source: draft-ietf-httpbis/latest/p3-payload.xml @ 1002

Last change on this file since 1002 was 1002, checked in by julian.reschke@…, 10 years ago

Use consistent syntax when talking about RFCs in prose (not references)

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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">
[981]15  <!ENTITY ID-MONTH "September">
[741]16  <!ENTITY ID-YEAR "2010">
[424]17  <!ENTITY notation                 "<xref target='Part1' x:rel='#notation' xmlns:x=''/>">
[205]18  <!ENTITY notation-abnf            "<xref target='Part1' x:rel='#notation.abnf' xmlns:x=''/>">
19  <!ENTITY basic-rules              "<xref target='Part1' x:rel='#basic.rules' xmlns:x=''/>">
[115]20  <!ENTITY caching-neg-resp         "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x=''/>">
[31]21  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x=''/>">
22  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x=''/>">
23  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x=''/>">
24  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x=''/>">
25  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x=''/>">
26  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x=''/>">
[115]27  <!ENTITY header-vary              "<xref target='Part6' x:rel='#header.vary' xmlns:x=''/>">
[31]28  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x=''/>">
29  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='' xmlns:x=''/>">
[580]30  <!ENTITY full-date                "<xref target='Part1' x:rel='' xmlns:x=''/>">
[457]31  <!ENTITY qvalue                   "<xref target='Part1' x:rel='#quality.values' xmlns:x=''/>">
[374]32  <!ENTITY uri                      "<xref target='Part1' x:rel='#uri' xmlns:x=''/>">
[823]33  <!ENTITY effective-request-uri    "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x=''/>">
[808]34  <!ENTITY compression-codings      "<xref target='Part1' x:rel='#compression.codings' xmlns:x=''/>">
35  <!ENTITY transfer-codings         "<xref target='Part1' x:rel='#transfer.codings' xmlns:x=''/>">
[673]36  <!ENTITY compress-coding          "<xref target='Part1' x:rel='#compress.coding' xmlns:x=''/>">
37  <!ENTITY deflate-coding           "<xref target='Part1' x:rel='#deflate.coding' xmlns:x=''/>">
38  <!ENTITY gzip-coding              "<xref target='Part1' x:rel='#gzip.coding' xmlns:x=''/>">
[716]39  <!ENTITY response-representation  "<xref target='Part2' x:rel='#identifying.response.associated.with.representation' xmlns:x=''/>">
41<?rfc toc="yes" ?>
[29]42<?rfc symrefs="yes" ?>
43<?rfc sortrefs="yes" ?>
[8]44<?rfc compact="yes"?>
45<?rfc subcompact="no" ?>
46<?rfc linkmailto="no" ?>
47<?rfc editing="no" ?>
[203]48<?rfc comments="yes"?>
49<?rfc inline="yes"?>
[799]50<?rfc rfcedstyle="yes"?>
[8]51<?rfc-ext allow-markup-in-artwork="yes" ?>
52<?rfc-ext include-references-in-index="yes" ?>
[308]53<rfc obsoletes="2616" category="std" x:maturity-level="draft"
[446]54     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
[153]55     xmlns:x=''>
[120]58  <title abbrev="HTTP/1.1, Part 3">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
[29]60  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
61    <organization abbrev="Day Software">Day Software</organization>
[8]62    <address>
63      <postal>
[29]64        <street>23 Corporate Plaza DR, Suite 280</street>
65        <city>Newport Beach</city>
[8]66        <region>CA</region>
[29]67        <code>92660</code>
68        <country>USA</country>
[8]69      </postal>
[29]70      <phone>+1-949-706-5300</phone>
71      <facsimile>+1-949-706-5305</facsimile>
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">
[29]122    <organization abbrev="Adobe Systems">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
215    mailing list ( The current issues list is
[848]216    at <eref target=""/>
[36]217    and related documents (including fancy diffs) can be found at
[324]218    <eref target=""/>.
[36]219  </t>
[153]220  <t>
[973]221    The changes in this draft are summarized in <xref target="changes.since.11"/>.
[153]222  </t>
226<section title="Introduction" anchor="introduction">
[163]228   This document defines HTTP/1.1 message payloads (a.k.a., content), the
[161]229   associated metadata header fields that define how the payload is intended
230   to be interpreted by a recipient, the request header fields that
[908]231   might influence content selection, and the various selection algorithms
[161]232   that are collectively referred to as HTTP content negotiation.
235   This document is currently disorganized in order to minimize the changes
236   between drafts and enable reviewers to see the smaller errata changes.
[980]237   A future draft will reorganize the sections to better reflect the content.
[161]238   In particular, the sections on entities will be renamed payload and moved
239   to the first half of the document, while the sections on content negotiation
240   and associated request header fields will be moved to the second half.  The
241   current mess reflects how widely dispersed these topics and associated
242   requirements had become in <xref target="RFC2616"/>.
[660]245<section title="Terminology" anchor="terminology">
247   This specification uses a number of terms to refer to the roles
248   played by participants in, and objects of, the HTTP communication.
251  <iref item="content negotiation"/>
252  <x:dfn>content negotiation</x:dfn>
253  <list>
254    <t>
255      The mechanism for selecting the appropriate representation when
[856]256      servicing a request. The representation in any response
[660]257      can be negotiated (including error responses).
258    </t>
259  </list>
[96]263<section title="Requirements" anchor="intro.requirements">
265   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
266   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
267   document are to be interpreted as described in <xref target="RFC2119"/>.
270   An implementation is not compliant if it fails to satisfy one or more
[847]271   of the "MUST" or "REQUIRED" level requirements for the protocols it
272   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
273   level and all the "SHOULD" level requirements for its protocols is said
274   to be "unconditionally compliant"; one that satisfies all the "MUST"
275   level requirements but not all the "SHOULD" level requirements for its
276   protocols is said to be "conditionally compliant".
[424]280<section title="Syntax Notation" anchor="notation">
[425]281  <x:anchor-alias value="ALPHA"/>
282  <x:anchor-alias value="CR"/>
283  <x:anchor-alias value="DIGIT"/>
284  <x:anchor-alias value="LF"/>
285  <x:anchor-alias value="OCTET"/>
286  <x:anchor-alias value="VCHAR"/>
287  <x:anchor-alias value="WSP"/>
[543]289  This specification uses the ABNF syntax defined in &notation; (which
290  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
291  <xref target="collected.abnf"/> shows the collected ABNF, with the list
292  rule expanded.
[425]295  The following core rules are included by
296  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
297  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
298  DIGIT (decimal 0-9), DQUOTE (double quote),
299  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
300  OCTET (any 8-bit sequence of data), SP (space),
301  VCHAR (any visible USASCII character),
302  and WSP (whitespace).
305<section title="Core Rules" anchor="core.rules">
[229]306  <x:anchor-alias value="token"/>
[810]307  <x:anchor-alias value="word"/>
[357]308  <x:anchor-alias value="OWS"/>
[424]310  The core rules below are defined in &basic-rules;:
312<figure><artwork type="abnf2616">
[229]313  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
[810]314  <x:ref>word</x:ref>           = &lt;word, defined in &basic-rules;&gt;
[357]315  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
319<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
[374]320  <x:anchor-alias value="absolute-URI"/>
[229]321  <x:anchor-alias value="Allow"/>
322  <x:anchor-alias value="Content-Length"/>
323  <x:anchor-alias value="Content-Range"/>
324  <x:anchor-alias value="Expires"/>
325  <x:anchor-alias value="Last-Modified"/>
[391]326  <x:anchor-alias value="partial-URI"/>
[457]327  <x:anchor-alias value="qvalue"/>
[206]329  The ABNF rules below are defined in other parts:
[207]331<figure><!--Part1--><artwork type="abnf2616">
[374]332  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
[229]333  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
[391]334  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
[457]335  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
337<figure><!--Part4--><artwork type="abnf2616">
[229]338  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
340<figure><!--Part5--><artwork type="abnf2616">
[229]341  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
343<figure><!--Part6--><artwork type="abnf2616">
[229]344  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
[8]352<section title="Protocol Parameters" anchor="protocol.parameters">
354<section title="Character Sets" anchor="character.sets">
356   HTTP uses the same definition of the term "character set" as that
357   described for MIME:
360   The term "character set" is used in this document to refer to a
361   method used with one or more tables to convert a sequence of octets
362   into a sequence of characters. Note that unconditional conversion in
[908]363   the other direction is not required, in that not all characters might
364   be available in a given character set and a character set might provide
[8]365   more than one sequence of octets to represent a particular character.
366   This definition is intended to allow various kinds of character
367   encoding, from simple single-table mappings such as US-ASCII to
368   complex table switching methods such as those that use ISO-2022's
369   techniques. However, the definition associated with a MIME character
370   set name &MUST; fully specify the mapping to be performed from octets
371   to characters. In particular, use of external profiling information
372   to determine the exact mapping is not permitted.
375  <t>
376    <x:h>Note:</x:h> This use of the term "character set" is more commonly
[879]377    referred to as a "character encoding". However, since HTTP and
[563]378    MIME share the same registry, it is important that the terminology
379    also be shared.
380  </t>
[229]382<t anchor="rule.charset">
383  <x:anchor-alias value="charset"/>
[8]384   HTTP character sets are identified by case-insensitive tokens. The
385   complete set of tokens is defined by the IANA Character Set registry
[91]386   (<eref target=""/>).
388<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
[229]389  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
392   Although HTTP allows an arbitrary token to be used as a charset
393   value, any token that has a predefined value within the IANA
[91]394   Character Set registry &MUST; represent the character set defined
[8]395   by that registry. Applications &SHOULD; limit their use of character
396   sets to those defined by the IANA registry.
[81]399   HTTP uses charset in two contexts: within an Accept-Charset request
[994]400   header field (in which the charset value is an unquoted token) and as the
401   value of a parameter in a Content-Type header field (within a request or
[81]402   response), in which case the parameter value of the charset parameter
[908]403   can be quoted.
[969]406   Implementors need to be aware of IETF character set requirements <xref target="RFC3629"/>
[8]407   <xref target="RFC2277"/>.
410<section title="Missing Charset" anchor="missing.charset">
[994]412   Some HTTP/1.0 software has interpreted a Content-Type header field without
[879]413   charset parameter incorrectly to mean "recipient should guess".
[211]414   Senders wishing to defeat this behavior &MAY; include a charset
415   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
416   it is known that it will not confuse the recipient.
419   Unfortunately, some older HTTP/1.0 clients did not deal properly with
420   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
421   charset label provided by the sender; and those user agents that have
422   a provision to "guess" a charset &MUST; use the charset from the
423   content-type field if they support that charset, rather than the
424   recipient's preference, when initially displaying a document. See
425   <xref target="canonicalization.and.text.defaults"/>.
430<section title="Content Codings" anchor="content.codings">
[229]431  <x:anchor-alias value="content-coding"/>
433   Content coding values indicate an encoding transformation that has
[866]434   been or can be applied to a representation. Content codings are primarily
435   used to allow a representation to be compressed or otherwise usefully
[8]436   transformed without losing the identity of its underlying media type
[866]437   and without loss of information. Frequently, the representation is stored in
[8]438   coded form, transmitted directly, and only decoded by the recipient.
440<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
[229]441  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
444   All content-coding values are case-insensitive. HTTP/1.1 uses
445   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
446   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
447   describes the content-coding, what is more important is that it
448   indicates what decoding mechanism will be required to remove the
449   encoding.
[673]452   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
453  <list>
454    <t>
455      See &compress-coding;.
456    </t>
457  </list>
[673]460   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
[8]461  <list>
462    <t>
[673]463      See &deflate-coding;.
[8]464    </t>
465  </list>
[673]468   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
469  <list>
470    <t>
471      See &gzip-coding;.
472    </t>
473  </list>
[673]476   identity<iref item="identity (Coding Format)"/><iref item="Coding Format" subitem="identity"/>
[8]477  <list><t>
478        The default (identity) encoding; the use of no transformation
479        whatsoever. This content-coding is used only in the Accept-Encoding
[994]480        header field, and &SHOULD-NOT;  be used in the Content-Encoding
481        header field.
[8]482  </t></list>
485<section title="Content Coding Registry" anchor="content.coding.registry">
[670]487   The HTTP Content Coding Registry defines the name space for the content
488   coding names.
491   Registrations &MUST; include the following fields:
492   <list style="symbols">
493     <t>Name</t>
494     <t>Description</t>
495     <t>Pointer to specification text</t>
496   </list>
[808]499   Names of content codings &MUST-NOT; overlap with names of transfer codings
500   (&transfer-codings;), unless the encoding transformation is identical (as it
501   is the case for the compression codings defined in
502   &compression-codings;).
[942]505   Values to be added to this name space require a specification
506   (see "Specification Required" in
[670]507   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
[8]508   conform to the purpose of content coding defined in this section.
511   The registry itself is maintained at
512   <eref target=""/>.
[8]518<section title="Media Types" anchor="media.types">
[229]519  <x:anchor-alias value="media-type"/>
520  <x:anchor-alias value="type"/>
521  <x:anchor-alias value="subtype"/>
[152]523   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
[8]524   and Accept (<xref target="header.accept"/>) header fields in order to provide
525   open and extensible data typing and type negotiation.
527<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]528  <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> )
529  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
530  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
[229]532<t anchor="rule.parameter">
533  <x:anchor-alias value="attribute"/>
534  <x:anchor-alias value="parameter"/>
535  <x:anchor-alias value="value"/>
[8]536   Parameters &MAY; follow the type/subtype in the form of attribute/value
[29]537   pairs.
[29]539<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]540  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
541  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
[810]542  <x:ref>value</x:ref>          = <x:ref>word</x:ref>
545   The type, subtype, and parameter attribute names are case-insensitive.
[370]546   Parameter values might or might not be case-sensitive, depending on the
547   semantics of the parameter name.  The presence or absence of a parameter might
[8]548   be significant to the processing of a media-type, depending on its
549   definition within the media type registry.
[908]552   A parameter value that matches the <x:ref>token</x:ref> production can be
[297]553   transmitted as either a token or within a quoted-string. The quoted and
554   unquoted values are equivalent.
[8]557   Note that some older HTTP applications do not recognize media type
558   parameters. When sending data to older HTTP applications,
559   implementations &SHOULD; only use media type parameters when they are
560   required by that type/subtype definition.
563   Media-type values are registered with the Internet Assigned Number
[91]564   Authority (IANA). The media type registration process is
[115]565   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
[8]566   discouraged.
569<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
[874]571   Internet media types are registered with a canonical form. A
572   representation transferred via HTTP messages &MUST; be in the
[8]573   appropriate canonical form prior to its transmission except for
574   "text" types, as defined in the next paragraph.
577   When in canonical form, media subtypes of the "text" type use CRLF as
578   the text line break. HTTP relaxes this requirement and allows the
579   transport of text media with plain CR or LF alone representing a line
[874]580   break when it is done consistently for an entire representation. HTTP
581   applications &MUST; accept CRLF, bare CR, and bare LF as indicating
582   a line break in text media received via HTTP. In
583   addition, if the text is in a character encoding that does not
[8]584   use octets 13 and 10 for CR and LF respectively, as is the case for
[874]585   some multi-byte character encodings, HTTP allows the use of whatever octet
586   sequences are defined by that character encoding to represent the
[8]587   equivalent of CR and LF for line breaks. This flexibility regarding
[874]588   line breaks applies only to text media in the payload body; a bare CR
[8]589   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
590   structures (such as header fields and multipart boundaries).
[874]593   If a representation is encoded with a content-coding, the underlying
[8]594   data &MUST; be in a form defined above prior to being encoded.
[211]597   The "charset" parameter is used with some media types to define the
[874]598   character encoding (<xref target="character.sets"/>) of the data. When no explicit charset
[211]599   parameter is provided by the sender, media subtypes of the "text"
600   type are defined to have a default charset value of "ISO-8859-1" when
[874]601   received via HTTP. Data in character encodings other than "ISO-8859-1" or
[211]602   its subsets &MUST; be labeled with an appropriate charset value. See
603   <xref target="missing.charset"/> for compatibility problems.
607<section title="Multipart Types" anchor="multipart.types">
609   MIME provides for a number of "multipart" types -- encapsulations of
[874]610   one or more representations within a single message-body. All multipart
[97]611   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
612   and &MUST; include a boundary parameter as part of the media type
[8]613   value. The message body is itself a protocol element and &MUST;
614   therefore use only CRLF to represent line breaks between body-parts.
617   In general, HTTP treats a multipart message-body no differently than
[852]618   any other media type: strictly as payload.  HTTP does not use the
619   multipart boundary as an indicator of message-body length.
[97]620   <!-- jre: re-insert removed text pointing to caching? -->
[852]621   In all other respects, an HTTP user agent &SHOULD; follow the same or similar
[8]622   behavior as a MIME user agent would upon receipt of a multipart type.
623   The MIME header fields within each body-part of a multipart message-body
624   do not have any significance to HTTP beyond that defined by
625   their MIME semantics.
628   If an application receives an unrecognized multipart subtype, the
629   application &MUST; treat it as being equivalent to "multipart/mixed".
632  <t>
633    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
634    for carrying form data suitable for processing via the POST
635    request method, as described in <xref target="RFC2388"/>.
636  </t>
641<section title="Language Tags" anchor="language.tags">
[229]642  <x:anchor-alias value="language-tag"/>
[690]644   A language tag, as defined in <xref target="RFC5646"/>, identifies a
[613]645   natural language spoken, written, or otherwise conveyed by human beings for
646   communication of information to other human beings. Computer languages are
647   explicitly excluded. HTTP uses language tags within the Accept-Language and
648   Content-Language fields.
[613]651   In summary, a language tag is composed of one or more parts: A primary
652   language subtag followed by a possibly empty series of subtags:
[613]654<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
[690]655  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
658   White space is not allowed within the tag and all tags are case-insensitive.
[613]659   The name space of language subtags is administered by the IANA (see
660   <eref target=""/>).
663  <preamble>Example tags include:</preamble>
664<artwork type="example">
665  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
[690]669   See <xref target="RFC5646"/> for further information.
[965]674<section title="Payload" anchor="payload">
[965]676   HTTP messages &MAY; transfer a payload if not otherwise restricted by
677   the request method or response status code.  The payload consists of
678   metadata, in the form of header fields, and data, in the form of the
679   sequence of octets in the message-body after any transfer-coding has
680   been decoded.
[965]682<iref item="payload"/>
684   A "<x:dfn>payload</x:dfn>" in HTTP is always a partial or complete
685   representation of some resource.  We use separate terms for payload
686   and representation because some messages contain only the associated
687   representation's header fields (e.g., responses to HEAD) or only some
688   part(s) of the representation (e.g., the 206 status code).
690<section title="Payload Header Fields" anchor="payload.header.fields">
691  <x:anchor-alias value="payload-header"/>
[965]693   HTTP header fields that specifically define the payload, rather than the
694   associated representation, are referred to as "payload header fields".
695   The following payload header fields are defined by HTTP/1.1:
698   <x:ref>Content-Length</x:ref>           ; &header-content-length;
699   <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
700   <x:ref>Content-Range</x:ref>            ; &header-content-range;
[874]704<section title="Payload Body" anchor="payload.body">
705  <x:anchor-alias value="payload-body"/>
[874]707   A payload body is only present in a message when a message-body is
708   present, as described in &message-body;. The payload body is obtained
[8]709   from the message-body by decoding any Transfer-Encoding that might
710   have been applied to ensure safe and proper transfer of the message.
[965]715<section title="Representation" anchor="representation">
716<iref item="representation"/>
[965]718   A "<x:dfn>representation</x:dfn>" is information in a format that can be readily
719   communicated from one party to another.  A resource representation
720   is information that reflects the state of that resource, as observed
721   at some point in the past (e.g., in a response to GET) or to be
722   desired at some point in the future (e.g., in a PUT request).
725   Most, but not all, representations transferred via HTTP are intended
726   to be a representation of the target resource (the resource identified
727   by the effective request URI).  The precise semantics of a representation
728   are determined by the type of message (request or response), the request
729   method, the response status code, and the representation metadata.
730   For example, the above semantic is true for the representation in any
731   200 (OK) response to GET and for the representation in any PUT request.
732   A 200 response to PUT, in contrast, contains either a representation
733   that describes the successful action or a representation of the target
734   resource, with the latter indicated by a Content-Location header field
735   with the same value as the effective request URI.  Likewise, response
736   messages with an error status code usually contain a representation that
737   describes the error and what next steps are suggested for resolving it.
740<section title="Representation Header Fields" anchor="representation.header.fields">
741  <x:anchor-alias value="representation-header"/>
743   Representation header fields define metadata about the representation data
744   enclosed in the message-body or, if no message-body is present, about
745   the representation that would have been transferred in a 200 response
746   to a simultaneous GET request with the same effective request URI.
749   The following header fields are defined as representation metadata:
752   <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
753   <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
754   <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
755   <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
756   <x:ref>Expires</x:ref>                  ; &header-expires;
757   <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
761<section title="Representation Data" anchor="">
762  <x:anchor-alias value="representation-data"/>
764   The representation body associated with an HTTP message is
765   either provided as the payload body of the message or
766   referred to by the message semantics and the effective request
767   URI.  The representation data is in a format and encoding defined by
768   the representation metadata header fields.
771   The data type of the representation data
772   is determined via the header fields Content-Type and Content-Encoding.
[8]773   These define a two-layer, ordered encoding model:
775<figure><artwork type="example">
[965]776  representation-data := Content-Encoding( Content-Type( bits ) )
[965]779   Content-Type specifies the media type of the underlying data, which
780   defines both the data format and how that data &SHOULD; be processed
781   by the recipient (within the scope of the request method semantics).
782   Any HTTP/1.1 message containing a payload body &SHOULD; include a
783   Content-Type header field defining the media type of the associated
784   representation unless that metadata is unknown to the sender.
[831]785   If the Content-Type header field is not present, it indicates that
[965]786   the sender does not know the media type of the representation;
787   recipients &MAY; either assume that the media type is
788   "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
[592]789   or examine the content to determine its type.
[965]792   In practice, resource owners do not always properly configure their origin
793   server to provide the correct Content-Type for a given representation,
794   with the result that some clients will examine a response body's content
795   and override the specified type.
[908]796   Clients that do so risk drawing incorrect conclusions, which might expose
[965]797   additional security risks (e.g., "privilege escalation").  Furthermore,
798   it is impossible to determine the sender's intent by examining the data
799   format: many data formats match multiple media types that differ only in
800   processing semantics.  Implementers are encouraged to provide a means of
801   disabling such "content sniffing" when it is used.
[908]804   Content-Encoding is used to indicate any additional content
[8]805   codings applied to the data, usually for the purpose of data
[965]806   compression, that are a property of the representation.  If
807   Content-Encoding is not present, then there is no additional
808   encoding beyond that defined by the Content-Type.
813<section title="Content Negotiation" anchor="content.negotiation">
[745]815   HTTP responses include a representation which contains information for
816   interpretation, whether by a human user or for further processing.
817   Often, the server has different ways of representing the
818   same information; for example, in different formats, languages,
819   or using different character encodings.
[745]822   HTTP clients and their users might have different or variable
823   capabilities, characteristics or preferences which would influence
824   which representation, among those available from the server,
825   would be best for the server to deliver. For this reason, HTTP
826   provides mechanisms for "content negotiation" -- a process of
827   allowing selection of a representation of a given resource,
828   when more than one is available.
[745]831   This specification defines two patterns of content negotiation;
832   "server-driven", where the server selects the representation based
833   upon the client's stated preferences, and "agent-driven" negotiation,
834   where the server provides a list of representations for the client to
835   choose from, based upon their metadata. In addition,  there are
836   other patterns: some applications use an "active content" pattern,
837   where the server returns active content which runs on the client
838   and, based on client available parameters, selects additional
839   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
840   has also been proposed.
843   These patterns are all widely used, and have trade-offs in applicability
844   and practicality. In particular, when the number of preferences or
845   capabilities to be expressed by a client are large (such as when many
846   different formats are supported by a user-agent), server-driven
[908]847   negotiation becomes unwieldy, and might not be appropriate. Conversely,
[745]848   when the number of representations to choose from is very large,
[908]849   agent-driven negotiation might not be appropriate.
852   Note that in all cases, the supplier of representations has the
853   responsibility for determining which representations might be
854   considered to be the "same information".
857<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
859   If the selection of the best representation for a response is made by
860   an algorithm located at the server, it is called server-driven
861   negotiation. Selection is based on the available representations of
[763]862   the response (the dimensions over which it can vary; e.g., language,
[8]863   content-coding, etc.) and the contents of particular header fields in
864   the request message or on other information pertaining to the request
865   (such as the network address of the client).
868   Server-driven negotiation is advantageous when the algorithm for
869   selecting from among the available representations is difficult to
870   describe to the user agent, or when the server desires to send its
871   "best guess" to the client along with the first response (hoping to
872   avoid the round-trip delay of a subsequent request if the "best
873   guess" is good enough for the user). In order to improve the server's
874   guess, the user agent &MAY; include request header fields (Accept,
875   Accept-Language, Accept-Encoding, etc.) which describe its
876   preferences for such a response.
879   Server-driven negotiation has disadvantages:
880  <list style="numbers">
881    <t>
882         It is impossible for the server to accurately determine what
883         might be "best" for any given user, since that would require
884         complete knowledge of both the capabilities of the user agent
885         and the intended use for the response (e.g., does the user want
886         to view it on screen or print it on paper?).
887    </t>
888    <t>
889         Having the user agent describe its capabilities in every
890         request can be both very inefficient (given that only a small
891         percentage of responses have multiple representations) and a
892         potential violation of the user's privacy.
893    </t>
894    <t>
895         It complicates the implementation of an origin server and the
896         algorithms for generating responses to a request.
897    </t>
898    <t>
[908]899         It might limit a public cache's ability to use the same response
[8]900         for multiple user's requests.
901    </t>
902  </list>
905   HTTP/1.1 includes the following request-header fields for enabling
906   server-driven negotiation through description of user agent
907   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
908   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
[745]909   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
910   However, an origin server is not limited to these dimensions and &MAY; vary
911   the response based on any aspect of the request, including information
[8]912   outside the request-header fields or within extension header fields
913   not defined by this specification.
916  <t>
917    <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
918    because new clients might not be recognized.
919  </t>
[115]922   The Vary header field (&header-vary;) can be used to express the parameters the
[8]923   server uses to select a representation that is subject to server-driven
[29]924   negotiation.
928<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
930   With agent-driven negotiation, selection of the best representation
931   for a response is performed by the user agent after receiving an
932   initial response from the origin server. Selection is based on a list
933   of the available representations of the response included within the
[874]934   header fields or body of the initial response, with each
[8]935   representation identified by its own URI. Selection from among the
[908]936   representations can be performed automatically (if the user agent is
[8]937   capable of doing so) or manually by the user selecting from a
938   generated (possibly hypertext) menu.
941   Agent-driven negotiation is advantageous when the response would vary
942   over commonly-used dimensions (such as type, language, or encoding),
943   when the origin server is unable to determine a user agent's
944   capabilities from examining the request, and generally when public
945   caches are used to distribute server load and reduce network usage.
948   Agent-driven negotiation suffers from the disadvantage of needing a
949   second request to obtain the best alternate representation. This
950   second request is only efficient when caching is used. In addition,
951   this specification does not define any mechanism for supporting
952   automatic selection, though it also does not prevent any such
953   mechanism from being developed as an extension and used within
954   HTTP/1.1.
[745]957   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
[8]958   status codes for enabling agent-driven negotiation when the server is
959   unwilling or unable to provide a varying response using server-driven
960   negotiation.
[8]965<section title="Header Field Definitions" anchor="header.fields">
[117]967   This section defines the syntax and semantics of HTTP/1.1 header fields
968   related to the payload of messages.
[8]971<section title="Accept" anchor="header.accept">
972  <iref primary="true" item="Accept header" x:for-anchor=""/>
973  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
[229]974  <x:anchor-alias value="Accept"/>
[357]975  <x:anchor-alias value="Accept-v"/>
[370]976  <x:anchor-alias value="accept-ext"/>
[229]977  <x:anchor-alias value="accept-params"/>
978  <x:anchor-alias value="media-range"/>
[698]980   The "Accept" request-header field can be used by user agents to specify
[994]981   response media types that are acceptable. Accept header fields can be used to
[698]982   indicate that the request is specifically limited to a small set of desired
983   types, as in the case of a request for an in-line image.
[370]985<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="Accept-v"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-ext"/>
[366]986  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
[357]987  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
[229]989  <x:ref>media-range</x:ref>    = ( "*/*"
[334]990                   / ( <x:ref>type</x:ref> "/" "*" )
991                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
[370]992                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
993  <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> )
[376]994  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref>
[810]995                   [ "=" <x:ref>word</x:ref> ]
998   The asterisk "*" character is used to group media types into ranges,
999   with "*/*" indicating all media types and "type/*" indicating all
1000   subtypes of that type. The media-range &MAY; include media type
1001   parameters that are applicable to that range.
1004   Each media-range &MAY; be followed by one or more accept-params,
1005   beginning with the "q" parameter for indicating a relative quality
1006   factor. The first "q" parameter (if any) separates the media-range
1007   parameter(s) from the accept-params. Quality factors allow the user
1008   or user agent to indicate the relative degree of preference for that
[457]1009   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
[8]1010   default value is q=1.
1013  <t>
1014    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
1015    parameters from Accept extension parameters is due to historical
1016    practice. Although this prevents any media type parameter named
1017    "q" from being used with a media range, such an event is believed
1018    to be unlikely given the lack of any "q" parameters in the IANA
1019    media type registry and the rare usage of any media type
1020    parameters in Accept. Future media types are discouraged from
1021    registering any parameter named "q".
1022  </t>
1025   The example
1027<figure><artwork type="example">
[357]1028  Accept: audio/*; q=0.2, audio/basic
1031   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
[879]1032   type if it is the best available after an 80% mark-down in quality".
1035   If no Accept header field is present, then it is assumed that the
1036   client accepts all media types. If an Accept header field is present,
1037   and if the server cannot send a response which is acceptable
1038   according to the combined Accept field value, then the server &SHOULD;
[137]1039   send a 406 (Not Acceptable) response.
1042   A more elaborate example is
1044<figure><artwork type="example">
[357]1045  Accept: text/plain; q=0.5, text/html,
1046          text/x-dvi; q=0.8, text/x-c
1049   Verbally, this would be interpreted as "text/html and text/x-c are
1050   the preferred media types, but if they do not exist, then send the
[866]1051   text/x-dvi representation, and if that does not exist, send the text/plain
[879]1052   representation".
1055   Media ranges can be overridden by more specific media ranges or
1056   specific media types. If more than one media range applies to a given
1057   type, the most specific reference has precedence. For example,
1059<figure><artwork type="example">
[357]1060  Accept: text/*, text/html, text/html;level=1, */*
1063   have the following precedence:
[459]1064   <list style="numbers">
1065    <t>text/html;level=1</t>
1066    <t>text/html</t>
1067    <t>text/*</t>
1068    <t>*/*</t>
1069   </list>
1072   The media type quality factor associated with a given type is
1073   determined by finding the media range with the highest precedence
1074   which matches that type. For example,
1076<figure><artwork type="example">
[357]1077  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1078          text/html;level=2;q=0.4, */*;q=0.5
1081   would cause the following values to be associated:
[459]1083<texttable align="left">
1084  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1085  <c>text/html;level=1</c>    <c>1</c>
1086  <c>text/html</c>            <c>0.7</c>
1087  <c>text/plain</c>           <c>0.3</c>
1088  <c>image/jpeg</c>           <c>0.5</c>
1089  <c>text/html;level=2</c>    <c>0.4</c>
1090  <c>text/html;level=3</c>    <c>0.7</c>
1093      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1094      values for certain media ranges. However, unless the user agent is
1095      a closed system which cannot interact with other rendering agents,
1096      this default set ought to be configurable by the user.
1100<section title="Accept-Charset" anchor="header.accept-charset">
1101  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1102  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
[229]1103  <x:anchor-alias value="Accept-Charset"/>
[357]1104  <x:anchor-alias value="Accept-Charset-v"/>
[698]1106   The "Accept-Charset" request-header field can be used by user agents to
1107   indicate what response character sets are acceptable. This field allows
[8]1108   clients capable of understanding more comprehensive or special-purpose
[698]1109   character sets to signal that capability to a server which is capable of
1110   representing documents in those character sets.
[357]1112<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
[366]1113  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
[357]1114          <x:ref>Accept-Charset-v</x:ref>
[376]1115  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1116                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1119   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1120   be given an associated quality value which represents the user's
1121   preference for that charset. The default value is q=1. An example is
1123<figure><artwork type="example">
[357]1124  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1127   The special value "*", if present in the Accept-Charset field,
1128   matches every character set (including ISO-8859-1) which is not
1129   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1130   in an Accept-Charset field, then all character sets not explicitly
1131   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1132   a quality value of 1 if not explicitly mentioned.
[994]1135   If no Accept-Charset header field is present, the default is that any
1136   character set is acceptable. If an Accept-Charset header field is present,
[8]1137   and if the server cannot send a response which is acceptable
[994]1138   according to the Accept-Charset header field, then the server &SHOULD; send
[137]1139   an error response with the 406 (Not Acceptable) status code, though
[8]1140   the sending of an unacceptable response is also allowed.
1144<section title="Accept-Encoding" anchor="header.accept-encoding">
1145  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1146  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
[229]1147  <x:anchor-alias value="Accept-Encoding"/>
[357]1148  <x:anchor-alias value="Accept-Encoding-v"/>
[229]1149  <x:anchor-alias value="codings"/>
[698]1151   The "Accept-Encoding" request-header field can be used by user agents to
1152   indicate what response content-codings (<xref target="content.codings"/>)
1153   are acceptable in the response.
[357]1155<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="Accept-Encoding-v"/><iref primary="true" item="Grammar" subitem="codings"/>
[366]1156  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
[357]1157                     <x:ref>Accept-Encoding-v</x:ref>
1158  <x:ref>Accept-Encoding-v</x:ref>  =
[370]1159                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
[357]1160  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
[248]1163   Each codings value &MAY; be given an associated quality value which
1164   represents the preference for that encoding. The default value is q=1.
[8]1167   Examples of its use are:
1169<figure><artwork type="example">
[357]1170  Accept-Encoding: compress, gzip
1171  Accept-Encoding:
1172  Accept-Encoding: *
1173  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1174  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1177   A server tests whether a content-coding is acceptable, according to
1178   an Accept-Encoding field, using these rules:
1179  <list style="numbers">
1180      <t>If the content-coding is one of the content-codings listed in
1181         the Accept-Encoding field, then it is acceptable, unless it is
[457]1182         accompanied by a qvalue of 0. (As defined in &qvalue;, a
[879]1183         qvalue of 0 means "not acceptable".)</t>
1185      <t>The special "*" symbol in an Accept-Encoding field matches any
1186         available content-coding not explicitly listed in the header
1187         field.</t>
1189      <t>If multiple content-codings are acceptable, then the acceptable
1190         content-coding with the highest non-zero qvalue is preferred.</t>
1192      <t>The "identity" content-coding is always acceptable, unless
1193         specifically refused because the Accept-Encoding field includes
1194         "identity;q=0", or because the field includes "*;q=0" and does
1195         not explicitly include the "identity" content-coding. If the
1196         Accept-Encoding field-value is empty, then only the "identity"
1197         encoding is acceptable.</t>
1198  </list>
1201   If an Accept-Encoding field is present in a request, and if the
1202   server cannot send a response which is acceptable according to the
[994]1203   Accept-Encoding header field, then the server &SHOULD; send an error response
[8]1204   with the 406 (Not Acceptable) status code.
1207   If no Accept-Encoding field is present in a request, the server &MAY;
1208   assume that the client will accept any content coding. In this case,
1209   if "identity" is one of the available content-codings, then the
1210   server &SHOULD; use the "identity" content-coding, unless it has
1211   additional information that a different content-coding is meaningful
1212   to the client.
1215  <t>
1216    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1217    and if the "identity" content-coding is unavailable, then
1218    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1219    "gzip" and "compress") are preferred; some older clients
1220    improperly display messages sent with other content-codings.  The
1221    server might also make this decision based on information about
1222    the particular user-agent or client.
1223  </t>
1226  <t>
1227    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1228    associated with content-codings. This means that qvalues will not
1229    work and are not permitted with x-gzip or x-compress.
1230  </t>
1234<section title="Accept-Language" anchor="header.accept-language">
1235  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1236  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
[229]1237  <x:anchor-alias value="Accept-Language"/>
[357]1238  <x:anchor-alias value="Accept-Language-v"/>
[229]1239  <x:anchor-alias value="language-range"/>
[698]1241   The "Accept-Language" request-header field can be used by user agents to
1242   indicate the set of natural languages that are preferred in the response.
1243   Language tags are defined in <xref target="language.tags"/>.
[357]1245<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="Accept-Language-v"/><iref primary="true" item="Grammar" subitem="language-range"/>
[366]1246  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
[357]1247                    <x:ref>Accept-Language-v</x:ref>
1248  <x:ref>Accept-Language-v</x:ref> =
[370]1249                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
[357]1250  <x:ref>language-range</x:ref>    =
[303]1251            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
[303]1254   Each language-range can be given an associated quality value which
[8]1255   represents an estimate of the user's preference for the languages
1256   specified by that range. The quality value defaults to "q=1". For
1257   example,
1259<figure><artwork type="example">
[357]1260  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1263   would mean: "I prefer Danish, but will accept British English and
[879]1264   other types of English".
[724]1265   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
[724]1268   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
1269   several matching schemes. Implementations can offer the most appropriate
1270   matching scheme for their requirements.
1273  <t>
[756]1274    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
[724]1275    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
1276    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
[563]1277  </t>
1280   It might be contrary to the privacy expectations of the user to send
[994]1281   an Accept-Language header field with the complete linguistic preferences of
[8]1282   the user in every request. For a discussion of this issue, see
[994]1283   <xref target=""/>.
1286   As intelligibility is highly dependent on the individual user, it is
1287   recommended that client applications make the choice of linguistic
1288   preference available to the user. If the choice is not made
1289   available, then the Accept-Language header field &MUST-NOT; be given in
1290   the request.
1293  <t>
1294    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1295    the user, we remind implementors of  the fact that users are not
1296    familiar with the details of language matching as described above,
[969]1297    and ought to be provided appropriate guidance. As an example, users
[563]1298    might assume that on selecting "en-gb", they will be served any
1299    kind of English document if British English is not available. A
1300    user agent might suggest in such a case to add "en" to get the
1301    best matching behavior.
1302  </t>
1306<section title="Content-Encoding" anchor="header.content-encoding">
1307  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1308  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
[229]1309  <x:anchor-alias value="Content-Encoding"/>
[357]1310  <x:anchor-alias value="Content-Encoding-v"/>
[965]1312   The "Content-Encoding" header field indicates what content-codings
[866]1313   have been applied to the representation, and thus what decoding mechanisms
[698]1314   must be applied in order to obtain the media-type referenced by the
1315   Content-Type header field. Content-Encoding is primarily used to allow a
[866]1316   representation to be compressed without losing the identity of its underlying
[698]1317   media type.
[357]1319<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
[366]1320  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
[357]1321  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1324   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1326<figure><artwork type="example">
[357]1327  Content-Encoding: gzip
[866]1330   The content-coding is a characteristic of the representation.
1331   Typically, the representation body is stored with this
[8]1332   encoding and is only decoded before rendering or analogous usage.
1333   However, a non-transparent proxy &MAY; modify the content-coding if the
1334   new coding is known to be acceptable to the recipient, unless the
1335   "no-transform" cache-control directive is present in the message.
[866]1338   If the content-coding of a representation is not "identity", then the
1339   representation metadata &MUST; include a Content-Encoding header
1340   field (<xref target="header.content-encoding"/>)
[8]1341   that lists the non-identity content-coding(s) used.
[874]1344   If the content-coding of a representation in a request message is not
[8]1345   acceptable to the origin server, the server &SHOULD; respond with a
1346   status code of 415 (Unsupported Media Type).
[866]1349   If multiple encodings have been applied to a representation, the content
[8]1350   codings &MUST; be listed in the order in which they were applied.
1351   Additional information about the encoding parameters &MAY; be provided
[866]1352   by other header fields not defined by this specification.
1356<section title="Content-Language" anchor="header.content-language">
1357  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1358  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
[229]1359  <x:anchor-alias value="Content-Language"/>
[357]1360  <x:anchor-alias value="Content-Language-v"/>
[965]1362   The "Content-Language" header field describes the natural
[866]1363   language(s) of the intended audience for the representation. Note that this might
[874]1364   not be equivalent to all the languages used within the representation.
[357]1366<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
[366]1367  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
[357]1368  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1371   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1372   Content-Language is to allow a user to identify and differentiate
[866]1373   representations according to the user's own preferred language. Thus, if the
[8]1374   body content is intended only for a Danish-literate audience, the
1375   appropriate field is
1377<figure><artwork type="example">
[357]1378  Content-Language: da
1381   If no Content-Language is specified, the default is that the content
1382   is intended for all language audiences. This might mean that the
1383   sender does not consider it to be specific to any natural language,
1384   or that the sender does not know for which language it is intended.
1387   Multiple languages &MAY; be listed for content that is intended for
1388   multiple audiences. For example, a rendition of the "Treaty of
[879]1389   Waitangi", presented simultaneously in the original Maori and English
[8]1390   versions, would call for
1392<figure><artwork type="example">
[357]1393  Content-Language: mi, en
[866]1396   However, just because multiple languages are present within a representation
[8]1397   does not mean that it is intended for multiple linguistic audiences.
1398   An example would be a beginner's language primer, such as "A First
[879]1399   Lesson in Latin", which is clearly intended to be used by an
[8]1400   English-literate audience. In this case, the Content-Language would
1401   properly only include "en".
1404   Content-Language &MAY; be applied to any media type -- it is not
1405   limited to textual documents.
1409<section title="Content-Location" anchor="header.content-location">
1410  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1411  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
[229]1412  <x:anchor-alias value="Content-Location"/>
[357]1413  <x:anchor-alias value="Content-Location-v"/>
[856]1415   The "Content-Location" header field supplies a URI that can be used
1416   as a specific identifier for the representation in this message.
1417   In other words, if one were to perform a GET on this URI at the time
1418   of this message's generation, then a 200 response would contain the
1419   same representation that is enclosed as payload in this message.
[357]1421<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
[366]1422  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
[357]1423                    <x:ref>Content-Location-v</x:ref>
1424  <x:ref>Content-Location-v</x:ref> =
[391]1425                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
[972]1428   The Content-Location value is not a replacement for the effective
[856]1429   Request URI (&effective-request-uri;).  It is representation metadata.
1430   It has the same syntax and semantics as the header field of the same name
[858]1431   defined for MIME body parts in <xref target="RFC2557" x:fmt="of" x:sec="4"/>.
[856]1432   However, its appearance in an HTTP message has some special implications
1433   for HTTP recipients.
[856]1436   If Content-Location is included in a response message and its value
[965]1437   is the same as the effective request URI, then the response payload
[856]1438   &SHOULD; be considered the current representation of that resource.
1439   For a GET or HEAD request, this is the same as the default semantics
1440   when no Content-Location is provided by the server.  For a state-changing
1441   method like PUT or POST, it implies that the server's response contains
1442   the new representation of that resource, thereby distinguishing it from
1443   representations that might only report about the action (e.g., "It worked!").
1444   This allows authoring applications to update their local copies without
1445   the need for a subsequent GET request.
[856]1448   If Content-Location is included in a response message and its value
[965]1449   differs from the effective request URI, then the origin server is
[856]1450   informing recipients that this representation has its own, presumably
1451   more specific, identifier.  For a GET or HEAD request, this is an
[965]1452   indication that the effective request URI identifies a resource that
[856]1453   is subject to content negotiation and the representation selected for
1454   this response can also be found at the identified URI.  For other
1455   methods, such a Content-Location indicates that this representation
1456   contains a report on the action's status and the same report is
1457   available (for future access with GET) at the given URI.  For
[908]1458   example, a purchase transaction made via the POST method might
[856]1459   include a receipt document as the payload of the 200 response;
1460   the Content-Location value provides an identifier for retrieving
1461   a copy of that same receipt in the future.
1464   If Content-Location is included in a request message, then it &MAY;
1465   be interpreted by the origin server as an indication of where the
1466   user agent originally obtained the content of the enclosed
1467   representation (prior to any subsequent modification of the content
1468   by that user agent).  In other words, the user agent is providing
1469   the same representation metadata that it received with the original
1470   representation.  However, such interpretation &MUST-NOT; be used to
1471   alter the semantics of the method requested by the client.  For
1472   example, if a client makes a PUT request on a negotiated resource
1473   and the origin server accepts that PUT (without redirection), then the
1474   new set of values for that resource is expected to be consistent with
1475   the one representation supplied in that PUT; the Content-Location
1476   cannot be used as a form of reverse content selection that
1477   identifies only one of the negotiated representations to be updated.
1478   If the user agent had wanted the latter semantics, it would have applied
1479   the PUT directly to the Content-Location URI.
1482   A Content-Location field received in a request message is transitory
1483   information that &SHOULD-NOT; be saved with other representation
1484   metadata for use in later responses.  The Content-Location's value
1485   might be saved for use in other contexts, such as within source links
1486   or other metadata.
1489   A cache cannot assume that a representation with a Content-Location
[8]1490   different from the URI used to retrieve it can be used to respond to
[856]1491   later requests on that Content-Location URI.
[965]1494   If the Content-Location value is a partial URI, the partial URI is
1495   interpreted relative to the effective request URI.
1499<section title="Content-MD5" anchor="header.content-md5">
1500  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1501  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
[229]1502  <x:anchor-alias value="Content-MD5"/>
[357]1503  <x:anchor-alias value="Content-MD5-v"/>
[965]1505   The "Content-MD5" header field, as defined in <xref target="RFC1864"/>, is
[874]1506   an MD5 digest of the payload body that provides an end-to-end message
1507   integrity check (MIC) of the payload body (the message-body after any
1508   transfer-coding is decoded). Note that a MIC is good for
1509   detecting accidental modification of the payload body in transit, but is not
[699]1510   proof against malicious attacks.
[357]1512<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
[366]1513  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
[357]1514  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1517   The Content-MD5 header field &MAY; be generated by an origin server or
[874]1518   client to function as an integrity check of the payload body. Only
1519   origin servers or user agents &MAY; generate the Content-MD5 header field;
[8]1520   proxies and gateways &MUST-NOT; generate it, as this would defeat its
[874]1521   value as an end-to-end integrity check. Any recipient &MAY; check that
1522   the digest value in this header field matches a corresponding digest
1523   calculated on payload body as received.
[874]1526   The MD5 digest is computed based on the content of the payload body,
1527   including any content-coding, but not including any transfer-coding
1528   applied to the message-body because such transfer-codings might be
1529   applied or removed anywhere along the request/response chain.
1530   If the message is received with a transfer-coding, that encoding &MUST;
1531   be decoded prior to checking the Content-MD5 value against the received
1532   payload.
1535   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1536   composite media-types (e.g., multipart/* and message/rfc822), but
1537   this does not change how the digest is computed as defined in the
1538   preceding paragraph.
[874]1541   There are several consequences of this. The payload for composite
[8]1542   types &MAY; contain many body-parts, each with its own MIME and HTTP
[994]1543   header fields (including Content-MD5, Content-Transfer-Encoding, and
1544   Content-Encoding header fields). If a body-part has a Content-Transfer-Encoding
1545   or Content-Encoding header field, it is assumed that the content
[8]1546   of the body-part has had the encoding applied, and the body-part is
1547   included in the Content-MD5 digest as is -- i.e., after the
1548   application. The Transfer-Encoding header field is not allowed within
1549   body-parts.
1552   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1553   computing or checking the digest: the line break convention used in
1554   the text actually transmitted &MUST; be left unaltered when computing
1555   the digest.
1558  <t>
[756]1559    <x:h>Note:</x:h> While the definition of Content-MD5 is exactly the same for
[563]1560    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1561    in which the application of Content-MD5 to HTTP entity-bodies
1562    differs from its application to MIME entity-bodies. One is that
1563    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1564    does use Transfer-Encoding and Content-Encoding. Another is that
1565    HTTP more frequently uses binary content types than MIME, so it is
1566    worth noting that, in such cases, the byte order used to compute
1567    the digest is the transmission byte order defined for the type.
1568    Lastly, HTTP allows transmission of text types with any of several
1569    line break conventions and not just the canonical form using CRLF.
1570  </t>
1574<section title="Content-Type" anchor="header.content-type">
1575  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1576  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
[229]1577  <x:anchor-alias value="Content-Type"/>
[357]1578  <x:anchor-alias value="Content-Type-v"/>
[965]1580   The "Content-Type" header field indicates the media type of the
[874]1581   representation. In the case of responses to the HEAD method, the media type is
[698]1582   that which would have been sent had the request been a GET.
[357]1584<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
[366]1585  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
[357]1586  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1589   Media types are defined in <xref target="media.types"/>. An example of the field is
1591<figure><artwork type="example">
[357]1592  Content-Type: text/html; charset=ISO-8859-4
[965]1595   Further discussion of Content-Type is provided in <xref target=""/>.
[29]1601<section title="IANA Considerations" anchor="IANA.considerations">
[921]1602<section title="Header Field Registration" anchor="header.field.registration">
[969]1604   The Message Header Field Registry located at <eref target=""/> shall be updated
[290]1605   with the permanent registrations below (see <xref target="RFC3864"/>):
[680]1607<?BEGININC p3-payload.iana-headers ?>
[253]1608<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
[290]1609<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
[253]1610   <ttcol>Header Field Name</ttcol>
1611   <ttcol>Protocol</ttcol>
1612   <ttcol>Status</ttcol>
1613   <ttcol>Reference</ttcol>
1615   <c>Accept</c>
1616   <c>http</c>
1617   <c>standard</c>
1618   <c>
1619      <xref target="header.accept"/>
1620   </c>
1621   <c>Accept-Charset</c>
1622   <c>http</c>
1623   <c>standard</c>
1624   <c>
1625      <xref target="header.accept-charset"/>
1626   </c>
1627   <c>Accept-Encoding</c>
1628   <c>http</c>
1629   <c>standard</c>
1630   <c>
1631      <xref target="header.accept-encoding"/>
1632   </c>
1633   <c>Accept-Language</c>
1634   <c>http</c>
1635   <c>standard</c>
1636   <c>
1637      <xref target="header.accept-language"/>
1638   </c>
1639   <c>Content-Encoding</c>
1640   <c>http</c>
1641   <c>standard</c>
1642   <c>
1643      <xref target="header.content-encoding"/>
1644   </c>
1645   <c>Content-Language</c>
1646   <c>http</c>
1647   <c>standard</c>
1648   <c>
1649      <xref target="header.content-language"/>
1650   </c>
1651   <c>Content-Location</c>
1652   <c>http</c>
1653   <c>standard</c>
1654   <c>
1655      <xref target="header.content-location"/>
1656   </c>
1657   <c>Content-MD5</c>
1658   <c>http</c>
1659   <c>standard</c>
1660   <c>
1661      <xref target="header.content-md5"/>
1662   </c>
1663   <c>Content-Type</c>
1664   <c>http</c>
1665   <c>standard</c>
1666   <c>
1667      <xref target="header.content-type"/>
1668   </c>
[291]1669   <c>MIME-Version</c>
1670   <c>http</c>
[937]1671   <c>standard</c>
[291]1672   <c>
1673      <xref target="mime-version"/>
1674   </c>
[680]1677<?ENDINC p3-payload.iana-headers ?>
[290]1679   The change controller is: "IETF ( - Internet Engineering Task Force".
[668]1683<section title="Content Coding Registry" anchor="content.coding.registration">
1685   The registration procedure for HTTP Content Codings is now defined
[670]1686   by <xref target="content.coding.registry"/> of this document.
1689   The HTTP Content Codings Registry located at <eref target=""/>
[969]1690   shall be updated with the registration below:
1692<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
[670]1693   <ttcol>Name</ttcol>
[668]1694   <ttcol>Description</ttcol>
1695   <ttcol>Reference</ttcol>
1696   <c>compress</c>
1697   <c>UNIX "compress" program method</c>
1698   <c>
[673]1699      &compress-coding;
[668]1700   </c>
1701   <c>deflate</c>
[806]1702   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1703   the "zlib" data format (<xref target="RFC1950"/>)
1704   </c>
[668]1705   <c>
[673]1706      &deflate-coding;
[668]1707   </c>
1708   <c>gzip</c>
1709   <c>Same as GNU zip <xref target="RFC1952"/></c>
1710   <c>
[673]1711      &gzip-coding;
[668]1712   </c>
1713   <c>identity</c>
1714   <c>No transformation</c>
1715   <c>
1716      <xref target="content.codings"/>
1717   </c>
[8]1723<section title="Security Considerations" anchor="security.considerations">
1725   This section is meant to inform application developers, information
1726   providers, and users of the security limitations in HTTP/1.1 as
1727   described by this document. The discussion does not include
1728   definitive solutions to the problems revealed, though it does make
1729   some suggestions for reducing security risks.
[994]1732<section title="Privacy Issues Connected to Accept Header Fields" anchor="">
[994]1734   Accept request-headers fields can reveal information about the user to all
1735   servers which are accessed. The Accept-Language header field in particular
[8]1736   can reveal information the user would consider to be of a private
1737   nature, because the understanding of particular languages is often
1738   strongly correlated to the membership of a particular ethnic group.
1739   User agents which offer the option to configure the contents of an
[994]1740   Accept-Language header field to be sent in every request are strongly
[8]1741   encouraged to let the configuration process include a message which
1742   makes the user aware of the loss of privacy involved.
1745   An approach that limits the loss of privacy would be for a user agent
[994]1746   to omit the sending of Accept-Language header fields by default, and to ask
1747   the user whether or not to start sending Accept-Language header fields to a
[8]1748   server if it detects, by looking for any Vary response-header fields
1749   generated by the server, that such sending could improve the quality
1750   of service.
1753   Elaborate user-customized accept header fields sent in every request,
1754   in particular if these include quality values, can be used by servers
1755   as relatively reliable and long-lived user identifiers. Such user
1756   identifiers would allow content providers to do click-trail tracking,
1757   and would allow collaborating content providers to match cross-server
1758   click-trails or form submissions of individual users. Note that for
1759   many users not behind a proxy, the network address of the host
1760   running the user agent will also serve as a long-lived user
1761   identifier. In environments where proxies are used to enhance
1762   privacy, user agents ought to be conservative in offering accept
1763   header configuration options to end users. As an extreme privacy
[994]1764   measure, proxies could filter the accept header fields in relayed requests.
[8]1765   General purpose user agents which provide a high degree of header
1766   configurability &SHOULD; warn users about the loss of privacy which can
1767   be involved.
1773<section title="Acknowledgments" anchor="ack">
[119]1778<references title="Normative References">
[121]1780<reference anchor="ISO-8859-1">
1781  <front>
1782    <title>
1783     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1784    </title>
1785    <author>
1786      <organization>International Organization for Standardization</organization>
1787    </author>
1788    <date year="1998"/>
1789  </front>
1790  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
[31]1793<reference anchor="Part1">
[119]1794  <front>
1795    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1796    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1797      <organization abbrev="Day Software">Day Software</organization>
1798      <address><email></email></address>
1799    </author>
1800    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1801      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1802      <address><email></email></address>
[119]1803    </author>
1804    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1805      <organization abbrev="HP">Hewlett-Packard Company</organization>
1806      <address><email></email></address>
1807    </author>
1808    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1809      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1810      <address><email></email></address>
1811    </author>
1812    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1813      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1814      <address><email></email></address>
1815    </author>
1816    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1817      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1818      <address><email></email></address>
1819    </author>
1820    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1821      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1822      <address><email></email></address>
1823    </author>
1824    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1825      <organization abbrev="W3C">World Wide Web Consortium</organization>
1826      <address><email></email></address>
1827    </author>
1828    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1829      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1830      <address><email></email></address>
1831    </author>
1832    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1833  </front>
1834  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1835  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1838<reference anchor="Part2">
[119]1839  <front>
1840    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1841    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1842      <organization abbrev="Day Software">Day Software</organization>
1843      <address><email></email></address>
1844    </author>
1845    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1846      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1847      <address><email></email></address>
[119]1848    </author>
1849    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1850      <organization abbrev="HP">Hewlett-Packard Company</organization>
1851      <address><email></email></address>
1852    </author>
1853    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1854      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1855      <address><email></email></address>
1856    </author>
1857    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1858      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1859      <address><email></email></address>
1860    </author>
1861    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1862      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1863      <address><email></email></address>
1864    </author>
1865    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1866      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1867      <address><email></email></address>
1868    </author>
1869    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1870      <organization abbrev="W3C">World Wide Web Consortium</organization>
1871      <address><email></email></address>
1872    </author>
1873    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1874      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1875      <address><email></email></address>
1876    </author>
1877    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1878  </front>
1879  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1880  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1883<reference anchor="Part4">
[119]1884  <front>
1885    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1886    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1887      <organization abbrev="Day Software">Day Software</organization>
1888      <address><email></email></address>
1889    </author>
1890    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1891      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1892      <address><email></email></address>
[119]1893    </author>
1894    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1895      <organization abbrev="HP">Hewlett-Packard Company</organization>
1896      <address><email></email></address>
1897    </author>
1898    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1899      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1900      <address><email></email></address>
1901    </author>
1902    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1903      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1904      <address><email></email></address>
1905    </author>
1906    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1907      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1908      <address><email></email></address>
1909    </author>
1910    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1911      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1912      <address><email></email></address>
1913    </author>
1914    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1915      <organization abbrev="W3C">World Wide Web Consortium</organization>
1916      <address><email></email></address>
1917    </author>
1918    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1919      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1920      <address><email></email></address>
1921    </author>
1922    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1923  </front>
1924  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1925  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1928<reference anchor="Part5">
[119]1929  <front>
1930    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1931    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1932      <organization abbrev="Day Software">Day Software</organization>
1933      <address><email></email></address>
1934    </author>
1935    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1936      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1937      <address><email></email></address>
[119]1938    </author>
1939    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1940      <organization abbrev="HP">Hewlett-Packard Company</organization>
1941      <address><email></email></address>
1942    </author>
1943    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1944      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1945      <address><email></email></address>
1946    </author>
1947    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1948      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1949      <address><email></email></address>
1950    </author>
1951    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1952      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1953      <address><email></email></address>
1954    </author>
1955    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1956      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1957      <address><email></email></address>
1958    </author>
1959    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1960      <organization abbrev="W3C">World Wide Web Consortium</organization>
1961      <address><email></email></address>
1962    </author>
1963    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1964      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1965      <address><email></email></address>
1966    </author>
1967    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1968  </front>
1969  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1970  <x:source href="p5-range.xml" basename="p5-range"/>
1973<reference anchor="Part6">
[119]1974  <front>
1975    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1976    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1977      <organization abbrev="Day Software">Day Software</organization>
1978      <address><email></email></address>
1979    </author>
1980    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1981      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1982      <address><email></email></address>
[119]1983    </author>
1984    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1985      <organization abbrev="HP">Hewlett-Packard Company</organization>
1986      <address><email></email></address>
1987    </author>
1988    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1989      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1990      <address><email></email></address>
1991    </author>
1992    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1993      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1994      <address><email></email></address>
1995    </author>
1996    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1997      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1998      <address><email></email></address>
1999    </author>
2000    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2001      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2002      <address><email></email></address>
2003    </author>
2004    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2005      <organization abbrev="W3C">World Wide Web Consortium</organization>
2006      <address><email></email></address>
2007    </author>
[601]2008    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
2009      <address><email></email></address>
2010    </author>
[119]2011    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2012      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2013      <address><email></email></address>
2014    </author>
2015    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2016  </front>
2017  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2018  <x:source href="p6-cache.xml" basename="p6-cache"/>
[131]2021<reference anchor="RFC1864">
2022  <front>
2023    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
2024    <author initials="J." surname="Myers" fullname="John G. Myers">
2025      <organization>Carnegie Mellon University</organization>
2026      <address><email></email></address>
2027    </author>
2028    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
2029      <organization>Dover Beach Consulting, Inc.</organization>
2030      <address><email></email></address>
2031    </author>
2032    <date month="October" year="1995"/>
2033  </front>
2034  <seriesInfo name="RFC" value="1864"/>
[122]2037<reference anchor="RFC1950">
2038  <front>
2039    <title>ZLIB Compressed Data Format Specification version 3.3</title>
2040    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2041      <organization>Aladdin Enterprises</organization>
2042      <address><email></email></address>
2043    </author>
[713]2044    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
[122]2045    <date month="May" year="1996"/>
2046  </front>
2047  <seriesInfo name="RFC" value="1950"/>
2048  <annotation>
[908]2049    RFC 1950 is an Informational RFC, thus it might be less stable than
[122]2050    this specification. On the other hand, this downward reference was
[277]2051    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2052    therefore it is unlikely to cause problems in practice. See also
2053    <xref target="BCP97"/>.
[122]2054  </annotation>
[806]2057<reference anchor="RFC1951">
2058  <front>
2059    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
2060    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2061      <organization>Aladdin Enterprises</organization>
2062      <address><email></email></address>
2063    </author>
2064    <date month="May" year="1996"/>
2065  </front>
2066  <seriesInfo name="RFC" value="1951"/>
2067  <annotation>
[908]2068    RFC 1951 is an Informational RFC, thus it might be less stable than
[806]2069    this specification. On the other hand, this downward reference was
2070    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2071    therefore it is unlikely to cause problems in practice. See also
2072    <xref target="BCP97"/>.
2073  </annotation>
[122]2076<reference anchor="RFC1952">
2077  <front>
2078    <title>GZIP file format specification version 4.3</title>
2079    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2080      <organization>Aladdin Enterprises</organization>
2081      <address><email></email></address>
2082    </author>
2083    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2084      <address><email></email></address>
2085    </author>
2086    <author initials="M." surname="Adler" fullname="Mark Adler">
2087      <address><email></email></address>
2088    </author>
2089    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2090      <address><email></email></address>
2091    </author>
2092    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2093      <address><email></email></address>
2094    </author>
2095    <date month="May" year="1996"/>
2096  </front>
2097  <seriesInfo name="RFC" value="1952"/>
2098  <annotation>
[908]2099    RFC 1952 is an Informational RFC, thus it might be less stable than
[122]2100    this specification. On the other hand, this downward reference was
[277]2101    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2102    therefore it is unlikely to cause problems in practice. See also
2103    <xref target="BCP97"/>.
[122]2104  </annotation>
[131]2107<reference anchor="RFC2045">
2108  <front>
2109    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2110    <author initials="N." surname="Freed" fullname="Ned Freed">
2111      <organization>Innosoft International, Inc.</organization>
2112      <address><email></email></address>
2113    </author>
2114    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2115      <organization>First Virtual Holdings</organization>
2116      <address><email></email></address>
2117    </author>
2118    <date month="November" year="1996"/>
2119  </front>
2120  <seriesInfo name="RFC" value="2045"/>
2123<reference anchor="RFC2046">
2124  <front>
2125    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2126    <author initials="N." surname="Freed" fullname="Ned Freed">
2127      <organization>Innosoft International, Inc.</organization>
2128      <address><email></email></address>
2129    </author>
2130    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2131      <organization>First Virtual Holdings</organization>
2132      <address><email></email></address>
2133    </author>
2134    <date month="November" year="1996"/>
2135  </front>
2136  <seriesInfo name="RFC" value="2046"/>
[119]2139<reference anchor="RFC2119">
2140  <front>
2141    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2142    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2143      <organization>Harvard University</organization>
2144      <address><email></email></address>
2145    </author>
2146    <date month="March" year="1997"/>
2147  </front>
2148  <seriesInfo name="BCP" value="14"/>
2149  <seriesInfo name="RFC" value="2119"/>
[303]2152<reference anchor='RFC4647'>
2153  <front>
2154    <title>Matching of Language Tags</title>
2155    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2156      <organization>Yahoo! Inc.</organization>
2157      <address><email></email></address>
2158    </author>
2159    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2160      <organization>Google</organization>
2161      <address><email></email></address>
2162    </author>
2163    <date year='2006' month='September' />
2164  </front>
2165  <seriesInfo name='BCP' value='47' />
2166  <seriesInfo name='RFC' value='4647' />
[425]2169<reference anchor="RFC5234">
2170  <front>
2171    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2172    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2173      <organization>Brandenburg InternetWorking</organization>
2174      <address>
[728]2175        <email></email>
2176      </address> 
[425]2177    </author>
2178    <author initials="P." surname="Overell" fullname="Paul Overell">
2179      <organization>THUS plc.</organization>
2180      <address>
[728]2181        <email></email>
2182      </address>
[425]2183    </author>
2184    <date month="January" year="2008"/>
2185  </front>
2186  <seriesInfo name="STD" value="68"/>
2187  <seriesInfo name="RFC" value="5234"/>
[690]2190<reference anchor='RFC5646'>
[613]2191  <front>
2192    <title>Tags for Identifying Languages</title>
2193    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
2194      <organization>Lab126</organization>
2195      <address><email></email></address>
2196    </author>
2197    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
2198      <organization>Google</organization>
2199      <address><email></email></address>
2200    </author>
[690]2201    <date month='September' year='2009' />
[613]2202  </front>
[690]2203  <seriesInfo name='BCP' value='47' />
2204  <seriesInfo name='RFC' value='5646' />
2209<references title="Informative References">
[129]2211<reference anchor="RFC1945">
2212  <front>
2213    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2214    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2215      <organization>MIT, Laboratory for Computer Science</organization>
2216      <address><email></email></address>
2217    </author>
2218    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2219      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2220      <address><email></email></address>
2221    </author>
2222    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2223      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2224      <address><email></email></address>
2225    </author>
2226    <date month="May" year="1996"/>
2227  </front>
2228  <seriesInfo name="RFC" value="1945"/>
2231<reference anchor="RFC2049">
2232  <front>
2233    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2234    <author initials="N." surname="Freed" fullname="Ned Freed">
2235      <organization>Innosoft International, Inc.</organization>
2236      <address><email></email></address>
2237    </author>
2238    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2239      <organization>First Virtual Holdings</organization>
2240      <address><email></email></address>
2241    </author>
2242    <date month="November" year="1996"/>
2243  </front>
2244  <seriesInfo name="RFC" value="2049"/>
[133]2247<reference anchor="RFC2068">
2248  <front>
2249    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2250    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2251      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2252      <address><email></email></address>
2253    </author>
2254    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2255      <organization>MIT Laboratory for Computer Science</organization>
2256      <address><email></email></address>
2257    </author>
2258    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2259      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2260      <address><email></email></address>
2261    </author>
2262    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2263      <organization>MIT Laboratory for Computer Science</organization>
2264      <address><email></email></address>
2265    </author>
2266    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2267      <organization>MIT Laboratory for Computer Science</organization>
2268      <address><email></email></address>
2269    </author>
2270    <date month="January" year="1997"/>
2271  </front>
2272  <seriesInfo name="RFC" value="2068"/>
[129]2275<reference anchor="RFC2076">
2276  <front>
2277    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2278    <author initials="J." surname="Palme" fullname="Jacob Palme">
2279      <organization>Stockholm University/KTH</organization>
2280      <address><email></email></address>
2281    </author>
2282    <date month="February" year="1997"/>
2283  </front>
2284  <seriesInfo name="RFC" value="2076"/>
2287<reference anchor="RFC2277">
2288  <front>
2289    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2290    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2291      <organization>UNINETT</organization>
2292      <address><email></email></address>
2293    </author>
2294    <date month="January" year="1998"/>
2295  </front>
2296  <seriesInfo name="BCP" value="18"/>
2297  <seriesInfo name="RFC" value="2277"/>
[745]2300<reference anchor='RFC2295'>
2301  <front>
2302    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
2303    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
2304      <organization>Technische Universiteit Eindhoven</organization>
2305      <address>
2306        <email></email>
2307      </address>
2308    </author>
2309    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
2310      <organization>Hewlett-Packard Company</organization>
2311      <address>
2312        <email></email>
2313      </address>
2314    </author>
2315    <date year='1998' month='March'/>
2316  </front>
2317  <seriesInfo name='RFC' value='2295'/>
[129]2320<reference anchor="RFC2388">
2321  <front>
2322    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2323    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2324      <organization>Xerox Palo Alto Research Center</organization>
2325      <address><email></email></address>
2326    </author>
2327    <date year="1998" month="August"/>
2328  </front>
2329  <seriesInfo name="RFC" value="2388"/>
2332<reference anchor="RFC2557">
2333  <front>
2334    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2335    <author initials="F." surname="Palme" fullname="Jacob Palme">
2336      <organization>Stockholm University and KTH</organization>
2337      <address><email></email></address>
2338    </author>
2339    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2340      <organization>Microsoft Corporation</organization>
2341      <address><email></email></address>
2342    </author>
2343    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2344      <organization>Lotus Development Corporation</organization>
2345      <address><email></email></address>
2346    </author>
2347    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2348      <address><email></email></address>
2349    </author>
2350    <date year="1999" month="March"/>
2351  </front>
2352  <seriesInfo name="RFC" value="2557"/>
[119]2355<reference anchor="RFC2616">
2356  <front>
2357    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2358    <author initials="R." surname="Fielding" fullname="R. Fielding">
2359      <organization>University of California, Irvine</organization>
2360      <address><email></email></address>
2361    </author>
2362    <author initials="J." surname="Gettys" fullname="J. Gettys">
2363      <organization>W3C</organization>
2364      <address><email></email></address>
2365    </author>
2366    <author initials="J." surname="Mogul" fullname="J. Mogul">
2367      <organization>Compaq Computer Corporation</organization>
2368      <address><email></email></address>
2369    </author>
2370    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2371      <organization>MIT Laboratory for Computer Science</organization>
2372      <address><email></email></address>
2373    </author>
2374    <author initials="L." surname="Masinter" fullname="L. Masinter">
2375      <organization>Xerox Corporation</organization>
2376      <address><email></email></address>
2377    </author>
2378    <author initials="P." surname="Leach" fullname="P. Leach">
2379      <organization>Microsoft Corporation</organization>
2380      <address><email></email></address>
2381    </author>
2382    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2383      <organization>W3C</organization>
2384      <address><email></email></address>
2385    </author>
2386    <date month="June" year="1999"/>
2387  </front>
2388  <seriesInfo name="RFC" value="2616"/>
[129]2391<reference anchor="RFC3629">
2392  <front>
2393    <title>UTF-8, a transformation format of ISO 10646</title>
2394    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2395      <organization>Alis Technologies</organization>
2396      <address><email></email></address>
2397    </author>
2398    <date month="November" year="2003"/>
2399  </front>
2400  <seriesInfo name="RFC" value="3629"/>
2401  <seriesInfo name="STD" value="63"/>
[253]2404<reference anchor='RFC3864'>
2405  <front>
2406    <title>Registration Procedures for Message Header Fields</title>
2407    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2408      <organization>Nine by Nine</organization>
2409      <address><email></email></address>
2410    </author>
2411    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2412      <organization>BEA Systems</organization>
2413      <address><email></email></address>
2414    </author>
2415    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2416      <organization>HP Labs</organization>
2417      <address><email></email></address>
2418    </author>
2419    <date year='2004' month='September' />
2420  </front>
2421  <seriesInfo name='BCP' value='90' />
2422  <seriesInfo name='RFC' value='3864' />
[200]2425<reference anchor="RFC4288">
2426  <front>
2427    <title>Media Type Specifications and Registration Procedures</title>
2428    <author initials="N." surname="Freed" fullname="N. Freed">
2429      <organization>Sun Microsystems</organization>
2430      <address>
2431        <email></email>
2432      </address>
2433    </author>
2434    <author initials="J." surname="Klensin" fullname="J. Klensin">
2435      <address>
2436        <email></email>
2437      </address>
2438    </author>
2439    <date year="2005" month="December"/>
2440  </front>
2441  <seriesInfo name="BCP" value="13"/>
2442  <seriesInfo name="RFC" value="4288"/>
[670]2445<reference anchor='RFC5226'>
2446  <front>
2447    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2448    <author initials='T.' surname='Narten' fullname='T. Narten'>
2449      <organization>IBM</organization>
2450      <address><email></email></address>
2451    </author>
2452    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
2453      <organization>Google</organization>
2454      <address><email></email></address>
2455    </author>
2456    <date year='2008' month='May' />
2457  </front>
2458  <seriesInfo name='BCP' value='26' />
2459  <seriesInfo name='RFC' value='5226' />
[327]2462<reference anchor="RFC5322">
2463  <front>
2464    <title>Internet Message Format</title>
2465    <author initials="P." surname="Resnick" fullname="P. Resnick">
2466      <organization>Qualcomm Incorporated</organization>
2467    </author>
2468    <date year="2008" month="October"/>
2469  </front>
2470  <seriesInfo name="RFC" value="5322"/>
[277]2473<reference anchor='BCP97'>
2474  <front>
2475    <title>Handling Normative References to Standards-Track Documents</title>
2476    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2477      <address>
2478        <email></email>
2479      </address>
2480    </author>
2481    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2482      <organization>MIT</organization>
2483      <address>
2484        <email></email>
2485      </address>
2486    </author>
2487    <date year='2007' month='June' />
2488  </front>
2489  <seriesInfo name='BCP' value='97' />
2490  <seriesInfo name='RFC' value='4897' />
[874]2496<section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
[327]2498   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]2499   allow a message-body to be transmitted in an open variety of
[8]2500   representations and with extensible mechanisms. However, RFC 2045
2501   discusses mail, and HTTP has a few features that are different from
[874]2502   those described in MIME. These differences were carefully chosen
[8]2503   to optimize performance over binary connections, to allow greater
2504   freedom in the use of new media types, to make date comparisons
2505   easier, and to acknowledge the practice of some early HTTP servers
2506   and clients.
[874]2509   This appendix describes specific areas where HTTP differs from MIME.
2510   Proxies and gateways to strict MIME environments &SHOULD; be
[8]2511   aware of these differences and provide the appropriate conversions
2512   where necessary. Proxies and gateways from MIME environments to HTTP
2513   also need to be aware of the differences because some conversions
2514   might be required.
[8]2517<section title="MIME-Version" anchor="mime-version">
[291]2518  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2519  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
[229]2520  <x:anchor-alias value="MIME-Version"/>
[357]2521  <x:anchor-alias value="MIME-Version-v"/>
2523   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2524   include a single MIME-Version general-header field to indicate what
2525   version of the MIME protocol was used to construct the message. Use
2526   of the MIME-Version header field indicates that the message is in
[115]2527   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
[8]2528   Proxies/gateways are responsible for ensuring full compliance (where
2529   possible) when exporting HTTP messages to strict MIME environments.
[357]2531<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
[366]2532  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
[357]2533  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2536   MIME version "1.0" is the default for use in HTTP/1.1. However,
2537   HTTP/1.1 message parsing and semantics are defined by this document
2538   and not the MIME specification.
2542<section title="Conversion to Canonical Form" anchor="">
[874]2544   MIME requires that an Internet mail body-part be converted to
[115]2545   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
[97]2546   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
[8]2547   allowed for subtypes of the "text" media type when transmitted over
[97]2548   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
[8]2549   line breaks as CRLF and forbids the use of CR or LF outside of line
2550   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2551   line break within text content when a message is transmitted over
2552   HTTP.
2555   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2556   environment &SHOULD; translate all line breaks within the text media
2557   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2558   canonical form of CRLF. Note, however, that this might be complicated
2559   by the presence of a Content-Encoding and by the fact that HTTP
2560   allows the use of some character sets which do not use octets 13 and
2561   10 to represent CR and LF, as is the case for some multi-byte
2562   character sets.
[969]2565   Conversion will break any cryptographic
[8]2566   checksums applied to the original content unless the original content
2567   is already in canonical form. Therefore, the canonical form is
2568   recommended for any content that uses such checksums in HTTP.
2573<section title="Conversion of Date Formats" anchor="">
2575   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2576   simplify the process of date comparison. Proxies and gateways from
2577   other protocols &SHOULD; ensure that any Date header field present in a
2578   message conforms to one of the HTTP/1.1 formats and rewrite the date
2579   if necessary.
[8]2583<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
[874]2585   MIME does not include any concept equivalent to HTTP/1.1's
[8]2586   Content-Encoding header field. Since this acts as a modifier on the
2587   media type, proxies and gateways from HTTP to MIME-compliant
2588   protocols &MUST; either change the value of the Content-Type header
[874]2589   field or decode the representation before forwarding the message. (Some
[8]2590   experimental applications of Content-Type for Internet mail have used
2591   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2592   a function equivalent to Content-Encoding. However, this parameter is
[874]2593   not part of the MIME standards).
2597<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
[874]2599   HTTP does not use the Content-Transfer-Encoding field of MIME.
2600   Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
[85]2601   remove any Content-Transfer-Encoding
[8]2602   prior to delivering the response message to an HTTP client.
2605   Proxies and gateways from HTTP to MIME-compliant protocols are
2606   responsible for ensuring that the message is in the correct format
2607   and encoding for safe transport on that protocol, where "safe
2608   transport" is defined by the limitations of the protocol being used.
2609   Such a proxy or gateway &SHOULD; label the data with an appropriate
2610   Content-Transfer-Encoding if doing so will improve the likelihood of
2611   safe transport over the destination protocol.
2615<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
[29]2617   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
[8]2618   Proxies/gateways &MUST; remove any transfer-coding prior to
2619   forwarding a message via a MIME-compliant protocol.
2623<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
[129]2625   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
[8]2626   need to be aware of MIME line length limitations. Since HTTP does not
2627   have this limitation, HTTP does not fold long lines. MHTML messages
2628   being transported by HTTP follow all conventions of MHTML, including
2629   line length limitations and folding, canonicalization, etc., since
2630   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2631   does not interpret the content or any MIME header lines that might be
2632   contained therein.
2637<section title="Additional Features" anchor="additional.features">
[97]2639   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
[8]2640   existing HTTP implementations, but not consistently and correctly
2641   across most HTTP/1.1 applications. Implementors are advised to be
2642   aware of these features, but cannot rely upon their presence in, or
2643   interoperability with, other HTTP/1.1 applications. Some of these
2644   describe proposed experimental features, and some describe features
2645   that experimental deployment found lacking that are now addressed in
2646   the base HTTP/1.1 specification.
[994]2649   A number of other header fields, such as Content-Disposition and Title,
[97]2650   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
[99]2654<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2656  Clarify contexts that charset is used in.
2657  (<xref target="character.sets"/>)
[712]2660  Remove base URI setting semantics for Content-Location due to poor
[714]2661  implementation support, which was caused by too many broken servers emitting
[994]2662  bogus Content-Location header fields, and also the potentially undesirable effect
[714]2663  of potentially breaking relative links in content-negotiated resources.
[712]2664  (<xref target="header.content-location"/>)
[104]2667  Remove reference to non-existant identity transfer-coding value tokens.
2668  (<xref target="no.content-transfer-encoding"/>)
[680]2672<?BEGININC p3-payload.abnf-appendix ?>
[427]2673<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
2675<artwork type="abnf" name="p3-payload.parsed-abnf">
2676<x:ref>Accept</x:ref> = "Accept:" OWS Accept-v
2677<x:ref>Accept-Charset</x:ref> = "Accept-Charset:" OWS Accept-Charset-v
2678<x:ref>Accept-Charset-v</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
[425]2679 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2680 qvalue ] ] )
[427]2681<x:ref>Accept-Encoding</x:ref> = "Accept-Encoding:" OWS Accept-Encoding-v
2682<x:ref>Accept-Encoding-v</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
[425]2683 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
[427]2684<x:ref>Accept-Language</x:ref> = "Accept-Language:" OWS Accept-Language-v
2685<x:ref>Accept-Language-v</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
[425]2686 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2687 ] )
[427]2688<x:ref>Accept-v</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
[425]2689 OWS media-range [ accept-params ] ] ) ]
[427]2691<x:ref>Content-Encoding</x:ref> = "Content-Encoding:" OWS Content-Encoding-v
2692<x:ref>Content-Encoding-v</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
[425]2693 content-coding ] )
[427]2694<x:ref>Content-Language</x:ref> = "Content-Language:" OWS Content-Language-v
2695<x:ref>Content-Language-v</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
[425]2696 language-tag ] )
[678]2697<x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in [Part1], Section 9.2&gt;
[427]2698<x:ref>Content-Location</x:ref> = "Content-Location:" OWS Content-Location-v
2699<x:ref>Content-Location-v</x:ref> = absolute-URI / partial-URI
2700<x:ref>Content-MD5</x:ref> = "Content-MD5:" OWS Content-MD5-v
2701<x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2702<x:ref>Content-Range</x:ref> = &lt;Content-Range, defined in [Part5], Section 5.2&gt;
2703<x:ref>Content-Type</x:ref> = "Content-Type:" OWS Content-Type-v
2704<x:ref>Content-Type-v</x:ref> = media-type
[538]2706<x:ref>Expires</x:ref> = &lt;Expires, defined in [Part6], Section 3.3&gt;
2708<x:ref>Last-Modified</x:ref> = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;
2710<x:ref>MIME-Version</x:ref> = "MIME-Version:" OWS MIME-Version-v
2711<x:ref>MIME-Version-v</x:ref> = 1*DIGIT "." 1*DIGIT
2713<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
[648]2715<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.6&gt;
[810]2716<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" word ]
[427]2717<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2718<x:ref>attribute</x:ref> = token
2720<x:ref>charset</x:ref> = token
2721<x:ref>codings</x:ref> = ( content-coding / "*" )
2722<x:ref>content-coding</x:ref> = token
[427]2724<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
[690]2725<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC5646], Section 2.1&gt;
2727<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
[425]2728 ";" OWS parameter )
[427]2729<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2731<x:ref>parameter</x:ref> = attribute "=" value
[648]2732<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.6&gt;
[678]2734<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 6.4&gt;
2736<x:ref>subtype</x:ref> = token
2738<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2739<x:ref>type</x:ref> = token
[810]2741<x:ref>value</x:ref> = word
2743<x:ref>word</x:ref> = &lt;word, defined in [Part1], Section 1.2.2&gt;
[532]2746<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2747; Accept defined but not used
[425]2748; Accept-Charset defined but not used
2749; Accept-Encoding defined but not used
2750; Accept-Language defined but not used
[968]2751; Content-Encoding defined but not used
2752; Content-Language defined but not used
2753; Content-Length defined but not used
2754; Content-Location defined but not used
2755; Content-MD5 defined but not used
2756; Content-Range defined but not used
2757; Content-Type defined but not used
2758; Expires defined but not used
2759; Last-Modified defined but not used
[425]2760; MIME-Version defined but not used
[680]2762<?ENDINC p3-payload.abnf-appendix ?>
[252]2764<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
[1002]2766<section title="Since RFC 2616">
2768  Extracted relevant partitions from <xref target="RFC2616"/>.
2772<section title="Since draft-ietf-httpbis-p3-payload-00">
[116]2774  Closed issues:
2775  <list style="symbols">
2776    <t>
[324]2777      <eref target=""/>:
[116]2778      "Media Type Registrations"
2779      (<eref target=""/>)
2780    </t>
2781    <t>
[324]2782      <eref target=""/>:
[116]2783      "Clarification regarding quoting of charset values"
2784      (<eref target=""/>)
2785    </t>
2786    <t>
[324]2787      <eref target=""/>:
[116]2788      "Remove 'identity' token references"
2789      (<eref target=""/>)
2790    </t>
2791    <t>
[324]2792      <eref target=""/>:
[126]2793      "Accept-Encoding BNF"
2794    </t>
2795    <t>
[324]2796      <eref target=""/>:
[152]2797      "Normative and Informative references"
2798    </t>
2799    <t>
[324]2800      <eref target=""/>:
[116]2801      "RFC1700 references"
2802    </t>
[122]2803    <t>
[324]2804      <eref target=""/>:
[200]2805      "Updating to RFC4288"
2806    </t>
2807    <t>
[324]2808      <eref target=""/>:
[129]2809      "Informative references"
2810    </t>
2811    <t>
[324]2812      <eref target=""/>:
[123]2813      "ISO-8859-1 Reference"
2814    </t>
2815    <t>
[324]2816      <eref target=""/>:
[122]2817      "Encoding References Normative"
2818    </t>
[131]2819    <t>
[324]2820      <eref target=""/>:
[131]2821      "Normative up-to-date references"
2822    </t>
[116]2823  </list>
[170]2827<section title="Since draft-ietf-httpbis-p3-payload-01">
[324]2829  Ongoing work on ABNF conversion (<eref target=""/>):
[205]2830  <list style="symbols">
2831    <t>
2832      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2833    </t>
2834  </list>
[252]2838<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
[232]2840  Closed issues:
2841  <list style="symbols">
2842    <t>
[324]2843      <eref target=""/>:
[251]2844      "Quoting Charsets"
2845    </t>
2846    <t>
[324]2847      <eref target=""/>:
[232]2848      "Classification for Allow header"
2849    </t>
[248]2850    <t>
[324]2851      <eref target=""/>:
[248]2852      "missing default for qvalue in description of Accept-Encoding"
2853    </t>
[232]2854  </list>
[994]2857  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
[253]2858  <list style="symbols">
2859    <t>
[994]2860      Reference RFC 3984, and update header field registrations for headers defined
[253]2861      in this document.
2862    </t>
2863  </list>
[267]2867<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
[269]2869  Closed issues:
2870  <list style="symbols">
2871    <t>
[297]2872      <eref target=""/>:
2873      "Quoting Charsets"
2874    </t>
2875    <t>
[303]2876      <eref target=""/>:
2877      "language tag matching (Accept-Language) vs RFC4647"
2878    </t>
2879    <t>
[277]2880      <eref target=""/>:
[269]2881      "RFC 1806 has been replaced by RFC2183"
2882    </t>
2883  </list>
2886  Other changes:
2887  <list style="symbols">
2888    <t>
2889      <eref target=""/>:
2890      "Encoding References Normative" -- rephrase the annotation and reference
2891      <xref target="BCP97"/>.
2892    </t>
2893  </list>
[269]2895 </section>
[323]2897<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
[327]2899  Closed issues:
2900  <list style="symbols">
2901    <t>
2902      <eref target=""/>:
2903      "RFC 2822 is updated by RFC 5322"
2904    </t>
2905  </list>
2908  Ongoing work on ABNF conversion (<eref target=""/>):
2909  <list style="symbols">
2910    <t>
2911      Use "/" instead of "|" for alternatives.
2912    </t>
[357]2913    <t>
2914      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2915      whitespace ("OWS") and required whitespace ("RWS").
2916    </t>
2917    <t>
2918      Rewrite ABNFs to spell out whitespace rules, factor out
[994]2919      header field value format definitions.
[357]2920    </t>
[334]2921  </list>
[382]2925<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
[385]2927  Closed issues:
2928  <list style="symbols">
2929    <t>
2930      <eref target=""/>:
2931      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
2932    </t>
2933  </list>
[543]2936  Final work on ABNF conversion (<eref target=""/>):
[421]2937  <list style="symbols">
2938    <t>
[424]2939      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
[421]2940    </t>
2941  </list>
2944  Other changes:
2945  <list style="symbols">
2946    <t>
2947      Move definition of quality values into Part 1.
2948    </t>
2949  </list>
[547]2953<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
[577]2955  Closed issues:
2956  <list style="symbols">
2957    <t>
2958      <eref target=""/>:
2959      "Content-Location isn't special"
2960    </t>
[592]2961    <t>
2962      <eref target=""/>:
2963      "Content Sniffing"
2964    </t>
[577]2965  </list>
[604]2969<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
[613]2971  Closed issues:
2972  <list style="symbols">
2973    <t>
[670]2974      <eref target=""/>:
[613]2975      "Updated reference for language tags"
2976    </t>
[663]2977    <t>
[716]2978      <eref target=""/>:
2979      "Clarify rules for determining what entities a response carries"
2980    </t>
2981    <t>
[712]2982      <eref target=""/>:
2983      "Content-Location base-setting problems"
2984    </t>
2985    <t>
[663]2986      <eref target=""/>:
2987      "Content Sniffing"
2988    </t>
[670]2989    <t>
2990      <eref target=""/>:
2991      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
2992    </t>
[673]2993    <t>
2994      <eref target=""/>:
2995      "move definitions of gzip/deflate/compress to part 1"
2996    </t>
[613]2997  </list>
3000  Partly resolved issues:
3001  <list style="symbols">
3002    <t>
3003      <eref target=""/>:
3004      "update IANA requirements wrt Transfer-Coding values" (add the
3005      IANA Considerations subsection)
3006    </t>
[668]3007    <t>
3008      <eref target=""/>:
3009      "update IANA requirements wrt Content-Coding values" (add the
3010      IANA Considerations subsection)
3011    </t>
[667]3012  </list>
[720]3016<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
[724]3018  Closed issues:
3019  <list style="symbols">
3020    <t>
[745]3021      <eref target=""/>:
3022      "Content Negotiation for media types"
3023    </t>
3024    <t>
[724]3025      <eref target=""/>:
3026      "Accept-Language: which RFC4647 filtering?"
3027    </t>
3028  </list>
[773]3032<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
[808]3034  Closed issues:
3035  <list style="symbols">
3036    <t>
[937]3037      <eref target=""/>:
3038      "MIME-Version not listed in P1, general header fields"
3039    </t>
3040    <t>
[808]3041      <eref target=""/>:
3042      "IANA registry for content/transfer encodings"
3043    </t>
[810]3044    <t>
[831]3045      <eref target=""/>:
3046      "Content Sniffing"
3047    </t>
3048    <t>
[810]3049      <eref target=""/>:
3050      "use of term "word" when talking about header structure"
3051    </t>
[808]3052  </list>
3055  Partly resolved issues:
3056  <list style="symbols">
3057    <t>
3058      <eref target=""/>:
3059      "Term for the requested resource's URI"
3060    </t>
3061  </list>
[841]3065<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.10">
[854]3067  Closed issues:
3068  <list style="symbols">
3069    <t>
[858]3070      <eref target=""/>:
3071      "Clarify 'Requested Variant'"
3072    </t>
3073    <t>
3074      <eref target=""/>:
3075      "Content-Location isn't special"
3076    </t>
3077    <t>
[854]3078      <eref target=""/>:
3079      "Delimiting messages with multipart/byteranges"
3080    </t>
[858]3081    <t>
3082      <eref target=""/>:
3083      "Clarify entity / representation / variant terminology"
3084    </t>
3085    <t>
3086      <eref target=""/>:
3087      "confusing req. language for Content-Location"
3088    </t>
3089    <t>
3090      <eref target=""/>:
3091      "Content-Location on 304 responses"
3092    </t>
[882]3093    <t>
3094      <eref target=""/>:
3095      "'requested resource' in content-encoding definition"
3096    </t>
[911]3097    <t>
3098      <eref target=""/>:
3099      "consider removing the 'changes from 2068' sections"
3100    </t>
[854]3101  </list>
3104  Partly resolved issues:
3105  <list style="symbols">
3106    <t>
3107      <eref target=""/>:
3108      "Content-MD5 and partial responses"
3109    </t>
3110  </list>
[973]3114<section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.since.11">
[987]3116  Closed issues:
3117  <list style="symbols">
3118    <t>
3119      <eref target=""/>:
3120      "Factor out Content-Disposition"
3121    </t>
3122  </list>
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