source: draft-ietf-httpbis/latest/p3-payload.xml @ 981

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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="quoted-string"/>
307  <x:anchor-alias value="token"/>
[810]308  <x:anchor-alias value="word"/>
[357]309  <x:anchor-alias value="OWS"/>
[424]311  The core rules below are defined in &basic-rules;:
313<figure><artwork type="abnf2616">
[229]314  <x:ref>quoted-string</x:ref>  = &lt;quoted-string, defined in &basic-rules;&gt;
315  <x:ref>token</x:ref>          = &lt;token, defined in &basic-rules;&gt;
[810]316  <x:ref>word</x:ref>           = &lt;word, defined in &basic-rules;&gt;
[357]317  <x:ref>OWS</x:ref>            = &lt;OWS, defined in &basic-rules;&gt;
321<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
[374]322  <x:anchor-alias value="absolute-URI"/>
[229]323  <x:anchor-alias value="Allow"/>
324  <x:anchor-alias value="Content-Length"/>
325  <x:anchor-alias value="Content-Range"/>
326  <x:anchor-alias value="Expires"/>
327  <x:anchor-alias value="Last-Modified"/>
[391]328  <x:anchor-alias value="partial-URI"/>
[457]329  <x:anchor-alias value="qvalue"/>
[206]331  The ABNF rules below are defined in other parts:
[207]333<figure><!--Part1--><artwork type="abnf2616">
[374]334  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in &uri;&gt;
[229]335  <x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in &header-content-length;&gt;
[391]336  <x:ref>partial-URI</x:ref>    = &lt;partial-URI, defined in &uri;&gt;
[457]337  <x:ref>qvalue</x:ref>         = &lt;qvalue, defined in &qvalue;&gt;
339<figure><!--Part4--><artwork type="abnf2616">
[229]340  <x:ref>Last-Modified</x:ref>  = &lt;Last-Modified, defined in &header-last-modified;&gt;
342<figure><!--Part5--><artwork type="abnf2616">
[229]343  <x:ref>Content-Range</x:ref>  = &lt;Content-Range, defined in &header-content-range;&gt;
345<figure><!--Part6--><artwork type="abnf2616">
[229]346  <x:ref>Expires</x:ref>        = &lt;Expires, defined in &header-expires;&gt;
[8]354<section title="Protocol Parameters" anchor="protocol.parameters">
356<section title="Character Sets" anchor="character.sets">
358   HTTP uses the same definition of the term "character set" as that
359   described for MIME:
362   The term "character set" is used in this document to refer to a
363   method used with one or more tables to convert a sequence of octets
364   into a sequence of characters. Note that unconditional conversion in
[908]365   the other direction is not required, in that not all characters might
366   be available in a given character set and a character set might provide
[8]367   more than one sequence of octets to represent a particular character.
368   This definition is intended to allow various kinds of character
369   encoding, from simple single-table mappings such as US-ASCII to
370   complex table switching methods such as those that use ISO-2022's
371   techniques. However, the definition associated with a MIME character
372   set name &MUST; fully specify the mapping to be performed from octets
373   to characters. In particular, use of external profiling information
374   to determine the exact mapping is not permitted.
377  <t>
378    <x:h>Note:</x:h> This use of the term "character set" is more commonly
[879]379    referred to as a "character encoding". However, since HTTP and
[563]380    MIME share the same registry, it is important that the terminology
381    also be shared.
382  </t>
[229]384<t anchor="rule.charset">
385  <x:anchor-alias value="charset"/>
[8]386   HTTP character sets are identified by case-insensitive tokens. The
387   complete set of tokens is defined by the IANA Character Set registry
[91]388   (<eref target=""/>).
390<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
[229]391  <x:ref>charset</x:ref> = <x:ref>token</x:ref>
394   Although HTTP allows an arbitrary token to be used as a charset
395   value, any token that has a predefined value within the IANA
[91]396   Character Set registry &MUST; represent the character set defined
[8]397   by that registry. Applications &SHOULD; limit their use of character
398   sets to those defined by the IANA registry.
[81]401   HTTP uses charset in two contexts: within an Accept-Charset request
402   header (in which the charset value is an unquoted token) and as the
[115]403   value of a parameter in a Content-Type header (within a request or
[81]404   response), in which case the parameter value of the charset parameter
[908]405   can be quoted.
[969]408   Implementors need to be aware of IETF character set requirements <xref target="RFC3629"/>
[8]409   <xref target="RFC2277"/>.
412<section title="Missing Charset" anchor="missing.charset">
414   Some HTTP/1.0 software has interpreted a Content-Type header without
[879]415   charset parameter incorrectly to mean "recipient should guess".
[211]416   Senders wishing to defeat this behavior &MAY; include a charset
417   parameter even when the charset is ISO-8859-1 (<xref target="ISO-8859-1"/>) and &SHOULD; do so when
418   it is known that it will not confuse the recipient.
421   Unfortunately, some older HTTP/1.0 clients did not deal properly with
422   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
423   charset label provided by the sender; and those user agents that have
424   a provision to "guess" a charset &MUST; use the charset from the
425   content-type field if they support that charset, rather than the
426   recipient's preference, when initially displaying a document. See
427   <xref target="canonicalization.and.text.defaults"/>.
432<section title="Content Codings" anchor="content.codings">
[229]433  <x:anchor-alias value="content-coding"/>
435   Content coding values indicate an encoding transformation that has
[866]436   been or can be applied to a representation. Content codings are primarily
437   used to allow a representation to be compressed or otherwise usefully
[8]438   transformed without losing the identity of its underlying media type
[866]439   and without loss of information. Frequently, the representation is stored in
[8]440   coded form, transmitted directly, and only decoded by the recipient.
442<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
[229]443  <x:ref>content-coding</x:ref>   = <x:ref>token</x:ref>
446   All content-coding values are case-insensitive. HTTP/1.1 uses
447   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
448   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
449   describes the content-coding, what is more important is that it
450   indicates what decoding mechanism will be required to remove the
451   encoding.
[673]454   compress<iref item="compress (Coding Format)"/><iref item="Coding Format" subitem="compress"/>
455  <list>
456    <t>
457      See &compress-coding;.
458    </t>
459  </list>
[673]462   deflate<iref item="deflate (Coding Format)"/><iref item="Coding Format" subitem="deflate"/>
[8]463  <list>
464    <t>
[673]465      See &deflate-coding;.
[8]466    </t>
467  </list>
[673]470   gzip<iref item="gzip (Coding Format)"/><iref item="Coding Format" subitem="gzip"/>
471  <list>
472    <t>
473      See &gzip-coding;.
474    </t>
475  </list>
[673]478   identity<iref item="identity (Coding Format)"/><iref item="Coding Format" subitem="identity"/>
[8]479  <list><t>
480        The default (identity) encoding; the use of no transformation
481        whatsoever. This content-coding is used only in the Accept-Encoding
482        header, and &SHOULD-NOT;  be used in the Content-Encoding
483        header.
484  </t></list>
487<section title="Content Coding Registry" anchor="content.coding.registry">
[670]489   The HTTP Content Coding Registry defines the name space for the content
490   coding names.
493   Registrations &MUST; include the following fields:
494   <list style="symbols">
495     <t>Name</t>
496     <t>Description</t>
497     <t>Pointer to specification text</t>
498   </list>
[808]501   Names of content codings &MUST-NOT; overlap with names of transfer codings
502   (&transfer-codings;), unless the encoding transformation is identical (as it
503   is the case for the compression codings defined in
504   &compression-codings;).
[942]507   Values to be added to this name space require a specification
508   (see "Specification Required" in
[670]509   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
[8]510   conform to the purpose of content coding defined in this section.
513   The registry itself is maintained at
514   <eref target=""/>.
[8]520<section title="Media Types" anchor="media.types">
[229]521  <x:anchor-alias value="media-type"/>
522  <x:anchor-alias value="type"/>
523  <x:anchor-alias value="subtype"/>
[152]525   HTTP uses Internet Media Types <xref target="RFC2046"/> in the Content-Type (<xref target="header.content-type"/>)
[8]526   and Accept (<xref target="header.accept"/>) header fields in order to provide
527   open and extensible data typing and type negotiation.
529<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]530  <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> )
531  <x:ref>type</x:ref>       = <x:ref>token</x:ref>
532  <x:ref>subtype</x:ref>    = <x:ref>token</x:ref>
[229]534<t anchor="rule.parameter">
535  <x:anchor-alias value="attribute"/>
536  <x:anchor-alias value="parameter"/>
537  <x:anchor-alias value="value"/>
[8]538   Parameters &MAY; follow the type/subtype in the form of attribute/value
[29]539   pairs.
[29]541<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]542  <x:ref>parameter</x:ref>      = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
543  <x:ref>attribute</x:ref>      = <x:ref>token</x:ref>
[810]544  <x:ref>value</x:ref>          = <x:ref>word</x:ref>
547   The type, subtype, and parameter attribute names are case-insensitive.
[370]548   Parameter values might or might not be case-sensitive, depending on the
549   semantics of the parameter name.  The presence or absence of a parameter might
[8]550   be significant to the processing of a media-type, depending on its
551   definition within the media type registry.
[908]554   A parameter value that matches the <x:ref>token</x:ref> production can be
[297]555   transmitted as either a token or within a quoted-string. The quoted and
556   unquoted values are equivalent.
[8]559   Note that some older HTTP applications do not recognize media type
560   parameters. When sending data to older HTTP applications,
561   implementations &SHOULD; only use media type parameters when they are
562   required by that type/subtype definition.
565   Media-type values are registered with the Internet Assigned Number
[91]566   Authority (IANA). The media type registration process is
[115]567   outlined in <xref target="RFC4288"/>. Use of non-registered media types is
[8]568   discouraged.
571<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
[874]573   Internet media types are registered with a canonical form. A
574   representation transferred via HTTP messages &MUST; be in the
[8]575   appropriate canonical form prior to its transmission except for
576   "text" types, as defined in the next paragraph.
579   When in canonical form, media subtypes of the "text" type use CRLF as
580   the text line break. HTTP relaxes this requirement and allows the
581   transport of text media with plain CR or LF alone representing a line
[874]582   break when it is done consistently for an entire representation. HTTP
583   applications &MUST; accept CRLF, bare CR, and bare LF as indicating
584   a line break in text media received via HTTP. In
585   addition, if the text is in a character encoding that does not
[8]586   use octets 13 and 10 for CR and LF respectively, as is the case for
[874]587   some multi-byte character encodings, HTTP allows the use of whatever octet
588   sequences are defined by that character encoding to represent the
[8]589   equivalent of CR and LF for line breaks. This flexibility regarding
[874]590   line breaks applies only to text media in the payload body; a bare CR
[8]591   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
592   structures (such as header fields and multipart boundaries).
[874]595   If a representation is encoded with a content-coding, the underlying
[8]596   data &MUST; be in a form defined above prior to being encoded.
[211]599   The "charset" parameter is used with some media types to define the
[874]600   character encoding (<xref target="character.sets"/>) of the data. When no explicit charset
[211]601   parameter is provided by the sender, media subtypes of the "text"
602   type are defined to have a default charset value of "ISO-8859-1" when
[874]603   received via HTTP. Data in character encodings other than "ISO-8859-1" or
[211]604   its subsets &MUST; be labeled with an appropriate charset value. See
605   <xref target="missing.charset"/> for compatibility problems.
609<section title="Multipart Types" anchor="multipart.types">
611   MIME provides for a number of "multipart" types -- encapsulations of
[874]612   one or more representations within a single message-body. All multipart
[97]613   types share a common syntax, as defined in <xref target="RFC2046" x:sec="5.1.1" x:fmt="of"/>,
614   and &MUST; include a boundary parameter as part of the media type
[8]615   value. The message body is itself a protocol element and &MUST;
616   therefore use only CRLF to represent line breaks between body-parts.
619   In general, HTTP treats a multipart message-body no differently than
[852]620   any other media type: strictly as payload.  HTTP does not use the
621   multipart boundary as an indicator of message-body length.
[97]622   <!-- jre: re-insert removed text pointing to caching? -->
[852]623   In all other respects, an HTTP user agent &SHOULD; follow the same or similar
[8]624   behavior as a MIME user agent would upon receipt of a multipart type.
625   The MIME header fields within each body-part of a multipart message-body
626   do not have any significance to HTTP beyond that defined by
627   their MIME semantics.
630   If an application receives an unrecognized multipart subtype, the
631   application &MUST; treat it as being equivalent to "multipart/mixed".
634  <t>
635    <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
636    for carrying form data suitable for processing via the POST
637    request method, as described in <xref target="RFC2388"/>.
638  </t>
643<section title="Language Tags" anchor="language.tags">
[229]644  <x:anchor-alias value="language-tag"/>
[690]646   A language tag, as defined in <xref target="RFC5646"/>, identifies a
[613]647   natural language spoken, written, or otherwise conveyed by human beings for
648   communication of information to other human beings. Computer languages are
649   explicitly excluded. HTTP uses language tags within the Accept-Language and
650   Content-Language fields.
[613]653   In summary, a language tag is composed of one or more parts: A primary
654   language subtag followed by a possibly empty series of subtags:
[613]656<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/>
[690]657  <x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in <xref target="RFC5646" x:sec="2.1"/>&gt;
660   White space is not allowed within the tag and all tags are case-insensitive.
[613]661   The name space of language subtags is administered by the IANA (see
662   <eref target=""/>).
665  <preamble>Example tags include:</preamble>
666<artwork type="example">
667  en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
[690]671   See <xref target="RFC5646"/> for further information.
[965]676<section title="Payload" anchor="payload">
[965]678   HTTP messages &MAY; transfer a payload if not otherwise restricted by
679   the request method or response status code.  The payload consists of
680   metadata, in the form of header fields, and data, in the form of the
681   sequence of octets in the message-body after any transfer-coding has
682   been decoded.
[965]684<iref item="payload"/>
686   A "<x:dfn>payload</x:dfn>" in HTTP is always a partial or complete
687   representation of some resource.  We use separate terms for payload
688   and representation because some messages contain only the associated
689   representation's header fields (e.g., responses to HEAD) or only some
690   part(s) of the representation (e.g., the 206 status code).
692<section title="Payload Header Fields" anchor="payload.header.fields">
693  <x:anchor-alias value="payload-header"/>
[965]695   HTTP header fields that specifically define the payload, rather than the
696   associated representation, are referred to as "payload header fields".
697   The following payload header fields are defined by HTTP/1.1:
700   <x:ref>Content-Length</x:ref>           ; &header-content-length;
701   <x:ref>Content-MD5</x:ref>              ; <xref target="header.content-md5"/>
702   <x:ref>Content-Range</x:ref>            ; &header-content-range;
[874]706<section title="Payload Body" anchor="payload.body">
707  <x:anchor-alias value="payload-body"/>
[874]709   A payload body is only present in a message when a message-body is
710   present, as described in &message-body;. The payload body is obtained
[8]711   from the message-body by decoding any Transfer-Encoding that might
712   have been applied to ensure safe and proper transfer of the message.
[965]717<section title="Representation" anchor="representation">
718<iref item="representation"/>
[965]720   A "<x:dfn>representation</x:dfn>" is information in a format that can be readily
721   communicated from one party to another.  A resource representation
722   is information that reflects the state of that resource, as observed
723   at some point in the past (e.g., in a response to GET) or to be
724   desired at some point in the future (e.g., in a PUT request).
727   Most, but not all, representations transferred via HTTP are intended
728   to be a representation of the target resource (the resource identified
729   by the effective request URI).  The precise semantics of a representation
730   are determined by the type of message (request or response), the request
731   method, the response status code, and the representation metadata.
732   For example, the above semantic is true for the representation in any
733   200 (OK) response to GET and for the representation in any PUT request.
734   A 200 response to PUT, in contrast, contains either a representation
735   that describes the successful action or a representation of the target
736   resource, with the latter indicated by a Content-Location header field
737   with the same value as the effective request URI.  Likewise, response
738   messages with an error status code usually contain a representation that
739   describes the error and what next steps are suggested for resolving it.
742<section title="Representation Header Fields" anchor="representation.header.fields">
743  <x:anchor-alias value="representation-header"/>
745   Representation header fields define metadata about the representation data
746   enclosed in the message-body or, if no message-body is present, about
747   the representation that would have been transferred in a 200 response
748   to a simultaneous GET request with the same effective request URI.
751   The following header fields are defined as representation metadata:
754   <x:ref>Content-Encoding</x:ref>         ; <xref target="header.content-encoding"/>
755   <x:ref>Content-Language</x:ref>         ; <xref target="header.content-language"/>
756   <x:ref>Content-Location</x:ref>         ; <xref target="header.content-location"/>
757   <x:ref>Content-Type</x:ref>             ; <xref target="header.content-type"/>
758   <x:ref>Expires</x:ref>                  ; &header-expires;
759   <x:ref>Last-Modified</x:ref>            ; &header-last-modified;
763<section title="Representation Data" anchor="">
764  <x:anchor-alias value="representation-data"/>
766   The representation body associated with an HTTP message is
767   either provided as the payload body of the message or
768   referred to by the message semantics and the effective request
769   URI.  The representation data is in a format and encoding defined by
770   the representation metadata header fields.
773   The data type of the representation data
774   is determined via the header fields Content-Type and Content-Encoding.
[8]775   These define a two-layer, ordered encoding model:
777<figure><artwork type="example">
[965]778  representation-data := Content-Encoding( Content-Type( bits ) )
[965]781   Content-Type specifies the media type of the underlying data, which
782   defines both the data format and how that data &SHOULD; be processed
783   by the recipient (within the scope of the request method semantics).
784   Any HTTP/1.1 message containing a payload body &SHOULD; include a
785   Content-Type header field defining the media type of the associated
786   representation unless that metadata is unknown to the sender.
[831]787   If the Content-Type header field is not present, it indicates that
[965]788   the sender does not know the media type of the representation;
789   recipients &MAY; either assume that the media type is
790   "application/octet-stream" (<xref target="RFC2046" x:fmt="," x:sec="4.5.1"/>)
[592]791   or examine the content to determine its type.
[965]794   In practice, resource owners do not always properly configure their origin
795   server to provide the correct Content-Type for a given representation,
796   with the result that some clients will examine a response body's content
797   and override the specified type.
[908]798   Clients that do so risk drawing incorrect conclusions, which might expose
[965]799   additional security risks (e.g., "privilege escalation").  Furthermore,
800   it is impossible to determine the sender's intent by examining the data
801   format: many data formats match multiple media types that differ only in
802   processing semantics.  Implementers are encouraged to provide a means of
803   disabling such "content sniffing" when it is used.
[908]806   Content-Encoding is used to indicate any additional content
[8]807   codings applied to the data, usually for the purpose of data
[965]808   compression, that are a property of the representation.  If
809   Content-Encoding is not present, then there is no additional
810   encoding beyond that defined by the Content-Type.
815<section title="Content Negotiation" anchor="content.negotiation">
[745]817   HTTP responses include a representation which contains information for
818   interpretation, whether by a human user or for further processing.
819   Often, the server has different ways of representing the
820   same information; for example, in different formats, languages,
821   or using different character encodings.
[745]824   HTTP clients and their users might have different or variable
825   capabilities, characteristics or preferences which would influence
826   which representation, among those available from the server,
827   would be best for the server to deliver. For this reason, HTTP
828   provides mechanisms for "content negotiation" -- a process of
829   allowing selection of a representation of a given resource,
830   when more than one is available.
[745]833   This specification defines two patterns of content negotiation;
834   "server-driven", where the server selects the representation based
835   upon the client's stated preferences, and "agent-driven" negotiation,
836   where the server provides a list of representations for the client to
837   choose from, based upon their metadata. In addition,  there are
838   other patterns: some applications use an "active content" pattern,
839   where the server returns active content which runs on the client
840   and, based on client available parameters, selects additional
841   resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)
842   has also been proposed.
845   These patterns are all widely used, and have trade-offs in applicability
846   and practicality. In particular, when the number of preferences or
847   capabilities to be expressed by a client are large (such as when many
848   different formats are supported by a user-agent), server-driven
[908]849   negotiation becomes unwieldy, and might not be appropriate. Conversely,
[745]850   when the number of representations to choose from is very large,
[908]851   agent-driven negotiation might not be appropriate.
854   Note that in all cases, the supplier of representations has the
855   responsibility for determining which representations might be
856   considered to be the "same information".
859<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
861   If the selection of the best representation for a response is made by
862   an algorithm located at the server, it is called server-driven
863   negotiation. Selection is based on the available representations of
[763]864   the response (the dimensions over which it can vary; e.g., language,
[8]865   content-coding, etc.) and the contents of particular header fields in
866   the request message or on other information pertaining to the request
867   (such as the network address of the client).
870   Server-driven negotiation is advantageous when the algorithm for
871   selecting from among the available representations is difficult to
872   describe to the user agent, or when the server desires to send its
873   "best guess" to the client along with the first response (hoping to
874   avoid the round-trip delay of a subsequent request if the "best
875   guess" is good enough for the user). In order to improve the server's
876   guess, the user agent &MAY; include request header fields (Accept,
877   Accept-Language, Accept-Encoding, etc.) which describe its
878   preferences for such a response.
881   Server-driven negotiation has disadvantages:
882  <list style="numbers">
883    <t>
884         It is impossible for the server to accurately determine what
885         might be "best" for any given user, since that would require
886         complete knowledge of both the capabilities of the user agent
887         and the intended use for the response (e.g., does the user want
888         to view it on screen or print it on paper?).
889    </t>
890    <t>
891         Having the user agent describe its capabilities in every
892         request can be both very inefficient (given that only a small
893         percentage of responses have multiple representations) and a
894         potential violation of the user's privacy.
895    </t>
896    <t>
897         It complicates the implementation of an origin server and the
898         algorithms for generating responses to a request.
899    </t>
900    <t>
[908]901         It might limit a public cache's ability to use the same response
[8]902         for multiple user's requests.
903    </t>
904  </list>
907   HTTP/1.1 includes the following request-header fields for enabling
908   server-driven negotiation through description of user agent
909   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
910   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
[745]911   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;).
912   However, an origin server is not limited to these dimensions and &MAY; vary
913   the response based on any aspect of the request, including information
[8]914   outside the request-header fields or within extension header fields
915   not defined by this specification.
918  <t>
919    <x:h>Note:</x:h> In practice, User-Agent based negotiation is fragile,
920    because new clients might not be recognized.
921  </t>
[115]924   The Vary header field (&header-vary;) can be used to express the parameters the
[8]925   server uses to select a representation that is subject to server-driven
[29]926   negotiation.
930<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
932   With agent-driven negotiation, selection of the best representation
933   for a response is performed by the user agent after receiving an
934   initial response from the origin server. Selection is based on a list
935   of the available representations of the response included within the
[874]936   header fields or body of the initial response, with each
[8]937   representation identified by its own URI. Selection from among the
[908]938   representations can be performed automatically (if the user agent is
[8]939   capable of doing so) or manually by the user selecting from a
940   generated (possibly hypertext) menu.
943   Agent-driven negotiation is advantageous when the response would vary
944   over commonly-used dimensions (such as type, language, or encoding),
945   when the origin server is unable to determine a user agent's
946   capabilities from examining the request, and generally when public
947   caches are used to distribute server load and reduce network usage.
950   Agent-driven negotiation suffers from the disadvantage of needing a
951   second request to obtain the best alternate representation. This
952   second request is only efficient when caching is used. In addition,
953   this specification does not define any mechanism for supporting
954   automatic selection, though it also does not prevent any such
955   mechanism from being developed as an extension and used within
956   HTTP/1.1.
[745]959   This specification defines the 300 (Multiple Choices) and 406 (Not Acceptable)
[8]960   status codes for enabling agent-driven negotiation when the server is
961   unwilling or unable to provide a varying response using server-driven
962   negotiation.
[8]967<section title="Header Field Definitions" anchor="header.fields">
[117]969   This section defines the syntax and semantics of HTTP/1.1 header fields
970   related to the payload of messages.
[8]973<section title="Accept" anchor="header.accept">
974  <iref primary="true" item="Accept header" x:for-anchor=""/>
975  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
[229]976  <x:anchor-alias value="Accept"/>
[357]977  <x:anchor-alias value="Accept-v"/>
[370]978  <x:anchor-alias value="accept-ext"/>
[229]979  <x:anchor-alias value="accept-params"/>
980  <x:anchor-alias value="media-range"/>
[698]982   The "Accept" request-header field can be used by user agents to specify
983   response media types that are acceptable. Accept headers can be used to
984   indicate that the request is specifically limited to a small set of desired
985   types, as in the case of a request for an in-line image.
[370]987<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]988  <x:ref>Accept</x:ref>   = "Accept" ":" <x:ref>OWS</x:ref> <x:ref>Accept-v</x:ref>
[357]989  <x:ref>Accept-v</x:ref> = #( <x:ref>media-range</x:ref> [ <x:ref>accept-params</x:ref> ] )
[229]991  <x:ref>media-range</x:ref>    = ( "*/*"
[334]992                   / ( <x:ref>type</x:ref> "/" "*" )
993                   / ( <x:ref>type</x:ref> "/" <x:ref>subtype</x:ref> )
[370]994                   ) *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
995  <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]996  <x:ref>accept-ext</x:ref>     = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref>
[810]997                   [ "=" <x:ref>word</x:ref> ]
1000   The asterisk "*" character is used to group media types into ranges,
1001   with "*/*" indicating all media types and "type/*" indicating all
1002   subtypes of that type. The media-range &MAY; include media type
1003   parameters that are applicable to that range.
1006   Each media-range &MAY; be followed by one or more accept-params,
1007   beginning with the "q" parameter for indicating a relative quality
1008   factor. The first "q" parameter (if any) separates the media-range
1009   parameter(s) from the accept-params. Quality factors allow the user
1010   or user agent to indicate the relative degree of preference for that
[457]1011   media-range, using the qvalue scale from 0 to 1 (&qvalue;). The
[8]1012   default value is q=1.
1015  <t>
1016    <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
1017    parameters from Accept extension parameters is due to historical
1018    practice. Although this prevents any media type parameter named
1019    "q" from being used with a media range, such an event is believed
1020    to be unlikely given the lack of any "q" parameters in the IANA
1021    media type registry and the rare usage of any media type
1022    parameters in Accept. Future media types are discouraged from
1023    registering any parameter named "q".
1024  </t>
1027   The example
1029<figure><artwork type="example">
[357]1030  Accept: audio/*; q=0.2, audio/basic
1033   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
[879]1034   type if it is the best available after an 80% mark-down in quality".
1037   If no Accept header field is present, then it is assumed that the
1038   client accepts all media types. If an Accept header field is present,
1039   and if the server cannot send a response which is acceptable
1040   according to the combined Accept field value, then the server &SHOULD;
[137]1041   send a 406 (Not Acceptable) response.
1044   A more elaborate example is
1046<figure><artwork type="example">
[357]1047  Accept: text/plain; q=0.5, text/html,
1048          text/x-dvi; q=0.8, text/x-c
1051   Verbally, this would be interpreted as "text/html and text/x-c are
1052   the preferred media types, but if they do not exist, then send the
[866]1053   text/x-dvi representation, and if that does not exist, send the text/plain
[879]1054   representation".
1057   Media ranges can be overridden by more specific media ranges or
1058   specific media types. If more than one media range applies to a given
1059   type, the most specific reference has precedence. For example,
1061<figure><artwork type="example">
[357]1062  Accept: text/*, text/html, text/html;level=1, */*
1065   have the following precedence:
[459]1066   <list style="numbers">
1067    <t>text/html;level=1</t>
1068    <t>text/html</t>
1069    <t>text/*</t>
1070    <t>*/*</t>
1071   </list>
1074   The media type quality factor associated with a given type is
1075   determined by finding the media range with the highest precedence
1076   which matches that type. For example,
1078<figure><artwork type="example">
[357]1079  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
1080          text/html;level=2;q=0.4, */*;q=0.5
1083   would cause the following values to be associated:
[459]1085<texttable align="left">
1086  <ttcol>Media Type</ttcol><ttcol>Quality Value</ttcol>
1087  <c>text/html;level=1</c>    <c>1</c>
1088  <c>text/html</c>            <c>0.7</c>
1089  <c>text/plain</c>           <c>0.3</c>
1090  <c>image/jpeg</c>           <c>0.5</c>
1091  <c>text/html;level=2</c>    <c>0.4</c>
1092  <c>text/html;level=3</c>    <c>0.7</c>
1095      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
1096      values for certain media ranges. However, unless the user agent is
1097      a closed system which cannot interact with other rendering agents,
1098      this default set ought to be configurable by the user.
1102<section title="Accept-Charset" anchor="header.accept-charset">
1103  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
1104  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
[229]1105  <x:anchor-alias value="Accept-Charset"/>
[357]1106  <x:anchor-alias value="Accept-Charset-v"/>
[698]1108   The "Accept-Charset" request-header field can be used by user agents to
1109   indicate what response character sets are acceptable. This field allows
[8]1110   clients capable of understanding more comprehensive or special-purpose
[698]1111   character sets to signal that capability to a server which is capable of
1112   representing documents in those character sets.
[357]1114<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/><iref primary="true" item="Grammar" subitem="Accept-Charset-v"/>
[366]1115  <x:ref>Accept-Charset</x:ref>   = "Accept-Charset" ":" <x:ref>OWS</x:ref>
[357]1116          <x:ref>Accept-Charset-v</x:ref>
[376]1117  <x:ref>Accept-Charset-v</x:ref> = 1#( ( <x:ref>charset</x:ref> / "*" )
1118                         [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
1121   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
1122   be given an associated quality value which represents the user's
1123   preference for that charset. The default value is q=1. An example is
1125<figure><artwork type="example">
[357]1126  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
1129   The special value "*", if present in the Accept-Charset field,
1130   matches every character set (including ISO-8859-1) which is not
1131   mentioned elsewhere in the Accept-Charset field. If no "*" is present
1132   in an Accept-Charset field, then all character sets not explicitly
1133   mentioned get a quality value of 0, except for ISO-8859-1, which gets
1134   a quality value of 1 if not explicitly mentioned.
1137   If no Accept-Charset header is present, the default is that any
1138   character set is acceptable. If an Accept-Charset header is present,
1139   and if the server cannot send a response which is acceptable
1140   according to the Accept-Charset header, then the server &SHOULD; send
[137]1141   an error response with the 406 (Not Acceptable) status code, though
[8]1142   the sending of an unacceptable response is also allowed.
1146<section title="Accept-Encoding" anchor="header.accept-encoding">
1147  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
1148  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
[229]1149  <x:anchor-alias value="Accept-Encoding"/>
[357]1150  <x:anchor-alias value="Accept-Encoding-v"/>
[229]1151  <x:anchor-alias value="codings"/>
[698]1153   The "Accept-Encoding" request-header field can be used by user agents to
1154   indicate what response content-codings (<xref target="content.codings"/>)
1155   are acceptable in the response.
[357]1157<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]1158  <x:ref>Accept-Encoding</x:ref>    = "Accept-Encoding" ":" <x:ref>OWS</x:ref>
[357]1159                     <x:ref>Accept-Encoding-v</x:ref>
1160  <x:ref>Accept-Encoding-v</x:ref>  =
[370]1161                     #( <x:ref>codings</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
[357]1162  <x:ref>codings</x:ref>            = ( <x:ref>content-coding</x:ref> / "*" )
[248]1165   Each codings value &MAY; be given an associated quality value which
1166   represents the preference for that encoding. The default value is q=1.
[8]1169   Examples of its use are:
1171<figure><artwork type="example">
[357]1172  Accept-Encoding: compress, gzip
1173  Accept-Encoding:
1174  Accept-Encoding: *
1175  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1176  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
1179   A server tests whether a content-coding is acceptable, according to
1180   an Accept-Encoding field, using these rules:
1181  <list style="numbers">
1182      <t>If the content-coding is one of the content-codings listed in
1183         the Accept-Encoding field, then it is acceptable, unless it is
[457]1184         accompanied by a qvalue of 0. (As defined in &qvalue;, a
[879]1185         qvalue of 0 means "not acceptable".)</t>
1187      <t>The special "*" symbol in an Accept-Encoding field matches any
1188         available content-coding not explicitly listed in the header
1189         field.</t>
1191      <t>If multiple content-codings are acceptable, then the acceptable
1192         content-coding with the highest non-zero qvalue is preferred.</t>
1194      <t>The "identity" content-coding is always acceptable, unless
1195         specifically refused because the Accept-Encoding field includes
1196         "identity;q=0", or because the field includes "*;q=0" and does
1197         not explicitly include the "identity" content-coding. If the
1198         Accept-Encoding field-value is empty, then only the "identity"
1199         encoding is acceptable.</t>
1200  </list>
1203   If an Accept-Encoding field is present in a request, and if the
1204   server cannot send a response which is acceptable according to the
1205   Accept-Encoding header, then the server &SHOULD; send an error response
1206   with the 406 (Not Acceptable) status code.
1209   If no Accept-Encoding field is present in a request, the server &MAY;
1210   assume that the client will accept any content coding. In this case,
1211   if "identity" is one of the available content-codings, then the
1212   server &SHOULD; use the "identity" content-coding, unless it has
1213   additional information that a different content-coding is meaningful
1214   to the client.
1217  <t>
1218    <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1219    and if the "identity" content-coding is unavailable, then
1220    content-codings commonly understood by HTTP/1.0 clients (i.e.,
1221    "gzip" and "compress") are preferred; some older clients
1222    improperly display messages sent with other content-codings.  The
1223    server might also make this decision based on information about
1224    the particular user-agent or client.
1225  </t>
1228  <t>
1229    <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1230    associated with content-codings. This means that qvalues will not
1231    work and are not permitted with x-gzip or x-compress.
1232  </t>
1236<section title="Accept-Language" anchor="header.accept-language">
1237  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1238  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
[229]1239  <x:anchor-alias value="Accept-Language"/>
[357]1240  <x:anchor-alias value="Accept-Language-v"/>
[229]1241  <x:anchor-alias value="language-range"/>
[698]1243   The "Accept-Language" request-header field can be used by user agents to
1244   indicate the set of natural languages that are preferred in the response.
1245   Language tags are defined in <xref target="language.tags"/>.
[357]1247<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]1248  <x:ref>Accept-Language</x:ref>   = "Accept-Language" ":" <x:ref>OWS</x:ref>
[357]1249                    <x:ref>Accept-Language-v</x:ref>
1250  <x:ref>Accept-Language-v</x:ref> =
[370]1251                    1#( <x:ref>language-range</x:ref> [ <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> ] )
[357]1252  <x:ref>language-range</x:ref>    =
[303]1253            &lt;language-range, defined in <xref target="RFC4647" x:fmt="," x:sec="2.1"/>&gt;
[303]1256   Each language-range can be given an associated quality value which
[8]1257   represents an estimate of the user's preference for the languages
1258   specified by that range. The quality value defaults to "q=1". For
1259   example,
1261<figure><artwork type="example">
[357]1262  Accept-Language: da, en-gb;q=0.8, en;q=0.7
1265   would mean: "I prefer Danish, but will accept British English and
[879]1266   other types of English".
[724]1267   (see also <xref target="RFC4647" x:sec="2.3" x:fmt="of"/>)
[724]1270   For matching, <xref target="RFC4647" x:sec="3" x:fmt="of"/> defines
1271   several matching schemes. Implementations can offer the most appropriate
1272   matching scheme for their requirements.
1275  <t>
[756]1276    <x:h>Note:</x:h> The "Basic Filtering" scheme (<xref target="RFC4647"
[724]1277    x:fmt="," x:sec="3.3.1"/>) is identical to the matching scheme that was
1278    previously defined in <xref target="RFC2616" x:fmt="of" x:sec="14.4"/>.
[563]1279  </t>
1282   It might be contrary to the privacy expectations of the user to send
1283   an Accept-Language header with the complete linguistic preferences of
1284   the user in every request. For a discussion of this issue, see
1285   <xref target=""/>.
1288   As intelligibility is highly dependent on the individual user, it is
1289   recommended that client applications make the choice of linguistic
1290   preference available to the user. If the choice is not made
1291   available, then the Accept-Language header field &MUST-NOT; be given in
1292   the request.
1295  <t>
1296    <x:h>Note:</x:h> When making the choice of linguistic preference available to
1297    the user, we remind implementors of  the fact that users are not
1298    familiar with the details of language matching as described above,
[969]1299    and ought to be provided appropriate guidance. As an example, users
[563]1300    might assume that on selecting "en-gb", they will be served any
1301    kind of English document if British English is not available. A
1302    user agent might suggest in such a case to add "en" to get the
1303    best matching behavior.
1304  </t>
1308<section title="Content-Encoding" anchor="header.content-encoding">
1309  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1310  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
[229]1311  <x:anchor-alias value="Content-Encoding"/>
[357]1312  <x:anchor-alias value="Content-Encoding-v"/>
[965]1314   The "Content-Encoding" header field indicates what content-codings
[866]1315   have been applied to the representation, and thus what decoding mechanisms
[698]1316   must be applied in order to obtain the media-type referenced by the
1317   Content-Type header field. Content-Encoding is primarily used to allow a
[866]1318   representation to be compressed without losing the identity of its underlying
[698]1319   media type.
[357]1321<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/><iref primary="true" item="Grammar" subitem="Content-Encoding-v"/>
[366]1322  <x:ref>Content-Encoding</x:ref>   = "Content-Encoding" ":" <x:ref>OWS</x:ref> <x:ref>Content-Encoding-v</x:ref>
[357]1323  <x:ref>Content-Encoding-v</x:ref> = 1#<x:ref>content-coding</x:ref>
1326   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1328<figure><artwork type="example">
[357]1329  Content-Encoding: gzip
[866]1332   The content-coding is a characteristic of the representation.
1333   Typically, the representation body is stored with this
[8]1334   encoding and is only decoded before rendering or analogous usage.
1335   However, a non-transparent proxy &MAY; modify the content-coding if the
1336   new coding is known to be acceptable to the recipient, unless the
1337   "no-transform" cache-control directive is present in the message.
[866]1340   If the content-coding of a representation is not "identity", then the
1341   representation metadata &MUST; include a Content-Encoding header
1342   field (<xref target="header.content-encoding"/>)
[8]1343   that lists the non-identity content-coding(s) used.
[874]1346   If the content-coding of a representation in a request message is not
[8]1347   acceptable to the origin server, the server &SHOULD; respond with a
1348   status code of 415 (Unsupported Media Type).
[866]1351   If multiple encodings have been applied to a representation, the content
[8]1352   codings &MUST; be listed in the order in which they were applied.
1353   Additional information about the encoding parameters &MAY; be provided
[866]1354   by other header fields not defined by this specification.
1358<section title="Content-Language" anchor="header.content-language">
1359  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1360  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
[229]1361  <x:anchor-alias value="Content-Language"/>
[357]1362  <x:anchor-alias value="Content-Language-v"/>
[965]1364   The "Content-Language" header field describes the natural
[866]1365   language(s) of the intended audience for the representation. Note that this might
[874]1366   not be equivalent to all the languages used within the representation.
[357]1368<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/><iref primary="true" item="Grammar" subitem="Content-Language-v"/>
[366]1369  <x:ref>Content-Language</x:ref>   = "Content-Language" ":" <x:ref>OWS</x:ref> <x:ref>Content-Language-v</x:ref>
[357]1370  <x:ref>Content-Language-v</x:ref> = 1#<x:ref>language-tag</x:ref>
1373   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1374   Content-Language is to allow a user to identify and differentiate
[866]1375   representations according to the user's own preferred language. Thus, if the
[8]1376   body content is intended only for a Danish-literate audience, the
1377   appropriate field is
1379<figure><artwork type="example">
[357]1380  Content-Language: da
1383   If no Content-Language is specified, the default is that the content
1384   is intended for all language audiences. This might mean that the
1385   sender does not consider it to be specific to any natural language,
1386   or that the sender does not know for which language it is intended.
1389   Multiple languages &MAY; be listed for content that is intended for
1390   multiple audiences. For example, a rendition of the "Treaty of
[879]1391   Waitangi", presented simultaneously in the original Maori and English
[8]1392   versions, would call for
1394<figure><artwork type="example">
[357]1395  Content-Language: mi, en
[866]1398   However, just because multiple languages are present within a representation
[8]1399   does not mean that it is intended for multiple linguistic audiences.
1400   An example would be a beginner's language primer, such as "A First
[879]1401   Lesson in Latin", which is clearly intended to be used by an
[8]1402   English-literate audience. In this case, the Content-Language would
1403   properly only include "en".
1406   Content-Language &MAY; be applied to any media type -- it is not
1407   limited to textual documents.
1411<section title="Content-Location" anchor="header.content-location">
1412  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1413  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
[229]1414  <x:anchor-alias value="Content-Location"/>
[357]1415  <x:anchor-alias value="Content-Location-v"/>
[856]1417   The "Content-Location" header field supplies a URI that can be used
1418   as a specific identifier for the representation in this message.
1419   In other words, if one were to perform a GET on this URI at the time
1420   of this message's generation, then a 200 response would contain the
1421   same representation that is enclosed as payload in this message.
[357]1423<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/><iref primary="true" item="Grammar" subitem="Content-Location-v"/>
[366]1424  <x:ref>Content-Location</x:ref>   = "Content-Location" ":" <x:ref>OWS</x:ref>
[357]1425                    <x:ref>Content-Location-v</x:ref>
1426  <x:ref>Content-Location-v</x:ref> =
[391]1427                    <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
[972]1430   The Content-Location value is not a replacement for the effective
[856]1431   Request URI (&effective-request-uri;).  It is representation metadata.
1432   It has the same syntax and semantics as the header field of the same name
[858]1433   defined for MIME body parts in <xref target="RFC2557" x:fmt="of" x:sec="4"/>.
[856]1434   However, its appearance in an HTTP message has some special implications
1435   for HTTP recipients.
[856]1438   If Content-Location is included in a response message and its value
[965]1439   is the same as the effective request URI, then the response payload
[856]1440   &SHOULD; be considered the current representation of that resource.
1441   For a GET or HEAD request, this is the same as the default semantics
1442   when no Content-Location is provided by the server.  For a state-changing
1443   method like PUT or POST, it implies that the server's response contains
1444   the new representation of that resource, thereby distinguishing it from
1445   representations that might only report about the action (e.g., "It worked!").
1446   This allows authoring applications to update their local copies without
1447   the need for a subsequent GET request.
[856]1450   If Content-Location is included in a response message and its value
[965]1451   differs from the effective request URI, then the origin server is
[856]1452   informing recipients that this representation has its own, presumably
1453   more specific, identifier.  For a GET or HEAD request, this is an
[965]1454   indication that the effective request URI identifies a resource that
[856]1455   is subject to content negotiation and the representation selected for
1456   this response can also be found at the identified URI.  For other
1457   methods, such a Content-Location indicates that this representation
1458   contains a report on the action's status and the same report is
1459   available (for future access with GET) at the given URI.  For
[908]1460   example, a purchase transaction made via the POST method might
[856]1461   include a receipt document as the payload of the 200 response;
1462   the Content-Location value provides an identifier for retrieving
1463   a copy of that same receipt in the future.
1466   If Content-Location is included in a request message, then it &MAY;
1467   be interpreted by the origin server as an indication of where the
1468   user agent originally obtained the content of the enclosed
1469   representation (prior to any subsequent modification of the content
1470   by that user agent).  In other words, the user agent is providing
1471   the same representation metadata that it received with the original
1472   representation.  However, such interpretation &MUST-NOT; be used to
1473   alter the semantics of the method requested by the client.  For
1474   example, if a client makes a PUT request on a negotiated resource
1475   and the origin server accepts that PUT (without redirection), then the
1476   new set of values for that resource is expected to be consistent with
1477   the one representation supplied in that PUT; the Content-Location
1478   cannot be used as a form of reverse content selection that
1479   identifies only one of the negotiated representations to be updated.
1480   If the user agent had wanted the latter semantics, it would have applied
1481   the PUT directly to the Content-Location URI.
1484   A Content-Location field received in a request message is transitory
1485   information that &SHOULD-NOT; be saved with other representation
1486   metadata for use in later responses.  The Content-Location's value
1487   might be saved for use in other contexts, such as within source links
1488   or other metadata.
1491   A cache cannot assume that a representation with a Content-Location
[8]1492   different from the URI used to retrieve it can be used to respond to
[856]1493   later requests on that Content-Location URI.
[965]1496   If the Content-Location value is a partial URI, the partial URI is
1497   interpreted relative to the effective request URI.
1501<section title="Content-MD5" anchor="header.content-md5">
1502  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1503  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
[229]1504  <x:anchor-alias value="Content-MD5"/>
[357]1505  <x:anchor-alias value="Content-MD5-v"/>
[965]1507   The "Content-MD5" header field, as defined in <xref target="RFC1864"/>, is
[874]1508   an MD5 digest of the payload body that provides an end-to-end message
1509   integrity check (MIC) of the payload body (the message-body after any
1510   transfer-coding is decoded). Note that a MIC is good for
1511   detecting accidental modification of the payload body in transit, but is not
[699]1512   proof against malicious attacks.
[357]1514<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="Content-MD5-v"/>
[366]1515  <x:ref>Content-MD5</x:ref>   = "Content-MD5" ":" <x:ref>OWS</x:ref> <x:ref>Content-MD5-v</x:ref>
[357]1516  <x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per <xref target="RFC1864"/>&gt;
1519   The Content-MD5 header field &MAY; be generated by an origin server or
[874]1520   client to function as an integrity check of the payload body. Only
1521   origin servers or user agents &MAY; generate the Content-MD5 header field;
[8]1522   proxies and gateways &MUST-NOT; generate it, as this would defeat its
[874]1523   value as an end-to-end integrity check. Any recipient &MAY; check that
1524   the digest value in this header field matches a corresponding digest
1525   calculated on payload body as received.
[874]1528   The MD5 digest is computed based on the content of the payload body,
1529   including any content-coding, but not including any transfer-coding
1530   applied to the message-body because such transfer-codings might be
1531   applied or removed anywhere along the request/response chain.
1532   If the message is received with a transfer-coding, that encoding &MUST;
1533   be decoded prior to checking the Content-MD5 value against the received
1534   payload.
1537   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1538   composite media-types (e.g., multipart/* and message/rfc822), but
1539   this does not change how the digest is computed as defined in the
1540   preceding paragraph.
[874]1543   There are several consequences of this. The payload for composite
[8]1544   types &MAY; contain many body-parts, each with its own MIME and HTTP
1545   headers (including Content-MD5, Content-Transfer-Encoding, and
1546   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1547   or Content-Encoding header, it is assumed that the content
1548   of the body-part has had the encoding applied, and the body-part is
1549   included in the Content-MD5 digest as is -- i.e., after the
1550   application. The Transfer-Encoding header field is not allowed within
1551   body-parts.
1554   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1555   computing or checking the digest: the line break convention used in
1556   the text actually transmitted &MUST; be left unaltered when computing
1557   the digest.
1560  <t>
[756]1561    <x:h>Note:</x:h> While the definition of Content-MD5 is exactly the same for
[563]1562    HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1563    in which the application of Content-MD5 to HTTP entity-bodies
1564    differs from its application to MIME entity-bodies. One is that
1565    HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1566    does use Transfer-Encoding and Content-Encoding. Another is that
1567    HTTP more frequently uses binary content types than MIME, so it is
1568    worth noting that, in such cases, the byte order used to compute
1569    the digest is the transmission byte order defined for the type.
1570    Lastly, HTTP allows transmission of text types with any of several
1571    line break conventions and not just the canonical form using CRLF.
1572  </t>
1576<section title="Content-Type" anchor="header.content-type">
1577  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1578  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
[229]1579  <x:anchor-alias value="Content-Type"/>
[357]1580  <x:anchor-alias value="Content-Type-v"/>
[965]1582   The "Content-Type" header field indicates the media type of the
[874]1583   representation. In the case of responses to the HEAD method, the media type is
[698]1584   that which would have been sent had the request been a GET.
[357]1586<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/><iref primary="true" item="Grammar" subitem="Content-Type-v"/>
[366]1587  <x:ref>Content-Type</x:ref>   = "Content-Type" ":" <x:ref>OWS</x:ref> <x:ref>Content-Type-v</x:ref>
[357]1588  <x:ref>Content-Type-v</x:ref> = <x:ref>media-type</x:ref>
1591   Media types are defined in <xref target="media.types"/>. An example of the field is
1593<figure><artwork type="example">
[357]1594  Content-Type: text/html; charset=ISO-8859-4
[965]1597   Further discussion of Content-Type is provided in <xref target=""/>.
[29]1603<section title="IANA Considerations" anchor="IANA.considerations">
[921]1604<section title="Header Field Registration" anchor="header.field.registration">
[969]1606   The Message Header Field Registry located at <eref target=""/> shall be updated
[290]1607   with the permanent registrations below (see <xref target="RFC3864"/>):
[680]1609<?BEGININC p3-payload.iana-headers ?>
[253]1610<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
[290]1611<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
[253]1612   <ttcol>Header Field Name</ttcol>
1613   <ttcol>Protocol</ttcol>
1614   <ttcol>Status</ttcol>
1615   <ttcol>Reference</ttcol>
1617   <c>Accept</c>
1618   <c>http</c>
1619   <c>standard</c>
1620   <c>
1621      <xref target="header.accept"/>
1622   </c>
1623   <c>Accept-Charset</c>
1624   <c>http</c>
1625   <c>standard</c>
1626   <c>
1627      <xref target="header.accept-charset"/>
1628   </c>
1629   <c>Accept-Encoding</c>
1630   <c>http</c>
1631   <c>standard</c>
1632   <c>
1633      <xref target="header.accept-encoding"/>
1634   </c>
1635   <c>Accept-Language</c>
1636   <c>http</c>
1637   <c>standard</c>
1638   <c>
1639      <xref target="header.accept-language"/>
1640   </c>
1641   <c>Content-Disposition</c>
1642   <c>http</c>
[937]1643   <c>standard</c>
[253]1644   <c>
1645      <xref target="content-disposition"/>
1646   </c>
1647   <c>Content-Encoding</c>
1648   <c>http</c>
1649   <c>standard</c>
1650   <c>
1651      <xref target="header.content-encoding"/>
1652   </c>
1653   <c>Content-Language</c>
1654   <c>http</c>
1655   <c>standard</c>
1656   <c>
1657      <xref target="header.content-language"/>
1658   </c>
1659   <c>Content-Location</c>
1660   <c>http</c>
1661   <c>standard</c>
1662   <c>
1663      <xref target="header.content-location"/>
1664   </c>
1665   <c>Content-MD5</c>
1666   <c>http</c>
1667   <c>standard</c>
1668   <c>
1669      <xref target="header.content-md5"/>
1670   </c>
1671   <c>Content-Type</c>
1672   <c>http</c>
1673   <c>standard</c>
1674   <c>
1675      <xref target="header.content-type"/>
1676   </c>
[291]1677   <c>MIME-Version</c>
1678   <c>http</c>
[937]1679   <c>standard</c>
[291]1680   <c>
1681      <xref target="mime-version"/>
1682   </c>
[680]1685<?ENDINC p3-payload.iana-headers ?>
[290]1687   The change controller is: "IETF ( - Internet Engineering Task Force".
[668]1691<section title="Content Coding Registry" anchor="content.coding.registration">
1693   The registration procedure for HTTP Content Codings is now defined
[670]1694   by <xref target="content.coding.registry"/> of this document.
1697   The HTTP Content Codings Registry located at <eref target=""/>
[969]1698   shall be updated with the registration below:
1700<texttable align="left" suppress-title="true" anchor="iana.content.coding.registration.table">
[670]1701   <ttcol>Name</ttcol>
[668]1702   <ttcol>Description</ttcol>
1703   <ttcol>Reference</ttcol>
1704   <c>compress</c>
1705   <c>UNIX "compress" program method</c>
1706   <c>
[673]1707      &compress-coding;
[668]1708   </c>
1709   <c>deflate</c>
[806]1710   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
1711   the "zlib" data format (<xref target="RFC1950"/>)
1712   </c>
[668]1713   <c>
[673]1714      &deflate-coding;
[668]1715   </c>
1716   <c>gzip</c>
1717   <c>Same as GNU zip <xref target="RFC1952"/></c>
1718   <c>
[673]1719      &gzip-coding;
[668]1720   </c>
1721   <c>identity</c>
1722   <c>No transformation</c>
1723   <c>
1724      <xref target="content.codings"/>
1725   </c>
[8]1731<section title="Security Considerations" anchor="security.considerations">
1733   This section is meant to inform application developers, information
1734   providers, and users of the security limitations in HTTP/1.1 as
1735   described by this document. The discussion does not include
1736   definitive solutions to the problems revealed, though it does make
1737   some suggestions for reducing security risks.
1740<section title="Privacy Issues Connected to Accept Headers" anchor="">
1742   Accept request-headers can reveal information about the user to all
1743   servers which are accessed. The Accept-Language header in particular
1744   can reveal information the user would consider to be of a private
1745   nature, because the understanding of particular languages is often
1746   strongly correlated to the membership of a particular ethnic group.
1747   User agents which offer the option to configure the contents of an
1748   Accept-Language header to be sent in every request are strongly
1749   encouraged to let the configuration process include a message which
1750   makes the user aware of the loss of privacy involved.
1753   An approach that limits the loss of privacy would be for a user agent
1754   to omit the sending of Accept-Language headers by default, and to ask
1755   the user whether or not to start sending Accept-Language headers to a
1756   server if it detects, by looking for any Vary response-header fields
1757   generated by the server, that such sending could improve the quality
1758   of service.
1761   Elaborate user-customized accept header fields sent in every request,
1762   in particular if these include quality values, can be used by servers
1763   as relatively reliable and long-lived user identifiers. Such user
1764   identifiers would allow content providers to do click-trail tracking,
1765   and would allow collaborating content providers to match cross-server
1766   click-trails or form submissions of individual users. Note that for
1767   many users not behind a proxy, the network address of the host
1768   running the user agent will also serve as a long-lived user
1769   identifier. In environments where proxies are used to enhance
1770   privacy, user agents ought to be conservative in offering accept
1771   header configuration options to end users. As an extreme privacy
1772   measure, proxies could filter the accept headers in relayed requests.
1773   General purpose user agents which provide a high degree of header
1774   configurability &SHOULD; warn users about the loss of privacy which can
1775   be involved.
1779<section title="Content-Disposition Issues" anchor="content-disposition.issues">
[269]1781   <xref target="RFC2183"/>, from which the often implemented Content-Disposition
[8]1782   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1783   serious security considerations. Content-Disposition is not part of
1784   the HTTP standard, but since it is widely implemented, we are
[269]1785   documenting its use and risks for implementors. See <xref target="RFC2183" x:fmt="of" x:sec="5"/>
1786   for details.
1792<section title="Acknowledgments" anchor="ack">
[119]1797<references title="Normative References">
[121]1799<reference anchor="ISO-8859-1">
1800  <front>
1801    <title>
1802     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
1803    </title>
1804    <author>
1805      <organization>International Organization for Standardization</organization>
1806    </author>
1807    <date year="1998"/>
1808  </front>
1809  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
[31]1812<reference anchor="Part1">
[119]1813  <front>
1814    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1815    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1816      <organization abbrev="Day Software">Day Software</organization>
1817      <address><email></email></address>
1818    </author>
1819    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1820      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1821      <address><email></email></address>
[119]1822    </author>
1823    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1824      <organization abbrev="HP">Hewlett-Packard Company</organization>
1825      <address><email></email></address>
1826    </author>
1827    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1828      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1829      <address><email></email></address>
1830    </author>
1831    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1832      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1833      <address><email></email></address>
1834    </author>
1835    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1836      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1837      <address><email></email></address>
1838    </author>
1839    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1840      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1841      <address><email></email></address>
1842    </author>
1843    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1844      <organization abbrev="W3C">World Wide Web Consortium</organization>
1845      <address><email></email></address>
1846    </author>
1847    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1848      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1849      <address><email></email></address>
1850    </author>
1851    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1852  </front>
1853  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1854  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1857<reference anchor="Part2">
[119]1858  <front>
1859    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1860    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1861      <organization abbrev="Day Software">Day Software</organization>
1862      <address><email></email></address>
1863    </author>
1864    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1865      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1866      <address><email></email></address>
[119]1867    </author>
1868    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1869      <organization abbrev="HP">Hewlett-Packard Company</organization>
1870      <address><email></email></address>
1871    </author>
1872    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1873      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1874      <address><email></email></address>
1875    </author>
1876    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1877      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1878      <address><email></email></address>
1879    </author>
1880    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1881      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1882      <address><email></email></address>
1883    </author>
1884    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1885      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1886      <address><email></email></address>
1887    </author>
1888    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1889      <organization abbrev="W3C">World Wide Web Consortium</organization>
1890      <address><email></email></address>
1891    </author>
1892    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1893      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1894      <address><email></email></address>
1895    </author>
1896    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1897  </front>
1898  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1899  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1902<reference anchor="Part4">
[119]1903  <front>
1904    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1905    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1906      <organization abbrev="Day Software">Day Software</organization>
1907      <address><email></email></address>
1908    </author>
1909    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1910      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1911      <address><email></email></address>
[119]1912    </author>
1913    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1914      <organization abbrev="HP">Hewlett-Packard Company</organization>
1915      <address><email></email></address>
1916    </author>
1917    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1918      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1919      <address><email></email></address>
1920    </author>
1921    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1922      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1923      <address><email></email></address>
1924    </author>
1925    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1926      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1927      <address><email></email></address>
1928    </author>
1929    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1930      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1931      <address><email></email></address>
1932    </author>
1933    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1934      <organization abbrev="W3C">World Wide Web Consortium</organization>
1935      <address><email></email></address>
1936    </author>
1937    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1938      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1939      <address><email></email></address>
1940    </author>
1941    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1942  </front>
1943  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1944  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1947<reference anchor="Part5">
[119]1948  <front>
1949    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1950    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1951      <organization abbrev="Day Software">Day Software</organization>
1952      <address><email></email></address>
1953    </author>
1954    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]1955      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1956      <address><email></email></address>
[119]1957    </author>
1958    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1959      <organization abbrev="HP">Hewlett-Packard Company</organization>
1960      <address><email></email></address>
1961    </author>
1962    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1963      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1964      <address><email></email></address>
1965    </author>
1966    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1967      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1968      <address><email></email></address>
1969    </author>
1970    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1971      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1972      <address><email></email></address>
1973    </author>
1974    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1975      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1976      <address><email></email></address>
1977    </author>
1978    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1979      <organization abbrev="W3C">World Wide Web Consortium</organization>
1980      <address><email></email></address>
1981    </author>
1982    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1983      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1984      <address><email></email></address>
1985    </author>
1986    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1987  </front>
1988  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1989  <x:source href="p5-range.xml" basename="p5-range"/>
1992<reference anchor="Part6">
[119]1993  <front>
1994    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1995    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1996      <organization abbrev="Day Software">Day Software</organization>
1997      <address><email></email></address>
1998    </author>
1999    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]2000      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
2001      <address><email></email></address>
[119]2002    </author>
2003    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2004      <organization abbrev="HP">Hewlett-Packard Company</organization>
2005      <address><email></email></address>
2006    </author>
2007    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2008      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2009      <address><email></email></address>
2010    </author>
2011    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2012      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2013      <address><email></email></address>
2014    </author>
2015    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2016      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2017      <address><email></email></address>
2018    </author>
2019    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2020      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2021      <address><email></email></address>
2022    </author>
2023    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2024      <organization abbrev="W3C">World Wide Web Consortium</organization>
2025      <address><email></email></address>
2026    </author>
[601]2027    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
2028      <address><email></email></address>
2029    </author>
[119]2030    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2031      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2032      <address><email></email></address>
2033    </author>
2034    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2035  </front>
2036  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2037  <x:source href="p6-cache.xml" basename="p6-cache"/>
[131]2040<reference anchor="RFC1864">
2041  <front>
2042    <title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
2043    <author initials="J." surname="Myers" fullname="John G. Myers">
2044      <organization>Carnegie Mellon University</organization>
2045      <address><email></email></address>
2046    </author>
2047    <author initials="M." surname="Rose" fullname="Marshall T. Rose">
2048      <organization>Dover Beach Consulting, Inc.</organization>
2049      <address><email></email></address>
2050    </author>
2051    <date month="October" year="1995"/>
2052  </front>
2053  <seriesInfo name="RFC" value="1864"/>
[122]2056<reference anchor="RFC1950">
2057  <front>
2058    <title>ZLIB Compressed Data Format Specification version 3.3</title>
2059    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2060      <organization>Aladdin Enterprises</organization>
2061      <address><email></email></address>
2062    </author>
[713]2063    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
[122]2064    <date month="May" year="1996"/>
2065  </front>
2066  <seriesInfo name="RFC" value="1950"/>
2067  <annotation>
[908]2068    RFC 1950 is an Informational RFC, thus it might be less stable than
[122]2069    this specification. On the other hand, this downward reference was
[277]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"/>.
[122]2073  </annotation>
[806]2076<reference anchor="RFC1951">
2077  <front>
2078    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
2079    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2080      <organization>Aladdin Enterprises</organization>
2081      <address><email></email></address>
2082    </author>
2083    <date month="May" year="1996"/>
2084  </front>
2085  <seriesInfo name="RFC" value="1951"/>
2086  <annotation>
[908]2087    RFC 1951 is an Informational RFC, thus it might be less stable than
[806]2088    this specification. On the other hand, this downward reference was
2089    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2090    therefore it is unlikely to cause problems in practice. See also
2091    <xref target="BCP97"/>.
2092  </annotation>
[122]2095<reference anchor="RFC1952">
2096  <front>
2097    <title>GZIP file format specification version 4.3</title>
2098    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
2099      <organization>Aladdin Enterprises</organization>
2100      <address><email></email></address>
2101    </author>
2102    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
2103      <address><email></email></address>
2104    </author>
2105    <author initials="M." surname="Adler" fullname="Mark Adler">
2106      <address><email></email></address>
2107    </author>
2108    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
2109      <address><email></email></address>
2110    </author>
2111    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
2112      <address><email></email></address>
2113    </author>
2114    <date month="May" year="1996"/>
2115  </front>
2116  <seriesInfo name="RFC" value="1952"/>
2117  <annotation>
[908]2118    RFC 1952 is an Informational RFC, thus it might be less stable than
[122]2119    this specification. On the other hand, this downward reference was
[277]2120    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
2121    therefore it is unlikely to cause problems in practice. See also
2122    <xref target="BCP97"/>.
[122]2123  </annotation>
[131]2126<reference anchor="RFC2045">
2127  <front>
2128    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
2129    <author initials="N." surname="Freed" fullname="Ned Freed">
2130      <organization>Innosoft International, Inc.</organization>
2131      <address><email></email></address>
2132    </author>
2133    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2134      <organization>First Virtual Holdings</organization>
2135      <address><email></email></address>
2136    </author>
2137    <date month="November" year="1996"/>
2138  </front>
2139  <seriesInfo name="RFC" value="2045"/>
2142<reference anchor="RFC2046">
2143  <front>
2144    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2145    <author initials="N." surname="Freed" fullname="Ned Freed">
2146      <organization>Innosoft International, Inc.</organization>
2147      <address><email></email></address>
2148    </author>
2149    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2150      <organization>First Virtual Holdings</organization>
2151      <address><email></email></address>
2152    </author>
2153    <date month="November" year="1996"/>
2154  </front>
2155  <seriesInfo name="RFC" value="2046"/>
[119]2158<reference anchor="RFC2119">
2159  <front>
2160    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2161    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2162      <organization>Harvard University</organization>
2163      <address><email></email></address>
2164    </author>
2165    <date month="March" year="1997"/>
2166  </front>
2167  <seriesInfo name="BCP" value="14"/>
2168  <seriesInfo name="RFC" value="2119"/>
[303]2171<reference anchor='RFC4647'>
2172  <front>
2173    <title>Matching of Language Tags</title>
2174    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
2175      <organization>Yahoo! Inc.</organization>
2176      <address><email></email></address>
2177    </author>
2178    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
2179      <organization>Google</organization>
2180      <address><email></email></address>
2181    </author>
2182    <date year='2006' month='September' />
2183  </front>
2184  <seriesInfo name='BCP' value='47' />
2185  <seriesInfo name='RFC' value='4647' />
[425]2188<reference anchor="RFC5234">
2189  <front>
2190    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2191    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2192      <organization>Brandenburg InternetWorking</organization>
2193      <address>
[728]2194        <email></email>
2195      </address> 
[425]2196    </author>
2197    <author initials="P." surname="Overell" fullname="Paul Overell">
2198      <organization>THUS plc.</organization>
2199      <address>
[728]2200        <email></email>
2201      </address>
[425]2202    </author>
2203    <date month="January" year="2008"/>
2204  </front>
2205  <seriesInfo name="STD" value="68"/>
2206  <seriesInfo name="RFC" value="5234"/>
[690]2209<reference anchor='RFC5646'>
[613]2210  <front>
2211    <title>Tags for Identifying Languages</title>
2212    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
2213      <organization>Lab126</organization>
2214      <address><email></email></address>
2215    </author>
2216    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
2217      <organization>Google</organization>
2218      <address><email></email></address>
2219    </author>
[690]2220    <date month='September' year='2009' />
[613]2221  </front>
[690]2222  <seriesInfo name='BCP' value='47' />
2223  <seriesInfo name='RFC' value='5646' />
2228<references title="Informative References">
[129]2230<reference anchor="RFC1945">
2231  <front>
2232    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2233    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2234      <organization>MIT, Laboratory for Computer Science</organization>
2235      <address><email></email></address>
2236    </author>
2237    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2238      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2239      <address><email></email></address>
2240    </author>
2241    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2242      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2243      <address><email></email></address>
2244    </author>
2245    <date month="May" year="1996"/>
2246  </front>
2247  <seriesInfo name="RFC" value="1945"/>
2250<reference anchor="RFC2049">
2251  <front>
2252    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2253    <author initials="N." surname="Freed" fullname="Ned Freed">
2254      <organization>Innosoft International, Inc.</organization>
2255      <address><email></email></address>
2256    </author>
2257    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2258      <organization>First Virtual Holdings</organization>
2259      <address><email></email></address>
2260    </author>
2261    <date month="November" year="1996"/>
2262  </front>
2263  <seriesInfo name="RFC" value="2049"/>
[133]2266<reference anchor="RFC2068">
2267  <front>
2268    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2269    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2270      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2271      <address><email></email></address>
2272    </author>
2273    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2274      <organization>MIT Laboratory for Computer Science</organization>
2275      <address><email></email></address>
2276    </author>
2277    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2278      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2279      <address><email></email></address>
2280    </author>
2281    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2282      <organization>MIT Laboratory for Computer Science</organization>
2283      <address><email></email></address>
2284    </author>
2285    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2286      <organization>MIT Laboratory for Computer Science</organization>
2287      <address><email></email></address>
2288    </author>
2289    <date month="January" year="1997"/>
2290  </front>
2291  <seriesInfo name="RFC" value="2068"/>
[129]2294<reference anchor="RFC2076">
2295  <front>
2296    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2297    <author initials="J." surname="Palme" fullname="Jacob Palme">
2298      <organization>Stockholm University/KTH</organization>
2299      <address><email></email></address>
2300    </author>
2301    <date month="February" year="1997"/>
2302  </front>
2303  <seriesInfo name="RFC" value="2076"/>
2306<reference anchor="RFC2183">
2307  <front>
2308    <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2309    <author initials="R." surname="Troost" fullname="Rens Troost">
2310      <organization>New Century Systems</organization>
2311      <address><email></email></address>
2312    </author>
2313    <author initials="S." surname="Dorner" fullname="Steve Dorner">
2314      <organization>QUALCOMM Incorporated</organization>
2315      <address><email></email></address>
2316    </author>
2317    <author initials="K." surname="Moore" fullname="Keith Moore">
2318      <organization>Department of Computer Science</organization>
2319      <address><email></email></address>
2320    </author>
2321    <date month="August" year="1997"/>
2322  </front>
2323  <seriesInfo name="RFC" value="2183"/>
2326<reference anchor="RFC2277">
2327  <front>
2328    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2329    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2330      <organization>UNINETT</organization>
2331      <address><email></email></address>
2332    </author>
2333    <date month="January" year="1998"/>
2334  </front>
2335  <seriesInfo name="BCP" value="18"/>
2336  <seriesInfo name="RFC" value="2277"/>
[745]2339<reference anchor='RFC2295'>
2340  <front>
2341    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
2342    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
2343      <organization>Technische Universiteit Eindhoven</organization>
2344      <address>
2345        <email></email>
2346      </address>
2347    </author>
2348    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
2349      <organization>Hewlett-Packard Company</organization>
2350      <address>
2351        <email></email>
2352      </address>
2353    </author>
2354    <date year='1998' month='March'/>
2355  </front>
2356  <seriesInfo name='RFC' value='2295'/>
[129]2359<reference anchor="RFC2388">
2360  <front>
2361    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
2362    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2363      <organization>Xerox Palo Alto Research Center</organization>
2364      <address><email></email></address>
2365    </author>
2366    <date year="1998" month="August"/>
2367  </front>
2368  <seriesInfo name="RFC" value="2388"/>
2371<reference anchor="RFC2557">
2372  <front>
2373    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2374    <author initials="F." surname="Palme" fullname="Jacob Palme">
2375      <organization>Stockholm University and KTH</organization>
2376      <address><email></email></address>
2377    </author>
2378    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2379      <organization>Microsoft Corporation</organization>
2380      <address><email></email></address>
2381    </author>
2382    <author initials="N." surname="Shelness" fullname="Nick Shelness">
2383      <organization>Lotus Development Corporation</organization>
2384      <address><email></email></address>
2385    </author>
2386    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
2387      <address><email></email></address>
2388    </author>
2389    <date year="1999" month="March"/>
2390  </front>
2391  <seriesInfo name="RFC" value="2557"/>
[119]2394<reference anchor="RFC2616">
2395  <front>
2396    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2397    <author initials="R." surname="Fielding" fullname="R. Fielding">
2398      <organization>University of California, Irvine</organization>
2399      <address><email></email></address>
2400    </author>
2401    <author initials="J." surname="Gettys" fullname="J. Gettys">
2402      <organization>W3C</organization>
2403      <address><email></email></address>
2404    </author>
2405    <author initials="J." surname="Mogul" fullname="J. Mogul">
2406      <organization>Compaq Computer Corporation</organization>
2407      <address><email></email></address>
2408    </author>
2409    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2410      <organization>MIT Laboratory for Computer Science</organization>
2411      <address><email></email></address>
2412    </author>
2413    <author initials="L." surname="Masinter" fullname="L. Masinter">
2414      <organization>Xerox Corporation</organization>
2415      <address><email></email></address>
2416    </author>
2417    <author initials="P." surname="Leach" fullname="P. Leach">
2418      <organization>Microsoft Corporation</organization>
2419      <address><email></email></address>
2420    </author>
2421    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2422      <organization>W3C</organization>
2423      <address><email></email></address>
2424    </author>
2425    <date month="June" year="1999"/>
2426  </front>
2427  <seriesInfo name="RFC" value="2616"/>
[129]2430<reference anchor="RFC3629">
2431  <front>
2432    <title>UTF-8, a transformation format of ISO 10646</title>
2433    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
2434      <organization>Alis Technologies</organization>
2435      <address><email></email></address>
2436    </author>
2437    <date month="November" year="2003"/>
2438  </front>
2439  <seriesInfo name="RFC" value="3629"/>
2440  <seriesInfo name="STD" value="63"/>
[253]2443<reference anchor='RFC3864'>
2444  <front>
2445    <title>Registration Procedures for Message Header Fields</title>
2446    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2447      <organization>Nine by Nine</organization>
2448      <address><email></email></address>
2449    </author>
2450    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2451      <organization>BEA Systems</organization>
2452      <address><email></email></address>
2453    </author>
2454    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2455      <organization>HP Labs</organization>
2456      <address><email></email></address>
2457    </author>
2458    <date year='2004' month='September' />
2459  </front>
2460  <seriesInfo name='BCP' value='90' />
2461  <seriesInfo name='RFC' value='3864' />
[200]2464<reference anchor="RFC4288">
2465  <front>
2466    <title>Media Type Specifications and Registration Procedures</title>
2467    <author initials="N." surname="Freed" fullname="N. Freed">
2468      <organization>Sun Microsystems</organization>
2469      <address>
2470        <email></email>
2471      </address>
2472    </author>
2473    <author initials="J." surname="Klensin" fullname="J. Klensin">
2474      <address>
2475        <email></email>
2476      </address>
2477    </author>
2478    <date year="2005" month="December"/>
2479  </front>
2480  <seriesInfo name="BCP" value="13"/>
2481  <seriesInfo name="RFC" value="4288"/>
[670]2484<reference anchor='RFC5226'>
2485  <front>
2486    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2487    <author initials='T.' surname='Narten' fullname='T. Narten'>
2488      <organization>IBM</organization>
2489      <address><email></email></address>
2490    </author>
2491    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
2492      <organization>Google</organization>
2493      <address><email></email></address>
2494    </author>
2495    <date year='2008' month='May' />
2496  </front>
2497  <seriesInfo name='BCP' value='26' />
2498  <seriesInfo name='RFC' value='5226' />
[327]2501<reference anchor="RFC5322">
2502  <front>
2503    <title>Internet Message Format</title>
2504    <author initials="P." surname="Resnick" fullname="P. Resnick">
2505      <organization>Qualcomm Incorporated</organization>
2506    </author>
2507    <date year="2008" month="October"/>
2508  </front> 
2509  <seriesInfo name="RFC" value="5322"/>
[277]2512<reference anchor='BCP97'>
2513  <front>
2514    <title>Handling Normative References to Standards-Track Documents</title>
2515    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
2516      <address>
2517        <email></email>
2518      </address>
2519    </author>
2520    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
2521      <organization>MIT</organization>
2522      <address>
2523        <email></email>
2524      </address>
2525    </author>
2526    <date year='2007' month='June' />
2527  </front>
2528  <seriesInfo name='BCP' value='97' />
2529  <seriesInfo name='RFC' value='4897' />
[874]2535<section title="Differences between HTTP and MIME" anchor="differences.between.http.and.mime">
[327]2537   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]2538   allow a message-body to be transmitted in an open variety of
[8]2539   representations and with extensible mechanisms. However, RFC 2045
2540   discusses mail, and HTTP has a few features that are different from
[874]2541   those described in MIME. These differences were carefully chosen
[8]2542   to optimize performance over binary connections, to allow greater
2543   freedom in the use of new media types, to make date comparisons
2544   easier, and to acknowledge the practice of some early HTTP servers
2545   and clients.
[874]2548   This appendix describes specific areas where HTTP differs from MIME.
2549   Proxies and gateways to strict MIME environments &SHOULD; be
[8]2550   aware of these differences and provide the appropriate conversions
2551   where necessary. Proxies and gateways from MIME environments to HTTP
2552   also need to be aware of the differences because some conversions
2553   might be required.
[8]2556<section title="MIME-Version" anchor="mime-version">
[291]2557  <iref primary="true" item="MIME-Version header" x:for-anchor=""/>
2558  <iref primary="true" item="Headers" subitem="MIME-Version" x:for-anchor=""/>
[229]2559  <x:anchor-alias value="MIME-Version"/>
[357]2560  <x:anchor-alias value="MIME-Version-v"/>
2562   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2563   include a single MIME-Version general-header field to indicate what
2564   version of the MIME protocol was used to construct the message. Use
2565   of the MIME-Version header field indicates that the message is in
[115]2566   full compliance with the MIME protocol (as defined in <xref target="RFC2045"/>).
[8]2567   Proxies/gateways are responsible for ensuring full compliance (where
2568   possible) when exporting HTTP messages to strict MIME environments.
[357]2570<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/><iref primary="true" item="Grammar" subitem="MIME-Version-v"/>
[366]2571  <x:ref>MIME-Version</x:ref>   = "MIME-Version" ":" <x:ref>OWS</x:ref> <x:ref>MIME-Version-v</x:ref>
[357]2572  <x:ref>MIME-Version-v</x:ref> = 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
2575   MIME version "1.0" is the default for use in HTTP/1.1. However,
2576   HTTP/1.1 message parsing and semantics are defined by this document
2577   and not the MIME specification.
2581<section title="Conversion to Canonical Form" anchor="">
[874]2583   MIME requires that an Internet mail body-part be converted to
[115]2584   canonical form prior to being transferred, as described in <xref target="RFC2049" x:fmt="of" x:sec="4"/>.
[97]2585   <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
[8]2586   allowed for subtypes of the "text" media type when transmitted over
[97]2587   HTTP. <xref target="RFC2046"/> requires that content with a type of "text" represent
[8]2588   line breaks as CRLF and forbids the use of CR or LF outside of line
2589   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2590   line break within text content when a message is transmitted over
2591   HTTP.
2594   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2595   environment &SHOULD; translate all line breaks within the text media
2596   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2597   canonical form of CRLF. Note, however, that this might be complicated
2598   by the presence of a Content-Encoding and by the fact that HTTP
2599   allows the use of some character sets which do not use octets 13 and
2600   10 to represent CR and LF, as is the case for some multi-byte
2601   character sets.
[969]2604   Conversion will break any cryptographic
[8]2605   checksums applied to the original content unless the original content
2606   is already in canonical form. Therefore, the canonical form is
2607   recommended for any content that uses such checksums in HTTP.
2612<section title="Conversion of Date Formats" anchor="">
2614   HTTP/1.1 uses a restricted set of date formats (&full-date;) to
2615   simplify the process of date comparison. Proxies and gateways from
2616   other protocols &SHOULD; ensure that any Date header field present in a
2617   message conforms to one of the HTTP/1.1 formats and rewrite the date
2618   if necessary.
[8]2622<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
[874]2624   MIME does not include any concept equivalent to HTTP/1.1's
[8]2625   Content-Encoding header field. Since this acts as a modifier on the
2626   media type, proxies and gateways from HTTP to MIME-compliant
2627   protocols &MUST; either change the value of the Content-Type header
[874]2628   field or decode the representation before forwarding the message. (Some
[8]2629   experimental applications of Content-Type for Internet mail have used
2630   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2631   a function equivalent to Content-Encoding. However, this parameter is
[874]2632   not part of the MIME standards).
2636<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
[874]2638   HTTP does not use the Content-Transfer-Encoding field of MIME.
2639   Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
[85]2640   remove any Content-Transfer-Encoding
[8]2641   prior to delivering the response message to an HTTP client.
2644   Proxies and gateways from HTTP to MIME-compliant protocols are
2645   responsible for ensuring that the message is in the correct format
2646   and encoding for safe transport on that protocol, where "safe
2647   transport" is defined by the limitations of the protocol being used.
2648   Such a proxy or gateway &SHOULD; label the data with an appropriate
2649   Content-Transfer-Encoding if doing so will improve the likelihood of
2650   safe transport over the destination protocol.
2654<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
[29]2656   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
[8]2657   Proxies/gateways &MUST; remove any transfer-coding prior to
2658   forwarding a message via a MIME-compliant protocol.
2662<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
[129]2664   HTTP implementations which share code with MHTML <xref target="RFC2557"/> implementations
[8]2665   need to be aware of MIME line length limitations. Since HTTP does not
2666   have this limitation, HTTP does not fold long lines. MHTML messages
2667   being transported by HTTP follow all conventions of MHTML, including
2668   line length limitations and folding, canonicalization, etc., since
2669   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2670   does not interpret the content or any MIME header lines that might be
2671   contained therein.
2676<section title="Additional Features" anchor="additional.features">
[97]2678   <xref target="RFC1945"/> and <xref target="RFC2068"/> document protocol elements used by some
[8]2679   existing HTTP implementations, but not consistently and correctly
2680   across most HTTP/1.1 applications. Implementors are advised to be
2681   aware of these features, but cannot rely upon their presence in, or
2682   interoperability with, other HTTP/1.1 applications. Some of these
2683   describe proposed experimental features, and some describe features
2684   that experimental deployment found lacking that are now addressed in
2685   the base HTTP/1.1 specification.
2688   A number of other headers, such as Content-Disposition and Title,
[97]2689   from SMTP and MIME are also often implemented (see <xref target="RFC2076"/>).
2692<section title="Content-Disposition" anchor="content-disposition">
2693<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2694<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
[229]2695  <x:anchor-alias value="content-disposition"/>
[357]2696  <x:anchor-alias value="content-disposition-v"/>
[229]2697  <x:anchor-alias value="disposition-type"/>
2698  <x:anchor-alias value="disposition-parm"/>
2699  <x:anchor-alias value="disp-extension-parm"/>
2700  <x:anchor-alias value="disp-extension-token"/>
2701  <x:anchor-alias value="filename-parm"/>
[697]2703   The "Content-Disposition" response-header field has been proposed as a
[8]2704   means for the origin server to suggest a default filename if the user
2705   requests that the content is saved to a file. This usage is derived
[269]2706   from the definition of Content-Disposition in <xref target="RFC2183"/>.
[357]2708<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-disposition"/><iref primary="true" item="Grammar" subitem="content-disposition-v"/><iref primary="true" item="Grammar" subitem="disposition-type"/><iref primary="true" item="Grammar" subitem="disposition-parm"/><iref primary="true" item="Grammar" subitem="filename-parm"/><iref primary="true" item="Grammar" subitem="disp-extension-token"/><iref primary="true" item="Grammar" subitem="disp-extension-parm"/>
[366]2709  <x:ref>content-disposition</x:ref> = "Content-Disposition" ":" <x:ref>OWS</x:ref>
[357]2710                        <x:ref>content-disposition-v</x:ref>
[376]2711  <x:ref>content-disposition-v</x:ref> = <x:ref>disposition-type</x:ref>
2712                          *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>disposition-parm</x:ref> )
[334]2713  <x:ref>disposition-type</x:ref> = "attachment" / <x:ref>disp-extension-token</x:ref>
2714  <x:ref>disposition-parm</x:ref> = <x:ref>filename-parm</x:ref> / <x:ref>disp-extension-parm</x:ref>
[229]2715  <x:ref>filename-parm</x:ref> = "filename" "=" <x:ref>quoted-string</x:ref>
2716  <x:ref>disp-extension-token</x:ref> = <x:ref>token</x:ref>
[810]2717  <x:ref>disp-extension-parm</x:ref> = <x:ref>token</x:ref> "=" <x:ref>word</x:ref>
2720   An example is
2722<figure><artwork type="example">
[458]2723  Content-Disposition: attachment; filename="fname.ext"
2726   The receiving user agent &SHOULD-NOT;  respect any directory path
2727   information present in the filename-parm parameter, which is the only
2728   parameter believed to apply to HTTP implementations at this time. The
2729   filename &SHOULD; be treated as a terminal component only.
2732   If this header is used in a response with the application/octet-stream
2733   content-type, the implied suggestion is that the user agent
[746]2734   should not display the response, but directly enter a "save response
2735   as..." dialog.
2738   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
[99]2743<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2745  Clarify contexts that charset is used in.
2746  (<xref target="character.sets"/>)
[712]2749  Remove base URI setting semantics for Content-Location due to poor
[714]2750  implementation support, which was caused by too many broken servers emitting
2751  bogus Content-Location headers, and also the potentially undesirable effect
2752  of potentially breaking relative links in content-negotiated resources.
[712]2753  (<xref target="header.content-location"/>)
[104]2756  Remove reference to non-existant identity transfer-coding value tokens.
2757  (<xref target="no.content-transfer-encoding"/>)
[680]2761<?BEGININC p3-payload.abnf-appendix ?>
[427]2762<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
2764<artwork type="abnf" name="p3-payload.parsed-abnf">
2765<x:ref>Accept</x:ref> = "Accept:" OWS Accept-v
2766<x:ref>Accept-Charset</x:ref> = "Accept-Charset:" OWS Accept-Charset-v
2767<x:ref>Accept-Charset-v</x:ref> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
[425]2768 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
2769 qvalue ] ] )
[427]2770<x:ref>Accept-Encoding</x:ref> = "Accept-Encoding:" OWS Accept-Encoding-v
2771<x:ref>Accept-Encoding-v</x:ref> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
[425]2772 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
[427]2773<x:ref>Accept-Language</x:ref> = "Accept-Language:" OWS Accept-Language-v
2774<x:ref>Accept-Language-v</x:ref> = *( "," OWS ) language-range [ OWS ";" OWS "q="
[425]2775 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
2776 ] )
[427]2777<x:ref>Accept-v</x:ref> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
[425]2778 OWS media-range [ accept-params ] ] ) ]
[427]2780<x:ref>Content-Encoding</x:ref> = "Content-Encoding:" OWS Content-Encoding-v
2781<x:ref>Content-Encoding-v</x:ref> = *( "," OWS ) content-coding *( OWS "," [ OWS
[425]2782 content-coding ] )
[427]2783<x:ref>Content-Language</x:ref> = "Content-Language:" OWS Content-Language-v
2784<x:ref>Content-Language-v</x:ref> = *( "," OWS ) language-tag *( OWS "," [ OWS
[425]2785 language-tag ] )
[678]2786<x:ref>Content-Length</x:ref> = &lt;Content-Length, defined in [Part1], Section 9.2&gt;
[427]2787<x:ref>Content-Location</x:ref> = "Content-Location:" OWS Content-Location-v
2788<x:ref>Content-Location-v</x:ref> = absolute-URI / partial-URI
2789<x:ref>Content-MD5</x:ref> = "Content-MD5:" OWS Content-MD5-v
2790<x:ref>Content-MD5-v</x:ref> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
2791<x:ref>Content-Range</x:ref> = &lt;Content-Range, defined in [Part5], Section 5.2&gt;
2792<x:ref>Content-Type</x:ref> = "Content-Type:" OWS Content-Type-v
2793<x:ref>Content-Type-v</x:ref> = media-type
[538]2795<x:ref>Expires</x:ref> = &lt;Expires, defined in [Part6], Section 3.3&gt;
2797<x:ref>Last-Modified</x:ref> = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;
2799<x:ref>MIME-Version</x:ref> = "MIME-Version:" OWS MIME-Version-v
2800<x:ref>MIME-Version-v</x:ref> = 1*DIGIT "." 1*DIGIT
2802<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
[648]2804<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.6&gt;
[810]2805<x:ref>accept-ext</x:ref> = OWS ";" OWS token [ "=" word ]
[427]2806<x:ref>accept-params</x:ref> = OWS ";" OWS "q=" qvalue *accept-ext
2807<x:ref>attribute</x:ref> = token
2809<x:ref>charset</x:ref> = token
2810<x:ref>codings</x:ref> = ( content-coding / "*" )
2811<x:ref>content-coding</x:ref> = token
2812<x:ref>content-disposition</x:ref> = "Content-Disposition:" OWS
[425]2813 content-disposition-v
[427]2814<x:ref>content-disposition-v</x:ref> = disposition-type *( OWS ";" OWS
[425]2815 disposition-parm )
[810]2817<x:ref>disp-extension-parm</x:ref> = token "=" word
[427]2818<x:ref>disp-extension-token</x:ref> = token
2819<x:ref>disposition-parm</x:ref> = filename-parm / disp-extension-parm
2820<x:ref>disposition-type</x:ref> = "attachment" / disp-extension-token
2822<x:ref>filename-parm</x:ref> = "filename=" quoted-string
2824<x:ref>language-range</x:ref> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
[690]2825<x:ref>language-tag</x:ref> = &lt;Language-Tag, defined in [RFC5646], Section 2.1&gt;
2827<x:ref>media-range</x:ref> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
[425]2828 ";" OWS parameter )
[427]2829<x:ref>media-type</x:ref> = type "/" subtype *( OWS ";" OWS parameter )
2831<x:ref>parameter</x:ref> = attribute "=" value
[648]2832<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.6&gt;
2834<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
[678]2835<x:ref>qvalue</x:ref> = &lt;qvalue, defined in [Part1], Section 6.4&gt;
2837<x:ref>subtype</x:ref> = token
2839<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
2840<x:ref>type</x:ref> = token
[810]2842<x:ref>value</x:ref> = word
2844<x:ref>word</x:ref> = &lt;word, defined in [Part1], Section 1.2.2&gt;
[532]2847<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
2848; Accept defined but not used
[425]2849; Accept-Charset defined but not used
2850; Accept-Encoding defined but not used
2851; Accept-Language defined but not used
[968]2852; Content-Encoding defined but not used
2853; Content-Language defined but not used
2854; Content-Length defined but not used
2855; Content-Location defined but not used
2856; Content-MD5 defined but not used
2857; Content-Range defined but not used
2858; Content-Type defined but not used
2859; Expires defined but not used
2860; Last-Modified defined but not used
[425]2861; MIME-Version defined but not used
2862; content-disposition defined but not used
[680]2864<?ENDINC p3-payload.abnf-appendix ?>
[252]2866<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2868<section title="Since RFC2616">
2870  Extracted relevant partitions from <xref target="RFC2616"/>.
2874<section title="Since draft-ietf-httpbis-p3-payload-00">
[116]2876  Closed issues:
2877  <list style="symbols"> 
2878    <t>
[324]2879      <eref target=""/>:
[116]2880      "Media Type Registrations"
2881      (<eref target=""/>)
2882    </t>
2883    <t>
[324]2884      <eref target=""/>:
[116]2885      "Clarification regarding quoting of charset values"
2886      (<eref target=""/>)
2887    </t>
2888    <t>
[324]2889      <eref target=""/>:
[116]2890      "Remove 'identity' token references"
2891      (<eref target=""/>)
2892    </t>
2893    <t>
[324]2894      <eref target=""/>:
[126]2895      "Accept-Encoding BNF"
2896    </t>
2897    <t>
[324]2898      <eref target=""/>:
[152]2899      "Normative and Informative references"
2900    </t>
2901    <t>
[324]2902      <eref target=""/>:
[116]2903      "RFC1700 references"
2904    </t>
[122]2905    <t>
[324]2906      <eref target=""/>:
[200]2907      "Updating to RFC4288"
2908    </t>
2909    <t>
[324]2910      <eref target=""/>:
[129]2911      "Informative references"
2912    </t>
2913    <t>
[324]2914      <eref target=""/>:
[123]2915      "ISO-8859-1 Reference"
2916    </t>
2917    <t>
[324]2918      <eref target=""/>:
[122]2919      "Encoding References Normative"
2920    </t>
[131]2921    <t>
[324]2922      <eref target=""/>:
[131]2923      "Normative up-to-date references"
2924    </t>
[116]2925  </list>
[170]2929<section title="Since draft-ietf-httpbis-p3-payload-01">
[324]2931  Ongoing work on ABNF conversion (<eref target=""/>):
[205]2932  <list style="symbols"> 
2933    <t>
2934      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2935    </t>
2936  </list>
[252]2940<section title="Since draft-ietf-httpbis-p3-payload-02" anchor="changes.since.02">
[232]2942  Closed issues:
2943  <list style="symbols"> 
2944    <t>
[324]2945      <eref target=""/>:
[251]2946      "Quoting Charsets"
2947    </t>
2948    <t>
[324]2949      <eref target=""/>:
[232]2950      "Classification for Allow header"
2951    </t>
[248]2952    <t>
[324]2953      <eref target=""/>:
[248]2954      "missing default for qvalue in description of Accept-Encoding"
2955    </t>
[232]2956  </list>
[324]2959  Ongoing work on IANA Message Header Registration (<eref target=""/>):
[253]2960  <list style="symbols"> 
2961    <t>
2962      Reference RFC 3984, and update header registrations for headers defined
2963      in this document.
2964    </t>
2965  </list>
[267]2969<section title="Since draft-ietf-httpbis-p3-payload-03" anchor="changes.since.03">
[269]2971  Closed issues:
2972  <list style="symbols"> 
2973    <t>
[297]2974      <eref target=""/>:
2975      "Quoting Charsets"
2976    </t>
2977    <t>
[303]2978      <eref target=""/>:
2979      "language tag matching (Accept-Language) vs RFC4647"
2980    </t>
2981    <t>
[277]2982      <eref target=""/>:
[269]2983      "RFC 1806 has been replaced by RFC2183"
2984    </t>
2985  </list>
2988  Other changes:
2989  <list style="symbols"> 
2990    <t>
2991      <eref target=""/>:
2992      "Encoding References Normative" -- rephrase the annotation and reference
2993      <xref target="BCP97"/>.
2994    </t>
2995  </list>
[269]2997 </section>
[323]2999<section title="Since draft-ietf-httpbis-p3-payload-04" anchor="changes.since.04">
[327]3001  Closed issues:
3002  <list style="symbols"> 
3003    <t>
3004      <eref target=""/>:
3005      "RFC 2822 is updated by RFC 5322"
3006    </t>
3007  </list>
3010  Ongoing work on ABNF conversion (<eref target=""/>):
3011  <list style="symbols"> 
3012    <t>
3013      Use "/" instead of "|" for alternatives.
3014    </t>
[357]3015    <t>
3016      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
3017      whitespace ("OWS") and required whitespace ("RWS").
3018    </t>
3019    <t>
3020      Rewrite ABNFs to spell out whitespace rules, factor out
3021      header value format definitions.
3022    </t>
[334]3023  </list>
[382]3027<section title="Since draft-ietf-httpbis-p3-payload-05" anchor="changes.since.05">
[385]3029  Closed issues:
3030  <list style="symbols"> 
3031    <t>
3032      <eref target=""/>:
3033      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
3034    </t>
3035  </list>
[543]3038  Final work on ABNF conversion (<eref target=""/>):
[421]3039  <list style="symbols"> 
3040    <t>
[424]3041      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
[421]3042    </t>
3043  </list>
3046  Other changes:
3047  <list style="symbols"> 
3048    <t>
3049      Move definition of quality values into Part 1.
3050    </t>
3051  </list>
[547]3055<section title="Since draft-ietf-httpbis-p3-payload-06" anchor="changes.since.06">
[577]3057  Closed issues:
3058  <list style="symbols"> 
3059    <t>
3060      <eref target=""/>:
3061      "Content-Location isn't special"
3062    </t>
[592]3063    <t>
3064      <eref target=""/>:
3065      "Content Sniffing"
3066    </t>
[577]3067  </list>
[604]3071<section title="Since draft-ietf-httpbis-p3-payload-07" anchor="changes.since.07">
[613]3073  Closed issues:
3074  <list style="symbols"> 
3075    <t>
[670]3076      <eref target=""/>:
[613]3077      "Updated reference for language tags"
3078    </t>
[663]3079    <t>
[716]3080      <eref target=""/>:
3081      "Clarify rules for determining what entities a response carries"
3082    </t>
3083    <t>
[712]3084      <eref target=""/>:
3085      "Content-Location base-setting problems"
3086    </t>
3087    <t>
[663]3088      <eref target=""/>:
3089      "Content Sniffing"
3090    </t>
[670]3091    <t>
3092      <eref target=""/>:
3093      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
3094    </t>
[673]3095    <t>
3096      <eref target=""/>:
3097      "move definitions of gzip/deflate/compress to part 1"
3098    </t>
[613]3099  </list>
3102  Partly resolved issues:
3103  <list style="symbols"> 
3104    <t>
3105      <eref target=""/>:
3106      "update IANA requirements wrt Transfer-Coding values" (add the
3107      IANA Considerations subsection)
3108    </t>
[668]3109    <t>
3110      <eref target=""/>:
3111      "update IANA requirements wrt Content-Coding values" (add the
3112      IANA Considerations subsection)
3113    </t>
[667]3114  </list>
[720]3118<section title="Since draft-ietf-httpbis-p3-payload-08" anchor="changes.since.08">
[724]3120  Closed issues:
3121  <list style="symbols"> 
3122    <t>
[745]3123      <eref target=""/>:
3124      "Content Negotiation for media types"
3125    </t>
3126    <t>
[724]3127      <eref target=""/>:
3128      "Accept-Language: which RFC4647 filtering?"
3129    </t>
3130  </list>
[773]3134<section title="Since draft-ietf-httpbis-p3-payload-09" anchor="changes.since.09">
[808]3136  Closed issues:
3137  <list style="symbols"> 
3138    <t>
[937]3139      <eref target=""/>:
3140      "MIME-Version not listed in P1, general header fields"
3141    </t>
3142    <t>
[808]3143      <eref target=""/>:
3144      "IANA registry for content/transfer encodings"
3145    </t>
[810]3146    <t>
[831]3147      <eref target=""/>:
3148      "Content Sniffing"
3149    </t>
3150    <t>
[810]3151      <eref target=""/>:
3152      "use of term "word" when talking about header structure"
3153    </t>
[808]3154  </list>
3157  Partly resolved issues:
3158  <list style="symbols"> 
3159    <t>
3160      <eref target=""/>:
3161      "Term for the requested resource's URI"
3162    </t>
3163  </list>
[841]3167<section title="Since draft-ietf-httpbis-p3-payload-10" anchor="changes.since.10">
[854]3169  Closed issues:
3170  <list style="symbols"> 
3171    <t>
[858]3172      <eref target=""/>:
3173      "Clarify 'Requested Variant'"
3174    </t>
3175    <t>
3176      <eref target=""/>:
3177      "Content-Location isn't special"
3178    </t>
3179    <t>
[854]3180      <eref target=""/>:
3181      "Delimiting messages with multipart/byteranges"
3182    </t>
[858]3183    <t>
3184      <eref target=""/>:
3185      "Clarify entity / representation / variant terminology"
3186    </t>
3187    <t>
3188      <eref target=""/>:
3189      "confusing req. language for Content-Location"
3190    </t>
3191    <t>
3192      <eref target=""/>:
3193      "Content-Location on 304 responses"
3194    </t>
[882]3195    <t>
3196      <eref target=""/>:
3197      "'requested resource' in content-encoding definition"
3198    </t>
[911]3199    <t>
3200      <eref target=""/>:
3201      "consider removing the 'changes from 2068' sections"
3202    </t>
[854]3203  </list>
3206  Partly resolved issues:
3207  <list style="symbols"> 
3208    <t>
3209      <eref target=""/>:
3210      "Content-MD5 and partial responses"
3211    </t>
3212  </list>
[973]3216<section title="Since draft-ietf-httpbis-p3-payload-11" anchor="changes.since.11">
3218  None yet.
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