source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1408

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "August">
16  <!ENTITY ID-YEAR "2011">
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-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-mime-version    "<xref target='Part3' x:rel='#mime-version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40]>
41<?rfc toc="yes" ?>
42<?rfc symrefs="yes" ?>
43<?rfc sortrefs="yes" ?>
44<?rfc compact="yes"?>
45<?rfc subcompact="no" ?>
46<?rfc linkmailto="no" ?>
47<?rfc editing="no" ?>
48<?rfc comments="yes"?>
49<?rfc inline="yes"?>
50<?rfc rfcedstyle="yes"?>
51<?rfc-ext allow-markup-in-artwork="yes" ?>
52<?rfc-ext include-references-in-index="yes" ?>
53<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="draft"
54     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
55     xmlns:x='http://purl.org/net/xml2rfc/ext'>
56<front>
57
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
59
60  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
61    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
62    <address>
63      <postal>
64        <street>345 Park Ave</street>
65        <city>San Jose</city>
66        <region>CA</region>
67        <code>95110</code>
68        <country>USA</country>
69      </postal>
70      <email>fielding@gbiv.com</email>
71      <uri>http://roy.gbiv.com/</uri>
72    </address>
73  </author>
74
75  <author initials="J." surname="Gettys" fullname="Jim Gettys">
76    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
77    <address>
78      <postal>
79        <street>21 Oak Knoll Road</street>
80        <city>Carlisle</city>
81        <region>MA</region>
82        <code>01741</code>
83        <country>USA</country>
84      </postal>
85      <email>jg@freedesktop.org</email>
86      <uri>http://gettys.wordpress.com/</uri>
87    </address>
88  </author>
89 
90  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
91    <organization abbrev="HP">Hewlett-Packard Company</organization>
92    <address>
93      <postal>
94        <street>HP Labs, Large Scale Systems Group</street>
95        <street>1501 Page Mill Road, MS 1177</street>
96        <city>Palo Alto</city>
97        <region>CA</region>
98        <code>94304</code>
99        <country>USA</country>
100      </postal>
101      <email>JeffMogul@acm.org</email>
102    </address>
103  </author>
104
105  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
106    <organization abbrev="Microsoft">Microsoft Corporation</organization>
107    <address>
108      <postal>
109        <street>1 Microsoft Way</street>
110        <city>Redmond</city>
111        <region>WA</region>
112        <code>98052</code>
113        <country>USA</country>
114      </postal>
115      <email>henrikn@microsoft.com</email>
116    </address>
117  </author>
118
119  <author initials="L." surname="Masinter" fullname="Larry Masinter">
120    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
121    <address>
122      <postal>
123        <street>345 Park Ave</street>
124        <city>San Jose</city>
125        <region>CA</region>
126        <code>95110</code>
127        <country>USA</country>
128      </postal>
129      <email>LMM@acm.org</email>
130      <uri>http://larry.masinter.net/</uri>
131    </address>
132  </author>
133 
134  <author initials="P." surname="Leach" fullname="Paul J. Leach">
135    <organization abbrev="Microsoft">Microsoft Corporation</organization>
136    <address>
137      <postal>
138        <street>1 Microsoft Way</street>
139        <city>Redmond</city>
140        <region>WA</region>
141        <code>98052</code>
142      </postal>
143      <email>paulle@microsoft.com</email>
144    </address>
145  </author>
146   
147  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
148    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
149    <address>
150      <postal>
151        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
152        <street>The Stata Center, Building 32</street>
153        <street>32 Vassar Street</street>
154        <city>Cambridge</city>
155        <region>MA</region>
156        <code>02139</code>
157        <country>USA</country>
158      </postal>
159      <email>timbl@w3.org</email>
160      <uri>http://www.w3.org/People/Berners-Lee/</uri>
161    </address>
162  </author>
163
164  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
165    <organization abbrev="W3C">World Wide Web Consortium</organization>
166    <address>
167      <postal>
168        <street>W3C / ERCIM</street>
169        <street>2004, rte des Lucioles</street>
170        <city>Sophia-Antipolis</city>
171        <region>AM</region>
172        <code>06902</code>
173        <country>France</country>
174      </postal>
175      <email>ylafon@w3.org</email>
176      <uri>http://www.raubacapeu.net/people/yves/</uri>
177    </address>
178  </author>
179
180  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
181    <organization abbrev="greenbytes">greenbytes GmbH</organization>
182    <address>
183      <postal>
184        <street>Hafenweg 16</street>
185        <city>Muenster</city><region>NW</region><code>48155</code>
186        <country>Germany</country>
187      </postal>
188      <phone>+49 251 2807760</phone>
189      <facsimile>+49 251 2807761</facsimile>
190      <email>julian.reschke@greenbytes.de</email>
191      <uri>http://greenbytes.de/tech/webdav/</uri>
192    </address>
193  </author>
194
195  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
196  <workgroup>HTTPbis Working Group</workgroup>
197
198<abstract>
199<t>
200   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
201   distributed, collaborative, hypertext information systems. HTTP has been in
202   use by the World Wide Web global information initiative since 1990. This
203   document is Part 1 of the seven-part specification that defines the protocol
204   referred to as "HTTP/1.1" and, taken together, obsoletes
205   <xref target="RFC2616" x:fmt="none">RFC 2616</xref> and moves it to historic
206   status, along with its predecessor <xref target="RFC2068" x:fmt="none">RFC
207   2068</xref>.
208</t>
209<t>
210   Part 1 provides an overview of HTTP and its associated terminology, defines
211   the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
212   the generic message syntax and parsing requirements for HTTP message frames,
213   and describes general security concerns for implementations.
214</t>
215<t>
216   This part also obsoletes RFCs <xref target="RFC2145" x:fmt="none">2145</xref>
217   (on HTTP version numbers) and <xref target="RFC2817" x:fmt="none">2817</xref>
218   (on using CONNECT for TLS upgrades) and moves them to historic status.
219</t>
220</abstract>
221
222<note title="Editorial Note (To be removed by RFC Editor)">
223  <t>
224    Discussion of this draft should take place on the HTTPBIS working group
225    mailing list (ietf-http-wg@w3.org), which is archived at
226    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
227  </t>
228  <t>
229    The current issues list is at
230    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
231    documents (including fancy diffs) can be found at
232    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
233  </t>
234  <t>
235    The changes in this draft are summarized in <xref target="changes.since.16"/>.
236  </t>
237</note>
238</front>
239<middle>
240<section title="Introduction" anchor="introduction">
241<t>
242   The Hypertext Transfer Protocol (HTTP) is an application-level
243   request/response protocol that uses extensible semantics and MIME-like
244   message payloads for flexible interaction with network-based hypertext
245   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
246   standard <xref target="RFC3986"/> to indicate the target resource and
247   relationships between resources.
248   Messages are passed in a format similar to that used by Internet mail
249   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
250   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
251   between HTTP and MIME messages).
252</t>
253<t>
254   HTTP is a generic interface protocol for information systems. It is
255   designed to hide the details of how a service is implemented by presenting
256   a uniform interface to clients that is independent of the types of
257   resources provided. Likewise, servers do not need to be aware of each
258   client's purpose: an HTTP request can be considered in isolation rather
259   than being associated with a specific type of client or a predetermined
260   sequence of application steps. The result is a protocol that can be used
261   effectively in many different contexts and for which implementations can
262   evolve independently over time.
263</t>
264<t>
265   HTTP is also designed for use as an intermediation protocol for translating
266   communication to and from non-HTTP information systems.
267   HTTP proxies and gateways can provide access to alternative information
268   services by translating their diverse protocols into a hypertext
269   format that can be viewed and manipulated by clients in the same way
270   as HTTP services.
271</t>
272<t>
273   One consequence of HTTP flexibility is that the protocol cannot be
274   defined in terms of what occurs behind the interface. Instead, we
275   are limited to defining the syntax of communication, the intent
276   of received communication, and the expected behavior of recipients.
277   If the communication is considered in isolation, then successful
278   actions ought to be reflected in corresponding changes to the
279   observable interface provided by servers. However, since multiple
280   clients might act in parallel and perhaps at cross-purposes, we
281   cannot require that such changes be observable beyond the scope
282   of a single response.
283</t>
284<t>
285   This document is Part 1 of the seven-part specification of HTTP,
286   defining the protocol referred to as "HTTP/1.1", obsoleting
287   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
288   Part 1 describes the architectural elements that are used or
289   referred to in HTTP, defines the "http" and "https" URI schemes,
290   describes overall network operation and connection management,
291   and defines HTTP message framing and forwarding requirements.
292   Our goal is to define all of the mechanisms necessary for HTTP message
293   handling that are independent of message semantics, thereby defining the
294   complete set of requirements for message parsers and
295   message-forwarding intermediaries.
296</t>
297
298<section title="Requirements" anchor="intro.requirements">
299<t>
300   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
301   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
302   document are to be interpreted as described in <xref target="RFC2119"/>.
303</t>
304<t>
305   An implementation is not compliant if it fails to satisfy one or more
306   of the "MUST" or "REQUIRED" level requirements for the protocols it
307   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
308   level and all the "SHOULD" level requirements for its protocols is said
309   to be "unconditionally compliant"; one that satisfies all the "MUST"
310   level requirements but not all the "SHOULD" level requirements for its
311   protocols is said to be "conditionally compliant".
312</t>
313</section>
314
315<section title="Syntax Notation" anchor="notation">
316<iref primary="true" item="Grammar" subitem="ALPHA"/>
317<iref primary="true" item="Grammar" subitem="CR"/>
318<iref primary="true" item="Grammar" subitem="CRLF"/>
319<iref primary="true" item="Grammar" subitem="CTL"/>
320<iref primary="true" item="Grammar" subitem="DIGIT"/>
321<iref primary="true" item="Grammar" subitem="DQUOTE"/>
322<iref primary="true" item="Grammar" subitem="HEXDIG"/>
323<iref primary="true" item="Grammar" subitem="LF"/>
324<iref primary="true" item="Grammar" subitem="OCTET"/>
325<iref primary="true" item="Grammar" subitem="SP"/>
326<iref primary="true" item="Grammar" subitem="VCHAR"/>
327<iref primary="true" item="Grammar" subitem="WSP"/>
328<t>
329   This specification uses the Augmented Backus-Naur Form (ABNF) notation
330   of <xref target="RFC5234"/>.
331</t>
332<t anchor="core.rules">
333  <x:anchor-alias value="ALPHA"/>
334  <x:anchor-alias value="CTL"/>
335  <x:anchor-alias value="CR"/>
336  <x:anchor-alias value="CRLF"/>
337  <x:anchor-alias value="DIGIT"/>
338  <x:anchor-alias value="DQUOTE"/>
339  <x:anchor-alias value="HEXDIG"/>
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  <x:anchor-alias value="WSP"/>
345   The following core rules are included by
346   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
347   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
348   DIGIT (decimal 0-9), DQUOTE (double quote),
349   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
350   OCTET (any 8-bit sequence of data), SP (space),
351   VCHAR (any visible <xref target="USASCII"/> character),
352   and WSP (whitespace).
353</t>
354<t>
355   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
356   "obsolete" grammar rules that appear for historical reasons.
357</t>
358
359<section title="ABNF Extension: #rule" anchor="notation.abnf">
360<t>
361  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
362  improve readability.
363</t>
364<t>
365  A construct "#" is defined, similar to "*", for defining comma-delimited
366  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
367  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
368  comma (",") and optional whitespace (OWS, <xref target="basic.rules"/>).   
369</t>
370<figure><preamble>
371  Thus,
372</preamble><artwork type="example">
373  1#element =&gt; element *( OWS "," OWS element )
374</artwork></figure>
375<figure><preamble>
376  and:
377</preamble><artwork type="example">
378  #element =&gt; [ 1#element ]
379</artwork></figure>
380<figure><preamble>
381  and for n &gt;= 1 and m &gt; 1:
382</preamble><artwork type="example">
383  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
384</artwork></figure>
385<t>
386  For compatibility with legacy list rules, recipients &SHOULD; accept empty
387  list elements. In other words, consumers would follow the list productions:
388</t>
389<figure><artwork type="example">
390  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
391 
392  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
393</artwork></figure>
394<t>
395  Note that empty elements do not contribute to the count of elements present,
396  though.
397</t>
398<t>
399  For example, given these ABNF productions:
400</t>
401<figure><artwork type="example">
402  example-list      = 1#example-list-elmt
403  example-list-elmt = token ; see <xref target="field.rules"/> 
404</artwork></figure>
405<t>
406  Then these are valid values for example-list (not including the double
407  quotes, which are present for delimitation only):
408</t>
409<figure><artwork type="example">
410  "foo,bar"
411  " foo ,bar,"
412  "  foo , ,bar,charlie   "
413  "foo ,bar,   charlie "
414</artwork></figure>
415<t>
416  But these values would be invalid, as at least one non-empty element is
417  required:
418</t>
419<figure><artwork type="example">
420  ""
421  ","
422  ",   ,"
423</artwork></figure>
424<t>
425  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
426  expanded as explained above.
427</t>
428</section>
429
430<section title="Basic Rules" anchor="basic.rules">
431<t anchor="rule.LWS">
432   This specification uses three rules to denote the use of linear
433   whitespace: OWS (optional whitespace), RWS (required whitespace), and
434   BWS ("bad" whitespace).
435</t>
436<t anchor="rule.OWS">
437   The OWS rule is used where zero or more linear whitespace octets might
438   appear. OWS &SHOULD; either not be produced or be produced as a single
439   SP. Multiple OWS octets that occur within field-content &SHOULD; either
440   be replaced with a single SP or transformed to all SP octets (each WSP
441   octet other than SP replaced with SP) before interpreting the field value
442   or forwarding the message downstream.
443</t>
444<t anchor="rule.RWS">
445   RWS is used when at least one linear whitespace octet is required to
446   separate field tokens. RWS &SHOULD; be produced as a single SP.
447   Multiple RWS octets that occur within field-content &SHOULD; either
448   be replaced with a single SP or transformed to all SP octets before
449   interpreting the field value or forwarding the message downstream.
450</t>
451<t anchor="rule.BWS">
452   BWS is used where the grammar allows optional whitespace for historical
453   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
454   recipients &MUST; accept such bad optional whitespace and remove it before
455   interpreting the field value or forwarding the message downstream.
456</t>
457<t anchor="rule.whitespace">
458  <x:anchor-alias value="BWS"/>
459  <x:anchor-alias value="OWS"/>
460  <x:anchor-alias value="RWS"/>
461  <x:anchor-alias value="obs-fold"/>
462</t>
463<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"/>
464  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
465                 ; "optional" whitespace
466  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
467                 ; "required" whitespace
468  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
469                 ; "bad" whitespace
470  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
471                 ; see <xref target="header.fields"/>
472</artwork></figure>
473</section>
474</section>
475</section>
476
477<section title="HTTP-related architecture" anchor="architecture">
478<t>
479   HTTP was created for the World Wide Web architecture
480   and has evolved over time to support the scalability needs of a worldwide
481   hypertext system. Much of that architecture is reflected in the terminology
482   and syntax productions used to define HTTP.
483</t>
484
485<section title="Client/Server Messaging" anchor="operation">
486<iref primary="true" item="client"/>
487<iref primary="true" item="server"/>
488<iref primary="true" item="connection"/>
489<t>
490   HTTP is a stateless request/response protocol that operates by exchanging
491   messages across a reliable transport or session-layer
492   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
493   program that establishes a connection to a server for the purpose of
494   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
495   program that accepts connections in order to service HTTP requests by
496   sending HTTP responses.
497</t>
498<iref primary="true" item="user agent"/>
499<iref primary="true" item="origin server"/>
500<iref primary="true" item="browser"/>
501<iref primary="true" item="spider"/>
502<iref primary="true" item="sender"/>
503<iref primary="true" item="recipient"/>
504<t>
505   Note that the terms client and server refer only to the roles that
506   these programs perform for a particular connection.  The same program
507   might act as a client on some connections and a server on others.  We use
508   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
509   such as a WWW browser, editor, or spider (web-traversing robot), and
510   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
511   authoritative responses to a request.  For general requirements, we use
512   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
513   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
514   message.
515</t>
516<t>
517   Most HTTP communication consists of a retrieval request (GET) for
518   a representation of some resource identified by a URI.  In the
519   simplest case, this might be accomplished via a single bidirectional
520   connection (===) between the user agent (UA) and the origin server (O).
521</t>
522<figure><artwork type="drawing">
523         request   &gt;
524    UA ======================================= O
525                                &lt;   response
526</artwork></figure>
527<iref primary="true" item="message"/>
528<iref primary="true" item="request"/>
529<iref primary="true" item="response"/>
530<t>
531   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
532   <x:dfn>message</x:dfn> (<xref target="request"/>), beginning with a method, URI, and
533   protocol version, followed by MIME-like header fields containing
534   request modifiers, client information, and payload metadata, an empty
535   line to indicate the end of the header section, and finally the payload
536   body (if any).
537</t>
538<t>
539   A server responds to the client's request by sending an HTTP <x:dfn>response</x:dfn>
540   <x:dfn>message</x:dfn> (<xref target="response"/>), beginning with a status line that
541   includes the protocol version, a success or error code, and textual
542   reason phrase, followed by MIME-like header fields containing server
543   information, resource metadata, and payload metadata, an empty line to
544   indicate the end of the header section, and finally the payload body (if any).
545</t>
546<t>
547   The following example illustrates a typical message exchange for a
548   GET request on the URI "http://www.example.com/hello.txt":
549</t>
550<figure><preamble>
551client request:
552</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
553GET /hello.txt HTTP/1.1
554User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
555Host: www.example.com
556Accept: */*
557
558</artwork></figure>
559<figure><preamble>
560server response:
561</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
562HTTP/1.1 200 OK
563Date: Mon, 27 Jul 2009 12:28:53 GMT
564Server: Apache
565Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
566ETag: "34aa387-d-1568eb00"
567Accept-Ranges: bytes
568Content-Length: <x:length-of target="exbody"/>
569Vary: Accept-Encoding
570Content-Type: text/plain
571
572<x:span anchor="exbody">Hello World!
573</x:span></artwork></figure>
574</section>
575
576<section title="Message Orientation and Buffering" anchor="message-orientation-and-buffering">
577<t>
578   Fundamentally, HTTP is a message-based protocol. Although message bodies can
579   be chunked (<xref target="chunked.encoding"/>) and implementations often
580   make parts of a message available progressively, this is not required, and
581   some widely-used implementations only make a message available when it is
582   complete. Furthermore, while most proxies will progressively stream messages,
583   some amount of buffering will take place, and some proxies might buffer
584   messages to perform transformations, check content or provide other services.
585</t>
586<t>
587   Therefore, extensions to and uses of HTTP cannot rely on the availability of
588   a partial message, or assume that messages will not be buffered. There are
589   strategies that can be used to test for buffering in a given connection, but
590   it should be understood that behaviors can differ across connections, and
591   between requests and responses.
592</t>
593<t>
594   Recipients &MUST; consider every message in a connection in isolation;
595   because HTTP is a stateless protocol, it cannot be assumed that two requests
596   on the same connection are from the same client or share any other common
597   attributes. In particular, intermediaries might mix requests from different
598   clients into a single server connection. Note that some existing HTTP
599   extensions (e.g., <xref target="RFC4559"/>) violate this requirement, thereby
600   potentially causing interoperability and security problems.
601</t>
602</section>
603
604<section title="Connections and Transport Independence" anchor="transport-independence">
605<t>
606   HTTP messaging is independent of the underlying transport or
607   session-layer connection protocol(s).  HTTP only presumes a reliable
608   transport with in-order delivery of requests and the corresponding
609   in-order delivery of responses.  The mapping of HTTP request and
610   response structures onto the data units of the underlying transport
611   protocol is outside the scope of this specification.
612</t>
613<t>
614   The specific connection protocols to be used for an interaction
615   are determined by client configuration and the target resource's URI.
616   For example, the "http" URI scheme
617   (<xref target="http.uri"/>) indicates a default connection of TCP
618   over IP, with a default TCP port of 80, but the client might be
619   configured to use a proxy via some other connection port or protocol
620   instead of using the defaults.
621</t>
622<t>
623   A connection might be used for multiple HTTP request/response exchanges,
624   as defined in <xref target="persistent.connections"/>.
625</t>
626</section>
627
628<section title="Intermediaries" anchor="intermediaries">
629<iref primary="true" item="intermediary"/>
630<t>
631   HTTP enables the use of intermediaries to satisfy requests through
632   a chain of connections.  There are three common forms of HTTP
633   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
634   a single intermediary might act as an origin server, proxy, gateway,
635   or tunnel, switching behavior based on the nature of each request.
636</t>
637<figure><artwork type="drawing">
638         &gt;             &gt;             &gt;             &gt;
639    <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>
640               &lt;             &lt;             &lt;             &lt;
641</artwork></figure>
642<t>
643   The figure above shows three intermediaries (A, B, and C) between the
644   user agent and origin server. A request or response message that
645   travels the whole chain will pass through four separate connections.
646   Some HTTP communication options
647   might apply only to the connection with the nearest, non-tunnel
648   neighbor, only to the end-points of the chain, or to all connections
649   along the chain. Although the diagram is linear, each participant might
650   be engaged in multiple, simultaneous communications. For example, B
651   might be receiving requests from many clients other than A, and/or
652   forwarding requests to servers other than C, at the same time that it
653   is handling A's request.
654</t>
655<t>
656<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
657<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
658   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
659   to describe various requirements in relation to the directional flow of a
660   message: all messages flow from upstream to downstream.
661   Likewise, we use the terms inbound and outbound to refer to
662   directions in relation to the request path:
663   "<x:dfn>inbound</x:dfn>" means toward the origin server and
664   "<x:dfn>outbound</x:dfn>" means toward the user agent.
665</t>
666<t><iref primary="true" item="proxy"/>
667   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
668   client, usually via local configuration rules, to receive requests
669   for some type(s) of absolute URI and attempt to satisfy those
670   requests via translation through the HTTP interface.  Some translations
671   are minimal, such as for proxy requests for "http" URIs, whereas
672   other requests might require translation to and from entirely different
673   application-layer protocols. Proxies are often used to group an
674   organization's HTTP requests through a common intermediary for the
675   sake of security, annotation services, or shared caching.
676</t>
677<t>
678<iref primary="true" item="transforming proxy"/>
679<iref primary="true" item="non-transforming proxy"/>
680   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
681   or configured to modify request or response messages in a semantically
682   meaningful way (i.e., modifications, beyond those required by normal
683   HTTP processing, that change the message in a way that would be
684   significant to the original sender or potentially significant to
685   downstream recipients).  For example, a transforming proxy might be
686   acting as a shared annotation server (modifying responses to include
687   references to a local annotation database), a malware filter, a
688   format transcoder, or an intranet-to-Internet privacy filter.  Such
689   transformations are presumed to be desired by the client (or client
690   organization) that selected the proxy and are beyond the scope of
691   this specification.  However, when a proxy is not intended to transform
692   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
693   requirements that preserve HTTP message semantics. See &status-203; and
694   &header-warning; for status and warning codes related to transformations.
695</t>
696<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
697<iref primary="true" item="accelerator"/>
698   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
699   is a receiving agent that acts
700   as a layer above some other server(s) and translates the received
701   requests to the underlying server's protocol.  Gateways are often
702   used to encapsulate legacy or untrusted information services, to
703   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
704   enable partitioning or load-balancing of HTTP services across
705   multiple machines.
706</t>
707<t>
708   A gateway behaves as an origin server on its outbound connection and
709   as a user agent on its inbound connection.
710   All HTTP requirements applicable to an origin server
711   also apply to the outbound communication of a gateway.
712   A gateway communicates with inbound servers using any protocol that
713   it desires, including private extensions to HTTP that are outside
714   the scope of this specification.  However, an HTTP-to-HTTP gateway
715   that wishes to interoperate with third-party HTTP servers &MUST;
716   comply with HTTP user agent requirements on the gateway's inbound
717   connection and &MUST; implement the Connection
718   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
719   header fields for both connections.
720</t>
721<t><iref primary="true" item="tunnel"/>
722   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
723   without changing the messages. Once active, a tunnel is not
724   considered a party to the HTTP communication, though the tunnel might
725   have been initiated by an HTTP request. A tunnel ceases to exist when
726   both ends of the relayed connection are closed. Tunnels are used to
727   extend a virtual connection through an intermediary, such as when
728   transport-layer security is used to establish private communication
729   through a shared firewall proxy.
730</t>
731<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
732<iref primary="true" item="captive portal"/>
733   In addition, there may exist network intermediaries that are not
734   considered part of the HTTP communication but nevertheless act as
735   filters or redirecting agents (usually violating HTTP semantics,
736   causing security problems, and otherwise making a mess of things).
737   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
738   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
739   or "<x:dfn>captive portal</x:dfn>",
740   differs from an HTTP proxy because it has not been selected by the client.
741   Instead, the network intermediary redirects outgoing TCP port 80 packets
742   (and occasionally other common port traffic) to an internal HTTP server.
743   Interception proxies are commonly found on public network access points,
744   as a means of enforcing account subscription prior to allowing use of
745   non-local Internet services, and within corporate firewalls to enforce
746   network usage policies.
747   They are indistinguishable from a man-in-the-middle attack.
748</t>
749</section>
750
751<section title="Caches" anchor="caches">
752<iref primary="true" item="cache"/>
753<t>
754   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
755   subsystem that controls its message storage, retrieval, and deletion.
756   A cache stores cacheable responses in order to reduce the response
757   time and network bandwidth consumption on future, equivalent
758   requests. Any client or server &MAY; employ a cache, though a cache
759   cannot be used by a server while it is acting as a tunnel.
760</t>
761<t>
762   The effect of a cache is that the request/response chain is shortened
763   if one of the participants along the chain has a cached response
764   applicable to that request. The following illustrates the resulting
765   chain if B has a cached copy of an earlier response from O (via C)
766   for a request which has not been cached by UA or A.
767</t>
768<figure><artwork type="drawing">
769            &gt;             &gt;
770       UA =========== A =========== B - - - - - - C - - - - - - O
771                  &lt;             &lt;
772</artwork></figure>
773<t><iref primary="true" item="cacheable"/>
774   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
775   the response message for use in answering subsequent requests.
776   Even when a response is cacheable, there might be additional
777   constraints placed by the client or by the origin server on when
778   that cached response can be used for a particular request. HTTP
779   requirements for cache behavior and cacheable responses are
780   defined in &caching-overview;
781</t>
782<t>
783   There are a wide variety of architectures and configurations
784   of caches and proxies deployed across the World Wide Web and
785   inside large organizations. These systems include national hierarchies
786   of proxy caches to save transoceanic bandwidth, systems that
787   broadcast or multicast cache entries, organizations that distribute
788   subsets of cached data via optical media, and so on.
789</t>
790</section>
791
792<section title="Protocol Versioning" anchor="http.version">
793  <x:anchor-alias value="HTTP-Version"/>
794  <x:anchor-alias value="HTTP-Prot-Name"/>
795<t>
796   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
797   versions of the protocol. This specification defines version "1.1".
798   The protocol version as a whole indicates the sender's compliance
799   with the set of requirements laid out in that version's corresponding
800   specification of HTTP.
801</t>
802<t>
803   The version of an HTTP message is indicated by an HTTP-Version field
804   in the first line of the message. HTTP-Version is case-sensitive.
805</t>
806<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
807  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
808  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
809</artwork></figure>
810<t>
811   The HTTP version number consists of two decimal digits separated by a "."
812   (period or decimal point).  The first digit ("major version") indicates the
813   HTTP messaging syntax, whereas the second digit ("minor version") indicates
814   the highest minor version to which the sender is at least conditionally
815   compliant and able to understand for future communication.  The minor
816   version advertises the sender's communication capabilities even when the
817   sender is only using a backwards-compatible subset of the protocol,
818   thereby letting the recipient know that more advanced features can
819   be used in response (by servers) or in future requests (by clients).
820</t>
821<t>
822   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
823   <xref target="RFC1945"/> or a recipient whose version is unknown,
824   the HTTP/1.1 message is constructed such that it can be interpreted
825   as a valid HTTP/1.0 message if all of the newer features are ignored.
826   This specification places recipient-version requirements on some
827   new features so that a compliant sender will only use compatible
828   features until it has determined, through configuration or the
829   receipt of a message, that the recipient supports HTTP/1.1.
830</t>
831<t>
832   The interpretation of an HTTP header field does not change
833   between minor versions of the same major version, though the default
834   behavior of a recipient in the absence of such a field can change.
835   Unless specified otherwise, header fields defined in HTTP/1.1 are
836   defined for all versions of HTTP/1.x.  In particular, the Host and
837   Connection header fields ought to be implemented by all HTTP/1.x
838   implementations whether or not they advertise compliance with HTTP/1.1.
839</t>
840<t>
841   New header fields can be defined such that, when they are
842   understood by a recipient, they might override or enhance the
843   interpretation of previously defined header fields.  When an
844   implementation receives an unrecognized header field, the recipient
845   &MUST; ignore that header field for local processing regardless of
846   the message's HTTP version.  An unrecognized header field received
847   by a proxy &MUST; be forwarded downstream unless the header field's
848   field-name is listed in the message's Connection header-field
849   (see <xref target="header.connection"/>).
850   These requirements allow HTTP's functionality to be enhanced without
851   requiring prior update of all compliant intermediaries.
852</t>
853<t>
854   Intermediaries that process HTTP messages (i.e., all intermediaries
855   other than those acting as a tunnel) &MUST; send their own HTTP-Version
856   in forwarded messages.  In other words, they &MUST-NOT; blindly
857   forward the first line of an HTTP message without ensuring that the
858   protocol version matches what the intermediary understands, and
859   is at least conditionally compliant to, for both the receiving and
860   sending of messages.  Forwarding an HTTP message without rewriting
861   the HTTP-Version might result in communication errors when downstream
862   recipients use the message sender's version to determine what features
863   are safe to use for later communication with that sender.
864</t>
865<t>
866   An HTTP client &SHOULD; send a request version equal to the highest
867   version for which the client is at least conditionally compliant and
868   whose major version is no higher than the highest version supported
869   by the server, if this is known.  An HTTP client &MUST-NOT; send a
870   version for which it is not at least conditionally compliant.
871</t>
872<t>
873   An HTTP client &MAY; send a lower request version if it is known that
874   the server incorrectly implements the HTTP specification, but only
875   after the client has attempted at least one normal request and determined
876   from the response status or header fields (e.g., Server) that the
877   server improperly handles higher request versions.
878</t>
879<t>
880   An HTTP server &SHOULD; send a response version equal to the highest
881   version for which the server is at least conditionally compliant and
882   whose major version is less than or equal to the one received in the
883   request.  An HTTP server &MUST-NOT; send a version for which it is not
884   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
885   Version Not Supported) response if it cannot send a response using the
886   major version used in the client's request.
887</t>
888<t>
889   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
890   if it is known or suspected that the client incorrectly implements the
891   HTTP specification and is incapable of correctly processing later
892   version responses, such as when a client fails to parse the version
893   number correctly or when an intermediary is known to blindly forward
894   the HTTP-Version even when it doesn't comply with the given minor
895   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
896   performed unless triggered by specific client attributes, such as when
897   one or more of the request header fields (e.g., User-Agent) uniquely
898   match the values sent by a client known to be in error.
899</t>
900<t>
901   The intention of HTTP's versioning design is that the major number
902   will only be incremented if an incompatible message syntax is
903   introduced, and that the minor number will only be incremented when
904   changes made to the protocol have the effect of adding to the message
905   semantics or implying additional capabilities of the sender.  However,
906   the minor version was not incremented for the changes introduced between
907   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
908   is specifically avoiding any such changes to the protocol.
909</t>
910</section>
911
912<section title="Uniform Resource Identifiers" anchor="uri">
913<iref primary="true" item="resource"/>
914<t>
915   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
916   throughout HTTP as the means for identifying resources. URI references
917   are used to target requests, indicate redirects, and define relationships.
918   HTTP does not limit what a resource might be; it merely defines an interface
919   that can be used to interact with a resource via HTTP. More information on
920   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
921</t>
922  <x:anchor-alias value="URI-reference"/>
923  <x:anchor-alias value="absolute-URI"/>
924  <x:anchor-alias value="relative-part"/>
925  <x:anchor-alias value="authority"/>
926  <x:anchor-alias value="path-abempty"/>
927  <x:anchor-alias value="path-absolute"/>
928  <x:anchor-alias value="port"/>
929  <x:anchor-alias value="query"/>
930  <x:anchor-alias value="uri-host"/>
931  <x:anchor-alias value="partial-URI"/>
932<t>
933   This specification adopts the definitions of "URI-reference",
934   "absolute-URI", "relative-part", "port", "host",
935   "path-abempty", "path-absolute", "query", and "authority" from the
936   URI generic syntax <xref target="RFC3986"/>.
937   In addition, we define a partial-URI rule for protocol elements
938   that allow a relative URI but not a fragment.
939</t>
940<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"/>
941  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
942  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
943  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
944  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
945  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
946  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
947  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
948  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
949  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
950 
951  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
952</artwork></figure>
953<t>
954   Each protocol element in HTTP that allows a URI reference will indicate
955   in its ABNF production whether the element allows any form of reference
956   (URI-reference), only a URI in absolute form (absolute-URI), only the
957   path and optional query components, or some combination of the above.
958   Unless otherwise indicated, URI references are parsed relative to the
959   effective request URI, which defines the default base URI for references
960   in both the request and its corresponding response.
961</t>
962
963<section title="http URI scheme" anchor="http.uri">
964  <x:anchor-alias value="http-URI"/>
965  <iref item="http URI scheme" primary="true"/>
966  <iref item="URI scheme" subitem="http" primary="true"/>
967<t>
968   The "http" URI scheme is hereby defined for the purpose of minting
969   identifiers according to their association with the hierarchical
970   namespace governed by a potential HTTP origin server listening for
971   TCP connections on a given port.
972</t>
973<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
974  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
975</artwork></figure>
976<t>
977   The HTTP origin server is identified by the generic syntax's
978   <x:ref>authority</x:ref> component, which includes a host identifier
979   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
980   The remainder of the URI, consisting of both the hierarchical path
981   component and optional query component, serves as an identifier for
982   a potential resource within that origin server's name space.
983</t>
984<t>
985   If the host identifier is provided as an IP literal or IPv4 address,
986   then the origin server is any listener on the indicated TCP port at
987   that IP address. If host is a registered name, then that name is
988   considered an indirect identifier and the recipient might use a name
989   resolution service, such as DNS, to find the address of a listener
990   for that host.
991   The host &MUST-NOT; be empty; if an "http" URI is received with an
992   empty host, then it &MUST; be rejected as invalid.
993   If the port subcomponent is empty or not given, then TCP port 80 is
994   assumed (the default reserved port for WWW services).
995</t>
996<t>
997   Regardless of the form of host identifier, access to that host is not
998   implied by the mere presence of its name or address. The host might or might
999   not exist and, even when it does exist, might or might not be running an
1000   HTTP server or listening to the indicated port. The "http" URI scheme
1001   makes use of the delegated nature of Internet names and addresses to
1002   establish a naming authority (whatever entity has the ability to place
1003   an HTTP server at that Internet name or address) and allows that
1004   authority to determine which names are valid and how they might be used.
1005</t>
1006<t>
1007   When an "http" URI is used within a context that calls for access to the
1008   indicated resource, a client &MAY; attempt access by resolving
1009   the host to an IP address, establishing a TCP connection to that address
1010   on the indicated port, and sending an HTTP request message to the server
1011   containing the URI's identifying data as described in <xref target="request"/>.
1012   If the server responds to that request with a non-interim HTTP response
1013   message, as described in <xref target="response"/>, then that response
1014   is considered an authoritative answer to the client's request.
1015</t>
1016<t>
1017   Although HTTP is independent of the transport protocol, the "http"
1018   scheme is specific to TCP-based services because the name delegation
1019   process depends on TCP for establishing authority.
1020   An HTTP service based on some other underlying connection protocol
1021   would presumably be identified using a different URI scheme, just as
1022   the "https" scheme (below) is used for servers that require an SSL/TLS
1023   transport layer on a connection. Other protocols might also be used to
1024   provide access to "http" identified resources &mdash; it is only the
1025   authoritative interface used for mapping the namespace that is
1026   specific to TCP.
1027</t>
1028<t>
1029   The URI generic syntax for authority also includes a deprecated
1030   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1031   for including user authentication information in the URI.  Some
1032   implementations make use of the userinfo component for internal
1033   configuration of authentication information, such as within command
1034   invocation options, configuration files, or bookmark lists, even
1035   though such usage might expose a user identifier or password.
1036   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
1037   delimiter) when transmitting an "http" URI in a message.  Recipients
1038   of HTTP messages that contain a URI reference &SHOULD; parse for the
1039   existence of userinfo and treat its presence as an error, likely
1040   indicating that the deprecated subcomponent is being used to obscure
1041   the authority for the sake of phishing attacks.
1042</t>
1043</section>
1044
1045<section title="https URI scheme" anchor="https.uri">
1046   <x:anchor-alias value="https-URI"/>
1047   <iref item="https URI scheme"/>
1048   <iref item="URI scheme" subitem="https"/>
1049<t>
1050   The "https" URI scheme is hereby defined for the purpose of minting
1051   identifiers according to their association with the hierarchical
1052   namespace governed by a potential HTTP origin server listening for
1053   SSL/TLS-secured connections on a given TCP port.
1054</t>
1055<t>
1056   All of the requirements listed above for the "http" scheme are also
1057   requirements for the "https" scheme, except that a default TCP port
1058   of 443 is assumed if the port subcomponent is empty or not given,
1059   and the TCP connection &MUST; be secured for privacy through the
1060   use of strong encryption prior to sending the first HTTP request.
1061</t>
1062<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1063  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1064</artwork></figure>
1065<t>
1066   Unlike the "http" scheme, responses to "https" identified requests
1067   are never "public" and thus &MUST-NOT; be reused for shared caching.
1068   They can, however, be reused in a private cache if the message is
1069   cacheable by default in HTTP or specifically indicated as such by
1070   the Cache-Control header field (&header-cache-control;).
1071</t>
1072<t>
1073   Resources made available via the "https" scheme have no shared
1074   identity with the "http" scheme even if their resource identifiers
1075   indicate the same authority (the same host listening to the same
1076   TCP port).  They are distinct name spaces and are considered to be
1077   distinct origin servers.  However, an extension to HTTP that is
1078   defined to apply to entire host domains, such as the Cookie protocol
1079   <xref target="RFC6265"/>, can allow information
1080   set by one service to impact communication with other services
1081   within a matching group of host domains.
1082</t>
1083<t>
1084   The process for authoritative access to an "https" identified
1085   resource is defined in <xref target="RFC2818"/>.
1086</t>
1087</section>
1088
1089<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1090<t>
1091   Since the "http" and "https" schemes conform to the URI generic syntax,
1092   such URIs are normalized and compared according to the algorithm defined
1093   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1094   described above for each scheme.
1095</t>
1096<t>
1097   If the port is equal to the default port for a scheme, the normal
1098   form is to elide the port subcomponent. Likewise, an empty path
1099   component is equivalent to an absolute path of "/", so the normal
1100   form is to provide a path of "/" instead. The scheme and host
1101   are case-insensitive and normally provided in lowercase; all
1102   other components are compared in a case-sensitive manner.
1103   Characters other than those in the "reserved" set are equivalent
1104   to their percent-encoded octets (see <xref target="RFC3986"
1105   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1106</t>
1107<t>
1108   For example, the following three URIs are equivalent:
1109</t>
1110<figure><artwork type="example">
1111   http://example.com:80/~smith/home.html
1112   http://EXAMPLE.com/%7Esmith/home.html
1113   http://EXAMPLE.com:/%7esmith/home.html
1114</artwork></figure>
1115</section>
1116</section>
1117</section>
1118
1119<section title="Message Format" anchor="http.message">
1120<x:anchor-alias value="generic-message"/>
1121<x:anchor-alias value="message.types"/>
1122<x:anchor-alias value="HTTP-message"/>
1123<x:anchor-alias value="start-line"/>
1124<iref item="header section"/>
1125<iref item="headers"/>
1126<iref item="header field"/>
1127<t>
1128   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1129   octets in a format similar to the Internet Message Format
1130   <xref target="RFC5322"/>: zero or more header fields (collectively
1131   referred to as the "headers" or the "header section"), an empty line
1132   indicating the end of the header section, and an optional message-body.
1133</t>
1134<t>
1135   An HTTP message can either be a request from client to server or a
1136   response from server to client.  Syntactically, the two types of message
1137   differ only in the start-line, which is either a Request-Line (for requests)
1138   or a Status-Line (for responses), and in the algorithm for determining
1139   the length of the message-body (<xref target="message.body"/>).
1140   In theory, a client could receive requests and a server could receive
1141   responses, distinguishing them by their different start-line formats,
1142   but in practice servers are implemented to only expect a request
1143   (a response is interpreted as an unknown or invalid request method)
1144   and clients are implemented to only expect a response.
1145</t>
1146<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1147  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1148                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1149                    <x:ref>CRLF</x:ref>
1150                    [ <x:ref>message-body</x:ref> ]
1151  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1152</artwork></figure>
1153<t>
1154   Implementations &MUST-NOT; send whitespace between the start-line and
1155   the first header field. The presence of such whitespace in a request
1156   might be an attempt to trick a server into ignoring that field or
1157   processing the line after it as a new request, either of which might
1158   result in a security vulnerability if other implementations within
1159   the request chain interpret the same message differently.
1160   Likewise, the presence of such whitespace in a response might be
1161   ignored by some clients or cause others to cease parsing.
1162</t>
1163
1164<section title="Message Parsing and Robustness" anchor="message.robustness">
1165<t>
1166   The normal procedure for parsing an HTTP message is to read the
1167   start-line into a structure, read each header field into a hash
1168   table by field name until the empty line, and then use the parsed
1169   data to determine if a message-body is expected.  If a message-body
1170   has been indicated, then it is read as a stream until an amount
1171   of octets equal to the message-body length is read or the connection
1172   is closed.
1173</t>
1174<t>
1175   Care must be taken to parse an HTTP message as a sequence
1176   of octets in an encoding that is a superset of US-ASCII.  Attempting
1177   to parse HTTP as a stream of Unicode characters in a character encoding
1178   like UTF-16 might introduce security flaws due to the differing ways
1179   that such parsers interpret invalid characters.
1180</t>
1181<t>
1182   Older HTTP/1.0 client implementations might send an extra CRLF
1183   after a POST request as a lame workaround for some early server
1184   applications that failed to read message-body content that was
1185   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1186   preface or follow a request with an extra CRLF.  If terminating
1187   the request message-body with a line-ending is desired, then the
1188   client &MUST; include the terminating CRLF octets as part of the
1189   message-body length.
1190</t>
1191<t>
1192   In the interest of robustness, servers &SHOULD; ignore at least one
1193   empty line received where a Request-Line is expected. In other words, if
1194   the server is reading the protocol stream at the beginning of a
1195   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1196   Likewise, although the line terminator for the start-line and header
1197   fields is the sequence CRLF, we recommend that recipients recognize a
1198   single LF as a line terminator and ignore any CR.
1199</t>
1200<t>
1201   When a server listening only for HTTP request messages, or processing
1202   what appears from the start-line to be an HTTP request message,
1203   receives a sequence of octets that does not match the HTTP-message
1204   grammar aside from the robustness exceptions listed above, the
1205   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1206</t>
1207</section>
1208
1209<section title="Header Fields" anchor="header.fields">
1210  <x:anchor-alias value="header-field"/>
1211  <x:anchor-alias value="field-content"/>
1212  <x:anchor-alias value="field-name"/>
1213  <x:anchor-alias value="field-value"/>
1214  <x:anchor-alias value="OWS"/>
1215<t>
1216   Each HTTP header field consists of a case-insensitive field name
1217   followed by a colon (":"), optional whitespace, and the field value.
1218</t>
1219<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"/>
1220  <x:ref>header-field</x:ref>   = <x:ref>field-name</x:ref> ":" <x:ref>OWS</x:ref> <x:ref>field-value</x:ref> <x:ref>OWS</x:ref>
1221  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1222  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1223  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1224</artwork></figure>
1225<t>
1226   The field-name token labels the corresponding field-value as having the
1227   semantics defined by that header field.  For example, the Date header field
1228   is defined in <xref target="header.date"/> as containing the origination
1229   timestamp for the message in which it appears.
1230</t>
1231<t>
1232   HTTP header fields are fully extensible: there is no limit on the
1233   introduction of new field names, each presumably defining new semantics,
1234   or on the number of header fields used in a given message.  Existing
1235   fields are defined in each part of this specification and in many other
1236   specifications outside the standards process.
1237   New header fields can be introduced without changing the protocol version
1238   if their defined semantics allow them to be safely ignored by recipients
1239   that do not recognize them.
1240</t>
1241<t>
1242   New HTTP header fields &SHOULD; be registered with IANA according
1243   to the procedures in <xref target="header.field.registration"/>.
1244   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1245   field-name is listed in the Connection header field
1246   (<xref target="header.connection"/>) or the proxy is specifically
1247   configured to block or otherwise transform such fields.
1248   Unrecognized header fields &SHOULD; be ignored by other recipients.
1249</t>
1250<t>
1251   The order in which header fields with differing field names are
1252   received is not significant. However, it is "good practice" to send
1253   header fields that contain control data first, such as Host on
1254   requests and Date on responses, so that implementations can decide
1255   when not to handle a message as early as possible.  A server &MUST;
1256   wait until the entire header section is received before interpreting
1257   a request message, since later header fields might include conditionals,
1258   authentication credentials, or deliberately misleading duplicate
1259   header fields that would impact request processing.
1260</t>
1261<t>
1262   Multiple header fields with the same field name &MUST-NOT; be
1263   sent in a message unless the entire field value for that
1264   header field is defined as a comma-separated list [i.e., #(values)].
1265   Multiple header fields with the same field name can be combined into
1266   one "field-name: field-value" pair, without changing the semantics of the
1267   message, by appending each subsequent field value to the combined
1268   field value in order, separated by a comma. The order in which
1269   header fields with the same field name are received is therefore
1270   significant to the interpretation of the combined field value;
1271   a proxy &MUST-NOT; change the order of these field values when
1272   forwarding a message.
1273</t>
1274<x:note>
1275  <t>
1276   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1277   practice can occur multiple times, but does not use the list syntax, and
1278   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1279   for details.) Also note that the Set-Cookie2 header field specified in
1280   <xref target="RFC2965"/> does not share this problem.
1281  </t>
1282</x:note>
1283
1284<section title="Field Parsing" anchor="field.parsing">
1285<t>
1286   No whitespace is allowed between the header field-name and colon.
1287   In the past, differences in the handling of such whitespace have led to
1288   security vulnerabilities in request routing and response handling.
1289   Any received request message that contains whitespace between a header
1290   field-name and colon &MUST; be rejected with a response code of 400
1291   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1292   message before forwarding the message downstream.
1293</t>
1294<t>
1295   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1296   preferred. The field value does not include any leading or trailing white
1297   space: OWS occurring before the first non-whitespace octet of the
1298   field value or after the last non-whitespace octet of the field value
1299   is ignored and &SHOULD; be removed before further processing (as this does
1300   not change the meaning of the header field).
1301</t>
1302<t>
1303   Historically, HTTP header field values could be extended over multiple
1304   lines by preceding each extra line with at least one space or horizontal
1305   tab octet (line folding). This specification deprecates such line
1306   folding except within the message/http media type
1307   (<xref target="internet.media.type.message.http"/>).
1308   HTTP senders &MUST-NOT; produce messages that include line folding
1309   (i.e., that contain any field-content that matches the obs-fold rule) unless
1310   the message is intended for packaging within the message/http media type.
1311   HTTP recipients &SHOULD; accept line folding and replace any embedded
1312   obs-fold whitespace with either a single SP or a matching number of SP
1313   octets (to avoid buffer copying) prior to interpreting the field value or
1314   forwarding the message downstream.
1315</t>
1316<t>
1317   Historically, HTTP has allowed field content with text in the ISO-8859-1
1318   <xref target="ISO-8859-1"/> character encoding and supported other
1319   character sets only through use of <xref target="RFC2047"/> encoding.
1320   In practice, most HTTP header field values use only a subset of the
1321   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1322   header fields &SHOULD; limit their field values to US-ASCII octets.
1323   Recipients &SHOULD; treat other (obs-text) octets in field content as
1324   opaque data.
1325</t>
1326</section>
1327
1328<section title="Field Length" anchor="field.length">
1329<t>
1330   HTTP does not place a pre-defined limit on the length of header fields,
1331   either in isolation or as a set. A server &MUST; be prepared to receive
1332   request header fields of unbounded length and respond with a 4xx status
1333   code if the received header field(s) would be longer than the server wishes
1334   to handle.
1335</t>
1336<t>
1337   A client that receives response headers that are longer than it wishes to
1338   handle can only treat it as a server error.
1339</t>
1340<t>
1341   Various ad-hoc limitations on header length are found in practice. It is
1342   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1343   combined header fields have 4000 or more octets.
1344</t>
1345</section>
1346
1347<section title="Common Field ABNF Rules" anchor="field.rules">
1348<t anchor="rule.token.separators">
1349  <x:anchor-alias value="tchar"/>
1350  <x:anchor-alias value="token"/>
1351  <x:anchor-alias value="special"/>
1352  <x:anchor-alias value="word"/>
1353   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1354   separated by whitespace or special characters. These special characters
1355   &MUST; be in a quoted string to be used within a parameter value (as defined
1356   in <xref target="transfer.codings"/>).
1357</t>
1358<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"/>
1359  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1360
1361  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1362<!--
1363  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1364 -->
1365  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1366                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1367                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1368                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1369
1370  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1371                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1372                 / "]" / "?" / "=" / "{" / "}"
1373</artwork></figure>
1374<t anchor="rule.quoted-string">
1375  <x:anchor-alias value="quoted-string"/>
1376  <x:anchor-alias value="qdtext"/>
1377  <x:anchor-alias value="obs-text"/>
1378   A string of text is parsed as a single word if it is quoted using
1379   double-quote marks.
1380</t>
1381<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"/>
1382  <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>
1383  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1384  <x:ref>obs-text</x:ref>       = %x80-FF
1385</artwork></figure>
1386<t anchor="rule.quoted-pair">
1387  <x:anchor-alias value="quoted-pair"/>
1388   The backslash octet ("\") can be used as a single-octet
1389   quoting mechanism within quoted-string constructs:
1390</t>
1391<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1392  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1393</artwork></figure>
1394<t>
1395   Recipients that process the value of the quoted-string &MUST; handle a
1396   quoted-pair as if it were replaced by the octet following the backslash.
1397</t>
1398<t>
1399   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1400   escaping (i.e., other than DQUOTE and the backslash octet).
1401</t>
1402<t anchor="rule.comment">
1403  <x:anchor-alias value="comment"/>
1404  <x:anchor-alias value="ctext"/>
1405   Comments can be included in some HTTP header fields by surrounding
1406   the comment text with parentheses. Comments are only allowed in
1407   fields containing "comment" as part of their field value definition.
1408</t>
1409<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1410  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1411  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1412</artwork></figure>
1413<t anchor="rule.quoted-cpair">
1414  <x:anchor-alias value="quoted-cpair"/>
1415   The backslash octet ("\") can be used as a single-octet
1416   quoting mechanism within comment constructs:
1417</t>
1418<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1419  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1420</artwork></figure>
1421<t>
1422   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1423   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1424</t>
1425</section>
1426</section>
1427
1428<section title="Message Body" anchor="message.body">
1429  <x:anchor-alias value="message-body"/>
1430<t>
1431   The message-body (if any) of an HTTP message is used to carry the
1432   payload body associated with the request or response.
1433</t>
1434<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1435  <x:ref>message-body</x:ref> = *OCTET
1436</artwork></figure>
1437<t>
1438   The message-body differs from the payload body only when a transfer-coding
1439   has been applied, as indicated by the Transfer-Encoding header field
1440   (<xref target="header.transfer-encoding"/>).  If more than one
1441   Transfer-Encoding header field is present in a message, the multiple
1442   field-values &MUST; be combined into one field-value, according to the
1443   algorithm defined in <xref target="header.fields"/>, before determining
1444   the message-body length.
1445</t>
1446<t>
1447   When one or more transfer-codings are applied to a payload in order to
1448   form the message-body, the Transfer-Encoding header field &MUST; contain
1449   the list of transfer-codings applied. Transfer-Encoding is a property of
1450   the message, not of the payload, and thus &MAY; be added or removed by
1451   any implementation along the request/response chain under the constraints
1452   found in <xref target="transfer.codings"/>.
1453</t>
1454<t>
1455   If a message is received that has multiple Content-Length header fields
1456   (<xref target="header.content-length"/>) with field-values consisting
1457   of the same decimal value, or a single Content-Length header field with
1458   a field value containing a list of identical decimal values (e.g.,
1459   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1460   header fields have been generated or combined by an upstream message
1461   processor, then the recipient &MUST; either reject the message as invalid
1462   or replace the duplicated field-values with a single valid Content-Length
1463   field containing that decimal value prior to determining the message-body
1464   length.
1465</t>
1466<t>
1467   The rules for when a message-body is allowed in a message differ for
1468   requests and responses.
1469</t>
1470<t>
1471   The presence of a message-body in a request is signaled by the
1472   inclusion of a Content-Length or Transfer-Encoding header field in
1473   the request's header fields, even if the request method does not
1474   define any use for a message-body.  This allows the request
1475   message framing algorithm to be independent of method semantics.
1476</t>
1477<t>
1478   For response messages, whether or not a message-body is included with
1479   a message is dependent on both the request method and the response
1480   status code (<xref target="status.code.and.reason.phrase"/>).
1481   Responses to the HEAD request method never include a message-body
1482   because the associated response header fields (e.g., Transfer-Encoding,
1483   Content-Length, etc.) only indicate what their values would have been
1484   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1485   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1486   All other responses do include a message-body, although the body
1487   &MAY; be of zero length.
1488</t>
1489<t>
1490   The length of the message-body is determined by one of the following
1491   (in order of precedence):
1492</t>
1493<t>
1494  <list style="numbers">
1495    <x:lt><t>
1496     Any response to a HEAD request and any response with a status
1497     code of 100-199, 204, or 304 is always terminated by the first
1498     empty line after the header fields, regardless of the header
1499     fields present in the message, and thus cannot contain a message-body.
1500    </t></x:lt>
1501    <x:lt><t>
1502     If a Transfer-Encoding header field is present
1503     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1504     is the final encoding, the message-body length is determined by reading
1505     and decoding the chunked data until the transfer-coding indicates the
1506     data is complete.
1507    </t>
1508    <t>
1509     If a Transfer-Encoding header field is present in a response and the
1510     "chunked" transfer-coding is not the final encoding, the message-body
1511     length is determined by reading the connection until it is closed by
1512     the server.
1513     If a Transfer-Encoding header field is present in a request and the
1514     "chunked" transfer-coding is not the final encoding, the message-body
1515     length cannot be determined reliably; the server &MUST; respond with
1516     the 400 (Bad Request) status code and then close the connection.
1517    </t>
1518    <t>
1519     If a message is received with both a Transfer-Encoding header field
1520     and a Content-Length header field, the Transfer-Encoding overrides
1521     the Content-Length.
1522     Such a message might indicate an attempt to perform request or response
1523     smuggling (bypass of security-related checks on message routing or content)
1524     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1525     be removed, prior to forwarding the message downstream, or replaced with
1526     the real message-body length after the transfer-coding is decoded.
1527    </t></x:lt>
1528    <x:lt><t>
1529     If a message is received without Transfer-Encoding and with either
1530     multiple Content-Length header fields having differing field-values or
1531     a single Content-Length header field having an invalid value, then the
1532     message framing is invalid and &MUST; be treated as an error to
1533     prevent request or response smuggling.
1534     If this is a request message, the server &MUST; respond with
1535     a 400 (Bad Request) status code and then close the connection.
1536     If this is a response message received by a proxy, the proxy
1537     &MUST; discard the received response, send a 502 (Bad Gateway)
1538     status code as its downstream response, and then close the connection.
1539     If this is a response message received by a user-agent, it &MUST; be
1540     treated as an error by discarding the message and closing the connection.
1541    </t></x:lt>
1542    <x:lt><t>
1543     If a valid Content-Length header field
1544     is present without Transfer-Encoding, its decimal value defines the
1545     message-body length in octets.  If the actual number of octets sent in
1546     the message is less than the indicated Content-Length, the recipient
1547     &MUST; consider the message to be incomplete and treat the connection
1548     as no longer usable.
1549     If the actual number of octets sent in the message is more than the indicated
1550     Content-Length, the recipient &MUST; only process the message-body up to the
1551     field value's number of octets; the remainder of the message &MUST; either
1552     be discarded or treated as the next message in a pipeline.  For the sake of
1553     robustness, a user-agent &MAY; attempt to detect and correct such an error
1554     in message framing if it is parsing the response to the last request on
1555     a connection and the connection has been closed by the server.
1556    </t></x:lt>
1557    <x:lt><t>
1558     If this is a request message and none of the above are true, then the
1559     message-body length is zero (no message-body is present).
1560    </t></x:lt>
1561    <x:lt><t>
1562     Otherwise, this is a response message without a declared message-body
1563     length, so the message-body length is determined by the number of octets
1564     received prior to the server closing the connection.
1565    </t></x:lt>
1566  </list>
1567</t>
1568<t>
1569   Since there is no way to distinguish a successfully completed,
1570   close-delimited message from a partially-received message interrupted
1571   by network failure, implementations &SHOULD; use encoding or
1572   length-delimited messages whenever possible.  The close-delimiting
1573   feature exists primarily for backwards compatibility with HTTP/1.0.
1574</t>
1575<t>
1576   A server &MAY; reject a request that contains a message-body but
1577   not a Content-Length by responding with 411 (Length Required).
1578</t>
1579<t>
1580   Unless a transfer-coding other than "chunked" has been applied,
1581   a client that sends a request containing a message-body &SHOULD;
1582   use a valid Content-Length header field if the message-body length
1583   is known in advance, rather than the "chunked" encoding, since some
1584   existing services respond to "chunked" with a 411 (Length Required)
1585   status code even though they understand the chunked encoding.  This
1586   is typically because such services are implemented via a gateway that
1587   requires a content-length in advance of being called and the server
1588   is unable or unwilling to buffer the entire request before processing.
1589</t>
1590<t>
1591   A client that sends a request containing a message-body &MUST; include a
1592   valid Content-Length header field if it does not know the server will
1593   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1594   of specific user configuration or by remembering the version of a prior
1595   received response.
1596</t>
1597</section>
1598
1599<section anchor="incomplete.messages" title="Incomplete Messages">
1600<t>
1601   Request messages that are prematurely terminated, possibly due to a
1602   cancelled connection or a server-imposed time-out exception, &MUST;
1603   result in closure of the connection; sending an HTTP/1.1 error response
1604   prior to closing the connection is &OPTIONAL;.
1605</t>
1606<t>
1607   Response messages that are prematurely terminated, usually by closure
1608   of the connection prior to receiving the expected number of octets or by
1609   failure to decode a transfer-encoded message-body, &MUST; be recorded
1610   as incomplete.  A response that terminates in the middle of the header
1611   block (before the empty line is received) cannot be assumed to convey the
1612   full semantics of the response and &MUST; be treated as an error.
1613</t>
1614<t>
1615   A message-body that uses the chunked transfer encoding is
1616   incomplete if the zero-sized chunk that terminates the encoding has not
1617   been received.  A message that uses a valid Content-Length is incomplete
1618   if the size of the message-body received (in octets) is less than the
1619   value given by Content-Length.  A response that has neither chunked
1620   transfer encoding nor Content-Length is terminated by closure of the
1621   connection, and thus is considered complete regardless of the number of
1622   message-body octets received, provided that the header block was received
1623   intact.
1624</t>
1625<t>
1626   A user agent &MUST-NOT; render an incomplete response message-body as if
1627   it were complete (i.e., some indication must be given to the user that an
1628   error occurred).  Cache requirements for incomplete responses are defined
1629   in &cache-incomplete;.
1630</t>
1631<t>
1632   A server &MUST; read the entire request message-body or close
1633   the connection after sending its response, since otherwise the
1634   remaining data on a persistent connection would be misinterpreted
1635   as the next request.  Likewise,
1636   a client &MUST; read the entire response message-body if it intends
1637   to reuse the same connection for a subsequent request.  Pipelining
1638   multiple requests on a connection is described in <xref target="pipelining"/>.
1639</t>
1640</section>
1641
1642<section title="General Header Fields" anchor="general.header.fields">
1643  <x:anchor-alias value="general-header"/>
1644<t>
1645   There are a few header fields which have general applicability for
1646   both request and response messages, but which do not apply to the
1647   payload being transferred. These header fields apply only to the
1648   message being transmitted.
1649</t>
1650<texttable align="left">
1651  <ttcol>Header Field Name</ttcol>
1652  <ttcol>Defined in...</ttcol>
1653 
1654  <c>Connection</c> <c><xref target="header.connection"/></c>
1655  <c>Date</c> <c><xref target="header.date"/></c>
1656  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1657  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1658  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1659  <c>Via</c> <c><xref target="header.via"/></c>
1660</texttable>
1661</section>
1662</section>
1663
1664<section title="Request" anchor="request">
1665  <x:anchor-alias value="Request"/>
1666<t>
1667   A request message from a client to a server begins with a
1668   Request-Line, followed by zero or more header fields, an empty
1669   line signifying the end of the header block, and an optional
1670   message body.
1671</t>
1672<!--                 Host                      ; should be moved here eventually -->
1673<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1674  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1675                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1676                  <x:ref>CRLF</x:ref>
1677                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1678</artwork></figure>
1679
1680<section title="Request-Line" anchor="request-line">
1681  <x:anchor-alias value="Request-Line"/>
1682<t>
1683   The Request-Line begins with a method token, followed by a single
1684   space (SP), the request-target, another single space (SP), the
1685   protocol version, and ending with CRLF.
1686</t>
1687<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1688  <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>
1689</artwork></figure>
1690
1691<section title="Method" anchor="method">
1692  <x:anchor-alias value="Method"/>
1693<t>
1694   The Method token indicates the request method to be performed on the
1695   target resource. The request method is case-sensitive.
1696</t>
1697<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1698  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1699</artwork></figure>
1700</section>
1701
1702<section title="request-target" anchor="request-target">
1703  <x:anchor-alias value="request-target"/>
1704<t>
1705   The request-target identifies the target resource upon which to apply
1706   the request.  In most cases, the user agent is provided a URI reference
1707   from which it determines an absolute URI for identifying the target
1708   resource.  When a request to the resource is initiated, all or part
1709   of that URI is used to construct the HTTP request-target.
1710</t>
1711<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1712  <x:ref>request-target</x:ref> = "*"
1713                 / <x:ref>absolute-URI</x:ref>
1714                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1715                 / <x:ref>authority</x:ref>
1716</artwork></figure>
1717<t>
1718   The four options for request-target are dependent on the nature of the
1719   request.
1720</t>   
1721<t><iref item="asterisk form (of request-target)"/>
1722   The asterisk "*" form of request-target, which &MUST-NOT; be used
1723   with any request method other than OPTIONS, means that the request
1724   applies to the server as a whole (the listening process) rather than
1725   to a specific named resource at that server.  For example,
1726</t>
1727<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1728OPTIONS * HTTP/1.1
1729</artwork></figure>
1730<t><iref item="absolute-URI form (of request-target)"/>
1731   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1732   proxy. The proxy is requested to either forward the request or service it
1733   from a valid cache, and then return the response. Note that the proxy &MAY;
1734   forward the request on to another proxy or directly to the server
1735   specified by the absolute-URI. In order to avoid request loops, a
1736   proxy that forwards requests to other proxies &MUST; be able to
1737   recognize and exclude all of its own server names, including
1738   any aliases, local variations, and the numeric IP address. An example
1739   Request-Line would be:
1740</t>
1741<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1742GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1743</artwork></figure>
1744<t>
1745   To allow for transition to absolute-URIs in all requests in future
1746   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1747   form in requests, even though HTTP/1.1 clients will only generate
1748   them in requests to proxies.
1749</t>
1750<t>
1751   If a proxy receives a host name that is not a fully qualified domain
1752   name, it &MAY; add its domain to the host name it received. If a proxy
1753   receives a fully qualified domain name, the proxy &MUST-NOT; change
1754   the host name.
1755</t>
1756<t><iref item="authority form (of request-target)"/>
1757   The "authority form" is only used by the CONNECT request method (&CONNECT;).
1758</t>
1759<t><iref item="origin form (of request-target)"/>
1760   The most common form of request-target is that used when making
1761   a request to an origin server ("origin form").
1762   In this case, the absolute path and query components of the URI
1763   &MUST; be transmitted as the request-target, and the authority component
1764   &MUST; be transmitted in a Host header field. For example, a client wishing
1765   to retrieve a representation of the resource, as identified above,
1766   directly from the origin server would open (or reuse) a TCP connection
1767   to port 80 of the host "www.example.org" and send the lines:
1768</t>
1769<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1770GET /pub/WWW/TheProject.html HTTP/1.1
1771Host: www.example.org
1772</artwork></figure>
1773<t>
1774   followed by the remainder of the Request. Note that the origin form
1775   of request-target always starts with an absolute path; if the target
1776   resource's URI path is empty, then an absolute path of "/" &MUST; be
1777   provided in the request-target.
1778</t>
1779<t>
1780   If a proxy receives an OPTIONS request with an absolute-URI form of
1781   request-target in which the URI has an empty path and no query component,
1782   then the last proxy on the request chain &MUST; use a request-target
1783   of "*" when it forwards the request to the indicated origin server.
1784</t>
1785<figure><preamble>   
1786   For example, the request
1787</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1788OPTIONS http://www.example.org:8001 HTTP/1.1
1789</artwork></figure>
1790<figure><preamble>   
1791  would be forwarded by the final proxy as
1792</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1793OPTIONS * HTTP/1.1
1794Host: www.example.org:8001
1795</artwork>
1796<postamble>
1797   after connecting to port 8001 of host "www.example.org".
1798</postamble>
1799</figure>
1800<t>
1801   The request-target is transmitted in the format specified in
1802   <xref target="http.uri"/>. If the request-target is percent-encoded
1803   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1804   &MUST; decode the request-target in order to
1805   properly interpret the request. Servers &SHOULD; respond to invalid
1806   request-targets with an appropriate status code.
1807</t>
1808<t>
1809   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1810   received request-target when forwarding it to the next inbound server,
1811   except as noted above to replace a null path-absolute with "/" or "*".
1812</t>
1813<x:note>
1814  <t>
1815    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1816    meaning of the request when the origin server is improperly using
1817    a non-reserved URI character for a reserved purpose.  Implementors
1818    need to be aware that some pre-HTTP/1.1 proxies have been known to
1819    rewrite the request-target.
1820  </t>
1821</x:note>
1822<t>
1823   HTTP does not place a pre-defined limit on the length of a request-target.
1824   A server &MUST; be prepared to receive URIs of unbounded length and
1825   respond with the 414 (URI Too Long) status code if the received
1826   request-target would be longer than the server wishes to handle
1827   (see &status-414;).
1828</t>
1829<t>
1830   Various ad-hoc limitations on request-target length are found in practice.
1831   It is &RECOMMENDED; that all HTTP senders and recipients support
1832   request-target lengths of 8000 or more octets.
1833</t>
1834<x:note>
1835  <t>
1836    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1837    are not part of the request-target and thus will not be transmitted
1838    in an HTTP request.
1839  </t>
1840</x:note>
1841</section>
1842</section>
1843
1844<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1845<t>
1846   The exact resource identified by an Internet request is determined by
1847   examining both the request-target and the Host header field.
1848</t>
1849<t>
1850   An origin server that does not allow resources to differ by the
1851   requested host &MAY; ignore the Host header field value when
1852   determining the resource identified by an HTTP/1.1 request. (But see
1853   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1854   for other requirements on Host support in HTTP/1.1.)
1855</t>
1856<t>
1857   An origin server that does differentiate resources based on the host
1858   requested (sometimes referred to as virtual hosts or vanity host
1859   names) &MUST; use the following rules for determining the requested
1860   resource on an HTTP/1.1 request:
1861  <list style="numbers">
1862    <t>If request-target is an absolute-URI, the host is part of the
1863     request-target. Any Host header field value in the request &MUST; be
1864     ignored.</t>
1865    <t>If the request-target is not an absolute-URI, and the request includes
1866     a Host header field, the host is determined by the Host header
1867     field value.</t>
1868    <t>If the host as determined by rule 1 or 2 is not a valid host on
1869     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1870  </list>
1871</t>
1872<t>
1873   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1874   attempt to use heuristics (e.g., examination of the URI path for
1875   something unique to a particular host) in order to determine what
1876   exact resource is being requested.
1877</t>
1878</section>
1879
1880<section title="Effective Request URI" anchor="effective.request.uri">
1881  <iref primary="true" item="effective request URI"/>
1882  <iref primary="true" item="target resource"/>
1883<t>
1884   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1885   for the target resource; instead, the URI needs to be inferred from the
1886   request-target, Host header field, and connection context. The result of
1887   this process is called the "effective request URI".  The "target resource"
1888   is the resource identified by the effective request URI.
1889</t>
1890<t>
1891   If the request-target is an absolute-URI, then the effective request URI is
1892   the request-target.
1893</t>
1894<t>
1895   If the request-target uses the path-absolute form or the asterisk form,
1896   and the Host header field is present, then the effective request URI is
1897   constructed by concatenating
1898</t>
1899<t>
1900  <list style="symbols">
1901    <t>
1902      the scheme name: "http" if the request was received over an insecure
1903      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1904      connection,
1905    </t>
1906    <t>
1907      the octet sequence "://",
1908    </t>
1909    <t>
1910      the authority component, as specified in the Host header field
1911      (<xref target="header.host"/>), and
1912    </t>
1913    <t>
1914      the request-target obtained from the Request-Line, unless the
1915      request-target is just the asterisk "*".
1916    </t>
1917  </list>
1918</t>
1919<t>
1920   If the request-target uses the path-absolute form or the asterisk form,
1921   and the Host header field is not present, then the effective request URI is
1922   undefined.
1923</t>
1924<t>
1925   Otherwise, when request-target uses the authority form, the effective
1926   request URI is undefined.
1927</t>
1928<figure>
1929<preamble>
1930   Example 1: the effective request URI for the message
1931</preamble> 
1932<artwork type="example" x:indent-with="  ">
1933GET /pub/WWW/TheProject.html HTTP/1.1
1934Host: www.example.org:8080
1935</artwork>
1936<postamble>
1937  (received over an insecure TCP connection) is "http", plus "://", plus the
1938  authority component "www.example.org:8080", plus the request-target
1939  "/pub/WWW/TheProject.html", thus
1940  "http://www.example.org:8080/pub/WWW/TheProject.html".
1941</postamble>
1942</figure>
1943<figure>
1944<preamble>
1945   Example 2: the effective request URI for the message
1946</preamble> 
1947<artwork type="example" x:indent-with="  ">
1948OPTIONS * HTTP/1.1
1949Host: www.example.org
1950</artwork>
1951<postamble>
1952  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1953  authority component "www.example.org", thus "https://www.example.org".
1954</postamble>
1955</figure>
1956<t>
1957   Effective request URIs are compared using the rules described in
1958   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1959   be treated as equivalent to an absolute path of "/".
1960</t> 
1961</section>
1962
1963</section>
1964
1965
1966<section title="Response" anchor="response">
1967  <x:anchor-alias value="Response"/>
1968<t>
1969   After receiving and interpreting a request message, a server responds
1970   with an HTTP response message.
1971</t>
1972<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1973  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1974                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1975                  <x:ref>CRLF</x:ref>
1976                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1977</artwork></figure>
1978
1979<section title="Status-Line" anchor="status-line">
1980  <x:anchor-alias value="Status-Line"/>
1981<t>
1982   The first line of a Response message is the Status-Line, consisting
1983   of the protocol version, a space (SP), the status code, another space,
1984   a possibly-empty textual phrase describing the status code, and
1985   ending with CRLF.
1986</t>
1987<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1988  <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>
1989</artwork></figure>
1990
1991<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1992  <x:anchor-alias value="Reason-Phrase"/>
1993  <x:anchor-alias value="Status-Code"/>
1994<t>
1995   The Status-Code element is a 3-digit integer result code of the
1996   attempt to understand and satisfy the request. These codes are fully
1997   defined in &status-codes;.  The Reason Phrase exists for the sole
1998   purpose of providing a textual description associated with the numeric
1999   status code, out of deference to earlier Internet application protocols
2000   that were more frequently used with interactive text clients.
2001   A client &SHOULD; ignore the content of the Reason Phrase.
2002</t>
2003<t>
2004   The first digit of the Status-Code defines the class of response. The
2005   last two digits do not have any categorization role. There are 5
2006   values for the first digit:
2007  <list style="symbols">
2008    <t>
2009      1xx: Informational - Request received, continuing process
2010    </t>
2011    <t>
2012      2xx: Success - The action was successfully received,
2013        understood, and accepted
2014    </t>
2015    <t>
2016      3xx: Redirection - Further action must be taken in order to
2017        complete the request
2018    </t>
2019    <t>
2020      4xx: Client Error - The request contains bad syntax or cannot
2021        be fulfilled
2022    </t>
2023    <t>
2024      5xx: Server Error - The server failed to fulfill an apparently
2025        valid request
2026    </t>
2027  </list>
2028</t>
2029<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
2030  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
2031  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
2032</artwork></figure>
2033</section>
2034</section>
2035
2036</section>
2037
2038
2039<section title="Protocol Parameters" anchor="protocol.parameters">
2040
2041<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
2042  <x:anchor-alias value="HTTP-date"/>
2043<t>
2044   HTTP applications have historically allowed three different formats
2045   for date/time stamps. However, the preferred format is a fixed-length subset
2046   of that defined by <xref target="RFC1123"/>:
2047</t>
2048<figure><artwork type="example" x:indent-with="  ">
2049Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2050</artwork></figure>
2051<t>
2052   The other formats are described here only for compatibility with obsolete
2053   implementations.
2054</t>
2055<figure><artwork type="example" x:indent-with="  ">
2056Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2057Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2058</artwork></figure>
2059<t>
2060   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2061   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2062   only generate the RFC 1123 format for representing HTTP-date values
2063   in header fields.
2064</t>
2065<t>
2066   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2067   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2068   equal to UTC (Coordinated Universal Time). This is indicated in the
2069   first two formats by the inclusion of "GMT" as the three-letter
2070   abbreviation for time zone, and &MUST; be assumed when reading the
2071   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2072   additional whitespace beyond that specifically included as SP in the
2073   grammar.
2074</t>
2075<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2076  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2077</artwork></figure>
2078<t anchor="preferred.date.format">
2079  <x:anchor-alias value="rfc1123-date"/>
2080  <x:anchor-alias value="time-of-day"/>
2081  <x:anchor-alias value="hour"/>
2082  <x:anchor-alias value="minute"/>
2083  <x:anchor-alias value="second"/>
2084  <x:anchor-alias value="day-name"/>
2085  <x:anchor-alias value="day"/>
2086  <x:anchor-alias value="month"/>
2087  <x:anchor-alias value="year"/>
2088  <x:anchor-alias value="GMT"/>
2089  Preferred format:
2090</t>
2091<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="time-of-day"/><iref primary="true" item="Grammar" subitem="hour"/><iref primary="true" item="Grammar" subitem="minute"/><iref primary="true" item="Grammar" subitem="second"/><iref primary="true" item="Grammar" subitem="day-name"/><iref primary="true" item="Grammar" subitem="day-name-l"/><iref primary="true" item="Grammar" subitem="day"/><iref primary="true" item="Grammar" subitem="month"/><iref primary="true" item="Grammar" subitem="year"/><iref primary="true" item="Grammar" subitem="GMT"/>
2092  <x:ref>rfc1123-date</x:ref> = <x:ref>day-name</x:ref> "," <x:ref>SP</x:ref> date1 <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
2093  ; fixed length subset of the format defined in
2094  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2095 
2096  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2097               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2098               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2099               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2100               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2101               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2102               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2103               
2104  <x:ref>date1</x:ref>        = <x:ref>day</x:ref> <x:ref>SP</x:ref> <x:ref>month</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
2105               ; e.g., 02 Jun 1982
2106
2107  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2108  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2109               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2110               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2111               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2112               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2113               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2114               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2115               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2116               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2117               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2118               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2119               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2120  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2121
2122  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2123
2124  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2125                 ; 00:00:00 - 23:59:59
2126                 
2127  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2128  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2129  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2130</artwork></figure>
2131<t>
2132  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2133  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2134  same as those defined for the RFC 5322 constructs
2135  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2136</t>
2137<t anchor="obsolete.date.formats">
2138  <x:anchor-alias value="obs-date"/>
2139  <x:anchor-alias value="rfc850-date"/>
2140  <x:anchor-alias value="asctime-date"/>
2141  <x:anchor-alias value="date1"/>
2142  <x:anchor-alias value="date2"/>
2143  <x:anchor-alias value="date3"/>
2144  <x:anchor-alias value="rfc1123-date"/>
2145  <x:anchor-alias value="day-name-l"/>
2146  Obsolete formats:
2147</t>
2148<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2149  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2150</artwork></figure>
2151<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2152  <x:ref>rfc850-date</x:ref>  = <x:ref>day-name-l</x:ref> "," <x:ref>SP</x:ref> <x:ref>date2</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
2153  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2154                 ; day-month-year (e.g., 02-Jun-82)
2155
2156  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2157         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2158         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2159         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2160         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2161         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2162         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2163</artwork></figure>
2164<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2165  <x:ref>asctime-date</x:ref> = <x:ref>day-name</x:ref> <x:ref>SP</x:ref> <x:ref>date3</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
2166  <x:ref>date3</x:ref>        = <x:ref>month</x:ref> <x:ref>SP</x:ref> ( 2<x:ref>DIGIT</x:ref> / ( <x:ref>SP</x:ref> 1<x:ref>DIGIT</x:ref> ))
2167                 ; month day (e.g., Jun  2)
2168</artwork></figure>
2169<x:note>
2170  <t>
2171    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2172    accepting date values that might have been sent by non-HTTP
2173    applications, as is sometimes the case when retrieving or posting
2174    messages via proxies/gateways to SMTP or NNTP.
2175  </t>
2176</x:note>
2177<x:note>
2178  <t>
2179    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2180    to their usage within the protocol stream. Clients and servers are
2181    not required to use these formats for user presentation, request
2182    logging, etc.
2183  </t>
2184</x:note>
2185</section>
2186
2187<section title="Transfer Codings" anchor="transfer.codings">
2188  <x:anchor-alias value="transfer-coding"/>
2189  <x:anchor-alias value="transfer-extension"/>
2190<t>
2191   Transfer-coding values are used to indicate an encoding
2192   transformation that has been, can be, or might need to be applied to a
2193   payload body in order to ensure "safe transport" through the network.
2194   This differs from a content coding in that the transfer-coding is a
2195   property of the message rather than a property of the representation
2196   that is being transferred.
2197</t>
2198<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2199  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2200                          / "compress" ; <xref target="compress.coding"/>
2201                          / "deflate" ; <xref target="deflate.coding"/>
2202                          / "gzip" ; <xref target="gzip.coding"/>
2203                          / <x:ref>transfer-extension</x:ref>
2204  <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> )
2205</artwork></figure>
2206<t anchor="rule.parameter">
2207  <x:anchor-alias value="attribute"/>
2208  <x:anchor-alias value="transfer-parameter"/>
2209  <x:anchor-alias value="value"/>
2210   Parameters are in the form of attribute/value pairs.
2211</t>
2212<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"/>
2213  <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>
2214  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2215  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2216</artwork></figure>
2217<t>
2218   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2219   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2220   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2221</t>
2222<t>
2223   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2224   MIME, which were designed to enable safe transport of binary data over a
2225   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2226   However, safe transport
2227   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2228   the only unsafe characteristic of message-bodies is the difficulty in
2229   determining the exact message body length (<xref target="message.body"/>),
2230   or the desire to encrypt data over a shared transport.
2231</t>
2232<t>
2233   A server that receives a request message with a transfer-coding it does
2234   not understand &SHOULD; respond with 501 (Not Implemented) and then
2235   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2236   client.
2237</t>
2238
2239<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2240  <iref item="chunked (Coding Format)"/>
2241  <iref item="Coding Format" subitem="chunked"/>
2242  <x:anchor-alias value="chunk"/>
2243  <x:anchor-alias value="Chunked-Body"/>
2244  <x:anchor-alias value="chunk-data"/>
2245  <x:anchor-alias value="chunk-ext"/>
2246  <x:anchor-alias value="chunk-ext-name"/>
2247  <x:anchor-alias value="chunk-ext-val"/>
2248  <x:anchor-alias value="chunk-size"/>
2249  <x:anchor-alias value="last-chunk"/>
2250  <x:anchor-alias value="trailer-part"/>
2251  <x:anchor-alias value="quoted-str-nf"/>
2252  <x:anchor-alias value="qdtext-nf"/>
2253<t>
2254   The chunked encoding modifies the body of a message in order to
2255   transfer it as a series of chunks, each with its own size indicator,
2256   followed by an &OPTIONAL; trailer containing header fields. This
2257   allows dynamically produced content to be transferred along with the
2258   information necessary for the recipient to verify that it has
2259   received the full message.
2260</t>
2261<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"/>
2262  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2263                   <x:ref>last-chunk</x:ref>
2264                   <x:ref>trailer-part</x:ref>
2265                   <x:ref>CRLF</x:ref>
2266 
2267  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2268                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2269  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2270  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2271 
2272  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2273                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2274  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2275  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2276  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2277  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2278 
2279  <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>
2280                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2281  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2282                 ; <x:ref>WSP</x:ref> / &lt;<x:ref>VCHAR</x:ref> except <x:ref>DQUOTE</x:ref> and "\"&gt; / <x:ref>obs-text</x:ref> 
2283</artwork></figure>
2284<t>
2285   The chunk-size field is a string of hex digits indicating the size of
2286   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2287   zero, followed by the trailer, which is terminated by an empty line.
2288</t>
2289<t>
2290   The trailer allows the sender to include additional HTTP header
2291   fields at the end of the message. The Trailer header field can be
2292   used to indicate which header fields are included in a trailer (see
2293   <xref target="header.trailer"/>).
2294</t>
2295<t>
2296   A server using chunked transfer-coding in a response &MUST-NOT; use the
2297   trailer for any header fields unless at least one of the following is
2298   true:
2299  <list style="numbers">
2300    <t>the request included a TE header field that indicates "trailers" is
2301     acceptable in the transfer-coding of the  response, as described in
2302     <xref target="header.te"/>; or,</t>
2303     
2304    <t>the trailer fields consist entirely of optional metadata, and the
2305    recipient could use the message (in a manner acceptable to the server where
2306    the field originated) without receiving it. In other words, the server that
2307    generated the header (often but not always the origin server) is willing to
2308    accept the possibility that the trailer fields might be silently discarded
2309    along the path to the client.</t>
2310  </list>
2311</t>
2312<t>
2313   This requirement prevents an interoperability failure when the
2314   message is being received by an HTTP/1.1 (or later) proxy and
2315   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2316   compliance with the protocol would have necessitated a possibly
2317   infinite buffer on the proxy.
2318</t>
2319<t>
2320   A process for decoding the "chunked" transfer-coding
2321   can be represented in pseudo-code as:
2322</t>
2323<figure><artwork type="code">
2324  length := 0
2325  read chunk-size, chunk-ext (if any) and CRLF
2326  while (chunk-size &gt; 0) {
2327     read chunk-data and CRLF
2328     append chunk-data to decoded-body
2329     length := length + chunk-size
2330     read chunk-size and CRLF
2331  }
2332  read header-field
2333  while (header-field not empty) {
2334     append header-field to existing header fields
2335     read header-field
2336  }
2337  Content-Length := length
2338  Remove "chunked" from Transfer-Encoding
2339</artwork></figure>
2340<t>
2341   All HTTP/1.1 applications &MUST; be able to receive and decode the
2342   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2343   they do not understand.
2344</t>
2345<t>
2346   Since "chunked" is the only transfer-coding required to be understood
2347   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2348   on a persistent connection.  Whenever a transfer-coding is applied to
2349   a payload body in a request, the final transfer-coding applied &MUST;
2350   be "chunked".  If a transfer-coding is applied to a response payload
2351   body, then either the final transfer-coding applied &MUST; be "chunked"
2352   or the message &MUST; be terminated by closing the connection. When the
2353   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2354   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2355   be applied more than once in a message-body.
2356</t>
2357</section>
2358
2359<section title="Compression Codings" anchor="compression.codings">
2360<t>
2361   The codings defined below can be used to compress the payload of a
2362   message.
2363</t>
2364<x:note><t>
2365   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2366   is not desirable and is discouraged for future encodings. Their
2367   use here is representative of historical practice, not good
2368   design.
2369</t></x:note>
2370<x:note><t>
2371   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2372   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2373   equivalent to "gzip" and "compress" respectively.
2374</t></x:note>
2375
2376<section title="Compress Coding" anchor="compress.coding">
2377<iref item="compress (Coding Format)"/>
2378<iref item="Coding Format" subitem="compress"/>
2379<t>
2380   The "compress" format is produced by the common UNIX file compression
2381   program "compress". This format is an adaptive Lempel-Ziv-Welch
2382   coding (LZW).
2383</t>
2384</section>
2385
2386<section title="Deflate Coding" anchor="deflate.coding">
2387<iref item="deflate (Coding Format)"/>
2388<iref item="Coding Format" subitem="deflate"/>
2389<t>
2390   The "deflate" format is defined as the "deflate" compression mechanism
2391   (described in <xref target="RFC1951"/>) used inside the "zlib"
2392   data format (<xref target="RFC1950"/>).
2393</t>
2394<x:note>
2395  <t>
2396    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2397    compressed data without the zlib wrapper.
2398   </t>
2399</x:note>
2400</section>
2401
2402<section title="Gzip Coding" anchor="gzip.coding">
2403<iref item="gzip (Coding Format)"/>
2404<iref item="Coding Format" subitem="gzip"/>
2405<t>
2406   The "gzip" format is produced by the file compression program
2407   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2408   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2409</t>
2410</section>
2411
2412</section>
2413
2414<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2415<t>
2416   The HTTP Transfer Coding Registry defines the name space for the transfer
2417   coding names.
2418</t>
2419<t>
2420   Registrations &MUST; include the following fields:
2421   <list style="symbols">
2422     <t>Name</t>
2423     <t>Description</t>
2424     <t>Pointer to specification text</t>
2425   </list>
2426</t>
2427<t>
2428   Names of transfer codings &MUST-NOT; overlap with names of content codings
2429   (&content-codings;), unless the encoding transformation is identical (as it
2430   is the case for the compression codings defined in
2431   <xref target="compression.codings"/>).
2432</t>
2433<t>
2434   Values to be added to this name space require a specification
2435   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2436   conform to the purpose of transfer coding defined in this section.
2437</t>
2438<t>
2439   The registry itself is maintained at
2440   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2441</t>
2442</section>
2443</section>
2444
2445<section title="Product Tokens" anchor="product.tokens">
2446  <x:anchor-alias value="product"/>
2447  <x:anchor-alias value="product-version"/>
2448<t>
2449   Product tokens are used to allow communicating applications to
2450   identify themselves by software name and version. Most fields using
2451   product tokens also allow sub-products which form a significant part
2452   of the application to be listed, separated by whitespace. By
2453   convention, the products are listed in order of their significance
2454   for identifying the application.
2455</t>
2456<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2457  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2458  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2459</artwork></figure>
2460<t>
2461   Examples:
2462</t>
2463<figure><artwork type="example">
2464  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2465  Server: Apache/0.8.4
2466</artwork></figure>
2467<t>
2468   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2469   used for advertising or other non-essential information. Although any
2470   token octet &MAY; appear in a product-version, this token &SHOULD;
2471   only be used for a version identifier (i.e., successive versions of
2472   the same product &SHOULD; only differ in the product-version portion of
2473   the product value).
2474</t>
2475</section>
2476
2477<section title="Quality Values" anchor="quality.values">
2478  <x:anchor-alias value="qvalue"/>
2479<t>
2480   Both transfer codings (TE request header field, <xref target="header.te"/>)
2481   and content negotiation (&content.negotiation;) use short "floating point"
2482   numbers to indicate the relative importance ("weight") of various
2483   negotiable parameters.  A weight is normalized to a real number in
2484   the range 0 through 1, where 0 is the minimum and 1 the maximum
2485   value. If a parameter has a quality value of 0, then content with
2486   this parameter is "not acceptable" for the client. HTTP/1.1
2487   applications &MUST-NOT; generate more than three digits after the
2488   decimal point. User configuration of these values &SHOULD; also be
2489   limited in this fashion.
2490</t>
2491<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2492  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2493                 / ( "1" [ "." 0*3("0") ] )
2494</artwork></figure>
2495<x:note>
2496  <t>
2497     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2498     relative degradation in desired quality.
2499  </t>
2500</x:note>
2501</section>
2502
2503</section>
2504
2505<section title="Connections" anchor="connections">
2506
2507<section title="Persistent Connections" anchor="persistent.connections">
2508
2509<section title="Purpose" anchor="persistent.purpose">
2510<t>
2511   Prior to persistent connections, a separate TCP connection was
2512   established for each request, increasing the load on HTTP servers
2513   and causing congestion on the Internet. The use of inline images and
2514   other associated data often requires a client to make multiple
2515   requests of the same server in a short amount of time. Analysis of
2516   these performance problems and results from a prototype
2517   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2518   measurements of actual HTTP/1.1 implementations show good
2519   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2520   T/TCP <xref target="Tou1998"/>.
2521</t>
2522<t>
2523   Persistent HTTP connections have a number of advantages:
2524  <list style="symbols">
2525      <t>
2526        By opening and closing fewer TCP connections, CPU time is saved
2527        in routers and hosts (clients, servers, proxies, gateways,
2528        tunnels, or caches), and memory used for TCP protocol control
2529        blocks can be saved in hosts.
2530      </t>
2531      <t>
2532        HTTP requests and responses can be pipelined on a connection.
2533        Pipelining allows a client to make multiple requests without
2534        waiting for each response, allowing a single TCP connection to
2535        be used much more efficiently, with much lower elapsed time.
2536      </t>
2537      <t>
2538        Network congestion is reduced by reducing the number of packets
2539        caused by TCP opens, and by allowing TCP sufficient time to
2540        determine the congestion state of the network.
2541      </t>
2542      <t>
2543        Latency on subsequent requests is reduced since there is no time
2544        spent in TCP's connection opening handshake.
2545      </t>
2546      <t>
2547        HTTP can evolve more gracefully, since errors can be reported
2548        without the penalty of closing the TCP connection. Clients using
2549        future versions of HTTP might optimistically try a new feature,
2550        but if communicating with an older server, retry with old
2551        semantics after an error is reported.
2552      </t>
2553    </list>
2554</t>
2555<t>
2556   HTTP implementations &SHOULD; implement persistent connections.
2557</t>
2558</section>
2559
2560<section title="Overall Operation" anchor="persistent.overall">
2561<t>
2562   A significant difference between HTTP/1.1 and earlier versions of
2563   HTTP is that persistent connections are the default behavior of any
2564   HTTP connection. That is, unless otherwise indicated, the client
2565   &SHOULD; assume that the server will maintain a persistent connection,
2566   even after error responses from the server.
2567</t>
2568<t>
2569   Persistent connections provide a mechanism by which a client and a
2570   server can signal the close of a TCP connection. This signaling takes
2571   place using the Connection header field (<xref target="header.connection"/>). Once a close
2572   has been signaled, the client &MUST-NOT; send any more requests on that
2573   connection.
2574</t>
2575
2576<section title="Negotiation" anchor="persistent.negotiation">
2577<t>
2578   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2579   maintain a persistent connection unless a Connection header field including
2580   the connection-token "close" was sent in the request. If the server
2581   chooses to close the connection immediately after sending the
2582   response, it &SHOULD; send a Connection header field including the
2583   connection-token "close".
2584</t>
2585<t>
2586   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2587   decide to keep it open based on whether the response from a server
2588   contains a Connection header field with the connection-token close. In case
2589   the client does not want to maintain a connection for more than that
2590   request, it &SHOULD; send a Connection header field including the
2591   connection-token close.
2592</t>
2593<t>
2594   If either the client or the server sends the close token in the
2595   Connection header field, that request becomes the last one for the
2596   connection.
2597</t>
2598<t>
2599   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2600   maintained for HTTP versions less than 1.1 unless it is explicitly
2601   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2602   compatibility with HTTP/1.0 clients.
2603</t>
2604<t>
2605   In order to remain persistent, all messages on the connection &MUST;
2606   have a self-defined message length (i.e., one not defined by closure
2607   of the connection), as described in <xref target="message.body"/>.
2608</t>
2609</section>
2610
2611<section title="Pipelining" anchor="pipelining">
2612<t>
2613   A client that supports persistent connections &MAY; "pipeline" its
2614   requests (i.e., send multiple requests without waiting for each
2615   response). A server &MUST; send its responses to those requests in the
2616   same order that the requests were received.
2617</t>
2618<t>
2619   Clients which assume persistent connections and pipeline immediately
2620   after connection establishment &SHOULD; be prepared to retry their
2621   connection if the first pipelined attempt fails. If a client does
2622   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2623   persistent. Clients &MUST; also be prepared to resend their requests if
2624   the server closes the connection before sending all of the
2625   corresponding responses.
2626</t>
2627<t>
2628   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2629   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2630   premature termination of the transport connection could lead to
2631   indeterminate results. A client wishing to send a non-idempotent
2632   request &SHOULD; wait to send that request until it has received the
2633   response status line for the previous request.
2634</t>
2635</section>
2636</section>
2637
2638<section title="Proxy Servers" anchor="persistent.proxy">
2639<t>
2640   It is especially important that proxies correctly implement the
2641   properties of the Connection header field as specified in <xref target="header.connection"/>.
2642</t>
2643<t>
2644   The proxy server &MUST; signal persistent connections separately with
2645   its clients and the origin servers (or other proxy servers) that it
2646   connects to. Each persistent connection applies to only one transport
2647   link.
2648</t>
2649<t>
2650   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2651   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2652   for information and discussion of the problems with the Keep-Alive header field
2653   implemented by many HTTP/1.0 clients).
2654</t>
2655
2656<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2657<!--<t>
2658  <cref anchor="TODO-end-to-end" source="jre">
2659    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2660    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2661  </cref>
2662</t>-->
2663<t>
2664   For the purpose of defining the behavior of caches and non-caching
2665   proxies, we divide HTTP header fields into two categories:
2666  <list style="symbols">
2667      <t>End-to-end header fields, which are  transmitted to the ultimate
2668        recipient of a request or response. End-to-end header fields in
2669        responses MUST be stored as part of a cache entry and &MUST; be
2670        transmitted in any response formed from a cache entry.</t>
2671
2672      <t>Hop-by-hop header fields, which are meaningful only for a single
2673        transport-level connection, and are not stored by caches or
2674        forwarded by proxies.</t>
2675  </list>
2676</t>
2677<t>
2678   The following HTTP/1.1 header fields are hop-by-hop header fields:
2679  <list style="symbols">
2680      <t>Connection</t>
2681      <t>Keep-Alive</t>
2682      <t>Proxy-Authenticate</t>
2683      <t>Proxy-Authorization</t>
2684      <t>TE</t>
2685      <t>Trailer</t>
2686      <t>Transfer-Encoding</t>
2687      <t>Upgrade</t>
2688  </list>
2689</t>
2690<t>
2691   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2692</t>
2693<t>
2694   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2695   (<xref target="header.connection"/>).
2696</t>
2697</section>
2698
2699<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2700<!--<t>
2701  <cref anchor="TODO-non-mod-headers" source="jre">
2702    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2703    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2704  </cref>
2705</t>-->
2706<t>
2707   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2708   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2709   modify an end-to-end header field unless the definition of that header field requires
2710   or specifically allows that.
2711</t>
2712<t>
2713   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2714   request or response, and it &MUST-NOT; add any of these fields if not
2715   already present:
2716  <list style="symbols">
2717    <t>Allow</t>
2718    <t>Content-Location</t>
2719    <t>Content-MD5</t>
2720    <t>ETag</t>
2721    <t>Last-Modified</t>
2722    <t>Server</t>
2723  </list>
2724</t>
2725<t>
2726   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2727   response:
2728  <list style="symbols">
2729    <t>Expires</t>
2730  </list>
2731</t>
2732<t>
2733   but it &MAY; add any of these fields if not already present. If an
2734   Expires header field is added, it &MUST; be given a field-value identical to
2735   that of the Date header field in that response.
2736</t>
2737<t>
2738   A proxy &MUST-NOT; modify or add any of the following fields in a
2739   message that contains the no-transform cache-control directive, or in
2740   any request:
2741  <list style="symbols">
2742    <t>Content-Encoding</t>
2743    <t>Content-Range</t>
2744    <t>Content-Type</t>
2745  </list>
2746</t>
2747<t>
2748   A transforming proxy &MAY; modify or add these fields to a message
2749   that does not include no-transform, but if it does so, it &MUST; add a
2750   Warning 214 (Transformation applied) if one does not already appear
2751   in the message (see &header-warning;).
2752</t>
2753<x:note>
2754  <t>
2755    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2756    cause authentication failures if stronger authentication
2757    mechanisms are introduced in later versions of HTTP. Such
2758    authentication mechanisms &MAY; rely on the values of header fields
2759    not listed here.
2760  </t>
2761</x:note>
2762<t>
2763   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2764   though it &MAY; change the message-body through application or removal
2765   of a transfer-coding (<xref target="transfer.codings"/>).
2766</t>
2767</section>
2768
2769</section>
2770
2771<section title="Practical Considerations" anchor="persistent.practical">
2772<t>
2773   Servers will usually have some time-out value beyond which they will
2774   no longer maintain an inactive connection. Proxy servers might make
2775   this a higher value since it is likely that the client will be making
2776   more connections through the same server. The use of persistent
2777   connections places no requirements on the length (or existence) of
2778   this time-out for either the client or the server.
2779</t>
2780<t>
2781   When a client or server wishes to time-out it &SHOULD; issue a graceful
2782   close on the transport connection. Clients and servers &SHOULD; both
2783   constantly watch for the other side of the transport close, and
2784   respond to it as appropriate. If a client or server does not detect
2785   the other side's close promptly it could cause unnecessary resource
2786   drain on the network.
2787</t>
2788<t>
2789   A client, server, or proxy &MAY; close the transport connection at any
2790   time. For example, a client might have started to send a new request
2791   at the same time that the server has decided to close the "idle"
2792   connection. From the server's point of view, the connection is being
2793   closed while it was idle, but from the client's point of view, a
2794   request is in progress.
2795</t>
2796<t>
2797   This means that clients, servers, and proxies &MUST; be able to recover
2798   from asynchronous close events. Client software &SHOULD; reopen the
2799   transport connection and retransmit the aborted sequence of requests
2800   without user interaction so long as the request sequence is
2801   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2802   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2803   human operator the choice of retrying the request(s). Confirmation by
2804   user-agent software with semantic understanding of the application
2805   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2806   be repeated if the second sequence of requests fails.
2807</t>
2808<t>
2809   Servers &SHOULD; always respond to at least one request per connection,
2810   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2811   middle of transmitting a response, unless a network or client failure
2812   is suspected.
2813</t>
2814<t>
2815   Clients (including proxies) &SHOULD; limit the number of simultaneous
2816   connections that they maintain to a given server (including proxies).
2817</t>
2818<t>
2819   Previous revisions of HTTP gave a specific number of connections as a
2820   ceiling, but this was found to be impractical for many applications. As a
2821   result, this specification does not mandate a particular maximum number of
2822   connections, but instead encourages clients to be conservative when opening
2823   multiple connections.
2824</t>
2825<t>
2826   In particular, while using multiple connections avoids the "head-of-line
2827   blocking" problem (whereby a request that takes significant server-side
2828   processing and/or has a large payload can block subsequent requests on the
2829   same connection), each connection used consumes server resources (sometimes
2830   significantly), and furthermore using multiple connections can cause
2831   undesirable side effects in congested networks.
2832</t>
2833<t>
2834   Note that servers might reject traffic that they deem abusive, including an
2835   excessive number of connections from a client.
2836</t>
2837</section>
2838</section>
2839
2840<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2841
2842<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2843<t>
2844   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2845   flow control mechanisms to resolve temporary overloads, rather than
2846   terminating connections with the expectation that clients will retry.
2847   The latter technique can exacerbate network congestion.
2848</t>
2849</section>
2850
2851<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2852<t>
2853   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2854   the network connection for an error status code while it is transmitting
2855   the request. If the client sees an error status code, it &SHOULD;
2856   immediately cease transmitting the body. If the body is being sent
2857   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2858   empty trailer &MAY; be used to prematurely mark the end of the message.
2859   If the body was preceded by a Content-Length header field, the client &MUST;
2860   close the connection.
2861</t>
2862</section>
2863
2864<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2865<t>
2866   The purpose of the 100 (Continue) status code (see &status-100;) is to
2867   allow a client that is sending a request message with a request body
2868   to determine if the origin server is willing to accept the request
2869   (based on the request header fields) before the client sends the request
2870   body. In some cases, it might either be inappropriate or highly
2871   inefficient for the client to send the body if the server will reject
2872   the message without looking at the body.
2873</t>
2874<t>
2875   Requirements for HTTP/1.1 clients:
2876  <list style="symbols">
2877    <t>
2878        If a client will wait for a 100 (Continue) response before
2879        sending the request body, it &MUST; send an Expect header
2880        field (&header-expect;) with the "100-continue" expectation.
2881    </t>
2882    <t>
2883        A client &MUST-NOT; send an Expect header field (&header-expect;)
2884        with the "100-continue" expectation if it does not intend
2885        to send a request body.
2886    </t>
2887  </list>
2888</t>
2889<t>
2890   Because of the presence of older implementations, the protocol allows
2891   ambiguous situations in which a client might send "Expect: 100-continue"
2892   without receiving either a 417 (Expectation Failed)
2893   or a 100 (Continue) status code. Therefore, when a client sends this
2894   header field to an origin server (possibly via a proxy) from which it
2895   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2896   wait for an indefinite period before sending the request body.
2897</t>
2898<t>
2899   Requirements for HTTP/1.1 origin servers:
2900  <list style="symbols">
2901    <t> Upon receiving a request which includes an Expect header
2902        field with the "100-continue" expectation, an origin server &MUST;
2903        either respond with 100 (Continue) status code and continue to read
2904        from the input stream, or respond with a final status code. The
2905        origin server &MUST-NOT; wait for the request body before sending
2906        the 100 (Continue) response. If it responds with a final status
2907        code, it &MAY; close the transport connection or it &MAY; continue
2908        to read and discard the rest of the request.  It &MUST-NOT;
2909        perform the request method if it returns a final status code.
2910    </t>
2911    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2912        the request message does not include an Expect header
2913        field with the "100-continue" expectation, and &MUST-NOT; send a
2914        100 (Continue) response if such a request comes from an HTTP/1.0
2915        (or earlier) client. There is an exception to this rule: for
2916        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2917        status code in response to an HTTP/1.1 PUT or POST request that does
2918        not include an Expect header field with the "100-continue"
2919        expectation. This exception, the purpose of which is
2920        to minimize any client processing delays associated with an
2921        undeclared wait for 100 (Continue) status code, applies only to
2922        HTTP/1.1 requests, and not to requests with any other HTTP-version
2923        value.
2924    </t>
2925    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2926        already received some or all of the request body for the
2927        corresponding request.
2928    </t>
2929    <t> An origin server that sends a 100 (Continue) response &MUST;
2930    ultimately send a final status code, once the request body is
2931        received and processed, unless it terminates the transport
2932        connection prematurely.
2933    </t>
2934    <t> If an origin server receives a request that does not include an
2935        Expect header field with the "100-continue" expectation,
2936        the request includes a request body, and the server responds
2937        with a final status code before reading the entire request body
2938        from the transport connection, then the server &SHOULD-NOT;  close
2939        the transport connection until it has read the entire request,
2940        or until the client closes the connection. Otherwise, the client
2941        might not reliably receive the response message. However, this
2942        requirement is not be construed as preventing a server from
2943        defending itself against denial-of-service attacks, or from
2944        badly broken client implementations.
2945      </t>
2946    </list>
2947</t>
2948<t>
2949   Requirements for HTTP/1.1 proxies:
2950  <list style="symbols">
2951    <t> If a proxy receives a request that includes an Expect header
2952        field with the "100-continue" expectation, and the proxy
2953        either knows that the next-hop server complies with HTTP/1.1 or
2954        higher, or does not know the HTTP version of the next-hop
2955        server, it &MUST; forward the request, including the Expect header
2956        field.
2957    </t>
2958    <t> If the proxy knows that the version of the next-hop server is
2959        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2960        respond with a 417 (Expectation Failed) status code.
2961    </t>
2962    <t> Proxies &SHOULD; maintain a record of the HTTP version
2963        numbers received from recently-referenced next-hop servers.
2964    </t>
2965    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2966        request message was received from an HTTP/1.0 (or earlier)
2967        client and did not include an Expect header field with
2968        the "100-continue" expectation. This requirement overrides the
2969        general rule for forwarding of 1xx responses (see &status-1xx;).
2970    </t>
2971  </list>
2972</t>
2973</section>
2974
2975<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2976<t>
2977   If an HTTP/1.1 client sends a request which includes a request body,
2978   but which does not include an Expect header field with the
2979   "100-continue" expectation, and if the client is not directly
2980   connected to an HTTP/1.1 origin server, and if the client sees the
2981   connection close before receiving a status line from the server, the
2982   client &SHOULD; retry the request.  If the client does retry this
2983   request, it &MAY; use the following "binary exponential backoff"
2984   algorithm to be assured of obtaining a reliable response:
2985  <list style="numbers">
2986    <t>
2987      Initiate a new connection to the server
2988    </t>
2989    <t>
2990      Transmit the request-line, header fields, and the CRLF that
2991      indicates the end of header fields.
2992    </t>
2993    <t>
2994      Initialize a variable R to the estimated round-trip time to the
2995         server (e.g., based on the time it took to establish the
2996         connection), or to a constant value of 5 seconds if the round-trip
2997         time is not available.
2998    </t>
2999    <t>
3000       Compute T = R * (2**N), where N is the number of previous
3001         retries of this request.
3002    </t>
3003    <t>
3004       Wait either for an error response from the server, or for T
3005         seconds (whichever comes first)
3006    </t>
3007    <t>
3008       If no error response is received, after T seconds transmit the
3009         body of the request.
3010    </t>
3011    <t>
3012       If client sees that the connection is closed prematurely,
3013         repeat from step 1 until the request is accepted, an error
3014         response is received, or the user becomes impatient and
3015         terminates the retry process.
3016    </t>
3017  </list>
3018</t>
3019<t>
3020   If at any point an error status code is received, the client
3021  <list style="symbols">
3022      <t>&SHOULD-NOT;  continue and</t>
3023
3024      <t>&SHOULD; close the connection if it has not completed sending the
3025        request message.</t>
3026    </list>
3027</t>
3028</section>
3029</section>
3030</section>
3031
3032
3033<section title="Miscellaneous notes that might disappear" anchor="misc">
3034<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
3035<t>
3036   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
3037</t>
3038</section>
3039
3040<section title="Use of HTTP for proxy communication" anchor="http.proxy">
3041<t>
3042   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
3043</t>
3044</section>
3045
3046<section title="Interception of HTTP for access control" anchor="http.intercept">
3047<t>
3048   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
3049</t>
3050</section>
3051
3052<section title="Use of HTTP by other protocols" anchor="http.others">
3053<t>
3054   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
3055   Extensions of HTTP like WebDAV.</cref>
3056</t>
3057
3058</section>
3059<section title="Use of HTTP by media type specification" anchor="http.media">
3060<t>
3061   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
3062</t>
3063</section>
3064</section>
3065
3066<section title="Header Field Definitions" anchor="header.field.definitions">
3067<t>
3068   This section defines the syntax and semantics of HTTP header fields
3069   related to message framing and transport protocols.
3070</t>
3071
3072<section title="Connection" anchor="header.connection">
3073  <iref primary="true" item="Connection header field" x:for-anchor=""/>
3074  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
3075  <x:anchor-alias value="Connection"/>
3076  <x:anchor-alias value="connection-token"/>
3077<t>
3078   The "Connection" header field allows the sender to specify
3079   options that are desired only for that particular connection.
3080   Such connection options &MUST; be removed or replaced before the
3081   message can be forwarded downstream by a proxy or gateway.
3082   This mechanism also allows the sender to indicate which HTTP
3083   header fields used in the message are only intended for the
3084   immediate recipient ("hop-by-hop"), as opposed to all recipients
3085   on the chain ("end-to-end"), enabling the message to be
3086   self-descriptive and allowing future connection-specific extensions
3087   to be deployed in HTTP without fear that they will be blindly
3088   forwarded by previously deployed intermediaries.
3089</t>
3090<t>
3091   The Connection header field's value has the following grammar:
3092</t>
3093<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
3094  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
3095  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
3096</artwork></figure>
3097<t>
3098   A proxy or gateway &MUST; parse a received Connection
3099   header field before a message is forwarded and, for each
3100   connection-token in this field, remove any header field(s) from
3101   the message with the same name as the connection-token, and then
3102   remove the Connection header field itself or replace it with the
3103   sender's own connection options for the forwarded message.
3104</t>
3105<t>
3106   A sender &MUST-NOT; include field-names in the Connection header
3107   field-value for fields that are defined as expressing constraints
3108   for all recipients in the request or response chain, such as the
3109   Cache-Control header field (&header-cache-control;).
3110</t>
3111<t>
3112   The connection options do not have to correspond to a header field
3113   present in the message, since a connection-specific header field
3114   might not be needed if there are no parameters associated with that
3115   connection option.  Recipients that trigger certain connection
3116   behavior based on the presence of connection options &MUST; do so
3117   based on the presence of the connection-token rather than only the
3118   presence of the optional header field.  In other words, if the
3119   connection option is received as a header field but not indicated
3120   within the Connection field-value, then the recipient &MUST; ignore
3121   the connection-specific header field because it has likely been
3122   forwarded by an intermediary that is only partially compliant.
3123</t>
3124<t>
3125   When defining new connection options, specifications ought to
3126   carefully consider existing deployed header fields and ensure
3127   that the new connection-token does not share the same name as
3128   an unrelated header field that might already be deployed.
3129   Defining a new connection-token essentially reserves that potential
3130   field-name for carrying additional information related to the
3131   connection option, since it would be unwise for senders to use
3132   that field-name for anything else.
3133</t>
3134<t>
3135   HTTP/1.1 defines the "close" connection option for the sender to
3136   signal that the connection will be closed after completion of the
3137   response. For example,
3138</t>
3139<figure><artwork type="example">
3140  Connection: close
3141</artwork></figure>
3142<t>
3143   in either the request or the response header fields indicates that
3144   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
3145   after the current request/response is complete.
3146</t>
3147<t>
3148   An HTTP/1.1 client that does not support persistent connections &MUST;
3149   include the "close" connection option in every request message.
3150</t>
3151<t>
3152   An HTTP/1.1 server that does not support persistent connections &MUST;
3153   include the "close" connection option in every response message that
3154   does not have a 1xx (Informational) status code.
3155</t>
3156</section>
3157
3158<section title="Content-Length" anchor="header.content-length">
3159  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
3160  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
3161  <x:anchor-alias value="Content-Length"/>
3162<t>
3163   The "Content-Length" header field indicates the size of the
3164   message-body, in decimal number of octets, for any message other than
3165   a response to a HEAD request or a response with a status code of 304.
3166   In the case of a response to a HEAD request, Content-Length indicates
3167   the size of the payload body (not including any potential transfer-coding)
3168   that would have been sent had the request been a GET.
3169   In the case of a 304 (Not Modified) response to a GET request,
3170   Content-Length indicates the size of the payload body (not including
3171   any potential transfer-coding) that would have been sent in a 200 (OK)
3172   response.
3173</t>
3174<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
3175  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
3176</artwork></figure>
3177<t>
3178   An example is
3179</t>
3180<figure><artwork type="example">
3181  Content-Length: 3495
3182</artwork></figure>
3183<t>
3184   Implementations &SHOULD; use this field to indicate the message-body
3185   length when no transfer-coding is being applied and the
3186   payload's body length can be determined prior to being transferred.
3187   <xref target="message.body"/> describes how recipients determine the length
3188   of a message-body.
3189</t>
3190<t>
3191   Any Content-Length greater than or equal to zero is a valid value.
3192</t>
3193<t>
3194   Note that the use of this field in HTTP is significantly different from
3195   the corresponding definition in MIME, where it is an optional field
3196   used within the "message/external-body" content-type.
3197</t>
3198</section>
3199
3200<section title="Date" anchor="header.date">
3201  <iref primary="true" item="Date header field" x:for-anchor=""/>
3202  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
3203  <x:anchor-alias value="Date"/>
3204<t>
3205   The "Date" header field represents the date and time at which
3206   the message was originated, having the same semantics as the Origination
3207   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
3208   The field value is an HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
3209   it &MUST; be sent in rfc1123-date format.
3210</t>
3211<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
3212  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
3213</artwork></figure>
3214<t>
3215   An example is
3216</t>
3217<figure><artwork type="example">
3218  Date: Tue, 15 Nov 1994 08:12:31 GMT
3219</artwork></figure>
3220<t>
3221   Origin servers &MUST; include a Date header field in all responses,
3222   except in these cases:
3223  <list style="numbers">
3224      <t>If the response status code is 100 (Continue) or 101 (Switching
3225         Protocols), the response &MAY; include a Date header field, at
3226         the server's option.</t>
3227
3228      <t>If the response status code conveys a server error, e.g., 500
3229         (Internal Server Error) or 503 (Service Unavailable), and it is
3230         inconvenient or impossible to generate a valid Date.</t>
3231
3232      <t>If the server does not have a clock that can provide a
3233         reasonable approximation of the current time, its responses
3234         &MUST-NOT; include a Date header field. In this case, the rules
3235         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3236  </list>
3237</t>
3238<t>
3239   A received message that does not have a Date header field &MUST; be
3240   assigned one by the recipient if the message will be cached by that
3241   recipient.
3242</t>
3243<t>
3244   Clients can use the Date header field as well; in order to keep request
3245   messages small, they are advised not to include it when it doesn't convey
3246   any useful information (as it is usually the case for requests that do not
3247   contain a payload).
3248</t>
3249<t>
3250   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3251   time subsequent to the generation of the message. It &SHOULD; represent
3252   the best available approximation of the date and time of message
3253   generation, unless the implementation has no means of generating a
3254   reasonably accurate date and time. In theory, the date ought to
3255   represent the moment just before the payload is generated. In
3256   practice, the date can be generated at any time during the message
3257   origination without affecting its semantic value.
3258</t>
3259
3260<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3261<t>
3262   Some origin server implementations might not have a clock available.
3263   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3264   values to a response, unless these values were associated
3265   with the resource by a system or user with a reliable clock. It &MAY;
3266   assign an Expires value that is known, at or before server
3267   configuration time, to be in the past (this allows "pre-expiration"
3268   of responses without storing separate Expires values for each
3269   resource).
3270</t>
3271</section>
3272</section>
3273
3274<section title="Host" anchor="header.host">
3275  <iref primary="true" item="Host header field" x:for-anchor=""/>
3276  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3277  <x:anchor-alias value="Host"/>
3278<t>
3279   The "Host" header field in a request provides the host and port
3280   information from the target resource's URI, enabling the origin
3281   server to distinguish between resources while servicing requests
3282   for multiple host names on a single IP address.  Since the Host
3283   field-value is critical information for handling a request, it
3284   &SHOULD; be sent as the first header field following the Request-Line.
3285</t>
3286<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
3287  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3288</artwork></figure>
3289<t>
3290   A client &MUST; send a Host header field in all HTTP/1.1 request
3291   messages.  If the target resource's URI includes an authority
3292   component, then the Host field-value &MUST; be identical to that
3293   authority component after excluding any userinfo (<xref target="http.uri"/>).
3294   If the authority component is missing or undefined for the target
3295   resource's URI, then the Host header field &MUST; be sent with an
3296   empty field-value.
3297</t>
3298<t>
3299   For example, a GET request to the origin server for
3300   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
3301</t>
3302<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3303GET /pub/WWW/ HTTP/1.1
3304Host: www.example.org
3305</artwork></figure>
3306<t>
3307   The Host header field &MUST; be sent in an HTTP/1.1 request even
3308   if the request-target is in the form of an absolute-URI, since this
3309   allows the Host information to be forwarded through ancient HTTP/1.0
3310   proxies that might not have implemented Host.
3311</t>
3312<t>
3313   When an HTTP/1.1 proxy receives a request with a request-target in
3314   the form of an absolute-URI, the proxy &MUST; ignore the received
3315   Host header field (if any) and instead replace it with the host
3316   information of the request-target.  When a proxy forwards a request,
3317   it &MUST; generate the Host header field based on the received
3318   absolute-URI rather than the received Host.
3319</t>
3320<t>
3321   Since the Host header field acts as an application-level routing
3322   mechanism, it is a frequent target for malware seeking to poison
3323   a shared cache or redirect a request to an unintended server.
3324   An interception proxy is particularly vulnerable if it relies on
3325   the Host header field value for redirecting requests to internal
3326   servers, or for use as a cache key in a shared cache, without
3327   first verifying that the intercepted connection is targeting a
3328   valid IP address for that host.
3329</t>
3330<t>
3331   A server &MUST; respond with a 400 (Bad Request) status code to
3332   any HTTP/1.1 request message that lacks a Host header field and
3333   to any request message that contains more than one Host header field
3334   or a Host header field with an invalid field-value.
3335</t>
3336<t>
3337   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3338   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3339   for other requirements relating to Host.
3340</t>
3341</section>
3342
3343<section title="TE" anchor="header.te">
3344  <iref primary="true" item="TE header field" x:for-anchor=""/>
3345  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3346  <x:anchor-alias value="TE"/>
3347  <x:anchor-alias value="t-codings"/>
3348  <x:anchor-alias value="te-params"/>
3349  <x:anchor-alias value="te-ext"/>
3350<t>
3351   The "TE" header field indicates what extension transfer-codings
3352   it is willing to accept in the response, and whether or not it is
3353   willing to accept trailer fields in a chunked transfer-coding.
3354</t>
3355<t>
3356   Its value consists of the keyword "trailers" and/or a comma-separated
3357   list of extension transfer-coding names with optional accept
3358   parameters (as described in <xref target="transfer.codings"/>).
3359</t>
3360<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"/>
3361  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
3362  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3363  <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> )
3364  <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> ]
3365</artwork></figure>
3366<t>
3367   The presence of the keyword "trailers" indicates that the client is
3368   willing to accept trailer fields in a chunked transfer-coding, as
3369   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3370   transfer-coding values even though it does not itself represent a
3371   transfer-coding.
3372</t>
3373<t>
3374   Examples of its use are:
3375</t>
3376<figure><artwork type="example">
3377  TE: deflate
3378  TE:
3379  TE: trailers, deflate;q=0.5
3380</artwork></figure>
3381<t>
3382   The TE header field only applies to the immediate connection.
3383   Therefore, the keyword &MUST; be supplied within a Connection header
3384   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3385</t>
3386<t>
3387   A server tests whether a transfer-coding is acceptable, according to
3388   a TE field, using these rules:
3389  <list style="numbers">
3390    <x:lt>
3391      <t>The "chunked" transfer-coding is always acceptable. If the
3392         keyword "trailers" is listed, the client indicates that it is
3393         willing to accept trailer fields in the chunked response on
3394         behalf of itself and any downstream clients. The implication is
3395         that, if given, the client is stating that either all
3396         downstream clients are willing to accept trailer fields in the
3397         forwarded response, or that it will attempt to buffer the
3398         response on behalf of downstream recipients.
3399      </t><t>
3400         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3401         chunked response such that a client can be assured of buffering
3402         the entire response.</t>
3403    </x:lt>
3404    <x:lt>
3405      <t>If the transfer-coding being tested is one of the transfer-codings
3406         listed in the TE field, then it is acceptable unless it
3407         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3408         qvalue of 0 means "not acceptable".)</t>
3409    </x:lt>
3410    <x:lt>
3411      <t>If multiple transfer-codings are acceptable, then the
3412         acceptable transfer-coding with the highest non-zero qvalue is
3413         preferred.  The "chunked" transfer-coding always has a qvalue
3414         of 1.</t>
3415    </x:lt>
3416  </list>
3417</t>
3418<t>
3419   If the TE field-value is empty or if no TE field is present, the only
3420   transfer-coding is "chunked". A message with no transfer-coding is
3421   always acceptable.
3422</t>
3423</section>
3424
3425<section title="Trailer" anchor="header.trailer">
3426  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3427  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3428  <x:anchor-alias value="Trailer"/>
3429<t>
3430   The "Trailer" header field indicates that the given set of
3431   header fields is present in the trailer of a message encoded with
3432   chunked transfer-coding.
3433</t>
3434<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
3435  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
3436</artwork></figure>
3437<t>
3438   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3439   message using chunked transfer-coding with a non-empty trailer. Doing
3440   so allows the recipient to know which header fields to expect in the
3441   trailer.
3442</t>
3443<t>
3444   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3445   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3446   trailer fields in a "chunked" transfer-coding.
3447</t>
3448<t>
3449   Message header fields listed in the Trailer header field &MUST-NOT;
3450   include the following header fields:
3451  <list style="symbols">
3452    <t>Transfer-Encoding</t>
3453    <t>Content-Length</t>
3454    <t>Trailer</t>
3455  </list>
3456</t>
3457</section>
3458
3459<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3460  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3461  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3462  <x:anchor-alias value="Transfer-Encoding"/>
3463<t>
3464   The "Transfer-Encoding" header field indicates what transfer-codings
3465   (if any) have been applied to the message body. It differs from
3466   Content-Encoding (&content-codings;) in that transfer-codings are a property
3467   of the message (and therefore are removed by intermediaries), whereas
3468   content-codings are not.
3469</t>
3470<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
3471  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3472</artwork></figure>
3473<t>
3474   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3475</t>
3476<figure><artwork type="example">
3477  Transfer-Encoding: chunked
3478</artwork></figure>
3479<t>
3480   If multiple encodings have been applied to a representation, the transfer-codings
3481   &MUST; be listed in the order in which they were applied.
3482   Additional information about the encoding parameters &MAY; be provided
3483   by other header fields not defined by this specification.
3484</t>
3485<t>
3486   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3487   header field.
3488</t>
3489</section>
3490
3491<section title="Upgrade" anchor="header.upgrade">
3492  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3493  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3494  <x:anchor-alias value="Upgrade"/>
3495<t>
3496   The "Upgrade" header field allows the client to specify what
3497   additional communication protocols it would like to use, if the server
3498   chooses to switch protocols. Servers can use it to indicate what protocols
3499   they are willing to switch to.
3500</t>
3501<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3502  <x:ref>Upgrade</x:ref> = 1#<x:ref>product</x:ref>
3503</artwork></figure>
3504<t>
3505   For example,
3506</t>
3507<figure><artwork type="example">
3508  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3509</artwork></figure>
3510<t>
3511   The Upgrade header field is intended to provide a simple mechanism
3512   for transition from HTTP/1.1 to some other, incompatible protocol. It
3513   does so by allowing the client to advertise its desire to use another
3514   protocol, such as a later version of HTTP with a higher major version
3515   number, even though the current request has been made using HTTP/1.1.
3516   This eases the difficult transition between incompatible protocols by
3517   allowing the client to initiate a request in the more commonly
3518   supported protocol while indicating to the server that it would like
3519   to use a "better" protocol if available (where "better" is determined
3520   by the server, possibly according to the nature of the request method
3521   or target resource).
3522</t>
3523<t>
3524   The Upgrade header field only applies to switching application-layer
3525   protocols upon the existing transport-layer connection. Upgrade
3526   cannot be used to insist on a protocol change; its acceptance and use
3527   by the server is optional. The capabilities and nature of the
3528   application-layer communication after the protocol change is entirely
3529   dependent upon the new protocol chosen, although the first action
3530   after changing the protocol &MUST; be a response to the initial HTTP
3531   request containing the Upgrade header field.
3532</t>
3533<t>
3534   The Upgrade header field only applies to the immediate connection.
3535   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3536   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3537   HTTP/1.1 message.
3538</t>
3539<t>
3540   The Upgrade header field cannot be used to indicate a switch to a
3541   protocol on a different connection. For that purpose, it is more
3542   appropriate to use a 3xx redirection response (&status-3xx;).
3543</t>
3544<t>
3545   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3546   Protocols) responses to indicate which protocol(s) are being switched to,
3547   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3548   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3549   response to indicate that they are willing to upgrade to one of the
3550   specified protocols.
3551</t>
3552<t>
3553   This specification only defines the protocol name "HTTP" for use by
3554   the family of Hypertext Transfer Protocols, as defined by the HTTP
3555   version rules of <xref target="http.version"/> and future updates to this
3556   specification. Additional tokens can be registered with IANA using the
3557   registration procedure defined below. 
3558</t>
3559
3560<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3561<t>
3562   The HTTP Upgrade Token Registry defines the name space for product
3563   tokens used to identify protocols in the Upgrade header field.
3564   Each registered token is associated with contact information and
3565   an optional set of specifications that details how the connection
3566   will be processed after it has been upgraded.
3567</t>
3568<t>
3569   Registrations are allowed on a First Come First Served basis as
3570   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3571   specifications need not be IETF documents or be subject to IESG review.
3572   Registrations are subject to the following rules:
3573  <list style="numbers">
3574    <t>A token, once registered, stays registered forever.</t>
3575    <t>The registration &MUST; name a responsible party for the
3576       registration.</t>
3577    <t>The registration &MUST; name a point of contact.</t>
3578    <t>The registration &MAY; name a set of specifications associated with that
3579       token. Such specifications need not be publicly available.</t>
3580    <t>The responsible party &MAY; change the registration at any time.
3581       The IANA will keep a record of all such changes, and make them
3582       available upon request.</t>
3583    <t>The responsible party for the first registration of a "product"
3584       token &MUST; approve later registrations of a "version" token
3585       together with that "product" token before they can be registered.</t>
3586    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3587       for a token. This will normally only be used in the case when a
3588       responsible party cannot be contacted.</t>
3589  </list>
3590</t>
3591</section>
3592
3593
3594</section>
3595
3596<section title="Via" anchor="header.via">
3597  <iref primary="true" item="Via header field" x:for-anchor=""/>
3598  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3599  <x:anchor-alias value="protocol-name"/>
3600  <x:anchor-alias value="protocol-version"/>
3601  <x:anchor-alias value="pseudonym"/>
3602  <x:anchor-alias value="received-by"/>
3603  <x:anchor-alias value="received-protocol"/>
3604  <x:anchor-alias value="Via"/>
3605<t>
3606   The "Via" header field &MUST; be sent by a proxy or gateway to
3607   indicate the intermediate protocols and recipients between the user
3608   agent and the server on requests, and between the origin server and
3609   the client on responses. It is analogous to the "Received" field
3610   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3611   and is intended to be used for tracking message forwards,
3612   avoiding request loops, and identifying the protocol capabilities of
3613   all senders along the request/response chain.
3614</t>
3615<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"/>
3616  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3617                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3618  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3619  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3620  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3621  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3622  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3623</artwork></figure>
3624<t>
3625   The received-protocol indicates the protocol version of the message
3626   received by the server or client along each segment of the
3627   request/response chain. The received-protocol version is appended to
3628   the Via field value when the message is forwarded so that information
3629   about the protocol capabilities of upstream applications remains
3630   visible to all recipients.
3631</t>
3632<t>
3633   The protocol-name is excluded if and only if it would be "HTTP". The
3634   received-by field is normally the host and optional port number of a
3635   recipient server or client that subsequently forwarded the message.
3636   However, if the real host is considered to be sensitive information,
3637   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3638   be assumed to be the default port of the received-protocol.
3639</t>
3640<t>
3641   Multiple Via field values represent each proxy or gateway that has
3642   forwarded the message. Each recipient &MUST; append its information
3643   such that the end result is ordered according to the sequence of
3644   forwarding applications.
3645</t>
3646<t>
3647   Comments &MAY; be used in the Via header field to identify the software
3648   of each recipient, analogous to the User-Agent and Server header fields.
3649   However, all comments in the Via field are optional and &MAY; be removed
3650   by any recipient prior to forwarding the message.
3651</t>
3652<t>
3653   For example, a request message could be sent from an HTTP/1.0 user
3654   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3655   forward the request to a public proxy at p.example.net, which completes
3656   the request by forwarding it to the origin server at www.example.com.
3657   The request received by www.example.com would then have the following
3658   Via header field:
3659</t>
3660<figure><artwork type="example">
3661  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3662</artwork></figure>
3663<t>
3664   A proxy or gateway used as a portal through a network firewall
3665   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3666   region unless it is explicitly enabled to do so. If not enabled, the
3667   received-by host of any host behind the firewall &SHOULD; be replaced
3668   by an appropriate pseudonym for that host.
3669</t>
3670<t>
3671   For organizations that have strong privacy requirements for hiding
3672   internal structures, a proxy or gateway &MAY; combine an ordered
3673   subsequence of Via header field entries with identical received-protocol
3674   values into a single such entry. For example,
3675</t>
3676<figure><artwork type="example">
3677  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3678</artwork></figure>
3679<t>
3680  could be collapsed to
3681</t>
3682<figure><artwork type="example">
3683  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3684</artwork></figure>
3685<t>
3686   Senders &SHOULD-NOT; combine multiple entries unless they are all
3687   under the same organizational control and the hosts have already been
3688   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3689   have different received-protocol values.
3690</t>
3691</section>
3692
3693</section>
3694
3695<section title="IANA Considerations" anchor="IANA.considerations">
3696
3697<section title="Header Field Registration" anchor="header.field.registration">
3698<t>
3699   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3700   with the permanent registrations below (see <xref target="RFC3864"/>):
3701</t>
3702<?BEGININC p1-messaging.iana-headers ?>
3703<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3704<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3705   <ttcol>Header Field Name</ttcol>
3706   <ttcol>Protocol</ttcol>
3707   <ttcol>Status</ttcol>
3708   <ttcol>Reference</ttcol>
3709
3710   <c>Connection</c>
3711   <c>http</c>
3712   <c>standard</c>
3713   <c>
3714      <xref target="header.connection"/>
3715   </c>
3716   <c>Content-Length</c>
3717   <c>http</c>
3718   <c>standard</c>
3719   <c>
3720      <xref target="header.content-length"/>
3721   </c>
3722   <c>Date</c>
3723   <c>http</c>
3724   <c>standard</c>
3725   <c>
3726      <xref target="header.date"/>
3727   </c>
3728   <c>Host</c>
3729   <c>http</c>
3730   <c>standard</c>
3731   <c>
3732      <xref target="header.host"/>
3733   </c>
3734   <c>TE</c>
3735   <c>http</c>
3736   <c>standard</c>
3737   <c>
3738      <xref target="header.te"/>
3739   </c>
3740   <c>Trailer</c>
3741   <c>http</c>
3742   <c>standard</c>
3743   <c>
3744      <xref target="header.trailer"/>
3745   </c>
3746   <c>Transfer-Encoding</c>
3747   <c>http</c>
3748   <c>standard</c>
3749   <c>
3750      <xref target="header.transfer-encoding"/>
3751   </c>
3752   <c>Upgrade</c>
3753   <c>http</c>
3754   <c>standard</c>
3755   <c>
3756      <xref target="header.upgrade"/>
3757   </c>
3758   <c>Via</c>
3759   <c>http</c>
3760   <c>standard</c>
3761   <c>
3762      <xref target="header.via"/>
3763   </c>
3764</texttable>
3765<!--(END)-->
3766<?ENDINC p1-messaging.iana-headers ?>
3767<t>
3768   Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
3769   HTTP header field would be in conflict with the use of the "close" connection
3770   option for the "Connection" header field (<xref target="header.connection"/>).
3771</t>
3772<texttable align="left" suppress-title="true">
3773   <ttcol>Header Field Name</ttcol>
3774   <ttcol>Protocol</ttcol>
3775   <ttcol>Status</ttcol>
3776   <ttcol>Reference</ttcol>
3777
3778   <c>Close</c>
3779   <c>http</c>
3780   <c>reserved</c>
3781   <c>
3782      <xref target="header.field.registration"/>
3783   </c>
3784</texttable>
3785<t>
3786   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3787</t>
3788</section>
3789
3790<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3791<t>
3792   The entries for the "http" and "https" URI Schemes in the registry located at
3793   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3794   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3795   and <xref target="https.uri" format="counter"/> of this document
3796   (see <xref target="RFC4395"/>).
3797</t>
3798</section>
3799
3800<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3801<t>
3802   This document serves as the specification for the Internet media types
3803   "message/http" and "application/http". The following is to be registered with
3804   IANA (see <xref target="RFC4288"/>).
3805</t>
3806<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3807<iref item="Media Type" subitem="message/http" primary="true"/>
3808<iref item="message/http Media Type" primary="true"/>
3809<t>
3810   The message/http type can be used to enclose a single HTTP request or
3811   response message, provided that it obeys the MIME restrictions for all
3812   "message" types regarding line length and encodings.
3813</t>
3814<t>
3815  <list style="hanging" x:indent="12em">
3816    <t hangText="Type name:">
3817      message
3818    </t>
3819    <t hangText="Subtype name:">
3820      http
3821    </t>
3822    <t hangText="Required parameters:">
3823      none
3824    </t>
3825    <t hangText="Optional parameters:">
3826      version, msgtype
3827      <list style="hanging">
3828        <t hangText="version:">
3829          The HTTP-Version number of the enclosed message
3830          (e.g., "1.1"). If not present, the version can be
3831          determined from the first line of the body.
3832        </t>
3833        <t hangText="msgtype:">
3834          The message type &mdash; "request" or "response". If not
3835          present, the type can be determined from the first
3836          line of the body.
3837        </t>
3838      </list>
3839    </t>
3840    <t hangText="Encoding considerations:">
3841      only "7bit", "8bit", or "binary" are permitted
3842    </t>
3843    <t hangText="Security considerations:">
3844      none
3845    </t>
3846    <t hangText="Interoperability considerations:">
3847      none
3848    </t>
3849    <t hangText="Published specification:">
3850      This specification (see <xref target="internet.media.type.message.http"/>).
3851    </t>
3852    <t hangText="Applications that use this media type:">
3853    </t>
3854    <t hangText="Additional information:">
3855      <list style="hanging">
3856        <t hangText="Magic number(s):">none</t>
3857        <t hangText="File extension(s):">none</t>
3858        <t hangText="Macintosh file type code(s):">none</t>
3859      </list>
3860    </t>
3861    <t hangText="Person and email address to contact for further information:">
3862      See Authors Section.
3863    </t>
3864    <t hangText="Intended usage:">
3865      COMMON
3866    </t>
3867    <t hangText="Restrictions on usage:">
3868      none
3869    </t>
3870    <t hangText="Author/Change controller:">
3871      IESG
3872    </t>
3873  </list>
3874</t>
3875</section>
3876<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3877<iref item="Media Type" subitem="application/http" primary="true"/>
3878<iref item="application/http Media Type" primary="true"/>
3879<t>
3880   The application/http type can be used to enclose a pipeline of one or more
3881   HTTP request or response messages (not intermixed).
3882</t>
3883<t>
3884  <list style="hanging" x:indent="12em">
3885    <t hangText="Type name:">
3886      application
3887    </t>
3888    <t hangText="Subtype name:">
3889      http
3890    </t>
3891    <t hangText="Required parameters:">
3892      none
3893    </t>
3894    <t hangText="Optional parameters:">
3895      version, msgtype
3896      <list style="hanging">
3897        <t hangText="version:">
3898          The HTTP-Version number of the enclosed messages
3899          (e.g., "1.1"). If not present, the version can be
3900          determined from the first line of the body.
3901        </t>
3902        <t hangText="msgtype:">
3903          The message type &mdash; "request" or "response". If not
3904          present, the type can be determined from the first
3905          line of the body.
3906        </t>
3907      </list>
3908    </t>
3909    <t hangText="Encoding considerations:">
3910      HTTP messages enclosed by this type
3911      are in "binary" format; use of an appropriate
3912      Content-Transfer-Encoding is required when
3913      transmitted via E-mail.
3914    </t>
3915    <t hangText="Security considerations:">
3916      none
3917    </t>
3918    <t hangText="Interoperability considerations:">
3919      none
3920    </t>
3921    <t hangText="Published specification:">
3922      This specification (see <xref target="internet.media.type.application.http"/>).
3923    </t>
3924    <t hangText="Applications that use this media type:">
3925    </t>
3926    <t hangText="Additional information:">
3927      <list style="hanging">
3928        <t hangText="Magic number(s):">none</t>
3929        <t hangText="File extension(s):">none</t>
3930        <t hangText="Macintosh file type code(s):">none</t>
3931      </list>
3932    </t>
3933    <t hangText="Person and email address to contact for further information:">
3934      See Authors Section.
3935    </t>
3936    <t hangText="Intended usage:">
3937      COMMON
3938    </t>
3939    <t hangText="Restrictions on usage:">
3940      none
3941    </t>
3942    <t hangText="Author/Change controller:">
3943      IESG
3944    </t>
3945  </list>
3946</t>
3947</section>
3948</section>
3949
3950<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3951<t>
3952   The registration procedure for HTTP Transfer Codings is now defined by
3953   <xref target="transfer.coding.registry"/> of this document.
3954</t>
3955<t>
3956   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3957   shall be updated with the registrations below:
3958</t>
3959<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3960   <ttcol>Name</ttcol>
3961   <ttcol>Description</ttcol>
3962   <ttcol>Reference</ttcol>
3963   <c>chunked</c>
3964   <c>Transfer in a series of chunks</c>
3965   <c>
3966      <xref target="chunked.encoding"/>
3967   </c>
3968   <c>compress</c>
3969   <c>UNIX "compress" program method</c>
3970   <c>
3971      <xref target="compress.coding"/>
3972   </c>
3973   <c>deflate</c>
3974   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3975   the "zlib" data format (<xref target="RFC1950"/>)
3976   </c>
3977   <c>
3978      <xref target="deflate.coding"/>
3979   </c>
3980   <c>gzip</c>
3981   <c>Same as GNU zip <xref target="RFC1952"/></c>
3982   <c>
3983      <xref target="gzip.coding"/>
3984   </c>
3985</texttable>
3986</section>
3987
3988<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3989<t>
3990   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3991   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3992   by <xref target="upgrade.token.registry"/> of this document.
3993</t>
3994<t>
3995   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3996   shall be updated with the registration below:
3997</t>
3998<texttable align="left" suppress-title="true">
3999   <ttcol>Value</ttcol>
4000   <ttcol>Description</ttcol>
4001   <ttcol>Reference</ttcol>
4002
4003   <c>HTTP</c>
4004   <c>Hypertext Transfer Protocol</c> 
4005   <c><xref target="http.version"/> of this specification</c>
4006
4007</texttable>
4008</section>
4009
4010</section>
4011
4012<section title="Security Considerations" anchor="security.considerations">
4013<t>
4014   This section is meant to inform application developers, information
4015   providers, and users of the security limitations in HTTP/1.1 as
4016   described by this document. The discussion does not include
4017   definitive solutions to the problems revealed, though it does make
4018   some suggestions for reducing security risks.
4019</t>
4020
4021<section title="Personal Information" anchor="personal.information">
4022<t>
4023   HTTP clients are often privy to large amounts of personal information
4024   (e.g., the user's name, location, mail address, passwords, encryption
4025   keys, etc.), and &SHOULD; be very careful to prevent unintentional
4026   leakage of this information.
4027   We very strongly recommend that a convenient interface be provided
4028   for the user to control dissemination of such information, and that
4029   designers and implementors be particularly careful in this area.
4030   History shows that errors in this area often create serious security
4031   and/or privacy problems and generate highly adverse publicity for the
4032   implementor's company.
4033</t>
4034</section>
4035
4036<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
4037<t>
4038   A server is in the position to save personal data about a user's
4039   requests which might identify their reading patterns or subjects of
4040   interest. This information is clearly confidential in nature and its
4041   handling can be constrained by law in certain countries. People using
4042   HTTP to provide data are responsible for ensuring that
4043   such material is not distributed without the permission of any
4044   individuals that are identifiable by the published results.
4045</t>
4046</section>
4047
4048<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
4049<t>
4050   Implementations of HTTP origin servers &SHOULD; be careful to restrict
4051   the documents returned by HTTP requests to be only those that were
4052   intended by the server administrators. If an HTTP server translates
4053   HTTP URIs directly into file system calls, the server &MUST; take
4054   special care not to serve files that were not intended to be
4055   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
4056   other operating systems use ".." as a path component to indicate a
4057   directory level above the current one. On such a system, an HTTP
4058   server &MUST; disallow any such construct in the request-target if it
4059   would otherwise allow access to a resource outside those intended to
4060   be accessible via the HTTP server. Similarly, files intended for
4061   reference only internally to the server (such as access control
4062   files, configuration files, and script code) &MUST; be protected from
4063   inappropriate retrieval, since they might contain sensitive
4064   information. Experience has shown that minor bugs in such HTTP server
4065   implementations have turned into security risks.
4066</t>
4067</section>
4068
4069<section title="DNS-related Attacks" anchor="dns.related.attacks">
4070<t>
4071   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
4072   generally prone to security attacks based on the deliberate misassociation
4073   of IP addresses and DNS names not protected by DNSSec. Clients need to be
4074   cautious in assuming the validity of an IP number/DNS name association unless
4075   the response is protected by DNSSec (<xref target="RFC4033"/>).
4076</t>
4077</section>
4078
4079<section title="Proxies and Caching" anchor="attack.proxies">
4080<t>
4081   By their very nature, HTTP proxies are men-in-the-middle, and
4082   represent an opportunity for man-in-the-middle attacks. Compromise of
4083   the systems on which the proxies run can result in serious security
4084   and privacy problems. Proxies have access to security-related
4085   information, personal information about individual users and
4086   organizations, and proprietary information belonging to users and
4087   content providers. A compromised proxy, or a proxy implemented or
4088   configured without regard to security and privacy considerations,
4089   might be used in the commission of a wide range of potential attacks.
4090</t>
4091<t>
4092   Proxy operators need to protect the systems on which proxies run as
4093   they would protect any system that contains or transports sensitive
4094   information. In particular, log information gathered at proxies often
4095   contains highly sensitive personal information, and/or information
4096   about organizations. Log information needs to be carefully guarded, and
4097   appropriate guidelines for use need to be developed and followed.
4098   (<xref target="abuse.of.server.log.information"/>).
4099</t>
4100<t>
4101   Proxy implementors need to consider the privacy and security
4102   implications of their design and coding decisions, and of the
4103   configuration options they provide to proxy operators (especially the
4104   default configuration).
4105</t>
4106<t>
4107   Users of a proxy need to be aware that proxies are no trustworthier than
4108   the people who run them; HTTP itself cannot solve this problem.
4109</t>
4110<t>
4111   The judicious use of cryptography, when appropriate, might suffice to
4112   protect against a broad range of security and privacy attacks. Such
4113   cryptography is beyond the scope of the HTTP/1.1 specification.
4114</t>
4115</section>
4116
4117<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
4118<t>
4119   Because HTTP uses mostly textual, character-delimited fields, attackers can
4120   overflow buffers in implementations, and/or perform a Denial of Service
4121   against implementations that accept fields with unlimited lengths.
4122</t>
4123<t>
4124   To promote interoperability, this specification makes specific
4125   recommendations for size limits on request-targets (<xref target="request-target"/>)
4126   and blocks of header fields (<xref target="header.fields"/>). These are
4127   minimum recommendations, chosen to be supportable even by implementations
4128   with limited resources; it is expected that most implementations will choose
4129   substantially higher limits.
4130</t>
4131<t>
4132   This specification also provides a way for servers to reject messages that
4133   have request-targets that are too long (&status-414;) or request entities
4134   that are too large (&status-4xx;).
4135</t>
4136<t>
4137   Other fields (including but not limited to request methods, response status
4138   phrases, header field-names, and body chunks) &SHOULD; be limited by
4139   implementations carefully, so as to not impede interoperability.
4140</t>
4141</section>
4142
4143<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
4144<t>
4145   They exist. They are hard to defend against. Research continues.
4146   Beware.
4147</t>
4148</section>
4149</section>
4150
4151<section title="Acknowledgments" anchor="acks">
4152<t>
4153   This document revision builds on the work that went into
4154   <xref target="RFC2616" format="none">RFC 2616</xref> and its predecessors.
4155   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for detailed
4156   acknowledgements.
4157</t>
4158<t>
4159  <cref anchor="todoacks">Insert HTTPbis-specific acknowledgements here.</cref>
4160</t>
4161<!--
4162
4163Acknowledgements TODO list
4164
4165- Jeff Hodges ("effective request URI")
4166
4167-->
4168</section>
4169
4170</middle>
4171<back>
4172
4173<references title="Normative References">
4174
4175<reference anchor="ISO-8859-1">
4176  <front>
4177    <title>
4178     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4179    </title>
4180    <author>
4181      <organization>International Organization for Standardization</organization>
4182    </author>
4183    <date year="1998"/>
4184  </front>
4185  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4186</reference>
4187
4188<reference anchor="Part2">
4189  <front>
4190    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4191    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4192      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4193      <address><email>fielding@gbiv.com</email></address>
4194    </author>
4195    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4196      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4197      <address><email>jg@freedesktop.org</email></address>
4198    </author>
4199    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4200      <organization abbrev="HP">Hewlett-Packard Company</organization>
4201      <address><email>JeffMogul@acm.org</email></address>
4202    </author>
4203    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4204      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4205      <address><email>henrikn@microsoft.com</email></address>
4206    </author>
4207    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4208      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4209      <address><email>LMM@acm.org</email></address>
4210    </author>
4211    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4212      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4213      <address><email>paulle@microsoft.com</email></address>
4214    </author>
4215    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4216      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4217      <address><email>timbl@w3.org</email></address>
4218    </author>
4219    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4220      <organization abbrev="W3C">World Wide Web Consortium</organization>
4221      <address><email>ylafon@w3.org</email></address>
4222    </author>
4223    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4224      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4225      <address><email>julian.reschke@greenbytes.de</email></address>
4226    </author>
4227    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4228  </front>
4229  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4230  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4231</reference>
4232
4233<reference anchor="Part3">
4234  <front>
4235    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4236    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4237      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4238      <address><email>fielding@gbiv.com</email></address>
4239    </author>
4240    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4241      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4242      <address><email>jg@freedesktop.org</email></address>
4243    </author>
4244    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4245      <organization abbrev="HP">Hewlett-Packard Company</organization>
4246      <address><email>JeffMogul@acm.org</email></address>
4247    </author>
4248    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4249      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4250      <address><email>henrikn@microsoft.com</email></address>
4251    </author>
4252    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4253      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4254      <address><email>LMM@acm.org</email></address>
4255    </author>
4256    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4257      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4258      <address><email>paulle@microsoft.com</email></address>
4259    </author>
4260    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4261      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4262      <address><email>timbl@w3.org</email></address>
4263    </author>
4264    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4265      <organization abbrev="W3C">World Wide Web Consortium</organization>
4266      <address><email>ylafon@w3.org</email></address>
4267    </author>
4268    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4269      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4270      <address><email>julian.reschke@greenbytes.de</email></address>
4271    </author>
4272    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4273  </front>
4274  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4275  <x:source href="p3-payload.xml" basename="p3-payload"/>
4276</reference>
4277
4278<reference anchor="Part6">
4279  <front>
4280    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4281    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4282      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4283      <address><email>fielding@gbiv.com</email></address>
4284    </author>
4285    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4286      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4287      <address><email>jg@freedesktop.org</email></address>
4288    </author>
4289    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4290      <organization abbrev="HP">Hewlett-Packard Company</organization>
4291      <address><email>JeffMogul@acm.org</email></address>
4292    </author>
4293    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4294      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4295      <address><email>henrikn@microsoft.com</email></address>
4296    </author>
4297    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4298      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4299      <address><email>LMM@acm.org</email></address>
4300    </author>
4301    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4302      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4303      <address><email>paulle@microsoft.com</email></address>
4304    </author>
4305    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4306      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4307      <address><email>timbl@w3.org</email></address>
4308    </author>
4309    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4310      <organization abbrev="W3C">World Wide Web Consortium</organization>
4311      <address><email>ylafon@w3.org</email></address>
4312    </author>
4313    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4314      <address><email>mnot@mnot.net</email></address>
4315    </author>
4316    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4317      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4318      <address><email>julian.reschke@greenbytes.de</email></address>
4319    </author>
4320    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4321  </front>
4322  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4323  <x:source href="p6-cache.xml" basename="p6-cache"/>
4324</reference>
4325
4326<reference anchor="RFC5234">
4327  <front>
4328    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4329    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4330      <organization>Brandenburg InternetWorking</organization>
4331      <address>
4332        <email>dcrocker@bbiw.net</email>
4333      </address> 
4334    </author>
4335    <author initials="P." surname="Overell" fullname="Paul Overell">
4336      <organization>THUS plc.</organization>
4337      <address>
4338        <email>paul.overell@thus.net</email>
4339      </address>
4340    </author>
4341    <date month="January" year="2008"/>
4342  </front>
4343  <seriesInfo name="STD" value="68"/>
4344  <seriesInfo name="RFC" value="5234"/>
4345</reference>
4346
4347<reference anchor="RFC2119">
4348  <front>
4349    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4350    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4351      <organization>Harvard University</organization>
4352      <address><email>sob@harvard.edu</email></address>
4353    </author>
4354    <date month="March" year="1997"/>
4355  </front>
4356  <seriesInfo name="BCP" value="14"/>
4357  <seriesInfo name="RFC" value="2119"/>
4358</reference>
4359
4360<reference anchor="RFC3986">
4361 <front>
4362  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4363  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4364    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4365    <address>
4366       <email>timbl@w3.org</email>
4367       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4368    </address>
4369  </author>
4370  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4371    <organization abbrev="Day Software">Day Software</organization>
4372    <address>
4373      <email>fielding@gbiv.com</email>
4374      <uri>http://roy.gbiv.com/</uri>
4375    </address>
4376  </author>
4377  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4378    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4379    <address>
4380      <email>LMM@acm.org</email>
4381      <uri>http://larry.masinter.net/</uri>
4382    </address>
4383  </author>
4384  <date month='January' year='2005'></date>
4385 </front>
4386 <seriesInfo name="STD" value="66"/>
4387 <seriesInfo name="RFC" value="3986"/>
4388</reference>
4389
4390<reference anchor="USASCII">
4391  <front>
4392    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4393    <author>
4394      <organization>American National Standards Institute</organization>
4395    </author>
4396    <date year="1986"/>
4397  </front>
4398  <seriesInfo name="ANSI" value="X3.4"/>
4399</reference>
4400
4401<reference anchor="RFC1950">
4402  <front>
4403    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4404    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4405      <organization>Aladdin Enterprises</organization>
4406      <address><email>ghost@aladdin.com</email></address>
4407    </author>
4408    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4409    <date month="May" year="1996"/>
4410  </front>
4411  <seriesInfo name="RFC" value="1950"/>
4412  <annotation>
4413    RFC 1950 is an Informational RFC, thus it might be less stable than
4414    this specification. On the other hand, this downward reference was
4415    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4416    therefore it is unlikely to cause problems in practice. See also
4417    <xref target="BCP97"/>.
4418  </annotation>
4419</reference>
4420
4421<reference anchor="RFC1951">
4422  <front>
4423    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4424    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4425      <organization>Aladdin Enterprises</organization>
4426      <address><email>ghost@aladdin.com</email></address>
4427    </author>
4428    <date month="May" year="1996"/>
4429  </front>
4430  <seriesInfo name="RFC" value="1951"/>
4431  <annotation>
4432    RFC 1951 is an Informational RFC, thus it might be less stable than
4433    this specification. On the other hand, this downward reference was
4434    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4435    therefore it is unlikely to cause problems in practice. See also
4436    <xref target="BCP97"/>.
4437  </annotation>
4438</reference>
4439
4440<reference anchor="RFC1952">
4441  <front>
4442    <title>GZIP file format specification version 4.3</title>
4443    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4444      <organization>Aladdin Enterprises</organization>
4445      <address><email>ghost@aladdin.com</email></address>
4446    </author>
4447    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4448      <address><email>gzip@prep.ai.mit.edu</email></address>
4449    </author>
4450    <author initials="M." surname="Adler" fullname="Mark Adler">
4451      <address><email>madler@alumni.caltech.edu</email></address>
4452    </author>
4453    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4454      <address><email>ghost@aladdin.com</email></address>
4455    </author>
4456    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4457      <address><email>randeg@alumni.rpi.edu</email></address>
4458    </author>
4459    <date month="May" year="1996"/>
4460  </front>
4461  <seriesInfo name="RFC" value="1952"/>
4462  <annotation>
4463    RFC 1952 is an Informational RFC, thus it might be less stable than
4464    this specification. On the other hand, this downward reference was
4465    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4466    therefore it is unlikely to cause problems in practice. See also
4467    <xref target="BCP97"/>.
4468  </annotation>
4469</reference>
4470
4471</references>
4472
4473<references title="Informative References">
4474
4475<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4476  <front>
4477    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4478    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4479    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4480    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4481    <author initials="H." surname="Lie" fullname="H. Lie"/>
4482    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4483    <date year="1997" month="September"/>
4484  </front>
4485  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4486</reference>
4487
4488<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4489  <front>
4490    <title>Improving HTTP Latency</title>
4491    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4492    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4493    <date year="1995" month="December"/>
4494  </front>
4495  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4496</reference>
4497
4498<reference anchor="RFC1123">
4499  <front>
4500    <title>Requirements for Internet Hosts - Application and Support</title>
4501    <author initials="R." surname="Braden" fullname="Robert Braden">
4502      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4503      <address><email>Braden@ISI.EDU</email></address>
4504    </author>
4505    <date month="October" year="1989"/>
4506  </front>
4507  <seriesInfo name="STD" value="3"/>
4508  <seriesInfo name="RFC" value="1123"/>
4509</reference>
4510
4511<reference anchor='RFC1919'>
4512  <front>
4513    <title>Classical versus Transparent IP Proxies</title>
4514    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4515      <address><email>mchatel@pax.eunet.ch</email></address>
4516    </author>
4517    <date year='1996' month='March' />
4518  </front>
4519  <seriesInfo name='RFC' value='1919' />
4520</reference>
4521
4522<reference anchor="RFC1945">
4523  <front>
4524    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4525    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4526      <organization>MIT, Laboratory for Computer Science</organization>
4527      <address><email>timbl@w3.org</email></address>
4528    </author>
4529    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4530      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4531      <address><email>fielding@ics.uci.edu</email></address>
4532    </author>
4533    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4534      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4535      <address><email>frystyk@w3.org</email></address>
4536    </author>
4537    <date month="May" year="1996"/>
4538  </front>
4539  <seriesInfo name="RFC" value="1945"/>
4540</reference>
4541
4542<reference anchor="RFC2045">
4543  <front>
4544    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4545    <author initials="N." surname="Freed" fullname="Ned Freed">
4546      <organization>Innosoft International, Inc.</organization>
4547      <address><email>ned@innosoft.com</email></address>
4548    </author>
4549    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4550      <organization>First Virtual Holdings</organization>
4551      <address><email>nsb@nsb.fv.com</email></address>
4552    </author>
4553    <date month="November" year="1996"/>
4554  </front>
4555  <seriesInfo name="RFC" value="2045"/>
4556</reference>
4557
4558<reference anchor="RFC2047">
4559  <front>
4560    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4561    <author initials="K." surname="Moore" fullname="Keith Moore">
4562      <organization>University of Tennessee</organization>
4563      <address><email>moore@cs.utk.edu</email></address>
4564    </author>
4565    <date month="November" year="1996"/>
4566  </front>
4567  <seriesInfo name="RFC" value="2047"/>
4568</reference>
4569
4570<reference anchor="RFC2068">
4571  <front>
4572    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4573    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4574      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4575      <address><email>fielding@ics.uci.edu</email></address>
4576    </author>
4577    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4578      <organization>MIT Laboratory for Computer Science</organization>
4579      <address><email>jg@w3.org</email></address>
4580    </author>
4581    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4582      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4583      <address><email>mogul@wrl.dec.com</email></address>
4584    </author>
4585    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4586      <organization>MIT Laboratory for Computer Science</organization>
4587      <address><email>frystyk@w3.org</email></address>
4588    </author>
4589    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4590      <organization>MIT Laboratory for Computer Science</organization>
4591      <address><email>timbl@w3.org</email></address>
4592    </author>
4593    <date month="January" year="1997"/>
4594  </front>
4595  <seriesInfo name="RFC" value="2068"/>
4596</reference>
4597
4598<reference anchor="RFC2145">
4599  <front>
4600    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4601    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4602      <organization>Western Research Laboratory</organization>
4603      <address><email>mogul@wrl.dec.com</email></address>
4604    </author>
4605    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4606      <organization>Department of Information and Computer Science</organization>
4607      <address><email>fielding@ics.uci.edu</email></address>
4608    </author>
4609    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4610      <organization>MIT Laboratory for Computer Science</organization>
4611      <address><email>jg@w3.org</email></address>
4612    </author>
4613    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4614      <organization>W3 Consortium</organization>
4615      <address><email>frystyk@w3.org</email></address>
4616    </author>
4617    <date month="May" year="1997"/>
4618  </front>
4619  <seriesInfo name="RFC" value="2145"/>
4620</reference>
4621
4622<reference anchor="RFC2616">
4623  <front>
4624    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4625    <author initials="R." surname="Fielding" fullname="R. Fielding">
4626      <organization>University of California, Irvine</organization>
4627      <address><email>fielding@ics.uci.edu</email></address>
4628    </author>
4629    <author initials="J." surname="Gettys" fullname="J. Gettys">
4630      <organization>W3C</organization>
4631      <address><email>jg@w3.org</email></address>
4632    </author>
4633    <author initials="J." surname="Mogul" fullname="J. Mogul">
4634      <organization>Compaq Computer Corporation</organization>
4635      <address><email>mogul@wrl.dec.com</email></address>
4636    </author>
4637    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4638      <organization>MIT Laboratory for Computer Science</organization>
4639      <address><email>frystyk@w3.org</email></address>
4640    </author>
4641    <author initials="L." surname="Masinter" fullname="L. Masinter">
4642      <organization>Xerox Corporation</organization>
4643      <address><email>masinter@parc.xerox.com</email></address>
4644    </author>
4645    <author initials="P." surname="Leach" fullname="P. Leach">
4646      <organization>Microsoft Corporation</organization>
4647      <address><email>paulle@microsoft.com</email></address>
4648    </author>
4649    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4650      <organization>W3C</organization>
4651      <address><email>timbl@w3.org</email></address>
4652    </author>
4653    <date month="June" year="1999"/>
4654  </front>
4655  <seriesInfo name="RFC" value="2616"/>
4656</reference>
4657
4658<reference anchor='RFC2817'>
4659  <front>
4660    <title>Upgrading to TLS Within HTTP/1.1</title>
4661    <author initials='R.' surname='Khare' fullname='R. Khare'>
4662      <organization>4K Associates / UC Irvine</organization>
4663      <address><email>rohit@4K-associates.com</email></address>
4664    </author>
4665    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4666      <organization>Agranat Systems, Inc.</organization>
4667      <address><email>lawrence@agranat.com</email></address>
4668    </author>
4669    <date year='2000' month='May' />
4670  </front>
4671  <seriesInfo name='RFC' value='2817' />
4672</reference>
4673
4674<reference anchor='RFC2818'>
4675  <front>
4676    <title>HTTP Over TLS</title>
4677    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4678      <organization>RTFM, Inc.</organization>
4679      <address><email>ekr@rtfm.com</email></address>
4680    </author>
4681    <date year='2000' month='May' />
4682  </front>
4683  <seriesInfo name='RFC' value='2818' />
4684</reference>
4685
4686<reference anchor='RFC2965'>
4687  <front>
4688    <title>HTTP State Management Mechanism</title>
4689    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4690      <organization>Bell Laboratories, Lucent Technologies</organization>
4691      <address><email>dmk@bell-labs.com</email></address>
4692    </author>
4693    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4694      <organization>Epinions.com, Inc.</organization>
4695      <address><email>lou@montulli.org</email></address>
4696    </author>
4697    <date year='2000' month='October' />
4698  </front>
4699  <seriesInfo name='RFC' value='2965' />
4700</reference>
4701
4702<reference anchor='RFC3040'>
4703  <front>
4704    <title>Internet Web Replication and Caching Taxonomy</title>
4705    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4706      <organization>Equinix, Inc.</organization>
4707    </author>
4708    <author initials='I.' surname='Melve' fullname='I. Melve'>
4709      <organization>UNINETT</organization>
4710    </author>
4711    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4712      <organization>CacheFlow Inc.</organization>
4713    </author>
4714    <date year='2001' month='January' />
4715  </front>
4716  <seriesInfo name='RFC' value='3040' />
4717</reference>
4718
4719<reference anchor='RFC3864'>
4720  <front>
4721    <title>Registration Procedures for Message Header Fields</title>
4722    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4723      <organization>Nine by Nine</organization>
4724      <address><email>GK-IETF@ninebynine.org</email></address>
4725    </author>
4726    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4727      <organization>BEA Systems</organization>
4728      <address><email>mnot@pobox.com</email></address>
4729    </author>
4730    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4731      <organization>HP Labs</organization>
4732      <address><email>JeffMogul@acm.org</email></address>
4733    </author>
4734    <date year='2004' month='September' />
4735  </front>
4736  <seriesInfo name='BCP' value='90' />
4737  <seriesInfo name='RFC' value='3864' />
4738</reference>
4739
4740<reference anchor='RFC4033'>
4741  <front>
4742    <title>DNS Security Introduction and Requirements</title>
4743    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4744    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4745    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4746    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4747    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4748    <date year='2005' month='March' />
4749  </front>
4750  <seriesInfo name='RFC' value='4033' />
4751</reference>
4752
4753<reference anchor="RFC4288">
4754  <front>
4755    <title>Media Type Specifications and Registration Procedures</title>
4756    <author initials="N." surname="Freed" fullname="N. Freed">
4757      <organization>Sun Microsystems</organization>
4758      <address>
4759        <email>ned.freed@mrochek.com</email>
4760      </address>
4761    </author>
4762    <author initials="J." surname="Klensin" fullname="J. Klensin">
4763      <address>
4764        <email>klensin+ietf@jck.com</email>
4765      </address>
4766    </author>
4767    <date year="2005" month="December"/>
4768  </front>
4769  <seriesInfo name="BCP" value="13"/>
4770  <seriesInfo name="RFC" value="4288"/>
4771</reference>
4772
4773<reference anchor='RFC4395'>
4774  <front>
4775    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4776    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4777      <organization>AT&amp;T Laboratories</organization>
4778      <address>
4779        <email>tony+urireg@maillennium.att.com</email>
4780      </address>
4781    </author>
4782    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4783      <organization>Qualcomm, Inc.</organization>
4784      <address>
4785        <email>hardie@qualcomm.com</email>
4786      </address>
4787    </author>
4788    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4789      <organization>Adobe Systems</organization>
4790      <address>
4791        <email>LMM@acm.org</email>
4792      </address>
4793    </author>
4794    <date year='2006' month='February' />
4795  </front>
4796  <seriesInfo name='BCP' value='115' />
4797  <seriesInfo name='RFC' value='4395' />
4798</reference>
4799
4800<reference anchor='RFC4559'>
4801  <front>
4802    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4803    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4804    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4805    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4806    <date year='2006' month='June' />
4807  </front>
4808  <seriesInfo name='RFC' value='4559' />
4809</reference>
4810
4811<reference anchor='RFC5226'>
4812  <front>
4813    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4814    <author initials='T.' surname='Narten' fullname='T. Narten'>
4815      <organization>IBM</organization>
4816      <address><email>narten@us.ibm.com</email></address>
4817    </author>
4818    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4819      <organization>Google</organization>
4820      <address><email>Harald@Alvestrand.no</email></address>
4821    </author>
4822    <date year='2008' month='May' />
4823  </front>
4824  <seriesInfo name='BCP' value='26' />
4825  <seriesInfo name='RFC' value='5226' />
4826</reference>
4827
4828<reference anchor="RFC5322">
4829  <front>
4830    <title>Internet Message Format</title>
4831    <author initials="P." surname="Resnick" fullname="P. Resnick">
4832      <organization>Qualcomm Incorporated</organization>
4833    </author>
4834    <date year="2008" month="October"/>
4835  </front> 
4836  <seriesInfo name="RFC" value="5322"/>
4837</reference>
4838
4839<reference anchor="RFC6265">
4840  <front>
4841    <title>HTTP State Management Mechanism</title>
4842    <author initials="A." surname="Barth" fullname="Adam Barth">
4843      <organization abbrev="U.C. Berkeley">
4844        University of California, Berkeley
4845      </organization>
4846      <address><email>abarth@eecs.berkeley.edu</email></address>
4847    </author>
4848    <date year="2011" month="April" />
4849  </front>
4850  <seriesInfo name="RFC" value="6265"/>
4851</reference>
4852
4853<reference anchor='BCP97'>
4854  <front>
4855    <title>Handling Normative References to Standards-Track Documents</title>
4856    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4857      <address>
4858        <email>klensin+ietf@jck.com</email>
4859      </address>
4860    </author>
4861    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4862      <organization>MIT</organization>
4863      <address>
4864        <email>hartmans-ietf@mit.edu</email>
4865      </address>
4866    </author>
4867    <date year='2007' month='June' />
4868  </front>
4869  <seriesInfo name='BCP' value='97' />
4870  <seriesInfo name='RFC' value='4897' />
4871</reference>
4872
4873<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4874  <front>
4875    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4876    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4877    <date year="2001" month="November"/>
4878  </front>
4879  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4880</reference>
4881
4882<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4883  <front>
4884    <title>Analysis of HTTP Performance Problems</title>
4885    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4886    <date/>
4887  </front>
4888</reference>
4889
4890<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4891  <front>
4892  <title>Analysis of HTTP Performance</title>
4893  <author initials="J." surname="Touch" fullname="Joe Touch">
4894    <organization>USC/Information Sciences Institute</organization>
4895    <address><email>touch@isi.edu</email></address>
4896  </author>
4897  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4898    <organization>USC/Information Sciences Institute</organization>
4899    <address><email>johnh@isi.edu</email></address>
4900  </author>
4901  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4902    <organization>USC/Information Sciences Institute</organization>
4903    <address><email>katia@isi.edu</email></address>
4904  </author>
4905  <date year="1998" month="Aug"/>
4906  </front>
4907  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4908  <annotation>(original report dated Aug. 1996)</annotation>
4909</reference>
4910
4911</references>
4912
4913
4914<section title="HTTP Version History" anchor="compatibility">
4915<t>
4916   HTTP has been in use by the World-Wide Web global information initiative
4917   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4918   was a simple protocol for hypertext data transfer across the Internet
4919   with only a single request method (GET) and no metadata.
4920   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4921   methods and MIME-like messaging that could include metadata about the data
4922   transferred and modifiers on the request/response semantics. However,
4923   HTTP/1.0 did not sufficiently take into consideration the effects of
4924   hierarchical proxies, caching, the need for persistent connections, or
4925   name-based virtual hosts. The proliferation of incompletely-implemented
4926   applications calling themselves "HTTP/1.0" further necessitated a
4927   protocol version change in order for two communicating applications
4928   to determine each other's true capabilities.
4929</t>
4930<t>
4931   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4932   requirements that enable reliable implementations, adding only
4933   those new features that will either be safely ignored by an HTTP/1.0
4934   recipient or only sent when communicating with a party advertising
4935   compliance with HTTP/1.1.
4936</t>
4937<t>
4938   It is beyond the scope of a protocol specification to mandate
4939   compliance with previous versions. HTTP/1.1 was deliberately
4940   designed, however, to make supporting previous versions easy.
4941   We would expect a general-purpose HTTP/1.1 server to understand
4942   any valid request in the format of HTTP/1.0 and respond appropriately
4943   with an HTTP/1.1 message that only uses features understood (or
4944   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4945   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4946</t>
4947<t>
4948   Since HTTP/0.9 did not support header fields in a request,
4949   there is no mechanism for it to support name-based virtual
4950   hosts (selection of resource by inspection of the Host header
4951   field).  Any server that implements name-based virtual hosts
4952   ought to disable support for HTTP/0.9.  Most requests that
4953   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4954   requests wherein a buggy client failed to properly encode
4955   linear whitespace found in a URI reference and placed in
4956   the request-target.
4957</t>
4958
4959<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4960<t>
4961   This section summarizes major differences between versions HTTP/1.0
4962   and HTTP/1.1.
4963</t>
4964
4965<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4966<t>
4967   The requirements that clients and servers support the Host header
4968   field (<xref target="header.host"/>), report an error if it is
4969   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4970   are among the most important changes defined by HTTP/1.1.
4971</t>
4972<t>
4973   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4974   addresses and servers; there was no other established mechanism for
4975   distinguishing the intended server of a request than the IP address
4976   to which that request was directed. The Host header field was
4977   introduced during the development of HTTP/1.1 and, though it was
4978   quickly implemented by most HTTP/1.0 browsers, additional requirements
4979   were placed on all HTTP/1.1 requests in order to ensure complete
4980   adoption.  At the time of this writing, most HTTP-based services
4981   are dependent upon the Host header field for targeting requests.
4982</t>
4983</section>
4984
4985<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4986<t>
4987   For most implementations of HTTP/1.0, each connection is established
4988   by the client prior to the request and closed by the server after
4989   sending the response. However, some implementations implement the
4990   Keep-Alive version of persistent connections described in
4991   <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4992</t>
4993<t>
4994   Some clients and servers might wish to be compatible with some
4995   previous implementations of persistent connections in HTTP/1.0
4996   clients and servers. Persistent connections in HTTP/1.0 are
4997   explicitly negotiated as they are not the default behavior. HTTP/1.0
4998   experimental implementations of persistent connections are faulty,
4999   and the new facilities in HTTP/1.1 are designed to rectify these
5000   problems. The problem was that some existing HTTP/1.0 clients might
5001   send Keep-Alive to a proxy server that doesn't understand
5002   Connection, which would then erroneously forward it to the next
5003   inbound server, which would establish the Keep-Alive connection and
5004   result in a hung HTTP/1.0 proxy waiting for the close on the
5005   response. The result is that HTTP/1.0 clients must be prevented from
5006   using Keep-Alive when talking to proxies.
5007</t>
5008<t>
5009   However, talking to proxies is the most important use of persistent
5010   connections, so that prohibition is clearly unacceptable. Therefore,
5011   we need some other mechanism for indicating a persistent connection
5012   is desired, which is safe to use even when talking to an old proxy
5013   that ignores Connection. Persistent connections are the default for
5014   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
5015   declaring non-persistence. See <xref target="header.connection"/>.
5016</t>
5017</section>
5018</section>
5019
5020<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
5021<t>
5022  Empty list elements in list productions have been deprecated.
5023  (<xref target="notation.abnf"/>)
5024</t>
5025<t>
5026  Rules about implicit linear whitespace between certain grammar productions
5027  have been removed; now it's only allowed when specifically pointed out
5028  in the ABNF.
5029  (<xref target="basic.rules"/>)
5030</t>
5031<t>
5032  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
5033  sensitive. Restrict the version numbers to be single digits due to the fact
5034  that implementations are known to handle multi-digit version numbers
5035  incorrectly.
5036  (<xref target="http.version"/>)
5037</t>
5038<t>
5039  Require that invalid whitespace around field-names be rejected.
5040  (<xref target="header.fields"/>)
5041</t>
5042<t> 
5043  The NUL octet is no longer allowed in comment and quoted-string
5044  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
5045  Non-ASCII content in header fields and reason phrase has been obsoleted and
5046  made opaque (the TEXT rule was removed).
5047  (<xref target="field.rules"/>)
5048</t>
5049<t>
5050  Require recipients to handle bogus Content-Length header fields as errors.
5051  (<xref target="message.body"/>)
5052</t>
5053<t>
5054  Remove reference to non-existent identity transfer-coding value tokens.
5055  (Sections <xref format="counter" target="message.body"/> and
5056  <xref format="counter" target="transfer.codings"/>)
5057</t>
5058<t>
5059  Update use of abs_path production from RFC 1808 to the path-absolute + query
5060  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5061  request method only.
5062  (<xref target="request-target"/>)
5063</t>
5064<t>
5065  Clarification that the chunk length does not include the count of the octets
5066  in the chunk header and trailer. Furthermore disallowed line folding
5067  in chunk extensions.
5068  (<xref target="chunked.encoding"/>)
5069</t>
5070<t>
5071  Remove hard limit of two connections per server.
5072  (<xref target="persistent.practical"/>)
5073</t>
5074<t>
5075  Change ABNF productions for header fields to only define the field value.
5076  (<xref target="header.field.definitions"/>)
5077</t>
5078<t>
5079  Clarify exactly when close connection options must be sent.
5080  (<xref target="header.connection"/>)
5081</t>
5082<t>
5083  Define the semantics of the "Upgrade" header field in responses other than
5084  101 (this was incorporated from <xref target="RFC2817"/>).
5085  (<xref target="header.upgrade"/>)
5086</t>
5087</section>
5088</section>
5089
5090<?BEGININC p1-messaging.abnf-appendix ?>
5091<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
5092<figure>
5093<artwork type="abnf" name="p1-messaging.parsed-abnf">
5094<x:ref>BWS</x:ref> = OWS
5095
5096<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5097<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5098 connection-token ] )
5099<x:ref>Content-Length</x:ref> = 1*DIGIT
5100
5101<x:ref>Date</x:ref> = HTTP-date
5102
5103<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
5104
5105<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5106<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" DIGIT "." DIGIT
5107<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
5108<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5109 ]
5110<x:ref>Host</x:ref> = uri-host [ ":" port ]
5111
5112<x:ref>Method</x:ref> = token
5113
5114<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
5115
5116<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
5117<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
5118<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5119<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5120<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5121
5122<x:ref>Status-Code</x:ref> = 3DIGIT
5123<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5124
5125<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5126<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5127<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5128 transfer-coding ] )
5129
5130<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5131<x:ref>Upgrade</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5132
5133<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5134 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5135 )
5136
5137<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5138<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5139<x:ref>attribute</x:ref> = token
5140<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5141
5142<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5143<x:ref>chunk-data</x:ref> = 1*OCTET
5144<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5145<x:ref>chunk-ext-name</x:ref> = token
5146<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5147<x:ref>chunk-size</x:ref> = 1*HEXDIG
5148<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5149<x:ref>connection-token</x:ref> = token
5150<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5151 / %x2A-5B ; '*'-'['
5152 / %x5D-7E ; ']'-'~'
5153 / obs-text
5154
5155<x:ref>date1</x:ref> = day SP month SP year
5156<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5157<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5158<x:ref>day</x:ref> = 2DIGIT
5159<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5160 / %x54.75.65 ; Tue
5161 / %x57.65.64 ; Wed
5162 / %x54.68.75 ; Thu
5163 / %x46.72.69 ; Fri
5164 / %x53.61.74 ; Sat
5165 / %x53.75.6E ; Sun
5166<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5167 / %x54.75.65.73.64.61.79 ; Tuesday
5168 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
5169 / %x54.68.75.72.73.64.61.79 ; Thursday
5170 / %x46.72.69.64.61.79 ; Friday
5171 / %x53.61.74.75.72.64.61.79 ; Saturday
5172 / %x53.75.6E.64.61.79 ; Sunday
5173
5174<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5175<x:ref>field-name</x:ref> = token
5176<x:ref>field-value</x:ref> = *( field-content / OWS )
5177
5178<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5179<x:ref>hour</x:ref> = 2DIGIT
5180<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5181<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5182
5183<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5184
5185<x:ref>message-body</x:ref> = *OCTET
5186<x:ref>minute</x:ref> = 2DIGIT
5187<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5188 / %x46.65.62 ; Feb
5189 / %x4D.61.72 ; Mar
5190 / %x41.70.72 ; Apr
5191 / %x4D.61.79 ; May
5192 / %x4A.75.6E ; Jun
5193 / %x4A.75.6C ; Jul
5194 / %x41.75.67 ; Aug
5195 / %x53.65.70 ; Sep
5196 / %x4F.63.74 ; Oct
5197 / %x4E.6F.76 ; Nov
5198 / %x44.65.63 ; Dec
5199
5200<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5201<x:ref>obs-fold</x:ref> = CRLF
5202<x:ref>obs-text</x:ref> = %x80-FF
5203
5204<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5205<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5206<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5207<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5208<x:ref>product</x:ref> = token [ "/" product-version ]
5209<x:ref>product-version</x:ref> = token
5210<x:ref>protocol-name</x:ref> = token
5211<x:ref>protocol-version</x:ref> = token
5212<x:ref>pseudonym</x:ref> = token
5213
5214<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5215 / %x5D-7E ; ']'-'~'
5216 / obs-text
5217<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5218 / %x5D-7E ; ']'-'~'
5219 / obs-text
5220<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5221<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5222<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5223<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5224<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5225<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5226
5227<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5228<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5229<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5230<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5231 / authority
5232<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5233<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5234
5235<x:ref>second</x:ref> = 2DIGIT
5236<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5237 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5238<x:ref>start-line</x:ref> = Request-Line / Status-Line
5239
5240<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5241<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5242 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5243<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5244<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5245<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5246<x:ref>token</x:ref> = 1*tchar
5247<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5248<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5249 transfer-extension
5250<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5251<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5252
5253<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5254
5255<x:ref>value</x:ref> = word
5256
5257<x:ref>word</x:ref> = token / quoted-string
5258
5259<x:ref>year</x:ref> = 4DIGIT
5260</artwork>
5261</figure>
5262<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5263; Chunked-Body defined but not used
5264; Connection defined but not used
5265; Content-Length defined but not used
5266; Date defined but not used
5267; HTTP-message defined but not used
5268; Host defined but not used
5269; Request defined but not used
5270; Response defined but not used
5271; TE defined but not used
5272; Trailer defined but not used
5273; Transfer-Encoding defined but not used
5274; URI-reference defined but not used
5275; Upgrade defined but not used
5276; Via defined but not used
5277; http-URI defined but not used
5278; https-URI defined but not used
5279; partial-URI defined but not used
5280; special defined but not used
5281</artwork></figure></section>
5282<?ENDINC p1-messaging.abnf-appendix ?>
5283
5284<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5285
5286<section title="Since RFC 2616">
5287<t>
5288  Extracted relevant partitions from <xref target="RFC2616"/>.
5289</t>
5290</section>
5291
5292<section title="Since draft-ietf-httpbis-p1-messaging-00">
5293<t>
5294  Closed issues:
5295  <list style="symbols"> 
5296    <t>
5297      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5298      "HTTP Version should be case sensitive"
5299      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5300    </t>
5301    <t>
5302      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5303      "'unsafe' characters"
5304      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5305    </t>
5306    <t>
5307      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5308      "Chunk Size Definition"
5309      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5310    </t>
5311    <t>
5312      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5313      "Message Length"
5314      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5315    </t>
5316    <t>
5317      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5318      "Media Type Registrations"
5319      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5320    </t>
5321    <t>
5322      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5323      "URI includes query"
5324      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5325    </t>
5326    <t>
5327      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5328      "No close on 1xx responses"
5329      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5330    </t>
5331    <t>
5332      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5333      "Remove 'identity' token references"
5334      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5335    </t>
5336    <t>
5337      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5338      "Import query BNF"
5339    </t>
5340    <t>
5341      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5342      "qdtext BNF"
5343    </t>
5344    <t>
5345      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5346      "Normative and Informative references"
5347    </t>
5348    <t>
5349      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5350      "RFC2606 Compliance"
5351    </t>
5352    <t>
5353      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5354      "RFC977 reference"
5355    </t>
5356    <t>
5357      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5358      "RFC1700 references"
5359    </t>
5360    <t>
5361      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5362      "inconsistency in date format explanation"
5363    </t>
5364    <t>
5365      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5366      "Date reference typo"
5367    </t>
5368    <t>
5369      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5370      "Informative references"
5371    </t>
5372    <t>
5373      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5374      "ISO-8859-1 Reference"
5375    </t>
5376    <t>
5377      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5378      "Normative up-to-date references"
5379    </t>
5380  </list>
5381</t>
5382<t>
5383  Other changes:
5384  <list style="symbols"> 
5385    <t>
5386      Update media type registrations to use RFC4288 template.
5387    </t>
5388    <t>
5389      Use names of RFC4234 core rules DQUOTE and WSP,
5390      fix broken ABNF for chunk-data
5391      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5392    </t>
5393  </list>
5394</t>
5395</section>
5396
5397<section title="Since draft-ietf-httpbis-p1-messaging-01">
5398<t>
5399  Closed issues:
5400  <list style="symbols"> 
5401    <t>
5402      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5403      "Bodies on GET (and other) requests"
5404    </t>
5405    <t>
5406      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5407      "Updating to RFC4288"
5408    </t>
5409    <t>
5410      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5411      "Status Code and Reason Phrase"
5412    </t>
5413    <t>
5414      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5415      "rel_path not used"
5416    </t>
5417  </list>
5418</t>
5419<t>
5420  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5421  <list style="symbols"> 
5422    <t>
5423      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5424      "trailer-part").
5425    </t>
5426    <t>
5427      Avoid underscore character in rule names ("http_URL" ->
5428      "http-URL", "abs_path" -> "path-absolute").
5429    </t>
5430    <t>
5431      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5432      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5433      have to be updated when switching over to RFC3986.
5434    </t>
5435    <t>
5436      Synchronize core rules with RFC5234.
5437    </t>
5438    <t>
5439      Get rid of prose rules that span multiple lines.
5440    </t>
5441    <t>
5442      Get rid of unused rules LOALPHA and UPALPHA.
5443    </t>
5444    <t>
5445      Move "Product Tokens" section (back) into Part 1, as "token" is used
5446      in the definition of the Upgrade header field.
5447    </t>
5448    <t>
5449      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5450    </t>
5451    <t>
5452      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5453    </t>
5454  </list>
5455</t>
5456</section>
5457
5458<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5459<t>
5460  Closed issues:
5461  <list style="symbols"> 
5462    <t>
5463      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5464      "HTTP-date vs. rfc1123-date"
5465    </t>
5466    <t>
5467      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5468      "WS in quoted-pair"
5469    </t>
5470  </list>
5471</t>
5472<t>
5473  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5474  <list style="symbols"> 
5475    <t>
5476      Reference RFC 3984, and update header field registrations for headers defined
5477      in this document.
5478    </t>
5479  </list>
5480</t>
5481<t>
5482  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5483  <list style="symbols"> 
5484    <t>
5485      Replace string literals when the string really is case-sensitive (HTTP-Version).
5486    </t>
5487  </list>
5488</t>
5489</section>
5490
5491<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5492<t>
5493  Closed issues:
5494  <list style="symbols"> 
5495    <t>
5496      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5497      "Connection closing"
5498    </t>
5499    <t>
5500      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5501      "Move registrations and registry information to IANA Considerations"
5502    </t>
5503    <t>
5504      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5505      "need new URL for PAD1995 reference"
5506    </t>
5507    <t>
5508      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5509      "IANA Considerations: update HTTP URI scheme registration"
5510    </t>
5511    <t>
5512      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5513      "Cite HTTPS URI scheme definition"
5514    </t>
5515    <t>
5516      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5517      "List-type headers vs Set-Cookie"
5518    </t>
5519  </list>
5520</t>
5521<t>
5522  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5523  <list style="symbols"> 
5524    <t>
5525      Replace string literals when the string really is case-sensitive (HTTP-Date).
5526    </t>
5527    <t>
5528      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5529    </t>
5530  </list>
5531</t>
5532</section>
5533
5534<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5535<t>
5536  Closed issues:
5537  <list style="symbols"> 
5538    <t>
5539      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5540      "Out-of-date reference for URIs"
5541    </t>
5542    <t>
5543      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5544      "RFC 2822 is updated by RFC 5322"
5545    </t>
5546  </list>
5547</t>
5548<t>
5549  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5550  <list style="symbols"> 
5551    <t>
5552      Use "/" instead of "|" for alternatives.
5553    </t>
5554    <t>
5555      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5556    </t>
5557    <t>
5558      Only reference RFC 5234's core rules.
5559    </t>
5560    <t>
5561      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5562      whitespace ("OWS") and required whitespace ("RWS").
5563    </t>
5564    <t>
5565      Rewrite ABNFs to spell out whitespace rules, factor out
5566      header field value format definitions.
5567    </t>
5568  </list>
5569</t>
5570</section>
5571
5572<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5573<t>
5574  Closed issues:
5575  <list style="symbols"> 
5576    <t>
5577      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5578      "Header LWS"
5579    </t>
5580    <t>
5581      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5582      "Sort 1.3 Terminology"
5583    </t>
5584    <t>
5585      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5586      "RFC2047 encoded words"
5587    </t>
5588    <t>
5589      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5590      "Character Encodings in TEXT"
5591    </t>
5592    <t>
5593      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5594      "Line Folding"
5595    </t>
5596    <t>
5597      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5598      "OPTIONS * and proxies"
5599    </t>
5600    <t>
5601      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5602      "Reason-Phrase BNF"
5603    </t>
5604    <t>
5605      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5606      "Use of TEXT"
5607    </t>
5608    <t>
5609      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5610      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5611    </t>
5612    <t>
5613      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5614      "RFC822 reference left in discussion of date formats"
5615    </t>
5616  </list>
5617</t>
5618<t>
5619  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5620  <list style="symbols"> 
5621    <t>
5622      Rewrite definition of list rules, deprecate empty list elements.
5623    </t>
5624    <t>
5625      Add appendix containing collected and expanded ABNF.
5626    </t>
5627  </list>
5628</t>
5629<t>
5630  Other changes:
5631  <list style="symbols"> 
5632    <t>
5633      Rewrite introduction; add mostly new Architecture Section.
5634    </t>
5635    <t>
5636      Move definition of quality values from Part 3 into Part 1;
5637      make TE request header field grammar independent of accept-params (defined in Part 3).
5638    </t>
5639  </list>
5640</t>
5641</section>
5642
5643<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5644<t>
5645  Closed issues:
5646  <list style="symbols"> 
5647    <t>
5648      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5649      "base for numeric protocol elements"
5650    </t>
5651    <t>
5652      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5653      "comment ABNF"
5654    </t>
5655  </list>
5656</t>
5657<t>
5658  Partly resolved issues:
5659  <list style="symbols"> 
5660    <t>
5661      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5662      "205 Bodies" (took out language that implied that there might be
5663      methods for which a request body MUST NOT be included)
5664    </t>
5665    <t>
5666      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5667      "editorial improvements around HTTP-date"
5668    </t>
5669  </list>
5670</t>
5671</section>
5672
5673<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5674<t>
5675  Closed issues:
5676  <list style="symbols"> 
5677    <t>
5678      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5679      "Repeating single-value headers"
5680    </t>
5681    <t>
5682      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5683      "increase connection limit"
5684    </t>
5685    <t>
5686      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5687      "IP addresses in URLs"
5688    </t>
5689    <t>
5690      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5691      "take over HTTP Upgrade Token Registry"
5692    </t>
5693    <t>
5694      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5695      "CR and LF in chunk extension values"
5696    </t>
5697    <t>
5698      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5699      "HTTP/0.9 support"
5700    </t>
5701    <t>
5702      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5703      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5704    </t>
5705    <t>
5706      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5707      "move definitions of gzip/deflate/compress to part 1"
5708    </t>
5709    <t>
5710      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5711      "disallow control characters in quoted-pair"
5712    </t>
5713  </list>
5714</t>
5715<t>
5716  Partly resolved issues:
5717  <list style="symbols"> 
5718    <t>
5719      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5720      "update IANA requirements wrt Transfer-Coding values" (add the
5721      IANA Considerations subsection)
5722    </t>
5723  </list>
5724</t>
5725</section>
5726
5727<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5728<t>
5729  Closed issues:
5730  <list style="symbols"> 
5731    <t>
5732      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5733      "header parsing, treatment of leading and trailing OWS"
5734    </t>
5735  </list>
5736</t>
5737<t>
5738  Partly resolved issues:
5739  <list style="symbols"> 
5740    <t>
5741      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5742      "Placement of 13.5.1 and 13.5.2"
5743    </t>
5744    <t>
5745      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5746      "use of term "word" when talking about header structure"
5747    </t>
5748  </list>
5749</t>
5750</section>
5751
5752<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5753<t>
5754  Closed issues:
5755  <list style="symbols"> 
5756    <t>
5757      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5758      "Clarification of the term 'deflate'"
5759    </t>
5760    <t>
5761      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5762      "OPTIONS * and proxies"
5763    </t>
5764    <t>
5765      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5766      "MIME-Version not listed in P1, general header fields"
5767    </t>
5768    <t>
5769      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5770      "IANA registry for content/transfer encodings"
5771    </t>
5772    <t>
5773      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5774      "Case-sensitivity of HTTP-date"
5775    </t>
5776    <t>
5777      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5778      "use of term "word" when talking about header structure"
5779    </t>
5780  </list>
5781</t>
5782<t>
5783  Partly resolved issues:
5784  <list style="symbols"> 
5785    <t>
5786      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5787      "Term for the requested resource's URI"
5788    </t>
5789  </list>
5790</t>
5791</section>
5792
5793<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5794<t>
5795  Closed issues:
5796  <list style="symbols">
5797    <t>
5798      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5799      "Connection Closing"
5800    </t>
5801    <t>
5802      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5803      "Delimiting messages with multipart/byteranges"
5804    </t>
5805    <t>
5806      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5807      "Handling multiple Content-Length headers"
5808    </t>
5809    <t>
5810      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5811      "Clarify entity / representation / variant terminology"
5812    </t>
5813    <t>
5814      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5815      "consider removing the 'changes from 2068' sections"
5816    </t>
5817  </list>
5818</t>
5819<t>
5820  Partly resolved issues:
5821  <list style="symbols"> 
5822    <t>
5823      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5824      "HTTP(s) URI scheme definitions"
5825    </t>
5826  </list>
5827</t>
5828</section>
5829
5830<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5831<t>
5832  Closed issues:
5833  <list style="symbols">
5834    <t>
5835      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5836      "Trailer requirements"
5837    </t>
5838    <t>
5839      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5840      "Text about clock requirement for caches belongs in p6"
5841    </t>
5842    <t>
5843      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5844      "effective request URI: handling of missing host in HTTP/1.0"
5845    </t>
5846    <t>
5847      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5848      "confusing Date requirements for clients"
5849    </t>
5850  </list>
5851</t>
5852<t>
5853  Partly resolved issues:
5854  <list style="symbols"> 
5855    <t>
5856      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5857      "Handling multiple Content-Length headers"
5858    </t>
5859  </list>
5860</t>
5861</section>
5862
5863<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5864<t>
5865  Closed issues:
5866  <list style="symbols">
5867    <t>
5868      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5869      "RFC2145 Normative"
5870    </t>
5871    <t>
5872      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5873      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5874    </t>
5875    <t>
5876      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5877      "define 'transparent' proxy"
5878    </t>
5879    <t>
5880      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5881      "Header Classification"
5882    </t>
5883    <t>
5884      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5885      "Is * usable as a request-uri for new methods?"
5886    </t>
5887    <t>
5888      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5889      "Migrate Upgrade details from RFC2817"
5890    </t>
5891    <t>
5892      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5893      "untangle ABNFs for header fields"
5894    </t>
5895    <t>
5896      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5897      "update RFC 2109 reference"
5898    </t>
5899  </list>
5900</t>
5901</section>
5902
5903<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5904<t>
5905  Closed issues:
5906  <list style="symbols">
5907    <t>
5908      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5909      "Allow is not in 13.5.2"
5910    </t>
5911    <t>
5912      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5913      "Handling multiple Content-Length headers"
5914    </t>
5915    <t>
5916      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5917      "untangle ABNFs for header fields"
5918    </t>
5919    <t>
5920      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5921      "Content-Length ABNF broken"
5922    </t>
5923  </list>
5924</t>
5925</section>
5926
5927<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5928<t>
5929  Closed issues:
5930  <list style="symbols">
5931    <t>
5932      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5933      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
5934    </t>
5935    <t>
5936      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5937      "Recommend minimum sizes for protocol elements"
5938    </t>
5939    <t>
5940      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5941      "Set expectations around buffering"
5942    </t>
5943    <t>
5944      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5945      "Considering messages in isolation"
5946    </t>
5947  </list>
5948</t>
5949</section>
5950
5951<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5952<t>
5953  Closed issues:
5954  <list style="symbols">
5955    <t>
5956      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5957      "DNS Spoofing / DNS Binding advice"
5958    </t>
5959    <t>
5960      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5961      "move RFCs 2145, 2616, 2817 to Historic status"
5962    </t>
5963    <t>
5964      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5965      "\-escaping in quoted strings"
5966    </t>
5967    <t>
5968      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5969      "'Close' should be reserved in the HTTP header field registry"
5970    </t>
5971  </list>
5972</t>
5973</section>
5974
5975<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5976<t>
5977  None yet.
5978</t>
5979</section>
5980
5981</section>
5982
5983</back>
5984</rfc>
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