source: draft-ietf-httpbis/15/draft-ietf-httpbis-p2-semantics-15.xml @ 1391

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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<?rfc rfcedstyle="yes"?>
17<!DOCTYPE rfc
18  PUBLIC "" "rfc2629.dtd">
19<rfc obsoletes="2616" updates="2817" category="std" ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p2-semantics-15">
20<front>
21
22  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
23
24  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
25    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
26    <address>
27      <postal>
28        <street>345 Park Ave</street>
29        <city>San Jose</city>
30        <region>CA</region>
31        <code>95110</code>
32        <country>USA</country>
33      </postal>
34      <email>fielding@gbiv.com</email>
35      <uri>http://roy.gbiv.com/</uri>
36    </address>
37  </author>
38
39  <author initials="J." surname="Gettys" fullname="Jim Gettys">
40    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
41    <address>
42      <postal>
43        <street>21 Oak Knoll Road</street>
44        <city>Carlisle</city>
45        <region>MA</region>
46        <code>01741</code>
47        <country>USA</country>
48      </postal>
49      <email>jg@freedesktop.org</email>
50      <uri>http://gettys.wordpress.com/</uri>
51    </address>
52  </author>
53 
54  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
55    <organization abbrev="HP">Hewlett-Packard Company</organization>
56    <address>
57      <postal>
58        <street>HP Labs, Large Scale Systems Group</street>
59        <street>1501 Page Mill Road, MS 1177</street>
60        <city>Palo Alto</city>
61        <region>CA</region>
62        <code>94304</code>
63        <country>USA</country>
64      </postal>
65      <email>JeffMogul@acm.org</email>
66    </address>
67  </author>
68
69  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
70    <organization abbrev="Microsoft">Microsoft Corporation</organization>
71    <address>
72      <postal>
73        <street>1 Microsoft Way</street>
74        <city>Redmond</city>
75        <region>WA</region>
76        <code>98052</code>
77        <country>USA</country>
78      </postal>
79      <email>henrikn@microsoft.com</email>
80    </address>
81  </author>
82
83  <author initials="L." surname="Masinter" fullname="Larry Masinter">
84    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
85    <address>
86      <postal>
87        <street>345 Park Ave</street>
88        <city>San Jose</city>
89        <region>CA</region>
90        <code>95110</code>
91        <country>USA</country>
92      </postal>
93      <email>LMM@acm.org</email>
94      <uri>http://larry.masinter.net/</uri>
95    </address>
96  </author>
97 
98  <author initials="P." surname="Leach" fullname="Paul J. Leach">
99    <organization abbrev="Microsoft">Microsoft Corporation</organization>
100    <address>
101      <postal>
102        <street>1 Microsoft Way</street>
103        <city>Redmond</city>
104        <region>WA</region>
105        <code>98052</code>
106      </postal>
107      <email>paulle@microsoft.com</email>
108    </address>
109  </author>
110   
111  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
112    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
113    <address>
114      <postal>
115        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
116        <street>The Stata Center, Building 32</street>
117        <street>32 Vassar Street</street>
118        <city>Cambridge</city>
119        <region>MA</region>
120        <code>02139</code>
121        <country>USA</country>
122      </postal>
123      <email>timbl@w3.org</email>
124      <uri>http://www.w3.org/People/Berners-Lee/</uri>
125    </address>
126  </author>
127
128  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
129    <organization abbrev="W3C">World Wide Web Consortium</organization>
130    <address>
131      <postal>
132        <street>W3C / ERCIM</street>
133        <street>2004, rte des Lucioles</street>
134        <city>Sophia-Antipolis</city>
135        <region>AM</region>
136        <code>06902</code>
137        <country>France</country>
138      </postal>
139      <email>ylafon@w3.org</email>
140      <uri>http://www.raubacapeu.net/people/yves/</uri>
141    </address>
142  </author>
143
144  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
145    <organization abbrev="greenbytes">greenbytes GmbH</organization>
146    <address>
147      <postal>
148        <street>Hafenweg 16</street>
149        <city>Muenster</city><region>NW</region><code>48155</code>
150        <country>Germany</country>
151      </postal>
152      <phone>+49 251 2807760</phone>
153      <facsimile>+49 251 2807761</facsimile>
154      <email>julian.reschke@greenbytes.de</email>
155      <uri>http://greenbytes.de/tech/webdav/</uri>
156    </address>
157  </author>
158
159  <date month="July" year="2011" day="11"/>
160  <workgroup>HTTPbis Working Group</workgroup>
161
162<abstract>
163<t>
164   The Hypertext Transfer Protocol (HTTP) is an application-level
165   protocol for distributed, collaborative, hypermedia information
166   systems. HTTP has been in use by the World Wide Web global information
167   initiative since 1990. This document is Part 2 of the seven-part specification
168   that defines the protocol referred to as "HTTP/1.1" and, taken together,
169   obsoletes RFC 2616.  Part 2 defines the semantics of HTTP messages
170   as expressed by request methods, request header fields, response status codes,
171   and response header fields.
172</t>
173</abstract>
174
175<note title="Editorial Note (To be removed by RFC Editor)">
176  <t>
177    Discussion of this draft should take place on the HTTPBIS working group
178    mailing list (ietf-http-wg@w3.org), which is archived at
179    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
180  </t>
181  <t>
182    The current issues list is at
183    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
184    documents (including fancy diffs) can be found at
185    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
186  </t>
187  <t>
188    The changes in this draft are summarized in <xref target="changes.since.14"/>.
189  </t>
190</note>
191</front>
192<middle>
193<section title="Introduction" anchor="introduction">
194<t>
195   This document defines HTTP/1.1 request and response semantics.  Each HTTP
196   message, as defined in <xref target="Part1"/>, is in the form of either a request or
197   a response.  An HTTP server listens on a connection for HTTP requests and
198   responds to each request, in the order received on that connection, with
199   one or more HTTP response messages.  This document defines the commonly
200   agreed upon semantics of the HTTP uniform interface, the intentions defined
201   by each request method, and the various response messages that might be
202   expected as a result of applying that method to the target resource.
203</t>
204<t>
205   This document is currently disorganized in order to minimize the changes
206   between drafts and enable reviewers to see the smaller errata changes.
207   A future draft will reorganize the sections to better reflect the content.
208   In particular, the sections will be ordered according to the typical
209   processing of an HTTP request message (after message parsing): resource
210   mapping, methods, request modifying header fields, response status,
211   status modifying header fields, and resource metadata.  The current mess
212   reflects how widely dispersed these topics and associated requirements
213   had become in <xref target="RFC2616"/>.
214</t>
215
216<section title="Requirements" anchor="intro.requirements">
217<t>
218   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
219   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
220   document are to be interpreted as described in <xref target="RFC2119"/>.
221</t>
222<t>
223   An implementation is not compliant if it fails to satisfy one or more
224   of the "MUST" or "REQUIRED" level requirements for the protocols it
225   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
226   level and all the "SHOULD" level requirements for its protocols is said
227   to be "unconditionally compliant"; one that satisfies all the "MUST"
228   level requirements but not all the "SHOULD" level requirements for its
229   protocols is said to be "conditionally compliant".
230</t>
231</section>
232
233<section title="Syntax Notation" anchor="notation">
234 
235 
236 
237 
238 
239<t>
240  This specification uses the ABNF syntax defined in Section 1.2 of <xref target="Part1"/> (which
241  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
242  <xref target="collected.abnf"/> shows the collected ABNF, with the list
243  rule expanded.
244</t>
245<t>
246  The following core rules are included by
247  reference, as defined in <xref target="RFC5234"/>, Appendix B.1:
248  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
249  DIGIT (decimal 0-9), DQUOTE (double quote),
250  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
251  OCTET (any 8-bit sequence of data), SP (space),
252  VCHAR (any visible USASCII character),
253  and WSP (whitespace).
254</t>
255
256<section title="Core Rules" anchor="core.rules">
257 
258 
259 
260 
261 
262<t>
263  The core rules below are defined in Section 1.2.2 of <xref target="Part1"/>:
264</t>
265<figure><artwork type="abnf2616"><![CDATA[
266  quoted-string = <quoted-string, defined in [Part1], Section 1.2.2>
267  token         = <token, defined in [Part1], Section 1.2.2>
268  OWS           = <OWS, defined in [Part1], Section 1.2.2>
269  RWS           = <RWS, defined in [Part1], Section 1.2.2>
270  obs-text      = <obs-text, defined in [Part1], Section 1.2.2>
271]]></artwork></figure>
272</section>
273
274<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
275 
276 
277 
278 
279 
280 
281<t>
282  The ABNF rules below are defined in other parts:
283</t>
284<figure><artwork type="abnf2616"><![CDATA[
285  absolute-URI  = <absolute-URI, defined in [Part1], Section 2.7>
286  comment       = <comment, defined in [Part1], Section 3.2>
287  HTTP-date     = <HTTP-date, defined in [Part1], Section 6.1>
288  partial-URI   = <partial-URI, defined in [Part1], Section 2.7>
289  product       = <product, defined in [Part1], Section 6.3>
290  URI-reference = <URI-reference, defined in [Part1], Section 2.7>
291]]></artwork></figure>
292</section>
293</section>
294</section>
295
296<section title="Method" anchor="method">
297 
298 
299<t>
300   The Method token indicates the request method to be performed on the target
301   resource (Section 4.3 of <xref target="Part1"/>). The method is case-sensitive.
302</t>
303<figure><iref primary="true" item="Grammar" subitem="Method"/><artwork type="abnf2616"><![CDATA[
304  Method         = token
305]]></artwork></figure>
306<t>
307   The list of methods allowed by a resource can be specified in an
308   Allow header field (<xref target="header.allow"/>). The status code of the response
309   always notifies the client whether a method is currently allowed on a
310   resource, since the set of allowed methods can change dynamically. An
311   origin server SHOULD respond with the status code 405 (Method Not Allowed)
312   if the method is known by the origin server but not allowed for the
313   resource, and 501 (Not Implemented) if the method is
314   unrecognized or not implemented by the origin server. The methods GET
315   and HEAD MUST be supported by all general-purpose servers. All other
316   methods are OPTIONAL; however, if the above methods are implemented,
317   they MUST be implemented with the same semantics as those specified
318   in <xref target="method.definitions"/>.
319</t>
320
321<section title="Overview of Methods" anchor="overview.of.methods">
322<t>
323  The methods listed below are defined in <xref target="method.definitions"/>.
324</t>
325<texttable align="left">
326  <ttcol>Method Name</ttcol><ttcol>Defined in...</ttcol>
327 
328  <c>OPTIONS</c> <c><xref target="OPTIONS"/></c>
329  <c>GET</c> <c><xref target="GET"/></c>
330  <c>HEAD</c> <c><xref target="HEAD"/></c>
331  <c>POST</c> <c><xref target="POST"/></c>
332  <c>PUT</c> <c><xref target="PUT"/></c>
333  <c>DELETE</c> <c><xref target="DELETE"/></c>
334  <c>TRACE</c> <c><xref target="TRACE"/></c>
335  <c>CONNECT</c> <c><xref target="CONNECT"/></c>
336</texttable>
337<t>
338  Note that this list is not exhaustive — it does not include request methods defined
339  in other specifications.
340</t>
341</section>
342
343<section title="Method Registry" anchor="method.registry">
344<t>
345  The HTTP Method Registry defines the name space for the Method token in the
346  Request line of an HTTP request.
347</t>
348<t>
349  Registrations MUST include the following fields:
350  <list style="symbols">
351    <t>Method Name (see <xref target="method"/>)</t>
352    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
353    <t>Pointer to specification text</t>
354  </list>
355</t>
356<t>
357  Values to be added to this name space are subject to IETF review
358  (<xref target="RFC5226"/>, Section 4.1).
359</t>
360<t>
361  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
362</t>
363
364<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
365<t>
366   When it is necessary to express new semantics for a HTTP request that
367   aren't specific to a single application or media type, and currently defined
368   methods are inadequate, it may be appropriate to register a new method.
369</t>
370<t>
371   HTTP methods are generic; that is, they are potentially applicable to any
372   resource, not just one particular media type, "type" of resource, or
373   application. As such, it is preferred that new HTTP methods be registered
374   in a document that isn't specific to a single application, so that this is
375   clear.
376</t>
377<t>
378   Due to the parsing rules defined in Section 3.3 of <xref target="Part1"/>, definitions of HTTP
379   methods cannot prohibit the presence of a message-body on either the request
380   or the response message (with responses to HEAD requests being the single
381   exception). Definitions of new methods cannot change this rule, but they can
382   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
383</t>
384<t>
385   New method definitions need to indicate whether they are safe (<xref target="safe.methods"/>), what semantics (if any) the request body has,
386   and whether they are idempotent (<xref target="idempotent.methods"/>).
387   They also need to state whether they can be cached (<xref target="Part6"/>); in
388   particular what conditions a cache may store the response, and under what
389   conditions such a stored response may be used to satisfy a subsequent
390   request.
391</t>
392</section>
393
394</section>
395</section>
396
397<section title="Request Header Fields" anchor="request.header.fields">
398 
399<t>
400   The request header fields allow the client to pass additional
401   information about the request, and about the client itself, to the
402   server. These fields act as request modifiers, with semantics
403   equivalent to the parameters on a programming language method
404   invocation.
405</t>
406<texttable align="left">
407  <ttcol>Header Field Name</ttcol>
408  <ttcol>Defined in...</ttcol>
409
410  <c>Accept</c> <c>Section 6.1 of <xref target="Part3"/></c>
411  <c>Accept-Charset</c> <c>Section 6.2 of <xref target="Part3"/></c>
412  <c>Accept-Encoding</c> <c>Section 6.3 of <xref target="Part3"/></c>
413  <c>Accept-Language</c> <c>Section 6.4 of <xref target="Part3"/></c>
414  <c>Authorization</c> <c>Section 4.1 of <xref target="Part7"/></c>
415  <c>Expect</c> <c><xref target="header.expect"/></c>
416  <c>From</c> <c><xref target="header.from"/></c>
417  <c>Host</c> <c>Section 9.4 of <xref target="Part1"/></c>
418  <c>If-Match</c> <c>Section 3.1 of <xref target="Part4"/></c>
419  <c>If-Modified-Since</c> <c>Section 3.3 of <xref target="Part4"/></c>
420  <c>If-None-Match</c> <c>Section 3.2 of <xref target="Part4"/></c>
421  <c>If-Range</c> <c>Section 5.3 of <xref target="Part5"/></c>
422  <c>If-Unmodified-Since</c> <c>Section 3.4 of <xref target="Part4"/></c>
423  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
424  <c>Proxy-Authorization</c> <c>Section 4.3 of <xref target="Part7"/></c>
425  <c>Range</c> <c>Section 5.4 of <xref target="Part5"/></c>
426  <c>Referer</c> <c><xref target="header.referer"/></c>
427  <c>TE</c> <c>Section 9.5 of <xref target="Part1"/></c>
428  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
429</texttable>
430</section>
431
432<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
433 
434 
435 
436<t>
437   The Status-Code element is a 3-digit integer result code of the attempt to
438   understand and satisfy the request.
439</t>
440<t>
441   The Reason-Phrase is intended to give a short textual description of the
442   Status-Code and is intended for a human user. The client does not need
443   to examine or display the Reason-Phrase.
444</t>
445<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[
446  Status-Code    = 3DIGIT
447  Reason-Phrase  = *( WSP / VCHAR / obs-text )
448]]></artwork></figure>
449<t>
450   HTTP status codes are extensible. HTTP applications are not required
451   to understand the meaning of all registered status codes, though such
452   understanding is obviously desirable. However, applications MUST
453   understand the class of any status code, as indicated by the first
454   digit, and treat any unrecognized response as being equivalent to the
455   x00 status code of that class, with the exception that an
456   unrecognized response MUST NOT be cached. For example, if an
457   unrecognized status code of 431 is received by the client, it can
458   safely assume that there was something wrong with its request and
459   treat the response as if it had received a 400 status code. In such
460   cases, user agents SHOULD present to the user the representation enclosed
461   with the response, since that representation is likely to include human-readable
462   information which will explain the unusual status.
463</t>
464
465<section title="Overview of Status Codes" anchor="overview.of.status.codes">
466<t> 
467   The status codes listed below are defined in <xref target="status.codes"/>
468   of this specification, Section 4 of <xref target="Part4"/>, Section 3 of <xref target="Part5"/>, and Section 3 of <xref target="Part7"/>.
469   The reason phrases listed here are only recommendations — they can be
470   replaced by local equivalents without affecting the protocol.
471</t>
472<texttable align="left">
473  <ttcol>Status-Code</ttcol>
474  <ttcol>Reason-Phrase</ttcol>
475  <ttcol>Defined in...</ttcol>
476 
477  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
478  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
479
480  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
481  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
482  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
483  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
484  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
485  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
486  <c>206</c> <c>Partial Content</c> <c>Section 3.1 of <xref target="Part5"/></c>
487
488  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
489  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
490  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
491  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
492  <c>304</c> <c>Not Modified</c> <c>Section 4.1 of <xref target="Part4"/></c>
493  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
494  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
495
496  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
497  <c>401</c> <c>Unauthorized</c> <c>Section 3.1 of <xref target="Part7"/></c>
498  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
499  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
500  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
501  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
502  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
503  <c>407</c> <c>Proxy Authentication Required</c> <c>Section 3.2 of <xref target="Part7"/></c>
504  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
505  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
506  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
507  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
508  <c>412</c> <c>Precondition Failed</c> <c>Section 4.2 of <xref target="Part4"/></c>
509  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
510  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
511  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
512  <c>416</c> <c>Requested range not satisfiable</c> <c>Section 3.2 of <xref target="Part5"/></c>
513  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
514  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
515
516  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
517  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
518  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
519  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
520  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
521  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
522</texttable>
523<t>
524   Note that this list is not exhaustive — it does not include
525   extension status codes defined in other specifications.
526</t>
527</section>
528
529<section title="Status Code Registry" anchor="status.code.registry">
530<t>
531  The HTTP Status Code Registry defines the name space for the Status-Code
532  token in the Status-Line of an HTTP response.
533</t>
534<t>
535  Values to be added to this name space are subject to IETF review
536  (<xref target="RFC5226"/>, Section 4.1).
537</t>
538<t>
539  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
540</t>
541
542<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
543<t>
544   When it is necessary to express new semantics for a HTTP response that
545   aren't specific to a single application or media type, and currently defined
546   status codes are inadequate, a new status code can be registered.
547</t>
548<t>
549   HTTP status codes are generic; that is, they are potentially applicable to
550   any resource, not just one particular media type, "type" of resource, or
551   application. As such, it is preferred that new HTTP status codes be
552   registered in a document that isn't specific to a single application, so
553   that this is clear.
554</t>
555<t>
556   Definitions of new HTTP status codes typically explain the request
557   conditions that produce a response containing the status code (e.g.,
558   combinations of request headers and/or method(s)), along with any
559   interactions with response headers (e.g., those that are required, those
560   that modify the semantics of the response).
561</t>
562<t>
563   New HTTP status codes are required to fall under one of the categories
564   defined in <xref target="status.codes"/>. To allow existing parsers to
565   properly handle them, new status codes cannot disallow a response body,
566   although they can mandate a zero-length response body. They can require the
567   presence of one or more particular HTTP response header(s).
568</t>
569<t>
570   Likewise, their definitions can specify that caches are allowed to use
571   heuristics to determine their freshness (see <xref target="Part6"/>; by default, it is
572   not allowed), and can define how to determine the resource which they
573   carry a representation for (see <xref target="identifying.response.associated.with.representation"/>; by default,
574   it is anonymous).
575</t>
576</section>
577
578</section>
579
580</section>
581
582<section title="Response Header Fields" anchor="response.header.fields">
583 
584<t>
585   The response header fields allow the server to pass additional
586   information about the response which cannot be placed in the Status-Line.
587   These header fields give information about the server and about
588   further access to the target resource (Section 4.3 of <xref target="Part1"/>).
589</t>
590<texttable align="left">
591  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
592
593  <c>Accept-Ranges</c> <c>Section 5.1 of <xref target="Part5"/></c>
594  <c>Age</c> <c>Section 3.1 of <xref target="Part6"/></c>
595  <c>Allow</c> <c><xref target="header.allow"/></c>
596  <c>ETag</c> <c>Section 2.2 of <xref target="Part4"/></c>
597  <c>Location</c> <c><xref target="header.location"/></c>
598  <c>Proxy-Authenticate</c> <c>Section 4.2 of <xref target="Part7"/></c>
599  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
600  <c>Server</c> <c><xref target="header.server"/></c>
601  <c>Vary</c> <c>Section 3.5 of <xref target="Part6"/></c>
602  <c>WWW-Authenticate</c> <c>Section 4.4 of <xref target="Part7"/></c>
603</texttable>
604</section>
605
606<section title="Representation" anchor="representation">
607<t>
608   Request and Response messages MAY transfer a representation if not otherwise
609   restricted by the request method or response status code. A representation
610   consists of metadata (representation header fields) and data (representation
611   body).  When a complete or partial representation is enclosed in an HTTP message,
612   it is referred to as the payload of the message. HTTP representations
613   are defined in <xref target="Part3"/>.
614</t>
615<t>
616   A representation body is only present in a message when a message-body is
617   present, as described in Section 3.3 of <xref target="Part1"/>. The representation body is obtained
618   from the message-body by decoding any Transfer-Encoding that might
619   have been applied to ensure safe and proper transfer of the message.
620</t>
621
622<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
623<t>
624   It is sometimes necessary to determine an identifier for the resource
625   associated with a representation.
626</t>
627<t>
628   An HTTP request representation, when present, is always associated with an
629   anonymous (i.e., unidentified) resource.
630</t>
631<t>
632   In the common case, an HTTP response is a representation of the target
633   resource (see Section 4.3 of <xref target="Part1"/>). However, this is not always the
634   case. To determine the URI of the resource a response is associated with,
635   the following rules are used (with the first applicable one being selected):
636</t>
637<t><list style="numbers">
638   <t>If the response status code is 200 or 203 and the request method was GET,
639   the response payload is a representation of the target resource.</t>
640   <t>If the response status code is 204, 206, or 304 and the request method was GET
641   or HEAD, the response payload is a partial representation of the target
642   resource (see Section 2.8 of <xref target="Part6"/>).</t>
643   <t>If the response has a Content-Location header field, and that URI is the same
644   as the effective request URI, the response payload is a representation of the
645   target resource.</t>
646   <t>If the response has a Content-Location header field, and that URI is not the
647   same as the effective request URI, then the response asserts that its
648   payload is a representation of the resource identified by the
649   Content-Location URI. However, such an assertion cannot be trusted unless
650   it can be verified by other means (not defined by HTTP).</t>
651   <t>Otherwise, the response is a representation of an anonymous (i.e.,
652   unidentified) resource.</t>
653</list></t>
654<t>
655  <cref anchor="TODO-req-uri">
656   The comparison function is going to have to be defined somewhere,
657   because we already need to compare URIs for things like cache invalidation.</cref>
658</t>
659</section>
660
661</section>
662
663
664<section title="Method Definitions" anchor="method.definitions">
665<t>
666   The set of common request methods for HTTP/1.1 is defined below. Although
667   this set can be expanded, additional methods cannot be assumed to
668   share the same semantics for separately extended clients and servers.
669</t>
670
671<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
672
673<section title="Safe Methods" anchor="safe.methods">
674<iref item="Safe Methods" primary="true"/>
675<t>
676   Implementors need to be aware that the software represents the user in
677   their interactions over the Internet, and need to allow
678   the user to be aware of any actions they take which might have an
679   unexpected significance to themselves or others.
680</t>
681<t>
682   In particular, the convention has been established that the GET, HEAD,
683   OPTIONS, and TRACE request methods SHOULD NOT have the significance
684   of taking an action other than retrieval. These request methods ought
685   to be considered "safe".
686   This allows user agents to represent other methods, such as POST, PUT
687   and DELETE, in a special way, so that the user is made aware of the
688   fact that a possibly unsafe action is being requested.
689</t>
690<t>
691   Naturally, it is not possible to ensure that the server does not
692   generate side-effects as a result of performing a GET request; in
693   fact, some dynamic resources consider that a feature. The important
694   distinction here is that the user did not request the side-effects,
695   so therefore cannot be held accountable for them.
696</t>
697</section>
698
699<section title="Idempotent Methods" anchor="idempotent.methods">
700<iref item="Idempotent Methods" primary="true"/>
701<t>
702   Request methods can also have the property of "idempotence" in that,
703   aside from error or expiration issues, the intended effect of multiple
704   identical requests is the same as for a single request.
705   PUT, DELETE, and all safe request methods are idempotent.
706   It is important to note that idempotence refers only to changes
707   requested by the client: a server is free to change its state due
708   to multiple requests for the purpose of tracking those requests,
709   versioning of results, etc.
710</t>
711</section>
712</section>
713
714<section title="OPTIONS" anchor="OPTIONS">
715 
716  <iref primary="true" item="OPTIONS method"/>
717  <iref primary="true" item="Methods" subitem="OPTIONS"/>
718<t>
719   The OPTIONS method requests information about the
720   communication options available on the request/response chain
721   identified by the effective request URI. This method allows a client to
722   determine the options and/or requirements associated with a resource,
723   or the capabilities of a server, without implying a resource action
724   or initiating a resource retrieval.
725</t>
726<t>
727   Responses to the OPTIONS method are not cacheable.
728</t>
729<t>
730   If the OPTIONS request includes a message-body (as indicated by the
731   presence of Content-Length or Transfer-Encoding), then the media type
732   MUST be indicated by a Content-Type field. Although this
733   specification does not define any use for such a body, future
734   extensions to HTTP might use the OPTIONS body to make more detailed
735   queries on the server.
736</t>
737<t>
738   If the request-target is an asterisk ("*"), the OPTIONS request is
739   intended to apply to the server in general rather than to a specific
740   resource. Since a server's communication options typically depend on
741   the resource, the "*" request is only useful as a "ping" or "no-op"
742   type of method; it does nothing beyond allowing the client to test
743   the capabilities of the server. For example, this can be used to test
744   a proxy for HTTP/1.1 compliance (or lack thereof).
745</t>
746<t>
747   If the request-target is not an asterisk, the OPTIONS request applies
748   only to the options that are available when communicating with that
749   resource.
750</t>
751<t>
752   A 200 response SHOULD include any header fields that indicate
753   optional features implemented by the server and applicable to that
754   resource (e.g., Allow), possibly including extensions not defined by
755   this specification. The response body, if any, SHOULD also include
756   information about the communication options. The format for such a
757   body is not defined by this specification, but might be defined by
758   future extensions to HTTP. Content negotiation MAY be used to select
759   the appropriate response format. If no response body is included, the
760   response MUST include a Content-Length field with a field-value of
761   "0".
762</t>
763<t>
764   The Max-Forwards header field MAY be used to target a
765   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
766   If no Max-Forwards field is present in the request, then the forwarded
767   request MUST NOT include a Max-Forwards field.
768</t>
769</section>
770
771<section title="GET" anchor="GET">
772 
773  <iref primary="true" item="GET method"/>
774  <iref primary="true" item="Methods" subitem="GET"/>
775<t>
776   The GET method requests transfer of a current representation of
777   the target resource.
778</t>
779<t>   
780   If the target resource is a data-producing process, it is the
781   produced data which shall be returned as the representation in the response and not
782   the source text of the process, unless that text happens to be the output of
783   the process.
784</t>
785<t>
786   The semantics of the GET method change to a "conditional GET" if the
787   request message includes an If-Modified-Since, If-Unmodified-Since,
788   If-Match, If-None-Match, or If-Range header field. A conditional GET
789   requests that the representation be transferred only under the
790   circumstances described by the conditional header field(s). The
791   conditional GET request is intended to reduce unnecessary network
792   usage by allowing cached representations to be refreshed without requiring
793   multiple requests or transferring data already held by the client.
794</t>
795<t>
796   The semantics of the GET method change to a "partial GET" if the
797   request message includes a Range header field. A partial GET requests
798   that only part of the representation be transferred, as described in Section 5.4 of <xref target="Part5"/>.
799   The partial GET request is intended to reduce unnecessary
800   network usage by allowing partially-retrieved representations to be
801   completed without transferring data already held by the client.
802</t>
803<t>
804   Bodies on GET requests have no defined semantics. Note that sending a body
805   on a GET request might cause some existing implementations to reject the
806   request.
807</t>
808<t>
809   The response to a GET request is cacheable and MAY be used to satisfy
810   subsequent GET and HEAD requests (see <xref target="Part6"/>).
811</t>
812<t>
813   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
814</t>
815</section>
816
817<section title="HEAD" anchor="HEAD">
818 
819  <iref primary="true" item="HEAD method"/>
820  <iref primary="true" item="Methods" subitem="HEAD"/>
821<t>
822   The HEAD method is identical to GET except that the server MUST NOT
823   return a message-body in the response. The metadata contained
824   in the HTTP header fields in response to a HEAD request SHOULD be identical
825   to the information sent in response to a GET request. This method can
826   be used for obtaining metadata about the representation implied by the
827   request without transferring the representation body. This method is
828   often used for testing hypertext links for validity, accessibility,
829   and recent modification.
830</t>
831<t>
832   The response to a HEAD request is cacheable and MAY be used to satisfy
833   a subsequent HEAD request; see <xref target="Part6"/>. It also MAY be used to update a previously cached
834   representation from that resource; if the new field values
835   indicate that the cached representation differs from the current representation (as
836   would be indicated by a change in Content-Length, Content-MD5, ETag
837   or Last-Modified), then the cache MUST treat the cache entry as
838   stale.
839</t>
840<t>
841   Bodies on HEAD requests have no defined semantics. Note that sending a body
842   on a HEAD request might cause some existing implementations to reject the
843   request.
844</t>
845</section>
846
847<section title="POST" anchor="POST">
848  <iref primary="true" item="POST method"/>
849  <iref primary="true" item="Methods" subitem="POST"/>
850<t>
851   The POST method requests that the origin server accept the
852   representation enclosed in the request as data to be processed by the
853   target resource. POST is designed to allow a uniform method to cover the
854   following functions:
855  <list style="symbols">
856    <t>
857      Annotation of existing resources;
858    </t>
859    <t>
860        Posting a message to a bulletin board, newsgroup, mailing list,
861        or similar group of articles;
862    </t>
863    <t>
864        Providing a block of data, such as the result of submitting a
865        form, to a data-handling process;
866    </t>
867    <t>
868        Extending a database through an append operation.
869    </t>
870  </list>
871</t>
872<t>
873   The actual function performed by the POST method is determined by the
874   server and is usually dependent on the effective request URI.
875</t>
876<t>
877   The action performed by the POST method might not result in a
878   resource that can be identified by a URI. In this case, either 200
879   (OK) or 204 (No Content) is the appropriate response status code,
880   depending on whether or not the response includes a representation that
881   describes the result.
882</t>
883<t>
884   If a resource has been created on the origin server, the response
885   SHOULD be 201 (Created) and contain a representation which describes the
886   status of the request and refers to the new resource, and a Location
887   header field (see <xref target="header.location"/>).
888</t>
889<t>
890   Responses to POST requests are only cacheable when they
891   include explicit freshness information (see Section 2.3.1 of <xref target="Part6"/>). A
892   cached POST response with a Content-Location header field
893   (see Section 6.7 of <xref target="Part3"/>) whose value is the effective
894   Request URI MAY be used to satisfy subsequent GET and HEAD requests.
895</t>
896<t>
897   Note that POST caching is not widely implemented.
898   However, the 303 (See Other) response can be used to direct the
899   user agent to retrieve a cacheable resource.
900</t>
901</section>
902
903<section title="PUT" anchor="PUT">
904  <iref primary="true" item="PUT method"/>
905  <iref primary="true" item="Methods" subitem="PUT"/>
906<t>
907   The PUT method requests that the state of the target resource
908   be created or replaced with the state defined by the representation
909   enclosed in the request message payload.  A successful PUT of a given
910   representation would suggest that a subsequent GET on that same target
911   resource will result in an equivalent representation being returned in
912   a 200 (OK) response.  However, there is no guarantee that such a state
913   change will be observable, since the target resource might be acted
914   upon by other user agents in parallel, or might be subject to dynamic
915   processing by the origin server, before any subsequent GET is received.
916   A successful response only implies that the user agent's intent was
917   achieved at the time of its processing by the origin server.
918</t>
919<t>   
920   If the target resource does not have a current representation and
921   the PUT successfully creates one, then the origin server MUST inform
922   the user agent by sending a 201 (Created) response.  If the target
923   resource does have a current representation and that representation is
924   successfully modified in accordance with the state of the enclosed
925   representation, then either a 200 (OK) or 204 (No Content) response
926   SHOULD be sent to indicate successful completion of the request.
927</t>
928<t>
929   Unrecognized header fields SHOULD be ignored (i.e., not saved
930   as part of the resource state).
931</t>
932<t>
933   An origin server SHOULD verify that the PUT representation is
934   consistent with any constraints which the server has for the target
935   resource that cannot or will not be changed by the PUT.  This is
936   particularly important when the origin server uses internal
937   configuration information related to the URI in order to set the
938   values for representation metadata on GET responses.  When a PUT
939   representation is inconsistent with the target resource, the origin
940   server SHOULD either make them consistent, by transforming the
941   representation or changing the resource configuration, or respond
942   with an appropriate error message containing sufficient information
943   to explain why the representation is unsuitable.  The 409 (Conflict)
944   or 415 (Unsupported Media Type) status codes are suggested, with the
945   latter being specific to constraints on Content-Type values.
946</t>
947<t>
948   For example, if the target resource is configured to always have a
949   Content-Type of "text/html" and the representation being PUT has a
950   Content-Type of "image/jpeg", then the origin server SHOULD do one of:
951   (a) reconfigure the target resource to reflect the new media type;
952   (b) transform the PUT representation to a format consistent with that
953   of the resource before saving it as the new resource state; or,
954   (c) reject the request with a 415 response indicating that the target
955   resource is limited to "text/html", perhaps including a link to a
956   different resource that would be a suitable target for the new
957   representation.
958</t>
959<t>
960   HTTP does not define exactly how a PUT method affects the state
961   of an origin server beyond what can be expressed by the intent of
962   the user agent request and the semantics of the origin server response.
963   It does not define what a resource might be, in any sense of that
964   word, beyond the interface provided via HTTP.  It does not define
965   how resource state is "stored", nor how such storage might change
966   as a result of a change in resource state, nor how the origin server
967   translates resource state into representations.  Generally speaking,
968   all implementation details behind the resource interface are
969   intentionally hidden by the server.
970</t>
971<t>
972   The fundamental difference between the POST and PUT methods is
973   highlighted by the different intent for the target resource.
974   The target resource in a POST request is intended to handle the
975   enclosed representation as a data-accepting process, such as for
976   a gateway to some other protocol or a document that accepts annotations.
977   In contrast, the target resource in a PUT request is intended to
978   take the enclosed representation as a new or replacement value.
979   Hence, the intent of PUT is idempotent and visible to intermediaries,
980   even though the exact effect is only known by the origin server.
981</t>
982<t>
983   Proper interpretation of a PUT request presumes that the user agent
984   knows what target resource is desired.  A service that is intended
985   to select a proper URI on behalf of the client, after receiving
986   a state-changing request, SHOULD be implemented using the POST
987   method rather than PUT.  If the origin server will not make the
988   requested PUT state change to the target resource and instead
989   wishes to have it applied to a different resource, such as when the
990   resource has been moved to a different URI, then the origin server
991   MUST send a 301 (Moved Permanently) response; the user agent MAY
992   then make its own decision regarding whether or not to redirect the
993   request.
994</t>
995<t>
996   A PUT request applied to the target resource MAY have side-effects
997   on other resources.  For example, an article might have a URI for
998   identifying "the current version" (a resource) which is separate
999   from the URIs identifying each particular version (different
1000   resources that at one point shared the same state as the current version
1001   resource).  A successful PUT request on "the current version" URI might
1002   therefore create a new version resource in addition to changing the
1003   state of the target resource, and might also cause links to be added
1004   between the related resources.
1005</t>
1006<t>
1007   An origin server SHOULD reject any PUT request that contains a
1008   Content-Range header field, since it might be misinterpreted as
1009   partial content (or might be partial content that is being mistakenly
1010   PUT as a full representation).  Partial content updates are
1011   possible by targeting a separately identified resource with state
1012   that overlaps a portion of the larger resource, or by using a
1013   different method that has been specifically defined for partial
1014   updates (for example, the PATCH method defined in
1015   <xref target="RFC5789"/>).
1016</t>
1017<t>
1018   Responses to the PUT method are not cacheable. If a PUT request passes
1019   through a cache that has one or more stored responses for the effective
1020   request URI, those stored responses will be invalidated (see
1021   Section 2.5 of <xref target="Part6"/>).
1022</t>
1023</section>
1024
1025<section title="DELETE" anchor="DELETE">
1026  <iref primary="true" item="DELETE method"/>
1027  <iref primary="true" item="Methods" subitem="DELETE"/>
1028<t>
1029   The DELETE method requests that the origin server delete the target
1030   resource. This method MAY be overridden by
1031   human intervention (or other means) on the origin server. The client cannot
1032   be guaranteed that the operation has been carried out, even if the
1033   status code returned from the origin server indicates that the action
1034   has been completed successfully. However, the server SHOULD NOT
1035   indicate success unless, at the time the response is given, it
1036   intends to delete the resource or move it to an inaccessible
1037   location.
1038</t>
1039<t>
1040   A successful response SHOULD be 200 (OK) if the response includes an
1041   representation describing the status, 202 (Accepted) if the action has not
1042   yet been enacted, or 204 (No Content) if the action has been enacted
1043   but the response does not include a representation.
1044</t>
1045<t>
1046   Bodies on DELETE requests have no defined semantics. Note that sending a body
1047   on a DELETE request might cause some existing implementations to reject the
1048   request.
1049</t>
1050<t>
1051   Responses to the DELETE method are not cacheable. If a DELETE request
1052   passes through a cache that has one or more stored responses for the
1053   effective request URI, those stored responses will be invalidated (see
1054   Section 2.5 of <xref target="Part6"/>).
1055</t>
1056</section>
1057
1058<section title="TRACE" anchor="TRACE">
1059 
1060  <iref primary="true" item="TRACE method"/>
1061  <iref primary="true" item="Methods" subitem="TRACE"/>
1062<t>
1063   The TRACE method requests a remote, application-layer loop-back
1064   of the request message. The final recipient of the request
1065   SHOULD reflect the message received back to the client as the
1066   message-body of a 200 (OK) response. The final recipient is either the
1067   origin server or the first proxy to receive a Max-Forwards
1068   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
1069   A TRACE request MUST NOT include a message-body.
1070</t>
1071<t>
1072   TRACE allows the client to see what is being received at the other
1073   end of the request chain and use that data for testing or diagnostic
1074   information. The value of the Via header field (Section 9.9 of <xref target="Part1"/>) is of
1075   particular interest, since it acts as a trace of the request chain.
1076   Use of the Max-Forwards header field allows the client to limit the
1077   length of the request chain, which is useful for testing a chain of
1078   proxies forwarding messages in an infinite loop.
1079</t>
1080<t>
1081   If the request is valid, the response SHOULD have a Content-Type of
1082   "message/http" (see Section 10.3.1 of <xref target="Part1"/>) and contain a message-body
1083   that encloses a copy of the entire request message.
1084   Responses to the TRACE method are not cacheable.
1085</t>
1086</section>
1087
1088<section title="CONNECT" anchor="CONNECT">
1089  <iref primary="true" item="CONNECT method"/>
1090  <iref primary="true" item="Methods" subitem="CONNECT"/>
1091<t>
1092   The CONNECT method requests that the proxy establish a tunnel
1093   to the request-target and then restrict its behavior to blind
1094   forwarding of packets until the connection is closed.
1095</t>
1096<t>
1097   When using CONNECT, the request-target MUST use the authority form
1098   (Section 4.1.2 of <xref target="Part1"/>); i.e., the request-target consists of only the
1099   host name and port number of the tunnel destination, separated by a colon.
1100   For example,
1101</t>
1102<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1103  CONNECT server.example.com:80 HTTP/1.1
1104  Host: server.example.com:80
1105 
1106  ]]></artwork></figure>
1107<t>
1108   Other HTTP mechanisms can be used normally with the CONNECT method —
1109   except end-to-end protocol Upgrade requests, since the
1110   tunnel must be established first.
1111</t>
1112<t>
1113   For example, proxy authentication might be used to establish the
1114   authority to create a tunnel:
1115</t>
1116<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1117  CONNECT server.example.com:80 HTTP/1.1
1118  Host: server.example.com:80
1119  Proxy-Authorization: basic aGVsbG86d29ybGQ=
1120 
1121  ]]></artwork></figure>
1122<t>
1123   Bodies on CONNECT requests have no defined semantics. Note that sending a body
1124   on a CONNECT request might cause some existing implementations to reject the
1125   request.
1126</t>
1127<t>
1128   Like any other pipelined HTTP/1.1 request, data to be tunnel may be
1129   sent immediately after the blank line. The usual caveats also apply:
1130   data may be discarded if the eventual response is negative, and the
1131   connection may be reset with no response if more than one TCP segment
1132   is outstanding.
1133</t>
1134
1135<section title="Establishing a Tunnel with CONNECT">
1136<t>
1137   Any successful (2xx) response to a CONNECT request indicates that the
1138   proxy has established a connection to the requested host and port,
1139   and has switched to tunneling the current connection to that server
1140   connection.
1141</t>
1142<t>
1143   It may be the case that the proxy itself can only reach the requested
1144   origin server through another proxy.  In this case, the first proxy
1145   SHOULD make a CONNECT request of that next proxy, requesting a tunnel
1146   to the authority.  A proxy MUST NOT respond with any 2xx status code
1147   unless it has either a direct or tunnel connection established to the
1148   authority.
1149</t>
1150<t>
1151   An origin server which receives a CONNECT request for itself MAY
1152   respond with a 2xx status code to indicate that a connection is
1153   established.
1154</t>
1155<t>
1156   If at any point either one of the peers gets disconnected, any
1157   outstanding data that came from that peer will be passed to the other
1158   one, and after that also the other connection will be terminated by
1159   the proxy. If there is outstanding data to that peer undelivered,
1160   that data will be discarded.
1161</t>
1162
1163</section>
1164</section>
1165</section>
1166
1167
1168<section title="Status Code Definitions" anchor="status.codes">
1169<t>
1170   Each Status-Code is described below, including any metadata required
1171   in the response.
1172</t>
1173
1174<section title="Informational 1xx" anchor="status.1xx">
1175<t>
1176   This class of status code indicates a provisional response,
1177   consisting only of the Status-Line and optional header fields, and is
1178   terminated by an empty line. There are no required header fields for this
1179   class of status code. Since HTTP/1.0 did not define any 1xx status
1180   codes, servers MUST NOT send a 1xx response to an HTTP/1.0 client
1181   except under experimental conditions.
1182</t>
1183<t>
1184   A client MUST be prepared to accept one or more 1xx status responses
1185   prior to a regular response, even if the client does not expect a 100
1186   (Continue) status message. Unexpected 1xx status responses MAY be
1187   ignored by a user agent.
1188</t>
1189<t>
1190   Proxies MUST forward 1xx responses, unless the connection between the
1191   proxy and its client has been closed, or unless the proxy itself
1192   requested the generation of the 1xx response. (For example, if a
1193   proxy adds a "Expect: 100-continue" field when it forwards a request,
1194   then it need not forward the corresponding 100 (Continue)
1195   response(s).)
1196</t>
1197
1198<section title="100 Continue" anchor="status.100">
1199  <iref primary="true" item="100 Continue (status code)"/>
1200  <iref primary="true" item="Status Codes" subitem="100 Continue"/>
1201<t>
1202   The client SHOULD continue with its request. This interim response is
1203   used to inform the client that the initial part of the request has
1204   been received and has not yet been rejected by the server. The client
1205   SHOULD continue by sending the remainder of the request or, if the
1206   request has already been completed, ignore this response. The server
1207   MUST send a final response after the request has been completed. See
1208   Section 7.2.3 of <xref target="Part1"/> for detailed discussion of the use and handling of this
1209   status code.
1210</t>
1211</section>
1212
1213<section title="101 Switching Protocols" anchor="status.101">
1214  <iref primary="true" item="101 Switching Protocols (status code)"/>
1215  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols"/>
1216<t>
1217   The server understands and is willing to comply with the client's
1218   request, via the Upgrade message header field (Section 9.8 of <xref target="Part1"/>), for a
1219   change in the application protocol being used on this connection. The
1220   server will switch protocols to those defined by the response's
1221   Upgrade header field immediately after the empty line which
1222   terminates the 101 response.
1223</t>
1224<t>
1225   The protocol SHOULD be switched only when it is advantageous to do
1226   so. For example, switching to a newer version of HTTP is advantageous
1227   over older versions, and switching to a real-time, synchronous
1228   protocol might be advantageous when delivering resources that use
1229   such features.
1230</t>
1231</section>
1232</section>
1233
1234<section title="Successful 2xx" anchor="status.2xx">
1235<t>
1236   This class of status code indicates that the client's request was
1237   successfully received, understood, and accepted.
1238</t>
1239
1240<section title="200 OK" anchor="status.200">
1241  <iref primary="true" item="200 OK (status code)"/>
1242  <iref primary="true" item="Status Codes" subitem="200 OK"/>
1243<t>
1244   The request has succeeded. The payload returned with the response
1245   is dependent on the method used in the request, for example:
1246  <list style="hanging">
1247    <t hangText="GET">
1248      a representation of the target resource is sent in the response;
1249    </t>
1250    <t hangText="HEAD">
1251      the same representation as GET, except without the message-body;
1252    </t>
1253    <t hangText="POST">
1254      a representation describing or containing the result of the action;
1255    </t>
1256    <t hangText="TRACE">
1257      a representation containing the request message as received by the
1258      end server.
1259    </t>
1260  </list>
1261</t>
1262<t>
1263   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine
1264   freshness for 200 responses.
1265</t>
1266</section>
1267
1268<section title="201 Created" anchor="status.201">
1269  <iref primary="true" item="201 Created (status code)"/>
1270  <iref primary="true" item="Status Codes" subitem="201 Created"/>
1271<t>
1272   The request has been fulfilled and has resulted in a new resource being
1273   created. The newly created resource can be referenced by the URI(s)
1274   returned in the payload of the response, with the most specific URI
1275   for the resource given by a Location header field. The response
1276   SHOULD include a payload containing a list of resource
1277   characteristics and location(s) from which the user or user agent can
1278   choose the one most appropriate. The payload format is specified by
1279   the media type given in the Content-Type header field. The origin
1280   server MUST create the resource before returning the 201 status code.
1281   If the action cannot be carried out immediately, the server SHOULD
1282   respond with 202 (Accepted) response instead.
1283</t>
1284<t>
1285   A 201 response MAY contain an ETag response header field indicating
1286   the current value of the entity-tag for the representation of the resource
1287   just created (see Section 2.2 of <xref target="Part4"/>).
1288</t>
1289</section>
1290
1291<section title="202 Accepted" anchor="status.202">
1292  <iref primary="true" item="202 Accepted (status code)"/>
1293  <iref primary="true" item="Status Codes" subitem="202 Accepted"/>
1294<t>
1295   The request has been accepted for processing, but the processing has
1296   not been completed.  The request might or might not eventually be
1297   acted upon, as it might be disallowed when processing actually takes
1298   place. There is no facility for re-sending a status code from an
1299   asynchronous operation such as this.
1300</t>
1301<t>
1302   The 202 response is intentionally non-committal. Its purpose is to
1303   allow a server to accept a request for some other process (perhaps a
1304   batch-oriented process that is only run once per day) without
1305   requiring that the user agent's connection to the server persist
1306   until the process is completed. The representation returned with this
1307   response SHOULD include an indication of the request's current status
1308   and either a pointer to a status monitor or some estimate of when the
1309   user can expect the request to be fulfilled.
1310</t>
1311</section>
1312
1313<section title="203 Non-Authoritative Information" anchor="status.203">
1314  <iref primary="true" item="203 Non-Authoritative Information (status code)"/>
1315  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information"/>
1316<t>
1317   The representation in the response has been transformed or otherwise
1318   modified by a transforming proxy (Section 2.4 of <xref target="Part1"/>).  Note that the
1319   behaviour of transforming intermediaries is controlled by the no-transform
1320   Cache-Control directive (Section 3.2 of <xref target="Part6"/>).
1321</t>
1322<t>
1323   This status code is only appropriate when the response status code would
1324   have been 200 (OK) otherwise. When the status code before transformation
1325   would have been different, the 214 Transformation Applied warn-code
1326   (Section 3.6 of <xref target="Part6"/>) is appropriate.
1327</t>
1328<t>
1329   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine
1330   freshness for 203 responses.
1331</t>
1332</section>
1333
1334<section title="204 No Content" anchor="status.204">
1335  <iref primary="true" item="204 No Content (status code)"/>
1336  <iref primary="true" item="Status Codes" subitem="204 No Content"/>
1337<t>
1338   The 204 (No Content) status code indicates that the server has
1339   successfully fulfilled the request and that there is no additional
1340   content to return in the response payload body.  Metadata in the
1341   response header fields refer to the target resource and its current
1342   representation after the requested action.
1343</t>
1344<t>
1345   For example, if a 204 status code is received in response to a PUT
1346   request and the response contains an ETag header field, then the PUT
1347   was successful and the ETag field-value contains the entity-tag for
1348   the new representation of that target resource.
1349</t>
1350<t>
1351   The 204 response allows a server to indicate that the action has been
1352   successfully applied to the target resource while implying that the
1353   user agent SHOULD NOT traverse away from its current "document view"
1354   (if any).  The server assumes that the user agent will provide some
1355   indication of the success to its user, in accord with its own interface,
1356   and apply any new or updated metadata in the response to the active
1357   representation.
1358</t>
1359<t>
1360   For example, a 204 status code is commonly used with document editing
1361   interfaces corresponding to a "save" action, such that the document
1362   being saved remains available to the user for editing. It is also
1363   frequently used with interfaces that expect automated data transfers
1364   to be prevalent, such as within distributed version control systems.
1365</t>
1366<t>
1367   The 204 response MUST NOT include a message-body, and thus is always
1368   terminated by the first empty line after the header fields.
1369</t>
1370</section>
1371
1372<section title="205 Reset Content" anchor="status.205">
1373  <iref primary="true" item="205 Reset Content (status code)"/>
1374  <iref primary="true" item="Status Codes" subitem="205 Reset Content"/>
1375<t>
1376   The server has fulfilled the request and the user agent SHOULD reset
1377   the document view which caused the request to be sent. This response
1378   is primarily intended to allow input for actions to take place via
1379   user input, followed by a clearing of the form in which the input is
1380   given so that the user can easily initiate another input action.
1381</t>
1382<t>   
1383   The message-body included with the response MUST be empty. Note that
1384   receivers still need to parse the response according to the algorithm defined
1385   in Section 3.3 of <xref target="Part1"/>.
1386</t>
1387</section>
1388
1389<section title="206 Partial Content" anchor="status.206">
1390  <iref primary="true" item="206 Partial Content (status code)"/>
1391  <iref primary="true" item="Status Codes" subitem="206 Partial Content"/>
1392 
1393<t>
1394   The server has fulfilled the partial GET request for the resource
1395   and the enclosed payload is a partial representation as defined in Section 3.1 of <xref target="Part5"/>.
1396</t>
1397<t>
1398   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine
1399   freshness for 206 responses.
1400</t>
1401</section>
1402</section>
1403
1404<section title="Redirection 3xx" anchor="status.3xx">
1405<t>
1406   This class of status code indicates that further action needs to be
1407   taken by the user agent in order to fulfill the request.  The action
1408   required MAY be carried out by the user agent without interaction
1409   with the user if and only if the method used in the second request is
1410   known to be "safe", as defined in <xref target="safe.methods"/>.
1411   A client SHOULD detect infinite redirection loops, since such loops
1412   generate network traffic for each redirection.
1413</t>
1414<t><list>
1415  <t>
1416    Note: An earlier version of this specification recommended a
1417    maximum of five redirections (<xref target="RFC2068"/>, Section 10.3).
1418    Content developers need to be aware that some clients might
1419    implement such a fixed limitation.
1420  </t>
1421</list></t>
1422
1423<section title="300 Multiple Choices" anchor="status.300">
1424  <iref primary="true" item="300 Multiple Choices (status code)"/>
1425  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices"/>
1426<t>
1427   The target resource has more than one
1428   representation, each with its own specific location, and agent-driven
1429   negotiation information (Section 5 of <xref target="Part3"/>) is being provided so that
1430   the user (or user agent) can select a preferred representation by
1431   redirecting its request to that location.
1432</t>
1433<t>
1434   Unless it was a HEAD request, the response SHOULD include a representation
1435   containing a list of representation metadata and location(s) from
1436   which the user or user agent can choose the one most appropriate. The
1437   data format is specified by the media type given in the Content-Type
1438   header field. Depending upon the format and the capabilities of
1439   the user agent, selection of the most appropriate choice MAY be
1440   performed automatically. However, this specification does not define
1441   any standard for such automatic selection.
1442</t>
1443<t>
1444   If the server has a preferred choice of representation, it SHOULD
1445   include the specific URI for that representation in the Location
1446   field; user agents MAY use the Location field value for automatic
1447   redirection.
1448</t>
1449<t>
1450   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine
1451   freshness for 300 responses.
1452</t>
1453
1454</section>
1455
1456<section title="301 Moved Permanently" anchor="status.301">
1457  <iref primary="true" item="301 Moved Permanently (status code)"/>
1458  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently"/>
1459<t>
1460   The target resource has been assigned a new permanent URI and any
1461   future references to this resource SHOULD use one of the returned
1462   URIs.  Clients with link editing capabilities ought to automatically
1463   re-link references to the effective request URI to one or more of the new
1464   references returned by the server, where possible.
1465</t>
1466<t>
1467   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine
1468   freshness for 301 responses.
1469</t>
1470<t>
1471   The new permanent URI SHOULD be given by the Location field in the
1472   response. Unless the request method was HEAD, the representation of the
1473   response SHOULD contain a short hypertext note with a hyperlink to
1474   the new URI(s).
1475</t>
1476<t>
1477   If the 301 status code is received in response to a request method
1478   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1479   then the request MAY be automatically redirected by the user agent without
1480   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
1481   request unless it can be confirmed by the user, since this might
1482   change the conditions under which the request was issued.
1483</t>
1484<t><list>
1485  <t>
1486    Note: When automatically redirecting a POST request after
1487    receiving a 301 status code, some existing HTTP/1.0 user agents
1488    will erroneously change it into a GET request.
1489  </t>
1490</list></t>
1491</section>
1492
1493<section title="302 Found" anchor="status.302">
1494  <iref primary="true" item="302 Found (status code)"/>
1495  <iref primary="true" item="Status Codes" subitem="302 Found"/>
1496<t>
1497   The target resource resides temporarily under a different URI.
1498   Since the redirection might be altered on occasion, the client SHOULD
1499   continue to use the effective request URI for future requests.
1500</t>
1501<t>
1502   The temporary URI SHOULD be given by the Location field in the
1503   response. Unless the request method was HEAD, the representation of the
1504   response SHOULD contain a short hypertext note with a hyperlink to
1505   the new URI(s).
1506</t>
1507<t>
1508   If the 302 status code is received in response to a request method
1509   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1510   then the request MAY be automatically redirected by the user agent without
1511   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
1512   request unless it can be confirmed by the user, since this might
1513   change the conditions under which the request was issued.
1514</t>
1515<t><list>
1516  <t>
1517    Note: HTTP/1.0 (<xref target="RFC1945"/>, Section 9.3)
1518    and the first version of HTTP/1.1 (<xref target="RFC2068"/>, Section 10.3.3)
1519    specify that the client is not allowed to change the method on the
1520    redirected request.  However, most existing user agent implementations
1521    treat 302 as if it were a 303 response, performing a GET on the Location
1522    field-value regardless of the original request method. Therefore, a
1523    previous version of this specification
1524    (<xref target="RFC2616"/>, Section 10.3.3) has added the
1525    status codes
1526    <xref target="status.303" format="none">303</xref> and
1527    <xref target="status.307" format="none">307</xref> for servers that wish
1528    to make unambiguously clear which kind of reaction is expected of the
1529    client.
1530  </t>
1531</list></t>
1532</section>
1533
1534<section title="303 See Other" anchor="status.303">
1535  <iref primary="true" item="303 See Other (status code)"/>
1536  <iref primary="true" item="Status Codes" subitem="303 See Other"/>
1537<t>
1538   The server directs the user agent to a different resource, indicated
1539   by a URI in the Location header field, that provides an indirect
1540   response to the original request.  The user agent MAY perform a GET
1541   request on the URI in the Location field in order to obtain a
1542   representation corresponding to the response, be redirected again,
1543   or end with an error status.  The Location URI is not a substitute
1544   reference for the effective request URI.
1545</t>
1546<t>
1547   The 303 status code is generally applicable to any HTTP method.  It is
1548   primarily used to allow the output of a POST action to redirect
1549   the user agent to a selected resource, since doing so provides the
1550   information corresponding to the POST response in a form that
1551   can be separately identified, bookmarked, and cached independent
1552   of the original request.
1553</t>
1554<t>
1555   A 303 response to a GET request indicates that the requested
1556   resource does not have a representation of its own that can be
1557   transferred by the server over HTTP.  The Location URI indicates a
1558   resource that is descriptive of the target resource, such that the
1559   follow-on representation might be useful to recipients without
1560   implying that it adequately represents the target resource.
1561   Note that answers to the questions of what can be represented, what
1562   representations are adequate, and what might be a useful description
1563   are outside the scope of HTTP and thus entirely determined by the
1564   URI owner(s).
1565</t>
1566<t>
1567   Except for responses to a HEAD request, the representation of a 303
1568   response SHOULD contain a short hypertext note with a hyperlink
1569   to the Location URI.
1570</t>
1571</section>
1572
1573<section title="304 Not Modified" anchor="status.304">
1574  <iref primary="true" item="304 Not Modified (status code)"/>
1575  <iref primary="true" item="Status Codes" subitem="304 Not Modified"/>
1576 
1577<t>
1578   The response to the request has not been modified since the conditions
1579   indicated by the client's conditional GET request, as defined in Section 4.1 of <xref target="Part4"/>.
1580</t>
1581</section>
1582
1583<section title="305 Use Proxy" anchor="status.305">
1584  <iref primary="true" item="305 Use Proxy (status code)"/>
1585  <iref primary="true" item="Status Codes" subitem="305 Use Proxy"/>
1586<t>
1587   The 305 status code was defined in a previous version of this specification
1588   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1589</t>
1590</section>
1591
1592<section title="306 (Unused)" anchor="status.306">
1593  <iref primary="true" item="306 (Unused) (status code)"/>
1594  <iref primary="true" item="Status Codes" subitem="306 (Unused)"/>
1595<t>
1596   The 306 status code was used in a previous version of the
1597   specification, is no longer used, and the code is reserved.
1598</t>
1599</section>
1600
1601<section title="307 Temporary Redirect" anchor="status.307">
1602  <iref primary="true" item="307 Temporary Redirect (status code)"/>
1603  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect"/>
1604<t>
1605   The target resource resides temporarily under a different URI.
1606   Since the redirection can change over time, the client SHOULD
1607   continue to use the effective request URI for future requests.
1608</t>
1609<t>
1610   The temporary URI SHOULD be given by the Location field in the
1611   response. Unless the request method was HEAD, the representation of the
1612   response SHOULD contain a short hypertext note with a hyperlink to
1613   the new URI(s), since many pre-HTTP/1.1 user agents do not
1614   understand the 307 status code. Therefore, the note SHOULD contain the
1615   information necessary for a user to repeat the original request on
1616   the new URI.
1617</t>
1618<t>
1619   If the 307 status code is received in response to a request method
1620   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1621   then the request MAY be automatically redirected by the user agent without
1622   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
1623   request unless it can be confirmed by the user, since this might
1624   change the conditions under which the request was issued.
1625</t>
1626</section>
1627</section>
1628
1629<section title="Client Error 4xx" anchor="status.4xx">
1630<t>
1631   The 4xx class of status code is intended for cases in which the
1632   client seems to have erred. Except when responding to a HEAD request,
1633   the server SHOULD include a representation containing an explanation of the
1634   error situation, and whether it is a temporary or permanent
1635   condition. These status codes are applicable to any request method.
1636   User agents SHOULD display any included representation to the user.
1637</t>
1638<t>
1639   If the client is sending data, a server implementation using TCP
1640   SHOULD be careful to ensure that the client acknowledges receipt of
1641   the packet(s) containing the response, before the server closes the
1642   input connection. If the client continues sending data to the server
1643   after the close, the server's TCP stack will send a reset packet to
1644   the client, which might erase the client's unacknowledged input buffers
1645   before they can be read and interpreted by the HTTP application.
1646</t>
1647
1648<section title="400 Bad Request" anchor="status.400">
1649  <iref primary="true" item="400 Bad Request (status code)"/>
1650  <iref primary="true" item="Status Codes" subitem="400 Bad Request"/>
1651<t>
1652   The request could not be understood by the server due to malformed
1653   syntax. The client SHOULD NOT repeat the request without
1654   modifications.
1655</t>
1656</section>
1657
1658<section title="401 Unauthorized" anchor="status.401">
1659  <iref primary="true" item="401 Unauthorized (status code)"/>
1660  <iref primary="true" item="Status Codes" subitem="401 Unauthorized"/>
1661 
1662<t>
1663   The request requires user authentication (see Section 3.1 of <xref target="Part7"/>).
1664</t>
1665</section>
1666
1667<section title="402 Payment Required" anchor="status.402">
1668  <iref primary="true" item="402 Payment Required (status code)"/>
1669  <iref primary="true" item="Status Codes" subitem="402 Payment Required"/>
1670<t>
1671   This code is reserved for future use.
1672</t>
1673</section>
1674
1675<section title="403 Forbidden" anchor="status.403">
1676  <iref primary="true" item="403 Forbidden (status code)"/>
1677  <iref primary="true" item="Status Codes" subitem="403 Forbidden"/>
1678<t>
1679   The server understood the request, but refuses to authorize it. Providing
1680   different user authentication credentials might be successful, but any
1681   credentials that were provided in the request are insufficient. The request
1682   SHOULD NOT be repeated with the same credentials.
1683</t>
1684<t>
1685   If the request method was not HEAD and the server wishes to make
1686   public why the request has not been fulfilled, it SHOULD describe the
1687   reason for the refusal in the representation.  If the server does not wish to
1688   make this information available to the client, the status code 404
1689   (Not Found) MAY be used instead.
1690</t>
1691</section>
1692
1693<section title="404 Not Found" anchor="status.404">
1694  <iref primary="true" item="404 Not Found (status code)"/>
1695  <iref primary="true" item="Status Codes" subitem="404 Not Found"/>
1696<t>
1697   The server has not found anything matching the effective request URI. No
1698   indication is given of whether the condition is temporary or
1699   permanent. The 410 (Gone) status code SHOULD be used if the server
1700   knows, through some internally configurable mechanism, that an old
1701   resource is permanently unavailable and has no forwarding address.
1702   This status code is commonly used when the server does not wish to
1703   reveal exactly why the request has been refused, or when no other
1704   response is applicable.
1705</t>
1706</section>
1707
1708<section title="405 Method Not Allowed" anchor="status.405">
1709  <iref primary="true" item="405 Method Not Allowed (status code)"/>
1710  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed"/>
1711<t>
1712   The method specified in the Request-Line is not allowed for the target
1713   resource. The response MUST include an Allow header field containing a
1714   list of valid methods for the requested resource.
1715</t>
1716</section>
1717
1718<section title="406 Not Acceptable" anchor="status.406">
1719  <iref primary="true" item="406 Not Acceptable (status code)"/>
1720  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable"/>
1721<t>
1722   The resource identified by the request is only capable of generating
1723   response representations which have content characteristics not acceptable
1724   according to the accept header fields sent in the request.
1725</t>
1726<t>
1727   Unless it was a HEAD request, the response SHOULD include a representation
1728   containing a list of available representation characteristics and location(s)
1729   from which the user or user agent can choose the one most
1730   appropriate. The data format is specified by the media type given
1731   in the Content-Type header field. Depending upon the format and the
1732   capabilities of the user agent, selection of the most appropriate
1733   choice MAY be performed automatically. However, this specification
1734   does not define any standard for such automatic selection.
1735</t>
1736<t><list>
1737  <t>
1738    Note: HTTP/1.1 servers are allowed to return responses which are
1739    not acceptable according to the accept header fields sent in the
1740    request. In some cases, this might even be preferable to sending a
1741    406 response. User agents are encouraged to inspect the header fields of
1742    an incoming response to determine if it is acceptable.
1743  </t>
1744</list></t>
1745<t>
1746   If the response could be unacceptable, a user agent SHOULD
1747   temporarily stop receipt of more data and query the user for a
1748   decision on further actions.
1749</t>
1750</section>
1751
1752<section title="407 Proxy Authentication Required" anchor="status.407">
1753  <iref primary="true" item="407 Proxy Authentication Required (status code)"/>
1754  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required"/>
1755<t>
1756   This code is similar to 401 (Unauthorized), but indicates that the
1757   client must first authenticate itself with the proxy (see Section 3.2 of <xref target="Part7"/>).
1758</t>
1759</section>
1760
1761<section title="408 Request Timeout" anchor="status.408">
1762  <iref primary="true" item="408 Request Timeout (status code)"/>
1763  <iref primary="true" item="Status Codes" subitem="408 Request Timeout"/>
1764<t>
1765   The client did not produce a request within the time that the server
1766   was prepared to wait. The client MAY repeat the request without
1767   modifications at any later time.
1768</t>
1769</section>
1770
1771<section title="409 Conflict" anchor="status.409">
1772  <iref primary="true" item="409 Conflict (status code)"/>
1773  <iref primary="true" item="Status Codes" subitem="409 Conflict"/>
1774<t>
1775   The request could not be completed due to a conflict with the current
1776   state of the resource. This code is only allowed in situations where
1777   it is expected that the user might be able to resolve the conflict
1778   and resubmit the request. The response body SHOULD include enough
1779   information for the user to recognize the source of the conflict.
1780   Ideally, the response representation would include enough information for the
1781   user or user agent to fix the problem; however, that might not be
1782   possible and is not required.
1783</t>
1784<t>
1785   Conflicts are most likely to occur in response to a PUT request. For
1786   example, if versioning were being used and the representation being PUT
1787   included changes to a resource which conflict with those made by an
1788   earlier (third-party) request, the server might use the 409 response
1789   to indicate that it can't complete the request. In this case, the
1790   response representation would likely contain a list of the differences
1791   between the two versions in a format defined by the response
1792   Content-Type.
1793</t>
1794</section>
1795
1796<section title="410 Gone" anchor="status.410">
1797  <iref primary="true" item="410 Gone (status code)"/>
1798  <iref primary="true" item="Status Codes" subitem="410 Gone"/>
1799<t>
1800   The target resource is no longer available at the server and no
1801   forwarding address is known. This condition is expected to be
1802   considered permanent. Clients with link editing capabilities SHOULD
1803   delete references to the effective request URI after user approval. If the
1804   server does not know, or has no facility to determine, whether or not
1805   the condition is permanent, the status code 404 (Not Found) SHOULD be
1806   used instead.
1807</t>
1808<t>
1809   The 410 response is primarily intended to assist the task of web
1810   maintenance by notifying the recipient that the resource is
1811   intentionally unavailable and that the server owners desire that
1812   remote links to that resource be removed. Such an event is common for
1813   limited-time, promotional services and for resources belonging to
1814   individuals no longer working at the server's site. It is not
1815   necessary to mark all permanently unavailable resources as "gone" or
1816   to keep the mark for any length of time — that is left to the
1817   discretion of the server owner.
1818</t>
1819<t>
1820   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine freshness
1821   for 410 responses.
1822</t>
1823
1824</section>
1825
1826<section title="411 Length Required" anchor="status.411">
1827  <iref primary="true" item="411 Length Required (status code)"/>
1828  <iref primary="true" item="Status Codes" subitem="411 Length Required"/>
1829<t>
1830   The server refuses to accept the request without a defined Content-Length.
1831   The client MAY repeat the request if it adds a valid
1832   Content-Length header field containing the length of the message-body
1833   in the request message.
1834</t>
1835</section>
1836
1837<section title="412 Precondition Failed" anchor="status.412">
1838  <iref primary="true" item="412 Precondition Failed (status code)"/>
1839  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed"/>
1840 
1841<t>
1842   The precondition given in one or more of the header fields
1843   evaluated to false when it was tested on the server, as defined in
1844   Section 4.2 of <xref target="Part4"/>.
1845</t>
1846</section>
1847
1848<section title="413 Request Representation Too Large" anchor="status.413">
1849  <iref primary="true" item="413 Request Representation Too Large (status code)"/>
1850  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large"/>
1851<t>
1852   The server is refusing to process a request because the request
1853   representation is larger than the server is willing or able to process. The
1854   server MAY close the connection to prevent the client from continuing
1855   the request.
1856</t>
1857<t>
1858   If the condition is temporary, the server SHOULD include a Retry-After
1859   header field to indicate that it is temporary and after what
1860   time the client MAY try again.
1861</t>
1862</section>
1863
1864<section title="414 URI Too Long" anchor="status.414">
1865  <iref primary="true" item="414 URI Too Long (status code)"/>
1866  <iref primary="true" item="Status Codes" subitem="414 URI Too Long"/>
1867<t>
1868   The server is refusing to service the request because the effective request URI
1869   is longer than the server is willing to interpret. This rare
1870   condition is only likely to occur when a client has improperly
1871   converted a POST request to a GET request with long query
1872   information, when the client has descended into a URI "black hole" of
1873   redirection (e.g., a redirected URI prefix that points to a suffix of
1874   itself), or when the server is under attack by a client attempting to
1875   exploit security holes present in some servers using fixed-length
1876   buffers for reading or manipulating the effective request URI.
1877</t>
1878</section>
1879
1880<section title="415 Unsupported Media Type" anchor="status.415">
1881  <iref primary="true" item="415 Unsupported Media Type (status code)"/>
1882  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type"/>
1883<t>
1884   The server is refusing to service the request because the request
1885   payload is in a format not supported by this request method on the
1886   target resource.
1887</t>
1888</section>
1889
1890<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1891  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)"/>
1892  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable"/>
1893 
1894<t>
1895   The request included a Range header field (Section 5.4 of <xref target="Part5"/>) and none of
1896   the range-specifier values in this field overlap the current extent
1897   of the selected resource. See Section 3.2 of <xref target="Part5"/>.
1898</t>
1899</section>
1900
1901<section title="417 Expectation Failed" anchor="status.417">
1902  <iref primary="true" item="417 Expectation Failed (status code)"/>
1903  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed"/>
1904<t>
1905   The expectation given in an Expect header field (see <xref target="header.expect"/>)
1906   could not be met by this server, or, if the server is a proxy,
1907   the server has unambiguous evidence that the request could not be met
1908   by the next-hop server.
1909</t>
1910</section>
1911
1912<section title="426 Upgrade Required" anchor="status.426">
1913  <iref primary="true" item="426 Upgrade Required (status code)"/>
1914  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required"/>
1915<t>
1916   The request can not be completed without a prior protocol upgrade. This
1917   response MUST include an Upgrade header field (Section 9.8 of <xref target="Part1"/>)
1918   specifying the required protocols.
1919</t>
1920<figure>
1921<preamble>Example:</preamble>
1922<artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1923  HTTP/1.1 426 Upgrade Required
1924  Upgrade: HTTP/2.0
1925  Connection: Upgrade
1926 
1927  ]]></artwork></figure>
1928<t>
1929   The server SHOULD include a message body in the 426 response which
1930   indicates in human readable form the reason for the error and describes any
1931   alternative courses which may be available to the user.
1932</t>
1933</section>
1934</section>
1935
1936<section title="Server Error 5xx" anchor="status.5xx">
1937<t>
1938   Response status codes beginning with the digit "5" indicate cases in
1939   which the server is aware that it has erred or is incapable of
1940   performing the request. Except when responding to a HEAD request, the
1941   server SHOULD include a representation containing an explanation of the
1942   error situation, and whether it is a temporary or permanent
1943   condition. User agents SHOULD display any included representation to the
1944   user. These response codes are applicable to any request method.
1945</t>
1946
1947<section title="500 Internal Server Error" anchor="status.500">
1948  <iref primary="true" item="500 Internal Server Error (status code)"/>
1949  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error"/>
1950<t>
1951   The server encountered an unexpected condition which prevented it
1952   from fulfilling the request.
1953</t>
1954</section>
1955
1956<section title="501 Not Implemented" anchor="status.501">
1957  <iref primary="true" item="501 Not Implemented (status code)"/>
1958  <iref primary="true" item="Status Codes" subitem="501 Not Implemented"/>
1959<t>
1960   The server does not support the functionality required to fulfill the
1961   request. This is the appropriate response when the server does not
1962   recognize the request method and is not capable of supporting it for
1963   any resource.
1964</t>
1965</section>
1966
1967<section title="502 Bad Gateway" anchor="status.502">
1968  <iref primary="true" item="502 Bad Gateway (status code)"/>
1969  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway"/>
1970<t>
1971   The server, while acting as a gateway or proxy, received an invalid
1972   response from the upstream server it accessed in attempting to
1973   fulfill the request.
1974</t>
1975</section>
1976
1977<section title="503 Service Unavailable" anchor="status.503">
1978  <iref primary="true" item="503 Service Unavailable (status code)"/>
1979  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable"/>
1980<t>
1981   The server is currently unable or unwilling to handle the request due to
1982   reasons such as temporary overloading, maintenance of the server, or rate
1983   limiting of the client.
1984</t>
1985<t>
1986   The implication is that this is a temporary condition which will be
1987   alleviated after some delay. If known, the length of the delay MAY be
1988   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
1989   If no Retry-After is given, the client SHOULD handle the response as it
1990   would for a 500 response.
1991</t>
1992<t><list>
1993  <t>
1994    Note: The existence of the 503 status code does not imply that a
1995    server must use it when becoming overloaded. Some servers might wish
1996    to simply refuse the connection.
1997  </t>
1998</list></t>
1999</section>
2000
2001<section title="504 Gateway Timeout" anchor="status.504">
2002  <iref primary="true" item="504 Gateway Timeout (status code)"/>
2003  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout"/>
2004<t>
2005   The server, while acting as a gateway or proxy, did not receive a
2006   timely response from the upstream server specified by the URI (e.g.,
2007   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2008   to access in attempting to complete the request.
2009</t>
2010<t><list>
2011  <t>
2012    Note to implementors: some deployed proxies are known to
2013    return 400 or 500 when DNS lookups time out.
2014  </t>
2015</list></t>
2016</section>
2017
2018<section title="505 HTTP Version Not Supported" anchor="status.505">
2019  <iref primary="true" item="505 HTTP Version Not Supported (status code)"/>
2020  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported"/>
2021<t>
2022   The server does not support, or refuses to support, the protocol
2023   version that was used in the request message. The server is
2024   indicating that it is unable or unwilling to complete the request
2025   using the same major version as the client, as described in Section 2.6 of <xref target="Part1"/>,
2026   other than with this error message. The response SHOULD contain
2027   a representation describing why that version is not supported and what other
2028   protocols are supported by that server.
2029</t>
2030
2031</section>
2032</section>
2033</section>
2034
2035
2036<section title="Header Field Definitions" anchor="header.fields">
2037<t>
2038   This section defines the syntax and semantics of HTTP/1.1 header fields
2039   related to request and response semantics.
2040</t>
2041
2042<section title="Allow" anchor="header.allow">
2043  <iref primary="true" item="Allow header field"/>
2044  <iref primary="true" item="Header Fields" subitem="Allow"/>
2045 
2046<t>
2047   The "Allow" header field lists the set of methods advertised as
2048   supported by the target resource. The purpose of this field is strictly to
2049   inform the recipient of valid request methods associated with the resource.
2050</t>
2051<figure><iref primary="true" item="Grammar" subitem="Allow"/><artwork type="abnf2616"><![CDATA[
2052  Allow = #Method
2053]]></artwork></figure>
2054<t>
2055   Example of use:
2056</t>
2057<figure><artwork type="example"><![CDATA[
2058  Allow: GET, HEAD, PUT
2059]]></artwork></figure>
2060<t>
2061   The actual set of allowed methods is defined by the origin server at the
2062   time of each request.
2063</t>
2064<t>
2065   A proxy MUST NOT modify the Allow header field — it does not need to
2066   understand all the methods specified in order to handle them according to
2067   the generic message handling rules.
2068</t>
2069</section>
2070
2071<section title="Expect" anchor="header.expect">
2072  <iref primary="true" item="Expect header field"/>
2073  <iref primary="true" item="Header Fields" subitem="Expect"/>
2074 
2075 
2076 
2077 
2078<t>
2079   The "Expect" header field is used to indicate that particular
2080   server behaviors are required by the client.
2081</t>
2082<figure><iref primary="true" item="Grammar" subitem="Expect"/><iref primary="true" item="Grammar" subitem="expectation"/><iref primary="true" item="Grammar" subitem="expectation-extension"/><iref primary="true" item="Grammar" subitem="expect-params"/><artwork type="abnf2616"><![CDATA[
2083  Expect       = 1#expectation
2084 
2085  expectation  = "100-continue" / expectation-extension
2086  expectation-extension = token [ "=" ( token / quoted-string )
2087                           *expect-params ]
2088  expect-params = ";" token [ "=" ( token / quoted-string ) ]
2089]]></artwork></figure>
2090<t>
2091   A server that does not understand or is unable to comply with any of
2092   the expectation values in the Expect field of a request MUST respond
2093   with appropriate error status code. The server MUST respond with a 417
2094   (Expectation Failed) status code if any of the expectations cannot be met
2095   or, if there are other problems with the request, some other 4xx
2096   status code.
2097</t>
2098<t>
2099   This header field is defined with extensible syntax to allow for
2100   future extensions. If a server receives a request containing an
2101   Expect field that includes an expectation-extension that it does not
2102   support, it MUST respond with a 417 (Expectation Failed) status code.
2103</t>
2104<t>
2105   Comparison of expectation values is case-insensitive for unquoted
2106   tokens (including the 100-continue token), and is case-sensitive for
2107   quoted-string expectation-extensions.
2108</t>
2109<t>
2110   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy MUST
2111   return a 417 (Expectation Failed) status code if it receives a request
2112   with an expectation that it cannot meet. However, the Expect
2113   header field itself is end-to-end; it MUST be forwarded if the
2114   request is forwarded.
2115</t>
2116<t>
2117   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
2118   Expect header field.
2119</t>
2120<t>
2121   See Section 7.2.3 of <xref target="Part1"/> for the use of the 100 (Continue) status code.
2122</t>
2123</section>
2124
2125<section title="From" anchor="header.from">
2126  <iref primary="true" item="From header field"/>
2127  <iref primary="true" item="Header Fields" subitem="From"/>
2128 
2129 
2130<t>
2131   The "From" header field, if given, SHOULD contain an Internet
2132   e-mail address for the human user who controls the requesting user
2133   agent. The address SHOULD be machine-usable, as defined by "mailbox"
2134   in Section 3.4 of <xref target="RFC5322"/>:
2135</t>
2136<figure><iref primary="true" item="Grammar" subitem="From"/><artwork type="abnf2616"><![CDATA[
2137  From    = mailbox
2138 
2139  mailbox = <mailbox, defined in [RFC5322], Section 3.4>
2140]]></artwork></figure>
2141<t>
2142   An example is:
2143</t>
2144<figure><artwork type="example"><![CDATA[
2145  From: webmaster@example.org
2146]]></artwork></figure>
2147<t>
2148   This header field MAY be used for logging purposes and as a means for
2149   identifying the source of invalid or unwanted requests. It SHOULD NOT
2150   be used as an insecure form of access protection. The interpretation
2151   of this field is that the request is being performed on behalf of the
2152   person given, who accepts responsibility for the method performed. In
2153   particular, robot agents SHOULD include this header field so that the
2154   person responsible for running the robot can be contacted if problems
2155   occur on the receiving end.
2156</t>
2157<t>
2158   The Internet e-mail address in this field MAY be separate from the
2159   Internet host which issued the request. For example, when a request
2160   is passed through a proxy the original issuer's address SHOULD be
2161   used.
2162</t>
2163<t>
2164   The client SHOULD NOT  send the From header field without the user's
2165   approval, as it might conflict with the user's privacy interests or
2166   their site's security policy. It is strongly recommended that the
2167   user be able to disable, enable, and modify the value of this field
2168   at any time prior to a request.
2169</t>
2170</section>
2171
2172<section title="Location" anchor="header.location">
2173  <iref primary="true" item="Location header field"/>
2174  <iref primary="true" item="Header Fields" subitem="Location"/>
2175 
2176<t>
2177   The "Location" header field is used to identify a newly created
2178   resource, or to redirect the recipient to a different location for
2179   completion of the request.
2180</t>
2181<t>
2182   For 201 (Created) responses, the Location is the URI of the new resource
2183   which was created by the request. For 3xx responses, the location SHOULD
2184   indicate the server's preferred URI for automatic redirection to the
2185   resource.
2186</t>
2187<t>
2188   The field value consists of a single URI-reference. When it has the form
2189   of a relative reference (<xref target="RFC3986"/>, Section 4.2),
2190   the final value is computed by resolving it against the effective request
2191   URI (<xref target="RFC3986"/>, Section 5).
2192</t>
2193<figure><iref primary="true" item="Grammar" subitem="Location"/><artwork type="abnf2616"><![CDATA[
2194  Location = URI-reference
2195]]></artwork></figure>
2196<figure>
2197<preamble>Examples are:</preamble><!--DO NOT DARE changing the vertical WSP below, it's necessary this way for xml2rfc-->
2198<artwork type="example"><![CDATA[
2199  Location: http://www.example.org/pub/WWW/People.html#tim
2200]]></artwork></figure><figure><artwork type="example"><![CDATA[  Location: /index.html
2201]]></artwork></figure>
2202<t>
2203   There are circumstances in which a fragment identifier in a Location URI
2204   would not be appropriate. For instance, when it appears in a 201 Created
2205   response, where the Location header field specifies the URI for the entire
2206   created resource.
2207</t>
2208<t><list>
2209  <t>
2210    Note: This specification does not define precedence rules
2211    for the case where the original URI, as navigated to by the user
2212    agent, and the Location header field value both contain fragment
2213    identifiers. Thus be aware that including fragment identifiers might
2214    inconvenience anyone relying on the semantics of the original URI's
2215    fragment identifier.
2216  </t>
2217</list></t>
2218<t><list>
2219  <t>
2220    Note: The Content-Location header field (Section 6.7 of <xref target="Part3"/>) differs
2221    from Location in that the Content-Location identifies the most specific
2222    resource corresponding to the enclosed representation.
2223    It is therefore possible for a response to contain header fields for
2224    both Location and Content-Location.
2225  </t>
2226</list></t>
2227</section>
2228
2229<section title="Max-Forwards" anchor="header.max-forwards">
2230  <iref primary="true" item="Max-Forwards header field"/>
2231  <iref primary="true" item="Header Fields" subitem="Max-Forwards"/>
2232 
2233<t>
2234   The "Max-Forwards" header field provides a mechanism with the
2235   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2236   methods to limit the number of times that the request is forwarded by
2237   proxies. This can be useful when the client is attempting to
2238   trace a request which appears to be failing or looping in mid-chain.
2239</t>
2240<figure><iref primary="true" item="Grammar" subitem="Max-Forwards"/><artwork type="abnf2616"><![CDATA[
2241  Max-Forwards = 1*DIGIT
2242]]></artwork></figure>
2243<t>
2244   The Max-Forwards value is a decimal integer indicating the remaining
2245   number of times this request message can be forwarded.
2246</t>
2247<t>
2248   Each recipient of a TRACE or OPTIONS request
2249   containing a Max-Forwards header field MUST check and update its
2250   value prior to forwarding the request. If the received value is zero
2251   (0), the recipient MUST NOT forward the request; instead, it MUST
2252   respond as the final recipient. If the received Max-Forwards value is
2253   greater than zero, then the forwarded message MUST contain an updated
2254   Max-Forwards field with a value decremented by one (1).
2255</t>
2256<t>
2257   The Max-Forwards header field MAY be ignored for all other request
2258   methods.
2259</t>
2260</section>
2261
2262<section title="Referer" anchor="header.referer">
2263  <iref primary="true" item="Referer header field"/>
2264  <iref primary="true" item="Header Fields" subitem="Referer"/>
2265 
2266<t>
2267   The "Referer" [sic] header field allows the client to specify the
2268   URI of the resource from which the effective request URI was obtained (the
2269   "referrer", although the header field is misspelled.).
2270</t>
2271<t>
2272   The Referer header field allows servers to generate lists of back-links to
2273   resources for interest, logging, optimized caching, etc. It also allows
2274   obsolete or mistyped links to be traced for maintenance. Some servers use
2275   Referer as a means of controlling where they allow links from (so-called
2276   "deep linking"), but legitimate requests do not always
2277   contain a Referer header field.
2278</t>
2279<t>
2280   If the effective request URI was obtained from a source that does not have its own
2281   URI (e.g., input from the user keyboard), the Referer field MUST either be
2282   sent with the value "about:blank", or not be sent at all. Note that this
2283   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2284</t>
2285<figure><iref primary="true" item="Grammar" subitem="Referer"/><artwork type="abnf2616"><![CDATA[
2286  Referer = absolute-URI / partial-URI
2287]]></artwork></figure>
2288<t>
2289   Example:
2290</t>
2291<figure><artwork type="example"><![CDATA[
2292  Referer: http://www.example.org/hypertext/Overview.html
2293]]></artwork></figure>
2294<t>
2295   If the field value is a relative URI, it SHOULD be interpreted
2296   relative to the effective request URI. The URI MUST NOT include a fragment. See
2297   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2298</t>
2299</section>
2300
2301<section title="Retry-After" anchor="header.retry-after">
2302  <iref primary="true" item="Retry-After header field"/>
2303  <iref primary="true" item="Header Fields" subitem="Retry-After"/>
2304 
2305<t>
2306   The header "Retry-After" field can be used with a 503 (Service
2307   Unavailable) response to indicate how long the service is expected to
2308   be unavailable to the requesting client. This field MAY also be used
2309   with any 3xx (Redirection) response to indicate the minimum time the
2310   user-agent is asked wait before issuing the redirected request.
2311</t>
2312<t>
2313   The value of this field can be either an HTTP-date or an integer number
2314   of seconds (in decimal) after the time of the response.
2315</t>
2316<figure><iref primary="true" item="Grammar" subitem="Retry-After"/><artwork type="abnf2616"><![CDATA[
2317  Retry-After = HTTP-date / delta-seconds
2318]]></artwork></figure>
2319<t anchor="rule.delta-seconds">
2320 
2321   Time spans are non-negative decimal integers, representing time in
2322   seconds.
2323</t>
2324<figure><iref primary="true" item="Grammar" subitem="delta-seconds"/><artwork type="abnf2616"><![CDATA[
2325  delta-seconds  = 1*DIGIT
2326]]></artwork></figure>
2327<t>
2328   Two examples of its use are
2329</t>
2330<figure><artwork type="example"><![CDATA[
2331  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2332  Retry-After: 120
2333]]></artwork></figure>
2334<t>
2335   In the latter example, the delay is 2 minutes.
2336</t>
2337</section>
2338
2339<section title="Server" anchor="header.server">
2340  <iref primary="true" item="Server header field"/>
2341  <iref primary="true" item="Header Fields" subitem="Server"/>
2342 
2343<t>
2344   The "Server" header field contains information about the
2345   software used by the origin server to handle the request.
2346</t>
2347<t>
2348   The field can contain multiple product tokens (Section 6.3 of <xref target="Part1"/>) and
2349   comments (Section 3.2 of <xref target="Part1"/>) identifying the server and any significant
2350   subproducts. The product tokens are listed in order of their significance
2351   for identifying the application.
2352</t>
2353<figure><iref primary="true" item="Grammar" subitem="Server"/><artwork type="abnf2616"><![CDATA[
2354  Server = product *( RWS ( product / comment ) )
2355]]></artwork></figure>
2356<t>
2357   Example:
2358</t>
2359<figure><artwork type="example"><![CDATA[
2360  Server: CERN/3.0 libwww/2.17
2361]]></artwork></figure>
2362<t>
2363   If the response is being forwarded through a proxy, the proxy
2364   application MUST NOT modify the Server header field. Instead, it
2365   MUST include a Via field (as described in Section 9.9 of <xref target="Part1"/>).
2366</t>
2367<t><list>
2368  <t>
2369    Note: Revealing the specific software version of the server might
2370    allow the server machine to become more vulnerable to attacks
2371    against software that is known to contain security holes. Server
2372    implementors are encouraged to make this field a configurable
2373    option.
2374  </t>
2375</list></t>
2376</section>
2377
2378<section title="User-Agent" anchor="header.user-agent">
2379  <iref primary="true" item="User-Agent header field"/>
2380  <iref primary="true" item="Header Fields" subitem="User-Agent"/>
2381 
2382<t>
2383   The "User-Agent" header field contains information about the user
2384   agent originating the request. User agents SHOULD include this field with
2385   requests.
2386</t>
2387<t>
2388   Typically, it is used for statistical purposes, the tracing of protocol
2389   violations, and tailoring responses to avoid particular user agent
2390   limitations.
2391</t>
2392<t>
2393   The field can contain multiple product tokens (Section 6.3 of <xref target="Part1"/>)
2394   and comments (Section 3.2 of <xref target="Part1"/>) identifying the agent and its
2395   significant subproducts. By convention, the product tokens are listed in
2396   order of their significance for identifying the application.
2397</t>
2398<t>
2399   Because this field is usually sent on every request a user agent makes,
2400   implementations are encouraged not to include needlessly fine-grained
2401   detail, and to limit (or even prohibit) the addition of subproducts by third
2402   parties. Overly long and detailed User-Agent field values make requests
2403   larger and can also be used to identify ("fingerprint") the user against
2404   their wishes.
2405</t>
2406<t>
2407   Likewise, implementations are encouraged not to use the product tokens of
2408   other implementations in order to declare compatibility with them, as this
2409   circumvents the purpose of the field. Finally, they are encouraged not to
2410   use comments to identify products; doing so makes the field value more
2411   difficult to parse.
2412</t>
2413<figure><iref primary="true" item="Grammar" subitem="User-Agent"/><artwork type="abnf2616"><![CDATA[
2414  User-Agent = product *( RWS ( product / comment ) )
2415]]></artwork></figure>
2416<t>
2417   Example:
2418</t>
2419<figure><artwork type="example"><![CDATA[
2420  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2421]]></artwork></figure>
2422</section>
2423
2424</section>
2425
2426<section title="IANA Considerations" anchor="IANA.considerations">
2427
2428<section title="Method Registry" anchor="method.registration">
2429<t>
2430  The registration procedure for HTTP request methods is defined by
2431  <xref target="method.registry"/> of this document.
2432</t>
2433<t>
2434   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2435   and be populated with the registrations below:
2436</t>
2437
2438<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2439<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2440   <ttcol>Method</ttcol>
2441   <ttcol>Safe</ttcol>
2442   <ttcol>Reference</ttcol>
2443   <c>CONNECT</c>
2444   <c>no</c>
2445   <c>
2446      <xref target="CONNECT"/>
2447   </c>
2448   <c>DELETE</c>
2449   <c>no</c>
2450   <c>
2451      <xref target="DELETE"/>
2452   </c>
2453   <c>GET</c>
2454   <c>yes</c>
2455   <c>
2456      <xref target="GET"/>
2457   </c>
2458   <c>HEAD</c>
2459   <c>yes</c>
2460   <c>
2461      <xref target="HEAD"/>
2462   </c>
2463   <c>OPTIONS</c>
2464   <c>yes</c>
2465   <c>
2466      <xref target="OPTIONS"/>
2467   </c>
2468   <c>POST</c>
2469   <c>no</c>
2470   <c>
2471      <xref target="POST"/>
2472   </c>
2473   <c>PUT</c>
2474   <c>no</c>
2475   <c>
2476      <xref target="PUT"/>
2477   </c>
2478   <c>TRACE</c>
2479   <c>yes</c>
2480   <c>
2481      <xref target="TRACE"/>
2482   </c>
2483</texttable>
2484<!--(END)-->
2485
2486</section>
2487
2488<section title="Status Code Registry" anchor="status.code.registration">
2489<t>
2490   The registration procedure for HTTP Status Codes — previously defined
2491   in Section 7.1 of <xref target="RFC2817"/> — is now defined
2492   by <xref target="status.code.registry"/> of this document.
2493</t>
2494<t>
2495   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2496   shall be updated with the registrations below:
2497</t>
2498
2499<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2500<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2501   <ttcol>Value</ttcol>
2502   <ttcol>Description</ttcol>
2503   <ttcol>Reference</ttcol>
2504   <c>100</c>
2505   <c>Continue</c>
2506   <c>
2507      <xref target="status.100"/>
2508   </c>
2509   <c>101</c>
2510   <c>Switching Protocols</c>
2511   <c>
2512      <xref target="status.101"/>
2513   </c>
2514   <c>200</c>
2515   <c>OK</c>
2516   <c>
2517      <xref target="status.200"/>
2518   </c>
2519   <c>201</c>
2520   <c>Created</c>
2521   <c>
2522      <xref target="status.201"/>
2523   </c>
2524   <c>202</c>
2525   <c>Accepted</c>
2526   <c>
2527      <xref target="status.202"/>
2528   </c>
2529   <c>203</c>
2530   <c>Non-Authoritative Information</c>
2531   <c>
2532      <xref target="status.203"/>
2533   </c>
2534   <c>204</c>
2535   <c>No Content</c>
2536   <c>
2537      <xref target="status.204"/>
2538   </c>
2539   <c>205</c>
2540   <c>Reset Content</c>
2541   <c>
2542      <xref target="status.205"/>
2543   </c>
2544   <c>300</c>
2545   <c>Multiple Choices</c>
2546   <c>
2547      <xref target="status.300"/>
2548   </c>
2549   <c>301</c>
2550   <c>Moved Permanently</c>
2551   <c>
2552      <xref target="status.301"/>
2553   </c>
2554   <c>302</c>
2555   <c>Found</c>
2556   <c>
2557      <xref target="status.302"/>
2558   </c>
2559   <c>303</c>
2560   <c>See Other</c>
2561   <c>
2562      <xref target="status.303"/>
2563   </c>
2564   <c>305</c>
2565   <c>Use Proxy</c>
2566   <c>
2567      <xref target="status.305"/>
2568   </c>
2569   <c>306</c>
2570   <c>(Unused)</c>
2571   <c>
2572      <xref target="status.306"/>
2573   </c>
2574   <c>307</c>
2575   <c>Temporary Redirect</c>
2576   <c>
2577      <xref target="status.307"/>
2578   </c>
2579   <c>400</c>
2580   <c>Bad Request</c>
2581   <c>
2582      <xref target="status.400"/>
2583   </c>
2584   <c>402</c>
2585   <c>Payment Required</c>
2586   <c>
2587      <xref target="status.402"/>
2588   </c>
2589   <c>403</c>
2590   <c>Forbidden</c>
2591   <c>
2592      <xref target="status.403"/>
2593   </c>
2594   <c>404</c>
2595   <c>Not Found</c>
2596   <c>
2597      <xref target="status.404"/>
2598   </c>
2599   <c>405</c>
2600   <c>Method Not Allowed</c>
2601   <c>
2602      <xref target="status.405"/>
2603   </c>
2604   <c>406</c>
2605   <c>Not Acceptable</c>
2606   <c>
2607      <xref target="status.406"/>
2608   </c>
2609   <c>407</c>
2610   <c>Proxy Authentication Required</c>
2611   <c>
2612      <xref target="status.407"/>
2613   </c>
2614   <c>408</c>
2615   <c>Request Timeout</c>
2616   <c>
2617      <xref target="status.408"/>
2618   </c>
2619   <c>409</c>
2620   <c>Conflict</c>
2621   <c>
2622      <xref target="status.409"/>
2623   </c>
2624   <c>410</c>
2625   <c>Gone</c>
2626   <c>
2627      <xref target="status.410"/>
2628   </c>
2629   <c>411</c>
2630   <c>Length Required</c>
2631   <c>
2632      <xref target="status.411"/>
2633   </c>
2634   <c>413</c>
2635   <c>Request Representation Too Large</c>
2636   <c>
2637      <xref target="status.413"/>
2638   </c>
2639   <c>414</c>
2640   <c>URI Too Long</c>
2641   <c>
2642      <xref target="status.414"/>
2643   </c>
2644   <c>415</c>
2645   <c>Unsupported Media Type</c>
2646   <c>
2647      <xref target="status.415"/>
2648   </c>
2649   <c>417</c>
2650   <c>Expectation Failed</c>
2651   <c>
2652      <xref target="status.417"/>
2653   </c>
2654   <c>426</c>
2655   <c>Upgrade Required</c>
2656   <c>
2657      <xref target="status.426"/>
2658   </c>
2659   <c>500</c>
2660   <c>Internal Server Error</c>
2661   <c>
2662      <xref target="status.500"/>
2663   </c>
2664   <c>501</c>
2665   <c>Not Implemented</c>
2666   <c>
2667      <xref target="status.501"/>
2668   </c>
2669   <c>502</c>
2670   <c>Bad Gateway</c>
2671   <c>
2672      <xref target="status.502"/>
2673   </c>
2674   <c>503</c>
2675   <c>Service Unavailable</c>
2676   <c>
2677      <xref target="status.503"/>
2678   </c>
2679   <c>504</c>
2680   <c>Gateway Timeout</c>
2681   <c>
2682      <xref target="status.504"/>
2683   </c>
2684   <c>505</c>
2685   <c>HTTP Version Not Supported</c>
2686   <c>
2687      <xref target="status.505"/>
2688   </c>
2689</texttable>
2690<!--(END)-->
2691
2692</section>
2693<section title="Header Field Registration" anchor="header.field.registration">
2694<t>
2695   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
2696   with the permanent registrations below (see <xref target="RFC3864"/>):
2697</t>
2698
2699<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2700<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2701   <ttcol>Header Field Name</ttcol>
2702   <ttcol>Protocol</ttcol>
2703   <ttcol>Status</ttcol>
2704   <ttcol>Reference</ttcol>
2705
2706   <c>Allow</c>
2707   <c>http</c>
2708   <c>standard</c>
2709   <c>
2710      <xref target="header.allow"/>
2711   </c>
2712   <c>Expect</c>
2713   <c>http</c>
2714   <c>standard</c>
2715   <c>
2716      <xref target="header.expect"/>
2717   </c>
2718   <c>From</c>
2719   <c>http</c>
2720   <c>standard</c>
2721   <c>
2722      <xref target="header.from"/>
2723   </c>
2724   <c>Location</c>
2725   <c>http</c>
2726   <c>standard</c>
2727   <c>
2728      <xref target="header.location"/>
2729   </c>
2730   <c>Max-Forwards</c>
2731   <c>http</c>
2732   <c>standard</c>
2733   <c>
2734      <xref target="header.max-forwards"/>
2735   </c>
2736   <c>Referer</c>
2737   <c>http</c>
2738   <c>standard</c>
2739   <c>
2740      <xref target="header.referer"/>
2741   </c>
2742   <c>Retry-After</c>
2743   <c>http</c>
2744   <c>standard</c>
2745   <c>
2746      <xref target="header.retry-after"/>
2747   </c>
2748   <c>Server</c>
2749   <c>http</c>
2750   <c>standard</c>
2751   <c>
2752      <xref target="header.server"/>
2753   </c>
2754   <c>User-Agent</c>
2755   <c>http</c>
2756   <c>standard</c>
2757   <c>
2758      <xref target="header.user-agent"/>
2759   </c>
2760</texttable>
2761<!--(END)-->
2762
2763<t>
2764   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2765</t>
2766</section>
2767</section>
2768
2769<section title="Security Considerations" anchor="security.considerations">
2770<t>
2771   This section is meant to inform application developers, information
2772   providers, and users of the security limitations in HTTP/1.1 as
2773   described by this document. The discussion does not include
2774   definitive solutions to the problems revealed, though it does make
2775   some suggestions for reducing security risks.
2776</t>
2777
2778<section title="Transfer of Sensitive Information" anchor="security.sensitive">
2779<t>
2780   Like any generic data transfer protocol, HTTP cannot regulate the
2781   content of the data that is transferred, nor is there any a priori
2782   method of determining the sensitivity of any particular piece of
2783   information within the context of any given request. Therefore,
2784   applications SHOULD supply as much control over this information as
2785   possible to the provider of that information. Four header fields are
2786   worth special mention in this context: Server, Via, Referer and From.
2787</t>
2788<t>
2789   Revealing the specific software version of the server might allow the
2790   server machine to become more vulnerable to attacks against software
2791   that is known to contain security holes. Implementors SHOULD make the
2792   Server header field a configurable option.
2793</t>
2794<t>
2795   Proxies which serve as a portal through a network firewall SHOULD
2796   take special precautions regarding the transfer of header information
2797   that identifies the hosts behind the firewall. In particular, they
2798   SHOULD remove, or replace with sanitized versions, any Via fields
2799   generated behind the firewall.
2800</t>
2801<t>
2802   The Referer header field allows reading patterns to be studied and reverse
2803   links drawn. Although it can be very useful, its power can be abused
2804   if user details are not separated from the information contained in
2805   the Referer. Even when the personal information has been removed, the
2806   Referer header field might indicate a private document's URI whose
2807   publication would be inappropriate.
2808</t>
2809<t>
2810   The information sent in the From field might conflict with the user's
2811   privacy interests or their site's security policy, and hence it
2812   SHOULD NOT  be transmitted without the user being able to disable,
2813   enable, and modify the contents of the field. The user MUST be able
2814   to set the contents of this field within a user preference or
2815   application defaults configuration.
2816</t>
2817<t>
2818   We suggest, though do not require, that a convenient toggle interface
2819   be provided for the user to enable or disable the sending of From and
2820   Referer information.
2821</t>
2822<t>
2823   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header fields can sometimes be used to determine
2824   that a specific client or server have a particular security hole which might
2825   be exploited. Unfortunately, this same information is often used for other
2826   valuable purposes for which HTTP currently has no better mechanism.
2827</t>
2828<t>
2829   Furthermore, the User-Agent header field may contain enough entropy to be
2830   used, possibly in conjunction with other material, to uniquely identify the
2831   user.
2832</t>
2833<t>
2834   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
2835   that was sent in request header fields within the body of their response.
2836   Clients SHOULD be careful with sensitive information, like Cookies,
2837   Authorization credentials, and other header fields that might be used to
2838   collect data from the client.
2839</t> 
2840</section>
2841
2842<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
2843<t>
2844   Because the source of a link might be private information or might
2845   reveal an otherwise private information source, it is strongly
2846   recommended that the user be able to select whether or not the
2847   Referer field is sent. For example, a browser client could have a
2848   toggle switch for browsing openly/anonymously, which would
2849   respectively enable/disable the sending of Referer and From
2850   information.
2851</t>
2852<t>
2853   Clients SHOULD NOT include a Referer header field in a (non-secure)
2854   HTTP request if the referring page was transferred with a secure
2855   protocol.
2856</t>
2857<t>
2858   Authors of services SHOULD NOT use GET-based forms for the submission of
2859   sensitive data because that data will be placed in the request-target. Many
2860   existing servers, proxies, and user agents log or display the request-target
2861   in places where it might be visible to third parties. Such services can
2862   use POST-based form submission instead.
2863</t>
2864</section>
2865
2866<section title="Location Headers and Spoofing" anchor="location.spoofing">
2867<t>
2868   If a single server supports multiple organizations that do not trust
2869   one another, then it MUST check the values of Location and Content-Location
2870   header fields in responses that are generated under control of
2871   said organizations to make sure that they do not attempt to
2872   invalidate resources over which they have no authority.
2873</t>
2874</section>
2875
2876<section title="Security Considerations for CONNECT">
2877<t>
2878   Since tunneled data is opaque to the proxy, there are additional
2879   risks to tunneling to other well-known or reserved ports.
2880   A HTTP client CONNECTing to port 25 could relay spam
2881   via SMTP, for example. As such, proxies SHOULD restrict CONNECT
2882   access to a small number of known ports.
2883</t>
2884</section>
2885
2886</section>
2887
2888<section title="Acknowledgments" anchor="ack">
2889</section>
2890</middle>
2891<back>
2892
2893<references title="Normative References">
2894
2895<reference anchor="Part1">
2896  <front>
2897    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2898    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2899      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
2900      <address><email>fielding@gbiv.com</email></address>
2901    </author>
2902    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2903      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
2904      <address><email>jg@freedesktop.org</email></address>
2905    </author>
2906    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2907      <organization abbrev="HP">Hewlett-Packard Company</organization>
2908      <address><email>JeffMogul@acm.org</email></address>
2909    </author>
2910    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2911      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2912      <address><email>henrikn@microsoft.com</email></address>
2913    </author>
2914    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2915      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
2916      <address><email>LMM@acm.org</email></address>
2917    </author>
2918    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2919      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2920      <address><email>paulle@microsoft.com</email></address>
2921    </author>
2922    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2923      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2924      <address><email>timbl@w3.org</email></address>
2925    </author>
2926    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2927      <organization abbrev="W3C">World Wide Web Consortium</organization>
2928      <address><email>ylafon@w3.org</email></address>
2929    </author>
2930    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2931      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2932      <address><email>julian.reschke@greenbytes.de</email></address>
2933    </author>
2934    <date month="July" year="2011"/>
2935  </front>
2936  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-15"/>
2937 
2938</reference>
2939
2940<reference anchor="Part3">
2941  <front>
2942    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2943    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2944      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
2945      <address><email>fielding@gbiv.com</email></address>
2946    </author>
2947    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2948      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
2949      <address><email>jg@freedesktop.org</email></address>
2950    </author>
2951    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2952      <organization abbrev="HP">Hewlett-Packard Company</organization>
2953      <address><email>JeffMogul@acm.org</email></address>
2954    </author>
2955    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2956      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2957      <address><email>henrikn@microsoft.com</email></address>
2958    </author>
2959    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2960      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
2961      <address><email>LMM@acm.org</email></address>
2962    </author>
2963    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2964      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2965      <address><email>paulle@microsoft.com</email></address>
2966    </author>
2967    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2968      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2969      <address><email>timbl@w3.org</email></address>
2970    </author>
2971    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2972      <organization abbrev="W3C">World Wide Web Consortium</organization>
2973      <address><email>ylafon@w3.org</email></address>
2974    </author>
2975    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2976      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2977      <address><email>julian.reschke@greenbytes.de</email></address>
2978    </author>
2979    <date month="July" year="2011"/>
2980  </front>
2981  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-15"/>
2982 
2983</reference>
2984
2985<reference anchor="Part4">
2986  <front>
2987    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2988    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2989      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
2990      <address><email>fielding@gbiv.com</email></address>
2991    </author>
2992    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2993      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
2994      <address><email>jg@freedesktop.org</email></address>
2995    </author>
2996    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2997      <organization abbrev="HP">Hewlett-Packard Company</organization>
2998      <address><email>JeffMogul@acm.org</email></address>
2999    </author>
3000    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3001      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3002      <address><email>henrikn@microsoft.com</email></address>
3003    </author>
3004    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3005      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3006      <address><email>LMM@acm.org</email></address>
3007    </author>
3008    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3009      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3010      <address><email>paulle@microsoft.com</email></address>
3011    </author>
3012    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3013      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3014      <address><email>timbl@w3.org</email></address>
3015    </author>
3016    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3017      <organization abbrev="W3C">World Wide Web Consortium</organization>
3018      <address><email>ylafon@w3.org</email></address>
3019    </author>
3020    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3021      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3022      <address><email>julian.reschke@greenbytes.de</email></address>
3023    </author>
3024    <date month="July" year="2011"/>
3025  </front>
3026  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-15"/>
3027 
3028</reference>
3029
3030<reference anchor="Part5">
3031  <front>
3032    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3033    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3034      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3035      <address><email>fielding@gbiv.com</email></address>
3036    </author>
3037    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3038      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3039      <address><email>jg@freedesktop.org</email></address>
3040    </author>
3041    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3042      <organization abbrev="HP">Hewlett-Packard Company</organization>
3043      <address><email>JeffMogul@acm.org</email></address>
3044    </author>
3045    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3046      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3047      <address><email>henrikn@microsoft.com</email></address>
3048    </author>
3049    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3050      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3051      <address><email>LMM@acm.org</email></address>
3052    </author>
3053    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3054      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3055      <address><email>paulle@microsoft.com</email></address>
3056    </author>
3057    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3058      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3059      <address><email>timbl@w3.org</email></address>
3060    </author>
3061    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3062      <organization abbrev="W3C">World Wide Web Consortium</organization>
3063      <address><email>ylafon@w3.org</email></address>
3064    </author>
3065    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3066      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3067      <address><email>julian.reschke@greenbytes.de</email></address>
3068    </author>
3069    <date month="July" year="2011"/>
3070  </front>
3071  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-15"/>
3072 
3073</reference>
3074
3075<reference anchor="Part6">
3076  <front>
3077    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3078    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3079      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3080      <address><email>fielding@gbiv.com</email></address>
3081    </author>
3082    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3083      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3084      <address><email>jg@freedesktop.org</email></address>
3085    </author>
3086    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3087      <organization abbrev="HP">Hewlett-Packard Company</organization>
3088      <address><email>JeffMogul@acm.org</email></address>
3089    </author>
3090    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3091      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3092      <address><email>henrikn@microsoft.com</email></address>
3093    </author>
3094    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3095      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3096      <address><email>LMM@acm.org</email></address>
3097    </author>
3098    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3099      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3100      <address><email>paulle@microsoft.com</email></address>
3101    </author>
3102    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3103      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3104      <address><email>timbl@w3.org</email></address>
3105    </author>
3106    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3107      <organization abbrev="W3C">World Wide Web Consortium</organization>
3108      <address><email>ylafon@w3.org</email></address>
3109    </author>
3110    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3111      <address><email>mnot@mnot.net</email></address>
3112    </author>
3113    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3114      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3115      <address><email>julian.reschke@greenbytes.de</email></address>
3116    </author>
3117    <date month="July" year="2011"/>
3118  </front>
3119  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-15"/>
3120 
3121</reference>
3122
3123<reference anchor="Part7">
3124  <front>
3125    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3126    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3127      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3128      <address><email>fielding@gbiv.com</email></address>
3129    </author>
3130    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3131      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3132      <address><email>jg@freedesktop.org</email></address>
3133    </author>
3134    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3135      <organization abbrev="HP">Hewlett-Packard Company</organization>
3136      <address><email>JeffMogul@acm.org</email></address>
3137    </author>
3138    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3139      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3140      <address><email>henrikn@microsoft.com</email></address>
3141    </author>
3142    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3143      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3144      <address><email>LMM@acm.org</email></address>
3145    </author>
3146    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3147      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3148      <address><email>paulle@microsoft.com</email></address>
3149    </author>
3150    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3151      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3152      <address><email>timbl@w3.org</email></address>
3153    </author>
3154    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3155      <organization abbrev="W3C">World Wide Web Consortium</organization>
3156      <address><email>ylafon@w3.org</email></address>
3157    </author>
3158    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3159      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3160      <address><email>julian.reschke@greenbytes.de</email></address>
3161    </author>
3162    <date month="July" year="2011"/>
3163  </front>
3164  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-15"/>
3165 
3166</reference>
3167
3168<reference anchor="RFC2119">
3169  <front>
3170    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3171    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3172      <organization>Harvard University</organization>
3173      <address><email>sob@harvard.edu</email></address>
3174    </author>
3175    <date month="March" year="1997"/>
3176  </front>
3177  <seriesInfo name="BCP" value="14"/>
3178  <seriesInfo name="RFC" value="2119"/>
3179</reference>
3180
3181<reference anchor="RFC3986">
3182 <front>
3183  <title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
3184  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3185    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3186    <address>
3187       <email>timbl@w3.org</email>
3188       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3189    </address>
3190  </author>
3191  <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3192    <organization abbrev="Day Software">Day Software</organization>
3193    <address>
3194      <email>fielding@gbiv.com</email>
3195      <uri>http://roy.gbiv.com/</uri>
3196    </address>
3197  </author>
3198  <author initials="L." surname="Masinter" fullname="Larry Masinter">
3199    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3200    <address>
3201      <email>LMM@acm.org</email>
3202      <uri>http://larry.masinter.net/</uri>
3203    </address>
3204  </author>
3205  <date month="January" year="2005"/>
3206 </front>
3207 <seriesInfo name="STD" value="66"/>
3208 <seriesInfo name="RFC" value="3986"/>
3209</reference>
3210
3211<reference anchor="RFC5234">
3212  <front>
3213    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3214    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3215      <organization>Brandenburg InternetWorking</organization>
3216      <address>
3217        <email>dcrocker@bbiw.net</email>
3218      </address> 
3219    </author>
3220    <author initials="P." surname="Overell" fullname="Paul Overell">
3221      <organization>THUS plc.</organization>
3222      <address>
3223        <email>paul.overell@thus.net</email>
3224      </address>
3225    </author>
3226    <date month="January" year="2008"/>
3227  </front>
3228  <seriesInfo name="STD" value="68"/>
3229  <seriesInfo name="RFC" value="5234"/>
3230</reference>
3231
3232</references>
3233
3234<references title="Informative References">
3235
3236<reference anchor="RFC1945">
3237  <front>
3238    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3239    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3240      <organization>MIT, Laboratory for Computer Science</organization>
3241      <address><email>timbl@w3.org</email></address>
3242    </author>
3243    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3244      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3245      <address><email>fielding@ics.uci.edu</email></address>
3246    </author>
3247    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3248      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3249      <address><email>frystyk@w3.org</email></address>
3250    </author>
3251    <date month="May" year="1996"/>
3252  </front>
3253  <seriesInfo name="RFC" value="1945"/>
3254</reference>
3255
3256<reference anchor="RFC2068">
3257  <front>
3258    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3259    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3260      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3261      <address><email>fielding@ics.uci.edu</email></address>
3262    </author>
3263    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3264      <organization>MIT Laboratory for Computer Science</organization>
3265      <address><email>jg@w3.org</email></address>
3266    </author>
3267    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3268      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3269      <address><email>mogul@wrl.dec.com</email></address>
3270    </author>
3271    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3272      <organization>MIT Laboratory for Computer Science</organization>
3273      <address><email>frystyk@w3.org</email></address>
3274    </author>
3275    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3276      <organization>MIT Laboratory for Computer Science</organization>
3277      <address><email>timbl@w3.org</email></address>
3278    </author>
3279    <date month="January" year="1997"/>
3280  </front>
3281  <seriesInfo name="RFC" value="2068"/>
3282</reference>
3283
3284<reference anchor="RFC2616">
3285  <front>
3286    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3287    <author initials="R." surname="Fielding" fullname="R. Fielding">
3288      <organization>University of California, Irvine</organization>
3289      <address><email>fielding@ics.uci.edu</email></address>
3290    </author>
3291    <author initials="J." surname="Gettys" fullname="J. Gettys">
3292      <organization>W3C</organization>
3293      <address><email>jg@w3.org</email></address>
3294    </author>
3295    <author initials="J." surname="Mogul" fullname="J. Mogul">
3296      <organization>Compaq Computer Corporation</organization>
3297      <address><email>mogul@wrl.dec.com</email></address>
3298    </author>
3299    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3300      <organization>MIT Laboratory for Computer Science</organization>
3301      <address><email>frystyk@w3.org</email></address>
3302    </author>
3303    <author initials="L." surname="Masinter" fullname="L. Masinter">
3304      <organization>Xerox Corporation</organization>
3305      <address><email>masinter@parc.xerox.com</email></address>
3306    </author>
3307    <author initials="P." surname="Leach" fullname="P. Leach">
3308      <organization>Microsoft Corporation</organization>
3309      <address><email>paulle@microsoft.com</email></address>
3310    </author>
3311    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3312      <organization>W3C</organization>
3313      <address><email>timbl@w3.org</email></address>
3314    </author>
3315    <date month="June" year="1999"/>
3316  </front>
3317  <seriesInfo name="RFC" value="2616"/>
3318</reference>
3319
3320<reference anchor="RFC2817">
3321  <front>
3322    <title>Upgrading to TLS Within HTTP/1.1</title>
3323    <author initials="R." surname="Khare" fullname="R. Khare">
3324      <organization>4K Associates / UC Irvine</organization>
3325      <address><email>rohit@4K-associates.com</email></address>
3326    </author>
3327    <author initials="S." surname="Lawrence" fullname="S. Lawrence">
3328      <organization>Agranat Systems, Inc.</organization>
3329      <address><email>lawrence@agranat.com</email></address>
3330    </author>
3331    <date year="2000" month="May"/>
3332  </front>
3333  <seriesInfo name="RFC" value="2817"/>
3334</reference>
3335
3336<reference anchor="RFC3864">
3337  <front>
3338    <title>Registration Procedures for Message Header Fields</title>
3339    <author initials="G." surname="Klyne" fullname="G. Klyne">
3340      <organization>Nine by Nine</organization>
3341      <address><email>GK-IETF@ninebynine.org</email></address>
3342    </author>
3343    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
3344      <organization>BEA Systems</organization>
3345      <address><email>mnot@pobox.com</email></address>
3346    </author>
3347    <author initials="J." surname="Mogul" fullname="J. Mogul">
3348      <organization>HP Labs</organization>
3349      <address><email>JeffMogul@acm.org</email></address>
3350    </author>
3351    <date year="2004" month="September"/>
3352  </front>
3353  <seriesInfo name="BCP" value="90"/>
3354  <seriesInfo name="RFC" value="3864"/>
3355</reference>
3356
3357<reference anchor="RFC5226">
3358  <front>
3359    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3360    <author initials="T." surname="Narten" fullname="T. Narten">
3361      <organization>IBM</organization>
3362      <address><email>narten@us.ibm.com</email></address>
3363    </author>
3364    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
3365      <organization>Google</organization>
3366      <address><email>Harald@Alvestrand.no</email></address>
3367    </author>
3368    <date year="2008" month="May"/>
3369  </front>
3370  <seriesInfo name="BCP" value="26"/>
3371  <seriesInfo name="RFC" value="5226"/>
3372</reference>
3373
3374<reference anchor="RFC5322">
3375  <front>
3376    <title>Internet Message Format</title>
3377    <author initials="P." surname="Resnick" fullname="P. Resnick">
3378      <organization>Qualcomm Incorporated</organization>
3379    </author>
3380    <date year="2008" month="October"/>
3381  </front> 
3382  <seriesInfo name="RFC" value="5322"/>
3383</reference>
3384
3385<reference anchor="RFC5789">
3386  <front>
3387    <title>PATCH Method for HTTP</title>
3388    <author initials="L." surname="Dusseault" fullname="L. Dusseault">
3389      <organization>Linden Lab</organization>
3390    </author>
3391    <author initials="J." surname="Snell" fullname="J. Snell"/>
3392    <date year="2010" month="March"/>
3393  </front>
3394  <seriesInfo name="RFC" value="5789"/>
3395</reference>
3396
3397</references>
3398
3399<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3400<t>
3401  This document takes over the Status Code Registry, previously defined
3402  in Section 7.1 of <xref target="RFC2817"/>.
3403  (<xref target="status.code.registry"/>)
3404</t>
3405<t>
3406  Clarify definition of POST.
3407  (<xref target="POST"/>)
3408</t>
3409<t>
3410  Remove requirement to handle all Content-* header fields; ban use of
3411  Content-Range with PUT.
3412  (<xref target="PUT"/>)
3413</t>
3414<t>
3415  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3416  (<xref target="CONNECT"/>)
3417</t>
3418<t>
3419  Broadened the definition of 203 (Non-Authoritative Information) to include
3420  cases of payload transformations as well.
3421  (<xref target="status.203"/>)
3422</t>
3423<t>
3424  Failed to consider that there are
3425  many other request methods that are safe to automatically redirect,
3426  and further that the user agent is able to make that determination
3427  based on the request method semantics.
3428  (Sections <xref format="counter" target="status.301"/>,
3429  <xref format="counter" target="status.302"/> and
3430  <xref format="counter" target="status.307"/>)
3431</t>
3432<t>
3433  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3434  It used to indicate that the target resource must be accessed through the
3435  proxy given by the Location field. The Location field gave the URI of the
3436  proxy. The recipient was expected to repeat this single request via the proxy.
3437  (<xref target="status.305"/>)
3438</t>
3439<t>
3440  Define status 426 (Upgrade Required) (this was incorporated from
3441  <xref target="RFC2817"/>).
3442  (<xref target="status.426"/>)
3443</t>
3444<t>
3445  Change ABNF productions for header fields to only define the field value.
3446  (<xref target="header.fields"/>)
3447</t>
3448<t>
3449  Reclassify "Allow" as response header field, removing the option to
3450  specify it in a PUT request.
3451  Relax the server requirement on the contents of the Allow header field and
3452  remove requirement on clients to always trust the header field value.
3453  (<xref target="header.allow"/>)
3454</t>
3455<t>
3456  Correct syntax of Location header field to allow URI references (including
3457  relative references and fragments), as referred symbol "absoluteURI" wasn't
3458  what was expected, and add some clarifications as to when use of fragments
3459  would not be appropriate.
3460  (<xref target="header.location"/>)
3461</t>
3462<t>
3463  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
3464  extension methods could have used it as well).
3465  (<xref target="header.max-forwards"/>)
3466</t>
3467<t>
3468  Allow Referer field value of "about:blank" as alternative to not specifying it.
3469  (<xref target="header.referer"/>)
3470</t>
3471<t>
3472  In the description of the Server header field, the Via field
3473  was described as a SHOULD. The requirement was and is stated
3474  correctly in the description of the Via header field in Section 9.9 of <xref target="Part1"/>.
3475  (<xref target="header.server"/>)
3476</t>
3477</section>
3478
3479
3480<section title="Collected ABNF" anchor="collected.abnf">
3481<figure>
3482<artwork type="abnf" name="p2-semantics.parsed-abnf"><![CDATA[
3483Allow = [ ( "," / Method ) *( OWS "," [ OWS Method ] ) ]
3484
3485Expect = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
3486
3487From = mailbox
3488
3489HTTP-date = <HTTP-date, defined in [Part1], Section 6.1>
3490
3491Location = URI-reference
3492
3493Max-Forwards = 1*DIGIT
3494Method = token
3495
3496OWS = <OWS, defined in [Part1], Section 1.2.2>
3497
3498RWS = <RWS, defined in [Part1], Section 1.2.2>
3499Reason-Phrase = *( WSP / VCHAR / obs-text )
3500Referer = absolute-URI / partial-URI
3501Retry-After = HTTP-date / delta-seconds
3502
3503Server = product *( RWS ( product / comment ) )
3504Status-Code = 3DIGIT
3505
3506URI-reference = <URI-reference, defined in [Part1], Section 2.7>
3507User-Agent = product *( RWS ( product / comment ) )
3508
3509absolute-URI = <absolute-URI, defined in [Part1], Section 2.7>
3510
3511comment = <comment, defined in [Part1], Section 3.2>
3512
3513delta-seconds = 1*DIGIT
3514
3515expect-params = ";" token [ "=" ( token / quoted-string ) ]
3516expectation = "100-continue" / expectation-extension
3517expectation-extension = token [ "=" ( token / quoted-string )
3518 *expect-params ]
3519
3520mailbox = <mailbox, defined in [RFC5322], Section 3.4>
3521
3522obs-text = <obs-text, defined in [Part1], Section 1.2.2>
3523
3524partial-URI = <partial-URI, defined in [Part1], Section 2.7>
3525product = <product, defined in [Part1], Section 6.3>
3526
3527quoted-string = <quoted-string, defined in [Part1], Section 1.2.2>
3528
3529token = <token, defined in [Part1], Section 1.2.2>
3530]]></artwork>
3531</figure>
3532<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
3533; Allow defined but not used
3534; Expect defined but not used
3535; From defined but not used
3536; Location defined but not used
3537; Max-Forwards defined but not used
3538; Reason-Phrase defined but not used
3539; Referer defined but not used
3540; Retry-After defined but not used
3541; Server defined but not used
3542; Status-Code defined but not used
3543; User-Agent defined but not used
3544]]></artwork></figure></section>
3545
3546
3547<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
3548
3549<section title="Since RFC 2616">
3550<t>
3551  Extracted relevant partitions from <xref target="RFC2616"/>.
3552</t>
3553</section>
3554
3555<section title="Since draft-ietf-httpbis-p2-semantics-00">
3556<t>
3557  Closed issues:
3558  <list style="symbols"> 
3559    <t>
3560      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
3561      "Via is a MUST"
3562      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
3563    </t>
3564    <t>
3565      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
3566      "Fragments allowed in Location"
3567      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
3568    </t>
3569    <t>
3570      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
3571      "Safe Methods vs Redirection"
3572      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
3573    </t>
3574    <t>
3575      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
3576      "Revise description of the POST method"
3577      (<eref target="http://purl.org/NET/http-errata#post"/>)
3578    </t>
3579    <t>
3580      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
3581      "Normative and Informative references"
3582    </t>
3583    <t>
3584      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
3585      "RFC2606 Compliance"
3586    </t>
3587    <t>
3588      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
3589      "Informative references"
3590    </t>
3591    <t>
3592      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
3593      "Redundant cross-references"
3594    </t>
3595  </list>
3596</t>
3597<t>
3598  Other changes:
3599  <list style="symbols"> 
3600    <t>
3601      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
3602    </t>
3603  </list>
3604</t>
3605</section>
3606
3607<section title="Since draft-ietf-httpbis-p2-semantics-01">
3608<t>
3609  Closed issues:
3610  <list style="symbols"> 
3611    <t>
3612      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
3613      "PUT side effects"
3614    </t>
3615    <t>
3616      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
3617      "Duplicate Host header requirements"
3618    </t>
3619  </list>
3620</t>
3621<t>
3622  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3623  <list style="symbols"> 
3624    <t>
3625      Move "Product Tokens" section (back) into Part 1, as "token" is used
3626      in the definition of the Upgrade header field.
3627    </t>
3628    <t>
3629      Add explicit references to BNF syntax and rules imported from other parts of the specification.
3630    </t>
3631    <t>
3632      Copy definition of delta-seconds from Part6 instead of referencing it.
3633    </t>
3634  </list>
3635</t>
3636</section>
3637
3638<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
3639<t>
3640  Closed issues:
3641  <list style="symbols"> 
3642    <t>
3643      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
3644      "Requiring Allow in 405 responses"
3645    </t>
3646    <t>
3647      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
3648      "Status Code Registry"
3649    </t>
3650    <t>
3651      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
3652      "Redirection vs. Location"
3653    </t>
3654    <t>
3655      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
3656      "Cacheability of 303 response"
3657    </t>
3658    <t>
3659      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
3660      "305 Use Proxy"
3661    </t>
3662    <t>
3663      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
3664      "Classification for Allow header"
3665    </t>
3666    <t>
3667      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
3668      "PUT - 'store under' vs 'store at'"
3669    </t>
3670  </list>
3671</t>
3672<t>
3673  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
3674  <list style="symbols"> 
3675    <t>
3676      Reference RFC 3984, and update header field registrations for headers defined
3677      in this document.
3678    </t>
3679  </list>
3680</t>
3681<t>
3682  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3683  <list style="symbols"> 
3684    <t>
3685      Replace string literals when the string really is case-sensitive (method).
3686    </t>
3687  </list>
3688</t>
3689</section>
3690
3691<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
3692<t>
3693  Closed issues:
3694  <list style="symbols"> 
3695    <t>
3696      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
3697      "OPTIONS request bodies"
3698    </t>
3699    <t>
3700      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
3701      "Description of CONNECT should refer to RFC2817"
3702    </t>
3703    <t>
3704      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
3705      "Location Content-Location reference request/response mixup"
3706    </t>
3707  </list>
3708</t>
3709<t>
3710  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
3711  <list style="symbols"> 
3712    <t>
3713      Added initial proposal for registration process, plus initial
3714      content (non-HTTP/1.1 methods to be added by a separate specification).
3715    </t>
3716  </list>
3717</t>
3718</section>
3719
3720<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
3721<t>
3722  Closed issues:
3723  <list style="symbols"> 
3724    <t>
3725      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
3726      "Content-*"
3727    </t>
3728    <t>
3729      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
3730      "RFC 2822 is updated by RFC 5322"
3731    </t>
3732  </list>
3733</t>
3734<t>
3735  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3736  <list style="symbols"> 
3737    <t>
3738      Use "/" instead of "|" for alternatives.
3739    </t>
3740    <t>
3741      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
3742      whitespace ("OWS") and required whitespace ("RWS").
3743    </t>
3744    <t>
3745      Rewrite ABNFs to spell out whitespace rules, factor out
3746      header field value format definitions.
3747    </t>
3748  </list>
3749</t>
3750</section>
3751
3752<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
3753<t>
3754  Closed issues:
3755  <list style="symbols"> 
3756    <t>
3757      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
3758      "Reason-Phrase BNF"
3759    </t>
3760  </list>
3761</t>
3762<t>
3763  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3764  <list style="symbols"> 
3765    <t>
3766      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
3767    </t>
3768  </list>
3769</t>
3770</section>
3771
3772<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
3773<t>
3774  Closed issues:
3775  <list style="symbols"> 
3776    <t>
3777      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
3778      "Clarify when Referer is sent"
3779    </t>
3780    <t>
3781      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
3782      "status codes vs methods"
3783    </t>
3784    <t>
3785      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
3786      "Do not require "updates" relation for specs that register status codes or method names"
3787    </t>
3788  </list>
3789</t>
3790</section>
3791
3792<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
3793<t>
3794  Closed issues:
3795  <list style="symbols"> 
3796    <t>
3797      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
3798      "Idempotency"
3799    </t>
3800    <t>
3801      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
3802      "TRACE security considerations"
3803    </t>
3804    <t>
3805      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
3806      "Clarify rules for determining what entities a response carries"
3807    </t>
3808    <t>
3809      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
3810      "update note citing RFC 1945 and 2068"
3811    </t>
3812    <t>
3813      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
3814      "update note about redirect limit"
3815    </t>
3816    <t>
3817      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
3818      "Location header ABNF should use 'URI'"
3819    </t>
3820    <t>
3821      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
3822      "fragments in Location vs status 303"
3823    </t>
3824    <t>
3825      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
3826      "move IANA registrations for optional status codes"
3827    </t>
3828  </list>
3829</t>
3830<t>
3831  Partly resolved issues:
3832  <list style="symbols"> 
3833    <t>
3834      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
3835      "Are OPTIONS and TRACE safe?"
3836    </t>
3837  </list>
3838</t>
3839</section>
3840
3841<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
3842<t>
3843  Closed issues:
3844  <list style="symbols"> 
3845    <t>
3846      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
3847      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
3848      status codes when fixing this previously)
3849    </t>
3850  </list>
3851</t>
3852</section>
3853
3854<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
3855<t>
3856  Closed issues:
3857  <list style="symbols"> 
3858    <t>
3859      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
3860      "Fragment combination / precedence during redirects"
3861    </t>
3862  </list>
3863</t>
3864<t>
3865  Partly resolved issues:
3866  <list style="symbols"> 
3867    <t>
3868      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
3869      "Location header payload handling"
3870    </t>
3871    <t>
3872      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
3873      "Term for the requested resource's URI"
3874    </t>
3875  </list>
3876</t>
3877</section>
3878
3879<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
3880<t>
3881  Closed issues:
3882  <list style="symbols"> 
3883    <t>
3884      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
3885      "Clarify 'Requested Variant'"
3886    </t>
3887    <t>
3888      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
3889      "Clarify entity / representation / variant terminology"
3890    </t>
3891    <t>
3892      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
3893      "Methods and Caching"
3894    </t>
3895    <t>
3896      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
3897      "OPTIONS vs Max-Forwards"
3898    </t>
3899    <t>
3900      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
3901      "Status codes and caching"
3902    </t>
3903    <t>
3904      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
3905      "consider removing the 'changes from 2068' sections"
3906    </t>
3907  </list>
3908</t>
3909</section>
3910
3911<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
3912<t>
3913  Closed issues:
3914  <list style="symbols"> 
3915    <t>
3916      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
3917      "Considerations for new status codes"
3918    </t>
3919    <t>
3920      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
3921      "Considerations for new methods"
3922    </t>
3923    <t>
3924      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
3925      "User-Agent guidelines" (relating to the 'User-Agent' header field)
3926    </t>
3927  </list>
3928</t>
3929</section>
3930
3931<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
3932<t>
3933  Closed issues:
3934  <list style="symbols"> 
3935    <t>
3936      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
3937      "Fragment combination / precedence during redirects" (added warning
3938      about having a fragid on the redirect may cause inconvenience in
3939      some cases)
3940    </t>
3941    <t>
3942      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
3943      "Content-* vs. PUT"
3944    </t>
3945    <t>
3946      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
3947      "205 Bodies"
3948    </t>
3949    <t>
3950      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
3951      "Understanding Content-* on non-PUT requests"
3952    </t>
3953    <t>
3954      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
3955      "Content-*"
3956    </t>
3957    <t>
3958      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
3959      "Header type defaulting"
3960    </t>
3961    <t>
3962      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
3963      "PUT - 'store under' vs 'store at'"
3964    </t>
3965    <t>
3966      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
3967      "duplicate ABNF for Reason-Phrase"
3968    </t>
3969    <t>
3970      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
3971      "Note special status of Content-* prefix in header registration procedures"
3972    </t>
3973    <t>
3974      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
3975      "Max-Forwards vs extension methods"
3976    </t>
3977    <t>
3978      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
3979      "What is the value space of HTTP status codes?" (actually fixed in
3980      draft-ietf-httpbis-p2-semantics-11)
3981    </t>
3982    <t>
3983      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
3984      "Header Classification"
3985    </t>
3986    <t>
3987      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
3988      "PUT side effect: invalidation or just stale?"
3989    </t>
3990    <t>
3991      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
3992      "proxies not supporting certain methods"
3993    </t>
3994    <t>
3995      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
3996      "Migrate CONNECT from RFC2817 to p2"
3997    </t>
3998    <t>
3999      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4000      "Migrate Upgrade details from RFC2817"
4001    </t>
4002    <t>
4003      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4004      "clarify PUT semantics'"
4005    </t>
4006    <t>
4007      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4008      "duplicate ABNF for 'Method'"
4009    </t>
4010    <t>
4011      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4012      "untangle ABNFs for header fields"
4013    </t>
4014  </list>
4015</t>
4016</section>
4017
4018<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4019<t>
4020  Closed issues:
4021  <list style="symbols"> 
4022    <t>
4023      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4024      "untangle ABNFs for header fields"
4025    </t>
4026    <t>
4027      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4028      "message-body in CONNECT request"
4029    </t>
4030  </list>
4031</t>
4032</section>
4033
4034<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4035<t>
4036  Closed issues:
4037  <list style="symbols"> 
4038    <t>
4039      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4040      "Clarify status code for rate limiting"
4041    </t>
4042    <t>
4043      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4044      "clarify 403 forbidden"
4045    </t>
4046    <t>
4047      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4048      "Clarify 203 Non-Authoritative Information"
4049    </t>
4050    <t>
4051      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4052      "update default reason phrase for 413"
4053    </t>
4054  </list>
4055</t>
4056</section>
4057</section>
4058
4059</back>
4060</rfc>
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