source: draft-ietf-httpbis/latest/p3-payload.xml @ 670

Last change on this file since 670 was 670, checked in by julian.reschke@…, 10 years ago

Rephrase registration procedures for Transfer/Content? Codings in terms of RFC5226, requiring Expert Review & Specification (see #188)

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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 "August">
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 header-fields            "<xref target='Part1' x:rel='#header.fields' 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='#date.time.formats.full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY qvalue                   "<xref target='Part1' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35]>
36<?rfc toc="yes" ?>
37<?rfc symrefs="yes" ?>
38<?rfc sortrefs="yes" ?>
39<?rfc compact="yes"?>
40<?rfc subcompact="no" ?>
41<?rfc linkmailto="no" ?>
42<?rfc editing="no" ?>
43<?rfc comments="yes"?>
44<?rfc inline="yes"?>
45<?rfc-ext allow-markup-in-artwork="yes" ?>
46<?rfc-ext include-references-in-index="yes" ?>
47<rfc obsoletes="2616" category="std" x:maturity-level="draft"
48     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
49     xmlns:x='http://purl.org/net/xml2rfc/ext'>
50<front>
51
52  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
53
54  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
55    <organization abbrev="Day Software">Day Software</organization>
56    <address>
57      <postal>
58        <street>23 Corporate Plaza DR, Suite 280</street>
59        <city>Newport Beach</city>
60        <region>CA</region>
61        <code>92660</code>
62        <country>USA</country>
63      </postal>
64      <phone>+1-949-706-5300</phone>
65      <facsimile>+1-949-706-5305</facsimile>
66      <email>fielding@gbiv.com</email>
67      <uri>http://roy.gbiv.com/</uri>
68    </address>
69  </author>
70
71  <author initials="J." surname="Gettys" fullname="Jim Gettys">
72    <organization>One Laptop per Child</organization>
73    <address>
74      <postal>
75        <street>21 Oak Knoll Road</street>
76        <city>Carlisle</city>
77        <region>MA</region>
78        <code>01741</code>
79        <country>USA</country>
80      </postal>
81      <email>jg@laptop.org</email>
82      <uri>http://www.laptop.org/</uri>
83    </address>
84  </author>
85 
86  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
87    <organization abbrev="HP">Hewlett-Packard Company</organization>
88    <address>
89      <postal>
90        <street>HP Labs, Large Scale Systems Group</street>
91        <street>1501 Page Mill Road, MS 1177</street>
92        <city>Palo Alto</city>
93        <region>CA</region>
94        <code>94304</code>
95        <country>USA</country>
96      </postal>
97      <email>JeffMogul@acm.org</email>
98    </address>
99  </author>
100
101  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
102    <organization abbrev="Microsoft">Microsoft Corporation</organization>
103    <address>
104      <postal>
105        <street>1 Microsoft Way</street>
106        <city>Redmond</city>
107        <region>WA</region>
108        <code>98052</code>
109        <country>USA</country>
110      </postal>
111      <email>henrikn@microsoft.com</email>
112    </address>
113  </author>
114
115  <author initials="L." surname="Masinter" fullname="Larry Masinter">
116    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
117    <address>
118      <postal>
119        <street>345 Park Ave</street>
120        <city>San Jose</city>
121        <region>CA</region>
122        <code>95110</code>
123        <country>USA</country>
124      </postal>
125      <email>LMM@acm.org</email>
126      <uri>http://larry.masinter.net/</uri>
127    </address>
128  </author>
129 
130  <author initials="P." surname="Leach" fullname="Paul J. Leach">
131    <organization abbrev="Microsoft">Microsoft Corporation</organization>
132    <address>
133      <postal>
134        <street>1 Microsoft Way</street>
135        <city>Redmond</city>
136        <region>WA</region>
137        <code>98052</code>
138      </postal>
139      <email>paulle@microsoft.com</email>
140    </address>
141  </author>
142   
143  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
144    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
145    <address>
146      <postal>
147        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
148        <street>The Stata Center, Building 32</street>
149        <street>32 Vassar Street</street>
150        <city>Cambridge</city>
151        <region>MA</region>
152        <code>02139</code>
153        <country>USA</country>
154      </postal>
155      <email>timbl@w3.org</email>
156      <uri>http://www.w3.org/People/Berners-Lee/</uri>
157    </address>
158  </author>
159
160  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
161    <organization abbrev="W3C">World Wide Web Consortium</organization>
162    <address>
163      <postal>
164        <street>W3C / ERCIM</street>
165        <street>2004, rte des Lucioles</street>
166        <city>Sophia-Antipolis</city>
167        <region>AM</region>
168        <code>06902</code>
169        <country>France</country>
170      </postal>
171      <email>ylafon@w3.org</email>
172      <uri>http://www.raubacapeu.net/people/yves/</uri>
173    </address>
174  </author>
175
176  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
177    <organization abbrev="greenbytes">greenbytes GmbH</organization>
178    <address>
179      <postal>
180        <street>Hafenweg 16</street>
181        <city>Muenster</city><region>NW</region><code>48155</code>
182        <country>Germany</country>
183      </postal>
184      <phone>+49 251 2807760</phone>
185      <facsimile>+49 251 2807761</facsimile>
186      <email>julian.reschke@greenbytes.de</email>
187      <uri>http://greenbytes.de/tech/webdav/</uri>
188    </address>
189  </author>
190
191  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
192  <workgroup>HTTPbis Working Group</workgroup>
193
194<abstract>
195<t>
196   The Hypertext Transfer Protocol (HTTP) is an application-level
197   protocol for distributed, collaborative, hypermedia information
198   systems. HTTP has been in use by the World Wide Web global information
199   initiative since 1990. This document is Part 3 of the seven-part specification
200   that defines the protocol referred to as "HTTP/1.1" and, taken together,
201   obsoletes RFC 2616.  Part 3 defines HTTP message content,
202   metadata, and content negotiation.
203</t>
204</abstract>
205
206<note title="Editorial Note (To be removed by RFC Editor)">
207  <t>
208    Discussion of this draft should take place on the HTTPBIS working group
209    mailing list (ietf-http-wg@w3.org). The current issues list is
210    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
211    and related documents (including fancy diffs) can be found at
212    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
213  </t>
214  <t>
215    The changes in this draft are summarized in <xref target="changes.since.07"/>.
216  </t>
217</note>
218</front>
219<middle>
220<section title="Introduction" anchor="introduction">
221<t>
222   This document defines HTTP/1.1 message payloads (a.k.a., content), the
223   associated metadata header fields that define how the payload is intended
224   to be interpreted by a recipient, the request header fields that
225   may influence content selection, and the various selection algorithms
226   that are collectively referred to as HTTP content negotiation.
227</t>
228<t>
229   This document is currently disorganized in order to minimize the changes
230   between drafts and enable reviewers to see the smaller errata changes.
231   The next draft will reorganize the sections to better reflect the content.
232   In particular, the sections on entities will be renamed payload and moved
233   to the first half of the document, while the sections on content negotiation
234   and associated request header fields will be moved to the second half.  The
235   current mess reflects how widely dispersed these topics and associated
236   requirements had become in <xref target="RFC2616"/>.
237</t>
238
239<section title="Terminology" anchor="terminology">
240<t>
241   This specification uses a number of terms to refer to the roles
242   played by participants in, and objects of, the HTTP communication.
243</t>
244<t>
245  <iref item="content negotiation"/>
246  <x:dfn>content negotiation</x:dfn>
247  <list>
248    <t>
249      The mechanism for selecting the appropriate representation when
250      servicing a request. The representation of entities in any response
251      can be negotiated (including error responses).
252    </t>
253  </list>
254</t>
255<t>
256  <iref item="entity"/>
257  <x:dfn>entity</x:dfn>
258  <list>
259    <t>
260      The information transferred as the payload of a request or
261      response. An entity consists of metadata in the form of
262      entity-header fields and content in the form of an entity-body.
263    </t>
264  </list>
265</t>
266<t>
267  <iref item="representation"/>
268  <x:dfn>representation</x:dfn>
269  <list>
270    <t>
271      An entity included with a response that is subject to content
272      negotiation. There may exist multiple
273      representations associated with a particular response status.
274    </t>
275  </list>
276</t>
277<t>
278  <iref item="variant"/>
279  <x:dfn>variant</x:dfn>
280  <list>
281    <t>
282      A resource may have one, or more than one, representation(s)
283      associated with it at any given instant. Each of these
284      representations is termed a `variant'.  Use of the term `variant'
285      does not necessarily imply that the resource is subject to content
286      negotiation.
287    </t>
288  </list>
289</t>
290</section>
291
292<section title="Requirements" anchor="intro.requirements">
293<t>
294   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
295   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
296   document are to be interpreted as described in <xref target="RFC2119"/>.
297</t>
298<t>
299   An implementation is not compliant if it fails to satisfy one or more
300   of the &MUST; or &REQUIRED; level requirements for the protocols it
301   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
302   level and all the &SHOULD; level requirements for its protocols is said
303   to be "unconditionally compliant"; one that satisfies all the &MUST;
304   level requirements but not all the &SHOULD; level requirements for its
305   protocols is said to be "conditionally compliant."
306</t>
307</section>
308
309<section title="Syntax Notation" anchor="notation">
310  <x:anchor-alias value="ALPHA"/>
311  <x:anchor-alias value="CR"/>
312  <x:anchor-alias value="DIGIT"/>
313  <x:anchor-alias value="LF"/>
314  <x:anchor-alias value="OCTET"/>
315  <x:anchor-alias value="VCHAR"/>
316  <x:anchor-alias value="WSP"/>
317<t>
318  This specification uses the ABNF syntax defined in &notation; (which
319  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
320  <xref target="collected.abnf"/> shows the collected ABNF, with the list
321  rule expanded.
322</t>
323<t>
324  The following core rules are included by
325  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
326  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
327  DIGIT (decimal 0-9), DQUOTE (double quote),
328  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
329  OCTET (any 8-bit sequence of data), SP (space),
330  VCHAR (any visible USASCII character),
331  and WSP (whitespace).
332</t>
333
334<section title="Core Rules" anchor="core.rules">
335  <x:anchor-alias value="quoted-string"/>
336  <x:anchor-alias value="token"/>
337  <x:anchor-alias value="OWS"/>
338<t>
339  The core rules below are defined in &basic-rules;:
340</t>
341<figure><artwork type="abnf2616">
342  <x:ref>quoted-string</x:ref>  = &lt;quoted-string, defined in &basic-rules;&gt;
343  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
344  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
345</artwork></figure>
346</section>
347
348<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
349  <x:anchor-alias value="absolute-URI"/>
350  <x:anchor-alias value="Allow"/>
351  <x:anchor-alias value="Content-Length"/>
352  <x:anchor-alias value="Content-Range"/>
353  <x:anchor-alias value="Expires"/>
354  <x:anchor-alias value="Last-Modified"/>
355  <x:anchor-alias value="header-field"/>
356  <x:anchor-alias value="partial-URI"/>
357  <x:anchor-alias value="qvalue"/>
358<t>
359  The ABNF rules below are defined in other parts:
360</t>
361<figure><!--Part1--><artwork type="abnf2616">
362  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
363  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
364  <x:ref>header-field</x:ref>   = &lt;header-field, defined in &header-fields;&gt;
365  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
366  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
367</artwork></figure>
368<figure><!--Part4--><artwork type="abnf2616">
369  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
370</artwork></figure>
371<figure><!--Part5--><artwork type="abnf2616">
372  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
373</artwork></figure>
374<figure><!--Part6--><artwork type="abnf2616">
375  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
376</artwork></figure>
377</section>
378
379</section>
380
381</section>
382
383<section title="Protocol Parameters" anchor="protocol.parameters">
384
385<section title="Character Sets" anchor="character.sets">
386<t>
387   HTTP uses the same definition of the term "character set" as that
388   described for MIME:
389</t>
390<t>
391   The term "character set" is used in this document to refer to a
392   method used with one or more tables to convert a sequence of octets
393   into a sequence of characters. Note that unconditional conversion in
394   the other direction is not required, in that not all characters may
395   be available in a given character set and a character set may provide
396   more than one sequence of octets to represent a particular character.
397   This definition is intended to allow various kinds of character
398   encoding, from simple single-table mappings such as US-ASCII to
399   complex table switching methods such as those that use ISO-2022's
400   techniques. However, the definition associated with a MIME character
401   set name &MUST; fully specify the mapping to be performed from octets
402   to characters. In particular, use of external profiling information
403   to determine the exact mapping is not permitted.
404</t>
405<x:note>
406  <t>
407    <x:h>Note:</x:h> This use of the term "character set" is more commonly
408    referred to as a "character encoding." However, since HTTP and
409    MIME share the same registry, it is important that the terminology
410    also be shared.
411  </t>
412</x:note>
413<t anchor="rule.charset">
414  <x:anchor-alias value="charset"/>
415   HTTP character sets are identified by case-insensitive tokens. The
416   complete set of tokens is defined by the IANA Character Set registry
417   (<eref target="http://www.iana.org/assignments/character-sets"/>).
418</t>
419<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
420  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
421</artwork></figure>
422<t>
423   Although HTTP allows an arbitrary token to be used as a charset
424   value, any token that has a predefined value within the IANA
425   Character Set registry &MUST; represent the character set defined
426   by that registry. Applications &SHOULD; limit their use of character
427   sets to those defined by the IANA registry.
428</t>
429<t>
430   HTTP uses charset in two contexts: within an Accept-Charset request
431   header (in which the charset value is an unquoted token) and as the
432   value of a parameter in a Content-Type header (within a request or
433   response), in which case the parameter value of the charset parameter
434   may be quoted.
435</t>
436<t>
437   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
438   <xref target="RFC2277"/>.
439</t>
440
441<section title="Missing Charset" anchor="missing.charset">
442<t>
443   Some HTTP/1.0 software has interpreted a Content-Type header without
444   charset parameter incorrectly to mean "recipient should guess."
445   Senders wishing to defeat this behavior &MAY; include a charset
446   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
447   it is known that it will not confuse the recipient.
448</t>
449<t>
450   Unfortunately, some older HTTP/1.0 clients did not deal properly with
451   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
452   charset label provided by the sender; and those user agents that have
453   a provision to "guess" a charset &MUST; use the charset from the
454   content-type field if they support that charset, rather than the
455   recipient's preference, when initially displaying a document. See
456   <xref target="canonicalization.and.text.defaults"/>.
457</t>
458</section>
459</section>
460
461<section title="Content Codings" anchor="content.codings">
462  <x:anchor-alias value="content-coding"/>
463<t>
464   Content coding values indicate an encoding transformation that has
465   been or can be applied to an entity. Content codings are primarily
466   used to allow a document to be compressed or otherwise usefully
467   transformed without losing the identity of its underlying media type
468   and without loss of information. Frequently, the entity is stored in
469   coded form, transmitted directly, and only decoded by the recipient.
470</t>
471<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
472  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
473</artwork></figure>
474<t>
475   All content-coding values are case-insensitive. HTTP/1.1 uses
476   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
477   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
478   describes the content-coding, what is more important is that it
479   indicates what decoding mechanism will be required to remove the
480   encoding.
481</t>
482<t>
483   The Internet Assigned Numbers Authority (IANA) acts as a registry for
484   content-coding value tokens. Initially, the registry contains the
485   following tokens:
486</t>
487<t>
488   gzip<iref item="gzip"/>
489  <list>
490    <t>
491        An encoding format produced by the file compression program
492        "gzip" (GNU zip) as described in <xref target="RFC1952"/>. This format is a
493        Lempel-Ziv coding (LZ77) with a 32 bit CRC.
494    </t>
495  </list>
496</t>
497<t>
498   compress<iref item="compress"/>
499  <list><t>
500        The encoding format produced by the common UNIX file compression
501        program "compress". This format is an adaptive Lempel-Ziv-Welch
502        coding (LZW).
503</t><t>
504        Use of program names for the identification of encoding formats
505        is not desirable and is discouraged for future encodings. Their
506        use here is representative of historical practice, not good
507        design. For compatibility with previous implementations of HTTP,
508        applications &SHOULD; consider "x-gzip" and "x-compress" to be
509        equivalent to "gzip" and "compress" respectively.
510  </t></list>
511</t>
512<t>
513   deflate<iref item="deflate"/>
514  <list><t>
515        The "zlib" format defined in <xref target="RFC1950"/> in combination with
516        the "deflate" compression mechanism described in <xref target="RFC1951"/>.
517  </t></list>
518</t>
519<t>
520   identity<iref item="identity"/>
521  <list><t>
522        The default (identity) encoding; the use of no transformation
523        whatsoever. This content-coding is used only in the Accept-Encoding
524        header, and &SHOULD-NOT;  be used in the Content-Encoding
525        header.
526  </t></list>
527</t>
528
529<section title="Content Coding Registry" anchor="content.coding.registry">
530<t>
531   The HTTP Content Coding Registry defines the name space for the content
532   coding names.
533</t>
534<t>
535   Registrations &MUST; include the following fields:
536   <list style="symbols">
537     <t>Name</t>
538     <t>Description</t>
539     <t>Pointer to specification text</t>
540   </list>
541</t>
542<t>
543   Values to be added to this name space require expert review and a specification
544   (see "Expert Review" and "Specification Required" in
545   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
546   conform to the purpose of content coding defined in this section.
547</t>
548<t>
549   The registry itself is maintained at
550   <eref target="http://www.iana.org/assignments/http-parameters"/>.
551</t>
552</section>
553
554</section>
555
556<section title="Media Types" anchor="media.types">
557  <x:anchor-alias value="media-type"/>
558  <x:anchor-alias value="type"/>
559  <x:anchor-alias value="subtype"/>
560<t>
561   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
562   and Accept (<xref target="header.accept"/>) header fields in order to provide
563   open and extensible data typing and type negotiation.
564</t>
565<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"/>
566  <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> )
567  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
568  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
569</artwork></figure>
570<t anchor="rule.parameter">
571  <x:anchor-alias value="attribute"/>
572  <x:anchor-alias value="parameter"/>
573  <x:anchor-alias value="value"/>
574   Parameters &MAY; follow the type/subtype in the form of attribute/value
575   pairs.
576</t>
577<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"/>
578  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
579  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
580  <x:ref>value</x:ref>          = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
581</artwork></figure>
582<t>
583   The type, subtype, and parameter attribute names are case-insensitive.
584   Parameter values might or might not be case-sensitive, depending on the
585   semantics of the parameter name.  The presence or absence of a parameter might
586   be significant to the processing of a media-type, depending on its
587   definition within the media type registry.
588</t>
589<t>
590   A parameter value that matches the <x:ref>token</x:ref> production may be
591   transmitted as either a token or within a quoted-string. The quoted and
592   unquoted values are equivalent.
593</t>
594<t>
595   Note that some older HTTP applications do not recognize media type
596   parameters. When sending data to older HTTP applications,
597   implementations &SHOULD; only use media type parameters when they are
598   required by that type/subtype definition.
599</t>
600<t>
601   Media-type values are registered with the Internet Assigned Number
602   Authority (IANA). The media type registration process is
603   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
604   discouraged.
605</t>
606
607<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
608<t>
609   Internet media types are registered with a canonical form. An
610   entity-body transferred via HTTP messages &MUST; be represented in the
611   appropriate canonical form prior to its transmission except for
612   "text" types, as defined in the next paragraph.
613</t>
614<t>
615   When in canonical form, media subtypes of the "text" type use CRLF as
616   the text line break. HTTP relaxes this requirement and allows the
617   transport of text media with plain CR or LF alone representing a line
618   break when it is done consistently for an entire entity-body. HTTP
619   applications &MUST; accept CRLF, bare CR, and bare LF as being
620   representative of a line break in text media received via HTTP. In
621   addition, if the text is represented in a character set that does not
622   use octets 13 and 10 for CR and LF respectively, as is the case for
623   some multi-byte character sets, HTTP allows the use of whatever octet
624   sequences are defined by that character set to represent the
625   equivalent of CR and LF for line breaks. This flexibility regarding
626   line breaks applies only to text media in the entity-body; a bare CR
627   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
628   structures (such as header fields and multipart boundaries).
629</t>
630<t>
631   If an entity-body is encoded with a content-coding, the underlying
632   data &MUST; be in a form defined above prior to being encoded.
633</t>
634<t>
635   The "charset" parameter is used with some media types to define the
636   character set (<xref target="character.sets"/>) of the data. When no explicit charset
637   parameter is provided by the sender, media subtypes of the "text"
638   type are defined to have a default charset value of "ISO-8859-1" when
639   received via HTTP. Data in character sets other than "ISO-8859-1" or
640   its subsets &MUST; be labeled with an appropriate charset value. See
641   <xref target="missing.charset"/> for compatibility problems.
642</t>
643</section>
644
645<section title="Multipart Types" anchor="multipart.types">
646<t>
647   MIME provides for a number of "multipart" types -- encapsulations of
648   one or more entities within a single message-body. All multipart
649   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
650   and &MUST; include a boundary parameter as part of the media type
651   value. The message body is itself a protocol element and &MUST;
652   therefore use only CRLF to represent line breaks between body-parts.
653   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
654   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
655   original multipart contains an epilogue). These restrictions exist in
656   order to preserve the self-delimiting nature of a multipart message-body,
657   wherein the "end" of the message-body is indicated by the
658   ending multipart boundary.
659</t>
660<t>
661   In general, HTTP treats a multipart message-body no differently than
662   any other media type: strictly as payload. The one exception is the
663   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
664   (Partial Content) response.
665   <!-- jre: re-insert removed text pointing to caching? -->
666   In all
667   other cases, an HTTP user agent &SHOULD; follow the same or similar
668   behavior as a MIME user agent would upon receipt of a multipart type.
669   The MIME header fields within each body-part of a multipart message-body
670   do not have any significance to HTTP beyond that defined by
671   their MIME semantics.
672</t>
673<t>
674   In general, an HTTP user agent &SHOULD; follow the same or similar
675   behavior as a MIME user agent would upon receipt of a multipart type.
676   If an application receives an unrecognized multipart subtype, the
677   application &MUST; treat it as being equivalent to "multipart/mixed".
678</t>
679<x:note>
680  <t>
681    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
682    for carrying form data suitable for processing via the POST
683    request method, as described in <xref target="RFC2388"/>.
684  </t>
685</x:note>
686</section>
687</section>
688
689<section title="Language Tags" anchor="language.tags">
690  <x:anchor-alias value="language-tag"/>
691<t>
692   A language tag, as defined in <xref target="RFC4646bis"/>, identifies a
693   natural language spoken, written, or otherwise conveyed by human beings for
694   communication of information to other human beings. Computer languages are
695   explicitly excluded. HTTP uses language tags within the Accept-Language and
696   Content-Language fields.
697</t>
698<t>
699   In summary, a language tag is composed of one or more parts: A primary
700   language subtag followed by a possibly empty series of subtags:
701</t>
702<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
703  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC4646bis" x:sec="2.1"/>&gt;
704</artwork></figure>
705<t>
706   White space is not allowed within the tag and all tags are case-insensitive.
707   The name space of language subtags is administered by the IANA (see
708   <eref target="http://www.iana.org/assignments/language-subtag-registry"/>).
709</t>
710<figure>
711  <preamble>Example tags include:</preamble>
712<artwork type="example">
713  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
714</artwork>
715</figure>
716<t>
717   See <xref target="RFC4646bis"/> for further information.
718</t>
719</section>
720</section>
721
722<section title="Entity" anchor="entity">
723<t>
724   Request and Response messages &MAY; transfer an entity if not otherwise
725   restricted by the request method or response status code. An entity
726   consists of entity-header fields and an entity-body, although some
727   responses will only include the entity-headers.
728</t>
729<t>
730   In this section, both sender and recipient refer to either the client
731   or the server, depending on who sends and who receives the entity.
732</t>
733
734<section title="Entity Header Fields" anchor="entity.header.fields">
735  <x:anchor-alias value="entity-header"/>
736  <x:anchor-alias value="extension-header"/>
737<t>
738   Entity-header fields define metainformation about the entity-body or,
739   if no body is present, about the resource identified by the request.
740</t>
741<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
742  <x:ref>entity-header</x:ref>  = <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
743                 / <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
744                 / <x:ref>Content-Length</x:ref>           ; &header-content-length;
745                 / <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
746                 / <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
747                 / <x:ref>Content-Range</x:ref>            ; &header-content-range;
748                 / <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
749                 / <x:ref>Expires</x:ref>                  ; &header-expires;
750                 / <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
751                 / <x:ref>extension-header</x:ref>
752 
753  <x:ref>extension-header</x:ref> = <x:ref>header-field</x:ref>
754</artwork></figure>
755<t>
756   The extension-header mechanism allows additional entity-header fields
757   to be defined without changing the protocol, but these fields cannot
758   be assumed to be recognizable by the recipient. Unrecognized header
759   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
760   transparent proxies.
761</t>
762</section>
763
764<section title="Entity Body" anchor="entity.body">
765  <x:anchor-alias value="entity-body"/>
766<t>
767   The entity-body (if any) sent with an HTTP request or response is in
768   a format and encoding defined by the entity-header fields.
769</t>
770<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
771  <x:ref>entity-body</x:ref>    = *<x:ref>OCTET</x:ref>
772</artwork></figure>
773<t>
774   An entity-body is only present in a message when a message-body is
775   present, as described in &message-body;. The entity-body is obtained
776   from the message-body by decoding any Transfer-Encoding that might
777   have been applied to ensure safe and proper transfer of the message.
778</t>
779
780<section title="Type" anchor="type">
781<t>
782   When an entity-body is included with a message, the data type of that
783   body is determined via the header fields Content-Type and Content-Encoding.
784   These define a two-layer, ordered encoding model:
785</t>
786<figure><artwork type="example">
787  entity-body := Content-Encoding( Content-Type( data ) )
788</artwork></figure>
789<t>
790   Content-Type specifies the media type of the underlying data. Any HTTP/1.1
791   message containing an entity-body &SHOULD; include a Content-Type header
792   field defining the media type of that body, unless that information is
793   unknown.  If the Content-Type header field is not present, it indicates that
794   the sender does not know the media type of the data; recipients &MAY;
795   either assume that it is "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
796   or examine the content to determine its type.
797</t>
798<t>
799   Content-Encoding may be used to indicate any additional content
800   codings applied to the data, usually for the purpose of data
801   compression, that are a property of the requested resource.  There is
802   no default encoding.
803</t>
804</section>
805   
806<section title="Entity Length" anchor="entity.length">
807<t>
808   The entity-length of a message is the length of the message-body
809   before any transfer-codings have been applied. &message-length; defines
810   how the transfer-length of a message-body is determined.
811</t>
812</section>
813</section>
814</section>
815
816<section title="Content Negotiation" anchor="content.negotiation">
817<t>
818   Most HTTP responses include an entity which contains information for
819   interpretation by a human user. Naturally, it is desirable to supply
820   the user with the "best available" entity corresponding to the
821   request. Unfortunately for servers and caches, not all users have the
822   same preferences for what is "best," and not all user agents are
823   equally capable of rendering all entity types. For that reason, HTTP
824   has provisions for several mechanisms for "content negotiation" --
825   the process of selecting the best representation for a given response
826   when there are multiple representations available.
827</t>
828<x:note>
829  <t>
830    <x:h>Note:</x:h> This is not called "format negotiation" because the
831    alternate representations may be of the same media type, but use
832    different capabilities of that type, be in different languages,
833    etc.
834  </t>
835</x:note>
836<t>
837   Any response containing an entity-body &MAY; be subject to negotiation,
838   including error responses.
839</t>
840<t>
841   There are two kinds of content negotiation which are possible in
842   HTTP: server-driven and agent-driven negotiation. These two kinds of
843   negotiation are orthogonal and thus may be used separately or in
844   combination. One method of combination, referred to as transparent
845   negotiation, occurs when a cache uses the agent-driven negotiation
846   information provided by the origin server in order to provide
847   server-driven negotiation for subsequent requests.
848</t>
849
850<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
851<t>
852   If the selection of the best representation for a response is made by
853   an algorithm located at the server, it is called server-driven
854   negotiation. Selection is based on the available representations of
855   the response (the dimensions over which it can vary; e.g. language,
856   content-coding, etc.) and the contents of particular header fields in
857   the request message or on other information pertaining to the request
858   (such as the network address of the client).
859</t>
860<t>
861   Server-driven negotiation is advantageous when the algorithm for
862   selecting from among the available representations is difficult to
863   describe to the user agent, or when the server desires to send its
864   "best guess" to the client along with the first response (hoping to
865   avoid the round-trip delay of a subsequent request if the "best
866   guess" is good enough for the user). In order to improve the server's
867   guess, the user agent &MAY; include request header fields (Accept,
868   Accept-Language, Accept-Encoding, etc.) which describe its
869   preferences for such a response.
870</t>
871<t>
872   Server-driven negotiation has disadvantages:
873  <list style="numbers">
874    <t>
875         It is impossible for the server to accurately determine what
876         might be "best" for any given user, since that would require
877         complete knowledge of both the capabilities of the user agent
878         and the intended use for the response (e.g., does the user want
879         to view it on screen or print it on paper?).
880    </t>
881    <t>
882         Having the user agent describe its capabilities in every
883         request can be both very inefficient (given that only a small
884         percentage of responses have multiple representations) and a
885         potential violation of the user's privacy.
886    </t>
887    <t>
888         It complicates the implementation of an origin server and the
889         algorithms for generating responses to a request.
890    </t>
891    <t>
892         It may limit a public cache's ability to use the same response
893         for multiple user's requests.
894    </t>
895  </list>
896</t>
897<t>
898   HTTP/1.1 includes the following request-header fields for enabling
899   server-driven negotiation through description of user agent
900   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
901   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
902   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;). However, an
903   origin server is not limited to these dimensions and &MAY; vary the
904   response based on any aspect of the request, including information
905   outside the request-header fields or within extension header fields
906   not defined by this specification.
907</t>
908<t>
909   The Vary header field (&header-vary;) can be used to express the parameters the
910   server uses to select a representation that is subject to server-driven
911   negotiation.
912</t>
913</section>
914
915<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
916<t>
917   With agent-driven negotiation, selection of the best representation
918   for a response is performed by the user agent after receiving an
919   initial response from the origin server. Selection is based on a list
920   of the available representations of the response included within the
921   header fields or entity-body of the initial response, with each
922   representation identified by its own URI. Selection from among the
923   representations may be performed automatically (if the user agent is
924   capable of doing so) or manually by the user selecting from a
925   generated (possibly hypertext) menu.
926</t>
927<t>
928   Agent-driven negotiation is advantageous when the response would vary
929   over commonly-used dimensions (such as type, language, or encoding),
930   when the origin server is unable to determine a user agent's
931   capabilities from examining the request, and generally when public
932   caches are used to distribute server load and reduce network usage.
933</t>
934<t>
935   Agent-driven negotiation suffers from the disadvantage of needing a
936   second request to obtain the best alternate representation. This
937   second request is only efficient when caching is used. In addition,
938   this specification does not define any mechanism for supporting
939   automatic selection, though it also does not prevent any such
940   mechanism from being developed as an extension and used within
941   HTTP/1.1.
942</t>
943<t>
944   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
945   status codes for enabling agent-driven negotiation when the server is
946   unwilling or unable to provide a varying response using server-driven
947   negotiation.
948</t>
949</section>
950
951<section title="Transparent Negotiation" anchor="transparent.negotiation">
952<t>
953   Transparent negotiation is a combination of both server-driven and
954   agent-driven negotiation. When a cache is supplied with a form of the
955   list of available representations of the response (as in agent-driven
956   negotiation) and the dimensions of variance are completely understood
957   by the cache, then the cache becomes capable of performing server-driven
958   negotiation on behalf of the origin server for subsequent
959   requests on that resource.
960</t>
961<t>
962   Transparent negotiation has the advantage of distributing the
963   negotiation work that would otherwise be required of the origin
964   server and also removing the second request delay of agent-driven
965   negotiation when the cache is able to correctly guess the right
966   response.
967</t>
968<t>
969   This specification does not define any mechanism for transparent
970   negotiation, though it also does not prevent any such mechanism from
971   being developed as an extension that could be used within HTTP/1.1.
972</t>
973</section>
974</section>
975
976<section title="Header Field Definitions" anchor="header.fields">
977<t>
978   This section defines the syntax and semantics of HTTP/1.1 header fields
979   related to the payload of messages.
980</t>
981<t>
982   For entity-header fields, both sender and recipient refer to either the
983   client or the server, depending on who sends and who receives the entity.
984</t>
985
986<section title="Accept" anchor="header.accept">
987  <iref primary="true" item="Accept header" x:for-anchor=""/>
988  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
989  <x:anchor-alias value="Accept"/>
990  <x:anchor-alias value="Accept-v"/>
991  <x:anchor-alias value="accept-ext"/>
992  <x:anchor-alias value="accept-params"/>
993  <x:anchor-alias value="media-range"/>
994<t>
995   The request-header field "Accept" can be used to specify certain media
996   types which are acceptable for the response. Accept headers can be
997   used to indicate that the request is specifically limited to a small
998   set of desired types, as in the case of a request for an in-line
999   image.
1000</t>
1001<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"/>
1002  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
1003  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
1004 
1005  <x:ref>media-range</x:ref>    = ( "*/*"
1006                   / ( <x:ref>type</x:ref> "/" "*" )
1007                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
1008                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
1009  <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> )
1010  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref>
1011                   [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
1012</artwork></figure>
1013<t>
1014   The asterisk "*" character is used to group media types into ranges,
1015   with "*/*" indicating all media types and "type/*" indicating all
1016   subtypes of that type. The media-range &MAY; include media type
1017   parameters that are applicable to that range.
1018</t>
1019<t>
1020   Each media-range &MAY; be followed by one or more accept-params,
1021   beginning with the "q" parameter for indicating a relative quality
1022   factor. The first "q" parameter (if any) separates the media-range
1023   parameter(s) from the accept-params. Quality factors allow the user
1024   or user agent to indicate the relative degree of preference for that
1025   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
1026   default value is q=1.
1027</t>
1028<x:note>
1029  <t>
1030    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
1031    parameters from Accept extension parameters is due to historical
1032    practice. Although this prevents any media type parameter named
1033    "q" from being used with a media range, such an event is believed
1034    to be unlikely given the lack of any "q" parameters in the IANA
1035    media type registry and the rare usage of any media type
1036    parameters in Accept. Future media types are discouraged from
1037    registering any parameter named "q".
1038  </t>
1039</x:note>
1040<t>
1041   The example
1042</t>
1043<figure><artwork type="example">
1044  Accept: audio/*; q=0.2, audio/basic
1045</artwork></figure>
1046<t>
1047   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
1048   type if it is the best available after an 80% mark-down in quality."
1049</t>
1050<t>
1051   If no Accept header field is present, then it is assumed that the
1052   client accepts all media types. If an Accept header field is present,
1053   and if the server cannot send a response which is acceptable
1054   according to the combined Accept field value, then the server &SHOULD;
1055   send a 406 (Not Acceptable) response.
1056</t>
1057<t>
1058   A more elaborate example is
1059</t>
1060<figure><artwork type="example">
1061  Accept: text/plain; q=0.5, text/html,
1062          text/x-dvi; q=0.8, text/x-c
1063</artwork></figure>
1064<t>
1065   Verbally, this would be interpreted as "text/html and text/x-c are
1066   the preferred media types, but if they do not exist, then send the
1067   text/x-dvi entity, and if that does not exist, send the text/plain
1068   entity."
1069</t>
1070<t>
1071   Media ranges can be overridden by more specific media ranges or
1072   specific media types. If more than one media range applies to a given
1073   type, the most specific reference has precedence. For example,
1074</t>
1075<figure><artwork type="example">
1076  Accept: text/*, text/html, text/html;level=1, */*
1077</artwork></figure>
1078<t>
1079   have the following precedence:
1080   <list style="numbers">
1081    <t>text/html;level=1</t>
1082    <t>text/html</t>
1083    <t>text/*</t>
1084    <t>*/*</t>
1085   </list>
1086</t>
1087<t>
1088   The media type quality factor associated with a given type is
1089   determined by finding the media range with the highest precedence
1090   which matches that type. For example,
1091</t>
1092<figure><artwork type="example">
1093  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1094          text/html;level=2;q=0.4, */*;q=0.5
1095</artwork></figure>
1096<t>
1097   would cause the following values to be associated:
1098</t>
1099<texttable align="left">
1100  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1101  <c>text/html;level=1</c>    <c>1</c>
1102  <c>text/html</c>            <c>0.7</c>
1103  <c>text/plain</c>           <c>0.3</c>
1104  <c>image/jpeg</c>           <c>0.5</c>
1105  <c>text/html;level=2</c>    <c>0.4</c>
1106  <c>text/html;level=3</c>    <c>0.7</c>
1107</texttable>
1108<t>
1109      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1110      values for certain media ranges. However, unless the user agent is
1111      a closed system which cannot interact with other rendering agents,
1112      this default set ought to be configurable by the user.
1113</t>
1114</section>
1115
1116<section title="Accept-Charset" anchor="header.accept-charset">
1117  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1118  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1119  <x:anchor-alias value="Accept-Charset"/>
1120  <x:anchor-alias value="Accept-Charset-v"/>
1121<t>
1122   The request-header field "Accept-Charset" can be used to indicate what
1123   character sets are acceptable for the response. This field allows
1124   clients capable of understanding more comprehensive or special-purpose
1125   character sets to signal that capability to a server which is
1126   capable of representing documents in those character sets.
1127</t>
1128<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
1129  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
1130          <x:ref>Accept-Charset-v</x:ref>
1131  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1132                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1133</artwork></figure>
1134<t>
1135   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1136   be given an associated quality value which represents the user's
1137   preference for that charset. The default value is q=1. An example is
1138</t>
1139<figure><artwork type="example">
1140  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1141</artwork></figure>
1142<t>
1143   The special value "*", if present in the Accept-Charset field,
1144   matches every character set (including ISO-8859-1) which is not
1145   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1146   in an Accept-Charset field, then all character sets not explicitly
1147   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1148   a quality value of 1 if not explicitly mentioned.
1149</t>
1150<t>
1151   If no Accept-Charset header is present, the default is that any
1152   character set is acceptable. If an Accept-Charset header is present,
1153   and if the server cannot send a response which is acceptable
1154   according to the Accept-Charset header, then the server &SHOULD; send
1155   an error response with the 406 (Not Acceptable) status code, though
1156   the sending of an unacceptable response is also allowed.
1157</t>
1158</section>
1159
1160<section title="Accept-Encoding" anchor="header.accept-encoding">
1161  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1162  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1163  <x:anchor-alias value="Accept-Encoding"/>
1164  <x:anchor-alias value="Accept-Encoding-v"/>
1165  <x:anchor-alias value="codings"/>
1166<t>
1167   The request-header field "Accept-Encoding" is similar to Accept, but
1168   restricts the content-codings (<xref target="content.codings"/>) that are acceptable in
1169   the response.
1170</t>
1171<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"/>
1172  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
1173                     <x:ref>Accept-Encoding-v</x:ref>
1174  <x:ref>Accept-Encoding-v</x:ref>  =
1175                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1176  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
1177</artwork></figure>
1178<t>
1179   Each codings value &MAY; be given an associated quality value which
1180   represents the preference for that encoding. The default value is q=1.
1181</t>
1182<t>
1183   Examples of its use are:
1184</t>
1185<figure><artwork type="example">
1186  Accept-Encoding: compress, gzip
1187  Accept-Encoding:
1188  Accept-Encoding: *
1189  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1190  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1191</artwork></figure>
1192<t>
1193   A server tests whether a content-coding is acceptable, according to
1194   an Accept-Encoding field, using these rules:
1195  <list style="numbers">
1196      <t>If the content-coding is one of the content-codings listed in
1197         the Accept-Encoding field, then it is acceptable, unless it is
1198         accompanied by a qvalue of 0. (As defined in &qvalue;, a
1199         qvalue of 0 means "not acceptable.")</t>
1200
1201      <t>The special "*" symbol in an Accept-Encoding field matches any
1202         available content-coding not explicitly listed in the header
1203         field.</t>
1204
1205      <t>If multiple content-codings are acceptable, then the acceptable
1206         content-coding with the highest non-zero qvalue is preferred.</t>
1207
1208      <t>The "identity" content-coding is always acceptable, unless
1209         specifically refused because the Accept-Encoding field includes
1210         "identity;q=0", or because the field includes "*;q=0" and does
1211         not explicitly include the "identity" content-coding. If the
1212         Accept-Encoding field-value is empty, then only the "identity"
1213         encoding is acceptable.</t>
1214  </list>
1215</t>
1216<t>
1217   If an Accept-Encoding field is present in a request, and if the
1218   server cannot send a response which is acceptable according to the
1219   Accept-Encoding header, then the server &SHOULD; send an error response
1220   with the 406 (Not Acceptable) status code.
1221</t>
1222<t>
1223   If no Accept-Encoding field is present in a request, the server &MAY;
1224   assume that the client will accept any content coding. In this case,
1225   if "identity" is one of the available content-codings, then the
1226   server &SHOULD; use the "identity" content-coding, unless it has
1227   additional information that a different content-coding is meaningful
1228   to the client.
1229</t>
1230<x:note>
1231  <t>
1232    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1233    and if the "identity" content-coding is unavailable, then
1234    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1235    "gzip" and "compress") are preferred; some older clients
1236    improperly display messages sent with other content-codings.  The
1237    server might also make this decision based on information about
1238    the particular user-agent or client.
1239  </t>
1240</x:note>
1241<x:note>
1242  <t>
1243    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1244    associated with content-codings. This means that qvalues will not
1245    work and are not permitted with x-gzip or x-compress.
1246  </t>
1247</x:note>
1248</section>
1249
1250<section title="Accept-Language" anchor="header.accept-language">
1251  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1252  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1253  <x:anchor-alias value="Accept-Language"/>
1254  <x:anchor-alias value="Accept-Language-v"/>
1255  <x:anchor-alias value="language-range"/>
1256<t>
1257   The request-header field "Accept-Language" is similar to Accept, but
1258   restricts the set of natural languages that are preferred as a
1259   response to the request. Language tags are defined in <xref target="language.tags"/>.
1260</t>
1261<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"/>
1262  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
1263                    <x:ref>Accept-Language-v</x:ref>
1264  <x:ref>Accept-Language-v</x:ref> =
1265                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1266  <x:ref>language-range</x:ref>    =
1267            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1268</artwork></figure>
1269<t>
1270   Each language-range can be given an associated quality value which
1271   represents an estimate of the user's preference for the languages
1272   specified by that range. The quality value defaults to "q=1". For
1273   example,
1274</t>
1275<figure><artwork type="example">
1276  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1277</artwork></figure>
1278<t>
1279   would mean: "I prefer Danish, but will accept British English and
1280   other types of English."
1281</t>
1282<t>
1283   For matching, the "Basic Filtering" matching scheme, defined in
1284   <xref target="RFC4647" x:sec="3.3.1" x:fmt="of"/>, is used:
1285</t>
1286<x:blockquote cite="http://tools.ietf.org/html/rfc4647#section-3.3.1">
1287  <t>
1288     A language range matches a
1289     particular language tag if, in a case-insensitive comparison, it
1290     exactly equals the tag, or if it exactly equals a prefix of the tag
1291     such that the first character following the prefix is "-".
1292  </t>
1293</x:blockquote> 
1294<t>
1295   The special range "*", if present in the Accept-Language field,
1296   matches every tag not matched by any other range present in the
1297   Accept-Language field.
1298</t>
1299<x:note>
1300  <t>
1301    <x:h>Note:</x:h> This use of a prefix matching rule does not imply that
1302    language tags are assigned to languages in such a way that it is
1303    always true that if a user understands a language with a certain
1304    tag, then this user will also understand all languages with tags
1305    for which this tag is a prefix. The prefix rule simply allows the
1306    use of prefix tags if this is the case.
1307  </t>
1308</x:note>
1309<t>
1310   The language quality factor assigned to a language-tag by the
1311   Accept-Language field is the quality value of the longest language-range
1312   in the field that matches the language-tag. If no language-range
1313   in the field matches the tag, the language quality factor
1314   assigned is 0. If no Accept-Language header is present in the
1315   request, the server
1316   &SHOULD; assume that all languages are equally acceptable. If an
1317   Accept-Language header is present, then all languages which are
1318   assigned a quality factor greater than 0 are acceptable.
1319</t>
1320<t>
1321   It might be contrary to the privacy expectations of the user to send
1322   an Accept-Language header with the complete linguistic preferences of
1323   the user in every request. For a discussion of this issue, see
1324   <xref target="privacy.issues.connected.to.accept.headers"/>.
1325</t>
1326<t>
1327   As intelligibility is highly dependent on the individual user, it is
1328   recommended that client applications make the choice of linguistic
1329   preference available to the user. If the choice is not made
1330   available, then the Accept-Language header field &MUST-NOT; be given in
1331   the request.
1332</t>
1333<x:note>
1334  <t>
1335    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1336    the user, we remind implementors of  the fact that users are not
1337    familiar with the details of language matching as described above,
1338    and should provide appropriate guidance. As an example, users
1339    might assume that on selecting "en-gb", they will be served any
1340    kind of English document if British English is not available. A
1341    user agent might suggest in such a case to add "en" to get the
1342    best matching behavior.
1343  </t>
1344</x:note>
1345</section>
1346
1347<section title="Content-Encoding" anchor="header.content-encoding">
1348  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1349  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1350  <x:anchor-alias value="Content-Encoding"/>
1351  <x:anchor-alias value="Content-Encoding-v"/>
1352<t>
1353   The entity-header field "Content-Encoding" is used as a modifier to the
1354   media-type. When present, its value indicates what additional content
1355   codings have been applied to the entity-body, and thus what decoding
1356   mechanisms must be applied in order to obtain the media-type
1357   referenced by the Content-Type header field. Content-Encoding is
1358   primarily used to allow a document to be compressed without losing
1359   the identity of its underlying media type.
1360</t>
1361<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
1362  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
1363  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1364</artwork></figure>
1365<t>
1366   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1367</t>
1368<figure><artwork type="example">
1369  Content-Encoding: gzip
1370</artwork></figure>
1371<t>
1372   The content-coding is a characteristic of the entity identified by
1373   the request-target. Typically, the entity-body is stored with this
1374   encoding and is only decoded before rendering or analogous usage.
1375   However, a non-transparent proxy &MAY; modify the content-coding if the
1376   new coding is known to be acceptable to the recipient, unless the
1377   "no-transform" cache-control directive is present in the message.
1378</t>
1379<t>
1380   If the content-coding of an entity is not "identity", then the
1381   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1382   that lists the non-identity content-coding(s) used.
1383</t>
1384<t>
1385   If the content-coding of an entity in a request message is not
1386   acceptable to the origin server, the server &SHOULD; respond with a
1387   status code of 415 (Unsupported Media Type).
1388</t>
1389<t>
1390   If multiple encodings have been applied to an entity, the content
1391   codings &MUST; be listed in the order in which they were applied.
1392   Additional information about the encoding parameters &MAY; be provided
1393   by other entity-header fields not defined by this specification.
1394</t>
1395</section>
1396
1397<section title="Content-Language" anchor="header.content-language">
1398  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1399  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1400  <x:anchor-alias value="Content-Language"/>
1401  <x:anchor-alias value="Content-Language-v"/>
1402<t>
1403   The entity-header field "Content-Language" describes the natural
1404   language(s) of the intended audience for the enclosed entity. Note
1405   that this might not be equivalent to all the languages used within
1406   the entity-body.
1407</t>
1408<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
1409  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
1410  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1411</artwork></figure>
1412<t>
1413   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1414   Content-Language is to allow a user to identify and differentiate
1415   entities according to the user's own preferred language. Thus, if the
1416   body content is intended only for a Danish-literate audience, the
1417   appropriate field is
1418</t>
1419<figure><artwork type="example">
1420  Content-Language: da
1421</artwork></figure>
1422<t>
1423   If no Content-Language is specified, the default is that the content
1424   is intended for all language audiences. This might mean that the
1425   sender does not consider it to be specific to any natural language,
1426   or that the sender does not know for which language it is intended.
1427</t>
1428<t>
1429   Multiple languages &MAY; be listed for content that is intended for
1430   multiple audiences. For example, a rendition of the "Treaty of
1431   Waitangi," presented simultaneously in the original Maori and English
1432   versions, would call for
1433</t>
1434<figure><artwork type="example">
1435  Content-Language: mi, en
1436</artwork></figure>
1437<t>
1438   However, just because multiple languages are present within an entity
1439   does not mean that it is intended for multiple linguistic audiences.
1440   An example would be a beginner's language primer, such as "A First
1441   Lesson in Latin," which is clearly intended to be used by an
1442   English-literate audience. In this case, the Content-Language would
1443   properly only include "en".
1444</t>
1445<t>
1446   Content-Language &MAY; be applied to any media type -- it is not
1447   limited to textual documents.
1448</t>
1449</section>
1450
1451<section title="Content-Location" anchor="header.content-location">
1452  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1453  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1454  <x:anchor-alias value="Content-Location"/>
1455  <x:anchor-alias value="Content-Location-v"/>
1456<t>
1457   The entity-header field "Content-Location" &MAY; be used to supply the
1458   resource location for the entity enclosed in the message when that
1459   entity is accessible from a location separate from the requested
1460   resource's URI. A server &SHOULD; provide a Content-Location for the
1461   variant corresponding to the response entity; especially in the case
1462   where a resource has multiple entities associated with it, and those
1463   entities actually have separate locations by which they might be
1464   individually accessed, the server &SHOULD; provide a Content-Location
1465   for the particular variant which is returned.
1466</t>
1467<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
1468  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
1469                    <x:ref>Content-Location-v</x:ref>
1470  <x:ref>Content-Location-v</x:ref> =
1471                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1472</artwork></figure>
1473<t>
1474   The value of Content-Location also defines the base URI for the
1475   entity.
1476</t>
1477<t>
1478   The Content-Location value is not a replacement for the original
1479   requested URI; it is only a statement of the location of the resource
1480   corresponding to this particular entity at the time of the request.
1481   Future requests &MAY; specify the Content-Location URI as the request-target
1482   if the desire is to identify the source of that particular
1483   entity.
1484</t>
1485<t>
1486   A cache cannot assume that an entity with a Content-Location
1487   different from the URI used to retrieve it can be used to respond to
1488   later requests on that Content-Location URI. However, the Content-Location
1489   can be used to differentiate between multiple entities
1490   retrieved from a single requested resource, as described in &caching-neg-resp;.
1491</t>
1492<t>
1493   If the Content-Location is a relative URI, the relative URI is
1494   interpreted relative to the request-target.
1495</t>
1496<t>
1497   The meaning of the Content-Location header in requests is
1498   undefined; servers are free to ignore it in those cases.
1499</t>
1500</section>
1501
1502<section title="Content-MD5" anchor="header.content-md5">
1503  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1504  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1505  <x:anchor-alias value="Content-MD5"/>
1506  <x:anchor-alias value="Content-MD5-v"/>
1507<t>
1508   The entity-header field "Content-MD5", as defined in <xref target="RFC1864"/>, is
1509   an MD5 digest of the entity-body for the purpose of providing an
1510   end-to-end message integrity check (MIC) of the entity-body. (Note: a
1511   MIC is good for detecting accidental modification of the entity-body
1512   in transit, but is not proof against malicious attacks.)
1513</t>
1514<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
1515  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
1516  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1517</artwork></figure>
1518<t>
1519   The Content-MD5 header field &MAY; be generated by an origin server or
1520   client to function as an integrity check of the entity-body. Only
1521   origin servers or clients &MAY; generate the Content-MD5 header field;
1522   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1523   value as an end-to-end integrity check. Any recipient of the entity-body,
1524   including gateways and proxies, &MAY; check that the digest value
1525   in this header field matches that of the entity-body as received.
1526</t>
1527<t>
1528   The MD5 digest is computed based on the content of the entity-body,
1529   including any content-coding that has been applied, but not including
1530   any transfer-encoding applied to the message-body. If the message is
1531   received with a transfer-encoding, that encoding &MUST; be removed
1532   prior to checking the Content-MD5 value against the received entity.
1533</t>
1534<t>
1535   This has the result that the digest is computed on the octets of the
1536   entity-body exactly as, and in the order that, they would be sent if
1537   no transfer-encoding were being applied.
1538</t>
1539<t>
1540   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1541   composite media-types (e.g., multipart/* and message/rfc822), but
1542   this does not change how the digest is computed as defined in the
1543   preceding paragraph.
1544</t>
1545<t>
1546   There are several consequences of this. The entity-body for composite
1547   types &MAY; contain many body-parts, each with its own MIME and HTTP
1548   headers (including Content-MD5, Content-Transfer-Encoding, and
1549   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1550   or Content-Encoding header, it is assumed that the content
1551   of the body-part has had the encoding applied, and the body-part is
1552   included in the Content-MD5 digest as is -- i.e., after the
1553   application. The Transfer-Encoding header field is not allowed within
1554   body-parts.
1555</t>
1556<t>
1557   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1558   computing or checking the digest: the line break convention used in
1559   the text actually transmitted &MUST; be left unaltered when computing
1560   the digest.
1561</t>
1562<x:note>
1563  <t>
1564    <x:h>Note:</x:h> while the definition of Content-MD5 is exactly the same for
1565    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1566    in which the application of Content-MD5 to HTTP entity-bodies
1567    differs from its application to MIME entity-bodies. One is that
1568    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1569    does use Transfer-Encoding and Content-Encoding. Another is that
1570    HTTP more frequently uses binary content types than MIME, so it is
1571    worth noting that, in such cases, the byte order used to compute
1572    the digest is the transmission byte order defined for the type.
1573    Lastly, HTTP allows transmission of text types with any of several
1574    line break conventions and not just the canonical form using CRLF.
1575  </t>
1576</x:note>
1577</section>
1578
1579<section title="Content-Type" anchor="header.content-type">
1580  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1581  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1582  <x:anchor-alias value="Content-Type"/>
1583  <x:anchor-alias value="Content-Type-v"/>
1584<t>
1585   The entity-header field "Content-Type" indicates the media type of the
1586   entity-body sent to the recipient or, in the case of the HEAD method,
1587   the media type that would have been sent had the request been a GET.
1588</t>
1589<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
1590  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
1591  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1592</artwork></figure>
1593<t>
1594   Media types are defined in <xref target="media.types"/>. An example of the field is
1595</t>
1596<figure><artwork type="example">
1597  Content-Type: text/html; charset=ISO-8859-4
1598</artwork></figure>
1599<t>
1600   Further discussion of methods for identifying the media type of an
1601   entity is provided in <xref target="type"/>.
1602</t>
1603</section>
1604
1605</section>
1606
1607<section title="IANA Considerations" anchor="IANA.considerations">
1608<section title="Message Header Registration" anchor="message.header.registration">
1609<t>
1610   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
1611   with the permanent registrations below (see <xref target="RFC3864"/>):
1612</t>
1613<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1614<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1615   <ttcol>Header Field Name</ttcol>
1616   <ttcol>Protocol</ttcol>
1617   <ttcol>Status</ttcol>
1618   <ttcol>Reference</ttcol>
1619
1620   <c>Accept</c>
1621   <c>http</c>
1622   <c>standard</c>
1623   <c>
1624      <xref target="header.accept"/>
1625   </c>
1626   <c>Accept-Charset</c>
1627   <c>http</c>
1628   <c>standard</c>
1629   <c>
1630      <xref target="header.accept-charset"/>
1631   </c>
1632   <c>Accept-Encoding</c>
1633   <c>http</c>
1634   <c>standard</c>
1635   <c>
1636      <xref target="header.accept-encoding"/>
1637   </c>
1638   <c>Accept-Language</c>
1639   <c>http</c>
1640   <c>standard</c>
1641   <c>
1642      <xref target="header.accept-language"/>
1643   </c>
1644   <c>Content-Disposition</c>
1645   <c>http</c>
1646   <c/>
1647   <c>
1648      <xref target="content-disposition"/>
1649   </c>
1650   <c>Content-Encoding</c>
1651   <c>http</c>
1652   <c>standard</c>
1653   <c>
1654      <xref target="header.content-encoding"/>
1655   </c>
1656   <c>Content-Language</c>
1657   <c>http</c>
1658   <c>standard</c>
1659   <c>
1660      <xref target="header.content-language"/>
1661   </c>
1662   <c>Content-Location</c>
1663   <c>http</c>
1664   <c>standard</c>
1665   <c>
1666      <xref target="header.content-location"/>
1667   </c>
1668   <c>Content-MD5</c>
1669   <c>http</c>
1670   <c>standard</c>
1671   <c>
1672      <xref target="header.content-md5"/>
1673   </c>
1674   <c>Content-Type</c>
1675   <c>http</c>
1676   <c>standard</c>
1677   <c>
1678      <xref target="header.content-type"/>
1679   </c>
1680   <c>MIME-Version</c>
1681   <c>http</c>
1682   <c/>
1683   <c>
1684      <xref target="mime-version"/>
1685   </c>
1686</texttable>
1687<!--(END)-->
1688<t>
1689   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1690</t>
1691</section>
1692
1693<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
1694<t>
1695   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1696   should be updated with the registrations below:
1697</t>
1698<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
1699   <ttcol>Registry Name</ttcol>
1700   <ttcol>Description</ttcol>
1701   <ttcol>Reference</ttcol>
1702   <c>compress</c>
1703   <c>UNIX "compress" program method</c>
1704   <c>
1705      <xref target="content.codings"/>
1706   </c>
1707   <c>deflate</c>
1708   <c>"zlib" format <xref target="RFC1950"/> with "deflate" compression</c>
1709   <c>
1710      <xref target="content.codings"/>
1711   </c>
1712   <c>gzip</c>
1713   <c>Same as GNU zip <xref target="RFC1952"/></c>
1714   <c>
1715      <xref target="content.codings"/>
1716   </c>
1717</texttable>
1718</section>
1719
1720<section title="Content Coding Registry" anchor="content.coding.registration">
1721<t>
1722   The registration procedure for HTTP Content Codings is now defined
1723   by <xref target="content.coding.registry"/> of this document.
1724</t>
1725<t>
1726   The HTTP Content Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
1727   should be updated with the registrations below:
1728</t>
1729<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
1730   <ttcol>Name</ttcol>
1731   <ttcol>Description</ttcol>
1732   <ttcol>Reference</ttcol>
1733   <c>compress</c>
1734   <c>UNIX "compress" program method</c>
1735   <c>
1736      <xref target="content.codings"/>
1737   </c>
1738   <c>deflate</c>
1739   <c>"zlib" format <xref target="RFC1950"/> with "deflate" compression</c>
1740   <c>
1741      <xref target="content.codings"/>
1742   </c>
1743   <c>gzip</c>
1744   <c>Same as GNU zip <xref target="RFC1952"/></c>
1745   <c>
1746      <xref target="content.codings"/>
1747   </c>
1748   <c>identity</c>
1749   <c>No transformation</c>
1750   <c>
1751      <xref target="content.codings"/>
1752   </c>
1753</texttable>
1754</section>
1755
1756</section>
1757
1758<section title="Security Considerations" anchor="security.considerations">
1759<t>
1760   This section is meant to inform application developers, information
1761   providers, and users of the security limitations in HTTP/1.1 as
1762   described by this document. The discussion does not include
1763   definitive solutions to the problems revealed, though it does make
1764   some suggestions for reducing security risks.
1765</t>
1766
1767<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1768<t>
1769   Accept request-headers can reveal information about the user to all
1770   servers which are accessed. The Accept-Language header in particular
1771   can reveal information the user would consider to be of a private
1772   nature, because the understanding of particular languages is often
1773   strongly correlated to the membership of a particular ethnic group.
1774   User agents which offer the option to configure the contents of an
1775   Accept-Language header to be sent in every request are strongly
1776   encouraged to let the configuration process include a message which
1777   makes the user aware of the loss of privacy involved.
1778</t>
1779<t>
1780   An approach that limits the loss of privacy would be for a user agent
1781   to omit the sending of Accept-Language headers by default, and to ask
1782   the user whether or not to start sending Accept-Language headers to a
1783   server if it detects, by looking for any Vary response-header fields
1784   generated by the server, that such sending could improve the quality
1785   of service.
1786</t>
1787<t>
1788   Elaborate user-customized accept header fields sent in every request,
1789   in particular if these include quality values, can be used by servers
1790   as relatively reliable and long-lived user identifiers. Such user
1791   identifiers would allow content providers to do click-trail tracking,
1792   and would allow collaborating content providers to match cross-server
1793   click-trails or form submissions of individual users. Note that for
1794   many users not behind a proxy, the network address of the host
1795   running the user agent will also serve as a long-lived user
1796   identifier. In environments where proxies are used to enhance
1797   privacy, user agents ought to be conservative in offering accept
1798   header configuration options to end users. As an extreme privacy
1799   measure, proxies could filter the accept headers in relayed requests.
1800   General purpose user agents which provide a high degree of header
1801   configurability &SHOULD; warn users about the loss of privacy which can
1802   be involved.
1803</t>
1804</section>
1805
1806<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1807<t>
1808   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
1809   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1810   serious security considerations. Content-Disposition is not part of
1811   the HTTP standard, but since it is widely implemented, we are
1812   documenting its use and risks for implementors. See <xref target="RFC2183" x:fmt="of" x:sec="5"/>
1813   for details.
1814</t>
1815</section>
1816
1817</section>
1818
1819<section title="Acknowledgments" anchor="ack">
1820</section>
1821</middle>
1822<back>
1823
1824<references title="Normative References">
1825
1826<reference anchor="ISO-8859-1">
1827  <front>
1828    <title>
1829     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1830    </title>
1831    <author>
1832      <organization>International Organization for Standardization</organization>
1833    </author>
1834    <date year="1998"/>
1835  </front>
1836  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1837</reference>
1838
1839<reference anchor="Part1">
1840  <front>
1841    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</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-p1-messaging-&ID-VERSION;"/>
1881  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1882</reference>
1883
1884<reference anchor="Part2">
1885  <front>
1886    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</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-p2-semantics-&ID-VERSION;"/>
1926  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1927</reference>
1928
1929<reference anchor="Part4">
1930  <front>
1931    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1932    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1933      <organization abbrev="Day Software">Day Software</organization>
1934      <address><email>fielding@gbiv.com</email></address>
1935    </author>
1936    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1937      <organization>One Laptop per Child</organization>
1938      <address><email>jg@laptop.org</email></address>
1939    </author>
1940    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1941      <organization abbrev="HP">Hewlett-Packard Company</organization>
1942      <address><email>JeffMogul@acm.org</email></address>
1943    </author>
1944    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1945      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1946      <address><email>henrikn@microsoft.com</email></address>
1947    </author>
1948    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1949      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1950      <address><email>LMM@acm.org</email></address>
1951    </author>
1952    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1953      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1954      <address><email>paulle@microsoft.com</email></address>
1955    </author>
1956    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1957      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1958      <address><email>timbl@w3.org</email></address>
1959    </author>
1960    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1961      <organization abbrev="W3C">World Wide Web Consortium</organization>
1962      <address><email>ylafon@w3.org</email></address>
1963    </author>
1964    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1965      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1966      <address><email>julian.reschke@greenbytes.de</email></address>
1967    </author>
1968    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1969  </front>
1970  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1971  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1972</reference>
1973
1974<reference anchor="Part5">
1975  <front>
1976    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1977    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1978      <organization abbrev="Day Software">Day Software</organization>
1979      <address><email>fielding@gbiv.com</email></address>
1980    </author>
1981    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1982      <organization>One Laptop per Child</organization>
1983      <address><email>jg@laptop.org</email></address>
1984    </author>
1985    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1986      <organization abbrev="HP">Hewlett-Packard Company</organization>
1987      <address><email>JeffMogul@acm.org</email></address>
1988    </author>
1989    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1990      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1991      <address><email>henrikn@microsoft.com</email></address>
1992    </author>
1993    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1994      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1995      <address><email>LMM@acm.org</email></address>
1996    </author>
1997    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1998      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1999      <address><email>paulle@microsoft.com</email></address>
2000    </author>
2001    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2002      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2003      <address><email>timbl@w3.org</email></address>
2004    </author>
2005    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2006      <organization abbrev="W3C">World Wide Web Consortium</organization>
2007      <address><email>ylafon@w3.org</email></address>
2008    </author>
2009    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2010      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2011      <address><email>julian.reschke@greenbytes.de</email></address>
2012    </author>
2013    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2014  </front>
2015  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
2016  <x:source href="p5-range.xml" basename="p5-range"/>
2017</reference>
2018
2019<reference anchor="Part6">
2020  <front>
2021    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2022    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2023      <organization abbrev="Day Software">Day Software</organization>
2024      <address><email>fielding@gbiv.com</email></address>
2025    </author>
2026    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2027      <organization>One Laptop per Child</organization>
2028      <address><email>jg@laptop.org</email></address>
2029    </author>
2030    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2031      <organization abbrev="HP">Hewlett-Packard Company</organization>
2032      <address><email>JeffMogul@acm.org</email></address>
2033    </author>
2034    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2035      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2036      <address><email>henrikn@microsoft.com</email></address>
2037    </author>
2038    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2039      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2040      <address><email>LMM@acm.org</email></address>
2041    </author>
2042    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2043      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2044      <address><email>paulle@microsoft.com</email></address>
2045    </author>
2046    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2047      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2048      <address><email>timbl@w3.org</email></address>
2049    </author>
2050    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2051      <organization abbrev="W3C">World Wide Web Consortium</organization>
2052      <address><email>ylafon@w3.org</email></address>
2053    </author>
2054    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
2055      <organization />
2056      <address><email>mnot@mnot.net</email></address>
2057    </author>
2058    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2059      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2060      <address><email>julian.reschke@greenbytes.de</email></address>
2061    </author>
2062    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2063  </front>
2064  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2065  <x:source href="p6-cache.xml" basename="p6-cache"/>
2066</reference>
2067
2068<reference anchor="RFC1864">
2069  <front>
2070    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
2071    <author initials="J." surname="Myers" fullname="John G. Myers">
2072      <organization>Carnegie Mellon University</organization>
2073      <address><email>jgm+@cmu.edu</email></address>
2074    </author>
2075    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
2076      <organization>Dover Beach Consulting, Inc.</organization>
2077      <address><email>mrose@dbc.mtview.ca.us</email></address>
2078    </author>
2079    <date month="October" year="1995"/>
2080  </front>
2081  <seriesInfo name="RFC" value="1864"/>
2082</reference>
2083
2084<reference anchor="RFC1950">
2085  <front>
2086    <title>ZLIB Compressed Data Format Specification version 3.3</title>
2087    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2088      <organization>Aladdin Enterprises</organization>
2089      <address><email>ghost@aladdin.com</email></address>
2090    </author>
2091    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2092      <organization/>
2093    </author>
2094    <date month="May" year="1996"/>
2095  </front>
2096  <seriesInfo name="RFC" value="1950"/>
2097  <annotation>
2098    RFC 1950 is an Informational RFC, thus it may be less stable than
2099    this specification. On the other hand, this downward reference was
2100    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2101    therefore it is unlikely to cause problems in practice. See also
2102    <xref target="BCP97"/>.
2103  </annotation>
2104</reference>
2105
2106<reference anchor="RFC1951">
2107  <front>
2108    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
2109    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2110      <organization>Aladdin Enterprises</organization>
2111      <address><email>ghost@aladdin.com</email></address>
2112    </author>
2113    <date month="May" year="1996"/>
2114  </front>
2115  <seriesInfo name="RFC" value="1951"/>
2116  <annotation>
2117    RFC 1951 is an Informational RFC, thus it may be less stable than
2118    this specification. On the other hand, this downward reference was
2119    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2120    therefore it is unlikely to cause problems in practice. See also
2121    <xref target="BCP97"/>.
2122  </annotation>
2123</reference>
2124
2125<reference anchor="RFC1952">
2126  <front>
2127    <title>GZIP file format specification version 4.3</title>
2128    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2129      <organization>Aladdin Enterprises</organization>
2130      <address><email>ghost@aladdin.com</email></address>
2131    </author>
2132    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2133      <organization/>
2134      <address><email>gzip@prep.ai.mit.edu</email></address>
2135    </author>
2136    <author initials="M." surname="Adler" fullname="Mark Adler">
2137      <organization/>
2138      <address><email>madler@alumni.caltech.edu</email></address>
2139    </author>
2140    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2141      <organization/>
2142      <address><email>ghost@aladdin.com</email></address>
2143    </author>
2144    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2145      <organization/>
2146      <address><email>randeg@alumni.rpi.edu</email></address>
2147    </author>
2148    <date month="May" year="1996"/>
2149  </front>
2150  <seriesInfo name="RFC" value="1952"/>
2151  <annotation>
2152    RFC 1952 is an Informational RFC, thus it may be less stable than
2153    this specification. On the other hand, this downward reference was
2154    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2155    therefore it is unlikely to cause problems in practice. See also
2156    <xref target="BCP97"/>.
2157  </annotation>
2158</reference>
2159
2160<reference anchor="RFC2045">
2161  <front>
2162    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2163    <author initials="N." surname="Freed" fullname="Ned Freed">
2164      <organization>Innosoft International, Inc.</organization>
2165      <address><email>ned@innosoft.com</email></address>
2166    </author>
2167    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2168      <organization>First Virtual Holdings</organization>
2169      <address><email>nsb@nsb.fv.com</email></address>
2170    </author>
2171    <date month="November" year="1996"/>
2172  </front>
2173  <seriesInfo name="RFC" value="2045"/>
2174</reference>
2175
2176<reference anchor="RFC2046">
2177  <front>
2178    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2179    <author initials="N." surname="Freed" fullname="Ned Freed">
2180      <organization>Innosoft International, Inc.</organization>
2181      <address><email>ned@innosoft.com</email></address>
2182    </author>
2183    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2184      <organization>First Virtual Holdings</organization>
2185      <address><email>nsb@nsb.fv.com</email></address>
2186    </author>
2187    <date month="November" year="1996"/>
2188  </front>
2189  <seriesInfo name="RFC" value="2046"/>
2190</reference>
2191
2192<reference anchor="RFC2119">
2193  <front>
2194    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2195    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2196      <organization>Harvard University</organization>
2197      <address><email>sob@harvard.edu</email></address>
2198    </author>
2199    <date month="March" year="1997"/>
2200  </front>
2201  <seriesInfo name="BCP" value="14"/>
2202  <seriesInfo name="RFC" value="2119"/>
2203</reference>
2204
2205<reference anchor='RFC4647'>
2206  <front>
2207    <title>Matching of Language Tags</title>
2208    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2209      <organization>Yahoo! Inc.</organization>
2210      <address><email>addison@inter-locale.com</email></address>
2211    </author>
2212    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2213      <organization>Google</organization>
2214      <address><email>mark.davis@macchiato.com</email></address>
2215    </author>
2216    <date year='2006' month='September' />
2217  </front>
2218  <seriesInfo name='BCP' value='47' />
2219  <seriesInfo name='RFC' value='4647' />
2220</reference>
2221
2222<reference anchor="RFC5234">
2223  <front>
2224    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2225    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2226      <organization>Brandenburg InternetWorking</organization>
2227      <address>
2228      <postal>
2229      <street>675 Spruce Dr.</street>
2230      <city>Sunnyvale</city>
2231      <region>CA</region>
2232      <code>94086</code>
2233      <country>US</country></postal>
2234      <phone>+1.408.246.8253</phone>
2235      <email>dcrocker@bbiw.net</email></address> 
2236    </author>
2237    <author initials="P." surname="Overell" fullname="Paul Overell">
2238      <organization>THUS plc.</organization>
2239      <address>
2240      <postal>
2241      <street>1/2 Berkeley Square</street>
2242      <street>99 Berkely Street</street>
2243      <city>Glasgow</city>
2244      <code>G3 7HR</code>
2245      <country>UK</country></postal>
2246      <email>paul.overell@thus.net</email></address>
2247    </author>
2248    <date month="January" year="2008"/>
2249  </front>
2250  <seriesInfo name="STD" value="68"/>
2251  <seriesInfo name="RFC" value="5234"/>
2252</reference>
2253
2254<reference anchor='RFC4646bis'>
2255  <front>
2256    <title>Tags for Identifying Languages</title>
2257    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
2258      <organization>Lab126</organization>
2259      <address><email>addison@inter-locale.com</email></address>
2260    </author>
2261    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
2262      <organization>Google</organization>
2263      <address><email>mark.davis@google.com</email></address>
2264    </author>
2265    <date month='June' day='11' year='2009' />
2266  </front>
2267  <seriesInfo name='Internet-Draft' value='draft-ietf-ltru-4646bis-23' />
2268</reference>
2269
2270</references>
2271
2272<references title="Informative References">
2273
2274<reference anchor="RFC1945">
2275  <front>
2276    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2277    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2278      <organization>MIT, Laboratory for Computer Science</organization>
2279      <address><email>timbl@w3.org</email></address>
2280    </author>
2281    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2282      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2283      <address><email>fielding@ics.uci.edu</email></address>
2284    </author>
2285    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2286      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2287      <address><email>frystyk@w3.org</email></address>
2288    </author>
2289    <date month="May" year="1996"/>
2290  </front>
2291  <seriesInfo name="RFC" value="1945"/>
2292</reference>
2293
2294<reference anchor="RFC2049">
2295  <front>
2296    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2297    <author initials="N." surname="Freed" fullname="Ned Freed">
2298      <organization>Innosoft International, Inc.</organization>
2299      <address><email>ned@innosoft.com</email></address>
2300    </author>
2301    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2302      <organization>First Virtual Holdings</organization>
2303      <address><email>nsb@nsb.fv.com</email></address>
2304    </author>
2305    <date month="November" year="1996"/>
2306  </front>
2307  <seriesInfo name="RFC" value="2049"/>
2308</reference>
2309
2310<reference anchor="RFC2068">
2311  <front>
2312    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2313    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2314      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2315      <address><email>fielding@ics.uci.edu</email></address>
2316    </author>
2317    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2318      <organization>MIT Laboratory for Computer Science</organization>
2319      <address><email>jg@w3.org</email></address>
2320    </author>
2321    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2322      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2323      <address><email>mogul@wrl.dec.com</email></address>
2324    </author>
2325    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2326      <organization>MIT Laboratory for Computer Science</organization>
2327      <address><email>frystyk@w3.org</email></address>
2328    </author>
2329    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2330      <organization>MIT Laboratory for Computer Science</organization>
2331      <address><email>timbl@w3.org</email></address>
2332    </author>
2333    <date month="January" year="1997"/>
2334  </front>
2335  <seriesInfo name="RFC" value="2068"/>
2336</reference>
2337
2338<reference anchor="RFC2076">
2339  <front>
2340    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2341    <author initials="J." surname="Palme" fullname="Jacob Palme">
2342      <organization>Stockholm University/KTH</organization>
2343      <address><email>jpalme@dsv.su.se</email></address>
2344    </author>
2345    <date month="February" year="1997"/>
2346  </front>
2347  <seriesInfo name="RFC" value="2076"/>
2348</reference>
2349
2350<reference anchor="RFC2183">
2351  <front>
2352    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2353    <author initials="R." surname="Troost" fullname="Rens Troost">
2354      <organization>New Century Systems</organization>
2355      <address><email>rens@century.com</email></address>
2356    </author>
2357    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2358      <organization>QUALCOMM Incorporated</organization>
2359      <address><email>sdorner@qualcomm.com</email></address>
2360    </author>
2361    <author initials="K." surname="Moore" fullname="Keith Moore">
2362      <organization>Department of Computer Science</organization>
2363      <address><email>moore@cs.utk.edu</email></address>
2364    </author>
2365    <date month="August" year="1997"/>
2366  </front>
2367  <seriesInfo name="RFC" value="2183"/>
2368</reference>
2369
2370<reference anchor="RFC2277">
2371  <front>
2372    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2373    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2374      <organization>UNINETT</organization>
2375      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
2376    </author>
2377    <date month="January" year="1998"/>
2378  </front>
2379  <seriesInfo name="BCP" value="18"/>
2380  <seriesInfo name="RFC" value="2277"/>
2381</reference>
2382
2383<reference anchor="RFC2388">
2384  <front>
2385    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2386    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2387      <organization>Xerox Palo Alto Research Center</organization>
2388      <address><email>masinter@parc.xerox.com</email></address>
2389    </author>
2390    <date year="1998" month="August"/>
2391  </front>
2392  <seriesInfo name="RFC" value="2388"/>
2393</reference>
2394
2395<reference anchor="RFC2557">
2396  <front>
2397    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2398    <author initials="F." surname="Palme" fullname="Jacob Palme">
2399      <organization>Stockholm University and KTH</organization>
2400      <address><email>jpalme@dsv.su.se</email></address>
2401    </author>
2402    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2403      <organization>Microsoft Corporation</organization>
2404      <address><email>alexhop@microsoft.com</email></address>
2405    </author>
2406    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2407      <organization>Lotus Development Corporation</organization>
2408      <address><email>Shelness@lotus.com</email></address>
2409    </author>
2410    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2411      <organization/>
2412      <address><email>stef@nma.com</email></address>
2413    </author>
2414    <date year="1999" month="March"/>
2415  </front>
2416  <seriesInfo name="RFC" value="2557"/>
2417</reference>
2418
2419<reference anchor="RFC2616">
2420  <front>
2421    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2422    <author initials="R." surname="Fielding" fullname="R. Fielding">
2423      <organization>University of California, Irvine</organization>
2424      <address><email>fielding@ics.uci.edu</email></address>
2425    </author>
2426    <author initials="J." surname="Gettys" fullname="J. Gettys">
2427      <organization>W3C</organization>
2428      <address><email>jg@w3.org</email></address>
2429    </author>
2430    <author initials="J." surname="Mogul" fullname="J. Mogul">
2431      <organization>Compaq Computer Corporation</organization>
2432      <address><email>mogul@wrl.dec.com</email></address>
2433    </author>
2434    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2435      <organization>MIT Laboratory for Computer Science</organization>
2436      <address><email>frystyk@w3.org</email></address>
2437    </author>
2438    <author initials="L." surname="Masinter" fullname="L. Masinter">
2439      <organization>Xerox Corporation</organization>
2440      <address><email>masinter@parc.xerox.com</email></address>
2441    </author>
2442    <author initials="P." surname="Leach" fullname="P. Leach">
2443      <organization>Microsoft Corporation</organization>
2444      <address><email>paulle@microsoft.com</email></address>
2445    </author>
2446    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2447      <organization>W3C</organization>
2448      <address><email>timbl@w3.org</email></address>
2449    </author>
2450    <date month="June" year="1999"/>
2451  </front>
2452  <seriesInfo name="RFC" value="2616"/>
2453</reference>
2454
2455<reference anchor="RFC3629">
2456  <front>
2457    <title>UTF-8, a transformation format of ISO 10646</title>
2458    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2459      <organization>Alis Technologies</organization>
2460      <address><email>fyergeau@alis.com</email></address>
2461    </author>
2462    <date month="November" year="2003"/>
2463  </front>
2464  <seriesInfo name="RFC" value="3629"/>
2465  <seriesInfo name="STD" value="63"/>
2466</reference>
2467
2468<reference anchor='RFC3864'>
2469  <front>
2470    <title>Registration Procedures for Message Header Fields</title>
2471    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2472      <organization>Nine by Nine</organization>
2473      <address><email>GK-IETF@ninebynine.org</email></address>
2474    </author>
2475    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2476      <organization>BEA Systems</organization>
2477      <address><email>mnot@pobox.com</email></address>
2478    </author>
2479    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2480      <organization>HP Labs</organization>
2481      <address><email>JeffMogul@acm.org</email></address>
2482    </author>
2483    <date year='2004' month='September' />
2484  </front>
2485  <seriesInfo name='BCP' value='90' />
2486  <seriesInfo name='RFC' value='3864' />
2487</reference>
2488
2489<reference anchor="RFC4288">
2490  <front>
2491    <title>Media Type Specifications and Registration Procedures</title>
2492    <author initials="N." surname="Freed" fullname="N. Freed">
2493      <organization>Sun Microsystems</organization>
2494      <address>
2495        <email>ned.freed@mrochek.com</email>
2496      </address>
2497    </author>
2498    <author initials="J." surname="Klensin" fullname="J. Klensin">
2499      <organization/>
2500      <address>
2501        <email>klensin+ietf@jck.com</email>
2502      </address>
2503    </author>
2504    <date year="2005" month="December"/>
2505  </front>
2506  <seriesInfo name="BCP" value="13"/>
2507  <seriesInfo name="RFC" value="4288"/>
2508</reference>
2509
2510<reference anchor='RFC5226'>
2511  <front>
2512    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2513    <author initials='T.' surname='Narten' fullname='T. Narten'>
2514      <organization>IBM</organization>
2515      <address><email>narten@us.ibm.com</email></address>
2516    </author>
2517    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
2518      <organization>Google</organization>
2519      <address><email>Harald@Alvestrand.no</email></address>
2520    </author>
2521    <date year='2008' month='May' />
2522  </front>
2523  <seriesInfo name='BCP' value='26' />
2524  <seriesInfo name='RFC' value='5226' />
2525</reference>
2526
2527<reference anchor="RFC5322">
2528  <front>
2529    <title>Internet Message Format</title>
2530    <author initials="P." surname="Resnick" fullname="P. Resnick">
2531      <organization>Qualcomm Incorporated</organization>
2532    </author>
2533    <date year="2008" month="October"/>
2534  </front> 
2535  <seriesInfo name="RFC" value="5322"/>
2536</reference>
2537
2538<reference anchor='BCP97'>
2539  <front>
2540    <title>Handling Normative References to Standards-Track Documents</title>
2541    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2542      <organization />
2543      <address>
2544        <email>klensin+ietf@jck.com</email>
2545      </address>
2546    </author>
2547    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2548      <organization>MIT</organization>
2549      <address>
2550        <email>hartmans-ietf@mit.edu</email>
2551      </address>
2552    </author>
2553    <date year='2007' month='June' />
2554  </front>
2555  <seriesInfo name='BCP' value='97' />
2556  <seriesInfo name='RFC' value='4897' />
2557</reference>
2558
2559
2560</references>
2561
2562<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2563<t>
2564   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
2565   allow entities to be transmitted in an open variety of
2566   representations and with extensible mechanisms. However, RFC 2045
2567   discusses mail, and HTTP has a few features that are different from
2568   those described in RFC 2045. These differences were carefully chosen
2569   to optimize performance over binary connections, to allow greater
2570   freedom in the use of new media types, to make date comparisons
2571   easier, and to acknowledge the practice of some early HTTP servers
2572   and clients.
2573</t>
2574<t>
2575   This appendix describes specific areas where HTTP differs from RFC
2576   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2577   aware of these differences and provide the appropriate conversions
2578   where necessary. Proxies and gateways from MIME environments to HTTP
2579   also need to be aware of the differences because some conversions
2580   might be required.
2581</t>
2582
2583<section title="MIME-Version" anchor="mime-version">
2584  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2585  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
2586  <x:anchor-alias value="MIME-Version"/>
2587  <x:anchor-alias value="MIME-Version-v"/>
2588<t>
2589   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2590   include a single MIME-Version general-header field to indicate what
2591   version of the MIME protocol was used to construct the message. Use
2592   of the MIME-Version header field indicates that the message is in
2593   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2594   Proxies/gateways are responsible for ensuring full compliance (where
2595   possible) when exporting HTTP messages to strict MIME environments.
2596</t>
2597<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
2598  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
2599  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2600</artwork></figure>
2601<t>
2602   MIME version "1.0" is the default for use in HTTP/1.1. However,
2603   HTTP/1.1 message parsing and semantics are defined by this document
2604   and not the MIME specification.
2605</t>
2606</section>
2607
2608<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2609<t>
2610   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2611   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2612   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2613   allowed for subtypes of the "text" media type when transmitted over
2614   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2615   line breaks as CRLF and forbids the use of CR or LF outside of line
2616   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2617   line break within text content when a message is transmitted over
2618   HTTP.
2619</t>
2620<t>
2621   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2622   environment &SHOULD; translate all line breaks within the text media
2623   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2624   canonical form of CRLF. Note, however, that this might be complicated
2625   by the presence of a Content-Encoding and by the fact that HTTP
2626   allows the use of some character sets which do not use octets 13 and
2627   10 to represent CR and LF, as is the case for some multi-byte
2628   character sets.
2629</t>
2630<t>
2631   Implementors should note that conversion will break any cryptographic
2632   checksums applied to the original content unless the original content
2633   is already in canonical form. Therefore, the canonical form is
2634   recommended for any content that uses such checksums in HTTP.
2635</t>
2636</section>
2637
2638
2639<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
2640<t>
2641   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2642   simplify the process of date comparison. Proxies and gateways from
2643   other protocols &SHOULD; ensure that any Date header field present in a
2644   message conforms to one of the HTTP/1.1 formats and rewrite the date
2645   if necessary.
2646</t>
2647</section>
2648
2649<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2650<t>
2651   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2652   Content-Encoding header field. Since this acts as a modifier on the
2653   media type, proxies and gateways from HTTP to MIME-compliant
2654   protocols &MUST; either change the value of the Content-Type header
2655   field or decode the entity-body before forwarding the message. (Some
2656   experimental applications of Content-Type for Internet mail have used
2657   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2658   a function equivalent to Content-Encoding. However, this parameter is
2659   not part of RFC 2045).
2660</t>
2661</section>
2662
2663<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2664<t>
2665   HTTP does not use the Content-Transfer-Encoding field of RFC
2666   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2667   remove any Content-Transfer-Encoding
2668   prior to delivering the response message to an HTTP client.
2669</t>
2670<t>
2671   Proxies and gateways from HTTP to MIME-compliant protocols are
2672   responsible for ensuring that the message is in the correct format
2673   and encoding for safe transport on that protocol, where "safe
2674   transport" is defined by the limitations of the protocol being used.
2675   Such a proxy or gateway &SHOULD; label the data with an appropriate
2676   Content-Transfer-Encoding if doing so will improve the likelihood of
2677   safe transport over the destination protocol.
2678</t>
2679</section>
2680
2681<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2682<t>
2683   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2684   Proxies/gateways &MUST; remove any transfer-coding prior to
2685   forwarding a message via a MIME-compliant protocol.
2686</t>
2687</section>
2688
2689<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2690<t>
2691   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2692   need to be aware of MIME line length limitations. Since HTTP does not
2693   have this limitation, HTTP does not fold long lines. MHTML messages
2694   being transported by HTTP follow all conventions of MHTML, including
2695   line length limitations and folding, canonicalization, etc., since
2696   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2697   does not interpret the content or any MIME header lines that might be
2698   contained therein.
2699</t>
2700</section>
2701</section>
2702
2703<section title="Additional Features" anchor="additional.features">
2704<t>
2705   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2706   existing HTTP implementations, but not consistently and correctly
2707   across most HTTP/1.1 applications. Implementors are advised to be
2708   aware of these features, but cannot rely upon their presence in, or
2709   interoperability with, other HTTP/1.1 applications. Some of these
2710   describe proposed experimental features, and some describe features
2711   that experimental deployment found lacking that are now addressed in
2712   the base HTTP/1.1 specification.
2713</t>
2714<t>
2715   A number of other headers, such as Content-Disposition and Title,
2716   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2717</t>
2718
2719<section title="Content-Disposition" anchor="content-disposition">
2720<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2721<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2722  <x:anchor-alias value="content-disposition"/>
2723  <x:anchor-alias value="content-disposition-v"/>
2724  <x:anchor-alias value="disposition-type"/>
2725  <x:anchor-alias value="disposition-parm"/>
2726  <x:anchor-alias value="disp-extension-parm"/>
2727  <x:anchor-alias value="disp-extension-token"/>
2728  <x:anchor-alias value="filename-parm"/>
2729<t>
2730   The Content-Disposition response-header field has been proposed as a
2731   means for the origin server to suggest a default filename if the user
2732   requests that the content is saved to a file. This usage is derived
2733   from the definition of Content-Disposition in <xref target="RFC2183"/>.
2734</t>
2735<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"/>
2736  <x:ref>content-disposition</x:ref> = "Content-Disposition" ":" <x:ref>OWS</x:ref>
2737                        <x:ref>content-disposition-v</x:ref>
2738  <x:ref>content-disposition-v</x:ref> = <x:ref>disposition-type</x:ref>
2739                          *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>disposition-parm</x:ref> )
2740  <x:ref>disposition-type</x:ref> = "attachment" / <x:ref>disp-extension-token</x:ref>
2741  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> / <x:ref>disp-extension-parm</x:ref>
2742  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2743  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
2744  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
2745</artwork></figure>
2746<t>
2747   An example is
2748</t>
2749<figure><artwork type="example">
2750  Content-Disposition: attachment; filename="fname.ext"
2751</artwork></figure>
2752<t>
2753   The receiving user agent &SHOULD-NOT;  respect any directory path
2754   information present in the filename-parm parameter, which is the only
2755   parameter believed to apply to HTTP implementations at this time. The
2756   filename &SHOULD; be treated as a terminal component only.
2757</t>
2758<t>
2759   If this header is used in a response with the application/octet-stream
2760   content-type, the implied suggestion is that the user agent
2761   should not display the response, but directly enter a `save response
2762   as...' dialog.
2763</t>
2764<t>
2765   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2766</t>
2767</section>
2768</section>
2769
2770<section title="Compatibility with Previous Versions" anchor="compatibility">
2771<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2772<t>
2773   Transfer-coding and message lengths all interact in ways that
2774   required fixing exactly when chunked encoding is used (to allow for
2775   transfer encoding that may not be self delimiting); it was important
2776   to straighten out exactly how message lengths are computed.
2777   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2778   <xref target="Part5"/> and <xref target="Part6"/>).
2779</t>
2780<t>
2781   Charset wildcarding is introduced to avoid explosion of character set
2782   names in accept headers. (<xref target="header.accept-charset"/>)
2783</t>
2784<t>
2785   Content-Base was deleted from the specification: it was not
2786   implemented widely, and there is no simple, safe way to introduce it
2787   without a robust extension mechanism. In addition, it is used in a
2788   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2789</t>
2790<t>
2791   A content-coding of "identity" was introduced, to solve problems
2792   discovered in caching. (<xref target="content.codings"/>)
2793</t>
2794<t>
2795   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
2796   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
2797   specification, but not commonly implemented. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.2"/>.
2798</t>
2799</section>
2800
2801<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2802<t>
2803  Clarify contexts that charset is used in.
2804  (<xref target="character.sets"/>)
2805</t>
2806<t>
2807  Remove reference to non-existant identity transfer-coding value tokens.
2808  (<xref target="no.content-transfer-encoding"/>)
2809</t>
2810</section>
2811
2812</section>
2813
2814<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
2815<figure>
2816<artwork type="abnf" name="p3-payload.parsed-abnf">
2817<x:ref>Accept</x:ref> = "Accept:" OWS Accept-v
2818<x:ref>Accept-Charset</x:ref> = "Accept-Charset:" OWS Accept-Charset-v
2819<x:ref>Accept-Charset-v</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
2820 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2821 qvalue ] ] )
2822<x:ref>Accept-Encoding</x:ref> = "Accept-Encoding:" OWS Accept-Encoding-v
2823<x:ref>Accept-Encoding-v</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
2824 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2825<x:ref>Accept-Language</x:ref> = "Accept-Language:" OWS Accept-Language-v
2826<x:ref>Accept-Language-v</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
2827 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2828 ] )
2829<x:ref>Accept-v</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2830 OWS media-range [ accept-params ] ] ) ]
2831
2832<x:ref>Content-Encoding</x:ref> = "Content-Encoding:" OWS Content-Encoding-v
2833<x:ref>Content-Encoding-v</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
2834 content-coding ] )
2835<x:ref>Content-Language</x:ref> = "Content-Language:" OWS Content-Language-v
2836<x:ref>Content-Language-v</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
2837 language-tag ] )
2838<x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in [Part1], Section 3.2&gt;
2839<x:ref>Content-Location</x:ref> = "Content-Location:" OWS Content-Location-v
2840<x:ref>Content-Location-v</x:ref> = absolute-URI / partial-URI
2841<x:ref>Content-MD5</x:ref> = "Content-MD5:" OWS Content-MD5-v
2842<x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2843<x:ref>Content-Range</x:ref> = &lt;Content-Range, defined in [Part5], Section 5.2&gt;
2844<x:ref>Content-Type</x:ref> = "Content-Type:" OWS Content-Type-v
2845<x:ref>Content-Type-v</x:ref> = media-type
2846
2847<x:ref>Expires</x:ref> = &lt;Expires, defined in [Part6], Section 3.3&gt;
2848
2849<x:ref>Last-Modified</x:ref> = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;
2850
2851<x:ref>MIME-Version</x:ref> = "MIME-Version:" OWS MIME-Version-v
2852<x:ref>MIME-Version-v</x:ref> = 1*DIGIT "." 1*DIGIT
2853
2854<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
2855
2856<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.6&gt;
2857<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
2858<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2859<x:ref>attribute</x:ref> = token
2860
2861<x:ref>charset</x:ref> = token
2862<x:ref>codings</x:ref> = ( content-coding / "*" )
2863<x:ref>content-coding</x:ref> = token
2864<x:ref>content-disposition</x:ref> = "Content-Disposition:" OWS
2865 content-disposition-v
2866<x:ref>content-disposition-v</x:ref> = disposition-type *( OWS ";" OWS
2867 disposition-parm )
2868
2869<x:ref>disp-extension-parm</x:ref> = token "=" ( token / quoted-string )
2870<x:ref>disp-extension-token</x:ref> = token
2871<x:ref>disposition-parm</x:ref> = filename-parm / disp-extension-parm
2872<x:ref>disposition-type</x:ref> = "attachment" / disp-extension-token
2873
2874<x:ref>entity-body</x:ref> = *OCTET
2875<x:ref>entity-header</x:ref> = Content-Encoding / Content-Language / Content-Length
2876 / Content-Location / Content-MD5 / Content-Range / Content-Type /
2877 Expires / Last-Modified / extension-header
2878<x:ref>extension-header</x:ref> = header-field
2879
2880<x:ref>filename-parm</x:ref> = "filename=" quoted-string
2881
2882<x:ref>header-field</x:ref> = &lt;header-field, defined in [Part1], Section 2.7.2&gt;
2883
2884<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
2885<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC4646bis], Section 2.1&gt;
2886
2887<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
2888 ";" OWS parameter )
2889<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2890
2891<x:ref>parameter</x:ref> = attribute "=" value
2892<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.6&gt;
2893
2894<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
2895<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 2.10.4&gt;
2896
2897<x:ref>subtype</x:ref> = token
2898
2899<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2900<x:ref>type</x:ref> = token
2901
2902<x:ref>value</x:ref> = token / quoted-string
2903</artwork>
2904</figure>
2905<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2906; Accept defined but not used
2907; Accept-Charset defined but not used
2908; Accept-Encoding defined but not used
2909; Accept-Language defined but not used
2910; MIME-Version defined but not used
2911; content-disposition defined but not used
2912; entity-body defined but not used
2913; entity-header defined but not used
2914</artwork></figure></section>
2915
2916<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2917
2918<section title="Since RFC2616">
2919<t>
2920  Extracted relevant partitions from <xref target="RFC2616"/>.
2921</t>
2922</section>
2923
2924<section title="Since draft-ietf-httpbis-p3-payload-00">
2925<t>
2926  Closed issues:
2927  <list style="symbols"> 
2928    <t>
2929      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
2930      "Media Type Registrations"
2931      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
2932    </t>
2933    <t>
2934      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/14"/>:
2935      "Clarification regarding quoting of charset values"
2936      (<eref target="http://purl.org/NET/http-errata#charactersets"/>)
2937    </t>
2938    <t>
2939      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
2940      "Remove 'identity' token references"
2941      (<eref target="http://purl.org/NET/http-errata#identity"/>)
2942    </t>
2943    <t>
2944      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/25"/>:
2945      "Accept-Encoding BNF"
2946    </t>
2947    <t>
2948      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2949      "Normative and Informative references"
2950    </t>
2951    <t>
2952      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
2953      "RFC1700 references"
2954    </t>
2955    <t>
2956      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
2957      "Updating to RFC4288"
2958    </t>
2959    <t>
2960      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2961      "Informative references"
2962    </t>
2963    <t>
2964      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
2965      "ISO-8859-1 Reference"
2966    </t>
2967    <t>
2968      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
2969      "Encoding References Normative"
2970    </t>
2971    <t>
2972      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
2973      "Normative up-to-date references"
2974    </t>
2975  </list>
2976</t>
2977</section>
2978
2979<section title="Since draft-ietf-httpbis-p3-payload-01">
2980<t>
2981  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2982  <list style="symbols"> 
2983    <t>
2984      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2985    </t>
2986  </list>
2987</t>
2988</section>
2989
2990<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2991<t>
2992  Closed issues:
2993  <list style="symbols"> 
2994    <t>
2995      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
2996      "Quoting Charsets"
2997    </t>
2998    <t>
2999      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
3000      "Classification for Allow header"
3001    </t>
3002    <t>
3003      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/115"/>:
3004      "missing default for qvalue in description of Accept-Encoding"
3005    </t>
3006  </list>
3007</t>
3008<t>
3009  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
3010  <list style="symbols"> 
3011    <t>
3012      Reference RFC 3984, and update header registrations for headers defined
3013      in this document.
3014    </t>
3015  </list>
3016</t>
3017</section>
3018
3019<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
3020<t>
3021  Closed issues:
3022  <list style="symbols"> 
3023    <t>
3024      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/67"/>:
3025      "Quoting Charsets"
3026    </t>
3027    <t>
3028      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/113"/>:
3029      "language tag matching (Accept-Language) vs RFC4647"
3030    </t>
3031    <t>
3032      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/121"/>:
3033      "RFC 1806 has been replaced by RFC2183"
3034    </t>
3035  </list>
3036</t>
3037<t>
3038  Other changes:
3039  <list style="symbols"> 
3040    <t>
3041      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/68"/>:
3042      "Encoding References Normative" -- rephrase the annotation and reference
3043      <xref target="BCP97"/>.
3044    </t>
3045  </list>
3046</t>
3047 </section>
3048
3049<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
3050<t>
3051  Closed issues:
3052  <list style="symbols"> 
3053    <t>
3054      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
3055      "RFC 2822 is updated by RFC 5322"
3056    </t>
3057  </list>
3058</t>
3059<t>
3060  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3061  <list style="symbols"> 
3062    <t>
3063      Use "/" instead of "|" for alternatives.
3064    </t>
3065    <t>
3066      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
3067      whitespace ("OWS") and required whitespace ("RWS").
3068    </t>
3069    <t>
3070      Rewrite ABNFs to spell out whitespace rules, factor out
3071      header value format definitions.
3072    </t>
3073  </list>
3074</t>
3075</section>
3076
3077<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
3078<t>
3079  Closed issues:
3080  <list style="symbols"> 
3081    <t>
3082      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
3083      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
3084    </t>
3085  </list>
3086</t>
3087<t>
3088  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3089  <list style="symbols"> 
3090    <t>
3091      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
3092    </t>
3093  </list>
3094</t>
3095<t>
3096  Other changes:
3097  <list style="symbols"> 
3098    <t>
3099      Move definition of quality values into Part 1.
3100    </t>
3101  </list>
3102</t>
3103</section>
3104
3105<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
3106<t>
3107  Closed issues:
3108  <list style="symbols"> 
3109    <t>
3110      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/80"/>:
3111      "Content-Location isn't special"
3112    </t>
3113    <t>
3114      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3115      "Content Sniffing"
3116    </t>
3117  </list>
3118</t>
3119</section>
3120
3121<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
3122<t>
3123  Closed issues:
3124  <list style="symbols"> 
3125    <t>
3126      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/13"/>:
3127      "Updated reference for language tags"
3128    </t>
3129    <t>
3130      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/155"/>:
3131      "Content Sniffing"
3132    </t>
3133    <t>
3134      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
3135      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
3136    </t>
3137  </list>
3138</t>
3139<t>
3140  Partly resolved issues:
3141  <list style="symbols"> 
3142    <t>
3143      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
3144      "update IANA requirements wrt Transfer-Coding values" (add the
3145      IANA Considerations subsection)
3146    </t>
3147    <t>
3148      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/149"/>:
3149      "update IANA requirements wrt Content-Coding values" (add the
3150      IANA Considerations subsection)
3151    </t>
3152  </list>
3153</t>
3154</section>
3155
3156</section>
3157
3158</back>
3159</rfc>
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