source: draft-ietf-httpbis/04/draft-ietf-httpbis-p2-semantics-04.xml @ 875

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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" updates="2817" category="std" ipr="full3978" docName="draft-ietf-httpbis-p2-semantics-04">
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="August" year="2008" day="29"/>
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    The changes in this draft are summarized in <xref target="changes.since.02"/>.
185  </t>
186</note>
187</front>
188<middle>
189<section title="Introduction" anchor="introduction">
190<t>
191   This document defines HTTP/1.1 request and response semantics.  Each HTTP
192   message, as defined in <xref target="Part1"/>, is in the form of either a request or
193   a response.  An HTTP server listens on a connection for HTTP requests and
194   responds to each request, in the order received on that connection, with
195   one or more HTTP response messages.  This document defines the commonly
196   agreed upon semantics of the HTTP uniform interface, the intentions defined
197   by each request method, and the various response messages that might be
198   expected as a result of applying that method for the requested resource.
199</t>
200<t>
201   This document is currently disorganized in order to minimize the changes
202   between drafts and enable reviewers to see the smaller errata changes.
203   The next draft will reorganize the sections to better reflect the content.
204   In particular, the sections will be ordered according to the typical
205   processing of an HTTP request message (after message parsing): resource
206   mapping, general header fields, methods, request modifiers, response
207   status, and resource metadata.  The current mess reflects how widely
208   dispersed these topics and associated requirements had become in
209   <xref target="RFC2616"/>.
210</t>
211
212<section title="Requirements" anchor="intro.requirements">
213<t>
214   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
215   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
216   document are to be interpreted as described in <xref target="RFC2119"/>.
217</t>
218<t>
219   An implementation is not compliant if it fails to satisfy one or more
220   of the MUST or REQUIRED level requirements for the protocols it
221   implements. An implementation that satisfies all the MUST or REQUIRED
222   level and all the SHOULD level requirements for its protocols is said
223   to be "unconditionally compliant"; one that satisfies all the MUST
224   level requirements but not all the SHOULD level requirements for its
225   protocols is said to be "conditionally compliant."
226</t>
227</section>
228</section>
229
230<section title="Notational Conventions and Generic Grammar" anchor="notation">
231 
232 
233 
234 
235<t>
236  This specification uses the ABNF syntax defined in Section 2.1 of <xref target="Part1"/> and
237  the core rules defined in Section 2.2 of <xref target="Part1"/>:
238  <cref anchor="abnf.dep">ABNF syntax and basic rules will be adopted from RFC 5234, see
239  &lt;http://tools.ietf.org/wg/httpbis/trac/ticket/36&gt;.</cref>
240</t>
241<figure><artwork type="abnf2616"><![CDATA[
242  DIGIT         = <DIGIT, defined in [Part1], Section 2.2>
243]]></artwork></figure>
244<figure><artwork type="abnf2616"><![CDATA[
245  comment       = <comment, defined in [Part1], Section 2.2>
246  quoted-string = <quoted-string, defined in [Part1], Section 2.2>
247  token         = <token, defined in [Part1], Section 2.2>
248]]></artwork></figure>
249<t anchor="abnf.dependencies">
250 
251 
252 
253 
254 
255 
256 
257 
258 
259 
260 
261 
262 
263 
264 
265 
266 
267 
268 
269 
270 
271 
272 
273 
274 
275  The ABNF rules below are defined in other parts:
276</t>
277<figure><!--Part1--><artwork type="abnf2616"><![CDATA[
278  absoluteURI   = <absoluteURI, defined in [Part1], Section 3.2.1>
279  fragment      = <fragment, defined in [Part1], Section 3.2.1>
280  Host          = <Host, defined in [Part1], Section 8.4>
281  HTTP-date     = <HTTP-date, defined in [Part1], Section 3.3.1>
282  product       = <product, defined in [Part1], Section 3.5>
283  relativeURI   = <relativeURI, defined in [Part1], Section 3.2.1>
284  TE            = <TE, defined in [Part1], Section 8.8>
285]]></artwork></figure>
286<figure><!--Part3--><artwork type="abnf2616"><![CDATA[
287  Accept        = <Accept, defined in [Part3], Section 6.1>
288  Accept-Charset =
289             <Accept-Charset, defined in [Part3], Section 6.2>
290  Accept-Encoding =
291             <Accept-Encoding, defined in [Part3], Section 6.3>
292  Accept-Language =
293             <Accept-Language, defined in [Part3], Section 6.4>
294]]></artwork></figure>
295<figure><!--Part4--><artwork type="abnf2616"><![CDATA[
296  ETag          = <ETag, defined in [Part4], Section 7.1>
297  If-Match      = <If-Match, defined in [Part4], Section 7.2>
298  If-Modified-Since =
299             <If-Modified-Since, defined in [Part4], Section 7.3>
300  If-None-Match = <If-None-Match, defined in [Part4], Section 7.4>
301  If-Unmodified-Since =
302             <If-Unmodified-Since, defined in [Part4], Section 7.5>
303]]></artwork></figure>
304<figure><!--Part5--><artwork type="abnf2616"><![CDATA[
305  Accept-Ranges = <Accept-Ranges, defined in [Part5], Section 6.1>
306  If-Range      = <If-Range, defined in [Part5], Section 6.3>
307  Range         = <Range, defined in [Part5], Section 6.4>
308]]></artwork></figure>
309<figure><!--Part6--><artwork type="abnf2616"><![CDATA[
310  Age           = <Age, defined in [Part6], Section 16.1>
311  Vary          = <Vary, defined in [Part6], Section 16.5>
312]]></artwork><!--Part7--></figure>
313<figure><artwork type="abnf2616"><![CDATA[
314  Authorization = <Authorization, defined in [Part7], Section 4.1>
315  Proxy-Authenticate =
316             <Proxy-Authenticate, defined in [Part7], Section 4.2>
317  Proxy-Authorization =
318             <Proxy-Authorization, defined in [Part7], Section 4.3>
319  WWW-Authenticate =
320             <WWW-Authenticate, defined in [Part7], Section 4.4>
321]]></artwork></figure>
322</section>
323
324<section title="Method" anchor="method">
325 
326 
327<t>
328   The Method  token indicates the method to be performed on the
329   resource identified by the Request-URI. The method is case-sensitive.
330</t>
331<figure><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/><artwork type="abnf2616"><![CDATA[
332  Method         = %x4F.50.54.49.4F.4E.53   ; "OPTIONS", Section 8.2
333                 | %x47.45.54               ; "GET", Section 8.3
334                 | %x48.45.41.44            ; "HEAD", Section 8.4
335                 | %x50.4F.53.54            ; "POST", Section 8.5
336                 | %x50.55.54               ; "PUT", Section 8.6
337                 | %x44.45.4C.45.54.45      ; "DELETE", Section 8.7
338                 | %x54.52.41.43.45         ; "TRACE", Section 8.8
339                 | %x43.4F.4E.4E.45.43.54   ; "CONNECT", Section 8.9
340                 | extension-method
341  extension-method = token
342]]></artwork></figure>
343<t>
344   The list of methods allowed by a resource can be specified in an
345   Allow header field (<xref target="header.allow"/>). The return code of the response
346   always notifies the client whether a method is currently allowed on a
347   resource, since the set of allowed methods can change dynamically. An
348   origin server SHOULD return the status code 405 (Method Not Allowed)
349   if the method is known by the origin server but not allowed for the
350   requested resource, and 501 (Not Implemented) if the method is
351   unrecognized or not implemented by the origin server. The methods GET
352   and HEAD MUST be supported by all general-purpose servers. All other
353   methods are OPTIONAL; however, if the above methods are implemented,
354   they MUST be implemented with the same semantics as those specified
355   in <xref target="method.definitions"/>.
356</t>
357
358<section title="Method Registry" anchor="method.registry">
359<t>
360  The HTTP Method Registry defines the name space for the Method token in the
361  Request line of an HTTP request.
362</t>
363<t>
364  Registrations MUST include the following fields:
365  <list style="symbols">
366    <t>Method Name (see <xref target="method"/>)</t>
367    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
368    <t>Pointer to specification text</t>
369  </list>
370</t>
371<t>
372  Values to be added to this name space are subject to IETF review
373  (<xref target="RFC5226"/>, Section 4.1).  Any document registering
374  new method names should be traceable through statuses of either 'Obsoletes'
375  or 'Updates' to this document.
376</t>
377<t>
378  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
379</t>
380</section>
381</section>
382
383<section title="Request Header Fields" anchor="request.header.fields">
384 
385 
386<t>
387   The request-header fields allow the client to pass additional
388   information about the request, and about the client itself, to the
389   server. These fields act as request modifiers, with semantics
390   equivalent to the parameters on a programming language method
391   invocation.
392</t>
393<figure><iref primary="true" item="Grammar" subitem="request-header"/><artwork type="abnf2616"><![CDATA[
394  request-header = Accept                   ; [Part3], Section 6.1
395                 | Accept-Charset           ; [Part3], Section 6.2
396                 | Accept-Encoding          ; [Part3], Section 6.3
397                 | Accept-Language          ; [Part3], Section 6.4
398                 | Authorization            ; [Part7], Section 4.1
399                 | Expect                   ; Section 10.2
400                 | From                     ; Section 10.3
401                 | Host                     ; [Part1], Section 8.4
402                 | If-Match                 ; [Part4], Section 7.2
403                 | If-Modified-Since        ; [Part4], Section 7.3
404                 | If-None-Match            ; [Part4], Section 7.4
405                 | If-Range                 ; [Part5], Section 6.3
406                 | If-Unmodified-Since      ; [Part4], Section 7.5
407                 | Max-Forwards             ; Section 10.5
408                 | Proxy-Authorization      ; [Part7], Section 4.3
409                 | Range                    ; [Part5], Section 6.4
410                 | Referer                  ; Section 10.6
411                 | TE                       ; [Part1], Section 8.8
412                 | User-Agent               ; Section 10.9
413]]></artwork></figure>
414<t>
415   Request-header field names can be extended reliably only in
416   combination with a change in the protocol version. However, new or
417   experimental header fields MAY be given the semantics of request-header
418   fields if all parties in the communication recognize them to
419   be request-header fields. Unrecognized header fields are treated as
420   entity-header fields.
421</t>
422</section>
423
424<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
425 
426 
427<t>
428   The Status-Code element is a 3-digit integer result code of the
429   attempt to understand and satisfy the request. The status codes listed
430   below are defined in <xref target="status.codes"/>.
431   The Reason-Phrase is intended to give a short
432   textual description of the Status-Code. The Status-Code is intended
433   for use by automata and the Reason-Phrase is intended for the human
434   user. The client is not required to examine or display the Reason-Phrase.
435</t>
436<t> 
437   The individual values of the numeric status codes defined for
438   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
439   presented below. The reason phrases listed here are only
440   recommendations -- they MAY be replaced by local equivalents without
441   affecting the protocol.
442</t>
443<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[
444  Status-Code    =
445         "100"  ; Section 9.1.1: Continue
446       | "101"  ; Section 9.1.2: Switching Protocols
447       | "200"  ; Section 9.2.1: OK
448       | "201"  ; Section 9.2.2: Created
449       | "202"  ; Section 9.2.3: Accepted
450       | "203"  ; Section 9.2.4: Non-Authoritative Information
451       | "204"  ; Section 9.2.5: No Content
452       | "205"  ; Section 9.2.6: Reset Content
453       | "206"  ; Section 9.2.7: Partial Content
454       | "300"  ; Section 9.3.1: Multiple Choices
455       | "301"  ; Section 9.3.2: Moved Permanently
456       | "302"  ; Section 9.3.3: Found
457       | "303"  ; Section 9.3.4: See Other
458       | "304"  ; Section 9.3.5: Not Modified
459       | "305"  ; Section 9.3.6: Use Proxy
460       | "307"  ; Section 9.3.8: Temporary Redirect
461       | "400"  ; Section 9.4.1: Bad Request
462       | "401"  ; Section 9.4.2: Unauthorized
463       | "402"  ; Section 9.4.3: Payment Required
464       | "403"  ; Section 9.4.4: Forbidden
465       | "404"  ; Section 9.4.5: Not Found
466       | "405"  ; Section 9.4.6: Method Not Allowed
467       | "406"  ; Section 9.4.7: Not Acceptable
468       | "407"  ; Section 9.4.8: Proxy Authentication Required
469       | "408"  ; Section 9.4.9: Request Time-out
470       | "409"  ; Section 9.4.10: Conflict
471       | "410"  ; Section 9.4.11: Gone
472       | "411"  ; Section 9.4.12: Length Required
473       | "412"  ; Section 9.4.13: Precondition Failed
474       | "413"  ; Section 9.4.14: Request Entity Too Large
475       | "414"  ; Section 9.4.15: Request-URI Too Large
476       | "415"  ; Section 9.4.16: Unsupported Media Type
477       | "416"  ; Section 9.4.17: Requested range not satisfiable
478       | "417"  ; Section 9.4.18: Expectation Failed
479       | "500"  ; Section 9.5.1: Internal Server Error
480       | "501"  ; Section 9.5.2: Not Implemented
481       | "502"  ; Section 9.5.3: Bad Gateway
482       | "503"  ; Section 9.5.4: Service Unavailable
483       | "504"  ; Section 9.5.5: Gateway Time-out
484       | "505"  ; Section 9.5.6: HTTP Version not supported
485       | extension-code
486
487  extension-code = 3DIGIT
488  Reason-Phrase  = *<TEXT, excluding CR, LF>
489]]></artwork></figure>
490<t>
491   HTTP status codes are extensible. HTTP applications are not required
492   to understand the meaning of all registered status codes, though such
493   understanding is obviously desirable. However, applications MUST
494   understand the class of any status code, as indicated by the first
495   digit, and treat any unrecognized response as being equivalent to the
496   x00 status code of that class, with the exception that an
497   unrecognized response MUST NOT be cached. For example, if an
498   unrecognized status code of 431 is received by the client, it can
499   safely assume that there was something wrong with its request and
500   treat the response as if it had received a 400 status code. In such
501   cases, user agents SHOULD present to the user the entity returned
502   with the response, since that entity is likely to include human-readable
503   information which will explain the unusual status.
504</t>
505
506<section title="Status Code Registry" anchor="status.code.registry">
507<t>
508  The HTTP Status Code Registry defines the name space for the Status-Code
509  token in the Status line of an HTTP response.
510</t>
511<t>
512  Values to be added to this name space are subject to IETF review
513  (<xref target="RFC5226"/>, Section 4.1).  Any document registering
514  new status codes should be traceable through statuses of either 'Obsoletes'
515  or 'Updates' to this document.
516</t>
517<t>
518  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
519</t>
520</section>
521
522</section>
523
524<section title="Response Header Fields" anchor="response.header.fields">
525 
526<t>
527   The response-header fields allow the server to pass additional
528   information about the response which cannot be placed in the Status-Line.
529   These header fields give information about the server and about
530   further access to the resource identified by the Request-URI.
531</t>
532<figure><iref primary="true" item="Grammar" subitem="response-header"/><artwork type="abnf2616"><![CDATA[
533  response-header = Accept-Ranges           ; [Part5], Section 6.1
534                  | Age                     ; [Part6], Section 16.1
535                  | Allow                   ; Section 10.1
536                  | ETag                    ; [Part4], Section 7.1
537                  | Location                ; Section 10.4
538                  | Proxy-Authenticate      ; [Part7], Section 4.2
539                  | Retry-After             ; Section 10.7
540                  | Server                  ; Section 10.8
541                  | Vary                    ; [Part6], Section 16.5
542                  | WWW-Authenticate        ; [Part7], Section 4.4
543]]></artwork></figure>
544<t>
545   Response-header field names can be extended reliably only in
546   combination with a change in the protocol version. However, new or
547   experimental header fields MAY be given the semantics of response-header
548   fields if all parties in the communication recognize them to
549   be response-header fields. Unrecognized header fields are treated as
550   entity-header fields.
551</t>
552</section>
553
554<section title="Entity" anchor="entity">
555<t>
556   Request and Response messages MAY transfer an entity if not otherwise
557   restricted by the request method or response status code. An entity
558   consists of entity-header fields and an entity-body, although some
559   responses will only include the entity-headers. HTTP entity-body and
560   entity-header fields are defined in <xref target="Part3"/>.
561</t>
562<t>
563   An entity-body is only present in a message when a message-body is
564   present, as described in Section 4.3 of <xref target="Part1"/>. The entity-body is obtained
565   from the message-body by decoding any Transfer-Encoding that might
566   have been applied to ensure safe and proper transfer of the message.
567</t>
568</section>
569
570
571<section title="Method Definitions" anchor="method.definitions">
572<t>
573   The set of common methods for HTTP/1.1 is defined below. Although
574   this set can be expanded, additional methods cannot be assumed to
575   share the same semantics for separately extended clients and servers.
576</t>
577
578<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
579
580<section title="Safe Methods" anchor="safe.methods">
581<iref item="Safe Methods" primary="true"/>
582<t>
583   Implementors should be aware that the software represents the user in
584   their interactions over the Internet, and should be careful to allow
585   the user to be aware of any actions they might take which may have an
586   unexpected significance to themselves or others.
587</t>
588<t>
589   In particular, the convention has been established that the GET and
590   HEAD methods SHOULD NOT  have the significance of taking an action
591   other than retrieval. These methods ought to be considered "safe".
592   This allows user agents to represent other methods, such as POST, PUT
593   and DELETE, in a special way, so that the user is made aware of the
594   fact that a possibly unsafe action is being requested.
595</t>
596<t>
597   Naturally, it is not possible to ensure that the server does not
598   generate side-effects as a result of performing a GET request; in
599   fact, some dynamic resources consider that a feature. The important
600   distinction here is that the user did not request the side-effects,
601   so therefore cannot be held accountable for them.
602</t>
603</section>
604
605<section title="Idempotent Methods" anchor="idempotent.methods">
606<iref item="Idempotent Methods" primary="true"/>
607<t>
608   Methods can also have the property of "idempotence" in that (aside
609   from error or expiration issues) the side-effects of N &gt; 0 identical
610   requests is the same as for a single request. The methods GET, HEAD,
611   PUT and DELETE share this property. Also, the methods OPTIONS and
612   TRACE SHOULD NOT  have side effects, and so are inherently idempotent.
613</t>
614<t>
615   However, it is possible that a sequence of several requests is non-idempotent,
616   even if all of the methods executed in that sequence are
617   idempotent. (A sequence is idempotent if a single execution of the
618   entire sequence always yields a result that is not changed by a
619   reexecution of all, or part, of that sequence.) For example, a
620   sequence is non-idempotent if its result depends on a value that is
621   later modified in the same sequence.
622</t>
623<t>
624   A sequence that never has side effects is idempotent, by definition
625   (provided that no concurrent operations are being executed on the
626   same set of resources).
627</t>
628</section>
629</section>
630
631<section title="OPTIONS" anchor="OPTIONS">
632 
633  <iref primary="true" item="OPTIONS method"/>
634  <iref primary="true" item="Methods" subitem="OPTIONS"/>
635<t>
636   The OPTIONS method represents a request for information about the
637   communication options available on the request/response chain
638   identified by the Request-URI. This method allows the client to
639   determine the options and/or requirements associated with a resource,
640   or the capabilities of a server, without implying a resource action
641   or initiating a resource retrieval.
642</t>
643<t>
644   Responses to this method are not cacheable.
645</t>
646<t>
647   If the OPTIONS request includes an entity-body (as indicated by the
648   presence of Content-Length or Transfer-Encoding), then the media type
649   MUST be indicated by a Content-Type field. Although this
650   specification does not define any use for such a body, future
651   extensions to HTTP might use the OPTIONS body to make more detailed
652   queries on the server.
653</t>
654<t>
655   If the Request-URI is an asterisk ("*"), the OPTIONS request is
656   intended to apply to the server in general rather than to a specific
657   resource. Since a server's communication options typically depend on
658   the resource, the "*" request is only useful as a "ping" or "no-op"
659   type of method; it does nothing beyond allowing the client to test
660   the capabilities of the server. For example, this can be used to test
661   a proxy for HTTP/1.1 compliance (or lack thereof).
662</t>
663<t>
664   If the Request-URI is not an asterisk, the OPTIONS request applies
665   only to the options that are available when communicating with that
666   resource.
667</t>
668<t>
669   A 200 response SHOULD include any header fields that indicate
670   optional features implemented by the server and applicable to that
671   resource (e.g., Allow), possibly including extensions not defined by
672   this specification. The response body, if any, SHOULD also include
673   information about the communication options. The format for such a
674   body is not defined by this specification, but might be defined by
675   future extensions to HTTP. Content negotiation MAY be used to select
676   the appropriate response format. If no response body is included, the
677   response MUST include a Content-Length field with a field-value of
678   "0".
679</t>
680<t>
681   The Max-Forwards request-header field MAY be used to target a
682   specific proxy in the request chain. When a proxy receives an OPTIONS
683   request on an absoluteURI for which request forwarding is permitted,
684   the proxy MUST check for a Max-Forwards field. If the Max-Forwards
685   field-value is zero ("0"), the proxy MUST NOT forward the message;
686   instead, the proxy SHOULD respond with its own communication options.
687   If the Max-Forwards field-value is an integer greater than zero, the
688   proxy MUST decrement the field-value when it forwards the request. If
689   no Max-Forwards field is present in the request, then the forwarded
690   request MUST NOT include a Max-Forwards field.
691</t>
692</section>
693
694<section title="GET" anchor="GET">
695 
696  <iref primary="true" item="GET method"/>
697  <iref primary="true" item="Methods" subitem="GET"/>
698<t>
699   The GET method means retrieve whatever information (in the form of an
700   entity) is identified by the Request-URI. If the Request-URI refers
701   to a data-producing process, it is the produced data which shall be
702   returned as the entity in the response and not the source text of the
703   process, unless that text happens to be the output of the process.
704</t>
705<t>
706   The semantics of the GET method change to a "conditional GET" if the
707   request message includes an If-Modified-Since, If-Unmodified-Since,
708   If-Match, If-None-Match, or If-Range header field. A conditional GET
709   method requests that the entity be transferred only under the
710   circumstances described by the conditional header field(s). The
711   conditional GET method is intended to reduce unnecessary network
712   usage by allowing cached entities to be refreshed without requiring
713   multiple requests or transferring data already held by the client.
714</t>
715<t>
716   The semantics of the GET method change to a "partial GET" if the
717   request message includes a Range header field. A partial GET requests
718   that only part of the entity be transferred, as described in Section 6.4 of <xref target="Part5"/>.
719   The partial GET method is intended to reduce unnecessary
720   network usage by allowing partially-retrieved entities to be
721   completed without transferring data already held by the client.
722</t>
723<t>
724   The response to a GET request is cacheable if and only if it meets
725   the requirements for HTTP caching described in <xref target="Part6"/>.
726</t>
727<t>
728   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
729</t>
730</section>
731
732<section title="HEAD" anchor="HEAD">
733 
734  <iref primary="true" item="HEAD method"/>
735  <iref primary="true" item="Methods" subitem="HEAD"/>
736<t>
737   The HEAD method is identical to GET except that the server MUST NOT
738   return a message-body in the response. The metainformation contained
739   in the HTTP headers in response to a HEAD request SHOULD be identical
740   to the information sent in response to a GET request. This method can
741   be used for obtaining metainformation about the entity implied by the
742   request without transferring the entity-body itself. This method is
743   often used for testing hypertext links for validity, accessibility,
744   and recent modification.
745</t>
746<t>
747   The response to a HEAD request MAY be cacheable in the sense that the
748   information contained in the response MAY be used to update a
749   previously cached entity from that resource. If the new field values
750   indicate that the cached entity differs from the current entity (as
751   would be indicated by a change in Content-Length, Content-MD5, ETag
752   or Last-Modified), then the cache MUST treat the cache entry as
753   stale.
754</t>
755</section>
756
757<section title="POST" anchor="POST">
758  <iref primary="true" item="POST method"/>
759  <iref primary="true" item="Methods" subitem="POST"/>
760<t>
761   The POST method is used to request that the origin server accept the
762   entity enclosed in the request as data to be processed by the resource
763   identified by the Request-URI in the Request-Line. POST is designed
764   to allow a uniform method to cover the following functions:
765  <list style="symbols">
766    <t>
767      Annotation of existing resources;
768    </t>
769    <t>
770        Posting a message to a bulletin board, newsgroup, mailing list,
771        or similar group of articles;
772    </t>
773    <t>
774        Providing a block of data, such as the result of submitting a
775        form, to a data-handling process;
776    </t>
777    <t>
778        Extending a database through an append operation.
779    </t>
780  </list>
781</t>
782<t>
783   The actual function performed by the POST method is determined by the
784   server and is usually dependent on the Request-URI.
785</t>
786<t>
787   The action performed by the POST method might not result in a
788   resource that can be identified by a URI. In this case, either 200
789   (OK) or 204 (No Content) is the appropriate response status,
790   depending on whether or not the response includes an entity that
791   describes the result.
792</t>
793<t>
794   If a resource has been created on the origin server, the response
795   SHOULD be 201 (Created) and contain an entity which describes the
796   status of the request and refers to the new resource, and a Location
797   header (see <xref target="header.location"/>).
798</t>
799<t>
800   Responses to this method are not cacheable, unless the response
801   includes appropriate Cache-Control or Expires header fields. However,
802   the 303 (See Other) response can be used to direct the user agent to
803   retrieve a cacheable resource.
804</t>
805</section>
806
807<section title="PUT" anchor="PUT">
808  <iref primary="true" item="PUT method"/>
809  <iref primary="true" item="Methods" subitem="PUT"/>
810<t>
811   The PUT method requests that the enclosed entity be stored at the
812   supplied Request-URI. If the Request-URI refers to an already
813   existing resource, the enclosed entity SHOULD be considered as a
814   modified version of the one residing on the origin server. If the
815   Request-URI does not point to an existing resource, and that URI is
816   capable of being defined as a new resource by the requesting user
817   agent, the origin server can create the resource with that URI. If a
818   new resource is created at the Request-URI, the origin server MUST
819         inform the user agent
820   via the 201 (Created) response. If an existing resource is modified,
821   either the 200 (OK) or 204 (No Content) response codes SHOULD be sent
822   to indicate successful completion of the request. If the resource
823   could not be created or modified with the Request-URI, an appropriate
824   error response SHOULD be given that reflects the nature of the
825   problem. The recipient of the entity MUST NOT ignore any Content-*
826   (e.g. Content-Range) headers that it does not understand or implement
827   and MUST return a 501 (Not Implemented) response in such cases.
828</t>
829<t>
830   If the request passes through a cache and the Request-URI identifies
831   one or more currently cached entities, those entries SHOULD be
832   treated as stale. Responses to this method are not cacheable.
833</t>
834<t>
835   The fundamental difference between the POST and PUT requests is
836   reflected in the different meaning of the Request-URI. The URI in a
837   POST request identifies the resource that will handle the enclosed
838   entity. That resource might be a data-accepting process, a gateway to
839   some other protocol, or a separate entity that accepts annotations.
840   In contrast, the URI in a PUT request identifies the entity enclosed
841   with the request -- the user agent knows what URI is intended and the
842   server MUST NOT attempt to apply the request to some other resource.
843   If the server desires that the request be applied to a different URI,
844   it MUST send a 301 (Moved Permanently) response; the user agent MAY
845   then make its own decision regarding whether or not to redirect the
846   request.
847</t>
848<t>
849   A single resource MAY be identified by many different URIs. For
850   example, an article might have a URI for identifying "the current
851   version" which is separate from the URI identifying each particular
852   version. In this case, a PUT request on a general URI might result in
853   several other URIs being defined by the origin server.
854</t>
855<t>
856   HTTP/1.1 does not define how a PUT method affects the state of an
857   origin server.
858</t>
859<t>
860   Unless otherwise specified for a particular entity-header, the
861   entity-headers in the PUT request SHOULD be applied to the resource
862   created or modified by the PUT.
863</t>
864</section>
865
866<section title="DELETE" anchor="DELETE">
867  <iref primary="true" item="DELETE method"/>
868  <iref primary="true" item="Methods" subitem="DELETE"/>
869<t>
870   The DELETE method requests that the origin server delete the resource
871   identified by the Request-URI. This method MAY be overridden by human
872   intervention (or other means) on the origin server. The client cannot
873   be guaranteed that the operation has been carried out, even if the
874   status code returned from the origin server indicates that the action
875   has been completed successfully. However, the server SHOULD NOT
876   indicate success unless, at the time the response is given, it
877   intends to delete the resource or move it to an inaccessible
878   location.
879</t>
880<t>
881   A successful response SHOULD be 200 (OK) if the response includes an
882   entity describing the status, 202 (Accepted) if the action has not
883   yet been enacted, or 204 (No Content) if the action has been enacted
884   but the response does not include an entity.
885</t>
886<t>
887   If the request passes through a cache and the Request-URI identifies
888   one or more currently cached entities, those entries SHOULD be
889   treated as stale. Responses to this method are not cacheable.
890</t>
891</section>
892
893<section title="TRACE" anchor="TRACE">
894 
895  <iref primary="true" item="TRACE method"/>
896  <iref primary="true" item="Methods" subitem="TRACE"/>
897<t>
898   The TRACE method is used to invoke a remote, application-layer loop-back
899   of the request message. The final recipient of the request
900   SHOULD reflect the message received back to the client as the
901   entity-body of a 200 (OK) response. The final recipient is either the
902   origin server or the first proxy or gateway to receive a Max-Forwards
903   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
904   MUST NOT include an entity.
905</t>
906<t>
907   TRACE allows the client to see what is being received at the other
908   end of the request chain and use that data for testing or diagnostic
909   information. The value of the Via header field (Section 8.9 of <xref target="Part1"/>) is of
910   particular interest, since it acts as a trace of the request chain.
911   Use of the Max-Forwards header field allows the client to limit the
912   length of the request chain, which is useful for testing a chain of
913   proxies forwarding messages in an infinite loop.
914</t>
915<t>
916   If the request is valid, the response SHOULD contain the entire
917   request message in the entity-body, with a Content-Type of
918   "message/http" (see Section 9.3.1 of <xref target="Part1"/>). Responses to this method
919   MUST NOT be cached.
920</t>
921</section>
922
923<section title="CONNECT" anchor="CONNECT">
924  <iref primary="true" item="CONNECT method"/>
925  <iref primary="true" item="Methods" subitem="CONNECT"/>
926<t>
927   This specification reserves the method name CONNECT for use with a
928   proxy that can dynamically switch to being a tunnel (e.g. SSL
929   tunneling <xref target="RFC2817"/>).
930</t>
931</section>
932</section>
933
934
935<section title="Status Code Definitions" anchor="status.codes">
936<t>
937   Each Status-Code is described below, including a description of which
938   method(s) it can follow and any metainformation required in the
939   response.
940</t>
941
942<section title="Informational 1xx" anchor="status.1xx">
943<t>
944   This class of status code indicates a provisional response,
945   consisting only of the Status-Line and optional headers, and is
946   terminated by an empty line. There are no required headers for this
947   class of status code. Since HTTP/1.0 did not define any 1xx status
948   codes, servers MUST NOT send a 1xx response to an HTTP/1.0 client
949   except under experimental conditions.
950</t>
951<t>
952   A client MUST be prepared to accept one or more 1xx status responses
953   prior to a regular response, even if the client does not expect a 100
954   (Continue) status message. Unexpected 1xx status responses MAY be
955   ignored by a user agent.
956</t>
957<t>
958   Proxies MUST forward 1xx responses, unless the connection between the
959   proxy and its client has been closed, or unless the proxy itself
960   requested the generation of the 1xx response. (For example, if a
961   proxy adds a "Expect: 100-continue" field when it forwards a request,
962   then it need not forward the corresponding 100 (Continue)
963   response(s).)
964</t>
965
966<section title="100 Continue" anchor="status.100">
967  <iref primary="true" item="100 Continue (status code)"/>
968  <iref primary="true" item="Status Codes" subitem="100 Continue"/>
969<t>
970   The client SHOULD continue with its request. This interim response is
971   used to inform the client that the initial part of the request has
972   been received and has not yet been rejected by the server. The client
973   SHOULD continue by sending the remainder of the request or, if the
974   request has already been completed, ignore this response. The server
975   MUST send a final response after the request has been completed. See
976   Section 7.2.3 of <xref target="Part1"/> for detailed discussion of the use and handling of this
977   status code.
978</t>
979</section>
980
981<section title="101 Switching Protocols" anchor="status.101">
982  <iref primary="true" item="101 Switching Protocols (status code)"/>
983  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols"/>
984<t>
985   The server understands and is willing to comply with the client's
986   request, via the Upgrade message header field (Section 6.4 of <xref target="Part5"/>), for a
987   change in the application protocol being used on this connection. The
988   server will switch protocols to those defined by the response's
989   Upgrade header field immediately after the empty line which
990   terminates the 101 response.
991</t>
992<t>
993   The protocol SHOULD be switched only when it is advantageous to do
994   so. For example, switching to a newer version of HTTP is advantageous
995   over older versions, and switching to a real-time, synchronous
996   protocol might be advantageous when delivering resources that use
997   such features.
998</t>
999</section>
1000</section>
1001
1002<section title="Successful 2xx" anchor="status.2xx">
1003<t>
1004   This class of status code indicates that the client's request was
1005   successfully received, understood, and accepted.
1006</t>
1007
1008<section title="200 OK" anchor="status.200">
1009  <iref primary="true" item="200 OK (status code)"/>
1010  <iref primary="true" item="Status Codes" subitem="200 OK"/>
1011<t>
1012   The request has succeeded. The information returned with the response
1013   is dependent on the method used in the request, for example:
1014  <list style="hanging">
1015    <t hangText="GET">
1016          an entity corresponding to the requested resource is sent in
1017          the response;
1018    </t>
1019    <t hangText="HEAD">
1020          the entity-header fields corresponding to the requested
1021          resource are sent in the response without any message-body;
1022    </t>
1023    <t hangText="POST">
1024      an entity describing or containing the result of the action;
1025    </t>
1026    <t hangText="TRACE">
1027      an entity containing the request message as received by the
1028      end server.
1029    </t>
1030  </list>
1031</t>
1032</section>
1033
1034<section title="201 Created" anchor="status.201">
1035  <iref primary="true" item="201 Created (status code)"/>
1036  <iref primary="true" item="Status Codes" subitem="201 Created"/>
1037<t>
1038   The request has been fulfilled and resulted in a new resource being
1039   created. The newly created resource can be referenced by the URI(s)
1040   returned in the entity of the response, with the most specific URI
1041   for the resource given by a Location header field. The response
1042   SHOULD include an entity containing a list of resource
1043   characteristics and location(s) from which the user or user agent can
1044   choose the one most appropriate. The entity format is specified by
1045   the media type given in the Content-Type header field. The origin
1046   server MUST create the resource before returning the 201 status code.
1047   If the action cannot be carried out immediately, the server SHOULD
1048   respond with 202 (Accepted) response instead.
1049</t>
1050<t>
1051   A 201 response MAY contain an ETag response header field indicating
1052   the current value of the entity tag for the requested variant just
1053   created, see Section 7.1 of <xref target="Part4"/>.
1054</t>
1055</section>
1056
1057<section title="202 Accepted" anchor="status.202">
1058  <iref primary="true" item="202 Accepted (status code)"/>
1059  <iref primary="true" item="Status Codes" subitem="202 Accepted"/>
1060<t>
1061   The request has been accepted for processing, but the processing has
1062   not been completed.  The request might or might not eventually be
1063   acted upon, as it might be disallowed when processing actually takes
1064   place. There is no facility for re-sending a status code from an
1065   asynchronous operation such as this.
1066</t>
1067<t>
1068   The 202 response is intentionally non-committal. Its purpose is to
1069   allow a server to accept a request for some other process (perhaps a
1070   batch-oriented process that is only run once per day) without
1071   requiring that the user agent's connection to the server persist
1072   until the process is completed. The entity returned with this
1073   response SHOULD include an indication of the request's current status
1074   and either a pointer to a status monitor or some estimate of when the
1075   user can expect the request to be fulfilled.
1076</t>
1077</section>
1078
1079<section title="203 Non-Authoritative Information" anchor="status.203">
1080  <iref primary="true" item="203 Non-Authoritative Information (status code)"/>
1081  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information"/>
1082<t>
1083   The returned metainformation in the entity-header is not the
1084   definitive set as available from the origin server, but is gathered
1085   from a local or a third-party copy. The set presented MAY be a subset
1086   or superset of the original version. For example, including local
1087   annotation information about the resource might result in a superset
1088   of the metainformation known by the origin server. Use of this
1089   response code is not required and is only appropriate when the
1090   response would otherwise be 200 (OK).
1091</t>
1092</section>
1093
1094<section title="204 No Content" anchor="status.204">
1095  <iref primary="true" item="204 No Content (status code)"/>
1096  <iref primary="true" item="Status Codes" subitem="204 No Content"/>
1097<t>
1098   The server has fulfilled the request but does not need to return an
1099   entity-body, and might want to return updated metainformation. The
1100   response MAY include new or updated metainformation in the form of
1101   entity-headers, which if present SHOULD be associated with the
1102   requested variant.
1103</t>
1104<t>
1105   If the client is a user agent, it SHOULD NOT  change its document view
1106   from that which caused the request to be sent. This response is
1107   primarily intended to allow input for actions to take place without
1108   causing a change to the user agent's active document view, although
1109   any new or updated metainformation SHOULD be applied to the document
1110   currently in the user agent's active view.
1111</t>
1112<t>
1113   The 204 response MUST NOT include a message-body, and thus is always
1114   terminated by the first empty line after the header fields.
1115</t>
1116</section>
1117
1118<section title="205 Reset Content" anchor="status.205">
1119  <iref primary="true" item="205 Reset Content (status code)"/>
1120  <iref primary="true" item="Status Codes" subitem="205 Reset Content"/>
1121<t>
1122   The server has fulfilled the request and the user agent SHOULD reset
1123   the document view which caused the request to be sent. This response
1124   is primarily intended to allow input for actions to take place via
1125   user input, followed by a clearing of the form in which the input is
1126   given so that the user can easily initiate another input action. The
1127   response MUST NOT include an entity.
1128</t>
1129</section>
1130
1131<section title="206 Partial Content" anchor="status.206">
1132  <iref primary="true" item="206 Partial Content (status code)"/>
1133  <iref primary="true" item="Status Codes" subitem="206 Partial Content"/>
1134<t>
1135   The server has fulfilled the partial GET request for the resource
1136   and the enclosed entity is a partial representation as defined in <xref target="Part5"/>.
1137</t>
1138</section>
1139</section>
1140
1141<section title="Redirection 3xx" anchor="status.3xx">
1142<t>
1143   This class of status code indicates that further action needs to be
1144   taken by the user agent in order to fulfill the request.  The action
1145   required MAY be carried out by the user agent without interaction
1146   with the user if and only if the method used in the second request is
1147   GET or HEAD. A client SHOULD detect infinite redirection loops, since
1148   such loops generate network traffic for each redirection.
1149  <list><t>
1150      Note: previous versions of this specification recommended a
1151      maximum of five redirections. Content developers should be aware
1152      that there might be clients that implement such a fixed
1153      limitation.
1154  </t></list>
1155</t>
1156
1157<section title="300 Multiple Choices" anchor="status.300">
1158  <iref primary="true" item="300 Multiple Choices (status code)"/>
1159  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices"/>
1160<t>
1161   The requested resource corresponds to any one of a set of
1162   representations, each with its own specific location, and agent-driven
1163   negotiation information (Section 5 of <xref target="Part3"/>) is being provided so that
1164   the user (or user agent) can select a preferred representation and
1165   redirect its request to that location.
1166</t>
1167<t>
1168   Unless it was a HEAD request, the response SHOULD include an entity
1169   containing a list of resource characteristics and location(s) from
1170   which the user or user agent can choose the one most appropriate. The
1171   entity format is specified by the media type given in the Content-Type
1172   header field. Depending upon the format and the capabilities of
1173   the user agent, selection of the most appropriate choice MAY be
1174   performed automatically. However, this specification does not define
1175   any standard for such automatic selection.
1176</t>
1177<t>
1178   If the server has a preferred choice of representation, it SHOULD
1179   include the specific URI for that representation in the Location
1180   field; user agents MAY use the Location field value for automatic
1181   redirection. This response is cacheable unless indicated otherwise.
1182</t>
1183</section>
1184
1185<section title="301 Moved Permanently" anchor="status.301">
1186  <iref primary="true" item="301 Moved Permanently (status code)"/>
1187  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently"/>
1188<t>
1189   The requested resource has been assigned a new permanent URI and any
1190   future references to this resource SHOULD use one of the returned
1191   URIs.  Clients with link editing capabilities ought to automatically
1192   re-link references to the Request-URI to one or more of the new
1193   references returned by the server, where possible. This response is
1194   cacheable unless indicated otherwise.
1195</t>
1196<t>
1197   The new permanent URI SHOULD be given by the Location field in the
1198   response. Unless the request method was HEAD, the entity of the
1199   response SHOULD contain a short hypertext note with a hyperlink to
1200   the new URI(s).
1201</t>
1202<t>
1203   If the 301 status code is received in response to a request method
1204   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1205   then the request MAY be automatically redirected by the user agent without
1206   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
1207   request unless it can be confirmed by the user, since this might
1208   change the conditions under which the request was issued.
1209  <list><t>
1210      Note: When automatically redirecting a POST request after
1211      receiving a 301 status code, some existing HTTP/1.0 user agents
1212      will erroneously change it into a GET request.
1213  </t></list>
1214</t>
1215</section>
1216
1217<section title="302 Found" anchor="status.302">
1218  <iref primary="true" item="302 Found (status code)"/>
1219  <iref primary="true" item="Status Codes" subitem="302 Found"/>
1220<t>
1221   The requested resource resides temporarily under a different URI.
1222   Since the redirection might be altered on occasion, the client SHOULD
1223   continue to use the Request-URI for future requests.  This response
1224   is only cacheable if indicated by a Cache-Control or Expires header
1225   field.
1226</t>
1227<t>
1228   The temporary URI SHOULD be given by the Location field in the
1229   response. Unless the request method was HEAD, the entity of the
1230   response SHOULD contain a short hypertext note with a hyperlink to
1231   the new URI(s).
1232</t>
1233<t>
1234   If the 302 status code is received in response to a request method
1235   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1236   then the request MAY be automatically redirected by the user agent without
1237   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
1238   request unless it can be confirmed by the user, since this might
1239   change the conditions under which the request was issued.
1240  <list><t>
1241      Note: <xref target="RFC1945"/> and <xref target="RFC2068"/> specify that the client is not allowed
1242      to change the method on the redirected request.  However, most
1243      existing user agent implementations treat 302 as if it were a 303
1244      response, performing a GET on the Location field-value regardless
1245      of the original request method. The status codes 303 and 307 have
1246      been added for servers that wish to make unambiguously clear which
1247      kind of reaction is expected of the client.
1248  </t></list>
1249</t>
1250</section>
1251
1252<section title="303 See Other" anchor="status.303">
1253  <iref primary="true" item="303 See Other (status code)"/>
1254  <iref primary="true" item="Status Codes" subitem="303 See Other"/>
1255<t>
1256   The server directs the user agent to a different resource, indicated
1257   by a URI in the Location header field, that provides an indirect
1258   response to the original request.  The user agent MAY perform a GET
1259   request on the URI in the Location field in order to obtain a
1260   representation corresponding to the response, be redirected again,
1261   or end with an error status.  The Location URI is not a substitute
1262   reference for the originally requested resource.
1263</t>
1264<t>
1265   The 303 status is generally applicable to any HTTP method.  It is
1266   primarily used to allow the output of a POST action to redirect
1267   the user agent to a selected resource, since doing so provides the
1268   information corresponding to the POST response in a form that
1269   can be separately identified, bookmarked, and cached independent
1270   of the original request.
1271</t>
1272<t>
1273   A 303 response to a GET request indicates that the requested
1274   resource does not have a representation of its own that can be
1275   transferred by the server over HTTP.  The Location URI indicates a
1276   resource that is descriptive of the requested resource such that
1277   the follow-on representation may be useful without implying that
1278   it adequately represents the previously requested resource.
1279   Note that answers to the questions of what can be represented, what
1280   representations are adequate, and what might be a useful description
1281   are outside the scope of HTTP and thus entirely determined by the
1282   resource owner(s).
1283</t>
1284<t>
1285   A 303 response SHOULD NOT be cached unless it is indicated as
1286   cacheable by Cache-Control or Expires header fields.  Except for
1287   responses to a HEAD request, the entity of a 303 response SHOULD
1288   contain a short hypertext note with a hyperlink to the Location URI.
1289</t>
1290</section>
1291
1292<section title="304 Not Modified" anchor="status.304">
1293  <iref primary="true" item="304 Not Modified (status code)"/>
1294  <iref primary="true" item="Status Codes" subitem="304 Not Modified"/>
1295<t>
1296   The response to the request has not been modified since the conditions
1297   indicated by the client's conditional GET request, as defined in <xref target="Part4"/>.
1298</t>
1299</section>
1300
1301<section title="305 Use Proxy" anchor="status.305">
1302  <iref primary="true" item="305 Use Proxy (status code)"/>
1303  <iref primary="true" item="Status Codes" subitem="305 Use Proxy"/>
1304<t>
1305   The 305 status was defined in a previous version of this specification
1306   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1307</t>
1308</section>
1309
1310<section title="306 (Unused)" anchor="status.306">
1311  <iref primary="true" item="306 (Unused) (status code)"/>
1312  <iref primary="true" item="Status Codes" subitem="306 (Unused)"/>
1313<t>
1314   The 306 status code was used in a previous version of the
1315   specification, is no longer used, and the code is reserved.
1316</t>
1317</section>
1318
1319<section title="307 Temporary Redirect" anchor="status.307">
1320  <iref primary="true" item="307 Temporary Redirect (status code)"/>
1321  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect"/>
1322<t>
1323   The requested resource resides temporarily under a different URI.
1324   Since the redirection MAY be altered on occasion, the client SHOULD
1325   continue to use the Request-URI for future requests.  This response
1326   is only cacheable if indicated by a Cache-Control or Expires header
1327   field.
1328</t>
1329<t>
1330   The temporary URI SHOULD be given by the Location field in the
1331   response. Unless the request method was HEAD, the entity of the
1332   response SHOULD contain a short hypertext note with a hyperlink to
1333   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1334   understand the 307 status. Therefore, the note SHOULD contain the
1335   information necessary for a user to repeat the original request on
1336   the new URI.
1337</t>
1338<t>
1339   If the 307 status code is received in response to a request method
1340   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1341   then the request MAY be automatically redirected by the user agent without
1342   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
1343   request unless it can be confirmed by the user, since this might
1344   change the conditions under which the request was issued.
1345</t>
1346</section>
1347</section>
1348
1349<section title="Client Error 4xx" anchor="status.4xx">
1350<t>
1351   The 4xx class of status code is intended for cases in which the
1352   client seems to have erred. Except when responding to a HEAD request,
1353   the server SHOULD include an entity containing an explanation of the
1354   error situation, and whether it is a temporary or permanent
1355   condition. These status codes are applicable to any request method.
1356   User agents SHOULD display any included entity to the user.
1357</t>
1358<t>
1359   If the client is sending data, a server implementation using TCP
1360   SHOULD be careful to ensure that the client acknowledges receipt of
1361   the packet(s) containing the response, before the server closes the
1362   input connection. If the client continues sending data to the server
1363   after the close, the server's TCP stack will send a reset packet to
1364   the client, which may erase the client's unacknowledged input buffers
1365   before they can be read and interpreted by the HTTP application.
1366</t>
1367
1368<section title="400 Bad Request" anchor="status.400">
1369  <iref primary="true" item="400 Bad Request (status code)"/>
1370  <iref primary="true" item="Status Codes" subitem="400 Bad Request"/>
1371<t>
1372   The request could not be understood by the server due to malformed
1373   syntax. The client SHOULD NOT  repeat the request without
1374   modifications.
1375</t>
1376</section>
1377
1378<section title="401 Unauthorized" anchor="status.401">
1379  <iref primary="true" item="401 Unauthorized (status code)"/>
1380  <iref primary="true" item="Status Codes" subitem="401 Unauthorized"/>
1381<t>
1382   The request requires user authentication (see <xref target="Part7"/>).
1383</t>
1384</section>
1385
1386<section title="402 Payment Required" anchor="status.402">
1387  <iref primary="true" item="402 Payment Required (status code)"/>
1388  <iref primary="true" item="Status Codes" subitem="402 Payment Required"/>
1389<t>
1390   This code is reserved for future use.
1391</t>
1392</section>
1393
1394<section title="403 Forbidden" anchor="status.403">
1395  <iref primary="true" item="403 Forbidden (status code)"/>
1396  <iref primary="true" item="Status Codes" subitem="403 Forbidden"/>
1397<t>
1398   The server understood the request, but is refusing to fulfill it.
1399   Authorization will not help and the request SHOULD NOT  be repeated.
1400   If the request method was not HEAD and the server wishes to make
1401   public why the request has not been fulfilled, it SHOULD describe the
1402   reason for the refusal in the entity.  If the server does not wish to
1403   make this information available to the client, the status code 404
1404   (Not Found) can be used instead.
1405</t>
1406</section>
1407
1408<section title="404 Not Found" anchor="status.404">
1409  <iref primary="true" item="404 Not Found (status code)"/>
1410  <iref primary="true" item="Status Codes" subitem="404 Not Found"/>
1411<t>
1412   The server has not found anything matching the Request-URI. No
1413   indication is given of whether the condition is temporary or
1414   permanent. The 410 (Gone) status code SHOULD be used if the server
1415   knows, through some internally configurable mechanism, that an old
1416   resource is permanently unavailable and has no forwarding address.
1417   This status code is commonly used when the server does not wish to
1418   reveal exactly why the request has been refused, or when no other
1419   response is applicable.
1420</t>
1421</section>
1422
1423<section title="405 Method Not Allowed" anchor="status.405">
1424  <iref primary="true" item="405 Method Not Allowed (status code)"/>
1425  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed"/>
1426<t>
1427   The method specified in the Request-Line is not allowed for the
1428   resource identified by the Request-URI. The response MUST include an
1429   Allow header containing a list of valid methods for the requested
1430   resource.
1431</t>
1432</section>
1433
1434<section title="406 Not Acceptable" anchor="status.406">
1435  <iref primary="true" item="406 Not Acceptable (status code)"/>
1436  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable"/>
1437<t>
1438   The resource identified by the request is only capable of generating
1439   response entities which have content characteristics not acceptable
1440   according to the accept headers sent in the request.
1441</t>
1442<t>
1443   Unless it was a HEAD request, the response SHOULD include an entity
1444   containing a list of available entity characteristics and location(s)
1445   from which the user or user agent can choose the one most
1446   appropriate. The entity format is specified by the media type given
1447   in the Content-Type header field. Depending upon the format and the
1448   capabilities of the user agent, selection of the most appropriate
1449   choice MAY be performed automatically. However, this specification
1450   does not define any standard for such automatic selection.
1451  <list><t>
1452      Note: HTTP/1.1 servers are allowed to return responses which are
1453      not acceptable according to the accept headers sent in the
1454      request. In some cases, this may even be preferable to sending a
1455      406 response. User agents are encouraged to inspect the headers of
1456      an incoming response to determine if it is acceptable.
1457  </t></list>
1458</t>
1459<t>
1460   If the response could be unacceptable, a user agent SHOULD
1461   temporarily stop receipt of more data and query the user for a
1462   decision on further actions.
1463</t>
1464</section>
1465
1466<section title="407 Proxy Authentication Required" anchor="status.407">
1467  <iref primary="true" item="407 Proxy Authentication Required (status code)"/>
1468  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required"/>
1469<t>
1470   This code is similar to 401 (Unauthorized), but indicates that the
1471   client must first authenticate itself with the proxy (see <xref target="Part7"/>).
1472</t>
1473</section>
1474
1475<section title="408 Request Timeout" anchor="status.408">
1476  <iref primary="true" item="408 Request Timeout (status code)"/>
1477  <iref primary="true" item="Status Codes" subitem="408 Request Timeout"/>
1478<t>
1479   The client did not produce a request within the time that the server
1480   was prepared to wait. The client MAY repeat the request without
1481   modifications at any later time.
1482</t>
1483</section>
1484
1485<section title="409 Conflict" anchor="status.409">
1486  <iref primary="true" item="409 Conflict (status code)"/>
1487  <iref primary="true" item="Status Codes" subitem="409 Conflict"/>
1488<t>
1489   The request could not be completed due to a conflict with the current
1490   state of the resource. This code is only allowed in situations where
1491   it is expected that the user might be able to resolve the conflict
1492   and resubmit the request. The response body SHOULD include enough
1493   information for the user to recognize the source of the conflict.
1494   Ideally, the response entity would include enough information for the
1495   user or user agent to fix the problem; however, that might not be
1496   possible and is not required.
1497</t>
1498<t>
1499   Conflicts are most likely to occur in response to a PUT request. For
1500   example, if versioning were being used and the entity being PUT
1501   included changes to a resource which conflict with those made by an
1502   earlier (third-party) request, the server might use the 409 response
1503   to indicate that it can't complete the request. In this case, the
1504   response entity would likely contain a list of the differences
1505   between the two versions in a format defined by the response
1506   Content-Type.
1507</t>
1508</section>
1509
1510<section title="410 Gone" anchor="status.410">
1511  <iref primary="true" item="410 Gone (status code)"/>
1512  <iref primary="true" item="Status Codes" subitem="410 Gone"/>
1513<t>
1514   The requested resource is no longer available at the server and no
1515   forwarding address is known. This condition is expected to be
1516   considered permanent. Clients with link editing capabilities SHOULD
1517   delete references to the Request-URI after user approval. If the
1518   server does not know, or has no facility to determine, whether or not
1519   the condition is permanent, the status code 404 (Not Found) SHOULD be
1520   used instead. This response is cacheable unless indicated otherwise.
1521</t>
1522<t>
1523   The 410 response is primarily intended to assist the task of web
1524   maintenance by notifying the recipient that the resource is
1525   intentionally unavailable and that the server owners desire that
1526   remote links to that resource be removed. Such an event is common for
1527   limited-time, promotional services and for resources belonging to
1528   individuals no longer working at the server's site. It is not
1529   necessary to mark all permanently unavailable resources as "gone" or
1530   to keep the mark for any length of time -- that is left to the
1531   discretion of the server owner.
1532</t>
1533</section>
1534
1535<section title="411 Length Required" anchor="status.411">
1536  <iref primary="true" item="411 Length Required (status code)"/>
1537  <iref primary="true" item="Status Codes" subitem="411 Length Required"/>
1538<t>
1539   The server refuses to accept the request without a defined Content-Length.
1540   The client MAY repeat the request if it adds a valid
1541   Content-Length header field containing the length of the message-body
1542   in the request message.
1543</t>
1544</section>
1545
1546<section title="412 Precondition Failed" anchor="status.412">
1547  <iref primary="true" item="412 Precondition Failed (status code)"/>
1548  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed"/>
1549<t>
1550   The precondition given in one or more of the request-header fields
1551   evaluated to false when it was tested on the server, as defined in
1552   <xref target="Part4"/>.
1553</t>
1554</section>
1555
1556<section title="413 Request Entity Too Large" anchor="status.413">
1557  <iref primary="true" item="413 Request Entity Too Large (status code)"/>
1558  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large"/>
1559<t>
1560   The server is refusing to process a request because the request
1561   entity is larger than the server is willing or able to process. The
1562   server MAY close the connection to prevent the client from continuing
1563   the request.
1564</t>
1565<t>
1566   If the condition is temporary, the server SHOULD include a Retry-After
1567   header field to indicate that it is temporary and after what
1568   time the client MAY try again.
1569</t>
1570</section>
1571
1572<section title="414 Request-URI Too Long" anchor="status.414">
1573  <iref primary="true" item="414 Request-URI Too Long (status code)"/>
1574  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long"/>
1575<t>
1576   The server is refusing to service the request because the Request-URI
1577   is longer than the server is willing to interpret. This rare
1578   condition is only likely to occur when a client has improperly
1579   converted a POST request to a GET request with long query
1580   information, when the client has descended into a URI "black hole" of
1581   redirection (e.g., a redirected URI prefix that points to a suffix of
1582   itself), or when the server is under attack by a client attempting to
1583   exploit security holes present in some servers using fixed-length
1584   buffers for reading or manipulating the Request-URI.
1585</t>
1586</section>
1587
1588<section title="415 Unsupported Media Type" anchor="status.415">
1589  <iref primary="true" item="415 Unsupported Media Type (status code)"/>
1590  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type"/>
1591<t>
1592   The server is refusing to service the request because the entity of
1593   the request is in a format not supported by the requested resource
1594   for the requested method.
1595</t>
1596</section>
1597
1598<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1599  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)"/>
1600  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable"/>
1601<t>
1602   The request included a Range request-header field (Section 6.4 of <xref target="Part5"/>) and none of
1603   the range-specifier values in this field overlap the current extent
1604   of the selected resource.
1605</t>
1606</section>
1607
1608<section title="417 Expectation Failed" anchor="status.417">
1609  <iref primary="true" item="417 Expectation Failed (status code)"/>
1610  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed"/>
1611<t>
1612   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1613   could not be met by this server, or, if the server is a proxy,
1614   the server has unambiguous evidence that the request could not be met
1615   by the next-hop server.
1616</t>
1617</section>
1618</section>
1619
1620<section title="Server Error 5xx" anchor="status.5xx">
1621<t>
1622   Response status codes beginning with the digit "5" indicate cases in
1623   which the server is aware that it has erred or is incapable of
1624   performing the request. Except when responding to a HEAD request, the
1625   server SHOULD include an entity containing an explanation of the
1626   error situation, and whether it is a temporary or permanent
1627   condition. User agents SHOULD display any included entity to the
1628   user. These response codes are applicable to any request method.
1629</t>
1630
1631<section title="500 Internal Server Error" anchor="status.500">
1632  <iref primary="true" item="500 Internal Server Error (status code)"/>
1633  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error"/>
1634<t>
1635   The server encountered an unexpected condition which prevented it
1636   from fulfilling the request.
1637</t>
1638</section>
1639
1640<section title="501 Not Implemented" anchor="status.501">
1641  <iref primary="true" item="501 Not Implemented (status code)"/>
1642  <iref primary="true" item="Status Codes" subitem="501 Not Implemented"/>
1643<t>
1644   The server does not support the functionality required to fulfill the
1645   request. This is the appropriate response when the server does not
1646   recognize the request method and is not capable of supporting it for
1647   any resource.
1648</t>
1649</section>
1650
1651<section title="502 Bad Gateway" anchor="status.502">
1652  <iref primary="true" item="502 Bad Gateway (status code)"/>
1653  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway"/>
1654<t>
1655   The server, while acting as a gateway or proxy, received an invalid
1656   response from the upstream server it accessed in attempting to
1657   fulfill the request.
1658</t>
1659</section>
1660
1661<section title="503 Service Unavailable" anchor="status.503">
1662  <iref primary="true" item="503 Service Unavailable (status code)"/>
1663  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable"/>
1664<t>
1665   The server is currently unable to handle the request due to a
1666   temporary overloading or maintenance of the server. The implication
1667   is that this is a temporary condition which will be alleviated after
1668   some delay. If known, the length of the delay MAY be indicated in a
1669   Retry-After header. If no Retry-After is given, the client SHOULD
1670   handle the response as it would for a 500 response.
1671  <list><t>
1672      Note: The existence of the 503 status code does not imply that a
1673      server must use it when becoming overloaded. Some servers may wish
1674      to simply refuse the connection.
1675  </t></list>
1676</t>
1677</section>
1678
1679<section title="504 Gateway Timeout" anchor="status.504">
1680  <iref primary="true" item="504 Gateway Timeout (status code)"/>
1681  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout"/>
1682<t>
1683   The server, while acting as a gateway or proxy, did not receive a
1684   timely response from the upstream server specified by the URI (e.g.
1685   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1686   to access in attempting to complete the request.
1687  <list><t>
1688      Note: Note to implementors: some deployed proxies are known to
1689      return 400 or 500 when DNS lookups time out.
1690  </t></list>
1691</t>
1692</section>
1693
1694<section title="505 HTTP Version Not Supported" anchor="status.505">
1695  <iref primary="true" item="505 HTTP Version Not Supported (status code)"/>
1696  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported"/>
1697<t>
1698   The server does not support, or refuses to support, the protocol
1699   version that was used in the request message. The server is
1700   indicating that it is unable or unwilling to complete the request
1701   using the same major version as the client, as described in Section 3.1 of <xref target="Part1"/>,
1702   other than with this error message. The response SHOULD contain
1703   an entity describing why that version is not supported and what other
1704   protocols are supported by that server.
1705</t>
1706
1707</section>
1708</section>
1709</section>
1710
1711
1712<section title="Header Field Definitions" anchor="header.fields">
1713<t>
1714   This section defines the syntax and semantics of HTTP/1.1 header fields
1715   related to request and response semantics.
1716</t>
1717<t>
1718   For entity-header fields, both sender and recipient refer to either the
1719   client or the server, depending on who sends and who receives the entity.
1720</t>
1721
1722<section title="Allow" anchor="header.allow">
1723  <iref primary="true" item="Allow header"/>
1724  <iref primary="true" item="Headers" subitem="Allow"/>
1725 
1726<t>
1727      The Allow response-header field lists the set of methods advertised as
1728      supported by the resource identified by the Request-URI. The purpose of
1729      this field is strictly to inform the recipient of valid methods
1730      associated with the resource. An Allow header field MUST be
1731      present in a 405 (Method Not Allowed) response.
1732</t>
1733<figure><iref primary="true" item="Grammar" subitem="Allow"/><artwork type="abnf2616"><![CDATA[
1734  Allow   = "Allow" ":" #Method
1735]]></artwork></figure>
1736<t>
1737      Example of use:
1738</t>
1739<figure><artwork type="example"><![CDATA[
1740       Allow: GET, HEAD, PUT
1741]]></artwork></figure>
1742<t>
1743      The actual set of allowed methods is defined
1744      by the origin server at the time of each request.
1745</t>
1746<t>
1747      A proxy MUST NOT modify the Allow header field even if it does not
1748      understand all the methods specified, since the user agent might
1749      have other means of communicating with the origin server.
1750</t>
1751</section>
1752
1753<section title="Expect" anchor="header.expect">
1754  <iref primary="true" item="Expect header"/>
1755  <iref primary="true" item="Headers" subitem="Expect"/>
1756 
1757 
1758 
1759 
1760<t>
1761   The Expect request-header field is used to indicate that particular
1762   server behaviors are required by the client.
1763</t>
1764<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[
1765  Expect       =  "Expect" ":" 1#expectation
1766 
1767  expectation  =  "100-continue" | expectation-extension
1768  expectation-extension =  token [ "=" ( token | quoted-string )
1769                           *expect-params ]
1770  expect-params =  ";" token [ "=" ( token | quoted-string ) ]
1771]]></artwork></figure>
1772<t>
1773   A server that does not understand or is unable to comply with any of
1774   the expectation values in the Expect field of a request MUST respond
1775   with appropriate error status. The server MUST respond with a 417
1776   (Expectation Failed) status if any of the expectations cannot be met
1777   or, if there are other problems with the request, some other 4xx
1778   status.
1779</t>
1780<t>
1781   This header field is defined with extensible syntax to allow for
1782   future extensions. If a server receives a request containing an
1783   Expect field that includes an expectation-extension that it does not
1784   support, it MUST respond with a 417 (Expectation Failed) status.
1785</t>
1786<t>
1787   Comparison of expectation values is case-insensitive for unquoted
1788   tokens (including the 100-continue token), and is case-sensitive for
1789   quoted-string expectation-extensions.
1790</t>
1791<t>
1792   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy MUST
1793   return a 417 (Expectation Failed) status if it receives a request
1794   with an expectation that it cannot meet. However, the Expect
1795   request-header itself is end-to-end; it MUST be forwarded if the
1796   request is forwarded.
1797</t>
1798<t>
1799   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1800   Expect header.
1801</t>
1802<t>
1803   See Section 7.2.3 of <xref target="Part1"/> for the use of the 100 (Continue) status.
1804</t>
1805</section>
1806
1807<section title="From" anchor="header.from">
1808  <iref primary="true" item="From header"/>
1809  <iref primary="true" item="Headers" subitem="From"/>
1810 
1811 
1812<t>
1813   The From request-header field, if given, SHOULD contain an Internet
1814   e-mail address for the human user who controls the requesting user
1815   agent. The address SHOULD be machine-usable, as defined by "mailbox"
1816   in Section 3.4 of <xref target="RFC2822"/>:
1817</t>
1818<figure><iref primary="true" item="Grammar" subitem="From"/><artwork type="abnf2616"><![CDATA[
1819  From    = "From" ":" mailbox
1820 
1821  mailbox = <mailbox, defined in [RFC2822], Section 3.4>
1822]]></artwork></figure>
1823<t>
1824   An example is:
1825</t>
1826<figure><artwork type="example"><![CDATA[
1827    From: webmaster@example.org
1828]]></artwork></figure>
1829<t>
1830   This header field MAY be used for logging purposes and as a means for
1831   identifying the source of invalid or unwanted requests. It SHOULD NOT
1832   be used as an insecure form of access protection. The interpretation
1833   of this field is that the request is being performed on behalf of the
1834   person given, who accepts responsibility for the method performed. In
1835   particular, robot agents SHOULD include this header so that the
1836   person responsible for running the robot can be contacted if problems
1837   occur on the receiving end.
1838</t>
1839<t>
1840   The Internet e-mail address in this field MAY be separate from the
1841   Internet host which issued the request. For example, when a request
1842   is passed through a proxy the original issuer's address SHOULD be
1843   used.
1844</t>
1845<t>
1846   The client SHOULD NOT  send the From header field without the user's
1847   approval, as it might conflict with the user's privacy interests or
1848   their site's security policy. It is strongly recommended that the
1849   user be able to disable, enable, and modify the value of this field
1850   at any time prior to a request.
1851</t>
1852</section>
1853
1854<section title="Location" anchor="header.location">
1855  <iref primary="true" item="Location header"/>
1856  <iref primary="true" item="Headers" subitem="Location"/>
1857 
1858<t>
1859   The Location response-header field is used for the identification of a
1860   new resource or to redirect the recipient to a location other than the
1861   Request-URI for completion of the request.  For 201 (Created)
1862   responses, the Location is that of the new resource which was created
1863   by the request. For 3xx responses, the location SHOULD indicate the
1864   server's preferred URI for automatic redirection to the resource. The
1865   field value consists of a single absolute URI.
1866</t>
1867<figure><iref primary="true" item="Grammar" subitem="Location"/><artwork type="abnf2616"><![CDATA[
1868  Location       = "Location" ":" absoluteURI [ "#" fragment ]
1869]]></artwork></figure>
1870<t>
1871   An example is:
1872</t>
1873<figure><artwork type="example"><![CDATA[
1874    Location: http://www.example.org/pub/WWW/People.html
1875]]></artwork></figure>
1876<t>
1877  <list><t>
1878      Note: The Content-Location header field (Section 6.7 of <xref target="Part3"/>) differs
1879      from Location in that the Content-Location identifies the original
1880      location of the entity enclosed in the response. It is therefore
1881      possible for a response to contain header fields for both Location
1882      and Content-Location.
1883  </t></list>
1884</t>
1885<t>
1886   There are circumstances in which a fragment identifier in a Location URL would not be appropriate:
1887   <list style="symbols">
1888      <t>With a 201 Created response, because in this usage the Location header specifies the URL for the entire created resource.</t>
1889      <t>With a 300 Multiple Choices, since the choice decision is intended to be made on resource characteristics and not fragment characteristics.</t>
1890      <t>With 305 Use Proxy.</t>
1891   </list>
1892</t>
1893</section>
1894
1895<section title="Max-Forwards" anchor="header.max-forwards">
1896  <iref primary="true" item="Max-Forwards header"/>
1897  <iref primary="true" item="Headers" subitem="Max-Forwards"/>
1898 
1899<t>
1900   The Max-Forwards request-header field provides a mechanism with the
1901   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1902   number of proxies or gateways that can forward the request to the
1903   next inbound server. This can be useful when the client is attempting
1904   to trace a request chain which appears to be failing or looping in
1905   mid-chain.
1906</t>
1907<figure><iref primary="true" item="Grammar" subitem="Max-Forwards"/><artwork type="abnf2616"><![CDATA[
1908  Max-Forwards   = "Max-Forwards" ":" 1*DIGIT
1909]]></artwork></figure>
1910<t>
1911   The Max-Forwards value is a decimal integer indicating the remaining
1912   number of times this request message may be forwarded.
1913</t>
1914<t>
1915   Each proxy or gateway recipient of a TRACE or OPTIONS request
1916   containing a Max-Forwards header field MUST check and update its
1917   value prior to forwarding the request. If the received value is zero
1918   (0), the recipient MUST NOT forward the request; instead, it MUST
1919   respond as the final recipient. If the received Max-Forwards value is
1920   greater than zero, then the forwarded message MUST contain an updated
1921   Max-Forwards field with a value decremented by one (1).
1922</t>
1923<t>
1924   The Max-Forwards header field MAY be ignored for all other methods
1925   defined by this specification and for any extension methods for which
1926   it is not explicitly referred to as part of that method definition.
1927</t>
1928</section>
1929
1930<section title="Referer" anchor="header.referer">
1931  <iref primary="true" item="Referer header"/>
1932  <iref primary="true" item="Headers" subitem="Referer"/>
1933 
1934<t>
1935   The Referer[sic] request-header field allows the client to specify,
1936   for the server's benefit, the address (URI) of the resource from
1937   which the Request-URI was obtained (the "referrer", although the
1938   header field is misspelled.) The Referer request-header allows a
1939   server to generate lists of back-links to resources for interest,
1940   logging, optimized caching, etc. It also allows obsolete or mistyped
1941   links to be traced for maintenance. The Referer field MUST NOT be
1942   sent if the Request-URI was obtained from a source that does not have
1943   its own URI, such as input from the user keyboard.
1944</t>
1945<figure><iref primary="true" item="Grammar" subitem="Referer"/><artwork type="abnf2616"><![CDATA[
1946  Referer        = "Referer" ":" ( absoluteURI | relativeURI )
1947]]></artwork></figure>
1948<t>
1949   Example:
1950</t>
1951<figure><artwork type="example"><![CDATA[
1952    Referer: http://www.example.org/hypertext/Overview.html
1953]]></artwork></figure>
1954<t>
1955   If the field value is a relative URI, it SHOULD be interpreted
1956   relative to the Request-URI. The URI MUST NOT include a fragment. See
1957   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
1958</t>
1959</section>
1960
1961<section title="Retry-After" anchor="header.retry-after">
1962  <iref primary="true" item="Retry-After header"/>
1963  <iref primary="true" item="Headers" subitem="Retry-After"/>
1964 
1965<t>
1966   The Retry-After response-header field can be used with a 503 (Service
1967   Unavailable) response to indicate how long the service is expected to
1968   be unavailable to the requesting client. This field MAY also be used
1969   with any 3xx (Redirection) response to indicate the minimum time the
1970   user-agent is asked wait before issuing the redirected request. The
1971   value of this field can be either an HTTP-date or an integer number
1972   of seconds (in decimal) after the time of the response.
1973</t>
1974<figure><iref primary="true" item="Grammar" subitem="Retry-After"/><artwork type="abnf2616"><![CDATA[
1975  Retry-After   = "Retry-After" ":" ( HTTP-date | delta-seconds )
1976]]></artwork></figure>
1977<t anchor="rule.delta-seconds">
1978 
1979   Time spans are non-negative decimal integers, representing time in
1980   seconds.
1981</t>
1982<figure><iref primary="true" item="Grammar" subitem="delta-seconds"/><artwork type="abnf2616"><![CDATA[
1983  delta-seconds  = 1*DIGIT
1984]]></artwork></figure>
1985<t>
1986   Two examples of its use are
1987</t>
1988<figure><artwork type="example"><![CDATA[
1989    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
1990    Retry-After: 120
1991]]></artwork></figure>
1992<t>
1993   In the latter example, the delay is 2 minutes.
1994</t>
1995</section>
1996
1997<section title="Server" anchor="header.server">
1998  <iref primary="true" item="Server header"/>
1999  <iref primary="true" item="Headers" subitem="Server"/>
2000 
2001<t>
2002   The Server response-header field contains information about the
2003   software used by the origin server to handle the request. The field
2004   can contain multiple product tokens (Section 3.5 of <xref target="Part1"/>) and comments
2005   identifying the server and any significant subproducts. The product
2006   tokens are listed in order of their significance for identifying the
2007   application.
2008</t>
2009<figure><iref primary="true" item="Grammar" subitem="Server"/><artwork type="abnf2616"><![CDATA[
2010  Server         = "Server" ":" 1*( product | comment )
2011]]></artwork></figure>
2012<t>
2013   Example:
2014</t>
2015<figure><artwork type="example"><![CDATA[
2016    Server: CERN/3.0 libwww/2.17
2017]]></artwork></figure>
2018<t>
2019   If the response is being forwarded through a proxy, the proxy
2020   application MUST NOT modify the Server response-header. Instead, it
2021   MUST include a Via field (as described in Section 8.9 of <xref target="Part1"/>).
2022  <list><t>
2023      Note: Revealing the specific software version of the server might
2024      allow the server machine to become more vulnerable to attacks
2025      against software that is known to contain security holes. Server
2026      implementors are encouraged to make this field a configurable
2027      option.
2028  </t></list>
2029</t>
2030</section>
2031
2032<section title="User-Agent" anchor="header.user-agent">
2033  <iref primary="true" item="User-Agent header"/>
2034  <iref primary="true" item="Headers" subitem="User-Agent"/>
2035 
2036<t>
2037   The User-Agent request-header field contains information about the
2038   user agent originating the request. This is for statistical purposes,
2039   the tracing of protocol violations, and automated recognition of user
2040   agents for the sake of tailoring responses to avoid particular user
2041   agent limitations. User agents SHOULD include this field with
2042   requests. The field can contain multiple product tokens (Section 3.5 of <xref target="Part1"/>)
2043   and comments identifying the agent and any subproducts which form a
2044   significant part of the user agent. By convention, the product tokens
2045   are listed in order of their significance for identifying the
2046   application.
2047</t>
2048<figure><iref primary="true" item="Grammar" subitem="User-Agent"/><artwork type="abnf2616"><![CDATA[
2049  User-Agent     = "User-Agent" ":" 1*( product | comment )
2050]]></artwork></figure>
2051<t>
2052   Example:
2053</t>
2054<figure><artwork type="example"><![CDATA[
2055    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2056]]></artwork></figure>
2057</section>
2058
2059</section>
2060
2061<section title="IANA Considerations" anchor="IANA.considerations">
2062
2063<section title="Method Registry" anchor="method.registration">
2064<t>
2065  The registration procedure for HTTP Methods is defined by
2066  <xref target="method.registry"/> of this document.
2067</t>
2068<t>
2069   The HTTP Method Registry located at <eref target="http://www.iana.org/assignments/http-methods"/>
2070   should be populated with the registrations below:
2071</t>
2072<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2073<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2074   <ttcol>Method</ttcol>
2075   <ttcol>Safe</ttcol>
2076   <ttcol>Reference</ttcol>
2077   <c>CONNECT</c>
2078   <c>no</c>
2079   <c>
2080      <xref target="CONNECT"/>
2081   </c>
2082   <c>DELETE</c>
2083   <c>no</c>
2084   <c>
2085      <xref target="DELETE"/>
2086   </c>
2087   <c>GET</c>
2088   <c>yes</c>
2089   <c>
2090      <xref target="GET"/>
2091   </c>
2092   <c>HEAD</c>
2093   <c>yes</c>
2094   <c>
2095      <xref target="HEAD"/>
2096   </c>
2097   <c>OPTIONS</c>
2098   <c>yes</c>
2099   <c>
2100      <xref target="OPTIONS"/>
2101   </c>
2102   <c>POST</c>
2103   <c>no</c>
2104   <c>
2105      <xref target="POST"/>
2106   </c>
2107   <c>PUT</c>
2108   <c>no</c>
2109   <c>
2110      <xref target="PUT"/>
2111   </c>
2112   <c>TRACE</c>
2113   <c>yes</c>
2114   <c>
2115      <xref target="TRACE"/>
2116   </c>
2117</texttable>
2118<!--(END)-->
2119</section>
2120
2121<section title="Status Code Registry" anchor="status.code.registration">
2122<t>
2123   The registration procedure for HTTP Status Codes -- previously defined
2124   in Section 7.1 of <xref target="RFC2817"/> -- is now defined
2125   by <xref target="status.code.registry"/> of this document.
2126</t>
2127<t>
2128   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2129   should be updated with the registrations below:
2130</t>
2131<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2132<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2133   <ttcol>Value</ttcol>
2134   <ttcol>Description</ttcol>
2135   <ttcol>Reference</ttcol>
2136   <c>100</c>
2137   <c>Continue</c>
2138   <c>
2139      <xref target="status.100"/>
2140   </c>
2141   <c>101</c>
2142   <c>Switching Protocols</c>
2143   <c>
2144      <xref target="status.101"/>
2145   </c>
2146   <c>200</c>
2147   <c>OK</c>
2148   <c>
2149      <xref target="status.200"/>
2150   </c>
2151   <c>201</c>
2152   <c>Created</c>
2153   <c>
2154      <xref target="status.201"/>
2155   </c>
2156   <c>202</c>
2157   <c>Accepted</c>
2158   <c>
2159      <xref target="status.202"/>
2160   </c>
2161   <c>203</c>
2162   <c>Non-Authoritative Information</c>
2163   <c>
2164      <xref target="status.203"/>
2165   </c>
2166   <c>204</c>
2167   <c>No Content</c>
2168   <c>
2169      <xref target="status.204"/>
2170   </c>
2171   <c>205</c>
2172   <c>Reset Content</c>
2173   <c>
2174      <xref target="status.205"/>
2175   </c>
2176   <c>206</c>
2177   <c>Partial Content</c>
2178   <c>
2179      <xref target="status.206"/>
2180   </c>
2181   <c>300</c>
2182   <c>Multiple Choices</c>
2183   <c>
2184      <xref target="status.300"/>
2185   </c>
2186   <c>301</c>
2187   <c>Moved Permanently</c>
2188   <c>
2189      <xref target="status.301"/>
2190   </c>
2191   <c>302</c>
2192   <c>Found</c>
2193   <c>
2194      <xref target="status.302"/>
2195   </c>
2196   <c>303</c>
2197   <c>See Other</c>
2198   <c>
2199      <xref target="status.303"/>
2200   </c>
2201   <c>304</c>
2202   <c>Not Modified</c>
2203   <c>
2204      <xref target="status.304"/>
2205   </c>
2206   <c>305</c>
2207   <c>Use Proxy</c>
2208   <c>
2209      <xref target="status.305"/>
2210   </c>
2211   <c>306</c>
2212   <c>(Unused)</c>
2213   <c>
2214      <xref target="status.306"/>
2215   </c>
2216   <c>307</c>
2217   <c>Temporary Redirect</c>
2218   <c>
2219      <xref target="status.307"/>
2220   </c>
2221   <c>400</c>
2222   <c>Bad Request</c>
2223   <c>
2224      <xref target="status.400"/>
2225   </c>
2226   <c>401</c>
2227   <c>Unauthorized</c>
2228   <c>
2229      <xref target="status.401"/>
2230   </c>
2231   <c>402</c>
2232   <c>Payment Required</c>
2233   <c>
2234      <xref target="status.402"/>
2235   </c>
2236   <c>403</c>
2237   <c>Forbidden</c>
2238   <c>
2239      <xref target="status.403"/>
2240   </c>
2241   <c>404</c>
2242   <c>Not Found</c>
2243   <c>
2244      <xref target="status.404"/>
2245   </c>
2246   <c>405</c>
2247   <c>Method Not Allowed</c>
2248   <c>
2249      <xref target="status.405"/>
2250   </c>
2251   <c>406</c>
2252   <c>Not Acceptable</c>
2253   <c>
2254      <xref target="status.406"/>
2255   </c>
2256   <c>407</c>
2257   <c>Proxy Authentication Required</c>
2258   <c>
2259      <xref target="status.407"/>
2260   </c>
2261   <c>408</c>
2262   <c>Request Timeout</c>
2263   <c>
2264      <xref target="status.408"/>
2265   </c>
2266   <c>409</c>
2267   <c>Conflict</c>
2268   <c>
2269      <xref target="status.409"/>
2270   </c>
2271   <c>410</c>
2272   <c>Gone</c>
2273   <c>
2274      <xref target="status.410"/>
2275   </c>
2276   <c>411</c>
2277   <c>Length Required</c>
2278   <c>
2279      <xref target="status.411"/>
2280   </c>
2281   <c>412</c>
2282   <c>Precondition Failed</c>
2283   <c>
2284      <xref target="status.412"/>
2285   </c>
2286   <c>413</c>
2287   <c>Request Entity Too Large</c>
2288   <c>
2289      <xref target="status.413"/>
2290   </c>
2291   <c>414</c>
2292   <c>Request-URI Too Long</c>
2293   <c>
2294      <xref target="status.414"/>
2295   </c>
2296   <c>415</c>
2297   <c>Unsupported Media Type</c>
2298   <c>
2299      <xref target="status.415"/>
2300   </c>
2301   <c>416</c>
2302   <c>Requested Range Not Satisfiable</c>
2303   <c>
2304      <xref target="status.416"/>
2305   </c>
2306   <c>417</c>
2307   <c>Expectation Failed</c>
2308   <c>
2309      <xref target="status.417"/>
2310   </c>
2311   <c>500</c>
2312   <c>Internal Server Error</c>
2313   <c>
2314      <xref target="status.500"/>
2315   </c>
2316   <c>501</c>
2317   <c>Not Implemented</c>
2318   <c>
2319      <xref target="status.501"/>
2320   </c>
2321   <c>502</c>
2322   <c>Bad Gateway</c>
2323   <c>
2324      <xref target="status.502"/>
2325   </c>
2326   <c>503</c>
2327   <c>Service Unavailable</c>
2328   <c>
2329      <xref target="status.503"/>
2330   </c>
2331   <c>504</c>
2332   <c>Gateway Timeout</c>
2333   <c>
2334      <xref target="status.504"/>
2335   </c>
2336   <c>505</c>
2337   <c>HTTP Version Not Supported</c>
2338   <c>
2339      <xref target="status.505"/>
2340   </c>
2341</texttable>
2342<!--(END)-->
2343</section>
2344<section title="Message Header Registration" anchor="message.header.registration">
2345<t>
2346   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2347   with the permanent registrations below (see <xref target="RFC3864"/>):
2348</t>
2349<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2350<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2351   <ttcol>Header Field Name</ttcol>
2352   <ttcol>Protocol</ttcol>
2353   <ttcol>Status</ttcol>
2354   <ttcol>Reference</ttcol>
2355   <c>Allow</c>
2356   <c>http</c>
2357   <c>standard</c>
2358   <c>
2359      <xref target="header.allow"/>
2360   </c>
2361   <c>Expect</c>
2362   <c>http</c>
2363   <c>standard</c>
2364   <c>
2365      <xref target="header.expect"/>
2366   </c>
2367   <c>From</c>
2368   <c>http</c>
2369   <c>standard</c>
2370   <c>
2371      <xref target="header.from"/>
2372   </c>
2373   <c>Location</c>
2374   <c>http</c>
2375   <c>standard</c>
2376   <c>
2377      <xref target="header.location"/>
2378   </c>
2379   <c>Max-Forwards</c>
2380   <c>http</c>
2381   <c>standard</c>
2382   <c>
2383      <xref target="header.max-forwards"/>
2384   </c>
2385   <c>Referer</c>
2386   <c>http</c>
2387   <c>standard</c>
2388   <c>
2389      <xref target="header.referer"/>
2390   </c>
2391   <c>Retry-After</c>
2392   <c>http</c>
2393   <c>standard</c>
2394   <c>
2395      <xref target="header.retry-after"/>
2396   </c>
2397   <c>Server</c>
2398   <c>http</c>
2399   <c>standard</c>
2400   <c>
2401      <xref target="header.server"/>
2402   </c>
2403   <c>User-Agent</c>
2404   <c>http</c>
2405   <c>standard</c>
2406   <c>
2407      <xref target="header.user-agent"/>
2408   </c>
2409</texttable>
2410<!--(END)-->
2411<t>
2412   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2413</t>
2414</section>
2415</section>
2416
2417<section title="Security Considerations" anchor="security.considerations">
2418<t>
2419   This section is meant to inform application developers, information
2420   providers, and users of the security limitations in HTTP/1.1 as
2421   described by this document. The discussion does not include
2422   definitive solutions to the problems revealed, though it does make
2423   some suggestions for reducing security risks.
2424</t>
2425
2426<section title="Transfer of Sensitive Information" anchor="security.sensitive">
2427<t>
2428   Like any generic data transfer protocol, HTTP cannot regulate the
2429   content of the data that is transferred, nor is there any a priori
2430   method of determining the sensitivity of any particular piece of
2431   information within the context of any given request. Therefore,
2432   applications SHOULD supply as much control over this information as
2433   possible to the provider of that information. Four header fields are
2434   worth special mention in this context: Server, Via, Referer and From.
2435</t>
2436<t>
2437   Revealing the specific software version of the server might allow the
2438   server machine to become more vulnerable to attacks against software
2439   that is known to contain security holes. Implementors SHOULD make the
2440   Server header field a configurable option.
2441</t>
2442<t>
2443   Proxies which serve as a portal through a network firewall SHOULD
2444   take special precautions regarding the transfer of header information
2445   that identifies the hosts behind the firewall. In particular, they
2446   SHOULD remove, or replace with sanitized versions, any Via fields
2447   generated behind the firewall.
2448</t>
2449<t>
2450   The Referer header allows reading patterns to be studied and reverse
2451   links drawn. Although it can be very useful, its power can be abused
2452   if user details are not separated from the information contained in
2453   the Referer. Even when the personal information has been removed, the
2454   Referer header might indicate a private document's URI whose
2455   publication would be inappropriate.
2456</t>
2457<t>
2458   The information sent in the From field might conflict with the user's
2459   privacy interests or their site's security policy, and hence it
2460   SHOULD NOT  be transmitted without the user being able to disable,
2461   enable, and modify the contents of the field. The user MUST be able
2462   to set the contents of this field within a user preference or
2463   application defaults configuration.
2464</t>
2465<t>
2466   We suggest, though do not require, that a convenient toggle interface
2467   be provided for the user to enable or disable the sending of From and
2468   Referer information.
2469</t>
2470<t>
2471   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2472   fields can sometimes be used to determine that a specific client or
2473   server have a particular security hole which might be exploited.
2474   Unfortunately, this same information is often used for other valuable
2475   purposes for which HTTP currently has no better mechanism.
2476</t>
2477</section>
2478
2479<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
2480<t>
2481   Because the source of a link might be private information or might
2482   reveal an otherwise private information source, it is strongly
2483   recommended that the user be able to select whether or not the
2484   Referer field is sent. For example, a browser client could have a
2485   toggle switch for browsing openly/anonymously, which would
2486   respectively enable/disable the sending of Referer and From
2487   information.
2488</t>
2489<t>
2490   Clients SHOULD NOT include a Referer header field in a (non-secure)
2491   HTTP request if the referring page was transferred with a secure
2492   protocol.
2493</t>
2494<t>
2495   Authors of services should not use
2496   GET-based forms for the submission of sensitive data because that
2497   data will be encoded in the Request-URI. Many existing
2498   servers, proxies, and user agents log or display the Request-URI in
2499   places where it might be visible to third parties. Such services can
2500   use POST-based form submission instead.
2501</t>
2502</section>
2503
2504<section title="Location Headers and Spoofing" anchor="location.spoofing">
2505<t>
2506   If a single server supports multiple organizations that do not trust
2507   one another, then it MUST check the values of Location and Content-Location
2508   headers in responses that are generated under control of
2509   said organizations to make sure that they do not attempt to
2510   invalidate resources over which they have no authority.
2511</t>
2512</section>
2513
2514</section>
2515
2516<section title="Acknowledgments" anchor="ack">
2517</section>
2518</middle>
2519<back>
2520
2521<references title="Normative References">
2522
2523<reference anchor="Part1">
2524  <front>
2525    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2526    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2527      <organization abbrev="Day Software">Day Software</organization>
2528      <address><email>fielding@gbiv.com</email></address>
2529    </author>
2530    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2531      <organization>One Laptop per Child</organization>
2532      <address><email>jg@laptop.org</email></address>
2533    </author>
2534    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2535      <organization abbrev="HP">Hewlett-Packard Company</organization>
2536      <address><email>JeffMogul@acm.org</email></address>
2537    </author>
2538    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2539      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2540      <address><email>henrikn@microsoft.com</email></address>
2541    </author>
2542    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2543      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2544      <address><email>LMM@acm.org</email></address>
2545    </author>
2546    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2547      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2548      <address><email>paulle@microsoft.com</email></address>
2549    </author>
2550    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2551      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2552      <address><email>timbl@w3.org</email></address>
2553    </author>
2554    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2555      <organization abbrev="W3C">World Wide Web Consortium</organization>
2556      <address><email>ylafon@w3.org</email></address>
2557    </author>
2558    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2559      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2560      <address><email>julian.reschke@greenbytes.de</email></address>
2561    </author>
2562    <date month="August" year="2008"/>
2563  </front>
2564  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-04"/>
2565 
2566</reference>
2567
2568<reference anchor="Part3">
2569  <front>
2570    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2571    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2572      <organization abbrev="Day Software">Day Software</organization>
2573      <address><email>fielding@gbiv.com</email></address>
2574    </author>
2575    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2576      <organization>One Laptop per Child</organization>
2577      <address><email>jg@laptop.org</email></address>
2578    </author>
2579    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2580      <organization abbrev="HP">Hewlett-Packard Company</organization>
2581      <address><email>JeffMogul@acm.org</email></address>
2582    </author>
2583    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2584      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2585      <address><email>henrikn@microsoft.com</email></address>
2586    </author>
2587    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2588      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2589      <address><email>LMM@acm.org</email></address>
2590    </author>
2591    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2592      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2593      <address><email>paulle@microsoft.com</email></address>
2594    </author>
2595    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2596      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2597      <address><email>timbl@w3.org</email></address>
2598    </author>
2599    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2600      <organization abbrev="W3C">World Wide Web Consortium</organization>
2601      <address><email>ylafon@w3.org</email></address>
2602    </author>
2603    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2604      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2605      <address><email>julian.reschke@greenbytes.de</email></address>
2606    </author>
2607    <date month="August" year="2008"/>
2608  </front>
2609  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-04"/>
2610 
2611</reference>
2612
2613<reference anchor="Part4">
2614  <front>
2615    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2616    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2617      <organization abbrev="Day Software">Day Software</organization>
2618      <address><email>fielding@gbiv.com</email></address>
2619    </author>
2620    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2621      <organization>One Laptop per Child</organization>
2622      <address><email>jg@laptop.org</email></address>
2623    </author>
2624    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2625      <organization abbrev="HP">Hewlett-Packard Company</organization>
2626      <address><email>JeffMogul@acm.org</email></address>
2627    </author>
2628    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2629      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2630      <address><email>henrikn@microsoft.com</email></address>
2631    </author>
2632    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2633      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2634      <address><email>LMM@acm.org</email></address>
2635    </author>
2636    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2637      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2638      <address><email>paulle@microsoft.com</email></address>
2639    </author>
2640    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2641      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2642      <address><email>timbl@w3.org</email></address>
2643    </author>
2644    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2645      <organization abbrev="W3C">World Wide Web Consortium</organization>
2646      <address><email>ylafon@w3.org</email></address>
2647    </author>
2648    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2649      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2650      <address><email>julian.reschke@greenbytes.de</email></address>
2651    </author>
2652    <date month="August" year="2008"/>
2653  </front>
2654  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-04"/>
2655 
2656</reference>
2657
2658<reference anchor="Part5">
2659  <front>
2660    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2661    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2662      <organization abbrev="Day Software">Day Software</organization>
2663      <address><email>fielding@gbiv.com</email></address>
2664    </author>
2665    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2666      <organization>One Laptop per Child</organization>
2667      <address><email>jg@laptop.org</email></address>
2668    </author>
2669    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2670      <organization abbrev="HP">Hewlett-Packard Company</organization>
2671      <address><email>JeffMogul@acm.org</email></address>
2672    </author>
2673    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2674      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2675      <address><email>henrikn@microsoft.com</email></address>
2676    </author>
2677    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2678      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2679      <address><email>LMM@acm.org</email></address>
2680    </author>
2681    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2682      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2683      <address><email>paulle@microsoft.com</email></address>
2684    </author>
2685    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2686      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2687      <address><email>timbl@w3.org</email></address>
2688    </author>
2689    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2690      <organization abbrev="W3C">World Wide Web Consortium</organization>
2691      <address><email>ylafon@w3.org</email></address>
2692    </author>
2693    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2694      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2695      <address><email>julian.reschke@greenbytes.de</email></address>
2696    </author>
2697    <date month="August" year="2008"/>
2698  </front>
2699  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-04"/>
2700 
2701</reference>
2702
2703<reference anchor="Part6">
2704  <front>
2705    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2706    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2707      <organization abbrev="Day Software">Day Software</organization>
2708      <address><email>fielding@gbiv.com</email></address>
2709    </author>
2710    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2711      <organization>One Laptop per Child</organization>
2712      <address><email>jg@laptop.org</email></address>
2713    </author>
2714    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2715      <organization abbrev="HP">Hewlett-Packard Company</organization>
2716      <address><email>JeffMogul@acm.org</email></address>
2717    </author>
2718    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2719      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2720      <address><email>henrikn@microsoft.com</email></address>
2721    </author>
2722    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2723      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2724      <address><email>LMM@acm.org</email></address>
2725    </author>
2726    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2727      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2728      <address><email>paulle@microsoft.com</email></address>
2729    </author>
2730    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2731      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2732      <address><email>timbl@w3.org</email></address>
2733    </author>
2734    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2735      <organization abbrev="W3C">World Wide Web Consortium</organization>
2736      <address><email>ylafon@w3.org</email></address>
2737    </author>
2738    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2739      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2740      <address><email>julian.reschke@greenbytes.de</email></address>
2741    </author>
2742    <date month="August" year="2008"/>
2743  </front>
2744  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-04"/>
2745 
2746</reference>
2747
2748<reference anchor="Part7">
2749  <front>
2750    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2751    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2752      <organization abbrev="Day Software">Day Software</organization>
2753      <address><email>fielding@gbiv.com</email></address>
2754    </author>
2755    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2756      <organization>One Laptop per Child</organization>
2757      <address><email>jg@laptop.org</email></address>
2758    </author>
2759    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2760      <organization abbrev="HP">Hewlett-Packard Company</organization>
2761      <address><email>JeffMogul@acm.org</email></address>
2762    </author>
2763    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2764      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2765      <address><email>henrikn@microsoft.com</email></address>
2766    </author>
2767    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2768      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2769      <address><email>LMM@acm.org</email></address>
2770    </author>
2771    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2772      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2773      <address><email>paulle@microsoft.com</email></address>
2774    </author>
2775    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2776      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2777      <address><email>timbl@w3.org</email></address>
2778    </author>
2779    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2780      <organization abbrev="W3C">World Wide Web Consortium</organization>
2781      <address><email>ylafon@w3.org</email></address>
2782    </author>
2783    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2784      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2785      <address><email>julian.reschke@greenbytes.de</email></address>
2786    </author>
2787    <date month="August" year="2008"/>
2788  </front>
2789  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-04"/>
2790 
2791</reference>
2792
2793<reference anchor="RFC2119">
2794  <front>
2795    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2796    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2797      <organization>Harvard University</organization>
2798      <address><email>sob@harvard.edu</email></address>
2799    </author>
2800    <date month="March" year="1997"/>
2801  </front>
2802  <seriesInfo name="BCP" value="14"/>
2803  <seriesInfo name="RFC" value="2119"/>
2804</reference>
2805
2806</references>
2807
2808<references title="Informative References">
2809
2810<reference anchor="RFC1945">
2811  <front>
2812    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2813    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2814      <organization>MIT, Laboratory for Computer Science</organization>
2815      <address><email>timbl@w3.org</email></address>
2816    </author>
2817    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2818      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2819      <address><email>fielding@ics.uci.edu</email></address>
2820    </author>
2821    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2822      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2823      <address><email>frystyk@w3.org</email></address>
2824    </author>
2825    <date month="May" year="1996"/>
2826  </front>
2827  <seriesInfo name="RFC" value="1945"/>
2828</reference>
2829
2830<reference anchor="RFC2068">
2831  <front>
2832    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2833    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2834      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2835      <address><email>fielding@ics.uci.edu</email></address>
2836    </author>
2837    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2838      <organization>MIT Laboratory for Computer Science</organization>
2839      <address><email>jg@w3.org</email></address>
2840    </author>
2841    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2842      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2843      <address><email>mogul@wrl.dec.com</email></address>
2844    </author>
2845    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2846      <organization>MIT Laboratory for Computer Science</organization>
2847      <address><email>frystyk@w3.org</email></address>
2848    </author>
2849    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2850      <organization>MIT Laboratory for Computer Science</organization>
2851      <address><email>timbl@w3.org</email></address>
2852    </author>
2853    <date month="January" year="1997"/>
2854  </front>
2855  <seriesInfo name="RFC" value="2068"/>
2856</reference>
2857
2858<reference anchor="RFC2616">
2859  <front>
2860    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2861    <author initials="R." surname="Fielding" fullname="R. Fielding">
2862      <organization>University of California, Irvine</organization>
2863      <address><email>fielding@ics.uci.edu</email></address>
2864    </author>
2865    <author initials="J." surname="Gettys" fullname="J. Gettys">
2866      <organization>W3C</organization>
2867      <address><email>jg@w3.org</email></address>
2868    </author>
2869    <author initials="J." surname="Mogul" fullname="J. Mogul">
2870      <organization>Compaq Computer Corporation</organization>
2871      <address><email>mogul@wrl.dec.com</email></address>
2872    </author>
2873    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2874      <organization>MIT Laboratory for Computer Science</organization>
2875      <address><email>frystyk@w3.org</email></address>
2876    </author>
2877    <author initials="L." surname="Masinter" fullname="L. Masinter">
2878      <organization>Xerox Corporation</organization>
2879      <address><email>masinter@parc.xerox.com</email></address>
2880    </author>
2881    <author initials="P." surname="Leach" fullname="P. Leach">
2882      <organization>Microsoft Corporation</organization>
2883      <address><email>paulle@microsoft.com</email></address>
2884    </author>
2885    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2886      <organization>W3C</organization>
2887      <address><email>timbl@w3.org</email></address>
2888    </author>
2889    <date month="June" year="1999"/>
2890  </front>
2891  <seriesInfo name="RFC" value="2616"/>
2892</reference>
2893
2894<reference anchor="RFC2817">
2895  <front>
2896    <title>Upgrading to TLS Within HTTP/1.1</title>
2897    <author initials="R." surname="Khare" fullname="R. Khare">
2898      <organization>4K Associates / UC Irvine</organization>
2899      <address><email>rohit@4K-associates.com</email></address>
2900    </author>
2901    <author initials="S." surname="Lawrence" fullname="S. Lawrence">
2902      <organization>Agranat Systems, Inc.</organization>
2903      <address><email>lawrence@agranat.com</email></address>
2904    </author>
2905    <date year="2000" month="May"/>
2906  </front>
2907  <seriesInfo name="RFC" value="2817"/>
2908</reference>
2909
2910<reference anchor="RFC2822">
2911  <front>
2912    <title>Internet Message Format</title>
2913    <author initials="P." surname="Resnick" fullname="P. Resnick">
2914      <organization>QUALCOMM Incorporated</organization>
2915    </author>
2916    <date year="2001" month="April"/>
2917  </front> 
2918  <seriesInfo name="RFC" value="2822"/>
2919</reference>
2920
2921<reference anchor="RFC3864">
2922  <front>
2923    <title>Registration Procedures for Message Header Fields</title>
2924    <author initials="G." surname="Klyne" fullname="G. Klyne">
2925      <organization>Nine by Nine</organization>
2926      <address><email>GK-IETF@ninebynine.org</email></address>
2927    </author>
2928    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
2929      <organization>BEA Systems</organization>
2930      <address><email>mnot@pobox.com</email></address>
2931    </author>
2932    <author initials="J." surname="Mogul" fullname="J. Mogul">
2933      <organization>HP Labs</organization>
2934      <address><email>JeffMogul@acm.org</email></address>
2935    </author>
2936    <date year="2004" month="September"/>
2937  </front>
2938  <seriesInfo name="BCP" value="90"/>
2939  <seriesInfo name="RFC" value="3864"/>
2940</reference>
2941
2942<reference anchor="RFC5226">
2943  <front>
2944    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2945    <author initials="T." surname="Narten" fullname="T. Narten">
2946      <organization>IBM</organization>
2947      <address><email>narten@us.ibm.com</email></address>
2948    </author>
2949    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
2950      <organization>Google</organization>
2951      <address><email>Harald@Alvestrand.no</email></address>
2952    </author>
2953    <date year="2008" month="May"/>
2954  </front>
2955  <seriesInfo name="BCP" value="26"/>
2956  <seriesInfo name="RFC" value="5226"/>
2957</reference>
2958
2959</references>
2960
2961<section title="Compatibility with Previous Versions" anchor="compatibility">
2962<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2963<t>
2964   Clarified which error code should be used for inbound server failures
2965   (e.g. DNS failures). (<xref target="status.504"/>).
2966</t>
2967<t>
2968   201 (Created) had a race that required an Etag be sent when a resource is
2969   first created. (<xref target="status.201"/>).
2970</t>
2971<t>
2972   Rewrite of message transmission requirements to make it much harder
2973   for implementors to get it wrong, as the consequences of errors here
2974   can have significant impact on the Internet, and to deal with the
2975   following problems:
2976  <list style="numbers">
2977      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
2978         this was incorrectly placing a requirement on the behavior of
2979         an implementation of a future version of HTTP/1.x</t>
2980
2981      <t>Made it clear that user-agents should retry requests, not
2982         "clients" in general.</t>
2983
2984      <t>Converted requirements for clients to ignore unexpected 100
2985         (Continue) responses, and for proxies to forward 100 responses,
2986         into a general requirement for 1xx responses.</t>
2987
2988      <t>Modified some TCP-specific language, to make it clearer that
2989         non-TCP transports are possible for HTTP.</t>
2990
2991      <t>Require that the origin server MUST NOT wait for the request
2992         body before it sends a required 100 (Continue) response.</t>
2993
2994      <t>Allow, rather than require, a server to omit 100 (Continue) if
2995         it has already seen some of the request body.</t>
2996
2997      <t>Allow servers to defend against denial-of-service attacks and
2998         broken clients.</t>
2999  </list>
3000</t>
3001<t>
3002   This change adds the Expect header and 417 status code.
3003</t>
3004<t>
3005   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
3006   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
3007</t>
3008<t>
3009   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
3010   implemented in previous versions of this specification. See Section 19.6.1 of <xref target="RFC2068"/>.
3011</t>
3012</section>
3013
3014<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3015<t>
3016  This document takes over the Status Code Registry, previously defined
3017  in Section 7.1 of <xref target="RFC2817"/>.
3018  (<xref target="status.code.registry"/>)
3019</t>
3020<t>
3021  Clarify definition of POST.
3022  (<xref target="POST"/>)
3023</t>
3024<t>
3025  Failed to consider that there are
3026  many other request methods that are safe to automatically redirect,
3027  and further that the user agent is able to make that determination
3028  based on the request method semantics.
3029  (Sections <xref format="counter" target="status.301"/>,
3030  <xref format="counter" target="status.302"/> and
3031  <xref format="counter" target="status.307"/>)
3032</t>
3033<t>
3034  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3035  It used to indicate that the requested resource must be accessed through the
3036  proxy given by the Location field. The Location field gave the URI of the
3037  proxy. The recipient was expected to repeat this single request via the proxy.
3038  (<xref target="status.305"/>)
3039</t>
3040<t>
3041  Reclassify Allow header as response header, removing the option to
3042  specify it in a PUT request.
3043  Relax the server requirement on the contents of the Allow header and
3044  remove requirement on clients to always trust the header value.
3045  (<xref target="header.allow"/>)
3046</t>
3047<t>
3048  Correct syntax of Location header to allow fragment,
3049  as referred symbol wasn't what was expected, and add some
3050  clarifications as to when it would not be appropriate.
3051  (<xref target="header.location"/>)
3052</t>
3053<t>
3054  In the description of the Server header, the Via field
3055  was described as a SHOULD. The requirement was and is stated
3056  correctly in the description of the Via header in Section 8.9 of <xref target="Part1"/>.
3057  (<xref target="header.server"/>)
3058</t>
3059</section>
3060
3061</section>
3062
3063<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
3064
3065<section title="Since RFC2616">
3066<t>
3067  Extracted relevant partitions from <xref target="RFC2616"/>.
3068</t>
3069</section>
3070
3071<section title="Since draft-ietf-httpbis-p2-semantics-00">
3072<t>
3073  Closed issues:
3074  <list style="symbols"> 
3075    <t>
3076      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
3077      "Via is a MUST"
3078      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
3079    </t>
3080    <t>
3081      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
3082      "Fragments allowed in Location"
3083      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
3084    </t>
3085    <t>
3086      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
3087      "Safe Methods vs Redirection"
3088      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
3089    </t>
3090    <t>
3091      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
3092      "Revise description of the POST method"
3093      (<eref target="http://purl.org/NET/http-errata#post"/>)
3094    </t>
3095    <t>
3096      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
3097      "Normative and Informative references"
3098    </t>
3099    <t>
3100      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
3101      "RFC2606 Compliance"
3102    </t>
3103    <t>
3104      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
3105      "Informative references"
3106    </t>
3107    <t>
3108      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
3109      "Redundant cross-references"
3110    </t>
3111  </list>
3112</t>
3113<t>
3114  Other changes:
3115  <list style="symbols"> 
3116    <t>
3117      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
3118    </t>
3119  </list>
3120</t>
3121</section>
3122
3123<section title="Since draft-ietf-httpbis-p2-semantics-01">
3124<t>
3125  Closed issues:
3126  <list style="symbols"> 
3127    <t>
3128      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
3129      "PUT side effects"
3130    </t>
3131    <t>
3132      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
3133      "Duplicate Host header requirements"
3134    </t>
3135  </list>
3136</t>
3137<t>
3138  Ongoing work on ABNF conversion (<eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3139  <list style="symbols"> 
3140    <t>
3141      Move "Product Tokens" section (back) into Part 1, as "token" is used
3142      in the definition of the Upgrade header.
3143    </t>
3144    <t>
3145      Add explicit references to BNF syntax and rules imported from other parts of the specification.
3146    </t>
3147    <t>
3148      Copy definition of delta-seconds from Part6 instead of referencing it.
3149    </t>
3150  </list>
3151</t>
3152</section>
3153
3154<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
3155<t>
3156  Closed issues:
3157  <list style="symbols"> 
3158    <t>
3159      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
3160      "Requiring Allow in 405 responses"
3161    </t>
3162    <t>
3163      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
3164      "Status Code Registry"
3165    </t>
3166    <t>
3167      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
3168      "Redirection vs. Location"
3169    </t>
3170    <t>
3171      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
3172      "Cacheability of 303 response"
3173    </t>
3174    <t>
3175      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
3176      "305 Use Proxy"
3177    </t>
3178    <t>
3179      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
3180      "Classification for Allow header"
3181    </t>
3182    <t>
3183      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
3184      "PUT - 'store under' vs 'store at'"
3185    </t>
3186  </list>
3187</t>
3188<t>
3189  Ongoing work on IANA Message Header Registration (<eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
3190  <list style="symbols"> 
3191    <t>
3192      Reference RFC 3984, and update header registrations for headers defined
3193      in this document.
3194    </t>
3195  </list>
3196</t>
3197<t>
3198  Ongoing work on ABNF conversion (<eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3199  <list style="symbols"> 
3200    <t>
3201      Replace string literals when the string really is case-sensitive (method).
3202    </t>
3203  </list>
3204</t>
3205</section>
3206
3207<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
3208<t>
3209  Closed issues:
3210  <list style="symbols"> 
3211    <t>
3212      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
3213      "OPTIONS request bodies"
3214    </t>
3215    <t>
3216      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
3217      "Description of CONNECT should refer to RFC2817"
3218    </t>
3219    <t>
3220      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
3221      "Location Content-Location reference request/response mixup"
3222    </t>
3223  </list>
3224</t>
3225<t>
3226  Ongoing work on Method Registry (<eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
3227  <list style="symbols"> 
3228    <t>
3229      Added initial proposal for registration process, plus initial
3230      content (non-HTTP/1.1 methods to be added by a separate specification).
3231    </t>
3232  </list>
3233</t>
3234</section>
3235
3236</section>
3237
3238</back>
3239</rfc>
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