source: draft-ietf-httpbis/19/draft-ietf-httpbis-p2-semantics-19.xml @ 1618

Last change on this file since 1618 was 1592, checked in by julian.reschke@…, 8 years ago

-19

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 166.0 KB
Line 
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-19">
20
21
22
23<front>
24
25  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
26
27  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
28    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
29    <address>
30      <postal>
31        <street>345 Park Ave</street>
32        <city>San Jose</city>
33        <region>CA</region>
34        <code>95110</code>
35        <country>USA</country>
36      </postal>
37      <email>fielding@gbiv.com</email>
38      <uri>http://roy.gbiv.com/</uri>
39    </address>
40  </author>
41
42  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
43    <organization abbrev="W3C">World Wide Web Consortium</organization>
44    <address>
45      <postal>
46        <street>W3C / ERCIM</street>
47        <street>2004, rte des Lucioles</street>
48        <city>Sophia-Antipolis</city>
49        <region>AM</region>
50        <code>06902</code>
51        <country>France</country>
52      </postal>
53      <email>ylafon@w3.org</email>
54      <uri>http://www.raubacapeu.net/people/yves/</uri>
55    </address>
56  </author>
57
58  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
59    <organization abbrev="greenbytes">greenbytes GmbH</organization>
60    <address>
61      <postal>
62        <street>Hafenweg 16</street>
63        <city>Muenster</city><region>NW</region><code>48155</code>
64        <country>Germany</country>
65      </postal>
66      <phone>+49 251 2807760</phone>
67      <facsimile>+49 251 2807761</facsimile>
68      <email>julian.reschke@greenbytes.de</email>
69      <uri>http://greenbytes.de/tech/webdav/</uri>
70    </address>
71  </author>
72
73  <date month="March" year="2012" day="12"/>
74  <workgroup>HTTPbis Working Group</workgroup>
75
76<abstract>
77<t>
78   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
79   distributed, collaborative, hypertext information systems. HTTP has been in
80   use by the World Wide Web global information initiative since 1990. This
81   document is Part 2 of the seven-part specification that defines the protocol
82   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
83</t>
84<t>
85   Part 2 defines the semantics of HTTP messages as expressed by request
86   methods, request header fields, response status codes, and response header
87   fields.
88</t>
89</abstract>
90
91<note title="Editorial Note (To be removed by RFC Editor)">
92  <t>
93    Discussion of this draft should take place on the HTTPBIS working group
94    mailing list (ietf-http-wg@w3.org), which is archived at
95    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
96  </t>
97  <t>
98    The current issues list is at
99    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
100    documents (including fancy diffs) can be found at
101    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
102  </t>
103  <t>
104    The changes in this draft are summarized in <xref target="changes.since.18"/>.
105  </t>
106</note>
107</front>
108<middle>
109<section title="Introduction" anchor="introduction">
110<t>
111   This document defines HTTP/1.1 request and response semantics.  Each HTTP
112   message, as defined in <xref target="Part1"/>, is in the form of either a request or
113   a response.  An HTTP server listens on a connection for HTTP requests and
114   responds to each request, in the order received on that connection, with
115   one or more HTTP response messages.  This document defines the commonly
116   agreed upon semantics of the HTTP uniform interface, the intentions defined
117   by each request method, and the various response messages that might be
118   expected as a result of applying that method to the target resource.
119</t>
120<t>
121   This document is currently disorganized in order to minimize the changes
122   between drafts and enable reviewers to see the smaller errata changes.
123   A future draft will reorganize the sections to better reflect the content.
124   In particular, the sections will be ordered according to the typical
125   processing of an HTTP request message (after message parsing): resource
126   mapping, methods, request modifying header fields, response status,
127   status modifying header fields, and resource metadata.  The current mess
128   reflects how widely dispersed these topics and associated requirements
129   had become in <xref target="RFC2616"/>.
130</t>
131
132<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
133<t>
134   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
135   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
136   document are to be interpreted as described in <xref target="RFC2119"/>.
137</t>
138<t>
139   This document defines conformance criteria for several roles in HTTP
140   communication, including Senders, Recipients, Clients, Servers, User-Agents,
141   Origin Servers, Intermediaries, Proxies and Gateways. See Section 2 of <xref target="Part1"/>
142   for definitions of these terms.
143</t>
144<t>
145   An implementation is considered conformant if it complies with all of the
146   requirements associated with its role(s). Note that SHOULD-level requirements
147   are relevant here, unless one of the documented exceptions is applicable.
148</t>
149<t>
150   This document also uses ABNF to define valid protocol elements
151   (<xref target="notation"/>). In addition to the prose requirements placed
152   upon them, Senders MUST NOT generate protocol elements that are invalid.
153</t>
154<t>
155   Unless noted otherwise, Recipients MAY take steps to recover a usable
156   protocol element from an invalid construct. However, HTTP does not define
157   specific error handling mechanisms, except in cases where it has direct
158   impact on security. This is because different uses of the protocol require
159   different error handling strategies; for example, a Web browser may wish to
160   transparently recover from a response where the Location header field
161   doesn't parse according to the ABNF, whereby in a systems control protocol
162   using HTTP, this type of error recovery could lead to dangerous consequences.
163</t>
164</section>
165
166<section title="Syntax Notation" anchor="notation">
167 
168 
169 
170 
171 
172 
173<t>
174   This specification uses the Augmented Backus-Naur Form (ABNF) notation
175   of <xref target="RFC5234"/> with the list rule extension defined in
176   Section 1.2 of <xref target="Part1"/>.  <xref target="collected.abnf"/> shows the collected ABNF
177   with the list rule expanded.
178</t>
179<t>
180  The following core rules are included by
181  reference, as defined in <xref target="RFC5234"/>, Appendix B.1:
182  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
183  DIGIT (decimal 0-9), DQUOTE (double quote),
184  HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
185  OCTET (any 8-bit sequence of data), SP (space), and
186  VCHAR (any visible US-ASCII character).
187</t>
188
189<section title="Core Rules" anchor="core.rules">
190 
191 
192 
193 
194 
195 
196<t>
197  The core rules below are defined in <xref target="Part1"/>:
198</t>
199<figure><artwork type="abnf2616"><![CDATA[
200  BWS           = <BWS, defined in [Part1], Section 3.2.1>
201  OWS           = <OWS, defined in [Part1], Section 3.2.1>
202  RWS           = <RWS, defined in [Part1], Section 3.2.1>
203  obs-text      = <obs-text, defined in [Part1], Section 3.2.4>
204  quoted-string = <quoted-string, defined in [Part1], Section 3.2.4>
205  token         = <token, defined in [Part1], Section 3.2.4>
206]]></artwork></figure>
207</section>
208
209<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
210 
211 
212 
213 
214<t>
215  The ABNF rules below are defined in other parts:
216</t>
217<figure><artwork type="abnf2616"><![CDATA[
218  absolute-URI  = <absolute-URI, defined in [Part1], Section 2.7>
219  comment       = <comment, defined in [Part1], Section 3.2.4>
220  partial-URI   = <partial-URI, defined in [Part1], Section 2.7>
221  URI-reference = <URI-reference, defined in [Part1], Section 2.7>
222]]></artwork></figure>
223</section>
224</section>
225</section>
226
227<section title="Method" anchor="method">
228 
229 
230<t>
231   The method token indicates the request method to be performed on the target
232   resource (Section 5.5 of <xref target="Part1"/>). The method is case-sensitive.
233</t>
234<figure><iref primary="true" item="Grammar" subitem="method"/><artwork type="abnf2616"><![CDATA[
235  method         = token
236]]></artwork></figure>
237<t>
238   The list of methods allowed by a resource can be specified in an
239   Allow header field (<xref target="header.allow"/>). The status code of the response
240   always notifies the client whether a method is currently allowed on a
241   resource, since the set of allowed methods can change dynamically. An
242   origin server SHOULD respond with the status code 405 (Method Not Allowed)
243   if the method is known by the origin server but not allowed for the
244   resource, and 501 (Not Implemented) if the method is
245   unrecognized or not implemented by the origin server. The methods GET
246   and HEAD MUST be supported by all general-purpose servers. All other
247   methods are OPTIONAL; however, if the above methods are implemented,
248   they MUST be implemented with the same semantics as those specified
249   in <xref target="method.definitions"/>.
250</t>
251
252<section title="Overview of Methods" anchor="overview.of.methods">
253<t>
254  The methods listed below are defined in <xref target="method.definitions"/>.
255</t>
256<texttable align="left">
257  <ttcol>Method Name</ttcol><ttcol>Defined in...</ttcol>
258 
259  <c>OPTIONS</c> <c><xref target="OPTIONS"/></c>
260  <c>GET</c> <c><xref target="GET"/></c>
261  <c>HEAD</c> <c><xref target="HEAD"/></c>
262  <c>POST</c> <c><xref target="POST"/></c>
263  <c>PUT</c> <c><xref target="PUT"/></c>
264  <c>DELETE</c> <c><xref target="DELETE"/></c>
265  <c>TRACE</c> <c><xref target="TRACE"/></c>
266  <c>CONNECT</c> <c><xref target="CONNECT"/></c>
267</texttable>
268<t>
269  Note that this list is not exhaustive — it does not include request methods defined
270  in other specifications.
271</t>
272</section>
273
274<section title="Method Registry" anchor="method.registry">
275<t>
276  The HTTP Method Registry defines the name space for the method token in the
277  Request line of an HTTP request.
278</t>
279<t>
280  Registrations MUST include the following fields:
281  <list style="symbols">
282    <t>Method Name (see <xref target="method"/>)</t>
283    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
284    <t>Pointer to specification text</t>
285  </list>
286</t>
287<t>
288  Values to be added to this name space require IETF Review
289  (see <xref target="RFC5226"/>, Section 4.1).
290</t>
291<t>
292  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
293</t>
294
295<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
296<t>
297   When it is necessary to express new semantics for a HTTP request that
298   aren't specific to a single application or media type, and currently defined
299   methods are inadequate, it may be appropriate to register a new method.
300</t>
301<t>
302   HTTP methods are generic; that is, they are potentially applicable to any
303   resource, not just one particular media type, "type" of resource, or
304   application. As such, it is preferred that new HTTP methods be registered
305   in a document that isn't specific to a single application, so that this is
306   clear.
307</t>
308<t>
309   Due to the parsing rules defined in Section 3.3 of <xref target="Part1"/>, definitions of HTTP
310   methods cannot prohibit the presence of a message body on either the request
311   or the response message (with responses to HEAD requests being the single
312   exception). Definitions of new methods cannot change this rule, but they can
313   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
314</t>
315<t>
316   New method definitions need to indicate whether they are safe (<xref target="safe.methods"/>), what semantics (if any) the request body has,
317   and whether they are idempotent (<xref target="idempotent.methods"/>).
318   They also need to state whether they can be cached (<xref target="Part6"/>); in
319   particular what conditions a cache may store the response, and under what
320   conditions such a stored response may be used to satisfy a subsequent
321   request.
322</t>
323</section>
324
325</section>
326</section>
327
328<section title="Header Fields" anchor="header.fields">
329<t>
330   Header fields are key value pairs that can be used to communicate data about
331   the message, its payload, the target resource, or about the connection
332   itself (i.e., control data).  See Section 3.2 of <xref target="Part1"/> for a general definition
333   of their syntax.
334</t>
335
336<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
337<t>
338   New header fields are registered using the procedures described in
339   <xref target="RFC3864"/>.
340</t>
341<t>
342   The requirements for header field names are defined in
343   Section 4.1 of <xref target="RFC3864"/>.  Authors of specifications
344   defining new fields are advised to keep the name as short as practical, and
345   not to prefix them with "X-" if they are to be registered (either
346   immediately or in the future).
347</t>
348<t>
349   New header field values typically have their syntax defined using ABNF
350   (<xref target="RFC5234"/>), using the extension defined in Section 3.2.5 of <xref target="Part1"/>
351   as necessary, and are usually constrained to the range of ASCII characters.
352   Header fields needing a greater range of characters can use an encoding
353   such as the one defined in <xref target="RFC5987"/>.
354</t>
355<t>
356   Because commas (",") are used as a generic delimiter between field-values,
357   they need to be treated with care if they are allowed in the field-value's
358   payload. Typically, components that might contain a comma are protected with
359   double-quotes using the quoted-string ABNF production (Section 3.2.4 of <xref target="Part1"/>).
360</t>
361<t>
362   For example, a textual date and a URI (either of which might contain a comma)
363   could be safely carried in field-values like these:
364</t>
365<figure><artwork type="example"><![CDATA[
366  Example-URI-Field: "http://example.com/a.html,foo",
367                     "http://without-a-comma.example.com/"
368  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
369]]></artwork></figure>
370<t>
371   Note that double quote delimiters almost always are used with the
372   quoted-string production; using a different syntax inside double quotes
373   will likely cause unnecessary confusion.
374</t>
375<t>
376   Many header fields use a format including (case-insensitively) named
377   parameters (for instance, Content-Type, defined in Section 6.8 of <xref target="Part3"/>).
378   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
379   parameter value enables recipients to use existing parser components. When
380   allowing both forms, the meaning of a parameter value ought to be
381   independent of the syntax used for it (for an example, see the notes on
382   parameter handling for media types in Section 2.3 of <xref target="Part3"/>).
383</t>
384<t>
385   Authors of specifications defining new header fields are advised to consider
386   documenting:
387  <list style="symbols">
388    <t>Whether the field is a single value, or whether it can be a list
389      (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
390      where the header field occurs multiple times (a sensible default would
391      be to ignore the header field, but this might not always be the right
392      choice).<vspace blankLines="1"/>Note that intermediaries and software libraries might combine
393      multiple header field instances into a single one, despite the header
394      field not allowing this. A robust format enables recipients to discover
395      these situations (good example: "Content-Type", as the comma can only
396      appear inside quoted strings; bad example: "Location", as a comma can
397      occur inside a URI).</t>
398    <t>Under what conditions the header field can be used; e.g., only in
399    responses or requests, in all messages, only on responses to a particular
400    request method.</t>
401    <t>Whether it is appropriate to list the field-name in the Connection header
402    (i.e., if the header is to be hop-by-hop, see Section 6.1 of <xref target="Part1"/>).</t>
403    <t>Under what conditions intermediaries are allowed to modify the header
404    field's value, insert or delete it.</t>
405    <t>How the header might interact with caching (see <xref target="Part6"/>).</t>
406    <t>Whether the header field is useful or allowable in trailers (see
407    Section 4.1 of <xref target="Part1"/>).</t>
408    <t>Whether the header field should be preserved across redirects.</t>
409  </list>
410</t>
411</section>
412
413<section title="Request Header Fields" anchor="request.header.fields">
414 
415<t>
416   The request header fields allow the client to pass additional
417   information about the request, and about the client itself, to the
418   server. These fields act as request modifiers, with semantics
419   equivalent to the parameters on a programming language method
420   invocation.
421</t>
422<texttable align="left">
423  <ttcol>Header Field Name</ttcol>
424  <ttcol>Defined in...</ttcol>
425
426  <c>Accept</c> <c>Section 6.1 of <xref target="Part3"/></c>
427  <c>Accept-Charset</c> <c>Section 6.2 of <xref target="Part3"/></c>
428  <c>Accept-Encoding</c> <c>Section 6.3 of <xref target="Part3"/></c>
429  <c>Accept-Language</c> <c>Section 6.4 of <xref target="Part3"/></c>
430  <c>Authorization</c> <c>Section 4.1 of <xref target="Part7"/></c>
431  <c>Expect</c> <c><xref target="header.expect"/></c>
432  <c>From</c> <c><xref target="header.from"/></c>
433  <c>Host</c> <c>Section 5.4 of <xref target="Part1"/></c>
434  <c>If-Match</c> <c>Section 3.1 of <xref target="Part4"/></c>
435  <c>If-Modified-Since</c> <c>Section 3.3 of <xref target="Part4"/></c>
436  <c>If-None-Match</c> <c>Section 3.2 of <xref target="Part4"/></c>
437  <c>If-Range</c> <c>Section 5.3 of <xref target="Part5"/></c>
438  <c>If-Unmodified-Since</c> <c>Section 3.4 of <xref target="Part4"/></c>
439  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
440  <c>Proxy-Authorization</c> <c>Section 4.3 of <xref target="Part7"/></c>
441  <c>Range</c> <c>Section 5.4 of <xref target="Part5"/></c>
442  <c>Referer</c> <c><xref target="header.referer"/></c>
443  <c>TE</c> <c>Section 4.3 of <xref target="Part1"/></c>
444  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
445</texttable>
446</section>
447
448<section title="Response Header Fields" anchor="response.header.fields">
449 
450<t>
451   The response header fields allow the server to pass additional
452   information about the response which cannot be placed in the status-line.
453   These header fields give information about the server and about
454   further access to the target resource (Section 5.5 of <xref target="Part1"/>).
455</t>
456<texttable align="left">
457  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
458
459  <c>Accept-Ranges</c> <c>Section 5.1 of <xref target="Part5"/></c>
460  <c>Age</c> <c>Section 3.1 of <xref target="Part6"/></c>
461  <c>Allow</c> <c><xref target="header.allow"/></c>
462  <c>Date</c> <c><xref target="header.date"/></c>
463  <c>ETag</c> <c>Section 2.3 of <xref target="Part4"/></c>
464  <c>Location</c> <c><xref target="header.location"/></c>
465  <c>Proxy-Authenticate</c> <c>Section 4.2 of <xref target="Part7"/></c>
466  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
467  <c>Server</c> <c><xref target="header.server"/></c>
468  <c>Vary</c> <c>Section 3.5 of <xref target="Part6"/></c>
469  <c>WWW-Authenticate</c> <c>Section 4.4 of <xref target="Part7"/></c>
470</texttable>
471</section>
472
473</section>
474
475<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
476 
477 
478 
479<t>
480   The status-code element is a 3-digit integer result code of the attempt to
481   understand and satisfy the request.
482</t>
483<t>
484   The reason-phrase is intended to give a short textual description of the
485   status-code and is intended for a human user. The client does not need
486   to examine or display the reason-phrase.
487</t>
488<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[
489  status-code    = 3DIGIT
490  reason-phrase  = *( HTAB / SP / VCHAR / obs-text )
491]]></artwork></figure>
492<t>
493   HTTP status codes are extensible. HTTP applications are not required
494   to understand the meaning of all registered status codes, though such
495   understanding is obviously desirable. However, applications MUST
496   understand the class of any status code, as indicated by the first
497   digit, and treat any unrecognized response as being equivalent to the
498   x00 status code of that class, with the exception that an
499   unrecognized response MUST NOT be cached. For example, if an
500   unrecognized status code of 431 is received by the client, it can
501   safely assume that there was something wrong with its request and
502   treat the response as if it had received a 400 status code. In such
503   cases, user agents SHOULD present to the user the representation enclosed
504   with the response, since that representation is likely to include human-readable
505   information which will explain the unusual status.
506</t>
507
508<section title="Overview of Status Codes" anchor="overview.of.status.codes">
509<t> 
510   The status codes listed below are defined in <xref target="status.codes"/>
511   of this specification, Section 4 of <xref target="Part4"/>, Section 3 of <xref target="Part5"/>, and Section 3 of <xref target="Part7"/>.
512   The reason phrases listed here are only recommendations — they can be
513   replaced by local equivalents without affecting the protocol.
514</t>
515<texttable align="left">
516  <ttcol>status-code</ttcol>
517  <ttcol>reason-phrase</ttcol>
518  <ttcol>Defined in...</ttcol>
519 
520  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
521  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
522
523  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
524  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
525  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
526  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
527  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
528  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
529  <c>206</c> <c>Partial Content</c> <c>Section 3.1 of <xref target="Part5"/></c>
530
531  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
532  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
533  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
534  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
535  <c>304</c> <c>Not Modified</c> <c>Section 4.1 of <xref target="Part4"/></c>
536  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
537  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
538
539  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
540  <c>401</c> <c>Unauthorized</c> <c>Section 3.1 of <xref target="Part7"/></c>
541  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
542  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
543  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
544  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
545  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
546  <c>407</c> <c>Proxy Authentication Required</c> <c>Section 3.2 of <xref target="Part7"/></c>
547  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
548  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
549  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
550  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
551  <c>412</c> <c>Precondition Failed</c> <c>Section 4.2 of <xref target="Part4"/></c>
552  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
553  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
554  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
555  <c>416</c> <c>Requested range not satisfiable</c> <c>Section 3.2 of <xref target="Part5"/></c>
556  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
557  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
558
559  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
560  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
561  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
562  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
563  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
564  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
565</texttable>
566<t>
567   Note that this list is not exhaustive — it does not include
568   extension status codes defined in other specifications.
569</t>
570</section>
571
572<section title="Status Code Registry" anchor="status.code.registry">
573<t>
574  The HTTP Status Code Registry defines the name space for the status-code
575  token in the status-line of an HTTP response.
576</t>
577<t>
578  Values to be added to this name space require IETF Review
579  (see <xref target="RFC5226"/>, Section 4.1).
580</t>
581<t>
582  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
583</t>
584
585<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
586<t>
587   When it is necessary to express new semantics for a HTTP response that
588   aren't specific to a single application or media type, and currently defined
589   status codes are inadequate, a new status code can be registered.
590</t>
591<t>
592   HTTP status codes are generic; that is, they are potentially applicable to
593   any resource, not just one particular media type, "type" of resource, or
594   application. As such, it is preferred that new HTTP status codes be
595   registered in a document that isn't specific to a single application, so
596   that this is clear.
597</t>
598<t>
599   Definitions of new HTTP status codes typically explain the request
600   conditions that produce a response containing the status code (e.g.,
601   combinations of request headers and/or method(s)), along with any
602   interactions with response headers (e.g., those that are required, those
603   that modify the semantics of the response).
604</t>
605<t>
606   New HTTP status codes are required to fall under one of the categories
607   defined in <xref target="status.codes"/>. To allow existing parsers to
608   properly handle them, new status codes cannot disallow a response body,
609   although they can mandate a zero-length response body. They can require the
610   presence of one or more particular HTTP response header(s).
611</t>
612<t>
613   Likewise, their definitions can specify that caches are allowed to use
614   heuristics to determine their freshness (see <xref target="Part6"/>; by default, it is
615   not allowed), and can define how to determine the resource which they
616   carry a representation for (see <xref target="identifying.response.associated.with.representation"/>; by default,
617   it is anonymous).
618</t>
619</section>
620
621</section>
622
623</section>
624
625<section title="Representation" anchor="representation">
626<t>
627   Request and Response messages MAY transfer a representation if not otherwise
628   restricted by the request method or response status code. A representation
629   consists of metadata (representation header fields) and data (representation
630   body).  When a complete or partial representation is enclosed in an HTTP message,
631   it is referred to as the payload of the message. HTTP representations
632   are defined in <xref target="Part3"/>.
633</t>
634<t>
635   A representation body is only present in a message when a message body is
636   present, as described in Section 3.3 of <xref target="Part1"/>. The representation body is obtained
637   from the message body by decoding any Transfer-Encoding that might
638   have been applied to ensure safe and proper transfer of the message.
639</t>
640
641<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
642<t>
643   It is sometimes necessary to determine an identifier for the resource
644   associated with a representation.
645</t>
646<t>
647   An HTTP request representation, when present, is always associated with an
648   anonymous (i.e., unidentified) resource.
649</t>
650<t>
651   In the common case, an HTTP response is a representation of the target
652   resource (see Section 5.5 of <xref target="Part1"/>). However, this is not always the
653   case. To determine the URI of the resource a response is associated with,
654   the following rules are used (with the first applicable one being selected):
655</t>
656<t><list style="numbers">
657   <t>If the response status code is 200 or 203 and the request method was GET,
658   the response payload is a representation of the target resource.</t>
659   <t>If the response status code is 204, 206, or 304 and the request method was GET
660   or HEAD, the response payload is a partial representation of the target
661   resource.</t>
662   <t>If the response has a Content-Location header field, and that URI is the same
663   as the effective request URI, the response payload is a representation of the
664   target resource.</t>
665   <t>If the response has a Content-Location header field, and that URI is not the
666   same as the effective request URI, then the response asserts that its
667   payload is a representation of the resource identified by the
668   Content-Location URI. However, such an assertion cannot be trusted unless
669   it can be verified by other means (not defined by HTTP).</t>
670   <t>Otherwise, the response is a representation of an anonymous (i.e.,
671   unidentified) resource.</t>
672</list></t>
673<t>
674  <cref anchor="TODO-req-uri">
675   The comparison function is going to have to be defined somewhere,
676   because we already need to compare URIs for things like cache invalidation.</cref>
677</t>
678</section>
679
680</section>
681
682
683<section title="Method Definitions" anchor="method.definitions">
684<t>
685   The set of common request methods for HTTP/1.1 is defined below. Although
686   this set can be expanded, additional methods cannot be assumed to
687   share the same semantics for separately extended clients and servers.
688</t>
689
690<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
691
692<section title="Safe Methods" anchor="safe.methods">
693<iref item="Safe Methods" primary="true"/>
694<t>
695   Implementors need to be aware that the software represents the user in
696   their interactions over the Internet, and need to allow
697   the user to be aware of any actions they take which might have an
698   unexpected significance to themselves or others.
699</t>
700<t>
701   In particular, the convention has been established that the GET, HEAD,
702   OPTIONS, and TRACE request methods SHOULD NOT have the significance
703   of taking an action other than retrieval. These request methods ought
704   to be considered "safe".
705   This allows user agents to represent other methods, such as POST, PUT
706   and DELETE, in a special way, so that the user is made aware of the
707   fact that a possibly unsafe action is being requested.
708</t>
709<t>
710   Naturally, it is not possible to ensure that the server does not
711   generate side-effects as a result of performing a GET request; in
712   fact, some dynamic resources consider that a feature. The important
713   distinction here is that the user did not request the side-effects,
714   so therefore cannot be held accountable for them.
715</t>
716</section>
717
718<section title="Idempotent Methods" anchor="idempotent.methods">
719<iref item="Idempotent Methods" primary="true"/>
720<t>
721   Request methods can also have the property of "idempotence" in that,
722   aside from error or expiration issues, the intended effect of multiple
723   identical requests is the same as for a single request.
724   PUT, DELETE, and all safe request methods are idempotent.
725   It is important to note that idempotence refers only to changes
726   requested by the client: a server is free to change its state due
727   to multiple requests for the purpose of tracking those requests,
728   versioning of results, etc.
729</t>
730</section>
731</section>
732
733<section title="OPTIONS" anchor="OPTIONS">
734 
735  <iref primary="true" item="OPTIONS method"/>
736  <iref primary="true" item="Methods" subitem="OPTIONS"/>
737<t>
738   The OPTIONS method requests information about the
739   communication options available on the request/response chain
740   identified by the effective request URI. This method allows a client to
741   determine the options and/or requirements associated with a resource,
742   or the capabilities of a server, without implying a resource action
743   or initiating a resource retrieval.
744</t>
745<t>
746   Responses to the OPTIONS method are not cacheable.
747</t>
748<t>
749   If the OPTIONS request includes a message body (as indicated by the
750   presence of Content-Length or Transfer-Encoding), then the media type
751   MUST be indicated by a Content-Type field. Although this
752   specification does not define any use for such a body, future
753   extensions to HTTP might use the OPTIONS body to make more detailed
754   queries on the server.
755</t>
756<t>
757   If the request-target (Section 5.3 of <xref target="Part1"/>) is an asterisk ("*"),
758   the OPTIONS request is
759   intended to apply to the server in general rather than to a specific
760   resource. Since a server's communication options typically depend on
761   the resource, the "*" request is only useful as a "ping" or "no-op"
762   type of method; it does nothing beyond allowing the client to test
763   the capabilities of the server. For example, this can be used to test
764   a proxy for HTTP/1.1 conformance (or lack thereof).
765</t>
766<t>
767   If the request-target is not an asterisk, the OPTIONS request applies
768   only to the options that are available when communicating with that
769   resource.
770</t>
771<t>
772   A 200 response SHOULD include any header fields that indicate
773   optional features implemented by the server and applicable to that
774   resource (e.g., Allow), possibly including extensions not defined by
775   this specification. The response body, if any, SHOULD also include
776   information about the communication options. The format for such a
777   body is not defined by this specification, but might be defined by
778   future extensions to HTTP. Content negotiation MAY be used to select
779   the appropriate response format. If no response body is included, the
780   response MUST include a Content-Length field with a field-value of
781   "0".
782</t>
783<t>
784   The Max-Forwards header field MAY be used to target a
785   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
786   If no Max-Forwards field is present in the request, then the forwarded
787   request MUST NOT include a Max-Forwards field.
788</t>
789</section>
790
791<section title="GET" anchor="GET">
792 
793  <iref primary="true" item="GET method"/>
794  <iref primary="true" item="Methods" subitem="GET"/>
795<t>
796   The GET method requests transfer of a current representation of
797   the target resource.
798</t>
799<t>  
800   If the target resource is a data-producing process, it is the
801   produced data which shall be returned as the representation in the response and not
802   the source text of the process, unless that text happens to be the output of
803   the process.
804</t>
805<t>
806   The semantics of the GET method change to a "conditional GET" if the
807   request message includes an If-Modified-Since, If-Unmodified-Since,
808   If-Match, If-None-Match, or If-Range header field. A conditional GET
809   requests that the representation be transferred only under the
810   circumstances described by the conditional header field(s). The
811   conditional GET request is intended to reduce unnecessary network
812   usage by allowing cached representations to be refreshed without requiring
813   multiple requests or transferring data already held by the client.
814</t>
815<t>
816   The semantics of the GET method change to a "partial GET" if the
817   request message includes a Range header field. A partial GET requests
818   that only part of the representation be transferred, as described in Section 5.4 of <xref target="Part5"/>.
819   The partial GET request is intended to reduce unnecessary
820   network usage by allowing partially-retrieved representations to be
821   completed without transferring data already held by the client.
822</t>
823<t>
824   Bodies on GET requests have no defined semantics. Note that sending a body
825   on a GET request might cause some existing implementations to reject the
826   request.
827</t>
828<t>
829   The response to a GET request is cacheable and MAY be used to satisfy
830   subsequent GET and HEAD requests (see <xref target="Part6"/>).
831</t>
832<t>
833   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
834</t>
835</section>
836
837<section title="HEAD" anchor="HEAD">
838 
839  <iref primary="true" item="HEAD method"/>
840  <iref primary="true" item="Methods" subitem="HEAD"/>
841<t>
842   The HEAD method is identical to GET except that the server MUST NOT
843   return a message body in the response. The metadata contained
844   in the HTTP header fields in response to a HEAD request SHOULD be identical
845   to the information sent in response to a GET request. This method can
846   be used for obtaining metadata about the representation implied by the
847   request without transferring the representation body. This method is
848   often used for testing hypertext links for validity, accessibility,
849   and recent modification.
850</t>
851<t>
852   The response to a HEAD request is cacheable and MAY be used to satisfy
853   a subsequent HEAD request. It also has potential side effects on
854   previously stored responses to GET; see Section 2.5 of <xref target="Part6"/>.
855</t>
856<t>
857   Bodies on HEAD requests have no defined semantics. Note that sending a body
858   on a HEAD request might cause some existing implementations to reject the
859   request.
860</t>
861</section>
862
863<section title="POST" anchor="POST">
864  <iref primary="true" item="POST method"/>
865  <iref primary="true" item="Methods" subitem="POST"/>
866<t>
867   The POST method requests that the origin server accept the
868   representation enclosed in the request as data to be processed by the
869   target resource. POST is designed to allow a uniform method to cover the
870   following functions:
871  <list style="symbols">
872    <t>
873      Annotation of existing resources;
874    </t>
875    <t>
876        Posting a message to a bulletin board, newsgroup, mailing list,
877        or similar group of articles;
878    </t>
879    <t>
880        Providing a block of data, such as the result of submitting a
881        form, to a data-handling process;
882    </t>
883    <t>
884        Extending a database through an append operation.
885    </t>
886  </list>
887</t>
888<t>
889   The actual function performed by the POST method is determined by the
890   server and is usually dependent on the effective request URI.
891</t>
892<t>
893   The action performed by the POST method might not result in a
894   resource that can be identified by a URI. In this case, either 200
895   (OK) or 204 (No Content) is the appropriate response status code,
896   depending on whether or not the response includes a representation that
897   describes the result.
898</t>
899<t>
900   If a resource has been created on the origin server, the response
901   SHOULD be 201 (Created) and contain a representation which describes the
902   status of the request and refers to the new resource, and a Location
903   header field (see <xref target="header.location"/>).
904</t>
905<t>
906   Responses to POST requests are only cacheable when they
907   include explicit freshness information (see Section 2.3.1 of <xref target="Part6"/>). A
908   cached POST response with a Content-Location header field
909   (see Section 6.7 of <xref target="Part3"/>) whose value is the effective
910   Request URI MAY be used to satisfy subsequent GET and HEAD requests.
911</t>
912<t>
913   Note that POST caching is not widely implemented.
914   However, the 303 (See Other) response can be used to direct the
915   user agent to retrieve a cacheable resource.
916</t>
917</section>
918
919<section title="PUT" anchor="PUT">
920  <iref primary="true" item="PUT method"/>
921  <iref primary="true" item="Methods" subitem="PUT"/>
922<t>
923   The PUT method requests that the state of the target resource
924   be created or replaced with the state defined by the representation
925   enclosed in the request message payload.  A successful PUT of a given
926   representation would suggest that a subsequent GET on that same target
927   resource will result in an equivalent representation being returned in
928   a 200 (OK) response.  However, there is no guarantee that such a state
929   change will be observable, since the target resource might be acted
930   upon by other user agents in parallel, or might be subject to dynamic
931   processing by the origin server, before any subsequent GET is received.
932   A successful response only implies that the user agent's intent was
933   achieved at the time of its processing by the origin server.
934</t>
935<t>  
936   If the target resource does not have a current representation and
937   the PUT successfully creates one, then the origin server MUST inform
938   the user agent by sending a 201 (Created) response.  If the target
939   resource does have a current representation and that representation is
940   successfully modified in accordance with the state of the enclosed
941   representation, then either a 200 (OK) or 204 (No Content) response
942   SHOULD be sent to indicate successful completion of the request.
943</t>
944<t>
945   Unrecognized header fields SHOULD be ignored (i.e., not saved
946   as part of the resource state).
947</t>
948<t>
949   An origin server SHOULD verify that the PUT representation is
950   consistent with any constraints which the server has for the target
951   resource that cannot or will not be changed by the PUT.  This is
952   particularly important when the origin server uses internal
953   configuration information related to the URI in order to set the
954   values for representation metadata on GET responses.  When a PUT
955   representation is inconsistent with the target resource, the origin
956   server SHOULD either make them consistent, by transforming the
957   representation or changing the resource configuration, or respond
958   with an appropriate error message containing sufficient information
959   to explain why the representation is unsuitable.  The 409 (Conflict)
960   or 415 (Unsupported Media Type) status codes are suggested, with the
961   latter being specific to constraints on Content-Type values.
962</t>
963<t>
964   For example, if the target resource is configured to always have a
965   Content-Type of "text/html" and the representation being PUT has a
966   Content-Type of "image/jpeg", then the origin server SHOULD do one of:
967   (a) reconfigure the target resource to reflect the new media type;
968   (b) transform the PUT representation to a format consistent with that
969   of the resource before saving it as the new resource state; or,
970   (c) reject the request with a 415 response indicating that the target
971   resource is limited to "text/html", perhaps including a link to a
972   different resource that would be a suitable target for the new
973   representation.
974</t>
975<t>
976   HTTP does not define exactly how a PUT method affects the state
977   of an origin server beyond what can be expressed by the intent of
978   the user agent request and the semantics of the origin server response.
979   It does not define what a resource might be, in any sense of that
980   word, beyond the interface provided via HTTP.  It does not define
981   how resource state is "stored", nor how such storage might change
982   as a result of a change in resource state, nor how the origin server
983   translates resource state into representations.  Generally speaking,
984   all implementation details behind the resource interface are
985   intentionally hidden by the server.
986</t>
987<t>
988   The fundamental difference between the POST and PUT methods is
989   highlighted by the different intent for the target resource.
990   The target resource in a POST request is intended to handle the
991   enclosed representation as a data-accepting process, such as for
992   a gateway to some other protocol or a document that accepts annotations.
993   In contrast, the target resource in a PUT request is intended to
994   take the enclosed representation as a new or replacement value.
995   Hence, the intent of PUT is idempotent and visible to intermediaries,
996   even though the exact effect is only known by the origin server.
997</t>
998<t>
999   Proper interpretation of a PUT request presumes that the user agent
1000   knows what target resource is desired.  A service that is intended
1001   to select a proper URI on behalf of the client, after receiving
1002   a state-changing request, SHOULD be implemented using the POST
1003   method rather than PUT.  If the origin server will not make the
1004   requested PUT state change to the target resource and instead
1005   wishes to have it applied to a different resource, such as when the
1006   resource has been moved to a different URI, then the origin server
1007   MUST send a 301 (Moved Permanently) response; the user agent MAY
1008   then make its own decision regarding whether or not to redirect the
1009   request.
1010</t>
1011<t>
1012   A PUT request applied to the target resource MAY have side-effects
1013   on other resources.  For example, an article might have a URI for
1014   identifying "the current version" (a resource) which is separate
1015   from the URIs identifying each particular version (different
1016   resources that at one point shared the same state as the current version
1017   resource).  A successful PUT request on "the current version" URI might
1018   therefore create a new version resource in addition to changing the
1019   state of the target resource, and might also cause links to be added
1020   between the related resources.
1021</t>
1022<t>
1023   An origin server SHOULD reject any PUT request that contains a
1024   Content-Range header field, since it might be misinterpreted as
1025   partial content (or might be partial content that is being mistakenly
1026   PUT as a full representation).  Partial content updates are
1027   possible by targeting a separately identified resource with state
1028   that overlaps a portion of the larger resource, or by using a
1029   different method that has been specifically defined for partial
1030   updates (for example, the PATCH method defined in
1031   <xref target="RFC5789"/>).
1032</t>
1033<t>
1034   Responses to the PUT method are not cacheable. If a PUT request passes
1035   through a cache that has one or more stored responses for the effective
1036   request URI, those stored responses will be invalidated (see
1037   Section 2.6 of <xref target="Part6"/>).
1038</t>
1039</section>
1040
1041<section title="DELETE" anchor="DELETE">
1042  <iref primary="true" item="DELETE method"/>
1043  <iref primary="true" item="Methods" subitem="DELETE"/>
1044<t>
1045   The DELETE method requests that the origin server delete the target
1046   resource. This method MAY be overridden by
1047   human intervention (or other means) on the origin server. The client cannot
1048   be guaranteed that the operation has been carried out, even if the
1049   status code returned from the origin server indicates that the action
1050   has been completed successfully. However, the server SHOULD NOT
1051   indicate success unless, at the time the response is given, it
1052   intends to delete the resource or move it to an inaccessible
1053   location.
1054</t>
1055<t>
1056   A successful response SHOULD be 200 (OK) if the response includes an
1057   representation describing the status, 202 (Accepted) if the action has not
1058   yet been enacted, or 204 (No Content) if the action has been enacted
1059   but the response does not include a representation.
1060</t>
1061<t>
1062   Bodies on DELETE requests have no defined semantics. Note that sending a body
1063   on a DELETE request might cause some existing implementations to reject the
1064   request.
1065</t>
1066<t>
1067   Responses to the DELETE method are not cacheable. If a DELETE request
1068   passes through a cache that has one or more stored responses for the
1069   effective request URI, those stored responses will be invalidated (see
1070   Section 2.6 of <xref target="Part6"/>).
1071</t>
1072</section>
1073
1074<section title="TRACE" anchor="TRACE">
1075 
1076  <iref primary="true" item="TRACE method"/>
1077  <iref primary="true" item="Methods" subitem="TRACE"/>
1078<t>
1079   The TRACE method requests a remote, application-layer loop-back
1080   of the request message. The final recipient of the request
1081   SHOULD reflect the message received back to the client as the
1082   message body of a 200 (OK) response. The final recipient is either the
1083   origin server or the first proxy to receive a Max-Forwards
1084   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
1085   A TRACE request MUST NOT include a message body.
1086</t>
1087<t>
1088   TRACE allows the client to see what is being received at the other
1089   end of the request chain and use that data for testing or diagnostic
1090   information. The value of the Via header field (Section 6.2 of <xref target="Part1"/>) is of
1091   particular interest, since it acts as a trace of the request chain.
1092   Use of the Max-Forwards header field allows the client to limit the
1093   length of the request chain, which is useful for testing a chain of
1094   proxies forwarding messages in an infinite loop.
1095</t>
1096<t>
1097   If the request is valid, the response SHOULD have a Content-Type of
1098   "message/http" (see Section 7.3.1 of <xref target="Part1"/>) and contain a message body
1099   that encloses a copy of the entire request message.
1100   Responses to the TRACE method are not cacheable.
1101</t>
1102</section>
1103
1104<section title="CONNECT" anchor="CONNECT">
1105  <iref primary="true" item="CONNECT method"/>
1106  <iref primary="true" item="Methods" subitem="CONNECT"/>
1107<t>
1108   The CONNECT method requests that the proxy establish a tunnel
1109   to the request-target and, if successful, thereafter restrict its behavior
1110   to blind forwarding of packets until the connection is closed.
1111</t>
1112<t>
1113   When using CONNECT, the request-target MUST use the authority form
1114   (Section 5.3 of <xref target="Part1"/>); i.e., the request-target consists of only the
1115   host name and port number of the tunnel destination, separated by a colon.
1116   For example,
1117</t>
1118<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1119  CONNECT server.example.com:80 HTTP/1.1
1120  Host: server.example.com:80
1121 
1122  ]]></artwork></figure>
1123<t>
1124   Any successful (2xx) response to a CONNECT request indicates that the
1125   proxy has established a connection to the requested host and port,
1126   and has switched to tunneling the current connection to that server
1127   connection.
1128   The tunneled data from the server begins immediately after the blank line
1129   that concludes the successful response's header block.
1130   A server SHOULD NOT send any Transfer-Encoding or Content-Length
1131   header fields in a successful response.
1132   A client MUST ignore any Content-Length or Transfer-Encoding header
1133   fields received in a successful response.
1134</t>
1135<t>
1136   Any response other than a successful response indicates that the tunnel
1137   has not yet been formed and that the connection remains governed by HTTP.
1138</t>
1139<t>
1140   Proxy authentication might be used to establish the
1141   authority to create a tunnel:
1142</t>
1143<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1144  CONNECT server.example.com:80 HTTP/1.1
1145  Host: server.example.com:80
1146  Proxy-Authorization: basic aGVsbG86d29ybGQ=
1147 
1148  ]]></artwork></figure>
1149<t>
1150   A message body on a CONNECT request has no defined semantics. Sending a
1151   body on a CONNECT request might cause existing implementations to reject
1152   the request.
1153</t>
1154<t>
1155   Similar to a pipelined HTTP/1.1 request, data to be tunneled from client
1156   to server MAY be sent immediately after the request (before a response
1157   is received). The usual caveats also apply:
1158   data may be discarded if the eventual response is negative, and the
1159   connection may be reset with no response if more than one TCP segment
1160   is outstanding.
1161</t>
1162<t>
1163   It may be the case that the proxy itself can only reach the requested
1164   origin server through another proxy.  In this case, the first proxy
1165   SHOULD make a CONNECT request of that next proxy, requesting a tunnel
1166   to the authority.  A proxy MUST NOT respond with any 2xx status code
1167   unless it has either a direct or tunnel connection established to the
1168   authority.
1169</t>
1170<t>
1171   If at any point either one of the peers gets disconnected, any
1172   outstanding data that came from that peer will be passed to the other
1173   one, and after that also the other connection will be terminated by
1174   the proxy. If there is outstanding data to that peer undelivered,
1175   that data will be discarded.
1176</t>
1177<t>
1178   An origin server which receives a CONNECT request for itself MAY
1179   respond with a 2xx status code to indicate that a connection is
1180   established.  However, most origin servers do not implement CONNECT.
1181</t>
1182</section>
1183</section>
1184
1185
1186<section title="Status Code Definitions" anchor="status.codes">
1187<t>
1188   The first digit of the status-code defines the class of response. The
1189   last two digits do not have any categorization role. There are 5
1190   values for the first digit:
1191  <list style="symbols">
1192    <t>
1193      1xx: Informational - Request received, continuing process
1194    </t>
1195    <t>
1196      2xx: Success - The action was successfully received,
1197        understood, and accepted
1198    </t>
1199    <t>
1200      3xx: Redirection - Further action must be taken in order to
1201        complete the request
1202    </t>
1203    <t>
1204      4xx: Client Error - The request contains bad syntax or cannot
1205        be fulfilled
1206    </t>
1207    <t>
1208      5xx: Server Error - The server failed to fulfill an apparently
1209        valid request
1210    </t>
1211  </list>
1212</t>
1213<t>
1214   Each status-code is described below, including any metadata required
1215   in the response.
1216</t>
1217<t>
1218   For most status codes the response can carry a payload, in which case a
1219   Content-Type header field indicates the payload's media type
1220   (Section 6.8 of <xref target="Part3"/>).
1221</t>
1222
1223<section title="Informational 1xx" anchor="status.1xx">
1224<t>
1225   This class of status code indicates a provisional response,
1226   consisting only of the status-line and optional header fields, and is
1227   terminated by an empty line. There are no required header fields for this
1228   class of status code. Since HTTP/1.0 did not define any 1xx status
1229   codes, servers MUST NOT send a 1xx response to an HTTP/1.0 client
1230   except under experimental conditions.
1231</t>
1232<t>
1233   A client MUST be prepared to accept one or more 1xx status responses
1234   prior to a regular response, even if the client does not expect a 100
1235   (Continue) status message. Unexpected 1xx status responses MAY be
1236   ignored by a user agent.
1237</t>
1238<t>
1239   Proxies MUST forward 1xx responses, unless the connection between the
1240   proxy and its client has been closed, or unless the proxy itself
1241   requested the generation of the 1xx response. (For example, if a
1242   proxy adds a "Expect: 100-continue" field when it forwards a request,
1243   then it need not forward the corresponding 100 (Continue)
1244   response(s).)
1245</t>
1246
1247<section title="100 Continue" anchor="status.100">
1248  <iref primary="true" item="100 Continue (status code)"/>
1249  <iref primary="true" item="Status Codes" subitem="100 Continue"/>
1250<t>
1251   The client SHOULD continue with its request. This interim response is
1252   used to inform the client that the initial part of the request has
1253   been received and has not yet been rejected by the server. The client
1254   SHOULD continue by sending the remainder of the request or, if the
1255   request has already been completed, ignore this response. The server
1256   MUST send a final response after the request has been completed. See
1257   Section 6.4.3 of <xref target="Part1"/> for detailed discussion of the use and handling of this
1258   status code.
1259</t>
1260</section>
1261
1262<section title="101 Switching Protocols" anchor="status.101">
1263  <iref primary="true" item="101 Switching Protocols (status code)"/>
1264  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols"/>
1265<t>
1266   The server understands and is willing to comply with the client's
1267   request, via the Upgrade message header field (Section 6.5 of <xref target="Part1"/>), for a
1268   change in the application protocol being used on this connection. The
1269   server will switch protocols to those defined by the response's
1270   Upgrade header field immediately after the empty line which
1271   terminates the 101 response.
1272</t>
1273<t>
1274   The protocol SHOULD be switched only when it is advantageous to do
1275   so. For example, switching to a newer version of HTTP is advantageous
1276   over older versions, and switching to a real-time, synchronous
1277   protocol might be advantageous when delivering resources that use
1278   such features.
1279</t>
1280</section>
1281</section>
1282
1283<section title="Successful 2xx" anchor="status.2xx">
1284<t>
1285   This class of status code indicates that the client's request was
1286   successfully received, understood, and accepted.
1287</t>
1288
1289<section title="200 OK" anchor="status.200">
1290  <iref primary="true" item="200 OK (status code)"/>
1291  <iref primary="true" item="Status Codes" subitem="200 OK"/>
1292<t>
1293   The request has succeeded. The payload returned with the response
1294   is dependent on the method used in the request, for example:
1295  <list style="hanging">
1296    <t hangText="GET">
1297      a representation of the target resource is sent in the response;
1298    </t>
1299    <t hangText="HEAD">
1300      the same representation as GET, except without the message body;
1301    </t>
1302    <t hangText="POST">
1303      a representation describing or containing the result of the action;
1304    </t>
1305    <t hangText="TRACE">
1306      a representation containing the request message as received by the
1307      end server.
1308    </t>
1309  </list>
1310</t>
1311<t>
1312   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine
1313   freshness for 200 responses.
1314</t>
1315</section>
1316
1317<section title="201 Created" anchor="status.201">
1318  <iref primary="true" item="201 Created (status code)"/>
1319  <iref primary="true" item="Status Codes" subitem="201 Created"/>
1320<t>
1321   The request has been fulfilled and has resulted in a new resource being
1322   created.
1323</t>
1324<t>
1325   The newly created resource is typically linked to from the response payload,
1326   with the most relevant URI also being carried in the Location header field.
1327   If the newly created resource's URI is the same as the Effective Request URI,
1328   this information can be omitted (e.g., in the case of a response to a PUT
1329   request). 
1330</t>
1331<t>
1332   The origin server MUST create the resource before returning the 201 status
1333   code. If the action cannot be carried out immediately, the server SHOULD
1334   respond with 202 (Accepted) response instead.
1335</t>
1336<t>
1337   A 201 response MAY contain an ETag response header field indicating
1338   the current value of the entity-tag for the representation of the resource
1339   just created (see Section 2.3 of <xref target="Part4"/>).
1340</t>
1341</section>
1342
1343<section title="202 Accepted" anchor="status.202">
1344  <iref primary="true" item="202 Accepted (status code)"/>
1345  <iref primary="true" item="Status Codes" subitem="202 Accepted"/>
1346<t>
1347   The request has been accepted for processing, but the processing has
1348   not been completed.  The request might or might not eventually be
1349   acted upon, as it might be disallowed when processing actually takes
1350   place. There is no facility for re-sending a status code from an
1351   asynchronous operation such as this.
1352</t>
1353<t>
1354   The 202 response is intentionally non-committal. Its purpose is to
1355   allow a server to accept a request for some other process (perhaps a
1356   batch-oriented process that is only run once per day) without
1357   requiring that the user agent's connection to the server persist
1358   until the process is completed. The representation returned with this
1359   response SHOULD include an indication of the request's current status
1360   and either a pointer to a status monitor or some estimate of when the
1361   user can expect the request to be fulfilled.
1362</t>
1363</section>
1364
1365<section title="203 Non-Authoritative Information" anchor="status.203">
1366  <iref primary="true" item="203 Non-Authoritative Information (status code)"/>
1367  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information"/>
1368<t>
1369   The representation in the response has been transformed or otherwise
1370   modified by a transforming proxy (Section 2.3 of <xref target="Part1"/>).  Note that the
1371   behavior of transforming intermediaries is controlled by the no-transform
1372   Cache-Control directive (Section 3.2 of <xref target="Part6"/>).
1373</t>
1374<t>
1375   This status code is only appropriate when the response status code would
1376   have been 200 (OK) otherwise. When the status code before transformation
1377   would have been different, the 214 Transformation Applied warn-code
1378   (Section 3.6 of <xref target="Part6"/>) is appropriate.
1379</t>
1380<t>
1381   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine
1382   freshness for 203 responses.
1383</t>
1384</section>
1385
1386<section title="204 No Content" anchor="status.204">
1387  <iref primary="true" item="204 No Content (status code)"/>
1388  <iref primary="true" item="Status Codes" subitem="204 No Content"/>
1389<t>
1390   The 204 (No Content) status code indicates that the server has
1391   successfully fulfilled the request and that there is no additional
1392   content to return in the response payload body.  Metadata in the
1393   response header fields refer to the target resource and its current
1394   representation after the requested action.
1395</t>
1396<t>
1397   For example, if a 204 status code is received in response to a PUT
1398   request and the response contains an ETag header field, then the PUT
1399   was successful and the ETag field-value contains the entity-tag for
1400   the new representation of that target resource.
1401</t>
1402<t>
1403   The 204 response allows a server to indicate that the action has been
1404   successfully applied to the target resource while implying that the
1405   user agent SHOULD NOT traverse away from its current "document view"
1406   (if any).  The server assumes that the user agent will provide some
1407   indication of the success to its user, in accord with its own interface,
1408   and apply any new or updated metadata in the response to the active
1409   representation.
1410</t>
1411<t>
1412   For example, a 204 status code is commonly used with document editing
1413   interfaces corresponding to a "save" action, such that the document
1414   being saved remains available to the user for editing. It is also
1415   frequently used with interfaces that expect automated data transfers
1416   to be prevalent, such as within distributed version control systems.
1417</t>
1418<t>
1419   The 204 response MUST NOT include a message body, and thus is always
1420   terminated by the first empty line after the header fields.
1421</t>
1422</section>
1423
1424<section title="205 Reset Content" anchor="status.205">
1425  <iref primary="true" item="205 Reset Content (status code)"/>
1426  <iref primary="true" item="Status Codes" subitem="205 Reset Content"/>
1427<t>
1428   The server has fulfilled the request and the user agent SHOULD reset
1429   the document view which caused the request to be sent. This response
1430   is primarily intended to allow input for actions to take place via
1431   user input, followed by a clearing of the form in which the input is
1432   given so that the user can easily initiate another input action.
1433</t>
1434<t>  
1435   The message body included with the response MUST be empty. Note that
1436   receivers still need to parse the response according to the algorithm defined
1437   in Section 3.3 of <xref target="Part1"/>.
1438</t>
1439</section>
1440</section>
1441
1442<section title="Redirection 3xx" anchor="status.3xx">
1443<t>
1444   This class of status code indicates that further action needs to be
1445   taken by the user agent in order to fulfill the request.  If the required
1446   action involves a subsequent HTTP request, it MAY be carried out by the
1447   user agent without interaction with the user if and only if the method used
1448   in the second request is known to be "safe", as defined in
1449   <xref target="safe.methods"/>.
1450</t>
1451<t>
1452   There are several types of redirects:
1453   <list style="numbers">
1454      <t>
1455          Redirects of the request to another URI, either temporarily or
1456          permanently. The new URI is specified in the Location header field.
1457          In this specification, the status codes 301 (Moved Permanently),
1458          302 (Found), and 307 (Temporary Redirect) fall under this category.
1459        </t>
1460      <t>
1461          Redirection to a new location that represents an indirect response to
1462          the request, such as the result of a POST operation to be retrieved
1463          with a subsequent GET request. This is status code 303 (See Other).
1464        </t>
1465      <t>
1466          Redirection offering a choice of matching resources for use by
1467          agent-driven content negotiation (Section 5.2 of <xref target="Part3"/>). This
1468          is status code 300 (Multiple Choices).
1469        </t>
1470      <t>
1471          Other kinds of redirection, such as to a cached result (status code 304
1472          (Not Modified), see Section 4.1 of <xref target="Part4"/>).
1473        </t>
1474   </list>
1475</t>
1476<t><list>
1477  <t>
1478    Note: In HTTP/1.0, only the status codes 301 (Moved Permanently)
1479    and 302 (Found) were defined for the first type of redirect, and the second
1480    type did not exist at all (<xref target="RFC1945"/>, Section 9.3).
1481    However it turned out that web forms using POST expected redirects to change
1482    the operation for the subsequent request to retrieval (GET). To address this
1483    use case, HTTP/1.1 introduced the second type of redirect with the status
1484    code 303 (See Other) (<xref target="RFC2068"/>, Section 10.3.4).
1485    As user agents did not change their behavior to maintain backwards
1486    compatibility, the first revision of HTTP/1.1 added yet another status code,
1487    307 (Temporary Redirect), for which the backwards compatibility problems did
1488    not apply (<xref target="RFC2616"/>, Section 10.3.8).
1489    Over 10 years later, most user agents still do method rewriting for
1490    status codes 301 and 302, therefore this specification makes that behavior
1491    conformant in case the original request was POST.
1492  </t>
1493</list></t>
1494<t>
1495   A Location header field on a 3xx response indicates that a client MAY
1496   automatically redirect to the URI provided; see <xref target="header.location"/>.
1497</t>
1498<t>
1499   Note that for methods not known to be "safe", as defined in <xref target="safe.methods"/>,
1500   automatic redirection needs to done with care, since the redirect might
1501   change the conditions under which the request was issued.
1502</t>
1503<t>
1504   Clients SHOULD detect and intervene in cyclical redirections (i.e.,
1505   "infinite" redirection loops).
1506</t>
1507<t><list>
1508  <t>
1509    Note: An earlier version of this specification recommended a
1510    maximum of five redirections (<xref target="RFC2068"/>, Section 10.3).
1511    Content developers need to be aware that some clients might
1512    implement such a fixed limitation.
1513  </t>
1514</list></t>
1515
1516<section title="300 Multiple Choices" anchor="status.300">
1517  <iref primary="true" item="300 Multiple Choices (status code)"/>
1518  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices"/>
1519<t>
1520   The target resource has more than one
1521   representation, each with its own specific location, and agent-driven
1522   negotiation information (Section 5 of <xref target="Part3"/>) is being provided so that
1523   the user (or user agent) can select a preferred representation by
1524   redirecting its request to that location.
1525</t>
1526<t>
1527   Unless it was a HEAD request, the response SHOULD include a representation
1528   containing a list of representation metadata and location(s) from
1529   which the user or user agent can choose the one most appropriate. Depending
1530   upon the format and the capabilities of
1531   the user agent, selection of the most appropriate choice MAY be
1532   performed automatically. However, this specification does not define
1533   any standard for such automatic selection.
1534</t>
1535<t>
1536   If the server has a preferred choice of representation, it SHOULD
1537   include the specific URI for that representation in the Location
1538   field; user agents MAY use the Location field value for automatic
1539   redirection.
1540</t>
1541<t>
1542   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine
1543   freshness for 300 responses.
1544</t>
1545
1546</section>
1547
1548<section title="301 Moved Permanently" anchor="status.301">
1549  <iref primary="true" item="301 Moved Permanently (status code)"/>
1550  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently"/>
1551<t>
1552   The target resource has been assigned a new permanent URI and any
1553   future references to this resource SHOULD use one of the returned
1554   URIs.  Clients with link editing capabilities ought to automatically
1555   re-link references to the effective request URI to one or more of the new
1556   references returned by the server, where possible.
1557</t>
1558<t>
1559   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine
1560   freshness for 301 responses.
1561</t>
1562<t>
1563   The new permanent URI SHOULD be given by the Location field in the
1564   response. A response payload can contain a short hypertext note with a
1565   hyperlink to the new URI(s).
1566</t>
1567<t><list>
1568  <t>
1569    Note: For historic reasons, user agents MAY change the
1570    request method from POST to GET for the subsequent request. If this
1571    behavior is undesired, status code 307 (Temporary Redirect) can be used
1572    instead.
1573  </t>
1574</list></t>
1575</section>
1576
1577<section title="302 Found" anchor="status.302">
1578  <iref primary="true" item="302 Found (status code)"/>
1579  <iref primary="true" item="Status Codes" subitem="302 Found"/>
1580<t>
1581   The target resource resides temporarily under a different URI.
1582   Since the redirection might be altered on occasion, the client SHOULD
1583   continue to use the effective request URI for future requests.
1584</t>
1585<t>
1586   The temporary URI SHOULD be given by the Location field in the
1587   response. A response payload can contain a short hypertext note with a
1588   hyperlink to the new URI(s).
1589</t>
1590<t><list>
1591  <t>
1592    Note: For historic reasons, user agents MAY change the
1593    request method from POST to GET for the subsequent request. If this
1594    behavior is undesired, status code 307 (Temporary Redirect) can be used
1595    instead.
1596  </t>
1597</list></t>
1598</section>
1599
1600<section title="303 See Other" anchor="status.303">
1601  <iref primary="true" item="303 See Other (status code)"/>
1602  <iref primary="true" item="Status Codes" subitem="303 See Other"/>
1603<t>
1604   The 303 status code indicates that the server is redirecting the
1605   user agent to a different resource, as indicated by a URI in the
1606   Location header field, that is intended to provide an indirect
1607   response to the original request.  In order to satisfy the original
1608   request, a user agent SHOULD perform a retrieval request using the
1609   Location URI (a GET or HEAD request if using HTTP), which
1610   may itself be redirected further, and present the eventual result as an
1611   answer to the original request.
1612   Note that the new URI in the Location header field is not considered
1613   equivalent to the effective request URI.
1614</t>
1615<t>
1616   This status code is generally applicable to any HTTP method.  It is
1617   primarily used to allow the output of a POST action to redirect
1618   the user agent to a selected resource, since doing so provides the
1619   information corresponding to the POST response in a form that
1620   can be separately identified, bookmarked, and cached independent
1621   of the original request.
1622</t>
1623<t>
1624   A 303 response to a GET request indicates that the requested
1625   resource does not have a representation of its own that can be
1626   transferred by the server over HTTP.  The Location URI indicates a
1627   resource that is descriptive of the target resource, such that the
1628   follow-on representation might be useful to recipients without
1629   implying that it adequately represents the target resource.
1630   Note that answers to the questions of what can be represented, what
1631   representations are adequate, and what might be a useful description
1632   are outside the scope of HTTP and thus entirely determined by the
1633   URI owner(s).
1634</t>
1635<t>
1636   Except for responses to a HEAD request, the representation of a 303
1637   response SHOULD contain a short hypertext note with a hyperlink
1638   to the Location URI.
1639</t>
1640</section>
1641
1642<section title="305 Use Proxy" anchor="status.305">
1643  <iref primary="true" item="305 Use Proxy (status code)"/>
1644  <iref primary="true" item="Status Codes" subitem="305 Use Proxy"/>
1645<t>
1646   The 305 status code was defined in a previous version of this specification
1647   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1648</t>
1649</section>
1650
1651<section title="306 (Unused)" anchor="status.306">
1652  <iref primary="true" item="306 (Unused) (status code)"/>
1653  <iref primary="true" item="Status Codes" subitem="306 (Unused)"/>
1654<t>
1655   The 306 status code was used in a previous version of the
1656   specification, is no longer used, and the code is reserved.
1657</t>
1658</section>
1659
1660<section title="307 Temporary Redirect" anchor="status.307">
1661  <iref primary="true" item="307 Temporary Redirect (status code)"/>
1662  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect"/>
1663<t>
1664   The target resource resides temporarily under a different URI.
1665   Since the redirection can change over time, the client SHOULD
1666   continue to use the effective request URI for future requests.
1667</t>
1668<t>
1669   The temporary URI SHOULD be given by the Location field in the
1670   response. A response payload can contain a short hypertext note with a
1671   hyperlink to the new URI(s).
1672</t>
1673<t><list>
1674  <t>
1675    Note: This status code is similar to 302 Found, except that
1676    it does not allow rewriting the request method from POST to GET. This
1677    specification defines no equivalent counterpart for 301 Moved Permanently.
1678  </t>
1679</list></t>
1680</section>
1681</section>
1682
1683<section title="Client Error 4xx" anchor="status.4xx">
1684<t>
1685   The 4xx class of status code is intended for cases in which the
1686   client seems to have erred. Except when responding to a HEAD request,
1687   the server SHOULD include a representation containing an explanation of the
1688   error situation, and whether it is a temporary or permanent
1689   condition. These status codes are applicable to any request method.
1690   User agents SHOULD display any included representation to the user.
1691</t>
1692
1693<section title="400 Bad Request" anchor="status.400">
1694  <iref primary="true" item="400 Bad Request (status code)"/>
1695  <iref primary="true" item="Status Codes" subitem="400 Bad Request"/>
1696<t>
1697   The server cannot or will not process the request, due to a client error (e.g.,
1698   malformed syntax).
1699</t>
1700</section>
1701
1702<section title="402 Payment Required" anchor="status.402">
1703  <iref primary="true" item="402 Payment Required (status code)"/>
1704  <iref primary="true" item="Status Codes" subitem="402 Payment Required"/>
1705<t>
1706   This code is reserved for future use.
1707</t>
1708</section>
1709
1710<section title="403 Forbidden" anchor="status.403">
1711  <iref primary="true" item="403 Forbidden (status code)"/>
1712  <iref primary="true" item="Status Codes" subitem="403 Forbidden"/>
1713<t>
1714   The server understood the request, but refuses to authorize it. Providing
1715   different user authentication credentials might be successful, but any
1716   credentials that were provided in the request are insufficient. The request
1717   SHOULD NOT be repeated with the same credentials.
1718</t>
1719<t>
1720   If the request method was not HEAD and the server wishes to make
1721   public why the request has not been fulfilled, it SHOULD describe the
1722   reason for the refusal in the representation.  If the server does not wish to
1723   make this information available to the client, the status code 404
1724   (Not Found) MAY be used instead.
1725</t>
1726</section>
1727
1728<section title="404 Not Found" anchor="status.404">
1729  <iref primary="true" item="404 Not Found (status code)"/>
1730  <iref primary="true" item="Status Codes" subitem="404 Not Found"/>
1731<t>
1732   The server has not found anything matching the effective request URI. No
1733   indication is given of whether the condition is temporary or
1734   permanent. The 410 (Gone) status code SHOULD be used if the server
1735   knows, through some internally configurable mechanism, that an old
1736   resource is permanently unavailable and has no forwarding address.
1737   This status code is commonly used when the server does not wish to
1738   reveal exactly why the request has been refused, or when no other
1739   response is applicable.
1740</t>
1741</section>
1742
1743<section title="405 Method Not Allowed" anchor="status.405">
1744  <iref primary="true" item="405 Method Not Allowed (status code)"/>
1745  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed"/>
1746<t>
1747   The method specified in the request-line is not allowed for the target
1748   resource. The response MUST include an Allow header field containing a
1749   list of valid methods for the requested resource.
1750</t>
1751</section>
1752
1753<section title="406 Not Acceptable" anchor="status.406">
1754  <iref primary="true" item="406 Not Acceptable (status code)"/>
1755  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable"/>
1756<t>
1757   The resource identified by the request is only capable of generating
1758   response representations which have content characteristics not acceptable
1759   according to the Accept and Accept-* header fields sent in the request
1760   (see Section 6 of <xref target="Part3"/>).
1761</t>
1762<t>
1763   Unless it was a HEAD request, the response SHOULD include a representation
1764   containing a list of available representation characteristics and location(s)
1765   from which the user or user agent can choose the one most
1766   appropriate. Depending upon the format and the
1767   capabilities of the user agent, selection of the most appropriate
1768   choice MAY be performed automatically. However, this specification
1769   does not define any standard for such automatic selection.
1770</t>
1771<t><list>
1772  <t>
1773    Note: HTTP/1.1 servers are allowed to return responses which are
1774    not acceptable according to the accept header fields sent in the
1775    request. In some cases, this might even be preferable to sending a
1776    406 response. User agents are encouraged to inspect the header fields of
1777    an incoming response to determine if it is acceptable.
1778  </t>
1779</list></t>
1780<t>
1781   If the response could be unacceptable, a user agent SHOULD
1782   temporarily stop receipt of more data and query the user for a
1783   decision on further actions.
1784</t>
1785</section>
1786
1787<section title="408 Request Timeout" anchor="status.408">
1788  <iref primary="true" item="408 Request Timeout (status code)"/>
1789  <iref primary="true" item="Status Codes" subitem="408 Request Timeout"/>
1790<t>
1791   The client did not produce a request within the time that the server
1792   was prepared to wait. The client MAY repeat the request without
1793   modifications at any later time.
1794</t>
1795</section>
1796
1797<section title="409 Conflict" anchor="status.409">
1798  <iref primary="true" item="409 Conflict (status code)"/>
1799  <iref primary="true" item="Status Codes" subitem="409 Conflict"/>
1800<t>
1801   The request could not be completed due to a conflict with the current
1802   state of the resource. This code is only allowed in situations where
1803   it is expected that the user might be able to resolve the conflict
1804   and resubmit the request. The response body SHOULD include enough
1805   information for the user to recognize the source of the conflict.
1806   Ideally, the response representation would include enough information for the
1807   user or user agent to fix the problem; however, that might not be
1808   possible and is not required.
1809</t>
1810<t>
1811   Conflicts are most likely to occur in response to a PUT request. For
1812   example, if versioning were being used and the representation being PUT
1813   included changes to a resource which conflict with those made by an
1814   earlier (third-party) request, the server might use the 409 response
1815   to indicate that it can't complete the request. In this case, the
1816   response representation would likely contain a list of the differences
1817   between the two versions.
1818</t>
1819</section>
1820
1821<section title="410 Gone" anchor="status.410">
1822  <iref primary="true" item="410 Gone (status code)"/>
1823  <iref primary="true" item="Status Codes" subitem="410 Gone"/>
1824<t>
1825   The target resource is no longer available at the server and no
1826   forwarding address is known. This condition is expected to be
1827   considered permanent. Clients with link editing capabilities SHOULD
1828   delete references to the effective request URI after user approval. If the
1829   server does not know, or has no facility to determine, whether or not
1830   the condition is permanent, the status code 404 (Not Found) SHOULD be
1831   used instead.
1832</t>
1833<t>
1834   The 410 response is primarily intended to assist the task of web
1835   maintenance by notifying the recipient that the resource is
1836   intentionally unavailable and that the server owners desire that
1837   remote links to that resource be removed. Such an event is common for
1838   limited-time, promotional services and for resources belonging to
1839   individuals no longer working at the server's site. It is not
1840   necessary to mark all permanently unavailable resources as "gone" or
1841   to keep the mark for any length of time — that is left to the
1842   discretion of the server owner.
1843</t>
1844<t>
1845   Caches MAY use a heuristic (see Section 2.3.1.1 of <xref target="Part6"/>) to determine freshness
1846   for 410 responses.
1847</t>
1848</section>
1849
1850<section title="411 Length Required" anchor="status.411">
1851  <iref primary="true" item="411 Length Required (status code)"/>
1852  <iref primary="true" item="Status Codes" subitem="411 Length Required"/>
1853<t>
1854   The server refuses to accept the request without a defined Content-Length.
1855   The client MAY repeat the request if it adds a valid
1856   Content-Length header field containing the length of the message body
1857   in the request message.
1858</t>
1859</section>
1860
1861<section title="413 Request Representation Too Large" anchor="status.413">
1862  <iref primary="true" item="413 Request Representation Too Large (status code)"/>
1863  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large"/>
1864<t>
1865   The server is refusing to process a request because the request
1866   representation is larger than the server is willing or able to process. The
1867   server MAY close the connection to prevent the client from continuing
1868   the request.
1869</t>
1870<t>
1871   If the condition is temporary, the server SHOULD include a Retry-After
1872   header field to indicate that it is temporary and after what
1873   time the client MAY try again.
1874</t>
1875</section>
1876
1877<section title="414 URI Too Long" anchor="status.414">
1878  <iref primary="true" item="414 URI Too Long (status code)"/>
1879  <iref primary="true" item="Status Codes" subitem="414 URI Too Long"/>
1880<t>
1881   The server is refusing to service the request because the effective request URI
1882   is longer than the server is willing to interpret. This rare
1883   condition is only likely to occur when a client has improperly
1884   converted a POST request to a GET request with long query
1885   information, when the client has descended into a URI "black hole" of
1886   redirection (e.g., a redirected URI prefix that points to a suffix of
1887   itself), or when the server is under attack by a client attempting to
1888   exploit security holes present in some servers using fixed-length
1889   buffers for reading or manipulating the request-target.
1890</t>
1891</section>
1892
1893<section title="415 Unsupported Media Type" anchor="status.415">
1894  <iref primary="true" item="415 Unsupported Media Type (status code)"/>
1895  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type"/>
1896<t>
1897   The server is refusing to service the request because the request
1898   payload is in a format not supported by this request method on the
1899   target resource.
1900</t>
1901</section>
1902
1903<section title="417 Expectation Failed" anchor="status.417">
1904  <iref primary="true" item="417 Expectation Failed (status code)"/>
1905  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed"/>
1906<t>
1907   The expectation given in an Expect header field (see <xref target="header.expect"/>)
1908   could not be met by this server, or, if the server is a proxy,
1909   the server has unambiguous evidence that the request could not be met
1910   by the next-hop server.
1911</t>
1912</section>
1913
1914<section title="426 Upgrade Required" anchor="status.426">
1915  <iref primary="true" item="426 Upgrade Required (status code)"/>
1916  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required"/>
1917<t>
1918   The request can not be completed without a prior protocol upgrade. This
1919   response MUST include an Upgrade header field (Section 6.5 of <xref target="Part1"/>)
1920   specifying the required protocols.
1921</t>
1922<figure>
1923<preamble>Example:</preamble>
1924<artwork type="message/http; msgtype=&#34;response&#34;"><![CDATA[
1925  HTTP/1.1 426 Upgrade Required
1926  Upgrade: HTTP/3.0
1927  Connection: Upgrade
1928  Content-Length: 53
1929  Content-Type: text/plain
1930 
1931  This service requires use of the HTTP/3.0 protocol.
1932  ]]></artwork></figure>
1933<t>
1934   The server SHOULD include a message body in the 426 response which
1935   indicates in human readable form the reason for the error and describes any
1936   alternative courses which may be available to the user.
1937</t>
1938</section>
1939</section>
1940
1941<section title="Server Error 5xx" anchor="status.5xx">
1942<t>
1943   Response status codes beginning with the digit "5" indicate cases in
1944   which the server is aware that it has erred or is incapable of
1945   performing the request. Except when responding to a HEAD request, the
1946   server SHOULD include a representation containing an explanation of the
1947   error situation, and whether it is a temporary or permanent
1948   condition. User agents SHOULD display any included representation to the
1949   user. These response codes are applicable to any request method.
1950</t>
1951
1952<section title="500 Internal Server Error" anchor="status.500">
1953  <iref primary="true" item="500 Internal Server Error (status code)"/>
1954  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error"/>
1955<t>
1956   The server encountered an unexpected condition which prevented it
1957   from fulfilling the request.
1958</t>
1959</section>
1960
1961<section title="501 Not Implemented" anchor="status.501">
1962  <iref primary="true" item="501 Not Implemented (status code)"/>
1963  <iref primary="true" item="Status Codes" subitem="501 Not Implemented"/>
1964<t>
1965   The server does not support the functionality required to fulfill the
1966   request. This is the appropriate response when the server does not
1967   recognize the request method and is not capable of supporting it for
1968   any resource.
1969</t>
1970</section>
1971
1972<section title="502 Bad Gateway" anchor="status.502">
1973  <iref primary="true" item="502 Bad Gateway (status code)"/>
1974  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway"/>
1975<t>
1976   The server, while acting as a gateway or proxy, received an invalid
1977   response from the upstream server it accessed in attempting to
1978   fulfill the request.
1979</t>
1980</section>
1981
1982<section title="503 Service Unavailable" anchor="status.503">
1983  <iref primary="true" item="503 Service Unavailable (status code)"/>
1984  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable"/>
1985<t>
1986   The server is currently unable to handle the request due to a
1987   temporary overloading or maintenance of the server.
1988</t>
1989<t>
1990   The implication is that this is a temporary condition which will be
1991   alleviated after some delay. If known, the length of the delay MAY be
1992   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
1993   If no Retry-After is given, the client SHOULD handle the response as it
1994   would for a 500 response.
1995</t>
1996<t><list>
1997  <t>
1998    Note: The existence of the 503 status code does not imply that a
1999    server must use it when becoming overloaded. Some servers might wish
2000    to simply refuse the connection.
2001  </t>
2002</list></t>
2003</section>
2004
2005<section title="504 Gateway Timeout" anchor="status.504">
2006  <iref primary="true" item="504 Gateway Timeout (status code)"/>
2007  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout"/>
2008<t>
2009   The server, while acting as a gateway or proxy, did not receive a
2010   timely response from the upstream server specified by the URI (e.g.,
2011   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2012   to access in attempting to complete the request.
2013</t>
2014<t><list>
2015  <t>
2016    Note to implementors: some deployed proxies are known to
2017    return 400 or 500 when DNS lookups time out.
2018  </t>
2019</list></t>
2020</section>
2021
2022<section title="505 HTTP Version Not Supported" anchor="status.505">
2023  <iref primary="true" item="505 HTTP Version Not Supported (status code)"/>
2024  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported"/>
2025<t>
2026   The server does not support, or refuses to support, the protocol
2027   version that was used in the request message. The server is
2028   indicating that it is unable or unwilling to complete the request
2029   using the same major version as the client, as described in Section 2.6 of <xref target="Part1"/>,
2030   other than with this error message. The response SHOULD contain
2031   a representation describing why that version is not supported and what other
2032   protocols are supported by that server.
2033</t>
2034
2035</section>
2036</section>
2037</section>
2038
2039
2040<section title="Date/Time Formats" anchor="http.date">
2041 
2042<t>
2043   HTTP applications have historically allowed three different formats
2044   for date/time stamps. However, the preferred format is a fixed-length subset
2045   of that defined by <xref target="RFC1123"/>:
2046</t>
2047<figure><artwork type="example"><![CDATA[
2048  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2049  ]]></artwork></figure>
2050<t>
2051   The other formats are described here only for compatibility with obsolete
2052   implementations.
2053</t>
2054<figure><artwork type="example"><![CDATA[
2055  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2056  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2057  ]]></artwork></figure>
2058<t>
2059   HTTP/1.1 clients and servers that parse a date value MUST accept
2060   all three formats (for compatibility with HTTP/1.0), though they MUST
2061   only generate the RFC 1123 format for representing HTTP-date values
2062   in header fields.
2063</t>
2064<t>
2065   All HTTP date/time stamps MUST be represented in Greenwich Mean Time
2066   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2067   equal to UTC (Coordinated Universal Time). This is indicated in the
2068   first two formats by the inclusion of "GMT" as the three-letter
2069   abbreviation for time zone, and MUST be assumed when reading the
2070   asctime format. HTTP-date is case sensitive and MUST NOT include
2071   additional whitespace beyond that specifically included as SP in the
2072   grammar.
2073</t>
2074<figure><iref primary="true" item="Grammar" subitem="HTTP-date"/><artwork type="abnf2616"><![CDATA[
2075  HTTP-date    = rfc1123-date / obs-date
2076]]></artwork></figure>
2077<t anchor="preferred.date.format">
2078 
2079 
2080 
2081 
2082 
2083 
2084 
2085 
2086 
2087 
2088  Preferred format:
2089</t>
2090<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[
2091  rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
2092  ; fixed length subset of the format defined in
2093  ; Section 5.2.14 of [RFC1123]
2094 
2095  day-name     = %x4D.6F.6E ; "Mon", case-sensitive
2096               / %x54.75.65 ; "Tue", case-sensitive
2097               / %x57.65.64 ; "Wed", case-sensitive
2098               / %x54.68.75 ; "Thu", case-sensitive
2099               / %x46.72.69 ; "Fri", case-sensitive
2100               / %x53.61.74 ; "Sat", case-sensitive
2101               / %x53.75.6E ; "Sun", case-sensitive
2102               
2103  date1        = day SP month SP year
2104               ; e.g., 02 Jun 1982
2105
2106  day          = 2DIGIT
2107  month        = %x4A.61.6E ; "Jan", case-sensitive
2108               / %x46.65.62 ; "Feb", case-sensitive
2109               / %x4D.61.72 ; "Mar", case-sensitive
2110               / %x41.70.72 ; "Apr", case-sensitive
2111               / %x4D.61.79 ; "May", case-sensitive
2112               / %x4A.75.6E ; "Jun", case-sensitive
2113               / %x4A.75.6C ; "Jul", case-sensitive
2114               / %x41.75.67 ; "Aug", case-sensitive
2115               / %x53.65.70 ; "Sep", case-sensitive
2116               / %x4F.63.74 ; "Oct", case-sensitive
2117               / %x4E.6F.76 ; "Nov", case-sensitive
2118               / %x44.65.63 ; "Dec", case-sensitive
2119  year         = 4DIGIT
2120
2121  GMT   = %x47.4D.54 ; "GMT", case-sensitive
2122
2123  time-of-day  = hour ":" minute ":" second
2124                 ; 00:00:00 - 23:59:59
2125                 
2126  hour         = 2DIGIT               
2127  minute       = 2DIGIT               
2128  second       = 2DIGIT               
2129]]></artwork></figure>
2130<t>
2131  The semantics of <xref target="preferred.date.format" format="none">day-name</xref>, <xref target="preferred.date.format" format="none">day</xref>,
2132  <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
2133  same as those defined for the RFC 5322 constructs
2134  with the corresponding name (<xref target="RFC5322"/>, Section 3.3).
2135</t>
2136<t anchor="obsolete.date.formats">
2137 
2138 
2139 
2140 
2141 
2142 
2143 
2144 
2145  Obsolete formats:
2146</t>
2147<figure><iref primary="true" item="Grammar" subitem="obs-date"/><artwork type="abnf2616"><![CDATA[
2148  obs-date     = rfc850-date / asctime-date
2149]]></artwork></figure>
2150<figure><iref primary="true" item="Grammar" subitem="rfc850-date"/><artwork type="abnf2616"><![CDATA[
2151  rfc850-date  = day-name-l "," SP date2 SP time-of-day SP GMT
2152  date2        = day "-" month "-" 2DIGIT
2153                 ; day-month-year (e.g., 02-Jun-82)
2154
2155  day-name-l   = %x4D.6F.6E.64.61.79 ; "Monday", case-sensitive
2156         / %x54.75.65.73.64.61.79 ; "Tuesday", case-sensitive
2157         / %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
2158         / %x54.68.75.72.73.64.61.79 ; "Thursday", case-sensitive
2159         / %x46.72.69.64.61.79 ; "Friday", case-sensitive
2160         / %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive
2161         / %x53.75.6E.64.61.79 ; "Sunday", case-sensitive
2162]]></artwork></figure>
2163<figure><iref primary="true" item="Grammar" subitem="asctime-date"/><artwork type="abnf2616"><![CDATA[
2164  asctime-date = day-name SP date3 SP time-of-day SP year
2165  date3        = month SP ( 2DIGIT / ( SP 1DIGIT ))
2166                 ; month day (e.g., Jun  2)
2167]]></artwork></figure>
2168<t><list>
2169  <t>
2170    Note: Recipients of date values are encouraged to be robust in
2171    accepting date values that might have been sent by non-HTTP
2172    applications, as is sometimes the case when retrieving or posting
2173    messages via proxies/gateways to SMTP or NNTP.
2174  </t>
2175</list></t>
2176<t><list>
2177  <t>
2178    Note: HTTP requirements for the date/time stamp format apply only
2179    to their usage within the protocol stream. Clients and servers are
2180    not required to use these formats for user presentation, request
2181    logging, etc.
2182  </t>
2183</list></t>
2184</section>
2185
2186<section title="Product Tokens" anchor="product.tokens">
2187 
2188 
2189<t>
2190   Product tokens are used to allow communicating applications to
2191   identify themselves by software name and version. Most fields using
2192   product tokens also allow sub-products which form a significant part
2193   of the application to be listed, separated by whitespace. By
2194   convention, the products are listed in order of their significance
2195   for identifying the application.
2196</t>
2197<figure><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/><artwork type="abnf2616"><![CDATA[
2198  product         = token ["/" product-version]
2199  product-version = token
2200]]></artwork></figure>
2201<t>
2202   Examples:
2203</t>
2204<figure><artwork type="example"><![CDATA[
2205  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2206  Server: Apache/0.8.4
2207]]></artwork></figure>
2208<t>
2209   Product tokens SHOULD be short and to the point. They MUST NOT be
2210   used for advertising or other non-essential information. Although any
2211   token octet MAY appear in a product-version, this token SHOULD
2212   only be used for a version identifier (i.e., successive versions of
2213   the same product SHOULD only differ in the product-version portion of
2214   the product value).
2215</t>
2216</section>
2217
2218
2219<section title="Header Field Definitions" anchor="header.field.definitions">
2220<t>
2221   This section defines the syntax and semantics of HTTP/1.1 header fields
2222   related to request and response semantics.
2223</t>
2224
2225<section title="Allow" anchor="header.allow">
2226  <iref primary="true" item="Allow header field"/>
2227  <iref primary="true" item="Header Fields" subitem="Allow"/>
2228 
2229<t>
2230   The "Allow" header field lists the set of methods advertised as
2231   supported by the target resource. The purpose of this field is strictly to
2232   inform the recipient of valid request methods associated with the resource.
2233</t>
2234<figure><iref primary="true" item="Grammar" subitem="Allow"/><artwork type="abnf2616"><![CDATA[
2235  Allow = #method
2236]]></artwork></figure>
2237<t>
2238   Example of use:
2239</t>
2240<figure><artwork type="example"><![CDATA[
2241  Allow: GET, HEAD, PUT
2242]]></artwork></figure>
2243<t>
2244   The actual set of allowed methods is defined by the origin server at the
2245   time of each request.
2246</t>
2247<t>
2248   A proxy MUST NOT modify the Allow header field — it does not need to
2249   understand all the methods specified in order to handle them according to
2250   the generic message handling rules.
2251</t>
2252</section>
2253
2254<section title="Date" anchor="header.date">
2255  <iref primary="true" item="Date header field"/>
2256  <iref primary="true" item="Header Fields" subitem="Date"/>
2257 
2258<t>
2259   The "Date" header field represents the date and time at which
2260   the message was originated, having the same semantics as the Origination
2261   Date Field (orig-date) defined in Section 3.6.1 of <xref target="RFC5322"/>.
2262   The field value is an HTTP-date, as defined in <xref target="http.date"/>;
2263   it MUST be sent in rfc1123-date format.
2264</t>
2265<figure><iref primary="true" item="Grammar" subitem="Date"/><artwork type="abnf2616"><![CDATA[
2266  Date = HTTP-date
2267]]></artwork></figure>
2268<t>
2269   An example is
2270</t>
2271<figure><artwork type="example"><![CDATA[
2272  Date: Tue, 15 Nov 1994 08:12:31 GMT
2273]]></artwork></figure>
2274<t>
2275   Origin servers MUST include a Date header field in all responses,
2276   except in these cases:
2277  <list style="numbers">
2278      <t>If the response status code is 100 (Continue) or 101 (Switching
2279         Protocols), the response MAY include a Date header field, at
2280         the server's option.</t>
2281
2282      <t>If the response status code conveys a server error, e.g., 500
2283         (Internal Server Error) or 503 (Service Unavailable), and it is
2284         inconvenient or impossible to generate a valid Date.</t>
2285
2286      <t>If the server does not have a clock that can provide a
2287         reasonable approximation of the current time, its responses
2288         MUST NOT include a Date header field.</t>
2289  </list>
2290</t>
2291<t>
2292   A received message that does not have a Date header field MUST be
2293   assigned one by the recipient if the message will be cached by that
2294   recipient.
2295</t>
2296<t>
2297   Clients can use the Date header field as well; in order to keep request
2298   messages small, they are advised not to include it when it doesn't convey
2299   any useful information (as is usually the case for requests that do not
2300   contain a payload).
2301</t>
2302<t>
2303   The HTTP-date sent in a Date header field SHOULD NOT represent a date and
2304   time subsequent to the generation of the message. It SHOULD represent
2305   the best available approximation of the date and time of message
2306   generation, unless the implementation has no means of generating a
2307   reasonably accurate date and time. In theory, the date ought to
2308   represent the moment just before the payload is generated. In
2309   practice, the date can be generated at any time during the message
2310   origination without affecting its semantic value.
2311</t>
2312</section>
2313
2314<section title="Expect" anchor="header.expect">
2315  <iref primary="true" item="Expect header field"/>
2316  <iref primary="true" item="Header Fields" subitem="Expect"/>
2317 
2318 
2319 
2320 
2321 
2322<t>
2323   The "Expect" header field is used to indicate that particular
2324   server behaviors are required by the client.
2325</t>
2326<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[
2327  Expect       = 1#expectation
2328 
2329  expectation  = expect-name [ BWS "=" BWS expect-value ]
2330                             *( OWS ";" [ OWS expect-param ] )
2331  expect-param = expect-name [ BWS "=" BWS expect-value ]
2332 
2333  expect-name  = token
2334  expect-value = token / quoted-string
2335]]></artwork></figure>
2336<t>
2337   If all received Expect header field(s) are syntactically valid but contain
2338   an expectation that the recipient does not understand or cannot comply with,
2339   the recipient MUST respond with a 417 (Expectation Failed) status code. A
2340   recipient of a syntactically invalid Expectation header field MUST respond
2341   with a 4xx status code other than 417.
2342</t>
2343<t>
2344   The only expectation defined by this specification is:
2345</t>
2346<t><iref primary="true" item="100-continue (expect value)"/><iref primary="true" item="Expect Values" subitem="100-continue"/>
2347  100-continue
2348   <list>
2349      <t>
2350        The "100-continue" expectation is defined Section 6.4.3 of <xref target="Part1"/>. It does not support
2351        any expect-params.
2352      </t>
2353   </list>
2354</t>
2355<t>
2356   Comparison is case-insensitive for names (expect-name), and case-sensitive
2357   for values (expect-value).
2358</t>
2359<t>
2360   The Expect mechanism is hop-by-hop: the above requirements apply to any
2361   server, including proxies. However, the Expect header field itself is
2362   end-to-end; it MUST be forwarded if the request is forwarded.
2363</t>
2364<t>
2365   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect
2366   header field.
2367</t>
2368</section>
2369
2370<section title="From" anchor="header.from">
2371  <iref primary="true" item="From header field"/>
2372  <iref primary="true" item="Header Fields" subitem="From"/>
2373 
2374 
2375<t>
2376   The "From" header field, if given, SHOULD contain an Internet
2377   e-mail address for the human user who controls the requesting user
2378   agent. The address SHOULD be machine-usable, as defined by "mailbox"
2379   in Section 3.4 of <xref target="RFC5322"/>:
2380</t>
2381<figure><iref primary="true" item="Grammar" subitem="From"/><artwork type="abnf2616"><![CDATA[
2382  From    = mailbox
2383 
2384  mailbox = <mailbox, defined in [RFC5322], Section 3.4>
2385]]></artwork></figure>
2386<t>
2387   An example is:
2388</t>
2389<figure><artwork type="example"><![CDATA[
2390  From: webmaster@example.org
2391]]></artwork></figure>
2392<t>
2393   This header field MAY be used for logging purposes and as a means for
2394   identifying the source of invalid or unwanted requests. It SHOULD NOT
2395   be used as an insecure form of access protection. The interpretation
2396   of this field is that the request is being performed on behalf of the
2397   person given, who accepts responsibility for the method performed. In
2398   particular, robot agents SHOULD include this header field so that the
2399   person responsible for running the robot can be contacted if problems
2400   occur on the receiving end.
2401</t>
2402<t>
2403   The Internet e-mail address in this field MAY be separate from the
2404   Internet host which issued the request. For example, when a request
2405   is passed through a proxy the original issuer's address SHOULD be
2406   used.
2407</t>
2408<t>
2409   The client SHOULD NOT  send the From header field without the user's
2410   approval, as it might conflict with the user's privacy interests or
2411   their site's security policy. It is strongly recommended that the
2412   user be able to disable, enable, and modify the value of this field
2413   at any time prior to a request.
2414</t>
2415</section>
2416
2417<section title="Location" anchor="header.location">
2418  <iref primary="true" item="Location header field"/>
2419  <iref primary="true" item="Header Fields" subitem="Location"/>
2420 
2421<t>
2422   The "Location" header field MAY be sent in responses to refer to
2423   a specific resource in accordance with the semantics of the status
2424   code.
2425</t>
2426<figure><iref primary="true" item="Grammar" subitem="Location"/><artwork type="abnf2616"><![CDATA[
2427  Location = URI-reference
2428]]></artwork></figure>
2429<t>
2430   For 201 (Created) responses, the Location is the URI of the new resource
2431   which was created by the request. For 3xx responses, the location SHOULD
2432   indicate the server's preferred URI for automatic redirection to the
2433   resource.
2434</t>
2435<t>
2436   The field value consists of a single URI-reference. When it has the form
2437   of a relative reference (<xref target="RFC3986"/>, Section 4.2),
2438   the final value is computed by resolving it against the effective request
2439   URI (<xref target="RFC3986"/>, Section 5). If the original URI, as
2440   navigated to by the user agent, did contain a fragment identifier, and the
2441   final value does not, then the original URI's fragment identifier is added
2442   to the final value.
2443</t>
2444<figure>
2445<preamble>For example, the original URI "http://www.example.org/~tim", combined with a field value given as:</preamble><!--DO NOT DARE changing the vertical spacing below, it's necessary this way for xml2rfc-->
2446<artwork type="example"><![CDATA[
2447  Location: /pub/WWW/People.html#tim
2448]]></artwork>
2449<postamble>would result in a final value of "http://www.example.org/pub/WWW/People.html#tim"</postamble>
2450</figure>
2451<figure>
2452<preamble>An original URI "http://www.example.org/index.html#larry", combined with a field value given as:</preamble><!--DO NOT DARE changing the vertical spacing below, it's necessary this way for xml2rfc-->
2453<artwork type="example"><![CDATA[
2454  Location: http://www.example.net/index.html
2455]]></artwork>
2456<postamble>would result in a final value of "http://www.example.net/index.html#larry", preserving the original fragment identifier.</postamble>
2457</figure>
2458<t><list>
2459  <t>
2460    Note: Some recipients attempt to recover from Location fields
2461    that are not valid URI references. This specification does not mandate or
2462    define such processing, but does allow it (see <xref target="intro.conformance.and.error.handling"/>).
2463  </t>
2464</list></t>
2465<t>
2466   There are circumstances in which a fragment identifier in a Location URI
2467   would not be appropriate. For instance, when it appears in a 201 Created
2468   response, where the Location header field specifies the URI for the entire
2469   created resource.
2470</t>
2471<t><list>
2472  <t>
2473    Note: The Content-Location header field (Section 6.7 of <xref target="Part3"/>) differs
2474    from Location in that the Content-Location identifies the most specific
2475    resource corresponding to the enclosed representation.
2476    It is therefore possible for a response to contain header fields for
2477    both Location and Content-Location.
2478  </t>
2479</list></t>
2480</section>
2481
2482<section title="Max-Forwards" anchor="header.max-forwards">
2483  <iref primary="true" item="Max-Forwards header field"/>
2484  <iref primary="true" item="Header Fields" subitem="Max-Forwards"/>
2485 
2486<t>
2487   The "Max-Forwards" header field provides a mechanism with the
2488   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2489   methods to limit the number of times that the request is forwarded by
2490   proxies. This can be useful when the client is attempting to
2491   trace a request which appears to be failing or looping mid-chain.
2492</t>
2493<figure><iref primary="true" item="Grammar" subitem="Max-Forwards"/><artwork type="abnf2616"><![CDATA[
2494  Max-Forwards = 1*DIGIT
2495]]></artwork></figure>
2496<t>
2497   The Max-Forwards value is a decimal integer indicating the remaining
2498   number of times this request message can be forwarded.
2499</t>
2500<t>
2501   Each recipient of a TRACE or OPTIONS request
2502   containing a Max-Forwards header field MUST check and update its
2503   value prior to forwarding the request. If the received value is zero
2504   (0), the recipient MUST NOT forward the request; instead, it MUST
2505   respond as the final recipient. If the received Max-Forwards value is
2506   greater than zero, then the forwarded message MUST contain an updated
2507   Max-Forwards field with a value decremented by one (1).
2508</t>
2509<t>
2510   The Max-Forwards header field MAY be ignored for all other request
2511   methods.
2512</t>
2513</section>
2514
2515<section title="Referer" anchor="header.referer">
2516  <iref primary="true" item="Referer header field"/>
2517  <iref primary="true" item="Header Fields" subitem="Referer"/>
2518 
2519<t>
2520   The "Referer" [sic] header field allows the client to specify the
2521   URI of the resource from which the target URI was obtained (the
2522   "referrer", although the header field is misspelled.).
2523</t>
2524<t>
2525   The Referer header field allows servers to generate lists of back-links to
2526   resources for interest, logging, optimized caching, etc. It also allows
2527   obsolete or mistyped links to be traced for maintenance. Some servers use
2528   Referer as a means of controlling where they allow links from (so-called
2529   "deep linking"), but legitimate requests do not always
2530   contain a Referer header field.
2531</t>
2532<t>
2533   If the target URI was obtained from a source that does not have its own
2534   URI (e.g., input from the user keyboard), the Referer field MUST either be
2535   sent with the value "about:blank", or not be sent at all. Note that this
2536   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2537</t>
2538<figure><iref primary="true" item="Grammar" subitem="Referer"/><artwork type="abnf2616"><![CDATA[
2539  Referer = absolute-URI / partial-URI
2540]]></artwork></figure>
2541<t>
2542   Example:
2543</t>
2544<figure><artwork type="example"><![CDATA[
2545  Referer: http://www.example.org/hypertext/Overview.html
2546]]></artwork></figure>
2547<t>
2548   If the field value is a relative URI, it SHOULD be interpreted
2549   relative to the effective request URI. The URI MUST NOT include a fragment. See
2550   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2551</t>
2552</section>
2553
2554<section title="Retry-After" anchor="header.retry-after">
2555  <iref primary="true" item="Retry-After header field"/>
2556  <iref primary="true" item="Header Fields" subitem="Retry-After"/>
2557 
2558<t>
2559   The header "Retry-After" field can be used with a 503 (Service
2560   Unavailable) response to indicate how long the service is expected to
2561   be unavailable to the requesting client. This field MAY also be used
2562   with any 3xx (Redirection) response to indicate the minimum time the
2563   user-agent is asked to wait before issuing the redirected request.
2564</t>
2565<t>
2566   The value of this field can be either an HTTP-date or an integer number
2567   of seconds (in decimal) after the time of the response.
2568</t>
2569<figure><iref primary="true" item="Grammar" subitem="Retry-After"/><artwork type="abnf2616"><![CDATA[
2570  Retry-After = HTTP-date / delta-seconds
2571]]></artwork></figure>
2572<t anchor="rule.delta-seconds">
2573 
2574   Time spans are non-negative decimal integers, representing time in
2575   seconds.
2576</t>
2577<figure><iref primary="true" item="Grammar" subitem="delta-seconds"/><artwork type="abnf2616"><![CDATA[
2578  delta-seconds  = 1*DIGIT
2579]]></artwork></figure>
2580<t>
2581   Two examples of its use are
2582</t>
2583<figure><artwork type="example"><![CDATA[
2584  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2585  Retry-After: 120
2586]]></artwork></figure>
2587<t>
2588   In the latter example, the delay is 2 minutes.
2589</t>
2590</section>
2591
2592<section title="Server" anchor="header.server">
2593  <iref primary="true" item="Server header field"/>
2594  <iref primary="true" item="Header Fields" subitem="Server"/>
2595 
2596<t>
2597   The "Server" header field contains information about the
2598   software used by the origin server to handle the request.
2599</t>
2600<t>
2601   The field can contain multiple
2602   product tokens (<xref target="product.tokens"/>) and
2603   comments (Section 3.2 of <xref target="Part1"/>) identifying the server and any significant
2604   subproducts. The product tokens are listed in order of their significance
2605   for identifying the application.
2606</t>
2607<figure><iref primary="true" item="Grammar" subitem="Server"/><artwork type="abnf2616"><![CDATA[
2608  Server = product *( RWS ( product / comment ) )
2609]]></artwork></figure>
2610<t>
2611   Example:
2612</t>
2613<figure><artwork type="example"><![CDATA[
2614  Server: CERN/3.0 libwww/2.17
2615]]></artwork></figure>
2616<t>
2617   If the response is being forwarded through a proxy, the proxy
2618   application MUST NOT modify the Server header field. Instead, it
2619   MUST include a Via field (as described in Section 6.2 of <xref target="Part1"/>).
2620</t>
2621<t><list>
2622  <t>
2623    Note: Revealing the specific software version of the server might
2624    allow the server machine to become more vulnerable to attacks
2625    against software that is known to contain security holes. Server
2626    implementors are encouraged to make this field a configurable
2627    option.
2628  </t>
2629</list></t>
2630</section>
2631
2632<section title="User-Agent" anchor="header.user-agent">
2633  <iref primary="true" item="User-Agent header field"/>
2634  <iref primary="true" item="Header Fields" subitem="User-Agent"/>
2635 
2636<t>
2637   The "User-Agent" header field contains information about the user
2638   agent originating the request. User agents SHOULD include this field with
2639   requests.
2640</t>
2641<t>
2642   Typically, it is used for statistical purposes, the tracing of protocol
2643   violations, and tailoring responses to avoid particular user agent
2644   limitations.
2645</t>
2646<t>
2647   The field can contain multiple
2648   product tokens (<xref target="product.tokens"/>)
2649   and comments (Section 3.2 of <xref target="Part1"/>) identifying the agent and its
2650   significant subproducts. By convention, the product tokens are listed in
2651   order of their significance for identifying the application.
2652</t>
2653<t>
2654   Because this field is usually sent on every request a user agent makes,
2655   implementations are encouraged not to include needlessly fine-grained
2656   detail, and to limit (or even prohibit) the addition of subproducts by third
2657   parties. Overly long and detailed User-Agent field values make requests
2658   larger and can also be used to identify ("fingerprint") the user against
2659   their wishes.
2660</t>
2661<t>
2662   Likewise, implementations are encouraged not to use the product tokens of
2663   other implementations in order to declare compatibility with them, as this
2664   circumvents the purpose of the field. Finally, they are encouraged not to
2665   use comments to identify products; doing so makes the field value more
2666   difficult to parse.
2667</t>
2668<figure><iref primary="true" item="Grammar" subitem="User-Agent"/><artwork type="abnf2616"><![CDATA[
2669  User-Agent = product *( RWS ( product / comment ) )
2670]]></artwork></figure>
2671<t>
2672   Example:
2673</t>
2674<figure><artwork type="example"><![CDATA[
2675  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2676]]></artwork></figure>
2677</section>
2678
2679</section>
2680
2681<section title="IANA Considerations" anchor="IANA.considerations">
2682
2683<section title="Method Registry" anchor="method.registration">
2684<t>
2685  The registration procedure for HTTP request methods is defined by
2686  <xref target="method.registry"/> of this document.
2687</t>
2688<t>
2689   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2690   and be populated with the registrations below:
2691</t>
2692
2693<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2694<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2695   <ttcol>Method</ttcol>
2696   <ttcol>Safe</ttcol>
2697   <ttcol>Reference</ttcol>
2698   <c>CONNECT</c>
2699   <c>no</c>
2700   <c>
2701      <xref target="CONNECT"/>
2702   </c>
2703   <c>DELETE</c>
2704   <c>no</c>
2705   <c>
2706      <xref target="DELETE"/>
2707   </c>
2708   <c>GET</c>
2709   <c>yes</c>
2710   <c>
2711      <xref target="GET"/>
2712   </c>
2713   <c>HEAD</c>
2714   <c>yes</c>
2715   <c>
2716      <xref target="HEAD"/>
2717   </c>
2718   <c>OPTIONS</c>
2719   <c>yes</c>
2720   <c>
2721      <xref target="OPTIONS"/>
2722   </c>
2723   <c>POST</c>
2724   <c>no</c>
2725   <c>
2726      <xref target="POST"/>
2727   </c>
2728   <c>PUT</c>
2729   <c>no</c>
2730   <c>
2731      <xref target="PUT"/>
2732   </c>
2733   <c>TRACE</c>
2734   <c>yes</c>
2735   <c>
2736      <xref target="TRACE"/>
2737   </c>
2738</texttable>
2739<!--(END)-->
2740
2741</section>
2742
2743<section title="Status Code Registry" anchor="status.code.registration">
2744<t>
2745   The registration procedure for HTTP Status Codes — previously defined
2746   in Section 7.1 of <xref target="RFC2817"/> — is now defined
2747   by <xref target="status.code.registry"/> of this document.
2748</t>
2749<t>
2750   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2751   shall be updated with the registrations below:
2752</t>
2753
2754<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2755<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2756   <ttcol>Value</ttcol>
2757   <ttcol>Description</ttcol>
2758   <ttcol>Reference</ttcol>
2759   <c>100</c>
2760   <c>Continue</c>
2761   <c>
2762      <xref target="status.100"/>
2763   </c>
2764   <c>101</c>
2765   <c>Switching Protocols</c>
2766   <c>
2767      <xref target="status.101"/>
2768   </c>
2769   <c>200</c>
2770   <c>OK</c>
2771   <c>
2772      <xref target="status.200"/>
2773   </c>
2774   <c>201</c>
2775   <c>Created</c>
2776   <c>
2777      <xref target="status.201"/>
2778   </c>
2779   <c>202</c>
2780   <c>Accepted</c>
2781   <c>
2782      <xref target="status.202"/>
2783   </c>
2784   <c>203</c>
2785   <c>Non-Authoritative Information</c>
2786   <c>
2787      <xref target="status.203"/>
2788   </c>
2789   <c>204</c>
2790   <c>No Content</c>
2791   <c>
2792      <xref target="status.204"/>
2793   </c>
2794   <c>205</c>
2795   <c>Reset Content</c>
2796   <c>
2797      <xref target="status.205"/>
2798   </c>
2799   <c>300</c>
2800   <c>Multiple Choices</c>
2801   <c>
2802      <xref target="status.300"/>
2803   </c>
2804   <c>301</c>
2805   <c>Moved Permanently</c>
2806   <c>
2807      <xref target="status.301"/>
2808   </c>
2809   <c>302</c>
2810   <c>Found</c>
2811   <c>
2812      <xref target="status.302"/>
2813   </c>
2814   <c>303</c>
2815   <c>See Other</c>
2816   <c>
2817      <xref target="status.303"/>
2818   </c>
2819   <c>305</c>
2820   <c>Use Proxy</c>
2821   <c>
2822      <xref target="status.305"/>
2823   </c>
2824   <c>306</c>
2825   <c>(Unused)</c>
2826   <c>
2827      <xref target="status.306"/>
2828   </c>
2829   <c>307</c>
2830   <c>Temporary Redirect</c>
2831   <c>
2832      <xref target="status.307"/>
2833   </c>
2834   <c>400</c>
2835   <c>Bad Request</c>
2836   <c>
2837      <xref target="status.400"/>
2838   </c>
2839   <c>402</c>
2840   <c>Payment Required</c>
2841   <c>
2842      <xref target="status.402"/>
2843   </c>
2844   <c>403</c>
2845   <c>Forbidden</c>
2846   <c>
2847      <xref target="status.403"/>
2848   </c>
2849   <c>404</c>
2850   <c>Not Found</c>
2851   <c>
2852      <xref target="status.404"/>
2853   </c>
2854   <c>405</c>
2855   <c>Method Not Allowed</c>
2856   <c>
2857      <xref target="status.405"/>
2858   </c>
2859   <c>406</c>
2860   <c>Not Acceptable</c>
2861   <c>
2862      <xref target="status.406"/>
2863   </c>
2864   <c>408</c>
2865   <c>Request Timeout</c>
2866   <c>
2867      <xref target="status.408"/>
2868   </c>
2869   <c>409</c>
2870   <c>Conflict</c>
2871   <c>
2872      <xref target="status.409"/>
2873   </c>
2874   <c>410</c>
2875   <c>Gone</c>
2876   <c>
2877      <xref target="status.410"/>
2878   </c>
2879   <c>411</c>
2880   <c>Length Required</c>
2881   <c>
2882      <xref target="status.411"/>
2883   </c>
2884   <c>413</c>
2885   <c>Request Representation Too Large</c>
2886   <c>
2887      <xref target="status.413"/>
2888   </c>
2889   <c>414</c>
2890   <c>URI Too Long</c>
2891   <c>
2892      <xref target="status.414"/>
2893   </c>
2894   <c>415</c>
2895   <c>Unsupported Media Type</c>
2896   <c>
2897      <xref target="status.415"/>
2898   </c>
2899   <c>417</c>
2900   <c>Expectation Failed</c>
2901   <c>
2902      <xref target="status.417"/>
2903   </c>
2904   <c>426</c>
2905   <c>Upgrade Required</c>
2906   <c>
2907      <xref target="status.426"/>
2908   </c>
2909   <c>500</c>
2910   <c>Internal Server Error</c>
2911   <c>
2912      <xref target="status.500"/>
2913   </c>
2914   <c>501</c>
2915   <c>Not Implemented</c>
2916   <c>
2917      <xref target="status.501"/>
2918   </c>
2919   <c>502</c>
2920   <c>Bad Gateway</c>
2921   <c>
2922      <xref target="status.502"/>
2923   </c>
2924   <c>503</c>
2925   <c>Service Unavailable</c>
2926   <c>
2927      <xref target="status.503"/>
2928   </c>
2929   <c>504</c>
2930   <c>Gateway Timeout</c>
2931   <c>
2932      <xref target="status.504"/>
2933   </c>
2934   <c>505</c>
2935   <c>HTTP Version Not Supported</c>
2936   <c>
2937      <xref target="status.505"/>
2938   </c>
2939</texttable>
2940<!--(END)-->
2941
2942</section>
2943<section title="Header Field Registration" anchor="header.field.registration">
2944<t>
2945   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
2946   with the permanent registrations below (see <xref target="RFC3864"/>):
2947</t>
2948
2949<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2950<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2951   <ttcol>Header Field Name</ttcol>
2952   <ttcol>Protocol</ttcol>
2953   <ttcol>Status</ttcol>
2954   <ttcol>Reference</ttcol>
2955
2956   <c>Allow</c>
2957   <c>http</c>
2958   <c>standard</c>
2959   <c>
2960      <xref target="header.allow"/>
2961   </c>
2962   <c>Date</c>
2963   <c>http</c>
2964   <c>standard</c>
2965   <c>
2966      <xref target="header.date"/>
2967   </c>
2968   <c>Expect</c>
2969   <c>http</c>
2970   <c>standard</c>
2971   <c>
2972      <xref target="header.expect"/>
2973   </c>
2974   <c>From</c>
2975   <c>http</c>
2976   <c>standard</c>
2977   <c>
2978      <xref target="header.from"/>
2979   </c>
2980   <c>Location</c>
2981   <c>http</c>
2982   <c>standard</c>
2983   <c>
2984      <xref target="header.location"/>
2985   </c>
2986   <c>Max-Forwards</c>
2987   <c>http</c>
2988   <c>standard</c>
2989   <c>
2990      <xref target="header.max-forwards"/>
2991   </c>
2992   <c>Referer</c>
2993   <c>http</c>
2994   <c>standard</c>
2995   <c>
2996      <xref target="header.referer"/>
2997   </c>
2998   <c>Retry-After</c>
2999   <c>http</c>
3000   <c>standard</c>
3001   <c>
3002      <xref target="header.retry-after"/>
3003   </c>
3004   <c>Server</c>
3005   <c>http</c>
3006   <c>standard</c>
3007   <c>
3008      <xref target="header.server"/>
3009   </c>
3010   <c>User-Agent</c>
3011   <c>http</c>
3012   <c>standard</c>
3013   <c>
3014      <xref target="header.user-agent"/>
3015   </c>
3016</texttable>
3017<!--(END)-->
3018
3019<t>
3020   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3021</t>
3022</section>
3023</section>
3024
3025<section title="Security Considerations" anchor="security.considerations">
3026<t>
3027   This section is meant to inform application developers, information
3028   providers, and users of the security limitations in HTTP/1.1 as
3029   described by this document. The discussion does not include
3030   definitive solutions to the problems revealed, though it does make
3031   some suggestions for reducing security risks.
3032</t>
3033
3034<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3035<t>
3036   Like any generic data transfer protocol, HTTP cannot regulate the
3037   content of the data that is transferred, nor is there any a priori
3038   method of determining the sensitivity of any particular piece of
3039   information within the context of any given request. Therefore,
3040   applications SHOULD supply as much control over this information as
3041   possible to the provider of that information. Four header fields are
3042   worth special mention in this context: Server, Via, Referer and From.
3043</t>
3044<t>
3045   Revealing the specific software version of the server might allow the
3046   server machine to become more vulnerable to attacks against software
3047   that is known to contain security holes. Implementors SHOULD make the
3048   Server header field a configurable option.
3049</t>
3050<t>
3051   Proxies which serve as a portal through a network firewall SHOULD
3052   take special precautions regarding the transfer of header information
3053   that identifies the hosts behind the firewall. In particular, they
3054   SHOULD remove, or replace with sanitized versions, any Via fields
3055   generated behind the firewall.
3056</t>
3057<t>
3058   The Referer header field allows reading patterns to be studied and reverse
3059   links drawn. Although it can be very useful, its power can be abused
3060   if user details are not separated from the information contained in
3061   the Referer. Even when the personal information has been removed, the
3062   Referer header field might indicate a private document's URI whose
3063   publication would be inappropriate.
3064</t>
3065<t>
3066   The information sent in the From field might conflict with the user's
3067   privacy interests or their site's security policy, and hence it
3068   SHOULD NOT  be transmitted without the user being able to disable,
3069   enable, and modify the contents of the field. The user MUST be able
3070   to set the contents of this field within a user preference or
3071   application defaults configuration.
3072</t>
3073<t>
3074   We suggest, though do not require, that a convenient toggle interface
3075   be provided for the user to enable or disable the sending of From and
3076   Referer information.
3077</t>
3078<t>
3079   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header fields can sometimes be used to determine
3080   that a specific client or server has a particular security hole which might
3081   be exploited. Unfortunately, this same information is often used for other
3082   valuable purposes for which HTTP currently has no better mechanism.
3083</t>
3084<t>
3085   Furthermore, the User-Agent header field may contain enough entropy to be
3086   used, possibly in conjunction with other material, to uniquely identify the
3087   user.
3088</t>
3089<t>
3090   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3091   that was sent in request header fields within the body of their response.
3092   Clients SHOULD be careful with sensitive information, like Cookies,
3093   Authorization credentials, and other header fields that might be used to
3094   collect data from the client.
3095</t>
3096</section>
3097
3098<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3099<t>
3100   Because the source of a link might be private information or might
3101   reveal an otherwise private information source, it is strongly
3102   recommended that the user be able to select whether or not the
3103   Referer field is sent. For example, a browser client could have a
3104   toggle switch for browsing openly/anonymously, which would
3105   respectively enable/disable the sending of Referer and From
3106   information.
3107</t>
3108<t>
3109   Clients SHOULD NOT include a Referer header field in a (non-secure)
3110   HTTP request if the referring page was transferred with a secure
3111   protocol.
3112</t>
3113<t>
3114   Authors of services SHOULD NOT use GET-based forms for the submission of
3115   sensitive data because that data will be placed in the request-target. Many
3116   existing servers, proxies, and user agents log or display the request-target
3117   in places where it might be visible to third parties. Such services can
3118   use POST-based form submission instead.
3119</t>
3120</section>
3121
3122<section title="Location Header Fields: Spoofing and Information Leakage" anchor="location.spoofing-leakage">
3123<t>
3124   If a single server supports multiple organizations that do not trust
3125   one another, then it MUST check the values of Location and Content-Location
3126   header fields in responses that are generated under control of
3127   said organizations to make sure that they do not attempt to
3128   invalidate resources over which they have no authority.
3129</t>
3130<t>
3131   Furthermore, appending the fragment identifier from one URI to another
3132   one obtained from a Location header field might leak confidential
3133   information to the target server — although the fragment identifier is
3134   not transmitted in the final request, it might be visible to the user agent
3135   through other means, such as scripting.
3136</t>
3137</section>
3138
3139<section title="Security Considerations for CONNECT">
3140<t>
3141   Since tunneled data is opaque to the proxy, there are additional
3142   risks to tunneling to other well-known or reserved ports.
3143   A HTTP client CONNECTing to port 25 could relay spam
3144   via SMTP, for example. As such, proxies SHOULD restrict CONNECT
3145   access to a small number of known ports.
3146</t>
3147</section>
3148
3149</section>
3150
3151<section title="Acknowledgments" anchor="acks">
3152<t>
3153  See Section 9 of <xref target="Part1"/>.
3154</t>
3155</section>
3156</middle>
3157<back>
3158
3159<references title="Normative References">
3160
3161<reference anchor="Part1">
3162  <front>
3163    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3164    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3165      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3166      <address><email>fielding@gbiv.com</email></address>
3167    </author>
3168    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3169      <organization abbrev="W3C">World Wide Web Consortium</organization>
3170      <address><email>ylafon@w3.org</email></address>
3171    </author>
3172    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3173      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3174      <address><email>julian.reschke@greenbytes.de</email></address>
3175    </author>
3176    <date month="March" year="2012"/>
3177  </front>
3178  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-19"/>
3179 
3180</reference>
3181
3182<reference anchor="Part3">
3183  <front>
3184    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3185    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3186      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3187      <address><email>fielding@gbiv.com</email></address>
3188    </author>
3189    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3190      <organization abbrev="W3C">World Wide Web Consortium</organization>
3191      <address><email>ylafon@w3.org</email></address>
3192    </author>
3193    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3194      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3195      <address><email>julian.reschke@greenbytes.de</email></address>
3196    </author>
3197    <date month="March" year="2012"/>
3198  </front>
3199  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-19"/>
3200 
3201</reference>
3202
3203<reference anchor="Part4">
3204  <front>
3205    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3206    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3207      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3208      <address><email>fielding@gbiv.com</email></address>
3209    </author>
3210    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3211      <organization abbrev="W3C">World Wide Web Consortium</organization>
3212      <address><email>ylafon@w3.org</email></address>
3213    </author>
3214    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3215      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3216      <address><email>julian.reschke@greenbytes.de</email></address>
3217    </author>
3218    <date month="March" year="2012"/>
3219  </front>
3220  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-19"/>
3221 
3222</reference>
3223
3224<reference anchor="Part5">
3225  <front>
3226    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3227    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3228      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3229      <address><email>fielding@gbiv.com</email></address>
3230    </author>
3231    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3232      <organization abbrev="W3C">World Wide Web Consortium</organization>
3233      <address><email>ylafon@w3.org</email></address>
3234    </author>
3235    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3236      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3237      <address><email>julian.reschke@greenbytes.de</email></address>
3238    </author>
3239    <date month="March" year="2012"/>
3240  </front>
3241  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-19"/>
3242 
3243</reference>
3244
3245<reference anchor="Part6">
3246  <front>
3247    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3248    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3249      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3250      <address><email>fielding@gbiv.com</email></address>
3251    </author>
3252    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3253      <organization abbrev="W3C">World Wide Web Consortium</organization>
3254      <address><email>ylafon@w3.org</email></address>
3255    </author>
3256    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3257      <organization>Rackspace</organization>
3258      <address><email>mnot@mnot.net</email></address>
3259    </author>
3260    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3261      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3262      <address><email>julian.reschke@greenbytes.de</email></address>
3263    </author>
3264    <date month="March" year="2012"/>
3265  </front>
3266  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-19"/>
3267 
3268</reference>
3269
3270<reference anchor="Part7">
3271  <front>
3272    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3273    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3274      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3275      <address><email>fielding@gbiv.com</email></address>
3276    </author>
3277    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3278      <organization abbrev="W3C">World Wide Web Consortium</organization>
3279      <address><email>ylafon@w3.org</email></address>
3280    </author>
3281    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3282      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3283      <address><email>julian.reschke@greenbytes.de</email></address>
3284    </author>
3285    <date month="March" year="2012"/>
3286  </front>
3287  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-19"/>
3288 
3289</reference>
3290
3291<reference anchor="RFC2119">
3292  <front>
3293    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3294    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3295      <organization>Harvard University</organization>
3296      <address><email>sob@harvard.edu</email></address>
3297    </author>
3298    <date month="March" year="1997"/>
3299  </front>
3300  <seriesInfo name="BCP" value="14"/>
3301  <seriesInfo name="RFC" value="2119"/>
3302</reference>
3303
3304<reference anchor="RFC3986">
3305 <front>
3306  <title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
3307  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3308    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3309    <address>
3310       <email>timbl@w3.org</email>
3311       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3312    </address>
3313  </author>
3314  <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3315    <organization abbrev="Day Software">Day Software</organization>
3316    <address>
3317      <email>fielding@gbiv.com</email>
3318      <uri>http://roy.gbiv.com/</uri>
3319    </address>
3320  </author>
3321  <author initials="L." surname="Masinter" fullname="Larry Masinter">
3322    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3323    <address>
3324      <email>LMM@acm.org</email>
3325      <uri>http://larry.masinter.net/</uri>
3326    </address>
3327  </author>
3328  <date month="January" year="2005"/>
3329 </front>
3330 <seriesInfo name="STD" value="66"/>
3331 <seriesInfo name="RFC" value="3986"/>
3332</reference>
3333
3334<reference anchor="RFC5234">
3335  <front>
3336    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3337    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3338      <organization>Brandenburg InternetWorking</organization>
3339      <address>
3340        <email>dcrocker@bbiw.net</email>
3341      </address> 
3342    </author>
3343    <author initials="P." surname="Overell" fullname="Paul Overell">
3344      <organization>THUS plc.</organization>
3345      <address>
3346        <email>paul.overell@thus.net</email>
3347      </address>
3348    </author>
3349    <date month="January" year="2008"/>
3350  </front>
3351  <seriesInfo name="STD" value="68"/>
3352  <seriesInfo name="RFC" value="5234"/>
3353</reference>
3354
3355</references>
3356
3357<references title="Informative References">
3358
3359<reference anchor="RFC1123">
3360  <front>
3361    <title>Requirements for Internet Hosts - Application and Support</title>
3362    <author initials="R." surname="Braden" fullname="Robert Braden">
3363      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3364      <address><email>Braden@ISI.EDU</email></address>
3365    </author>
3366    <date month="October" year="1989"/>
3367  </front>
3368  <seriesInfo name="STD" value="3"/>
3369  <seriesInfo name="RFC" value="1123"/>
3370</reference>
3371
3372<reference anchor="RFC1945">
3373  <front>
3374    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3375    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3376      <organization>MIT, Laboratory for Computer Science</organization>
3377      <address><email>timbl@w3.org</email></address>
3378    </author>
3379    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3380      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3381      <address><email>fielding@ics.uci.edu</email></address>
3382    </author>
3383    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3384      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3385      <address><email>frystyk@w3.org</email></address>
3386    </author>
3387    <date month="May" year="1996"/>
3388  </front>
3389  <seriesInfo name="RFC" value="1945"/>
3390</reference>
3391
3392<reference anchor="RFC2068">
3393  <front>
3394    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3395    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3396      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3397      <address><email>fielding@ics.uci.edu</email></address>
3398    </author>
3399    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3400      <organization>MIT Laboratory for Computer Science</organization>
3401      <address><email>jg@w3.org</email></address>
3402    </author>
3403    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3404      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3405      <address><email>mogul@wrl.dec.com</email></address>
3406    </author>
3407    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3408      <organization>MIT Laboratory for Computer Science</organization>
3409      <address><email>frystyk@w3.org</email></address>
3410    </author>
3411    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3412      <organization>MIT Laboratory for Computer Science</organization>
3413      <address><email>timbl@w3.org</email></address>
3414    </author>
3415    <date month="January" year="1997"/>
3416  </front>
3417  <seriesInfo name="RFC" value="2068"/>
3418</reference>
3419
3420<reference anchor="RFC2616">
3421  <front>
3422    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3423    <author initials="R." surname="Fielding" fullname="R. Fielding">
3424      <organization>University of California, Irvine</organization>
3425      <address><email>fielding@ics.uci.edu</email></address>
3426    </author>
3427    <author initials="J." surname="Gettys" fullname="J. Gettys">
3428      <organization>W3C</organization>
3429      <address><email>jg@w3.org</email></address>
3430    </author>
3431    <author initials="J." surname="Mogul" fullname="J. Mogul">
3432      <organization>Compaq Computer Corporation</organization>
3433      <address><email>mogul@wrl.dec.com</email></address>
3434    </author>
3435    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3436      <organization>MIT Laboratory for Computer Science</organization>
3437      <address><email>frystyk@w3.org</email></address>
3438    </author>
3439    <author initials="L." surname="Masinter" fullname="L. Masinter">
3440      <organization>Xerox Corporation</organization>
3441      <address><email>masinter@parc.xerox.com</email></address>
3442    </author>
3443    <author initials="P." surname="Leach" fullname="P. Leach">
3444      <organization>Microsoft Corporation</organization>
3445      <address><email>paulle@microsoft.com</email></address>
3446    </author>
3447    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3448      <organization>W3C</organization>
3449      <address><email>timbl@w3.org</email></address>
3450    </author>
3451    <date month="June" year="1999"/>
3452  </front>
3453  <seriesInfo name="RFC" value="2616"/>
3454</reference>
3455
3456<reference anchor="RFC2817">
3457  <front>
3458    <title>Upgrading to TLS Within HTTP/1.1</title>
3459    <author initials="R." surname="Khare" fullname="R. Khare">
3460      <organization>4K Associates / UC Irvine</organization>
3461      <address><email>rohit@4K-associates.com</email></address>
3462    </author>
3463    <author initials="S." surname="Lawrence" fullname="S. Lawrence">
3464      <organization>Agranat Systems, Inc.</organization>
3465      <address><email>lawrence@agranat.com</email></address>
3466    </author>
3467    <date year="2000" month="May"/>
3468  </front>
3469  <seriesInfo name="RFC" value="2817"/>
3470</reference>
3471
3472<reference anchor="RFC3864">
3473  <front>
3474    <title>Registration Procedures for Message Header Fields</title>
3475    <author initials="G." surname="Klyne" fullname="G. Klyne">
3476      <organization>Nine by Nine</organization>
3477      <address><email>GK-IETF@ninebynine.org</email></address>
3478    </author>
3479    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
3480      <organization>BEA Systems</organization>
3481      <address><email>mnot@pobox.com</email></address>
3482    </author>
3483    <author initials="J." surname="Mogul" fullname="J. Mogul">
3484      <organization>HP Labs</organization>
3485      <address><email>JeffMogul@acm.org</email></address>
3486    </author>
3487    <date year="2004" month="September"/>
3488  </front>
3489  <seriesInfo name="BCP" value="90"/>
3490  <seriesInfo name="RFC" value="3864"/>
3491</reference>
3492
3493<reference anchor="RFC5226">
3494  <front>
3495    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3496    <author initials="T." surname="Narten" fullname="T. Narten">
3497      <organization>IBM</organization>
3498      <address><email>narten@us.ibm.com</email></address>
3499    </author>
3500    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
3501      <organization>Google</organization>
3502      <address><email>Harald@Alvestrand.no</email></address>
3503    </author>
3504    <date year="2008" month="May"/>
3505  </front>
3506  <seriesInfo name="BCP" value="26"/>
3507  <seriesInfo name="RFC" value="5226"/>
3508</reference>
3509
3510<reference anchor="RFC5322">
3511  <front>
3512    <title>Internet Message Format</title>
3513    <author initials="P." surname="Resnick" fullname="P. Resnick">
3514      <organization>Qualcomm Incorporated</organization>
3515    </author>
3516    <date year="2008" month="October"/>
3517  </front>
3518  <seriesInfo name="RFC" value="5322"/>
3519</reference>
3520
3521<reference anchor="RFC5789">
3522  <front>
3523    <title>PATCH Method for HTTP</title>
3524    <author initials="L." surname="Dusseault" fullname="L. Dusseault">
3525      <organization>Linden Lab</organization>
3526    </author>
3527    <author initials="J." surname="Snell" fullname="J. Snell"/>
3528    <date year="2010" month="March"/>
3529  </front>
3530  <seriesInfo name="RFC" value="5789"/>
3531</reference>
3532
3533<reference anchor="RFC5987">
3534        <front>
3535    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3536    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3537      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3538      <address>
3539        <postal>
3540          <street>Hafenweg 16</street>
3541          <city>Muenster</city><region>NW</region><code>48155</code>
3542          <country>Germany</country>
3543        </postal>
3544        <email>julian.reschke@greenbytes.de</email>     
3545        <uri>http://greenbytes.de/tech/webdav/</uri>   
3546      </address>
3547    </author>
3548    <date month="August" year="2010"/>
3549  </front>
3550  <seriesInfo name="RFC" value="5987"/>
3551</reference>
3552
3553</references>
3554
3555<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3556<t>
3557  This document takes over the Status Code Registry, previously defined
3558  in Section 7.1 of <xref target="RFC2817"/>.
3559  (<xref target="status.code.registry"/>)
3560</t>
3561<t>
3562  Clarify definition of POST.
3563  (<xref target="POST"/>)
3564</t>
3565<t>
3566  Remove requirement to handle all Content-* header fields; ban use of
3567  Content-Range with PUT.
3568  (<xref target="PUT"/>)
3569</t>
3570<t>
3571  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3572  (<xref target="CONNECT"/>)
3573</t>
3574<t>
3575  Broadened the definition of 203 (Non-Authoritative Information) to include
3576  cases of payload transformations as well.
3577  (<xref target="status.203"/>)
3578</t>
3579<t>
3580  Status codes 301, 302, and 307: removed the normative requirements on both
3581  response payloads and user interaction.
3582  (<xref target="status.3xx"/>)
3583</t>
3584<t>
3585  Failed to consider that there are many other request methods that are safe
3586  to automatically redirect, and further that the user agent is able to make
3587  that determination based on the request method semantics.
3588  Furthermore, allow user agents to rewrite the method from POST to GET
3589  for status codes 301 and 302.
3590  (Sections <xref format="counter" target="status.301"/>,
3591  <xref format="counter" target="status.302"/> and
3592  <xref format="counter" target="status.307"/>)
3593</t>
3594<t>
3595  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3596  It used to indicate that the target resource must be accessed through the
3597  proxy given by the Location field. The Location field gave the URI of the
3598  proxy. The recipient was expected to repeat this single request via the proxy.
3599  (<xref target="status.305"/>)
3600</t>
3601<t>
3602  Define status 426 (Upgrade Required) (this was incorporated from
3603  <xref target="RFC2817"/>).
3604  (<xref target="status.426"/>)
3605</t>
3606<t>
3607  Change ABNF productions for header fields to only define the field value.
3608  (<xref target="header.field.definitions"/>)
3609</t>
3610<t>
3611  Reclassify "Allow" as response header field, removing the option to
3612  specify it in a PUT request.
3613  Relax the server requirement on the contents of the Allow header field and
3614  remove requirement on clients to always trust the header field value.
3615  (<xref target="header.allow"/>)
3616</t>
3617<t>
3618  The ABNF for the Expect header field has been both fixed (allowing parameters
3619  for value-less expectations as well) and simplified (allowing trailing
3620  semicolons after "100-continue" when they were invalid before).
3621  (<xref target="header.expect"/>)
3622</t>
3623<t>
3624  Correct syntax of Location header field to allow URI references (including
3625  relative references and fragments), as referred symbol "absoluteURI" wasn't
3626  what was expected, and add some clarifications as to when use of fragments
3627  would not be appropriate.
3628  (<xref target="header.location"/>)
3629</t>
3630<t>
3631  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
3632  extension methods could have used it as well).
3633  (<xref target="header.max-forwards"/>)
3634</t>
3635<t>
3636  Allow Referer field value of "about:blank" as alternative to not specifying it.
3637  (<xref target="header.referer"/>)
3638</t>
3639<t>
3640  In the description of the Server header field, the Via field
3641  was described as a SHOULD. The requirement was and is stated
3642  correctly in the description of the Via header field in Section 6.2 of <xref target="Part1"/>.
3643  (<xref target="header.server"/>)
3644</t>
3645</section>
3646
3647
3648<section title="Collected ABNF" anchor="collected.abnf">
3649<figure>
3650<artwork type="abnf" name="p2-semantics.parsed-abnf"><![CDATA[
3651Allow = [ ( "," / method ) *( OWS "," [ OWS method ] ) ]
3652
3653BWS = <BWS, defined in [Part1], Section 3.2.1>
3654
3655Date = HTTP-date
3656
3657Expect = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
3658
3659From = mailbox
3660
3661GMT = %x47.4D.54 ; GMT
3662
3663HTTP-date = rfc1123-date / obs-date
3664
3665Location = URI-reference
3666
3667Max-Forwards = 1*DIGIT
3668
3669OWS = <OWS, defined in [Part1], Section 3.2.1>
3670
3671RWS = <RWS, defined in [Part1], Section 3.2.1>
3672Referer = absolute-URI / partial-URI
3673Retry-After = HTTP-date / delta-seconds
3674
3675Server = product *( RWS ( product / comment ) )
3676
3677URI-reference = <URI-reference, defined in [Part1], Section 2.7>
3678User-Agent = product *( RWS ( product / comment ) )
3679
3680absolute-URI = <absolute-URI, defined in [Part1], Section 2.7>
3681asctime-date = day-name SP date3 SP time-of-day SP year
3682
3683comment = <comment, defined in [Part1], Section 3.2.4>
3684
3685date1 = day SP month SP year
3686date2 = day "-" month "-" 2DIGIT
3687date3 = month SP ( 2DIGIT / ( SP DIGIT ) )
3688day = 2DIGIT
3689day-name = %x4D.6F.6E ; Mon
3690 / %x54.75.65 ; Tue
3691 / %x57.65.64 ; Wed
3692 / %x54.68.75 ; Thu
3693 / %x46.72.69 ; Fri
3694 / %x53.61.74 ; Sat
3695 / %x53.75.6E ; Sun
3696day-name-l = %x4D.6F.6E.64.61.79 ; Monday
3697 / %x54.75.65.73.64.61.79 ; Tuesday
3698 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
3699 / %x54.68.75.72.73.64.61.79 ; Thursday
3700 / %x46.72.69.64.61.79 ; Friday
3701 / %x53.61.74.75.72.64.61.79 ; Saturday
3702 / %x53.75.6E.64.61.79 ; Sunday
3703delta-seconds = 1*DIGIT
3704
3705expect-name = token
3706expect-param = expect-name [ BWS "=" BWS expect-value ]
3707expect-value = token / quoted-string
3708expectation = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
3709 OWS expect-param ] )
3710
3711hour = 2DIGIT
3712
3713mailbox = <mailbox, defined in [RFC5322], Section 3.4>
3714method = token
3715minute = 2DIGIT
3716month = %x4A.61.6E ; Jan
3717 / %x46.65.62 ; Feb
3718 / %x4D.61.72 ; Mar
3719 / %x41.70.72 ; Apr
3720 / %x4D.61.79 ; May
3721 / %x4A.75.6E ; Jun
3722 / %x4A.75.6C ; Jul
3723 / %x41.75.67 ; Aug
3724 / %x53.65.70 ; Sep
3725 / %x4F.63.74 ; Oct
3726 / %x4E.6F.76 ; Nov
3727 / %x44.65.63 ; Dec
3728
3729obs-date = rfc850-date / asctime-date
3730obs-text = <obs-text, defined in [Part1], Section 3.2.4>
3731
3732partial-URI = <partial-URI, defined in [Part1], Section 2.7>
3733product = token [ "/" product-version ]
3734product-version = token
3735
3736quoted-string = <quoted-string, defined in [Part1], Section 3.2.4>
3737
3738reason-phrase = *( HTAB / SP / VCHAR / obs-text )
3739rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
3740rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
3741
3742second = 2DIGIT
3743status-code = 3DIGIT
3744
3745time-of-day = hour ":" minute ":" second
3746token = <token, defined in [Part1], Section 3.2.4>
3747
3748year = 4DIGIT
3749]]></artwork>
3750</figure>
3751<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
3752; Allow defined but not used
3753; Date defined but not used
3754; Expect defined but not used
3755; From defined but not used
3756; Location defined but not used
3757; Max-Forwards defined but not used
3758; Referer defined but not used
3759; Retry-After defined but not used
3760; Server defined but not used
3761; User-Agent defined but not used
3762; reason-phrase defined but not used
3763; status-code defined but not used
3764]]></artwork></figure></section>
3765
3766
3767<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
3768
3769<section title="Since RFC 2616">
3770<t>
3771  Extracted relevant partitions from <xref target="RFC2616"/>.
3772</t>
3773</section>
3774
3775<section title="Since draft-ietf-httpbis-p2-semantics-00">
3776<t>
3777  Closed issues:
3778  <list style="symbols">
3779    <t>
3780      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
3781      "Via is a MUST"
3782      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
3783    </t>
3784    <t>
3785      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
3786      "Fragments allowed in Location"
3787      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
3788    </t>
3789    <t>
3790      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
3791      "Safe Methods vs Redirection"
3792      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
3793    </t>
3794    <t>
3795      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
3796      "Revise description of the POST method"
3797      (<eref target="http://purl.org/NET/http-errata#post"/>)
3798    </t>
3799    <t>
3800      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
3801      "Normative and Informative references"
3802    </t>
3803    <t>
3804      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
3805      "RFC2606 Compliance"
3806    </t>
3807    <t>
3808      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
3809      "Informative references"
3810    </t>
3811    <t>
3812      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
3813      "Redundant cross-references"
3814    </t>
3815  </list>
3816</t>
3817<t>
3818  Other changes:
3819  <list style="symbols">
3820    <t>
3821      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
3822    </t>
3823  </list>
3824</t>
3825</section>
3826
3827<section title="Since draft-ietf-httpbis-p2-semantics-01">
3828<t>
3829  Closed issues:
3830  <list style="symbols">
3831    <t>
3832      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
3833      "PUT side effects"
3834    </t>
3835    <t>
3836      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
3837      "Duplicate Host header requirements"
3838    </t>
3839  </list>
3840</t>
3841<t>
3842  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3843  <list style="symbols">
3844    <t>
3845      Move "Product Tokens" section (back) into Part 1, as "token" is used
3846      in the definition of the Upgrade header field.
3847    </t>
3848    <t>
3849      Add explicit references to BNF syntax and rules imported from other parts of the specification.
3850    </t>
3851    <t>
3852      Copy definition of delta-seconds from Part6 instead of referencing it.
3853    </t>
3854  </list>
3855</t>
3856</section>
3857
3858<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
3859<t>
3860  Closed issues:
3861  <list style="symbols">
3862    <t>
3863      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
3864      "Requiring Allow in 405 responses"
3865    </t>
3866    <t>
3867      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
3868      "Status Code Registry"
3869    </t>
3870    <t>
3871      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
3872      "Redirection vs. Location"
3873    </t>
3874    <t>
3875      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
3876      "Cacheability of 303 response"
3877    </t>
3878    <t>
3879      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
3880      "305 Use Proxy"
3881    </t>
3882    <t>
3883      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
3884      "Classification for Allow header"
3885    </t>
3886    <t>
3887      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
3888      "PUT - 'store under' vs 'store at'"
3889    </t>
3890  </list>
3891</t>
3892<t>
3893  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
3894  <list style="symbols">
3895    <t>
3896      Reference RFC 3984, and update header field registrations for headers defined
3897      in this document.
3898    </t>
3899  </list>
3900</t>
3901<t>
3902  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3903  <list style="symbols">
3904    <t>
3905      Replace string literals when the string really is case-sensitive (method).
3906    </t>
3907  </list>
3908</t>
3909</section>
3910
3911<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
3912<t>
3913  Closed issues:
3914  <list style="symbols">
3915    <t>
3916      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
3917      "OPTIONS request bodies"
3918    </t>
3919    <t>
3920      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
3921      "Description of CONNECT should refer to RFC2817"
3922    </t>
3923    <t>
3924      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
3925      "Location Content-Location reference request/response mixup"
3926    </t>
3927  </list>
3928</t>
3929<t>
3930  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
3931  <list style="symbols">
3932    <t>
3933      Added initial proposal for registration process, plus initial
3934      content (non-HTTP/1.1 methods to be added by a separate specification).
3935    </t>
3936  </list>
3937</t>
3938</section>
3939
3940<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
3941<t>
3942  Closed issues:
3943  <list style="symbols">
3944    <t>
3945      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
3946      "Content-*"
3947    </t>
3948    <t>
3949      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
3950      "RFC 2822 is updated by RFC 5322"
3951    </t>
3952  </list>
3953</t>
3954<t>
3955  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3956  <list style="symbols">
3957    <t>
3958      Use "/" instead of "|" for alternatives.
3959    </t>
3960    <t>
3961      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
3962      whitespace ("OWS") and required whitespace ("RWS").
3963    </t>
3964    <t>
3965      Rewrite ABNFs to spell out whitespace rules, factor out
3966      header field value format definitions.
3967    </t>
3968  </list>
3969</t>
3970</section>
3971
3972<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
3973<t>
3974  Closed issues:
3975  <list style="symbols">
3976    <t>
3977      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
3978      "reason-phrase BNF"
3979    </t>
3980  </list>
3981</t>
3982<t>
3983  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3984  <list style="symbols">
3985    <t>
3986      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
3987    </t>
3988  </list>
3989</t>
3990</section>
3991
3992<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
3993<t>
3994  Closed issues:
3995  <list style="symbols">
3996    <t>
3997      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
3998      "Clarify when Referer is sent"
3999    </t>
4000    <t>
4001      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4002      "status codes vs methods"
4003    </t>
4004    <t>
4005      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4006      "Do not require "updates" relation for specs that register status codes or method names"
4007    </t>
4008  </list>
4009</t>
4010</section>
4011
4012<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4013<t>
4014  Closed issues:
4015  <list style="symbols">
4016    <t>
4017      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4018      "Idempotency"
4019    </t>
4020    <t>
4021      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4022      "TRACE security considerations"
4023    </t>
4024    <t>
4025      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4026      "Clarify rules for determining what entities a response carries"
4027    </t>
4028    <t>
4029      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4030      "update note citing RFC 1945 and 2068"
4031    </t>
4032    <t>
4033      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4034      "update note about redirect limit"
4035    </t>
4036    <t>
4037      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4038      "Location header ABNF should use 'URI'"
4039    </t>
4040    <t>
4041      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4042      "fragments in Location vs status 303"
4043    </t>
4044    <t>
4045      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4046      "move IANA registrations for optional status codes"
4047    </t>
4048  </list>
4049</t>
4050<t>
4051  Partly resolved issues:
4052  <list style="symbols">
4053    <t>
4054      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4055      "Are OPTIONS and TRACE safe?"
4056    </t>
4057  </list>
4058</t>
4059</section>
4060
4061<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4062<t>
4063  Closed issues:
4064  <list style="symbols">
4065    <t>
4066      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4067      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4068      status codes when fixing this previously)
4069    </t>
4070  </list>
4071</t>
4072</section>
4073
4074<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4075<t>
4076  Closed issues:
4077  <list style="symbols">
4078    <t>
4079      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4080      "Fragment combination / precedence during redirects"
4081    </t>
4082  </list>
4083</t>
4084<t>
4085  Partly resolved issues:
4086  <list style="symbols">
4087    <t>
4088      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4089      "Location header payload handling"
4090    </t>
4091    <t>
4092      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4093      "Term for the requested resource's URI"
4094    </t>
4095  </list>
4096</t>
4097</section>
4098
4099<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4100<t>
4101  Closed issues:
4102  <list style="symbols">
4103    <t>
4104      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4105      "Clarify 'Requested Variant'"
4106    </t>
4107    <t>
4108      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4109      "Clarify entity / representation / variant terminology"
4110    </t>
4111    <t>
4112      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4113      "Methods and Caching"
4114    </t>
4115    <t>
4116      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4117      "OPTIONS vs Max-Forwards"
4118    </t>
4119    <t>
4120      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4121      "Status codes and caching"
4122    </t>
4123    <t>
4124      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4125      "consider removing the 'changes from 2068' sections"
4126    </t>
4127  </list>
4128</t>
4129</section>
4130
4131<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4132<t>
4133  Closed issues:
4134  <list style="symbols">
4135    <t>
4136      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4137      "Considerations for new status codes"
4138    </t>
4139    <t>
4140      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4141      "Considerations for new methods"
4142    </t>
4143    <t>
4144      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4145      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4146    </t>
4147  </list>
4148</t>
4149</section>
4150
4151<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4152<t>
4153  Closed issues:
4154  <list style="symbols">
4155    <t>
4156      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4157      "Fragment combination / precedence during redirects" (added warning
4158      about having a fragid on the redirect may cause inconvenience in
4159      some cases)
4160    </t>
4161    <t>
4162      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4163      "Content-* vs. PUT"
4164    </t>
4165    <t>
4166      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4167      "205 Bodies"
4168    </t>
4169    <t>
4170      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4171      "Understanding Content-* on non-PUT requests"
4172    </t>
4173    <t>
4174      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4175      "Content-*"
4176    </t>
4177    <t>
4178      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4179      "Header type defaulting"
4180    </t>
4181    <t>
4182      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4183      "PUT - 'store under' vs 'store at'"
4184    </t>
4185    <t>
4186      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4187      "duplicate ABNF for reason-phrase"
4188    </t>
4189    <t>
4190      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4191      "Note special status of Content-* prefix in header registration procedures"
4192    </t>
4193    <t>
4194      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4195      "Max-Forwards vs extension methods"
4196    </t>
4197    <t>
4198      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4199      "What is the value space of HTTP status codes?" (actually fixed in
4200      draft-ietf-httpbis-p2-semantics-11)
4201    </t>
4202    <t>
4203      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4204      "Header Classification"
4205    </t>
4206    <t>
4207      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4208      "PUT side effect: invalidation or just stale?"
4209    </t>
4210    <t>
4211      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4212      "proxies not supporting certain methods"
4213    </t>
4214    <t>
4215      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4216      "Migrate CONNECT from RFC2817 to p2"
4217    </t>
4218    <t>
4219      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4220      "Migrate Upgrade details from RFC2817"
4221    </t>
4222    <t>
4223      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4224      "clarify PUT semantics'"
4225    </t>
4226    <t>
4227      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4228      "duplicate ABNF for 'Method'"
4229    </t>
4230    <t>
4231      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4232      "untangle ABNFs for header fields"
4233    </t>
4234  </list>
4235</t>
4236</section>
4237
4238<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4239<t>
4240  Closed issues:
4241  <list style="symbols">
4242    <t>
4243      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4244      "untangle ABNFs for header fields"
4245    </t>
4246    <t>
4247      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4248      "message body in CONNECT request"
4249    </t>
4250  </list>
4251</t>
4252</section>
4253
4254<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4255<t>
4256  Closed issues:
4257  <list style="symbols">
4258    <t>
4259      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4260      "Clarify status code for rate limiting"
4261    </t>
4262    <t>
4263      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4264      "clarify 403 forbidden"
4265    </t>
4266    <t>
4267      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4268      "Clarify 203 Non-Authoritative Information"
4269    </t>
4270    <t>
4271      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4272      "update default reason phrase for 413"
4273    </t>
4274  </list>
4275</t>
4276</section>
4277
4278<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4279<t>
4280  Closed issues:
4281  <list style="symbols">
4282    <t>
4283      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4284      "Strength of requirements on Accept re: 406"
4285    </t>
4286    <t>
4287      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4288      "400 response isn't generic"
4289    </t>
4290  </list>
4291</t>
4292</section>
4293
4294<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4295<t>
4296  Closed issues:
4297  <list style="symbols">
4298    <t>
4299      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4300      "Redirects and non-GET methods"
4301    </t>
4302    <t>
4303      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
4304      "Document HTTP's error-handling philosophy"
4305    </t>
4306    <t>
4307      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4308      "Considerations for new headers"
4309    </t>
4310    <t>
4311      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4312      "clarify 303 redirect on HEAD"
4313    </t>
4314  </list>
4315</t>
4316</section>
4317
4318<section title="Since draft-ietf-httpbis-p2-semantics-17" anchor="changes.since.17">
4319<t>
4320  Closed issues:
4321  <list style="symbols">
4322    <t>
4323      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4324      "Location header payload handling"
4325    </t>
4326    <t>
4327      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4328      "Clarify status code for rate limiting" (change backed out because
4329      a new status code is being defined for this purpose)
4330    </t>
4331    <t>
4332      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4333      "should there be a permanent variant of 307"
4334    </t>
4335    <t>
4336      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/325"/>:
4337      "When are Location's semantics triggered?"
4338    </t>
4339    <t>
4340      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/327"/>:
4341      "'expect' grammar missing OWS"
4342    </t>
4343    <t>
4344      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/329"/>:
4345      "header field considerations: quoted-string vs use of double quotes"
4346    </t>
4347  </list>
4348</t>
4349</section>
4350
4351<section title="Since draft-ietf-httpbis-p2-semantics-18" anchor="changes.since.18">
4352<t>
4353  Closed issues:
4354  <list style="symbols">
4355    <t>
4356      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/227"/>:
4357      "Combining HEAD responses"
4358    </t>
4359    <t>
4360      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/238"/>:
4361      "Requirements for user intervention during redirects"
4362    </t>
4363    <t>
4364      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
4365      "message-body in CONNECT response"
4366    </t>
4367    <t>
4368      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/295"/>:
4369      "Applying original fragment to 'plain' redirected URI"
4370    </t>
4371    <t>
4372      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
4373      "Misplaced text on connection handling in p2"
4374    </t>
4375    <t>
4376      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/331"/>:
4377      "clarify that 201 doesn't require Location header fields"
4378    </t>
4379    <t>
4380      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/332"/>:
4381      "relax requirements on hypertext in 3/4/5xx error responses"
4382    </t>
4383    <t>
4384      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/333"/>:
4385      "example for 426 response should have a payload"
4386    </t>
4387    <t>
4388      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/336"/>:
4389      "drop indirection entries for status codes"
4390    </t>
4391  </list>
4392</t>
4393</section>
4394
4395</section>
4396
4397</back>
4398</rfc>
Note: See TracBrowser for help on using the repository browser.