Additional information:">
3672      <list style="hanging">
3673        <t hangText="Magic number(s):">none</t>
3674        <t hangText="File extension(s):">none</t>
3675        <t hangText="Macintosh file type code(s):">none</t>
3676      </list>
3677    </t>
3678    <t hangText="Person and email address to contact for further information:">
3679      See Authors Section.
3680    </t>
3681    <t hangText="Intended usage:">
3682      COMMON
3683    </t>
3684    <t hangText="Restrictions on usage:">
3685      none
3686    </t>
3687    <t hangText="Author/Change controller:">
3688      IESG
3689    </t>
3690  </list>
3691</t>
3692</section>
3693</section>
3694
3695<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3696<t>
3697   The registration procedure for HTTP Transfer Codings is now defined by
3698   <xref target="transfer.coding.registry"/> of this document.
3699</t>
3700<t>
3701   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3702   shall be updated with the registrations below:
3703</t>
3704<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3705   <ttcol>Name</ttcol>
3706   <ttcol>Description</ttcol>
3707   <ttcol>Reference</ttcol>
3708   <c>chunked</c>
3709   <c>Transfer in a series of chunks</c>
3710   <c>
3711      <xref target="chunked.encoding"/>
3712   </c>
3713   <c>compress</c>
3714   <c>UNIX "compress" program method</c>
3715   <c>
3716      <xref target="compress.coding"/>
3717   </c>
3718   <c>deflate</c>
3719   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3720   the "zlib" data format (<xref target="RFC1950"/>)
3721   </c>
3722   <c>
3723      <xref target="deflate.coding"/>
3724   </c>
3725   <c>gzip</c>
3726   <c>Same as GNU zip <xref target="RFC1952"/></c>
3727   <c>
3728      <xref target="gzip.coding"/>
3729   </c>
3730</texttable>
3731</section>
3732
3733<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3734<t>
3735   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3736   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3737   by <xref target="upgrade.token.registry"/> of this document.
3738</t>
3739<t>
3740   The HTTP Upgrade Token Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3741   shall be updated with the registration below:
3742</t>
3743<texttable align="left" suppress-title="true">
3744   <ttcol>Value</ttcol>
3745   <ttcol>Description</ttcol>
3746   <ttcol>Reference</ttcol>
3747
3748   <c>HTTP</c>
3749   <c>Hypertext Transfer Protocol</c> 
3750   <c><xref target="http.version"/> of this specification</c>
3751
3752</texttable>
3753</section>
3754
3755</section>
3756
3757<section title="Security Considerations" anchor="security.considerations">
3758<t>
3759   This section is meant to inform application developers, information
3760   providers, and users of the security limitations in HTTP/1.1 as
3761   described by this document. The discussion does not include
3762   definitive solutions to the problems revealed, though it does make
3763   some suggestions for reducing security risks.
3764</t>
3765
3766<section title="Personal Information" anchor="personal.information">
3767<t>
3768   HTTP clients are often privy to large amounts of personal information
3769   (e.g., the user's name, location, mail address, passwords, encryption
3770   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3771   leakage of this information.
3772   We very strongly recommend that a convenient interface be provided
3773   for the user to control dissemination of such information, and that
3774   designers and implementors be particularly careful in this area.
3775   History shows that errors in this area often create serious security
3776   and/or privacy problems and generate highly adverse publicity for the
3777   implementor's company.
3778</t>
3779</section>
3780
3781<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3782<t>
3783   A server is in the position to save personal data about a user's
3784   requests which might identify their reading patterns or subjects of
3785   interest. This information is clearly confidential in nature and its
3786   handling can be constrained by law in certain countries. People using
3787   HTTP to provide data are responsible for ensuring that
3788   such material is not distributed without the permission of any
3789   individuals that are identifiable by the published results.
3790</t>
3791</section>
3792
3793<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3794<t>
3795   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3796   the documents returned by HTTP requests to be only those that were
3797   intended by the server administrators. If an HTTP server translates
3798   HTTP URIs directly into file system calls, the server &MUST; take
3799   special care not to serve files that were not intended to be
3800   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3801   other operating systems use ".." as a path component to indicate a
3802   directory level above the current one. On such a system, an HTTP
3803   server &MUST; disallow any such construct in the request-target if it
3804   would otherwise allow access to a resource outside those intended to
3805   be accessible via the HTTP server. Similarly, files intended for
3806   reference only internally to the server (such as access control
3807   files, configuration files, and script code) &MUST; be protected from
3808   inappropriate retrieval, since they might contain sensitive
3809   information. Experience has shown that minor bugs in such HTTP server
3810   implementations have turned into security risks.
3811</t>
3812</section>
3813
3814<section title="DNS-related Attacks" anchor="dns.related.attacks">
3815<t>
3816   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3817   generally prone to security attacks based on the deliberate misassociation
3818   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3819   cautious in assuming the validity of an IP number/DNS name association unless
3820   the response is protected by DNSSec (<xref target="RFC4033"/>).
3821</t>
3822</section>
3823
3824<section title="Proxies and Caching" anchor="attack.proxies">
3825<t>
3826   By their very nature, HTTP proxies are men-in-the-middle, and
3827   represent an opportunity for man-in-the-middle attacks. Compromise of
3828   the systems on which the proxies run can result in serious security
3829   and privacy problems. Proxies have access to security-related
3830   information, personal information about individual users and
3831   organizations, and proprietary information belonging to users and
3832   content providers. A compromised proxy, or a proxy implemented or
3833   configured without regard to security and privacy considerations,
3834   might be used in the commission of a wide range of potential attacks.
3835</t>
3836<t>
3837   Proxy operators need to protect the systems on which proxies run as
3838   they would protect any system that contains or transports sensitive
3839   information. In particular, log information gathered at proxies often
3840   contains highly sensitive personal information, and/or information
3841   about organizations. Log information needs to be carefully guarded, and
3842   appropriate guidelines for use need to be developed and followed.
3843   (<xref target="abuse.of.server.log.information"/>).
3844</t>
3845<t>
3846   Proxy implementors need to consider the privacy and security
3847   implications of their design and coding decisions, and of the
3848   configuration options they provide to proxy operators (especially the
3849   default configuration).
3850</t>
3851<t>
3852   Users of a proxy need to be aware that proxies are no more trustworthy than
3853   the people who run them; HTTP itself cannot solve this problem.
3854</t>
3855<t>
3856   The judicious use of cryptography, when appropriate, might suffice to
3857   protect against a broad range of security and privacy attacks. Such
3858   cryptography is beyond the scope of the HTTP/1.1 specification.
3859</t>
3860</section>
3861
3862<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3863<t>
3864   Because HTTP uses mostly textual, character-delimited fields, attackers can
3865   overflow buffers in implementations, and/or perform a Denial of Service
3866   against implementations that accept fields with unlimited lengths.
3867</t>
3868<t>
3869   To promote interoperability, this specification makes specific
3870   recommendations for size limits on request-targets (<xref target="request-target"/>)
3871   and blocks of header fields (<xref target="header.fields"/>). These are
3872   minimum recommendations, chosen to be supportable even by implementations
3873   with limited resources; it is expected that most implementations will choose
3874   substantially higher limits.
3875</t>
3876<t>
3877   This specification also provides a way for servers to reject messages that
3878   have request-targets that are too long (&status-414;) or request entities
3879   that are too large (&status-4xx;).
3880</t>
3881<t>
3882   Other fields (including but not limited to request methods, response status
3883   phrases, header field-names, and body chunks) &SHOULD; be limited by
3884   implementations carefully, so as to not impede interoperability.
3885</t>
3886</section>
3887
3888<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3889<t>
3890   They exist. They are hard to defend against. Research continues.
3891   Beware.
3892</t>
3893</section>
3894</section>
3895
3896<section title="Acknowledgments" anchor="acks">
3897<t>
3898   This document revision builds on the work that went into
3899   <xref target="RFC2616" format="none">RFC 2616</xref> and its predecessors.
3900   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for detailed
3901   acknowledgements.
3902</t>
3903<t>
3904   Since 1999, many contributors have helped by reporting bugs, asking
3905   smart questions, drafting and reviewing text, and discussing open issues:
3906</t>
3907<?BEGININC acks ?>
3908<t>Adam Barth,
3909Adam Roach,
3910Addison Phillips,
3911Adrian Chadd,
3912Adrien de Croy,
3913Alan Ford,
3914Alan Ruttenberg,
3915Albert Lunde,
3916Alex Rousskov,
3917Alexey Melnikov,
3918Alisha Smith,
3919Amichai Rothman,
3920Amit Klein,
3921Amos Jeffries,
3922Andreas Maier,
3923Andreas Petersson,
3924Anne van Kesteren,
3925Anthony Bryan,
3926Asbjorn Ulsberg,
3927Balachander Krishnamurthy,
3928Barry Leiba,
3929Ben Laurie,
3930Benjamin Niven-Jenkins,
3931Bil Corry,
3932Bill Burke,
3933Bjoern Hoehrmann,
3934Bob Scheifler,
3935Boris Zbarsky,
3936Brett Slatkin,
3937Brian Kell,
3938Brian McBarron,
3939Brian Pane,
3940Brian Smith,
3941Bryce Nesbitt,
3942Cameron Heavon-Jones,
3943Carl Kugler,
3944Carsten Bormann,
3945Charles Fry,
3946Chris Newman,
3947Cyrus Daboo,
3948Dale Robert Anderson,
3949Dan Winship,
3950Daniel Stenberg,
3951Dave Cridland,
3952Dave Crocker,
3953Dave Kristol,
3954David Booth,
3955David Singer,
3956David W. Morris,
3957Diwakar Shetty,
3958Dmitry Kurochkin,
3959Drummond Reed,
3960Duane Wessels,
3961Edward Lee,
3962Eliot Lear,
3963Eran Hammer-Lahav,
3964Eric D. Williams,
3965Eric J. Bowman,
3966Eric Lawrence,
3967Erik Aronesty,
3968Florian Weimer,
3969Frank Ellermann,
3970Fred Bohle,
3971Geoffrey Sneddon,
3972Gervase Markham,
3973Greg Wilkins,
3974Harald Tveit Alvestrand,
3975Harry Halpin,
3976Helge Hess,
3977Henrik Nordstrom,
3978Henry S. Thompson,
3979Henry Story,
3980Herbert van de Sompel,
3981Howard Melman,
3982Hugo Haas,
3983Ian Hickson,
3984Ingo Struck,
3985J. Ross Nicoll,
3986James H. Manger,
3987James Lacey,
3988James M. Snell,
3989Jamie Lokier,
3990Jan Algermissen,
3991Jeff Hodges (for coming up with the term 'effective Request-URI'),
3992Jeff Walden,
3993Jim Luther,
3994Joe D. Williams,
3995Joe Gregorio,
3996Joe Orton,
3997John C. Klensin,
3998John C. Mallery,
3999John Cowan,
4000John Kemp,
4001John Panzer,
4002John Schneider,
4003John Stracke,
4004Jonas Sicking,
4005Jonathan Billington,
4006Jonathan Moore,
4007Jonathan Rees,
4008Jordi Ros,
4009Joris Dobbelsteen,
4010Josh Cohen,
4011Julien Pierre,
4012Jungshik Shin,
4013Justin Chapweske,
4014Justin Erenkrantz,
4015Justin James,
4016Kalvinder Singh,
4017Karl Dubost,
4018Keith Hoffman,
4019Keith Moore,
4020Koen Holtman,
4021Konstantin Voronkov,
4022Kris Zyp,
4023Lisa Dusseault,
4024Maciej Stachowiak,
4025Marc Schneider,
4026Marc Slemko,
4027Mark Baker,
4028Mark Nottingham (Working Group chair),
4029Mark Pauley,
4030Markus Lanthaler,
4031Martin J. Duerst,
4032Martin Thomson,
4033Matt Lynch,
4034Matthew Cox,
4035Max Clark,
4036Michael Burrows,
4037Michael Hausenblas,
4038Mike Amundsen,
4039Mike Belshe,
4040Mike Kelly,
4041Mike Schinkel,
4042Miles Sabin,
4043Mykyta Yevstifeyev,
4044Nathan Rixham,
4045Nicholas Shanks,
4046Nico Williams,
4047Nicolas Alvarez,
4048Nicolas Mailhot,
4049Noah Slater,
4050Pablo Castro,
4051Pat Hayes,
4052Patrick R. McManus,
4053Paul E. Jones,
4054Paul Hoffman,
4055Paul Marquess,
4056Peter Saint-Andre,
4057Peter Watkins,
4058Phil Archer,
4059Phillip Hallam-Baker,
4060Poul-Henning Kamp,
4061Preethi Natarajan,
4062Ray Polk,
4063Reto Bachmann-Gmuer,
4064Richard Cyganiak,
4065Robert Brewer,
4066Robert Collins,
4067Robert O'Callahan,
4068Robert Olofsson,
4069Robert Sayre,
4070Robert Siemer,
4071Robert de Wilde,
4072Roberto Javier Godoy,
4073Ronny Widjaja,
4074S. Mike Dierken,
4075Salvatore Loreto,
4076Sam Johnston,
4077Sam Ruby,
4078Scott Lawrence (for maintaining the original issues list),
4079Sean B. Palmer,
4080Shane McCarron,
4081Stefan Eissing,
4082Stefan Tilkov,
4083Stefanos Harhalakis,
4084Stephane Bortzmeyer,
4085Stephen Farrell,
4086Stuart Williams,
4087Subbu Allamaraju,
4088Sylvain Hellegouarch,
4089Tapan Divekar,
4090Ted Hardie,
4091Thomas Broyer,
4092Thomas Nordin,
4093Thomas Roessler,
4094Tim Morgan,
4095Tim Olsen,
4096Travis Snoozy,
4097Tyler Close,
4098Vincent Murphy,
4099Wenbo Zhu,
4100Werner Baumann,
4101Wilbur Streett,
4102Wilfredo Sanchez Vega,
4103William A. Rowe Jr.,
4104William Chan,
4105Willy Tarreau,
4106Xiaoshu Wang,
4107Yaron Goland,
4108Yngve Nysaeter Pettersen,
4109Yogesh Bang,
4110Yutaka Oiwa,
4111Zed A. Shaw, and
4112Zhong Yu.
4113</t>
4114<?ENDINC acks ?>
4115</section>
4116
4117</middle>
4118<back>
4119
4120<references title="Normative References">
4121
4122<reference anchor="ISO-8859-1">
4123  <front>
4124    <title>
4125     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4126    </title>
4127    <author>
4128      <organization>International Organization for Standardization</organization>
4129    </author>
4130    <date year="1998"/>
4131  </front>
4132  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4133</reference>
4134
4135<reference anchor="Part2">
4136  <front>
4137    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4138    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4139      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4140      <address><email>fielding@gbiv.com</email></address>
4141    </author>
4142    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4143      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4144      <address><email>jg@freedesktop.org</email></address>
4145    </author>
4146    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4147      <organization abbrev="HP">Hewlett-Packard Company</organization>
4148      <address><email>JeffMogul@acm.org</email></address>
4149    </author>
4150    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4151      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4152      <address><email>henrikn@microsoft.com</email></address>
4153    </author>
4154    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4155      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4156      <address><email>LMM@acm.org</email></address>
4157    </author>
4158    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4159      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4160      <address><email>paulle@microsoft.com</email></address>
4161    </author>
4162    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4163      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4164      <address><email>timbl@w3.org</email></address>
4165    </author>
4166    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4167      <organization abbrev="W3C">World Wide Web Consortium</organization>
4168      <address><email>ylafon@w3.org</email></address>
4169    </author>
4170    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4171      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4172      <address><email>julian.reschke@greenbytes.de</email></address>
4173    </author>
4174    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4175  </front>
4176  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4177  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4178</reference>
4179
4180<reference anchor="Part3">
4181  <front>
4182    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4183    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4184      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4185      <address><email>fielding@gbiv.com</email></address>
4186    </author>
4187    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4188      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4189      <address><email>jg@freedesktop.org</email></address>
4190    </author>
4191    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4192      <organization abbrev="HP">Hewlett-Packard Company</organization>
4193      <address><email>JeffMogul@acm.org</email></address>
4194    </author>
4195    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4196      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4197      <address><email>henrikn@microsoft.com</email></address>
4198    </author>
4199    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4200      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4201      <address><email>LMM@acm.org</email></address>
4202    </author>
4203    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4204      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4205      <address><email>paulle@microsoft.com</email></address>
4206    </author>
4207    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4208      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4209      <address><email>timbl@w3.org</email></address>
4210    </author>
4211    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4212      <organization abbrev="W3C">World Wide Web Consortium</organization>
4213      <address><email>ylafon@w3.org</email></address>
4214    </author>
4215    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4216      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4217      <address><email>julian.reschke@greenbytes.de</email></address>
4218    </author>
4219    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4220  </front>
4221  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4222  <x:source href="p3-payload.xml" basename="p3-payload"/>
4223</reference>
4224
4225<reference anchor="Part6">
4226  <front>
4227    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4228    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4229      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4230      <address><email>fielding@gbiv.com</email></address>
4231    </author>
4232    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4233      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4234      <address><email>jg@freedesktop.org</email></address>
4235    </author>
4236    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4237      <organization abbrev="HP">Hewlett-Packard Company</organization>
4238      <address><email>JeffMogul@acm.org</email></address>
4239    </author>
4240    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4241      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4242      <address><email>henrikn@microsoft.com</email></address>
4243    </author>
4244    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4245      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4246      <address><email>LMM@acm.org</email></address>
4247    </author>
4248    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4249      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4250      <address><email>paulle@microsoft.com</email></address>
4251    </author>
4252    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4253      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4254      <address><email>timbl@w3.org</email></address>
4255    </author>
4256    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4257      <organization abbrev="W3C">World Wide Web Consortium</organization>
4258      <address><email>ylafon@w3.org</email></address>
4259    </author>
4260    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4261      <organization>Rackspace</organization>
4262      <address><email>mnot@mnot.net</email></address>
4263    </author>
4264    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4265      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4266      <address><email>julian.reschke@greenbytes.de</email></address>
4267    </author>
4268    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4269  </front>
4270  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4271  <x:source href="p6-cache.xml" basename="p6-cache"/>
4272</reference>
4273
4274<reference anchor="RFC5234">
4275  <front>
4276    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4277    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4278      <organization>Brandenburg InternetWorking</organization>
4279      <address>
4280        <email>dcrocker@bbiw.net</email>
4281      </address> 
4282    </author>
4283    <author initials="P." surname="Overell" fullname="Paul Overell">
4284      <organization>THUS plc.</organization>
4285      <address>
4286        <email>paul.overell@thus.net</email>
4287      </address>
4288    </author>
4289    <date month="January" year="2008"/>
4290  </front>
4291  <seriesInfo name="STD" value="68"/>
4292  <seriesInfo name="RFC" value="5234"/>
4293</reference>
4294
4295<reference anchor="RFC2119">
4296  <front>
4297    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4298    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4299      <organization>Harvard University</organization>
4300      <address><email>sob@harvard.edu</email></address>
4301    </author>
4302    <date month="March" year="1997"/>
4303  </front>
4304  <seriesInfo name="BCP" value="14"/>
4305  <seriesInfo name="RFC" value="2119"/>
4306</reference>
4307
4308<reference anchor="RFC3986">
4309 <front>
4310  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4311  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4312    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4313    <address>
4314       <email>timbl@w3.org</email>
4315       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4316    </address>
4317  </author>
4318  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4319    <organization abbrev="Day Software">Day Software</organization>
4320    <address>
4321      <email>fielding@gbiv.com</email>
4322      <uri>http://roy.gbiv.com/</uri>
4323    </address>
4324  </author>
4325  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4326    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4327    <address>
4328      <email>LMM@acm.org</email>
4329      <uri>http://larry.masinter.net/</uri>
4330    </address>
4331  </author>
4332  <date month='January' year='2005'></date>
4333 </front>
4334 <seriesInfo name="STD" value="66"/>
4335 <seriesInfo name="RFC" value="3986"/>
4336</reference>
4337
4338<reference anchor="USASCII">
4339  <front>
4340    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4341    <author>
4342      <organization>American National Standards Institute</organization>
4343    </author>
4344    <date year="1986"/>
4345  </front>
4346  <seriesInfo name="ANSI" value="X3.4"/>
4347</reference>
4348
4349<reference anchor="RFC1950">
4350  <front>
4351    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4352    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4353      <organization>Aladdin Enterprises</organization>
4354      <address><email>ghost@aladdin.com</email></address>
4355    </author>
4356    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4357    <date month="May" year="1996"/>
4358  </front>
4359  <seriesInfo name="RFC" value="1950"/>
4360  <!--<annotation>
4361    RFC 1950 is an Informational RFC, thus it might be less stable than
4362    this specification. On the other hand, this downward reference was
4363    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4364    therefore it is unlikely to cause problems in practice. See also
4365    <xref target="BCP97"/>.
4366  </annotation>-->
4367</reference>
4368
4369<reference anchor="RFC1951">
4370  <front>
4371    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4372    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4373      <organization>Aladdin Enterprises</organization>
4374      <address><email>ghost@aladdin.com</email></address>
4375    </author>
4376    <date month="May" year="1996"/>
4377  </front>
4378  <seriesInfo name="RFC" value="1951"/>
4379  <!--<annotation>
4380    RFC 1951 is an Informational RFC, thus it might be less stable than
4381    this specification. On the other hand, this downward reference was
4382    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4383    therefore it is unlikely to cause problems in practice. See also
4384    <xref target="BCP97"/>.
4385  </annotation>-->
4386</reference>
4387
4388<reference anchor="RFC1952">
4389  <front>
4390    <title>GZIP file format specification version 4.3</title>
4391    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4392      <organization>Aladdin Enterprises</organization>
4393      <address><email>ghost@aladdin.com</email></address>
4394    </author>
4395    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4396      <address><email>gzip@prep.ai.mit.edu</email></address>
4397    </author>
4398    <author initials="M." surname="Adler" fullname="Mark Adler">
4399      <address><email>madler@alumni.caltech.edu</email></address>
4400    </author>
4401    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4402      <address><email>ghost@aladdin.com</email></address>
4403    </author>
4404    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4405      <address><email>randeg@alumni.rpi.edu</email></address>
4406    </author>
4407    <date month="May" year="1996"/>
4408  </front>
4409  <seriesInfo name="RFC" value="1952"/>
4410  <!--<annotation>
4411    RFC 1952 is an Informational RFC, thus it might be less stable than
4412    this specification. On the other hand, this downward reference was
4413    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4414    therefore it is unlikely to cause problems in practice. See also
4415    <xref target="BCP97"/>.
4416  </annotation>-->
4417</reference>
4418
4419</references>
4420
4421<references title="Informative References">
4422
4423<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4424  <front>
4425    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4426    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4427    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4428    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4429    <author initials="H." surname="Lie" fullname="H. Lie"/>
4430    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4431    <date year="1997" month="September"/>
4432  </front>
4433  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4434</reference>
4435
4436<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4437  <front>
4438    <title>Improving HTTP Latency</title>
4439    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4440    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4441    <date year="1995" month="December"/>
4442  </front>
4443  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4444</reference>
4445
4446<reference anchor='RFC1919'>
4447  <front>
4448    <title>Classical versus Transparent IP Proxies</title>
4449    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4450      <address><email>mchatel@pax.eunet.ch</email></address>
4451    </author>
4452    <date year='1996' month='March' />
4453  </front>
4454  <seriesInfo name='RFC' value='1919' />
4455</reference>
4456
4457<reference anchor="RFC1945">
4458  <front>
4459    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4460    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4461      <organization>MIT, Laboratory for Computer Science</organization>
4462      <address><email>timbl@w3.org</email></address>
4463    </author>
4464    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4465      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4466      <address><email>fielding@ics.uci.edu</email></address>
4467    </author>
4468    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4469      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4470      <address><email>frystyk@w3.org</email></address>
4471    </author>
4472    <date month="May" year="1996"/>
4473  </front>
4474  <seriesInfo name="RFC" value="1945"/>
4475</reference>
4476
4477<reference anchor="RFC2045">
4478  <front>
4479    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4480    <author initials="N." surname="Freed" fullname="Ned Freed">
4481      <organization>Innosoft International, Inc.</organization>
4482      <address><email>ned@innosoft.com</email></address>
4483    </author>
4484    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4485      <organization>First Virtual Holdings</organization>
4486      <address><email>nsb@nsb.fv.com</email></address>
4487    </author>
4488    <date month="November" year="1996"/>
4489  </front>
4490  <seriesInfo name="RFC" value="2045"/>
4491</reference>
4492
4493<reference anchor="RFC2047">
4494  <front>
4495    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4496    <author initials="K." surname="Moore" fullname="Keith Moore">
4497      <organization>University of Tennessee</organization>
4498      <address><email>moore@cs.utk.edu</email></address>
4499    </author>
4500    <date month="November" year="1996"/>
4501  </front>
4502  <seriesInfo name="RFC" value="2047"/>
4503</reference>
4504
4505<reference anchor="RFC2068">
4506  <front>
4507    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4508    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4509      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4510      <address><email>fielding@ics.uci.edu</email></address>
4511    </author>
4512    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4513      <organization>MIT Laboratory for Computer Science</organization>
4514      <address><email>jg@w3.org</email></address>
4515    </author>
4516    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4517      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4518      <address><email>mogul@wrl.dec.com</email></address>
4519    </author>
4520    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4521      <organization>MIT Laboratory for Computer Science</organization>
4522      <address><email>frystyk@w3.org</email></address>
4523    </author>
4524    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4525      <organization>MIT Laboratory for Computer Science</organization>
4526      <address><email>timbl@w3.org</email></address>
4527    </author>
4528    <date month="January" year="1997"/>
4529  </front>
4530  <seriesInfo name="RFC" value="2068"/>
4531</reference>
4532
4533<reference anchor="RFC2145">
4534  <front>
4535    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4536    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4537      <organization>Western Research Laboratory</organization>
4538      <address><email>mogul@wrl.dec.com</email></address>
4539    </author>
4540    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4541      <organization>Department of Information and Computer Science</organization>
4542      <address><email>fielding@ics.uci.edu</email></address>
4543    </author>
4544    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4545      <organization>MIT Laboratory for Computer Science</organization>
4546      <address><email>jg@w3.org</email></address>
4547    </author>
4548    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4549      <organization>W3 Consortium</organization>
4550      <address><email>frystyk@w3.org</email></address>
4551    </author>
4552    <date month="May" year="1997"/>
4553  </front>
4554  <seriesInfo name="RFC" value="2145"/>
4555</reference>
4556
4557<reference anchor="RFC2616">
4558  <front>
4559    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4560    <author initials="R." surname="Fielding" fullname="R. Fielding">
4561      <organization>University of California, Irvine</organization>
4562      <address><email>fielding@ics.uci.edu</email></address>
4563    </author>
4564    <author initials="J." surname="Gettys" fullname="J. Gettys">
4565      <organization>W3C</organization>
4566      <address><email>jg@w3.org</email></address>
4567    </author>
4568    <author initials="J." surname="Mogul" fullname="J. Mogul">
4569      <organization>Compaq Computer Corporation</organization>
4570      <address><email>mogul@wrl.dec.com</email></address>
4571    </author>
4572    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4573      <organization>MIT Laboratory for Computer Science</organization>
4574      <address><email>frystyk@w3.org</email></address>
4575    </author>
4576    <author initials="L." surname="Masinter" fullname="L. Masinter">
4577      <organization>Xerox Corporation</organization>
4578      <address><email>masinter@parc.xerox.com</email></address>
4579    </author>
4580    <author initials="P." surname="Leach" fullname="P. Leach">
4581      <organization>Microsoft Corporation</organization>
4582      <address><email>paulle@microsoft.com</email></address>
4583    </author>
4584    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4585      <organization>W3C</organization>
4586      <address><email>timbl@w3.org</email></address>
4587    </author>
4588    <date month="June" year="1999"/>
4589  </front>
4590  <seriesInfo name="RFC" value="2616"/>
4591</reference>
4592
4593<reference anchor='RFC2817'>
4594  <front>
4595    <title>Upgrading to TLS Within HTTP/1.1</title>
4596    <author initials='R.' surname='Khare' fullname='R. Khare'>
4597      <organization>4K Associates / UC Irvine</organization>
4598      <address><email>rohit@4K-associates.com</email></address>
4599    </author>
4600    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4601      <organization>Agranat Systems, Inc.</organization>
4602      <address><email>lawrence@agranat.com</email></address>
4603    </author>
4604    <date year='2000' month='May' />
4605  </front>
4606  <seriesInfo name='RFC' value='2817' />
4607</reference>
4608
4609<reference anchor='RFC2818'>
4610  <front>
4611    <title>HTTP Over TLS</title>
4612    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4613      <organization>RTFM, Inc.</organization>
4614      <address><email>ekr@rtfm.com</email></address>
4615    </author>
4616    <date year='2000' month='May' />
4617  </front>
4618  <seriesInfo name='RFC' value='2818' />
4619</reference>
4620
4621<reference anchor='RFC2965'>
4622  <front>
4623    <title>HTTP State Management Mechanism</title>
4624    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4625      <organization>Bell Laboratories, Lucent Technologies</organization>
4626      <address><email>dmk@bell-labs.com</email></address>
4627    </author>
4628    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4629      <organization>Epinions.com, Inc.</organization>
4630      <address><email>lou@montulli.org</email></address>
4631    </author>
4632    <date year='2000' month='October' />
4633  </front>
4634  <seriesInfo name='RFC' value='2965' />
4635</reference>
4636
4637<reference anchor='RFC3040'>
4638  <front>
4639    <title>Internet Web Replication and Caching Taxonomy</title>
4640    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4641      <organization>Equinix, Inc.</organization>
4642    </author>
4643    <author initials='I.' surname='Melve' fullname='I. Melve'>
4644      <organization>UNINETT</organization>
4645    </author>
4646    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4647      <organization>CacheFlow Inc.</organization>
4648    </author>
4649    <date year='2001' month='January' />
4650  </front>
4651  <seriesInfo name='RFC' value='3040' />
4652</reference>
4653
4654<reference anchor='RFC3864'>
4655  <front>
4656    <title>Registration Procedures for Message Header Fields</title>
4657    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4658      <organization>Nine by Nine</organization>
4659      <address><email>GK-IETF@ninebynine.org</email></address>
4660    </author>
4661    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4662      <organization>BEA Systems</organization>
4663      <address><email>mnot@pobox.com</email></address>
4664    </author>
4665    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4666      <organization>HP Labs</organization>
4667      <address><email>JeffMogul@acm.org</email></address>
4668    </author>
4669    <date year='2004' month='September' />
4670  </front>
4671  <seriesInfo name='BCP' value='90' />
4672  <seriesInfo name='RFC' value='3864' />
4673</reference>
4674
4675<reference anchor='RFC4033'>
4676  <front>
4677    <title>DNS Security Introduction and Requirements</title>
4678    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4679    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4680    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4681    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4682    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4683    <date year='2005' month='March' />
4684  </front>
4685  <seriesInfo name='RFC' value='4033' />
4686</reference>
4687
4688<reference anchor="RFC4288">
4689  <front>
4690    <title>Media Type Specifications and Registration Procedures</title>
4691    <author initials="N." surname="Freed" fullname="N. Freed">
4692      <organization>Sun Microsystems</organization>
4693      <address>
4694        <email>ned.freed@mrochek.com</email>
4695      </address>
4696    </author>
4697    <author initials="J." surname="Klensin" fullname="J. Klensin">
4698      <address>
4699        <email>klensin+ietf@jck.com</email>
4700      </address>
4701    </author>
4702    <date year="2005" month="December"/>
4703  </front>
4704  <seriesInfo name="BCP" value="13"/>
4705  <seriesInfo name="RFC" value="4288"/>
4706</reference>
4707
4708<reference anchor='RFC4395'>
4709  <front>
4710    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4711    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4712      <organization>AT&amp;T Laboratories</organization>
4713      <address>
4714        <email>tony+urireg@maillennium.att.com</email>
4715      </address>
4716    </author>
4717    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4718      <organization>Qualcomm, Inc.</organization>
4719      <address>
4720        <email>hardie@qualcomm.com</email>
4721      </address>
4722    </author>
4723    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4724      <organization>Adobe Systems</organization>
4725      <address>
4726        <email>LMM@acm.org</email>
4727      </address>
4728    </author>
4729    <date year='2006' month='February' />
4730  </front>
4731  <seriesInfo name='BCP' value='115' />
4732  <seriesInfo name='RFC' value='4395' />
4733</reference>
4734
4735<reference anchor='RFC4559'>
4736  <front>
4737    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4738    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4739    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4740    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4741    <date year='2006' month='June' />
4742  </front>
4743  <seriesInfo name='RFC' value='4559' />
4744</reference>
4745
4746<reference anchor='RFC5226'>
4747  <front>
4748    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4749    <author initials='T.' surname='Narten' fullname='T. Narten'>
4750      <organization>IBM</organization>
4751      <address><email>narten@us.ibm.com</email></address>
4752    </author>
4753    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4754      <organization>Google</organization>
4755      <address><email>Harald@Alvestrand.no</email></address>
4756    </author>
4757    <date year='2008' month='May' />
4758  </front>
4759  <seriesInfo name='BCP' value='26' />
4760  <seriesInfo name='RFC' value='5226' />
4761</reference>
4762
4763<reference anchor="RFC5322">
4764  <front>
4765    <title>Internet Message Format</title>
4766    <author initials="P." surname="Resnick" fullname="P. Resnick">
4767      <organization>Qualcomm Incorporated</organization>
4768    </author>
4769    <date year="2008" month="October"/>
4770  </front> 
4771  <seriesInfo name="RFC" value="5322"/>
4772</reference>
4773
4774<reference anchor="RFC6265">
4775  <front>
4776    <title>HTTP State Management Mechanism</title>
4777    <author initials="A." surname="Barth" fullname="Adam Barth">
4778      <organization abbrev="U.C. Berkeley">
4779        University of California, Berkeley
4780      </organization>
4781      <address><email>abarth@eecs.berkeley.edu</email></address>
4782    </author>
4783    <date year="2011" month="April" />
4784  </front>
4785  <seriesInfo name="RFC" value="6265"/>
4786</reference>
4787
4788<!--<reference anchor='BCP97'>
4789  <front>
4790    <title>Handling Normative References to Standards-Track Documents</title>
4791    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4792      <address>
4793        <email>klensin+ietf@jck.com</email>
4794      </address>
4795    </author>
4796    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4797      <organization>MIT</organization>
4798      <address>
4799        <email>hartmans-ietf@mit.edu</email>
4800      </address>
4801    </author>
4802    <date year='2007' month='June' />
4803  </front>
4804  <seriesInfo name='BCP' value='97' />
4805  <seriesInfo name='RFC' value='4897' />
4806</reference>-->
4807
4808<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4809  <front>
4810    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4811    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4812    <date year="2001" month="November"/>
4813  </front>
4814  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4815</reference>
4816
4817<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4818  <front>
4819    <title>Analysis of HTTP Performance Problems</title>
4820    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4821    <date/>
4822  </front>
4823</reference>
4824
4825<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4826  <front>
4827  <title>Analysis of HTTP Performance</title>
4828  <author initials="J." surname="Touch" fullname="Joe Touch">
4829    <organization>USC/Information Sciences Institute</organization>
4830    <address><email>touch@isi.edu</email></address>
4831  </author>
4832  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4833    <organization>USC/Information Sciences Institute</organization>
4834    <address><email>johnh@isi.edu</email></address>
4835  </author>
4836  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4837    <organization>USC/Information Sciences Institute</organization>
4838    <address><email>katia@isi.edu</email></address>
4839  </author>
4840  <date year="1998" month="Aug"/>
4841  </front>
4842  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4843  <annotation>(original report dated Aug. 1996)</annotation>
4844</reference>
4845
4846</references>
4847
4848
4849<section title="HTTP Version History" anchor="compatibility">
4850<t>
4851   HTTP has been in use by the World-Wide Web global information initiative
4852   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4853   was a simple protocol for hypertext data transfer across the Internet
4854   with only a single request method (GET) and no metadata.
4855   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4856   methods and MIME-like messaging that could include metadata about the data
4857   transferred and modifiers on the request/response semantics. However,
4858   HTTP/1.0 did not sufficiently take into consideration the effects of
4859   hierarchical proxies, caching, the need for persistent connections, or
4860   name-based virtual hosts. The proliferation of incompletely-implemented
4861   applications calling themselves "HTTP/1.0" further necessitated a
4862   protocol version change in order for two communicating applications
4863   to determine each other's true capabilities.
4864</t>
4865<t>
4866   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4867   requirements that enable reliable implementations, adding only
4868   those new features that will either be safely ignored by an HTTP/1.0
4869   recipient or only sent when communicating with a party advertising
4870   conformance with HTTP/1.1.
4871</t>
4872<t>
4873   It is beyond the scope of a protocol specification to mandate
4874   conformance with previous versions. HTTP/1.1 was deliberately
4875   designed, however, to make supporting previous versions easy.
4876   We would expect a general-purpose HTTP/1.1 server to understand
4877   any valid request in the format of HTTP/1.0 and respond appropriately
4878   with an HTTP/1.1 message that only uses features understood (or
4879   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4880   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4881</t>
4882<t>
4883   Since HTTP/0.9 did not support header fields in a request,
4884   there is no mechanism for it to support name-based virtual
4885   hosts (selection of resource by inspection of the Host header
4886   field).  Any server that implements name-based virtual hosts
4887   ought to disable support for HTTP/0.9.  Most requests that
4888   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4889   requests wherein a buggy client failed to properly encode
4890   linear whitespace found in a URI reference and placed in
4891   the request-target.
4892</t>
4893
4894<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4895<t>
4896   This section summarizes major differences between versions HTTP/1.0
4897   and HTTP/1.1.
4898</t>
4899
4900<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4901<t>
4902   The requirements that clients and servers support the Host header
4903   field (<xref target="header.host"/>), report an error if it is
4904   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4905   are among the most important changes defined by HTTP/1.1.
4906</t>
4907<t>
4908   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4909   addresses and servers; there was no other established mechanism for
4910   distinguishing the intended server of a request than the IP address
4911   to which that request was directed. The Host header field was
4912   introduced during the development of HTTP/1.1 and, though it was
4913   quickly implemented by most HTTP/1.0 browsers, additional requirements
4914   were placed on all HTTP/1.1 requests in order to ensure complete
4915   adoption.  At the time of this writing, most HTTP-based services
4916   are dependent upon the Host header field for targeting requests.
4917</t>
4918</section>
4919
4920<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4921<t>
4922   In HTTP/1.0, each connection is established by the client prior to the
4923   request and closed by the server after sending the response. However, some
4924   implementations implement the explicitly negotiated ("Keep-Alive") version
4925   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4926   target="RFC2068"/>.
4927</t>
4928<t>
4929   Some clients and servers might wish to be compatible with these previous
4930   approaches to persistent connections, by explicitly negotiating for them
4931   with a "Connection: keep-alive" request header field. However, some
4932   experimental implementations of HTTP/1.0 persistent connections are faulty;
4933   for example, if a HTTP/1.0 proxy server doesn't understand Connection, it
4934   will erroneously forward that header to the next inbound server, which
4935   would result in a hung connection.
4936</t>
4937<t>
4938   One attempted solution was the introduction of a Proxy-Connection header,
4939   targeted specifically at proxies. In practice, this was also unworkable,
4940   because proxies are often deployed in multiple layers, bringing about the
4941   same problem discussed above.
4942</t>
4943<t>
4944   As a result, clients are encouraged not to send the Proxy-Connection header
4945   in any requests.
4946</t>
4947<t>
4948   Clients are also encouraged to consider the use of Connection: keep-alive
4949   in requests carefully; while they can enable persistent connections with
4950   HTTP/1.0 servers, clients using them need will need to monitor the
4951   connection for "hung" requests (which indicate that the client ought stop
4952   sending the header), and this mechanism ought not be used by clients at all
4953   when a proxy is being used.
4954</t>
4955</section>
4956</section>
4957
4958<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4959<t>
4960  Empty list elements in list productions have been deprecated.
4961  (<xref target="abnf.extension"/>)
4962</t>
4963<t>
4964  Rules about implicit linear whitespace between certain grammar productions
4965  have been removed; now whitespace is only allowed where specifically
4966  defined in the ABNF.
4967  (<xref target="whitespace"/>)
4968</t>
4969<t>
4970  Clarify that the string "HTTP" in the HTTP-version ABFN production is case
4971  sensitive. Restrict the version numbers to be single digits due to the fact
4972  that implementations are known to handle multi-digit version numbers
4973  incorrectly.
4974  (<xref target="http.version"/>)
4975</t>
4976<t>
4977  Require that invalid whitespace around field-names be rejected.
4978  (<xref target="header.fields"/>)
4979</t>
4980<t> 
4981  The NUL octet is no longer allowed in comment and quoted-string
4982  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4983  Non-ASCII content in header fields and reason phrase has been obsoleted and
4984  made opaque (the TEXT rule was removed).
4985  (<xref target="field.components"/>)
4986</t>
4987<t>
4988  Require recipients to handle bogus Content-Length header fields as errors.
4989  (<xref target="message.body"/>)
4990</t>
4991<t>
4992  Remove reference to non-existent identity transfer-coding value tokens.
4993  (Sections <xref format="counter" target="message.body"/> and
4994  <xref format="counter" target="transfer.codings"/>)
4995</t>
4996<t>
4997  Update use of abs_path production from RFC 1808 to the path-absolute + query
4998  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4999  request method only.
5000  (<xref target="request-target"/>)
5001</t>
5002<t>
5003  Clarification that the chunk length does not include the count of the octets
5004  in the chunk header and trailer. Furthermore disallowed line folding
5005  in chunk extensions, and deprecate their use.
5006  (<xref target="chunked.encoding"/>)
5007</t>
5008<t>
5009  Remove hard limit of two connections per server.
5010  Remove requirement to retry a sequence of requests as long it was idempotent.
5011  Remove requirements about when servers are allowed to close connections
5012  prematurely.
5013  (<xref target="persistent.practical"/>)
5014</t>
5015<t>
5016  Remove requirement to retry requests under certain cirumstances when the
5017  server prematurely closes the connection.
5018  (<xref target="message.transmission.requirements"/>)
5019</t>
5020<t>
5021  Change ABNF productions for header fields to only define the field value.
5022  (<xref target="header.field.definitions"/>)
5023</t>
5024<t>
5025  Clarify exactly when close connection options must be sent.
5026  (<xref target="header.connection"/>)
5027</t>
5028<t>
5029  Define the semantics of the "Upgrade" header field in responses other than
5030  101 (this was incorporated from <xref target="RFC2817"/>).
5031  (<xref target="header.upgrade"/>)
5032</t>
5033</section>
5034</section>
5035
5036<?BEGININC p1-messaging.abnf-appendix ?>
5037<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
5038<figure>
5039<artwork type="abnf" name="p1-messaging.parsed-abnf">
5040<x:ref>BWS</x:ref> = OWS
5041
5042<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5043 connection-token ] )
5044<x:ref>Content-Length</x:ref> = 1*DIGIT
5045
5046<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5047 ]
5048<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
5049<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
5050<x:ref>Host</x:ref> = uri-host [ ":" port ]
5051
5052<x:ref>OWS</x:ref> = *( SP / HTAB )
5053
5054<x:ref>RWS</x:ref> = 1*( SP / HTAB )
5055
5056<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5057<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5058<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5059 transfer-coding ] )
5060
5061<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5062<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
5063
5064<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5065 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5066 )
5067
5068<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5069<x:ref>attribute</x:ref> = token
5070<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5071
5072<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5073<x:ref>chunk-data</x:ref> = 1*OCTET
5074<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5075<x:ref>chunk-ext-name</x:ref> = token
5076<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5077<x:ref>chunk-size</x:ref> = 1*HEXDIG
5078<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
5079<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5080<x:ref>connection-token</x:ref> = token
5081<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5082 / %x2A-5B ; '*'-'['
5083 / %x5D-7E ; ']'-'~'
5084 / obs-text
5085
5086<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5087<x:ref>field-name</x:ref> = token
5088<x:ref>field-value</x:ref> = *( field-content / obs-fold )
5089
5090<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
5091<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5092<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5093
5094<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
5095
5096<x:ref>message-body</x:ref> = *OCTET
5097<x:ref>method</x:ref> = token
5098
5099<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
5100<x:ref>obs-text</x:ref> = %x80-FF
5101
5102<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5103<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5104<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5105<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5106<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
5107<x:ref>protocol-name</x:ref> = token
5108<x:ref>protocol-version</x:ref> = token
5109<x:ref>pseudonym</x:ref> = token
5110
5111<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5112 / %x5D-7E ; ']'-'~'
5113 / obs-text
5114<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
5115 / %x5D-7E ; ']'-'~'
5116 / obs-text
5117<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5118<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5119<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5120<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5121<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5122<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5123
5124<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5125<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5126<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5127<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5128<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
5129<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5130 / authority
5131
5132<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5133 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5134<x:ref>start-line</x:ref> = request-line / status-line
5135<x:ref>status-code</x:ref> = 3DIGIT
5136<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
5137
5138<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5139<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5140 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5141<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5142<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5143<x:ref>token</x:ref> = 1*tchar
5144<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5145<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5146 transfer-extension
5147<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5148<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5149
5150<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5151
5152<x:ref>value</x:ref> = word
5153
5154<x:ref>word</x:ref> = token / quoted-string
5155</artwork>
5156</figure>
5157<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5158; Connection defined but not used
5159; Content-Length defined but not used
5160; HTTP-message defined but not used
5161; Host defined but not used
5162; TE defined but not used
5163; Trailer defined but not used
5164; Transfer-Encoding defined but not used
5165; URI-reference defined but not used
5166; Upgrade defined but not used
5167; Via defined but not used
5168; chunked-body defined but not used
5169; http-URI defined but not used
5170; https-URI defined but not used
5171; partial-URI defined but not used
5172; special defined but not used
5173</artwork></figure></section>
5174<?ENDINC p1-messaging.abnf-appendix ?>
5175
5176<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5177
5178<section title="Since RFC 2616">
5179<t>
5180  Extracted relevant partitions from <xref target="RFC2616"/>.
5181</t>
5182</section>
5183
5184<section title="Since draft-ietf-httpbis-p1-messaging-00">
5185<t>
5186  Closed issues:
5187  <list style="symbols"> 
5188    <t>
5189      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5190      "HTTP Version should be case sensitive"
5191      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5192    </t>
5193    <t>
5194      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5195      "'unsafe' characters"
5196      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5197    </t>
5198    <t>
5199      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5200      "Chunk Size Definition"
5201      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5202    </t>
5203    <t>
5204      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5205      "Message Length"
5206      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5207    </t>
5208    <t>
5209      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5210      "Media Type Registrations"
5211      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5212    </t>
5213    <t>
5214      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5215      "URI includes query"
5216      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5217    </t>
5218    <t>
5219      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5220      "No close on 1xx responses"
5221      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5222    </t>
5223    <t>
5224      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5225      "Remove 'identity' token references"
5226      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5227    </t>
5228    <t>
5229      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5230      "Import query BNF"
5231    </t>
5232    <t>
5233      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5234      "qdtext BNF"
5235    </t>
5236    <t>
5237      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5238      "Normative and Informative references"
5239    </t>
5240    <t>
5241      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5242      "RFC2606 Compliance"
5243    </t>
5244    <t>
5245      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5246      "RFC977 reference"
5247    </t>
5248    <t>
5249      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5250      "RFC1700 references"
5251    </t>
5252    <t>
5253      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5254      "inconsistency in date format explanation"
5255    </t>
5256    <t>
5257      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5258      "Date reference typo"
5259    </t>
5260    <t>
5261      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5262      "Informative references"
5263    </t>
5264    <t>
5265      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5266      "ISO-8859-1 Reference"
5267    </t>
5268    <t>
5269      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5270      "Normative up-to-date references"
5271    </t>
5272  </list>
5273</t>
5274<t>
5275  Other changes:
5276  <list style="symbols"> 
5277    <t>
5278      Update media type registrations to use RFC4288 template.
5279    </t>
5280    <t>
5281      Use names of RFC4234 core rules DQUOTE and HTAB,
5282      fix broken ABNF for chunk-data
5283      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5284    </t>
5285  </list>
5286</t>
5287</section>
5288
5289<section title="Since draft-ietf-httpbis-p1-messaging-01">
5290<t>
5291  Closed issues:
5292  <list style="symbols"> 
5293    <t>
5294      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5295      "Bodies on GET (and other) requests"
5296    </t>
5297    <t>
5298      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5299      "Updating to RFC4288"
5300    </t>
5301    <t>
5302      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5303      "Status Code and Reason Phrase"
5304    </t>
5305    <t>
5306      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5307      "rel_path not used"
5308    </t>
5309  </list>
5310</t>
5311<t>
5312  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5313  <list style="symbols"> 
5314    <t>
5315      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5316      "trailer-part").
5317    </t>
5318    <t>
5319      Avoid underscore character in rule names ("http_URL" ->
5320      "http-URL", "abs_path" -> "path-absolute").
5321    </t>
5322    <t>
5323      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5324      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5325      have to be updated when switching over to RFC3986.
5326    </t>
5327    <t>
5328      Synchronize core rules with RFC5234.
5329    </t>
5330    <t>
5331      Get rid of prose rules that span multiple lines.
5332    </t>
5333    <t>
5334      Get rid of unused rules LOALPHA and UPALPHA.
5335    </t>
5336    <t>
5337      Move "Product Tokens" section (back) into Part 1, as "token" is used
5338      in the definition of the Upgrade header field.
5339    </t>
5340    <t>
5341      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5342    </t>
5343    <t>
5344      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5345    </t>
5346  </list>
5347</t>
5348</section>
5349
5350<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5351<t>
5352  Closed issues:
5353  <list style="symbols"> 
5354    <t>
5355      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5356      "HTTP-date vs. rfc1123-date"
5357    </t>
5358    <t>
5359      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5360      "WS in quoted-pair"
5361    </t>
5362  </list>
5363</t>
5364<t>
5365  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5366  <list style="symbols"> 
5367    <t>
5368      Reference RFC 3984, and update header field registrations for headers defined
5369      in this document.
5370    </t>
5371  </list>
5372</t>
5373<t>
5374  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5375  <list style="symbols"> 
5376    <t>
5377      Replace string literals when the string really is case-sensitive (HTTP-version).
5378    </t>
5379  </list>
5380</t>
5381</section>
5382
5383<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5384<t>
5385  Closed issues:
5386  <list style="symbols"> 
5387    <t>
5388      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5389      "Connection closing"
5390    </t>
5391    <t>
5392      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5393      "Move registrations and registry information to IANA Considerations"
5394    </t>
5395    <t>
5396      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5397      "need new URL for PAD1995 reference"
5398    </t>
5399    <t>
5400      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5401      "IANA Considerations: update HTTP URI scheme registration"
5402    </t>
5403    <t>
5404      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5405      "Cite HTTPS URI scheme definition"
5406    </t>
5407    <t>
5408      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5409      "List-type headers vs Set-Cookie"
5410    </t>
5411  </list>
5412</t>
5413<t>
5414  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5415  <list style="symbols"> 
5416    <t>
5417      Replace string literals when the string really is case-sensitive (HTTP-Date).
5418    </t>
5419    <t>
5420      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5421    </t>
5422  </list>
5423</t>
5424</section>
5425
5426<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5427<t>
5428  Closed issues:
5429  <list style="symbols"> 
5430    <t>
5431      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5432      "Out-of-date reference for URIs"
5433    </t>
5434    <t>
5435      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5436      "RFC 2822 is updated by RFC 5322"
5437    </t>
5438  </list>
5439</t>
5440<t>
5441  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5442  <list style="symbols"> 
5443    <t>
5444      Use "/" instead of "|" for alternatives.
5445    </t>
5446    <t>
5447      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5448    </t>
5449    <t>
5450      Only reference RFC 5234's core rules.
5451    </t>
5452    <t>
5453      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5454      whitespace ("OWS") and required whitespace ("RWS").
5455    </t>
5456    <t>
5457      Rewrite ABNFs to spell out whitespace rules, factor out
5458      header field value format definitions.
5459    </t>
5460  </list>
5461</t>
5462</section>
5463
5464<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5465<t>
5466  Closed issues:
5467  <list style="symbols"> 
5468    <t>
5469      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5470      "Header LWS"
5471    </t>
5472    <t>
5473      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5474      "Sort 1.3 Terminology"
5475    </t>
5476    <t>
5477      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5478      "RFC2047 encoded words"
5479    </t>
5480    <t>
5481      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5482      "Character Encodings in TEXT"
5483    </t>
5484    <t>
5485      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5486      "Line Folding"
5487    </t>
5488    <t>
5489      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5490      "OPTIONS * and proxies"
5491    </t>
5492    <t>
5493      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5494      "reason-phrase BNF"
5495    </t>
5496    <t>
5497      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5498      "Use of TEXT"
5499    </t>
5500    <t>
5501      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5502      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5503    </t>
5504    <t>
5505      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5506      "RFC822 reference left in discussion of date formats"
5507    </t>
5508  </list>
5509</t>
5510<t>
5511  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5512  <list style="symbols"> 
5513    <t>
5514      Rewrite definition of list rules, deprecate empty list elements.
5515    </t>
5516    <t>
5517      Add appendix containing collected and expanded ABNF.
5518    </t>
5519  </list>
5520</t>
5521<t>
5522  Other changes:
5523  <list style="symbols"> 
5524    <t>
5525      Rewrite introduction; add mostly new Architecture Section.
5526    </t>
5527    <t>
5528      Move definition of quality values from Part 3 into Part 1;
5529      make TE request header field grammar independent of accept-params (defined in Part 3).
5530    </t>
5531  </list>
5532</t>
5533</section>
5534
5535<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5536<t>
5537  Closed issues:
5538  <list style="symbols"> 
5539    <t>
5540      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5541      "base for numeric protocol elements"
5542    </t>
5543    <t>
5544      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5545      "comment ABNF"
5546    </t>
5547  </list>
5548</t>
5549<t>
5550  Partly resolved issues:
5551  <list style="symbols"> 
5552    <t>
5553      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5554      "205 Bodies" (took out language that implied that there might be
5555      methods for which a request body MUST NOT be included)
5556    </t>
5557    <t>
5558      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5559      "editorial improvements around HTTP-date"
5560    </t>
5561  </list>
5562</t>
5563</section>
5564
5565<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5566<t>
5567  Closed issues:
5568  <list style="symbols"> 
5569    <t>
5570      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5571      "Repeating single-value headers"
5572    </t>
5573    <t>
5574      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5575      "increase connection limit"
5576    </t>
5577    <t>
5578      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5579      "IP addresses in URLs"
5580    </t>
5581    <t>
5582      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5583      "take over HTTP Upgrade Token Registry"
5584    </t>
5585    <t>
5586      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5587      "CR and LF in chunk extension values"
5588    </t>
5589    <t>
5590      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5591      "HTTP/0.9 support"
5592    </t>
5593    <t>
5594      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5595      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5596    </t>
5597    <t>
5598      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5599      "move definitions of gzip/deflate/compress to part 1"
5600    </t>
5601    <t>
5602      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5603      "disallow control characters in quoted-pair"
5604    </t>
5605  </list>
5606</t>
5607<t>
5608  Partly resolved issues:
5609  <list style="symbols"> 
5610    <t>
5611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5612      "update IANA requirements wrt Transfer-Coding values" (add the
5613      IANA Considerations subsection)
5614    </t>
5615  </list>
5616</t>
5617</section>
5618
5619<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5620<t>
5621  Closed issues:
5622  <list style="symbols"> 
5623    <t>
5624      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5625      "header parsing, treatment of leading and trailing OWS"
5626    </t>
5627  </list>
5628</t>
5629<t>
5630  Partly resolved issues:
5631  <list style="symbols"> 
5632    <t>
5633      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5634      "Placement of 13.5.1 and 13.5.2"
5635    </t>
5636    <t>
5637      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5638      "use of term "word" when talking about header structure"
5639    </t>
5640  </list>
5641</t>
5642</section>
5643
5644<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5645<t>
5646  Closed issues:
5647  <list style="symbols"> 
5648    <t>
5649      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5650      "Clarification of the term 'deflate'"
5651    </t>
5652    <t>
5653      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5654      "OPTIONS * and proxies"
5655    </t>
5656    <t>
5657      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5658      "MIME-Version not listed in P1, general header fields"
5659    </t>
5660    <t>
5661      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5662      "IANA registry for content/transfer encodings"
5663    </t>
5664    <t>
5665      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5666      "Case-sensitivity of HTTP-date"
5667    </t>
5668    <t>
5669      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5670      "use of term "word" when talking about header structure"
5671    </t>
5672  </list>
5673</t>
5674<t>
5675  Partly resolved issues:
5676  <list style="symbols"> 
5677    <t>
5678      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5679      "Term for the requested resource's URI"
5680    </t>
5681  </list>
5682</t>
5683</section>
5684
5685<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5686<t>
5687  Closed issues:
5688  <list style="symbols">
5689    <t>
5690      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5691      "Connection Closing"
5692    </t>
5693    <t>
5694      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5695      "Delimiting messages with multipart/byteranges"
5696    </t>
5697    <t>
5698      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5699      "Handling multiple Content-Length headers"
5700    </t>
5701    <t>
5702      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5703      "Clarify entity / representation / variant terminology"
5704    </t>
5705    <t>
5706      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5707      "consider removing the 'changes from 2068' sections"
5708    </t>
5709  </list>
5710</t>
5711<t>
5712  Partly resolved issues:
5713  <list style="symbols"> 
5714    <t>
5715      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5716      "HTTP(s) URI scheme definitions"
5717    </t>
5718  </list>
5719</t>
5720</section>
5721
5722<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5723<t>
5724  Closed issues:
5725  <list style="symbols">
5726    <t>
5727      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5728      "Trailer requirements"
5729    </t>
5730    <t>
5731      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5732      "Text about clock requirement for caches belongs in p6"
5733    </t>
5734    <t>
5735      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5736      "effective request URI: handling of missing host in HTTP/1.0"
5737    </t>
5738    <t>
5739      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5740      "confusing Date requirements for clients"
5741    </t>
5742  </list>
5743</t>
5744<t>
5745  Partly resolved issues:
5746  <list style="symbols"> 
5747    <t>
5748      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5749      "Handling multiple Content-Length headers"
5750    </t>
5751  </list>
5752</t>
5753</section>
5754
5755<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5756<t>
5757  Closed issues:
5758  <list style="symbols">
5759    <t>
5760      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5761      "RFC2145 Normative"
5762    </t>
5763    <t>
5764      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5765      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5766    </t>
5767    <t>
5768      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5769      "define 'transparent' proxy"
5770    </t>
5771    <t>
5772      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5773      "Header Classification"
5774    </t>
5775    <t>
5776      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5777      "Is * usable as a request-uri for new methods?"
5778    </t>
5779    <t>
5780      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5781      "Migrate Upgrade details from RFC2817"
5782    </t>
5783    <t>
5784      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5785      "untangle ABNFs for header fields"
5786    </t>
5787    <t>
5788      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5789      "update RFC 2109 reference"
5790    </t>
5791  </list>
5792</t>
5793</section>
5794
5795<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5796<t>
5797  Closed issues:
5798  <list style="symbols">
5799    <t>
5800      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5801      "Allow is not in 13.5.2"
5802    </t>
5803    <t>
5804      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5805      "Handling multiple Content-Length headers"
5806    </t>
5807    <t>
5808      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5809      "untangle ABNFs for header fields"
5810    </t>
5811    <t>
5812      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5813      "Content-Length ABNF broken"
5814    </t>
5815  </list>
5816</t>
5817</section>
5818
5819<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5820<t>
5821  Closed issues:
5822  <list style="symbols">
5823    <t>
5824      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5825      "HTTP-version should be redefined as fixed length pair of DIGIT . DIGIT"
5826    </t>
5827    <t>
5828      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5829      "Recommend minimum sizes for protocol elements"
5830    </t>
5831    <t>
5832      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5833      "Set expectations around buffering"
5834    </t>
5835    <t>
5836      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5837      "Considering messages in isolation"
5838    </t>
5839  </list>
5840</t>
5841</section>
5842
5843<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5844<t>
5845  Closed issues:
5846  <list style="symbols">
5847    <t>
5848      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5849      "DNS Spoofing / DNS Binding advice"
5850    </t>
5851    <t>
5852      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5853      "move RFCs 2145, 2616, 2817 to Historic status"
5854    </t>
5855    <t>
5856      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5857      "\-escaping in quoted strings"
5858    </t>
5859    <t>
5860      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5861      "'Close' should be reserved in the HTTP header field registry"
5862    </t>
5863  </list>
5864</t>
5865</section>
5866
5867<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5868<t>
5869  Closed issues:
5870  <list style="symbols">
5871    <t>
5872      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5873      "Document HTTP's error-handling philosophy"
5874    </t>
5875    <t>
5876      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5877      "Explain header registration"
5878    </t>
5879    <t>
5880      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5881      "Revise Acknowledgements Sections"
5882    </t>
5883    <t>
5884      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5885      "Retrying Requests"
5886    </t>
5887    <t>
5888      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5889      "Closing the connection on server error"
5890    </t>
5891  </list>
5892</t>
5893</section>
5894
5895<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5896<t>
5897  Closed issues:
5898  <list style="symbols">
5899    <t>
5900      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/166"/>:
5901      "Clarify 'User Agent'"
5902    </t>
5903    <t>
5904      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/300"/>:
5905      "Define non-final responses"
5906    </t>
5907    <t>
5908      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
5909      "intended maturity level vs normative references"
5910    </t>
5911    <t>
5912      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/324"/>:
5913      "Intermediary rewriting of queries"
5914    </t>
5915    <t>
5916      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/158"/>:
5917      "Proxy-Connection and Keep-Alive"
5918    </t>
5919  </list>
5920</t>
5921</section>
5922
5923<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5924<t>
5925  Closed issues:
5926  <list style="symbols">
5927    <t>
5928      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
5929      "Misplaced text on connection handling in p2"
5930    </t>
5931    <t>
5932      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/335"/>:
5933      "wording of line folding rule"
5934    </t>
5935    <t>
5936      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/343"/>:
5937      "chunk-extensions"
5938    </t>
5939  </list>
5940</t>
5941</section>
5942
5943</section>
5944
5945</back>
5946</rfc>
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