source: draft-ietf-httpbis/latest/p3-payload.xml @ 36

Last change on this file since 36 was 36, checked in by fielding@…, 12 years ago

Add an editorial note about status and list.
Streamline the new references and place them up front.

  • Property svn:eol-style set to native
File size: 106.1 KB
Line 
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, 2617" 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 and RFC 2617.  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://www.w3.org/Protocols/HTTP/1.1/rfc2616bis/issues/"/>
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   Implementors should be aware of IETF character set requirements <xref target="RFC2279"/>
242   <xref target="RFC2277"/>.
243</t>
244
245<section title="Missing Charset" anchor="missing.charset">
246<t>
247   Some HTTP/1.0 software has interpreted a Content-Type header without
248   charset parameter incorrectly to mean "recipient should guess."
249   Senders wishing to defeat this behavior &MAY; include a charset
250   parameter even when the charset is ISO-8859-1 and &SHOULD; do so when
251   it is known that it will not confuse the recipient.
252</t>
253<t>
254   Unfortunately, some older HTTP/1.0 clients did not deal properly with
255   an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
256   charset label provided by the sender; and those user agents that have
257   a provision to "guess" a charset &MUST; use the charset from the
258   content-type field if they support that charset, rather than the
259   recipient's preference, when initially displaying a document. See
260   <xref target="canonicalization.and.text.defaults"/>.
261</t>
262</section>
263</section>
264
265<section title="Content Codings" anchor="content.codings">
266<t>
267   Content coding values indicate an encoding transformation that has
268   been or can be applied to an entity. Content codings are primarily
269   used to allow a document to be compressed or otherwise usefully
270   transformed without losing the identity of its underlying media type
271   and without loss of information. Frequently, the entity is stored in
272   coded form, transmitted directly, and only decoded by the recipient.
273</t>
274<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="content-coding"/>
275    content-coding   = token
276</artwork></figure>
277<t>
278   All content-coding values are case-insensitive. HTTP/1.1 uses
279   content-coding values in the Accept-Encoding (<xref target="header.accept-encoding"/>) and
280   Content-Encoding (<xref target="header.content-encoding"/>) header fields. Although the value
281   describes the content-coding, what is more important is that it
282   indicates what decoding mechanism will be required to remove the
283   encoding.
284</t>
285<t>
286   The Internet Assigned Numbers Authority (IANA) acts as a registry for
287   content-coding value tokens. Initially, the registry contains the
288   following tokens:
289</t>
290<t>
291   gzip<iref item="gzip"/>
292  <list>
293    <t>
294        An encoding format produced by the file compression program
295        "gzip" (GNU zip) as described in RFC 1952 <xref target="RFC1952"/>. This format is a
296        Lempel-Ziv coding (LZ77) with a 32 bit CRC.
297    </t>
298  </list>
299</t>
300<t>
301   compress<iref item="compress"/>
302  <list><t>
303        The encoding format produced by the common UNIX file compression
304        program "compress". This format is an adaptive Lempel-Ziv-Welch
305        coding (LZW).
306</t><t>
307        Use of program names for the identification of encoding formats
308        is not desirable and is discouraged for future encodings. Their
309        use here is representative of historical practice, not good
310        design. For compatibility with previous implementations of HTTP,
311        applications &SHOULD; consider "x-gzip" and "x-compress" to be
312        equivalent to "gzip" and "compress" respectively.
313  </t></list>
314</t>
315<t>
316   deflate<iref item="deflate"/>
317  <list><t>
318        The "zlib" format defined in RFC 1950 <xref target="RFC1950"/> in combination with
319        the "deflate" compression mechanism described in RFC 1951 <xref target="RFC1951"/>.
320  </t></list>
321</t>
322<t>
323   identity<iref item="identity"/>
324  <list><t>
325        The default (identity) encoding; the use of no transformation
326        whatsoever. This content-coding is used only in the Accept-Encoding
327        header, and &SHOULD-NOT;  be used in the Content-Encoding
328        header.
329  </t></list>
330</t>
331<t>
332   New content-coding value tokens &SHOULD; be registered; to allow
333   interoperability between clients and servers, specifications of the
334   content coding algorithms needed to implement a new value &SHOULD; be
335   publicly available and adequate for independent implementation, and
336   conform to the purpose of content coding defined in this section.
337</t>
338</section>
339
340<section title="Media Types" anchor="media.types">
341<t>
342   HTTP uses Internet Media Types <xref target="RFC1590"/> in the Content-Type (<xref target="header.content-type"/>)
343   and Accept (<xref target="header.accept"/>) header fields in order to provide
344   open and extensible data typing and type negotiation.
345</t>
346<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"/>
347    media-type     = type "/" subtype *( ";" parameter )
348    type           = token
349    subtype        = token
350</artwork></figure>
351<t>
352   Parameters &MAY; follow the type/subtype in the form of attribute/value
353   pairs.
354</t>
355<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"/>
356    parameter               = attribute "=" value
357    attribute               = token
358    value                   = token | quoted-string
359</artwork></figure>
360<t>
361   The type, subtype, and parameter attribute names are case-insensitive.
362   Parameter values might or might not be case-sensitive,
363   depending on the semantics of the parameter name. Linear white space
364   (LWS) &MUST-NOT; be used between the type and subtype, nor between an
365   attribute and its value. The presence or absence of a parameter might
366   be significant to the processing of a media-type, depending on its
367   definition within the media type registry.
368</t>
369<t>
370   Note that some older HTTP applications do not recognize media type
371   parameters. When sending data to older HTTP applications,
372   implementations &SHOULD; only use media type parameters when they are
373   required by that type/subtype definition.
374</t>
375<t>
376   Media-type values are registered with the Internet Assigned Number
377   Authority (IANA <xref target="RFC1700"/>). The media type registration process is
378   outlined in RFC 1590 <xref target="RFC1590"/>. Use of non-registered media types is
379   discouraged.
380</t>
381
382<section title="Canonicalization and Text Defaults" anchor="canonicalization.and.text.defaults">
383<t>
384   Internet media types are registered with a canonical form. An
385   entity-body transferred via HTTP messages &MUST; be represented in the
386   appropriate canonical form prior to its transmission except for
387   "text" types, as defined in the next paragraph.
388</t>
389<t>
390   When in canonical form, media subtypes of the "text" type use CRLF as
391   the text line break. HTTP relaxes this requirement and allows the
392   transport of text media with plain CR or LF alone representing a line
393   break when it is done consistently for an entire entity-body. HTTP
394   applications &MUST; accept CRLF, bare CR, and bare LF as being
395   representative of a line break in text media received via HTTP. In
396   addition, if the text is represented in a character set that does not
397   use octets 13 and 10 for CR and LF respectively, as is the case for
398   some multi-byte character sets, HTTP allows the use of whatever octet
399   sequences are defined by that character set to represent the
400   equivalent of CR and LF for line breaks. This flexibility regarding
401   line breaks applies only to text media in the entity-body; a bare CR
402   or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
403   structures (such as header fields and multipart boundaries).
404</t>
405<t>
406   If an entity-body is encoded with a content-coding, the underlying
407   data &MUST; be in a form defined above prior to being encoded.
408</t>
409<t>
410   The "charset" parameter is used with some media types to define the
411   character set (<xref target="character.sets"/>) of the data. When no explicit charset
412   parameter is provided by the sender, media subtypes of the "text"
413   type are defined to have a default charset value of "ISO-8859-1" when
414   received via HTTP. Data in character sets other than "ISO-8859-1" or
415   its subsets &MUST; be labeled with an appropriate charset value. See
416   <xref target="missing.charset"/> for compatibility problems.
417</t>
418</section>
419
420<section title="Multipart Types" anchor="multipart.types">
421<t>
422   MIME provides for a number of "multipart" types -- encapsulations of
423   one or more entities within a single message-body. All multipart
424   types share a common syntax, as defined in section <xref target="RFC2046" x:sec="5.1.1" x:fmt="number"/> of RFC 2046
425   <xref target="RFC2046"/>, and &MUST; include a boundary parameter as part of the media type
426   value. The message body is itself a protocol element and &MUST;
427   therefore use only CRLF to represent line breaks between body-parts.
428   Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
429   empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
430   original multipart contains an epilogue). These restrictions exist in
431   order to preserve the self-delimiting nature of a multipart message-body,
432   wherein the "end" of the message-body is indicated by the
433   ending multipart boundary.
434</t>
435<t>
436   In general, HTTP treats a multipart message-body no differently than
437   any other media type: strictly as payload. The one exception is the
438   "multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
439   (Partial Content) response. In all
440   other cases, an HTTP user agent &SHOULD; follow the same or similar
441   behavior as a MIME user agent would upon receipt of a multipart type.
442   The MIME header fields within each body-part of a multipart message-body
443   do not have any significance to HTTP beyond that defined by
444   their MIME semantics.
445</t>
446<t>
447   In general, 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   If an application receives an unrecognized multipart subtype, the
450   application &MUST; treat it as being equivalent to "multipart/mixed".
451</t>
452<t><list><t>
453      <x:h>Note:</x:h> The "multipart/form-data" type has been specifically defined
454      for carrying form data suitable for processing via the POST
455      request method, as described in RFC 1867 <xref target="RFC1867"/>.
456</t></list></t>
457</section>
458</section>
459
460<section title="Quality Values" anchor="quality.values">
461<t>
462   HTTP content negotiation (<xref target="content.negotiation"/>) uses short "floating point"
463   numbers to indicate the relative importance ("weight") of various
464   negotiable parameters.  A weight is normalized to a real number in
465   the range 0 through 1, where 0 is the minimum and 1 the maximum
466   value. If a parameter has a quality value of 0, then content with
467   this parameter is `not acceptable' for the client. HTTP/1.1
468   applications &MUST-NOT; generate more than three digits after the
469   decimal point. User configuration of these values &SHOULD; also be
470   limited in this fashion.
471</t>
472<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
473    qvalue         = ( "0" [ "." 0*3DIGIT ] )
474                   | ( "1" [ "." 0*3("0") ] )
475</artwork></figure>
476<t>
477   "Quality values" is a misnomer, since these values merely represent
478   relative degradation in desired quality.
479</t>
480</section>
481
482<section title="Language Tags" anchor="language.tags">
483<t>
484   A language tag identifies a natural language spoken, written, or
485   otherwise conveyed by human beings for communication of information
486   to other human beings. Computer languages are explicitly excluded.
487   HTTP uses language tags within the Accept-Language and Content-Language
488   fields.
489</t>
490<t>
491   The syntax and registry of HTTP language tags is the same as that
492   defined by RFC 1766 <xref target="RFC1766"/>. In summary, a language tag is composed of 1
493   or more parts: A primary language tag and a possibly empty series of
494   subtags:
495</t>
496<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"/>
497     language-tag  = primary-tag *( "-" subtag )
498     primary-tag   = 1*8ALPHA
499     subtag        = 1*8ALPHA
500</artwork></figure>
501<t>
502   White space is not allowed within the tag and all tags are case-insensitive.
503   The name space of language tags is administered by the
504   IANA. Example tags include:
505</t>
506<figure><artwork type="example">
507    en, en-US, en-cockney, i-cherokee, x-pig-latin
508</artwork></figure>
509<t>
510   where any two-letter primary-tag is an ISO-639 language abbreviation
511   and any two-letter initial subtag is an ISO-3166 country code. (The
512   last three tags above are not registered tags; all but the last are
513   examples of tags which could be registered in future.)
514</t>
515</section>
516</section>
517
518<section title="Entity" anchor="entity">
519<t>
520   Request and Response messages &MAY; transfer an entity if not otherwise
521   restricted by the request method or response status code. An entity
522   consists of entity-header fields and an entity-body, although some
523   responses will only include the entity-headers.
524</t>
525<t>
526   In this section, both sender and recipient refer to either the client
527   or the server, depending on who sends and who receives the entity.
528</t>
529
530<section title="Entity Header Fields" anchor="entity.header.fields">
531<t>
532   Entity-header fields define metainformation about the entity-body or,
533   if no body is present, about the resource identified by the request.
534   Some of this metainformation is &OPTIONAL;; some might be &REQUIRED; by
535   portions of this specification.
536</t>
537<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-header"/><iref primary="true" item="Grammar" subitem="extension-header"/>
538    entity-header  = Allow                    ; &header-allow;
539                   | Content-Encoding         ; <xref target="header.content-encoding"/>
540                   | Content-Language         ; <xref target="header.content-language"/>
541                   | Content-Length           ; &header-content-length;
542                   | Content-Location         ; <xref target="header.content-location"/>
543                   | Content-MD5              ; <xref target="header.content-md5"/>
544                   | Content-Range            ; &header-content-range;
545                   | Content-Type             ; <xref target="header.content-type"/>
546                   | Expires                  ; &header-expires;
547                   | Last-Modified            ; &header-last-modified;
548                   | extension-header
549
550    extension-header = message-header
551</artwork></figure>
552<t>
553   The extension-header mechanism allows additional entity-header fields
554   to be defined without changing the protocol, but these fields cannot
555   be assumed to be recognizable by the recipient. Unrecognized header
556   fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
557   transparent proxies.
558</t>
559</section>
560
561<section title="Entity Body" anchor="entity.body">
562<t>
563   The entity-body (if any) sent with an HTTP request or response is in
564   a format and encoding defined by the entity-header fields.
565</t>
566<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="entity-body"/>
567    entity-body    = *OCTET
568</artwork></figure>
569<t>
570   An entity-body is only present in a message when a message-body is
571   present, as described in &message-body;. The entity-body is obtained
572   from the message-body by decoding any Transfer-Encoding that might
573   have been applied to ensure safe and proper transfer of the message.
574</t>
575
576<section title="Type" anchor="type">
577<t>
578   When an entity-body is included with a message, the data type of that
579   body is determined via the header fields Content-Type and Content-Encoding.
580   These define a two-layer, ordered encoding model:
581</t>
582<figure><artwork type="example">
583    entity-body := Content-Encoding( Content-Type( data ) )
584</artwork></figure>
585<t>
586   Content-Type specifies the media type of the underlying data.
587   Content-Encoding may be used to indicate any additional content
588   codings applied to the data, usually for the purpose of data
589   compression, that are a property of the requested resource. There is
590   no default encoding.
591</t>
592<t>
593   Any HTTP/1.1 message containing an entity-body &SHOULD; include a
594   Content-Type header field defining the media type of that body. If
595   and only if the media type is not given by a Content-Type field, the
596   recipient &MAY; attempt to guess the media type via inspection of its
597   content and/or the name extension(s) of the URI used to identify the
598   resource. If the media type remains unknown, the recipient &SHOULD;
599   treat it as type "application/octet-stream".
600</t>
601</section>
602   
603<section title="Entity Length" anchor="entity.length">
604<t>
605   The entity-length of a message is the length of the message-body
606   before any transfer-codings have been applied. &message-length; defines
607   how the transfer-length of a message-body is determined.
608</t>
609</section>
610</section>
611</section>
612
613<section title="Content Negotiation" anchor="content.negotiation">
614<t>
615   Most HTTP responses include an entity which contains information for
616   interpretation by a human user. Naturally, it is desirable to supply
617   the user with the "best available" entity corresponding to the
618   request. Unfortunately for servers and caches, not all users have the
619   same preferences for what is "best," and not all user agents are
620   equally capable of rendering all entity types. For that reason, HTTP
621   has provisions for several mechanisms for "content negotiation" --
622   the process of selecting the best representation for a given response
623   when there are multiple representations available.
624  <list><t>
625      <x:h>Note:</x:h> This is not called "format negotiation" because the
626      alternate representations may be of the same media type, but use
627      different capabilities of that type, be in different languages,
628      etc.
629  </t></list>
630</t>
631<t>
632   Any response containing an entity-body &MAY; be subject to negotiation,
633   including error responses.
634</t>
635<t>
636   There are two kinds of content negotiation which are possible in
637   HTTP: server-driven and agent-driven negotiation. These two kinds of
638   negotiation are orthogonal and thus may be used separately or in
639   combination. One method of combination, referred to as transparent
640   negotiation, occurs when a cache uses the agent-driven negotiation
641   information provided by the origin server in order to provide
642   server-driven negotiation for subsequent requests.
643</t>
644
645<section title="Server-driven Negotiation" anchor="server-driven.negotiation">
646<t>
647   If the selection of the best representation for a response is made by
648   an algorithm located at the server, it is called server-driven
649   negotiation. Selection is based on the available representations of
650   the response (the dimensions over which it can vary; e.g. language,
651   content-coding, etc.) and the contents of particular header fields in
652   the request message or on other information pertaining to the request
653   (such as the network address of the client).
654</t>
655<t>
656   Server-driven negotiation is advantageous when the algorithm for
657   selecting from among the available representations is difficult to
658   describe to the user agent, or when the server desires to send its
659   "best guess" to the client along with the first response (hoping to
660   avoid the round-trip delay of a subsequent request if the "best
661   guess" is good enough for the user). In order to improve the server's
662   guess, the user agent &MAY; include request header fields (Accept,
663   Accept-Language, Accept-Encoding, etc.) which describe its
664   preferences for such a response.
665</t>
666<t>
667   Server-driven negotiation has disadvantages:
668  <list style="numbers">
669    <t>
670         It is impossible for the server to accurately determine what
671         might be "best" for any given user, since that would require
672         complete knowledge of both the capabilities of the user agent
673         and the intended use for the response (e.g., does the user want
674         to view it on screen or print it on paper?).
675    </t>
676    <t>
677         Having the user agent describe its capabilities in every
678         request can be both very inefficient (given that only a small
679         percentage of responses have multiple representations) and a
680         potential violation of the user's privacy.
681    </t>
682    <t>
683         It complicates the implementation of an origin server and the
684         algorithms for generating responses to a request.
685    </t>
686    <t>
687         It may limit a public cache's ability to use the same response
688         for multiple user's requests.
689    </t>
690  </list>
691</t>
692<t>
693   HTTP/1.1 includes the following request-header fields for enabling
694   server-driven negotiation through description of user agent
695   capabilities and user preferences: Accept (<xref target="header.accept"/>), Accept-Charset
696   (<xref target="header.accept-charset"/>), Accept-Encoding (<xref target="header.accept-encoding"/>), Accept-Language
697   (<xref target="header.accept-language"/>), and User-Agent (&header-user-agent;). However, an
698   origin server is not limited to these dimensions and &MAY; vary the
699   response based on any aspect of the request, including information
700   outside the request-header fields or within extension header fields
701   not defined by this specification.
702</t>
703<t>
704   The Vary header field &caching; can be used to express the parameters the
705   server uses to select a representation that is subject to server-driven
706   negotiation.
707</t>
708</section>
709
710<section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">
711<t>
712   With agent-driven negotiation, selection of the best representation
713   for a response is performed by the user agent after receiving an
714   initial response from the origin server. Selection is based on a list
715   of the available representations of the response included within the
716   header fields or entity-body of the initial response, with each
717   representation identified by its own URI. Selection from among the
718   representations may be performed automatically (if the user agent is
719   capable of doing so) or manually by the user selecting from a
720   generated (possibly hypertext) menu.
721</t>
722<t>
723   Agent-driven negotiation is advantageous when the response would vary
724   over commonly-used dimensions (such as type, language, or encoding),
725   when the origin server is unable to determine a user agent's
726   capabilities from examining the request, and generally when public
727   caches are used to distribute server load and reduce network usage.
728</t>
729<t>
730   Agent-driven negotiation suffers from the disadvantage of needing a
731   second request to obtain the best alternate representation. This
732   second request is only efficient when caching is used. In addition,
733   this specification does not define any mechanism for supporting
734   automatic selection, though it also does not prevent any such
735   mechanism from being developed as an extension and used within
736   HTTP/1.1.
737</t>
738<t>
739   HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
740   status codes for enabling agent-driven negotiation when the server is
741   unwilling or unable to provide a varying response using server-driven
742   negotiation.
743</t>
744</section>
745
746<section title="Transparent Negotiation" anchor="transparent.negotiation">
747<t>
748   Transparent negotiation is a combination of both server-driven and
749   agent-driven negotiation. When a cache is supplied with a form of the
750   list of available representations of the response (as in agent-driven
751   negotiation) and the dimensions of variance are completely understood
752   by the cache, then the cache becomes capable of performing server-driven
753   negotiation on behalf of the origin server for subsequent
754   requests on that resource.
755</t>
756<t>
757   Transparent negotiation has the advantage of distributing the
758   negotiation work that would otherwise be required of the origin
759   server and also removing the second request delay of agent-driven
760   negotiation when the cache is able to correctly guess the right
761   response.
762</t>
763<t>
764   This specification does not define any mechanism for transparent
765   negotiation, though it also does not prevent any such mechanism from
766   being developed as an extension that could be used within HTTP/1.1.
767</t>
768</section>
769</section>
770<section title="Header Field Definitions" anchor="header.fields">
771<t>
772   This section defines the syntax and semantics of all standard
773   HTTP/1.1 header fields. For entity-header fields, both sender and
774   recipient refer to either the client or the server, depending on who
775   sends and who receives the entity.
776</t>
777<section title="Accept" anchor="header.accept">
778  <iref primary="true" item="Accept header" x:for-anchor=""/>
779  <iref primary="true" item="Headers" subitem="Accept" x:for-anchor=""/>
780<t>
781   The Accept request-header field can be used to specify certain media
782   types which are acceptable for the response. Accept headers can be
783   used to indicate that the request is specifically limited to a small
784   set of desired types, as in the case of a request for an in-line
785   image.
786</t>
787<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"/>
788    Accept         = "Accept" ":"
789                     #( media-range [ accept-params ] )
790
791    media-range    = ( "*/*"
792                     | ( type "/" "*" )
793                     | ( type "/" subtype )
794                     ) *( ";" parameter )
795    accept-params  = ";" "q" "=" qvalue *( accept-extension )
796    accept-extension = ";" token [ "=" ( token | quoted-string ) ]
797</artwork></figure>
798<t>
799   The asterisk "*" character is used to group media types into ranges,
800   with "*/*" indicating all media types and "type/*" indicating all
801   subtypes of that type. The media-range &MAY; include media type
802   parameters that are applicable to that range.
803</t>
804<t>
805   Each media-range &MAY; be followed by one or more accept-params,
806   beginning with the "q" parameter for indicating a relative quality
807   factor. The first "q" parameter (if any) separates the media-range
808   parameter(s) from the accept-params. Quality factors allow the user
809   or user agent to indicate the relative degree of preference for that
810   media-range, using the qvalue scale from 0 to 1 (<xref target="quality.values"/>). The
811   default value is q=1.
812  <list><t>
813      <x:h>Note:</x:h> Use of the "q" parameter name to separate media type
814      parameters from Accept extension parameters is due to historical
815      practice. Although this prevents any media type parameter named
816      "q" from being used with a media range, such an event is believed
817      to be unlikely given the lack of any "q" parameters in the IANA
818      media type registry and the rare usage of any media type
819      parameters in Accept. Future media types are discouraged from
820      registering any parameter named "q".
821  </t></list>
822</t>
823<t>
824   The example
825</t>
826<figure><artwork type="example">
827    Accept: audio/*; q=0.2, audio/basic
828</artwork></figure>
829<t>
830   &SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
831   type if it is the best available after an 80% mark-down in quality."
832</t>
833<t>
834   If no Accept header field is present, then it is assumed that the
835   client accepts all media types. If an Accept header field is present,
836   and if the server cannot send a response which is acceptable
837   according to the combined Accept field value, then the server &SHOULD;
838   send a 406 (not acceptable) response.
839</t>
840<t>
841   A more elaborate example is
842</t>
843<figure><artwork type="example">
844    Accept: text/plain; q=0.5, text/html,
845            text/x-dvi; q=0.8, text/x-c
846</artwork></figure>
847<t>
848   Verbally, this would be interpreted as "text/html and text/x-c are
849   the preferred media types, but if they do not exist, then send the
850   text/x-dvi entity, and if that does not exist, send the text/plain
851   entity."
852</t>
853<t>
854   Media ranges can be overridden by more specific media ranges or
855   specific media types. If more than one media range applies to a given
856   type, the most specific reference has precedence. For example,
857</t>
858<figure><artwork type="example">
859    Accept: text/*, text/html, text/html;level=1, */*
860</artwork></figure>
861<t>
862   have the following precedence:
863</t>
864<figure><artwork type="example">
865    1) text/html;level=1
866    2) text/html
867    3) text/*
868    4) */*
869</artwork></figure>
870<t>
871   The media type quality factor associated with a given type is
872   determined by finding the media range with the highest precedence
873   which matches that type. For example,
874</t>
875<figure><artwork type="example">
876    Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
877            text/html;level=2;q=0.4, */*;q=0.5
878</artwork></figure>
879<t>
880   would cause the following values to be associated:
881</t>
882<figure><artwork type="example">
883    text/html;level=1         = 1
884    text/html                 = 0.7
885    text/plain                = 0.3
886    image/jpeg                = 0.5
887    text/html;level=2         = 0.4
888    text/html;level=3         = 0.7
889</artwork></figure>
890<t>
891      <x:h>Note:</x:h> A user agent might be provided with a default set of quality
892      values for certain media ranges. However, unless the user agent is
893      a closed system which cannot interact with other rendering agents,
894      this default set ought to be configurable by the user.
895</t>
896</section>
897
898<section title="Accept-Charset" anchor="header.accept-charset">
899  <iref primary="true" item="Accept-Charset header" x:for-anchor=""/>
900  <iref primary="true" item="Headers" subitem="Accept-Charset" x:for-anchor=""/>
901<t>
902   The Accept-Charset request-header field can be used to indicate what
903   character sets are acceptable for the response. This field allows
904   clients capable of understanding more comprehensive or special-purpose
905   character sets to signal that capability to a server which is
906   capable of representing documents in those character sets.
907</t>
908<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Charset"/>
909   Accept-Charset = "Accept-Charset" ":"
910           1#( ( charset | "*" )[ ";" "q" "=" qvalue ] )
911</artwork></figure>
912<t>
913   Character set values are described in <xref target="character.sets"/>. Each charset &MAY;
914   be given an associated quality value which represents the user's
915   preference for that charset. The default value is q=1. An example is
916</t>
917<figure><artwork type="example">
918   Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
919</artwork></figure>
920<t>
921   The special value "*", if present in the Accept-Charset field,
922   matches every character set (including ISO-8859-1) which is not
923   mentioned elsewhere in the Accept-Charset field. If no "*" is present
924   in an Accept-Charset field, then all character sets not explicitly
925   mentioned get a quality value of 0, except for ISO-8859-1, which gets
926   a quality value of 1 if not explicitly mentioned.
927</t>
928<t>
929   If no Accept-Charset header is present, the default is that any
930   character set is acceptable. If an Accept-Charset header is present,
931   and if the server cannot send a response which is acceptable
932   according to the Accept-Charset header, then the server &SHOULD; send
933   an error response with the 406 (not acceptable) status code, though
934   the sending of an unacceptable response is also allowed.
935</t>
936</section>
937
938<section title="Accept-Encoding" anchor="header.accept-encoding">
939  <iref primary="true" item="Accept-Encoding header" x:for-anchor=""/>
940  <iref primary="true" item="Headers" subitem="Accept-Encoding" x:for-anchor=""/>
941<t>
942   The Accept-Encoding request-header field is similar to Accept, but
943   restricts the content-codings (<xref target="content.codings"/>) that are acceptable in
944   the response.
945</t>
946<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Encoding"/><iref primary="true" item="Grammar" subitem="codings"/>
947    Accept-Encoding  = "Accept-Encoding" ":"
948                       1#( codings [ ";" "q" "=" qvalue ] )
949    codings          = ( content-coding | "*" )
950</artwork></figure>
951<t>
952   Examples of its use are:
953</t>
954<figure><artwork type="example">
955    Accept-Encoding: compress, gzip
956    Accept-Encoding:
957    Accept-Encoding: *
958    Accept-Encoding: compress;q=0.5, gzip;q=1.0
959    Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
960</artwork></figure>
961<t>
962   A server tests whether a content-coding is acceptable, according to
963   an Accept-Encoding field, using these rules:
964  <list style="numbers">
965      <t>If the content-coding is one of the content-codings listed in
966         the Accept-Encoding field, then it is acceptable, unless it is
967         accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
968         qvalue of 0 means "not acceptable.")</t>
969
970      <t>The special "*" symbol in an Accept-Encoding field matches any
971         available content-coding not explicitly listed in the header
972         field.</t>
973
974      <t>If multiple content-codings are acceptable, then the acceptable
975         content-coding with the highest non-zero qvalue is preferred.</t>
976
977      <t>The "identity" content-coding is always acceptable, unless
978         specifically refused because the Accept-Encoding field includes
979         "identity;q=0", or because the field includes "*;q=0" and does
980         not explicitly include the "identity" content-coding. If the
981         Accept-Encoding field-value is empty, then only the "identity"
982         encoding is acceptable.</t>
983  </list>
984</t>
985<t>
986   If an Accept-Encoding field is present in a request, and if the
987   server cannot send a response which is acceptable according to the
988   Accept-Encoding header, then the server &SHOULD; send an error response
989   with the 406 (Not Acceptable) status code.
990</t>
991<t>
992   If no Accept-Encoding field is present in a request, the server &MAY;
993   assume that the client will accept any content coding. In this case,
994   if "identity" is one of the available content-codings, then the
995   server &SHOULD; use the "identity" content-coding, unless it has
996   additional information that a different content-coding is meaningful
997   to the client.
998  <list><t>
999      <x:h>Note:</x:h> If the request does not include an Accept-Encoding field,
1000      and if the "identity" content-coding is unavailable, then
1001      content-codings commonly understood by HTTP/1.0 clients (i.e.,
1002      "gzip" and "compress") are preferred; some older clients
1003      improperly display messages sent with other content-codings.  The
1004      server might also make this decision based on information about
1005      the particular user-agent or client.
1006    </t><t>
1007      <x:h>Note:</x:h> Most HTTP/1.0 applications do not recognize or obey qvalues
1008      associated with content-codings. This means that qvalues will not
1009      work and are not permitted with x-gzip or x-compress.
1010    </t></list>
1011</t>
1012</section>
1013
1014<section title="Accept-Language" anchor="header.accept-language">
1015  <iref primary="true" item="Accept-Language header" x:for-anchor=""/>
1016  <iref primary="true" item="Headers" subitem="Accept-Language" x:for-anchor=""/>
1017<t>
1018   The Accept-Language request-header field is similar to Accept, but
1019   restricts the set of natural languages that are preferred as a
1020   response to the request. Language tags are defined in <xref target="language.tags"/>.
1021</t>
1022<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Accept-Language"/><iref primary="true" item="Grammar" subitem="language-range"/>
1023    Accept-Language = "Accept-Language" ":"
1024                      1#( language-range [ ";" "q" "=" qvalue ] )
1025    language-range  = ( ( 1*8ALPHA *( "-" 1*8ALPHA ) ) | "*" )
1026</artwork></figure>
1027<t>
1028   Each language-range &MAY; be given an associated quality value which
1029   represents an estimate of the user's preference for the languages
1030   specified by that range. The quality value defaults to "q=1". For
1031   example,
1032</t>
1033<figure><artwork type="example">
1034    Accept-Language: da, en-gb;q=0.8, en;q=0.7
1035</artwork></figure>
1036<t>
1037   would mean: "I prefer Danish, but will accept British English and
1038   other types of English." A language-range matches a language-tag if
1039   it exactly equals the tag, or if it exactly equals a prefix of the
1040   tag such that the first tag character following the prefix is "-".
1041   The special range "*", if present in the Accept-Language field,
1042   matches every tag not matched by any other range present in the
1043   Accept-Language field.
1044  <list><t>
1045      <x:h>Note:</x:h> This use of a prefix matching rule does not imply that
1046      language tags are assigned to languages in such a way that it is
1047      always true that if a user understands a language with a certain
1048      tag, then this user will also understand all languages with tags
1049      for which this tag is a prefix. The prefix rule simply allows the
1050      use of prefix tags if this is the case.
1051  </t></list>
1052</t>
1053<t>
1054   The language quality factor assigned to a language-tag by the
1055   Accept-Language field is the quality value of the longest language-range
1056   in the field that matches the language-tag. If no language-range
1057   in the field matches the tag, the language quality factor
1058   assigned is 0. If no Accept-Language header is present in the
1059   request, the server
1060   &SHOULD; assume that all languages are equally acceptable. If an
1061   Accept-Language header is present, then all languages which are
1062   assigned a quality factor greater than 0 are acceptable.
1063</t>
1064<t>
1065   It might be contrary to the privacy expectations of the user to send
1066   an Accept-Language header with the complete linguistic preferences of
1067   the user in every request. For a discussion of this issue, see
1068   <xref target="privacy.issues.connected.to.accept.headers"/>.
1069</t>
1070<t>
1071   As intelligibility is highly dependent on the individual user, it is
1072   recommended that client applications make the choice of linguistic
1073   preference available to the user. If the choice is not made
1074   available, then the Accept-Language header field &MUST-NOT; be given in
1075   the request.
1076  <list><t>
1077      <x:h>Note:</x:h> When making the choice of linguistic preference available to
1078      the user, we remind implementors of  the fact that users are not
1079      familiar with the details of language matching as described above,
1080      and should provide appropriate guidance. As an example, users
1081      might assume that on selecting "en-gb", they will be served any
1082      kind of English document if British English is not available. A
1083      user agent might suggest in such a case to add "en" to get the
1084      best matching behavior.
1085  </t></list>
1086</t>
1087</section>
1088
1089<section title="Content-Encoding" anchor="header.content-encoding">
1090  <iref primary="true" item="Content-Encoding header" x:for-anchor=""/>
1091  <iref primary="true" item="Headers" subitem="Content-Encoding" x:for-anchor=""/>
1092<t>
1093   The Content-Encoding entity-header field is used as a modifier to the
1094   media-type. When present, its value indicates what additional content
1095   codings have been applied to the entity-body, and thus what decoding
1096   mechanisms must be applied in order to obtain the media-type
1097   referenced by the Content-Type header field. Content-Encoding is
1098   primarily used to allow a document to be compressed without losing
1099   the identity of its underlying media type.
1100</t>
1101<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Encoding"/>
1102    Content-Encoding  = "Content-Encoding" ":" 1#content-coding
1103</artwork></figure>
1104<t>
1105   Content codings are defined in <xref target="content.codings"/>. An example of its use is
1106</t>
1107<figure><artwork type="example">
1108    Content-Encoding: gzip
1109</artwork></figure>
1110<t>
1111   The content-coding is a characteristic of the entity identified by
1112   the Request-URI. Typically, the entity-body is stored with this
1113   encoding and is only decoded before rendering or analogous usage.
1114   However, a non-transparent proxy &MAY; modify the content-coding if the
1115   new coding is known to be acceptable to the recipient, unless the
1116   "no-transform" cache-control directive is present in the message.
1117</t>
1118<t>
1119   If the content-coding of an entity is not "identity", then the
1120   response &MUST; include a Content-Encoding entity-header (<xref target="header.content-encoding"/>)
1121   that lists the non-identity content-coding(s) used.
1122</t>
1123<t>
1124   If the content-coding of an entity in a request message is not
1125   acceptable to the origin server, the server &SHOULD; respond with a
1126   status code of 415 (Unsupported Media Type).
1127</t>
1128<t>
1129   If multiple encodings have been applied to an entity, the content
1130   codings &MUST; be listed in the order in which they were applied.
1131   Additional information about the encoding parameters &MAY; be provided
1132   by other entity-header fields not defined by this specification.
1133</t>
1134</section>
1135
1136<section title="Content-Language" anchor="header.content-language">
1137  <iref primary="true" item="Content-Language header" x:for-anchor=""/>
1138  <iref primary="true" item="Headers" subitem="Content-Language" x:for-anchor=""/>
1139<t>
1140   The Content-Language entity-header field describes the natural
1141   language(s) of the intended audience for the enclosed entity. Note
1142   that this might not be equivalent to all the languages used within
1143   the entity-body.
1144</t>
1145<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Language"/>
1146    Content-Language  = "Content-Language" ":" 1#language-tag
1147</artwork></figure>
1148<t>
1149   Language tags are defined in <xref target="language.tags"/>. The primary purpose of
1150   Content-Language is to allow a user to identify and differentiate
1151   entities according to the user's own preferred language. Thus, if the
1152   body content is intended only for a Danish-literate audience, the
1153   appropriate field is
1154</t>
1155<figure><artwork type="example">
1156    Content-Language: da
1157</artwork></figure>
1158<t>
1159   If no Content-Language is specified, the default is that the content
1160   is intended for all language audiences. This might mean that the
1161   sender does not consider it to be specific to any natural language,
1162   or that the sender does not know for which language it is intended.
1163</t>
1164<t>
1165   Multiple languages &MAY; be listed for content that is intended for
1166   multiple audiences. For example, a rendition of the "Treaty of
1167   Waitangi," presented simultaneously in the original Maori and English
1168   versions, would call for
1169</t>
1170<figure><artwork type="example">
1171    Content-Language: mi, en
1172</artwork></figure>
1173<t>
1174   However, just because multiple languages are present within an entity
1175   does not mean that it is intended for multiple linguistic audiences.
1176   An example would be a beginner's language primer, such as "A First
1177   Lesson in Latin," which is clearly intended to be used by an
1178   English-literate audience. In this case, the Content-Language would
1179   properly only include "en".
1180</t>
1181<t>
1182   Content-Language &MAY; be applied to any media type -- it is not
1183   limited to textual documents.
1184</t>
1185</section>
1186
1187<section title="Content-Location" anchor="header.content-location">
1188  <iref primary="true" item="Content-Location header" x:for-anchor=""/>
1189  <iref primary="true" item="Headers" subitem="Content-Location" x:for-anchor=""/>
1190<t>
1191   The Content-Location entity-header field &MAY; be used to supply the
1192   resource location for the entity enclosed in the message when that
1193   entity is accessible from a location separate from the requested
1194   resource's URI. A server &SHOULD; provide a Content-Location for the
1195   variant corresponding to the response entity; especially in the case
1196   where a resource has multiple entities associated with it, and those
1197   entities actually have separate locations by which they might be
1198   individually accessed, the server &SHOULD; provide a Content-Location
1199   for the particular variant which is returned.
1200</t>
1201<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Location"/>
1202    Content-Location = "Content-Location" ":"
1203                      ( absoluteURI | relativeURI )
1204</artwork></figure>
1205<t>
1206   The value of Content-Location also defines the base URI for the
1207   entity.
1208</t>
1209<t>
1210   The Content-Location value is not a replacement for the original
1211   requested URI; it is only a statement of the location of the resource
1212   corresponding to this particular entity at the time of the request.
1213   Future requests &MAY; specify the Content-Location URI as the request-URI
1214   if the desire is to identify the source of that particular
1215   entity.
1216</t>
1217<t>
1218   A cache cannot assume that an entity with a Content-Location
1219   different from the URI used to retrieve it can be used to respond to
1220   later requests on that Content-Location URI. However, the Content-Location
1221   can be used to differentiate between multiple entities
1222   retrieved from a single requested resource, as described in &caching;.
1223</t>
1224<t>
1225   If the Content-Location is a relative URI, the relative URI is
1226   interpreted relative to the Request-URI.
1227</t>
1228<t>
1229   The meaning of the Content-Location header in PUT or POST requests is
1230   undefined; servers are free to ignore it in those cases.
1231</t>
1232</section>
1233
1234<section title="Content-MD5" anchor="header.content-md5">
1235  <iref primary="true" item="Content-MD5 header" x:for-anchor=""/>
1236  <iref primary="true" item="Headers" subitem="Content-MD5" x:for-anchor=""/>
1237<t>
1238   The Content-MD5 entity-header field, as defined in RFC 1864 <xref target="RFC1864"/>, is
1239   an MD5 digest of the entity-body for the purpose of providing an
1240   end-to-end message integrity check (MIC) of the entity-body. (Note: a
1241   MIC is good for detecting accidental modification of the entity-body
1242   in transit, but is not proof against malicious attacks.)
1243</t>
1244<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-MD5"/><iref primary="true" item="Grammar" subitem="md5-digest"/>
1245     Content-MD5   = "Content-MD5" ":" md5-digest
1246     md5-digest   = &lt;base64 of 128 bit MD5 digest as per RFC 1864&gt;
1247</artwork></figure>
1248<t>
1249   The Content-MD5 header field &MAY; be generated by an origin server or
1250   client to function as an integrity check of the entity-body. Only
1251   origin servers or clients &MAY; generate the Content-MD5 header field;
1252   proxies and gateways &MUST-NOT; generate it, as this would defeat its
1253   value as an end-to-end integrity check. Any recipient of the entity-body,
1254   including gateways and proxies, &MAY; check that the digest value
1255   in this header field matches that of the entity-body as received.
1256</t>
1257<t>
1258   The MD5 digest is computed based on the content of the entity-body,
1259   including any content-coding that has been applied, but not including
1260   any transfer-encoding applied to the message-body. If the message is
1261   received with a transfer-encoding, that encoding &MUST; be removed
1262   prior to checking the Content-MD5 value against the received entity.
1263</t>
1264<t>
1265   This has the result that the digest is computed on the octets of the
1266   entity-body exactly as, and in the order that, they would be sent if
1267   no transfer-encoding were being applied.
1268</t>
1269<t>
1270   HTTP extends RFC 1864 to permit the digest to be computed for MIME
1271   composite media-types (e.g., multipart/* and message/rfc822), but
1272   this does not change how the digest is computed as defined in the
1273   preceding paragraph.
1274</t>
1275<t>
1276   There are several consequences of this. The entity-body for composite
1277   types &MAY; contain many body-parts, each with its own MIME and HTTP
1278   headers (including Content-MD5, Content-Transfer-Encoding, and
1279   Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
1280   or Content-Encoding header, it is assumed that the content
1281   of the body-part has had the encoding applied, and the body-part is
1282   included in the Content-MD5 digest as is -- i.e., after the
1283   application. The Transfer-Encoding header field is not allowed within
1284   body-parts.
1285</t>
1286<t>
1287   Conversion of all line breaks to CRLF &MUST-NOT; be done before
1288   computing or checking the digest: the line break convention used in
1289   the text actually transmitted &MUST; be left unaltered when computing
1290   the digest.
1291  <list><t>
1292      <x:h>Note:</x:h> while the definition of Content-MD5 is exactly the same for
1293      HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
1294      in which the application of Content-MD5 to HTTP entity-bodies
1295      differs from its application to MIME entity-bodies. One is that
1296      HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
1297      does use Transfer-Encoding and Content-Encoding. Another is that
1298      HTTP more frequently uses binary content types than MIME, so it is
1299      worth noting that, in such cases, the byte order used to compute
1300      the digest is the transmission byte order defined for the type.
1301      Lastly, HTTP allows transmission of text types with any of several
1302      line break conventions and not just the canonical form using CRLF.
1303  </t></list>
1304</t>
1305</section>
1306
1307<section title="Content-Type" anchor="header.content-type">
1308  <iref primary="true" item="Content-Type header" x:for-anchor=""/>
1309  <iref primary="true" item="Headers" subitem="Content-Type" x:for-anchor=""/>
1310<t>
1311   The Content-Type entity-header field indicates the media type of the
1312   entity-body sent to the recipient or, in the case of the HEAD method,
1313   the media type that would have been sent had the request been a GET.
1314</t>
1315<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Type"/>
1316    Content-Type   = "Content-Type" ":" media-type
1317</artwork></figure>
1318<t>
1319   Media types are defined in <xref target="media.types"/>. An example of the field is
1320</t>
1321<figure><artwork type="example">
1322    Content-Type: text/html; charset=ISO-8859-4
1323</artwork></figure>
1324<t>
1325   Further discussion of methods for identifying the media type of an
1326   entity is provided in <xref target="type"/>.
1327</t>
1328</section>
1329
1330</section>
1331
1332<section title="IANA Considerations" anchor="IANA.considerations">
1333<t>
1334   TBD.
1335</t>
1336</section>
1337
1338<section title="Security Considerations" anchor="security.considerations">
1339<t>
1340   This section is meant to inform application developers, information
1341   providers, and users of the security limitations in HTTP/1.1 as
1342   described by this document. The discussion does not include
1343   definitive solutions to the problems revealed, though it does make
1344   some suggestions for reducing security risks.
1345</t>
1346
1347<section title="Privacy Issues Connected to Accept Headers" anchor="privacy.issues.connected.to.accept.headers">
1348<t>
1349   Accept request-headers can reveal information about the user to all
1350   servers which are accessed. The Accept-Language header in particular
1351   can reveal information the user would consider to be of a private
1352   nature, because the understanding of particular languages is often
1353   strongly correlated to the membership of a particular ethnic group.
1354   User agents which offer the option to configure the contents of an
1355   Accept-Language header to be sent in every request are strongly
1356   encouraged to let the configuration process include a message which
1357   makes the user aware of the loss of privacy involved.
1358</t>
1359<t>
1360   An approach that limits the loss of privacy would be for a user agent
1361   to omit the sending of Accept-Language headers by default, and to ask
1362   the user whether or not to start sending Accept-Language headers to a
1363   server if it detects, by looking for any Vary response-header fields
1364   generated by the server, that such sending could improve the quality
1365   of service.
1366</t>
1367<t>
1368   Elaborate user-customized accept header fields sent in every request,
1369   in particular if these include quality values, can be used by servers
1370   as relatively reliable and long-lived user identifiers. Such user
1371   identifiers would allow content providers to do click-trail tracking,
1372   and would allow collaborating content providers to match cross-server
1373   click-trails or form submissions of individual users. Note that for
1374   many users not behind a proxy, the network address of the host
1375   running the user agent will also serve as a long-lived user
1376   identifier. In environments where proxies are used to enhance
1377   privacy, user agents ought to be conservative in offering accept
1378   header configuration options to end users. As an extreme privacy
1379   measure, proxies could filter the accept headers in relayed requests.
1380   General purpose user agents which provide a high degree of header
1381   configurability &SHOULD; warn users about the loss of privacy which can
1382   be involved.
1383</t>
1384</section>
1385
1386<section title="Content-Disposition Issues" anchor="content-disposition.issues">
1387<t>
1388   RFC 1806 <xref target="RFC1806"/>, from which the often implemented Content-Disposition
1389   (see <xref target="content-disposition"/>) header in HTTP is derived, has a number of very
1390   serious security considerations. Content-Disposition is not part of
1391   the HTTP standard, but since it is widely implemented, we are
1392   documenting its use and risks for implementors. See RFC 2183 <xref target="RFC2183"/>
1393   (which updates RFC 1806) for details.
1394</t>
1395</section>
1396
1397</section>
1398
1399<section title="Acknowledgments" anchor="ack">
1400<t>
1401   Based on an XML translation of RFC 2616 by Julian Reschke.
1402</t>
1403</section>
1404</middle>
1405<back>
1406<references>
1407
1408<reference anchor="Part1">
1409   <front>
1410      <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1411      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1412         <organization abbrev="Day Software">Day Software</organization>
1413         <address><email>fielding@gbiv.com</email></address>
1414      </author>
1415      <author initials="J." surname="Gettys" fullname="Jim Gettys">
1416         <organization>One Laptop per Child</organization>
1417         <address><email>jg@laptop.org</email></address>
1418      </author>
1419      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1420         <organization abbrev="HP">Hewlett-Packard Company</organization>
1421         <address><email>JeffMogul@acm.org</email></address>
1422      </author>
1423      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1424         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1425         <address><email>henrikn@microsoft.com</email></address>
1426      </author>
1427      <author initials="L." surname="Masinter" fullname="Larry Masinter">
1428         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1429         <address><email>LMM@acm.org</email></address>
1430      </author>
1431      <author initials="P." surname="Leach" fullname="Paul J. Leach">
1432         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1433         <address><email>paulle@microsoft.com</email></address>
1434      </author>
1435      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1436         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1437         <address><email>timbl@w3.org</email></address>
1438      </author>
1439      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1440   </front>
1441   <seriesInfo name="Internet-Draft" value="draft-fielding-p1-messaging-&ID-VERSION;"/>
1442   <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1443</reference>
1444
1445<reference anchor="Part2">
1446   <front>
1447      <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1448      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1449         <organization abbrev="Day Software">Day Software</organization>
1450         <address><email>fielding@gbiv.com</email></address>
1451      </author>
1452      <author initials="J." surname="Gettys" fullname="Jim Gettys">
1453         <organization>One Laptop per Child</organization>
1454         <address><email>jg@laptop.org</email></address>
1455      </author>
1456      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1457         <organization abbrev="HP">Hewlett-Packard Company</organization>
1458         <address><email>JeffMogul@acm.org</email></address>
1459      </author>
1460      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1461         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1462         <address><email>henrikn@microsoft.com</email></address>
1463      </author>
1464      <author initials="L." surname="Masinter" fullname="Larry Masinter">
1465         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1466         <address><email>LMM@acm.org</email></address>
1467      </author>
1468      <author initials="P." surname="Leach" fullname="Paul J. Leach">
1469         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1470         <address><email>paulle@microsoft.com</email></address>
1471      </author>
1472      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1473         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1474         <address><email>timbl@w3.org</email></address>
1475      </author>
1476      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1477   </front>
1478   <seriesInfo name="Internet-Draft" value="draft-fielding-p2-semantics-&ID-VERSION;"/>
1479   <x:source href="p2-semantics.xml" basename="p2-semantics"/>
1480</reference>
1481
1482<reference anchor="Part4">
1483   <front>
1484      <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1485      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1486         <organization abbrev="Day Software">Day Software</organization>
1487         <address><email>fielding@gbiv.com</email></address>
1488      </author>
1489      <author initials="J." surname="Gettys" fullname="Jim Gettys">
1490         <organization>One Laptop per Child</organization>
1491         <address><email>jg@laptop.org</email></address>
1492      </author>
1493      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1494         <organization abbrev="HP">Hewlett-Packard Company</organization>
1495         <address><email>JeffMogul@acm.org</email></address>
1496      </author>
1497      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1498         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1499         <address><email>henrikn@microsoft.com</email></address>
1500      </author>
1501      <author initials="L." surname="Masinter" fullname="Larry Masinter">
1502         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1503         <address><email>LMM@acm.org</email></address>
1504      </author>
1505      <author initials="P." surname="Leach" fullname="Paul J. Leach">
1506         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1507         <address><email>paulle@microsoft.com</email></address>
1508      </author>
1509      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1510         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1511         <address><email>timbl@w3.org</email></address>
1512      </author>
1513      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1514   </front>
1515   <seriesInfo name="Internet-Draft" value="draft-fielding-p4-conditional-&ID-VERSION;"/>
1516   <x:source href="p4-conditional.xml" basename="p4-conditional"/>
1517</reference>
1518
1519<reference anchor="Part5">
1520   <front>
1521      <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1522      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1523         <organization abbrev="Day Software">Day Software</organization>
1524         <address><email>fielding@gbiv.com</email></address>
1525      </author>
1526      <author initials="J." surname="Gettys" fullname="Jim Gettys">
1527         <organization>One Laptop per Child</organization>
1528         <address><email>jg@laptop.org</email></address>
1529      </author>
1530      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1531         <organization abbrev="HP">Hewlett-Packard Company</organization>
1532         <address><email>JeffMogul@acm.org</email></address>
1533      </author>
1534      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1535         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1536         <address><email>henrikn@microsoft.com</email></address>
1537      </author>
1538      <author initials="L." surname="Masinter" fullname="Larry Masinter">
1539         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1540         <address><email>LMM@acm.org</email></address>
1541      </author>
1542      <author initials="P." surname="Leach" fullname="Paul J. Leach">
1543         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1544         <address><email>paulle@microsoft.com</email></address>
1545      </author>
1546      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1547         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1548         <address><email>timbl@w3.org</email></address>
1549      </author>
1550      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1551   </front>
1552   <seriesInfo name="Internet-Draft" value="draft-fielding-p5-range-&ID-VERSION;"/>
1553   <x:source href="p5-range.xml" basename="p5-range"/>
1554</reference>
1555
1556<reference anchor="Part6">
1557   <front>
1558      <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1559      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1560         <organization abbrev="Day Software">Day Software</organization>
1561         <address><email>fielding@gbiv.com</email></address>
1562      </author>
1563      <author initials="J." surname="Gettys" fullname="Jim Gettys">
1564         <organization>One Laptop per Child</organization>
1565         <address><email>jg@laptop.org</email></address>
1566      </author>
1567      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1568         <organization abbrev="HP">Hewlett-Packard Company</organization>
1569         <address><email>JeffMogul@acm.org</email></address>
1570      </author>
1571      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1572         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1573         <address><email>henrikn@microsoft.com</email></address>
1574      </author>
1575      <author initials="L." surname="Masinter" fullname="Larry Masinter">
1576         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1577         <address><email>LMM@acm.org</email></address>
1578      </author>
1579      <author initials="P." surname="Leach" fullname="Paul J. Leach">
1580         <organization abbrev="Microsoft">Microsoft Corporation</organization>
1581         <address><email>paulle@microsoft.com</email></address>
1582      </author>
1583      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1584         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1585         <address><email>timbl@w3.org</email></address>
1586      </author>
1587      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1588   </front>
1589   <seriesInfo name="Internet-Draft" value="draft-fielding-p6-cache-&ID-VERSION;"/>
1590   <x:source href="p6-cache.xml" basename="p6-cache"/>
1591</reference>
1592
1593<reference anchor="RFC2616">
1594   <front>
1595      <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
1596      <author initials="R." surname="Fielding" fullname="R. Fielding">
1597         <organization>University of California, Irvine</organization>
1598         <address><email>fielding@ics.uci.edu</email></address>
1599      </author>
1600      <author initials="J." surname="Gettys" fullname="J. Gettys">
1601         <organization>W3C</organization>
1602         <address><email>jg@w3.org</email></address>
1603      </author>
1604      <author initials="J." surname="Mogul" fullname="J. Mogul">
1605         <organization>Compaq Computer Corporation</organization>
1606         <address><email>mogul@wrl.dec.com</email></address>
1607      </author>
1608      <author initials="H." surname="Frystyk" fullname="H. Frystyk">
1609         <organization>MIT Laboratory for Computer Science</organization>
1610         <address><email>frystyk@w3.org</email></address>
1611      </author>
1612      <author initials="L." surname="Masinter" fullname="L. Masinter">
1613         <organization>Xerox Corporation</organization>
1614         <address><email>masinter@parc.xerox.com</email></address>
1615      </author>
1616      <author initials="P." surname="Leach" fullname="P. Leach">
1617         <organization>Microsoft Corporation</organization>
1618         <address><email>paulle@microsoft.com</email></address>
1619      </author>
1620      <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
1621         <organization>W3C</organization>
1622         <address><email>timbl@w3.org</email></address>
1623      </author>
1624      <date month="June" year="1999"/>
1625   </front>
1626   <seriesInfo name="RFC" value="2616"/>
1627</reference>
1628
1629<reference anchor="RFC1766">
1630<front>
1631<title abbrev="Language Tag">Tags for the Identification of Languages</title>
1632<author initials="H." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
1633<organization>UNINETT</organization>
1634<address>
1635<postal>
1636<street>Pb. 6883 Elgeseter</street>
1637<city>Trondheim</city>
1638<region/>
1639<code>N-7002</code>
1640<country>NO</country></postal>
1641<phone>+47 73 597094</phone>
1642<email>Harald.T.Alvestrand@uninett.no</email></address></author>
1643<date month="March" year="1995"/>
1644</front>
1645<seriesInfo name="RFC" value="1766"/>
1646</reference>
1647
1648<reference anchor="RFC2045">
1649<front>
1650<title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
1651<author initials="N." surname="Freed" fullname="Ned Freed">
1652<organization>Innosoft International, Inc.</organization>
1653<address>
1654<postal>
1655<street>1050 East Garvey Avenue South</street>
1656<city>West Covina</city>
1657<region>CA</region>
1658<code>91790</code>
1659<country>US</country></postal>
1660<phone>+1 818 919 3600</phone>
1661<facsimile>+1 818 919 3614</facsimile>
1662<email>ned@innosoft.com</email></address></author>
1663<author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
1664<organization>First Virtual Holdings</organization>
1665<address>
1666<postal>
1667<street>25 Washington Avenue</street>
1668<city>Morristown</city>
1669<region>NJ</region>
1670<code>07960</code>
1671<country>US</country></postal>
1672<phone>+1 201 540 8967</phone>
1673<facsimile>+1 201 993 3032</facsimile>
1674<email>nsb@nsb.fv.com</email></address></author>
1675<date month="November" year="1996"/>
1676</front>
1677<seriesInfo name="RFC" value="2045"/>
1678</reference>
1679
1680<reference anchor="RFC822">
1681<front>
1682<title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
1683<author initials="D.H." surname="Crocker" fullname="David H. Crocker">
1684<organization>University of Delaware, Dept. of Electrical Engineering</organization>
1685<address>
1686<postal>
1687<street/>
1688<city>Newark</city>
1689<region>DE</region>
1690<code>19711</code>
1691<country>US</country></postal>
1692<email>DCrocker@UDel-Relay</email></address></author>
1693<date month="August" day="13" year="1982"/></front>
1694<seriesInfo name="STD" value="11"/>
1695<seriesInfo name="RFC" value="822"/>
1696</reference>
1697
1698<reference anchor="RFC1867">
1699<front>
1700<title>Form-based File Upload in HTML</title>
1701<author initials="L." surname="Masinter" fullname="Larry Masinter">
1702<organization>Xerox Palo Alto Research Center</organization>
1703<address>
1704<postal>
1705<street>3333 Coyote Hill Road</street>
1706<city>Palo Alto</city>
1707<region>CA</region>
1708<code>94304</code>
1709<country>US</country></postal>
1710<phone>+1 415 812 4365</phone>
1711<facsimile>+1 415 812 4333</facsimile>
1712<email>masinter@parc.xerox.com</email></address></author>
1713<author initials="E." surname="Nebel" fullname="Ernesto Nebel">
1714<organization>XSoft, Xerox Corporation</organization>
1715<address>
1716<postal>
1717<street>10875 Rancho Bernardo Road</street>
1718<street>Suite 200</street>
1719<city>San Diego</city>
1720<region>CA</region>
1721<code>92127-2116</code>
1722<country>US</country></postal>
1723<phone>+1 619 676 7817</phone>
1724<facsimile>+1 619 676 7865</facsimile>
1725<email>nebel@xsoft.sd.xerox.com</email></address></author>
1726<date month="November" year="1995"/>
1727</front>
1728<seriesInfo name="RFC" value="1867"/>
1729</reference>
1730
1731<reference anchor="RFC1590">
1732<front>
1733<title>Media Type Registration Procedure</title>
1734<author initials="J." surname="Postel" fullname="Jon Postel">
1735<organization>USC/Information Sciences Institute</organization>
1736<address>
1737<postal>
1738<street>4676 Admiralty Way</street>
1739<city>Marina del Rey</city>
1740<region>CA</region>
1741<code>90292</code>
1742<country>US</country></postal>
1743<phone>+1 310 822 1511</phone>
1744<facsimile>+1 310 823 6714</facsimile>
1745<email>Postel@ISI.EDU</email></address></author>
1746<date month="November" year="1996"/>
1747</front>
1748<seriesInfo name="RFC" value="1590"/>
1749</reference>
1750
1751<reference anchor="RFC1700">
1752<front>
1753<title abbrev="Assigned Numbers">Assigned Numbers</title>
1754<author initials="J." surname="Reynolds" fullname="Joyce K. Reynolds">
1755<organization>USC/Information Sciences Institute</organization>
1756<address>
1757<postal>
1758<street>4676 Admiralty Way</street>
1759<city>Marina del Rey</city>
1760<region>CA</region>
1761<code>90292-6695</code>
1762<country>US</country></postal>
1763<phone>+1 310 822 1511</phone>
1764<email>jkrey@isi.edu</email></address></author>
1765<author initials="J." surname="Postel" fullname="Jon Postel">
1766<organization>USC/Information Sciences Institute</organization>
1767<address>
1768<postal>
1769<street>4676 Admiralty Way</street>
1770<city>Marina del Rey</city>
1771<region>CA</region>
1772<code>90292-6695</code>
1773<country>US</country></postal>
1774<phone>+1 310 822 1511</phone>
1775<email>postel@isi.edu</email></address></author>
1776<date month="October" year="1994"/>
1777<abstract>
1778<t/></abstract></front>
1779<seriesInfo name="STD" value="2"/>
1780<seriesInfo name="RFC" value="1700"/>
1781</reference>
1782
1783<reference anchor="RFC1864">
1784<front>
1785<title abbrev="Content-MD5 Header Field">The Content-MD5 Header Field</title>
1786<author initials="J." surname="Myers" fullname="John G. Myers">
1787<organization>Carnegie Mellon University</organization>
1788<address>
1789<phone/>
1790<email>jgm+@cmu.edu</email></address></author>
1791<author initials="M." surname="Rose" fullname="Marshall T. Rose">
1792<organization>Dover Beach Consulting, Inc.</organization>
1793<address>
1794<phone/>
1795<email>mrose@dbc.mtview.ca.us</email></address></author>
1796<date month="October" year="1995"/>
1797</front>
1798<seriesInfo name="RFC" value="1864"/>
1799</reference>
1800
1801
1802<reference anchor="RFC1952">
1803<front>
1804<title>GZIP file format specification version 4.3</title>
1805<author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1806<organization>Aladdin Enterprises</organization>
1807<address>
1808<postal>
1809<street>203 Santa Margarita Ave.</street>
1810<city>Menlo Park</city>
1811<region>CA</region>
1812<code>94025</code>
1813<country>US</country></postal>
1814<phone>+1 415 322 0103</phone>
1815<facsimile>+1 415 322 1734</facsimile>
1816<email>ghost@aladdin.com</email></address></author>
1817<author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1818<organization/>
1819<address>
1820<postal>
1821<street/>
1822<city/>
1823<region/>
1824<code/>
1825<country/></postal>
1826<phone/>
1827<email>gzip@prep.ai.mit.edu</email></address></author>
1828<author initials="M." surname="Adler" fullname="Mark Adler">
1829<organization/>
1830<address>
1831<postal>
1832<street/>
1833<city/>
1834<region/>
1835<code/>
1836<country/></postal>
1837<phone/>
1838<email>madler@alumni.caltech.edu</email></address></author>
1839<author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1840<organization/>
1841<address>
1842<postal>
1843<street/>
1844<city/>
1845<region/>
1846<code/>
1847<country/></postal>
1848<phone/>
1849<email>ghost@aladdin.com</email></address></author>
1850<author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
1851<organization/>
1852<address>
1853<postal>
1854<street/>
1855<city/>
1856<region/>
1857<code/>
1858<country/></postal>
1859<phone/>
1860<email>randeg@alumni.rpi.edu</email></address></author>
1861<date month="May" year="1996"/>
1862</front>
1863<seriesInfo name="RFC" value="1952"/>
1864</reference>
1865
1866<reference anchor="RFC1951">
1867<front>
1868<title>DEFLATE Compressed Data Format Specification version 1.3</title>
1869<author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
1870<organization>Aladdin Enterprises</organization>
1871<address>
1872<postal>
1873<street>203 Santa Margarita Ave.</street>
1874<city>Menlo Park</city>
1875<region>CA</region>
1876<code>94025</code>
1877<country>US</country></postal>
1878<phone>+1 415 322 0103</phone>
1879<facsimile>+1 415 322 1734</facsimile>
1880<email>ghost@aladdin.com</email></address></author>
1881<date month="May" year="1996"/>
1882<abstract>
1883<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>
1884<seriesInfo name="RFC" value="1951"/>
1885</reference>
1886
1887<reference anchor="RFC1950">
1888<front>
1889<title>ZLIB Compressed Data Format Specification version 3.3</title>
1890<author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
1891<organization>Aladdin Enterprises</organization>
1892<address>
1893<postal>
1894<street>203 Santa Margarita Ave.</street>
1895<city>Menlo Park</city>
1896<region>CA</region>
1897<code>94025</code>
1898<country>US</country></postal>
1899<phone>+1 415 322 0103</phone>
1900<facsimile>+1 415 322 1734</facsimile>
1901<email>ghost@aladdin.com</email></address></author>
1902<author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
1903<organization/></author>
1904<date month="May" year="1996"/>
1905<abstract>
1906<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
1907   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>
1908<seriesInfo name="RFC" value="1950"/>
1909</reference>
1910
1911<reference anchor="RFC2068">
1912<front>
1913<title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
1914<author initials="R." surname="Fielding" fullname="Roy T. Fielding">
1915<organization>University of California, Irvine, Department of Information and Computer Science</organization>
1916<address>
1917<postal>
1918<street/>
1919<city>Irvine</city>
1920<region>CA</region>
1921<code>92717-3425</code>
1922<country>US</country></postal>
1923<facsimile>+1 714 824 4056</facsimile>
1924<email>fielding@ics.uci.edu</email></address></author>
1925<author initials="J." surname="Gettys" fullname="Jim Gettys">
1926<organization>MIT Laboratory for Computer Science</organization>
1927<address>
1928<postal>
1929<street>545 Technology Square</street>
1930<city>Cambridge</city>
1931<region>MA</region>
1932<code>02139</code>
1933<country>US</country></postal>
1934<facsimile>+1 617 258 8682</facsimile>
1935<email>jg@w3.org</email></address></author>
1936<author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1937<organization>Digital Equipment Corporation, Western Research Laboratory</organization>
1938<address>
1939<postal>
1940<street>250 University Avenue</street>
1941<city>Palo Alto</city>
1942<region>CA</region>
1943<code>94301</code>
1944<country>US</country></postal>
1945<email>mogul@wrl.dec.com</email></address></author>
1946<author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
1947<organization>MIT Laboratory for Computer Science</organization>
1948<address>
1949<postal>
1950<street>545 Technology Square</street>
1951<city>Cambridge</city>
1952<region>MA</region>
1953<code>02139</code>
1954<country>US</country></postal>
1955<facsimile>+1 617 258 8682</facsimile>
1956<email>frystyk@w3.org</email></address></author>
1957<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1958<organization>MIT Laboratory for Computer Science</organization>
1959<address>
1960<postal>
1961<street>545 Technology Square</street>
1962<city>Cambridge</city>
1963<region>MA</region>
1964<code>02139</code>
1965<country>US</country></postal>
1966<facsimile>+1 617 258 8682</facsimile>
1967<email>timbl@w3.org</email></address></author>
1968<date month="January" year="1997"/>
1969<abstract>
1970<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>
1971<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>
1972<seriesInfo name="RFC" value="2068"/>
1973</reference>
1974
1975<reference anchor="RFC1806">
1976<front>
1977<title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header</title>
1978<author initials="R." surname="Troost" fullname="Rens Troost">
1979<organization>New Century Systems</organization>
1980<address>
1981<postal>
1982<street>324 East 41st Street #804</street>
1983<city>New York</city>
1984<region>NY</region>
1985<code>10017</code>
1986<country>US</country></postal>
1987<phone>+1 212 557 2050</phone>
1988<facsimile>+1 212 557 2049</facsimile>
1989<email>rens@century.com</email></address></author>
1990<author initials="S." surname="Dorner" fullname="Steve Dorner">
1991<organization>QUALCOMM Incorporated</organization>
1992<address>
1993<postal>
1994<street>6455 Lusk Boulevard</street>
1995<city>San Diego</city>
1996<region>CA</region>
1997<code>92121</code>
1998<country>US</country></postal>
1999<email>sdorner@qualcomm.com</email></address></author>
2000<date month="June" year="1995"/>
2001<abstract>
2002<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>
2003<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>
2004<seriesInfo name="RFC" value="1806"/>
2005</reference>
2006
2007<reference anchor="RFC2076">
2008<front>
2009<title abbrev="Internet Message Headers">Common Internet Message Headers</title>
2010<author initials="J." surname="Palme" fullname="Jacob Palme">
2011<organization>Stockholm University/KTH</organization>
2012<address>
2013<postal>
2014<street>Electrum 230</street>
2015<street>S-164 40 Kista</street>
2016<country>SE</country></postal>
2017<phone>+46 8 161667</phone>
2018<facsimile>+46 8 7830829</facsimile>
2019<email>jpalme@dsv.su.se</email></address></author>
2020<date month="February" year="1997"/>
2021<abstract>
2022<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>
2023<seriesInfo name="RFC" value="2076"/>
2024</reference>
2025
2026<reference anchor="RFC2279">
2027<front>
2028<title abbrev="UTF-8">UTF-8, a transformation format of ISO 10646</title>
2029<author initials="F." surname="Yergeau" fullname="Francois Yergeau">
2030<organization>Alis Technologies</organization>
2031<address>
2032<postal>
2033<street>100, boul. Alexis-Nihon</street>
2034<street>Suite 600</street>
2035<city>Montreal</city>
2036<region>Quebec</region>
2037<code>H4M 2P2</code>
2038<country>CA</country></postal>
2039<phone>+1 514 747 2547</phone>
2040<facsimile>+1 514 747 2561</facsimile>
2041<email>fyergeau@alis.com</email></address></author>
2042<date month="January" year="1998"/>
2043<abstract>
2044<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>
2045<seriesInfo name="RFC" value="2279"/>
2046</reference>
2047
2048<reference anchor="RFC2046">
2049<front>
2050<title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
2051<author initials="N." surname="Freed" fullname="Ned Freed">
2052<organization>Innosoft International, Inc.</organization>
2053<address>
2054<postal>
2055<street>1050 East Garvey Avenue South</street>
2056<city>West Covina</city>
2057<region>CA</region>
2058<code>91790</code>
2059<country>US</country></postal>
2060<phone>+1 818 919 3600</phone>
2061<facsimile>+1 818 919 3614</facsimile>
2062<email>ned@innosoft.com</email></address></author>
2063<author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2064<organization>First Virtual Holdings</organization>
2065<address>
2066<postal>
2067<street>25 Washington Avenue</street>
2068<city>Morristown</city>
2069<region>NJ</region>
2070<code>07960</code>
2071<country>US</country></postal>
2072<phone>+1 201 540 8967</phone>
2073<facsimile>+1 201 993 3032</facsimile>
2074<email>nsb@nsb.fv.com</email></address></author>
2075<date month="November" year="1996"/>
2076</front>
2077<seriesInfo name="RFC" value="2046"/>
2078</reference>
2079
2080<reference anchor="RFC2277">
2081<front>
2082<title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
2083<author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
2084<organization>UNINETT</organization>
2085<address>
2086<postal>
2087<street>P.O.Box 6883 Elgeseter</street>
2088<street>N-7002 TRONDHEIM</street>
2089<country>NORWAY</country></postal>
2090<phone>+47 73 59 70 94</phone>
2091<email>Harald.T.Alvestrand@uninett.no</email></address></author>
2092<date month="January" year="1998"/>
2093<area>Applications</area>
2094<keyword>Internet Engineering Task Force</keyword>
2095<keyword>character encoding</keyword></front>
2096<seriesInfo name="BCP" value="18"/>
2097<seriesInfo name="RFC" value="2277"/>
2098</reference>
2099
2100<reference anchor="RFC2110">
2101<front>
2102<title abbrev="MHTML">MIME E-mail Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
2103<author initials="J." surname="Palme" fullname="Jacob Palme">
2104<organization>Stockholm University and KTH</organization>
2105<address>
2106<postal>
2107<street>Electrum 230</street>
2108<street>S-164 40 Kista</street>
2109<country>Sweden</country></postal>
2110<phone>+46-8-16 16 67</phone>
2111<facsimile>+46-8-783 08 29</facsimile>
2112<email>jpalme@dsv.su.se</email></address></author>
2113<author initials="A." surname="Hopmann" fullname="Alex Hopmann">
2114<organization>Microsoft Corporation</organization>
2115<address>
2116<postal>
2117<street>3590 North First Street</street>
2118<street>Suite 300</street>
2119<street>San Jose</street>
2120<street>CA 95134</street>
2121<street>Working group chairman:</street></postal>
2122<email>alexhop@microsoft.com</email></address></author>
2123<date month="March" year="1997"/>
2124<area>Applications</area>
2125<keyword>encapsulate</keyword>
2126<keyword>hypertext markup language</keyword>
2127<keyword>mail</keyword>
2128<keyword>multipurpose internet mail extensions</keyword>
2129</front>
2130<seriesInfo name="RFC" value="2110"/>
2131</reference>
2132
2133<reference anchor="RFC2049">
2134<front>
2135<title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
2136<author initials="N." surname="Freed" fullname="Ned Freed">
2137<organization>Innosoft International, Inc.</organization>
2138<address>
2139<postal>
2140<street>1050 East Garvey Avenue South</street>
2141<street>West Covina</street>
2142<street>CA 91790</street>
2143<country>USA</country></postal>
2144<phone>+1 818 919 3600</phone>
2145<facsimile>+1 818 919 3614</facsimile>
2146<email>ned@innosoft.com</email></address></author>
2147<author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
2148<organization>First Virtual Holdings</organization>
2149<address>
2150<postal>
2151<street>25 Washington Avenue</street>
2152<street>Morristown</street>
2153<street>NJ 07960</street>
2154<country>USA</country></postal>
2155<phone>+1 201 540 8967</phone>
2156<facsimile>+1 201 993 3032</facsimile>
2157<email>nsb@nsb.fv.com</email></address></author>
2158<date month="November" year="1996"/>
2159<area>Applications</area>
2160<keyword>mail</keyword>
2161<keyword>multipurpose internet mail extensions</keyword>
2162</front>
2163<seriesInfo name="RFC" value="2049"/>
2164</reference>
2165
2166<reference anchor="RFC2183">
2167<front>
2168<title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
2169<author initials="R." surname="Troost" fullname="Rens Troost">
2170<organization>New Century Systems</organization>
2171<address>
2172<postal>
2173<street>324 East 41st Street #804</street>
2174<street>New York</street>
2175<street>NY</street>
2176<street>10017</street>
2177<country>USA</country></postal>
2178<phone>+1 (212) 557-2050</phone>
2179<facsimile>+1 (212) 557-2049</facsimile>
2180<email>rens@century.com</email></address></author>
2181<author initials="S." surname="Dorner" fullname="Steve Dorner">
2182<organization>QUALCOMM Incorporated</organization>
2183<address>
2184<postal>
2185<street>6455 Lusk Boulevard</street>
2186<street>San Diego</street>
2187<street>CA 92121</street>
2188<country>USA</country></postal>
2189<email>sdorner@qualcomm.com</email></address></author>
2190<author initials="K." surname="Moore" fullname="Keith Moore">
2191<organization>Department of Computer Science</organization>
2192<address>
2193<postal>
2194<street>University of Tennessee</street>
2195<street>Knoxville</street>
2196<street>107 Ayres Hall</street>
2197<street>Knoxville TN  37996-1301</street>
2198<country>USA</country></postal>
2199<phone>+1 (423) 974-5067</phone>
2200<facsimile>+1 (423) 974-8296</facsimile>
2201<email>moore@cs.utk.edu</email></address></author>
2202<date month="August" year="1997"/>
2203<area>Applications</area>
2204<keyword>MIME</keyword>
2205<keyword>internet message</keyword>
2206<keyword>multipurpose internet mail extensions</keyword>
2207</front>
2208<seriesInfo name="RFC" value="2183"/>
2209</reference>
2210
2211</references>
2212
2213<section title="Differences Between HTTP Entities and RFC 2045 Entities" anchor="differences.between.http.entities.and.rfc.2045.entities">
2214<t>
2215   HTTP/1.1 uses many of the constructs defined for Internet Mail (RFC
2216   822 <xref target="RFC822"/>) and the Multipurpose Internet Mail Extensions (MIME <xref target="RFC2045"/>) to
2217   allow entities to be transmitted in an open variety of
2218   representations and with extensible mechanisms. However, RFC 2045
2219   discusses mail, and HTTP has a few features that are different from
2220   those described in RFC 2045. These differences were carefully chosen
2221   to optimize performance over binary connections, to allow greater
2222   freedom in the use of new media types, to make date comparisons
2223   easier, and to acknowledge the practice of some early HTTP servers
2224   and clients.
2225</t>
2226<t>
2227   This appendix describes specific areas where HTTP differs from RFC
2228   2045. Proxies and gateways to strict MIME environments &SHOULD; be
2229   aware of these differences and provide the appropriate conversions
2230   where necessary. Proxies and gateways from MIME environments to HTTP
2231   also need to be aware of the differences because some conversions
2232   might be required.
2233</t>
2234<section title="MIME-Version" anchor="mime-version">
2235<t>
2236   HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
2237   include a single MIME-Version general-header field to indicate what
2238   version of the MIME protocol was used to construct the message. Use
2239   of the MIME-Version header field indicates that the message is in
2240   full compliance with the MIME protocol (as defined in RFC 2045<xref target="RFC2045"/>).
2241   Proxies/gateways are responsible for ensuring full compliance (where
2242   possible) when exporting HTTP messages to strict MIME environments.
2243</t>
2244<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="MIME-Version"/>
2245    MIME-Version   = "MIME-Version" ":" 1*DIGIT "." 1*DIGIT
2246</artwork></figure>
2247<t>
2248   MIME version "1.0" is the default for use in HTTP/1.1. However,
2249   HTTP/1.1 message parsing and semantics are defined by this document
2250   and not the MIME specification.
2251</t>
2252</section>
2253
2254<section title="Conversion to Canonical Form" anchor="conversion.to.canonical.form">
2255<t>
2256   RFC 2045 <xref target="RFC2045"/> requires that an Internet mail entity be converted to
2257   canonical form prior to being transferred, as described in section <xref target="RFC2049" x:fmt="number" x:sec="4"/>
2258   of RFC 2049 <xref target="RFC2049"/>. <xref target="canonicalization.and.text.defaults"/> of this document describes the forms
2259   allowed for subtypes of the "text" media type when transmitted over
2260   HTTP. RFC 2046 requires that content with a type of "text" represent
2261   line breaks as CRLF and forbids the use of CR or LF outside of line
2262   break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
2263   line break within text content when a message is transmitted over
2264   HTTP.
2265</t>
2266<t>
2267   Where it is possible, a proxy or gateway from HTTP to a strict MIME
2268   environment &SHOULD; translate all line breaks within the text media
2269   types described in <xref target="canonicalization.and.text.defaults"/> of this document to the RFC 2049
2270   canonical form of CRLF. Note, however, that this might be complicated
2271   by the presence of a Content-Encoding and by the fact that HTTP
2272   allows the use of some character sets which do not use octets 13 and
2273   10 to represent CR and LF, as is the case for some multi-byte
2274   character sets.
2275</t>
2276<t>
2277   Implementors should note that conversion will break any cryptographic
2278   checksums applied to the original content unless the original content
2279   is already in canonical form. Therefore, the canonical form is
2280   recommended for any content that uses such checksums in HTTP.
2281</t>
2282</section>
2283
2284<section title="Introduction of Content-Encoding" anchor="introduction.of.content-encoding">
2285<t>
2286   RFC 2045 does not include any concept equivalent to HTTP/1.1's
2287   Content-Encoding header field. Since this acts as a modifier on the
2288   media type, proxies and gateways from HTTP to MIME-compliant
2289   protocols &MUST; either change the value of the Content-Type header
2290   field or decode the entity-body before forwarding the message. (Some
2291   experimental applications of Content-Type for Internet mail have used
2292   a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
2293   a function equivalent to Content-Encoding. However, this parameter is
2294   not part of RFC 2045).
2295</t>
2296</section>
2297
2298<section title="No Content-Transfer-Encoding" anchor="no.content-transfer-encoding">
2299<t>
2300   HTTP does not use the Content-Transfer-Encoding (CTE) field of RFC
2301   2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
2302   remove any non-identity CTE ("quoted-printable" or "base64") encoding
2303   prior to delivering the response message to an HTTP client.
2304</t>
2305<t>
2306   Proxies and gateways from HTTP to MIME-compliant protocols are
2307   responsible for ensuring that the message is in the correct format
2308   and encoding for safe transport on that protocol, where "safe
2309   transport" is defined by the limitations of the protocol being used.
2310   Such a proxy or gateway &SHOULD; label the data with an appropriate
2311   Content-Transfer-Encoding if doing so will improve the likelihood of
2312   safe transport over the destination protocol.
2313</t>
2314</section>
2315
2316<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
2317<t>
2318   HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
2319   Proxies/gateways &MUST; remove any transfer-coding prior to
2320   forwarding a message via a MIME-compliant protocol.
2321</t>
2322</section>
2323
2324<section title="MHTML and Line Length Limitations" anchor="mhtml.line.length">
2325<t>
2326   HTTP implementations which share code with MHTML <xref target="RFC2110"/> implementations
2327   need to be aware of MIME line length limitations. Since HTTP does not
2328   have this limitation, HTTP does not fold long lines. MHTML messages
2329   being transported by HTTP follow all conventions of MHTML, including
2330   line length limitations and folding, canonicalization, etc., since
2331   HTTP transports all message-bodies as payload (see <xref target="multipart.types"/>) and
2332   does not interpret the content or any MIME header lines that might be
2333   contained therein.
2334</t>
2335</section>
2336</section>
2337
2338<section title="Additional Features" anchor="additional.features">
2339<t>
2340   RFC 1945 and RFC 2068 document protocol elements used by some
2341   existing HTTP implementations, but not consistently and correctly
2342   across most HTTP/1.1 applications. Implementors are advised to be
2343   aware of these features, but cannot rely upon their presence in, or
2344   interoperability with, other HTTP/1.1 applications. Some of these
2345   describe proposed experimental features, and some describe features
2346   that experimental deployment found lacking that are now addressed in
2347   the base HTTP/1.1 specification.
2348</t>
2349<t>
2350   A number of other headers, such as Content-Disposition and Title,
2351   from SMTP and MIME are also often implemented (see RFC 2076 <xref target="RFC2076"/>).
2352</t>
2353
2354<section title="Content-Disposition" anchor="content-disposition">
2355<iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
2356<iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
2357<t>
2358   The Content-Disposition response-header field has been proposed as a
2359   means for the origin server to suggest a default filename if the user
2360   requests that the content is saved to a file. This usage is derived
2361   from the definition of Content-Disposition in RFC 1806 <xref target="RFC1806"/>.
2362</t>
2363<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"/>
2364     content-disposition = "Content-Disposition" ":"
2365                           disposition-type *( ";" disposition-parm )
2366     disposition-type = "attachment" | disp-extension-token
2367     disposition-parm = filename-parm | disp-extension-parm
2368     filename-parm = "filename" "=" quoted-string
2369     disp-extension-token = token
2370     disp-extension-parm = token "=" ( token | quoted-string )
2371</artwork></figure>
2372<t>
2373   An example is
2374</t>
2375<figure><artwork type="example">
2376     Content-Disposition: attachment; filename="fname.ext"
2377</artwork></figure>
2378<t>
2379   The receiving user agent &SHOULD-NOT;  respect any directory path
2380   information present in the filename-parm parameter, which is the only
2381   parameter believed to apply to HTTP implementations at this time. The
2382   filename &SHOULD; be treated as a terminal component only.
2383</t>
2384<t>
2385   If this header is used in a response with the application/octet-stream
2386   content-type, the implied suggestion is that the user agent
2387   should not display the response, but directly enter a `save response
2388   as...' dialog.
2389</t>
2390<t>
2391   See <xref target="content-disposition.issues"/> for Content-Disposition security issues.
2392</t>
2393</section>
2394</section>
2395
2396<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2397<t>
2398   Charset wildcarding is introduced to avoid explosion of character set
2399   names in accept headers. (<xref target="header.accept-charset"/>)
2400</t>
2401<t>
2402   Content-Base was deleted from the specification: it was not
2403   implemented widely, and there is no simple, safe way to introduce it
2404   without a robust extension mechanism. In addition, it is used in a
2405   similar, but not identical fashion in MHTML <xref target="RFC2110"/>.
2406</t>
2407<t>
2408   A content-coding of "identity" was introduced, to solve problems
2409   discovered in caching. (<xref target="content.codings"/>)
2410</t>
2411<t>
2412   Quality Values of zero should indicate that "I don't want something"
2413   to allow clients to refuse a representation. (<xref target="quality.values"/>)
2414</t>
2415<t>
2416   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
2417   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
2418   specification, but not commonly implemented. See RFC 2068 <xref target="RFC2068"/>.
2419</t>
2420</section>
2421</back>
2422</rfc>
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