source: draft-ietf-httpbis/02/draft-ietf-httpbis-p2-semantics-02.xml @ 872

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1<?xml version="1.0" encoding="UTF-8"?>
2<!--
3    This XML document is the output of clean-for-DTD.xslt; a tool that strips
4    extensions to RFC2629(bis) from documents for processing with xml2rfc.
5-->
6<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
7<?rfc toc="yes" ?>
8<?rfc symrefs="yes" ?>
9<?rfc sortrefs="yes" ?>
10<?rfc compact="yes"?>
11<?rfc subcompact="no" ?>
12<?rfc linkmailto="no" ?>
13<?rfc editing="no" ?>
14<?rfc comments="yes"?>
15<?rfc inline="yes"?>
16<!DOCTYPE rfc
17  PUBLIC "" "rfc2629.dtd">
18<rfc obsoletes="2616" category="std" ipr="full3978" docName="draft-ietf-httpbis-p2-semantics-02">
19<front>
20
21  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
22
23  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
24    <organization abbrev="Day Software">Day Software</organization>
25    <address>
26      <postal>
27        <street>23 Corporate Plaza DR, Suite 280</street>
28        <city>Newport Beach</city>
29        <region>CA</region>
30        <code>92660</code>
31        <country>USA</country>
32      </postal>
33      <phone>+1-949-706-5300</phone>
34      <facsimile>+1-949-706-5305</facsimile>
35      <email>fielding@gbiv.com</email>
36      <uri>http://roy.gbiv.com/</uri>
37    </address>
38  </author>
39
40  <author initials="J." surname="Gettys" fullname="Jim Gettys">
41    <organization>One Laptop per Child</organization>
42    <address>
43      <postal>
44        <street>21 Oak Knoll Road</street>
45        <city>Carlisle</city>
46        <region>MA</region>
47        <code>01741</code>
48        <country>USA</country>
49      </postal>
50      <email>jg@laptop.org</email>
51      <uri>http://www.laptop.org/</uri>
52    </address>
53  </author>
54 
55  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
56    <organization abbrev="HP">Hewlett-Packard Company</organization>
57    <address>
58      <postal>
59        <street>HP Labs, Large Scale Systems Group</street>
60        <street>1501 Page Mill Road, MS 1177</street>
61        <city>Palo Alto</city>
62        <region>CA</region>
63        <code>94304</code>
64        <country>USA</country>
65      </postal>
66      <email>JeffMogul@acm.org</email>
67    </address>
68  </author>
69
70  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
71    <organization abbrev="Microsoft">Microsoft Corporation</organization>
72    <address>
73      <postal>
74        <street>1 Microsoft Way</street>
75        <city>Redmond</city>
76        <region>WA</region>
77        <code>98052</code>
78        <country>USA</country>
79      </postal>
80      <email>henrikn@microsoft.com</email>
81    </address>
82  </author>
83
84  <author initials="L." surname="Masinter" fullname="Larry Masinter">
85    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
86    <address>
87      <postal>
88        <street>345 Park Ave</street>
89        <city>San Jose</city>
90        <region>CA</region>
91        <code>95110</code>
92        <country>USA</country>
93      </postal>
94      <email>LMM@acm.org</email>
95      <uri>http://larry.masinter.net/</uri>
96    </address>
97  </author>
98 
99  <author initials="P." surname="Leach" fullname="Paul J. Leach">
100    <organization abbrev="Microsoft">Microsoft Corporation</organization>
101    <address>
102      <postal>
103        <street>1 Microsoft Way</street>
104        <city>Redmond</city>
105        <region>WA</region>
106        <code>98052</code>
107      </postal>
108      <email>paulle@microsoft.com</email>
109    </address>
110  </author>
111   
112  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
113    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
114    <address>
115      <postal>
116        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
117        <street>The Stata Center, Building 32</street>
118        <street>32 Vassar Street</street>
119        <city>Cambridge</city>
120        <region>MA</region>
121        <code>02139</code>
122        <country>USA</country>
123      </postal>
124      <email>timbl@w3.org</email>
125      <uri>http://www.w3.org/People/Berners-Lee/</uri>
126    </address>
127  </author>
128
129  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
130    <organization abbrev="W3C">World Wide Web Consortium</organization>
131    <address>
132      <postal>
133        <street>W3C / ERCIM</street>
134        <street>2004, rte des Lucioles</street>
135        <city>Sophia-Antipolis</city>
136        <region>AM</region>
137        <code>06902</code>
138        <country>France</country>
139      </postal>
140      <email>ylafon@w3.org</email>
141      <uri>http://www.raubacapeu.net/people/yves/</uri>
142    </address>
143  </author>
144
145  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
146    <organization abbrev="greenbytes">greenbytes GmbH</organization>
147    <address>
148      <postal>
149        <street>Hafenweg 16</street>
150        <city>Muenster</city><region>NW</region><code>48155</code>
151        <country>Germany</country>
152      </postal>
153      <phone>+49 251 2807760</phone>   
154      <facsimile>+49 251 2807761</facsimile>   
155      <email>julian.reschke@greenbytes.de</email>       
156      <uri>http://greenbytes.de/tech/webdav/</uri>     
157    </address>
158  </author>
159
160  <date month="February" year="2008" day="24"/>
161
162<abstract>
163<t>
164   The Hypertext Transfer Protocol (HTTP) is an application-level
165   protocol for distributed, collaborative, hypermedia information
166   systems. HTTP has been in use by the World Wide Web global information
167   initiative since 1990. This document is Part 2 of the seven-part specification
168   that defines the protocol referred to as "HTTP/1.1" and, taken together,
169   obsoletes RFC 2616.  Part 2 defines the semantics of HTTP messages
170   as expressed by request methods, request-header fields, response status codes,
171   and response-header fields.
172</t>
173</abstract>
174
175<note title="Editorial Note (To be removed by RFC Editor)">
176  <t>
177    Discussion of this draft should take place on the HTTPBIS working group
178    mailing list (ietf-http-wg@w3.org). The current issues list is
179    at <eref target="http://www.tools.ietf.org/wg/httpbis/trac/report/11"/>
180    and related documents (including fancy diffs) can be found at
181    <eref target="http://www.tools.ietf.org/wg/httpbis/"/>.
182  </t>
183  <t>
184    This draft incorporates those issue resolutions that were either
185    collected in the original RFC2616 errata list (<eref target="http://purl.org/NET/http-errata"/>),
186    or which were agreed upon on the mailing list between October 2006 and
187    November 2007 (as published in "draft-lafon-rfc2616bis-03").
188  </t>
189</note>
190</front>
191<middle>
192<section title="Introduction" anchor="introduction">
193<t>
194   This document defines HTTP/1.1 request and response semantics.  Each HTTP
195   message, as defined in <xref target="Part1"/>, is in the form of either a request or
196   a response.  An HTTP server listens on a connection for HTTP requests and
197   responds to each request, in the order received on that connection, with
198   one or more HTTP response messages.  This document defines the commonly
199   agreed upon semantics of the HTTP uniform interface, the intentions defined
200   by each request method, and the various response messages that might be
201   expected as a result of applying that method for the requested resource.
202</t>
203<t>
204   This document is currently disorganized in order to minimize the changes
205   between drafts and enable reviewers to see the smaller errata changes.
206   The next draft will reorganize the sections to better reflect the content.
207   In particular, the sections will be ordered according to the typical
208   processing of an HTTP request message (after message parsing): resource
209   mapping, general header fields, methods, request modifiers, response
210   status, and resource metadata.  The current mess reflects how widely
211   dispersed these topics and associated requirements had become in
212   <xref target="RFC2616"/>.
213</t>
214
215<section title="Requirements" anchor="intro.requirements">
216<t>
217   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
218   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
219   document are to be interpreted as described in <xref target="RFC2119"/>.
220</t>
221<t>
222   An implementation is not compliant if it fails to satisfy one or more
223   of the MUST or REQUIRED level requirements for the protocols it
224   implements. An implementation that satisfies all the MUST or REQUIRED
225   level and all the SHOULD level requirements for its protocols is said
226   to be "unconditionally compliant"; one that satisfies all the MUST
227   level requirements but not all the SHOULD level requirements for its
228   protocols is said to be "conditionally compliant."
229</t>
230</section>
231</section>
232
233<section title="Notational Conventions and Generic Grammar" anchor="notation">
234<t>
235  This specification uses the ABNF syntax defined in Section 2.1 of <xref target="Part1"/> and
236  the core rules defined in Section 2.2 of <xref target="Part1"/>:
237  <cref anchor="abnf.dep">ABNF syntax and basic rules will be adopted from RFC 5234, see
238  &lt;http://tools.ietf.org/wg/httpbis/trac/ticket/36&gt;.</cref>
239</t>
240<figure><artwork type="abnf2616"><![CDATA[
241  DIGIT         = <DIGIT, defined in [Part1], Section 2.2>
242]]></artwork></figure>
243<figure><artwork type="abnf2616"><![CDATA[
244  comment       = <comment, defined in [Part1], Section 2.2>
245  quoted-string = <quoted-string, defined in [Part1], Section 2.2>
246  token         = <token, defined in [Part1], Section 2.2>
247]]></artwork></figure>
248<t anchor="abnf.dependencies">
249  The ABNF rules below are defined in other parts:
250</t>
251<figure><!--Part1--><artwork type="abnf2616"><![CDATA[
252  absoluteURI   = <absoluteURI, defined in [Part1], Section 3.2.1>
253  fragment      = <fragment, defined in [Part1], Section 3.2.1>
254  Host          = <Host, defined in [Part1], Section 8.4>
255  HTTP-date     = <HTTP-date, defined in [Part1], Section 3.3.1>
256  product       = <product, defined in [Part1], Section 3.5>
257  relativeURI   = <relativeURI, defined in [Part1], Section 3.2.1>
258  TE            = <TE, defined in [Part1], Section 8.8>
259]]></artwork></figure>
260<figure><!--Part3--><artwork type="abnf2616"><![CDATA[
261  Accept        = <Accept, defined in [Part3], Section 6.1>
262  Accept-Charset =
263             <Accept-Charset, defined in [Part3], Section 6.2>
264  Accept-Encoding =
265             <Accept-Encoding, defined in [Part3], Section 6.3>
266  Accept-Language =
267             <Accept-Language, defined in [Part3], Section 6.4>
268]]></artwork></figure>
269<figure><!--Part4--><artwork type="abnf2616"><![CDATA[
270  ETag          = <ETag, defined in [Part4], Section 7.1>
271  If-Match      = <If-Match, defined in [Part4], Section 7.2>
272  If-Modified-Since =
273             <If-Modified-Since, defined in [Part4], Section 7.3>
274  If-None-Match = <If-None-Match, defined in [Part4], Section 7.4>
275  If-Unmodified-Since =
276             <If-Unmodified-Since, defined in [Part4], Section 7.5>
277]]></artwork></figure>
278<figure><!--Part5--><artwork type="abnf2616"><![CDATA[
279  Accept-Ranges = <Accept-Ranges, defined in [Part5], Section 6.1>
280  If-Range      = <If-Range, defined in [Part5], Section 6.3>
281  Range         = <Range, defined in [Part5], Section 6.4>
282]]></artwork></figure>
283<figure><!--Part6--><artwork type="abnf2616"><![CDATA[
284  Age           = <Age, defined in [Part6], Section 16.1>
285  Vary          = <Vary, defined in [Part6], Section 16.5>
286]]></artwork><!--Part7--></figure>
287<figure><artwork type="abnf2616"><![CDATA[
288  Authorization = <Authorization, defined in [Part7], Section 4.1>
289  Proxy-Authenticate =
290             <Proxy-Authenticate, defined in [Part7], Section 4.2>
291  Proxy-Authorization =
292             <Proxy-Authorization, defined in [Part7], Section 4.3>
293  WWW-Authenticate =
294             <WWW-Authenticate, defined in [Part7], Section 4.4>
295]]></artwork></figure>
296</section>
297
298<section title="Method" anchor="method">
299<t>
300   The Method  token indicates the method to be performed on the
301   resource identified by the Request-URI. The method is case-sensitive.
302</t>
303<figure><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/><artwork type="abnf2616"><![CDATA[
304  Method         = "OPTIONS"                ; Section 8.2
305                 | "GET"                    ; Section 8.3
306                 | "HEAD"                   ; Section 8.4
307                 | "POST"                   ; Section 8.5
308                 | "PUT"                    ; Section 8.6
309                 | "DELETE"                 ; Section 8.7
310                 | "TRACE"                  ; Section 8.8
311                 | "CONNECT"                ; Section 8.9
312                 | extension-method
313  extension-method = token
314]]></artwork></figure>
315<t>
316   The list of methods allowed by a resource can be specified in an
317   Allow header field (<xref target="header.allow"/>). The return code of the response
318   always notifies the client whether a method is currently allowed on a
319   resource, since the set of allowed methods can change dynamically. An
320   origin server SHOULD return the status code 405 (Method Not Allowed)
321   if the method is known by the origin server but not allowed for the
322   requested resource, and 501 (Not Implemented) if the method is
323   unrecognized or not implemented by the origin server. The methods GET
324   and HEAD MUST be supported by all general-purpose servers. All other
325   methods are OPTIONAL; however, if the above methods are implemented,
326   they MUST be implemented with the same semantics as those specified
327   in <xref target="method.definitions"/>.
328</t>
329</section>
330
331<section title="Request Header Fields" anchor="request.header.fields">
332<t>
333   The request-header fields allow the client to pass additional
334   information about the request, and about the client itself, to the
335   server. These fields act as request modifiers, with semantics
336   equivalent to the parameters on a programming language method
337   invocation.
338</t>
339<figure><iref primary="true" item="Grammar" subitem="request-header"/><artwork type="abnf2616"><![CDATA[
340  request-header = Accept                   ; [Part3], Section 6.1
341                 | Accept-Charset           ; [Part3], Section 6.2
342                 | Accept-Encoding          ; [Part3], Section 6.3
343                 | Accept-Language          ; [Part3], Section 6.4
344                 | Authorization            ; [Part7], Section 4.1
345                 | Expect                   ; Section 10.2
346                 | From                     ; Section 10.3
347                 | Host                     ; [Part1], Section 8.4
348                 | If-Match                 ; [Part4], Section 7.2
349                 | If-Modified-Since        ; [Part4], Section 7.3
350                 | If-None-Match            ; [Part4], Section 7.4
351                 | If-Range                 ; [Part5], Section 6.3
352                 | If-Unmodified-Since      ; [Part4], Section 7.5
353                 | Max-Forwards             ; Section 10.5
354                 | Proxy-Authorization      ; [Part7], Section 4.3
355                 | Range                    ; [Part5], Section 6.4
356                 | Referer                  ; Section 10.6
357                 | TE                       ; [Part1], Section 8.8
358                 | User-Agent               ; Section 10.9
359]]></artwork></figure>
360<t>
361   Request-header field names can be extended reliably only in
362   combination with a change in the protocol version. However, new or
363   experimental header fields MAY be given the semantics of request-header
364   fields if all parties in the communication recognize them to
365   be request-header fields. Unrecognized header fields are treated as
366   entity-header fields.
367</t>
368</section>
369
370<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
371<t>
372   The Status-Code element is a 3-digit integer result code of the
373   attempt to understand and satisfy the request. The status codes listed
374   below are defined in <xref target="status.codes"/>.
375   The Reason-Phrase is intended to give a short
376   textual description of the Status-Code. The Status-Code is intended
377   for use by automata and the Reason-Phrase is intended for the human
378   user. The client is not required to examine or display the Reason-Phrase.
379</t>
380<t> 
381   The individual values of the numeric status codes defined for
382   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
383   presented below. The reason phrases listed here are only
384   recommendations -- they MAY be replaced by local equivalents without
385   affecting the protocol.
386</t>
387<figure><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/><artwork type="abnf2616"><![CDATA[
388  Status-Code    =
389         "100"  ; Section 9.1.1: Continue
390       | "101"  ; Section 9.1.2: Switching Protocols
391       | "200"  ; Section 9.2.1: OK
392       | "201"  ; Section 9.2.2: Created
393       | "202"  ; Section 9.2.3: Accepted
394       | "203"  ; Section 9.2.4: Non-Authoritative Information
395       | "204"  ; Section 9.2.5: No Content
396       | "205"  ; Section 9.2.6: Reset Content
397       | "206"  ; Section 9.2.7: Partial Content
398       | "300"  ; Section 9.3.1: Multiple Choices
399       | "301"  ; Section 9.3.2: Moved Permanently
400       | "302"  ; Section 9.3.3: Found
401       | "303"  ; Section 9.3.4: See Other
402       | "304"  ; Section 9.3.5: Not Modified
403       | "305"  ; Section 9.3.6: Use Proxy
404       | "307"  ; Section 9.3.8: Temporary Redirect
405       | "400"  ; Section 9.4.1: Bad Request
406       | "401"  ; Section 9.4.2: Unauthorized
407       | "402"  ; Section 9.4.3: Payment Required
408       | "403"  ; Section 9.4.4: Forbidden
409       | "404"  ; Section 9.4.5: Not Found
410       | "405"  ; Section 9.4.6: Method Not Allowed
411       | "406"  ; Section 9.4.7: Not Acceptable
412       | "407"  ; Section 9.4.8: Proxy Authentication Required
413       | "408"  ; Section 9.4.9: Request Time-out
414       | "409"  ; Section 9.4.10: Conflict
415       | "410"  ; Section 9.4.11: Gone
416       | "411"  ; Section 9.4.12: Length Required
417       | "412"  ; Section 9.4.13: Precondition Failed
418       | "413"  ; Section 9.4.14: Request Entity Too Large
419       | "414"  ; Section 9.4.15: Request-URI Too Large
420       | "415"  ; Section 9.4.16: Unsupported Media Type
421       | "416"  ; Section 9.4.17: Requested range not satisfiable
422       | "417"  ; Section 9.4.18: Expectation Failed
423       | "500"  ; Section 9.5.1: Internal Server Error
424       | "501"  ; Section 9.5.2: Not Implemented
425       | "502"  ; Section 9.5.3: Bad Gateway
426       | "503"  ; Section 9.5.4: Service Unavailable
427       | "504"  ; Section 9.5.5: Gateway Time-out
428       | "505"  ; Section 9.5.6: HTTP Version not supported
429       | extension-code
430
431  extension-code = 3DIGIT
432  Reason-Phrase  = *<TEXT, excluding CR, LF>
433]]></artwork></figure>
434<t>
435   HTTP status codes are extensible. HTTP applications are not required
436   to understand the meaning of all registered status codes, though such
437   understanding is obviously desirable. However, applications MUST
438   understand the class of any status code, as indicated by the first
439   digit, and treat any unrecognized response as being equivalent to the
440   x00 status code of that class, with the exception that an
441   unrecognized response MUST NOT be cached. For example, if an
442   unrecognized status code of 431 is received by the client, it can
443   safely assume that there was something wrong with its request and
444   treat the response as if it had received a 400 status code. In such
445   cases, user agents SHOULD present to the user the entity returned
446   with the response, since that entity is likely to include human-readable
447   information which will explain the unusual status.
448</t>
449</section>
450
451<section title="Response Header Fields" anchor="response.header.fields">
452<t>
453   The response-header fields allow the server to pass additional
454   information about the response which cannot be placed in the Status-Line.
455   These header fields give information about the server and about
456   further access to the resource identified by the Request-URI.
457</t>
458<figure><iref primary="true" item="Grammar" subitem="response-header"/><artwork type="abnf2616"><![CDATA[
459  response-header = Accept-Ranges           ; [Part5], Section 6.1
460                  | Age                     ; [Part6], Section 16.1
461                  | ETag                    ; [Part4], Section 7.1
462                  | Location                ; Section 10.4
463                  | Proxy-Authenticate      ; [Part7], Section 4.2
464                  | Retry-After             ; Section 10.7
465                  | Server                  ; Section 10.8
466                  | Vary                    ; [Part6], Section 16.5
467                  | WWW-Authenticate        ; [Part7], Section 4.4
468]]></artwork></figure>
469<t>
470   Response-header field names can be extended reliably only in
471   combination with a change in the protocol version. However, new or
472   experimental header fields MAY be given the semantics of response-header
473   fields if all parties in the communication recognize them to
474   be response-header fields. Unrecognized header fields are treated as
475   entity-header fields.
476</t>
477</section>
478
479<section title="Entity" anchor="entity">
480<t>
481   Request and Response messages MAY transfer an entity if not otherwise
482   restricted by the request method or response status code. An entity
483   consists of entity-header fields and an entity-body, although some
484   responses will only include the entity-headers. HTTP entity-body and
485   entity-header fields are defined in <xref target="Part3"/>.
486</t>
487<t>
488   An entity-body is only present in a message when a message-body is
489   present, as described in Section 4.3 of <xref target="Part1"/>. The entity-body is obtained
490   from the message-body by decoding any Transfer-Encoding that might
491   have been applied to ensure safe and proper transfer of the message.
492</t>
493</section>
494
495
496<section title="Method Definitions" anchor="method.definitions">
497<t>
498   The set of common methods for HTTP/1.1 is defined below. Although
499   this set can be expanded, additional methods cannot be assumed to
500   share the same semantics for separately extended clients and servers.
501</t>
502
503<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
504
505<section title="Safe Methods" anchor="safe.methods">
506<t>
507   Implementors should be aware that the software represents the user in
508   their interactions over the Internet, and should be careful to allow
509   the user to be aware of any actions they might take which may have an
510   unexpected significance to themselves or others.
511</t>
512<t>
513   In particular, the convention has been established that the GET and
514   HEAD methods SHOULD NOT  have the significance of taking an action
515   other than retrieval. These methods ought to be considered "safe".
516   This allows user agents to represent other methods, such as POST, PUT
517   and DELETE, in a special way, so that the user is made aware of the
518   fact that a possibly unsafe action is being requested.
519</t>
520<t>
521   Naturally, it is not possible to ensure that the server does not
522   generate side-effects as a result of performing a GET request; in
523   fact, some dynamic resources consider that a feature. The important
524   distinction here is that the user did not request the side-effects,
525   so therefore cannot be held accountable for them.
526</t>
527</section>
528
529<section title="Idempotent Methods" anchor="idempotent.methods">
530<t>
531   Methods can also have the property of "idempotence" in that (aside
532   from error or expiration issues) the side-effects of N &gt; 0 identical
533   requests is the same as for a single request. The methods GET, HEAD,
534   PUT and DELETE share this property. Also, the methods OPTIONS and
535   TRACE SHOULD NOT  have side effects, and so are inherently idempotent.
536</t>
537<t>
538   However, it is possible that a sequence of several requests is non-idempotent,
539   even if all of the methods executed in that sequence are
540   idempotent. (A sequence is idempotent if a single execution of the
541   entire sequence always yields a result that is not changed by a
542   reexecution of all, or part, of that sequence.) For example, a
543   sequence is non-idempotent if its result depends on a value that is
544   later modified in the same sequence.
545</t>
546<t>
547   A sequence that never has side effects is idempotent, by definition
548   (provided that no concurrent operations are being executed on the
549   same set of resources).
550</t>
551</section>
552</section>
553
554<section title="OPTIONS" anchor="OPTIONS">
555  <iref primary="true" item="OPTIONS method"/>
556  <iref primary="true" item="Methods" subitem="OPTIONS"/>
557<t>
558   The OPTIONS method represents a request for information about the
559   communication options available on the request/response chain
560   identified by the Request-URI. This method allows the client to
561   determine the options and/or requirements associated with a resource,
562   or the capabilities of a server, without implying a resource action
563   or initiating a resource retrieval.
564</t>
565<t>
566   Responses to this method are not cacheable.
567</t>
568<t>
569   If the OPTIONS request includes an entity-body (as indicated by the
570   presence of Content-Length or Transfer-Encoding), then the media type
571   MUST be indicated by a Content-Type field. Although this
572   specification does not define any use for such a body, future
573   extensions to HTTP might use the OPTIONS body to make more detailed
574   queries on the server. A server that does not support such an
575   extension MAY discard the request body.
576</t>
577<t>
578   If the Request-URI is an asterisk ("*"), the OPTIONS request is
579   intended to apply to the server in general rather than to a specific
580   resource. Since a server's communication options typically depend on
581   the resource, the "*" request is only useful as a "ping" or "no-op"
582   type of method; it does nothing beyond allowing the client to test
583   the capabilities of the server. For example, this can be used to test
584   a proxy for HTTP/1.1 compliance (or lack thereof).
585</t>
586<t>
587   If the Request-URI is not an asterisk, the OPTIONS request applies
588   only to the options that are available when communicating with that
589   resource.
590</t>
591<t>
592   A 200 response SHOULD include any header fields that indicate
593   optional features implemented by the server and applicable to that
594   resource (e.g., Allow), possibly including extensions not defined by
595   this specification. The response body, if any, SHOULD also include
596   information about the communication options. The format for such a
597   body is not defined by this specification, but might be defined by
598   future extensions to HTTP. Content negotiation MAY be used to select
599   the appropriate response format. If no response body is included, the
600   response MUST include a Content-Length field with a field-value of
601   "0".
602</t>
603<t>
604   The Max-Forwards request-header field MAY be used to target a
605   specific proxy in the request chain. When a proxy receives an OPTIONS
606   request on an absoluteURI for which request forwarding is permitted,
607   the proxy MUST check for a Max-Forwards field. If the Max-Forwards
608   field-value is zero ("0"), the proxy MUST NOT forward the message;
609   instead, the proxy SHOULD respond with its own communication options.
610   If the Max-Forwards field-value is an integer greater than zero, the
611   proxy MUST decrement the field-value when it forwards the request. If
612   no Max-Forwards field is present in the request, then the forwarded
613   request MUST NOT include a Max-Forwards field.
614</t>
615</section>
616
617<section title="GET" anchor="GET">
618  <iref primary="true" item="GET method"/>
619  <iref primary="true" item="Methods" subitem="GET"/>
620<t>
621   The GET method means retrieve whatever information (in the form of an
622   entity) is identified by the Request-URI. If the Request-URI refers
623   to a data-producing process, it is the produced data which shall be
624   returned as the entity in the response and not the source text of the
625   process, unless that text happens to be the output of the process.
626</t>
627<t>
628   The semantics of the GET method change to a "conditional GET" if the
629   request message includes an If-Modified-Since, If-Unmodified-Since,
630   If-Match, If-None-Match, or If-Range header field. A conditional GET
631   method requests that the entity be transferred only under the
632   circumstances described by the conditional header field(s). The
633   conditional GET method is intended to reduce unnecessary network
634   usage by allowing cached entities to be refreshed without requiring
635   multiple requests or transferring data already held by the client.
636</t>
637<t>
638   The semantics of the GET method change to a "partial GET" if the
639   request message includes a Range header field. A partial GET requests
640   that only part of the entity be transferred, as described in Section 6.4 of <xref target="Part5"/>.
641   The partial GET method is intended to reduce unnecessary
642   network usage by allowing partially-retrieved entities to be
643   completed without transferring data already held by the client.
644</t>
645<t>
646   The response to a GET request is cacheable if and only if it meets
647   the requirements for HTTP caching described in <xref target="Part6"/>.
648</t>
649<t>
650   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
651</t>
652</section>
653
654<section title="HEAD" anchor="HEAD">
655  <iref primary="true" item="HEAD method"/>
656  <iref primary="true" item="Methods" subitem="HEAD"/>
657<t>
658   The HEAD method is identical to GET except that the server MUST NOT
659   return a message-body in the response. The metainformation contained
660   in the HTTP headers in response to a HEAD request SHOULD be identical
661   to the information sent in response to a GET request. This method can
662   be used for obtaining metainformation about the entity implied by the
663   request without transferring the entity-body itself. This method is
664   often used for testing hypertext links for validity, accessibility,
665   and recent modification.
666</t>
667<t>
668   The response to a HEAD request MAY be cacheable in the sense that the
669   information contained in the response MAY be used to update a
670   previously cached entity from that resource. If the new field values
671   indicate that the cached entity differs from the current entity (as
672   would be indicated by a change in Content-Length, Content-MD5, ETag
673   or Last-Modified), then the cache MUST treat the cache entry as
674   stale.
675</t>
676</section>
677
678<section title="POST" anchor="POST">
679  <iref primary="true" item="POST method"/>
680  <iref primary="true" item="Methods" subitem="POST"/>
681<t>
682   The POST method is used to request that the origin server accept the
683   entity enclosed in the request as data to be processed by the resource
684   identified by the Request-URI in the Request-Line. POST is designed
685   to allow a uniform method to cover the following functions:
686  <list style="symbols">
687    <t>
688      Annotation of existing resources;
689    </t>
690    <t>
691        Posting a message to a bulletin board, newsgroup, mailing list,
692        or similar group of articles;
693    </t>
694    <t>
695        Providing a block of data, such as the result of submitting a
696        form, to a data-handling process;
697    </t>
698    <t>
699        Extending a database through an append operation.
700    </t>
701  </list>
702</t>
703<t>
704   The actual function performed by the POST method is determined by the
705   server and is usually dependent on the Request-URI.
706</t>
707<t>
708   The action performed by the POST method might not result in a
709   resource that can be identified by a URI. In this case, either 200
710   (OK) or 204 (No Content) is the appropriate response status,
711   depending on whether or not the response includes an entity that
712   describes the result.
713</t>
714<t>
715   If a resource has been created on the origin server, the response
716   SHOULD be 201 (Created) and contain an entity which describes the
717   status of the request and refers to the new resource, and a Location
718   header (see <xref target="header.location"/>).
719</t>
720<t>
721   Responses to this method are not cacheable, unless the response
722   includes appropriate Cache-Control or Expires header fields. However,
723   the 303 (See Other) response can be used to direct the user agent to
724   retrieve a cacheable resource.
725</t>
726</section>
727
728<section title="PUT" anchor="PUT">
729  <iref primary="true" item="PUT method"/>
730  <iref primary="true" item="Methods" subitem="PUT"/>
731<t>
732   The PUT method requests that the enclosed entity be stored under the
733   supplied Request-URI. If the Request-URI refers to an already
734   existing resource, the enclosed entity SHOULD be considered as a
735   modified version of the one residing on the origin server. If the
736   Request-URI does not point to an existing resource, and that URI is
737   capable of being defined as a new resource by the requesting user
738   agent, the origin server can create the resource with that URI. If a
739   new resource is created at the Request-URI, the origin server MUST
740         inform the user agent
741   via the 201 (Created) response. If an existing resource is modified,
742   either the 200 (OK) or 204 (No Content) response codes SHOULD be sent
743   to indicate successful completion of the request. If the resource
744   could not be created or modified with the Request-URI, an appropriate
745   error response SHOULD be given that reflects the nature of the
746   problem. The recipient of the entity MUST NOT ignore any Content-*
747   (e.g. Content-Range) headers that it does not understand or implement
748   and MUST return a 501 (Not Implemented) response in such cases.
749</t>
750<t>
751   If the request passes through a cache and the Request-URI identifies
752   one or more currently cached entities, those entries SHOULD be
753   treated as stale. Responses to this method are not cacheable.
754</t>
755<t>
756   The fundamental difference between the POST and PUT requests is
757   reflected in the different meaning of the Request-URI. The URI in a
758   POST request identifies the resource that will handle the enclosed
759   entity. That resource might be a data-accepting process, a gateway to
760   some other protocol, or a separate entity that accepts annotations.
761   In contrast, the URI in a PUT request identifies the entity enclosed
762   with the request -- the user agent knows what URI is intended and the
763   server MUST NOT attempt to apply the request to some other resource.
764   If the server desires that the request be applied to a different URI,
765   it MUST send a 301 (Moved Permanently) response; the user agent MAY
766   then make its own decision regarding whether or not to redirect the
767   request.
768</t>
769<t>
770   A single resource MAY be identified by many different URIs. For
771   example, an article might have a URI for identifying "the current
772   version" which is separate from the URI identifying each particular
773   version. In this case, a PUT request on a general URI might result in
774   several other URIs being defined by the origin server.
775</t>
776<t>
777   HTTP/1.1 does not define how a PUT method affects the state of an
778   origin server.
779</t>
780<t>
781   Unless otherwise specified for a particular entity-header, the
782   entity-headers in the PUT request SHOULD be applied to the resource
783   created or modified by the PUT.
784</t>
785</section>
786
787<section title="DELETE" anchor="DELETE">
788  <iref primary="true" item="DELETE method"/>
789  <iref primary="true" item="Methods" subitem="DELETE"/>
790<t>
791   The DELETE method requests that the origin server delete the resource
792   identified by the Request-URI. This method MAY be overridden by human
793   intervention (or other means) on the origin server. The client cannot
794   be guaranteed that the operation has been carried out, even if the
795   status code returned from the origin server indicates that the action
796   has been completed successfully. However, the server SHOULD NOT
797   indicate success unless, at the time the response is given, it
798   intends to delete the resource or move it to an inaccessible
799   location.
800</t>
801<t>
802   A successful response SHOULD be 200 (OK) if the response includes an
803   entity describing the status, 202 (Accepted) if the action has not
804   yet been enacted, or 204 (No Content) if the action has been enacted
805   but the response does not include an entity.
806</t>
807<t>
808   If the request passes through a cache and the Request-URI identifies
809   one or more currently cached entities, those entries SHOULD be
810   treated as stale. Responses to this method are not cacheable.
811</t>
812</section>
813
814<section title="TRACE" anchor="TRACE">
815  <iref primary="true" item="TRACE method"/>
816  <iref primary="true" item="Methods" subitem="TRACE"/>
817<t>
818   The TRACE method is used to invoke a remote, application-layer loop-back
819   of the request message. The final recipient of the request
820   SHOULD reflect the message received back to the client as the
821   entity-body of a 200 (OK) response. The final recipient is either the
822   origin server or the first proxy or gateway to receive a Max-Forwards
823   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
824   MUST NOT include an entity.
825</t>
826<t>
827   TRACE allows the client to see what is being received at the other
828   end of the request chain and use that data for testing or diagnostic
829   information. The value of the Via header field (Section 8.9 of <xref target="Part1"/>) is of
830   particular interest, since it acts as a trace of the request chain.
831   Use of the Max-Forwards header field allows the client to limit the
832   length of the request chain, which is useful for testing a chain of
833   proxies forwarding messages in an infinite loop.
834</t>
835<t>
836   If the request is valid, the response SHOULD contain the entire
837   request message in the entity-body, with a Content-Type of
838   "message/http". Responses to this method MUST NOT be cached.
839</t>
840</section>
841
842<section title="CONNECT" anchor="CONNECT">
843  <iref primary="true" item="CONNECT method"/>
844  <iref primary="true" item="Methods" subitem="CONNECT"/>
845<t>
846   This specification reserves the method name CONNECT for use with a
847   proxy that can dynamically switch to being a tunnel (e.g. SSL
848   tunneling <xref target="Luo1998"/>).
849</t>
850</section>
851</section>
852
853
854<section title="Status Code Definitions" anchor="status.codes">
855<t>
856   Each Status-Code is described below, including a description of which
857   method(s) it can follow and any metainformation required in the
858   response.
859</t>
860
861<section title="Informational 1xx" anchor="status.1xx">
862<t>
863   This class of status code indicates a provisional response,
864   consisting only of the Status-Line and optional headers, and is
865   terminated by an empty line. There are no required headers for this
866   class of status code. Since HTTP/1.0 did not define any 1xx status
867   codes, servers MUST NOT send a 1xx response to an HTTP/1.0 client
868   except under experimental conditions.
869</t>
870<t>
871   A client MUST be prepared to accept one or more 1xx status responses
872   prior to a regular response, even if the client does not expect a 100
873   (Continue) status message. Unexpected 1xx status responses MAY be
874   ignored by a user agent.
875</t>
876<t>
877   Proxies MUST forward 1xx responses, unless the connection between the
878   proxy and its client has been closed, or unless the proxy itself
879   requested the generation of the 1xx response. (For example, if a
880   proxy adds a "Expect: 100-continue" field when it forwards a request,
881   then it need not forward the corresponding 100 (Continue)
882   response(s).)
883</t>
884
885<section title="100 Continue" anchor="status.100">
886  <iref primary="true" item="100 Continue (status code)"/>
887  <iref primary="true" item="Status Codes" subitem="100 Continue"/>
888<t>
889   The client SHOULD continue with its request. This interim response is
890   used to inform the client that the initial part of the request has
891   been received and has not yet been rejected by the server. The client
892   SHOULD continue by sending the remainder of the request or, if the
893   request has already been completed, ignore this response. The server
894   MUST send a final response after the request has been completed. See
895   Section 7.2.3 of <xref target="Part1"/> for detailed discussion of the use and handling of this
896   status code.
897</t>
898</section>
899
900<section title="101 Switching Protocols" anchor="status.101">
901  <iref primary="true" item="101 Switching Protocols (status code)"/>
902  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols"/>
903<t>
904   The server understands and is willing to comply with the client's
905   request, via the Upgrade message header field (Section 6.4 of <xref target="Part5"/>), for a
906   change in the application protocol being used on this connection. The
907   server will switch protocols to those defined by the response's
908   Upgrade header field immediately after the empty line which
909   terminates the 101 response.
910</t>
911<t>
912   The protocol SHOULD be switched only when it is advantageous to do
913   so. For example, switching to a newer version of HTTP is advantageous
914   over older versions, and switching to a real-time, synchronous
915   protocol might be advantageous when delivering resources that use
916   such features.
917</t>
918</section>
919</section>
920
921<section title="Successful 2xx" anchor="status.2xx">
922<t>
923   This class of status code indicates that the client's request was
924   successfully received, understood, and accepted.
925</t>
926
927<section title="200 OK" anchor="status.200">
928  <iref primary="true" item="200 OK (status code)"/>
929  <iref primary="true" item="Status Codes" subitem="200 OK"/>
930<t>
931   The request has succeeded. The information returned with the response
932   is dependent on the method used in the request, for example:
933  <list style="hanging">
934    <t hangText="GET">
935          an entity corresponding to the requested resource is sent in
936          the response;
937    </t>
938    <t hangText="HEAD">
939          the entity-header fields corresponding to the requested
940          resource are sent in the response without any message-body;
941    </t>
942    <t hangText="POST">
943      an entity describing or containing the result of the action;
944    </t>
945    <t hangText="TRACE">
946      an entity containing the request message as received by the
947      end server.
948    </t>
949  </list>
950</t>
951</section>
952
953<section title="201 Created" anchor="status.201">
954  <iref primary="true" item="201 Created (status code)"/>
955  <iref primary="true" item="Status Codes" subitem="201 Created"/>
956<t>
957   The request has been fulfilled and resulted in a new resource being
958   created. The newly created resource can be referenced by the URI(s)
959   returned in the entity of the response, with the most specific URI
960   for the resource given by a Location header field. The response
961   SHOULD include an entity containing a list of resource
962   characteristics and location(s) from which the user or user agent can
963   choose the one most appropriate. The entity format is specified by
964   the media type given in the Content-Type header field. The origin
965   server MUST create the resource before returning the 201 status code.
966   If the action cannot be carried out immediately, the server SHOULD
967   respond with 202 (Accepted) response instead.
968</t>
969<t>
970   A 201 response MAY contain an ETag response header field indicating
971   the current value of the entity tag for the requested variant just
972   created, see Section 7.1 of <xref target="Part4"/>.
973</t>
974</section>
975
976<section title="202 Accepted" anchor="status.202">
977  <iref primary="true" item="202 Accepted (status code)"/>
978  <iref primary="true" item="Status Codes" subitem="202 Accepted"/>
979<t>
980   The request has been accepted for processing, but the processing has
981   not been completed.  The request might or might not eventually be
982   acted upon, as it might be disallowed when processing actually takes
983   place. There is no facility for re-sending a status code from an
984   asynchronous operation such as this.
985</t>
986<t>
987   The 202 response is intentionally non-committal. Its purpose is to
988   allow a server to accept a request for some other process (perhaps a
989   batch-oriented process that is only run once per day) without
990   requiring that the user agent's connection to the server persist
991   until the process is completed. The entity returned with this
992   response SHOULD include an indication of the request's current status
993   and either a pointer to a status monitor or some estimate of when the
994   user can expect the request to be fulfilled.
995</t>
996</section>
997
998<section title="203 Non-Authoritative Information" anchor="status.203">
999  <iref primary="true" item="203 Non-Authoritative Information (status code)"/>
1000  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information"/>
1001<t>
1002   The returned metainformation in the entity-header is not the
1003   definitive set as available from the origin server, but is gathered
1004   from a local or a third-party copy. The set presented MAY be a subset
1005   or superset of the original version. For example, including local
1006   annotation information about the resource might result in a superset
1007   of the metainformation known by the origin server. Use of this
1008   response code is not required and is only appropriate when the
1009   response would otherwise be 200 (OK).
1010</t>
1011</section>
1012
1013<section title="204 No Content" anchor="status.204">
1014  <iref primary="true" item="204 No Content (status code)"/>
1015  <iref primary="true" item="Status Codes" subitem="204 No Content"/>
1016<t>
1017   The server has fulfilled the request but does not need to return an
1018   entity-body, and might want to return updated metainformation. The
1019   response MAY include new or updated metainformation in the form of
1020   entity-headers, which if present SHOULD be associated with the
1021   requested variant.
1022</t>
1023<t>
1024   If the client is a user agent, it SHOULD NOT  change its document view
1025   from that which caused the request to be sent. This response is
1026   primarily intended to allow input for actions to take place without
1027   causing a change to the user agent's active document view, although
1028   any new or updated metainformation SHOULD be applied to the document
1029   currently in the user agent's active view.
1030</t>
1031<t>
1032   The 204 response MUST NOT include a message-body, and thus is always
1033   terminated by the first empty line after the header fields.
1034</t>
1035</section>
1036
1037<section title="205 Reset Content" anchor="status.205">
1038  <iref primary="true" item="205 Reset Content (status code)"/>
1039  <iref primary="true" item="Status Codes" subitem="205 Reset Content"/>
1040<t>
1041   The server has fulfilled the request and the user agent SHOULD reset
1042   the document view which caused the request to be sent. This response
1043   is primarily intended to allow input for actions to take place via
1044   user input, followed by a clearing of the form in which the input is
1045   given so that the user can easily initiate another input action. The
1046   response MUST NOT include an entity.
1047</t>
1048</section>
1049
1050<section title="206 Partial Content" anchor="status.206">
1051  <iref primary="true" item="206 Partial Content (status code)"/>
1052  <iref primary="true" item="Status Codes" subitem="206 Partial Content"/>
1053<t>
1054   The server has fulfilled the partial GET request for the resource
1055   and the enclosed entity is a partial representation as defined in <xref target="Part5"/>.
1056</t>
1057</section>
1058</section>
1059
1060<section title="Redirection 3xx" anchor="status.3xx">
1061<t>
1062   This class of status code indicates that further action needs to be
1063   taken by the user agent in order to fulfill the request.  The action
1064   required MAY be carried out by the user agent without interaction
1065   with the user if and only if the method used in the second request is
1066   GET or HEAD. A client SHOULD detect infinite redirection loops, since
1067   such loops generate network traffic for each redirection.
1068  <list><t>
1069      Note: previous versions of this specification recommended a
1070      maximum of five redirections. Content developers should be aware
1071      that there might be clients that implement such a fixed
1072      limitation.
1073  </t></list>
1074</t>
1075
1076<section title="300 Multiple Choices" anchor="status.300">
1077  <iref primary="true" item="300 Multiple Choices (status code)"/>
1078  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices"/>
1079<t>
1080   The requested resource corresponds to any one of a set of
1081   representations, each with its own specific location, and agent-driven
1082   negotiation information (Section 5 of <xref target="Part3"/>) is being provided so that
1083   the user (or user agent) can select a preferred representation and
1084   redirect its request to that location.
1085</t>
1086<t>
1087   Unless it was a HEAD request, the response SHOULD include an entity
1088   containing a list of resource characteristics and location(s) from
1089   which the user or user agent can choose the one most appropriate. The
1090   entity format is specified by the media type given in the Content-Type
1091   header field. Depending upon the format and the capabilities of
1092   the user agent, selection of the most appropriate choice MAY be
1093   performed automatically. However, this specification does not define
1094   any standard for such automatic selection.
1095</t>
1096<t>
1097   If the server has a preferred choice of representation, it SHOULD
1098   include the specific URI for that representation in the Location
1099   field; user agents MAY use the Location field value for automatic
1100   redirection. This response is cacheable unless indicated otherwise.
1101</t>
1102</section>
1103
1104<section title="301 Moved Permanently" anchor="status.301">
1105  <iref primary="true" item="301 Moved Permanently (status code)"/>
1106  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently"/>
1107<t>
1108   The requested resource has been assigned a new permanent URI and any
1109   future references to this resource SHOULD use one of the returned
1110   URIs.  Clients with link editing capabilities ought to automatically
1111   re-link references to the Request-URI to one or more of the new
1112   references returned by the server, where possible. This response is
1113   cacheable unless indicated otherwise.
1114</t>
1115<t>
1116   The new permanent URI SHOULD be given by the Location field in the
1117   response. Unless the request method was HEAD, the entity of the
1118   response SHOULD contain a short hypertext note with a hyperlink to
1119   the new URI(s).
1120</t>
1121<t>
1122   If the 301 status code is received in response to a request method
1123   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1124   then the request MAY be automatically redirected by the user agent without
1125   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
1126   request unless it can be confirmed by the user, since this might
1127   change the conditions under which the request was issued.
1128  <list><t>
1129      Note: When automatically redirecting a POST request after
1130      receiving a 301 status code, some existing HTTP/1.0 user agents
1131      will erroneously change it into a GET request.
1132  </t></list>
1133</t>
1134</section>
1135
1136<section title="302 Found" anchor="status.302">
1137  <iref primary="true" item="302 Found (status code)"/>
1138  <iref primary="true" item="Status Codes" subitem="302 Found"/>
1139<t>
1140   The requested resource resides temporarily under a different URI.
1141   Since the redirection might be altered on occasion, the client SHOULD
1142   continue to use the Request-URI for future requests.  This response
1143   is only cacheable if indicated by a Cache-Control or Expires header
1144   field.
1145</t>
1146<t>
1147   The temporary URI SHOULD be given by the Location field in the
1148   response. Unless the request method was HEAD, the entity of the
1149   response SHOULD contain a short hypertext note with a hyperlink to
1150   the new URI(s).
1151</t>
1152<t>
1153   If the 302 status code is received in response to a request method
1154   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1155   then the request MAY be automatically redirected by the user agent without
1156   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
1157   request unless it can be confirmed by the user, since this might
1158   change the conditions under which the request was issued.
1159  <list><t>
1160      Note: <xref target="RFC1945"/> and <xref target="RFC2068"/> specify that the client is not allowed
1161      to change the method on the redirected request.  However, most
1162      existing user agent implementations treat 302 as if it were a 303
1163      response, performing a GET on the Location field-value regardless
1164      of the original request method. The status codes 303 and 307 have
1165      been added for servers that wish to make unambiguously clear which
1166      kind of reaction is expected of the client.
1167  </t></list>
1168</t>
1169</section>
1170
1171<section title="303 See Other" anchor="status.303">
1172  <iref primary="true" item="303 See Other (status code)"/>
1173  <iref primary="true" item="Status Codes" subitem="303 See Other"/>
1174<t>
1175   The response to the request can be found under a different URI and
1176   SHOULD be retrieved using a GET method on that resource. This method
1177   exists primarily to allow the output of a POST-activated script to
1178   redirect the user agent to a selected resource. The new URI is not a
1179   substitute reference for the originally requested resource. The 303
1180   response MUST NOT be cached, but the response to the second
1181   (redirected) request might be cacheable.
1182</t>
1183<t>
1184   The different URI SHOULD be given by the Location field in the
1185   response. Unless the request method was HEAD, the entity of the
1186   response SHOULD contain a short hypertext note with a hyperlink to
1187   the new URI(s).
1188  <list><t>
1189      Note: Many pre-HTTP/1.1 user agents do not understand the 303
1190      status. When interoperability with such clients is a concern, the
1191      302 status code may be used instead, since most user agents react
1192      to a 302 response as described here for 303.
1193  </t></list>
1194</t>
1195</section>
1196
1197<section title="304 Not Modified" anchor="status.304">
1198  <iref primary="true" item="304 Not Modified (status code)"/>
1199  <iref primary="true" item="Status Codes" subitem="304 Not Modified"/>
1200<t>
1201   The response to the request has not been modified since the conditions
1202   indicated by the client's conditional GET request, as defined in <xref target="Part4"/>.
1203</t>
1204</section>
1205
1206<section title="305 Use Proxy" anchor="status.305">
1207  <iref primary="true" item="305 Use Proxy (status code)"/>
1208  <iref primary="true" item="Status Codes" subitem="305 Use Proxy"/>
1209<t>
1210   The requested resource MUST be accessed through the proxy given by
1211   the Location field. The Location field gives the URI of the proxy.
1212   The recipient is expected to repeat this single request via the
1213   proxy. 305 responses MUST only be generated by origin servers.
1214  <list><t>
1215      Note: <xref target="RFC2068"/> was not clear that 305 was intended to redirect a
1216      single request, and to be generated by origin servers only.  Not
1217      observing these limitations has significant security consequences.
1218  </t></list>
1219</t>
1220</section>
1221
1222<section title="306 (Unused)" anchor="status.306">
1223  <iref primary="true" item="306 (Unused) (status code)"/>
1224  <iref primary="true" item="Status Codes" subitem="306 (Unused)"/>
1225<t>
1226   The 306 status code was used in a previous version of the
1227   specification, is no longer used, and the code is reserved.
1228</t>
1229</section>
1230
1231<section title="307 Temporary Redirect" anchor="status.307">
1232  <iref primary="true" item="307 Temporary Redirect (status code)"/>
1233  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect"/>
1234<t>
1235   The requested resource resides temporarily under a different URI.
1236   Since the redirection MAY be altered on occasion, the client SHOULD
1237   continue to use the Request-URI for future requests.  This response
1238   is only cacheable if indicated by a Cache-Control or Expires header
1239   field.
1240</t>
1241<t>
1242   The temporary URI SHOULD be given by the Location field in the
1243   response. Unless the request method was HEAD, the entity of the
1244   response SHOULD contain a short hypertext note with a hyperlink to
1245   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1246   understand the 307 status. Therefore, the note SHOULD contain the
1247   information necessary for a user to repeat the original request on
1248   the new URI.
1249</t>
1250<t>
1251   If the 307 status code is received in response to a request method
1252   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1253   then the request MAY be automatically redirected by the user agent without
1254   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
1255   request unless it can be confirmed by the user, since this might
1256   change the conditions under which the request was issued.
1257</t>
1258</section>
1259</section>
1260
1261<section title="Client Error 4xx" anchor="status.4xx">
1262<t>
1263   The 4xx class of status code is intended for cases in which the
1264   client seems to have erred. Except when responding to a HEAD request,
1265   the server SHOULD include an entity containing an explanation of the
1266   error situation, and whether it is a temporary or permanent
1267   condition. These status codes are applicable to any request method.
1268   User agents SHOULD display any included entity to the user.
1269</t>
1270<t>
1271   If the client is sending data, a server implementation using TCP
1272   SHOULD be careful to ensure that the client acknowledges receipt of
1273   the packet(s) containing the response, before the server closes the
1274   input connection. If the client continues sending data to the server
1275   after the close, the server's TCP stack will send a reset packet to
1276   the client, which may erase the client's unacknowledged input buffers
1277   before they can be read and interpreted by the HTTP application.
1278</t>
1279
1280<section title="400 Bad Request" anchor="status.400">
1281  <iref primary="true" item="400 Bad Request (status code)"/>
1282  <iref primary="true" item="Status Codes" subitem="400 Bad Request"/>
1283<t>
1284   The request could not be understood by the server due to malformed
1285   syntax. The client SHOULD NOT  repeat the request without
1286   modifications.
1287</t>
1288</section>
1289
1290<section title="401 Unauthorized" anchor="status.401">
1291  <iref primary="true" item="401 Unauthorized (status code)"/>
1292  <iref primary="true" item="Status Codes" subitem="401 Unauthorized"/>
1293<t>
1294   The request requires user authentication (see <xref target="Part7"/>).
1295</t>
1296</section>
1297
1298<section title="402 Payment Required" anchor="status.402">
1299  <iref primary="true" item="402 Payment Required (status code)"/>
1300  <iref primary="true" item="Status Codes" subitem="402 Payment Required"/>
1301<t>
1302   This code is reserved for future use.
1303</t>
1304</section>
1305
1306<section title="403 Forbidden" anchor="status.403">
1307  <iref primary="true" item="403 Forbidden (status code)"/>
1308  <iref primary="true" item="Status Codes" subitem="403 Forbidden"/>
1309<t>
1310   The server understood the request, but is refusing to fulfill it.
1311   Authorization will not help and the request SHOULD NOT  be repeated.
1312   If the request method was not HEAD and the server wishes to make
1313   public why the request has not been fulfilled, it SHOULD describe the
1314   reason for the refusal in the entity.  If the server does not wish to
1315   make this information available to the client, the status code 404
1316   (Not Found) can be used instead.
1317</t>
1318</section>
1319
1320<section title="404 Not Found" anchor="status.404">
1321  <iref primary="true" item="404 Not Found (status code)"/>
1322  <iref primary="true" item="Status Codes" subitem="404 Not Found"/>
1323<t>
1324   The server has not found anything matching the Request-URI. No
1325   indication is given of whether the condition is temporary or
1326   permanent. The 410 (Gone) status code SHOULD be used if the server
1327   knows, through some internally configurable mechanism, that an old
1328   resource is permanently unavailable and has no forwarding address.
1329   This status code is commonly used when the server does not wish to
1330   reveal exactly why the request has been refused, or when no other
1331   response is applicable.
1332</t>
1333</section>
1334
1335<section title="405 Method Not Allowed" anchor="status.405">
1336  <iref primary="true" item="405 Method Not Allowed (status code)"/>
1337  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed"/>
1338<t>
1339   The method specified in the Request-Line is not allowed for the
1340   resource identified by the Request-URI. The response MUST include an
1341   Allow header containing a list of valid methods for the requested
1342   resource.
1343</t>
1344</section>
1345
1346<section title="406 Not Acceptable" anchor="status.406">
1347  <iref primary="true" item="406 Not Acceptable (status code)"/>
1348  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable"/>
1349<t>
1350   The resource identified by the request is only capable of generating
1351   response entities which have content characteristics not acceptable
1352   according to the accept headers sent in the request.
1353</t>
1354<t>
1355   Unless it was a HEAD request, the response SHOULD include an entity
1356   containing a list of available entity characteristics and location(s)
1357   from which the user or user agent can choose the one most
1358   appropriate. The entity format is specified by the media type given
1359   in the Content-Type header field. Depending upon the format and the
1360   capabilities of the user agent, selection of the most appropriate
1361   choice MAY be performed automatically. However, this specification
1362   does not define any standard for such automatic selection.
1363  <list><t>
1364      Note: HTTP/1.1 servers are allowed to return responses which are
1365      not acceptable according to the accept headers sent in the
1366      request. In some cases, this may even be preferable to sending a
1367      406 response. User agents are encouraged to inspect the headers of
1368      an incoming response to determine if it is acceptable.
1369  </t></list>
1370</t>
1371<t>
1372   If the response could be unacceptable, a user agent SHOULD
1373   temporarily stop receipt of more data and query the user for a
1374   decision on further actions.
1375</t>
1376</section>
1377
1378<section title="407 Proxy Authentication Required" anchor="status.407">
1379  <iref primary="true" item="407 Proxy Authentication Required (status code)"/>
1380  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required"/>
1381<t>
1382   This code is similar to 401 (Unauthorized), but indicates that the
1383   client must first authenticate itself with the proxy (see <xref target="Part7"/>).
1384</t>
1385</section>
1386
1387<section title="408 Request Timeout" anchor="status.408">
1388  <iref primary="true" item="408 Request Timeout (status code)"/>
1389  <iref primary="true" item="Status Codes" subitem="408 Request Timeout"/>
1390<t>
1391   The client did not produce a request within the time that the server
1392   was prepared to wait. The client MAY repeat the request without
1393   modifications at any later time.
1394</t>
1395</section>
1396
1397<section title="409 Conflict" anchor="status.409">
1398  <iref primary="true" item="409 Conflict (status code)"/>
1399  <iref primary="true" item="Status Codes" subitem="409 Conflict"/>
1400<t>
1401   The request could not be completed due to a conflict with the current
1402   state of the resource. This code is only allowed in situations where
1403   it is expected that the user might be able to resolve the conflict
1404   and resubmit the request. The response body SHOULD include enough
1405   information for the user to recognize the source of the conflict.
1406   Ideally, the response entity would include enough information for the
1407   user or user agent to fix the problem; however, that might not be
1408   possible and is not required.
1409</t>
1410<t>
1411   Conflicts are most likely to occur in response to a PUT request. For
1412   example, if versioning were being used and the entity being PUT
1413   included changes to a resource which conflict with those made by an
1414   earlier (third-party) request, the server might use the 409 response
1415   to indicate that it can't complete the request. In this case, the
1416   response entity would likely contain a list of the differences
1417   between the two versions in a format defined by the response
1418   Content-Type.
1419</t>
1420</section>
1421
1422<section title="410 Gone" anchor="status.410">
1423  <iref primary="true" item="410 Gone (status code)"/>
1424  <iref primary="true" item="Status Codes" subitem="410 Gone"/>
1425<t>
1426   The requested resource is no longer available at the server and no
1427   forwarding address is known. This condition is expected to be
1428   considered permanent. Clients with link editing capabilities SHOULD
1429   delete references to the Request-URI after user approval. If the
1430   server does not know, or has no facility to determine, whether or not
1431   the condition is permanent, the status code 404 (Not Found) SHOULD be
1432   used instead. This response is cacheable unless indicated otherwise.
1433</t>
1434<t>
1435   The 410 response is primarily intended to assist the task of web
1436   maintenance by notifying the recipient that the resource is
1437   intentionally unavailable and that the server owners desire that
1438   remote links to that resource be removed. Such an event is common for
1439   limited-time, promotional services and for resources belonging to
1440   individuals no longer working at the server's site. It is not
1441   necessary to mark all permanently unavailable resources as "gone" or
1442   to keep the mark for any length of time -- that is left to the
1443   discretion of the server owner.
1444</t>
1445</section>
1446
1447<section title="411 Length Required" anchor="status.411">
1448  <iref primary="true" item="411 Length Required (status code)"/>
1449  <iref primary="true" item="Status Codes" subitem="411 Length Required"/>
1450<t>
1451   The server refuses to accept the request without a defined Content-Length.
1452   The client MAY repeat the request if it adds a valid
1453   Content-Length header field containing the length of the message-body
1454   in the request message.
1455</t>
1456</section>
1457
1458<section title="412 Precondition Failed" anchor="status.412">
1459  <iref primary="true" item="412 Precondition Failed (status code)"/>
1460  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed"/>
1461<t>
1462   The precondition given in one or more of the request-header fields
1463   evaluated to false when it was tested on the server, as defined in
1464   <xref target="Part4"/>.
1465</t>
1466</section>
1467
1468<section title="413 Request Entity Too Large" anchor="status.413">
1469  <iref primary="true" item="413 Request Entity Too Large (status code)"/>
1470  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large"/>
1471<t>
1472   The server is refusing to process a request because the request
1473   entity is larger than the server is willing or able to process. The
1474   server MAY close the connection to prevent the client from continuing
1475   the request.
1476</t>
1477<t>
1478   If the condition is temporary, the server SHOULD include a Retry-After
1479   header field to indicate that it is temporary and after what
1480   time the client MAY try again.
1481</t>
1482</section>
1483
1484<section title="414 Request-URI Too Long" anchor="status.414">
1485  <iref primary="true" item="414 Request-URI Too Long (status code)"/>
1486  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long"/>
1487<t>
1488   The server is refusing to service the request because the Request-URI
1489   is longer than the server is willing to interpret. This rare
1490   condition is only likely to occur when a client has improperly
1491   converted a POST request to a GET request with long query
1492   information, when the client has descended into a URI "black hole" of
1493   redirection (e.g., a redirected URI prefix that points to a suffix of
1494   itself), or when the server is under attack by a client attempting to
1495   exploit security holes present in some servers using fixed-length
1496   buffers for reading or manipulating the Request-URI.
1497</t>
1498</section>
1499
1500<section title="415 Unsupported Media Type" anchor="status.415">
1501  <iref primary="true" item="415 Unsupported Media Type (status code)"/>
1502  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type"/>
1503<t>
1504   The server is refusing to service the request because the entity of
1505   the request is in a format not supported by the requested resource
1506   for the requested method.
1507</t>
1508</section>
1509
1510<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1511  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)"/>
1512  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable"/>
1513<t>
1514   The request included a Range request-header field (Section 6.4 of <xref target="Part5"/>) and none of
1515   the range-specifier values in this field overlap the current extent
1516   of the selected resource.
1517</t>
1518</section>
1519
1520<section title="417 Expectation Failed" anchor="status.417">
1521  <iref primary="true" item="417 Expectation Failed (status code)"/>
1522  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed"/>
1523<t>
1524   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1525   could not be met by this server, or, if the server is a proxy,
1526   the server has unambiguous evidence that the request could not be met
1527   by the next-hop server.
1528</t>
1529</section>
1530</section>
1531
1532<section title="Server Error 5xx" anchor="status.5xx">
1533<t>
1534   Response status codes beginning with the digit "5" indicate cases in
1535   which the server is aware that it has erred or is incapable of
1536   performing the request. Except when responding to a HEAD request, the
1537   server SHOULD include an entity containing an explanation of the
1538   error situation, and whether it is a temporary or permanent
1539   condition. User agents SHOULD display any included entity to the
1540   user. These response codes are applicable to any request method.
1541</t>
1542
1543<section title="500 Internal Server Error" anchor="status.500">
1544  <iref primary="true" item="500 Internal Server Error (status code)"/>
1545  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error"/>
1546<t>
1547   The server encountered an unexpected condition which prevented it
1548   from fulfilling the request.
1549</t>
1550</section>
1551
1552<section title="501 Not Implemented" anchor="status.501">
1553  <iref primary="true" item="501 Not Implemented (status code)"/>
1554  <iref primary="true" item="Status Codes" subitem="501 Not Implemented"/>
1555<t>
1556   The server does not support the functionality required to fulfill the
1557   request. This is the appropriate response when the server does not
1558   recognize the request method and is not capable of supporting it for
1559   any resource.
1560</t>
1561</section>
1562
1563<section title="502 Bad Gateway" anchor="status.502">
1564  <iref primary="true" item="502 Bad Gateway (status code)"/>
1565  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway"/>
1566<t>
1567   The server, while acting as a gateway or proxy, received an invalid
1568   response from the upstream server it accessed in attempting to
1569   fulfill the request.
1570</t>
1571</section>
1572
1573<section title="503 Service Unavailable" anchor="status.503">
1574  <iref primary="true" item="503 Service Unavailable (status code)"/>
1575  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable"/>
1576<t>
1577   The server is currently unable to handle the request due to a
1578   temporary overloading or maintenance of the server. The implication
1579   is that this is a temporary condition which will be alleviated after
1580   some delay. If known, the length of the delay MAY be indicated in a
1581   Retry-After header. If no Retry-After is given, the client SHOULD
1582   handle the response as it would for a 500 response.
1583  <list><t>
1584      Note: The existence of the 503 status code does not imply that a
1585      server must use it when becoming overloaded. Some servers may wish
1586      to simply refuse the connection.
1587  </t></list>
1588</t>
1589</section>
1590
1591<section title="504 Gateway Timeout" anchor="status.504">
1592  <iref primary="true" item="504 Gateway Timeout (status code)"/>
1593  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout"/>
1594<t>
1595   The server, while acting as a gateway or proxy, did not receive a
1596   timely response from the upstream server specified by the URI (e.g.
1597   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1598   to access in attempting to complete the request.
1599  <list><t>
1600      Note: Note to implementors: some deployed proxies are known to
1601      return 400 or 500 when DNS lookups time out.
1602  </t></list>
1603</t>
1604</section>
1605
1606<section title="505 HTTP Version Not Supported" anchor="status.505">
1607  <iref primary="true" item="505 HTTP Version Not Supported (status code)"/>
1608  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported"/>
1609<t>
1610   The server does not support, or refuses to support, the protocol
1611   version that was used in the request message. The server is
1612   indicating that it is unable or unwilling to complete the request
1613   using the same major version as the client, as described in Section 3.1 of <xref target="Part1"/>,
1614   other than with this error message. The response SHOULD contain
1615   an entity describing why that version is not supported and what other
1616   protocols are supported by that server.
1617</t>
1618
1619</section>
1620</section>
1621</section>
1622
1623
1624<section title="Header Field Definitions" anchor="header.fields">
1625<t>
1626   This section defines the syntax and semantics of HTTP/1.1 header fields
1627   related to request and response semantics.
1628</t>
1629<t>
1630   For entity-header fields, both sender and recipient refer to either the
1631   client or the server, depending on who sends and who receives the entity.
1632</t>
1633
1634<section title="Allow" anchor="header.allow">
1635  <iref primary="true" item="Allow header"/>
1636  <iref primary="true" item="Headers" subitem="Allow"/>
1637<t>
1638      The Allow entity-header field lists the set of methods supported
1639      by the resource identified by the Request-URI. The purpose of this
1640      field is strictly to inform the recipient of valid methods
1641      associated with the resource. An Allow header field MUST be
1642      present in a 405 (Method Not Allowed) response.
1643</t>
1644<figure><iref primary="true" item="Grammar" subitem="Allow"/><artwork type="abnf2616"><![CDATA[
1645  Allow   = "Allow" ":" #Method
1646]]></artwork></figure>
1647<t>
1648      Example of use:
1649</t>
1650<figure><artwork type="example"><![CDATA[
1651       Allow: GET, HEAD, PUT
1652]]></artwork></figure>
1653<t>
1654      This field cannot prevent a client from trying other methods.
1655      However, the indications given by the Allow header field value
1656      SHOULD be followed. The actual set of allowed methods is defined
1657      by the origin server at the time of each request.
1658</t>
1659<t>
1660      The Allow header field MAY be provided with a PUT request to
1661      recommend the methods to be supported by the new or modified
1662      resource. The server is not required to support these methods and
1663      SHOULD include an Allow header in the response giving the actual
1664      supported methods.
1665</t>
1666<t>
1667      A proxy MUST NOT modify the Allow header field even if it does not
1668      understand all the methods specified, since the user agent might
1669      have other means of communicating with the origin server.
1670</t>
1671</section>
1672
1673<section title="Expect" anchor="header.expect">
1674  <iref primary="true" item="Expect header"/>
1675  <iref primary="true" item="Headers" subitem="Expect"/>
1676<t>
1677   The Expect request-header field is used to indicate that particular
1678   server behaviors are required by the client.
1679</t>
1680<figure><iref primary="true" item="Grammar" subitem="Expect"/><iref primary="true" item="Grammar" subitem="expectation"/><iref primary="true" item="Grammar" subitem="expectation-extension"/><iref primary="true" item="Grammar" subitem="expect-params"/><artwork type="abnf2616"><![CDATA[
1681  Expect       =  "Expect" ":" 1#expectation
1682 
1683  expectation  =  "100-continue" | expectation-extension
1684  expectation-extension =  token [ "=" ( token | quoted-string )
1685                           *expect-params ]
1686  expect-params =  ";" token [ "=" ( token | quoted-string ) ]
1687]]></artwork></figure>
1688<t>
1689   A server that does not understand or is unable to comply with any of
1690   the expectation values in the Expect field of a request MUST respond
1691   with appropriate error status. The server MUST respond with a 417
1692   (Expectation Failed) status if any of the expectations cannot be met
1693   or, if there are other problems with the request, some other 4xx
1694   status.
1695</t>
1696<t>
1697   This header field is defined with extensible syntax to allow for
1698   future extensions. If a server receives a request containing an
1699   Expect field that includes an expectation-extension that it does not
1700   support, it MUST respond with a 417 (Expectation Failed) status.
1701</t>
1702<t>
1703   Comparison of expectation values is case-insensitive for unquoted
1704   tokens (including the 100-continue token), and is case-sensitive for
1705   quoted-string expectation-extensions.
1706</t>
1707<t>
1708   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy MUST
1709   return a 417 (Expectation Failed) status if it receives a request
1710   with an expectation that it cannot meet. However, the Expect
1711   request-header itself is end-to-end; it MUST be forwarded if the
1712   request is forwarded.
1713</t>
1714<t>
1715   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1716   Expect header.
1717</t>
1718<t>
1719   See Section 7.2.3 of <xref target="Part1"/> for the use of the 100 (Continue) status.
1720</t>
1721</section>
1722
1723<section title="From" anchor="header.from">
1724  <iref primary="true" item="From header"/>
1725  <iref primary="true" item="Headers" subitem="From"/>
1726<t>
1727   The From request-header field, if given, SHOULD contain an Internet
1728   e-mail address for the human user who controls the requesting user
1729   agent. The address SHOULD be machine-usable, as defined by "mailbox"
1730   in Section 3.4 of <xref target="RFC2822"/>:
1731</t>
1732<figure><iref primary="true" item="Grammar" subitem="From"/><artwork type="abnf2616"><![CDATA[
1733  From    = "From" ":" mailbox
1734 
1735  mailbox = <mailbox, defined in [RFC2822], Section 3.4>
1736]]></artwork></figure>
1737<t>
1738   An example is:
1739</t>
1740<figure><artwork type="example"><![CDATA[
1741    From: webmaster@example.org
1742]]></artwork></figure>
1743<t>
1744   This header field MAY be used for logging purposes and as a means for
1745   identifying the source of invalid or unwanted requests. It SHOULD NOT
1746   be used as an insecure form of access protection. The interpretation
1747   of this field is that the request is being performed on behalf of the
1748   person given, who accepts responsibility for the method performed. In
1749   particular, robot agents SHOULD include this header so that the
1750   person responsible for running the robot can be contacted if problems
1751   occur on the receiving end.
1752</t>
1753<t>
1754   The Internet e-mail address in this field MAY be separate from the
1755   Internet host which issued the request. For example, when a request
1756   is passed through a proxy the original issuer's address SHOULD be
1757   used.
1758</t>
1759<t>
1760   The client SHOULD NOT  send the From header field without the user's
1761   approval, as it might conflict with the user's privacy interests or
1762   their site's security policy. It is strongly recommended that the
1763   user be able to disable, enable, and modify the value of this field
1764   at any time prior to a request.
1765</t>
1766</section>
1767
1768<section title="Location" anchor="header.location">
1769  <iref primary="true" item="Location header"/>
1770  <iref primary="true" item="Headers" subitem="Location"/>
1771<t>
1772   The Location response-header field is used to redirect the recipient
1773   to a location other than the Request-URI for completion of the
1774   request or identification of a new resource. For 201 (Created)
1775   responses, the Location is that of the new resource which was created
1776   by the request. For 3xx responses, the location SHOULD indicate the
1777   server's preferred URI for automatic redirection to the resource. The
1778   field value consists of a single absolute URI.
1779</t>
1780<figure><iref primary="true" item="Grammar" subitem="Location"/><artwork type="abnf2616"><![CDATA[
1781  Location       = "Location" ":" absoluteURI [ "#" fragment ]
1782]]></artwork></figure>
1783<t>
1784   An example is:
1785</t>
1786<figure><artwork type="example"><![CDATA[
1787    Location: http://www.example.org/pub/WWW/People.html
1788]]></artwork></figure>
1789<t>
1790  <list><t>
1791      Note: The Content-Location header field (Section 6.7 of <xref target="Part3"/>) differs
1792      from Location in that the Content-Location identifies the original
1793      location of the entity enclosed in the request. It is therefore
1794      possible for a response to contain header fields for both Location
1795      and Content-Location.
1796  </t></list>
1797</t>
1798<t>
1799   There are circumstances in which a fragment identifier in a Location URL would not be appropriate:
1800   <list style="symbols">
1801      <t>With a 201 Created response, because in this usage the Location header specifies the URL for the entire created resource.</t>
1802      <t>With a 300 Multiple Choices, since the choice decision is intended to be made on resource characteristics and not fragment characteristics.</t>
1803      <t>With 305 Use Proxy.</t>
1804   </list>
1805</t>
1806</section>
1807
1808<section title="Max-Forwards" anchor="header.max-forwards">
1809  <iref primary="true" item="Max-Forwards header"/>
1810  <iref primary="true" item="Headers" subitem="Max-Forwards"/>
1811<t>
1812   The Max-Forwards request-header field provides a mechanism with the
1813   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1814   number of proxies or gateways that can forward the request to the
1815   next inbound server. This can be useful when the client is attempting
1816   to trace a request chain which appears to be failing or looping in
1817   mid-chain.
1818</t>
1819<figure><iref primary="true" item="Grammar" subitem="Max-Forwards"/><artwork type="abnf2616"><![CDATA[
1820  Max-Forwards   = "Max-Forwards" ":" 1*DIGIT
1821]]></artwork></figure>
1822<t>
1823   The Max-Forwards value is a decimal integer indicating the remaining
1824   number of times this request message may be forwarded.
1825</t>
1826<t>
1827   Each proxy or gateway recipient of a TRACE or OPTIONS request
1828   containing a Max-Forwards header field MUST check and update its
1829   value prior to forwarding the request. If the received value is zero
1830   (0), the recipient MUST NOT forward the request; instead, it MUST
1831   respond as the final recipient. If the received Max-Forwards value is
1832   greater than zero, then the forwarded message MUST contain an updated
1833   Max-Forwards field with a value decremented by one (1).
1834</t>
1835<t>
1836   The Max-Forwards header field MAY be ignored for all other methods
1837   defined by this specification and for any extension methods for which
1838   it is not explicitly referred to as part of that method definition.
1839</t>
1840</section>
1841
1842<section title="Referer" anchor="header.referer">
1843  <iref primary="true" item="Referer header"/>
1844  <iref primary="true" item="Headers" subitem="Referer"/>
1845<t>
1846   The Referer[sic] request-header field allows the client to specify,
1847   for the server's benefit, the address (URI) of the resource from
1848   which the Request-URI was obtained (the "referrer", although the
1849   header field is misspelled.) The Referer request-header allows a
1850   server to generate lists of back-links to resources for interest,
1851   logging, optimized caching, etc. It also allows obsolete or mistyped
1852   links to be traced for maintenance. The Referer field MUST NOT be
1853   sent if the Request-URI was obtained from a source that does not have
1854   its own URI, such as input from the user keyboard.
1855</t>
1856<figure><iref primary="true" item="Grammar" subitem="Referer"/><artwork type="abnf2616"><![CDATA[
1857  Referer        = "Referer" ":" ( absoluteURI | relativeURI )
1858]]></artwork></figure>
1859<t>
1860   Example:
1861</t>
1862<figure><artwork type="example"><![CDATA[
1863    Referer: http://www.example.org/hypertext/Overview.html
1864]]></artwork></figure>
1865<t>
1866   If the field value is a relative URI, it SHOULD be interpreted
1867   relative to the Request-URI. The URI MUST NOT include a fragment. See
1868   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
1869</t>
1870</section>
1871
1872<section title="Retry-After" anchor="header.retry-after">
1873  <iref primary="true" item="Retry-After header"/>
1874  <iref primary="true" item="Headers" subitem="Retry-After"/>
1875<t>
1876   The Retry-After response-header field can be used with a 503 (Service
1877   Unavailable) response to indicate how long the service is expected to
1878   be unavailable to the requesting client. This field MAY also be used
1879   with any 3xx (Redirection) response to indicate the minimum time the
1880   user-agent is asked wait before issuing the redirected request. The
1881   value of this field can be either an HTTP-date or an integer number
1882   of seconds (in decimal) after the time of the response.
1883</t>
1884<figure><iref primary="true" item="Grammar" subitem="Retry-After"/><artwork type="abnf2616"><![CDATA[
1885  Retry-After   = "Retry-After" ":" ( HTTP-date | delta-seconds )
1886]]></artwork></figure>
1887<t>
1888   Time spans are non-negative decimal integers, representing time in
1889   seconds.
1890</t>
1891<figure><iref primary="true" item="Grammar" subitem="delta-seconds"/><artwork type="abnf2616"><![CDATA[
1892  delta-seconds  = 1*DIGIT
1893]]></artwork></figure>
1894<t>
1895   Two examples of its use are
1896</t>
1897<figure><artwork type="example"><![CDATA[
1898    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
1899    Retry-After: 120
1900]]></artwork></figure>
1901<t>
1902   In the latter example, the delay is 2 minutes.
1903</t>
1904</section>
1905
1906<section title="Server" anchor="header.server">
1907  <iref primary="true" item="Server header"/>
1908  <iref primary="true" item="Headers" subitem="Server"/>
1909<t>
1910   The Server response-header field contains information about the
1911   software used by the origin server to handle the request. The field
1912   can contain multiple product tokens (Section 3.5 of <xref target="Part1"/>) and comments
1913   identifying the server and any significant subproducts. The product
1914   tokens are listed in order of their significance for identifying the
1915   application.
1916</t>
1917<figure><iref primary="true" item="Grammar" subitem="Server"/><artwork type="abnf2616"><![CDATA[
1918  Server         = "Server" ":" 1*( product | comment )
1919]]></artwork></figure>
1920<t>
1921   Example:
1922</t>
1923<figure><artwork type="example"><![CDATA[
1924    Server: CERN/3.0 libwww/2.17
1925]]></artwork></figure>
1926<t>
1927   If the response is being forwarded through a proxy, the proxy
1928   application MUST NOT modify the Server response-header. Instead, it
1929   MUST include a Via field (as described in Section 8.9 of <xref target="Part1"/>).
1930  <list><t>
1931      Note: Revealing the specific software version of the server might
1932      allow the server machine to become more vulnerable to attacks
1933      against software that is known to contain security holes. Server
1934      implementors are encouraged to make this field a configurable
1935      option.
1936  </t></list>
1937</t>
1938</section>
1939
1940<section title="User-Agent" anchor="header.user-agent">
1941  <iref primary="true" item="User-Agent header"/>
1942  <iref primary="true" item="Headers" subitem="User-Agent"/>
1943<t>
1944   The User-Agent request-header field contains information about the
1945   user agent originating the request. This is for statistical purposes,
1946   the tracing of protocol violations, and automated recognition of user
1947   agents for the sake of tailoring responses to avoid particular user
1948   agent limitations. User agents SHOULD include this field with
1949   requests. The field can contain multiple product tokens (Section 3.5 of <xref target="Part1"/>)
1950   and comments identifying the agent and any subproducts which form a
1951   significant part of the user agent. By convention, the product tokens
1952   are listed in order of their significance for identifying the
1953   application.
1954</t>
1955<figure><iref primary="true" item="Grammar" subitem="User-Agent"/><artwork type="abnf2616"><![CDATA[
1956  User-Agent     = "User-Agent" ":" 1*( product | comment )
1957]]></artwork></figure>
1958<t>
1959   Example:
1960</t>
1961<figure><artwork type="example"><![CDATA[
1962    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1963]]></artwork></figure>
1964</section>
1965
1966</section>
1967
1968<section title="IANA Considerations" anchor="IANA.considerations">
1969<t>
1970   <cref>TBD.</cref>
1971</t>
1972</section>
1973
1974<section title="Security Considerations" anchor="security.considerations">
1975<t>
1976   This section is meant to inform application developers, information
1977   providers, and users of the security limitations in HTTP/1.1 as
1978   described by this document. The discussion does not include
1979   definitive solutions to the problems revealed, though it does make
1980   some suggestions for reducing security risks.
1981</t>
1982
1983<section title="Transfer of Sensitive Information" anchor="security.sensitive">
1984<t>
1985   Like any generic data transfer protocol, HTTP cannot regulate the
1986   content of the data that is transferred, nor is there any a priori
1987   method of determining the sensitivity of any particular piece of
1988   information within the context of any given request. Therefore,
1989   applications SHOULD supply as much control over this information as
1990   possible to the provider of that information. Four header fields are
1991   worth special mention in this context: Server, Via, Referer and From.
1992</t>
1993<t>
1994   Revealing the specific software version of the server might allow the
1995   server machine to become more vulnerable to attacks against software
1996   that is known to contain security holes. Implementors SHOULD make the
1997   Server header field a configurable option.
1998</t>
1999<t>
2000   Proxies which serve as a portal through a network firewall SHOULD
2001   take special precautions regarding the transfer of header information
2002   that identifies the hosts behind the firewall. In particular, they
2003   SHOULD remove, or replace with sanitized versions, any Via fields
2004   generated behind the firewall.
2005</t>
2006<t>
2007   The Referer header allows reading patterns to be studied and reverse
2008   links drawn. Although it can be very useful, its power can be abused
2009   if user details are not separated from the information contained in
2010   the Referer. Even when the personal information has been removed, the
2011   Referer header might indicate a private document's URI whose
2012   publication would be inappropriate.
2013</t>
2014<t>
2015   The information sent in the From field might conflict with the user's
2016   privacy interests or their site's security policy, and hence it
2017   SHOULD NOT  be transmitted without the user being able to disable,
2018   enable, and modify the contents of the field. The user MUST be able
2019   to set the contents of this field within a user preference or
2020   application defaults configuration.
2021</t>
2022<t>
2023   We suggest, though do not require, that a convenient toggle interface
2024   be provided for the user to enable or disable the sending of From and
2025   Referer information.
2026</t>
2027<t>
2028   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2029   fields can sometimes be used to determine that a specific client or
2030   server have a particular security hole which might be exploited.
2031   Unfortunately, this same information is often used for other valuable
2032   purposes for which HTTP currently has no better mechanism.
2033</t>
2034</section>
2035
2036<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
2037<t>
2038   Because the source of a link might be private information or might
2039   reveal an otherwise private information source, it is strongly
2040   recommended that the user be able to select whether or not the
2041   Referer field is sent. For example, a browser client could have a
2042   toggle switch for browsing openly/anonymously, which would
2043   respectively enable/disable the sending of Referer and From
2044   information.
2045</t>
2046<t>
2047   Clients SHOULD NOT include a Referer header field in a (non-secure)
2048   HTTP request if the referring page was transferred with a secure
2049   protocol.
2050</t>
2051<t>
2052   Authors of services should not use
2053   GET-based forms for the submission of sensitive data because that
2054   data will be encoded in the Request-URI. Many existing
2055   servers, proxies, and user agents log or display the Request-URI in
2056   places where it might be visible to third parties. Such services can
2057   use POST-based form submission instead.
2058</t>
2059</section>
2060
2061<section title="Location Headers and Spoofing" anchor="location.spoofing">
2062<t>
2063   If a single server supports multiple organizations that do not trust
2064   one another, then it MUST check the values of Location and Content-Location
2065   headers in responses that are generated under control of
2066   said organizations to make sure that they do not attempt to
2067   invalidate resources over which they have no authority.
2068</t>
2069</section>
2070
2071</section>
2072
2073<section title="Acknowledgments" anchor="ack">
2074</section>
2075</middle>
2076<back>
2077
2078<references title="Normative References">
2079
2080<reference anchor="Part1">
2081  <front>
2082    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2083    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2084      <organization abbrev="Day Software">Day Software</organization>
2085      <address><email>fielding@gbiv.com</email></address>
2086    </author>
2087    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2088      <organization>One Laptop per Child</organization>
2089      <address><email>jg@laptop.org</email></address>
2090    </author>
2091    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2092      <organization abbrev="HP">Hewlett-Packard Company</organization>
2093      <address><email>JeffMogul@acm.org</email></address>
2094    </author>
2095    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2096      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2097      <address><email>henrikn@microsoft.com</email></address>
2098    </author>
2099    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2100      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2101      <address><email>LMM@acm.org</email></address>
2102    </author>
2103    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2104      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2105      <address><email>paulle@microsoft.com</email></address>
2106    </author>
2107    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2108      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2109      <address><email>timbl@w3.org</email></address>
2110    </author>
2111    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2112      <organization abbrev="W3C">World Wide Web Consortium</organization>
2113      <address><email>ylafon@w3.org</email></address>
2114    </author>
2115    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2116      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2117      <address><email>julian.reschke@greenbytes.de</email></address>
2118    </author>
2119    <date month="February" year="2008"/>
2120  </front>
2121  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-02"/>
2122 
2123</reference>
2124
2125<reference anchor="Part3">
2126  <front>
2127    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2128    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2129      <organization abbrev="Day Software">Day Software</organization>
2130      <address><email>fielding@gbiv.com</email></address>
2131    </author>
2132    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2133      <organization>One Laptop per Child</organization>
2134      <address><email>jg@laptop.org</email></address>
2135    </author>
2136    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2137      <organization abbrev="HP">Hewlett-Packard Company</organization>
2138      <address><email>JeffMogul@acm.org</email></address>
2139    </author>
2140    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2141      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2142      <address><email>henrikn@microsoft.com</email></address>
2143    </author>
2144    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2145      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2146      <address><email>LMM@acm.org</email></address>
2147    </author>
2148    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2149      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2150      <address><email>paulle@microsoft.com</email></address>
2151    </author>
2152    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2153      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2154      <address><email>timbl@w3.org</email></address>
2155    </author>
2156    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2157      <organization abbrev="W3C">World Wide Web Consortium</organization>
2158      <address><email>ylafon@w3.org</email></address>
2159    </author>
2160    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2161      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2162      <address><email>julian.reschke@greenbytes.de</email></address>
2163    </author>
2164    <date month="February" year="2008"/>
2165  </front>
2166  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-02"/>
2167 
2168</reference>
2169
2170<reference anchor="Part4">
2171  <front>
2172    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2173    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2174      <organization abbrev="Day Software">Day Software</organization>
2175      <address><email>fielding@gbiv.com</email></address>
2176    </author>
2177    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2178      <organization>One Laptop per Child</organization>
2179      <address><email>jg@laptop.org</email></address>
2180    </author>
2181    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2182      <organization abbrev="HP">Hewlett-Packard Company</organization>
2183      <address><email>JeffMogul@acm.org</email></address>
2184    </author>
2185    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2186      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2187      <address><email>henrikn@microsoft.com</email></address>
2188    </author>
2189    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2190      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2191      <address><email>LMM@acm.org</email></address>
2192    </author>
2193    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2194      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2195      <address><email>paulle@microsoft.com</email></address>
2196    </author>
2197    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2198      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2199      <address><email>timbl@w3.org</email></address>
2200    </author>
2201    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2202      <organization abbrev="W3C">World Wide Web Consortium</organization>
2203      <address><email>ylafon@w3.org</email></address>
2204    </author>
2205    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2206      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2207      <address><email>julian.reschke@greenbytes.de</email></address>
2208    </author>
2209    <date month="February" year="2008"/>
2210  </front>
2211  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-02"/>
2212 
2213</reference>
2214
2215<reference anchor="Part5">
2216  <front>
2217    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2218    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2219      <organization abbrev="Day Software">Day Software</organization>
2220      <address><email>fielding@gbiv.com</email></address>
2221    </author>
2222    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2223      <organization>One Laptop per Child</organization>
2224      <address><email>jg@laptop.org</email></address>
2225    </author>
2226    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2227      <organization abbrev="HP">Hewlett-Packard Company</organization>
2228      <address><email>JeffMogul@acm.org</email></address>
2229    </author>
2230    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2231      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2232      <address><email>henrikn@microsoft.com</email></address>
2233    </author>
2234    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2235      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2236      <address><email>LMM@acm.org</email></address>
2237    </author>
2238    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2239      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2240      <address><email>paulle@microsoft.com</email></address>
2241    </author>
2242    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2243      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2244      <address><email>timbl@w3.org</email></address>
2245    </author>
2246    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2247      <organization abbrev="W3C">World Wide Web Consortium</organization>
2248      <address><email>ylafon@w3.org</email></address>
2249    </author>
2250    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2251      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2252      <address><email>julian.reschke@greenbytes.de</email></address>
2253    </author>
2254    <date month="February" year="2008"/>
2255  </front>
2256  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-02"/>
2257 
2258</reference>
2259
2260<reference anchor="Part6">
2261  <front>
2262    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2263    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2264      <organization abbrev="Day Software">Day Software</organization>
2265      <address><email>fielding@gbiv.com</email></address>
2266    </author>
2267    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2268      <organization>One Laptop per Child</organization>
2269      <address><email>jg@laptop.org</email></address>
2270    </author>
2271    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2272      <organization abbrev="HP">Hewlett-Packard Company</organization>
2273      <address><email>JeffMogul@acm.org</email></address>
2274    </author>
2275    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2276      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2277      <address><email>henrikn@microsoft.com</email></address>
2278    </author>
2279    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2280      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2281      <address><email>LMM@acm.org</email></address>
2282    </author>
2283    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2284      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2285      <address><email>paulle@microsoft.com</email></address>
2286    </author>
2287    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2288      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2289      <address><email>timbl@w3.org</email></address>
2290    </author>
2291    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2292      <organization abbrev="W3C">World Wide Web Consortium</organization>
2293      <address><email>ylafon@w3.org</email></address>
2294    </author>
2295    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2296      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2297      <address><email>julian.reschke@greenbytes.de</email></address>
2298    </author>
2299    <date month="February" year="2008"/>
2300  </front>
2301  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-02"/>
2302 
2303</reference>
2304
2305<reference anchor="Part7">
2306  <front>
2307    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2308    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2309      <organization abbrev="Day Software">Day Software</organization>
2310      <address><email>fielding@gbiv.com</email></address>
2311    </author>
2312    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2313      <organization>One Laptop per Child</organization>
2314      <address><email>jg@laptop.org</email></address>
2315    </author>
2316    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2317      <organization abbrev="HP">Hewlett-Packard Company</organization>
2318      <address><email>JeffMogul@acm.org</email></address>
2319    </author>
2320    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2321      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2322      <address><email>henrikn@microsoft.com</email></address>
2323    </author>
2324    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2325      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2326      <address><email>LMM@acm.org</email></address>
2327    </author>
2328    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2329      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2330      <address><email>paulle@microsoft.com</email></address>
2331    </author>
2332    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2333      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2334      <address><email>timbl@w3.org</email></address>
2335    </author>
2336    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2337      <organization abbrev="W3C">World Wide Web Consortium</organization>
2338      <address><email>ylafon@w3.org</email></address>
2339    </author>
2340    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2341      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2342      <address><email>julian.reschke@greenbytes.de</email></address>
2343    </author>
2344    <date month="February" year="2008"/>
2345  </front>
2346  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-02"/>
2347 
2348</reference>
2349
2350<reference anchor="RFC2119">
2351  <front>
2352    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2353    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2354      <organization>Harvard University</organization>
2355      <address><email>sob@harvard.edu</email></address>
2356    </author>
2357    <date month="March" year="1997"/>
2358  </front>
2359  <seriesInfo name="BCP" value="14"/>
2360  <seriesInfo name="RFC" value="2119"/>
2361</reference>
2362
2363</references>
2364
2365<references title="Informative References">
2366
2367<reference anchor="Luo1998">
2368  <front>
2369    <title>Tunneling TCP based protocols through Web proxy servers</title>
2370    <author initials="A." surname="Luotonen" fullname="A. Luotonen">
2371      <organization/>
2372    </author>
2373    <date year="1998" month="August"/>
2374  </front>
2375  <seriesInfo name="Internet-Draft" value="draft-luotonen-web-proxy-tunneling-01"/>
2376</reference>
2377
2378<reference anchor="RFC1945">
2379  <front>
2380    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2381    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2382      <organization>MIT, Laboratory for Computer Science</organization>
2383      <address><email>timbl@w3.org</email></address>
2384    </author>
2385    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2386      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2387      <address><email>fielding@ics.uci.edu</email></address>
2388    </author>
2389    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2390      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2391      <address><email>frystyk@w3.org</email></address>
2392    </author>
2393    <date month="May" year="1996"/>
2394  </front>
2395  <seriesInfo name="RFC" value="1945"/>
2396</reference>
2397
2398<reference anchor="RFC2068">
2399  <front>
2400    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2401    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2402      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2403      <address><email>fielding@ics.uci.edu</email></address>
2404    </author>
2405    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2406      <organization>MIT Laboratory for Computer Science</organization>
2407      <address><email>jg@w3.org</email></address>
2408    </author>
2409    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2410      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2411      <address><email>mogul@wrl.dec.com</email></address>
2412    </author>
2413    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2414      <organization>MIT Laboratory for Computer Science</organization>
2415      <address><email>frystyk@w3.org</email></address>
2416    </author>
2417    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2418      <organization>MIT Laboratory for Computer Science</organization>
2419      <address><email>timbl@w3.org</email></address>
2420    </author>
2421    <date month="January" year="1997"/>
2422  </front>
2423  <seriesInfo name="RFC" value="2068"/>
2424</reference>
2425
2426<reference anchor="RFC2616">
2427  <front>
2428    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2429    <author initials="R." surname="Fielding" fullname="R. Fielding">
2430      <organization>University of California, Irvine</organization>
2431      <address><email>fielding@ics.uci.edu</email></address>
2432    </author>
2433    <author initials="J." surname="Gettys" fullname="J. Gettys">
2434      <organization>W3C</organization>
2435      <address><email>jg@w3.org</email></address>
2436    </author>
2437    <author initials="J." surname="Mogul" fullname="J. Mogul">
2438      <organization>Compaq Computer Corporation</organization>
2439      <address><email>mogul@wrl.dec.com</email></address>
2440    </author>
2441    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2442      <organization>MIT Laboratory for Computer Science</organization>
2443      <address><email>frystyk@w3.org</email></address>
2444    </author>
2445    <author initials="L." surname="Masinter" fullname="L. Masinter">
2446      <organization>Xerox Corporation</organization>
2447      <address><email>masinter@parc.xerox.com</email></address>
2448    </author>
2449    <author initials="P." surname="Leach" fullname="P. Leach">
2450      <organization>Microsoft Corporation</organization>
2451      <address><email>paulle@microsoft.com</email></address>
2452    </author>
2453    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2454      <organization>W3C</organization>
2455      <address><email>timbl@w3.org</email></address>
2456    </author>
2457    <date month="June" year="1999"/>
2458  </front>
2459  <seriesInfo name="RFC" value="2616"/>
2460</reference>
2461
2462<reference anchor="RFC2822">
2463  <front>
2464    <title>Internet Message Format</title>
2465    <author initials="P." surname="Resnick" fullname="P. Resnick">
2466      <organization>QUALCOMM Incorporated</organization>
2467    </author>
2468    <date year="2001" month="April"/>
2469  </front> 
2470  <seriesInfo name="RFC" value="2822"/>
2471</reference>
2472
2473</references>
2474
2475<section title="Compatibility with Previous Versions" anchor="compatibility">
2476<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2477<t>
2478   Clarified which error code should be used for inbound server failures
2479   (e.g. DNS failures). (<xref target="status.504"/>).
2480</t>
2481<t>
2482   201 (Created) had a race that required an Etag be sent when a resource is
2483   first created. (<xref target="status.201"/>).
2484</t>
2485<t>
2486   Rewrite of message transmission requirements to make it much harder
2487   for implementors to get it wrong, as the consequences of errors here
2488   can have significant impact on the Internet, and to deal with the
2489   following problems:
2490  <list style="numbers">
2491      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
2492         this was incorrectly placing a requirement on the behavior of
2493         an implementation of a future version of HTTP/1.x</t>
2494
2495      <t>Made it clear that user-agents should retry requests, not
2496         "clients" in general.</t>
2497
2498      <t>Converted requirements for clients to ignore unexpected 100
2499         (Continue) responses, and for proxies to forward 100 responses,
2500         into a general requirement for 1xx responses.</t>
2501
2502      <t>Modified some TCP-specific language, to make it clearer that
2503         non-TCP transports are possible for HTTP.</t>
2504
2505      <t>Require that the origin server MUST NOT wait for the request
2506         body before it sends a required 100 (Continue) response.</t>
2507
2508      <t>Allow, rather than require, a server to omit 100 (Continue) if
2509         it has already seen some of the request body.</t>
2510
2511      <t>Allow servers to defend against denial-of-service attacks and
2512         broken clients.</t>
2513  </list>
2514</t>
2515<t>
2516   This change adds the Expect header and 417 status code.
2517</t>
2518<t>
2519   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
2520   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
2521</t>
2522<t>
2523   The PATCH<iref item="PATCH method" primary="true"/><iref item="Methods" subitem="PATCH" primary="true"/>, LINK<iref item="LINK method" primary="true"/><iref item="Methods" subitem="LINK" primary="true"/>, UNLINK<iref item="UNLINK method" primary="true"/><iref item="Methods" subitem="UNLINK" primary="true"/> methods were defined but not commonly
2524   implemented in previous versions of this specification. See <xref target="RFC2068"/>.
2525</t>
2526</section>
2527
2528<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2529<t>
2530  Clarify definition of POST.
2531  (<xref target="POST"/>)
2532</t>
2533<t>
2534  Failed to consider that there are
2535  many other request methods that are safe to automatically redirect,
2536  and further that the user agent is able to make that determination
2537  based on the request method semantics.
2538  (Sections <xref format="counter" target="status.301"/>,
2539  <xref format="counter" target="status.302"/> and
2540  <xref format="counter" target="status.307"/> )
2541</t>
2542<t>
2543  Correct syntax of Location header to allow fragment,
2544  as referred symbol wasn't what was expected, and add some
2545  clarifications as to when it would not be appropriate.
2546  (<xref target="header.location"/>)
2547</t>
2548<t>
2549  In the description of the Server header, the Via field
2550  was described as a SHOULD. The requirement was and is stated
2551  correctly in the description of the Via header in Section 8.9 of <xref target="Part1"/>.
2552  (<xref target="header.server"/>)
2553</t>
2554</section>
2555
2556</section>
2557
2558<section title="Change Log (to be removed by RFC Editor before publication)">
2559
2560<section title="Since RFC2616">
2561<t>
2562  Extracted relevant partitions from <xref target="RFC2616"/>.
2563</t>
2564</section>
2565
2566<section title="Since draft-ietf-httpbis-p2-semantics-00">
2567<t>
2568  Closed issues:
2569  <list style="symbols"> 
2570    <t>
2571      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
2572      "Via is a MUST"
2573      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
2574    </t>
2575    <t>
2576      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
2577      "Fragments allowed in Location"
2578      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
2579    </t>
2580    <t>
2581      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
2582      "Safe Methods vs Redirection"
2583      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
2584    </t>
2585    <t>
2586      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
2587      "Revise description of the POST method"
2588      (<eref target="http://purl.org/NET/http-errata#post"/>)
2589    </t>
2590    <t>
2591      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2592      "Normative and Informative references"
2593    </t>
2594    <t>
2595      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
2596      "RFC2606 Compliance"
2597    </t>
2598    <t>
2599      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2600      "Informative references"
2601    </t>
2602    <t>
2603      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
2604      "Redundant cross-references"
2605    </t>
2606  </list>
2607</t>
2608<t>
2609  Other changes:
2610  <list style="symbols"> 
2611    <t>
2612      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
2613    </t>
2614  </list>
2615</t>
2616</section>
2617
2618<section title="Since draft-ietf-httpbis-p2-semantics-01">
2619<t>
2620  Closed issues:
2621  <list style="symbols"> 
2622    <t>
2623      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
2624      "PUT side effects"
2625    </t>
2626    <t>
2627      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
2628      "Duplicate Host header requirements"
2629    </t>
2630  </list>
2631</t>
2632<t>
2633  Ongoing work on ABNF conversion (<eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2634  <list style="symbols"> 
2635    <t>
2636      Move "Product Tokens" section (back) into Part 1, as "token" is used
2637      in the definition of the Upgrade header.
2638    </t>
2639    <t>
2640      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2641    </t>
2642    <t>
2643      Copy definition of delta-seconds from Part6 instead of referencing it.
2644    </t>
2645  </list>
2646</t>
2647</section>
2648
2649</section>
2650
2651</back>
2652</rfc>
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