source: draft-ietf-httpbis/latest/p3-payload.xml @ 1234

Last change on this file since 1234 was 1234, checked in by julian.reschke@…, 9 years ago

rewrite header field ABNFs to only specify the field value (see #276)

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File size: 126.3 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "March">
16  <!ENTITY ID-YEAR "2011">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY notation                 "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY notation-abnf            "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY basic-rules              "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY full-date                "<xref target='Part1' x:rel='#date.time.formats.full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY qvalue                   "<xref target='Part1' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY effective-request-uri    "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY compression-codings      "<xref target='Part1' x:rel='#compression.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY transfer-codings         "<xref target='Part1' x:rel='#transfer.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY compress-coding          "<xref target='Part1' x:rel='#compress.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY deflate-coding           "<xref target='Part1' x:rel='#deflate.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY gzip-coding              "<xref target='Part1' x:rel='#gzip.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY response-representation  "<xref target='Part2' x:rel='#identifying.response.associated.with.representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41]>
42<?rfc toc="yes" ?>
43<?rfc symrefs="yes" ?>
44<?rfc sortrefs="yes" ?>
45<?rfc compact="yes"?>
46<?rfc subcompact="no" ?>
47<?rfc linkmailto="no" ?>
48<?rfc editing="no" ?>
49<?rfc comments="yes"?>
50<?rfc inline="yes"?>
51<?rfc rfcedstyle="yes"?>
52<?rfc-ext allow-markup-in-artwork="yes" ?>
53<?rfc-ext include-references-in-index="yes" ?>
54<rfc obsoletes="2616" category="std" x:maturity-level="draft"
55     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
56     xmlns:x='http://purl.org/net/xml2rfc/ext'>
57<front>
58
59  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
60
61  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
62    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
63    <address>
64      <postal>
65        <street>345 Park Ave</street>
66        <city>San Jose</city>
67        <region>CA</region>
68        <code>95110</code>
69        <country>USA</country>
70      </postal>
71      <email>fielding@gbiv.com</email>
72      <uri>http://roy.gbiv.com/</uri>
73    </address>
74  </author>
75
76  <author initials="J." surname="Gettys" fullname="Jim Gettys">
77    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
78    <address>
79      <postal>
80        <street>21 Oak Knoll Road</street>
81        <city>Carlisle</city>
82        <region>MA</region>
83        <code>01741</code>
84        <country>USA</country>
85      </postal>
86      <email>jg@freedesktop.org</email>
87      <uri>http://gettys.wordpress.com/</uri>
88    </address>
89  </author>
90 
91  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
92    <organization abbrev="HP">Hewlett-Packard Company</organization>
93    <address>
94      <postal>
95        <street>HP Labs, Large Scale Systems Group</street>
96        <street>1501 Page Mill Road, MS 1177</street>
97        <city>Palo Alto</city>
98        <region>CA</region>
99        <code>94304</code>
100        <country>USA</country>
101      </postal>
102      <email>JeffMogul@acm.org</email>
103    </address>
104  </author>
105
106  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
107    <organization abbrev="Microsoft">Microsoft Corporation</organization>
108    <address>
109      <postal>
110        <street>1 Microsoft Way</street>
111        <city>Redmond</city>
112        <region>WA</region>
113        <code>98052</code>
114        <country>USA</country>
115      </postal>
116      <email>henrikn@microsoft.com</email>
117    </address>
118  </author>
119
120  <author initials="L." surname="Masinter" fullname="Larry Masinter">
121    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
122    <address>
123      <postal>
124        <street>345 Park Ave</street>
125        <city>San Jose</city>
126        <region>CA</region>
127        <code>95110</code>
128        <country>USA</country>
129      </postal>
130      <email>LMM@acm.org</email>
131      <uri>http://larry.masinter.net/</uri>
132    </address>
133  </author>
134 
135  <author initials="P." surname="Leach" fullname="Paul J. Leach">
136    <organization abbrev="Microsoft">Microsoft Corporation</organization>
137    <address>
138      <postal>
139        <street>1 Microsoft Way</street>
140        <city>Redmond</city>
141        <region>WA</region>
142        <code>98052</code>
143      </postal>
144      <email>paulle@microsoft.com</email>
145    </address>
146  </author>
147   
148  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
149    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
150    <address>
151      <postal>
152        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
153        <street>The Stata Center, Building 32</street>
154        <street>32 Vassar Street</street>
155        <city>Cambridge</city>
156        <region>MA</region>
157        <code>02139</code>
158        <country>USA</country>
159      </postal>
160      <email>timbl@w3.org</email>
161      <uri>http://www.w3.org/People/Berners-Lee/</uri>
162    </address>
163  </author>
164
165  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
166    <organization abbrev="W3C">World Wide Web Consortium</organization>
167    <address>
168      <postal>
169        <street>W3C / ERCIM</street>
170        <street>2004, rte des Lucioles</street>
171        <city>Sophia-Antipolis</city>
172        <region>AM</region>
173        <code>06902</code>
174        <country>France</country>
175      </postal>
176      <email>ylafon@w3.org</email>
177      <uri>http://www.raubacapeu.net/people/yves/</uri>
178    </address>
179  </author>
180
181  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
182    <organization abbrev="greenbytes">greenbytes GmbH</organization>
183    <address>
184      <postal>
185        <street>Hafenweg 16</street>
186        <city>Muenster</city><region>NW</region><code>48155</code>
187        <country>Germany</country>
188      </postal>
189      <phone>+49 251 2807760</phone>
190      <facsimile>+49 251 2807761</facsimile>
191      <email>julian.reschke@greenbytes.de</email>
192      <uri>http://greenbytes.de/tech/webdav/</uri>
193    </address>
194  </author>
195
196  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
197  <workgroup>HTTPbis Working Group</workgroup>
198
199<abstract>
200<t>
201   The Hypertext Transfer Protocol (HTTP) is an application-level
202   protocol for distributed, collaborative, hypermedia information
203   systems. HTTP has been in use by the World Wide Web global information
204   initiative since 1990. This document is Part 3 of the seven-part specification
205   that defines the protocol referred to as "HTTP/1.1" and, taken together,
206   obsoletes RFC 2616.  Part 3 defines HTTP message content,
207   metadata, and content negotiation.
208</t>
209</abstract>
210
211<note title="Editorial Note (To be removed by RFC Editor)">
212  <t>
213    Discussion of this draft should take place on the HTTPBIS working group
214    mailing list (ietf-http-wg@w3.org). The current issues list is
215    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/>
216    and related documents (including fancy diffs) can be found at
217    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
218  </t>
219  <t>
220    The changes in this draft are summarized in <xref target="changes.since.13"/>.
221  </t>
222</note>
223</front>
224<middle>
225<section title="Introduction" anchor="introduction">
226<t>
227   This document defines HTTP/1.1 message payloads (a.k.a., content), the
228   associated metadata header fields that define how the payload is intended
229   to be interpreted by a recipient, the request header fields that
230   might influence content selection, and the various selection algorithms
231   that are collectively referred to as HTTP content negotiation.
232</t>
233<t>
234   This document is currently disorganized in order to minimize the changes
235   between drafts and enable reviewers to see the smaller errata changes.
236   A future draft will reorganize the sections to better reflect the content.
237   In particular, the sections on entities will be renamed payload and moved
238   to the first half of the document, while the sections on content negotiation
239   and associated request header fields will be moved to the second half.  The
240   current mess reflects how widely dispersed these topics and associated
241   requirements had become in <xref target="RFC2616"/>.
242</t>
243
244<section title="Terminology" anchor="terminology">
245<t>
246   This specification uses a number of terms to refer to the roles
247   played by participants in, and objects of, the HTTP communication.
248</t>
249<t>
250  <iref item="content negotiation"/>
251  <x:dfn>content negotiation</x:dfn>
252  <list>
253    <t>
254      The mechanism for selecting the appropriate representation when
255      servicing a request. The representation in any response
256      can be negotiated (including error responses).
257    </t>
258  </list>
259</t>
260</section>
261
262<section title="Requirements" anchor="intro.requirements">
263<t>
264   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
265   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
266   document are to be interpreted as described in <xref target="RFC2119"/>.
267</t>
268<t>
269   An implementation is not compliant if it fails to satisfy one or more
270   of the "MUST" or "REQUIRED" level requirements for the protocols it
271   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
272   level and all the "SHOULD" level requirements for its protocols is said
273   to be "unconditionally compliant"; one that satisfies all the "MUST"
274   level requirements but not all the "SHOULD" level requirements for its
275   protocols is said to be "conditionally compliant".
276</t>
277</section>
278
279<section title="Syntax Notation" anchor="notation">
280  <x:anchor-alias value="ALPHA"/>
281  <x:anchor-alias value="CR"/>
282  <x:anchor-alias value="DIGIT"/>
283  <x:anchor-alias value="LF"/>
284  <x:anchor-alias value="OCTET"/>
285  <x:anchor-alias value="VCHAR"/>
286  <x:anchor-alias value="WSP"/>
287<t>
288  This specification uses the ABNF syntax defined in &notation; (which
289  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
290  <xref target="collected.abnf"/> shows the collected ABNF, with the list
291  rule expanded.
292</t>
293<t>
294  The following core rules are included by
295  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
296  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
297  DIGIT (decimal 0-9), DQUOTE (double quote),
298  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
299  OCTET (any 8-bit sequence of data), SP (space),
300  VCHAR (any visible USASCII character),
301  and WSP (whitespace).
302</t>
303
304<section title="Core Rules" anchor="core.rules">
305  <x:anchor-alias value="token"/>
306  <x:anchor-alias value="word"/>
307  <x:anchor-alias value="OWS"/>
308<t>
309  The core rules below are defined in &basic-rules;:
310</t>
311<figure><artwork type="abnf2616">
312  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
313  <x:ref>word</x:ref>           = &lt;word, defined in &basic-rules;&gt;
314  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
315</artwork></figure>
316</section>
317
318<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
319  <x:anchor-alias value="absolute-URI"/>
320  <x:anchor-alias value="partial-URI"/>
321  <x:anchor-alias value="qvalue"/>
322<t>
323  The ABNF rules below are defined in other parts:
324</t>
325<figure><!--Part1--><artwork type="abnf2616">
326  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
327  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
328  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
329</artwork></figure>
330</section>
331
332</section>
333
334</section>
335
336<section title="Protocol Parameters" anchor="protocol.parameters">
337
338<section title="Character Encodings (charset)" anchor="character.sets">
339<t>
340   HTTP uses charset names to indicate the character encoding of a
341   textual representation.
342</t>
343<t anchor="rule.charset">
344  <x:anchor-alias value="charset"/>
345   A character encoding is identified by a case-insensitive token. The
346   complete set of tokens is defined by the IANA Character Set registry
347   (<eref target="http://www.iana.org/assignments/character-sets"/>).
348</t>
349<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
350  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
351</artwork></figure>
352<t>
353   Although HTTP allows an arbitrary token to be used as a charset
354   value, any token that has a predefined value within the IANA
355   Character Set registry &MUST; represent the character encoding defined
356   by that registry. Applications &SHOULD; limit their use of character
357   encodings to those defined within the IANA registry.
358</t>
359<t>
360   HTTP uses charset in two contexts: within an Accept-Charset request
361   header field (in which the charset value is an unquoted token) and as the
362   value of a parameter in a Content-Type header field (within a request or
363   response), in which case the parameter value of the charset parameter
364   can be quoted.
365</t>
366<t>
367   Implementors need to be aware of IETF character set requirements <xref target="RFC3629"/>
368   <xref target="RFC2277"/>.
369</t>
370
371<section title="Missing Charset" anchor="missing.charset">
372<t>
373   Some HTTP/1.0 software has interpreted a Content-Type header field without
374   charset parameter incorrectly to mean "recipient should guess".
375   Senders wishing to defeat this behavior &MAY; include a charset
376   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
377   it is known that it will not confuse the recipient.
378</t>
379<t>
380   Unfortunately, some older HTTP/1.0 clients did not deal properly with
381   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
382   charset label provided by the sender; and those user agents that have
383   a provision to "guess" a charset &MUST; use the charset from the
384   content-type field if they support that charset, rather than the
385   recipient's preference, when initially displaying a document. See
386   <xref target="canonicalization.and.text.defaults"/>.
387</t>
388</section>
389</section>
390
391<section title="Content Codings" anchor="content.codings">
392  <x:anchor-alias value="content-coding"/>
393<t>
394   Content coding values indicate an encoding transformation that has
395   been or can be applied to a representation. Content codings are primarily
396   used to allow a representation to be compressed or otherwise usefully
397   transformed without losing the identity of its underlying media type
398   and without loss of information. Frequently, the representation is stored in
399   coded form, transmitted directly, and only decoded by the recipient.
400</t>
401<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
402  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
403</artwork></figure>
404<t>
405   All content-coding values are case-insensitive. HTTP/1.1 uses
406   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
407   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
408   describes the content-coding, what is more important is that it
409   indicates what decoding mechanism will be required to remove the
410   encoding.
411</t>
412<t>
413   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
414  <list>
415    <t>
416      See &compress-coding;.
417    </t>
418  </list>
419</t>
420<t>
421   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
422  <list>
423    <t>
424      See &deflate-coding;.
425    </t>
426  </list>
427</t>
428<t>
429   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
430  <list>
431    <t>
432      See &gzip-coding;.
433    </t>
434  </list>
435</t>
436<t>
437   identity<iref item="identity (Coding Format)"/><iref item="Coding Format" subitem="identity"/>
438  <list><t>
439        The default (identity) encoding; the use of no transformation
440        whatsoever. This content-coding is used only in the Accept-Encoding
441        header field, and &SHOULD-NOT;  be used in the Content-Encoding
442        header field.
443  </t></list>
444</t>
445
446<section title="Content Coding Registry" anchor="content.coding.registry">
447<t>
448   The HTTP Content Coding Registry defines the name space for the content
449   coding names.
450</t>
451<t>
452   Registrations &MUST; include the following fields:
453   <list style="symbols">
454     <t>Name</t>
455     <t>Description</t>
456     <t>Pointer to specification text</t>
457   </list>
458</t>
459<t>
460   Names of content codings &MUST-NOT; overlap with names of transfer codings
461   (&transfer-codings;), unless the encoding transformation is identical (as it
462   is the case for the compression codings defined in
463   &compression-codings;).
464</t>
465<t>
466   Values to be added to this name space require a specification
467   (see "Specification Required" in
468   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
469   conform to the purpose of content coding defined in this section.
470</t>
471<t>
472   The registry itself is maintained at
473   <eref target="http://www.iana.org/assignments/http-parameters"/>.
474</t>
475</section>
476
477</section>
478
479<section title="Media Types" anchor="media.types">
480  <x:anchor-alias value="media-type"/>
481  <x:anchor-alias value="type"/>
482  <x:anchor-alias value="subtype"/>
483<t>
484   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
485   and Accept (<xref target="header.accept"/>) header fields in order to provide
486   open and extensible data typing and type negotiation.
487</t>
488<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="media-type"/><iref primary="true" item="Grammar" subitem="type"/><iref primary="true" item="Grammar" subitem="subtype"/>
489  <x:ref>media-type</x:ref> = <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
490  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
491  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
492</artwork></figure>
493<t anchor="rule.parameter">
494  <x:anchor-alias value="attribute"/>
495  <x:anchor-alias value="parameter"/>
496  <x:anchor-alias value="value"/>
497   The type/subtype &MAY; be followed by parameters in the form of
498   attribute/value pairs.
499</t>
500<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/>
501  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
502  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
503  <x:ref>value</x:ref>          = <x:ref>word</x:ref>
504</artwork></figure>
505<t>
506   The type, subtype, and parameter attribute names are case-insensitive.
507   Parameter values might or might not be case-sensitive, depending on the
508   semantics of the parameter name.  The presence or absence of a parameter might
509   be significant to the processing of a media-type, depending on its
510   definition within the media type registry.
511</t>
512<t>
513   A parameter value that matches the <x:ref>token</x:ref> production can be
514   transmitted as either a token or within a quoted-string. The quoted and
515   unquoted values are equivalent.
516</t>
517<t>
518   Note that some older HTTP applications do not recognize media type
519   parameters. When sending data to older HTTP applications,
520   implementations &SHOULD; only use media type parameters when they are
521   required by that type/subtype definition.
522</t>
523<t>
524   Media-type values are registered with the Internet Assigned Number
525   Authority (IANA). The media type registration process is
526   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
527   discouraged.
528</t>
529
530<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
531<t>
532   Internet media types are registered with a canonical form. A
533   representation transferred via HTTP messages &MUST; be in the
534   appropriate canonical form prior to its transmission except for
535   "text" types, as defined in the next paragraph.
536</t>
537<t>
538   When in canonical form, media subtypes of the "text" type use CRLF as
539   the text line break. HTTP relaxes this requirement and allows the
540   transport of text media with plain CR or LF alone representing a line
541   break when it is done consistently for an entire representation. HTTP
542   applications &MUST; accept CRLF, bare CR, and bare LF as indicating
543   a line break in text media received via HTTP. In
544   addition, if the text is in a character encoding that does not
545   use octets 13 and 10 for CR and LF respectively, as is the case for
546   some multi-byte character encodings, HTTP allows the use of whatever octet
547   sequences are defined by that character encoding to represent the
548   equivalent of CR and LF for line breaks. This flexibility regarding
549   line breaks applies only to text media in the payload body; a bare CR
550   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
551   structures (such as header fields and multipart boundaries).
552</t>
553<t>
554   If a representation is encoded with a content-coding, the underlying
555   data &MUST; be in a form defined above prior to being encoded.
556</t>
557<t>
558   The "charset" parameter is used with some media types to define the
559   character encoding (<xref target="character.sets"/>) of the data. When no explicit charset
560   parameter is provided by the sender, media subtypes of the "text"
561   type are defined to have a default charset value of "ISO-8859-1" when
562   received via HTTP. Data in character encodings other than "ISO-8859-1" or
563   its subsets &MUST; be labeled with an appropriate charset value. See
564   <xref target="missing.charset"/> for compatibility problems.
565</t>
566</section>
567
568<section title="Multipart Types" anchor="multipart.types">
569<t>
570   MIME provides for a number of "multipart" types &mdash; encapsulations of
571   one or more representations within a single message-body. All multipart
572   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
573   and &MUST; include a boundary parameter as part of the media type
574   value. The message body is itself a protocol element and &MUST;
575   therefore use only CRLF to represent line breaks between body-parts.
576</t>
577<t>
578   In general, HTTP treats a multipart message-body no differently than
579   any other media type: strictly as payload.  HTTP does not use the
580   multipart boundary as an indicator of message-body length.
581   <!-- jre: re-insert removed text pointing to caching? -->
582   In all other respects, an HTTP user agent &SHOULD; follow the same or similar
583   behavior as a MIME user agent would upon receipt of a multipart type.
584   The MIME header fields within each body-part of a multipart message-body
585   do not have any significance to HTTP beyond that defined by
586   their MIME semantics.
587</t>
588<t>
589   If an application receives an unrecognized multipart subtype, the
590   application &MUST; treat it as being equivalent to "multipart/mixed".
591</t>
592<x:note>
593  <t>
594    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
595    for carrying form data suitable for processing via the POST
596    request method, as described in <xref target="RFC2388"/>.
597  </t>
598</x:note>
599</section>
600</section>
601
602<section title="Language Tags" anchor="language.tags">
603  <x:anchor-alias value="language-tag"/>
604<t>
605   A language tag, as defined in <xref target="RFC5646"/>, identifies a
606   natural language spoken, written, or otherwise conveyed by human beings for
607   communication of information to other human beings. Computer languages are
608   explicitly excluded. HTTP uses language tags within the Accept-Language and
609   Content-Language fields.
610</t>
611<t>
612   In summary, a language tag is composed of one or more parts: A primary
613   language subtag followed by a possibly empty series of subtags:
614</t>
615<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
616  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
617</artwork></figure>
618<t>
619   White space is not allowed within the tag and all tags are case-insensitive.
620   The name space of language subtags is administered by the IANA (see
621   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
622</t>
623<figure>
624  <preamble>Example tags include:</preamble>
625<artwork type="example">
626  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
627</artwork>
628</figure>
629<t>
630   See <xref target="RFC5646"/> for further information.
631</t>
632</section>
633</section>
634
635<section title="Payload" anchor="payload">
636<t>
637   HTTP messages &MAY; transfer a payload if not otherwise restricted by
638   the request method or response status code.  The payload consists of
639   metadata, in the form of header fields, and data, in the form of the
640   sequence of octets in the message-body after any transfer-coding has
641   been decoded.
642</t>
643<iref item="payload"/>
644<t>   
645   A "<x:dfn>payload</x:dfn>" in HTTP is always a partial or complete
646   representation of some resource.  We use separate terms for payload
647   and representation because some messages contain only the associated
648   representation's header fields (e.g., responses to HEAD) or only some
649   part(s) of the representation (e.g., the 206 status code).
650</t>
651<section title="Payload Header Fields" anchor="payload.header.fields">
652  <x:anchor-alias value="payload-header"/>
653<t>
654   HTTP header fields that specifically define the payload, rather than the
655   associated representation, are referred to as "payload header fields".
656   The following payload header fields are defined by HTTP/1.1:
657</t>
658<texttable align="left">
659  <ttcol>Header Field Name</ttcol>
660  <ttcol>Defined in...</ttcol>
661
662  <c>Content-Length</c> <c>&header-content-length;</c>
663  <c>Content-MD5</c> <c><xref target="header.content-md5"/></c>
664  <c>Content-Range</c> <c>&header-content-range;</c>
665</texttable>
666</section>
667
668<section title="Payload Body" anchor="payload.body">
669  <x:anchor-alias value="payload-body"/>
670<t>
671   A payload body is only present in a message when a message-body is
672   present, as described in &message-body;. The payload body is obtained
673   from the message-body by decoding any Transfer-Encoding that might
674   have been applied to ensure safe and proper transfer of the message.
675</t>
676</section>
677</section>
678
679<section title="Representation" anchor="representation">
680<iref item="representation"/>
681<t>
682   A "<x:dfn>representation</x:dfn>" is information in a format that can be readily
683   communicated from one party to another.  A resource representation
684   is information that reflects the state of that resource, as observed
685   at some point in the past (e.g., in a response to GET) or to be
686   desired at some point in the future (e.g., in a PUT request).
687</t>
688<t>
689   Most, but not all, representations transferred via HTTP are intended
690   to be a representation of the target resource (the resource identified
691   by the effective request URI).  The precise semantics of a representation
692   are determined by the type of message (request or response), the request
693   method, the response status code, and the representation metadata.
694   For example, the above semantic is true for the representation in any
695   200 (OK) response to GET and for the representation in any PUT request.
696   A 200 response to PUT, in contrast, contains either a representation
697   that describes the successful action or a representation of the target
698   resource, with the latter indicated by a Content-Location header field
699   with the same value as the effective request URI.  Likewise, response
700   messages with an error status code usually contain a representation that
701   describes the error and what next steps are suggested for resolving it.
702</t>
703
704<section title="Representation Header Fields" anchor="representation.header.fields">
705  <x:anchor-alias value="representation-header"/>
706<t>
707   Representation header fields define metadata about the representation data
708   enclosed in the message-body or, if no message-body is present, about
709   the representation that would have been transferred in a 200 response
710   to a simultaneous GET request with the same effective request URI.
711</t>
712<t>
713   The following header fields are defined as representation metadata:
714</t>
715<texttable align="left">
716  <ttcol>Header Field Name</ttcol>
717  <ttcol>Defined in...</ttcol>
718
719  <c>Content-Encoding</c> <c><xref target="header.content-encoding"/></c>
720  <c>Content-Language</c> <c><xref target="header.content-language"/></c>
721  <c>Content-Location</c> <c><xref target="header.content-location"/></c>
722  <c>Content-Type</c> <c><xref target="header.content-type"/></c>
723  <c>Expires</c> <c>&header-expires;</c>
724  <c>Last-Modified</c> <c>&header-last-modified;</c>
725</texttable>
726</section>
727
728<section title="Representation Data" anchor="representation.data">
729  <x:anchor-alias value="representation-data"/>
730<t>
731   The representation body associated with an HTTP message is
732   either provided as the payload body of the message or
733   referred to by the message semantics and the effective request
734   URI.  The representation data is in a format and encoding defined by
735   the representation metadata header fields.
736</t>
737<t>
738   The data type of the representation data
739   is determined via the header fields Content-Type and Content-Encoding.
740   These define a two-layer, ordered encoding model:
741</t>
742<figure><artwork type="example">
743  representation-data := Content-Encoding( Content-Type( bits ) )
744</artwork></figure>
745<t>
746   Content-Type specifies the media type of the underlying data, which
747   defines both the data format and how that data &SHOULD; be processed
748   by the recipient (within the scope of the request method semantics).
749   Any HTTP/1.1 message containing a payload body &SHOULD; include a
750   Content-Type header field defining the media type of the associated
751   representation unless that metadata is unknown to the sender.
752   If the Content-Type header field is not present, it indicates that
753   the sender does not know the media type of the representation;
754   recipients &MAY; either assume that the media type is
755   "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
756   or examine the content to determine its type.
757</t>
758<t>
759   In practice, resource owners do not always properly configure their origin
760   server to provide the correct Content-Type for a given representation,
761   with the result that some clients will examine a response body's content
762   and override the specified type.
763   Clients that do so risk drawing incorrect conclusions, which might expose
764   additional security risks (e.g., "privilege escalation").  Furthermore,
765   it is impossible to determine the sender's intent by examining the data
766   format: many data formats match multiple media types that differ only in
767   processing semantics.  Implementers are encouraged to provide a means of
768   disabling such "content sniffing" when it is used.
769</t>
770<t>
771   Content-Encoding is used to indicate any additional content
772   codings applied to the data, usually for the purpose of data
773   compression, that are a property of the representation.  If
774   Content-Encoding is not present, then there is no additional
775   encoding beyond that defined by the Content-Type.
776</t>
777</section>
778</section>
779
780<section title="Content Negotiation" anchor="content.negotiation">
781<t>
782   HTTP responses include a representation which contains information for
783   interpretation, whether by a human user or for further processing.
784   Often, the server has different ways of representing the
785   same information; for example, in different formats, languages,
786   or using different character encodings.
787</t>
788<t>
789   HTTP clients and their users might have different or variable
790   capabilities, characteristics or preferences which would influence
791   which representation, among those available from the server,
792   would be best for the server to deliver. For this reason, HTTP
793   provides mechanisms for "content negotiation" &mdash; a process of
794   allowing selection of a representation of a given resource,
795   when more than one is available.
796</t>
797<t>
798   This specification defines two patterns of content negotiation;
799   "server-driven", where the server selects the representation based
800   upon the client's stated preferences, and "agent-driven" negotiation,
801   where the server provides a list of representations for the client to
802   choose from, based upon their metadata. In addition,  there are
803   other patterns: some applications use an "active content" pattern,
804   where the server returns active content which runs on the client
805   and, based on client available parameters, selects additional
806   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
807   has also been proposed.
808</t>
809<t>
810   These patterns are all widely used, and have trade-offs in applicability
811   and practicality. In particular, when the number of preferences or
812   capabilities to be expressed by a client are large (such as when many
813   different formats are supported by a user-agent), server-driven
814   negotiation becomes unwieldy, and might not be appropriate. Conversely,
815   when the number of representations to choose from is very large,
816   agent-driven negotiation might not be appropriate.
817</t>
818<t>
819   Note that in all cases, the supplier of representations has the
820   responsibility for determining which representations might be
821   considered to be the "same information".
822</t>
823
824<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
825<t>
826   If the selection of the best representation for a response is made by
827   an algorithm located at the server, it is called server-driven
828   negotiation. Selection is based on the available representations of
829   the response (the dimensions over which it can vary; e.g., language,
830   content-coding, etc.) and the contents of particular header fields in
831   the request message or on other information pertaining to the request
832   (such as the network address of the client).
833</t>
834<t>
835   Server-driven negotiation is advantageous when the algorithm for
836   selecting from among the available representations is difficult to
837   describe to the user agent, or when the server desires to send its
838   "best guess" to the client along with the first response (hoping to
839   avoid the round-trip delay of a subsequent request if the "best
840   guess" is good enough for the user). In order to improve the server's
841   guess, the user agent &MAY; include request header fields (Accept,
842   Accept-Language, Accept-Encoding, etc.) which describe its
843   preferences for such a response.
844</t>
845<t>
846   Server-driven negotiation has disadvantages:
847  <list style="numbers">
848    <t>
849         It is impossible for the server to accurately determine what
850         might be "best" for any given user, since that would require
851         complete knowledge of both the capabilities of the user agent
852         and the intended use for the response (e.g., does the user want
853         to view it on screen or print it on paper?).
854    </t>
855    <t>
856         Having the user agent describe its capabilities in every
857         request can be both very inefficient (given that only a small
858         percentage of responses have multiple representations) and a
859         potential violation of the user's privacy.
860    </t>
861    <t>
862         It complicates the implementation of an origin server and the
863         algorithms for generating responses to a request.
864    </t>
865    <t>
866         It might limit a public cache's ability to use the same response
867         for multiple user's requests.
868    </t>
869  </list>
870</t>
871<t>
872   HTTP/1.1 includes the following header fields for enabling
873   server-driven negotiation through description of user agent
874   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
875   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
876   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
877   However, an origin server is not limited to these dimensions and &MAY; vary
878   the response based on any aspect of the request, including aspects
879   of the connection (e.g., IP address) or information within extension
880   header fields not defined by this specification.
881</t>
882<x:note>
883  <t>
884    <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
885    because new clients might not be recognized.
886  </t>
887</x:note>
888<t>
889   The Vary header field (&header-vary;) can be used to express the parameters the
890   server uses to select a representation that is subject to server-driven
891   negotiation.
892</t>
893</section>
894
895<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
896<t>
897   With agent-driven negotiation, selection of the best representation
898   for a response is performed by the user agent after receiving an
899   initial response from the origin server. Selection is based on a list
900   of the available representations of the response included within the
901   header fields or body of the initial response, with each
902   representation identified by its own URI. Selection from among the
903   representations can be performed automatically (if the user agent is
904   capable of doing so) or manually by the user selecting from a
905   generated (possibly hypertext) menu.
906</t>
907<t>
908   Agent-driven negotiation is advantageous when the response would vary
909   over commonly-used dimensions (such as type, language, or encoding),
910   when the origin server is unable to determine a user agent's
911   capabilities from examining the request, and generally when public
912   caches are used to distribute server load and reduce network usage.
913</t>
914<t>
915   Agent-driven negotiation suffers from the disadvantage of needing a
916   second request to obtain the best alternate representation. This
917   second request is only efficient when caching is used. In addition,
918   this specification does not define any mechanism for supporting
919   automatic selection, though it also does not prevent any such
920   mechanism from being developed as an extension and used within
921   HTTP/1.1.
922</t>
923<t>
924   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
925   status codes for enabling agent-driven negotiation when the server is
926   unwilling or unable to provide a varying response using server-driven
927   negotiation.
928</t>
929</section>
930</section>
931
932<section title="Header Field Definitions" anchor="header.fields">
933<t>
934   This section defines the syntax and semantics of HTTP/1.1 header fields
935   related to the payload of messages.
936</t>
937
938<section title="Accept" anchor="header.accept">
939  <iref primary="true" item="Accept header field" x:for-anchor=""/>
940  <iref primary="true" item="Header Fields" subitem="Accept" x:for-anchor=""/>
941  <x:anchor-alias value="Accept"/>
942  <x:anchor-alias value="accept-ext"/>
943  <x:anchor-alias value="accept-params"/>
944  <x:anchor-alias value="media-range"/>
945<t>
946   The "Accept" header field can be used by user agents to specify
947   response media types that are acceptable. Accept header fields can be used to
948   indicate that the request is specifically limited to a small set of desired
949   types, as in the case of a request for an in-line image.
950</t>
951<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-ext"/>
952  <x:ref>Accept</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
953 
954  <x:ref>media-range</x:ref>    = ( "*/*"
955                   / ( <x:ref>type</x:ref> "/" "*" )
956                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
957                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
958  <x:ref>accept-params</x:ref>  = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>accept-ext</x:ref> )
959  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
960</artwork></figure>
961<t>
962   The asterisk "*" character is used to group media types into ranges,
963   with "*/*" indicating all media types and "type/*" indicating all
964   subtypes of that type. The media-range &MAY; include media type
965   parameters that are applicable to that range.
966</t>
967<t>
968   Each media-range &MAY; be followed by one or more accept-params,
969   beginning with the "q" parameter for indicating a relative quality
970   factor. The first "q" parameter (if any) separates the media-range
971   parameter(s) from the accept-params. Quality factors allow the user
972   or user agent to indicate the relative degree of preference for that
973   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
974   default value is q=1.
975</t>
976<x:note>
977  <t>
978    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
979    parameters from Accept extension parameters is due to historical
980    practice. Although this prevents any media type parameter named
981    "q" from being used with a media range, such an event is believed
982    to be unlikely given the lack of any "q" parameters in the IANA
983    media type registry and the rare usage of any media type
984    parameters in Accept. Future media types are discouraged from
985    registering any parameter named "q".
986  </t>
987</x:note>
988<t>
989   The example
990</t>
991<figure><artwork type="example">
992  Accept: audio/*; q=0.2, audio/basic
993</artwork></figure>
994<t>
995   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
996   type if it is the best available after an 80% mark-down in quality".
997</t>
998<t>
999   If no Accept header field is present, then it is assumed that the
1000   client accepts all media types. If an Accept header field is present,
1001   and if the server cannot send a response which is acceptable
1002   according to the combined Accept field value, then the server &SHOULD;
1003   send a 406 (Not Acceptable) response.
1004</t>
1005<t>
1006   A more elaborate example is
1007</t>
1008<figure><artwork type="example">
1009  Accept: text/plain; q=0.5, text/html,
1010          text/x-dvi; q=0.8, text/x-c
1011</artwork></figure>
1012<t>
1013   Verbally, this would be interpreted as "text/html and text/x-c are
1014   the preferred media types, but if they do not exist, then send the
1015   text/x-dvi representation, and if that does not exist, send the text/plain
1016   representation".
1017</t>
1018<t>
1019   Media ranges can be overridden by more specific media ranges or
1020   specific media types. If more than one media range applies to a given
1021   type, the most specific reference has precedence. For example,
1022</t>
1023<figure><artwork type="example">
1024  Accept: text/*, text/html, text/html;level=1, */*
1025</artwork></figure>
1026<t>
1027   have the following precedence:
1028   <list style="numbers">
1029    <t>text/html;level=1</t>
1030    <t>text/html</t>
1031    <t>text/*</t>
1032    <t>*/*</t>
1033   </list>
1034</t>
1035<t>
1036   The media type quality factor associated with a given type is
1037   determined by finding the media range with the highest precedence
1038   which matches that type. For example,
1039</t>
1040<figure><artwork type="example">
1041  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1042          text/html;level=2;q=0.4, */*;q=0.5
1043</artwork></figure>
1044<t>
1045   would cause the following values to be associated:
1046</t>
1047<texttable align="left">
1048  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1049  <c>text/html;level=1</c>    <c>1</c>
1050  <c>text/html</c>            <c>0.7</c>
1051  <c>text/plain</c>           <c>0.3</c>
1052  <c>image/jpeg</c>           <c>0.5</c>
1053  <c>text/html;level=2</c>    <c>0.4</c>
1054  <c>text/html;level=3</c>    <c>0.7</c>
1055</texttable>
1056<t>
1057      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1058      values for certain media ranges. However, unless the user agent is
1059      a closed system which cannot interact with other rendering agents,
1060      this default set ought to be configurable by the user.
1061</t>
1062</section>
1063
1064<section title="Accept-Charset" anchor="header.accept-charset">
1065  <iref primary="true" item="Accept-Charset header field" x:for-anchor=""/>
1066  <iref primary="true" item="Header Fields" subitem="Accept-Charset" x:for-anchor=""/>
1067  <x:anchor-alias value="Accept-Charset"/>
1068<t>
1069   The "Accept-Charset" header field can be used by user agents to
1070   indicate what character encodings are acceptable in a response
1071   payload. This field allows
1072   clients capable of understanding more comprehensive or special-purpose
1073   character encodings to signal that capability to a server which is capable of
1074   representing documents in those character encodings.
1075</t>
1076<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/>
1077  <x:ref>Accept-Charset</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1078                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1079</artwork></figure>
1080<t>
1081   Character encoding values (a.k.a., charsets) are described in
1082   <xref target="character.sets"/>. Each charset &MAY; be given an
1083   associated quality value which represents the user's preference
1084   for that charset. The default value is q=1. An example is
1085</t>
1086<figure><artwork type="example">
1087  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1088</artwork></figure>
1089<t>
1090   The special value "*", if present in the Accept-Charset field,
1091   matches every character encoding (including ISO-8859-1) which is not
1092   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1093   in an Accept-Charset field, then all character encodings not explicitly
1094   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1095   a quality value of 1 if not explicitly mentioned.
1096</t>
1097<t>
1098   If no Accept-Charset header field is present, the default is that any
1099   character encoding is acceptable. If an Accept-Charset header field is present,
1100   and if the server cannot send a response which is acceptable
1101   according to the Accept-Charset header field, then the server &SHOULD; send
1102   an error response with the 406 (Not Acceptable) status code, though
1103   the sending of an unacceptable response is also allowed.
1104</t>
1105</section>
1106
1107<section title="Accept-Encoding" anchor="header.accept-encoding">
1108  <iref primary="true" item="Accept-Encoding header field" x:for-anchor=""/>
1109  <iref primary="true" item="Header Fields" subitem="Accept-Encoding" x:for-anchor=""/>
1110  <x:anchor-alias value="Accept-Encoding"/>
1111  <x:anchor-alias value="codings"/>
1112<t>
1113   The "Accept-Encoding" header field can be used by user agents to
1114   indicate what response content-codings (<xref target="content.codings"/>)
1115   are acceptable in the response.
1116</t>
1117<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/>
1118  <x:ref>Accept-Encoding</x:ref>  = #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1119  <x:ref>codings</x:ref>          = ( <x:ref>content-coding</x:ref> / "*" )
1120</artwork></figure>
1121<t>
1122   Each codings value &MAY; be given an associated quality value which
1123   represents the preference for that encoding. The default value is q=1.
1124</t>
1125<t>
1126   Examples of its use are:
1127</t>
1128<figure><artwork type="example">
1129  Accept-Encoding: compress, gzip
1130  Accept-Encoding:
1131  Accept-Encoding: *
1132  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1133  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1134</artwork></figure>
1135<t>
1136   A server tests whether a content-coding is acceptable, according to
1137   an Accept-Encoding field, using these rules:
1138  <list style="numbers">
1139      <t>If the content-coding is one of the content-codings listed in
1140         the Accept-Encoding field, then it is acceptable, unless it is
1141         accompanied by a qvalue of 0. (As defined in &qvalue;, a
1142         qvalue of 0 means "not acceptable".)</t>
1143
1144      <t>The special "*" symbol in an Accept-Encoding field matches any
1145         available content-coding not explicitly listed in the header
1146         field.</t>
1147
1148      <t>If multiple content-codings are acceptable, then the acceptable
1149         content-coding with the highest non-zero qvalue is preferred.</t>
1150
1151      <t>The "identity" content-coding is always acceptable, unless
1152         specifically refused because the Accept-Encoding field includes
1153         "identity;q=0", or because the field includes "*;q=0" and does
1154         not explicitly include the "identity" content-coding. If the
1155         Accept-Encoding field-value is empty, then only the "identity"
1156         encoding is acceptable.</t>
1157  </list>
1158</t>
1159<t>
1160   If an Accept-Encoding field is present in a request, and if the
1161   server cannot send a response which is acceptable according to the
1162   Accept-Encoding header field, then the server &SHOULD; send an error response
1163   with the 406 (Not Acceptable) status code.
1164</t>
1165<t>
1166   If no Accept-Encoding field is present in a request, the server &MAY;
1167   assume that the client will accept any content coding. In this case,
1168   if "identity" is one of the available content-codings, then the
1169   server &SHOULD; use the "identity" content-coding, unless it has
1170   additional information that a different content-coding is meaningful
1171   to the client.
1172</t>
1173<x:note>
1174  <t>
1175    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1176    and if the "identity" content-coding is unavailable, then
1177    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1178    "gzip" and "compress") are preferred; some older clients
1179    improperly display messages sent with other content-codings.  The
1180    server might also make this decision based on information about
1181    the particular user-agent or client.
1182  </t>
1183</x:note>
1184<x:note>
1185  <t>
1186    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1187    associated with content-codings. This means that qvalues will not
1188    work and are not permitted with x-gzip or x-compress.
1189  </t>
1190</x:note>
1191</section>
1192
1193<section title="Accept-Language" anchor="header.accept-language">
1194  <iref primary="true" item="Accept-Language header field" x:for-anchor=""/>
1195  <iref primary="true" item="Header Fields" subitem="Accept-Language" x:for-anchor=""/>
1196  <x:anchor-alias value="Accept-Language"/>
1197  <x:anchor-alias value="language-range"/>
1198<t>
1199   The "Accept-Language" header field can be used by user agents to
1200   indicate the set of natural languages that are preferred in the response.
1201   Language tags are defined in <xref target="language.tags"/>.
1202</t>
1203<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/>
1204  <x:ref>Accept-Language</x:ref> =
1205                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1206  <x:ref>language-range</x:ref>  =
1207            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1208</artwork></figure>
1209<t>
1210   Each language-range can be given an associated quality value which
1211   represents an estimate of the user's preference for the languages
1212   specified by that range. The quality value defaults to "q=1". For
1213   example,
1214</t>
1215<figure><artwork type="example">
1216  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1217</artwork></figure>
1218<t>
1219   would mean: "I prefer Danish, but will accept British English and
1220   other types of English".
1221   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
1222</t>
1223<t>
1224   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
1225   several matching schemes. Implementations can offer the most appropriate
1226   matching scheme for their requirements.
1227</t>
1228<x:note>
1229  <t>
1230    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
1231    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
1232    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
1233  </t>
1234</x:note>
1235<t>
1236   It might be contrary to the privacy expectations of the user to send
1237   an Accept-Language header field with the complete linguistic preferences of
1238   the user in every request. For a discussion of this issue, see
1239   <xref target="privacy.issues.connected.to.accept.header.fields"/>.
1240</t>
1241<t>
1242   As intelligibility is highly dependent on the individual user, it is
1243   recommended that client applications make the choice of linguistic
1244   preference available to the user. If the choice is not made
1245   available, then the Accept-Language header field &MUST-NOT; be given in
1246   the request.
1247</t>
1248<x:note>
1249  <t>
1250    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1251    the user, we remind implementors of  the fact that users are not
1252    familiar with the details of language matching as described above,
1253    and ought to be provided appropriate guidance. As an example, users
1254    might assume that on selecting "en-gb", they will be served any
1255    kind of English document if British English is not available. A
1256    user agent might suggest in such a case to add "en" to get the
1257    best matching behavior.
1258  </t>
1259</x:note>
1260</section>
1261
1262<section title="Content-Encoding" anchor="header.content-encoding">
1263  <iref primary="true" item="Content-Encoding header field" x:for-anchor=""/>
1264  <iref primary="true" item="Header Fields" subitem="Content-Encoding" x:for-anchor=""/>
1265  <x:anchor-alias value="Content-Encoding"/>
1266<t>
1267   The "Content-Encoding" header field indicates what content-codings
1268   have been applied to the representation, and thus what decoding mechanisms
1269   must be applied in order to obtain the media-type referenced by the
1270   Content-Type header field. Content-Encoding is primarily used to allow a
1271   representation to be compressed without losing the identity of its underlying
1272   media type.
1273</t>
1274<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/>
1275  <x:ref>Content-Encoding</x:ref> = 1#<x:ref>content-coding</x:ref>
1276</artwork></figure>
1277<t>
1278   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1279</t>
1280<figure><artwork type="example">
1281  Content-Encoding: gzip
1282</artwork></figure>
1283<t>
1284   The content-coding is a characteristic of the representation.
1285   Typically, the representation body is stored with this
1286   encoding and is only decoded before rendering or analogous usage.
1287   However, a transforming proxy &MAY; modify the content-coding if the
1288   new coding is known to be acceptable to the recipient, unless the
1289   "no-transform" cache-control directive is present in the message.
1290</t>
1291<t>
1292   If the content-coding of a representation is not "identity", then the
1293   representation metadata &MUST; include a Content-Encoding header
1294   field (<xref target="header.content-encoding"/>)
1295   that lists the non-identity content-coding(s) used.
1296</t>
1297<t>
1298   If the content-coding of a representation in a request message is not
1299   acceptable to the origin server, the server &SHOULD; respond with a
1300   status code of 415 (Unsupported Media Type).
1301</t>
1302<t>
1303   If multiple encodings have been applied to a representation, the content
1304   codings &MUST; be listed in the order in which they were applied.
1305   Additional information about the encoding parameters &MAY; be provided
1306   by other header fields not defined by this specification.
1307</t>
1308</section>
1309
1310<section title="Content-Language" anchor="header.content-language">
1311  <iref primary="true" item="Content-Language header field" x:for-anchor=""/>
1312  <iref primary="true" item="Header Fields" subitem="Content-Language" x:for-anchor=""/>
1313  <x:anchor-alias value="Content-Language"/>
1314<t>
1315   The "Content-Language" header field describes the natural
1316   language(s) of the intended audience for the representation. Note that this might
1317   not be equivalent to all the languages used within the representation.
1318</t>
1319<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/>
1320  <x:ref>Content-Language</x:ref> = 1#<x:ref>language-tag</x:ref>
1321</artwork></figure>
1322<t>
1323   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1324   Content-Language is to allow a user to identify and differentiate
1325   representations according to the user's own preferred language. Thus, if the
1326   body content is intended only for a Danish-literate audience, the
1327   appropriate field is
1328</t>
1329<figure><artwork type="example">
1330  Content-Language: da
1331</artwork></figure>
1332<t>
1333   If no Content-Language is specified, the default is that the content
1334   is intended for all language audiences. This might mean that the
1335   sender does not consider it to be specific to any natural language,
1336   or that the sender does not know for which language it is intended.
1337</t>
1338<t>
1339   Multiple languages &MAY; be listed for content that is intended for
1340   multiple audiences. For example, a rendition of the "Treaty of
1341   Waitangi", presented simultaneously in the original Maori and English
1342   versions, would call for
1343</t>
1344<figure><artwork type="example">
1345  Content-Language: mi, en
1346</artwork></figure>
1347<t>
1348   However, just because multiple languages are present within a representation
1349   does not mean that it is intended for multiple linguistic audiences.
1350   An example would be a beginner's language primer, such as "A First
1351   Lesson in Latin", which is clearly intended to be used by an
1352   English-literate audience. In this case, the Content-Language would
1353   properly only include "en".
1354</t>
1355<t>
1356   Content-Language &MAY; be applied to any media type &mdash; it is not
1357   limited to textual documents.
1358</t>
1359</section>
1360
1361<section title="Content-Location" anchor="header.content-location">
1362  <iref primary="true" item="Content-Location header field" x:for-anchor=""/>
1363  <iref primary="true" item="Header Fields" subitem="Content-Location" x:for-anchor=""/>
1364  <x:anchor-alias value="Content-Location"/>
1365<t>
1366   The "Content-Location" header field supplies a URI that can be used
1367   as a specific identifier for the representation in this message.
1368   In other words, if one were to perform a GET on this URI at the time
1369   of this message's generation, then a 200 response would contain the
1370   same representation that is enclosed as payload in this message.
1371</t>
1372<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/>
1373  <x:ref>Content-Location</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1374</artwork></figure>
1375<t>
1376   The Content-Location value is not a replacement for the effective
1377   Request URI (&effective-request-uri;).  It is representation metadata.
1378   It has the same syntax and semantics as the header field of the same name
1379   defined for MIME body parts in <xref target="RFC2557" x:fmt="of" x:sec="4"/>.
1380   However, its appearance in an HTTP message has some special implications
1381   for HTTP recipients.
1382</t>
1383<t>
1384   If Content-Location is included in a response message and its value
1385   is the same as the effective request URI, then the response payload
1386   &SHOULD; be considered the current representation of that resource.
1387   For a GET or HEAD request, this is the same as the default semantics
1388   when no Content-Location is provided by the server.  For a state-changing
1389   request like PUT or POST, it implies that the server's response contains
1390   the new representation of that resource, thereby distinguishing it from
1391   representations that might only report about the action (e.g., "It worked!").
1392   This allows authoring applications to update their local copies without
1393   the need for a subsequent GET request.
1394</t>
1395<t>
1396   If Content-Location is included in a response message and its value
1397   differs from the effective request URI, then the origin server is
1398   informing recipients that this representation has its own, presumably
1399   more specific, identifier.  For a GET or HEAD request, this is an
1400   indication that the effective request URI identifies a resource that
1401   is subject to content negotiation and the representation selected for
1402   this response can also be found at the identified URI.  For other
1403   methods, such a Content-Location indicates that this representation
1404   contains a report on the action's status and the same report is
1405   available (for future access with GET) at the given URI.  For
1406   example, a purchase transaction made via a POST request might
1407   include a receipt document as the payload of the 200 response;
1408   the Content-Location value provides an identifier for retrieving
1409   a copy of that same receipt in the future.
1410</t>
1411<t>
1412   If Content-Location is included in a request message, then it &MAY;
1413   be interpreted by the origin server as an indication of where the
1414   user agent originally obtained the content of the enclosed
1415   representation (prior to any subsequent modification of the content
1416   by that user agent).  In other words, the user agent is providing
1417   the same representation metadata that it received with the original
1418   representation.  However, such interpretation &MUST-NOT; be used to
1419   alter the semantics of the method requested by the client.  For
1420   example, if a client makes a PUT request on a negotiated resource
1421   and the origin server accepts that PUT (without redirection), then the
1422   new set of values for that resource is expected to be consistent with
1423   the one representation supplied in that PUT; the Content-Location
1424   cannot be used as a form of reverse content selection that
1425   identifies only one of the negotiated representations to be updated.
1426   If the user agent had wanted the latter semantics, it would have applied
1427   the PUT directly to the Content-Location URI.
1428</t>
1429<t>
1430   A Content-Location field received in a request message is transitory
1431   information that &SHOULD-NOT; be saved with other representation
1432   metadata for use in later responses.  The Content-Location's value
1433   might be saved for use in other contexts, such as within source links
1434   or other metadata.
1435</t>
1436<t>
1437   A cache cannot assume that a representation with a Content-Location
1438   different from the URI used to retrieve it can be used to respond to
1439   later requests on that Content-Location URI.
1440</t>
1441<t>
1442   If the Content-Location value is a partial URI, the partial URI is
1443   interpreted relative to the effective request URI.
1444</t>
1445</section>
1446
1447<section title="Content-MD5" anchor="header.content-md5">
1448  <iref primary="true" item="Content-MD5 header field" x:for-anchor=""/>
1449  <iref primary="true" item="Header Fields" subitem="Content-MD5" x:for-anchor=""/>
1450  <x:anchor-alias value="Content-MD5"/>
1451<t>
1452   The "Content-MD5" header field, as defined in <xref target="RFC1864"/>, is
1453   an MD5 digest of the payload body that provides an end-to-end message
1454   integrity check (MIC) of the payload body (the message-body after any
1455   transfer-coding is decoded). Note that a MIC is good for
1456   detecting accidental modification of the payload body in transit, but is not
1457   proof against malicious attacks.
1458</t>
1459<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/>
1460  <x:ref>Content-MD5</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1461</artwork></figure>
1462<t>
1463   The Content-MD5 header field &MAY; be generated by an origin server or
1464   client to function as an integrity check of the payload body. Only
1465   origin servers or user agents &MAY; generate the Content-MD5 header field;
1466   proxies &MUST-NOT; generate it, as this would defeat its
1467   value as an end-to-end integrity check. Any recipient &MAY; check that
1468   the digest value in this header field matches a corresponding digest
1469   calculated on payload body as received.
1470</t>
1471<t>
1472   The MD5 digest is computed based on the content of the payload body,
1473   including any content-coding, but not including any transfer-coding
1474   applied to the message-body because such transfer-codings might be
1475   applied or removed anywhere along the request/response chain.
1476   If the message is received with a transfer-coding, that encoding &MUST;
1477   be decoded prior to checking the Content-MD5 value against the received
1478   payload.
1479</t>
1480<t>
1481   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1482   composite media-types (e.g., multipart/* and message/rfc822), but
1483   this does not change how the digest is computed as defined in the
1484   preceding paragraph.
1485</t>
1486<t>
1487   There are several consequences of this. The payload for composite
1488   types &MAY; contain many body-parts, each with its own MIME and HTTP
1489   header fields (including Content-MD5, Content-Transfer-Encoding, and
1490   Content-Encoding header fields). If a body-part has a Content-Transfer-Encoding
1491   or Content-Encoding header field, it is assumed that the content
1492   of the body-part has had the encoding applied, and the body-part is
1493   included in the Content-MD5 digest as is &mdash; i.e., after the
1494   application. The Transfer-Encoding header field is not allowed within
1495   body-parts.
1496</t>
1497<t>
1498   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1499   computing or checking the digest: the line break convention used in
1500   the text actually transmitted &MUST; be left unaltered when computing
1501   the digest.
1502</t>
1503<x:note>
1504  <t>
1505    <x:h>Note:</x:h> While the definition of Content-MD5 is exactly the same for
1506    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1507    in which the application of Content-MD5 to HTTP entity-bodies
1508    differs from its application to MIME entity-bodies. One is that
1509    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1510    does use Transfer-Encoding and Content-Encoding. Another is that
1511    HTTP more frequently uses binary content types than MIME, so it is
1512    worth noting that, in such cases, the byte order used to compute
1513    the digest is the transmission byte order defined for the type.
1514    Lastly, HTTP allows transmission of text types with any of several
1515    line break conventions and not just the canonical form using CRLF.
1516  </t>
1517</x:note>
1518</section>
1519
1520<section title="Content-Type" anchor="header.content-type">
1521  <iref primary="true" item="Content-Type header field" x:for-anchor=""/>
1522  <iref primary="true" item="Header Fields" subitem="Content-Type" x:for-anchor=""/>
1523  <x:anchor-alias value="Content-Type"/>
1524<t>
1525   The "Content-Type" header field indicates the media type of the
1526   representation. In the case of responses to the HEAD method, the media type is
1527   that which would have been sent had the request been a GET.
1528</t>
1529<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/>
1530  <x:ref>Content-Type</x:ref> = <x:ref>media-type</x:ref>
1531</artwork></figure>
1532<t>
1533   Media types are defined in <xref target="media.types"/>. An example of the field is
1534</t>
1535<figure><artwork type="example">
1536  Content-Type: text/html; charset=ISO-8859-4
1537</artwork></figure>
1538<t>
1539   Further discussion of Content-Type is provided in <xref target="representation.data"/>.
1540</t>
1541</section>
1542
1543</section>
1544
1545<section title="IANA Considerations" anchor="IANA.considerations">
1546<section title="Header Field Registration" anchor="header.field.registration">
1547<t>
1548   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
1549   with the permanent registrations below (see <xref target="RFC3864"/>):
1550</t>
1551<?BEGININC p3-payload.iana-headers ?>
1552<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1553<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1554   <ttcol>Header Field Name</ttcol>
1555   <ttcol>Protocol</ttcol>
1556   <ttcol>Status</ttcol>
1557   <ttcol>Reference</ttcol>
1558
1559   <c>Accept</c>
1560   <c>http</c>
1561   <c>standard</c>
1562   <c>
1563      <xref target="header.accept"/>
1564   </c>
1565   <c>Accept-Charset</c>
1566   <c>http</c>
1567   <c>standard</c>
1568   <c>
1569      <xref target="header.accept-charset"/>
1570   </c>
1571   <c>Accept-Encoding</c>
1572   <c>http</c>
1573   <c>standard</c>
1574   <c>
1575      <xref target="header.accept-encoding"/>
1576   </c>
1577   <c>Accept-Language</c>
1578   <c>http</c>
1579   <c>standard</c>
1580   <c>
1581      <xref target="header.accept-language"/>
1582   </c>
1583   <c>Content-Encoding</c>
1584   <c>http</c>
1585   <c>standard</c>
1586   <c>
1587      <xref target="header.content-encoding"/>
1588   </c>
1589   <c>Content-Language</c>
1590   <c>http</c>
1591   <c>standard</c>
1592   <c>
1593      <xref target="header.content-language"/>
1594   </c>
1595   <c>Content-Location</c>
1596   <c>http</c>
1597   <c>standard</c>
1598   <c>
1599      <xref target="header.content-location"/>
1600   </c>
1601   <c>Content-MD5</c>
1602   <c>http</c>
1603   <c>standard</c>
1604   <c>
1605      <xref target="header.content-md5"/>
1606   </c>
1607   <c>Content-Type</c>
1608   <c>http</c>
1609   <c>standard</c>
1610   <c>
1611      <xref target="header.content-type"/>
1612   </c>
1613   <c>MIME-Version</c>
1614   <c>http</c>
1615   <c>standard</c>
1616   <c>
1617      <xref target="mime-version"/>
1618   </c>
1619</texttable>
1620<!--(END)-->
1621<?ENDINC p3-payload.iana-headers ?>
1622<t>
1623   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1624</t>
1625</section>
1626
1627<section title="Content Coding Registry" anchor="content.coding.registration">
1628<t>
1629   The registration procedure for HTTP Content Codings is now defined
1630   by <xref target="content.coding.registry"/> of this document.
1631</t>
1632<t>
1633   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1634   shall be updated with the registration below:
1635</t>
1636<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
1637   <ttcol>Name</ttcol>
1638   <ttcol>Description</ttcol>
1639   <ttcol>Reference</ttcol>
1640   <c>compress</c>
1641   <c>UNIX "compress" program method</c>
1642   <c>
1643      &compress-coding;
1644   </c>
1645   <c>deflate</c>
1646   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1647   the "zlib" data format (<xref target="RFC1950"/>)
1648   </c>
1649   <c>
1650      &deflate-coding;
1651   </c>
1652   <c>gzip</c>
1653   <c>Same as GNU zip <xref target="RFC1952"/></c>
1654   <c>
1655      &gzip-coding;
1656   </c>
1657   <c>identity</c>
1658   <c>No transformation</c>
1659   <c>
1660      <xref target="content.codings"/>
1661   </c>
1662</texttable>
1663</section>
1664
1665</section>
1666
1667<section title="Security Considerations" anchor="security.considerations">
1668<t>
1669   This section is meant to inform application developers, information
1670   providers, and users of the security limitations in HTTP/1.1 as
1671   described by this document. The discussion does not include
1672   definitive solutions to the problems revealed, though it does make
1673   some suggestions for reducing security risks.
1674</t>
1675
1676<section title="Privacy Issues Connected to Accept Header Fields" anchor="privacy.issues.connected.to.accept.header.fields">
1677<t>
1678   Accept headers fields can reveal information about the user to all
1679   servers which are accessed. The Accept-Language header field in particular
1680   can reveal information the user would consider to be of a private
1681   nature, because the understanding of particular languages is often
1682   strongly correlated to the membership of a particular ethnic group.
1683   User agents which offer the option to configure the contents of an
1684   Accept-Language header field to be sent in every request are strongly
1685   encouraged to let the configuration process include a message which
1686   makes the user aware of the loss of privacy involved.
1687</t>
1688<t>
1689   An approach that limits the loss of privacy would be for a user agent
1690   to omit the sending of Accept-Language header fields by default, and to ask
1691   the user whether or not to start sending Accept-Language header fields to a
1692   server if it detects, by looking for any Vary header fields
1693   generated by the server, that such sending could improve the quality
1694   of service.
1695</t>
1696<t>
1697   Elaborate user-customized accept header fields sent in every request,
1698   in particular if these include quality values, can be used by servers
1699   as relatively reliable and long-lived user identifiers. Such user
1700   identifiers would allow content providers to do click-trail tracking,
1701   and would allow collaborating content providers to match cross-server
1702   click-trails or form submissions of individual users. Note that for
1703   many users not behind a proxy, the network address of the host
1704   running the user agent will also serve as a long-lived user
1705   identifier. In environments where proxies are used to enhance
1706   privacy, user agents ought to be conservative in offering accept
1707   header configuration options to end users. As an extreme privacy
1708   measure, proxies could filter the accept header fields in relayed requests.
1709   General purpose user agents which provide a high degree of header
1710   configurability &SHOULD; warn users about the loss of privacy which can
1711   be involved.
1712</t>
1713</section>
1714
1715</section>
1716
1717<section title="Acknowledgments" anchor="ack">
1718</section>
1719</middle>
1720<back>
1721
1722<references title="Normative References">
1723
1724<reference anchor="ISO-8859-1">
1725  <front>
1726    <title>
1727     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1728    </title>
1729    <author>
1730      <organization>International Organization for Standardization</organization>
1731    </author>
1732    <date year="1998"/>
1733  </front>
1734  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1735</reference>
1736
1737<reference anchor="Part1">
1738  <front>
1739    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1740    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1741      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1742      <address><email>fielding@gbiv.com</email></address>
1743    </author>
1744    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1745      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1746      <address><email>jg@freedesktop.org</email></address>
1747    </author>
1748    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1749      <organization abbrev="HP">Hewlett-Packard Company</organization>
1750      <address><email>JeffMogul@acm.org</email></address>
1751    </author>
1752    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1753      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1754      <address><email>henrikn@microsoft.com</email></address>
1755    </author>
1756    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1757      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1758      <address><email>LMM@acm.org</email></address>
1759    </author>
1760    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1761      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1762      <address><email>paulle@microsoft.com</email></address>
1763    </author>
1764    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1765      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1766      <address><email>timbl@w3.org</email></address>
1767    </author>
1768    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1769      <organization abbrev="W3C">World Wide Web Consortium</organization>
1770      <address><email>ylafon@w3.org</email></address>
1771    </author>
1772    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1773      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1774      <address><email>julian.reschke@greenbytes.de</email></address>
1775    </author>
1776    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1777  </front>
1778  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1779  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1780</reference>
1781
1782<reference anchor="Part2">
1783  <front>
1784    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1785    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1786      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1787      <address><email>fielding@gbiv.com</email></address>
1788    </author>
1789    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1790      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1791      <address><email>jg@freedesktop.org</email></address>
1792    </author>
1793    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1794      <organization abbrev="HP">Hewlett-Packard Company</organization>
1795      <address><email>JeffMogul@acm.org</email></address>
1796    </author>
1797    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1798      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1799      <address><email>henrikn@microsoft.com</email></address>
1800    </author>
1801    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1802      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1803      <address><email>LMM@acm.org</email></address>
1804    </author>
1805    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1806      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1807      <address><email>paulle@microsoft.com</email></address>
1808    </author>
1809    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1810      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1811      <address><email>timbl@w3.org</email></address>
1812    </author>
1813    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1814      <organization abbrev="W3C">World Wide Web Consortium</organization>
1815      <address><email>ylafon@w3.org</email></address>
1816    </author>
1817    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1818      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1819      <address><email>julian.reschke@greenbytes.de</email></address>
1820    </author>
1821    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1822  </front>
1823  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1824  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1825</reference>
1826
1827<reference anchor="Part4">
1828  <front>
1829    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1830    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1831      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1832      <address><email>fielding@gbiv.com</email></address>
1833    </author>
1834    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1835      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1836      <address><email>jg@freedesktop.org</email></address>
1837    </author>
1838    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1839      <organization abbrev="HP">Hewlett-Packard Company</organization>
1840      <address><email>JeffMogul@acm.org</email></address>
1841    </author>
1842    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1843      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1844      <address><email>henrikn@microsoft.com</email></address>
1845    </author>
1846    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1847      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1848      <address><email>LMM@acm.org</email></address>
1849    </author>
1850    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1851      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1852      <address><email>paulle@microsoft.com</email></address>
1853    </author>
1854    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1855      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1856      <address><email>timbl@w3.org</email></address>
1857    </author>
1858    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1859      <organization abbrev="W3C">World Wide Web Consortium</organization>
1860      <address><email>ylafon@w3.org</email></address>
1861    </author>
1862    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1863      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1864      <address><email>julian.reschke@greenbytes.de</email></address>
1865    </author>
1866    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1867  </front>
1868  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1869  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1870</reference>
1871
1872<reference anchor="Part5">
1873  <front>
1874    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1875    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1876      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1877      <address><email>fielding@gbiv.com</email></address>
1878    </author>
1879    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1880      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1881      <address><email>jg@freedesktop.org</email></address>
1882    </author>
1883    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1884      <organization abbrev="HP">Hewlett-Packard Company</organization>
1885      <address><email>JeffMogul@acm.org</email></address>
1886    </author>
1887    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1888      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1889      <address><email>henrikn@microsoft.com</email></address>
1890    </author>
1891    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1892      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1893      <address><email>LMM@acm.org</email></address>
1894    </author>
1895    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1896      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1897      <address><email>paulle@microsoft.com</email></address>
1898    </author>
1899    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1900      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1901      <address><email>timbl@w3.org</email></address>
1902    </author>
1903    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1904      <organization abbrev="W3C">World Wide Web Consortium</organization>
1905      <address><email>ylafon@w3.org</email></address>
1906    </author>
1907    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1908      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1909      <address><email>julian.reschke@greenbytes.de</email></address>
1910    </author>
1911    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1912  </front>
1913  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1914  <x:source href="p5-range.xml" basename="p5-range"/>
1915</reference>
1916
1917<reference anchor="Part6">
1918  <front>
1919    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1920    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1921      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1922      <address><email>fielding@gbiv.com</email></address>
1923    </author>
1924    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1925      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1926      <address><email>jg@freedesktop.org</email></address>
1927    </author>
1928    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1929      <organization abbrev="HP">Hewlett-Packard Company</organization>
1930      <address><email>JeffMogul@acm.org</email></address>
1931    </author>
1932    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1933      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1934      <address><email>henrikn@microsoft.com</email></address>
1935    </author>
1936    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1937      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1938      <address><email>LMM@acm.org</email></address>
1939    </author>
1940    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1941      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1942      <address><email>paulle@microsoft.com</email></address>
1943    </author>
1944    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1945      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1946      <address><email>timbl@w3.org</email></address>
1947    </author>
1948    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1949      <organization abbrev="W3C">World Wide Web Consortium</organization>
1950      <address><email>ylafon@w3.org</email></address>
1951    </author>
1952    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1953      <address><email>mnot@mnot.net</email></address>
1954    </author>
1955    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1956      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1957      <address><email>julian.reschke@greenbytes.de</email></address>
1958    </author>
1959    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1960  </front>
1961  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1962  <x:source href="p6-cache.xml" basename="p6-cache"/>
1963</reference>
1964
1965<reference anchor="RFC1864">
1966  <front>
1967    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1968    <author initials="J." surname="Myers" fullname="John G. Myers">
1969      <organization>Carnegie Mellon University</organization>
1970      <address><email>jgm+@cmu.edu</email></address>
1971    </author>
1972    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
1973      <organization>Dover Beach Consulting, Inc.</organization>
1974      <address><email>mrose@dbc.mtview.ca.us</email></address>
1975    </author>
1976    <date month="October" year="1995"/>
1977  </front>
1978  <seriesInfo name="RFC" value="1864"/>
1979</reference>
1980
1981<reference anchor="RFC1950">
1982  <front>
1983    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1984    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1985      <organization>Aladdin Enterprises</organization>
1986      <address><email>ghost@aladdin.com</email></address>
1987    </author>
1988    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
1989    <date month="May" year="1996"/>
1990  </front>
1991  <seriesInfo name="RFC" value="1950"/>
1992  <annotation>
1993    RFC 1950 is an Informational RFC, thus it might be less stable than
1994    this specification. On the other hand, this downward reference was
1995    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1996    therefore it is unlikely to cause problems in practice. See also
1997    <xref target="BCP97"/>.
1998  </annotation>
1999</reference>
2000
2001<reference anchor="RFC1951">
2002  <front>
2003    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
2004    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2005      <organization>Aladdin Enterprises</organization>
2006      <address><email>ghost@aladdin.com</email></address>
2007    </author>
2008    <date month="May" year="1996"/>
2009  </front>
2010  <seriesInfo name="RFC" value="1951"/>
2011  <annotation>
2012    RFC 1951 is an Informational RFC, thus it might be less stable than
2013    this specification. On the other hand, this downward reference was
2014    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2015    therefore it is unlikely to cause problems in practice. See also
2016    <xref target="BCP97"/>.
2017  </annotation>
2018</reference>
2019
2020<reference anchor="RFC1952">
2021  <front>
2022    <title>GZIP file format specification version 4.3</title>
2023    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2024      <organization>Aladdin Enterprises</organization>
2025      <address><email>ghost@aladdin.com</email></address>
2026    </author>
2027    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2028      <address><email>gzip@prep.ai.mit.edu</email></address>
2029    </author>
2030    <author initials="M." surname="Adler" fullname="Mark Adler">
2031      <address><email>madler@alumni.caltech.edu</email></address>
2032    </author>
2033    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2034      <address><email>ghost@aladdin.com</email></address>
2035    </author>
2036    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2037      <address><email>randeg@alumni.rpi.edu</email></address>
2038    </author>
2039    <date month="May" year="1996"/>
2040  </front>
2041  <seriesInfo name="RFC" value="1952"/>
2042  <annotation>
2043    RFC 1952 is an Informational RFC, thus it might be less stable than
2044    this specification. On the other hand, this downward reference was
2045    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2046    therefore it is unlikely to cause problems in practice. See also
2047    <xref target="BCP97"/>.
2048  </annotation>
2049</reference>
2050
2051<reference anchor="RFC2045">
2052  <front>
2053    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2054    <author initials="N." surname="Freed" fullname="Ned Freed">
2055      <organization>Innosoft International, Inc.</organization>
2056      <address><email>ned@innosoft.com</email></address>
2057    </author>
2058    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2059      <organization>First Virtual Holdings</organization>
2060      <address><email>nsb@nsb.fv.com</email></address>
2061    </author>
2062    <date month="November" year="1996"/>
2063  </front>
2064  <seriesInfo name="RFC" value="2045"/>
2065</reference>
2066
2067<reference anchor="RFC2046">
2068  <front>
2069    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2070    <author initials="N." surname="Freed" fullname="Ned Freed">
2071      <organization>Innosoft International, Inc.</organization>
2072      <address><email>ned@innosoft.com</email></address>
2073    </author>
2074    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2075      <organization>First Virtual Holdings</organization>
2076      <address><email>nsb@nsb.fv.com</email></address>
2077    </author>
2078    <date month="November" year="1996"/>
2079  </front>
2080  <seriesInfo name="RFC" value="2046"/>
2081</reference>
2082
2083<reference anchor="RFC2119">
2084  <front>
2085    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2086    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2087      <organization>Harvard University</organization>
2088      <address><email>sob@harvard.edu</email></address>
2089    </author>
2090    <date month="March" year="1997"/>
2091  </front>
2092  <seriesInfo name="BCP" value="14"/>
2093  <seriesInfo name="RFC" value="2119"/>
2094</reference>
2095
2096<reference anchor='RFC4647'>
2097  <front>
2098    <title>Matching of Language Tags</title>
2099    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2100      <organization>Yahoo! Inc.</organization>
2101      <address><email>addison@inter-locale.com</email></address>
2102    </author>
2103    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2104      <organization>Google</organization>
2105      <address><email>mark.davis@macchiato.com</email></address>
2106    </author>
2107    <date year='2006' month='September' />
2108  </front>
2109  <seriesInfo name='BCP' value='47' />
2110  <seriesInfo name='RFC' value='4647' />
2111</reference>
2112
2113<reference anchor="RFC5234">
2114  <front>
2115    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2116    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2117      <organization>Brandenburg InternetWorking</organization>
2118      <address>
2119        <email>dcrocker@bbiw.net</email>
2120      </address> 
2121    </author>
2122    <author initials="P." surname="Overell" fullname="Paul Overell">
2123      <organization>THUS plc.</organization>
2124      <address>
2125        <email>paul.overell@thus.net</email>
2126      </address>
2127    </author>
2128    <date month="January" year="2008"/>
2129  </front>
2130  <seriesInfo name="STD" value="68"/>
2131  <seriesInfo name="RFC" value="5234"/>
2132</reference>
2133
2134<reference anchor='RFC5646'>
2135  <front>
2136    <title>Tags for Identifying Languages</title>
2137    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
2138      <organization>Lab126</organization>
2139      <address><email>addison@inter-locale.com</email></address>
2140    </author>
2141    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
2142      <organization>Google</organization>
2143      <address><email>mark.davis@google.com</email></address>
2144    </author>
2145    <date month='September' year='2009' />
2146  </front>
2147  <seriesInfo name='BCP' value='47' />
2148  <seriesInfo name='RFC' value='5646' />
2149</reference>
2150
2151</references>
2152
2153<references title="Informative References">
2154
2155<reference anchor="RFC1945">
2156  <front>
2157    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2158    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2159      <organization>MIT, Laboratory for Computer Science</organization>
2160      <address><email>timbl@w3.org</email></address>
2161    </author>
2162    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2163      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2164      <address><email>fielding@ics.uci.edu</email></address>
2165    </author>
2166    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2167      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2168      <address><email>frystyk@w3.org</email></address>
2169    </author>
2170    <date month="May" year="1996"/>
2171  </front>
2172  <seriesInfo name="RFC" value="1945"/>
2173</reference>
2174
2175<reference anchor="RFC2049">
2176  <front>
2177    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2178    <author initials="N." surname="Freed" fullname="Ned Freed">
2179      <organization>Innosoft International, Inc.</organization>
2180      <address><email>ned@innosoft.com</email></address>
2181    </author>
2182    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2183      <organization>First Virtual Holdings</organization>
2184      <address><email>nsb@nsb.fv.com</email></address>
2185    </author>
2186    <date month="November" year="1996"/>
2187  </front>
2188  <seriesInfo name="RFC" value="2049"/>
2189</reference>
2190
2191<reference anchor="RFC2068">
2192  <front>
2193    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2194    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2195      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2196      <address><email>fielding@ics.uci.edu</email></address>
2197    </author>
2198    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2199      <organization>MIT Laboratory for Computer Science</organization>
2200      <address><email>jg@w3.org</email></address>
2201    </author>
2202    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2203      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2204      <address><email>mogul@wrl.dec.com</email></address>
2205    </author>
2206    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2207      <organization>MIT Laboratory for Computer Science</organization>
2208      <address><email>frystyk@w3.org</email></address>
2209    </author>
2210    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2211      <organization>MIT Laboratory for Computer Science</organization>
2212      <address><email>timbl@w3.org</email></address>
2213    </author>
2214    <date month="January" year="1997"/>
2215  </front>
2216  <seriesInfo name="RFC" value="2068"/>
2217</reference>
2218
2219<reference anchor="RFC2076">
2220  <front>
2221    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2222    <author initials="J." surname="Palme" fullname="Jacob Palme">
2223      <organization>Stockholm University/KTH</organization>
2224      <address><email>jpalme@dsv.su.se</email></address>
2225    </author>
2226    <date month="February" year="1997"/>
2227  </front>
2228  <seriesInfo name="RFC" value="2076"/>
2229</reference>
2230
2231<reference anchor="RFC2277">
2232  <front>
2233    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2234    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2235      <organization>UNINETT</organization>
2236      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2237    </author>
2238    <date month="January" year="1998"/>
2239  </front>
2240  <seriesInfo name="BCP" value="18"/>
2241  <seriesInfo name="RFC" value="2277"/>
2242</reference>
2243
2244<reference anchor='RFC2295'>
2245  <front>
2246    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
2247    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
2248      <organization>Technische Universiteit Eindhoven</organization>
2249      <address>
2250        <email>koen@win.tue.nl</email>
2251      </address>
2252    </author>
2253    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
2254      <organization>Hewlett-Packard Company</organization>
2255      <address>
2256        <email>mutz@hpl.hp.com</email>
2257      </address>
2258    </author>
2259    <date year='1998' month='March'/>
2260  </front>
2261  <seriesInfo name='RFC' value='2295'/>
2262</reference>
2263
2264<reference anchor="RFC2388">
2265  <front>
2266    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2267    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2268      <organization>Xerox Palo Alto Research Center</organization>
2269      <address><email>masinter@parc.xerox.com</email></address>
2270    </author>
2271    <date year="1998" month="August"/>
2272  </front>
2273  <seriesInfo name="RFC" value="2388"/>
2274</reference>
2275
2276<reference anchor="RFC2557">
2277  <front>
2278    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2279    <author initials="F." surname="Palme" fullname="Jacob Palme">
2280      <organization>Stockholm University and KTH</organization>
2281      <address><email>jpalme@dsv.su.se</email></address>
2282    </author>
2283    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2284      <organization>Microsoft Corporation</organization>
2285      <address><email>alexhop@microsoft.com</email></address>
2286    </author>
2287    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2288      <organization>Lotus Development Corporation</organization>
2289      <address><email>Shelness@lotus.com</email></address>
2290    </author>
2291    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2292      <address><email>stef@nma.com</email></address>
2293    </author>
2294    <date year="1999" month="March"/>
2295  </front>
2296  <seriesInfo name="RFC" value="2557"/>
2297</reference>
2298
2299<reference anchor="RFC2616">
2300  <front>
2301    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2302    <author initials="R." surname="Fielding" fullname="R. Fielding">
2303      <organization>University of California, Irvine</organization>
2304      <address><email>fielding@ics.uci.edu</email></address>
2305    </author>
2306    <author initials="J." surname="Gettys" fullname="J. Gettys">
2307      <organization>W3C</organization>
2308      <address><email>jg@w3.org</email></address>
2309    </author>
2310    <author initials="J." surname="Mogul" fullname="J. Mogul">
2311      <organization>Compaq Computer Corporation</organization>
2312      <address><email>mogul@wrl.dec.com</email></address>
2313    </author>
2314    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2315      <organization>MIT Laboratory for Computer Science</organization>
2316      <address><email>frystyk@w3.org</email></address>
2317    </author>
2318    <author initials="L." surname="Masinter" fullname="L. Masinter">
2319      <organization>Xerox Corporation</organization>
2320      <address><email>masinter@parc.xerox.com</email></address>
2321    </author>
2322    <author initials="P." surname="Leach" fullname="P. Leach">
2323      <organization>Microsoft Corporation</organization>
2324      <address><email>paulle@microsoft.com</email></address>
2325    </author>
2326    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2327      <organization>W3C</organization>
2328      <address><email>timbl@w3.org</email></address>
2329    </author>
2330    <date month="June" year="1999"/>
2331  </front>
2332  <seriesInfo name="RFC" value="2616"/>
2333</reference>
2334
2335<reference anchor="RFC3629">
2336  <front>
2337    <title>UTF-8, a transformation format of ISO 10646</title>
2338    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2339      <organization>Alis Technologies</organization>
2340      <address><email>fyergeau@alis.com</email></address>
2341    </author>
2342    <date month="November" year="2003"/>
2343  </front>
2344  <seriesInfo name="STD" value="63"/>
2345  <seriesInfo name="RFC" value="3629"/>
2346</reference>
2347
2348<reference anchor='RFC3864'>
2349  <front>
2350    <title>Registration Procedures for Message Header Fields</title>
2351    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2352      <organization>Nine by Nine</organization>
2353      <address><email>GK-IETF@ninebynine.org</email></address>
2354    </author>
2355    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2356      <organization>BEA Systems</organization>
2357      <address><email>mnot@pobox.com</email></address>
2358    </author>
2359    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2360      <organization>HP Labs</organization>
2361      <address><email>JeffMogul@acm.org</email></address>
2362    </author>
2363    <date year='2004' month='September' />
2364  </front>
2365  <seriesInfo name='BCP' value='90' />
2366  <seriesInfo name='RFC' value='3864' />
2367</reference>
2368
2369<reference anchor="RFC4288">
2370  <front>
2371    <title>Media Type Specifications and Registration Procedures</title>
2372    <author initials="N." surname="Freed" fullname="N. Freed">
2373      <organization>Sun Microsystems</organization>
2374      <address>
2375        <email>ned.freed@mrochek.com</email>
2376      </address>
2377    </author>
2378    <author initials="J." surname="Klensin" fullname="J. Klensin">
2379      <address>
2380        <email>klensin+ietf@jck.com</email>
2381      </address>
2382    </author>
2383    <date year="2005" month="December"/>
2384  </front>
2385  <seriesInfo name="BCP" value="13"/>
2386  <seriesInfo name="RFC" value="4288"/>
2387</reference>
2388
2389<reference anchor='RFC5226'>
2390  <front>
2391    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2392    <author initials='T.' surname='Narten' fullname='T. Narten'>
2393      <organization>IBM</organization>
2394      <address><email>narten@us.ibm.com</email></address>
2395    </author>
2396    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
2397      <organization>Google</organization>
2398      <address><email>Harald@Alvestrand.no</email></address>
2399    </author>
2400    <date year='2008' month='May' />
2401  </front>
2402  <seriesInfo name='BCP' value='26' />
2403  <seriesInfo name='RFC' value='5226' />
2404</reference>
2405
2406<reference anchor="RFC5322">
2407  <front>
2408    <title>Internet Message Format</title>
2409    <author initials="P." surname="Resnick" fullname="P. Resnick">
2410      <organization>Qualcomm Incorporated</organization>
2411    </author>
2412    <date year="2008" month="October"/>
2413  </front> 
2414  <seriesInfo name="RFC" value="5322"/>
2415</reference>
2416
2417<reference anchor='BCP97'>
2418  <front>
2419    <title>Handling Normative References to Standards-Track Documents</title>
2420    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2421      <address>
2422        <email>klensin+ietf@jck.com</email>
2423      </address>
2424    </author>
2425    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2426      <organization>MIT</organization>
2427      <address>
2428        <email>hartmans-ietf@mit.edu</email>
2429      </address>
2430    </author>
2431    <date year='2007' month='June' />
2432  </front>
2433  <seriesInfo name='BCP' value='97' />
2434  <seriesInfo name='RFC' value='4897' />
2435</reference>
2436
2437
2438</references>
2439
2440<section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
2441<t>
2442   HTTP/1.1 uses many of the constructs defined for Internet Mail (<xref target="RFC5322"/>) and the Multipurpose Internet Mail Extensions (MIME <xref target="RFC2045"/>) to
2443   allow a message-body to be transmitted in an open variety of
2444   representations and with extensible mechanisms. However, RFC 2045
2445   discusses mail, and HTTP has a few features that are different from
2446   those described in MIME. These differences were carefully chosen
2447   to optimize performance over binary connections, to allow greater
2448   freedom in the use of new media types, to make date comparisons
2449   easier, and to acknowledge the practice of some early HTTP servers
2450   and clients.
2451</t>
2452<t>
2453   This appendix describes specific areas where HTTP differs from MIME.
2454   Proxies and gateways to strict MIME environments &SHOULD; be
2455   aware of these differences and provide the appropriate conversions
2456   where necessary. Proxies and gateways from MIME environments to HTTP
2457   also need to be aware of the differences because some conversions
2458   might be required.
2459</t>
2460
2461<section title="MIME-Version" anchor="mime-version">
2462  <iref primary="true" item="MIME-Version header field" x:for-anchor=""/>
2463  <iref primary="true" item="Header Fields" subitem="MIME-Version" x:for-anchor=""/>
2464  <x:anchor-alias value="MIME-Version"/>
2465<t>
2466   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2467   include a single MIME-Version header field to indicate what
2468   version of the MIME protocol was used to construct the message. Use
2469   of the MIME-Version header field indicates that the message is in
2470   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2471   Proxies/gateways are responsible for ensuring full compliance (where
2472   possible) when exporting HTTP messages to strict MIME environments.
2473</t>
2474<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/>
2475  <x:ref>MIME-Version</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2476</artwork></figure>
2477<t>
2478   MIME version "1.0" is the default for use in HTTP/1.1. However,
2479   HTTP/1.1 message parsing and semantics are defined by this document
2480   and not the MIME specification.
2481</t>
2482</section>
2483
2484<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2485<t>
2486   MIME requires that an Internet mail body-part be converted to
2487   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2488   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2489   allowed for subtypes of the "text" media type when transmitted over
2490   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2491   line breaks as CRLF and forbids the use of CR or LF outside of line
2492   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2493   line break within text content when a message is transmitted over
2494   HTTP.
2495</t>
2496<t>
2497   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2498   environment &SHOULD; translate all line breaks within the text media
2499   types described in <xref target="canonicalization.and.text.defaults"/>
2500   of this document to the RFC 2049
2501   canonical form of CRLF. Note, however, that this might be complicated
2502   by the presence of a Content-Encoding and by the fact that HTTP
2503   allows the use of some character encodings which do not use octets 13 and
2504   10 to represent CR and LF, respectively, as is the case for some multi-byte
2505   character encodings.
2506</t>
2507<t>
2508   Conversion will break any cryptographic
2509   checksums applied to the original content unless the original content
2510   is already in canonical form. Therefore, the canonical form is
2511   recommended for any content that uses such checksums in HTTP.
2512</t>
2513</section>
2514
2515
2516<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2517<t>
2518   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2519   simplify the process of date comparison. Proxies and gateways from
2520   other protocols &SHOULD; ensure that any Date header field present in a
2521   message conforms to one of the HTTP/1.1 formats and rewrite the date
2522   if necessary.
2523</t>
2524</section>
2525
2526<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2527<t>
2528   MIME does not include any concept equivalent to HTTP/1.1's
2529   Content-Encoding header field. Since this acts as a modifier on the
2530   media type, proxies and gateways from HTTP to MIME-compliant
2531   protocols &MUST; either change the value of the Content-Type header
2532   field or decode the representation before forwarding the message. (Some
2533   experimental applications of Content-Type for Internet mail have used
2534   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2535   a function equivalent to Content-Encoding. However, this parameter is
2536   not part of the MIME standards).
2537</t>
2538</section>
2539
2540<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2541<t>
2542   HTTP does not use the Content-Transfer-Encoding field of MIME.
2543   Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2544   remove any Content-Transfer-Encoding
2545   prior to delivering the response message to an HTTP client.
2546</t>
2547<t>
2548   Proxies and gateways from HTTP to MIME-compliant protocols are
2549   responsible for ensuring that the message is in the correct format
2550   and encoding for safe transport on that protocol, where "safe
2551   transport" is defined by the limitations of the protocol being used.
2552   Such a proxy or gateway &SHOULD; label the data with an appropriate
2553   Content-Transfer-Encoding if doing so will improve the likelihood of
2554   safe transport over the destination protocol.
2555</t>
2556</section>
2557
2558<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2559<t>
2560   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2561   Proxies/gateways &MUST; remove any transfer-coding prior to
2562   forwarding a message via a MIME-compliant protocol.
2563</t>
2564</section>
2565
2566<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2567<t>
2568   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2569   need to be aware of MIME line length limitations. Since HTTP does not
2570   have this limitation, HTTP does not fold long lines. MHTML messages
2571   being transported by HTTP follow all conventions of MHTML, including
2572   line length limitations and folding, canonicalization, etc., since
2573   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2574   does not interpret the content or any MIME header lines that might be
2575   contained therein.
2576</t>
2577</section>
2578</section>
2579
2580<section title="Additional Features" anchor="additional.features">
2581<t>
2582   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2583   existing HTTP implementations, but not consistently and correctly
2584   across most HTTP/1.1 applications. Implementors are advised to be
2585   aware of these features, but cannot rely upon their presence in, or
2586   interoperability with, other HTTP/1.1 applications. Some of these
2587   describe proposed experimental features, and some describe features
2588   that experimental deployment found lacking that are now addressed in
2589   the base HTTP/1.1 specification.
2590</t>
2591<t>
2592   A number of other header fields, such as Content-Disposition and Title,
2593   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2594</t>
2595</section>
2596
2597<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2598<t>
2599  Clarify contexts that charset is used in.
2600  (<xref target="character.sets"/>)
2601</t>
2602<t>
2603  Change ABNF productions for header fields to only define the field value.
2604  (<xref target="header.fields"/>)
2605</t>
2606<t>
2607  Remove base URI setting semantics for Content-Location due to poor
2608  implementation support, which was caused by too many broken servers emitting
2609  bogus Content-Location header fields, and also the potentially undesirable effect
2610  of potentially breaking relative links in content-negotiated resources.
2611  (<xref target="header.content-location"/>)
2612</t>
2613<t>
2614  Remove reference to non-existant identity transfer-coding value tokens.
2615  (<xref target="no.content-transfer-encoding"/>)
2616</t>
2617</section>
2618
2619<?BEGININC p3-payload.abnf-appendix ?>
2620<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
2621<figure>
2622<artwork type="abnf" name="p3-payload.parsed-abnf">
2623<x:ref>Accept</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2624 OWS media-range [ accept-params ] ] ) ]
2625<x:ref>Accept-Charset</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2626 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2627 qvalue ] ] )
2628<x:ref>Accept-Encoding</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] ) )
2629 *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2630<x:ref>Accept-Language</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
2631 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2632 ] )
2633
2634<x:ref>Content-Encoding</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
2635 content-coding ] )
2636<x:ref>Content-Language</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
2637 language-tag ] )
2638<x:ref>Content-Location</x:ref> = absolute-URI / partial-URI
2639<x:ref>Content-MD5</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2640<x:ref>Content-Type</x:ref> = media-type
2641
2642<x:ref>MIME-Version</x:ref> = 1*DIGIT "." 1*DIGIT
2643
2644<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
2645
2646<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.6&gt;
2647<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" word ]
2648<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2649<x:ref>attribute</x:ref> = token
2650
2651<x:ref>charset</x:ref> = token
2652<x:ref>codings</x:ref> = ( content-coding / "*" )
2653<x:ref>content-coding</x:ref> = token
2654
2655<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
2656<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC5646], Section 2.1&gt;
2657
2658<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2659 ";" OWS parameter )
2660<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2661
2662<x:ref>parameter</x:ref> = attribute "=" value
2663<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.6&gt;
2664
2665<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 6.4&gt;
2666
2667<x:ref>subtype</x:ref> = token
2668
2669<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2670<x:ref>type</x:ref> = token
2671
2672<x:ref>value</x:ref> = word
2673
2674<x:ref>word</x:ref> = &lt;word, defined in [Part1], Section 1.2.2&gt;
2675</artwork>
2676</figure>
2677<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2678; Accept defined but not used
2679; Accept-Charset defined but not used
2680; Accept-Encoding defined but not used
2681; Accept-Language defined but not used
2682; Content-Encoding defined but not used
2683; Content-Language defined but not used
2684; Content-Location defined but not used
2685; Content-MD5 defined but not used
2686; Content-Type defined but not used
2687; MIME-Version defined but not used
2688</artwork></figure></section>
2689<?ENDINC p3-payload.abnf-appendix ?>
2690
2691<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2692
2693<section title="Since RFC 2616">
2694<t>
2695  Extracted relevant partitions from <xref target="RFC2616"/>.
2696</t>
2697</section>
2698
2699<section title="Since draft-ietf-httpbis-p3-payload-00">
2700<t>
2701  Closed issues:
2702  <list style="symbols"> 
2703    <t>
2704      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2705      "Media Type Registrations"
2706      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2707    </t>
2708    <t>
2709      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2710      "Clarification regarding quoting of charset values"
2711      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2712    </t>
2713    <t>
2714      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2715      "Remove 'identity' token references"
2716      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2717    </t>
2718    <t>
2719      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2720      "Accept-Encoding BNF"
2721    </t>
2722    <t>
2723      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2724      "Normative and Informative references"
2725    </t>
2726    <t>
2727      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2728      "RFC1700 references"
2729    </t>
2730    <t>
2731      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2732      "Updating to RFC4288"
2733    </t>
2734    <t>
2735      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2736      "Informative references"
2737    </t>
2738    <t>
2739      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2740      "ISO-8859-1 Reference"
2741    </t>
2742    <t>
2743      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2744      "Encoding References Normative"
2745    </t>
2746    <t>
2747      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2748      "Normative up-to-date references"
2749    </t>
2750  </list>
2751</t>
2752</section>
2753
2754<section title="Since draft-ietf-httpbis-p3-payload-01">
2755<t>
2756  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2757  <list style="symbols"> 
2758    <t>
2759      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2760    </t>
2761  </list>
2762</t>
2763</section>
2764
2765<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2766<t>
2767  Closed issues:
2768  <list style="symbols"> 
2769    <t>
2770      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2771      "Quoting Charsets"
2772    </t>
2773    <t>
2774      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2775      "Classification for Allow header"
2776    </t>
2777    <t>
2778      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2779      "missing default for qvalue in description of Accept-Encoding"
2780    </t>
2781  </list>
2782</t>
2783<t>
2784  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2785  <list style="symbols"> 
2786    <t>
2787      Reference RFC 3984, and update header field registrations for headers defined
2788      in this document.
2789    </t>
2790  </list>
2791</t>
2792</section>
2793
2794<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2795<t>
2796  Closed issues:
2797  <list style="symbols"> 
2798    <t>
2799      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2800      "Quoting Charsets"
2801    </t>
2802    <t>
2803      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2804      "language tag matching (Accept-Language) vs RFC4647"
2805    </t>
2806    <t>
2807      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2808      "RFC 1806 has been replaced by RFC2183"
2809    </t>
2810  </list>
2811</t>
2812<t>
2813  Other changes:
2814  <list style="symbols"> 
2815    <t>
2816      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2817      "Encoding References Normative" &mdash; rephrase the annotation and reference
2818      <xref target="BCP97"/>.
2819    </t>
2820  </list>
2821</t>
2822 </section>
2823
2824<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2825<t>
2826  Closed issues:
2827  <list style="symbols"> 
2828    <t>
2829      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2830      "RFC 2822 is updated by RFC 5322"
2831    </t>
2832  </list>
2833</t>
2834<t>
2835  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2836  <list style="symbols"> 
2837    <t>
2838      Use "/" instead of "|" for alternatives.
2839    </t>
2840    <t>
2841      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2842      whitespace ("OWS") and required whitespace ("RWS").
2843    </t>
2844    <t>
2845      Rewrite ABNFs to spell out whitespace rules, factor out
2846      header field value format definitions.
2847    </t>
2848  </list>
2849</t>
2850</section>
2851
2852<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2853<t>
2854  Closed issues:
2855  <list style="symbols"> 
2856    <t>
2857      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2858      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2859    </t>
2860  </list>
2861</t>
2862<t>
2863  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2864  <list style="symbols"> 
2865    <t>
2866      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2867    </t>
2868  </list>
2869</t>
2870<t>
2871  Other changes:
2872  <list style="symbols"> 
2873    <t>
2874      Move definition of quality values into Part 1.
2875    </t>
2876  </list>
2877</t>
2878</section>
2879
2880<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
2881<t>
2882  Closed issues:
2883  <list style="symbols"> 
2884    <t>
2885      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
2886      "Content-Location isn't special"
2887    </t>
2888    <t>
2889      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2890      "Content Sniffing"
2891    </t>
2892  </list>
2893</t>
2894</section>
2895
2896<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
2897<t>
2898  Closed issues:
2899  <list style="symbols"> 
2900    <t>
2901      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
2902      "Updated reference for language tags"
2903    </t>
2904    <t>
2905      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
2906      "Clarify rules for determining what entities a response carries"
2907    </t>
2908    <t>
2909      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/154"/>:
2910      "Content-Location base-setting problems"
2911    </t>
2912    <t>
2913      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2914      "Content Sniffing"
2915    </t>
2916    <t>
2917      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
2918      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
2919    </t>
2920    <t>
2921      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
2922      "move definitions of gzip/deflate/compress to part 1"
2923    </t>
2924  </list>
2925</t>
2926<t>
2927  Partly resolved issues:
2928  <list style="symbols"> 
2929    <t>
2930      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
2931      "update IANA requirements wrt Transfer-Coding values" (add the
2932      IANA Considerations subsection)
2933    </t>
2934    <t>
2935      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
2936      "update IANA requirements wrt Content-Coding values" (add the
2937      IANA Considerations subsection)
2938    </t>
2939  </list>
2940</t>
2941</section>
2942
2943<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
2944<t>
2945  Closed issues:
2946  <list style="symbols"> 
2947    <t>
2948      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/81"/>:
2949      "Content Negotiation for media types"
2950    </t>
2951    <t>
2952      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/181"/>:
2953      "Accept-Language: which RFC4647 filtering?"
2954    </t>
2955  </list>
2956</t>
2957</section>
2958
2959<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
2960<t>
2961  Closed issues:
2962  <list style="symbols"> 
2963    <t>
2964      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
2965      "MIME-Version not listed in P1, general header fields"
2966    </t>
2967    <t>
2968      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
2969      "IANA registry for content/transfer encodings"
2970    </t>
2971    <t>
2972      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
2973      "Content Sniffing"
2974    </t>
2975    <t>
2976      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
2977      "use of term "word" when talking about header structure"
2978    </t>
2979  </list>
2980</t>
2981<t>
2982  Partly resolved issues:
2983  <list style="symbols"> 
2984    <t>
2985      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
2986      "Term for the requested resource's URI"
2987    </t>
2988  </list>
2989</t>
2990</section>
2991
2992<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.10">
2993<t>
2994  Closed issues:
2995  <list style="symbols"> 
2996    <t>
2997      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
2998      "Clarify 'Requested Variant'"
2999    </t>
3000    <t>
3001      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
3002      "Content-Location isn't special"
3003    </t>
3004    <t>
3005      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
3006      "Delimiting messages with multipart/byteranges"
3007    </t>
3008    <t>
3009      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
3010      "Clarify entity / representation / variant terminology"
3011    </t>
3012    <t>
3013      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/136"/>:
3014      "confusing req. language for Content-Location"
3015    </t>
3016    <t>
3017      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/167"/>:
3018      "Content-Location on 304 responses"
3019    </t>
3020    <t>
3021      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/183"/>:
3022      "'requested resource' in content-encoding definition"
3023    </t>
3024    <t>
3025      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
3026      "consider removing the 'changes from 2068' sections"
3027    </t>
3028  </list>
3029</t>
3030<t>
3031  Partly resolved issues:
3032  <list style="symbols"> 
3033    <t>
3034      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/178"/>:
3035      "Content-MD5 and partial responses"
3036    </t>
3037  </list>
3038</t>
3039</section>
3040
3041<section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.since.11">
3042<t>
3043  Closed issues:
3044  <list style="symbols"> 
3045    <t>
3046      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/123"/>:
3047      "Factor out Content-Disposition"
3048    </t>
3049  </list>
3050</t>
3051</section>
3052
3053<section title="Since draft-ietf-httpbis-p3-payload-12" anchor="changes.since.12">
3054<t>
3055  Closed issues:
3056  <list style="symbols"> 
3057    <t>
3058      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
3059      "Header Classification"
3060    </t>
3061    <t>
3062      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
3063      "untangle ABNFs for header fields"
3064    </t>
3065    <t>
3066      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/277"/>:
3067      "potentially misleading MAY in media-type def"
3068    </t>
3069  </list>
3070</t>
3071</section>
3072
3073<section title="Since draft-ietf-httpbis-p3-payload-13" anchor="changes.since.13">
3074<t>
3075  Closed issues:
3076  <list style="symbols"> 
3077    <t>
3078      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
3079      "untangle ABNFs for header fields"
3080    </t>
3081  </list>
3082</t>
3083</section>
3084
3085</section>
3086
3087</back>
3088</rfc>
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