source: draft-ietf-httpbis/09/draft-ietf-httpbis-p2-semantics-09.xml @ 772

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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="pre5378Trust200902" docName="draft-ietf-httpbis-p2-semantics-09">
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="March" year="2010" day="8"/>
161  <workgroup>HTTPbis Working Group</workgroup>
162
163<abstract>
164<t>
165   The Hypertext Transfer Protocol (HTTP) is an application-level
166   protocol for distributed, collaborative, hypermedia information
167   systems. HTTP has been in use by the World Wide Web global information
168   initiative since 1990. This document is Part 2 of the seven-part specification
169   that defines the protocol referred to as "HTTP/1.1" and, taken together,
170   obsoletes RFC 2616.  Part 2 defines the semantics of HTTP messages
171   as expressed by request methods, request-header fields, response status codes,
172   and response-header fields.
173</t>
174</abstract>
175
176<note title="Editorial Note (To be removed by RFC Editor)">
177  <t>
178    Discussion of this draft should take place on the HTTPBIS working group
179    mailing list (ietf-http-wg@w3.org). The current issues list is
180    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
181    and related documents (including fancy diffs) can be found at
182    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
183  </t>
184  <t>
185    The changes in this draft are summarized in <xref target="changes.since.08"/>.
186  </t>
187</note>
188</front>
189<middle>
190<section title="Introduction" anchor="introduction">
191<t>
192   This document defines HTTP/1.1 request and response semantics.  Each HTTP
193   message, as defined in <xref target="Part1"/>, is in the form of either a request or
194   a response.  An HTTP server listens on a connection for HTTP requests and
195   responds to each request, in the order received on that connection, with
196   one or more HTTP response messages.  This document defines the commonly
197   agreed upon semantics of the HTTP uniform interface, the intentions defined
198   by each request method, and the various response messages that might be
199   expected as a result of applying that method for the requested resource.
200</t>
201<t>
202   This document is currently disorganized in order to minimize the changes
203   between drafts and enable reviewers to see the smaller errata changes.
204   The next draft will reorganize the sections to better reflect the content.
205   In particular, the sections will be ordered according to the typical
206   processing of an HTTP request message (after message parsing): resource
207   mapping, general header fields, methods, request modifiers, response
208   status, and resource metadata.  The current mess reflects how widely
209   dispersed these topics and associated requirements had become in
210   <xref target="RFC2616"/>.
211</t>
212
213<section title="Requirements" anchor="intro.requirements">
214<t>
215   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
216   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
217   document are to be interpreted as described in <xref target="RFC2119"/>.
218</t>
219<t>
220   An implementation is not compliant if it fails to satisfy one or more
221   of the MUST or REQUIRED level requirements for the protocols it
222   implements. An implementation that satisfies all the MUST or REQUIRED
223   level and all the SHOULD level requirements for its protocols is said
224   to be "unconditionally compliant"; one that satisfies all the MUST
225   level requirements but not all the SHOULD level requirements for its
226   protocols is said to be "conditionally compliant."
227</t>
228</section>
229
230<section title="Syntax Notation" anchor="notation">
231 
232 
233 
234 
235 
236<t>
237  This specification uses the ABNF syntax defined in Section 1.2 of <xref target="Part1"/> (which
238  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
239  <xref target="collected.abnf"/> shows the collected ABNF, with the list
240  rule expanded.
241</t>
242<t>
243  The following core rules are included by
244  reference, as defined in <xref target="RFC5234"/>, Appendix B.1:
245  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
246  DIGIT (decimal 0-9), DQUOTE (double quote),
247  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
248  OCTET (any 8-bit sequence of data), SP (space),
249  VCHAR (any visible USASCII character),
250  and WSP (whitespace).
251</t>
252
253<section title="Core Rules" anchor="core.rules">
254 
255 
256 
257 
258 
259<t>
260  The core rules below are defined in Section 1.2.2 of <xref target="Part1"/>:
261</t>
262<figure><artwork type="abnf2616"><![CDATA[
263  quoted-string = <quoted-string, defined in [Part1], Section 1.2.2>
264  token         = <token, defined in [Part1], Section 1.2.2>
265  OWS           = <OWS, defined in [Part1], Section 1.2.2>
266  RWS           = <RWS, defined in [Part1], Section 1.2.2>
267  obs-text      = <obs-text, defined in [Part1], Section 1.2.2>
268]]></artwork></figure>
269</section>
270
271<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
272 
273 
274 
275 
276 
277 
278 
279 
280 
281 
282 
283 
284 
285 
286 
287 
288 
289 
290 
291 
292 
293 
294 
295 
296 
297 
298<t>
299  The ABNF rules below are defined in other parts:
300</t>
301<figure><artwork type="abnf2616"><![CDATA[
302  absolute-URI  = <absolute-URI, defined in [Part1], Section 2.6>
303  comment       = <comment, defined in [Part1], Section 3.2>
304  Host          = <Host, defined in [Part1], Section 2.6>
305  HTTP-date     = <HTTP-date, defined in [Part1], Section 6.1>
306  partial-URI   = <partial-URI, defined in [Part1], Section 2.6>
307  product       = <product, defined in [Part1], Section 6.3>
308  TE            = <TE, defined in [Part1], Section 9.8>
309  URI           = <URI, defined in [Part1], Section 2.6>
310]]></artwork></figure>
311<figure><artwork type="abnf2616"><![CDATA[
312  Accept        = <Accept, defined in [Part3], Section 5.1>
313  Accept-Charset =
314             <Accept-Charset, defined in [Part3], Section 5.2>
315  Accept-Encoding =
316             <Accept-Encoding, defined in [Part3], Section 5.3>
317  Accept-Language =
318             <Accept-Language, defined in [Part3], Section 5.4>
319]]></artwork></figure>
320<figure><artwork type="abnf2616"><![CDATA[
321  ETag          = <ETag, defined in [Part4], Section 6.1>
322  If-Match      = <If-Match, defined in [Part4], Section 6.2>
323  If-Modified-Since =
324             <If-Modified-Since, defined in [Part4], Section 6.3>
325  If-None-Match = <If-None-Match, defined in [Part4], Section 6.4>
326  If-Unmodified-Since =
327             <If-Unmodified-Since, defined in [Part4], Section 6.5>
328]]></artwork></figure>
329<figure><artwork type="abnf2616"><![CDATA[
330  Accept-Ranges = <Accept-Ranges, defined in [Part5], Section 5.1>
331  If-Range      = <If-Range, defined in [Part5], Section 5.3>
332  Range         = <Range, defined in [Part5], Section 5.4>
333]]></artwork></figure>
334<figure><artwork type="abnf2616"><![CDATA[
335  Age           = <Age, defined in [Part6], Section 3.1>
336  Vary          = <Vary, defined in [Part6], Section 3.5>
337]]></artwork></figure>
338<figure><artwork type="abnf2616"><![CDATA[
339  Authorization = <Authorization, defined in [Part7], Section 3.1>
340  Proxy-Authenticate =
341             <Proxy-Authenticate, defined in [Part7], Section 3.2>
342  Proxy-Authorization =
343             <Proxy-Authorization, defined in [Part7], Section 3.3>
344  WWW-Authenticate =
345             <WWW-Authenticate, defined in [Part7], Section 3.4>
346]]></artwork></figure>
347</section>
348</section>
349</section>
350
351<section title="Method" anchor="method">
352 
353 
354<t>
355   The Method  token indicates the method to be performed on the
356   resource identified by the request-target. The method is case-sensitive.
357</t>
358<figure><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/><artwork type="abnf2616"><![CDATA[
359  Method         = %x4F.50.54.49.4F.4E.53   ; "OPTIONS", Section 7.2
360                 / %x47.45.54               ; "GET", Section 7.3
361                 / %x48.45.41.44            ; "HEAD", Section 7.4
362                 / %x50.4F.53.54            ; "POST", Section 7.5
363                 / %x50.55.54               ; "PUT", Section 7.6
364                 / %x44.45.4C.45.54.45      ; "DELETE", Section 7.7
365                 / %x54.52.41.43.45         ; "TRACE", Section 7.8
366                 / %x43.4F.4E.4E.45.43.54   ; "CONNECT", Section 7.9
367                 / extension-method
368  extension-method = token
369]]></artwork></figure>
370<t>
371   The list of methods allowed by a resource can be specified in an
372   Allow header field (<xref target="header.allow"/>). The return code of the response
373   always notifies the client whether a method is currently allowed on a
374   resource, since the set of allowed methods can change dynamically. An
375   origin server SHOULD return the status code 405 (Method Not Allowed)
376   if the method is known by the origin server but not allowed for the
377   requested resource, and 501 (Not Implemented) if the method is
378   unrecognized or not implemented by the origin server. The methods GET
379   and HEAD MUST be supported by all general-purpose servers. All other
380   methods are OPTIONAL; however, if the above methods are implemented,
381   they MUST be implemented with the same semantics as those specified
382   in <xref target="method.definitions"/>.
383</t>
384
385<section title="Method Registry" anchor="method.registry">
386<t>
387  The HTTP Method Registry defines the name space for the Method token in the
388  Request line of an HTTP request.
389</t>
390<t>
391  Registrations MUST include the following fields:
392  <list style="symbols">
393    <t>Method Name (see <xref target="method"/>)</t>
394    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
395    <t>Pointer to specification text</t>
396  </list>
397</t>
398<t>
399  Values to be added to this name space are subject to IETF review
400  (<xref target="RFC5226"/>, Section 4.1).
401</t>
402<t>
403  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
404</t>
405</section>
406</section>
407
408<section title="Request Header Fields" anchor="request.header.fields">
409 
410<t>
411   The request-header fields allow the client to pass additional
412   information about the request, and about the client itself, to the
413   server. These fields act as request modifiers, with semantics
414   equivalent to the parameters on a programming language method
415   invocation.
416</t>
417<figure><iref primary="true" item="Grammar" subitem="request-header"/><artwork type="abnf2616"><![CDATA[
418  request-header = Accept                   ; [Part3], Section 5.1
419                 / Accept-Charset           ; [Part3], Section 5.2
420                 / Accept-Encoding          ; [Part3], Section 5.3
421                 / Accept-Language          ; [Part3], Section 5.4
422                 / Authorization            ; [Part7], Section 3.1
423                 / Expect                   ; Section 9.2
424                 / From                     ; Section 9.3
425                 / Host                     ; [Part1], Section 9.4
426                 / If-Match                 ; [Part4], Section 6.2
427                 / If-Modified-Since        ; [Part4], Section 6.3
428                 / If-None-Match            ; [Part4], Section 6.4
429                 / If-Range                 ; [Part5], Section 5.3
430                 / If-Unmodified-Since      ; [Part4], Section 6.5
431                 / Max-Forwards             ; Section 9.5
432                 / Proxy-Authorization      ; [Part7], Section 3.3
433                 / Range                    ; [Part5], Section 5.4
434                 / Referer                  ; Section 9.6
435                 / TE                       ; [Part1], Section 9.8
436                 / User-Agent               ; Section 9.9
437]]></artwork></figure>
438<t>
439   Request-header field names can be extended reliably only in
440   combination with a change in the protocol version. However, new or
441   experimental header fields MAY be given the semantics of request-header
442   fields if all parties in the communication recognize them to
443   be request-header fields. Unrecognized header fields are treated as
444   entity-header fields.
445</t>
446</section>
447
448<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
449 
450 
451 
452<t>
453   The Status-Code element is a 3-digit integer result code of the
454   attempt to understand and satisfy the request. The status codes listed
455   below are defined in <xref target="status.codes"/>.
456   The Reason-Phrase is intended to give a short
457   textual description of the Status-Code. The Status-Code is intended
458   for use by automata and the Reason-Phrase is intended for the human
459   user. The client is not required to examine or display the Reason-Phrase.
460</t>
461<t> 
462   The individual values of the numeric status codes defined for
463   HTTP/1.1, and an example set of corresponding Reason-Phrase values, are
464   presented below. The reason phrases listed here are only
465   recommendations -- they MAY be replaced by local equivalents without
466   affecting the protocol.
467</t>
468<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[
469  Status-Code    =
470         "100"  ; Section 8.1.1: Continue
471       / "101"  ; Section 8.1.2: Switching Protocols
472       / "200"  ; Section 8.2.1: OK
473       / "201"  ; Section 8.2.2: Created
474       / "202"  ; Section 8.2.3: Accepted
475       / "203"  ; Section 8.2.4: Non-Authoritative Information
476       / "204"  ; Section 8.2.5: No Content
477       / "205"  ; Section 8.2.6: Reset Content
478       / "206"  ; [Part5], Section 3.1: Partial Content
479       / "300"  ; Section 8.3.1: Multiple Choices
480       / "301"  ; Section 8.3.2: Moved Permanently
481       / "302"  ; Section 8.3.3: Found
482       / "303"  ; Section 8.3.4: See Other
483       / "304"  ; [Part4], Section 3.1: Not Modified
484       / "305"  ; Section 8.3.6: Use Proxy
485       / "307"  ; Section 8.3.8: Temporary Redirect
486       / "400"  ; Section 8.4.1: Bad Request
487       / "401"  ; [Part7], Section 2.1: Unauthorized
488       / "402"  ; Section 8.4.3: Payment Required
489       / "403"  ; Section 8.4.4: Forbidden
490       / "404"  ; Section 8.4.5: Not Found
491       / "405"  ; Section 8.4.6: Method Not Allowed
492       / "406"  ; Section 8.4.7: Not Acceptable
493       / "407"  ; [Part7], Section 2.2: Proxy Authentication Required
494       / "408"  ; Section 8.4.9: Request Time-out
495       / "409"  ; Section 8.4.10: Conflict
496       / "410"  ; Section 8.4.11: Gone
497       / "411"  ; Section 8.4.12: Length Required
498       / "412"  ; [Part4], Section 3.2: Precondition Failed
499       / "413"  ; Section 8.4.14: Request Entity Too Large
500       / "414"  ; Section 8.4.15: URI Too Long
501       / "415"  ; Section 8.4.16: Unsupported Media Type
502       / "416"  ; status-416;: Requested range not satisfiable
503       / "417"  ; Section 8.4.18: Expectation Failed
504       / "500"  ; Section 8.5.1: Internal Server Error
505       / "501"  ; Section 8.5.2: Not Implemented
506       / "502"  ; Section 8.5.3: Bad Gateway
507       / "503"  ; Section 8.5.4: Service Unavailable
508       / "504"  ; Section 8.5.5: Gateway Time-out
509       / "505"  ; Section 8.5.6: HTTP Version not supported
510       / extension-code
511
512  extension-code = 3DIGIT
513  Reason-Phrase  = *( WSP / VCHAR / obs-text )
514]]></artwork></figure>
515<t>
516   HTTP status codes are extensible. HTTP applications are not required
517   to understand the meaning of all registered status codes, though such
518   understanding is obviously desirable. However, applications MUST
519   understand the class of any status code, as indicated by the first
520   digit, and treat any unrecognized response as being equivalent to the
521   x00 status code of that class, with the exception that an
522   unrecognized response MUST NOT be cached. For example, if an
523   unrecognized status code of 431 is received by the client, it can
524   safely assume that there was something wrong with its request and
525   treat the response as if it had received a 400 status code. In such
526   cases, user agents SHOULD present to the user the entity returned
527   with the response, since that entity is likely to include human-readable
528   information which will explain the unusual status.
529</t>
530
531<section title="Status Code Registry" anchor="status.code.registry">
532<t>
533  The HTTP Status Code Registry defines the name space for the Status-Code
534  token in the Status line of an HTTP response.
535</t>
536<t>
537  Values to be added to this name space are subject to IETF review
538  (<xref target="RFC5226"/>, Section 4.1).
539</t>
540<t>
541  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
542</t>
543</section>
544
545</section>
546
547<section title="Response Header Fields" anchor="response.header.fields">
548 
549<t>
550   The response-header fields allow the server to pass additional
551   information about the response which cannot be placed in the Status-Line.
552   These header fields give information about the server and about
553   further access to the resource identified by the request-target.
554</t>
555<figure><iref primary="true" item="Grammar" subitem="response-header"/><artwork type="abnf2616"><![CDATA[
556  response-header = Accept-Ranges           ; [Part5], Section 5.1
557                  / Age                     ; [Part6], Section 3.1
558                  / Allow                   ; Section 9.1
559                  / ETag                    ; [Part4], Section 6.1
560                  / Location                ; Section 9.4
561                  / Proxy-Authenticate      ; [Part7], Section 3.2
562                  / Retry-After             ; Section 9.7
563                  / Server                  ; Section 9.8
564                  / Vary                    ; [Part6], Section 3.5
565                  / WWW-Authenticate        ; [Part7], Section 3.4
566]]></artwork></figure>
567<t>
568   Response-header field names can be extended reliably only in
569   combination with a change in the protocol version. However, new or
570   experimental header fields MAY be given the semantics of response-header
571   fields if all parties in the communication recognize them to
572   be response-header fields. Unrecognized header fields are treated as
573   entity-header fields.
574</t>
575</section>
576
577<section title="Entity" anchor="entity">
578<t>
579   Request and Response messages MAY transfer an entity if not otherwise
580   restricted by the request method or response status code. An entity
581   consists of entity-header fields and an entity-body, although some
582   responses will only include the entity-headers. HTTP entity-body and
583   entity-header fields are defined in <xref target="Part3"/>.
584</t>
585<t>
586   An entity-body is only present in a message when a message-body is
587   present, as described in Section 3.3 of <xref target="Part1"/>. The entity-body is obtained
588   from the message-body by decoding any Transfer-Encoding that might
589   have been applied to ensure safe and proper transfer of the message.
590</t>
591
592<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
593<t>
594   It is sometimes necessary to determine the identity of the resource
595   associated with a representation.
596</t>
597<t>
598   An HTTP request representation, when present, is always associated with an
599   anonymous (i.e., unidentified) resource.
600</t>
601<t>
602   In the common case, an HTTP response is a representation of the resource
603   located at the request-URI. However, this is not always the case. To
604   determine the URI of the resource a response is associated with, the
605   following rules are used (with the first applicable one being selected):
606</t>
607<t><list style="numbers">
608   <t>If the response status code is 200 or 203 and the request method was GET,
609   the response is a representation of the resource at the request-URI.</t>
610   <t>If the response status is 204, 206, or 304 and the request method was GET
611   or HEAD, the response is a partial representation of the resource at the
612   request-URI (see Section 2.7 of <xref target="Part6"/>).</t>
613   <t>If the response has a Content-Location header, and that URI is the same
614   as the request-URI <cref anchor="TODO-missref-requri">(see [ref])</cref>, the response is a representation of the
615   resource at the request-URI.</t>
616   <t>If the response has a Content-Location header, and that URI is not the
617   same as the request-URI, the response asserts that it is a representation of
618   the resource at the Content-Location URI (but it may not be).</t>
619   <t>Otherwise, the response is a representation of an anonymous (i.e.,
620   unidentified) resource.</t>
621</list></t>
622<t>
623  <cref anchor="TODO-req-uri">
624   Note that "request-URI" is used here; however, we need to come up with a
625   term to denote "the URI that can be inferred from examining the
626   request-target and the Host header." (see &lt;http://tools.ietf.org/wg/httpbis/trac/ticket/196&gt;).
627   Also, the comparison function is going to have to be defined somewhere,
628   because we already need to compare URIs for things like cache invalidation.</cref>
629</t>
630</section>
631
632</section>
633
634
635<section title="Method Definitions" anchor="method.definitions">
636<t>
637   The set of common methods for HTTP/1.1 is defined below. Although
638   this set can be expanded, additional methods cannot be assumed to
639   share the same semantics for separately extended clients and servers.
640</t>
641
642<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
643
644<section title="Safe Methods" anchor="safe.methods">
645<iref item="Safe Methods" primary="true"/>
646<t>
647   Implementors should be aware that the software represents the user in
648   their interactions over the Internet, and should be careful to allow
649   the user to be aware of any actions they might take which may have an
650   unexpected significance to themselves or others.
651</t>
652<t>
653   In particular, the convention has been established that the GET, HEAD,
654   OPTIONS, and TRACE methods SHOULD NOT  have the significance of taking an action
655   other than retrieval. These methods ought to be considered "safe".
656   This allows user agents to represent other methods, such as POST, PUT
657   and DELETE, in a special way, so that the user is made aware of the
658   fact that a possibly unsafe action is being requested.
659</t>
660<t>
661   Naturally, it is not possible to ensure that the server does not
662   generate side-effects as a result of performing a GET request; in
663   fact, some dynamic resources consider that a feature. The important
664   distinction here is that the user did not request the side-effects,
665   so therefore cannot be held accountable for them.
666</t>
667</section>
668
669<section title="Idempotent Methods" anchor="idempotent.methods">
670<iref item="Idempotent Methods" primary="true"/>
671<t>
672   Methods can also have the property of "idempotence" in that, aside
673   from error or expiration issues, the intended effect of multiple
674   identical requests is the same as for a single request.
675   The methods PUT, DELETE, and all safe methods are idempotent.
676   It is important to note that idempotence refers only to changes
677   requested by the client: a server is free to change its state due
678   to multiple requests for the purpose of tracking those requests,
679   versioning of results, etc.
680</t>
681</section>
682</section>
683
684<section title="OPTIONS" anchor="OPTIONS">
685 
686  <iref primary="true" item="OPTIONS method"/>
687  <iref primary="true" item="Methods" subitem="OPTIONS"/>
688<t>
689   The OPTIONS method represents a request for information about the
690   communication options available on the request/response chain
691   identified by the request-target. This method allows the client to
692   determine the options and/or requirements associated with a resource,
693   or the capabilities of a server, without implying a resource action
694   or initiating a resource retrieval.
695</t>
696<t>
697   Responses to this method are not cacheable.
698</t>
699<t>
700   If the OPTIONS request includes an entity-body (as indicated by the
701   presence of Content-Length or Transfer-Encoding), then the media type
702   MUST be indicated by a Content-Type field. Although this
703   specification does not define any use for such a body, future
704   extensions to HTTP might use the OPTIONS body to make more detailed
705   queries on the server.
706</t>
707<t>
708   If the request-target is an asterisk ("*"), the OPTIONS request is
709   intended to apply to the server in general rather than to a specific
710   resource. Since a server's communication options typically depend on
711   the resource, the "*" request is only useful as a "ping" or "no-op"
712   type of method; it does nothing beyond allowing the client to test
713   the capabilities of the server. For example, this can be used to test
714   a proxy for HTTP/1.1 compliance (or lack thereof).
715</t>
716<t>
717   If the request-target is not an asterisk, the OPTIONS request applies
718   only to the options that are available when communicating with that
719   resource.
720</t>
721<t>
722   A 200 response SHOULD include any header fields that indicate
723   optional features implemented by the server and applicable to that
724   resource (e.g., Allow), possibly including extensions not defined by
725   this specification. The response body, if any, SHOULD also include
726   information about the communication options. The format for such a
727   body is not defined by this specification, but might be defined by
728   future extensions to HTTP. Content negotiation MAY be used to select
729   the appropriate response format. If no response body is included, the
730   response MUST include a Content-Length field with a field-value of
731   "0".
732</t>
733<t>
734   The Max-Forwards request-header field MAY be used to target a
735   specific proxy in the request chain. When a proxy receives an OPTIONS
736   request on an absolute-URI for which request forwarding is permitted,
737   the proxy MUST check for a Max-Forwards field. If the Max-Forwards
738   field-value is zero ("0"), the proxy MUST NOT forward the message;
739   instead, the proxy SHOULD respond with its own communication options.
740   If the Max-Forwards field-value is an integer greater than zero, the
741   proxy MUST decrement the field-value when it forwards the request. If
742   no Max-Forwards field is present in the request, then the forwarded
743   request MUST NOT include a Max-Forwards field.
744</t>
745</section>
746
747<section title="GET" anchor="GET">
748 
749  <iref primary="true" item="GET method"/>
750  <iref primary="true" item="Methods" subitem="GET"/>
751<t>
752   The GET method means retrieve whatever information (in the form of an
753   entity) currently corresponds to the resource identified by the
754   request-target.
755</t>
756<t>   
757   If the request-target identifies a data-producing process, it is the
758   produced data which shall be returned as the entity in the response and not
759   the source text of the process, unless that text happens to be the output of
760   the process.
761</t>
762<t>
763   The semantics of the GET method change to a "conditional GET" if the
764   request message includes an If-Modified-Since, If-Unmodified-Since,
765   If-Match, If-None-Match, or If-Range header field. A conditional GET
766   method requests that the entity be transferred only under the
767   circumstances described by the conditional header field(s). The
768   conditional GET method is intended to reduce unnecessary network
769   usage by allowing cached entities to be refreshed without requiring
770   multiple requests or transferring data already held by the client.
771</t>
772<t>
773   The semantics of the GET method change to a "partial GET" if the
774   request message includes a Range header field. A partial GET requests
775   that only part of the entity be transferred, as described in Section 5.4 of <xref target="Part5"/>.
776   The partial GET method is intended to reduce unnecessary
777   network usage by allowing partially-retrieved entities to be
778   completed without transferring data already held by the client.
779</t>
780<t>
781   The response to a GET request is cacheable if and only if it meets
782   the requirements for HTTP caching described in <xref target="Part6"/>.
783</t>
784<t>
785   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
786</t>
787</section>
788
789<section title="HEAD" anchor="HEAD">
790 
791  <iref primary="true" item="HEAD method"/>
792  <iref primary="true" item="Methods" subitem="HEAD"/>
793<t>
794   The HEAD method is identical to GET except that the server MUST NOT
795   return a message-body in the response. The metainformation contained
796   in the HTTP headers in response to a HEAD request SHOULD be identical
797   to the information sent in response to a GET request. This method can
798   be used for obtaining metainformation about the entity implied by the
799   request without transferring the entity-body itself. This method is
800   often used for testing hypertext links for validity, accessibility,
801   and recent modification.
802</t>
803<t>
804   The response to a HEAD request MAY be cacheable in the sense that the
805   information contained in the response MAY be used to update a
806   previously cached entity from that resource. If the new field values
807   indicate that the cached entity differs from the current entity (as
808   would be indicated by a change in Content-Length, Content-MD5, ETag
809   or Last-Modified), then the cache MUST treat the cache entry as
810   stale.
811</t>
812</section>
813
814<section title="POST" anchor="POST">
815  <iref primary="true" item="POST method"/>
816  <iref primary="true" item="Methods" subitem="POST"/>
817<t>
818   The POST method is used to request that the origin server accept the
819   entity enclosed in the request as data to be processed by the resource
820   identified by the request-target in the Request-Line. POST is designed
821   to allow a uniform method to cover the following functions:
822  <list style="symbols">
823    <t>
824      Annotation of existing resources;
825    </t>
826    <t>
827        Posting a message to a bulletin board, newsgroup, mailing list,
828        or similar group of articles;
829    </t>
830    <t>
831        Providing a block of data, such as the result of submitting a
832        form, to a data-handling process;
833    </t>
834    <t>
835        Extending a database through an append operation.
836    </t>
837  </list>
838</t>
839<t>
840   The actual function performed by the POST method is determined by the
841   server and is usually dependent on the request-target.
842</t>
843<t>
844   The action performed by the POST method might not result in a
845   resource that can be identified by a URI. In this case, either 200
846   (OK) or 204 (No Content) is the appropriate response status,
847   depending on whether or not the response includes an entity that
848   describes the result.
849</t>
850<t>
851   If a resource has been created on the origin server, the response
852   SHOULD be 201 (Created) and contain an entity which describes the
853   status of the request and refers to the new resource, and a Location
854   header (see <xref target="header.location"/>).
855</t>
856<t>
857   Responses to this method are not cacheable, unless the response
858   includes appropriate Cache-Control or Expires header fields. However,
859   the 303 (See Other) response can be used to direct the user agent to
860   retrieve a cacheable resource.
861</t>
862</section>
863
864<section title="PUT" anchor="PUT">
865  <iref primary="true" item="PUT method"/>
866  <iref primary="true" item="Methods" subitem="PUT"/>
867<t>
868   The PUT method requests that the enclosed entity be stored at the
869   supplied request-target. If the request-target refers to an already
870   existing resource, the enclosed entity SHOULD be considered as a
871   modified version of the one residing on the origin server. If the
872   request-target does not point to an existing resource, and that URI is
873   capable of being defined as a new resource by the requesting user
874   agent, the origin server can create the resource with that URI. If a
875   new resource is created at the request-target, the origin server MUST
876   inform the user agent
877   via the 201 (Created) response. If an existing resource is modified,
878   either the 200 (OK) or 204 (No Content) response codes SHOULD be sent
879   to indicate successful completion of the request. If the resource
880   could not be created or modified with the request-target, an appropriate
881   error response SHOULD be given that reflects the nature of the
882   problem. The recipient of the entity MUST NOT ignore any Content-*
883   headers (headers starting with the prefix "Content-") that it does
884   not understand or implement
885   and MUST return a 501 (Not Implemented) response in such cases.
886</t>
887<t>
888   If the request passes through a cache and the request-target identifies
889   one or more currently cached entities, those entries SHOULD be
890   treated as stale. Responses to this method are not cacheable.
891</t>
892<t>
893   The fundamental difference between the POST and PUT requests is
894   reflected in the different meaning of the request-target. The URI in a
895   POST request identifies the resource that will handle the enclosed
896   entity. That resource might be a data-accepting process, a gateway to
897   some other protocol, or a separate entity that accepts annotations.
898   In contrast, the URI in a PUT request identifies the entity enclosed
899   with the request -- the user agent knows what URI is intended and the
900   server MUST NOT attempt to apply the request to some other resource.
901   If the server desires that the request be applied to a different URI,
902   it MUST send a 301 (Moved Permanently) response; the user agent MAY
903   then make its own decision regarding whether or not to redirect the
904   request.
905</t>
906<t>
907   A single resource MAY be identified by many different URIs. For
908   example, an article might have a URI for identifying "the current
909   version" which is separate from the URI identifying each particular
910   version. In this case, a PUT request on a general URI might result in
911   several other URIs being defined by the origin server.
912</t>
913<t>
914   HTTP/1.1 does not define how a PUT method affects the state of an
915   origin server.
916</t>
917<t>
918   Unless otherwise specified for a particular entity-header, the
919   entity-headers in the PUT request SHOULD be applied to the resource
920   created or modified by the PUT.
921</t>
922</section>
923
924<section title="DELETE" anchor="DELETE">
925  <iref primary="true" item="DELETE method"/>
926  <iref primary="true" item="Methods" subitem="DELETE"/>
927<t>
928   The DELETE method requests that the origin server delete the resource
929   identified by the request-target. This method MAY be overridden by human
930   intervention (or other means) on the origin server. The client cannot
931   be guaranteed that the operation has been carried out, even if the
932   status code returned from the origin server indicates that the action
933   has been completed successfully. However, the server SHOULD NOT
934   indicate success unless, at the time the response is given, it
935   intends to delete the resource or move it to an inaccessible
936   location.
937</t>
938<t>
939   A successful response SHOULD be 200 (OK) if the response includes an
940   entity describing the status, 202 (Accepted) if the action has not
941   yet been enacted, or 204 (No Content) if the action has been enacted
942   but the response does not include an entity.
943</t>
944<t>
945   If the request passes through a cache and the request-target identifies
946   one or more currently cached entities, those entries SHOULD be
947   treated as stale. Responses to this method are not cacheable.
948</t>
949</section>
950
951<section title="TRACE" anchor="TRACE">
952 
953  <iref primary="true" item="TRACE method"/>
954  <iref primary="true" item="Methods" subitem="TRACE"/>
955<t>
956   The TRACE method is used to invoke a remote, application-layer loop-back
957   of the request message. The final recipient of the request
958   SHOULD reflect the message received back to the client as the
959   entity-body of a 200 (OK) response. The final recipient is either the
960   origin server or the first proxy or gateway to receive a Max-Forwards
961   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
962   MUST NOT include an entity.
963</t>
964<t>
965   TRACE allows the client to see what is being received at the other
966   end of the request chain and use that data for testing or diagnostic
967   information. The value of the Via header field (Section 9.9 of <xref target="Part1"/>) is of
968   particular interest, since it acts as a trace of the request chain.
969   Use of the Max-Forwards header field allows the client to limit the
970   length of the request chain, which is useful for testing a chain of
971   proxies forwarding messages in an infinite loop.
972</t>
973<t>
974   If the request is valid, the response SHOULD contain the entire
975   request message in the entity-body, with a Content-Type of
976   "message/http" (see Section 10.3.1 of <xref target="Part1"/>). Responses to this method
977   MUST NOT be cached.
978</t>
979</section>
980
981<section title="CONNECT" anchor="CONNECT">
982  <iref primary="true" item="CONNECT method"/>
983  <iref primary="true" item="Methods" subitem="CONNECT"/>
984<t>
985   This specification reserves the method name CONNECT for use with a
986   proxy that can dynamically switch to being a tunnel (e.g., SSL
987   tunneling <xref target="RFC2817"/>).
988</t>
989</section>
990</section>
991
992
993<section title="Status Code Definitions" anchor="status.codes">
994<t>
995   Each Status-Code is described below, including any metainformation required
996   in the response.
997</t>
998
999<section title="Informational 1xx" anchor="status.1xx">
1000<t>
1001   This class of status code indicates a provisional response,
1002   consisting only of the Status-Line and optional headers, and is
1003   terminated by an empty line. There are no required headers for this
1004   class of status code. Since HTTP/1.0 did not define any 1xx status
1005   codes, servers MUST NOT send a 1xx response to an HTTP/1.0 client
1006   except under experimental conditions.
1007</t>
1008<t>
1009   A client MUST be prepared to accept one or more 1xx status responses
1010   prior to a regular response, even if the client does not expect a 100
1011   (Continue) status message. Unexpected 1xx status responses MAY be
1012   ignored by a user agent.
1013</t>
1014<t>
1015   Proxies MUST forward 1xx responses, unless the connection between the
1016   proxy and its client has been closed, or unless the proxy itself
1017   requested the generation of the 1xx response. (For example, if a
1018   proxy adds a "Expect: 100-continue" field when it forwards a request,
1019   then it need not forward the corresponding 100 (Continue)
1020   response(s).)
1021</t>
1022
1023<section title="100 Continue" anchor="status.100">
1024  <iref primary="true" item="100 Continue (status code)"/>
1025  <iref primary="true" item="Status Codes" subitem="100 Continue"/>
1026<t>
1027   The client SHOULD continue with its request. This interim response is
1028   used to inform the client that the initial part of the request has
1029   been received and has not yet been rejected by the server. The client
1030   SHOULD continue by sending the remainder of the request or, if the
1031   request has already been completed, ignore this response. The server
1032   MUST send a final response after the request has been completed. See
1033   Section 7.2.3 of <xref target="Part1"/> for detailed discussion of the use and handling of this
1034   status code.
1035</t>
1036</section>
1037
1038<section title="101 Switching Protocols" anchor="status.101">
1039  <iref primary="true" item="101 Switching Protocols (status code)"/>
1040  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols"/>
1041<t>
1042   The server understands and is willing to comply with the client's
1043   request, via the Upgrade message header field (Section 5.4 of <xref target="Part5"/>), for a
1044   change in the application protocol being used on this connection. The
1045   server will switch protocols to those defined by the response's
1046   Upgrade header field immediately after the empty line which
1047   terminates the 101 response.
1048</t>
1049<t>
1050   The protocol SHOULD be switched only when it is advantageous to do
1051   so. For example, switching to a newer version of HTTP is advantageous
1052   over older versions, and switching to a real-time, synchronous
1053   protocol might be advantageous when delivering resources that use
1054   such features.
1055</t>
1056</section>
1057</section>
1058
1059<section title="Successful 2xx" anchor="status.2xx">
1060<t>
1061   This class of status code indicates that the client's request was
1062   successfully received, understood, and accepted.
1063</t>
1064
1065<section title="200 OK" anchor="status.200">
1066  <iref primary="true" item="200 OK (status code)"/>
1067  <iref primary="true" item="Status Codes" subitem="200 OK"/>
1068<t>
1069   The request has succeeded. The information returned with the response
1070   is dependent on the method used in the request, for example:
1071  <list style="hanging">
1072    <t hangText="GET">
1073          an entity corresponding to the requested resource is sent in
1074          the response;
1075    </t>
1076    <t hangText="HEAD">
1077          the entity-header fields corresponding to the requested
1078          resource are sent in the response without any message-body;
1079    </t>
1080    <t hangText="POST">
1081      an entity describing or containing the result of the action;
1082    </t>
1083    <t hangText="TRACE">
1084      an entity containing the request message as received by the
1085      end server.
1086    </t>
1087  </list>
1088</t>
1089</section>
1090
1091<section title="201 Created" anchor="status.201">
1092  <iref primary="true" item="201 Created (status code)"/>
1093  <iref primary="true" item="Status Codes" subitem="201 Created"/>
1094<t>
1095   The request has been fulfilled and has resulted in a new resource being
1096   created. The newly created resource can be referenced by the URI(s)
1097   returned in the entity of the response, with the most specific URI
1098   for the resource given by a Location header field. The response
1099   SHOULD include an entity containing a list of resource
1100   characteristics and location(s) from which the user or user agent can
1101   choose the one most appropriate. The entity format is specified by
1102   the media type given in the Content-Type header field. The origin
1103   server MUST create the resource before returning the 201 status code.
1104   If the action cannot be carried out immediately, the server SHOULD
1105   respond with 202 (Accepted) response instead.
1106</t>
1107<t>
1108   A 201 response MAY contain an ETag response header field indicating
1109   the current value of the entity tag for the requested variant just
1110   created, see Section 6.1 of <xref target="Part4"/>.
1111</t>
1112</section>
1113
1114<section title="202 Accepted" anchor="status.202">
1115  <iref primary="true" item="202 Accepted (status code)"/>
1116  <iref primary="true" item="Status Codes" subitem="202 Accepted"/>
1117<t>
1118   The request has been accepted for processing, but the processing has
1119   not been completed.  The request might or might not eventually be
1120   acted upon, as it might be disallowed when processing actually takes
1121   place. There is no facility for re-sending a status code from an
1122   asynchronous operation such as this.
1123</t>
1124<t>
1125   The 202 response is intentionally non-committal. Its purpose is to
1126   allow a server to accept a request for some other process (perhaps a
1127   batch-oriented process that is only run once per day) without
1128   requiring that the user agent's connection to the server persist
1129   until the process is completed. The entity returned with this
1130   response SHOULD include an indication of the request's current status
1131   and either a pointer to a status monitor or some estimate of when the
1132   user can expect the request to be fulfilled.
1133</t>
1134</section>
1135
1136<section title="203 Non-Authoritative Information" anchor="status.203">
1137  <iref primary="true" item="203 Non-Authoritative Information (status code)"/>
1138  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information"/>
1139<t>
1140   The returned metainformation in the entity-header is not the
1141   definitive set as available from the origin server, but is gathered
1142   from a local or a third-party copy. The set presented MAY be a subset
1143   or superset of the original version. For example, including local
1144   annotation information about the resource might result in a superset
1145   of the metainformation known by the origin server. Use of this
1146   response code is not required and is only appropriate when the
1147   response would otherwise be 200 (OK).
1148</t>
1149</section>
1150
1151<section title="204 No Content" anchor="status.204">
1152  <iref primary="true" item="204 No Content (status code)"/>
1153  <iref primary="true" item="Status Codes" subitem="204 No Content"/>
1154<t>
1155   The server has fulfilled the request but does not need to return an
1156   entity-body, and might want to return updated metainformation. The
1157   response MAY include new or updated metainformation in the form of
1158   entity-headers, which if present SHOULD be associated with the
1159   requested variant.
1160</t>
1161<t>
1162   If the client is a user agent, it SHOULD NOT  change its document view
1163   from that which caused the request to be sent. This response is
1164   primarily intended to allow input for actions to take place without
1165   causing a change to the user agent's active document view, although
1166   any new or updated metainformation SHOULD be applied to the document
1167   currently in the user agent's active view.
1168</t>
1169<t>
1170   The 204 response MUST NOT include a message-body, and thus is always
1171   terminated by the first empty line after the header fields.
1172</t>
1173</section>
1174
1175<section title="205 Reset Content" anchor="status.205">
1176  <iref primary="true" item="205 Reset Content (status code)"/>
1177  <iref primary="true" item="Status Codes" subitem="205 Reset Content"/>
1178<t>
1179   The server has fulfilled the request and the user agent SHOULD reset
1180   the document view which caused the request to be sent. This response
1181   is primarily intended to allow input for actions to take place via
1182   user input, followed by a clearing of the form in which the input is
1183   given so that the user can easily initiate another input action. The
1184   response MUST NOT include an entity.
1185</t>
1186</section>
1187
1188<section title="206 Partial Content" anchor="status.206">
1189  <iref primary="true" item="206 Partial Content (status code)"/>
1190  <iref primary="true" item="Status Codes" subitem="206 Partial Content"/>
1191 
1192<t>
1193   The server has fulfilled the partial GET request for the resource
1194   and the enclosed entity is a partial representation as defined in Section 3.1 of <xref target="Part5"/>.
1195</t>
1196</section>
1197</section>
1198
1199<section title="Redirection 3xx" anchor="status.3xx">
1200<t>
1201   This class of status code indicates that further action needs to be
1202   taken by the user agent in order to fulfill the request.  The action
1203   required MAY be carried out by the user agent without interaction
1204   with the user if and only if the method used in the second request is
1205   known to be "safe", as defined in <xref target="safe.methods"/>.
1206   A client SHOULD detect infinite redirection loops, since such loops
1207   generate network traffic for each redirection.
1208</t>
1209<t><list>
1210  <t>
1211    Note: An earlier version of this specification recommended a
1212    maximum of five redirections (<xref target="RFC2068"/>, Section 10.3).
1213    Content developers should be aware that there might be clients that
1214    implement such a fixed limitation.
1215  </t>
1216</list></t>
1217
1218<section title="300 Multiple Choices" anchor="status.300">
1219  <iref primary="true" item="300 Multiple Choices (status code)"/>
1220  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices"/>
1221<t>
1222   The requested resource corresponds to any one of a set of
1223   representations, each with its own specific location, and agent-driven
1224   negotiation information (Section 4 of <xref target="Part3"/>) is being provided so that
1225   the user (or user agent) can select a preferred representation and
1226   redirect its request to that location.
1227</t>
1228<t>
1229   Unless it was a HEAD request, the response SHOULD include an entity
1230   containing a list of resource characteristics and location(s) from
1231   which the user or user agent can choose the one most appropriate. The
1232   entity format is specified by the media type given in the Content-Type
1233   header field. Depending upon the format and the capabilities of
1234   the user agent, selection of the most appropriate choice MAY be
1235   performed automatically. However, this specification does not define
1236   any standard for such automatic selection.
1237</t>
1238<t>
1239   If the server has a preferred choice of representation, it SHOULD
1240   include the specific URI for that representation in the Location
1241   field; user agents MAY use the Location field value for automatic
1242   redirection. This response is cacheable unless indicated otherwise.
1243</t>
1244</section>
1245
1246<section title="301 Moved Permanently" anchor="status.301">
1247  <iref primary="true" item="301 Moved Permanently (status code)"/>
1248  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently"/>
1249<t>
1250   The requested resource has been assigned a new permanent URI and any
1251   future references to this resource SHOULD use one of the returned
1252   URIs.  Clients with link editing capabilities ought to automatically
1253   re-link references to the request-target to one or more of the new
1254   references returned by the server, where possible. This response is
1255   cacheable unless indicated otherwise.
1256</t>
1257<t>
1258   The new permanent URI SHOULD be given by the Location field in the
1259   response. Unless the request method was HEAD, the entity of the
1260   response SHOULD contain a short hypertext note with a hyperlink to
1261   the new URI(s).
1262</t>
1263<t>
1264   If the 301 status code is received in response to a request method
1265   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1266   then the request MAY be automatically redirected by the user agent without
1267   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
1268   request unless it can be confirmed by the user, since this might
1269   change the conditions under which the request was issued.
1270</t>
1271<t><list>
1272  <t>
1273    Note: When automatically redirecting a POST request after
1274    receiving a 301 status code, some existing HTTP/1.0 user agents
1275    will erroneously change it into a GET request.
1276  </t>
1277</list></t>
1278</section>
1279
1280<section title="302 Found" anchor="status.302">
1281  <iref primary="true" item="302 Found (status code)"/>
1282  <iref primary="true" item="Status Codes" subitem="302 Found"/>
1283<t>
1284   The requested resource resides temporarily under a different URI.
1285   Since the redirection might be altered on occasion, the client SHOULD
1286   continue to use the request-target for future requests.  This response
1287   is only cacheable if indicated by a Cache-Control or Expires header
1288   field.
1289</t>
1290<t>
1291   The temporary URI SHOULD be given by the Location field in the
1292   response. Unless the request method was HEAD, the entity of the
1293   response SHOULD contain a short hypertext note with a hyperlink to
1294   the new URI(s).
1295</t>
1296<t>
1297   If the 302 status code is received in response to a request method
1298   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1299   then the request MAY be automatically redirected by the user agent without
1300   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
1301   request unless it can be confirmed by the user, since this might
1302   change the conditions under which the request was issued.
1303</t>
1304<t><list>
1305  <t>
1306    Note: HTTP/1.0 (<xref target="RFC1945"/>, Section 9.3)
1307    and the first version of HTTP/1.1 (<xref target="RFC2068"/>, Section 10.3.3)
1308    specify that the client is not allowed to change the method on the
1309    redirected request.  However, most existing user agent implementations
1310    treat 302 as if it were a 303 response, performing a GET on the Location
1311    field-value regardless of the original request method. Therefore, a
1312    previous version of this specification
1313    (<xref target="RFC2616"/>, Section 10.3.3) has added the
1314    status codes
1315    <xref target="status.303" format="none">303</xref> and
1316    <xref target="status.307" format="none">307</xref> for servers that wish
1317    to make unambiguously clear which kind of reaction is expected of the
1318    client.
1319  </t>
1320</list></t>
1321</section>
1322
1323<section title="303 See Other" anchor="status.303">
1324  <iref primary="true" item="303 See Other (status code)"/>
1325  <iref primary="true" item="Status Codes" subitem="303 See Other"/>
1326<t>
1327   The server directs the user agent to a different resource, indicated
1328   by a URI in the Location header field, that provides an indirect
1329   response to the original request.  The user agent MAY perform a GET
1330   request on the URI in the Location field in order to obtain a
1331   representation corresponding to the response, be redirected again,
1332   or end with an error status.  The Location URI is not a substitute
1333   reference for the originally requested resource.
1334</t>
1335<t>
1336   The 303 status is generally applicable to any HTTP method.  It is
1337   primarily used to allow the output of a POST action to redirect
1338   the user agent to a selected resource, since doing so provides the
1339   information corresponding to the POST response in a form that
1340   can be separately identified, bookmarked, and cached independent
1341   of the original request.
1342</t>
1343<t>
1344   A 303 response to a GET request indicates that the requested
1345   resource does not have a representation of its own that can be
1346   transferred by the server over HTTP.  The Location URI indicates a
1347   resource that is descriptive of the requested resource such that
1348   the follow-on representation may be useful without implying that
1349   it adequately represents the previously requested resource.
1350   Note that answers to the questions of what can be represented, what
1351   representations are adequate, and what might be a useful description
1352   are outside the scope of HTTP and thus entirely determined by the
1353   URI owner(s).
1354</t>
1355<t>
1356   A 303 response SHOULD NOT be cached unless it is indicated as
1357   cacheable by Cache-Control or Expires header fields.  Except for
1358   responses to a HEAD request, the entity of a 303 response SHOULD
1359   contain a short hypertext note with a hyperlink to the Location URI.
1360</t>
1361</section>
1362
1363<section title="304 Not Modified" anchor="status.304">
1364  <iref primary="true" item="304 Not Modified (status code)"/>
1365  <iref primary="true" item="Status Codes" subitem="304 Not Modified"/>
1366 
1367<t>
1368   The response to the request has not been modified since the conditions
1369   indicated by the client's conditional GET request, as defined in Section 3.1 of <xref target="Part4"/>.
1370</t>
1371</section>
1372
1373<section title="305 Use Proxy" anchor="status.305">
1374  <iref primary="true" item="305 Use Proxy (status code)"/>
1375  <iref primary="true" item="Status Codes" subitem="305 Use Proxy"/>
1376<t>
1377   The 305 status was defined in a previous version of this specification
1378   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1379</t>
1380</section>
1381
1382<section title="306 (Unused)" anchor="status.306">
1383  <iref primary="true" item="306 (Unused) (status code)"/>
1384  <iref primary="true" item="Status Codes" subitem="306 (Unused)"/>
1385<t>
1386   The 306 status code was used in a previous version of the
1387   specification, is no longer used, and the code is reserved.
1388</t>
1389</section>
1390
1391<section title="307 Temporary Redirect" anchor="status.307">
1392  <iref primary="true" item="307 Temporary Redirect (status code)"/>
1393  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect"/>
1394<t>
1395   The requested resource resides temporarily under a different URI.
1396   Since the redirection MAY be altered on occasion, the client SHOULD
1397   continue to use the request-target for future requests.  This response
1398   is only cacheable if indicated by a Cache-Control or Expires header
1399   field.
1400</t>
1401<t>
1402   The temporary URI SHOULD be given by the Location field in the
1403   response. Unless the request method was HEAD, the entity of the
1404   response SHOULD contain a short hypertext note with a hyperlink to
1405   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1406   understand the 307 status. Therefore, the note SHOULD contain the
1407   information necessary for a user to repeat the original request on
1408   the new URI.
1409</t>
1410<t>
1411   If the 307 status code is received in response to a request method
1412   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1413   then the request MAY be automatically redirected by the user agent without
1414   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
1415   request unless it can be confirmed by the user, since this might
1416   change the conditions under which the request was issued.
1417</t>
1418</section>
1419</section>
1420
1421<section title="Client Error 4xx" anchor="status.4xx">
1422<t>
1423   The 4xx class of status code is intended for cases in which the
1424   client seems to have erred. Except when responding to a HEAD request,
1425   the server SHOULD include an entity containing an explanation of the
1426   error situation, and whether it is a temporary or permanent
1427   condition. These status codes are applicable to any request method.
1428   User agents SHOULD display any included entity to the user.
1429</t>
1430<t>
1431   If the client is sending data, a server implementation using TCP
1432   SHOULD be careful to ensure that the client acknowledges receipt of
1433   the packet(s) containing the response, before the server closes the
1434   input connection. If the client continues sending data to the server
1435   after the close, the server's TCP stack will send a reset packet to
1436   the client, which may erase the client's unacknowledged input buffers
1437   before they can be read and interpreted by the HTTP application.
1438</t>
1439
1440<section title="400 Bad Request" anchor="status.400">
1441  <iref primary="true" item="400 Bad Request (status code)"/>
1442  <iref primary="true" item="Status Codes" subitem="400 Bad Request"/>
1443<t>
1444   The request could not be understood by the server due to malformed
1445   syntax. The client SHOULD NOT  repeat the request without
1446   modifications.
1447</t>
1448</section>
1449
1450<section title="401 Unauthorized" anchor="status.401">
1451  <iref primary="true" item="401 Unauthorized (status code)"/>
1452  <iref primary="true" item="Status Codes" subitem="401 Unauthorized"/>
1453 
1454<t>
1455   The request requires user authentication (see Section 2.1 of <xref target="Part7"/>).
1456</t>
1457</section>
1458
1459<section title="402 Payment Required" anchor="status.402">
1460  <iref primary="true" item="402 Payment Required (status code)"/>
1461  <iref primary="true" item="Status Codes" subitem="402 Payment Required"/>
1462<t>
1463   This code is reserved for future use.
1464</t>
1465</section>
1466
1467<section title="403 Forbidden" anchor="status.403">
1468  <iref primary="true" item="403 Forbidden (status code)"/>
1469  <iref primary="true" item="Status Codes" subitem="403 Forbidden"/>
1470<t>
1471   The server understood the request, but is refusing to fulfill it.
1472   Authorization will not help and the request SHOULD NOT  be repeated.
1473   If the request method was not HEAD and the server wishes to make
1474   public why the request has not been fulfilled, it SHOULD describe the
1475   reason for the refusal in the entity.  If the server does not wish to
1476   make this information available to the client, the status code 404
1477   (Not Found) can be used instead.
1478</t>
1479</section>
1480
1481<section title="404 Not Found" anchor="status.404">
1482  <iref primary="true" item="404 Not Found (status code)"/>
1483  <iref primary="true" item="Status Codes" subitem="404 Not Found"/>
1484<t>
1485   The server has not found anything matching the request-target. No
1486   indication is given of whether the condition is temporary or
1487   permanent. The 410 (Gone) status code SHOULD be used if the server
1488   knows, through some internally configurable mechanism, that an old
1489   resource is permanently unavailable and has no forwarding address.
1490   This status code is commonly used when the server does not wish to
1491   reveal exactly why the request has been refused, or when no other
1492   response is applicable.
1493</t>
1494</section>
1495
1496<section title="405 Method Not Allowed" anchor="status.405">
1497  <iref primary="true" item="405 Method Not Allowed (status code)"/>
1498  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed"/>
1499<t>
1500   The method specified in the Request-Line is not allowed for the
1501   resource identified by the request-target. The response MUST include an
1502   Allow header containing a list of valid methods for the requested
1503   resource.
1504</t>
1505</section>
1506
1507<section title="406 Not Acceptable" anchor="status.406">
1508  <iref primary="true" item="406 Not Acceptable (status code)"/>
1509  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable"/>
1510<t>
1511   The resource identified by the request is only capable of generating
1512   response entities which have content characteristics not acceptable
1513   according to the accept headers sent in the request.
1514</t>
1515<t>
1516   Unless it was a HEAD request, the response SHOULD include an entity
1517   containing a list of available entity characteristics and location(s)
1518   from which the user or user agent can choose the one most
1519   appropriate. The entity format is specified by the media type given
1520   in the Content-Type header field. Depending upon the format and the
1521   capabilities of the user agent, selection of the most appropriate
1522   choice MAY be performed automatically. However, this specification
1523   does not define any standard for such automatic selection.
1524</t>
1525<t><list>
1526  <t>
1527    Note: HTTP/1.1 servers are allowed to return responses which are
1528    not acceptable according to the accept headers sent in the
1529    request. In some cases, this may even be preferable to sending a
1530    406 response. User agents are encouraged to inspect the headers of
1531    an incoming response to determine if it is acceptable.
1532  </t>
1533</list></t>
1534<t>
1535   If the response could be unacceptable, a user agent SHOULD
1536   temporarily stop receipt of more data and query the user for a
1537   decision on further actions.
1538</t>
1539</section>
1540
1541<section title="407 Proxy Authentication Required" anchor="status.407">
1542  <iref primary="true" item="407 Proxy Authentication Required (status code)"/>
1543  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required"/>
1544<t>
1545   This code is similar to 401 (Unauthorized), but indicates that the
1546   client must first authenticate itself with the proxy (see Section 2.2 of <xref target="Part7"/>).
1547</t>
1548</section>
1549
1550<section title="408 Request Timeout" anchor="status.408">
1551  <iref primary="true" item="408 Request Timeout (status code)"/>
1552  <iref primary="true" item="Status Codes" subitem="408 Request Timeout"/>
1553<t>
1554   The client did not produce a request within the time that the server
1555   was prepared to wait. The client MAY repeat the request without
1556   modifications at any later time.
1557</t>
1558</section>
1559
1560<section title="409 Conflict" anchor="status.409">
1561  <iref primary="true" item="409 Conflict (status code)"/>
1562  <iref primary="true" item="Status Codes" subitem="409 Conflict"/>
1563<t>
1564   The request could not be completed due to a conflict with the current
1565   state of the resource. This code is only allowed in situations where
1566   it is expected that the user might be able to resolve the conflict
1567   and resubmit the request. The response body SHOULD include enough
1568   information for the user to recognize the source of the conflict.
1569   Ideally, the response entity would include enough information for the
1570   user or user agent to fix the problem; however, that might not be
1571   possible and is not required.
1572</t>
1573<t>
1574   Conflicts are most likely to occur in response to a PUT request. For
1575   example, if versioning were being used and the entity being PUT
1576   included changes to a resource which conflict with those made by an
1577   earlier (third-party) request, the server might use the 409 response
1578   to indicate that it can't complete the request. In this case, the
1579   response entity would likely contain a list of the differences
1580   between the two versions in a format defined by the response
1581   Content-Type.
1582</t>
1583</section>
1584
1585<section title="410 Gone" anchor="status.410">
1586  <iref primary="true" item="410 Gone (status code)"/>
1587  <iref primary="true" item="Status Codes" subitem="410 Gone"/>
1588<t>
1589   The requested resource is no longer available at the server and no
1590   forwarding address is known. This condition is expected to be
1591   considered permanent. Clients with link editing capabilities SHOULD
1592   delete references to the request-target after user approval. If the
1593   server does not know, or has no facility to determine, whether or not
1594   the condition is permanent, the status code 404 (Not Found) SHOULD be
1595   used instead. This response is cacheable unless indicated otherwise.
1596</t>
1597<t>
1598   The 410 response is primarily intended to assist the task of web
1599   maintenance by notifying the recipient that the resource is
1600   intentionally unavailable and that the server owners desire that
1601   remote links to that resource be removed. Such an event is common for
1602   limited-time, promotional services and for resources belonging to
1603   individuals no longer working at the server's site. It is not
1604   necessary to mark all permanently unavailable resources as "gone" or
1605   to keep the mark for any length of time -- that is left to the
1606   discretion of the server owner.
1607</t>
1608</section>
1609
1610<section title="411 Length Required" anchor="status.411">
1611  <iref primary="true" item="411 Length Required (status code)"/>
1612  <iref primary="true" item="Status Codes" subitem="411 Length Required"/>
1613<t>
1614   The server refuses to accept the request without a defined Content-Length.
1615   The client MAY repeat the request if it adds a valid
1616   Content-Length header field containing the length of the message-body
1617   in the request message.
1618</t>
1619</section>
1620
1621<section title="412 Precondition Failed" anchor="status.412">
1622  <iref primary="true" item="412 Precondition Failed (status code)"/>
1623  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed"/>
1624 
1625<t>
1626   The precondition given in one or more of the request-header fields
1627   evaluated to false when it was tested on the server, as defined in
1628   Section 3.2 of <xref target="Part4"/>.
1629</t>
1630</section>
1631
1632<section title="413 Request Entity Too Large" anchor="status.413">
1633  <iref primary="true" item="413 Request Entity Too Large (status code)"/>
1634  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large"/>
1635<t>
1636   The server is refusing to process a request because the request
1637   entity is larger than the server is willing or able to process. The
1638   server MAY close the connection to prevent the client from continuing
1639   the request.
1640</t>
1641<t>
1642   If the condition is temporary, the server SHOULD include a Retry-After
1643   header field to indicate that it is temporary and after what
1644   time the client MAY try again.
1645</t>
1646</section>
1647
1648<section title="414 URI Too Long" anchor="status.414">
1649  <iref primary="true" item="414 URI Too Long (status code)"/>
1650  <iref primary="true" item="Status Codes" subitem="414 URI Too Long"/>
1651<t>
1652   The server is refusing to service the request because the request-target
1653   is longer than the server is willing to interpret. This rare
1654   condition is only likely to occur when a client has improperly
1655   converted a POST request to a GET request with long query
1656   information, when the client has descended into a URI "black hole" of
1657   redirection (e.g., a redirected URI prefix that points to a suffix of
1658   itself), or when the server is under attack by a client attempting to
1659   exploit security holes present in some servers using fixed-length
1660   buffers for reading or manipulating the request-target.
1661</t>
1662</section>
1663
1664<section title="415 Unsupported Media Type" anchor="status.415">
1665  <iref primary="true" item="415 Unsupported Media Type (status code)"/>
1666  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type"/>
1667<t>
1668   The server is refusing to service the request because the entity of
1669   the request is in a format not supported by the requested resource
1670   for the requested method.
1671</t>
1672</section>
1673
1674<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1675  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)"/>
1676  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable"/>
1677 
1678<t>
1679   The request included a Range request-header field (Section 5.4 of <xref target="Part5"/>) and none of
1680   the range-specifier values in this field overlap the current extent
1681   of the selected resource. See Section 3.2 of <xref target="Part5"/>
1682</t>
1683</section>
1684
1685<section title="417 Expectation Failed" anchor="status.417">
1686  <iref primary="true" item="417 Expectation Failed (status code)"/>
1687  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed"/>
1688<t>
1689   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1690   could not be met by this server, or, if the server is a proxy,
1691   the server has unambiguous evidence that the request could not be met
1692   by the next-hop server.
1693</t>
1694</section>
1695</section>
1696
1697<section title="Server Error 5xx" anchor="status.5xx">
1698<t>
1699   Response status codes beginning with the digit "5" indicate cases in
1700   which the server is aware that it has erred or is incapable of
1701   performing the request. Except when responding to a HEAD request, the
1702   server SHOULD include an entity containing an explanation of the
1703   error situation, and whether it is a temporary or permanent
1704   condition. User agents SHOULD display any included entity to the
1705   user. These response codes are applicable to any request method.
1706</t>
1707
1708<section title="500 Internal Server Error" anchor="status.500">
1709  <iref primary="true" item="500 Internal Server Error (status code)"/>
1710  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error"/>
1711<t>
1712   The server encountered an unexpected condition which prevented it
1713   from fulfilling the request.
1714</t>
1715</section>
1716
1717<section title="501 Not Implemented" anchor="status.501">
1718  <iref primary="true" item="501 Not Implemented (status code)"/>
1719  <iref primary="true" item="Status Codes" subitem="501 Not Implemented"/>
1720<t>
1721   The server does not support the functionality required to fulfill the
1722   request. This is the appropriate response when the server does not
1723   recognize the request method and is not capable of supporting it for
1724   any resource.
1725</t>
1726</section>
1727
1728<section title="502 Bad Gateway" anchor="status.502">
1729  <iref primary="true" item="502 Bad Gateway (status code)"/>
1730  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway"/>
1731<t>
1732   The server, while acting as a gateway or proxy, received an invalid
1733   response from the upstream server it accessed in attempting to
1734   fulfill the request.
1735</t>
1736</section>
1737
1738<section title="503 Service Unavailable" anchor="status.503">
1739  <iref primary="true" item="503 Service Unavailable (status code)"/>
1740  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable"/>
1741<t>
1742   The server is currently unable to handle the request due to a
1743   temporary overloading or maintenance of the server. The implication
1744   is that this is a temporary condition which will be alleviated after
1745   some delay. If known, the length of the delay MAY be indicated in a
1746   Retry-After header. If no Retry-After is given, the client SHOULD
1747   handle the response as it would for a 500 response.
1748</t>
1749<t><list>
1750  <t>
1751    Note: The existence of the 503 status code does not imply that a
1752    server must use it when becoming overloaded. Some servers may wish
1753    to simply refuse the connection.
1754  </t>
1755</list></t>
1756</section>
1757
1758<section title="504 Gateway Timeout" anchor="status.504">
1759  <iref primary="true" item="504 Gateway Timeout (status code)"/>
1760  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout"/>
1761<t>
1762   The server, while acting as a gateway or proxy, did not receive a
1763   timely response from the upstream server specified by the URI (e.g.,
1764   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
1765   to access in attempting to complete the request.
1766</t>
1767<t><list>
1768  <t>
1769    Note to implementors: some deployed proxies are known to
1770    return 400 or 500 when DNS lookups time out.
1771  </t>
1772</list></t>
1773</section>
1774
1775<section title="505 HTTP Version Not Supported" anchor="status.505">
1776  <iref primary="true" item="505 HTTP Version Not Supported (status code)"/>
1777  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported"/>
1778<t>
1779   The server does not support, or refuses to support, the protocol
1780   version that was used in the request message. The server is
1781   indicating that it is unable or unwilling to complete the request
1782   using the same major version as the client, as described in Section 2.5 of <xref target="Part1"/>,
1783   other than with this error message. The response SHOULD contain
1784   an entity describing why that version is not supported and what other
1785   protocols are supported by that server.
1786</t>
1787
1788</section>
1789</section>
1790</section>
1791
1792
1793<section title="Header Field Definitions" anchor="header.fields">
1794<t>
1795   This section defines the syntax and semantics of HTTP/1.1 header fields
1796   related to request and response semantics.
1797</t>
1798<t>
1799   For entity-header fields, both sender and recipient refer to either the
1800   client or the server, depending on who sends and who receives the entity.
1801</t>
1802
1803<section title="Allow" anchor="header.allow">
1804  <iref primary="true" item="Allow header"/>
1805  <iref primary="true" item="Headers" subitem="Allow"/>
1806 
1807 
1808<t>
1809   The "Allow" response-header field lists the set of methods advertised as
1810   supported by the resource identified by the request-target. The purpose of
1811   this field is strictly to inform the recipient of valid methods
1812   associated with the resource.
1813</t>
1814<figure><iref primary="true" item="Grammar" subitem="Allow"/><iref primary="true" item="Grammar" subitem="Allow-v"/><artwork type="abnf2616"><![CDATA[
1815  Allow   = "Allow" ":" OWS Allow-v
1816  Allow-v = #Method
1817]]></artwork></figure>
1818<t>
1819      Example of use:
1820</t>
1821<figure><artwork type="example"><![CDATA[
1822  Allow: GET, HEAD, PUT
1823]]></artwork></figure>
1824<t>
1825      The actual set of allowed methods is defined
1826      by the origin server at the time of each request.
1827</t>
1828<t>
1829      A proxy MUST NOT modify the Allow header field even if it does not
1830      understand all the methods specified, since the user agent might
1831      have other means of communicating with the origin server.
1832</t>
1833</section>
1834
1835<section title="Expect" anchor="header.expect">
1836  <iref primary="true" item="Expect header"/>
1837  <iref primary="true" item="Headers" subitem="Expect"/>
1838 
1839 
1840 
1841 
1842 
1843<t>
1844   The "Expect" request-header field is used to indicate that particular
1845   server behaviors are required by the client.
1846</t>
1847<figure><iref primary="true" item="Grammar" subitem="Expect"/><iref primary="true" item="Grammar" subitem="Expect-v"/><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[
1848  Expect       = "Expect" ":" OWS Expect-v
1849  Expect-v     = 1#expectation
1850 
1851  expectation  = "100-continue" / expectation-extension
1852  expectation-extension = token [ "=" ( token / quoted-string )
1853                           *expect-params ]
1854  expect-params = ";" token [ "=" ( token / quoted-string ) ]
1855]]></artwork></figure>
1856<t>
1857   A server that does not understand or is unable to comply with any of
1858   the expectation values in the Expect field of a request MUST respond
1859   with appropriate error status. The server MUST respond with a 417
1860   (Expectation Failed) status if any of the expectations cannot be met
1861   or, if there are other problems with the request, some other 4xx
1862   status.
1863</t>
1864<t>
1865   This header field is defined with extensible syntax to allow for
1866   future extensions. If a server receives a request containing an
1867   Expect field that includes an expectation-extension that it does not
1868   support, it MUST respond with a 417 (Expectation Failed) status.
1869</t>
1870<t>
1871   Comparison of expectation values is case-insensitive for unquoted
1872   tokens (including the 100-continue token), and is case-sensitive for
1873   quoted-string expectation-extensions.
1874</t>
1875<t>
1876   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy MUST
1877   return a 417 (Expectation Failed) status if it receives a request
1878   with an expectation that it cannot meet. However, the Expect
1879   request-header itself is end-to-end; it MUST be forwarded if the
1880   request is forwarded.
1881</t>
1882<t>
1883   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1884   Expect header.
1885</t>
1886<t>
1887   See Section 7.2.3 of <xref target="Part1"/> for the use of the 100 (Continue) status.
1888</t>
1889</section>
1890
1891<section title="From" anchor="header.from">
1892  <iref primary="true" item="From header"/>
1893  <iref primary="true" item="Headers" subitem="From"/>
1894 
1895 
1896 
1897<t>
1898   The "From" request-header field, if given, SHOULD contain an Internet
1899   e-mail address for the human user who controls the requesting user
1900   agent. The address SHOULD be machine-usable, as defined by "mailbox"
1901   in Section 3.4 of <xref target="RFC5322"/>:
1902</t>
1903<figure><iref primary="true" item="Grammar" subitem="From"/><iref primary="true" item="Grammar" subitem="From-v"/><artwork type="abnf2616"><![CDATA[
1904  From    = "From" ":" OWS From-v
1905  From-v  = mailbox
1906 
1907  mailbox = <mailbox, defined in [RFC5322], Section 3.4>
1908]]></artwork></figure>
1909<t>
1910   An example is:
1911</t>
1912<figure><artwork type="example"><![CDATA[
1913  From: webmaster@example.org
1914]]></artwork></figure>
1915<t>
1916   This header field MAY be used for logging purposes and as a means for
1917   identifying the source of invalid or unwanted requests. It SHOULD NOT
1918   be used as an insecure form of access protection. The interpretation
1919   of this field is that the request is being performed on behalf of the
1920   person given, who accepts responsibility for the method performed. In
1921   particular, robot agents SHOULD include this header so that the
1922   person responsible for running the robot can be contacted if problems
1923   occur on the receiving end.
1924</t>
1925<t>
1926   The Internet e-mail address in this field MAY be separate from the
1927   Internet host which issued the request. For example, when a request
1928   is passed through a proxy the original issuer's address SHOULD be
1929   used.
1930</t>
1931<t>
1932   The client SHOULD NOT  send the From header field without the user's
1933   approval, as it might conflict with the user's privacy interests or
1934   their site's security policy. It is strongly recommended that the
1935   user be able to disable, enable, and modify the value of this field
1936   at any time prior to a request.
1937</t>
1938</section>
1939
1940<section title="Location" anchor="header.location">
1941  <iref primary="true" item="Location header"/>
1942  <iref primary="true" item="Headers" subitem="Location"/>
1943 
1944 
1945<t>
1946   The "Location" response-header field is used to identify a newly created
1947   resource, or to redirect the recipient to a different location for
1948   completion of the request.
1949</t>
1950<t>
1951   For 201 (Created) responses, the Location is the URI of the new resource
1952   which was created by the request. For 3xx responses, the location SHOULD
1953   indicate the server's preferred URI for automatic redirection to the
1954   resource.
1955</t>
1956<t>
1957   The field value consists of a single URI.
1958</t>
1959<figure><iref primary="true" item="Grammar" subitem="Location"/><iref primary="true" item="Grammar" subitem="Location-v"/><artwork type="abnf2616"><![CDATA[
1960  Location       = "Location" ":" OWS Location-v
1961  Location-v     = URI
1962]]></artwork></figure>
1963<t>
1964   An example is:
1965</t>
1966<figure><artwork type="example"><![CDATA[
1967  Location: http://www.example.org/pub/WWW/People.html
1968]]></artwork></figure>
1969<t>
1970   There are circumstances in which a fragment identifier in a Location URI would not be appropriate:
1971   <list style="symbols">
1972      <t>With a 201 Created response, because in this usage the Location header specifies the URI for the entire created resource.</t>
1973      <t>With 305 Use Proxy.</t>
1974   </list>
1975</t>
1976<t><list>
1977  <t>
1978    Note: The Content-Location header field (Section 5.7 of <xref target="Part3"/>) differs
1979    from Location in that the Content-Location identifies the original
1980    location of the entity enclosed in the response. It is therefore
1981    possible for a response to contain header fields for both Location
1982    and Content-Location.
1983  </t>
1984</list></t>
1985</section>
1986
1987<section title="Max-Forwards" anchor="header.max-forwards">
1988  <iref primary="true" item="Max-Forwards header"/>
1989  <iref primary="true" item="Headers" subitem="Max-Forwards"/>
1990 
1991 
1992<t>
1993   The "Max-Forwards" request-header field provides a mechanism with the
1994   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
1995   methods to limit the number of times that the request is forwarded by
1996   proxies or gateways. This can be useful when the client is attempting to
1997   trace a request which appears to be failing or looping in mid-chain.
1998</t>
1999<figure><iref primary="true" item="Grammar" subitem="Max-Forwards"/><iref primary="true" item="Grammar" subitem="Max-Forwards-v"/><artwork type="abnf2616"><![CDATA[
2000  Max-Forwards   = "Max-Forwards" ":" OWS Max-Forwards-v
2001  Max-Forwards-v = 1*DIGIT
2002]]></artwork></figure>
2003<t>
2004   The Max-Forwards value is a decimal integer indicating the remaining
2005   number of times this request message may be forwarded.
2006</t>
2007<t>
2008   Each proxy or gateway recipient of a TRACE or OPTIONS request
2009   containing a Max-Forwards header field MUST check and update its
2010   value prior to forwarding the request. If the received value is zero
2011   (0), the recipient MUST NOT forward the request; instead, it MUST
2012   respond as the final recipient. If the received Max-Forwards value is
2013   greater than zero, then the forwarded message MUST contain an updated
2014   Max-Forwards field with a value decremented by one (1).
2015</t>
2016<t>
2017   The Max-Forwards header field MAY be ignored for all other methods
2018   defined by this specification and for any extension methods for which
2019   it is not explicitly referred to as part of that method definition.
2020</t>
2021</section>
2022
2023<section title="Referer" anchor="header.referer">
2024  <iref primary="true" item="Referer header"/>
2025  <iref primary="true" item="Headers" subitem="Referer"/>
2026 
2027 
2028<t>
2029   The "Referer" [sic] request-header field allows the client to specify the
2030   URI of the resource from which the request-target was obtained (the
2031   "referrer", although the header field is misspelled.).
2032</t>
2033<t>
2034   The Referer header allows servers to generate lists of back-links to
2035   resources for interest, logging, optimized caching, etc. It also allows
2036   obsolete or mistyped links to be traced for maintenance. Some servers use
2037   Referer as a means of controlling where they allow links from (so-called
2038   "deep linking"), but it should be noted that legitimate requests are not
2039   required to contain a Referer header field.
2040</t>
2041<t>
2042   If the request-target was obtained from a source that does not have its own
2043   URI (e.g., input from the user keyboard), the Referer field MUST either be
2044   sent with the value "about:blank", or not be sent at all. Note that this
2045   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2046</t>
2047<figure><iref primary="true" item="Grammar" subitem="Referer"/><iref primary="true" item="Grammar" subitem="Referer-v"/><artwork type="abnf2616"><![CDATA[
2048  Referer        = "Referer" ":" OWS Referer-v
2049  Referer-v      = absolute-URI / partial-URI
2050]]></artwork></figure>
2051<t>
2052   Example:
2053</t>
2054<figure><artwork type="example"><![CDATA[
2055  Referer: http://www.example.org/hypertext/Overview.html
2056]]></artwork></figure>
2057<t>
2058   If the field value is a relative URI, it SHOULD be interpreted
2059   relative to the request-target. The URI MUST NOT include a fragment. See
2060   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2061</t>
2062</section>
2063
2064<section title="Retry-After" anchor="header.retry-after">
2065  <iref primary="true" item="Retry-After header"/>
2066  <iref primary="true" item="Headers" subitem="Retry-After"/>
2067 
2068 
2069<t>
2070   The response-header "Retry-After" field can be used with a 503 (Service
2071   Unavailable) response to indicate how long the service is expected to
2072   be unavailable to the requesting client. This field MAY also be used
2073   with any 3xx (Redirection) response to indicate the minimum time the
2074   user-agent is asked wait before issuing the redirected request.
2075</t>
2076<t>
2077   The value of this field can be either an HTTP-date or an integer number
2078   of seconds (in decimal) after the time of the response.
2079</t>
2080<figure><iref primary="true" item="Grammar" subitem="Retry-After"/><iref primary="true" item="Grammar" subitem="Retry-After-v"/><artwork type="abnf2616"><![CDATA[
2081  Retry-After   = "Retry-After" ":" OWS Retry-After-v
2082  Retry-After-v = HTTP-date / delta-seconds
2083]]></artwork></figure>
2084<t anchor="rule.delta-seconds">
2085 
2086   Time spans are non-negative decimal integers, representing time in
2087   seconds.
2088</t>
2089<figure><iref primary="true" item="Grammar" subitem="delta-seconds"/><artwork type="abnf2616"><![CDATA[
2090  delta-seconds  = 1*DIGIT
2091]]></artwork></figure>
2092<t>
2093   Two examples of its use are
2094</t>
2095<figure><artwork type="example"><![CDATA[
2096  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2097  Retry-After: 120
2098]]></artwork></figure>
2099<t>
2100   In the latter example, the delay is 2 minutes.
2101</t>
2102</section>
2103
2104<section title="Server" anchor="header.server">
2105  <iref primary="true" item="Server header"/>
2106  <iref primary="true" item="Headers" subitem="Server"/>
2107 
2108 
2109<t>
2110   The "Server" response-header field contains information about the
2111   software used by the origin server to handle the request.
2112</t>
2113<t>
2114   The field can contain multiple product tokens (Section 6.3 of <xref target="Part1"/>) and
2115   comments (Section 3.2 of <xref target="Part1"/>) identifying the server and any significant
2116   subproducts. The product tokens are listed in order of their significance
2117   for identifying the application.
2118</t>
2119<figure><iref primary="true" item="Grammar" subitem="Server"/><iref primary="true" item="Grammar" subitem="Server-v"/><artwork type="abnf2616"><![CDATA[
2120  Server         = "Server" ":" OWS Server-v
2121  Server-v       = product
2122                   *( RWS ( product / comment ) )
2123]]></artwork></figure>
2124<t>
2125   Example:
2126</t>
2127<figure><artwork type="example"><![CDATA[
2128  Server: CERN/3.0 libwww/2.17
2129]]></artwork></figure>
2130<t>
2131   If the response is being forwarded through a proxy, the proxy
2132   application MUST NOT modify the Server response-header. Instead, it
2133   MUST include a Via field (as described in Section 9.9 of <xref target="Part1"/>).
2134</t>
2135<t><list>
2136  <t>
2137    Note: Revealing the specific software version of the server might
2138    allow the server machine to become more vulnerable to attacks
2139    against software that is known to contain security holes. Server
2140    implementors are encouraged to make this field a configurable
2141    option.
2142  </t>
2143</list></t>
2144</section>
2145
2146<section title="User-Agent" anchor="header.user-agent">
2147  <iref primary="true" item="User-Agent header"/>
2148  <iref primary="true" item="Headers" subitem="User-Agent"/>
2149 
2150 
2151<t>
2152   The "User-Agent" request-header field contains information about the
2153   user agent originating the request. This is for statistical purposes,
2154   the tracing of protocol violations, and automated recognition of user
2155   agents for the sake of tailoring responses to avoid particular user
2156   agent limitations.
2157</t>
2158<t>
2159   User agents SHOULD include this field with requests. The field can contain
2160   multiple product tokens (Section 6.3 of <xref target="Part1"/>) and comments (Section 3.2 of <xref target="Part1"/>)
2161   identifying the agent and any subproducts which form a significant part of
2162   the user agent. By convention, the product tokens are listed in order of
2163   their significance for identifying the application.
2164</t>
2165<figure><iref primary="true" item="Grammar" subitem="User-Agent"/><iref primary="true" item="Grammar" subitem="User-Agent-v"/><artwork type="abnf2616"><![CDATA[
2166  User-Agent     = "User-Agent" ":" OWS User-Agent-v
2167  User-Agent-v   = product
2168                   *( RWS ( product / comment ) )
2169]]></artwork></figure>
2170<t>
2171   Example:
2172</t>
2173<figure><artwork type="example"><![CDATA[
2174  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2175]]></artwork></figure>
2176</section>
2177
2178</section>
2179
2180<section title="IANA Considerations" anchor="IANA.considerations">
2181
2182<section title="Method Registry" anchor="method.registration">
2183<t>
2184  The registration procedure for HTTP Methods is defined by
2185  <xref target="method.registry"/> of this document.
2186</t>
2187<t>
2188   The HTTP Method Registry located at <eref target="http://www.iana.org/assignments/http-methods"/>
2189   should be populated with the registrations below:
2190</t>
2191
2192<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2193<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2194   <ttcol>Method</ttcol>
2195   <ttcol>Safe</ttcol>
2196   <ttcol>Reference</ttcol>
2197   <c>CONNECT</c>
2198   <c>no</c>
2199   <c>
2200      <xref target="CONNECT"/>
2201   </c>
2202   <c>DELETE</c>
2203   <c>no</c>
2204   <c>
2205      <xref target="DELETE"/>
2206   </c>
2207   <c>GET</c>
2208   <c>yes</c>
2209   <c>
2210      <xref target="GET"/>
2211   </c>
2212   <c>HEAD</c>
2213   <c>yes</c>
2214   <c>
2215      <xref target="HEAD"/>
2216   </c>
2217   <c>OPTIONS</c>
2218   <c>yes</c>
2219   <c>
2220      <xref target="OPTIONS"/>
2221   </c>
2222   <c>POST</c>
2223   <c>no</c>
2224   <c>
2225      <xref target="POST"/>
2226   </c>
2227   <c>PUT</c>
2228   <c>no</c>
2229   <c>
2230      <xref target="PUT"/>
2231   </c>
2232   <c>TRACE</c>
2233   <c>yes</c>
2234   <c>
2235      <xref target="TRACE"/>
2236   </c>
2237</texttable>
2238<!--(END)-->
2239
2240</section>
2241
2242<section title="Status Code Registry" anchor="status.code.registration">
2243<t>
2244   The registration procedure for HTTP Status Codes -- previously defined
2245   in Section 7.1 of <xref target="RFC2817"/> -- is now defined
2246   by <xref target="status.code.registry"/> of this document.
2247</t>
2248<t>
2249   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2250   should be updated with the registrations below:
2251</t>
2252
2253<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2254<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2255   <ttcol>Value</ttcol>
2256   <ttcol>Description</ttcol>
2257   <ttcol>Reference</ttcol>
2258   <c>100</c>
2259   <c>Continue</c>
2260   <c>
2261      <xref target="status.100"/>
2262   </c>
2263   <c>101</c>
2264   <c>Switching Protocols</c>
2265   <c>
2266      <xref target="status.101"/>
2267   </c>
2268   <c>200</c>
2269   <c>OK</c>
2270   <c>
2271      <xref target="status.200"/>
2272   </c>
2273   <c>201</c>
2274   <c>Created</c>
2275   <c>
2276      <xref target="status.201"/>
2277   </c>
2278   <c>202</c>
2279   <c>Accepted</c>
2280   <c>
2281      <xref target="status.202"/>
2282   </c>
2283   <c>203</c>
2284   <c>Non-Authoritative Information</c>
2285   <c>
2286      <xref target="status.203"/>
2287   </c>
2288   <c>204</c>
2289   <c>No Content</c>
2290   <c>
2291      <xref target="status.204"/>
2292   </c>
2293   <c>205</c>
2294   <c>Reset Content</c>
2295   <c>
2296      <xref target="status.205"/>
2297   </c>
2298   <c>300</c>
2299   <c>Multiple Choices</c>
2300   <c>
2301      <xref target="status.300"/>
2302   </c>
2303   <c>301</c>
2304   <c>Moved Permanently</c>
2305   <c>
2306      <xref target="status.301"/>
2307   </c>
2308   <c>302</c>
2309   <c>Found</c>
2310   <c>
2311      <xref target="status.302"/>
2312   </c>
2313   <c>303</c>
2314   <c>See Other</c>
2315   <c>
2316      <xref target="status.303"/>
2317   </c>
2318   <c>305</c>
2319   <c>Use Proxy</c>
2320   <c>
2321      <xref target="status.305"/>
2322   </c>
2323   <c>306</c>
2324   <c>(Unused)</c>
2325   <c>
2326      <xref target="status.306"/>
2327   </c>
2328   <c>307</c>
2329   <c>Temporary Redirect</c>
2330   <c>
2331      <xref target="status.307"/>
2332   </c>
2333   <c>400</c>
2334   <c>Bad Request</c>
2335   <c>
2336      <xref target="status.400"/>
2337   </c>
2338   <c>402</c>
2339   <c>Payment Required</c>
2340   <c>
2341      <xref target="status.402"/>
2342   </c>
2343   <c>403</c>
2344   <c>Forbidden</c>
2345   <c>
2346      <xref target="status.403"/>
2347   </c>
2348   <c>404</c>
2349   <c>Not Found</c>
2350   <c>
2351      <xref target="status.404"/>
2352   </c>
2353   <c>405</c>
2354   <c>Method Not Allowed</c>
2355   <c>
2356      <xref target="status.405"/>
2357   </c>
2358   <c>406</c>
2359   <c>Not Acceptable</c>
2360   <c>
2361      <xref target="status.406"/>
2362   </c>
2363   <c>407</c>
2364   <c>Proxy Authentication Required</c>
2365   <c>
2366      <xref target="status.407"/>
2367   </c>
2368   <c>408</c>
2369   <c>Request Timeout</c>
2370   <c>
2371      <xref target="status.408"/>
2372   </c>
2373   <c>409</c>
2374   <c>Conflict</c>
2375   <c>
2376      <xref target="status.409"/>
2377   </c>
2378   <c>410</c>
2379   <c>Gone</c>
2380   <c>
2381      <xref target="status.410"/>
2382   </c>
2383   <c>411</c>
2384   <c>Length Required</c>
2385   <c>
2386      <xref target="status.411"/>
2387   </c>
2388   <c>413</c>
2389   <c>Request Entity Too Large</c>
2390   <c>
2391      <xref target="status.413"/>
2392   </c>
2393   <c>414</c>
2394   <c>URI Too Long</c>
2395   <c>
2396      <xref target="status.414"/>
2397   </c>
2398   <c>415</c>
2399   <c>Unsupported Media Type</c>
2400   <c>
2401      <xref target="status.415"/>
2402   </c>
2403   <c>417</c>
2404   <c>Expectation Failed</c>
2405   <c>
2406      <xref target="status.417"/>
2407   </c>
2408   <c>500</c>
2409   <c>Internal Server Error</c>
2410   <c>
2411      <xref target="status.500"/>
2412   </c>
2413   <c>501</c>
2414   <c>Not Implemented</c>
2415   <c>
2416      <xref target="status.501"/>
2417   </c>
2418   <c>502</c>
2419   <c>Bad Gateway</c>
2420   <c>
2421      <xref target="status.502"/>
2422   </c>
2423   <c>503</c>
2424   <c>Service Unavailable</c>
2425   <c>
2426      <xref target="status.503"/>
2427   </c>
2428   <c>504</c>
2429   <c>Gateway Timeout</c>
2430   <c>
2431      <xref target="status.504"/>
2432   </c>
2433   <c>505</c>
2434   <c>HTTP Version Not Supported</c>
2435   <c>
2436      <xref target="status.505"/>
2437   </c>
2438</texttable>
2439<!--(END)-->
2440
2441</section>
2442<section title="Message Header Registration" anchor="message.header.registration">
2443<t>
2444   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2445   with the permanent registrations below (see <xref target="RFC3864"/>):
2446</t>
2447
2448<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2449<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2450   <ttcol>Header Field Name</ttcol>
2451   <ttcol>Protocol</ttcol>
2452   <ttcol>Status</ttcol>
2453   <ttcol>Reference</ttcol>
2454
2455   <c>Allow</c>
2456   <c>http</c>
2457   <c>standard</c>
2458   <c>
2459      <xref target="header.allow"/>
2460   </c>
2461   <c>Expect</c>
2462   <c>http</c>
2463   <c>standard</c>
2464   <c>
2465      <xref target="header.expect"/>
2466   </c>
2467   <c>From</c>
2468   <c>http</c>
2469   <c>standard</c>
2470   <c>
2471      <xref target="header.from"/>
2472   </c>
2473   <c>Location</c>
2474   <c>http</c>
2475   <c>standard</c>
2476   <c>
2477      <xref target="header.location"/>
2478   </c>
2479   <c>Max-Forwards</c>
2480   <c>http</c>
2481   <c>standard</c>
2482   <c>
2483      <xref target="header.max-forwards"/>
2484   </c>
2485   <c>Referer</c>
2486   <c>http</c>
2487   <c>standard</c>
2488   <c>
2489      <xref target="header.referer"/>
2490   </c>
2491   <c>Retry-After</c>
2492   <c>http</c>
2493   <c>standard</c>
2494   <c>
2495      <xref target="header.retry-after"/>
2496   </c>
2497   <c>Server</c>
2498   <c>http</c>
2499   <c>standard</c>
2500   <c>
2501      <xref target="header.server"/>
2502   </c>
2503   <c>User-Agent</c>
2504   <c>http</c>
2505   <c>standard</c>
2506   <c>
2507      <xref target="header.user-agent"/>
2508   </c>
2509</texttable>
2510<!--(END)-->
2511
2512<t>
2513   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2514</t>
2515</section>
2516</section>
2517
2518<section title="Security Considerations" anchor="security.considerations">
2519<t>
2520   This section is meant to inform application developers, information
2521   providers, and users of the security limitations in HTTP/1.1 as
2522   described by this document. The discussion does not include
2523   definitive solutions to the problems revealed, though it does make
2524   some suggestions for reducing security risks.
2525</t>
2526
2527<section title="Transfer of Sensitive Information" anchor="security.sensitive">
2528<t>
2529   Like any generic data transfer protocol, HTTP cannot regulate the
2530   content of the data that is transferred, nor is there any a priori
2531   method of determining the sensitivity of any particular piece of
2532   information within the context of any given request. Therefore,
2533   applications SHOULD supply as much control over this information as
2534   possible to the provider of that information. Four header fields are
2535   worth special mention in this context: Server, Via, Referer and From.
2536</t>
2537<t>
2538   Revealing the specific software version of the server might allow the
2539   server machine to become more vulnerable to attacks against software
2540   that is known to contain security holes. Implementors SHOULD make the
2541   Server header field a configurable option.
2542</t>
2543<t>
2544   Proxies which serve as a portal through a network firewall SHOULD
2545   take special precautions regarding the transfer of header information
2546   that identifies the hosts behind the firewall. In particular, they
2547   SHOULD remove, or replace with sanitized versions, any Via fields
2548   generated behind the firewall.
2549</t>
2550<t>
2551   The Referer header allows reading patterns to be studied and reverse
2552   links drawn. Although it can be very useful, its power can be abused
2553   if user details are not separated from the information contained in
2554   the Referer. Even when the personal information has been removed, the
2555   Referer header might indicate a private document's URI whose
2556   publication would be inappropriate.
2557</t>
2558<t>
2559   The information sent in the From field might conflict with the user's
2560   privacy interests or their site's security policy, and hence it
2561   SHOULD NOT  be transmitted without the user being able to disable,
2562   enable, and modify the contents of the field. The user MUST be able
2563   to set the contents of this field within a user preference or
2564   application defaults configuration.
2565</t>
2566<t>
2567   We suggest, though do not require, that a convenient toggle interface
2568   be provided for the user to enable or disable the sending of From and
2569   Referer information.
2570</t>
2571<t>
2572   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2573   fields can sometimes be used to determine that a specific client or
2574   server have a particular security hole which might be exploited.
2575   Unfortunately, this same information is often used for other valuable
2576   purposes for which HTTP currently has no better mechanism.
2577</t>
2578<t>
2579   Some methods, like TRACE (<xref target="TRACE"/>) may expose
2580   information sent in request headers in the response entity.
2581   Clients SHOULD be careful with sensitive information, like Cookies,
2582   Authorization credentials and other headers that might be used to
2583   collect data from the client.
2584</t> 
2585</section>
2586
2587<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
2588<t>
2589   Because the source of a link might be private information or might
2590   reveal an otherwise private information source, it is strongly
2591   recommended that the user be able to select whether or not the
2592   Referer field is sent. For example, a browser client could have a
2593   toggle switch for browsing openly/anonymously, which would
2594   respectively enable/disable the sending of Referer and From
2595   information.
2596</t>
2597<t>
2598   Clients SHOULD NOT include a Referer header field in a (non-secure)
2599   HTTP request if the referring page was transferred with a secure
2600   protocol.
2601</t>
2602<t>
2603   Authors of services should not use
2604   GET-based forms for the submission of sensitive data because that
2605   data will be encoded in the Request-target. Many existing
2606   servers, proxies, and user agents log or display the Request-target in
2607   places where it might be visible to third parties. Such services can
2608   use POST-based form submission instead.
2609</t>
2610</section>
2611
2612<section title="Location Headers and Spoofing" anchor="location.spoofing">
2613<t>
2614   If a single server supports multiple organizations that do not trust
2615   one another, then it MUST check the values of Location and Content-Location
2616   headers in responses that are generated under control of
2617   said organizations to make sure that they do not attempt to
2618   invalidate resources over which they have no authority.
2619</t>
2620</section>
2621
2622</section>
2623
2624<section title="Acknowledgments" anchor="ack">
2625</section>
2626</middle>
2627<back>
2628
2629<references title="Normative References">
2630
2631<reference anchor="Part1">
2632  <front>
2633    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2634    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2635      <organization abbrev="Day Software">Day Software</organization>
2636      <address><email>fielding@gbiv.com</email></address>
2637    </author>
2638    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2639      <organization>One Laptop per Child</organization>
2640      <address><email>jg@laptop.org</email></address>
2641    </author>
2642    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2643      <organization abbrev="HP">Hewlett-Packard Company</organization>
2644      <address><email>JeffMogul@acm.org</email></address>
2645    </author>
2646    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2647      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2648      <address><email>henrikn@microsoft.com</email></address>
2649    </author>
2650    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2651      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2652      <address><email>LMM@acm.org</email></address>
2653    </author>
2654    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2655      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2656      <address><email>paulle@microsoft.com</email></address>
2657    </author>
2658    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2659      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2660      <address><email>timbl@w3.org</email></address>
2661    </author>
2662    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2663      <organization abbrev="W3C">World Wide Web Consortium</organization>
2664      <address><email>ylafon@w3.org</email></address>
2665    </author>
2666    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2667      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2668      <address><email>julian.reschke@greenbytes.de</email></address>
2669    </author>
2670    <date month="March" year="2010"/>
2671  </front>
2672  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-09"/>
2673 
2674</reference>
2675
2676<reference anchor="Part3">
2677  <front>
2678    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2679    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2680      <organization abbrev="Day Software">Day Software</organization>
2681      <address><email>fielding@gbiv.com</email></address>
2682    </author>
2683    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2684      <organization>One Laptop per Child</organization>
2685      <address><email>jg@laptop.org</email></address>
2686    </author>
2687    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2688      <organization abbrev="HP">Hewlett-Packard Company</organization>
2689      <address><email>JeffMogul@acm.org</email></address>
2690    </author>
2691    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2692      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2693      <address><email>henrikn@microsoft.com</email></address>
2694    </author>
2695    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2696      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2697      <address><email>LMM@acm.org</email></address>
2698    </author>
2699    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2700      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2701      <address><email>paulle@microsoft.com</email></address>
2702    </author>
2703    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2704      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2705      <address><email>timbl@w3.org</email></address>
2706    </author>
2707    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2708      <organization abbrev="W3C">World Wide Web Consortium</organization>
2709      <address><email>ylafon@w3.org</email></address>
2710    </author>
2711    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2712      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2713      <address><email>julian.reschke@greenbytes.de</email></address>
2714    </author>
2715    <date month="March" year="2010"/>
2716  </front>
2717  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-09"/>
2718 
2719</reference>
2720
2721<reference anchor="Part4">
2722  <front>
2723    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2724    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2725      <organization abbrev="Day Software">Day Software</organization>
2726      <address><email>fielding@gbiv.com</email></address>
2727    </author>
2728    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2729      <organization>One Laptop per Child</organization>
2730      <address><email>jg@laptop.org</email></address>
2731    </author>
2732    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2733      <organization abbrev="HP">Hewlett-Packard Company</organization>
2734      <address><email>JeffMogul@acm.org</email></address>
2735    </author>
2736    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2737      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2738      <address><email>henrikn@microsoft.com</email></address>
2739    </author>
2740    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2741      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2742      <address><email>LMM@acm.org</email></address>
2743    </author>
2744    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2745      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2746      <address><email>paulle@microsoft.com</email></address>
2747    </author>
2748    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2749      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2750      <address><email>timbl@w3.org</email></address>
2751    </author>
2752    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2753      <organization abbrev="W3C">World Wide Web Consortium</organization>
2754      <address><email>ylafon@w3.org</email></address>
2755    </author>
2756    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2757      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2758      <address><email>julian.reschke@greenbytes.de</email></address>
2759    </author>
2760    <date month="March" year="2010"/>
2761  </front>
2762  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-09"/>
2763 
2764</reference>
2765
2766<reference anchor="Part5">
2767  <front>
2768    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2769    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2770      <organization abbrev="Day Software">Day Software</organization>
2771      <address><email>fielding@gbiv.com</email></address>
2772    </author>
2773    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2774      <organization>One Laptop per Child</organization>
2775      <address><email>jg@laptop.org</email></address>
2776    </author>
2777    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2778      <organization abbrev="HP">Hewlett-Packard Company</organization>
2779      <address><email>JeffMogul@acm.org</email></address>
2780    </author>
2781    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2782      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2783      <address><email>henrikn@microsoft.com</email></address>
2784    </author>
2785    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2786      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2787      <address><email>LMM@acm.org</email></address>
2788    </author>
2789    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2790      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2791      <address><email>paulle@microsoft.com</email></address>
2792    </author>
2793    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2794      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2795      <address><email>timbl@w3.org</email></address>
2796    </author>
2797    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2798      <organization abbrev="W3C">World Wide Web Consortium</organization>
2799      <address><email>ylafon@w3.org</email></address>
2800    </author>
2801    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2802      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2803      <address><email>julian.reschke@greenbytes.de</email></address>
2804    </author>
2805    <date month="March" year="2010"/>
2806  </front>
2807  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-09"/>
2808 
2809</reference>
2810
2811<reference anchor="Part6">
2812  <front>
2813    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2814    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2815      <organization abbrev="Day Software">Day Software</organization>
2816      <address><email>fielding@gbiv.com</email></address>
2817    </author>
2818    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2819      <organization>One Laptop per Child</organization>
2820      <address><email>jg@laptop.org</email></address>
2821    </author>
2822    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2823      <organization abbrev="HP">Hewlett-Packard Company</organization>
2824      <address><email>JeffMogul@acm.org</email></address>
2825    </author>
2826    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2827      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2828      <address><email>henrikn@microsoft.com</email></address>
2829    </author>
2830    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2831      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2832      <address><email>LMM@acm.org</email></address>
2833    </author>
2834    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2835      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2836      <address><email>paulle@microsoft.com</email></address>
2837    </author>
2838    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2839      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2840      <address><email>timbl@w3.org</email></address>
2841    </author>
2842    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2843      <organization abbrev="W3C">World Wide Web Consortium</organization>
2844      <address><email>ylafon@w3.org</email></address>
2845    </author>
2846    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
2847      <address><email>mnot@mnot.net</email></address>
2848    </author>
2849    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2850      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2851      <address><email>julian.reschke@greenbytes.de</email></address>
2852    </author>
2853    <date month="March" year="2010"/>
2854  </front>
2855  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-09"/>
2856 
2857</reference>
2858
2859<reference anchor="Part7">
2860  <front>
2861    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2862    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2863      <organization abbrev="Day Software">Day Software</organization>
2864      <address><email>fielding@gbiv.com</email></address>
2865    </author>
2866    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2867      <organization>One Laptop per Child</organization>
2868      <address><email>jg@laptop.org</email></address>
2869    </author>
2870    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2871      <organization abbrev="HP">Hewlett-Packard Company</organization>
2872      <address><email>JeffMogul@acm.org</email></address>
2873    </author>
2874    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2875      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2876      <address><email>henrikn@microsoft.com</email></address>
2877    </author>
2878    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2879      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2880      <address><email>LMM@acm.org</email></address>
2881    </author>
2882    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2883      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2884      <address><email>paulle@microsoft.com</email></address>
2885    </author>
2886    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2887      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2888      <address><email>timbl@w3.org</email></address>
2889    </author>
2890    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2891      <organization abbrev="W3C">World Wide Web Consortium</organization>
2892      <address><email>ylafon@w3.org</email></address>
2893    </author>
2894    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2895      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2896      <address><email>julian.reschke@greenbytes.de</email></address>
2897    </author>
2898    <date month="March" year="2010"/>
2899  </front>
2900  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-09"/>
2901 
2902</reference>
2903
2904<reference anchor="RFC2119">
2905  <front>
2906    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2907    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2908      <organization>Harvard University</organization>
2909      <address><email>sob@harvard.edu</email></address>
2910    </author>
2911    <date month="March" year="1997"/>
2912  </front>
2913  <seriesInfo name="BCP" value="14"/>
2914  <seriesInfo name="RFC" value="2119"/>
2915</reference>
2916
2917<reference anchor="RFC5234">
2918  <front>
2919    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2920    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2921      <organization>Brandenburg InternetWorking</organization>
2922      <address>
2923        <email>dcrocker@bbiw.net</email>
2924      </address> 
2925    </author>
2926    <author initials="P." surname="Overell" fullname="Paul Overell">
2927      <organization>THUS plc.</organization>
2928      <address>
2929        <email>paul.overell@thus.net</email>
2930      </address>
2931    </author>
2932    <date month="January" year="2008"/>
2933  </front>
2934  <seriesInfo name="STD" value="68"/>
2935  <seriesInfo name="RFC" value="5234"/>
2936</reference>
2937
2938</references>
2939
2940<references title="Informative References">
2941
2942<reference anchor="RFC1945">
2943  <front>
2944    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2945    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2946      <organization>MIT, Laboratory for Computer Science</organization>
2947      <address><email>timbl@w3.org</email></address>
2948    </author>
2949    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2950      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2951      <address><email>fielding@ics.uci.edu</email></address>
2952    </author>
2953    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2954      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2955      <address><email>frystyk@w3.org</email></address>
2956    </author>
2957    <date month="May" year="1996"/>
2958  </front>
2959  <seriesInfo name="RFC" value="1945"/>
2960</reference>
2961
2962<reference anchor="RFC2068">
2963  <front>
2964    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2965    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2966      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2967      <address><email>fielding@ics.uci.edu</email></address>
2968    </author>
2969    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2970      <organization>MIT Laboratory for Computer Science</organization>
2971      <address><email>jg@w3.org</email></address>
2972    </author>
2973    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2974      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2975      <address><email>mogul@wrl.dec.com</email></address>
2976    </author>
2977    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2978      <organization>MIT Laboratory for Computer Science</organization>
2979      <address><email>frystyk@w3.org</email></address>
2980    </author>
2981    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2982      <organization>MIT Laboratory for Computer Science</organization>
2983      <address><email>timbl@w3.org</email></address>
2984    </author>
2985    <date month="January" year="1997"/>
2986  </front>
2987  <seriesInfo name="RFC" value="2068"/>
2988</reference>
2989
2990<reference anchor="RFC2616">
2991  <front>
2992    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2993    <author initials="R." surname="Fielding" fullname="R. Fielding">
2994      <organization>University of California, Irvine</organization>
2995      <address><email>fielding@ics.uci.edu</email></address>
2996    </author>
2997    <author initials="J." surname="Gettys" fullname="J. Gettys">
2998      <organization>W3C</organization>
2999      <address><email>jg@w3.org</email></address>
3000    </author>
3001    <author initials="J." surname="Mogul" fullname="J. Mogul">
3002      <organization>Compaq Computer Corporation</organization>
3003      <address><email>mogul@wrl.dec.com</email></address>
3004    </author>
3005    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3006      <organization>MIT Laboratory for Computer Science</organization>
3007      <address><email>frystyk@w3.org</email></address>
3008    </author>
3009    <author initials="L." surname="Masinter" fullname="L. Masinter">
3010      <organization>Xerox Corporation</organization>
3011      <address><email>masinter@parc.xerox.com</email></address>
3012    </author>
3013    <author initials="P." surname="Leach" fullname="P. Leach">
3014      <organization>Microsoft Corporation</organization>
3015      <address><email>paulle@microsoft.com</email></address>
3016    </author>
3017    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3018      <organization>W3C</organization>
3019      <address><email>timbl@w3.org</email></address>
3020    </author>
3021    <date month="June" year="1999"/>
3022  </front>
3023  <seriesInfo name="RFC" value="2616"/>
3024</reference>
3025
3026<reference anchor="RFC2817">
3027  <front>
3028    <title>Upgrading to TLS Within HTTP/1.1</title>
3029    <author initials="R." surname="Khare" fullname="R. Khare">
3030      <organization>4K Associates / UC Irvine</organization>
3031      <address><email>rohit@4K-associates.com</email></address>
3032    </author>
3033    <author initials="S." surname="Lawrence" fullname="S. Lawrence">
3034      <organization>Agranat Systems, Inc.</organization>
3035      <address><email>lawrence@agranat.com</email></address>
3036    </author>
3037    <date year="2000" month="May"/>
3038  </front>
3039  <seriesInfo name="RFC" value="2817"/>
3040</reference>
3041
3042<reference anchor="RFC3864">
3043  <front>
3044    <title>Registration Procedures for Message Header Fields</title>
3045    <author initials="G." surname="Klyne" fullname="G. Klyne">
3046      <organization>Nine by Nine</organization>
3047      <address><email>GK-IETF@ninebynine.org</email></address>
3048    </author>
3049    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
3050      <organization>BEA Systems</organization>
3051      <address><email>mnot@pobox.com</email></address>
3052    </author>
3053    <author initials="J." surname="Mogul" fullname="J. Mogul">
3054      <organization>HP Labs</organization>
3055      <address><email>JeffMogul@acm.org</email></address>
3056    </author>
3057    <date year="2004" month="September"/>
3058  </front>
3059  <seriesInfo name="BCP" value="90"/>
3060  <seriesInfo name="RFC" value="3864"/>
3061</reference>
3062
3063<reference anchor="RFC5226">
3064  <front>
3065    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3066    <author initials="T." surname="Narten" fullname="T. Narten">
3067      <organization>IBM</organization>
3068      <address><email>narten@us.ibm.com</email></address>
3069    </author>
3070    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
3071      <organization>Google</organization>
3072      <address><email>Harald@Alvestrand.no</email></address>
3073    </author>
3074    <date year="2008" month="May"/>
3075  </front>
3076  <seriesInfo name="BCP" value="26"/>
3077  <seriesInfo name="RFC" value="5226"/>
3078</reference>
3079
3080<reference anchor="RFC5322">
3081  <front>
3082    <title>Internet Message Format</title>
3083    <author initials="P." surname="Resnick" fullname="P. Resnick">
3084      <organization>Qualcomm Incorporated</organization>
3085    </author>
3086    <date year="2008" month="October"/>
3087  </front> 
3088  <seriesInfo name="RFC" value="5322"/>
3089</reference>
3090
3091</references>
3092
3093<section title="Compatibility with Previous Versions" anchor="compatibility">
3094<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
3095<t>
3096   Clarified which error code should be used for inbound server failures
3097   (e.g., DNS failures). (<xref target="status.504"/>).
3098</t>
3099<t>
3100   201 (Created) had a race that required an Etag be sent when a resource is
3101   first created. (<xref target="status.201"/>).
3102</t>
3103<t>
3104   303 (See Also) and 307 (Temporary Redirect) added to address user agent
3105   failure to implement status code 302 properly.
3106   (Section <xref target="status.303" format="counter"/> and <xref target="status.307" format="counter"/>)
3107</t>
3108<t>
3109   Rewrite of message transmission requirements to make it much harder
3110   for implementors to get it wrong, as the consequences of errors here
3111   can have significant impact on the Internet, and to deal with the
3112   following problems:
3113  <list style="numbers">
3114      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
3115         this was incorrectly placing a requirement on the behavior of
3116         an implementation of a future version of HTTP/1.x</t>
3117
3118      <t>Made it clear that user-agents should retry requests, not
3119         "clients" in general.</t>
3120
3121      <t>Converted requirements for clients to ignore unexpected 100
3122         (Continue) responses, and for proxies to forward 100 responses,
3123         into a general requirement for 1xx responses.</t>
3124
3125      <t>Modified some TCP-specific language, to make it clearer that
3126         non-TCP transports are possible for HTTP.</t>
3127
3128      <t>Require that the origin server MUST NOT wait for the request
3129         body before it sends a required 100 (Continue) response.</t>
3130
3131      <t>Allow, rather than require, a server to omit 100 (Continue) if
3132         it has already seen some of the request body.</t>
3133
3134      <t>Allow servers to defend against denial-of-service attacks and
3135         broken clients.</t>
3136  </list>
3137</t>
3138<t>
3139   This change adds the Expect header and 417 status code.
3140</t>
3141<t>
3142   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
3143   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
3144</t>
3145<t>
3146   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
3147   implemented in previous versions of this specification. See Section 19.6.1 of <xref target="RFC2068"/>.
3148</t>
3149</section>
3150
3151<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3152<t>
3153  This document takes over the Status Code Registry, previously defined
3154  in Section 7.1 of <xref target="RFC2817"/>.
3155  (<xref target="status.code.registry"/>)
3156</t>
3157<t>
3158  Clarify definition of POST.
3159  (<xref target="POST"/>)
3160</t>
3161<t>
3162  Failed to consider that there are
3163  many other request methods that are safe to automatically redirect,
3164  and further that the user agent is able to make that determination
3165  based on the request method semantics.
3166  (Sections <xref format="counter" target="status.301"/>,
3167  <xref format="counter" target="status.302"/> and
3168  <xref format="counter" target="status.307"/>)
3169</t>
3170<t>
3171  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3172  It used to indicate that the requested resource must be accessed through the
3173  proxy given by the Location field. The Location field gave the URI of the
3174  proxy. The recipient was expected to repeat this single request via the proxy.
3175  (<xref target="status.305"/>)
3176</t>
3177<t>
3178  Reclassify Allow header as response header, removing the option to
3179  specify it in a PUT request.
3180  Relax the server requirement on the contents of the Allow header and
3181  remove requirement on clients to always trust the header value.
3182  (<xref target="header.allow"/>)
3183</t>
3184<t>
3185  Correct syntax of Location header to allow fragment,
3186  as referred symbol wasn't what was expected, and add some
3187  clarifications as to when it would not be appropriate.
3188  (<xref target="header.location"/>)
3189</t>
3190<t>
3191  Allow Referer value of "about:blank" as alternative to not specifying it.
3192  (<xref target="header.referer"/>)
3193</t>
3194<t>
3195  In the description of the Server header, the Via field
3196  was described as a SHOULD. The requirement was and is stated
3197  correctly in the description of the Via header in Section 9.9 of <xref target="Part1"/>.
3198  (<xref target="header.server"/>)
3199</t>
3200</section>
3201
3202</section>
3203
3204
3205<section title="Collected ABNF" anchor="collected.abnf">
3206<figure>
3207<artwork type="abnf" name="p2-semantics.parsed-abnf"><![CDATA[
3208Accept = <Accept, defined in [Part3], Section 5.1>
3209Accept-Charset = <Accept-Charset, defined in [Part3], Section 5.2>
3210Accept-Encoding = <Accept-Encoding, defined in [Part3], Section 5.3>
3211Accept-Language = <Accept-Language, defined in [Part3], Section 5.4>
3212Accept-Ranges = <Accept-Ranges, defined in [Part5], Section 5.1>
3213Age = <Age, defined in [Part6], Section 3.1>
3214Allow = "Allow:" OWS Allow-v
3215Allow-v = [ ( "," / Method ) *( OWS "," [ OWS Method ] ) ]
3216Authorization = <Authorization, defined in [Part7], Section 3.1>
3217
3218ETag = <ETag, defined in [Part4], Section 6.1>
3219Expect = "Expect:" OWS Expect-v
3220Expect-v = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
3221
3222From = "From:" OWS From-v
3223From-v = mailbox
3224
3225HTTP-date = <HTTP-date, defined in [Part1], Section 6.1>
3226Host = <Host, defined in [Part1], Section 2.6>
3227
3228If-Match = <If-Match, defined in [Part4], Section 6.2>
3229If-Modified-Since =
3230 <If-Modified-Since, defined in [Part4], Section 6.3>
3231If-None-Match = <If-None-Match, defined in [Part4], Section 6.4>
3232If-Range = <If-Range, defined in [Part5], Section 5.3>
3233If-Unmodified-Since =
3234 <If-Unmodified-Since, defined in [Part4], Section 6.5>
3235
3236Location = "Location:" OWS Location-v
3237Location-v = URI
3238
3239Max-Forwards = "Max-Forwards:" OWS Max-Forwards-v
3240Max-Forwards-v = 1*DIGIT
3241Method = %x4F.50.54.49.4F.4E.53 ; OPTIONS
3242 / %x47.45.54 ; GET
3243 / %x48.45.41.44 ; HEAD
3244 / %x50.4F.53.54 ; POST
3245 / %x50.55.54 ; PUT
3246 / %x44.45.4C.45.54.45 ; DELETE
3247 / %x54.52.41.43.45 ; TRACE
3248 / %x43.4F.4E.4E.45.43.54 ; CONNECT
3249 / extension-method
3250
3251OWS = <OWS, defined in [Part1], Section 1.2.2>
3252
3253Proxy-Authenticate =
3254 <Proxy-Authenticate, defined in [Part7], Section 3.2>
3255Proxy-Authorization =
3256 <Proxy-Authorization, defined in [Part7], Section 3.3>
3257
3258RWS = <RWS, defined in [Part1], Section 1.2.2>
3259Range = <Range, defined in [Part5], Section 5.4>
3260Reason-Phrase = *( WSP / VCHAR / obs-text )
3261Referer = "Referer:" OWS Referer-v
3262Referer-v = absolute-URI / partial-URI
3263Retry-After = "Retry-After:" OWS Retry-After-v
3264Retry-After-v = HTTP-date / delta-seconds
3265
3266Server = "Server:" OWS Server-v
3267Server-v = product *( RWS ( product / comment ) )
3268Status-Code = "100" / "101" / "200" / "201" / "202" / "203" / "204" /
3269 "205" / "206" / "300" / "301" / "302" / "303" / "304" / "305" /
3270 "307" / "400" / "401" / "402" / "403" / "404" / "405" / "406" /
3271 "407" / "408" / "409" / "410" / "411" / "412" / "413" / "414" /
3272 "415" / "416" / "417" / "500" / "501" / "502" / "503" / "504" /
3273 "505" / extension-code
3274
3275TE = <TE, defined in [Part1], Section 9.8>
3276
3277URI = <URI, defined in [Part1], Section 2.6>
3278User-Agent = "User-Agent:" OWS User-Agent-v
3279User-Agent-v = product *( RWS ( product / comment ) )
3280
3281Vary = <Vary, defined in [Part6], Section 3.5>
3282
3283WWW-Authenticate =
3284 <WWW-Authenticate, defined in [Part7], Section 3.4>
3285
3286absolute-URI = <absolute-URI, defined in [Part1], Section 2.6>
3287
3288comment = <comment, defined in [Part1], Section 3.2>
3289
3290delta-seconds = 1*DIGIT
3291
3292expect-params = ";" token [ "=" ( token / quoted-string ) ]
3293expectation = "100-continue" / expectation-extension
3294expectation-extension = token [ "=" ( token / quoted-string )
3295 *expect-params ]
3296extension-code = 3DIGIT
3297extension-method = token
3298
3299mailbox = <mailbox, defined in [RFC5322], Section 3.4>
3300
3301obs-text = <obs-text, defined in [Part1], Section 1.2.2>
3302
3303partial-URI = <partial-URI, defined in [Part1], Section 2.6>
3304product = <product, defined in [Part1], Section 6.3>
3305
3306quoted-string = <quoted-string, defined in [Part1], Section 1.2.2>
3307
3308request-header = Accept / Accept-Charset / Accept-Encoding /
3309 Accept-Language / Authorization / Expect / From / Host / If-Match /
3310 If-Modified-Since / If-None-Match / If-Range / If-Unmodified-Since /
3311 Max-Forwards / Proxy-Authorization / Range / Referer / TE /
3312 User-Agent
3313response-header = Accept-Ranges / Age / Allow / ETag / Location /
3314 Proxy-Authenticate / Retry-After / Server / Vary / WWW-Authenticate
3315
3316token = <token, defined in [Part1], Section 1.2.2>
3317]]></artwork>
3318</figure>
3319<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
3320; Reason-Phrase defined but not used
3321; Status-Code defined but not used
3322; request-header defined but not used
3323; response-header defined but not used
3324]]></artwork></figure></section>
3325
3326
3327<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
3328
3329<section title="Since RFC2616">
3330<t>
3331  Extracted relevant partitions from <xref target="RFC2616"/>.
3332</t>
3333</section>
3334
3335<section title="Since draft-ietf-httpbis-p2-semantics-00">
3336<t>
3337  Closed issues:
3338  <list style="symbols"> 
3339    <t>
3340      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
3341      "Via is a MUST"
3342      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
3343    </t>
3344    <t>
3345      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
3346      "Fragments allowed in Location"
3347      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
3348    </t>
3349    <t>
3350      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
3351      "Safe Methods vs Redirection"
3352      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
3353    </t>
3354    <t>
3355      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
3356      "Revise description of the POST method"
3357      (<eref target="http://purl.org/NET/http-errata#post"/>)
3358    </t>
3359    <t>
3360      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
3361      "Normative and Informative references"
3362    </t>
3363    <t>
3364      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
3365      "RFC2606 Compliance"
3366    </t>
3367    <t>
3368      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
3369      "Informative references"
3370    </t>
3371    <t>
3372      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
3373      "Redundant cross-references"
3374    </t>
3375  </list>
3376</t>
3377<t>
3378  Other changes:
3379  <list style="symbols"> 
3380    <t>
3381      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
3382    </t>
3383  </list>
3384</t>
3385</section>
3386
3387<section title="Since draft-ietf-httpbis-p2-semantics-01">
3388<t>
3389  Closed issues:
3390  <list style="symbols"> 
3391    <t>
3392      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
3393      "PUT side effects"
3394    </t>
3395    <t>
3396      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
3397      "Duplicate Host header requirements"
3398    </t>
3399  </list>
3400</t>
3401<t>
3402  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3403  <list style="symbols"> 
3404    <t>
3405      Move "Product Tokens" section (back) into Part 1, as "token" is used
3406      in the definition of the Upgrade header.
3407    </t>
3408    <t>
3409      Add explicit references to BNF syntax and rules imported from other parts of the specification.
3410    </t>
3411    <t>
3412      Copy definition of delta-seconds from Part6 instead of referencing it.
3413    </t>
3414  </list>
3415</t>
3416</section>
3417
3418<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
3419<t>
3420  Closed issues:
3421  <list style="symbols"> 
3422    <t>
3423      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
3424      "Requiring Allow in 405 responses"
3425    </t>
3426    <t>
3427      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
3428      "Status Code Registry"
3429    </t>
3430    <t>
3431      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
3432      "Redirection vs. Location"
3433    </t>
3434    <t>
3435      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
3436      "Cacheability of 303 response"
3437    </t>
3438    <t>
3439      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
3440      "305 Use Proxy"
3441    </t>
3442    <t>
3443      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
3444      "Classification for Allow header"
3445    </t>
3446    <t>
3447      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
3448      "PUT - 'store under' vs 'store at'"
3449    </t>
3450  </list>
3451</t>
3452<t>
3453  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
3454  <list style="symbols"> 
3455    <t>
3456      Reference RFC 3984, and update header registrations for headers defined
3457      in this document.
3458    </t>
3459  </list>
3460</t>
3461<t>
3462  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3463  <list style="symbols"> 
3464    <t>
3465      Replace string literals when the string really is case-sensitive (method).
3466    </t>
3467  </list>
3468</t>
3469</section>
3470
3471<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
3472<t>
3473  Closed issues:
3474  <list style="symbols"> 
3475    <t>
3476      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
3477      "OPTIONS request bodies"
3478    </t>
3479    <t>
3480      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
3481      "Description of CONNECT should refer to RFC2817"
3482    </t>
3483    <t>
3484      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
3485      "Location Content-Location reference request/response mixup"
3486    </t>
3487  </list>
3488</t>
3489<t>
3490  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
3491  <list style="symbols"> 
3492    <t>
3493      Added initial proposal for registration process, plus initial
3494      content (non-HTTP/1.1 methods to be added by a separate specification).
3495    </t>
3496  </list>
3497</t>
3498</section>
3499
3500<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
3501<t>
3502  Closed issues:
3503  <list style="symbols"> 
3504    <t>
3505      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
3506      "Content-*"
3507    </t>
3508    <t>
3509      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
3510      "RFC 2822 is updated by RFC 5322"
3511    </t>
3512  </list>
3513</t>
3514<t>
3515  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3516  <list style="symbols"> 
3517    <t>
3518      Use "/" instead of "|" for alternatives.
3519    </t>
3520    <t>
3521      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
3522      whitespace ("OWS") and required whitespace ("RWS").
3523    </t>
3524    <t>
3525      Rewrite ABNFs to spell out whitespace rules, factor out
3526      header value format definitions.
3527    </t>
3528  </list>
3529</t>
3530</section>
3531
3532<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
3533<t>
3534  Closed issues:
3535  <list style="symbols"> 
3536    <t>
3537      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
3538      "Reason-Phrase BNF"
3539    </t>
3540  </list>
3541</t>
3542<t>
3543  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3544  <list style="symbols"> 
3545    <t>
3546      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
3547    </t>
3548  </list>
3549</t>
3550</section>
3551
3552<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
3553<t>
3554  Closed issues:
3555  <list style="symbols"> 
3556    <t>
3557      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
3558      "Clarify when Referer is sent"
3559    </t>
3560    <t>
3561      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
3562      "status codes vs methods"
3563    </t>
3564    <t>
3565      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
3566      "Do not require "updates" relation for specs that register status codes or method names"
3567    </t>
3568  </list>
3569</t>
3570</section>
3571
3572<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
3573<t>
3574  Closed issues:
3575  <list style="symbols"> 
3576    <t>
3577      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
3578      "Idempotency"
3579    </t>
3580    <t>
3581      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
3582      "TRACE security considerations"
3583    </t>
3584    <t>
3585      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
3586      "Clarify rules for determining what entities a response carries"
3587    </t>
3588    <t>
3589      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
3590      "update note citing RFC 1945 and 2068"
3591    </t>
3592    <t>
3593      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
3594      "update note about redirect limit"
3595    </t>
3596    <t>
3597      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
3598      "Location header ABNF should use 'URI'"
3599    </t>
3600    <t>
3601      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
3602      "fragments in Location vs status 303"
3603    </t>
3604    <t>
3605      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
3606      "move IANA registrations for optional status codes"
3607    </t>
3608  </list>
3609</t>
3610<t>
3611  Partly resolved issues:
3612  <list style="symbols"> 
3613    <t>
3614      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
3615      "Are OPTIONS and TRACE safe?"
3616    </t>
3617  </list>
3618</t>
3619</section>
3620
3621<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
3622<t>
3623  Closed issues:
3624  <list style="symbols"> 
3625    <t>
3626      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
3627      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
3628      status codes when fixing this previously)
3629    </t>
3630  </list>
3631</t>
3632</section>
3633
3634</section>
3635
3636</back>
3637</rfc>
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