source: draft-ietf-httpbis/06/p3-payload.xml @ 784

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Prepare submission of draft -06 on Monday, March 09.

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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 "06">
15  <!ENTITY ID-MONTH "March">
16  <!ENTITY ID-YEAR "2009">
17  <!ENTITY notation                 "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY notation-abnf            "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY basic-rules              "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY message-length           "<xref target='Part1' x:rel='#message.length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY message-headers          "<xref target='Part1' x:rel='#message.headers' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY full-date                "<xref target='Part1' x:rel='#full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY qvalue                   "<xref target='Part1' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35]>
36<?rfc toc="yes" ?>
37<?rfc symrefs="yes" ?>
38<?rfc sortrefs="yes" ?>
39<?rfc compact="yes"?>
40<?rfc subcompact="no" ?>
41<?rfc linkmailto="no" ?>
42<?rfc editing="no" ?>
43<?rfc comments="yes"?>
44<?rfc inline="yes"?>
45<?rfc-ext allow-markup-in-artwork="yes" ?>
46<?rfc-ext include-references-in-index="yes" ?>
47<rfc obsoletes="2616" category="std" x:maturity-level="draft"
48     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
49     xmlns:x='http://purl.org/net/xml2rfc/ext'>
50<front>
51
52  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
53
54  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
55    <organization abbrev="Day Software">Day Software</organization>
56    <address>
57      <postal>
58        <street>23 Corporate Plaza DR, Suite 280</street>
59        <city>Newport Beach</city>
60        <region>CA</region>
61        <code>92660</code>
62        <country>USA</country>
63      </postal>
64      <phone>+1-949-706-5300</phone>
65      <facsimile>+1-949-706-5305</facsimile>
66      <email>fielding@gbiv.com</email>
67      <uri>http://roy.gbiv.com/</uri>
68    </address>
69  </author>
70
71  <author initials="J." surname="Gettys" fullname="Jim Gettys">
72    <organization>One Laptop per Child</organization>
73    <address>
74      <postal>
75        <street>21 Oak Knoll Road</street>
76        <city>Carlisle</city>
77        <region>MA</region>
78        <code>01741</code>
79        <country>USA</country>
80      </postal>
81      <email>jg@laptop.org</email>
82      <uri>http://www.laptop.org/</uri>
83    </address>
84  </author>
85 
86  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
87    <organization abbrev="HP">Hewlett-Packard Company</organization>
88    <address>
89      <postal>
90        <street>HP Labs, Large Scale Systems Group</street>
91        <street>1501 Page Mill Road, MS 1177</street>
92        <city>Palo Alto</city>
93        <region>CA</region>
94        <code>94304</code>
95        <country>USA</country>
96      </postal>
97      <email>JeffMogul@acm.org</email>
98    </address>
99  </author>
100
101  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
102    <organization abbrev="Microsoft">Microsoft Corporation</organization>
103    <address>
104      <postal>
105        <street>1 Microsoft Way</street>
106        <city>Redmond</city>
107        <region>WA</region>
108        <code>98052</code>
109        <country>USA</country>
110      </postal>
111      <email>henrikn@microsoft.com</email>
112    </address>
113  </author>
114
115  <author initials="L." surname="Masinter" fullname="Larry Masinter">
116    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
117    <address>
118      <postal>
119        <street>345 Park Ave</street>
120        <city>San Jose</city>
121        <region>CA</region>
122        <code>95110</code>
123        <country>USA</country>
124      </postal>
125      <email>LMM@acm.org</email>
126      <uri>http://larry.masinter.net/</uri>
127    </address>
128  </author>
129 
130  <author initials="P." surname="Leach" fullname="Paul J. Leach">
131    <organization abbrev="Microsoft">Microsoft Corporation</organization>
132    <address>
133      <postal>
134        <street>1 Microsoft Way</street>
135        <city>Redmond</city>
136        <region>WA</region>
137        <code>98052</code>
138      </postal>
139      <email>paulle@microsoft.com</email>
140    </address>
141  </author>
142   
143  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
144    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
145    <address>
146      <postal>
147        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
148        <street>The Stata Center, Building 32</street>
149        <street>32 Vassar Street</street>
150        <city>Cambridge</city>
151        <region>MA</region>
152        <code>02139</code>
153        <country>USA</country>
154      </postal>
155      <email>timbl@w3.org</email>
156      <uri>http://www.w3.org/People/Berners-Lee/</uri>
157    </address>
158  </author>
159
160  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
161    <organization abbrev="W3C">World Wide Web Consortium</organization>
162    <address>
163      <postal>
164        <street>W3C / ERCIM</street>
165        <street>2004, rte des Lucioles</street>
166        <city>Sophia-Antipolis</city>
167        <region>AM</region>
168        <code>06902</code>
169        <country>France</country>
170      </postal>
171      <email>ylafon@w3.org</email>
172      <uri>http://www.raubacapeu.net/people/yves/</uri>
173    </address>
174  </author>
175
176  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
177    <organization abbrev="greenbytes">greenbytes GmbH</organization>
178    <address>
179      <postal>
180        <street>Hafenweg 16</street>
181        <city>Muenster</city><region>NW</region><code>48155</code>
182        <country>Germany</country>
183      </postal>
184      <phone>+49 251 2807760</phone>   
185      <facsimile>+49 251 2807761</facsimile>   
186      <email>julian.reschke@greenbytes.de</email>       
187      <uri>http://greenbytes.de/tech/webdav/</uri>     
188    </address>
189  </author>
190
191  <date month="&ID-MONTH;" year="&ID-YEAR;" day="9"/>
192  <workgroup>HTTPbis Working Group</workgroup>
193
194<abstract>
195<t>
196   The Hypertext Transfer Protocol (HTTP) is an application-level
197   protocol for distributed, collaborative, hypermedia information
198   systems. HTTP has been in use by the World Wide Web global information
199   initiative since 1990. This document is Part 3 of the seven-part specification
200   that defines the protocol referred to as "HTTP/1.1" and, taken together,
201   obsoletes RFC 2616.  Part 3 defines HTTP message content,
202   metadata, and content negotiation.
203</t>
204</abstract>
205
206<note title="Editorial Note (To be removed by RFC Editor)">
207  <t>
208    Discussion of this draft should take place on the HTTPBIS working group
209    mailing list (ietf-http-wg@w3.org). The current issues list is
210    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
211    and related documents (including fancy diffs) can be found at
212    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
213  </t>
214  <t>
215    The changes in this draft are summarized in <xref target="changes.since.05"/>.
216  </t>
217</note>
218</front>
219<middle>
220<section title="Introduction" anchor="introduction">
221<t>
222   This document defines HTTP/1.1 message payloads (a.k.a., content), the
223   associated metadata header fields that define how the payload is intended
224   to be interpreted by a recipient, the request header fields that
225   may influence content selection, and the various selection algorithms
226   that are collectively referred to as HTTP content negotiation.
227</t>
228<t>
229   This document is currently disorganized in order to minimize the changes
230   between drafts and enable reviewers to see the smaller errata changes.
231   The next draft will reorganize the sections to better reflect the content.
232   In particular, the sections on entities will be renamed payload and moved
233   to the first half of the document, while the sections on content negotiation
234   and associated request header fields will be moved to the second half.  The
235   current mess reflects how widely dispersed these topics and associated
236   requirements had become in <xref target="RFC2616"/>.
237</t>
238
239<section title="Requirements" anchor="intro.requirements">
240<t>
241   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
242   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
243   document are to be interpreted as described in <xref target="RFC2119"/>.
244</t>
245<t>
246   An implementation is not compliant if it fails to satisfy one or more
247   of the &MUST; or &REQUIRED; level requirements for the protocols it
248   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
249   level and all the &SHOULD; level requirements for its protocols is said
250   to be "unconditionally compliant"; one that satisfies all the &MUST;
251   level requirements but not all the &SHOULD; level requirements for its
252   protocols is said to be "conditionally compliant."
253</t>
254</section>
255
256<section title="Syntax Notation" anchor="notation">
257  <x:anchor-alias value="ALPHA"/>
258  <x:anchor-alias value="CR"/>
259  <x:anchor-alias value="DIGIT"/>
260  <x:anchor-alias value="LF"/>
261  <x:anchor-alias value="OCTET"/>
262  <x:anchor-alias value="VCHAR"/>
263  <x:anchor-alias value="WSP"/>
264<t>
265  This specification uses the ABNF syntax defined in &notation; (which
266  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
267  <xref target="collected.abnf"/> shows the collected ABNF, with the list
268  rule expanded.
269</t>
270<t>
271  The following core rules are included by
272  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
273  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
274  DIGIT (decimal 0-9), DQUOTE (double quote),
275  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
276  OCTET (any 8-bit sequence of data), SP (space),
277  VCHAR (any visible USASCII character),
278  and WSP (whitespace).
279</t>
280
281<section title="Core Rules" anchor="core.rules">
282  <x:anchor-alias value="quoted-string"/>
283  <x:anchor-alias value="token"/>
284  <x:anchor-alias value="OWS"/>
285<t>
286  The core rules below are defined in &basic-rules;:
287</t>
288<figure><artwork type="abnf2616">
289  <x:ref>quoted-string</x:ref>  = &lt;quoted-string, defined in &basic-rules;&gt;
290  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
291  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
292</artwork></figure>
293</section>
294
295<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
296  <x:anchor-alias value="absolute-URI"/>
297  <x:anchor-alias value="Allow"/>
298  <x:anchor-alias value="Content-Length"/>
299  <x:anchor-alias value="Content-Range"/>
300  <x:anchor-alias value="Expires"/>
301  <x:anchor-alias value="Last-Modified"/>
302  <x:anchor-alias value="message-header"/>
303  <x:anchor-alias value="partial-URI"/>
304  <x:anchor-alias value="qvalue"/>
305<t>
306  The ABNF rules below are defined in other parts:
307</t>
308<figure><!--Part1--><artwork type="abnf2616">
309  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
310  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
311  <x:ref>message-header</x:ref> = &lt;message-header, defined in &message-headers;&gt;
312  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
313  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
314</artwork></figure>
315<figure><!--Part4--><artwork type="abnf2616">
316  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
317</artwork></figure>
318<figure><!--Part5--><artwork type="abnf2616">
319  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
320</artwork></figure>
321<figure><!--Part6--><artwork type="abnf2616">
322  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
323</artwork></figure>
324</section>
325
326</section>
327
328</section>
329
330<section title="Protocol Parameters" anchor="protocol.parameters">
331
332<section title="Character Sets" anchor="character.sets">
333<t>
334   HTTP uses the same definition of the term "character set" as that
335   described for MIME:
336</t>
337<t>
338   The term "character set" is used in this document to refer to a
339   method used with one or more tables to convert a sequence of octets
340   into a sequence of characters. Note that unconditional conversion in
341   the other direction is not required, in that not all characters may
342   be available in a given character set and a character set may provide
343   more than one sequence of octets to represent a particular character.
344   This definition is intended to allow various kinds of character
345   encoding, from simple single-table mappings such as US-ASCII to
346   complex table switching methods such as those that use ISO-2022's
347   techniques. However, the definition associated with a MIME character
348   set name &MUST; fully specify the mapping to be performed from octets
349   to characters. In particular, use of external profiling information
350   to determine the exact mapping is not permitted.
351</t>
352<t><list><t>
353      <x:h>Note:</x:h> This use of the term "character set" is more commonly
354      referred to as a "character encoding." However, since HTTP and
355      MIME share the same registry, it is important that the terminology
356      also be shared.
357</t></list></t>
358<t anchor="rule.charset">
359  <x:anchor-alias value="charset"/>
360   HTTP character sets are identified by case-insensitive tokens. The
361   complete set of tokens is defined by the IANA Character Set registry
362   (<eref target="http://www.iana.org/assignments/character-sets"/>).
363</t>
364<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
365  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
366</artwork></figure>
367<t>
368   Although HTTP allows an arbitrary token to be used as a charset
369   value, any token that has a predefined value within the IANA
370   Character Set registry &MUST; represent the character set defined
371   by that registry. Applications &SHOULD; limit their use of character
372   sets to those defined by the IANA registry.
373</t>
374<t>
375   HTTP uses charset in two contexts: within an Accept-Charset request
376   header (in which the charset value is an unquoted token) and as the
377   value of a parameter in a Content-Type header (within a request or
378   response), in which case the parameter value of the charset parameter
379   may be quoted.
380</t>
381<t>
382   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
383   <xref target="RFC2277"/>.
384</t>
385
386<section title="Missing Charset" anchor="missing.charset">
387<t>
388   Some HTTP/1.0 software has interpreted a Content-Type header without
389   charset parameter incorrectly to mean "recipient should guess."
390   Senders wishing to defeat this behavior &MAY; include a charset
391   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
392   it is known that it will not confuse the recipient.
393</t>
394<t>
395   Unfortunately, some older HTTP/1.0 clients did not deal properly with
396   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
397   charset label provided by the sender; and those user agents that have
398   a provision to "guess" a charset &MUST; use the charset from the
399   content-type field if they support that charset, rather than the
400   recipient's preference, when initially displaying a document. See
401   <xref target="canonicalization.and.text.defaults"/>.
402</t>
403</section>
404</section>
405
406<section title="Content Codings" anchor="content.codings">
407  <x:anchor-alias value="content-coding"/>
408<t>
409   Content coding values indicate an encoding transformation that has
410   been or can be applied to an entity. Content codings are primarily
411   used to allow a document to be compressed or otherwise usefully
412   transformed without losing the identity of its underlying media type
413   and without loss of information. Frequently, the entity is stored in
414   coded form, transmitted directly, and only decoded by the recipient.
415</t>
416<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
417  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
418</artwork></figure>
419<t>
420   All content-coding values are case-insensitive. HTTP/1.1 uses
421   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
422   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
423   describes the content-coding, what is more important is that it
424   indicates what decoding mechanism will be required to remove the
425   encoding.
426</t>
427<t>
428   The Internet Assigned Numbers Authority (IANA) acts as a registry for
429   content-coding value tokens. Initially, the registry contains the
430   following tokens:
431</t>
432<t>
433   gzip<iref item="gzip"/>
434  <list>
435    <t>
436        An encoding format produced by the file compression program
437        "gzip" (GNU zip) as described in <xref target="RFC1952"/>. This format is a
438        Lempel-Ziv coding (LZ77) with a 32 bit CRC.
439    </t>
440  </list>
441</t>
442<t>
443   compress<iref item="compress"/>
444  <list><t>
445        The encoding format produced by the common UNIX file compression
446        program "compress". This format is an adaptive Lempel-Ziv-Welch
447        coding (LZW).
448</t><t>
449        Use of program names for the identification of encoding formats
450        is not desirable and is discouraged for future encodings. Their
451        use here is representative of historical practice, not good
452        design. For compatibility with previous implementations of HTTP,
453        applications &SHOULD; consider "x-gzip" and "x-compress" to be
454        equivalent to "gzip" and "compress" respectively.
455  </t></list>
456</t>
457<t>
458   deflate<iref item="deflate"/>
459  <list><t>
460        The "zlib" format defined in <xref target="RFC1950"/> in combination with
461        the "deflate" compression mechanism described in <xref target="RFC1951"/>.
462  </t></list>
463</t>
464<t>
465   identity<iref item="identity"/>
466  <list><t>
467        The default (identity) encoding; the use of no transformation
468        whatsoever. This content-coding is used only in the Accept-Encoding
469        header, and &SHOULD-NOT;  be used in the Content-Encoding
470        header.
471  </t></list>
472</t>
473<t>
474   New content-coding value tokens &SHOULD; be registered; to allow
475   interoperability between clients and servers, specifications of the
476   content coding algorithms needed to implement a new value &SHOULD; be
477   publicly available and adequate for independent implementation, and
478   conform to the purpose of content coding defined in this section.
479</t>
480</section>
481
482<section title="Media Types" anchor="media.types">
483  <x:anchor-alias value="media-type"/>
484  <x:anchor-alias value="type"/>
485  <x:anchor-alias value="subtype"/>
486<t>
487   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
488   and Accept (<xref target="header.accept"/>) header fields in order to provide
489   open and extensible data typing and type negotiation.
490</t>
491<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"/>
492  <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> )
493  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
494  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
495</artwork></figure>
496<t anchor="rule.parameter">
497  <x:anchor-alias value="attribute"/>
498  <x:anchor-alias value="parameter"/>
499  <x:anchor-alias value="value"/>
500   Parameters &MAY; follow the type/subtype in the form of attribute/value
501   pairs.
502</t>
503<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"/>
504  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
505  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
506  <x:ref>value</x:ref>          = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
507</artwork></figure>
508<t>
509   The type, subtype, and parameter attribute names are case-insensitive.
510   Parameter values might or might not be case-sensitive, depending on the
511   semantics of the parameter name.  The presence or absence of a parameter might
512   be significant to the processing of a media-type, depending on its
513   definition within the media type registry.
514</t>
515<t>
516   A parameter value that matches the <x:ref>token</x:ref> production may be
517   transmitted as either a token or within a quoted-string. The quoted and
518   unquoted values are equivalent.
519</t>
520<t>
521   Note that some older HTTP applications do not recognize media type
522   parameters. When sending data to older HTTP applications,
523   implementations &SHOULD; only use media type parameters when they are
524   required by that type/subtype definition.
525</t>
526<t>
527   Media-type values are registered with the Internet Assigned Number
528   Authority (IANA). The media type registration process is
529   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
530   discouraged.
531</t>
532
533<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
534<t>
535   Internet media types are registered with a canonical form. An
536   entity-body transferred via HTTP messages &MUST; be represented in the
537   appropriate canonical form prior to its transmission except for
538   "text" types, as defined in the next paragraph.
539</t>
540<t>
541   When in canonical form, media subtypes of the "text" type use CRLF as
542   the text line break. HTTP relaxes this requirement and allows the
543   transport of text media with plain CR or LF alone representing a line
544   break when it is done consistently for an entire entity-body. HTTP
545   applications &MUST; accept CRLF, bare CR, and bare LF as being
546   representative of a line break in text media received via HTTP. In
547   addition, if the text is represented in a character set that does not
548   use octets 13 and 10 for CR and LF respectively, as is the case for
549   some multi-byte character sets, HTTP allows the use of whatever octet
550   sequences are defined by that character set to represent the
551   equivalent of CR and LF for line breaks. This flexibility regarding
552   line breaks applies only to text media in the entity-body; a bare CR
553   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
554   structures (such as header fields and multipart boundaries).
555</t>
556<t>
557   If an entity-body is encoded with a content-coding, the underlying
558   data &MUST; be in a form defined above prior to being encoded.
559</t>
560<t>
561   The "charset" parameter is used with some media types to define the
562   character set (<xref target="character.sets"/>) of the data. When no explicit charset
563   parameter is provided by the sender, media subtypes of the "text"
564   type are defined to have a default charset value of "ISO-8859-1" when
565   received via HTTP. Data in character sets other than "ISO-8859-1" or
566   its subsets &MUST; be labeled with an appropriate charset value. See
567   <xref target="missing.charset"/> for compatibility problems.
568</t>
569</section>
570
571<section title="Multipart Types" anchor="multipart.types">
572<t>
573   MIME provides for a number of "multipart" types -- encapsulations of
574   one or more entities within a single message-body. All multipart
575   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
576   and &MUST; include a boundary parameter as part of the media type
577   value. The message body is itself a protocol element and &MUST;
578   therefore use only CRLF to represent line breaks between body-parts.
579   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
580   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
581   original multipart contains an epilogue). These restrictions exist in
582   order to preserve the self-delimiting nature of a multipart message-body,
583   wherein the "end" of the message-body is indicated by the
584   ending multipart boundary.
585</t>
586<t>
587   In general, HTTP treats a multipart message-body no differently than
588   any other media type: strictly as payload. The one exception is the
589   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
590   (Partial Content) response.
591   <!-- jre: re-insert removed text pointing to caching? -->
592   In all
593   other cases, an HTTP user agent &SHOULD; follow the same or similar
594   behavior as a MIME user agent would upon receipt of a multipart type.
595   The MIME header fields within each body-part of a multipart message-body
596   do not have any significance to HTTP beyond that defined by
597   their MIME semantics.
598</t>
599<t>
600   In general, an HTTP user agent &SHOULD; follow the same or similar
601   behavior as a MIME user agent would upon receipt of a multipart type.
602   If an application receives an unrecognized multipart subtype, the
603   application &MUST; treat it as being equivalent to "multipart/mixed".
604</t>
605<t><list><t>
606      <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
607      for carrying form data suitable for processing via the POST
608      request method, as described in <xref target="RFC2388"/>.
609</t></list></t>
610</section>
611</section>
612
613<section title="Language Tags" anchor="language.tags">
614  <x:anchor-alias value="language-tag"/>
615  <x:anchor-alias value="primary-tag"/>
616  <x:anchor-alias value="subtag"/>
617<t>
618   A language tag identifies a natural language spoken, written, or
619   otherwise conveyed by human beings for communication of information
620   to other human beings. Computer languages are explicitly excluded.
621   HTTP uses language tags within the Accept-Language and Content-Language
622   fields.
623</t>
624<t>
625   The syntax and registry of HTTP language tags is the same as that
626   defined by <xref target="RFC1766"/>. In summary, a language tag is composed of 1
627   or more parts: A primary language tag and a possibly empty series of
628   subtags:
629</t>
630<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/><iref primary="true" item="Grammar" subitem="primary-tag"/><iref primary="true" item="Grammar" subitem="subtag"/>
631  <x:ref>language-tag</x:ref>  = <x:ref>primary-tag</x:ref> *( "-" <x:ref>subtag</x:ref> )
632  <x:ref>primary-tag</x:ref>   = 1*8<x:ref>ALPHA</x:ref>
633  <x:ref>subtag</x:ref>        = 1*8<x:ref>ALPHA</x:ref>
634</artwork></figure>
635<t>
636   White space is not allowed within the tag and all tags are case-insensitive.
637   The name space of language tags is administered by the
638   IANA. Example tags include:
639</t>
640<figure><artwork type="example">
641  en, en-US, en-cockney, i-cherokee, x-pig-latin
642</artwork></figure>
643<t>
644   where any two-letter primary-tag is an ISO-639 language abbreviation
645   and any two-letter initial subtag is an ISO-3166 country code. (The
646   last three tags above are not registered tags; all but the last are
647   examples of tags which could be registered in future.)
648</t>
649</section>
650</section>
651
652<section title="Entity" anchor="entity">
653<t>
654   Request and Response messages &MAY; transfer an entity if not otherwise
655   restricted by the request method or response status code. An entity
656   consists of entity-header fields and an entity-body, although some
657   responses will only include the entity-headers.
658</t>
659<t>
660   In this section, both sender and recipient refer to either the client
661   or the server, depending on who sends and who receives the entity.
662</t>
663
664<section title="Entity Header Fields" anchor="entity.header.fields">
665  <x:anchor-alias value="entity-header"/>
666  <x:anchor-alias value="extension-header"/>
667<t>
668   Entity-header fields define metainformation about the entity-body or,
669   if no body is present, about the resource identified by the request.
670</t>
671<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
672  <x:ref>entity-header</x:ref>  = <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
673                 / <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
674                 / <x:ref>Content-Length</x:ref>           ; &header-content-length;
675                 / <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
676                 / <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
677                 / <x:ref>Content-Range</x:ref>            ; &header-content-range;
678                 / <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
679                 / <x:ref>Expires</x:ref>                  ; &header-expires;
680                 / <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
681                 / <x:ref>extension-header</x:ref>
682 
683  <x:ref>extension-header</x:ref> = <x:ref>message-header</x:ref>
684</artwork></figure>
685<t>
686   The extension-header mechanism allows additional entity-header fields
687   to be defined without changing the protocol, but these fields cannot
688   be assumed to be recognizable by the recipient. Unrecognized header
689   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
690   transparent proxies.
691</t>
692</section>
693
694<section title="Entity Body" anchor="entity.body">
695  <x:anchor-alias value="entity-body"/>
696<t>
697   The entity-body (if any) sent with an HTTP request or response is in
698   a format and encoding defined by the entity-header fields.
699</t>
700<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
701  <x:ref>entity-body</x:ref>    = *<x:ref>OCTET</x:ref>
702</artwork></figure>
703<t>
704   An entity-body is only present in a message when a message-body is
705   present, as described in &message-body;. The entity-body is obtained
706   from the message-body by decoding any Transfer-Encoding that might
707   have been applied to ensure safe and proper transfer of the message.
708</t>
709
710<section title="Type" anchor="type">
711<t>
712   When an entity-body is included with a message, the data type of that
713   body is determined via the header fields Content-Type and Content-Encoding.
714   These define a two-layer, ordered encoding model:
715</t>
716<figure><artwork type="example">
717  entity-body := Content-Encoding( Content-Type( data ) )
718</artwork></figure>
719<t>
720   Content-Type specifies the media type of the underlying data.
721   Content-Encoding may be used to indicate any additional content
722   codings applied to the data, usually for the purpose of data
723   compression, that are a property of the requested resource. There is
724   no default encoding.
725</t>
726<t>
727   Any HTTP/1.1 message containing an entity-body &SHOULD; include a
728   Content-Type header field defining the media type of that body. If
729   and only if the media type is not given by a Content-Type field, the
730   recipient &MAY; attempt to guess the media type via inspection of its
731   content and/or the name extension(s) of the URI used to identify the
732   resource. If the media type remains unknown, the recipient &SHOULD;
733   treat it as type "application/octet-stream".
734</t>
735</section>
736   
737<section title="Entity Length" anchor="entity.length">
738<t>
739   The entity-length of a message is the length of the message-body
740   before any transfer-codings have been applied. &message-length; defines
741   how the transfer-length of a message-body is determined.
742</t>
743</section>
744</section>
745</section>
746
747<section title="Content Negotiation" anchor="content.negotiation">
748<t>
749   Most HTTP responses include an entity which contains information for
750   interpretation by a human user. Naturally, it is desirable to supply
751   the user with the "best available" entity corresponding to the
752   request. Unfortunately for servers and caches, not all users have the
753   same preferences for what is "best," and not all user agents are
754   equally capable of rendering all entity types. For that reason, HTTP
755   has provisions for several mechanisms for "content negotiation" --
756   the process of selecting the best representation for a given response
757   when there are multiple representations available.
758  <list><t>
759      <x:h>Note:</x:h> This is not called "format negotiation" because the
760      alternate representations may be of the same media type, but use
761      different capabilities of that type, be in different languages,
762      etc.
763  </t></list>
764</t>
765<t>
766   Any response containing an entity-body &MAY; be subject to negotiation,
767   including error responses.
768</t>
769<t>
770   There are two kinds of content negotiation which are possible in
771   HTTP: server-driven and agent-driven negotiation. These two kinds of
772   negotiation are orthogonal and thus may be used separately or in
773   combination. One method of combination, referred to as transparent
774   negotiation, occurs when a cache uses the agent-driven negotiation
775   information provided by the origin server in order to provide
776   server-driven negotiation for subsequent requests.
777</t>
778
779<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
780<t>
781   If the selection of the best representation for a response is made by
782   an algorithm located at the server, it is called server-driven
783   negotiation. Selection is based on the available representations of
784   the response (the dimensions over which it can vary; e.g. language,
785   content-coding, etc.) and the contents of particular header fields in
786   the request message or on other information pertaining to the request
787   (such as the network address of the client).
788</t>
789<t>
790   Server-driven negotiation is advantageous when the algorithm for
791   selecting from among the available representations is difficult to
792   describe to the user agent, or when the server desires to send its
793   "best guess" to the client along with the first response (hoping to
794   avoid the round-trip delay of a subsequent request if the "best
795   guess" is good enough for the user). In order to improve the server's
796   guess, the user agent &MAY; include request header fields (Accept,
797   Accept-Language, Accept-Encoding, etc.) which describe its
798   preferences for such a response.
799</t>
800<t>
801   Server-driven negotiation has disadvantages:
802  <list style="numbers">
803    <t>
804         It is impossible for the server to accurately determine what
805         might be "best" for any given user, since that would require
806         complete knowledge of both the capabilities of the user agent
807         and the intended use for the response (e.g., does the user want
808         to view it on screen or print it on paper?).
809    </t>
810    <t>
811         Having the user agent describe its capabilities in every
812         request can be both very inefficient (given that only a small
813         percentage of responses have multiple representations) and a
814         potential violation of the user's privacy.
815    </t>
816    <t>
817         It complicates the implementation of an origin server and the
818         algorithms for generating responses to a request.
819    </t>
820    <t>
821         It may limit a public cache's ability to use the same response
822         for multiple user's requests.
823    </t>
824  </list>
825</t>
826<t>
827   HTTP/1.1 includes the following request-header fields for enabling
828   server-driven negotiation through description of user agent
829   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
830   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
831   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;). However, an
832   origin server is not limited to these dimensions and &MAY; vary the
833   response based on any aspect of the request, including information
834   outside the request-header fields or within extension header fields
835   not defined by this specification.
836</t>
837<t>
838   The Vary header field (&header-vary;) can be used to express the parameters the
839   server uses to select a representation that is subject to server-driven
840   negotiation.
841</t>
842</section>
843
844<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
845<t>
846   With agent-driven negotiation, selection of the best representation
847   for a response is performed by the user agent after receiving an
848   initial response from the origin server. Selection is based on a list
849   of the available representations of the response included within the
850   header fields or entity-body of the initial response, with each
851   representation identified by its own URI. Selection from among the
852   representations may be performed automatically (if the user agent is
853   capable of doing so) or manually by the user selecting from a
854   generated (possibly hypertext) menu.
855</t>
856<t>
857   Agent-driven negotiation is advantageous when the response would vary
858   over commonly-used dimensions (such as type, language, or encoding),
859   when the origin server is unable to determine a user agent's
860   capabilities from examining the request, and generally when public
861   caches are used to distribute server load and reduce network usage.
862</t>
863<t>
864   Agent-driven negotiation suffers from the disadvantage of needing a
865   second request to obtain the best alternate representation. This
866   second request is only efficient when caching is used. In addition,
867   this specification does not define any mechanism for supporting
868   automatic selection, though it also does not prevent any such
869   mechanism from being developed as an extension and used within
870   HTTP/1.1.
871</t>
872<t>
873   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
874   status codes for enabling agent-driven negotiation when the server is
875   unwilling or unable to provide a varying response using server-driven
876   negotiation.
877</t>
878</section>
879
880<section title="Transparent Negotiation" anchor="transparent.negotiation">
881<t>
882   Transparent negotiation is a combination of both server-driven and
883   agent-driven negotiation. When a cache is supplied with a form of the
884   list of available representations of the response (as in agent-driven
885   negotiation) and the dimensions of variance are completely understood
886   by the cache, then the cache becomes capable of performing server-driven
887   negotiation on behalf of the origin server for subsequent
888   requests on that resource.
889</t>
890<t>
891   Transparent negotiation has the advantage of distributing the
892   negotiation work that would otherwise be required of the origin
893   server and also removing the second request delay of agent-driven
894   negotiation when the cache is able to correctly guess the right
895   response.
896</t>
897<t>
898   This specification does not define any mechanism for transparent
899   negotiation, though it also does not prevent any such mechanism from
900   being developed as an extension that could be used within HTTP/1.1.
901</t>
902</section>
903</section>
904
905<section title="Header Field Definitions" anchor="header.fields">
906<t>
907   This section defines the syntax and semantics of HTTP/1.1 header fields
908   related to the payload of messages.
909</t>
910<t>
911   For entity-header fields, both sender and recipient refer to either the
912   client or the server, depending on who sends and who receives the entity.
913</t>
914
915<section title="Accept" anchor="header.accept">
916  <iref primary="true" item="Accept header" x:for-anchor=""/>
917  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
918  <x:anchor-alias value="Accept"/>
919  <x:anchor-alias value="Accept-v"/>
920  <x:anchor-alias value="accept-ext"/>
921  <x:anchor-alias value="accept-params"/>
922  <x:anchor-alias value="media-range"/>
923<t>
924   The request-header field "Accept" can be used to specify certain media
925   types which are acceptable for the response. Accept headers can be
926   used to indicate that the request is specifically limited to a small
927   set of desired types, as in the case of a request for an in-line
928   image.
929</t>
930<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="Accept-v"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-ext"/>
931  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
932  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
933 
934  <x:ref>media-range</x:ref>    = ( "*/*"
935                   / ( <x:ref>type</x:ref> "/" "*" )
936                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
937                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
938  <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> )
939  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref>
940                   [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
941</artwork></figure>
942<t>
943   The asterisk "*" character is used to group media types into ranges,
944   with "*/*" indicating all media types and "type/*" indicating all
945   subtypes of that type. The media-range &MAY; include media type
946   parameters that are applicable to that range.
947</t>
948<t>
949   Each media-range &MAY; be followed by one or more accept-params,
950   beginning with the "q" parameter for indicating a relative quality
951   factor. The first "q" parameter (if any) separates the media-range
952   parameter(s) from the accept-params. Quality factors allow the user
953   or user agent to indicate the relative degree of preference for that
954   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
955   default value is q=1.
956  <list><t>
957      <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
958      parameters from Accept extension parameters is due to historical
959      practice. Although this prevents any media type parameter named
960      "q" from being used with a media range, such an event is believed
961      to be unlikely given the lack of any "q" parameters in the IANA
962      media type registry and the rare usage of any media type
963      parameters in Accept. Future media types are discouraged from
964      registering any parameter named "q".
965  </t></list>
966</t>
967<t>
968   The example
969</t>
970<figure><artwork type="example">
971  Accept: audio/*; q=0.2, audio/basic
972</artwork></figure>
973<t>
974   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
975   type if it is the best available after an 80% mark-down in quality."
976</t>
977<t>
978   If no Accept header field is present, then it is assumed that the
979   client accepts all media types. If an Accept header field is present,
980   and if the server cannot send a response which is acceptable
981   according to the combined Accept field value, then the server &SHOULD;
982   send a 406 (Not Acceptable) response.
983</t>
984<t>
985   A more elaborate example is
986</t>
987<figure><artwork type="example">
988  Accept: text/plain; q=0.5, text/html,
989          text/x-dvi; q=0.8, text/x-c
990</artwork></figure>
991<t>
992   Verbally, this would be interpreted as "text/html and text/x-c are
993   the preferred media types, but if they do not exist, then send the
994   text/x-dvi entity, and if that does not exist, send the text/plain
995   entity."
996</t>
997<t>
998   Media ranges can be overridden by more specific media ranges or
999   specific media types. If more than one media range applies to a given
1000   type, the most specific reference has precedence. For example,
1001</t>
1002<figure><artwork type="example">
1003  Accept: text/*, text/html, text/html;level=1, */*
1004</artwork></figure>
1005<t>
1006   have the following precedence:
1007   <list style="numbers">
1008    <t>text/html;level=1</t>
1009    <t>text/html</t>
1010    <t>text/*</t>
1011    <t>*/*</t>
1012   </list>
1013</t>
1014<t>
1015   The media type quality factor associated with a given type is
1016   determined by finding the media range with the highest precedence
1017   which matches that type. For example,
1018</t>
1019<figure><artwork type="example">
1020  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1021          text/html;level=2;q=0.4, */*;q=0.5
1022</artwork></figure>
1023<t>
1024   would cause the following values to be associated:
1025</t>
1026<texttable align="left">
1027  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1028  <c>text/html;level=1</c>    <c>1</c>
1029  <c>text/html</c>            <c>0.7</c>
1030  <c>text/plain</c>           <c>0.3</c>
1031  <c>image/jpeg</c>           <c>0.5</c>
1032  <c>text/html;level=2</c>    <c>0.4</c>
1033  <c>text/html;level=3</c>    <c>0.7</c>
1034</texttable>
1035<t>
1036      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1037      values for certain media ranges. However, unless the user agent is
1038      a closed system which cannot interact with other rendering agents,
1039      this default set ought to be configurable by the user.
1040</t>
1041</section>
1042
1043<section title="Accept-Charset" anchor="header.accept-charset">
1044  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1045  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1046  <x:anchor-alias value="Accept-Charset"/>
1047  <x:anchor-alias value="Accept-Charset-v"/>
1048<t>
1049   The request-header field "Accept-Charset" can be used to indicate what
1050   character sets are acceptable for the response. This field allows
1051   clients capable of understanding more comprehensive or special-purpose
1052   character sets to signal that capability to a server which is
1053   capable of representing documents in those character sets.
1054</t>
1055<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
1056  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
1057          <x:ref>Accept-Charset-v</x:ref>
1058  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1059                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1060</artwork></figure>
1061<t>
1062   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1063   be given an associated quality value which represents the user's
1064   preference for that charset. The default value is q=1. An example is
1065</t>
1066<figure><artwork type="example">
1067  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1068</artwork></figure>
1069<t>
1070   The special value "*", if present in the Accept-Charset field,
1071   matches every character set (including ISO-8859-1) which is not
1072   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1073   in an Accept-Charset field, then all character sets not explicitly
1074   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1075   a quality value of 1 if not explicitly mentioned.
1076</t>
1077<t>
1078   If no Accept-Charset header is present, the default is that any
1079   character set is acceptable. If an Accept-Charset header is present,
1080   and if the server cannot send a response which is acceptable
1081   according to the Accept-Charset header, then the server &SHOULD; send
1082   an error response with the 406 (Not Acceptable) status code, though
1083   the sending of an unacceptable response is also allowed.
1084</t>
1085</section>
1086
1087<section title="Accept-Encoding" anchor="header.accept-encoding">
1088  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1089  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1090  <x:anchor-alias value="Accept-Encoding"/>
1091  <x:anchor-alias value="Accept-Encoding-v"/>
1092  <x:anchor-alias value="codings"/>
1093<t>
1094   The request-header field "Accept-Encoding" is similar to Accept, but
1095   restricts the content-codings (<xref target="content.codings"/>) that are acceptable in
1096   the response.
1097</t>
1098<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="Accept-Encoding-v"/><iref primary="true" item="Grammar" subitem="codings"/>
1099  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
1100                     <x:ref>Accept-Encoding-v</x:ref>
1101  <x:ref>Accept-Encoding-v</x:ref>  =
1102                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1103  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
1104</artwork></figure>
1105<t>
1106   Each codings value &MAY; be given an associated quality value which
1107   represents the preference for that encoding. The default value is q=1.
1108</t>
1109<t>
1110   Examples of its use are:
1111</t>
1112<figure><artwork type="example">
1113  Accept-Encoding: compress, gzip
1114  Accept-Encoding:
1115  Accept-Encoding: *
1116  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1117  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1118</artwork></figure>
1119<t>
1120   A server tests whether a content-coding is acceptable, according to
1121   an Accept-Encoding field, using these rules:
1122  <list style="numbers">
1123      <t>If the content-coding is one of the content-codings listed in
1124         the Accept-Encoding field, then it is acceptable, unless it is
1125         accompanied by a qvalue of 0. (As defined in &qvalue;, a
1126         qvalue of 0 means "not acceptable.")</t>
1127
1128      <t>The special "*" symbol in an Accept-Encoding field matches any
1129         available content-coding not explicitly listed in the header
1130         field.</t>
1131
1132      <t>If multiple content-codings are acceptable, then the acceptable
1133         content-coding with the highest non-zero qvalue is preferred.</t>
1134
1135      <t>The "identity" content-coding is always acceptable, unless
1136         specifically refused because the Accept-Encoding field includes
1137         "identity;q=0", or because the field includes "*;q=0" and does
1138         not explicitly include the "identity" content-coding. If the
1139         Accept-Encoding field-value is empty, then only the "identity"
1140         encoding is acceptable.</t>
1141  </list>
1142</t>
1143<t>
1144   If an Accept-Encoding field is present in a request, and if the
1145   server cannot send a response which is acceptable according to the
1146   Accept-Encoding header, then the server &SHOULD; send an error response
1147   with the 406 (Not Acceptable) status code.
1148</t>
1149<t>
1150   If no Accept-Encoding field is present in a request, the server &MAY;
1151   assume that the client will accept any content coding. In this case,
1152   if "identity" is one of the available content-codings, then the
1153   server &SHOULD; use the "identity" content-coding, unless it has
1154   additional information that a different content-coding is meaningful
1155   to the client.
1156  <list><t>
1157      <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1158      and if the "identity" content-coding is unavailable, then
1159      content-codings commonly understood by HTTP/1.0 clients (i.e.,
1160      "gzip" and "compress") are preferred; some older clients
1161      improperly display messages sent with other content-codings.  The
1162      server might also make this decision based on information about
1163      the particular user-agent or client.
1164    </t><t>
1165      <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1166      associated with content-codings. This means that qvalues will not
1167      work and are not permitted with x-gzip or x-compress.
1168    </t></list>
1169</t>
1170</section>
1171
1172<section title="Accept-Language" anchor="header.accept-language">
1173  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1174  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1175  <x:anchor-alias value="Accept-Language"/>
1176  <x:anchor-alias value="Accept-Language-v"/>
1177  <x:anchor-alias value="language-range"/>
1178<t>
1179   The request-header field "Accept-Language" is similar to Accept, but
1180   restricts the set of natural languages that are preferred as a
1181   response to the request. Language tags are defined in <xref target="language.tags"/>.
1182</t>
1183<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="Accept-Language-v"/><iref primary="true" item="Grammar" subitem="language-range"/>
1184  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
1185                    <x:ref>Accept-Language-v</x:ref>
1186  <x:ref>Accept-Language-v</x:ref> =
1187                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1188  <x:ref>language-range</x:ref>    =
1189            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1190</artwork></figure>
1191<t>
1192   Each language-range can be given an associated quality value which
1193   represents an estimate of the user's preference for the languages
1194   specified by that range. The quality value defaults to "q=1". For
1195   example,
1196</t>
1197<figure><artwork type="example">
1198  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1199</artwork></figure>
1200<t>
1201   would mean: "I prefer Danish, but will accept British English and
1202   other types of English."
1203</t>
1204<t>
1205   For matching, the "Basic Filtering" matching scheme, defined in
1206   <xref target="RFC4647" x:sec="3.3.1" x:fmt="of"/>, is used:
1207</t>
1208<x:blockquote cite="http://tools.ietf.org/html/rfc4647#section-3.3.1">
1209  <t>
1210     A language range matches a
1211     particular language tag if, in a case-insensitive comparison, it
1212     exactly equals the tag, or if it exactly equals a prefix of the tag
1213     such that the first character following the prefix is "-".
1214  </t>
1215</x:blockquote> 
1216<t>
1217   The special range "*", if present in the Accept-Language field,
1218   matches every tag not matched by any other range present in the
1219   Accept-Language field.
1220  <list><t>
1221      <x:h>Note:</x:h> This use of a prefix matching rule does not imply that
1222      language tags are assigned to languages in such a way that it is
1223      always true that if a user understands a language with a certain
1224      tag, then this user will also understand all languages with tags
1225      for which this tag is a prefix. The prefix rule simply allows the
1226      use of prefix tags if this is the case.
1227  </t></list>
1228</t>
1229<t>
1230   The language quality factor assigned to a language-tag by the
1231   Accept-Language field is the quality value of the longest language-range
1232   in the field that matches the language-tag. If no language-range
1233   in the field matches the tag, the language quality factor
1234   assigned is 0. If no Accept-Language header is present in the
1235   request, the server
1236   &SHOULD; assume that all languages are equally acceptable. If an
1237   Accept-Language header is present, then all languages which are
1238   assigned a quality factor greater than 0 are acceptable.
1239</t>
1240<t>
1241   It might be contrary to the privacy expectations of the user to send
1242   an Accept-Language header with the complete linguistic preferences of
1243   the user in every request. For a discussion of this issue, see
1244   <xref target="privacy.issues.connected.to.accept.headers"/>.
1245</t>
1246<t>
1247   As intelligibility is highly dependent on the individual user, it is
1248   recommended that client applications make the choice of linguistic
1249   preference available to the user. If the choice is not made
1250   available, then the Accept-Language header field &MUST-NOT; be given in
1251   the request.
1252  <list><t>
1253      <x:h>Note:</x:h> When making the choice of linguistic preference available to
1254      the user, we remind implementors of  the fact that users are not
1255      familiar with the details of language matching as described above,
1256      and should provide appropriate guidance. As an example, users
1257      might assume that on selecting "en-gb", they will be served any
1258      kind of English document if British English is not available. A
1259      user agent might suggest in such a case to add "en" to get the
1260      best matching behavior.
1261  </t></list>
1262</t>
1263</section>
1264
1265<section title="Content-Encoding" anchor="header.content-encoding">
1266  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1267  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1268  <x:anchor-alias value="Content-Encoding"/>
1269  <x:anchor-alias value="Content-Encoding-v"/>
1270<t>
1271   The entity-header field "Content-Encoding" is used as a modifier to the
1272   media-type. When present, its value indicates what additional content
1273   codings have been applied to the entity-body, and thus what decoding
1274   mechanisms must be applied in order to obtain the media-type
1275   referenced by the Content-Type header field. Content-Encoding is
1276   primarily used to allow a document to be compressed without losing
1277   the identity of its underlying media type.
1278</t>
1279<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
1280  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
1281  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1282</artwork></figure>
1283<t>
1284   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1285</t>
1286<figure><artwork type="example">
1287  Content-Encoding: gzip
1288</artwork></figure>
1289<t>
1290   The content-coding is a characteristic of the entity identified by
1291   the request-target. Typically, the entity-body is stored with this
1292   encoding and is only decoded before rendering or analogous usage.
1293   However, a non-transparent proxy &MAY; modify the content-coding if the
1294   new coding is known to be acceptable to the recipient, unless the
1295   "no-transform" cache-control directive is present in the message.
1296</t>
1297<t>
1298   If the content-coding of an entity is not "identity", then the
1299   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1300   that lists the non-identity content-coding(s) used.
1301</t>
1302<t>
1303   If the content-coding of an entity in a request message is not
1304   acceptable to the origin server, the server &SHOULD; respond with a
1305   status code of 415 (Unsupported Media Type).
1306</t>
1307<t>
1308   If multiple encodings have been applied to an entity, the content
1309   codings &MUST; be listed in the order in which they were applied.
1310   Additional information about the encoding parameters &MAY; be provided
1311   by other entity-header fields not defined by this specification.
1312</t>
1313</section>
1314
1315<section title="Content-Language" anchor="header.content-language">
1316  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1317  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1318  <x:anchor-alias value="Content-Language"/>
1319  <x:anchor-alias value="Content-Language-v"/>
1320<t>
1321   The entity-header field "Content-Language" describes the natural
1322   language(s) of the intended audience for the enclosed entity. Note
1323   that this might not be equivalent to all the languages used within
1324   the entity-body.
1325</t>
1326<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
1327  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
1328  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1329</artwork></figure>
1330<t>
1331   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1332   Content-Language is to allow a user to identify and differentiate
1333   entities according to the user's own preferred language. Thus, if the
1334   body content is intended only for a Danish-literate audience, the
1335   appropriate field is
1336</t>
1337<figure><artwork type="example">
1338  Content-Language: da
1339</artwork></figure>
1340<t>
1341   If no Content-Language is specified, the default is that the content
1342   is intended for all language audiences. This might mean that the
1343   sender does not consider it to be specific to any natural language,
1344   or that the sender does not know for which language it is intended.
1345</t>
1346<t>
1347   Multiple languages &MAY; be listed for content that is intended for
1348   multiple audiences. For example, a rendition of the "Treaty of
1349   Waitangi," presented simultaneously in the original Maori and English
1350   versions, would call for
1351</t>
1352<figure><artwork type="example">
1353  Content-Language: mi, en
1354</artwork></figure>
1355<t>
1356   However, just because multiple languages are present within an entity
1357   does not mean that it is intended for multiple linguistic audiences.
1358   An example would be a beginner's language primer, such as "A First
1359   Lesson in Latin," which is clearly intended to be used by an
1360   English-literate audience. In this case, the Content-Language would
1361   properly only include "en".
1362</t>
1363<t>
1364   Content-Language &MAY; be applied to any media type -- it is not
1365   limited to textual documents.
1366</t>
1367</section>
1368
1369<section title="Content-Location" anchor="header.content-location">
1370  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1371  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1372  <x:anchor-alias value="Content-Location"/>
1373  <x:anchor-alias value="Content-Location-v"/>
1374<t>
1375   The entity-header field "Content-Location" &MAY; be used to supply the
1376   resource location for the entity enclosed in the message when that
1377   entity is accessible from a location separate from the requested
1378   resource's URI. A server &SHOULD; provide a Content-Location for the
1379   variant corresponding to the response entity; especially in the case
1380   where a resource has multiple entities associated with it, and those
1381   entities actually have separate locations by which they might be
1382   individually accessed, the server &SHOULD; provide a Content-Location
1383   for the particular variant which is returned.
1384</t>
1385<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
1386  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
1387                    <x:ref>Content-Location-v</x:ref>
1388  <x:ref>Content-Location-v</x:ref> =
1389                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1390</artwork></figure>
1391<t>
1392   The value of Content-Location also defines the base URI for the
1393   entity.
1394</t>
1395<t>
1396   The Content-Location value is not a replacement for the original
1397   requested URI; it is only a statement of the location of the resource
1398   corresponding to this particular entity at the time of the request.
1399   Future requests &MAY; specify the Content-Location URI as the request-target
1400   if the desire is to identify the source of that particular
1401   entity.
1402</t>
1403<t>
1404   A cache cannot assume that an entity with a Content-Location
1405   different from the URI used to retrieve it can be used to respond to
1406   later requests on that Content-Location URI. However, the Content-Location
1407   can be used to differentiate between multiple entities
1408   retrieved from a single requested resource, as described in &caching-neg-resp;.
1409</t>
1410<t>
1411   If the Content-Location is a relative URI, the relative URI is
1412   interpreted relative to the request-target.
1413</t>
1414<t>
1415   The meaning of the Content-Location header in PUT or POST requests is
1416   undefined; servers are free to ignore it in those cases.
1417</t>
1418</section>
1419
1420<section title="Content-MD5" anchor="header.content-md5">
1421  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1422  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1423  <x:anchor-alias value="Content-MD5"/>
1424  <x:anchor-alias value="Content-MD5-v"/>
1425<t>
1426   The entity-header field "Content-MD5", as defined in <xref target="RFC1864"/>, is
1427   an MD5 digest of the entity-body for the purpose of providing an
1428   end-to-end message integrity check (MIC) of the entity-body. (Note: a
1429   MIC is good for detecting accidental modification of the entity-body
1430   in transit, but is not proof against malicious attacks.)
1431</t>
1432<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
1433  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
1434  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1435</artwork></figure>
1436<t>
1437   The Content-MD5 header field &MAY; be generated by an origin server or
1438   client to function as an integrity check of the entity-body. Only
1439   origin servers or clients &MAY; generate the Content-MD5 header field;
1440   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1441   value as an end-to-end integrity check. Any recipient of the entity-body,
1442   including gateways and proxies, &MAY; check that the digest value
1443   in this header field matches that of the entity-body as received.
1444</t>
1445<t>
1446   The MD5 digest is computed based on the content of the entity-body,
1447   including any content-coding that has been applied, but not including
1448   any transfer-encoding applied to the message-body. If the message is
1449   received with a transfer-encoding, that encoding &MUST; be removed
1450   prior to checking the Content-MD5 value against the received entity.
1451</t>
1452<t>
1453   This has the result that the digest is computed on the octets of the
1454   entity-body exactly as, and in the order that, they would be sent if
1455   no transfer-encoding were being applied.
1456</t>
1457<t>
1458   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1459   composite media-types (e.g., multipart/* and message/rfc822), but
1460   this does not change how the digest is computed as defined in the
1461   preceding paragraph.
1462</t>
1463<t>
1464   There are several consequences of this. The entity-body for composite
1465   types &MAY; contain many body-parts, each with its own MIME and HTTP
1466   headers (including Content-MD5, Content-Transfer-Encoding, and
1467   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1468   or Content-Encoding header, it is assumed that the content
1469   of the body-part has had the encoding applied, and the body-part is
1470   included in the Content-MD5 digest as is -- i.e., after the
1471   application. The Transfer-Encoding header field is not allowed within
1472   body-parts.
1473</t>
1474<t>
1475   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1476   computing or checking the digest: the line break convention used in
1477   the text actually transmitted &MUST; be left unaltered when computing
1478   the digest.
1479  <list><t>
1480      <x:h>Note:</x:h> while the definition of Content-MD5 is exactly the same for
1481      HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1482      in which the application of Content-MD5 to HTTP entity-bodies
1483      differs from its application to MIME entity-bodies. One is that
1484      HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1485      does use Transfer-Encoding and Content-Encoding. Another is that
1486      HTTP more frequently uses binary content types than MIME, so it is
1487      worth noting that, in such cases, the byte order used to compute
1488      the digest is the transmission byte order defined for the type.
1489      Lastly, HTTP allows transmission of text types with any of several
1490      line break conventions and not just the canonical form using CRLF.
1491  </t></list>
1492</t>
1493</section>
1494
1495<section title="Content-Type" anchor="header.content-type">
1496  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1497  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1498  <x:anchor-alias value="Content-Type"/>
1499  <x:anchor-alias value="Content-Type-v"/>
1500<t>
1501   The entity-header field "Content-Type" indicates the media type of the
1502   entity-body sent to the recipient or, in the case of the HEAD method,
1503   the media type that would have been sent had the request been a GET.
1504</t>
1505<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
1506  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
1507  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1508</artwork></figure>
1509<t>
1510   Media types are defined in <xref target="media.types"/>. An example of the field is
1511</t>
1512<figure><artwork type="example">
1513  Content-Type: text/html; charset=ISO-8859-4
1514</artwork></figure>
1515<t>
1516   Further discussion of methods for identifying the media type of an
1517   entity is provided in <xref target="type"/>.
1518</t>
1519</section>
1520
1521</section>
1522
1523<section title="IANA Considerations" anchor="IANA.considerations">
1524<section title="Message Header Registration" anchor="message.header.registration">
1525<t>
1526   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
1527   with the permanent registrations below (see <xref target="RFC3864"/>):
1528</t>
1529<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1530<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1531   <ttcol>Header Field Name</ttcol>
1532   <ttcol>Protocol</ttcol>
1533   <ttcol>Status</ttcol>
1534   <ttcol>Reference</ttcol>
1535
1536   <c>Accept</c>
1537   <c>http</c>
1538   <c>standard</c>
1539   <c>
1540      <xref target="header.accept"/>
1541   </c>
1542   <c>Accept-Charset</c>
1543   <c>http</c>
1544   <c>standard</c>
1545   <c>
1546      <xref target="header.accept-charset"/>
1547   </c>
1548   <c>Accept-Encoding</c>
1549   <c>http</c>
1550   <c>standard</c>
1551   <c>
1552      <xref target="header.accept-encoding"/>
1553   </c>
1554   <c>Accept-Language</c>
1555   <c>http</c>
1556   <c>standard</c>
1557   <c>
1558      <xref target="header.accept-language"/>
1559   </c>
1560   <c>Content-Disposition</c>
1561   <c>http</c>
1562   <c/>
1563   <c>
1564      <xref target="content-disposition"/>
1565   </c>
1566   <c>Content-Encoding</c>
1567   <c>http</c>
1568   <c>standard</c>
1569   <c>
1570      <xref target="header.content-encoding"/>
1571   </c>
1572   <c>Content-Language</c>
1573   <c>http</c>
1574   <c>standard</c>
1575   <c>
1576      <xref target="header.content-language"/>
1577   </c>
1578   <c>Content-Location</c>
1579   <c>http</c>
1580   <c>standard</c>
1581   <c>
1582      <xref target="header.content-location"/>
1583   </c>
1584   <c>Content-MD5</c>
1585   <c>http</c>
1586   <c>standard</c>
1587   <c>
1588      <xref target="header.content-md5"/>
1589   </c>
1590   <c>Content-Type</c>
1591   <c>http</c>
1592   <c>standard</c>
1593   <c>
1594      <xref target="header.content-type"/>
1595   </c>
1596   <c>MIME-Version</c>
1597   <c>http</c>
1598   <c/>
1599   <c>
1600      <xref target="mime-version"/>
1601   </c>
1602</texttable>
1603<!--(END)-->
1604<t>
1605   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1606</t>
1607</section>
1608</section>
1609
1610<section title="Security Considerations" anchor="security.considerations">
1611<t>
1612   This section is meant to inform application developers, information
1613   providers, and users of the security limitations in HTTP/1.1 as
1614   described by this document. The discussion does not include
1615   definitive solutions to the problems revealed, though it does make
1616   some suggestions for reducing security risks.
1617</t>
1618
1619<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1620<t>
1621   Accept request-headers can reveal information about the user to all
1622   servers which are accessed. The Accept-Language header in particular
1623   can reveal information the user would consider to be of a private
1624   nature, because the understanding of particular languages is often
1625   strongly correlated to the membership of a particular ethnic group.
1626   User agents which offer the option to configure the contents of an
1627   Accept-Language header to be sent in every request are strongly
1628   encouraged to let the configuration process include a message which
1629   makes the user aware of the loss of privacy involved.
1630</t>
1631<t>
1632   An approach that limits the loss of privacy would be for a user agent
1633   to omit the sending of Accept-Language headers by default, and to ask
1634   the user whether or not to start sending Accept-Language headers to a
1635   server if it detects, by looking for any Vary response-header fields
1636   generated by the server, that such sending could improve the quality
1637   of service.
1638</t>
1639<t>
1640   Elaborate user-customized accept header fields sent in every request,
1641   in particular if these include quality values, can be used by servers
1642   as relatively reliable and long-lived user identifiers. Such user
1643   identifiers would allow content providers to do click-trail tracking,
1644   and would allow collaborating content providers to match cross-server
1645   click-trails or form submissions of individual users. Note that for
1646   many users not behind a proxy, the network address of the host
1647   running the user agent will also serve as a long-lived user
1648   identifier. In environments where proxies are used to enhance
1649   privacy, user agents ought to be conservative in offering accept
1650   header configuration options to end users. As an extreme privacy
1651   measure, proxies could filter the accept headers in relayed requests.
1652   General purpose user agents which provide a high degree of header
1653   configurability &SHOULD; warn users about the loss of privacy which can
1654   be involved.
1655</t>
1656</section>
1657
1658<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1659<t>
1660   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
1661   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1662   serious security considerations. Content-Disposition is not part of
1663   the HTTP standard, but since it is widely implemented, we are
1664   documenting its use and risks for implementors. See <xref target="RFC2183" x:fmt="of" x:sec="5"/>
1665   for details.
1666</t>
1667</section>
1668
1669</section>
1670
1671<section title="Acknowledgments" anchor="ack">
1672</section>
1673</middle>
1674<back>
1675
1676<references title="Normative References">
1677
1678<reference anchor="ISO-8859-1">
1679  <front>
1680    <title>
1681     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1682    </title>
1683    <author>
1684      <organization>International Organization for Standardization</organization>
1685    </author>
1686    <date year="1998"/>
1687  </front>
1688  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1689</reference>
1690
1691<reference anchor="Part1">
1692  <front>
1693    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1694    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1695      <organization abbrev="Day Software">Day Software</organization>
1696      <address><email>fielding@gbiv.com</email></address>
1697    </author>
1698    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1699      <organization>One Laptop per Child</organization>
1700      <address><email>jg@laptop.org</email></address>
1701    </author>
1702    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1703      <organization abbrev="HP">Hewlett-Packard Company</organization>
1704      <address><email>JeffMogul@acm.org</email></address>
1705    </author>
1706    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1707      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1708      <address><email>henrikn@microsoft.com</email></address>
1709    </author>
1710    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1711      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1712      <address><email>LMM@acm.org</email></address>
1713    </author>
1714    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1715      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1716      <address><email>paulle@microsoft.com</email></address>
1717    </author>
1718    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1719      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1720      <address><email>timbl@w3.org</email></address>
1721    </author>
1722    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1723      <organization abbrev="W3C">World Wide Web Consortium</organization>
1724      <address><email>ylafon@w3.org</email></address>
1725    </author>
1726    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1727      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1728      <address><email>julian.reschke@greenbytes.de</email></address>
1729    </author>
1730    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1731  </front>
1732  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1733  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1734</reference>
1735
1736<reference anchor="Part2">
1737  <front>
1738    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1739    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1740      <organization abbrev="Day Software">Day Software</organization>
1741      <address><email>fielding@gbiv.com</email></address>
1742    </author>
1743    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1744      <organization>One Laptop per Child</organization>
1745      <address><email>jg@laptop.org</email></address>
1746    </author>
1747    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1748      <organization abbrev="HP">Hewlett-Packard Company</organization>
1749      <address><email>JeffMogul@acm.org</email></address>
1750    </author>
1751    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1752      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1753      <address><email>henrikn@microsoft.com</email></address>
1754    </author>
1755    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1756      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1757      <address><email>LMM@acm.org</email></address>
1758    </author>
1759    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1760      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1761      <address><email>paulle@microsoft.com</email></address>
1762    </author>
1763    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1764      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1765      <address><email>timbl@w3.org</email></address>
1766    </author>
1767    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1768      <organization abbrev="W3C">World Wide Web Consortium</organization>
1769      <address><email>ylafon@w3.org</email></address>
1770    </author>
1771    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1772      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1773      <address><email>julian.reschke@greenbytes.de</email></address>
1774    </author>
1775    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1776  </front>
1777  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1778  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1779</reference>
1780
1781<reference anchor="Part4">
1782  <front>
1783    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1784    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1785      <organization abbrev="Day Software">Day Software</organization>
1786      <address><email>fielding@gbiv.com</email></address>
1787    </author>
1788    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1789      <organization>One Laptop per Child</organization>
1790      <address><email>jg@laptop.org</email></address>
1791    </author>
1792    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1793      <organization abbrev="HP">Hewlett-Packard Company</organization>
1794      <address><email>JeffMogul@acm.org</email></address>
1795    </author>
1796    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1797      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1798      <address><email>henrikn@microsoft.com</email></address>
1799    </author>
1800    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1801      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1802      <address><email>LMM@acm.org</email></address>
1803    </author>
1804    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1805      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1806      <address><email>paulle@microsoft.com</email></address>
1807    </author>
1808    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1809      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1810      <address><email>timbl@w3.org</email></address>
1811    </author>
1812    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1813      <organization abbrev="W3C">World Wide Web Consortium</organization>
1814      <address><email>ylafon@w3.org</email></address>
1815    </author>
1816    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1817      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1818      <address><email>julian.reschke@greenbytes.de</email></address>
1819    </author>
1820    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1821  </front>
1822  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1823  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1824</reference>
1825
1826<reference anchor="Part5">
1827  <front>
1828    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1829    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1830      <organization abbrev="Day Software">Day Software</organization>
1831      <address><email>fielding@gbiv.com</email></address>
1832    </author>
1833    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1834      <organization>One Laptop per Child</organization>
1835      <address><email>jg@laptop.org</email></address>
1836    </author>
1837    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1838      <organization abbrev="HP">Hewlett-Packard Company</organization>
1839      <address><email>JeffMogul@acm.org</email></address>
1840    </author>
1841    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1842      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1843      <address><email>henrikn@microsoft.com</email></address>
1844    </author>
1845    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1846      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1847      <address><email>LMM@acm.org</email></address>
1848    </author>
1849    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1850      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1851      <address><email>paulle@microsoft.com</email></address>
1852    </author>
1853    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1854      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1855      <address><email>timbl@w3.org</email></address>
1856    </author>
1857    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1858      <organization abbrev="W3C">World Wide Web Consortium</organization>
1859      <address><email>ylafon@w3.org</email></address>
1860    </author>
1861    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1862      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1863      <address><email>julian.reschke@greenbytes.de</email></address>
1864    </author>
1865    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1866  </front>
1867  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1868  <x:source href="p5-range.xml" basename="p5-range"/>
1869</reference>
1870
1871<reference anchor="Part6">
1872  <front>
1873    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1874    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1875      <organization abbrev="Day Software">Day Software</organization>
1876      <address><email>fielding@gbiv.com</email></address>
1877    </author>
1878    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1879      <organization>One Laptop per Child</organization>
1880      <address><email>jg@laptop.org</email></address>
1881    </author>
1882    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1883      <organization abbrev="HP">Hewlett-Packard Company</organization>
1884      <address><email>JeffMogul@acm.org</email></address>
1885    </author>
1886    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1887      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1888      <address><email>henrikn@microsoft.com</email></address>
1889    </author>
1890    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1891      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1892      <address><email>LMM@acm.org</email></address>
1893    </author>
1894    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1895      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1896      <address><email>paulle@microsoft.com</email></address>
1897    </author>
1898    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1899      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1900      <address><email>timbl@w3.org</email></address>
1901    </author>
1902    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1903      <organization abbrev="W3C">World Wide Web Consortium</organization>
1904      <address><email>ylafon@w3.org</email></address>
1905    </author>
1906    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1907      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1908      <address><email>julian.reschke@greenbytes.de</email></address>
1909    </author>
1910    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1911  </front>
1912  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1913  <x:source href="p6-cache.xml" basename="p6-cache"/>
1914</reference>
1915
1916<reference anchor="RFC1766">
1917  <front>
1918    <title abbrev="Language Tag">Tags for the Identification of Languages</title>
1919    <author initials="H." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
1920      <organization>UNINETT</organization>
1921      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
1922    </author>
1923    <date month="March" year="1995"/>
1924  </front>
1925  <seriesInfo name="RFC" value="1766"/>
1926</reference>
1927
1928<reference anchor="RFC1864">
1929  <front>
1930    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1931    <author initials="J." surname="Myers" fullname="John G. Myers">
1932      <organization>Carnegie Mellon University</organization>
1933      <address><email>jgm+@cmu.edu</email></address>
1934    </author>
1935    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
1936      <organization>Dover Beach Consulting, Inc.</organization>
1937      <address><email>mrose@dbc.mtview.ca.us</email></address>
1938    </author>
1939    <date month="October" year="1995"/>
1940  </front>
1941  <seriesInfo name="RFC" value="1864"/>
1942</reference>
1943
1944<reference anchor="RFC1950">
1945  <front>
1946    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1947    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1948      <organization>Aladdin Enterprises</organization>
1949      <address><email>ghost@aladdin.com</email></address>
1950    </author>
1951    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1952      <organization/>
1953    </author>
1954    <date month="May" year="1996"/>
1955  </front>
1956  <seriesInfo name="RFC" value="1950"/>
1957  <annotation>
1958    RFC 1950 is an Informational RFC, thus it may be less stable than
1959    this specification. On the other hand, this downward reference was
1960    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1961    therefore it is unlikely to cause problems in practice. See also
1962    <xref target="BCP97"/>.
1963  </annotation>
1964</reference>
1965
1966<reference anchor="RFC1951">
1967  <front>
1968    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1969    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1970      <organization>Aladdin Enterprises</organization>
1971      <address><email>ghost@aladdin.com</email></address>
1972    </author>
1973    <date month="May" year="1996"/>
1974  </front>
1975  <seriesInfo name="RFC" value="1951"/>
1976  <annotation>
1977    RFC 1951 is an Informational RFC, thus it may be less stable than
1978    this specification. On the other hand, this downward reference was
1979    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1980    therefore it is unlikely to cause problems in practice. See also
1981    <xref target="BCP97"/>.
1982  </annotation>
1983</reference>
1984
1985<reference anchor="RFC1952">
1986  <front>
1987    <title>GZIP file format specification version 4.3</title>
1988    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1989      <organization>Aladdin Enterprises</organization>
1990      <address><email>ghost@aladdin.com</email></address>
1991    </author>
1992    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1993      <organization/>
1994      <address><email>gzip@prep.ai.mit.edu</email></address>
1995    </author>
1996    <author initials="M." surname="Adler" fullname="Mark Adler">
1997      <organization/>
1998      <address><email>madler@alumni.caltech.edu</email></address>
1999    </author>
2000    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2001      <organization/>
2002      <address><email>ghost@aladdin.com</email></address>
2003    </author>
2004    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2005      <organization/>
2006      <address><email>randeg@alumni.rpi.edu</email></address>
2007    </author>
2008    <date month="May" year="1996"/>
2009  </front>
2010  <seriesInfo name="RFC" value="1952"/>
2011  <annotation>
2012    RFC 1952 is an Informational RFC, thus it may 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="RFC2045">
2021  <front>
2022    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2023    <author initials="N." surname="Freed" fullname="Ned Freed">
2024      <organization>Innosoft International, Inc.</organization>
2025      <address><email>ned@innosoft.com</email></address>
2026    </author>
2027    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2028      <organization>First Virtual Holdings</organization>
2029      <address><email>nsb@nsb.fv.com</email></address>
2030    </author>
2031    <date month="November" year="1996"/>
2032  </front>
2033  <seriesInfo name="RFC" value="2045"/>
2034</reference>
2035
2036<reference anchor="RFC2046">
2037  <front>
2038    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2039    <author initials="N." surname="Freed" fullname="Ned Freed">
2040      <organization>Innosoft International, Inc.</organization>
2041      <address><email>ned@innosoft.com</email></address>
2042    </author>
2043    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2044      <organization>First Virtual Holdings</organization>
2045      <address><email>nsb@nsb.fv.com</email></address>
2046    </author>
2047    <date month="November" year="1996"/>
2048  </front>
2049  <seriesInfo name="RFC" value="2046"/>
2050</reference>
2051
2052<reference anchor="RFC2119">
2053  <front>
2054    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2055    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2056      <organization>Harvard University</organization>
2057      <address><email>sob@harvard.edu</email></address>
2058    </author>
2059    <date month="March" year="1997"/>
2060  </front>
2061  <seriesInfo name="BCP" value="14"/>
2062  <seriesInfo name="RFC" value="2119"/>
2063</reference>
2064
2065<reference anchor='RFC4647'>
2066  <front>
2067    <title>Matching of Language Tags</title>
2068    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2069      <organization>Yahoo! Inc.</organization>
2070      <address><email>addison@inter-locale.com</email></address>
2071    </author>
2072    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2073      <organization>Google</organization>
2074      <address><email>mark.davis@macchiato.com</email></address>
2075    </author>
2076    <date year='2006' month='September' />
2077  </front>
2078  <seriesInfo name='BCP' value='47' />
2079  <seriesInfo name='RFC' value='4647' />
2080</reference>
2081
2082<reference anchor="RFC5234">
2083  <front>
2084    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2085    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2086      <organization>Brandenburg InternetWorking</organization>
2087      <address>
2088      <postal>
2089      <street>675 Spruce Dr.</street>
2090      <city>Sunnyvale</city>
2091      <region>CA</region>
2092      <code>94086</code>
2093      <country>US</country></postal>
2094      <phone>+1.408.246.8253</phone>
2095      <email>dcrocker@bbiw.net</email></address> 
2096    </author>
2097    <author initials="P." surname="Overell" fullname="Paul Overell">
2098      <organization>THUS plc.</organization>
2099      <address>
2100      <postal>
2101      <street>1/2 Berkeley Square</street>
2102      <street>99 Berkely Street</street>
2103      <city>Glasgow</city>
2104      <code>G3 7HR</code>
2105      <country>UK</country></postal>
2106      <email>paul.overell@thus.net</email></address>
2107    </author>
2108    <date month="January" year="2008"/>
2109  </front>
2110  <seriesInfo name="STD" value="68"/>
2111  <seriesInfo name="RFC" value="5234"/>
2112</reference>
2113
2114</references>
2115
2116<references title="Informative References">
2117
2118<reference anchor="RFC1945">
2119  <front>
2120    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2121    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2122      <organization>MIT, Laboratory for Computer Science</organization>
2123      <address><email>timbl@w3.org</email></address>
2124    </author>
2125    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2126      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2127      <address><email>fielding@ics.uci.edu</email></address>
2128    </author>
2129    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2130      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2131      <address><email>frystyk@w3.org</email></address>
2132    </author>
2133    <date month="May" year="1996"/>
2134  </front>
2135  <seriesInfo name="RFC" value="1945"/>
2136</reference>
2137
2138<reference anchor="RFC2049">
2139  <front>
2140    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2141    <author initials="N." surname="Freed" fullname="Ned Freed">
2142      <organization>Innosoft International, Inc.</organization>
2143      <address><email>ned@innosoft.com</email></address>
2144    </author>
2145    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2146      <organization>First Virtual Holdings</organization>
2147      <address><email>nsb@nsb.fv.com</email></address>
2148    </author>
2149    <date month="November" year="1996"/>
2150  </front>
2151  <seriesInfo name="RFC" value="2049"/>
2152</reference>
2153
2154<reference anchor="RFC2068">
2155  <front>
2156    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2157    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2158      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2159      <address><email>fielding@ics.uci.edu</email></address>
2160    </author>
2161    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2162      <organization>MIT Laboratory for Computer Science</organization>
2163      <address><email>jg@w3.org</email></address>
2164    </author>
2165    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2166      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2167      <address><email>mogul@wrl.dec.com</email></address>
2168    </author>
2169    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2170      <organization>MIT Laboratory for Computer Science</organization>
2171      <address><email>frystyk@w3.org</email></address>
2172    </author>
2173    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2174      <organization>MIT Laboratory for Computer Science</organization>
2175      <address><email>timbl@w3.org</email></address>
2176    </author>
2177    <date month="January" year="1997"/>
2178  </front>
2179  <seriesInfo name="RFC" value="2068"/>
2180</reference>
2181
2182<reference anchor="RFC2076">
2183  <front>
2184    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2185    <author initials="J." surname="Palme" fullname="Jacob Palme">
2186      <organization>Stockholm University/KTH</organization>
2187      <address><email>jpalme@dsv.su.se</email></address>
2188    </author>
2189    <date month="February" year="1997"/>
2190  </front>
2191  <seriesInfo name="RFC" value="2076"/>
2192</reference>
2193
2194<reference anchor="RFC2183">
2195  <front>
2196    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2197    <author initials="R." surname="Troost" fullname="Rens Troost">
2198      <organization>New Century Systems</organization>
2199      <address><email>rens@century.com</email></address>
2200    </author>
2201    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2202      <organization>QUALCOMM Incorporated</organization>
2203      <address><email>sdorner@qualcomm.com</email></address>
2204    </author>
2205    <author initials="K." surname="Moore" fullname="Keith Moore">
2206      <organization>Department of Computer Science</organization>
2207      <address><email>moore@cs.utk.edu</email></address>
2208    </author>
2209    <date month="August" year="1997"/>
2210  </front>
2211  <seriesInfo name="RFC" value="2183"/>
2212</reference>
2213
2214<reference anchor="RFC2277">
2215  <front>
2216    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2217    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2218      <organization>UNINETT</organization>
2219      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2220    </author>
2221    <date month="January" year="1998"/>
2222  </front>
2223  <seriesInfo name="BCP" value="18"/>
2224  <seriesInfo name="RFC" value="2277"/>
2225</reference>
2226
2227<reference anchor="RFC2388">
2228  <front>
2229    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2230    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2231      <organization>Xerox Palo Alto Research Center</organization>
2232      <address><email>masinter@parc.xerox.com</email></address>
2233    </author>
2234    <date year="1998" month="August"/>
2235  </front>
2236  <seriesInfo name="RFC" value="2388"/>
2237</reference>
2238
2239<reference anchor="RFC2557">
2240  <front>
2241    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2242    <author initials="F." surname="Palme" fullname="Jacob Palme">
2243      <organization>Stockholm University and KTH</organization>
2244      <address><email>jpalme@dsv.su.se</email></address>
2245    </author>
2246    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2247      <organization>Microsoft Corporation</organization>
2248      <address><email>alexhop@microsoft.com</email></address>
2249    </author>
2250    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2251      <organization>Lotus Development Corporation</organization>
2252      <address><email>Shelness@lotus.com</email></address>
2253    </author>
2254    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2255      <organization/>
2256      <address><email>stef@nma.com</email></address>
2257    </author>
2258    <date year="1999" month="March"/>
2259  </front>
2260  <seriesInfo name="RFC" value="2557"/>
2261</reference>
2262
2263<reference anchor="RFC2616">
2264  <front>
2265    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2266    <author initials="R." surname="Fielding" fullname="R. Fielding">
2267      <organization>University of California, Irvine</organization>
2268      <address><email>fielding@ics.uci.edu</email></address>
2269    </author>
2270    <author initials="J." surname="Gettys" fullname="J. Gettys">
2271      <organization>W3C</organization>
2272      <address><email>jg@w3.org</email></address>
2273    </author>
2274    <author initials="J." surname="Mogul" fullname="J. Mogul">
2275      <organization>Compaq Computer Corporation</organization>
2276      <address><email>mogul@wrl.dec.com</email></address>
2277    </author>
2278    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2279      <organization>MIT Laboratory for Computer Science</organization>
2280      <address><email>frystyk@w3.org</email></address>
2281    </author>
2282    <author initials="L." surname="Masinter" fullname="L. Masinter">
2283      <organization>Xerox Corporation</organization>
2284      <address><email>masinter@parc.xerox.com</email></address>
2285    </author>
2286    <author initials="P." surname="Leach" fullname="P. Leach">
2287      <organization>Microsoft Corporation</organization>
2288      <address><email>paulle@microsoft.com</email></address>
2289    </author>
2290    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2291      <organization>W3C</organization>
2292      <address><email>timbl@w3.org</email></address>
2293    </author>
2294    <date month="June" year="1999"/>
2295  </front>
2296  <seriesInfo name="RFC" value="2616"/>
2297</reference>
2298
2299<reference anchor="RFC3629">
2300  <front>
2301    <title>UTF-8, a transformation format of ISO 10646</title>
2302    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2303      <organization>Alis Technologies</organization>
2304      <address><email>fyergeau@alis.com</email></address>
2305    </author>
2306    <date month="November" year="2003"/>
2307  </front>
2308  <seriesInfo name="RFC" value="3629"/>
2309  <seriesInfo name="STD" value="63"/>
2310</reference>
2311
2312<reference anchor='RFC3864'>
2313  <front>
2314    <title>Registration Procedures for Message Header Fields</title>
2315    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2316      <organization>Nine by Nine</organization>
2317      <address><email>GK-IETF@ninebynine.org</email></address>
2318    </author>
2319    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2320      <organization>BEA Systems</organization>
2321      <address><email>mnot@pobox.com</email></address>
2322    </author>
2323    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2324      <organization>HP Labs</organization>
2325      <address><email>JeffMogul@acm.org</email></address>
2326    </author>
2327    <date year='2004' month='September' />
2328  </front>
2329  <seriesInfo name='BCP' value='90' />
2330  <seriesInfo name='RFC' value='3864' />
2331</reference>
2332
2333<reference anchor="RFC4288">
2334  <front>
2335    <title>Media Type Specifications and Registration Procedures</title>
2336    <author initials="N." surname="Freed" fullname="N. Freed">
2337      <organization>Sun Microsystems</organization>
2338      <address>
2339        <email>ned.freed@mrochek.com</email>
2340      </address>
2341    </author>
2342    <author initials="J." surname="Klensin" fullname="J. Klensin">
2343      <organization/>
2344      <address>
2345        <email>klensin+ietf@jck.com</email>
2346      </address>
2347    </author>
2348    <date year="2005" month="December"/>
2349  </front>
2350  <seriesInfo name="BCP" value="13"/>
2351  <seriesInfo name="RFC" value="4288"/>
2352</reference>
2353
2354<reference anchor="RFC5322">
2355  <front>
2356    <title>Internet Message Format</title>
2357    <author initials="P." surname="Resnick" fullname="P. Resnick">
2358      <organization>Qualcomm Incorporated</organization>
2359    </author>
2360    <date year="2008" month="October"/>
2361  </front> 
2362  <seriesInfo name="RFC" value="5322"/>
2363</reference>
2364
2365<reference anchor='BCP97'>
2366  <front>
2367    <title>Handling Normative References to Standards-Track Documents</title>
2368    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2369      <organization />
2370      <address>
2371        <email>klensin+ietf@jck.com</email>
2372      </address>
2373    </author>
2374    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2375      <organization>MIT</organization>
2376      <address>
2377        <email>hartmans-ietf@mit.edu</email>
2378      </address>
2379    </author>
2380    <date year='2007' month='June' />
2381  </front>
2382  <seriesInfo name='BCP' value='97' />
2383  <seriesInfo name='RFC' value='4897' />
2384</reference>
2385
2386
2387</references>
2388
2389<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2390<t>
2391   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
2392   allow entities to be transmitted in an open variety of
2393   representations and with extensible mechanisms. However, RFC 2045
2394   discusses mail, and HTTP has a few features that are different from
2395   those described in RFC 2045. These differences were carefully chosen
2396   to optimize performance over binary connections, to allow greater
2397   freedom in the use of new media types, to make date comparisons
2398   easier, and to acknowledge the practice of some early HTTP servers
2399   and clients.
2400</t>
2401<t>
2402   This appendix describes specific areas where HTTP differs from RFC
2403   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2404   aware of these differences and provide the appropriate conversions
2405   where necessary. Proxies and gateways from MIME environments to HTTP
2406   also need to be aware of the differences because some conversions
2407   might be required.
2408</t>
2409
2410<section title="MIME-Version" anchor="mime-version">
2411  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2412  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
2413  <x:anchor-alias value="MIME-Version"/>
2414  <x:anchor-alias value="MIME-Version-v"/>
2415<t>
2416   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2417   include a single MIME-Version general-header field to indicate what
2418   version of the MIME protocol was used to construct the message. Use
2419   of the MIME-Version header field indicates that the message is in
2420   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2421   Proxies/gateways are responsible for ensuring full compliance (where
2422   possible) when exporting HTTP messages to strict MIME environments.
2423</t>
2424<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
2425  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
2426  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2427</artwork></figure>
2428<t>
2429   MIME version "1.0" is the default for use in HTTP/1.1. However,
2430   HTTP/1.1 message parsing and semantics are defined by this document
2431   and not the MIME specification.
2432</t>
2433</section>
2434
2435<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2436<t>
2437   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2438   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2439   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2440   allowed for subtypes of the "text" media type when transmitted over
2441   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2442   line breaks as CRLF and forbids the use of CR or LF outside of line
2443   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2444   line break within text content when a message is transmitted over
2445   HTTP.
2446</t>
2447<t>
2448   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2449   environment &SHOULD; translate all line breaks within the text media
2450   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2451   canonical form of CRLF. Note, however, that this might be complicated
2452   by the presence of a Content-Encoding and by the fact that HTTP
2453   allows the use of some character sets which do not use octets 13 and
2454   10 to represent CR and LF, as is the case for some multi-byte
2455   character sets.
2456</t>
2457<t>
2458   Implementors should note that conversion will break any cryptographic
2459   checksums applied to the original content unless the original content
2460   is already in canonical form. Therefore, the canonical form is
2461   recommended for any content that uses such checksums in HTTP.
2462</t>
2463</section>
2464
2465
2466<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2467<t>
2468   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2469   simplify the process of date comparison. Proxies and gateways from
2470   other protocols &SHOULD; ensure that any Date header field present in a
2471   message conforms to one of the HTTP/1.1 formats and rewrite the date
2472   if necessary.
2473</t>
2474</section>
2475
2476<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2477<t>
2478   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2479   Content-Encoding header field. Since this acts as a modifier on the
2480   media type, proxies and gateways from HTTP to MIME-compliant
2481   protocols &MUST; either change the value of the Content-Type header
2482   field or decode the entity-body before forwarding the message. (Some
2483   experimental applications of Content-Type for Internet mail have used
2484   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2485   a function equivalent to Content-Encoding. However, this parameter is
2486   not part of RFC 2045).
2487</t>
2488</section>
2489
2490<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2491<t>
2492   HTTP does not use the Content-Transfer-Encoding field of RFC
2493   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2494   remove any Content-Transfer-Encoding
2495   prior to delivering the response message to an HTTP client.
2496</t>
2497<t>
2498   Proxies and gateways from HTTP to MIME-compliant protocols are
2499   responsible for ensuring that the message is in the correct format
2500   and encoding for safe transport on that protocol, where "safe
2501   transport" is defined by the limitations of the protocol being used.
2502   Such a proxy or gateway &SHOULD; label the data with an appropriate
2503   Content-Transfer-Encoding if doing so will improve the likelihood of
2504   safe transport over the destination protocol.
2505</t>
2506</section>
2507
2508<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2509<t>
2510   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2511   Proxies/gateways &MUST; remove any transfer-coding prior to
2512   forwarding a message via a MIME-compliant protocol.
2513</t>
2514</section>
2515
2516<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2517<t>
2518   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2519   need to be aware of MIME line length limitations. Since HTTP does not
2520   have this limitation, HTTP does not fold long lines. MHTML messages
2521   being transported by HTTP follow all conventions of MHTML, including
2522   line length limitations and folding, canonicalization, etc., since
2523   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2524   does not interpret the content or any MIME header lines that might be
2525   contained therein.
2526</t>
2527</section>
2528</section>
2529
2530<section title="Additional Features" anchor="additional.features">
2531<t>
2532   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2533   existing HTTP implementations, but not consistently and correctly
2534   across most HTTP/1.1 applications. Implementors are advised to be
2535   aware of these features, but cannot rely upon their presence in, or
2536   interoperability with, other HTTP/1.1 applications. Some of these
2537   describe proposed experimental features, and some describe features
2538   that experimental deployment found lacking that are now addressed in
2539   the base HTTP/1.1 specification.
2540</t>
2541<t>
2542   A number of other headers, such as Content-Disposition and Title,
2543   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2544</t>
2545
2546<section title="Content-Disposition" anchor="content-disposition">
2547<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2548<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2549  <x:anchor-alias value="content-disposition"/>
2550  <x:anchor-alias value="content-disposition-v"/>
2551  <x:anchor-alias value="disposition-type"/>
2552  <x:anchor-alias value="disposition-parm"/>
2553  <x:anchor-alias value="disp-extension-parm"/>
2554  <x:anchor-alias value="disp-extension-token"/>
2555  <x:anchor-alias value="filename-parm"/>
2556<t>
2557   The Content-Disposition response-header field has been proposed as a
2558   means for the origin server to suggest a default filename if the user
2559   requests that the content is saved to a file. This usage is derived
2560   from the definition of Content-Disposition in <xref target="RFC2183"/>.
2561</t>
2562<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-disposition"/><iref primary="true" item="Grammar" subitem="content-disposition-v"/><iref primary="true" item="Grammar" subitem="disposition-type"/><iref primary="true" item="Grammar" subitem="disposition-parm"/><iref primary="true" item="Grammar" subitem="filename-parm"/><iref primary="true" item="Grammar" subitem="disp-extension-token"/><iref primary="true" item="Grammar" subitem="disp-extension-parm"/>
2563  <x:ref>content-disposition</x:ref> = "Content-Disposition" ":" <x:ref>OWS</x:ref>
2564                        <x:ref>content-disposition-v</x:ref>
2565  <x:ref>content-disposition-v</x:ref> = <x:ref>disposition-type</x:ref>
2566                          *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>disposition-parm</x:ref> )
2567  <x:ref>disposition-type</x:ref> = "attachment" / <x:ref>disp-extension-token</x:ref>
2568  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> / <x:ref>disp-extension-parm</x:ref>
2569  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2570  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
2571  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
2572</artwork></figure>
2573<t>
2574   An example is
2575</t>
2576<figure><artwork type="example">
2577  Content-Disposition: attachment; filename="fname.ext"
2578</artwork></figure>
2579<t>
2580   The receiving user agent &SHOULD-NOT;  respect any directory path
2581   information present in the filename-parm parameter, which is the only
2582   parameter believed to apply to HTTP implementations at this time. The
2583   filename &SHOULD; be treated as a terminal component only.
2584</t>
2585<t>
2586   If this header is used in a response with the application/octet-stream
2587   content-type, the implied suggestion is that the user agent
2588   should not display the response, but directly enter a `save response
2589   as...' dialog.
2590</t>
2591<t>
2592   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2593</t>
2594</section>
2595</section>
2596
2597<section title="Compatibility with Previous Versions" anchor="compatibility">
2598<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2599<t>
2600   Transfer-coding and message lengths all interact in ways that
2601   required fixing exactly when chunked encoding is used (to allow for
2602   transfer encoding that may not be self delimiting); it was important
2603   to straighten out exactly how message lengths are computed.
2604   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2605   <xref target="Part5"/> and <xref target="Part6"/>).
2606</t>
2607<t>
2608   Charset wildcarding is introduced to avoid explosion of character set
2609   names in accept headers. (<xref target="header.accept-charset"/>)
2610</t>
2611<t>
2612   Content-Base was deleted from the specification: it was not
2613   implemented widely, and there is no simple, safe way to introduce it
2614   without a robust extension mechanism. In addition, it is used in a
2615   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2616</t>
2617<t>
2618   A content-coding of "identity" was introduced, to solve problems
2619   discovered in caching. (<xref target="content.codings"/>)
2620</t>
2621<t>
2622   The Alternates<iref item="Alternates header" primary="true"/><iref item="Headers" subitem="Alternate" primary="true"/>, Content-Version<iref item="Content-Version header" primary="true"/><iref item="Headers" subitem="Content-Version" primary="true"/>, Derived-From<iref item="Derived-From header" primary="true"/><iref item="Headers" subitem="Derived-From" primary="true"/>, Link<iref item="Link header" primary="true"/><iref item="Headers" subitem="Link" primary="true"/>, URI<iref item="URI header" primary="true"/><iref item="Headers" subitem="URI" primary="true"/>, Public<iref item="Public header" primary="true"/><iref item="Headers" subitem="Public" primary="true"/> and
2623   Content-Base<iref item="Content-Base header" primary="true"/><iref item="Headers" subitem="Content-Base" primary="true"/> header fields were defined in previous versions of this
2624   specification, but not commonly implemented. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.2"/>.
2625</t>
2626</section>
2627
2628<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2629<t>
2630  Clarify contexts that charset is used in.
2631  (<xref target="character.sets"/>)
2632</t>
2633<t>
2634  Remove reference to non-existant identity transfer-coding value tokens.
2635  (<xref target="no.content-transfer-encoding"/>)
2636</t>
2637</section>
2638
2639</section>
2640
2641<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
2642<figure>
2643<artwork type="abnf" name="p3-payload.parsed-abnf">
2644<x:ref>Accept</x:ref> = "Accept:" OWS Accept-v
2645<x:ref>Accept-Charset</x:ref> = "Accept-Charset:" OWS Accept-Charset-v
2646<x:ref>Accept-Charset-v</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2647 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2648 qvalue ] ] )
2649<x:ref>Accept-Encoding</x:ref> = "Accept-Encoding:" OWS Accept-Encoding-v
2650<x:ref>Accept-Encoding-v</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
2651 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2652<x:ref>Accept-Language</x:ref> = "Accept-Language:" OWS Accept-Language-v
2653<x:ref>Accept-Language-v</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
2654 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2655 ] )
2656<x:ref>Accept-v</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2657 OWS media-range [ accept-params ] ] ) ]
2658
2659<x:ref>Content-Encoding</x:ref> = "Content-Encoding:" OWS Content-Encoding-v
2660<x:ref>Content-Encoding-v</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
2661 content-coding ] )
2662<x:ref>Content-Language</x:ref> = "Content-Language:" OWS Content-Language-v
2663<x:ref>Content-Language-v</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
2664 language-tag ] )
2665<x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in [Part1], Section 8.2&gt;
2666<x:ref>Content-Location</x:ref> = "Content-Location:" OWS Content-Location-v
2667<x:ref>Content-Location-v</x:ref> = absolute-URI / partial-URI
2668<x:ref>Content-MD5</x:ref> = "Content-MD5:" OWS Content-MD5-v
2669<x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2670<x:ref>Content-Range</x:ref> = &lt;Content-Range, defined in [Part5], Section 5.2&gt;
2671<x:ref>Content-Type</x:ref> = "Content-Type:" OWS Content-Type-v
2672<x:ref>Content-Type-v</x:ref> = media-type
2673
2674<x:ref>Expires</x:ref> = &lt;Expires, defined in [Part6], Section 3.3&gt;
2675
2676<x:ref>Last-Modified</x:ref> = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;
2677
2678<x:ref>MIME-Version</x:ref> = "MIME-Version:" OWS MIME-Version-v
2679<x:ref>MIME-Version-v</x:ref> = 1*DIGIT "." 1*DIGIT
2680
2681<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
2682
2683<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.1&gt;
2684<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
2685<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2686<x:ref>attribute</x:ref> = token
2687
2688<x:ref>charset</x:ref> = token
2689<x:ref>codings</x:ref> = ( content-coding / "*" )
2690<x:ref>content-coding</x:ref> = token
2691<x:ref>content-disposition</x:ref> = "Content-Disposition:" OWS
2692 content-disposition-v
2693<x:ref>content-disposition-v</x:ref> = disposition-type *( OWS ";" OWS
2694 disposition-parm )
2695
2696<x:ref>disp-extension-parm</x:ref> = token "=" ( token / quoted-string )
2697<x:ref>disp-extension-token</x:ref> = token
2698<x:ref>disposition-parm</x:ref> = filename-parm / disp-extension-parm
2699<x:ref>disposition-type</x:ref> = "attachment" / disp-extension-token
2700
2701<x:ref>entity-body</x:ref> = *OCTET
2702<x:ref>entity-header</x:ref> = Content-Encoding / Content-Language / Content-Length
2703 / Content-Location / Content-MD5 / Content-Range / Content-Type /
2704 Expires / Last-Modified / extension-header
2705<x:ref>extension-header</x:ref> = message-header
2706
2707<x:ref>filename-parm</x:ref> = "filename=" quoted-string
2708
2709<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
2710<x:ref>language-tag</x:ref> = primary-tag *( "-" subtag )
2711
2712<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2713 ";" OWS parameter )
2714<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2715<x:ref>message-header</x:ref> = &lt;message-header, defined in [Part1], Section 4.2&gt;
2716
2717<x:ref>parameter</x:ref> = attribute "=" value
2718<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.1&gt;
2719<x:ref>primary-tag</x:ref> = 1*8ALPHA
2720
2721<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
2722<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 3.5&gt;
2723
2724<x:ref>subtag</x:ref> = 1*8ALPHA
2725<x:ref>subtype</x:ref> = token
2726
2727<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2728<x:ref>type</x:ref> = token
2729
2730<x:ref>value</x:ref> = token / quoted-string
2731
2732
2733</artwork>
2734</figure>
2735<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2736; Accept defined but not used
2737; Accept-Charset defined but not used
2738; Accept-Encoding defined but not used
2739; Accept-Language defined but not used
2740; MIME-Version defined but not used
2741; content-disposition defined but not used
2742; entity-body defined but not used
2743; entity-header defined but not used
2744</artwork></figure></section>
2745
2746<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2747
2748<section title="Since RFC2616">
2749<t>
2750  Extracted relevant partitions from <xref target="RFC2616"/>.
2751</t>
2752</section>
2753
2754<section title="Since draft-ietf-httpbis-p3-payload-00">
2755<t>
2756  Closed issues:
2757  <list style="symbols"> 
2758    <t>
2759      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2760      "Media Type Registrations"
2761      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2762    </t>
2763    <t>
2764      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2765      "Clarification regarding quoting of charset values"
2766      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2767    </t>
2768    <t>
2769      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2770      "Remove 'identity' token references"
2771      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2772    </t>
2773    <t>
2774      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2775      "Accept-Encoding BNF"
2776    </t>
2777    <t>
2778      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2779      "Normative and Informative references"
2780    </t>
2781    <t>
2782      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2783      "RFC1700 references"
2784    </t>
2785    <t>
2786      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2787      "Updating to RFC4288"
2788    </t>
2789    <t>
2790      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2791      "Informative references"
2792    </t>
2793    <t>
2794      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2795      "ISO-8859-1 Reference"
2796    </t>
2797    <t>
2798      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2799      "Encoding References Normative"
2800    </t>
2801    <t>
2802      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2803      "Normative up-to-date references"
2804    </t>
2805  </list>
2806</t>
2807</section>
2808
2809<section title="Since draft-ietf-httpbis-p3-payload-01">
2810<t>
2811  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2812  <list style="symbols"> 
2813    <t>
2814      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2815    </t>
2816  </list>
2817</t>
2818</section>
2819
2820<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2821<t>
2822  Closed issues:
2823  <list style="symbols"> 
2824    <t>
2825      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2826      "Quoting Charsets"
2827    </t>
2828    <t>
2829      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2830      "Classification for Allow header"
2831    </t>
2832    <t>
2833      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2834      "missing default for qvalue in description of Accept-Encoding"
2835    </t>
2836  </list>
2837</t>
2838<t>
2839  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2840  <list style="symbols"> 
2841    <t>
2842      Reference RFC 3984, and update header registrations for headers defined
2843      in this document.
2844    </t>
2845  </list>
2846</t>
2847</section>
2848
2849<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2850<t>
2851  Closed issues:
2852  <list style="symbols"> 
2853    <t>
2854      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2855      "Quoting Charsets"
2856    </t>
2857    <t>
2858      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2859      "language tag matching (Accept-Language) vs RFC4647"
2860    </t>
2861    <t>
2862      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2863      "RFC 1806 has been replaced by RFC2183"
2864    </t>
2865  </list>
2866</t>
2867<t>
2868  Other changes:
2869  <list style="symbols"> 
2870    <t>
2871      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2872      "Encoding References Normative" -- rephrase the annotation and reference
2873      <xref target="BCP97"/>.
2874    </t>
2875  </list>
2876</t>
2877 </section>
2878
2879<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2880<t>
2881  Closed issues:
2882  <list style="symbols"> 
2883    <t>
2884      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2885      "RFC 2822 is updated by RFC 5322"
2886    </t>
2887  </list>
2888</t>
2889<t>
2890  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2891  <list style="symbols"> 
2892    <t>
2893      Use "/" instead of "|" for alternatives.
2894    </t>
2895    <t>
2896      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2897      whitespace ("OWS") and required whitespace ("RWS").
2898    </t>
2899    <t>
2900      Rewrite ABNFs to spell out whitespace rules, factor out
2901      header value format definitions.
2902    </t>
2903  </list>
2904</t>
2905</section>
2906
2907<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2908<t>
2909  Closed issues:
2910  <list style="symbols"> 
2911    <t>
2912      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2913      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2914    </t>
2915  </list>
2916</t>
2917<t>
2918  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2919  <list style="symbols"> 
2920    <t>
2921      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2922    </t>
2923  </list>
2924</t>
2925<t>
2926  Other changes:
2927  <list style="symbols"> 
2928    <t>
2929      Move definition of quality values into Part 1.
2930    </t>
2931  </list>
2932</t>
2933</section>
2934
2935</section>
2936
2937</back>
2938</rfc>
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