source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1537

Last change on this file since 1537 was 1537, checked in by fielding@…, 8 years ago

Revert [1471] and move the 1xx note to a normaltive section on associating
one or more responses to the corresponding request(s). Requirements do not
belong in the intro and the text provided was not sufficient to answer #300.

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 243.5 KB
Line 
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 "February">
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-Prot-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-Prot-Name"/>
718  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
719  <x:ref>HTTP-Prot-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 an HTTP header field does not change
744   between minor versions of the same major 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   The 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   See &method; for further information, such as the list of methods defined
1133   by this specification, the IANA registry, and considerations for new methods.
1134</t>
1135</section>
1136
1137<section title="request-target" anchor="request-target">
1138  <x:anchor-alias value="request-target"/>
1139<t>
1140   The request-target identifies the target resource upon which to apply
1141   the request.  The four options for request-target are described in
1142   <xref target="request-target-types"/>.
1143</t>
1144<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1145  <x:ref>request-target</x:ref> = "*"
1146                 / <x:ref>absolute-URI</x:ref>
1147                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1148                 / <x:ref>authority</x:ref>
1149</artwork></figure>
1150<t>
1151   HTTP does not place a pre-defined limit on the length of a request-target.
1152   A server &MUST; be prepared to receive URIs of unbounded length and
1153   respond with the 414 (URI Too Long) status code if the received
1154   request-target would be longer than the server wishes to handle
1155   (see &status-414;).
1156</t>
1157<t>
1158   Various ad-hoc limitations on request-target length are found in practice.
1159   It is &RECOMMENDED; that all HTTP senders and recipients support
1160   request-target lengths of 8000 or more octets.
1161</t>
1162<x:note>
1163  <t>
1164    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1165    are not part of the request-target and thus will not be transmitted
1166    in an HTTP request.
1167  </t>
1168</x:note>
1169</section>
1170</section>
1171
1172<section title="Response Status-Line" anchor="status.line">
1173  <x:anchor-alias value="Response"/>
1174  <x:anchor-alias value="Status-Line"/>
1175<t>
1176   The first line of a Response message is the Status-Line, consisting
1177   of the protocol version, a space (SP), the status code, another space,
1178   a possibly-empty textual phrase describing the status code, and
1179   ending with CRLF.
1180</t>
1181<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1182  <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>
1183</artwork></figure>
1184
1185<section title="Status Code" anchor="status.code">
1186  <x:anchor-alias value="Status-Code"/>
1187<t>
1188   The Status-Code element is a 3-digit integer result code of the attempt to
1189   understand and satisfy the request. See &status-code-reasonphr; for
1190   further information, such as the list of status codes defined by this
1191   specification, the IANA registry, and considerations for new status codes.
1192</t>
1193<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/>
1194  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1195</artwork></figure>
1196</section>
1197
1198<section title="Reason Phrase" anchor="reason.phrase">
1199  <x:anchor-alias value="Reason-Phrase"/>
1200<t>   
1201   The Reason Phrase exists for the sole purpose of providing a textual
1202   description associated with the numeric status code, out of deference to
1203   earlier Internet application protocols that were more frequently used with
1204   interactive text clients. A client &SHOULD; ignore the content of the Reason
1205   Phrase.
1206</t>
1207<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1208  <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> )
1209</artwork></figure>
1210</section>
1211</section>
1212</section>
1213
1214<section title="Header Fields" anchor="header.fields">
1215  <x:anchor-alias value="header-field"/>
1216  <x:anchor-alias value="field-content"/>
1217  <x:anchor-alias value="field-name"/>
1218  <x:anchor-alias value="field-value"/>
1219  <x:anchor-alias value="OWS"/>
1220<t>
1221   Each HTTP header field consists of a case-insensitive field name
1222   followed by a colon (":"), optional whitespace, and the field value.
1223</t>
1224<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"/>
1225  <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>
1226  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1227  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1228  <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> )
1229</artwork></figure>
1230<t>
1231   The field-name token labels the corresponding field-value as having the
1232   semantics defined by that header field.  For example, the Date header field
1233   is defined in &header-date; as containing the origination
1234   timestamp for the message in which it appears.
1235</t>
1236<t>
1237   HTTP header fields are fully extensible: there is no limit on the
1238   introduction of new field names, each presumably defining new semantics,
1239   or on the number of header fields used in a given message.  Existing
1240   fields are defined in each part of this specification and in many other
1241   specifications outside the standards process.
1242   New header fields can be introduced without changing the protocol version
1243   if their defined semantics allow them to be safely ignored by recipients
1244   that do not recognize them.
1245</t>
1246<t>
1247   New HTTP header fields &SHOULD; be registered with IANA according
1248   to the procedures in &cons-new-header-fields;.
1249   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1250   field-name is listed in the Connection header field
1251   (<xref target="header.connection"/>) or the proxy is specifically
1252   configured to block or otherwise transform such fields.
1253   Unrecognized header fields &SHOULD; be ignored by other recipients.
1254</t>
1255<t>
1256   The order in which header fields with differing field names are
1257   received is not significant. However, it is "good practice" to send
1258   header fields that contain control data first, such as Host on
1259   requests and Date on responses, so that implementations can decide
1260   when not to handle a message as early as possible.  A server &MUST;
1261   wait until the entire header section is received before interpreting
1262   a request message, since later header fields might include conditionals,
1263   authentication credentials, or deliberately misleading duplicate
1264   header fields that would impact request processing.
1265</t>
1266<t>
1267   Multiple header fields with the same field name &MUST-NOT; be
1268   sent in a message unless the entire field value for that
1269   header field is defined as a comma-separated list [i.e., #(values)].
1270   Multiple header fields with the same field name can be combined into
1271   one "field-name: field-value" pair, without changing the semantics of the
1272   message, by appending each subsequent field value to the combined
1273   field value in order, separated by a comma. The order in which
1274   header fields with the same field name are received is therefore
1275   significant to the interpretation of the combined field value;
1276   a proxy &MUST-NOT; change the order of these field values when
1277   forwarding a message.
1278</t>
1279<x:note>
1280  <t>
1281   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1282   practice can occur multiple times, but does not use the list syntax, and
1283   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1284   for details.) Also note that the Set-Cookie2 header field specified in
1285   <xref target="RFC2965"/> does not share this problem.
1286  </t>
1287</x:note>
1288
1289<section title="Whitespace" anchor="whitespace">
1290<t anchor="rule.LWS">
1291   This specification uses three rules to denote the use of linear
1292   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1293   BWS ("bad" whitespace).
1294</t>
1295<t anchor="rule.OWS">
1296   The OWS rule is used where zero or more linear whitespace octets might
1297   appear. OWS &SHOULD; either not be produced or be produced as a single
1298   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1299   be replaced with a single SP or transformed to all SP octets (each
1300   octet other than SP replaced with SP) before interpreting the field value
1301   or forwarding the message downstream.
1302</t>
1303<t anchor="rule.RWS">
1304   RWS is used when at least one linear whitespace octet is required to
1305   separate field tokens. RWS &SHOULD; be produced as a single SP.
1306   Multiple RWS octets that occur within field-content &SHOULD; either
1307   be replaced with a single SP or transformed to all SP octets before
1308   interpreting the field value or forwarding the message downstream.
1309</t>
1310<t anchor="rule.BWS">
1311   BWS is used where the grammar allows optional whitespace for historical
1312   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
1313   recipients &MUST; accept such bad optional whitespace and remove it before
1314   interpreting the field value or forwarding the message downstream.
1315</t>
1316<t anchor="rule.whitespace">
1317  <x:anchor-alias value="BWS"/>
1318  <x:anchor-alias value="OWS"/>
1319  <x:anchor-alias value="RWS"/>
1320  <x:anchor-alias value="obs-fold"/>
1321</t>
1322<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"/>
1323  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> / obs-fold )
1324                 ; "optional" whitespace
1325  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> / obs-fold )
1326                 ; "required" whitespace
1327  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1328                 ; "bad" whitespace
1329  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1330                 ; obsolete line folding
1331                 ; see <xref target="field.parsing"/>
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-content 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 associated with the request or response.
1554</t>
1555<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1556  <x:ref>message-body</x:ref> = *OCTET
1557</artwork></figure>
1558<t>
1559   The message-body differs from the payload body only when a transfer-coding
1560   has been applied, as indicated by the Transfer-Encoding header field
1561   (<xref target="header.transfer-encoding"/>).  If more than one
1562   Transfer-Encoding header field is present in a message, the multiple
1563   field-values &MUST; be combined into one field-value, according to the
1564   algorithm defined in <xref target="header.fields"/>, before determining
1565   the message-body length.
1566</t>
1567<t>
1568   When one or more transfer-codings are applied to a payload in order to
1569   form the message-body, the Transfer-Encoding header field &MUST; contain
1570   the list of transfer-codings applied. Transfer-Encoding is a property of
1571   the message, not of the payload, and thus &MAY; be added or removed by
1572   any implementation along the request/response chain under the constraints
1573   found in <xref target="transfer.codings"/>.
1574</t>
1575<t>
1576   If a message is received that has multiple Content-Length header fields
1577   (<xref target="header.content-length"/>) with field-values consisting
1578   of the same decimal value, or a single Content-Length header field with
1579   a field value containing a list of identical decimal values (e.g.,
1580   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1581   header fields have been generated or combined by an upstream message
1582   processor, then the recipient &MUST; either reject the message as invalid
1583   or replace the duplicated field-values with a single valid Content-Length
1584   field containing that decimal value prior to determining the message-body
1585   length.
1586</t>
1587<t>
1588   The rules for when a message-body is allowed in a message differ for
1589   requests and responses.
1590</t>
1591<t>
1592   The presence of a message-body in a request is signaled by the
1593   inclusion of a Content-Length or Transfer-Encoding header field in
1594   the request's header fields, even if the request method does not
1595   define any use for a message-body.  This allows the request
1596   message framing algorithm to be independent of method semantics.
1597</t>
1598<t>
1599   For response messages, whether or not a message-body is included with
1600   a message is dependent on both the request method and the response
1601   status code (<xref target="status.code"/>).
1602   Responses to the HEAD request method never include a message-body
1603   because the associated response header fields (e.g., Transfer-Encoding,
1604   Content-Length, etc.) only indicate what their values would have been
1605   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1606   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1607   All other responses do include a message-body, although the body
1608   &MAY; be of zero length.
1609</t>
1610<t>
1611   The length of the message-body is determined by one of the following
1612   (in order of precedence):
1613</t>
1614<t>
1615  <list style="numbers">
1616    <x:lt><t>
1617     Any response to a HEAD request and any response with a status
1618     code of 100-199, 204, or 304 is always terminated by the first
1619     empty line after the header fields, regardless of the header
1620     fields present in the message, and thus cannot contain a message-body.
1621    </t></x:lt>
1622    <x:lt><t>
1623     If a Transfer-Encoding header field is present
1624     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1625     is the final encoding, the message-body length is determined by reading
1626     and decoding the chunked data until the transfer-coding indicates the
1627     data is complete.
1628    </t>
1629    <t>
1630     If a Transfer-Encoding header field is present in a response and the
1631     "chunked" transfer-coding is not the final encoding, the message-body
1632     length is determined by reading the connection until it is closed by
1633     the server.
1634     If a Transfer-Encoding header field is present in a request and the
1635     "chunked" transfer-coding is not the final encoding, the message-body
1636     length cannot be determined reliably; the server &MUST; respond with
1637     the 400 (Bad Request) status code and then close the connection.
1638    </t>
1639    <t>
1640     If a message is received with both a Transfer-Encoding header field
1641     and a Content-Length header field, the Transfer-Encoding overrides
1642     the Content-Length.
1643     Such a message might indicate an attempt to perform request or response
1644     smuggling (bypass of security-related checks on message routing or content)
1645     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1646     be removed, prior to forwarding the message downstream, or replaced with
1647     the real message-body length after the transfer-coding is decoded.
1648    </t></x:lt>
1649    <x:lt><t>
1650     If a message is received without Transfer-Encoding and with either
1651     multiple Content-Length header fields having differing field-values or
1652     a single Content-Length header field having an invalid value, then the
1653     message framing is invalid and &MUST; be treated as an error to
1654     prevent request or response smuggling.
1655     If this is a request message, the server &MUST; respond with
1656     a 400 (Bad Request) status code and then close the connection.
1657     If this is a response message received by a proxy, the proxy
1658     &MUST; discard the received response, send a 502 (Bad Gateway)
1659     status code as its downstream response, and then close the connection.
1660     If this is a response message received by a user-agent, it &MUST; be
1661     treated as an error by discarding the message and closing the connection.
1662    </t></x:lt>
1663    <x:lt><t>
1664     If a valid Content-Length header field
1665     is present without Transfer-Encoding, its decimal value defines the
1666     message-body length in octets.  If the actual number of octets sent in
1667     the message is less than the indicated Content-Length, the recipient
1668     &MUST; consider the message to be incomplete and treat the connection
1669     as no longer usable.
1670     If the actual number of octets sent in the message is more than the indicated
1671     Content-Length, the recipient &MUST; only process the message-body up to the
1672     field value's number of octets; the remainder of the message &MUST; either
1673     be discarded or treated as the next message in a pipeline.  For the sake of
1674     robustness, a user-agent &MAY; attempt to detect and correct such an error
1675     in message framing if it is parsing the response to the last request on
1676     a connection and the connection has been closed by the server.
1677    </t></x:lt>
1678    <x:lt><t>
1679     If this is a request message and none of the above are true, then the
1680     message-body length is zero (no message-body is present).
1681    </t></x:lt>
1682    <x:lt><t>
1683     Otherwise, this is a response message without a declared message-body
1684     length, so the message-body length is determined by the number of octets
1685     received prior to the server closing the connection.
1686    </t></x:lt>
1687  </list>
1688</t>
1689<t>
1690   Since there is no way to distinguish a successfully completed,
1691   close-delimited message from a partially-received message interrupted
1692   by network failure, implementations &SHOULD; use encoding or
1693   length-delimited messages whenever possible.  The close-delimiting
1694   feature exists primarily for backwards compatibility with HTTP/1.0.
1695</t>
1696<t>
1697   A server &MAY; reject a request that contains a message-body but
1698   not a Content-Length by responding with 411 (Length Required).
1699</t>
1700<t>
1701   Unless a transfer-coding other than "chunked" has been applied,
1702   a client that sends a request containing a message-body &SHOULD;
1703   use a valid Content-Length header field if the message-body length
1704   is known in advance, rather than the "chunked" encoding, since some
1705   existing services respond to "chunked" with a 411 (Length Required)
1706   status code even though they understand the chunked encoding.  This
1707   is typically because such services are implemented via a gateway that
1708   requires a content-length in advance of being called and the server
1709   is unable or unwilling to buffer the entire request before processing.
1710</t>
1711<t>
1712   A client that sends a request containing a message-body &MUST; include a
1713   valid Content-Length header field if it does not know the server will
1714   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1715   of specific user configuration or by remembering the version of a prior
1716   received response.
1717</t>
1718</section>
1719
1720<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1721<t>
1722   Request messages that are prematurely terminated, possibly due to a
1723   cancelled connection or a server-imposed time-out exception, &MUST;
1724   result in closure of the connection; sending an HTTP/1.1 error response
1725   prior to closing the connection is &OPTIONAL;.
1726</t>
1727<t>
1728   Response messages that are prematurely terminated, usually by closure
1729   of the connection prior to receiving the expected number of octets or by
1730   failure to decode a transfer-encoded message-body, &MUST; be recorded
1731   as incomplete.  A response that terminates in the middle of the header
1732   block (before the empty line is received) cannot be assumed to convey the
1733   full semantics of the response and &MUST; be treated as an error.
1734</t>
1735<t>
1736   A message-body that uses the chunked transfer encoding is
1737   incomplete if the zero-sized chunk that terminates the encoding has not
1738   been received.  A message that uses a valid Content-Length is incomplete
1739   if the size of the message-body received (in octets) is less than the
1740   value given by Content-Length.  A response that has neither chunked
1741   transfer encoding nor Content-Length is terminated by closure of the
1742   connection, and thus is considered complete regardless of the number of
1743   message-body octets received, provided that the header block was received
1744   intact.
1745</t>
1746<t>
1747   A user agent &MUST-NOT; render an incomplete response message-body as if
1748   it were complete (i.e., some indication must be given to the user that an
1749   error occurred).  Cache requirements for incomplete responses are defined
1750   in &cache-incomplete;.
1751</t>
1752<t>
1753   A server &MUST; read the entire request message-body or close
1754   the connection after sending its response, since otherwise the
1755   remaining data on a persistent connection would be misinterpreted
1756   as the next request.  Likewise,
1757   a client &MUST; read the entire response message-body if it intends
1758   to reuse the same connection for a subsequent request.  Pipelining
1759   multiple requests on a connection is described in <xref target="pipelining"/>.
1760</t>
1761</section>
1762
1763<section title="Message Parsing Robustness" anchor="message.robustness">
1764<t>
1765   Older HTTP/1.0 client implementations might send an extra CRLF
1766   after a POST request as a lame workaround for some early server
1767   applications that failed to read message-body content that was
1768   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1769   preface or follow a request with an extra CRLF.  If terminating
1770   the request message-body with a line-ending is desired, then the
1771   client &MUST; include the terminating CRLF octets as part of the
1772   message-body length.
1773</t>
1774<t>
1775   In the interest of robustness, servers &SHOULD; ignore at least one
1776   empty line received where a Request-Line is expected. In other words, if
1777   the server is reading the protocol stream at the beginning of a
1778   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1779   Likewise, although the line terminator for the start-line and header
1780   fields is the sequence CRLF, we recommend that recipients recognize a
1781   single LF as a line terminator and ignore any CR.
1782</t>
1783<t>
1784   When a server listening only for HTTP request messages, or processing
1785   what appears from the start-line to be an HTTP request message,
1786   receives a sequence of octets that does not match the HTTP-message
1787   grammar aside from the robustness exceptions listed above, the
1788   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1789</t>
1790</section>
1791</section>
1792
1793<section title="Message Routing" anchor="message.routing">
1794<t>
1795   In most cases, the user agent is provided a URI reference
1796   from which it determines an absolute URI for identifying the target
1797   resource.  When a request to the resource is initiated, all or part
1798   of that URI is used to construct the HTTP request-target.
1799</t>
1800
1801<section title="Types of Request Target" anchor="request-target-types">
1802<t>
1803   The proper format choice of the four options available to request-target
1804   depends on the method being requested and if the request is being made to
1805   a proxy.
1806</t>   
1807<t anchor="origin-form"><iref item="origin form (of request-target)"/>
1808   The most common form of request-target is that used when making
1809   a request to an origin server ("origin form") to access a resource
1810   identified by an "http" (<xref target="http.uri"/>) or
1811   "https" (<xref target="https.uri"/>) URI.
1812   In this case, the absolute path and query components of the URI
1813   &MUST; be transmitted as the request-target and the authority component
1814   (excluding any userinfo) &MUST; be transmitted in a Host header field.
1815   For example, a client wishing to retrieve a representation of the resource
1816   identified as
1817</t>
1818<figure><artwork x:indent-with="  ">
1819http://www.example.org/where?q=now
1820</artwork></figure>
1821<t>
1822   directly from the origin server would open (or reuse) a TCP connection
1823   to port 80 of the host "www.example.org" and send the lines:
1824</t>
1825<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1826GET /where?q=now HTTP/1.1
1827Host: www.example.org
1828</artwork></figure>
1829<t>
1830   followed by the remainder of the request. Note that the origin form
1831   of request-target always starts with an absolute path. If the target
1832   resource's URI path is empty, then an absolute path of "/" &MUST; be
1833   provided in the request-target.
1834</t>
1835<t>
1836   If the request-target is percent-encoded
1837   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1838   &MUST; decode the request-target in order to
1839   properly interpret the request. Servers &SHOULD; respond to invalid
1840   request-targets with an appropriate status code.
1841</t>
1842<t anchor="absolute-URI-form"><iref item="absolute-URI form (of request-target)"/>
1843   The "absolute-URI" form of request-target is &REQUIRED; when the request
1844   is being made to a proxy.  The proxy is requested to either forward the
1845   request or service it from a valid cache, and then return the response.
1846   Note that the proxy &MAY; forward the request on to another proxy or
1847   directly to the server specified by the absolute-URI.
1848   In order to avoid request loops, a proxy that forwards requests to other
1849   proxies &MUST; be able to recognize and exclude all of its own server
1850   names, including any aliases, local variations, or literal IP addresses.
1851   An example Request-Line would be:
1852</t>
1853<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1854GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1855</artwork></figure>
1856<t>
1857   To allow for transition to absolute-URIs in all requests in future
1858   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1859   form in requests, even though HTTP/1.1 clients will only generate
1860   them in requests to proxies.
1861</t>
1862<t>
1863   If a proxy receives a host name that is not a fully qualified domain
1864   name, it &MAY; add its domain to the host name it received. If a proxy
1865   receives a fully qualified domain name, the proxy &MUST-NOT; change
1866   the host name.
1867</t>
1868<t anchor="authority-form"><iref item="authority form (of request-target)"/>
1869   The "authority form" of request-target, which &MUST-NOT; be used
1870   with any request method other than CONNECT, is used to establish a
1871   tunnel through one or more proxies (&CONNECT;).  For example,
1872</t>
1873<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1874CONNECT www.example.com:80 HTTP/1.1
1875</artwork></figure>
1876<t anchor="asterix-form"><iref item="asterisk form (of request-target)"/>
1877   The asterisk ("*") form of request-target, which &MUST-NOT; be used
1878   with any request method other than OPTIONS, means that the request
1879   applies to the server as a whole (the listening process) rather than
1880   to a specific named resource at that server.  For example,
1881</t>
1882<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1883OPTIONS * HTTP/1.1
1884</artwork></figure>
1885<t>
1886   If a proxy receives an OPTIONS request with an absolute-URI form of
1887   request-target in which the URI has an empty path and no query component,
1888   then the last proxy on the request chain &MUST; use a request-target
1889   of "*" when it forwards the request to the indicated origin server.
1890</t>
1891<figure><preamble>   
1892   For example, the request
1893</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1894OPTIONS http://www.example.org:8001 HTTP/1.1
1895</artwork></figure>
1896<figure><preamble>   
1897  would be forwarded by the final proxy as
1898</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1899OPTIONS * HTTP/1.1
1900Host: www.example.org:8001
1901</artwork>
1902<postamble>
1903   after connecting to port 8001 of host "www.example.org".
1904</postamble>
1905</figure>
1906<t>
1907   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" and "query"
1908   parts of the received request-target when forwarding it to the next inbound
1909   server, except as noted above to replace a null path-absolute with "/" or
1910   "*".
1911</t>
1912</section>
1913
1914<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1915<t>
1916   The exact resource identified by an Internet request is determined by
1917   examining both the request-target and the Host header field.
1918</t>
1919<t>
1920   An origin server that does not allow resources to differ by the
1921   requested host &MAY; ignore the Host header field value when
1922   determining the resource identified by an HTTP/1.1 request. (But see
1923   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1924   for other requirements on Host support in HTTP/1.1.)
1925</t>
1926<t>
1927   An origin server that does differentiate resources based on the host
1928   requested (sometimes referred to as virtual hosts or vanity host
1929   names) &MUST; use the following rules for determining the requested
1930   resource on an HTTP/1.1 request:
1931  <list style="numbers">
1932    <t>If request-target is an absolute-URI, the host is part of the
1933     request-target. Any Host header field value in the request &MUST; be
1934     ignored.</t>
1935    <t>If the request-target is not an absolute-URI, and the request includes
1936     a Host header field, the host is determined by the Host header
1937     field value.</t>
1938    <t>If the host as determined by rule 1 or 2 is not a valid host on
1939     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1940  </list>
1941</t>
1942<t>
1943   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1944   attempt to use heuristics (e.g., examination of the URI path for
1945   something unique to a particular host) in order to determine what
1946   exact resource is being requested.
1947</t>
1948</section>
1949
1950<section title="Effective Request URI" anchor="effective.request.uri">
1951  <iref primary="true" item="effective request URI"/>
1952  <iref primary="true" item="target resource"/>
1953<t>
1954   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1955   for the target resource; instead, the URI needs to be inferred from the
1956   request-target, Host header field, and connection context. The result of
1957   this process is called the "effective request URI".  The "target resource"
1958   is the resource identified by the effective request URI.
1959</t>
1960<t>
1961   If the request-target is an absolute-URI, then the effective request URI is
1962   the request-target.
1963</t>
1964<t>
1965   If the request-target uses the origin form or the asterisk form,
1966   and the Host header field is present, then the effective request URI is
1967   constructed by concatenating
1968</t>
1969<t>
1970  <list style="symbols">
1971    <t>
1972      the scheme name: "http" if the request was received over an insecure
1973      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1974      connection,
1975    </t>
1976    <t>
1977      the octet sequence "://",
1978    </t>
1979    <t>
1980      the authority component, as specified in the Host header field
1981      (<xref target="header.host"/>), and
1982    </t>
1983    <t>
1984      the request-target obtained from the Request-Line, unless the
1985      request-target is just the asterisk "*".
1986    </t>
1987  </list>
1988</t>
1989<t>
1990   If the request-target uses the origin form or the asterisk form,
1991   and the Host header field is not present, then the effective request URI is
1992   undefined.
1993</t>
1994<t>
1995   Otherwise, when request-target uses the authority form, the effective
1996   request URI is undefined.
1997</t>
1998<figure>
1999<preamble>
2000   Example 1: the effective request URI for the message
2001</preamble> 
2002<artwork type="example" x:indent-with="  ">
2003GET /pub/WWW/TheProject.html HTTP/1.1
2004Host: www.example.org:8080
2005</artwork>
2006<postamble>
2007  (received over an insecure TCP connection) is "http", plus "://", plus the
2008  authority component "www.example.org:8080", plus the request-target
2009  "/pub/WWW/TheProject.html", thus
2010  "http://www.example.org:8080/pub/WWW/TheProject.html".
2011</postamble>
2012</figure>
2013<figure>
2014<preamble>
2015   Example 2: the effective request URI for the message
2016</preamble> 
2017<artwork type="example" x:indent-with="  ">
2018OPTIONS * HTTP/1.1
2019Host: www.example.org
2020</artwork>
2021<postamble>
2022  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
2023  authority component "www.example.org", thus "https://www.example.org".
2024</postamble>
2025</figure>
2026<t>
2027   Effective request URIs are compared using the rules described in
2028   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
2029   be treated as equivalent to an absolute path of "/".
2030</t> 
2031</section>
2032
2033<section title="Associating Response to Request" anchor="associating.request.response">
2034<t>
2035   HTTP does not include a request identifier for associating a given
2036   request message with its corresponding one or more response messages.
2037   Hence, it relies on the order of response arrival to correspond exactly
2038   to the order in which requests are made on the same connection.
2039   More than one response message per request only occurs when one or more
2040   informational responses (1xx, see &status-1xx;) precede a final response
2041   to the same request.
2042</t>
2043<t>
2044   A client that uses persistent connections and sends more than one request
2045   per connection &MUST; maintain a list of outstanding requests in the
2046   order sent on that connection and &MUST; associate each received response
2047   message to the highest ordered request that has not yet received a final
2048   (non-1xx) response.
2049</t>
2050</section>
2051</section>
2052
2053
2054<section title="Protocol Parameters" anchor="protocol.parameters">
2055
2056<section title="Transfer Codings" anchor="transfer.codings">
2057  <x:anchor-alias value="transfer-coding"/>
2058  <x:anchor-alias value="transfer-extension"/>
2059<t>
2060   Transfer-coding values are used to indicate an encoding
2061   transformation that has been, can be, or might need to be applied to a
2062   payload body in order to ensure "safe transport" through the network.
2063   This differs from a content coding in that the transfer-coding is a
2064   property of the message rather than a property of the representation
2065   that is being transferred.
2066</t>
2067<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2068  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2069                          / "compress" ; <xref target="compress.coding"/>
2070                          / "deflate" ; <xref target="deflate.coding"/>
2071                          / "gzip" ; <xref target="gzip.coding"/>
2072                          / <x:ref>transfer-extension</x:ref>
2073  <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> )
2074</artwork></figure>
2075<t anchor="rule.parameter">
2076  <x:anchor-alias value="attribute"/>
2077  <x:anchor-alias value="transfer-parameter"/>
2078  <x:anchor-alias value="value"/>
2079   Parameters are in the form of attribute/value pairs.
2080</t>
2081<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"/>
2082  <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>
2083  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2084  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2085</artwork></figure>
2086<t>
2087   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2088   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2089   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2090</t>
2091<t>
2092   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2093   MIME, which were designed to enable safe transport of binary data over a
2094   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2095   However, safe transport
2096   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2097   the only unsafe characteristic of message-bodies is the difficulty in
2098   determining the exact message body length (<xref target="message.body"/>),
2099   or the desire to encrypt data over a shared transport.
2100</t>
2101<t>
2102   A server that receives a request message with a transfer-coding it does
2103   not understand &SHOULD; respond with 501 (Not Implemented) and then
2104   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2105   client.
2106</t>
2107
2108<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2109  <iref item="chunked (Coding Format)"/>
2110  <iref item="Coding Format" subitem="chunked"/>
2111  <x:anchor-alias value="chunk"/>
2112  <x:anchor-alias value="Chunked-Body"/>
2113  <x:anchor-alias value="chunk-data"/>
2114  <x:anchor-alias value="chunk-ext"/>
2115  <x:anchor-alias value="chunk-ext-name"/>
2116  <x:anchor-alias value="chunk-ext-val"/>
2117  <x:anchor-alias value="chunk-size"/>
2118  <x:anchor-alias value="last-chunk"/>
2119  <x:anchor-alias value="trailer-part"/>
2120  <x:anchor-alias value="quoted-str-nf"/>
2121  <x:anchor-alias value="qdtext-nf"/>
2122<t>
2123   The chunked encoding modifies the body of a message in order to
2124   transfer it as a series of chunks, each with its own size indicator,
2125   followed by an &OPTIONAL; trailer containing header fields. This
2126   allows dynamically produced content to be transferred along with the
2127   information necessary for the recipient to verify that it has
2128   received the full message.
2129</t>
2130<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"/>
2131  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2132                   <x:ref>last-chunk</x:ref>
2133                   <x:ref>trailer-part</x:ref>
2134                   <x:ref>CRLF</x:ref>
2135 
2136  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2137                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2138  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2139  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2140 
2141  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref>
2142                      [ "=" <x:ref>chunk-ext-val</x:ref> ] )
2143  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2144  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2145  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2146  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2147 
2148  <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>
2149                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2150  <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>
2151</artwork></figure>
2152<t>
2153   The chunk-size field is a string of hex digits indicating the size of
2154   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2155   zero, followed by the trailer, which is terminated by an empty line.
2156</t>
2157<t>
2158   The trailer allows the sender to include additional HTTP header
2159   fields at the end of the message. The Trailer header field can be
2160   used to indicate which header fields are included in a trailer (see
2161   <xref target="header.trailer"/>).
2162</t>
2163<t>
2164   A server using chunked transfer-coding in a response &MUST-NOT; use the
2165   trailer for any header fields unless at least one of the following is
2166   true:
2167  <list style="numbers">
2168    <t>the request included a TE header field that indicates "trailers" is
2169     acceptable in the transfer-coding of the  response, as described in
2170     <xref target="header.te"/>; or,</t>
2171     
2172    <t>the trailer fields consist entirely of optional metadata, and the
2173    recipient could use the message (in a manner acceptable to the server where
2174    the field originated) without receiving it. In other words, the server that
2175    generated the header (often but not always the origin server) is willing to
2176    accept the possibility that the trailer fields might be silently discarded
2177    along the path to the client.</t>
2178  </list>
2179</t>
2180<t>
2181   This requirement prevents an interoperability failure when the
2182   message is being received by an HTTP/1.1 (or later) proxy and
2183   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2184   conformance with the protocol would have necessitated a possibly
2185   infinite buffer on the proxy.
2186</t>
2187<t>
2188   A process for decoding the "chunked" transfer-coding
2189   can be represented in pseudo-code as:
2190</t>
2191<figure><artwork type="code">
2192  length := 0
2193  read chunk-size, chunk-ext (if any) and CRLF
2194  while (chunk-size &gt; 0) {
2195     read chunk-data and CRLF
2196     append chunk-data to decoded-body
2197     length := length + chunk-size
2198     read chunk-size and CRLF
2199  }
2200  read header-field
2201  while (header-field not empty) {
2202     append header-field to existing header fields
2203     read header-field
2204  }
2205  Content-Length := length
2206  Remove "chunked" from Transfer-Encoding
2207</artwork></figure>
2208<t>
2209   All HTTP/1.1 applications &MUST; be able to receive and decode the
2210   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2211   they do not understand.
2212</t>
2213<t>
2214   Use of chunk-ext extensions by senders is deprecated; they &SHOULD-NOT; be
2215   sent and definition of new chunk-extensions is discouraged.
2216</t>
2217<t>
2218   Since "chunked" is the only transfer-coding required to be understood
2219   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2220   on a persistent connection.  Whenever a transfer-coding is applied to
2221   a payload body in a request, the final transfer-coding applied &MUST;
2222   be "chunked".  If a transfer-coding is applied to a response payload
2223   body, then either the final transfer-coding applied &MUST; be "chunked"
2224   or the message &MUST; be terminated by closing the connection. When the
2225   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2226   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2227   be applied more than once in a message-body.
2228</t>
2229</section>
2230
2231<section title="Compression Codings" anchor="compression.codings">
2232<t>
2233   The codings defined below can be used to compress the payload of a
2234   message.
2235</t>
2236<x:note><t>
2237   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2238   is not desirable and is discouraged for future encodings. Their
2239   use here is representative of historical practice, not good
2240   design.
2241</t></x:note>
2242<x:note><t>
2243   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2244   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2245   equivalent to "gzip" and "compress" respectively.
2246</t></x:note>
2247
2248<section title="Compress Coding" anchor="compress.coding">
2249<iref item="compress (Coding Format)"/>
2250<iref item="Coding Format" subitem="compress"/>
2251<t>
2252   The "compress" format is produced by the common UNIX file compression
2253   program "compress". This format is an adaptive Lempel-Ziv-Welch
2254   coding (LZW).
2255</t>
2256</section>
2257
2258<section title="Deflate Coding" anchor="deflate.coding">
2259<iref item="deflate (Coding Format)"/>
2260<iref item="Coding Format" subitem="deflate"/>
2261<t>
2262   The "deflate" format is defined as the "deflate" compression mechanism
2263   (described in <xref target="RFC1951"/>) used inside the "zlib"
2264   data format (<xref target="RFC1950"/>).
2265</t>
2266<x:note>
2267  <t>
2268    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2269    compressed data without the zlib wrapper.
2270   </t>
2271</x:note>
2272</section>
2273
2274<section title="Gzip Coding" anchor="gzip.coding">
2275<iref item="gzip (Coding Format)"/>
2276<iref item="Coding Format" subitem="gzip"/>
2277<t>
2278   The "gzip" format is produced by the file compression program
2279   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2280   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2281</t>
2282</section>
2283
2284</section>
2285
2286<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2287<t>
2288   The HTTP Transfer Coding Registry defines the name space for the transfer
2289   coding names.
2290</t>
2291<t>
2292   Registrations &MUST; include the following fields:
2293   <list style="symbols">
2294     <t>Name</t>
2295     <t>Description</t>
2296     <t>Pointer to specification text</t>
2297   </list>
2298</t>
2299<t>
2300   Names of transfer codings &MUST-NOT; overlap with names of content codings
2301   (&content-codings;), unless the encoding transformation is identical (as it
2302   is the case for the compression codings defined in
2303   <xref target="compression.codings"/>).
2304</t>
2305<t>
2306   Values to be added to this name space require a specification
2307   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2308   conform to the purpose of transfer coding defined in this section.
2309</t>
2310<t>
2311   The registry itself is maintained at
2312   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2313</t>
2314</section>
2315</section>
2316
2317<section title="Product Tokens" anchor="product.tokens">
2318  <x:anchor-alias value="product"/>
2319  <x:anchor-alias value="product-version"/>
2320<t>
2321   Product tokens are used to allow communicating applications to
2322   identify themselves by software name and version. Most fields using
2323   product tokens also allow sub-products which form a significant part
2324   of the application to be listed, separated by whitespace. By
2325   convention, the products are listed in order of their significance
2326   for identifying the application.
2327</t>
2328<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2329  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2330  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2331</artwork></figure>
2332<t>
2333   Examples:
2334</t>
2335<figure><artwork type="example">
2336  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2337  Server: Apache/0.8.4
2338</artwork></figure>
2339<t>
2340   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2341   used for advertising or other non-essential information. Although any
2342   token octet &MAY; appear in a product-version, this token &SHOULD;
2343   only be used for a version identifier (i.e., successive versions of
2344   the same product &SHOULD; only differ in the product-version portion of
2345   the product value).
2346</t>
2347</section>
2348
2349<section title="Quality Values" anchor="quality.values">
2350  <x:anchor-alias value="qvalue"/>
2351<t>
2352   Both transfer codings (TE request header field, <xref target="header.te"/>)
2353   and content negotiation (&content.negotiation;) use short "floating point"
2354   numbers to indicate the relative importance ("weight") of various
2355   negotiable parameters.  A weight is normalized to a real number in
2356   the range 0 through 1, where 0 is the minimum and 1 the maximum
2357   value. If a parameter has a quality value of 0, then content with
2358   this parameter is "not acceptable" for the client. HTTP/1.1
2359   applications &MUST-NOT; generate more than three digits after the
2360   decimal point. User configuration of these values &SHOULD; also be
2361   limited in this fashion.
2362</t>
2363<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2364  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2365                 / ( "1" [ "." 0*3("0") ] )
2366</artwork></figure>
2367<x:note>
2368  <t>
2369     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2370     relative degradation in desired quality.
2371  </t>
2372</x:note>
2373</section>
2374
2375</section>
2376
2377<section title="Connections" anchor="connections">
2378
2379<section title="Persistent Connections" anchor="persistent.connections">
2380
2381<section title="Purpose" anchor="persistent.purpose">
2382<t>
2383   Prior to persistent connections, a separate TCP connection was
2384   established for each request, increasing the load on HTTP servers
2385   and causing congestion on the Internet. The use of inline images and
2386   other associated data often requires a client to make multiple
2387   requests of the same server in a short amount of time. Analysis of
2388   these performance problems and results from a prototype
2389   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2390   measurements of actual HTTP/1.1 implementations show good
2391   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2392   T/TCP <xref target="Tou1998"/>.
2393</t>
2394<t>
2395   Persistent HTTP connections have a number of advantages:
2396  <list style="symbols">
2397      <t>
2398        By opening and closing fewer TCP connections, CPU time is saved
2399        in routers and hosts (clients, servers, proxies, gateways,
2400        tunnels, or caches), and memory used for TCP protocol control
2401        blocks can be saved in hosts.
2402      </t>
2403      <t>
2404        HTTP requests and responses can be pipelined on a connection.
2405        Pipelining allows a client to make multiple requests without
2406        waiting for each response, allowing a single TCP connection to
2407        be used much more efficiently, with much lower elapsed time.
2408      </t>
2409      <t>
2410        Network congestion is reduced by reducing the number of packets
2411        caused by TCP opens, and by allowing TCP sufficient time to
2412        determine the congestion state of the network.
2413      </t>
2414      <t>
2415        Latency on subsequent requests is reduced since there is no time
2416        spent in TCP's connection opening handshake.
2417      </t>
2418      <t>
2419        HTTP can evolve more gracefully, since errors can be reported
2420        without the penalty of closing the TCP connection. Clients using
2421        future versions of HTTP might optimistically try a new feature,
2422        but if communicating with an older server, retry with old
2423        semantics after an error is reported.
2424      </t>
2425    </list>
2426</t>
2427<t>
2428   HTTP implementations &SHOULD; implement persistent connections.
2429</t>
2430</section>
2431
2432<section title="Overall Operation" anchor="persistent.overall">
2433<t>
2434   A significant difference between HTTP/1.1 and earlier versions of
2435   HTTP is that persistent connections are the default behavior of any
2436   HTTP connection. That is, unless otherwise indicated, the client
2437   &SHOULD; assume that the server will maintain a persistent connection,
2438   even after error responses from the server.
2439</t>
2440<t>
2441   Persistent connections provide a mechanism by which a client and a
2442   server can signal the close of a TCP connection. This signaling takes
2443   place using the Connection header field (<xref target="header.connection"/>). Once a close
2444   has been signaled, the client &MUST-NOT; send any more requests on that
2445   connection.
2446</t>
2447
2448<section title="Negotiation" anchor="persistent.negotiation">
2449<t>
2450   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2451   maintain a persistent connection unless a Connection header field including
2452   the connection-token "close" was sent in the request. If the server
2453   chooses to close the connection immediately after sending the
2454   response, it &SHOULD; send a Connection header field including the
2455   connection-token "close".
2456</t>
2457<t>
2458   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2459   decide to keep it open based on whether the response from a server
2460   contains a Connection header field with the connection-token close. In case
2461   the client does not want to maintain a connection for more than that
2462   request, it &SHOULD; send a Connection header field including the
2463   connection-token close.
2464</t>
2465<t>
2466   If either the client or the server sends the close token in the
2467   Connection header field, that request becomes the last one for the
2468   connection.
2469</t>
2470<t>
2471   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2472   maintained for HTTP versions less than 1.1 unless it is explicitly
2473   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2474   compatibility with HTTP/1.0 clients.
2475</t>
2476<t>
2477   In order to remain persistent, all messages on the connection &MUST;
2478   have a self-defined message length (i.e., one not defined by closure
2479   of the connection), as described in <xref target="message.body"/>.
2480</t>
2481</section>
2482
2483<section title="Pipelining" anchor="pipelining">
2484<t>
2485   A client that supports persistent connections &MAY; "pipeline" its
2486   requests (i.e., send multiple requests without waiting for each
2487   response). A server &MUST; send its responses to those requests in the
2488   same order that the requests were received.
2489</t>
2490<t>
2491   Clients which assume persistent connections and pipeline immediately
2492   after connection establishment &SHOULD; be prepared to retry their
2493   connection if the first pipelined attempt fails. If a client does
2494   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2495   persistent. Clients &MUST; also be prepared to resend their requests if
2496   the server closes the connection before sending all of the
2497   corresponding responses.
2498</t>
2499<t>
2500   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2501   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2502   premature termination of the transport connection could lead to
2503   indeterminate results. A client wishing to send a non-idempotent
2504   request &SHOULD; wait to send that request until it has received the
2505   response status line for the previous request.
2506</t>
2507</section>
2508</section>
2509
2510<section title="Proxy Servers" anchor="persistent.proxy">
2511<t>
2512   It is especially important that proxies correctly implement the
2513   properties of the Connection header field as specified in <xref target="header.connection"/>.
2514</t>
2515<t>
2516   The proxy server &MUST; signal persistent connections separately with
2517   its clients and the origin servers (or other proxy servers) that it
2518   connects to. Each persistent connection applies to only one transport
2519   link.
2520</t>
2521<t>
2522   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2523   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2524   for information and discussion of the problems with the Keep-Alive header field
2525   implemented by many HTTP/1.0 clients).
2526</t>
2527
2528<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2529<!--<t>
2530  <cref anchor="TODO-end-to-end" source="jre">
2531    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2532    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2533  </cref>
2534</t>-->
2535<t>
2536   For the purpose of defining the behavior of caches and non-caching
2537   proxies, we divide HTTP header fields into two categories:
2538  <list style="symbols">
2539      <t>End-to-end header fields, which are  transmitted to the ultimate
2540        recipient of a request or response. End-to-end header fields in
2541        responses MUST be stored as part of a cache entry and &MUST; be
2542        transmitted in any response formed from a cache entry.</t>
2543
2544      <t>Hop-by-hop header fields, which are meaningful only for a single
2545        transport-level connection, and are not stored by caches or
2546        forwarded by proxies.</t>
2547  </list>
2548</t>
2549<t>
2550   The following HTTP/1.1 header fields are hop-by-hop header fields:
2551  <list style="symbols">
2552      <t>Connection</t>
2553      <t>Keep-Alive</t>
2554      <t>Proxy-Authenticate</t>
2555      <t>Proxy-Authorization</t>
2556      <t>TE</t>
2557      <t>Trailer</t>
2558      <t>Transfer-Encoding</t>
2559      <t>Upgrade</t>
2560  </list>
2561</t>
2562<t>
2563   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2564</t>
2565<t>
2566   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2567   (<xref target="header.connection"/>).
2568</t>
2569</section>
2570
2571<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2572<!--<t>
2573  <cref anchor="TODO-non-mod-headers" source="jre">
2574    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2575    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2576  </cref>
2577</t>-->
2578<t>
2579   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2580   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2581   modify an end-to-end header field unless the definition of that header field requires
2582   or specifically allows that.
2583</t>
2584<t>
2585   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2586   request or response, and it &MUST-NOT; add any of these fields if not
2587   already present:
2588  <list style="symbols">
2589    <t>Allow</t>
2590    <t>Content-Location</t>
2591    <t>Content-MD5</t>
2592    <t>ETag</t>
2593    <t>Last-Modified</t>
2594    <t>Server</t>
2595  </list>
2596</t>
2597<t>
2598   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2599   response:
2600  <list style="symbols">
2601    <t>Expires</t>
2602  </list>
2603</t>
2604<t>
2605   but it &MAY; add any of these fields if not already present. If an
2606   Expires header field is added, it &MUST; be given a field-value identical to
2607   that of the Date header field in that response.
2608</t>
2609<t>
2610   A proxy &MUST-NOT; modify or add any of the following fields in a
2611   message that contains the no-transform cache-control directive, or in
2612   any request:
2613  <list style="symbols">
2614    <t>Content-Encoding</t>
2615    <t>Content-Range</t>
2616    <t>Content-Type</t>
2617  </list>
2618</t>
2619<t>
2620   A transforming proxy &MAY; modify or add these fields to a message
2621   that does not include no-transform, but if it does so, it &MUST; add a
2622   Warning 214 (Transformation applied) if one does not already appear
2623   in the message (see &header-warning;).
2624</t>
2625<x:note>
2626  <t>
2627    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2628    cause authentication failures if stronger authentication
2629    mechanisms are introduced in later versions of HTTP. Such
2630    authentication mechanisms &MAY; rely on the values of header fields
2631    not listed here.
2632  </t>
2633</x:note>
2634<t>
2635   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2636   though it &MAY; change the message-body through application or removal
2637   of a transfer-coding (<xref target="transfer.codings"/>).
2638</t>
2639</section>
2640
2641</section>
2642
2643<section title="Practical Considerations" anchor="persistent.practical">
2644<t>
2645   Servers will usually have some time-out value beyond which they will
2646   no longer maintain an inactive connection. Proxy servers might make
2647   this a higher value since it is likely that the client will be making
2648   more connections through the same server. The use of persistent
2649   connections places no requirements on the length (or existence) of
2650   this time-out for either the client or the server.
2651</t>
2652<t>
2653   When a client or server wishes to time-out it &SHOULD; issue a graceful
2654   close on the transport connection. Clients and servers &SHOULD; both
2655   constantly watch for the other side of the transport close, and
2656   respond to it as appropriate. If a client or server does not detect
2657   the other side's close promptly it could cause unnecessary resource
2658   drain on the network.
2659</t>
2660<t>
2661   A client, server, or proxy &MAY; close the transport connection at any
2662   time. For example, a client might have started to send a new request
2663   at the same time that the server has decided to close the "idle"
2664   connection. From the server's point of view, the connection is being
2665   closed while it was idle, but from the client's point of view, a
2666   request is in progress.
2667</t>
2668<t>
2669   Clients (including proxies) &SHOULD; limit the number of simultaneous
2670   connections that they maintain to a given server (including proxies).
2671</t>
2672<t>
2673   Previous revisions of HTTP gave a specific number of connections as a
2674   ceiling, but this was found to be impractical for many applications. As a
2675   result, this specification does not mandate a particular maximum number of
2676   connections, but instead encourages clients to be conservative when opening
2677   multiple connections.
2678</t>
2679<t>
2680   In particular, while using multiple connections avoids the "head-of-line
2681   blocking" problem (whereby a request that takes significant server-side
2682   processing and/or has a large payload can block subsequent requests on the
2683   same connection), each connection used consumes server resources (sometimes
2684   significantly), and furthermore using multiple connections can cause
2685   undesirable side effects in congested networks.
2686</t>
2687<t>
2688   Note that servers might reject traffic that they deem abusive, including an
2689   excessive number of connections from a client.
2690</t>
2691</section>
2692
2693<section title="Retrying Requests" anchor="persistent.retrying.requests">
2694<t>
2695   Senders can close the transport connection at any time. Therefore,
2696   clients, servers, and proxies &MUST; be able to recover
2697   from asynchronous close events. Client software &MAY; reopen the
2698   transport connection and retransmit the aborted sequence of requests
2699   without user interaction so long as the request sequence is
2700   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2701   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2702   human operator the choice of retrying the request(s). Confirmation by
2703   user-agent software with semantic understanding of the application
2704   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2705   be repeated if the second sequence of requests fails.
2706</t>
2707</section>
2708
2709</section>
2710
2711<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2712
2713<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2714<t>
2715   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2716   flow control mechanisms to resolve temporary overloads, rather than
2717   terminating connections with the expectation that clients will retry.
2718   The latter technique can exacerbate network congestion.
2719</t>
2720</section>
2721
2722<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2723<t>
2724   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2725   the network connection for an error status code while it is transmitting
2726   the request. If the client sees an error status code, it &SHOULD;
2727   immediately cease transmitting the body. If the body is being sent
2728   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2729   empty trailer &MAY; be used to prematurely mark the end of the message.
2730   If the body was preceded by a Content-Length header field, the client &MUST;
2731   close the connection.
2732</t>
2733</section>
2734
2735<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2736<t>
2737   The purpose of the 100 (Continue) status code (see &status-100;) is to
2738   allow a client that is sending a request message with a request body
2739   to determine if the origin server is willing to accept the request
2740   (based on the request header fields) before the client sends the request
2741   body. In some cases, it might either be inappropriate or highly
2742   inefficient for the client to send the body if the server will reject
2743   the message without looking at the body.
2744</t>
2745<t>
2746   Requirements for HTTP/1.1 clients:
2747  <list style="symbols">
2748    <t>
2749        If a client will wait for a 100 (Continue) response before
2750        sending the request body, it &MUST; send an Expect header
2751        field (&header-expect;) with the "100-continue" expectation.
2752    </t>
2753    <t>
2754        A client &MUST-NOT; send an Expect header field (&header-expect;)
2755        with the "100-continue" expectation if it does not intend
2756        to send a request body.
2757    </t>
2758  </list>
2759</t>
2760<t>
2761   Because of the presence of older implementations, the protocol allows
2762   ambiguous situations in which a client might send "Expect: 100-continue"
2763   without receiving either a 417 (Expectation Failed)
2764   or a 100 (Continue) status code. Therefore, when a client sends this
2765   header field to an origin server (possibly via a proxy) from which it
2766   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2767   wait for an indefinite period before sending the request body.
2768</t>
2769<t>
2770   Requirements for HTTP/1.1 origin servers:
2771  <list style="symbols">
2772    <t> Upon receiving a request which includes an Expect header
2773        field with the "100-continue" expectation, an origin server &MUST;
2774        either respond with 100 (Continue) status code and continue to read
2775        from the input stream, or respond with a final status code. The
2776        origin server &MUST-NOT; wait for the request body before sending
2777        the 100 (Continue) response. If it responds with a final status
2778        code, it &MAY; close the transport connection or it &MAY; continue
2779        to read and discard the rest of the request.  It &MUST-NOT;
2780        perform the request method if it returns a final status code.
2781    </t>
2782    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2783        the request message does not include an Expect header
2784        field with the "100-continue" expectation, and &MUST-NOT; send a
2785        100 (Continue) response if such a request comes from an HTTP/1.0
2786        (or earlier) client. There is an exception to this rule: for
2787        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2788        status code in response to an HTTP/1.1 PUT or POST request that does
2789        not include an Expect header field with the "100-continue"
2790        expectation. This exception, the purpose of which is
2791        to minimize any client processing delays associated with an
2792        undeclared wait for 100 (Continue) status code, applies only to
2793        HTTP/1.1 requests, and not to requests with any other HTTP-version
2794        value.
2795    </t>
2796    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2797        already received some or all of the request body for the
2798        corresponding request.
2799    </t>
2800    <t> An origin server that sends a 100 (Continue) response &MUST;
2801        ultimately send a final status code, once the request body is
2802        received and processed, unless it terminates the transport
2803        connection prematurely.
2804    </t>
2805    <t> If an origin server receives a request that does not include an
2806        Expect header field with the "100-continue" expectation,
2807        the request includes a request body, and the server responds
2808        with a final status code before reading the entire request body
2809        from the transport connection, then the server &SHOULD-NOT;  close
2810        the transport connection until it has read the entire request,
2811        or until the client closes the connection. Otherwise, the client
2812        might not reliably receive the response message. However, this
2813        requirement ought not be construed as preventing a server from
2814        defending itself against denial-of-service attacks, or from
2815        badly broken client implementations.
2816      </t>
2817    </list>
2818</t>
2819<t>
2820   Requirements for HTTP/1.1 proxies:
2821  <list style="symbols">
2822    <t> If a proxy receives a request that includes an Expect header
2823        field with the "100-continue" expectation, and the proxy
2824        either knows that the next-hop server complies with HTTP/1.1 or
2825        higher, or does not know the HTTP version of the next-hop
2826        server, it &MUST; forward the request, including the Expect header
2827        field.
2828    </t>
2829    <t> If the proxy knows that the version of the next-hop server is
2830        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2831        respond with a 417 (Expectation Failed) status code.
2832    </t>
2833    <t> Proxies &SHOULD; maintain a record of the HTTP version
2834        numbers received from recently-referenced next-hop servers.
2835    </t>
2836    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2837        request message was received from an HTTP/1.0 (or earlier)
2838        client and did not include an Expect header field with
2839        the "100-continue" expectation. This requirement overrides the
2840        general rule for forwarding of 1xx responses (see &status-1xx;).
2841    </t>
2842  </list>
2843</t>
2844</section>
2845
2846<section title="Closing Connections on Error" anchor="closing.connections.on.error">
2847<t>
2848   If the client is sending data, a server implementation using TCP
2849   &SHOULD; be careful to ensure that the client acknowledges receipt of
2850   the packet(s) containing the response, before the server closes the
2851   input connection. If the client continues sending data to the server
2852   after the close, the server's TCP stack will send a reset packet to
2853   the client, which might erase the client's unacknowledged input buffers
2854   before they can be read and interpreted by the HTTP application.
2855</t>
2856</section>
2857
2858</section>
2859</section>
2860
2861
2862<section title="Miscellaneous notes that might disappear" anchor="misc">
2863<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2864<t>
2865   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2866</t>
2867</section>
2868
2869<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2870<t>
2871   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2872</t>
2873</section>
2874
2875<section title="Interception of HTTP for access control" anchor="http.intercept">
2876<t>
2877   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2878</t>
2879</section>
2880
2881<section title="Use of HTTP by other protocols" anchor="http.others">
2882<t>
2883   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2884   Extensions of HTTP like WebDAV.</cref>
2885</t>
2886
2887</section>
2888<section title="Use of HTTP by media type specification" anchor="http.media">
2889<t>
2890   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2891</t>
2892</section>
2893</section>
2894
2895<section title="Header Field Definitions" anchor="header.field.definitions">
2896<t>
2897   This section defines the syntax and semantics of HTTP header fields
2898   related to message origination, framing, and routing.
2899</t>
2900<texttable align="left">
2901  <ttcol>Header Field Name</ttcol>
2902  <ttcol>Defined in...</ttcol>
2903 
2904  <c>Connection</c> <c><xref target="header.connection"/></c>
2905  <c>Content-Length</c> <c><xref target="header.content-length"/></c>
2906  <c>Host</c> <c><xref target="header.host"/></c>
2907  <c>TE</c> <c><xref target="header.te"/></c>
2908  <c>Trailer</c> <c><xref target="header.trailer"/></c>
2909  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
2910  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
2911  <c>Via</c> <c><xref target="header.via"/></c>
2912</texttable>
2913
2914<section title="Connection" anchor="header.connection">
2915  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2916  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2917  <x:anchor-alias value="Connection"/>
2918  <x:anchor-alias value="connection-token"/>
2919<t>
2920   The "Connection" header field allows the sender to specify
2921   options that are desired only for that particular connection.
2922   Such connection options &MUST; be removed or replaced before the
2923   message can be forwarded downstream by a proxy or gateway.
2924   This mechanism also allows the sender to indicate which HTTP
2925   header fields used in the message are only intended for the
2926   immediate recipient ("hop-by-hop"), as opposed to all recipients
2927   on the chain ("end-to-end"), enabling the message to be
2928   self-descriptive and allowing future connection-specific extensions
2929   to be deployed in HTTP without fear that they will be blindly
2930   forwarded by previously deployed intermediaries.
2931</t>
2932<t>
2933   The Connection header field's value has the following grammar:
2934</t>
2935<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2936  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
2937  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2938</artwork></figure>
2939<t>
2940   A proxy or gateway &MUST; parse a received Connection
2941   header field before a message is forwarded and, for each
2942   connection-token in this field, remove any header field(s) from
2943   the message with the same name as the connection-token, and then
2944   remove the Connection header field itself or replace it with the
2945   sender's own connection options for the forwarded message.
2946</t>
2947<t>
2948   A sender &MUST-NOT; include field-names in the Connection header
2949   field-value for fields that are defined as expressing constraints
2950   for all recipients in the request or response chain, such as the
2951   Cache-Control header field (&header-cache-control;).
2952</t>
2953<t>
2954   The connection options do not have to correspond to a header field
2955   present in the message, since a connection-specific header field
2956   might not be needed if there are no parameters associated with that
2957   connection option.  Recipients that trigger certain connection
2958   behavior based on the presence of connection options &MUST; do so
2959   based on the presence of the connection-token rather than only the
2960   presence of the optional header field.  In other words, if the
2961   connection option is received as a header field but not indicated
2962   within the Connection field-value, then the recipient &MUST; ignore
2963   the connection-specific header field because it has likely been
2964   forwarded by an intermediary that is only partially conformant.
2965</t>
2966<t>
2967   When defining new connection options, specifications ought to
2968   carefully consider existing deployed header fields and ensure
2969   that the new connection-token does not share the same name as
2970   an unrelated header field that might already be deployed.
2971   Defining a new connection-token essentially reserves that potential
2972   field-name for carrying additional information related to the
2973   connection option, since it would be unwise for senders to use
2974   that field-name for anything else.
2975</t>
2976<t>
2977   HTTP/1.1 defines the "close" connection option for the sender to
2978   signal that the connection will be closed after completion of the
2979   response. For example,
2980</t>
2981<figure><artwork type="example">
2982  Connection: close
2983</artwork></figure>
2984<t>
2985   in either the request or the response header fields indicates that
2986   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2987   after the current request/response is complete.
2988</t>
2989<t>
2990   An HTTP/1.1 client that does not support persistent connections &MUST;
2991   include the "close" connection option in every request message.
2992</t>
2993<t>
2994   An HTTP/1.1 server that does not support persistent connections &MUST;
2995   include the "close" connection option in every response message that
2996   does not have a 1xx (Informational) status code.
2997</t>
2998</section>
2999
3000<section title="Content-Length" anchor="header.content-length">
3001  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
3002  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
3003  <x:anchor-alias value="Content-Length"/>
3004<t>
3005   The "Content-Length" header field indicates the size of the
3006   message-body, in decimal number of octets, for any message other than
3007   a response to a HEAD request or a response with a status code of 304.
3008   In the case of a response to a HEAD request, Content-Length indicates
3009   the size of the payload body (not including any potential transfer-coding)
3010   that would have been sent had the request been a GET.
3011   In the case of a 304 (Not Modified) response to a GET request,
3012   Content-Length indicates the size of the payload body (not including
3013   any potential transfer-coding) that would have been sent in a 200 (OK)
3014   response.
3015</t>
3016<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
3017  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
3018</artwork></figure>
3019<t>
3020   An example is
3021</t>
3022<figure><artwork type="example">
3023  Content-Length: 3495
3024</artwork></figure>
3025<t>
3026   Implementations &SHOULD; use this field to indicate the message-body
3027   length when no transfer-coding is being applied and the
3028   payload's body length can be determined prior to being transferred.
3029   <xref target="message.body"/> describes how recipients determine the length
3030   of a message-body.
3031</t>
3032<t>
3033   Any Content-Length greater than or equal to zero is a valid value.
3034</t>
3035<t>
3036   Note that the use of this field in HTTP is significantly different from
3037   the corresponding definition in MIME, where it is an optional field
3038   used within the "message/external-body" content-type.
3039</t>
3040</section>
3041
3042<section title="Host" anchor="header.host">
3043  <iref primary="true" item="Host header field" x:for-anchor=""/>
3044  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3045  <x:anchor-alias value="Host"/>
3046<t>
3047   The "Host" header field in a request provides the host and port
3048   information from the target resource's URI, enabling the origin
3049   server to distinguish between resources while servicing requests
3050   for multiple host names on a single IP address.  Since the Host
3051   field-value is critical information for handling a request, it
3052   &SHOULD; be sent as the first header field following the Request-Line.
3053</t>
3054<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
3055  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3056</artwork></figure>
3057<t>
3058   A client &MUST; send a Host header field in all HTTP/1.1 request
3059   messages.  If the target resource's URI includes an authority
3060   component, then the Host field-value &MUST; be identical to that
3061   authority component after excluding any userinfo (<xref target="http.uri"/>).
3062   If the authority component is missing or undefined for the target
3063   resource's URI, then the Host header field &MUST; be sent with an
3064   empty field-value.
3065</t>
3066<t>
3067   For example, a GET request to the origin server for
3068   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
3069</t>
3070<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3071GET /pub/WWW/ HTTP/1.1
3072Host: www.example.org
3073</artwork></figure>
3074<t>
3075   The Host header field &MUST; be sent in an HTTP/1.1 request even
3076   if the request-target is in the form of an absolute-URI, since this
3077   allows the Host information to be forwarded through ancient HTTP/1.0
3078   proxies that might not have implemented Host.
3079</t>
3080<t>
3081   When an HTTP/1.1 proxy receives a request with a request-target in
3082   the form of an absolute-URI, the proxy &MUST; ignore the received
3083   Host header field (if any) and instead replace it with the host
3084   information of the request-target.  When a proxy forwards a request,
3085   it &MUST; generate the Host header field based on the received
3086   absolute-URI rather than the received Host.
3087</t>
3088<t>
3089   Since the Host header field acts as an application-level routing
3090   mechanism, it is a frequent target for malware seeking to poison
3091   a shared cache or redirect a request to an unintended server.
3092   An interception proxy is particularly vulnerable if it relies on
3093   the Host header field value for redirecting requests to internal
3094   servers, or for use as a cache key in a shared cache, without
3095   first verifying that the intercepted connection is targeting a
3096   valid IP address for that host.
3097</t>
3098<t>
3099   A server &MUST; respond with a 400 (Bad Request) status code to
3100   any HTTP/1.1 request message that lacks a Host header field and
3101   to any request message that contains more than one Host header field
3102   or a Host header field with an invalid field-value.
3103</t>
3104<t>
3105   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3106   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3107   for other requirements relating to Host.
3108</t>
3109</section>
3110
3111<section title="TE" anchor="header.te">
3112  <iref primary="true" item="TE header field" x:for-anchor=""/>
3113  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3114  <x:anchor-alias value="TE"/>
3115  <x:anchor-alias value="t-codings"/>
3116  <x:anchor-alias value="te-params"/>
3117  <x:anchor-alias value="te-ext"/>
3118<t>
3119   The "TE" header field indicates what extension transfer-codings
3120   the client is willing to accept in the response, and whether or not it is
3121   willing to accept trailer fields in a chunked transfer-coding.
3122</t>
3123<t>
3124   Its value consists of the keyword "trailers" and/or a comma-separated
3125   list of extension transfer-coding names with optional accept
3126   parameters (as described in <xref target="transfer.codings"/>).
3127</t>
3128<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"/>
3129  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
3130  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3131  <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> )
3132  <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> ]
3133</artwork></figure>
3134<t>
3135   The presence of the keyword "trailers" indicates that the client is
3136   willing to accept trailer fields in a chunked transfer-coding, as
3137   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3138   transfer-coding values even though it does not itself represent a
3139   transfer-coding.
3140</t>
3141<t>
3142   Examples of its use are:
3143</t>
3144<figure><artwork type="example">
3145  TE: deflate
3146  TE:
3147  TE: trailers, deflate;q=0.5
3148</artwork></figure>
3149<t>
3150   The TE header field only applies to the immediate connection.
3151   Therefore, the keyword &MUST; be supplied within a Connection header
3152   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3153</t>
3154<t>
3155   A server tests whether a transfer-coding is acceptable, according to
3156   a TE field, using these rules:
3157  <list style="numbers">
3158    <x:lt>
3159      <t>The "chunked" transfer-coding is always acceptable. If the
3160         keyword "trailers" is listed, the client indicates that it is
3161         willing to accept trailer fields in the chunked response on
3162         behalf of itself and any downstream clients. The implication is
3163         that, if given, the client is stating that either all
3164         downstream clients are willing to accept trailer fields in the
3165         forwarded response, or that it will attempt to buffer the
3166         response on behalf of downstream recipients.
3167      </t><t>
3168         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3169         chunked response such that a client can be assured of buffering
3170         the entire response.</t>
3171    </x:lt>
3172    <x:lt>
3173      <t>If the transfer-coding being tested is one of the transfer-codings
3174         listed in the TE field, then it is acceptable unless it
3175         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3176         qvalue of 0 means "not acceptable".)</t>
3177    </x:lt>
3178    <x:lt>
3179      <t>If multiple transfer-codings are acceptable, then the
3180         acceptable transfer-coding with the highest non-zero qvalue is
3181         preferred.  The "chunked" transfer-coding always has a qvalue
3182         of 1.</t>
3183    </x:lt>
3184  </list>
3185</t>
3186<t>
3187   If the TE field-value is empty or if no TE field is present, the only
3188   acceptable transfer-coding is "chunked". A message with no transfer-coding is
3189   always acceptable.
3190</t>
3191</section>
3192
3193<section title="Trailer" anchor="header.trailer">
3194  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3195  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3196  <x:anchor-alias value="Trailer"/>
3197<t>
3198   The "Trailer" header field indicates that the given set of
3199   header fields is present in the trailer of a message encoded with
3200   chunked transfer-coding.
3201</t>
3202<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
3203  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
3204</artwork></figure>
3205<t>
3206   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3207   message using chunked transfer-coding with a non-empty trailer. Doing
3208   so allows the recipient to know which header fields to expect in the
3209   trailer.
3210</t>
3211<t>
3212   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3213   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3214   trailer fields in a "chunked" transfer-coding.
3215</t>
3216<t>
3217   Message header fields listed in the Trailer header field &MUST-NOT;
3218   include the following header fields:
3219  <list style="symbols">
3220    <t>Transfer-Encoding</t>
3221    <t>Content-Length</t>
3222    <t>Trailer</t>
3223  </list>
3224</t>
3225</section>
3226
3227<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3228  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3229  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3230  <x:anchor-alias value="Transfer-Encoding"/>
3231<t>
3232   The "Transfer-Encoding" header field indicates what transfer-codings
3233   (if any) have been applied to the message body. It differs from
3234   Content-Encoding (&content-codings;) in that transfer-codings are a property
3235   of the message (and therefore are removed by intermediaries), whereas
3236   content-codings are not.
3237</t>
3238<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
3239  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3240</artwork></figure>
3241<t>
3242   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3243</t>
3244<figure><artwork type="example">
3245  Transfer-Encoding: chunked
3246</artwork></figure>
3247<t>
3248   If multiple encodings have been applied to a representation, the transfer-codings
3249   &MUST; be listed in the order in which they were applied.
3250   Additional information about the encoding parameters &MAY; be provided
3251   by other header fields not defined by this specification.
3252</t>
3253<t>
3254   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3255   header field.
3256</t>
3257</section>
3258
3259<section title="Upgrade" anchor="header.upgrade">
3260  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3261  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3262  <x:anchor-alias value="Upgrade"/>
3263<t>
3264   The "Upgrade" header field allows the client to specify what
3265   additional communication protocols it would like to use, if the server
3266   chooses to switch protocols. Servers can use it to indicate what protocols
3267   they are willing to switch to.
3268</t>
3269<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3270  <x:ref>Upgrade</x:ref> = 1#<x:ref>product</x:ref>
3271</artwork></figure>
3272<t>
3273   For example,
3274</t>
3275<figure><artwork type="example">
3276  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3277</artwork></figure>
3278<t>
3279   The Upgrade header field is intended to provide a simple mechanism
3280   for transitioning from HTTP/1.1 to some other, incompatible protocol. It
3281   does so by allowing the client to advertise its desire to use another
3282   protocol, such as a later version of HTTP with a higher major version
3283   number, even though the current request has been made using HTTP/1.1.
3284   This eases the difficult transition between incompatible protocols by
3285   allowing the client to initiate a request in the more commonly
3286   supported protocol while indicating to the server that it would like
3287   to use a "better" protocol if available (where "better" is determined
3288   by the server, possibly according to the nature of the request method
3289   or target resource).
3290</t>
3291<t>
3292   The Upgrade header field only applies to switching application-layer
3293   protocols upon the existing transport-layer connection. Upgrade
3294   cannot be used to insist on a protocol change; its acceptance and use
3295   by the server is optional. The capabilities and nature of the
3296   application-layer communication after the protocol change is entirely
3297   dependent upon the new protocol chosen, although the first action
3298   after changing the protocol &MUST; be a response to the initial HTTP
3299   request containing the Upgrade header field.
3300</t>
3301<t>
3302   The Upgrade header field only applies to the immediate connection.
3303   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3304   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3305   HTTP/1.1 message.
3306</t>
3307<t>
3308   The Upgrade header field cannot be used to indicate a switch to a
3309   protocol on a different connection. For that purpose, it is more
3310   appropriate to use a 3xx redirection response (&status-3xx;).
3311</t>
3312<t>
3313   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3314   Protocols) responses to indicate which protocol(s) are being switched to,
3315   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3316   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3317   response to indicate that they are willing to upgrade to one of the
3318   specified protocols.
3319</t>
3320<t>
3321   This specification only defines the protocol name "HTTP" for use by
3322   the family of Hypertext Transfer Protocols, as defined by the HTTP
3323   version rules of <xref target="http.version"/> and future updates to this
3324   specification. Additional tokens can be registered with IANA using the
3325   registration procedure defined below. 
3326</t>
3327
3328<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3329<t>
3330   The HTTP Upgrade Token Registry defines the name space for product
3331   tokens used to identify protocols in the Upgrade header field.
3332   Each registered token is associated with contact information and
3333   an optional set of specifications that details how the connection
3334   will be processed after it has been upgraded.
3335</t>
3336<t>
3337   Registrations are allowed on a First Come First Served basis as
3338   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3339   specifications need not be IETF documents or be subject to IESG review.
3340   Registrations are subject to the following rules:
3341  <list style="numbers">
3342    <t>A token, once registered, stays registered forever.</t>
3343    <t>The registration &MUST; name a responsible party for the
3344       registration.</t>
3345    <t>The registration &MUST; name a point of contact.</t>
3346    <t>The registration &MAY; name a set of specifications associated with that
3347       token. Such specifications need not be publicly available.</t>
3348    <t>The responsible party &MAY; change the registration at any time.
3349       The IANA will keep a record of all such changes, and make them
3350       available upon request.</t>
3351    <t>The responsible party for the first registration of a "product"
3352       token &MUST; approve later registrations of a "version" token
3353       together with that "product" token before they can be registered.</t>
3354    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3355       for a token. This will normally only be used in the case when a
3356       responsible party cannot be contacted.</t>
3357  </list>
3358</t>
3359</section>
3360
3361
3362</section>
3363
3364<section title="Via" anchor="header.via">
3365  <iref primary="true" item="Via header field" x:for-anchor=""/>
3366  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3367  <x:anchor-alias value="protocol-name"/>
3368  <x:anchor-alias value="protocol-version"/>
3369  <x:anchor-alias value="pseudonym"/>
3370  <x:anchor-alias value="received-by"/>
3371  <x:anchor-alias value="received-protocol"/>
3372  <x:anchor-alias value="Via"/>
3373<t>
3374   The "Via" header field &MUST; be sent by a proxy or gateway to
3375   indicate the intermediate protocols and recipients between the user
3376   agent and the server on requests, and between the origin server and
3377   the client on responses. It is analogous to the "Received" field
3378   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3379   and is intended to be used for tracking message forwards,
3380   avoiding request loops, and identifying the protocol capabilities of
3381   all senders along the request/response chain.
3382</t>
3383<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"/>
3384  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3385                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3386  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3387  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3388  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3389  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3390  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3391</artwork></figure>
3392<t>
3393   The received-protocol indicates the protocol version of the message
3394   received by the server or client along each segment of the
3395   request/response chain. The received-protocol version is appended to
3396   the Via field value when the message is forwarded so that information
3397   about the protocol capabilities of upstream applications remains
3398   visible to all recipients.
3399</t>
3400<t>
3401   The protocol-name is excluded if and only if it would be "HTTP". The
3402   received-by field is normally the host and optional port number of a
3403   recipient server or client that subsequently forwarded the message.
3404   However, if the real host is considered to be sensitive information,
3405   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3406   be assumed to be the default port of the received-protocol.
3407</t>
3408<t>
3409   Multiple Via field values represent each proxy or gateway that has
3410   forwarded the message. Each recipient &MUST; append its information
3411   such that the end result is ordered according to the sequence of
3412   forwarding applications.
3413</t>
3414<t>
3415   Comments &MAY; be used in the Via header field to identify the software
3416   of each recipient, analogous to the User-Agent and Server header fields.
3417   However, all comments in the Via field are optional and &MAY; be removed
3418   by any recipient prior to forwarding the message.
3419</t>
3420<t>
3421   For example, a request message could be sent from an HTTP/1.0 user
3422   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3423   forward the request to a public proxy at p.example.net, which completes
3424   the request by forwarding it to the origin server at www.example.com.
3425   The request received by www.example.com would then have the following
3426   Via header field:
3427</t>
3428<figure><artwork type="example">
3429  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3430</artwork></figure>
3431<t>
3432   A proxy or gateway used as a portal through a network firewall
3433   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3434   region unless it is explicitly enabled to do so. If not enabled, the
3435   received-by host of any host behind the firewall &SHOULD; be replaced
3436   by an appropriate pseudonym for that host.
3437</t>
3438<t>
3439   For organizations that have strong privacy requirements for hiding
3440   internal structures, a proxy or gateway &MAY; combine an ordered
3441   subsequence of Via header field entries with identical received-protocol
3442   values into a single such entry. For example,
3443</t>
3444<figure><artwork type="example">
3445  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3446</artwork></figure>
3447<t>
3448  could be collapsed to
3449</t>
3450<figure><artwork type="example">
3451  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3452</artwork></figure>
3453<t>
3454   Senders &SHOULD-NOT; combine multiple entries unless they are all
3455   under the same organizational control and the hosts have already been
3456   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3457   have different received-protocol values.
3458</t>
3459</section>
3460
3461</section>
3462
3463<section title="IANA Considerations" anchor="IANA.considerations">
3464
3465<section title="Header Field Registration" anchor="header.field.registration">
3466<t>
3467   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3468   with the permanent registrations below (see <xref target="RFC3864"/>):
3469</t>
3470<?BEGININC p1-messaging.iana-headers ?>
3471<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3472<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3473   <ttcol>Header Field Name</ttcol>
3474   <ttcol>Protocol</ttcol>
3475   <ttcol>Status</ttcol>
3476   <ttcol>Reference</ttcol>
3477
3478   <c>Connection</c>
3479   <c>http</c>
3480   <c>standard</c>
3481   <c>
3482      <xref target="header.connection"/>
3483   </c>
3484   <c>Content-Length</c>
3485   <c>http</c>
3486   <c>standard</c>
3487   <c>
3488      <xref target="header.content-length"/>
3489   </c>
3490   <c>Host</c>
3491   <c>http</c>
3492   <c>standard</c>
3493   <c>
3494      <xref target="header.host"/>
3495   </c>
3496   <c>TE</c>
3497   <c>http</c>
3498   <c>standard</c>
3499   <c>
3500      <xref target="header.te"/>
3501   </c>
3502   <c>Trailer</c>
3503   <c>http</c>
3504   <c>standard</c>
3505   <c>
3506      <xref target="header.trailer"/>
3507   </c>
3508   <c>Transfer-Encoding</c>
3509   <c>http</c>
3510   <c>standard</c>
3511   <c>
3512      <xref target="header.transfer-encoding"/>
3513   </c>
3514   <c>Upgrade</c>
3515   <c>http</c>
3516   <c>standard</c>
3517   <c>
3518      <xref target="header.upgrade"/>
3519   </c>
3520   <c>Via</c>
3521   <c>http</c>
3522   <c>standard</c>
3523   <c>
3524      <xref target="header.via"/>
3525   </c>
3526</texttable>
3527<!--(END)-->
3528<?ENDINC p1-messaging.iana-headers ?>
3529<t>
3530   Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
3531   HTTP header field would be in conflict with the use of the "close" connection
3532   option for the "Connection" header field (<xref target="header.connection"/>).
3533</t>
3534<texttable align="left" suppress-title="true">
3535   <ttcol>Header Field Name</ttcol>
3536   <ttcol>Protocol</ttcol>
3537   <ttcol>Status</ttcol>
3538   <ttcol>Reference</ttcol>
3539
3540   <c>Close</c>
3541   <c>http</c>
3542   <c>reserved</c>
3543   <c>
3544      <xref target="header.field.registration"/>
3545   </c>
3546</texttable>
3547<t>
3548   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3549</t>
3550</section>
3551
3552<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3553<t>
3554   The entries for the "http" and "https" URI Schemes in the registry located at
3555   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3556   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3557   and <xref target="https.uri" format="counter"/> of this document
3558   (see <xref target="RFC4395"/>).
3559</t>
3560</section>
3561
3562<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3563<t>
3564   This document serves as the specification for the Internet media types
3565   "message/http" and "application/http". The following is to be registered with
3566   IANA (see <xref target="RFC4288"/>).
3567</t>
3568<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3569<iref item="Media Type" subitem="message/http" primary="true"/>
3570<iref item="message/http Media Type" primary="true"/>
3571<t>
3572   The message/http type can be used to enclose a single HTTP request or
3573   response message, provided that it obeys the MIME restrictions for all
3574   "message" types regarding line length and encodings.
3575</t>
3576<t>
3577  <list style="hanging" x:indent="12em">
3578    <t hangText="Type name:">
3579      message
3580    </t>
3581    <t hangText="Subtype name:">
3582      http
3583    </t>
3584    <t hangText="Required parameters:">
3585      none
3586    </t>
3587    <t hangText="Optional parameters:">
3588      version, msgtype
3589      <list style="hanging">
3590        <t hangText="version:">
3591          The HTTP-Version number of the enclosed message
3592          (e.g., "1.1"). If not present, the version can be
3593          determined from the first line of the body.
3594        </t>
3595        <t hangText="msgtype:">
3596          The message type &mdash; "request" or "response". If not
3597          present, the type can be determined from the first
3598          line of the body.
3599        </t>
3600      </list>
3601    </t>
3602    <t hangText="Encoding considerations:">
3603      only "7bit", "8bit", or "binary" are permitted
3604    </t>
3605    <t hangText="Security considerations:">
3606      none
3607    </t>
3608    <t hangText="Interoperability considerations:">
3609      none
3610    </t>
3611    <t hangText="Published specification:">
3612      This specification (see <xref target="internet.media.type.message.http"/>).
3613    </t>
3614    <t hangText="Applications that use this media type:">
3615    </t>
3616    <t hangText="Additional information:">
3617      <list style="hanging">
3618        <t hangText="Magic number(s):">none</t>
3619        <t hangText="File extension(s):">none</t>
3620        <t hangText="Macintosh file type code(s):">none</t>
3621      </list>
3622    </t>
3623    <t hangText="Person and email address to contact for further information:">
3624      See Authors Section.
3625    </t>
3626    <t hangText="Intended usage:">
3627      COMMON
3628    </t>
3629    <t hangText="Restrictions on usage:">
3630      none
3631    </t>
3632    <t hangText="Author/Change controller:">
3633      IESG
3634    </t>
3635  </list>
3636</t>
3637</section>
3638<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3639<iref item="Media Type" subitem="application/http" primary="true"/>
3640<iref item="application/http Media Type" primary="true"/>
3641<t>
3642   The application/http type can be used to enclose a pipeline of one or more
3643   HTTP request or response messages (not intermixed).
3644</t>
3645<t>
3646  <list style="hanging" x:indent="12em">
3647    <t hangText="Type name:">
3648      application
3649    </t>
3650    <t hangText="Subtype name:">
3651      http
3652    </t>
3653    <t hangText="Required parameters:">
3654      none
3655    </t>
3656    <t hangText="Optional parameters:">
3657      version, msgtype
3658      <list style="hanging">
3659        <t hangText="version:">
3660          The HTTP-Version number of the enclosed messages
3661          (e.g., "1.1"). If not present, the version can be
3662          determined from the first line of the body.
3663        </t>
3664        <t hangText="msgtype:">
3665          The message type &mdash; "request" or "response". If not
3666          present, the type can be determined from the first
3667          line of the body.
3668        </t>
3669      </list>
3670    </t>
3671    <t hangText="Encoding considerations:">
3672      HTTP messages enclosed by this type
3673      are in "binary" format; use of an appropriate
3674      Content-Transfer-Encoding is required when
3675      transmitted via E-mail.
3676    </t>
3677    <t hangText="Security considerations:">
3678      none
3679    </t>
3680    <t hangText="Interoperability considerations:">
3681      none
3682    </t>
3683    <t hangText="Published specification:">
3684      This specification (see <xref target="internet.media.type.application.http"/>).
3685    </t>
3686    <t hangText="Applications that use this media type:">
3687    </t>
3688    <t hangText="Additional information:">
3689      <list style="hanging">
3690        <t hangText="Magic number(s):">none</t>
3691        <t hangText="File extension(s):">none</t>
3692        <t hangText="Macintosh file type code(s):">none</t>
3693      </list>
3694    </t>
3695    <t hangText="Person and email address to contact for further information:">
3696      See Authors Section.
3697    </t>
3698    <t hangText="Intended usage:">
3699      COMMON
3700    </t>
3701    <t hangText="Restrictions on usage:">
3702      none
3703    </t>
3704    <t hangText="Author/Change controller:">
3705      IESG
3706    </t>
3707  </list>
3708</t>
3709</section>
3710</section>
3711
3712<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3713<t>
3714   The registration procedure for HTTP Transfer Codings is now defined by
3715   <xref target="transfer.coding.registry"/> of this document.
3716</t>
3717<t>
3718   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3719   shall be updated with the registrations below:
3720</t>
3721<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3722   <ttcol>Name</ttcol>
3723   <ttcol>Description</ttcol>
3724   <ttcol>Reference</ttcol>
3725   <c>chunked</c>
3726   <c>Transfer in a series of chunks</c>
3727   <c>
3728      <xref target="chunked.encoding"/>
3729   </c>
3730   <c>compress</c>
3731   <c>UNIX "compress" program method</c>
3732   <c>
3733      <xref target="compress.coding"/>
3734   </c>
3735   <c>deflate</c>
3736   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3737   the "zlib" data format (<xref target="RFC1950"/>)
3738   </c>
3739   <c>
3740      <xref target="deflate.coding"/>
3741   </c>
3742   <c>gzip</c>
3743   <c>Same as GNU zip <xref target="RFC1952"/></c>
3744   <c>
3745      <xref target="gzip.coding"/>
3746   </c>
3747</texttable>
3748</section>
3749
3750<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3751<t>
3752   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3753   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3754   by <xref target="upgrade.token.registry"/> of this document.
3755</t>
3756<t>
3757   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3758   shall be updated with the registration below:
3759</t>
3760<texttable align="left" suppress-title="true">
3761   <ttcol>Value</ttcol>
3762   <ttcol>Description</ttcol>
3763   <ttcol>Reference</ttcol>
3764
3765   <c>HTTP</c>
3766   <c>Hypertext Transfer Protocol</c> 
3767   <c><xref target="http.version"/> of this specification</c>
3768
3769</texttable>
3770</section>
3771
3772</section>
3773
3774<section title="Security Considerations" anchor="security.considerations">
3775<t>
3776   This section is meant to inform application developers, information
3777   providers, and users of the security limitations in HTTP/1.1 as
3778   described by this document. The discussion does not include
3779   definitive solutions to the problems revealed, though it does make
3780   some suggestions for reducing security risks.
3781</t>
3782
3783<section title="Personal Information" anchor="personal.information">
3784<t>
3785   HTTP clients are often privy to large amounts of personal information
3786   (e.g., the user's name, location, mail address, passwords, encryption
3787   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3788   leakage of this information.
3789   We very strongly recommend that a convenient interface be provided
3790   for the user to control dissemination of such information, and that
3791   designers and implementors be particularly careful in this area.
3792   History shows that errors in this area often create serious security
3793   and/or privacy problems and generate highly adverse publicity for the
3794   implementor's company.
3795</t>
3796</section>
3797
3798<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3799<t>
3800   A server is in the position to save personal data about a user's
3801   requests which might identify their reading patterns or subjects of
3802   interest. This information is clearly confidential in nature and its
3803   handling can be constrained by law in certain countries. People using
3804   HTTP to provide data are responsible for ensuring that
3805   such material is not distributed without the permission of any
3806   individuals that are identifiable by the published results.
3807</t>
3808</section>
3809
3810<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3811<t>
3812   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3813   the documents returned by HTTP requests to be only those that were
3814   intended by the server administrators. If an HTTP server translates
3815   HTTP URIs directly into file system calls, the server &MUST; take
3816   special care not to serve files that were not intended to be
3817   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3818   other operating systems use ".." as a path component to indicate a
3819   directory level above the current one. On such a system, an HTTP
3820   server &MUST; disallow any such construct in the request-target if it
3821   would otherwise allow access to a resource outside those intended to
3822   be accessible via the HTTP server. Similarly, files intended for
3823   reference only internally to the server (such as access control
3824   files, configuration files, and script code) &MUST; be protected from
3825   inappropriate retrieval, since they might contain sensitive
3826   information. Experience has shown that minor bugs in such HTTP server
3827   implementations have turned into security risks.
3828</t>
3829</section>
3830
3831<section title="DNS-related Attacks" anchor="dns.related.attacks">
3832<t>
3833   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3834   generally prone to security attacks based on the deliberate misassociation
3835   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3836   cautious in assuming the validity of an IP number/DNS name association unless
3837   the response is protected by DNSSec (<xref target="RFC4033"/>).
3838</t>
3839</section>
3840
3841<section title="Proxies and Caching" anchor="attack.proxies">
3842<t>
3843   By their very nature, HTTP proxies are men-in-the-middle, and
3844   represent an opportunity for man-in-the-middle attacks. Compromise of
3845   the systems on which the proxies run can result in serious security
3846   and privacy problems. Proxies have access to security-related
3847   information, personal information about individual users and
3848   organizations, and proprietary information belonging to users and
3849   content providers. A compromised proxy, or a proxy implemented or
3850   configured without regard to security and privacy considerations,
3851   might be used in the commission of a wide range of potential attacks.
3852</t>
3853<t>
3854   Proxy operators need to protect the systems on which proxies run as
3855   they would protect any system that contains or transports sensitive
3856   information. In particular, log information gathered at proxies often
3857   contains highly sensitive personal information, and/or information
3858   about organizations. Log information needs to be carefully guarded, and
3859   appropriate guidelines for use need to be developed and followed.
3860   (<xref target="abuse.of.server.log.information"/>).
3861</t>
3862<t>
3863   Proxy implementors need to consider the privacy and security
3864   implications of their design and coding decisions, and of the
3865   configuration options they provide to proxy operators (especially the
3866   default configuration).
3867</t>
3868<t>
3869   Users of a proxy need to be aware that proxies are no more trustworthy than
3870   the people who run them; HTTP itself cannot solve this problem.
3871</t>
3872<t>
3873   The judicious use of cryptography, when appropriate, might suffice to
3874   protect against a broad range of security and privacy attacks. Such
3875   cryptography is beyond the scope of the HTTP/1.1 specification.
3876</t>
3877</section>
3878
3879<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3880<t>
3881   Because HTTP uses mostly textual, character-delimited fields, attackers can
3882   overflow buffers in implementations, and/or perform a Denial of Service
3883   against implementations that accept fields with unlimited lengths.
3884</t>
3885<t>
3886   To promote interoperability, this specification makes specific
3887   recommendations for size limits on request-targets (<xref target="request-target"/>)
3888   and blocks of header fields (<xref target="header.fields"/>). These are
3889   minimum recommendations, chosen to be supportable even by implementations
3890   with limited resources; it is expected that most implementations will choose
3891   substantially higher limits.
3892</t>
3893<t>
3894   This specification also provides a way for servers to reject messages that
3895   have request-targets that are too long (&status-414;) or request entities
3896   that are too large (&status-4xx;).
3897</t>
3898<t>
3899   Other fields (including but not limited to request methods, response status
3900   phrases, header field-names, and body chunks) &SHOULD; be limited by
3901   implementations carefully, so as to not impede interoperability.
3902</t>
3903</section>
3904
3905<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3906<t>
3907   They exist. They are hard to defend against. Research continues.
3908   Beware.
3909</t>
3910</section>
3911</section>
3912
3913<section title="Acknowledgments" anchor="acks">
3914<t>
3915   This document revision builds on the work that went into
3916   <xref target="RFC2616" format="none">RFC 2616</xref> and its predecessors.
3917   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for detailed
3918   acknowledgements.
3919</t>
3920<t>
3921   Since 1999, many contributors have helped by reporting bugs, asking
3922   smart questions, drafting and reviewing text, and discussing open issues:
3923</t>
3924<?BEGININC acks ?>
3925<t>Adam Barth,
3926Adam Roach,
3927Addison Phillips,
3928Adrian Chadd,
3929Adrien de Croy,
3930Alan Ford,
3931Alan Ruttenberg,
3932Albert Lunde,
3933Alex Rousskov,
3934Alexey Melnikov,
3935Alisha Smith,
3936Amichai Rothman,
3937Amit Klein,
3938Amos Jeffries,
3939Andreas Maier,
3940Andreas Petersson,
3941Anne van Kesteren,
3942Anthony Bryan,
3943Asbjorn Ulsberg,
3944Balachander Krishnamurthy,
3945Barry Leiba,
3946Ben Laurie,
3947Benjamin Niven-Jenkins,
3948Bil Corry,
3949Bill Burke,
3950Bjoern Hoehrmann,
3951Bob Scheifler,
3952Boris Zbarsky,
3953Brett Slatkin,
3954Brian Kell,
3955Brian McBarron,
3956Brian Pane,
3957Brian Smith,
3958Bryce Nesbitt,
3959Cameron Heavon-Jones,
3960Carl Kugler,
3961Carsten Bormann,
3962Charles Fry,
3963Chris Newman,
3964Cyrus Daboo,
3965Dale Robert Anderson,
3966Dan Winship,
3967Daniel Stenberg,
3968Dave Cridland,
3969Dave Crocker,
3970Dave Kristol,
3971David Booth,
3972David Singer,
3973David W. Morris,
3974Diwakar Shetty,
3975Dmitry Kurochkin,
3976Drummond Reed,
3977Duane Wessels,
3978Edward Lee,
3979Eliot Lear,
3980Eran Hammer-Lahav,
3981Eric D. Williams,
3982Eric J. Bowman,
3983Eric Lawrence,
3984Erik Aronesty,
3985Florian Weimer,
3986Frank Ellermann,
3987Fred Bohle,
3988Geoffrey Sneddon,
3989Gervase Markham,
3990Greg Wilkins,
3991Harald Tveit Alvestrand,
3992Harry Halpin,
3993Helge Hess,
3994Henrik Nordstrom,
3995Henry S. Thompson,
3996Henry Story,
3997Herbert van de Sompel,
3998Howard Melman,
3999Hugo Haas,
4000Ian Hickson,
4001Ingo Struck,
4002J. Ross Nicoll,
4003James H. Manger,
4004James Lacey,
4005James M. Snell,
4006Jamie Lokier,
4007Jan Algermissen,
4008Jeff Hodges (for coming up with the term 'effective Request-URI'),
4009Jeff Walden,
4010Jim Luther,
4011Joe D. Williams,
4012Joe Gregorio,
4013Joe Orton,
4014John C. Klensin,
4015John C. Mallery,
4016John Cowan,
4017John Kemp,
4018John Panzer,
4019John Schneider,
4020John Stracke,
4021Jonas Sicking,
4022Jonathan Billington,
4023Jonathan Moore,
4024Jonathan Rees,
4025Jordi Ros,
4026Joris Dobbelsteen,
4027Josh Cohen,
4028Julien Pierre,
4029Jungshik Shin,
4030Justin Chapweske,
4031Justin Erenkrantz,
4032Justin James,
4033Kalvinder Singh,
4034Karl Dubost,
4035Keith Hoffman,
4036Keith Moore,
4037Koen Holtman,
4038Konstantin Voronkov,
4039Kris Zyp,
4040Lisa Dusseault,
4041Maciej Stachowiak,
4042Marc Schneider,
4043Marc Slemko,
4044Mark Baker,
4045Mark Nottingham (Working Group chair),
4046Mark Pauley,
4047Markus Lanthaler,
4048Martin J. Duerst,
4049Martin Thomson,
4050Matt Lynch,
4051Matthew Cox,
4052Max Clark,
4053Michael Burrows,
4054Michael Hausenblas,
4055Mike Amundsen,
4056Mike Kelly,
4057Mike Schinkel,
4058Miles Sabin,
4059Mykyta Yevstifeyev,
4060Nathan Rixham,
4061Nicholas Shanks,
4062Nico Williams,
4063Nicolas Alvarez,
4064Noah Slater,
4065Pablo Castro,
4066Pat Hayes,
4067Patrick R. McManus,
4068Paul E. Jones,
4069Paul Hoffman,
4070Paul Marquess,
4071Peter Saint-Andre,
4072Peter Watkins,
4073Phil Archer,
4074Phillip Hallam-Baker,
4075Poul-Henning Kamp,
4076Preethi Natarajan,
4077Ray Polk,
4078Reto Bachmann-Gmuer,
4079Richard Cyganiak,
4080Robert Brewer,
4081Robert Collins,
4082Robert O'Callahan,
4083Robert Olofsson,
4084Robert Sayre,
4085Robert Siemer,
4086Robert de Wilde,
4087Roberto Javier Godoy,
4088Ronny Widjaja,
4089S. Mike Dierken,
4090Salvatore Loreto,
4091Sam Johnston,
4092Sam Ruby,
4093Scott Lawrence (for maintaining the original issues list),
4094Sean B. Palmer,
4095Shane McCarron,
4096Stefan Eissing,
4097Stefan Tilkov,
4098Stefanos Harhalakis,
4099Stephane Bortzmeyer,
4100Stuart Williams,
4101Subbu Allamaraju,
4102Sylvain Hellegouarch,
4103Tapan Divekar,
4104Ted Hardie,
4105Thomas Broyer,
4106Thomas Nordin,
4107Thomas Roessler,
4108Tim Morgan,
4109Tim Olsen,
4110Travis Snoozy,
4111Tyler Close,
4112Vincent Murphy,
4113Wenbo Zhu,
4114Werner Baumann,
4115Wilbur Streett,
4116Wilfredo Sanchez Vega,
4117William A. Rowe Jr.,
4118William Chan,
4119Willy Tarreau,
4120Xiaoshu Wang,
4121Yaron Goland,
4122Yngve Nysaeter Pettersen,
4123Yogesh Bang,
4124Yutaka Oiwa,
4125Zed A. Shaw, and
4126Zhong Yu.
4127</t>
4128<?ENDINC acks ?>
4129</section>
4130
4131</middle>
4132<back>
4133
4134<references title="Normative References">
4135
4136<reference anchor="ISO-8859-1">
4137  <front>
4138    <title>
4139     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4140    </title>
4141    <author>
4142      <organization>International Organization for Standardization</organization>
4143    </author>
4144    <date year="1998"/>
4145  </front>
4146  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4147</reference>
4148
4149<reference anchor="Part2">
4150  <front>
4151    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4152    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4153      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4154      <address><email>fielding@gbiv.com</email></address>
4155    </author>
4156    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4157      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4158      <address><email>jg@freedesktop.org</email></address>
4159    </author>
4160    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4161      <organization abbrev="HP">Hewlett-Packard Company</organization>
4162      <address><email>JeffMogul@acm.org</email></address>
4163    </author>
4164    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4165      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4166      <address><email>henrikn@microsoft.com</email></address>
4167    </author>
4168    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4169      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4170      <address><email>LMM@acm.org</email></address>
4171    </author>
4172    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4173      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4174      <address><email>paulle@microsoft.com</email></address>
4175    </author>
4176    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4177      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4178      <address><email>timbl@w3.org</email></address>
4179    </author>
4180    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4181      <organization abbrev="W3C">World Wide Web Consortium</organization>
4182      <address><email>ylafon@w3.org</email></address>
4183    </author>
4184    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4185      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4186      <address><email>julian.reschke@greenbytes.de</email></address>
4187    </author>
4188    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4189  </front>
4190  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4191  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4192</reference>
4193
4194<reference anchor="Part3">
4195  <front>
4196    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4197    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4198      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4199      <address><email>fielding@gbiv.com</email></address>
4200    </author>
4201    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4202      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4203      <address><email>jg@freedesktop.org</email></address>
4204    </author>
4205    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4206      <organization abbrev="HP">Hewlett-Packard Company</organization>
4207      <address><email>JeffMogul@acm.org</email></address>
4208    </author>
4209    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4210      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4211      <address><email>henrikn@microsoft.com</email></address>
4212    </author>
4213    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4214      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4215      <address><email>LMM@acm.org</email></address>
4216    </author>
4217    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4218      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4219      <address><email>paulle@microsoft.com</email></address>
4220    </author>
4221    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4222      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4223      <address><email>timbl@w3.org</email></address>
4224    </author>
4225    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4226      <organization abbrev="W3C">World Wide Web Consortium</organization>
4227      <address><email>ylafon@w3.org</email></address>
4228    </author>
4229    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4230      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4231      <address><email>julian.reschke@greenbytes.de</email></address>
4232    </author>
4233    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4234  </front>
4235  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4236  <x:source href="p3-payload.xml" basename="p3-payload"/>
4237</reference>
4238
4239<reference anchor="Part6">
4240  <front>
4241    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4242    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4243      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4244      <address><email>fielding@gbiv.com</email></address>
4245    </author>
4246    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4247      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4248      <address><email>jg@freedesktop.org</email></address>
4249    </author>
4250    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4251      <organization abbrev="HP">Hewlett-Packard Company</organization>
4252      <address><email>JeffMogul@acm.org</email></address>
4253    </author>
4254    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4255      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4256      <address><email>henrikn@microsoft.com</email></address>
4257    </author>
4258    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4259      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4260      <address><email>LMM@acm.org</email></address>
4261    </author>
4262    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4263      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4264      <address><email>paulle@microsoft.com</email></address>
4265    </author>
4266    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4267      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4268      <address><email>timbl@w3.org</email></address>
4269    </author>
4270    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4271      <organization abbrev="W3C">World Wide Web Consortium</organization>
4272      <address><email>ylafon@w3.org</email></address>
4273    </author>
4274    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4275      <organization>Rackspace</organization>
4276      <address><email>mnot@mnot.net</email></address>
4277    </author>
4278    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4279      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4280      <address><email>julian.reschke@greenbytes.de</email></address>
4281    </author>
4282    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4283  </front>
4284  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4285  <x:source href="p6-cache.xml" basename="p6-cache"/>
4286</reference>
4287
4288<reference anchor="RFC5234">
4289  <front>
4290    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4291    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4292      <organization>Brandenburg InternetWorking</organization>
4293      <address>
4294        <email>dcrocker@bbiw.net</email>
4295      </address> 
4296    </author>
4297    <author initials="P." surname="Overell" fullname="Paul Overell">
4298      <organization>THUS plc.</organization>
4299      <address>
4300        <email>paul.overell@thus.net</email>
4301      </address>
4302    </author>
4303    <date month="January" year="2008"/>
4304  </front>
4305  <seriesInfo name="STD" value="68"/>
4306  <seriesInfo name="RFC" value="5234"/>
4307</reference>
4308
4309<reference anchor="RFC2119">
4310  <front>
4311    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4312    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4313      <organization>Harvard University</organization>
4314      <address><email>sob@harvard.edu</email></address>
4315    </author>
4316    <date month="March" year="1997"/>
4317  </front>
4318  <seriesInfo name="BCP" value="14"/>
4319  <seriesInfo name="RFC" value="2119"/>
4320</reference>
4321
4322<reference anchor="RFC3986">
4323 <front>
4324  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4325  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4326    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4327    <address>
4328       <email>timbl@w3.org</email>
4329       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4330    </address>
4331  </author>
4332  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4333    <organization abbrev="Day Software">Day Software</organization>
4334    <address>
4335      <email>fielding@gbiv.com</email>
4336      <uri>http://roy.gbiv.com/</uri>
4337    </address>
4338  </author>
4339  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4340    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4341    <address>
4342      <email>LMM@acm.org</email>
4343      <uri>http://larry.masinter.net/</uri>
4344    </address>
4345  </author>
4346  <date month='January' year='2005'></date>
4347 </front>
4348 <seriesInfo name="STD" value="66"/>
4349 <seriesInfo name="RFC" value="3986"/>
4350</reference>
4351
4352<reference anchor="USASCII">
4353  <front>
4354    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4355    <author>
4356      <organization>American National Standards Institute</organization>
4357    </author>
4358    <date year="1986"/>
4359  </front>
4360  <seriesInfo name="ANSI" value="X3.4"/>
4361</reference>
4362
4363<reference anchor="RFC1950">
4364  <front>
4365    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4366    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4367      <organization>Aladdin Enterprises</organization>
4368      <address><email>ghost@aladdin.com</email></address>
4369    </author>
4370    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4371    <date month="May" year="1996"/>
4372  </front>
4373  <seriesInfo name="RFC" value="1950"/>
4374  <!--<annotation>
4375    RFC 1950 is an Informational RFC, thus it might be less stable than
4376    this specification. On the other hand, this downward reference was
4377    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4378    therefore it is unlikely to cause problems in practice. See also
4379    <xref target="BCP97"/>.
4380  </annotation>-->
4381</reference>
4382
4383<reference anchor="RFC1951">
4384  <front>
4385    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4386    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4387      <organization>Aladdin Enterprises</organization>
4388      <address><email>ghost@aladdin.com</email></address>
4389    </author>
4390    <date month="May" year="1996"/>
4391  </front>
4392  <seriesInfo name="RFC" value="1951"/>
4393  <!--<annotation>
4394    RFC 1951 is an Informational RFC, thus it might be less stable than
4395    this specification. On the other hand, this downward reference was
4396    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4397    therefore it is unlikely to cause problems in practice. See also
4398    <xref target="BCP97"/>.
4399  </annotation>-->
4400</reference>
4401
4402<reference anchor="RFC1952">
4403  <front>
4404    <title>GZIP file format specification version 4.3</title>
4405    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4406      <organization>Aladdin Enterprises</organization>
4407      <address><email>ghost@aladdin.com</email></address>
4408    </author>
4409    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4410      <address><email>gzip@prep.ai.mit.edu</email></address>
4411    </author>
4412    <author initials="M." surname="Adler" fullname="Mark Adler">
4413      <address><email>madler@alumni.caltech.edu</email></address>
4414    </author>
4415    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4416      <address><email>ghost@aladdin.com</email></address>
4417    </author>
4418    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4419      <address><email>randeg@alumni.rpi.edu</email></address>
4420    </author>
4421    <date month="May" year="1996"/>
4422  </front>
4423  <seriesInfo name="RFC" value="1952"/>
4424  <!--<annotation>
4425    RFC 1952 is an Informational RFC, thus it might be less stable than
4426    this specification. On the other hand, this downward reference was
4427    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4428    therefore it is unlikely to cause problems in practice. See also
4429    <xref target="BCP97"/>.
4430  </annotation>-->
4431</reference>
4432
4433</references>
4434
4435<references title="Informative References">
4436
4437<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4438  <front>
4439    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4440    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4441    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4442    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4443    <author initials="H." surname="Lie" fullname="H. Lie"/>
4444    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4445    <date year="1997" month="September"/>
4446  </front>
4447  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4448</reference>
4449
4450<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4451  <front>
4452    <title>Improving HTTP Latency</title>
4453    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4454    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4455    <date year="1995" month="December"/>
4456  </front>
4457  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4458</reference>
4459
4460<reference anchor='RFC1919'>
4461  <front>
4462    <title>Classical versus Transparent IP Proxies</title>
4463    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4464      <address><email>mchatel@pax.eunet.ch</email></address>
4465    </author>
4466    <date year='1996' month='March' />
4467  </front>
4468  <seriesInfo name='RFC' value='1919' />
4469</reference>
4470
4471<reference anchor="RFC1945">
4472  <front>
4473    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4474    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4475      <organization>MIT, Laboratory for Computer Science</organization>
4476      <address><email>timbl@w3.org</email></address>
4477    </author>
4478    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4479      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4480      <address><email>fielding@ics.uci.edu</email></address>
4481    </author>
4482    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4483      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4484      <address><email>frystyk@w3.org</email></address>
4485    </author>
4486    <date month="May" year="1996"/>
4487  </front>
4488  <seriesInfo name="RFC" value="1945"/>
4489</reference>
4490
4491<reference anchor="RFC2045">
4492  <front>
4493    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4494    <author initials="N." surname="Freed" fullname="Ned Freed">
4495      <organization>Innosoft International, Inc.</organization>
4496      <address><email>ned@innosoft.com</email></address>
4497    </author>
4498    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4499      <organization>First Virtual Holdings</organization>
4500      <address><email>nsb@nsb.fv.com</email></address>
4501    </author>
4502    <date month="November" year="1996"/>
4503  </front>
4504  <seriesInfo name="RFC" value="2045"/>
4505</reference>
4506
4507<reference anchor="RFC2047">
4508  <front>
4509    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4510    <author initials="K." surname="Moore" fullname="Keith Moore">
4511      <organization>University of Tennessee</organization>
4512      <address><email>moore@cs.utk.edu</email></address>
4513    </author>
4514    <date month="November" year="1996"/>
4515  </front>
4516  <seriesInfo name="RFC" value="2047"/>
4517</reference>
4518
4519<reference anchor="RFC2068">
4520  <front>
4521    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4522    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4523      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4524      <address><email>fielding@ics.uci.edu</email></address>
4525    </author>
4526    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4527      <organization>MIT Laboratory for Computer Science</organization>
4528      <address><email>jg@w3.org</email></address>
4529    </author>
4530    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4531      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4532      <address><email>mogul@wrl.dec.com</email></address>
4533    </author>
4534    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4535      <organization>MIT Laboratory for Computer Science</organization>
4536      <address><email>frystyk@w3.org</email></address>
4537    </author>
4538    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4539      <organization>MIT Laboratory for Computer Science</organization>
4540      <address><email>timbl@w3.org</email></address>
4541    </author>
4542    <date month="January" year="1997"/>
4543  </front>
4544  <seriesInfo name="RFC" value="2068"/>
4545</reference>
4546
4547<reference anchor="RFC2145">
4548  <front>
4549    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4550    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4551      <organization>Western Research Laboratory</organization>
4552      <address><email>mogul@wrl.dec.com</email></address>
4553    </author>
4554    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4555      <organization>Department of Information and Computer Science</organization>
4556      <address><email>fielding@ics.uci.edu</email></address>
4557    </author>
4558    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4559      <organization>MIT Laboratory for Computer Science</organization>
4560      <address><email>jg@w3.org</email></address>
4561    </author>
4562    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4563      <organization>W3 Consortium</organization>
4564      <address><email>frystyk@w3.org</email></address>
4565    </author>
4566    <date month="May" year="1997"/>
4567  </front>
4568  <seriesInfo name="RFC" value="2145"/>
4569</reference>
4570
4571<reference anchor="RFC2616">
4572  <front>
4573    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4574    <author initials="R." surname="Fielding" fullname="R. Fielding">
4575      <organization>University of California, Irvine</organization>
4576      <address><email>fielding@ics.uci.edu</email></address>
4577    </author>
4578    <author initials="J." surname="Gettys" fullname="J. Gettys">
4579      <organization>W3C</organization>
4580      <address><email>jg@w3.org</email></address>
4581    </author>
4582    <author initials="J." surname="Mogul" fullname="J. Mogul">
4583      <organization>Compaq Computer Corporation</organization>
4584      <address><email>mogul@wrl.dec.com</email></address>
4585    </author>
4586    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4587      <organization>MIT Laboratory for Computer Science</organization>
4588      <address><email>frystyk@w3.org</email></address>
4589    </author>
4590    <author initials="L." surname="Masinter" fullname="L. Masinter">
4591      <organization>Xerox Corporation</organization>
4592      <address><email>masinter@parc.xerox.com</email></address>
4593    </author>
4594    <author initials="P." surname="Leach" fullname="P. Leach">
4595      <organization>Microsoft Corporation</organization>
4596      <address><email>paulle@microsoft.com</email></address>
4597    </author>
4598    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4599      <organization>W3C</organization>
4600      <address><email>timbl@w3.org</email></address>
4601    </author>
4602    <date month="June" year="1999"/>
4603  </front>
4604  <seriesInfo name="RFC" value="2616"/>
4605</reference>
4606
4607<reference anchor='RFC2817'>
4608  <front>
4609    <title>Upgrading to TLS Within HTTP/1.1</title>
4610    <author initials='R.' surname='Khare' fullname='R. Khare'>
4611      <organization>4K Associates / UC Irvine</organization>
4612      <address><email>rohit@4K-associates.com</email></address>
4613    </author>
4614    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4615      <organization>Agranat Systems, Inc.</organization>
4616      <address><email>lawrence@agranat.com</email></address>
4617    </author>
4618    <date year='2000' month='May' />
4619  </front>
4620  <seriesInfo name='RFC' value='2817' />
4621</reference>
4622
4623<reference anchor='RFC2818'>
4624  <front>
4625    <title>HTTP Over TLS</title>
4626    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4627      <organization>RTFM, Inc.</organization>
4628      <address><email>ekr@rtfm.com</email></address>
4629    </author>
4630    <date year='2000' month='May' />
4631  </front>
4632  <seriesInfo name='RFC' value='2818' />
4633</reference>
4634
4635<reference anchor='RFC2965'>
4636  <front>
4637    <title>HTTP State Management Mechanism</title>
4638    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4639      <organization>Bell Laboratories, Lucent Technologies</organization>
4640      <address><email>dmk@bell-labs.com</email></address>
4641    </author>
4642    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4643      <organization>Epinions.com, Inc.</organization>
4644      <address><email>lou@montulli.org</email></address>
4645    </author>
4646    <date year='2000' month='October' />
4647  </front>
4648  <seriesInfo name='RFC' value='2965' />
4649</reference>
4650
4651<reference anchor='RFC3040'>
4652  <front>
4653    <title>Internet Web Replication and Caching Taxonomy</title>
4654    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4655      <organization>Equinix, Inc.</organization>
4656    </author>
4657    <author initials='I.' surname='Melve' fullname='I. Melve'>
4658      <organization>UNINETT</organization>
4659    </author>
4660    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4661      <organization>CacheFlow Inc.</organization>
4662    </author>
4663    <date year='2001' month='January' />
4664  </front>
4665  <seriesInfo name='RFC' value='3040' />
4666</reference>
4667
4668<reference anchor='RFC3864'>
4669  <front>
4670    <title>Registration Procedures for Message Header Fields</title>
4671    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4672      <organization>Nine by Nine</organization>
4673      <address><email>GK-IETF@ninebynine.org</email></address>
4674    </author>
4675    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4676      <organization>BEA Systems</organization>
4677      <address><email>mnot@pobox.com</email></address>
4678    </author>
4679    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4680      <organization>HP Labs</organization>
4681      <address><email>JeffMogul@acm.org</email></address>
4682    </author>
4683    <date year='2004' month='September' />
4684  </front>
4685  <seriesInfo name='BCP' value='90' />
4686  <seriesInfo name='RFC' value='3864' />
4687</reference>
4688
4689<reference anchor='RFC4033'>
4690  <front>
4691    <title>DNS Security Introduction and Requirements</title>
4692    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4693    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4694    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4695    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4696    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4697    <date year='2005' month='March' />
4698  </front>
4699  <seriesInfo name='RFC' value='4033' />
4700</reference>
4701
4702<reference anchor="RFC4288">
4703  <front>
4704    <title>Media Type Specifications and Registration Procedures</title>
4705    <author initials="N." surname="Freed" fullname="N. Freed">
4706      <organization>Sun Microsystems</organization>
4707      <address>
4708        <email>ned.freed@mrochek.com</email>
4709      </address>
4710    </author>
4711    <author initials="J." surname="Klensin" fullname="J. Klensin">
4712      <address>
4713        <email>klensin+ietf@jck.com</email>
4714      </address>
4715    </author>
4716    <date year="2005" month="December"/>
4717  </front>
4718  <seriesInfo name="BCP" value="13"/>
4719  <seriesInfo name="RFC" value="4288"/>
4720</reference>
4721
4722<reference anchor='RFC4395'>
4723  <front>
4724    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4725    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4726      <organization>AT&amp;T Laboratories</organization>
4727      <address>
4728        <email>tony+urireg@maillennium.att.com</email>
4729      </address>
4730    </author>
4731    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4732      <organization>Qualcomm, Inc.</organization>
4733      <address>
4734        <email>hardie@qualcomm.com</email>
4735      </address>
4736    </author>
4737    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4738      <organization>Adobe Systems</organization>
4739      <address>
4740        <email>LMM@acm.org</email>
4741      </address>
4742    </author>
4743    <date year='2006' month='February' />
4744  </front>
4745  <seriesInfo name='BCP' value='115' />
4746  <seriesInfo name='RFC' value='4395' />
4747</reference>
4748
4749<reference anchor='RFC4559'>
4750  <front>
4751    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4752    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4753    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4754    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4755    <date year='2006' month='June' />
4756  </front>
4757  <seriesInfo name='RFC' value='4559' />
4758</reference>
4759
4760<reference anchor='RFC5226'>
4761  <front>
4762    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4763    <author initials='T.' surname='Narten' fullname='T. Narten'>
4764      <organization>IBM</organization>
4765      <address><email>narten@us.ibm.com</email></address>
4766    </author>
4767    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4768      <organization>Google</organization>
4769      <address><email>Harald@Alvestrand.no</email></address>
4770    </author>
4771    <date year='2008' month='May' />
4772  </front>
4773  <seriesInfo name='BCP' value='26' />
4774  <seriesInfo name='RFC' value='5226' />
4775</reference>
4776
4777<reference anchor="RFC5322">
4778  <front>
4779    <title>Internet Message Format</title>
4780    <author initials="P." surname="Resnick" fullname="P. Resnick">
4781      <organization>Qualcomm Incorporated</organization>
4782    </author>
4783    <date year="2008" month="October"/>
4784  </front> 
4785  <seriesInfo name="RFC" value="5322"/>
4786</reference>
4787
4788<reference anchor="RFC6265">
4789  <front>
4790    <title>HTTP State Management Mechanism</title>
4791    <author initials="A." surname="Barth" fullname="Adam Barth">
4792      <organization abbrev="U.C. Berkeley">
4793        University of California, Berkeley
4794      </organization>
4795      <address><email>abarth@eecs.berkeley.edu</email></address>
4796    </author>
4797    <date year="2011" month="April" />
4798  </front>
4799  <seriesInfo name="RFC" value="6265"/>
4800</reference>
4801
4802<!--<reference anchor='BCP97'>
4803  <front>
4804    <title>Handling Normative References to Standards-Track Documents</title>
4805    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4806      <address>
4807        <email>klensin+ietf@jck.com</email>
4808      </address>
4809    </author>
4810    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4811      <organization>MIT</organization>
4812      <address>
4813        <email>hartmans-ietf@mit.edu</email>
4814      </address>
4815    </author>
4816    <date year='2007' month='June' />
4817  </front>
4818  <seriesInfo name='BCP' value='97' />
4819  <seriesInfo name='RFC' value='4897' />
4820</reference>-->
4821
4822<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4823  <front>
4824    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4825    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4826    <date year="2001" month="November"/>
4827  </front>
4828  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4829</reference>
4830
4831<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4832  <front>
4833    <title>Analysis of HTTP Performance Problems</title>
4834    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4835    <date/>
4836  </front>
4837</reference>
4838
4839<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4840  <front>
4841  <title>Analysis of HTTP Performance</title>
4842  <author initials="J." surname="Touch" fullname="Joe Touch">
4843    <organization>USC/Information Sciences Institute</organization>
4844    <address><email>touch@isi.edu</email></address>
4845  </author>
4846  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4847    <organization>USC/Information Sciences Institute</organization>
4848    <address><email>johnh@isi.edu</email></address>
4849  </author>
4850  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4851    <organization>USC/Information Sciences Institute</organization>
4852    <address><email>katia@isi.edu</email></address>
4853  </author>
4854  <date year="1998" month="Aug"/>
4855  </front>
4856  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4857  <annotation>(original report dated Aug. 1996)</annotation>
4858</reference>
4859
4860</references>
4861
4862
4863<section title="HTTP Version History" anchor="compatibility">
4864<t>
4865   HTTP has been in use by the World-Wide Web global information initiative
4866   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4867   was a simple protocol for hypertext data transfer across the Internet
4868   with only a single request method (GET) and no metadata.
4869   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4870   methods and MIME-like messaging that could include metadata about the data
4871   transferred and modifiers on the request/response semantics. However,
4872   HTTP/1.0 did not sufficiently take into consideration the effects of
4873   hierarchical proxies, caching, the need for persistent connections, or
4874   name-based virtual hosts. The proliferation of incompletely-implemented
4875   applications calling themselves "HTTP/1.0" further necessitated a
4876   protocol version change in order for two communicating applications
4877   to determine each other's true capabilities.
4878</t>
4879<t>
4880   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4881   requirements that enable reliable implementations, adding only
4882   those new features that will either be safely ignored by an HTTP/1.0
4883   recipient or only sent when communicating with a party advertising
4884   conformance with HTTP/1.1.
4885</t>
4886<t>
4887   It is beyond the scope of a protocol specification to mandate
4888   conformance with previous versions. HTTP/1.1 was deliberately
4889   designed, however, to make supporting previous versions easy.
4890   We would expect a general-purpose HTTP/1.1 server to understand
4891   any valid request in the format of HTTP/1.0 and respond appropriately
4892   with an HTTP/1.1 message that only uses features understood (or
4893   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4894   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4895</t>
4896<t>
4897   Since HTTP/0.9 did not support header fields in a request,
4898   there is no mechanism for it to support name-based virtual
4899   hosts (selection of resource by inspection of the Host header
4900   field).  Any server that implements name-based virtual hosts
4901   ought to disable support for HTTP/0.9.  Most requests that
4902   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4903   requests wherein a buggy client failed to properly encode
4904   linear whitespace found in a URI reference and placed in
4905   the request-target.
4906</t>
4907
4908<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4909<t>
4910   This section summarizes major differences between versions HTTP/1.0
4911   and HTTP/1.1.
4912</t>
4913
4914<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4915<t>
4916   The requirements that clients and servers support the Host header
4917   field (<xref target="header.host"/>), report an error if it is
4918   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4919   are among the most important changes defined by HTTP/1.1.
4920</t>
4921<t>
4922   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4923   addresses and servers; there was no other established mechanism for
4924   distinguishing the intended server of a request than the IP address
4925   to which that request was directed. The Host header field was
4926   introduced during the development of HTTP/1.1 and, though it was
4927   quickly implemented by most HTTP/1.0 browsers, additional requirements
4928   were placed on all HTTP/1.1 requests in order to ensure complete
4929   adoption.  At the time of this writing, most HTTP-based services
4930   are dependent upon the Host header field for targeting requests.
4931</t>
4932</section>
4933
4934<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4935<t>
4936   In HTTP/1.0, each connection is established by the client prior to the
4937   request and closed by the server after sending the response. However, some
4938   implementations implement the explicitly negotiated ("Keep-Alive") version
4939   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4940   target="RFC2068"/>.
4941</t>
4942<t>
4943   Some clients and servers might wish to be compatible with these previous
4944   approaches to persistent connections, by explicitly negotiating for them
4945   with a "Connection: keep-alive" request header field. However, some
4946   experimental implementations of HTTP/1.0 persistent connections are faulty;
4947   for example, if a HTTP/1.0 proxy server doesn't understand Connection, it
4948   will erroneously forward that header to the next inbound server, which
4949   would result in a hung connection.
4950</t>
4951<t>
4952   One attempted solution was the introduction of a Proxy-Connection header,
4953   targeted specifically at proxies. In practice, this was also unworkable,
4954   because proxies are often deployed in multiple layers, bringing about the
4955   same problem discussed above.
4956</t>
4957<t>
4958   As a result, clients are encouraged not to send the Proxy-Connection header
4959   in any requests.
4960</t>
4961<t>
4962   Clients are also encouraged to consider the use of Connection: keep-alive
4963   in requests carefully; while they can enable persistent connections with
4964   HTTP/1.0 servers, clients using them need will need to monitor the
4965   connection for "hung" requests (which indicate that the client ought stop
4966   sending the header), and this mechanism ought not be used by clients at all
4967   when a proxy is being used.
4968</t>
4969</section>
4970</section>
4971
4972<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4973<t>
4974  Empty list elements in list productions have been deprecated.
4975  (<xref target="abnf.extension"/>)
4976</t>
4977<t>
4978  Rules about implicit linear whitespace between certain grammar productions
4979  have been removed; now whitespace is only allowed where specifically
4980  defined in the ABNF.
4981  (<xref target="whitespace"/>)
4982</t>
4983<t>
4984  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
4985  sensitive. Restrict the version numbers to be single digits due to the fact
4986  that implementations are known to handle multi-digit version numbers
4987  incorrectly.
4988  (<xref target="http.version"/>)
4989</t>
4990<t>
4991  Require that invalid whitespace around field-names be rejected.
4992  (<xref target="header.fields"/>)
4993</t>
4994<t> 
4995  The NUL octet is no longer allowed in comment and quoted-string
4996  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4997  Non-ASCII content in header fields and reason phrase has been obsoleted and
4998  made opaque (the TEXT rule was removed).
4999  (<xref target="field.components"/>)
5000</t>
5001<t>
5002  Require recipients to handle bogus Content-Length header fields as errors.
5003  (<xref target="message.body"/>)
5004</t>
5005<t>
5006  Remove reference to non-existent identity transfer-coding value tokens.
5007  (Sections <xref format="counter" target="message.body"/> and
5008  <xref format="counter" target="transfer.codings"/>)
5009</t>
5010<t>
5011  Update use of abs_path production from RFC 1808 to the path-absolute + query
5012  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5013  request method only.
5014  (<xref target="request-target"/>)
5015</t>
5016<t>
5017  Clarification that the chunk length does not include the count of the octets
5018  in the chunk header and trailer. Furthermore disallowed line folding
5019  in chunk extensions, and deprecate their use.
5020  (<xref target="chunked.encoding"/>)
5021</t>
5022<t>
5023  Remove hard limit of two connections per server.
5024  Remove requirement to retry a sequence of requests as long it was idempotent.
5025  Remove requirements about when servers are allowed to close connections
5026  prematurely.
5027  (<xref target="persistent.practical"/>)
5028</t>
5029<t>
5030  Remove requirement to retry requests under certain cirumstances when the
5031  server prematurely closes the connection.
5032  (<xref target="message.transmission.requirements"/>)
5033</t>
5034<t>
5035  Change ABNF productions for header fields to only define the field value.
5036  (<xref target="header.field.definitions"/>)
5037</t>
5038<t>
5039  Clarify exactly when close connection options must be sent.
5040  (<xref target="header.connection"/>)
5041</t>
5042<t>
5043  Define the semantics of the "Upgrade" header field in responses other than
5044  101 (this was incorporated from <xref target="RFC2817"/>).
5045  (<xref target="header.upgrade"/>)
5046</t>
5047</section>
5048</section>
5049
5050<?BEGININC p1-messaging.abnf-appendix ?>
5051<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
5052<figure>
5053<artwork type="abnf" name="p1-messaging.parsed-abnf">
5054<x:ref>BWS</x:ref> = OWS
5055
5056<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5057<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5058 connection-token ] )
5059<x:ref>Content-Length</x:ref> = 1*DIGIT
5060
5061<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5062<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" DIGIT "." DIGIT
5063<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5064 ]
5065<x:ref>Host</x:ref> = uri-host [ ":" port ]
5066
5067<x:ref>Method</x:ref> = token
5068
5069<x:ref>OWS</x:ref> = *( SP / HTAB / obs-fold )
5070
5071<x:ref>RWS</x:ref> = 1*( SP / HTAB / obs-fold )
5072<x:ref>Reason-Phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5073<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5074
5075<x:ref>Status-Code</x:ref> = 3DIGIT
5076<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5077
5078<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5079<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5080<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5081 transfer-coding ] )
5082
5083<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5084<x:ref>Upgrade</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5085
5086<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5087 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5088 )
5089
5090<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5091<x:ref>attribute</x:ref> = token
5092<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5093
5094<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5095<x:ref>chunk-data</x:ref> = 1*OCTET
5096<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5097<x:ref>chunk-ext-name</x:ref> = token
5098<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5099<x:ref>chunk-size</x:ref> = 1*HEXDIG
5100<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5101<x:ref>connection-token</x:ref> = token
5102<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5103 / %x2A-5B ; '*'-'['
5104 / %x5D-7E ; ']'-'~'
5105 / obs-text
5106
5107<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5108<x:ref>field-name</x:ref> = token
5109<x:ref>field-value</x:ref> = *( field-content / obs-fold )
5110
5111<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
5112<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5113<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5114
5115<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
5116
5117<x:ref>message-body</x:ref> = *OCTET
5118
5119<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
5120<x:ref>obs-text</x:ref> = %x80-FF
5121
5122<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5123<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5124<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5125<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5126<x:ref>product</x:ref> = token [ "/" product-version ]
5127<x:ref>product-version</x:ref> = token
5128<x:ref>protocol-name</x:ref> = token
5129<x:ref>protocol-version</x:ref> = token
5130<x:ref>pseudonym</x:ref> = token
5131
5132<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5133 / %x5D-7E ; ']'-'~'
5134 / obs-text
5135<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
5136 / %x5D-7E ; ']'-'~'
5137 / obs-text
5138<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5139<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5140<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5141<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5142<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5143<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5144
5145<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5146<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5147<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5148<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5149 / authority
5150
5151<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5152 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5153<x:ref>start-line</x:ref> = Request-Line / Status-Line
5154
5155<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5156<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5157 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5158<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5159<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5160<x:ref>token</x:ref> = 1*tchar
5161<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5162<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5163 transfer-extension
5164<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5165<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5166
5167<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5168
5169<x:ref>value</x:ref> = word
5170
5171<x:ref>word</x:ref> = token / quoted-string
5172</artwork>
5173</figure>
5174<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5175; Chunked-Body defined but not used
5176; Connection defined but not used
5177; Content-Length defined but not used
5178; HTTP-message defined but not used
5179; Host defined but not used
5180; TE defined but not used
5181; Trailer defined but not used
5182; Transfer-Encoding defined but not used
5183; URI-reference defined but not used
5184; Upgrade defined but not used
5185; Via defined but not used
5186; http-URI defined but not used
5187; https-URI defined but not used
5188; partial-URI defined but not used
5189; special defined but not used
5190</artwork></figure></section>
5191<?ENDINC p1-messaging.abnf-appendix ?>
5192
5193<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5194
5195<section title="Since RFC 2616">
5196<t>
5197  Extracted relevant partitions from <xref target="RFC2616"/>.
5198</t>
5199</section>
5200
5201<section title="Since draft-ietf-httpbis-p1-messaging-00">
5202<t>
5203  Closed issues:
5204  <list style="symbols"> 
5205    <t>
5206      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5207      "HTTP Version should be case sensitive"
5208      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5209    </t>
5210    <t>
5211      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5212      "'unsafe' characters"
5213      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5214    </t>
5215    <t>
5216      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5217      "Chunk Size Definition"
5218      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5219    </t>
5220    <t>
5221      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5222      "Message Length"
5223      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5224    </t>
5225    <t>
5226      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5227      "Media Type Registrations"
5228      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5229    </t>
5230    <t>
5231      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5232      "URI includes query"
5233      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5234    </t>
5235    <t>
5236      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5237      "No close on 1xx responses"
5238      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5239    </t>
5240    <t>
5241      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5242      "Remove 'identity' token references"
5243      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5244    </t>
5245    <t>
5246      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5247      "Import query BNF"
5248    </t>
5249    <t>
5250      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5251      "qdtext BNF"
5252    </t>
5253    <t>
5254      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5255      "Normative and Informative references"
5256    </t>
5257    <t>
5258      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5259      "RFC2606 Compliance"
5260    </t>
5261    <t>
5262      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5263      "RFC977 reference"
5264    </t>
5265    <t>
5266      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5267      "RFC1700 references"
5268    </t>
5269    <t>
5270      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5271      "inconsistency in date format explanation"
5272    </t>
5273    <t>
5274      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5275      "Date reference typo"
5276    </t>
5277    <t>
5278      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5279      "Informative references"
5280    </t>
5281    <t>
5282      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5283      "ISO-8859-1 Reference"
5284    </t>
5285    <t>
5286      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5287      "Normative up-to-date references"
5288    </t>
5289  </list>
5290</t>
5291<t>
5292  Other changes:
5293  <list style="symbols"> 
5294    <t>
5295      Update media type registrations to use RFC4288 template.
5296    </t>
5297    <t>
5298      Use names of RFC4234 core rules DQUOTE and HTAB,
5299      fix broken ABNF for chunk-data
5300      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5301    </t>
5302  </list>
5303</t>
5304</section>
5305
5306<section title="Since draft-ietf-httpbis-p1-messaging-01">
5307<t>
5308  Closed issues:
5309  <list style="symbols"> 
5310    <t>
5311      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5312      "Bodies on GET (and other) requests"
5313    </t>
5314    <t>
5315      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5316      "Updating to RFC4288"
5317    </t>
5318    <t>
5319      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5320      "Status Code and Reason Phrase"
5321    </t>
5322    <t>
5323      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5324      "rel_path not used"
5325    </t>
5326  </list>
5327</t>
5328<t>
5329  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5330  <list style="symbols"> 
5331    <t>
5332      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5333      "trailer-part").
5334    </t>
5335    <t>
5336      Avoid underscore character in rule names ("http_URL" ->
5337      "http-URL", "abs_path" -> "path-absolute").
5338    </t>
5339    <t>
5340      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5341      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5342      have to be updated when switching over to RFC3986.
5343    </t>
5344    <t>
5345      Synchronize core rules with RFC5234.
5346    </t>
5347    <t>
5348      Get rid of prose rules that span multiple lines.
5349    </t>
5350    <t>
5351      Get rid of unused rules LOALPHA and UPALPHA.
5352    </t>
5353    <t>
5354      Move "Product Tokens" section (back) into Part 1, as "token" is used
5355      in the definition of the Upgrade header field.
5356    </t>
5357    <t>
5358      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5359    </t>
5360    <t>
5361      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5362    </t>
5363  </list>
5364</t>
5365</section>
5366
5367<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5368<t>
5369  Closed issues:
5370  <list style="symbols"> 
5371    <t>
5372      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5373      "HTTP-date vs. rfc1123-date"
5374    </t>
5375    <t>
5376      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5377      "WS in quoted-pair"
5378    </t>
5379  </list>
5380</t>
5381<t>
5382  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5383  <list style="symbols"> 
5384    <t>
5385      Reference RFC 3984, and update header field registrations for headers defined
5386      in this document.
5387    </t>
5388  </list>
5389</t>
5390<t>
5391  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5392  <list style="symbols"> 
5393    <t>
5394      Replace string literals when the string really is case-sensitive (HTTP-Version).
5395    </t>
5396  </list>
5397</t>
5398</section>
5399
5400<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5401<t>
5402  Closed issues:
5403  <list style="symbols"> 
5404    <t>
5405      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5406      "Connection closing"
5407    </t>
5408    <t>
5409      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5410      "Move registrations and registry information to IANA Considerations"
5411    </t>
5412    <t>
5413      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5414      "need new URL for PAD1995 reference"
5415    </t>
5416    <t>
5417      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5418      "IANA Considerations: update HTTP URI scheme registration"
5419    </t>
5420    <t>
5421      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5422      "Cite HTTPS URI scheme definition"
5423    </t>
5424    <t>
5425      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5426      "List-type headers vs Set-Cookie"
5427    </t>
5428  </list>
5429</t>
5430<t>
5431  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5432  <list style="symbols"> 
5433    <t>
5434      Replace string literals when the string really is case-sensitive (HTTP-Date).
5435    </t>
5436    <t>
5437      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5438    </t>
5439  </list>
5440</t>
5441</section>
5442
5443<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5444<t>
5445  Closed issues:
5446  <list style="symbols"> 
5447    <t>
5448      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5449      "Out-of-date reference for URIs"
5450    </t>
5451    <t>
5452      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5453      "RFC 2822 is updated by RFC 5322"
5454    </t>
5455  </list>
5456</t>
5457<t>
5458  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5459  <list style="symbols"> 
5460    <t>
5461      Use "/" instead of "|" for alternatives.
5462    </t>
5463    <t>
5464      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5465    </t>
5466    <t>
5467      Only reference RFC 5234's core rules.
5468    </t>
5469    <t>
5470      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5471      whitespace ("OWS") and required whitespace ("RWS").
5472    </t>
5473    <t>
5474      Rewrite ABNFs to spell out whitespace rules, factor out
5475      header field value format definitions.
5476    </t>
5477  </list>
5478</t>
5479</section>
5480
5481<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5482<t>
5483  Closed issues:
5484  <list style="symbols"> 
5485    <t>
5486      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5487      "Header LWS"
5488    </t>
5489    <t>
5490      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5491      "Sort 1.3 Terminology"
5492    </t>
5493    <t>
5494      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5495      "RFC2047 encoded words"
5496    </t>
5497    <t>
5498      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5499      "Character Encodings in TEXT"
5500    </t>
5501    <t>
5502      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5503      "Line Folding"
5504    </t>
5505    <t>
5506      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5507      "OPTIONS * and proxies"
5508    </t>
5509    <t>
5510      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5511      "Reason-Phrase BNF"
5512    </t>
5513    <t>
5514      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5515      "Use of TEXT"
5516    </t>
5517    <t>
5518      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5519      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5520    </t>
5521    <t>
5522      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5523      "RFC822 reference left in discussion of date formats"
5524    </t>
5525  </list>
5526</t>
5527<t>
5528  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5529  <list style="symbols"> 
5530    <t>
5531      Rewrite definition of list rules, deprecate empty list elements.
5532    </t>
5533    <t>
5534      Add appendix containing collected and expanded ABNF.
5535    </t>
5536  </list>
5537</t>
5538<t>
5539  Other changes:
5540  <list style="symbols"> 
5541    <t>
5542      Rewrite introduction; add mostly new Architecture Section.
5543    </t>
5544    <t>
5545      Move definition of quality values from Part 3 into Part 1;
5546      make TE request header field grammar independent of accept-params (defined in Part 3).
5547    </t>
5548  </list>
5549</t>
5550</section>
5551
5552<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5553<t>
5554  Closed issues:
5555  <list style="symbols"> 
5556    <t>
5557      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5558      "base for numeric protocol elements"
5559    </t>
5560    <t>
5561      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5562      "comment ABNF"
5563    </t>
5564  </list>
5565</t>
5566<t>
5567  Partly resolved issues:
5568  <list style="symbols"> 
5569    <t>
5570      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5571      "205 Bodies" (took out language that implied that there might be
5572      methods for which a request body MUST NOT be included)
5573    </t>
5574    <t>
5575      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5576      "editorial improvements around HTTP-date"
5577    </t>
5578  </list>
5579</t>
5580</section>
5581
5582<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5583<t>
5584  Closed issues:
5585  <list style="symbols"> 
5586    <t>
5587      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5588      "Repeating single-value headers"
5589    </t>
5590    <t>
5591      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5592      "increase connection limit"
5593    </t>
5594    <t>
5595      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5596      "IP addresses in URLs"
5597    </t>
5598    <t>
5599      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5600      "take over HTTP Upgrade Token Registry"
5601    </t>
5602    <t>
5603      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5604      "CR and LF in chunk extension values"
5605    </t>
5606    <t>
5607      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5608      "HTTP/0.9 support"
5609    </t>
5610    <t>
5611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5612      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5613    </t>
5614    <t>
5615      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5616      "move definitions of gzip/deflate/compress to part 1"
5617    </t>
5618    <t>
5619      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5620      "disallow control characters in quoted-pair"
5621    </t>
5622  </list>
5623</t>
5624<t>
5625  Partly resolved issues:
5626  <list style="symbols"> 
5627    <t>
5628      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5629      "update IANA requirements wrt Transfer-Coding values" (add the
5630      IANA Considerations subsection)
5631    </t>
5632  </list>
5633</t>
5634</section>
5635
5636<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5637<t>
5638  Closed issues:
5639  <list style="symbols"> 
5640    <t>
5641      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5642      "header parsing, treatment of leading and trailing OWS"
5643    </t>
5644  </list>
5645</t>
5646<t>
5647  Partly resolved issues:
5648  <list style="symbols"> 
5649    <t>
5650      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5651      "Placement of 13.5.1 and 13.5.2"
5652    </t>
5653    <t>
5654      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5655      "use of term "word" when talking about header structure"
5656    </t>
5657  </list>
5658</t>
5659</section>
5660
5661<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5662<t>
5663  Closed issues:
5664  <list style="symbols"> 
5665    <t>
5666      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5667      "Clarification of the term 'deflate'"
5668    </t>
5669    <t>
5670      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5671      "OPTIONS * and proxies"
5672    </t>
5673    <t>
5674      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5675      "MIME-Version not listed in P1, general header fields"
5676    </t>
5677    <t>
5678      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5679      "IANA registry for content/transfer encodings"
5680    </t>
5681    <t>
5682      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5683      "Case-sensitivity of HTTP-date"
5684    </t>
5685    <t>
5686      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5687      "use of term "word" when talking about header structure"
5688    </t>
5689  </list>
5690</t>
5691<t>
5692  Partly resolved issues:
5693  <list style="symbols"> 
5694    <t>
5695      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5696      "Term for the requested resource's URI"
5697    </t>
5698  </list>
5699</t>
5700</section>
5701
5702<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5703<t>
5704  Closed issues:
5705  <list style="symbols">
5706    <t>
5707      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5708      "Connection Closing"
5709    </t>
5710    <t>
5711      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5712      "Delimiting messages with multipart/byteranges"
5713    </t>
5714    <t>
5715      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5716      "Handling multiple Content-Length headers"
5717    </t>
5718    <t>
5719      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5720      "Clarify entity / representation / variant terminology"
5721    </t>
5722    <t>
5723      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5724      "consider removing the 'changes from 2068' sections"
5725    </t>
5726  </list>
5727</t>
5728<t>
5729  Partly resolved issues:
5730  <list style="symbols"> 
5731    <t>
5732      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5733      "HTTP(s) URI scheme definitions"
5734    </t>
5735  </list>
5736</t>
5737</section>
5738
5739<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5740<t>
5741  Closed issues:
5742  <list style="symbols">
5743    <t>
5744      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5745      "Trailer requirements"
5746    </t>
5747    <t>
5748      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5749      "Text about clock requirement for caches belongs in p6"
5750    </t>
5751    <t>
5752      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5753      "effective request URI: handling of missing host in HTTP/1.0"
5754    </t>
5755    <t>
5756      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5757      "confusing Date requirements for clients"
5758    </t>
5759  </list>
5760</t>
5761<t>
5762  Partly resolved issues:
5763  <list style="symbols"> 
5764    <t>
5765      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5766      "Handling multiple Content-Length headers"
5767    </t>
5768  </list>
5769</t>
5770</section>
5771
5772<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5773<t>
5774  Closed issues:
5775  <list style="symbols">
5776    <t>
5777      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5778      "RFC2145 Normative"
5779    </t>
5780    <t>
5781      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5782      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5783    </t>
5784    <t>
5785      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5786      "define 'transparent' proxy"
5787    </t>
5788    <t>
5789      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5790      "Header Classification"
5791    </t>
5792    <t>
5793      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5794      "Is * usable as a request-uri for new methods?"
5795    </t>
5796    <t>
5797      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5798      "Migrate Upgrade details from RFC2817"
5799    </t>
5800    <t>
5801      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5802      "untangle ABNFs for header fields"
5803    </t>
5804    <t>
5805      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5806      "update RFC 2109 reference"
5807    </t>
5808  </list>
5809</t>
5810</section>
5811
5812<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5813<t>
5814  Closed issues:
5815  <list style="symbols">
5816    <t>
5817      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5818      "Allow is not in 13.5.2"
5819    </t>
5820    <t>
5821      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5822      "Handling multiple Content-Length headers"
5823    </t>
5824    <t>
5825      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5826      "untangle ABNFs for header fields"
5827    </t>
5828    <t>
5829      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5830      "Content-Length ABNF broken"
5831    </t>
5832  </list>
5833</t>
5834</section>
5835
5836<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5837<t>
5838  Closed issues:
5839  <list style="symbols">
5840    <t>
5841      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5842      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
5843    </t>
5844    <t>
5845      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5846      "Recommend minimum sizes for protocol elements"
5847    </t>
5848    <t>
5849      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5850      "Set expectations around buffering"
5851    </t>
5852    <t>
5853      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5854      "Considering messages in isolation"
5855    </t>
5856  </list>
5857</t>
5858</section>
5859
5860<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5861<t>
5862  Closed issues:
5863  <list style="symbols">
5864    <t>
5865      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5866      "DNS Spoofing / DNS Binding advice"
5867    </t>
5868    <t>
5869      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5870      "move RFCs 2145, 2616, 2817 to Historic status"
5871    </t>
5872    <t>
5873      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5874      "\-escaping in quoted strings"
5875    </t>
5876    <t>
5877      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5878      "'Close' should be reserved in the HTTP header field registry"
5879    </t>
5880  </list>
5881</t>
5882</section>
5883
5884<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5885<t>
5886  Closed issues:
5887  <list style="symbols">
5888    <t>
5889      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5890      "Document HTTP's error-handling philosophy"
5891    </t>
5892    <t>
5893      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5894      "Explain header registration"
5895    </t>
5896    <t>
5897      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5898      "Revise Acknowledgements Sections"
5899    </t>
5900    <t>
5901      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5902      "Retrying Requests"
5903    </t>
5904    <t>
5905      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5906      "Closing the connection on server error"
5907    </t>
5908  </list>
5909</t>
5910</section>
5911
5912<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5913<t>
5914  Closed issues:
5915  <list style="symbols">
5916    <t>
5917      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/166"/>:
5918      "Clarify 'User Agent'"
5919    </t>
5920    <t>
5921      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/300"/>:
5922      "Define non-final responses"
5923    </t>
5924    <t>
5925      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
5926      "intended maturity level vs normative references"
5927    </t>
5928    <t>
5929      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/324"/>:
5930      "Intermediary rewriting of queries"
5931    </t>
5932    <t>
5933      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/158"/>:
5934      "Proxy-Connection and Keep-Alive"
5935    </t>
5936  </list>
5937</t>
5938</section>
5939
5940<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5941<t>
5942  Closed issues:
5943  <list style="symbols">
5944    <t>
5945      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
5946      "Misplaced text on connection handling in p2"
5947    </t>
5948    <t>
5949      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/343"/>:
5950      "chunk-extensions"
5951    </t>
5952  </list>
5953</t>
5954</section>
5955
5956</section>
5957
5958</back>
5959</rfc>
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