source: draft-ietf-httpbis/18/draft-ietf-httpbis-p2-semantics-18.xml @ 2323

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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-18">
20
21
22<front>
23
24  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
25
26  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
27    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
28    <address>
29      <postal>
30        <street>345 Park Ave</street>
31        <city>San Jose</city>
32        <region>CA</region>
33        <code>95110</code>
34        <country>USA</country>
35      </postal>
36      <email>fielding@gbiv.com</email>
37      <uri>http://roy.gbiv.com/</uri>
38    </address>
39  </author>
40
41  <author initials="J." surname="Gettys" fullname="Jim Gettys">
42    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
43    <address>
44      <postal>
45        <street>21 Oak Knoll Road</street>
46        <city>Carlisle</city>
47        <region>MA</region>
48        <code>01741</code>
49        <country>USA</country>
50      </postal>
51      <email>jg@freedesktop.org</email>
52      <uri>http://gettys.wordpress.com/</uri>
53    </address>
54  </author>
55 
56  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
57    <organization abbrev="HP">Hewlett-Packard Company</organization>
58    <address>
59      <postal>
60        <street>HP Labs, Large Scale Systems Group</street>
61        <street>1501 Page Mill Road, MS 1177</street>
62        <city>Palo Alto</city>
63        <region>CA</region>
64        <code>94304</code>
65        <country>USA</country>
66      </postal>
67      <email>JeffMogul@acm.org</email>
68    </address>
69  </author>
70
71  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
72    <organization abbrev="Microsoft">Microsoft Corporation</organization>
73    <address>
74      <postal>
75        <street>1 Microsoft Way</street>
76        <city>Redmond</city>
77        <region>WA</region>
78        <code>98052</code>
79        <country>USA</country>
80      </postal>
81      <email>henrikn@microsoft.com</email>
82    </address>
83  </author>
84
85  <author initials="L." surname="Masinter" fullname="Larry Masinter">
86    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
87    <address>
88      <postal>
89        <street>345 Park Ave</street>
90        <city>San Jose</city>
91        <region>CA</region>
92        <code>95110</code>
93        <country>USA</country>
94      </postal>
95      <email>LMM@acm.org</email>
96      <uri>http://larry.masinter.net/</uri>
97    </address>
98  </author>
99 
100  <author initials="P." surname="Leach" fullname="Paul J. Leach">
101    <organization abbrev="Microsoft">Microsoft Corporation</organization>
102    <address>
103      <postal>
104        <street>1 Microsoft Way</street>
105        <city>Redmond</city>
106        <region>WA</region>
107        <code>98052</code>
108      </postal>
109      <email>paulle@microsoft.com</email>
110    </address>
111  </author>
112   
113  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
114    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
115    <address>
116      <postal>
117        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
118        <street>The Stata Center, Building 32</street>
119        <street>32 Vassar Street</street>
120        <city>Cambridge</city>
121        <region>MA</region>
122        <code>02139</code>
123        <country>USA</country>
124      </postal>
125      <email>timbl@w3.org</email>
126      <uri>http://www.w3.org/People/Berners-Lee/</uri>
127    </address>
128  </author>
129
130  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
131    <organization abbrev="W3C">World Wide Web Consortium</organization>
132    <address>
133      <postal>
134        <street>W3C / ERCIM</street>
135        <street>2004, rte des Lucioles</street>
136        <city>Sophia-Antipolis</city>
137        <region>AM</region>
138        <code>06902</code>
139        <country>France</country>
140      </postal>
141      <email>ylafon@w3.org</email>
142      <uri>http://www.raubacapeu.net/people/yves/</uri>
143    </address>
144  </author>
145
146  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
147    <organization abbrev="greenbytes">greenbytes GmbH</organization>
148    <address>
149      <postal>
150        <street>Hafenweg 16</street>
151        <city>Muenster</city><region>NW</region><code>48155</code>
152        <country>Germany</country>
153      </postal>
154      <phone>+49 251 2807760</phone>
155      <facsimile>+49 251 2807761</facsimile>
156      <email>julian.reschke@greenbytes.de</email>
157      <uri>http://greenbytes.de/tech/webdav/</uri>
158    </address>
159  </author>
160
161  <date month="January" year="2012" day="4"/>
162  <workgroup>HTTPbis Working Group</workgroup>
163
164<abstract>
165<t>
166   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
167   distributed, collaborative, hypertext information systems. HTTP has been in
168   use by the World Wide Web global information initiative since 1990. This
169   document is Part 2 of the seven-part specification that defines the protocol
170   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
171</t>
172<t>
173   Part 2 defines the semantics of HTTP messages as expressed by request
174   methods, request header fields, response status codes, and response header
175   fields.
176</t>
177</abstract>
178
179<note title="Editorial Note (To be removed by RFC Editor)">
180  <t>
181    Discussion of this draft should take place on the HTTPBIS working group
182    mailing list (ietf-http-wg@w3.org), which is archived at
183    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
184  </t>
185  <t>
186    The current issues list is at
187    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
188    documents (including fancy diffs) can be found at
189    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
190  </t>
191  <t>
192    The changes in this draft are summarized in <xref target="changes.since.17"/>.
193  </t>
194</note>
195</front>
196<middle>
197<section title="Introduction" anchor="introduction">
198<t>
199   This document defines HTTP/1.1 request and response semantics.  Each HTTP
200   message, as defined in <xref target="Part1"/>, is in the form of either a request or
201   a response.  An HTTP server listens on a connection for HTTP requests and
202   responds to each request, in the order received on that connection, with
203   one or more HTTP response messages.  This document defines the commonly
204   agreed upon semantics of the HTTP uniform interface, the intentions defined
205   by each request method, and the various response messages that might be
206   expected as a result of applying that method to the target resource.
207</t>
208<t>
209   This document is currently disorganized in order to minimize the changes
210   between drafts and enable reviewers to see the smaller errata changes.
211   A future draft will reorganize the sections to better reflect the content.
212   In particular, the sections will be ordered according to the typical
213   processing of an HTTP request message (after message parsing): resource
214   mapping, methods, request modifying header fields, response status,
215   status modifying header fields, and resource metadata.  The current mess
216   reflects how widely dispersed these topics and associated requirements
217   had become in <xref target="RFC2616"/>.
218</t>
219
220<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
221<t>
222   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
223   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
224   document are to be interpreted as described in <xref target="RFC2119"/>.
225</t>
226<t>
227   This document defines conformance criteria for several roles in HTTP
228   communication, including Senders, Recipients, Clients, Servers, User-Agents,
229   Origin Servers, Intermediaries, Proxies and Gateways. See Section 2 of <xref target="Part1"/>
230   for definitions of these terms.
231</t>
232<t>
233   An implementation is considered conformant if it complies with all of the
234   requirements associated with its role(s). Note that SHOULD-level requirements
235   are relevant here, unless one of the documented exceptions is applicable.
236</t>
237<t>
238   This document also uses ABNF to define valid protocol elements
239   (<xref target="notation"/>). In addition to the prose requirements placed
240   upon them, Senders MUST NOT generate protocol elements that are invalid.
241</t>
242<t>
243   Unless noted otherwise, Recipients MAY take steps to recover a usable
244   protocol element from an invalid construct. However, HTTP does not define
245   specific error handling mechanisms, except in cases where it has direct
246   impact on security. This is because different uses of the protocol require
247   different error handling strategies; for example, a Web browser may wish to
248   transparently recover from a response where the Location header field
249   doesn't parse according to the ABNF, whereby in a systems control protocol
250   using HTTP, this type of error recovery could lead to dangerous consequences.
251</t>
252</section>
253
254<section title="Syntax Notation" anchor="notation">
255 
256 
257 
258 
259 
260 
261<t>
262  This specification uses the ABNF syntax defined in Section 1.2 of <xref target="Part1"/> (which
263  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
264  <xref target="collected.abnf"/> shows the collected ABNF, with the list
265  rule expanded.
266</t>
267<t>
268  The following core rules are included by
269  reference, as defined in <xref target="RFC5234"/>, Appendix B.1:
270  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
271  DIGIT (decimal 0-9), DQUOTE (double quote),
272  HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
273  OCTET (any 8-bit sequence of data), SP (space), and
274  VCHAR (any visible US-ASCII character).
275</t>
276
277<section title="Core Rules" anchor="core.rules">
278 
279 
280 
281 
282 
283 
284<t>
285  The core rules below are defined in <xref target="Part1"/>:
286</t>
287<figure><artwork type="abnf2616"><![CDATA[
288  BWS           = <BWS, defined in [Part1], Section 1.2.2>
289  OWS           = <OWS, defined in [Part1], Section 1.2.2>
290  RWS           = <RWS, defined in [Part1], Section 1.2.2>
291  obs-text      = <obs-text, defined in [Part1], Section 1.2.2>
292  quoted-string = <quoted-string, defined in [Part1], Section 3.2.3>
293  token         = <token, defined in [Part1], Section 3.2.3>
294]]></artwork></figure>
295</section>
296
297<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
298 
299 
300 
301 
302 
303<t>
304  The ABNF rules below are defined in other parts:
305</t>
306<figure><artwork type="abnf2616"><![CDATA[
307  absolute-URI  = <absolute-URI, defined in [Part1], Section 2.7>
308  comment       = <comment, defined in [Part1], Section 3.2>
309  partial-URI   = <partial-URI, defined in [Part1], Section 2.7>
310  product       = <product, defined in [Part1], Section 5.2>
311  URI-reference = <URI-reference, defined in [Part1], Section 2.7>
312]]></artwork></figure>
313</section>
314</section>
315</section>
316
317<section title="Method" anchor="method">
318 
319 
320<t>
321   The Method token indicates the request method to be performed on the target
322   resource (Section 4.3 of <xref target="Part1"/>). The method is case-sensitive.
323</t>
324<figure><iref primary="true" item="Grammar" subitem="Method"/><artwork type="abnf2616"><![CDATA[
325  Method         = token
326]]></artwork></figure>
327<t>
328   The list of methods allowed by a resource can be specified in an
329   Allow header field (<xref target="header.allow"/>). The status code of the response
330   always notifies the client whether a method is currently allowed on a
331   resource, since the set of allowed methods can change dynamically. An
332   origin server SHOULD respond with the status code 405 (Method Not Allowed)
333   if the method is known by the origin server but not allowed for the
334   resource, and 501 (Not Implemented) if the method is
335   unrecognized or not implemented by the origin server. The methods GET
336   and HEAD MUST be supported by all general-purpose servers. All other
337   methods are OPTIONAL; however, if the above methods are implemented,
338   they MUST be implemented with the same semantics as those specified
339   in <xref target="method.definitions"/>.
340</t>
341
342<section title="Overview of Methods" anchor="overview.of.methods">
343<t>
344  The methods listed below are defined in <xref target="method.definitions"/>.
345</t>
346<texttable align="left">
347  <ttcol>Method Name</ttcol><ttcol>Defined in...</ttcol>
348 
349  <c>OPTIONS</c> <c><xref target="OPTIONS"/></c>
350  <c>GET</c> <c><xref target="GET"/></c>
351  <c>HEAD</c> <c><xref target="HEAD"/></c>
352  <c>POST</c> <c><xref target="POST"/></c>
353  <c>PUT</c> <c><xref target="PUT"/></c>
354  <c>DELETE</c> <c><xref target="DELETE"/></c>
355  <c>TRACE</c> <c><xref target="TRACE"/></c>
356  <c>CONNECT</c> <c><xref target="CONNECT"/></c>
357</texttable>
358<t>
359  Note that this list is not exhaustive — it does not include request methods defined
360  in other specifications.
361</t>
362</section>
363
364<section title="Method Registry" anchor="method.registry">
365<t>
366  The HTTP Method Registry defines the name space for the Method token in the
367  Request line of an HTTP request.
368</t>
369<t>
370  Registrations MUST include the following fields:
371  <list style="symbols">
372    <t>Method Name (see <xref target="method"/>)</t>
373    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
374    <t>Pointer to specification text</t>
375  </list>
376</t>
377<t>
378  Values to be added to this name space are subject to IETF review
379  (<xref target="RFC5226"/>, Section 4.1).
380</t>
381<t>
382  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
383</t>
384
385<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
386<t>
387   When it is necessary to express new semantics for a HTTP request that
388   aren't specific to a single application or media type, and currently defined
389   methods are inadequate, it may be appropriate to register a new method.
390</t>
391<t>
392   HTTP methods are generic; that is, they are potentially applicable to any
393   resource, not just one particular media type, "type" of resource, or
394   application. As such, it is preferred that new HTTP methods be registered
395   in a document that isn't specific to a single application, so that this is
396   clear.
397</t>
398<t>
399   Due to the parsing rules defined in Section 3.3 of <xref target="Part1"/>, definitions of HTTP
400   methods cannot prohibit the presence of a message-body on either the request
401   or the response message (with responses to HEAD requests being the single
402   exception). Definitions of new methods cannot change this rule, but they can
403   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
404</t>
405<t>
406   New method definitions need to indicate whether they are safe (<xref target="safe.methods"/>), what semantics (if any) the request body has,
407   and whether they are idempotent (<xref target="idempotent.methods"/>).
408   They also need to state whether they can be cached (<xref target="Part6"/>); in
409   particular what conditions a cache may store the response, and under what
410   conditions such a stored response may be used to satisfy a subsequent
411   request.
412</t>
413</section>
414
415</section>
416</section>
417
418<section title="Header Fields" anchor="header.fields">
419<t>
420   Header fields are key value pairs that can be used to communicate data about
421   the message, its payload, the target resource, or about the connection
422   itself (i.e., control data).  See Section 3.2 of <xref target="Part1"/> for a general definition
423   of their syntax.
424</t>
425
426<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
427<t>
428   New header fields are registered using the procedures described in
429   <xref target="RFC3864"/>.
430</t>
431<t>
432   The requirements for header field names are defined in
433   Section 4.1 of <xref target="RFC3864"/>.  Authors of specifications
434   defining new fields are advised to keep the name as short as practical, and
435   not to prefix them with "X-" if they are to be registered (either
436   immediately or in the future).
437</t>
438<t>
439   New header field values typically have their syntax defined using ABNF
440   (<xref target="RFC5234"/>), using the extensions defined in Section 1.2.1 of <xref target="Part1"/>
441   as necessary, and are usually constrained to the range of ASCII characters.
442   Header fields needing a greater range of characters can use an encoding
443   such as the one defined in <xref target="RFC5987"/>.
444</t>
445<t>
446   Because commas (",") are used as a generic delimiter between field-values,
447   they need to be treated with care if they are allowed in the field-value's
448   payload. Typically, components that might contain a comma are protected with
449   double-quotes using the quoted-string ABNF production (Section 3.2.3 of <xref target="Part1"/>).
450</t>
451<t>
452   For example, a textual date and a URI (either of which might contain a comma)
453   could be safely carried in field-values like these:
454</t>
455<figure><artwork type="example"><![CDATA[
456  Example-URI-Field: "http://example.com/a.html,foo",
457                     "http://without-a-comma.example.com/"
458  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
459]]></artwork></figure>
460<t>
461   Note that double quote delimiters almost always are used with the
462   quoted-string production; using a different syntax inside double quotes
463   will likely cause unnecessary confusion.
464</t>
465<t>
466   Many header fields use a format including (case-insensitively) named
467   parameters (for instance, Content-Type, defined in Section 6.8 of <xref target="Part3"/>).
468   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
469   parameter value enables recipients to use existing parser components. When
470   allowing both forms, the meaning of a parameter value ought to be
471   independent of the syntax used for it (for an example, see the notes on
472   parameter handling for media types in Section 2.3 of <xref target="Part3"/>).
473</t>
474<t>
475   Authors of specifications defining new header fields are advised to consider
476   documenting:
477  <list style="symbols">
478    <t>Whether the field is a single value, or whether it can be a list
479      (delimited by commas; see Section 3.2 of <xref target="Part1"/>).<vspace blankLines="1"/>If it does not use the list syntax, document how to treat messages
480      where the header field occurs multiple times (a sensible default would
481      be to ignore the header field, but this might not always be the right
482      choice).<vspace blankLines="1"/>Note that intermediaries and software libraries might combine
483      multiple header field instances into a single one, despite the header
484      field not allowing this. A robust format enables recipients to discover
485      these situations (good example: "Content-Type", as the comma can only
486      appear inside quoted strings; bad example: "Location", as a comma can
487      occur inside a URI).</t>
488    <t>Under what conditions the header field can be used; e.g., only in
489    responses or requests, in all messages, only on responses to a particular
490    request method.</t>
491    <t>Whether it is appropriate to list the field-name in the Connection header
492    (i.e., if the header is to be hop-by-hop, see Section 8.1 of <xref target="Part1"/>).</t>
493    <t>Under what conditions intermediaries are allowed to modify the header
494    field's value, insert or delete it.</t>
495    <t>How the header might interact with caching (see <xref target="Part6"/>).</t>
496    <t>Whether the header field is useful or allowable in trailers (see
497    Section 5.1.1 of <xref target="Part1"/>).</t>
498    <t>Whether the header field should be preserved across redirects.</t>
499  </list>
500</t>
501</section>
502
503<section title="Request Header Fields" anchor="request.header.fields">
504 
505<t>
506   The request header fields allow the client to pass additional
507   information about the request, and about the client itself, to the
508   server. These fields act as request modifiers, with semantics
509   equivalent to the parameters on a programming language method
510   invocation.
511</t>
512<texttable align="left">
513  <ttcol>Header Field Name</ttcol>
514  <ttcol>Defined in...</ttcol>
515
516  <c>Accept</c> <c>Section 6.1 of <xref target="Part3"/></c>
517  <c>Accept-Charset</c> <c>Section 6.2 of <xref target="Part3"/></c>
518  <c>Accept-Encoding</c> <c>Section 6.3 of <xref target="Part3"/></c>
519  <c>Accept-Language</c> <c>Section 6.4 of <xref target="Part3"/></c>
520  <c>Authorization</c> <c>Section 4.1 of <xref target="Part7"/></c>
521  <c>Expect</c> <c><xref target="header.expect"/></c>
522  <c>From</c> <c><xref target="header.from"/></c>
523  <c>Host</c> <c>Section 8.3 of <xref target="Part1"/></c>
524  <c>If-Match</c> <c>Section 3.1 of <xref target="Part4"/></c>
525  <c>If-Modified-Since</c> <c>Section 3.3 of <xref target="Part4"/></c>
526  <c>If-None-Match</c> <c>Section 3.2 of <xref target="Part4"/></c>
527  <c>If-Range</c> <c>Section 5.3 of <xref target="Part5"/></c>
528  <c>If-Unmodified-Since</c> <c>Section 3.4 of <xref target="Part4"/></c>
529  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
530  <c>Proxy-Authorization</c> <c>Section 4.3 of <xref target="Part7"/></c>
531  <c>Range</c> <c>Section 5.4 of <xref target="Part5"/></c>
532  <c>Referer</c> <c><xref target="header.referer"/></c>
533  <c>TE</c> <c>Section 8.4 of <xref target="Part1"/></c>
534  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
535</texttable>
536</section>
537
538<section title="Response Header Fields" anchor="response.header.fields">
539 
540<t>
541   The response header fields allow the server to pass additional
542   information about the response which cannot be placed in the Status-Line.
543   These header fields give information about the server and about
544   further access to the target resource (Section 4.3 of <xref target="Part1"/>).
545</t>
546<texttable align="left">
547  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
548
549  <c>Accept-Ranges</c> <c>Section 5.1 of <xref target="Part5"/></c>
550  <c>Age</c> <c>Section 3.1 of <xref target="Part6"/></c>
551  <c>Allow</c> <c><xref target="header.allow"/></c>
552  <c>Date</c> <c><xref target="header.date"/></c>
553  <c>ETag</c> <c>Section 2.3 of <xref target="Part4"/></c>
554  <c>Location</c> <c><xref target="header.location"/></c>
555  <c>Proxy-Authenticate</c> <c>Section 4.2 of <xref target="Part7"/></c>
556  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
557  <c>Server</c> <c><xref target="header.server"/></c>
558  <c>Vary</c> <c>Section 3.5 of <xref target="Part6"/></c>
559  <c>WWW-Authenticate</c> <c>Section 4.4 of <xref target="Part7"/></c>
560</texttable>
561</section>
562
563</section>
564
565<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
566 
567 
568 
569<t>
570   The Status-Code element is a 3-digit integer result code of the attempt to
571   understand and satisfy the request.
572</t>
573<t>
574   The Reason-Phrase is intended to give a short textual description of the
575   Status-Code and is intended for a human user. The client does not need
576   to examine or display the Reason-Phrase.
577</t>
578<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[
579  Status-Code    = 3DIGIT
580  Reason-Phrase  = *( HTAB / SP / VCHAR / obs-text )
581]]></artwork></figure>
582<t>
583   HTTP status codes are extensible. HTTP applications are not required
584   to understand the meaning of all registered status codes, though such
585   understanding is obviously desirable. However, applications MUST
586   understand the class of any status code, as indicated by the first
587   digit, and treat any unrecognized response as being equivalent to the
588   x00 status code of that class, with the exception that an
589   unrecognized response MUST NOT be cached. For example, if an
590   unrecognized status code of 431 is received by the client, it can
591   safely assume that there was something wrong with its request and
592   treat the response as if it had received a 400 status code. In such
593   cases, user agents SHOULD present to the user the representation enclosed
594   with the response, since that representation is likely to include human-readable
595   information which will explain the unusual status.
596</t>
597
598<section title="Overview of Status Codes" anchor="overview.of.status.codes">
599<t> 
600   The status codes listed below are defined in <xref target="status.codes"/>
601   of this specification, Section 4 of <xref target="Part4"/>, Section 3 of <xref target="Part5"/>, and Section 3 of <xref target="Part7"/>.
602   The reason phrases listed here are only recommendations — they can be
603   replaced by local equivalents without affecting the protocol.
604</t>
605<texttable align="left">
606  <ttcol>Status-Code</ttcol>
607  <ttcol>Reason-Phrase</ttcol>
608  <ttcol>Defined in...</ttcol>
609 
610  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
611  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
612
613  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
614  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
615  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
616  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
617  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
618  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
619  <c>206</c> <c>Partial Content</c> <c>Section 3.1 of <xref target="Part5"/></c>
620
621  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
622  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
623  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
624  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
625  <c>304</c> <c>Not Modified</c> <c>Section 4.1 of <xref target="Part4"/></c>
626  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
627  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
628
629  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
630  <c>401</c> <c>Unauthorized</c> <c>Section 3.1 of <xref target="Part7"/></c>
631  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
632  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
633  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
634  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
635  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
636  <c>407</c> <c>Proxy Authentication Required</c> <c>Section 3.2 of <xref target="Part7"/></c>
637  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
638  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
639  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
640  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
641  <c>412</c> <c>Precondition Failed</c> <c>Section 4.2 of <xref target="Part4"/></c>
642  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
643  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
644  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
645  <c>416</c> <c>Requested range not satisfiable</c> <c>Section 3.2 of <xref target="Part5"/></c>
646  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
647  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
648
649  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
650  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
651  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
652  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
653  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
654  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
655</texttable>
656<t>
657   Note that this list is not exhaustive — it does not include
658   extension status codes defined in other specifications.
659</t>
660</section>
661
662<section title="Status Code Registry" anchor="status.code.registry">
663<t>
664  The HTTP Status Code Registry defines the name space for the Status-Code
665  token in the Status-Line of an HTTP response.
666</t>
667<t>
668  Values to be added to this name space are subject to IETF review
669  (<xref target="RFC5226"/>, Section 4.1).
670</t>
671<t>
672  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
673</t>
674
675<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
676<t>
677   When it is necessary to express new semantics for a HTTP response that
678   aren't specific to a single application or media type, and currently defined
679   status codes are inadequate, a new status code can be registered.
680</t>
681<t>
682   HTTP status codes are generic; that is, they are potentially applicable to
683   any resource, not just one particular media type, "type" of resource, or
684   application. As such, it is preferred that new HTTP status codes be
685   registered in a document that isn't specific to a single application, so
686   that this is clear.
687</t>
688<t>
689   Definitions of new HTTP status codes typically explain the request
690   conditions that produce a response containing the status code (e.g.,
691   combinations of request headers and/or method(s)), along with any
692   interactions with response headers (e.g., those that are required, those
693   that modify the semantics of the response).
694</t>
695<t>
696   New HTTP status codes are required to fall under one of the categories
697   defined in <xref target="status.codes"/>. To allow existing parsers to
698   properly handle them, new status codes cannot disallow a response body,
699   although they can mandate a zero-length response body. They can require the
700   presence of one or more particular HTTP response header(s).
701</t>
702<t>
703   Likewise, their definitions can specify that caches are allowed to use
704   heuristics to determine their freshness (see <xref target="Part6"/>; by default, it is
705   not allowed), and can define how to determine the resource which they
706   carry a representation for (see <xref target="identifying.response.associated.with.representation"/>; by default,
707   it is anonymous).
708</t>
709</section>
710
711</section>
712
713</section>
714
715<section title="Representation" anchor="representation">
716<t>
717   Request and Response messages MAY transfer a representation if not otherwise
718   restricted by the request method or response status code. A representation
719   consists of metadata (representation header fields) and data (representation
720   body).  When a complete or partial representation is enclosed in an HTTP message,
721   it is referred to as the payload of the message. HTTP representations
722   are defined in <xref target="Part3"/>.
723</t>
724<t>
725   A representation body is only present in a message when a message-body is
726   present, as described in Section 3.3 of <xref target="Part1"/>. The representation body is obtained
727   from the message-body by decoding any Transfer-Encoding that might
728   have been applied to ensure safe and proper transfer of the message.
729</t>
730
731<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
732<t>
733   It is sometimes necessary to determine an identifier for the resource
734   associated with a representation.
735</t>
736<t>
737   An HTTP request representation, when present, is always associated with an
738   anonymous (i.e., unidentified) resource.
739</t>
740<t>
741   In the common case, an HTTP response is a representation of the target
742   resource (see Section 4.3 of <xref target="Part1"/>). However, this is not always the
743   case. To determine the URI of the resource a response is associated with,
744   the following rules are used (with the first applicable one being selected):
745</t>
746<t><list style="numbers">
747   <t>If the response status code is 200 or 203 and the request method was GET,
748   the response payload is a representation of the target resource.</t>
749   <t>If the response status code is 204, 206, or 304 and the request method was GET
750   or HEAD, the response payload is a partial representation of the target
751   resource.</t>
752   <t>If the response has a Content-Location header field, and that URI is the same
753   as the effective request URI, the response payload is a representation of the
754   target resource.</t>
755   <t>If the response has a Content-Location header field, and that URI is not the
756   same as the effective request URI, then the response asserts that its
757   payload is a representation of the resource identified by the
758   Content-Location URI. However, such an assertion cannot be trusted unless
759   it can be verified by other means (not defined by HTTP).</t>
760   <t>Otherwise, the response is a representation of an anonymous (i.e.,
761   unidentified) resource.</t>
762</list></t>
763<t>
764  <cref anchor="TODO-req-uri">
765   The comparison function is going to have to be defined somewhere,
766   because we already need to compare URIs for things like cache invalidation.</cref>
767</t>
768</section>
769
770</section>
771
772
773<section title="Method Definitions" anchor="method.definitions">
774<t>
775   The set of common request methods for HTTP/1.1 is defined below. Although
776   this set can be expanded, additional methods cannot be assumed to
777   share the same semantics for separately extended clients and servers.
778</t>
779
780<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
781
782<section title="Safe Methods" anchor="safe.methods">
783<iref item="Safe Methods" primary="true"/>
784<t>
785   Implementors need to be aware that the software represents the user in
786   their interactions over the Internet, and need to allow
787   the user to be aware of any actions they take which might have an
788   unexpected significance to themselves or others.
789</t>
790<t>
791   In particular, the convention has been established that the GET, HEAD,
792   OPTIONS, and TRACE request methods SHOULD NOT have the significance
793   of taking an action other than retrieval. These request methods ought
794   to be considered "safe".
795   This allows user agents to represent other methods, such as POST, PUT
796   and DELETE, in a special way, so that the user is made aware of the
797   fact that a possibly unsafe action is being requested.
798</t>
799<t>
800   Naturally, it is not possible to ensure that the server does not
801   generate side-effects as a result of performing a GET request; in
802   fact, some dynamic resources consider that a feature. The important
803   distinction here is that the user did not request the side-effects,
804   so therefore cannot be held accountable for them.
805</t>
806</section>
807
808<section title="Idempotent Methods" anchor="idempotent.methods">
809<iref item="Idempotent Methods" primary="true"/>
810<t>
811   Request methods can also have the property of "idempotence" in that,
812   aside from error or expiration issues, the intended effect of multiple
813   identical requests is the same as for a single request.
814   PUT, DELETE, and all safe request methods are idempotent.
815   It is important to note that idempotence refers only to changes
816   requested by the client: a server is free to change its state due
817   to multiple requests for the purpose of tracking those requests,
818   versioning of results, etc.
819</t>
820</section>
821</section>
822
823<section title="OPTIONS" anchor="OPTIONS">
824 
825  <iref primary="true" item="OPTIONS method"/>
826  <iref primary="true" item="Methods" subitem="OPTIONS"/>
827<t>
828   The OPTIONS method requests information about the
829   communication options available on the request/response chain
830   identified by the effective request URI. This method allows a client to
831   determine the options and/or requirements associated with a resource,
832   or the capabilities of a server, without implying a resource action
833   or initiating a resource retrieval.
834</t>
835<t>
836   Responses to the OPTIONS method are not cacheable.
837</t>
838<t>
839   If the OPTIONS request includes a message-body (as indicated by the
840   presence of Content-Length or Transfer-Encoding), then the media type
841   MUST be indicated by a Content-Type field. Although this
842   specification does not define any use for such a body, future
843   extensions to HTTP might use the OPTIONS body to make more detailed
844   queries on the server.
845</t>
846<t>
847   If the request-target is an asterisk ("*"), the OPTIONS request is
848   intended to apply to the server in general rather than to a specific
849   resource. Since a server's communication options typically depend on
850   the resource, the "*" request is only useful as a "ping" or "no-op"
851   type of method; it does nothing beyond allowing the client to test
852   the capabilities of the server. For example, this can be used to test
853   a proxy for HTTP/1.1 compliance (or lack thereof).
854</t>
855<t>
856   If the request-target is not an asterisk, the OPTIONS request applies
857   only to the options that are available when communicating with that
858   resource.
859</t>
860<t>
861   A 200 response SHOULD include any header fields that indicate
862   optional features implemented by the server and applicable to that
863   resource (e.g., Allow), possibly including extensions not defined by
864   this specification. The response body, if any, SHOULD also include
865   information about the communication options. The format for such a
866   body is not defined by this specification, but might be defined by
867   future extensions to HTTP. Content negotiation MAY be used to select
868   the appropriate response format. If no response body is included, the
869   response MUST include a Content-Length field with a field-value of
870   "0".
871</t>
872<t>
873   The Max-Forwards header field MAY be used to target a
874   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
875   If no Max-Forwards field is present in the request, then the forwarded
876   request MUST NOT include a Max-Forwards field.
877</t>
878</section>
879
880<section title="GET" anchor="GET">
881 
882  <iref primary="true" item="GET method"/>
883  <iref primary="true" item="Methods" subitem="GET"/>
884<t>
885   The GET method requests transfer of a current representation of
886   the target resource.
887</t>
888<t>   
889   If the target resource is a data-producing process, it is the
890   produced data which shall be returned as the representation in the response and not
891   the source text of the process, unless that text happens to be the output of
892   the process.
893</t>
894<t>
895   The semantics of the GET method change to a "conditional GET" if the
896   request message includes an If-Modified-Since, If-Unmodified-Since,
897   If-Match, If-None-Match, or If-Range header field. A conditional GET
898   requests that the representation be transferred only under the
899   circumstances described by the conditional header field(s). The
900   conditional GET request is intended to reduce unnecessary network
901   usage by allowing cached representations to be refreshed without requiring
902   multiple requests or transferring data already held by the client.
903</t>
904<t>
905   The semantics of the GET method change to a "partial GET" if the
906   request message includes a Range header field. A partial GET requests
907   that only part of the representation be transferred, as described in Section 5.4 of <xref target="Part5"/>.
908   The partial GET request is intended to reduce unnecessary
909   network usage by allowing partially-retrieved representations to be
910   completed without transferring data already held by the client.
911</t>
912<t>
913   Bodies on GET requests have no defined semantics. Note that sending a body
914   on a GET request might cause some existing implementations to reject the
915   request.
916</t>
917<t>
918   The response to a GET request is cacheable and MAY be used to satisfy
919   subsequent GET and HEAD requests (see <xref target="Part6"/>).
920</t>
921<t>
922   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
923</t>
924</section>
925
926<section title="HEAD" anchor="HEAD">
927 
928  <iref primary="true" item="HEAD method"/>
929  <iref primary="true" item="Methods" subitem="HEAD"/>
930<t>
931   The HEAD method is identical to GET except that the server MUST NOT
932   return a message-body in the response. The metadata contained
933   in the HTTP header fields in response to a HEAD request SHOULD be identical
934   to the information sent in response to a GET request. This method can
935   be used for obtaining metadata about the representation implied by the
936   request without transferring the representation body. This method is
937   often used for testing hypertext links for validity, accessibility,
938   and recent modification.
939</t>
940<t>
941   The response to a HEAD request is cacheable and MAY be used to satisfy
942   a subsequent HEAD request; see <xref target="Part6"/>. It also MAY be used to update a previously cached
943   representation from that resource; if the new field values
944   indicate that the cached representation differs from the current representation (as
945   would be indicated by a change in Content-Length, ETag
946   or Last-Modified), then the cache MUST treat the cache entry as
947   stale.
948</t>
949<t>
950   Bodies on HEAD requests have no defined semantics. Note that sending a body
951   on a HEAD request might cause some existing implementations to reject the
952   request.
953</t>
954</section>
955
956<section title="POST" anchor="POST">
957  <iref primary="true" item="POST method"/>
958  <iref primary="true" item="Methods" subitem="POST"/>
959<t>
960   The POST method requests that the origin server accept the
961   representation enclosed in the request as data to be processed by the
962   target resource. POST is designed to allow a uniform method to cover the
963   following functions:
964  <list style="symbols">
965    <t>
966      Annotation of existing resources;
967    </t>
968    <t>
969        Posting a message to a bulletin board, newsgroup, mailing list,
970        or similar group of articles;
971    </t>
972    <t>
973        Providing a block of data, such as the result of submitting a
974        form, to a data-handling process;
975    </t>
976    <t>
977        Extending a database through an append operation.
978    </t>
979  </list>
980</t>
981<t>
982   The actual function performed by the POST method is determined by the
983   server and is usually dependent on the effective request URI.
984</t>
985<t>
986   The action performed by the POST method might not result in a
987   resource that can be identified by a URI. In this case, either 200
988   (OK) or 204 (No Content) is the appropriate response status code,
989   depending on whether or not the response includes a representation that
990   describes the result.
991</t>
992<t>
993   If a resource has been created on the origin server, the response
994   SHOULD be 201 (Created) and contain a representation which describes the
995   status of the request and refers to the new resource, and a Location
996   header field (see <xref target="header.location"/>).
997</t>
998<t>
999   Responses to POST requests are only cacheable when they
1000   include explicit freshness information (see Section 2.3.1 of <xref target="Part6"/>). A
1001   cached POST response with a Content-Location header field
1002   (see Section 6.7 of <xref target="Part3"/>) whose value is the effective
1003   Request URI MAY be used to satisfy subsequent GET and HEAD requests.
1004</t>
1005<t>
1006   Note that POST caching is not widely implemented.
1007   However, the 303 (See Other) response can be used to direct the
1008   user agent to retrieve a cacheable resource.
1009</t>
1010</section>
1011
1012<section title="PUT" anchor="PUT">
1013  <iref primary="true" item="PUT method"/>
1014  <iref primary="true" item="Methods" subitem="PUT"/>
1015<t>
1016   The PUT method requests that the state of the target resource
1017   be created or replaced with the state defined by the representation
1018   enclosed in the request message payload.  A successful PUT of a given
1019   representation would suggest that a subsequent GET on that same target
1020   resource will result in an equivalent representation being returned in
1021   a 200 (OK) response.  However, there is no guarantee that such a state
1022   change will be observable, since the target resource might be acted
1023   upon by other user agents in parallel, or might be subject to dynamic
1024   processing by the origin server, before any subsequent GET is received.
1025   A successful response only implies that the user agent's intent was
1026   achieved at the time of its processing by the origin server.
1027</t>
1028<t>   
1029   If the target resource does not have a current representation and
1030   the PUT successfully creates one, then the origin server MUST inform
1031   the user agent by sending a 201 (Created) response.  If the target
1032   resource does have a current representation and that representation is
1033   successfully modified in accordance with the state of the enclosed
1034   representation, then either a 200 (OK) or 204 (No Content) response
1035   SHOULD be sent to indicate successful completion of the request.
1036</t>
1037<t>
1038   Unrecognized header fields SHOULD be ignored (i.e., not saved
1039   as part of the resource state).
1040</t>
1041<t>
1042   An origin server SHOULD verify that the PUT representation is
1043   consistent with any constraints which the server has for the target
1044   resource that cannot or will not be changed by the PUT.  This is
1045   particularly important when the origin server uses internal
1046   configuration information related to the URI in order to set the
1047   values for representation metadata on GET responses.  When a PUT
1048   representation is inconsistent with the target resource, the origin
1049   server SHOULD either make them consistent, by transforming the
1050   representation or changing the resource configuration, or respond
1051   with an appropriate error message containing sufficient information
1052   to explain why the representation is unsuitable.  The 409 (Conflict)
1053   or 415 (Unsupported Media Type) status codes are suggested, with the
1054   latter being specific to constraints on Content-Type values.
1055</t>
1056<t>
1057   For example, if the target resource is configured to always have a
1058   Content-Type of "text/html" and the representation being PUT has a
1059   Content-Type of "image/jpeg", then the origin server SHOULD do one of:
1060   (a) reconfigure the target resource to reflect the new media type;
1061   (b) transform the PUT representation to a format consistent with that
1062   of the resource before saving it as the new resource state; or,
1063   (c) reject the request with a 415 response indicating that the target
1064   resource is limited to "text/html", perhaps including a link to a
1065   different resource that would be a suitable target for the new
1066   representation.
1067</t>
1068<t>
1069   HTTP does not define exactly how a PUT method affects the state
1070   of an origin server beyond what can be expressed by the intent of
1071   the user agent request and the semantics of the origin server response.
1072   It does not define what a resource might be, in any sense of that
1073   word, beyond the interface provided via HTTP.  It does not define
1074   how resource state is "stored", nor how such storage might change
1075   as a result of a change in resource state, nor how the origin server
1076   translates resource state into representations.  Generally speaking,
1077   all implementation details behind the resource interface are
1078   intentionally hidden by the server.
1079</t>
1080<t>
1081   The fundamental difference between the POST and PUT methods is
1082   highlighted by the different intent for the target resource.
1083   The target resource in a POST request is intended to handle the
1084   enclosed representation as a data-accepting process, such as for
1085   a gateway to some other protocol or a document that accepts annotations.
1086   In contrast, the target resource in a PUT request is intended to
1087   take the enclosed representation as a new or replacement value.
1088   Hence, the intent of PUT is idempotent and visible to intermediaries,
1089   even though the exact effect is only known by the origin server.
1090</t>
1091<t>
1092   Proper interpretation of a PUT request presumes that the user agent
1093   knows what target resource is desired.  A service that is intended
1094   to select a proper URI on behalf of the client, after receiving
1095   a state-changing request, SHOULD be implemented using the POST
1096   method rather than PUT.  If the origin server will not make the
1097   requested PUT state change to the target resource and instead
1098   wishes to have it applied to a different resource, such as when the
1099   resource has been moved to a different URI, then the origin server
1100   MUST send a 301 (Moved Permanently) response; the user agent MAY
1101   then make its own decision regarding whether or not to redirect the
1102   request.
1103</t>
1104<t>
1105   A PUT request applied to the target resource MAY have side-effects
1106   on other resources.  For example, an article might have a URI for
1107   identifying "the current version" (a resource) which is separate
1108   from the URIs identifying each particular version (different
1109   resources that at one point shared the same state as the current version
1110   resource).  A successful PUT request on "the current version" URI might
1111   therefore create a new version resource in addition to changing the
1112   state of the target resource, and might also cause links to be added
1113   between the related resources.
1114</t>
1115<t>
1116   An origin server SHOULD reject any PUT request that contains a
1117   Content-Range header field, since it might be misinterpreted as
1118   partial content (or might be partial content that is being mistakenly
1119   PUT as a full representation).  Partial content updates are
1120   possible by targeting a separately identified resource with state
1121   that overlaps a portion of the larger resource, or by using a
1122   different method that has been specifically defined for partial
1123   updates (for example, the PATCH method defined in
1124   <xref target="RFC5789"/>).
1125</t>
1126<t>
1127   Responses to the PUT method are not cacheable. If a PUT request passes
1128   through a cache that has one or more stored responses for the effective
1129   request URI, those stored responses will be invalidated (see
1130   Section 2.5 of <xref target="Part6"/>).
1131</t>
1132</section>
1133
1134<section title="DELETE" anchor="DELETE">
1135  <iref primary="true" item="DELETE method"/>
1136  <iref primary="true" item="Methods" subitem="DELETE"/>
1137<t>
1138   The DELETE method requests that the origin server delete the target
1139   resource. This method MAY be overridden by
1140   human intervention (or other means) on the origin server. The client cannot
1141   be guaranteed that the operation has been carried out, even if the
1142   status code returned from the origin server indicates that the action
1143   has been completed successfully. However, the server SHOULD NOT
1144   indicate success unless, at the time the response is given, it
1145   intends to delete the resource or move it to an inaccessible
1146   location.
1147</t>
1148<t>
1149   A successful response SHOULD be 200 (OK) if the response includes an
1150   representation describing the status, 202 (Accepted) if the action has not
1151   yet been enacted, or 204 (No Content) if the action has been enacted
1152   but the response does not include a representation.
1153</t>
1154<t>
1155   Bodies on DELETE requests have no defined semantics. Note that sending a body
1156   on a DELETE request might cause some existing implementations to reject the
1157   request.
1158</t>
1159<t>
1160   Responses to the DELETE method are not cacheable. If a DELETE request
1161   passes through a cache that has one or more stored responses for the
1162   effective request URI, those stored responses will be invalidated (see
1163   Section 2.5 of <xref target="Part6"/>).
1164</t>
1165</section>
1166
1167<section title="TRACE" anchor="TRACE">
1168 
1169  <iref primary="true" item="TRACE method"/>
1170  <iref primary="true" item="Methods" subitem="TRACE"/>
1171<t>
1172   The TRACE method requests a remote, application-layer loop-back
1173   of the request message. The final recipient of the request
1174   SHOULD reflect the message received back to the client as the
1175   message-body of a 200 (OK) response. The final recipient is either the
1176   origin server or the first proxy to receive a Max-Forwards
1177   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
1178   A TRACE request MUST NOT include a message-body.
1179</t>
1180<t>
1181   TRACE allows the client to see what is being received at the other
1182   end of the request chain and use that data for testing or diagnostic
1183   information. The value of the Via header field (Section 8.8 of <xref target="Part1"/>) is of
1184   particular interest, since it acts as a trace of the request chain.
1185   Use of the Max-Forwards header field allows the client to limit the
1186   length of the request chain, which is useful for testing a chain of
1187   proxies forwarding messages in an infinite loop.
1188</t>
1189<t>
1190   If the request is valid, the response SHOULD have a Content-Type of
1191   "message/http" (see Section 9.3.1 of <xref target="Part1"/>) and contain a message-body
1192   that encloses a copy of the entire request message.
1193   Responses to the TRACE method are not cacheable.
1194</t>
1195</section>
1196
1197<section title="CONNECT" anchor="CONNECT">
1198  <iref primary="true" item="CONNECT method"/>
1199  <iref primary="true" item="Methods" subitem="CONNECT"/>
1200<t>
1201   The CONNECT method requests that the proxy establish a tunnel
1202   to the request-target and then restrict its behavior to blind
1203   forwarding of packets until the connection is closed.
1204</t>
1205<t>
1206   When using CONNECT, the request-target MUST use the authority form
1207   (Section 3.1.1.2 of <xref target="Part1"/>); i.e., the request-target consists of only the
1208   host name and port number of the tunnel destination, separated by a colon.
1209   For example,
1210</t>
1211<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1212  CONNECT server.example.com:80 HTTP/1.1
1213  Host: server.example.com:80
1214 
1215  ]]></artwork></figure>
1216<t>
1217   Other HTTP mechanisms can be used normally with the CONNECT method —
1218   except end-to-end protocol Upgrade requests, since the
1219   tunnel must be established first.
1220</t>
1221<t>
1222   For example, proxy authentication might be used to establish the
1223   authority to create a tunnel:
1224</t>
1225<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1226  CONNECT server.example.com:80 HTTP/1.1
1227  Host: server.example.com:80
1228  Proxy-Authorization: basic aGVsbG86d29ybGQ=
1229 
1230  ]]></artwork></figure>
1231<t>
1232   Bodies on CONNECT requests have no defined semantics. Note that sending a body
1233   on a CONNECT request might cause some existing implementations to reject the
1234   request.
1235</t>
1236<t>
1237   Like any other pipelined HTTP/1.1 request, data to be tunnel may be
1238   sent immediately after the blank line. The usual caveats also apply:
1239   data may be discarded if the eventual response is negative, and the
1240   connection may be reset with no response if more than one TCP segment
1241   is outstanding.
1242</t>
1243
1244<section title="Establishing a Tunnel with CONNECT">
1245<t>
1246   Any successful (2xx) response to a CONNECT request indicates that the
1247   proxy has established a connection to the requested host and port,
1248   and has switched to tunneling the current connection to that server
1249   connection.
1250</t>
1251<t>
1252   It may be the case that the proxy itself can only reach the requested
1253   origin server through another proxy.  In this case, the first proxy
1254   SHOULD make a CONNECT request of that next proxy, requesting a tunnel
1255   to the authority.  A proxy MUST NOT respond with any 2xx status code
1256   unless it has either a direct or tunnel connection established to the
1257   authority.
1258</t>
1259<t>
1260   An origin server which receives a CONNECT request for itself MAY
1261   respond with a 2xx status code to indicate that a connection is
1262   established.
1263</t>
1264<t>
1265   If at any point either one of the peers gets disconnected, any
1266   outstanding data that came from that peer will be passed to the other
1267   one, and after that also the other connection will be terminated by
1268   the proxy. If there is outstanding data to that peer undelivered,
1269   that data will be discarded.
1270</t>
1271
1272</section>
1273</section>
1274</section>
1275
1276
1277<section title="Status Code Definitions" anchor="status.codes">
1278<t>
1279   The first digit of the Status-Code defines the class of response. The
1280   last two digits do not have any categorization role. There are 5
1281   values for the first digit:
1282  <list style="symbols">
1283    <t>
1284      1xx: Informational - Request received, continuing process
1285    </t>
1286    <t>
1287      2xx: Success - The action was successfully received,
1288        understood, and accepted
1289    </t>
1290    <t>
1291      3xx: Redirection - Further action must be taken in order to
1292        complete the request
1293    </t>
1294    <t>
1295      4xx: Client Error - The request contains bad syntax or cannot
1296        be fulfilled
1297    </t>
1298    <t>
1299      5xx: Server Error - The server failed to fulfill an apparently
1300        valid request
1301    </t>
1302  </list>
1303</t>
1304<t>
1305   Each Status-Code is described below, including any metadata required
1306   in the response.
1307</t>
1308
1309<section title="Informational 1xx" anchor="status.1xx">
1310<t>
1311   This class of status code indicates a provisional response,
1312   consisting only of the Status-Line and optional header fields, and is
1313   terminated by an empty line. There are no required header fields for this
1314   class of status code. Since HTTP/1.0 did not define any 1xx status
1315   codes, servers MUST NOT send a 1xx response to an HTTP/1.0 client
1316   except under experimental conditions.
1317</t>
1318<t>
1319   A client MUST be prepared to accept one or more 1xx status responses
1320   prior to a regular response, even if the client does not expect a 100
1321   (Continue) status message. Unexpected 1xx status responses MAY be
1322   ignored by a user agent.
1323</t>
1324<t>
1325   Proxies MUST forward 1xx responses, unless the connection between the
1326   proxy and its client has been closed, or unless the proxy itself
1327   requested the generation of the 1xx response. (For example, if a
1328   proxy adds a "Expect: 100-continue" field when it forwards a request,
1329   then it need not forward the corresponding 100 (Continue)
1330   response(s).)
1331</t>
1332
1333<section title="100 Continue" anchor="status.100">
1334  <iref primary="true" item="100 Continue (status code)"/>
1335  <iref primary="true" item="Status Codes" subitem="100 Continue"/>
1336<t>
1337   The client SHOULD continue with its request. This interim response is
1338   used to inform the client that the initial part of the request has
1339   been received and has not yet been rejected by the server. The client
1340   SHOULD continue by sending the remainder of the request or, if the
1341   request has already been completed, ignore this response. The server
1342   MUST send a final response after the request has been completed. See
1343   Section 6.2.3 of <xref target="Part1"/> for detailed discussion of the use and handling of this
1344   status code.
1345</t>
1346</section>
1347
1348<section title="101 Switching Protocols" anchor="status.101">
1349  <iref primary="true" item="101 Switching Protocols (status code)"/>
1350  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols"/>
1351<t>
1352   The server understands and is willing to comply with the client's
1353   request, via the Upgrade message header field (Section 8.7 of <xref target="Part1"/>), for a
1354   change in the application protocol being used on this connection. The
1355   server will switch protocols to those defined by the response's
1356   Upgrade header field immediately after the empty line which
1357   terminates the 101 response.
1358</t>
1359<t>
1360   The protocol SHOULD be switched only when it is advantageous to do
1361   so. For example, switching to a newer version of HTTP is advantageous
1362   over older versions, and switching to a real-time, synchronous
1363   protocol might be advantageous when delivering resources that use
1364   such features.
1365</t>
1366</section>
1367</section>
1368
1369<section title="Successful 2xx" anchor="status.2xx">
1370<t>
1371   This class of status code indicates that the client's request was
1372   successfully received, understood, and accepted.
1373</t>
1374
1375<section title="200 OK" anchor="status.200">
1376  <iref primary="true" item="200 OK (status code)"/>
1377  <iref primary="true" item="Status Codes" subitem="200 OK"/>
1378<t>
1379   The request has succeeded. The payload returned with the response
1380   is dependent on the method used in the request, for example:
1381  <list style="hanging">
1382    <t hangText="GET">
1383      a representation of the target resource is sent in the response;
1384    </t>
1385    <t hangText="HEAD">
1386      the same representation as GET, except without the message-body;
1387    </t>
1388    <t hangText="POST">
1389      a representation describing or containing the result of the action;
1390    </t>
1391    <t hangText="TRACE">
1392      a representation containing the request message as received by the
1393      end server.
1394    </t>
1395  </list>
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 200 responses.
1400</t>
1401</section>
1402
1403<section title="201 Created" anchor="status.201">
1404  <iref primary="true" item="201 Created (status code)"/>
1405  <iref primary="true" item="Status Codes" subitem="201 Created"/>
1406<t>
1407   The request has been fulfilled and has resulted in a new resource being
1408   created. The newly created resource can be referenced by the URI(s)
1409   returned in the payload of the response, with the most specific URI
1410   for the resource given by a Location header field. The response
1411   SHOULD include a payload containing a list of resource
1412   characteristics and location(s) from which the user or user agent can
1413   choose the one most appropriate. The payload format is specified by
1414   the media type given in the Content-Type header field. The origin
1415   server MUST create the resource before returning the 201 status code.
1416   If the action cannot be carried out immediately, the server SHOULD
1417   respond with 202 (Accepted) response instead.
1418</t>
1419<t>
1420   A 201 response MAY contain an ETag response header field indicating
1421   the current value of the entity-tag for the representation of the resource
1422   just created (see Section 2.3 of <xref target="Part4"/>).
1423</t>
1424</section>
1425
1426<section title="202 Accepted" anchor="status.202">
1427  <iref primary="true" item="202 Accepted (status code)"/>
1428  <iref primary="true" item="Status Codes" subitem="202 Accepted"/>
1429<t>
1430   The request has been accepted for processing, but the processing has
1431   not been completed.  The request might or might not eventually be
1432   acted upon, as it might be disallowed when processing actually takes
1433   place. There is no facility for re-sending a status code from an
1434   asynchronous operation such as this.
1435</t>
1436<t>
1437   The 202 response is intentionally non-committal. Its purpose is to
1438   allow a server to accept a request for some other process (perhaps a
1439   batch-oriented process that is only run once per day) without
1440   requiring that the user agent's connection to the server persist
1441   until the process is completed. The representation returned with this
1442   response SHOULD include an indication of the request's current status
1443   and either a pointer to a status monitor or some estimate of when the
1444   user can expect the request to be fulfilled.
1445</t>
1446</section>
1447
1448<section title="203 Non-Authoritative Information" anchor="status.203">
1449  <iref primary="true" item="203 Non-Authoritative Information (status code)"/>
1450  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information"/>
1451<t>
1452   The representation in the response has been transformed or otherwise
1453   modified by a transforming proxy (Section 2.4 of <xref target="Part1"/>).  Note that the
1454   behaviour of transforming intermediaries is controlled by the no-transform
1455   Cache-Control directive (Section 3.2 of <xref target="Part6"/>).
1456</t>
1457<t>
1458   This status code is only appropriate when the response status code would
1459   have been 200 (OK) otherwise. When the status code before transformation
1460   would have been different, the 214 Transformation Applied warn-code
1461   (Section 3.6 of <xref target="Part6"/>) is appropriate.
1462</t>
1463<t>
1464   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine
1465   freshness for 203 responses.
1466</t>
1467</section>
1468
1469<section title="204 No Content" anchor="status.204">
1470  <iref primary="true" item="204 No Content (status code)"/>
1471  <iref primary="true" item="Status Codes" subitem="204 No Content"/>
1472<t>
1473   The 204 (No Content) status code indicates that the server has
1474   successfully fulfilled the request and that there is no additional
1475   content to return in the response payload body.  Metadata in the
1476   response header fields refer to the target resource and its current
1477   representation after the requested action.
1478</t>
1479<t>
1480   For example, if a 204 status code is received in response to a PUT
1481   request and the response contains an ETag header field, then the PUT
1482   was successful and the ETag field-value contains the entity-tag for
1483   the new representation of that target resource.
1484</t>
1485<t>
1486   The 204 response allows a server to indicate that the action has been
1487   successfully applied to the target resource while implying that the
1488   user agent SHOULD NOT traverse away from its current "document view"
1489   (if any).  The server assumes that the user agent will provide some
1490   indication of the success to its user, in accord with its own interface,
1491   and apply any new or updated metadata in the response to the active
1492   representation.
1493</t>
1494<t>
1495   For example, a 204 status code is commonly used with document editing
1496   interfaces corresponding to a "save" action, such that the document
1497   being saved remains available to the user for editing. It is also
1498   frequently used with interfaces that expect automated data transfers
1499   to be prevalent, such as within distributed version control systems.
1500</t>
1501<t>
1502   The 204 response MUST NOT include a message-body, and thus is always
1503   terminated by the first empty line after the header fields.
1504</t>
1505</section>
1506
1507<section title="205 Reset Content" anchor="status.205">
1508  <iref primary="true" item="205 Reset Content (status code)"/>
1509  <iref primary="true" item="Status Codes" subitem="205 Reset Content"/>
1510<t>
1511   The server has fulfilled the request and the user agent SHOULD reset
1512   the document view which caused the request to be sent. This response
1513   is primarily intended to allow input for actions to take place via
1514   user input, followed by a clearing of the form in which the input is
1515   given so that the user can easily initiate another input action.
1516</t>
1517<t>   
1518   The message-body included with the response MUST be empty. Note that
1519   receivers still need to parse the response according to the algorithm defined
1520   in Section 3.3 of <xref target="Part1"/>.
1521</t>
1522</section>
1523
1524<section title="206 Partial Content" anchor="status.206">
1525  <iref primary="true" item="206 Partial Content (status code)"/>
1526  <iref primary="true" item="Status Codes" subitem="206 Partial Content"/>
1527 
1528<t>
1529   The server has fulfilled the partial GET request for the resource
1530   and the enclosed payload is a partial representation as defined in Section 3.1 of <xref target="Part5"/>.
1531</t>
1532<t>
1533   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine
1534   freshness for 206 responses.
1535</t>
1536</section>
1537</section>
1538
1539<section title="Redirection 3xx" anchor="status.3xx">
1540<t>
1541   This class of status code indicates that further action needs to be
1542   taken by the user agent in order to fulfill the request.  If the required
1543   action involves a subsequent HTTP request, it MAY be carried out by the
1544   user agent without interaction with the user if and only if the method used
1545   in the second request is known to be "safe", as defined in
1546   <xref target="safe.methods"/>.
1547</t>
1548<t>
1549   There are several types of redirects:
1550   <list style="numbers">
1551      <t>
1552          Redirects of the request to another URI, either temporarily or
1553          permanently. The new URI is specified in the Location header field.
1554          In this specification, the status codes 301 (Moved Permanently),
1555          302 (Found), and 307 (Temporary Redirect) fall under this category.
1556        </t>
1557      <t>
1558          Redirection to a new location that represents an indirect response to
1559          the request, such as the result of a POST operation to be retrieved
1560          with a subsequent GET request. This is status code 303 (See Other).
1561        </t>
1562      <t>
1563          Redirection offering a choice of matching resources for use by
1564          agent-driven content negotiation (Section 5.2 of <xref target="Part3"/>). This
1565          is status code 300 (Multiple Choices).
1566        </t>
1567      <t>
1568          Other kinds of redirection, such as to a cached result (status code 304
1569          (Not Modified)).
1570        </t>
1571   </list>
1572</t>
1573<t><list>
1574  <t>
1575    Note: In HTTP/1.0, only the status codes 301 (Moved Permanently)
1576    and 302 (Found) were defined for the first type of redirect, and the second
1577    type did not exist at all (<xref target="RFC1945"/>, Section 9.3).
1578    However it turned out that web forms using POST expected redirects to change
1579    the operation for the subsequent request to retrieval (GET). To address this
1580    use case, HTTP/1.1 introduced the second type of redirect with the status
1581    code 303 (See Other) (<xref target="RFC2068"/>, Section 10.3.4).
1582    As user agents did not change their behavior to maintain backwards
1583    compatibility, the first revision of HTTP/1.1 added yet another status code,
1584    307 (Temporary Redirect), for which the backwards compatibility problems did
1585    not apply (<xref target="RFC2616"/>, Section 10.3.8).
1586    Over 10 years later, most user agents still do method rewriting for
1587    status codes 301 and 302, therefore this specification makes that behavior
1588    compliant in case the original request was POST.
1589  </t>
1590</list></t>
1591<t>
1592   A Location header field on a 3xx response indicates that a client MAY
1593   automatically redirect to the URI provided; see <xref target="header.location"/>.
1594</t>
1595<t>
1596   Clients SHOULD detect and intervene in cyclical redirections (i.e.,
1597   "infinite" redirection loops).
1598</t>
1599<t><list>
1600  <t>
1601    Note: An earlier version of this specification recommended a
1602    maximum of five redirections (<xref target="RFC2068"/>, Section 10.3).
1603    Content developers need to be aware that some clients might
1604    implement such a fixed limitation.
1605  </t>
1606</list></t>
1607
1608<section title="300 Multiple Choices" anchor="status.300">
1609  <iref primary="true" item="300 Multiple Choices (status code)"/>
1610  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices"/>
1611<t>
1612   The target resource has more than one
1613   representation, each with its own specific location, and agent-driven
1614   negotiation information (Section 5 of <xref target="Part3"/>) is being provided so that
1615   the user (or user agent) can select a preferred representation by
1616   redirecting its request to that location.
1617</t>
1618<t>
1619   Unless it was a HEAD request, the response SHOULD include a representation
1620   containing a list of representation metadata and location(s) from
1621   which the user or user agent can choose the one most appropriate. The
1622   data format is specified by the media type given in the Content-Type
1623   header field. Depending upon the format and the capabilities of
1624   the user agent, selection of the most appropriate choice MAY be
1625   performed automatically. However, this specification does not define
1626   any standard for such automatic selection.
1627</t>
1628<t>
1629   If the server has a preferred choice of representation, it SHOULD
1630   include the specific URI for that representation in the Location
1631   field; user agents MAY use the Location field value for automatic
1632   redirection.
1633</t>
1634<t>
1635   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine
1636   freshness for 300 responses.
1637</t>
1638
1639</section>
1640
1641<section title="301 Moved Permanently" anchor="status.301">
1642  <iref primary="true" item="301 Moved Permanently (status code)"/>
1643  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently"/>
1644<t>
1645   The target resource has been assigned a new permanent URI and any
1646   future references to this resource SHOULD use one of the returned
1647   URIs.  Clients with link editing capabilities ought to automatically
1648   re-link references to the effective request URI to one or more of the new
1649   references returned by the server, where possible.
1650</t>
1651<t>
1652   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine
1653   freshness for 301 responses.
1654</t>
1655<t>
1656   The new permanent URI SHOULD be given by the Location field in the
1657   response. Unless the request method was HEAD, the representation of the
1658   response SHOULD contain a short hypertext note with a hyperlink to
1659   the new URI(s).
1660</t>
1661<t>
1662   If the 301 status code is received in response to a request method
1663   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1664   then the request MAY be automatically redirected by the user agent without
1665   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
1666   request unless it can be confirmed by the user, since this might
1667   change the conditions under which the request was issued.
1668</t>
1669<t><list>
1670  <t>
1671    Note: For historic reasons, user agents MAY change the
1672    request method from POST to GET for the subsequent request. If this
1673    behavior is undesired, status code 307 (Temporary Redirect) can be used
1674    instead.
1675  </t>
1676</list></t>
1677</section>
1678
1679<section title="302 Found" anchor="status.302">
1680  <iref primary="true" item="302 Found (status code)"/>
1681  <iref primary="true" item="Status Codes" subitem="302 Found"/>
1682<t>
1683   The target resource resides temporarily under a different URI.
1684   Since the redirection might be altered on occasion, the client SHOULD
1685   continue to use the effective request URI for future requests.
1686</t>
1687<t>
1688   The temporary URI SHOULD be given by the Location field in the
1689   response. Unless the request method was HEAD, the representation of the
1690   response SHOULD contain a short hypertext note with a hyperlink to
1691   the new URI(s).
1692</t>
1693<t>
1694   If the 302 status code is received in response to a request method
1695   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1696   then the request MAY be automatically redirected by the user agent without
1697   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
1698   request unless it can be confirmed by the user, since this might
1699   change the conditions under which the request was issued.
1700</t>
1701<t><list>
1702  <t>
1703    Note: For historic reasons, user agents MAY change the
1704    request method from POST to GET for the subsequent request. If this
1705    behavior is undesired, status code 307 (Temporary Redirect) can be used
1706    instead.
1707    <cref anchor="issue312">but see &lt;http://trac.tools.ietf.org/wg/httpbis/trac/ticket/312&gt;</cref>
1708  </t>
1709</list></t>
1710</section>
1711
1712<section title="303 See Other" anchor="status.303">
1713  <iref primary="true" item="303 See Other (status code)"/>
1714  <iref primary="true" item="Status Codes" subitem="303 See Other"/>
1715<t>
1716   The 303 status code indicates that the server is redirecting the
1717   user agent to a different resource, as indicated by a URI in the
1718   Location header field, that is intended to provide an indirect
1719   response to the original request.  In order to satisfy the original
1720   request, a user agent SHOULD perform a retrieval request using the
1721   Location URI (a GET or HEAD request if using HTTP), which
1722   may itself be redirected further, and present the eventual result as an
1723   answer to the original request.
1724   Note that the new URI in the Location header field is not considered
1725   equivalent to the effective request URI.
1726</t>
1727<t>
1728   This status code is generally applicable to any HTTP method.  It is
1729   primarily used to allow the output of a POST action to redirect
1730   the user agent to a selected resource, since doing so provides the
1731   information corresponding to the POST response in a form that
1732   can be separately identified, bookmarked, and cached independent
1733   of the original request.
1734</t>
1735<t>
1736   A 303 response to a GET request indicates that the requested
1737   resource does not have a representation of its own that can be
1738   transferred by the server over HTTP.  The Location URI indicates a
1739   resource that is descriptive of the target resource, such that the
1740   follow-on representation might be useful to recipients without
1741   implying that it adequately represents the target resource.
1742   Note that answers to the questions of what can be represented, what
1743   representations are adequate, and what might be a useful description
1744   are outside the scope of HTTP and thus entirely determined by the
1745   URI owner(s).
1746</t>
1747<t>
1748   Except for responses to a HEAD request, the representation of a 303
1749   response SHOULD contain a short hypertext note with a hyperlink
1750   to the Location URI.
1751</t>
1752</section>
1753
1754<section title="304 Not Modified" anchor="status.304">
1755  <iref primary="true" item="304 Not Modified (status code)"/>
1756  <iref primary="true" item="Status Codes" subitem="304 Not Modified"/>
1757 
1758<t>
1759   The response to the request has not been modified since the conditions
1760   indicated by the client's conditional GET request, as defined in Section 4.1 of <xref target="Part4"/>.
1761</t>
1762</section>
1763
1764<section title="305 Use Proxy" anchor="status.305">
1765  <iref primary="true" item="305 Use Proxy (status code)"/>
1766  <iref primary="true" item="Status Codes" subitem="305 Use Proxy"/>
1767<t>
1768   The 305 status code was defined in a previous version of this specification
1769   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1770</t>
1771</section>
1772
1773<section title="306 (Unused)" anchor="status.306">
1774  <iref primary="true" item="306 (Unused) (status code)"/>
1775  <iref primary="true" item="Status Codes" subitem="306 (Unused)"/>
1776<t>
1777   The 306 status code was used in a previous version of the
1778   specification, is no longer used, and the code is reserved.
1779</t>
1780</section>
1781
1782<section title="307 Temporary Redirect" anchor="status.307">
1783  <iref primary="true" item="307 Temporary Redirect (status code)"/>
1784  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect"/>
1785<t>
1786   The target resource resides temporarily under a different URI.
1787   Since the redirection can change over time, the client SHOULD
1788   continue to use the effective request URI for future requests.
1789</t>
1790<t>
1791   The temporary URI SHOULD be given by the Location field in the
1792   response. Unless the request method was HEAD, the representation of the
1793   response SHOULD contain a short hypertext note with a hyperlink to
1794   the new URI(s), since many pre-HTTP/1.1 user agents do not
1795   understand the 307 status code. Therefore, the note SHOULD contain the
1796   information necessary for a user to repeat the original request on
1797   the new URI.
1798</t>
1799<t>
1800   If the 307 status code is received in response to a request method
1801   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1802   then the request MAY be automatically redirected by the user agent without
1803   confirmation.  Otherwise, the user agent MUST NOT automatically redirect the
1804   request unless it can be confirmed by the user, since this might
1805   change the conditions under which the request was issued.
1806</t>
1807<t><list>
1808  <t>
1809    Note: This status code is similar to 302 Found, except that
1810    it does not allow rewriting the request method from POST to GET. This
1811    specification defines no equivalent counterpart for 301 Moved Permanently.
1812  </t>
1813</list></t>
1814</section>
1815</section>
1816
1817<section title="Client Error 4xx" anchor="status.4xx">
1818<t>
1819   The 4xx class of status code is intended for cases in which the
1820   client seems to have erred. Except when responding to a HEAD request,
1821   the server SHOULD include a representation containing an explanation of the
1822   error situation, and whether it is a temporary or permanent
1823   condition. These status codes are applicable to any request method.
1824   User agents SHOULD display any included representation to the user.
1825</t>
1826<t>
1827   If the client is sending data, a server implementation using TCP
1828   SHOULD be careful to ensure that the client acknowledges receipt of
1829   the packet(s) containing the response, before the server closes the
1830   input connection. If the client continues sending data to the server
1831   after the close, the server's TCP stack will send a reset packet to
1832   the client, which might erase the client's unacknowledged input buffers
1833   before they can be read and interpreted by the HTTP application.
1834</t>
1835
1836<section title="400 Bad Request" anchor="status.400">
1837  <iref primary="true" item="400 Bad Request (status code)"/>
1838  <iref primary="true" item="Status Codes" subitem="400 Bad Request"/>
1839<t>
1840   The server cannot or will not process the request, due to a client error (e.g.,
1841   malformed syntax).</t>
1842</section>
1843
1844<section title="401 Unauthorized" anchor="status.401">
1845  <iref primary="true" item="401 Unauthorized (status code)"/>
1846  <iref primary="true" item="Status Codes" subitem="401 Unauthorized"/>
1847 
1848<t>
1849   The request requires user authentication (see Section 3.1 of <xref target="Part7"/>).
1850</t>
1851</section>
1852
1853<section title="402 Payment Required" anchor="status.402">
1854  <iref primary="true" item="402 Payment Required (status code)"/>
1855  <iref primary="true" item="Status Codes" subitem="402 Payment Required"/>
1856<t>
1857   This code is reserved for future use.
1858</t>
1859</section>
1860
1861<section title="403 Forbidden" anchor="status.403">
1862  <iref primary="true" item="403 Forbidden (status code)"/>
1863  <iref primary="true" item="Status Codes" subitem="403 Forbidden"/>
1864<t>
1865   The server understood the request, but refuses to authorize it. Providing
1866   different user authentication credentials might be successful, but any
1867   credentials that were provided in the request are insufficient. The request
1868   SHOULD NOT be repeated with the same credentials.
1869</t>
1870<t>
1871   If the request method was not HEAD and the server wishes to make
1872   public why the request has not been fulfilled, it SHOULD describe the
1873   reason for the refusal in the representation.  If the server does not wish to
1874   make this information available to the client, the status code 404
1875   (Not Found) MAY be used instead.
1876</t>
1877</section>
1878
1879<section title="404 Not Found" anchor="status.404">
1880  <iref primary="true" item="404 Not Found (status code)"/>
1881  <iref primary="true" item="Status Codes" subitem="404 Not Found"/>
1882<t>
1883   The server has not found anything matching the effective request URI. No
1884   indication is given of whether the condition is temporary or
1885   permanent. The 410 (Gone) status code SHOULD be used if the server
1886   knows, through some internally configurable mechanism, that an old
1887   resource is permanently unavailable and has no forwarding address.
1888   This status code is commonly used when the server does not wish to
1889   reveal exactly why the request has been refused, or when no other
1890   response is applicable.
1891</t>
1892</section>
1893
1894<section title="405 Method Not Allowed" anchor="status.405">
1895  <iref primary="true" item="405 Method Not Allowed (status code)"/>
1896  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed"/>
1897<t>
1898   The method specified in the Request-Line is not allowed for the target
1899   resource. The response MUST include an Allow header field containing a
1900   list of valid methods for the requested resource.
1901</t>
1902</section>
1903
1904<section title="406 Not Acceptable" anchor="status.406">
1905  <iref primary="true" item="406 Not Acceptable (status code)"/>
1906  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable"/>
1907<t>
1908   The resource identified by the request is only capable of generating
1909   response representations which have content characteristics not acceptable
1910   according to the Accept and Accept-* header fields sent in the request
1911   (see Section 6 of <xref target="Part3"/>).
1912</t>
1913<t>
1914   Unless it was a HEAD request, the response SHOULD include a representation
1915   containing a list of available representation characteristics and location(s)
1916   from which the user or user agent can choose the one most
1917   appropriate. The data format is specified by the media type given
1918   in the Content-Type header field. Depending upon the format and the
1919   capabilities of the user agent, selection of the most appropriate
1920   choice MAY be performed automatically. However, this specification
1921   does not define any standard for such automatic selection.
1922</t>
1923<t><list>
1924  <t>
1925    Note: HTTP/1.1 servers are allowed to return responses which are
1926    not acceptable according to the accept header fields sent in the
1927    request. In some cases, this might even be preferable to sending a
1928    406 response. User agents are encouraged to inspect the header fields of
1929    an incoming response to determine if it is acceptable.
1930  </t>
1931</list></t>
1932<t>
1933   If the response could be unacceptable, a user agent SHOULD
1934   temporarily stop receipt of more data and query the user for a
1935   decision on further actions.
1936</t>
1937</section>
1938
1939<section title="407 Proxy Authentication Required" anchor="status.407">
1940  <iref primary="true" item="407 Proxy Authentication Required (status code)"/>
1941  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required"/>
1942<t>
1943   This code is similar to 401 (Unauthorized), but indicates that the
1944   client must first authenticate itself with the proxy (see Section 3.2 of <xref target="Part7"/>).
1945</t>
1946</section>
1947
1948<section title="408 Request Timeout" anchor="status.408">
1949  <iref primary="true" item="408 Request Timeout (status code)"/>
1950  <iref primary="true" item="Status Codes" subitem="408 Request Timeout"/>
1951<t>
1952   The client did not produce a request within the time that the server
1953   was prepared to wait. The client MAY repeat the request without
1954   modifications at any later time.
1955</t>
1956</section>
1957
1958<section title="409 Conflict" anchor="status.409">
1959  <iref primary="true" item="409 Conflict (status code)"/>
1960  <iref primary="true" item="Status Codes" subitem="409 Conflict"/>
1961<t>
1962   The request could not be completed due to a conflict with the current
1963   state of the resource. This code is only allowed in situations where
1964   it is expected that the user might be able to resolve the conflict
1965   and resubmit the request. The response body SHOULD include enough
1966   information for the user to recognize the source of the conflict.
1967   Ideally, the response representation would include enough information for the
1968   user or user agent to fix the problem; however, that might not be
1969   possible and is not required.
1970</t>
1971<t>
1972   Conflicts are most likely to occur in response to a PUT request. For
1973   example, if versioning were being used and the representation being PUT
1974   included changes to a resource which conflict with those made by an
1975   earlier (third-party) request, the server might use the 409 response
1976   to indicate that it can't complete the request. In this case, the
1977   response representation would likely contain a list of the differences
1978   between the two versions in a format defined by the response
1979   Content-Type.
1980</t>
1981</section>
1982
1983<section title="410 Gone" anchor="status.410">
1984  <iref primary="true" item="410 Gone (status code)"/>
1985  <iref primary="true" item="Status Codes" subitem="410 Gone"/>
1986<t>
1987   The target resource is no longer available at the server and no
1988   forwarding address is known. This condition is expected to be
1989   considered permanent. Clients with link editing capabilities SHOULD
1990   delete references to the effective request URI after user approval. If the
1991   server does not know, or has no facility to determine, whether or not
1992   the condition is permanent, the status code 404 (Not Found) SHOULD be
1993   used instead.
1994</t>
1995<t>
1996   The 410 response is primarily intended to assist the task of web
1997   maintenance by notifying the recipient that the resource is
1998   intentionally unavailable and that the server owners desire that
1999   remote links to that resource be removed. Such an event is common for
2000   limited-time, promotional services and for resources belonging to
2001   individuals no longer working at the server's site. It is not
2002   necessary to mark all permanently unavailable resources as "gone" or
2003   to keep the mark for any length of time — that is left to the
2004   discretion of the server owner.
2005</t>
2006<t>
2007   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine freshness
2008   for 410 responses.
2009</t>
2010
2011</section>
2012
2013<section title="411 Length Required" anchor="status.411">
2014  <iref primary="true" item="411 Length Required (status code)"/>
2015  <iref primary="true" item="Status Codes" subitem="411 Length Required"/>
2016<t>
2017   The server refuses to accept the request without a defined Content-Length.
2018   The client MAY repeat the request if it adds a valid
2019   Content-Length header field containing the length of the message-body
2020   in the request message.
2021</t>
2022</section>
2023
2024<section title="412 Precondition Failed" anchor="status.412">
2025  <iref primary="true" item="412 Precondition Failed (status code)"/>
2026  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed"/>
2027 
2028<t>
2029   The precondition given in one or more of the header fields
2030   evaluated to false when it was tested on the server, as defined in
2031   Section 4.2 of <xref target="Part4"/>.
2032</t>
2033</section>
2034
2035<section title="413 Request Representation Too Large" anchor="status.413">
2036  <iref primary="true" item="413 Request Representation Too Large (status code)"/>
2037  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large"/>
2038<t>
2039   The server is refusing to process a request because the request
2040   representation is larger than the server is willing or able to process. The
2041   server MAY close the connection to prevent the client from continuing
2042   the request.
2043</t>
2044<t>
2045   If the condition is temporary, the server SHOULD include a Retry-After
2046   header field to indicate that it is temporary and after what
2047   time the client MAY try again.
2048</t>
2049</section>
2050
2051<section title="414 URI Too Long" anchor="status.414">
2052  <iref primary="true" item="414 URI Too Long (status code)"/>
2053  <iref primary="true" item="Status Codes" subitem="414 URI Too Long"/>
2054<t>
2055   The server is refusing to service the request because the effective request URI
2056   is longer than the server is willing to interpret. This rare
2057   condition is only likely to occur when a client has improperly
2058   converted a POST request to a GET request with long query
2059   information, when the client has descended into a URI "black hole" of
2060   redirection (e.g., a redirected URI prefix that points to a suffix of
2061   itself), or when the server is under attack by a client attempting to
2062   exploit security holes present in some servers using fixed-length
2063   buffers for reading or manipulating the effective request URI.
2064</t>
2065</section>
2066
2067<section title="415 Unsupported Media Type" anchor="status.415">
2068  <iref primary="true" item="415 Unsupported Media Type (status code)"/>
2069  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type"/>
2070<t>
2071   The server is refusing to service the request because the request
2072   payload is in a format not supported by this request method on the
2073   target resource.
2074</t>
2075</section>
2076
2077<section title="416 Requested Range Not Satisfiable" anchor="status.416">
2078  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)"/>
2079  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable"/>
2080 
2081<t>
2082   The request included a Range header field (Section 5.4 of <xref target="Part5"/>) and none of
2083   the range-specifier values in this field overlap the current extent
2084   of the selected resource. See Section 3.2 of <xref target="Part5"/>.
2085</t>
2086</section>
2087
2088<section title="417 Expectation Failed" anchor="status.417">
2089  <iref primary="true" item="417 Expectation Failed (status code)"/>
2090  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed"/>
2091<t>
2092   The expectation given in an Expect header field (see <xref target="header.expect"/>)
2093   could not be met by this server, or, if the server is a proxy,
2094   the server has unambiguous evidence that the request could not be met
2095   by the next-hop server.
2096</t>
2097</section>
2098
2099<section title="426 Upgrade Required" anchor="status.426">
2100  <iref primary="true" item="426 Upgrade Required (status code)"/>
2101  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required"/>
2102<t>
2103   The request can not be completed without a prior protocol upgrade. This
2104   response MUST include an Upgrade header field (Section 8.7 of <xref target="Part1"/>)
2105   specifying the required protocols.
2106</t>
2107<figure>
2108<preamble>Example:</preamble>
2109<artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
2110  HTTP/1.1 426 Upgrade Required
2111  Upgrade: HTTP/2.0
2112  Connection: Upgrade
2113 
2114  ]]></artwork></figure>
2115<t>
2116   The server SHOULD include a message body in the 426 response which
2117   indicates in human readable form the reason for the error and describes any
2118   alternative courses which may be available to the user.
2119</t>
2120</section>
2121</section>
2122
2123<section title="Server Error 5xx" anchor="status.5xx">
2124<t>
2125   Response status codes beginning with the digit "5" indicate cases in
2126   which the server is aware that it has erred or is incapable of
2127   performing the request. Except when responding to a HEAD request, the
2128   server SHOULD include a representation containing an explanation of the
2129   error situation, and whether it is a temporary or permanent
2130   condition. User agents SHOULD display any included representation to the
2131   user. These response codes are applicable to any request method.
2132</t>
2133
2134<section title="500 Internal Server Error" anchor="status.500">
2135  <iref primary="true" item="500 Internal Server Error (status code)"/>
2136  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error"/>
2137<t>
2138   The server encountered an unexpected condition which prevented it
2139   from fulfilling the request.
2140</t>
2141</section>
2142
2143<section title="501 Not Implemented" anchor="status.501">
2144  <iref primary="true" item="501 Not Implemented (status code)"/>
2145  <iref primary="true" item="Status Codes" subitem="501 Not Implemented"/>
2146<t>
2147   The server does not support the functionality required to fulfill the
2148   request. This is the appropriate response when the server does not
2149   recognize the request method and is not capable of supporting it for
2150   any resource.
2151</t>
2152</section>
2153
2154<section title="502 Bad Gateway" anchor="status.502">
2155  <iref primary="true" item="502 Bad Gateway (status code)"/>
2156  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway"/>
2157<t>
2158   The server, while acting as a gateway or proxy, received an invalid
2159   response from the upstream server it accessed in attempting to
2160   fulfill the request.
2161</t>
2162</section>
2163
2164<section title="503 Service Unavailable" anchor="status.503">
2165  <iref primary="true" item="503 Service Unavailable (status code)"/>
2166  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable"/>
2167<t>
2168   The server is currently unable to handle the request due to a
2169   temporary overloading or maintenance of the server.
2170</t>
2171<t>
2172   The implication is that this is a temporary condition which will be
2173   alleviated after some delay. If known, the length of the delay MAY be
2174   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2175   If no Retry-After is given, the client SHOULD handle the response as it
2176   would for a 500 response.
2177</t>
2178<t><list>
2179  <t>
2180    Note: The existence of the 503 status code does not imply that a
2181    server must use it when becoming overloaded. Some servers might wish
2182    to simply refuse the connection.
2183  </t>
2184</list></t>
2185</section>
2186
2187<section title="504 Gateway Timeout" anchor="status.504">
2188  <iref primary="true" item="504 Gateway Timeout (status code)"/>
2189  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout"/>
2190<t>
2191   The server, while acting as a gateway or proxy, did not receive a
2192   timely response from the upstream server specified by the URI (e.g.,
2193   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2194   to access in attempting to complete the request.
2195</t>
2196<t><list>
2197  <t>
2198    Note to implementors: some deployed proxies are known to
2199    return 400 or 500 when DNS lookups time out.
2200  </t>
2201</list></t>
2202</section>
2203
2204<section title="505 HTTP Version Not Supported" anchor="status.505">
2205  <iref primary="true" item="505 HTTP Version Not Supported (status code)"/>
2206  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported"/>
2207<t>
2208   The server does not support, or refuses to support, the protocol
2209   version that was used in the request message. The server is
2210   indicating that it is unable or unwilling to complete the request
2211   using the same major version as the client, as described in Section 2.6 of <xref target="Part1"/>,
2212   other than with this error message. The response SHOULD contain
2213   a representation describing why that version is not supported and what other
2214   protocols are supported by that server.
2215</t>
2216
2217</section>
2218</section>
2219</section>
2220
2221
2222<section title="Date/Time Formats" anchor="http.date">
2223 
2224<t>
2225   HTTP applications have historically allowed three different formats
2226   for date/time stamps. However, the preferred format is a fixed-length subset
2227   of that defined by <xref target="RFC1123"/>:
2228</t>
2229<figure><artwork type="example"><![CDATA[
2230  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2231  ]]></artwork></figure>
2232<t>
2233   The other formats are described here only for compatibility with obsolete
2234   implementations.
2235</t>
2236<figure><artwork type="example"><![CDATA[
2237  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2238  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2239  ]]></artwork></figure>
2240<t>
2241   HTTP/1.1 clients and servers that parse a date value MUST accept
2242   all three formats (for compatibility with HTTP/1.0), though they MUST
2243   only generate the RFC 1123 format for representing HTTP-date values
2244   in header fields.
2245</t>
2246<t>
2247   All HTTP date/time stamps MUST be represented in Greenwich Mean Time
2248   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2249   equal to UTC (Coordinated Universal Time). This is indicated in the
2250   first two formats by the inclusion of "GMT" as the three-letter
2251   abbreviation for time zone, and MUST be assumed when reading the
2252   asctime format. HTTP-date is case sensitive and MUST NOT include
2253   additional whitespace beyond that specifically included as SP in the
2254   grammar.
2255</t>
2256<figure><iref primary="true" item="Grammar" subitem="HTTP-date"/><artwork type="abnf2616"><![CDATA[
2257  HTTP-date    = rfc1123-date / obs-date
2258]]></artwork></figure>
2259<t anchor="preferred.date.format">
2260 
2261 
2262 
2263 
2264 
2265 
2266 
2267 
2268 
2269 
2270  Preferred format:
2271</t>
2272<figure><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="time-of-day"/><iref primary="true" item="Grammar" subitem="hour"/><iref primary="true" item="Grammar" subitem="minute"/><iref primary="true" item="Grammar" subitem="second"/><iref primary="true" item="Grammar" subitem="day-name"/><iref primary="true" item="Grammar" subitem="day-name-l"/><iref primary="true" item="Grammar" subitem="day"/><iref primary="true" item="Grammar" subitem="month"/><iref primary="true" item="Grammar" subitem="year"/><iref primary="true" item="Grammar" subitem="GMT"/><artwork type="abnf2616"><![CDATA[
2273  rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
2274  ; fixed length subset of the format defined in
2275  ; Section 5.2.14 of [RFC1123]
2276 
2277  day-name     = %x4D.6F.6E ; "Mon", case-sensitive
2278               / %x54.75.65 ; "Tue", case-sensitive
2279               / %x57.65.64 ; "Wed", case-sensitive
2280               / %x54.68.75 ; "Thu", case-sensitive
2281               / %x46.72.69 ; "Fri", case-sensitive
2282               / %x53.61.74 ; "Sat", case-sensitive
2283               / %x53.75.6E ; "Sun", case-sensitive
2284               
2285  date1        = day SP month SP year
2286               ; e.g., 02 Jun 1982
2287
2288  day          = 2DIGIT
2289  month        = %x4A.61.6E ; "Jan", case-sensitive
2290               / %x46.65.62 ; "Feb", case-sensitive
2291               / %x4D.61.72 ; "Mar", case-sensitive
2292               / %x41.70.72 ; "Apr", case-sensitive
2293               / %x4D.61.79 ; "May", case-sensitive
2294               / %x4A.75.6E ; "Jun", case-sensitive
2295               / %x4A.75.6C ; "Jul", case-sensitive
2296               / %x41.75.67 ; "Aug", case-sensitive
2297               / %x53.65.70 ; "Sep", case-sensitive
2298               / %x4F.63.74 ; "Oct", case-sensitive
2299               / %x4E.6F.76 ; "Nov", case-sensitive
2300               / %x44.65.63 ; "Dec", case-sensitive
2301  year         = 4DIGIT
2302
2303  GMT   = %x47.4D.54 ; "GMT", case-sensitive
2304
2305  time-of-day  = hour ":" minute ":" second
2306                 ; 00:00:00 - 23:59:59
2307                 
2308  hour         = 2DIGIT               
2309  minute       = 2DIGIT               
2310  second       = 2DIGIT               
2311]]></artwork></figure>
2312<t>
2313  The semantics of <xref target="preferred.date.format" format="none">day-name</xref>, <xref target="preferred.date.format" format="none">day</xref>,
2314  <xref target="preferred.date.format" format="none">month</xref>, <xref target="preferred.date.format" format="none">year</xref>, and <xref target="preferred.date.format" format="none">time-of-day</xref> are the
2315  same as those defined for the RFC 5322 constructs
2316  with the corresponding name (<xref target="RFC5322"/>, Section 3.3).
2317</t>
2318<t anchor="obsolete.date.formats">
2319 
2320 
2321 
2322 
2323 
2324 
2325 
2326 
2327  Obsolete formats:
2328</t>
2329<figure><iref primary="true" item="Grammar" subitem="obs-date"/><artwork type="abnf2616"><![CDATA[
2330  obs-date     = rfc850-date / asctime-date
2331]]></artwork></figure>
2332<figure><iref primary="true" item="Grammar" subitem="rfc850-date"/><artwork type="abnf2616"><![CDATA[
2333  rfc850-date  = day-name-l "," SP date2 SP time-of-day SP GMT
2334  date2        = day "-" month "-" 2DIGIT
2335                 ; day-month-year (e.g., 02-Jun-82)
2336
2337  day-name-l   = %x4D.6F.6E.64.61.79 ; "Monday", case-sensitive
2338         / %x54.75.65.73.64.61.79 ; "Tuesday", case-sensitive
2339         / %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
2340         / %x54.68.75.72.73.64.61.79 ; "Thursday", case-sensitive
2341         / %x46.72.69.64.61.79 ; "Friday", case-sensitive
2342         / %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive
2343         / %x53.75.6E.64.61.79 ; "Sunday", case-sensitive
2344]]></artwork></figure>
2345<figure><iref primary="true" item="Grammar" subitem="asctime-date"/><artwork type="abnf2616"><![CDATA[
2346  asctime-date = day-name SP date3 SP time-of-day SP year
2347  date3        = month SP ( 2DIGIT / ( SP 1DIGIT ))
2348                 ; month day (e.g., Jun  2)
2349]]></artwork></figure>
2350<t><list>
2351  <t>
2352    Note: Recipients of date values are encouraged to be robust in
2353    accepting date values that might have been sent by non-HTTP
2354    applications, as is sometimes the case when retrieving or posting
2355    messages via proxies/gateways to SMTP or NNTP.
2356  </t>
2357</list></t>
2358<t><list>
2359  <t>
2360    Note: HTTP requirements for the date/time stamp format apply only
2361    to their usage within the protocol stream. Clients and servers are
2362    not required to use these formats for user presentation, request
2363    logging, etc.
2364  </t>
2365</list></t>
2366</section>
2367
2368
2369<section title="Header Field Definitions" anchor="header.field.definitions">
2370<t>
2371   This section defines the syntax and semantics of HTTP/1.1 header fields
2372   related to request and response semantics.
2373</t>
2374
2375<section title="Allow" anchor="header.allow">
2376  <iref primary="true" item="Allow header field"/>
2377  <iref primary="true" item="Header Fields" subitem="Allow"/>
2378 
2379<t>
2380   The "Allow" header field lists the set of methods advertised as
2381   supported by the target resource. The purpose of this field is strictly to
2382   inform the recipient of valid request methods associated with the resource.
2383</t>
2384<figure><iref primary="true" item="Grammar" subitem="Allow"/><artwork type="abnf2616"><![CDATA[
2385  Allow = #Method
2386]]></artwork></figure>
2387<t>
2388   Example of use:
2389</t>
2390<figure><artwork type="example"><![CDATA[
2391  Allow: GET, HEAD, PUT
2392]]></artwork></figure>
2393<t>
2394   The actual set of allowed methods is defined by the origin server at the
2395   time of each request.
2396</t>
2397<t>
2398   A proxy MUST NOT modify the Allow header field — it does not need to
2399   understand all the methods specified in order to handle them according to
2400   the generic message handling rules.
2401</t>
2402</section>
2403
2404<section title="Date" anchor="header.date">
2405  <iref primary="true" item="Date header field"/>
2406  <iref primary="true" item="Header Fields" subitem="Date"/>
2407 
2408<t>
2409   The "Date" header field represents the date and time at which
2410   the message was originated, having the same semantics as the Origination
2411   Date Field (orig-date) defined in Section 3.6.1 of <xref target="RFC5322"/>.
2412   The field value is an HTTP-date, as defined in <xref target="http.date"/>;
2413   it MUST be sent in rfc1123-date format.
2414</t>
2415<figure><iref primary="true" item="Grammar" subitem="Date"/><artwork type="abnf2616"><![CDATA[
2416  Date = HTTP-date
2417]]></artwork></figure>
2418<t>
2419   An example is
2420</t>
2421<figure><artwork type="example"><![CDATA[
2422  Date: Tue, 15 Nov 1994 08:12:31 GMT
2423]]></artwork></figure>
2424<t>
2425   Origin servers MUST include a Date header field in all responses,
2426   except in these cases:
2427  <list style="numbers">
2428      <t>If the response status code is 100 (Continue) or 101 (Switching
2429         Protocols), the response MAY include a Date header field, at
2430         the server's option.</t>
2431
2432      <t>If the response status code conveys a server error, e.g., 500
2433         (Internal Server Error) or 503 (Service Unavailable), and it is
2434         inconvenient or impossible to generate a valid Date.</t>
2435
2436      <t>If the server does not have a clock that can provide a
2437         reasonable approximation of the current time, its responses
2438         MUST NOT include a Date header field.</t>
2439  </list>
2440</t>
2441<t>
2442   A received message that does not have a Date header field MUST be
2443   assigned one by the recipient if the message will be cached by that
2444   recipient.
2445</t>
2446<t>
2447   Clients can use the Date header field as well; in order to keep request
2448   messages small, they are advised not to include it when it doesn't convey
2449   any useful information (as it is usually the case for requests that do not
2450   contain a payload).
2451</t>
2452<t>
2453   The HTTP-date sent in a Date header field SHOULD NOT represent a date and
2454   time subsequent to the generation of the message. It SHOULD represent
2455   the best available approximation of the date and time of message
2456   generation, unless the implementation has no means of generating a
2457   reasonably accurate date and time. In theory, the date ought to
2458   represent the moment just before the payload is generated. In
2459   practice, the date can be generated at any time during the message
2460   origination without affecting its semantic value.
2461</t>
2462</section>
2463
2464<section title="Expect" anchor="header.expect">
2465  <iref primary="true" item="Expect header field"/>
2466  <iref primary="true" item="Header Fields" subitem="Expect"/>
2467 
2468 
2469 
2470 
2471 
2472<t>
2473   The "Expect" header field is used to indicate that particular
2474   server behaviors are required by the client.
2475</t>
2476<figure><iref primary="true" item="Grammar" subitem="Expect"/><iref primary="true" item="Grammar" subitem="expectation"/><iref primary="true" item="Grammar" subitem="expect-param"/><iref primary="true" item="Grammar" subitem="expect-value"/><iref primary="true" item="Grammar" subitem="expect-name"/><artwork type="abnf2616"><![CDATA[
2477  Expect       = 1#expectation
2478 
2479  expectation  = expect-name [ BWS "=" BWS expect-value ]
2480                             *( OWS ";" [ OWS expect-param ] )
2481  expect-param = expect-name [ BWS "=" BWS expect-value ]
2482 
2483  expect-name  = token
2484  expect-value = token / quoted-string
2485]]></artwork></figure>
2486<t>
2487   If all received Expect header field(s) are syntactically valid but contain
2488   an expectation that the recipient does not understand or cannot comply with,
2489   the recipient MUST respond with a 417 (Expectation Failed) status code. A
2490   recipient of a syntactically invalid Expectation header field MUST respond
2491   with a 4xx status code other than 417.
2492</t>
2493<t>
2494   The only expectation defined by this specification is:
2495</t>
2496<t><iref primary="true" item="100-continue (expect value)"/><iref primary="true" item="Expect Values" subitem="100-continue"/>
2497  100-continue
2498   <list>
2499      <t>
2500        The "100-continue" expectation is defined Section 6.2.3 of <xref target="Part1"/>. It does not support
2501        any expect-params.
2502      </t>
2503   </list>
2504</t>
2505<t>
2506   Comparison is case-insensitive for names (expect-name), and case-sensitive
2507   for values (expect-value).
2508</t>
2509<t>
2510   The Expect mechanism is hop-by-hop: the above requirements apply to any
2511   server, including proxies. However, the Expect header field itself is
2512   end-to-end; it MUST be forwarded if the request is forwarded.
2513</t>
2514<t>
2515   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect
2516   header field.
2517</t>
2518</section>
2519
2520<section title="From" anchor="header.from">
2521  <iref primary="true" item="From header field"/>
2522  <iref primary="true" item="Header Fields" subitem="From"/>
2523 
2524 
2525<t>
2526   The "From" header field, if given, SHOULD contain an Internet
2527   e-mail address for the human user who controls the requesting user
2528   agent. The address SHOULD be machine-usable, as defined by "mailbox"
2529   in Section 3.4 of <xref target="RFC5322"/>:
2530</t>
2531<figure><iref primary="true" item="Grammar" subitem="From"/><artwork type="abnf2616"><![CDATA[
2532  From    = mailbox
2533 
2534  mailbox = <mailbox, defined in [RFC5322], Section 3.4>
2535]]></artwork></figure>
2536<t>
2537   An example is:
2538</t>
2539<figure><artwork type="example"><![CDATA[
2540  From: webmaster@example.org
2541]]></artwork></figure>
2542<t>
2543   This header field MAY be used for logging purposes and as a means for
2544   identifying the source of invalid or unwanted requests. It SHOULD NOT
2545   be used as an insecure form of access protection. The interpretation
2546   of this field is that the request is being performed on behalf of the
2547   person given, who accepts responsibility for the method performed. In
2548   particular, robot agents SHOULD include this header field so that the
2549   person responsible for running the robot can be contacted if problems
2550   occur on the receiving end.
2551</t>
2552<t>
2553   The Internet e-mail address in this field MAY be separate from the
2554   Internet host which issued the request. For example, when a request
2555   is passed through a proxy the original issuer's address SHOULD be
2556   used.
2557</t>
2558<t>
2559   The client SHOULD NOT  send the From header field without the user's
2560   approval, as it might conflict with the user's privacy interests or
2561   their site's security policy. It is strongly recommended that the
2562   user be able to disable, enable, and modify the value of this field
2563   at any time prior to a request.
2564</t>
2565</section>
2566
2567<section title="Location" anchor="header.location">
2568  <iref primary="true" item="Location header field"/>
2569  <iref primary="true" item="Header Fields" subitem="Location"/>
2570 
2571<t>
2572   The "Location" header field is used to identify a newly created
2573   resource, or to redirect the recipient to a different location for
2574   completion of the request.
2575</t>
2576<t>
2577   For 201 (Created) responses, the Location is the URI of the new resource
2578   which was created by the request. For 3xx responses, the location SHOULD
2579   indicate the server's preferred URI for automatic redirection to the
2580   resource.
2581</t>
2582<t>
2583   The field value consists of a single URI-reference. When it has the form
2584   of a relative reference (<xref target="RFC3986"/>, Section 4.2),
2585   the final value is computed by resolving it against the effective request
2586   URI (<xref target="RFC3986"/>, Section 5).
2587</t>
2588<figure><iref primary="true" item="Grammar" subitem="Location"/><artwork type="abnf2616"><![CDATA[
2589  Location = URI-reference
2590]]></artwork></figure>
2591<figure>
2592<preamble>Examples are:</preamble><!--DO NOT DARE changing the vertical spacing below, it's necessary this way for xml2rfc-->
2593<artwork type="example"><![CDATA[
2594  Location: http://www.example.org/pub/WWW/People.html#tim
2595]]></artwork></figure><figure><artwork type="example"><![CDATA[  Location: /index.html
2596]]></artwork></figure>
2597<t><list>
2598  <t>
2599    Note: Some recipients attempt to recover from Location fields
2600    that are not valid URI references. This specification does not mandate or
2601    define such processing, but does allow it (see <xref target="intro.conformance.and.error.handling"/>).
2602  </t>
2603</list></t>
2604<t>
2605   There are circumstances in which a fragment identifier in a Location URI
2606   would not be appropriate. For instance, when it appears in a 201 Created
2607   response, where the Location header field specifies the URI for the entire
2608   created resource.
2609</t>
2610<t><list>
2611  <t>
2612    Note: This specification does not define precedence rules
2613    for the case where the original URI, as navigated to by the user
2614    agent, and the Location header field value both contain fragment
2615    identifiers. Thus be aware that including fragment identifiers might
2616    inconvenience anyone relying on the semantics of the original URI's
2617    fragment identifier.
2618  </t>
2619</list></t>
2620<t><list>
2621  <t>
2622    Note: The Content-Location header field (Section 6.7 of <xref target="Part3"/>) differs
2623    from Location in that the Content-Location identifies the most specific
2624    resource corresponding to the enclosed representation.
2625    It is therefore possible for a response to contain header fields for
2626    both Location and Content-Location.
2627  </t>
2628</list></t>
2629</section>
2630
2631<section title="Max-Forwards" anchor="header.max-forwards">
2632  <iref primary="true" item="Max-Forwards header field"/>
2633  <iref primary="true" item="Header Fields" subitem="Max-Forwards"/>
2634 
2635<t>
2636   The "Max-Forwards" header field provides a mechanism with the
2637   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2638   methods to limit the number of times that the request is forwarded by
2639   proxies. This can be useful when the client is attempting to
2640   trace a request which appears to be failing or looping in mid-chain.
2641</t>
2642<figure><iref primary="true" item="Grammar" subitem="Max-Forwards"/><artwork type="abnf2616"><![CDATA[
2643  Max-Forwards = 1*DIGIT
2644]]></artwork></figure>
2645<t>
2646   The Max-Forwards value is a decimal integer indicating the remaining
2647   number of times this request message can be forwarded.
2648</t>
2649<t>
2650   Each recipient of a TRACE or OPTIONS request
2651   containing a Max-Forwards header field MUST check and update its
2652   value prior to forwarding the request. If the received value is zero
2653   (0), the recipient MUST NOT forward the request; instead, it MUST
2654   respond as the final recipient. If the received Max-Forwards value is
2655   greater than zero, then the forwarded message MUST contain an updated
2656   Max-Forwards field with a value decremented by one (1).
2657</t>
2658<t>
2659   The Max-Forwards header field MAY be ignored for all other request
2660   methods.
2661</t>
2662</section>
2663
2664<section title="Referer" anchor="header.referer">
2665  <iref primary="true" item="Referer header field"/>
2666  <iref primary="true" item="Header Fields" subitem="Referer"/>
2667 
2668<t>
2669   The "Referer" [sic] header field allows the client to specify the
2670   URI of the resource from which the effective request URI was obtained (the
2671   "referrer", although the header field is misspelled.).
2672</t>
2673<t>
2674   The Referer header field allows servers to generate lists of back-links to
2675   resources for interest, logging, optimized caching, etc. It also allows
2676   obsolete or mistyped links to be traced for maintenance. Some servers use
2677   Referer as a means of controlling where they allow links from (so-called
2678   "deep linking"), but legitimate requests do not always
2679   contain a Referer header field.
2680</t>
2681<t>
2682   If the effective request URI was obtained from a source that does not have its own
2683   URI (e.g., input from the user keyboard), the Referer field MUST either be
2684   sent with the value "about:blank", or not be sent at all. Note that this
2685   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2686</t>
2687<figure><iref primary="true" item="Grammar" subitem="Referer"/><artwork type="abnf2616"><![CDATA[
2688  Referer = absolute-URI / partial-URI
2689]]></artwork></figure>
2690<t>
2691   Example:
2692</t>
2693<figure><artwork type="example"><![CDATA[
2694  Referer: http://www.example.org/hypertext/Overview.html
2695]]></artwork></figure>
2696<t>
2697   If the field value is a relative URI, it SHOULD be interpreted
2698   relative to the effective request URI. The URI MUST NOT include a fragment. See
2699   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2700</t>
2701</section>
2702
2703<section title="Retry-After" anchor="header.retry-after">
2704  <iref primary="true" item="Retry-After header field"/>
2705  <iref primary="true" item="Header Fields" subitem="Retry-After"/>
2706 
2707<t>
2708   The header "Retry-After" field can be used with a 503 (Service
2709   Unavailable) response to indicate how long the service is expected to
2710   be unavailable to the requesting client. This field MAY also be used
2711   with any 3xx (Redirection) response to indicate the minimum time the
2712   user-agent is asked wait before issuing the redirected request.
2713</t>
2714<t>
2715   The value of this field can be either an HTTP-date or an integer number
2716   of seconds (in decimal) after the time of the response.
2717</t>
2718<figure><iref primary="true" item="Grammar" subitem="Retry-After"/><artwork type="abnf2616"><![CDATA[
2719  Retry-After = HTTP-date / delta-seconds
2720]]></artwork></figure>
2721<t anchor="rule.delta-seconds">
2722 
2723   Time spans are non-negative decimal integers, representing time in
2724   seconds.
2725</t>
2726<figure><iref primary="true" item="Grammar" subitem="delta-seconds"/><artwork type="abnf2616"><![CDATA[
2727  delta-seconds  = 1*DIGIT
2728]]></artwork></figure>
2729<t>
2730   Two examples of its use are
2731</t>
2732<figure><artwork type="example"><![CDATA[
2733  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2734  Retry-After: 120
2735]]></artwork></figure>
2736<t>
2737   In the latter example, the delay is 2 minutes.
2738</t>
2739</section>
2740
2741<section title="Server" anchor="header.server">
2742  <iref primary="true" item="Server header field"/>
2743  <iref primary="true" item="Header Fields" subitem="Server"/>
2744 
2745<t>
2746   The "Server" header field contains information about the
2747   software used by the origin server to handle the request.
2748</t>
2749<t>
2750   The field can contain multiple product tokens (Section 5.2 of <xref target="Part1"/>) and
2751   comments (Section 3.2 of <xref target="Part1"/>) identifying the server and any significant
2752   subproducts. The product tokens are listed in order of their significance
2753   for identifying the application.
2754</t>
2755<figure><iref primary="true" item="Grammar" subitem="Server"/><artwork type="abnf2616"><![CDATA[
2756  Server = product *( RWS ( product / comment ) )
2757]]></artwork></figure>
2758<t>
2759   Example:
2760</t>
2761<figure><artwork type="example"><![CDATA[
2762  Server: CERN/3.0 libwww/2.17
2763]]></artwork></figure>
2764<t>
2765   If the response is being forwarded through a proxy, the proxy
2766   application MUST NOT modify the Server header field. Instead, it
2767   MUST include a Via field (as described in Section 8.8 of <xref target="Part1"/>).
2768</t>
2769<t><list>
2770  <t>
2771    Note: Revealing the specific software version of the server might
2772    allow the server machine to become more vulnerable to attacks
2773    against software that is known to contain security holes. Server
2774    implementors are encouraged to make this field a configurable
2775    option.
2776  </t>
2777</list></t>
2778</section>
2779
2780<section title="User-Agent" anchor="header.user-agent">
2781  <iref primary="true" item="User-Agent header field"/>
2782  <iref primary="true" item="Header Fields" subitem="User-Agent"/>
2783 
2784<t>
2785   The "User-Agent" header field contains information about the user
2786   agent originating the request. User agents SHOULD include this field with
2787   requests.
2788</t>
2789<t>
2790   Typically, it is used for statistical purposes, the tracing of protocol
2791   violations, and tailoring responses to avoid particular user agent
2792   limitations.
2793</t>
2794<t>
2795   The field can contain multiple product tokens (Section 5.2 of <xref target="Part1"/>)
2796   and comments (Section 3.2 of <xref target="Part1"/>) identifying the agent and its
2797   significant subproducts. By convention, the product tokens are listed in
2798   order of their significance for identifying the application.
2799</t>
2800<t>
2801   Because this field is usually sent on every request a user agent makes,
2802   implementations are encouraged not to include needlessly fine-grained
2803   detail, and to limit (or even prohibit) the addition of subproducts by third
2804   parties. Overly long and detailed User-Agent field values make requests
2805   larger and can also be used to identify ("fingerprint") the user against
2806   their wishes.
2807</t>
2808<t>
2809   Likewise, implementations are encouraged not to use the product tokens of
2810   other implementations in order to declare compatibility with them, as this
2811   circumvents the purpose of the field. Finally, they are encouraged not to
2812   use comments to identify products; doing so makes the field value more
2813   difficult to parse.
2814</t>
2815<figure><iref primary="true" item="Grammar" subitem="User-Agent"/><artwork type="abnf2616"><![CDATA[
2816  User-Agent = product *( RWS ( product / comment ) )
2817]]></artwork></figure>
2818<t>
2819   Example:
2820</t>
2821<figure><artwork type="example"><![CDATA[
2822  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2823]]></artwork></figure>
2824</section>
2825
2826</section>
2827
2828<section title="IANA Considerations" anchor="IANA.considerations">
2829
2830<section title="Method Registry" anchor="method.registration">
2831<t>
2832  The registration procedure for HTTP request methods is defined by
2833  <xref target="method.registry"/> of this document.
2834</t>
2835<t>
2836   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2837   and be populated with the registrations below:
2838</t>
2839
2840<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2841<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2842   <ttcol>Method</ttcol>
2843   <ttcol>Safe</ttcol>
2844   <ttcol>Reference</ttcol>
2845   <c>CONNECT</c>
2846   <c>no</c>
2847   <c>
2848      <xref target="CONNECT"/>
2849   </c>
2850   <c>DELETE</c>
2851   <c>no</c>
2852   <c>
2853      <xref target="DELETE"/>
2854   </c>
2855   <c>GET</c>
2856   <c>yes</c>
2857   <c>
2858      <xref target="GET"/>
2859   </c>
2860   <c>HEAD</c>
2861   <c>yes</c>
2862   <c>
2863      <xref target="HEAD"/>
2864   </c>
2865   <c>OPTIONS</c>
2866   <c>yes</c>
2867   <c>
2868      <xref target="OPTIONS"/>
2869   </c>
2870   <c>POST</c>
2871   <c>no</c>
2872   <c>
2873      <xref target="POST"/>
2874   </c>
2875   <c>PUT</c>
2876   <c>no</c>
2877   <c>
2878      <xref target="PUT"/>
2879   </c>
2880   <c>TRACE</c>
2881   <c>yes</c>
2882   <c>
2883      <xref target="TRACE"/>
2884   </c>
2885</texttable>
2886<!--(END)-->
2887
2888</section>
2889
2890<section title="Status Code Registry" anchor="status.code.registration">
2891<t>
2892   The registration procedure for HTTP Status Codes — previously defined
2893   in Section 7.1 of <xref target="RFC2817"/> — is now defined
2894   by <xref target="status.code.registry"/> of this document.
2895</t>
2896<t>
2897   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2898   shall be updated with the registrations below:
2899</t>
2900
2901<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2902<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2903   <ttcol>Value</ttcol>
2904   <ttcol>Description</ttcol>
2905   <ttcol>Reference</ttcol>
2906   <c>100</c>
2907   <c>Continue</c>
2908   <c>
2909      <xref target="status.100"/>
2910   </c>
2911   <c>101</c>
2912   <c>Switching Protocols</c>
2913   <c>
2914      <xref target="status.101"/>
2915   </c>
2916   <c>200</c>
2917   <c>OK</c>
2918   <c>
2919      <xref target="status.200"/>
2920   </c>
2921   <c>201</c>
2922   <c>Created</c>
2923   <c>
2924      <xref target="status.201"/>
2925   </c>
2926   <c>202</c>
2927   <c>Accepted</c>
2928   <c>
2929      <xref target="status.202"/>
2930   </c>
2931   <c>203</c>
2932   <c>Non-Authoritative Information</c>
2933   <c>
2934      <xref target="status.203"/>
2935   </c>
2936   <c>204</c>
2937   <c>No Content</c>
2938   <c>
2939      <xref target="status.204"/>
2940   </c>
2941   <c>205</c>
2942   <c>Reset Content</c>
2943   <c>
2944      <xref target="status.205"/>
2945   </c>
2946   <c>300</c>
2947   <c>Multiple Choices</c>
2948   <c>
2949      <xref target="status.300"/>
2950   </c>
2951   <c>301</c>
2952   <c>Moved Permanently</c>
2953   <c>
2954      <xref target="status.301"/>
2955   </c>
2956   <c>302</c>
2957   <c>Found</c>
2958   <c>
2959      <xref target="status.302"/>
2960   </c>
2961   <c>303</c>
2962   <c>See Other</c>
2963   <c>
2964      <xref target="status.303"/>
2965   </c>
2966   <c>305</c>
2967   <c>Use Proxy</c>
2968   <c>
2969      <xref target="status.305"/>
2970   </c>
2971   <c>306</c>
2972   <c>(Unused)</c>
2973   <c>
2974      <xref target="status.306"/>
2975   </c>
2976   <c>307</c>
2977   <c>Temporary Redirect</c>
2978   <c>
2979      <xref target="status.307"/>
2980   </c>
2981   <c>400</c>
2982   <c>Bad Request</c>
2983   <c>
2984      <xref target="status.400"/>
2985   </c>
2986   <c>402</c>
2987   <c>Payment Required</c>
2988   <c>
2989      <xref target="status.402"/>
2990   </c>
2991   <c>403</c>
2992   <c>Forbidden</c>
2993   <c>
2994      <xref target="status.403"/>
2995   </c>
2996   <c>404</c>
2997   <c>Not Found</c>
2998   <c>
2999      <xref target="status.404"/>
3000   </c>
3001   <c>405</c>
3002   <c>Method Not Allowed</c>
3003   <c>
3004      <xref target="status.405"/>
3005   </c>
3006   <c>406</c>
3007   <c>Not Acceptable</c>
3008   <c>
3009      <xref target="status.406"/>
3010   </c>
3011   <c>407</c>
3012   <c>Proxy Authentication Required</c>
3013   <c>
3014      <xref target="status.407"/>
3015   </c>
3016   <c>408</c>
3017   <c>Request Timeout</c>
3018   <c>
3019      <xref target="status.408"/>
3020   </c>
3021   <c>409</c>
3022   <c>Conflict</c>
3023   <c>
3024      <xref target="status.409"/>
3025   </c>
3026   <c>410</c>
3027   <c>Gone</c>
3028   <c>
3029      <xref target="status.410"/>
3030   </c>
3031   <c>411</c>
3032   <c>Length Required</c>
3033   <c>
3034      <xref target="status.411"/>
3035   </c>
3036   <c>413</c>
3037   <c>Request Representation Too Large</c>
3038   <c>
3039      <xref target="status.413"/>
3040   </c>
3041   <c>414</c>
3042   <c>URI Too Long</c>
3043   <c>
3044      <xref target="status.414"/>
3045   </c>
3046   <c>415</c>
3047   <c>Unsupported Media Type</c>
3048   <c>
3049      <xref target="status.415"/>
3050   </c>
3051   <c>417</c>
3052   <c>Expectation Failed</c>
3053   <c>
3054      <xref target="status.417"/>
3055   </c>
3056   <c>426</c>
3057   <c>Upgrade Required</c>
3058   <c>
3059      <xref target="status.426"/>
3060   </c>
3061   <c>500</c>
3062   <c>Internal Server Error</c>
3063   <c>
3064      <xref target="status.500"/>
3065   </c>
3066   <c>501</c>
3067   <c>Not Implemented</c>
3068   <c>
3069      <xref target="status.501"/>
3070   </c>
3071   <c>502</c>
3072   <c>Bad Gateway</c>
3073   <c>
3074      <xref target="status.502"/>
3075   </c>
3076   <c>503</c>
3077   <c>Service Unavailable</c>
3078   <c>
3079      <xref target="status.503"/>
3080   </c>
3081   <c>504</c>
3082   <c>Gateway Timeout</c>
3083   <c>
3084      <xref target="status.504"/>
3085   </c>
3086   <c>505</c>
3087   <c>HTTP Version Not Supported</c>
3088   <c>
3089      <xref target="status.505"/>
3090   </c>
3091</texttable>
3092<!--(END)-->
3093
3094</section>
3095<section title="Header Field Registration" anchor="header.field.registration">
3096<t>
3097   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3098   with the permanent registrations below (see <xref target="RFC3864"/>):
3099</t>
3100
3101<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3102<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3103   <ttcol>Header Field Name</ttcol>
3104   <ttcol>Protocol</ttcol>
3105   <ttcol>Status</ttcol>
3106   <ttcol>Reference</ttcol>
3107
3108   <c>Allow</c>
3109   <c>http</c>
3110   <c>standard</c>
3111   <c>
3112      <xref target="header.allow"/>
3113   </c>
3114   <c>Date</c>
3115   <c>http</c>
3116   <c>standard</c>
3117   <c>
3118      <xref target="header.date"/>
3119   </c>
3120   <c>Expect</c>
3121   <c>http</c>
3122   <c>standard</c>
3123   <c>
3124      <xref target="header.expect"/>
3125   </c>
3126   <c>From</c>
3127   <c>http</c>
3128   <c>standard</c>
3129   <c>
3130      <xref target="header.from"/>
3131   </c>
3132   <c>Location</c>
3133   <c>http</c>
3134   <c>standard</c>
3135   <c>
3136      <xref target="header.location"/>
3137   </c>
3138   <c>Max-Forwards</c>
3139   <c>http</c>
3140   <c>standard</c>
3141   <c>
3142      <xref target="header.max-forwards"/>
3143   </c>
3144   <c>Referer</c>
3145   <c>http</c>
3146   <c>standard</c>
3147   <c>
3148      <xref target="header.referer"/>
3149   </c>
3150   <c>Retry-After</c>
3151   <c>http</c>
3152   <c>standard</c>
3153   <c>
3154      <xref target="header.retry-after"/>
3155   </c>
3156   <c>Server</c>
3157   <c>http</c>
3158   <c>standard</c>
3159   <c>
3160      <xref target="header.server"/>
3161   </c>
3162   <c>User-Agent</c>
3163   <c>http</c>
3164   <c>standard</c>
3165   <c>
3166      <xref target="header.user-agent"/>
3167   </c>
3168</texttable>
3169<!--(END)-->
3170
3171<t>
3172   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3173</t>
3174</section>
3175</section>
3176
3177<section title="Security Considerations" anchor="security.considerations">
3178<t>
3179   This section is meant to inform application developers, information
3180   providers, and users of the security limitations in HTTP/1.1 as
3181   described by this document. The discussion does not include
3182   definitive solutions to the problems revealed, though it does make
3183   some suggestions for reducing security risks.
3184</t>
3185
3186<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3187<t>
3188   Like any generic data transfer protocol, HTTP cannot regulate the
3189   content of the data that is transferred, nor is there any a priori
3190   method of determining the sensitivity of any particular piece of
3191   information within the context of any given request. Therefore,
3192   applications SHOULD supply as much control over this information as
3193   possible to the provider of that information. Four header fields are
3194   worth special mention in this context: Server, Via, Referer and From.
3195</t>
3196<t>
3197   Revealing the specific software version of the server might allow the
3198   server machine to become more vulnerable to attacks against software
3199   that is known to contain security holes. Implementors SHOULD make the
3200   Server header field a configurable option.
3201</t>
3202<t>
3203   Proxies which serve as a portal through a network firewall SHOULD
3204   take special precautions regarding the transfer of header information
3205   that identifies the hosts behind the firewall. In particular, they
3206   SHOULD remove, or replace with sanitized versions, any Via fields
3207   generated behind the firewall.
3208</t>
3209<t>
3210   The Referer header field allows reading patterns to be studied and reverse
3211   links drawn. Although it can be very useful, its power can be abused
3212   if user details are not separated from the information contained in
3213   the Referer. Even when the personal information has been removed, the
3214   Referer header field might indicate a private document's URI whose
3215   publication would be inappropriate.
3216</t>
3217<t>
3218   The information sent in the From field might conflict with the user's
3219   privacy interests or their site's security policy, and hence it
3220   SHOULD NOT  be transmitted without the user being able to disable,
3221   enable, and modify the contents of the field. The user MUST be able
3222   to set the contents of this field within a user preference or
3223   application defaults configuration.
3224</t>
3225<t>
3226   We suggest, though do not require, that a convenient toggle interface
3227   be provided for the user to enable or disable the sending of From and
3228   Referer information.
3229</t>
3230<t>
3231   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header fields can sometimes be used to determine
3232   that a specific client or server have a particular security hole which might
3233   be exploited. Unfortunately, this same information is often used for other
3234   valuable purposes for which HTTP currently has no better mechanism.
3235</t>
3236<t>
3237   Furthermore, the User-Agent header field may contain enough entropy to be
3238   used, possibly in conjunction with other material, to uniquely identify the
3239   user.
3240</t>
3241<t>
3242   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3243   that was sent in request header fields within the body of their response.
3244   Clients SHOULD be careful with sensitive information, like Cookies,
3245   Authorization credentials, and other header fields that might be used to
3246   collect data from the client.
3247</t> 
3248</section>
3249
3250<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3251<t>
3252   Because the source of a link might be private information or might
3253   reveal an otherwise private information source, it is strongly
3254   recommended that the user be able to select whether or not the
3255   Referer field is sent. For example, a browser client could have a
3256   toggle switch for browsing openly/anonymously, which would
3257   respectively enable/disable the sending of Referer and From
3258   information.
3259</t>
3260<t>
3261   Clients SHOULD NOT include a Referer header field in a (non-secure)
3262   HTTP request if the referring page was transferred with a secure
3263   protocol.
3264</t>
3265<t>
3266   Authors of services SHOULD NOT use GET-based forms for the submission of
3267   sensitive data because that data will be placed in the request-target. Many
3268   existing servers, proxies, and user agents log or display the request-target
3269   in places where it might be visible to third parties. Such services can
3270   use POST-based form submission instead.
3271</t>
3272</section>
3273
3274<section title="Location Headers and Spoofing" anchor="location.spoofing">
3275<t>
3276   If a single server supports multiple organizations that do not trust
3277   one another, then it MUST check the values of Location and Content-Location
3278   header fields in responses that are generated under control of
3279   said organizations to make sure that they do not attempt to
3280   invalidate resources over which they have no authority.
3281</t>
3282</section>
3283
3284<section title="Security Considerations for CONNECT">
3285<t>
3286   Since tunneled data is opaque to the proxy, there are additional
3287   risks to tunneling to other well-known or reserved ports.
3288   A HTTP client CONNECTing to port 25 could relay spam
3289   via SMTP, for example. As such, proxies SHOULD restrict CONNECT
3290   access to a small number of known ports.
3291</t>
3292</section>
3293
3294</section>
3295
3296<section title="Acknowledgments" anchor="acks">
3297<t>
3298  See Section 11 of <xref target="Part1"/>.
3299</t>
3300</section>
3301</middle>
3302<back>
3303
3304<references title="Normative References">
3305
3306<reference anchor="Part1">
3307  <front>
3308    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3309    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3310      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3311      <address><email>fielding@gbiv.com</email></address>
3312    </author>
3313    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3314      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3315      <address><email>jg@freedesktop.org</email></address>
3316    </author>
3317    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3318      <organization abbrev="HP">Hewlett-Packard Company</organization>
3319      <address><email>JeffMogul@acm.org</email></address>
3320    </author>
3321    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3322      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3323      <address><email>henrikn@microsoft.com</email></address>
3324    </author>
3325    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3326      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3327      <address><email>LMM@acm.org</email></address>
3328    </author>
3329    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3330      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3331      <address><email>paulle@microsoft.com</email></address>
3332    </author>
3333    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3334      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3335      <address><email>timbl@w3.org</email></address>
3336    </author>
3337    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3338      <organization abbrev="W3C">World Wide Web Consortium</organization>
3339      <address><email>ylafon@w3.org</email></address>
3340    </author>
3341    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3342      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3343      <address><email>julian.reschke@greenbytes.de</email></address>
3344    </author>
3345    <date month="January" year="2012"/>
3346  </front>
3347  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-18"/>
3348 
3349</reference>
3350
3351<reference anchor="Part3">
3352  <front>
3353    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3354    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3355      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3356      <address><email>fielding@gbiv.com</email></address>
3357    </author>
3358    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3359      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3360      <address><email>jg@freedesktop.org</email></address>
3361    </author>
3362    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3363      <organization abbrev="HP">Hewlett-Packard Company</organization>
3364      <address><email>JeffMogul@acm.org</email></address>
3365    </author>
3366    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3367      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3368      <address><email>henrikn@microsoft.com</email></address>
3369    </author>
3370    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3371      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3372      <address><email>LMM@acm.org</email></address>
3373    </author>
3374    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3375      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3376      <address><email>paulle@microsoft.com</email></address>
3377    </author>
3378    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3379      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3380      <address><email>timbl@w3.org</email></address>
3381    </author>
3382    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3383      <organization abbrev="W3C">World Wide Web Consortium</organization>
3384      <address><email>ylafon@w3.org</email></address>
3385    </author>
3386    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3387      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3388      <address><email>julian.reschke@greenbytes.de</email></address>
3389    </author>
3390    <date month="January" year="2012"/>
3391  </front>
3392  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-18"/>
3393 
3394</reference>
3395
3396<reference anchor="Part4">
3397  <front>
3398    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3399    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3400      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3401      <address><email>fielding@gbiv.com</email></address>
3402    </author>
3403    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3404      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3405      <address><email>jg@freedesktop.org</email></address>
3406    </author>
3407    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3408      <organization abbrev="HP">Hewlett-Packard Company</organization>
3409      <address><email>JeffMogul@acm.org</email></address>
3410    </author>
3411    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3412      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3413      <address><email>henrikn@microsoft.com</email></address>
3414    </author>
3415    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3416      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3417      <address><email>LMM@acm.org</email></address>
3418    </author>
3419    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3420      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3421      <address><email>paulle@microsoft.com</email></address>
3422    </author>
3423    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3424      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3425      <address><email>timbl@w3.org</email></address>
3426    </author>
3427    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3428      <organization abbrev="W3C">World Wide Web Consortium</organization>
3429      <address><email>ylafon@w3.org</email></address>
3430    </author>
3431    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3432      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3433      <address><email>julian.reschke@greenbytes.de</email></address>
3434    </author>
3435    <date month="January" year="2012"/>
3436  </front>
3437  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-18"/>
3438 
3439</reference>
3440
3441<reference anchor="Part5">
3442  <front>
3443    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3444    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3445      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3446      <address><email>fielding@gbiv.com</email></address>
3447    </author>
3448    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3449      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3450      <address><email>jg@freedesktop.org</email></address>
3451    </author>
3452    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3453      <organization abbrev="HP">Hewlett-Packard Company</organization>
3454      <address><email>JeffMogul@acm.org</email></address>
3455    </author>
3456    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3457      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3458      <address><email>henrikn@microsoft.com</email></address>
3459    </author>
3460    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3461      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3462      <address><email>LMM@acm.org</email></address>
3463    </author>
3464    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3465      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3466      <address><email>paulle@microsoft.com</email></address>
3467    </author>
3468    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3469      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3470      <address><email>timbl@w3.org</email></address>
3471    </author>
3472    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3473      <organization abbrev="W3C">World Wide Web Consortium</organization>
3474      <address><email>ylafon@w3.org</email></address>
3475    </author>
3476    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3477      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3478      <address><email>julian.reschke@greenbytes.de</email></address>
3479    </author>
3480    <date month="January" year="2012"/>
3481  </front>
3482  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-18"/>
3483 
3484</reference>
3485
3486<reference anchor="Part6">
3487  <front>
3488    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3489    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3490      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3491      <address><email>fielding@gbiv.com</email></address>
3492    </author>
3493    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3494      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3495      <address><email>jg@freedesktop.org</email></address>
3496    </author>
3497    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3498      <organization abbrev="HP">Hewlett-Packard Company</organization>
3499      <address><email>JeffMogul@acm.org</email></address>
3500    </author>
3501    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3502      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3503      <address><email>henrikn@microsoft.com</email></address>
3504    </author>
3505    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3506      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3507      <address><email>LMM@acm.org</email></address>
3508    </author>
3509    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3510      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3511      <address><email>paulle@microsoft.com</email></address>
3512    </author>
3513    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3514      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3515      <address><email>timbl@w3.org</email></address>
3516    </author>
3517    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3518      <organization abbrev="W3C">World Wide Web Consortium</organization>
3519      <address><email>ylafon@w3.org</email></address>
3520    </author>
3521    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3522      <organization>Rackspace</organization>
3523      <address><email>mnot@mnot.net</email></address>
3524    </author>
3525    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3526      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3527      <address><email>julian.reschke@greenbytes.de</email></address>
3528    </author>
3529    <date month="January" year="2012"/>
3530  </front>
3531  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-18"/>
3532 
3533</reference>
3534
3535<reference anchor="Part7">
3536  <front>
3537    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3538    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3539      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3540      <address><email>fielding@gbiv.com</email></address>
3541    </author>
3542    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3543      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3544      <address><email>jg@freedesktop.org</email></address>
3545    </author>
3546    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3547      <organization abbrev="HP">Hewlett-Packard Company</organization>
3548      <address><email>JeffMogul@acm.org</email></address>
3549    </author>
3550    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3551      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3552      <address><email>henrikn@microsoft.com</email></address>
3553    </author>
3554    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3555      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3556      <address><email>LMM@acm.org</email></address>
3557    </author>
3558    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3559      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3560      <address><email>paulle@microsoft.com</email></address>
3561    </author>
3562    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3563      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3564      <address><email>timbl@w3.org</email></address>
3565    </author>
3566    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3567      <organization abbrev="W3C">World Wide Web Consortium</organization>
3568      <address><email>ylafon@w3.org</email></address>
3569    </author>
3570    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3571      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3572      <address><email>julian.reschke@greenbytes.de</email></address>
3573    </author>
3574    <date month="January" year="2012"/>
3575  </front>
3576  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-18"/>
3577 
3578</reference>
3579
3580<reference anchor="RFC2119">
3581  <front>
3582    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3583    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3584      <organization>Harvard University</organization>
3585      <address><email>sob@harvard.edu</email></address>
3586    </author>
3587    <date month="March" year="1997"/>
3588  </front>
3589  <seriesInfo name="BCP" value="14"/>
3590  <seriesInfo name="RFC" value="2119"/>
3591</reference>
3592
3593<reference anchor="RFC3986">
3594 <front>
3595  <title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
3596  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3597    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3598    <address>
3599       <email>timbl@w3.org</email>
3600       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3601    </address>
3602  </author>
3603  <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3604    <organization abbrev="Day Software">Day Software</organization>
3605    <address>
3606      <email>fielding@gbiv.com</email>
3607      <uri>http://roy.gbiv.com/</uri>
3608    </address>
3609  </author>
3610  <author initials="L." surname="Masinter" fullname="Larry Masinter">
3611    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3612    <address>
3613      <email>LMM@acm.org</email>
3614      <uri>http://larry.masinter.net/</uri>
3615    </address>
3616  </author>
3617  <date month="January" year="2005"/>
3618 </front>
3619 <seriesInfo name="STD" value="66"/>
3620 <seriesInfo name="RFC" value="3986"/>
3621</reference>
3622
3623<reference anchor="RFC5234">
3624  <front>
3625    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3626    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3627      <organization>Brandenburg InternetWorking</organization>
3628      <address>
3629        <email>dcrocker@bbiw.net</email>
3630      </address> 
3631    </author>
3632    <author initials="P." surname="Overell" fullname="Paul Overell">
3633      <organization>THUS plc.</organization>
3634      <address>
3635        <email>paul.overell@thus.net</email>
3636      </address>
3637    </author>
3638    <date month="January" year="2008"/>
3639  </front>
3640  <seriesInfo name="STD" value="68"/>
3641  <seriesInfo name="RFC" value="5234"/>
3642</reference>
3643
3644</references>
3645
3646<references title="Informative References">
3647
3648<reference anchor="RFC1123">
3649  <front>
3650    <title>Requirements for Internet Hosts - Application and Support</title>
3651    <author initials="R." surname="Braden" fullname="Robert Braden">
3652      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3653      <address><email>Braden@ISI.EDU</email></address>
3654    </author>
3655    <date month="October" year="1989"/>
3656  </front>
3657  <seriesInfo name="STD" value="3"/>
3658  <seriesInfo name="RFC" value="1123"/>
3659</reference>
3660
3661<reference anchor="RFC1945">
3662  <front>
3663    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3664    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3665      <organization>MIT, Laboratory for Computer Science</organization>
3666      <address><email>timbl@w3.org</email></address>
3667    </author>
3668    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3669      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3670      <address><email>fielding@ics.uci.edu</email></address>
3671    </author>
3672    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3673      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3674      <address><email>frystyk@w3.org</email></address>
3675    </author>
3676    <date month="May" year="1996"/>
3677  </front>
3678  <seriesInfo name="RFC" value="1945"/>
3679</reference>
3680
3681<reference anchor="RFC2068">
3682  <front>
3683    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3684    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3685      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3686      <address><email>fielding@ics.uci.edu</email></address>
3687    </author>
3688    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3689      <organization>MIT Laboratory for Computer Science</organization>
3690      <address><email>jg@w3.org</email></address>
3691    </author>
3692    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3693      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3694      <address><email>mogul@wrl.dec.com</email></address>
3695    </author>
3696    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3697      <organization>MIT Laboratory for Computer Science</organization>
3698      <address><email>frystyk@w3.org</email></address>
3699    </author>
3700    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3701      <organization>MIT Laboratory for Computer Science</organization>
3702      <address><email>timbl@w3.org</email></address>
3703    </author>
3704    <date month="January" year="1997"/>
3705  </front>
3706  <seriesInfo name="RFC" value="2068"/>
3707</reference>
3708
3709<reference anchor="RFC2616">
3710  <front>
3711    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3712    <author initials="R." surname="Fielding" fullname="R. Fielding">
3713      <organization>University of California, Irvine</organization>
3714      <address><email>fielding@ics.uci.edu</email></address>
3715    </author>
3716    <author initials="J." surname="Gettys" fullname="J. Gettys">
3717      <organization>W3C</organization>
3718      <address><email>jg@w3.org</email></address>
3719    </author>
3720    <author initials="J." surname="Mogul" fullname="J. Mogul">
3721      <organization>Compaq Computer Corporation</organization>
3722      <address><email>mogul@wrl.dec.com</email></address>
3723    </author>
3724    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3725      <organization>MIT Laboratory for Computer Science</organization>
3726      <address><email>frystyk@w3.org</email></address>
3727    </author>
3728    <author initials="L." surname="Masinter" fullname="L. Masinter">
3729      <organization>Xerox Corporation</organization>
3730      <address><email>masinter@parc.xerox.com</email></address>
3731    </author>
3732    <author initials="P." surname="Leach" fullname="P. Leach">
3733      <organization>Microsoft Corporation</organization>
3734      <address><email>paulle@microsoft.com</email></address>
3735    </author>
3736    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3737      <organization>W3C</organization>
3738      <address><email>timbl@w3.org</email></address>
3739    </author>
3740    <date month="June" year="1999"/>
3741  </front>
3742  <seriesInfo name="RFC" value="2616"/>
3743</reference>
3744
3745<reference anchor="RFC2817">
3746  <front>
3747    <title>Upgrading to TLS Within HTTP/1.1</title>
3748    <author initials="R." surname="Khare" fullname="R. Khare">
3749      <organization>4K Associates / UC Irvine</organization>
3750      <address><email>rohit@4K-associates.com</email></address>
3751    </author>
3752    <author initials="S." surname="Lawrence" fullname="S. Lawrence">
3753      <organization>Agranat Systems, Inc.</organization>
3754      <address><email>lawrence@agranat.com</email></address>
3755    </author>
3756    <date year="2000" month="May"/>
3757  </front>
3758  <seriesInfo name="RFC" value="2817"/>
3759</reference>
3760
3761<reference anchor="RFC3864">
3762  <front>
3763    <title>Registration Procedures for Message Header Fields</title>
3764    <author initials="G." surname="Klyne" fullname="G. Klyne">
3765      <organization>Nine by Nine</organization>
3766      <address><email>GK-IETF@ninebynine.org</email></address>
3767    </author>
3768    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
3769      <organization>BEA Systems</organization>
3770      <address><email>mnot@pobox.com</email></address>
3771    </author>
3772    <author initials="J." surname="Mogul" fullname="J. Mogul">
3773      <organization>HP Labs</organization>
3774      <address><email>JeffMogul@acm.org</email></address>
3775    </author>
3776    <date year="2004" month="September"/>
3777  </front>
3778  <seriesInfo name="BCP" value="90"/>
3779  <seriesInfo name="RFC" value="3864"/>
3780</reference>
3781
3782<reference anchor="RFC5226">
3783  <front>
3784    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3785    <author initials="T." surname="Narten" fullname="T. Narten">
3786      <organization>IBM</organization>
3787      <address><email>narten@us.ibm.com</email></address>
3788    </author>
3789    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
3790      <organization>Google</organization>
3791      <address><email>Harald@Alvestrand.no</email></address>
3792    </author>
3793    <date year="2008" month="May"/>
3794  </front>
3795  <seriesInfo name="BCP" value="26"/>
3796  <seriesInfo name="RFC" value="5226"/>
3797</reference>
3798
3799<reference anchor="RFC5322">
3800  <front>
3801    <title>Internet Message Format</title>
3802    <author initials="P." surname="Resnick" fullname="P. Resnick">
3803      <organization>Qualcomm Incorporated</organization>
3804    </author>
3805    <date year="2008" month="October"/>
3806  </front> 
3807  <seriesInfo name="RFC" value="5322"/>
3808</reference>
3809
3810<reference anchor="RFC5789">
3811  <front>
3812    <title>PATCH Method for HTTP</title>
3813    <author initials="L." surname="Dusseault" fullname="L. Dusseault">
3814      <organization>Linden Lab</organization>
3815    </author>
3816    <author initials="J." surname="Snell" fullname="J. Snell"/>
3817    <date year="2010" month="March"/>
3818  </front>
3819  <seriesInfo name="RFC" value="5789"/>
3820</reference>
3821
3822<reference anchor="RFC5987">
3823        <front>
3824    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3825    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3826      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3827      <address>
3828        <postal>
3829          <street>Hafenweg 16</street>
3830          <city>Muenster</city><region>NW</region><code>48155</code>
3831          <country>Germany</country>
3832        </postal>
3833        <email>julian.reschke@greenbytes.de</email>     
3834        <uri>http://greenbytes.de/tech/webdav/</uri>   
3835      </address>
3836    </author>
3837    <date month="August" year="2010"/>
3838  </front>
3839  <seriesInfo name="RFC" value="5987"/>
3840</reference>
3841
3842</references>
3843
3844<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3845<t>
3846  This document takes over the Status Code Registry, previously defined
3847  in Section 7.1 of <xref target="RFC2817"/>.
3848  (<xref target="status.code.registry"/>)
3849</t>
3850<t>
3851  Clarify definition of POST.
3852  (<xref target="POST"/>)
3853</t>
3854<t>
3855  Remove requirement to handle all Content-* header fields; ban use of
3856  Content-Range with PUT.
3857  (<xref target="PUT"/>)
3858</t>
3859<t>
3860  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3861  (<xref target="CONNECT"/>)
3862</t>
3863<t>
3864  Broadened the definition of 203 (Non-Authoritative Information) to include
3865  cases of payload transformations as well.
3866  (<xref target="status.203"/>)
3867</t>
3868<t>
3869  Failed to consider that there are many other request methods that are safe
3870  to automatically redirect, and further that the user agent is able to make
3871  that determination based on the request method semantics.
3872  Furthermore, allow user agents to rewrite the method from POST to GET
3873  for status codes 301 and 302.
3874  (Sections <xref format="counter" target="status.301"/>,
3875  <xref format="counter" target="status.302"/> and
3876  <xref format="counter" target="status.307"/>)
3877</t>
3878<t>
3879  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3880  It used to indicate that the target resource must be accessed through the
3881  proxy given by the Location field. The Location field gave the URI of the
3882  proxy. The recipient was expected to repeat this single request via the proxy.
3883  (<xref target="status.305"/>)
3884</t>
3885<t>
3886  Define status 426 (Upgrade Required) (this was incorporated from
3887  <xref target="RFC2817"/>).
3888  (<xref target="status.426"/>)
3889</t>
3890<t>
3891  Change ABNF productions for header fields to only define the field value.
3892  (<xref target="header.field.definitions"/>)
3893</t>
3894<t>
3895  Reclassify "Allow" as response header field, removing the option to
3896  specify it in a PUT request.
3897  Relax the server requirement on the contents of the Allow header field and
3898  remove requirement on clients to always trust the header field value.
3899  (<xref target="header.allow"/>)
3900</t>
3901<t>
3902  The ABNF for the Expect header field has been both fixed (allowing parameters
3903  for value-less expectations as well) and simplified (allowing trailing
3904  semicolons after "100-continue" when they were invalid before).
3905  (<xref target="header.expect"/>)
3906</t>
3907<t>
3908  Correct syntax of Location header field to allow URI references (including
3909  relative references and fragments), as referred symbol "absoluteURI" wasn't
3910  what was expected, and add some clarifications as to when use of fragments
3911  would not be appropriate.
3912  (<xref target="header.location"/>)
3913</t>
3914<t>
3915  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
3916  extension methods could have used it as well).
3917  (<xref target="header.max-forwards"/>)
3918</t>
3919<t>
3920  Allow Referer field value of "about:blank" as alternative to not specifying it.
3921  (<xref target="header.referer"/>)
3922</t>
3923<t>
3924  In the description of the Server header field, the Via field
3925  was described as a SHOULD. The requirement was and is stated
3926  correctly in the description of the Via header field in Section 8.8 of <xref target="Part1"/>.
3927  (<xref target="header.server"/>)
3928</t>
3929</section>
3930
3931
3932<section title="Collected ABNF" anchor="collected.abnf">
3933<figure>
3934<artwork type="abnf" name="p2-semantics.parsed-abnf"><![CDATA[
3935Allow = [ ( "," / Method ) *( OWS "," [ OWS Method ] ) ]
3936
3937BWS = <BWS, defined in [Part1], Section 1.2.2>
3938
3939Date = HTTP-date
3940
3941Expect = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
3942
3943From = mailbox
3944
3945GMT = %x47.4D.54 ; GMT
3946
3947HTTP-date = rfc1123-date / obs-date
3948
3949Location = URI-reference
3950
3951Max-Forwards = 1*DIGIT
3952Method = token
3953
3954OWS = <OWS, defined in [Part1], Section 1.2.2>
3955
3956RWS = <RWS, defined in [Part1], Section 1.2.2>
3957Reason-Phrase = *( HTAB / SP / VCHAR / obs-text )
3958Referer = absolute-URI / partial-URI
3959Retry-After = HTTP-date / delta-seconds
3960
3961Server = product *( RWS ( product / comment ) )
3962Status-Code = 3DIGIT
3963
3964URI-reference = <URI-reference, defined in [Part1], Section 2.7>
3965User-Agent = product *( RWS ( product / comment ) )
3966
3967absolute-URI = <absolute-URI, defined in [Part1], Section 2.7>
3968asctime-date = day-name SP date3 SP time-of-day SP year
3969
3970comment = <comment, defined in [Part1], Section 3.2>
3971
3972date1 = day SP month SP year
3973date2 = day "-" month "-" 2DIGIT
3974date3 = month SP ( 2DIGIT / ( SP DIGIT ) )
3975day = 2DIGIT
3976day-name = %x4D.6F.6E ; Mon
3977 / %x54.75.65 ; Tue
3978 / %x57.65.64 ; Wed
3979 / %x54.68.75 ; Thu
3980 / %x46.72.69 ; Fri
3981 / %x53.61.74 ; Sat
3982 / %x53.75.6E ; Sun
3983day-name-l = %x4D.6F.6E.64.61.79 ; Monday
3984 / %x54.75.65.73.64.61.79 ; Tuesday
3985 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
3986 / %x54.68.75.72.73.64.61.79 ; Thursday
3987 / %x46.72.69.64.61.79 ; Friday
3988 / %x53.61.74.75.72.64.61.79 ; Saturday
3989 / %x53.75.6E.64.61.79 ; Sunday
3990delta-seconds = 1*DIGIT
3991
3992expect-name = token
3993expect-param = expect-name [ BWS "=" BWS expect-value ]
3994expect-value = token / quoted-string
3995expectation = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
3996 OWS expect-param ] )
3997
3998hour = 2DIGIT
3999
4000mailbox = <mailbox, defined in [RFC5322], Section 3.4>
4001minute = 2DIGIT
4002month = %x4A.61.6E ; Jan
4003 / %x46.65.62 ; Feb
4004 / %x4D.61.72 ; Mar
4005 / %x41.70.72 ; Apr
4006 / %x4D.61.79 ; May
4007 / %x4A.75.6E ; Jun
4008 / %x4A.75.6C ; Jul
4009 / %x41.75.67 ; Aug
4010 / %x53.65.70 ; Sep
4011 / %x4F.63.74 ; Oct
4012 / %x4E.6F.76 ; Nov
4013 / %x44.65.63 ; Dec
4014
4015obs-date = rfc850-date / asctime-date
4016obs-text = <obs-text, defined in [Part1], Section 1.2.2>
4017
4018partial-URI = <partial-URI, defined in [Part1], Section 2.7>
4019product = <product, defined in [Part1], Section 5.2>
4020
4021quoted-string = <quoted-string, defined in [Part1], Section 3.2.3>
4022
4023rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
4024rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
4025
4026second = 2DIGIT
4027
4028time-of-day = hour ":" minute ":" second
4029token = <token, defined in [Part1], Section 3.2.3>
4030
4031year = 4DIGIT
4032]]></artwork>
4033</figure>
4034<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
4035; Allow defined but not used
4036; Date defined but not used
4037; Expect defined but not used
4038; From defined but not used
4039; Location defined but not used
4040; Max-Forwards defined but not used
4041; Reason-Phrase defined but not used
4042; Referer defined but not used
4043; Retry-After defined but not used
4044; Server defined but not used
4045; Status-Code defined but not used
4046; User-Agent defined but not used
4047]]></artwork></figure></section>
4048
4049
4050<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4051
4052<section title="Since RFC 2616">
4053<t>
4054  Extracted relevant partitions from <xref target="RFC2616"/>.
4055</t>
4056</section>
4057
4058<section title="Since draft-ietf-httpbis-p2-semantics-00">
4059<t>
4060  Closed issues:
4061  <list style="symbols"> 
4062    <t>
4063      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
4064      "Via is a MUST"
4065      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
4066    </t>
4067    <t>
4068      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
4069      "Fragments allowed in Location"
4070      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
4071    </t>
4072    <t>
4073      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4074      "Safe Methods vs Redirection"
4075      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
4076    </t>
4077    <t>
4078      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
4079      "Revise description of the POST method"
4080      (<eref target="http://purl.org/NET/http-errata#post"/>)
4081    </t>
4082    <t>
4083      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4084      "Normative and Informative references"
4085    </t>
4086    <t>
4087      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4088      "RFC2606 Compliance"
4089    </t>
4090    <t>
4091      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4092      "Informative references"
4093    </t>
4094    <t>
4095      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
4096      "Redundant cross-references"
4097    </t>
4098  </list>
4099</t>
4100<t>
4101  Other changes:
4102  <list style="symbols"> 
4103    <t>
4104      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
4105    </t>
4106  </list>
4107</t>
4108</section>
4109
4110<section title="Since draft-ietf-httpbis-p2-semantics-01">
4111<t>
4112  Closed issues:
4113  <list style="symbols"> 
4114    <t>
4115      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
4116      "PUT side effects"
4117    </t>
4118    <t>
4119      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
4120      "Duplicate Host header requirements"
4121    </t>
4122  </list>
4123</t>
4124<t>
4125  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4126  <list style="symbols"> 
4127    <t>
4128      Move "Product Tokens" section (back) into Part 1, as "token" is used
4129      in the definition of the Upgrade header field.
4130    </t>
4131    <t>
4132      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4133    </t>
4134    <t>
4135      Copy definition of delta-seconds from Part6 instead of referencing it.
4136    </t>
4137  </list>
4138</t>
4139</section>
4140
4141<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
4142<t>
4143  Closed issues:
4144  <list style="symbols"> 
4145    <t>
4146      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
4147      "Requiring Allow in 405 responses"
4148    </t>
4149    <t>
4150      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
4151      "Status Code Registry"
4152    </t>
4153    <t>
4154      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
4155      "Redirection vs. Location"
4156    </t>
4157    <t>
4158      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
4159      "Cacheability of 303 response"
4160    </t>
4161    <t>
4162      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
4163      "305 Use Proxy"
4164    </t>
4165    <t>
4166      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
4167      "Classification for Allow header"
4168    </t>
4169    <t>
4170      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4171      "PUT - 'store under' vs 'store at'"
4172    </t>
4173  </list>
4174</t>
4175<t>
4176  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4177  <list style="symbols"> 
4178    <t>
4179      Reference RFC 3984, and update header field registrations for headers defined
4180      in this document.
4181    </t>
4182  </list>
4183</t>
4184<t>
4185  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4186  <list style="symbols"> 
4187    <t>
4188      Replace string literals when the string really is case-sensitive (method).
4189    </t>
4190  </list>
4191</t>
4192</section>
4193
4194<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
4195<t>
4196  Closed issues:
4197  <list style="symbols"> 
4198    <t>
4199      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
4200      "OPTIONS request bodies"
4201    </t>
4202    <t>
4203      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
4204      "Description of CONNECT should refer to RFC2817"
4205    </t>
4206    <t>
4207      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
4208      "Location Content-Location reference request/response mixup"
4209    </t>
4210  </list>
4211</t>
4212<t>
4213  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
4214  <list style="symbols"> 
4215    <t>
4216      Added initial proposal for registration process, plus initial
4217      content (non-HTTP/1.1 methods to be added by a separate specification).
4218    </t>
4219  </list>
4220</t>
4221</section>
4222
4223<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
4224<t>
4225  Closed issues:
4226  <list style="symbols"> 
4227    <t>
4228      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4229      "Content-*"
4230    </t>
4231    <t>
4232      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4233      "RFC 2822 is updated by RFC 5322"
4234    </t>
4235  </list>
4236</t>
4237<t>
4238  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4239  <list style="symbols"> 
4240    <t>
4241      Use "/" instead of "|" for alternatives.
4242    </t>
4243    <t>
4244      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4245      whitespace ("OWS") and required whitespace ("RWS").
4246    </t>
4247    <t>
4248      Rewrite ABNFs to spell out whitespace rules, factor out
4249      header field value format definitions.
4250    </t>
4251  </list>
4252</t>
4253</section>
4254
4255<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
4256<t>
4257  Closed issues:
4258  <list style="symbols"> 
4259    <t>
4260      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4261      "Reason-Phrase BNF"
4262    </t>
4263  </list>
4264</t>
4265<t>
4266  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4267  <list style="symbols"> 
4268    <t>
4269      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4270    </t>
4271  </list>
4272</t>
4273</section>
4274
4275<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4276<t>
4277  Closed issues:
4278  <list style="symbols"> 
4279    <t>
4280      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4281      "Clarify when Referer is sent"
4282    </t>
4283    <t>
4284      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4285      "status codes vs methods"
4286    </t>
4287    <t>
4288      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4289      "Do not require "updates" relation for specs that register status codes or method names"
4290    </t>
4291  </list>
4292</t>
4293</section>
4294
4295<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4296<t>
4297  Closed issues:
4298  <list style="symbols"> 
4299    <t>
4300      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4301      "Idempotency"
4302    </t>
4303    <t>
4304      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4305      "TRACE security considerations"
4306    </t>
4307    <t>
4308      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4309      "Clarify rules for determining what entities a response carries"
4310    </t>
4311    <t>
4312      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4313      "update note citing RFC 1945 and 2068"
4314    </t>
4315    <t>
4316      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4317      "update note about redirect limit"
4318    </t>
4319    <t>
4320      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4321      "Location header ABNF should use 'URI'"
4322    </t>
4323    <t>
4324      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4325      "fragments in Location vs status 303"
4326    </t>
4327    <t>
4328      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4329      "move IANA registrations for optional status codes"
4330    </t>
4331  </list>
4332</t>
4333<t>
4334  Partly resolved issues:
4335  <list style="symbols"> 
4336    <t>
4337      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4338      "Are OPTIONS and TRACE safe?"
4339    </t>
4340  </list>
4341</t>
4342</section>
4343
4344<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4345<t>
4346  Closed issues:
4347  <list style="symbols"> 
4348    <t>
4349      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4350      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4351      status codes when fixing this previously)
4352    </t>
4353  </list>
4354</t>
4355</section>
4356
4357<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4358<t>
4359  Closed issues:
4360  <list style="symbols"> 
4361    <t>
4362      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4363      "Fragment combination / precedence during redirects"
4364    </t>
4365  </list>
4366</t>
4367<t>
4368  Partly resolved issues:
4369  <list style="symbols"> 
4370    <t>
4371      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4372      "Location header payload handling"
4373    </t>
4374    <t>
4375      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4376      "Term for the requested resource's URI"
4377    </t>
4378  </list>
4379</t>
4380</section>
4381
4382<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4383<t>
4384  Closed issues:
4385  <list style="symbols"> 
4386    <t>
4387      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4388      "Clarify 'Requested Variant'"
4389    </t>
4390    <t>
4391      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4392      "Clarify entity / representation / variant terminology"
4393    </t>
4394    <t>
4395      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4396      "Methods and Caching"
4397    </t>
4398    <t>
4399      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4400      "OPTIONS vs Max-Forwards"
4401    </t>
4402    <t>
4403      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4404      "Status codes and caching"
4405    </t>
4406    <t>
4407      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4408      "consider removing the 'changes from 2068' sections"
4409    </t>
4410  </list>
4411</t>
4412</section>
4413
4414<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4415<t>
4416  Closed issues:
4417  <list style="symbols"> 
4418    <t>
4419      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4420      "Considerations for new status codes"
4421    </t>
4422    <t>
4423      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4424      "Considerations for new methods"
4425    </t>
4426    <t>
4427      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4428      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4429    </t>
4430  </list>
4431</t>
4432</section>
4433
4434<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4435<t>
4436  Closed issues:
4437  <list style="symbols"> 
4438    <t>
4439      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4440      "Fragment combination / precedence during redirects" (added warning
4441      about having a fragid on the redirect may cause inconvenience in
4442      some cases)
4443    </t>
4444    <t>
4445      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4446      "Content-* vs. PUT"
4447    </t>
4448    <t>
4449      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4450      "205 Bodies"
4451    </t>
4452    <t>
4453      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4454      "Understanding Content-* on non-PUT requests"
4455    </t>
4456    <t>
4457      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4458      "Content-*"
4459    </t>
4460    <t>
4461      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4462      "Header type defaulting"
4463    </t>
4464    <t>
4465      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4466      "PUT - 'store under' vs 'store at'"
4467    </t>
4468    <t>
4469      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4470      "duplicate ABNF for Reason-Phrase"
4471    </t>
4472    <t>
4473      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4474      "Note special status of Content-* prefix in header registration procedures"
4475    </t>
4476    <t>
4477      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4478      "Max-Forwards vs extension methods"
4479    </t>
4480    <t>
4481      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4482      "What is the value space of HTTP status codes?" (actually fixed in
4483      draft-ietf-httpbis-p2-semantics-11)
4484    </t>
4485    <t>
4486      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4487      "Header Classification"
4488    </t>
4489    <t>
4490      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4491      "PUT side effect: invalidation or just stale?"
4492    </t>
4493    <t>
4494      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4495      "proxies not supporting certain methods"
4496    </t>
4497    <t>
4498      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4499      "Migrate CONNECT from RFC2817 to p2"
4500    </t>
4501    <t>
4502      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4503      "Migrate Upgrade details from RFC2817"
4504    </t>
4505    <t>
4506      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4507      "clarify PUT semantics'"
4508    </t>
4509    <t>
4510      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4511      "duplicate ABNF for 'Method'"
4512    </t>
4513    <t>
4514      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4515      "untangle ABNFs for header fields"
4516    </t>
4517  </list>
4518</t>
4519</section>
4520
4521<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4522<t>
4523  Closed issues:
4524  <list style="symbols"> 
4525    <t>
4526      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4527      "untangle ABNFs for header fields"
4528    </t>
4529    <t>
4530      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4531      "message-body in CONNECT request"
4532    </t>
4533  </list>
4534</t>
4535</section>
4536
4537<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4538<t>
4539  Closed issues:
4540  <list style="symbols"> 
4541    <t>
4542      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4543      "Clarify status code for rate limiting"
4544    </t>
4545    <t>
4546      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4547      "clarify 403 forbidden"
4548    </t>
4549    <t>
4550      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4551      "Clarify 203 Non-Authoritative Information"
4552    </t>
4553    <t>
4554      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4555      "update default reason phrase for 413"
4556    </t>
4557  </list>
4558</t>
4559</section>
4560
4561<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4562<t>
4563  Closed issues:
4564  <list style="symbols"> 
4565    <t>
4566      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4567      "Strength of requirements on Accept re: 406"
4568    </t>
4569    <t>
4570      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4571      "400 response isn't generic"
4572    </t>
4573  </list>
4574</t>
4575</section>
4576
4577<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4578<t>
4579  Closed issues:
4580  <list style="symbols"> 
4581    <t>
4582      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4583      "Redirects and non-GET methods"
4584    </t>
4585    <t>
4586      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
4587      "Document HTTP's error-handling philosophy"
4588    </t>
4589    <t>
4590      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4591      "Considerations for new headers"
4592    </t>
4593    <t>
4594      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4595      "clarify 303 redirect on HEAD"
4596    </t>
4597  </list>
4598</t>
4599</section>
4600
4601<section title="Since draft-ietf-httpbis-p2-semantics-17" anchor="changes.since.17">
4602<t>
4603  Closed issues:
4604  <list style="symbols"> 
4605    <t>
4606      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4607      "Location header payload handling"
4608    </t>
4609    <t>
4610      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4611      "Clarify status code for rate limiting" (change backed out because
4612      a new status code is being defined for this purpose)
4613    </t>
4614    <t>
4615      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4616      "should there be a permanent variant of 307"
4617    </t>
4618    <t>
4619      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/325"/>:
4620      "When are Location's semantics triggered?"
4621    </t>
4622    <t>
4623      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/327"/>:
4624      "'expect' grammar missing OWS"
4625    </t>
4626    <t>
4627      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/329"/>:
4628      "header field considerations: quoted-string vs use of double quotes"
4629    </t>
4630  </list>
4631</t>
4632</section>
4633
4634</section>
4635
4636</back>
4637</rfc>
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