source: draft-ietf-httpbis/latest/p3-payload.xml @ 301

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>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 "August">
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    The changes in this draft are summarized in <xref target="changes.since.02"/>.
212  </t>
216<section title="Introduction" anchor="introduction">
218   This document defines HTTP/1.1 message payloads (a.k.a., content), the
219   associated metadata header fields that define how the payload is intended
220   to be interpreted by a recipient, the request header fields that
221   may influence content selection, and the various selection algorithms
222   that are collectively referred to as HTTP content negotiation.
225   This document is currently disorganized in order to minimize the changes
226   between drafts and enable reviewers to see the smaller errata changes.
227   The next draft will reorganize the sections to better reflect the content.
228   In particular, the sections on entities will be renamed payload and moved
229   to the first half of the document, while the sections on content negotiation
230   and associated request header fields will be moved to the second half.  The
231   current mess reflects how widely dispersed these topics and associated
232   requirements had become in <xref target="RFC2616"/>.
235<section title="Requirements" anchor="intro.requirements">
237   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
238   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
239   document are to be interpreted as described in <xref target="RFC2119"/>.
242   An implementation is not compliant if it fails to satisfy one or more
243   of the &MUST; or &REQUIRED; level requirements for the protocols it
244   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
245   level and all the &SHOULD; level requirements for its protocols is said
246   to be "unconditionally compliant"; one that satisfies all the &MUST;
247   level requirements but not all the &SHOULD; level requirements for its
248   protocols is said to be "conditionally compliant."
253<section title="Notational Conventions and Generic Grammar" anchor="notation">
254  <x:anchor-alias value="ALPHA"/>
255  <x:anchor-alias value="DIGIT"/>
256  <x:anchor-alias value="OCTET"/>
257  <x:anchor-alias value="quoted-string"/>
258  <x:anchor-alias value="token"/>
260  This specification uses the ABNF syntax defined in &notation-abnf; and
261  the core rules defined in &basic-rules;:
262  <cref anchor="abnf.dep">ABNF syntax and basic rules will be adopted from RFC 5234, see
263  <eref target=""/>.</cref>
265<figure><artwork type="abnf2616">
266  <x:ref>ALPHA</x:ref>          = &lt;ALPHA, defined in &basic-rules;&gt;
267  <x:ref>DIGIT</x:ref>          = &lt;DIGIT, defined in &basic-rules;&gt;
268  <x:ref>OCTET</x:ref>          = &lt;OCTET, defined in &basic-rules;&gt;
270<figure><artwork type="abnf2616">
271  <x:ref>quoted-string</x:ref>  = &lt;quoted-string, defined in &basic-rules;&gt;
272  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
274<t anchor="abnf.dependencies">
275  <x:anchor-alias value="absoluteURI"/>
276  <x:anchor-alias value="Allow"/>
277  <x:anchor-alias value="Content-Length"/>
278  <x:anchor-alias value="Content-Range"/>
279  <x:anchor-alias value="Expires"/>
280  <x:anchor-alias value="Last-Modified"/>
281  <x:anchor-alias value="message-header"/>
282  <x:anchor-alias value="relativeURI"/>
283  The ABNF rules below are defined in other parts:
285<figure><!--Part1--><artwork type="abnf2616">
286  <x:ref>absoluteURI</x:ref>    = &lt;absoluteURI, defined in &general-syntax;&gt;
287  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
288  <x:ref>relativeURI</x:ref>    = &lt;relativeURI, defined in &general-syntax;&gt;
289  <x:ref>message-header</x:ref> = &lt;message-header, defined in &message-headers;&gt;
291<figure><!--Part4--><artwork type="abnf2616">
292  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
294<figure><!--Part5--><artwork type="abnf2616">
295  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
297<figure><!--Part6--><artwork type="abnf2616">
298  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
302<section title="Protocol Parameters" anchor="protocol.parameters">
304<section title="Character Sets" anchor="character.sets">
306   HTTP uses the same definition of the term "character set" as that
307   described for MIME:
310   The term "character set" is used in this document to refer to a
311   method used with one or more tables to convert a sequence of octets
312   into a sequence of characters. Note that unconditional conversion in
313   the other direction is not required, in that not all characters may
314   be available in a given character set and a character set may provide
315   more than one sequence of octets to represent a particular character.
316   This definition is intended to allow various kinds of character
317   encoding, from simple single-table mappings such as US-ASCII to
318   complex table switching methods such as those that use ISO-2022's
319   techniques. However, the definition associated with a MIME character
320   set name &MUST; fully specify the mapping to be performed from octets
321   to characters. In particular, use of external profiling information
322   to determine the exact mapping is not permitted.
325      <x:h>Note:</x:h> This use of the term "character set" is more commonly
326      referred to as a "character encoding." However, since HTTP and
327      MIME share the same registry, it is important that the terminology
328      also be shared.
330<t anchor="rule.charset">
331  <x:anchor-alias value="charset"/>
332   HTTP character sets are identified by case-insensitive tokens. The
333   complete set of tokens is defined by the IANA Character Set registry
334   (<eref target=""/>).
336<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
337  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
340   Although HTTP allows an arbitrary token to be used as a charset
341   value, any token that has a predefined value within the IANA
342   Character Set registry &MUST; represent the character set defined
343   by that registry. Applications &SHOULD; limit their use of character
344   sets to those defined by the IANA registry.
347   HTTP uses charset in two contexts: within an Accept-Charset request
348   header (in which the charset value is an unquoted token) and as the
349   value of a parameter in a Content-Type header (within a request or
350   response), in which case the parameter value of the charset parameter
351   may be quoted.
354   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
355   <xref target="RFC2277"/>.
358<section title="Missing Charset" anchor="missing.charset">
360   Some HTTP/1.0 software has interpreted a Content-Type header without
361   charset parameter incorrectly to mean "recipient should guess."
362   Senders wishing to defeat this behavior &MAY; include a charset
363   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
364   it is known that it will not confuse the recipient.
367   Unfortunately, some older HTTP/1.0 clients did not deal properly with
368   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
369   charset label provided by the sender; and those user agents that have
370   a provision to "guess" a charset &MUST; use the charset from the
371   content-type field if they support that charset, rather than the
372   recipient's preference, when initially displaying a document. See
373   <xref target="canonicalization.and.text.defaults"/>.
378<section title="Content Codings" anchor="content.codings">
379  <x:anchor-alias value="content-coding"/>
381   Content coding values indicate an encoding transformation that has
382   been or can be applied to an entity. Content codings are primarily
383   used to allow a document to be compressed or otherwise usefully
384   transformed without losing the identity of its underlying media type
385   and without loss of information. Frequently, the entity is stored in
386   coded form, transmitted directly, and only decoded by the recipient.
388<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
389  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
392   All content-coding values are case-insensitive. HTTP/1.1 uses
393   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
394   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
395   describes the content-coding, what is more important is that it
396   indicates what decoding mechanism will be required to remove the
397   encoding.
400   The Internet Assigned Numbers Authority (IANA) acts as a registry for
401   content-coding value tokens. Initially, the registry contains the
402   following tokens:
405   gzip<iref item="gzip"/>
406  <list>
407    <t>
408        An encoding format produced by the file compression program
409        "gzip" (GNU zip) as described in <xref target="RFC1952"/>. This format is a
410        Lempel-Ziv coding (LZ77) with a 32 bit CRC.
411    </t>
412  </list>
415   compress<iref item="compress"/>
416  <list><t>
417        The encoding format produced by the common UNIX file compression
418        program "compress". This format is an adaptive Lempel-Ziv-Welch
419        coding (LZW).
421        Use of program names for the identification of encoding formats
422        is not desirable and is discouraged for future encodings. Their
423        use here is representative of historical practice, not good
424        design. For compatibility with previous implementations of HTTP,
425        applications &SHOULD; consider "x-gzip" and "x-compress" to be
426        equivalent to "gzip" and "compress" respectively.
427  </t></list>
430   deflate<iref item="deflate"/>
431  <list><t>
432        The "zlib" format defined in <xref target="RFC1950"/> in combination with
433        the "deflate" compression mechanism described in <xref target="RFC1951"/>.
434  </t></list>
437   identity<iref item="identity"/>
438  <list><t>
439        The default (identity) encoding; the use of no transformation
440        whatsoever. This content-coding is used only in the Accept-Encoding
441        header, and &SHOULD-NOT;  be used in the Content-Encoding
442        header.
443  </t></list>
446   New content-coding value tokens &SHOULD; be registered; to allow
447   interoperability between clients and servers, specifications of the
448   content coding algorithms needed to implement a new value &SHOULD; be
449   publicly available and adequate for independent implementation, and
450   conform to the purpose of content coding defined in this section.
454<section title="Media Types" anchor="media.types">
455  <x:anchor-alias value="media-type"/>
456  <x:anchor-alias value="type"/>
457  <x:anchor-alias value="subtype"/>
459   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
460   and Accept (<xref target="header.accept"/>) header fields in order to provide
461   open and extensible data typing and type negotiation.
463<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"/>
464  <x:ref>media-type</x:ref>     = <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> *( ";" <x:ref>parameter</x:ref> )
465  <x:ref>type</x:ref>           = <x:ref>token</x:ref>
466  <x:ref>subtype</x:ref>        = <x:ref>token</x:ref>
468<t anchor="rule.parameter">
469  <x:anchor-alias value="attribute"/>
470  <x:anchor-alias value="parameter"/>
471  <x:anchor-alias value="value"/>
472   Parameters &MAY; follow the type/subtype in the form of attribute/value
473   pairs.
475<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"/>
476  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
477  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
478  <x:ref>value</x:ref>          = <x:ref>token</x:ref> | <x:ref>quoted-string</x:ref>
481   The type, subtype, and parameter attribute names are case-insensitive.
482   Parameter values might or might not be case-sensitive,
483   depending on the semantics of the parameter name. Linear white space
484   (LWS) &MUST-NOT; be used between the type and subtype, nor between an
485   attribute and its value. The presence or absence of a parameter might
486   be significant to the processing of a media-type, depending on its
487   definition within the media type registry.
490   A parameter value that matches the <x:ref>token</x:ref> production may be
491   transmitted as either a token or within a quoted-string. The quoted and
492   unquoted values are equivalent.
495   Note that some older HTTP applications do not recognize media type
496   parameters. When sending data to older HTTP applications,
497   implementations &SHOULD; only use media type parameters when they are
498   required by that type/subtype definition.
501   Media-type values are registered with the Internet Assigned Number
502   Authority (IANA). The media type registration process is
503   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
504   discouraged.
507<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
509   Internet media types are registered with a canonical form. An
510   entity-body transferred via HTTP messages &MUST; be represented in the
511   appropriate canonical form prior to its transmission except for
512   "text" types, as defined in the next paragraph.
515   When in canonical form, media subtypes of the "text" type use CRLF as
516   the text line break. HTTP relaxes this requirement and allows the
517   transport of text media with plain CR or LF alone representing a line
518   break when it is done consistently for an entire entity-body. HTTP
519   applications &MUST; accept CRLF, bare CR, and bare LF as being
520   representative of a line break in text media received via HTTP. In
521   addition, if the text is represented in a character set that does not
522   use octets 13 and 10 for CR and LF respectively, as is the case for
523   some multi-byte character sets, HTTP allows the use of whatever octet
524   sequences are defined by that character set to represent the
525   equivalent of CR and LF for line breaks. This flexibility regarding
526   line breaks applies only to text media in the entity-body; a bare CR
527   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
528   structures (such as header fields and multipart boundaries).
531   If an entity-body is encoded with a content-coding, the underlying
532   data &MUST; be in a form defined above prior to being encoded.
535   The "charset" parameter is used with some media types to define the
536   character set (<xref target="character.sets"/>) of the data. When no explicit charset
537   parameter is provided by the sender, media subtypes of the "text"
538   type are defined to have a default charset value of "ISO-8859-1" when
539   received via HTTP. Data in character sets other than "ISO-8859-1" or
540   its subsets &MUST; be labeled with an appropriate charset value. See
541   <xref target="missing.charset"/> for compatibility problems.
545<section title="Multipart Types" anchor="multipart.types">
547   MIME provides for a number of "multipart" types -- encapsulations of
548   one or more entities within a single message-body. All multipart
549   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
550   and &MUST; include a boundary parameter as part of the media type
551   value. The message body is itself a protocol element and &MUST;
552   therefore use only CRLF to represent line breaks between body-parts.
553   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
554   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
555   original multipart contains an epilogue). These restrictions exist in
556   order to preserve the self-delimiting nature of a multipart message-body,
557   wherein the "end" of the message-body is indicated by the
558   ending multipart boundary.
561   In general, HTTP treats a multipart message-body no differently than
562   any other media type: strictly as payload. The one exception is the
563   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
564   (Partial Content) response.
565   <!-- jre: re-insert removed text pointing to caching? -->
566   In all
567   other cases, an HTTP user agent &SHOULD; follow the same or similar
568   behavior as a MIME user agent would upon receipt of a multipart type.
569   The MIME header fields within each body-part of a multipart message-body
570   do not have any significance to HTTP beyond that defined by
571   their MIME semantics.
574   In general, an HTTP user agent &SHOULD; follow the same or similar
575   behavior as a MIME user agent would upon receipt of a multipart type.
576   If an application receives an unrecognized multipart subtype, the
577   application &MUST; treat it as being equivalent to "multipart/mixed".
580      <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
581      for carrying form data suitable for processing via the POST
582      request method, as described in <xref target="RFC2388"/>.
587<section title="Quality Values" anchor="quality.values">
588  <x:anchor-alias value="qvalue"/>
590   HTTP content negotiation (<xref target="content.negotiation"/>) uses short "floating point"
591   numbers to indicate the relative importance ("weight") of various
592   negotiable parameters.  A weight is normalized to a real number in
593   the range 0 through 1, where 0 is the minimum and 1 the maximum
594   value. If a parameter has a quality value of 0, then content with
595   this parameter is `not acceptable' for the client. HTTP/1.1
596   applications &MUST-NOT; generate more than three digits after the
597   decimal point. User configuration of these values &SHOULD; also be
598   limited in this fashion.
600<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
601  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
602                 | ( "1" [ "." 0*3("0") ] )
605   "Quality values" is a misnomer, since these values merely represent
606   relative degradation in desired quality.
610<section title="Language Tags" anchor="language.tags">
611  <x:anchor-alias value="language-tag"/>
612  <x:anchor-alias value="primary-tag"/>
613  <x:anchor-alias value="subtag"/>
615   A language tag identifies a natural language spoken, written, or
616   otherwise conveyed by human beings for communication of information
617   to other human beings. Computer languages are explicitly excluded.
618   HTTP uses language tags within the Accept-Language and Content-Language
619   fields.
622   The syntax and registry of HTTP language tags is the same as that
623   defined by <xref target="RFC1766"/>. In summary, a language tag is composed of 1
624   or more parts: A primary language tag and a possibly empty series of
625   subtags:
627<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"/>
628  <x:ref>language-tag</x:ref>  = <x:ref>primary-tag</x:ref> *( "-" <x:ref>subtag</x:ref> )
629  <x:ref>primary-tag</x:ref>   = 1*8<x:ref>ALPHA</x:ref>
630  <x:ref>subtag</x:ref>        = 1*8<x:ref>ALPHA</x:ref>
633   White space is not allowed within the tag and all tags are case-insensitive.
634   The name space of language tags is administered by the
635   IANA. Example tags include:
637<figure><artwork type="example">
638    en, en-US, en-cockney, i-cherokee, x-pig-latin
641   where any two-letter primary-tag is an ISO-639 language abbreviation
642   and any two-letter initial subtag is an ISO-3166 country code. (The
643   last three tags above are not registered tags; all but the last are
644   examples of tags which could be registered in future.)
649<section title="Entity" anchor="entity">
651   Request and Response messages &MAY; transfer an entity if not otherwise
652   restricted by the request method or response status code. An entity
653   consists of entity-header fields and an entity-body, although some
654   responses will only include the entity-headers.
657   In this section, both sender and recipient refer to either the client
658   or the server, depending on who sends and who receives the entity.
661<section title="Entity Header Fields" anchor="entity.header.fields">
662  <x:anchor-alias value="entity-header"/>
663  <x:anchor-alias value="extension-header"/>
665   Entity-header fields define metainformation about the entity-body or,
666   if no body is present, about the resource identified by the request.
668<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
669  <x:ref>entity-header</x:ref>  = <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
670                 | <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
671                 | <x:ref>Content-Length</x:ref>           ; &header-content-length;
672                 | <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
673                 | <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
674                 | <x:ref>Content-Range</x:ref>            ; &header-content-range;
675                 | <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
676                 | <x:ref>Expires</x:ref>                  ; &header-expires;
677                 | <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
678                 | <x:ref>extension-header</x:ref>
680  <x:ref>extension-header</x:ref> = <x:ref>message-header</x:ref>
683   The extension-header mechanism allows additional entity-header fields
684   to be defined without changing the protocol, but these fields cannot
685   be assumed to be recognizable by the recipient. Unrecognized header
686   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
687   transparent proxies.
691<section title="Entity Body" anchor="entity.body">
692  <x:anchor-alias value="entity-body"/>
694   The entity-body (if any) sent with an HTTP request or response is in
695   a format and encoding defined by the entity-header fields.
697<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
698  <x:ref>entity-body</x:ref>    = *<x:ref>OCTET</x:ref>
701   An entity-body is only present in a message when a message-body is
702   present, as described in &message-body;. The entity-body is obtained
703   from the message-body by decoding any Transfer-Encoding that might
704   have been applied to ensure safe and proper transfer of the message.
707<section title="Type" anchor="type">
709   When an entity-body is included with a message, the data type of that
710   body is determined via the header fields Content-Type and Content-Encoding.
711   These define a two-layer, ordered encoding model:
713<figure><artwork type="example">
714    entity-body := Content-Encoding( Content-Type( data ) )
717   Content-Type specifies the media type of the underlying data.
718   Content-Encoding may be used to indicate any additional content
719   codings applied to the data, usually for the purpose of data
720   compression, that are a property of the requested resource. There is
721   no default encoding.
724   Any HTTP/1.1 message containing an entity-body &SHOULD; include a
725   Content-Type header field defining the media type of that body. If
726   and only if the media type is not given by a Content-Type field, the
727   recipient &MAY; attempt to guess the media type via inspection of its
728   content and/or the name extension(s) of the URI used to identify the
729   resource. If the media type remains unknown, the recipient &SHOULD;
730   treat it as type "application/octet-stream".
734<section title="Entity Length" anchor="entity.length">
736   The entity-length of a message is the length of the message-body
737   before any transfer-codings have been applied. &message-length; defines
738   how the transfer-length of a message-body is determined.
744<section title="Content Negotiation" anchor="content.negotiation">
746   Most HTTP responses include an entity which contains information for
747   interpretation by a human user. Naturally, it is desirable to supply
748   the user with the "best available" entity corresponding to the
749   request. Unfortunately for servers and caches, not all users have the
750   same preferences for what is "best," and not all user agents are
751   equally capable of rendering all entity types. For that reason, HTTP
752   has provisions for several mechanisms for "content negotiation" --
753   the process of selecting the best representation for a given response
754   when there are multiple representations available.
755  <list><t>
756      <x:h>Note:</x:h> This is not called "format negotiation" because the
757      alternate representations may be of the same media type, but use
758      different capabilities of that type, be in different languages,
759      etc.
760  </t></list>
763   Any response containing an entity-body &MAY; be subject to negotiation,
764   including error responses.
767   There are two kinds of content negotiation which are possible in
768   HTTP: server-driven and agent-driven negotiation. These two kinds of
769   negotiation are orthogonal and thus may be used separately or in
770   combination. One method of combination, referred to as transparent
771   negotiation, occurs when a cache uses the agent-driven negotiation
772   information provided by the origin server in order to provide
773   server-driven negotiation for subsequent requests.
776<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
778   If the selection of the best representation for a response is made by
779   an algorithm located at the server, it is called server-driven
780   negotiation. Selection is based on the available representations of
781   the response (the dimensions over which it can vary; e.g. language,
782   content-coding, etc.) and the contents of particular header fields in
783   the request message or on other information pertaining to the request
784   (such as the network address of the client).
787   Server-driven negotiation is advantageous when the algorithm for
788   selecting from among the available representations is difficult to
789   describe to the user agent, or when the server desires to send its
790   "best guess" to the client along with the first response (hoping to
791   avoid the round-trip delay of a subsequent request if the "best
792   guess" is good enough for the user). In order to improve the server's
793   guess, the user agent &MAY; include request header fields (Accept,
794   Accept-Language, Accept-Encoding, etc.) which describe its
795   preferences for such a response.
798   Server-driven negotiation has disadvantages:
799  <list style="numbers">
800    <t>
801         It is impossible for the server to accurately determine what
802         might be "best" for any given user, since that would require
803         complete knowledge of both the capabilities of the user agent
804         and the intended use for the response (e.g., does the user want
805         to view it on screen or print it on paper?).
806    </t>
807    <t>
808         Having the user agent describe its capabilities in every
809         request can be both very inefficient (given that only a small
810         percentage of responses have multiple representations) and a
811         potential violation of the user's privacy.
812    </t>
813    <t>
814         It complicates the implementation of an origin server and the
815         algorithms for generating responses to a request.
816    </t>
817    <t>
818         It may limit a public cache's ability to use the same response
819         for multiple user's requests.
820    </t>
821  </list>
824   HTTP/1.1 includes the following request-header fields for enabling
825   server-driven negotiation through description of user agent
826   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
827   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
828   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;). However, an
829   origin server is not limited to these dimensions and &MAY; vary the
830   response based on any aspect of the request, including information
831   outside the request-header fields or within extension header fields
832   not defined by this specification.
835   The Vary header field (&header-vary;) can be used to express the parameters the
836   server uses to select a representation that is subject to server-driven
837   negotiation.
841<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
843   With agent-driven negotiation, selection of the best representation
844   for a response is performed by the user agent after receiving an
845   initial response from the origin server. Selection is based on a list
846   of the available representations of the response included within the
847   header fields or entity-body of the initial response, with each
848   representation identified by its own URI. Selection from among the
849   representations may be performed automatically (if the user agent is
850   capable of doing so) or manually by the user selecting from a
851   generated (possibly hypertext) menu.
854   Agent-driven negotiation is advantageous when the response would vary
855   over commonly-used dimensions (such as type, language, or encoding),
856   when the origin server is unable to determine a user agent's
857   capabilities from examining the request, and generally when public
858   caches are used to distribute server load and reduce network usage.
861   Agent-driven negotiation suffers from the disadvantage of needing a
862   second request to obtain the best alternate representation. This
863   second request is only efficient when caching is used. In addition,
864   this specification does not define any mechanism for supporting
865   automatic selection, though it also does not prevent any such
866   mechanism from being developed as an extension and used within
867   HTTP/1.1.
870   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
871   status codes for enabling agent-driven negotiation when the server is
872   unwilling or unable to provide a varying response using server-driven
873   negotiation.
877<section title="Transparent Negotiation" anchor="transparent.negotiation">
879   Transparent negotiation is a combination of both server-driven and
880   agent-driven negotiation. When a cache is supplied with a form of the
881   list of available representations of the response (as in agent-driven
882   negotiation) and the dimensions of variance are completely understood
883   by the cache, then the cache becomes capable of performing server-driven
884   negotiation on behalf of the origin server for subsequent
885   requests on that resource.
888   Transparent negotiation has the advantage of distributing the
889   negotiation work that would otherwise be required of the origin
890   server and also removing the second request delay of agent-driven
891   negotiation when the cache is able to correctly guess the right
892   response.
895   This specification does not define any mechanism for transparent
896   negotiation, though it also does not prevent any such mechanism from
897   being developed as an extension that could be used within HTTP/1.1.
902<section title="Header Field Definitions" anchor="header.fields">
904   This section defines the syntax and semantics of HTTP/1.1 header fields
905   related to the payload of messages.
908   For entity-header fields, both sender and recipient refer to either the
909   client or the server, depending on who sends and who receives the entity.
912<section title="Accept" anchor="header.accept">
913  <iref primary="true" item="Accept header" x:for-anchor=""/>
914  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
915  <x:anchor-alias value="Accept"/>
916  <x:anchor-alias value="accept-extension"/>
917  <x:anchor-alias value="accept-params"/>
918  <x:anchor-alias value="media-range"/>
920   The Accept request-header field can be used to specify certain media
921   types which are acceptable for the response. Accept headers can be
922   used to indicate that the request is specifically limited to a small
923   set of desired types, as in the case of a request for an in-line
924   image.
926<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"/>
927  <x:ref>Accept</x:ref>         = "Accept" ":"
928                   #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
930  <x:ref>media-range</x:ref>    = ( "*/*"
931                   | ( <x:ref>type</x:ref> "/" "*" )
932                   | ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
933                   ) *( ";" <x:ref>parameter</x:ref> )
934  <x:ref>accept-params</x:ref>  = ";" "q" "=" <x:ref>qvalue</x:ref> *( <x:ref>accept-extension</x:ref> )
935  <x:ref>accept-extension</x:ref> = ";" <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> | <x:ref>quoted-string</x:ref> ) ]
938   The asterisk "*" character is used to group media types into ranges,
939   with "*/*" indicating all media types and "type/*" indicating all
940   subtypes of that type. The media-range &MAY; include media type
941   parameters that are applicable to that range.
944   Each media-range &MAY; be followed by one or more accept-params,
945   beginning with the "q" parameter for indicating a relative quality
946   factor. The first "q" parameter (if any) separates the media-range
947   parameter(s) from the accept-params. Quality factors allow the user
948   or user agent to indicate the relative degree of preference for that
949   media-range, using the qvalue scale from 0 to 1 (<xref target="quality.values"/>). The
950   default value is q=1.
951  <list><t>
952      <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
953      parameters from Accept extension parameters is due to historical
954      practice. Although this prevents any media type parameter named
955      "q" from being used with a media range, such an event is believed
956      to be unlikely given the lack of any "q" parameters in the IANA
957      media type registry and the rare usage of any media type
958      parameters in Accept. Future media types are discouraged from
959      registering any parameter named "q".
960  </t></list>
963   The example
965<figure><artwork type="example">
966    Accept: audio/*; q=0.2, audio/basic
969   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
970   type if it is the best available after an 80% mark-down in quality."
973   If no Accept header field is present, then it is assumed that the
974   client accepts all media types. If an Accept header field is present,
975   and if the server cannot send a response which is acceptable
976   according to the combined Accept field value, then the server &SHOULD;
977   send a 406 (Not Acceptable) response.
980   A more elaborate example is
982<figure><artwork type="example">
983    Accept: text/plain; q=0.5, text/html,
984            text/x-dvi; q=0.8, text/x-c
987   Verbally, this would be interpreted as "text/html and text/x-c are
988   the preferred media types, but if they do not exist, then send the
989   text/x-dvi entity, and if that does not exist, send the text/plain
990   entity."
993   Media ranges can be overridden by more specific media ranges or
994   specific media types. If more than one media range applies to a given
995   type, the most specific reference has precedence. For example,
997<figure><artwork type="example">
998    Accept: text/*, text/html, text/html;level=1, */*
1001   have the following precedence:
1003<figure><artwork type="example">
1004    1) text/html;level=1
1005    2) text/html
1006    3) text/*
1007    4) */*
1010   The media type quality factor associated with a given type is
1011   determined by finding the media range with the highest precedence
1012   which matches that type. For example,
1014<figure><artwork type="example">
1015    Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1016            text/html;level=2;q=0.4, */*;q=0.5
1019   would cause the following values to be associated:
1021<figure><artwork type="example">
1022    text/html;level=1         = 1
1023    text/html                 = 0.7
1024    text/plain                = 0.3
1025    image/jpeg                = 0.5
1026    text/html;level=2         = 0.4
1027    text/html;level=3         = 0.7
1030      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1031      values for certain media ranges. However, unless the user agent is
1032      a closed system which cannot interact with other rendering agents,
1033      this default set ought to be configurable by the user.
1037<section title="Accept-Charset" anchor="header.accept-charset">
1038  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1039  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1040  <x:anchor-alias value="Accept-Charset"/>
1042   The Accept-Charset request-header field can be used to indicate what
1043   character sets are acceptable for the response. This field allows
1044   clients capable of understanding more comprehensive or special-purpose
1045   character sets to signal that capability to a server which is
1046   capable of representing documents in those character sets.
1048<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/>
1049  <x:ref>Accept-Charset</x:ref> = "Accept-Charset" ":"
1050          1#( ( <x:ref>charset</x:ref> | "*" ) [ ";" "q" "=" <x:ref>qvalue</x:ref> ] )
1053   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1054   be given an associated quality value which represents the user's
1055   preference for that charset. The default value is q=1. An example is
1057<figure><artwork type="example">
1058   Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1061   The special value "*", if present in the Accept-Charset field,
1062   matches every character set (including ISO-8859-1) which is not
1063   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1064   in an Accept-Charset field, then all character sets not explicitly
1065   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1066   a quality value of 1 if not explicitly mentioned.
1069   If no Accept-Charset header is present, the default is that any
1070   character set is acceptable. If an Accept-Charset header is present,
1071   and if the server cannot send a response which is acceptable
1072   according to the Accept-Charset header, then the server &SHOULD; send
1073   an error response with the 406 (Not Acceptable) status code, though
1074   the sending of an unacceptable response is also allowed.
1078<section title="Accept-Encoding" anchor="header.accept-encoding">
1079  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1080  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1081  <x:anchor-alias value="Accept-Encoding"/>
1082  <x:anchor-alias value="codings"/>
1084   The Accept-Encoding request-header field is similar to Accept, but
1085   restricts the content-codings (<xref target="content.codings"/>) that are acceptable in
1086   the response.
1088<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/>
1089  <x:ref>Accept-Encoding</x:ref>  = "Accept-Encoding" ":"
1090                     #( <x:ref>codings</x:ref> [ ";" "q" "=" <x:ref>qvalue</x:ref> ] )
1091  <x:ref>codings</x:ref>          = ( <x:ref>content-coding</x:ref> | "*" )
1094   Each codings value &MAY; be given an associated quality value which
1095   represents the preference for that encoding. The default value is q=1.
1098   Examples of its use are:
1100<figure><artwork type="example">
1101    Accept-Encoding: compress, gzip
1102    Accept-Encoding:
1103    Accept-Encoding: *
1104    Accept-Encoding: compress;q=0.5, gzip;q=1.0
1105    Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1108   A server tests whether a content-coding is acceptable, according to
1109   an Accept-Encoding field, using these rules:
1110  <list style="numbers">
1111      <t>If the content-coding is one of the content-codings listed in
1112         the Accept-Encoding field, then it is acceptable, unless it is
1113         accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
1114         qvalue of 0 means "not acceptable.")</t>
1116      <t>The special "*" symbol in an Accept-Encoding field matches any
1117         available content-coding not explicitly listed in the header
1118         field.</t>
1120      <t>If multiple content-codings are acceptable, then the acceptable
1121         content-coding with the highest non-zero qvalue is preferred.</t>
1123      <t>The "identity" content-coding is always acceptable, unless
1124         specifically refused because the Accept-Encoding field includes
1125         "identity;q=0", or because the field includes "*;q=0" and does
1126         not explicitly include the "identity" content-coding. If the
1127         Accept-Encoding field-value is empty, then only the "identity"
1128         encoding is acceptable.</t>
1129  </list>
1132   If an Accept-Encoding field is present in a request, and if the
1133   server cannot send a response which is acceptable according to the
1134   Accept-Encoding header, then the server &SHOULD; send an error response
1135   with the 406 (Not Acceptable) status code.
1138   If no Accept-Encoding field is present in a request, the server &MAY;
1139   assume that the client will accept any content coding. In this case,
1140   if "identity" is one of the available content-codings, then the
1141   server &SHOULD; use the "identity" content-coding, unless it has
1142   additional information that a different content-coding is meaningful
1143   to the client.
1144  <list><t>
1145      <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1146      and if the "identity" content-coding is unavailable, then
1147      content-codings commonly understood by HTTP/1.0 clients (i.e.,
1148      "gzip" and "compress") are preferred; some older clients
1149      improperly display messages sent with other content-codings.  The
1150      server might also make this decision based on information about
1151      the particular user-agent or client.
1152    </t><t>
1153      <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1154      associated with content-codings. This means that qvalues will not
1155      work and are not permitted with x-gzip or x-compress.
1156    </t></list>
1160<section title="Accept-Language" anchor="header.accept-language">
1161  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1162  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1163  <x:anchor-alias value="Accept-Language"/>
1164  <x:anchor-alias value="language-range"/>
1166   The Accept-Language request-header field is similar to Accept, but
1167   restricts the set of natural languages that are preferred as a
1168   response to the request. Language tags are defined in <xref target="language.tags"/>.
1170<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/>
1171  <x:ref>Accept-Language</x:ref> = "Accept-Language" ":"
1172                    1#( <x:ref>language-range</x:ref> [ ";" "q" "=" <x:ref>qvalue</x:ref> ] )
1173  <x:ref>language-range</x:ref>  = ( ( 1*8<x:ref>ALPHA</x:ref> *( "-" 1*8<x:ref>ALPHA</x:ref> ) ) | "*" )
1176   Each language-range &MAY; be given an associated quality value which
1177   represents an estimate of the user's preference for the languages
1178   specified by that range. The quality value defaults to "q=1". For
1179   example,
1181<figure><artwork type="example">
1182    Accept-Language: da, en-gb;q=0.8, en;q=0.7
1185   would mean: "I prefer Danish, but will accept British English and
1186   other types of English." A language-range matches a language-tag if
1187   it exactly equals the tag, or if it exactly equals a prefix of the
1188   tag such that the first tag character following the prefix is "-".
1189   The special range "*", if present in the Accept-Language field,
1190   matches every tag not matched by any other range present in the
1191   Accept-Language field.
1192  <list><t>
1193      <x:h>Note:</x:h> This use of a prefix matching rule does not imply that
1194      language tags are assigned to languages in such a way that it is
1195      always true that if a user understands a language with a certain
1196      tag, then this user will also understand all languages with tags
1197      for which this tag is a prefix. The prefix rule simply allows the
1198      use of prefix tags if this is the case.
1199  </t></list>
1202   The language quality factor assigned to a language-tag by the
1203   Accept-Language field is the quality value of the longest language-range
1204   in the field that matches the language-tag. If no language-range
1205   in the field matches the tag, the language quality factor
1206   assigned is 0. If no Accept-Language header is present in the
1207   request, the server
1208   &SHOULD; assume that all languages are equally acceptable. If an
1209   Accept-Language header is present, then all languages which are
1210   assigned a quality factor greater than 0 are acceptable.
1213   It might be contrary to the privacy expectations of the user to send
1214   an Accept-Language header with the complete linguistic preferences of
1215   the user in every request. For a discussion of this issue, see
1216   <xref target=""/>.
1219   As intelligibility is highly dependent on the individual user, it is
1220   recommended that client applications make the choice of linguistic
1221   preference available to the user. If the choice is not made
1222   available, then the Accept-Language header field &MUST-NOT; be given in
1223   the request.
1224  <list><t>
1225      <x:h>Note:</x:h> When making the choice of linguistic preference available to
1226      the user, we remind implementors of  the fact that users are not
1227      familiar with the details of language matching as described above,
1228      and should provide appropriate guidance. As an example, users
1229      might assume that on selecting "en-gb", they will be served any
1230      kind of English document if British English is not available. A
1231      user agent might suggest in such a case to add "en" to get the
1232      best matching behavior.
1233  </t></list>
1237<section title="Content-Encoding" anchor="header.content-encoding">
1238  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1239  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1240  <x:anchor-alias value="Content-Encoding"/>
1242   The Content-Encoding entity-header field is used as a modifier to the
1243   media-type. When present, its value indicates what additional content
1244   codings have been applied to the entity-body, and thus what decoding
1245   mechanisms must be applied in order to obtain the media-type
1246   referenced by the Content-Type header field. Content-Encoding is
1247   primarily used to allow a document to be compressed without losing
1248   the identity of its underlying media type.
1250<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/>
1251  <x:ref>Content-Encoding</x:ref>  = "Content-Encoding" ":" 1#<x:ref>content-coding</x:ref>
1254   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1256<figure><artwork type="example">
1257    Content-Encoding: gzip
1260   The content-coding is a characteristic of the entity identified by
1261   the Request-URI. Typically, the entity-body is stored with this
1262   encoding and is only decoded before rendering or analogous usage.
1263   However, a non-transparent proxy &MAY; modify the content-coding if the
1264   new coding is known to be acceptable to the recipient, unless the
1265   "no-transform" cache-control directive is present in the message.
1268   If the content-coding of an entity is not "identity", then the
1269   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1270   that lists the non-identity content-coding(s) used.
1273   If the content-coding of an entity in a request message is not
1274   acceptable to the origin server, the server &SHOULD; respond with a
1275   status code of 415 (Unsupported Media Type).
1278   If multiple encodings have been applied to an entity, the content
1279   codings &MUST; be listed in the order in which they were applied.
1280   Additional information about the encoding parameters &MAY; be provided
1281   by other entity-header fields not defined by this specification.
1285<section title="Content-Language" anchor="header.content-language">
1286  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1287  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1288  <x:anchor-alias value="Content-Language"/>
1290   The Content-Language entity-header field describes the natural
1291   language(s) of the intended audience for the enclosed entity. Note
1292   that this might not be equivalent to all the languages used within
1293   the entity-body.
1295<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/>
1296  <x:ref>Content-Language</x:ref>  = "Content-Language" ":" 1#<x:ref>language-tag</x:ref>
1299   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1300   Content-Language is to allow a user to identify and differentiate
1301   entities according to the user's own preferred language. Thus, if the
1302   body content is intended only for a Danish-literate audience, the
1303   appropriate field is
1305<figure><artwork type="example">
1306    Content-Language: da
1309   If no Content-Language is specified, the default is that the content
1310   is intended for all language audiences. This might mean that the
1311   sender does not consider it to be specific to any natural language,
1312   or that the sender does not know for which language it is intended.
1315   Multiple languages &MAY; be listed for content that is intended for
1316   multiple audiences. For example, a rendition of the "Treaty of
1317   Waitangi," presented simultaneously in the original Maori and English
1318   versions, would call for
1320<figure><artwork type="example">
1321    Content-Language: mi, en
1324   However, just because multiple languages are present within an entity
1325   does not mean that it is intended for multiple linguistic audiences.
1326   An example would be a beginner's language primer, such as "A First
1327   Lesson in Latin," which is clearly intended to be used by an
1328   English-literate audience. In this case, the Content-Language would
1329   properly only include "en".
1332   Content-Language &MAY; be applied to any media type -- it is not
1333   limited to textual documents.
1337<section title="Content-Location" anchor="header.content-location">
1338  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1339  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1340  <x:anchor-alias value="Content-Location"/>
1342   The Content-Location entity-header field &MAY; be used to supply the
1343   resource location for the entity enclosed in the message when that
1344   entity is accessible from a location separate from the requested
1345   resource's URI. A server &SHOULD; provide a Content-Location for the
1346   variant corresponding to the response entity; especially in the case
1347   where a resource has multiple entities associated with it, and those
1348   entities actually have separate locations by which they might be
1349   individually accessed, the server &SHOULD; provide a Content-Location
1350   for the particular variant which is returned.
1352<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/>
1353  <x:ref>Content-Location</x:ref> = "Content-Location" ":"
1354                    ( <x:ref>absoluteURI</x:ref> | <x:ref>relativeURI</x:ref> )
1357   The value of Content-Location also defines the base URI for the
1358   entity.
1361   The Content-Location value is not a replacement for the original
1362   requested URI; it is only a statement of the location of the resource
1363   corresponding to this particular entity at the time of the request.
1364   Future requests &MAY; specify the Content-Location URI as the request-URI
1365   if the desire is to identify the source of that particular
1366   entity.
1369   A cache cannot assume that an entity with a Content-Location
1370   different from the URI used to retrieve it can be used to respond to
1371   later requests on that Content-Location URI. However, the Content-Location
1372   can be used to differentiate between multiple entities
1373   retrieved from a single requested resource, as described in &caching-neg-resp;.
1376   If the Content-Location is a relative URI, the relative URI is
1377   interpreted relative to the Request-URI.
1380   The meaning of the Content-Location header in PUT or POST requests is
1381   undefined; servers are free to ignore it in those cases.
1385<section title="Content-MD5" anchor="header.content-md5">
1386  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1387  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1388  <x:anchor-alias value="Content-MD5"/>
1389  <x:anchor-alias value="md5-digest"/>
1391   The Content-MD5 entity-header field, as defined in <xref target="RFC1864"/>, is
1392   an MD5 digest of the entity-body for the purpose of providing an
1393   end-to-end message integrity check (MIC) of the entity-body. (Note: a
1394   MIC is good for detecting accidental modification of the entity-body
1395   in transit, but is not proof against malicious attacks.)
1397<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="md5-digest"/>
1398  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>md5-digest</x:ref>
1399  <x:ref>md5-digest</x:ref>    = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1402   The Content-MD5 header field &MAY; be generated by an origin server or
1403   client to function as an integrity check of the entity-body. Only
1404   origin servers or clients &MAY; generate the Content-MD5 header field;
1405   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1406   value as an end-to-end integrity check. Any recipient of the entity-body,
1407   including gateways and proxies, &MAY; check that the digest value
1408   in this header field matches that of the entity-body as received.
1411   The MD5 digest is computed based on the content of the entity-body,
1412   including any content-coding that has been applied, but not including
1413   any transfer-encoding applied to the message-body. If the message is
1414   received with a transfer-encoding, that encoding &MUST; be removed
1415   prior to checking the Content-MD5 value against the received entity.
1418   This has the result that the digest is computed on the octets of the
1419   entity-body exactly as, and in the order that, they would be sent if
1420   no transfer-encoding were being applied.
1423   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1424   composite media-types (e.g., multipart/* and message/rfc822), but
1425   this does not change how the digest is computed as defined in the
1426   preceding paragraph.
1429   There are several consequences of this. The entity-body for composite
1430   types &MAY; contain many body-parts, each with its own MIME and HTTP
1431   headers (including Content-MD5, Content-Transfer-Encoding, and
1432   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1433   or Content-Encoding header, it is assumed that the content
1434   of the body-part has had the encoding applied, and the body-part is
1435   included in the Content-MD5 digest as is -- i.e., after the
1436   application. The Transfer-Encoding header field is not allowed within
1437   body-parts.
1440   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1441   computing or checking the digest: the line break convention used in
1442   the text actually transmitted &MUST; be left unaltered when computing
1443   the digest.
1444  <list><t>
1445      <x:h>Note:</x:h> while the definition of Content-MD5 is exactly the same for
1446      HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1447      in which the application of Content-MD5 to HTTP entity-bodies
1448      differs from its application to MIME entity-bodies. One is that
1449      HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1450      does use Transfer-Encoding and Content-Encoding. Another is that
1451      HTTP more frequently uses binary content types than MIME, so it is
1452      worth noting that, in such cases, the byte order used to compute
1453      the digest is the transmission byte order defined for the type.
1454      Lastly, HTTP allows transmission of text types with any of several
1455      line break conventions and not just the canonical form using CRLF.
1456  </t></list>
1460<section title="Content-Type" anchor="header.content-type">
1461  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1462  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1463  <x:anchor-alias value="Content-Type"/>
1465   The Content-Type entity-header field indicates the media type of the
1466   entity-body sent to the recipient or, in the case of the HEAD method,
1467   the media type that would have been sent had the request been a GET.
1469<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/>
1470  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>media-type</x:ref>
1473   Media types are defined in <xref target="media.types"/>. An example of the field is
1475<figure><artwork type="example">
1476    Content-Type: text/html; charset=ISO-8859-4
1479   Further discussion of methods for identifying the media type of an
1480   entity is provided in <xref target="type"/>.
1486<section title="IANA Considerations" anchor="IANA.considerations">
1487<section title="Message Header Registration" anchor="message.header.registration">
1489   The Message Header Registry located at <eref target=""/> should be updated
1490   with the permanent registrations below (see <xref target="RFC3864"/>):
1492<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1493<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1494   <ttcol>Header Field Name</ttcol>
1495   <ttcol>Protocol</ttcol>
1496   <ttcol>Status</ttcol>
1497   <ttcol>Reference</ttcol>
1499   <c>Accept</c>
1500   <c>http</c>
1501   <c>standard</c>
1502   <c>
1503      <xref target="header.accept"/>
1504   </c>
1505   <c>Accept-Charset</c>
1506   <c>http</c>
1507   <c>standard</c>
1508   <c>
1509      <xref target="header.accept-charset"/>
1510   </c>
1511   <c>Accept-Encoding</c>
1512   <c>http</c>
1513   <c>standard</c>
1514   <c>
1515      <xref target="header.accept-encoding"/>
1516   </c>
1517   <c>Accept-Language</c>
1518   <c>http</c>
1519   <c>standard</c>
1520   <c>
1521      <xref target="header.accept-language"/>
1522   </c>
1523   <c>Content-Disposition</c>
1524   <c>http</c>
1525   <c/>
1526   <c>
1527      <xref target="content-disposition"/>
1528   </c>
1529   <c>Content-Encoding</c>
1530   <c>http</c>
1531   <c>standard</c>
1532   <c>
1533      <xref target="header.content-encoding"/>
1534   </c>
1535   <c>Content-Language</c>
1536   <c>http</c>
1537   <c>standard</c>
1538   <c>
1539      <xref target="header.content-language"/>
1540   </c>
1541   <c>Content-Location</c>
1542   <c>http</c>
1543   <c>standard</c>
1544   <c>
1545      <xref target="header.content-location"/>
1546   </c>
1547   <c>Content-MD5</c>
1548   <c>http</c>
1549   <c>standard</c>
1550   <c>
1551      <xref target="header.content-md5"/>
1552   </c>
1553   <c>Content-Type</c>
1554   <c>http</c>
1555   <c>standard</c>
1556   <c>
1557      <xref target="header.content-type"/>
1558   </c>
1559   <c>MIME-Version</c>
1560   <c>http</c>
1561   <c/>
1562   <c>
1563      <xref target="mime-version"/>
1564   </c>
1568   The change controller is: "IETF ( - Internet Engineering Task Force".
1573<section title="Security Considerations" anchor="security.considerations">
1575   This section is meant to inform application developers, information
1576   providers, and users of the security limitations in HTTP/1.1 as
1577   described by this document. The discussion does not include
1578   definitive solutions to the problems revealed, though it does make
1579   some suggestions for reducing security risks.
1582<section title="Privacy Issues Connected to Accept Headers" anchor="">
1584   Accept request-headers can reveal information about the user to all
1585   servers which are accessed. The Accept-Language header in particular
1586   can reveal information the user would consider to be of a private
1587   nature, because the understanding of particular languages is often
1588   strongly correlated to the membership of a particular ethnic group.
1589   User agents which offer the option to configure the contents of an
1590   Accept-Language header to be sent in every request are strongly
1591   encouraged to let the configuration process include a message which
1592   makes the user aware of the loss of privacy involved.
1595   An approach that limits the loss of privacy would be for a user agent
1596   to omit the sending of Accept-Language headers by default, and to ask
1597   the user whether or not to start sending Accept-Language headers to a
1598   server if it detects, by looking for any Vary response-header fields
1599   generated by the server, that such sending could improve the quality
1600   of service.
1603   Elaborate user-customized accept header fields sent in every request,
1604   in particular if these include quality values, can be used by servers
1605   as relatively reliable and long-lived user identifiers. Such user
1606   identifiers would allow content providers to do click-trail tracking,
1607   and would allow collaborating content providers to match cross-server
1608   click-trails or form submissions of individual users. Note that for
1609   many users not behind a proxy, the network address of the host
1610   running the user agent will also serve as a long-lived user
1611   identifier. In environments where proxies are used to enhance
1612   privacy, user agents ought to be conservative in offering accept
1613   header configuration options to end users. As an extreme privacy
1614   measure, proxies could filter the accept headers in relayed requests.
1615   General purpose user agents which provide a high degree of header
1616   configurability &SHOULD; warn users about the loss of privacy which can
1617   be involved.
1621<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1623   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
1624   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1625   serious security considerations. Content-Disposition is not part of
1626   the HTTP standard, but since it is widely implemented, we are
1627   documenting its use and risks for implementors. See <xref target="RFC2183" x:fmt="of" x:sec="5"/>
1628   for details.
1634<section title="Acknowledgments" anchor="ack">
1639<references title="Normative References">
1641<reference anchor="ISO-8859-1">
1642  <front>
1643    <title>
1644     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1645    </title>
1646    <author>
1647      <organization>International Organization for Standardization</organization>
1648    </author>
1649    <date year="1998"/>
1650  </front>
1651  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1654<reference anchor="Part1">
1655  <front>
1656    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1657    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1658      <organization abbrev="Day Software">Day Software</organization>
1659      <address><email></email></address>
1660    </author>
1661    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1662      <organization>One Laptop per Child</organization>
1663      <address><email></email></address>
1664    </author>
1665    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1666      <organization abbrev="HP">Hewlett-Packard Company</organization>
1667      <address><email></email></address>
1668    </author>
1669    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1670      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1671      <address><email></email></address>
1672    </author>
1673    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1674      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1675      <address><email></email></address>
1676    </author>
1677    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1678      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1679      <address><email></email></address>
1680    </author>
1681    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1682      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1683      <address><email></email></address>
1684    </author>
1685    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1686      <organization abbrev="W3C">World Wide Web Consortium</organization>
1687      <address><email></email></address>
1688    </author>
1689    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1690      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1691      <address><email></email></address>
1692    </author>
1693    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1694  </front>
1695  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1696  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1699<reference anchor="Part2">
1700  <front>
1701    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1702    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1703      <organization abbrev="Day Software">Day Software</organization>
1704      <address><email></email></address>
1705    </author>
1706    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1707      <organization>One Laptop per Child</organization>
1708      <address><email></email></address>
1709    </author>
1710    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1711      <organization abbrev="HP">Hewlett-Packard Company</organization>
1712      <address><email></email></address>
1713    </author>
1714    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1715      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1716      <address><email></email></address>
1717    </author>
1718    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1719      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1720      <address><email></email></address>
1721    </author>
1722    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1723      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1724      <address><email></email></address>
1725    </author>
1726    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1727      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1728      <address><email></email></address>
1729    </author>
1730    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1731      <organization abbrev="W3C">World Wide Web Consortium</organization>
1732      <address><email></email></address>
1733    </author>
1734    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1735      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1736      <address><email></email></address>
1737    </author>
1738    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1739  </front>
1740  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1741  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1744<reference anchor="Part4">
1745  <front>
1746    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1747    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1748      <organization abbrev="Day Software">Day Software</organization>
1749      <address><email></email></address>
1750    </author>
1751    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1752      <organization>One Laptop per Child</organization>
1753      <address><email></email></address>
1754    </author>
1755    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1756      <organization abbrev="HP">Hewlett-Packard Company</organization>
1757      <address><email></email></address>
1758    </author>
1759    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1760      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1761      <address><email></email></address>
1762    </author>
1763    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1764      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1765      <address><email></email></address>
1766    </author>
1767    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1768      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1769      <address><email></email></address>
1770    </author>
1771    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1772      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1773      <address><email></email></address>
1774    </author>
1775    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1776      <organization abbrev="W3C">World Wide Web Consortium</organization>
1777      <address><email></email></address>
1778    </author>
1779    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1780      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1781      <address><email></email></address>
1782    </author>
1783    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1784  </front>
1785  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1786  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1789<reference anchor="Part5">
1790  <front>
1791    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1792    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1793      <organization abbrev="Day Software">Day Software</organization>
1794      <address><email></email></address>
1795    </author>
1796    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1797      <organization>One Laptop per Child</organization>
1798      <address><email></email></address>
1799    </author>
1800    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1801      <organization abbrev="HP">Hewlett-Packard Company</organization>
1802      <address><email></email></address>
1803    </author>
1804    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1805      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1806      <address><email></email></address>
1807    </author>
1808    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1809      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1810      <address><email></email></address>
1811    </author>
1812    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1813      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1814      <address><email></email></address>
1815    </author>
1816    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1817      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1818      <address><email></email></address>
1819    </author>
1820    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1821      <organization abbrev="W3C">World Wide Web Consortium</organization>
1822      <address><email></email></address>
1823    </author>
1824    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1825      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1826      <address><email></email></address>
1827    </author>
1828    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1829  </front>
1830  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1831  <x:source href="p5-range.xml" basename="p5-range"/>
1834<reference anchor="Part6">
1835  <front>
1836    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1837    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1838      <organization abbrev="Day Software">Day Software</organization>
1839      <address><email></email></address>
1840    </author>
1841    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1842      <organization>One Laptop per Child</organization>
1843      <address><email></email></address>
1844    </author>
1845    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1846      <organization abbrev="HP">Hewlett-Packard Company</organization>
1847      <address><email></email></address>
1848    </author>
1849    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1850      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1851      <address><email></email></address>
1852    </author>
1853    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1854      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1855      <address><email></email></address>
1856    </author>
1857    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1858      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1859      <address><email></email></address>
1860    </author>
1861    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1862      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1863      <address><email></email></address>
1864    </author>
1865    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1866      <organization abbrev="W3C">World Wide Web Consortium</organization>
1867      <address><email></email></address>
1868    </author>
1869    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1870      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1871      <address><email></email></address>
1872    </author>
1873    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1874  </front>
1875  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1876  <x:source href="p6-cache.xml" basename="p6-cache"/>
1879<reference anchor="RFC1766">
1880  <front>
1881    <title abbrev="Language Tag">Tags for the Identification of Languages</title>
1882    <author initials="H." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
1883      <organization>UNINETT</organization>
1884      <address><email></email></address>
1885    </author>
1886    <date month="March" year="1995"/>
1887  </front>
1888  <seriesInfo name="RFC" value="1766"/>
1891<reference anchor="RFC1864">
1892  <front>
1893    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1894    <author initials="J." surname="Myers" fullname="John G. Myers">
1895      <organization>Carnegie Mellon University</organization>
1896      <address><email></email></address>
1897    </author>
1898    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
1899      <organization>Dover Beach Consulting, Inc.</organization>
1900      <address><email></email></address>
1901    </author>
1902    <date month="October" year="1995"/>
1903  </front>
1904  <seriesInfo name="RFC" value="1864"/>
1907<reference anchor="RFC1950">
1908  <front>
1909    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1910    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1911      <organization>Aladdin Enterprises</organization>
1912      <address><email></email></address>
1913    </author>
1914    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1915      <organization/>
1916    </author>
1917    <date month="May" year="1996"/>
1918  </front>
1919  <seriesInfo name="RFC" value="1950"/>
1920  <annotation>
1921    RFC 1950 is an Informational RFC, thus it may be less stable than
1922    this specification. On the other hand, this downward reference was
1923    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1924    therefore it is unlikely to cause problems in practice. See also
1925    <xref target="BCP97"/>.
1926  </annotation>
1929<reference anchor="RFC1951">
1930  <front>
1931    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1932    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1933      <organization>Aladdin Enterprises</organization>
1934      <address><email></email></address>
1935    </author>
1936    <date month="May" year="1996"/>
1937  </front>
1938  <seriesInfo name="RFC" value="1951"/>
1939  <annotation>
1940    RFC 1951 is an Informational RFC, thus it may be less stable than
1941    this specification. On the other hand, this downward reference was
1942    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1943    therefore it is unlikely to cause problems in practice. See also
1944    <xref target="BCP97"/>.
1945  </annotation>
1948<reference anchor="RFC1952">
1949  <front>
1950    <title>GZIP file format specification version 4.3</title>
1951    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1952      <organization>Aladdin Enterprises</organization>
1953      <address><email></email></address>
1954    </author>
1955    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1956      <organization/>
1957      <address><email></email></address>
1958    </author>
1959    <author initials="M." surname="Adler" fullname="Mark Adler">
1960      <organization/>
1961      <address><email></email></address>
1962    </author>
1963    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1964      <organization/>
1965      <address><email></email></address>
1966    </author>
1967    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
1968      <organization/>
1969      <address><email></email></address>
1970    </author>
1971    <date month="May" year="1996"/>
1972  </front>
1973  <seriesInfo name="RFC" value="1952"/>
1974  <annotation>
1975    RFC 1952 is an Informational RFC, thus it may be less stable than
1976    this specification. On the other hand, this downward reference was
1977    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1978    therefore it is unlikely to cause problems in practice. See also
1979    <xref target="BCP97"/>.
1980  </annotation>
1983<reference anchor="RFC2045">
1984  <front>
1985    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
1986    <author initials="N." surname="Freed" fullname="Ned Freed">
1987      <organization>Innosoft International, Inc.</organization>
1988      <address><email></email></address>
1989    </author>
1990    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1991      <organization>First Virtual Holdings</organization>
1992      <address><email></email></address>
1993    </author>
1994    <date month="November" year="1996"/>
1995  </front>
1996  <seriesInfo name="RFC" value="2045"/>
1999<reference anchor="RFC2046">
2000  <front>
2001    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2002    <author initials="N." surname="Freed" fullname="Ned Freed">
2003      <organization>Innosoft International, Inc.</organization>
2004      <address><email></email></address>
2005    </author>
2006    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2007      <organization>First Virtual Holdings</organization>
2008      <address><email></email></address>
2009    </author>
2010    <date month="November" year="1996"/>
2011  </front>
2012  <seriesInfo name="RFC" value="2046"/>
2015<reference anchor="RFC2119">
2016  <front>
2017    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2018    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2019      <organization>Harvard University</organization>
2020      <address><email></email></address>
2021    </author>
2022    <date month="March" year="1997"/>
2023  </front>
2024  <seriesInfo name="BCP" value="14"/>
2025  <seriesInfo name="RFC" value="2119"/>
2030<references title="Informative References">
2032<reference anchor="RFC1945">
2033  <front>
2034    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2035    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2036      <organization>MIT, Laboratory for Computer Science</organization>
2037      <address><email></email></address>
2038    </author>
2039    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2040      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2041      <address><email></email></address>
2042    </author>
2043    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2044      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2045      <address><email></email></address>
2046    </author>
2047    <date month="May" year="1996"/>
2048  </front>
2049  <seriesInfo name="RFC" value="1945"/>
2052<reference anchor="RFC2049">
2053  <front>
2054    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2055    <author initials="N." surname="Freed" fullname="Ned Freed">
2056      <organization>Innosoft International, Inc.</organization>
2057      <address><email></email></address>
2058    </author>
2059    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2060      <organization>First Virtual Holdings</organization>
2061      <address><email></email></address>
2062    </author>
2063    <date month="November" year="1996"/>
2064  </front>
2065  <seriesInfo name="RFC" value="2049"/>
2068<reference anchor="RFC2068">
2069  <front>
2070    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2071    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2072      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2073      <address><email></email></address>
2074    </author>
2075    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2076      <organization>MIT Laboratory for Computer Science</organization>
2077      <address><email></email></address>
2078    </author>
2079    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2080      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2081      <address><email></email></address>
2082    </author>
2083    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2084      <organization>MIT Laboratory for Computer Science</organization>
2085      <address><email></email></address>
2086    </author>
2087    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2088      <organization>MIT Laboratory for Computer Science</organization>
2089      <address><email></email></address>
2090    </author>
2091    <date month="January" year="1997"/>
2092  </front>
2093  <seriesInfo name="RFC" value="2068"/>
2096<reference anchor="RFC2076">
2097  <front>
2098    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2099    <author initials="J." surname="Palme" fullname="Jacob Palme">
2100      <organization>Stockholm University/KTH</organization>
2101      <address><email></email></address>
2102    </author>
2103    <date month="February" year="1997"/>
2104  </front>
2105  <seriesInfo name="RFC" value="2076"/>
2108<reference anchor="RFC2183">
2109  <front>
2110    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2111    <author initials="R." surname="Troost" fullname="Rens Troost">
2112      <organization>New Century Systems</organization>
2113      <address><email></email></address>
2114    </author>
2115    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2116      <organization>QUALCOMM Incorporated</organization>
2117      <address><email></email></address>
2118    </author>
2119    <author initials="K." surname="Moore" fullname="Keith Moore">
2120      <organization>Department of Computer Science</organization>
2121      <address><email></email></address>
2122    </author>
2123    <date month="August" year="1997"/>
2124  </front>
2125  <seriesInfo name="RFC" value="2183"/>
2128<reference anchor="RFC2277">
2129  <front>
2130    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2131    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2132      <organization>UNINETT</organization>
2133      <address><email></email></address>
2134    </author>
2135    <date month="January" year="1998"/>
2136  </front>
2137  <seriesInfo name="BCP" value="18"/>
2138  <seriesInfo name="RFC" value="2277"/>
2141<reference anchor="RFC2388">
2142  <front>
2143    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2144    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2145      <organization>Xerox Palo Alto Research Center</organization>
2146      <address><email></email></address>
2147    </author>
2148    <date year="1998" month="August"/>
2149  </front>
2150  <seriesInfo name="RFC" value="2388"/>
2153<reference anchor="RFC2557">
2154  <front>
2155    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2156    <author initials="F." surname="Palme" fullname="Jacob Palme">
2157      <organization>Stockholm University and KTH</organization>
2158      <address><email></email></address>
2159    </author>
2160    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2161      <organization>Microsoft Corporation</organization>
2162      <address><email></email></address>
2163    </author>
2164    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2165      <organization>Lotus Development Corporation</organization>
2166      <address><email></email></address>
2167    </author>
2168    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2169      <organization/>
2170      <address><email></email></address>
2171    </author>
2172    <date year="1999" month="March"/>
2173  </front>
2174  <seriesInfo name="RFC" value="2557"/>
2177<reference anchor="RFC2616">
2178  <front>
2179    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2180    <author initials="R." surname="Fielding" fullname="R. Fielding">
2181      <organization>University of California, Irvine</organization>
2182      <address><email></email></address>
2183    </author>
2184    <author initials="J." surname="Gettys" fullname="J. Gettys">
2185      <organization>W3C</organization>
2186      <address><email></email></address>
2187    </author>
2188    <author initials="J." surname="Mogul" fullname="J. Mogul">
2189      <organization>Compaq Computer Corporation</organization>
2190      <address><email></email></address>
2191    </author>
2192    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2193      <organization>MIT Laboratory for Computer Science</organization>
2194      <address><email></email></address>
2195    </author>
2196    <author initials="L." surname="Masinter" fullname="L. Masinter">
2197      <organization>Xerox Corporation</organization>
2198      <address><email></email></address>
2199    </author>
2200    <author initials="P." surname="Leach" fullname="P. Leach">
2201      <organization>Microsoft Corporation</organization>
2202      <address><email></email></address>
2203    </author>
2204    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2205      <organization>W3C</organization>
2206      <address><email></email></address>
2207    </author>
2208    <date month="June" year="1999"/>
2209  </front>
2210  <seriesInfo name="RFC" value="2616"/>
2213<reference anchor="RFC2822">
2214  <front>
2215    <title>Internet Message Format</title>
2216    <author initials="P." surname="Resnick" fullname="P. Resnick">
2217      <organization>QUALCOMM Incorporated</organization>
2218    </author>
2219    <date year="2001" month="April"/>
2220  </front>
2221  <seriesInfo name="RFC" value="2822"/>
2224<reference anchor="RFC3629">
2225  <front>
2226    <title>UTF-8, a transformation format of ISO 10646</title>
2227    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2228      <organization>Alis Technologies</organization>
2229      <address><email></email></address>
2230    </author>
2231    <date month="November" year="2003"/>
2232  </front>
2233  <seriesInfo name="RFC" value="3629"/>
2234  <seriesInfo name="STD" value="63"/>
2237<reference anchor='RFC3864'>
2238  <front>
2239    <title>Registration Procedures for Message Header Fields</title>
2240    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2241      <organization>Nine by Nine</organization>
2242      <address><email></email></address>
2243    </author>
2244    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2245      <organization>BEA Systems</organization>
2246      <address><email></email></address>
2247    </author>
2248    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2249      <organization>HP Labs</organization>
2250      <address><email></email></address>
2251    </author>
2252    <date year='2004' month='September' />
2253  </front>
2254  <seriesInfo name='BCP' value='90' />
2255  <seriesInfo name='RFC' value='3864' />
2258<reference anchor="RFC4288">
2259  <front>
2260    <title>Media Type Specifications and Registration Procedures</title>
2261    <author initials="N." surname="Freed" fullname="N. Freed">
2262      <organization>Sun Microsystems</organization>
2263      <address>
2264        <email></email>
2265      </address>
2266    </author>
2267    <author initials="J." surname="Klensin" fullname="J. Klensin">
2268      <organization/>
2269      <address>
2270        <email></email>
2271      </address>
2272    </author>
2273    <date year="2005" month="December"/>
2274  </front>
2275  <seriesInfo name="BCP" value="13"/>
2276  <seriesInfo name="RFC" value="4288"/>
2279<reference anchor='BCP97'>
2280  <front>
2281    <title>Handling Normative References to Standards-Track Documents</title>
2282    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2283      <organization />
2284      <address>
2285        <email></email>
2286      </address>
2287    </author>
2288    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2289      <organization>MIT</organization>
2290      <address>
2291        <email></email>
2292      </address>
2293    </author>
2294    <date year='2007' month='June' />
2295  </front>
2296  <seriesInfo name='BCP' value='97' />
2297  <seriesInfo name='RFC' value='4897' />
2303<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2305   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
2306   allow entities to be transmitted in an open variety of
2307   representations and with extensible mechanisms. However, RFC 2045
2308   discusses mail, and HTTP has a few features that are different from
2309   those described in RFC 2045. These differences were carefully chosen
2310   to optimize performance over binary connections, to allow greater
2311   freedom in the use of new media types, to make date comparisons
2312   easier, and to acknowledge the practice of some early HTTP servers
2313   and clients.
2316   This appendix describes specific areas where HTTP differs from RFC
2317   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2318   aware of these differences and provide the appropriate conversions
2319   where necessary. Proxies and gateways from MIME environments to HTTP
2320   also need to be aware of the differences because some conversions
2321   might be required.
2324<section title="MIME-Version" anchor="mime-version">
2325  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2326  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
2327  <x:anchor-alias value="MIME-Version"/>
2329   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2330   include a single MIME-Version general-header field to indicate what
2331   version of the MIME protocol was used to construct the message. Use
2332   of the MIME-Version header field indicates that the message is in
2333   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2334   Proxies/gateways are responsible for ensuring full compliance (where
2335   possible) when exporting HTTP messages to strict MIME environments.
2337<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/>
2338  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2341   MIME version "1.0" is the default for use in HTTP/1.1. However,
2342   HTTP/1.1 message parsing and semantics are defined by this document
2343   and not the MIME specification.
2347<section title="Conversion to Canonical Form" anchor="">
2349   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2350   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2351   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2352   allowed for subtypes of the "text" media type when transmitted over
2353   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2354   line breaks as CRLF and forbids the use of CR or LF outside of line
2355   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2356   line break within text content when a message is transmitted over
2357   HTTP.
2360   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2361   environment &SHOULD; translate all line breaks within the text media
2362   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2363   canonical form of CRLF. Note, however, that this might be complicated
2364   by the presence of a Content-Encoding and by the fact that HTTP
2365   allows the use of some character sets which do not use octets 13 and
2366   10 to represent CR and LF, as is the case for some multi-byte
2367   character sets.
2370   Implementors should note that conversion will break any cryptographic
2371   checksums applied to the original content unless the original content
2372   is already in canonical form. Therefore, the canonical form is
2373   recommended for any content that uses such checksums in HTTP.
2377<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2379   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2380   Content-Encoding header field. Since this acts as a modifier on the
2381   media type, proxies and gateways from HTTP to MIME-compliant
2382   protocols &MUST; either change the value of the Content-Type header
2383   field or decode the entity-body before forwarding the message. (Some
2384   experimental applications of Content-Type for Internet mail have used
2385   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2386   a function equivalent to Content-Encoding. However, this parameter is
2387   not part of RFC 2045).
2391<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2393   HTTP does not use the Content-Transfer-Encoding field of RFC
2394   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2395   remove any Content-Transfer-Encoding
2396   prior to delivering the response message to an HTTP client.
2399   Proxies and gateways from HTTP to MIME-compliant protocols are
2400   responsible for ensuring that the message is in the correct format
2401   and encoding for safe transport on that protocol, where "safe
2402   transport" is defined by the limitations of the protocol being used.
2403   Such a proxy or gateway &SHOULD; label the data with an appropriate
2404   Content-Transfer-Encoding if doing so will improve the likelihood of
2405   safe transport over the destination protocol.
2409<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2411   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2412   Proxies/gateways &MUST; remove any transfer-coding prior to
2413   forwarding a message via a MIME-compliant protocol.
2417<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2419   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2420   need to be aware of MIME line length limitations. Since HTTP does not
2421   have this limitation, HTTP does not fold long lines. MHTML messages
2422   being transported by HTTP follow all conventions of MHTML, including
2423   line length limitations and folding, canonicalization, etc., since
2424   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2425   does not interpret the content or any MIME header lines that might be
2426   contained therein.
2431<section title="Additional Features" anchor="additional.features">
2433   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2434   existing HTTP implementations, but not consistently and correctly
2435   across most HTTP/1.1 applications. Implementors are advised to be
2436   aware of these features, but cannot rely upon their presence in, or
2437   interoperability with, other HTTP/1.1 applications. Some of these
2438   describe proposed experimental features, and some describe features
2439   that experimental deployment found lacking that are now addressed in
2440   the base HTTP/1.1 specification.
2443   A number of other headers, such as Content-Disposition and Title,
2444   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2447<section title="Content-Disposition" anchor="content-disposition">
2448<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2449<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2450  <x:anchor-alias value="content-disposition"/>
2451  <x:anchor-alias value="disposition-type"/>
2452  <x:anchor-alias value="disposition-parm"/>
2453  <x:anchor-alias value="disp-extension-parm"/>
2454  <x:anchor-alias value="disp-extension-token"/>
2455  <x:anchor-alias value="filename-parm"/>
2457   The Content-Disposition response-header field has been proposed as a
2458   means for the origin server to suggest a default filename if the user
2459   requests that the content is saved to a file. This usage is derived
2460   from the definition of Content-Disposition in <xref target="RFC2183"/>.
2462<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"/>
2463  <x:ref>content-disposition</x:ref> = "Content-Disposition" ":"
2464                        <x:ref>disposition-type</x:ref> *( ";" <x:ref>disposition-parm</x:ref> )
2465  <x:ref>disposition-type</x:ref> = "attachment" | <x:ref>disp-extension-token</x:ref>
2466  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> | <x:ref>disp-extension-parm</x:ref>
2467  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2468  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
2469  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" ( <x:ref>token</x:ref> | <x:ref>quoted-string</x:ref> )
2472   An example is
2474<figure><artwork type="example">
2475     Content-Disposition: attachment; filename="fname.ext"
2478   The receiving user agent &SHOULD-NOT;  respect any directory path
2479   information present in the filename-parm parameter, which is the only
2480   parameter believed to apply to HTTP implementations at this time. The
2481   filename &SHOULD; be treated as a terminal component only.
2484   If this header is used in a response with the application/octet-stream
2485   content-type, the implied suggestion is that the user agent
2486   should not display the response, but directly enter a `save response
2487   as...' dialog.
2490   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2495<section title="Compatibility with Previous Versions" anchor="compatibility">
2496<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2498   Transfer-coding and message lengths all interact in ways that
2499   required fixing exactly when chunked encoding is used (to allow for
2500   transfer encoding that may not be self delimiting); it was important
2501   to straighten out exactly how message lengths are computed.
2502   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2503   <xref target="Part5"/> and <xref target="Part6"/>).
2506   Charset wildcarding is introduced to avoid explosion of character set
2507   names in accept headers. (<xref target="header.accept-charset"/>)
2510   Content-Base was deleted from the specification: it was not
2511   implemented widely, and there is no simple, safe way to introduce it
2512   without a robust extension mechanism. In addition, it is used in a
2513   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2516   A content-coding of "identity" was introduced, to solve problems
2517   discovered in caching. (<xref target="content.codings"/>)
2520   Quality Values of zero should indicate that "I don't want something"
2521   to allow clients to refuse a representation. (<xref target="quality.values"/>)
2524   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
2525   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
2526   specification, but not commonly implemented. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.2"/>.
2530<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2532  Clarify contexts that charset is used in.
2533  (<xref target="character.sets"/>)
2536  Remove reference to non-existant identity transfer-coding value tokens.
2537  (<xref target="no.content-transfer-encoding"/>)
2543<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2545<section title="Since RFC2616">
2547  Extracted relevant partitions from <xref target="RFC2616"/>.
2551<section title="Since draft-ietf-httpbis-p3-payload-00">
2553  Closed issues:
2554  <list style="symbols">
2555    <t>
2556      <eref target=""/>:
2557      "Media Type Registrations"
2558      (<eref target=""/>)
2559    </t>
2560    <t>
2561      <eref target=""/>:
2562      "Clarification regarding quoting of charset values"
2563      (<eref target=""/>)
2564    </t>
2565    <t>
2566      <eref target=""/>:
2567      "Remove 'identity' token references"
2568      (<eref target=""/>)
2569    </t>
2570    <t>
2571      <eref target=""/>:
2572      "Accept-Encoding BNF"
2573    </t>
2574    <t>
2575      <eref target=""/>:
2576      "Normative and Informative references"
2577    </t>
2578    <t>
2579      <eref target=""/>:
2580      "RFC1700 references"
2581    </t>
2582    <t>
2583      <eref target=""/>:
2584      "Updating to RFC4288"
2585    </t>
2586    <t>
2587      <eref target=""/>:
2588      "Informative references"
2589    </t>
2590    <t>
2591      <eref target=""/>:
2592      "ISO-8859-1 Reference"
2593    </t>
2594    <t>
2595      <eref target=""/>:
2596      "Encoding References Normative"
2597    </t>
2598    <t>
2599      <eref target=""/>:
2600      "Normative up-to-date references"
2601    </t>
2602  </list>
2606<section title="Since draft-ietf-httpbis-p3-payload-01">
2608  Ongoing work on ABNF conversion (<eref target=""/>):
2609  <list style="symbols">
2610    <t>
2611      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2612    </t>
2613  </list>
2617<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2619  Closed issues:
2620  <list style="symbols">
2621    <t>
2622      <eref target=""/>:
2623      "Quoting Charsets"
2624    </t>
2625    <t>
2626      <eref target=""/>:
2627      "Classification for Allow header"
2628    </t>
2629    <t>
2630      <eref target=""/>:
2631      "missing default for qvalue in description of Accept-Encoding"
2632    </t>
2633  </list>
2636  Ongoing work on IANA Message Header Registration (<eref target=""/>):
2637  <list style="symbols">
2638    <t>
2639      Reference RFC 3984, and update header registrations for headers defined
2640      in this document.
2641    </t>
2642  </list>
2646<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2648  Closed issues:
2649  <list style="symbols">
2650    <t>
2651      <eref target=""/>:
2652      "Quoting Charsets"
2653    </t>
2654    <t>
2655      <eref target=""/>:
2656      "RFC 1806 has been replaced by RFC2183"
2657    </t>
2658  </list>
2661  Other changes:
2662  <list style="symbols">
2663    <t>
2664      <eref target=""/>:
2665      "Encoding References Normative" -- rephrase the annotation and reference
2666      <xref target="BCP97"/>.
2667    </t>
2668  </list>
2670 </section>
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