source: draft-ietf-httpbis/latest/p3-payload.xml @ 1364

Last change on this file since 1364 was 1364, checked in by julian.reschke@…, 8 years ago

remove historical Acks (see #219)

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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">
[1321]15  <!ENTITY ID-MONTH "July">
[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=''/>">
[1364]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=''/>">
[115]22  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x=''/>">
[31]23  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x=''/>">
24  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x=''/>">
25  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x=''/>">
26  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x=''/>">
27  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x=''/>">
28  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x=''/>">
[115]29  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x=''/>">
[31]30  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x=''/>">
31  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='' xmlns:x=''/>">
[580]32  <!ENTITY full-date                "<xref target='Part1' x:rel='' xmlns:x=''/>">
[457]33  <!ENTITY qvalue                   "<xref target='Part1' x:rel='#quality.values' xmlns:x=''/>">
[374]34  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x=''/>">
[823]35  <!ENTITY effective-request-uri    "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x=''/>">
[808]36  <!ENTITY compression-codings      "<xref target='Part1' x:rel='#compression.codings' xmlns:x=''/>">
37  <!ENTITY transfer-codings         "<xref target='Part1' x:rel='#transfer.codings' xmlns:x=''/>">
[673]38  <!ENTITY compress-coding          "<xref target='Part1' x:rel='#compress.coding' xmlns:x=''/>">
39  <!ENTITY deflate-coding           "<xref target='Part1' x:rel='#deflate.coding' xmlns:x=''/>">
40  <!ENTITY gzip-coding              "<xref target='Part1' x:rel='#gzip.coding' xmlns:x=''/>">
[716]41  <!ENTITY response-representation  "<xref target='Part2' x:rel='#identifying.response.associated.with.representation' xmlns:x=''/>">
43<?rfc toc="yes" ?>
[29]44<?rfc symrefs="yes" ?>
45<?rfc sortrefs="yes" ?>
[8]46<?rfc compact="yes"?>
47<?rfc subcompact="no" ?>
48<?rfc linkmailto="no" ?>
49<?rfc editing="no" ?>
[203]50<?rfc comments="yes"?>
51<?rfc inline="yes"?>
[799]52<?rfc rfcedstyle="yes"?>
[8]53<?rfc-ext allow-markup-in-artwork="yes" ?>
54<?rfc-ext include-references-in-index="yes" ?>
[308]55<rfc obsoletes="2616" category="std" x:maturity-level="draft"
[446]56     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
[153]57     xmlns:x=''>
[120]60  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
[29]62  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]63    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[8]64    <address>
65      <postal>
[1106]66        <street>345 Park Ave</street>
67        <city>San Jose</city>
[8]68        <region>CA</region>
[1106]69        <code>95110</code>
[29]70        <country>USA</country>
[8]71      </postal>
[29]72      <email></email>
73      <uri></uri>
[8]74    </address>
75  </author>
[29]77  <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]78    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
[8]79    <address>
80      <postal>
[29]81        <street>21 Oak Knoll Road</street>
82        <city>Carlisle</city>
[8]83        <region>MA</region>
[29]84        <code>01741</code>
85        <country>USA</country>
[8]86      </postal>
[844]87      <email></email>
88      <uri></uri>
[8]89    </address>
90  </author>
92  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
[29]93    <organization abbrev="HP">Hewlett-Packard Company</organization>
[8]94    <address>
95      <postal>
[29]96        <street>HP Labs, Large Scale Systems Group</street>
97        <street>1501 Page Mill Road, MS 1177</street>
[8]98        <city>Palo Alto</city>
99        <region>CA</region>
[29]100        <code>94304</code>
101        <country>USA</country>
[8]102      </postal>
[29]103      <email></email>
[8]104    </address>
105  </author>
107  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
[29]108    <organization abbrev="Microsoft">Microsoft Corporation</organization>
[8]109    <address>
110      <postal>
[29]111        <street>1 Microsoft Way</street>
112        <city>Redmond</city>
113        <region>WA</region>
114        <code>98052</code>
115        <country>USA</country>
[8]116      </postal>
[29]117      <email></email>
[8]118    </address>
119  </author>
121  <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]122    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[8]123    <address>
124      <postal>
[29]125        <street>345 Park Ave</street>
126        <city>San Jose</city>
[8]127        <region>CA</region>
[29]128        <code>95110</code>
129        <country>USA</country>
[8]130      </postal>
[29]131      <email></email>
132      <uri></uri>
[8]133    </address>
134  </author>
136  <author initials="P." surname="Leach" fullname="Paul J. Leach">
137    <organization abbrev="Microsoft">Microsoft Corporation</organization>
138    <address>
139      <postal>
140        <street>1 Microsoft Way</street>
141        <city>Redmond</city>
142        <region>WA</region>
143        <code>98052</code>
144      </postal>
145      <email></email>
146    </address>
147  </author>
149  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
150    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
151    <address>
152      <postal>
[34]153        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
154        <street>The Stata Center, Building 32</street>
155        <street>32 Vassar Street</street>
[8]156        <city>Cambridge</city>
157        <region>MA</region>
158        <code>02139</code>
[29]159        <country>USA</country>
[8]160      </postal>
161      <email></email>
[34]162      <uri></uri>
[8]163    </address>
164  </author>
[95]166  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
[94]167    <organization abbrev="W3C">World Wide Web Consortium</organization>
168    <address>
169      <postal>
170        <street>W3C / ERCIM</street>
171        <street>2004, rte des Lucioles</street>
172        <city>Sophia-Antipolis</city>
173        <region>AM</region>
174        <code>06902</code>
175        <country>France</country>
176      </postal>
177      <email></email>
178      <uri></uri>
179    </address>
180  </author>
[95]182  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
183    <organization abbrev="greenbytes">greenbytes GmbH</organization>
184    <address>
185      <postal>
186        <street>Hafenweg 16</street>
187        <city>Muenster</city><region>NW</region><code>48155</code>
188        <country>Germany</country>
189      </postal>
[609]190      <phone>+49 251 2807760</phone>
191      <facsimile>+49 251 2807761</facsimile>
192      <email></email>
193      <uri></uri>
[95]194    </address>
195  </author>
[31]197  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
[440]198  <workgroup>HTTPbis Working Group</workgroup>
202   The Hypertext Transfer Protocol (HTTP) is an application-level
203   protocol for distributed, collaborative, hypermedia information
[29]204   systems. HTTP has been in use by the World Wide Web global information
[35]205   initiative since 1990. This document is Part 3 of the seven-part specification
[29]206   that defines the protocol referred to as "HTTP/1.1" and, taken together,
[42]207   obsoletes RFC 2616.  Part 3 defines HTTP message content,
[29]208   metadata, and content negotiation.
212<note title="Editorial Note (To be removed by RFC Editor)">
213  <t>
214    Discussion of this draft should take place on the HTTPBIS working group
[1268]215    mailing list (, which is archived at
216    <eref target=""/>.
217  </t>
218  <t>
219    The current issues list is at
220    <eref target=""/> and related
221    documents (including fancy diffs) can be found at
[324]222    <eref target=""/>.
[36]223  </t>
[153]224  <t>
[1326]225    The changes in this draft are summarized in <xref target="changes.since.15"/>.
[153]226  </t>
230<section title="Introduction" anchor="introduction">
[163]232   This document defines HTTP/1.1 message payloads (a.k.a., content), the
[161]233   associated metadata header fields that define how the payload is intended
234   to be interpreted by a recipient, the request header fields that
[908]235   might influence content selection, and the various selection algorithms
[161]236   that are collectively referred to as HTTP content negotiation.
239   This document is currently disorganized in order to minimize the changes
240   between drafts and enable reviewers to see the smaller errata changes.
[980]241   A future draft will reorganize the sections to better reflect the content.
[161]242   In particular, the sections on entities will be renamed payload and moved
243   to the first half of the document, while the sections on content negotiation
244   and associated request header fields will be moved to the second half.  The
245   current mess reflects how widely dispersed these topics and associated
246   requirements had become in <xref target="RFC2616"/>.
[660]249<section title="Terminology" anchor="terminology">
251   This specification uses a number of terms to refer to the roles
252   played by participants in, and objects of, the HTTP communication.
255  <iref item="content negotiation"/>
256  <x:dfn>content negotiation</x:dfn>
257  <list>
258    <t>
259      The mechanism for selecting the appropriate representation when
[856]260      servicing a request. The representation in any response
[660]261      can be negotiated (including error responses).
262    </t>
263  </list>
[96]267<section title="Requirements" anchor="intro.requirements">
269   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
270   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
271   document are to be interpreted as described in <xref target="RFC2119"/>.
274   An implementation is not compliant if it fails to satisfy one or more
[847]275   of the "MUST" or "REQUIRED" level requirements for the protocols it
276   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
277   level and all the "SHOULD" level requirements for its protocols is said
278   to be "unconditionally compliant"; one that satisfies all the "MUST"
279   level requirements but not all the "SHOULD" level requirements for its
280   protocols is said to be "conditionally compliant".
[424]284<section title="Syntax Notation" anchor="notation">
[425]285  <x:anchor-alias value="ALPHA"/>
286  <x:anchor-alias value="CR"/>
287  <x:anchor-alias value="DIGIT"/>
288  <x:anchor-alias value="LF"/>
289  <x:anchor-alias value="OCTET"/>
290  <x:anchor-alias value="VCHAR"/>
291  <x:anchor-alias value="WSP"/>
[543]293  This specification uses the ABNF syntax defined in &notation; (which
294  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
295  <xref target="collected.abnf"/> shows the collected ABNF, with the list
296  rule expanded.
[425]299  The following core rules are included by
300  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
301  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
302  DIGIT (decimal 0-9), DQUOTE (double quote),
303  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
304  OCTET (any 8-bit sequence of data), SP (space),
305  VCHAR (any visible USASCII character),
306  and WSP (whitespace).
309<section title="Core Rules" anchor="core.rules">
[229]310  <x:anchor-alias value="token"/>
[810]311  <x:anchor-alias value="word"/>
[357]312  <x:anchor-alias value="OWS"/>
[424]314  The core rules below are defined in &basic-rules;:
316<figure><artwork type="abnf2616">
[229]317  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
[810]318  <x:ref>word</x:ref>           = &lt;word, defined in &basic-rules;&gt;
[357]319  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
323<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
[374]324  <x:anchor-alias value="absolute-URI"/>
[391]325  <x:anchor-alias value="partial-URI"/>
[457]326  <x:anchor-alias value="qvalue"/>
[206]328  The ABNF rules below are defined in other parts:
[207]330<figure><!--Part1--><artwork type="abnf2616">
[374]331  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
[391]332  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
[457]333  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
[8]341<section title="Protocol Parameters" anchor="protocol.parameters">
[1176]343<section title="Character Encodings (charset)" anchor="character.sets">
[1176]345   HTTP uses charset names to indicate the character encoding of a
346   textual representation.
[229]348<t anchor="rule.charset">
349  <x:anchor-alias value="charset"/>
[1176]350   A character encoding is identified by a case-insensitive token. The
[8]351   complete set of tokens is defined by the IANA Character Set registry
[91]352   (<eref target=""/>).
354<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
[229]355  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
358   Although HTTP allows an arbitrary token to be used as a charset
359   value, any token that has a predefined value within the IANA
[1176]360   Character Set registry &MUST; represent the character encoding defined
[8]361   by that registry. Applications &SHOULD; limit their use of character
[1176]362   encodings to those defined within the IANA registry.
[81]365   HTTP uses charset in two contexts: within an Accept-Charset request
[994]366   header field (in which the charset value is an unquoted token) and as the
367   value of a parameter in a Content-Type header field (within a request or
[81]368   response), in which case the parameter value of the charset parameter
[908]369   can be quoted.
[969]372   Implementors need to be aware of IETF character set requirements <xref target="RFC3629"/>
[8]373   <xref target="RFC2277"/>.
377<section title="Content Codings" anchor="content.codings">
[229]378  <x:anchor-alias value="content-coding"/>
380   Content coding values indicate an encoding transformation that has
[866]381   been or can be applied to a representation. Content codings are primarily
382   used to allow a representation to be compressed or otherwise usefully
[8]383   transformed without losing the identity of its underlying media type
[866]384   and without loss of information. Frequently, the representation is stored in
[8]385   coded form, transmitted directly, and only decoded by the recipient.
387<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
[229]388  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
391   All content-coding values are case-insensitive. HTTP/1.1 uses
392   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
393   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
394   describes the content-coding, what is more important is that it
395   indicates what decoding mechanism will be required to remove the
396   encoding.
[673]399   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
400  <list>
401    <t>
402      See &compress-coding;.
403    </t>
404  </list>
[673]407   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
[8]408  <list>
409    <t>
[673]410      See &deflate-coding;.
[8]411    </t>
412  </list>
[673]415   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
416  <list>
417    <t>
418      See &gzip-coding;.
419    </t>
420  </list>
[673]423   identity<iref item="identity (Coding Format)"/><iref item="Coding Format" subitem="identity"/>
[8]424  <list><t>
425        The default (identity) encoding; the use of no transformation
426        whatsoever. This content-coding is used only in the Accept-Encoding
[994]427        header field, and &SHOULD-NOT;  be used in the Content-Encoding
428        header field.
[8]429  </t></list>
432<section title="Content Coding Registry" anchor="content.coding.registry">
[670]434   The HTTP Content Coding Registry defines the name space for the content
435   coding names.
438   Registrations &MUST; include the following fields:
439   <list style="symbols">
440     <t>Name</t>
441     <t>Description</t>
442     <t>Pointer to specification text</t>
443   </list>
[808]446   Names of content codings &MUST-NOT; overlap with names of transfer codings
447   (&transfer-codings;), unless the encoding transformation is identical (as it
448   is the case for the compression codings defined in
449   &compression-codings;).
[942]452   Values to be added to this name space require a specification
453   (see "Specification Required" in
[670]454   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
[8]455   conform to the purpose of content coding defined in this section.
458   The registry itself is maintained at
459   <eref target=""/>.
[8]465<section title="Media Types" anchor="media.types">
[229]466  <x:anchor-alias value="media-type"/>
467  <x:anchor-alias value="type"/>
468  <x:anchor-alias value="subtype"/>
[152]470   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
[8]471   and Accept (<xref target="header.accept"/>) header fields in order to provide
472   open and extensible data typing and type negotiation.
474<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]475  <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> )
476  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
477  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
[229]479<t anchor="rule.parameter">
480  <x:anchor-alias value="attribute"/>
481  <x:anchor-alias value="parameter"/>
482  <x:anchor-alias value="value"/>
[1153]483   The type/subtype &MAY; be followed by parameters in the form of
484   attribute/value pairs.
[29]486<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]487  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
488  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
[810]489  <x:ref>value</x:ref>          = <x:ref>word</x:ref>
492   The type, subtype, and parameter attribute names are case-insensitive.
[370]493   Parameter values might or might not be case-sensitive, depending on the
494   semantics of the parameter name.  The presence or absence of a parameter might
[8]495   be significant to the processing of a media-type, depending on its
496   definition within the media type registry.
[908]499   A parameter value that matches the <x:ref>token</x:ref> production can be
[297]500   transmitted as either a token or within a quoted-string. The quoted and
501   unquoted values are equivalent.
[8]504   Note that some older HTTP applications do not recognize media type
505   parameters. When sending data to older HTTP applications,
506   implementations &SHOULD; only use media type parameters when they are
507   required by that type/subtype definition.
510   Media-type values are registered with the Internet Assigned Number
[91]511   Authority (IANA). The media type registration process is
[115]512   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
[8]513   discouraged.
516<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
[874]518   Internet media types are registered with a canonical form. A
519   representation transferred via HTTP messages &MUST; be in the
[8]520   appropriate canonical form prior to its transmission except for
521   "text" types, as defined in the next paragraph.
524   When in canonical form, media subtypes of the "text" type use CRLF as
525   the text line break. HTTP relaxes this requirement and allows the
526   transport of text media with plain CR or LF alone representing a line
[874]527   break when it is done consistently for an entire representation. HTTP
528   applications &MUST; accept CRLF, bare CR, and bare LF as indicating
529   a line break in text media received via HTTP. In
530   addition, if the text is in a character encoding that does not
[8]531   use octets 13 and 10 for CR and LF respectively, as is the case for
[874]532   some multi-byte character encodings, HTTP allows the use of whatever octet
533   sequences are defined by that character encoding to represent the
[8]534   equivalent of CR and LF for line breaks. This flexibility regarding
[874]535   line breaks applies only to text media in the payload body; a bare CR
[8]536   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
537   structures (such as header fields and multipart boundaries).
[874]540   If a representation is encoded with a content-coding, the underlying
[8]541   data &MUST; be in a form defined above prior to being encoded.
545<section title="Multipart Types" anchor="multipart.types">
[1101]547   MIME provides for a number of "multipart" types &mdash; encapsulations of
[874]548   one or more representations within a single message-body. All multipart
[97]549   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
550   and &MUST; include a boundary parameter as part of the media type
[8]551   value. The message body is itself a protocol element and &MUST;
552   therefore use only CRLF to represent line breaks between body-parts.
555   In general, HTTP treats a multipart message-body no differently than
[852]556   any other media type: strictly as payload.  HTTP does not use the
557   multipart boundary as an indicator of message-body length.
[97]558   <!-- jre: re-insert removed text pointing to caching? -->
[852]559   In all other respects, an HTTP user agent &SHOULD; follow the same or similar
[8]560   behavior as a MIME user agent would upon receipt of a multipart type.
561   The MIME header fields within each body-part of a multipart message-body
562   do not have any significance to HTTP beyond that defined by
563   their MIME semantics.
566   If an application receives an unrecognized multipart subtype, the
567   application &MUST; treat it as being equivalent to "multipart/mixed".
570  <t>
571    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
572    for carrying form data suitable for processing via the POST
573    request method, as described in <xref target="RFC2388"/>.
574  </t>
579<section title="Language Tags" anchor="language.tags">
[229]580  <x:anchor-alias value="language-tag"/>
[690]582   A language tag, as defined in <xref target="RFC5646"/>, identifies a
[613]583   natural language spoken, written, or otherwise conveyed by human beings for
584   communication of information to other human beings. Computer languages are
585   explicitly excluded. HTTP uses language tags within the Accept-Language and
586   Content-Language fields.
[613]589   In summary, a language tag is composed of one or more parts: A primary
590   language subtag followed by a possibly empty series of subtags:
[613]592<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
[690]593  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
596   White space is not allowed within the tag and all tags are case-insensitive.
[613]597   The name space of language subtags is administered by the IANA (see
598   <eref target=""/>).
601  <preamble>Example tags include:</preamble>
602<artwork type="example">
603  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
[690]607   See <xref target="RFC5646"/> for further information.
[965]612<section title="Payload" anchor="payload">
[965]614   HTTP messages &MAY; transfer a payload if not otherwise restricted by
615   the request method or response status code.  The payload consists of
616   metadata, in the form of header fields, and data, in the form of the
617   sequence of octets in the message-body after any transfer-coding has
618   been decoded.
[965]620<iref item="payload"/>
622   A "<x:dfn>payload</x:dfn>" in HTTP is always a partial or complete
623   representation of some resource.  We use separate terms for payload
624   and representation because some messages contain only the associated
625   representation's header fields (e.g., responses to HEAD) or only some
626   part(s) of the representation (e.g., the 206 status code).
628<section title="Payload Header Fields" anchor="payload.header.fields">
629  <x:anchor-alias value="payload-header"/>
[965]631   HTTP header fields that specifically define the payload, rather than the
632   associated representation, are referred to as "payload header fields".
633   The following payload header fields are defined by HTTP/1.1:
[1138]635<texttable align="left">
636  <ttcol>Header Field Name</ttcol>
637  <ttcol>Defined in...</ttcol>
639  <c>Content-Length</c> <c>&header-content-length;</c>
640  <c>Content-Range</c> <c>&header-content-range;</c>
[874]644<section title="Payload Body" anchor="payload.body">
645  <x:anchor-alias value="payload-body"/>
[874]647   A payload body is only present in a message when a message-body is
648   present, as described in &message-body;. The payload body is obtained
[8]649   from the message-body by decoding any Transfer-Encoding that might
650   have been applied to ensure safe and proper transfer of the message.
[965]655<section title="Representation" anchor="representation">
656<iref item="representation"/>
[965]658   A "<x:dfn>representation</x:dfn>" is information in a format that can be readily
659   communicated from one party to another.  A resource representation
660   is information that reflects the state of that resource, as observed
661   at some point in the past (e.g., in a response to GET) or to be
662   desired at some point in the future (e.g., in a PUT request).
665   Most, but not all, representations transferred via HTTP are intended
666   to be a representation of the target resource (the resource identified
667   by the effective request URI).  The precise semantics of a representation
668   are determined by the type of message (request or response), the request
669   method, the response status code, and the representation metadata.
670   For example, the above semantic is true for the representation in any
671   200 (OK) response to GET and for the representation in any PUT request.
672   A 200 response to PUT, in contrast, contains either a representation
673   that describes the successful action or a representation of the target
674   resource, with the latter indicated by a Content-Location header field
675   with the same value as the effective request URI.  Likewise, response
676   messages with an error status code usually contain a representation that
677   describes the error and what next steps are suggested for resolving it.
680<section title="Representation Header Fields" anchor="representation.header.fields">
681  <x:anchor-alias value="representation-header"/>
683   Representation header fields define metadata about the representation data
684   enclosed in the message-body or, if no message-body is present, about
685   the representation that would have been transferred in a 200 response
686   to a simultaneous GET request with the same effective request URI.
689   The following header fields are defined as representation metadata:
[1138]691<texttable align="left">
692  <ttcol>Header Field Name</ttcol>
693  <ttcol>Defined in...</ttcol>
695  <c>Content-Encoding</c> <c><xref target="header.content-encoding"/></c>
696  <c>Content-Language</c> <c><xref target="header.content-language"/></c>
697  <c>Content-Location</c> <c><xref target="header.content-location"/></c>
698  <c>Content-Type</c> <c><xref target="header.content-type"/></c>
699  <c>Expires</c> <c>&header-expires;</c>
700  <c>Last-Modified</c> <c>&header-last-modified;</c>
704<section title="Representation Data" anchor="">
705  <x:anchor-alias value="representation-data"/>
707   The representation body associated with an HTTP message is
708   either provided as the payload body of the message or
709   referred to by the message semantics and the effective request
710   URI.  The representation data is in a format and encoding defined by
711   the representation metadata header fields.
714   The data type of the representation data
715   is determined via the header fields Content-Type and Content-Encoding.
[8]716   These define a two-layer, ordered encoding model:
718<figure><artwork type="example">
[965]719  representation-data := Content-Encoding( Content-Type( bits ) )
[965]722   Content-Type specifies the media type of the underlying data, which
723   defines both the data format and how that data &SHOULD; be processed
724   by the recipient (within the scope of the request method semantics).
725   Any HTTP/1.1 message containing a payload body &SHOULD; include a
726   Content-Type header field defining the media type of the associated
727   representation unless that metadata is unknown to the sender.
[831]728   If the Content-Type header field is not present, it indicates that
[965]729   the sender does not know the media type of the representation;
730   recipients &MAY; either assume that the media type is
731   "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
[592]732   or examine the content to determine its type.
[965]735   In practice, resource owners do not always properly configure their origin
736   server to provide the correct Content-Type for a given representation,
737   with the result that some clients will examine a response body's content
738   and override the specified type.
[908]739   Clients that do so risk drawing incorrect conclusions, which might expose
[965]740   additional security risks (e.g., "privilege escalation").  Furthermore,
741   it is impossible to determine the sender's intent by examining the data
742   format: many data formats match multiple media types that differ only in
743   processing semantics.  Implementers are encouraged to provide a means of
744   disabling such "content sniffing" when it is used.
[908]747   Content-Encoding is used to indicate any additional content
[8]748   codings applied to the data, usually for the purpose of data
[965]749   compression, that are a property of the representation.  If
750   Content-Encoding is not present, then there is no additional
751   encoding beyond that defined by the Content-Type.
756<section title="Content Negotiation" anchor="content.negotiation">
[745]758   HTTP responses include a representation which contains information for
759   interpretation, whether by a human user or for further processing.
760   Often, the server has different ways of representing the
761   same information; for example, in different formats, languages,
762   or using different character encodings.
[745]765   HTTP clients and their users might have different or variable
766   capabilities, characteristics or preferences which would influence
767   which representation, among those available from the server,
768   would be best for the server to deliver. For this reason, HTTP
[1101]769   provides mechanisms for "content negotiation" &mdash; a process of
[745]770   allowing selection of a representation of a given resource,
771   when more than one is available.
[745]774   This specification defines two patterns of content negotiation;
775   "server-driven", where the server selects the representation based
776   upon the client's stated preferences, and "agent-driven" negotiation,
777   where the server provides a list of representations for the client to
778   choose from, based upon their metadata. In addition,  there are
779   other patterns: some applications use an "active content" pattern,
780   where the server returns active content which runs on the client
781   and, based on client available parameters, selects additional
782   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
783   has also been proposed.
786   These patterns are all widely used, and have trade-offs in applicability
787   and practicality. In particular, when the number of preferences or
788   capabilities to be expressed by a client are large (such as when many
789   different formats are supported by a user-agent), server-driven
[908]790   negotiation becomes unwieldy, and might not be appropriate. Conversely,
[745]791   when the number of representations to choose from is very large,
[908]792   agent-driven negotiation might not be appropriate.
795   Note that in all cases, the supplier of representations has the
796   responsibility for determining which representations might be
797   considered to be the "same information".
800<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
802   If the selection of the best representation for a response is made by
803   an algorithm located at the server, it is called server-driven
804   negotiation. Selection is based on the available representations of
[763]805   the response (the dimensions over which it can vary; e.g., language,
[8]806   content-coding, etc.) and the contents of particular header fields in
807   the request message or on other information pertaining to the request
808   (such as the network address of the client).
811   Server-driven negotiation is advantageous when the algorithm for
812   selecting from among the available representations is difficult to
813   describe to the user agent, or when the server desires to send its
814   "best guess" to the client along with the first response (hoping to
815   avoid the round-trip delay of a subsequent request if the "best
816   guess" is good enough for the user). In order to improve the server's
817   guess, the user agent &MAY; include request header fields (Accept,
818   Accept-Language, Accept-Encoding, etc.) which describe its
819   preferences for such a response.
822   Server-driven negotiation has disadvantages:
823  <list style="numbers">
824    <t>
825         It is impossible for the server to accurately determine what
826         might be "best" for any given user, since that would require
827         complete knowledge of both the capabilities of the user agent
828         and the intended use for the response (e.g., does the user want
829         to view it on screen or print it on paper?).
830    </t>
831    <t>
832         Having the user agent describe its capabilities in every
833         request can be both very inefficient (given that only a small
834         percentage of responses have multiple representations) and a
835         potential violation of the user's privacy.
836    </t>
837    <t>
838         It complicates the implementation of an origin server and the
839         algorithms for generating responses to a request.
840    </t>
841    <t>
[908]842         It might limit a public cache's ability to use the same response
[8]843         for multiple user's requests.
844    </t>
845  </list>
[1335]848   Server-driven negotiation allows the user agent to specify its preferences,
849   but it cannot expect responses to always honour them. For example, the origin
850   server might not implement server-driven negotiation, or it might decide that
851   sending a response that doesn't conform to them is better than sending a 406
852   (Not Acceptable) response.
855   Many of the mechanisms for expressing preferences use quality values to
856   declare relative preference. See &qvalue; for more information.
[1163]859   HTTP/1.1 includes the following header fields for enabling
[8]860   server-driven negotiation through description of user agent
861   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
862   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
[745]863   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
864   However, an origin server is not limited to these dimensions and &MAY; vary
[1163]865   the response based on any aspect of the request, including aspects
866   of the connection (e.g., IP address) or information within extension
867   header fields not defined by this specification.
870  <t>
871    <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
872    because new clients might not be recognized.
873  </t>
[115]876   The Vary header field (&header-vary;) can be used to express the parameters the
[8]877   server uses to select a representation that is subject to server-driven
[29]878   negotiation.
882<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
884   With agent-driven negotiation, selection of the best representation
885   for a response is performed by the user agent after receiving an
886   initial response from the origin server. Selection is based on a list
887   of the available representations of the response included within the
[874]888   header fields or body of the initial response, with each
[8]889   representation identified by its own URI. Selection from among the
[908]890   representations can be performed automatically (if the user agent is
[8]891   capable of doing so) or manually by the user selecting from a
892   generated (possibly hypertext) menu.
895   Agent-driven negotiation is advantageous when the response would vary
896   over commonly-used dimensions (such as type, language, or encoding),
897   when the origin server is unable to determine a user agent's
898   capabilities from examining the request, and generally when public
899   caches are used to distribute server load and reduce network usage.
902   Agent-driven negotiation suffers from the disadvantage of needing a
903   second request to obtain the best alternate representation. This
904   second request is only efficient when caching is used. In addition,
905   this specification does not define any mechanism for supporting
906   automatic selection, though it also does not prevent any such
907   mechanism from being developed as an extension and used within
908   HTTP/1.1.
[745]911   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
[8]912   status codes for enabling agent-driven negotiation when the server is
913   unwilling or unable to provide a varying response using server-driven
914   negotiation.
[8]919<section title="Header Field Definitions" anchor="header.fields">
[117]921   This section defines the syntax and semantics of HTTP/1.1 header fields
922   related to the payload of messages.
[8]925<section title="Accept" anchor="header.accept">
[1120]926  <iref primary="true" item="Accept header field" x:for-anchor=""/>
927  <iref primary="true" item="Header Fields" subitem="Accept" x:for-anchor=""/>
[229]928  <x:anchor-alias value="Accept"/>
[370]929  <x:anchor-alias value="accept-ext"/>
[229]930  <x:anchor-alias value="accept-params"/>
931  <x:anchor-alias value="media-range"/>
[1163]933   The "Accept" header field can be used by user agents to specify
[994]934   response media types that are acceptable. Accept header fields can be used to
[698]935   indicate that the request is specifically limited to a small set of desired
936   types, as in the case of a request for an in-line image.
[1234]938<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"/>
939  <x:ref>Accept</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
[229]941  <x:ref>media-range</x:ref>    = ( "*/*"
[334]942                   / ( <x:ref>type</x:ref> "/" "*" )
943                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
[370]944                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
945  <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]946  <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> ]
949   The asterisk "*" character is used to group media types into ranges,
950   with "*/*" indicating all media types and "type/*" indicating all
951   subtypes of that type. The media-range &MAY; include media type
952   parameters that are applicable to that range.
955   Each media-range &MAY; be followed by one or more accept-params,
956   beginning with the "q" parameter for indicating a relative quality
957   factor. The first "q" parameter (if any) separates the media-range
958   parameter(s) from the accept-params. Quality factors allow the user
959   or user agent to indicate the relative degree of preference for that
[457]960   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
[8]961   default value is q=1.
964  <t>
965    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
966    parameters from Accept extension parameters is due to historical
967    practice. Although this prevents any media type parameter named
968    "q" from being used with a media range, such an event is believed
969    to be unlikely given the lack of any "q" parameters in the IANA
970    media type registry and the rare usage of any media type
971    parameters in Accept. Future media types are discouraged from
972    registering any parameter named "q".
973  </t>
976   The example
978<figure><artwork type="example">
[357]979  Accept: audio/*; q=0.2, audio/basic
982   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
[879]983   type if it is the best available after an 80% mark-down in quality".
986   If no Accept header field is present, then it is assumed that the
[1335]987   client accepts all media types. If an Accept header field is present in a
988   request, but the server cannot send a response which is acceptable, then
989   the server can either send a response in another format, or a 406 (Not
990   Acceptable) response.
993   A more elaborate example is
995<figure><artwork type="example">
[357]996  Accept: text/plain; q=0.5, text/html,
997          text/x-dvi; q=0.8, text/x-c
1000   Verbally, this would be interpreted as "text/html and text/x-c are
1001   the preferred media types, but if they do not exist, then send the
[866]1002   text/x-dvi representation, and if that does not exist, send the text/plain
[879]1003   representation".
1006   Media ranges can be overridden by more specific media ranges or
1007   specific media types. If more than one media range applies to a given
1008   type, the most specific reference has precedence. For example,
1010<figure><artwork type="example">
[1244]1011  Accept: text/*, text/plain, text/plain;format=flowed, */*
1014   have the following precedence:
[459]1015   <list style="numbers">
[1244]1016    <t>text/plain;format=flowed</t>
1017    <t>text/plain</t>
[459]1018    <t>text/*</t>
1019    <t>*/*</t>
1020   </list>
1023   The media type quality factor associated with a given type is
1024   determined by finding the media range with the highest precedence
1025   which matches that type. For example,
1027<figure><artwork type="example">
[357]1028  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1029          text/html;level=2;q=0.4, */*;q=0.5
1032   would cause the following values to be associated:
[459]1034<texttable align="left">
1035  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1036  <c>text/html;level=1</c>    <c>1</c>
1037  <c>text/html</c>            <c>0.7</c>
1038  <c>text/plain</c>           <c>0.3</c>
1039  <c>image/jpeg</c>           <c>0.5</c>
1040  <c>text/html;level=2</c>    <c>0.4</c>
1041  <c>text/html;level=3</c>    <c>0.7</c>
1044      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1045      values for certain media ranges. However, unless the user agent is
1046      a closed system which cannot interact with other rendering agents,
1047      this default set ought to be configurable by the user.
1051<section title="Accept-Charset" anchor="header.accept-charset">
[1120]1052  <iref primary="true" item="Accept-Charset header field" x:for-anchor=""/>
1053  <iref primary="true" item="Header Fields" subitem="Accept-Charset" x:for-anchor=""/>
[229]1054  <x:anchor-alias value="Accept-Charset"/>
[1163]1056   The "Accept-Charset" header field can be used by user agents to
[1176]1057   indicate what character encodings are acceptable in a response
1058   payload. This field allows
[8]1059   clients capable of understanding more comprehensive or special-purpose
[1176]1060   character encodings to signal that capability to a server which is capable of
1061   representing documents in those character encodings.
[1234]1063<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/>
1064  <x:ref>Accept-Charset</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
[376]1065                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
[1176]1068   Character encoding values (a.k.a., charsets) are described in
1069   <xref target="character.sets"/>. Each charset &MAY; be given an
1070   associated quality value which represents the user's preference
1071   for that charset. The default value is q=1. An example is
1073<figure><artwork type="example">
[357]1074  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1077   The special value "*", if present in the Accept-Charset field,
[1240]1078   matches every character encoding which is not mentioned elsewhere in the
1079   Accept-Charset field. If no "*" is present in an Accept-Charset field, then
1080   all character encodings not explicitly mentioned get a quality value of 0.
[994]1083   If no Accept-Charset header field is present, the default is that any
[1335]1084   character encoding is acceptable. If an Accept-Charset header field is
1085   present in a request, but the server cannot send a response which is
1086   acceptable, then the server can either use another character encoding, or
1087   send a 406 (Not Acceptable) response.
1091<section title="Accept-Encoding" anchor="header.accept-encoding">
[1120]1092  <iref primary="true" item="Accept-Encoding header field" x:for-anchor=""/>
1093  <iref primary="true" item="Header Fields" subitem="Accept-Encoding" x:for-anchor=""/>
[229]1094  <x:anchor-alias value="Accept-Encoding"/>
1095  <x:anchor-alias value="codings"/>
[1163]1097   The "Accept-Encoding" header field can be used by user agents to
[698]1098   indicate what response content-codings (<xref target="content.codings"/>)
1099   are acceptable in the response.
[1234]1101<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/>
1102  <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> ] )
1103  <x:ref>codings</x:ref>          = ( <x:ref>content-coding</x:ref> / "*" )
[248]1106   Each codings value &MAY; be given an associated quality value which
1107   represents the preference for that encoding. The default value is q=1.
[8]1110   Examples of its use are:
1112<figure><artwork type="example">
[357]1113  Accept-Encoding: compress, gzip
1114  Accept-Encoding:
1115  Accept-Encoding: *
1116  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1117  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1120   A server tests whether a content-coding is acceptable, according to
1121   an Accept-Encoding field, using these rules:
1122  <list style="numbers">
1123      <t>If the content-coding is one of the content-codings listed in
1124         the Accept-Encoding field, then it is acceptable, unless it is
[457]1125         accompanied by a qvalue of 0. (As defined in &qvalue;, a
[879]1126         qvalue of 0 means "not acceptable".)</t>
1128      <t>The special "*" symbol in an Accept-Encoding field matches any
1129         available content-coding not explicitly listed in the header
1130         field.</t>
1132      <t>If multiple content-codings are acceptable, then the acceptable
1133         content-coding with the highest non-zero qvalue is preferred.</t>
1135      <t>The "identity" content-coding is always acceptable, unless
1136         specifically refused because the Accept-Encoding field includes
1137         "identity;q=0", or because the field includes "*;q=0" and does
1138         not explicitly include the "identity" content-coding. If the
1139         Accept-Encoding field-value is empty, then only the "identity"
1140         encoding is acceptable.</t>
1141  </list>
[1335]1144   If an Accept-Encoding field is present in a request, but the server cannot
1145   send a response which is acceptable, then the server &SHOULD; send a
1146   response without any encoding (i.e., the "identity" encoding).
1149   If no Accept-Encoding field is present in a request, the server &MAY;
1150   assume that the client will accept any content coding. In this case,
1151   if "identity" is one of the available content-codings, then the
1152   server &SHOULD; use the "identity" content-coding, unless it has
1153   additional information that a different content-coding is meaningful
1154   to the client.
1157  <t>
1158    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1159    and if the "identity" content-coding is unavailable, then
1160    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1161    "gzip" and "compress") are preferred; some older clients
1162    improperly display messages sent with other content-codings.  The
1163    server might also make this decision based on information about
1164    the particular user-agent or client.
1165  </t>
1168  <t>
1169    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1170    associated with content-codings. This means that qvalues will not
1171    work and are not permitted with x-gzip or x-compress.
1172  </t>
1176<section title="Accept-Language" anchor="header.accept-language">
[1120]1177  <iref primary="true" item="Accept-Language header field" x:for-anchor=""/>
1178  <iref primary="true" item="Header Fields" subitem="Accept-Language" x:for-anchor=""/>
[229]1179  <x:anchor-alias value="Accept-Language"/>
1180  <x:anchor-alias value="language-range"/>
[1163]1182   The "Accept-Language" header field can be used by user agents to
[698]1183   indicate the set of natural languages that are preferred in the response.
1184   Language tags are defined in <xref target="language.tags"/>.
[1234]1186<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/>
1187  <x:ref>Accept-Language</x:ref> =
[370]1188                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
[1234]1189  <x:ref>language-range</x:ref>  =
[303]1190            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
[303]1193   Each language-range can be given an associated quality value which
[8]1194   represents an estimate of the user's preference for the languages
1195   specified by that range. The quality value defaults to "q=1". For
1196   example,
1198<figure><artwork type="example">
[357]1199  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1202   would mean: "I prefer Danish, but will accept British English and
[879]1203   other types of English".
[724]1204   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
[724]1207   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
1208   several matching schemes. Implementations can offer the most appropriate
1209   matching scheme for their requirements.
1212  <t>
[756]1213    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
[724]1214    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
1215    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
[563]1216  </t>
1219   It might be contrary to the privacy expectations of the user to send
[994]1220   an Accept-Language header field with the complete linguistic preferences of
[8]1221   the user in every request. For a discussion of this issue, see
[994]1222   <xref target=""/>.
1225   As intelligibility is highly dependent on the individual user, it is
1226   recommended that client applications make the choice of linguistic
1227   preference available to the user. If the choice is not made
1228   available, then the Accept-Language header field &MUST-NOT; be given in
1229   the request.
1232  <t>
1233    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1234    the user, we remind implementors of  the fact that users are not
1235    familiar with the details of language matching as described above,
[969]1236    and ought to be provided appropriate guidance. As an example, users
[563]1237    might assume that on selecting "en-gb", they will be served any
1238    kind of English document if British English is not available. A
1239    user agent might suggest in such a case to add "en" to get the
1240    best matching behavior.
1241  </t>
1245<section title="Content-Encoding" anchor="header.content-encoding">
[1120]1246  <iref primary="true" item="Content-Encoding header field" x:for-anchor=""/>
1247  <iref primary="true" item="Header Fields" subitem="Content-Encoding" x:for-anchor=""/>
[229]1248  <x:anchor-alias value="Content-Encoding"/>
[965]1250   The "Content-Encoding" header field indicates what content-codings
[866]1251   have been applied to the representation, and thus what decoding mechanisms
[698]1252   must be applied in order to obtain the media-type referenced by the
1253   Content-Type header field. Content-Encoding is primarily used to allow a
[866]1254   representation to be compressed without losing the identity of its underlying
[698]1255   media type.
[1234]1257<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/>
1258  <x:ref>Content-Encoding</x:ref> = 1#<x:ref>content-coding</x:ref>
1261   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1263<figure><artwork type="example">
[357]1264  Content-Encoding: gzip
[866]1267   The content-coding is a characteristic of the representation.
1268   Typically, the representation body is stored with this
[8]1269   encoding and is only decoded before rendering or analogous usage.
[1107]1270   However, a transforming proxy &MAY; modify the content-coding if the
[8]1271   new coding is known to be acceptable to the recipient, unless the
1272   "no-transform" cache-control directive is present in the message.
[866]1275   If the content-coding of a representation is not "identity", then the
1276   representation metadata &MUST; include a Content-Encoding header
1277   field (<xref target="header.content-encoding"/>)
[8]1278   that lists the non-identity content-coding(s) used.
[874]1281   If the content-coding of a representation in a request message is not
[8]1282   acceptable to the origin server, the server &SHOULD; respond with a
1283   status code of 415 (Unsupported Media Type).
[866]1286   If multiple encodings have been applied to a representation, the content
[8]1287   codings &MUST; be listed in the order in which they were applied.
1288   Additional information about the encoding parameters &MAY; be provided
[866]1289   by other header fields not defined by this specification.
1293<section title="Content-Language" anchor="header.content-language">
[1120]1294  <iref primary="true" item="Content-Language header field" x:for-anchor=""/>
1295  <iref primary="true" item="Header Fields" subitem="Content-Language" x:for-anchor=""/>
[229]1296  <x:anchor-alias value="Content-Language"/>
[965]1298   The "Content-Language" header field describes the natural
[866]1299   language(s) of the intended audience for the representation. Note that this might
[874]1300   not be equivalent to all the languages used within the representation.
[1234]1302<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/>
1303  <x:ref>Content-Language</x:ref> = 1#<x:ref>language-tag</x:ref>
1306   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1307   Content-Language is to allow a user to identify and differentiate
[866]1308   representations according to the user's own preferred language. Thus, if the
[8]1309   body content is intended only for a Danish-literate audience, the
1310   appropriate field is
1312<figure><artwork type="example">
[357]1313  Content-Language: da
1316   If no Content-Language is specified, the default is that the content
1317   is intended for all language audiences. This might mean that the
1318   sender does not consider it to be specific to any natural language,
1319   or that the sender does not know for which language it is intended.
1322   Multiple languages &MAY; be listed for content that is intended for
1323   multiple audiences. For example, a rendition of the "Treaty of
[879]1324   Waitangi", presented simultaneously in the original Maori and English
[8]1325   versions, would call for
1327<figure><artwork type="example">
[357]1328  Content-Language: mi, en
[866]1331   However, just because multiple languages are present within a representation
[8]1332   does not mean that it is intended for multiple linguistic audiences.
1333   An example would be a beginner's language primer, such as "A First
[879]1334   Lesson in Latin", which is clearly intended to be used by an
[8]1335   English-literate audience. In this case, the Content-Language would
1336   properly only include "en".
[1101]1339   Content-Language &MAY; be applied to any media type &mdash; it is not
[8]1340   limited to textual documents.
1344<section title="Content-Location" anchor="header.content-location">
[1120]1345  <iref primary="true" item="Content-Location header field" x:for-anchor=""/>
1346  <iref primary="true" item="Header Fields" subitem="Content-Location" x:for-anchor=""/>
[229]1347  <x:anchor-alias value="Content-Location"/>
[856]1349   The "Content-Location" header field supplies a URI that can be used
1350   as a specific identifier for the representation in this message.
1351   In other words, if one were to perform a GET on this URI at the time
1352   of this message's generation, then a 200 response would contain the
1353   same representation that is enclosed as payload in this message.
[1234]1355<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/>
1356  <x:ref>Content-Location</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
[972]1359   The Content-Location value is not a replacement for the effective
[856]1360   Request URI (&effective-request-uri;).  It is representation metadata.
1361   It has the same syntax and semantics as the header field of the same name
[858]1362   defined for MIME body parts in <xref target="RFC2557" x:fmt="of" x:sec="4"/>.
[856]1363   However, its appearance in an HTTP message has some special implications
1364   for HTTP recipients.
[856]1367   If Content-Location is included in a response message and its value
[965]1368   is the same as the effective request URI, then the response payload
[856]1369   &SHOULD; be considered the current representation of that resource.
1370   For a GET or HEAD request, this is the same as the default semantics
1371   when no Content-Location is provided by the server.  For a state-changing
[1161]1372   request like PUT or POST, it implies that the server's response contains
[856]1373   the new representation of that resource, thereby distinguishing it from
1374   representations that might only report about the action (e.g., "It worked!").
1375   This allows authoring applications to update their local copies without
1376   the need for a subsequent GET request.
[856]1379   If Content-Location is included in a response message and its value
[965]1380   differs from the effective request URI, then the origin server is
[856]1381   informing recipients that this representation has its own, presumably
1382   more specific, identifier.  For a GET or HEAD request, this is an
[965]1383   indication that the effective request URI identifies a resource that
[856]1384   is subject to content negotiation and the representation selected for
1385   this response can also be found at the identified URI.  For other
1386   methods, such a Content-Location indicates that this representation
1387   contains a report on the action's status and the same report is
1388   available (for future access with GET) at the given URI.  For
[1161]1389   example, a purchase transaction made via a POST request might
[856]1390   include a receipt document as the payload of the 200 response;
1391   the Content-Location value provides an identifier for retrieving
1392   a copy of that same receipt in the future.
1395   If Content-Location is included in a request message, then it &MAY;
1396   be interpreted by the origin server as an indication of where the
1397   user agent originally obtained the content of the enclosed
1398   representation (prior to any subsequent modification of the content
1399   by that user agent).  In other words, the user agent is providing
1400   the same representation metadata that it received with the original
1401   representation.  However, such interpretation &MUST-NOT; be used to
1402   alter the semantics of the method requested by the client.  For
1403   example, if a client makes a PUT request on a negotiated resource
1404   and the origin server accepts that PUT (without redirection), then the
1405   new set of values for that resource is expected to be consistent with
1406   the one representation supplied in that PUT; the Content-Location
1407   cannot be used as a form of reverse content selection that
1408   identifies only one of the negotiated representations to be updated.
1409   If the user agent had wanted the latter semantics, it would have applied
1410   the PUT directly to the Content-Location URI.
1413   A Content-Location field received in a request message is transitory
1414   information that &SHOULD-NOT; be saved with other representation
1415   metadata for use in later responses.  The Content-Location's value
1416   might be saved for use in other contexts, such as within source links
1417   or other metadata.
1420   A cache cannot assume that a representation with a Content-Location
[8]1421   different from the URI used to retrieve it can be used to respond to
[856]1422   later requests on that Content-Location URI.
[965]1425   If the Content-Location value is a partial URI, the partial URI is
1426   interpreted relative to the effective request URI.
1430<section title="Content-Type" anchor="header.content-type">
[1120]1431  <iref primary="true" item="Content-Type header field" x:for-anchor=""/>
1432  <iref primary="true" item="Header Fields" subitem="Content-Type" x:for-anchor=""/>
[229]1433  <x:anchor-alias value="Content-Type"/>
[965]1435   The "Content-Type" header field indicates the media type of the
[874]1436   representation. In the case of responses to the HEAD method, the media type is
[698]1437   that which would have been sent had the request been a GET.
[1234]1439<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/>
1440  <x:ref>Content-Type</x:ref> = <x:ref>media-type</x:ref>
1443   Media types are defined in <xref target="media.types"/>. An example of the field is
1445<figure><artwork type="example">
[357]1446  Content-Type: text/html; charset=ISO-8859-4
[965]1449   Further discussion of Content-Type is provided in <xref target=""/>.
[29]1455<section title="IANA Considerations" anchor="IANA.considerations">
[921]1456<section title="Header Field Registration" anchor="header.field.registration">
[969]1458   The Message Header Field Registry located at <eref target=""/> shall be updated
[290]1459   with the permanent registrations below (see <xref target="RFC3864"/>):
[680]1461<?BEGININC p3-payload.iana-headers ?>
[253]1462<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
[290]1463<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
[253]1464   <ttcol>Header Field Name</ttcol>
1465   <ttcol>Protocol</ttcol>
1466   <ttcol>Status</ttcol>
1467   <ttcol>Reference</ttcol>
1469   <c>Accept</c>
1470   <c>http</c>
1471   <c>standard</c>
1472   <c>
1473      <xref target="header.accept"/>
1474   </c>
1475   <c>Accept-Charset</c>
1476   <c>http</c>
1477   <c>standard</c>
1478   <c>
1479      <xref target="header.accept-charset"/>
1480   </c>
1481   <c>Accept-Encoding</c>
1482   <c>http</c>
1483   <c>standard</c>
1484   <c>
1485      <xref target="header.accept-encoding"/>
1486   </c>
1487   <c>Accept-Language</c>
1488   <c>http</c>
1489   <c>standard</c>
1490   <c>
1491      <xref target="header.accept-language"/>
1492   </c>
1493   <c>Content-Encoding</c>
1494   <c>http</c>
1495   <c>standard</c>
1496   <c>
1497      <xref target="header.content-encoding"/>
1498   </c>
1499   <c>Content-Language</c>
1500   <c>http</c>
1501   <c>standard</c>
1502   <c>
1503      <xref target="header.content-language"/>
1504   </c>
1505   <c>Content-Location</c>
1506   <c>http</c>
1507   <c>standard</c>
1508   <c>
1509      <xref target="header.content-location"/>
1510   </c>
1511   <c>Content-Type</c>
1512   <c>http</c>
1513   <c>standard</c>
1514   <c>
1515      <xref target="header.content-type"/>
1516   </c>
[291]1517   <c>MIME-Version</c>
1518   <c>http</c>
[937]1519   <c>standard</c>
[291]1520   <c>
1521      <xref target="mime-version"/>
1522   </c>
[680]1525<?ENDINC p3-payload.iana-headers ?>
[290]1527   The change controller is: "IETF ( - Internet Engineering Task Force".
[668]1531<section title="Content Coding Registry" anchor="content.coding.registration">
1533   The registration procedure for HTTP Content Codings is now defined
[670]1534   by <xref target="content.coding.registry"/> of this document.
1537   The HTTP Content Codings Registry located at <eref target=""/>
[969]1538   shall be updated with the registration below:
1540<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
[670]1541   <ttcol>Name</ttcol>
[668]1542   <ttcol>Description</ttcol>
1543   <ttcol>Reference</ttcol>
1544   <c>compress</c>
1545   <c>UNIX "compress" program method</c>
1546   <c>
[673]1547      &compress-coding;
[668]1548   </c>
1549   <c>deflate</c>
[806]1550   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1551   the "zlib" data format (<xref target="RFC1950"/>)
1552   </c>
[668]1553   <c>
[673]1554      &deflate-coding;
[668]1555   </c>
1556   <c>gzip</c>
1557   <c>Same as GNU zip <xref target="RFC1952"/></c>
1558   <c>
[673]1559      &gzip-coding;
[668]1560   </c>
1561   <c>identity</c>
1562   <c>No transformation</c>
1563   <c>
1564      <xref target="content.codings"/>
1565   </c>
[8]1571<section title="Security Considerations" anchor="security.considerations">
1573   This section is meant to inform application developers, information
1574   providers, and users of the security limitations in HTTP/1.1 as
1575   described by this document. The discussion does not include
1576   definitive solutions to the problems revealed, though it does make
1577   some suggestions for reducing security risks.
[994]1580<section title="Privacy Issues Connected to Accept Header Fields" anchor="">
[1163]1582   Accept headers fields can reveal information about the user to all
[994]1583   servers which are accessed. The Accept-Language header field in particular
[8]1584   can reveal information the user would consider to be of a private
1585   nature, because the understanding of particular languages is often
1586   strongly correlated to the membership of a particular ethnic group.
1587   User agents which offer the option to configure the contents of an
[994]1588   Accept-Language header field to be sent in every request are strongly
[8]1589   encouraged to let the configuration process include a message which
1590   makes the user aware of the loss of privacy involved.
1593   An approach that limits the loss of privacy would be for a user agent
[994]1594   to omit the sending of Accept-Language header fields by default, and to ask
1595   the user whether or not to start sending Accept-Language header fields to a
[1163]1596   server if it detects, by looking for any Vary header fields
[8]1597   generated by the server, that such sending could improve the quality
1598   of service.
1601   Elaborate user-customized accept header fields sent in every request,
1602   in particular if these include quality values, can be used by servers
1603   as relatively reliable and long-lived user identifiers. Such user
1604   identifiers would allow content providers to do click-trail tracking,
1605   and would allow collaborating content providers to match cross-server
1606   click-trails or form submissions of individual users. Note that for
1607   many users not behind a proxy, the network address of the host
1608   running the user agent will also serve as a long-lived user
1609   identifier. In environments where proxies are used to enhance
1610   privacy, user agents ought to be conservative in offering accept
1611   header configuration options to end users. As an extreme privacy
[994]1612   measure, proxies could filter the accept header fields in relayed requests.
[8]1613   General purpose user agents which provide a high degree of header
1614   configurability &SHOULD; warn users about the loss of privacy which can
1615   be involved.
[1364]1621<section title="Acknowledgments" anchor="acks">
1623  See &acks;.
[119]1629<references title="Normative References">
[31]1631<reference anchor="Part1">
[119]1632  <front>
1633    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1634    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]1635      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1636      <address><email></email></address>
1637    </author>
1638    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1639      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1640      <address><email></email></address>
[119]1641    </author>
1642    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1643      <organization abbrev="HP">Hewlett-Packard Company</organization>
1644      <address><email></email></address>
1645    </author>
1646    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1647      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1648      <address><email></email></address>
1649    </author>
1650    <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]1651      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1652      <address><email></email></address>
1653    </author>
1654    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1655      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1656      <address><email></email></address>
1657    </author>
1658    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1659      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1660      <address><email></email></address>
1661    </author>
1662    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1663      <organization abbrev="W3C">World Wide Web Consortium</organization>
1664      <address><email></email></address>
1665    </author>
1666    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1667      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1668      <address><email></email></address>
1669    </author>
1670    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1671  </front>
1672  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1673  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1676<reference anchor="Part2">
[119]1677  <front>
1678    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1679    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]1680      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1681      <address><email></email></address>
1682    </author>
1683    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1684      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1685      <address><email></email></address>
[119]1686    </author>
1687    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1688      <organization abbrev="HP">Hewlett-Packard Company</organization>
1689      <address><email></email></address>
1690    </author>
1691    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1692      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1693      <address><email></email></address>
1694    </author>
1695    <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]1696      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1697      <address><email></email></address>
1698    </author>
1699    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1700      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1701      <address><email></email></address>
1702    </author>
1703    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1704      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1705      <address><email></email></address>
1706    </author>
1707    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1708      <organization abbrev="W3C">World Wide Web Consortium</organization>
1709      <address><email></email></address>
1710    </author>
1711    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1712      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1713      <address><email></email></address>
1714    </author>
1715    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1716  </front>
1717  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1718  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1721<reference anchor="Part4">
[119]1722  <front>
1723    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1724    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]1725      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1726      <address><email></email></address>
1727    </author>
1728    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1729      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1730      <address><email></email></address>
[119]1731    </author>
1732    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1733      <organization abbrev="HP">Hewlett-Packard Company</organization>
1734      <address><email></email></address>
1735    </author>
1736    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1737      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1738      <address><email></email></address>
1739    </author>
1740    <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]1741      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1742      <address><email></email></address>
1743    </author>
1744    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1745      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1746      <address><email></email></address>
1747    </author>
1748    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1749      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1750      <address><email></email></address>
1751    </author>
1752    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1753      <organization abbrev="W3C">World Wide Web Consortium</organization>
1754      <address><email></email></address>
1755    </author>
1756    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1757      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1758      <address><email></email></address>
1759    </author>
1760    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1761  </front>
1762  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1763  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1766<reference anchor="Part5">
[119]1767  <front>
1768    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1769    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]1770      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1771      <address><email></email></address>
1772    </author>
1773    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1774      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1775      <address><email></email></address>
[119]1776    </author>
1777    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1778      <organization abbrev="HP">Hewlett-Packard Company</organization>
1779      <address><email></email></address>
1780    </author>
1781    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1782      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1783      <address><email></email></address>
1784    </author>
1785    <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]1786      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1787      <address><email></email></address>
1788    </author>
1789    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1790      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1791      <address><email></email></address>
1792    </author>
1793    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1794      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1795      <address><email></email></address>
1796    </author>
1797    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1798      <organization abbrev="W3C">World Wide Web Consortium</organization>
1799      <address><email></email></address>
1800    </author>
1801    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1802      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1803      <address><email></email></address>
1804    </author>
1805    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1806  </front>
1807  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1808  <x:source href="p5-range.xml" basename="p5-range"/>
1811<reference anchor="Part6">
[119]1812  <front>
1813    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1814    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]1815      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1816      <address><email></email></address>
1817    </author>
1818    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1819      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1820      <address><email></email></address>
[119]1821    </author>
1822    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1823      <organization abbrev="HP">Hewlett-Packard Company</organization>
1824      <address><email></email></address>
1825    </author>
1826    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1827      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1828      <address><email></email></address>
1829    </author>
1830    <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]1831      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]1832      <address><email></email></address>
1833    </author>
1834    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1835      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1836      <address><email></email></address>
1837    </author>
1838    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1839      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1840      <address><email></email></address>
1841    </author>
1842    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1843      <organization abbrev="W3C">World Wide Web Consortium</organization>
1844      <address><email></email></address>
1845    </author>
[601]1846    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1847      <address><email></email></address>
1848    </author>
[119]1849    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1850      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1851      <address><email></email></address>
1852    </author>
1853    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1854  </front>
1855  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1856  <x:source href="p6-cache.xml" basename="p6-cache"/>
[122]1859<reference anchor="RFC1950">
1860  <front>
1861    <title>ZLIB Compressed Data Format Specification version 3.3</title>
1862    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1863      <organization>Aladdin Enterprises</organization>
1864      <address><email></email></address>
1865    </author>
[713]1866    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
[122]1867    <date month="May" year="1996"/>
1868  </front>
1869  <seriesInfo name="RFC" value="1950"/>
1870  <annotation>
[908]1871    RFC 1950 is an Informational RFC, thus it might be less stable than
[122]1872    this specification. On the other hand, this downward reference was
[277]1873    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1874    therefore it is unlikely to cause problems in practice. See also
1875    <xref target="BCP97"/>.
[122]1876  </annotation>
[806]1879<reference anchor="RFC1951">
1880  <front>
1881    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
1882    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1883      <organization>Aladdin Enterprises</organization>
1884      <address><email></email></address>
1885    </author>
1886    <date month="May" year="1996"/>
1887  </front>
1888  <seriesInfo name="RFC" value="1951"/>
1889  <annotation>
[908]1890    RFC 1951 is an Informational RFC, thus it might be less stable than
[806]1891    this specification. On the other hand, this downward reference was
1892    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1893    therefore it is unlikely to cause problems in practice. See also
1894    <xref target="BCP97"/>.
1895  </annotation>
[122]1898<reference anchor="RFC1952">
1899  <front>
1900    <title>GZIP file format specification version 4.3</title>
1901    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1902      <organization>Aladdin Enterprises</organization>
1903      <address><email></email></address>
1904    </author>
1905    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1906      <address><email></email></address>
1907    </author>
1908    <author initials="M." surname="Adler" fullname="Mark Adler">
1909      <address><email></email></address>
1910    </author>
1911    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1912      <address><email></email></address>
1913    </author>
1914    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
1915      <address><email></email></address>
1916    </author>
1917    <date month="May" year="1996"/>
1918  </front>
1919  <seriesInfo name="RFC" value="1952"/>
1920  <annotation>
[908]1921    RFC 1952 is an Informational RFC, thus it might be less stable than
[122]1922    this specification. On the other hand, this downward reference was
[277]1923    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
1924    therefore it is unlikely to cause problems in practice. See also
1925    <xref target="BCP97"/>.
[122]1926  </annotation>
[131]1929<reference anchor="RFC2045">
1930  <front>
1931    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
1932    <author initials="N." surname="Freed" fullname="Ned Freed">
1933      <organization>Innosoft International, Inc.</organization>
1934      <address><email></email></address>
1935    </author>
1936    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1937      <organization>First Virtual Holdings</organization>
1938      <address><email></email></address>
1939    </author>
1940    <date month="November" year="1996"/>
1941  </front>
1942  <seriesInfo name="RFC" value="2045"/>
1945<reference anchor="RFC2046">
1946  <front>
1947    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
1948    <author initials="N." surname="Freed" fullname="Ned Freed">
1949      <organization>Innosoft International, Inc.</organization>
1950      <address><email></email></address>
1951    </author>
1952    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1953      <organization>First Virtual Holdings</organization>
1954      <address><email></email></address>
1955    </author>
1956    <date month="November" year="1996"/>
1957  </front>
1958  <seriesInfo name="RFC" value="2046"/>
[119]1961<reference anchor="RFC2119">
1962  <front>
1963    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
1964    <author initials="S." surname="Bradner" fullname="Scott Bradner">
1965      <organization>Harvard University</organization>
1966      <address><email></email></address>
1967    </author>
1968    <date month="March" year="1997"/>
1969  </front>
1970  <seriesInfo name="BCP" value="14"/>
1971  <seriesInfo name="RFC" value="2119"/>
[303]1974<reference anchor='RFC4647'>
1975  <front>
1976    <title>Matching of Language Tags</title>
1977    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
1978      <organization>Yahoo! Inc.</organization>
1979      <address><email></email></address>
1980    </author>
1981    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
1982      <organization>Google</organization>
1983      <address><email></email></address>
1984    </author>
1985    <date year='2006' month='September' />
1986  </front>
1987  <seriesInfo name='BCP' value='47' />
1988  <seriesInfo name='RFC' value='4647' />
[425]1991<reference anchor="RFC5234">
1992  <front>
1993    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
1994    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
1995      <organization>Brandenburg InternetWorking</organization>
1996      <address>
[728]1997        <email></email>
1998      </address> 
[425]1999    </author>
2000    <author initials="P." surname="Overell" fullname="Paul Overell">
2001      <organization>THUS plc.</organization>
2002      <address>
[728]2003        <email></email>
2004      </address>
[425]2005    </author>
2006    <date month="January" year="2008"/>
2007  </front>
2008  <seriesInfo name="STD" value="68"/>
2009  <seriesInfo name="RFC" value="5234"/>
[690]2012<reference anchor='RFC5646'>
[613]2013  <front>
2014    <title>Tags for Identifying Languages</title>
2015    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
2016      <organization>Lab126</organization>
2017      <address><email></email></address>
2018    </author>
2019    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
2020      <organization>Google</organization>
2021      <address><email></email></address>
2022    </author>
[690]2023    <date month='September' year='2009' />
[613]2024  </front>
[690]2025  <seriesInfo name='BCP' value='47' />
2026  <seriesInfo name='RFC' value='5646' />
2031<references title="Informative References">
[129]2033<reference anchor="RFC1945">
2034  <front>
2035    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2036    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2037      <organization>MIT, Laboratory for Computer Science</organization>
2038      <address><email></email></address>
2039    </author>
2040    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2041      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2042      <address><email></email></address>
2043    </author>
2044    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2045      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2046      <address><email></email></address>
2047    </author>
2048    <date month="May" year="1996"/>
2049  </front>
2050  <seriesInfo name="RFC" value="1945"/>
2053<reference anchor="RFC2049">
2054  <front>
2055    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2056    <author initials="N." surname="Freed" fullname="Ned Freed">
2057      <organization>Innosoft International, Inc.</organization>
2058      <address><email></email></address>
2059    </author>
2060    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2061      <organization>First Virtual Holdings</organization>
2062      <address><email></email></address>
2063    </author>
2064    <date month="November" year="1996"/>
2065  </front>
2066  <seriesInfo name="RFC" value="2049"/>
[133]2069<reference anchor="RFC2068">
2070  <front>
2071    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2072    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2073      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2074      <address><email></email></address>
2075    </author>
2076    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2077      <organization>MIT Laboratory for Computer Science</organization>
2078      <address><email></email></address>
2079    </author>
2080    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2081      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2082      <address><email></email></address>
2083    </author>
2084    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2085      <organization>MIT Laboratory for Computer Science</organization>
2086      <address><email></email></address>
2087    </author>
2088    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2089      <organization>MIT Laboratory for Computer Science</organization>
2090      <address><email></email></address>
2091    </author>
2092    <date month="January" year="1997"/>
2093  </front>
2094  <seriesInfo name="RFC" value="2068"/>
[129]2097<reference anchor="RFC2076">
2098  <front>
2099    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2100    <author initials="J." surname="Palme" fullname="Jacob Palme">
2101      <organization>Stockholm University/KTH</organization>
2102      <address><email></email></address>
2103    </author>
2104    <date month="February" year="1997"/>
2105  </front>
2106  <seriesInfo name="RFC" value="2076"/>
2109<reference anchor="RFC2277">
2110  <front>
2111    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2112    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2113      <organization>UNINETT</organization>
2114      <address><email></email></address>
2115    </author>
2116    <date month="January" year="1998"/>
2117  </front>
2118  <seriesInfo name="BCP" value="18"/>
2119  <seriesInfo name="RFC" value="2277"/>
[745]2122<reference anchor='RFC2295'>
2123  <front>
2124    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
2125    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
2126      <organization>Technische Universiteit Eindhoven</organization>
2127      <address>
2128        <email></email>
2129      </address>
2130    </author>
2131    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
2132      <organization>Hewlett-Packard Company</organization>
2133      <address>
2134        <email></email>
2135      </address>
2136    </author>
2137    <date year='1998' month='March'/>
2138  </front>
2139  <seriesInfo name='RFC' value='2295'/>
[129]2142<reference anchor="RFC2388">
2143  <front>
2144    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2145    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2146      <organization>Xerox Palo Alto Research Center</organization>
2147      <address><email></email></address>
2148    </author>
2149    <date year="1998" month="August"/>
2150  </front>
2151  <seriesInfo name="RFC" value="2388"/>
2154<reference anchor="RFC2557">
2155  <front>
2156    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2157    <author initials="F." surname="Palme" fullname="Jacob Palme">
2158      <organization>Stockholm University and KTH</organization>
2159      <address><email></email></address>
2160    </author>
2161    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2162      <organization>Microsoft Corporation</organization>
2163      <address><email></email></address>
2164    </author>
2165    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2166      <organization>Lotus Development Corporation</organization>
2167      <address><email></email></address>
2168    </author>
2169    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2170      <address><email></email></address>
2171    </author>
2172    <date year="1999" month="March"/>
2173  </front>
2174  <seriesInfo name="RFC" value="2557"/>
[119]2177<reference anchor="RFC2616">
2178  <front>
2179    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2180    <author initials="R." surname="Fielding" fullname="R. Fielding">
2181      <organization>University of California, Irvine</organization>
2182      <address><email></email></address>
2183    </author>
2184    <author initials="J." surname="Gettys" fullname="J. Gettys">
2185      <organization>W3C</organization>
2186      <address><email></email></address>
2187    </author>
2188    <author initials="J." surname="Mogul" fullname="J. Mogul">
2189      <organization>Compaq Computer Corporation</organization>
2190      <address><email></email></address>
2191    </author>
2192    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2193      <organization>MIT Laboratory for Computer Science</organization>
2194      <address><email></email></address>
2195    </author>
2196    <author initials="L." surname="Masinter" fullname="L. Masinter">
2197      <organization>Xerox Corporation</organization>
2198      <address><email></email></address>
2199    </author>
2200    <author initials="P." surname="Leach" fullname="P. Leach">
2201      <organization>Microsoft Corporation</organization>
2202      <address><email></email></address>
2203    </author>
2204    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2205      <organization>W3C</organization>
2206      <address><email></email></address>
2207    </author>
2208    <date month="June" year="1999"/>
2209  </front>
2210  <seriesInfo name="RFC" value="2616"/>
[129]2213<reference anchor="RFC3629">
2214  <front>
2215    <title>UTF-8, a transformation format of ISO 10646</title>
2216    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2217      <organization>Alis Technologies</organization>
2218      <address><email></email></address>
2219    </author>
2220    <date month="November" year="2003"/>
2221  </front>
[1003]2222  <seriesInfo name="STD" value="63"/>
[129]2223  <seriesInfo name="RFC" value="3629"/>
[253]2226<reference anchor='RFC3864'>
2227  <front>
2228    <title>Registration Procedures for Message Header Fields</title>
2229    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2230      <organization>Nine by Nine</organization>
2231      <address><email></email></address>
2232    </author>
2233    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2234      <organization>BEA Systems</organization>
2235      <address><email></email></address>
2236    </author>
2237    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2238      <organization>HP Labs</organization>
2239      <address><email></email></address>
2240    </author>
2241    <date year='2004' month='September' />
2242  </front>
2243  <seriesInfo name='BCP' value='90' />
2244  <seriesInfo name='RFC' value='3864' />
[200]2247<reference anchor="RFC4288">
2248  <front>
2249    <title>Media Type Specifications and Registration Procedures</title>
2250    <author initials="N." surname="Freed" fullname="N. Freed">
2251      <organization>Sun Microsystems</organization>
2252      <address>
2253        <email></email>
2254      </address>
2255    </author>
2256    <author initials="J." surname="Klensin" fullname="J. Klensin">
2257      <address>
2258        <email></email>
2259      </address>
2260    </author>
2261    <date year="2005" month="December"/>
2262  </front>
2263  <seriesInfo name="BCP" value="13"/>
2264  <seriesInfo name="RFC" value="4288"/>
[670]2267<reference anchor='RFC5226'>
2268  <front>
2269    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2270    <author initials='T.' surname='Narten' fullname='T. Narten'>
2271      <organization>IBM</organization>
2272      <address><email></email></address>
2273    </author>
2274    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
2275      <organization>Google</organization>
2276      <address><email></email></address>
2277    </author>
2278    <date year='2008' month='May' />
2279  </front>
2280  <seriesInfo name='BCP' value='26' />
2281  <seriesInfo name='RFC' value='5226' />
[327]2284<reference anchor="RFC5322">
2285  <front>
2286    <title>Internet Message Format</title>
2287    <author initials="P." surname="Resnick" fullname="P. Resnick">
2288      <organization>Qualcomm Incorporated</organization>
2289    </author>
2290    <date year="2008" month="October"/>
2291  </front> 
2292  <seriesInfo name="RFC" value="5322"/>
[1267]2295<reference anchor="RFC6151">
2296  <front>
2297    <title>Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms</title>
2298    <author initials="S." surname="Turner" fullname="S. Turner"/>
2299    <author initials="L." surname="Chen" fullname="L. Chen"/>
2300    <date year="2011" month="March" />
[1308]2301  </front>
[1267]2302  <seriesInfo name="RFC" value="6151" />
[277]2305<reference anchor='BCP97'>
2306  <front>
2307    <title>Handling Normative References to Standards-Track Documents</title>
2308    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2309      <address>
2310        <email></email>
2311      </address>
2312    </author>
2313    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2314      <organization>MIT</organization>
2315      <address>
2316        <email></email>
2317      </address>
2318    </author>
2319    <date year='2007' month='June' />
2320  </front>
2321  <seriesInfo name='BCP' value='97' />
2322  <seriesInfo name='RFC' value='4897' />
[1307]2325<reference anchor="RFC6266">
[1308]2326  <front>
[1259]2327    <title abbrev="Content-Disposition in HTTP">Use of the Content-Disposition Header Field
2328    in the Hypertext Transfer Protocol (HTTP)</title>
2329    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
2330      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2331      <address>
[1308]2332        <email></email>
[1259]2333      </address>
2334    </author>
[1307]2335    <date month="June" year="2011"/>
[1259]2336  </front>
[1307]2337  <seriesInfo name='RFC' value='6266' />
[874]2342<section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
[327]2344   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]2345   allow a message-body to be transmitted in an open variety of
[8]2346   representations and with extensible mechanisms. However, RFC 2045
2347   discusses mail, and HTTP has a few features that are different from
[874]2348   those described in MIME. These differences were carefully chosen
[8]2349   to optimize performance over binary connections, to allow greater
2350   freedom in the use of new media types, to make date comparisons
2351   easier, and to acknowledge the practice of some early HTTP servers
2352   and clients.
[874]2355   This appendix describes specific areas where HTTP differs from MIME.
2356   Proxies and gateways to strict MIME environments &SHOULD; be
[8]2357   aware of these differences and provide the appropriate conversions
2358   where necessary. Proxies and gateways from MIME environments to HTTP
2359   also need to be aware of the differences because some conversions
2360   might be required.
[8]2363<section title="MIME-Version" anchor="mime-version">
[1120]2364  <iref primary="true" item="MIME-Version header field" x:for-anchor=""/>
2365  <iref primary="true" item="Header Fields" subitem="MIME-Version" x:for-anchor=""/>
[229]2366  <x:anchor-alias value="MIME-Version"/>
2368   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
[1163]2369   include a single MIME-Version header field to indicate what
[8]2370   version of the MIME protocol was used to construct the message. Use
2371   of the MIME-Version header field indicates that the message is in
[115]2372   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
[8]2373   Proxies/gateways are responsible for ensuring full compliance (where
2374   possible) when exporting HTTP messages to strict MIME environments.
[1234]2376<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/>
2377  <x:ref>MIME-Version</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2380   MIME version "1.0" is the default for use in HTTP/1.1. However,
2381   HTTP/1.1 message parsing and semantics are defined by this document
2382   and not the MIME specification.
2386<section title="Conversion to Canonical Form" anchor="">
[874]2388   MIME requires that an Internet mail body-part be converted to
[115]2389   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
[97]2390   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
[8]2391   allowed for subtypes of the "text" media type when transmitted over
[97]2392   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
[8]2393   line breaks as CRLF and forbids the use of CR or LF outside of line
2394   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2395   line break within text content when a message is transmitted over
2396   HTTP.
2399   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2400   environment &SHOULD; translate all line breaks within the text media
[1176]2401   types described in <xref target="canonicalization.and.text.defaults"/>
2402   of this document to the RFC 2049
[8]2403   canonical form of CRLF. Note, however, that this might be complicated
2404   by the presence of a Content-Encoding and by the fact that HTTP
[1176]2405   allows the use of some character encodings which do not use octets 13 and
2406   10 to represent CR and LF, respectively, as is the case for some multi-byte
2407   character encodings.
[969]2410   Conversion will break any cryptographic
[8]2411   checksums applied to the original content unless the original content
2412   is already in canonical form. Therefore, the canonical form is
2413   recommended for any content that uses such checksums in HTTP.
2418<section title="Conversion of Date Formats" anchor="">
2420   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2421   simplify the process of date comparison. Proxies and gateways from
2422   other protocols &SHOULD; ensure that any Date header field present in a
2423   message conforms to one of the HTTP/1.1 formats and rewrite the date
2424   if necessary.
[8]2428<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
[874]2430   MIME does not include any concept equivalent to HTTP/1.1's
[8]2431   Content-Encoding header field. Since this acts as a modifier on the
2432   media type, proxies and gateways from HTTP to MIME-compliant
2433   protocols &MUST; either change the value of the Content-Type header
[874]2434   field or decode the representation before forwarding the message. (Some
[8]2435   experimental applications of Content-Type for Internet mail have used
2436   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2437   a function equivalent to Content-Encoding. However, this parameter is
[874]2438   not part of the MIME standards).
2442<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
[874]2444   HTTP does not use the Content-Transfer-Encoding field of MIME.
2445   Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
[85]2446   remove any Content-Transfer-Encoding
[8]2447   prior to delivering the response message to an HTTP client.
2450   Proxies and gateways from HTTP to MIME-compliant protocols are
2451   responsible for ensuring that the message is in the correct format
2452   and encoding for safe transport on that protocol, where "safe
2453   transport" is defined by the limitations of the protocol being used.
2454   Such a proxy or gateway &SHOULD; label the data with an appropriate
2455   Content-Transfer-Encoding if doing so will improve the likelihood of
2456   safe transport over the destination protocol.
2460<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
[29]2462   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
[8]2463   Proxies/gateways &MUST; remove any transfer-coding prior to
2464   forwarding a message via a MIME-compliant protocol.
2468<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
[129]2470   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
[8]2471   need to be aware of MIME line length limitations. Since HTTP does not
2472   have this limitation, HTTP does not fold long lines. MHTML messages
2473   being transported by HTTP follow all conventions of MHTML, including
2474   line length limitations and folding, canonicalization, etc., since
2475   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2476   does not interpret the content or any MIME header lines that might be
2477   contained therein.
2482<section title="Additional Features" anchor="additional.features">
[97]2484   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
[8]2485   existing HTTP implementations, but not consistently and correctly
2486   across most HTTP/1.1 applications. Implementors are advised to be
2487   aware of these features, but cannot rely upon their presence in, or
2488   interoperability with, other HTTP/1.1 applications. Some of these
2489   describe proposed experimental features, and some describe features
2490   that experimental deployment found lacking that are now addressed in
2491   the base HTTP/1.1 specification.
[994]2494   A number of other header fields, such as Content-Disposition and Title,
[1307]2495   from SMTP and MIME are also often implemented (see <xref target="RFC6266"/>
2496   and <xref target="RFC2076"/>).
[99]2500<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2502  Clarify contexts that charset is used in.
2503  (<xref target="character.sets"/>)
[1240]2506  Remove the default character encoding for text media types; the default
2507  now is whatever the media type definition says.
2508  (<xref target="canonicalization.and.text.defaults"/>)
[1234]2511  Change ABNF productions for header fields to only define the field value.
2512  (<xref target="header.fields"/>)
[1308]2515  Remove definition of Content-MD5 header field because it was inconsistently
2516  implemented with respect to partial responses, and also because of known
2517  deficiencies in the hash algorithm itself (see <xref target="RFC6151"/> for details).
[1267]2518  (<xref target="header.fields"/>)
[1240]2521  Remove ISO-8859-1 special-casing in Accept-Charset.
2522  (<xref target="header.accept-charset"/>)
[712]2525  Remove base URI setting semantics for Content-Location due to poor
[714]2526  implementation support, which was caused by too many broken servers emitting
[994]2527  bogus Content-Location header fields, and also the potentially undesirable effect
[714]2528  of potentially breaking relative links in content-negotiated resources.
[712]2529  (<xref target="header.content-location"/>)
[1308]2532  Remove discussion of Content-Disposition header field, it is now defined
2533  by <xref target="RFC6266"/>.
[1259]2534  (<xref target="additional.features"/>)
[104]2537  Remove reference to non-existant identity transfer-coding value tokens.
2538  (<xref target="no.content-transfer-encoding"/>)
[680]2542<?BEGININC p3-payload.abnf-appendix ?>
[427]2543<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
2545<artwork type="abnf" name="p3-payload.parsed-abnf">
[1234]2546<x:ref>Accept</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
2547 OWS media-range [ accept-params ] ] ) ]
2548<x:ref>Accept-Charset</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
[425]2549 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2550 qvalue ] ] )
[1234]2551<x:ref>Accept-Encoding</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] ) )
2552 *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
2553<x:ref>Accept-Language</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
[425]2554 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2555 ] )
[1234]2557<x:ref>Content-Encoding</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
[425]2558 content-coding ] )
[1234]2559<x:ref>Content-Language</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
[425]2560 language-tag ] )
[1234]2561<x:ref>Content-Location</x:ref> = absolute-URI / partial-URI
2562<x:ref>Content-Type</x:ref> = media-type
[1234]2564<x:ref>MIME-Version</x:ref> = 1*DIGIT "." 1*DIGIT
2566<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
[1318]2568<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
[810]2569<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" word ]
[427]2570<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2571<x:ref>attribute</x:ref> = token
2573<x:ref>charset</x:ref> = token
2574<x:ref>codings</x:ref> = ( content-coding / "*" )
2575<x:ref>content-coding</x:ref> = token
[427]2577<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
[690]2578<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC5646], Section 2.1&gt;
2580<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
[425]2581 ";" OWS parameter )
[427]2582<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2584<x:ref>parameter</x:ref> = attribute "=" value
[1318]2585<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
[678]2587<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 6.4&gt;
2589<x:ref>subtype</x:ref> = token
2591<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2592<x:ref>type</x:ref> = token
[810]2594<x:ref>value</x:ref> = word
2596<x:ref>word</x:ref> = &lt;word, defined in [Part1], Section 1.2.2&gt;
[532]2599<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2600; Accept defined but not used
[425]2601; Accept-Charset defined but not used
2602; Accept-Encoding defined but not used
2603; Accept-Language defined but not used
[968]2604; Content-Encoding defined but not used
2605; Content-Language defined but not used
2606; Content-Location defined but not used
2607; Content-Type defined but not used
[425]2608; MIME-Version defined but not used
[680]2610<?ENDINC p3-payload.abnf-appendix ?>
[252]2612<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
[1002]2614<section title="Since RFC 2616">
2616  Extracted relevant partitions from <xref target="RFC2616"/>.
2620<section title="Since draft-ietf-httpbis-p3-payload-00">
[116]2622  Closed issues:
2623  <list style="symbols"> 
2624    <t>
[324]2625      <eref target=""/>:
[116]2626      "Media Type Registrations"
2627      (<eref target=""/>)
2628    </t>
2629    <t>
[324]2630      <eref target=""/>:
[116]2631      "Clarification regarding quoting of charset values"
2632      (<eref target=""/>)
2633    </t>
2634    <t>
[324]2635      <eref target=""/>:
[116]2636      "Remove 'identity' token references"
2637      (<eref target=""/>)
2638    </t>
2639    <t>
[324]2640      <eref target=""/>:
[126]2641      "Accept-Encoding BNF"
2642    </t>
2643    <t>
[324]2644      <eref target=""/>:
[152]2645      "Normative and Informative references"
2646    </t>
2647    <t>
[324]2648      <eref target=""/>:
[116]2649      "RFC1700 references"
2650    </t>
[122]2651    <t>
[324]2652      <eref target=""/>:
[200]2653      "Updating to RFC4288"
2654    </t>
2655    <t>
[324]2656      <eref target=""/>:
[129]2657      "Informative references"
2658    </t>
2659    <t>
[324]2660      <eref target=""/>:
[123]2661      "ISO-8859-1 Reference"
2662    </t>
2663    <t>
[324]2664      <eref target=""/>:
[122]2665      "Encoding References Normative"
2666    </t>
[131]2667    <t>
[324]2668      <eref target=""/>:
[131]2669      "Normative up-to-date references"
2670    </t>
[116]2671  </list>
[170]2675<section title="Since draft-ietf-httpbis-p3-payload-01">
[324]2677  Ongoing work on ABNF conversion (<eref target=""/>):
[205]2678  <list style="symbols"> 
2679    <t>
2680      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2681    </t>
2682  </list>
[252]2686<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
[232]2688  Closed issues:
2689  <list style="symbols"> 
2690    <t>
[324]2691      <eref target=""/>:
[251]2692      "Quoting Charsets"
2693    </t>
2694    <t>
[324]2695      <eref target=""/>:
[232]2696      "Classification for Allow header"
2697    </t>
[248]2698    <t>
[324]2699      <eref target=""/>:
[248]2700      "missing default for qvalue in description of Accept-Encoding"
2701    </t>
[232]2702  </list>
[994]2705  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
[253]2706  <list style="symbols"> 
2707    <t>
[994]2708      Reference RFC 3984, and update header field registrations for headers defined
[253]2709      in this document.
2710    </t>
2711  </list>
[267]2715<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
[269]2717  Closed issues:
2718  <list style="symbols"> 
2719    <t>
[297]2720      <eref target=""/>:
2721      "Quoting Charsets"
2722    </t>
2723    <t>
[303]2724      <eref target=""/>:
2725      "language tag matching (Accept-Language) vs RFC4647"
2726    </t>
2727    <t>
[277]2728      <eref target=""/>:
[269]2729      "RFC 1806 has been replaced by RFC2183"
2730    </t>
2731  </list>
2734  Other changes:
2735  <list style="symbols"> 
2736    <t>
2737      <eref target=""/>:
[1101]2738      "Encoding References Normative" &mdash; rephrase the annotation and reference
[277]2739      <xref target="BCP97"/>.
2740    </t>
2741  </list>
[269]2743 </section>
[323]2745<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
[327]2747  Closed issues:
2748  <list style="symbols"> 
2749    <t>
2750      <eref target=""/>:
2751      "RFC 2822 is updated by RFC 5322"
2752    </t>
2753  </list>
2756  Ongoing work on ABNF conversion (<eref target=""/>):
2757  <list style="symbols"> 
2758    <t>
2759      Use "/" instead of "|" for alternatives.
2760    </t>
[357]2761    <t>
2762      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2763      whitespace ("OWS") and required whitespace ("RWS").
2764    </t>
2765    <t>
2766      Rewrite ABNFs to spell out whitespace rules, factor out
[994]2767      header field value format definitions.
[357]2768    </t>
[334]2769  </list>
[382]2773<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
[385]2775  Closed issues:
2776  <list style="symbols"> 
2777    <t>
2778      <eref target=""/>:
2779      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2780    </t>
2781  </list>
[543]2784  Final work on ABNF conversion (<eref target=""/>):
[421]2785  <list style="symbols"> 
2786    <t>
[424]2787      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
[421]2788    </t>
2789  </list>
2792  Other changes:
2793  <list style="symbols"> 
2794    <t>
2795      Move definition of quality values into Part 1.
2796    </t>
2797  </list>
[547]2801<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
[577]2803  Closed issues:
2804  <list style="symbols"> 
2805    <t>
2806      <eref target=""/>:
2807      "Content-Location isn't special"
2808    </t>
[592]2809    <t>
2810      <eref target=""/>:
2811      "Content Sniffing"
2812    </t>
[577]2813  </list>
[604]2817<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
[613]2819  Closed issues:
2820  <list style="symbols"> 
2821    <t>
[670]2822      <eref target=""/>:
[613]2823      "Updated reference for language tags"
2824    </t>
[663]2825    <t>
[716]2826      <eref target=""/>:
2827      "Clarify rules for determining what entities a response carries"
2828    </t>
2829    <t>
[712]2830      <eref target=""/>:
2831      "Content-Location base-setting problems"
2832    </t>
2833    <t>
[663]2834      <eref target=""/>:
2835      "Content Sniffing"
2836    </t>
[670]2837    <t>
2838      <eref target=""/>:
2839      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
2840    </t>
[673]2841    <t>
2842      <eref target=""/>:
2843      "move definitions of gzip/deflate/compress to part 1"
2844    </t>
[613]2845  </list>
2848  Partly resolved issues:
2849  <list style="symbols"> 
2850    <t>
2851      <eref target=""/>:
2852      "update IANA requirements wrt Transfer-Coding values" (add the
2853      IANA Considerations subsection)
2854    </t>
[668]2855    <t>
2856      <eref target=""/>:
2857      "update IANA requirements wrt Content-Coding values" (add the
2858      IANA Considerations subsection)
2859    </t>
[667]2860  </list>
[720]2864<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
[724]2866  Closed issues:
2867  <list style="symbols"> 
2868    <t>
[745]2869      <eref target=""/>:
2870      "Content Negotiation for media types"
2871    </t>
2872    <t>
[724]2873      <eref target=""/>:
2874      "Accept-Language: which RFC4647 filtering?"
2875    </t>
2876  </list>
[773]2880<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
[808]2882  Closed issues:
2883  <list style="symbols"> 
2884    <t>
[937]2885      <eref target=""/>:
2886      "MIME-Version not listed in P1, general header fields"
2887    </t>
2888    <t>
[808]2889      <eref target=""/>:
2890      "IANA registry for content/transfer encodings"
2891    </t>
[810]2892    <t>
[831]2893      <eref target=""/>:
2894      "Content Sniffing"
2895    </t>
2896    <t>
[810]2897      <eref target=""/>:
2898      "use of term "word" when talking about header structure"
2899    </t>
[808]2900  </list>
2903  Partly resolved issues:
2904  <list style="symbols"> 
2905    <t>
2906      <eref target=""/>:
2907      "Term for the requested resource's URI"
2908    </t>
2909  </list>
[841]2913<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.10">
[854]2915  Closed issues:
2916  <list style="symbols"> 
2917    <t>
[858]2918      <eref target=""/>:
2919      "Clarify 'Requested Variant'"
2920    </t>
2921    <t>
2922      <eref target=""/>:
2923      "Content-Location isn't special"
2924    </t>
2925    <t>
[854]2926      <eref target=""/>:
2927      "Delimiting messages with multipart/byteranges"
2928    </t>
[858]2929    <t>
2930      <eref target=""/>:
2931      "Clarify entity / representation / variant terminology"
2932    </t>
2933    <t>
2934      <eref target=""/>:
2935      "confusing req. language for Content-Location"
2936    </t>
2937    <t>
2938      <eref target=""/>:
2939      "Content-Location on 304 responses"
2940    </t>
[882]2941    <t>
2942      <eref target=""/>:
2943      "'requested resource' in content-encoding definition"
2944    </t>
[911]2945    <t>
2946      <eref target=""/>:
2947      "consider removing the 'changes from 2068' sections"
2948    </t>
[854]2949  </list>
2952  Partly resolved issues:
2953  <list style="symbols"> 
2954    <t>
2955      <eref target=""/>:
2956      "Content-MD5 and partial responses"
2957    </t>
2958  </list>
[973]2962<section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.since.11">
[987]2964  Closed issues:
2965  <list style="symbols"> 
2966    <t>
2967      <eref target=""/>:
2968      "Factor out Content-Disposition"
2969    </t>
2970  </list>
[1052]2974<section title="Since draft-ietf-httpbis-p3-payload-12" anchor="changes.since.12">
[1153]2976  Closed issues:
2977  <list style="symbols"> 
2978    <t>
[1165]2979      <eref target=""/>:
2980      "Header Classification"
2981    </t>
2982    <t>
[1167]2983      <eref target=""/>:
2984      "untangle ABNFs for header fields"
2985    </t>
2986    <t>
[1153]2987      <eref target=""/>:
2988      "potentially misleading MAY in media-type def"
2989    </t>
2990  </list>
[1180]2994<section title="Since draft-ietf-httpbis-p3-payload-13" anchor="changes.since.13">
[1234]2996  Closed issues:
2997  <list style="symbols"> 
2998    <t>
[1240]2999      <eref target=""/>:
3000      "Default charsets for text media types"
3001    </t>
3002    <t>
[1267]3003      <eref target=""/>:
3004      "Content-MD5 and partial responses"
3005    </t>
3006    <t>
[1234]3007      <eref target=""/>:
3008      "untangle ABNFs for header fields"
3009    </t>
[1244]3010    <t>
3011      <eref target=""/>:
3012      "confusing undefined parameter in media range example"
3013    </t>
[1234]3014  </list>
[1271]3018<section title="Since draft-ietf-httpbis-p3-payload-14" anchor="changes.since.14">
[1328]3020  None.
[1326]3024<section title="Since draft-ietf-httpbis-p3-payload-15" anchor="changes.since.15">
[1335]3026  Closed issues:
3027  <list style="symbols"> 
3028    <t>
3029      <eref target=""/>:
3030      "Strength of requirements on Accept re: 406"
3031    </t>
3032  </list>
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