source: draft-ietf-httpbis/latest/p2-semantics.xml @ 96

Last change on this file since 96 was 96, checked in by julian.reschke@…, 12 years ago

Add "Requirements" subsection everywhere (including reference to RFC2119), add missing bcp14 markup.

  • Property svn:eol-style set to native
File size: 119.5 KB
Line 
1<?xml version="1.0" encoding="utf-8"?>
2<!DOCTYPE rfc [
3  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
4  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
5  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
6  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
7  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
8  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
9  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
10  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
11  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
12  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
13  <!ENTITY ID-VERSION "latest">
14  <!ENTITY ID-MONTH "December">
15  <!ENTITY ID-YEAR "2007">
16  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
17  <!ENTITY payload                    "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY conditional                "<xref target='Part4' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY range                      "<xref target='Part5' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY caching                    "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY auth                       "<xref target='Part7' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY diff2045entity             "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY http-url                   "<xref target='Part1' x:rel='#http-url' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY header-authorization       "<xref target='Part7' x:rel='#header.authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY header-host                "<xref target='Part1' x:rel='#header.host' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY header-upgrade             "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.upgrade' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
57  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
58  <!ENTITY message-transmission-req   "<xref target='Part1' x:rel='#message.transmission.requirements' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
59]>
60<?rfc toc="yes" ?>
61<?rfc symrefs="yes" ?>
62<?rfc sortrefs="yes" ?>
63<?rfc compact="yes"?>
64<?rfc subcompact="no" ?>
65<?rfc linkmailto="no" ?>
66<?rfc editing="no" ?>
67<?rfc-ext allow-markup-in-artwork="yes" ?>
68<?rfc-ext include-references-in-index="yes" ?>
69<rfc obsoletes="2068, 2616" category="std"
70     ipr="full3978" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
71     xmlns:x='http://purl.org/net/xml2rfc/ext' xmlns:ed="http://greenbytes.de/2002/rfcedit">
72<front>
73
74  <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
75
76  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
77    <organization abbrev="Day Software">Day Software</organization>
78    <address>
79      <postal>
80        <street>23 Corporate Plaza DR, Suite 280</street>
81        <city>Newport Beach</city>
82        <region>CA</region>
83        <code>92660</code>
84        <country>USA</country>
85      </postal>
86      <phone>+1-949-706-5300</phone>
87      <facsimile>+1-949-706-5305</facsimile>
88      <email>fielding@gbiv.com</email>
89      <uri>http://roy.gbiv.com/</uri>
90    </address>
91  </author>
92
93  <author initials="J." surname="Gettys" fullname="Jim Gettys">
94    <organization>One Laptop per Child</organization>
95    <address>
96      <postal>
97        <street>21 Oak Knoll Road</street>
98        <city>Carlisle</city>
99        <region>MA</region>
100        <code>01741</code>
101        <country>USA</country>
102      </postal>
103      <email>jg@laptop.org</email>
104      <uri>http://www.laptop.org/</uri>
105    </address>
106  </author>
107 
108  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
109    <organization abbrev="HP">Hewlett-Packard Company</organization>
110    <address>
111      <postal>
112        <street>HP Labs, Large Scale Systems Group</street>
113        <street>1501 Page Mill Road, MS 1177</street>
114        <city>Palo Alto</city>
115        <region>CA</region>
116        <code>94304</code>
117        <country>USA</country>
118      </postal>
119      <email>JeffMogul@acm.org</email>
120    </address>
121  </author>
122
123  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
124    <organization abbrev="Microsoft">Microsoft Corporation</organization>
125    <address>
126      <postal>
127        <street>1 Microsoft Way</street>
128        <city>Redmond</city>
129        <region>WA</region>
130        <code>98052</code>
131        <country>USA</country>
132      </postal>
133      <email>henrikn@microsoft.com</email>
134    </address>
135  </author>
136
137  <author initials="L." surname="Masinter" fullname="Larry Masinter">
138    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
139    <address>
140      <postal>
141        <street>345 Park Ave</street>
142        <city>San Jose</city>
143        <region>CA</region>
144        <code>95110</code>
145        <country>USA</country>
146      </postal>
147      <email>LMM@acm.org</email>
148      <uri>http://larry.masinter.net/</uri>
149    </address>
150  </author>
151 
152  <author initials="P." surname="Leach" fullname="Paul J. Leach">
153    <organization abbrev="Microsoft">Microsoft Corporation</organization>
154    <address>
155      <postal>
156        <street>1 Microsoft Way</street>
157        <city>Redmond</city>
158        <region>WA</region>
159        <code>98052</code>
160      </postal>
161      <email>paulle@microsoft.com</email>
162    </address>
163  </author>
164   
165  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
166    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
167    <address>
168      <postal>
169        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
170        <street>The Stata Center, Building 32</street>
171        <street>32 Vassar Street</street>
172        <city>Cambridge</city>
173        <region>MA</region>
174        <code>02139</code>
175        <country>USA</country>
176      </postal>
177      <email>timbl@w3.org</email>
178      <uri>http://www.w3.org/People/Berners-Lee/</uri>
179    </address>
180  </author>
181
182  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
183    <organization abbrev="W3C">World Wide Web Consortium</organization>
184    <address>
185      <postal>
186        <street>W3C / ERCIM</street>
187        <street>2004, rte des Lucioles</street>
188        <city>Sophia-Antipolis</city>
189        <region>AM</region>
190        <code>06902</code>
191        <country>France</country>
192      </postal>
193      <email>ylafon@w3.org</email>
194      <uri>http://www.raubacapeu.net/people/yves/</uri>
195    </address>
196  </author>
197
198  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
199    <organization abbrev="greenbytes">greenbytes GmbH</organization>
200    <address>
201      <postal>
202        <street>Hafenweg 16</street>
203        <city>Muenster</city><region>NW</region><code>48155</code>
204        <country>Germany</country>
205      </postal>
206      <phone>+49 251 2807760</phone>   
207      <facsimile>+49 251 2807761</facsimile>   
208      <email>julian.reschke@greenbytes.de</email>       
209      <uri>http://greenbytes.de/tech/webdav/</uri>     
210    </address>
211  </author>
212
213  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
214
215<abstract>
216<t>
217   The Hypertext Transfer Protocol (HTTP) is an application-level
218   protocol for distributed, collaborative, hypermedia information
219   systems. HTTP has been in use by the World Wide Web global information
220   initiative since 1990. This document is Part 2 of the seven-part specification
221   that defines the protocol referred to as "HTTP/1.1" and, taken together,
222   obsoletes RFC 2616.  Part 2 defines the semantics of HTTP messages
223   as expressed by request methods, request-header fields, response status codes,
224   and response-header fields.
225</t>
226</abstract>
227
228<note title="Editorial Note (To be removed by RFC Editor)">
229  <t>
230    This version of the HTTP specification contains only minimal editorial
231    changes from <xref target="RFC2616"/> (abstract, introductory paragraph,
232    and authors' addresses).  All other changes are due to partitioning the
233    original into seven mostly independent parts.  The intent is for readers
234    of future drafts to able to use draft 00 as the basis for comparison
235    when the WG makes later changes to the specification text.  This draft
236    will shortly be followed by draft 01 (containing the first round of changes
237    that have already been agreed to on the mailing list). There is no point in
238    reviewing this draft other than to verify that the partitioning has been
239    done correctly.  Roy T. Fielding, Yves Lafon, and Julian Reschke
240    will be the editors after draft 00 is submitted.
241  </t>
242  <t>
243    Discussion of this draft should take place on the HTTPBIS working group
244    mailing list (ietf-http-wg@w3.org). The current issues list is
245    at <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/report/11"/>
246    and related documents (including fancy diffs) can be found at
247    <eref target="http://www3.tools.ietf.org/wg/httpbis/"/>.
248  </t>
249</note>
250</front>
251<middle>
252<section title="Introduction" anchor="introduction">
253<t>
254   This document will define aspects of HTTP related to request and response
255   semantics. Right now it only includes the extracted relevant sections of
256   RFC 2616 with only minor edits.
257</t>
258<t>
259   The HTTP protocol is a request/response protocol. A client sends a
260   request to the server in the form of a request method, URI, and
261   protocol version, followed by a MIME-like message containing request
262   modifiers, client information, and possible body content over a
263   connection with a server. The server responds with a status line,
264   including the message's protocol version and a success or error code,
265   followed by a MIME-like message containing server information, entity
266   metainformation, and possible entity-body content. The relationship
267   between HTTP and MIME is described in &diff2045entity;.
268</t>
269
270<section title="Requirements" anchor="intro.requirements">
271<t>
272   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
273   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
274   document are to be interpreted as described in <xref target="RFC2119"/>.
275</t>
276<t>
277   An implementation is not compliant if it fails to satisfy one or more
278   of the &MUST; or &REQUIRED; level requirements for the protocols it
279   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
280   level and all the &SHOULD; level requirements for its protocols is said
281   to be "unconditionally compliant"; one that satisfies all the &MUST;
282   level requirements but not all the &SHOULD; level requirements for its
283   protocols is said to be "conditionally compliant."
284</t>
285</section>
286</section>
287
288<section title="Product Tokens" anchor="product.tokens">
289<t>
290   Product tokens are used to allow communicating applications to
291   identify themselves by software name and version. Most fields using
292   product tokens also allow sub-products which form a significant part
293   of the application to be listed, separated by white space. By
294   convention, the products are listed in order of their significance
295   for identifying the application.
296</t>
297<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
298    product         = token ["/" product-version]
299    product-version = token
300</artwork></figure>
301<t>
302   Examples:
303</t>
304<figure><artwork type="example">
305    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
306    Server: Apache/0.8.4
307</artwork></figure>
308<t>
309   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
310   used for advertising or other non-essential information. Although any
311   token character &MAY; appear in a product-version, this token &SHOULD;
312   only be used for a version identifier (i.e., successive versions of
313   the same product &SHOULD; only differ in the product-version portion of
314   the product value).
315</t>
316</section>
317
318<section title="Method" anchor="method">
319<t>
320   The Method  token indicates the method to be performed on the
321   resource identified by the Request-URI. The method is case-sensitive.
322</t>
323<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
324    Method         = "OPTIONS"                ; <xref target="OPTIONS"/>
325                   | "GET"                    ; <xref target="GET"/>
326                   | "HEAD"                   ; <xref target="HEAD"/>
327                   | "POST"                   ; <xref target="POST"/>
328                   | "PUT"                    ; <xref target="PUT"/>
329                   | "DELETE"                 ; <xref target="DELETE"/>
330                   | "TRACE"                  ; <xref target="TRACE"/>
331                   | "CONNECT"                ; <xref target="CONNECT"/>
332                   | extension-method
333    extension-method = token
334</artwork></figure>
335<t>
336   The list of methods allowed by a resource can be specified in an
337   Allow header field (<xref target="header.allow"/>). The return code of the response
338   always notifies the client whether a method is currently allowed on a
339   resource, since the set of allowed methods can change dynamically. An
340   origin server &SHOULD; return the status code 405 (Method Not Allowed)
341   if the method is known by the origin server but not allowed for the
342   requested resource, and 501 (Not Implemented) if the method is
343   unrecognized or not implemented by the origin server. The methods GET
344   and HEAD &MUST; be supported by all general-purpose servers. All other
345   methods are &OPTIONAL;; however, if the above methods are implemented,
346   they &MUST; be implemented with the same semantics as those specified
347   in <xref target="method.definitions"/>.
348</t>
349</section>
350
351<section title="Request Header Fields" anchor="request.header.fields">
352<t>
353   The request-header fields allow the client to pass additional
354   information about the request, and about the client itself, to the
355   server. These fields act as request modifiers, with semantics
356   equivalent to the parameters on a programming language method
357   invocation.
358</t>
359<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-header"/>
360    request-header = Accept                   ; &header-accept;
361                   | Accept-Charset           ; &header-accept-charset;
362                   | Accept-Encoding          ; &header-accept-encoding;
363                   | Accept-Language          ; &header-accept-language;
364                   | Authorization            ; &header-authorization;
365                   | Expect                   ; <xref target="header.expect"/>
366                   | From                     ; <xref target="header.from"/>
367                   | Host                     ; &header-host;
368                   | If-Match                 ; &header-if-match;
369                   | If-Modified-Since        ; &header-if-modified-since;
370                   | If-None-Match            ; &header-if-none-match;
371                   | If-Range                 ; &header-if-range;
372                   | If-Unmodified-Since      ; &header-if-unmodified-since;
373                   | Max-Forwards             ; <xref target="header.max-forwards"/>
374                   | Proxy-Authorization      ; &header-proxy-authorization;
375                   | Range                    ; &header-range;
376                   | Referer                  ; <xref target="header.referer"/>
377                   | TE                       ; &header-te;
378                   | User-Agent               ; <xref target="header.user-agent"/>
379</artwork></figure>
380<t>
381   Request-header field names can be extended reliably only in
382   combination with a change in the protocol version. However, new or
383   experimental header fields &MAY; be given the semantics of request-header
384   fields if all parties in the communication recognize them to
385   be request-header fields. Unrecognized header fields are treated as
386   entity-header fields.
387</t>
388</section>
389
390<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
391<t>
392   The Status-Code element is a 3-digit integer result code of the
393   attempt to understand and satisfy the request. These codes are fully
394   defined in <xref target="status.codes"/>. The Reason-Phrase is intended to give a short
395   textual description of the Status-Code. The Status-Code is intended
396   for use by automata and the Reason-Phrase is intended for the human
397   user. The client is not required to examine or display the Reason-Phrase.
398</t>
399<t> 
400   The individual values of the numeric status codes defined for
401   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
402   presented below. The reason phrases listed here are only
403   recommendations -- they &MAY; be replaced by local equivalents without
404   affecting the protocol.
405</t>
406<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
407   Status-Code    =
408         "100"  ; <xref target="status.100"/>: Continue
409       | "101"  ; <xref target="status.101"/>: Switching Protocols
410       | "200"  ; <xref target="status.200"/>: OK
411       | "201"  ; <xref target="status.201"/>: Created
412       | "202"  ; <xref target="status.202"/>: Accepted
413       | "203"  ; <xref target="status.203"/>: Non-Authoritative Information
414       | "204"  ; <xref target="status.204"/>: No Content
415       | "205"  ; <xref target="status.205"/>: Reset Content
416       | "206"  ; <xref target="status.206"/>: Partial Content
417       | "300"  ; <xref target="status.300"/>: Multiple Choices
418       | "301"  ; <xref target="status.301"/>: Moved Permanently
419       | "302"  ; <xref target="status.302"/>: Found
420       | "303"  ; <xref target="status.303"/>: See Other
421       | "304"  ; <xref target="status.304"/>: Not Modified
422       | "305"  ; <xref target="status.305"/>: Use Proxy
423       | "307"  ; <xref target="status.307"/>: Temporary Redirect
424       | "400"  ; <xref target="status.400"/>: Bad Request
425       | "401"  ; <xref target="status.401"/>: Unauthorized
426       | "402"  ; <xref target="status.402"/>: Payment Required
427       | "403"  ; <xref target="status.403"/>: Forbidden
428       | "404"  ; <xref target="status.404"/>: Not Found
429       | "405"  ; <xref target="status.405"/>: Method Not Allowed
430       | "406"  ; <xref target="status.406"/>: Not Acceptable
431       | "407"  ; <xref target="status.407"/>: Proxy Authentication Required
432       | "408"  ; <xref target="status.408"/>: Request Time-out
433       | "409"  ; <xref target="status.409"/>: Conflict
434       | "410"  ; <xref target="status.410"/>: Gone
435       | "411"  ; <xref target="status.411"/>: Length Required
436       | "412"  ; <xref target="status.412"/>: Precondition Failed
437       | "413"  ; <xref target="status.413"/>: Request Entity Too Large
438       | "414"  ; <xref target="status.414"/>: Request-URI Too Large
439       | "415"  ; <xref target="status.415"/>: Unsupported Media Type
440       | "416"  ; <xref target="status.416"/>: Requested range not satisfiable
441       | "417"  ; <xref target="status.417"/>: Expectation Failed
442       | "500"  ; <xref target="status.500"/>: Internal Server Error
443       | "501"  ; <xref target="status.501"/>: Not Implemented
444       | "502"  ; <xref target="status.502"/>: Bad Gateway
445       | "503"  ; <xref target="status.503"/>: Service Unavailable
446       | "504"  ; <xref target="status.504"/>: Gateway Time-out
447       | "505"  ; <xref target="status.505"/>: HTTP Version not supported
448       | extension-code
449
450   extension-code = 3DIGIT
451   Reason-Phrase  = *&lt;TEXT, excluding CR, LF&gt;
452</artwork></figure>
453<t>
454   HTTP status codes are extensible. HTTP applications are not required
455   to understand the meaning of all registered status codes, though such
456   understanding is obviously desirable. However, applications &MUST;
457   understand the class of any status code, as indicated by the first
458   digit, and treat any unrecognized response as being equivalent to the
459   x00 status code of that class, with the exception that an
460   unrecognized response &MUST-NOT; be cached. For example, if an
461   unrecognized status code of 431 is received by the client, it can
462   safely assume that there was something wrong with its request and
463   treat the response as if it had received a 400 status code. In such
464   cases, user agents &SHOULD; present to the user the entity returned
465   with the response, since that entity is likely to include human-readable
466   information which will explain the unusual status.
467</t>
468</section>
469
470<section title="Response Header Fields" anchor="response.header.fields">
471<t>
472   The response-header fields allow the server to pass additional
473   information about the response which cannot be placed in the Status-Line.
474   These header fields give information about the server and about
475   further access to the resource identified by the Request-URI.
476</t>
477<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="response-header"/>
478    response-header = Accept-Ranges           ; &header-accept-ranges;
479                    | Age                     ; &header-age;
480                    | ETag                    ; &header-etag;
481                    | Location                ; <xref target="header.location"/>
482                    | Proxy-Authenticate      ; &header-proxy-authenticate;
483                    | Retry-After             ; <xref target="header.retry-after"/>
484                    | Server                  ; <xref target="header.server"/>
485                    | Vary                    ; &header-vary;
486                    | WWW-Authenticate        ; &header-www-authenticate;
487</artwork></figure>
488<t>
489   Response-header field names can be extended reliably only in
490   combination with a change in the protocol version. However, new or
491   experimental header fields &MAY; be given the semantics of response-header
492   fields if all parties in the communication recognize them to
493   be response-header fields. Unrecognized header fields are treated as
494   entity-header fields.
495</t>
496</section>
497
498<section title="Entity" anchor="entity">
499<t>
500   Request and Response messages &MAY; transfer an entity if not otherwise
501   restricted by the request method or response status code. An entity
502   consists of entity-header fields and an entity-body, although some
503   responses will only include the entity-headers. HTTP entity-body and
504   entity-header fields are defined in &payload;.
505</t>
506<t>
507   An entity-body is only present in a message when a message-body is
508   present, as described in &message-body;. The entity-body is obtained
509   from the message-body by decoding any Transfer-Encoding that might
510   have been applied to ensure safe and proper transfer of the message.
511</t>
512</section>
513
514
515<section title="Method Definitions" anchor="method.definitions">
516<t>
517   The set of common methods for HTTP/1.1 is defined below. Although
518   this set can be expanded, additional methods cannot be assumed to
519   share the same semantics for separately extended clients and servers.
520
521   The Host request-header field (&header-host;) &MUST; accompany all
522   HTTP/1.1 requests.
523</t>
524
525<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
526
527<section title="Safe Methods" anchor="safe.methods">
528<t>
529   Implementors should be aware that the software represents the user in
530   their interactions over the Internet, and should be careful to allow
531   the user to be aware of any actions they might take which may have an
532   unexpected significance to themselves or others.
533</t>
534<t>
535   In particular, the convention has been established that the GET and
536   HEAD methods &SHOULD-NOT;  have the significance of taking an action
537   other than retrieval. These methods ought to be considered "safe".
538   This allows user agents to represent other methods, such as POST, PUT
539   and DELETE, in a special way, so that the user is made aware of the
540   fact that a possibly unsafe action is being requested.
541</t>
542<t>
543   Naturally, it is not possible to ensure that the server does not
544   generate side-effects as a result of performing a GET request; in
545   fact, some dynamic resources consider that a feature. The important
546   distinction here is that the user did not request the side-effects,
547   so therefore cannot be held accountable for them.
548</t>
549</section>
550
551<section title="Idempotent Methods" anchor="idempotent.methods">
552<t>
553   Methods can also have the property of "idempotence" in that (aside
554   from error or expiration issues) the side-effects of N &gt; 0 identical
555   requests is the same as for a single request. The methods GET, HEAD,
556   PUT and DELETE share this property. Also, the methods OPTIONS and
557   TRACE &SHOULD-NOT;  have side effects, and so are inherently idempotent.
558</t>
559<t>
560   However, it is possible that a sequence of several requests is non-idempotent,
561   even if all of the methods executed in that sequence are
562   idempotent. (A sequence is idempotent if a single execution of the
563   entire sequence always yields a result that is not changed by a
564   reexecution of all, or part, of that sequence.) For example, a
565   sequence is non-idempotent if its result depends on a value that is
566   later modified in the same sequence.
567</t>
568<t>
569   A sequence that never has side effects is idempotent, by definition
570   (provided that no concurrent operations are being executed on the
571   same set of resources).
572</t>
573</section>
574</section>
575
576<section title="OPTIONS" anchor="OPTIONS">
577  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
578  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
579<t>
580   The OPTIONS method represents a request for information about the
581   communication options available on the request/response chain
582   identified by the Request-URI. This method allows the client to
583   determine the options and/or requirements associated with a resource,
584   or the capabilities of a server, without implying a resource action
585   or initiating a resource retrieval.
586</t>
587<t>
588   Responses to this method are not cacheable.
589</t>
590<t>
591   If the OPTIONS request includes an entity-body (as indicated by the
592   presence of Content-Length or Transfer-Encoding), then the media type
593   &MUST; be indicated by a Content-Type field. Although this
594   specification does not define any use for such a body, future
595   extensions to HTTP might use the OPTIONS body to make more detailed
596   queries on the server. A server that does not support such an
597   extension &MAY; discard the request body.
598</t>
599<t>
600   If the Request-URI is an asterisk ("*"), the OPTIONS request is
601   intended to apply to the server in general rather than to a specific
602   resource. Since a server's communication options typically depend on
603   the resource, the "*" request is only useful as a "ping" or "no-op"
604   type of method; it does nothing beyond allowing the client to test
605   the capabilities of the server. For example, this can be used to test
606   a proxy for HTTP/1.1 compliance (or lack thereof).
607</t>
608<t>
609   If the Request-URI is not an asterisk, the OPTIONS request applies
610   only to the options that are available when communicating with that
611   resource.
612</t>
613<t>
614   A 200 response &SHOULD; include any header fields that indicate
615   optional features implemented by the server and applicable to that
616   resource (e.g., Allow), possibly including extensions not defined by
617   this specification. The response body, if any, &SHOULD; also include
618   information about the communication options. The format for such a
619   body is not defined by this specification, but might be defined by
620   future extensions to HTTP. Content negotiation &MAY; be used to select
621   the appropriate response format. If no response body is included, the
622   response &MUST; include a Content-Length field with a field-value of
623   "0".
624</t>
625<t>
626   The Max-Forwards request-header field &MAY; be used to target a
627   specific proxy in the request chain. When a proxy receives an OPTIONS
628   request on an absoluteURI for which request forwarding is permitted,
629   the proxy &MUST; check for a Max-Forwards field. If the Max-Forwards
630   field-value is zero ("0"), the proxy &MUST-NOT; forward the message;
631   instead, the proxy &SHOULD; respond with its own communication options.
632   If the Max-Forwards field-value is an integer greater than zero, the
633   proxy &MUST; decrement the field-value when it forwards the request. If
634   no Max-Forwards field is present in the request, then the forwarded
635   request &MUST-NOT; include a Max-Forwards field.
636</t>
637</section>
638
639<section title="GET" anchor="GET">
640  <iref primary="true" item="GET method" x:for-anchor=""/>
641  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
642<t>
643   The GET method means retrieve whatever information (in the form of an
644   entity) is identified by the Request-URI. If the Request-URI refers
645   to a data-producing process, it is the produced data which shall be
646   returned as the entity in the response and not the source text of the
647   process, unless that text happens to be the output of the process.
648</t>
649<t>
650   The semantics of the GET method change to a "conditional GET" if the
651   request message includes an If-Modified-Since, If-Unmodified-Since,
652   If-Match, If-None-Match, or If-Range header field. A conditional GET
653   method requests that the entity be transferred only under the
654   circumstances described by the conditional header field(s). The
655   conditional GET method is intended to reduce unnecessary network
656   usage by allowing cached entities to be refreshed without requiring
657   multiple requests or transferring data already held by the client.
658</t>
659<t>
660   The semantics of the GET method change to a "partial GET" if the
661   request message includes a Range header field. A partial GET requests
662   that only part of the entity be transferred, as described in &header-range;.
663   The partial GET method is intended to reduce unnecessary
664   network usage by allowing partially-retrieved entities to be
665   completed without transferring data already held by the client.
666</t>
667<t>
668   The response to a GET request is cacheable if and only if it meets
669   the requirements for HTTP caching described in &caching;.
670</t>
671<t>
672   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
673</t>
674</section>
675
676<section title="HEAD" anchor="HEAD">
677  <iref primary="true" item="HEAD method" x:for-anchor=""/>
678  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
679<t>
680   The HEAD method is identical to GET except that the server &MUST-NOT;
681   return a message-body in the response. The metainformation contained
682   in the HTTP headers in response to a HEAD request &SHOULD; be identical
683   to the information sent in response to a GET request. This method can
684   be used for obtaining metainformation about the entity implied by the
685   request without transferring the entity-body itself. This method is
686   often used for testing hypertext links for validity, accessibility,
687   and recent modification.
688</t>
689<t>
690   The response to a HEAD request &MAY; be cacheable in the sense that the
691   information contained in the response &MAY; be used to update a
692   previously cached entity from that resource. If the new field values
693   indicate that the cached entity differs from the current entity (as
694   would be indicated by a change in Content-Length, Content-MD5, ETag
695   or Last-Modified), then the cache &MUST; treat the cache entry as
696   stale.
697</t>
698</section>
699
700<section title="POST" anchor="POST">
701  <iref primary="true" item="POST method" x:for-anchor=""/>
702  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
703<t>
704   The POST method is used to request that the origin server accept the
705   entity enclosed in the request as data to be processed by the resource
706   identified by the Request-URI in the Request-Line. POST is designed
707   to allow a uniform method to cover the following functions:
708  <list style="symbols">
709    <t>
710      Annotation of existing resources;
711    </t>
712    <t>
713        Posting a message to a bulletin board, newsgroup, mailing list,
714        or similar group of articles;
715    </t>
716    <t>
717        Providing a block of data, such as the result of submitting a
718        form, to a data-handling process;
719    </t>
720    <t>
721        Extending a database through an append operation.
722    </t>
723  </list>
724</t>
725<t>
726   The actual function performed by the POST method is determined by the
727   server and is usually dependent on the Request-URI.
728</t>
729<t>
730   The action performed by the POST method might not result in a
731   resource that can be identified by a URI. In this case, either 200
732   (OK) or 204 (No Content) is the appropriate response status,
733   depending on whether or not the response includes an entity that
734   describes the result.
735</t>
736<t>
737   If a resource has been created on the origin server, the response
738   &SHOULD; be 201 (Created) and contain an entity which describes the
739   status of the request and refers to the new resource, and a Location
740   header (see <xref target="header.location"/>).
741</t>
742<t>
743   Responses to this method are not cacheable, unless the response
744   includes appropriate Cache-Control or Expires header fields. However,
745   the 303 (See Other) response can be used to direct the user agent to
746   retrieve a cacheable resource.
747</t>
748<t>
749   POST requests &MUST; obey the message transmission requirements set out
750   in &message-transmission-req;.
751</t>
752<t>
753   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
754</t>
755</section>
756
757<section title="PUT" anchor="PUT">
758  <iref primary="true" item="PUT method" x:for-anchor=""/>
759  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
760<t>
761   The PUT method requests that the enclosed entity be stored under the
762   supplied Request-URI. If the Request-URI refers to an already
763   existing resource, the enclosed entity &SHOULD; be considered as a
764   modified version of the one residing on the origin server. If the
765   Request-URI does not point to an existing resource, and that URI is
766   capable of being defined as a new resource by the requesting user
767   agent, the origin server can create the resource with that URI. If a
768   new resource is created, the origin server &MUST; inform the user agent
769   via the 201 (Created) response. If an existing resource is modified,
770   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
771   to indicate successful completion of the request. If the resource
772   could not be created or modified with the Request-URI, an appropriate
773   error response &SHOULD; be given that reflects the nature of the
774   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
775   (e.g. Content-Range) headers that it does not understand or implement
776   and &MUST; return a 501 (Not Implemented) response in such cases.
777</t>
778<t>
779   If the request passes through a cache and the Request-URI identifies
780   one or more currently cached entities, those entries &SHOULD; be
781   treated as stale. Responses to this method are not cacheable.
782</t>
783<t>
784   The fundamental difference between the POST and PUT requests is
785   reflected in the different meaning of the Request-URI. The URI in a
786   POST request identifies the resource that will handle the enclosed
787   entity. That resource might be a data-accepting process, a gateway to
788   some other protocol, or a separate entity that accepts annotations.
789   In contrast, the URI in a PUT request identifies the entity enclosed
790   with the request -- the user agent knows what URI is intended and the
791   server &MUST-NOT; attempt to apply the request to some other resource.
792   If the server desires that the request be applied to a different URI,
793   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
794   then make its own decision regarding whether or not to redirect the
795   request.
796</t>
797<t>
798   A single resource &MAY; be identified by many different URIs. For
799   example, an article might have a URI for identifying "the current
800   version" which is separate from the URI identifying each particular
801   version. In this case, a PUT request on a general URI might result in
802   several other URIs being defined by the origin server.
803</t>
804<t>
805   HTTP/1.1 does not define how a PUT method affects the state of an
806   origin server.
807</t>
808<t>
809   PUT requests &MUST; obey the message transmission requirements set out
810   in &message-transmission-req;.
811</t>
812<t>
813   Unless otherwise specified for a particular entity-header, the
814   entity-headers in the PUT request &SHOULD; be applied to the resource
815   created or modified by the PUT.
816</t>
817</section>
818
819<section title="DELETE" anchor="DELETE">
820  <iref primary="true" item="DELETE method" x:for-anchor=""/>
821  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
822<t>
823   The DELETE method requests that the origin server delete the resource
824   identified by the Request-URI. This method &MAY; be overridden by human
825   intervention (or other means) on the origin server. The client cannot
826   be guaranteed that the operation has been carried out, even if the
827   status code returned from the origin server indicates that the action
828   has been completed successfully. However, the server &SHOULD-NOT; 
829   indicate success unless, at the time the response is given, it
830   intends to delete the resource or move it to an inaccessible
831   location.
832</t>
833<t>
834   A successful response &SHOULD; be 200 (OK) if the response includes an
835   entity describing the status, 202 (Accepted) if the action has not
836   yet been enacted, or 204 (No Content) if the action has been enacted
837   but the response does not include an entity.
838</t>
839<t>
840   If the request passes through a cache and the Request-URI identifies
841   one or more currently cached entities, those entries &SHOULD; be
842   treated as stale. Responses to this method are not cacheable.
843</t>
844</section>
845
846<section title="TRACE" anchor="TRACE">
847  <iref primary="true" item="TRACE method" x:for-anchor=""/>
848  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
849<t>
850   The TRACE method is used to invoke a remote, application-layer loop-back
851   of the request message. The final recipient of the request
852   &SHOULD; reflect the message received back to the client as the
853   entity-body of a 200 (OK) response. The final recipient is either the
854   origin server or the first proxy or gateway to receive a Max-Forwards
855   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
856   &MUST-NOT; include an entity.
857</t>
858<t>
859   TRACE allows the client to see what is being received at the other
860   end of the request chain and use that data for testing or diagnostic
861   information. The value of the Via header field (&header-via;) is of
862   particular interest, since it acts as a trace of the request chain.
863   Use of the Max-Forwards header field allows the client to limit the
864   length of the request chain, which is useful for testing a chain of
865   proxies forwarding messages in an infinite loop.
866</t>
867<t>
868   If the request is valid, the response &SHOULD; contain the entire
869   request message in the entity-body, with a Content-Type of
870   "message/http". Responses to this method &MUST-NOT; be cached.
871</t>
872</section>
873
874<section title="CONNECT" anchor="CONNECT">
875  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
876  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
877<t>
878   This specification reserves the method name CONNECT for use with a
879   proxy that can dynamically switch to being a tunnel (e.g. SSL
880   tunneling <xref target="Luo1998"/>).
881</t>
882</section>
883</section>
884
885
886<section title="Status Code Definitions" anchor="status.codes">
887<t>
888   Each Status-Code is described below, including a description of which
889   method(s) it can follow and any metainformation required in the
890   response.
891</t>
892
893<section title="Informational 1xx" anchor="status.1xx">
894<t>
895   This class of status code indicates a provisional response,
896   consisting only of the Status-Line and optional headers, and is
897   terminated by an empty line. There are no required headers for this
898   class of status code. Since HTTP/1.0 did not define any 1xx status
899   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
900   except under experimental conditions.
901</t>
902<t>
903   A client &MUST; be prepared to accept one or more 1xx status responses
904   prior to a regular response, even if the client does not expect a 100
905   (Continue) status message. Unexpected 1xx status responses &MAY; be
906   ignored by a user agent.
907</t>
908<t>
909   Proxies &MUST; forward 1xx responses, unless the connection between the
910   proxy and its client has been closed, or unless the proxy itself
911   requested the generation of the 1xx response. (For example, if a
912   proxy adds a "Expect: 100-continue" field when it forwards a request,
913   then it need not forward the corresponding 100 (Continue)
914   response(s).)
915</t>
916
917<section title="100 Continue" anchor="status.100">
918  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
919  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
920<t>
921   The client &SHOULD; continue with its request. This interim response is
922   used to inform the client that the initial part of the request has
923   been received and has not yet been rejected by the server. The client
924   &SHOULD; continue by sending the remainder of the request or, if the
925   request has already been completed, ignore this response. The server
926   &MUST; send a final response after the request has been completed. See
927   &use100; for detailed discussion of the use and handling of this
928   status code.
929</t>
930</section>
931
932<section title="101 Switching Protocols" anchor="status.101">
933  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
934  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
935<t>
936   The server understands and is willing to comply with the client's
937   request, via the Upgrade message header field (&header-upgrade;), for a
938   change in the application protocol being used on this connection. The
939   server will switch protocols to those defined by the response's
940   Upgrade header field immediately after the empty line which
941   terminates the 101 response.
942</t>
943<t>
944   The protocol &SHOULD; be switched only when it is advantageous to do
945   so. For example, switching to a newer version of HTTP is advantageous
946   over older versions, and switching to a real-time, synchronous
947   protocol might be advantageous when delivering resources that use
948   such features.
949</t>
950</section>
951</section>
952
953<section title="Successful 2xx" anchor="status.2xx">
954<t>
955   This class of status code indicates that the client's request was
956   successfully received, understood, and accepted.
957</t>
958
959<section title="200 OK" anchor="status.200">
960  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
961  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
962<t>
963   The request has succeeded. The information returned with the response
964   is dependent on the method used in the request, for example:
965  <list style="hanging">
966    <t hangText="GET">
967          an entity corresponding to the requested resource is sent in
968          the response;
969    </t>
970    <t hangText="HEAD">
971          the entity-header fields corresponding to the requested
972          resource are sent in the response without any message-body;
973    </t>
974    <t hangText="POST">
975      an entity describing or containing the result of the action;
976    </t>
977    <t hangText="TRACE">
978      an entity containing the request message as received by the
979      end server.
980    </t>
981  </list>
982</t>
983</section>
984
985<section title="201 Created" anchor="status.201">
986  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
987  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
988<t>
989   The request has been fulfilled and resulted in a new resource being
990   created. The newly created resource can be referenced by the URI(s)
991   returned in the entity of the response, with the most specific URI
992   for the resource given by a Location header field. The response
993   &SHOULD; include an entity containing a list of resource
994   characteristics and location(s) from which the user or user agent can
995   choose the one most appropriate. The entity format is specified by
996   the media type given in the Content-Type header field. The origin
997   server &MUST; create the resource before returning the 201 status code.
998   If the action cannot be carried out immediately, the server &SHOULD;
999   respond with 202 (Accepted) response instead.
1000</t>
1001<t>
1002   A 201 response &MAY; contain an ETag response header field indicating
1003   the current value of the entity tag for the requested variant just
1004   created, see &header-etag;.
1005</t>
1006</section>
1007
1008<section title="202 Accepted" anchor="status.202">
1009  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1010  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1011<t>
1012   The request has been accepted for processing, but the processing has
1013   not been completed.  The request might or might not eventually be
1014   acted upon, as it might be disallowed when processing actually takes
1015   place. There is no facility for re-sending a status code from an
1016   asynchronous operation such as this.
1017</t>
1018<t>
1019   The 202 response is intentionally non-committal. Its purpose is to
1020   allow a server to accept a request for some other process (perhaps a
1021   batch-oriented process that is only run once per day) without
1022   requiring that the user agent's connection to the server persist
1023   until the process is completed. The entity returned with this
1024   response &SHOULD; include an indication of the request's current status
1025   and either a pointer to a status monitor or some estimate of when the
1026   user can expect the request to be fulfilled.
1027</t>
1028</section>
1029
1030<section title="203 Non-Authoritative Information" anchor="status.203">
1031  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1032  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1033<t>
1034   The returned metainformation in the entity-header is not the
1035   definitive set as available from the origin server, but is gathered
1036   from a local or a third-party copy. The set presented &MAY; be a subset
1037   or superset of the original version. For example, including local
1038   annotation information about the resource might result in a superset
1039   of the metainformation known by the origin server. Use of this
1040   response code is not required and is only appropriate when the
1041   response would otherwise be 200 (OK).
1042</t>
1043</section>
1044
1045<section title="204 No Content" anchor="status.204">
1046  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1047  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1048<t>
1049   The server has fulfilled the request but does not need to return an
1050   entity-body, and might want to return updated metainformation. The
1051   response &MAY; include new or updated metainformation in the form of
1052   entity-headers, which if present &SHOULD; be associated with the
1053   requested variant.
1054</t>
1055<t>
1056   If the client is a user agent, it &SHOULD-NOT;  change its document view
1057   from that which caused the request to be sent. This response is
1058   primarily intended to allow input for actions to take place without
1059   causing a change to the user agent's active document view, although
1060   any new or updated metainformation &SHOULD; be applied to the document
1061   currently in the user agent's active view.
1062</t>
1063<t>
1064   The 204 response &MUST-NOT; include a message-body, and thus is always
1065   terminated by the first empty line after the header fields.
1066</t>
1067</section>
1068
1069<section title="205 Reset Content" anchor="status.205">
1070  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1071  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1072<t>
1073   The server has fulfilled the request and the user agent &SHOULD; reset
1074   the document view which caused the request to be sent. This response
1075   is primarily intended to allow input for actions to take place via
1076   user input, followed by a clearing of the form in which the input is
1077   given so that the user can easily initiate another input action. The
1078   response &MUST-NOT; include an entity.
1079</t>
1080</section>
1081
1082<section title="206 Partial Content" anchor="status.206">
1083  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1084  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1085<t>
1086   The server has fulfilled the partial GET request for the resource
1087   and the enclosed entity is a partial representation as defined in &range;.
1088</t>
1089</section>
1090</section>
1091
1092<section title="Redirection 3xx" anchor="status.3xx">
1093<t>
1094   This class of status code indicates that further action needs to be
1095   taken by the user agent in order to fulfill the request.  The action
1096   required &MAY; be carried out by the user agent without interaction
1097   with the user if and only if the method used in the second request is
1098   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1099   such loops generate network traffic for each redirection.
1100  <list><t>
1101      <x:h>Note:</x:h> previous versions of this specification recommended a
1102      maximum of five redirections. Content developers should be aware
1103      that there might be clients that implement such a fixed
1104      limitation.
1105  </t></list>
1106</t>
1107
1108<section title="300 Multiple Choices" anchor="status.300">
1109  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1110  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1111<t>
1112   The requested resource corresponds to any one of a set of
1113   representations, each with its own specific location, and agent-driven
1114   negotiation information (&content-negotiation;) is being provided so that
1115   the user (or user agent) can select a preferred representation and
1116   redirect its request to that location.
1117</t>
1118<t>
1119   Unless it was a HEAD request, the response &SHOULD; include an entity
1120   containing a list of resource characteristics and location(s) from
1121   which the user or user agent can choose the one most appropriate. The
1122   entity format is specified by the media type given in the Content-Type
1123   header field. Depending upon the format and the capabilities of
1124   the user agent, selection of the most appropriate choice &MAY; be
1125   performed automatically. However, this specification does not define
1126   any standard for such automatic selection.
1127</t>
1128<t>
1129   If the server has a preferred choice of representation, it &SHOULD;
1130   include the specific URI for that representation in the Location
1131   field; user agents &MAY; use the Location field value for automatic
1132   redirection. This response is cacheable unless indicated otherwise.
1133</t>
1134</section>
1135
1136<section title="301 Moved Permanently" anchor="status.301">
1137  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1138  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1139<t>
1140   The requested resource has been assigned a new permanent URI and any
1141   future references to this resource &SHOULD; use one of the returned
1142   URIs.  Clients with link editing capabilities ought to automatically
1143   re-link references to the Request-URI to one or more of the new
1144   references returned by the server, where possible. This response is
1145   cacheable unless indicated otherwise.
1146</t>
1147<t>
1148   The new permanent URI &SHOULD; be given by the Location field in the
1149   response. Unless the request method was HEAD, the entity of the
1150   response &SHOULD; contain a short hypertext note with a hyperlink to
1151   the new URI(s).
1152</t>
1153<t>
1154   If the 301 status code is received in response to a request method
1155   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1156   then the request &MAY; be automatically redirected by the user agent without
1157   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1158   request unless it can be confirmed by the user, since this might
1159   change the conditions under which the request was issued.
1160  <list><t>
1161      <x:h>Note:</x:h> When automatically redirecting a POST request after
1162      receiving a 301 status code, some existing HTTP/1.0 user agents
1163      will erroneously change it into a GET request.
1164  </t></list>
1165</t>
1166</section>
1167
1168<section title="302 Found" anchor="status.302">
1169  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1170  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1171<t>
1172   The requested resource resides temporarily under a different URI.
1173   Since the redirection might be altered on occasion, the client &SHOULD;
1174   continue to use the Request-URI for future requests.  This response
1175   is only cacheable if indicated by a Cache-Control or Expires header
1176   field.
1177</t>
1178<t>
1179   The temporary URI &SHOULD; be given by the Location field in the
1180   response. Unless the request method was HEAD, the entity of the
1181   response &SHOULD; contain a short hypertext note with a hyperlink to
1182   the new URI(s).
1183</t>
1184<t>
1185   If the 302 status code is received in response to a request method
1186   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1187   then the request &MAY; be automatically redirected by the user agent without
1188   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1189   request unless it can be confirmed by the user, since this might
1190   change the conditions under which the request was issued.
1191  <list><t>
1192      <x:h>Note:</x:h> RFC 1945 and RFC 2068 specify that the client is not allowed
1193      to change the method on the redirected request.  However, most
1194      existing user agent implementations treat 302 as if it were a 303
1195      response, performing a GET on the Location field-value regardless
1196      of the original request method. The status codes 303 and 307 have
1197      been added for servers that wish to make unambiguously clear which
1198      kind of reaction is expected of the client.
1199  </t></list>
1200</t>
1201</section>
1202
1203<section title="303 See Other" anchor="status.303">
1204  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1205  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1206<t>
1207   The response to the request can be found under a different URI and
1208   &SHOULD; be retrieved using a GET method on that resource. This method
1209   exists primarily to allow the output of a POST-activated script to
1210   redirect the user agent to a selected resource. The new URI is not a
1211   substitute reference for the originally requested resource. The 303
1212   response &MUST-NOT; be cached, but the response to the second
1213   (redirected) request might be cacheable.
1214</t>
1215<t>
1216   The different URI &SHOULD; be given by the Location field in the
1217   response. Unless the request method was HEAD, the entity of the
1218   response &SHOULD; contain a short hypertext note with a hyperlink to
1219   the new URI(s).
1220  <list><t>
1221      <x:h>Note:</x:h> Many pre-HTTP/1.1 user agents do not understand the 303
1222      status. When interoperability with such clients is a concern, the
1223      302 status code may be used instead, since most user agents react
1224      to a 302 response as described here for 303.
1225  </t></list>
1226</t>
1227</section>
1228
1229<section title="304 Not Modified" anchor="status.304">
1230  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1231  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1232<t>
1233   The response to the request has not been modified since the conditions
1234   indicated by the client's conditional GET request, as defined in &conditional;.
1235</t>
1236</section>
1237
1238<section title="305 Use Proxy" anchor="status.305">
1239  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1240  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1241<t>
1242   The requested resource &MUST; be accessed through the proxy given by
1243   the Location field. The Location field gives the URI of the proxy.
1244   The recipient is expected to repeat this single request via the
1245   proxy. 305 responses &MUST; only be generated by origin servers.
1246  <list><t>
1247      <x:h>Note:</x:h> RFC 2068 was not clear that 305 was intended to redirect a
1248      single request, and to be generated by origin servers only.  Not
1249      observing these limitations has significant security consequences.
1250  </t></list>
1251</t>
1252</section>
1253
1254<section title="306 (Unused)" anchor="status.306">
1255  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1256  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1257<t>
1258   The 306 status code was used in a previous version of the
1259   specification, is no longer used, and the code is reserved.
1260</t>
1261</section>
1262
1263<section title="307 Temporary Redirect" anchor="status.307">
1264  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1265  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1266<t>
1267   The requested resource resides temporarily under a different URI.
1268   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1269   continue to use the Request-URI for future requests.  This response
1270   is only cacheable if indicated by a Cache-Control or Expires header
1271   field.
1272</t>
1273<t>
1274   The temporary URI &SHOULD; be given by the Location field in the
1275   response. Unless the request method was HEAD, the entity of the
1276   response &SHOULD; contain a short hypertext note with a hyperlink to
1277   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1278   understand the 307 status. Therefore, the note &SHOULD; contain the
1279   information necessary for a user to repeat the original request on
1280   the new URI.
1281</t>
1282<t>
1283   If the 307 status code is received in response to a request method
1284   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1285   then the request &MAY; be automatically redirected by the user agent without
1286   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1287   request unless it can be confirmed by the user, since this might
1288   change the conditions under which the request was issued.
1289</t>
1290</section>
1291</section>
1292
1293<section title="Client Error 4xx" anchor="status.4xx">
1294<t>
1295   The 4xx class of status code is intended for cases in which the
1296   client seems to have erred. Except when responding to a HEAD request,
1297   the server &SHOULD; include an entity containing an explanation of the
1298   error situation, and whether it is a temporary or permanent
1299   condition. These status codes are applicable to any request method.
1300   User agents &SHOULD; display any included entity to the user.
1301</t>
1302<t>
1303   If the client is sending data, a server implementation using TCP
1304   &SHOULD; be careful to ensure that the client acknowledges receipt of
1305   the packet(s) containing the response, before the server closes the
1306   input connection. If the client continues sending data to the server
1307   after the close, the server's TCP stack will send a reset packet to
1308   the client, which may erase the client's unacknowledged input buffers
1309   before they can be read and interpreted by the HTTP application.
1310</t>
1311
1312<section title="400 Bad Request" anchor="status.400">
1313  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1314  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1315<t>
1316   The request could not be understood by the server due to malformed
1317   syntax. The client &SHOULD-NOT;  repeat the request without
1318   modifications.
1319</t>
1320</section>
1321
1322<section title="401 Unauthorized" anchor="status.401">
1323  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1324  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1325<t>
1326   The request requires user authentication (see &auth;).
1327</t>
1328</section>
1329
1330<section title="402 Payment Required" anchor="status.402">
1331  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1332  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1333<t>
1334   This code is reserved for future use.
1335</t>
1336</section>
1337
1338<section title="403 Forbidden" anchor="status.403">
1339  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1340  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1341<t>
1342   The server understood the request, but is refusing to fulfill it.
1343   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1344   If the request method was not HEAD and the server wishes to make
1345   public why the request has not been fulfilled, it &SHOULD; describe the
1346   reason for the refusal in the entity.  If the server does not wish to
1347   make this information available to the client, the status code 404
1348   (Not Found) can be used instead.
1349</t>
1350</section>
1351
1352<section title="404 Not Found" anchor="status.404">
1353  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1354  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1355<t>
1356   The server has not found anything matching the Request-URI. No
1357   indication is given of whether the condition is temporary or
1358   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1359   knows, through some internally configurable mechanism, that an old
1360   resource is permanently unavailable and has no forwarding address.
1361   This status code is commonly used when the server does not wish to
1362   reveal exactly why the request has been refused, or when no other
1363   response is applicable.
1364</t>
1365</section>
1366
1367<section title="405 Method Not Allowed" anchor="status.405">
1368  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1369  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1370<t>
1371   The method specified in the Request-Line is not allowed for the
1372   resource identified by the Request-URI. The response &MUST; include an
1373   Allow header containing a list of valid methods for the requested
1374   resource.
1375</t>
1376</section>
1377
1378<section title="406 Not Acceptable" anchor="status.406">
1379  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1380  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1381<t>
1382   The resource identified by the request is only capable of generating
1383   response entities which have content characteristics not acceptable
1384   according to the accept headers sent in the request.
1385</t>
1386<t>
1387   Unless it was a HEAD request, the response &SHOULD; include an entity
1388   containing a list of available entity characteristics and location(s)
1389   from which the user or user agent can choose the one most
1390   appropriate. The entity format is specified by the media type given
1391   in the Content-Type header field. Depending upon the format and the
1392   capabilities of the user agent, selection of the most appropriate
1393   choice &MAY; be performed automatically. However, this specification
1394   does not define any standard for such automatic selection.
1395  <list><t>
1396      <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1397      not acceptable according to the accept headers sent in the
1398      request. In some cases, this may even be preferable to sending a
1399      406 response. User agents are encouraged to inspect the headers of
1400      an incoming response to determine if it is acceptable.
1401  </t></list>
1402</t>
1403<t>
1404   If the response could be unacceptable, a user agent &SHOULD;
1405   temporarily stop receipt of more data and query the user for a
1406   decision on further actions.
1407</t>
1408</section>
1409
1410<section title="407 Proxy Authentication Required" anchor="status.407">
1411  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1412  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1413<t>
1414   This code is similar to 401 (Unauthorized), but indicates that the
1415   client must first authenticate itself with the proxy (see &auth;).
1416</t>
1417</section>
1418
1419<section title="408 Request Timeout" anchor="status.408">
1420  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1421  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1422<t>
1423   The client did not produce a request within the time that the server
1424   was prepared to wait. The client &MAY; repeat the request without
1425   modifications at any later time.
1426</t>
1427</section>
1428
1429<section title="409 Conflict" anchor="status.409">
1430  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1431  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1432<t>
1433   The request could not be completed due to a conflict with the current
1434   state of the resource. This code is only allowed in situations where
1435   it is expected that the user might be able to resolve the conflict
1436   and resubmit the request. The response body &SHOULD; include enough
1437   information for the user to recognize the source of the conflict.
1438   Ideally, the response entity would include enough information for the
1439   user or user agent to fix the problem; however, that might not be
1440   possible and is not required.
1441</t>
1442<t>
1443   Conflicts are most likely to occur in response to a PUT request. For
1444   example, if versioning were being used and the entity being PUT
1445   included changes to a resource which conflict with those made by an
1446   earlier (third-party) request, the server might use the 409 response
1447   to indicate that it can't complete the request. In this case, the
1448   response entity would likely contain a list of the differences
1449   between the two versions in a format defined by the response
1450   Content-Type.
1451</t>
1452</section>
1453
1454<section title="410 Gone" anchor="status.410">
1455  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1456  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1457<t>
1458   The requested resource is no longer available at the server and no
1459   forwarding address is known. This condition is expected to be
1460   considered permanent. Clients with link editing capabilities &SHOULD;
1461   delete references to the Request-URI after user approval. If the
1462   server does not know, or has no facility to determine, whether or not
1463   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1464   used instead. This response is cacheable unless indicated otherwise.
1465</t>
1466<t>
1467   The 410 response is primarily intended to assist the task of web
1468   maintenance by notifying the recipient that the resource is
1469   intentionally unavailable and that the server owners desire that
1470   remote links to that resource be removed. Such an event is common for
1471   limited-time, promotional services and for resources belonging to
1472   individuals no longer working at the server's site. It is not
1473   necessary to mark all permanently unavailable resources as "gone" or
1474   to keep the mark for any length of time -- that is left to the
1475   discretion of the server owner.
1476</t>
1477</section>
1478
1479<section title="411 Length Required" anchor="status.411">
1480  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1481  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1482<t>
1483   The server refuses to accept the request without a defined Content-Length.
1484   The client &MAY; repeat the request if it adds a valid
1485   Content-Length header field containing the length of the message-body
1486   in the request message.
1487</t>
1488</section>
1489
1490<section title="412 Precondition Failed" anchor="status.412">
1491  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1492  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1493<t>
1494   The precondition given in one or more of the request-header fields
1495   evaluated to false when it was tested on the server, as defined in
1496   &conditional;.
1497</t>
1498</section>
1499
1500<section title="413 Request Entity Too Large" anchor="status.413">
1501  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1502  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1503<t>
1504   The server is refusing to process a request because the request
1505   entity is larger than the server is willing or able to process. The
1506   server &MAY; close the connection to prevent the client from continuing
1507   the request.
1508</t>
1509<t>
1510   If the condition is temporary, the server &SHOULD; include a Retry-After
1511   header field to indicate that it is temporary and after what
1512   time the client &MAY; try again.
1513</t>
1514</section>
1515
1516<section title="414 Request-URI Too Long" anchor="status.414">
1517  <iref primary="true" item="414 Request-URI Too Long (status code)" x:for-anchor=""/>
1518  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long" x:for-anchor=""/>
1519<t>
1520   The server is refusing to service the request because the Request-URI
1521   is longer than the server is willing to interpret. This rare
1522   condition is only likely to occur when a client has improperly
1523   converted a POST request to a GET request with long query
1524   information, when the client has descended into a URI "black hole" of
1525   redirection (e.g., a redirected URI prefix that points to a suffix of
1526   itself), or when the server is under attack by a client attempting to
1527   exploit security holes present in some servers using fixed-length
1528   buffers for reading or manipulating the Request-URI.
1529</t>
1530</section>
1531
1532<section title="415 Unsupported Media Type" anchor="status.415">
1533  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1534  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1535<t>
1536   The server is refusing to service the request because the entity of
1537   the request is in a format not supported by the requested resource
1538   for the requested method.
1539</t>
1540</section>
1541
1542<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1543  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1544  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1545<t>
1546   The request included a Range request-header field (&header-range;) and none of
1547   the range-specifier values in this field overlap the current extent
1548   of the selected resource.
1549</t>
1550</section>
1551
1552<section title="417 Expectation Failed" anchor="status.417">
1553  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1554  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1555<t>
1556   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1557   could not be met by this server, or, if the server is a proxy,
1558   the server has unambiguous evidence that the request could not be met
1559   by the next-hop server.
1560</t>
1561</section>
1562</section>
1563
1564<section title="Server Error 5xx" anchor="status.5xx">
1565<t>
1566   Response status codes beginning with the digit "5" indicate cases in
1567   which the server is aware that it has erred or is incapable of
1568   performing the request. Except when responding to a HEAD request, the
1569   server &SHOULD; include an entity containing an explanation of the
1570   error situation, and whether it is a temporary or permanent
1571   condition. User agents &SHOULD; display any included entity to the
1572   user. These response codes are applicable to any request method.
1573</t>
1574
1575<section title="500 Internal Server Error" anchor="status.500">
1576  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1577  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1578<t>
1579   The server encountered an unexpected condition which prevented it
1580   from fulfilling the request.
1581</t>
1582</section>
1583
1584<section title="501 Not Implemented" anchor="status.501">
1585  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1586  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1587<t>
1588   The server does not support the functionality required to fulfill the
1589   request. This is the appropriate response when the server does not
1590   recognize the request method and is not capable of supporting it for
1591   any resource.
1592</t>
1593</section>
1594
1595<section title="502 Bad Gateway" anchor="status.502">
1596  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1597  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1598<t>
1599   The server, while acting as a gateway or proxy, received an invalid
1600   response from the upstream server it accessed in attempting to
1601   fulfill the request.
1602</t>
1603</section>
1604
1605<section title="503 Service Unavailable" anchor="status.503">
1606  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1607  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1608<t>
1609   The server is currently unable to handle the request due to a
1610   temporary overloading or maintenance of the server. The implication
1611   is that this is a temporary condition which will be alleviated after
1612   some delay. If known, the length of the delay &MAY; be indicated in a
1613   Retry-After header. If no Retry-After is given, the client &SHOULD;
1614   handle the response as it would for a 500 response.
1615  <list><t>
1616      <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1617      server must use it when becoming overloaded. Some servers may wish
1618      to simply refuse the connection.
1619  </t></list>
1620</t>
1621</section>
1622
1623<section title="504 Gateway Timeout" anchor="status.504">
1624  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1625  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1626<t>
1627   The server, while acting as a gateway or proxy, did not receive a
1628   timely response from the upstream server specified by the URI (e.g.
1629   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1630   to access in attempting to complete the request.
1631  <list><t>
1632      <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1633      return 400 or 500 when DNS lookups time out.
1634  </t></list>
1635</t>
1636</section>
1637
1638<section title="505 HTTP Version Not Supported" anchor="status.505">
1639  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1640  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1641<t>
1642   The server does not support, or refuses to support, the HTTP protocol
1643   version that was used in the request message. The server is
1644   indicating that it is unable or unwilling to complete the request
1645   using the same major version as the client, as described in &http-version;,
1646   other than with this error message. The response &SHOULD; contain
1647   an entity describing why that version is not supported and what other
1648   protocols are supported by that server.
1649</t>
1650
1651</section>
1652</section>
1653</section>
1654
1655
1656<section title="Header Field Definitions" anchor="header.fields">
1657<t>
1658   This section defines the syntax and semantics of all standard
1659   HTTP/1.1 header fields. For entity-header fields, both sender and
1660   recipient refer to either the client or the server, depending on who
1661   sends and who receives the entity.
1662</t>
1663
1664<section title="Allow" anchor="header.allow">
1665  <iref primary="true" item="Allow header" x:for-anchor=""/>
1666  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1667<t>
1668      The Allow entity-header field lists the set of methods supported
1669      by the resource identified by the Request-URI. The purpose of this
1670      field is strictly to inform the recipient of valid methods
1671      associated with the resource. An Allow header field &MUST; be
1672      present in a 405 (Method Not Allowed) response.
1673</t>
1674<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
1675       Allow   = "Allow" ":" #Method
1676</artwork></figure>
1677<t>
1678      Example of use:
1679</t>
1680<figure><artwork type="example">
1681       Allow: GET, HEAD, PUT
1682</artwork></figure>
1683<t>
1684      This field cannot prevent a client from trying other methods.
1685      However, the indications given by the Allow header field value
1686      &SHOULD; be followed. The actual set of allowed methods is defined
1687      by the origin server at the time of each request.
1688</t>
1689<t>
1690      The Allow header field &MAY; be provided with a PUT request to
1691      recommend the methods to be supported by the new or modified
1692      resource. The server is not required to support these methods and
1693      &SHOULD; include an Allow header in the response giving the actual
1694      supported methods.
1695</t>
1696<t>
1697      A proxy &MUST-NOT; modify the Allow header field even if it does not
1698      understand all the methods specified, since the user agent might
1699      have other means of communicating with the origin server.
1700</t>
1701</section>
1702
1703<section title="Expect" anchor="header.expect">
1704  <iref primary="true" item="Expect header" x:for-anchor=""/>
1705  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1706<t>
1707   The Expect request-header field is used to indicate that particular
1708   server behaviors are required by the client.
1709</t>
1710<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Expect"/><iref primary="true" item="Grammar" subitem="expectation"/><iref primary="true" item="Grammar" subitem="expectation-extension"/><iref primary="true" item="Grammar" subitem="expect-params"/>
1711   Expect       =  "Expect" ":" 1#expectation
1712
1713   expectation  =  "100-continue" | expectation-extension
1714   expectation-extension =  token [ "=" ( token | quoted-string )
1715                            *expect-params ]
1716   expect-params =  ";" token [ "=" ( token | quoted-string ) ]
1717</artwork></figure>
1718<t>
1719   A server that does not understand or is unable to comply with any of
1720   the expectation values in the Expect field of a request &MUST; respond
1721   with appropriate error status. The server &MUST; respond with a 417
1722   (Expectation Failed) status if any of the expectations cannot be met
1723   or, if there are other problems with the request, some other 4xx
1724   status.
1725</t>
1726<t>
1727   This header field is defined with extensible syntax to allow for
1728   future extensions. If a server receives a request containing an
1729   Expect field that includes an expectation-extension that it does not
1730   support, it &MUST; respond with a 417 (Expectation Failed) status.
1731</t>
1732<t>
1733   Comparison of expectation values is case-insensitive for unquoted
1734   tokens (including the 100-continue token), and is case-sensitive for
1735   quoted-string expectation-extensions.
1736</t>
1737<t>
1738   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1739   return a 417 (Expectation Failed) status if it receives a request
1740   with an expectation that it cannot meet. However, the Expect
1741   request-header itself is end-to-end; it &MUST; be forwarded if the
1742   request is forwarded.
1743</t>
1744<t>
1745   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1746   Expect header.
1747</t>
1748<t>
1749   See &use100; for the use of the 100 (continue) status.
1750</t>
1751</section>
1752
1753<section title="From" anchor="header.from">
1754  <iref primary="true" item="From header" x:for-anchor=""/>
1755  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1756<t>
1757   The From request-header field, if given, &SHOULD; contain an Internet
1758   e-mail address for the human user who controls the requesting user
1759   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1760   in RFC 822 <xref target="RFC822"/> as updated by RFC 1123 <xref target="RFC1123"/>:
1761</t>
1762<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
1763    From   = "From" ":" mailbox
1764</artwork></figure>
1765<t>
1766   An example is:
1767</t>
1768<figure><artwork type="example">
1769    From: webmaster@example.org
1770</artwork></figure>
1771<t>
1772   This header field &MAY; be used for logging purposes and as a means for
1773   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
1774   be used as an insecure form of access protection. The interpretation
1775   of this field is that the request is being performed on behalf of the
1776   person given, who accepts responsibility for the method performed. In
1777   particular, robot agents &SHOULD; include this header so that the
1778   person responsible for running the robot can be contacted if problems
1779   occur on the receiving end.
1780</t>
1781<t>
1782   The Internet e-mail address in this field &MAY; be separate from the
1783   Internet host which issued the request. For example, when a request
1784   is passed through a proxy the original issuer's address &SHOULD; be
1785   used.
1786</t>
1787<t>
1788   The client &SHOULD-NOT;  send the From header field without the user's
1789   approval, as it might conflict with the user's privacy interests or
1790   their site's security policy. It is strongly recommended that the
1791   user be able to disable, enable, and modify the value of this field
1792   at any time prior to a request.
1793</t>
1794</section>
1795
1796<section title="Location" anchor="header.location">
1797  <iref primary="true" item="Location header" x:for-anchor=""/>
1798  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1799<t>
1800   The Location response-header field is used to redirect the recipient
1801   to a location other than the Request-URI for completion of the
1802   request or identification of a new resource. For 201 (Created)
1803   responses, the Location is that of the new resource which was created
1804   by the request. For 3xx responses, the location &SHOULD; indicate the
1805   server's preferred URI for automatic redirection to the resource. The
1806   field value consists of a single absolute URI.
1807</t>
1808<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
1809    Location       = "Location" ":" absoluteURI [ "#" fragment ]
1810</artwork></figure>
1811<t>
1812   An example is:
1813</t>
1814<figure><artwork type="example">
1815    Location: http://www.example.org/pub/WWW/People.html
1816</artwork></figure>
1817<t>
1818  <list><t>
1819      <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1820      from Location in that the Content-Location identifies the original
1821      location of the entity enclosed in the request. It is therefore
1822      possible for a response to contain header fields for both Location
1823      and Content-Location.
1824  </t></list>
1825</t>
1826</section>
1827
1828<section title="Max-Forwards" anchor="header.max-forwards">
1829  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
1830  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
1831<t>
1832   The Max-Forwards request-header field provides a mechanism with the
1833   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1834   number of proxies or gateways that can forward the request to the
1835   next inbound server. This can be useful when the client is attempting
1836   to trace a request chain which appears to be failing or looping in
1837   mid-chain.
1838</t>
1839<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
1840    Max-Forwards   = "Max-Forwards" ":" 1*DIGIT
1841</artwork></figure>
1842<t>
1843   The Max-Forwards value is a decimal integer indicating the remaining
1844   number of times this request message may be forwarded.
1845</t>
1846<t>
1847   Each proxy or gateway recipient of a TRACE or OPTIONS request
1848   containing a Max-Forwards header field &MUST; check and update its
1849   value prior to forwarding the request. If the received value is zero
1850   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
1851   respond as the final recipient. If the received Max-Forwards value is
1852   greater than zero, then the forwarded message &MUST; contain an updated
1853   Max-Forwards field with a value decremented by one (1).
1854</t>
1855<t>
1856   The Max-Forwards header field &MAY; be ignored for all other methods
1857   defined by this specification and for any extension methods for which
1858   it is not explicitly referred to as part of that method definition.
1859</t>
1860</section>
1861
1862<section title="Referer" anchor="header.referer">
1863  <iref primary="true" item="Referer header" x:for-anchor=""/>
1864  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
1865<t>
1866   The Referer[sic] request-header field allows the client to specify,
1867   for the server's benefit, the address (URI) of the resource from
1868   which the Request-URI was obtained (the "referrer", although the
1869   header field is misspelled.) The Referer request-header allows a
1870   server to generate lists of back-links to resources for interest,
1871   logging, optimized caching, etc. It also allows obsolete or mistyped
1872   links to be traced for maintenance. The Referer field &MUST-NOT; be
1873   sent if the Request-URI was obtained from a source that does not have
1874   its own URI, such as input from the user keyboard.
1875</t>
1876<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
1877    Referer        = "Referer" ":" ( absoluteURI | relativeURI )
1878</artwork></figure>
1879<t>
1880   Example:
1881</t>
1882<figure><artwork type="example">
1883    Referer: http://www.example.org/hypertext/Overview.html
1884</artwork></figure>
1885<t>
1886   If the field value is a relative URI, it &SHOULD; be interpreted
1887   relative to the Request-URI. The URI &MUST-NOT; include a fragment. See
1888   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
1889</t>
1890</section>
1891
1892<section title="Retry-After" anchor="header.retry-after">
1893  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
1894  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
1895<t>
1896   The Retry-After response-header field can be used with a 503 (Service
1897   Unavailable) response to indicate how long the service is expected to
1898   be unavailable to the requesting client. This field &MAY; also be used
1899   with any 3xx (Redirection) response to indicate the minimum time the
1900   user-agent is asked wait before issuing the redirected request. The
1901   value of this field can be either an HTTP-date or an integer number
1902   of seconds (in decimal) after the time of the response.
1903</t>
1904<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
1905    Retry-After  = "Retry-After" ":" ( HTTP-date | delta-seconds )
1906</artwork></figure>
1907<t>
1908   Two examples of its use are
1909</t>
1910<figure><artwork type="example">
1911    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
1912    Retry-After: 120
1913</artwork></figure>
1914<t>
1915   In the latter example, the delay is 2 minutes.
1916</t>
1917</section>
1918
1919<section title="Server" anchor="header.server">
1920  <iref primary="true" item="Server header" x:for-anchor=""/>
1921  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
1922<t>
1923   The Server response-header field contains information about the
1924   software used by the origin server to handle the request. The field
1925   can contain multiple product tokens (<xref target="product.tokens"/>) and comments
1926   identifying the server and any significant subproducts. The product
1927   tokens are listed in order of their significance for identifying the
1928   application.
1929</t>
1930<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
1931    Server         = "Server" ":" 1*( product | comment )
1932</artwork></figure>
1933<t>
1934   Example:
1935</t>
1936<figure><artwork type="example">
1937    Server: CERN/3.0 libwww/2.17
1938</artwork></figure>
1939<t>
1940   If the response is being forwarded through a proxy, the proxy
1941   application &MUST-NOT; modify the Server response-header. Instead, it
1942   &MUST; include a Via field (as described in &header-via;).
1943  <list><t>
1944      <x:h>Note:</x:h> Revealing the specific software version of the server might
1945      allow the server machine to become more vulnerable to attacks
1946      against software that is known to contain security holes. Server
1947      implementors are encouraged to make this field a configurable
1948      option.
1949  </t></list>
1950</t>
1951</section>
1952
1953<section title="User-Agent" anchor="header.user-agent">
1954  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
1955  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
1956<t>
1957   The User-Agent request-header field contains information about the
1958   user agent originating the request. This is for statistical purposes,
1959   the tracing of protocol violations, and automated recognition of user
1960   agents for the sake of tailoring responses to avoid particular user
1961   agent limitations. User agents &SHOULD; include this field with
1962   requests. The field can contain multiple product tokens (<xref target="product.tokens"/>)
1963   and comments identifying the agent and any subproducts which form a
1964   significant part of the user agent. By convention, the product tokens
1965   are listed in order of their significance for identifying the
1966   application.
1967</t>
1968<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
1969    User-Agent     = "User-Agent" ":" 1*( product | comment )
1970</artwork></figure>
1971<t>
1972   Example:
1973</t>
1974<figure><artwork type="example">
1975    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1976</artwork></figure>
1977</section>
1978
1979</section>
1980
1981<section title="IANA Considerations" anchor="IANA.considerations">
1982<t>
1983   TBD.
1984</t>
1985</section>
1986
1987<section title="Security Considerations" anchor="security.considerations">
1988<t>
1989   This section is meant to inform application developers, information
1990   providers, and users of the security limitations in HTTP/1.1 as
1991   described by this document. The discussion does not include
1992   definitive solutions to the problems revealed, though it does make
1993   some suggestions for reducing security risks.
1994</t>
1995
1996<section title="Transfer of Sensitive Information" anchor="security.sensitive">
1997<t>
1998   Like any generic data transfer protocol, HTTP cannot regulate the
1999   content of the data that is transferred, nor is there any a priori
2000   method of determining the sensitivity of any particular piece of
2001   information within the context of any given request. Therefore,
2002   applications &SHOULD; supply as much control over this information as
2003   possible to the provider of that information. Four header fields are
2004   worth special mention in this context: Server, Via, Referer and From.
2005</t>
2006<t>
2007   Revealing the specific software version of the server might allow the
2008   server machine to become more vulnerable to attacks against software
2009   that is known to contain security holes. Implementors &SHOULD; make the
2010   Server header field a configurable option.
2011</t>
2012<t>
2013   Proxies which serve as a portal through a network firewall &SHOULD;
2014   take special precautions regarding the transfer of header information
2015   that identifies the hosts behind the firewall. In particular, they
2016   &SHOULD; remove, or replace with sanitized versions, any Via fields
2017   generated behind the firewall.
2018</t>
2019<t>
2020   The Referer header allows reading patterns to be studied and reverse
2021   links drawn. Although it can be very useful, its power can be abused
2022   if user details are not separated from the information contained in
2023   the Referer. Even when the personal information has been removed, the
2024   Referer header might indicate a private document's URI whose
2025   publication would be inappropriate.
2026</t>
2027<t>
2028   The information sent in the From field might conflict with the user's
2029   privacy interests or their site's security policy, and hence it
2030   &SHOULD-NOT;  be transmitted without the user being able to disable,
2031   enable, and modify the contents of the field. The user &MUST; be able
2032   to set the contents of this field within a user preference or
2033   application defaults configuration.
2034</t>
2035<t>
2036   We suggest, though do not require, that a convenient toggle interface
2037   be provided for the user to enable or disable the sending of From and
2038   Referer information.
2039</t>
2040<t>
2041   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2042   fields can sometimes be used to determine that a specific client or
2043   server have a particular security hole which might be exploited.
2044   Unfortunately, this same information is often used for other valuable
2045   purposes for which HTTP currently has no better mechanism.
2046</t>
2047</section>
2048
2049<section title="Encoding Sensitive Information in URI's" anchor="encoding.sensitive.information.in.uris">
2050<t>
2051   Because the source of a link might be private information or might
2052   reveal an otherwise private information source, it is strongly
2053   recommended that the user be able to select whether or not the
2054   Referer field is sent. For example, a browser client could have a
2055   toggle switch for browsing openly/anonymously, which would
2056   respectively enable/disable the sending of Referer and From
2057   information.
2058</t>
2059<t>
2060   Clients &SHOULD-NOT;  include a Referer header field in a (non-secure)
2061   HTTP request if the referring page was transferred with a secure
2062   protocol.
2063</t>
2064<t>
2065   Authors of services which use the HTTP protocol &SHOULD-NOT;  use GET
2066   based forms for the submission of sensitive data, because this will
2067   cause this data to be encoded in the Request-URI. Many existing
2068   servers, proxies, and user agents will log the request URI in some
2069   place where it might be visible to third parties. Servers can use
2070   POST-based form submission instead
2071</t>
2072</section>
2073
2074<section title="Location Headers and Spoofing" anchor="location.spoofing">
2075<t>
2076   If a single server supports multiple organizations that do not trust
2077   one another, then it &MUST; check the values of Location and Content-Location
2078   headers in responses that are generated under control of
2079   said organizations to make sure that they do not attempt to
2080   invalidate resources over which they have no authority.
2081</t>
2082</section>
2083
2084</section>
2085
2086<section title="Acknowledgments" anchor="ack">
2087</section>
2088</middle>
2089<back>
2090<references>
2091
2092<reference anchor="Part1">
2093   <front>
2094      <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2095      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2096         <organization abbrev="Day Software">Day Software</organization>
2097         <address><email>fielding@gbiv.com</email></address>
2098      </author>
2099      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2100         <organization>One Laptop per Child</organization>
2101         <address><email>jg@laptop.org</email></address>
2102      </author>
2103      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2104         <organization abbrev="HP">Hewlett-Packard Company</organization>
2105         <address><email>JeffMogul@acm.org</email></address>
2106      </author>
2107      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2108         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2109         <address><email>henrikn@microsoft.com</email></address>
2110      </author>
2111      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2112         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2113         <address><email>LMM@acm.org</email></address>
2114      </author>
2115      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2116         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2117         <address><email>paulle@microsoft.com</email></address>
2118      </author>
2119      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2120         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2121         <address><email>timbl@w3.org</email></address>
2122      </author>
2123      <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2124         <organization abbrev="W3C">World Wide Web Consortium</organization>
2125         <address><email>ylafon@w3.org</email></address>
2126      </author>
2127      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2128         <organization abbrev="greenbytes">greenbytes GmbH</organization>
2129         <address><email>julian.reschke@greenbytes.de</email></address>
2130      </author>
2131      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2132   </front>
2133   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
2134   <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2135</reference>
2136
2137<reference anchor="Part3">
2138   <front>
2139      <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2140      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2141         <organization abbrev="Day Software">Day Software</organization>
2142         <address><email>fielding@gbiv.com</email></address>
2143      </author>
2144      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2145         <organization>One Laptop per Child</organization>
2146         <address><email>jg@laptop.org</email></address>
2147      </author>
2148      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2149         <organization abbrev="HP">Hewlett-Packard Company</organization>
2150         <address><email>JeffMogul@acm.org</email></address>
2151      </author>
2152      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2153         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2154         <address><email>henrikn@microsoft.com</email></address>
2155      </author>
2156      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2157         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2158         <address><email>LMM@acm.org</email></address>
2159      </author>
2160      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2161         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2162         <address><email>paulle@microsoft.com</email></address>
2163      </author>
2164      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2165         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2166         <address><email>timbl@w3.org</email></address>
2167      </author>
2168      <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2169         <organization abbrev="W3C">World Wide Web Consortium</organization>
2170         <address><email>ylafon@w3.org</email></address>
2171      </author>
2172      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2173         <organization abbrev="greenbytes">greenbytes GmbH</organization>
2174         <address><email>julian.reschke@greenbytes.de</email></address>
2175      </author>
2176      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2177   </front>
2178   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
2179   <x:source href="p3-payload.xml" basename="p3-payload"/>
2180</reference>
2181
2182<reference anchor="Part4">
2183   <front>
2184      <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2185      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2186         <organization abbrev="Day Software">Day Software</organization>
2187         <address><email>fielding@gbiv.com</email></address>
2188      </author>
2189      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2190         <organization>One Laptop per Child</organization>
2191         <address><email>jg@laptop.org</email></address>
2192      </author>
2193      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2194         <organization abbrev="HP">Hewlett-Packard Company</organization>
2195         <address><email>JeffMogul@acm.org</email></address>
2196      </author>
2197      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2198         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2199         <address><email>henrikn@microsoft.com</email></address>
2200      </author>
2201      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2202         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2203         <address><email>LMM@acm.org</email></address>
2204      </author>
2205      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2206         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2207         <address><email>paulle@microsoft.com</email></address>
2208      </author>
2209      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2210         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2211         <address><email>timbl@w3.org</email></address>
2212      </author>
2213      <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2214         <organization abbrev="W3C">World Wide Web Consortium</organization>
2215         <address><email>ylafon@w3.org</email></address>
2216      </author>
2217      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2218         <organization abbrev="greenbytes">greenbytes GmbH</organization>
2219         <address><email>julian.reschke@greenbytes.de</email></address>
2220      </author>
2221      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2222   </front>
2223   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
2224   <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2225</reference>
2226
2227<reference anchor="Part5">
2228   <front>
2229      <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2230      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2231         <organization abbrev="Day Software">Day Software</organization>
2232         <address><email>fielding@gbiv.com</email></address>
2233      </author>
2234      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2235         <organization>One Laptop per Child</organization>
2236         <address><email>jg@laptop.org</email></address>
2237      </author>
2238      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2239         <organization abbrev="HP">Hewlett-Packard Company</organization>
2240         <address><email>JeffMogul@acm.org</email></address>
2241      </author>
2242      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2243         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2244         <address><email>henrikn@microsoft.com</email></address>
2245      </author>
2246      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2247         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2248         <address><email>LMM@acm.org</email></address>
2249      </author>
2250      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2251         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2252         <address><email>paulle@microsoft.com</email></address>
2253      </author>
2254      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2255         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2256         <address><email>timbl@w3.org</email></address>
2257      </author>
2258      <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2259         <organization abbrev="W3C">World Wide Web Consortium</organization>
2260         <address><email>ylafon@w3.org</email></address>
2261      </author>
2262      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2263         <organization abbrev="greenbytes">greenbytes GmbH</organization>
2264         <address><email>julian.reschke@greenbytes.de</email></address>
2265      </author>
2266      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2267   </front>
2268   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
2269   <x:source href="p5-range.xml" basename="p5-range"/>
2270</reference>
2271
2272<reference anchor="Part6">
2273   <front>
2274      <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2275      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2276         <organization abbrev="Day Software">Day Software</organization>
2277         <address><email>fielding@gbiv.com</email></address>
2278      </author>
2279      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2280         <organization>One Laptop per Child</organization>
2281         <address><email>jg@laptop.org</email></address>
2282      </author>
2283      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2284         <organization abbrev="HP">Hewlett-Packard Company</organization>
2285         <address><email>JeffMogul@acm.org</email></address>
2286      </author>
2287      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2288         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2289         <address><email>henrikn@microsoft.com</email></address>
2290      </author>
2291      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2292         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2293         <address><email>LMM@acm.org</email></address>
2294      </author>
2295      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2296         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2297         <address><email>paulle@microsoft.com</email></address>
2298      </author>
2299      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2300         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2301         <address><email>timbl@w3.org</email></address>
2302      </author>
2303      <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2304         <organization abbrev="W3C">World Wide Web Consortium</organization>
2305         <address><email>ylafon@w3.org</email></address>
2306      </author>
2307      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2308         <organization abbrev="greenbytes">greenbytes GmbH</organization>
2309         <address><email>julian.reschke@greenbytes.de</email></address>
2310      </author>
2311      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2312   </front>
2313   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2314   <x:source href="p6-cache.xml" basename="p6-cache"/>
2315</reference>
2316
2317<reference anchor="Part7">
2318   <front>
2319      <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2320      <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2321         <organization abbrev="Day Software">Day Software</organization>
2322         <address><email>fielding@gbiv.com</email></address>
2323      </author>
2324      <author initials="J." surname="Gettys" fullname="Jim Gettys">
2325         <organization>One Laptop per Child</organization>
2326         <address><email>jg@laptop.org</email></address>
2327      </author>
2328      <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2329         <organization abbrev="HP">Hewlett-Packard Company</organization>
2330         <address><email>JeffMogul@acm.org</email></address>
2331      </author>
2332      <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2333         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2334         <address><email>henrikn@microsoft.com</email></address>
2335      </author>
2336      <author initials="L." surname="Masinter" fullname="Larry Masinter">
2337         <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2338         <address><email>LMM@acm.org</email></address>
2339      </author>
2340      <author initials="P." surname="Leach" fullname="Paul J. Leach">
2341         <organization abbrev="Microsoft">Microsoft Corporation</organization>
2342         <address><email>paulle@microsoft.com</email></address>
2343      </author>
2344      <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2345         <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2346         <address><email>timbl@w3.org</email></address>
2347      </author>
2348      <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2349         <organization abbrev="W3C">World Wide Web Consortium</organization>
2350         <address><email>ylafon@w3.org</email></address>
2351      </author>
2352      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2353         <organization abbrev="greenbytes">greenbytes GmbH</organization>
2354         <address><email>julian.reschke@greenbytes.de</email></address>
2355      </author>
2356      <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2357   </front>
2358   <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
2359   <x:source href="p7-auth.xml" basename="p7-auth"/>
2360</reference>
2361
2362<reference anchor="RFC2616">
2363   <front>
2364      <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2365      <author initials="R." surname="Fielding" fullname="R. Fielding">
2366         <organization>University of California, Irvine</organization>
2367         <address><email>fielding@ics.uci.edu</email></address>
2368      </author>
2369      <author initials="J." surname="Gettys" fullname="J. Gettys">
2370         <organization>W3C</organization>
2371         <address><email>jg@w3.org</email></address>
2372      </author>
2373      <author initials="J." surname="Mogul" fullname="J. Mogul">
2374         <organization>Compaq Computer Corporation</organization>
2375         <address><email>mogul@wrl.dec.com</email></address>
2376      </author>
2377      <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2378         <organization>MIT Laboratory for Computer Science</organization>
2379         <address><email>frystyk@w3.org</email></address>
2380      </author>
2381      <author initials="L." surname="Masinter" fullname="L. Masinter">
2382         <organization>Xerox Corporation</organization>
2383         <address><email>masinter@parc.xerox.com</email></address>
2384      </author>
2385      <author initials="P." surname="Leach" fullname="P. Leach">
2386         <organization>Microsoft Corporation</organization>
2387         <address><email>paulle@microsoft.com</email></address>
2388      </author>
2389      <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2390         <organization>W3C</organization>
2391         <address><email>timbl@w3.org</email></address>
2392      </author>
2393      <date month="June" year="1999"/>
2394   </front>
2395   <seriesInfo name="RFC" value="2616"/>
2396</reference>
2397
2398<reference anchor="RFC1123">
2399<front>
2400<title>Requirements for Internet Hosts - Application and Support</title>
2401<author initials="R." surname="Braden" fullname="Robert Braden">
2402<organization>University of Southern California (USC), Information Sciences Institute</organization>
2403<address>
2404<postal>
2405<street>4676 Admiralty Way</street>
2406<city>Marina del Rey</city>
2407<region>CA</region>
2408<code>90292-6695</code>
2409<country>US</country></postal>
2410<phone>+1 213 822 1511</phone>
2411<email>Braden@ISI.EDU</email></address></author>
2412<date month="October" year="1989"/></front>
2413<seriesInfo name="STD" value="3"/>
2414<seriesInfo name="RFC" value="1123"/>
2415</reference>
2416
2417<reference anchor="RFC822">
2418<front>
2419<title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
2420<author initials="D.H." surname="Crocker" fullname="David H. Crocker">
2421<organization>University of Delaware, Dept. of Electrical Engineering</organization>
2422<address>
2423<postal>
2424<street/>
2425<city>Newark</city>
2426<region>DE</region>
2427<code>19711</code>
2428<country>US</country></postal>
2429<email>DCrocker@UDel-Relay</email></address></author>
2430<date month="August" day="13" year="1982"/></front>
2431<seriesInfo name="STD" value="11"/>
2432<seriesInfo name="RFC" value="822"/>
2433</reference>
2434
2435<reference anchor="RFC2068">
2436<front>
2437<title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2438<author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2439<organization>University of California, Irvine, Department of Information and Computer Science</organization>
2440<address>
2441<postal>
2442<street/>
2443<city>Irvine</city>
2444<region>CA</region>
2445<code>92717-3425</code>
2446<country>US</country></postal>
2447<facsimile>+1 714 824 4056</facsimile>
2448<email>fielding@ics.uci.edu</email></address></author>
2449<author initials="J." surname="Gettys" fullname="Jim Gettys">
2450<organization>MIT Laboratory for Computer Science</organization>
2451<address>
2452<postal>
2453<street>545 Technology Square</street>
2454<city>Cambridge</city>
2455<region>MA</region>
2456<code>02139</code>
2457<country>US</country></postal>
2458<facsimile>+1 617 258 8682</facsimile>
2459<email>jg@w3.org</email></address></author>
2460<author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2461<organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2462<address>
2463<postal>
2464<street>250 University Avenue</street>
2465<city>Palo Alto</city>
2466<region>CA</region>
2467<code>94301</code>
2468<country>US</country></postal>
2469<email>mogul@wrl.dec.com</email></address></author>
2470<author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2471<organization>MIT Laboratory for Computer Science</organization>
2472<address>
2473<postal>
2474<street>545 Technology Square</street>
2475<city>Cambridge</city>
2476<region>MA</region>
2477<code>02139</code>
2478<country>US</country></postal>
2479<facsimile>+1 617 258 8682</facsimile>
2480<email>frystyk@w3.org</email></address></author>
2481<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2482<organization>MIT Laboratory for Computer Science</organization>
2483<address>
2484<postal>
2485<street>545 Technology Square</street>
2486<city>Cambridge</city>
2487<region>MA</region>
2488<code>02139</code>
2489<country>US</country></postal>
2490<facsimile>+1 617 258 8682</facsimile>
2491<email>timbl@w3.org</email></address></author>
2492<date month="January" year="1997"/>
2493<abstract>
2494<t>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. It is a generic, stateless, object-oriented protocol which can be used for many tasks, such as name servers and distributed object management systems, through extension of its request methods. A feature of HTTP is the typing and negotiation of data representation, allowing systems to be built independently of the data being transferred.</t>
2495<t>HTTP has been in use by the World-Wide Web global information initiative since 1990. This specification defines the protocol referred to as "HTTP/1.1".</t></abstract></front>
2496<seriesInfo name="RFC" value="2068"/>
2497</reference>
2498
2499<reference anchor="RFC2119">
2500  <front>
2501    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2502    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2503      <organization>Harvard University</organization>
2504      <address><email>sob@harvard.edu</email></address>
2505    </author>
2506    <date month="March" year="1997"/>
2507  </front>
2508  <seriesInfo name="BCP" value="14"/>
2509  <seriesInfo name="RFC" value="2119"/>
2510</reference>
2511
2512<reference anchor="Luo1998">
2513<front>
2514<title>Tunneling TCP based protocols through Web proxy servers</title>
2515<author initials="A." surname="Luotonen" fullname="A. Luotonen">
2516  <organization/>
2517</author>
2518<date/>
2519</front>
2520<seriesInfo name="" value="Work in Progress"/>
2521</reference>
2522
2523</references>
2524
2525<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2526<t>
2527   Clarified which error code should be used for inbound server failures
2528   (e.g. DNS failures). (<xref target="status.504"/>).
2529</t>
2530<t>
2531   CREATE had a race that required an Etag be sent when a resource is
2532   first created. (<xref target="status.201"/>).
2533</t>
2534<t>
2535   Rewrite of message transmission requirements to make it much harder
2536   for implementors to get it wrong, as the consequences of errors here
2537   can have significant impact on the Internet, and to deal with the
2538   following problems:
2539  <list style="numbers">
2540      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
2541         this was incorrectly placing a requirement on the behavior of
2542         an implementation of a future version of HTTP/1.x</t>
2543
2544      <t>Made it clear that user-agents should retry requests, not
2545         "clients" in general.</t>
2546
2547      <t>Converted requirements for clients to ignore unexpected 100
2548         (Continue) responses, and for proxies to forward 100 responses,
2549         into a general requirement for 1xx responses.</t>
2550
2551      <t>Modified some TCP-specific language, to make it clearer that
2552         non-TCP transports are possible for HTTP.</t>
2553
2554      <t>Require that the origin server &MUST-NOT; wait for the request
2555         body before it sends a required 100 (Continue) response.</t>
2556
2557      <t>Allow, rather than require, a server to omit 100 (Continue) if
2558         it has already seen some of the request body.</t>
2559
2560      <t>Allow servers to defend against denial-of-service attacks and
2561         broken clients.</t>
2562  </list>
2563</t>
2564<t>
2565   This change adds the Expect header and 417 status code.
2566</t>
2567<t>
2568   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
2569   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
2570</t>
2571<t>
2572   The PATCH<iref item="PATCH method" primary="true"/><iref item="Methods" subitem="PATCH" primary="true"/>, LINK<iref item="LINK method" primary="true"/><iref item="Methods" subitem="LINK" primary="true"/>, UNLINK<iref item="UNLINK method" primary="true"/><iref item="Methods" subitem="UNLINK" primary="true"/> methods were defined but not commonly
2573   implemented in previous versions of this specification. See RFC 2068
2574   <xref target="RFC2068"/>.
2575</t>
2576</section>
2577</back>
2578</rfc>
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