source: draft-ietf-httpbis/latest/p3-payload.xml @ 81

Last change on this file since 81 was 81, checked in by fielding@…, 12 years ago

Resolve #14: Clarification regarding quoting of charset values

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1<?xml version="1.0" encoding="utf-8"?>
2<!DOCTYPE rfc [
3  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
4  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
5  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
6  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
7  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
8  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
9  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
10  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
11  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
12  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
13  <!ENTITY ID-VERSION "latest">
14  <!ENTITY ID-MONTH "December">
15  <!ENTITY ID-YEAR "2007">
16  <!ENTITY caching                  "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
17  <!ENTITY header-transfer-encoding "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY header-allow             "<xref target='Part2' x:rel='#header.allow' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY header-content-length    "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY header-content-range     "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY header-expires           "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY header-last-modified     "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY header-user-agent        "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY message-body             "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY message-length           "<xref target='Part1' x:rel='#message.length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY multipart-byteranges     "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27]>
28<?rfc toc="yes" ?>
29<?rfc symrefs="yes" ?>
30<?rfc sortrefs="yes" ?>
31<?rfc compact="yes"?>
32<?rfc subcompact="no" ?>
33<?rfc linkmailto="no" ?>
34<?rfc editing="no" ?>
35<?rfc-ext allow-markup-in-artwork="yes" ?>
36<?rfc-ext include-references-in-index="yes" ?>
37<rfc obsoletes="2068, 2616" category="std"
38     ipr="full3978" docName="draft-ietf-httpbis-p3-payload-&ID-VERSION;"
39     xmlns:x='http://purl.org/net/xml2rfc/ext' xmlns:ed="http://greenbytes.de/2002/rfcedit">
40<front>
41
42  <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
43
44  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
45    <organization abbrev="Day Software">Day Software</organization>
46    <address>
47      <postal>
48        <street>23 Corporate Plaza DR, Suite 280</street>
49        <city>Newport Beach</city>
50        <region>CA</region>
51        <code>92660</code>
52        <country>USA</country>
53      </postal>
54      <phone>+1-949-706-5300</phone>
55      <facsimile>+1-949-706-5305</facsimile>
56      <email>fielding@gbiv.com</email>
57      <uri>http://roy.gbiv.com/</uri>
58    </address>
59  </author>
60
61  <author initials="J." surname="Gettys" fullname="Jim Gettys">
62    <organization>One Laptop per Child</organization>
63    <address>
64      <postal>
65        <street>21 Oak Knoll Road</street>
66        <city>Carlisle</city>
67        <region>MA</region>
68        <code>01741</code>
69        <country>USA</country>
70      </postal>
71      <email>jg@laptop.org</email>
72      <uri>http://www.laptop.org/</uri>
73    </address>
74  </author>
75 
76  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
77    <organization abbrev="HP">Hewlett-Packard Company</organization>
78    <address>
79      <postal>
80        <street>HP Labs, Large Scale Systems Group</street>
81        <street>1501 Page Mill Road, MS 1177</street>
82        <city>Palo Alto</city>
83        <region>CA</region>
84        <code>94304</code>
85        <country>USA</country>
86      </postal>
87      <email>JeffMogul@acm.org</email>
88    </address>
89  </author>
90
91  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
92    <organization abbrev="Microsoft">Microsoft Corporation</organization>
93    <address>
94      <postal>
95        <street>1 Microsoft Way</street>
96        <city>Redmond</city>
97        <region>WA</region>
98        <code>98052</code>
99        <country>USA</country>
100      </postal>
101      <email>henrikn@microsoft.com</email>
102    </address>
103  </author>
104
105  <author initials="L." surname="Masinter" fullname="Larry Masinter">
106    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
107    <address>
108      <postal>
109        <street>345 Park Ave</street>
110        <city>San Jose</city>
111        <region>CA</region>
112        <code>95110</code>
113        <country>USA</country>
114      </postal>
115      <email>LMM@acm.org</email>
116      <uri>http://larry.masinter.net/</uri>
117    </address>
118  </author>
119 
120  <author initials="P." surname="Leach" fullname="Paul J. Leach">
121    <organization abbrev="Microsoft">Microsoft Corporation</organization>
122    <address>
123      <postal>
124        <street>1 Microsoft Way</street>
125        <city>Redmond</city>
126        <region>WA</region>
127        <code>98052</code>
128      </postal>
129      <email>paulle@microsoft.com</email>
130    </address>
131  </author>
132   
133  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
134    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
135    <address>
136      <postal>
137        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
138        <street>The Stata Center, Building 32</street>
139        <street>32 Vassar Street</street>
140        <city>Cambridge</city>
141        <region>MA</region>
142        <code>02139</code>
143        <country>USA</country>
144      </postal>
145      <email>timbl@w3.org</email>
146      <uri>http://www.w3.org/People/Berners-Lee/</uri>
147    </address>
148  </author>
149
150  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
151
152<abstract>
153<t>
154   The Hypertext Transfer Protocol (HTTP) is an application-level
155   protocol for distributed, collaborative, hypermedia information
156   systems. HTTP has been in use by the World Wide Web global information
157   initiative since 1990. This document is Part 3 of the seven-part specification
158   that defines the protocol referred to as "HTTP/1.1" and, taken together,
159   obsoletes RFC 2616.  Part 3 defines HTTP message content,
160   metadata, and content negotiation.
161</t>
162</abstract>
163
164<note title="Editorial Note (To be removed by RFC Editor)">
165  <t>
166    This version of the HTTP specification contains only minimal editorial
167    changes from <xref target="RFC2616"/> (abstract, introductory paragraph,
168    and authors' addresses).  All other changes are due to partitioning the
169    original into seven mostly independent parts.  The intent is for readers
170    of future drafts to able to use draft 00 as the basis for comparison
171    when the WG makes later changes to the specification text.  This draft
172    will shortly be followed by draft 01 (containing the first round of changes
173    that have already been agreed to on the mailing list). There is no point in
174    reviewing this draft other than to verify that the partitioning has been
175    done correctly.  Roy T. Fielding, Yves Lafon, and Julian Reschke
176    will be the editors after draft 00 is submitted.
177  </t>
178  <t>
179    Discussion of this draft should take place on the HTTPBIS working group
180    mailing list (ietf-http-wg@w3.org). The current issues list is
181    at <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/report/11"/>
182    and related documents (including fancy diffs) can be found at
183    <eref target="http://www3.tools.ietf.org/wg/httpbis/"/>.
184  </t>
185</note>
186</front>
187<middle>
188<section title="Introduction" anchor="introduction">
189<t>
190   This document will define aspects of HTTP related to the payload of
191   messages (message content), including metadata and media types, along
192   with HTTP content negotiation.  Right now it only includes the extracted
193   relevant sections of RFC 2616 without edit.
194</t>
195</section>
196
197<section title="Protocol Parameters" anchor="protocol.parameters">
198
199<section title="Character Sets" anchor="character.sets">
200<t>
201   HTTP uses the same definition of the term "character set" as that
202   described for MIME:
203</t>
204<t>
205   The term "character set" is used in this document to refer to a
206   method used with one or more tables to convert a sequence of octets
207   into a sequence of characters. Note that unconditional conversion in
208   the other direction is not required, in that not all characters may
209   be available in a given character set and a character set may provide
210   more than one sequence of octets to represent a particular character.
211   This definition is intended to allow various kinds of character
212   encoding, from simple single-table mappings such as US-ASCII to
213   complex table switching methods such as those that use ISO-2022's
214   techniques. However, the definition associated with a MIME character
215   set name &MUST; fully specify the mapping to be performed from octets
216   to characters. In particular, use of external profiling information
217   to determine the exact mapping is not permitted.
218</t>
219<t><list><t>
220      <x:h>Note:</x:h> This use of the term "character set" is more commonly
221      referred to as a "character encoding." However, since HTTP and
222      MIME share the same registry, it is important that the terminology
223      also be shared.
224</t></list></t>
225<t>
226   HTTP character sets are identified by case-insensitive tokens. The
227   complete set of tokens is defined by the IANA Character Set registry
228   <xref target="RFC1700"/>.
229</t>
230<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="charset"/>
231    charset = token
232</artwork></figure>
233<t>
234   Although HTTP allows an arbitrary token to be used as a charset
235   value, any token that has a predefined value within the IANA
236   Character Set registry <xref target="RFC1700"/> &MUST; represent the character set defined
237   by that registry. Applications &SHOULD; limit their use of character
238   sets to those defined by the IANA registry.
239</t>
240<t>
241   HTTP uses charset in two contexts: within an Accept-Charset request
242   header (in which the charset value is an unquoted token) and as the
243   value of a parameter in a Content-type header (within a request or
244   response), in which case the parameter value of the charset parameter
245   may be quoted.
246</t>
247<t>
248   Implementors should be aware of IETF character set requirements <xref target="RFC2279"/>
249   <xref target="RFC2277"/>.
250</t>
251
252<section title="Missing Charset" anchor="missing.charset">
253<t>
254   Some HTTP/1.0 software has interpreted a Content-Type header without
255   charset parameter incorrectly to mean "recipient should guess."
256   Senders wishing to defeat this behavior &MAY; include a charset
257   parameter even when the charset is ISO-8859-1 and &SHOULD; do so when
258   it is known that it will not confuse the recipient.
259</t>
260<t>
261   Unfortunately, some older HTTP/1.0 clients did not deal properly with
262   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
263   charset label provided by the sender; and those user agents that have
264   a provision to "guess" a charset &MUST; use the charset from the
265   content-type field if they support that charset, rather than the
266   recipient's preference, when initially displaying a document. See
267   <xref target="canonicalization.and.text.defaults"/>.
268</t>
269</section>
270</section>
271
272<section title="Content Codings" anchor="content.codings">
273<t>
274   Content coding values indicate an encoding transformation that has
275   been or can be applied to an entity. Content codings are primarily
276   used to allow a document to be compressed or otherwise usefully
277   transformed without losing the identity of its underlying media type
278   and without loss of information. Frequently, the entity is stored in
279   coded form, transmitted directly, and only decoded by the recipient.
280</t>
281<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
282    content-coding   = token
283</artwork></figure>
284<t>
285   All content-coding values are case-insensitive. HTTP/1.1 uses
286   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
287   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
288   describes the content-coding, what is more important is that it
289   indicates what decoding mechanism will be required to remove the
290   encoding.
291</t>
292<t>
293   The Internet Assigned Numbers Authority (IANA) acts as a registry for
294   content-coding value tokens. Initially, the registry contains the
295   following tokens:
296</t>
297<t>
298   gzip<iref item="gzip"/>
299  <list>
300    <t>
301        An encoding format produced by the file compression program
302        "gzip" (GNU zip) as described in RFC 1952 <xref target="RFC1952"/>. This format is a
303        Lempel-Ziv coding (LZ77) with a 32 bit CRC.
304    </t>
305  </list>
306</t>
307<t>
308   compress<iref item="compress"/>
309  <list><t>
310        The encoding format produced by the common UNIX file compression
311        program "compress". This format is an adaptive Lempel-Ziv-Welch
312        coding (LZW).
313</t><t>
314        Use of program names for the identification of encoding formats
315        is not desirable and is discouraged for future encodings. Their
316        use here is representative of historical practice, not good
317        design. For compatibility with previous implementations of HTTP,
318        applications &SHOULD; consider "x-gzip" and "x-compress" to be
319        equivalent to "gzip" and "compress" respectively.
320  </t></list>
321</t>
322<t>
323   deflate<iref item="deflate"/>
324  <list><t>
325        The "zlib" format defined in RFC 1950 <xref target="RFC1950"/> in combination with
326        the "deflate" compression mechanism described in RFC 1951 <xref target="RFC1951"/>.
327  </t></list>
328</t>
329<t>
330   identity<iref item="identity"/>
331  <list><t>
332        The default (identity) encoding; the use of no transformation
333        whatsoever. This content-coding is used only in the Accept-Encoding
334        header, and &SHOULD-NOT;  be used in the Content-Encoding
335        header.
336  </t></list>
337</t>
338<t>
339   New content-coding value tokens &SHOULD; be registered; to allow
340   interoperability between clients and servers, specifications of the
341   content coding algorithms needed to implement a new value &SHOULD; be
342   publicly available and adequate for independent implementation, and
343   conform to the purpose of content coding defined in this section.
344</t>
345</section>
346
347<section title="Media Types" anchor="media.types">
348<t>
349   HTTP uses Internet Media Types <xref target="RFC4288"/> in the Content-Type (<xref target="header.content-type"/>)
350   and Accept (<xref target="header.accept"/>) header fields in order to provide
351   open and extensible data typing and type negotiation.
352</t>
353<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"/>
354    media-type     = type "/" subtype *( ";" parameter )
355    type           = token
356    subtype        = token
357</artwork></figure>
358<t>
359   Parameters &MAY; follow the type/subtype in the form of attribute/value
360   pairs.
361</t>
362<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"/>
363    parameter               = attribute "=" value
364    attribute               = token
365    value                   = token | quoted-string
366</artwork></figure>
367<t>
368   The type, subtype, and parameter attribute names are case-insensitive.
369   Parameter values might or might not be case-sensitive,
370   depending on the semantics of the parameter name. Linear white space
371   (LWS) &MUST-NOT; be used between the type and subtype, nor between an
372   attribute and its value. The presence or absence of a parameter might
373   be significant to the processing of a media-type, depending on its
374   definition within the media type registry.
375</t>
376<t>
377   Note that some older HTTP applications do not recognize media type
378   parameters. When sending data to older HTTP applications,
379   implementations &SHOULD; only use media type parameters when they are
380   required by that type/subtype definition.
381</t>
382<t>
383   Media-type values are registered with the Internet Assigned Number
384   Authority (IANA <xref target="RFC1700"/>). The media type registration process is
385   outlined in RFC 4288 <xref target="RFC4288"/>. Use of non-registered media types is
386   discouraged.
387</t>
388
389<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
390<t>
391   Internet media types are registered with a canonical form. An
392   entity-body transferred via HTTP messages &MUST; be represented in the
393   appropriate canonical form prior to its transmission except for
394   "text" types, as defined in the next paragraph.
395</t>
396<t>
397   When in canonical form, media subtypes of the "text" type use CRLF as
398   the text line break. HTTP relaxes this requirement and allows the
399   transport of text media with plain CR or LF alone representing a line
400   break when it is done consistently for an entire entity-body. HTTP
401   applications &MUST; accept CRLF, bare CR, and bare LF as being
402   representative of a line break in text media received via HTTP. In
403   addition, if the text is represented in a character set that does not
404   use octets 13 and 10 for CR and LF respectively, as is the case for
405   some multi-byte character sets, HTTP allows the use of whatever octet
406   sequences are defined by that character set to represent the
407   equivalent of CR and LF for line breaks. This flexibility regarding
408   line breaks applies only to text media in the entity-body; a bare CR
409   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
410   structures (such as header fields and multipart boundaries).
411</t>
412<t>
413   If an entity-body is encoded with a content-coding, the underlying
414   data &MUST; be in a form defined above prior to being encoded.
415</t>
416<t>
417   The "charset" parameter is used with some media types to define the
418   character set (<xref target="character.sets"/>) of the data. When no explicit charset
419   parameter is provided by the sender, media subtypes of the "text"
420   type are defined to have a default charset value of "ISO-8859-1" when
421   received via HTTP. Data in character sets other than "ISO-8859-1" or
422   its subsets &MUST; be labeled with an appropriate charset value. See
423   <xref target="missing.charset"/> for compatibility problems.
424</t>
425</section>
426
427<section title="Multipart Types" anchor="multipart.types">
428<t>
429   MIME provides for a number of "multipart" types -- encapsulations of
430   one or more entities within a single message-body. All multipart
431   types share a common syntax, as defined in section <xref target="RFC2046" x:sec="5.1.1" x:fmt="number"/> of RFC 2046
432   <xref target="RFC2046"/>, and &MUST; include a boundary parameter as part of the media type
433   value. The message body is itself a protocol element and &MUST;
434   therefore use only CRLF to represent line breaks between body-parts.
435   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
436   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
437   original multipart contains an epilogue). These restrictions exist in
438   order to preserve the self-delimiting nature of a multipart message-body,
439   wherein the "end" of the message-body is indicated by the
440   ending multipart boundary.
441</t>
442<t>
443   In general, HTTP treats a multipart message-body no differently than
444   any other media type: strictly as payload. The one exception is the
445   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
446   (Partial Content) response. In all
447   other cases, an HTTP user agent &SHOULD; follow the same or similar
448   behavior as a MIME user agent would upon receipt of a multipart type.
449   The MIME header fields within each body-part of a multipart message-body
450   do not have any significance to HTTP beyond that defined by
451   their MIME semantics.
452</t>
453<t>
454   In general, an HTTP user agent &SHOULD; follow the same or similar
455   behavior as a MIME user agent would upon receipt of a multipart type.
456   If an application receives an unrecognized multipart subtype, the
457   application &MUST; treat it as being equivalent to "multipart/mixed".
458</t>
459<t><list><t>
460      <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
461      for carrying form data suitable for processing via the POST
462      request method, as described in RFC 1867 <xref target="RFC1867"/>.
463</t></list></t>
464</section>
465</section>
466
467<section title="Quality Values" anchor="quality.values">
468<t>
469   HTTP content negotiation (<xref target="content.negotiation"/>) uses short "floating point"
470   numbers to indicate the relative importance ("weight") of various
471   negotiable parameters.  A weight is normalized to a real number in
472   the range 0 through 1, where 0 is the minimum and 1 the maximum
473   value. If a parameter has a quality value of 0, then content with
474   this parameter is `not acceptable' for the client. HTTP/1.1
475   applications &MUST-NOT; generate more than three digits after the
476   decimal point. User configuration of these values &SHOULD; also be
477   limited in this fashion.
478</t>
479<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
480    qvalue         = ( "0" [ "." 0*3DIGIT ] )
481                   | ( "1" [ "." 0*3("0") ] )
482</artwork></figure>
483<t>
484   "Quality values" is a misnomer, since these values merely represent
485   relative degradation in desired quality.
486</t>
487</section>
488
489<section title="Language Tags" anchor="language.tags">
490<t>
491   A language tag identifies a natural language spoken, written, or
492   otherwise conveyed by human beings for communication of information
493   to other human beings. Computer languages are explicitly excluded.
494   HTTP uses language tags within the Accept-Language and Content-Language
495   fields.
496</t>
497<t>
498   The syntax and registry of HTTP language tags is the same as that
499   defined by RFC 1766 <xref target="RFC1766"/>. In summary, a language tag is composed of 1
500   or more parts: A primary language tag and a possibly empty series of
501   subtags:
502</t>
503<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="language-tag"/><iref primary="true" item="Grammar" subitem="primary-tag"/><iref primary="true" item="Grammar" subitem="subtag"/>
504     language-tag  = primary-tag *( "-" subtag )
505     primary-tag   = 1*8ALPHA
506     subtag        = 1*8ALPHA
507</artwork></figure>
508<t>
509   White space is not allowed within the tag and all tags are case-insensitive.
510   The name space of language tags is administered by the
511   IANA. Example tags include:
512</t>
513<figure><artwork type="example">
514    en, en-US, en-cockney, i-cherokee, x-pig-latin
515</artwork></figure>
516<t>
517   where any two-letter primary-tag is an ISO-639 language abbreviation
518   and any two-letter initial subtag is an ISO-3166 country code. (The
519   last three tags above are not registered tags; all but the last are
520   examples of tags which could be registered in future.)
521</t>
522</section>
523</section>
524
525<section title="Entity" anchor="entity">
526<t>
527   Request and Response messages &MAY; transfer an entity if not otherwise
528   restricted by the request method or response status code. An entity
529   consists of entity-header fields and an entity-body, although some
530   responses will only include the entity-headers.
531</t>
532<t>
533   In this section, both sender and recipient refer to either the client
534   or the server, depending on who sends and who receives the entity.
535</t>
536
537<section title="Entity Header Fields" anchor="entity.header.fields">
538<t>
539   Entity-header fields define metainformation about the entity-body or,
540   if no body is present, about the resource identified by the request.
541   Some of this metainformation is &OPTIONAL;; some might be &REQUIRED; by
542   portions of this specification.
543</t>
544<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
545    entity-header  = Allow                    ; &header-allow;
546                   | Content-Encoding         ; <xref target="header.content-encoding"/>
547                   | Content-Language         ; <xref target="header.content-language"/>
548                   | Content-Length           ; &header-content-length;
549                   | Content-Location         ; <xref target="header.content-location"/>
550                   | Content-MD5              ; <xref target="header.content-md5"/>
551                   | Content-Range            ; &header-content-range;
552                   | Content-Type             ; <xref target="header.content-type"/>
553                   | Expires                  ; &header-expires;
554                   | Last-Modified            ; &header-last-modified;
555                   | extension-header
556
557    extension-header = message-header
558</artwork></figure>
559<t>
560   The extension-header mechanism allows additional entity-header fields
561   to be defined without changing the protocol, but these fields cannot
562   be assumed to be recognizable by the recipient. Unrecognized header
563   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
564   transparent proxies.
565</t>
566</section>
567
568<section title="Entity Body" anchor="entity.body">
569<t>
570   The entity-body (if any) sent with an HTTP request or response is in
571   a format and encoding defined by the entity-header fields.
572</t>
573<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
574    entity-body    = *OCTET
575</artwork></figure>
576<t>
577   An entity-body is only present in a message when a message-body is
578   present, as described in &message-body;. The entity-body is obtained
579   from the message-body by decoding any Transfer-Encoding that might
580   have been applied to ensure safe and proper transfer of the message.
581</t>
582
583<section title="Type" anchor="type">
584<t>
585   When an entity-body is included with a message, the data type of that
586   body is determined via the header fields Content-Type and Content-Encoding.
587   These define a two-layer, ordered encoding model:
588</t>
589<figure><artwork type="example">
590    entity-body := Content-Encoding( Content-Type( data ) )
591</artwork></figure>
592<t>
593   Content-Type specifies the media type of the underlying data.
594   Content-Encoding may be used to indicate any additional content
595   codings applied to the data, usually for the purpose of data
596   compression, that are a property of the requested resource. There is
597   no default encoding.
598</t>
599<t>
600   Any HTTP/1.1 message containing an entity-body &SHOULD; include a
601   Content-Type header field defining the media type of that body. If
602   and only if the media type is not given by a Content-Type field, the
603   recipient &MAY; attempt to guess the media type via inspection of its
604   content and/or the name extension(s) of the URI used to identify the
605   resource. If the media type remains unknown, the recipient &SHOULD;
606   treat it as type "application/octet-stream".
607</t>
608</section>
609   
610<section title="Entity Length" anchor="entity.length">
611<t>
612   The entity-length of a message is the length of the message-body
613   before any transfer-codings have been applied. &message-length; defines
614   how the transfer-length of a message-body is determined.
615</t>
616</section>
617</section>
618</section>
619
620<section title="Content Negotiation" anchor="content.negotiation">
621<t>
622   Most HTTP responses include an entity which contains information for
623   interpretation by a human user. Naturally, it is desirable to supply
624   the user with the "best available" entity corresponding to the
625   request. Unfortunately for servers and caches, not all users have the
626   same preferences for what is "best," and not all user agents are
627   equally capable of rendering all entity types. For that reason, HTTP
628   has provisions for several mechanisms for "content negotiation" --
629   the process of selecting the best representation for a given response
630   when there are multiple representations available.
631  <list><t>
632      <x:h>Note:</x:h> This is not called "format negotiation" because the
633      alternate representations may be of the same media type, but use
634      different capabilities of that type, be in different languages,
635      etc.
636  </t></list>
637</t>
638<t>
639   Any response containing an entity-body &MAY; be subject to negotiation,
640   including error responses.
641</t>
642<t>
643   There are two kinds of content negotiation which are possible in
644   HTTP: server-driven and agent-driven negotiation. These two kinds of
645   negotiation are orthogonal and thus may be used separately or in
646   combination. One method of combination, referred to as transparent
647   negotiation, occurs when a cache uses the agent-driven negotiation
648   information provided by the origin server in order to provide
649   server-driven negotiation for subsequent requests.
650</t>
651
652<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
653<t>
654   If the selection of the best representation for a response is made by
655   an algorithm located at the server, it is called server-driven
656   negotiation. Selection is based on the available representations of
657   the response (the dimensions over which it can vary; e.g. language,
658   content-coding, etc.) and the contents of particular header fields in
659   the request message or on other information pertaining to the request
660   (such as the network address of the client).
661</t>
662<t>
663   Server-driven negotiation is advantageous when the algorithm for
664   selecting from among the available representations is difficult to
665   describe to the user agent, or when the server desires to send its
666   "best guess" to the client along with the first response (hoping to
667   avoid the round-trip delay of a subsequent request if the "best
668   guess" is good enough for the user). In order to improve the server's
669   guess, the user agent &MAY; include request header fields (Accept,
670   Accept-Language, Accept-Encoding, etc.) which describe its
671   preferences for such a response.
672</t>
673<t>
674   Server-driven negotiation has disadvantages:
675  <list style="numbers">
676    <t>
677         It is impossible for the server to accurately determine what
678         might be "best" for any given user, since that would require
679         complete knowledge of both the capabilities of the user agent
680         and the intended use for the response (e.g., does the user want
681         to view it on screen or print it on paper?).
682    </t>
683    <t>
684         Having the user agent describe its capabilities in every
685         request can be both very inefficient (given that only a small
686         percentage of responses have multiple representations) and a
687         potential violation of the user's privacy.
688    </t>
689    <t>
690         It complicates the implementation of an origin server and the
691         algorithms for generating responses to a request.
692    </t>
693    <t>
694         It may limit a public cache's ability to use the same response
695         for multiple user's requests.
696    </t>
697  </list>
698</t>
699<t>
700   HTTP/1.1 includes the following request-header fields for enabling
701   server-driven negotiation through description of user agent
702   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
703   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
704   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;). However, an
705   origin server is not limited to these dimensions and &MAY; vary the
706   response based on any aspect of the request, including information
707   outside the request-header fields or within extension header fields
708   not defined by this specification.
709</t>
710<t>
711   The Vary header field &caching; can be used to express the parameters the
712   server uses to select a representation that is subject to server-driven
713   negotiation.
714</t>
715</section>
716
717<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
718<t>
719   With agent-driven negotiation, selection of the best representation
720   for a response is performed by the user agent after receiving an
721   initial response from the origin server. Selection is based on a list
722   of the available representations of the response included within the
723   header fields or entity-body of the initial response, with each
724   representation identified by its own URI. Selection from among the
725   representations may be performed automatically (if the user agent is
726   capable of doing so) or manually by the user selecting from a
727   generated (possibly hypertext) menu.
728</t>
729<t>
730   Agent-driven negotiation is advantageous when the response would vary
731   over commonly-used dimensions (such as type, language, or encoding),
732   when the origin server is unable to determine a user agent's
733   capabilities from examining the request, and generally when public
734   caches are used to distribute server load and reduce network usage.
735</t>
736<t>
737   Agent-driven negotiation suffers from the disadvantage of needing a
738   second request to obtain the best alternate representation. This
739   second request is only efficient when caching is used. In addition,
740   this specification does not define any mechanism for supporting
741   automatic selection, though it also does not prevent any such
742   mechanism from being developed as an extension and used within
743   HTTP/1.1.
744</t>
745<t>
746   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
747   status codes for enabling agent-driven negotiation when the server is
748   unwilling or unable to provide a varying response using server-driven
749   negotiation.
750</t>
751</section>
752
753<section title="Transparent Negotiation" anchor="transparent.negotiation">
754<t>
755   Transparent negotiation is a combination of both server-driven and
756   agent-driven negotiation. When a cache is supplied with a form of the
757   list of available representations of the response (as in agent-driven
758   negotiation) and the dimensions of variance are completely understood
759   by the cache, then the cache becomes capable of performing server-driven
760   negotiation on behalf of the origin server for subsequent
761   requests on that resource.
762</t>
763<t>
764   Transparent negotiation has the advantage of distributing the
765   negotiation work that would otherwise be required of the origin
766   server and also removing the second request delay of agent-driven
767   negotiation when the cache is able to correctly guess the right
768   response.
769</t>
770<t>
771   This specification does not define any mechanism for transparent
772   negotiation, though it also does not prevent any such mechanism from
773   being developed as an extension that could be used within HTTP/1.1.
774</t>
775</section>
776</section>
777<section title="Header Field Definitions" anchor="header.fields">
778<t>
779   This section defines the syntax and semantics of all standard
780   HTTP/1.1 header fields. For entity-header fields, both sender and
781   recipient refer to either the client or the server, depending on who
782   sends and who receives the entity.
783</t>
784<section title="Accept" anchor="header.accept">
785  <iref primary="true" item="Accept header" x:for-anchor=""/>
786  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
787<t>
788   The Accept request-header field can be used to specify certain media
789   types which are acceptable for the response. Accept headers can be
790   used to indicate that the request is specifically limited to a small
791   set of desired types, as in the case of a request for an in-line
792   image.
793</t>
794<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept"/><iref primary="true" item="Grammar" subitem="media-range"/><iref primary="true" item="Grammar" subitem="accept-params"/><iref primary="true" item="Grammar" subitem="accept-extension"/>
795    Accept         = "Accept" ":"
796                     #( media-range [ accept-params ] )
797
798    media-range    = ( "*/*"
799                     | ( type "/" "*" )
800                     | ( type "/" subtype )
801                     ) *( ";" parameter )
802    accept-params  = ";" "q" "=" qvalue *( accept-extension )
803    accept-extension = ";" token [ "=" ( token | quoted-string ) ]
804</artwork></figure>
805<t>
806   The asterisk "*" character is used to group media types into ranges,
807   with "*/*" indicating all media types and "type/*" indicating all
808   subtypes of that type. The media-range &MAY; include media type
809   parameters that are applicable to that range.
810</t>
811<t>
812   Each media-range &MAY; be followed by one or more accept-params,
813   beginning with the "q" parameter for indicating a relative quality
814   factor. The first "q" parameter (if any) separates the media-range
815   parameter(s) from the accept-params. Quality factors allow the user
816   or user agent to indicate the relative degree of preference for that
817   media-range, using the qvalue scale from 0 to 1 (<xref target="quality.values"/>). The
818   default value is q=1.
819  <list><t>
820      <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
821      parameters from Accept extension parameters is due to historical
822      practice. Although this prevents any media type parameter named
823      "q" from being used with a media range, such an event is believed
824      to be unlikely given the lack of any "q" parameters in the IANA
825      media type registry and the rare usage of any media type
826      parameters in Accept. Future media types are discouraged from
827      registering any parameter named "q".
828  </t></list>
829</t>
830<t>
831   The example
832</t>
833<figure><artwork type="example">
834    Accept: audio/*; q=0.2, audio/basic
835</artwork></figure>
836<t>
837   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
838   type if it is the best available after an 80% mark-down in quality."
839</t>
840<t>
841   If no Accept header field is present, then it is assumed that the
842   client accepts all media types. If an Accept header field is present,
843   and if the server cannot send a response which is acceptable
844   according to the combined Accept field value, then the server &SHOULD;
845   send a 406 (not acceptable) response.
846</t>
847<t>
848   A more elaborate example is
849</t>
850<figure><artwork type="example">
851    Accept: text/plain; q=0.5, text/html,
852            text/x-dvi; q=0.8, text/x-c
853</artwork></figure>
854<t>
855   Verbally, this would be interpreted as "text/html and text/x-c are
856   the preferred media types, but if they do not exist, then send the
857   text/x-dvi entity, and if that does not exist, send the text/plain
858   entity."
859</t>
860<t>
861   Media ranges can be overridden by more specific media ranges or
862   specific media types. If more than one media range applies to a given
863   type, the most specific reference has precedence. For example,
864</t>
865<figure><artwork type="example">
866    Accept: text/*, text/html, text/html;level=1, */*
867</artwork></figure>
868<t>
869   have the following precedence:
870</t>
871<figure><artwork type="example">
872    1) text/html;level=1
873    2) text/html
874    3) text/*
875    4) */*
876</artwork></figure>
877<t>
878   The media type quality factor associated with a given type is
879   determined by finding the media range with the highest precedence
880   which matches that type. For example,
881</t>
882<figure><artwork type="example">
883    Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
884            text/html;level=2;q=0.4, */*;q=0.5
885</artwork></figure>
886<t>
887   would cause the following values to be associated:
888</t>
889<figure><artwork type="example">
890    text/html;level=1         = 1
891    text/html                 = 0.7
892    text/plain                = 0.3
893    image/jpeg                = 0.5
894    text/html;level=2         = 0.4
895    text/html;level=3         = 0.7
896</artwork></figure>
897<t>
898      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
899      values for certain media ranges. However, unless the user agent is
900      a closed system which cannot interact with other rendering agents,
901      this default set ought to be configurable by the user.
902</t>
903</section>
904
905<section title="Accept-Charset" anchor="header.accept-charset">
906  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
907  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
908<t>
909   The Accept-Charset request-header field can be used to indicate what
910   character sets are acceptable for the response. This field allows
911   clients capable of understanding more comprehensive or special-purpose
912   character sets to signal that capability to a server which is
913   capable of representing documents in those character sets.
914</t>
915<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/>
916   Accept-Charset = "Accept-Charset" ":"
917           1#( ( charset | "*" )[ ";" "q" "=" qvalue ] )
918</artwork></figure>
919<t>
920   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
921   be given an associated quality value which represents the user's
922   preference for that charset. The default value is q=1. An example is
923</t>
924<figure><artwork type="example">
925   Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
926</artwork></figure>
927<t>
928   The special value "*", if present in the Accept-Charset field,
929   matches every character set (including ISO-8859-1) which is not
930   mentioned elsewhere in the Accept-Charset field. If no "*" is present
931   in an Accept-Charset field, then all character sets not explicitly
932   mentioned get a quality value of 0, except for ISO-8859-1, which gets
933   a quality value of 1 if not explicitly mentioned.
934</t>
935<t>
936   If no Accept-Charset header is present, the default is that any
937   character set is acceptable. If an Accept-Charset header is present,
938   and if the server cannot send a response which is acceptable
939   according to the Accept-Charset header, then the server &SHOULD; send
940   an error response with the 406 (not acceptable) status code, though
941   the sending of an unacceptable response is also allowed.
942</t>
943</section>
944
945<section title="Accept-Encoding" anchor="header.accept-encoding">
946  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
947  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
948<t>
949   The Accept-Encoding request-header field is similar to Accept, but
950   restricts the content-codings (<xref target="content.codings"/>) that are acceptable in
951   the response.
952</t>
953<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/>
954    Accept-Encoding  = "Accept-Encoding" ":"
955                       1#( codings [ ";" "q" "=" qvalue ] )
956    codings          = ( content-coding | "*" )
957</artwork></figure>
958<t>
959   Examples of its use are:
960</t>
961<figure><artwork type="example">
962    Accept-Encoding: compress, gzip
963    Accept-Encoding:
964    Accept-Encoding: *
965    Accept-Encoding: compress;q=0.5, gzip;q=1.0
966    Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
967</artwork></figure>
968<t>
969   A server tests whether a content-coding is acceptable, according to
970   an Accept-Encoding field, using these rules:
971  <list style="numbers">
972      <t>If the content-coding is one of the content-codings listed in
973         the Accept-Encoding field, then it is acceptable, unless it is
974         accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
975         qvalue of 0 means "not acceptable.")</t>
976
977      <t>The special "*" symbol in an Accept-Encoding field matches any
978         available content-coding not explicitly listed in the header
979         field.</t>
980
981      <t>If multiple content-codings are acceptable, then the acceptable
982         content-coding with the highest non-zero qvalue is preferred.</t>
983
984      <t>The "identity" content-coding is always acceptable, unless
985         specifically refused because the Accept-Encoding field includes
986         "identity;q=0", or because the field includes "*;q=0" and does
987         not explicitly include the "identity" content-coding. If the
988         Accept-Encoding field-value is empty, then only the "identity"
989         encoding is acceptable.</t>
990  </list>
991</t>
992<t>
993   If an Accept-Encoding field is present in a request, and if the
994   server cannot send a response which is acceptable according to the
995   Accept-Encoding header, then the server &SHOULD; send an error response
996   with the 406 (Not Acceptable) status code.
997</t>
998<t>
999   If no Accept-Encoding field is present in a request, the server &MAY;
1000   assume that the client will accept any content coding. In this case,
1001   if "identity" is one of the available content-codings, then the
1002   server &SHOULD; use the "identity" content-coding, unless it has
1003   additional information that a different content-coding is meaningful
1004   to the client.
1005  <list><t>
1006      <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1007      and if the "identity" content-coding is unavailable, then
1008      content-codings commonly understood by HTTP/1.0 clients (i.e.,
1009      "gzip" and "compress") are preferred; some older clients
1010      improperly display messages sent with other content-codings.  The
1011      server might also make this decision based on information about
1012      the particular user-agent or client.
1013    </t><t>
1014      <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1015      associated with content-codings. This means that qvalues will not
1016      work and are not permitted with x-gzip or x-compress.
1017    </t></list>
1018</t>
1019</section>
1020
1021<section title="Accept-Language" anchor="header.accept-language">
1022  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1023  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1024<t>
1025   The Accept-Language request-header field is similar to Accept, but
1026   restricts the set of natural languages that are preferred as a
1027   response to the request. Language tags are defined in <xref target="language.tags"/>.
1028</t>
1029<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/>
1030    Accept-Language = "Accept-Language" ":"
1031                      1#( language-range [ ";" "q" "=" qvalue ] )
1032    language-range  = ( ( 1*8ALPHA *( "-" 1*8ALPHA ) ) | "*" )
1033</artwork></figure>
1034<t>
1035   Each language-range &MAY; be given an associated quality value which
1036   represents an estimate of the user's preference for the languages
1037   specified by that range. The quality value defaults to "q=1". For
1038   example,
1039</t>
1040<figure><artwork type="example">
1041    Accept-Language: da, en-gb;q=0.8, en;q=0.7
1042</artwork></figure>
1043<t>
1044   would mean: "I prefer Danish, but will accept British English and
1045   other types of English." A language-range matches a language-tag if
1046   it exactly equals the tag, or if it exactly equals a prefix of the
1047   tag such that the first tag character following the prefix is "-".
1048   The special range "*", if present in the Accept-Language field,
1049   matches every tag not matched by any other range present in the
1050   Accept-Language field.
1051  <list><t>
1052      <x:h>Note:</x:h> This use of a prefix matching rule does not imply that
1053      language tags are assigned to languages in such a way that it is
1054      always true that if a user understands a language with a certain
1055      tag, then this user will also understand all languages with tags
1056      for which this tag is a prefix. The prefix rule simply allows the
1057      use of prefix tags if this is the case.
1058  </t></list>
1059</t>
1060<t>
1061   The language quality factor assigned to a language-tag by the
1062   Accept-Language field is the quality value of the longest language-range
1063   in the field that matches the language-tag. If no language-range
1064   in the field matches the tag, the language quality factor
1065   assigned is 0. If no Accept-Language header is present in the
1066   request, the server
1067   &SHOULD; assume that all languages are equally acceptable. If an
1068   Accept-Language header is present, then all languages which are
1069   assigned a quality factor greater than 0 are acceptable.
1070</t>
1071<t>
1072   It might be contrary to the privacy expectations of the user to send
1073   an Accept-Language header with the complete linguistic preferences of
1074   the user in every request. For a discussion of this issue, see
1075   <xref target="privacy.issues.connected.to.accept.headers"/>.
1076</t>
1077<t>
1078   As intelligibility is highly dependent on the individual user, it is
1079   recommended that client applications make the choice of linguistic
1080   preference available to the user. If the choice is not made
1081   available, then the Accept-Language header field &MUST-NOT; be given in
1082   the request.
1083  <list><t>
1084      <x:h>Note:</x:h> When making the choice of linguistic preference available to
1085      the user, we remind implementors of  the fact that users are not
1086      familiar with the details of language matching as described above,
1087      and should provide appropriate guidance. As an example, users
1088      might assume that on selecting "en-gb", they will be served any
1089      kind of English document if British English is not available. A
1090      user agent might suggest in such a case to add "en" to get the
1091      best matching behavior.
1092  </t></list>
1093</t>
1094</section>
1095
1096<section title="Content-Encoding" anchor="header.content-encoding">
1097  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1098  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1099<t>
1100   The Content-Encoding entity-header field is used as a modifier to the
1101   media-type. When present, its value indicates what additional content
1102   codings have been applied to the entity-body, and thus what decoding
1103   mechanisms must be applied in order to obtain the media-type
1104   referenced by the Content-Type header field. Content-Encoding is
1105   primarily used to allow a document to be compressed without losing
1106   the identity of its underlying media type.
1107</t>
1108<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/>
1109    Content-Encoding  = "Content-Encoding" ":" 1#content-coding
1110</artwork></figure>
1111<t>
1112   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1113</t>
1114<figure><artwork type="example">
1115    Content-Encoding: gzip
1116</artwork></figure>
1117<t>
1118   The content-coding is a characteristic of the entity identified by
1119   the Request-URI. Typically, the entity-body is stored with this
1120   encoding and is only decoded before rendering or analogous usage.
1121   However, a non-transparent proxy &MAY; modify the content-coding if the
1122   new coding is known to be acceptable to the recipient, unless the
1123   "no-transform" cache-control directive is present in the message.
1124</t>
1125<t>
1126   If the content-coding of an entity is not "identity", then the
1127   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1128   that lists the non-identity content-coding(s) used.
1129</t>
1130<t>
1131   If the content-coding of an entity in a request message is not
1132   acceptable to the origin server, the server &SHOULD; respond with a
1133   status code of 415 (Unsupported Media Type).
1134</t>
1135<t>
1136   If multiple encodings have been applied to an entity, the content
1137   codings &MUST; be listed in the order in which they were applied.
1138   Additional information about the encoding parameters &MAY; be provided
1139   by other entity-header fields not defined by this specification.
1140</t>
1141</section>
1142
1143<section title="Content-Language" anchor="header.content-language">
1144  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1145  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1146<t>
1147   The Content-Language entity-header field describes the natural
1148   language(s) of the intended audience for the enclosed entity. Note
1149   that this might not be equivalent to all the languages used within
1150   the entity-body.
1151</t>
1152<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/>
1153    Content-Language  = "Content-Language" ":" 1#language-tag
1154</artwork></figure>
1155<t>
1156   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1157   Content-Language is to allow a user to identify and differentiate
1158   entities according to the user's own preferred language. Thus, if the
1159   body content is intended only for a Danish-literate audience, the
1160   appropriate field is
1161</t>
1162<figure><artwork type="example">
1163    Content-Language: da
1164</artwork></figure>
1165<t>
1166   If no Content-Language is specified, the default is that the content
1167   is intended for all language audiences. This might mean that the
1168   sender does not consider it to be specific to any natural language,
1169   or that the sender does not know for which language it is intended.
1170</t>
1171<t>
1172   Multiple languages &MAY; be listed for content that is intended for
1173   multiple audiences. For example, a rendition of the "Treaty of
1174   Waitangi," presented simultaneously in the original Maori and English
1175   versions, would call for
1176</t>
1177<figure><artwork type="example">
1178    Content-Language: mi, en
1179</artwork></figure>
1180<t>
1181   However, just because multiple languages are present within an entity
1182   does not mean that it is intended for multiple linguistic audiences.
1183   An example would be a beginner's language primer, such as "A First
1184   Lesson in Latin," which is clearly intended to be used by an
1185   English-literate audience. In this case, the Content-Language would
1186   properly only include "en".
1187</t>
1188<t>
1189   Content-Language &MAY; be applied to any media type -- it is not
1190   limited to textual documents.
1191</t>
1192</section>
1193
1194<section title="Content-Location" anchor="header.content-location">
1195  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1196  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1197<t>
1198   The Content-Location entity-header field &MAY; be used to supply the
1199   resource location for the entity enclosed in the message when that
1200   entity is accessible from a location separate from the requested
1201   resource's URI. A server &SHOULD; provide a Content-Location for the
1202   variant corresponding to the response entity; especially in the case
1203   where a resource has multiple entities associated with it, and those
1204   entities actually have separate locations by which they might be
1205   individually accessed, the server &SHOULD; provide a Content-Location
1206   for the particular variant which is returned.
1207</t>
1208<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/>
1209    Content-Location = "Content-Location" ":"
1210                      ( absoluteURI | relativeURI )
1211</artwork></figure>
1212<t>
1213   The value of Content-Location also defines the base URI for the
1214   entity.
1215</t>
1216<t>
1217   The Content-Location value is not a replacement for the original
1218   requested URI; it is only a statement of the location of the resource
1219   corresponding to this particular entity at the time of the request.
1220   Future requests &MAY; specify the Content-Location URI as the request-URI
1221   if the desire is to identify the source of that particular
1222   entity.
1223</t>
1224<t>
1225   A cache cannot assume that an entity with a Content-Location
1226   different from the URI used to retrieve it can be used to respond to
1227   later requests on that Content-Location URI. However, the Content-Location
1228   can be used to differentiate between multiple entities
1229   retrieved from a single requested resource, as described in &caching;.
1230</t>
1231<t>
1232   If the Content-Location is a relative URI, the relative URI is
1233   interpreted relative to the Request-URI.
1234</t>
1235<t>
1236   The meaning of the Content-Location header in PUT or POST requests is
1237   undefined; servers are free to ignore it in those cases.
1238</t>
1239</section>
1240
1241<section title="Content-MD5" anchor="header.content-md5">
1242  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1243  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1244<t>
1245   The Content-MD5 entity-header field, as defined in RFC 1864 <xref target="RFC1864"/>, is
1246   an MD5 digest of the entity-body for the purpose of providing an
1247   end-to-end message integrity check (MIC) of the entity-body. (Note: a
1248   MIC is good for detecting accidental modification of the entity-body
1249   in transit, but is not proof against malicious attacks.)
1250</t>
1251<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="md5-digest"/>
1252     Content-MD5   = "Content-MD5" ":" md5-digest
1253     md5-digest   = &lt;base64 of 128 bit MD5 digest as per RFC 1864&gt;
1254</artwork></figure>
1255<t>
1256   The Content-MD5 header field &MAY; be generated by an origin server or
1257   client to function as an integrity check of the entity-body. Only
1258   origin servers or clients &MAY; generate the Content-MD5 header field;
1259   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1260   value as an end-to-end integrity check. Any recipient of the entity-body,
1261   including gateways and proxies, &MAY; check that the digest value
1262   in this header field matches that of the entity-body as received.
1263</t>
1264<t>
1265   The MD5 digest is computed based on the content of the entity-body,
1266   including any content-coding that has been applied, but not including
1267   any transfer-encoding applied to the message-body. If the message is
1268   received with a transfer-encoding, that encoding &MUST; be removed
1269   prior to checking the Content-MD5 value against the received entity.
1270</t>
1271<t>
1272   This has the result that the digest is computed on the octets of the
1273   entity-body exactly as, and in the order that, they would be sent if
1274   no transfer-encoding were being applied.
1275</t>
1276<t>
1277   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1278   composite media-types (e.g., multipart/* and message/rfc822), but
1279   this does not change how the digest is computed as defined in the
1280   preceding paragraph.
1281</t>
1282<t>
1283   There are several consequences of this. The entity-body for composite
1284   types &MAY; contain many body-parts, each with its own MIME and HTTP
1285   headers (including Content-MD5, Content-Transfer-Encoding, and
1286   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1287   or Content-Encoding header, it is assumed that the content
1288   of the body-part has had the encoding applied, and the body-part is
1289   included in the Content-MD5 digest as is -- i.e., after the
1290   application. The Transfer-Encoding header field is not allowed within
1291   body-parts.
1292</t>
1293<t>
1294   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1295   computing or checking the digest: the line break convention used in
1296   the text actually transmitted &MUST; be left unaltered when computing
1297   the digest.
1298  <list><t>
1299      <x:h>Note:</x:h> while the definition of Content-MD5 is exactly the same for
1300      HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1301      in which the application of Content-MD5 to HTTP entity-bodies
1302      differs from its application to MIME entity-bodies. One is that
1303      HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1304      does use Transfer-Encoding and Content-Encoding. Another is that
1305      HTTP more frequently uses binary content types than MIME, so it is
1306      worth noting that, in such cases, the byte order used to compute
1307      the digest is the transmission byte order defined for the type.
1308      Lastly, HTTP allows transmission of text types with any of several
1309      line break conventions and not just the canonical form using CRLF.
1310  </t></list>
1311</t>
1312</section>
1313
1314<section title="Content-Type" anchor="header.content-type">
1315  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1316  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1317<t>
1318   The Content-Type entity-header field indicates the media type of the
1319   entity-body sent to the recipient or, in the case of the HEAD method,
1320   the media type that would have been sent had the request been a GET.
1321</t>
1322<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/>
1323    Content-Type   = "Content-Type" ":" media-type
1324</artwork></figure>
1325<t>
1326   Media types are defined in <xref target="media.types"/>. An example of the field is
1327</t>
1328<figure><artwork type="example">
1329    Content-Type: text/html; charset=ISO-8859-4
1330</artwork></figure>
1331<t>
1332   Further discussion of methods for identifying the media type of an
1333   entity is provided in <xref target="type"/>.
1334</t>
1335</section>
1336
1337</section>
1338
1339<section title="IANA Considerations" anchor="IANA.considerations">
1340<t>
1341   TBD.
1342</t>
1343</section>
1344
1345<section title="Security Considerations" anchor="security.considerations">
1346<t>
1347   This section is meant to inform application developers, information
1348   providers, and users of the security limitations in HTTP/1.1 as
1349   described by this document. The discussion does not include
1350   definitive solutions to the problems revealed, though it does make
1351   some suggestions for reducing security risks.
1352</t>
1353
1354<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1355<t>
1356   Accept request-headers can reveal information about the user to all
1357   servers which are accessed. The Accept-Language header in particular
1358   can reveal information the user would consider to be of a private
1359   nature, because the understanding of particular languages is often
1360   strongly correlated to the membership of a particular ethnic group.
1361   User agents which offer the option to configure the contents of an
1362   Accept-Language header to be sent in every request are strongly
1363   encouraged to let the configuration process include a message which
1364   makes the user aware of the loss of privacy involved.
1365</t>
1366<t>
1367   An approach that limits the loss of privacy would be for a user agent
1368   to omit the sending of Accept-Language headers by default, and to ask
1369   the user whether or not to start sending Accept-Language headers to a
1370   server if it detects, by looking for any Vary response-header fields
1371   generated by the server, that such sending could improve the quality
1372   of service.
1373</t>
1374<t>
1375   Elaborate user-customized accept header fields sent in every request,
1376   in particular if these include quality values, can be used by servers
1377   as relatively reliable and long-lived user identifiers. Such user
1378   identifiers would allow content providers to do click-trail tracking,
1379   and would allow collaborating content providers to match cross-server
1380   click-trails or form submissions of individual users. Note that for
1381   many users not behind a proxy, the network address of the host
1382   running the user agent will also serve as a long-lived user
1383   identifier. In environments where proxies are used to enhance
1384   privacy, user agents ought to be conservative in offering accept
1385   header configuration options to end users. As an extreme privacy
1386   measure, proxies could filter the accept headers in relayed requests.
1387   General purpose user agents which provide a high degree of header
1388   configurability &SHOULD; warn users about the loss of privacy which can
1389   be involved.
1390</t>
1391</section>
1392
1393<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1394<t>
1395   RFC 1806 <xref target="RFC1806"/>, from which the often implemented Content-Disposition
1396   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1397   serious security considerations. Content-Disposition is not part of
1398   the HTTP standard, but since it is widely implemented, we are
1399   documenting its use and risks for implementors. See RFC 2183 <xref target="RFC2183"/>
1400   (which updates RFC 1806) for details.
1401</t>
1402</section>
1403
1404</section>
1405
1406<section title="Acknowledgments" anchor="ack">
1407<t>
1408   Based on an XML translation of RFC 2616 by Julian Reschke.
1409</t>
1410</section>
1411</middle>
1412<back>
1413<references>
1414
1415<reference anchor="Part1">
1416   <front>
1417      <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1418      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1419         <organization abbrev="Day Software">Day Software</organization>
1420         <address><email>fielding@gbiv.com</email></address>
1421      </author>
1422      <author initials="J." surname="Gettys" fullname="Jim Gettys">
1423         <organization>One Laptop per Child</organization>
1424         <address><email>jg@laptop.org</email></address>
1425      </author>
1426      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1427         <organization abbrev="HP">Hewlett-Packard Company</organization>
1428         <address><email>JeffMogul@acm.org</email></address>
1429      </author>
1430      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1431         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1432         <address><email>henrikn@microsoft.com</email></address>
1433      </author>
1434      <author initials="L." surname="Masinter" fullname="Larry Masinter">
1435         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1436         <address><email>LMM@acm.org</email></address>
1437      </author>
1438      <author initials="P." surname="Leach" fullname="Paul J. Leach">
1439         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1440         <address><email>paulle@microsoft.com</email></address>
1441      </author>
1442      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1443         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1444         <address><email>timbl@w3.org</email></address>
1445      </author>
1446      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1447   </front>
1448   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1449   <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1450</reference>
1451
1452<reference anchor="Part2">
1453   <front>
1454      <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1455      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1456         <organization abbrev="Day Software">Day Software</organization>
1457         <address><email>fielding@gbiv.com</email></address>
1458      </author>
1459      <author initials="J." surname="Gettys" fullname="Jim Gettys">
1460         <organization>One Laptop per Child</organization>
1461         <address><email>jg@laptop.org</email></address>
1462      </author>
1463      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1464         <organization abbrev="HP">Hewlett-Packard Company</organization>
1465         <address><email>JeffMogul@acm.org</email></address>
1466      </author>
1467      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1468         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1469         <address><email>henrikn@microsoft.com</email></address>
1470      </author>
1471      <author initials="L." surname="Masinter" fullname="Larry Masinter">
1472         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1473         <address><email>LMM@acm.org</email></address>
1474      </author>
1475      <author initials="P." surname="Leach" fullname="Paul J. Leach">
1476         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1477         <address><email>paulle@microsoft.com</email></address>
1478      </author>
1479      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1480         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1481         <address><email>timbl@w3.org</email></address>
1482      </author>
1483      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1484   </front>
1485   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
1486   <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1487</reference>
1488
1489<reference anchor="Part4">
1490   <front>
1491      <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1492      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1493         <organization abbrev="Day Software">Day Software</organization>
1494         <address><email>fielding@gbiv.com</email></address>
1495      </author>
1496      <author initials="J." surname="Gettys" fullname="Jim Gettys">
1497         <organization>One Laptop per Child</organization>
1498         <address><email>jg@laptop.org</email></address>
1499      </author>
1500      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1501         <organization abbrev="HP">Hewlett-Packard Company</organization>
1502         <address><email>JeffMogul@acm.org</email></address>
1503      </author>
1504      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1505         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1506         <address><email>henrikn@microsoft.com</email></address>
1507      </author>
1508      <author initials="L." surname="Masinter" fullname="Larry Masinter">
1509         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1510         <address><email>LMM@acm.org</email></address>
1511      </author>
1512      <author initials="P." surname="Leach" fullname="Paul J. Leach">
1513         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1514         <address><email>paulle@microsoft.com</email></address>
1515      </author>
1516      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1517         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1518         <address><email>timbl@w3.org</email></address>
1519      </author>
1520      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1521   </front>
1522   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
1523   <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1524</reference>
1525
1526<reference anchor="Part5">
1527   <front>
1528      <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1529      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1530         <organization abbrev="Day Software">Day Software</organization>
1531         <address><email>fielding@gbiv.com</email></address>
1532      </author>
1533      <author initials="J." surname="Gettys" fullname="Jim Gettys">
1534         <organization>One Laptop per Child</organization>
1535         <address><email>jg@laptop.org</email></address>
1536      </author>
1537      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1538         <organization abbrev="HP">Hewlett-Packard Company</organization>
1539         <address><email>JeffMogul@acm.org</email></address>
1540      </author>
1541      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1542         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1543         <address><email>henrikn@microsoft.com</email></address>
1544      </author>
1545      <author initials="L." surname="Masinter" fullname="Larry Masinter">
1546         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1547         <address><email>LMM@acm.org</email></address>
1548      </author>
1549      <author initials="P." surname="Leach" fullname="Paul J. Leach">
1550         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1551         <address><email>paulle@microsoft.com</email></address>
1552      </author>
1553      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1554         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1555         <address><email>timbl@w3.org</email></address>
1556      </author>
1557      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1558   </front>
1559   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1560   <x:source href="p5-range.xml" basename="p5-range"/>
1561</reference>
1562
1563<reference anchor="Part6">
1564   <front>
1565      <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1566      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1567         <organization abbrev="Day Software">Day Software</organization>
1568         <address><email>fielding@gbiv.com</email></address>
1569      </author>
1570      <author initials="J." surname="Gettys" fullname="Jim Gettys">
1571         <organization>One Laptop per Child</organization>
1572         <address><email>jg@laptop.org</email></address>
1573      </author>
1574      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1575         <organization abbrev="HP">Hewlett-Packard Company</organization>
1576         <address><email>JeffMogul@acm.org</email></address>
1577      </author>
1578      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1579         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1580         <address><email>henrikn@microsoft.com</email></address>
1581      </author>
1582      <author initials="L." surname="Masinter" fullname="Larry Masinter">
1583         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1584         <address><email>LMM@acm.org</email></address>
1585      </author>
1586      <author initials="P." surname="Leach" fullname="Paul J. Leach">
1587         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1588         <address><email>paulle@microsoft.com</email></address>
1589      </author>
1590      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1591         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1592         <address><email>timbl@w3.org</email></address>
1593      </author>
1594      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1595   </front>
1596   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1597   <x:source href="p6-cache.xml" basename="p6-cache"/>
1598</reference>
1599
1600<reference anchor="RFC2616">
1601   <front>
1602      <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
1603      <author initials="R." surname="Fielding" fullname="R. Fielding">
1604         <organization>University of California, Irvine</organization>
1605         <address><email>fielding@ics.uci.edu</email></address>
1606      </author>
1607      <author initials="J." surname="Gettys" fullname="J. Gettys">
1608         <organization>W3C</organization>
1609         <address><email>jg@w3.org</email></address>
1610      </author>
1611      <author initials="J." surname="Mogul" fullname="J. Mogul">
1612         <organization>Compaq Computer Corporation</organization>
1613         <address><email>mogul@wrl.dec.com</email></address>
1614      </author>
1615      <author initials="H." surname="Frystyk" fullname="H. Frystyk">
1616         <organization>MIT Laboratory for Computer Science</organization>
1617         <address><email>frystyk@w3.org</email></address>
1618      </author>
1619      <author initials="L." surname="Masinter" fullname="L. Masinter">
1620         <organization>Xerox Corporation</organization>
1621         <address><email>masinter@parc.xerox.com</email></address>
1622      </author>
1623      <author initials="P." surname="Leach" fullname="P. Leach">
1624         <organization>Microsoft Corporation</organization>
1625         <address><email>paulle@microsoft.com</email></address>
1626      </author>
1627      <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
1628         <organization>W3C</organization>
1629         <address><email>timbl@w3.org</email></address>
1630      </author>
1631      <date month="June" year="1999"/>
1632   </front>
1633   <seriesInfo name="RFC" value="2616"/>
1634</reference>
1635
1636<reference anchor="RFC1766">
1637<front>
1638<title abbrev="Language Tag">Tags for the Identification of Languages</title>
1639<author initials="H." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
1640<organization>UNINETT</organization>
1641<address>
1642<postal>
1643<street>Pb. 6883 Elgeseter</street>
1644<city>Trondheim</city>
1645<region/>
1646<code>N-7002</code>
1647<country>NO</country></postal>
1648<phone>+47 73 597094</phone>
1649<email>Harald.T.Alvestrand@uninett.no</email></address></author>
1650<date month="March" year="1995"/>
1651</front>
1652<seriesInfo name="RFC" value="1766"/>
1653</reference>
1654
1655<reference anchor="RFC2045">
1656<front>
1657<title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
1658<author initials="N." surname="Freed" fullname="Ned Freed">
1659<organization>Innosoft International, Inc.</organization>
1660<address>
1661<postal>
1662<street>1050 East Garvey Avenue South</street>
1663<city>West Covina</city>
1664<region>CA</region>
1665<code>91790</code>
1666<country>US</country></postal>
1667<phone>+1 818 919 3600</phone>
1668<facsimile>+1 818 919 3614</facsimile>
1669<email>ned@innosoft.com</email></address></author>
1670<author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1671<organization>First Virtual Holdings</organization>
1672<address>
1673<postal>
1674<street>25 Washington Avenue</street>
1675<city>Morristown</city>
1676<region>NJ</region>
1677<code>07960</code>
1678<country>US</country></postal>
1679<phone>+1 201 540 8967</phone>
1680<facsimile>+1 201 993 3032</facsimile>
1681<email>nsb@nsb.fv.com</email></address></author>
1682<date month="November" year="1996"/>
1683</front>
1684<seriesInfo name="RFC" value="2045"/>
1685</reference>
1686
1687<reference anchor="RFC822">
1688<front>
1689<title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
1690<author initials="D.H." surname="Crocker" fullname="David H. Crocker">
1691<organization>University of Delaware, Dept. of Electrical Engineering</organization>
1692<address>
1693<postal>
1694<street/>
1695<city>Newark</city>
1696<region>DE</region>
1697<code>19711</code>
1698<country>US</country></postal>
1699<email>DCrocker@UDel-Relay</email></address></author>
1700<date month="August" day="13" year="1982"/></front>
1701<seriesInfo name="STD" value="11"/>
1702<seriesInfo name="RFC" value="822"/>
1703</reference>
1704
1705<reference anchor="RFC1867">
1706<front>
1707<title>Form-based File Upload in HTML</title>
1708<author initials="L." surname="Masinter" fullname="Larry Masinter">
1709<organization>Xerox Palo Alto Research Center</organization>
1710<address>
1711<postal>
1712<street>3333 Coyote Hill Road</street>
1713<city>Palo Alto</city>
1714<region>CA</region>
1715<code>94304</code>
1716<country>US</country></postal>
1717<phone>+1 415 812 4365</phone>
1718<facsimile>+1 415 812 4333</facsimile>
1719<email>masinter@parc.xerox.com</email></address></author>
1720<author initials="E." surname="Nebel" fullname="Ernesto Nebel">
1721<organization>XSoft, Xerox Corporation</organization>
1722<address>
1723<postal>
1724<street>10875 Rancho Bernardo Road</street>
1725<street>Suite 200</street>
1726<city>San Diego</city>
1727<region>CA</region>
1728<code>92127-2116</code>
1729<country>US</country></postal>
1730<phone>+1 619 676 7817</phone>
1731<facsimile>+1 619 676 7865</facsimile>
1732<email>nebel@xsoft.sd.xerox.com</email></address></author>
1733<date month="November" year="1995"/>
1734</front>
1735<seriesInfo name="RFC" value="1867"/>
1736</reference>
1737
1738<reference anchor="RFC4288">
1739  <front>
1740    <title>Media Type Specifications and Registration Procedures</title>
1741    <author initials="N." surname="Freed" fullname="N. Freed">
1742      <organization>Sun Microsystems</organization>
1743      <address>
1744        <email>ned.freed@mrochek.com</email>
1745      </address>
1746    </author>
1747    <author initials="J." surname="Klensin" fullname="J. Klensin">
1748      <organization/>
1749      <address>
1750        <email>klensin+ietf@jck.com</email>
1751      </address>
1752    </author>
1753    <date year="2005" month="December"/>
1754  </front>
1755  <seriesInfo name="BCP" value="13"/>
1756  <seriesInfo name="RFC" value="4288"/>
1757</reference>
1758
1759<reference anchor="RFC1700">
1760<front>
1761<title abbrev="Assigned Numbers">Assigned Numbers</title>
1762<author initials="J." surname="Reynolds" fullname="Joyce K. Reynolds">
1763<organization>USC/Information Sciences Institute</organization>
1764<address>
1765<postal>
1766<street>4676 Admiralty Way</street>
1767<city>Marina del Rey</city>
1768<region>CA</region>
1769<code>90292-6695</code>
1770<country>US</country></postal>
1771<phone>+1 310 822 1511</phone>
1772<email>jkrey@isi.edu</email></address></author>
1773<author initials="J." surname="Postel" fullname="Jon Postel">
1774<organization>USC/Information Sciences Institute</organization>
1775<address>
1776<postal>
1777<street>4676 Admiralty Way</street>
1778<city>Marina del Rey</city>
1779<region>CA</region>
1780<code>90292-6695</code>
1781<country>US</country></postal>
1782<phone>+1 310 822 1511</phone>
1783<email>postel@isi.edu</email></address></author>
1784<date month="October" year="1994"/>
1785<abstract>
1786<t/></abstract></front>
1787<seriesInfo name="STD" value="2"/>
1788<seriesInfo name="RFC" value="1700"/>
1789</reference>
1790
1791<reference anchor="RFC1864">
1792<front>
1793<title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1794<author initials="J." surname="Myers" fullname="John G. Myers">
1795<organization>Carnegie Mellon University</organization>
1796<address>
1797<phone/>
1798<email>jgm+@cmu.edu</email></address></author>
1799<author initials="M." surname="Rose" fullname="Marshall T. Rose">
1800<organization>Dover Beach Consulting, Inc.</organization>
1801<address>
1802<phone/>
1803<email>mrose@dbc.mtview.ca.us</email></address></author>
1804<date month="October" year="1995"/>
1805</front>
1806<seriesInfo name="RFC" value="1864"/>
1807</reference>
1808
1809
1810<reference anchor="RFC1952">
1811<front>
1812<title>GZIP file format specification version 4.3</title>
1813<author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1814<organization>Aladdin Enterprises</organization>
1815<address>
1816<postal>
1817<street>203 Santa Margarita Ave.</street>
1818<city>Menlo Park</city>
1819<region>CA</region>
1820<code>94025</code>
1821<country>US</country></postal>
1822<phone>+1 415 322 0103</phone>
1823<facsimile>+1 415 322 1734</facsimile>
1824<email>ghost@aladdin.com</email></address></author>
1825<author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1826<organization/>
1827<address>
1828<postal>
1829<street/>
1830<city/>
1831<region/>
1832<code/>
1833<country/></postal>
1834<phone/>
1835<email>gzip@prep.ai.mit.edu</email></address></author>
1836<author initials="M." surname="Adler" fullname="Mark Adler">
1837<organization/>
1838<address>
1839<postal>
1840<street/>
1841<city/>
1842<region/>
1843<code/>
1844<country/></postal>
1845<phone/>
1846<email>madler@alumni.caltech.edu</email></address></author>
1847<author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1848<organization/>
1849<address>
1850<postal>
1851<street/>
1852<city/>
1853<region/>
1854<code/>
1855<country/></postal>
1856<phone/>
1857<email>ghost@aladdin.com</email></address></author>
1858<author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
1859<organization/>
1860<address>
1861<postal>
1862<street/>
1863<city/>
1864<region/>
1865<code/>
1866<country/></postal>
1867<phone/>
1868<email>randeg@alumni.rpi.edu</email></address></author>
1869<date month="May" year="1996"/>
1870</front>
1871<seriesInfo name="RFC" value="1952"/>
1872</reference>
1873
1874<reference anchor="RFC1951">
1875<front>
1876<title>DEFLATE Compressed Data Format Specification version 1.3</title>
1877<author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1878<organization>Aladdin Enterprises</organization>
1879<address>
1880<postal>
1881<street>203 Santa Margarita Ave.</street>
1882<city>Menlo Park</city>
1883<region>CA</region>
1884<code>94025</code>
1885<country>US</country></postal>
1886<phone>+1 415 322 0103</phone>
1887<facsimile>+1 415 322 1734</facsimile>
1888<email>ghost@aladdin.com</email></address></author>
1889<date month="May" year="1996"/>
1890<abstract>
1891<t>This specification defines a lossless compressed data format that compresses data using a combination of the LZ77 algorithm and Huffman coding, with efficiency comparable to the best currently available general-purpose compression methods.  The data can be produced or consumed, even for an arbitrarily long sequentially presented input data stream, using only an a priori bounded amount of intermediate storage.  The format can be implemented readily in a manner not covered by patents.</t></abstract></front>
1892<seriesInfo name="RFC" value="1951"/>
1893</reference>
1894
1895<reference anchor="RFC1950">
1896<front>
1897<title>ZLIB Compressed Data Format Specification version 3.3</title>
1898<author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1899<organization>Aladdin Enterprises</organization>
1900<address>
1901<postal>
1902<street>203 Santa Margarita Ave.</street>
1903<city>Menlo Park</city>
1904<region>CA</region>
1905<code>94025</code>
1906<country>US</country></postal>
1907<phone>+1 415 322 0103</phone>
1908<facsimile>+1 415 322 1734</facsimile>
1909<email>ghost@aladdin.com</email></address></author>
1910<author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1911<organization/></author>
1912<date month="May" year="1996"/>
1913<abstract>
1914<t>This specification defines a lossless compressed data format.  The data can be produced or consumed, even for an arbitrarily long sequentially presented input data stream, using only an a priori bounded amount of intermediate storage.  The format presently uses the DEFLATE compression method but can be easily extended to use
1915   other compression methods.  It can be implemented readily in a manner not covered by patents.  This specification also defines the ADLER-32 checksum (an extension and improvement of the Fletcher checksum), used for detection of data corruption, and provides an algorithm for computing it.</t></abstract></front>
1916<seriesInfo name="RFC" value="1950"/>
1917</reference>
1918
1919<reference anchor="RFC2068">
1920<front>
1921<title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
1922<author initials="R." surname="Fielding" fullname="Roy T. Fielding">
1923<organization>University of California, Irvine, Department of Information and Computer Science</organization>
1924<address>
1925<postal>
1926<street/>
1927<city>Irvine</city>
1928<region>CA</region>
1929<code>92717-3425</code>
1930<country>US</country></postal>
1931<facsimile>+1 714 824 4056</facsimile>
1932<email>fielding@ics.uci.edu</email></address></author>
1933<author initials="J." surname="Gettys" fullname="Jim Gettys">
1934<organization>MIT Laboratory for Computer Science</organization>
1935<address>
1936<postal>
1937<street>545 Technology Square</street>
1938<city>Cambridge</city>
1939<region>MA</region>
1940<code>02139</code>
1941<country>US</country></postal>
1942<facsimile>+1 617 258 8682</facsimile>
1943<email>jg@w3.org</email></address></author>
1944<author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1945<organization>Digital Equipment Corporation, Western Research Laboratory</organization>
1946<address>
1947<postal>
1948<street>250 University Avenue</street>
1949<city>Palo Alto</city>
1950<region>CA</region>
1951<code>94301</code>
1952<country>US</country></postal>
1953<email>mogul@wrl.dec.com</email></address></author>
1954<author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
1955<organization>MIT Laboratory for Computer Science</organization>
1956<address>
1957<postal>
1958<street>545 Technology Square</street>
1959<city>Cambridge</city>
1960<region>MA</region>
1961<code>02139</code>
1962<country>US</country></postal>
1963<facsimile>+1 617 258 8682</facsimile>
1964<email>frystyk@w3.org</email></address></author>
1965<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1966<organization>MIT Laboratory for Computer Science</organization>
1967<address>
1968<postal>
1969<street>545 Technology Square</street>
1970<city>Cambridge</city>
1971<region>MA</region>
1972<code>02139</code>
1973<country>US</country></postal>
1974<facsimile>+1 617 258 8682</facsimile>
1975<email>timbl@w3.org</email></address></author>
1976<date month="January" year="1997"/>
1977<abstract>
1978<t>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. It is a generic, stateless, object-oriented protocol which can be used for many tasks, such as name servers and distributed object management systems, through extension of its request methods. A feature of HTTP is the typing and negotiation of data representation, allowing systems to be built independently of the data being transferred.</t>
1979<t>HTTP has been in use by the World-Wide Web global information initiative since 1990. This specification defines the protocol referred to as "HTTP/1.1".</t></abstract></front>
1980<seriesInfo name="RFC" value="2068"/>
1981</reference>
1982
1983<reference anchor="RFC1806">
1984<front>
1985<title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header</title>
1986<author initials="R." surname="Troost" fullname="Rens Troost">
1987<organization>New Century Systems</organization>
1988<address>
1989<postal>
1990<street>324 East 41st Street #804</street>
1991<city>New York</city>
1992<region>NY</region>
1993<code>10017</code>
1994<country>US</country></postal>
1995<phone>+1 212 557 2050</phone>
1996<facsimile>+1 212 557 2049</facsimile>
1997<email>rens@century.com</email></address></author>
1998<author initials="S." surname="Dorner" fullname="Steve Dorner">
1999<organization>QUALCOMM Incorporated</organization>
2000<address>
2001<postal>
2002<street>6455 Lusk Boulevard</street>
2003<city>San Diego</city>
2004<region>CA</region>
2005<code>92121</code>
2006<country>US</country></postal>
2007<email>sdorner@qualcomm.com</email></address></author>
2008<date month="June" year="1995"/>
2009<abstract>
2010<t>This memo provides a mechanism whereby messages conforming to the("MIME") specification can convey presentational information.  It specifies a new "Content-Disposition" header, optional and valid for anyentity ("message" or "body part"). Two values for this header are described in this memo; one for the ordinary linear presentation of the body part, and another to facilitate the use of mail to transfer files. It is expected that more values will be defined in the future, and procedures are defined for extending this set of values.</t>
2011<t>This document is intended as an extension to. As such, the reader is assumed to be familiar with, and. The information presented herein supplements but does not replace that found in those documents.</t></abstract></front>
2012<seriesInfo name="RFC" value="1806"/>
2013</reference>
2014
2015<reference anchor="RFC2076">
2016<front>
2017<title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2018<author initials="J." surname="Palme" fullname="Jacob Palme">
2019<organization>Stockholm University/KTH</organization>
2020<address>
2021<postal>
2022<street>Electrum 230</street>
2023<street>S-164 40 Kista</street>
2024<country>SE</country></postal>
2025<phone>+46 8 161667</phone>
2026<facsimile>+46 8 7830829</facsimile>
2027<email>jpalme@dsv.su.se</email></address></author>
2028<date month="February" year="1997"/>
2029<abstract>
2030<t>This memo contains a table of commonly occurring headers in headings of e-mail messages. The document compiles information from other RFCs such as RFC 822, RFC 1036, RFC 1123, RFC 1327, RFC 1496, RFC 1521, RFC 1766, RFC 1806, RFC 1864 and RFC 1911. A few commonly occurring headers which are not defined in RFCs are also included. For each header, the memo gives a short description and a reference to the RFC in which the header is defined.</t></abstract></front>
2031<seriesInfo name="RFC" value="2076"/>
2032</reference>
2033
2034<reference anchor="RFC2279">
2035<front>
2036<title abbrev="UTF-8">UTF-8, a transformation format of ISO 10646</title>
2037<author initials="F." surname="Yergeau" fullname="Francois Yergeau">
2038<organization>Alis Technologies</organization>
2039<address>
2040<postal>
2041<street>100, boul. Alexis-Nihon</street>
2042<street>Suite 600</street>
2043<city>Montreal</city>
2044<region>Quebec</region>
2045<code>H4M 2P2</code>
2046<country>CA</country></postal>
2047<phone>+1 514 747 2547</phone>
2048<facsimile>+1 514 747 2561</facsimile>
2049<email>fyergeau@alis.com</email></address></author>
2050<date month="January" year="1998"/>
2051<abstract>
2052<t>ISO/IEC 10646-1 defines a multi-octet character set called the Universal Character Set (UCS) which encompasses most of the world's writing systems. Multi-octet characters, however, are not compatible with many current applications and protocols, and this has led to the development of a few so-called UCS transformation formats (UTF), each with different characteristics.  UTF-8, the object of this memo, has the characteristic of preserving the full US-ASCII range, providing compatibility with file systems, parsers and other software that rely on US-ASCII values but are transparent to other values. This memo updates and replaces RFC 2044, in particular addressing the question of versions of the relevant standards.</t></abstract></front>
2053<seriesInfo name="RFC" value="2279"/>
2054</reference>
2055
2056<reference anchor="RFC2046">
2057<front>
2058<title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2059<author initials="N." surname="Freed" fullname="Ned Freed">
2060<organization>Innosoft International, Inc.</organization>
2061<address>
2062<postal>
2063<street>1050 East Garvey Avenue South</street>
2064<city>West Covina</city>
2065<region>CA</region>
2066<code>91790</code>
2067<country>US</country></postal>
2068<phone>+1 818 919 3600</phone>
2069<facsimile>+1 818 919 3614</facsimile>
2070<email>ned@innosoft.com</email></address></author>
2071<author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2072<organization>First Virtual Holdings</organization>
2073<address>
2074<postal>
2075<street>25 Washington Avenue</street>
2076<city>Morristown</city>
2077<region>NJ</region>
2078<code>07960</code>
2079<country>US</country></postal>
2080<phone>+1 201 540 8967</phone>
2081<facsimile>+1 201 993 3032</facsimile>
2082<email>nsb@nsb.fv.com</email></address></author>
2083<date month="November" year="1996"/>
2084</front>
2085<seriesInfo name="RFC" value="2046"/>
2086</reference>
2087
2088<reference anchor="RFC2277">
2089<front>
2090<title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2091<author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2092<organization>UNINETT</organization>
2093<address>
2094<postal>
2095<street>P.O.Box 6883 Elgeseter</street>
2096<street>N-7002 TRONDHEIM</street>
2097<country>NORWAY</country></postal>
2098<phone>+47 73 59 70 94</phone>
2099<email>Harald.T.Alvestrand@uninett.no</email></address></author>
2100<date month="January" year="1998"/>
2101<area>Applications</area>
2102<keyword>Internet Engineering Task Force</keyword>
2103<keyword>character encoding</keyword></front>
2104<seriesInfo name="BCP" value="18"/>
2105<seriesInfo name="RFC" value="2277"/>
2106</reference>
2107
2108<reference anchor="RFC2110">
2109<front>
2110<title abbrev="MHTML">MIME E-mail Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2111<author initials="J." surname="Palme" fullname="Jacob Palme">
2112<organization>Stockholm University and KTH</organization>
2113<address>
2114<postal>
2115<street>Electrum 230</street>
2116<street>S-164 40 Kista</street>
2117<country>Sweden</country></postal>
2118<phone>+46-8-16 16 67</phone>
2119<facsimile>+46-8-783 08 29</facsimile>
2120<email>jpalme@dsv.su.se</email></address></author>
2121<author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2122<organization>Microsoft Corporation</organization>
2123<address>
2124<postal>
2125<street>3590 North First Street</street>
2126<street>Suite 300</street>
2127<street>San Jose</street>
2128<street>CA 95134</street>
2129<street>Working group chairman:</street></postal>
2130<email>alexhop@microsoft.com</email></address></author>
2131<date month="March" year="1997"/>
2132<area>Applications</area>
2133<keyword>encapsulate</keyword>
2134<keyword>hypertext markup language</keyword>
2135<keyword>mail</keyword>
2136<keyword>multipurpose internet mail extensions</keyword>
2137</front>
2138<seriesInfo name="RFC" value="2110"/>
2139</reference>
2140
2141<reference anchor="RFC2049">
2142<front>
2143<title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2144<author initials="N." surname="Freed" fullname="Ned Freed">
2145<organization>Innosoft International, Inc.</organization>
2146<address>
2147<postal>
2148<street>1050 East Garvey Avenue South</street>
2149<street>West Covina</street>
2150<street>CA 91790</street>
2151<country>USA</country></postal>
2152<phone>+1 818 919 3600</phone>
2153<facsimile>+1 818 919 3614</facsimile>
2154<email>ned@innosoft.com</email></address></author>
2155<author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2156<organization>First Virtual Holdings</organization>
2157<address>
2158<postal>
2159<street>25 Washington Avenue</street>
2160<street>Morristown</street>
2161<street>NJ 07960</street>
2162<country>USA</country></postal>
2163<phone>+1 201 540 8967</phone>
2164<facsimile>+1 201 993 3032</facsimile>
2165<email>nsb@nsb.fv.com</email></address></author>
2166<date month="November" year="1996"/>
2167<area>Applications</area>
2168<keyword>mail</keyword>
2169<keyword>multipurpose internet mail extensions</keyword>
2170</front>
2171<seriesInfo name="RFC" value="2049"/>
2172</reference>
2173
2174<reference anchor="RFC2183">
2175<front>
2176<title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2177<author initials="R." surname="Troost" fullname="Rens Troost">
2178<organization>New Century Systems</organization>
2179<address>
2180<postal>
2181<street>324 East 41st Street #804</street>
2182<street>New York</street>
2183<street>NY</street>
2184<street>10017</street>
2185<country>USA</country></postal>
2186<phone>+1 (212) 557-2050</phone>
2187<facsimile>+1 (212) 557-2049</facsimile>
2188<email>rens@century.com</email></address></author>
2189<author initials="S." surname="Dorner" fullname="Steve Dorner">
2190<organization>QUALCOMM Incorporated</organization>
2191<address>
2192<postal>
2193<street>6455 Lusk Boulevard</street>
2194<street>San Diego</street>
2195<street>CA 92121</street>
2196<country>USA</country></postal>
2197<email>sdorner@qualcomm.com</email></address></author>
2198<author initials="K." surname="Moore" fullname="Keith Moore">
2199<organization>Department of Computer Science</organization>
2200<address>
2201<postal>
2202<street>University of Tennessee</street>
2203<street>Knoxville</street>
2204<street>107 Ayres Hall</street>
2205<street>Knoxville TN  37996-1301</street>
2206<country>USA</country></postal>
2207<phone>+1 (423) 974-5067</phone>
2208<facsimile>+1 (423) 974-8296</facsimile>
2209<email>moore@cs.utk.edu</email></address></author>
2210<date month="August" year="1997"/>
2211<area>Applications</area>
2212<keyword>MIME</keyword>
2213<keyword>internet message</keyword>
2214<keyword>multipurpose internet mail extensions</keyword>
2215</front>
2216<seriesInfo name="RFC" value="2183"/>
2217</reference>
2218
2219</references>
2220
2221<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2222<t>
2223   HTTP/1.1 uses many of the constructs defined for Internet Mail (RFC
2224   822 <xref target="RFC822"/>) and the Multipurpose Internet Mail Extensions (MIME <xref target="RFC2045"/>) to
2225   allow entities to be transmitted in an open variety of
2226   representations and with extensible mechanisms. However, RFC 2045
2227   discusses mail, and HTTP has a few features that are different from
2228   those described in RFC 2045. These differences were carefully chosen
2229   to optimize performance over binary connections, to allow greater
2230   freedom in the use of new media types, to make date comparisons
2231   easier, and to acknowledge the practice of some early HTTP servers
2232   and clients.
2233</t>
2234<t>
2235   This appendix describes specific areas where HTTP differs from RFC
2236   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2237   aware of these differences and provide the appropriate conversions
2238   where necessary. Proxies and gateways from MIME environments to HTTP
2239   also need to be aware of the differences because some conversions
2240   might be required.
2241</t>
2242<section title="MIME-Version" anchor="mime-version">
2243<t>
2244   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2245   include a single MIME-Version general-header field to indicate what
2246   version of the MIME protocol was used to construct the message. Use
2247   of the MIME-Version header field indicates that the message is in
2248   full compliance with the MIME protocol (as defined in RFC 2045<xref target="RFC2045"/>).
2249   Proxies/gateways are responsible for ensuring full compliance (where
2250   possible) when exporting HTTP messages to strict MIME environments.
2251</t>
2252<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/>
2253    MIME-Version   = "MIME-Version" ":" 1*DIGIT "." 1*DIGIT
2254</artwork></figure>
2255<t>
2256   MIME version "1.0" is the default for use in HTTP/1.1. However,
2257   HTTP/1.1 message parsing and semantics are defined by this document
2258   and not the MIME specification.
2259</t>
2260</section>
2261
2262<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2263<t>
2264   RFC 2045 <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2265   canonical form prior to being transferred, as described in section <xref target="RFC2049" x:fmt="number" x:sec="4"/>
2266   of RFC 2049 <xref target="RFC2049"/>. <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2267   allowed for subtypes of the "text" media type when transmitted over
2268   HTTP. RFC 2046 requires that content with a type of "text" represent
2269   line breaks as CRLF and forbids the use of CR or LF outside of line
2270   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2271   line break within text content when a message is transmitted over
2272   HTTP.
2273</t>
2274<t>
2275   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2276   environment &SHOULD; translate all line breaks within the text media
2277   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2278   canonical form of CRLF. Note, however, that this might be complicated
2279   by the presence of a Content-Encoding and by the fact that HTTP
2280   allows the use of some character sets which do not use octets 13 and
2281   10 to represent CR and LF, as is the case for some multi-byte
2282   character sets.
2283</t>
2284<t>
2285   Implementors should note that conversion will break any cryptographic
2286   checksums applied to the original content unless the original content
2287   is already in canonical form. Therefore, the canonical form is
2288   recommended for any content that uses such checksums in HTTP.
2289</t>
2290</section>
2291
2292<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2293<t>
2294   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2295   Content-Encoding header field. Since this acts as a modifier on the
2296   media type, proxies and gateways from HTTP to MIME-compliant
2297   protocols &MUST; either change the value of the Content-Type header
2298   field or decode the entity-body before forwarding the message. (Some
2299   experimental applications of Content-Type for Internet mail have used
2300   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2301   a function equivalent to Content-Encoding. However, this parameter is
2302   not part of RFC 2045).
2303</t>
2304</section>
2305
2306<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2307<t>
2308   HTTP does not use the Content-Transfer-Encoding (CTE) field of RFC
2309   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2310   remove any non-identity CTE ("quoted-printable" or "base64") encoding
2311   prior to delivering the response message to an HTTP client.
2312</t>
2313<t>
2314   Proxies and gateways from HTTP to MIME-compliant protocols are
2315   responsible for ensuring that the message is in the correct format
2316   and encoding for safe transport on that protocol, where "safe
2317   transport" is defined by the limitations of the protocol being used.
2318   Such a proxy or gateway &SHOULD; label the data with an appropriate
2319   Content-Transfer-Encoding if doing so will improve the likelihood of
2320   safe transport over the destination protocol.
2321</t>
2322</section>
2323
2324<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2325<t>
2326   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2327   Proxies/gateways &MUST; remove any transfer-coding prior to
2328   forwarding a message via a MIME-compliant protocol.
2329</t>
2330</section>
2331
2332<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2333<t>
2334   HTTP implementations which share code with MHTML <xref target="RFC2110"/> implementations
2335   need to be aware of MIME line length limitations. Since HTTP does not
2336   have this limitation, HTTP does not fold long lines. MHTML messages
2337   being transported by HTTP follow all conventions of MHTML, including
2338   line length limitations and folding, canonicalization, etc., since
2339   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2340   does not interpret the content or any MIME header lines that might be
2341   contained therein.
2342</t>
2343</section>
2344</section>
2345
2346<section title="Additional Features" anchor="additional.features">
2347<t>
2348   RFC 1945 and RFC 2068 document protocol elements used by some
2349   existing HTTP implementations, but not consistently and correctly
2350   across most HTTP/1.1 applications. Implementors are advised to be
2351   aware of these features, but cannot rely upon their presence in, or
2352   interoperability with, other HTTP/1.1 applications. Some of these
2353   describe proposed experimental features, and some describe features
2354   that experimental deployment found lacking that are now addressed in
2355   the base HTTP/1.1 specification.
2356</t>
2357<t>
2358   A number of other headers, such as Content-Disposition and Title,
2359   from SMTP and MIME are also often implemented (see RFC 2076 <xref target="RFC2076"/>).
2360</t>
2361
2362<section title="Content-Disposition" anchor="content-disposition">
2363<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2364<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2365<t>
2366   The Content-Disposition response-header field has been proposed as a
2367   means for the origin server to suggest a default filename if the user
2368   requests that the content is saved to a file. This usage is derived
2369   from the definition of Content-Disposition in RFC 1806 <xref target="RFC1806"/>.
2370</t>
2371<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-disposition"/><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"/>
2372     content-disposition = "Content-Disposition" ":"
2373                           disposition-type *( ";" disposition-parm )
2374     disposition-type = "attachment" | disp-extension-token
2375     disposition-parm = filename-parm | disp-extension-parm
2376     filename-parm = "filename" "=" quoted-string
2377     disp-extension-token = token
2378     disp-extension-parm = token "=" ( token | quoted-string )
2379</artwork></figure>
2380<t>
2381   An example is
2382</t>
2383<figure><artwork type="example">
2384     Content-Disposition: attachment; filename="fname.ext"
2385</artwork></figure>
2386<t>
2387   The receiving user agent &SHOULD-NOT;  respect any directory path
2388   information present in the filename-parm parameter, which is the only
2389   parameter believed to apply to HTTP implementations at this time. The
2390   filename &SHOULD; be treated as a terminal component only.
2391</t>
2392<t>
2393   If this header is used in a response with the application/octet-stream
2394   content-type, the implied suggestion is that the user agent
2395   should not display the response, but directly enter a `save response
2396   as...' dialog.
2397</t>
2398<t>
2399   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2400</t>
2401</section>
2402</section>
2403
2404<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2405<t>
2406   Charset wildcarding is introduced to avoid explosion of character set
2407   names in accept headers. (<xref target="header.accept-charset"/>)
2408</t>
2409<t>
2410   Content-Base was deleted from the specification: it was not
2411   implemented widely, and there is no simple, safe way to introduce it
2412   without a robust extension mechanism. In addition, it is used in a
2413   similar, but not identical fashion in MHTML <xref target="RFC2110"/>.
2414</t>
2415<t>
2416   A content-coding of "identity" was introduced, to solve problems
2417   discovered in caching. (<xref target="content.codings"/>)
2418</t>
2419<t>
2420   Quality Values of zero should indicate that "I don't want something"
2421   to allow clients to refuse a representation. (<xref target="quality.values"/>)
2422</t>
2423<t>
2424   The Alternates<iref item="Alternates header" primary="true"/><iref item="Headers" subitem="Alternate" primary="true"/>, Content-Version<iref item="Content-Version header" primary="true"/><iref item="Headers" subitem="Content-Version" primary="true"/>, Derived-From<iref item="Derived-From header" primary="true"/><iref item="Headers" subitem="Derived-From" primary="true"/>, Link<iref item="Link header" primary="true"/><iref item="Headers" subitem="Link" primary="true"/>, URI<iref item="URI header" primary="true"/><iref item="Headers" subitem="URI" primary="true"/>, Public<iref item="Public header" primary="true"/><iref item="Headers" subitem="Public" primary="true"/> and
2425   Content-Base<iref item="Content-Base header" primary="true"/><iref item="Headers" subitem="Content-Base" primary="true"/> header fields were defined in previous versions of this
2426   specification, but not commonly implemented. See RFC 2068 <xref target="RFC2068"/>.
2427</t>
2428</section>
2429</back>
2430</rfc>
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