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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-08">
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 day="26" month="October" year="2009"/>
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.07"/>.
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's, 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 (first match winning):
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>(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) is identified by the request-target. If the request-target refers
754   to a data-producing process, it is the produced data which shall be
755   returned as the entity in the response and not the source text of the
756   process, unless that text happens to be the output of the process.
757</t>
758<t>
759   The semantics of the GET method change to a "conditional GET" if the
760   request message includes an If-Modified-Since, If-Unmodified-Since,
761   If-Match, If-None-Match, or If-Range header field. A conditional GET
762   method requests that the entity be transferred only under the
763   circumstances described by the conditional header field(s). The
764   conditional GET method is intended to reduce unnecessary network
765   usage by allowing cached entities to be refreshed without requiring
766   multiple requests or transferring data already held by the client.
767</t>
768<t>
769   The semantics of the GET method change to a "partial GET" if the
770   request message includes a Range header field. A partial GET requests
771   that only part of the entity be transferred, as described in Section 5.4 of <xref target="Part5"/>.
772   The partial GET method is intended to reduce unnecessary
773   network usage by allowing partially-retrieved entities to be
774   completed without transferring data already held by the client.
775</t>
776<t>
777   The response to a GET request is cacheable if and only if it meets
778   the requirements for HTTP caching described in <xref target="Part6"/>.
779</t>
780<t>
781   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
782</t>
783</section>
784
785<section title="HEAD" anchor="HEAD">
786 
787  <iref primary="true" item="HEAD method"/>
788  <iref primary="true" item="Methods" subitem="HEAD"/>
789<t>
790   The HEAD method is identical to GET except that the server MUST NOT
791   return a message-body in the response. The metainformation contained
792   in the HTTP headers in response to a HEAD request SHOULD be identical
793   to the information sent in response to a GET request. This method can
794   be used for obtaining metainformation about the entity implied by the
795   request without transferring the entity-body itself. This method is
796   often used for testing hypertext links for validity, accessibility,
797   and recent modification.
798</t>
799<t>
800   The response to a HEAD request MAY be cacheable in the sense that the
801   information contained in the response MAY be used to update a
802   previously cached entity from that resource. If the new field values
803   indicate that the cached entity differs from the current entity (as
804   would be indicated by a change in Content-Length, Content-MD5, ETag
805   or Last-Modified), then the cache MUST treat the cache entry as
806   stale.
807</t>
808</section>
809
810<section title="POST" anchor="POST">
811  <iref primary="true" item="POST method"/>
812  <iref primary="true" item="Methods" subitem="POST"/>
813<t>
814   The POST method is used to request that the origin server accept the
815   entity enclosed in the request as data to be processed by the resource
816   identified by the request-target in the Request-Line. POST is designed
817   to allow a uniform method to cover the following functions:
818  <list style="symbols">
819    <t>
820      Annotation of existing resources;
821    </t>
822    <t>
823        Posting a message to a bulletin board, newsgroup, mailing list,
824        or similar group of articles;
825    </t>
826    <t>
827        Providing a block of data, such as the result of submitting a
828        form, to a data-handling process;
829    </t>
830    <t>
831        Extending a database through an append operation.
832    </t>
833  </list>
834</t>
835<t>
836   The actual function performed by the POST method is determined by the
837   server and is usually dependent on the request-target.
838</t>
839<t>
840   The action performed by the POST method might not result in a
841   resource that can be identified by a URI. In this case, either 200
842   (OK) or 204 (No Content) is the appropriate response status,
843   depending on whether or not the response includes an entity that
844   describes the result.
845</t>
846<t>
847   If a resource has been created on the origin server, the response
848   SHOULD be 201 (Created) and contain an entity which describes the
849   status of the request and refers to the new resource, and a Location
850   header (see <xref target="header.location"/>).
851</t>
852<t>
853   Responses to this method are not cacheable, unless the response
854   includes appropriate Cache-Control or Expires header fields. However,
855   the 303 (See Other) response can be used to direct the user agent to
856   retrieve a cacheable resource.
857</t>
858</section>
859
860<section title="PUT" anchor="PUT">
861  <iref primary="true" item="PUT method"/>
862  <iref primary="true" item="Methods" subitem="PUT"/>
863<t>
864   The PUT method requests that the enclosed entity be stored at the
865   supplied request-target. If the request-target refers to an already
866   existing resource, the enclosed entity SHOULD be considered as a
867   modified version of the one residing on the origin server. If the
868   request-target does not point to an existing resource, and that URI is
869   capable of being defined as a new resource by the requesting user
870   agent, the origin server can create the resource with that URI. If a
871   new resource is created at the request-target, the origin server MUST
872   inform the user agent
873   via the 201 (Created) response. If an existing resource is modified,
874   either the 200 (OK) or 204 (No Content) response codes SHOULD be sent
875   to indicate successful completion of the request. If the resource
876   could not be created or modified with the request-target, an appropriate
877   error response SHOULD be given that reflects the nature of the
878   problem. The recipient of the entity MUST NOT ignore any Content-*
879   headers (headers starting with the prefix 'Content-') that it does
880   not understand or implement
881   and MUST return a 501 (Not Implemented) response in such cases.
882</t>
883<t>
884   If the request passes through a cache and the request-target identifies
885   one or more currently cached entities, those entries SHOULD be
886   treated as stale. Responses to this method are not cacheable.
887</t>
888<t>
889   The fundamental difference between the POST and PUT requests is
890   reflected in the different meaning of the request-target. The URI in a
891   POST request identifies the resource that will handle the enclosed
892   entity. That resource might be a data-accepting process, a gateway to
893   some other protocol, or a separate entity that accepts annotations.
894   In contrast, the URI in a PUT request identifies the entity enclosed
895   with the request -- the user agent knows what URI is intended and the
896   server MUST NOT attempt to apply the request to some other resource.
897   If the server desires that the request be applied to a different URI,
898   it MUST send a 301 (Moved Permanently) response; the user agent MAY
899   then make its own decision regarding whether or not to redirect the
900   request.
901</t>
902<t>
903   A single resource MAY be identified by many different URIs. For
904   example, an article might have a URI for identifying "the current
905   version" which is separate from the URI identifying each particular
906   version. In this case, a PUT request on a general URI might result in
907   several other URIs being defined by the origin server.
908</t>
909<t>
910   HTTP/1.1 does not define how a PUT method affects the state of an
911   origin server.
912</t>
913<t>
914   Unless otherwise specified for a particular entity-header, the
915   entity-headers in the PUT request SHOULD be applied to the resource
916   created or modified by the PUT.
917</t>
918</section>
919
920<section title="DELETE" anchor="DELETE">
921  <iref primary="true" item="DELETE method"/>
922  <iref primary="true" item="Methods" subitem="DELETE"/>
923<t>
924   The DELETE method requests that the origin server delete the resource
925   identified by the request-target. This method MAY be overridden by human
926   intervention (or other means) on the origin server. The client cannot
927   be guaranteed that the operation has been carried out, even if the
928   status code returned from the origin server indicates that the action
929   has been completed successfully. However, the server SHOULD NOT
930   indicate success unless, at the time the response is given, it
931   intends to delete the resource or move it to an inaccessible
932   location.
933</t>
934<t>
935   A successful response SHOULD be 200 (OK) if the response includes an
936   entity describing the status, 202 (Accepted) if the action has not
937   yet been enacted, or 204 (No Content) if the action has been enacted
938   but the response does not include an entity.
939</t>
940<t>
941   If the request passes through a cache and the request-target identifies
942   one or more currently cached entities, those entries SHOULD be
943   treated as stale. Responses to this method are not cacheable.
944</t>
945</section>
946
947<section title="TRACE" anchor="TRACE">
948 
949  <iref primary="true" item="TRACE method"/>
950  <iref primary="true" item="Methods" subitem="TRACE"/>
951<t>
952   The TRACE method is used to invoke a remote, application-layer loop-back
953   of the request message. The final recipient of the request
954   SHOULD reflect the message received back to the client as the
955   entity-body of a 200 (OK) response. The final recipient is either the
956   origin server or the first proxy or gateway to receive a Max-Forwards
957   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
958   MUST NOT include an entity.
959</t>
960<t>
961   TRACE allows the client to see what is being received at the other
962   end of the request chain and use that data for testing or diagnostic
963   information. The value of the Via header field (Section 9.9 of <xref target="Part1"/>) is of
964   particular interest, since it acts as a trace of the request chain.
965   Use of the Max-Forwards header field allows the client to limit the
966   length of the request chain, which is useful for testing a chain of
967   proxies forwarding messages in an infinite loop.
968</t>
969<t>
970   If the request is valid, the response SHOULD contain the entire
971   request message in the entity-body, with a Content-Type of
972   "message/http" (see Section 10.3.1 of <xref target="Part1"/>). Responses to this method
973   MUST NOT be cached.
974</t>
975</section>
976
977<section title="CONNECT" anchor="CONNECT">
978  <iref primary="true" item="CONNECT method"/>
979  <iref primary="true" item="Methods" subitem="CONNECT"/>
980<t>
981   This specification reserves the method name CONNECT for use with a
982   proxy that can dynamically switch to being a tunnel (e.g. SSL
983   tunneling <xref target="RFC2817"/>).
984</t>
985</section>
986</section>
987
988
989<section title="Status Code Definitions" anchor="status.codes">
990<t>
991   Each Status-Code is described below, including any metainformation required
992   in the response.
993</t>
994
995<section title="Informational 1xx" anchor="status.1xx">
996<t>
997   This class of status code indicates a provisional response,
998   consisting only of the Status-Line and optional headers, and is
999   terminated by an empty line. There are no required headers for this
1000   class of status code. Since HTTP/1.0 did not define any 1xx status
1001   codes, servers MUST NOT send a 1xx response to an HTTP/1.0 client
1002   except under experimental conditions.
1003</t>
1004<t>
1005   A client MUST be prepared to accept one or more 1xx status responses
1006   prior to a regular response, even if the client does not expect a 100
1007   (Continue) status message. Unexpected 1xx status responses MAY be
1008   ignored by a user agent.
1009</t>
1010<t>
1011   Proxies MUST forward 1xx responses, unless the connection between the
1012   proxy and its client has been closed, or unless the proxy itself
1013   requested the generation of the 1xx response. (For example, if a
1014   proxy adds a "Expect: 100-continue" field when it forwards a request,
1015   then it need not forward the corresponding 100 (Continue)
1016   response(s).)
1017</t>
1018
1019<section title="100 Continue" anchor="status.100">
1020  <iref primary="true" item="100 Continue (status code)"/>
1021  <iref primary="true" item="Status Codes" subitem="100 Continue"/>
1022<t>
1023   The client SHOULD continue with its request. This interim response is
1024   used to inform the client that the initial part of the request has
1025   been received and has not yet been rejected by the server. The client
1026   SHOULD continue by sending the remainder of the request or, if the
1027   request has already been completed, ignore this response. The server
1028   MUST send a final response after the request has been completed. See
1029   Section 7.2.3 of <xref target="Part1"/> for detailed discussion of the use and handling of this
1030   status code.
1031</t>
1032</section>
1033
1034<section title="101 Switching Protocols" anchor="status.101">
1035  <iref primary="true" item="101 Switching Protocols (status code)"/>
1036  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols"/>
1037<t>
1038   The server understands and is willing to comply with the client's
1039   request, via the Upgrade message header field (Section 5.4 of <xref target="Part5"/>), for a
1040   change in the application protocol being used on this connection. The
1041   server will switch protocols to those defined by the response's
1042   Upgrade header field immediately after the empty line which
1043   terminates the 101 response.
1044</t>
1045<t>
1046   The protocol SHOULD be switched only when it is advantageous to do
1047   so. For example, switching to a newer version of HTTP is advantageous
1048   over older versions, and switching to a real-time, synchronous
1049   protocol might be advantageous when delivering resources that use
1050   such features.
1051</t>
1052</section>
1053</section>
1054
1055<section title="Successful 2xx" anchor="status.2xx">
1056<t>
1057   This class of status code indicates that the client's request was
1058   successfully received, understood, and accepted.
1059</t>
1060
1061<section title="200 OK" anchor="status.200">
1062  <iref primary="true" item="200 OK (status code)"/>
1063  <iref primary="true" item="Status Codes" subitem="200 OK"/>
1064<t>
1065   The request has succeeded. The information returned with the response
1066   is dependent on the method used in the request, for example:
1067  <list style="hanging">
1068    <t hangText="GET">
1069          an entity corresponding to the requested resource is sent in
1070          the response;
1071    </t>
1072    <t hangText="HEAD">
1073          the entity-header fields corresponding to the requested
1074          resource are sent in the response without any message-body;
1075    </t>
1076    <t hangText="POST">
1077      an entity describing or containing the result of the action;
1078    </t>
1079    <t hangText="TRACE">
1080      an entity containing the request message as received by the
1081      end server.
1082    </t>
1083  </list>
1084</t>
1085</section>
1086
1087<section title="201 Created" anchor="status.201">
1088  <iref primary="true" item="201 Created (status code)"/>
1089  <iref primary="true" item="Status Codes" subitem="201 Created"/>
1090<t>
1091   The request has been fulfilled and resulted in a new resource being
1092   created. The newly created resource can be referenced by the URI(s)
1093   returned in the entity of the response, with the most specific URI
1094   for the resource given by a Location header field. The response
1095   SHOULD include an entity containing a list of resource
1096   characteristics and location(s) from which the user or user agent can
1097   choose the one most appropriate. The entity format is specified by
1098   the media type given in the Content-Type header field. The origin
1099   server MUST create the resource before returning the 201 status code.
1100   If the action cannot be carried out immediately, the server SHOULD
1101   respond with 202 (Accepted) response instead.
1102</t>
1103<t>
1104   A 201 response MAY contain an ETag response header field indicating
1105   the current value of the entity tag for the requested variant just
1106   created, see Section 6.1 of <xref target="Part4"/>.
1107</t>
1108</section>
1109
1110<section title="202 Accepted" anchor="status.202">
1111  <iref primary="true" item="202 Accepted (status code)"/>
1112  <iref primary="true" item="Status Codes" subitem="202 Accepted"/>
1113<t>
1114   The request has been accepted for processing, but the processing has
1115   not been completed.  The request might or might not eventually be
1116   acted upon, as it might be disallowed when processing actually takes
1117   place. There is no facility for re-sending a status code from an
1118   asynchronous operation such as this.
1119</t>
1120<t>
1121   The 202 response is intentionally non-committal. Its purpose is to
1122   allow a server to accept a request for some other process (perhaps a
1123   batch-oriented process that is only run once per day) without
1124   requiring that the user agent's connection to the server persist
1125   until the process is completed. The entity returned with this
1126   response SHOULD include an indication of the request's current status
1127   and either a pointer to a status monitor or some estimate of when the
1128   user can expect the request to be fulfilled.
1129</t>
1130</section>
1131
1132<section title="203 Non-Authoritative Information" anchor="status.203">
1133  <iref primary="true" item="203 Non-Authoritative Information (status code)"/>
1134  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information"/>
1135<t>
1136   The returned metainformation in the entity-header is not the
1137   definitive set as available from the origin server, but is gathered
1138   from a local or a third-party copy. The set presented MAY be a subset
1139   or superset of the original version. For example, including local
1140   annotation information about the resource might result in a superset
1141   of the metainformation known by the origin server. Use of this
1142   response code is not required and is only appropriate when the
1143   response would otherwise be 200 (OK).
1144</t>
1145</section>
1146
1147<section title="204 No Content" anchor="status.204">
1148  <iref primary="true" item="204 No Content (status code)"/>
1149  <iref primary="true" item="Status Codes" subitem="204 No Content"/>
1150<t>
1151   The server has fulfilled the request but does not need to return an
1152   entity-body, and might want to return updated metainformation. The
1153   response MAY include new or updated metainformation in the form of
1154   entity-headers, which if present SHOULD be associated with the
1155   requested variant.
1156</t>
1157<t>
1158   If the client is a user agent, it SHOULD NOT  change its document view
1159   from that which caused the request to be sent. This response is
1160   primarily intended to allow input for actions to take place without
1161   causing a change to the user agent's active document view, although
1162   any new or updated metainformation SHOULD be applied to the document
1163   currently in the user agent's active view.
1164</t>
1165<t>
1166   The 204 response MUST NOT include a message-body, and thus is always
1167   terminated by the first empty line after the header fields.
1168</t>
1169</section>
1170
1171<section title="205 Reset Content" anchor="status.205">
1172  <iref primary="true" item="205 Reset Content (status code)"/>
1173  <iref primary="true" item="Status Codes" subitem="205 Reset Content"/>
1174<t>
1175   The server has fulfilled the request and the user agent SHOULD reset
1176   the document view which caused the request to be sent. This response
1177   is primarily intended to allow input for actions to take place via
1178   user input, followed by a clearing of the form in which the input is
1179   given so that the user can easily initiate another input action. The
1180   response MUST NOT include an entity.
1181</t>
1182</section>
1183
1184<section title="206 Partial Content" anchor="status.206">
1185  <iref primary="true" item="206 Partial Content (status code)"/>
1186  <iref primary="true" item="Status Codes" subitem="206 Partial Content"/>
1187 
1188<t>
1189   The server has fulfilled the partial GET request for the resource
1190   and the enclosed entity is a partial representation as defined in Section 3.1 of <xref target="Part5"/>.
1191</t>
1192</section>
1193</section>
1194
1195<section title="Redirection 3xx" anchor="status.3xx">
1196<t>
1197   This class of status code indicates that further action needs to be
1198   taken by the user agent in order to fulfill the request.  The action
1199   required MAY be carried out by the user agent without interaction
1200   with the user if and only if the method used in the second request is
1201   GET or HEAD. A client SHOULD detect infinite redirection loops, since
1202   such loops generate network traffic for each redirection.
1203</t>
1204<t><list>
1205  <t>
1206    Note: an earlier version of this specification recommended a
1207    maximum of five redirections (<xref target="RFC2068"/>, Section 10.3).
1208    Content developers should be aware that there might be clients that
1209    implement such a fixed limitation.
1210  </t>
1211</list></t>
1212
1213<section title="300 Multiple Choices" anchor="status.300">
1214  <iref primary="true" item="300 Multiple Choices (status code)"/>
1215  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices"/>
1216<t>
1217   The requested resource corresponds to any one of a set of
1218   representations, each with its own specific location, and agent-driven
1219   negotiation information (Section 4 of <xref target="Part3"/>) is being provided so that
1220   the user (or user agent) can select a preferred representation and
1221   redirect its request to that location.
1222</t>
1223<t>
1224   Unless it was a HEAD request, the response SHOULD include an entity
1225   containing a list of resource characteristics and location(s) from
1226   which the user or user agent can choose the one most appropriate. The
1227   entity format is specified by the media type given in the Content-Type
1228   header field. Depending upon the format and the capabilities of
1229   the user agent, selection of the most appropriate choice MAY be
1230   performed automatically. However, this specification does not define
1231   any standard for such automatic selection.
1232</t>
1233<t>
1234   If the server has a preferred choice of representation, it SHOULD
1235   include the specific URI for that representation in the Location
1236   field; user agents MAY use the Location field value for automatic
1237   redirection. This response is cacheable unless indicated otherwise.
1238</t>
1239</section>
1240
1241<section title="301 Moved Permanently" anchor="status.301">
1242  <iref primary="true" item="301 Moved Permanently (status code)"/>
1243  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently"/>
1244<t>
1245   The requested resource has been assigned a new permanent URI and any
1246   future references to this resource SHOULD use one of the returned
1247   URIs.  Clients with link editing capabilities ought to automatically
1248   re-link references to the request-target to one or more of the new
1249   references returned by the server, where possible. This response is
1250   cacheable unless indicated otherwise.
1251</t>
1252<t>
1253   The new permanent URI SHOULD be given by the Location field in the
1254   response. Unless the request method was HEAD, the entity of the
1255   response SHOULD contain a short hypertext note with a hyperlink to
1256   the new URI(s).
1257</t>
1258<t>
1259   If the 301 status code is received in response to a request method
1260   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1261   then the request MAY be automatically redirected by the user agent without
1262   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
1263   request unless it can be confirmed by the user, since this might
1264   change the conditions under which the request was issued.
1265</t>
1266<t><list>
1267  <t>
1268    Note: When automatically redirecting a POST request after
1269    receiving a 301 status code, some existing HTTP/1.0 user agents
1270    will erroneously change it into a GET request.
1271  </t>
1272</list></t>
1273</section>
1274
1275<section title="302 Found" anchor="status.302">
1276  <iref primary="true" item="302 Found (status code)"/>
1277  <iref primary="true" item="Status Codes" subitem="302 Found"/>
1278<t>
1279   The requested resource resides temporarily under a different URI.
1280   Since the redirection might be altered on occasion, the client SHOULD
1281   continue to use the request-target for future requests.  This response
1282   is only cacheable if indicated by a Cache-Control or Expires header
1283   field.
1284</t>
1285<t>
1286   The temporary URI SHOULD be given by the Location field in the
1287   response. Unless the request method was HEAD, the entity of the
1288   response SHOULD contain a short hypertext note with a hyperlink to
1289   the new URI(s).
1290</t>
1291<t>
1292   If the 302 status code is received in response to a request method
1293   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1294   then the request MAY be automatically redirected by the user agent without
1295   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
1296   request unless it can be confirmed by the user, since this might
1297   change the conditions under which the request was issued.
1298</t>
1299<t><list>
1300  <t>
1301    Note: HTTP/1.0 (<xref target="RFC1945"/>, Section 9.3)
1302    and the first version of HTTP/1.1 (<xref target="RFC2068"/>, Section 10.3.3)
1303    specify that the client is not allowed to change the method on the
1304    redirected request.  However, most existing user agent implementations
1305    treat 302 as if it were a 303 response, performing a GET on the Location
1306    field-value regardless of the original request method. Therefore, a
1307    previous version of this specification
1308    (<xref target="RFC2616"/>, Section 10.3.3) has added the
1309    status codes
1310    <xref target="status.303" format="none">303</xref> and
1311    <xref target="status.307" format="none">307</xref> for servers that wish
1312    to make unambiguously clear which kind of reaction is expected of the
1313    client.
1314  </t>
1315</list></t>
1316</section>
1317
1318<section title="303 See Other" anchor="status.303">
1319  <iref primary="true" item="303 See Other (status code)"/>
1320  <iref primary="true" item="Status Codes" subitem="303 See Other"/>
1321<t>
1322   The server directs the user agent to a different resource, indicated
1323   by a URI in the Location header field, that provides an indirect
1324   response to the original request.  The user agent MAY perform a GET
1325   request on the URI in the Location field in order to obtain a
1326   representation corresponding to the response, be redirected again,
1327   or end with an error status.  The Location URI is not a substitute
1328   reference for the originally requested resource.
1329</t>
1330<t>
1331   The 303 status is generally applicable to any HTTP method.  It is
1332   primarily used to allow the output of a POST action to redirect
1333   the user agent to a selected resource, since doing so provides the
1334   information corresponding to the POST response in a form that
1335   can be separately identified, bookmarked, and cached independent
1336   of the original request.
1337</t>
1338<t>
1339   A 303 response to a GET request indicates that the requested
1340   resource does not have a representation of its own that can be
1341   transferred by the server over HTTP.  The Location URI indicates a
1342   resource that is descriptive of the requested resource such that
1343   the follow-on representation may be useful without implying that
1344   it adequately represents the previously requested resource.
1345   Note that answers to the questions of what can be represented, what
1346   representations are adequate, and what might be a useful description
1347   are outside the scope of HTTP and thus entirely determined by the
1348   URI owner(s).
1349</t>
1350<t>
1351   A 303 response SHOULD NOT be cached unless it is indicated as
1352   cacheable by Cache-Control or Expires header fields.  Except for
1353   responses to a HEAD request, the entity of a 303 response SHOULD
1354   contain a short hypertext note with a hyperlink to the Location URI.
1355</t>
1356</section>
1357
1358<section title="304 Not Modified" anchor="status.304">
1359  <iref primary="true" item="304 Not Modified (status code)"/>
1360  <iref primary="true" item="Status Codes" subitem="304 Not Modified"/>
1361 
1362<t>
1363   The response to the request has not been modified since the conditions
1364   indicated by the client's conditional GET request, as defined in Section 3.1 of <xref target="Part4"/>.
1365</t>
1366</section>
1367
1368<section title="305 Use Proxy" anchor="status.305">
1369  <iref primary="true" item="305 Use Proxy (status code)"/>
1370  <iref primary="true" item="Status Codes" subitem="305 Use Proxy"/>
1371<t>
1372   The 305 status was defined in a previous version of this specification
1373   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1374</t>
1375</section>
1376
1377<section title="306 (Unused)" anchor="status.306">
1378  <iref primary="true" item="306 (Unused) (status code)"/>
1379  <iref primary="true" item="Status Codes" subitem="306 (Unused)"/>
1380<t>
1381   The 306 status code was used in a previous version of the
1382   specification, is no longer used, and the code is reserved.
1383</t>
1384</section>
1385
1386<section title="307 Temporary Redirect" anchor="status.307">
1387  <iref primary="true" item="307 Temporary Redirect (status code)"/>
1388  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect"/>
1389<t>
1390   The requested resource resides temporarily under a different URI.
1391   Since the redirection MAY be altered on occasion, the client SHOULD
1392   continue to use the request-target for future requests.  This response
1393   is only cacheable if indicated by a Cache-Control or Expires header
1394   field.
1395</t>
1396<t>
1397   The temporary URI SHOULD be given by the Location field in the
1398   response. Unless the request method was HEAD, the entity of the
1399   response SHOULD contain a short hypertext note with a hyperlink to
1400   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1401   understand the 307 status. Therefore, the note SHOULD contain the
1402   information necessary for a user to repeat the original request on
1403   the new URI.
1404</t>
1405<t>
1406   If the 307 status code is received in response to a request method
1407   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1408   then the request MAY be automatically redirected by the user agent without
1409   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
1410   request unless it can be confirmed by the user, since this might
1411   change the conditions under which the request was issued.
1412</t>
1413</section>
1414</section>
1415
1416<section title="Client Error 4xx" anchor="status.4xx">
1417<t>
1418   The 4xx class of status code is intended for cases in which the
1419   client seems to have erred. Except when responding to a HEAD request,
1420   the server SHOULD include an entity containing an explanation of the
1421   error situation, and whether it is a temporary or permanent
1422   condition. These status codes are applicable to any request method.
1423   User agents SHOULD display any included entity to the user.
1424</t>
1425<t>
1426   If the client is sending data, a server implementation using TCP
1427   SHOULD be careful to ensure that the client acknowledges receipt of
1428   the packet(s) containing the response, before the server closes the
1429   input connection. If the client continues sending data to the server
1430   after the close, the server's TCP stack will send a reset packet to
1431   the client, which may erase the client's unacknowledged input buffers
1432   before they can be read and interpreted by the HTTP application.
1433</t>
1434
1435<section title="400 Bad Request" anchor="status.400">
1436  <iref primary="true" item="400 Bad Request (status code)"/>
1437  <iref primary="true" item="Status Codes" subitem="400 Bad Request"/>
1438<t>
1439   The request could not be understood by the server due to malformed
1440   syntax. The client SHOULD NOT  repeat the request without
1441   modifications.
1442</t>
1443</section>
1444
1445<section title="401 Unauthorized" anchor="status.401">
1446  <iref primary="true" item="401 Unauthorized (status code)"/>
1447  <iref primary="true" item="Status Codes" subitem="401 Unauthorized"/>
1448 
1449<t>
1450   The request requires user authentication (see Section 2.1 of <xref target="Part7"/>).
1451</t>
1452</section>
1453
1454<section title="402 Payment Required" anchor="status.402">
1455  <iref primary="true" item="402 Payment Required (status code)"/>
1456  <iref primary="true" item="Status Codes" subitem="402 Payment Required"/>
1457<t>
1458   This code is reserved for future use.
1459</t>
1460</section>
1461
1462<section title="403 Forbidden" anchor="status.403">
1463  <iref primary="true" item="403 Forbidden (status code)"/>
1464  <iref primary="true" item="Status Codes" subitem="403 Forbidden"/>
1465<t>
1466   The server understood the request, but is refusing to fulfill it.
1467   Authorization will not help and the request SHOULD NOT  be repeated.
1468   If the request method was not HEAD and the server wishes to make
1469   public why the request has not been fulfilled, it SHOULD describe the
1470   reason for the refusal in the entity.  If the server does not wish to
1471   make this information available to the client, the status code 404
1472   (Not Found) can be used instead.
1473</t>
1474</section>
1475
1476<section title="404 Not Found" anchor="status.404">
1477  <iref primary="true" item="404 Not Found (status code)"/>
1478  <iref primary="true" item="Status Codes" subitem="404 Not Found"/>
1479<t>
1480   The server has not found anything matching the request-target. No
1481   indication is given of whether the condition is temporary or
1482   permanent. The 410 (Gone) status code SHOULD be used if the server
1483   knows, through some internally configurable mechanism, that an old
1484   resource is permanently unavailable and has no forwarding address.
1485   This status code is commonly used when the server does not wish to
1486   reveal exactly why the request has been refused, or when no other
1487   response is applicable.
1488</t>
1489</section>
1490
1491<section title="405 Method Not Allowed" anchor="status.405">
1492  <iref primary="true" item="405 Method Not Allowed (status code)"/>
1493  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed"/>
1494<t>
1495   The method specified in the Request-Line is not allowed for the
1496   resource identified by the request-target. The response MUST include an
1497   Allow header containing a list of valid methods for the requested
1498   resource.
1499</t>
1500</section>
1501
1502<section title="406 Not Acceptable" anchor="status.406">
1503  <iref primary="true" item="406 Not Acceptable (status code)"/>
1504  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable"/>
1505<t>
1506   The resource identified by the request is only capable of generating
1507   response entities which have content characteristics not acceptable
1508   according to the accept headers sent in the request.
1509</t>
1510<t>
1511   Unless it was a HEAD request, the response SHOULD include an entity
1512   containing a list of available entity characteristics and location(s)
1513   from which the user or user agent can choose the one most
1514   appropriate. The entity format is specified by the media type given
1515   in the Content-Type header field. Depending upon the format and the
1516   capabilities of the user agent, selection of the most appropriate
1517   choice MAY be performed automatically. However, this specification
1518   does not define any standard for such automatic selection.
1519</t>
1520<t><list>
1521  <t>
1522    Note: HTTP/1.1 servers are allowed to return responses which are
1523    not acceptable according to the accept headers sent in the
1524    request. In some cases, this may even be preferable to sending a
1525    406 response. User agents are encouraged to inspect the headers of
1526    an incoming response to determine if it is acceptable.
1527  </t>
1528</list></t>
1529<t>
1530   If the response could be unacceptable, a user agent SHOULD
1531   temporarily stop receipt of more data and query the user for a
1532   decision on further actions.
1533</t>
1534</section>
1535
1536<section title="407 Proxy Authentication Required" anchor="status.407">
1537  <iref primary="true" item="407 Proxy Authentication Required (status code)"/>
1538  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required"/>
1539<t>
1540   This code is similar to 401 (Unauthorized), but indicates that the
1541   client must first authenticate itself with the proxy (see Section 2.2 of <xref target="Part7"/>).
1542</t>
1543</section>
1544
1545<section title="408 Request Timeout" anchor="status.408">
1546  <iref primary="true" item="408 Request Timeout (status code)"/>
1547  <iref primary="true" item="Status Codes" subitem="408 Request Timeout"/>
1548<t>
1549   The client did not produce a request within the time that the server
1550   was prepared to wait. The client MAY repeat the request without
1551   modifications at any later time.
1552</t>
1553</section>
1554
1555<section title="409 Conflict" anchor="status.409">
1556  <iref primary="true" item="409 Conflict (status code)"/>
1557  <iref primary="true" item="Status Codes" subitem="409 Conflict"/>
1558<t>
1559   The request could not be completed due to a conflict with the current
1560   state of the resource. This code is only allowed in situations where
1561   it is expected that the user might be able to resolve the conflict
1562   and resubmit the request. The response body SHOULD include enough
1563   information for the user to recognize the source of the conflict.
1564   Ideally, the response entity would include enough information for the
1565   user or user agent to fix the problem; however, that might not be
1566   possible and is not required.
1567</t>
1568<t>
1569   Conflicts are most likely to occur in response to a PUT request. For
1570   example, if versioning were being used and the entity being PUT
1571   included changes to a resource which conflict with those made by an
1572   earlier (third-party) request, the server might use the 409 response
1573   to indicate that it can't complete the request. In this case, the
1574   response entity would likely contain a list of the differences
1575   between the two versions in a format defined by the response
1576   Content-Type.
1577</t>
1578</section>
1579
1580<section title="410 Gone" anchor="status.410">
1581  <iref primary="true" item="410 Gone (status code)"/>
1582  <iref primary="true" item="Status Codes" subitem="410 Gone"/>
1583<t>
1584   The requested resource is no longer available at the server and no
1585   forwarding address is known. This condition is expected to be
1586   considered permanent. Clients with link editing capabilities SHOULD
1587   delete references to the request-target after user approval. If the
1588   server does not know, or has no facility to determine, whether or not
1589   the condition is permanent, the status code 404 (Not Found) SHOULD be
1590   used instead. This response is cacheable unless indicated otherwise.
1591</t>
1592<t>
1593   The 410 response is primarily intended to assist the task of web
1594   maintenance by notifying the recipient that the resource is
1595   intentionally unavailable and that the server owners desire that
1596   remote links to that resource be removed. Such an event is common for
1597   limited-time, promotional services and for resources belonging to
1598   individuals no longer working at the server's site. It is not
1599   necessary to mark all permanently unavailable resources as "gone" or
1600   to keep the mark for any length of time -- that is left to the
1601   discretion of the server owner.
1602</t>
1603</section>
1604
1605<section title="411 Length Required" anchor="status.411">
1606  <iref primary="true" item="411 Length Required (status code)"/>
1607  <iref primary="true" item="Status Codes" subitem="411 Length Required"/>
1608<t>
1609   The server refuses to accept the request without a defined Content-Length.
1610   The client MAY repeat the request if it adds a valid
1611   Content-Length header field containing the length of the message-body
1612   in the request message.
1613</t>
1614</section>
1615
1616<section title="412 Precondition Failed" anchor="status.412">
1617  <iref primary="true" item="412 Precondition Failed (status code)"/>
1618  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed"/>
1619 
1620<t>
1621   The precondition given in one or more of the request-header fields
1622   evaluated to false when it was tested on the server, as defined in
1623   Section 3.2 of <xref target="Part4"/>.
1624</t>
1625</section>
1626
1627<section title="413 Request Entity Too Large" anchor="status.413">
1628  <iref primary="true" item="413 Request Entity Too Large (status code)"/>
1629  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large"/>
1630<t>
1631   The server is refusing to process a request because the request
1632   entity is larger than the server is willing or able to process. The
1633   server MAY close the connection to prevent the client from continuing
1634   the request.
1635</t>
1636<t>
1637   If the condition is temporary, the server SHOULD include a Retry-After
1638   header field to indicate that it is temporary and after what
1639   time the client MAY try again.
1640</t>
1641</section>
1642
1643<section title="414 URI Too Long" anchor="status.414">
1644  <iref primary="true" item="414 URI Too Long (status code)"/>
1645  <iref primary="true" item="Status Codes" subitem="414 URI Too Long"/>
1646<t>
1647   The server is refusing to service the request because the request-target
1648   is longer than the server is willing to interpret. This rare
1649   condition is only likely to occur when a client has improperly
1650   converted a POST request to a GET request with long query
1651   information, when the client has descended into a URI "black hole" of
1652   redirection (e.g., a redirected URI prefix that points to a suffix of
1653   itself), or when the server is under attack by a client attempting to
1654   exploit security holes present in some servers using fixed-length
1655   buffers for reading or manipulating the request-target.
1656</t>
1657</section>
1658
1659<section title="415 Unsupported Media Type" anchor="status.415">
1660  <iref primary="true" item="415 Unsupported Media Type (status code)"/>
1661  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type"/>
1662<t>
1663   The server is refusing to service the request because the entity of
1664   the request is in a format not supported by the requested resource
1665   for the requested method.
1666</t>
1667</section>
1668
1669<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1670  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)"/>
1671  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable"/>
1672 
1673<t>
1674   The request included a Range request-header field (Section 5.4 of <xref target="Part5"/>) and none of
1675   the range-specifier values in this field overlap the current extent
1676   of the selected resource. See Section 3.2 of <xref target="Part5"/>
1677</t>
1678</section>
1679
1680<section title="417 Expectation Failed" anchor="status.417">
1681  <iref primary="true" item="417 Expectation Failed (status code)"/>
1682  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed"/>
1683<t>
1684   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1685   could not be met by this server, or, if the server is a proxy,
1686   the server has unambiguous evidence that the request could not be met
1687   by the next-hop server.
1688</t>
1689</section>
1690</section>
1691
1692<section title="Server Error 5xx" anchor="status.5xx">
1693<t>
1694   Response status codes beginning with the digit "5" indicate cases in
1695   which the server is aware that it has erred or is incapable of
1696   performing the request. Except when responding to a HEAD request, the
1697   server SHOULD include an entity containing an explanation of the
1698   error situation, and whether it is a temporary or permanent
1699   condition. User agents SHOULD display any included entity to the
1700   user. These response codes are applicable to any request method.
1701</t>
1702
1703<section title="500 Internal Server Error" anchor="status.500">
1704  <iref primary="true" item="500 Internal Server Error (status code)"/>
1705  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error"/>
1706<t>
1707   The server encountered an unexpected condition which prevented it
1708   from fulfilling the request.
1709</t>
1710</section>
1711
1712<section title="501 Not Implemented" anchor="status.501">
1713  <iref primary="true" item="501 Not Implemented (status code)"/>
1714  <iref primary="true" item="Status Codes" subitem="501 Not Implemented"/>
1715<t>
1716   The server does not support the functionality required to fulfill the
1717   request. This is the appropriate response when the server does not
1718   recognize the request method and is not capable of supporting it for
1719   any resource.
1720</t>
1721</section>
1722
1723<section title="502 Bad Gateway" anchor="status.502">
1724  <iref primary="true" item="502 Bad Gateway (status code)"/>
1725  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway"/>
1726<t>
1727   The server, while acting as a gateway or proxy, received an invalid
1728   response from the upstream server it accessed in attempting to
1729   fulfill the request.
1730</t>
1731</section>
1732
1733<section title="503 Service Unavailable" anchor="status.503">
1734  <iref primary="true" item="503 Service Unavailable (status code)"/>
1735  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable"/>
1736<t>
1737   The server is currently unable to handle the request due to a
1738   temporary overloading or maintenance of the server. The implication
1739   is that this is a temporary condition which will be alleviated after
1740   some delay. If known, the length of the delay MAY be indicated in a
1741   Retry-After header. If no Retry-After is given, the client SHOULD
1742   handle the response as it would for a 500 response.
1743</t>
1744<t><list>
1745  <t>
1746    Note: The existence of the 503 status code does not imply that a
1747    server must use it when becoming overloaded. Some servers may wish
1748    to simply refuse the connection.
1749  </t>
1750</list></t>
1751</section>
1752
1753<section title="504 Gateway Timeout" anchor="status.504">
1754  <iref primary="true" item="504 Gateway Timeout (status code)"/>
1755  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout"/>
1756<t>
1757   The server, while acting as a gateway or proxy, did not receive a
1758   timely response from the upstream server specified by the URI (e.g.
1759   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1760   to access in attempting to complete the request.
1761</t>
1762<t><list>
1763  <t>
1764    Note: Note to implementors: some deployed proxies are known to
1765    return 400 or 500 when DNS lookups time out.
1766  </t>
1767</list></t>
1768</section>
1769
1770<section title="505 HTTP Version Not Supported" anchor="status.505">
1771  <iref primary="true" item="505 HTTP Version Not Supported (status code)"/>
1772  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported"/>
1773<t>
1774   The server does not support, or refuses to support, the protocol
1775   version that was used in the request message. The server is
1776   indicating that it is unable or unwilling to complete the request
1777   using the same major version as the client, as described in Section 2.5 of <xref target="Part1"/>,
1778   other than with this error message. The response SHOULD contain
1779   an entity describing why that version is not supported and what other
1780   protocols are supported by that server.
1781</t>
1782
1783</section>
1784</section>
1785</section>
1786
1787
1788<section title="Header Field Definitions" anchor="header.fields">
1789<t>
1790   This section defines the syntax and semantics of HTTP/1.1 header fields
1791   related to request and response semantics.
1792</t>
1793<t>
1794   For entity-header fields, both sender and recipient refer to either the
1795   client or the server, depending on who sends and who receives the entity.
1796</t>
1797
1798<section title="Allow" anchor="header.allow">
1799  <iref primary="true" item="Allow header"/>
1800  <iref primary="true" item="Headers" subitem="Allow"/>
1801 
1802 
1803<t>
1804   The "Allow" response-header field lists the set of methods advertised as
1805   supported by the resource identified by the request-target. The purpose of
1806   this field is strictly to inform the recipient of valid methods
1807   associated with the resource.
1808</t>
1809<figure><iref primary="true" item="Grammar" subitem="Allow"/><iref primary="true" item="Grammar" subitem="Allow-v"/><artwork type="abnf2616"><![CDATA[
1810  Allow   = "Allow" ":" OWS Allow-v
1811  Allow-v = #Method
1812]]></artwork></figure>
1813<t>
1814      Example of use:
1815</t>
1816<figure><artwork type="example"><![CDATA[
1817  Allow: GET, HEAD, PUT
1818]]></artwork></figure>
1819<t>
1820      The actual set of allowed methods is defined
1821      by the origin server at the time of each request.
1822</t>
1823<t>
1824      A proxy MUST NOT modify the Allow header field even if it does not
1825      understand all the methods specified, since the user agent might
1826      have other means of communicating with the origin server.
1827</t>
1828</section>
1829
1830<section title="Expect" anchor="header.expect">
1831  <iref primary="true" item="Expect header"/>
1832  <iref primary="true" item="Headers" subitem="Expect"/>
1833 
1834 
1835 
1836 
1837 
1838<t>
1839   The "Expect" request-header field is used to indicate that particular
1840   server behaviors are required by the client.
1841</t>
1842<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[
1843  Expect       = "Expect" ":" OWS Expect-v
1844  Expect-v     = 1#expectation
1845 
1846  expectation  = "100-continue" / expectation-extension
1847  expectation-extension = token [ "=" ( token / quoted-string )
1848                           *expect-params ]
1849  expect-params = ";" token [ "=" ( token / quoted-string ) ]
1850]]></artwork></figure>
1851<t>
1852   A server that does not understand or is unable to comply with any of
1853   the expectation values in the Expect field of a request MUST respond
1854   with appropriate error status. The server MUST respond with a 417
1855   (Expectation Failed) status if any of the expectations cannot be met
1856   or, if there are other problems with the request, some other 4xx
1857   status.
1858</t>
1859<t>
1860   This header field is defined with extensible syntax to allow for
1861   future extensions. If a server receives a request containing an
1862   Expect field that includes an expectation-extension that it does not
1863   support, it MUST respond with a 417 (Expectation Failed) status.
1864</t>
1865<t>
1866   Comparison of expectation values is case-insensitive for unquoted
1867   tokens (including the 100-continue token), and is case-sensitive for
1868   quoted-string expectation-extensions.
1869</t>
1870<t>
1871   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy MUST
1872   return a 417 (Expectation Failed) status if it receives a request
1873   with an expectation that it cannot meet. However, the Expect
1874   request-header itself is end-to-end; it MUST be forwarded if the
1875   request is forwarded.
1876</t>
1877<t>
1878   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1879   Expect header.
1880</t>
1881<t>
1882   See Section 7.2.3 of <xref target="Part1"/> for the use of the 100 (Continue) status.
1883</t>
1884</section>
1885
1886<section title="From" anchor="header.from">
1887  <iref primary="true" item="From header"/>
1888  <iref primary="true" item="Headers" subitem="From"/>
1889 
1890 
1891 
1892<t>
1893   The "From" request-header field, if given, SHOULD contain an Internet
1894   e-mail address for the human user who controls the requesting user
1895   agent. The address SHOULD be machine-usable, as defined by "mailbox"
1896   in Section 3.4 of <xref target="RFC5322"/>:
1897</t>
1898<figure><iref primary="true" item="Grammar" subitem="From"/><iref primary="true" item="Grammar" subitem="From-v"/><artwork type="abnf2616"><![CDATA[
1899  From    = "From" ":" OWS From-v
1900  From-v  = mailbox
1901 
1902  mailbox = <mailbox, defined in [RFC5322], Section 3.4>
1903]]></artwork></figure>
1904<t>
1905   An example is:
1906</t>
1907<figure><artwork type="example"><![CDATA[
1908  From: webmaster@example.org
1909]]></artwork></figure>
1910<t>
1911   This header field MAY be used for logging purposes and as a means for
1912   identifying the source of invalid or unwanted requests. It SHOULD NOT
1913   be used as an insecure form of access protection. The interpretation
1914   of this field is that the request is being performed on behalf of the
1915   person given, who accepts responsibility for the method performed. In
1916   particular, robot agents SHOULD include this header so that the
1917   person responsible for running the robot can be contacted if problems
1918   occur on the receiving end.
1919</t>
1920<t>
1921   The Internet e-mail address in this field MAY be separate from the
1922   Internet host which issued the request. For example, when a request
1923   is passed through a proxy the original issuer's address SHOULD be
1924   used.
1925</t>
1926<t>
1927   The client SHOULD NOT  send the From header field without the user's
1928   approval, as it might conflict with the user's privacy interests or
1929   their site's security policy. It is strongly recommended that the
1930   user be able to disable, enable, and modify the value of this field
1931   at any time prior to a request.
1932</t>
1933</section>
1934
1935<section title="Location" anchor="header.location">
1936  <iref primary="true" item="Location header"/>
1937  <iref primary="true" item="Headers" subitem="Location"/>
1938 
1939 
1940<t>
1941   The "Location" response-header field is used to identify a newly created
1942   resource, or to redirect the recipient to a different location for
1943   completion of the request.
1944</t>
1945<t>
1946   For 201 (Created) responses, the Location is the URI of the new resource
1947   which was created by the request. For 3xx responses, the location SHOULD
1948   indicate the server's preferred URI for automatic redirection to the
1949   resource.
1950</t>
1951<t>
1952   The field value consists of a single URI.
1953</t>
1954<figure><iref primary="true" item="Grammar" subitem="Location"/><iref primary="true" item="Grammar" subitem="Location-v"/><artwork type="abnf2616"><![CDATA[
1955  Location       = "Location" ":" OWS Location-v
1956  Location-v     = URI
1957]]></artwork></figure>
1958<t>
1959   An example is:
1960</t>
1961<figure><artwork type="example"><![CDATA[
1962  Location: http://www.example.org/pub/WWW/People.html
1963]]></artwork></figure>
1964<t>
1965   There are circumstances in which a fragment identifier in a Location URI would not be appropriate:
1966   <list style="symbols">
1967      <t>With a 201 Created response, because in this usage the Location header specifies the URI for the entire created resource.</t>
1968      <t>With 305 Use Proxy.</t>
1969   </list>
1970</t>
1971<t><list>
1972  <t>
1973    Note: The Content-Location header field (Section 5.7 of <xref target="Part3"/>) differs
1974    from Location in that the Content-Location identifies the original
1975    location of the entity enclosed in the response. It is therefore
1976    possible for a response to contain header fields for both Location
1977    and Content-Location.
1978  </t>
1979</list></t>
1980</section>
1981
1982<section title="Max-Forwards" anchor="header.max-forwards">
1983  <iref primary="true" item="Max-Forwards header"/>
1984  <iref primary="true" item="Headers" subitem="Max-Forwards"/>
1985 
1986 
1987<t>
1988   The "Max-Forwards" request-header field provides a mechanism with the
1989   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
1990   methods to limit the number of times that the request is forwarded by
1991   proxies or gateways. This can be useful when the client is attempting to
1992   trace a request which appears to be failing or looping in mid-chain.
1993</t>
1994<figure><iref primary="true" item="Grammar" subitem="Max-Forwards"/><iref primary="true" item="Grammar" subitem="Max-Forwards-v"/><artwork type="abnf2616"><![CDATA[
1995  Max-Forwards   = "Max-Forwards" ":" OWS Max-Forwards-v
1996  Max-Forwards-v = 1*DIGIT
1997]]></artwork></figure>
1998<t>
1999   The Max-Forwards value is a decimal integer indicating the remaining
2000   number of times this request message may be forwarded.
2001</t>
2002<t>
2003   Each proxy or gateway recipient of a TRACE or OPTIONS request
2004   containing a Max-Forwards header field MUST check and update its
2005   value prior to forwarding the request. If the received value is zero
2006   (0), the recipient MUST NOT forward the request; instead, it MUST
2007   respond as the final recipient. If the received Max-Forwards value is
2008   greater than zero, then the forwarded message MUST contain an updated
2009   Max-Forwards field with a value decremented by one (1).
2010</t>
2011<t>
2012   The Max-Forwards header field MAY be ignored for all other methods
2013   defined by this specification and for any extension methods for which
2014   it is not explicitly referred to as part of that method definition.
2015</t>
2016</section>
2017
2018<section title="Referer" anchor="header.referer">
2019  <iref primary="true" item="Referer header"/>
2020  <iref primary="true" item="Headers" subitem="Referer"/>
2021 
2022 
2023<t>
2024   The "Referer" [sic] request-header field allows the client to specify the
2025   URI of the resource from which the request-target was obtained (the
2026   "referrer", although the header field is misspelled.).
2027</t>
2028<t>
2029   The Referer header allows servers to generate lists of back-links to
2030   resources for interest, logging, optimized caching, etc. It also allows
2031   obsolete or mistyped links to be traced for maintenance. Some servers use
2032   Referer as a means of controlling where they allow links from (so-called
2033   "deep linking"), but it should be noted that legitimate requests are not
2034   required to contain a Referer header field.
2035</t>
2036<t>
2037   If the request-target was obtained from a source that does not have its own
2038   URI (e.g., input from the user keyboard), the Referer field MUST either be
2039   sent with the value "about:blank", or not be sent at all. Note that this
2040   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2041</t>
2042<figure><iref primary="true" item="Grammar" subitem="Referer"/><iref primary="true" item="Grammar" subitem="Referer-v"/><artwork type="abnf2616"><![CDATA[
2043  Referer        = "Referer" ":" OWS Referer-v
2044  Referer-v      = absolute-URI / partial-URI
2045]]></artwork></figure>
2046<t>
2047   Example:
2048</t>
2049<figure><artwork type="example"><![CDATA[
2050  Referer: http://www.example.org/hypertext/Overview.html
2051]]></artwork></figure>
2052<t>
2053   If the field value is a relative URI, it SHOULD be interpreted
2054   relative to the request-target. The URI MUST NOT include a fragment. See
2055   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2056</t>
2057</section>
2058
2059<section title="Retry-After" anchor="header.retry-after">
2060  <iref primary="true" item="Retry-After header"/>
2061  <iref primary="true" item="Headers" subitem="Retry-After"/>
2062 
2063 
2064<t>
2065   The response-header "Retry-After" field can be used with a 503 (Service
2066   Unavailable) response to indicate how long the service is expected to
2067   be unavailable to the requesting client. This field MAY also be used
2068   with any 3xx (Redirection) response to indicate the minimum time the
2069   user-agent is asked wait before issuing the redirected request.
2070</t>
2071<t>
2072   The value of this field can be either an HTTP-date or an integer number
2073   of seconds (in decimal) after the time of the response.
2074</t>
2075<figure><iref primary="true" item="Grammar" subitem="Retry-After"/><iref primary="true" item="Grammar" subitem="Retry-After-v"/><artwork type="abnf2616"><![CDATA[
2076  Retry-After   = "Retry-After" ":" OWS Retry-After-v
2077  Retry-After-v = HTTP-date / delta-seconds
2078]]></artwork></figure>
2079<t anchor="rule.delta-seconds">
2080 
2081   Time spans are non-negative decimal integers, representing time in
2082   seconds.
2083</t>
2084<figure><iref primary="true" item="Grammar" subitem="delta-seconds"/><artwork type="abnf2616"><![CDATA[
2085  delta-seconds  = 1*DIGIT
2086]]></artwork></figure>
2087<t>
2088   Two examples of its use are
2089</t>
2090<figure><artwork type="example"><![CDATA[
2091  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2092  Retry-After: 120
2093]]></artwork></figure>
2094<t>
2095   In the latter example, the delay is 2 minutes.
2096</t>
2097</section>
2098
2099<section title="Server" anchor="header.server">
2100  <iref primary="true" item="Server header"/>
2101  <iref primary="true" item="Headers" subitem="Server"/>
2102 
2103 
2104<t>
2105   The "Server" response-header field contains information about the
2106   software used by the origin server to handle the request.
2107</t>
2108<t>
2109   The field can contain multiple product tokens (Section 6.3 of <xref target="Part1"/>) and
2110   comments (Section 3.2 of <xref target="Part1"/>) identifying the server and any significant
2111   subproducts. The product tokens are listed in order of their significance
2112   for identifying the application.
2113</t>
2114<figure><iref primary="true" item="Grammar" subitem="Server"/><iref primary="true" item="Grammar" subitem="Server-v"/><artwork type="abnf2616"><![CDATA[
2115  Server         = "Server" ":" OWS Server-v
2116  Server-v       = product
2117                   *( RWS ( product / comment ) )
2118]]></artwork></figure>
2119<t>
2120   Example:
2121</t>
2122<figure><artwork type="example"><![CDATA[
2123  Server: CERN/3.0 libwww/2.17
2124]]></artwork></figure>
2125<t>
2126   If the response is being forwarded through a proxy, the proxy
2127   application MUST NOT modify the Server response-header. Instead, it
2128   MUST include a Via field (as described in Section 9.9 of <xref target="Part1"/>).
2129</t>
2130<t><list>
2131  <t>
2132    Note: Revealing the specific software version of the server might
2133    allow the server machine to become more vulnerable to attacks
2134    against software that is known to contain security holes. Server
2135    implementors are encouraged to make this field a configurable
2136    option.
2137  </t>
2138</list></t>
2139</section>
2140
2141<section title="User-Agent" anchor="header.user-agent">
2142  <iref primary="true" item="User-Agent header"/>
2143  <iref primary="true" item="Headers" subitem="User-Agent"/>
2144 
2145 
2146<t>
2147   The "User-Agent" request-header field contains information about the
2148   user agent originating the request. This is for statistical purposes,
2149   the tracing of protocol violations, and automated recognition of user
2150   agents for the sake of tailoring responses to avoid particular user
2151   agent limitations.
2152</t>
2153<t>
2154   User agents SHOULD include this field with requests. The field can contain
2155   multiple product tokens (Section 6.3 of <xref target="Part1"/>) and comments (Section 3.2 of <xref target="Part1"/>)
2156   identifying the agent and any subproducts which form a significant part of
2157   the user agent. By convention, the product tokens are listed in order of
2158   their significance for identifying the application.
2159</t>
2160<figure><iref primary="true" item="Grammar" subitem="User-Agent"/><iref primary="true" item="Grammar" subitem="User-Agent-v"/><artwork type="abnf2616"><![CDATA[
2161  User-Agent     = "User-Agent" ":" OWS User-Agent-v
2162  User-Agent-v   = product
2163                   *( RWS ( product / comment ) )
2164]]></artwork></figure>
2165<t>
2166   Example:
2167</t>
2168<figure><artwork type="example"><![CDATA[
2169  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2170]]></artwork></figure>
2171</section>
2172
2173</section>
2174
2175<section title="IANA Considerations" anchor="IANA.considerations">
2176
2177<section title="Method Registry" anchor="method.registration">
2178<t>
2179  The registration procedure for HTTP Methods is defined by
2180  <xref target="method.registry"/> of this document.
2181</t>
2182<t>
2183   The HTTP Method Registry located at <eref target="http://www.iana.org/assignments/http-methods"/>
2184   should be populated with the registrations below:
2185</t>
2186
2187<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2188<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2189   <ttcol>Method</ttcol>
2190   <ttcol>Safe</ttcol>
2191   <ttcol>Reference</ttcol>
2192   <c>CONNECT</c>
2193   <c>no</c>
2194   <c>
2195      <xref target="CONNECT"/>
2196   </c>
2197   <c>DELETE</c>
2198   <c>no</c>
2199   <c>
2200      <xref target="DELETE"/>
2201   </c>
2202   <c>GET</c>
2203   <c>yes</c>
2204   <c>
2205      <xref target="GET"/>
2206   </c>
2207   <c>HEAD</c>
2208   <c>yes</c>
2209   <c>
2210      <xref target="HEAD"/>
2211   </c>
2212   <c>OPTIONS</c>
2213   <c>yes</c>
2214   <c>
2215      <xref target="OPTIONS"/>
2216   </c>
2217   <c>POST</c>
2218   <c>no</c>
2219   <c>
2220      <xref target="POST"/>
2221   </c>
2222   <c>PUT</c>
2223   <c>no</c>
2224   <c>
2225      <xref target="PUT"/>
2226   </c>
2227   <c>TRACE</c>
2228   <c>yes</c>
2229   <c>
2230      <xref target="TRACE"/>
2231   </c>
2232</texttable>
2233<!--(END)-->
2234
2235</section>
2236
2237<section title="Status Code Registry" anchor="status.code.registration">
2238<t>
2239   The registration procedure for HTTP Status Codes -- previously defined
2240   in Section 7.1 of <xref target="RFC2817"/> -- is now defined
2241   by <xref target="status.code.registry"/> of this document.
2242</t>
2243<t>
2244   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2245   should be updated with the registrations below:
2246</t>
2247
2248<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2249<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2250   <ttcol>Value</ttcol>
2251   <ttcol>Description</ttcol>
2252   <ttcol>Reference</ttcol>
2253   <c>100</c>
2254   <c>Continue</c>
2255   <c>
2256      <xref target="status.100"/>
2257   </c>
2258   <c>101</c>
2259   <c>Switching Protocols</c>
2260   <c>
2261      <xref target="status.101"/>
2262   </c>
2263   <c>200</c>
2264   <c>OK</c>
2265   <c>
2266      <xref target="status.200"/>
2267   </c>
2268   <c>201</c>
2269   <c>Created</c>
2270   <c>
2271      <xref target="status.201"/>
2272   </c>
2273   <c>202</c>
2274   <c>Accepted</c>
2275   <c>
2276      <xref target="status.202"/>
2277   </c>
2278   <c>203</c>
2279   <c>Non-Authoritative Information</c>
2280   <c>
2281      <xref target="status.203"/>
2282   </c>
2283   <c>204</c>
2284   <c>No Content</c>
2285   <c>
2286      <xref target="status.204"/>
2287   </c>
2288   <c>205</c>
2289   <c>Reset Content</c>
2290   <c>
2291      <xref target="status.205"/>
2292   </c>
2293   <c>300</c>
2294   <c>Multiple Choices</c>
2295   <c>
2296      <xref target="status.300"/>
2297   </c>
2298   <c>301</c>
2299   <c>Moved Permanently</c>
2300   <c>
2301      <xref target="status.301"/>
2302   </c>
2303   <c>302</c>
2304   <c>Found</c>
2305   <c>
2306      <xref target="status.302"/>
2307   </c>
2308   <c>303</c>
2309   <c>See Other</c>
2310   <c>
2311      <xref target="status.303"/>
2312   </c>
2313   <c>305</c>
2314   <c>Use Proxy</c>
2315   <c>
2316      <xref target="status.305"/>
2317   </c>
2318   <c>306</c>
2319   <c>(Unused)</c>
2320   <c>
2321      <xref target="status.306"/>
2322   </c>
2323   <c>307</c>
2324   <c>Temporary Redirect</c>
2325   <c>
2326      <xref target="status.307"/>
2327   </c>
2328   <c>400</c>
2329   <c>Bad Request</c>
2330   <c>
2331      <xref target="status.400"/>
2332   </c>
2333   <c>402</c>
2334   <c>Payment Required</c>
2335   <c>
2336      <xref target="status.402"/>
2337   </c>
2338   <c>403</c>
2339   <c>Forbidden</c>
2340   <c>
2341      <xref target="status.403"/>
2342   </c>
2343   <c>404</c>
2344   <c>Not Found</c>
2345   <c>
2346      <xref target="status.404"/>
2347   </c>
2348   <c>405</c>
2349   <c>Method Not Allowed</c>
2350   <c>
2351      <xref target="status.405"/>
2352   </c>
2353   <c>406</c>
2354   <c>Not Acceptable</c>
2355   <c>
2356      <xref target="status.406"/>
2357   </c>
2358   <c>407</c>
2359   <c>Proxy Authentication Required</c>
2360   <c>
2361      <xref target="status.407"/>
2362   </c>
2363   <c>408</c>
2364   <c>Request Timeout</c>
2365   <c>
2366      <xref target="status.408"/>
2367   </c>
2368   <c>409</c>
2369   <c>Conflict</c>
2370   <c>
2371      <xref target="status.409"/>
2372   </c>
2373   <c>410</c>
2374   <c>Gone</c>
2375   <c>
2376      <xref target="status.410"/>
2377   </c>
2378   <c>411</c>
2379   <c>Length Required</c>
2380   <c>
2381      <xref target="status.411"/>
2382   </c>
2383   <c>413</c>
2384   <c>Request Entity Too Large</c>
2385   <c>
2386      <xref target="status.413"/>
2387   </c>
2388   <c>414</c>
2389   <c>URI Too Long</c>
2390   <c>
2391      <xref target="status.414"/>
2392   </c>
2393   <c>415</c>
2394   <c>Unsupported Media Type</c>
2395   <c>
2396      <xref target="status.415"/>
2397   </c>
2398   <c>417</c>
2399   <c>Expectation Failed</c>
2400   <c>
2401      <xref target="status.417"/>
2402   </c>
2403   <c>500</c>
2404   <c>Internal Server Error</c>
2405   <c>
2406      <xref target="status.500"/>
2407   </c>
2408   <c>501</c>
2409   <c>Not Implemented</c>
2410   <c>
2411      <xref target="status.501"/>
2412   </c>
2413   <c>502</c>
2414   <c>Bad Gateway</c>
2415   <c>
2416      <xref target="status.502"/>
2417   </c>
2418   <c>503</c>
2419   <c>Service Unavailable</c>
2420   <c>
2421      <xref target="status.503"/>
2422   </c>
2423   <c>504</c>
2424   <c>Gateway Timeout</c>
2425   <c>
2426      <xref target="status.504"/>
2427   </c>
2428   <c>505</c>
2429   <c>HTTP Version Not Supported</c>
2430   <c>
2431      <xref target="status.505"/>
2432   </c>
2433</texttable>
2434<!--(END)-->
2435
2436</section>
2437<section title="Message Header Registration" anchor="message.header.registration">
2438<t>
2439   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2440   with the permanent registrations below (see <xref target="RFC3864"/>):
2441</t>
2442
2443<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2444<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2445   <ttcol>Header Field Name</ttcol>
2446   <ttcol>Protocol</ttcol>
2447   <ttcol>Status</ttcol>
2448   <ttcol>Reference</ttcol>
2449
2450   <c>Allow</c>
2451   <c>http</c>
2452   <c>standard</c>
2453   <c>
2454      <xref target="header.allow"/>
2455   </c>
2456   <c>Expect</c>
2457   <c>http</c>
2458   <c>standard</c>
2459   <c>
2460      <xref target="header.expect"/>
2461   </c>
2462   <c>From</c>
2463   <c>http</c>
2464   <c>standard</c>
2465   <c>
2466      <xref target="header.from"/>
2467   </c>
2468   <c>Location</c>
2469   <c>http</c>
2470   <c>standard</c>
2471   <c>
2472      <xref target="header.location"/>
2473   </c>
2474   <c>Max-Forwards</c>
2475   <c>http</c>
2476   <c>standard</c>
2477   <c>
2478      <xref target="header.max-forwards"/>
2479   </c>
2480   <c>Referer</c>
2481   <c>http</c>
2482   <c>standard</c>
2483   <c>
2484      <xref target="header.referer"/>
2485   </c>
2486   <c>Retry-After</c>
2487   <c>http</c>
2488   <c>standard</c>
2489   <c>
2490      <xref target="header.retry-after"/>
2491   </c>
2492   <c>Server</c>
2493   <c>http</c>
2494   <c>standard</c>
2495   <c>
2496      <xref target="header.server"/>
2497   </c>
2498   <c>User-Agent</c>
2499   <c>http</c>
2500   <c>standard</c>
2501   <c>
2502      <xref target="header.user-agent"/>
2503   </c>
2504</texttable>
2505<!--(END)-->
2506
2507<t>
2508   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2509</t>
2510</section>
2511</section>
2512
2513<section title="Security Considerations" anchor="security.considerations">
2514<t>
2515   This section is meant to inform application developers, information
2516   providers, and users of the security limitations in HTTP/1.1 as
2517   described by this document. The discussion does not include
2518   definitive solutions to the problems revealed, though it does make
2519   some suggestions for reducing security risks.
2520</t>
2521
2522<section title="Transfer of Sensitive Information" anchor="security.sensitive">
2523<t>
2524   Like any generic data transfer protocol, HTTP cannot regulate the
2525   content of the data that is transferred, nor is there any a priori
2526   method of determining the sensitivity of any particular piece of
2527   information within the context of any given request. Therefore,
2528   applications SHOULD supply as much control over this information as
2529   possible to the provider of that information. Four header fields are
2530   worth special mention in this context: Server, Via, Referer and From.
2531</t>
2532<t>
2533   Revealing the specific software version of the server might allow the
2534   server machine to become more vulnerable to attacks against software
2535   that is known to contain security holes. Implementors SHOULD make the
2536   Server header field a configurable option.
2537</t>
2538<t>
2539   Proxies which serve as a portal through a network firewall SHOULD
2540   take special precautions regarding the transfer of header information
2541   that identifies the hosts behind the firewall. In particular, they
2542   SHOULD remove, or replace with sanitized versions, any Via fields
2543   generated behind the firewall.
2544</t>
2545<t>
2546   The Referer header allows reading patterns to be studied and reverse
2547   links drawn. Although it can be very useful, its power can be abused
2548   if user details are not separated from the information contained in
2549   the Referer. Even when the personal information has been removed, the
2550   Referer header might indicate a private document's URI whose
2551   publication would be inappropriate.
2552</t>
2553<t>
2554   The information sent in the From field might conflict with the user's
2555   privacy interests or their site's security policy, and hence it
2556   SHOULD NOT  be transmitted without the user being able to disable,
2557   enable, and modify the contents of the field. The user MUST be able
2558   to set the contents of this field within a user preference or
2559   application defaults configuration.
2560</t>
2561<t>
2562   We suggest, though do not require, that a convenient toggle interface
2563   be provided for the user to enable or disable the sending of From and
2564   Referer information.
2565</t>
2566<t>
2567   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2568   fields can sometimes be used to determine that a specific client or
2569   server have a particular security hole which might be exploited.
2570   Unfortunately, this same information is often used for other valuable
2571   purposes for which HTTP currently has no better mechanism.
2572</t>
2573<t>
2574   Some methods, like TRACE (<xref target="TRACE"/>) may expose
2575   information sent in request headers in the response entity.
2576   Clients SHOULD be careful with sensitive information, like Cookies,
2577   Authorization credentials and other headers that might be used to
2578   collect data from the client.
2579</t>
2580</section>
2581
2582<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
2583<t>
2584   Because the source of a link might be private information or might
2585   reveal an otherwise private information source, it is strongly
2586   recommended that the user be able to select whether or not the
2587   Referer field is sent. For example, a browser client could have a
2588   toggle switch for browsing openly/anonymously, which would
2589   respectively enable/disable the sending of Referer and From
2590   information.
2591</t>
2592<t>
2593   Clients SHOULD NOT include a Referer header field in a (non-secure)
2594   HTTP request if the referring page was transferred with a secure
2595   protocol.
2596</t>
2597<t>
2598   Authors of services should not use
2599   GET-based forms for the submission of sensitive data because that
2600   data will be encoded in the Request-target. Many existing
2601   servers, proxies, and user agents log or display the Request-target in
2602   places where it might be visible to third parties. Such services can
2603   use POST-based form submission instead.
2604</t>
2605</section>
2606
2607<section title="Location Headers and Spoofing" anchor="location.spoofing">
2608<t>
2609   If a single server supports multiple organizations that do not trust
2610   one another, then it MUST check the values of Location and Content-Location
2611   headers in responses that are generated under control of
2612   said organizations to make sure that they do not attempt to
2613   invalidate resources over which they have no authority.
2614</t>
2615</section>
2616
2617</section>
2618
2619<section title="Acknowledgments" anchor="ack">
2620</section>
2621</middle>
2622<back>
2623
2624<references title="Normative References">
2625
2626<reference anchor="Part1">
2627  <front>
2628    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2629    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2630      <organization abbrev="Day Software">Day Software</organization>
2631      <address><email>fielding@gbiv.com</email></address>
2632    </author>
2633    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2634      <organization>One Laptop per Child</organization>
2635      <address><email>jg@laptop.org</email></address>
2636    </author>
2637    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2638      <organization abbrev="HP">Hewlett-Packard Company</organization>
2639      <address><email>JeffMogul@acm.org</email></address>
2640    </author>
2641    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2642      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2643      <address><email>henrikn@microsoft.com</email></address>
2644    </author>
2645    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2646      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2647      <address><email>LMM@acm.org</email></address>
2648    </author>
2649    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2650      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2651      <address><email>paulle@microsoft.com</email></address>
2652    </author>
2653    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2654      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2655      <address><email>timbl@w3.org</email></address>
2656    </author>
2657    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2658      <organization abbrev="W3C">World Wide Web Consortium</organization>
2659      <address><email>ylafon@w3.org</email></address>
2660    </author>
2661    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2662      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2663      <address><email>julian.reschke@greenbytes.de</email></address>
2664    </author>
2665    <date month="October" year="2009"/>
2666  </front>
2667  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-08"/>
2668 
2669</reference>
2670
2671<reference anchor="Part3">
2672  <front>
2673    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2674    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2675      <organization abbrev="Day Software">Day Software</organization>
2676      <address><email>fielding@gbiv.com</email></address>
2677    </author>
2678    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2679      <organization>One Laptop per Child</organization>
2680      <address><email>jg@laptop.org</email></address>
2681    </author>
2682    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2683      <organization abbrev="HP">Hewlett-Packard Company</organization>
2684      <address><email>JeffMogul@acm.org</email></address>
2685    </author>
2686    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2687      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2688      <address><email>henrikn@microsoft.com</email></address>
2689    </author>
2690    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2691      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2692      <address><email>LMM@acm.org</email></address>
2693    </author>
2694    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2695      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2696      <address><email>paulle@microsoft.com</email></address>
2697    </author>
2698    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2699      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2700      <address><email>timbl@w3.org</email></address>
2701    </author>
2702    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2703      <organization abbrev="W3C">World Wide Web Consortium</organization>
2704      <address><email>ylafon@w3.org</email></address>
2705    </author>
2706    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2707      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2708      <address><email>julian.reschke@greenbytes.de</email></address>
2709    </author>
2710    <date month="October" year="2009"/>
2711  </front>
2712  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-08"/>
2713 
2714</reference>
2715
2716<reference anchor="Part4">
2717  <front>
2718    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2719    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2720      <organization abbrev="Day Software">Day Software</organization>
2721      <address><email>fielding@gbiv.com</email></address>
2722    </author>
2723    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2724      <organization>One Laptop per Child</organization>
2725      <address><email>jg@laptop.org</email></address>
2726    </author>
2727    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2728      <organization abbrev="HP">Hewlett-Packard Company</organization>
2729      <address><email>JeffMogul@acm.org</email></address>
2730    </author>
2731    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2732      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2733      <address><email>henrikn@microsoft.com</email></address>
2734    </author>
2735    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2736      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2737      <address><email>LMM@acm.org</email></address>
2738    </author>
2739    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2740      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2741      <address><email>paulle@microsoft.com</email></address>
2742    </author>
2743    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2744      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2745      <address><email>timbl@w3.org</email></address>
2746    </author>
2747    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2748      <organization abbrev="W3C">World Wide Web Consortium</organization>
2749      <address><email>ylafon@w3.org</email></address>
2750    </author>
2751    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2752      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2753      <address><email>julian.reschke@greenbytes.de</email></address>
2754    </author>
2755    <date month="October" year="2009"/>
2756  </front>
2757  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-08"/>
2758 
2759</reference>
2760
2761<reference anchor="Part5">
2762  <front>
2763    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2764    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2765      <organization abbrev="Day Software">Day Software</organization>
2766      <address><email>fielding@gbiv.com</email></address>
2767    </author>
2768    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2769      <organization>One Laptop per Child</organization>
2770      <address><email>jg@laptop.org</email></address>
2771    </author>
2772    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2773      <organization abbrev="HP">Hewlett-Packard Company</organization>
2774      <address><email>JeffMogul@acm.org</email></address>
2775    </author>
2776    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2777      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2778      <address><email>henrikn@microsoft.com</email></address>
2779    </author>
2780    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2781      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2782      <address><email>LMM@acm.org</email></address>
2783    </author>
2784    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2785      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2786      <address><email>paulle@microsoft.com</email></address>
2787    </author>
2788    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2789      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2790      <address><email>timbl@w3.org</email></address>
2791    </author>
2792    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2793      <organization abbrev="W3C">World Wide Web Consortium</organization>
2794      <address><email>ylafon@w3.org</email></address>
2795    </author>
2796    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2797      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2798      <address><email>julian.reschke@greenbytes.de</email></address>
2799    </author>
2800    <date month="October" year="2009"/>
2801  </front>
2802  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-08"/>
2803 
2804</reference>
2805
2806<reference anchor="Part6">
2807  <front>
2808    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2809    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2810      <organization abbrev="Day Software">Day Software</organization>
2811      <address><email>fielding@gbiv.com</email></address>
2812    </author>
2813    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2814      <organization>One Laptop per Child</organization>
2815      <address><email>jg@laptop.org</email></address>
2816    </author>
2817    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2818      <organization abbrev="HP">Hewlett-Packard Company</organization>
2819      <address><email>JeffMogul@acm.org</email></address>
2820    </author>
2821    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2822      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2823      <address><email>henrikn@microsoft.com</email></address>
2824    </author>
2825    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2826      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2827      <address><email>LMM@acm.org</email></address>
2828    </author>
2829    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2830      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2831      <address><email>paulle@microsoft.com</email></address>
2832    </author>
2833    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2834      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2835      <address><email>timbl@w3.org</email></address>
2836    </author>
2837    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2838      <organization abbrev="W3C">World Wide Web Consortium</organization>
2839      <address><email>ylafon@w3.org</email></address>
2840    </author>
2841    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
2842      <address><email>mnot@mnot.net</email></address>
2843    </author>
2844    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2845      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2846      <address><email>julian.reschke@greenbytes.de</email></address>
2847    </author>
2848    <date month="October" year="2009"/>
2849  </front>
2850  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-08"/>
2851 
2852</reference>
2853
2854<reference anchor="Part7">
2855  <front>
2856    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2857    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2858      <organization abbrev="Day Software">Day Software</organization>
2859      <address><email>fielding@gbiv.com</email></address>
2860    </author>
2861    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2862      <organization>One Laptop per Child</organization>
2863      <address><email>jg@laptop.org</email></address>
2864    </author>
2865    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2866      <organization abbrev="HP">Hewlett-Packard Company</organization>
2867      <address><email>JeffMogul@acm.org</email></address>
2868    </author>
2869    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2870      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2871      <address><email>henrikn@microsoft.com</email></address>
2872    </author>
2873    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2874      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2875      <address><email>LMM@acm.org</email></address>
2876    </author>
2877    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2878      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2879      <address><email>paulle@microsoft.com</email></address>
2880    </author>
2881    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2882      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2883      <address><email>timbl@w3.org</email></address>
2884    </author>
2885    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2886      <organization abbrev="W3C">World Wide Web Consortium</organization>
2887      <address><email>ylafon@w3.org</email></address>
2888    </author>
2889    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2890      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2891      <address><email>julian.reschke@greenbytes.de</email></address>
2892    </author>
2893    <date month="October" year="2009"/>
2894  </front>
2895  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-08"/>
2896 
2897</reference>
2898
2899<reference anchor="RFC2119">
2900  <front>
2901    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2902    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2903      <organization>Harvard University</organization>
2904      <address><email>sob@harvard.edu</email></address>
2905    </author>
2906    <date month="March" year="1997"/>
2907  </front>
2908  <seriesInfo name="BCP" value="14"/>
2909  <seriesInfo name="RFC" value="2119"/>
2910</reference>
2911
2912<reference anchor="RFC5234">
2913  <front>
2914    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2915    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2916      <organization>Brandenburg InternetWorking</organization>
2917      <address>
2918      <postal>
2919      <street>675 Spruce Dr.</street>
2920      <city>Sunnyvale</city>
2921      <region>CA</region>
2922      <code>94086</code>
2923      <country>US</country></postal>
2924      <phone>+1.408.246.8253</phone>
2925      <email>dcrocker@bbiw.net</email></address> 
2926    </author>
2927    <author initials="P." surname="Overell" fullname="Paul Overell">
2928      <organization>THUS plc.</organization>
2929      <address>
2930      <postal>
2931      <street>1/2 Berkeley Square</street>
2932      <street>99 Berkely Street</street>
2933      <city>Glasgow</city>
2934      <code>G3 7HR</code>
2935      <country>UK</country></postal>
2936      <email>paul.overell@thus.net</email></address>
2937    </author>
2938    <date month="January" year="2008"/>
2939  </front>
2940  <seriesInfo name="STD" value="68"/>
2941  <seriesInfo name="RFC" value="5234"/>
2942</reference>
2943
2944</references>
2945
2946<references title="Informative References">
2947
2948<reference anchor="RFC1945">
2949  <front>
2950    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2951    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2952      <organization>MIT, Laboratory for Computer Science</organization>
2953      <address><email>timbl@w3.org</email></address>
2954    </author>
2955    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2956      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2957      <address><email>fielding@ics.uci.edu</email></address>
2958    </author>
2959    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2960      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2961      <address><email>frystyk@w3.org</email></address>
2962    </author>
2963    <date month="May" year="1996"/>
2964  </front>
2965  <seriesInfo name="RFC" value="1945"/>
2966</reference>
2967
2968<reference anchor="RFC2068">
2969  <front>
2970    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2971    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2972      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2973      <address><email>fielding@ics.uci.edu</email></address>
2974    </author>
2975    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2976      <organization>MIT Laboratory for Computer Science</organization>
2977      <address><email>jg@w3.org</email></address>
2978    </author>
2979    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2980      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2981      <address><email>mogul@wrl.dec.com</email></address>
2982    </author>
2983    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2984      <organization>MIT Laboratory for Computer Science</organization>
2985      <address><email>frystyk@w3.org</email></address>
2986    </author>
2987    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2988      <organization>MIT Laboratory for Computer Science</organization>
2989      <address><email>timbl@w3.org</email></address>
2990    </author>
2991    <date month="January" year="1997"/>
2992  </front>
2993  <seriesInfo name="RFC" value="2068"/>
2994</reference>
2995
2996<reference anchor="RFC2616">
2997  <front>
2998    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2999    <author initials="R." surname="Fielding" fullname="R. Fielding">
3000      <organization>University of California, Irvine</organization>
3001      <address><email>fielding@ics.uci.edu</email></address>
3002    </author>
3003    <author initials="J." surname="Gettys" fullname="J. Gettys">
3004      <organization>W3C</organization>
3005      <address><email>jg@w3.org</email></address>
3006    </author>
3007    <author initials="J." surname="Mogul" fullname="J. Mogul">
3008      <organization>Compaq Computer Corporation</organization>
3009      <address><email>mogul@wrl.dec.com</email></address>
3010    </author>
3011    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3012      <organization>MIT Laboratory for Computer Science</organization>
3013      <address><email>frystyk@w3.org</email></address>
3014    </author>
3015    <author initials="L." surname="Masinter" fullname="L. Masinter">
3016      <organization>Xerox Corporation</organization>
3017      <address><email>masinter@parc.xerox.com</email></address>
3018    </author>
3019    <author initials="P." surname="Leach" fullname="P. Leach">
3020      <organization>Microsoft Corporation</organization>
3021      <address><email>paulle@microsoft.com</email></address>
3022    </author>
3023    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3024      <organization>W3C</organization>
3025      <address><email>timbl@w3.org</email></address>
3026    </author>
3027    <date month="June" year="1999"/>
3028  </front>
3029  <seriesInfo name="RFC" value="2616"/>
3030</reference>
3031
3032<reference anchor="RFC2817">
3033  <front>
3034    <title>Upgrading to TLS Within HTTP/1.1</title>
3035    <author initials="R." surname="Khare" fullname="R. Khare">
3036      <organization>4K Associates / UC Irvine</organization>
3037      <address><email>rohit@4K-associates.com</email></address>
3038    </author>
3039    <author initials="S." surname="Lawrence" fullname="S. Lawrence">
3040      <organization>Agranat Systems, Inc.</organization>
3041      <address><email>lawrence@agranat.com</email></address>
3042    </author>
3043    <date year="2000" month="May"/>
3044  </front>
3045  <seriesInfo name="RFC" value="2817"/>
3046</reference>
3047
3048<reference anchor="RFC3864">
3049  <front>
3050    <title>Registration Procedures for Message Header Fields</title>
3051    <author initials="G." surname="Klyne" fullname="G. Klyne">
3052      <organization>Nine by Nine</organization>
3053      <address><email>GK-IETF@ninebynine.org</email></address>
3054    </author>
3055    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
3056      <organization>BEA Systems</organization>
3057      <address><email>mnot@pobox.com</email></address>
3058    </author>
3059    <author initials="J." surname="Mogul" fullname="J. Mogul">
3060      <organization>HP Labs</organization>
3061      <address><email>JeffMogul@acm.org</email></address>
3062    </author>
3063    <date year="2004" month="September"/>
3064  </front>
3065  <seriesInfo name="BCP" value="90"/>
3066  <seriesInfo name="RFC" value="3864"/>
3067</reference>
3068
3069<reference anchor="RFC5226">
3070  <front>
3071    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3072    <author initials="T." surname="Narten" fullname="T. Narten">
3073      <organization>IBM</organization>
3074      <address><email>narten@us.ibm.com</email></address>
3075    </author>
3076    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
3077      <organization>Google</organization>
3078      <address><email>Harald@Alvestrand.no</email></address>
3079    </author>
3080    <date year="2008" month="May"/>
3081  </front>
3082  <seriesInfo name="BCP" value="26"/>
3083  <seriesInfo name="RFC" value="5226"/>
3084</reference>
3085
3086<reference anchor="RFC5322">
3087  <front>
3088    <title>Internet Message Format</title>
3089    <author initials="P." surname="Resnick" fullname="P. Resnick">
3090      <organization>Qualcomm Incorporated</organization>
3091    </author>
3092    <date year="2008" month="October"/>
3093  </front>
3094  <seriesInfo name="RFC" value="5322"/>
3095</reference>
3096
3097</references>
3098
3099<section title="Compatibility with Previous Versions" anchor="compatibility">
3100<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
3101<t>
3102   Clarified which error code should be used for inbound server failures
3103   (e.g. DNS failures). (<xref target="status.504"/>).
3104</t>
3105<t>
3106   201 (Created) had a race that required an Etag be sent when a resource is
3107   first created. (<xref target="status.201"/>).
3108</t>
3109<t>
3110   303 (See Also) and 307 (Temporary Redirect) added to address user agent
3111   failure to implement status code 302 properly.
3112   (Section <xref target="status.303" format="counter"/> and <xref target="status.307" format="counter"/>)
3113</t>
3114<t>
3115   Rewrite of message transmission requirements to make it much harder
3116   for implementors to get it wrong, as the consequences of errors here
3117   can have significant impact on the Internet, and to deal with the
3118   following problems:
3119  <list style="numbers">
3120      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
3121         this was incorrectly placing a requirement on the behavior of
3122         an implementation of a future version of HTTP/1.x</t>
3123
3124      <t>Made it clear that user-agents should retry requests, not
3125         "clients" in general.</t>
3126
3127      <t>Converted requirements for clients to ignore unexpected 100
3128         (Continue) responses, and for proxies to forward 100 responses,
3129         into a general requirement for 1xx responses.</t>
3130
3131      <t>Modified some TCP-specific language, to make it clearer that
3132         non-TCP transports are possible for HTTP.</t>
3133
3134      <t>Require that the origin server MUST NOT wait for the request
3135         body before it sends a required 100 (Continue) response.</t>
3136
3137      <t>Allow, rather than require, a server to omit 100 (Continue) if
3138         it has already seen some of the request body.</t>
3139
3140      <t>Allow servers to defend against denial-of-service attacks and
3141         broken clients.</t>
3142  </list>
3143</t>
3144<t>
3145   This change adds the Expect header and 417 status code.
3146</t>
3147<t>
3148   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
3149   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
3150</t>
3151<t>
3152   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
3153   implemented in previous versions of this specification. See Section 19.6.1 of <xref target="RFC2068"/>.
3154</t>
3155</section>
3156
3157<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3158<t>
3159  This document takes over the Status Code Registry, previously defined
3160  in Section 7.1 of <xref target="RFC2817"/>.
3161  (<xref target="status.code.registry"/>)
3162</t>
3163<t>
3164  Clarify definition of POST.
3165  (<xref target="POST"/>)
3166</t>
3167<t>
3168  Failed to consider that there are
3169  many other request methods that are safe to automatically redirect,
3170  and further that the user agent is able to make that determination
3171  based on the request method semantics.
3172  (Sections <xref format="counter" target="status.301"/>,
3173  <xref format="counter" target="status.302"/> and
3174  <xref format="counter" target="status.307"/>)
3175</t>
3176<t>
3177  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3178  It used to indicate that the requested resource must be accessed through the
3179  proxy given by the Location field. The Location field gave the URI of the
3180  proxy. The recipient was expected to repeat this single request via the proxy.
3181  (<xref target="status.305"/>)
3182</t>
3183<t>
3184  Reclassify Allow header as response header, removing the option to
3185  specify it in a PUT request.
3186  Relax the server requirement on the contents of the Allow header and
3187  remove requirement on clients to always trust the header value.
3188  (<xref target="header.allow"/>)
3189</t>
3190<t>
3191  Correct syntax of Location header to allow fragment,
3192  as referred symbol wasn't what was expected, and add some
3193  clarifications as to when it would not be appropriate.
3194  (<xref target="header.location"/>)
3195</t>
3196<t>
3197  Allow Referer value of "about:blank" as alternative to not specifying it.
3198  (<xref target="header.referer"/>)
3199</t>
3200<t>
3201  In the description of the Server header, the Via field
3202  was described as a SHOULD. The requirement was and is stated
3203  correctly in the description of the Via header in Section 9.9 of <xref target="Part1"/>.
3204  (<xref target="header.server"/>)
3205</t>
3206</section>
3207
3208</section>
3209
3210
3211<section title="Collected ABNF" anchor="collected.abnf">
3212<figure>
3213<artwork type="abnf" name="p2-semantics.parsed-abnf"><![CDATA[
3214Accept = <Accept, defined in [Part3], Section 5.1>
3215Accept-Charset = <Accept-Charset, defined in [Part3], Section 5.2>
3216Accept-Encoding = <Accept-Encoding, defined in [Part3], Section 5.3>
3217Accept-Language = <Accept-Language, defined in [Part3], Section 5.4>
3218Accept-Ranges = <Accept-Ranges, defined in [Part5], Section 5.1>
3219Age = <Age, defined in [Part6], Section 3.1>
3220Allow = "Allow:" OWS Allow-v
3221Allow-v = [ ( "," / Method ) *( OWS "," [ OWS Method ] ) ]
3222Authorization = <Authorization, defined in [Part7], Section 3.1>
3223
3224ETag = <ETag, defined in [Part4], Section 6.1>
3225Expect = "Expect:" OWS Expect-v
3226Expect-v = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
3227
3228From = "From:" OWS From-v
3229From-v = mailbox
3230
3231HTTP-date = <HTTP-date, defined in [Part1], Section 6.1>
3232Host = <Host, defined in [Part1], Section 2.6>
3233
3234If-Match = <If-Match, defined in [Part4], Section 6.2>
3235If-Modified-Since =
3236 <If-Modified-Since, defined in [Part4], Section 6.3>
3237If-None-Match = <If-None-Match, defined in [Part4], Section 6.4>
3238If-Range = <If-Range, defined in [Part5], Section 5.3>
3239If-Unmodified-Since =
3240 <If-Unmodified-Since, defined in [Part4], Section 6.5>
3241
3242Location = "Location:" OWS Location-v
3243Location-v = URI
3244
3245Max-Forwards = "Max-Forwards:" OWS Max-Forwards-v
3246Max-Forwards-v = 1*DIGIT
3247Method = %x4F.50.54.49.4F.4E.53 ; OPTIONS
3248 / %x47.45.54 ; GET
3249 / %x48.45.41.44 ; HEAD
3250 / %x50.4F.53.54 ; POST
3251 / %x50.55.54 ; PUT
3252 / %x44.45.4C.45.54.45 ; DELETE
3253 / %x54.52.41.43.45 ; TRACE
3254 / %x43.4F.4E.4E.45.43.54 ; CONNECT
3255 / extension-method
3256
3257OWS = <OWS, defined in [Part1], Section 1.2.2>
3258
3259Proxy-Authenticate =
3260 <Proxy-Authenticate, defined in [Part7], Section 3.2>
3261Proxy-Authorization =
3262 <Proxy-Authorization, defined in [Part7], Section 3.3>
3263
3264RWS = <RWS, defined in [Part1], Section 1.2.2>
3265Range = <Range, defined in [Part5], Section 5.4>
3266Reason-Phrase = *( WSP / VCHAR / obs-text )
3267Referer = "Referer:" OWS Referer-v
3268Referer-v = absolute-URI / partial-URI
3269Retry-After = "Retry-After:" OWS Retry-After-v
3270Retry-After-v = HTTP-date / delta-seconds
3271
3272Server = "Server:" OWS Server-v
3273Server-v = product *( RWS ( product / comment ) )
3274Status-Code = "100" / "101" / "200" / "201" / "202" / "203" / "204" /
3275 "205" / "206" / "300" / "301" / "302" / "303" / "304" / "305" /
3276 "307" / "400" / "401" / "402" / "403" / "404" / "405" / "406" /
3277 "407" / "408" / "409" / "410" / "411" / "412" / "413" / "414" /
3278 "415" / "416" / "417" / "500" / "501" / "502" / "503" / "504" /
3279 "505" / extension-code
3280
3281TE = <TE, defined in [Part1], Section 9.8>
3282
3283URI = <URI, defined in [Part1], Section 2.6>
3284User-Agent = "User-Agent:" OWS User-Agent-v
3285User-Agent-v = product *( RWS ( product / comment ) )
3286
3287Vary = <Vary, defined in [Part6], Section 3.5>
3288
3289WWW-Authenticate =
3290 <WWW-Authenticate, defined in [Part7], Section 3.4>
3291
3292absolute-URI = <absolute-URI, defined in [Part1], Section 2.6>
3293
3294comment = <comment, defined in [Part1], Section 3.2>
3295
3296delta-seconds = 1*DIGIT
3297
3298expect-params = ";" token [ "=" ( token / quoted-string ) ]
3299expectation = "100-continue" / expectation-extension
3300expectation-extension = token [ "=" ( token / quoted-string )
3301 *expect-params ]
3302extension-code = 3DIGIT
3303extension-method = token
3304
3305mailbox = <mailbox, defined in [RFC5322], Section 3.4>
3306
3307obs-text = <obs-text, defined in [Part1], Section 1.2.2>
3308
3309partial-URI = <partial-URI, defined in [Part1], Section 2.6>
3310product = <product, defined in [Part1], Section 6.3>
3311
3312quoted-string = <quoted-string, defined in [Part1], Section 1.2.2>
3313
3314request-header = Accept / Accept-Charset / Accept-Encoding /
3315 Accept-Language / Authorization / Expect / From / Host / If-Match /
3316 If-Modified-Since / If-None-Match / If-Range / If-Unmodified-Since /
3317 Max-Forwards / Proxy-Authorization / Range / Referer / TE /
3318 User-Agent
3319response-header = Accept-Ranges / Age / Allow / ETag / Location /
3320 Proxy-Authenticate / Retry-After / Server / Vary / WWW-Authenticate
3321
3322token = <token, defined in [Part1], Section 1.2.2>
3323]]></artwork>
3324</figure>
3325<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
3326; Reason-Phrase defined but not used
3327; Status-Code defined but not used
3328; request-header defined but not used
3329; response-header defined but not used
3330]]></artwork></figure></section>
3331
3332
3333<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
3334
3335<section title="Since RFC2616">
3336<t>
3337  Extracted relevant partitions from <xref target="RFC2616"/>.
3338</t>
3339</section>
3340
3341<section title="Since draft-ietf-httpbis-p2-semantics-00">
3342<t>
3343  Closed issues:
3344  <list style="symbols">
3345    <t>
3346      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
3347      "Via is a MUST"
3348      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
3349    </t>
3350    <t>
3351      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
3352      "Fragments allowed in Location"
3353      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
3354    </t>
3355    <t>
3356      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
3357      "Safe Methods vs Redirection"
3358      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
3359    </t>
3360    <t>
3361      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
3362      "Revise description of the POST method"
3363      (<eref target="http://purl.org/NET/http-errata#post"/>)
3364    </t>
3365    <t>
3366      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
3367      "Normative and Informative references"
3368    </t>
3369    <t>
3370      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
3371      "RFC2606 Compliance"
3372    </t>
3373    <t>
3374      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
3375      "Informative references"
3376    </t>
3377    <t>
3378      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
3379      "Redundant cross-references"
3380    </t>
3381  </list>
3382</t>
3383<t>
3384  Other changes:
3385  <list style="symbols">
3386    <t>
3387      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
3388    </t>
3389  </list>
3390</t>
3391</section>
3392
3393<section title="Since draft-ietf-httpbis-p2-semantics-01">
3394<t>
3395  Closed issues:
3396  <list style="symbols">
3397    <t>
3398      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
3399      "PUT side effects"
3400    </t>
3401    <t>
3402      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
3403      "Duplicate Host header requirements"
3404    </t>
3405  </list>
3406</t>
3407<t>
3408  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3409  <list style="symbols">
3410    <t>
3411      Move "Product Tokens" section (back) into Part 1, as "token" is used
3412      in the definition of the Upgrade header.
3413    </t>
3414    <t>
3415      Add explicit references to BNF syntax and rules imported from other parts of the specification.
3416    </t>
3417    <t>
3418      Copy definition of delta-seconds from Part6 instead of referencing it.
3419    </t>
3420  </list>
3421</t>
3422</section>
3423
3424<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
3425<t>
3426  Closed issues:
3427  <list style="symbols">
3428    <t>
3429      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
3430      "Requiring Allow in 405 responses"
3431    </t>
3432    <t>
3433      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
3434      "Status Code Registry"
3435    </t>
3436    <t>
3437      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
3438      "Redirection vs. Location"
3439    </t>
3440    <t>
3441      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
3442      "Cacheability of 303 response"
3443    </t>
3444    <t>
3445      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
3446      "305 Use Proxy"
3447    </t>
3448    <t>
3449      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
3450      "Classification for Allow header"
3451    </t>
3452    <t>
3453      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
3454      "PUT - 'store under' vs 'store at'"
3455    </t>
3456  </list>
3457</t>
3458<t>
3459  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
3460  <list style="symbols">
3461    <t>
3462      Reference RFC 3984, and update header registrations for headers defined
3463      in this document.
3464    </t>
3465  </list>
3466</t>
3467<t>
3468  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3469  <list style="symbols">
3470    <t>
3471      Replace string literals when the string really is case-sensitive (method).
3472    </t>
3473  </list>
3474</t>
3475</section>
3476
3477<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
3478<t>
3479  Closed issues:
3480  <list style="symbols">
3481    <t>
3482      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
3483      "OPTIONS request bodies"
3484    </t>
3485    <t>
3486      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
3487      "Description of CONNECT should refer to RFC2817"
3488    </t>
3489    <t>
3490      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
3491      "Location Content-Location reference request/response mixup"
3492    </t>
3493  </list>
3494</t>
3495<t>
3496  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
3497  <list style="symbols">
3498    <t>
3499      Added initial proposal for registration process, plus initial
3500      content (non-HTTP/1.1 methods to be added by a separate specification).
3501    </t>
3502  </list>
3503</t>
3504</section>
3505
3506<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
3507<t>
3508  Closed issues:
3509  <list style="symbols">
3510    <t>
3511      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
3512      "Content-*"
3513    </t>
3514    <t>
3515      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
3516      "RFC 2822 is updated by RFC 5322"
3517    </t>
3518  </list>
3519</t>
3520<t>
3521  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3522  <list style="symbols">
3523    <t>
3524      Use "/" instead of "|" for alternatives.
3525    </t>
3526    <t>
3527      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
3528      whitespace ("OWS") and required whitespace ("RWS").
3529    </t>
3530    <t>
3531      Rewrite ABNFs to spell out whitespace rules, factor out
3532      header value format definitions.
3533    </t>
3534  </list>
3535</t>
3536</section>
3537
3538<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
3539<t>
3540  Closed issues:
3541  <list style="symbols">
3542    <t>
3543      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
3544      "Reason-Phrase BNF"
3545    </t>
3546  </list>
3547</t>
3548<t>
3549  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3550  <list style="symbols">
3551    <t>
3552      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
3553    </t>
3554  </list>
3555</t>
3556</section>
3557
3558<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
3559<t>
3560  Closed issues:
3561  <list style="symbols">
3562    <t>
3563      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
3564      "Clarify when Referer is sent"
3565    </t>
3566    <t>
3567      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
3568      "status codes vs methods"
3569    </t>
3570    <t>
3571      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
3572      "Do not require "updates" relation for specs that register status codes or method names"
3573    </t>
3574  </list>
3575</t>
3576</section>
3577
3578<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
3579<t>
3580  Closed issues:
3581  <list style="symbols">
3582    <t>
3583      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
3584      "Idempotency"
3585    </t>
3586    <t>
3587      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
3588      "TRACE security considerations"
3589    </t>
3590    <t>
3591      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
3592      "Clarify rules for determining what entities a response carries"
3593    </t>
3594    <t>
3595      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
3596      "update note citing RFC 1945 and 2068"
3597    </t>
3598    <t>
3599      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
3600      "update note about redirect limit"
3601    </t>
3602    <t>
3603      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
3604      "Location header ABNF should use 'URI'"
3605    </t>
3606    <t>
3607      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
3608      "fragments in Location vs status 303"
3609    </t>
3610    <t>
3611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
3612      "move IANA registrations for optional status codes"
3613    </t>
3614  </list>
3615</t>
3616<t>
3617  Partly resolved issues:
3618  <list style="symbols">
3619    <t>
3620      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
3621      "Are OPTIONS and TRACE safe?"
3622    </t>
3623  </list>
3624</t>
3625
3626</section>
3627
3628</section>
3629
3630</back>
3631</rfc>
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