source: draft-ietf-httpbis/latest/p3-payload.xml @ 251

Last change on this file since 251 was 251, checked in by julian.reschke@…, 14 years ago

Resolve #67: media-range: token and quoted-string notation for parameters is equivalent (closes #67).

  • Property svn:eol-style set to native
File size: 112.5 KB
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=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "May">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY notation-abnf            "<xref target='Part1' x:rel='#notation.abnf' xmlns:x=''/>">
18  <!ENTITY basic-rules              "<xref target='Part1' x:rel='#basic.rules' xmlns:x=''/>">
19  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x=''/>">
20  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x=''/>">
21  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x=''/>">
22  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x=''/>">
23  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x=''/>">
24  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x=''/>">
25  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x=''/>">
26  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x=''/>">
27  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x=''/>">
28  <!ENTITY message-length           "<xref target='Part1' x:rel='#message.length' xmlns:x=''/>">
29  <!ENTITY message-headers          "<xref target='Part1' x:rel='#message.headers' xmlns:x=''/>">
30  <!ENTITY general-syntax           "<xref target='Part1' x:rel='#general.syntax' xmlns:x=''/>">
31  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='' xmlns:x=''/>">
33<?rfc toc="yes" ?>
34<?rfc symrefs="yes" ?>
35<?rfc sortrefs="yes" ?>
36<?rfc compact="yes"?>
37<?rfc subcompact="no" ?>
38<?rfc linkmailto="no" ?>
39<?rfc editing="no" ?>
40<?rfc comments="yes"?>
41<?rfc inline="yes"?>
42<?rfc-ext allow-markup-in-artwork="yes" ?>
43<?rfc-ext include-references-in-index="yes" ?>
44<rfc obsoletes="2616" category="std"
45     ipr="full3978" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
46     xmlns:x=''>
49  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
51  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
52    <organization abbrev="Day Software">Day Software</organization>
53    <address>
54      <postal>
55        <street>23 Corporate Plaza DR, Suite 280</street>
56        <city>Newport Beach</city>
57        <region>CA</region>
58        <code>92660</code>
59        <country>USA</country>
60      </postal>
61      <phone>+1-949-706-5300</phone>
62      <facsimile>+1-949-706-5305</facsimile>
63      <email></email>
64      <uri></uri>
65    </address>
66  </author>
68  <author initials="J." surname="Gettys" fullname="Jim Gettys">
69    <organization>One Laptop per Child</organization>
70    <address>
71      <postal>
72        <street>21 Oak Knoll Road</street>
73        <city>Carlisle</city>
74        <region>MA</region>
75        <code>01741</code>
76        <country>USA</country>
77      </postal>
78      <email></email>
79      <uri></uri>
80    </address>
81  </author>
83  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
84    <organization abbrev="HP">Hewlett-Packard Company</organization>
85    <address>
86      <postal>
87        <street>HP Labs, Large Scale Systems Group</street>
88        <street>1501 Page Mill Road, MS 1177</street>
89        <city>Palo Alto</city>
90        <region>CA</region>
91        <code>94304</code>
92        <country>USA</country>
93      </postal>
94      <email></email>
95    </address>
96  </author>
98  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
99    <organization abbrev="Microsoft">Microsoft Corporation</organization>
100    <address>
101      <postal>
102        <street>1 Microsoft Way</street>
103        <city>Redmond</city>
104        <region>WA</region>
105        <code>98052</code>
106        <country>USA</country>
107      </postal>
108      <email></email>
109    </address>
110  </author>
112  <author initials="L." surname="Masinter" fullname="Larry Masinter">
113    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
114    <address>
115      <postal>
116        <street>345 Park Ave</street>
117        <city>San Jose</city>
118        <region>CA</region>
119        <code>95110</code>
120        <country>USA</country>
121      </postal>
122      <email></email>
123      <uri></uri>
124    </address>
125  </author>
127  <author initials="P." surname="Leach" fullname="Paul J. Leach">
128    <organization abbrev="Microsoft">Microsoft Corporation</organization>
129    <address>
130      <postal>
131        <street>1 Microsoft Way</street>
132        <city>Redmond</city>
133        <region>WA</region>
134        <code>98052</code>
135      </postal>
136      <email></email>
137    </address>
138  </author>
140  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
141    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
142    <address>
143      <postal>
144        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
145        <street>The Stata Center, Building 32</street>
146        <street>32 Vassar Street</street>
147        <city>Cambridge</city>
148        <region>MA</region>
149        <code>02139</code>
150        <country>USA</country>
151      </postal>
152      <email></email>
153      <uri></uri>
154    </address>
155  </author>
157  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
158    <organization abbrev="W3C">World Wide Web Consortium</organization>
159    <address>
160      <postal>
161        <street>W3C / ERCIM</street>
162        <street>2004, rte des Lucioles</street>
163        <city>Sophia-Antipolis</city>
164        <region>AM</region>
165        <code>06902</code>
166        <country>France</country>
167      </postal>
168      <email></email>
169      <uri></uri>
170    </address>
171  </author>
173  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
174    <organization abbrev="greenbytes">greenbytes GmbH</organization>
175    <address>
176      <postal>
177        <street>Hafenweg 16</street>
178        <city>Muenster</city><region>NW</region><code>48155</code>
179        <country>Germany</country>
180      </postal>
181      <phone>+49 251 2807760</phone>   
182      <facsimile>+49 251 2807761</facsimile>   
183      <email></email>       
184      <uri></uri>     
185    </address>
186  </author>
188  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
192   The Hypertext Transfer Protocol (HTTP) is an application-level
193   protocol for distributed, collaborative, hypermedia information
194   systems. HTTP has been in use by the World Wide Web global information
195   initiative since 1990. This document is Part 3 of the seven-part specification
196   that defines the protocol referred to as "HTTP/1.1" and, taken together,
197   obsoletes RFC 2616.  Part 3 defines HTTP message content,
198   metadata, and content negotiation.
202<note title="Editorial Note (To be removed by RFC Editor)">
203  <t>
204    Discussion of this draft should take place on the HTTPBIS working group
205    mailing list ( The current issues list is
206    at <eref target=""/>
207    and related documents (including fancy diffs) can be found at
208    <eref target=""/>.
209  </t>
210  <t>
211    This draft incorporates those issue resolutions that were either
212    collected in the original RFC2616 errata list (<eref target=""/>),
213    or which were agreed upon on the mailing list between October 2006 and
214    November 2007 (as published in "draft-lafon-rfc2616bis-03").
215  </t>
219<section title="Introduction" anchor="introduction">
221   This document defines HTTP/1.1 message payloads (a.k.a., content), the
222   associated metadata header fields that define how the payload is intended
223   to be interpreted by a recipient, the request header fields that
224   may influence content selection, and the various selection algorithms
225   that are collectively referred to as HTTP content negotiation.
228   This document is currently disorganized in order to minimize the changes
229   between drafts and enable reviewers to see the smaller errata changes.
230   The next draft will reorganize the sections to better reflect the content.
231   In particular, the sections on entities will be renamed payload and moved
232   to the first half of the document, while the sections on content negotiation
233   and associated request header fields will be moved to the second half.  The
234   current mess reflects how widely dispersed these topics and associated
235   requirements had become in <xref target="RFC2616"/>.
238<section title="Requirements" anchor="intro.requirements">
240   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
241   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
242   document are to be interpreted as described in <xref target="RFC2119"/>.
245   An implementation is not compliant if it fails to satisfy one or more
246   of the &MUST; or &REQUIRED; level requirements for the protocols it
247   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
248   level and all the &SHOULD; level requirements for its protocols is said
249   to be "unconditionally compliant"; one that satisfies all the &MUST;
250   level requirements but not all the &SHOULD; level requirements for its
251   protocols is said to be "conditionally compliant."
256<section title="Notational Conventions and Generic Grammar" anchor="notation">
257  <x:anchor-alias value="ALPHA"/>
258  <x:anchor-alias value="DIGIT"/>
259  <x:anchor-alias value="OCTET"/>
260  <x:anchor-alias value="quoted-string"/>
261  <x:anchor-alias value="token"/>
263  This specification uses the ABNF syntax defined in &notation-abnf; and
264  the core rules defined in &basic-rules;:
265  <cref anchor="abnf.dep">ABNF syntax and basic rules will be adopted from RFC 5234, see
266  <eref target=""/>.</cref>
268<figure><artwork type="abnf2616">
269  <x:ref>ALPHA</x:ref>          = &lt;ALPHA, defined in &basic-rules;&gt;
270  <x:ref>DIGIT</x:ref>          = &lt;DIGIT, defined in &basic-rules;&gt;
271  <x:ref>OCTET</x:ref>          = &lt;OCTET, defined in &basic-rules;&gt;
273<figure><artwork type="abnf2616">
274  <x:ref>quoted-string</x:ref>  = &lt;quoted-string, defined in &basic-rules;&gt;
275  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
277<t anchor="abnf.dependencies">
278  <x:anchor-alias value="absoluteURI"/>
279  <x:anchor-alias value="Allow"/>
280  <x:anchor-alias value="Content-Length"/>
281  <x:anchor-alias value="Content-Range"/>
282  <x:anchor-alias value="Expires"/>
283  <x:anchor-alias value="Last-Modified"/>
284  <x:anchor-alias value="message-header"/>
285  <x:anchor-alias value="relativeURI"/>
286  The ABNF rules below are defined in other parts:
288<figure><!--Part1--><artwork type="abnf2616">
289  <x:ref>absoluteURI</x:ref>    = &lt;absoluteURI, defined in &general-syntax;&gt;
290  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
291  <x:ref>relativeURI</x:ref>    = &lt;relativeURI, defined in &general-syntax;&gt;
292  <x:ref>message-header</x:ref> = &lt;message-header, defined in &message-headers;&gt;
294<figure><!--Part4--><artwork type="abnf2616">
295  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
297<figure><!--Part5--><artwork type="abnf2616">
298  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
300<figure><!--Part6--><artwork type="abnf2616">
301  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
305<section title="Protocol Parameters" anchor="protocol.parameters">
307<section title="Character Sets" anchor="character.sets">
309   HTTP uses the same definition of the term "character set" as that
310   described for MIME:
313   The term "character set" is used in this document to refer to a
314   method used with one or more tables to convert a sequence of octets
315   into a sequence of characters. Note that unconditional conversion in
316   the other direction is not required, in that not all characters may
317   be available in a given character set and a character set may provide
318   more than one sequence of octets to represent a particular character.
319   This definition is intended to allow various kinds of character
320   encoding, from simple single-table mappings such as US-ASCII to
321   complex table switching methods such as those that use ISO-2022's
322   techniques. However, the definition associated with a MIME character
323   set name &MUST; fully specify the mapping to be performed from octets
324   to characters. In particular, use of external profiling information
325   to determine the exact mapping is not permitted.
328      <x:h>Note:</x:h> This use of the term "character set" is more commonly
329      referred to as a "character encoding." However, since HTTP and
330      MIME share the same registry, it is important that the terminology
331      also be shared.
333<t anchor="rule.charset">
334  <x:anchor-alias value="charset"/>
335   HTTP character sets are identified by case-insensitive tokens. The
336   complete set of tokens is defined by the IANA Character Set registry
337   (<eref target=""/>).
339<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
340  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
343   Although HTTP allows an arbitrary token to be used as a charset
344   value, any token that has a predefined value within the IANA
345   Character Set registry &MUST; represent the character set defined
346   by that registry. Applications &SHOULD; limit their use of character
347   sets to those defined by the IANA registry.
350   HTTP uses charset in two contexts: within an Accept-Charset request
351   header (in which the charset value is an unquoted token) and as the
352   value of a parameter in a Content-Type header (within a request or
353   response), in which case the parameter value of the charset parameter
354   may be quoted.
357   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
358   <xref target="RFC2277"/>.
361<section title="Missing Charset" anchor="missing.charset">
363   Some HTTP/1.0 software has interpreted a Content-Type header without
364   charset parameter incorrectly to mean "recipient should guess."
365   Senders wishing to defeat this behavior &MAY; include a charset
366   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
367   it is known that it will not confuse the recipient.
370   Unfortunately, some older HTTP/1.0 clients did not deal properly with
371   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
372   charset label provided by the sender; and those user agents that have
373   a provision to "guess" a charset &MUST; use the charset from the
374   content-type field if they support that charset, rather than the
375   recipient's preference, when initially displaying a document. See
376   <xref target="canonicalization.and.text.defaults"/>.
381<section title="Content Codings" anchor="content.codings">
382  <x:anchor-alias value="content-coding"/>
384   Content coding values indicate an encoding transformation that has
385   been or can be applied to an entity. Content codings are primarily
386   used to allow a document to be compressed or otherwise usefully
387   transformed without losing the identity of its underlying media type
388   and without loss of information. Frequently, the entity is stored in
389   coded form, transmitted directly, and only decoded by the recipient.
391<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
392  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
395   All content-coding values are case-insensitive. HTTP/1.1 uses
396   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
397   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
398   describes the content-coding, what is more important is that it
399   indicates what decoding mechanism will be required to remove the
400   encoding.
403   The Internet Assigned Numbers Authority (IANA) acts as a registry for
404   content-coding value tokens. Initially, the registry contains the
405   following tokens:
408   gzip<iref item="gzip"/>
409  <list>
410    <t>
411        An encoding format produced by the file compression program
412        "gzip" (GNU zip) as described in <xref target="RFC1952"/>. This format is a
413        Lempel-Ziv coding (LZ77) with a 32 bit CRC.
414    </t>
415  </list>
418   compress<iref item="compress"/>
419  <list><t>
420        The encoding format produced by the common UNIX file compression
421        program "compress". This format is an adaptive Lempel-Ziv-Welch
422        coding (LZW).
424        Use of program names for the identification of encoding formats
425        is not desirable and is discouraged for future encodings. Their
426        use here is representative of historical practice, not good
427        design. For compatibility with previous implementations of HTTP,
428        applications &SHOULD; consider "x-gzip" and "x-compress" to be
429        equivalent to "gzip" and "compress" respectively.
430  </t></list>
433   deflate<iref item="deflate"/>
434  <list><t>
435        The "zlib" format defined in <xref target="RFC1950"/> in combination with
436        the "deflate" compression mechanism described in <xref target="RFC1951"/>.
437  </t></list>
440   identity<iref item="identity"/>
441  <list><t>
442        The default (identity) encoding; the use of no transformation
443        whatsoever. This content-coding is used only in the Accept-Encoding
444        header, and &SHOULD-NOT;  be used in the Content-Encoding
445        header.
446  </t></list>
449   New content-coding value tokens &SHOULD; be registered; to allow
450   interoperability between clients and servers, specifications of the
451   content coding algorithms needed to implement a new value &SHOULD; be
452   publicly available and adequate for independent implementation, and
453   conform to the purpose of content coding defined in this section.
457<section title="Media Types" anchor="media.types">
458  <x:anchor-alias value="media-type"/>
459  <x:anchor-alias value="type"/>
460  <x:anchor-alias value="subtype"/>
462   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
463   and Accept (<xref target="header.accept"/>) header fields in order to provide
464   open and extensible data typing and type negotiation.
466<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"/>
467  <x:ref>media-type</x:ref>     = <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> *( ";" <x:ref>parameter</x:ref> )
468  <x:ref>type</x:ref>           = <x:ref>token</x:ref>
469  <x:ref>subtype</x:ref>        = <x:ref>token</x:ref>
471<t anchor="rule.parameter">
472  <x:anchor-alias value="attribute"/>
473  <x:anchor-alias value="parameter"/>
474  <x:anchor-alias value="value"/>
475   Parameters &MAY; follow the type/subtype in the form of attribute/value
476   pairs.
478<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"/>
479  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
480  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
481  <x:ref>value</x:ref>          = <x:ref>token</x:ref> | <x:ref>quoted-string</x:ref>
484   The type, subtype, and parameter attribute names are case-insensitive.
485   Parameter values might or might not be case-sensitive,
486   depending on the semantics of the parameter name. Linear white space
487   (LWS) &MUST-NOT; be used between the type and subtype, nor between an
488   attribute and its value. The presence or absence of a parameter might
489   be significant to the processing of a media-type, depending on its
490   definition within the media type registry.
493   All parameters defined as a token are also allowed to occur as quoted-string;
494   both notations are equivalent.
497   Note that some older HTTP applications do not recognize media type
498   parameters. When sending data to older HTTP applications,
499   implementations &SHOULD; only use media type parameters when they are
500   required by that type/subtype definition.
503   Media-type values are registered with the Internet Assigned Number
504   Authority (IANA). The media type registration process is
505   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
506   discouraged.
509<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
511   Internet media types are registered with a canonical form. An
512   entity-body transferred via HTTP messages &MUST; be represented in the
513   appropriate canonical form prior to its transmission except for
514   "text" types, as defined in the next paragraph.
517   When in canonical form, media subtypes of the "text" type use CRLF as
518   the text line break. HTTP relaxes this requirement and allows the
519   transport of text media with plain CR or LF alone representing a line
520   break when it is done consistently for an entire entity-body. HTTP
521   applications &MUST; accept CRLF, bare CR, and bare LF as being
522   representative of a line break in text media received via HTTP. In
523   addition, if the text is represented in a character set that does not
524   use octets 13 and 10 for CR and LF respectively, as is the case for
525   some multi-byte character sets, HTTP allows the use of whatever octet
526   sequences are defined by that character set to represent the
527   equivalent of CR and LF for line breaks. This flexibility regarding
528   line breaks applies only to text media in the entity-body; a bare CR
529   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
530   structures (such as header fields and multipart boundaries).
533   If an entity-body is encoded with a content-coding, the underlying
534   data &MUST; be in a form defined above prior to being encoded.
537   The "charset" parameter is used with some media types to define the
538   character set (<xref target="character.sets"/>) of the data. When no explicit charset
539   parameter is provided by the sender, media subtypes of the "text"
540   type are defined to have a default charset value of "ISO-8859-1" when
541   received via HTTP. Data in character sets other than "ISO-8859-1" or
542   its subsets &MUST; be labeled with an appropriate charset value. See
543   <xref target="missing.charset"/> for compatibility problems.
547<section title="Multipart Types" anchor="multipart.types">
549   MIME provides for a number of "multipart" types -- encapsulations of
550   one or more entities within a single message-body. All multipart
551   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
552   and &MUST; include a boundary parameter as part of the media type
553   value. The message body is itself a protocol element and &MUST;
554   therefore use only CRLF to represent line breaks between body-parts.
555   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
556   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
557   original multipart contains an epilogue). These restrictions exist in
558   order to preserve the self-delimiting nature of a multipart message-body,
559   wherein the "end" of the message-body is indicated by the
560   ending multipart boundary.
563   In general, HTTP treats a multipart message-body no differently than
564   any other media type: strictly as payload. The one exception is the
565   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
566   (Partial Content) response.
567   <!-- jre: re-insert removed text pointing to caching? -->
568   In all
569   other cases, an HTTP user agent &SHOULD; follow the same or similar
570   behavior as a MIME user agent would upon receipt of a multipart type.
571   The MIME header fields within each body-part of a multipart message-body
572   do not have any significance to HTTP beyond that defined by
573   their MIME semantics.
576   In general, an HTTP user agent &SHOULD; follow the same or similar
577   behavior as a MIME user agent would upon receipt of a multipart type.
578   If an application receives an unrecognized multipart subtype, the
579   application &MUST; treat it as being equivalent to "multipart/mixed".
582      <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
583      for carrying form data suitable for processing via the POST
584      request method, as described in <xref target="RFC2388"/>.
589<section title="Quality Values" anchor="quality.values">
590  <x:anchor-alias value="qvalue"/>
592   HTTP content negotiation (<xref target="content.negotiation"/>) uses short "floating point"
593   numbers to indicate the relative importance ("weight") of various
594   negotiable parameters.  A weight is normalized to a real number in
595   the range 0 through 1, where 0 is the minimum and 1 the maximum
596   value. If a parameter has a quality value of 0, then content with
597   this parameter is `not acceptable' for the client. HTTP/1.1
598   applications &MUST-NOT; generate more than three digits after the
599   decimal point. User configuration of these values &SHOULD; also be
600   limited in this fashion.
602<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
603  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
604                 | ( "1" [ "." 0*3("0") ] )
607   "Quality values" is a misnomer, since these values merely represent
608   relative degradation in desired quality.
612<section title="Language Tags" anchor="language.tags">
613  <x:anchor-alias value="language-tag"/>
614  <x:anchor-alias value="primary-tag"/>
615  <x:anchor-alias value="subtag"/>
617   A language tag identifies a natural language spoken, written, or
618   otherwise conveyed by human beings for communication of information
619   to other human beings. Computer languages are explicitly excluded.
620   HTTP uses language tags within the Accept-Language and Content-Language
621   fields.
624   The syntax and registry of HTTP language tags is the same as that
625   defined by <xref target="RFC1766"/>. In summary, a language tag is composed of 1
626   or more parts: A primary language tag and a possibly empty series of
627   subtags:
629<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/><iref primary="true" item="Grammar" subitem="primary-tag"/><iref primary="true" item="Grammar" subitem="subtag"/>
630  <x:ref>language-tag</x:ref>  = <x:ref>primary-tag</x:ref> *( "-" <x:ref>subtag</x:ref> )
631  <x:ref>primary-tag</x:ref>   = 1*8<x:ref>ALPHA</x:ref>
632  <x:ref>subtag</x:ref>        = 1*8<x:ref>ALPHA</x:ref>
635   White space is not allowed within the tag and all tags are case-insensitive.
636   The name space of language tags is administered by the
637   IANA. Example tags include:
639<figure><artwork type="example">
640    en, en-US, en-cockney, i-cherokee, x-pig-latin
643   where any two-letter primary-tag is an ISO-639 language abbreviation
644   and any two-letter initial subtag is an ISO-3166 country code. (The
645   last three tags above are not registered tags; all but the last are
646   examples of tags which could be registered in future.)
651<section title="Entity" anchor="entity">
653   Request and Response messages &MAY; transfer an entity if not otherwise
654   restricted by the request method or response status code. An entity
655   consists of entity-header fields and an entity-body, although some
656   responses will only include the entity-headers.
659   In this section, both sender and recipient refer to either the client
660   or the server, depending on who sends and who receives the entity.
663<section title="Entity Header Fields" anchor="entity.header.fields">
664  <x:anchor-alias value="entity-header"/>
665  <x:anchor-alias value="extension-header"/>
667   Entity-header fields define metainformation about the entity-body or,
668   if no body is present, about the resource identified by the request.
670<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
671  <x:ref>entity-header</x:ref>  = <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
672                 | <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
673                 | <x:ref>Content-Length</x:ref>           ; &header-content-length;
674                 | <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
675                 | <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
676                 | <x:ref>Content-Range</x:ref>            ; &header-content-range;
677                 | <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
678                 | <x:ref>Expires</x:ref>                  ; &header-expires;
679                 | <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
680                 | <x:ref>extension-header</x:ref>
682  <x:ref>extension-header</x:ref> = <x:ref>message-header</x:ref>
685   The extension-header mechanism allows additional entity-header fields
686   to be defined without changing the protocol, but these fields cannot
687   be assumed to be recognizable by the recipient. Unrecognized header
688   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
689   transparent proxies.
693<section title="Entity Body" anchor="entity.body">
694  <x:anchor-alias value="entity-body"/>
696   The entity-body (if any) sent with an HTTP request or response is in
697   a format and encoding defined by the entity-header fields.
699<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
700  <x:ref>entity-body</x:ref>    = *<x:ref>OCTET</x:ref>
703   An entity-body is only present in a message when a message-body is
704   present, as described in &message-body;. The entity-body is obtained
705   from the message-body by decoding any Transfer-Encoding that might
706   have been applied to ensure safe and proper transfer of the message.
709<section title="Type" anchor="type">
711   When an entity-body is included with a message, the data type of that
712   body is determined via the header fields Content-Type and Content-Encoding.
713   These define a two-layer, ordered encoding model:
715<figure><artwork type="example">
716    entity-body := Content-Encoding( Content-Type( data ) )
719   Content-Type specifies the media type of the underlying data.
720   Content-Encoding may be used to indicate any additional content
721   codings applied to the data, usually for the purpose of data
722   compression, that are a property of the requested resource. There is
723   no default encoding.
726   Any HTTP/1.1 message containing an entity-body &SHOULD; include a
727   Content-Type header field defining the media type of that body. If
728   and only if the media type is not given by a Content-Type field, the
729   recipient &MAY; attempt to guess the media type via inspection of its
730   content and/or the name extension(s) of the URI used to identify the
731   resource. If the media type remains unknown, the recipient &SHOULD;
732   treat it as type "application/octet-stream".
736<section title="Entity Length" anchor="entity.length">
738   The entity-length of a message is the length of the message-body
739   before any transfer-codings have been applied. &message-length; defines
740   how the transfer-length of a message-body is determined.
746<section title="Content Negotiation" anchor="content.negotiation">
748   Most HTTP responses include an entity which contains information for
749   interpretation by a human user. Naturally, it is desirable to supply
750   the user with the "best available" entity corresponding to the
751   request. Unfortunately for servers and caches, not all users have the
752   same preferences for what is "best," and not all user agents are
753   equally capable of rendering all entity types. For that reason, HTTP
754   has provisions for several mechanisms for "content negotiation" --
755   the process of selecting the best representation for a given response
756   when there are multiple representations available.
757  <list><t>
758      <x:h>Note:</x:h> This is not called "format negotiation" because the
759      alternate representations may be of the same media type, but use
760      different capabilities of that type, be in different languages,
761      etc.
762  </t></list>
765   Any response containing an entity-body &MAY; be subject to negotiation,
766   including error responses.
769   There are two kinds of content negotiation which are possible in
770   HTTP: server-driven and agent-driven negotiation. These two kinds of
771   negotiation are orthogonal and thus may be used separately or in
772   combination. One method of combination, referred to as transparent
773   negotiation, occurs when a cache uses the agent-driven negotiation
774   information provided by the origin server in order to provide
775   server-driven negotiation for subsequent requests.
778<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
780   If the selection of the best representation for a response is made by
781   an algorithm located at the server, it is called server-driven
782   negotiation. Selection is based on the available representations of
783   the response (the dimensions over which it can vary; e.g. language,
784   content-coding, etc.) and the contents of particular header fields in
785   the request message or on other information pertaining to the request
786   (such as the network address of the client).
789   Server-driven negotiation is advantageous when the algorithm for
790   selecting from among the available representations is difficult to
791   describe to the user agent, or when the server desires to send its
792   "best guess" to the client along with the first response (hoping to
793   avoid the round-trip delay of a subsequent request if the "best
794   guess" is good enough for the user). In order to improve the server's
795   guess, the user agent &MAY; include request header fields (Accept,
796   Accept-Language, Accept-Encoding, etc.) which describe its
797   preferences for such a response.
800   Server-driven negotiation has disadvantages:
801  <list style="numbers">
802    <t>
803         It is impossible for the server to accurately determine what
804         might be "best" for any given user, since that would require
805         complete knowledge of both the capabilities of the user agent
806         and the intended use for the response (e.g., does the user want
807         to view it on screen or print it on paper?).
808    </t>
809    <t>
810         Having the user agent describe its capabilities in every
811         request can be both very inefficient (given that only a small
812         percentage of responses have multiple representations) and a
813         potential violation of the user's privacy.
814    </t>
815    <t>
816         It complicates the implementation of an origin server and the
817         algorithms for generating responses to a request.
818    </t>
819    <t>
820         It may limit a public cache's ability to use the same response
821         for multiple user's requests.
822    </t>
823  </list>
826   HTTP/1.1 includes the following request-header fields for enabling
827   server-driven negotiation through description of user agent
828   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
829   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
830   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;). However, an
831   origin server is not limited to these dimensions and &MAY; vary the
832   response based on any aspect of the request, including information
833   outside the request-header fields or within extension header fields
834   not defined by this specification.
837   The Vary header field (&header-vary;) can be used to express the parameters the
838   server uses to select a representation that is subject to server-driven
839   negotiation.
843<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
845   With agent-driven negotiation, selection of the best representation
846   for a response is performed by the user agent after receiving an
847   initial response from the origin server. Selection is based on a list
848   of the available representations of the response included within the
849   header fields or entity-body of the initial response, with each
850   representation identified by its own URI. Selection from among the
851   representations may be performed automatically (if the user agent is
852   capable of doing so) or manually by the user selecting from a
853   generated (possibly hypertext) menu.
856   Agent-driven negotiation is advantageous when the response would vary
857   over commonly-used dimensions (such as type, language, or encoding),
858   when the origin server is unable to determine a user agent's
859   capabilities from examining the request, and generally when public
860   caches are used to distribute server load and reduce network usage.
863   Agent-driven negotiation suffers from the disadvantage of needing a
864   second request to obtain the best alternate representation. This
865   second request is only efficient when caching is used. In addition,
866   this specification does not define any mechanism for supporting
867   automatic selection, though it also does not prevent any such
868   mechanism from being developed as an extension and used within
869   HTTP/1.1.
872   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
873   status codes for enabling agent-driven negotiation when the server is
874   unwilling or unable to provide a varying response using server-driven
875   negotiation.
879<section title="Transparent Negotiation" anchor="transparent.negotiation">
881   Transparent negotiation is a combination of both server-driven and
882   agent-driven negotiation. When a cache is supplied with a form of the
883   list of available representations of the response (as in agent-driven
884   negotiation) and the dimensions of variance are completely understood
885   by the cache, then the cache becomes capable of performing server-driven
886   negotiation on behalf of the origin server for subsequent
887   requests on that resource.
890   Transparent negotiation has the advantage of distributing the
891   negotiation work that would otherwise be required of the origin
892   server and also removing the second request delay of agent-driven
893   negotiation when the cache is able to correctly guess the right
894   response.
897   This specification does not define any mechanism for transparent
898   negotiation, though it also does not prevent any such mechanism from
899   being developed as an extension that could be used within HTTP/1.1.
904<section title="Header Field Definitions" anchor="header.fields">
906   This section defines the syntax and semantics of HTTP/1.1 header fields
907   related to the payload of messages.
910   For entity-header fields, both sender and recipient refer to either the
911   client or the server, depending on who sends and who receives the entity.
914<section title="Accept" anchor="header.accept">
915  <iref primary="true" item="Accept header" x:for-anchor=""/>
916  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
917  <x:anchor-alias value="Accept"/>
918  <x:anchor-alias value="accept-extension"/>
919  <x:anchor-alias value="accept-params"/>
920  <x:anchor-alias value="media-range"/>
922   The Accept request-header field can be used to specify certain media
923   types which are acceptable for the response. Accept headers can be
924   used to indicate that the request is specifically limited to a small
925   set of desired types, as in the case of a request for an in-line
926   image.
928<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-extension"/>
929  <x:ref>Accept</x:ref>         = "Accept" ":"
930                   #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
932  <x:ref>media-range</x:ref>    = ( "*/*"
933                   | ( <x:ref>type</x:ref> "/" "*" )
934                   | ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
935                   ) *( ";" <x:ref>parameter</x:ref> )
936  <x:ref>accept-params</x:ref>  = ";" "q" "=" <x:ref>qvalue</x:ref> *( <x:ref>accept-extension</x:ref> )
937  <x:ref>accept-extension</x:ref> = ";" <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> | <x:ref>quoted-string</x:ref> ) ]
940   The asterisk "*" character is used to group media types into ranges,
941   with "*/*" indicating all media types and "type/*" indicating all
942   subtypes of that type. The media-range &MAY; include media type
943   parameters that are applicable to that range.
946   Each media-range &MAY; be followed by one or more accept-params,
947   beginning with the "q" parameter for indicating a relative quality
948   factor. The first "q" parameter (if any) separates the media-range
949   parameter(s) from the accept-params. Quality factors allow the user
950   or user agent to indicate the relative degree of preference for that
951   media-range, using the qvalue scale from 0 to 1 (<xref target="quality.values"/>). The
952   default value is q=1.
953  <list><t>
954      <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
955      parameters from Accept extension parameters is due to historical
956      practice. Although this prevents any media type parameter named
957      "q" from being used with a media range, such an event is believed
958      to be unlikely given the lack of any "q" parameters in the IANA
959      media type registry and the rare usage of any media type
960      parameters in Accept. Future media types are discouraged from
961      registering any parameter named "q".
962  </t></list>
965   The example
967<figure><artwork type="example">
968    Accept: audio/*; q=0.2, audio/basic
971   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
972   type if it is the best available after an 80% mark-down in quality."
975   If no Accept header field is present, then it is assumed that the
976   client accepts all media types. If an Accept header field is present,
977   and if the server cannot send a response which is acceptable
978   according to the combined Accept field value, then the server &SHOULD;
979   send a 406 (Not Acceptable) response.
982   A more elaborate example is
984<figure><artwork type="example">
985    Accept: text/plain; q=0.5, text/html,
986            text/x-dvi; q=0.8, text/x-c
989   Verbally, this would be interpreted as "text/html and text/x-c are
990   the preferred media types, but if they do not exist, then send the
991   text/x-dvi entity, and if that does not exist, send the text/plain
992   entity."
995   Media ranges can be overridden by more specific media ranges or
996   specific media types. If more than one media range applies to a given
997   type, the most specific reference has precedence. For example,
999<figure><artwork type="example">
1000    Accept: text/*, text/html, text/html;level=1, */*
1003   have the following precedence:
1005<figure><artwork type="example">
1006    1) text/html;level=1
1007    2) text/html
1008    3) text/*
1009    4) */*
1012   The media type quality factor associated with a given type is
1013   determined by finding the media range with the highest precedence
1014   which matches that type. For example,
1016<figure><artwork type="example">
1017    Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1018            text/html;level=2;q=0.4, */*;q=0.5
1021   would cause the following values to be associated:
1023<figure><artwork type="example">
1024    text/html;level=1         = 1
1025    text/html                 = 0.7
1026    text/plain                = 0.3
1027    image/jpeg                = 0.5
1028    text/html;level=2         = 0.4
1029    text/html;level=3         = 0.7
1032      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1033      values for certain media ranges. However, unless the user agent is
1034      a closed system which cannot interact with other rendering agents,
1035      this default set ought to be configurable by the user.
1039<section title="Accept-Charset" anchor="header.accept-charset">
1040  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1041  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1042  <x:anchor-alias value="Accept-Charset"/>
1044   The Accept-Charset request-header field can be used to indicate what
1045   character sets are acceptable for the response. This field allows
1046   clients capable of understanding more comprehensive or special-purpose
1047   character sets to signal that capability to a server which is
1048   capable of representing documents in those character sets.
1050<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/>
1051  <x:ref>Accept-Charset</x:ref> = "Accept-Charset" ":"
1052          1#( ( <x:ref>charset</x:ref> | "*" ) [ ";" "q" "=" <x:ref>qvalue</x:ref> ] )
1055   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1056   be given an associated quality value which represents the user's
1057   preference for that charset. The default value is q=1. An example is
1059<figure><artwork type="example">
1060   Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1063   The special value "*", if present in the Accept-Charset field,
1064   matches every character set (including ISO-8859-1) which is not
1065   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1066   in an Accept-Charset field, then all character sets not explicitly
1067   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1068   a quality value of 1 if not explicitly mentioned.
1071   If no Accept-Charset header is present, the default is that any
1072   character set is acceptable. If an Accept-Charset header is present,
1073   and if the server cannot send a response which is acceptable
1074   according to the Accept-Charset header, then the server &SHOULD; send
1075   an error response with the 406 (Not Acceptable) status code, though
1076   the sending of an unacceptable response is also allowed.
1080<section title="Accept-Encoding" anchor="header.accept-encoding">
1081  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1082  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1083  <x:anchor-alias value="Accept-Encoding"/>
1084  <x:anchor-alias value="codings"/>
1086   The Accept-Encoding request-header field is similar to Accept, but
1087   restricts the content-codings (<xref target="content.codings"/>) that are acceptable in
1088   the response.
1090<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/>
1091  <x:ref>Accept-Encoding</x:ref>  = "Accept-Encoding" ":"
1092                     #( <x:ref>codings</x:ref> [ ";" "q" "=" <x:ref>qvalue</x:ref> ] )
1093  <x:ref>codings</x:ref>          = ( <x:ref>content-coding</x:ref> | "*" )
1096   Each codings value &MAY; be given an associated quality value which
1097   represents the preference for that encoding. The default value is q=1.
1100   Examples of its use are:
1102<figure><artwork type="example">
1103    Accept-Encoding: compress, gzip
1104    Accept-Encoding:
1105    Accept-Encoding: *
1106    Accept-Encoding: compress;q=0.5, gzip;q=1.0
1107    Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1110   A server tests whether a content-coding is acceptable, according to
1111   an Accept-Encoding field, using these rules:
1112  <list style="numbers">
1113      <t>If the content-coding is one of the content-codings listed in
1114         the Accept-Encoding field, then it is acceptable, unless it is
1115         accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
1116         qvalue of 0 means "not acceptable.")</t>
1118      <t>The special "*" symbol in an Accept-Encoding field matches any
1119         available content-coding not explicitly listed in the header
1120         field.</t>
1122      <t>If multiple content-codings are acceptable, then the acceptable
1123         content-coding with the highest non-zero qvalue is preferred.</t>
1125      <t>The "identity" content-coding is always acceptable, unless
1126         specifically refused because the Accept-Encoding field includes
1127         "identity;q=0", or because the field includes "*;q=0" and does
1128         not explicitly include the "identity" content-coding. If the
1129         Accept-Encoding field-value is empty, then only the "identity"
1130         encoding is acceptable.</t>
1131  </list>
1134   If an Accept-Encoding field is present in a request, and if the
1135   server cannot send a response which is acceptable according to the
1136   Accept-Encoding header, then the server &SHOULD; send an error response
1137   with the 406 (Not Acceptable) status code.
1140   If no Accept-Encoding field is present in a request, the server &MAY;
1141   assume that the client will accept any content coding. In this case,
1142   if "identity" is one of the available content-codings, then the
1143   server &SHOULD; use the "identity" content-coding, unless it has
1144   additional information that a different content-coding is meaningful
1145   to the client.
1146  <list><t>
1147      <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1148      and if the "identity" content-coding is unavailable, then
1149      content-codings commonly understood by HTTP/1.0 clients (i.e.,
1150      "gzip" and "compress") are preferred; some older clients
1151      improperly display messages sent with other content-codings.  The
1152      server might also make this decision based on information about
1153      the particular user-agent or client.
1154    </t><t>
1155      <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1156      associated with content-codings. This means that qvalues will not
1157      work and are not permitted with x-gzip or x-compress.
1158    </t></list>
1162<section title="Accept-Language" anchor="header.accept-language">
1163  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1164  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1165  <x:anchor-alias value="Accept-Language"/>
1166  <x:anchor-alias value="language-range"/>
1168   The Accept-Language request-header field is similar to Accept, but
1169   restricts the set of natural languages that are preferred as a
1170   response to the request. Language tags are defined in <xref target="language.tags"/>.
1172<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/>
1173  <x:ref>Accept-Language</x:ref> = "Accept-Language" ":"
1174                    1#( <x:ref>language-range</x:ref> [ ";" "q" "=" <x:ref>qvalue</x:ref> ] )
1175  <x:ref>language-range</x:ref>  = ( ( 1*8<x:ref>ALPHA</x:ref> *( "-" 1*8<x:ref>ALPHA</x:ref> ) ) | "*" )
1178   Each language-range &MAY; be given an associated quality value which
1179   represents an estimate of the user's preference for the languages
1180   specified by that range. The quality value defaults to "q=1". For
1181   example,
1183<figure><artwork type="example">
1184    Accept-Language: da, en-gb;q=0.8, en;q=0.7
1187   would mean: "I prefer Danish, but will accept British English and
1188   other types of English." A language-range matches a language-tag if
1189   it exactly equals the tag, or if it exactly equals a prefix of the
1190   tag such that the first tag character following the prefix is "-".
1191   The special range "*", if present in the Accept-Language field,
1192   matches every tag not matched by any other range present in the
1193   Accept-Language field.
1194  <list><t>
1195      <x:h>Note:</x:h> This use of a prefix matching rule does not imply that
1196      language tags are assigned to languages in such a way that it is
1197      always true that if a user understands a language with a certain
1198      tag, then this user will also understand all languages with tags
1199      for which this tag is a prefix. The prefix rule simply allows the
1200      use of prefix tags if this is the case.
1201  </t></list>
1204   The language quality factor assigned to a language-tag by the
1205   Accept-Language field is the quality value of the longest language-range
1206   in the field that matches the language-tag. If no language-range
1207   in the field matches the tag, the language quality factor
1208   assigned is 0. If no Accept-Language header is present in the
1209   request, the server
1210   &SHOULD; assume that all languages are equally acceptable. If an
1211   Accept-Language header is present, then all languages which are
1212   assigned a quality factor greater than 0 are acceptable.
1215   It might be contrary to the privacy expectations of the user to send
1216   an Accept-Language header with the complete linguistic preferences of
1217   the user in every request. For a discussion of this issue, see
1218   <xref target=""/>.
1221   As intelligibility is highly dependent on the individual user, it is
1222   recommended that client applications make the choice of linguistic
1223   preference available to the user. If the choice is not made
1224   available, then the Accept-Language header field &MUST-NOT; be given in
1225   the request.
1226  <list><t>
1227      <x:h>Note:</x:h> When making the choice of linguistic preference available to
1228      the user, we remind implementors of  the fact that users are not
1229      familiar with the details of language matching as described above,
1230      and should provide appropriate guidance. As an example, users
1231      might assume that on selecting "en-gb", they will be served any
1232      kind of English document if British English is not available. A
1233      user agent might suggest in such a case to add "en" to get the
1234      best matching behavior.
1235  </t></list>
1239<section title="Content-Encoding" anchor="header.content-encoding">
1240  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1241  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1242  <x:anchor-alias value="Content-Encoding"/>
1244   The Content-Encoding entity-header field is used as a modifier to the
1245   media-type. When present, its value indicates what additional content
1246   codings have been applied to the entity-body, and thus what decoding
1247   mechanisms must be applied in order to obtain the media-type
1248   referenced by the Content-Type header field. Content-Encoding is
1249   primarily used to allow a document to be compressed without losing
1250   the identity of its underlying media type.
1252<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/>
1253  <x:ref>Content-Encoding</x:ref>  = "Content-Encoding" ":" 1#<x:ref>content-coding</x:ref>
1256   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1258<figure><artwork type="example">
1259    Content-Encoding: gzip
1262   The content-coding is a characteristic of the entity identified by
1263   the Request-URI. Typically, the entity-body is stored with this
1264   encoding and is only decoded before rendering or analogous usage.
1265   However, a non-transparent proxy &MAY; modify the content-coding if the
1266   new coding is known to be acceptable to the recipient, unless the
1267   "no-transform" cache-control directive is present in the message.
1270   If the content-coding of an entity is not "identity", then the
1271   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1272   that lists the non-identity content-coding(s) used.
1275   If the content-coding of an entity in a request message is not
1276   acceptable to the origin server, the server &SHOULD; respond with a
1277   status code of 415 (Unsupported Media Type).
1280   If multiple encodings have been applied to an entity, the content
1281   codings &MUST; be listed in the order in which they were applied.
1282   Additional information about the encoding parameters &MAY; be provided
1283   by other entity-header fields not defined by this specification.
1287<section title="Content-Language" anchor="header.content-language">
1288  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1289  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1290  <x:anchor-alias value="Content-Language"/>
1292   The Content-Language entity-header field describes the natural
1293   language(s) of the intended audience for the enclosed entity. Note
1294   that this might not be equivalent to all the languages used within
1295   the entity-body.
1297<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/>
1298  <x:ref>Content-Language</x:ref>  = "Content-Language" ":" 1#<x:ref>language-tag</x:ref>
1301   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1302   Content-Language is to allow a user to identify and differentiate
1303   entities according to the user's own preferred language. Thus, if the
1304   body content is intended only for a Danish-literate audience, the
1305   appropriate field is
1307<figure><artwork type="example">
1308    Content-Language: da
1311   If no Content-Language is specified, the default is that the content
1312   is intended for all language audiences. This might mean that the
1313   sender does not consider it to be specific to any natural language,
1314   or that the sender does not know for which language it is intended.
1317   Multiple languages &MAY; be listed for content that is intended for
1318   multiple audiences. For example, a rendition of the "Treaty of
1319   Waitangi," presented simultaneously in the original Maori and English
1320   versions, would call for
1322<figure><artwork type="example">
1323    Content-Language: mi, en
1326   However, just because multiple languages are present within an entity
1327   does not mean that it is intended for multiple linguistic audiences.
1328   An example would be a beginner's language primer, such as "A First
1329   Lesson in Latin," which is clearly intended to be used by an
1330   English-literate audience. In this case, the Content-Language would
1331   properly only include "en".
1334   Content-Language &MAY; be applied to any media type -- it is not
1335   limited to textual documents.
1339<section title="Content-Location" anchor="header.content-location">
1340  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1341  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1342  <x:anchor-alias value="Content-Location"/>
1344   The Content-Location entity-header field &MAY; be used to supply the
1345   resource location for the entity enclosed in the message when that
1346   entity is accessible from a location separate from the requested
1347   resource's URI. A server &SHOULD; provide a Content-Location for the
1348   variant corresponding to the response entity; especially in the case
1349   where a resource has multiple entities associated with it, and those
1350   entities actually have separate locations by which they might be
1351   individually accessed, the server &SHOULD; provide a Content-Location
1352   for the particular variant which is returned.
1354<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/>
1355  <x:ref>Content-Location</x:ref> = "Content-Location" ":"
1356                    ( <x:ref>absoluteURI</x:ref> | <x:ref>relativeURI</x:ref> )
1359   The value of Content-Location also defines the base URI for the
1360   entity.
1363   The Content-Location value is not a replacement for the original
1364   requested URI; it is only a statement of the location of the resource
1365   corresponding to this particular entity at the time of the request.
1366   Future requests &MAY; specify the Content-Location URI as the request-URI
1367   if the desire is to identify the source of that particular
1368   entity.
1371   A cache cannot assume that an entity with a Content-Location
1372   different from the URI used to retrieve it can be used to respond to
1373   later requests on that Content-Location URI. However, the Content-Location
1374   can be used to differentiate between multiple entities
1375   retrieved from a single requested resource, as described in &caching-neg-resp;.
1378   If the Content-Location is a relative URI, the relative URI is
1379   interpreted relative to the Request-URI.
1382   The meaning of the Content-Location header in PUT or POST requests is
1383   undefined; servers are free to ignore it in those cases.
1387<section title="Content-MD5" anchor="header.content-md5">
1388  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1389  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1390  <x:anchor-alias value="Content-MD5"/>
1391  <x:anchor-alias value="md5-digest"/>
1393   The Content-MD5 entity-header field, as defined in <xref target="RFC1864"/>, is
1394   an MD5 digest of the entity-body for the purpose of providing an
1395   end-to-end message integrity check (MIC) of the entity-body. (Note: a
1396   MIC is good for detecting accidental modification of the entity-body
1397   in transit, but is not proof against malicious attacks.)
1399<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="md5-digest"/>
1400  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>md5-digest</x:ref>
1401  <x:ref>md5-digest</x:ref>    = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1404   The Content-MD5 header field &MAY; be generated by an origin server or
1405   client to function as an integrity check of the entity-body. Only
1406   origin servers or clients &MAY; generate the Content-MD5 header field;
1407   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1408   value as an end-to-end integrity check. Any recipient of the entity-body,
1409   including gateways and proxies, &MAY; check that the digest value
1410   in this header field matches that of the entity-body as received.
1413   The MD5 digest is computed based on the content of the entity-body,
1414   including any content-coding that has been applied, but not including
1415   any transfer-encoding applied to the message-body. If the message is
1416   received with a transfer-encoding, that encoding &MUST; be removed
1417   prior to checking the Content-MD5 value against the received entity.
1420   This has the result that the digest is computed on the octets of the
1421   entity-body exactly as, and in the order that, they would be sent if
1422   no transfer-encoding were being applied.
1425   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1426   composite media-types (e.g., multipart/* and message/rfc822), but
1427   this does not change how the digest is computed as defined in the
1428   preceding paragraph.
1431   There are several consequences of this. The entity-body for composite
1432   types &MAY; contain many body-parts, each with its own MIME and HTTP
1433   headers (including Content-MD5, Content-Transfer-Encoding, and
1434   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1435   or Content-Encoding header, it is assumed that the content
1436   of the body-part has had the encoding applied, and the body-part is
1437   included in the Content-MD5 digest as is -- i.e., after the
1438   application. The Transfer-Encoding header field is not allowed within
1439   body-parts.
1442   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1443   computing or checking the digest: the line break convention used in
1444   the text actually transmitted &MUST; be left unaltered when computing
1445   the digest.
1446  <list><t>
1447      <x:h>Note:</x:h> while the definition of Content-MD5 is exactly the same for
1448      HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1449      in which the application of Content-MD5 to HTTP entity-bodies
1450      differs from its application to MIME entity-bodies. One is that
1451      HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1452      does use Transfer-Encoding and Content-Encoding. Another is that
1453      HTTP more frequently uses binary content types than MIME, so it is
1454      worth noting that, in such cases, the byte order used to compute
1455      the digest is the transmission byte order defined for the type.
1456      Lastly, HTTP allows transmission of text types with any of several
1457      line break conventions and not just the canonical form using CRLF.
1458  </t></list>
1462<section title="Content-Type" anchor="header.content-type">
1463  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1464  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1465  <x:anchor-alias value="Content-Type"/>
1467   The Content-Type entity-header field indicates the media type of the
1468   entity-body sent to the recipient or, in the case of the HEAD method,
1469   the media type that would have been sent had the request been a GET.
1471<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/>
1472  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>media-type</x:ref>
1475   Media types are defined in <xref target="media.types"/>. An example of the field is
1477<figure><artwork type="example">
1478    Content-Type: text/html; charset=ISO-8859-4
1481   Further discussion of methods for identifying the media type of an
1482   entity is provided in <xref target="type"/>.
1488<section title="IANA Considerations" anchor="IANA.considerations">
1490   <cref>TBD.</cref>
1494<section title="Security Considerations" anchor="security.considerations">
1496   This section is meant to inform application developers, information
1497   providers, and users of the security limitations in HTTP/1.1 as
1498   described by this document. The discussion does not include
1499   definitive solutions to the problems revealed, though it does make
1500   some suggestions for reducing security risks.
1503<section title="Privacy Issues Connected to Accept Headers" anchor="">
1505   Accept request-headers can reveal information about the user to all
1506   servers which are accessed. The Accept-Language header in particular
1507   can reveal information the user would consider to be of a private
1508   nature, because the understanding of particular languages is often
1509   strongly correlated to the membership of a particular ethnic group.
1510   User agents which offer the option to configure the contents of an
1511   Accept-Language header to be sent in every request are strongly
1512   encouraged to let the configuration process include a message which
1513   makes the user aware of the loss of privacy involved.
1516   An approach that limits the loss of privacy would be for a user agent
1517   to omit the sending of Accept-Language headers by default, and to ask
1518   the user whether or not to start sending Accept-Language headers to a
1519   server if it detects, by looking for any Vary response-header fields
1520   generated by the server, that such sending could improve the quality
1521   of service.
1524   Elaborate user-customized accept header fields sent in every request,
1525   in particular if these include quality values, can be used by servers
1526   as relatively reliable and long-lived user identifiers. Such user
1527   identifiers would allow content providers to do click-trail tracking,
1528   and would allow collaborating content providers to match cross-server
1529   click-trails or form submissions of individual users. Note that for
1530   many users not behind a proxy, the network address of the host
1531   running the user agent will also serve as a long-lived user
1532   identifier. In environments where proxies are used to enhance
1533   privacy, user agents ought to be conservative in offering accept
1534   header configuration options to end users. As an extreme privacy
1535   measure, proxies could filter the accept headers in relayed requests.
1536   General purpose user agents which provide a high degree of header
1537   configurability &SHOULD; warn users about the loss of privacy which can
1538   be involved.
1542<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1544   <xref target="RFC1806"/>, from which the often implemented Content-Disposition
1545   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1546   serious security considerations. Content-Disposition is not part of
1547   the HTTP standard, but since it is widely implemented, we are
1548   documenting its use and risks for implementors. See <xref target="RFC2183"/>
1549   (which updates <xref target="RFC1806"/>) for details.
1555<section title="Acknowledgments" anchor="ack">
1560<references title="Normative References">
1562<reference anchor="ISO-8859-1">
1563  <front>
1564    <title>
1565     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1566    </title>
1567    <author>
1568      <organization>International Organization for Standardization</organization>
1569    </author>
1570    <date year="1998"/>
1571  </front>
1572  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1575<reference anchor="Part1">
1576  <front>
1577    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1578    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1579      <organization abbrev="Day Software">Day Software</organization>
1580      <address><email></email></address>
1581    </author>
1582    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1583      <organization>One Laptop per Child</organization>
1584      <address><email></email></address>
1585    </author>
1586    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1587      <organization abbrev="HP">Hewlett-Packard Company</organization>
1588      <address><email></email></address>
1589    </author>
1590    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1591      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1592      <address><email></email></address>
1593    </author>
1594    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1595      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1596      <address><email></email></address>
1597    </author>
1598    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1599      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1600      <address><email></email></address>
1601    </author>
1602    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1603      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1604      <address><email></email></address>
1605    </author>
1606    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1607      <organization abbrev="W3C">World Wide Web Consortium</organization>
1608      <address><email></email></address>
1609    </author>
1610    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1611      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1612      <address><email></email></address>
1613    </author>
1614    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1615  </front>
1616  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1617  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1620<reference anchor="Part2">
1621  <front>
1622    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1623    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1624      <organization abbrev="Day Software">Day Software</organization>
1625      <address><email></email></address>
1626    </author>
1627    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1628      <organization>One Laptop per Child</organization>
1629      <address><email></email></address>
1630    </author>
1631    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1632      <organization abbrev="HP">Hewlett-Packard Company</organization>
1633      <address><email></email></address>
1634    </author>
1635    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1636      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1637      <address><email></email></address>
1638    </author>
1639    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1640      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1641      <address><email></email></address>
1642    </author>
1643    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1644      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1645      <address><email></email></address>
1646    </author>
1647    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1648      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1649      <address><email></email></address>
1650    </author>
1651    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1652      <organization abbrev="W3C">World Wide Web Consortium</organization>
1653      <address><email></email></address>
1654    </author>
1655    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1656      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1657      <address><email></email></address>
1658    </author>
1659    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1660  </front>
1661  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1662  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1665<reference anchor="Part4">
1666  <front>
1667    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1668    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1669      <organization abbrev="Day Software">Day Software</organization>
1670      <address><email></email></address>
1671    </author>
1672    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1673      <organization>One Laptop per Child</organization>
1674      <address><email></email></address>
1675    </author>
1676    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1677      <organization abbrev="HP">Hewlett-Packard Company</organization>
1678      <address><email></email></address>
1679    </author>
1680    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1681      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1682      <address><email></email></address>
1683    </author>
1684    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1685      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1686      <address><email></email></address>
1687    </author>
1688    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1689      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1690      <address><email></email></address>
1691    </author>
1692    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1693      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1694      <address><email></email></address>
1695    </author>
1696    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1697      <organization abbrev="W3C">World Wide Web Consortium</organization>
1698      <address><email></email></address>
1699    </author>
1700    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1701      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1702      <address><email></email></address>
1703    </author>
1704    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1705  </front>
1706  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1707  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1710<reference anchor="Part5">
1711  <front>
1712    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1713    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1714      <organization abbrev="Day Software">Day Software</organization>
1715      <address><email></email></address>
1716    </author>
1717    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1718      <organization>One Laptop per Child</organization>
1719      <address><email></email></address>
1720    </author>
1721    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1722      <organization abbrev="HP">Hewlett-Packard Company</organization>
1723      <address><email></email></address>
1724    </author>
1725    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1726      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1727      <address><email></email></address>
1728    </author>
1729    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1730      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1731      <address><email></email></address>
1732    </author>
1733    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1734      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1735      <address><email></email></address>
1736    </author>
1737    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1738      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1739      <address><email></email></address>
1740    </author>
1741    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1742      <organization abbrev="W3C">World Wide Web Consortium</organization>
1743      <address><email></email></address>
1744    </author>
1745    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1746      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1747      <address><email></email></address>
1748    </author>
1749    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1750  </front>
1751  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1752  <x:source href="p5-range.xml" basename="p5-range"/>
1755<reference anchor="Part6">
1756  <front>
1757    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1758    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1759      <organization abbrev="Day Software">Day Software</organization>
1760      <address><email></email></address>
1761    </author>
1762    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1763      <organization>One Laptop per Child</organization>
1764      <address><email></email></address>
1765    </author>
1766    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1767      <organization abbrev="HP">Hewlett-Packard Company</organization>
1768      <address><email></email></address>
1769    </author>
1770    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1771      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1772      <address><email></email></address>
1773    </author>
1774    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1775      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1776      <address><email></email></address>
1777    </author>
1778    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1779      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1780      <address><email></email></address>
1781    </author>
1782    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1783      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1784      <address><email></email></address>
1785    </author>
1786    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1787      <organization abbrev="W3C">World Wide Web Consortium</organization>
1788      <address><email></email></address>
1789    </author>
1790    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1791      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1792      <address><email></email></address>
1793    </author>
1794    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1795  </front>
1796  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1797  <x:source href="p6-cache.xml" basename="p6-cache"/>
1800<reference anchor="RFC1766">
1801  <front>
1802    <title abbrev="Language Tag">Tags for the Identification of Languages</title>
1803    <author initials="H." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
1804      <organization>UNINETT</organization>
1805      <address><email></email></address>
1806    </author>
1807    <date month="March" year="1995"/>
1808  </front>
1809  <seriesInfo name="RFC" value="1766"/>
1812<reference anchor="RFC1864">
1813  <front>
1814    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1815    <author initials="J." surname="Myers" fullname="John G. Myers">
1816      <organization>Carnegie Mellon University</organization>
1817      <address><email></email></address>
1818    </author>
1819    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
1820      <organization>Dover Beach Consulting, Inc.</organization>
1821      <address><email></email></address>
1822    </author>
1823    <date month="October" year="1995"/>
1824  </front>
1825  <seriesInfo name="RFC" value="1864"/>
1828<reference anchor="RFC1950">
1829  <front>
1830    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1831    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1832      <organization>Aladdin Enterprises</organization>
1833      <address><email></email></address>
1834    </author>
1835    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1836      <organization/>
1837    </author>
1838    <date month="May" year="1996"/>
1839  </front>
1840  <seriesInfo name="RFC" value="1950"/>
1841  <annotation>
1842    RFC1950 is an Informational RFC, thus it may be less stable than
1843    this specification. On the other hand, this downward reference was
1844    present since <xref target="RFC2068"/> (published in 1997), therefore it is unlikely
1845    to cause problems in practice.
1846  </annotation>
1849<reference anchor="RFC1951">
1850  <front>
1851    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1852    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1853      <organization>Aladdin Enterprises</organization>
1854      <address><email></email></address>
1855    </author>
1856    <date month="May" year="1996"/>
1857  </front>
1858  <seriesInfo name="RFC" value="1951"/>
1859  <annotation>
1860    RFC1951 is an Informational RFC, thus it may be less stable than
1861    this specification. On the other hand, this downward reference was
1862    present since <xref target="RFC2068"/> (published in 1997), therefore it is unlikely
1863    to cause problems in practice.
1864  </annotation>
1867<reference anchor="RFC1952">
1868  <front>
1869    <title>GZIP file format specification version 4.3</title>
1870    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1871      <organization>Aladdin Enterprises</organization>
1872      <address><email></email></address>
1873    </author>
1874    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1875      <organization/>
1876      <address><email></email></address>
1877    </author>
1878    <author initials="M." surname="Adler" fullname="Mark Adler">
1879      <organization/>
1880      <address><email></email></address>
1881    </author>
1882    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1883      <organization/>
1884      <address><email></email></address>
1885    </author>
1886    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
1887      <organization/>
1888      <address><email></email></address>
1889    </author>
1890    <date month="May" year="1996"/>
1891  </front>
1892  <seriesInfo name="RFC" value="1952"/>
1893  <annotation>
1894    RFC1952 is an Informational RFC, thus it may be less stable than
1895    this specification. On the other hand, this downward reference was
1896    present since <xref target="RFC2068"/> (published in 1997), therefore it is unlikely
1897    to cause problems in practice.
1898  </annotation>
1901<reference anchor="RFC2045">
1902  <front>
1903    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
1904    <author initials="N." surname="Freed" fullname="Ned Freed">
1905      <organization>Innosoft International, Inc.</organization>
1906      <address><email></email></address>
1907    </author>
1908    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1909      <organization>First Virtual Holdings</organization>
1910      <address><email></email></address>
1911    </author>
1912    <date month="November" year="1996"/>
1913  </front>
1914  <seriesInfo name="RFC" value="2045"/>
1917<reference anchor="RFC2046">
1918  <front>
1919    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
1920    <author initials="N." surname="Freed" fullname="Ned Freed">
1921      <organization>Innosoft International, Inc.</organization>
1922      <address><email></email></address>
1923    </author>
1924    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1925      <organization>First Virtual Holdings</organization>
1926      <address><email></email></address>
1927    </author>
1928    <date month="November" year="1996"/>
1929  </front>
1930  <seriesInfo name="RFC" value="2046"/>
1933<reference anchor="RFC2119">
1934  <front>
1935    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
1936    <author initials="S." surname="Bradner" fullname="Scott Bradner">
1937      <organization>Harvard University</organization>
1938      <address><email></email></address>
1939    </author>
1940    <date month="March" year="1997"/>
1941  </front>
1942  <seriesInfo name="BCP" value="14"/>
1943  <seriesInfo name="RFC" value="2119"/>
1948<references title="Informative References">
1950<reference anchor="RFC1806">
1951  <front>
1952    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header</title>
1953    <author initials="R." surname="Troost" fullname="Rens Troost">
1954      <organization>New Century Systems</organization>
1955      <address><email></email></address>
1956    </author>
1957    <author initials="S." surname="Dorner" fullname="Steve Dorner">
1958      <organization>QUALCOMM Incorporated</organization>
1959      <address><email></email></address>
1960    </author>
1961    <date month="June" year="1995"/>
1962  </front>
1963  <seriesInfo name="RFC" value="1806"/>
1966<reference anchor="RFC1945">
1967  <front>
1968    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
1969    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1970      <organization>MIT, Laboratory for Computer Science</organization>
1971      <address><email></email></address>
1972    </author>
1973    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
1974      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
1975      <address><email></email></address>
1976    </author>
1977    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
1978      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
1979      <address><email></email></address>
1980    </author>
1981    <date month="May" year="1996"/>
1982  </front>
1983  <seriesInfo name="RFC" value="1945"/>
1986<reference anchor="RFC2049">
1987  <front>
1988    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
1989    <author initials="N." surname="Freed" fullname="Ned Freed">
1990      <organization>Innosoft International, Inc.</organization>
1991      <address><email></email></address>
1992    </author>
1993    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1994      <organization>First Virtual Holdings</organization>
1995      <address><email></email></address>
1996    </author>
1997    <date month="November" year="1996"/>
1998  </front>
1999  <seriesInfo name="RFC" value="2049"/>
2002<reference anchor="RFC2068">
2003  <front>
2004    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2005    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2006      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2007      <address><email></email></address>
2008    </author>
2009    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2010      <organization>MIT Laboratory for Computer Science</organization>
2011      <address><email></email></address>
2012    </author>
2013    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2014      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2015      <address><email></email></address>
2016    </author>
2017    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2018      <organization>MIT Laboratory for Computer Science</organization>
2019      <address><email></email></address>
2020    </author>
2021    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2022      <organization>MIT Laboratory for Computer Science</organization>
2023      <address><email></email></address>
2024    </author>
2025    <date month="January" year="1997"/>
2026  </front>
2027  <seriesInfo name="RFC" value="2068"/>
2030<reference anchor="RFC2076">
2031  <front>
2032    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2033    <author initials="J." surname="Palme" fullname="Jacob Palme">
2034      <organization>Stockholm University/KTH</organization>
2035      <address><email></email></address>
2036    </author>
2037    <date month="February" year="1997"/>
2038  </front>
2039  <seriesInfo name="RFC" value="2076"/>
2042<reference anchor="RFC2183">
2043  <front>
2044    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2045    <author initials="R." surname="Troost" fullname="Rens Troost">
2046      <organization>New Century Systems</organization>
2047      <address><email></email></address>
2048    </author>
2049    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2050      <organization>QUALCOMM Incorporated</organization>
2051      <address><email></email></address>
2052    </author>
2053    <author initials="K." surname="Moore" fullname="Keith Moore">
2054      <organization>Department of Computer Science</organization>
2055      <address><email></email></address>
2056    </author>
2057    <date month="August" year="1997"/>
2058  </front>
2059  <seriesInfo name="RFC" value="2183"/>
2062<reference anchor="RFC2277">
2063  <front>
2064    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2065    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2066      <organization>UNINETT</organization>
2067      <address><email></email></address>
2068    </author>
2069    <date month="January" year="1998"/>
2070  </front>
2071  <seriesInfo name="BCP" value="18"/>
2072  <seriesInfo name="RFC" value="2277"/>
2075<reference anchor="RFC2388">
2076  <front>
2077    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2078    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2079      <organization>Xerox Palo Alto Research Center</organization>
2080      <address><email></email></address>
2081    </author>
2082    <date year="1998" month="August"/>
2083  </front>
2084  <seriesInfo name="RFC" value="2388"/>
2087<reference anchor="RFC2557">
2088  <front>
2089    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2090    <author initials="F." surname="Palme" fullname="Jacob Palme">
2091      <organization>Stockholm University and KTH</organization>
2092      <address><email></email></address>
2093    </author>
2094    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2095      <organization>Microsoft Corporation</organization>
2096      <address><email></email></address>
2097    </author>
2098    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2099      <organization>Lotus Development Corporation</organization>
2100      <address><email></email></address>
2101    </author>
2102    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2103      <organization/>
2104      <address><email></email></address>
2105    </author>
2106    <date year="1999" month="March"/>
2107  </front>
2108  <seriesInfo name="RFC" value="2557"/>
2111<reference anchor="RFC2616">
2112  <front>
2113    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2114    <author initials="R." surname="Fielding" fullname="R. Fielding">
2115      <organization>University of California, Irvine</organization>
2116      <address><email></email></address>
2117    </author>
2118    <author initials="J." surname="Gettys" fullname="J. Gettys">
2119      <organization>W3C</organization>
2120      <address><email></email></address>
2121    </author>
2122    <author initials="J." surname="Mogul" fullname="J. Mogul">
2123      <organization>Compaq Computer Corporation</organization>
2124      <address><email></email></address>
2125    </author>
2126    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2127      <organization>MIT Laboratory for Computer Science</organization>
2128      <address><email></email></address>
2129    </author>
2130    <author initials="L." surname="Masinter" fullname="L. Masinter">
2131      <organization>Xerox Corporation</organization>
2132      <address><email></email></address>
2133    </author>
2134    <author initials="P." surname="Leach" fullname="P. Leach">
2135      <organization>Microsoft Corporation</organization>
2136      <address><email></email></address>
2137    </author>
2138    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2139      <organization>W3C</organization>
2140      <address><email></email></address>
2141    </author>
2142    <date month="June" year="1999"/>
2143  </front>
2144  <seriesInfo name="RFC" value="2616"/>
2147<reference anchor="RFC2822">
2148  <front>
2149    <title>Internet Message Format</title>
2150    <author initials="P." surname="Resnick" fullname="P. Resnick">
2151      <organization>QUALCOMM Incorporated</organization>
2152    </author>
2153    <date year="2001" month="April"/>
2154  </front>
2155  <seriesInfo name="RFC" value="2822"/>
2158<reference anchor="RFC3629">
2159  <front>
2160    <title>UTF-8, a transformation format of ISO 10646</title>
2161    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2162      <organization>Alis Technologies</organization>
2163      <address><email></email></address>
2164    </author>
2165    <date month="November" year="2003"/>
2166  </front>
2167  <seriesInfo name="RFC" value="3629"/>
2168  <seriesInfo name="STD" value="63"/>
2171<reference anchor="RFC4288">
2172  <front>
2173    <title>Media Type Specifications and Registration Procedures</title>
2174    <author initials="N." surname="Freed" fullname="N. Freed">
2175      <organization>Sun Microsystems</organization>
2176      <address>
2177        <email></email>
2178      </address>
2179    </author>
2180    <author initials="J." surname="Klensin" fullname="J. Klensin">
2181      <organization/>
2182      <address>
2183        <email></email>
2184      </address>
2185    </author>
2186    <date year="2005" month="December"/>
2187  </front>
2188  <seriesInfo name="BCP" value="13"/>
2189  <seriesInfo name="RFC" value="4288"/>
2194<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2196   HTTP/1.1 uses many of the constructs defined for Internet Mail (<xref target="RFC2822"/>) and the Multipurpose Internet Mail Extensions (MIME <xref target="RFC2045"/>) to
2197   allow entities to be transmitted in an open variety of
2198   representations and with extensible mechanisms. However, RFC 2045
2199   discusses mail, and HTTP has a few features that are different from
2200   those described in RFC 2045. These differences were carefully chosen
2201   to optimize performance over binary connections, to allow greater
2202   freedom in the use of new media types, to make date comparisons
2203   easier, and to acknowledge the practice of some early HTTP servers
2204   and clients.
2207   This appendix describes specific areas where HTTP differs from RFC
2208   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2209   aware of these differences and provide the appropriate conversions
2210   where necessary. Proxies and gateways from MIME environments to HTTP
2211   also need to be aware of the differences because some conversions
2212   might be required.
2215<section title="MIME-Version" anchor="mime-version">
2216  <x:anchor-alias value="MIME-Version"/>
2218   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2219   include a single MIME-Version general-header field to indicate what
2220   version of the MIME protocol was used to construct the message. Use
2221   of the MIME-Version header field indicates that the message is in
2222   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2223   Proxies/gateways are responsible for ensuring full compliance (where
2224   possible) when exporting HTTP messages to strict MIME environments.
2226<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/>
2227  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2230   MIME version "1.0" is the default for use in HTTP/1.1. However,
2231   HTTP/1.1 message parsing and semantics are defined by this document
2232   and not the MIME specification.
2236<section title="Conversion to Canonical Form" anchor="">
2238   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2239   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2240   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2241   allowed for subtypes of the "text" media type when transmitted over
2242   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2243   line breaks as CRLF and forbids the use of CR or LF outside of line
2244   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2245   line break within text content when a message is transmitted over
2246   HTTP.
2249   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2250   environment &SHOULD; translate all line breaks within the text media
2251   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2252   canonical form of CRLF. Note, however, that this might be complicated
2253   by the presence of a Content-Encoding and by the fact that HTTP
2254   allows the use of some character sets which do not use octets 13 and
2255   10 to represent CR and LF, as is the case for some multi-byte
2256   character sets.
2259   Implementors should note that conversion will break any cryptographic
2260   checksums applied to the original content unless the original content
2261   is already in canonical form. Therefore, the canonical form is
2262   recommended for any content that uses such checksums in HTTP.
2266<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2268   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2269   Content-Encoding header field. Since this acts as a modifier on the
2270   media type, proxies and gateways from HTTP to MIME-compliant
2271   protocols &MUST; either change the value of the Content-Type header
2272   field or decode the entity-body before forwarding the message. (Some
2273   experimental applications of Content-Type for Internet mail have used
2274   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2275   a function equivalent to Content-Encoding. However, this parameter is
2276   not part of RFC 2045).
2280<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2282   HTTP does not use the Content-Transfer-Encoding field of RFC
2283   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2284   remove any Content-Transfer-Encoding
2285   prior to delivering the response message to an HTTP client.
2288   Proxies and gateways from HTTP to MIME-compliant protocols are
2289   responsible for ensuring that the message is in the correct format
2290   and encoding for safe transport on that protocol, where "safe
2291   transport" is defined by the limitations of the protocol being used.
2292   Such a proxy or gateway &SHOULD; label the data with an appropriate
2293   Content-Transfer-Encoding if doing so will improve the likelihood of
2294   safe transport over the destination protocol.
2298<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2300   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2301   Proxies/gateways &MUST; remove any transfer-coding prior to
2302   forwarding a message via a MIME-compliant protocol.
2306<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2308   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2309   need to be aware of MIME line length limitations. Since HTTP does not
2310   have this limitation, HTTP does not fold long lines. MHTML messages
2311   being transported by HTTP follow all conventions of MHTML, including
2312   line length limitations and folding, canonicalization, etc., since
2313   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2314   does not interpret the content or any MIME header lines that might be
2315   contained therein.
2320<section title="Additional Features" anchor="additional.features">
2322   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2323   existing HTTP implementations, but not consistently and correctly
2324   across most HTTP/1.1 applications. Implementors are advised to be
2325   aware of these features, but cannot rely upon their presence in, or
2326   interoperability with, other HTTP/1.1 applications. Some of these
2327   describe proposed experimental features, and some describe features
2328   that experimental deployment found lacking that are now addressed in
2329   the base HTTP/1.1 specification.
2332   A number of other headers, such as Content-Disposition and Title,
2333   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2336<section title="Content-Disposition" anchor="content-disposition">
2337<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2338<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2339  <x:anchor-alias value="content-disposition"/>
2340  <x:anchor-alias value="disposition-type"/>
2341  <x:anchor-alias value="disposition-parm"/>
2342  <x:anchor-alias value="disp-extension-parm"/>
2343  <x:anchor-alias value="disp-extension-token"/>
2344  <x:anchor-alias value="filename-parm"/>
2346   The Content-Disposition response-header field has been proposed as a
2347   means for the origin server to suggest a default filename if the user
2348   requests that the content is saved to a file. This usage is derived
2349   from the definition of Content-Disposition in <xref target="RFC1806"/>.
2351<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-disposition"/><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"/>
2352  <x:ref>content-disposition</x:ref> = "Content-Disposition" ":"
2353                        <x:ref>disposition-type</x:ref> *( ";" <x:ref>disposition-parm</x:ref> )
2354  <x:ref>disposition-type</x:ref> = "attachment" | <x:ref>disp-extension-token</x:ref>
2355  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> | <x:ref>disp-extension-parm</x:ref>
2356  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2357  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
2358  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" ( <x:ref>token</x:ref> | <x:ref>quoted-string</x:ref> )
2361   An example is
2363<figure><artwork type="example">
2364     Content-Disposition: attachment; filename="fname.ext"
2367   The receiving user agent &SHOULD-NOT;  respect any directory path
2368   information present in the filename-parm parameter, which is the only
2369   parameter believed to apply to HTTP implementations at this time. The
2370   filename &SHOULD; be treated as a terminal component only.
2373   If this header is used in a response with the application/octet-stream
2374   content-type, the implied suggestion is that the user agent
2375   should not display the response, but directly enter a `save response
2376   as...' dialog.
2379   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2384<section title="Compatibility with Previous Versions" anchor="compatibility">
2385<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2387   Transfer-coding and message lengths all interact in ways that
2388   required fixing exactly when chunked encoding is used (to allow for
2389   transfer encoding that may not be self delimiting); it was important
2390   to straighten out exactly how message lengths are computed.
2391   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2392   <xref target="Part5"/> and <xref target="Part6"/>).
2395   Charset wildcarding is introduced to avoid explosion of character set
2396   names in accept headers. (<xref target="header.accept-charset"/>)
2399   Content-Base was deleted from the specification: it was not
2400   implemented widely, and there is no simple, safe way to introduce it
2401   without a robust extension mechanism. In addition, it is used in a
2402   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2405   A content-coding of "identity" was introduced, to solve problems
2406   discovered in caching. (<xref target="content.codings"/>)
2409   Quality Values of zero should indicate that "I don't want something"
2410   to allow clients to refuse a representation. (<xref target="quality.values"/>)
2413   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
2414   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
2415   specification, but not commonly implemented. See <xref target="RFC2068"/>.
2419<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2421  Clarify contexts that charset is used in.
2422  (<xref target="character.sets"/>)
2425  Remove reference to non-existant identity transfer-coding value tokens.
2426  (<xref target="no.content-transfer-encoding"/>)
2432<section title="Change Log (to be removed by RFC Editor before publication)">
2434<section title="Since RFC2616">
2436  Extracted relevant partitions from <xref target="RFC2616"/>.
2440<section title="Since draft-ietf-httpbis-p3-payload-00">
2442  Closed issues:
2443  <list style="symbols">
2444    <t>
2445      <eref target=""/>:
2446      "Media Type Registrations"
2447      (<eref target=""/>)
2448    </t>
2449    <t>
2450      <eref target=""/>:
2451      "Clarification regarding quoting of charset values"
2452      (<eref target=""/>)
2453    </t>
2454    <t>
2455      <eref target=""/>:
2456      "Remove 'identity' token references"
2457      (<eref target=""/>)
2458    </t>
2459    <t>
2460      <eref target=""/>:
2461      "Accept-Encoding BNF"
2462    </t>
2463    <t>
2464      <eref target=""/>:
2465      "Normative and Informative references"
2466    </t>
2467    <t>
2468      <eref target=""/>:
2469      "RFC1700 references"
2470    </t>
2471    <t>
2472      <eref target=""/>:
2473      "Updating to RFC4288"
2474    </t>
2475    <t>
2476      <eref target=""/>:
2477      "Informative references"
2478    </t>
2479    <t>
2480      <eref target=""/>:
2481      "ISO-8859-1 Reference"
2482    </t>
2483    <t>
2484      <eref target=""/>:
2485      "Encoding References Normative"
2486    </t>
2487    <t>
2488      <eref target=""/>:
2489      "Normative up-to-date references"
2490    </t>
2491  </list>
2495<section title="Since draft-ietf-httpbis-p3-payload-01">
2497  Ongoing work on ABNF conversion (<eref target=""/>):
2498  <list style="symbols">
2499    <t>
2500      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2501    </t>
2502  </list>
2506<section title="Since draft-ietf-httpbis-p3-payload-02">
2508  Closed issues:
2509  <list style="symbols">
2510    <t>
2511      <eref target=""/>:
2512      "Quoting Charsets"
2513    </t>
2514    <t>
2515      <eref target=""/>:
2516      "Classification for Allow header"
2517    </t>
2518    <t>
2519      <eref target=""/>:
2520      "missing default for qvalue in description of Accept-Encoding"
2521    </t>
2522  </list>
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