source: draft-ietf-httpbis/latest/p3-payload.xml @ 439

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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 "January">
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="full3978" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
48     xmlns:x='http://purl.org/net/xml2rfc/ext'>
49<front>
50
51  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
52
53  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
54    <organization abbrev="Day Software">Day Software</organization>
55    <address>
56      <postal>
57        <street>23 Corporate Plaza DR, Suite 280</street>
58        <city>Newport Beach</city>
59        <region>CA</region>
60        <code>92660</code>
61        <country>USA</country>
62      </postal>
63      <phone>+1-949-706-5300</phone>
64      <facsimile>+1-949-706-5305</facsimile>
65      <email>fielding@gbiv.com</email>
66      <uri>http://roy.gbiv.com/</uri>
67    </address>
68  </author>
69
70  <author initials="J." surname="Gettys" fullname="Jim Gettys">
71    <organization>One Laptop per Child</organization>
72    <address>
73      <postal>
74        <street>21 Oak Knoll Road</street>
75        <city>Carlisle</city>
76        <region>MA</region>
77        <code>01741</code>
78        <country>USA</country>
79      </postal>
80      <email>jg@laptop.org</email>
81      <uri>http://www.laptop.org/</uri>
82    </address>
83  </author>
84 
85  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
86    <organization abbrev="HP">Hewlett-Packard Company</organization>
87    <address>
88      <postal>
89        <street>HP Labs, Large Scale Systems Group</street>
90        <street>1501 Page Mill Road, MS 1177</street>
91        <city>Palo Alto</city>
92        <region>CA</region>
93        <code>94304</code>
94        <country>USA</country>
95      </postal>
96      <email>JeffMogul@acm.org</email>
97    </address>
98  </author>
99
100  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
101    <organization abbrev="Microsoft">Microsoft Corporation</organization>
102    <address>
103      <postal>
104        <street>1 Microsoft Way</street>
105        <city>Redmond</city>
106        <region>WA</region>
107        <code>98052</code>
108        <country>USA</country>
109      </postal>
110      <email>henrikn@microsoft.com</email>
111    </address>
112  </author>
113
114  <author initials="L." surname="Masinter" fullname="Larry Masinter">
115    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
116    <address>
117      <postal>
118        <street>345 Park Ave</street>
119        <city>San Jose</city>
120        <region>CA</region>
121        <code>95110</code>
122        <country>USA</country>
123      </postal>
124      <email>LMM@acm.org</email>
125      <uri>http://larry.masinter.net/</uri>
126    </address>
127  </author>
128 
129  <author initials="P." surname="Leach" fullname="Paul J. Leach">
130    <organization abbrev="Microsoft">Microsoft Corporation</organization>
131    <address>
132      <postal>
133        <street>1 Microsoft Way</street>
134        <city>Redmond</city>
135        <region>WA</region>
136        <code>98052</code>
137      </postal>
138      <email>paulle@microsoft.com</email>
139    </address>
140  </author>
141   
142  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
143    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
144    <address>
145      <postal>
146        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
147        <street>The Stata Center, Building 32</street>
148        <street>32 Vassar Street</street>
149        <city>Cambridge</city>
150        <region>MA</region>
151        <code>02139</code>
152        <country>USA</country>
153      </postal>
154      <email>timbl@w3.org</email>
155      <uri>http://www.w3.org/People/Berners-Lee/</uri>
156    </address>
157  </author>
158
159  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
160    <organization abbrev="W3C">World Wide Web Consortium</organization>
161    <address>
162      <postal>
163        <street>W3C / ERCIM</street>
164        <street>2004, rte des Lucioles</street>
165        <city>Sophia-Antipolis</city>
166        <region>AM</region>
167        <code>06902</code>
168        <country>France</country>
169      </postal>
170      <email>ylafon@w3.org</email>
171      <uri>http://www.raubacapeu.net/people/yves/</uri>
172    </address>
173  </author>
174
175  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
176    <organization abbrev="greenbytes">greenbytes GmbH</organization>
177    <address>
178      <postal>
179        <street>Hafenweg 16</street>
180        <city>Muenster</city><region>NW</region><code>48155</code>
181        <country>Germany</country>
182      </postal>
183      <phone>+49 251 2807760</phone>   
184      <facsimile>+49 251 2807761</facsimile>   
185      <email>julian.reschke@greenbytes.de</email>       
186      <uri>http://greenbytes.de/tech/webdav/</uri>     
187    </address>
188  </author>
189
190  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
191
192<abstract>
193<t>
194   The Hypertext Transfer Protocol (HTTP) is an application-level
195   protocol for distributed, collaborative, hypermedia information
196   systems. HTTP has been in use by the World Wide Web global information
197   initiative since 1990. This document is Part 3 of the seven-part specification
198   that defines the protocol referred to as "HTTP/1.1" and, taken together,
199   obsoletes RFC 2616.  Part 3 defines HTTP message content,
200   metadata, and content negotiation.
201</t>
202</abstract>
203
204<note title="Editorial Note (To be removed by RFC Editor)">
205  <t>
206    Discussion of this draft should take place on the HTTPBIS working group
207    mailing list (ietf-http-wg@w3.org). The current issues list is
208    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
209    and related documents (including fancy diffs) can be found at
210    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
211  </t>
212  <t>
213    The changes in this draft are summarized in <xref target="changes.since.05"/>.
214  </t>
215</note>
216</front>
217<middle>
218<section title="Introduction" anchor="introduction">
219<t>
220   This document defines HTTP/1.1 message payloads (a.k.a., content), the
221   associated metadata header fields that define how the payload is intended
222   to be interpreted by a recipient, the request header fields that
223   may influence content selection, and the various selection algorithms
224   that are collectively referred to as HTTP content negotiation.
225</t>
226<t>
227   This document is currently disorganized in order to minimize the changes
228   between drafts and enable reviewers to see the smaller errata changes.
229   The next draft will reorganize the sections to better reflect the content.
230   In particular, the sections on entities will be renamed payload and moved
231   to the first half of the document, while the sections on content negotiation
232   and associated request header fields will be moved to the second half.  The
233   current mess reflects how widely dispersed these topics and associated
234   requirements had become in <xref target="RFC2616"/>.
235</t>
236
237<section title="Requirements" anchor="intro.requirements">
238<t>
239   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
240   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
241   document are to be interpreted as described in <xref target="RFC2119"/>.
242</t>
243<t>
244   An implementation is not compliant if it fails to satisfy one or more
245   of the &MUST; or &REQUIRED; level requirements for the protocols it
246   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
247   level and all the &SHOULD; level requirements for its protocols is said
248   to be "unconditionally compliant"; one that satisfies all the &MUST;
249   level requirements but not all the &SHOULD; level requirements for its
250   protocols is said to be "conditionally compliant."
251</t>
252</section>
253
254<section title="Syntax Notation" anchor="notation">
255  <x:anchor-alias value="ALPHA"/>
256  <x:anchor-alias value="CR"/>
257  <x:anchor-alias value="DIGIT"/>
258  <x:anchor-alias value="LF"/>
259  <x:anchor-alias value="OCTET"/>
260  <x:anchor-alias value="VCHAR"/>
261  <x:anchor-alias value="WSP"/>
262<t>
263  This specification uses the ABNF syntax defined in &notation;.
264  The following core rules are included by
265  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
266  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
267  DIGIT (decimal 0-9), DQUOTE (double quote),
268  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
269  OCTET (any 8-bit sequence of data), SP (space),
270  VCHAR (any visible USASCII character),
271  and WSP (whitespace).
272</t>
273
274<section title="Core Rules" anchor="core.rules">
275  <x:anchor-alias value="quoted-string"/>
276  <x:anchor-alias value="token"/>
277  <x:anchor-alias value="OWS"/>
278<t>
279  The core rules below are defined in &basic-rules;:
280</t>
281<figure><artwork type="abnf2616">
282  <x:ref>quoted-string</x:ref>  = &lt;quoted-string, defined in &basic-rules;&gt;
283  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
284  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
285</artwork></figure>
286</section>
287
288<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
289  <x:anchor-alias value="absolute-URI"/>
290  <x:anchor-alias value="Allow"/>
291  <x:anchor-alias value="Content-Length"/>
292  <x:anchor-alias value="Content-Range"/>
293  <x:anchor-alias value="Expires"/>
294  <x:anchor-alias value="Last-Modified"/>
295  <x:anchor-alias value="message-header"/>
296  <x:anchor-alias value="partial-URI"/>
297<t>
298  The ABNF rules below are defined in other parts:
299</t>
300<figure><!--Part1--><artwork type="abnf2616">
301  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
302  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
303  <x:ref>message-header</x:ref> = &lt;message-header, defined in &message-headers;&gt;
304  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
305</artwork></figure>
306<figure><!--Part4--><artwork type="abnf2616">
307  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
308</artwork></figure>
309<figure><!--Part5--><artwork type="abnf2616">
310  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
311</artwork></figure>
312<figure><!--Part6--><artwork type="abnf2616">
313  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
314</artwork></figure>
315</section>
316
317</section>
318
319</section>
320
321<section title="Protocol Parameters" anchor="protocol.parameters">
322
323<section title="Character Sets" anchor="character.sets">
324<t>
325   HTTP uses the same definition of the term "character set" as that
326   described for MIME:
327</t>
328<t>
329   The term "character set" is used in this document to refer to a
330   method used with one or more tables to convert a sequence of octets
331   into a sequence of characters. Note that unconditional conversion in
332   the other direction is not required, in that not all characters may
333   be available in a given character set and a character set may provide
334   more than one sequence of octets to represent a particular character.
335   This definition is intended to allow various kinds of character
336   encoding, from simple single-table mappings such as US-ASCII to
337   complex table switching methods such as those that use ISO-2022's
338   techniques. However, the definition associated with a MIME character
339   set name &MUST; fully specify the mapping to be performed from octets
340   to characters. In particular, use of external profiling information
341   to determine the exact mapping is not permitted.
342</t>
343<t><list><t>
344      <x:h>Note:</x:h> This use of the term "character set" is more commonly
345      referred to as a "character encoding." However, since HTTP and
346      MIME share the same registry, it is important that the terminology
347      also be shared.
348</t></list></t>
349<t anchor="rule.charset">
350  <x:anchor-alias value="charset"/>
351   HTTP character sets are identified by case-insensitive tokens. The
352   complete set of tokens is defined by the IANA Character Set registry
353   (<eref target="http://www.iana.org/assignments/character-sets"/>).
354</t>
355<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
356  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
357</artwork></figure>
358<t>
359   Although HTTP allows an arbitrary token to be used as a charset
360   value, any token that has a predefined value within the IANA
361   Character Set registry &MUST; represent the character set defined
362   by that registry. Applications &SHOULD; limit their use of character
363   sets to those defined by the IANA registry.
364</t>
365<t>
366   HTTP uses charset in two contexts: within an Accept-Charset request
367   header (in which the charset value is an unquoted token) and as the
368   value of a parameter in a Content-Type header (within a request or
369   response), in which case the parameter value of the charset parameter
370   may be quoted.
371</t>
372<t>
373   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
374   <xref target="RFC2277"/>.
375</t>
376
377<section title="Missing Charset" anchor="missing.charset">
378<t>
379   Some HTTP/1.0 software has interpreted a Content-Type header without
380   charset parameter incorrectly to mean "recipient should guess."
381   Senders wishing to defeat this behavior &MAY; include a charset
382   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
383   it is known that it will not confuse the recipient.
384</t>
385<t>
386   Unfortunately, some older HTTP/1.0 clients did not deal properly with
387   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
388   charset label provided by the sender; and those user agents that have
389   a provision to "guess" a charset &MUST; use the charset from the
390   content-type field if they support that charset, rather than the
391   recipient's preference, when initially displaying a document. See
392   <xref target="canonicalization.and.text.defaults"/>.
393</t>
394</section>
395</section>
396
397<section title="Content Codings" anchor="content.codings">
398  <x:anchor-alias value="content-coding"/>
399<t>
400   Content coding values indicate an encoding transformation that has
401   been or can be applied to an entity. Content codings are primarily
402   used to allow a document to be compressed or otherwise usefully
403   transformed without losing the identity of its underlying media type
404   and without loss of information. Frequently, the entity is stored in
405   coded form, transmitted directly, and only decoded by the recipient.
406</t>
407<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
408  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
409</artwork></figure>
410<t>
411   All content-coding values are case-insensitive. HTTP/1.1 uses
412   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
413   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
414   describes the content-coding, what is more important is that it
415   indicates what decoding mechanism will be required to remove the
416   encoding.
417</t>
418<t>
419   The Internet Assigned Numbers Authority (IANA) acts as a registry for
420   content-coding value tokens. Initially, the registry contains the
421   following tokens:
422</t>
423<t>
424   gzip<iref item="gzip"/>
425  <list>
426    <t>
427        An encoding format produced by the file compression program
428        "gzip" (GNU zip) as described in <xref target="RFC1952"/>. This format is a
429        Lempel-Ziv coding (LZ77) with a 32 bit CRC.
430    </t>
431  </list>
432</t>
433<t>
434   compress<iref item="compress"/>
435  <list><t>
436        The encoding format produced by the common UNIX file compression
437        program "compress". This format is an adaptive Lempel-Ziv-Welch
438        coding (LZW).
439</t><t>
440        Use of program names for the identification of encoding formats
441        is not desirable and is discouraged for future encodings. Their
442        use here is representative of historical practice, not good
443        design. For compatibility with previous implementations of HTTP,
444        applications &SHOULD; consider "x-gzip" and "x-compress" to be
445        equivalent to "gzip" and "compress" respectively.
446  </t></list>
447</t>
448<t>
449   deflate<iref item="deflate"/>
450  <list><t>
451        The "zlib" format defined in <xref target="RFC1950"/> in combination with
452        the "deflate" compression mechanism described in <xref target="RFC1951"/>.
453  </t></list>
454</t>
455<t>
456   identity<iref item="identity"/>
457  <list><t>
458        The default (identity) encoding; the use of no transformation
459        whatsoever. This content-coding is used only in the Accept-Encoding
460        header, and &SHOULD-NOT;  be used in the Content-Encoding
461        header.
462  </t></list>
463</t>
464<t>
465   New content-coding value tokens &SHOULD; be registered; to allow
466   interoperability between clients and servers, specifications of the
467   content coding algorithms needed to implement a new value &SHOULD; be
468   publicly available and adequate for independent implementation, and
469   conform to the purpose of content coding defined in this section.
470</t>
471</section>
472
473<section title="Media Types" anchor="media.types">
474  <x:anchor-alias value="media-type"/>
475  <x:anchor-alias value="type"/>
476  <x:anchor-alias value="subtype"/>
477<t>
478   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
479   and Accept (<xref target="header.accept"/>) header fields in order to provide
480   open and extensible data typing and type negotiation.
481</t>
482<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"/>
483  <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> )
484  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
485  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
486</artwork></figure>
487<t anchor="rule.parameter">
488  <x:anchor-alias value="attribute"/>
489  <x:anchor-alias value="parameter"/>
490  <x:anchor-alias value="value"/>
491   Parameters &MAY; follow the type/subtype in the form of attribute/value
492   pairs.
493</t>
494<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"/>
495  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
496  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
497  <x:ref>value</x:ref>          = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
498</artwork></figure>
499<t>
500   The type, subtype, and parameter attribute names are case-insensitive.
501   Parameter values might or might not be case-sensitive, depending on the
502   semantics of the parameter name.  The presence or absence of a parameter might
503   be significant to the processing of a media-type, depending on its
504   definition within the media type registry.
505</t>
506<t>
507   A parameter value that matches the <x:ref>token</x:ref> production may be
508   transmitted as either a token or within a quoted-string. The quoted and
509   unquoted values are equivalent.
510</t>
511<t>
512   Note that some older HTTP applications do not recognize media type
513   parameters. When sending data to older HTTP applications,
514   implementations &SHOULD; only use media type parameters when they are
515   required by that type/subtype definition.
516</t>
517<t>
518   Media-type values are registered with the Internet Assigned Number
519   Authority (IANA). The media type registration process is
520   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
521   discouraged.
522</t>
523
524<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
525<t>
526   Internet media types are registered with a canonical form. An
527   entity-body transferred via HTTP messages &MUST; be represented in the
528   appropriate canonical form prior to its transmission except for
529   "text" types, as defined in the next paragraph.
530</t>
531<t>
532   When in canonical form, media subtypes of the "text" type use CRLF as
533   the text line break. HTTP relaxes this requirement and allows the
534   transport of text media with plain CR or LF alone representing a line
535   break when it is done consistently for an entire entity-body. HTTP
536   applications &MUST; accept CRLF, bare CR, and bare LF as being
537   representative of a line break in text media received via HTTP. In
538   addition, if the text is represented in a character set that does not
539   use octets 13 and 10 for CR and LF respectively, as is the case for
540   some multi-byte character sets, HTTP allows the use of whatever octet
541   sequences are defined by that character set to represent the
542   equivalent of CR and LF for line breaks. This flexibility regarding
543   line breaks applies only to text media in the entity-body; a bare CR
544   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
545   structures (such as header fields and multipart boundaries).
546</t>
547<t>
548   If an entity-body is encoded with a content-coding, the underlying
549   data &MUST; be in a form defined above prior to being encoded.
550</t>
551<t>
552   The "charset" parameter is used with some media types to define the
553   character set (<xref target="character.sets"/>) of the data. When no explicit charset
554   parameter is provided by the sender, media subtypes of the "text"
555   type are defined to have a default charset value of "ISO-8859-1" when
556   received via HTTP. Data in character sets other than "ISO-8859-1" or
557   its subsets &MUST; be labeled with an appropriate charset value. See
558   <xref target="missing.charset"/> for compatibility problems.
559</t>
560</section>
561
562<section title="Multipart Types" anchor="multipart.types">
563<t>
564   MIME provides for a number of "multipart" types -- encapsulations of
565   one or more entities within a single message-body. All multipart
566   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
567   and &MUST; include a boundary parameter as part of the media type
568   value. The message body is itself a protocol element and &MUST;
569   therefore use only CRLF to represent line breaks between body-parts.
570   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
571   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
572   original multipart contains an epilogue). These restrictions exist in
573   order to preserve the self-delimiting nature of a multipart message-body,
574   wherein the "end" of the message-body is indicated by the
575   ending multipart boundary.
576</t>
577<t>
578   In general, HTTP treats a multipart message-body no differently than
579   any other media type: strictly as payload. The one exception is the
580   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
581   (Partial Content) response.
582   <!-- jre: re-insert removed text pointing to caching? -->
583   In all
584   other cases, an HTTP user agent &SHOULD; follow the same or similar
585   behavior as a MIME user agent would upon receipt of a multipart type.
586   The MIME header fields within each body-part of a multipart message-body
587   do not have any significance to HTTP beyond that defined by
588   their MIME semantics.
589</t>
590<t>
591   In general, an HTTP user agent &SHOULD; follow the same or similar
592   behavior as a MIME user agent would upon receipt of a multipart type.
593   If an application receives an unrecognized multipart subtype, the
594   application &MUST; treat it as being equivalent to "multipart/mixed".
595</t>
596<t><list><t>
597      <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
598      for carrying form data suitable for processing via the POST
599      request method, as described in <xref target="RFC2388"/>.
600</t></list></t>
601</section>
602</section>
603
604<section title="Quality Values" anchor="quality.values">
605  <x:anchor-alias value="qvalue"/>
606<t>
607   HTTP content negotiation (<xref target="content.negotiation"/>) uses short "floating point"
608   numbers to indicate the relative importance ("weight") of various
609   negotiable parameters.  A weight is normalized to a real number in
610   the range 0 through 1, where 0 is the minimum and 1 the maximum
611   value. If a parameter has a quality value of 0, then content with
612   this parameter is `not acceptable' for the client. HTTP/1.1
613   applications &MUST-NOT; generate more than three digits after the
614   decimal point. User configuration of these values &SHOULD; also be
615   limited in this fashion.
616</t>
617<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
618  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
619                 / ( "1" [ "." 0*3("0") ] )
620</artwork></figure>
621<t>
622   "Quality values" is a misnomer, since these values merely represent
623   relative degradation in desired quality.
624</t>
625</section>
626
627<section title="Language Tags" anchor="language.tags">
628  <x:anchor-alias value="language-tag"/>
629  <x:anchor-alias value="primary-tag"/>
630  <x:anchor-alias value="subtag"/>
631<t>
632   A language tag identifies a natural language spoken, written, or
633   otherwise conveyed by human beings for communication of information
634   to other human beings. Computer languages are explicitly excluded.
635   HTTP uses language tags within the Accept-Language and Content-Language
636   fields.
637</t>
638<t>
639   The syntax and registry of HTTP language tags is the same as that
640   defined by <xref target="RFC1766"/>. In summary, a language tag is composed of 1
641   or more parts: A primary language tag and a possibly empty series of
642   subtags:
643</t>
644<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"/>
645  <x:ref>language-tag</x:ref>  = <x:ref>primary-tag</x:ref> *( "-" <x:ref>subtag</x:ref> )
646  <x:ref>primary-tag</x:ref>   = 1*8<x:ref>ALPHA</x:ref>
647  <x:ref>subtag</x:ref>        = 1*8<x:ref>ALPHA</x:ref>
648</artwork></figure>
649<t>
650   White space is not allowed within the tag and all tags are case-insensitive.
651   The name space of language tags is administered by the
652   IANA. Example tags include:
653</t>
654<figure><artwork type="example">
655    en, en-US, en-cockney, i-cherokee, x-pig-latin
656</artwork></figure>
657<t>
658   where any two-letter primary-tag is an ISO-639 language abbreviation
659   and any two-letter initial subtag is an ISO-3166 country code. (The
660   last three tags above are not registered tags; all but the last are
661   examples of tags which could be registered in future.)
662</t>
663</section>
664</section>
665
666<section title="Entity" anchor="entity">
667<t>
668   Request and Response messages &MAY; transfer an entity if not otherwise
669   restricted by the request method or response status code. An entity
670   consists of entity-header fields and an entity-body, although some
671   responses will only include the entity-headers.
672</t>
673<t>
674   In this section, both sender and recipient refer to either the client
675   or the server, depending on who sends and who receives the entity.
676</t>
677
678<section title="Entity Header Fields" anchor="entity.header.fields">
679  <x:anchor-alias value="entity-header"/>
680  <x:anchor-alias value="extension-header"/>
681<t>
682   Entity-header fields define metainformation about the entity-body or,
683   if no body is present, about the resource identified by the request.
684</t>
685<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
686  <x:ref>entity-header</x:ref>  = <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
687                 / <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
688                 / <x:ref>Content-Length</x:ref>           ; &header-content-length;
689                 / <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
690                 / <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
691                 / <x:ref>Content-Range</x:ref>            ; &header-content-range;
692                 / <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
693                 / <x:ref>Expires</x:ref>                  ; &header-expires;
694                 / <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
695                 / <x:ref>extension-header</x:ref>
696 
697  <x:ref>extension-header</x:ref> = <x:ref>message-header</x:ref>
698</artwork></figure>
699<t>
700   The extension-header mechanism allows additional entity-header fields
701   to be defined without changing the protocol, but these fields cannot
702   be assumed to be recognizable by the recipient. Unrecognized header
703   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
704   transparent proxies.
705</t>
706</section>
707
708<section title="Entity Body" anchor="entity.body">
709  <x:anchor-alias value="entity-body"/>
710<t>
711   The entity-body (if any) sent with an HTTP request or response is in
712   a format and encoding defined by the entity-header fields.
713</t>
714<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
715  <x:ref>entity-body</x:ref>    = *<x:ref>OCTET</x:ref>
716</artwork></figure>
717<t>
718   An entity-body is only present in a message when a message-body is
719   present, as described in &message-body;. The entity-body is obtained
720   from the message-body by decoding any Transfer-Encoding that might
721   have been applied to ensure safe and proper transfer of the message.
722</t>
723
724<section title="Type" anchor="type">
725<t>
726   When an entity-body is included with a message, the data type of that
727   body is determined via the header fields Content-Type and Content-Encoding.
728   These define a two-layer, ordered encoding model:
729</t>
730<figure><artwork type="example">
731    entity-body := Content-Encoding( Content-Type( data ) )
732</artwork></figure>
733<t>
734   Content-Type specifies the media type of the underlying data.
735   Content-Encoding may be used to indicate any additional content
736   codings applied to the data, usually for the purpose of data
737   compression, that are a property of the requested resource. There is
738   no default encoding.
739</t>
740<t>
741   Any HTTP/1.1 message containing an entity-body &SHOULD; include a
742   Content-Type header field defining the media type of that body. If
743   and only if the media type is not given by a Content-Type field, the
744   recipient &MAY; attempt to guess the media type via inspection of its
745   content and/or the name extension(s) of the URI used to identify the
746   resource. If the media type remains unknown, the recipient &SHOULD;
747   treat it as type "application/octet-stream".
748</t>
749</section>
750   
751<section title="Entity Length" anchor="entity.length">
752<t>
753   The entity-length of a message is the length of the message-body
754   before any transfer-codings have been applied. &message-length; defines
755   how the transfer-length of a message-body is determined.
756</t>
757</section>
758</section>
759</section>
760
761<section title="Content Negotiation" anchor="content.negotiation">
762<t>
763   Most HTTP responses include an entity which contains information for
764   interpretation by a human user. Naturally, it is desirable to supply
765   the user with the "best available" entity corresponding to the
766   request. Unfortunately for servers and caches, not all users have the
767   same preferences for what is "best," and not all user agents are
768   equally capable of rendering all entity types. For that reason, HTTP
769   has provisions for several mechanisms for "content negotiation" --
770   the process of selecting the best representation for a given response
771   when there are multiple representations available.
772  <list><t>
773      <x:h>Note:</x:h> This is not called "format negotiation" because the
774      alternate representations may be of the same media type, but use
775      different capabilities of that type, be in different languages,
776      etc.
777  </t></list>
778</t>
779<t>
780   Any response containing an entity-body &MAY; be subject to negotiation,
781   including error responses.
782</t>
783<t>
784   There are two kinds of content negotiation which are possible in
785   HTTP: server-driven and agent-driven negotiation. These two kinds of
786   negotiation are orthogonal and thus may be used separately or in
787   combination. One method of combination, referred to as transparent
788   negotiation, occurs when a cache uses the agent-driven negotiation
789   information provided by the origin server in order to provide
790   server-driven negotiation for subsequent requests.
791</t>
792
793<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
794<t>
795   If the selection of the best representation for a response is made by
796   an algorithm located at the server, it is called server-driven
797   negotiation. Selection is based on the available representations of
798   the response (the dimensions over which it can vary; e.g. language,
799   content-coding, etc.) and the contents of particular header fields in
800   the request message or on other information pertaining to the request
801   (such as the network address of the client).
802</t>
803<t>
804   Server-driven negotiation is advantageous when the algorithm for
805   selecting from among the available representations is difficult to
806   describe to the user agent, or when the server desires to send its
807   "best guess" to the client along with the first response (hoping to
808   avoid the round-trip delay of a subsequent request if the "best
809   guess" is good enough for the user). In order to improve the server's
810   guess, the user agent &MAY; include request header fields (Accept,
811   Accept-Language, Accept-Encoding, etc.) which describe its
812   preferences for such a response.
813</t>
814<t>
815   Server-driven negotiation has disadvantages:
816  <list style="numbers">
817    <t>
818         It is impossible for the server to accurately determine what
819         might be "best" for any given user, since that would require
820         complete knowledge of both the capabilities of the user agent
821         and the intended use for the response (e.g., does the user want
822         to view it on screen or print it on paper?).
823    </t>
824    <t>
825         Having the user agent describe its capabilities in every
826         request can be both very inefficient (given that only a small
827         percentage of responses have multiple representations) and a
828         potential violation of the user's privacy.
829    </t>
830    <t>
831         It complicates the implementation of an origin server and the
832         algorithms for generating responses to a request.
833    </t>
834    <t>
835         It may limit a public cache's ability to use the same response
836         for multiple user's requests.
837    </t>
838  </list>
839</t>
840<t>
841   HTTP/1.1 includes the following request-header fields for enabling
842   server-driven negotiation through description of user agent
843   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
844   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
845   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;). However, an
846   origin server is not limited to these dimensions and &MAY; vary the
847   response based on any aspect of the request, including information
848   outside the request-header fields or within extension header fields
849   not defined by this specification.
850</t>
851<t>
852   The Vary header field (&header-vary;) can be used to express the parameters the
853   server uses to select a representation that is subject to server-driven
854   negotiation.
855</t>
856</section>
857
858<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
859<t>
860   With agent-driven negotiation, selection of the best representation
861   for a response is performed by the user agent after receiving an
862   initial response from the origin server. Selection is based on a list
863   of the available representations of the response included within the
864   header fields or entity-body of the initial response, with each
865   representation identified by its own URI. Selection from among the
866   representations may be performed automatically (if the user agent is
867   capable of doing so) or manually by the user selecting from a
868   generated (possibly hypertext) menu.
869</t>
870<t>
871   Agent-driven negotiation is advantageous when the response would vary
872   over commonly-used dimensions (such as type, language, or encoding),
873   when the origin server is unable to determine a user agent's
874   capabilities from examining the request, and generally when public
875   caches are used to distribute server load and reduce network usage.
876</t>
877<t>
878   Agent-driven negotiation suffers from the disadvantage of needing a
879   second request to obtain the best alternate representation. This
880   second request is only efficient when caching is used. In addition,
881   this specification does not define any mechanism for supporting
882   automatic selection, though it also does not prevent any such
883   mechanism from being developed as an extension and used within
884   HTTP/1.1.
885</t>
886<t>
887   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
888   status codes for enabling agent-driven negotiation when the server is
889   unwilling or unable to provide a varying response using server-driven
890   negotiation.
891</t>
892</section>
893
894<section title="Transparent Negotiation" anchor="transparent.negotiation">
895<t>
896   Transparent negotiation is a combination of both server-driven and
897   agent-driven negotiation. When a cache is supplied with a form of the
898   list of available representations of the response (as in agent-driven
899   negotiation) and the dimensions of variance are completely understood
900   by the cache, then the cache becomes capable of performing server-driven
901   negotiation on behalf of the origin server for subsequent
902   requests on that resource.
903</t>
904<t>
905   Transparent negotiation has the advantage of distributing the
906   negotiation work that would otherwise be required of the origin
907   server and also removing the second request delay of agent-driven
908   negotiation when the cache is able to correctly guess the right
909   response.
910</t>
911<t>
912   This specification does not define any mechanism for transparent
913   negotiation, though it also does not prevent any such mechanism from
914   being developed as an extension that could be used within HTTP/1.1.
915</t>
916</section>
917</section>
918
919<section title="Header Field Definitions" anchor="header.fields">
920<t>
921   This section defines the syntax and semantics of HTTP/1.1 header fields
922   related to the payload of messages.
923</t>
924<t>
925   For entity-header fields, both sender and recipient refer to either the
926   client or the server, depending on who sends and who receives the entity.
927</t>
928
929<section title="Accept" anchor="header.accept">
930  <iref primary="true" item="Accept header" x:for-anchor=""/>
931  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
932  <x:anchor-alias value="Accept"/>
933  <x:anchor-alias value="Accept-v"/>
934  <x:anchor-alias value="accept-ext"/>
935  <x:anchor-alias value="accept-params"/>
936  <x:anchor-alias value="media-range"/>
937<t>
938   The request-header field "Accept" can be used to specify certain media
939   types which are acceptable for the response. Accept headers can be
940   used to indicate that the request is specifically limited to a small
941   set of desired types, as in the case of a request for an in-line
942   image.
943</t>
944<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"/>
945  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
946  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
947 
948  <x:ref>media-range</x:ref>    = ( "*/*"
949                   / ( <x:ref>type</x:ref> "/" "*" )
950                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
951                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
952  <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> )
953  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref>
954                   [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
955</artwork></figure>
956<t>
957   The asterisk "*" character is used to group media types into ranges,
958   with "*/*" indicating all media types and "type/*" indicating all
959   subtypes of that type. The media-range &MAY; include media type
960   parameters that are applicable to that range.
961</t>
962<t>
963   Each media-range &MAY; be followed by one or more accept-params,
964   beginning with the "q" parameter for indicating a relative quality
965   factor. The first "q" parameter (if any) separates the media-range
966   parameter(s) from the accept-params. Quality factors allow the user
967   or user agent to indicate the relative degree of preference for that
968   media-range, using the qvalue scale from 0 to 1 (<xref target="quality.values"/>). The
969   default value is q=1.
970  <list><t>
971      <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
972      parameters from Accept extension parameters is due to historical
973      practice. Although this prevents any media type parameter named
974      "q" from being used with a media range, such an event is believed
975      to be unlikely given the lack of any "q" parameters in the IANA
976      media type registry and the rare usage of any media type
977      parameters in Accept. Future media types are discouraged from
978      registering any parameter named "q".
979  </t></list>
980</t>
981<t>
982   The example
983</t>
984<figure><artwork type="example">
985  Accept: audio/*; q=0.2, audio/basic
986</artwork></figure>
987<t>
988   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
989   type if it is the best available after an 80% mark-down in quality."
990</t>
991<t>
992   If no Accept header field is present, then it is assumed that the
993   client accepts all media types. If an Accept header field is present,
994   and if the server cannot send a response which is acceptable
995   according to the combined Accept field value, then the server &SHOULD;
996   send a 406 (Not Acceptable) response.
997</t>
998<t>
999   A more elaborate example is
1000</t>
1001<figure><artwork type="example">
1002  Accept: text/plain; q=0.5, text/html,
1003          text/x-dvi; q=0.8, text/x-c
1004</artwork></figure>
1005<t>
1006   Verbally, this would be interpreted as "text/html and text/x-c are
1007   the preferred media types, but if they do not exist, then send the
1008   text/x-dvi entity, and if that does not exist, send the text/plain
1009   entity."
1010</t>
1011<t>
1012   Media ranges can be overridden by more specific media ranges or
1013   specific media types. If more than one media range applies to a given
1014   type, the most specific reference has precedence. For example,
1015</t>
1016<figure><artwork type="example">
1017  Accept: text/*, text/html, text/html;level=1, */*
1018</artwork></figure>
1019<t>
1020   have the following precedence:
1021</t>
1022<figure><artwork type="example">
1023    1) text/html;level=1
1024    2) text/html
1025    3) text/*
1026    4) */*
1027</artwork></figure>
1028<t>
1029   The media type quality factor associated with a given type is
1030   determined by finding the media range with the highest precedence
1031   which matches that type. For example,
1032</t>
1033<figure><artwork type="example">
1034  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1035          text/html;level=2;q=0.4, */*;q=0.5
1036</artwork></figure>
1037<t>
1038   would cause the following values to be associated:
1039</t>
1040<figure><artwork type="example">
1041    text/html;level=1         = 1
1042    text/html                 = 0.7
1043    text/plain                = 0.3
1044    image/jpeg                = 0.5
1045    text/html;level=2         = 0.4
1046    text/html;level=3         = 0.7
1047</artwork></figure>
1048<t>
1049      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1050      values for certain media ranges. However, unless the user agent is
1051      a closed system which cannot interact with other rendering agents,
1052      this default set ought to be configurable by the user.
1053</t>
1054</section>
1055
1056<section title="Accept-Charset" anchor="header.accept-charset">
1057  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1058  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1059  <x:anchor-alias value="Accept-Charset"/>
1060  <x:anchor-alias value="Accept-Charset-v"/>
1061<t>
1062   The request-header field "Accept-Charset" can be used to indicate what
1063   character sets are acceptable for the response. This field allows
1064   clients capable of understanding more comprehensive or special-purpose
1065   character sets to signal that capability to a server which is
1066   capable of representing documents in those character sets.
1067</t>
1068<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
1069  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
1070          <x:ref>Accept-Charset-v</x:ref>
1071  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1072                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1073</artwork></figure>
1074<t>
1075   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1076   be given an associated quality value which represents the user's
1077   preference for that charset. The default value is q=1. An example is
1078</t>
1079<figure><artwork type="example">
1080  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1081</artwork></figure>
1082<t>
1083   The special value "*", if present in the Accept-Charset field,
1084   matches every character set (including ISO-8859-1) which is not
1085   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1086   in an Accept-Charset field, then all character sets not explicitly
1087   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1088   a quality value of 1 if not explicitly mentioned.
1089</t>
1090<t>
1091   If no Accept-Charset header is present, the default is that any
1092   character set is acceptable. If an Accept-Charset header is present,
1093   and if the server cannot send a response which is acceptable
1094   according to the Accept-Charset header, then the server &SHOULD; send
1095   an error response with the 406 (Not Acceptable) status code, though
1096   the sending of an unacceptable response is also allowed.
1097</t>
1098</section>
1099
1100<section title="Accept-Encoding" anchor="header.accept-encoding">
1101  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1102  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1103  <x:anchor-alias value="Accept-Encoding"/>
1104  <x:anchor-alias value="Accept-Encoding-v"/>
1105  <x:anchor-alias value="codings"/>
1106<t>
1107   The request-header field "Accept-Encoding" is similar to Accept, but
1108   restricts the content-codings (<xref target="content.codings"/>) that are acceptable in
1109   the response.
1110</t>
1111<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"/>
1112  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
1113                     <x:ref>Accept-Encoding-v</x:ref>
1114  <x:ref>Accept-Encoding-v</x:ref>  =
1115                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1116  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
1117</artwork></figure>
1118<t>
1119   Each codings value &MAY; be given an associated quality value which
1120   represents the preference for that encoding. The default value is q=1.
1121</t>
1122<t>
1123   Examples of its use are:
1124</t>
1125<figure><artwork type="example">
1126  Accept-Encoding: compress, gzip
1127  Accept-Encoding:
1128  Accept-Encoding: *
1129  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1130  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1131</artwork></figure>
1132<t>
1133   A server tests whether a content-coding is acceptable, according to
1134   an Accept-Encoding field, using these rules:
1135  <list style="numbers">
1136      <t>If the content-coding is one of the content-codings listed in
1137         the Accept-Encoding field, then it is acceptable, unless it is
1138         accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
1139         qvalue of 0 means "not acceptable.")</t>
1140
1141      <t>The special "*" symbol in an Accept-Encoding field matches any
1142         available content-coding not explicitly listed in the header
1143         field.</t>
1144
1145      <t>If multiple content-codings are acceptable, then the acceptable
1146         content-coding with the highest non-zero qvalue is preferred.</t>
1147
1148      <t>The "identity" content-coding is always acceptable, unless
1149         specifically refused because the Accept-Encoding field includes
1150         "identity;q=0", or because the field includes "*;q=0" and does
1151         not explicitly include the "identity" content-coding. If the
1152         Accept-Encoding field-value is empty, then only the "identity"
1153         encoding is acceptable.</t>
1154  </list>
1155</t>
1156<t>
1157   If an Accept-Encoding field is present in a request, and if the
1158   server cannot send a response which is acceptable according to the
1159   Accept-Encoding header, then the server &SHOULD; send an error response
1160   with the 406 (Not Acceptable) status code.
1161</t>
1162<t>
1163   If no Accept-Encoding field is present in a request, the server &MAY;
1164   assume that the client will accept any content coding. In this case,
1165   if "identity" is one of the available content-codings, then the
1166   server &SHOULD; use the "identity" content-coding, unless it has
1167   additional information that a different content-coding is meaningful
1168   to the client.
1169  <list><t>
1170      <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1171      and if the "identity" content-coding is unavailable, then
1172      content-codings commonly understood by HTTP/1.0 clients (i.e.,
1173      "gzip" and "compress") are preferred; some older clients
1174      improperly display messages sent with other content-codings.  The
1175      server might also make this decision based on information about
1176      the particular user-agent or client.
1177    </t><t>
1178      <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1179      associated with content-codings. This means that qvalues will not
1180      work and are not permitted with x-gzip or x-compress.
1181    </t></list>
1182</t>
1183</section>
1184
1185<section title="Accept-Language" anchor="header.accept-language">
1186  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1187  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1188  <x:anchor-alias value="Accept-Language"/>
1189  <x:anchor-alias value="Accept-Language-v"/>
1190  <x:anchor-alias value="language-range"/>
1191<t>
1192   The request-header field "Accept-Language" is similar to Accept, but
1193   restricts the set of natural languages that are preferred as a
1194   response to the request. Language tags are defined in <xref target="language.tags"/>.
1195</t>
1196<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"/>
1197  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
1198                    <x:ref>Accept-Language-v</x:ref>
1199  <x:ref>Accept-Language-v</x:ref> =
1200                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1201  <x:ref>language-range</x:ref>    =
1202            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1203</artwork></figure>
1204<t>
1205   Each language-range can be given an associated quality value which
1206   represents an estimate of the user's preference for the languages
1207   specified by that range. The quality value defaults to "q=1". For
1208   example,
1209</t>
1210<figure><artwork type="example">
1211  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1212</artwork></figure>
1213<t>
1214   would mean: "I prefer Danish, but will accept British English and
1215   other types of English."
1216</t>
1217<t>
1218   For matching, the "Basic Filtering" matching scheme, defined in
1219   <xref target="RFC4647" x:sec="3.3.1" x:fmt="of"/>, is used:
1220</t>
1221<x:blockquote cite="http://tools.ietf.org/html/rfc4647#section-3.3.1">
1222  <t>
1223     A language range matches a
1224     particular language tag if, in a case-insensitive comparison, it
1225     exactly equals the tag, or if it exactly equals a prefix of the tag
1226     such that the first character following the prefix is "-".
1227  </t>
1228</x:blockquote> 
1229<t>
1230   The special range "*", if present in the Accept-Language field,
1231   matches every tag not matched by any other range present in the
1232   Accept-Language field.
1233  <list><t>
1234      <x:h>Note:</x:h> This use of a prefix matching rule does not imply that
1235      language tags are assigned to languages in such a way that it is
1236      always true that if a user understands a language with a certain
1237      tag, then this user will also understand all languages with tags
1238      for which this tag is a prefix. The prefix rule simply allows the
1239      use of prefix tags if this is the case.
1240  </t></list>
1241</t>
1242<t>
1243   The language quality factor assigned to a language-tag by the
1244   Accept-Language field is the quality value of the longest language-range
1245   in the field that matches the language-tag. If no language-range
1246   in the field matches the tag, the language quality factor
1247   assigned is 0. If no Accept-Language header is present in the
1248   request, the server
1249   &SHOULD; assume that all languages are equally acceptable. If an
1250   Accept-Language header is present, then all languages which are
1251   assigned a quality factor greater than 0 are acceptable.
1252</t>
1253<t>
1254   It might be contrary to the privacy expectations of the user to send
1255   an Accept-Language header with the complete linguistic preferences of
1256   the user in every request. For a discussion of this issue, see
1257   <xref target="privacy.issues.connected.to.accept.headers"/>.
1258</t>
1259<t>
1260   As intelligibility is highly dependent on the individual user, it is
1261   recommended that client applications make the choice of linguistic
1262   preference available to the user. If the choice is not made
1263   available, then the Accept-Language header field &MUST-NOT; be given in
1264   the request.
1265  <list><t>
1266      <x:h>Note:</x:h> When making the choice of linguistic preference available to
1267      the user, we remind implementors of  the fact that users are not
1268      familiar with the details of language matching as described above,
1269      and should provide appropriate guidance. As an example, users
1270      might assume that on selecting "en-gb", they will be served any
1271      kind of English document if British English is not available. A
1272      user agent might suggest in such a case to add "en" to get the
1273      best matching behavior.
1274  </t></list>
1275</t>
1276</section>
1277
1278<section title="Content-Encoding" anchor="header.content-encoding">
1279  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1280  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1281  <x:anchor-alias value="Content-Encoding"/>
1282  <x:anchor-alias value="Content-Encoding-v"/>
1283<t>
1284   The entity-header field "Content-Encoding" is used as a modifier to the
1285   media-type. When present, its value indicates what additional content
1286   codings have been applied to the entity-body, and thus what decoding
1287   mechanisms must be applied in order to obtain the media-type
1288   referenced by the Content-Type header field. Content-Encoding is
1289   primarily used to allow a document to be compressed without losing
1290   the identity of its underlying media type.
1291</t>
1292<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
1293  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
1294  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1295</artwork></figure>
1296<t>
1297   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1298</t>
1299<figure><artwork type="example">
1300  Content-Encoding: gzip
1301</artwork></figure>
1302<t>
1303   The content-coding is a characteristic of the entity identified by
1304   the request-target. Typically, the entity-body is stored with this
1305   encoding and is only decoded before rendering or analogous usage.
1306   However, a non-transparent proxy &MAY; modify the content-coding if the
1307   new coding is known to be acceptable to the recipient, unless the
1308   "no-transform" cache-control directive is present in the message.
1309</t>
1310<t>
1311   If the content-coding of an entity is not "identity", then the
1312   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1313   that lists the non-identity content-coding(s) used.
1314</t>
1315<t>
1316   If the content-coding of an entity in a request message is not
1317   acceptable to the origin server, the server &SHOULD; respond with a
1318   status code of 415 (Unsupported Media Type).
1319</t>
1320<t>
1321   If multiple encodings have been applied to an entity, the content
1322   codings &MUST; be listed in the order in which they were applied.
1323   Additional information about the encoding parameters &MAY; be provided
1324   by other entity-header fields not defined by this specification.
1325</t>
1326</section>
1327
1328<section title="Content-Language" anchor="header.content-language">
1329  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1330  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1331  <x:anchor-alias value="Content-Language"/>
1332  <x:anchor-alias value="Content-Language-v"/>
1333<t>
1334   The entity-header field "Content-Language" describes the natural
1335   language(s) of the intended audience for the enclosed entity. Note
1336   that this might not be equivalent to all the languages used within
1337   the entity-body.
1338</t>
1339<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
1340  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
1341  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1342</artwork></figure>
1343<t>
1344   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1345   Content-Language is to allow a user to identify and differentiate
1346   entities according to the user's own preferred language. Thus, if the
1347   body content is intended only for a Danish-literate audience, the
1348   appropriate field is
1349</t>
1350<figure><artwork type="example">
1351  Content-Language: da
1352</artwork></figure>
1353<t>
1354   If no Content-Language is specified, the default is that the content
1355   is intended for all language audiences. This might mean that the
1356   sender does not consider it to be specific to any natural language,
1357   or that the sender does not know for which language it is intended.
1358</t>
1359<t>
1360   Multiple languages &MAY; be listed for content that is intended for
1361   multiple audiences. For example, a rendition of the "Treaty of
1362   Waitangi," presented simultaneously in the original Maori and English
1363   versions, would call for
1364</t>
1365<figure><artwork type="example">
1366  Content-Language: mi, en
1367</artwork></figure>
1368<t>
1369   However, just because multiple languages are present within an entity
1370   does not mean that it is intended for multiple linguistic audiences.
1371   An example would be a beginner's language primer, such as "A First
1372   Lesson in Latin," which is clearly intended to be used by an
1373   English-literate audience. In this case, the Content-Language would
1374   properly only include "en".
1375</t>
1376<t>
1377   Content-Language &MAY; be applied to any media type -- it is not
1378   limited to textual documents.
1379</t>
1380</section>
1381
1382<section title="Content-Location" anchor="header.content-location">
1383  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1384  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1385  <x:anchor-alias value="Content-Location"/>
1386  <x:anchor-alias value="Content-Location-v"/>
1387<t>
1388   The entity-header field "Content-Location" &MAY; be used to supply the
1389   resource location for the entity enclosed in the message when that
1390   entity is accessible from a location separate from the requested
1391   resource's URI. A server &SHOULD; provide a Content-Location for the
1392   variant corresponding to the response entity; especially in the case
1393   where a resource has multiple entities associated with it, and those
1394   entities actually have separate locations by which they might be
1395   individually accessed, the server &SHOULD; provide a Content-Location
1396   for the particular variant which is returned.
1397</t>
1398<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
1399  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
1400                    <x:ref>Content-Location-v</x:ref>
1401  <x:ref>Content-Location-v</x:ref> =
1402                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1403</artwork></figure>
1404<t>
1405   The value of Content-Location also defines the base URI for the
1406   entity.
1407</t>
1408<t>
1409   The Content-Location value is not a replacement for the original
1410   requested URI; it is only a statement of the location of the resource
1411   corresponding to this particular entity at the time of the request.
1412   Future requests &MAY; specify the Content-Location URI as the request-target
1413   if the desire is to identify the source of that particular
1414   entity.
1415</t>
1416<t>
1417   A cache cannot assume that an entity with a Content-Location
1418   different from the URI used to retrieve it can be used to respond to
1419   later requests on that Content-Location URI. However, the Content-Location
1420   can be used to differentiate between multiple entities
1421   retrieved from a single requested resource, as described in &caching-neg-resp;.
1422</t>
1423<t>
1424   If the Content-Location is a relative URI, the relative URI is
1425   interpreted relative to the request-target.
1426</t>
1427<t>
1428   The meaning of the Content-Location header in PUT or POST requests is
1429   undefined; servers are free to ignore it in those cases.
1430</t>
1431</section>
1432
1433<section title="Content-MD5" anchor="header.content-md5">
1434  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1435  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1436  <x:anchor-alias value="Content-MD5"/>
1437  <x:anchor-alias value="Content-MD5-v"/>
1438<t>
1439   The entity-header field "Content-MD5", as defined in <xref target="RFC1864"/>, is
1440   an MD5 digest of the entity-body for the purpose of providing an
1441   end-to-end message integrity check (MIC) of the entity-body. (Note: a
1442   MIC is good for detecting accidental modification of the entity-body
1443   in transit, but is not proof against malicious attacks.)
1444</t>
1445<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
1446  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
1447  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1448</artwork></figure>
1449<t>
1450   The Content-MD5 header field &MAY; be generated by an origin server or
1451   client to function as an integrity check of the entity-body. Only
1452   origin servers or clients &MAY; generate the Content-MD5 header field;
1453   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1454   value as an end-to-end integrity check. Any recipient of the entity-body,
1455   including gateways and proxies, &MAY; check that the digest value
1456   in this header field matches that of the entity-body as received.
1457</t>
1458<t>
1459   The MD5 digest is computed based on the content of the entity-body,
1460   including any content-coding that has been applied, but not including
1461   any transfer-encoding applied to the message-body. If the message is
1462   received with a transfer-encoding, that encoding &MUST; be removed
1463   prior to checking the Content-MD5 value against the received entity.
1464</t>
1465<t>
1466   This has the result that the digest is computed on the octets of the
1467   entity-body exactly as, and in the order that, they would be sent if
1468   no transfer-encoding were being applied.
1469</t>
1470<t>
1471   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1472   composite media-types (e.g., multipart/* and message/rfc822), but
1473   this does not change how the digest is computed as defined in the
1474   preceding paragraph.
1475</t>
1476<t>
1477   There are several consequences of this. The entity-body for composite
1478   types &MAY; contain many body-parts, each with its own MIME and HTTP
1479   headers (including Content-MD5, Content-Transfer-Encoding, and
1480   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1481   or Content-Encoding header, it is assumed that the content
1482   of the body-part has had the encoding applied, and the body-part is
1483   included in the Content-MD5 digest as is -- i.e., after the
1484   application. The Transfer-Encoding header field is not allowed within
1485   body-parts.
1486</t>
1487<t>
1488   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1489   computing or checking the digest: the line break convention used in
1490   the text actually transmitted &MUST; be left unaltered when computing
1491   the digest.
1492  <list><t>
1493      <x:h>Note:</x:h> while the definition of Content-MD5 is exactly the same for
1494      HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1495      in which the application of Content-MD5 to HTTP entity-bodies
1496      differs from its application to MIME entity-bodies. One is that
1497      HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1498      does use Transfer-Encoding and Content-Encoding. Another is that
1499      HTTP more frequently uses binary content types than MIME, so it is
1500      worth noting that, in such cases, the byte order used to compute
1501      the digest is the transmission byte order defined for the type.
1502      Lastly, HTTP allows transmission of text types with any of several
1503      line break conventions and not just the canonical form using CRLF.
1504  </t></list>
1505</t>
1506</section>
1507
1508<section title="Content-Type" anchor="header.content-type">
1509  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1510  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1511  <x:anchor-alias value="Content-Type"/>
1512  <x:anchor-alias value="Content-Type-v"/>
1513<t>
1514   The entity-header field "Content-Type" indicates the media type of the
1515   entity-body sent to the recipient or, in the case of the HEAD method,
1516   the media type that would have been sent had the request been a GET.
1517</t>
1518<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
1519  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
1520  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1521</artwork></figure>
1522<t>
1523   Media types are defined in <xref target="media.types"/>. An example of the field is
1524</t>
1525<figure><artwork type="example">
1526  Content-Type: text/html; charset=ISO-8859-4
1527</artwork></figure>
1528<t>
1529   Further discussion of methods for identifying the media type of an
1530   entity is provided in <xref target="type"/>.
1531</t>
1532</section>
1533
1534</section>
1535
1536<section title="IANA Considerations" anchor="IANA.considerations">
1537<section title="Message Header Registration" anchor="message.header.registration">
1538<t>
1539   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
1540   with the permanent registrations below (see <xref target="RFC3864"/>):
1541</t>
1542<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1543<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1544   <ttcol>Header Field Name</ttcol>
1545   <ttcol>Protocol</ttcol>
1546   <ttcol>Status</ttcol>
1547   <ttcol>Reference</ttcol>
1548
1549   <c>Accept</c>
1550   <c>http</c>
1551   <c>standard</c>
1552   <c>
1553      <xref target="header.accept"/>
1554   </c>
1555   <c>Accept-Charset</c>
1556   <c>http</c>
1557   <c>standard</c>
1558   <c>
1559      <xref target="header.accept-charset"/>
1560   </c>
1561   <c>Accept-Encoding</c>
1562   <c>http</c>
1563   <c>standard</c>
1564   <c>
1565      <xref target="header.accept-encoding"/>
1566   </c>
1567   <c>Accept-Language</c>
1568   <c>http</c>
1569   <c>standard</c>
1570   <c>
1571      <xref target="header.accept-language"/>
1572   </c>
1573   <c>Content-Disposition</c>
1574   <c>http</c>
1575   <c/>
1576   <c>
1577      <xref target="content-disposition"/>
1578   </c>
1579   <c>Content-Encoding</c>
1580   <c>http</c>
1581   <c>standard</c>
1582   <c>
1583      <xref target="header.content-encoding"/>
1584   </c>
1585   <c>Content-Language</c>
1586   <c>http</c>
1587   <c>standard</c>
1588   <c>
1589      <xref target="header.content-language"/>
1590   </c>
1591   <c>Content-Location</c>
1592   <c>http</c>
1593   <c>standard</c>
1594   <c>
1595      <xref target="header.content-location"/>
1596   </c>
1597   <c>Content-MD5</c>
1598   <c>http</c>
1599   <c>standard</c>
1600   <c>
1601      <xref target="header.content-md5"/>
1602   </c>
1603   <c>Content-Type</c>
1604   <c>http</c>
1605   <c>standard</c>
1606   <c>
1607      <xref target="header.content-type"/>
1608   </c>
1609   <c>MIME-Version</c>
1610   <c>http</c>
1611   <c/>
1612   <c>
1613      <xref target="mime-version"/>
1614   </c>
1615</texttable>
1616<!--(END)-->
1617<t>
1618   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1619</t>
1620</section>
1621</section>
1622
1623<section title="Security Considerations" anchor="security.considerations">
1624<t>
1625   This section is meant to inform application developers, information
1626   providers, and users of the security limitations in HTTP/1.1 as
1627   described by this document. The discussion does not include
1628   definitive solutions to the problems revealed, though it does make
1629   some suggestions for reducing security risks.
1630</t>
1631
1632<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1633<t>
1634   Accept request-headers can reveal information about the user to all
1635   servers which are accessed. The Accept-Language header in particular
1636   can reveal information the user would consider to be of a private
1637   nature, because the understanding of particular languages is often
1638   strongly correlated to the membership of a particular ethnic group.
1639   User agents which offer the option to configure the contents of an
1640   Accept-Language header to be sent in every request are strongly
1641   encouraged to let the configuration process include a message which
1642   makes the user aware of the loss of privacy involved.
1643</t>
1644<t>
1645   An approach that limits the loss of privacy would be for a user agent
1646   to omit the sending of Accept-Language headers by default, and to ask
1647   the user whether or not to start sending Accept-Language headers to a
1648   server if it detects, by looking for any Vary response-header fields
1649   generated by the server, that such sending could improve the quality
1650   of service.
1651</t>
1652<t>
1653   Elaborate user-customized accept header fields sent in every request,
1654   in particular if these include quality values, can be used by servers
1655   as relatively reliable and long-lived user identifiers. Such user
1656   identifiers would allow content providers to do click-trail tracking,
1657   and would allow collaborating content providers to match cross-server
1658   click-trails or form submissions of individual users. Note that for
1659   many users not behind a proxy, the network address of the host
1660   running the user agent will also serve as a long-lived user
1661   identifier. In environments where proxies are used to enhance
1662   privacy, user agents ought to be conservative in offering accept
1663   header configuration options to end users. As an extreme privacy
1664   measure, proxies could filter the accept headers in relayed requests.
1665   General purpose user agents which provide a high degree of header
1666   configurability &SHOULD; warn users about the loss of privacy which can
1667   be involved.
1668</t>
1669</section>
1670
1671<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1672<t>
1673   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
1674   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1675   serious security considerations. Content-Disposition is not part of
1676   the HTTP standard, but since it is widely implemented, we are
1677   documenting its use and risks for implementors. See <xref target="RFC2183" x:fmt="of" x:sec="5"/>
1678   for details.
1679</t>
1680</section>
1681
1682</section>
1683
1684<section title="Acknowledgments" anchor="ack">
1685</section>
1686</middle>
1687<back>
1688
1689<references title="Normative References">
1690
1691<reference anchor="ISO-8859-1">
1692  <front>
1693    <title>
1694     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1695    </title>
1696    <author>
1697      <organization>International Organization for Standardization</organization>
1698    </author>
1699    <date year="1998"/>
1700  </front>
1701  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1702</reference>
1703
1704<reference anchor="Part1">
1705  <front>
1706    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1707    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1708      <organization abbrev="Day Software">Day Software</organization>
1709      <address><email>fielding@gbiv.com</email></address>
1710    </author>
1711    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1712      <organization>One Laptop per Child</organization>
1713      <address><email>jg@laptop.org</email></address>
1714    </author>
1715    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1716      <organization abbrev="HP">Hewlett-Packard Company</organization>
1717      <address><email>JeffMogul@acm.org</email></address>
1718    </author>
1719    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1720      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1721      <address><email>henrikn@microsoft.com</email></address>
1722    </author>
1723    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1724      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1725      <address><email>LMM@acm.org</email></address>
1726    </author>
1727    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1728      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1729      <address><email>paulle@microsoft.com</email></address>
1730    </author>
1731    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1732      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1733      <address><email>timbl@w3.org</email></address>
1734    </author>
1735    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1736      <organization abbrev="W3C">World Wide Web Consortium</organization>
1737      <address><email>ylafon@w3.org</email></address>
1738    </author>
1739    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1740      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1741      <address><email>julian.reschke@greenbytes.de</email></address>
1742    </author>
1743    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1744  </front>
1745  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1746  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1747</reference>
1748
1749<reference anchor="Part2">
1750  <front>
1751    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1752    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1753      <organization abbrev="Day Software">Day Software</organization>
1754      <address><email>fielding@gbiv.com</email></address>
1755    </author>
1756    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1757      <organization>One Laptop per Child</organization>
1758      <address><email>jg@laptop.org</email></address>
1759    </author>
1760    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1761      <organization abbrev="HP">Hewlett-Packard Company</organization>
1762      <address><email>JeffMogul@acm.org</email></address>
1763    </author>
1764    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1765      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1766      <address><email>henrikn@microsoft.com</email></address>
1767    </author>
1768    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1769      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1770      <address><email>LMM@acm.org</email></address>
1771    </author>
1772    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1773      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1774      <address><email>paulle@microsoft.com</email></address>
1775    </author>
1776    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1777      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1778      <address><email>timbl@w3.org</email></address>
1779    </author>
1780    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1781      <organization abbrev="W3C">World Wide Web Consortium</organization>
1782      <address><email>ylafon@w3.org</email></address>
1783    </author>
1784    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1785      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1786      <address><email>julian.reschke@greenbytes.de</email></address>
1787    </author>
1788    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1789  </front>
1790  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1791  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1792</reference>
1793
1794<reference anchor="Part4">
1795  <front>
1796    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1797    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1798      <organization abbrev="Day Software">Day Software</organization>
1799      <address><email>fielding@gbiv.com</email></address>
1800    </author>
1801    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1802      <organization>One Laptop per Child</organization>
1803      <address><email>jg@laptop.org</email></address>
1804    </author>
1805    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1806      <organization abbrev="HP">Hewlett-Packard Company</organization>
1807      <address><email>JeffMogul@acm.org</email></address>
1808    </author>
1809    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1810      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1811      <address><email>henrikn@microsoft.com</email></address>
1812    </author>
1813    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1814      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1815      <address><email>LMM@acm.org</email></address>
1816    </author>
1817    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1818      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1819      <address><email>paulle@microsoft.com</email></address>
1820    </author>
1821    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1822      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1823      <address><email>timbl@w3.org</email></address>
1824    </author>
1825    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1826      <organization abbrev="W3C">World Wide Web Consortium</organization>
1827      <address><email>ylafon@w3.org</email></address>
1828    </author>
1829    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1830      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1831      <address><email>julian.reschke@greenbytes.de</email></address>
1832    </author>
1833    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1834  </front>
1835  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1836  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1837</reference>
1838
1839<reference anchor="Part5">
1840  <front>
1841    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1842    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1843      <organization abbrev="Day Software">Day Software</organization>
1844      <address><email>fielding@gbiv.com</email></address>
1845    </author>
1846    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1847      <organization>One Laptop per Child</organization>
1848      <address><email>jg@laptop.org</email></address>
1849    </author>
1850    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1851      <organization abbrev="HP">Hewlett-Packard Company</organization>
1852      <address><email>JeffMogul@acm.org</email></address>
1853    </author>
1854    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1855      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1856      <address><email>henrikn@microsoft.com</email></address>
1857    </author>
1858    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1859      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1860      <address><email>LMM@acm.org</email></address>
1861    </author>
1862    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1863      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1864      <address><email>paulle@microsoft.com</email></address>
1865    </author>
1866    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1867      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1868      <address><email>timbl@w3.org</email></address>
1869    </author>
1870    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1871      <organization abbrev="W3C">World Wide Web Consortium</organization>
1872      <address><email>ylafon@w3.org</email></address>
1873    </author>
1874    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1875      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1876      <address><email>julian.reschke@greenbytes.de</email></address>
1877    </author>
1878    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1879  </front>
1880  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1881  <x:source href="p5-range.xml" basename="p5-range"/>
1882</reference>
1883
1884<reference anchor="Part6">
1885  <front>
1886    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1887    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1888      <organization abbrev="Day Software">Day Software</organization>
1889      <address><email>fielding@gbiv.com</email></address>
1890    </author>
1891    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1892      <organization>One Laptop per Child</organization>
1893      <address><email>jg@laptop.org</email></address>
1894    </author>
1895    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1896      <organization abbrev="HP">Hewlett-Packard Company</organization>
1897      <address><email>JeffMogul@acm.org</email></address>
1898    </author>
1899    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1900      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1901      <address><email>henrikn@microsoft.com</email></address>
1902    </author>
1903    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1904      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1905      <address><email>LMM@acm.org</email></address>
1906    </author>
1907    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1908      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1909      <address><email>paulle@microsoft.com</email></address>
1910    </author>
1911    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1912      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1913      <address><email>timbl@w3.org</email></address>
1914    </author>
1915    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1916      <organization abbrev="W3C">World Wide Web Consortium</organization>
1917      <address><email>ylafon@w3.org</email></address>
1918    </author>
1919    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1920      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1921      <address><email>julian.reschke@greenbytes.de</email></address>
1922    </author>
1923    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1924  </front>
1925  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1926  <x:source href="p6-cache.xml" basename="p6-cache"/>
1927</reference>
1928
1929<reference anchor="RFC1766">
1930  <front>
1931    <title abbrev="Language Tag">Tags for the Identification of Languages</title>
1932    <author initials="H." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
1933      <organization>UNINETT</organization>
1934      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
1935    </author>
1936    <date month="March" year="1995"/>
1937  </front>
1938  <seriesInfo name="RFC" value="1766"/>
1939</reference>
1940
1941<reference anchor="RFC1864">
1942  <front>
1943    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1944    <author initials="J." surname="Myers" fullname="John G. Myers">
1945      <organization>Carnegie Mellon University</organization>
1946      <address><email>jgm+@cmu.edu</email></address>
1947    </author>
1948    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
1949      <organization>Dover Beach Consulting, Inc.</organization>
1950      <address><email>mrose@dbc.mtview.ca.us</email></address>
1951    </author>
1952    <date month="October" year="1995"/>
1953  </front>
1954  <seriesInfo name="RFC" value="1864"/>
1955</reference>
1956
1957<reference anchor="RFC1950">
1958  <front>
1959    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1960    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1961      <organization>Aladdin Enterprises</organization>
1962      <address><email>ghost@aladdin.com</email></address>
1963    </author>
1964    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1965      <organization/>
1966    </author>
1967    <date month="May" year="1996"/>
1968  </front>
1969  <seriesInfo name="RFC" value="1950"/>
1970  <annotation>
1971    RFC 1950 is an Informational RFC, thus it may be less stable than
1972    this specification. On the other hand, this downward reference was
1973    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1974    therefore it is unlikely to cause problems in practice. See also
1975    <xref target="BCP97"/>.
1976  </annotation>
1977</reference>
1978
1979<reference anchor="RFC1951">
1980  <front>
1981    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1982    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1983      <organization>Aladdin Enterprises</organization>
1984      <address><email>ghost@aladdin.com</email></address>
1985    </author>
1986    <date month="May" year="1996"/>
1987  </front>
1988  <seriesInfo name="RFC" value="1951"/>
1989  <annotation>
1990    RFC 1951 is an Informational RFC, thus it may be less stable than
1991    this specification. On the other hand, this downward reference was
1992    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1993    therefore it is unlikely to cause problems in practice. See also
1994    <xref target="BCP97"/>.
1995  </annotation>
1996</reference>
1997
1998<reference anchor="RFC1952">
1999  <front>
2000    <title>GZIP file format specification version 4.3</title>
2001    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2002      <organization>Aladdin Enterprises</organization>
2003      <address><email>ghost@aladdin.com</email></address>
2004    </author>
2005    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2006      <organization/>
2007      <address><email>gzip@prep.ai.mit.edu</email></address>
2008    </author>
2009    <author initials="M." surname="Adler" fullname="Mark Adler">
2010      <organization/>
2011      <address><email>madler@alumni.caltech.edu</email></address>
2012    </author>
2013    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2014      <organization/>
2015      <address><email>ghost@aladdin.com</email></address>
2016    </author>
2017    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2018      <organization/>
2019      <address><email>randeg@alumni.rpi.edu</email></address>
2020    </author>
2021    <date month="May" year="1996"/>
2022  </front>
2023  <seriesInfo name="RFC" value="1952"/>
2024  <annotation>
2025    RFC 1952 is an Informational RFC, thus it may be less stable than
2026    this specification. On the other hand, this downward reference was
2027    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2028    therefore it is unlikely to cause problems in practice. See also
2029    <xref target="BCP97"/>.
2030  </annotation>
2031</reference>
2032
2033<reference anchor="RFC2045">
2034  <front>
2035    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2036    <author initials="N." surname="Freed" fullname="Ned Freed">
2037      <organization>Innosoft International, Inc.</organization>
2038      <address><email>ned@innosoft.com</email></address>
2039    </author>
2040    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2041      <organization>First Virtual Holdings</organization>
2042      <address><email>nsb@nsb.fv.com</email></address>
2043    </author>
2044    <date month="November" year="1996"/>
2045  </front>
2046  <seriesInfo name="RFC" value="2045"/>
2047</reference>
2048
2049<reference anchor="RFC2046">
2050  <front>
2051    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2052    <author initials="N." surname="Freed" fullname="Ned Freed">
2053      <organization>Innosoft International, Inc.</organization>
2054      <address><email>ned@innosoft.com</email></address>
2055    </author>
2056    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2057      <organization>First Virtual Holdings</organization>
2058      <address><email>nsb@nsb.fv.com</email></address>
2059    </author>
2060    <date month="November" year="1996"/>
2061  </front>
2062  <seriesInfo name="RFC" value="2046"/>
2063</reference>
2064
2065<reference anchor="RFC2119">
2066  <front>
2067    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2068    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2069      <organization>Harvard University</organization>
2070      <address><email>sob@harvard.edu</email></address>
2071    </author>
2072    <date month="March" year="1997"/>
2073  </front>
2074  <seriesInfo name="BCP" value="14"/>
2075  <seriesInfo name="RFC" value="2119"/>
2076</reference>
2077
2078<reference anchor='RFC4647'>
2079  <front>
2080    <title>Matching of Language Tags</title>
2081    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2082      <organization>Yahoo! Inc.</organization>
2083      <address><email>addison@inter-locale.com</email></address>
2084    </author>
2085    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2086      <organization>Google</organization>
2087      <address><email>mark.davis@macchiato.com</email></address>
2088    </author>
2089    <date year='2006' month='September' />
2090  </front>
2091  <seriesInfo name='BCP' value='47' />
2092  <seriesInfo name='RFC' value='4647' />
2093</reference>
2094
2095<reference anchor="RFC5234">
2096  <front>
2097    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2098    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2099      <organization>Brandenburg InternetWorking</organization>
2100      <address>
2101      <postal>
2102      <street>675 Spruce Dr.</street>
2103      <city>Sunnyvale</city>
2104      <region>CA</region>
2105      <code>94086</code>
2106      <country>US</country></postal>
2107      <phone>+1.408.246.8253</phone>
2108      <email>dcrocker@bbiw.net</email></address> 
2109    </author>
2110    <author initials="P." surname="Overell" fullname="Paul Overell">
2111      <organization>THUS plc.</organization>
2112      <address>
2113      <postal>
2114      <street>1/2 Berkeley Square</street>
2115      <street>99 Berkely Street</street>
2116      <city>Glasgow</city>
2117      <code>G3 7HR</code>
2118      <country>UK</country></postal>
2119      <email>paul.overell@thus.net</email></address>
2120    </author>
2121    <date month="January" year="2008"/>
2122  </front>
2123  <seriesInfo name="STD" value="68"/>
2124  <seriesInfo name="RFC" value="5234"/>
2125</reference>
2126
2127</references>
2128
2129<references title="Informative References">
2130
2131<reference anchor="RFC1945">
2132  <front>
2133    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2134    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2135      <organization>MIT, Laboratory for Computer Science</organization>
2136      <address><email>timbl@w3.org</email></address>
2137    </author>
2138    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2139      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2140      <address><email>fielding@ics.uci.edu</email></address>
2141    </author>
2142    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2143      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2144      <address><email>frystyk@w3.org</email></address>
2145    </author>
2146    <date month="May" year="1996"/>
2147  </front>
2148  <seriesInfo name="RFC" value="1945"/>
2149</reference>
2150
2151<reference anchor="RFC2049">
2152  <front>
2153    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2154    <author initials="N." surname="Freed" fullname="Ned Freed">
2155      <organization>Innosoft International, Inc.</organization>
2156      <address><email>ned@innosoft.com</email></address>
2157    </author>
2158    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2159      <organization>First Virtual Holdings</organization>
2160      <address><email>nsb@nsb.fv.com</email></address>
2161    </author>
2162    <date month="November" year="1996"/>
2163  </front>
2164  <seriesInfo name="RFC" value="2049"/>
2165</reference>
2166
2167<reference anchor="RFC2068">
2168  <front>
2169    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2170    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2171      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2172      <address><email>fielding@ics.uci.edu</email></address>
2173    </author>
2174    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2175      <organization>MIT Laboratory for Computer Science</organization>
2176      <address><email>jg@w3.org</email></address>
2177    </author>
2178    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2179      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2180      <address><email>mogul@wrl.dec.com</email></address>
2181    </author>
2182    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2183      <organization>MIT Laboratory for Computer Science</organization>
2184      <address><email>frystyk@w3.org</email></address>
2185    </author>
2186    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2187      <organization>MIT Laboratory for Computer Science</organization>
2188      <address><email>timbl@w3.org</email></address>
2189    </author>
2190    <date month="January" year="1997"/>
2191  </front>
2192  <seriesInfo name="RFC" value="2068"/>
2193</reference>
2194
2195<reference anchor="RFC2076">
2196  <front>
2197    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2198    <author initials="J." surname="Palme" fullname="Jacob Palme">
2199      <organization>Stockholm University/KTH</organization>
2200      <address><email>jpalme@dsv.su.se</email></address>
2201    </author>
2202    <date month="February" year="1997"/>
2203  </front>
2204  <seriesInfo name="RFC" value="2076"/>
2205</reference>
2206
2207<reference anchor="RFC2183">
2208  <front>
2209    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2210    <author initials="R." surname="Troost" fullname="Rens Troost">
2211      <organization>New Century Systems</organization>
2212      <address><email>rens@century.com</email></address>
2213    </author>
2214    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2215      <organization>QUALCOMM Incorporated</organization>
2216      <address><email>sdorner@qualcomm.com</email></address>
2217    </author>
2218    <author initials="K." surname="Moore" fullname="Keith Moore">
2219      <organization>Department of Computer Science</organization>
2220      <address><email>moore@cs.utk.edu</email></address>
2221    </author>
2222    <date month="August" year="1997"/>
2223  </front>
2224  <seriesInfo name="RFC" value="2183"/>
2225</reference>
2226
2227<reference anchor="RFC2277">
2228  <front>
2229    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2230    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2231      <organization>UNINETT</organization>
2232      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2233    </author>
2234    <date month="January" year="1998"/>
2235  </front>
2236  <seriesInfo name="BCP" value="18"/>
2237  <seriesInfo name="RFC" value="2277"/>
2238</reference>
2239
2240<reference anchor="RFC2388">
2241  <front>
2242    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2243    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2244      <organization>Xerox Palo Alto Research Center</organization>
2245      <address><email>masinter@parc.xerox.com</email></address>
2246    </author>
2247    <date year="1998" month="August"/>
2248  </front>
2249  <seriesInfo name="RFC" value="2388"/>
2250</reference>
2251
2252<reference anchor="RFC2557">
2253  <front>
2254    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2255    <author initials="F." surname="Palme" fullname="Jacob Palme">
2256      <organization>Stockholm University and KTH</organization>
2257      <address><email>jpalme@dsv.su.se</email></address>
2258    </author>
2259    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2260      <organization>Microsoft Corporation</organization>
2261      <address><email>alexhop@microsoft.com</email></address>
2262    </author>
2263    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2264      <organization>Lotus Development Corporation</organization>
2265      <address><email>Shelness@lotus.com</email></address>
2266    </author>
2267    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2268      <organization/>
2269      <address><email>stef@nma.com</email></address>
2270    </author>
2271    <date year="1999" month="March"/>
2272  </front>
2273  <seriesInfo name="RFC" value="2557"/>
2274</reference>
2275
2276<reference anchor="RFC2616">
2277  <front>
2278    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2279    <author initials="R." surname="Fielding" fullname="R. Fielding">
2280      <organization>University of California, Irvine</organization>
2281      <address><email>fielding@ics.uci.edu</email></address>
2282    </author>
2283    <author initials="J." surname="Gettys" fullname="J. Gettys">
2284      <organization>W3C</organization>
2285      <address><email>jg@w3.org</email></address>
2286    </author>
2287    <author initials="J." surname="Mogul" fullname="J. Mogul">
2288      <organization>Compaq Computer Corporation</organization>
2289      <address><email>mogul@wrl.dec.com</email></address>
2290    </author>
2291    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2292      <organization>MIT Laboratory for Computer Science</organization>
2293      <address><email>frystyk@w3.org</email></address>
2294    </author>
2295    <author initials="L." surname="Masinter" fullname="L. Masinter">
2296      <organization>Xerox Corporation</organization>
2297      <address><email>masinter@parc.xerox.com</email></address>
2298    </author>
2299    <author initials="P." surname="Leach" fullname="P. Leach">
2300      <organization>Microsoft Corporation</organization>
2301      <address><email>paulle@microsoft.com</email></address>
2302    </author>
2303    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2304      <organization>W3C</organization>
2305      <address><email>timbl@w3.org</email></address>
2306    </author>
2307    <date month="June" year="1999"/>
2308  </front>
2309  <seriesInfo name="RFC" value="2616"/>
2310</reference>
2311
2312<reference anchor="RFC3629">
2313  <front>
2314    <title>UTF-8, a transformation format of ISO 10646</title>
2315    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2316      <organization>Alis Technologies</organization>
2317      <address><email>fyergeau@alis.com</email></address>
2318    </author>
2319    <date month="November" year="2003"/>
2320  </front>
2321  <seriesInfo name="RFC" value="3629"/>
2322  <seriesInfo name="STD" value="63"/>
2323</reference>
2324
2325<reference anchor='RFC3864'>
2326  <front>
2327    <title>Registration Procedures for Message Header Fields</title>
2328    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2329      <organization>Nine by Nine</organization>
2330      <address><email>GK-IETF@ninebynine.org</email></address>
2331    </author>
2332    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2333      <organization>BEA Systems</organization>
2334      <address><email>mnot@pobox.com</email></address>
2335    </author>
2336    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2337      <organization>HP Labs</organization>
2338      <address><email>JeffMogul@acm.org</email></address>
2339    </author>
2340    <date year='2004' month='September' />
2341  </front>
2342  <seriesInfo name='BCP' value='90' />
2343  <seriesInfo name='RFC' value='3864' />
2344</reference>
2345
2346<reference anchor="RFC4288">
2347  <front>
2348    <title>Media Type Specifications and Registration Procedures</title>
2349    <author initials="N." surname="Freed" fullname="N. Freed">
2350      <organization>Sun Microsystems</organization>
2351      <address>
2352        <email>ned.freed@mrochek.com</email>
2353      </address>
2354    </author>
2355    <author initials="J." surname="Klensin" fullname="J. Klensin">
2356      <organization/>
2357      <address>
2358        <email>klensin+ietf@jck.com</email>
2359      </address>
2360    </author>
2361    <date year="2005" month="December"/>
2362  </front>
2363  <seriesInfo name="BCP" value="13"/>
2364  <seriesInfo name="RFC" value="4288"/>
2365</reference>
2366
2367<reference anchor="RFC5322">
2368  <front>
2369    <title>Internet Message Format</title>
2370    <author initials="P." surname="Resnick" fullname="P. Resnick">
2371      <organization>Qualcomm Incorporated</organization>
2372    </author>
2373    <date year="2008" month="October"/>
2374  </front> 
2375  <seriesInfo name="RFC" value="5322"/>
2376</reference>
2377
2378<reference anchor='BCP97'>
2379  <front>
2380    <title>Handling Normative References to Standards-Track Documents</title>
2381    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2382      <organization />
2383      <address>
2384        <email>klensin+ietf@jck.com</email>
2385      </address>
2386    </author>
2387    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2388      <organization>MIT</organization>
2389      <address>
2390        <email>hartmans-ietf@mit.edu</email>
2391      </address>
2392    </author>
2393    <date year='2007' month='June' />
2394  </front>
2395  <seriesInfo name='BCP' value='97' />
2396  <seriesInfo name='RFC' value='4897' />
2397</reference>
2398
2399
2400</references>
2401
2402<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2403<t>
2404   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
2405   allow entities to be transmitted in an open variety of
2406   representations and with extensible mechanisms. However, RFC 2045
2407   discusses mail, and HTTP has a few features that are different from
2408   those described in RFC 2045. These differences were carefully chosen
2409   to optimize performance over binary connections, to allow greater
2410   freedom in the use of new media types, to make date comparisons
2411   easier, and to acknowledge the practice of some early HTTP servers
2412   and clients.
2413</t>
2414<t>
2415   This appendix describes specific areas where HTTP differs from RFC
2416   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2417   aware of these differences and provide the appropriate conversions
2418   where necessary. Proxies and gateways from MIME environments to HTTP
2419   also need to be aware of the differences because some conversions
2420   might be required.
2421</t>
2422
2423<section title="MIME-Version" anchor="mime-version">
2424  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2425  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
2426  <x:anchor-alias value="MIME-Version"/>
2427  <x:anchor-alias value="MIME-Version-v"/>
2428<t>
2429   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2430   include a single MIME-Version general-header field to indicate what
2431   version of the MIME protocol was used to construct the message. Use
2432   of the MIME-Version header field indicates that the message is in
2433   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2434   Proxies/gateways are responsible for ensuring full compliance (where
2435   possible) when exporting HTTP messages to strict MIME environments.
2436</t>
2437<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
2438  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
2439  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2440</artwork></figure>
2441<t>
2442   MIME version "1.0" is the default for use in HTTP/1.1. However,
2443   HTTP/1.1 message parsing and semantics are defined by this document
2444   and not the MIME specification.
2445</t>
2446</section>
2447
2448<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2449<t>
2450   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2451   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2452   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2453   allowed for subtypes of the "text" media type when transmitted over
2454   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2455   line breaks as CRLF and forbids the use of CR or LF outside of line
2456   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2457   line break within text content when a message is transmitted over
2458   HTTP.
2459</t>
2460<t>
2461   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2462   environment &SHOULD; translate all line breaks within the text media
2463   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2464   canonical form of CRLF. Note, however, that this might be complicated
2465   by the presence of a Content-Encoding and by the fact that HTTP
2466   allows the use of some character sets which do not use octets 13 and
2467   10 to represent CR and LF, as is the case for some multi-byte
2468   character sets.
2469</t>
2470<t>
2471   Implementors should note that conversion will break any cryptographic
2472   checksums applied to the original content unless the original content
2473   is already in canonical form. Therefore, the canonical form is
2474   recommended for any content that uses such checksums in HTTP.
2475</t>
2476</section>
2477
2478
2479<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2480<t>
2481   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2482   simplify the process of date comparison. Proxies and gateways from
2483   other protocols &SHOULD; ensure that any Date header field present in a
2484   message conforms to one of the HTTP/1.1 formats and rewrite the date
2485   if necessary.
2486</t>
2487</section>
2488
2489<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2490<t>
2491   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2492   Content-Encoding header field. Since this acts as a modifier on the
2493   media type, proxies and gateways from HTTP to MIME-compliant
2494   protocols &MUST; either change the value of the Content-Type header
2495   field or decode the entity-body before forwarding the message. (Some
2496   experimental applications of Content-Type for Internet mail have used
2497   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2498   a function equivalent to Content-Encoding. However, this parameter is
2499   not part of RFC 2045).
2500</t>
2501</section>
2502
2503<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2504<t>
2505   HTTP does not use the Content-Transfer-Encoding field of RFC
2506   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2507   remove any Content-Transfer-Encoding
2508   prior to delivering the response message to an HTTP client.
2509</t>
2510<t>
2511   Proxies and gateways from HTTP to MIME-compliant protocols are
2512   responsible for ensuring that the message is in the correct format
2513   and encoding for safe transport on that protocol, where "safe
2514   transport" is defined by the limitations of the protocol being used.
2515   Such a proxy or gateway &SHOULD; label the data with an appropriate
2516   Content-Transfer-Encoding if doing so will improve the likelihood of
2517   safe transport over the destination protocol.
2518</t>
2519</section>
2520
2521<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2522<t>
2523   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2524   Proxies/gateways &MUST; remove any transfer-coding prior to
2525   forwarding a message via a MIME-compliant protocol.
2526</t>
2527</section>
2528
2529<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2530<t>
2531   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2532   need to be aware of MIME line length limitations. Since HTTP does not
2533   have this limitation, HTTP does not fold long lines. MHTML messages
2534   being transported by HTTP follow all conventions of MHTML, including
2535   line length limitations and folding, canonicalization, etc., since
2536   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2537   does not interpret the content or any MIME header lines that might be
2538   contained therein.
2539</t>
2540</section>
2541</section>
2542
2543<section title="Additional Features" anchor="additional.features">
2544<t>
2545   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2546   existing HTTP implementations, but not consistently and correctly
2547   across most HTTP/1.1 applications. Implementors are advised to be
2548   aware of these features, but cannot rely upon their presence in, or
2549   interoperability with, other HTTP/1.1 applications. Some of these
2550   describe proposed experimental features, and some describe features
2551   that experimental deployment found lacking that are now addressed in
2552   the base HTTP/1.1 specification.
2553</t>
2554<t>
2555   A number of other headers, such as Content-Disposition and Title,
2556   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2557</t>
2558
2559<section title="Content-Disposition" anchor="content-disposition">
2560<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2561<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2562  <x:anchor-alias value="content-disposition"/>
2563  <x:anchor-alias value="content-disposition-v"/>
2564  <x:anchor-alias value="disposition-type"/>
2565  <x:anchor-alias value="disposition-parm"/>
2566  <x:anchor-alias value="disp-extension-parm"/>
2567  <x:anchor-alias value="disp-extension-token"/>
2568  <x:anchor-alias value="filename-parm"/>
2569<t>
2570   The Content-Disposition response-header field has been proposed as a
2571   means for the origin server to suggest a default filename if the user
2572   requests that the content is saved to a file. This usage is derived
2573   from the definition of Content-Disposition in <xref target="RFC2183"/>.
2574</t>
2575<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"/>
2576  <x:ref>content-disposition</x:ref> = "Content-Disposition" ":" <x:ref>OWS</x:ref>
2577                        <x:ref>content-disposition-v</x:ref>
2578  <x:ref>content-disposition-v</x:ref> = <x:ref>disposition-type</x:ref>
2579                          *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>disposition-parm</x:ref> )
2580  <x:ref>disposition-type</x:ref> = "attachment" / <x:ref>disp-extension-token</x:ref>
2581  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> / <x:ref>disp-extension-parm</x:ref>
2582  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2583  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
2584  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
2585</artwork></figure>
2586<t>
2587   An example is
2588</t>
2589<figure><artwork type="example">
2590   Content-Disposition: attachment; filename="fname.ext"
2591</artwork></figure>
2592<t>
2593   The receiving user agent &SHOULD-NOT;  respect any directory path
2594   information present in the filename-parm parameter, which is the only
2595   parameter believed to apply to HTTP implementations at this time. The
2596   filename &SHOULD; be treated as a terminal component only.
2597</t>
2598<t>
2599   If this header is used in a response with the application/octet-stream
2600   content-type, the implied suggestion is that the user agent
2601   should not display the response, but directly enter a `save response
2602   as...' dialog.
2603</t>
2604<t>
2605   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2606</t>
2607</section>
2608</section>
2609
2610<section title="Compatibility with Previous Versions" anchor="compatibility">
2611<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2612<t>
2613   Transfer-coding and message lengths all interact in ways that
2614   required fixing exactly when chunked encoding is used (to allow for
2615   transfer encoding that may not be self delimiting); it was important
2616   to straighten out exactly how message lengths are computed.
2617   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2618   <xref target="Part5"/> and <xref target="Part6"/>).
2619</t>
2620<t>
2621   Charset wildcarding is introduced to avoid explosion of character set
2622   names in accept headers. (<xref target="header.accept-charset"/>)
2623</t>
2624<t>
2625   Content-Base was deleted from the specification: it was not
2626   implemented widely, and there is no simple, safe way to introduce it
2627   without a robust extension mechanism. In addition, it is used in a
2628   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2629</t>
2630<t>
2631   A content-coding of "identity" was introduced, to solve problems
2632   discovered in caching. (<xref target="content.codings"/>)
2633</t>
2634<t>
2635   Quality Values of zero should indicate that "I don't want something"
2636   to allow clients to refuse a representation. (<xref target="quality.values"/>)
2637</t>
2638<t>
2639   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
2640   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
2641   specification, but not commonly implemented. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.2"/>.
2642</t>
2643</section>
2644
2645<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2646<t>
2647  Clarify contexts that charset is used in.
2648  (<xref target="character.sets"/>)
2649</t>
2650<t>
2651  Remove reference to non-existant identity transfer-coding value tokens.
2652  (<xref target="no.content-transfer-encoding"/>)
2653</t>
2654</section>
2655
2656</section>
2657
2658<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
2659<figure>
2660<artwork type="abnf" name="p3-payload.parsed-abnf">
2661<x:ref>Accept</x:ref> = "Accept:" OWS Accept-v
2662<x:ref>Accept-Charset</x:ref> = "Accept-Charset:" OWS Accept-Charset-v
2663<x:ref>Accept-Charset-v</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2664 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2665 qvalue ] ] )
2666<x:ref>Accept-Encoding</x:ref> = "Accept-Encoding:" OWS Accept-Encoding-v
2667<x:ref>Accept-Encoding-v</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
2668 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2669<x:ref>Accept-Language</x:ref> = "Accept-Language:" OWS Accept-Language-v
2670<x:ref>Accept-Language-v</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
2671 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2672 ] )
2673<x:ref>Accept-v</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2674 OWS media-range [ accept-params ] ] ) ]
2675
2676<x:ref>Content-Encoding</x:ref> = "Content-Encoding:" OWS Content-Encoding-v
2677<x:ref>Content-Encoding-v</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
2678 content-coding ] )
2679<x:ref>Content-Language</x:ref> = "Content-Language:" OWS Content-Language-v
2680<x:ref>Content-Language-v</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
2681 language-tag ] )
2682<x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in [Part1], Section 8.2&gt;
2683<x:ref>Content-Location</x:ref> = "Content-Location:" OWS Content-Location-v
2684<x:ref>Content-Location-v</x:ref> = absolute-URI / partial-URI
2685<x:ref>Content-MD5</x:ref> = "Content-MD5:" OWS Content-MD5-v
2686<x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2687<x:ref>Content-Range</x:ref> = &lt;Content-Range, defined in [Part5], Section 5.2&gt;
2688<x:ref>Content-Type</x:ref> = "Content-Type:" OWS Content-Type-v
2689<x:ref>Content-Type-v</x:ref> = media-type
2690
2691<x:ref>Expires</x:ref> = &lt;Expires, defined in [Part6], Section 15.3&gt;
2692
2693<x:ref>Last-Modified</x:ref> = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;
2694
2695<x:ref>MIME-Version</x:ref> = "MIME-Version:" OWS MIME-Version-v
2696<x:ref>MIME-Version-v</x:ref> = 1*DIGIT "." 1*DIGIT
2697
2698<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
2699
2700<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.1&gt;
2701<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
2702<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2703<x:ref>attribute</x:ref> = token
2704
2705<x:ref>charset</x:ref> = token
2706<x:ref>codings</x:ref> = ( content-coding / "*" )
2707<x:ref>content-coding</x:ref> = token
2708<x:ref>content-disposition</x:ref> = "Content-Disposition:" OWS
2709 content-disposition-v
2710<x:ref>content-disposition-v</x:ref> = disposition-type *( OWS ";" OWS
2711 disposition-parm )
2712
2713<x:ref>disp-extension-parm</x:ref> = token "=" ( token / quoted-string )
2714<x:ref>disp-extension-token</x:ref> = token
2715<x:ref>disposition-parm</x:ref> = filename-parm / disp-extension-parm
2716<x:ref>disposition-type</x:ref> = "attachment" / disp-extension-token
2717
2718<x:ref>entity-body</x:ref> = *OCTET
2719<x:ref>entity-header</x:ref> = Content-Encoding / Content-Language / Content-Length
2720 / Content-Location / Content-MD5 / Content-Range / Content-Type /
2721 Expires / Last-Modified / extension-header
2722<x:ref>extension-header</x:ref> = message-header
2723
2724<x:ref>filename-parm</x:ref> = "filename=" quoted-string
2725
2726<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
2727<x:ref>language-tag</x:ref> = primary-tag *( "-" subtag )
2728
2729<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2730 ";" OWS parameter )
2731<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2732<x:ref>message-header</x:ref> = &lt;message-header, defined in [Part1], Section 4.2&gt;
2733
2734<x:ref>parameter</x:ref> = attribute "=" value
2735<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.1&gt;
2736<x:ref>primary-tag</x:ref> = 1*8ALPHA
2737
2738<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
2739<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
2740
2741<x:ref>subtag</x:ref> = 1*8ALPHA
2742<x:ref>subtype</x:ref> = token
2743
2744<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2745<x:ref>type</x:ref> = token
2746
2747<x:ref>value</x:ref> = token / quoted-string
2748
2749; Accept defined but not used
2750; Accept-Charset defined but not used
2751; Accept-Encoding defined but not used
2752; Accept-Language defined but not used
2753; MIME-Version defined but not used
2754; content-disposition defined but not used
2755; entity-body defined but not used
2756; entity-header defined but not used
2757
2758
2759</artwork>
2760</figure>
2761</section>
2762
2763<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2764
2765<section title="Since RFC2616">
2766<t>
2767  Extracted relevant partitions from <xref target="RFC2616"/>.
2768</t>
2769</section>
2770
2771<section title="Since draft-ietf-httpbis-p3-payload-00">
2772<t>
2773  Closed issues:
2774  <list style="symbols"> 
2775    <t>
2776      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2777      "Media Type Registrations"
2778      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2779    </t>
2780    <t>
2781      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2782      "Clarification regarding quoting of charset values"
2783      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2784    </t>
2785    <t>
2786      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2787      "Remove 'identity' token references"
2788      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2789    </t>
2790    <t>
2791      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2792      "Accept-Encoding BNF"
2793    </t>
2794    <t>
2795      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2796      "Normative and Informative references"
2797    </t>
2798    <t>
2799      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2800      "RFC1700 references"
2801    </t>
2802    <t>
2803      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2804      "Updating to RFC4288"
2805    </t>
2806    <t>
2807      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2808      "Informative references"
2809    </t>
2810    <t>
2811      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2812      "ISO-8859-1 Reference"
2813    </t>
2814    <t>
2815      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2816      "Encoding References Normative"
2817    </t>
2818    <t>
2819      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2820      "Normative up-to-date references"
2821    </t>
2822  </list>
2823</t>
2824</section>
2825
2826<section title="Since draft-ietf-httpbis-p3-payload-01">
2827<t>
2828  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2829  <list style="symbols"> 
2830    <t>
2831      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2832    </t>
2833  </list>
2834</t>
2835</section>
2836
2837<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2838<t>
2839  Closed issues:
2840  <list style="symbols"> 
2841    <t>
2842      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2843      "Quoting Charsets"
2844    </t>
2845    <t>
2846      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2847      "Classification for Allow header"
2848    </t>
2849    <t>
2850      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
2851      "missing default for qvalue in description of Accept-Encoding"
2852    </t>
2853  </list>
2854</t>
2855<t>
2856  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2857  <list style="symbols"> 
2858    <t>
2859      Reference RFC 3984, and update header registrations for headers defined
2860      in this document.
2861    </t>
2862  </list>
2863</t>
2864</section>
2865
2866<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2867<t>
2868  Closed issues:
2869  <list style="symbols"> 
2870    <t>
2871      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2872      "Quoting Charsets"
2873    </t>
2874    <t>
2875      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
2876      "language tag matching (Accept-Language) vs RFC4647"
2877    </t>
2878    <t>
2879      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
2880      "RFC 1806 has been replaced by RFC2183"
2881    </t>
2882  </list>
2883</t>
2884<t>
2885  Other changes:
2886  <list style="symbols"> 
2887    <t>
2888      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2889      "Encoding References Normative" -- rephrase the annotation and reference
2890      <xref target="BCP97"/>.
2891    </t>
2892  </list>
2893</t>
2894 </section>
2895
2896<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2897<t>
2898  Closed issues:
2899  <list style="symbols"> 
2900    <t>
2901      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
2902      "RFC 2822 is updated by RFC 5322"
2903    </t>
2904  </list>
2905</t>
2906<t>
2907  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2908  <list style="symbols"> 
2909    <t>
2910      Use "/" instead of "|" for alternatives.
2911    </t>
2912    <t>
2913      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2914      whitespace ("OWS") and required whitespace ("RWS").
2915    </t>
2916    <t>
2917      Rewrite ABNFs to spell out whitespace rules, factor out
2918      header value format definitions.
2919    </t>
2920  </list>
2921</t>
2922</section>
2923
2924<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2925<t>
2926  Closed issues:
2927  <list style="symbols"> 
2928    <t>
2929      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
2930      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2931    </t>
2932  </list>
2933</t>
2934<t>
2935  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2936  <list style="symbols"> 
2937    <t>
2938      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2939    </t>
2940  </list>
2941</t>
2942</section>
2943
2944</section>
2945
2946</back>
2947</rfc>
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