source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1101

Last change on this file since 1101 was 1101, checked in by julian.reschke@…, 9 years ago

use mdash for long dashes, make use of dashes consistent

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Line 
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "January">
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='#errors.or.incomplete.response.cache.behavior' 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 request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' 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="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="Day Software">Day Software</organization>
62    <address>
63      <postal>
64        <street>23 Corporate Plaza DR, Suite 280</street>
65        <city>Newport Beach</city>
66        <region>CA</region>
67        <code>92660</code>
68        <country>USA</country>
69      </postal>
70      <phone>+1-949-706-5300</phone>
71      <facsimile>+1-949-706-5305</facsimile>
72      <email>fielding@gbiv.com</email>
73      <uri>http://roy.gbiv.com/</uri>
74    </address>
75  </author>
76
77  <author initials="J." surname="Gettys" fullname="Jim Gettys">
78    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
79    <address>
80      <postal>
81        <street>21 Oak Knoll Road</street>
82        <city>Carlisle</city>
83        <region>MA</region>
84        <code>01741</code>
85        <country>USA</country>
86      </postal>
87      <email>jg@freedesktop.org</email>
88      <uri>http://gettys.wordpress.com/</uri>
89    </address>
90  </author>
91 
92  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
93    <organization abbrev="HP">Hewlett-Packard Company</organization>
94    <address>
95      <postal>
96        <street>HP Labs, Large Scale Systems Group</street>
97        <street>1501 Page Mill Road, MS 1177</street>
98        <city>Palo Alto</city>
99        <region>CA</region>
100        <code>94304</code>
101        <country>USA</country>
102      </postal>
103      <email>JeffMogul@acm.org</email>
104    </address>
105  </author>
106
107  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
108    <organization abbrev="Microsoft">Microsoft Corporation</organization>
109    <address>
110      <postal>
111        <street>1 Microsoft Way</street>
112        <city>Redmond</city>
113        <region>WA</region>
114        <code>98052</code>
115        <country>USA</country>
116      </postal>
117      <email>henrikn@microsoft.com</email>
118    </address>
119  </author>
120
121  <author initials="L." surname="Masinter" fullname="Larry Masinter">
122    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
123    <address>
124      <postal>
125        <street>345 Park Ave</street>
126        <city>San Jose</city>
127        <region>CA</region>
128        <code>95110</code>
129        <country>USA</country>
130      </postal>
131      <email>LMM@acm.org</email>
132      <uri>http://larry.masinter.net/</uri>
133    </address>
134  </author>
135 
136  <author initials="P." surname="Leach" fullname="Paul J. Leach">
137    <organization abbrev="Microsoft">Microsoft Corporation</organization>
138    <address>
139      <postal>
140        <street>1 Microsoft Way</street>
141        <city>Redmond</city>
142        <region>WA</region>
143        <code>98052</code>
144      </postal>
145      <email>paulle@microsoft.com</email>
146    </address>
147  </author>
148   
149  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
150    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
151    <address>
152      <postal>
153        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
154        <street>The Stata Center, Building 32</street>
155        <street>32 Vassar Street</street>
156        <city>Cambridge</city>
157        <region>MA</region>
158        <code>02139</code>
159        <country>USA</country>
160      </postal>
161      <email>timbl@w3.org</email>
162      <uri>http://www.w3.org/People/Berners-Lee/</uri>
163    </address>
164  </author>
165
166  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
167    <organization abbrev="W3C">World Wide Web Consortium</organization>
168    <address>
169      <postal>
170        <street>W3C / ERCIM</street>
171        <street>2004, rte des Lucioles</street>
172        <city>Sophia-Antipolis</city>
173        <region>AM</region>
174        <code>06902</code>
175        <country>France</country>
176      </postal>
177      <email>ylafon@w3.org</email>
178      <uri>http://www.raubacapeu.net/people/yves/</uri>
179    </address>
180  </author>
181
182  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
183    <organization abbrev="greenbytes">greenbytes GmbH</organization>
184    <address>
185      <postal>
186        <street>Hafenweg 16</street>
187        <city>Muenster</city><region>NW</region><code>48155</code>
188        <country>Germany</country>
189      </postal>
190      <phone>+49 251 2807760</phone>
191      <facsimile>+49 251 2807761</facsimile>
192      <email>julian.reschke@greenbytes.de</email>
193      <uri>http://greenbytes.de/tech/webdav/</uri>
194    </address>
195  </author>
196
197  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
198  <workgroup>HTTPbis Working Group</workgroup>
199
200<abstract>
201<t>
202   The Hypertext Transfer Protocol (HTTP) is an application-level
203   protocol for distributed, collaborative, hypertext information
204   systems. HTTP has been in use by the World Wide Web global information
205   initiative since 1990. This document is Part 1 of the seven-part specification
206   that defines the protocol referred to as "HTTP/1.1" and, taken together,
207   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
208   its associated terminology, defines the "http" and "https" Uniform
209   Resource Identifier (URI) schemes, defines the generic message syntax
210   and parsing requirements for HTTP message frames, and describes
211   general security concerns for implementations.
212</t>
213</abstract>
214
215<note title="Editorial Note (To be removed by RFC Editor)">
216  <t>
217    Discussion of this draft should take place on the HTTPBIS working group
218    mailing list (ietf-http-wg@w3.org). The current issues list is
219    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/>
220    and related documents (including fancy diffs) can be found at
221    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
222  </t>
223  <t>
224    The changes in this draft are summarized in <xref target="changes.since.12"/>.
225  </t>
226</note>
227</front>
228<middle>
229<section title="Introduction" anchor="introduction">
230<t>
231   The Hypertext Transfer Protocol (HTTP) is an application-level
232   request/response protocol that uses extensible semantics and MIME-like
233   message payloads for flexible interaction with network-based hypertext
234   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
235   standard <xref target="RFC3986"/> to indicate request targets and
236   relationships between resources.
237   Messages are passed in a format similar to that used by Internet mail
238   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
239   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
240   between HTTP and MIME messages).
241</t>
242<t>
243   HTTP is a generic interface protocol for information systems. It is
244   designed to hide the details of how a service is implemented by presenting
245   a uniform interface to clients that is independent of the types of
246   resources provided. Likewise, servers do not need to be aware of each
247   client's purpose: an HTTP request can be considered in isolation rather
248   than being associated with a specific type of client or a predetermined
249   sequence of application steps. The result is a protocol that can be used
250   effectively in many different contexts and for which implementations can
251   evolve independently over time.
252</t>
253<t>
254   HTTP is also designed for use as an intermediation protocol for translating
255   communication to and from non-HTTP information systems.
256   HTTP proxies and gateways can provide access to alternative information
257   services by translating their diverse protocols into a hypertext
258   format that can be viewed and manipulated by clients in the same way
259   as HTTP services.
260</t>
261<t>
262   One consequence of HTTP flexibility is that the protocol cannot be
263   defined in terms of what occurs behind the interface. Instead, we
264   are limited to defining the syntax of communication, the intent
265   of received communication, and the expected behavior of recipients.
266   If the communication is considered in isolation, then successful
267   actions ought to be reflected in corresponding changes to the
268   observable interface provided by servers. However, since multiple
269   clients might act in parallel and perhaps at cross-purposes, we
270   cannot require that such changes be observable beyond the scope
271   of a single response.
272</t>
273<t>
274   This document is Part 1 of the seven-part specification of HTTP,
275   defining the protocol referred to as "HTTP/1.1" and obsoleting
276   <xref target="RFC2616"/>.
277   Part 1 describes the architectural elements that are used or
278   referred to in HTTP, defines the "http" and "https" URI schemes,
279   describes overall network operation and connection management,
280   and defines HTTP message framing and forwarding requirements.
281   Our goal is to define all of the mechanisms necessary for HTTP message
282   handling that are independent of message semantics, thereby defining the
283   complete set of requirements for message parsers and
284   message-forwarding intermediaries.
285</t>
286
287<section title="Requirements" anchor="intro.requirements">
288<t>
289   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
290   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
291   document are to be interpreted as described in <xref target="RFC2119"/>.
292</t>
293<t>
294   An implementation is not compliant if it fails to satisfy one or more
295   of the "MUST" or "REQUIRED" level requirements for the protocols it
296   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
297   level and all the "SHOULD" level requirements for its protocols is said
298   to be "unconditionally compliant"; one that satisfies all the "MUST"
299   level requirements but not all the "SHOULD" level requirements for its
300   protocols is said to be "conditionally compliant".
301</t>
302</section>
303
304<section title="Syntax Notation" anchor="notation">
305<iref primary="true" item="Grammar" subitem="ALPHA"/>
306<iref primary="true" item="Grammar" subitem="CR"/>
307<iref primary="true" item="Grammar" subitem="CRLF"/>
308<iref primary="true" item="Grammar" subitem="CTL"/>
309<iref primary="true" item="Grammar" subitem="DIGIT"/>
310<iref primary="true" item="Grammar" subitem="DQUOTE"/>
311<iref primary="true" item="Grammar" subitem="HEXDIG"/>
312<iref primary="true" item="Grammar" subitem="LF"/>
313<iref primary="true" item="Grammar" subitem="OCTET"/>
314<iref primary="true" item="Grammar" subitem="SP"/>
315<iref primary="true" item="Grammar" subitem="VCHAR"/>
316<iref primary="true" item="Grammar" subitem="WSP"/>
317<t>
318   This specification uses the Augmented Backus-Naur Form (ABNF) notation
319   of <xref target="RFC5234"/>.
320</t>
321<t anchor="core.rules">
322  <x:anchor-alias value="ALPHA"/>
323  <x:anchor-alias value="CTL"/>
324  <x:anchor-alias value="CR"/>
325  <x:anchor-alias value="CRLF"/>
326  <x:anchor-alias value="DIGIT"/>
327  <x:anchor-alias value="DQUOTE"/>
328  <x:anchor-alias value="HEXDIG"/>
329  <x:anchor-alias value="LF"/>
330  <x:anchor-alias value="OCTET"/>
331  <x:anchor-alias value="SP"/>
332  <x:anchor-alias value="VCHAR"/>
333  <x:anchor-alias value="WSP"/>
334   The following core rules are included by
335   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
336   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
337   DIGIT (decimal 0-9), DQUOTE (double quote),
338   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
339   OCTET (any 8-bit sequence of data), SP (space),
340   VCHAR (any visible <xref target="USASCII"/> character),
341   and WSP (whitespace).
342</t>
343<t>
344   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
345   "obsolete" grammar rules that appear for historical reasons.
346</t>
347
348<section title="ABNF Extension: #rule" anchor="notation.abnf">
349<t>
350  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
351  improve readability.
352</t>
353<t>
354  A construct "#" is defined, similar to "*", for defining comma-delimited
355  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
356  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
357  comma (",") and optional whitespace (OWS,
358  <xref target="basic.rules"/>).   
359</t>
360<figure><preamble>
361  Thus,
362</preamble><artwork type="example">
363  1#element =&gt; element *( OWS "," OWS element )
364</artwork></figure>
365<figure><preamble>
366  and:
367</preamble><artwork type="example">
368  #element =&gt; [ 1#element ]
369</artwork></figure>
370<figure><preamble>
371  and for n &gt;= 1 and m &gt; 1:
372</preamble><artwork type="example">
373  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
374</artwork></figure>
375<t>
376  For compatibility with legacy list rules, recipients &SHOULD; accept empty
377  list elements. In other words, consumers would follow the list productions:
378</t>
379<figure><artwork type="example">
380  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
381 
382  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
383</artwork></figure>
384<t>
385  Note that empty elements do not contribute to the count of elements present,
386  though.
387</t>
388<t>
389  For example, given these ABNF productions:
390</t>
391<figure><artwork type="example">
392  example-list      = 1#example-list-elmt
393  example-list-elmt = token ; see <xref target="basic.rules"/> 
394</artwork></figure>
395<t>
396  Then these are valid values for example-list (not including the double
397  quotes, which are present for delimitation only):
398</t>
399<figure><artwork type="example">
400  "foo,bar"
401  " foo ,bar,"
402  "  foo , ,bar,charlie   "
403  "foo ,bar,   charlie "
404</artwork></figure>
405<t>
406  But these values would be invalid, as at least one non-empty element is
407  required:
408</t>
409<figure><artwork type="example">
410  ""
411  ","
412  ",   ,"
413</artwork></figure>
414<t>
415  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
416  expanded as explained above.
417</t>
418</section>
419
420<section title="Basic Rules" anchor="basic.rules">
421<t anchor="rule.CRLF">
422  <x:anchor-alias value="CRLF"/>
423   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
424   protocol elements other than the message-body
425   (see <xref target="tolerant.applications"/> for tolerant applications).
426</t>
427<t anchor="rule.LWS">
428   This specification uses three rules to denote the use of linear
429   whitespace: OWS (optional whitespace), RWS (required whitespace), and
430   BWS ("bad" whitespace).
431</t>
432<t>
433   The OWS rule is used where zero or more linear whitespace characters might
434   appear. OWS &SHOULD; either not be produced or be produced as a single SP
435   character. Multiple OWS characters that occur within field-content &SHOULD;
436   be replaced with a single SP before interpreting the field value or
437   forwarding the message downstream.
438</t>
439<t>
440   RWS is used when at least one linear whitespace character is required to
441   separate field tokens. RWS &SHOULD; be produced as a single SP character.
442   Multiple RWS characters that occur within field-content &SHOULD; be
443   replaced with a single SP before interpreting the field value or
444   forwarding the message downstream.
445</t>
446<t>
447   BWS is used where the grammar allows optional whitespace for historical
448   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
449   recipients &MUST; accept such bad optional whitespace and remove it before
450   interpreting the field value or forwarding the message downstream.
451</t>
452<t anchor="rule.whitespace">
453  <x:anchor-alias value="BWS"/>
454  <x:anchor-alias value="OWS"/>
455  <x:anchor-alias value="RWS"/>
456  <x:anchor-alias value="obs-fold"/>
457</t>
458<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"/>
459  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
460                 ; "optional" whitespace
461  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
462                 ; "required" whitespace
463  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
464                 ; "bad" whitespace
465  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
466                 ; see <xref target="header.fields"/>
467</artwork></figure>
468<t anchor="rule.token.separators">
469  <x:anchor-alias value="tchar"/>
470  <x:anchor-alias value="token"/>
471  <x:anchor-alias value="special"/>
472  <x:anchor-alias value="word"/>
473   Many HTTP/1.1 header field values consist of words (token or quoted-string)
474   separated by whitespace or special characters. These special characters
475   &MUST; be in a quoted string to be used within a parameter value (as defined
476   in <xref target="transfer.codings"/>).
477</t>
478<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"/>
479  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
480
481  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
482<!--
483  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
484 -->
485  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
486                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
487                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
488                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
489
490  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
491                 / ";" / ":" / "\" / DQUOTE / "/" / "["
492                 / "]" / "?" / "=" / "{" / "}"
493</artwork></figure>
494<t anchor="rule.quoted-string">
495  <x:anchor-alias value="quoted-string"/>
496  <x:anchor-alias value="qdtext"/>
497  <x:anchor-alias value="obs-text"/>
498   A string of text is parsed as a single word if it is quoted using
499   double-quote marks.
500</t>
501<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"/>
502  <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>
503  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
504                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except <x:ref>DQUOTE</x:ref> and "\"&gt; / <x:ref>obs-text</x:ref> 
505  <x:ref>obs-text</x:ref>       = %x80-FF
506</artwork></figure>
507<t anchor="rule.quoted-pair">
508  <x:anchor-alias value="quoted-pair"/>
509   The backslash character ("\") can be used as a single-character
510   quoting mechanism within quoted-string constructs:
511</t>
512<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
513  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
514</artwork></figure>
515<t>
516   Producers &SHOULD-NOT; escape characters that do not require escaping
517   (i.e., other than DQUOTE and the backslash character).
518</t>
519</section>
520
521<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
522  <x:anchor-alias value="request-header"/>
523  <x:anchor-alias value="response-header"/>
524  <x:anchor-alias value="Cache-Control"/>
525  <x:anchor-alias value="Pragma"/>
526  <x:anchor-alias value="Warning"/>
527  <x:anchor-alias value="MIME-Version"/>
528<t>
529  The ABNF rules below are defined in other parts:
530</t>
531<figure><!-- Part2--><artwork type="abnf2616">
532  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
533  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
534</artwork></figure>
535<figure><!-- Part3--><artwork type="abnf2616">
536  <x:ref>MIME-Version</x:ref>    = &lt;MIME-Version, defined in &header-mime-version;&gt;
537</artwork></figure>
538<figure><!-- Part6--><artwork type="abnf2616">
539  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
540  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
541  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
542</artwork></figure>
543</section>
544
545</section>
546</section>
547
548<section title="HTTP-related architecture" anchor="architecture">
549<t>
550   HTTP was created for the World Wide Web architecture
551   and has evolved over time to support the scalability needs of a worldwide
552   hypertext system. Much of that architecture is reflected in the terminology
553   and syntax productions used to define HTTP.
554</t>
555
556<section title="Client/Server Messaging" anchor="operation">
557<iref primary="true" item="client"/>
558<iref primary="true" item="server"/>
559<iref primary="true" item="connection"/>
560<t>
561   HTTP is a stateless request/response protocol that operates by exchanging
562   messages across a reliable transport or session-layer connection. An HTTP
563   "client" is a program that establishes a connection to a server for the
564   purpose of sending one or more HTTP requests.  An HTTP "server" is a
565   program that accepts connections in order to service HTTP requests by
566   sending HTTP responses.
567</t>
568<iref primary="true" item="user agent"/>
569<iref primary="true" item="origin server"/>
570<iref primary="true" item="browser"/>
571<iref primary="true" item="spider"/>
572<t>
573   Note that the terms client and server refer only to the roles that
574   these programs perform for a particular connection.  The same program
575   might act as a client on some connections and a server on others.  We use
576   the term "user agent" to refer to the program that initiates a request,
577   such as a WWW browser, editor, or spider (web-traversing robot), and
578   the term "origin server" to refer to the program that can originate
579   authoritative responses to a request.  For general requirements, we use
580   the term "sender" to refer to whichever component sent a given message
581   and the term "recipient" to refer to any component that receives the
582   message.
583</t>
584<t>
585   Most HTTP communication consists of a retrieval request (GET) for
586   a representation of some resource identified by a URI.  In the
587   simplest case, this might be accomplished via a single bidirectional
588   connection (===) between the user agent (UA) and the origin server (O).
589</t>
590<figure><artwork type="drawing">
591         request   &gt;
592    UA ======================================= O
593                                &lt;   response
594</artwork></figure>
595<iref primary="true" item="message"/>
596<iref primary="true" item="request"/>
597<iref primary="true" item="response"/>
598<t>
599   A client sends an HTTP request to the server in the form of a request
600   message (<xref target="request"/>), beginning with a method, URI, and
601   protocol version, followed by MIME-like header fields containing
602   request modifiers, client information, and payload metadata, an empty
603   line to indicate the end of the header section, and finally the payload
604   body (if any).
605</t>
606<t>
607   A server responds to the client's request by sending an HTTP response
608   message (<xref target="response"/>), beginning with a status line that
609   includes the protocol version, a success or error code, and textual
610   reason phrase, followed by MIME-like header fields containing server
611   information, resource metadata, and payload metadata, an empty line to
612   indicate the end of the header section, and finally the payload body (if any).
613</t>
614<t>
615   The following example illustrates a typical message exchange for a
616   GET request on the URI "http://www.example.com/hello.txt":
617</t>
618<figure><preamble>
619client request:
620</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
621GET /hello.txt HTTP/1.1
622User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
623Host: www.example.com
624Accept: */*
625
626</artwork></figure>
627<figure><preamble>
628server response:
629</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
630HTTP/1.1 200 OK
631Date: Mon, 27 Jul 2009 12:28:53 GMT
632Server: Apache
633Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
634ETag: "34aa387-d-1568eb00"
635Accept-Ranges: bytes
636Content-Length: <x:length-of target="exbody"/>
637Vary: Accept-Encoding
638Content-Type: text/plain
639
640<x:span anchor="exbody">Hello World!
641</x:span></artwork></figure>
642</section>
643
644<section title="Intermediaries" anchor="intermediaries">
645<iref primary="true" item="intermediary"/>
646<t>
647   A more complicated situation occurs when one or more intermediaries
648   are present in the request/response chain. There are three common
649   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
650   a single intermediary might act as an origin server, proxy, gateway,
651   or tunnel, switching behavior based on the nature of each request.
652</t>
653<figure><artwork type="drawing">
654         &gt;             &gt;             &gt;             &gt;
655    UA =========== A =========== B =========== C =========== O
656               &lt;             &lt;             &lt;             &lt;
657</artwork></figure>
658<t>
659   The figure above shows three intermediaries (A, B, and C) between the
660   user agent and origin server. A request or response message that
661   travels the whole chain will pass through four separate connections.
662   Some HTTP communication options
663   might apply only to the connection with the nearest, non-tunnel
664   neighbor, only to the end-points of the chain, or to all connections
665   along the chain. Although the diagram is linear, each participant might
666   be engaged in multiple, simultaneous communications. For example, B
667   might be receiving requests from many clients other than A, and/or
668   forwarding requests to servers other than C, at the same time that it
669   is handling A's request.
670</t>
671<t>
672<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
673<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
674   We use the terms "upstream" and "downstream" to describe various
675   requirements in relation to the directional flow of a message:
676   all messages flow from upstream to downstream.
677   Likewise, we use the terms "inbound" and "outbound" to refer to
678   directions in relation to the request path: "inbound" means toward
679   the origin server and "outbound" means toward the user agent.
680</t>
681<t><iref primary="true" item="proxy"/>
682   A "proxy" is a message forwarding agent that is selected by the
683   client, usually via local configuration rules, to receive requests
684   for some type(s) of absolute URI and attempt to satisfy those
685   requests via translation through the HTTP interface.  Some translations
686   are minimal, such as for proxy requests for "http" URIs, whereas
687   other requests might require translation to and from entirely different
688   application-layer protocols. Proxies are often used to group an
689   organization's HTTP requests through a common intermediary for the
690   sake of security, annotation services, or shared caching.
691</t>
692<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
693   A "gateway" (a.k.a., "reverse proxy") is a receiving agent that acts
694   as a layer above some other server(s) and translates the received
695   requests to the underlying server's protocol.  Gateways are often
696   used for load balancing or partitioning HTTP services across
697   multiple machines.
698   Unlike a proxy, a gateway receives requests as if it were the
699   origin server for the target resource; the requesting client
700   will not be aware that it is communicating with a gateway.
701   A gateway communicates with the client as if the gateway is the
702   origin server and thus is subject to all of the requirements on
703   origin servers for that connection.  A gateway communicates
704   with inbound servers using any protocol it desires, including
705   private extensions to HTTP that are outside the scope of this
706   specification.
707</t>
708<t><iref primary="true" item="tunnel"/>
709   A "tunnel" acts as a blind relay between two connections
710   without changing the messages. Once active, a tunnel is not
711   considered a party to the HTTP communication, though the tunnel might
712   have been initiated by an HTTP request. A tunnel ceases to exist when
713   both ends of the relayed connection are closed. Tunnels are used to
714   extend a virtual connection through an intermediary, such as when
715   transport-layer security is used to establish private communication
716   through a shared firewall proxy.
717</t>
718</section>
719
720<section title="Caches" anchor="caches">
721<iref primary="true" item="cache"/>
722<t>
723   A "cache" is a local store of previous response messages and the
724   subsystem that controls its message storage, retrieval, and deletion.
725   A cache stores cacheable responses in order to reduce the response
726   time and network bandwidth consumption on future, equivalent
727   requests. Any client or server &MAY; employ a cache, though a cache
728   cannot be used by a server while it is acting as a tunnel.
729</t>
730<t>
731   The effect of a cache is that the request/response chain is shortened
732   if one of the participants along the chain has a cached response
733   applicable to that request. The following illustrates the resulting
734   chain if B has a cached copy of an earlier response from O (via C)
735   for a request which has not been cached by UA or A.
736</t>
737<figure><artwork type="drawing">
738            &gt;             &gt;
739       UA =========== A =========== B - - - - - - C - - - - - - O
740                  &lt;             &lt;
741</artwork></figure>
742<t><iref primary="true" item="cacheable"/>
743   A response is "cacheable" if a cache is allowed to store a copy of
744   the response message for use in answering subsequent requests.
745   Even when a response is cacheable, there might be additional
746   constraints placed by the client or by the origin server on when
747   that cached response can be used for a particular request. HTTP
748   requirements for cache behavior and cacheable responses are
749   defined in &caching-overview;
750</t>
751<t>
752   There are a wide variety of architectures and configurations
753   of caches and proxies deployed across the World Wide Web and
754   inside large organizations. These systems include national hierarchies
755   of proxy caches to save transoceanic bandwidth, systems that
756   broadcast or multicast cache entries, organizations that distribute
757   subsets of cached data via optical media, and so on.
758</t>
759</section>
760
761<section title="Transport Independence" anchor="transport-independence">
762<t>
763  HTTP systems are used in a wide variety of environments, from
764  corporate intranets with high-bandwidth links to long-distance
765  communication over low-power radio links and intermittent connectivity.
766</t>
767<t>
768   HTTP communication usually takes place over TCP/IP connections. The
769   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
770   not preclude HTTP from being implemented on top of any other protocol
771   on the Internet, or on other networks. HTTP only presumes a reliable
772   transport; any protocol that provides such guarantees can be used;
773   the mapping of the HTTP/1.1 request and response structures onto the
774   transport data units of the protocol in question is outside the scope
775   of this specification.
776</t>
777<t>
778   In HTTP/1.0, most implementations used a new connection for each
779   request/response exchange. In HTTP/1.1, a connection might be used for
780   one or more request/response exchanges, although connections might be
781   closed for a variety of reasons (see <xref target="persistent.connections"/>).
782</t>
783</section>
784
785<section title="HTTP Version" anchor="http.version">
786  <x:anchor-alias value="HTTP-Version"/>
787  <x:anchor-alias value="HTTP-Prot-Name"/>
788<t>
789   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
790   of the protocol. The protocol versioning policy is intended to allow
791   the sender to indicate the format of a message and its capacity for
792   understanding further HTTP communication, rather than the features
793   obtained via that communication. No change is made to the version
794   number for the addition of message components which do not affect
795   communication behavior or which only add to extensible field values.
796   The &lt;minor&gt; number is incremented when the changes made to the
797   protocol add features which do not change the general message parsing
798   algorithm, but which might add to the message semantics and imply
799   additional capabilities of the sender. The &lt;major&gt; number is
800   incremented when the format of a message within the protocol is
801   changed. See <xref target="RFC2145"/> for a fuller explanation.
802</t>
803<t>
804   The version of an HTTP message is indicated by an HTTP-Version field
805   in the first line of the message. HTTP-Version is case-sensitive.
806</t>
807<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
808  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
809  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
810</artwork></figure>
811<t>
812   Note that the major and minor numbers &MUST; be treated as separate
813   integers and that each &MAY; be incremented higher than a single digit.
814   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
815   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
816   &MUST-NOT; be sent.
817</t>
818<t>
819   An application that sends a request or response message that includes
820   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
821   with this specification. Applications that are at least conditionally
822   compliant with this specification &SHOULD; use an HTTP-Version of
823   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
824   not compatible with HTTP/1.0. For more details on when to send
825   specific HTTP-Version values, see <xref target="RFC2145"/>.
826</t>
827<t>
828   The HTTP version of an application is the highest HTTP version for
829   which the application is at least conditionally compliant.
830</t>
831<t>
832   Proxy and gateway applications need to be careful when forwarding
833   messages in protocol versions different from that of the application.
834   Since the protocol version indicates the protocol capability of the
835   sender, a proxy/gateway &MUST-NOT; send a message with a version
836   indicator which is greater than its actual version. If a higher
837   version request is received, the proxy/gateway &MUST; either downgrade
838   the request version, or respond with an error, or switch to tunnel
839   behavior.
840</t>
841<t>
842   Due to interoperability problems with HTTP/1.0 proxies discovered
843   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
844   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
845   they support. The proxy/gateway's response to that request &MUST; be in
846   the same major version as the request.
847</t>
848<x:note>
849  <t>
850    <x:h>Note:</x:h> Converting between versions of HTTP might involve modification
851    of header fields required or forbidden by the versions involved.
852  </t>
853</x:note>
854</section>
855
856<section title="Uniform Resource Identifiers" anchor="uri">
857<iref primary="true" item="resource"/>
858<t>
859   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
860   throughout HTTP as the means for identifying resources. URI references
861   are used to target requests, indicate redirects, and define relationships.
862   HTTP does not limit what a resource might be; it merely defines an interface
863   that can be used to interact with a resource via HTTP. More information on
864   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
865</t>
866  <x:anchor-alias value="URI-reference"/>
867  <x:anchor-alias value="absolute-URI"/>
868  <x:anchor-alias value="relative-part"/>
869  <x:anchor-alias value="authority"/>
870  <x:anchor-alias value="path-abempty"/>
871  <x:anchor-alias value="path-absolute"/>
872  <x:anchor-alias value="port"/>
873  <x:anchor-alias value="query"/>
874  <x:anchor-alias value="uri-host"/>
875  <x:anchor-alias value="partial-URI"/>
876<t>
877   This specification adopts the definitions of "URI-reference",
878   "absolute-URI", "relative-part", "port", "host",
879   "path-abempty", "path-absolute", "query", and "authority" from
880   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
881   protocol elements that allow a relative URI without a fragment.
882</t>
883<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"/>
884  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
885  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
886  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
887  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
888  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
889  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
890  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
891  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
892  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
893 
894  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
895</artwork></figure>
896<t>
897   Each protocol element in HTTP that allows a URI reference will indicate in
898   its ABNF production whether the element allows only a URI in absolute form
899   (absolute-URI), any relative reference (relative-ref), or some other subset
900   of the URI-reference grammar. Unless otherwise indicated, URI references
901   are parsed relative to the request target (the default base URI for both
902   the request and its corresponding response).
903</t>
904
905<section title="http URI scheme" anchor="http.uri">
906  <x:anchor-alias value="http-URI"/>
907  <iref item="http URI scheme" primary="true"/>
908  <iref item="URI scheme" subitem="http" primary="true"/>
909<t>
910   The "http" URI scheme is hereby defined for the purpose of minting
911   identifiers according to their association with the hierarchical
912   namespace governed by a potential HTTP origin server listening for
913   TCP connections on a given port.
914   The HTTP server is identified via the generic syntax's
915   <x:ref>authority</x:ref> component, which includes a host
916   identifier and optional TCP port, and the remainder of the URI is
917   considered to be identifying data corresponding to a resource for
918   which that server might provide an HTTP interface.
919</t>
920<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
921  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
922</artwork></figure>
923<t>
924   The host identifier within an <x:ref>authority</x:ref> component is
925   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
926   provided as an IP literal or IPv4 address, then the HTTP server is any
927   listener on the indicated TCP port at that IP address. If host is a
928   registered name, then that name is considered an indirect identifier
929   and the recipient might use a name resolution service, such as DNS,
930   to find the address of a listener for that host.
931   The host &MUST-NOT; be empty; if an "http" URI is received with an
932   empty host, then it &MUST; be rejected as invalid.
933   If the port subcomponent is empty or not given, then TCP port 80 is
934   assumed (the default reserved port for WWW services).
935</t>
936<t>
937   Regardless of the form of host identifier, access to that host is not
938   implied by the mere presence of its name or address. The host might or might
939   not exist and, even when it does exist, might or might not be running an
940   HTTP server or listening to the indicated port. The "http" URI scheme
941   makes use of the delegated nature of Internet names and addresses to
942   establish a naming authority (whatever entity has the ability to place
943   an HTTP server at that Internet name or address) and allows that
944   authority to determine which names are valid and how they might be used.
945</t>
946<t>
947   When an "http" URI is used within a context that calls for access to the
948   indicated resource, a client &MAY; attempt access by resolving
949   the host to an IP address, establishing a TCP connection to that address
950   on the indicated port, and sending an HTTP request message to the server
951   containing the URI's identifying data as described in <xref target="request"/>.
952   If the server responds to that request with a non-interim HTTP response
953   message, as described in <xref target="response"/>, then that response
954   is considered an authoritative answer to the client's request.
955</t>
956<t>
957   Although HTTP is independent of the transport protocol, the "http"
958   scheme is specific to TCP-based services because the name delegation
959   process depends on TCP for establishing authority.
960   An HTTP service based on some other underlying connection protocol
961   would presumably be identified using a different URI scheme, just as
962   the "https" scheme (below) is used for servers that require an SSL/TLS
963   transport layer on a connection. Other protocols might also be used to
964   provide access to "http" identified resources &mdash; it is only the
965   authoritative interface used for mapping the namespace that is
966   specific to TCP.
967</t>
968<t>
969   The URI generic syntax for authority also includes a deprecated
970   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
971   for including user authentication information in the URI.  The userinfo
972   subcomponent (and its "@" delimiter) &MUST-NOT; be used in an "http"
973   URI.  URI reference recipients &SHOULD; parse for the existence of
974   userinfo and treat its presence as an error, likely indicating that
975   the deprecated subcomponent is being used to obscure the authority
976   for the sake of phishing attacks.
977</t>
978</section>
979
980<section title="https URI scheme" anchor="https.uri">
981   <x:anchor-alias value="https-URI"/>
982   <iref item="https URI scheme"/>
983   <iref item="URI scheme" subitem="https"/>
984<t>
985   The "https" URI scheme is hereby defined for the purpose of minting
986   identifiers according to their association with the hierarchical
987   namespace governed by a potential HTTP origin server listening for
988   SSL/TLS-secured connections on a given TCP port.
989</t>
990<t>
991   All of the requirements listed above for the "http" scheme are also
992   requirements for the "https" scheme, except that a default TCP port
993   of 443 is assumed if the port subcomponent is empty or not given,
994   and the TCP connection &MUST; be secured for privacy through the
995   use of strong encryption prior to sending the first HTTP request.
996</t>
997<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
998  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
999</artwork></figure>
1000<t>
1001   Unlike the "http" scheme, responses to "https" identified requests
1002   are never "public" and thus are ineligible for shared caching.
1003   Their default is "private" and might be further constrained via use
1004   of the Cache-Control header field.
1005</t>
1006<t>
1007   Resources made available via the "https" scheme have no shared
1008   identity with the "http" scheme even if their resource identifiers
1009   only differ by the single "s" in the scheme name.  They are
1010   different services governed by different authorities.  However,
1011   some extensions to HTTP that apply to entire host domains, such
1012   as the Cookie protocol, do allow one service to effect communication
1013   with the other services based on host domain matching.
1014</t>
1015<t>
1016   The process for authoritative access to an "https" identified
1017   resource is defined in <xref target="RFC2818"/>.
1018</t>
1019</section>
1020
1021<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1022<t>
1023   Since the "http" and "https" schemes conform to the URI generic syntax,
1024   such URIs are normalized and compared according to the algorithm defined
1025   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1026   described above for each scheme.
1027</t>
1028<t>
1029   If the port is equal to the default port for a scheme, the normal
1030   form is to elide the port subcomponent. Likewise, an empty path
1031   component is equivalent to an absolute path of "/", so the normal
1032   form is to provide a path of "/" instead. The scheme and host
1033   are case-insensitive and normally provided in lowercase; all
1034   other components are compared in a case-sensitive manner.
1035   Characters other than those in the "reserved" set are equivalent
1036   to their percent-encoded octets (see <xref target="RFC3986"
1037   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1038</t>
1039<t>
1040   For example, the following three URIs are equivalent:
1041</t>
1042<figure><artwork type="example">
1043   http://example.com:80/~smith/home.html
1044   http://EXAMPLE.com/%7Esmith/home.html
1045   http://EXAMPLE.com:/%7esmith/home.html
1046</artwork></figure>
1047<t>
1048   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
1049   If path-abempty is the empty string (i.e., there is no slash "/"
1050   path separator following the authority), then the "http" URI
1051   &MUST; be given as "/" when
1052   used as a request-target (<xref target="request-target"/>). If a proxy
1053   receives a host name which is not a fully qualified domain name, it
1054   &MAY; add its domain to the host name it received. If a proxy receives
1055   a fully qualified domain name, the proxy &MUST-NOT; change the host
1056   name.
1057</t>
1058</section>
1059</section>
1060</section>
1061
1062<section title="HTTP Message" anchor="http.message">
1063<x:anchor-alias value="generic-message"/>
1064<x:anchor-alias value="message.types"/>
1065<x:anchor-alias value="HTTP-message"/>
1066<x:anchor-alias value="start-line"/>
1067<iref item="header section"/>
1068<iref item="headers"/>
1069<iref item="header field"/>
1070<t>
1071   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1072   characters in a format similar to the Internet Message Format
1073   <xref target="RFC5322"/>: zero or more header fields (collectively
1074   referred to as the "headers" or the "header section"), an empty line
1075   indicating the end of the header section, and an optional message-body.
1076</t>
1077<t>
1078   An HTTP message can either be a request from client to server or a
1079   response from server to client.  Syntactically, the two types of message
1080   differ only in the start-line, which is either a Request-Line (for requests)
1081   or a Status-Line (for responses), and in the algorithm for determining
1082   the length of the message-body (<xref target="message.body"/>).
1083   In theory, a client could receive requests and a server could receive
1084   responses, distinguishing them by their different start-line formats,
1085   but in practice servers are implemented to only expect a request
1086   (a response is interpreted as an unknown or invalid request method)
1087   and clients are implemented to only expect a response.
1088</t>
1089<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1090  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1091                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1092                    <x:ref>CRLF</x:ref>
1093                    [ <x:ref>message-body</x:ref> ]
1094  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1095</artwork></figure>
1096<t>
1097   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1098   header field. The presence of whitespace might be an attempt to trick a
1099   noncompliant implementation of HTTP into ignoring that field or processing
1100   the next line as a new request, either of which might result in security
1101   issues when implementations within the request chain interpret the
1102   same message differently. HTTP/1.1 servers &MUST; reject such a message
1103   with a 400 (Bad Request) response.
1104</t>
1105
1106<section title="Message Parsing Robustness" anchor="message.robustness">
1107<t>
1108   In the interest of robustness, servers &SHOULD; ignore at least one
1109   empty line received where a Request-Line is expected. In other words, if
1110   the server is reading the protocol stream at the beginning of a
1111   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1112</t>
1113<t>
1114   Some old HTTP/1.0 client implementations generate an extra CRLF
1115   after a POST request as a lame workaround for some early server
1116   applications that failed to read message-body content that was
1117   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1118   preface or follow a request with an extra CRLF.  If terminating
1119   the request message-body with a line-ending is desired, then the
1120   client &MUST; include the terminating CRLF octets as part of the
1121   message-body length.
1122</t>
1123<t>
1124   The normal procedure for parsing an HTTP message is to read the
1125   start-line into a structure, read each header field into a hash
1126   table by field name until the empty line, and then use the parsed
1127   data to determine if a message-body is expected.  If a message-body
1128   has been indicated, then it is read as a stream until an amount
1129   of octets equal to the message-body length is read or the connection
1130   is closed.  Care must be taken to parse an HTTP message as a sequence
1131   of octets in an encoding that is a superset of US-ASCII.  Attempting
1132   to parse HTTP as a stream of Unicode characters in a character encoding
1133   like UTF-16 might introduce security flaws due to the differing ways
1134   that such parsers interpret invalid characters.
1135</t>
1136<t>
1137   HTTP allows the set of defined header fields to be extended without
1138   changing the protocol version (see <xref target="header.field.registration"/>).
1139   However, such fields might not be recognized by a downstream recipient
1140   and might be stripped by non-transparent intermediaries.
1141   Unrecognized header fields &MUST; be forwarded by transparent proxies
1142   and &SHOULD; be ignored by a recipient.
1143</t>
1144</section>
1145
1146<section title="Header Fields" anchor="header.fields">
1147  <x:anchor-alias value="header-field"/>
1148  <x:anchor-alias value="field-content"/>
1149  <x:anchor-alias value="field-name"/>
1150  <x:anchor-alias value="field-value"/>
1151  <x:anchor-alias value="OWS"/>
1152<t>
1153   Each HTTP header field consists of a case-insensitive field name
1154   followed by a colon (":"), optional whitespace, and the field value.
1155</t>
1156<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"/>
1157  <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>
1158  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1159  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1160  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1161</artwork></figure>
1162<t>
1163   No whitespace is allowed between the header field name and colon. For
1164   security reasons, any request message received containing such whitespace
1165   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1166   &MUST; remove any such whitespace from a response message before
1167   forwarding the message downstream.
1168</t>
1169<t>
1170   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1171   preferred. The field value does not include any leading or trailing white
1172   space: OWS occurring before the first non-whitespace character of the
1173   field value or after the last non-whitespace character of the field value
1174   is ignored and &SHOULD; be removed before further processing (as this does
1175   not change the meaning of the header field).
1176</t>
1177<t>
1178   The order in which header fields with differing field names are
1179   received is not significant. However, it is "good practice" to send
1180   header fields that contain control data first, such as Host on
1181   requests and Date on responses, so that implementations can decide
1182   when not to handle a message as early as possible.  A server &MUST;
1183   wait until the entire header section is received before interpreting
1184   a request message, since later header fields might include conditionals,
1185   authentication credentials, or deliberately misleading duplicate
1186   header fields that would impact request processing.
1187</t>
1188<t>
1189   Multiple header fields with the same field name &MUST-NOT; be
1190   sent in a message unless the entire field value for that
1191   header field is defined as a comma-separated list [i.e., #(values)].
1192   Multiple header fields with the same field name can be combined into
1193   one "field-name: field-value" pair, without changing the semantics of the
1194   message, by appending each subsequent field value to the combined
1195   field value in order, separated by a comma. The order in which
1196   header fields with the same field name are received is therefore
1197   significant to the interpretation of the combined field value;
1198   a proxy &MUST-NOT; change the order of these field values when
1199   forwarding a message.
1200</t>
1201<x:note>
1202  <t>
1203   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1204   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1205   can occur multiple times, but does not use the list syntax, and thus cannot
1206   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1207   for details.) Also note that the Set-Cookie2 header field specified in
1208   <xref target="RFC2965"/> does not share this problem.
1209  </t>
1210</x:note>
1211<t>
1212   Historically, HTTP header field values could be extended over multiple
1213   lines by preceding each extra line with at least one space or horizontal
1214   tab character (line folding). This specification deprecates such line
1215   folding except within the message/http media type
1216   (<xref target="internet.media.type.message.http"/>).
1217   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1218   (i.e., that contain any field-content that matches the obs-fold rule) unless
1219   the message is intended for packaging within the message/http media type.
1220   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1221   obs-fold whitespace with a single SP prior to interpreting the field value
1222   or forwarding the message downstream.
1223</t>
1224<t>
1225   Historically, HTTP has allowed field content with text in the ISO-8859-1
1226   <xref target="ISO-8859-1"/> character encoding and supported other
1227   character sets only through use of <xref target="RFC2047"/> encoding.
1228   In practice, most HTTP header field values use only a subset of the
1229   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1230   header fields &SHOULD; limit their field values to US-ASCII characters.
1231   Recipients &SHOULD; treat other (obs-text) octets in field content as
1232   opaque data.
1233</t>
1234<t anchor="rule.comment">
1235  <x:anchor-alias value="comment"/>
1236  <x:anchor-alias value="ctext"/>
1237   Comments can be included in some HTTP header fields by surrounding
1238   the comment text with parentheses. Comments are only allowed in
1239   fields containing "comment" as part of their field value definition.
1240</t>
1241<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1242  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1243  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1244                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1245</artwork></figure>
1246<t anchor="rule.quoted-cpair">
1247  <x:anchor-alias value="quoted-cpair"/>
1248   The backslash character ("\") can be used as a single-character
1249   quoting mechanism within comment constructs:
1250</t>
1251<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1252  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1253</artwork></figure>
1254<t>
1255   Producers &SHOULD-NOT; escape characters that do not require escaping
1256   (i.e., other than the backslash character "\" and the parentheses "(" and
1257   ")").
1258</t>
1259</section>
1260
1261<section title="Message Body" anchor="message.body">
1262  <x:anchor-alias value="message-body"/>
1263<t>
1264   The message-body (if any) of an HTTP message is used to carry the
1265   payload body associated with the request or response.
1266</t>
1267<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1268  <x:ref>message-body</x:ref> = *OCTET
1269</artwork></figure>
1270<t>
1271   The message-body differs from the payload body only when a transfer-coding
1272   has been applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).  When one or more transfer-codings are
1273   applied to a payload in order to form the message-body, the
1274   Transfer-Encoding header field &MUST; contain the list of
1275   transfer-codings applied. Transfer-Encoding is a property of the message,
1276   not of the payload, and thus &MAY; be added or removed by any implementation
1277   along the request/response chain under the constraints found in
1278   <xref target="transfer.codings"/>.
1279</t>
1280<t>
1281   The rules for when a message-body is allowed in a message differ for
1282   requests and responses.
1283</t>
1284<t>
1285   The presence of a message-body in a request is signaled by the
1286   inclusion of a Content-Length or Transfer-Encoding header field in
1287   the request's header fields, even if the request method does not
1288   define any use for a message-body.  This allows the request
1289   message framing algorithm to be independent of method semantics.
1290</t>
1291<t>
1292   For response messages, whether or not a message-body is included with
1293   a message is dependent on both the request method and the response
1294   status code (<xref target="status.code.and.reason.phrase"/>).
1295   Responses to the HEAD request method never include a message-body
1296   because the associated response header fields (e.g., Transfer-Encoding,
1297   Content-Length, etc.) only indicate what their values would have been
1298   if the method had been GET.  All 1xx (Informational), 204 (No Content),
1299   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1300   All other responses do include a message-body, although the body
1301   &MAY; be of zero length.
1302</t>
1303<t>
1304   The length of the message-body is determined by one of the following
1305   (in order of precedence):
1306</t>
1307<t>
1308  <list style="numbers">
1309    <x:lt><t>
1310     Any response to a HEAD request and any response with a status
1311     code of 100-199, 204, or 304 is always terminated by the first
1312     empty line after the header fields, regardless of the header
1313     fields present in the message, and thus cannot contain a message-body.
1314    </t></x:lt>
1315    <x:lt><t>
1316     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1317     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1318     is the final encoding, the message-body length is determined by reading
1319     and decoding the chunked data until the transfer-coding indicates the
1320     data is complete.
1321    </t>
1322    <t>
1323     If a Transfer-Encoding header field is present in a response and the
1324     "chunked" transfer-coding is not the final encoding, the message-body
1325     length is determined by reading the connection until it is closed by
1326     the server.
1327     If a Transfer-Encoding header field is present in a request and the
1328     "chunked" transfer-coding is not the final encoding, the message-body
1329     length cannot be determined reliably; the server &MUST; respond with
1330     the 400 (Bad Request) status code and then close the connection.
1331    </t>
1332    <t>
1333     If a message is received with both a Transfer-Encoding header field and a
1334     Content-Length header field, the Transfer-Encoding overrides the Content-Length.
1335     Such a message might indicate an attempt to perform request or response
1336     smuggling (bypass of security-related checks on message routing or content)
1337     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1338     be removed, prior to forwarding the message downstream, or replaced with
1339     the real message-body length after the transfer-coding is decoded.
1340    </t></x:lt>
1341    <x:lt><t>
1342     If a message is received without Transfer-Encoding and with either
1343     multiple Content-Length header fields or a single Content-Length header
1344     field with an invalid value, then the message framing is invalid and
1345     &MUST; be treated as an error to prevent request or response smuggling.
1346     If this is a request message, the server &MUST; respond with
1347     a 400 (Bad Request) status code and then close the connection.
1348     If this is a response message received by a proxy or gateway, the proxy
1349     or gateway &MUST; discard the received response, send a 502 (Bad Gateway)
1350     status code as its downstream response, and then close the connection.
1351     If this is a response message received by a user-agent, it &SHOULD; be
1352     treated as an error by discarding the message and closing the connection.
1353    </t></x:lt>
1354    <x:lt><t>
1355     If a valid Content-Length header field (<xref target="header.content-length"/>)
1356     is present without Transfer-Encoding, its decimal value defines the
1357     message-body length in octets.  If the actual number of octets sent in
1358     the message is less than the indicated Content-Length, the recipient
1359     &MUST; consider the message to be incomplete and treat the connection
1360     as no longer usable.
1361     If the actual number of octets sent in the message is more than the indicated
1362     Content-Length, the recipient &MUST; only process the message-body up to the
1363     field value's number of octets; the remainder of the message &MUST; either
1364     be discarded or treated as the next message in a pipeline.  For the sake of
1365     robustness, a user-agent &MAY; attempt to detect and correct such an error
1366     in message framing if it is parsing the response to the last request on
1367     on a connection and the connection has been closed by the server.
1368    </t></x:lt>
1369    <x:lt><t>
1370     If this is a request message and none of the above are true, then the
1371     message-body length is zero (no message-body is present).
1372    </t></x:lt>
1373    <x:lt><t>
1374     Otherwise, this is a response message without a declared message-body
1375     length, so the message-body length is determined by the number of octets
1376     received prior to the server closing the connection.
1377    </t></x:lt>
1378  </list>
1379</t>
1380<t>
1381   Since there is no way to distinguish a successfully completed,
1382   close-delimited message from a partially-received message interrupted
1383   by network failure, implementations &SHOULD; use encoding or
1384   length-delimited messages whenever possible.  The close-delimiting
1385   feature exists primarily for backwards compatibility with HTTP/1.0.
1386</t>
1387<t>
1388   A server &MAY; reject a request that contains a message-body but
1389   not a Content-Length by responding with 411 (Length Required).
1390</t>
1391<t>
1392   Unless a transfer-coding other than "chunked" has been applied,
1393   a client that sends a request containing a message-body &SHOULD;
1394   use a valid Content-Length header field if the message-body length
1395   is known in advance, rather than the "chunked" encoding, since some
1396   existing services respond to "chunked" with a 411 (Length Required)
1397   status code even though they understand the chunked encoding.  This
1398   is typically because such services are implemented via a gateway that
1399   requires a content-length in advance of being called and the server
1400   is unable or unwilling to buffer the entire request before processing.
1401</t>
1402<t>
1403   A client that sends a request containing a message-body &MUST; include a
1404   valid Content-Length header field if it does not know the server will
1405   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1406   of specific user configuration or by remembering the version of a prior
1407   received response.
1408</t>
1409<t>
1410   Request messages that are prematurely terminated, possibly due to a
1411   cancelled connection or a server-imposed time-out exception, &MUST;
1412   result in closure of the connection; sending an HTTP/1.1 error response
1413   prior to closing the connection is &OPTIONAL;.
1414   Response messages that are prematurely terminated, usually by closure
1415   of the connection prior to receiving the expected number of octets or by
1416   failure to decode a transfer-encoded message-body, &MUST; be recorded
1417   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1418   message-body as if it were complete (i.e., some indication must be given
1419   to the user that an error occurred).  Cache requirements for incomplete
1420   responses are defined in &cache-incomplete;.
1421</t>
1422<t>
1423   A server &MUST; read the entire request message-body or close
1424   the connection after sending its response, since otherwise the
1425   remaining data on a persistent connection would be misinterpreted
1426   as the next request.  Likewise,
1427   a client &MUST; read the entire response message-body if it intends
1428   to reuse the same connection for a subsequent request.  Pipelining
1429   multiple requests on a connection is described in <xref target="pipelining"/>.
1430</t>
1431</section>
1432
1433<section title="General Header Fields" anchor="general.header.fields">
1434  <x:anchor-alias value="general-header"/>
1435<t>
1436   There are a few header fields which have general applicability for
1437   both request and response messages, but which do not apply to the
1438   payload being transferred. These header fields apply only to the
1439   message being transmitted.
1440</t>
1441<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1442  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1443                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1444                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1445                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1446                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1447                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1448                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1449                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1450                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1451                 / <x:ref>MIME-Version</x:ref>             ; &header-mime-version;
1452</artwork></figure>
1453<t>
1454   General-header field names can be extended reliably only in
1455   combination with a change in the protocol version. However, new or
1456   experimental header fields might be given the semantics of general
1457   header fields if all parties in the communication recognize them to
1458   be general-header fields.
1459</t>
1460</section>
1461</section>
1462
1463<section title="Request" anchor="request">
1464  <x:anchor-alias value="Request"/>
1465<t>
1466   A request message from a client to a server includes, within the
1467   first line of that message, the method to be applied to the resource,
1468   the identifier of the resource, and the protocol version in use.
1469</t>
1470<!--                 Host                      ; should be moved here eventually -->
1471<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1472  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1473                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1474                  <x:ref>CRLF</x:ref>
1475                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1476</artwork></figure>
1477
1478<section title="Request-Line" anchor="request-line">
1479  <x:anchor-alias value="Request-Line"/>
1480<t>
1481   The Request-Line begins with a method token, followed by the
1482   request-target and the protocol version, and ending with CRLF. The
1483   elements are separated by SP characters. No CR or LF is allowed
1484   except in the final CRLF sequence.
1485</t>
1486<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1487  <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>
1488</artwork></figure>
1489
1490<section title="Method" anchor="method">
1491  <x:anchor-alias value="Method"/>
1492<t>
1493   The Method  token indicates the method to be performed on the
1494   resource identified by the request-target. The method is case-sensitive.
1495</t>
1496<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1497  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1498</artwork></figure>
1499</section>
1500
1501<section title="request-target" anchor="request-target">
1502  <x:anchor-alias value="request-target"/>
1503<t>
1504   The request-target identifies the resource upon which to apply the request.
1505</t>
1506<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1507  <x:ref>request-target</x:ref> = "*"
1508                 / <x:ref>absolute-URI</x:ref>
1509                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1510                 / <x:ref>authority</x:ref>
1511</artwork></figure>
1512<t>
1513   The four options for request-target are dependent on the nature of the
1514   request.
1515</t>   
1516<t><iref item="asterisk form (of request-target)"/>
1517   The asterisk "*" ("asterisk form") means that the request does not apply to a
1518   particular resource, but to the server itself. This is only allowed for the
1519   OPTIONS method. Thus, the only valid example is
1520</t>
1521<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1522OPTIONS * HTTP/1.1
1523</artwork></figure>
1524<t><iref item="absolute-URI form (of request-target)"/>
1525   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1526   proxy. The proxy is requested to forward the request or service it
1527   from a valid cache, and return the response. Note that the proxy &MAY;
1528   forward the request on to another proxy or directly to the server
1529   specified by the absolute-URI. In order to avoid request loops, a
1530   proxy &MUST; be able to recognize all of its server names, including
1531   any aliases, local variations, and the numeric IP address. An example
1532   Request-Line would be:
1533</t>
1534<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1535GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1536</artwork></figure>
1537<t>
1538   To allow for transition to absolute-URIs in all requests in future
1539   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1540   form in requests, even though HTTP/1.1 clients will only generate
1541   them in requests to proxies.
1542</t>
1543<t><iref item="authority form (of request-target)"/>
1544   The "authority form" is only used by the CONNECT method (&CONNECT;).
1545</t>
1546<t><iref item="path-absolute form (of request-target)"/>
1547   The most common form of request-target is that used to identify a
1548   resource on an origin server or gateway ("path-absolute form"). In this case the absolute
1549   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1550   the request-target, and the network location of the URI (authority) &MUST;
1551   be transmitted in a Host header field. For example, a client wishing
1552   to retrieve the resource above directly from the origin server would
1553   create a TCP connection to port 80 of the host "www.example.org" and send
1554   the lines:
1555</t>
1556<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1557GET /pub/WWW/TheProject.html HTTP/1.1
1558Host: www.example.org
1559</artwork></figure>
1560<t>
1561   followed by the remainder of the Request. Note that the absolute path
1562   cannot be empty; if none is present in the original URI, it &MUST; be
1563   given as "/" (the server root).
1564</t>
1565<t>
1566   If a proxy receives a request without any path in the request-target and
1567   the method specified is capable of supporting the asterisk form of
1568   request-target, then the last proxy on the request chain &MUST; forward the
1569   request with "*" as the final request-target.
1570</t>
1571<figure><preamble>   
1572   For example, the request
1573</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1574OPTIONS http://www.example.org:8001 HTTP/1.1
1575</artwork></figure>
1576<figure><preamble>   
1577  would be forwarded by the proxy as
1578</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1579OPTIONS * HTTP/1.1
1580Host: www.example.org:8001
1581</artwork>
1582<postamble>
1583   after connecting to port 8001 of host "www.example.org".
1584</postamble>
1585</figure>
1586<t>
1587   The request-target is transmitted in the format specified in
1588   <xref target="http.uri"/>. If the request-target is percent-encoded
1589   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1590   &MUST; decode the request-target in order to
1591   properly interpret the request. Servers &SHOULD; respond to invalid
1592   request-targets with an appropriate status code.
1593</t>
1594<t>
1595   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1596   received request-target when forwarding it to the next inbound server,
1597   except as noted above to replace a null path-absolute with "/" or "*".
1598</t>
1599<x:note>
1600  <t>
1601    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1602    meaning of the request when the origin server is improperly using
1603    a non-reserved URI character for a reserved purpose.  Implementors
1604    need to be aware that some pre-HTTP/1.1 proxies have been known to
1605    rewrite the request-target.
1606  </t>
1607</x:note>
1608<t>
1609   HTTP does not place a pre-defined limit on the length of a request-target.
1610   A server &MUST; be prepared to receive URIs of unbounded length and
1611   respond with the 414 (URI Too Long) status code if the received
1612   request-target would be longer than the server wishes to handle
1613   (see &status-414;).
1614</t>
1615<t>
1616   Various ad-hoc limitations on request-target length are found in practice.
1617   It is &RECOMMENDED; that all HTTP senders and recipients support
1618   request-target lengths of 8000 or more octets.
1619</t>
1620<x:note>
1621  <t>
1622    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1623    are not part of the request-target and thus will not be transmitted
1624    in an HTTP request.
1625  </t>
1626</x:note>
1627</section>
1628</section>
1629
1630<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1631<t>
1632   The exact resource identified by an Internet request is determined by
1633   examining both the request-target and the Host header field.
1634</t>
1635<t>
1636   An origin server that does not allow resources to differ by the
1637   requested host &MAY; ignore the Host header field value when
1638   determining the resource identified by an HTTP/1.1 request. (But see
1639   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1640   for other requirements on Host support in HTTP/1.1.)
1641</t>
1642<t>
1643   An origin server that does differentiate resources based on the host
1644   requested (sometimes referred to as virtual hosts or vanity host
1645   names) &MUST; use the following rules for determining the requested
1646   resource on an HTTP/1.1 request:
1647  <list style="numbers">
1648    <t>If request-target is an absolute-URI, the host is part of the
1649     request-target. Any Host header field value in the request &MUST; be
1650     ignored.</t>
1651    <t>If the request-target is not an absolute-URI, and the request includes
1652     a Host header field, the host is determined by the Host header
1653     field value.</t>
1654    <t>If the host as determined by rule 1 or 2 is not a valid host on
1655     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1656  </list>
1657</t>
1658<t>
1659   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1660   attempt to use heuristics (e.g., examination of the URI path for
1661   something unique to a particular host) in order to determine what
1662   exact resource is being requested.
1663</t>
1664</section>
1665
1666<section title="Effective Request URI" anchor="effective.request.uri">
1667  <iref primary="true" item="effective request URI"/>
1668  <iref primary="true" item="target resource"/>
1669<t>
1670   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1671   for the target resource; instead, the URI needs to be inferred from the
1672   request-target, Host header field, and connection context. The result of
1673   this process is called the "effective request URI".  The "target resource"
1674   is the resource identified by the effective request URI.
1675</t>
1676<t>
1677   If the request-target is an absolute-URI, then the effective request URI is
1678   the request-target.
1679</t>
1680<t>
1681   If the request-target uses the path-absolute form or the asterisk form,
1682   and the Host header field is present, then the effective request URI is
1683   constructed by concatenating
1684</t>
1685<t>
1686  <list style="symbols">
1687    <t>
1688      the scheme name: "http" if the request was received over an insecure
1689      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1690      connection,
1691    </t>
1692    <t>
1693      the character sequence "://",
1694    </t>
1695    <t>
1696      the authority component, as specified in the Host header field
1697      (<xref target="header.host"/>), and
1698    </t>
1699    <t>
1700      the request-target obtained from the Request-Line, unless the
1701      request-target is just the asterisk "*".
1702    </t>
1703  </list>
1704</t>
1705<t>
1706   If the request-target uses the path-absolute form or the asterisk form,
1707   and the Host header field is not present, then the effective request URI is
1708   undefined.
1709</t>
1710<t>
1711   Otherwise, when request-target uses the authority form, the effective
1712   request URI is undefined.
1713</t>
1714<figure>
1715<preamble>
1716   Example 1: the effective request URI for the message
1717</preamble> 
1718<artwork type="example" x:indent-with="  ">
1719GET /pub/WWW/TheProject.html HTTP/1.1
1720Host: www.example.org:8080
1721</artwork>
1722<postamble>
1723  (received over an insecure TCP connection) is "http", plus "://", plus the
1724  authority component "www.example.org:8080", plus the request-target
1725  "/pub/WWW/TheProject.html", thus
1726  "http://www.example.org:8080/pub/WWW/TheProject.html".
1727</postamble>
1728</figure>
1729<figure>
1730<preamble>
1731   Example 2: the effective request URI for the message
1732</preamble> 
1733<artwork type="example" x:indent-with="  ">
1734GET * HTTP/1.1
1735Host: www.example.org
1736</artwork>
1737<postamble>
1738  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1739  authority component "www.example.org", thus "https://www.example.org".
1740</postamble>
1741</figure>
1742<t>
1743   Effective request URIs are compared using the rules described in
1744   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1745   be treated as equivalent to an absolute path of "/".
1746</t> 
1747</section>
1748
1749</section>
1750
1751
1752<section title="Response" anchor="response">
1753  <x:anchor-alias value="Response"/>
1754<t>
1755   After receiving and interpreting a request message, a server responds
1756   with an HTTP response message.
1757</t>
1758<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1759  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1760                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1761                  <x:ref>CRLF</x:ref>
1762                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1763</artwork></figure>
1764
1765<section title="Status-Line" anchor="status-line">
1766  <x:anchor-alias value="Status-Line"/>
1767<t>
1768   The first line of a Response message is the Status-Line, consisting
1769   of the protocol version followed by a numeric status code and its
1770   associated textual phrase, with each element separated by SP
1771   characters. No CR or LF is allowed except in the final CRLF sequence.
1772</t>
1773<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1774  <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>
1775</artwork></figure>
1776
1777<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1778  <x:anchor-alias value="Reason-Phrase"/>
1779  <x:anchor-alias value="Status-Code"/>
1780<t>
1781   The Status-Code element is a 3-digit integer result code of the
1782   attempt to understand and satisfy the request. These codes are fully
1783   defined in &status-codes;.  The Reason Phrase exists for the sole
1784   purpose of providing a textual description associated with the numeric
1785   status code, out of deference to earlier Internet application protocols
1786   that were more frequently used with interactive text clients.
1787   A client &SHOULD; ignore the content of the Reason Phrase.
1788</t>
1789<t>
1790   The first digit of the Status-Code defines the class of response. The
1791   last two digits do not have any categorization role. There are 5
1792   values for the first digit:
1793  <list style="symbols">
1794    <t>
1795      1xx: Informational - Request received, continuing process
1796    </t>
1797    <t>
1798      2xx: Success - The action was successfully received,
1799        understood, and accepted
1800    </t>
1801    <t>
1802      3xx: Redirection - Further action must be taken in order to
1803        complete the request
1804    </t>
1805    <t>
1806      4xx: Client Error - The request contains bad syntax or cannot
1807        be fulfilled
1808    </t>
1809    <t>
1810      5xx: Server Error - The server failed to fulfill an apparently
1811        valid request
1812    </t>
1813  </list>
1814</t>
1815<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1816  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1817  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1818</artwork></figure>
1819</section>
1820</section>
1821
1822</section>
1823
1824
1825<section title="Protocol Parameters" anchor="protocol.parameters">
1826
1827<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1828  <x:anchor-alias value="HTTP-date"/>
1829<t>
1830   HTTP applications have historically allowed three different formats
1831   for date/time stamps. However, the preferred format is a fixed-length subset
1832   of that defined by <xref target="RFC1123"/>:
1833</t>
1834<figure><artwork type="example" x:indent-with="  ">
1835Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1836</artwork></figure>
1837<t>
1838   The other formats are described here only for compatibility with obsolete
1839   implementations.
1840</t>
1841<figure><artwork type="example" x:indent-with="  ">
1842Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1843Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1844</artwork></figure>
1845<t>
1846   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1847   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1848   only generate the RFC 1123 format for representing HTTP-date values
1849   in header fields. See <xref target="tolerant.applications"/> for further information.
1850</t>
1851<t>
1852   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1853   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1854   equal to UTC (Coordinated Universal Time). This is indicated in the
1855   first two formats by the inclusion of "GMT" as the three-letter
1856   abbreviation for time zone, and &MUST; be assumed when reading the
1857   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1858   additional whitespace beyond that specifically included as SP in the
1859   grammar.
1860</t>
1861<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1862  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1863</artwork></figure>
1864<t anchor="preferred.date.format">
1865  <x:anchor-alias value="rfc1123-date"/>
1866  <x:anchor-alias value="time-of-day"/>
1867  <x:anchor-alias value="hour"/>
1868  <x:anchor-alias value="minute"/>
1869  <x:anchor-alias value="second"/>
1870  <x:anchor-alias value="day-name"/>
1871  <x:anchor-alias value="day"/>
1872  <x:anchor-alias value="month"/>
1873  <x:anchor-alias value="year"/>
1874  <x:anchor-alias value="GMT"/>
1875  Preferred format:
1876</t>
1877<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"/>
1878  <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>
1879  ; fixed length subset of the format defined in
1880  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
1881 
1882  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1883               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1884               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1885               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1886               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1887               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1888               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1889               
1890  <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>
1891               ; e.g., 02 Jun 1982
1892
1893  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1894  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1895               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1896               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1897               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1898               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1899               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1900               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1901               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1902               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1903               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1904               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1905               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1906  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1907
1908  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1909
1910  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1911                 ; 00:00:00 - 23:59:59
1912                 
1913  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1914  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1915  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1916</artwork></figure>
1917<t>
1918  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1919  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1920  same as those defined for the RFC 5322 constructs
1921  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1922</t>
1923<t anchor="obsolete.date.formats">
1924  <x:anchor-alias value="obs-date"/>
1925  <x:anchor-alias value="rfc850-date"/>
1926  <x:anchor-alias value="asctime-date"/>
1927  <x:anchor-alias value="date1"/>
1928  <x:anchor-alias value="date2"/>
1929  <x:anchor-alias value="date3"/>
1930  <x:anchor-alias value="rfc1123-date"/>
1931  <x:anchor-alias value="day-name-l"/>
1932  Obsolete formats:
1933</t>
1934<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1935  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
1936</artwork></figure>
1937<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1938  <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>
1939  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1940                 ; day-month-year (e.g., 02-Jun-82)
1941
1942  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1943         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1944         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1945         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1946         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1947         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1948         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1949</artwork></figure>
1950<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1951  <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>
1952  <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> ))
1953                 ; month day (e.g., Jun  2)
1954</artwork></figure>
1955<x:note>
1956  <t>
1957    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1958    accepting date values that might have been sent by non-HTTP
1959    applications, as is sometimes the case when retrieving or posting
1960    messages via proxies/gateways to SMTP or NNTP.
1961  </t>
1962</x:note>
1963<x:note>
1964  <t>
1965    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1966    to their usage within the protocol stream. Clients and servers are
1967    not required to use these formats for user presentation, request
1968    logging, etc.
1969  </t>
1970</x:note>
1971</section>
1972
1973<section title="Transfer Codings" anchor="transfer.codings">
1974  <x:anchor-alias value="transfer-coding"/>
1975  <x:anchor-alias value="transfer-extension"/>
1976<t>
1977   Transfer-coding values are used to indicate an encoding
1978   transformation that has been, can be, or might need to be applied to a
1979   payload body in order to ensure "safe transport" through the network.
1980   This differs from a content coding in that the transfer-coding is a
1981   property of the message rather than a property of the representation
1982   that is being transferred.
1983</t>
1984<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1985  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
1986                          / "compress" ; <xref target="compress.coding"/>
1987                          / "deflate" ; <xref target="deflate.coding"/>
1988                          / "gzip" ; <xref target="gzip.coding"/>
1989                          / <x:ref>transfer-extension</x:ref>
1990  <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> )
1991</artwork></figure>
1992<t anchor="rule.parameter">
1993  <x:anchor-alias value="attribute"/>
1994  <x:anchor-alias value="transfer-parameter"/>
1995  <x:anchor-alias value="value"/>
1996   Parameters are in the form of attribute/value pairs.
1997</t>
1998<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"/>
1999  <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>
2000  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2001  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2002</artwork></figure>
2003<t>
2004   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2005   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2006   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2007</t>
2008<t>
2009   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2010   MIME, which were designed to enable safe transport of binary data over a
2011   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2012   However, safe transport
2013   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2014   the only unsafe characteristic of message-bodies is the difficulty in
2015   determining the exact message body length (<xref target="message.body"/>),
2016   or the desire to encrypt data over a shared transport.
2017</t>
2018<t>
2019   A server that receives a request message with a transfer-coding it does
2020   not understand &SHOULD; respond with 501 (Not Implemented) and then
2021   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2022   client.
2023</t>
2024
2025<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2026  <iref item="chunked (Coding Format)"/>
2027  <iref item="Coding Format" subitem="chunked"/>
2028  <x:anchor-alias value="chunk"/>
2029  <x:anchor-alias value="Chunked-Body"/>
2030  <x:anchor-alias value="chunk-data"/>
2031  <x:anchor-alias value="chunk-ext"/>
2032  <x:anchor-alias value="chunk-ext-name"/>
2033  <x:anchor-alias value="chunk-ext-val"/>
2034  <x:anchor-alias value="chunk-size"/>
2035  <x:anchor-alias value="last-chunk"/>
2036  <x:anchor-alias value="trailer-part"/>
2037  <x:anchor-alias value="quoted-str-nf"/>
2038  <x:anchor-alias value="qdtext-nf"/>
2039<t>
2040   The chunked encoding modifies the body of a message in order to
2041   transfer it as a series of chunks, each with its own size indicator,
2042   followed by an &OPTIONAL; trailer containing header fields. This
2043   allows dynamically produced content to be transferred along with the
2044   information necessary for the recipient to verify that it has
2045   received the full message.
2046</t>
2047<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"/>
2048  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2049                   <x:ref>last-chunk</x:ref>
2050                   <x:ref>trailer-part</x:ref>
2051                   <x:ref>CRLF</x:ref>
2052 
2053  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2054                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2055  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2056  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2057 
2058  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2059                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2060  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2061  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2062  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2063  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2064 
2065  <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>
2066                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2067  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2068                 ; <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> 
2069</artwork></figure>
2070<t>
2071   The chunk-size field is a string of hex digits indicating the size of
2072   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2073   zero, followed by the trailer, which is terminated by an empty line.
2074</t>
2075<t>
2076   The trailer allows the sender to include additional HTTP header
2077   fields at the end of the message. The Trailer header field can be
2078   used to indicate which header fields are included in a trailer (see
2079   <xref target="header.trailer"/>).
2080</t>
2081<t>
2082   A server using chunked transfer-coding in a response &MUST-NOT; use the
2083   trailer for any header fields unless at least one of the following is
2084   true:
2085  <list style="numbers">
2086    <t>the request included a TE header field that indicates "trailers" is
2087     acceptable in the transfer-coding of the  response, as described in
2088     <xref target="header.te"/>; or,</t>
2089     
2090    <t>the trailer fields consist entirely of optional metadata, and the
2091    recipient could use the message (in a manner acceptable to the server where
2092    the field originated) without receiving it. In other words, the server that
2093    generated the header (often but not always the origin server) is willing to
2094    accept the possibility that the trailer fields might be silently discarded
2095    along the path to the client.</t>
2096  </list>
2097</t>
2098<t>
2099   This requirement prevents an interoperability failure when the
2100   message is being received by an HTTP/1.1 (or later) proxy and
2101   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2102   compliance with the protocol would have necessitated a possibly
2103   infinite buffer on the proxy.
2104</t>
2105<t>
2106   A process for decoding the "chunked" transfer-coding
2107   can be represented in pseudo-code as:
2108</t>
2109<figure><artwork type="code">
2110  length := 0
2111  read chunk-size, chunk-ext (if any) and CRLF
2112  while (chunk-size &gt; 0) {
2113     read chunk-data and CRLF
2114     append chunk-data to decoded-body
2115     length := length + chunk-size
2116     read chunk-size and CRLF
2117  }
2118  read header-field
2119  while (header-field not empty) {
2120     append header-field to existing header fields
2121     read header-field
2122  }
2123  Content-Length := length
2124  Remove "chunked" from Transfer-Encoding
2125</artwork></figure>
2126<t>
2127   All HTTP/1.1 applications &MUST; be able to receive and decode the
2128   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2129   they do not understand.
2130</t>
2131<t>
2132   Since "chunked" is the only transfer-coding required to be understood
2133   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2134   on a persistent connection.  Whenever a transfer-coding is applied to
2135   a payload body in a request, the final transfer-coding applied &MUST;
2136   be "chunked".  If a transfer-coding is applied to a response payload
2137   body, then either the final transfer-coding applied &MUST; be "chunked"
2138   or the message &MUST; be terminated by closing the connection. When the
2139   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2140   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2141   be applied more than once in a message-body.
2142</t>
2143</section>
2144
2145<section title="Compression Codings" anchor="compression.codings">
2146<t>
2147   The codings defined below can be used to compress the payload of a
2148   message.
2149</t>
2150<x:note><t>
2151   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2152   is not desirable and is discouraged for future encodings. Their
2153   use here is representative of historical practice, not good
2154   design.
2155</t></x:note>
2156<x:note><t>
2157   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2158   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2159   equivalent to "gzip" and "compress" respectively.
2160</t></x:note>
2161
2162<section title="Compress Coding" anchor="compress.coding">
2163<iref item="compress (Coding Format)"/>
2164<iref item="Coding Format" subitem="compress"/>
2165<t>
2166   The "compress" format is produced by the common UNIX file compression
2167   program "compress". This format is an adaptive Lempel-Ziv-Welch
2168   coding (LZW).
2169</t>
2170</section>
2171
2172<section title="Deflate Coding" anchor="deflate.coding">
2173<iref item="deflate (Coding Format)"/>
2174<iref item="Coding Format" subitem="deflate"/>
2175<t>
2176   The "deflate" format is defined as the "deflate" compression mechanism
2177   (described in <xref target="RFC1951"/>) used inside the "zlib"
2178   data format (<xref target="RFC1950"/>).
2179</t>
2180<x:note>
2181  <t>
2182    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2183    compressed data without the zlib wrapper.
2184   </t>
2185</x:note>
2186</section>
2187
2188<section title="Gzip Coding" anchor="gzip.coding">
2189<iref item="gzip (Coding Format)"/>
2190<iref item="Coding Format" subitem="gzip"/>
2191<t>
2192   The "gzip" format is produced by the file compression program
2193   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2194   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2195</t>
2196</section>
2197
2198</section>
2199
2200<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2201<t>
2202   The HTTP Transfer Coding Registry defines the name space for the transfer
2203   coding names.
2204</t>
2205<t>
2206   Registrations &MUST; include the following fields:
2207   <list style="symbols">
2208     <t>Name</t>
2209     <t>Description</t>
2210     <t>Pointer to specification text</t>
2211   </list>
2212</t>
2213<t>
2214   Names of transfer codings &MUST-NOT; overlap with names of content codings
2215   (&content-codings;), unless the encoding transformation is identical (as it
2216   is the case for the compression codings defined in
2217   <xref target="compression.codings"/>).
2218</t>
2219<t>
2220   Values to be added to this name space require a specification
2221   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2222   conform to the purpose of transfer coding defined in this section.
2223</t>
2224<t>
2225   The registry itself is maintained at
2226   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2227</t>
2228</section>
2229</section>
2230
2231<section title="Product Tokens" anchor="product.tokens">
2232  <x:anchor-alias value="product"/>
2233  <x:anchor-alias value="product-version"/>
2234<t>
2235   Product tokens are used to allow communicating applications to
2236   identify themselves by software name and version. Most fields using
2237   product tokens also allow sub-products which form a significant part
2238   of the application to be listed, separated by whitespace. By
2239   convention, the products are listed in order of their significance
2240   for identifying the application.
2241</t>
2242<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2243  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2244  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2245</artwork></figure>
2246<t>
2247   Examples:
2248</t>
2249<figure><artwork type="example">
2250  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2251  Server: Apache/0.8.4
2252</artwork></figure>
2253<t>
2254   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2255   used for advertising or other non-essential information. Although any
2256   token character &MAY; appear in a product-version, this token &SHOULD;
2257   only be used for a version identifier (i.e., successive versions of
2258   the same product &SHOULD; only differ in the product-version portion of
2259   the product value).
2260</t>
2261</section>
2262
2263<section title="Quality Values" anchor="quality.values">
2264  <x:anchor-alias value="qvalue"/>
2265<t>
2266   Both transfer codings (TE request header field, <xref target="header.te"/>)
2267   and content negotiation (&content.negotiation;) use short "floating point"
2268   numbers to indicate the relative importance ("weight") of various
2269   negotiable parameters.  A weight is normalized to a real number in
2270   the range 0 through 1, where 0 is the minimum and 1 the maximum
2271   value. If a parameter has a quality value of 0, then content with
2272   this parameter is "not acceptable" for the client. HTTP/1.1
2273   applications &MUST-NOT; generate more than three digits after the
2274   decimal point. User configuration of these values &SHOULD; also be
2275   limited in this fashion.
2276</t>
2277<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2278  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2279                 / ( "1" [ "." 0*3("0") ] )
2280</artwork></figure>
2281<x:note>
2282  <t>
2283     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2284     relative degradation in desired quality.
2285  </t>
2286</x:note>
2287</section>
2288
2289</section>
2290
2291<section title="Connections" anchor="connections">
2292
2293<section title="Persistent Connections" anchor="persistent.connections">
2294
2295<section title="Purpose" anchor="persistent.purpose">
2296<t>
2297   Prior to persistent connections, a separate TCP connection was
2298   established to fetch each URL, increasing the load on HTTP servers
2299   and causing congestion on the Internet. The use of inline images and
2300   other associated data often requires a client to make multiple
2301   requests of the same server in a short amount of time. Analysis of
2302   these performance problems and results from a prototype
2303   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2304   measurements of actual HTTP/1.1 implementations show good
2305   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2306   T/TCP <xref target="Tou1998"/>.
2307</t>
2308<t>
2309   Persistent HTTP connections have a number of advantages:
2310  <list style="symbols">
2311      <t>
2312        By opening and closing fewer TCP connections, CPU time is saved
2313        in routers and hosts (clients, servers, proxies, gateways,
2314        tunnels, or caches), and memory used for TCP protocol control
2315        blocks can be saved in hosts.
2316      </t>
2317      <t>
2318        HTTP requests and responses can be pipelined on a connection.
2319        Pipelining allows a client to make multiple requests without
2320        waiting for each response, allowing a single TCP connection to
2321        be used much more efficiently, with much lower elapsed time.
2322      </t>
2323      <t>
2324        Network congestion is reduced by reducing the number of packets
2325        caused by TCP opens, and by allowing TCP sufficient time to
2326        determine the congestion state of the network.
2327      </t>
2328      <t>
2329        Latency on subsequent requests is reduced since there is no time
2330        spent in TCP's connection opening handshake.
2331      </t>
2332      <t>
2333        HTTP can evolve more gracefully, since errors can be reported
2334        without the penalty of closing the TCP connection. Clients using
2335        future versions of HTTP might optimistically try a new feature,
2336        but if communicating with an older server, retry with old
2337        semantics after an error is reported.
2338      </t>
2339    </list>
2340</t>
2341<t>
2342   HTTP implementations &SHOULD; implement persistent connections.
2343</t>
2344</section>
2345
2346<section title="Overall Operation" anchor="persistent.overall">
2347<t>
2348   A significant difference between HTTP/1.1 and earlier versions of
2349   HTTP is that persistent connections are the default behavior of any
2350   HTTP connection. That is, unless otherwise indicated, the client
2351   &SHOULD; assume that the server will maintain a persistent connection,
2352   even after error responses from the server.
2353</t>
2354<t>
2355   Persistent connections provide a mechanism by which a client and a
2356   server can signal the close of a TCP connection. This signaling takes
2357   place using the Connection header field (<xref target="header.connection"/>). Once a close
2358   has been signaled, the client &MUST-NOT; send any more requests on that
2359   connection.
2360</t>
2361
2362<section title="Negotiation" anchor="persistent.negotiation">
2363<t>
2364   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2365   maintain a persistent connection unless a Connection header field including
2366   the connection-token "close" was sent in the request. If the server
2367   chooses to close the connection immediately after sending the
2368   response, it &SHOULD; send a Connection header field including the
2369   connection-token "close".
2370</t>
2371<t>
2372   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2373   decide to keep it open based on whether the response from a server
2374   contains a Connection header field with the connection-token close. In case
2375   the client does not want to maintain a connection for more than that
2376   request, it &SHOULD; send a Connection header field including the
2377   connection-token close.
2378</t>
2379<t>
2380   If either the client or the server sends the close token in the
2381   Connection header field, that request becomes the last one for the
2382   connection.
2383</t>
2384<t>
2385   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2386   maintained for HTTP versions less than 1.1 unless it is explicitly
2387   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2388   compatibility with HTTP/1.0 clients.
2389</t>
2390<t>
2391   In order to remain persistent, all messages on the connection &MUST;
2392   have a self-defined message length (i.e., one not defined by closure
2393   of the connection), as described in <xref target="message.body"/>.
2394</t>
2395</section>
2396
2397<section title="Pipelining" anchor="pipelining">
2398<t>
2399   A client that supports persistent connections &MAY; "pipeline" its
2400   requests (i.e., send multiple requests without waiting for each
2401   response). A server &MUST; send its responses to those requests in the
2402   same order that the requests were received.
2403</t>
2404<t>
2405   Clients which assume persistent connections and pipeline immediately
2406   after connection establishment &SHOULD; be prepared to retry their
2407   connection if the first pipelined attempt fails. If a client does
2408   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2409   persistent. Clients &MUST; also be prepared to resend their requests if
2410   the server closes the connection before sending all of the
2411   corresponding responses.
2412</t>
2413<t>
2414   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2415   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2416   premature termination of the transport connection could lead to
2417   indeterminate results. A client wishing to send a non-idempotent
2418   request &SHOULD; wait to send that request until it has received the
2419   response status line for the previous request.
2420</t>
2421</section>
2422</section>
2423
2424<section title="Proxy Servers" anchor="persistent.proxy">
2425<t>
2426   It is especially important that proxies correctly implement the
2427   properties of the Connection header field as specified in <xref target="header.connection"/>.
2428</t>
2429<t>
2430   The proxy server &MUST; signal persistent connections separately with
2431   its clients and the origin servers (or other proxy servers) that it
2432   connects to. Each persistent connection applies to only one transport
2433   link.
2434</t>
2435<t>
2436   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2437   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2438   for information and discussion of the problems with the Keep-Alive header field
2439   implemented by many HTTP/1.0 clients).
2440</t>
2441
2442<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2443<!--<t>
2444  <cref anchor="TODO-end-to-end" source="jre">
2445    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2446    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2447  </cref>
2448</t>-->
2449<t>
2450   For the purpose of defining the behavior of caches and non-caching
2451   proxies, we divide HTTP header fields into two categories:
2452  <list style="symbols">
2453      <t>End-to-end header fields, which are  transmitted to the ultimate
2454        recipient of a request or response. End-to-end header fields in
2455        responses MUST be stored as part of a cache entry and &MUST; be
2456        transmitted in any response formed from a cache entry.</t>
2457
2458      <t>Hop-by-hop header fields, which are meaningful only for a single
2459        transport-level connection, and are not stored by caches or
2460        forwarded by proxies.</t>
2461  </list>
2462</t>
2463<t>
2464   The following HTTP/1.1 header fields are hop-by-hop header fields:
2465  <list style="symbols">
2466      <t>Connection</t>
2467      <t>Keep-Alive</t>
2468      <t>Proxy-Authenticate</t>
2469      <t>Proxy-Authorization</t>
2470      <t>TE</t>
2471      <t>Trailer</t>
2472      <t>Transfer-Encoding</t>
2473      <t>Upgrade</t>
2474  </list>
2475</t>
2476<t>
2477   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2478</t>
2479<t>
2480   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2481   (<xref target="header.connection"/>).
2482</t>
2483</section>
2484
2485<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2486<!--<t>
2487  <cref anchor="TODO-non-mod-headers" source="jre">
2488    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2489    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2490  </cref>
2491</t>-->
2492<t>
2493   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2494   value of certain end-to-end header fields. A transparent proxy &SHOULD-NOT;
2495   modify an end-to-end header field unless the definition of that header field requires
2496   or specifically allows that.
2497</t>
2498<t>
2499   A transparent proxy &MUST-NOT; modify any of the following fields in a
2500   request or response, and it &MUST-NOT; add any of these fields if not
2501   already present:
2502  <list style="symbols">
2503      <t>Content-Location</t>
2504      <t>Content-MD5</t>
2505      <t>ETag</t>
2506      <t>Last-Modified</t>
2507  </list>
2508</t>
2509<t>
2510   A transparent proxy &MUST-NOT; modify any of the following fields in a
2511   response:
2512  <list style="symbols">
2513    <t>Expires</t>
2514  </list>
2515</t>
2516<t>
2517   but it &MAY; add any of these fields if not already present. If an
2518   Expires header field is added, it &MUST; be given a field-value identical to
2519   that of the Date header field in that response.
2520</t>
2521<t>
2522   A proxy &MUST-NOT; modify or add any of the following fields in a
2523   message that contains the no-transform cache-control directive, or in
2524   any request:
2525  <list style="symbols">
2526    <t>Content-Encoding</t>
2527    <t>Content-Range</t>
2528    <t>Content-Type</t>
2529  </list>
2530</t>
2531<t>
2532   A non-transparent proxy &MAY; modify or add these fields to a message
2533   that does not include no-transform, but if it does so, it &MUST; add a
2534   Warning 214 (Transformation applied) if one does not already appear
2535   in the message (see &header-warning;).
2536</t>
2537<x:note>
2538  <t>
2539    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2540    cause authentication failures if stronger authentication
2541    mechanisms are introduced in later versions of HTTP. Such
2542    authentication mechanisms &MAY; rely on the values of header fields
2543    not listed here.
2544  </t>
2545</x:note>
2546<t>
2547   A transparent proxy &MUST; preserve the message payload (&payload;),
2548   though it &MAY; change the message-body through application or removal
2549   of a transfer-coding (<xref target="transfer.codings"/>).
2550</t>
2551</section>
2552
2553</section>
2554
2555<section title="Practical Considerations" anchor="persistent.practical">
2556<t>
2557   Servers will usually have some time-out value beyond which they will
2558   no longer maintain an inactive connection. Proxy servers might make
2559   this a higher value since it is likely that the client will be making
2560   more connections through the same server. The use of persistent
2561   connections places no requirements on the length (or existence) of
2562   this time-out for either the client or the server.
2563</t>
2564<t>
2565   When a client or server wishes to time-out it &SHOULD; issue a graceful
2566   close on the transport connection. Clients and servers &SHOULD; both
2567   constantly watch for the other side of the transport close, and
2568   respond to it as appropriate. If a client or server does not detect
2569   the other side's close promptly it could cause unnecessary resource
2570   drain on the network.
2571</t>
2572<t>
2573   A client, server, or proxy &MAY; close the transport connection at any
2574   time. For example, a client might have started to send a new request
2575   at the same time that the server has decided to close the "idle"
2576   connection. From the server's point of view, the connection is being
2577   closed while it was idle, but from the client's point of view, a
2578   request is in progress.
2579</t>
2580<t>
2581   This means that clients, servers, and proxies &MUST; be able to recover
2582   from asynchronous close events. Client software &SHOULD; reopen the
2583   transport connection and retransmit the aborted sequence of requests
2584   without user interaction so long as the request sequence is
2585   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2586   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2587   human operator the choice of retrying the request(s). Confirmation by
2588   user-agent software with semantic understanding of the application
2589   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2590   be repeated if the second sequence of requests fails.
2591</t>
2592<t>
2593   Servers &SHOULD; always respond to at least one request per connection,
2594   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2595   middle of transmitting a response, unless a network or client failure
2596   is suspected.
2597</t>
2598<t>
2599   Clients (including proxies) &SHOULD; limit the number of simultaneous
2600   connections that they maintain to a given server (including proxies).
2601</t>
2602<t>
2603   Previous revisions of HTTP gave a specific number of connections as a
2604   ceiling, but this was found to be impractical for many applications. As a
2605   result, this specification does not mandate a particular maximum number of
2606   connections, but instead encourages clients to be conservative when opening
2607   multiple connections.
2608</t>
2609<t>
2610   In particular, while using multiple connections avoids the "head-of-line
2611   blocking" problem (whereby a request that takes significant server-side
2612   processing and/or has a large payload can block subsequent requests on the
2613   same connection), each connection used consumes server resources (sometimes
2614   significantly), and furthermore using multiple connections can cause
2615   undesirable side effects in congested networks.
2616</t>
2617<t>
2618   Note that servers might reject traffic that they deem abusive, including an
2619   excessive number of connections from a client.
2620</t>
2621</section>
2622</section>
2623
2624<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2625
2626<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2627<t>
2628   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2629   flow control mechanisms to resolve temporary overloads, rather than
2630   terminating connections with the expectation that clients will retry.
2631   The latter technique can exacerbate network congestion.
2632</t>
2633</section>
2634
2635<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2636<t>
2637   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2638   the network connection for an error status code while it is transmitting
2639   the request. If the client sees an error status code, it &SHOULD;
2640   immediately cease transmitting the body. If the body is being sent
2641   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2642   empty trailer &MAY; be used to prematurely mark the end of the message.
2643   If the body was preceded by a Content-Length header field, the client &MUST;
2644   close the connection.
2645</t>
2646</section>
2647
2648<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2649<t>
2650   The purpose of the 100 (Continue) status code (see &status-100;) is to
2651   allow a client that is sending a request message with a request body
2652   to determine if the origin server is willing to accept the request
2653   (based on the request header fields) before the client sends the request
2654   body. In some cases, it might either be inappropriate or highly
2655   inefficient for the client to send the body if the server will reject
2656   the message without looking at the body.
2657</t>
2658<t>
2659   Requirements for HTTP/1.1 clients:
2660  <list style="symbols">
2661    <t>
2662        If a client will wait for a 100 (Continue) response before
2663        sending the request body, it &MUST; send an Expect request-header
2664        field (&header-expect;) with the "100-continue" expectation.
2665    </t>
2666    <t>
2667        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2668        with the "100-continue" expectation if it does not intend
2669        to send a request body.
2670    </t>
2671  </list>
2672</t>
2673<t>
2674   Because of the presence of older implementations, the protocol allows
2675   ambiguous situations in which a client might send "Expect: 100-continue"
2676   without receiving either a 417 (Expectation Failed)
2677   or a 100 (Continue) status code. Therefore, when a client sends this
2678   header field to an origin server (possibly via a proxy) from which it
2679   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2680   wait for an indefinite period before sending the request body.
2681</t>
2682<t>
2683   Requirements for HTTP/1.1 origin servers:
2684  <list style="symbols">
2685    <t> Upon receiving a request which includes an Expect request-header
2686        field with the "100-continue" expectation, an origin server &MUST;
2687        either respond with 100 (Continue) status code and continue to read
2688        from the input stream, or respond with a final status code. The
2689        origin server &MUST-NOT; wait for the request body before sending
2690        the 100 (Continue) response. If it responds with a final status
2691        code, it &MAY; close the transport connection or it &MAY; continue
2692        to read and discard the rest of the request.  It &MUST-NOT;
2693        perform the requested method if it returns a final status code.
2694    </t>
2695    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2696        the request message does not include an Expect request-header
2697        field with the "100-continue" expectation, and &MUST-NOT; send a
2698        100 (Continue) response if such a request comes from an HTTP/1.0
2699        (or earlier) client. There is an exception to this rule: for
2700        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2701        status code in response to an HTTP/1.1 PUT or POST request that does
2702        not include an Expect request-header field with the "100-continue"
2703        expectation. This exception, the purpose of which is
2704        to minimize any client processing delays associated with an
2705        undeclared wait for 100 (Continue) status code, applies only to
2706        HTTP/1.1 requests, and not to requests with any other HTTP-version
2707        value.
2708    </t>
2709    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2710        already received some or all of the request body for the
2711        corresponding request.
2712    </t>
2713    <t> An origin server that sends a 100 (Continue) response &MUST;
2714    ultimately send a final status code, once the request body is
2715        received and processed, unless it terminates the transport
2716        connection prematurely.
2717    </t>
2718    <t> If an origin server receives a request that does not include an
2719        Expect request-header field with the "100-continue" expectation,
2720        the request includes a request body, and the server responds
2721        with a final status code before reading the entire request body
2722        from the transport connection, then the server &SHOULD-NOT;  close
2723        the transport connection until it has read the entire request,
2724        or until the client closes the connection. Otherwise, the client
2725        might not reliably receive the response message. However, this
2726        requirement is not be construed as preventing a server from
2727        defending itself against denial-of-service attacks, or from
2728        badly broken client implementations.
2729      </t>
2730    </list>
2731</t>
2732<t>
2733   Requirements for HTTP/1.1 proxies:
2734  <list style="symbols">
2735    <t> If a proxy receives a request that includes an Expect request-header
2736        field with the "100-continue" expectation, and the proxy
2737        either knows that the next-hop server complies with HTTP/1.1 or
2738        higher, or does not know the HTTP version of the next-hop
2739        server, it &MUST; forward the request, including the Expect header
2740        field.
2741    </t>
2742    <t> If the proxy knows that the version of the next-hop server is
2743        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2744        respond with a 417 (Expectation Failed) status code.
2745    </t>
2746    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2747        numbers received from recently-referenced next-hop servers.
2748    </t>
2749    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2750        request message was received from an HTTP/1.0 (or earlier)
2751        client and did not include an Expect request-header field with
2752        the "100-continue" expectation. This requirement overrides the
2753        general rule for forwarding of 1xx responses (see &status-1xx;).
2754    </t>
2755  </list>
2756</t>
2757</section>
2758
2759<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2760<t>
2761   If an HTTP/1.1 client sends a request which includes a request body,
2762   but which does not include an Expect request-header field with the
2763   "100-continue" expectation, and if the client is not directly
2764   connected to an HTTP/1.1 origin server, and if the client sees the
2765   connection close before receiving a status line from the server, the
2766   client &SHOULD; retry the request.  If the client does retry this
2767   request, it &MAY; use the following "binary exponential backoff"
2768   algorithm to be assured of obtaining a reliable response:
2769  <list style="numbers">
2770    <t>
2771      Initiate a new connection to the server
2772    </t>
2773    <t>
2774      Transmit the request-header fields
2775    </t>
2776    <t>
2777      Initialize a variable R to the estimated round-trip time to the
2778         server (e.g., based on the time it took to establish the
2779         connection), or to a constant value of 5 seconds if the round-trip
2780         time is not available.
2781    </t>
2782    <t>
2783       Compute T = R * (2**N), where N is the number of previous
2784         retries of this request.
2785    </t>
2786    <t>
2787       Wait either for an error response from the server, or for T
2788         seconds (whichever comes first)
2789    </t>
2790    <t>
2791       If no error response is received, after T seconds transmit the
2792         body of the request.
2793    </t>
2794    <t>
2795       If client sees that the connection is closed prematurely,
2796         repeat from step 1 until the request is accepted, an error
2797         response is received, or the user becomes impatient and
2798         terminates the retry process.
2799    </t>
2800  </list>
2801</t>
2802<t>
2803   If at any point an error status code is received, the client
2804  <list style="symbols">
2805      <t>&SHOULD-NOT;  continue and</t>
2806
2807      <t>&SHOULD; close the connection if it has not completed sending the
2808        request message.</t>
2809    </list>
2810</t>
2811</section>
2812</section>
2813</section>
2814
2815
2816<section title="Miscellaneous notes that might disappear" anchor="misc">
2817<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2818<t>
2819   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2820</t>
2821</section>
2822
2823<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2824<t>
2825   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2826</t>
2827</section>
2828
2829<section title="Interception of HTTP for access control" anchor="http.intercept">
2830<t>
2831   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2832</t>
2833</section>
2834
2835<section title="Use of HTTP by other protocols" anchor="http.others">
2836<t>
2837   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2838   Extensions of HTTP like WebDAV.</cref>
2839</t>
2840
2841</section>
2842<section title="Use of HTTP by media type specification" anchor="http.media">
2843<t>
2844   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2845</t>
2846</section>
2847</section>
2848
2849<section title="Header Field Definitions" anchor="header.field.definitions">
2850<t>
2851   This section defines the syntax and semantics of HTTP/1.1 header fields
2852   related to message framing and transport protocols.
2853</t>
2854
2855<section title="Connection" anchor="header.connection">
2856  <iref primary="true" item="Connection header" x:for-anchor=""/>
2857  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2858  <x:anchor-alias value="Connection"/>
2859  <x:anchor-alias value="connection-token"/>
2860  <x:anchor-alias value="Connection-v"/>
2861<t>
2862   The "Connection" general-header field allows the sender to specify
2863   options that are desired for that particular connection and &MUST-NOT;
2864   be communicated by proxies over further connections.
2865</t>
2866<t>
2867   The Connection header field's value has the following grammar:
2868</t>
2869<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="Connection-v"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2870  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2871  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2872  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2873</artwork></figure>
2874<t>
2875   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2876   message is forwarded and, for each connection-token in this field,
2877   remove any header field(s) from the message with the same name as the
2878   connection-token. Connection options are signaled by the presence of
2879   a connection-token in the Connection header field, not by any
2880   corresponding additional header field(s), since the additional header
2881   field might not be sent if there are no parameters associated with that
2882   connection option.
2883</t>
2884<t>
2885   Message header fields listed in the Connection header field &MUST-NOT; include
2886   end-to-end header fields, such as Cache-Control.
2887</t>
2888<t>
2889   HTTP/1.1 defines the "close" connection option for the sender to
2890   signal that the connection will be closed after completion of the
2891   response. For example,
2892</t>
2893<figure><artwork type="example">
2894  Connection: close
2895</artwork></figure>
2896<t>
2897   in either the request or the response header fields indicates that
2898   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2899   after the current request/response is complete.
2900</t>
2901<t>
2902   An HTTP/1.1 client that does not support persistent connections &MUST;
2903   include the "close" connection option in every request message.
2904</t>
2905<t>
2906   An HTTP/1.1 server that does not support persistent connections &MUST;
2907   include the "close" connection option in every response message that
2908   does not have a 1xx (Informational) status code.
2909</t>
2910<t>
2911   A system receiving an HTTP/1.0 (or lower-version) message that
2912   includes a Connection header field &MUST;, for each connection-token in this
2913   field, remove and ignore any header field(s) from the message with
2914   the same name as the connection-token. This protects against mistaken
2915   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2916</t>
2917</section>
2918
2919<section title="Content-Length" anchor="header.content-length">
2920  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2921  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2922  <x:anchor-alias value="Content-Length"/>
2923  <x:anchor-alias value="Content-Length-v"/>
2924<t>
2925   The "Content-Length" header field indicates the size of the
2926   message-body, in decimal number of octets, for any message other than
2927   a response to the HEAD method or a response with a status code of 304.
2928   In the case of responses to the HEAD method, it indicates the size of
2929   the payload body (not including any potential transfer-coding) that
2930   would have been sent had the request been a GET.
2931   In the case of the 304 (Not Modified) response, it indicates the size of
2932   the payload body (not including any potential transfer-coding) that
2933   would have been sent in a 200 (OK) response.
2934</t>
2935<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2936  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2937  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2938</artwork></figure>
2939<t>
2940   An example is
2941</t>
2942<figure><artwork type="example">
2943  Content-Length: 3495
2944</artwork></figure>
2945<t>
2946   Implementations &SHOULD; use this field to indicate the message-body
2947   length when no transfer-coding is being applied and the
2948   payload's body length can be determined prior to being transferred.
2949   <xref target="message.body"/> describes how recipients determine the length
2950   of a message-body.
2951</t>
2952<t>
2953   Any Content-Length greater than or equal to zero is a valid value.
2954</t>
2955<t>
2956   Note that the use of this field in HTTP is significantly different from
2957   the corresponding definition in MIME, where it is an optional field
2958   used within the "message/external-body" content-type.
2959</t>
2960</section>
2961
2962<section title="Date" anchor="header.date">
2963  <iref primary="true" item="Date header" x:for-anchor=""/>
2964  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2965  <x:anchor-alias value="Date"/>
2966  <x:anchor-alias value="Date-v"/>
2967<t>
2968   The "Date" general-header field represents the date and time at which
2969   the message was originated, having the same semantics as the Origination
2970   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2971   The field value is an HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
2972   it &MUST; be sent in rfc1123-date format.
2973</t>
2974<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2975  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2976  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2977</artwork></figure>
2978<t>
2979   An example is
2980</t>
2981<figure><artwork type="example">
2982  Date: Tue, 15 Nov 1994 08:12:31 GMT
2983</artwork></figure>
2984<t>
2985   Origin servers &MUST; include a Date header field in all responses,
2986   except in these cases:
2987  <list style="numbers">
2988      <t>If the response status code is 100 (Continue) or 101 (Switching
2989         Protocols), the response &MAY; include a Date header field, at
2990         the server's option.</t>
2991
2992      <t>If the response status code conveys a server error, e.g., 500
2993         (Internal Server Error) or 503 (Service Unavailable), and it is
2994         inconvenient or impossible to generate a valid Date.</t>
2995
2996      <t>If the server does not have a clock that can provide a
2997         reasonable approximation of the current time, its responses
2998         &MUST-NOT; include a Date header field. In this case, the rules
2999         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3000  </list>
3001</t>
3002<t>
3003   A received message that does not have a Date header field &MUST; be
3004   assigned one by the recipient if the message will be cached by that
3005   recipient or gatewayed via a protocol which requires a Date.
3006</t>
3007<t>
3008   Clients can use the Date header field as well; in order to keep request
3009   messages small, they are advised not to include it when it doesn't convey
3010   any useful information (as it is usually the case for requests that do not
3011   contain a payload).
3012</t>
3013<t>
3014   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3015   time subsequent to the generation of the message. It &SHOULD; represent
3016   the best available approximation of the date and time of message
3017   generation, unless the implementation has no means of generating a
3018   reasonably accurate date and time. In theory, the date ought to
3019   represent the moment just before the payload is generated. In
3020   practice, the date can be generated at any time during the message
3021   origination without affecting its semantic value.
3022</t>
3023
3024<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3025<t>
3026   Some origin server implementations might not have a clock available.
3027   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3028   values to a response, unless these values were associated
3029   with the resource by a system or user with a reliable clock. It &MAY;
3030   assign an Expires value that is known, at or before server
3031   configuration time, to be in the past (this allows "pre-expiration"
3032   of responses without storing separate Expires values for each
3033   resource).
3034</t>
3035</section>
3036</section>
3037
3038<section title="Host" anchor="header.host">
3039  <iref primary="true" item="Host header" x:for-anchor=""/>
3040  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
3041  <x:anchor-alias value="Host"/>
3042  <x:anchor-alias value="Host-v"/>
3043<t>
3044   The "Host" request-header field specifies the Internet host and port
3045   number of the resource being requested, allowing the origin server or
3046   gateway to differentiate between internally-ambiguous URLs, such as the root
3047   "/" URL of a server for multiple host names on a single IP address.
3048</t>
3049<t>   
3050   The Host field value &MUST; represent the naming authority of the origin
3051   server or gateway given by the original URL obtained from the user or
3052   referring resource (generally an http URI, as described in
3053   <xref target="http.uri"/>).
3054</t>
3055<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3056  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3057  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3058</artwork></figure>
3059<t>
3060   A "host" without any trailing port information implies the default
3061   port for the service requested (e.g., "80" for an HTTP URL). For
3062   example, a request on the origin server for
3063   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
3064</t>
3065<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3066GET /pub/WWW/ HTTP/1.1
3067Host: www.example.org
3068</artwork></figure>
3069<t>
3070   A client &MUST; include a Host header field in all HTTP/1.1 request
3071   messages. If the requested URI does not include an Internet host
3072   name for the service being requested, then the Host header field &MUST;
3073   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
3074   request message it forwards does contain an appropriate Host header
3075   field that identifies the service being requested by the proxy. All
3076   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
3077   status code to any HTTP/1.1 request message which lacks a Host header
3078   field.
3079</t>
3080<t>
3081   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3082   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3083   for other requirements relating to Host.
3084</t>
3085</section>
3086
3087<section title="TE" anchor="header.te">
3088  <iref primary="true" item="TE header" x:for-anchor=""/>
3089  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
3090  <x:anchor-alias value="TE"/>
3091  <x:anchor-alias value="TE-v"/>
3092  <x:anchor-alias value="t-codings"/>
3093  <x:anchor-alias value="te-params"/>
3094  <x:anchor-alias value="te-ext"/>
3095<t>
3096   The "TE" request-header field indicates what extension transfer-codings
3097   it is willing to accept in the response, and whether or not it is
3098   willing to accept trailer fields in a chunked transfer-coding.
3099</t>
3100<t>
3101   Its value consists of the keyword "trailers" and/or a comma-separated
3102   list of extension transfer-coding names with optional accept
3103   parameters (as described in <xref target="transfer.codings"/>).
3104</t>
3105<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="TE-v"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
3106  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3107  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3108  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3109  <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> )
3110  <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> ]
3111</artwork></figure>
3112<t>
3113   The presence of the keyword "trailers" indicates that the client is
3114   willing to accept trailer fields in a chunked transfer-coding, as
3115   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3116   transfer-coding values even though it does not itself represent a
3117   transfer-coding.
3118</t>
3119<t>
3120   Examples of its use are:
3121</t>
3122<figure><artwork type="example">
3123  TE: deflate
3124  TE:
3125  TE: trailers, deflate;q=0.5
3126</artwork></figure>
3127<t>
3128   The TE header field only applies to the immediate connection.
3129   Therefore, the keyword &MUST; be supplied within a Connection header
3130   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3131</t>
3132<t>
3133   A server tests whether a transfer-coding is acceptable, according to
3134   a TE field, using these rules:
3135  <list style="numbers">
3136    <x:lt>
3137      <t>The "chunked" transfer-coding is always acceptable. If the
3138         keyword "trailers" is listed, the client indicates that it is
3139         willing to accept trailer fields in the chunked response on
3140         behalf of itself and any downstream clients. The implication is
3141         that, if given, the client is stating that either all
3142         downstream clients are willing to accept trailer fields in the
3143         forwarded response, or that it will attempt to buffer the
3144         response on behalf of downstream recipients.
3145      </t><t>
3146         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3147         chunked response such that a client can be assured of buffering
3148         the entire response.</t>
3149    </x:lt>
3150    <x:lt>
3151      <t>If the transfer-coding being tested is one of the transfer-codings
3152         listed in the TE field, then it is acceptable unless it
3153         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3154         qvalue of 0 means "not acceptable".)</t>
3155    </x:lt>
3156    <x:lt>
3157      <t>If multiple transfer-codings are acceptable, then the
3158         acceptable transfer-coding with the highest non-zero qvalue is
3159         preferred.  The "chunked" transfer-coding always has a qvalue
3160         of 1.</t>
3161    </x:lt>
3162  </list>
3163</t>
3164<t>
3165   If the TE field-value is empty or if no TE field is present, the only
3166   transfer-coding is "chunked". A message with no transfer-coding is
3167   always acceptable.
3168</t>
3169</section>
3170
3171<section title="Trailer" anchor="header.trailer">
3172  <iref primary="true" item="Trailer header" x:for-anchor=""/>
3173  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
3174  <x:anchor-alias value="Trailer"/>
3175  <x:anchor-alias value="Trailer-v"/>
3176<t>
3177   The "Trailer" general-header field indicates that the given set of
3178   header fields is present in the trailer of a message encoded with
3179   chunked transfer-coding.
3180</t>
3181<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3182  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3183  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3184</artwork></figure>
3185<t>
3186   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3187   message using chunked transfer-coding with a non-empty trailer. Doing
3188   so allows the recipient to know which header fields to expect in the
3189   trailer.
3190</t>
3191<t>
3192   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3193   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3194   trailer fields in a "chunked" transfer-coding.
3195</t>
3196<t>
3197   Message header fields listed in the Trailer header field &MUST-NOT;
3198   include the following header fields:
3199  <list style="symbols">
3200    <t>Transfer-Encoding</t>
3201    <t>Content-Length</t>
3202    <t>Trailer</t>
3203  </list>
3204</t>
3205</section>
3206
3207<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3208  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
3209  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
3210  <x:anchor-alias value="Transfer-Encoding"/>
3211  <x:anchor-alias value="Transfer-Encoding-v"/>
3212<t>
3213   The "Transfer-Encoding" general-header field indicates what transfer-codings
3214   (if any) have been applied to the message body. It differs from
3215   Content-Encoding (&content-codings;) in that transfer-codings are a property
3216   of the message (and therefore are removed by intermediaries), whereas
3217   content-codings are not.
3218</t>
3219<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3220  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3221                        <x:ref>Transfer-Encoding-v</x:ref>
3222  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3223</artwork></figure>
3224<t>
3225   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3226</t>
3227<figure><artwork type="example">
3228  Transfer-Encoding: chunked
3229</artwork></figure>
3230<t>
3231   If multiple encodings have been applied to a representation, the transfer-codings
3232   &MUST; be listed in the order in which they were applied.
3233   Additional information about the encoding parameters &MAY; be provided
3234   by other header fields not defined by this specification.
3235</t>
3236<t>
3237   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3238   header field.
3239</t>
3240</section>
3241
3242<section title="Upgrade" anchor="header.upgrade">
3243  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
3244  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
3245  <x:anchor-alias value="Upgrade"/>
3246  <x:anchor-alias value="Upgrade-v"/>
3247<t>
3248   The "Upgrade" general-header field allows the client to specify what
3249   additional communication protocols it would like to use, if the server
3250   chooses to switch protocols. Servers can use it to indicate what protocols
3251   they are willing to switch to.
3252</t>
3253<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3254  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3255  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3256</artwork></figure>
3257<t>
3258   For example,
3259</t>
3260<figure><artwork type="example">
3261  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3262</artwork></figure>
3263<t>
3264   The Upgrade header field is intended to provide a simple mechanism
3265   for transition from HTTP/1.1 to some other, incompatible protocol. It
3266   does so by allowing the client to advertise its desire to use another
3267   protocol, such as a later version of HTTP with a higher major version
3268   number, even though the current request has been made using HTTP/1.1.
3269   This eases the difficult transition between incompatible protocols by
3270   allowing the client to initiate a request in the more commonly
3271   supported protocol while indicating to the server that it would like
3272   to use a "better" protocol if available (where "better" is determined
3273   by the server, possibly according to the nature of the method and/or
3274   resource being requested).
3275</t>
3276<t>
3277   The Upgrade header field only applies to switching application-layer
3278   protocols upon the existing transport-layer connection. Upgrade
3279   cannot be used to insist on a protocol change; its acceptance and use
3280   by the server is optional. The capabilities and nature of the
3281   application-layer communication after the protocol change is entirely
3282   dependent upon the new protocol chosen, although the first action
3283   after changing the protocol &MUST; be a response to the initial HTTP
3284   request containing the Upgrade header field.
3285</t>
3286<t>
3287   The Upgrade header field only applies to the immediate connection.
3288   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3289   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3290   HTTP/1.1 message.
3291</t>
3292<t>
3293   The Upgrade header field cannot be used to indicate a switch to a
3294   protocol on a different connection. For that purpose, it is more
3295   appropriate to use a 3xx redirection response (&status-3xx;).
3296</t>
3297<t>
3298   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3299   Protocols) responses to indicate which protocol(s) are being switched to,
3300   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3301   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3302   response to indicate that they are willing to upgrade to one of the
3303   specified protocols.
3304</t>
3305<t>
3306   This specification only defines the protocol name "HTTP" for use by
3307   the family of Hypertext Transfer Protocols, as defined by the HTTP
3308   version rules of <xref target="http.version"/> and future updates to this
3309   specification. Additional tokens can be registered with IANA using the
3310   registration procedure defined below. 
3311</t>
3312
3313<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3314<t>
3315   The HTTP Upgrade Token Registry defines the name space for product
3316   tokens used to identify protocols in the Upgrade header field.
3317   Each registered token is associated with contact information and
3318   an optional set of specifications that details how the connection
3319   will be processed after it has been upgraded.
3320</t>
3321<t>
3322   Registrations are allowed on a First Come First Served basis as
3323   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3324   specifications need not be IETF documents or be subject to IESG review.
3325   Registrations are subject to the following rules:
3326  <list style="numbers">
3327    <t>A token, once registered, stays registered forever.</t>
3328    <t>The registration &MUST; name a responsible party for the
3329       registration.</t>
3330    <t>The registration &MUST; name a point of contact.</t>
3331    <t>The registration &MAY; name a set of specifications associated with that
3332       token. Such specifications need not be publicly available.</t>
3333    <t>The responsible party &MAY; change the registration at any time.
3334       The IANA will keep a record of all such changes, and make them
3335       available upon request.</t>
3336    <t>The responsible party for the first registration of a "product"
3337       token &MUST; approve later registrations of a "version" token
3338       together with that "product" token before they can be registered.</t>
3339    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3340       for a token. This will normally only be used in the case when a
3341       responsible party cannot be contacted.</t>
3342  </list>
3343</t>
3344</section>
3345
3346
3347</section>
3348
3349<section title="Via" anchor="header.via">
3350  <iref primary="true" item="Via header" x:for-anchor=""/>
3351  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
3352  <x:anchor-alias value="protocol-name"/>
3353  <x:anchor-alias value="protocol-version"/>
3354  <x:anchor-alias value="pseudonym"/>
3355  <x:anchor-alias value="received-by"/>
3356  <x:anchor-alias value="received-protocol"/>
3357  <x:anchor-alias value="Via"/>
3358  <x:anchor-alias value="Via-v"/>
3359<t>
3360   The "Via" general-header field &MUST; be used by gateways and proxies to
3361   indicate the intermediate protocols and recipients between the user
3362   agent and the server on requests, and between the origin server and
3363   the client on responses. It is analogous to the "Received" field defined in
3364   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3365   avoiding request loops, and identifying the protocol capabilities of
3366   all senders along the request/response chain.
3367</t>
3368<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="Via-v"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/>
3369  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3370  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3371                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3372  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3373  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3374  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3375  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3376  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3377</artwork></figure>
3378<t>
3379   The received-protocol indicates the protocol version of the message
3380   received by the server or client along each segment of the
3381   request/response chain. The received-protocol version is appended to
3382   the Via field value when the message is forwarded so that information
3383   about the protocol capabilities of upstream applications remains
3384   visible to all recipients.
3385</t>
3386<t>
3387   The protocol-name is optional if and only if it would be "HTTP". The
3388   received-by field is normally the host and optional port number of a
3389   recipient server or client that subsequently forwarded the message.
3390   However, if the real host is considered to be sensitive information,
3391   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3392   be assumed to be the default port of the received-protocol.
3393</t>
3394<t>
3395   Multiple Via field values represent each proxy or gateway that has
3396   forwarded the message. Each recipient &MUST; append its information
3397   such that the end result is ordered according to the sequence of
3398   forwarding applications.
3399</t>
3400<t>
3401   Comments &MAY; be used in the Via header field to identify the software
3402   of the recipient proxy or gateway, analogous to the User-Agent and
3403   Server header fields. However, all comments in the Via field are
3404   optional and &MAY; be removed by any recipient prior to forwarding the
3405   message.
3406</t>
3407<t>
3408   For example, a request message could be sent from an HTTP/1.0 user
3409   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3410   forward the request to a public proxy at p.example.net, which completes
3411   the request by forwarding it to the origin server at www.example.com.
3412   The request received by www.example.com would then have the following
3413   Via header field:
3414</t>
3415<figure><artwork type="example">
3416  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3417</artwork></figure>
3418<t>
3419   Proxies and gateways used as a portal through a network firewall
3420   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3421   the firewall region. This information &SHOULD; only be propagated if
3422   explicitly enabled. If not enabled, the received-by host of any host
3423   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3424   for that host.
3425</t>
3426<t>
3427   For organizations that have strong privacy requirements for hiding
3428   internal structures, a proxy &MAY; combine an ordered subsequence of
3429   Via header field entries with identical received-protocol values into
3430   a single such entry. For example,
3431</t>
3432<figure><artwork type="example">
3433  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3434</artwork></figure>
3435<t>
3436  could be collapsed to
3437</t>
3438<figure><artwork type="example">
3439  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3440</artwork></figure>
3441<t>
3442   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3443   under the same organizational control and the hosts have already been
3444   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3445   have different received-protocol values.
3446</t>
3447</section>
3448
3449</section>
3450
3451<section title="IANA Considerations" anchor="IANA.considerations">
3452
3453<section title="Header Field Registration" anchor="header.field.registration">
3454<t>
3455   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3456   with the permanent registrations below (see <xref target="RFC3864"/>):
3457</t>
3458<?BEGININC p1-messaging.iana-headers ?>
3459<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3460<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3461   <ttcol>Header Field Name</ttcol>
3462   <ttcol>Protocol</ttcol>
3463   <ttcol>Status</ttcol>
3464   <ttcol>Reference</ttcol>
3465
3466   <c>Connection</c>
3467   <c>http</c>
3468   <c>standard</c>
3469   <c>
3470      <xref target="header.connection"/>
3471   </c>
3472   <c>Content-Length</c>
3473   <c>http</c>
3474   <c>standard</c>
3475   <c>
3476      <xref target="header.content-length"/>
3477   </c>
3478   <c>Date</c>
3479   <c>http</c>
3480   <c>standard</c>
3481   <c>
3482      <xref target="header.date"/>
3483   </c>
3484   <c>Host</c>
3485   <c>http</c>
3486   <c>standard</c>
3487   <c>
3488      <xref target="header.host"/>
3489   </c>
3490   <c>TE</c>
3491   <c>http</c>
3492   <c>standard</c>
3493   <c>
3494      <xref target="header.te"/>
3495   </c>
3496   <c>Trailer</c>
3497   <c>http</c>
3498   <c>standard</c>
3499   <c>
3500      <xref target="header.trailer"/>
3501   </c>
3502   <c>Transfer-Encoding</c>
3503   <c>http</c>
3504   <c>standard</c>
3505   <c>
3506      <xref target="header.transfer-encoding"/>
3507   </c>
3508   <c>Upgrade</c>
3509   <c>http</c>
3510   <c>standard</c>
3511   <c>
3512      <xref target="header.upgrade"/>
3513   </c>
3514   <c>Via</c>
3515   <c>http</c>
3516   <c>standard</c>
3517   <c>
3518      <xref target="header.via"/>
3519   </c>
3520</texttable>
3521<!--(END)-->
3522<?ENDINC p1-messaging.iana-headers ?>
3523<t>
3524   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3525</t>
3526</section>
3527
3528<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3529<t>
3530   The entries for the "http" and "https" URI Schemes in the registry located at
3531   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3532   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3533   and <xref target="https.uri" format="counter"/> of this document
3534   (see <xref target="RFC4395"/>).
3535</t>
3536</section>
3537
3538<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3539<t>
3540   This document serves as the specification for the Internet media types
3541   "message/http" and "application/http". The following is to be registered with
3542   IANA (see <xref target="RFC4288"/>).
3543</t>
3544<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3545<iref item="Media Type" subitem="message/http" primary="true"/>
3546<iref item="message/http Media Type" primary="true"/>
3547<t>
3548   The message/http type can be used to enclose a single HTTP request or
3549   response message, provided that it obeys the MIME restrictions for all
3550   "message" types regarding line length and encodings.
3551</t>
3552<t>
3553  <list style="hanging" x:indent="12em">
3554    <t hangText="Type name:">
3555      message
3556    </t>
3557    <t hangText="Subtype name:">
3558      http
3559    </t>
3560    <t hangText="Required parameters:">
3561      none
3562    </t>
3563    <t hangText="Optional parameters:">
3564      version, msgtype
3565      <list style="hanging">
3566        <t hangText="version:">
3567          The HTTP-Version number of the enclosed message
3568          (e.g., "1.1"). If not present, the version can be
3569          determined from the first line of the body.
3570        </t>
3571        <t hangText="msgtype:">
3572          The message type &mdash; "request" or "response". If not
3573          present, the type can be determined from the first
3574          line of the body.
3575        </t>
3576      </list>
3577    </t>
3578    <t hangText="Encoding considerations:">
3579      only "7bit", "8bit", or "binary" are permitted
3580    </t>
3581    <t hangText="Security considerations:">
3582      none
3583    </t>
3584    <t hangText="Interoperability considerations:">
3585      none
3586    </t>
3587    <t hangText="Published specification:">
3588      This specification (see <xref target="internet.media.type.message.http"/>).
3589    </t>
3590    <t hangText="Applications that use this media type:">
3591    </t>
3592    <t hangText="Additional information:">
3593      <list style="hanging">
3594        <t hangText="Magic number(s):">none</t>
3595        <t hangText="File extension(s):">none</t>
3596        <t hangText="Macintosh file type code(s):">none</t>
3597      </list>
3598    </t>
3599    <t hangText="Person and email address to contact for further information:">
3600      See Authors Section.
3601    </t>
3602    <t hangText="Intended usage:">
3603      COMMON
3604    </t>
3605    <t hangText="Restrictions on usage:">
3606      none
3607    </t>
3608    <t hangText="Author/Change controller:">
3609      IESG
3610    </t>
3611  </list>
3612</t>
3613</section>
3614<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3615<iref item="Media Type" subitem="application/http" primary="true"/>
3616<iref item="application/http Media Type" primary="true"/>
3617<t>
3618   The application/http type can be used to enclose a pipeline of one or more
3619   HTTP request or response messages (not intermixed).
3620</t>
3621<t>
3622  <list style="hanging" x:indent="12em">
3623    <t hangText="Type name:">
3624      application
3625    </t>
3626    <t hangText="Subtype name:">
3627      http
3628    </t>
3629    <t hangText="Required parameters:">
3630      none
3631    </t>
3632    <t hangText="Optional parameters:">
3633      version, msgtype
3634      <list style="hanging">
3635        <t hangText="version:">
3636          The HTTP-Version number of the enclosed messages
3637          (e.g., "1.1"). If not present, the version can be
3638          determined from the first line of the body.
3639        </t>
3640        <t hangText="msgtype:">
3641          The message type &mdash; "request" or "response". If not
3642          present, the type can be determined from the first
3643          line of the body.
3644        </t>
3645      </list>
3646    </t>
3647    <t hangText="Encoding considerations:">
3648      HTTP messages enclosed by this type
3649      are in "binary" format; use of an appropriate
3650      Content-Transfer-Encoding is required when
3651      transmitted via E-mail.
3652    </t>
3653    <t hangText="Security considerations:">
3654      none
3655    </t>
3656    <t hangText="Interoperability considerations:">
3657      none
3658    </t>
3659    <t hangText="Published specification:">
3660      This specification (see <xref target="internet.media.type.application.http"/>).
3661    </t>
3662    <t hangText="Applications that use this media type:">
3663    </t>
3664    <t hangText="Additional information:">
3665      <list style="hanging">
3666        <t hangText="Magic number(s):">none</t>
3667        <t hangText="File extension(s):">none</t>
3668        <t hangText="Macintosh file type code(s):">none</t>
3669      </list>
3670    </t>
3671    <t hangText="Person and email address to contact for further information:">
3672      See Authors Section.
3673    </t>
3674    <t hangText="Intended usage:">
3675      COMMON
3676    </t>
3677    <t hangText="Restrictions on usage:">
3678      none
3679    </t>
3680    <t hangText="Author/Change controller:">
3681      IESG
3682    </t>
3683  </list>
3684</t>
3685</section>
3686</section>
3687
3688<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3689<t>
3690   The registration procedure for HTTP Transfer Codings is now defined by
3691   <xref target="transfer.coding.registry"/> of this document.
3692</t>
3693<t>
3694   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3695   shall be updated with the registrations below:
3696</t>
3697<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3698   <ttcol>Name</ttcol>
3699   <ttcol>Description</ttcol>
3700   <ttcol>Reference</ttcol>
3701   <c>chunked</c>
3702   <c>Transfer in a series of chunks</c>
3703   <c>
3704      <xref target="chunked.encoding"/>
3705   </c>
3706   <c>compress</c>
3707   <c>UNIX "compress" program method</c>
3708   <c>
3709      <xref target="compress.coding"/>
3710   </c>
3711   <c>deflate</c>
3712   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3713   the "zlib" data format (<xref target="RFC1950"/>)
3714   </c>
3715   <c>
3716      <xref target="deflate.coding"/>
3717   </c>
3718   <c>gzip</c>
3719   <c>Same as GNU zip <xref target="RFC1952"/></c>
3720   <c>
3721      <xref target="gzip.coding"/>
3722   </c>
3723</texttable>
3724</section>
3725
3726<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3727<t>
3728   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3729   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3730   by <xref target="upgrade.token.registry"/> of this document.
3731</t>
3732<t>
3733   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3734   shall be updated with the registration below:
3735</t>
3736<texttable align="left" suppress-title="true">
3737   <ttcol>Value</ttcol>
3738   <ttcol>Description</ttcol>
3739   <ttcol>Reference</ttcol>
3740
3741   <c>HTTP</c>
3742   <c>Hypertext Transfer Protocol</c> 
3743   <c><xref target="http.version"/> of this specification</c>
3744<!-- IANA should add this without our instructions; emailed on June 05, 2009
3745   <c>TLS/1.0</c>
3746   <c>Transport Layer Security</c>
3747   <c><xref target="RFC2817"/></c> -->
3748
3749</texttable>
3750</section>
3751
3752</section>
3753
3754<section title="Security Considerations" anchor="security.considerations">
3755<t>
3756   This section is meant to inform application developers, information
3757   providers, and users of the security limitations in HTTP/1.1 as
3758   described by this document. The discussion does not include
3759   definitive solutions to the problems revealed, though it does make
3760   some suggestions for reducing security risks.
3761</t>
3762
3763<section title="Personal Information" anchor="personal.information">
3764<t>
3765   HTTP clients are often privy to large amounts of personal information
3766   (e.g., the user's name, location, mail address, passwords, encryption
3767   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3768   leakage of this information.
3769   We very strongly recommend that a convenient interface be provided
3770   for the user to control dissemination of such information, and that
3771   designers and implementors be particularly careful in this area.
3772   History shows that errors in this area often create serious security
3773   and/or privacy problems and generate highly adverse publicity for the
3774   implementor's company.
3775</t>
3776</section>
3777
3778<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3779<t>
3780   A server is in the position to save personal data about a user's
3781   requests which might identify their reading patterns or subjects of
3782   interest. This information is clearly confidential in nature and its
3783   handling can be constrained by law in certain countries. People using
3784   HTTP to provide data are responsible for ensuring that
3785   such material is not distributed without the permission of any
3786   individuals that are identifiable by the published results.
3787</t>
3788</section>
3789
3790<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3791<t>
3792   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3793   the documents returned by HTTP requests to be only those that were
3794   intended by the server administrators. If an HTTP server translates
3795   HTTP URIs directly into file system calls, the server &MUST; take
3796   special care not to serve files that were not intended to be
3797   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3798   other operating systems use ".." as a path component to indicate a
3799   directory level above the current one. On such a system, an HTTP
3800   server &MUST; disallow any such construct in the request-target if it
3801   would otherwise allow access to a resource outside those intended to
3802   be accessible via the HTTP server. Similarly, files intended for
3803   reference only internally to the server (such as access control
3804   files, configuration files, and script code) &MUST; be protected from
3805   inappropriate retrieval, since they might contain sensitive
3806   information. Experience has shown that minor bugs in such HTTP server
3807   implementations have turned into security risks.
3808</t>
3809</section>
3810
3811<section title="DNS Spoofing" anchor="dns.spoofing">
3812<t>
3813   Clients using HTTP rely heavily on the Domain Name Service, and are
3814   thus generally prone to security attacks based on the deliberate
3815   mis-association of IP addresses and DNS names. Clients need to be
3816   cautious in assuming the continuing validity of an IP number/DNS name
3817   association.
3818</t>
3819<t>
3820   In particular, HTTP clients &SHOULD; rely on their name resolver for
3821   confirmation of an IP number/DNS name association, rather than
3822   caching the result of previous host name lookups. Many platforms
3823   already can cache host name lookups locally when appropriate, and
3824   they &SHOULD; be configured to do so. It is proper for these lookups to
3825   be cached, however, only when the TTL (Time To Live) information
3826   reported by the name server makes it likely that the cached
3827   information will remain useful.
3828</t>
3829<t>
3830   If HTTP clients cache the results of host name lookups in order to
3831   achieve a performance improvement, they &MUST; observe the TTL
3832   information reported by DNS.
3833</t>
3834<t>
3835   If HTTP clients do not observe this rule, they could be spoofed when
3836   a previously-accessed server's IP address changes. As network
3837   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3838   possibility of this form of attack will grow. Observing this
3839   requirement thus reduces this potential security vulnerability.
3840</t>
3841<t>
3842   This requirement also improves the load-balancing behavior of clients
3843   for replicated servers using the same DNS name and reduces the
3844   likelihood of a user's experiencing failure in accessing sites which
3845   use that strategy.
3846</t>
3847</section>
3848
3849<section title="Proxies and Caching" anchor="attack.proxies">
3850<t>
3851   By their very nature, HTTP proxies are men-in-the-middle, and
3852   represent an opportunity for man-in-the-middle attacks. Compromise of
3853   the systems on which the proxies run can result in serious security
3854   and privacy problems. Proxies have access to security-related
3855   information, personal information about individual users and
3856   organizations, and proprietary information belonging to users and
3857   content providers. A compromised proxy, or a proxy implemented or
3858   configured without regard to security and privacy considerations,
3859   might be used in the commission of a wide range of potential attacks.
3860</t>
3861<t>
3862   Proxy operators need to protect the systems on which proxies run as
3863   they would protect any system that contains or transports sensitive
3864   information. In particular, log information gathered at proxies often
3865   contains highly sensitive personal information, and/or information
3866   about organizations. Log information needs to be carefully guarded, and
3867   appropriate guidelines for use need to be developed and followed.
3868   (<xref target="abuse.of.server.log.information"/>).
3869</t>
3870<t>
3871   Proxy implementors need to consider the privacy and security
3872   implications of their design and coding decisions, and of the
3873   configuration options they provide to proxy operators (especially the
3874   default configuration).
3875</t>
3876<t>
3877   Users of a proxy need to be aware that proxies are no trustworthier than
3878   the people who run them; HTTP itself cannot solve this problem.
3879</t>
3880<t>
3881   The judicious use of cryptography, when appropriate, might suffice to
3882   protect against a broad range of security and privacy attacks. Such
3883   cryptography is beyond the scope of the HTTP/1.1 specification.
3884</t>
3885</section>
3886
3887<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3888<t>
3889   They exist. They are hard to defend against. Research continues.
3890   Beware.
3891</t>
3892</section>
3893</section>
3894
3895<section title="Acknowledgments" anchor="ack">
3896<t>
3897   HTTP has evolved considerably over the years. It has
3898   benefited from a large and active developer community &mdash; the many
3899   people who have participated on the www-talk mailing list &mdash; and it is
3900   that community which has been most responsible for the success of
3901   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3902   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3903   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3904   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3905   VanHeyningen deserve special recognition for their efforts in
3906   defining early aspects of the protocol.
3907</t>
3908<t>
3909   This document has benefited greatly from the comments of all those
3910   participating in the HTTP-WG. In addition to those already mentioned,
3911   the following individuals have contributed to this specification:
3912</t>
3913<t>
3914   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3915   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
3916   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3917   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3918   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3919   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3920   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3921   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3922   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3923   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3924   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3925   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
3926</t>
3927<t>
3928   Thanks to the "cave men" of Palo Alto. You know who you are.
3929</t>
3930<t>
3931   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3932   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3933   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3934   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3935   Larry Masinter for their help. And thanks go particularly to Jeff
3936   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3937</t>
3938<t>
3939   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3940   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3941   discovery of many of the problems that this document attempts to
3942   rectify.
3943</t>
3944<t>
3945   This specification makes heavy use of the augmented BNF and generic
3946   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3947   reuses many of the definitions provided by Nathaniel Borenstein and
3948   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3949   specification will help reduce past confusion over the relationship
3950   between HTTP and Internet mail message formats.
3951</t>
3952<!--
3953
3954Acknowledgements TODO list
3955
3956- Jeff Hodges ("effective request URI")
3957
3958-->
3959</section>
3960
3961</middle>
3962<back>
3963
3964<references title="Normative References">
3965
3966<reference anchor="ISO-8859-1">
3967  <front>
3968    <title>
3969     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3970    </title>
3971    <author>
3972      <organization>International Organization for Standardization</organization>
3973    </author>
3974    <date year="1998"/>
3975  </front>
3976  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3977</reference>
3978
3979<reference anchor="Part2">
3980  <front>
3981    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3982    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3983      <organization abbrev="Day Software">Day Software</organization>
3984      <address><email>fielding@gbiv.com</email></address>
3985    </author>
3986    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3987      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3988      <address><email>jg@freedesktop.org</email></address>
3989    </author>
3990    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3991      <organization abbrev="HP">Hewlett-Packard Company</organization>
3992      <address><email>JeffMogul@acm.org</email></address>
3993    </author>
3994    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3995      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3996      <address><email>henrikn@microsoft.com</email></address>
3997    </author>
3998    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3999      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4000      <address><email>LMM@acm.org</email></address>
4001    </author>
4002    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4003      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4004      <address><email>paulle@microsoft.com</email></address>
4005    </author>
4006    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4007      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4008      <address><email>timbl@w3.org</email></address>
4009    </author>
4010    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4011      <organization abbrev="W3C">World Wide Web Consortium</organization>
4012      <address><email>ylafon@w3.org</email></address>
4013    </author>
4014    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4015      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4016      <address><email>julian.reschke@greenbytes.de</email></address>
4017    </author>
4018    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4019  </front>
4020  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4021  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4022</reference>
4023
4024<reference anchor="Part3">
4025  <front>
4026    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4027    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4028      <organization abbrev="Day Software">Day Software</organization>
4029      <address><email>fielding@gbiv.com</email></address>
4030    </author>
4031    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4032      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4033      <address><email>jg@freedesktop.org</email></address>
4034    </author>
4035    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4036      <organization abbrev="HP">Hewlett-Packard Company</organization>
4037      <address><email>JeffMogul@acm.org</email></address>
4038    </author>
4039    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4040      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4041      <address><email>henrikn@microsoft.com</email></address>
4042    </author>
4043    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4044      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4045      <address><email>LMM@acm.org</email></address>
4046    </author>
4047    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4048      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4049      <address><email>paulle@microsoft.com</email></address>
4050    </author>
4051    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4052      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4053      <address><email>timbl@w3.org</email></address>
4054    </author>
4055    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4056      <organization abbrev="W3C">World Wide Web Consortium</organization>
4057      <address><email>ylafon@w3.org</email></address>
4058    </author>
4059    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4060      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4061      <address><email>julian.reschke@greenbytes.de</email></address>
4062    </author>
4063    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4064  </front>
4065  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4066  <x:source href="p3-payload.xml" basename="p3-payload"/>
4067</reference>
4068
4069<reference anchor="Part6">
4070  <front>
4071    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4072    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4073      <organization abbrev="Day Software">Day Software</organization>
4074      <address><email>fielding@gbiv.com</email></address>
4075    </author>
4076    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4077      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4078      <address><email>jg@freedesktop.org</email></address>
4079    </author>
4080    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4081      <organization abbrev="HP">Hewlett-Packard Company</organization>
4082      <address><email>JeffMogul@acm.org</email></address>
4083    </author>
4084    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4085      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4086      <address><email>henrikn@microsoft.com</email></address>
4087    </author>
4088    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4089      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4090      <address><email>LMM@acm.org</email></address>
4091    </author>
4092    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4093      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4094      <address><email>paulle@microsoft.com</email></address>
4095    </author>
4096    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4097      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4098      <address><email>timbl@w3.org</email></address>
4099    </author>
4100    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4101      <organization abbrev="W3C">World Wide Web Consortium</organization>
4102      <address><email>ylafon@w3.org</email></address>
4103    </author>
4104    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4105      <address><email>mnot@mnot.net</email></address>
4106    </author>
4107    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4108      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4109      <address><email>julian.reschke@greenbytes.de</email></address>
4110    </author>
4111    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4112  </front>
4113  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4114  <x:source href="p6-cache.xml" basename="p6-cache"/>
4115</reference>
4116
4117<reference anchor="RFC5234">
4118  <front>
4119    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4120    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4121      <organization>Brandenburg InternetWorking</organization>
4122      <address>
4123        <email>dcrocker@bbiw.net</email>
4124      </address> 
4125    </author>
4126    <author initials="P." surname="Overell" fullname="Paul Overell">
4127      <organization>THUS plc.</organization>
4128      <address>
4129        <email>paul.overell@thus.net</email>
4130      </address>
4131    </author>
4132    <date month="January" year="2008"/>
4133  </front>
4134  <seriesInfo name="STD" value="68"/>
4135  <seriesInfo name="RFC" value="5234"/>
4136</reference>
4137
4138<reference anchor="RFC2119">
4139  <front>
4140    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4141    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4142      <organization>Harvard University</organization>
4143      <address><email>sob@harvard.edu</email></address>
4144    </author>
4145    <date month="March" year="1997"/>
4146  </front>
4147  <seriesInfo name="BCP" value="14"/>
4148  <seriesInfo name="RFC" value="2119"/>
4149</reference>
4150
4151<reference anchor="RFC3986">
4152 <front>
4153  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4154  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4155    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4156    <address>
4157       <email>timbl@w3.org</email>
4158       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4159    </address>
4160  </author>
4161  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4162    <organization abbrev="Day Software">Day Software</organization>
4163    <address>
4164      <email>fielding@gbiv.com</email>
4165      <uri>http://roy.gbiv.com/</uri>
4166    </address>
4167  </author>
4168  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4169    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4170    <address>
4171      <email>LMM@acm.org</email>
4172      <uri>http://larry.masinter.net/</uri>
4173    </address>
4174  </author>
4175  <date month='January' year='2005'></date>
4176 </front>
4177 <seriesInfo name="STD" value="66"/>
4178 <seriesInfo name="RFC" value="3986"/>
4179</reference>
4180
4181<reference anchor="USASCII">
4182  <front>
4183    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4184    <author>
4185      <organization>American National Standards Institute</organization>
4186    </author>
4187    <date year="1986"/>
4188  </front>
4189  <seriesInfo name="ANSI" value="X3.4"/>
4190</reference>
4191
4192<reference anchor="RFC1950">
4193  <front>
4194    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4195    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4196      <organization>Aladdin Enterprises</organization>
4197      <address><email>ghost@aladdin.com</email></address>
4198    </author>
4199    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4200    <date month="May" year="1996"/>
4201  </front>
4202  <seriesInfo name="RFC" value="1950"/>
4203  <annotation>
4204    RFC 1950 is an Informational RFC, thus it might be less stable than
4205    this specification. On the other hand, this downward reference was
4206    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4207    therefore it is unlikely to cause problems in practice. See also
4208    <xref target="BCP97"/>.
4209  </annotation>
4210</reference>
4211
4212<reference anchor="RFC1951">
4213  <front>
4214    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4215    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4216      <organization>Aladdin Enterprises</organization>
4217      <address><email>ghost@aladdin.com</email></address>
4218    </author>
4219    <date month="May" year="1996"/>
4220  </front>
4221  <seriesInfo name="RFC" value="1951"/>
4222  <annotation>
4223    RFC 1951 is an Informational RFC, thus it might be less stable than
4224    this specification. On the other hand, this downward reference was
4225    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4226    therefore it is unlikely to cause problems in practice. See also
4227    <xref target="BCP97"/>.
4228  </annotation>
4229</reference>
4230
4231<reference anchor="RFC1952">
4232  <front>
4233    <title>GZIP file format specification version 4.3</title>
4234    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4235      <organization>Aladdin Enterprises</organization>
4236      <address><email>ghost@aladdin.com</email></address>
4237    </author>
4238    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4239      <address><email>gzip@prep.ai.mit.edu</email></address>
4240    </author>
4241    <author initials="M." surname="Adler" fullname="Mark Adler">
4242      <address><email>madler@alumni.caltech.edu</email></address>
4243    </author>
4244    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4245      <address><email>ghost@aladdin.com</email></address>
4246    </author>
4247    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4248      <address><email>randeg@alumni.rpi.edu</email></address>
4249    </author>
4250    <date month="May" year="1996"/>
4251  </front>
4252  <seriesInfo name="RFC" value="1952"/>
4253  <annotation>
4254    RFC 1952 is an Informational RFC, thus it might be less stable than
4255    this specification. On the other hand, this downward reference was
4256    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4257    therefore it is unlikely to cause problems in practice. See also
4258    <xref target="BCP97"/>.
4259  </annotation>
4260</reference>
4261
4262</references>
4263
4264<references title="Informative References">
4265
4266<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4267  <front>
4268    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4269    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4270    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4271    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4272    <author initials="H." surname="Lie" fullname="H. Lie"/>
4273    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4274    <date year="1997" month="September"/>
4275  </front>
4276  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4277</reference>
4278
4279<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4280  <front>
4281    <title>Improving HTTP Latency</title>
4282    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4283    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4284    <date year="1995" month="December"/>
4285  </front>
4286  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4287</reference>
4288
4289<reference anchor="RFC1123">
4290  <front>
4291    <title>Requirements for Internet Hosts - Application and Support</title>
4292    <author initials="R." surname="Braden" fullname="Robert Braden">
4293      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4294      <address><email>Braden@ISI.EDU</email></address>
4295    </author>
4296    <date month="October" year="1989"/>
4297  </front>
4298  <seriesInfo name="STD" value="3"/>
4299  <seriesInfo name="RFC" value="1123"/>
4300</reference>
4301
4302<reference anchor="RFC1900">
4303  <front>
4304    <title>Renumbering Needs Work</title>
4305    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4306      <organization>CERN, Computing and Networks Division</organization>
4307      <address><email>brian@dxcoms.cern.ch</email></address>
4308    </author>
4309    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4310      <organization>cisco Systems</organization>
4311      <address><email>yakov@cisco.com</email></address>
4312    </author>
4313    <date month="February" year="1996"/>
4314  </front>
4315  <seriesInfo name="RFC" value="1900"/>
4316</reference>
4317
4318<reference anchor="RFC1945">
4319  <front>
4320    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4321    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4322      <organization>MIT, Laboratory for Computer Science</organization>
4323      <address><email>timbl@w3.org</email></address>
4324    </author>
4325    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4326      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4327      <address><email>fielding@ics.uci.edu</email></address>
4328    </author>
4329    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4330      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4331      <address><email>frystyk@w3.org</email></address>
4332    </author>
4333    <date month="May" year="1996"/>
4334  </front>
4335  <seriesInfo name="RFC" value="1945"/>
4336</reference>
4337
4338<reference anchor="RFC2045">
4339  <front>
4340    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4341    <author initials="N." surname="Freed" fullname="Ned Freed">
4342      <organization>Innosoft International, Inc.</organization>
4343      <address><email>ned@innosoft.com</email></address>
4344    </author>
4345    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4346      <organization>First Virtual Holdings</organization>
4347      <address><email>nsb@nsb.fv.com</email></address>
4348    </author>
4349    <date month="November" year="1996"/>
4350  </front>
4351  <seriesInfo name="RFC" value="2045"/>
4352</reference>
4353
4354<reference anchor="RFC2047">
4355  <front>
4356    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4357    <author initials="K." surname="Moore" fullname="Keith Moore">
4358      <organization>University of Tennessee</organization>
4359      <address><email>moore@cs.utk.edu</email></address>
4360    </author>
4361    <date month="November" year="1996"/>
4362  </front>
4363  <seriesInfo name="RFC" value="2047"/>
4364</reference>
4365
4366<reference anchor="RFC2068">
4367  <front>
4368    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4369    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4370      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4371      <address><email>fielding@ics.uci.edu</email></address>
4372    </author>
4373    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4374      <organization>MIT Laboratory for Computer Science</organization>
4375      <address><email>jg@w3.org</email></address>
4376    </author>
4377    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4378      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4379      <address><email>mogul@wrl.dec.com</email></address>
4380    </author>
4381    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4382      <organization>MIT Laboratory for Computer Science</organization>
4383      <address><email>frystyk@w3.org</email></address>
4384    </author>
4385    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4386      <organization>MIT Laboratory for Computer Science</organization>
4387      <address><email>timbl@w3.org</email></address>
4388    </author>
4389    <date month="January" year="1997"/>
4390  </front>
4391  <seriesInfo name="RFC" value="2068"/>
4392</reference>
4393
4394<reference anchor='RFC2109'>
4395  <front>
4396    <title>HTTP State Management Mechanism</title>
4397    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
4398      <organization>Bell Laboratories, Lucent Technologies</organization>
4399      <address><email>dmk@bell-labs.com</email></address>
4400    </author>
4401    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4402      <organization>Netscape Communications Corp.</organization>
4403      <address><email>montulli@netscape.com</email></address>
4404    </author>
4405    <date year='1997' month='February' />
4406  </front>
4407  <seriesInfo name='RFC' value='2109' />
4408</reference>
4409
4410<reference anchor="RFC2145">
4411  <front>
4412    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4413    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4414      <organization>Western Research Laboratory</organization>
4415      <address><email>mogul@wrl.dec.com</email></address>
4416    </author>
4417    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4418      <organization>Department of Information and Computer Science</organization>
4419      <address><email>fielding@ics.uci.edu</email></address>
4420    </author>
4421    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4422      <organization>MIT Laboratory for Computer Science</organization>
4423      <address><email>jg@w3.org</email></address>
4424    </author>
4425    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4426      <organization>W3 Consortium</organization>
4427      <address><email>frystyk@w3.org</email></address>
4428    </author>
4429    <date month="May" year="1997"/>
4430  </front>
4431  <seriesInfo name="RFC" value="2145"/>
4432</reference>
4433
4434<reference anchor="RFC2616">
4435  <front>
4436    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4437    <author initials="R." surname="Fielding" fullname="R. Fielding">
4438      <organization>University of California, Irvine</organization>
4439      <address><email>fielding@ics.uci.edu</email></address>
4440    </author>
4441    <author initials="J." surname="Gettys" fullname="J. Gettys">
4442      <organization>W3C</organization>
4443      <address><email>jg@w3.org</email></address>
4444    </author>
4445    <author initials="J." surname="Mogul" fullname="J. Mogul">
4446      <organization>Compaq Computer Corporation</organization>
4447      <address><email>mogul@wrl.dec.com</email></address>
4448    </author>
4449    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4450      <organization>MIT Laboratory for Computer Science</organization>
4451      <address><email>frystyk@w3.org</email></address>
4452    </author>
4453    <author initials="L." surname="Masinter" fullname="L. Masinter">
4454      <organization>Xerox Corporation</organization>
4455      <address><email>masinter@parc.xerox.com</email></address>
4456    </author>
4457    <author initials="P." surname="Leach" fullname="P. Leach">
4458      <organization>Microsoft Corporation</organization>
4459      <address><email>paulle@microsoft.com</email></address>
4460    </author>
4461    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4462      <organization>W3C</organization>
4463      <address><email>timbl@w3.org</email></address>
4464    </author>
4465    <date month="June" year="1999"/>
4466  </front>
4467  <seriesInfo name="RFC" value="2616"/>
4468</reference>
4469
4470<reference anchor='RFC2817'>
4471  <front>
4472    <title>Upgrading to TLS Within HTTP/1.1</title>
4473    <author initials='R.' surname='Khare' fullname='R. Khare'>
4474      <organization>4K Associates / UC Irvine</organization>
4475      <address><email>rohit@4K-associates.com</email></address>
4476    </author>
4477    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4478      <organization>Agranat Systems, Inc.</organization>
4479      <address><email>lawrence@agranat.com</email></address>
4480    </author>
4481    <date year='2000' month='May' />
4482  </front>
4483  <seriesInfo name='RFC' value='2817' />
4484</reference>
4485
4486<reference anchor='RFC2818'>
4487  <front>
4488    <title>HTTP Over TLS</title>
4489    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4490      <organization>RTFM, Inc.</organization>
4491      <address><email>ekr@rtfm.com</email></address>
4492    </author>
4493    <date year='2000' month='May' />
4494  </front>
4495  <seriesInfo name='RFC' value='2818' />
4496</reference>
4497
4498<reference anchor='RFC2965'>
4499  <front>
4500    <title>HTTP State Management Mechanism</title>
4501    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4502      <organization>Bell Laboratories, Lucent Technologies</organization>
4503      <address><email>dmk@bell-labs.com</email></address>
4504    </author>
4505    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4506      <organization>Epinions.com, Inc.</organization>
4507      <address><email>lou@montulli.org</email></address>
4508    </author>
4509    <date year='2000' month='October' />
4510  </front>
4511  <seriesInfo name='RFC' value='2965' />
4512</reference>
4513
4514<reference anchor='RFC3864'>
4515  <front>
4516    <title>Registration Procedures for Message Header Fields</title>
4517    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4518      <organization>Nine by Nine</organization>
4519      <address><email>GK-IETF@ninebynine.org</email></address>
4520    </author>
4521    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4522      <organization>BEA Systems</organization>
4523      <address><email>mnot@pobox.com</email></address>
4524    </author>
4525    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4526      <organization>HP Labs</organization>
4527      <address><email>JeffMogul@acm.org</email></address>
4528    </author>
4529    <date year='2004' month='September' />
4530  </front>
4531  <seriesInfo name='BCP' value='90' />
4532  <seriesInfo name='RFC' value='3864' />
4533</reference>
4534
4535<reference anchor="RFC4288">
4536  <front>
4537    <title>Media Type Specifications and Registration Procedures</title>
4538    <author initials="N." surname="Freed" fullname="N. Freed">
4539      <organization>Sun Microsystems</organization>
4540      <address>
4541        <email>ned.freed@mrochek.com</email>
4542      </address>
4543    </author>
4544    <author initials="J." surname="Klensin" fullname="J. Klensin">
4545      <address>
4546        <email>klensin+ietf@jck.com</email>
4547      </address>
4548    </author>
4549    <date year="2005" month="December"/>
4550  </front>
4551  <seriesInfo name="BCP" value="13"/>
4552  <seriesInfo name="RFC" value="4288"/>
4553</reference>
4554
4555<reference anchor='RFC4395'>
4556  <front>
4557    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4558    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4559      <organization>AT&amp;T Laboratories</organization>
4560      <address>
4561        <email>tony+urireg@maillennium.att.com</email>
4562      </address>
4563    </author>
4564    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4565      <organization>Qualcomm, Inc.</organization>
4566      <address>
4567        <email>hardie@qualcomm.com</email>
4568      </address>
4569    </author>
4570    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4571      <organization>Adobe Systems</organization>
4572      <address>
4573        <email>LMM@acm.org</email>
4574      </address>
4575    </author>
4576    <date year='2006' month='February' />
4577  </front>
4578  <seriesInfo name='BCP' value='115' />
4579  <seriesInfo name='RFC' value='4395' />
4580</reference>
4581
4582<reference anchor='RFC5226'>
4583  <front>
4584    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4585    <author initials='T.' surname='Narten' fullname='T. Narten'>
4586      <organization>IBM</organization>
4587      <address><email>narten@us.ibm.com</email></address>
4588    </author>
4589    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4590      <organization>Google</organization>
4591      <address><email>Harald@Alvestrand.no</email></address>
4592    </author>
4593    <date year='2008' month='May' />
4594  </front>
4595  <seriesInfo name='BCP' value='26' />
4596  <seriesInfo name='RFC' value='5226' />
4597</reference>
4598
4599<reference anchor="RFC5322">
4600  <front>
4601    <title>Internet Message Format</title>
4602    <author initials="P." surname="Resnick" fullname="P. Resnick">
4603      <organization>Qualcomm Incorporated</organization>
4604    </author>
4605    <date year="2008" month="October"/>
4606  </front> 
4607  <seriesInfo name="RFC" value="5322"/>
4608</reference>
4609
4610<reference anchor='BCP97'>
4611  <front>
4612    <title>Handling Normative References to Standards-Track Documents</title>
4613    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4614      <address>
4615        <email>klensin+ietf@jck.com</email>
4616      </address>
4617    </author>
4618    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4619      <organization>MIT</organization>
4620      <address>
4621        <email>hartmans-ietf@mit.edu</email>
4622      </address>
4623    </author>
4624    <date year='2007' month='June' />
4625  </front>
4626  <seriesInfo name='BCP' value='97' />
4627  <seriesInfo name='RFC' value='4897' />
4628</reference>
4629
4630<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4631  <front>
4632    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4633    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4634    <date year="2001" month="November"/>
4635  </front>
4636  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4637</reference>
4638
4639<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4640  <front>
4641    <title>Analysis of HTTP Performance Problems</title>
4642    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4643    <date/>
4644  </front>
4645</reference>
4646
4647<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4648  <front>
4649  <title>Analysis of HTTP Performance</title>
4650  <author initials="J." surname="Touch" fullname="Joe Touch">
4651    <organization>USC/Information Sciences Institute</organization>
4652    <address><email>touch@isi.edu</email></address>
4653  </author>
4654  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4655    <organization>USC/Information Sciences Institute</organization>
4656    <address><email>johnh@isi.edu</email></address>
4657  </author>
4658  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4659    <organization>USC/Information Sciences Institute</organization>
4660    <address><email>katia@isi.edu</email></address>
4661  </author>
4662  <date year="1998" month="Aug"/>
4663  </front>
4664  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4665  <annotation>(original report dated Aug. 1996)</annotation>
4666</reference>
4667
4668</references>
4669
4670
4671<section title="Tolerant Applications" anchor="tolerant.applications">
4672<t>
4673   Although this document specifies the requirements for the generation
4674   of HTTP/1.1 messages, not all applications will be correct in their
4675   implementation. We therefore recommend that operational applications
4676   be tolerant of deviations whenever those deviations can be
4677   interpreted unambiguously.
4678</t>
4679<t>
4680   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4681   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4682   &SHOULD; accept any amount of WSP characters between fields, even though
4683   only a single SP is required.
4684</t>
4685<t>
4686   The line terminator for header fields is the sequence CRLF.
4687   However, we recommend that applications, when parsing such headers fields,
4688   recognize a single LF as a line terminator and ignore the leading CR.
4689</t>
4690<t>
4691   The character set of a representation &SHOULD; be labeled as the lowest
4692   common denominator of the character codes used within that representation, with
4693   the exception that not labeling the representation is preferred over labeling
4694   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4695</t>
4696<t>
4697   Additional rules for requirements on parsing and encoding of dates
4698   and other potential problems with date encodings include:
4699</t>
4700<t>
4701  <list style="symbols">
4702     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4703        which appears to be more than 50 years in the future is in fact
4704        in the past (this helps solve the "year 2000" problem).</t>
4705
4706     <t>Although all date formats are specified to be case-sensitive,
4707        recipients &SHOULD; match day, week and timezone names
4708        case-insensitively.</t>
4709             
4710     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4711        Expires date as earlier than the proper value, but &MUST-NOT;
4712        internally represent a parsed Expires date as later than the
4713        proper value.</t>
4714
4715     <t>All expiration-related calculations &MUST; be done in GMT. The
4716        local time zone &MUST-NOT; influence the calculation or comparison
4717        of an age or expiration time.</t>
4718
4719     <t>If an HTTP header field incorrectly carries a date value with a time
4720        zone other than GMT, it &MUST; be converted into GMT using the
4721        most conservative possible conversion.</t>
4722  </list>
4723</t>
4724</section>
4725
4726<section title="Compatibility with Previous Versions" anchor="compatibility">
4727<t>
4728   HTTP has been in use by the World-Wide Web global information initiative
4729   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4730   was a simple protocol for hypertext data transfer across the Internet
4731   with only a single method and no metadata.
4732   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4733   methods and MIME-like messaging that could include metadata about the data
4734   transferred and modifiers on the request/response semantics. However,
4735   HTTP/1.0 did not sufficiently take into consideration the effects of
4736   hierarchical proxies, caching, the need for persistent connections, or
4737   name-based virtual hosts. The proliferation of incompletely-implemented
4738   applications calling themselves "HTTP/1.0" further necessitated a
4739   protocol version change in order for two communicating applications
4740   to determine each other's true capabilities.
4741</t>
4742<t>
4743   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4744   requirements that enable reliable implementations, adding only
4745   those new features that will either be safely ignored by an HTTP/1.0
4746   recipient or only sent when communicating with a party advertising
4747   compliance with HTTP/1.1.
4748</t>
4749<t>
4750   It is beyond the scope of a protocol specification to mandate
4751   compliance with previous versions. HTTP/1.1 was deliberately
4752   designed, however, to make supporting previous versions easy. It is
4753   worth noting that, at the time of composing this specification, we would
4754   expect general-purpose HTTP/1.1 servers to:
4755  <list style="symbols">
4756     <t>understand any valid request in the format of HTTP/1.0 and
4757        1.1;</t>
4758
4759     <t>respond appropriately with a message in the same major version
4760        used by the client.</t>
4761  </list>
4762</t>
4763<t>
4764   And we would expect HTTP/1.1 clients to:
4765  <list style="symbols">
4766     <t>understand any valid response in the format of HTTP/1.0 or
4767        1.1.</t>
4768  </list>
4769</t>
4770<t>
4771   For most implementations of HTTP/1.0, each connection is established
4772   by the client prior to the request and closed by the server after
4773   sending the response. Some implementations implement the Keep-Alive
4774   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4775</t>
4776
4777<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4778<t>
4779   This section summarizes major differences between versions HTTP/1.0
4780   and HTTP/1.1.
4781</t>
4782
4783<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4784<t>
4785   The requirements that clients and servers support the Host request-header
4786   field (<xref target="header.host"/>), report an error if it is
4787   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4788   are among the most important changes defined by this
4789   specification.
4790</t>
4791<t>
4792   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4793   addresses and servers; there was no other established mechanism for
4794   distinguishing the intended server of a request than the IP address
4795   to which that request was directed. The changes outlined above will
4796   allow the Internet, once older HTTP clients are no longer common, to
4797   support multiple Web sites from a single IP address, greatly
4798   simplifying large operational Web servers, where allocation of many
4799   IP addresses to a single host has created serious problems. The
4800   Internet will also be able to recover the IP addresses that have been
4801   allocated for the sole purpose of allowing special-purpose domain
4802   names to be used in root-level HTTP URLs. Given the rate of growth of
4803   the Web, and the number of servers already deployed, it is extremely
4804   important that all implementations of HTTP (including updates to
4805   existing HTTP/1.0 applications) correctly implement these
4806   requirements:
4807  <list style="symbols">
4808     <t>Both clients and servers &MUST; support the Host request-header field.</t>
4809
4810     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header field.</t>
4811
4812     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4813        request does not include a Host request-header field.</t>
4814
4815     <t>Servers &MUST; accept absolute URIs.</t>
4816  </list>
4817</t>
4818</section>
4819</section>
4820
4821<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4822<t>
4823   Some clients and servers might wish to be compatible with some
4824   previous implementations of persistent connections in HTTP/1.0
4825   clients and servers. Persistent connections in HTTP/1.0 are
4826   explicitly negotiated as they are not the default behavior. HTTP/1.0
4827   experimental implementations of persistent connections are faulty,
4828   and the new facilities in HTTP/1.1 are designed to rectify these
4829   problems. The problem was that some existing HTTP/1.0 clients might
4830   send Keep-Alive to a proxy server that doesn't understand
4831   Connection, which would then erroneously forward it to the next
4832   inbound server, which would establish the Keep-Alive connection and
4833   result in a hung HTTP/1.0 proxy waiting for the close on the
4834   response. The result is that HTTP/1.0 clients must be prevented from
4835   using Keep-Alive when talking to proxies.
4836</t>
4837<t>
4838   However, talking to proxies is the most important use of persistent
4839   connections, so that prohibition is clearly unacceptable. Therefore,
4840   we need some other mechanism for indicating a persistent connection
4841   is desired, which is safe to use even when talking to an old proxy
4842   that ignores Connection. Persistent connections are the default for
4843   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4844   declaring non-persistence. See <xref target="header.connection"/>.
4845</t>
4846<t>
4847   The original HTTP/1.0 form of persistent connections (the Connection:
4848   Keep-Alive and Keep-Alive header field) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4849</t>
4850</section>
4851
4852<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4853<t>
4854  Empty list elements in list productions have been deprecated.
4855  (<xref target="notation.abnf"/>)
4856</t>
4857<t>
4858  Rules about implicit linear whitespace between certain grammar productions
4859  have been removed; now it's only allowed when specifically pointed out
4860  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4861  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4862  Non-ASCII content in header fields and reason phrase has been obsoleted and
4863  made opaque (the TEXT rule was removed)
4864  (<xref target="basic.rules"/>)
4865</t>
4866<t>
4867  Clarify that HTTP-Version is case sensitive.
4868  (<xref target="http.version"/>)
4869</t>
4870<t>
4871  Require that invalid whitespace around field-names be rejected.
4872  (<xref target="header.fields"/>)
4873</t>
4874<t>
4875  Require recipients to handle bogus Content-Length header fields as errors.
4876  (<xref target="message.body"/>)
4877</t>
4878<t>
4879  Remove reference to non-existent identity transfer-coding value tokens.
4880  (Sections <xref format="counter" target="message.body"/> and
4881  <xref format="counter" target="transfer.codings"/>)
4882</t>
4883<t>
4884  Update use of abs_path production from RFC 1808 to the path-absolute + query
4885  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4886  method only.
4887  (<xref target="request-target"/>)
4888</t>
4889<t>
4890  Clarification that the chunk length does not include the count of the octets
4891  in the chunk header and trailer. Furthermore disallowed line folding
4892  in chunk extensions.
4893  (<xref target="chunked.encoding"/>)
4894</t>
4895<t>
4896  Remove hard limit of two connections per server.
4897  (<xref target="persistent.practical"/>)
4898</t>
4899<t>
4900  Clarify exactly when close connection options must be sent.
4901  (<xref target="header.connection"/>)
4902</t>
4903<t>
4904  Define the semantics of the "Upgrade" header field in responses other than
4905  101 (this was incorporated from <xref target="RFC2817"/>).
4906  (<xref target="header.upgrade"/>)
4907</t>
4908</section>
4909</section>
4910
4911<?BEGININC p1-messaging.abnf-appendix ?>
4912<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4913<figure>
4914<artwork type="abnf" name="p1-messaging.parsed-abnf">
4915<x:ref>BWS</x:ref> = OWS
4916
4917<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4918<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4919<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4920<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4921 connection-token ] )
4922<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4923<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4924
4925<x:ref>Date</x:ref> = "Date:" OWS Date-v
4926<x:ref>Date-v</x:ref> = HTTP-date
4927
4928<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4929
4930<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4931<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4932<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4933<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4934 ]
4935<x:ref>Host</x:ref> = "Host:" OWS Host-v
4936<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4937
4938<x:ref>MIME-Version</x:ref> = &lt;MIME-Version, defined in [Part3], Appendix A.1&gt;
4939<x:ref>Method</x:ref> = token
4940
4941<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4942
4943<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4944
4945<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4946<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4947<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
4948<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4949<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
4950
4951<x:ref>Status-Code</x:ref> = 3DIGIT
4952<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4953
4954<x:ref>TE</x:ref> = "TE:" OWS TE-v
4955<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4956<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4957<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4958<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4959<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4960 transfer-coding ] )
4961
4962<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4963<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4964<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4965
4966<x:ref>Via</x:ref> = "Via:" OWS Via-v
4967<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4968 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4969 ] )
4970
4971<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4972
4973<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4974<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4975<x:ref>attribute</x:ref> = token
4976<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4977
4978<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4979<x:ref>chunk-data</x:ref> = 1*OCTET
4980<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4981<x:ref>chunk-ext-name</x:ref> = token
4982<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4983<x:ref>chunk-size</x:ref> = 1*HEXDIG
4984<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4985<x:ref>connection-token</x:ref> = token
4986<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4987 / %x2A-5B ; '*'-'['
4988 / %x5D-7E ; ']'-'~'
4989 / obs-text
4990
4991<x:ref>date1</x:ref> = day SP month SP year
4992<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4993<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4994<x:ref>day</x:ref> = 2DIGIT
4995<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4996 / %x54.75.65 ; Tue
4997 / %x57.65.64 ; Wed
4998 / %x54.68.75 ; Thu
4999 / %x46.72.69 ; Fri
5000 / %x53.61.74 ; Sat
5001 / %x53.75.6E ; Sun
5002<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5003 / %x54.75.65.73.64.61.79 ; Tuesday
5004 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
5005 / %x54.68.75.72.73.64.61.79 ; Thursday
5006 / %x46.72.69.64.61.79 ; Friday
5007 / %x53.61.74.75.72.64.61.79 ; Saturday
5008 / %x53.75.6E.64.61.79 ; Sunday
5009
5010<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5011<x:ref>field-name</x:ref> = token
5012<x:ref>field-value</x:ref> = *( field-content / OWS )
5013
5014<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
5015 / Transfer-Encoding / Upgrade / Via / Warning / MIME-Version
5016
5017<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5018<x:ref>hour</x:ref> = 2DIGIT
5019<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5020<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5021
5022<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5023
5024<x:ref>message-body</x:ref> = *OCTET
5025<x:ref>minute</x:ref> = 2DIGIT
5026<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5027 / %x46.65.62 ; Feb
5028 / %x4D.61.72 ; Mar
5029 / %x41.70.72 ; Apr
5030 / %x4D.61.79 ; May
5031 / %x4A.75.6E ; Jun
5032 / %x4A.75.6C ; Jul
5033 / %x41.75.67 ; Aug
5034 / %x53.65.70 ; Sep
5035 / %x4F.63.74 ; Oct
5036 / %x4E.6F.76 ; Nov
5037 / %x44.65.63 ; Dec
5038
5039<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5040<x:ref>obs-fold</x:ref> = CRLF
5041<x:ref>obs-text</x:ref> = %x80-FF
5042
5043<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5044<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5045<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5046<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5047<x:ref>product</x:ref> = token [ "/" product-version ]
5048<x:ref>product-version</x:ref> = token
5049<x:ref>protocol-name</x:ref> = token
5050<x:ref>protocol-version</x:ref> = token
5051<x:ref>pseudonym</x:ref> = token
5052
5053<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5054 / %x5D-7E ; ']'-'~'
5055 / obs-text
5056<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5057 / %x5D-7E ; ']'-'~'
5058 / obs-text
5059<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5060<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5061<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5062<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5063<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5064<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5065
5066<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5067<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5068<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5069<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
5070<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5071 / authority
5072<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
5073<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5074<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5075
5076<x:ref>second</x:ref> = 2DIGIT
5077<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5078 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5079<x:ref>start-line</x:ref> = Request-Line / Status-Line
5080
5081<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5082<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5083 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5084<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5085<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5086<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5087<x:ref>token</x:ref> = 1*tchar
5088<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5089<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5090 transfer-extension
5091<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5092<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5093
5094<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5095
5096<x:ref>value</x:ref> = word
5097
5098<x:ref>word</x:ref> = token / quoted-string
5099
5100<x:ref>year</x:ref> = 4DIGIT
5101</artwork>
5102</figure>
5103<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5104; Chunked-Body defined but not used
5105; Content-Length defined but not used
5106; HTTP-message defined but not used
5107; Host defined but not used
5108; Request defined but not used
5109; Response defined but not used
5110; TE defined but not used
5111; URI-reference defined but not used
5112; general-header defined but not used
5113; http-URI defined but not used
5114; https-URI defined but not used
5115; partial-URI defined but not used
5116; request-header defined but not used
5117; response-header defined but not used
5118; special defined but not used
5119</artwork></figure></section>
5120<?ENDINC p1-messaging.abnf-appendix ?>
5121
5122<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5123
5124<section title="Since RFC 2616">
5125<t>
5126  Extracted relevant partitions from <xref target="RFC2616"/>.
5127</t>
5128</section>
5129
5130<section title="Since draft-ietf-httpbis-p1-messaging-00">
5131<t>
5132  Closed issues:
5133  <list style="symbols"> 
5134    <t>
5135      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5136      "HTTP Version should be case sensitive"
5137      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5138    </t>
5139    <t>
5140      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5141      "'unsafe' characters"
5142      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5143    </t>
5144    <t>
5145      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5146      "Chunk Size Definition"
5147      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5148    </t>
5149    <t>
5150      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5151      "Message Length"
5152      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5153    </t>
5154    <t>
5155      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5156      "Media Type Registrations"
5157      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5158    </t>
5159    <t>
5160      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5161      "URI includes query"
5162      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5163    </t>
5164    <t>
5165      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5166      "No close on 1xx responses"
5167      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5168    </t>
5169    <t>
5170      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5171      "Remove 'identity' token references"
5172      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5173    </t>
5174    <t>
5175      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5176      "Import query BNF"
5177    </t>
5178    <t>
5179      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5180      "qdtext BNF"
5181    </t>
5182    <t>
5183      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5184      "Normative and Informative references"
5185    </t>
5186    <t>
5187      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5188      "RFC2606 Compliance"
5189    </t>
5190    <t>
5191      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5192      "RFC977 reference"
5193    </t>
5194    <t>
5195      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5196      "RFC1700 references"
5197    </t>
5198    <t>
5199      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5200      "inconsistency in date format explanation"
5201    </t>
5202    <t>
5203      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5204      "Date reference typo"
5205    </t>
5206    <t>
5207      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5208      "Informative references"
5209    </t>
5210    <t>
5211      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5212      "ISO-8859-1 Reference"
5213    </t>
5214    <t>
5215      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5216      "Normative up-to-date references"
5217    </t>
5218  </list>
5219</t>
5220<t>
5221  Other changes:
5222  <list style="symbols"> 
5223    <t>
5224      Update media type registrations to use RFC4288 template.
5225    </t>
5226    <t>
5227      Use names of RFC4234 core rules DQUOTE and WSP,
5228      fix broken ABNF for chunk-data
5229      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5230    </t>
5231  </list>
5232</t>
5233</section>
5234
5235<section title="Since draft-ietf-httpbis-p1-messaging-01">
5236<t>
5237  Closed issues:
5238  <list style="symbols"> 
5239    <t>
5240      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5241      "Bodies on GET (and other) requests"
5242    </t>
5243    <t>
5244      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5245      "Updating to RFC4288"
5246    </t>
5247    <t>
5248      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5249      "Status Code and Reason Phrase"
5250    </t>
5251    <t>
5252      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5253      "rel_path not used"
5254    </t>
5255  </list>
5256</t>
5257<t>
5258  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5259  <list style="symbols"> 
5260    <t>
5261      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5262      "trailer-part").
5263    </t>
5264    <t>
5265      Avoid underscore character in rule names ("http_URL" ->
5266      "http-URL", "abs_path" -> "path-absolute").
5267    </t>
5268    <t>
5269      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5270      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5271      have to be updated when switching over to RFC3986.
5272    </t>
5273    <t>
5274      Synchronize core rules with RFC5234.
5275    </t>
5276    <t>
5277      Get rid of prose rules that span multiple lines.
5278    </t>
5279    <t>
5280      Get rid of unused rules LOALPHA and UPALPHA.
5281    </t>
5282    <t>
5283      Move "Product Tokens" section (back) into Part 1, as "token" is used
5284      in the definition of the Upgrade header field.
5285    </t>
5286    <t>
5287      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5288    </t>
5289    <t>
5290      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5291    </t>
5292  </list>
5293</t>
5294</section>
5295
5296<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5297<t>
5298  Closed issues:
5299  <list style="symbols"> 
5300    <t>
5301      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5302      "HTTP-date vs. rfc1123-date"
5303    </t>
5304    <t>
5305      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5306      "WS in quoted-pair"
5307    </t>
5308  </list>
5309</t>
5310<t>
5311  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5312  <list style="symbols"> 
5313    <t>
5314      Reference RFC 3984, and update header field registrations for headers defined
5315      in this document.
5316    </t>
5317  </list>
5318</t>
5319<t>
5320  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5321  <list style="symbols"> 
5322    <t>
5323      Replace string literals when the string really is case-sensitive (HTTP-Version).
5324    </t>
5325  </list>
5326</t>
5327</section>
5328
5329<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5330<t>
5331  Closed issues:
5332  <list style="symbols"> 
5333    <t>
5334      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5335      "Connection closing"
5336    </t>
5337    <t>
5338      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5339      "Move registrations and registry information to IANA Considerations"
5340    </t>
5341    <t>
5342      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5343      "need new URL for PAD1995 reference"
5344    </t>
5345    <t>
5346      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5347      "IANA Considerations: update HTTP URI scheme registration"
5348    </t>
5349    <t>
5350      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5351      "Cite HTTPS URI scheme definition"
5352    </t>
5353    <t>
5354      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5355      "List-type headers vs Set-Cookie"
5356    </t>
5357  </list>
5358</t>
5359<t>
5360  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5361  <list style="symbols"> 
5362    <t>
5363      Replace string literals when the string really is case-sensitive (HTTP-Date).
5364    </t>
5365    <t>
5366      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5367    </t>
5368  </list>
5369</t>
5370</section>
5371
5372<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5373<t>
5374  Closed issues:
5375  <list style="symbols"> 
5376    <t>
5377      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5378      "Out-of-date reference for URIs"
5379    </t>
5380    <t>
5381      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5382      "RFC 2822 is updated by RFC 5322"
5383    </t>
5384  </list>
5385</t>
5386<t>
5387  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5388  <list style="symbols"> 
5389    <t>
5390      Use "/" instead of "|" for alternatives.
5391    </t>
5392    <t>
5393      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5394    </t>
5395    <t>
5396      Only reference RFC 5234's core rules.
5397    </t>
5398    <t>
5399      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5400      whitespace ("OWS") and required whitespace ("RWS").
5401    </t>
5402    <t>
5403      Rewrite ABNFs to spell out whitespace rules, factor out
5404      header field value format definitions.
5405    </t>
5406  </list>
5407</t>
5408</section>
5409
5410<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5411<t>
5412  Closed issues:
5413  <list style="symbols"> 
5414    <t>
5415      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5416      "Header LWS"
5417    </t>
5418    <t>
5419      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5420      "Sort 1.3 Terminology"
5421    </t>
5422    <t>
5423      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5424      "RFC2047 encoded words"
5425    </t>
5426    <t>
5427      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5428      "Character Encodings in TEXT"
5429    </t>
5430    <t>
5431      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5432      "Line Folding"
5433    </t>
5434    <t>
5435      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5436      "OPTIONS * and proxies"
5437    </t>
5438    <t>
5439      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5440      "Reason-Phrase BNF"
5441    </t>
5442    <t>
5443      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5444      "Use of TEXT"
5445    </t>
5446    <t>
5447      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5448      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5449    </t>
5450    <t>
5451      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5452      "RFC822 reference left in discussion of date formats"
5453    </t>
5454  </list>
5455</t>
5456<t>
5457  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5458  <list style="symbols"> 
5459    <t>
5460      Rewrite definition of list rules, deprecate empty list elements.
5461    </t>
5462    <t>
5463      Add appendix containing collected and expanded ABNF.
5464    </t>
5465  </list>
5466</t>
5467<t>
5468  Other changes:
5469  <list style="symbols"> 
5470    <t>
5471      Rewrite introduction; add mostly new Architecture Section.
5472    </t>
5473    <t>
5474      Move definition of quality values from Part 3 into Part 1;
5475      make TE request header field grammar independent of accept-params (defined in Part 3).
5476    </t>
5477  </list>
5478</t>
5479</section>
5480
5481<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5482<t>
5483  Closed issues:
5484  <list style="symbols"> 
5485    <t>
5486      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5487      "base for numeric protocol elements"
5488    </t>
5489    <t>
5490      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5491      "comment ABNF"
5492    </t>
5493  </list>
5494</t>
5495<t>
5496  Partly resolved issues:
5497  <list style="symbols"> 
5498    <t>
5499      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5500      "205 Bodies" (took out language that implied that there might be
5501      methods for which a request body MUST NOT be included)
5502    </t>
5503    <t>
5504      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5505      "editorial improvements around HTTP-date"
5506    </t>
5507  </list>
5508</t>
5509</section>
5510
5511<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5512<t>
5513  Closed issues:
5514  <list style="symbols"> 
5515    <t>
5516      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5517      "Repeating single-value headers"
5518    </t>
5519    <t>
5520      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5521      "increase connection limit"
5522    </t>
5523    <t>
5524      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5525      "IP addresses in URLs"
5526    </t>
5527    <t>
5528      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5529      "take over HTTP Upgrade Token Registry"
5530    </t>
5531    <t>
5532      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5533      "CR and LF in chunk extension values"
5534    </t>
5535    <t>
5536      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5537      "HTTP/0.9 support"
5538    </t>
5539    <t>
5540      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5541      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5542    </t>
5543    <t>
5544      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5545      "move definitions of gzip/deflate/compress to part 1"
5546    </t>
5547    <t>
5548      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5549      "disallow control characters in quoted-pair"
5550    </t>
5551  </list>
5552</t>
5553<t>
5554  Partly resolved issues:
5555  <list style="symbols"> 
5556    <t>
5557      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5558      "update IANA requirements wrt Transfer-Coding values" (add the
5559      IANA Considerations subsection)
5560    </t>
5561  </list>
5562</t>
5563</section>
5564
5565<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5566<t>
5567  Closed issues:
5568  <list style="symbols"> 
5569    <t>
5570      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5571      "header parsing, treatment of leading and trailing OWS"
5572    </t>
5573  </list>
5574</t>
5575<t>
5576  Partly resolved issues:
5577  <list style="symbols"> 
5578    <t>
5579      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5580      "Placement of 13.5.1 and 13.5.2"
5581    </t>
5582    <t>
5583      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5584      "use of term "word" when talking about header structure"
5585    </t>
5586  </list>
5587</t>
5588</section>
5589
5590<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5591<t>
5592  Closed issues:
5593  <list style="symbols"> 
5594    <t>
5595      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5596      "Clarification of the term 'deflate'"
5597    </t>
5598    <t>
5599      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5600      "OPTIONS * and proxies"
5601    </t>
5602    <t>
5603      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5604      "MIME-Version not listed in P1, general header fields"
5605    </t>
5606    <t>
5607      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5608      "IANA registry for content/transfer encodings"
5609    </t>
5610    <t>
5611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5612      "Case-sensitivity of HTTP-date"
5613    </t>
5614    <t>
5615      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5616      "use of term "word" when talking about header structure"
5617    </t>
5618  </list>
5619</t>
5620<t>
5621  Partly resolved issues:
5622  <list style="symbols"> 
5623    <t>
5624      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5625      "Term for the requested resource's URI"
5626    </t>
5627  </list>
5628</t>
5629</section>
5630
5631<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5632<t>
5633  Closed issues:
5634  <list style="symbols">
5635    <t>
5636      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5637      "Connection Closing"
5638    </t>
5639    <t>
5640      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5641      "Delimiting messages with multipart/byteranges"
5642    </t>
5643    <t>
5644      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5645      "Handling multiple Content-Length headers"
5646    </t>
5647    <t>
5648      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5649      "Clarify entity / representation / variant terminology"
5650    </t>
5651    <t>
5652      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5653      "consider removing the 'changes from 2068' sections"
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/159"/>:
5662      "HTTP(s) URI scheme definitions"
5663    </t>
5664  </list>
5665</t>
5666</section>
5667
5668<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5669<t>
5670  Closed issues:
5671  <list style="symbols">
5672    <t>
5673      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5674      "Trailer requirements"
5675    </t>
5676    <t>
5677      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5678      "Text about clock requirement for caches belongs in p6"
5679    </t>
5680    <t>
5681      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5682      "effective request URI: handling of missing host in HTTP/1.0"
5683    </t>
5684    <t>
5685      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5686      "confusing Date requirements for clients"
5687    </t>
5688  </list>
5689</t>
5690<t>
5691  Partly resolved issues:
5692  <list style="symbols"> 
5693    <t>
5694      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5695      "Handling multiple Content-Length headers"
5696    </t>
5697  </list>
5698</t>
5699</section>
5700
5701<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5702<t>
5703  Closed issues:
5704  <list style="symbols">
5705    <t>
5706      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5707      "Is * usable as a request-uri for new methods?"
5708    </t>
5709    <t>
5710      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5711      "Migrate Upgrade details from RFC2817"
5712    </t>
5713  </list>
5714</t>
5715</section>
5716
5717</section>
5718
5719</back>
5720</rfc>
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