source: draft-ietf-httpbis/latest/p3-payload.xml @ 421

Last change on this file since 421 was 421, checked in by julian.reschke@…, 14 years ago

add collected abnf appendices (related to #36)

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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 "November">
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 multipart-byteranges     "<xref target='Part5' x:rel='' xmlns:x=''/>">
31  <!ENTITY full-date                "<xref target='Part1' x:rel='' xmlns:x=''/>">
32  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x=''/>">
34<?rfc toc="yes" ?>
35<?rfc symrefs="yes" ?>
36<?rfc sortrefs="yes" ?>
37<?rfc compact="yes"?>
38<?rfc subcompact="no" ?>
39<?rfc linkmailto="no" ?>
40<?rfc editing="no" ?>
41<?rfc comments="yes"?>
42<?rfc inline="yes"?>
43<?rfc-ext allow-markup-in-artwork="yes" ?>
44<?rfc-ext include-references-in-index="yes" ?>
45<rfc obsoletes="2616" category="std" x:maturity-level="draft"
46     ipr="full3978" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
47     xmlns:x=''>
50  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
52  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
53    <organization abbrev="Day Software">Day Software</organization>
54    <address>
55      <postal>
56        <street>23 Corporate Plaza DR, Suite 280</street>
57        <city>Newport Beach</city>
58        <region>CA</region>
59        <code>92660</code>
60        <country>USA</country>
61      </postal>
62      <phone>+1-949-706-5300</phone>
63      <facsimile>+1-949-706-5305</facsimile>
64      <email></email>
65      <uri></uri>
66    </address>
67  </author>
69  <author initials="J." surname="Gettys" fullname="Jim Gettys">
70    <organization>One Laptop per Child</organization>
71    <address>
72      <postal>
73        <street>21 Oak Knoll Road</street>
74        <city>Carlisle</city>
75        <region>MA</region>
76        <code>01741</code>
77        <country>USA</country>
78      </postal>
79      <email></email>
80      <uri></uri>
81    </address>
82  </author>
84  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
85    <organization abbrev="HP">Hewlett-Packard Company</organization>
86    <address>
87      <postal>
88        <street>HP Labs, Large Scale Systems Group</street>
89        <street>1501 Page Mill Road, MS 1177</street>
90        <city>Palo Alto</city>
91        <region>CA</region>
92        <code>94304</code>
93        <country>USA</country>
94      </postal>
95      <email></email>
96    </address>
97  </author>
99  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
100    <organization abbrev="Microsoft">Microsoft Corporation</organization>
101    <address>
102      <postal>
103        <street>1 Microsoft Way</street>
104        <city>Redmond</city>
105        <region>WA</region>
106        <code>98052</code>
107        <country>USA</country>
108      </postal>
109      <email></email>
110    </address>
111  </author>
113  <author initials="L." surname="Masinter" fullname="Larry Masinter">
114    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
115    <address>
116      <postal>
117        <street>345 Park Ave</street>
118        <city>San Jose</city>
119        <region>CA</region>
120        <code>95110</code>
121        <country>USA</country>
122      </postal>
123      <email></email>
124      <uri></uri>
125    </address>
126  </author>
128  <author initials="P." surname="Leach" fullname="Paul J. Leach">
129    <organization abbrev="Microsoft">Microsoft Corporation</organization>
130    <address>
131      <postal>
132        <street>1 Microsoft Way</street>
133        <city>Redmond</city>
134        <region>WA</region>
135        <code>98052</code>
136      </postal>
137      <email></email>
138    </address>
139  </author>
141  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
142    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
143    <address>
144      <postal>
145        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
146        <street>The Stata Center, Building 32</street>
147        <street>32 Vassar Street</street>
148        <city>Cambridge</city>
149        <region>MA</region>
150        <code>02139</code>
151        <country>USA</country>
152      </postal>
153      <email></email>
154      <uri></uri>
155    </address>
156  </author>
158  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
159    <organization abbrev="W3C">World Wide Web Consortium</organization>
160    <address>
161      <postal>
162        <street>W3C / ERCIM</street>
163        <street>2004, rte des Lucioles</street>
164        <city>Sophia-Antipolis</city>
165        <region>AM</region>
166        <code>06902</code>
167        <country>France</country>
168      </postal>
169      <email></email>
170      <uri></uri>
171    </address>
172  </author>
174  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
175    <organization abbrev="greenbytes">greenbytes GmbH</organization>
176    <address>
177      <postal>
178        <street>Hafenweg 16</street>
179        <city>Muenster</city><region>NW</region><code>48155</code>
180        <country>Germany</country>
181      </postal>
182      <phone>+49 251 2807760</phone>   
183      <facsimile>+49 251 2807761</facsimile>   
184      <email></email>       
185      <uri></uri>     
186    </address>
187  </author>
189  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
193   The Hypertext Transfer Protocol (HTTP) is an application-level
194   protocol for distributed, collaborative, hypermedia information
195   systems. HTTP has been in use by the World Wide Web global information
196   initiative since 1990. This document is Part 3 of the seven-part specification
197   that defines the protocol referred to as "HTTP/1.1" and, taken together,
198   obsoletes RFC 2616.  Part 3 defines HTTP message content,
199   metadata, and content negotiation.
203<note title="Editorial Note (To be removed by RFC Editor)">
204  <t>
205    Discussion of this draft should take place on the HTTPBIS working group
206    mailing list ( The current issues list is
207    at <eref target=""/>
208    and related documents (including fancy diffs) can be found at
209    <eref target=""/>.
210  </t>
211  <t>
212    The changes in this draft are summarized in <xref target="changes.since.05"/>.
213  </t>
217<section title="Introduction" anchor="introduction">
219   This document defines HTTP/1.1 message payloads (a.k.a., content), the
220   associated metadata header fields that define how the payload is intended
221   to be interpreted by a recipient, the request header fields that
222   may influence content selection, and the various selection algorithms
223   that are collectively referred to as HTTP content negotiation.
226   This document is currently disorganized in order to minimize the changes
227   between drafts and enable reviewers to see the smaller errata changes.
228   The next draft will reorganize the sections to better reflect the content.
229   In particular, the sections on entities will be renamed payload and moved
230   to the first half of the document, while the sections on content negotiation
231   and associated request header fields will be moved to the second half.  The
232   current mess reflects how widely dispersed these topics and associated
233   requirements had become in <xref target="RFC2616"/>.
236<section title="Requirements" anchor="intro.requirements">
238   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
239   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
240   document are to be interpreted as described in <xref target="RFC2119"/>.
243   An implementation is not compliant if it fails to satisfy one or more
244   of the &MUST; or &REQUIRED; level requirements for the protocols it
245   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
246   level and all the &SHOULD; level requirements for its protocols is said
247   to be "unconditionally compliant"; one that satisfies all the &MUST;
248   level requirements but not all the &SHOULD; level requirements for its
249   protocols is said to be "conditionally compliant."
254<section title="Notational Conventions and Generic Grammar" anchor="notation">
255  <x:anchor-alias value="ALPHA"/>
256  <x:anchor-alias value="DIGIT"/>
257  <x:anchor-alias value="OCTET"/>
258  <x:anchor-alias value="quoted-string"/>
259  <x:anchor-alias value="token"/>
260  <x:anchor-alias value="OWS"/>
262  This specification uses the ABNF syntax defined in &notation-abnf; and
263  the core rules defined in &basic-rules;:
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;
273  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
275<t anchor="abnf.dependencies">
276  <x:anchor-alias value="absolute-URI"/>
277  <x:anchor-alias value="Allow"/>
278  <x:anchor-alias value="Content-Length"/>
279  <x:anchor-alias value="Content-Range"/>
280  <x:anchor-alias value="Expires"/>
281  <x:anchor-alias value="Last-Modified"/>
282  <x:anchor-alias value="message-header"/>
283  <x:anchor-alias value="partial-URI"/>
284  The ABNF rules below are defined in other parts:
286<figure><!--Part1--><artwork type="abnf2616">
287  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
288  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
289  <x:ref>message-header</x:ref> = &lt;message-header, defined in &message-headers;&gt;
290  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
292<figure><!--Part4--><artwork type="abnf2616">
293  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
295<figure><!--Part5--><artwork type="abnf2616">
296  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
298<figure><!--Part6--><artwork type="abnf2616">
299  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
303<section title="Protocol Parameters" anchor="protocol.parameters">
305<section title="Character Sets" anchor="character.sets">
307   HTTP uses the same definition of the term "character set" as that
308   described for MIME:
311   The term "character set" is used in this document to refer to a
312   method used with one or more tables to convert a sequence of octets
313   into a sequence of characters. Note that unconditional conversion in
314   the other direction is not required, in that not all characters may
315   be available in a given character set and a character set may provide
316   more than one sequence of octets to represent a particular character.
317   This definition is intended to allow various kinds of character
318   encoding, from simple single-table mappings such as US-ASCII to
319   complex table switching methods such as those that use ISO-2022's
320   techniques. However, the definition associated with a MIME character
321   set name &MUST; fully specify the mapping to be performed from octets
322   to characters. In particular, use of external profiling information
323   to determine the exact mapping is not permitted.
326      <x:h>Note:</x:h> This use of the term "character set" is more commonly
327      referred to as a "character encoding." However, since HTTP and
328      MIME share the same registry, it is important that the terminology
329      also be shared.
331<t anchor="rule.charset">
332  <x:anchor-alias value="charset"/>
333   HTTP character sets are identified by case-insensitive tokens. The
334   complete set of tokens is defined by the IANA Character Set registry
335   (<eref target=""/>).
337<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
338  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
341   Although HTTP allows an arbitrary token to be used as a charset
342   value, any token that has a predefined value within the IANA
343   Character Set registry &MUST; represent the character set defined
344   by that registry. Applications &SHOULD; limit their use of character
345   sets to those defined by the IANA registry.
348   HTTP uses charset in two contexts: within an Accept-Charset request
349   header (in which the charset value is an unquoted token) and as the
350   value of a parameter in a Content-Type header (within a request or
351   response), in which case the parameter value of the charset parameter
352   may be quoted.
355   Implementors should be aware of IETF character set requirements <xref target="RFC3629"/>
356   <xref target="RFC2277"/>.
359<section title="Missing Charset" anchor="missing.charset">
361   Some HTTP/1.0 software has interpreted a Content-Type header without
362   charset parameter incorrectly to mean "recipient should guess."
363   Senders wishing to defeat this behavior &MAY; include a charset
364   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
365   it is known that it will not confuse the recipient.
368   Unfortunately, some older HTTP/1.0 clients did not deal properly with
369   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
370   charset label provided by the sender; and those user agents that have
371   a provision to "guess" a charset &MUST; use the charset from the
372   content-type field if they support that charset, rather than the
373   recipient's preference, when initially displaying a document. See
374   <xref target="canonicalization.and.text.defaults"/>.
379<section title="Content Codings" anchor="content.codings">
380  <x:anchor-alias value="content-coding"/>
382   Content coding values indicate an encoding transformation that has
383   been or can be applied to an entity. Content codings are primarily
384   used to allow a document to be compressed or otherwise usefully
385   transformed without losing the identity of its underlying media type
386   and without loss of information. Frequently, the entity is stored in
387   coded form, transmitted directly, and only decoded by the recipient.
389<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
390  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
393   All content-coding values are case-insensitive. HTTP/1.1 uses
394   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
395   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
396   describes the content-coding, what is more important is that it
397   indicates what decoding mechanism will be required to remove the
398   encoding.
401   The Internet Assigned Numbers Authority (IANA) acts as a registry for
402   content-coding value tokens. Initially, the registry contains the
403   following tokens:
406   gzip<iref item="gzip"/>
407  <list>
408    <t>
409        An encoding format produced by the file compression program
410        "gzip" (GNU zip) as described in <xref target="RFC1952"/>. This format is a
411        Lempel-Ziv coding (LZ77) with a 32 bit CRC.
412    </t>
413  </list>
416   compress<iref item="compress"/>
417  <list><t>
418        The encoding format produced by the common UNIX file compression
419        program "compress". This format is an adaptive Lempel-Ziv-Welch
420        coding (LZW).
422        Use of program names for the identification of encoding formats
423        is not desirable and is discouraged for future encodings. Their
424        use here is representative of historical practice, not good
425        design. For compatibility with previous implementations of HTTP,
426        applications &SHOULD; consider "x-gzip" and "x-compress" to be
427        equivalent to "gzip" and "compress" respectively.
428  </t></list>
431   deflate<iref item="deflate"/>
432  <list><t>
433        The "zlib" format defined in <xref target="RFC1950"/> in combination with
434        the "deflate" compression mechanism described in <xref target="RFC1951"/>.
435  </t></list>
438   identity<iref item="identity"/>
439  <list><t>
440        The default (identity) encoding; the use of no transformation
441        whatsoever. This content-coding is used only in the Accept-Encoding
442        header, and &SHOULD-NOT;  be used in the Content-Encoding
443        header.
444  </t></list>
447   New content-coding value tokens &SHOULD; be registered; to allow
448   interoperability between clients and servers, specifications of the
449   content coding algorithms needed to implement a new value &SHOULD; be
450   publicly available and adequate for independent implementation, and
451   conform to the purpose of content coding defined in this section.
455<section title="Media Types" anchor="media.types">
456  <x:anchor-alias value="media-type"/>
457  <x:anchor-alias value="type"/>
458  <x:anchor-alias value="subtype"/>
460   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
461   and Accept (<xref target="header.accept"/>) header fields in order to provide
462   open and extensible data typing and type negotiation.
464<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"/>
465  <x:ref>media-type</x:ref> = <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
466  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
467  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
469<t anchor="rule.parameter">
470  <x:anchor-alias value="attribute"/>
471  <x:anchor-alias value="parameter"/>
472  <x:anchor-alias value="value"/>
473   Parameters &MAY; follow the type/subtype in the form of attribute/value
474   pairs.
476<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"/>
477  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
478  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
479  <x:ref>value</x:ref>          = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
482   The type, subtype, and parameter attribute names are case-insensitive.
483   Parameter values might or might not be case-sensitive, depending on the
484   semantics of the parameter name.  The presence or absence of a parameter might
485   be significant to the processing of a media-type, depending on its
486   definition within the media type registry.
489   A parameter value that matches the <x:ref>token</x:ref> production may be
490   transmitted as either a token or within a quoted-string. The quoted and
491   unquoted values are equivalent.
494   Note that some older HTTP applications do not recognize media type
495   parameters. When sending data to older HTTP applications,
496   implementations &SHOULD; only use media type parameters when they are
497   required by that type/subtype definition.
500   Media-type values are registered with the Internet Assigned Number
501   Authority (IANA). The media type registration process is
502   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
503   discouraged.
506<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
508   Internet media types are registered with a canonical form. An
509   entity-body transferred via HTTP messages &MUST; be represented in the
510   appropriate canonical form prior to its transmission except for
511   "text" types, as defined in the next paragraph.
514   When in canonical form, media subtypes of the "text" type use CRLF as
515   the text line break. HTTP relaxes this requirement and allows the
516   transport of text media with plain CR or LF alone representing a line
517   break when it is done consistently for an entire entity-body. HTTP
518   applications &MUST; accept CRLF, bare CR, and bare LF as being
519   representative of a line break in text media received via HTTP. In
520   addition, if the text is represented in a character set that does not
521   use octets 13 and 10 for CR and LF respectively, as is the case for
522   some multi-byte character sets, HTTP allows the use of whatever octet
523   sequences are defined by that character set to represent the
524   equivalent of CR and LF for line breaks. This flexibility regarding
525   line breaks applies only to text media in the entity-body; a bare CR
526   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
527   structures (such as header fields and multipart boundaries).
530   If an entity-body is encoded with a content-coding, the underlying
531   data &MUST; be in a form defined above prior to being encoded.
534   The "charset" parameter is used with some media types to define the
535   character set (<xref target="character.sets"/>) of the data. When no explicit charset
536   parameter is provided by the sender, media subtypes of the "text"
537   type are defined to have a default charset value of "ISO-8859-1" when
538   received via HTTP. Data in character sets other than "ISO-8859-1" or
539   its subsets &MUST; be labeled with an appropriate charset value. See
540   <xref target="missing.charset"/> for compatibility problems.
544<section title="Multipart Types" anchor="multipart.types">
546   MIME provides for a number of "multipart" types -- encapsulations of
547   one or more entities within a single message-body. All multipart
548   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
549   and &MUST; include a boundary parameter as part of the media type
550   value. The message body is itself a protocol element and &MUST;
551   therefore use only CRLF to represent line breaks between body-parts.
552   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
553   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
554   original multipart contains an epilogue). These restrictions exist in
555   order to preserve the self-delimiting nature of a multipart message-body,
556   wherein the "end" of the message-body is indicated by the
557   ending multipart boundary.
560   In general, HTTP treats a multipart message-body no differently than
561   any other media type: strictly as payload. The one exception is the
562   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
563   (Partial Content) response.
564   <!-- jre: re-insert removed text pointing to caching? -->
565   In all
566   other cases, an HTTP user agent &SHOULD; follow the same or similar
567   behavior as a MIME user agent would upon receipt of a multipart type.
568   The MIME header fields within each body-part of a multipart message-body
569   do not have any significance to HTTP beyond that defined by
570   their MIME semantics.
573   In general, an HTTP user agent &SHOULD; follow the same or similar
574   behavior as a MIME user agent would upon receipt of a multipart type.
575   If an application receives an unrecognized multipart subtype, the
576   application &MUST; treat it as being equivalent to "multipart/mixed".
579      <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
580      for carrying form data suitable for processing via the POST
581      request method, as described in <xref target="RFC2388"/>.
586<section title="Quality Values" anchor="quality.values">
587  <x:anchor-alias value="qvalue"/>
589   HTTP content negotiation (<xref target="content.negotiation"/>) uses short "floating point"
590   numbers to indicate the relative importance ("weight") of various
591   negotiable parameters.  A weight is normalized to a real number in
592   the range 0 through 1, where 0 is the minimum and 1 the maximum
593   value. If a parameter has a quality value of 0, then content with
594   this parameter is `not acceptable' for the client. HTTP/1.1
595   applications &MUST-NOT; generate more than three digits after the
596   decimal point. User configuration of these values &SHOULD; also be
597   limited in this fashion.
599<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
600  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
601                 / ( "1" [ "." 0*3("0") ] )
604   "Quality values" is a misnomer, since these values merely represent
605   relative degradation in desired quality.
609<section title="Language Tags" anchor="language.tags">
610  <x:anchor-alias value="language-tag"/>
611  <x:anchor-alias value="primary-tag"/>
612  <x:anchor-alias value="subtag"/>
614   A language tag identifies a natural language spoken, written, or
615   otherwise conveyed by human beings for communication of information
616   to other human beings. Computer languages are explicitly excluded.
617   HTTP uses language tags within the Accept-Language and Content-Language
618   fields.
621   The syntax and registry of HTTP language tags is the same as that
622   defined by <xref target="RFC1766"/>. In summary, a language tag is composed of 1
623   or more parts: A primary language tag and a possibly empty series of
624   subtags:
626<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"/>
627  <x:ref>language-tag</x:ref>  = <x:ref>primary-tag</x:ref> *( "-" <x:ref>subtag</x:ref> )
628  <x:ref>primary-tag</x:ref>   = 1*8<x:ref>ALPHA</x:ref>
629  <x:ref>subtag</x:ref>        = 1*8<x:ref>ALPHA</x:ref>
632   White space is not allowed within the tag and all tags are case-insensitive.
633   The name space of language tags is administered by the
634   IANA. Example tags include:
636<figure><artwork type="example">
637    en, en-US, en-cockney, i-cherokee, x-pig-latin
640   where any two-letter primary-tag is an ISO-639 language abbreviation
641   and any two-letter initial subtag is an ISO-3166 country code. (The
642   last three tags above are not registered tags; all but the last are
643   examples of tags which could be registered in future.)
648<section title="Entity" anchor="entity">
650   Request and Response messages &MAY; transfer an entity if not otherwise
651   restricted by the request method or response status code. An entity
652   consists of entity-header fields and an entity-body, although some
653   responses will only include the entity-headers.
656   In this section, both sender and recipient refer to either the client
657   or the server, depending on who sends and who receives the entity.
660<section title="Entity Header Fields" anchor="entity.header.fields">
661  <x:anchor-alias value="entity-header"/>
662  <x:anchor-alias value="extension-header"/>
664   Entity-header fields define metainformation about the entity-body or,
665   if no body is present, about the resource identified by the request.
667<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
668  <x:ref>entity-header</x:ref>  = <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
669                 / <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
670                 / <x:ref>Content-Length</x:ref>           ; &header-content-length;
671                 / <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
672                 / <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
673                 / <x:ref>Content-Range</x:ref>            ; &header-content-range;
674                 / <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
675                 / <x:ref>Expires</x:ref>                  ; &header-expires;
676                 / <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
677                 / <x:ref>extension-header</x:ref>
679  <x:ref>extension-header</x:ref> = <x:ref>message-header</x:ref>
682   The extension-header mechanism allows additional entity-header fields
683   to be defined without changing the protocol, but these fields cannot
684   be assumed to be recognizable by the recipient. Unrecognized header
685   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
686   transparent proxies.
690<section title="Entity Body" anchor="entity.body">
691  <x:anchor-alias value="entity-body"/>
693   The entity-body (if any) sent with an HTTP request or response is in
694   a format and encoding defined by the entity-header fields.
696<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
697  <x:ref>entity-body</x:ref>    = *<x:ref>OCTET</x:ref>
700   An entity-body is only present in a message when a message-body is
701   present, as described in &message-body;. The entity-body is obtained
702   from the message-body by decoding any Transfer-Encoding that might
703   have been applied to ensure safe and proper transfer of the message.
706<section title="Type" anchor="type">
708   When an entity-body is included with a message, the data type of that
709   body is determined via the header fields Content-Type and Content-Encoding.
710   These define a two-layer, ordered encoding model:
712<figure><artwork type="example">
713    entity-body := Content-Encoding( Content-Type( data ) )
716   Content-Type specifies the media type of the underlying data.
717   Content-Encoding may be used to indicate any additional content
718   codings applied to the data, usually for the purpose of data
719   compression, that are a property of the requested resource. There is
720   no default encoding.
723   Any HTTP/1.1 message containing an entity-body &SHOULD; include a
724   Content-Type header field defining the media type of that body. If
725   and only if the media type is not given by a Content-Type field, the
726   recipient &MAY; attempt to guess the media type via inspection of its
727   content and/or the name extension(s) of the URI used to identify the
728   resource. If the media type remains unknown, the recipient &SHOULD;
729   treat it as type "application/octet-stream".
733<section title="Entity Length" anchor="entity.length">
735   The entity-length of a message is the length of the message-body
736   before any transfer-codings have been applied. &message-length; defines
737   how the transfer-length of a message-body is determined.
743<section title="Content Negotiation" anchor="content.negotiation">
745   Most HTTP responses include an entity which contains information for
746   interpretation by a human user. Naturally, it is desirable to supply
747   the user with the "best available" entity corresponding to the
748   request. Unfortunately for servers and caches, not all users have the
749   same preferences for what is "best," and not all user agents are
750   equally capable of rendering all entity types. For that reason, HTTP
751   has provisions for several mechanisms for "content negotiation" --
752   the process of selecting the best representation for a given response
753   when there are multiple representations available.
754  <list><t>
755      <x:h>Note:</x:h> This is not called "format negotiation" because the
756      alternate representations may be of the same media type, but use
757      different capabilities of that type, be in different languages,
758      etc.
759  </t></list>
762   Any response containing an entity-body &MAY; be subject to negotiation,
763   including error responses.
766   There are two kinds of content negotiation which are possible in
767   HTTP: server-driven and agent-driven negotiation. These two kinds of
768   negotiation are orthogonal and thus may be used separately or in
769   combination. One method of combination, referred to as transparent
770   negotiation, occurs when a cache uses the agent-driven negotiation
771   information provided by the origin server in order to provide
772   server-driven negotiation for subsequent requests.
775<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
777   If the selection of the best representation for a response is made by
778   an algorithm located at the server, it is called server-driven
779   negotiation. Selection is based on the available representations of
780   the response (the dimensions over which it can vary; e.g. language,
781   content-coding, etc.) and the contents of particular header fields in
782   the request message or on other information pertaining to the request
783   (such as the network address of the client).
786   Server-driven negotiation is advantageous when the algorithm for
787   selecting from among the available representations is difficult to
788   describe to the user agent, or when the server desires to send its
789   "best guess" to the client along with the first response (hoping to
790   avoid the round-trip delay of a subsequent request if the "best
791   guess" is good enough for the user). In order to improve the server's
792   guess, the user agent &MAY; include request header fields (Accept,
793   Accept-Language, Accept-Encoding, etc.) which describe its
794   preferences for such a response.
797   Server-driven negotiation has disadvantages:
798  <list style="numbers">
799    <t>
800         It is impossible for the server to accurately determine what
801         might be "best" for any given user, since that would require
802         complete knowledge of both the capabilities of the user agent
803         and the intended use for the response (e.g., does the user want
804         to view it on screen or print it on paper?).
805    </t>
806    <t>
807         Having the user agent describe its capabilities in every
808         request can be both very inefficient (given that only a small
809         percentage of responses have multiple representations) and a
810         potential violation of the user's privacy.
811    </t>
812    <t>
813         It complicates the implementation of an origin server and the
814         algorithms for generating responses to a request.
815    </t>
816    <t>
817         It may limit a public cache's ability to use the same response
818         for multiple user's requests.
819    </t>
820  </list>
823   HTTP/1.1 includes the following request-header fields for enabling
824   server-driven negotiation through description of user agent
825   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
826   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
827   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;). However, an
828   origin server is not limited to these dimensions and &MAY; vary the
829   response based on any aspect of the request, including information
830   outside the request-header fields or within extension header fields
831   not defined by this specification.
834   The Vary header field (&header-vary;) can be used to express the parameters the
835   server uses to select a representation that is subject to server-driven
836   negotiation.
840<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
842   With agent-driven negotiation, selection of the best representation
843   for a response is performed by the user agent after receiving an
844   initial response from the origin server. Selection is based on a list
845   of the available representations of the response included within the
846   header fields or entity-body of the initial response, with each
847   representation identified by its own URI. Selection from among the
848   representations may be performed automatically (if the user agent is
849   capable of doing so) or manually by the user selecting from a
850   generated (possibly hypertext) menu.
853   Agent-driven negotiation is advantageous when the response would vary
854   over commonly-used dimensions (such as type, language, or encoding),
855   when the origin server is unable to determine a user agent's
856   capabilities from examining the request, and generally when public
857   caches are used to distribute server load and reduce network usage.
860   Agent-driven negotiation suffers from the disadvantage of needing a
861   second request to obtain the best alternate representation. This
862   second request is only efficient when caching is used. In addition,
863   this specification does not define any mechanism for supporting
864   automatic selection, though it also does not prevent any such
865   mechanism from being developed as an extension and used within
866   HTTP/1.1.
869   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
870   status codes for enabling agent-driven negotiation when the server is
871   unwilling or unable to provide a varying response using server-driven
872   negotiation.
876<section title="Transparent Negotiation" anchor="transparent.negotiation">
878   Transparent negotiation is a combination of both server-driven and
879   agent-driven negotiation. When a cache is supplied with a form of the
880   list of available representations of the response (as in agent-driven
881   negotiation) and the dimensions of variance are completely understood
882   by the cache, then the cache becomes capable of performing server-driven
883   negotiation on behalf of the origin server for subsequent
884   requests on that resource.
887   Transparent negotiation has the advantage of distributing the
888   negotiation work that would otherwise be required of the origin
889   server and also removing the second request delay of agent-driven
890   negotiation when the cache is able to correctly guess the right
891   response.
894   This specification does not define any mechanism for transparent
895   negotiation, though it also does not prevent any such mechanism from
896   being developed as an extension that could be used within HTTP/1.1.
901<section title="Header Field Definitions" anchor="header.fields">
903   This section defines the syntax and semantics of HTTP/1.1 header fields
904   related to the payload of messages.
907   For entity-header fields, both sender and recipient refer to either the
908   client or the server, depending on who sends and who receives the entity.
911<section title="Accept" anchor="header.accept">
912  <iref primary="true" item="Accept header" x:for-anchor=""/>
913  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
914  <x:anchor-alias value="Accept"/>
915  <x:anchor-alias value="Accept-v"/>
916  <x:anchor-alias value="accept-ext"/>
917  <x:anchor-alias value="accept-params"/>
918  <x:anchor-alias value="media-range"/>
920   The request-header field "Accept" 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="Accept-v"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-ext"/>
927  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
928  <x:ref>Accept-v</x:ref> = #( <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>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
934  <x:ref>accept-params</x:ref>  = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>accept-ext</x:ref> )
935  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref>
936                   [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
939   The asterisk "*" character is used to group media types into ranges,
940   with "*/*" indicating all media types and "type/*" indicating all
941   subtypes of that type. The media-range &MAY; include media type
942   parameters that are applicable to that range.
945   Each media-range &MAY; be followed by one or more accept-params,
946   beginning with the "q" parameter for indicating a relative quality
947   factor. The first "q" parameter (if any) separates the media-range
948   parameter(s) from the accept-params. Quality factors allow the user
949   or user agent to indicate the relative degree of preference for that
950   media-range, using the qvalue scale from 0 to 1 (<xref target="quality.values"/>). The
951   default value is q=1.
952  <list><t>
953      <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
954      parameters from Accept extension parameters is due to historical
955      practice. Although this prevents any media type parameter named
956      "q" from being used with a media range, such an event is believed
957      to be unlikely given the lack of any "q" parameters in the IANA
958      media type registry and the rare usage of any media type
959      parameters in Accept. Future media types are discouraged from
960      registering any parameter named "q".
961  </t></list>
964   The example
966<figure><artwork type="example">
967  Accept: audio/*; q=0.2, audio/basic
970   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
971   type if it is the best available after an 80% mark-down in quality."
974   If no Accept header field is present, then it is assumed that the
975   client accepts all media types. If an Accept header field is present,
976   and if the server cannot send a response which is acceptable
977   according to the combined Accept field value, then the server &SHOULD;
978   send a 406 (Not Acceptable) response.
981   A more elaborate example is
983<figure><artwork type="example">
984  Accept: text/plain; q=0.5, text/html,
985          text/x-dvi; q=0.8, text/x-c
988   Verbally, this would be interpreted as "text/html and text/x-c are
989   the preferred media types, but if they do not exist, then send the
990   text/x-dvi entity, and if that does not exist, send the text/plain
991   entity."
994   Media ranges can be overridden by more specific media ranges or
995   specific media types. If more than one media range applies to a given
996   type, the most specific reference has precedence. For example,
998<figure><artwork type="example">
999  Accept: text/*, text/html, text/html;level=1, */*
1002   have the following precedence:
1004<figure><artwork type="example">
1005    1) text/html;level=1
1006    2) text/html
1007    3) text/*
1008    4) */*
1011   The media type quality factor associated with a given type is
1012   determined by finding the media range with the highest precedence
1013   which matches that type. For example,
1015<figure><artwork type="example">
1016  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1017          text/html;level=2;q=0.4, */*;q=0.5
1020   would cause the following values to be associated:
1022<figure><artwork type="example">
1023    text/html;level=1         = 1
1024    text/html                 = 0.7
1025    text/plain                = 0.3
1026    image/jpeg                = 0.5
1027    text/html;level=2         = 0.4
1028    text/html;level=3         = 0.7
1031      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1032      values for certain media ranges. However, unless the user agent is
1033      a closed system which cannot interact with other rendering agents,
1034      this default set ought to be configurable by the user.
1038<section title="Accept-Charset" anchor="header.accept-charset">
1039  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1040  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
1041  <x:anchor-alias value="Accept-Charset"/>
1042  <x:anchor-alias value="Accept-Charset-v"/>
1044   The request-header field "Accept-Charset" can be used to indicate what
1045   character sets are acceptable for the response. This field allows
1046   clients capable of understanding more comprehensive or special-purpose
1047   character sets to signal that capability to a server which is
1048   capable of representing documents in those character sets.
1050<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
1051  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
1052          <x:ref>Accept-Charset-v</x:ref>
1053  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1054                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1057   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1058   be given an associated quality value which represents the user's
1059   preference for that charset. The default value is q=1. An example is
1061<figure><artwork type="example">
1062  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1065   The special value "*", if present in the Accept-Charset field,
1066   matches every character set (including ISO-8859-1) which is not
1067   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1068   in an Accept-Charset field, then all character sets not explicitly
1069   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1070   a quality value of 1 if not explicitly mentioned.
1073   If no Accept-Charset header is present, the default is that any
1074   character set is acceptable. If an Accept-Charset header is present,
1075   and if the server cannot send a response which is acceptable
1076   according to the Accept-Charset header, then the server &SHOULD; send
1077   an error response with the 406 (Not Acceptable) status code, though
1078   the sending of an unacceptable response is also allowed.
1082<section title="Accept-Encoding" anchor="header.accept-encoding">
1083  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1084  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
1085  <x:anchor-alias value="Accept-Encoding"/>
1086  <x:anchor-alias value="Accept-Encoding-v"/>
1087  <x:anchor-alias value="codings"/>
1089   The request-header field "Accept-Encoding" is similar to Accept, but
1090   restricts the content-codings (<xref target="content.codings"/>) that are acceptable in
1091   the response.
1093<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="Accept-Encoding-v"/><iref primary="true" item="Grammar" subitem="codings"/>
1094  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
1095                     <x:ref>Accept-Encoding-v</x:ref>
1096  <x:ref>Accept-Encoding-v</x:ref>  =
1097                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1098  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
1101   Each codings value &MAY; be given an associated quality value which
1102   represents the preference for that encoding. The default value is q=1.
1105   Examples of its use are:
1107<figure><artwork type="example">
1108  Accept-Encoding: compress, gzip
1109  Accept-Encoding:
1110  Accept-Encoding: *
1111  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1112  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1115   A server tests whether a content-coding is acceptable, according to
1116   an Accept-Encoding field, using these rules:
1117  <list style="numbers">
1118      <t>If the content-coding is one of the content-codings listed in
1119         the Accept-Encoding field, then it is acceptable, unless it is
1120         accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
1121         qvalue of 0 means "not acceptable.")</t>
1123      <t>The special "*" symbol in an Accept-Encoding field matches any
1124         available content-coding not explicitly listed in the header
1125         field.</t>
1127      <t>If multiple content-codings are acceptable, then the acceptable
1128         content-coding with the highest non-zero qvalue is preferred.</t>
1130      <t>The "identity" content-coding is always acceptable, unless
1131         specifically refused because the Accept-Encoding field includes
1132         "identity;q=0", or because the field includes "*;q=0" and does
1133         not explicitly include the "identity" content-coding. If the
1134         Accept-Encoding field-value is empty, then only the "identity"
1135         encoding is acceptable.</t>
1136  </list>
1139   If an Accept-Encoding field is present in a request, and if the
1140   server cannot send a response which is acceptable according to the
1141   Accept-Encoding header, then the server &SHOULD; send an error response
1142   with the 406 (Not Acceptable) status code.
1145   If no Accept-Encoding field is present in a request, the server &MAY;
1146   assume that the client will accept any content coding. In this case,
1147   if "identity" is one of the available content-codings, then the
1148   server &SHOULD; use the "identity" content-coding, unless it has
1149   additional information that a different content-coding is meaningful
1150   to the client.
1151  <list><t>
1152      <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1153      and if the "identity" content-coding is unavailable, then
1154      content-codings commonly understood by HTTP/1.0 clients (i.e.,
1155      "gzip" and "compress") are preferred; some older clients
1156      improperly display messages sent with other content-codings.  The
1157      server might also make this decision based on information about
1158      the particular user-agent or client.
1159    </t><t>
1160      <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1161      associated with content-codings. This means that qvalues will not
1162      work and are not permitted with x-gzip or x-compress.
1163    </t></list>
1167<section title="Accept-Language" anchor="header.accept-language">
1168  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1169  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1170  <x:anchor-alias value="Accept-Language"/>
1171  <x:anchor-alias value="Accept-Language-v"/>
1172  <x:anchor-alias value="language-range"/>
1174   The request-header field "Accept-Language" is similar to Accept, but
1175   restricts the set of natural languages that are preferred as a
1176   response to the request. Language tags are defined in <xref target="language.tags"/>.
1178<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="Accept-Language-v"/><iref primary="true" item="Grammar" subitem="language-range"/>
1179  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
1180                    <x:ref>Accept-Language-v</x:ref>
1181  <x:ref>Accept-Language-v</x:ref> =
1182                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1183  <x:ref>language-range</x:ref>    =
1184            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
1187   Each language-range can be given an associated quality value which
1188   represents an estimate of the user's preference for the languages
1189   specified by that range. The quality value defaults to "q=1". For
1190   example,
1192<figure><artwork type="example">
1193  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1196   would mean: "I prefer Danish, but will accept British English and
1197   other types of English."
1200   For matching, the "Basic Filtering" matching scheme, defined in
1201   <xref target="RFC4647" x:sec="3.3.1" x:fmt="of"/>, is used:
1203<x:blockquote cite="">
1204  <t>
1205     A language range matches a
1206     particular language tag if, in a case-insensitive comparison, it
1207     exactly equals the tag, or if it exactly equals a prefix of the tag
1208     such that the first character following the prefix is "-".
1209  </t>
1212   The special range "*", if present in the Accept-Language field,
1213   matches every tag not matched by any other range present in the
1214   Accept-Language field.
1215  <list><t>
1216      <x:h>Note:</x:h> This use of a prefix matching rule does not imply that
1217      language tags are assigned to languages in such a way that it is
1218      always true that if a user understands a language with a certain
1219      tag, then this user will also understand all languages with tags
1220      for which this tag is a prefix. The prefix rule simply allows the
1221      use of prefix tags if this is the case.
1222  </t></list>
1225   The language quality factor assigned to a language-tag by the
1226   Accept-Language field is the quality value of the longest language-range
1227   in the field that matches the language-tag. If no language-range
1228   in the field matches the tag, the language quality factor
1229   assigned is 0. If no Accept-Language header is present in the
1230   request, the server
1231   &SHOULD; assume that all languages are equally acceptable. If an
1232   Accept-Language header is present, then all languages which are
1233   assigned a quality factor greater than 0 are acceptable.
1236   It might be contrary to the privacy expectations of the user to send
1237   an Accept-Language header with the complete linguistic preferences of
1238   the user in every request. For a discussion of this issue, see
1239   <xref target=""/>.
1242   As intelligibility is highly dependent on the individual user, it is
1243   recommended that client applications make the choice of linguistic
1244   preference available to the user. If the choice is not made
1245   available, then the Accept-Language header field &MUST-NOT; be given in
1246   the request.
1247  <list><t>
1248      <x:h>Note:</x:h> When making the choice of linguistic preference available to
1249      the user, we remind implementors of  the fact that users are not
1250      familiar with the details of language matching as described above,
1251      and should provide appropriate guidance. As an example, users
1252      might assume that on selecting "en-gb", they will be served any
1253      kind of English document if British English is not available. A
1254      user agent might suggest in such a case to add "en" to get the
1255      best matching behavior.
1256  </t></list>
1260<section title="Content-Encoding" anchor="header.content-encoding">
1261  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1262  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1263  <x:anchor-alias value="Content-Encoding"/>
1264  <x:anchor-alias value="Content-Encoding-v"/>
1266   The entity-header field "Content-Encoding" is used as a modifier to the
1267   media-type. When present, its value indicates what additional content
1268   codings have been applied to the entity-body, and thus what decoding
1269   mechanisms must be applied in order to obtain the media-type
1270   referenced by the Content-Type header field. Content-Encoding is
1271   primarily used to allow a document to be compressed without losing
1272   the identity of its underlying media type.
1274<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
1275  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
1276  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1279   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1281<figure><artwork type="example">
1282  Content-Encoding: gzip
1285   The content-coding is a characteristic of the entity identified by
1286   the request-target. Typically, the entity-body is stored with this
1287   encoding and is only decoded before rendering or analogous usage.
1288   However, a non-transparent proxy &MAY; modify the content-coding if the
1289   new coding is known to be acceptable to the recipient, unless the
1290   "no-transform" cache-control directive is present in the message.
1293   If the content-coding of an entity is not "identity", then the
1294   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1295   that lists the non-identity content-coding(s) used.
1298   If the content-coding of an entity in a request message is not
1299   acceptable to the origin server, the server &SHOULD; respond with a
1300   status code of 415 (Unsupported Media Type).
1303   If multiple encodings have been applied to an entity, the content
1304   codings &MUST; be listed in the order in which they were applied.
1305   Additional information about the encoding parameters &MAY; be provided
1306   by other entity-header fields not defined by this specification.
1310<section title="Content-Language" anchor="header.content-language">
1311  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1312  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1313  <x:anchor-alias value="Content-Language"/>
1314  <x:anchor-alias value="Content-Language-v"/>
1316   The entity-header field "Content-Language" describes the natural
1317   language(s) of the intended audience for the enclosed entity. Note
1318   that this might not be equivalent to all the languages used within
1319   the entity-body.
1321<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
1322  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
1323  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1326   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1327   Content-Language is to allow a user to identify and differentiate
1328   entities according to the user's own preferred language. Thus, if the
1329   body content is intended only for a Danish-literate audience, the
1330   appropriate field is
1332<figure><artwork type="example">
1333  Content-Language: da
1336   If no Content-Language is specified, the default is that the content
1337   is intended for all language audiences. This might mean that the
1338   sender does not consider it to be specific to any natural language,
1339   or that the sender does not know for which language it is intended.
1342   Multiple languages &MAY; be listed for content that is intended for
1343   multiple audiences. For example, a rendition of the "Treaty of
1344   Waitangi," presented simultaneously in the original Maori and English
1345   versions, would call for
1347<figure><artwork type="example">
1348  Content-Language: mi, en
1351   However, just because multiple languages are present within an entity
1352   does not mean that it is intended for multiple linguistic audiences.
1353   An example would be a beginner's language primer, such as "A First
1354   Lesson in Latin," which is clearly intended to be used by an
1355   English-literate audience. In this case, the Content-Language would
1356   properly only include "en".
1359   Content-Language &MAY; be applied to any media type -- it is not
1360   limited to textual documents.
1364<section title="Content-Location" anchor="header.content-location">
1365  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1366  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1367  <x:anchor-alias value="Content-Location"/>
1368  <x:anchor-alias value="Content-Location-v"/>
1370   The entity-header field "Content-Location" &MAY; be used to supply the
1371   resource location for the entity enclosed in the message when that
1372   entity is accessible from a location separate from the requested
1373   resource's URI. A server &SHOULD; provide a Content-Location for the
1374   variant corresponding to the response entity; especially in the case
1375   where a resource has multiple entities associated with it, and those
1376   entities actually have separate locations by which they might be
1377   individually accessed, the server &SHOULD; provide a Content-Location
1378   for the particular variant which is returned.
1380<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
1381  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
1382                    <x:ref>Content-Location-v</x:ref>
1383  <x:ref>Content-Location-v</x:ref> =
1384                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
1387   The value of Content-Location also defines the base URI for the
1388   entity.
1391   The Content-Location value is not a replacement for the original
1392   requested URI; it is only a statement of the location of the resource
1393   corresponding to this particular entity at the time of the request.
1394   Future requests &MAY; specify the Content-Location URI as the request-target
1395   if the desire is to identify the source of that particular
1396   entity.
1399   A cache cannot assume that an entity with a Content-Location
1400   different from the URI used to retrieve it can be used to respond to
1401   later requests on that Content-Location URI. However, the Content-Location
1402   can be used to differentiate between multiple entities
1403   retrieved from a single requested resource, as described in &caching-neg-resp;.
1406   If the Content-Location is a relative URI, the relative URI is
1407   interpreted relative to the request-target.
1410   The meaning of the Content-Location header in PUT or POST requests is
1411   undefined; servers are free to ignore it in those cases.
1415<section title="Content-MD5" anchor="header.content-md5">
1416  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1417  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1418  <x:anchor-alias value="Content-MD5"/>
1419  <x:anchor-alias value="Content-MD5-v"/>
1421   The entity-header field "Content-MD5", as defined in <xref target="RFC1864"/>, is
1422   an MD5 digest of the entity-body for the purpose of providing an
1423   end-to-end message integrity check (MIC) of the entity-body. (Note: a
1424   MIC is good for detecting accidental modification of the entity-body
1425   in transit, but is not proof against malicious attacks.)
1427<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
1428  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
1429  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1432   The Content-MD5 header field &MAY; be generated by an origin server or
1433   client to function as an integrity check of the entity-body. Only
1434   origin servers or clients &MAY; generate the Content-MD5 header field;
1435   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1436   value as an end-to-end integrity check. Any recipient of the entity-body,
1437   including gateways and proxies, &MAY; check that the digest value
1438   in this header field matches that of the entity-body as received.
1441   The MD5 digest is computed based on the content of the entity-body,
1442   including any content-coding that has been applied, but not including
1443   any transfer-encoding applied to the message-body. If the message is
1444   received with a transfer-encoding, that encoding &MUST; be removed
1445   prior to checking the Content-MD5 value against the received entity.
1448   This has the result that the digest is computed on the octets of the
1449   entity-body exactly as, and in the order that, they would be sent if
1450   no transfer-encoding were being applied.
1453   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1454   composite media-types (e.g., multipart/* and message/rfc822), but
1455   this does not change how the digest is computed as defined in the
1456   preceding paragraph.
1459   There are several consequences of this. The entity-body for composite
1460   types &MAY; contain many body-parts, each with its own MIME and HTTP
1461   headers (including Content-MD5, Content-Transfer-Encoding, and
1462   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1463   or Content-Encoding header, it is assumed that the content
1464   of the body-part has had the encoding applied, and the body-part is
1465   included in the Content-MD5 digest as is -- i.e., after the
1466   application. The Transfer-Encoding header field is not allowed within
1467   body-parts.
1470   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1471   computing or checking the digest: the line break convention used in
1472   the text actually transmitted &MUST; be left unaltered when computing
1473   the digest.
1474  <list><t>
1475      <x:h>Note:</x:h> while the definition of Content-MD5 is exactly the same for
1476      HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1477      in which the application of Content-MD5 to HTTP entity-bodies
1478      differs from its application to MIME entity-bodies. One is that
1479      HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1480      does use Transfer-Encoding and Content-Encoding. Another is that
1481      HTTP more frequently uses binary content types than MIME, so it is
1482      worth noting that, in such cases, the byte order used to compute
1483      the digest is the transmission byte order defined for the type.
1484      Lastly, HTTP allows transmission of text types with any of several
1485      line break conventions and not just the canonical form using CRLF.
1486  </t></list>
1490<section title="Content-Type" anchor="header.content-type">
1491  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1492  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1493  <x:anchor-alias value="Content-Type"/>
1494  <x:anchor-alias value="Content-Type-v"/>
1496   The entity-header field "Content-Type" indicates the media type of the
1497   entity-body sent to the recipient or, in the case of the HEAD method,
1498   the media type that would have been sent had the request been a GET.
1500<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
1501  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
1502  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1505   Media types are defined in <xref target="media.types"/>. An example of the field is
1507<figure><artwork type="example">
1508  Content-Type: text/html; charset=ISO-8859-4
1511   Further discussion of methods for identifying the media type of an
1512   entity is provided in <xref target="type"/>.
1518<section title="IANA Considerations" anchor="IANA.considerations">
1519<section title="Message Header Registration" anchor="message.header.registration">
1521   The Message Header Registry located at <eref target=""/> should be updated
1522   with the permanent registrations below (see <xref target="RFC3864"/>):
1524<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1525<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1526   <ttcol>Header Field Name</ttcol>
1527   <ttcol>Protocol</ttcol>
1528   <ttcol>Status</ttcol>
1529   <ttcol>Reference</ttcol>
1531   <c>Accept</c>
1532   <c>http</c>
1533   <c>standard</c>
1534   <c>
1535      <xref target="header.accept"/>
1536   </c>
1537   <c>Accept-Charset</c>
1538   <c>http</c>
1539   <c>standard</c>
1540   <c>
1541      <xref target="header.accept-charset"/>
1542   </c>
1543   <c>Accept-Encoding</c>
1544   <c>http</c>
1545   <c>standard</c>
1546   <c>
1547      <xref target="header.accept-encoding"/>
1548   </c>
1549   <c>Accept-Language</c>
1550   <c>http</c>
1551   <c>standard</c>
1552   <c>
1553      <xref target="header.accept-language"/>
1554   </c>
1555   <c>Content-Disposition</c>
1556   <c>http</c>
1557   <c/>
1558   <c>
1559      <xref target="content-disposition"/>
1560   </c>
1561   <c>Content-Encoding</c>
1562   <c>http</c>
1563   <c>standard</c>
1564   <c>
1565      <xref target="header.content-encoding"/>
1566   </c>
1567   <c>Content-Language</c>
1568   <c>http</c>
1569   <c>standard</c>
1570   <c>
1571      <xref target="header.content-language"/>
1572   </c>
1573   <c>Content-Location</c>
1574   <c>http</c>
1575   <c>standard</c>
1576   <c>
1577      <xref target="header.content-location"/>
1578   </c>
1579   <c>Content-MD5</c>
1580   <c>http</c>
1581   <c>standard</c>
1582   <c>
1583      <xref target="header.content-md5"/>
1584   </c>
1585   <c>Content-Type</c>
1586   <c>http</c>
1587   <c>standard</c>
1588   <c>
1589      <xref target="header.content-type"/>
1590   </c>
1591   <c>MIME-Version</c>
1592   <c>http</c>
1593   <c/>
1594   <c>
1595      <xref target="mime-version"/>
1596   </c>
1600   The change controller is: "IETF ( - Internet Engineering Task Force".
1605<section title="Security Considerations" anchor="security.considerations">
1607   This section is meant to inform application developers, information
1608   providers, and users of the security limitations in HTTP/1.1 as
1609   described by this document. The discussion does not include
1610   definitive solutions to the problems revealed, though it does make
1611   some suggestions for reducing security risks.
1614<section title="Privacy Issues Connected to Accept Headers" anchor="">
1616   Accept request-headers can reveal information about the user to all
1617   servers which are accessed. The Accept-Language header in particular
1618   can reveal information the user would consider to be of a private
1619   nature, because the understanding of particular languages is often
1620   strongly correlated to the membership of a particular ethnic group.
1621   User agents which offer the option to configure the contents of an
1622   Accept-Language header to be sent in every request are strongly
1623   encouraged to let the configuration process include a message which
1624   makes the user aware of the loss of privacy involved.
1627   An approach that limits the loss of privacy would be for a user agent
1628   to omit the sending of Accept-Language headers by default, and to ask
1629   the user whether or not to start sending Accept-Language headers to a
1630   server if it detects, by looking for any Vary response-header fields
1631   generated by the server, that such sending could improve the quality
1632   of service.
1635   Elaborate user-customized accept header fields sent in every request,
1636   in particular if these include quality values, can be used by servers
1637   as relatively reliable and long-lived user identifiers. Such user
1638   identifiers would allow content providers to do click-trail tracking,
1639   and would allow collaborating content providers to match cross-server
1640   click-trails or form submissions of individual users. Note that for
1641   many users not behind a proxy, the network address of the host
1642   running the user agent will also serve as a long-lived user
1643   identifier. In environments where proxies are used to enhance
1644   privacy, user agents ought to be conservative in offering accept
1645   header configuration options to end users. As an extreme privacy
1646   measure, proxies could filter the accept headers in relayed requests.
1647   General purpose user agents which provide a high degree of header
1648   configurability &SHOULD; warn users about the loss of privacy which can
1649   be involved.
1653<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1655   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
1656   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1657   serious security considerations. Content-Disposition is not part of
1658   the HTTP standard, but since it is widely implemented, we are
1659   documenting its use and risks for implementors. See <xref target="RFC2183" x:fmt="of" x:sec="5"/>
1660   for details.
1666<section title="Acknowledgments" anchor="ack">
1671<references title="Normative References">
1673<reference anchor="ISO-8859-1">
1674  <front>
1675    <title>
1676     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1677    </title>
1678    <author>
1679      <organization>International Organization for Standardization</organization>
1680    </author>
1681    <date year="1998"/>
1682  </front>
1683  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
1686<reference anchor="Part1">
1687  <front>
1688    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1689    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1690      <organization abbrev="Day Software">Day Software</organization>
1691      <address><email></email></address>
1692    </author>
1693    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1694      <organization>One Laptop per Child</organization>
1695      <address><email></email></address>
1696    </author>
1697    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1698      <organization abbrev="HP">Hewlett-Packard Company</organization>
1699      <address><email></email></address>
1700    </author>
1701    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1702      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1703      <address><email></email></address>
1704    </author>
1705    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1706      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1707      <address><email></email></address>
1708    </author>
1709    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1710      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1711      <address><email></email></address>
1712    </author>
1713    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1714      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1715      <address><email></email></address>
1716    </author>
1717    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1718      <organization abbrev="W3C">World Wide Web Consortium</organization>
1719      <address><email></email></address>
1720    </author>
1721    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1722      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1723      <address><email></email></address>
1724    </author>
1725    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1726  </front>
1727  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1728  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1731<reference anchor="Part2">
1732  <front>
1733    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1734    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1735      <organization abbrev="Day Software">Day Software</organization>
1736      <address><email></email></address>
1737    </author>
1738    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1739      <organization>One Laptop per Child</organization>
1740      <address><email></email></address>
1741    </author>
1742    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1743      <organization abbrev="HP">Hewlett-Packard Company</organization>
1744      <address><email></email></address>
1745    </author>
1746    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1747      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1748      <address><email></email></address>
1749    </author>
1750    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1751      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1752      <address><email></email></address>
1753    </author>
1754    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1755      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1756      <address><email></email></address>
1757    </author>
1758    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1759      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1760      <address><email></email></address>
1761    </author>
1762    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1763      <organization abbrev="W3C">World Wide Web Consortium</organization>
1764      <address><email></email></address>
1765    </author>
1766    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1767      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1768      <address><email></email></address>
1769    </author>
1770    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1771  </front>
1772  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1773  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1776<reference anchor="Part4">
1777  <front>
1778    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1779    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1780      <organization abbrev="Day Software">Day Software</organization>
1781      <address><email></email></address>
1782    </author>
1783    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1784      <organization>One Laptop per Child</organization>
1785      <address><email></email></address>
1786    </author>
1787    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1788      <organization abbrev="HP">Hewlett-Packard Company</organization>
1789      <address><email></email></address>
1790    </author>
1791    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1792      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1793      <address><email></email></address>
1794    </author>
1795    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1796      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1797      <address><email></email></address>
1798    </author>
1799    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1800      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1801      <address><email></email></address>
1802    </author>
1803    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1804      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1805      <address><email></email></address>
1806    </author>
1807    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1808      <organization abbrev="W3C">World Wide Web Consortium</organization>
1809      <address><email></email></address>
1810    </author>
1811    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1812      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1813      <address><email></email></address>
1814    </author>
1815    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1816  </front>
1817  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1818  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1821<reference anchor="Part5">
1822  <front>
1823    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1824    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1825      <organization abbrev="Day Software">Day Software</organization>
1826      <address><email></email></address>
1827    </author>
1828    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1829      <organization>One Laptop per Child</organization>
1830      <address><email></email></address>
1831    </author>
1832    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1833      <organization abbrev="HP">Hewlett-Packard Company</organization>
1834      <address><email></email></address>
1835    </author>
1836    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1837      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1838      <address><email></email></address>
1839    </author>
1840    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1841      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1842      <address><email></email></address>
1843    </author>
1844    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1845      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1846      <address><email></email></address>
1847    </author>
1848    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1849      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1850      <address><email></email></address>
1851    </author>
1852    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1853      <organization abbrev="W3C">World Wide Web Consortium</organization>
1854      <address><email></email></address>
1855    </author>
1856    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1857      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1858      <address><email></email></address>
1859    </author>
1860    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1861  </front>
1862  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1863  <x:source href="p5-range.xml" basename="p5-range"/>
1866<reference anchor="Part6">
1867  <front>
1868    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1869    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1870      <organization abbrev="Day Software">Day Software</organization>
1871      <address><email></email></address>
1872    </author>
1873    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1874      <organization>One Laptop per Child</organization>
1875      <address><email></email></address>
1876    </author>
1877    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1878      <organization abbrev="HP">Hewlett-Packard Company</organization>
1879      <address><email></email></address>
1880    </author>
1881    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1882      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1883      <address><email></email></address>
1884    </author>
1885    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1886      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1887      <address><email></email></address>
1888    </author>
1889    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1890      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1891      <address><email></email></address>
1892    </author>
1893    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1894      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1895      <address><email></email></address>
1896    </author>
1897    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1898      <organization abbrev="W3C">World Wide Web Consortium</organization>
1899      <address><email></email></address>
1900    </author>
1901    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1902      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1903      <address><email></email></address>
1904    </author>
1905    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1906  </front>
1907  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1908  <x:source href="p6-cache.xml" basename="p6-cache"/>
1911<reference anchor="RFC1766">
1912  <front>
1913    <title abbrev="Language Tag">Tags for the Identification of Languages</title>
1914    <author initials="H." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
1915      <organization>UNINETT</organization>
1916      <address><email></email></address>
1917    </author>
1918    <date month="March" year="1995"/>
1919  </front>
1920  <seriesInfo name="RFC" value="1766"/>
1923<reference anchor="RFC1864">
1924  <front>
1925    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1926    <author initials="J." surname="Myers" fullname="John G. Myers">
1927      <organization>Carnegie Mellon University</organization>
1928      <address><email></email></address>
1929    </author>
1930    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
1931      <organization>Dover Beach Consulting, Inc.</organization>
1932      <address><email></email></address>
1933    </author>
1934    <date month="October" year="1995"/>
1935  </front>
1936  <seriesInfo name="RFC" value="1864"/>
1939<reference anchor="RFC1950">
1940  <front>
1941    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1942    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1943      <organization>Aladdin Enterprises</organization>
1944      <address><email></email></address>
1945    </author>
1946    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1947      <organization/>
1948    </author>
1949    <date month="May" year="1996"/>
1950  </front>
1951  <seriesInfo name="RFC" value="1950"/>
1952  <annotation>
1953    RFC 1950 is an Informational RFC, thus it may be less stable than
1954    this specification. On the other hand, this downward reference was
1955    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1956    therefore it is unlikely to cause problems in practice. See also
1957    <xref target="BCP97"/>.
1958  </annotation>
1961<reference anchor="RFC1951">
1962  <front>
1963    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1964    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1965      <organization>Aladdin Enterprises</organization>
1966      <address><email></email></address>
1967    </author>
1968    <date month="May" year="1996"/>
1969  </front>
1970  <seriesInfo name="RFC" value="1951"/>
1971  <annotation>
1972    RFC 1951 is an Informational RFC, thus it may be less stable than
1973    this specification. On the other hand, this downward reference was
1974    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1975    therefore it is unlikely to cause problems in practice. See also
1976    <xref target="BCP97"/>.
1977  </annotation>
1980<reference anchor="RFC1952">
1981  <front>
1982    <title>GZIP file format specification version 4.3</title>
1983    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1984      <organization>Aladdin Enterprises</organization>
1985      <address><email></email></address>
1986    </author>
1987    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1988      <organization/>
1989      <address><email></email></address>
1990    </author>
1991    <author initials="M." surname="Adler" fullname="Mark Adler">
1992      <organization/>
1993      <address><email></email></address>
1994    </author>
1995    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1996      <organization/>
1997      <address><email></email></address>
1998    </author>
1999    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2000      <organization/>
2001      <address><email></email></address>
2002    </author>
2003    <date month="May" year="1996"/>
2004  </front>
2005  <seriesInfo name="RFC" value="1952"/>
2006  <annotation>
2007    RFC 1952 is an Informational RFC, thus it may be less stable than
2008    this specification. On the other hand, this downward reference was
2009    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2010    therefore it is unlikely to cause problems in practice. See also
2011    <xref target="BCP97"/>.
2012  </annotation>
2015<reference anchor="RFC2045">
2016  <front>
2017    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2018    <author initials="N." surname="Freed" fullname="Ned Freed">
2019      <organization>Innosoft International, Inc.</organization>
2020      <address><email></email></address>
2021    </author>
2022    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2023      <organization>First Virtual Holdings</organization>
2024      <address><email></email></address>
2025    </author>
2026    <date month="November" year="1996"/>
2027  </front>
2028  <seriesInfo name="RFC" value="2045"/>
2031<reference anchor="RFC2046">
2032  <front>
2033    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2034    <author initials="N." surname="Freed" fullname="Ned Freed">
2035      <organization>Innosoft International, Inc.</organization>
2036      <address><email></email></address>
2037    </author>
2038    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2039      <organization>First Virtual Holdings</organization>
2040      <address><email></email></address>
2041    </author>
2042    <date month="November" year="1996"/>
2043  </front>
2044  <seriesInfo name="RFC" value="2046"/>
2047<reference anchor="RFC2119">
2048  <front>
2049    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2050    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2051      <organization>Harvard University</organization>
2052      <address><email></email></address>
2053    </author>
2054    <date month="March" year="1997"/>
2055  </front>
2056  <seriesInfo name="BCP" value="14"/>
2057  <seriesInfo name="RFC" value="2119"/>
2060<reference anchor='RFC4647'>
2061  <front>
2062    <title>Matching of Language Tags</title>
2063    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2064      <organization>Yahoo! Inc.</organization>
2065      <address><email></email></address>
2066    </author>
2067    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2068      <organization>Google</organization>
2069      <address><email></email></address>
2070    </author>
2071    <date year='2006' month='September' />
2072  </front>
2073  <seriesInfo name='BCP' value='47' />
2074  <seriesInfo name='RFC' value='4647' />
2079<references title="Informative References">
2081<reference anchor="RFC1945">
2082  <front>
2083    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2084    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2085      <organization>MIT, Laboratory for Computer Science</organization>
2086      <address><email></email></address>
2087    </author>
2088    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2089      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2090      <address><email></email></address>
2091    </author>
2092    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2093      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2094      <address><email></email></address>
2095    </author>
2096    <date month="May" year="1996"/>
2097  </front>
2098  <seriesInfo name="RFC" value="1945"/>
2101<reference anchor="RFC2049">
2102  <front>
2103    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2104    <author initials="N." surname="Freed" fullname="Ned Freed">
2105      <organization>Innosoft International, Inc.</organization>
2106      <address><email></email></address>
2107    </author>
2108    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2109      <organization>First Virtual Holdings</organization>
2110      <address><email></email></address>
2111    </author>
2112    <date month="November" year="1996"/>
2113  </front>
2114  <seriesInfo name="RFC" value="2049"/>
2117<reference anchor="RFC2068">
2118  <front>
2119    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2120    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2121      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2122      <address><email></email></address>
2123    </author>
2124    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2125      <organization>MIT Laboratory for Computer Science</organization>
2126      <address><email></email></address>
2127    </author>
2128    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2129      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2130      <address><email></email></address>
2131    </author>
2132    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2133      <organization>MIT Laboratory for Computer Science</organization>
2134      <address><email></email></address>
2135    </author>
2136    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2137      <organization>MIT Laboratory for Computer Science</organization>
2138      <address><email></email></address>
2139    </author>
2140    <date month="January" year="1997"/>
2141  </front>
2142  <seriesInfo name="RFC" value="2068"/>
2145<reference anchor="RFC2076">
2146  <front>
2147    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2148    <author initials="J." surname="Palme" fullname="Jacob Palme">
2149      <organization>Stockholm University/KTH</organization>
2150      <address><email></email></address>
2151    </author>
2152    <date month="February" year="1997"/>
2153  </front>
2154  <seriesInfo name="RFC" value="2076"/>
2157<reference anchor="RFC2183">
2158  <front>
2159    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2160    <author initials="R." surname="Troost" fullname="Rens Troost">
2161      <organization>New Century Systems</organization>
2162      <address><email></email></address>
2163    </author>
2164    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2165      <organization>QUALCOMM Incorporated</organization>
2166      <address><email></email></address>
2167    </author>
2168    <author initials="K." surname="Moore" fullname="Keith Moore">
2169      <organization>Department of Computer Science</organization>
2170      <address><email></email></address>
2171    </author>
2172    <date month="August" year="1997"/>
2173  </front>
2174  <seriesInfo name="RFC" value="2183"/>
2177<reference anchor="RFC2277">
2178  <front>
2179    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2180    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2181      <organization>UNINETT</organization>
2182      <address><email></email></address>
2183    </author>
2184    <date month="January" year="1998"/>
2185  </front>
2186  <seriesInfo name="BCP" value="18"/>
2187  <seriesInfo name="RFC" value="2277"/>
2190<reference anchor="RFC2388">
2191  <front>
2192    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2193    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2194      <organization>Xerox Palo Alto Research Center</organization>
2195      <address><email></email></address>
2196    </author>
2197    <date year="1998" month="August"/>
2198  </front>
2199  <seriesInfo name="RFC" value="2388"/>
2202<reference anchor="RFC2557">
2203  <front>
2204    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2205    <author initials="F." surname="Palme" fullname="Jacob Palme">
2206      <organization>Stockholm University and KTH</organization>
2207      <address><email></email></address>
2208    </author>
2209    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2210      <organization>Microsoft Corporation</organization>
2211      <address><email></email></address>
2212    </author>
2213    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2214      <organization>Lotus Development Corporation</organization>
2215      <address><email></email></address>
2216    </author>
2217    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2218      <organization/>
2219      <address><email></email></address>
2220    </author>
2221    <date year="1999" month="March"/>
2222  </front>
2223  <seriesInfo name="RFC" value="2557"/>
2226<reference anchor="RFC2616">
2227  <front>
2228    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2229    <author initials="R." surname="Fielding" fullname="R. Fielding">
2230      <organization>University of California, Irvine</organization>
2231      <address><email></email></address>
2232    </author>
2233    <author initials="J." surname="Gettys" fullname="J. Gettys">
2234      <organization>W3C</organization>
2235      <address><email></email></address>
2236    </author>
2237    <author initials="J." surname="Mogul" fullname="J. Mogul">
2238      <organization>Compaq Computer Corporation</organization>
2239      <address><email></email></address>
2240    </author>
2241    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2242      <organization>MIT Laboratory for Computer Science</organization>
2243      <address><email></email></address>
2244    </author>
2245    <author initials="L." surname="Masinter" fullname="L. Masinter">
2246      <organization>Xerox Corporation</organization>
2247      <address><email></email></address>
2248    </author>
2249    <author initials="P." surname="Leach" fullname="P. Leach">
2250      <organization>Microsoft Corporation</organization>
2251      <address><email></email></address>
2252    </author>
2253    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2254      <organization>W3C</organization>
2255      <address><email></email></address>
2256    </author>
2257    <date month="June" year="1999"/>
2258  </front>
2259  <seriesInfo name="RFC" value="2616"/>
2262<reference anchor="RFC3629">
2263  <front>
2264    <title>UTF-8, a transformation format of ISO 10646</title>
2265    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2266      <organization>Alis Technologies</organization>
2267      <address><email></email></address>
2268    </author>
2269    <date month="November" year="2003"/>
2270  </front>
2271  <seriesInfo name="RFC" value="3629"/>
2272  <seriesInfo name="STD" value="63"/>
2275<reference anchor='RFC3864'>
2276  <front>
2277    <title>Registration Procedures for Message Header Fields</title>
2278    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2279      <organization>Nine by Nine</organization>
2280      <address><email></email></address>
2281    </author>
2282    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2283      <organization>BEA Systems</organization>
2284      <address><email></email></address>
2285    </author>
2286    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2287      <organization>HP Labs</organization>
2288      <address><email></email></address>
2289    </author>
2290    <date year='2004' month='September' />
2291  </front>
2292  <seriesInfo name='BCP' value='90' />
2293  <seriesInfo name='RFC' value='3864' />
2296<reference anchor="RFC4288">
2297  <front>
2298    <title>Media Type Specifications and Registration Procedures</title>
2299    <author initials="N." surname="Freed" fullname="N. Freed">
2300      <organization>Sun Microsystems</organization>
2301      <address>
2302        <email></email>
2303      </address>
2304    </author>
2305    <author initials="J." surname="Klensin" fullname="J. Klensin">
2306      <organization/>
2307      <address>
2308        <email></email>
2309      </address>
2310    </author>
2311    <date year="2005" month="December"/>
2312  </front>
2313  <seriesInfo name="BCP" value="13"/>
2314  <seriesInfo name="RFC" value="4288"/>
2317<reference anchor="RFC5322">
2318  <front>
2319    <title>Internet Message Format</title>
2320    <author initials="P." surname="Resnick" fullname="P. Resnick">
2321      <organization>Qualcomm Incorporated</organization>
2322    </author>
2323    <date year="2008" month="October"/>
2324  </front>
2325  <seriesInfo name="RFC" value="5322"/>
2328<reference anchor='BCP97'>
2329  <front>
2330    <title>Handling Normative References to Standards-Track Documents</title>
2331    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2332      <organization />
2333      <address>
2334        <email></email>
2335      </address>
2336    </author>
2337    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2338      <organization>MIT</organization>
2339      <address>
2340        <email></email>
2341      </address>
2342    </author>
2343    <date year='2007' month='June' />
2344  </front>
2345  <seriesInfo name='BCP' value='97' />
2346  <seriesInfo name='RFC' value='4897' />
2352<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2354   HTTP/1.1 uses many of the constructs defined for Internet Mail (<xref target="RFC5322"/>) and the Multipurpose Internet Mail Extensions (MIME <xref target="RFC2045"/>) to
2355   allow entities to be transmitted in an open variety of
2356   representations and with extensible mechanisms. However, RFC 2045
2357   discusses mail, and HTTP has a few features that are different from
2358   those described in RFC 2045. These differences were carefully chosen
2359   to optimize performance over binary connections, to allow greater
2360   freedom in the use of new media types, to make date comparisons
2361   easier, and to acknowledge the practice of some early HTTP servers
2362   and clients.
2365   This appendix describes specific areas where HTTP differs from RFC
2366   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2367   aware of these differences and provide the appropriate conversions
2368   where necessary. Proxies and gateways from MIME environments to HTTP
2369   also need to be aware of the differences because some conversions
2370   might be required.
2373<section title="MIME-Version" anchor="mime-version">
2374  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2375  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
2376  <x:anchor-alias value="MIME-Version"/>
2377  <x:anchor-alias value="MIME-Version-v"/>
2379   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2380   include a single MIME-Version general-header field to indicate what
2381   version of the MIME protocol was used to construct the message. Use
2382   of the MIME-Version header field indicates that the message is in
2383   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
2384   Proxies/gateways are responsible for ensuring full compliance (where
2385   possible) when exporting HTTP messages to strict MIME environments.
2387<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
2388  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
2389  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2392   MIME version "1.0" is the default for use in HTTP/1.1. However,
2393   HTTP/1.1 message parsing and semantics are defined by this document
2394   and not the MIME specification.
2398<section title="Conversion to Canonical Form" anchor="">
2400   <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2401   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
2402   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2403   allowed for subtypes of the "text" media type when transmitted over
2404   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
2405   line breaks as CRLF and forbids the use of CR or LF outside of line
2406   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2407   line break within text content when a message is transmitted over
2408   HTTP.
2411   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2412   environment &SHOULD; translate all line breaks within the text media
2413   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2414   canonical form of CRLF. Note, however, that this might be complicated
2415   by the presence of a Content-Encoding and by the fact that HTTP
2416   allows the use of some character sets which do not use octets 13 and
2417   10 to represent CR and LF, as is the case for some multi-byte
2418   character sets.
2421   Implementors should note that conversion will break any cryptographic
2422   checksums applied to the original content unless the original content
2423   is already in canonical form. Therefore, the canonical form is
2424   recommended for any content that uses such checksums in HTTP.
2429<section title="Conversion of Date Formats" anchor="">
2431   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2432   simplify the process of date comparison. Proxies and gateways from
2433   other protocols &SHOULD; ensure that any Date header field present in a
2434   message conforms to one of the HTTP/1.1 formats and rewrite the date
2435   if necessary.
2439<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2441   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2442   Content-Encoding header field. Since this acts as a modifier on the
2443   media type, proxies and gateways from HTTP to MIME-compliant
2444   protocols &MUST; either change the value of the Content-Type header
2445   field or decode the entity-body before forwarding the message. (Some
2446   experimental applications of Content-Type for Internet mail have used
2447   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2448   a function equivalent to Content-Encoding. However, this parameter is
2449   not part of RFC 2045).
2453<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2455   HTTP does not use the Content-Transfer-Encoding field of RFC
2456   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2457   remove any Content-Transfer-Encoding
2458   prior to delivering the response message to an HTTP client.
2461   Proxies and gateways from HTTP to MIME-compliant protocols are
2462   responsible for ensuring that the message is in the correct format
2463   and encoding for safe transport on that protocol, where "safe
2464   transport" is defined by the limitations of the protocol being used.
2465   Such a proxy or gateway &SHOULD; label the data with an appropriate
2466   Content-Transfer-Encoding if doing so will improve the likelihood of
2467   safe transport over the destination protocol.
2471<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2473   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2474   Proxies/gateways &MUST; remove any transfer-coding prior to
2475   forwarding a message via a MIME-compliant protocol.
2479<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2481   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
2482   need to be aware of MIME line length limitations. Since HTTP does not
2483   have this limitation, HTTP does not fold long lines. MHTML messages
2484   being transported by HTTP follow all conventions of MHTML, including
2485   line length limitations and folding, canonicalization, etc., since
2486   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2487   does not interpret the content or any MIME header lines that might be
2488   contained therein.
2493<section title="Additional Features" anchor="additional.features">
2495   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
2496   existing HTTP implementations, but not consistently and correctly
2497   across most HTTP/1.1 applications. Implementors are advised to be
2498   aware of these features, but cannot rely upon their presence in, or
2499   interoperability with, other HTTP/1.1 applications. Some of these
2500   describe proposed experimental features, and some describe features
2501   that experimental deployment found lacking that are now addressed in
2502   the base HTTP/1.1 specification.
2505   A number of other headers, such as Content-Disposition and Title,
2506   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2509<section title="Content-Disposition" anchor="content-disposition">
2510<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2511<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2512  <x:anchor-alias value="content-disposition"/>
2513  <x:anchor-alias value="content-disposition-v"/>
2514  <x:anchor-alias value="disposition-type"/>
2515  <x:anchor-alias value="disposition-parm"/>
2516  <x:anchor-alias value="disp-extension-parm"/>
2517  <x:anchor-alias value="disp-extension-token"/>
2518  <x:anchor-alias value="filename-parm"/>
2520   The Content-Disposition response-header field has been proposed as a
2521   means for the origin server to suggest a default filename if the user
2522   requests that the content is saved to a file. This usage is derived
2523   from the definition of Content-Disposition in <xref target="RFC2183"/>.
2525<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-disposition"/><iref primary="true" item="Grammar" subitem="content-disposition-v"/><iref primary="true" item="Grammar" subitem="disposition-type"/><iref primary="true" item="Grammar" subitem="disposition-parm"/><iref primary="true" item="Grammar" subitem="filename-parm"/><iref primary="true" item="Grammar" subitem="disp-extension-token"/><iref primary="true" item="Grammar" subitem="disp-extension-parm"/>
2526  <x:ref>content-disposition</x:ref> = "Content-Disposition" ":" <x:ref>OWS</x:ref>
2527                        <x:ref>content-disposition-v</x:ref>
2528  <x:ref>content-disposition-v</x:ref> = <x:ref>disposition-type</x:ref>
2529                          *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>disposition-parm</x:ref> )
2530  <x:ref>disposition-type</x:ref> = "attachment" / <x:ref>disp-extension-token</x:ref>
2531  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> / <x:ref>disp-extension-parm</x:ref>
2532  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2533  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
2534  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
2537   An example is
2539<figure><artwork type="example">
2540   Content-Disposition: attachment; filename="fname.ext"
2543   The receiving user agent &SHOULD-NOT;  respect any directory path
2544   information present in the filename-parm parameter, which is the only
2545   parameter believed to apply to HTTP implementations at this time. The
2546   filename &SHOULD; be treated as a terminal component only.
2549   If this header is used in a response with the application/octet-stream
2550   content-type, the implied suggestion is that the user agent
2551   should not display the response, but directly enter a `save response
2552   as...' dialog.
2555   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2560<section title="Compatibility with Previous Versions" anchor="compatibility">
2561<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2563   Transfer-coding and message lengths all interact in ways that
2564   required fixing exactly when chunked encoding is used (to allow for
2565   transfer encoding that may not be self delimiting); it was important
2566   to straighten out exactly how message lengths are computed.
2567   (<xref target="entity.length"/>, see also <xref target="Part1"/>,
2568   <xref target="Part5"/> and <xref target="Part6"/>).
2571   Charset wildcarding is introduced to avoid explosion of character set
2572   names in accept headers. (<xref target="header.accept-charset"/>)
2575   Content-Base was deleted from the specification: it was not
2576   implemented widely, and there is no simple, safe way to introduce it
2577   without a robust extension mechanism. In addition, it is used in a
2578   similar, but not identical fashion in MHTML <xref target="RFC2557"/>.
2581   A content-coding of "identity" was introduced, to solve problems
2582   discovered in caching. (<xref target="content.codings"/>)
2585   Quality Values of zero should indicate that "I don't want something"
2586   to allow clients to refuse a representation. (<xref target="quality.values"/>)
2589   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
2590   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
2591   specification, but not commonly implemented. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.2"/>.
2595<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2597  Clarify contexts that charset is used in.
2598  (<xref target="character.sets"/>)
2601  Remove reference to non-existant identity transfer-coding value tokens.
2602  (<xref target="no.content-transfer-encoding"/>)
2608<section title="Collected ABNF" anchor="collected.abnf">
2609   <figure>
2610      <artwork type="abnf" name="p3-payload.parsed-abnf">ALPHA = &lt;ALPHA, defined in [Part1], Section 1.2.2&gt;&#xD;
2611Accept = "Accept:" OWS Accept-v&#xD;
2612Accept-Charset = "Accept-Charset:" OWS Accept-Charset-v&#xD;
2613Accept-Charset-v = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="&#xD;
2614 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="&#xD;
2615 qvalue ] ] )&#xD;
2616Accept-Encoding = "Accept-Encoding:" OWS Accept-Encoding-v&#xD;
2617Accept-Encoding-v = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )&#xD;
2618 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]&#xD;
2619Accept-Language = "Accept-Language:" OWS Accept-Language-v&#xD;
2620Accept-Language-v = *( "," OWS ) language-range [ OWS ";" OWS "q="&#xD;
2621 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]&#xD;
2622 ] )&#xD;
2623Accept-v = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [&#xD;
2624 OWS media-range [ accept-params ] ] ) ]&#xD;
2625Content-Encoding = "Content-Encoding:" OWS Content-Encoding-v&#xD;
2626Content-Encoding-v = *( "," OWS ) content-coding *( OWS "," [ OWS&#xD;
2627 content-coding ] )&#xD;
2628Content-Language = "Content-Language:" OWS Content-Language-v&#xD;
2629Content-Language-v = *( "," OWS ) language-tag *( OWS "," [ OWS&#xD;
2630 language-tag ] )&#xD;
2631Content-Length = &lt;Content-Length, defined in [Part1], Section 8.2&gt;&#xD;
2632Content-Location = "Content-Location:" OWS Content-Location-v&#xD;
2633Content-Location-v = absolute-URI / partial-URI&#xD;
2634Content-MD5 = "Content-MD5:" OWS Content-MD5-v&#xD;
2635Content-MD5-v = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;&#xD;
2636Content-Range = &lt;Content-Range, defined in [Part5], Section 6.2&gt;&#xD;
2637Content-Type = "Content-Type:" OWS Content-Type-v&#xD;
2638Content-Type-v = media-type&#xD;
2639DIGIT = &lt;DIGIT, defined in [Part1], Section 1.2.2&gt;&#xD;
2640Expires = &lt;Expires, defined in [Part6], Section 16.3&gt;&#xD;
2641Last-Modified = &lt;Last-Modified, defined in [Part4], Section 7.6&gt;&#xD;
2642MIME-Version = "MIME-Version:" OWS MIME-Version-v&#xD;
2643MIME-Version-v = 1*DIGIT "." 1*DIGIT&#xD;
2644OCTET = &lt;OCTET, defined in [Part1], Section 1.2.2&gt;&#xD;
2645OWS = &lt;OWS, defined in [Part1], Section 1.2.2&gt;&#xD;
2646absolute-URI = &lt;absolute-URI, defined in [Part1], Section 2.1&gt;&#xD;
2647accept-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ]&#xD;
2648accept-params = OWS ";" OWS "q=" qvalue *accept-ext&#xD;
2649attribute = token&#xD;
2650charset = token&#xD;
2651codings = ( content-coding / "*" )&#xD;
2652content-coding = token&#xD;
2653content-disposition = "Content-Disposition:" OWS&#xD;
2654 content-disposition-v&#xD;
2655content-disposition-v = disposition-type *( OWS ";" OWS&#xD;
2656 disposition-parm )&#xD;
2657disp-extension-parm = token "=" ( token / quoted-string )&#xD;
2658disp-extension-token = token&#xD;
2659disposition-parm = filename-parm / disp-extension-parm&#xD;
2660disposition-type = "attachment" / disp-extension-token&#xD;
2661entity-body = *OCTET&#xD;
2662entity-header = Content-Encoding / Content-Language / Content-Length&#xD;
2663 / Content-Location / Content-MD5 / Content-Range / Content-Type /&#xD;
2664 Expires / Last-Modified / extension-header&#xD;
2665extension-header = message-header&#xD;
2666filename-parm = "filename=" quoted-string&#xD;
2667language-range = &lt;language-range, defined in [RFC4647], Section 2.1&gt;&#xD;
2668language-tag = primary-tag *( "-" subtag )&#xD;
2669media-range = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS&#xD;
2670 ";" OWS parameter )&#xD;
2671media-type = type "/" subtype *( OWS ";" OWS parameter )&#xD;
2672message-header = &lt;message-header, defined in [Part1], Section 4.2&gt;&#xD;
2673parameter = attribute "=" value&#xD;
2674partial-URI = &lt;partial-URI, defined in [Part1], Section 2.1&gt;&#xD;
2675primary-tag = 1*8ALPHA&#xD;
2676quoted-string = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;&#xD;
2677qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )&#xD;
2678subtag = 1*8ALPHA&#xD;
2679subtype = token&#xD;
2680token = &lt;token, defined in [Part1], Section 1.2.2&gt;&#xD;
2681type = token&#xD;
2682value = token / quoted-string&#xD;
2683; Accept defined but not used&#xD;
2684; Accept-Charset defined but not used&#xD;
2685; Accept-Encoding defined but not used&#xD;
2686; Accept-Language defined but not used&#xD;
2687; MIME-Version defined but not used&#xD;
2688; content-disposition defined but not used&#xD;
2689; entity-body defined but not used&#xD;
2690; entity-header defined but not used&#xD;
2692   </figure>
2695<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2697<section title="Since RFC2616">
2699  Extracted relevant partitions from <xref target="RFC2616"/>.
2703<section title="Since draft-ietf-httpbis-p3-payload-00">
2705  Closed issues:
2706  <list style="symbols">
2707    <t>
2708      <eref target=""/>:
2709      "Media Type Registrations"
2710      (<eref target=""/>)
2711    </t>
2712    <t>
2713      <eref target=""/>:
2714      "Clarification regarding quoting of charset values"
2715      (<eref target=""/>)
2716    </t>
2717    <t>
2718      <eref target=""/>:
2719      "Remove 'identity' token references"
2720      (<eref target=""/>)
2721    </t>
2722    <t>
2723      <eref target=""/>:
2724      "Accept-Encoding BNF"
2725    </t>
2726    <t>
2727      <eref target=""/>:
2728      "Normative and Informative references"
2729    </t>
2730    <t>
2731      <eref target=""/>:
2732      "RFC1700 references"
2733    </t>
2734    <t>
2735      <eref target=""/>:
2736      "Updating to RFC4288"
2737    </t>
2738    <t>
2739      <eref target=""/>:
2740      "Informative references"
2741    </t>
2742    <t>
2743      <eref target=""/>:
2744      "ISO-8859-1 Reference"
2745    </t>
2746    <t>
2747      <eref target=""/>:
2748      "Encoding References Normative"
2749    </t>
2750    <t>
2751      <eref target=""/>:
2752      "Normative up-to-date references"
2753    </t>
2754  </list>
2758<section title="Since draft-ietf-httpbis-p3-payload-01">
2760  Ongoing work on ABNF conversion (<eref target=""/>):
2761  <list style="symbols">
2762    <t>
2763      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2764    </t>
2765  </list>
2769<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
2771  Closed issues:
2772  <list style="symbols">
2773    <t>
2774      <eref target=""/>:
2775      "Quoting Charsets"
2776    </t>
2777    <t>
2778      <eref target=""/>:
2779      "Classification for Allow header"
2780    </t>
2781    <t>
2782      <eref target=""/>:
2783      "missing default for qvalue in description of Accept-Encoding"
2784    </t>
2785  </list>
2788  Ongoing work on IANA Message Header Registration (<eref target=""/>):
2789  <list style="symbols">
2790    <t>
2791      Reference RFC 3984, and update header registrations for headers defined
2792      in this document.
2793    </t>
2794  </list>
2798<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
2800  Closed issues:
2801  <list style="symbols">
2802    <t>
2803      <eref target=""/>:
2804      "Quoting Charsets"
2805    </t>
2806    <t>
2807      <eref target=""/>:
2808      "language tag matching (Accept-Language) vs RFC4647"
2809    </t>
2810    <t>
2811      <eref target=""/>:
2812      "RFC 1806 has been replaced by RFC2183"
2813    </t>
2814  </list>
2817  Other changes:
2818  <list style="symbols">
2819    <t>
2820      <eref target=""/>:
2821      "Encoding References Normative" -- rephrase the annotation and reference
2822      <xref target="BCP97"/>.
2823    </t>
2824  </list>
2826 </section>
2828<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
2830  Closed issues:
2831  <list style="symbols">
2832    <t>
2833      <eref target=""/>:
2834      "RFC 2822 is updated by RFC 5322"
2835    </t>
2836  </list>
2839  Ongoing work on ABNF conversion (<eref target=""/>):
2840  <list style="symbols">
2841    <t>
2842      Use "/" instead of "|" for alternatives.
2843    </t>
2844    <t>
2845      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2846      whitespace ("OWS") and required whitespace ("RWS").
2847    </t>
2848    <t>
2849      Rewrite ABNFs to spell out whitespace rules, factor out
2850      header value format definitions.
2851    </t>
2852  </list>
2856<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
2858  Closed issues:
2859  <list style="symbols">
2860    <t>
2861      <eref target=""/>:
2862      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2863    </t>
2864  </list>
2867  Ongoing work on ABNF conversion (<eref target=""/>):
2868  <list style="symbols">
2869    <t>
2870      Add appendix containing collected and expanded ABNF.
2871    </t>
2872  </list>
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