source: draft-ietf-httpbis/latest/p2-semantics.xml @ 94

Last change on this file since 94 was 94, checked in by ylafon@…, 12 years ago

added Yves Lafon in authors section

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