source: draft-ietf-httpbis/latest/p3-payload.xml @ 424

Last change on this file since 424 was 424, checked in by julian.reschke@…, 11 years ago

reorganize ABNF introductions to match Part1 (related to #36)

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File size: 125.9 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "November">
16  <!ENTITY ID-YEAR "2008">
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 uri                      "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34]>
35<?rfc toc="yes" ?>
36<?rfc symrefs="yes" ?>
37<?rfc sortrefs="yes" ?>
38<?rfc compact="yes"?>
39<?rfc subcompact="no" ?>
40<?rfc linkmailto="no" ?>
41<?rfc editing="no" ?>
42<?rfc comments="yes"?>
43<?rfc inline="yes"?>
44<?rfc-ext allow-markup-in-artwork="yes" ?>
45<?rfc-ext include-references-in-index="yes" ?>
46<rfc obsoletes="2616" category="std" x:maturity-level="draft"
47     ipr="full3978" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
48     xmlns:x='http://purl.org/net/xml2rfc/ext'>
49<front>
50
51  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
52
53  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
54    <organization abbrev="Day Software">Day Software</organization>
55    <address>
56      <postal>
57        <street>23 Corporate Plaza DR, Suite 280</street>
58        <city>Newport Beach</city>
59        <region>CA</region>
60        <code>92660</code>
61        <country>USA</country>
62      </postal>
63      <phone>+1-949-706-5300</phone>
64      <facsimile>+1-949-706-5305</facsimile>
65      <email>fielding@gbiv.com</email>
66      <uri>http://roy.gbiv.com/</uri>
67    </address>
68  </author>
69
70  <author initials="J." surname="Gettys" fullname="Jim Gettys">
71    <organization>One Laptop per Child</organization>
72    <address>
73      <postal>
74        <street>21 Oak Knoll Road</street>
75        <city>Carlisle</city>
76        <region>MA</region>
77        <code>01741</code>
78        <country>USA</country>
79      </postal>
80      <email>jg@laptop.org</email>
81      <uri>http://www.laptop.org/</uri>
82    </address>
83  </author>
84 
85  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
86    <organization abbrev="HP">Hewlett-Packard Company</organization>
87    <address>
88      <postal>
89        <street>HP Labs, Large Scale Systems Group</street>
90        <street>1501 Page Mill Road, MS 1177</street>
91        <city>Palo Alto</city>
92        <region>CA</region>
93        <code>94304</code>
94        <country>USA</country>
95      </postal>
96      <email>JeffMogul@acm.org</email>
97    </address>
98  </author>
99
100  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
101    <organization abbrev="Microsoft">Microsoft Corporation</organization>
102    <address>
103      <postal>
104        <street>1 Microsoft Way</street>
105        <city>Redmond</city>
106        <region>WA</region>
107        <code>98052</code>
108        <country>USA</country>
109      </postal>
110      <email>henrikn@microsoft.com</email>
111    </address>
112  </author>
113
114  <author initials="L." surname="Masinter" fullname="Larry Masinter">
115    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
116    <address>
117      <postal>
118        <street>345 Park Ave</street>
119        <city>San Jose</city>
120        <region>CA</region>
121        <code>95110</code>
122        <country>USA</country>
123      </postal>
124      <email>LMM@acm.org</email>
125      <uri>http://larry.masinter.net/</uri>
126    </address>
127  </author>
128 
129  <author initials="P." surname="Leach" fullname="Paul J. Leach">
130    <organization abbrev="Microsoft">Microsoft Corporation</organization>
131    <address>
132      <postal>
133        <street>1 Microsoft Way</street>
134        <city>Redmond</city>
135        <region>WA</region>
136        <code>98052</code>
137      </postal>
138      <email>paulle@microsoft.com</email>
139    </address>
140  </author>
141   
142  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
143    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
144    <address>
145      <postal>
146        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
147        <street>The Stata Center, Building 32</street>
148        <street>32 Vassar Street</street>
149        <city>Cambridge</city>
150        <region>MA</region>
151        <code>02139</code>
152        <country>USA</country>
153      </postal>
154      <email>timbl@w3.org</email>
155      <uri>http://www.w3.org/People/Berners-Lee/</uri>
156    </address>
157  </author>
158
159  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
160    <organization abbrev="W3C">World Wide Web Consortium</organization>
161    <address>
162      <postal>
163        <street>W3C / ERCIM</street>
164        <street>2004, rte des Lucioles</street>
165        <city>Sophia-Antipolis</city>
166        <region>AM</region>
167        <code>06902</code>
168        <country>France</country>
169      </postal>
170      <email>ylafon@w3.org</email>
171      <uri>http://www.raubacapeu.net/people/yves/</uri>
172    </address>
173  </author>
174
175  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
176    <organization abbrev="greenbytes">greenbytes GmbH</organization>
177    <address>
178      <postal>
179        <street>Hafenweg 16</street>
180        <city>Muenster</city><region>NW</region><code>48155</code>
181        <country>Germany</country>
182      </postal>
183      <phone>+49 251 2807760</phone>   
184      <facsimile>+49 251 2807761</facsimile>   
185      <email>julian.reschke@greenbytes.de</email>       
186      <uri>http://greenbytes.de/tech/webdav/</uri>     
187    </address>
188  </author>
189
190  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
191
192<abstract>
193<t>
194   The Hypertext Transfer Protocol (HTTP) is an application-level
195   protocol for distributed, collaborative, hypermedia information
196   systems. HTTP has been in use by the World Wide Web global information
197   initiative since 1990. This document is Part 3 of the seven-part specification
198   that defines the protocol referred to as "HTTP/1.1" and, taken together,
199   obsoletes RFC 2616.  Part 3 defines HTTP message content,
200   metadata, and content negotiation.
201</t>
202</abstract>
203
204<note title="Editorial Note (To be removed by RFC Editor)">
205  <t>
206    Discussion of this draft should take place on the HTTPBIS working group
207    mailing list (ietf-http-wg@w3.org). The current issues list is
208    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
209    and related documents (including fancy diffs) can be found at
210    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
211  </t>
212  <t>
213    The changes in this draft are summarized in <xref target="changes.since.05"/>.
214  </t>
215</note>
216</front>
217<middle>
218<section title="Introduction" anchor="introduction">
219<t>
220   This document defines HTTP/1.1 message payloads (a.k.a., content), the
221   associated metadata header fields that define how the payload is intended
222   to be interpreted by a recipient, the request header fields that
223   may influence content selection, and the various selection algorithms
224   that are collectively referred to as HTTP content negotiation.
225</t>
226<t>
227   This document is currently disorganized in order to minimize the changes
228   between drafts and enable reviewers to see the smaller errata changes.
229   The next draft will reorganize the sections to better reflect the content.
230   In particular, the sections on entities will be renamed payload and moved
231   to the first half of the document, while the sections on content negotiation
232   and associated request header fields will be moved to the second half.  The
233   current mess reflects how widely dispersed these topics and associated
234   requirements had become in <xref target="RFC2616"/>.
235</t>
236
237<section title="Requirements" anchor="intro.requirements">
238<t>
239   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
240   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
241   document are to be interpreted as described in <xref target="RFC2119"/>.
242</t>
243<t>
244   An implementation is not compliant if it fails to satisfy one or more
245   of the &MUST; or &REQUIRED; level requirements for the protocols it
246   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
247   level and all the &SHOULD; level requirements for its protocols is said
248   to be "unconditionally compliant"; one that satisfies all the &MUST;
249   level requirements but not all the &SHOULD; level requirements for its
250   protocols is said to be "conditionally compliant."
251</t>
252</section>
253
254<section title="Syntax Notation" anchor="notation">
255<t>
256  This specification uses the ABNF syntax defined in &notation;.
257</t>
258
259<section title="Core Rules" anchor="core.rules">
260  <x:anchor-alias value="ALPHA"/>
261  <x:anchor-alias value="DIGIT"/>
262  <x:anchor-alias value="OCTET"/>
263  <x:anchor-alias value="quoted-string"/>
264  <x:anchor-alias value="token"/>
265  <x:anchor-alias value="OWS"/>
266<t>
267  The core rules below are defined in &basic-rules;:
268</t>
269<figure><artwork type="abnf2616">
270  <x:ref>ALPHA</x:ref>          = &lt;ALPHA, defined in &basic-rules;&gt;
271  <x:ref>DIGIT</x:ref>          = &lt;DIGIT, defined in &basic-rules;&gt;
272  <x:ref>OCTET</x:ref>          = &lt;OCTET, defined in &basic-rules;&gt;
273</artwork></figure>
274<figure><artwork type="abnf2616">
275  <x:ref>quoted-string</x:ref>  = &lt;quoted-string, defined in &basic-rules;&gt;
276  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
277  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
278</artwork></figure>
279</section>
280
281<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
282  <x:anchor-alias value="absolute-URI"/>
283  <x:anchor-alias value="Allow"/>
284  <x:anchor-alias value="Content-Length"/>
285  <x:anchor-alias value="Content-Range"/>
286  <x:anchor-alias value="Expires"/>
287  <x:anchor-alias value="Last-Modified"/>
288  <x:anchor-alias value="message-header"/>
289  <x:anchor-alias value="partial-URI"/>
290<t>
291  The ABNF rules below are defined in other parts:
292</t>
293<figure><!--Part1--><artwork type="abnf2616">
294  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
295  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
296  <x:ref>message-header</x:ref> = &lt;message-header, defined in &message-headers;&gt;
297  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
298</artwork></figure>
299<figure><!--Part4--><artwork type="abnf2616">
300  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
301</artwork></figure>
302<figure><!--Part5--><artwork type="abnf2616">
303  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
304</artwork></figure>
305<figure><!--Part6--><artwork type="abnf2616">
306  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
307</artwork></figure>
308</section>
309
310</section>
311
312</section>
313
314<section title="Protocol Parameters" anchor="protocol.parameters">
315
316<section title="Character Sets" anchor="character.sets">
317<t>
318   HTTP uses the same definition of the term "character set" as that
319   described for MIME:
320</t>
321<t>
322   The term "character set" is used in this document to refer to a
323   method used with one or more tables to convert a sequence of octets
324   into a sequence of characters. Note that unconditional conversion in
325   the other direction is not required, in that not all characters may
326   be available in a given character set and a character set may provide
327   more than one sequence of octets to represent a particular character.
328   This definition is intended to allow various kinds of character
329   encoding, from simple single-table mappings such as US-ASCII to
330   complex table switching methods such as those that use ISO-2022's
331   techniques. However, the definition associated with a MIME character
332   set name &MUST; fully specify the mapping to be performed from octets
333   to characters. In particular, use of external profiling information
334   to determine the exact mapping is not permitted.
335</t>
336<t><list><t>
337      <x:h>Note:</x:h> This use of the term "character set" is more commonly
338      referred to as a "character encoding." However, since HTTP and
339      MIME share the same registry, it is important that the terminology
340      also be shared.
341</t></list></t>
342<t anchor="rule.charset">
343  <x:anchor-alias value="charset"/>
344   HTTP character sets are identified by case-insensitive tokens. The
345   complete set of tokens is defined by the IANA Character Set registry
346   (<eref target="http://www.iana.org/assignments/character-sets"/>).
347</t>
348<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
349  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
350</artwork></figure>
351<t>
352   Although HTTP allows an arbitrary token to be used as a charset
353   value, any token that has a predefined value within the IANA
354   Character Set registry &MUST; represent the character set defined
355   by that registry. Applications &SHOULD; limit their use of character
356   sets to those defined by the IANA registry.
357</t>
358<t>
359   HTTP uses charset in two contexts: within an Accept-Charset request
360   header (in which the charset value is an unquoted token) and as the
361   value of a parameter in a Content-Type header (within a request or
362   response), in which case the parameter value of the charset parameter
363   may be quoted.
364</t>
365<t>
366   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
367   <xref target="RFC2277"/>.
368</t>
369
370<section title="Missing Charset" anchor="missing.charset">
371<t>
372   Some HTTP/1.0 software has interpreted a Content-Type header without
373   charset parameter incorrectly to mean "recipient should guess."
374   Senders wishing to defeat this behavior &MAY; include a charset
375   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
376   it is known that it will not confuse the recipient.
377</t>
378<t>
379   Unfortunately, some older HTTP/1.0 clients did not deal properly with
380   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
381   charset label provided by the sender; and those user agents that have
382   a provision to "guess" a charset &MUST; use the charset from the
383   content-type field if they support that charset, rather than the
384   recipient's preference, when initially displaying a document. See
385   <xref target="canonicalization.and.text.defaults"/>.
386</t>
387</section>
388</section>
389
390<section title="Content Codings" anchor="content.codings">
391  <x:anchor-alias value="content-coding"/>
392<t>
393   Content coding values indicate an encoding transformation that has
394   been or can be applied to an entity. Content codings are primarily
395   used to allow a document to be compressed or otherwise usefully
396   transformed without losing the identity of its underlying media type
397   and without loss of information. Frequently, the entity is stored in
398   coded form, transmitted directly, and only decoded by the recipient.
399</t>
400<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
401  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
402</artwork></figure>
403<t>
404   All content-coding values are case-insensitive. HTTP/1.1 uses
405   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
406   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
407   describes the content-coding, what is more important is that it
408   indicates what decoding mechanism will be required to remove the
409   encoding.
410</t>
411<t>
412   The Internet Assigned Numbers Authority (IANA) acts as a registry for
413   content-coding value tokens. Initially, the registry contains the
414   following tokens:
415</t>
416<t>
417   gzip<iref item="gzip"/>
418  <list>
419    <t>
420        An encoding format produced by the file compression program
421        "gzip" (GNU zip) as described in <xref target="RFC1952"/>. This format is a
422        Lempel-Ziv coding (LZ77) with a 32 bit CRC.
423    </t>
424  </list>
425</t>
426<t>
427   compress<iref item="compress"/>
428  <list><t>
429        The encoding format produced by the common UNIX file compression
430        program "compress". This format is an adaptive Lempel-Ziv-Welch
431        coding (LZW).
432</t><t>
433        Use of program names for the identification of encoding formats
434        is not desirable and is discouraged for future encodings. Their
435        use here is representative of historical practice, not good
436        design. For compatibility with previous implementations of HTTP,
437        applications &SHOULD; consider "x-gzip" and "x-compress" to be
438        equivalent to "gzip" and "compress" respectively.
439  </t></list>
440</t>
441<t>
442   deflate<iref item="deflate"/>
443  <list><t>
444        The "zlib" format defined in <xref target="RFC1950"/> in combination with
445        the "deflate" compression mechanism described in <xref target="RFC1951"/>.
446  </t></list>
447</t>
448<t>
449   identity<iref item="identity"/>
450  <list><t>
451        The default (identity) encoding; the use of no transformation
452        whatsoever. This content-coding is used only in the Accept-Encoding
453        header, and &SHOULD-NOT;  be used in the Content-Encoding
454        header.
455  </t></list>
456</t>
457<t>
458   New content-coding value tokens &SHOULD; be registered; to allow
459   interoperability between clients and servers, specifications of the
460   content coding algorithms needed to implement a new value &SHOULD; be
461   publicly available and adequate for independent implementation, and
462   conform to the purpose of content coding defined in this section.
463</t>
464</section>
465
466<section title="Media Types" anchor="media.types">
467  <x:anchor-alias value="media-type"/>
468  <x:anchor-alias value="type"/>
469  <x:anchor-alias value="subtype"/>
470<t>
471   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
472   and Accept (<xref target="header.accept"/>) header fields in order to provide
473   open and extensible data typing and type negotiation.
474</t>
475<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"/>
476  <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> )
477  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
478  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
479</artwork></figure>
480<t anchor="rule.parameter">
481  <x:anchor-alias value="attribute"/>
482  <x:anchor-alias value="parameter"/>
483  <x:anchor-alias value="value"/>
484   Parameters &MAY; follow the type/subtype in the form of attribute/value
485   pairs.
486</t>
487<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"/>
488  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
489  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
490  <x:ref>value</x:ref>          = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
491</artwork></figure>
492<t>
493   The type, subtype, and parameter attribute names are case-insensitive.
494   Parameter values might or might not be case-sensitive, depending on the
495   semantics of the parameter name.  The presence or absence of a parameter might
496   be significant to the processing of a media-type, depending on its
497   definition within the media type registry.
498</t>
499<t>
500   A parameter value that matches the <x:ref>token</x:ref> production may be
501   transmitted as either a token or within a quoted-string. The quoted and
502   unquoted values are equivalent.
503</t>
504<t>
505   Note that some older HTTP applications do not recognize media type
506   parameters. When sending data to older HTTP applications,
507   implementations &SHOULD; only use media type parameters when they are
508   required by that type/subtype definition.
509</t>
510<t>
511   Media-type values are registered with the Internet Assigned Number
512   Authority (IANA). The media type registration process is
513   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
514   discouraged.
515</t>
516
517<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
518<t>
519   Internet media types are registered with a canonical form. An
520   entity-body transferred via HTTP messages &MUST; be represented in the
521   appropriate canonical form prior to its transmission except for
522   "text" types, as defined in the next paragraph.
523</t>
524<t>
525   When in canonical form, media subtypes of the "text" type use CRLF as
526   the text line break. HTTP relaxes this requirement and allows the
527   transport of text media with plain CR or LF alone representing a line
528   break when it is done consistently for an entire entity-body. HTTP
529   applications &MUST; accept CRLF, bare CR, and bare LF as being
530   representative of a line break in text media received via HTTP. In
531   addition, if the text is represented in a character set that does not
532   use octets 13 and 10 for CR and LF respectively, as is the case for
533   some multi-byte character sets, HTTP allows the use of whatever octet
534   sequences are defined by that character set to represent the
535   equivalent of CR and LF for line breaks. This flexibility regarding
536   line breaks applies only to text media in the entity-body; a bare CR
537   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
538   structures (such as header fields and multipart boundaries).
539</t>
540<t>
541   If an entity-body is encoded with a content-coding, the underlying
542   data &MUST; be in a form defined above prior to being encoded.
543</t>
544<t>
545   The "charset" parameter is used with some media types to define the
546   character set (<xref target="character.sets"/>) of the data. When no explicit charset
547   parameter is provided by the sender, media subtypes of the "text"
548   type are defined to have a default charset value of "ISO-8859-1" when
549   received via HTTP. Data in character sets other than "ISO-8859-1" or
550   its subsets &MUST; be labeled with an appropriate charset value. See
551   <xref target="missing.charset"/> for compatibility problems.
552</t>
553</section>
554
555<section title="Multipart Types" anchor="multipart.types">
556<t>
557   MIME provides for a number of "multipart" types -- encapsulations of
558   one or more entities within a single message-body. All multipart
559   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
560   and &MUST; include a boundary parameter as part of the media type
561   value. The message body is itself a protocol element and &MUST;
562   therefore use only CRLF to represent line breaks between body-parts.
563   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
564   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
565   original multipart contains an epilogue). These restrictions exist in
566   order to preserve the self-delimiting nature of a multipart message-body,
567   wherein the "end" of the message-body is indicated by the
568   ending multipart boundary.
569</t>
570<t>
571   In general, HTTP treats a multipart message-body no differently than
572   any other media type: strictly as payload. The one exception is the
573   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
574   (Partial Content) response.
575   <!-- jre: re-insert removed text pointing to caching? -->
576   In all
577   other cases, an HTTP user agent &SHOULD; follow the same or similar
578   behavior as a MIME user agent would upon receipt of a multipart type.
579   The MIME header fields within each body-part of a multipart message-body
580   do not have any significance to HTTP beyond that defined by
581   their MIME semantics.
582</t>
583<t>
584   In general, an HTTP user agent &SHOULD; follow the same or similar
585   behavior as a MIME user agent would upon receipt of a multipart type.
586   If an application receives an unrecognized multipart subtype, the
587   application &MUST; treat it as being equivalent to "multipart/mixed".
588</t>
589<t><list><t>
590      <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
591      for carrying form data suitable for processing via the POST
592      request method, as described in <xref target="RFC2388"/>.
593</t></list></t>
594</section>
595</section>
596
597<section title="Quality Values" anchor="quality.values">
598  <x:anchor-alias value="qvalue"/>
599<t>
600   HTTP content negotiation (<xref target="content.negotiation"/>) uses short "floating point"
601   numbers to indicate the relative importance ("weight") of various
602   negotiable parameters.  A weight is normalized to a real number in
603   the range 0 through 1, where 0 is the minimum and 1 the maximum
604   value. If a parameter has a quality value of 0, then content with
605   this parameter is `not acceptable' for the client. HTTP/1.1
606   applications &MUST-NOT; generate more than three digits after the
607   decimal point. User configuration of these values &SHOULD; also be
608   limited in this fashion.
609</t>
610<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
611  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
612                 / ( "1" [ "." 0*3("0") ] )
613</artwork></figure>
614<t>
615   "Quality values" is a misnomer, since these values merely represent
616   relative degradation in desired quality.
617</t>
618</section>
619
620<section title="Language Tags" anchor="language.tags">
621  <x:anchor-alias value="language-tag"/>
622  <x:anchor-alias value="primary-tag"/>
623  <x:anchor-alias value="subtag"/>
624<t>
625   A language tag identifies a natural language spoken, written, or
626   otherwise conveyed by human beings for communication of information
627   to other human beings. Computer languages are explicitly excluded.
628   HTTP uses language tags within the Accept-Language and Content-Language
629   fields.
630</t>
631<t>
632   The syntax and registry of HTTP language tags is the same as that
633   defined by <xref target="RFC1766"/>. In summary, a language tag is composed of 1
634   or more parts: A primary language tag and a possibly empty series of
635   subtags:
636</t>
637<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"/>
638  <x:ref>language-tag</x:ref>  = <x:ref>primary-tag</x:ref> *( "-" <x:ref>subtag</x:ref> )
639  <x:ref>primary-tag</x:ref>   = 1*8<x:ref>ALPHA</x:ref>
640  <x:ref>subtag</x:ref>        = 1*8<x:ref>ALPHA</x:ref>
641</artwork></figure>
642<t>
643   White space is not allowed within the tag and all tags are case-insensitive.
644   The name space of language tags is administered by the
645   IANA. Example tags include:
646</t>
647<figure><artwork type="example">
648    en, en-US, en-cockney, i-cherokee, x-pig-latin
649</artwork></figure>
650<t>
651   where any two-letter primary-tag is an ISO-639 language abbreviation
652   and any two-letter initial subtag is an ISO-3166 country code. (The
653   last three tags above are not registered tags; all but the last are
654   examples of tags which could be registered in future.)
655</t>
656</section>
657</section>
658
659<section title="Entity" anchor="entity">
660<t>
661   Request and Response messages &MAY; transfer an entity if not otherwise
662   restricted by the request method or response status code. An entity
663   consists of entity-header fields and an entity-body, although some
664   responses will only include the entity-headers.
665</t>
666<t>
667   In this section, both sender and recipient refer to either the client
668   or the server, depending on who sends and who receives the entity.
669</t>
670
671<section title="Entity Header Fields" anchor="entity.header.fields">
672  <x:anchor-alias value="entity-header"/>
673  <x:anchor-alias value="extension-header"/>
674<t>
675   Entity-header fields define metainformation about the entity-body or,
676   if no body is present, about the resource identified by the request.
677</t>
678<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
679  <x:ref>entity-header</x:ref>  = <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
680                 / <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
681                 / <x:ref>Content-Length</x:ref>           ; &header-content-length;
682                 / <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
683                 / <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
684                 / <x:ref>Content-Range</x:ref>            ; &header-content-range;
685                 / <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
686                 / <x:ref>Expires</x:ref>                  ; &header-expires;
687                 / <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
688                 / <x:ref>extension-header</x:ref>
689 
690  <x:ref>extension-header</x:ref> = <x:ref>message-header</x:ref>
691</artwork></figure>
692<t>
693   The extension-header mechanism allows additional entity-header fields
694   to be defined without changing the protocol, but these fields cannot
695   be assumed to be recognizable by the recipient. Unrecognized header
696   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
697   transparent proxies.
698</t>
699</section>
700
701<section title="Entity Body" anchor="entity.body">
702  <x:anchor-alias value="entity-body"/>
703<t>
704   The entity-body (if any) sent with an HTTP request or response is in
705   a format and encoding defined by the entity-header fields.
706</t>
707<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
708  <x:ref>entity-body</x:ref>    = *<x:ref>OCTET</x:ref>
709</artwork></figure>
710<t>
711   An entity-body is only present in a message when a message-body is
712   present, as described in &message-body;. The entity-body is obtained
713   from the message-body by decoding any Transfer-Encoding that might
714   have been applied to ensure safe and proper transfer of the message.
715</t>
716
717<section title="Type" anchor="type">
718<t>
719   When an entity-body is included with a message, the data type of that
720   body is determined via the header fields Content-Type and Content-Encoding.
721   These define a two-layer, ordered encoding model:
722</t>
723<figure><artwork type="example">
724    entity-body := Content-Encoding( Content-Type( data ) )
725</artwork></figure>
726<t>
727   Content-Type specifies the media type of the underlying data.
728   Content-Encoding may be used to indicate any additional content
729   codings applied to the data, usually for the purpose of data
730   compression, that are a property of the requested resource. There is
731   no default encoding.
732</t>
733<t>
734   Any HTTP/1.1 message containing an entity-body &SHOULD; include a
735   Content-Type header field defining the media type of that body. If
736   and only if the media type is not given by a Content-Type field, the
737   recipient &MAY; attempt to guess the media type via inspection of its
738   content and/or the name extension(s) of the URI used to identify the
739   resource. If the media type remains unknown, the recipient &SHOULD;
740   treat it as type "application/octet-stream".
741</t>
742</section>
743   
744<section title="Entity Length" anchor="entity.length">
745<t>
746   The entity-length of a message is the length of the message-body
747   before any transfer-codings have been applied. &message-length; defines
748   how the transfer-length of a message-body is determined.
749</t>
750</section>
751</section>
752</section>
753
754<section title="Content Negotiation" anchor="content.negotiation">
755<t>
756   Most HTTP responses include an entity which contains information for
757   interpretation by a human user. Naturally, it is desirable to supply
758   the user with the "best available" entity corresponding to the
759   request. Unfortunately for servers and caches, not all users have the
760   same preferences for what is "best," and not all user agents are
761   equally capable of rendering all entity types. For that reason, HTTP
762   has provisions for several mechanisms for "content negotiation" --
763   the process of selecting the best representation for a given response
764   when there are multiple representations available.
765  <list><t>
766      <x:h>Note:</x:h> This is not called "format negotiation" because the
767      alternate representations may be of the same media type, but use
768      different capabilities of that type, be in different languages,
769      etc.
770  </t></list>
771</t>
772<t>
773   Any response containing an entity-body &MAY; be subject to negotiation,
774   including error responses.
775</t>
776<t>
777   There are two kinds of content negotiation which are possible in
778   HTTP: server-driven and agent-driven negotiation. These two kinds of
779   negotiation are orthogonal and thus may be used separately or in
780   combination. One method of combination, referred to as transparent
781   negotiation, occurs when a cache uses the agent-driven negotiation
782   information provided by the origin server in order to provide
783   server-driven negotiation for subsequent requests.
784</t>
785
786<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
787<t>
788   If the selection of the best representation for a response is made by
789   an algorithm located at the server, it is called server-driven
790   negotiation. Selection is based on the available representations of
791   the response (the dimensions over which it can vary; e.g. language,
792   content-coding, etc.) and the contents of particular header fields in
793   the request message or on other information pertaining to the request
794   (such as the network address of the client).
795</t>
796<t>
797   Server-driven negotiation is advantageous when the algorithm for
798   selecting from among the available representations is difficult to
799   describe to the user agent, or when the server desires to send its
800   "best guess" to the client along with the first response (hoping to
801   avoid the round-trip delay of a subsequent request if the "best
802   guess" is good enough for the user). In order to improve the server's
803   guess, the user agent &MAY; include request header fields (Accept,
804   Accept-Language, Accept-Encoding, etc.) which describe its
805   preferences for such a response.
806</t>
807<t>
808   Server-driven negotiation has disadvantages:
809  <list style="numbers">
810    <t>
811         It is impossible for the server to accurately determine what
812         might be "best" for any given user, since that would require
813         complete knowledge of both the capabilities of the user agent
814         and the intended use for the response (e.g., does the user want
815         to view it on screen or print it on paper?).
816    </t>
817    <t>
818         Having the user agent describe its capabilities in every
819         request can be both very inefficient (given that only a small
820         percentage of responses have multiple representations) and a
821         potential violation of the user's privacy.
822    </t>
823    <t>
824         It complicates the implementation of an origin server and the
825         algorithms for generating responses to a request.
826    </t>
827    <t>
828         It may limit a public cache's ability to use the same response
829         for multiple user's requests.
830    </t>
831  </list>
832</t>
833<t>
834   HTTP/1.1 includes the following request-header fields for enabling
835   server-driven negotiation through description of user agent
836   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
837   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
838   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;). However, an
839   origin server is not limited to these dimensions and &MAY; vary the
840   response based on any aspect of the request, including information
841   outside the request-header fields or within extension header fields
842   not defined by this specification.
843</t>
844<t>
845   The Vary header field (&header-vary;) can be used to express the parameters the
846   server uses to select a representation that is subject to server-driven
847   negotiation.
848</t>
849</section>
850
851<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
852<t>
853   With agent-driven negotiation, selection of the best representation
854   for a response is performed by the user agent after receiving an
855   initial response from the origin server. Selection is based on a list
856   of the available representations of the response included within the
857   header fields or entity-body of the initial response, with each
858   representation identified by its own URI. Selection from among the
859   representations may be performed automatically (if the user agent is
860   capable of doing so) or manually by the user selecting from a
861   generated (possibly hypertext) menu.
862</t>
863<t>
864   Agent-driven negotiation is advantageous when the response would vary
865   over commonly-used dimensions (such as type, language, or encoding),
866   when the origin server is unable to determine a user agent's
867   capabilities from examining the request, and generally when public
868   caches are used to distribute server load and reduce network usage.
869</t>
870<t>
871   Agent-driven negotiation suffers from the disadvantage of needing a
872   second request to obtain the best alternate representation. This
873   second request is only efficient when caching is used. In addition,
874   this specification does not define any mechanism for supporting
875   automatic selection, though it also does not prevent any such
876   mechanism from being developed as an extension and used within
877   HTTP/1.1.
878</t>
879<t>
880   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
881   status codes for enabling agent-driven negotiation when the server is
882   unwilling or unable to provide a varying response using server-driven
883   negotiation.
884</t>
885</section>
886
887<section title="Transparent Negotiation" anchor="transparent.negotiation">
888<t>
889   Transparent negotiation is a combination of both server-driven and
890   agent-driven negotiation. When a cache is supplied with a form of the
891   list of available representations of the response (as in agent-driven
892   negotiation) and the dimensions of variance are completely understood
893   by the cache, then the cache becomes capable of performing server-driven
894   negotiation on behalf of the origin server for subsequent
895   requests on that resource.
896</t>
897<t>
898   Transparent negotiation has the advantage of distributing the
899   negotiation work that would otherwise be required of the origin
900   server and also removing the second request delay of agent-driven
901   negotiation when the cache is able to correctly guess the right
902   response.
903</t>
904<t>
905   This specification does not define any mechanism for transparent
906   negotiation, though it also does not prevent any such mechanism from
907   being developed as an extension that could be used within HTTP/1.1.
908</t>
909</section>
910</section>
911
912<section title="Header Field Definitions" anchor="header.fields">
913<t>
914   This section defines the syntax and semantics of HTTP/1.1 header fields
915   related to the payload of messages.
916</t>
917<t>
918   For entity-header fields, both sender and recipient refer to either the
919   client or the server, depending on who sends and who receives the entity.
920</t>
921
922<section title="Accept" anchor="header.accept">
923  <iref primary="true" item="Accept header" x:for-anchor=""/>
924  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
925  <x:anchor-alias value="Accept"/>
926  <x:anchor-alias value="Accept-v"/>
927  <x:anchor-alias value="accept-ext"/>
928  <x:anchor-alias value="accept-params"/>
929  <x:anchor-alias value="media-range"/>
930<t>
931   The request-header field "Accept" can be used to specify certain media
932   types which are acceptable for the response. Accept headers can be
933   used to indicate that the request is specifically limited to a small
934   set of desired types, as in the case of a request for an in-line
935   image.
936</t>
937<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"/>
938  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
939  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
940 
941  <x:ref>media-range</x:ref>    = ( "*/*"
942                   / ( <x:ref>type</x:ref> "/" "*" )
943                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
944                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
945  <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> )
946  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref>
947                   [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
948</artwork></figure>
949<t>
950   The asterisk "*" character is used to group media types into ranges,
951   with "*/*" indicating all media types and "type/*" indicating all
952   subtypes of that type. The media-range &MAY; include media type
953   parameters that are applicable to that range.
954</t>
955<t>
956   Each media-range &MAY; be followed by one or more accept-params,
957   beginning with the "q" parameter for indicating a relative quality
958   factor. The first "q" parameter (if any) separates the media-range
959   parameter(s) from the accept-params. Quality factors allow the user
960   or user agent to indicate the relative degree of preference for that
961   media-range, using the qvalue scale from 0 to 1 (<xref target="quality.values"/>). The
962   default value is q=1.
963  <list><t>
964      <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
965      parameters from Accept extension parameters is due to historical
966      practice. Although this prevents any media type parameter named
967      "q" from being used with a media range, such an event is believed
968      to be unlikely given the lack of any "q" parameters in the IANA
969      media type registry and the rare usage of any media type
970      parameters in Accept. Future media types are discouraged from
971      registering any parameter named "q".
972  </t></list>
973</t>
974<t>
975   The example
976</t>
977<figure><artwork type="example">
978  Accept: audio/*; q=0.2, audio/basic
979</artwork></figure>
980<t>
981   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
982   type if it is the best available after an 80% mark-down in quality."
983</t>
984<t>
985   If no Accept header field is present, then it is assumed that the
986   client accepts all media types. If an Accept header field is present,
987   and if the server cannot send a response which is acceptable
988   according to the combined Accept field value, then the server &SHOULD;
989   send a 406 (Not Acceptable) response.
990</t>
991<t>
992   A more elaborate example is
993</t>
994<figure><artwork type="example">
995  Accept: text/plain; q=0.5, text/html,
996          text/x-dvi; q=0.8, text/x-c
997</artwork></figure>
998<t>
999   Verbally, this would be interpreted as "text/html and text/x-c are
1000   the preferred media types, but if they do not exist, then send the
1001   text/x-dvi entity, and if that does not exist, send the text/plain
1002   entity."
1003</t>
1004<t>
1005   Media ranges can be overridden by more specific media ranges or
1006   specific media types. If more than one media range applies to a given
1007   type, the most specific reference has precedence. For example,
1008</t>
1009<figure><artwork type="example">
1010  Accept: text/*, text/html, text/html;level=1, */*
1011</artwork></figure>
1012<t>
1013   have the following precedence:
1014</t>
1015<figure><artwork type="example">
1016    1) text/html;level=1
1017    2) text/html
1018    3) text/*
1019    4) */*
1020</artwork></figure>
1021<t>
1022   The media type quality factor associated with a given type is
1023   determined by finding the media range with the highest precedence
1024   which matches that type. For example,
1025</t>
1026<figure><artwork type="example">
1027  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1028          text/html;level=2;q=0.4, */*;q=0.5
1029</artwork></figure>
1030<t>
1031   would cause the following values to be associated:
1032</t>
1033<figure><artwork type="example">
1034    text/html;level=1         = 1
1035    text/html                 = 0.7
1036    text/plain                = 0.3
1037    image/jpeg                = 0.5
1038    text/html;level=2         = 0.4
1039    text/html;level=3         = 0.7
1040</artwork></figure>
1041<t>
1042      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1043      values for certain media ranges. However, unless the user agent is
1044      a closed system which cannot interact with other rendering agents,
1045      this default set ought to be configurable by the user.
1046</t>
1047</section>
1048
1049<section title="Accept-Charset" anchor="header.accept-charset">
1050  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1051  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1052  <x:anchor-alias value="Accept-Charset"/>
1053  <x:anchor-alias value="Accept-Charset-v"/>
1054<t>
1055   The request-header field "Accept-Charset" can be used to indicate what
1056   character sets are acceptable for the response. This field allows
1057   clients capable of understanding more comprehensive or special-purpose
1058   character sets to signal that capability to a server which is
1059   capable of representing documents in those character sets.
1060</t>
1061<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
1062  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
1063          <x:ref>Accept-Charset-v</x:ref>
1064  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1065                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1066</artwork></figure>
1067<t>
1068   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1069   be given an associated quality value which represents the user's
1070   preference for that charset. The default value is q=1. An example is
1071</t>
1072<figure><artwork type="example">
1073  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1074</artwork></figure>
1075<t>
1076   The special value "*", if present in the Accept-Charset field,
1077   matches every character set (including ISO-8859-1) which is not
1078   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1079   in an Accept-Charset field, then all character sets not explicitly
1080   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1081   a quality value of 1 if not explicitly mentioned.
1082</t>
1083<t>
1084   If no Accept-Charset header is present, the default is that any
1085   character set is acceptable. If an Accept-Charset header is present,
1086   and if the server cannot send a response which is acceptable
1087   according to the Accept-Charset header, then the server &SHOULD; send
1088   an error response with the 406 (Not Acceptable) status code, though
1089   the sending of an unacceptable response is also allowed.
1090</t>
1091</section>
1092
1093<section title="Accept-Encoding" anchor="header.accept-encoding">
1094  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1095  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1096  <x:anchor-alias value="Accept-Encoding"/>
1097  <x:anchor-alias value="Accept-Encoding-v"/>
1098  <x:anchor-alias value="codings"/>
1099<t>
1100   The request-header field "Accept-Encoding" is similar to Accept, but
1101   restricts the content-codings (<xref target="content.codings"/>) that are acceptable in
1102   the response.
1103</t>
1104<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"/>
1105  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
1106                     <x:ref>Accept-Encoding-v</x:ref>
1107  <x:ref>Accept-Encoding-v</x:ref>  =
1108                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1109  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
1110</artwork></figure>
1111<t>
1112   Each codings value &MAY; be given an associated quality value which
1113   represents the preference for that encoding. The default value is q=1.
1114</t>
1115<t>
1116   Examples of its use are:
1117</t>
1118<figure><artwork type="example">
1119  Accept-Encoding: compress, gzip
1120  Accept-Encoding:
1121  Accept-Encoding: *
1122  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1123  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1124</artwork></figure>
1125<t>
1126   A server tests whether a content-coding is acceptable, according to
1127   an Accept-Encoding field, using these rules:
1128  <list style="numbers">
1129      <t>If the content-coding is one of the content-codings listed in
1130         the Accept-Encoding field, then it is acceptable, unless it is
1131         accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
1132         qvalue of 0 means "not acceptable.")</t>
1133
1134      <t>The special "*" symbol in an Accept-Encoding field matches any
1135         available content-coding not explicitly listed in the header
1136         field.</t>
1137
1138      <t>If multiple content-codings are acceptable, then the acceptable
1139         content-coding with the highest non-zero qvalue is preferred.</t>
1140
1141      <t>The "identity" content-coding is always acceptable, unless
1142         specifically refused because the Accept-Encoding field includes
1143         "identity;q=0", or because the field includes "*;q=0" and does
1144         not explicitly include the "identity" content-coding. If the
1145         Accept-Encoding field-value is empty, then only the "identity"
1146         encoding is acceptable.</t>
1147  </list>
1148</t>
1149<t>
1150   If an Accept-Encoding field is present in a request, and if the
1151   server cannot send a response which is acceptable according to the
1152   Accept-Encoding header, then the server &SHOULD; send an error response
1153   with the 406 (Not Acceptable) status code.
1154</t>
1155<t>
1156   If no Accept-Encoding field is present in a request, the server &MAY;
1157   assume that the client will accept any content coding. In this case,
1158   if "identity" is one of the available content-codings, then the
1159   server &SHOULD; use the "identity" content-coding, unless it has
1160   additional information that a different content-coding is meaningful
1161   to the client.
1162  <list><t>
1163      <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1164      and if the "identity" content-coding is unavailable, then
1165      content-codings commonly understood by HTTP/1.0 clients (i.e.,
1166      "gzip" and "compress") are preferred; some older clients
1167      improperly display messages sent with other content-codings.  The
1168      server might also make this decision based on information about
1169      the particular user-agent or client.
1170    </t><t>
1171      <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1172      associated with content-codings. This means that qvalues will not
1173      work and are not permitted with x-gzip or x-compress.
1174    </t></list>
1175</t>
1176</section>
1177
1178<section title="Accept-Language" anchor="header.accept-language">
1179  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1180  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1181  <x:anchor-alias value="Accept-Language"/>
1182  <x:anchor-alias value="Accept-Language-v"/>
1183  <x:anchor-alias value="language-range"/>
1184<t>
1185   The request-header field "Accept-Language" is similar to Accept, but
1186   restricts the set of natural languages that are preferred as a
1187   response to the request. Language tags are defined in <xref target="language.tags"/>.
1188</t>
1189<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"/>
1190  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
1191                    <x:ref>Accept-Language-v</x:ref>
1192  <x:ref>Accept-Language-v</x:ref> =
1193                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1194  <x:ref>language-range</x:ref>    =
1195            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1196</artwork></figure>
1197<t>
1198   Each language-range can be given an associated quality value which
1199   represents an estimate of the user's preference for the languages
1200   specified by that range. The quality value defaults to "q=1". For
1201   example,
1202</t>
1203<figure><artwork type="example">
1204  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1205</artwork></figure>
1206<t>
1207   would mean: "I prefer Danish, but will accept British English and
1208   other types of English."
1209</t>
1210<t>
1211   For matching, the "Basic Filtering" matching scheme, defined in
1212   <xref target="RFC4647" x:sec="3.3.1" x:fmt="of"/>, is used:
1213</t>
1214<x:blockquote cite="http://tools.ietf.org/html/rfc4647#section-3.3.1">
1215  <t>
1216     A language range matches a
1217     particular language tag if, in a case-insensitive comparison, it
1218     exactly equals the tag, or if it exactly equals a prefix of the tag
1219     such that the first character following the prefix is "-".
1220  </t>
1221</x:blockquote> 
1222<t>
1223   The special range "*", if present in the Accept-Language field,
1224   matches every tag not matched by any other range present in the
1225   Accept-Language field.
1226  <list><t>
1227      <x:h>Note:</x:h> This use of a prefix matching rule does not imply that
1228      language tags are assigned to languages in such a way that it is
1229      always true that if a user understands a language with a certain
1230      tag, then this user will also understand all languages with tags
1231      for which this tag is a prefix. The prefix rule simply allows the
1232      use of prefix tags if this is the case.
1233  </t></list>
1234</t>
1235<t>
1236   The language quality factor assigned to a language-tag by the
1237   Accept-Language field is the quality value of the longest language-range
1238   in the field that matches the language-tag. If no language-range
1239   in the field matches the tag, the language quality factor
1240   assigned is 0. If no Accept-Language header is present in the
1241   request, the server
1242   &SHOULD; assume that all languages are equally acceptable. If an
1243   Accept-Language header is present, then all languages which are
1244   assigned a quality factor greater than 0 are acceptable.
1245</t>
1246<t>
1247   It might be contrary to the privacy expectations of the user to send
1248   an Accept-Language header with the complete linguistic preferences of
1249   the user in every request. For a discussion of this issue, see
1250   <xref target="privacy.issues.connected.to.accept.headers"/>.
1251</t>
1252<t>
1253   As intelligibility is highly dependent on the individual user, it is
1254   recommended that client applications make the choice of linguistic
1255   preference available to the user. If the choice is not made
1256   available, then the Accept-Language header field &MUST-NOT; be given in
1257   the request.
1258  <list><t>
1259      <x:h>Note:</x:h> When making the choice of linguistic preference available to
1260      the user, we remind implementors of  the fact that users are not
1261      familiar with the details of language matching as described above,
1262      and should provide appropriate guidance. As an example, users
1263      might assume that on selecting "en-gb", they will be served any
1264      kind of English document if British English is not available. A
1265      user agent might suggest in such a case to add "en" to get the
1266      best matching behavior.
1267  </t></list>
1268</t>
1269</section>
1270
1271<section title="Content-Encoding" anchor="header.content-encoding">
1272  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1273  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1274  <x:anchor-alias value="Content-Encoding"/>
1275  <x:anchor-alias value="Content-Encoding-v"/>
1276<t>
1277   The entity-header field "Content-Encoding" is used as a modifier to the
1278   media-type. When present, its value indicates what additional content
1279   codings have been applied to the entity-body, and thus what decoding
1280   mechanisms must be applied in order to obtain the media-type
1281   referenced by the Content-Type header field. Content-Encoding is
1282   primarily used to allow a document to be compressed without losing
1283   the identity of its underlying media type.
1284</t>
1285<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
1286  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
1287  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1288</artwork></figure>
1289<t>
1290   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1291</t>
1292<figure><artwork type="example">
1293  Content-Encoding: gzip
1294</artwork></figure>
1295<t>
1296   The content-coding is a characteristic of the entity identified by
1297   the request-target. Typically, the entity-body is stored with this
1298   encoding and is only decoded before rendering or analogous usage.
1299   However, a non-transparent proxy &MAY; modify the content-coding if the
1300   new coding is known to be acceptable to the recipient, unless the
1301   "no-transform" cache-control directive is present in the message.
1302</t>
1303<t>
1304   If the content-coding of an entity is not "identity", then the
1305   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1306   that lists the non-identity content-coding(s) used.
1307</t>
1308<t>
1309   If the content-coding of an entity in a request message is not
1310   acceptable to the origin server, the server &SHOULD; respond with a
1311   status code of 415 (Unsupported Media Type).
1312</t>
1313<t>
1314   If multiple encodings have been applied to an entity, the content
1315   codings &MUST; be listed in the order in which they were applied.
1316   Additional information about the encoding parameters &MAY; be provided
1317   by other entity-header fields not defined by this specification.
1318</t>
1319</section>
1320
1321<section title="Content-Language" anchor="header.content-language">
1322  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1323  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1324  <x:anchor-alias value="Content-Language"/>
1325  <x:anchor-alias value="Content-Language-v"/>
1326<t>
1327   The entity-header field "Content-Language" describes the natural
1328   language(s) of the intended audience for the enclosed entity. Note
1329   that this might not be equivalent to all the languages used within
1330   the entity-body.
1331</t>
1332<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
1333  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
1334  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1335</artwork></figure>
1336<t>
1337   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1338   Content-Language is to allow a user to identify and differentiate
1339   entities according to the user's own preferred language. Thus, if the
1340   body content is intended only for a Danish-literate audience, the
1341   appropriate field is
1342</t>
1343<figure><artwork type="example">
1344  Content-Language: da
1345</artwork></figure>
1346<t>
1347   If no Content-Language is specified, the default is that the content
1348   is intended for all language audiences. This might mean that the
1349   sender does not consider it to be specific to any natural language,
1350   or that the sender does not know for which language it is intended.
1351</t>
1352<t>
1353   Multiple languages &MAY; be listed for content that is intended for
1354   multiple audiences. For example, a rendition of the "Treaty of
1355   Waitangi," presented simultaneously in the original Maori and English
1356   versions, would call for
1357</t>
1358<figure><artwork type="example">
1359  Content-Language: mi, en
1360</artwork></figure>
1361<t>
1362   However, just because multiple languages are present within an entity
1363   does not mean that it is intended for multiple linguistic audiences.
1364   An example would be a beginner's language primer, such as "A First
1365   Lesson in Latin," which is clearly intended to be used by an
1366   English-literate audience. In this case, the Content-Language would
1367   properly only include "en".
1368</t>
1369<t>
1370   Content-Language &MAY; be applied to any media type -- it is not
1371   limited to textual documents.
1372</t>
1373</section>
1374
1375<section title="Content-Location" anchor="header.content-location">
1376  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1377  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1378  <x:anchor-alias value="Content-Location"/>
1379  <x:anchor-alias value="Content-Location-v"/>
1380<t>
1381   The entity-header field "Content-Location" &MAY; be used to supply the
1382   resource location for the entity enclosed in the message when that
1383   entity is accessible from a location separate from the requested
1384   resource's URI. A server &SHOULD; provide a Content-Location for the
1385   variant corresponding to the response entity; especially in the case
1386   where a resource has multiple entities associated with it, and those
1387   entities actually have separate locations by which they might be
1388   individually accessed, the server &SHOULD; provide a Content-Location
1389   for the particular variant which is returned.
1390</t>
1391<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
1392  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
1393                    <x:ref>Content-Location-v</x:ref>
1394  <x:ref>Content-Location-v</x:ref> =
1395                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1396</artwork></figure>
1397<t>
1398   The value of Content-Location also defines the base URI for the
1399   entity.
1400</t>
1401<t>
1402   The Content-Location value is not a replacement for the original
1403   requested URI; it is only a statement of the location of the resource
1404   corresponding to this particular entity at the time of the request.
1405   Future requests &MAY; specify the Content-Location URI as the request-target
1406   if the desire is to identify the source of that particular
1407   entity.
1408</t>
1409<t>
1410   A cache cannot assume that an entity with a Content-Location
1411   different from the URI used to retrieve it can be used to respond to
1412   later requests on that Content-Location URI. However, the Content-Location
1413   can be used to differentiate between multiple entities
1414   retrieved from a single requested resource, as described in &caching-neg-resp;.
1415</t>
1416<t>
1417   If the Content-Location is a relative URI, the relative URI is
1418   interpreted relative to the request-target.
1419</t>
1420<t>
1421   The meaning of the Content-Location header in PUT or POST requests is
1422   undefined; servers are free to ignore it in those cases.
1423</t>
1424</section>
1425
1426<section title="Content-MD5" anchor="header.content-md5">
1427  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1428  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1429  <x:anchor-alias value="Content-MD5"/>
1430  <x:anchor-alias value="Content-MD5-v"/>
1431<t>
1432   The entity-header field "Content-MD5", as defined in <xref target="RFC1864"/>, is
1433   an MD5 digest of the entity-body for the purpose of providing an
1434   end-to-end message integrity check (MIC) of the entity-body. (Note: a
1435   MIC is good for detecting accidental modification of the entity-body
1436   in transit, but is not proof against malicious attacks.)
1437</t>
1438<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
1439  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
1440  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1441</artwork></figure>
1442<t>
1443   The Content-MD5 header field &MAY; be generated by an origin server or
1444   client to function as an integrity check of the entity-body. Only
1445   origin servers or clients &MAY; generate the Content-MD5 header field;
1446   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1447   value as an end-to-end integrity check. Any recipient of the entity-body,
1448   including gateways and proxies, &MAY; check that the digest value
1449   in this header field matches that of the entity-body as received.
1450</t>
1451<t>
1452   The MD5 digest is computed based on the content of the entity-body,
1453   including any content-coding that has been applied, but not including
1454   any transfer-encoding applied to the message-body. If the message is
1455   received with a transfer-encoding, that encoding &MUST; be removed
1456   prior to checking the Content-MD5 value against the received entity.
1457</t>
1458<t>
1459   This has the result that the digest is computed on the octets of the
1460   entity-body exactly as, and in the order that, they would be sent if
1461   no transfer-encoding were being applied.
1462</t>
1463<t>
1464   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1465   composite media-types (e.g., multipart/* and message/rfc822), but
1466   this does not change how the digest is computed as defined in the
1467   preceding paragraph.
1468</t>
1469<t>
1470   There are several consequences of this. The entity-body for composite
1471   types &MAY; contain many body-parts, each with its own MIME and HTTP
1472   headers (including Content-MD5, Content-Transfer-Encoding, and
1473   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1474   or Content-Encoding header, it is assumed that the content
1475   of the body-part has had the encoding applied, and the body-part is
1476   included in the Content-MD5 digest as is -- i.e., after the
1477   application. The Transfer-Encoding header field is not allowed within
1478   body-parts.
1479</t>
1480<t>
1481   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1482   computing or checking the digest: the line break convention used in
1483   the text actually transmitted &MUST; be left unaltered when computing
1484   the digest.
1485  <list><t>
1486      <x:h>Note:</x:h> while the definition of Content-MD5 is exactly the same for
1487      HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1488      in which the application of Content-MD5 to HTTP entity-bodies
1489      differs from its application to MIME entity-bodies. One is that
1490      HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1491      does use Transfer-Encoding and Content-Encoding. Another is that
1492      HTTP more frequently uses binary content types than MIME, so it is
1493      worth noting that, in such cases, the byte order used to compute
1494      the digest is the transmission byte order defined for the type.
1495      Lastly, HTTP allows transmission of text types with any of several
1496      line break conventions and not just the canonical form using CRLF.
1497  </t></list>
1498</t>
1499</section>
1500
1501<section title="Content-Type" anchor="header.content-type">
1502  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1503  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1504  <x:anchor-alias value="Content-Type"/>
1505  <x:anchor-alias value="Content-Type-v"/>
1506<t>
1507   The entity-header field "Content-Type" indicates the media type of the
1508   entity-body sent to the recipient or, in the case of the HEAD method,
1509   the media type that would have been sent had the request been a GET.
1510</t>
1511<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
1512  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
1513  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1514</artwork></figure>
1515<t>
1516   Media types are defined in <xref target="media.types"/>. An example of the field is
1517</t>
1518<figure><artwork type="example">
1519  Content-Type: text/html; charset=ISO-8859-4
1520</artwork></figure>
1521<t>
1522   Further discussion of methods for identifying the media type of an
1523   entity is provided in <xref target="type"/>.
1524</t>
1525</section>
1526
1527</section>
1528
1529<section title="IANA Considerations" anchor="IANA.considerations">
1530<section title="Message Header Registration" anchor="message.header.registration">
1531<t>
1532   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
1533   with the permanent registrations below (see <xref target="RFC3864"/>):
1534</t>
1535<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1536<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1537   <ttcol>Header Field Name</ttcol>
1538   <ttcol>Protocol</ttcol>
1539   <ttcol>Status</ttcol>
1540   <ttcol>Reference</ttcol>
1541
1542   <c>Accept</c>
1543   <c>http</c>
1544   <c>standard</c>
1545   <c>
1546      <xref target="header.accept"/>
1547   </c>
1548   <c>Accept-Charset</c>
1549   <c>http</c>
1550   <c>standard</c>
1551   <c>
1552      <xref target="header.accept-charset"/>
1553   </c>
1554   <c>Accept-Encoding</c>
1555   <c>http</c>
1556   <c>standard</c>
1557   <c>
1558      <xref target="header.accept-encoding"/>
1559   </c>
1560   <c>Accept-Language</c>
1561   <c>http</c>
1562   <c>standard</c>
1563   <c>
1564      <xref target="header.accept-language"/>
1565   </c>
1566   <c>Content-Disposition</c>
1567   <c>http</c>
1568   <c/>
1569   <c>
1570      <xref target="content-disposition"/>
1571   </c>
1572   <c>Content-Encoding</c>
1573   <c>http</c>
1574   <c>standard</c>
1575   <c>
1576      <xref target="header.content-encoding"/>
1577   </c>
1578   <c>Content-Language</c>
1579   <c>http</c>
1580   <c>standard</c>
1581   <c>
1582      <xref target="header.content-language"/>
1583   </c>
1584   <c>Content-Location</c>
1585   <c>http</c>
1586   <c>standard</c>
1587   <c>
1588      <xref target="header.content-location"/>
1589   </c>
1590   <c>Content-MD5</c>
1591   <c>http</c>
1592   <c>standard</c>
1593   <c>
1594      <xref target="header.content-md5"/>
1595   </c>
1596   <c>Content-Type</c>
1597   <c>http</c>
1598   <c>standard</c>
1599   <c>
1600      <xref target="header.content-type"/>
1601   </c>
1602   <c>MIME-Version</c>
1603   <c>http</c>
1604   <c/>
1605   <c>
1606      <xref target="mime-version"/>
1607   </c>
1608</texttable>
1609<!--(END)-->
1610<t>
1611   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1612</t>
1613</section>
1614</section>
1615
1616<section title="Security Considerations" anchor="security.considerations">
1617<t>
1618   This section is meant to inform application developers, information
1619   providers, and users of the security limitations in HTTP/1.1 as
1620   described by this document. The discussion does not include
1621   definitive solutions to the problems revealed, though it does make
1622   some suggestions for reducing security risks.
1623</t>
1624
1625<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1626<t>
1627   Accept request-headers can reveal information about the user to all
1628   servers which are accessed. The Accept-Language header in particular
1629   can reveal information the user would consider to be of a private
1630   nature, because the understanding of particular languages is often
1631   strongly correlated to the membership of a particular ethnic group.
1632   User agents which offer the option to configure the contents of an
1633   Accept-Language header to be sent in every request are strongly
1634   encouraged to let the configuration process include a message which
1635   makes the user aware of the loss of privacy involved.
1636</t>
1637<t>
1638   An approach that limits the loss of privacy would be for a user agent
1639   to omit the sending of Accept-Language headers by default, and to ask
1640   the user whether or not to start sending Accept-Language headers to a
1641   server if it detects, by looking for any Vary response-header fields
1642   generated by the server, that such sending could improve the quality
1643   of service.
1644</t>
1645<t>
1646   Elaborate user-customized accept header fields sent in every request,
1647   in particular if these include quality values, can be used by servers
1648   as relatively reliable and long-lived user identifiers. Such user
1649   identifiers would allow content providers to do click-trail tracking,
1650   and would allow collaborating content providers to match cross-server
1651   click-trails or form submissions of individual users. Note that for
1652   many users not behind a proxy, the network address of the host
1653   running the user agent will also serve as a long-lived user
1654   identifier. In environments where proxies are used to enhance
1655   privacy, user agents ought to be conservative in offering accept
1656   header configuration options to end users. As an extreme privacy
1657   measure, proxies could filter the accept headers in relayed requests.
1658   General purpose user agents which provide a high degree of header
1659   configurability &SHOULD; warn users about the loss of privacy which can
1660   be involved.
1661</t>
1662</section>
1663
1664<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1665<t>
1666   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
1667   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1668   serious security considerations. Content-Disposition is not part of
1669   the HTTP standard, but since it is widely implemented, we are
1670   documenting its use and risks for implementors. See <xref target="RFC2183" x:fmt="of" x:sec="5"/>
1671   for details.
1672</t>
1673</section>
1674
1675</section>
1676
1677<section title="Acknowledgments" anchor="ack">
1678</section>
1679</middle>
1680<back>
1681
1682<references title="Normative References">
1683
1684<reference anchor="ISO-8859-1">
1685  <front>
1686    <title>
1687     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1688    </title>
1689    <author>
1690      <organization>International Organization for Standardization</organization>
1691    </author>
1692    <date year="1998"/>
1693  </front>
1694  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1695</reference>
1696
1697<reference anchor="Part1">
1698  <front>
1699    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1700    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1701      <organization abbrev="Day Software">Day Software</organization>
1702      <address><email>fielding@gbiv.com</email></address>
1703    </author>
1704    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1705      <organization>One Laptop per Child</organization>
1706      <address><email>jg@laptop.org</email></address>
1707    </author>
1708    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1709      <organization abbrev="HP">Hewlett-Packard Company</organization>
1710      <address><email>JeffMogul@acm.org</email></address>
1711    </author>
1712    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1713      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1714      <address><email>henrikn@microsoft.com</email></address>
1715    </author>
1716    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1717      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1718      <address><email>LMM@acm.org</email></address>
1719    </author>
1720    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1721      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1722      <address><email>paulle@microsoft.com</email></address>
1723    </author>
1724    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1725      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1726      <address><email>timbl@w3.org</email></address>
1727    </author>
1728    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1729      <organization abbrev="W3C">World Wide Web Consortium</organization>
1730      <address><email>ylafon@w3.org</email></address>
1731    </author>
1732    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1733      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1734      <address><email>julian.reschke@greenbytes.de</email></address>
1735    </author>
1736    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1737  </front>
1738  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1739  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1740</reference>
1741
1742<reference anchor="Part2">
1743  <front>
1744    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1745    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1746      <organization abbrev="Day Software">Day Software</organization>
1747      <address><email>fielding@gbiv.com</email></address>
1748    </author>
1749    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1750      <organization>One Laptop per Child</organization>
1751      <address><email>jg@laptop.org</email></address>
1752    </author>
1753    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1754      <organization abbrev="HP">Hewlett-Packard Company</organization>
1755      <address><email>JeffMogul@acm.org</email></address>
1756    </author>
1757    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1758      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1759      <address><email>henrikn@microsoft.com</email></address>
1760    </author>
1761    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1762      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1763      <address><email>LMM@acm.org</email></address>
1764    </author>
1765    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1766      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1767      <address><email>paulle@microsoft.com</email></address>
1768    </author>
1769    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1770      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1771      <address><email>timbl@w3.org</email></address>
1772    </author>
1773    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1774      <organization abbrev="W3C">World Wide Web Consortium</organization>
1775      <address><email>ylafon@w3.org</email></address>
1776    </author>
1777    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1778      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1779      <address><email>julian.reschke@greenbytes.de</email></address>
1780    </author>
1781    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1782  </front>
1783  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1784  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1785</reference>
1786
1787<reference anchor="Part4">
1788  <front>
1789    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1790    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1791      <organization abbrev="Day Software">Day Software</organization>
1792      <address><email>fielding@gbiv.com</email></address>
1793    </author>
1794    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1795      <organization>One Laptop per Child</organization>
1796      <address><email>jg@laptop.org</email></address>
1797    </author>
1798    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1799      <organization abbrev="HP">Hewlett-Packard Company</organization>
1800      <address><email>JeffMogul@acm.org</email></address>
1801    </author>
1802    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1803      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1804      <address><email>henrikn@microsoft.com</email></address>
1805    </author>
1806    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1807      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1808      <address><email>LMM@acm.org</email></address>
1809    </author>
1810    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1811      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1812      <address><email>paulle@microsoft.com</email></address>
1813    </author>
1814    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1815      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1816      <address><email>timbl@w3.org</email></address>
1817    </author>
1818    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1819      <organization abbrev="W3C">World Wide Web Consortium</organization>
1820      <address><email>ylafon@w3.org</email></address>
1821    </author>
1822    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1823      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1824      <address><email>julian.reschke@greenbytes.de</email></address>
1825    </author>
1826    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1827  </front>
1828  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1829  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1830</reference>
1831
1832<reference anchor="Part5">
1833  <front>
1834    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1835    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1836      <organization abbrev="Day Software">Day Software</organization>
1837      <address><email>fielding@gbiv.com</email></address>
1838    </author>
1839    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1840      <organization>One Laptop per Child</organization>
1841      <address><email>jg@laptop.org</email></address>
1842    </author>
1843    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1844      <organization abbrev="HP">Hewlett-Packard Company</organization>
1845      <address><email>JeffMogul@acm.org</email></address>
1846    </author>
1847    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1848      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1849      <address><email>henrikn@microsoft.com</email></address>
1850    </author>
1851    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1852      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1853      <address><email>LMM@acm.org</email></address>
1854    </author>
1855    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1856      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1857      <address><email>paulle@microsoft.com</email></address>
1858    </author>
1859    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1860      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1861      <address><email>timbl@w3.org</email></address>
1862    </author>
1863    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1864      <organization abbrev="W3C">World Wide Web Consortium</organization>
1865      <address><email>ylafon@w3.org</email></address>
1866    </author>
1867    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1868      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1869      <address><email>julian.reschke@greenbytes.de</email></address>
1870    </author>
1871    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1872  </front>
1873  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1874  <x:source href="p5-range.xml" basename="p5-range"/>
1875</reference>
1876
1877<reference anchor="Part6">
1878  <front>
1879    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1880    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1881      <organization abbrev="Day Software">Day Software</organization>
1882      <address><email>fielding@gbiv.com</email></address>
1883    </author>
1884    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1885      <organization>One Laptop per Child</organization>
1886      <address><email>jg@laptop.org</email></address>
1887    </author>
1888    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1889      <organization abbrev="HP">Hewlett-Packard Company</organization>
1890      <address><email>JeffMogul@acm.org</email></address>
1891    </author>
1892    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1893      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1894      <address><email>henrikn@microsoft.com</email></address>
1895    </author>
1896    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1897      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1898      <address><email>LMM@acm.org</email></address>
1899    </author>
1900    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1901      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1902      <address><email>paulle@microsoft.com</email></address>
1903    </author>
1904    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1905      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1906      <address><email>timbl@w3.org</email></address>
1907    </author>
1908    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1909      <organization abbrev="W3C">World Wide Web Consortium</organization>
1910      <address><email>ylafon@w3.org</email></address>
1911    </author>
1912    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1913      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1914      <address><email>julian.reschke@greenbytes.de</email></address>
1915    </author>
1916    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1917  </front>
1918  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1919  <x:source href="p6-cache.xml" basename="p6-cache"/>
1920</reference>
1921
1922<reference anchor="RFC1766">
1923  <front>
1924    <title abbrev="Language Tag">Tags for the Identification of Languages</title>
1925    <author initials="H." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
1926      <organization>UNINETT</organization>
1927      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
1928    </author>
1929    <date month="March" year="1995"/>
1930  </front>
1931  <seriesInfo name="RFC" value="1766"/>
1932</reference>
1933
1934<reference anchor="RFC1864">
1935  <front>
1936    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1937    <author initials="J." surname="Myers" fullname="John G. Myers">
1938      <organization>Carnegie Mellon University</organization>
1939      <address><email>jgm+@cmu.edu</email></address>
1940    </author>
1941    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
1942      <organization>Dover Beach Consulting, Inc.</organization>
1943      <address><email>mrose@dbc.mtview.ca.us</email></address>
1944    </author>
1945    <date month="October" year="1995"/>
1946  </front>
1947  <seriesInfo name="RFC" value="1864"/>
1948</reference>
1949
1950<reference anchor="RFC1950">
1951  <front>
1952    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1953    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1954      <organization>Aladdin Enterprises</organization>
1955      <address><email>ghost@aladdin.com</email></address>
1956    </author>
1957    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1958      <organization/>
1959    </author>
1960    <date month="May" year="1996"/>
1961  </front>
1962  <seriesInfo name="RFC" value="1950"/>
1963  <annotation>
1964    RFC 1950 is an Informational RFC, thus it may be less stable than
1965    this specification. On the other hand, this downward reference was
1966    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1967    therefore it is unlikely to cause problems in practice. See also
1968    <xref target="BCP97"/>.
1969  </annotation>
1970</reference>
1971
1972<reference anchor="RFC1951">
1973  <front>
1974    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1975    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1976      <organization>Aladdin Enterprises</organization>
1977      <address><email>ghost@aladdin.com</email></address>
1978    </author>
1979    <date month="May" year="1996"/>
1980  </front>
1981  <seriesInfo name="RFC" value="1951"/>
1982  <annotation>
1983    RFC 1951 is an Informational RFC, thus it may be less stable than
1984    this specification. On the other hand, this downward reference was
1985    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1986    therefore it is unlikely to cause problems in practice. See also
1987    <xref target="BCP97"/>.
1988  </annotation>
1989</reference>
1990
1991<reference anchor="RFC1952">
1992  <front>
1993    <title>GZIP file format specification version 4.3</title>
1994    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1995      <organization>Aladdin Enterprises</organization>
1996      <address><email>ghost@aladdin.com</email></address>
1997    </author>
1998    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1999      <organization/>
2000      <address><email>gzip@prep.ai.mit.edu</email></address>
2001    </author>
2002    <author initials="M." surname="Adler" fullname="Mark Adler">
2003      <organization/>
2004      <address><email>madler@alumni.caltech.edu</email></address>
2005    </author>
2006    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2007      <organization/>
2008      <address><email>ghost@aladdin.com</email></address>
2009    </author>
2010    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2011      <organization/>
2012      <address><email>randeg@alumni.rpi.edu</email></address>
2013    </author>
2014    <date month="May" year="1996"/>
2015  </front>
2016  <seriesInfo name="RFC" value="1952"/>
2017  <annotation>
2018    RFC 1952 is an Informational RFC, thus it may be less stable than
2019    this specification. On the other hand, this downward reference was
2020    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2021    therefore it is unlikely to cause problems in practice. See also
2022    <xref target="BCP97"/>.
2023  </annotation>
2024</reference>
2025
2026<reference anchor="RFC2045">
2027  <front>
2028    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2029    <author initials="N." surname="Freed" fullname="Ned Freed">
2030      <organization>Innosoft International, Inc.</organization>
2031      <address><email>ned@innosoft.com</email></address>
2032    </author>
2033    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2034      <organization>First Virtual Holdings</organization>
2035      <address><email>nsb@nsb.fv.com</email></address>
2036    </author>
2037    <date month="November" year="1996"/>
2038  </front>
2039  <seriesInfo name="RFC" value="2045"/>
2040</reference>
2041
2042<reference anchor="RFC2046">
2043  <front>
2044    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2045    <author initials="N." surname="Freed" fullname="Ned Freed">
2046      <organization>Innosoft International, Inc.</organization>
2047      <address><email>ned@innosoft.com</email></address>
2048    </author>
2049    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2050      <organization>First Virtual Holdings</organization>
2051      <address><email>nsb@nsb.fv.com</email></address>
2052    </author>
2053    <date month="November" year="1996"/>
2054  </front>
2055  <seriesInfo name="RFC" value="2046"/>
2056</reference>
2057
2058<reference anchor="RFC2119">
2059  <front>
2060    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2061    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2062      <organization>Harvard University</organization>
2063      <address><email>sob@harvard.edu</email></address>
2064    </author>
2065    <date month="March" year="1997"/>
2066  </front>
2067  <seriesInfo name="BCP" value="14"/>
2068  <seriesInfo name="RFC" value="2119"/>
2069</reference>
2070
2071<reference anchor='RFC4647'>
2072  <front>
2073    <title>Matching of Language Tags</title>
2074    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2075      <organization>Yahoo! Inc.</organization>
2076      <address><email>addison@inter-locale.com</email></address>
2077    </author>
2078    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2079      <organization>Google</organization>
2080      <address><email>mark.davis@macchiato.com</email></address>
2081    </author>
2082    <date year='2006' month='September' />
2083  </front>
2084  <seriesInfo name='BCP' value='47' />
2085  <seriesInfo name='RFC' value='4647' />
2086</reference>
2087
2088</references>
2089
2090<references title="Informative References">
2091
2092<reference anchor="RFC1945">
2093  <front>
2094    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2095    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2096      <organization>MIT, Laboratory for Computer Science</organization>
2097      <address><email>timbl@w3.org</email></address>
2098    </author>
2099    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2100      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2101      <address><email>fielding@ics.uci.edu</email></address>
2102    </author>
2103    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2104      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2105      <address><email>frystyk@w3.org</email></address>
2106    </author>
2107    <date month="May" year="1996"/>
2108  </front>
2109  <seriesInfo name="RFC" value="1945"/>
2110</reference>
2111
2112<reference anchor="RFC2049">
2113  <front>
2114    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2115    <author initials="N." surname="Freed" fullname="Ned Freed">
2116      <organization>Innosoft International, Inc.</organization>
2117      <address><email>ned@innosoft.com</email></address>
2118    </author>
2119    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2120      <organization>First Virtual Holdings</organization>
2121      <address><email>nsb@nsb.fv.com</email></address>
2122    </author>
2123    <date month="November" year="1996"/>
2124  </front>
2125  <seriesInfo name="RFC" value="2049"/>
2126</reference>
2127
2128<reference anchor="RFC2068">
2129  <front>
2130    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2131    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2132      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2133      <address><email>fielding@ics.uci.edu</email></address>
2134    </author>
2135    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2136      <organization>MIT Laboratory for Computer Science</organization>
2137      <address><email>jg@w3.org</email></address>
2138    </author>
2139    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2140      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2141      <address><email>mogul@wrl.dec.com</email></address>
2142    </author>
2143    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2144      <organization>MIT Laboratory for Computer Science</organization>
2145      <address><email>frystyk@w3.org</email></address>
2146    </author>
2147    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2148      <organization>MIT Laboratory for Computer Science</organization>
2149      <address><email>timbl@w3.org</email></address>
2150    </author>
2151    <date month="January" year="1997"/>
2152  </front>
2153  <seriesInfo name="RFC" value="2068"/>
2154</reference>
2155
2156<reference anchor="RFC2076">
2157  <front>
2158    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2159    <author initials="J." surname="Palme" fullname="Jacob Palme">
2160      <organization>Stockholm University/KTH</organization>
2161      <address><email>jpalme@dsv.su.se</email></address>
2162    </author>
2163    <date month="February" year="1997"/>
2164  </front>
2165  <seriesInfo name="RFC" value="2076"/>
2166</reference>
2167
2168<reference anchor="RFC2183">
2169  <front>
2170    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2171    <author initials="R." surname="Troost" fullname="Rens Troost">
2172      <organization>New Century Systems</organization>
2173      <address><email>rens@century.com</email></address>
2174    </author>
2175    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2176      <organization>QUALCOMM Incorporated</organization>
2177      <address><email>sdorner@qualcomm.com</email></address>
2178    </author>
2179    <author initials="K." surname="Moore" fullname="Keith Moore">
2180      <organization>Department of Computer Science</organization>
2181      <address><email>moore@cs.utk.edu</email></address>
2182    </author>
2183    <date month="August" year="1997"/>
2184  </front>
2185  <seriesInfo name="RFC" value="2183"/>
2186</reference>
2187
2188<reference anchor="RFC2277">
2189  <front>
2190    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2191    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2192      <organization>UNINETT</organization>
2193      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2194    </author>
2195    <date month="January" year="1998"/>
2196  </front>
2197  <seriesInfo name="BCP" value="18"/>
2198  <seriesInfo name="RFC" value="2277"/>
2199</reference>
2200
2201<reference anchor="RFC2388">
2202  <front>
2203    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2204    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2205      <organization>Xerox Palo Alto Research Center</organization>
2206      <address><email>masinter@parc.xerox.com</email></address>
2207    </author>
2208    <date year="1998" month="August"/>
2209  </front>
2210  <seriesInfo name="RFC" value="2388"/>
2211</reference>
2212
2213<reference anchor="RFC2557">
2214  <front>
2215    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2216    <author initials="F." surname="Palme" fullname="Jacob Palme">
2217      <organization>Stockholm University and KTH</organization>
2218      <address><email>jpalme@dsv.su.se</email></address>
2219    </author>
2220    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2221      <organization>Microsoft Corporation</organization>
2222      <address><email>alexhop@microsoft.com</email></address>
2223    </author>
2224    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2225      <organization>Lotus Development Corporation</organization>
2226      <address><email>Shelness@lotus.com</email></address>
2227    </author>
2228    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2229      <organization/>
2230      <address><email>stef@nma.com</email></address>
2231    </author>
2232    <date year="1999" month="March"/>
2233  </front>
2234  <seriesInfo name="RFC" value="2557"/>
2235</reference>
2236
2237<reference anchor="RFC2616">
2238  <front>
2239    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2240    <author initials="R." surname="Fielding" fullname="R. Fielding">
2241      <organization>University of California, Irvine</organization>
2242      <address><email>fielding@ics.uci.edu</email></address>
2243    </author>
2244    <author initials="J." surname="Gettys" fullname="J. Gettys">
2245      <organization>W3C</organization>
2246      <address><email>jg@w3.org</email></address>
2247    </author>
2248    <author initials="J." surname="Mogul" fullname="J. Mogul">
2249      <organization>Compaq Computer Corporation</organization>
2250      <address><email>mogul@wrl.dec.com</email></address>
2251    </author>
2252    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2253      <organization>MIT Laboratory for Computer Science</organization>
2254      <address><email>frystyk@w3.org</email></address>
2255    </author>
2256    <author initials="L." surname="Masinter" fullname="L. Masinter">
2257      <organization>Xerox Corporation</organization>
2258      <address><email>masinter@parc.xerox.com</email></address>
2259    </author>
2260    <author initials="P." surname="Leach" fullname="P. Leach">
2261      <organization>Microsoft Corporation</organization>
2262      <address><email>paulle@microsoft.com</email></address>
2263    </author>
2264    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2265      <organization>W3C</organization>
2266      <address><email>timbl@w3.org</email></address>
2267    </author>
2268    <date month="June" year="1999"/>
2269  </front>
2270  <seriesInfo name="RFC" value="2616"/>
2271</reference>
2272
2273<reference anchor="RFC3629">
2274  <front>
2275    <title>UTF-8, a transformation format of ISO 10646</title>
2276    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2277      <organization>Alis Technologies</organization>
2278      <address><email>fyergeau@alis.com</email></address>
2279    </author>
2280    <date month="November" year="2003"/>
2281  </front>
2282  <seriesInfo name="RFC" value="3629"/>
2283  <seriesInfo name="STD" value="63"/>
2284</reference>
2285
2286<reference anchor='RFC3864'>
2287  <front>
2288    <title>Registration Procedures for Message Header Fields</title>
2289    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2290      <organization>Nine by Nine</organization>
2291      <address><email>GK-IETF@ninebynine.org</email></address>
2292    </author>
2293    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2294      <organization>BEA Systems</organization>
2295      <address><email>mnot@pobox.com</email></address>
2296    </author>
2297    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2298      <organization>HP Labs</organization>
2299      <address><email>JeffMogul@acm.org</email></address>
2300    </author>
2301    <date year='2004' month='September' />
2302  </front>
2303  <seriesInfo name='BCP' value='90' />
2304  <seriesInfo name='RFC' value='3864' />
2305</reference>
2306
2307<reference anchor="RFC4288">
2308  <front>
2309    <title>Media Type Specifications and Registration Procedures</title>
2310    <author initials="N." surname="Freed" fullname="N. Freed">
2311      <organization>Sun Microsystems</organization>
2312      <address>
2313        <email>ned.freed@mrochek.com</email>
2314      </address>
2315    </author>
2316    <author initials="J." surname="Klensin" fullname="J. Klensin">
2317      <organization/>
2318      <address>
2319        <email>klensin+ietf@jck.com</email>
2320      </address>
2321    </author>
2322    <date year="2005" month="December"/>
2323  </front>
2324  <seriesInfo name="BCP" value="13"/>
2325  <seriesInfo name="RFC" value="4288"/>
2326</reference>
2327
2328<reference anchor="RFC5322">
2329  <front>
2330    <title>Internet Message Format</title>
2331    <author initials="P." surname="Resnick" fullname="P. Resnick">
2332      <organization>Qualcomm Incorporated</organization>
2333    </author>
2334    <date year="2008" month="October"/>
2335  </front> 
2336  <seriesInfo name="RFC" value="5322"/>
2337</reference>
2338
2339<reference anchor='BCP97'>
2340  <front>
2341    <title>Handling Normative References to Standards-Track Documents</title>
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    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2349      <organization>MIT</organization>
2350      <address>
2351        <email>hartmans-ietf@mit.edu</email>
2352      </address>
2353    </author>
2354    <date year='2007' month='June' />
2355  </front>
2356  <seriesInfo name='BCP' value='97' />
2357  <seriesInfo name='RFC' value='4897' />
2358</reference>
2359
2360
2361</references>
2362
2363<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2364<t>
2365   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
2366   allow entities to be transmitted in an open variety of
2367   representations and with extensible mechanisms. However, RFC 2045
2368   discusses mail, and HTTP has a few features that are different from
2369   those described in RFC 2045. These differences were carefully chosen
2370   to optimize performance over binary connections, to allow greater
2371   freedom in the use of new media types, to make date comparisons
2372   easier, and to acknowledge the practice of some early HTTP servers
2373   and clients.
2374</t>
2375<t>
2376   This appendix describes specific areas where HTTP differs from RFC
2377   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2378   aware of these differences and provide the appropriate conversions
2379   where necessary. Proxies and gateways from MIME environments to HTTP
2380   also need to be aware of the differences because some conversions
2381   might be required.
2382</t>
2383
2384<section title="MIME-Version" anchor="mime-version">
2385  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2386  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
2387  <x:anchor-alias value="MIME-Version"/>
2388  <x:anchor-alias value="MIME-Version-v"/>
2389<t>
2390   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2391   include a single MIME-Version general-header field to indicate what
2392   version of the MIME protocol was used to construct the message. Use
2393   of the MIME-Version header field indicates that the message is in
2394   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2395   Proxies/gateways are responsible for ensuring full compliance (where
2396   possible) when exporting HTTP messages to strict MIME environments.
2397</t>
2398<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
2399  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
2400  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2401</artwork></figure>
2402<t>
2403   MIME version "1.0" is the default for use in HTTP/1.1. However,
2404   HTTP/1.1 message parsing and semantics are defined by this document
2405   and not the MIME specification.
2406</t>
2407</section>
2408
2409<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2410<t>
2411   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2412   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2413   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2414   allowed for subtypes of the "text" media type when transmitted over
2415   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2416   line breaks as CRLF and forbids the use of CR or LF outside of line
2417   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2418   line break within text content when a message is transmitted over
2419   HTTP.
2420</t>
2421<t>
2422   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2423   environment &SHOULD; translate all line breaks within the text media
2424   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2425   canonical form of CRLF. Note, however, that this might be complicated
2426   by the presence of a Content-Encoding and by the fact that HTTP
2427   allows the use of some character sets which do not use octets 13 and
2428   10 to represent CR and LF, as is the case for some multi-byte
2429   character sets.
2430</t>
2431<t>
2432   Implementors should note that conversion will break any cryptographic
2433   checksums applied to the original content unless the original content
2434   is already in canonical form. Therefore, the canonical form is
2435   recommended for any content that uses such checksums in HTTP.
2436</t>
2437</section>
2438
2439
2440<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2441<t>
2442   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2443   simplify the process of date comparison. Proxies and gateways from
2444   other protocols &SHOULD; ensure that any Date header field present in a
2445   message conforms to one of the HTTP/1.1 formats and rewrite the date
2446   if necessary.
2447</t>
2448</section>
2449
2450<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2451<t>
2452   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2453   Content-Encoding header field. Since this acts as a modifier on the
2454   media type, proxies and gateways from HTTP to MIME-compliant
2455   protocols &MUST; either change the value of the Content-Type header
2456   field or decode the entity-body before forwarding the message. (Some
2457   experimental applications of Content-Type for Internet mail have used
2458   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2459   a function equivalent to Content-Encoding. However, this parameter is
2460   not part of RFC 2045).
2461</t>
2462</section>
2463
2464<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2465<t>
2466   HTTP does not use the Content-Transfer-Encoding field of RFC
2467   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2468   remove any Content-Transfer-Encoding
2469   prior to delivering the response message to an HTTP client.
2470</t>
2471<t>
2472   Proxies and gateways from HTTP to MIME-compliant protocols are
2473   responsible for ensuring that the message is in the correct format
2474   and encoding for safe transport on that protocol, where "safe
2475   transport" is defined by the limitations of the protocol being used.
2476   Such a proxy or gateway &SHOULD; label the data with an appropriate
2477   Content-Transfer-Encoding if doing so will improve the likelihood of
2478   safe transport over the destination protocol.
2479</t>
2480</section>
2481
2482<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2483<t>
2484   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2485   Proxies/gateways &MUST; remove any transfer-coding prior to
2486   forwarding a message via a MIME-compliant protocol.
2487</t>
2488</section>
2489
2490<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2491<t>
2492   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2493   need to be aware of MIME line length limitations. Since HTTP does not
2494   have this limitation, HTTP does not fold long lines. MHTML messages
2495   being transported by HTTP follow all conventions of MHTML, including
2496   line length limitations and folding, canonicalization, etc., since
2497   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2498   does not interpret the content or any MIME header lines that might be
2499   contained therein.
2500</t>
2501</section>
2502</section>
2503
2504<section title="Additional Features" anchor="additional.features">
2505<t>
2506   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2507   existing HTTP implementations, but not consistently and correctly
2508   across most HTTP/1.1 applications. Implementors are advised to be
2509   aware of these features, but cannot rely upon their presence in, or
2510   interoperability with, other HTTP/1.1 applications. Some of these
2511   describe proposed experimental features, and some describe features
2512   that experimental deployment found lacking that are now addressed in
2513   the base HTTP/1.1 specification.
2514</t>
2515<t>
2516   A number of other headers, such as Content-Disposition and Title,
2517   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2518</t>
2519
2520<section title="Content-Disposition" anchor="content-disposition">
2521<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2522<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2523  <x:anchor-alias value="content-disposition"/>
2524  <x:anchor-alias value="content-disposition-v"/>
2525  <x:anchor-alias value="disposition-type"/>
2526  <x:anchor-alias value="disposition-parm"/>
2527  <x:anchor-alias value="disp-extension-parm"/>
2528  <x:anchor-alias value="disp-extension-token"/>
2529  <x:anchor-alias value="filename-parm"/>
2530<t>
2531   The Content-Disposition response-header field has been proposed as a
2532   means for the origin server to suggest a default filename if the user
2533   requests that the content is saved to a file. This usage is derived
2534   from the definition of Content-Disposition in <xref target="RFC2183"/>.
2535</t>
2536<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"/>
2537  <x:ref>content-disposition</x:ref> = "Content-Disposition" ":" <x:ref>OWS</x:ref>
2538                        <x:ref>content-disposition-v</x:ref>
2539  <x:ref>content-disposition-v</x:ref> = <x:ref>disposition-type</x:ref>
2540                          *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>disposition-parm</x:ref> )
2541  <x:ref>disposition-type</x:ref> = "attachment" / <x:ref>disp-extension-token</x:ref>
2542  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> / <x:ref>disp-extension-parm</x:ref>
2543  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2544  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
2545  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
2546</artwork></figure>
2547<t>
2548   An example is
2549</t>
2550<figure><artwork type="example">
2551   Content-Disposition: attachment; filename="fname.ext"
2552</artwork></figure>
2553<t>
2554   The receiving user agent &SHOULD-NOT;  respect any directory path
2555   information present in the filename-parm parameter, which is the only
2556   parameter believed to apply to HTTP implementations at this time. The
2557   filename &SHOULD; be treated as a terminal component only.
2558</t>
2559<t>
2560   If this header is used in a response with the application/octet-stream
2561   content-type, the implied suggestion is that the user agent
2562   should not display the response, but directly enter a `save response
2563   as...' dialog.
2564</t>
2565<t>
2566   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2567</t>
2568</section>
2569</section>
2570
2571<section title="Compatibility with Previous Versions" anchor="compatibility">
2572<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2573<t>
2574   Transfer-coding and message lengths all interact in ways that
2575   required fixing exactly when chunked encoding is used (to allow for
2576   transfer encoding that may not be self delimiting); it was important
2577   to straighten out exactly how message lengths are computed.
2578   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2579   <xref target="Part5"/> and <xref target="Part6"/>).
2580</t>
2581<t>
2582   Charset wildcarding is introduced to avoid explosion of character set
2583   names in accept headers. (<xref target="header.accept-charset"/>)
2584</t>
2585<t>
2586   Content-Base was deleted from the specification: it was not
2587   implemented widely, and there is no simple, safe way to introduce it
2588   without a robust extension mechanism. In addition, it is used in a
2589   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2590</t>
2591<t>
2592   A content-coding of "identity" was introduced, to solve problems
2593   discovered in caching. (<xref target="content.codings"/>)
2594</t>
2595<t>
2596   Quality Values of zero should indicate that "I don't want something"
2597   to allow clients to refuse a representation. (<xref target="quality.values"/>)
2598</t>
2599<t>
2600   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
2601   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
2602   specification, but not commonly implemented. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.2"/>.
2603</t>
2604</section>
2605
2606<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2607<t>
2608  Clarify contexts that charset is used in.
2609  (<xref target="character.sets"/>)
2610</t>
2611<t>
2612  Remove reference to non-existant identity transfer-coding value tokens.
2613  (<xref target="no.content-transfer-encoding"/>)
2614</t>
2615</section>
2616
2617</section>
2618
2619<section title="Collected ABNF" anchor="collected.abnf">
2620   <figure>
2621      <artwork type="abnf" name="p3-payload.parsed-abnf">ALPHA = &lt;ALPHA, defined in [Part1], Section 1.2.2&gt;&#xD;
2622Accept = "Accept:" OWS Accept-v&#xD;
2623Accept-Charset = "Accept-Charset:" OWS Accept-Charset-v&#xD;
2624Accept-Charset-v = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="&#xD;
2625 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="&#xD;
2626 qvalue ] ] )&#xD;
2627Accept-Encoding = "Accept-Encoding:" OWS Accept-Encoding-v&#xD;
2628Accept-Encoding-v = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )&#xD;
2629 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]&#xD;
2630Accept-Language = "Accept-Language:" OWS Accept-Language-v&#xD;
2631Accept-Language-v = *( "," OWS ) language-range [ OWS ";" OWS "q="&#xD;
2632 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]&#xD;
2633 ] )&#xD;
2634Accept-v = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [&#xD;
2635 OWS media-range [ accept-params ] ] ) ]&#xD;
2636Content-Encoding = "Content-Encoding:" OWS Content-Encoding-v&#xD;
2637Content-Encoding-v = *( "," OWS ) content-coding *( OWS "," [ OWS&#xD;
2638 content-coding ] )&#xD;
2639Content-Language = "Content-Language:" OWS Content-Language-v&#xD;
2640Content-Language-v = *( "," OWS ) language-tag *( OWS "," [ OWS&#xD;
2641 language-tag ] )&#xD;
2642Content-Length = &lt;Content-Length, defined in [Part1], Section 8.2&gt;&#xD;
2643Content-Location = "Content-Location:" OWS Content-Location-v&#xD;
2644Content-Location-v = absolute-URI / partial-URI&#xD;
2645Content-MD5 = "Content-MD5:" OWS Content-MD5-v&#xD;
2646Content-MD5-v = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;&#xD;
2647Content-Range = &lt;Content-Range, defined in [Part5], Section 5.2&gt;&#xD;
2648Content-Type = "Content-Type:" OWS Content-Type-v&#xD;
2649Content-Type-v = media-type&#xD;
2650DIGIT = &lt;DIGIT, defined in [Part1], Section 1.2.2&gt;&#xD;
2651Expires = &lt;Expires, defined in [Part6], Section 15.3&gt;&#xD;
2652Last-Modified = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;&#xD;
2653MIME-Version = "MIME-Version:" OWS MIME-Version-v&#xD;
2654MIME-Version-v = 1*DIGIT "." 1*DIGIT&#xD;
2655OCTET = &lt;OCTET, defined in [Part1], Section 1.2.2&gt;&#xD;
2656OWS = &lt;OWS, defined in [Part1], Section 1.2.2&gt;&#xD;
2657absolute-URI = &lt;absolute-URI, defined in [Part1], Section 2.1&gt;&#xD;
2658accept-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ]&#xD;
2659accept-params = OWS ";" OWS "q=" qvalue *accept-ext&#xD;
2660attribute = token&#xD;
2661charset = token&#xD;
2662codings = ( content-coding / "*" )&#xD;
2663content-coding = token&#xD;
2664content-disposition = "Content-Disposition:" OWS&#xD;
2665 content-disposition-v&#xD;
2666content-disposition-v = disposition-type *( OWS ";" OWS&#xD;
2667 disposition-parm )&#xD;
2668disp-extension-parm = token "=" ( token / quoted-string )&#xD;
2669disp-extension-token = token&#xD;
2670disposition-parm = filename-parm / disp-extension-parm&#xD;
2671disposition-type = "attachment" / disp-extension-token&#xD;
2672entity-body = *OCTET&#xD;
2673entity-header = Content-Encoding / Content-Language / Content-Length&#xD;
2674 / Content-Location / Content-MD5 / Content-Range / Content-Type /&#xD;
2675 Expires / Last-Modified / extension-header&#xD;
2676extension-header = message-header&#xD;
2677filename-parm = "filename=" quoted-string&#xD;
2678language-range = &lt;language-range, defined in [RFC4647], Section 2.1&gt;&#xD;
2679language-tag = primary-tag *( "-" subtag )&#xD;
2680media-range = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS&#xD;
2681 ";" OWS parameter )&#xD;
2682media-type = type "/" subtype *( OWS ";" OWS parameter )&#xD;
2683message-header = &lt;message-header, defined in [Part1], Section 4.2&gt;&#xD;
2684parameter = attribute "=" value&#xD;
2685partial-URI = &lt;partial-URI, defined in [Part1], Section 2.1&gt;&#xD;
2686primary-tag = 1*8ALPHA&#xD;
2687quoted-string = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;&#xD;
2688qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )&#xD;
2689subtag = 1*8ALPHA&#xD;
2690subtype = token&#xD;
2691token = &lt;token, defined in [Part1], Section 1.2.2&gt;&#xD;
2692type = token&#xD;
2693value = token / quoted-string&#xD;
2694; Accept defined but not used&#xD;
2695; Accept-Charset defined but not used&#xD;
2696; Accept-Encoding defined but not used&#xD;
2697; Accept-Language defined but not used&#xD;
2698; MIME-Version defined but not used&#xD;
2699; content-disposition defined but not used&#xD;
2700; entity-body defined but not used&#xD;
2701; entity-header defined but not used&#xD;
2702</artwork>
2703   </figure>
2704</section>
2705
2706<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2707
2708<section title="Since RFC2616">
2709<t>
2710  Extracted relevant partitions from <xref target="RFC2616"/>.
2711</t>
2712</section>
2713
2714<section title="Since draft-ietf-httpbis-p3-payload-00">
2715<t>
2716  Closed issues:
2717  <list style="symbols"> 
2718    <t>
2719      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2720      "Media Type Registrations"
2721      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2722    </t>
2723    <t>
2724      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2725      "Clarification regarding quoting of charset values"
2726      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2727    </t>
2728    <t>
2729      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2730      "Remove 'identity' token references"
2731      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2732    </t>
2733    <t>
2734      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2735      "Accept-Encoding BNF"
2736    </t>
2737    <t>
2738      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2739      "Normative and Informative references"
2740    </t>
2741    <t>
2742      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2743      "RFC1700 references"
2744    </t>
2745    <t>
2746      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2747      "Updating to RFC4288"
2748    </t>
2749    <t>
2750      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2751      "Informative references"
2752    </t>
2753    <t>
2754      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2755      "ISO-8859-1 Reference"
2756    </t>
2757    <t>
2758      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2759      "Encoding References Normative"
2760    </t>
2761    <t>
2762      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2763      "Normative up-to-date references"
2764    </t>
2765  </list>
2766</t>
2767</section>
2768
2769<section title="Since draft-ietf-httpbis-p3-payload-01">
2770<t>
2771  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2772  <list style="symbols"> 
2773    <t>
2774      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2775    </t>
2776  </list>
2777</t>
2778</section>
2779
2780<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2781<t>
2782  Closed issues:
2783  <list style="symbols"> 
2784    <t>
2785      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2786      "Quoting Charsets"
2787    </t>
2788    <t>
2789      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2790      "Classification for Allow header"
2791    </t>
2792    <t>
2793      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2794      "missing default for qvalue in description of Accept-Encoding"
2795    </t>
2796  </list>
2797</t>
2798<t>
2799  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2800  <list style="symbols"> 
2801    <t>
2802      Reference RFC 3984, and update header registrations for headers defined
2803      in this document.
2804    </t>
2805  </list>
2806</t>
2807</section>
2808
2809<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2810<t>
2811  Closed issues:
2812  <list style="symbols"> 
2813    <t>
2814      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2815      "Quoting Charsets"
2816    </t>
2817    <t>
2818      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2819      "language tag matching (Accept-Language) vs RFC4647"
2820    </t>
2821    <t>
2822      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2823      "RFC 1806 has been replaced by RFC2183"
2824    </t>
2825  </list>
2826</t>
2827<t>
2828  Other changes:
2829  <list style="symbols"> 
2830    <t>
2831      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2832      "Encoding References Normative" -- rephrase the annotation and reference
2833      <xref target="BCP97"/>.
2834    </t>
2835  </list>
2836</t>
2837 </section>
2838
2839<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2840<t>
2841  Closed issues:
2842  <list style="symbols"> 
2843    <t>
2844      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2845      "RFC 2822 is updated by RFC 5322"
2846    </t>
2847  </list>
2848</t>
2849<t>
2850  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2851  <list style="symbols"> 
2852    <t>
2853      Use "/" instead of "|" for alternatives.
2854    </t>
2855    <t>
2856      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2857      whitespace ("OWS") and required whitespace ("RWS").
2858    </t>
2859    <t>
2860      Rewrite ABNFs to spell out whitespace rules, factor out
2861      header value format definitions.
2862    </t>
2863  </list>
2864</t>
2865</section>
2866
2867<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2868<t>
2869  Closed issues:
2870  <list style="symbols"> 
2871    <t>
2872      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2873      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2874    </t>
2875  </list>
2876</t>
2877<t>
2878  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2879  <list style="symbols"> 
2880    <t>
2881      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2882    </t>
2883  </list>
2884</t>
2885</section>
2886
2887</section>
2888
2889</back>
2890</rfc>
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