source: draft-ietf-httpbis/latest/p3-payload.xml @ 446

Last change on this file since 446 was 446, checked in by julian.reschke@…, 11 years ago

Update to latest version of rfc2629.xslt, and add experimental version of xml2rfc.tcl (supporting the new IPR escape clause), use that clause in P1..P7 (but not for the method registrations).

  • Property svn:eol-style set to native
File size: 127.6 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 "February">
16  <!ENTITY ID-YEAR "2009">
17  <!ENTITY notation                 "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY notation-abnf            "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY basic-rules              "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY message-length           "<xref target='Part1' x:rel='#message.length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY message-headers          "<xref target='Part1' x:rel='#message.headers' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY full-date                "<xref target='Part1' x:rel='#full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY 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="pre5378Trust200902" 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  <workgroup>HTTPbis Working Group</workgroup>
192
193<abstract>
194<t>
195   The Hypertext Transfer Protocol (HTTP) is an application-level
196   protocol for distributed, collaborative, hypermedia information
197   systems. HTTP has been in use by the World Wide Web global information
198   initiative since 1990. This document is Part 3 of the seven-part specification
199   that defines the protocol referred to as "HTTP/1.1" and, taken together,
200   obsoletes RFC 2616.  Part 3 defines HTTP message content,
201   metadata, and content negotiation.
202</t>
203</abstract>
204
205<note title="Editorial Note (To be removed by RFC Editor)">
206  <t>
207    Discussion of this draft should take place on the HTTPBIS working group
208    mailing list (ietf-http-wg@w3.org). The current issues list is
209    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
210    and related documents (including fancy diffs) can be found at
211    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
212  </t>
213  <t>
214    The changes in this draft are summarized in <xref target="changes.since.05"/>.
215  </t>
216</note>
217</front>
218<middle>
219<section title="Introduction" anchor="introduction">
220<t>
221   This document defines HTTP/1.1 message payloads (a.k.a., content), the
222   associated metadata header fields that define how the payload is intended
223   to be interpreted by a recipient, the request header fields that
224   may influence content selection, and the various selection algorithms
225   that are collectively referred to as HTTP content negotiation.
226</t>
227<t>
228   This document is currently disorganized in order to minimize the changes
229   between drafts and enable reviewers to see the smaller errata changes.
230   The next draft will reorganize the sections to better reflect the content.
231   In particular, the sections on entities will be renamed payload and moved
232   to the first half of the document, while the sections on content negotiation
233   and associated request header fields will be moved to the second half.  The
234   current mess reflects how widely dispersed these topics and associated
235   requirements had become in <xref target="RFC2616"/>.
236</t>
237
238<section title="Requirements" anchor="intro.requirements">
239<t>
240   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
241   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
242   document are to be interpreted as described in <xref target="RFC2119"/>.
243</t>
244<t>
245   An implementation is not compliant if it fails to satisfy one or more
246   of the &MUST; or &REQUIRED; level requirements for the protocols it
247   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
248   level and all the &SHOULD; level requirements for its protocols is said
249   to be "unconditionally compliant"; one that satisfies all the &MUST;
250   level requirements but not all the &SHOULD; level requirements for its
251   protocols is said to be "conditionally compliant."
252</t>
253</section>
254
255<section title="Syntax Notation" anchor="notation">
256  <x:anchor-alias value="ALPHA"/>
257  <x:anchor-alias value="CR"/>
258  <x:anchor-alias value="DIGIT"/>
259  <x:anchor-alias value="LF"/>
260  <x:anchor-alias value="OCTET"/>
261  <x:anchor-alias value="VCHAR"/>
262  <x:anchor-alias value="WSP"/>
263<t>
264  This specification uses the ABNF syntax defined in &notation;.
265  The following core rules are included by
266  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
267  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
268  DIGIT (decimal 0-9), DQUOTE (double quote),
269  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
270  OCTET (any 8-bit sequence of data), SP (space),
271  VCHAR (any visible USASCII character),
272  and WSP (whitespace).
273</t>
274
275<section title="Core Rules" anchor="core.rules">
276  <x:anchor-alias value="quoted-string"/>
277  <x:anchor-alias value="token"/>
278  <x:anchor-alias value="OWS"/>
279<t>
280  The core rules below are defined in &basic-rules;:
281</t>
282<figure><artwork type="abnf2616">
283  <x:ref>quoted-string</x:ref>  = &lt;quoted-string, defined in &basic-rules;&gt;
284  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
285  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
286</artwork></figure>
287</section>
288
289<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
290  <x:anchor-alias value="absolute-URI"/>
291  <x:anchor-alias value="Allow"/>
292  <x:anchor-alias value="Content-Length"/>
293  <x:anchor-alias value="Content-Range"/>
294  <x:anchor-alias value="Expires"/>
295  <x:anchor-alias value="Last-Modified"/>
296  <x:anchor-alias value="message-header"/>
297  <x:anchor-alias value="partial-URI"/>
298<t>
299  The ABNF rules below are defined in other parts:
300</t>
301<figure><!--Part1--><artwork type="abnf2616">
302  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
303  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
304  <x:ref>message-header</x:ref> = &lt;message-header, defined in &message-headers;&gt;
305  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
306</artwork></figure>
307<figure><!--Part4--><artwork type="abnf2616">
308  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
309</artwork></figure>
310<figure><!--Part5--><artwork type="abnf2616">
311  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
312</artwork></figure>
313<figure><!--Part6--><artwork type="abnf2616">
314  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
315</artwork></figure>
316</section>
317
318</section>
319
320</section>
321
322<section title="Protocol Parameters" anchor="protocol.parameters">
323
324<section title="Character Sets" anchor="character.sets">
325<t>
326   HTTP uses the same definition of the term "character set" as that
327   described for MIME:
328</t>
329<t>
330   The term "character set" is used in this document to refer to a
331   method used with one or more tables to convert a sequence of octets
332   into a sequence of characters. Note that unconditional conversion in
333   the other direction is not required, in that not all characters may
334   be available in a given character set and a character set may provide
335   more than one sequence of octets to represent a particular character.
336   This definition is intended to allow various kinds of character
337   encoding, from simple single-table mappings such as US-ASCII to
338   complex table switching methods such as those that use ISO-2022's
339   techniques. However, the definition associated with a MIME character
340   set name &MUST; fully specify the mapping to be performed from octets
341   to characters. In particular, use of external profiling information
342   to determine the exact mapping is not permitted.
343</t>
344<t><list><t>
345      <x:h>Note:</x:h> This use of the term "character set" is more commonly
346      referred to as a "character encoding." However, since HTTP and
347      MIME share the same registry, it is important that the terminology
348      also be shared.
349</t></list></t>
350<t anchor="rule.charset">
351  <x:anchor-alias value="charset"/>
352   HTTP character sets are identified by case-insensitive tokens. The
353   complete set of tokens is defined by the IANA Character Set registry
354   (<eref target="http://www.iana.org/assignments/character-sets"/>).
355</t>
356<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
357  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
358</artwork></figure>
359<t>
360   Although HTTP allows an arbitrary token to be used as a charset
361   value, any token that has a predefined value within the IANA
362   Character Set registry &MUST; represent the character set defined
363   by that registry. Applications &SHOULD; limit their use of character
364   sets to those defined by the IANA registry.
365</t>
366<t>
367   HTTP uses charset in two contexts: within an Accept-Charset request
368   header (in which the charset value is an unquoted token) and as the
369   value of a parameter in a Content-Type header (within a request or
370   response), in which case the parameter value of the charset parameter
371   may be quoted.
372</t>
373<t>
374   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
375   <xref target="RFC2277"/>.
376</t>
377
378<section title="Missing Charset" anchor="missing.charset">
379<t>
380   Some HTTP/1.0 software has interpreted a Content-Type header without
381   charset parameter incorrectly to mean "recipient should guess."
382   Senders wishing to defeat this behavior &MAY; include a charset
383   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
384   it is known that it will not confuse the recipient.
385</t>
386<t>
387   Unfortunately, some older HTTP/1.0 clients did not deal properly with
388   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
389   charset label provided by the sender; and those user agents that have
390   a provision to "guess" a charset &MUST; use the charset from the
391   content-type field if they support that charset, rather than the
392   recipient's preference, when initially displaying a document. See
393   <xref target="canonicalization.and.text.defaults"/>.
394</t>
395</section>
396</section>
397
398<section title="Content Codings" anchor="content.codings">
399  <x:anchor-alias value="content-coding"/>
400<t>
401   Content coding values indicate an encoding transformation that has
402   been or can be applied to an entity. Content codings are primarily
403   used to allow a document to be compressed or otherwise usefully
404   transformed without losing the identity of its underlying media type
405   and without loss of information. Frequently, the entity is stored in
406   coded form, transmitted directly, and only decoded by the recipient.
407</t>
408<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
409  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
410</artwork></figure>
411<t>
412   All content-coding values are case-insensitive. HTTP/1.1 uses
413   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
414   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
415   describes the content-coding, what is more important is that it
416   indicates what decoding mechanism will be required to remove the
417   encoding.
418</t>
419<t>
420   The Internet Assigned Numbers Authority (IANA) acts as a registry for
421   content-coding value tokens. Initially, the registry contains the
422   following tokens:
423</t>
424<t>
425   gzip<iref item="gzip"/>
426  <list>
427    <t>
428        An encoding format produced by the file compression program
429        "gzip" (GNU zip) as described in <xref target="RFC1952"/>. This format is a
430        Lempel-Ziv coding (LZ77) with a 32 bit CRC.
431    </t>
432  </list>
433</t>
434<t>
435   compress<iref item="compress"/>
436  <list><t>
437        The encoding format produced by the common UNIX file compression
438        program "compress". This format is an adaptive Lempel-Ziv-Welch
439        coding (LZW).
440</t><t>
441        Use of program names for the identification of encoding formats
442        is not desirable and is discouraged for future encodings. Their
443        use here is representative of historical practice, not good
444        design. For compatibility with previous implementations of HTTP,
445        applications &SHOULD; consider "x-gzip" and "x-compress" to be
446        equivalent to "gzip" and "compress" respectively.
447  </t></list>
448</t>
449<t>
450   deflate<iref item="deflate"/>
451  <list><t>
452        The "zlib" format defined in <xref target="RFC1950"/> in combination with
453        the "deflate" compression mechanism described in <xref target="RFC1951"/>.
454  </t></list>
455</t>
456<t>
457   identity<iref item="identity"/>
458  <list><t>
459        The default (identity) encoding; the use of no transformation
460        whatsoever. This content-coding is used only in the Accept-Encoding
461        header, and &SHOULD-NOT;  be used in the Content-Encoding
462        header.
463  </t></list>
464</t>
465<t>
466   New content-coding value tokens &SHOULD; be registered; to allow
467   interoperability between clients and servers, specifications of the
468   content coding algorithms needed to implement a new value &SHOULD; be
469   publicly available and adequate for independent implementation, and
470   conform to the purpose of content coding defined in this section.
471</t>
472</section>
473
474<section title="Media Types" anchor="media.types">
475  <x:anchor-alias value="media-type"/>
476  <x:anchor-alias value="type"/>
477  <x:anchor-alias value="subtype"/>
478<t>
479   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
480   and Accept (<xref target="header.accept"/>) header fields in order to provide
481   open and extensible data typing and type negotiation.
482</t>
483<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"/>
484  <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> )
485  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
486  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
487</artwork></figure>
488<t anchor="rule.parameter">
489  <x:anchor-alias value="attribute"/>
490  <x:anchor-alias value="parameter"/>
491  <x:anchor-alias value="value"/>
492   Parameters &MAY; follow the type/subtype in the form of attribute/value
493   pairs.
494</t>
495<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"/>
496  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
497  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
498  <x:ref>value</x:ref>          = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
499</artwork></figure>
500<t>
501   The type, subtype, and parameter attribute names are case-insensitive.
502   Parameter values might or might not be case-sensitive, depending on the
503   semantics of the parameter name.  The presence or absence of a parameter might
504   be significant to the processing of a media-type, depending on its
505   definition within the media type registry.
506</t>
507<t>
508   A parameter value that matches the <x:ref>token</x:ref> production may be
509   transmitted as either a token or within a quoted-string. The quoted and
510   unquoted values are equivalent.
511</t>
512<t>
513   Note that some older HTTP applications do not recognize media type
514   parameters. When sending data to older HTTP applications,
515   implementations &SHOULD; only use media type parameters when they are
516   required by that type/subtype definition.
517</t>
518<t>
519   Media-type values are registered with the Internet Assigned Number
520   Authority (IANA). The media type registration process is
521   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
522   discouraged.
523</t>
524
525<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
526<t>
527   Internet media types are registered with a canonical form. An
528   entity-body transferred via HTTP messages &MUST; be represented in the
529   appropriate canonical form prior to its transmission except for
530   "text" types, as defined in the next paragraph.
531</t>
532<t>
533   When in canonical form, media subtypes of the "text" type use CRLF as
534   the text line break. HTTP relaxes this requirement and allows the
535   transport of text media with plain CR or LF alone representing a line
536   break when it is done consistently for an entire entity-body. HTTP
537   applications &MUST; accept CRLF, bare CR, and bare LF as being
538   representative of a line break in text media received via HTTP. In
539   addition, if the text is represented in a character set that does not
540   use octets 13 and 10 for CR and LF respectively, as is the case for
541   some multi-byte character sets, HTTP allows the use of whatever octet
542   sequences are defined by that character set to represent the
543   equivalent of CR and LF for line breaks. This flexibility regarding
544   line breaks applies only to text media in the entity-body; a bare CR
545   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
546   structures (such as header fields and multipart boundaries).
547</t>
548<t>
549   If an entity-body is encoded with a content-coding, the underlying
550   data &MUST; be in a form defined above prior to being encoded.
551</t>
552<t>
553   The "charset" parameter is used with some media types to define the
554   character set (<xref target="character.sets"/>) of the data. When no explicit charset
555   parameter is provided by the sender, media subtypes of the "text"
556   type are defined to have a default charset value of "ISO-8859-1" when
557   received via HTTP. Data in character sets other than "ISO-8859-1" or
558   its subsets &MUST; be labeled with an appropriate charset value. See
559   <xref target="missing.charset"/> for compatibility problems.
560</t>
561</section>
562
563<section title="Multipart Types" anchor="multipart.types">
564<t>
565   MIME provides for a number of "multipart" types -- encapsulations of
566   one or more entities within a single message-body. All multipart
567   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
568   and &MUST; include a boundary parameter as part of the media type
569   value. The message body is itself a protocol element and &MUST;
570   therefore use only CRLF to represent line breaks between body-parts.
571   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
572   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
573   original multipart contains an epilogue). These restrictions exist in
574   order to preserve the self-delimiting nature of a multipart message-body,
575   wherein the "end" of the message-body is indicated by the
576   ending multipart boundary.
577</t>
578<t>
579   In general, HTTP treats a multipart message-body no differently than
580   any other media type: strictly as payload. The one exception is the
581   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
582   (Partial Content) response.
583   <!-- jre: re-insert removed text pointing to caching? -->
584   In all
585   other cases, an HTTP user agent &SHOULD; follow the same or similar
586   behavior as a MIME user agent would upon receipt of a multipart type.
587   The MIME header fields within each body-part of a multipart message-body
588   do not have any significance to HTTP beyond that defined by
589   their MIME semantics.
590</t>
591<t>
592   In general, an HTTP user agent &SHOULD; follow the same or similar
593   behavior as a MIME user agent would upon receipt of a multipart type.
594   If an application receives an unrecognized multipart subtype, the
595   application &MUST; treat it as being equivalent to "multipart/mixed".
596</t>
597<t><list><t>
598      <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
599      for carrying form data suitable for processing via the POST
600      request method, as described in <xref target="RFC2388"/>.
601</t></list></t>
602</section>
603</section>
604
605<section title="Quality Values" anchor="quality.values">
606  <x:anchor-alias value="qvalue"/>
607<t>
608   HTTP content negotiation (<xref target="content.negotiation"/>) uses short "floating point"
609   numbers to indicate the relative importance ("weight") of various
610   negotiable parameters.  A weight is normalized to a real number in
611   the range 0 through 1, where 0 is the minimum and 1 the maximum
612   value. If a parameter has a quality value of 0, then content with
613   this parameter is `not acceptable' for the client. HTTP/1.1
614   applications &MUST-NOT; generate more than three digits after the
615   decimal point. User configuration of these values &SHOULD; also be
616   limited in this fashion.
617</t>
618<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
619  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
620                 / ( "1" [ "." 0*3("0") ] )
621</artwork></figure>
622<t>
623   "Quality values" is a misnomer, since these values merely represent
624   relative degradation in desired quality.
625</t>
626</section>
627
628<section title="Language Tags" anchor="language.tags">
629  <x:anchor-alias value="language-tag"/>
630  <x:anchor-alias value="primary-tag"/>
631  <x:anchor-alias value="subtag"/>
632<t>
633   A language tag identifies a natural language spoken, written, or
634   otherwise conveyed by human beings for communication of information
635   to other human beings. Computer languages are explicitly excluded.
636   HTTP uses language tags within the Accept-Language and Content-Language
637   fields.
638</t>
639<t>
640   The syntax and registry of HTTP language tags is the same as that
641   defined by <xref target="RFC1766"/>. In summary, a language tag is composed of 1
642   or more parts: A primary language tag and a possibly empty series of
643   subtags:
644</t>
645<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"/>
646  <x:ref>language-tag</x:ref>  = <x:ref>primary-tag</x:ref> *( "-" <x:ref>subtag</x:ref> )
647  <x:ref>primary-tag</x:ref>   = 1*8<x:ref>ALPHA</x:ref>
648  <x:ref>subtag</x:ref>        = 1*8<x:ref>ALPHA</x:ref>
649</artwork></figure>
650<t>
651   White space is not allowed within the tag and all tags are case-insensitive.
652   The name space of language tags is administered by the
653   IANA. Example tags include:
654</t>
655<figure><artwork type="example">
656    en, en-US, en-cockney, i-cherokee, x-pig-latin
657</artwork></figure>
658<t>
659   where any two-letter primary-tag is an ISO-639 language abbreviation
660   and any two-letter initial subtag is an ISO-3166 country code. (The
661   last three tags above are not registered tags; all but the last are
662   examples of tags which could be registered in future.)
663</t>
664</section>
665</section>
666
667<section title="Entity" anchor="entity">
668<t>
669   Request and Response messages &MAY; transfer an entity if not otherwise
670   restricted by the request method or response status code. An entity
671   consists of entity-header fields and an entity-body, although some
672   responses will only include the entity-headers.
673</t>
674<t>
675   In this section, both sender and recipient refer to either the client
676   or the server, depending on who sends and who receives the entity.
677</t>
678
679<section title="Entity Header Fields" anchor="entity.header.fields">
680  <x:anchor-alias value="entity-header"/>
681  <x:anchor-alias value="extension-header"/>
682<t>
683   Entity-header fields define metainformation about the entity-body or,
684   if no body is present, about the resource identified by the request.
685</t>
686<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
687  <x:ref>entity-header</x:ref>  = <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
688                 / <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
689                 / <x:ref>Content-Length</x:ref>           ; &header-content-length;
690                 / <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
691                 / <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
692                 / <x:ref>Content-Range</x:ref>            ; &header-content-range;
693                 / <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
694                 / <x:ref>Expires</x:ref>                  ; &header-expires;
695                 / <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
696                 / <x:ref>extension-header</x:ref>
697 
698  <x:ref>extension-header</x:ref> = <x:ref>message-header</x:ref>
699</artwork></figure>
700<t>
701   The extension-header mechanism allows additional entity-header fields
702   to be defined without changing the protocol, but these fields cannot
703   be assumed to be recognizable by the recipient. Unrecognized header
704   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
705   transparent proxies.
706</t>
707</section>
708
709<section title="Entity Body" anchor="entity.body">
710  <x:anchor-alias value="entity-body"/>
711<t>
712   The entity-body (if any) sent with an HTTP request or response is in
713   a format and encoding defined by the entity-header fields.
714</t>
715<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
716  <x:ref>entity-body</x:ref>    = *<x:ref>OCTET</x:ref>
717</artwork></figure>
718<t>
719   An entity-body is only present in a message when a message-body is
720   present, as described in &message-body;. The entity-body is obtained
721   from the message-body by decoding any Transfer-Encoding that might
722   have been applied to ensure safe and proper transfer of the message.
723</t>
724
725<section title="Type" anchor="type">
726<t>
727   When an entity-body is included with a message, the data type of that
728   body is determined via the header fields Content-Type and Content-Encoding.
729   These define a two-layer, ordered encoding model:
730</t>
731<figure><artwork type="example">
732    entity-body := Content-Encoding( Content-Type( data ) )
733</artwork></figure>
734<t>
735   Content-Type specifies the media type of the underlying data.
736   Content-Encoding may be used to indicate any additional content
737   codings applied to the data, usually for the purpose of data
738   compression, that are a property of the requested resource. There is
739   no default encoding.
740</t>
741<t>
742   Any HTTP/1.1 message containing an entity-body &SHOULD; include a
743   Content-Type header field defining the media type of that body. If
744   and only if the media type is not given by a Content-Type field, the
745   recipient &MAY; attempt to guess the media type via inspection of its
746   content and/or the name extension(s) of the URI used to identify the
747   resource. If the media type remains unknown, the recipient &SHOULD;
748   treat it as type "application/octet-stream".
749</t>
750</section>
751   
752<section title="Entity Length" anchor="entity.length">
753<t>
754   The entity-length of a message is the length of the message-body
755   before any transfer-codings have been applied. &message-length; defines
756   how the transfer-length of a message-body is determined.
757</t>
758</section>
759</section>
760</section>
761
762<section title="Content Negotiation" anchor="content.negotiation">
763<t>
764   Most HTTP responses include an entity which contains information for
765   interpretation by a human user. Naturally, it is desirable to supply
766   the user with the "best available" entity corresponding to the
767   request. Unfortunately for servers and caches, not all users have the
768   same preferences for what is "best," and not all user agents are
769   equally capable of rendering all entity types. For that reason, HTTP
770   has provisions for several mechanisms for "content negotiation" --
771   the process of selecting the best representation for a given response
772   when there are multiple representations available.
773  <list><t>
774      <x:h>Note:</x:h> This is not called "format negotiation" because the
775      alternate representations may be of the same media type, but use
776      different capabilities of that type, be in different languages,
777      etc.
778  </t></list>
779</t>
780<t>
781   Any response containing an entity-body &MAY; be subject to negotiation,
782   including error responses.
783</t>
784<t>
785   There are two kinds of content negotiation which are possible in
786   HTTP: server-driven and agent-driven negotiation. These two kinds of
787   negotiation are orthogonal and thus may be used separately or in
788   combination. One method of combination, referred to as transparent
789   negotiation, occurs when a cache uses the agent-driven negotiation
790   information provided by the origin server in order to provide
791   server-driven negotiation for subsequent requests.
792</t>
793
794<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
795<t>
796   If the selection of the best representation for a response is made by
797   an algorithm located at the server, it is called server-driven
798   negotiation. Selection is based on the available representations of
799   the response (the dimensions over which it can vary; e.g. language,
800   content-coding, etc.) and the contents of particular header fields in
801   the request message or on other information pertaining to the request
802   (such as the network address of the client).
803</t>
804<t>
805   Server-driven negotiation is advantageous when the algorithm for
806   selecting from among the available representations is difficult to
807   describe to the user agent, or when the server desires to send its
808   "best guess" to the client along with the first response (hoping to
809   avoid the round-trip delay of a subsequent request if the "best
810   guess" is good enough for the user). In order to improve the server's
811   guess, the user agent &MAY; include request header fields (Accept,
812   Accept-Language, Accept-Encoding, etc.) which describe its
813   preferences for such a response.
814</t>
815<t>
816   Server-driven negotiation has disadvantages:
817  <list style="numbers">
818    <t>
819         It is impossible for the server to accurately determine what
820         might be "best" for any given user, since that would require
821         complete knowledge of both the capabilities of the user agent
822         and the intended use for the response (e.g., does the user want
823         to view it on screen or print it on paper?).
824    </t>
825    <t>
826         Having the user agent describe its capabilities in every
827         request can be both very inefficient (given that only a small
828         percentage of responses have multiple representations) and a
829         potential violation of the user's privacy.
830    </t>
831    <t>
832         It complicates the implementation of an origin server and the
833         algorithms for generating responses to a request.
834    </t>
835    <t>
836         It may limit a public cache's ability to use the same response
837         for multiple user's requests.
838    </t>
839  </list>
840</t>
841<t>
842   HTTP/1.1 includes the following request-header fields for enabling
843   server-driven negotiation through description of user agent
844   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
845   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
846   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;). However, an
847   origin server is not limited to these dimensions and &MAY; vary the
848   response based on any aspect of the request, including information
849   outside the request-header fields or within extension header fields
850   not defined by this specification.
851</t>
852<t>
853   The Vary header field (&header-vary;) can be used to express the parameters the
854   server uses to select a representation that is subject to server-driven
855   negotiation.
856</t>
857</section>
858
859<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
860<t>
861   With agent-driven negotiation, selection of the best representation
862   for a response is performed by the user agent after receiving an
863   initial response from the origin server. Selection is based on a list
864   of the available representations of the response included within the
865   header fields or entity-body of the initial response, with each
866   representation identified by its own URI. Selection from among the
867   representations may be performed automatically (if the user agent is
868   capable of doing so) or manually by the user selecting from a
869   generated (possibly hypertext) menu.
870</t>
871<t>
872   Agent-driven negotiation is advantageous when the response would vary
873   over commonly-used dimensions (such as type, language, or encoding),
874   when the origin server is unable to determine a user agent's
875   capabilities from examining the request, and generally when public
876   caches are used to distribute server load and reduce network usage.
877</t>
878<t>
879   Agent-driven negotiation suffers from the disadvantage of needing a
880   second request to obtain the best alternate representation. This
881   second request is only efficient when caching is used. In addition,
882   this specification does not define any mechanism for supporting
883   automatic selection, though it also does not prevent any such
884   mechanism from being developed as an extension and used within
885   HTTP/1.1.
886</t>
887<t>
888   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
889   status codes for enabling agent-driven negotiation when the server is
890   unwilling or unable to provide a varying response using server-driven
891   negotiation.
892</t>
893</section>
894
895<section title="Transparent Negotiation" anchor="transparent.negotiation">
896<t>
897   Transparent negotiation is a combination of both server-driven and
898   agent-driven negotiation. When a cache is supplied with a form of the
899   list of available representations of the response (as in agent-driven
900   negotiation) and the dimensions of variance are completely understood
901   by the cache, then the cache becomes capable of performing server-driven
902   negotiation on behalf of the origin server for subsequent
903   requests on that resource.
904</t>
905<t>
906   Transparent negotiation has the advantage of distributing the
907   negotiation work that would otherwise be required of the origin
908   server and also removing the second request delay of agent-driven
909   negotiation when the cache is able to correctly guess the right
910   response.
911</t>
912<t>
913   This specification does not define any mechanism for transparent
914   negotiation, though it also does not prevent any such mechanism from
915   being developed as an extension that could be used within HTTP/1.1.
916</t>
917</section>
918</section>
919
920<section title="Header Field Definitions" anchor="header.fields">
921<t>
922   This section defines the syntax and semantics of HTTP/1.1 header fields
923   related to the payload of messages.
924</t>
925<t>
926   For entity-header fields, both sender and recipient refer to either the
927   client or the server, depending on who sends and who receives the entity.
928</t>
929
930<section title="Accept" anchor="header.accept">
931  <iref primary="true" item="Accept header" x:for-anchor=""/>
932  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
933  <x:anchor-alias value="Accept"/>
934  <x:anchor-alias value="Accept-v"/>
935  <x:anchor-alias value="accept-ext"/>
936  <x:anchor-alias value="accept-params"/>
937  <x:anchor-alias value="media-range"/>
938<t>
939   The request-header field "Accept" can be used to specify certain media
940   types which are acceptable for the response. Accept headers can be
941   used to indicate that the request is specifically limited to a small
942   set of desired types, as in the case of a request for an in-line
943   image.
944</t>
945<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"/>
946  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
947  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
948 
949  <x:ref>media-range</x:ref>    = ( "*/*"
950                   / ( <x:ref>type</x:ref> "/" "*" )
951                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
952                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
953  <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> )
954  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref>
955                   [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
956</artwork></figure>
957<t>
958   The asterisk "*" character is used to group media types into ranges,
959   with "*/*" indicating all media types and "type/*" indicating all
960   subtypes of that type. The media-range &MAY; include media type
961   parameters that are applicable to that range.
962</t>
963<t>
964   Each media-range &MAY; be followed by one or more accept-params,
965   beginning with the "q" parameter for indicating a relative quality
966   factor. The first "q" parameter (if any) separates the media-range
967   parameter(s) from the accept-params. Quality factors allow the user
968   or user agent to indicate the relative degree of preference for that
969   media-range, using the qvalue scale from 0 to 1 (<xref target="quality.values"/>). The
970   default value is q=1.
971  <list><t>
972      <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
973      parameters from Accept extension parameters is due to historical
974      practice. Although this prevents any media type parameter named
975      "q" from being used with a media range, such an event is believed
976      to be unlikely given the lack of any "q" parameters in the IANA
977      media type registry and the rare usage of any media type
978      parameters in Accept. Future media types are discouraged from
979      registering any parameter named "q".
980  </t></list>
981</t>
982<t>
983   The example
984</t>
985<figure><artwork type="example">
986  Accept: audio/*; q=0.2, audio/basic
987</artwork></figure>
988<t>
989   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
990   type if it is the best available after an 80% mark-down in quality."
991</t>
992<t>
993   If no Accept header field is present, then it is assumed that the
994   client accepts all media types. If an Accept header field is present,
995   and if the server cannot send a response which is acceptable
996   according to the combined Accept field value, then the server &SHOULD;
997   send a 406 (Not Acceptable) response.
998</t>
999<t>
1000   A more elaborate example is
1001</t>
1002<figure><artwork type="example">
1003  Accept: text/plain; q=0.5, text/html,
1004          text/x-dvi; q=0.8, text/x-c
1005</artwork></figure>
1006<t>
1007   Verbally, this would be interpreted as "text/html and text/x-c are
1008   the preferred media types, but if they do not exist, then send the
1009   text/x-dvi entity, and if that does not exist, send the text/plain
1010   entity."
1011</t>
1012<t>
1013   Media ranges can be overridden by more specific media ranges or
1014   specific media types. If more than one media range applies to a given
1015   type, the most specific reference has precedence. For example,
1016</t>
1017<figure><artwork type="example">
1018  Accept: text/*, text/html, text/html;level=1, */*
1019</artwork></figure>
1020<t>
1021   have the following precedence:
1022</t>
1023<figure><artwork type="example">
1024    1) text/html;level=1
1025    2) text/html
1026    3) text/*
1027    4) */*
1028</artwork></figure>
1029<t>
1030   The media type quality factor associated with a given type is
1031   determined by finding the media range with the highest precedence
1032   which matches that type. For example,
1033</t>
1034<figure><artwork type="example">
1035  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1036          text/html;level=2;q=0.4, */*;q=0.5
1037</artwork></figure>
1038<t>
1039   would cause the following values to be associated:
1040</t>
1041<figure><artwork type="example">
1042    text/html;level=1         = 1
1043    text/html                 = 0.7
1044    text/plain                = 0.3
1045    image/jpeg                = 0.5
1046    text/html;level=2         = 0.4
1047    text/html;level=3         = 0.7
1048</artwork></figure>
1049<t>
1050      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1051      values for certain media ranges. However, unless the user agent is
1052      a closed system which cannot interact with other rendering agents,
1053      this default set ought to be configurable by the user.
1054</t>
1055</section>
1056
1057<section title="Accept-Charset" anchor="header.accept-charset">
1058  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1059  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1060  <x:anchor-alias value="Accept-Charset"/>
1061  <x:anchor-alias value="Accept-Charset-v"/>
1062<t>
1063   The request-header field "Accept-Charset" can be used to indicate what
1064   character sets are acceptable for the response. This field allows
1065   clients capable of understanding more comprehensive or special-purpose
1066   character sets to signal that capability to a server which is
1067   capable of representing documents in those character sets.
1068</t>
1069<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
1070  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
1071          <x:ref>Accept-Charset-v</x:ref>
1072  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1073                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1074</artwork></figure>
1075<t>
1076   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1077   be given an associated quality value which represents the user's
1078   preference for that charset. The default value is q=1. An example is
1079</t>
1080<figure><artwork type="example">
1081  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1082</artwork></figure>
1083<t>
1084   The special value "*", if present in the Accept-Charset field,
1085   matches every character set (including ISO-8859-1) which is not
1086   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1087   in an Accept-Charset field, then all character sets not explicitly
1088   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1089   a quality value of 1 if not explicitly mentioned.
1090</t>
1091<t>
1092   If no Accept-Charset header is present, the default is that any
1093   character set is acceptable. If an Accept-Charset header is present,
1094   and if the server cannot send a response which is acceptable
1095   according to the Accept-Charset header, then the server &SHOULD; send
1096   an error response with the 406 (Not Acceptable) status code, though
1097   the sending of an unacceptable response is also allowed.
1098</t>
1099</section>
1100
1101<section title="Accept-Encoding" anchor="header.accept-encoding">
1102  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1103  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1104  <x:anchor-alias value="Accept-Encoding"/>
1105  <x:anchor-alias value="Accept-Encoding-v"/>
1106  <x:anchor-alias value="codings"/>
1107<t>
1108   The request-header field "Accept-Encoding" is similar to Accept, but
1109   restricts the content-codings (<xref target="content.codings"/>) that are acceptable in
1110   the response.
1111</t>
1112<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"/>
1113  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
1114                     <x:ref>Accept-Encoding-v</x:ref>
1115  <x:ref>Accept-Encoding-v</x:ref>  =
1116                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1117  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
1118</artwork></figure>
1119<t>
1120   Each codings value &MAY; be given an associated quality value which
1121   represents the preference for that encoding. The default value is q=1.
1122</t>
1123<t>
1124   Examples of its use are:
1125</t>
1126<figure><artwork type="example">
1127  Accept-Encoding: compress, gzip
1128  Accept-Encoding:
1129  Accept-Encoding: *
1130  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1131  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1132</artwork></figure>
1133<t>
1134   A server tests whether a content-coding is acceptable, according to
1135   an Accept-Encoding field, using these rules:
1136  <list style="numbers">
1137      <t>If the content-coding is one of the content-codings listed in
1138         the Accept-Encoding field, then it is acceptable, unless it is
1139         accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
1140         qvalue of 0 means "not acceptable.")</t>
1141
1142      <t>The special "*" symbol in an Accept-Encoding field matches any
1143         available content-coding not explicitly listed in the header
1144         field.</t>
1145
1146      <t>If multiple content-codings are acceptable, then the acceptable
1147         content-coding with the highest non-zero qvalue is preferred.</t>
1148
1149      <t>The "identity" content-coding is always acceptable, unless
1150         specifically refused because the Accept-Encoding field includes
1151         "identity;q=0", or because the field includes "*;q=0" and does
1152         not explicitly include the "identity" content-coding. If the
1153         Accept-Encoding field-value is empty, then only the "identity"
1154         encoding is acceptable.</t>
1155  </list>
1156</t>
1157<t>
1158   If an Accept-Encoding field is present in a request, and if the
1159   server cannot send a response which is acceptable according to the
1160   Accept-Encoding header, then the server &SHOULD; send an error response
1161   with the 406 (Not Acceptable) status code.
1162</t>
1163<t>
1164   If no Accept-Encoding field is present in a request, the server &MAY;
1165   assume that the client will accept any content coding. In this case,
1166   if "identity" is one of the available content-codings, then the
1167   server &SHOULD; use the "identity" content-coding, unless it has
1168   additional information that a different content-coding is meaningful
1169   to the client.
1170  <list><t>
1171      <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1172      and if the "identity" content-coding is unavailable, then
1173      content-codings commonly understood by HTTP/1.0 clients (i.e.,
1174      "gzip" and "compress") are preferred; some older clients
1175      improperly display messages sent with other content-codings.  The
1176      server might also make this decision based on information about
1177      the particular user-agent or client.
1178    </t><t>
1179      <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1180      associated with content-codings. This means that qvalues will not
1181      work and are not permitted with x-gzip or x-compress.
1182    </t></list>
1183</t>
1184</section>
1185
1186<section title="Accept-Language" anchor="header.accept-language">
1187  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1188  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1189  <x:anchor-alias value="Accept-Language"/>
1190  <x:anchor-alias value="Accept-Language-v"/>
1191  <x:anchor-alias value="language-range"/>
1192<t>
1193   The request-header field "Accept-Language" is similar to Accept, but
1194   restricts the set of natural languages that are preferred as a
1195   response to the request. Language tags are defined in <xref target="language.tags"/>.
1196</t>
1197<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"/>
1198  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
1199                    <x:ref>Accept-Language-v</x:ref>
1200  <x:ref>Accept-Language-v</x:ref> =
1201                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1202  <x:ref>language-range</x:ref>    =
1203            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1204</artwork></figure>
1205<t>
1206   Each language-range can be given an associated quality value which
1207   represents an estimate of the user's preference for the languages
1208   specified by that range. The quality value defaults to "q=1". For
1209   example,
1210</t>
1211<figure><artwork type="example">
1212  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1213</artwork></figure>
1214<t>
1215   would mean: "I prefer Danish, but will accept British English and
1216   other types of English."
1217</t>
1218<t>
1219   For matching, the "Basic Filtering" matching scheme, defined in
1220   <xref target="RFC4647" x:sec="3.3.1" x:fmt="of"/>, is used:
1221</t>
1222<x:blockquote cite="http://tools.ietf.org/html/rfc4647#section-3.3.1">
1223  <t>
1224     A language range matches a
1225     particular language tag if, in a case-insensitive comparison, it
1226     exactly equals the tag, or if it exactly equals a prefix of the tag
1227     such that the first character following the prefix is "-".
1228  </t>
1229</x:blockquote> 
1230<t>
1231   The special range "*", if present in the Accept-Language field,
1232   matches every tag not matched by any other range present in the
1233   Accept-Language field.
1234  <list><t>
1235      <x:h>Note:</x:h> This use of a prefix matching rule does not imply that
1236      language tags are assigned to languages in such a way that it is
1237      always true that if a user understands a language with a certain
1238      tag, then this user will also understand all languages with tags
1239      for which this tag is a prefix. The prefix rule simply allows the
1240      use of prefix tags if this is the case.
1241  </t></list>
1242</t>
1243<t>
1244   The language quality factor assigned to a language-tag by the
1245   Accept-Language field is the quality value of the longest language-range
1246   in the field that matches the language-tag. If no language-range
1247   in the field matches the tag, the language quality factor
1248   assigned is 0. If no Accept-Language header is present in the
1249   request, the server
1250   &SHOULD; assume that all languages are equally acceptable. If an
1251   Accept-Language header is present, then all languages which are
1252   assigned a quality factor greater than 0 are acceptable.
1253</t>
1254<t>
1255   It might be contrary to the privacy expectations of the user to send
1256   an Accept-Language header with the complete linguistic preferences of
1257   the user in every request. For a discussion of this issue, see
1258   <xref target="privacy.issues.connected.to.accept.headers"/>.
1259</t>
1260<t>
1261   As intelligibility is highly dependent on the individual user, it is
1262   recommended that client applications make the choice of linguistic
1263   preference available to the user. If the choice is not made
1264   available, then the Accept-Language header field &MUST-NOT; be given in
1265   the request.
1266  <list><t>
1267      <x:h>Note:</x:h> When making the choice of linguistic preference available to
1268      the user, we remind implementors of  the fact that users are not
1269      familiar with the details of language matching as described above,
1270      and should provide appropriate guidance. As an example, users
1271      might assume that on selecting "en-gb", they will be served any
1272      kind of English document if British English is not available. A
1273      user agent might suggest in such a case to add "en" to get the
1274      best matching behavior.
1275  </t></list>
1276</t>
1277</section>
1278
1279<section title="Content-Encoding" anchor="header.content-encoding">
1280  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1281  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1282  <x:anchor-alias value="Content-Encoding"/>
1283  <x:anchor-alias value="Content-Encoding-v"/>
1284<t>
1285   The entity-header field "Content-Encoding" is used as a modifier to the
1286   media-type. When present, its value indicates what additional content
1287   codings have been applied to the entity-body, and thus what decoding
1288   mechanisms must be applied in order to obtain the media-type
1289   referenced by the Content-Type header field. Content-Encoding is
1290   primarily used to allow a document to be compressed without losing
1291   the identity of its underlying media type.
1292</t>
1293<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
1294  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
1295  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1296</artwork></figure>
1297<t>
1298   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1299</t>
1300<figure><artwork type="example">
1301  Content-Encoding: gzip
1302</artwork></figure>
1303<t>
1304   The content-coding is a characteristic of the entity identified by
1305   the request-target. Typically, the entity-body is stored with this
1306   encoding and is only decoded before rendering or analogous usage.
1307   However, a non-transparent proxy &MAY; modify the content-coding if the
1308   new coding is known to be acceptable to the recipient, unless the
1309   "no-transform" cache-control directive is present in the message.
1310</t>
1311<t>
1312   If the content-coding of an entity is not "identity", then the
1313   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1314   that lists the non-identity content-coding(s) used.
1315</t>
1316<t>
1317   If the content-coding of an entity in a request message is not
1318   acceptable to the origin server, the server &SHOULD; respond with a
1319   status code of 415 (Unsupported Media Type).
1320</t>
1321<t>
1322   If multiple encodings have been applied to an entity, the content
1323   codings &MUST; be listed in the order in which they were applied.
1324   Additional information about the encoding parameters &MAY; be provided
1325   by other entity-header fields not defined by this specification.
1326</t>
1327</section>
1328
1329<section title="Content-Language" anchor="header.content-language">
1330  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1331  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1332  <x:anchor-alias value="Content-Language"/>
1333  <x:anchor-alias value="Content-Language-v"/>
1334<t>
1335   The entity-header field "Content-Language" describes the natural
1336   language(s) of the intended audience for the enclosed entity. Note
1337   that this might not be equivalent to all the languages used within
1338   the entity-body.
1339</t>
1340<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
1341  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
1342  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1343</artwork></figure>
1344<t>
1345   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1346   Content-Language is to allow a user to identify and differentiate
1347   entities according to the user's own preferred language. Thus, if the
1348   body content is intended only for a Danish-literate audience, the
1349   appropriate field is
1350</t>
1351<figure><artwork type="example">
1352  Content-Language: da
1353</artwork></figure>
1354<t>
1355   If no Content-Language is specified, the default is that the content
1356   is intended for all language audiences. This might mean that the
1357   sender does not consider it to be specific to any natural language,
1358   or that the sender does not know for which language it is intended.
1359</t>
1360<t>
1361   Multiple languages &MAY; be listed for content that is intended for
1362   multiple audiences. For example, a rendition of the "Treaty of
1363   Waitangi," presented simultaneously in the original Maori and English
1364   versions, would call for
1365</t>
1366<figure><artwork type="example">
1367  Content-Language: mi, en
1368</artwork></figure>
1369<t>
1370   However, just because multiple languages are present within an entity
1371   does not mean that it is intended for multiple linguistic audiences.
1372   An example would be a beginner's language primer, such as "A First
1373   Lesson in Latin," which is clearly intended to be used by an
1374   English-literate audience. In this case, the Content-Language would
1375   properly only include "en".
1376</t>
1377<t>
1378   Content-Language &MAY; be applied to any media type -- it is not
1379   limited to textual documents.
1380</t>
1381</section>
1382
1383<section title="Content-Location" anchor="header.content-location">
1384  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1385  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1386  <x:anchor-alias value="Content-Location"/>
1387  <x:anchor-alias value="Content-Location-v"/>
1388<t>
1389   The entity-header field "Content-Location" &MAY; be used to supply the
1390   resource location for the entity enclosed in the message when that
1391   entity is accessible from a location separate from the requested
1392   resource's URI. A server &SHOULD; provide a Content-Location for the
1393   variant corresponding to the response entity; especially in the case
1394   where a resource has multiple entities associated with it, and those
1395   entities actually have separate locations by which they might be
1396   individually accessed, the server &SHOULD; provide a Content-Location
1397   for the particular variant which is returned.
1398</t>
1399<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
1400  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
1401                    <x:ref>Content-Location-v</x:ref>
1402  <x:ref>Content-Location-v</x:ref> =
1403                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1404</artwork></figure>
1405<t>
1406   The value of Content-Location also defines the base URI for the
1407   entity.
1408</t>
1409<t>
1410   The Content-Location value is not a replacement for the original
1411   requested URI; it is only a statement of the location of the resource
1412   corresponding to this particular entity at the time of the request.
1413   Future requests &MAY; specify the Content-Location URI as the request-target
1414   if the desire is to identify the source of that particular
1415   entity.
1416</t>
1417<t>
1418   A cache cannot assume that an entity with a Content-Location
1419   different from the URI used to retrieve it can be used to respond to
1420   later requests on that Content-Location URI. However, the Content-Location
1421   can be used to differentiate between multiple entities
1422   retrieved from a single requested resource, as described in &caching-neg-resp;.
1423</t>
1424<t>
1425   If the Content-Location is a relative URI, the relative URI is
1426   interpreted relative to the request-target.
1427</t>
1428<t>
1429   The meaning of the Content-Location header in PUT or POST requests is
1430   undefined; servers are free to ignore it in those cases.
1431</t>
1432</section>
1433
1434<section title="Content-MD5" anchor="header.content-md5">
1435  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1436  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1437  <x:anchor-alias value="Content-MD5"/>
1438  <x:anchor-alias value="Content-MD5-v"/>
1439<t>
1440   The entity-header field "Content-MD5", as defined in <xref target="RFC1864"/>, is
1441   an MD5 digest of the entity-body for the purpose of providing an
1442   end-to-end message integrity check (MIC) of the entity-body. (Note: a
1443   MIC is good for detecting accidental modification of the entity-body
1444   in transit, but is not proof against malicious attacks.)
1445</t>
1446<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
1447  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
1448  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1449</artwork></figure>
1450<t>
1451   The Content-MD5 header field &MAY; be generated by an origin server or
1452   client to function as an integrity check of the entity-body. Only
1453   origin servers or clients &MAY; generate the Content-MD5 header field;
1454   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1455   value as an end-to-end integrity check. Any recipient of the entity-body,
1456   including gateways and proxies, &MAY; check that the digest value
1457   in this header field matches that of the entity-body as received.
1458</t>
1459<t>
1460   The MD5 digest is computed based on the content of the entity-body,
1461   including any content-coding that has been applied, but not including
1462   any transfer-encoding applied to the message-body. If the message is
1463   received with a transfer-encoding, that encoding &MUST; be removed
1464   prior to checking the Content-MD5 value against the received entity.
1465</t>
1466<t>
1467   This has the result that the digest is computed on the octets of the
1468   entity-body exactly as, and in the order that, they would be sent if
1469   no transfer-encoding were being applied.
1470</t>
1471<t>
1472   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1473   composite media-types (e.g., multipart/* and message/rfc822), but
1474   this does not change how the digest is computed as defined in the
1475   preceding paragraph.
1476</t>
1477<t>
1478   There are several consequences of this. The entity-body for composite
1479   types &MAY; contain many body-parts, each with its own MIME and HTTP
1480   headers (including Content-MD5, Content-Transfer-Encoding, and
1481   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1482   or Content-Encoding header, it is assumed that the content
1483   of the body-part has had the encoding applied, and the body-part is
1484   included in the Content-MD5 digest as is -- i.e., after the
1485   application. The Transfer-Encoding header field is not allowed within
1486   body-parts.
1487</t>
1488<t>
1489   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1490   computing or checking the digest: the line break convention used in
1491   the text actually transmitted &MUST; be left unaltered when computing
1492   the digest.
1493  <list><t>
1494      <x:h>Note:</x:h> while the definition of Content-MD5 is exactly the same for
1495      HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1496      in which the application of Content-MD5 to HTTP entity-bodies
1497      differs from its application to MIME entity-bodies. One is that
1498      HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1499      does use Transfer-Encoding and Content-Encoding. Another is that
1500      HTTP more frequently uses binary content types than MIME, so it is
1501      worth noting that, in such cases, the byte order used to compute
1502      the digest is the transmission byte order defined for the type.
1503      Lastly, HTTP allows transmission of text types with any of several
1504      line break conventions and not just the canonical form using CRLF.
1505  </t></list>
1506</t>
1507</section>
1508
1509<section title="Content-Type" anchor="header.content-type">
1510  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1511  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1512  <x:anchor-alias value="Content-Type"/>
1513  <x:anchor-alias value="Content-Type-v"/>
1514<t>
1515   The entity-header field "Content-Type" indicates the media type of the
1516   entity-body sent to the recipient or, in the case of the HEAD method,
1517   the media type that would have been sent had the request been a GET.
1518</t>
1519<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
1520  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
1521  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1522</artwork></figure>
1523<t>
1524   Media types are defined in <xref target="media.types"/>. An example of the field is
1525</t>
1526<figure><artwork type="example">
1527  Content-Type: text/html; charset=ISO-8859-4
1528</artwork></figure>
1529<t>
1530   Further discussion of methods for identifying the media type of an
1531   entity is provided in <xref target="type"/>.
1532</t>
1533</section>
1534
1535</section>
1536
1537<section title="IANA Considerations" anchor="IANA.considerations">
1538<section title="Message Header Registration" anchor="message.header.registration">
1539<t>
1540   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
1541   with the permanent registrations below (see <xref target="RFC3864"/>):
1542</t>
1543<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1544<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1545   <ttcol>Header Field Name</ttcol>
1546   <ttcol>Protocol</ttcol>
1547   <ttcol>Status</ttcol>
1548   <ttcol>Reference</ttcol>
1549
1550   <c>Accept</c>
1551   <c>http</c>
1552   <c>standard</c>
1553   <c>
1554      <xref target="header.accept"/>
1555   </c>
1556   <c>Accept-Charset</c>
1557   <c>http</c>
1558   <c>standard</c>
1559   <c>
1560      <xref target="header.accept-charset"/>
1561   </c>
1562   <c>Accept-Encoding</c>
1563   <c>http</c>
1564   <c>standard</c>
1565   <c>
1566      <xref target="header.accept-encoding"/>
1567   </c>
1568   <c>Accept-Language</c>
1569   <c>http</c>
1570   <c>standard</c>
1571   <c>
1572      <xref target="header.accept-language"/>
1573   </c>
1574   <c>Content-Disposition</c>
1575   <c>http</c>
1576   <c/>
1577   <c>
1578      <xref target="content-disposition"/>
1579   </c>
1580   <c>Content-Encoding</c>
1581   <c>http</c>
1582   <c>standard</c>
1583   <c>
1584      <xref target="header.content-encoding"/>
1585   </c>
1586   <c>Content-Language</c>
1587   <c>http</c>
1588   <c>standard</c>
1589   <c>
1590      <xref target="header.content-language"/>
1591   </c>
1592   <c>Content-Location</c>
1593   <c>http</c>
1594   <c>standard</c>
1595   <c>
1596      <xref target="header.content-location"/>
1597   </c>
1598   <c>Content-MD5</c>
1599   <c>http</c>
1600   <c>standard</c>
1601   <c>
1602      <xref target="header.content-md5"/>
1603   </c>
1604   <c>Content-Type</c>
1605   <c>http</c>
1606   <c>standard</c>
1607   <c>
1608      <xref target="header.content-type"/>
1609   </c>
1610   <c>MIME-Version</c>
1611   <c>http</c>
1612   <c/>
1613   <c>
1614      <xref target="mime-version"/>
1615   </c>
1616</texttable>
1617<!--(END)-->
1618<t>
1619   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1620</t>
1621</section>
1622</section>
1623
1624<section title="Security Considerations" anchor="security.considerations">
1625<t>
1626   This section is meant to inform application developers, information
1627   providers, and users of the security limitations in HTTP/1.1 as
1628   described by this document. The discussion does not include
1629   definitive solutions to the problems revealed, though it does make
1630   some suggestions for reducing security risks.
1631</t>
1632
1633<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1634<t>
1635   Accept request-headers can reveal information about the user to all
1636   servers which are accessed. The Accept-Language header in particular
1637   can reveal information the user would consider to be of a private
1638   nature, because the understanding of particular languages is often
1639   strongly correlated to the membership of a particular ethnic group.
1640   User agents which offer the option to configure the contents of an
1641   Accept-Language header to be sent in every request are strongly
1642   encouraged to let the configuration process include a message which
1643   makes the user aware of the loss of privacy involved.
1644</t>
1645<t>
1646   An approach that limits the loss of privacy would be for a user agent
1647   to omit the sending of Accept-Language headers by default, and to ask
1648   the user whether or not to start sending Accept-Language headers to a
1649   server if it detects, by looking for any Vary response-header fields
1650   generated by the server, that such sending could improve the quality
1651   of service.
1652</t>
1653<t>
1654   Elaborate user-customized accept header fields sent in every request,
1655   in particular if these include quality values, can be used by servers
1656   as relatively reliable and long-lived user identifiers. Such user
1657   identifiers would allow content providers to do click-trail tracking,
1658   and would allow collaborating content providers to match cross-server
1659   click-trails or form submissions of individual users. Note that for
1660   many users not behind a proxy, the network address of the host
1661   running the user agent will also serve as a long-lived user
1662   identifier. In environments where proxies are used to enhance
1663   privacy, user agents ought to be conservative in offering accept
1664   header configuration options to end users. As an extreme privacy
1665   measure, proxies could filter the accept headers in relayed requests.
1666   General purpose user agents which provide a high degree of header
1667   configurability &SHOULD; warn users about the loss of privacy which can
1668   be involved.
1669</t>
1670</section>
1671
1672<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1673<t>
1674   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
1675   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1676   serious security considerations. Content-Disposition is not part of
1677   the HTTP standard, but since it is widely implemented, we are
1678   documenting its use and risks for implementors. See <xref target="RFC2183" x:fmt="of" x:sec="5"/>
1679   for details.
1680</t>
1681</section>
1682
1683</section>
1684
1685<section title="Acknowledgments" anchor="ack">
1686</section>
1687</middle>
1688<back>
1689
1690<references title="Normative References">
1691
1692<reference anchor="ISO-8859-1">
1693  <front>
1694    <title>
1695     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1696    </title>
1697    <author>
1698      <organization>International Organization for Standardization</organization>
1699    </author>
1700    <date year="1998"/>
1701  </front>
1702  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1703</reference>
1704
1705<reference anchor="Part1">
1706  <front>
1707    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1708    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1709      <organization abbrev="Day Software">Day Software</organization>
1710      <address><email>fielding@gbiv.com</email></address>
1711    </author>
1712    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1713      <organization>One Laptop per Child</organization>
1714      <address><email>jg@laptop.org</email></address>
1715    </author>
1716    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1717      <organization abbrev="HP">Hewlett-Packard Company</organization>
1718      <address><email>JeffMogul@acm.org</email></address>
1719    </author>
1720    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1721      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1722      <address><email>henrikn@microsoft.com</email></address>
1723    </author>
1724    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1725      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1726      <address><email>LMM@acm.org</email></address>
1727    </author>
1728    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1729      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1730      <address><email>paulle@microsoft.com</email></address>
1731    </author>
1732    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1733      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1734      <address><email>timbl@w3.org</email></address>
1735    </author>
1736    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1737      <organization abbrev="W3C">World Wide Web Consortium</organization>
1738      <address><email>ylafon@w3.org</email></address>
1739    </author>
1740    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1741      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1742      <address><email>julian.reschke@greenbytes.de</email></address>
1743    </author>
1744    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1745  </front>
1746  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1747  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1748</reference>
1749
1750<reference anchor="Part2">
1751  <front>
1752    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1753    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1754      <organization abbrev="Day Software">Day Software</organization>
1755      <address><email>fielding@gbiv.com</email></address>
1756    </author>
1757    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1758      <organization>One Laptop per Child</organization>
1759      <address><email>jg@laptop.org</email></address>
1760    </author>
1761    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1762      <organization abbrev="HP">Hewlett-Packard Company</organization>
1763      <address><email>JeffMogul@acm.org</email></address>
1764    </author>
1765    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1766      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1767      <address><email>henrikn@microsoft.com</email></address>
1768    </author>
1769    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1770      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1771      <address><email>LMM@acm.org</email></address>
1772    </author>
1773    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1774      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1775      <address><email>paulle@microsoft.com</email></address>
1776    </author>
1777    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1778      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1779      <address><email>timbl@w3.org</email></address>
1780    </author>
1781    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1782      <organization abbrev="W3C">World Wide Web Consortium</organization>
1783      <address><email>ylafon@w3.org</email></address>
1784    </author>
1785    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1786      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1787      <address><email>julian.reschke@greenbytes.de</email></address>
1788    </author>
1789    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1790  </front>
1791  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1792  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1793</reference>
1794
1795<reference anchor="Part4">
1796  <front>
1797    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1798    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1799      <organization abbrev="Day Software">Day Software</organization>
1800      <address><email>fielding@gbiv.com</email></address>
1801    </author>
1802    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1803      <organization>One Laptop per Child</organization>
1804      <address><email>jg@laptop.org</email></address>
1805    </author>
1806    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1807      <organization abbrev="HP">Hewlett-Packard Company</organization>
1808      <address><email>JeffMogul@acm.org</email></address>
1809    </author>
1810    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1811      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1812      <address><email>henrikn@microsoft.com</email></address>
1813    </author>
1814    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1815      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1816      <address><email>LMM@acm.org</email></address>
1817    </author>
1818    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1819      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1820      <address><email>paulle@microsoft.com</email></address>
1821    </author>
1822    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1823      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1824      <address><email>timbl@w3.org</email></address>
1825    </author>
1826    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1827      <organization abbrev="W3C">World Wide Web Consortium</organization>
1828      <address><email>ylafon@w3.org</email></address>
1829    </author>
1830    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1831      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1832      <address><email>julian.reschke@greenbytes.de</email></address>
1833    </author>
1834    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1835  </front>
1836  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1837  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1838</reference>
1839
1840<reference anchor="Part5">
1841  <front>
1842    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1843    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1844      <organization abbrev="Day Software">Day Software</organization>
1845      <address><email>fielding@gbiv.com</email></address>
1846    </author>
1847    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1848      <organization>One Laptop per Child</organization>
1849      <address><email>jg@laptop.org</email></address>
1850    </author>
1851    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1852      <organization abbrev="HP">Hewlett-Packard Company</organization>
1853      <address><email>JeffMogul@acm.org</email></address>
1854    </author>
1855    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1856      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1857      <address><email>henrikn@microsoft.com</email></address>
1858    </author>
1859    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1860      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1861      <address><email>LMM@acm.org</email></address>
1862    </author>
1863    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1864      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1865      <address><email>paulle@microsoft.com</email></address>
1866    </author>
1867    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1868      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1869      <address><email>timbl@w3.org</email></address>
1870    </author>
1871    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1872      <organization abbrev="W3C">World Wide Web Consortium</organization>
1873      <address><email>ylafon@w3.org</email></address>
1874    </author>
1875    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1876      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1877      <address><email>julian.reschke@greenbytes.de</email></address>
1878    </author>
1879    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1880  </front>
1881  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1882  <x:source href="p5-range.xml" basename="p5-range"/>
1883</reference>
1884
1885<reference anchor="Part6">
1886  <front>
1887    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1888    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1889      <organization abbrev="Day Software">Day Software</organization>
1890      <address><email>fielding@gbiv.com</email></address>
1891    </author>
1892    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1893      <organization>One Laptop per Child</organization>
1894      <address><email>jg@laptop.org</email></address>
1895    </author>
1896    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1897      <organization abbrev="HP">Hewlett-Packard Company</organization>
1898      <address><email>JeffMogul@acm.org</email></address>
1899    </author>
1900    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1901      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1902      <address><email>henrikn@microsoft.com</email></address>
1903    </author>
1904    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1905      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1906      <address><email>LMM@acm.org</email></address>
1907    </author>
1908    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1909      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1910      <address><email>paulle@microsoft.com</email></address>
1911    </author>
1912    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1913      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1914      <address><email>timbl@w3.org</email></address>
1915    </author>
1916    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1917      <organization abbrev="W3C">World Wide Web Consortium</organization>
1918      <address><email>ylafon@w3.org</email></address>
1919    </author>
1920    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1921      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1922      <address><email>julian.reschke@greenbytes.de</email></address>
1923    </author>
1924    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1925  </front>
1926  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1927  <x:source href="p6-cache.xml" basename="p6-cache"/>
1928</reference>
1929
1930<reference anchor="RFC1766">
1931  <front>
1932    <title abbrev="Language Tag">Tags for the Identification of Languages</title>
1933    <author initials="H." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
1934      <organization>UNINETT</organization>
1935      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
1936    </author>
1937    <date month="March" year="1995"/>
1938  </front>
1939  <seriesInfo name="RFC" value="1766"/>
1940</reference>
1941
1942<reference anchor="RFC1864">
1943  <front>
1944    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1945    <author initials="J." surname="Myers" fullname="John G. Myers">
1946      <organization>Carnegie Mellon University</organization>
1947      <address><email>jgm+@cmu.edu</email></address>
1948    </author>
1949    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
1950      <organization>Dover Beach Consulting, Inc.</organization>
1951      <address><email>mrose@dbc.mtview.ca.us</email></address>
1952    </author>
1953    <date month="October" year="1995"/>
1954  </front>
1955  <seriesInfo name="RFC" value="1864"/>
1956</reference>
1957
1958<reference anchor="RFC1950">
1959  <front>
1960    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1961    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1962      <organization>Aladdin Enterprises</organization>
1963      <address><email>ghost@aladdin.com</email></address>
1964    </author>
1965    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1966      <organization/>
1967    </author>
1968    <date month="May" year="1996"/>
1969  </front>
1970  <seriesInfo name="RFC" value="1950"/>
1971  <annotation>
1972    RFC 1950 is an Informational RFC, thus it may be less stable than
1973    this specification. On the other hand, this downward reference was
1974    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1975    therefore it is unlikely to cause problems in practice. See also
1976    <xref target="BCP97"/>.
1977  </annotation>
1978</reference>
1979
1980<reference anchor="RFC1951">
1981  <front>
1982    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1983    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1984      <organization>Aladdin Enterprises</organization>
1985      <address><email>ghost@aladdin.com</email></address>
1986    </author>
1987    <date month="May" year="1996"/>
1988  </front>
1989  <seriesInfo name="RFC" value="1951"/>
1990  <annotation>
1991    RFC 1951 is an Informational RFC, thus it may be less stable than
1992    this specification. On the other hand, this downward reference was
1993    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1994    therefore it is unlikely to cause problems in practice. See also
1995    <xref target="BCP97"/>.
1996  </annotation>
1997</reference>
1998
1999<reference anchor="RFC1952">
2000  <front>
2001    <title>GZIP file format specification version 4.3</title>
2002    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2003      <organization>Aladdin Enterprises</organization>
2004      <address><email>ghost@aladdin.com</email></address>
2005    </author>
2006    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2007      <organization/>
2008      <address><email>gzip@prep.ai.mit.edu</email></address>
2009    </author>
2010    <author initials="M." surname="Adler" fullname="Mark Adler">
2011      <organization/>
2012      <address><email>madler@alumni.caltech.edu</email></address>
2013    </author>
2014    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2015      <organization/>
2016      <address><email>ghost@aladdin.com</email></address>
2017    </author>
2018    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2019      <organization/>
2020      <address><email>randeg@alumni.rpi.edu</email></address>
2021    </author>
2022    <date month="May" year="1996"/>
2023  </front>
2024  <seriesInfo name="RFC" value="1952"/>
2025  <annotation>
2026    RFC 1952 is an Informational RFC, thus it may be less stable than
2027    this specification. On the other hand, this downward reference was
2028    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2029    therefore it is unlikely to cause problems in practice. See also
2030    <xref target="BCP97"/>.
2031  </annotation>
2032</reference>
2033
2034<reference anchor="RFC2045">
2035  <front>
2036    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2037    <author initials="N." surname="Freed" fullname="Ned Freed">
2038      <organization>Innosoft International, Inc.</organization>
2039      <address><email>ned@innosoft.com</email></address>
2040    </author>
2041    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2042      <organization>First Virtual Holdings</organization>
2043      <address><email>nsb@nsb.fv.com</email></address>
2044    </author>
2045    <date month="November" year="1996"/>
2046  </front>
2047  <seriesInfo name="RFC" value="2045"/>
2048</reference>
2049
2050<reference anchor="RFC2046">
2051  <front>
2052    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2053    <author initials="N." surname="Freed" fullname="Ned Freed">
2054      <organization>Innosoft International, Inc.</organization>
2055      <address><email>ned@innosoft.com</email></address>
2056    </author>
2057    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2058      <organization>First Virtual Holdings</organization>
2059      <address><email>nsb@nsb.fv.com</email></address>
2060    </author>
2061    <date month="November" year="1996"/>
2062  </front>
2063  <seriesInfo name="RFC" value="2046"/>
2064</reference>
2065
2066<reference anchor="RFC2119">
2067  <front>
2068    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2069    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2070      <organization>Harvard University</organization>
2071      <address><email>sob@harvard.edu</email></address>
2072    </author>
2073    <date month="March" year="1997"/>
2074  </front>
2075  <seriesInfo name="BCP" value="14"/>
2076  <seriesInfo name="RFC" value="2119"/>
2077</reference>
2078
2079<reference anchor='RFC4647'>
2080  <front>
2081    <title>Matching of Language Tags</title>
2082    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2083      <organization>Yahoo! Inc.</organization>
2084      <address><email>addison@inter-locale.com</email></address>
2085    </author>
2086    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2087      <organization>Google</organization>
2088      <address><email>mark.davis@macchiato.com</email></address>
2089    </author>
2090    <date year='2006' month='September' />
2091  </front>
2092  <seriesInfo name='BCP' value='47' />
2093  <seriesInfo name='RFC' value='4647' />
2094</reference>
2095
2096<reference anchor="RFC5234">
2097  <front>
2098    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2099    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2100      <organization>Brandenburg InternetWorking</organization>
2101      <address>
2102      <postal>
2103      <street>675 Spruce Dr.</street>
2104      <city>Sunnyvale</city>
2105      <region>CA</region>
2106      <code>94086</code>
2107      <country>US</country></postal>
2108      <phone>+1.408.246.8253</phone>
2109      <email>dcrocker@bbiw.net</email></address> 
2110    </author>
2111    <author initials="P." surname="Overell" fullname="Paul Overell">
2112      <organization>THUS plc.</organization>
2113      <address>
2114      <postal>
2115      <street>1/2 Berkeley Square</street>
2116      <street>99 Berkely Street</street>
2117      <city>Glasgow</city>
2118      <code>G3 7HR</code>
2119      <country>UK</country></postal>
2120      <email>paul.overell@thus.net</email></address>
2121    </author>
2122    <date month="January" year="2008"/>
2123  </front>
2124  <seriesInfo name="STD" value="68"/>
2125  <seriesInfo name="RFC" value="5234"/>
2126</reference>
2127
2128</references>
2129
2130<references title="Informative References">
2131
2132<reference anchor="RFC1945">
2133  <front>
2134    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2135    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2136      <organization>MIT, Laboratory for Computer Science</organization>
2137      <address><email>timbl@w3.org</email></address>
2138    </author>
2139    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2140      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2141      <address><email>fielding@ics.uci.edu</email></address>
2142    </author>
2143    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2144      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2145      <address><email>frystyk@w3.org</email></address>
2146    </author>
2147    <date month="May" year="1996"/>
2148  </front>
2149  <seriesInfo name="RFC" value="1945"/>
2150</reference>
2151
2152<reference anchor="RFC2049">
2153  <front>
2154    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2155    <author initials="N." surname="Freed" fullname="Ned Freed">
2156      <organization>Innosoft International, Inc.</organization>
2157      <address><email>ned@innosoft.com</email></address>
2158    </author>
2159    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2160      <organization>First Virtual Holdings</organization>
2161      <address><email>nsb@nsb.fv.com</email></address>
2162    </author>
2163    <date month="November" year="1996"/>
2164  </front>
2165  <seriesInfo name="RFC" value="2049"/>
2166</reference>
2167
2168<reference anchor="RFC2068">
2169  <front>
2170    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2171    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2172      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2173      <address><email>fielding@ics.uci.edu</email></address>
2174    </author>
2175    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2176      <organization>MIT Laboratory for Computer Science</organization>
2177      <address><email>jg@w3.org</email></address>
2178    </author>
2179    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2180      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2181      <address><email>mogul@wrl.dec.com</email></address>
2182    </author>
2183    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2184      <organization>MIT Laboratory for Computer Science</organization>
2185      <address><email>frystyk@w3.org</email></address>
2186    </author>
2187    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2188      <organization>MIT Laboratory for Computer Science</organization>
2189      <address><email>timbl@w3.org</email></address>
2190    </author>
2191    <date month="January" year="1997"/>
2192  </front>
2193  <seriesInfo name="RFC" value="2068"/>
2194</reference>
2195
2196<reference anchor="RFC2076">
2197  <front>
2198    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2199    <author initials="J." surname="Palme" fullname="Jacob Palme">
2200      <organization>Stockholm University/KTH</organization>
2201      <address><email>jpalme@dsv.su.se</email></address>
2202    </author>
2203    <date month="February" year="1997"/>
2204  </front>
2205  <seriesInfo name="RFC" value="2076"/>
2206</reference>
2207
2208<reference anchor="RFC2183">
2209  <front>
2210    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2211    <author initials="R." surname="Troost" fullname="Rens Troost">
2212      <organization>New Century Systems</organization>
2213      <address><email>rens@century.com</email></address>
2214    </author>
2215    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2216      <organization>QUALCOMM Incorporated</organization>
2217      <address><email>sdorner@qualcomm.com</email></address>
2218    </author>
2219    <author initials="K." surname="Moore" fullname="Keith Moore">
2220      <organization>Department of Computer Science</organization>
2221      <address><email>moore@cs.utk.edu</email></address>
2222    </author>
2223    <date month="August" year="1997"/>
2224  </front>
2225  <seriesInfo name="RFC" value="2183"/>
2226</reference>
2227
2228<reference anchor="RFC2277">
2229  <front>
2230    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2231    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2232      <organization>UNINETT</organization>
2233      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2234    </author>
2235    <date month="January" year="1998"/>
2236  </front>
2237  <seriesInfo name="BCP" value="18"/>
2238  <seriesInfo name="RFC" value="2277"/>
2239</reference>
2240
2241<reference anchor="RFC2388">
2242  <front>
2243    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2244    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2245      <organization>Xerox Palo Alto Research Center</organization>
2246      <address><email>masinter@parc.xerox.com</email></address>
2247    </author>
2248    <date year="1998" month="August"/>
2249  </front>
2250  <seriesInfo name="RFC" value="2388"/>
2251</reference>
2252
2253<reference anchor="RFC2557">
2254  <front>
2255    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2256    <author initials="F." surname="Palme" fullname="Jacob Palme">
2257      <organization>Stockholm University and KTH</organization>
2258      <address><email>jpalme@dsv.su.se</email></address>
2259    </author>
2260    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2261      <organization>Microsoft Corporation</organization>
2262      <address><email>alexhop@microsoft.com</email></address>
2263    </author>
2264    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2265      <organization>Lotus Development Corporation</organization>
2266      <address><email>Shelness@lotus.com</email></address>
2267    </author>
2268    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2269      <organization/>
2270      <address><email>stef@nma.com</email></address>
2271    </author>
2272    <date year="1999" month="March"/>
2273  </front>
2274  <seriesInfo name="RFC" value="2557"/>
2275</reference>
2276
2277<reference anchor="RFC2616">
2278  <front>
2279    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2280    <author initials="R." surname="Fielding" fullname="R. Fielding">
2281      <organization>University of California, Irvine</organization>
2282      <address><email>fielding@ics.uci.edu</email></address>
2283    </author>
2284    <author initials="J." surname="Gettys" fullname="J. Gettys">
2285      <organization>W3C</organization>
2286      <address><email>jg@w3.org</email></address>
2287    </author>
2288    <author initials="J." surname="Mogul" fullname="J. Mogul">
2289      <organization>Compaq Computer Corporation</organization>
2290      <address><email>mogul@wrl.dec.com</email></address>
2291    </author>
2292    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2293      <organization>MIT Laboratory for Computer Science</organization>
2294      <address><email>frystyk@w3.org</email></address>
2295    </author>
2296    <author initials="L." surname="Masinter" fullname="L. Masinter">
2297      <organization>Xerox Corporation</organization>
2298      <address><email>masinter@parc.xerox.com</email></address>
2299    </author>
2300    <author initials="P." surname="Leach" fullname="P. Leach">
2301      <organization>Microsoft Corporation</organization>
2302      <address><email>paulle@microsoft.com</email></address>
2303    </author>
2304    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2305      <organization>W3C</organization>
2306      <address><email>timbl@w3.org</email></address>
2307    </author>
2308    <date month="June" year="1999"/>
2309  </front>
2310  <seriesInfo name="RFC" value="2616"/>
2311</reference>
2312
2313<reference anchor="RFC3629">
2314  <front>
2315    <title>UTF-8, a transformation format of ISO 10646</title>
2316    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2317      <organization>Alis Technologies</organization>
2318      <address><email>fyergeau@alis.com</email></address>
2319    </author>
2320    <date month="November" year="2003"/>
2321  </front>
2322  <seriesInfo name="RFC" value="3629"/>
2323  <seriesInfo name="STD" value="63"/>
2324</reference>
2325
2326<reference anchor='RFC3864'>
2327  <front>
2328    <title>Registration Procedures for Message Header Fields</title>
2329    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2330      <organization>Nine by Nine</organization>
2331      <address><email>GK-IETF@ninebynine.org</email></address>
2332    </author>
2333    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2334      <organization>BEA Systems</organization>
2335      <address><email>mnot@pobox.com</email></address>
2336    </author>
2337    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2338      <organization>HP Labs</organization>
2339      <address><email>JeffMogul@acm.org</email></address>
2340    </author>
2341    <date year='2004' month='September' />
2342  </front>
2343  <seriesInfo name='BCP' value='90' />
2344  <seriesInfo name='RFC' value='3864' />
2345</reference>
2346
2347<reference anchor="RFC4288">
2348  <front>
2349    <title>Media Type Specifications and Registration Procedures</title>
2350    <author initials="N." surname="Freed" fullname="N. Freed">
2351      <organization>Sun Microsystems</organization>
2352      <address>
2353        <email>ned.freed@mrochek.com</email>
2354      </address>
2355    </author>
2356    <author initials="J." surname="Klensin" fullname="J. Klensin">
2357      <organization/>
2358      <address>
2359        <email>klensin+ietf@jck.com</email>
2360      </address>
2361    </author>
2362    <date year="2005" month="December"/>
2363  </front>
2364  <seriesInfo name="BCP" value="13"/>
2365  <seriesInfo name="RFC" value="4288"/>
2366</reference>
2367
2368<reference anchor="RFC5322">
2369  <front>
2370    <title>Internet Message Format</title>
2371    <author initials="P." surname="Resnick" fullname="P. Resnick">
2372      <organization>Qualcomm Incorporated</organization>
2373    </author>
2374    <date year="2008" month="October"/>
2375  </front> 
2376  <seriesInfo name="RFC" value="5322"/>
2377</reference>
2378
2379<reference anchor='BCP97'>
2380  <front>
2381    <title>Handling Normative References to Standards-Track Documents</title>
2382    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2383      <organization />
2384      <address>
2385        <email>klensin+ietf@jck.com</email>
2386      </address>
2387    </author>
2388    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2389      <organization>MIT</organization>
2390      <address>
2391        <email>hartmans-ietf@mit.edu</email>
2392      </address>
2393    </author>
2394    <date year='2007' month='June' />
2395  </front>
2396  <seriesInfo name='BCP' value='97' />
2397  <seriesInfo name='RFC' value='4897' />
2398</reference>
2399
2400
2401</references>
2402
2403<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2404<t>
2405   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
2406   allow entities to be transmitted in an open variety of
2407   representations and with extensible mechanisms. However, RFC 2045
2408   discusses mail, and HTTP has a few features that are different from
2409   those described in RFC 2045. These differences were carefully chosen
2410   to optimize performance over binary connections, to allow greater
2411   freedom in the use of new media types, to make date comparisons
2412   easier, and to acknowledge the practice of some early HTTP servers
2413   and clients.
2414</t>
2415<t>
2416   This appendix describes specific areas where HTTP differs from RFC
2417   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2418   aware of these differences and provide the appropriate conversions
2419   where necessary. Proxies and gateways from MIME environments to HTTP
2420   also need to be aware of the differences because some conversions
2421   might be required.
2422</t>
2423
2424<section title="MIME-Version" anchor="mime-version">
2425  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2426  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
2427  <x:anchor-alias value="MIME-Version"/>
2428  <x:anchor-alias value="MIME-Version-v"/>
2429<t>
2430   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2431   include a single MIME-Version general-header field to indicate what
2432   version of the MIME protocol was used to construct the message. Use
2433   of the MIME-Version header field indicates that the message is in
2434   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2435   Proxies/gateways are responsible for ensuring full compliance (where
2436   possible) when exporting HTTP messages to strict MIME environments.
2437</t>
2438<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
2439  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
2440  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2441</artwork></figure>
2442<t>
2443   MIME version "1.0" is the default for use in HTTP/1.1. However,
2444   HTTP/1.1 message parsing and semantics are defined by this document
2445   and not the MIME specification.
2446</t>
2447</section>
2448
2449<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2450<t>
2451   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2452   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2453   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2454   allowed for subtypes of the "text" media type when transmitted over
2455   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2456   line breaks as CRLF and forbids the use of CR or LF outside of line
2457   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2458   line break within text content when a message is transmitted over
2459   HTTP.
2460</t>
2461<t>
2462   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2463   environment &SHOULD; translate all line breaks within the text media
2464   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2465   canonical form of CRLF. Note, however, that this might be complicated
2466   by the presence of a Content-Encoding and by the fact that HTTP
2467   allows the use of some character sets which do not use octets 13 and
2468   10 to represent CR and LF, as is the case for some multi-byte
2469   character sets.
2470</t>
2471<t>
2472   Implementors should note that conversion will break any cryptographic
2473   checksums applied to the original content unless the original content
2474   is already in canonical form. Therefore, the canonical form is
2475   recommended for any content that uses such checksums in HTTP.
2476</t>
2477</section>
2478
2479
2480<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2481<t>
2482   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2483   simplify the process of date comparison. Proxies and gateways from
2484   other protocols &SHOULD; ensure that any Date header field present in a
2485   message conforms to one of the HTTP/1.1 formats and rewrite the date
2486   if necessary.
2487</t>
2488</section>
2489
2490<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2491<t>
2492   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2493   Content-Encoding header field. Since this acts as a modifier on the
2494   media type, proxies and gateways from HTTP to MIME-compliant
2495   protocols &MUST; either change the value of the Content-Type header
2496   field or decode the entity-body before forwarding the message. (Some
2497   experimental applications of Content-Type for Internet mail have used
2498   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2499   a function equivalent to Content-Encoding. However, this parameter is
2500   not part of RFC 2045).
2501</t>
2502</section>
2503
2504<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2505<t>
2506   HTTP does not use the Content-Transfer-Encoding field of RFC
2507   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2508   remove any Content-Transfer-Encoding
2509   prior to delivering the response message to an HTTP client.
2510</t>
2511<t>
2512   Proxies and gateways from HTTP to MIME-compliant protocols are
2513   responsible for ensuring that the message is in the correct format
2514   and encoding for safe transport on that protocol, where "safe
2515   transport" is defined by the limitations of the protocol being used.
2516   Such a proxy or gateway &SHOULD; label the data with an appropriate
2517   Content-Transfer-Encoding if doing so will improve the likelihood of
2518   safe transport over the destination protocol.
2519</t>
2520</section>
2521
2522<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2523<t>
2524   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2525   Proxies/gateways &MUST; remove any transfer-coding prior to
2526   forwarding a message via a MIME-compliant protocol.
2527</t>
2528</section>
2529
2530<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2531<t>
2532   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2533   need to be aware of MIME line length limitations. Since HTTP does not
2534   have this limitation, HTTP does not fold long lines. MHTML messages
2535   being transported by HTTP follow all conventions of MHTML, including
2536   line length limitations and folding, canonicalization, etc., since
2537   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2538   does not interpret the content or any MIME header lines that might be
2539   contained therein.
2540</t>
2541</section>
2542</section>
2543
2544<section title="Additional Features" anchor="additional.features">
2545<t>
2546   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2547   existing HTTP implementations, but not consistently and correctly
2548   across most HTTP/1.1 applications. Implementors are advised to be
2549   aware of these features, but cannot rely upon their presence in, or
2550   interoperability with, other HTTP/1.1 applications. Some of these
2551   describe proposed experimental features, and some describe features
2552   that experimental deployment found lacking that are now addressed in
2553   the base HTTP/1.1 specification.
2554</t>
2555<t>
2556   A number of other headers, such as Content-Disposition and Title,
2557   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2558</t>
2559
2560<section title="Content-Disposition" anchor="content-disposition">
2561<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2562<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2563  <x:anchor-alias value="content-disposition"/>
2564  <x:anchor-alias value="content-disposition-v"/>
2565  <x:anchor-alias value="disposition-type"/>
2566  <x:anchor-alias value="disposition-parm"/>
2567  <x:anchor-alias value="disp-extension-parm"/>
2568  <x:anchor-alias value="disp-extension-token"/>
2569  <x:anchor-alias value="filename-parm"/>
2570<t>
2571   The Content-Disposition response-header field has been proposed as a
2572   means for the origin server to suggest a default filename if the user
2573   requests that the content is saved to a file. This usage is derived
2574   from the definition of Content-Disposition in <xref target="RFC2183"/>.
2575</t>
2576<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"/>
2577  <x:ref>content-disposition</x:ref> = "Content-Disposition" ":" <x:ref>OWS</x:ref>
2578                        <x:ref>content-disposition-v</x:ref>
2579  <x:ref>content-disposition-v</x:ref> = <x:ref>disposition-type</x:ref>
2580                          *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>disposition-parm</x:ref> )
2581  <x:ref>disposition-type</x:ref> = "attachment" / <x:ref>disp-extension-token</x:ref>
2582  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> / <x:ref>disp-extension-parm</x:ref>
2583  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2584  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
2585  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
2586</artwork></figure>
2587<t>
2588   An example is
2589</t>
2590<figure><artwork type="example">
2591   Content-Disposition: attachment; filename="fname.ext"
2592</artwork></figure>
2593<t>
2594   The receiving user agent &SHOULD-NOT;  respect any directory path
2595   information present in the filename-parm parameter, which is the only
2596   parameter believed to apply to HTTP implementations at this time. The
2597   filename &SHOULD; be treated as a terminal component only.
2598</t>
2599<t>
2600   If this header is used in a response with the application/octet-stream
2601   content-type, the implied suggestion is that the user agent
2602   should not display the response, but directly enter a `save response
2603   as...' dialog.
2604</t>
2605<t>
2606   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2607</t>
2608</section>
2609</section>
2610
2611<section title="Compatibility with Previous Versions" anchor="compatibility">
2612<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2613<t>
2614   Transfer-coding and message lengths all interact in ways that
2615   required fixing exactly when chunked encoding is used (to allow for
2616   transfer encoding that may not be self delimiting); it was important
2617   to straighten out exactly how message lengths are computed.
2618   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2619   <xref target="Part5"/> and <xref target="Part6"/>).
2620</t>
2621<t>
2622   Charset wildcarding is introduced to avoid explosion of character set
2623   names in accept headers. (<xref target="header.accept-charset"/>)
2624</t>
2625<t>
2626   Content-Base was deleted from the specification: it was not
2627   implemented widely, and there is no simple, safe way to introduce it
2628   without a robust extension mechanism. In addition, it is used in a
2629   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2630</t>
2631<t>
2632   A content-coding of "identity" was introduced, to solve problems
2633   discovered in caching. (<xref target="content.codings"/>)
2634</t>
2635<t>
2636   Quality Values of zero should indicate that "I don't want something"
2637   to allow clients to refuse a representation. (<xref target="quality.values"/>)
2638</t>
2639<t>
2640   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
2641   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
2642   specification, but not commonly implemented. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.2"/>.
2643</t>
2644</section>
2645
2646<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2647<t>
2648  Clarify contexts that charset is used in.
2649  (<xref target="character.sets"/>)
2650</t>
2651<t>
2652  Remove reference to non-existant identity transfer-coding value tokens.
2653  (<xref target="no.content-transfer-encoding"/>)
2654</t>
2655</section>
2656
2657</section>
2658
2659<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
2660<figure>
2661<artwork type="abnf" name="p3-payload.parsed-abnf">
2662<x:ref>Accept</x:ref> = "Accept:" OWS Accept-v
2663<x:ref>Accept-Charset</x:ref> = "Accept-Charset:" OWS Accept-Charset-v
2664<x:ref>Accept-Charset-v</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2665 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2666 qvalue ] ] )
2667<x:ref>Accept-Encoding</x:ref> = "Accept-Encoding:" OWS Accept-Encoding-v
2668<x:ref>Accept-Encoding-v</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
2669 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2670<x:ref>Accept-Language</x:ref> = "Accept-Language:" OWS Accept-Language-v
2671<x:ref>Accept-Language-v</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
2672 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2673 ] )
2674<x:ref>Accept-v</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2675 OWS media-range [ accept-params ] ] ) ]
2676
2677<x:ref>Content-Encoding</x:ref> = "Content-Encoding:" OWS Content-Encoding-v
2678<x:ref>Content-Encoding-v</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
2679 content-coding ] )
2680<x:ref>Content-Language</x:ref> = "Content-Language:" OWS Content-Language-v
2681<x:ref>Content-Language-v</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
2682 language-tag ] )
2683<x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in [Part1], Section 8.2&gt;
2684<x:ref>Content-Location</x:ref> = "Content-Location:" OWS Content-Location-v
2685<x:ref>Content-Location-v</x:ref> = absolute-URI / partial-URI
2686<x:ref>Content-MD5</x:ref> = "Content-MD5:" OWS Content-MD5-v
2687<x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2688<x:ref>Content-Range</x:ref> = &lt;Content-Range, defined in [Part5], Section 5.2&gt;
2689<x:ref>Content-Type</x:ref> = "Content-Type:" OWS Content-Type-v
2690<x:ref>Content-Type-v</x:ref> = media-type
2691
2692<x:ref>Expires</x:ref> = &lt;Expires, defined in [Part6], Section 15.3&gt;
2693
2694<x:ref>Last-Modified</x:ref> = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;
2695
2696<x:ref>MIME-Version</x:ref> = "MIME-Version:" OWS MIME-Version-v
2697<x:ref>MIME-Version-v</x:ref> = 1*DIGIT "." 1*DIGIT
2698
2699<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
2700
2701<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.1&gt;
2702<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
2703<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2704<x:ref>attribute</x:ref> = token
2705
2706<x:ref>charset</x:ref> = token
2707<x:ref>codings</x:ref> = ( content-coding / "*" )
2708<x:ref>content-coding</x:ref> = token
2709<x:ref>content-disposition</x:ref> = "Content-Disposition:" OWS
2710 content-disposition-v
2711<x:ref>content-disposition-v</x:ref> = disposition-type *( OWS ";" OWS
2712 disposition-parm )
2713
2714<x:ref>disp-extension-parm</x:ref> = token "=" ( token / quoted-string )
2715<x:ref>disp-extension-token</x:ref> = token
2716<x:ref>disposition-parm</x:ref> = filename-parm / disp-extension-parm
2717<x:ref>disposition-type</x:ref> = "attachment" / disp-extension-token
2718
2719<x:ref>entity-body</x:ref> = *OCTET
2720<x:ref>entity-header</x:ref> = Content-Encoding / Content-Language / Content-Length
2721 / Content-Location / Content-MD5 / Content-Range / Content-Type /
2722 Expires / Last-Modified / extension-header
2723<x:ref>extension-header</x:ref> = message-header
2724
2725<x:ref>filename-parm</x:ref> = "filename=" quoted-string
2726
2727<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
2728<x:ref>language-tag</x:ref> = primary-tag *( "-" subtag )
2729
2730<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2731 ";" OWS parameter )
2732<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2733<x:ref>message-header</x:ref> = &lt;message-header, defined in [Part1], Section 4.2&gt;
2734
2735<x:ref>parameter</x:ref> = attribute "=" value
2736<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.1&gt;
2737<x:ref>primary-tag</x:ref> = 1*8ALPHA
2738
2739<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
2740<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
2741
2742<x:ref>subtag</x:ref> = 1*8ALPHA
2743<x:ref>subtype</x:ref> = token
2744
2745<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2746<x:ref>type</x:ref> = token
2747
2748<x:ref>value</x:ref> = token / quoted-string
2749
2750; Accept defined but not used
2751; Accept-Charset defined but not used
2752; Accept-Encoding defined but not used
2753; Accept-Language defined but not used
2754; MIME-Version defined but not used
2755; content-disposition defined but not used
2756; entity-body defined but not used
2757; entity-header defined but not used
2758
2759
2760</artwork>
2761</figure>
2762</section>
2763
2764<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2765
2766<section title="Since RFC2616">
2767<t>
2768  Extracted relevant partitions from <xref target="RFC2616"/>.
2769</t>
2770</section>
2771
2772<section title="Since draft-ietf-httpbis-p3-payload-00">
2773<t>
2774  Closed issues:
2775  <list style="symbols"> 
2776    <t>
2777      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2778      "Media Type Registrations"
2779      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2780    </t>
2781    <t>
2782      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2783      "Clarification regarding quoting of charset values"
2784      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2785    </t>
2786    <t>
2787      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2788      "Remove 'identity' token references"
2789      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2790    </t>
2791    <t>
2792      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2793      "Accept-Encoding BNF"
2794    </t>
2795    <t>
2796      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2797      "Normative and Informative references"
2798    </t>
2799    <t>
2800      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2801      "RFC1700 references"
2802    </t>
2803    <t>
2804      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2805      "Updating to RFC4288"
2806    </t>
2807    <t>
2808      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2809      "Informative references"
2810    </t>
2811    <t>
2812      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2813      "ISO-8859-1 Reference"
2814    </t>
2815    <t>
2816      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2817      "Encoding References Normative"
2818    </t>
2819    <t>
2820      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2821      "Normative up-to-date references"
2822    </t>
2823  </list>
2824</t>
2825</section>
2826
2827<section title="Since draft-ietf-httpbis-p3-payload-01">
2828<t>
2829  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2830  <list style="symbols"> 
2831    <t>
2832      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2833    </t>
2834  </list>
2835</t>
2836</section>
2837
2838<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2839<t>
2840  Closed issues:
2841  <list style="symbols"> 
2842    <t>
2843      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2844      "Quoting Charsets"
2845    </t>
2846    <t>
2847      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2848      "Classification for Allow header"
2849    </t>
2850    <t>
2851      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2852      "missing default for qvalue in description of Accept-Encoding"
2853    </t>
2854  </list>
2855</t>
2856<t>
2857  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2858  <list style="symbols"> 
2859    <t>
2860      Reference RFC 3984, and update header registrations for headers defined
2861      in this document.
2862    </t>
2863  </list>
2864</t>
2865</section>
2866
2867<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2868<t>
2869  Closed issues:
2870  <list style="symbols"> 
2871    <t>
2872      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2873      "Quoting Charsets"
2874    </t>
2875    <t>
2876      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2877      "language tag matching (Accept-Language) vs RFC4647"
2878    </t>
2879    <t>
2880      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2881      "RFC 1806 has been replaced by RFC2183"
2882    </t>
2883  </list>
2884</t>
2885<t>
2886  Other changes:
2887  <list style="symbols"> 
2888    <t>
2889      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2890      "Encoding References Normative" -- rephrase the annotation and reference
2891      <xref target="BCP97"/>.
2892    </t>
2893  </list>
2894</t>
2895 </section>
2896
2897<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2898<t>
2899  Closed issues:
2900  <list style="symbols"> 
2901    <t>
2902      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2903      "RFC 2822 is updated by RFC 5322"
2904    </t>
2905  </list>
2906</t>
2907<t>
2908  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2909  <list style="symbols"> 
2910    <t>
2911      Use "/" instead of "|" for alternatives.
2912    </t>
2913    <t>
2914      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2915      whitespace ("OWS") and required whitespace ("RWS").
2916    </t>
2917    <t>
2918      Rewrite ABNFs to spell out whitespace rules, factor out
2919      header value format definitions.
2920    </t>
2921  </list>
2922</t>
2923</section>
2924
2925<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2926<t>
2927  Closed issues:
2928  <list style="symbols"> 
2929    <t>
2930      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2931      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2932    </t>
2933  </list>
2934</t>
2935<t>
2936  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2937  <list style="symbols"> 
2938    <t>
2939      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2940    </t>
2941  </list>
2942</t>
2943</section>
2944
2945</section>
2946
2947</back>
2948</rfc>
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