source: draft-ietf-httpbis/latest/p3-payload.xml @ 1401

Last change on this file since 1401 was 1401, checked in by julian.reschke@…, 8 years ago

prepare for publication of -16 on Aug 24.

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[29]1<?xml version="1.0" encoding="utf-8"?>
[101]2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
[8]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>">
[29]14  <!ENTITY ID-VERSION "latest">
[1368]15  <!ENTITY ID-MONTH "August">
[1099]16  <!ENTITY ID-YEAR "2011">
[1101]17  <!ENTITY mdash "&#8212;">
[424]18  <!ENTITY notation                 "<xref target='Part1' x:rel='#notation' xmlns:x=''/>">
[205]19  <!ENTITY notation-abnf            "<xref target='Part1' x:rel='#notation.abnf' xmlns:x=''/>">
[1399]20  <!ENTITY acks                     "<xref target='Part1' x:rel='#acks' xmlns:x=''/>">
[205]21  <!ENTITY basic-rules              "<xref target='Part1' x:rel='#basic.rules' xmlns:x=''/>">
[1396]22  <!ENTITY field-rules              "<xref target='Part1' x:rel='#field.rules' xmlns:x=''/>">
[115]23  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x=''/>">
[31]24  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x=''/>">
25  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x=''/>">
26  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x=''/>">
27  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x=''/>">
28  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x=''/>">
29  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x=''/>">
[115]30  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x=''/>">
[31]31  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x=''/>">
32  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='' xmlns:x=''/>">
[580]33  <!ENTITY full-date                "<xref target='Part1' x:rel='' xmlns:x=''/>">
[457]34  <!ENTITY qvalue                   "<xref target='Part1' x:rel='#quality.values' xmlns:x=''/>">
[374]35  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x=''/>">
[823]36  <!ENTITY effective-request-uri    "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x=''/>">
[808]37  <!ENTITY compression-codings      "<xref target='Part1' x:rel='#compression.codings' xmlns:x=''/>">
38  <!ENTITY transfer-codings         "<xref target='Part1' x:rel='#transfer.codings' xmlns:x=''/>">
[673]39  <!ENTITY compress-coding          "<xref target='Part1' x:rel='#compress.coding' xmlns:x=''/>">
40  <!ENTITY deflate-coding           "<xref target='Part1' x:rel='#deflate.coding' xmlns:x=''/>">
41  <!ENTITY gzip-coding              "<xref target='Part1' x:rel='#gzip.coding' xmlns:x=''/>">
[716]42  <!ENTITY response-representation  "<xref target='Part2' x:rel='#identifying.response.associated.with.representation' xmlns:x=''/>">
44<?rfc toc="yes" ?>
[29]45<?rfc symrefs="yes" ?>
46<?rfc sortrefs="yes" ?>
[8]47<?rfc compact="yes"?>
48<?rfc subcompact="no" ?>
49<?rfc linkmailto="no" ?>
50<?rfc editing="no" ?>
[203]51<?rfc comments="yes"?>
52<?rfc inline="yes"?>
[799]53<?rfc rfcedstyle="yes"?>
[8]54<?rfc-ext allow-markup-in-artwork="yes" ?>
55<?rfc-ext include-references-in-index="yes" ?>
[308]56<rfc obsoletes="2616" category="std" x:maturity-level="draft"
[446]57     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
[153]58     xmlns:x=''>
[120]61  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
[29]63  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]64    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[8]65    <address>
66      <postal>
[1106]67        <street>345 Park Ave</street>
68        <city>San Jose</city>
[8]69        <region>CA</region>
[1106]70        <code>95110</code>
[29]71        <country>USA</country>
[8]72      </postal>
[29]73      <email></email>
74      <uri></uri>
[8]75    </address>
76  </author>
[29]78  <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]79    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
[8]80    <address>
81      <postal>
[29]82        <street>21 Oak Knoll Road</street>
83        <city>Carlisle</city>
[8]84        <region>MA</region>
[29]85        <code>01741</code>
86        <country>USA</country>
[8]87      </postal>
[844]88      <email></email>
89      <uri></uri>
[8]90    </address>
91  </author>
93  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
[29]94    <organization abbrev="HP">Hewlett-Packard Company</organization>
[8]95    <address>
96      <postal>
[29]97        <street>HP Labs, Large Scale Systems Group</street>
98        <street>1501 Page Mill Road, MS 1177</street>
[8]99        <city>Palo Alto</city>
100        <region>CA</region>
[29]101        <code>94304</code>
102        <country>USA</country>
[8]103      </postal>
[29]104      <email></email>
[8]105    </address>
106  </author>
108  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
[29]109    <organization abbrev="Microsoft">Microsoft Corporation</organization>
[8]110    <address>
111      <postal>
[29]112        <street>1 Microsoft Way</street>
113        <city>Redmond</city>
114        <region>WA</region>
115        <code>98052</code>
116        <country>USA</country>
[8]117      </postal>
[29]118      <email></email>
[8]119    </address>
120  </author>
122  <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]123    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[8]124    <address>
125      <postal>
[29]126        <street>345 Park Ave</street>
127        <city>San Jose</city>
[8]128        <region>CA</region>
[29]129        <code>95110</code>
130        <country>USA</country>
[8]131      </postal>
[29]132      <email></email>
133      <uri></uri>
[8]134    </address>
135  </author>
137  <author initials="P." surname="Leach" fullname="Paul J. Leach">
138    <organization abbrev="Microsoft">Microsoft Corporation</organization>
139    <address>
140      <postal>
141        <street>1 Microsoft Way</street>
142        <city>Redmond</city>
143        <region>WA</region>
144        <code>98052</code>
145      </postal>
146      <email></email>
147    </address>
148  </author>
150  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
151    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
152    <address>
153      <postal>
[34]154        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
155        <street>The Stata Center, Building 32</street>
156        <street>32 Vassar Street</street>
[8]157        <city>Cambridge</city>
158        <region>MA</region>
159        <code>02139</code>
[29]160        <country>USA</country>
[8]161      </postal>
162      <email></email>
[34]163      <uri></uri>
[8]164    </address>
165  </author>
[95]167  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
[94]168    <organization abbrev="W3C">World Wide Web Consortium</organization>
169    <address>
170      <postal>
171        <street>W3C / ERCIM</street>
172        <street>2004, rte des Lucioles</street>
173        <city>Sophia-Antipolis</city>
174        <region>AM</region>
175        <code>06902</code>
176        <country>France</country>
177      </postal>
178      <email></email>
179      <uri></uri>
180    </address>
181  </author>
[95]183  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
184    <organization abbrev="greenbytes">greenbytes GmbH</organization>
185    <address>
186      <postal>
187        <street>Hafenweg 16</street>
188        <city>Muenster</city><region>NW</region><code>48155</code>
189        <country>Germany</country>
190      </postal>
[609]191      <phone>+49 251 2807760</phone>
192      <facsimile>+49 251 2807761</facsimile>
193      <email></email>
194      <uri></uri>
[95]195    </address>
196  </author>
[31]198  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
[440]199  <workgroup>HTTPbis Working Group</workgroup>
[1373]203   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
204   distributed, collaborative, hypertext information systems. HTTP has been in
205   use by the World Wide Web global information initiative since 1990. This
206   document is Part 3 of the seven-part specification that defines the protocol
207   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
210   Part 3 defines HTTP message content, metadata, and content negotiation.
214<note title="Editorial Note (To be removed by RFC Editor)">
215  <t>
216    Discussion of this draft should take place on the HTTPBIS working group
[1268]217    mailing list (, which is archived at
218    <eref target=""/>.
219  </t>
220  <t>
221    The current issues list is at
222    <eref target=""/> and related
223    documents (including fancy diffs) can be found at
[324]224    <eref target=""/>.
[36]225  </t>
[153]226  <t>
[1401]227    The changes in this draft are summarized in <xref target="changes.since.16"/>.
[153]228  </t>
232<section title="Introduction" anchor="introduction">
[163]234   This document defines HTTP/1.1 message payloads (a.k.a., content), the
[161]235   associated metadata header fields that define how the payload is intended
236   to be interpreted by a recipient, the request header fields that
[908]237   might influence content selection, and the various selection algorithms
[161]238   that are collectively referred to as HTTP content negotiation.
241   This document is currently disorganized in order to minimize the changes
242   between drafts and enable reviewers to see the smaller errata changes.
[980]243   A future draft will reorganize the sections to better reflect the content.
[161]244   In particular, the sections on entities will be renamed payload and moved
245   to the first half of the document, while the sections on content negotiation
246   and associated request header fields will be moved to the second half.  The
247   current mess reflects how widely dispersed these topics and associated
248   requirements had become in <xref target="RFC2616"/>.
[660]251<section title="Terminology" anchor="terminology">
253   This specification uses a number of terms to refer to the roles
254   played by participants in, and objects of, the HTTP communication.
257  <iref item="content negotiation"/>
258  <x:dfn>content negotiation</x:dfn>
259  <list>
260    <t>
261      The mechanism for selecting the appropriate representation when
[856]262      servicing a request. The representation in any response
[660]263      can be negotiated (including error responses).
264    </t>
265  </list>
[96]269<section title="Requirements" anchor="intro.requirements">
271   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
272   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
273   document are to be interpreted as described in <xref target="RFC2119"/>.
276   An implementation is not compliant if it fails to satisfy one or more
[847]277   of the "MUST" or "REQUIRED" level requirements for the protocols it
278   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
279   level and all the "SHOULD" level requirements for its protocols is said
280   to be "unconditionally compliant"; one that satisfies all the "MUST"
281   level requirements but not all the "SHOULD" level requirements for its
282   protocols is said to be "conditionally compliant".
[424]286<section title="Syntax Notation" anchor="notation">
[425]287  <x:anchor-alias value="ALPHA"/>
288  <x:anchor-alias value="CR"/>
289  <x:anchor-alias value="DIGIT"/>
290  <x:anchor-alias value="LF"/>
291  <x:anchor-alias value="OCTET"/>
292  <x:anchor-alias value="VCHAR"/>
293  <x:anchor-alias value="WSP"/>
[543]295  This specification uses the ABNF syntax defined in &notation; (which
296  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
297  <xref target="collected.abnf"/> shows the collected ABNF, with the list
298  rule expanded.
[425]301  The following core rules are included by
302  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
303  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
304  DIGIT (decimal 0-9), DQUOTE (double quote),
305  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
306  OCTET (any 8-bit sequence of data), SP (space),
307  VCHAR (any visible USASCII character),
308  and WSP (whitespace).
311<section title="Core Rules" anchor="core.rules">
[229]312  <x:anchor-alias value="token"/>
[810]313  <x:anchor-alias value="word"/>
[357]314  <x:anchor-alias value="OWS"/>
[1396]316  The core rules below are defined in <xref target="Part1"/>:
318<figure><artwork type="abnf2616">
[357]319  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
[1396]320  <x:ref>token</x:ref>          = &lt;token, defined in &field-rules;&gt;
321  <x:ref>word</x:ref>           = &lt;word, defined in &field-rules;&gt;
325<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
[374]326  <x:anchor-alias value="absolute-URI"/>
[391]327  <x:anchor-alias value="partial-URI"/>
[457]328  <x:anchor-alias value="qvalue"/>
[206]330  The ABNF rules below are defined in other parts:
[207]332<figure><!--Part1--><artwork type="abnf2616">
[374]333  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
[391]334  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
[457]335  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
[8]343<section title="Protocol Parameters" anchor="protocol.parameters">
[1176]345<section title="Character Encodings (charset)" anchor="character.sets">
[1176]347   HTTP uses charset names to indicate the character encoding of a
348   textual representation.
[229]350<t anchor="rule.charset">
351  <x:anchor-alias value="charset"/>
[1176]352   A character encoding is identified by a case-insensitive token. The
[8]353   complete set of tokens is defined by the IANA Character Set registry
[91]354   (<eref target=""/>).
356<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
[229]357  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
360   Although HTTP allows an arbitrary token to be used as a charset
361   value, any token that has a predefined value within the IANA
[1176]362   Character Set registry &MUST; represent the character encoding defined
[8]363   by that registry. Applications &SHOULD; limit their use of character
[1176]364   encodings to those defined within the IANA registry.
[81]367   HTTP uses charset in two contexts: within an Accept-Charset request
[994]368   header field (in which the charset value is an unquoted token) and as the
369   value of a parameter in a Content-Type header field (within a request or
[81]370   response), in which case the parameter value of the charset parameter
[908]371   can be quoted.
[969]374   Implementors need to be aware of IETF character set requirements <xref target="RFC3629"/>
[8]375   <xref target="RFC2277"/>.
379<section title="Content Codings" anchor="content.codings">
[229]380  <x:anchor-alias value="content-coding"/>
382   Content coding values indicate an encoding transformation that has
[866]383   been or can be applied to a representation. Content codings are primarily
384   used to allow a representation to be compressed or otherwise usefully
[8]385   transformed without losing the identity of its underlying media type
[866]386   and without loss of information. Frequently, the representation is stored in
[8]387   coded form, transmitted directly, and only decoded by the recipient.
389<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
[229]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.
[673]401   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
402  <list>
403    <t>
404      See &compress-coding;.
405    </t>
406  </list>
[673]409   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
[8]410  <list>
411    <t>
[673]412      See &deflate-coding;.
[8]413    </t>
414  </list>
[673]417   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
418  <list>
419    <t>
420      See &gzip-coding;.
421    </t>
422  </list>
[673]425   identity<iref item="identity (Coding Format)"/><iref item="Coding Format" subitem="identity"/>
[8]426  <list><t>
427        The default (identity) encoding; the use of no transformation
428        whatsoever. This content-coding is used only in the Accept-Encoding
[994]429        header field, and &SHOULD-NOT;  be used in the Content-Encoding
430        header field.
[8]431  </t></list>
434<section title="Content Coding Registry" anchor="content.coding.registry">
[670]436   The HTTP Content Coding Registry defines the name space for the content
437   coding names.
440   Registrations &MUST; include the following fields:
441   <list style="symbols">
442     <t>Name</t>
443     <t>Description</t>
444     <t>Pointer to specification text</t>
445   </list>
[808]448   Names of content codings &MUST-NOT; overlap with names of transfer codings
449   (&transfer-codings;), unless the encoding transformation is identical (as it
450   is the case for the compression codings defined in
451   &compression-codings;).
[942]454   Values to be added to this name space require a specification
455   (see "Specification Required" in
[670]456   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
[8]457   conform to the purpose of content coding defined in this section.
460   The registry itself is maintained at
461   <eref target=""/>.
[8]467<section title="Media Types" anchor="media.types">
[229]468  <x:anchor-alias value="media-type"/>
469  <x:anchor-alias value="type"/>
470  <x:anchor-alias value="subtype"/>
[152]472   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
[8]473   and Accept (<xref target="header.accept"/>) header fields in order to provide
474   open and extensible data typing and type negotiation.
476<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"/>
[357]477  <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> )
478  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
479  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
[229]481<t anchor="rule.parameter">
482  <x:anchor-alias value="attribute"/>
483  <x:anchor-alias value="parameter"/>
484  <x:anchor-alias value="value"/>
[1153]485   The type/subtype &MAY; be followed by parameters in the form of
486   attribute/value pairs.
[29]488<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"/>
[250]489  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
490  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
[810]491  <x:ref>value</x:ref>          = <x:ref>word</x:ref>
494   The type, subtype, and parameter attribute names are case-insensitive.
[370]495   Parameter values might or might not be case-sensitive, depending on the
496   semantics of the parameter name.  The presence or absence of a parameter might
[8]497   be significant to the processing of a media-type, depending on its
498   definition within the media type registry.
[908]501   A parameter value that matches the <x:ref>token</x:ref> production can be
[297]502   transmitted as either a token or within a quoted-string. The quoted and
503   unquoted values are equivalent.
[8]506   Note that some older HTTP applications do not recognize media type
507   parameters. When sending data to older HTTP applications,
508   implementations &SHOULD; only use media type parameters when they are
509   required by that type/subtype definition.
512   Media-type values are registered with the Internet Assigned Number
[91]513   Authority (IANA). The media type registration process is
[115]514   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
[8]515   discouraged.
518<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
[874]520   Internet media types are registered with a canonical form. A
521   representation transferred via HTTP messages &MUST; be in the
[8]522   appropriate canonical form prior to its transmission except for
523   "text" types, as defined in the next paragraph.
526   When in canonical form, media subtypes of the "text" type use CRLF as
527   the text line break. HTTP relaxes this requirement and allows the
528   transport of text media with plain CR or LF alone representing a line
[874]529   break when it is done consistently for an entire representation. HTTP
530   applications &MUST; accept CRLF, bare CR, and bare LF as indicating
531   a line break in text media received via HTTP. In
532   addition, if the text is in a character encoding that does not
[8]533   use octets 13 and 10 for CR and LF respectively, as is the case for
[874]534   some multi-byte character encodings, HTTP allows the use of whatever octet
535   sequences are defined by that character encoding to represent the
[8]536   equivalent of CR and LF for line breaks. This flexibility regarding
[874]537   line breaks applies only to text media in the payload body; a bare CR
[8]538   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
539   structures (such as header fields and multipart boundaries).
[874]542   If a representation is encoded with a content-coding, the underlying
[8]543   data &MUST; be in a form defined above prior to being encoded.
547<section title="Multipart Types" anchor="multipart.types">
[1101]549   MIME provides for a number of "multipart" types &mdash; encapsulations of
[874]550   one or more representations within a single message-body. All multipart
[97]551   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
552   and &MUST; include a boundary parameter as part of the media type
[8]553   value. The message body is itself a protocol element and &MUST;
554   therefore use only CRLF to represent line breaks between body-parts.
557   In general, HTTP treats a multipart message-body no differently than
[852]558   any other media type: strictly as payload.  HTTP does not use the
559   multipart boundary as an indicator of message-body length.
[97]560   <!-- jre: re-insert removed text pointing to caching? -->
[852]561   In all other respects, an HTTP user agent &SHOULD; follow the same or similar
[8]562   behavior as a MIME user agent would upon receipt of a multipart type.
563   The MIME header fields within each body-part of a multipart message-body
564   do not have any significance to HTTP beyond that defined by
565   their MIME semantics.
568   If an application receives an unrecognized multipart subtype, the
569   application &MUST; treat it as being equivalent to "multipart/mixed".
572  <t>
573    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
574    for carrying form data suitable for processing via the POST
575    request method, as described in <xref target="RFC2388"/>.
576  </t>
581<section title="Language Tags" anchor="language.tags">
[229]582  <x:anchor-alias value="language-tag"/>
[690]584   A language tag, as defined in <xref target="RFC5646"/>, identifies a
[613]585   natural language spoken, written, or otherwise conveyed by human beings for
586   communication of information to other human beings. Computer languages are
587   explicitly excluded. HTTP uses language tags within the Accept-Language and
588   Content-Language fields.
[613]591   In summary, a language tag is composed of one or more parts: A primary
592   language subtag followed by a possibly empty series of subtags:
[613]594<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
[690]595  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
598   White space is not allowed within the tag and all tags are case-insensitive.
[613]599   The name space of language subtags is administered by the IANA (see
600   <eref target=""/>).
603  <preamble>Example tags include:</preamble>
604<artwork type="example">
605  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
[690]609   See <xref target="RFC5646"/> for further information.
[965]614<section title="Payload" anchor="payload">
[965]616   HTTP messages &MAY; transfer a payload if not otherwise restricted by
617   the request method or response status code.  The payload consists of
618   metadata, in the form of header fields, and data, in the form of the
619   sequence of octets in the message-body after any transfer-coding has
620   been decoded.
[965]622<iref item="payload"/>
624   A "<x:dfn>payload</x:dfn>" in HTTP is always a partial or complete
625   representation of some resource.  We use separate terms for payload
626   and representation because some messages contain only the associated
627   representation's header fields (e.g., responses to HEAD) or only some
628   part(s) of the representation (e.g., the 206 status code).
630<section title="Payload Header Fields" anchor="payload.header.fields">
631  <x:anchor-alias value="payload-header"/>
[965]633   HTTP header fields that specifically define the payload, rather than the
634   associated representation, are referred to as "payload header fields".
635   The following payload header fields are defined by HTTP/1.1:
[1138]637<texttable align="left">
638  <ttcol>Header Field Name</ttcol>
639  <ttcol>Defined in...</ttcol>
641  <c>Content-Length</c> <c>&header-content-length;</c>
642  <c>Content-Range</c> <c>&header-content-range;</c>
[874]646<section title="Payload Body" anchor="payload.body">
647  <x:anchor-alias value="payload-body"/>
[874]649   A payload body is only present in a message when a message-body is
650   present, as described in &message-body;. The payload body is obtained
[8]651   from the message-body by decoding any Transfer-Encoding that might
652   have been applied to ensure safe and proper transfer of the message.
[965]657<section title="Representation" anchor="representation">
658<iref item="representation"/>
[965]660   A "<x:dfn>representation</x:dfn>" is information in a format that can be readily
661   communicated from one party to another.  A resource representation
662   is information that reflects the state of that resource, as observed
663   at some point in the past (e.g., in a response to GET) or to be
664   desired at some point in the future (e.g., in a PUT request).
667   Most, but not all, representations transferred via HTTP are intended
668   to be a representation of the target resource (the resource identified
669   by the effective request URI).  The precise semantics of a representation
670   are determined by the type of message (request or response), the request
671   method, the response status code, and the representation metadata.
672   For example, the above semantic is true for the representation in any
673   200 (OK) response to GET and for the representation in any PUT request.
674   A 200 response to PUT, in contrast, contains either a representation
675   that describes the successful action or a representation of the target
676   resource, with the latter indicated by a Content-Location header field
677   with the same value as the effective request URI.  Likewise, response
678   messages with an error status code usually contain a representation that
679   describes the error and what next steps are suggested for resolving it.
682<section title="Representation Header Fields" anchor="representation.header.fields">
683  <x:anchor-alias value="representation-header"/>
685   Representation header fields define metadata about the representation data
686   enclosed in the message-body or, if no message-body is present, about
687   the representation that would have been transferred in a 200 response
688   to a simultaneous GET request with the same effective request URI.
691   The following header fields are defined as representation metadata:
[1138]693<texttable align="left">
694  <ttcol>Header Field Name</ttcol>
695  <ttcol>Defined in...</ttcol>
697  <c>Content-Encoding</c> <c><xref target="header.content-encoding"/></c>
698  <c>Content-Language</c> <c><xref target="header.content-language"/></c>
699  <c>Content-Location</c> <c><xref target="header.content-location"/></c>
700  <c>Content-Type</c> <c><xref target="header.content-type"/></c>
701  <c>Expires</c> <c>&header-expires;</c>
702  <c>Last-Modified</c> <c>&header-last-modified;</c>
706<section title="Representation Data" anchor="">
707  <x:anchor-alias value="representation-data"/>
709   The representation body associated with an HTTP message is
710   either provided as the payload body of the message or
711   referred to by the message semantics and the effective request
712   URI.  The representation data is in a format and encoding defined by
713   the representation metadata header fields.
716   The data type of the representation data
717   is determined via the header fields Content-Type and Content-Encoding.
[8]718   These define a two-layer, ordered encoding model:
720<figure><artwork type="example">
[965]721  representation-data := Content-Encoding( Content-Type( bits ) )
[965]724   Content-Type specifies the media type of the underlying data, which
725   defines both the data format and how that data &SHOULD; be processed
726   by the recipient (within the scope of the request method semantics).
727   Any HTTP/1.1 message containing a payload body &SHOULD; include a
728   Content-Type header field defining the media type of the associated
729   representation unless that metadata is unknown to the sender.
[831]730   If the Content-Type header field is not present, it indicates that
[965]731   the sender does not know the media type of the representation;
732   recipients &MAY; either assume that the media type is
733   "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
[592]734   or examine the content to determine its type.
[965]737   In practice, resource owners do not always properly configure their origin
738   server to provide the correct Content-Type for a given representation,
739   with the result that some clients will examine a response body's content
740   and override the specified type.
[908]741   Clients that do so risk drawing incorrect conclusions, which might expose
[965]742   additional security risks (e.g., "privilege escalation").  Furthermore,
743   it is impossible to determine the sender's intent by examining the data
744   format: many data formats match multiple media types that differ only in
745   processing semantics.  Implementers are encouraged to provide a means of
746   disabling such "content sniffing" when it is used.
[908]749   Content-Encoding is used to indicate any additional content
[8]750   codings applied to the data, usually for the purpose of data
[965]751   compression, that are a property of the representation.  If
752   Content-Encoding is not present, then there is no additional
753   encoding beyond that defined by the Content-Type.
758<section title="Content Negotiation" anchor="content.negotiation">
[745]760   HTTP responses include a representation which contains information for
761   interpretation, whether by a human user or for further processing.
762   Often, the server has different ways of representing the
763   same information; for example, in different formats, languages,
764   or using different character encodings.
[745]767   HTTP clients and their users might have different or variable
768   capabilities, characteristics or preferences which would influence
769   which representation, among those available from the server,
770   would be best for the server to deliver. For this reason, HTTP
[1101]771   provides mechanisms for "content negotiation" &mdash; a process of
[745]772   allowing selection of a representation of a given resource,
773   when more than one is available.
[745]776   This specification defines two patterns of content negotiation;
777   "server-driven", where the server selects the representation based
778   upon the client's stated preferences, and "agent-driven" negotiation,
779   where the server provides a list of representations for the client to
780   choose from, based upon their metadata. In addition,  there are
781   other patterns: some applications use an "active content" pattern,
782   where the server returns active content which runs on the client
783   and, based on client available parameters, selects additional
784   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
785   has also been proposed.
788   These patterns are all widely used, and have trade-offs in applicability
789   and practicality. In particular, when the number of preferences or
790   capabilities to be expressed by a client are large (such as when many
791   different formats are supported by a user-agent), server-driven
[908]792   negotiation becomes unwieldy, and might not be appropriate. Conversely,
[745]793   when the number of representations to choose from is very large,
[908]794   agent-driven negotiation might not be appropriate.
797   Note that in all cases, the supplier of representations has the
798   responsibility for determining which representations might be
799   considered to be the "same information".
802<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
804   If the selection of the best representation for a response is made by
805   an algorithm located at the server, it is called server-driven
806   negotiation. Selection is based on the available representations of
[763]807   the response (the dimensions over which it can vary; e.g., language,
[8]808   content-coding, etc.) and the contents of particular header fields in
809   the request message or on other information pertaining to the request
810   (such as the network address of the client).
813   Server-driven negotiation is advantageous when the algorithm for
814   selecting from among the available representations is difficult to
815   describe to the user agent, or when the server desires to send its
816   "best guess" to the client along with the first response (hoping to
817   avoid the round-trip delay of a subsequent request if the "best
818   guess" is good enough for the user). In order to improve the server's
819   guess, the user agent &MAY; include request header fields (Accept,
820   Accept-Language, Accept-Encoding, etc.) which describe its
821   preferences for such a response.
824   Server-driven negotiation has disadvantages:
825  <list style="numbers">
826    <t>
827         It is impossible for the server to accurately determine what
828         might be "best" for any given user, since that would require
829         complete knowledge of both the capabilities of the user agent
830         and the intended use for the response (e.g., does the user want
831         to view it on screen or print it on paper?).
832    </t>
833    <t>
834         Having the user agent describe its capabilities in every
835         request can be both very inefficient (given that only a small
836         percentage of responses have multiple representations) and a
837         potential violation of the user's privacy.
838    </t>
839    <t>
840         It complicates the implementation of an origin server and the
841         algorithms for generating responses to a request.
842    </t>
843    <t>
[908]844         It might limit a public cache's ability to use the same response
[8]845         for multiple user's requests.
846    </t>
847  </list>
[1335]850   Server-driven negotiation allows the user agent to specify its preferences,
851   but it cannot expect responses to always honour them. For example, the origin
852   server might not implement server-driven negotiation, or it might decide that
853   sending a response that doesn't conform to them is better than sending a 406
854   (Not Acceptable) response.
857   Many of the mechanisms for expressing preferences use quality values to
858   declare relative preference. See &qvalue; for more information.
[1163]861   HTTP/1.1 includes the following header fields for enabling
[8]862   server-driven negotiation through description of user agent
863   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
864   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
[745]865   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
866   However, an origin server is not limited to these dimensions and &MAY; vary
[1163]867   the response based on any aspect of the request, including aspects
868   of the connection (e.g., IP address) or information within extension
869   header fields not defined by this specification.
872  <t>
873    <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
874    because new clients might not be recognized.
875  </t>
[115]878   The Vary header field (&header-vary;) can be used to express the parameters the
[8]879   server uses to select a representation that is subject to server-driven
[29]880   negotiation.
884<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
886   With agent-driven negotiation, selection of the best representation
887   for a response is performed by the user agent after receiving an
888   initial response from the origin server. Selection is based on a list
889   of the available representations of the response included within the
[874]890   header fields or body of the initial response, with each
[8]891   representation identified by its own URI. Selection from among the
[908]892   representations can be performed automatically (if the user agent is
[8]893   capable of doing so) or manually by the user selecting from a
894   generated (possibly hypertext) menu.
897   Agent-driven negotiation is advantageous when the response would vary
898   over commonly-used dimensions (such as type, language, or encoding),
899   when the origin server is unable to determine a user agent's
900   capabilities from examining the request, and generally when public
901   caches are used to distribute server load and reduce network usage.
904   Agent-driven negotiation suffers from the disadvantage of needing a
905   second request to obtain the best alternate representation. This
906   second request is only efficient when caching is used. In addition,
907   this specification does not define any mechanism for supporting
908   automatic selection, though it also does not prevent any such
909   mechanism from being developed as an extension and used within
910   HTTP/1.1.
[745]913   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
[8]914   status codes for enabling agent-driven negotiation when the server is
915   unwilling or unable to provide a varying response using server-driven
916   negotiation.
[8]921<section title="Header Field Definitions" anchor="header.fields">
[117]923   This section defines the syntax and semantics of HTTP/1.1 header fields
924   related to the payload of messages.
[8]927<section title="Accept" anchor="header.accept">
[1120]928  <iref primary="true" item="Accept header field" x:for-anchor=""/>
929  <iref primary="true" item="Header Fields" subitem="Accept" x:for-anchor=""/>
[229]930  <x:anchor-alias value="Accept"/>
[370]931  <x:anchor-alias value="accept-ext"/>
[229]932  <x:anchor-alias value="accept-params"/>
933  <x:anchor-alias value="media-range"/>
[1163]935   The "Accept" header field can be used by user agents to specify
[994]936   response media types that are acceptable. Accept header fields can be used to
[698]937   indicate that the request is specifically limited to a small set of desired
938   types, as in the case of a request for an in-line image.
[1234]940<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-ext"/>
941  <x:ref>Accept</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
[229]943  <x:ref>media-range</x:ref>    = ( "*/*"
[334]944                   / ( <x:ref>type</x:ref> "/" "*" )
945                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
[370]946                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
947  <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> )
[1039]948  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
951   The asterisk "*" character is used to group media types into ranges,
952   with "*/*" indicating all media types and "type/*" indicating all
953   subtypes of that type. The media-range &MAY; include media type
954   parameters that are applicable to that range.
957   Each media-range &MAY; be followed by one or more accept-params,
958   beginning with the "q" parameter for indicating a relative quality
959   factor. The first "q" parameter (if any) separates the media-range
960   parameter(s) from the accept-params. Quality factors allow the user
961   or user agent to indicate the relative degree of preference for that
[457]962   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
[8]963   default value is q=1.
966  <t>
967    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
968    parameters from Accept extension parameters is due to historical
969    practice. Although this prevents any media type parameter named
970    "q" from being used with a media range, such an event is believed
971    to be unlikely given the lack of any "q" parameters in the IANA
972    media type registry and the rare usage of any media type
973    parameters in Accept. Future media types are discouraged from
974    registering any parameter named "q".
975  </t>
978   The example
980<figure><artwork type="example">
[357]981  Accept: audio/*; q=0.2, audio/basic
984   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
[879]985   type if it is the best available after an 80% mark-down in quality".
988   If no Accept header field is present, then it is assumed that the
[1335]989   client accepts all media types. If an Accept header field is present in a
990   request, but the server cannot send a response which is acceptable, then
991   the server can either send a response in another format, or a 406 (Not
992   Acceptable) response.
995   A more elaborate example is
997<figure><artwork type="example">
[357]998  Accept: text/plain; q=0.5, text/html,
999          text/x-dvi; q=0.8, text/x-c
1002   Verbally, this would be interpreted as "text/html and text/x-c are
1003   the preferred media types, but if they do not exist, then send the
[866]1004   text/x-dvi representation, and if that does not exist, send the text/plain
[879]1005   representation".
1008   Media ranges can be overridden by more specific media ranges or
1009   specific media types. If more than one media range applies to a given
1010   type, the most specific reference has precedence. For example,
1012<figure><artwork type="example">
[1244]1013  Accept: text/*, text/plain, text/plain;format=flowed, */*
1016   have the following precedence:
[459]1017   <list style="numbers">
[1244]1018    <t>text/plain;format=flowed</t>
1019    <t>text/plain</t>
[459]1020    <t>text/*</t>
1021    <t>*/*</t>
1022   </list>
1025   The media type quality factor associated with a given type is
1026   determined by finding the media range with the highest precedence
1027   which matches that type. For example,
1029<figure><artwork type="example">
[357]1030  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1031          text/html;level=2;q=0.4, */*;q=0.5
1034   would cause the following values to be associated:
[459]1036<texttable align="left">
1037  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1038  <c>text/html;level=1</c>    <c>1</c>
1039  <c>text/html</c>            <c>0.7</c>
1040  <c>text/plain</c>           <c>0.3</c>
1041  <c>image/jpeg</c>           <c>0.5</c>
1042  <c>text/html;level=2</c>    <c>0.4</c>
1043  <c>text/html;level=3</c>    <c>0.7</c>
1046      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1047      values for certain media ranges. However, unless the user agent is
1048      a closed system which cannot interact with other rendering agents,
1049      this default set ought to be configurable by the user.
1053<section title="Accept-Charset" anchor="header.accept-charset">
[1120]1054  <iref primary="true" item="Accept-Charset header field" x:for-anchor=""/>
1055  <iref primary="true" item="Header Fields" subitem="Accept-Charset" x:for-anchor=""/>
[229]1056  <x:anchor-alias value="Accept-Charset"/>
[1163]1058   The "Accept-Charset" header field can be used by user agents to
[1176]1059   indicate what character encodings are acceptable in a response
1060   payload. This field allows
[8]1061   clients capable of understanding more comprehensive or special-purpose
[1176]1062   character encodings to signal that capability to a server which is capable of
1063   representing documents in those character encodings.
[1234]1065<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/>
1066  <x:ref>Accept-Charset</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
[376]1067                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
[1176]1070   Character encoding values (a.k.a., charsets) are described in
1071   <xref target="character.sets"/>. Each charset &MAY; be given an
1072   associated quality value which represents the user's preference
1073   for that charset. The default value is q=1. An example is
1075<figure><artwork type="example">
[357]1076  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1079   The special value "*", if present in the Accept-Charset field,
[1240]1080   matches every character encoding which is not mentioned elsewhere in the
1081   Accept-Charset field. If no "*" is present in an Accept-Charset field, then
1082   all character encodings not explicitly mentioned get a quality value of 0.
[994]1085   If no Accept-Charset header field is present, the default is that any
[1335]1086   character encoding is acceptable. If an Accept-Charset header field is
1087   present in a request, but the server cannot send a response which is
1088   acceptable, then the server can either use another character encoding, or
1089   send a 406 (Not Acceptable) response.
1093<section title="Accept-Encoding" anchor="header.accept-encoding">
[1120]1094  <iref primary="true" item="Accept-Encoding header field" x:for-anchor=""/>
1095  <iref primary="true" item="Header Fields" subitem="Accept-Encoding" x:for-anchor=""/>
[229]1096  <x:anchor-alias value="Accept-Encoding"/>
1097  <x:anchor-alias value="codings"/>
[1163]1099   The "Accept-Encoding" header field can be used by user agents to
[698]1100   indicate what response content-codings (<xref target="content.codings"/>)
1101   are acceptable in the response.
[1234]1103<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/>
1104  <x:ref>Accept-Encoding</x:ref>  = #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1105  <x:ref>codings</x:ref>          = ( <x:ref>content-coding</x:ref> / "*" )
[248]1108   Each codings value &MAY; be given an associated quality value which
1109   represents the preference for that encoding. The default value is q=1.
[8]1112   Examples of its use are:
1114<figure><artwork type="example">
[357]1115  Accept-Encoding: compress, gzip
1116  Accept-Encoding:
1117  Accept-Encoding: *
1118  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1119  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1122   A server tests whether a content-coding is acceptable, according to
1123   an Accept-Encoding field, using these rules:
1124  <list style="numbers">
1125      <t>If the content-coding is one of the content-codings listed in
1126         the Accept-Encoding field, then it is acceptable, unless it is
[457]1127         accompanied by a qvalue of 0. (As defined in &qvalue;, a
[879]1128         qvalue of 0 means "not acceptable".)</t>
1130      <t>The special "*" symbol in an Accept-Encoding field matches any
1131         available content-coding not explicitly listed in the header
1132         field.</t>
1134      <t>If multiple content-codings are acceptable, then the acceptable
1135         content-coding with the highest non-zero qvalue is preferred.</t>
1137      <t>The "identity" content-coding is always acceptable, unless
1138         specifically refused because the Accept-Encoding field includes
1139         "identity;q=0", or because the field includes "*;q=0" and does
1140         not explicitly include the "identity" content-coding. If the
1141         Accept-Encoding field-value is empty, then only the "identity"
1142         encoding is acceptable.</t>
1143  </list>
[1335]1146   If an Accept-Encoding field is present in a request, but the server cannot
1147   send a response which is acceptable, then the server &SHOULD; send a
1148   response without any encoding (i.e., the "identity" encoding).
1151   If no Accept-Encoding field is present in a request, the server &MAY;
1152   assume that the client will accept any content coding. In this case,
1153   if "identity" is one of the available content-codings, then the
1154   server &SHOULD; use the "identity" content-coding, unless it has
1155   additional information that a different content-coding is meaningful
1156   to the client.
1159  <t>
1160    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1161    and if the "identity" content-coding is unavailable, then
1162    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1163    "gzip" and "compress") are preferred; some older clients
1164    improperly display messages sent with other content-codings.  The
1165    server might also make this decision based on information about
1166    the particular user-agent or client.
1167  </t>
1170  <t>
1171    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1172    associated with content-codings. This means that qvalues will not
1173    work and are not permitted with x-gzip or x-compress.
1174  </t>
1178<section title="Accept-Language" anchor="header.accept-language">
[1120]1179  <iref primary="true" item="Accept-Language header field" x:for-anchor=""/>
1180  <iref primary="true" item="Header Fields" subitem="Accept-Language" x:for-anchor=""/>
[229]1181  <x:anchor-alias value="Accept-Language"/>
1182  <x:anchor-alias value="language-range"/>
[1163]1184   The "Accept-Language" header field can be used by user agents to
[698]1185   indicate the set of natural languages that are preferred in the response.
1186   Language tags are defined in <xref target="language.tags"/>.
[1234]1188<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/>
1189  <x:ref>Accept-Language</x:ref> =
[370]1190                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
[1234]1191  <x:ref>language-range</x:ref>  =
[303]1192            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
[303]1195   Each language-range can be given an associated quality value which
[8]1196   represents an estimate of the user's preference for the languages
1197   specified by that range. The quality value defaults to "q=1". For
1198   example,
1200<figure><artwork type="example">
[357]1201  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1204   would mean: "I prefer Danish, but will accept British English and
[879]1205   other types of English".
[724]1206   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
[724]1209   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
1210   several matching schemes. Implementations can offer the most appropriate
1211   matching scheme for their requirements.
1214  <t>
[756]1215    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
[724]1216    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
1217    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
[563]1218  </t>
1221   It might be contrary to the privacy expectations of the user to send
[994]1222   an Accept-Language header field with the complete linguistic preferences of
[8]1223   the user in every request. For a discussion of this issue, see
[994]1224   <xref target=""/>.
1227   As intelligibility is highly dependent on the individual user, it is
1228   recommended that client applications make the choice of linguistic
1229   preference available to the user. If the choice is not made
1230   available, then the Accept-Language header field &MUST-NOT; be given in
1231   the request.
1234  <t>
1235    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1236    the user, we remind implementors of  the fact that users are not
1237    familiar with the details of language matching as described above,
[969]1238    and ought to be provided appropriate guidance. As an example, users
[563]1239    might assume that on selecting "en-gb", they will be served any
1240    kind of English document if British English is not available. A
1241    user agent might suggest in such a case to add "en" to get the
1242    best matching behavior.
1243  </t>
1247<section title="Content-Encoding" anchor="header.content-encoding">
[1120]1248  <iref primary="true" item="Content-Encoding header field" x:for-anchor=""/>
1249  <iref primary="true" item="Header Fields" subitem="Content-Encoding" x:for-anchor=""/>
[229]1250  <x:anchor-alias value="Content-Encoding"/>
[965]1252   The "Content-Encoding" header field indicates what content-codings
[866]1253   have been applied to the representation, and thus what decoding mechanisms
[698]1254   must be applied in order to obtain the media-type referenced by the
1255   Content-Type header field. Content-Encoding is primarily used to allow a
[866]1256   representation to be compressed without losing the identity of its underlying
[698]1257   media type.
[1234]1259<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/>
1260  <x:ref>Content-Encoding</x:ref> = 1#<x:ref>content-coding</x:ref>
1263   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1265<figure><artwork type="example">
[357]1266  Content-Encoding: gzip
[866]1269   The content-coding is a characteristic of the representation.
1270   Typically, the representation body is stored with this
[8]1271   encoding and is only decoded before rendering or analogous usage.
[1107]1272   However, a transforming proxy &MAY; modify the content-coding if the
[8]1273   new coding is known to be acceptable to the recipient, unless the
1274   "no-transform" cache-control directive is present in the message.
[866]1277   If the content-coding of a representation is not "identity", then the
1278   representation metadata &MUST; include a Content-Encoding header
1279   field (<xref target="header.content-encoding"/>)
[8]1280   that lists the non-identity content-coding(s) used.
[874]1283   If the content-coding of a representation in a request message is not
[8]1284   acceptable to the origin server, the server &SHOULD; respond with a
1285   status code of 415 (Unsupported Media Type).
[866]1288   If multiple encodings have been applied to a representation, the content
[8]1289   codings &MUST; be listed in the order in which they were applied.
1290   Additional information about the encoding parameters &MAY; be provided
[866]1291   by other header fields not defined by this specification.
1295<section title="Content-Language" anchor="header.content-language">
[1120]1296  <iref primary="true" item="Content-Language header field" x:for-anchor=""/>
1297  <iref primary="true" item="Header Fields" subitem="Content-Language" x:for-anchor=""/>
[229]1298  <x:anchor-alias value="Content-Language"/>
[965]1300   The "Content-Language" header field describes the natural
[866]1301   language(s) of the intended audience for the representation. Note that this might
[874]1302   not be equivalent to all the languages used within the representation.
[1234]1304<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/>
1305  <x:ref>Content-Language</x:ref> = 1#<x:ref>language-tag</x:ref>
1308   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1309   Content-Language is to allow a user to identify and differentiate
[866]1310   representations according to the user's own preferred language. Thus, if the
[8]1311   body content is intended only for a Danish-literate audience, the
1312   appropriate field is
1314<figure><artwork type="example">
[357]1315  Content-Language: da
1318   If no Content-Language is specified, the default is that the content
1319   is intended for all language audiences. This might mean that the
1320   sender does not consider it to be specific to any natural language,
1321   or that the sender does not know for which language it is intended.
1324   Multiple languages &MAY; be listed for content that is intended for
1325   multiple audiences. For example, a rendition of the "Treaty of
[879]1326   Waitangi", presented simultaneously in the original Maori and English
[8]1327   versions, would call for
1329<figure><artwork type="example">
[357]1330  Content-Language: mi, en
[866]1333   However, just because multiple languages are present within a representation
[8]1334   does not mean that it is intended for multiple linguistic audiences.
1335   An example would be a beginner's language primer, such as "A First
[879]1336   Lesson in Latin", which is clearly intended to be used by an
[8]1337   English-literate audience. In this case, the Content-Language would
1338   properly only include "en".
[1101]1341   Content-Language &MAY; be applied to any media type &mdash; it is not
[8]1342   limited to textual documents.
1346<section title="Content-Location" anchor="header.content-location">
[1120]1347  <iref primary="true" item="Content-Location header field" x:for-anchor=""/>
1348  <iref primary="true" item="Header Fields" subitem="Content-Location" x:for-anchor=""/>
[229]1349  <x:anchor-alias value="Content-Location"/>
[856]1351   The "Content-Location" header field supplies a URI that can be used
1352   as a specific identifier for the representation in this message.
1353   In other words, if one were to perform a GET on this URI at the time
1354   of this message's generation, then a 200 response would contain the
1355   same representation that is enclosed as payload in this message.
[1234]1357<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/>
1358  <x:ref>Content-Location</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
[972]1361   The Content-Location value is not a replacement for the effective
[856]1362   Request URI (&effective-request-uri;).  It is representation metadata.
1363   It has the same syntax and semantics as the header field of the same name
[858]1364   defined for MIME body parts in <xref target="RFC2557" x:fmt="of" x:sec="4"/>.
[856]1365   However, its appearance in an HTTP message has some special implications
1366   for HTTP recipients.
[856]1369   If Content-Location is included in a response message and its value
[965]1370   is the same as the effective request URI, then the response payload
[856]1371   &SHOULD; be considered the current representation of that resource.
1372   For a GET or HEAD request, this is the same as the default semantics
1373   when no Content-Location is provided by the server.  For a state-changing
[1161]1374   request like PUT or POST, it implies that the server's response contains
[856]1375   the new representation of that resource, thereby distinguishing it from
1376   representations that might only report about the action (e.g., "It worked!").
1377   This allows authoring applications to update their local copies without
1378   the need for a subsequent GET request.
[856]1381   If Content-Location is included in a response message and its value
[965]1382   differs from the effective request URI, then the origin server is
[856]1383   informing recipients that this representation has its own, presumably
1384   more specific, identifier.  For a GET or HEAD request, this is an
[965]1385   indication that the effective request URI identifies a resource that
[856]1386   is subject to content negotiation and the representation selected for
1387   this response can also be found at the identified URI.  For other
1388   methods, such a Content-Location indicates that this representation
1389   contains a report on the action's status and the same report is
1390   available (for future access with GET) at the given URI.  For
[1161]1391   example, a purchase transaction made via a POST request might
[856]1392   include a receipt document as the payload of the 200 response;
1393   the Content-Location value provides an identifier for retrieving
1394   a copy of that same receipt in the future.
1397   If Content-Location is included in a request message, then it &MAY;
1398   be interpreted by the origin server as an indication of where the
1399   user agent originally obtained the content of the enclosed
1400   representation (prior to any subsequent modification of the content
1401   by that user agent).  In other words, the user agent is providing
1402   the same representation metadata that it received with the original
1403   representation.  However, such interpretation &MUST-NOT; be used to
1404   alter the semantics of the method requested by the client.  For
1405   example, if a client makes a PUT request on a negotiated resource
1406   and the origin server accepts that PUT (without redirection), then the
1407   new set of values for that resource is expected to be consistent with
1408   the one representation supplied in that PUT; the Content-Location
1409   cannot be used as a form of reverse content selection that
1410   identifies only one of the negotiated representations to be updated.
1411   If the user agent had wanted the latter semantics, it would have applied
1412   the PUT directly to the Content-Location URI.
1415   A Content-Location field received in a request message is transitory
1416   information that &SHOULD-NOT; be saved with other representation
1417   metadata for use in later responses.  The Content-Location's value
1418   might be saved for use in other contexts, such as within source links
1419   or other metadata.
1422   A cache cannot assume that a representation with a Content-Location
[8]1423   different from the URI used to retrieve it can be used to respond to
[856]1424   later requests on that Content-Location URI.
[965]1427   If the Content-Location value is a partial URI, the partial URI is
1428   interpreted relative to the effective request URI.
1432<section title="Content-Type" anchor="header.content-type">
[1120]1433  <iref primary="true" item="Content-Type header field" x:for-anchor=""/>
1434  <iref primary="true" item="Header Fields" subitem="Content-Type" x:for-anchor=""/>
[229]1435  <x:anchor-alias value="Content-Type"/>
[965]1437   The "Content-Type" header field indicates the media type of the
[874]1438   representation. In the case of responses to the HEAD method, the media type is
[698]1439   that which would have been sent had the request been a GET.
[1234]1441<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/>
1442  <x:ref>Content-Type</x:ref> = <x:ref>media-type</x:ref>
1445   Media types are defined in <xref target="media.types"/>. An example of the field is
1447<figure><artwork type="example">
[357]1448  Content-Type: text/html; charset=ISO-8859-4
[965]1451   Further discussion of Content-Type is provided in <xref target=""/>.
[29]1457<section title="IANA Considerations" anchor="IANA.considerations">
[921]1458<section title="Header Field Registration" anchor="header.field.registration">
[969]1460   The Message Header Field Registry located at <eref target=""/> shall be updated
[290]1461   with the permanent registrations below (see <xref target="RFC3864"/>):
[680]1463<?BEGININC p3-payload.iana-headers ?>
[253]1464<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
[290]1465<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
[253]1466   <ttcol>Header Field Name</ttcol>
1467   <ttcol>Protocol</ttcol>
1468   <ttcol>Status</ttcol>
1469   <ttcol>Reference</ttcol>
1471   <c>Accept</c>
1472   <c>http</c>
1473   <c>standard</c>
1474   <c>
1475      <xref target="header.accept"/>
1476   </c>
1477   <c>Accept-Charset</c>
1478   <c>http</c>
1479   <c>standard</c>
1480   <c>
1481      <xref target="header.accept-charset"/>
1482   </c>
1483   <c>Accept-Encoding</c>
1484   <c>http</c>
1485   <c>standard</c>
1486   <c>
1487      <xref target="header.accept-encoding"/>
1488   </c>
1489   <c>Accept-Language</c>
1490   <c>http</c>
1491   <c>standard</c>
1492   <c>
1493      <xref target="header.accept-language"/>
1494   </c>
1495   <c>Content-Encoding</c>
1496   <c>http</c>
1497   <c>standard</c>
1498   <c>
1499      <xref target="header.content-encoding"/>
1500   </c>
1501   <c>Content-Language</c>
1502   <c>http</c>
1503   <c>standard</c>
1504   <c>
1505      <xref target="header.content-language"/>
1506   </c>
1507   <c>Content-Location</c>
1508   <c>http</c>
1509   <c>standard</c>
1510   <c>
1511      <xref target="header.content-location"/>
1512   </c>
1513   <c>Content-Type</c>
1514   <c>http</c>
1515   <c>standard</c>
1516   <c>
1517      <xref target="header.content-type"/>
1518   </c>
[291]1519   <c>MIME-Version</c>
1520   <c>http</c>
[937]1521   <c>standard</c>
[291]1522   <c>
1523      <xref target="mime-version"/>
1524   </c>
[680]1527<?ENDINC p3-payload.iana-headers ?>
[290]1529   The change controller is: "IETF ( - Internet Engineering Task Force".
[668]1533<section title="Content Coding Registry" anchor="content.coding.registration">
1535   The registration procedure for HTTP Content Codings is now defined
[670]1536   by <xref target="content.coding.registry"/> of this document.
1539   The HTTP Content Codings Registry located at <eref target=""/>
[969]1540   shall be updated with the registration below:
1542<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
[670]1543   <ttcol>Name</ttcol>
[668]1544   <ttcol>Description</ttcol>
1545   <ttcol>Reference</ttcol>
1546   <c>compress</c>
1547   <c>UNIX "compress" program method</c>
1548   <c>
[673]1549      &compress-coding;
[668]1550   </c>
1551   <c>deflate</c>
[806]1552   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1553   the "zlib" data format (<xref target="RFC1950"/>)
1554   </c>
[668]1555   <c>
[673]1556      &deflate-coding;
[668]1557   </c>
1558   <c>gzip</c>
1559   <c>Same as GNU zip <xref target="RFC1952"/></c>
1560   <c>
[673]1561      &gzip-coding;
[668]1562   </c>
1563   <c>identity</c>
1564   <c>No transformation</c>
1565   <c>
1566      <xref target="content.codings"/>
1567   </c>
[8]1573<section title="Security Considerations" anchor="security.considerations">
1575   This section is meant to inform application developers, information
1576   providers, and users of the security limitations in HTTP/1.1 as
1577   described by this document. The discussion does not include
1578   definitive solutions to the problems revealed, though it does make
1579   some suggestions for reducing security risks.
[994]1582<section title="Privacy Issues Connected to Accept Header Fields" anchor="">
[1163]1584   Accept headers fields can reveal information about the user to all
[994]1585   servers which are accessed. The Accept-Language header field in particular
[8]1586   can reveal information the user would consider to be of a private
1587   nature, because the understanding of particular languages is often
1588   strongly correlated to the membership of a particular ethnic group.
1589   User agents which offer the option to configure the contents of an
[994]1590   Accept-Language header field to be sent in every request are strongly
[8]1591   encouraged to let the configuration process include a message which
1592   makes the user aware of the loss of privacy involved.
1595   An approach that limits the loss of privacy would be for a user agent
[994]1596   to omit the sending of Accept-Language header fields by default, and to ask
1597   the user whether or not to start sending Accept-Language header fields to a
[1163]1598   server if it detects, by looking for any Vary header fields
[8]1599   generated by the server, that such sending could improve the quality
1600   of service.
1603   Elaborate user-customized accept header fields sent in every request,
1604   in particular if these include quality values, can be used by servers
1605   as relatively reliable and long-lived user identifiers. Such user
1606   identifiers would allow content providers to do click-trail tracking,
1607   and would allow collaborating content providers to match cross-server
1608   click-trails or form submissions of individual users. Note that for
1609   many users not behind a proxy, the network address of the host
1610   running the user agent will also serve as a long-lived user
1611   identifier. In environments where proxies are used to enhance
1612   privacy, user agents ought to be conservative in offering accept
1613   header configuration options to end users. As an extreme privacy
[994]1614   measure, proxies could filter the accept header fields in relayed requests.
[8]1615   General purpose user agents which provide a high degree of header
1616   configurability &SHOULD; warn users about the loss of privacy which can
1617   be involved.
[1364]1623<section title="Acknowledgments" anchor="acks">
1625  See &acks;.
[119]1631<references title="Normative References">
[31]1633<reference anchor="Part1">
[119]1634  <front>
1635    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1636    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]1637      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1638      <address><email></email></address>
1639    </author>
1640    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1641      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1642      <address><email></email></address>
[119]1643    </author>
1644    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1645      <organization abbrev="HP">Hewlett-Packard Company</organization>
1646      <address><email></email></address>
1647    </author>
1648    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1649      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1650      <address><email></email></address>
1651    </author>
1652    <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]1653      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1654      <address><email></email></address>
1655    </author>
1656    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1657      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1658      <address><email></email></address>
1659    </author>
1660    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1661      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1662      <address><email></email></address>
1663    </author>
1664    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1665      <organization abbrev="W3C">World Wide Web Consortium</organization>
1666      <address><email></email></address>
1667    </author>
1668    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1669      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1670      <address><email></email></address>
1671    </author>
1672    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1673  </front>
1674  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1675  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1678<reference anchor="Part2">
[119]1679  <front>
1680    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1681    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]1682      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1683      <address><email></email></address>
1684    </author>
1685    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1686      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1687      <address><email></email></address>
[119]1688    </author>
1689    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1690      <organization abbrev="HP">Hewlett-Packard Company</organization>
1691      <address><email></email></address>
1692    </author>
1693    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1694      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1695      <address><email></email></address>
1696    </author>
1697    <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]1698      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1699      <address><email></email></address>
1700    </author>
1701    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1702      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1703      <address><email></email></address>
1704    </author>
1705    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1706      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1707      <address><email></email></address>
1708    </author>
1709    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1710      <organization abbrev="W3C">World Wide Web Consortium</organization>
1711      <address><email></email></address>
1712    </author>
1713    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1714      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1715      <address><email></email></address>
1716    </author>
1717    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1718  </front>
1719  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1720  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1723<reference anchor="Part4">
[119]1724  <front>
1725    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1726    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]1727      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1728      <address><email></email></address>
1729    </author>
1730    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1731      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1732      <address><email></email></address>
[119]1733    </author>
1734    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1735      <organization abbrev="HP">Hewlett-Packard Company</organization>
1736      <address><email></email></address>
1737    </author>
1738    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1739      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1740      <address><email></email></address>
1741    </author>
1742    <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]1743      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1744      <address><email></email></address>
1745    </author>
1746    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1747      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1748      <address><email></email></address>
1749    </author>
1750    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1751      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1752      <address><email></email></address>
1753    </author>
1754    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1755      <organization abbrev="W3C">World Wide Web Consortium</organization>
1756      <address><email></email></address>
1757    </author>
1758    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1759      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1760      <address><email></email></address>
1761    </author>
1762    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1763  </front>
1764  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1765  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1768<reference anchor="Part5">
[119]1769  <front>
1770    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1771    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]1772      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1773      <address><email></email></address>
1774    </author>
1775    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1776      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1777      <address><email></email></address>
[119]1778    </author>
1779    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1780      <organization abbrev="HP">Hewlett-Packard Company</organization>
1781      <address><email></email></address>
1782    </author>
1783    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1784      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1785      <address><email></email></address>
1786    </author>
1787    <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]1788      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1789      <address><email></email></address>
1790    </author>
1791    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1792      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1793      <address><email></email></address>
1794    </author>
1795    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1796      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1797      <address><email></email></address>
1798    </author>
1799    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1800      <organization abbrev="W3C">World Wide Web Consortium</organization>
1801      <address><email></email></address>
1802    </author>
1803    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1804      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1805      <address><email></email></address>
1806    </author>
1807    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1808  </front>
1809  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1810  <x:source href="p5-range.xml" basename="p5-range"/>
1813<reference anchor="Part6">
[119]1814  <front>
1815    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1816    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]1817      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1818      <address><email></email></address>
1819    </author>
1820    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1821      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1822      <address><email></email></address>
[119]1823    </author>
1824    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1825      <organization abbrev="HP">Hewlett-Packard Company</organization>
1826      <address><email></email></address>
1827    </author>
1828    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1829      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1830      <address><email></email></address>
1831    </author>
1832    <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]1833      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1834      <address><email></email></address>
1835    </author>
1836    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1837      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1838      <address><email></email></address>
1839    </author>
1840    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1841      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1842      <address><email></email></address>
1843    </author>
1844    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1845      <organization abbrev="W3C">World Wide Web Consortium</organization>
1846      <address><email></email></address>
1847    </author>
[601]1848    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1849      <address><email></email></address>
1850    </author>
[119]1851    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1852      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1853      <address><email></email></address>
1854    </author>
1855    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1856  </front>
1857  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1858  <x:source href="p6-cache.xml" basename="p6-cache"/>
[122]1861<reference anchor="RFC1950">
1862  <front>
1863    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1864    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1865      <organization>Aladdin Enterprises</organization>
1866      <address><email></email></address>
1867    </author>
[713]1868    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
[122]1869    <date month="May" year="1996"/>
1870  </front>
1871  <seriesInfo name="RFC" value="1950"/>
1872  <annotation>
[908]1873    RFC 1950 is an Informational RFC, thus it might be less stable than
[122]1874    this specification. On the other hand, this downward reference was
[277]1875    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1876    therefore it is unlikely to cause problems in practice. See also
1877    <xref target="BCP97"/>.
[122]1878  </annotation>
[806]1881<reference anchor="RFC1951">
1882  <front>
1883    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1884    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1885      <organization>Aladdin Enterprises</organization>
1886      <address><email></email></address>
1887    </author>
1888    <date month="May" year="1996"/>
1889  </front>
1890  <seriesInfo name="RFC" value="1951"/>
1891  <annotation>
[908]1892    RFC 1951 is an Informational RFC, thus it might be less stable than
[806]1893    this specification. On the other hand, this downward reference was
1894    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1895    therefore it is unlikely to cause problems in practice. See also
1896    <xref target="BCP97"/>.
1897  </annotation>
[122]1900<reference anchor="RFC1952">
1901  <front>
1902    <title>GZIP file format specification version 4.3</title>
1903    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1904      <organization>Aladdin Enterprises</organization>
1905      <address><email></email></address>
1906    </author>
1907    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1908      <address><email></email></address>
1909    </author>
1910    <author initials="M." surname="Adler" fullname="Mark Adler">
1911      <address><email></email></address>
1912    </author>
1913    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1914      <address><email></email></address>
1915    </author>
1916    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
1917      <address><email></email></address>
1918    </author>
1919    <date month="May" year="1996"/>
1920  </front>
1921  <seriesInfo name="RFC" value="1952"/>
1922  <annotation>
[908]1923    RFC 1952 is an Informational RFC, thus it might be less stable than
[122]1924    this specification. On the other hand, this downward reference was
[277]1925    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1926    therefore it is unlikely to cause problems in practice. See also
1927    <xref target="BCP97"/>.
[122]1928  </annotation>
[131]1931<reference anchor="RFC2045">
1932  <front>
1933    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
1934    <author initials="N." surname="Freed" fullname="Ned Freed">
1935      <organization>Innosoft International, Inc.</organization>
1936      <address><email></email></address>
1937    </author>
1938    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1939      <organization>First Virtual Holdings</organization>
1940      <address><email></email></address>
1941    </author>
1942    <date month="November" year="1996"/>
1943  </front>
1944  <seriesInfo name="RFC" value="2045"/>
1947<reference anchor="RFC2046">
1948  <front>
1949    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
1950    <author initials="N." surname="Freed" fullname="Ned Freed">
1951      <organization>Innosoft International, Inc.</organization>
1952      <address><email></email></address>
1953    </author>
1954    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1955      <organization>First Virtual Holdings</organization>
1956      <address><email></email></address>
1957    </author>
1958    <date month="November" year="1996"/>
1959  </front>
1960  <seriesInfo name="RFC" value="2046"/>
[119]1963<reference anchor="RFC2119">
1964  <front>
1965    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
1966    <author initials="S." surname="Bradner" fullname="Scott Bradner">
1967      <organization>Harvard University</organization>
1968      <address><email></email></address>
1969    </author>
1970    <date month="March" year="1997"/>
1971  </front>
1972  <seriesInfo name="BCP" value="14"/>
1973  <seriesInfo name="RFC" value="2119"/>
[303]1976<reference anchor='RFC4647'>
1977  <front>
1978    <title>Matching of Language Tags</title>
1979    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
1980      <organization>Yahoo! Inc.</organization>
1981      <address><email></email></address>
1982    </author>
1983    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
1984      <organization>Google</organization>
1985      <address><email></email></address>
1986    </author>
1987    <date year='2006' month='September' />
1988  </front>
1989  <seriesInfo name='BCP' value='47' />
1990  <seriesInfo name='RFC' value='4647' />
[425]1993<reference anchor="RFC5234">
1994  <front>
1995    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
1996    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
1997      <organization>Brandenburg InternetWorking</organization>
1998      <address>
[728]1999        <email></email>
2000      </address> 
[425]2001    </author>
2002    <author initials="P." surname="Overell" fullname="Paul Overell">
2003      <organization>THUS plc.</organization>
2004      <address>
[728]2005        <email></email>
2006      </address>
[425]2007    </author>
2008    <date month="January" year="2008"/>
2009  </front>
2010  <seriesInfo name="STD" value="68"/>
2011  <seriesInfo name="RFC" value="5234"/>
[690]2014<reference anchor='RFC5646'>
[613]2015  <front>
2016    <title>Tags for Identifying Languages</title>
2017    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
2018      <organization>Lab126</organization>
2019      <address><email></email></address>
2020    </author>
2021    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
2022      <organization>Google</organization>
2023      <address><email></email></address>
2024    </author>
[690]2025    <date month='September' year='2009' />
[613]2026  </front>
[690]2027  <seriesInfo name='BCP' value='47' />
2028  <seriesInfo name='RFC' value='5646' />
2033<references title="Informative References">
[129]2035<reference anchor="RFC1945">
2036  <front>
2037    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2038    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2039      <organization>MIT, Laboratory for Computer Science</organization>
2040      <address><email></email></address>
2041    </author>
2042    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2043      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2044      <address><email></email></address>
2045    </author>
2046    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2047      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2048      <address><email></email></address>
2049    </author>
2050    <date month="May" year="1996"/>
2051  </front>
2052  <seriesInfo name="RFC" value="1945"/>
2055<reference anchor="RFC2049">
2056  <front>
2057    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2058    <author initials="N." surname="Freed" fullname="Ned Freed">
2059      <organization>Innosoft International, Inc.</organization>
2060      <address><email></email></address>
2061    </author>
2062    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2063      <organization>First Virtual Holdings</organization>
2064      <address><email></email></address>
2065    </author>
2066    <date month="November" year="1996"/>
2067  </front>
2068  <seriesInfo name="RFC" value="2049"/>
[133]2071<reference anchor="RFC2068">
2072  <front>
2073    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2074    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2075      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2076      <address><email></email></address>
2077    </author>
2078    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2079      <organization>MIT Laboratory for Computer Science</organization>
2080      <address><email></email></address>
2081    </author>
2082    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2083      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2084      <address><email></email></address>
2085    </author>
2086    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2087      <organization>MIT Laboratory for Computer Science</organization>
2088      <address><email></email></address>
2089    </author>
2090    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2091      <organization>MIT Laboratory for Computer Science</organization>
2092      <address><email></email></address>
2093    </author>
2094    <date month="January" year="1997"/>
2095  </front>
2096  <seriesInfo name="RFC" value="2068"/>
[129]2099<reference anchor="RFC2076">
2100  <front>
2101    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2102    <author initials="J." surname="Palme" fullname="Jacob Palme">
2103      <organization>Stockholm University/KTH</organization>
2104      <address><email></email></address>
2105    </author>
2106    <date month="February" year="1997"/>
2107  </front>
2108  <seriesInfo name="RFC" value="2076"/>
2111<reference anchor="RFC2277">
2112  <front>
2113    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2114    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2115      <organization>UNINETT</organization>
2116      <address><email></email></address>
2117    </author>
2118    <date month="January" year="1998"/>
2119  </front>
2120  <seriesInfo name="BCP" value="18"/>
2121  <seriesInfo name="RFC" value="2277"/>
[745]2124<reference anchor='RFC2295'>
2125  <front>
2126    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
2127    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
2128      <organization>Technische Universiteit Eindhoven</organization>
2129      <address>
2130        <email></email>
2131      </address>
2132    </author>
2133    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
2134      <organization>Hewlett-Packard Company</organization>
2135      <address>
2136        <email></email>
2137      </address>
2138    </author>
2139    <date year='1998' month='March'/>
2140  </front>
2141  <seriesInfo name='RFC' value='2295'/>
[129]2144<reference anchor="RFC2388">
2145  <front>
2146    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2147    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2148      <organization>Xerox Palo Alto Research Center</organization>
2149      <address><email></email></address>
2150    </author>
2151    <date year="1998" month="August"/>
2152  </front>
2153  <seriesInfo name="RFC" value="2388"/>
2156<reference anchor="RFC2557">
2157  <front>
2158    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2159    <author initials="F." surname="Palme" fullname="Jacob Palme">
2160      <organization>Stockholm University and KTH</organization>
2161      <address><email></email></address>
2162    </author>
2163    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2164      <organization>Microsoft Corporation</organization>
2165      <address><email></email></address>
2166    </author>
2167    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2168      <organization>Lotus Development Corporation</organization>
2169      <address><email></email></address>
2170    </author>
2171    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2172      <address><email></email></address>
2173    </author>
2174    <date year="1999" month="March"/>
2175  </front>
2176  <seriesInfo name="RFC" value="2557"/>
[119]2179<reference anchor="RFC2616">
2180  <front>
2181    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2182    <author initials="R." surname="Fielding" fullname="R. Fielding">
2183      <organization>University of California, Irvine</organization>
2184      <address><email></email></address>
2185    </author>
2186    <author initials="J." surname="Gettys" fullname="J. Gettys">
2187      <organization>W3C</organization>
2188      <address><email></email></address>
2189    </author>
2190    <author initials="J." surname="Mogul" fullname="J. Mogul">
2191      <organization>Compaq Computer Corporation</organization>
2192      <address><email></email></address>
2193    </author>
2194    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2195      <organization>MIT Laboratory for Computer Science</organization>
2196      <address><email></email></address>
2197    </author>
2198    <author initials="L." surname="Masinter" fullname="L. Masinter">
2199      <organization>Xerox Corporation</organization>
2200      <address><email></email></address>
2201    </author>
2202    <author initials="P." surname="Leach" fullname="P. Leach">
2203      <organization>Microsoft Corporation</organization>
2204      <address><email></email></address>
2205    </author>
2206    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2207      <organization>W3C</organization>
2208      <address><email></email></address>
2209    </author>
2210    <date month="June" year="1999"/>
2211  </front>
2212  <seriesInfo name="RFC" value="2616"/>
[129]2215<reference anchor="RFC3629">
2216  <front>
2217    <title>UTF-8, a transformation format of ISO 10646</title>
2218    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2219      <organization>Alis Technologies</organization>
2220      <address><email></email></address>
2221    </author>
2222    <date month="November" year="2003"/>
2223  </front>
[1003]2224  <seriesInfo name="STD" value="63"/>
[129]2225  <seriesInfo name="RFC" value="3629"/>
[253]2228<reference anchor='RFC3864'>
2229  <front>
2230    <title>Registration Procedures for Message Header Fields</title>
2231    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2232      <organization>Nine by Nine</organization>
2233      <address><email></email></address>
2234    </author>
2235    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2236      <organization>BEA Systems</organization>
2237      <address><email></email></address>
2238    </author>
2239    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2240      <organization>HP Labs</organization>
2241      <address><email></email></address>
2242    </author>
2243    <date year='2004' month='September' />
2244  </front>
2245  <seriesInfo name='BCP' value='90' />
2246  <seriesInfo name='RFC' value='3864' />
[200]2249<reference anchor="RFC4288">
2250  <front>
2251    <title>Media Type Specifications and Registration Procedures</title>
2252    <author initials="N." surname="Freed" fullname="N. Freed">
2253      <organization>Sun Microsystems</organization>
2254      <address>
2255        <email></email>
2256      </address>
2257    </author>
2258    <author initials="J." surname="Klensin" fullname="J. Klensin">
2259      <address>
2260        <email></email>
2261      </address>
2262    </author>
2263    <date year="2005" month="December"/>
2264  </front>
2265  <seriesInfo name="BCP" value="13"/>
2266  <seriesInfo name="RFC" value="4288"/>
[670]2269<reference anchor='RFC5226'>
2270  <front>
2271    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2272    <author initials='T.' surname='Narten' fullname='T. Narten'>
2273      <organization>IBM</organization>
2274      <address><email></email></address>
2275    </author>
2276    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
2277      <organization>Google</organization>
2278      <address><email></email></address>
2279    </author>
2280    <date year='2008' month='May' />
2281  </front>
2282  <seriesInfo name='BCP' value='26' />
2283  <seriesInfo name='RFC' value='5226' />
[327]2286<reference anchor="RFC5322">
2287  <front>
2288    <title>Internet Message Format</title>
2289    <author initials="P." surname="Resnick" fullname="P. Resnick">
2290      <organization>Qualcomm Incorporated</organization>
2291    </author>
2292    <date year="2008" month="October"/>
2293  </front> 
2294  <seriesInfo name="RFC" value="5322"/>
[1267]2297<reference anchor="RFC6151">
2298  <front>
2299    <title>Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms</title>
2300    <author initials="S." surname="Turner" fullname="S. Turner"/>
2301    <author initials="L." surname="Chen" fullname="L. Chen"/>
2302    <date year="2011" month="March" />
[1308]2303  </front>
[1267]2304  <seriesInfo name="RFC" value="6151" />
[277]2307<reference anchor='BCP97'>
2308  <front>
2309    <title>Handling Normative References to Standards-Track Documents</title>
2310    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2311      <address>
2312        <email></email>
2313      </address>
2314    </author>
2315    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2316      <organization>MIT</organization>
2317      <address>
2318        <email></email>
2319      </address>
2320    </author>
2321    <date year='2007' month='June' />
2322  </front>
2323  <seriesInfo name='BCP' value='97' />
2324  <seriesInfo name='RFC' value='4897' />
[1307]2327<reference anchor="RFC6266">
[1308]2328  <front>
[1259]2329    <title abbrev="Content-Disposition in HTTP">Use of the Content-Disposition Header Field
2330    in the Hypertext Transfer Protocol (HTTP)</title>
2331    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
2332      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2333      <address>
[1308]2334        <email></email>
[1259]2335      </address>
2336    </author>
[1307]2337    <date month="June" year="2011"/>
[1259]2338  </front>
[1307]2339  <seriesInfo name='RFC' value='6266' />
[874]2344<section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
[327]2346   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
[874]2347   allow a message-body to be transmitted in an open variety of
[8]2348   representations and with extensible mechanisms. However, RFC 2045
2349   discusses mail, and HTTP has a few features that are different from
[874]2350   those described in MIME. These differences were carefully chosen
[8]2351   to optimize performance over binary connections, to allow greater
2352   freedom in the use of new media types, to make date comparisons
2353   easier, and to acknowledge the practice of some early HTTP servers
2354   and clients.
[874]2357   This appendix describes specific areas where HTTP differs from MIME.
2358   Proxies and gateways to strict MIME environments &SHOULD; be
[8]2359   aware of these differences and provide the appropriate conversions
2360   where necessary. Proxies and gateways from MIME environments to HTTP
2361   also need to be aware of the differences because some conversions
2362   might be required.
[8]2365<section title="MIME-Version" anchor="mime-version">
[1120]2366  <iref primary="true" item="MIME-Version header field" x:for-anchor=""/>
2367  <iref primary="true" item="Header Fields" subitem="MIME-Version" x:for-anchor=""/>
[229]2368  <x:anchor-alias value="MIME-Version"/>
2370   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
[1163]2371   include a single MIME-Version header field to indicate what
[8]2372   version of the MIME protocol was used to construct the message. Use
2373   of the MIME-Version header field indicates that the message is in
[115]2374   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
[8]2375   Proxies/gateways are responsible for ensuring full compliance (where
2376   possible) when exporting HTTP messages to strict MIME environments.
[1234]2378<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/>
2379  <x:ref>MIME-Version</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2382   MIME version "1.0" is the default for use in HTTP/1.1. However,
2383   HTTP/1.1 message parsing and semantics are defined by this document
2384   and not the MIME specification.
2388<section title="Conversion to Canonical Form" anchor="">
[874]2390   MIME requires that an Internet mail body-part be converted to
[115]2391   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
[97]2392   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
[8]2393   allowed for subtypes of the "text" media type when transmitted over
[97]2394   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
[8]2395   line breaks as CRLF and forbids the use of CR or LF outside of line
2396   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2397   line break within text content when a message is transmitted over
2398   HTTP.
2401   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2402   environment &SHOULD; translate all line breaks within the text media
[1176]2403   types described in <xref target="canonicalization.and.text.defaults"/>
2404   of this document to the RFC 2049
[8]2405   canonical form of CRLF. Note, however, that this might be complicated
2406   by the presence of a Content-Encoding and by the fact that HTTP
[1176]2407   allows the use of some character encodings which do not use octets 13 and
2408   10 to represent CR and LF, respectively, as is the case for some multi-byte
2409   character encodings.
[969]2412   Conversion will break any cryptographic
[8]2413   checksums applied to the original content unless the original content
2414   is already in canonical form. Therefore, the canonical form is
2415   recommended for any content that uses such checksums in HTTP.
2420<section title="Conversion of Date Formats" anchor="">
2422   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2423   simplify the process of date comparison. Proxies and gateways from
2424   other protocols &SHOULD; ensure that any Date header field present in a
2425   message conforms to one of the HTTP/1.1 formats and rewrite the date
2426   if necessary.
[8]2430<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
[874]2432   MIME does not include any concept equivalent to HTTP/1.1's
[8]2433   Content-Encoding header field. Since this acts as a modifier on the
2434   media type, proxies and gateways from HTTP to MIME-compliant
2435   protocols &MUST; either change the value of the Content-Type header
[874]2436   field or decode the representation before forwarding the message. (Some
[8]2437   experimental applications of Content-Type for Internet mail have used
2438   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2439   a function equivalent to Content-Encoding. However, this parameter is
[874]2440   not part of the MIME standards).
2444<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
[874]2446   HTTP does not use the Content-Transfer-Encoding field of MIME.
2447   Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
[85]2448   remove any Content-Transfer-Encoding
[8]2449   prior to delivering the response message to an HTTP client.
2452   Proxies and gateways from HTTP to MIME-compliant protocols are
2453   responsible for ensuring that the message is in the correct format
2454   and encoding for safe transport on that protocol, where "safe
2455   transport" is defined by the limitations of the protocol being used.
2456   Such a proxy or gateway &SHOULD; label the data with an appropriate
2457   Content-Transfer-Encoding if doing so will improve the likelihood of
2458   safe transport over the destination protocol.
2462<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
[29]2464   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
[8]2465   Proxies/gateways &MUST; remove any transfer-coding prior to
2466   forwarding a message via a MIME-compliant protocol.
2470<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
[129]2472   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
[8]2473   need to be aware of MIME line length limitations. Since HTTP does not
2474   have this limitation, HTTP does not fold long lines. MHTML messages
2475   being transported by HTTP follow all conventions of MHTML, including
2476   line length limitations and folding, canonicalization, etc., since
2477   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2478   does not interpret the content or any MIME header lines that might be
2479   contained therein.
2484<section title="Additional Features" anchor="additional.features">
[97]2486   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
[8]2487   existing HTTP implementations, but not consistently and correctly
2488   across most HTTP/1.1 applications. Implementors are advised to be
2489   aware of these features, but cannot rely upon their presence in, or
2490   interoperability with, other HTTP/1.1 applications. Some of these
2491   describe proposed experimental features, and some describe features
2492   that experimental deployment found lacking that are now addressed in
2493   the base HTTP/1.1 specification.
[994]2496   A number of other header fields, such as Content-Disposition and Title,
[1307]2497   from SMTP and MIME are also often implemented (see <xref target="RFC6266"/>
2498   and <xref target="RFC2076"/>).
[99]2502<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2504  Clarify contexts that charset is used in.
2505  (<xref target="character.sets"/>)
[1240]2508  Remove the default character encoding for text media types; the default
2509  now is whatever the media type definition says.
2510  (<xref target="canonicalization.and.text.defaults"/>)
[1234]2513  Change ABNF productions for header fields to only define the field value.
2514  (<xref target="header.fields"/>)
[1308]2517  Remove definition of Content-MD5 header field because it was inconsistently
2518  implemented with respect to partial responses, and also because of known
2519  deficiencies in the hash algorithm itself (see <xref target="RFC6151"/> for details).
[1267]2520  (<xref target="header.fields"/>)
[1240]2523  Remove ISO-8859-1 special-casing in Accept-Charset.
2524  (<xref target="header.accept-charset"/>)
[712]2527  Remove base URI setting semantics for Content-Location due to poor
[714]2528  implementation support, which was caused by too many broken servers emitting
[994]2529  bogus Content-Location header fields, and also the potentially undesirable effect
[714]2530  of potentially breaking relative links in content-negotiated resources.
[712]2531  (<xref target="header.content-location"/>)
[1308]2534  Remove discussion of Content-Disposition header field, it is now defined
2535  by <xref target="RFC6266"/>.
[1259]2536  (<xref target="additional.features"/>)
[104]2539  Remove reference to non-existant identity transfer-coding value tokens.
2540  (<xref target="no.content-transfer-encoding"/>)
[680]2544<?BEGININC p3-payload.abnf-appendix ?>
[427]2545<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
2547<artwork type="abnf" name="p3-payload.parsed-abnf">
[1234]2548<x:ref>Accept</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2549 OWS media-range [ accept-params ] ] ) ]
2550<x:ref>Accept-Charset</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
[425]2551 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2552 qvalue ] ] )
[1234]2553<x:ref>Accept-Encoding</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] ) )
2554 *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2555<x:ref>Accept-Language</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
[425]2556 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2557 ] )
[1234]2559<x:ref>Content-Encoding</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
[425]2560 content-coding ] )
[1234]2561<x:ref>Content-Language</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
[425]2562 language-tag ] )
[1234]2563<x:ref>Content-Location</x:ref> = absolute-URI / partial-URI
2564<x:ref>Content-Type</x:ref> = media-type
[1234]2566<x:ref>MIME-Version</x:ref> = 1*DIGIT "." 1*DIGIT
2568<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
[1318]2570<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
[810]2571<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" word ]
[427]2572<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2573<x:ref>attribute</x:ref> = token
2575<x:ref>charset</x:ref> = token
2576<x:ref>codings</x:ref> = ( content-coding / "*" )
2577<x:ref>content-coding</x:ref> = token
[427]2579<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
[690]2580<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC5646], Section 2.1&gt;
2582<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
[425]2583 ";" OWS parameter )
[427]2584<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2586<x:ref>parameter</x:ref> = attribute "=" value
[1318]2587<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
[678]2589<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 6.4&gt;
2591<x:ref>subtype</x:ref> = token
[1396]2593<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.3&gt;
[427]2594<x:ref>type</x:ref> = token
[810]2596<x:ref>value</x:ref> = word
[1396]2598<x:ref>word</x:ref> = &lt;word, defined in [Part1], Section 3.2.3&gt;
[532]2601<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2602; Accept defined but not used
[425]2603; Accept-Charset defined but not used
2604; Accept-Encoding defined but not used
2605; Accept-Language defined but not used
[968]2606; Content-Encoding defined but not used
2607; Content-Language defined but not used
2608; Content-Location defined but not used
2609; Content-Type defined but not used
[425]2610; MIME-Version defined but not used
[680]2612<?ENDINC p3-payload.abnf-appendix ?>
[252]2614<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
[1002]2616<section title="Since RFC 2616">
2618  Extracted relevant partitions from <xref target="RFC2616"/>.
2622<section title="Since draft-ietf-httpbis-p3-payload-00">
[116]2624  Closed issues:
2625  <list style="symbols"> 
2626    <t>
[324]2627      <eref target=""/>:
[116]2628      "Media Type Registrations"
2629      (<eref target=""/>)
2630    </t>
2631    <t>
[324]2632      <eref target=""/>:
[116]2633      "Clarification regarding quoting of charset values"
2634      (<eref target=""/>)
2635    </t>
2636    <t>
[324]2637      <eref target=""/>:
[116]2638      "Remove 'identity' token references"
2639      (<eref target=""/>)
2640    </t>
2641    <t>
[324]2642      <eref target=""/>:
[126]2643      "Accept-Encoding BNF"
2644    </t>
2645    <t>
[324]2646      <eref target=""/>:
[152]2647      "Normative and Informative references"
2648    </t>
2649    <t>
[324]2650      <eref target=""/>:
[116]2651      "RFC1700 references"
2652    </t>
[122]2653    <t>
[324]2654      <eref target=""/>:
[200]2655      "Updating to RFC4288"
2656    </t>
2657    <t>
[324]2658      <eref target=""/>:
[129]2659      "Informative references"
2660    </t>
2661    <t>
[324]2662      <eref target=""/>:
[123]2663      "ISO-8859-1 Reference"
2664    </t>
2665    <t>
[324]2666      <eref target=""/>:
[122]2667      "Encoding References Normative"
2668    </t>
[131]2669    <t>
[324]2670      <eref target=""/>:
[131]2671      "Normative up-to-date references"
2672    </t>
[116]2673  </list>
[170]2677<section title="Since draft-ietf-httpbis-p3-payload-01">
[324]2679  Ongoing work on ABNF conversion (<eref target=""/>):
[205]2680  <list style="symbols"> 
2681    <t>
2682      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2683    </t>
2684  </list>
[252]2688<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
[232]2690  Closed issues:
2691  <list style="symbols"> 
2692    <t>
[324]2693      <eref target=""/>:
[251]2694      "Quoting Charsets"
2695    </t>
2696    <t>
[324]2697      <eref target=""/>:
[232]2698      "Classification for Allow header"
2699    </t>
[248]2700    <t>
[324]2701      <eref target=""/>:
[248]2702      "missing default for qvalue in description of Accept-Encoding"
2703    </t>
[232]2704  </list>
[994]2707  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
[253]2708  <list style="symbols"> 
2709    <t>
[994]2710      Reference RFC 3984, and update header field registrations for headers defined
[253]2711      in this document.
2712    </t>
2713  </list>
[267]2717<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
[269]2719  Closed issues:
2720  <list style="symbols"> 
2721    <t>
[297]2722      <eref target=""/>:
2723      "Quoting Charsets"
2724    </t>
2725    <t>
[303]2726      <eref target=""/>:
2727      "language tag matching (Accept-Language) vs RFC4647"
2728    </t>
2729    <t>
[277]2730      <eref target=""/>:
[269]2731      "RFC 1806 has been replaced by RFC2183"
2732    </t>
2733  </list>
2736  Other changes:
2737  <list style="symbols"> 
2738    <t>
2739      <eref target=""/>:
[1101]2740      "Encoding References Normative" &mdash; rephrase the annotation and reference
[277]2741      <xref target="BCP97"/>.
2742    </t>
2743  </list>
[269]2745 </section>
[323]2747<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
[327]2749  Closed issues:
2750  <list style="symbols"> 
2751    <t>
2752      <eref target=""/>:
2753      "RFC 2822 is updated by RFC 5322"
2754    </t>
2755  </list>
2758  Ongoing work on ABNF conversion (<eref target=""/>):
2759  <list style="symbols"> 
2760    <t>
2761      Use "/" instead of "|" for alternatives.
2762    </t>
[357]2763    <t>
2764      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2765      whitespace ("OWS") and required whitespace ("RWS").
2766    </t>
2767    <t>
2768      Rewrite ABNFs to spell out whitespace rules, factor out
[994]2769      header field value format definitions.
[357]2770    </t>
[334]2771  </list>
[382]2775<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
[385]2777  Closed issues:
2778  <list style="symbols"> 
2779    <t>
2780      <eref target=""/>:
2781      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2782    </t>
2783  </list>
[543]2786  Final work on ABNF conversion (<eref target=""/>):
[421]2787  <list style="symbols"> 
2788    <t>
[424]2789      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
[421]2790    </t>
2791  </list>
2794  Other changes:
2795  <list style="symbols"> 
2796    <t>
2797      Move definition of quality values into Part 1.
2798    </t>
2799  </list>
[547]2803<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
[577]2805  Closed issues:
2806  <list style="symbols"> 
2807    <t>
2808      <eref target=""/>:
2809      "Content-Location isn't special"
2810    </t>
[592]2811    <t>
2812      <eref target=""/>:
2813      "Content Sniffing"
2814    </t>
[577]2815  </list>
[604]2819<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
[613]2821  Closed issues:
2822  <list style="symbols"> 
2823    <t>
[670]2824      <eref target=""/>:
[613]2825      "Updated reference for language tags"
2826    </t>
[663]2827    <t>
[716]2828      <eref target=""/>:
2829      "Clarify rules for determining what entities a response carries"
2830    </t>
2831    <t>
[712]2832      <eref target=""/>:
2833      "Content-Location base-setting problems"
2834    </t>
2835    <t>
[663]2836      <eref target=""/>:
2837      "Content Sniffing"
2838    </t>
[670]2839    <t>
2840      <eref target=""/>:
2841      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
2842    </t>
[673]2843    <t>
2844      <eref target=""/>:
2845      "move definitions of gzip/deflate/compress to part 1"
2846    </t>
[613]2847  </list>
2850  Partly resolved issues:
2851  <list style="symbols"> 
2852    <t>
2853      <eref target=""/>:
2854      "update IANA requirements wrt Transfer-Coding values" (add the
2855      IANA Considerations subsection)
2856    </t>
[668]2857    <t>
2858      <eref target=""/>:
2859      "update IANA requirements wrt Content-Coding values" (add the
2860      IANA Considerations subsection)
2861    </t>
[667]2862  </list>
[720]2866<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
[724]2868  Closed issues:
2869  <list style="symbols"> 
2870    <t>
[745]2871      <eref target=""/>:
2872      "Content Negotiation for media types"
2873    </t>
2874    <t>
[724]2875      <eref target=""/>:
2876      "Accept-Language: which RFC4647 filtering?"
2877    </t>
2878  </list>
[773]2882<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
[808]2884  Closed issues:
2885  <list style="symbols"> 
2886    <t>
[937]2887      <eref target=""/>:
2888      "MIME-Version not listed in P1, general header fields"
2889    </t>
2890    <t>
[808]2891      <eref target=""/>:
2892      "IANA registry for content/transfer encodings"
2893    </t>
[810]2894    <t>
[831]2895      <eref target=""/>:
2896      "Content Sniffing"
2897    </t>
2898    <t>
[810]2899      <eref target=""/>:
2900      "use of term "word" when talking about header structure"
2901    </t>
[808]2902  </list>
2905  Partly resolved issues:
2906  <list style="symbols"> 
2907    <t>
2908      <eref target=""/>:
2909      "Term for the requested resource's URI"
2910    </t>
2911  </list>
[841]2915<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.10">
[854]2917  Closed issues:
2918  <list style="symbols"> 
2919    <t>
[858]2920      <eref target=""/>:
2921      "Clarify 'Requested Variant'"
2922    </t>
2923    <t>
2924      <eref target=""/>:
2925      "Content-Location isn't special"
2926    </t>
2927    <t>
[854]2928      <eref target=""/>:
2929      "Delimiting messages with multipart/byteranges"
2930    </t>
[858]2931    <t>
2932      <eref target=""/>:
2933      "Clarify entity / representation / variant terminology"
2934    </t>
2935    <t>
2936      <eref target=""/>:
2937      "confusing req. language for Content-Location"
2938    </t>
2939    <t>
2940      <eref target=""/>:
2941      "Content-Location on 304 responses"
2942    </t>
[882]2943    <t>
2944      <eref target=""/>:
2945      "'requested resource' in content-encoding definition"
2946    </t>
[911]2947    <t>
2948      <eref target=""/>:
2949      "consider removing the 'changes from 2068' sections"
2950    </t>
[854]2951  </list>
2954  Partly resolved issues:
2955  <list style="symbols"> 
2956    <t>
2957      <eref target=""/>:
2958      "Content-MD5 and partial responses"
2959    </t>
2960  </list>
[973]2964<section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.since.11">
[987]2966  Closed issues:
2967  <list style="symbols"> 
2968    <t>
2969      <eref target=""/>:
2970      "Factor out Content-Disposition"
2971    </t>
2972  </list>
[1052]2976<section title="Since draft-ietf-httpbis-p3-payload-12" anchor="changes.since.12">
[1153]2978  Closed issues:
2979  <list style="symbols"> 
2980    <t>
[1165]2981      <eref target=""/>:
2982      "Header Classification"
2983    </t>
2984    <t>
[1167]2985      <eref target=""/>:
2986      "untangle ABNFs for header fields"
2987    </t>
2988    <t>
[1153]2989      <eref target=""/>:
2990      "potentially misleading MAY in media-type def"
2991    </t>
2992  </list>
[1180]2996<section title="Since draft-ietf-httpbis-p3-payload-13" anchor="changes.since.13">
[1234]2998  Closed issues:
2999  <list style="symbols"> 
3000    <t>
[1240]3001      <eref target=""/>:
3002      "Default charsets for text media types"
3003    </t>
3004    <t>
[1267]3005      <eref target=""/>:
3006      "Content-MD5 and partial responses"
3007    </t>
3008    <t>
[1234]3009      <eref target=""/>:
3010      "untangle ABNFs for header fields"
3011    </t>
[1244]3012    <t>
3013      <eref target=""/>:
3014      "confusing undefined parameter in media range example"
3015    </t>
[1234]3016  </list>
[1271]3020<section title="Since draft-ietf-httpbis-p3-payload-14" anchor="changes.since.14">
[1328]3022  None.
[1326]3026<section title="Since draft-ietf-httpbis-p3-payload-15" anchor="changes.since.15">
[1335]3028  Closed issues:
3029  <list style="symbols"> 
3030    <t>
3031      <eref target=""/>:
3032      "Strength of requirements on Accept re: 406"
3033    </t>
3034  </list>
[1401]3038<section title="Since draft-ietf-httpbis-p3-payload-16" anchor="changes.since.16">
3040  None yet.
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