source: draft-ietf-httpbis/latest/p2-semantics.xml @ 34

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update address for TimBL

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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]>
59<?rfc toc="yes" ?>
60<?rfc symrefs="yes" ?>
61<?rfc sortrefs="yes" ?>
62<?rfc compact="yes"?>
63<?rfc subcompact="no" ?>
64<?rfc linkmailto="no" ?>
65<?rfc editing="no" ?>
66<?rfc-ext allow-markup-in-artwork="yes" ?>
67<?rfc-ext include-references-in-index="yes" ?>
68<rfc obsoletes="2068, 2616, 2617" category="std"
69     ipr="full3978" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
70     xmlns:x='http://purl.org/net/xml2rfc/ext' xmlns:ed="http://greenbytes.de/2002/rfcedit">
71<front>
72
73  <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
74
75  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
76    <organization abbrev="Day Software">Day Software</organization>
77    <address>
78      <postal>
79        <street>23 Corporate Plaza DR, Suite 280</street>
80        <city>Newport Beach</city>
81        <region>CA</region>
82        <code>92660</code>
83        <country>USA</country>
84      </postal>
85      <phone>+1-949-706-5300</phone>
86      <facsimile>+1-949-706-5305</facsimile>
87      <email>fielding@gbiv.com</email>
88      <uri>http://roy.gbiv.com/</uri>
89    </address>
90  </author>
91
92  <author initials="J." surname="Gettys" fullname="Jim Gettys">
93    <organization>One Laptop per Child</organization>
94    <address>
95      <postal>
96        <street>21 Oak Knoll Road</street>
97        <city>Carlisle</city>
98        <region>MA</region>
99        <code>01741</code>
100        <country>USA</country>
101      </postal>
102      <email>jg@laptop.org</email>
103      <uri>http://www.laptop.org/</uri>
104    </address>
105  </author>
106 
107  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
108    <organization abbrev="HP">Hewlett-Packard Company</organization>
109    <address>
110      <postal>
111        <street>HP Labs, Large Scale Systems Group</street>
112        <street>1501 Page Mill Road, MS 1177</street>
113        <city>Palo Alto</city>
114        <region>CA</region>
115        <code>94304</code>
116        <country>USA</country>
117      </postal>
118      <email>JeffMogul@acm.org</email>
119    </address>
120  </author>
121
122  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
123    <organization abbrev="Microsoft">Microsoft Corporation</organization>
124    <address>
125      <postal>
126        <street>1 Microsoft Way</street>
127        <city>Redmond</city>
128        <region>WA</region>
129        <code>98052</code>
130        <country>USA</country>
131      </postal>
132      <email>henrikn@microsoft.com</email>
133    </address>
134  </author>
135
136  <author initials="L." surname="Masinter" fullname="Larry Masinter">
137    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
138    <address>
139      <postal>
140        <street>345 Park Ave</street>
141        <city>San Jose</city>
142        <region>CA</region>
143        <code>95110</code>
144        <country>USA</country>
145      </postal>
146      <email>LMM@acm.org</email>
147      <uri>http://larry.masinter.net/</uri>
148    </address>
149  </author>
150 
151  <author initials="P." surname="Leach" fullname="Paul J. Leach">
152    <organization abbrev="Microsoft">Microsoft Corporation</organization>
153    <address>
154      <postal>
155        <street>1 Microsoft Way</street>
156        <city>Redmond</city>
157        <region>WA</region>
158        <code>98052</code>
159      </postal>
160      <email>paulle@microsoft.com</email>
161    </address>
162  </author>
163   
164  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
165    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
166    <address>
167      <postal>
168        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
169        <street>The Stata Center, Building 32</street>
170        <street>32 Vassar Street</street>
171        <city>Cambridge</city>
172        <region>MA</region>
173        <code>02139</code>
174        <country>USA</country>
175      </postal>
176      <email>timbl@w3.org</email>
177      <uri>http://www.w3.org/People/Berners-Lee/</uri>
178    </address>
179  </author>
180
181  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
182
183<abstract>
184<t>
185   The Hypertext Transfer Protocol (HTTP) is an application-level
186   protocol for distributed, collaborative, hypermedia information
187   systems. HTTP has been in use by the World Wide Web global information
188   initiative since 1990. This document is Part 2 of the eight-part specification
189   that defines the protocol referred to as "HTTP/1.1" and, taken together,
190   updates RFC 2616 and RFC 2617.  Part 2 defines the semantics of HTTP messages
191   as expressed by request methods, request-header fields, response status codes,
192   and response-header fields.
193</t>
194</abstract>
195</front>
196<middle>
197<section title="Introduction" anchor="introduction">
198<t>
199   This document will define aspects of HTTP related to request and response
200   semantics. Right now it only includes the extracted relevant sections of
201   RFC 2616 with only minor edits.
202</t>
203<t>
204   The HTTP protocol is a request/response protocol. A client sends a
205   request to the server in the form of a request method, URI, and
206   protocol version, followed by a MIME-like message containing request
207   modifiers, client information, and possible body content over a
208   connection with a server. The server responds with a status line,
209   including the message's protocol version and a success or error code,
210   followed by a MIME-like message containing server information, entity
211   metainformation, and possible entity-body content. The relationship
212   between HTTP and MIME is described in &diff2045entity;.
213</t>
214</section>
215
216<section title="Product Tokens" anchor="product.tokens">
217<t>
218   Product tokens are used to allow communicating applications to
219   identify themselves by software name and version. Most fields using
220   product tokens also allow sub-products which form a significant part
221   of the application to be listed, separated by white space. By
222   convention, the products are listed in order of their significance
223   for identifying the application.
224</t>
225<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
226    product         = token ["/" product-version]
227    product-version = token
228</artwork></figure>
229<t>
230   Examples:
231</t>
232<figure><artwork type="example">
233    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
234    Server: Apache/0.8.4
235</artwork></figure>
236<t>
237   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
238   used for advertising or other non-essential information. Although any
239   token character &MAY; appear in a product-version, this token &SHOULD;
240   only be used for a version identifier (i.e., successive versions of
241   the same product &SHOULD; only differ in the product-version portion of
242   the product value).
243</t>
244</section>
245
246<section title="Method" anchor="method">
247<t>
248   The Method  token indicates the method to be performed on the
249   resource identified by the Request-URI. The method is case-sensitive.
250</t>
251<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
252    Method         = "OPTIONS"                ; <xref target="OPTIONS"/>
253                   | "GET"                    ; <xref target="GET"/>
254                   | "HEAD"                   ; <xref target="HEAD"/>
255                   | "POST"                   ; <xref target="POST"/>
256                   | "PUT"                    ; <xref target="PUT"/>
257                   | "DELETE"                 ; <xref target="DELETE"/>
258                   | "TRACE"                  ; <xref target="TRACE"/>
259                   | "CONNECT"                ; <xref target="CONNECT"/>
260                   | extension-method
261    extension-method = token
262</artwork></figure>
263<t>
264   The list of methods allowed by a resource can be specified in an
265   Allow header field (<xref target="header.allow"/>). The return code of the response
266   always notifies the client whether a method is currently allowed on a
267   resource, since the set of allowed methods can change dynamically. An
268   origin server &SHOULD; return the status code 405 (Method Not Allowed)
269   if the method is known by the origin server but not allowed for the
270   requested resource, and 501 (Not Implemented) if the method is
271   unrecognized or not implemented by the origin server. The methods GET
272   and HEAD &MUST; be supported by all general-purpose servers. All other
273   methods are &OPTIONAL;; however, if the above methods are implemented,
274   they &MUST; be implemented with the same semantics as those specified
275   in <xref target="method.definitions"/>.
276</t>
277</section>
278
279<section title="Request Header Fields" anchor="request.header.fields">
280<t>
281   The request-header fields allow the client to pass additional
282   information about the request, and about the client itself, to the
283   server. These fields act as request modifiers, with semantics
284   equivalent to the parameters on a programming language method
285   invocation.
286</t>
287<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-header"/>
288    request-header = Accept                   ; &header-accept;
289                   | Accept-Charset           ; &header-accept-charset;
290                   | Accept-Encoding          ; &header-accept-encoding;
291                   | Accept-Language          ; &header-accept-language;
292                   | Authorization            ; &header-authorization;
293                   | Expect                   ; <xref target="header.expect"/>
294                   | From                     ; <xref target="header.from"/>
295                   | Host                     ; &header-host;
296                   | If-Match                 ; &header-if-match;
297                   | If-Modified-Since        ; &header-if-modified-since;
298                   | If-None-Match            ; &header-if-none-match;
299                   | If-Range                 ; &header-if-range;
300                   | If-Unmodified-Since      ; &header-if-unmodified-since;
301                   | Max-Forwards             ; <xref target="header.max-forwards"/>
302                   | Proxy-Authorization      ; &header-proxy-authorization;
303                   | Range                    ; &header-range;
304                   | Referer                  ; <xref target="header.referer"/>
305                   | TE                       ; &header-te;
306                   | User-Agent               ; <xref target="header.user-agent"/>
307</artwork></figure>
308<t>
309   Request-header field names can be extended reliably only in
310   combination with a change in the protocol version. However, new or
311   experimental header fields &MAY; be given the semantics of request-header
312   fields if all parties in the communication recognize them to
313   be request-header fields. Unrecognized header fields are treated as
314   entity-header fields.
315</t>
316</section>
317
318<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
319<t>
320   The Status-Code element is a 3-digit integer result code of the
321   attempt to understand and satisfy the request. These codes are fully
322   defined in <xref target="status.codes"/>. The Reason-Phrase is intended to give a short
323   textual description of the Status-Code. The Status-Code is intended
324   for use by automata and the Reason-Phrase is intended for the human
325   user. The client is not required to examine or display the Reason-Phrase.
326</t>
327<t> 
328   The individual values of the numeric status codes defined for
329   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
330   presented below. The reason phrases listed here are only
331   recommendations -- they &MAY; be replaced by local equivalents without
332   affecting the protocol.
333</t>
334<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"/>
335   Status-Code    =
336         "100"  ; <xref target="status.100"/>: Continue
337       | "101"  ; <xref target="status.101"/>: Switching Protocols
338       | "200"  ; <xref target="status.200"/>: OK
339       | "201"  ; <xref target="status.201"/>: Created
340       | "202"  ; <xref target="status.202"/>: Accepted
341       | "203"  ; <xref target="status.203"/>: Non-Authoritative Information
342       | "204"  ; <xref target="status.204"/>: No Content
343       | "205"  ; <xref target="status.205"/>: Reset Content
344       | "206"  ; <xref target="status.206"/>: Partial Content
345       | "300"  ; <xref target="status.300"/>: Multiple Choices
346       | "301"  ; <xref target="status.301"/>: Moved Permanently
347       | "302"  ; <xref target="status.302"/>: Found
348       | "303"  ; <xref target="status.303"/>: See Other
349       | "304"  ; <xref target="status.304"/>: Not Modified
350       | "305"  ; <xref target="status.305"/>: Use Proxy
351       | "307"  ; <xref target="status.307"/>: Temporary Redirect
352       | "400"  ; <xref target="status.400"/>: Bad Request
353       | "401"  ; <xref target="status.401"/>: Unauthorized
354       | "402"  ; <xref target="status.402"/>: Payment Required
355       | "403"  ; <xref target="status.403"/>: Forbidden
356       | "404"  ; <xref target="status.404"/>: Not Found
357       | "405"  ; <xref target="status.405"/>: Method Not Allowed
358       | "406"  ; <xref target="status.406"/>: Not Acceptable
359       | "407"  ; <xref target="status.407"/>: Proxy Authentication Required
360       | "408"  ; <xref target="status.408"/>: Request Time-out
361       | "409"  ; <xref target="status.409"/>: Conflict
362       | "410"  ; <xref target="status.410"/>: Gone
363       | "411"  ; <xref target="status.411"/>: Length Required
364       | "412"  ; <xref target="status.412"/>: Precondition Failed
365       | "413"  ; <xref target="status.413"/>: Request Entity Too Large
366       | "414"  ; <xref target="status.414"/>: Request-URI Too Large
367       | "415"  ; <xref target="status.415"/>: Unsupported Media Type
368       | "416"  ; <xref target="status.416"/>: Requested range not satisfiable
369       | "417"  ; <xref target="status.417"/>: Expectation Failed
370       | "500"  ; <xref target="status.500"/>: Internal Server Error
371       | "501"  ; <xref target="status.501"/>: Not Implemented
372       | "502"  ; <xref target="status.502"/>: Bad Gateway
373       | "503"  ; <xref target="status.503"/>: Service Unavailable
374       | "504"  ; <xref target="status.504"/>: Gateway Time-out
375       | "505"  ; <xref target="status.505"/>: HTTP Version not supported
376       | extension-code
377
378   extension-code = 3DIGIT
379   Reason-Phrase  = *&lt;TEXT, excluding CR, LF&gt;
380</artwork></figure>
381<t>
382   HTTP status codes are extensible. HTTP applications are not required
383   to understand the meaning of all registered status codes, though such
384   understanding is obviously desirable. However, applications &MUST;
385   understand the class of any status code, as indicated by the first
386   digit, and treat any unrecognized response as being equivalent to the
387   x00 status code of that class, with the exception that an
388   unrecognized response &MUST-NOT; be cached. For example, if an
389   unrecognized status code of 431 is received by the client, it can
390   safely assume that there was something wrong with its request and
391   treat the response as if it had received a 400 status code. In such
392   cases, user agents &SHOULD; present to the user the entity returned
393   with the response, since that entity is likely to include human-readable
394   information which will explain the unusual status.
395</t>
396</section>
397
398<section title="Response Header Fields" anchor="response.header.fields">
399<t>
400   The response-header fields allow the server to pass additional
401   information about the response which cannot be placed in the Status-Line.
402   These header fields give information about the server and about
403   further access to the resource identified by the Request-URI.
404</t>
405<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="response-header"/>
406    response-header = Accept-Ranges           ; &header-accept-ranges;
407                    | Age                     ; &header-age;
408                    | ETag                    ; &header-etag;
409                    | Location                ; <xref target="header.location"/>
410                    | Proxy-Authenticate      ; &header-proxy-authenticate;
411                    | Retry-After             ; <xref target="header.retry-after"/>
412                    | Server                  ; <xref target="header.server"/>
413                    | Vary                    ; &header-vary;
414                    | WWW-Authenticate        ; &header-www-authenticate;
415</artwork></figure>
416<t>
417   Response-header field names can be extended reliably only in
418   combination with a change in the protocol version. However, new or
419   experimental header fields &MAY; be given the semantics of response-header
420   fields if all parties in the communication recognize them to
421   be response-header fields. Unrecognized header fields are treated as
422   entity-header fields.
423</t>
424</section>
425
426<section title="Entity" anchor="entity">
427<t>
428   Request and Response messages &MAY; transfer an entity if not otherwise
429   restricted by the request method or response status code. An entity
430   consists of entity-header fields and an entity-body, although some
431   responses will only include the entity-headers. HTTP entity-body and
432   entity-header fields are defined in &payload;.
433</t>
434<t>
435   An entity-body is only present in a message when a message-body is
436   present, as described in &message-body;. The entity-body is obtained
437   from the message-body by decoding any Transfer-Encoding that might
438   have been applied to ensure safe and proper transfer of the message.
439</t>
440</section>
441
442
443<section title="Method Definitions" anchor="method.definitions">
444<t>
445   The set of common methods for HTTP/1.1 is defined below. Although
446   this set can be expanded, additional methods cannot be assumed to
447   share the same semantics for separately extended clients and servers.
448
449   The Host request-header field (&header-host;) &MUST; accompany all
450   HTTP/1.1 requests.
451</t>
452
453<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
454
455<section title="Safe Methods" anchor="safe.methods">
456<t>
457   Implementors should be aware that the software represents the user in
458   their interactions over the Internet, and should be careful to allow
459   the user to be aware of any actions they might take which may have an
460   unexpected significance to themselves or others.
461</t>
462<t>
463   In particular, the convention has been established that the GET and
464   HEAD methods &SHOULD-NOT;  have the significance of taking an action
465   other than retrieval. These methods ought to be considered "safe".
466   This allows user agents to represent other methods, such as POST, PUT
467   and DELETE, in a special way, so that the user is made aware of the
468   fact that a possibly unsafe action is being requested.
469</t>
470<t>
471   Naturally, it is not possible to ensure that the server does not
472   generate side-effects as a result of performing a GET request; in
473   fact, some dynamic resources consider that a feature. The important
474   distinction here is that the user did not request the side-effects,
475   so therefore cannot be held accountable for them.
476</t>
477</section>
478
479<section title="Idempotent Methods" anchor="idempotent.methods">
480<t>
481   Methods can also have the property of "idempotence" in that (aside
482   from error or expiration issues) the side-effects of N &gt; 0 identical
483   requests is the same as for a single request. The methods GET, HEAD,
484   PUT and DELETE share this property. Also, the methods OPTIONS and
485   TRACE &SHOULD-NOT;  have side effects, and so are inherently idempotent.
486</t>
487<t>
488   However, it is possible that a sequence of several requests is non-idempotent,
489   even if all of the methods executed in that sequence are
490   idempotent. (A sequence is idempotent if a single execution of the
491   entire sequence always yields a result that is not changed by a
492   reexecution of all, or part, of that sequence.) For example, a
493   sequence is non-idempotent if its result depends on a value that is
494   later modified in the same sequence.
495</t>
496<t>
497   A sequence that never has side effects is idempotent, by definition
498   (provided that no concurrent operations are being executed on the
499   same set of resources).
500</t>
501</section>
502</section>
503
504<section title="OPTIONS" anchor="OPTIONS">
505  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
506  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
507<t>
508   The OPTIONS method represents a request for information about the
509   communication options available on the request/response chain
510   identified by the Request-URI. This method allows the client to
511   determine the options and/or requirements associated with a resource,
512   or the capabilities of a server, without implying a resource action
513   or initiating a resource retrieval.
514</t>
515<t>
516   Responses to this method are not cacheable.
517</t>
518<t>
519   If the OPTIONS request includes an entity-body (as indicated by the
520   presence of Content-Length or Transfer-Encoding), then the media type
521   &MUST; be indicated by a Content-Type field. Although this
522   specification does not define any use for such a body, future
523   extensions to HTTP might use the OPTIONS body to make more detailed
524   queries on the server. A server that does not support such an
525   extension &MAY; discard the request body.
526</t>
527<t>
528   If the Request-URI is an asterisk ("*"), the OPTIONS request is
529   intended to apply to the server in general rather than to a specific
530   resource. Since a server's communication options typically depend on
531   the resource, the "*" request is only useful as a "ping" or "no-op"
532   type of method; it does nothing beyond allowing the client to test
533   the capabilities of the server. For example, this can be used to test
534   a proxy for HTTP/1.1 compliance (or lack thereof).
535</t>
536<t>
537   If the Request-URI is not an asterisk, the OPTIONS request applies
538   only to the options that are available when communicating with that
539   resource.
540</t>
541<t>
542   A 200 response &SHOULD; include any header fields that indicate
543   optional features implemented by the server and applicable to that
544   resource (e.g., Allow), possibly including extensions not defined by
545   this specification. The response body, if any, &SHOULD; also include
546   information about the communication options. The format for such a
547   body is not defined by this specification, but might be defined by
548   future extensions to HTTP. Content negotiation &MAY; be used to select
549   the appropriate response format. If no response body is included, the
550   response &MUST; include a Content-Length field with a field-value of
551   "0".
552</t>
553<t>
554   The Max-Forwards request-header field &MAY; be used to target a
555   specific proxy in the request chain. When a proxy receives an OPTIONS
556   request on an absoluteURI for which request forwarding is permitted,
557   the proxy &MUST; check for a Max-Forwards field. If the Max-Forwards
558   field-value is zero ("0"), the proxy &MUST-NOT; forward the message;
559   instead, the proxy &SHOULD; respond with its own communication options.
560   If the Max-Forwards field-value is an integer greater than zero, the
561   proxy &MUST; decrement the field-value when it forwards the request. If
562   no Max-Forwards field is present in the request, then the forwarded
563   request &MUST-NOT; include a Max-Forwards field.
564</t>
565</section>
566
567<section title="GET" anchor="GET">
568  <iref primary="true" item="GET method" x:for-anchor=""/>
569  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
570<t>
571   The GET method means retrieve whatever information (in the form of an
572   entity) is identified by the Request-URI. If the Request-URI refers
573   to a data-producing process, it is the produced data which shall be
574   returned as the entity in the response and not the source text of the
575   process, unless that text happens to be the output of the process.
576</t>
577<t>
578   The semantics of the GET method change to a "conditional GET" if the
579   request message includes an If-Modified-Since, If-Unmodified-Since,
580   If-Match, If-None-Match, or If-Range header field. A conditional GET
581   method requests that the entity be transferred only under the
582   circumstances described by the conditional header field(s). The
583   conditional GET method is intended to reduce unnecessary network
584   usage by allowing cached entities to be refreshed without requiring
585   multiple requests or transferring data already held by the client.
586</t>
587<t>
588   The semantics of the GET method change to a "partial GET" if the
589   request message includes a Range header field. A partial GET requests
590   that only part of the entity be transferred, as described in &header-range;.
591   The partial GET method is intended to reduce unnecessary
592   network usage by allowing partially-retrieved entities to be
593   completed without transferring data already held by the client.
594</t>
595<t>
596   The response to a GET request is cacheable if and only if it meets
597   the requirements for HTTP caching described in &caching;.
598</t>
599<t>
600   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
601</t>
602</section>
603
604<section title="HEAD" anchor="HEAD">
605  <iref primary="true" item="HEAD method" x:for-anchor=""/>
606  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
607<t>
608   The HEAD method is identical to GET except that the server &MUST-NOT;
609   return a message-body in the response. The metainformation contained
610   in the HTTP headers in response to a HEAD request &SHOULD; be identical
611   to the information sent in response to a GET request. This method can
612   be used for obtaining metainformation about the entity implied by the
613   request without transferring the entity-body itself. This method is
614   often used for testing hypertext links for validity, accessibility,
615   and recent modification.
616</t>
617<t>
618   The response to a HEAD request &MAY; be cacheable in the sense that the
619   information contained in the response &MAY; be used to update a
620   previously cached entity from that resource. If the new field values
621   indicate that the cached entity differs from the current entity (as
622   would be indicated by a change in Content-Length, Content-MD5, ETag
623   or Last-Modified), then the cache &MUST; treat the cache entry as
624   stale.
625</t>
626</section>
627
628<section title="POST" anchor="POST">
629  <iref primary="true" item="POST method" x:for-anchor=""/>
630  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
631<t>
632   The POST method is used to request that the origin server accept the
633   entity enclosed in the request as a new subordinate of the resource
634   identified by the Request-URI in the Request-Line. POST is designed
635   to allow a uniform method to cover the following functions:
636  <list style="symbols">
637    <t>
638      Annotation of existing resources;
639    </t>
640    <t>
641        Posting a message to a bulletin board, newsgroup, mailing list,
642        or similar group of articles;
643    </t>
644    <t>
645        Providing a block of data, such as the result of submitting a
646        form, to a data-handling process;
647    </t>
648    <t>
649        Extending a database through an append operation.
650    </t>
651  </list>
652</t>
653<t>
654   The actual function performed by the POST method is determined by the
655   server and is usually dependent on the Request-URI. The posted entity
656   is subordinate to that URI in the same way that a file is subordinate
657   to a directory containing it, a news article is subordinate to a
658   newsgroup to which it is posted, or a record is subordinate to a
659   database.
660</t>
661<t>
662   The action performed by the POST method might not result in a
663   resource that can be identified by a URI. In this case, either 200
664   (OK) or 204 (No Content) is the appropriate response status,
665   depending on whether or not the response includes an entity that
666   describes the result.
667</t>
668<t>
669   If a resource has been created on the origin server, the response
670   &SHOULD; be 201 (Created) and contain an entity which describes the
671   status of the request and refers to the new resource, and a Location
672   header (see <xref target="header.location"/>).
673</t>
674<t>
675   Responses to this method are not cacheable, unless the response
676   includes appropriate Cache-Control or Expires header fields. However,
677   the 303 (See Other) response can be used to direct the user agent to
678   retrieve a cacheable resource.
679</t>
680<t>
681   POST requests &MUST; obey the message transmission requirements set out
682   in [message.transmission.requirements].
683</t>
684<t>
685   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
686</t>
687</section>
688
689<section title="PUT" anchor="PUT">
690  <iref primary="true" item="PUT method" x:for-anchor=""/>
691  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
692<t>
693   The PUT method requests that the enclosed entity be stored under the
694   supplied Request-URI. If the Request-URI refers to an already
695   existing resource, the enclosed entity &SHOULD; be considered as a
696   modified version of the one residing on the origin server. If the
697   Request-URI does not point to an existing resource, and that URI is
698   capable of being defined as a new resource by the requesting user
699   agent, the origin server can create the resource with that URI. If a
700   new resource is created, the origin server &MUST; inform the user agent
701   via the 201 (Created) response. If an existing resource is modified,
702   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
703   to indicate successful completion of the request. If the resource
704   could not be created or modified with the Request-URI, an appropriate
705   error response &SHOULD; be given that reflects the nature of the
706   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
707   (e.g. Content-Range) headers that it does not understand or implement
708   and &MUST; return a 501 (Not Implemented) response in such cases.
709</t>
710<t>
711   If the request passes through a cache and the Request-URI identifies
712   one or more currently cached entities, those entries &SHOULD; be
713   treated as stale. Responses to this method are not cacheable.
714</t>
715<t>
716   The fundamental difference between the POST and PUT requests is
717   reflected in the different meaning of the Request-URI. The URI in a
718   POST request identifies the resource that will handle the enclosed
719   entity. That resource might be a data-accepting process, a gateway to
720   some other protocol, or a separate entity that accepts annotations.
721   In contrast, the URI in a PUT request identifies the entity enclosed
722   with the request -- the user agent knows what URI is intended and the
723   server &MUST-NOT; attempt to apply the request to some other resource.
724   If the server desires that the request be applied to a different URI,
725   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
726   then make its own decision regarding whether or not to redirect the
727   request.
728</t>
729<t>
730   A single resource &MAY; be identified by many different URIs. For
731   example, an article might have a URI for identifying "the current
732   version" which is separate from the URI identifying each particular
733   version. In this case, a PUT request on a general URI might result in
734   several other URIs being defined by the origin server.
735</t>
736<t>
737   HTTP/1.1 does not define how a PUT method affects the state of an
738   origin server.
739</t>
740<t>
741   PUT requests &MUST; obey the message transmission requirements set out
742   in [message.transmission.requirements].
743</t>
744<t>
745   Unless otherwise specified for a particular entity-header, the
746   entity-headers in the PUT request &SHOULD; be applied to the resource
747   created or modified by the PUT.
748</t>
749</section>
750
751<section title="DELETE" anchor="DELETE">
752  <iref primary="true" item="DELETE method" x:for-anchor=""/>
753  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
754<t>
755   The DELETE method requests that the origin server delete the resource
756   identified by the Request-URI. This method &MAY; be overridden by human
757   intervention (or other means) on the origin server. The client cannot
758   be guaranteed that the operation has been carried out, even if the
759   status code returned from the origin server indicates that the action
760   has been completed successfully. However, the server &SHOULD-NOT;
761   indicate success unless, at the time the response is given, it
762   intends to delete the resource or move it to an inaccessible
763   location.
764</t>
765<t>
766   A successful response &SHOULD; be 200 (OK) if the response includes an
767   entity describing the status, 202 (Accepted) if the action has not
768   yet been enacted, or 204 (No Content) if the action has been enacted
769   but the response does not include an entity.
770</t>
771<t>
772   If the request passes through a cache and the Request-URI identifies
773   one or more currently cached entities, those entries &SHOULD; be
774   treated as stale. Responses to this method are not cacheable.
775</t>
776</section>
777
778<section title="TRACE" anchor="TRACE">
779  <iref primary="true" item="TRACE method" x:for-anchor=""/>
780  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
781<t>
782   The TRACE method is used to invoke a remote, application-layer loop-back
783   of the request message. The final recipient of the request
784   &SHOULD; reflect the message received back to the client as the
785   entity-body of a 200 (OK) response. The final recipient is either the
786   origin server or the first proxy or gateway to receive a Max-Forwards
787   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
788   &MUST-NOT; include an entity.
789</t>
790<t>
791   TRACE allows the client to see what is being received at the other
792   end of the request chain and use that data for testing or diagnostic
793   information. The value of the Via header field (&header-via;) is of
794   particular interest, since it acts as a trace of the request chain.
795   Use of the Max-Forwards header field allows the client to limit the
796   length of the request chain, which is useful for testing a chain of
797   proxies forwarding messages in an infinite loop.
798</t>
799<t>
800   If the request is valid, the response &SHOULD; contain the entire
801   request message in the entity-body, with a Content-Type of
802   "message/http". Responses to this method &MUST-NOT; be cached.
803</t>
804</section>
805
806<section title="CONNECT" anchor="CONNECT">
807  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
808  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
809<t>
810   This specification reserves the method name CONNECT for use with a
811   proxy that can dynamically switch to being a tunnel (e.g. SSL
812   tunneling <xref target="Luo1998"/>).
813</t>
814</section>
815</section>
816
817
818<section title="Status Code Definitions" anchor="status.codes">
819<t>
820   Each Status-Code is described below, including a description of which
821   method(s) it can follow and any metainformation required in the
822   response.
823</t>
824
825<section title="Informational 1xx" anchor="status.1xx">
826<t>
827   This class of status code indicates a provisional response,
828   consisting only of the Status-Line and optional headers, and is
829   terminated by an empty line. There are no required headers for this
830   class of status code. Since HTTP/1.0 did not define any 1xx status
831   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
832   except under experimental conditions.
833</t>
834<t>
835   A client &MUST; be prepared to accept one or more 1xx status responses
836   prior to a regular response, even if the client does not expect a 100
837   (Continue) status message. Unexpected 1xx status responses &MAY; be
838   ignored by a user agent.
839</t>
840<t>
841   Proxies &MUST; forward 1xx responses, unless the connection between the
842   proxy and its client has been closed, or unless the proxy itself
843   requested the generation of the 1xx response. (For example, if a
844   proxy adds a "Expect: 100-continue" field when it forwards a request,
845   then it need not forward the corresponding 100 (Continue)
846   response(s).)
847</t>
848
849<section title="100 Continue" anchor="status.100">
850  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
851  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
852<t>
853   The client &SHOULD; continue with its request. This interim response is
854   used to inform the client that the initial part of the request has
855   been received and has not yet been rejected by the server. The client
856   &SHOULD; continue by sending the remainder of the request or, if the
857   request has already been completed, ignore this response. The server
858   &MUST; send a final response after the request has been completed. See
859   &use100; for detailed discussion of the use and handling of this
860   status code.
861</t>
862</section>
863
864<section title="101 Switching Protocols" anchor="status.101">
865  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
866  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
867<t>
868   The server understands and is willing to comply with the client's
869   request, via the Upgrade message header field (&header-upgrade;), for a
870   change in the application protocol being used on this connection. The
871   server will switch protocols to those defined by the response's
872   Upgrade header field immediately after the empty line which
873   terminates the 101 response.
874</t>
875<t>
876   The protocol &SHOULD; be switched only when it is advantageous to do
877   so. For example, switching to a newer version of HTTP is advantageous
878   over older versions, and switching to a real-time, synchronous
879   protocol might be advantageous when delivering resources that use
880   such features.
881</t>
882</section>
883</section>
884
885<section title="Successful 2xx" anchor="status.2xx">
886<t>
887   This class of status code indicates that the client's request was
888   successfully received, understood, and accepted.
889</t>
890
891<section title="200 OK" anchor="status.200">
892  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
893  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
894<t>
895   The request has succeeded. The information returned with the response
896   is dependent on the method used in the request, for example:
897  <list style="hanging">
898    <t hangText="GET">
899          an entity corresponding to the requested resource is sent in
900          the response;
901    </t>
902    <t hangText="HEAD">
903          the entity-header fields corresponding to the requested
904          resource are sent in the response without any message-body;
905    </t>
906    <t hangText="POST">
907      an entity describing or containing the result of the action;
908    </t>
909    <t hangText="TRACE">
910      an entity containing the request message as received by the
911      end server.
912    </t>
913  </list>
914</t>
915</section>
916
917<section title="201 Created" anchor="status.201">
918  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
919  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
920<t>
921   The request has been fulfilled and resulted in a new resource being
922   created. The newly created resource can be referenced by the URI(s)
923   returned in the entity of the response, with the most specific URI
924   for the resource given by a Location header field. The response
925   &SHOULD; include an entity containing a list of resource
926   characteristics and location(s) from which the user or user agent can
927   choose the one most appropriate. The entity format is specified by
928   the media type given in the Content-Type header field. The origin
929   server &MUST; create the resource before returning the 201 status code.
930   If the action cannot be carried out immediately, the server &SHOULD;
931   respond with 202 (Accepted) response instead.
932</t>
933<t>
934   A 201 response &MAY; contain an ETag response header field indicating
935   the current value of the entity tag for the requested variant just
936   created, see &header-etag;.
937</t>
938</section>
939
940<section title="202 Accepted" anchor="status.202">
941  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
942  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
943<t>
944   The request has been accepted for processing, but the processing has
945   not been completed.  The request might or might not eventually be
946   acted upon, as it might be disallowed when processing actually takes
947   place. There is no facility for re-sending a status code from an
948   asynchronous operation such as this.
949</t>
950<t>
951   The 202 response is intentionally non-committal. Its purpose is to
952   allow a server to accept a request for some other process (perhaps a
953   batch-oriented process that is only run once per day) without
954   requiring that the user agent's connection to the server persist
955   until the process is completed. The entity returned with this
956   response &SHOULD; include an indication of the request's current status
957   and either a pointer to a status monitor or some estimate of when the
958   user can expect the request to be fulfilled.
959</t>
960</section>
961
962<section title="203 Non-Authoritative Information" anchor="status.203">
963  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
964  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
965<t>
966   The returned metainformation in the entity-header is not the
967   definitive set as available from the origin server, but is gathered
968   from a local or a third-party copy. The set presented &MAY; be a subset
969   or superset of the original version. For example, including local
970   annotation information about the resource might result in a superset
971   of the metainformation known by the origin server. Use of this
972   response code is not required and is only appropriate when the
973   response would otherwise be 200 (OK).
974</t>
975</section>
976
977<section title="204 No Content" anchor="status.204">
978  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
979  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
980<t>
981   The server has fulfilled the request but does not need to return an
982   entity-body, and might want to return updated metainformation. The
983   response &MAY; include new or updated metainformation in the form of
984   entity-headers, which if present &SHOULD; be associated with the
985   requested variant.
986</t>
987<t>
988   If the client is a user agent, it &SHOULD-NOT;  change its document view
989   from that which caused the request to be sent. This response is
990   primarily intended to allow input for actions to take place without
991   causing a change to the user agent's active document view, although
992   any new or updated metainformation &SHOULD; be applied to the document
993   currently in the user agent's active view.
994</t>
995<t>
996   The 204 response &MUST-NOT; include a message-body, and thus is always
997   terminated by the first empty line after the header fields.
998</t>
999</section>
1000
1001<section title="205 Reset Content" anchor="status.205">
1002  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1003  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1004<t>
1005   The server has fulfilled the request and the user agent &SHOULD; reset
1006   the document view which caused the request to be sent. This response
1007   is primarily intended to allow input for actions to take place via
1008   user input, followed by a clearing of the form in which the input is
1009   given so that the user can easily initiate another input action. The
1010   response &MUST-NOT; include an entity.
1011</t>
1012</section>
1013
1014<section title="206 Partial Content" anchor="status.206">
1015  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1016  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1017<t>
1018   The server has fulfilled the partial GET request for the resource
1019   and the enclosed entity is a partial representation as defined in &range;.
1020</t>
1021</section>
1022</section>
1023
1024<section title="Redirection 3xx" anchor="status.3xx">
1025<t>
1026   This class of status code indicates that further action needs to be
1027   taken by the user agent in order to fulfill the request.  The action
1028   required &MAY; be carried out by the user agent without interaction
1029   with the user if and only if the method used in the second request is
1030   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1031   such loops generate network traffic for each redirection.
1032  <list><t>
1033      <x:h>Note:</x:h> previous versions of this specification recommended a
1034      maximum of five redirections. Content developers should be aware
1035      that there might be clients that implement such a fixed
1036      limitation.
1037  </t></list>
1038</t>
1039
1040<section title="300 Multiple Choices" anchor="status.300">
1041  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1042  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1043<t>
1044   The requested resource corresponds to any one of a set of
1045   representations, each with its own specific location, and agent-driven
1046   negotiation information (&content-negotiation;) is being provided so that
1047   the user (or user agent) can select a preferred representation and
1048   redirect its request to that location.
1049</t>
1050<t>
1051   Unless it was a HEAD request, the response &SHOULD; include an entity
1052   containing a list of resource characteristics and location(s) from
1053   which the user or user agent can choose the one most appropriate. The
1054   entity format is specified by the media type given in the Content-Type
1055   header field. Depending upon the format and the capabilities of
1056   the user agent, selection of the most appropriate choice &MAY; be
1057   performed automatically. However, this specification does not define
1058   any standard for such automatic selection.
1059</t>
1060<t>
1061   If the server has a preferred choice of representation, it &SHOULD;
1062   include the specific URI for that representation in the Location
1063   field; user agents &MAY; use the Location field value for automatic
1064   redirection. This response is cacheable unless indicated otherwise.
1065</t>
1066</section>
1067
1068<section title="301 Moved Permanently" anchor="status.301">
1069  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1070  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1071<t>
1072   The requested resource has been assigned a new permanent URI and any
1073   future references to this resource &SHOULD; use one of the returned
1074   URIs.  Clients with link editing capabilities ought to automatically
1075   re-link references to the Request-URI to one or more of the new
1076   references returned by the server, where possible. This response is
1077   cacheable unless indicated otherwise.
1078</t>
1079<t>
1080   The new permanent URI &SHOULD; be given by the Location field in the
1081   response. Unless the request method was HEAD, the entity of the
1082   response &SHOULD; contain a short hypertext note with a hyperlink to
1083   the new URI(s).
1084</t>
1085<t>
1086   If the 301 status code is received in response to a request other
1087   than GET or HEAD, the user agent &MUST-NOT; automatically redirect the
1088   request unless it can be confirmed by the user, since this might
1089   change the conditions under which the request was issued.
1090  <list><t>
1091      <x:h>Note:</x:h> When automatically redirecting a POST request after
1092      receiving a 301 status code, some existing HTTP/1.0 user agents
1093      will erroneously change it into a GET request.
1094  </t></list>
1095</t>
1096</section>
1097
1098<section title="302 Found" anchor="status.302">
1099  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1100  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1101<t>
1102   The requested resource resides temporarily under a different URI.
1103   Since the redirection might be altered on occasion, the client &SHOULD;
1104   continue to use the Request-URI for future requests.  This response
1105   is only cacheable if indicated by a Cache-Control or Expires header
1106   field.
1107</t>
1108<t>
1109   The temporary URI &SHOULD; be given by the Location field in the
1110   response. Unless the request method was HEAD, the entity of the
1111   response &SHOULD; contain a short hypertext note with a hyperlink to
1112   the new URI(s).
1113</t>
1114<t>
1115   If the 302 status code is received in response to a request other
1116   than GET or HEAD, the user agent &MUST-NOT; automatically redirect the
1117   request unless it can be confirmed by the user, since this might
1118   change the conditions under which the request was issued.
1119  <list><t>
1120      <x:h>Note:</x:h> RFC 1945 and RFC 2068 specify that the client is not allowed
1121      to change the method on the redirected request.  However, most
1122      existing user agent implementations treat 302 as if it were a 303
1123      response, performing a GET on the Location field-value regardless
1124      of the original request method. The status codes 303 and 307 have
1125      been added for servers that wish to make unambiguously clear which
1126      kind of reaction is expected of the client.
1127  </t></list>
1128</t>
1129</section>
1130
1131<section title="303 See Other" anchor="status.303">
1132  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1133  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1134<t>
1135   The response to the request can be found under a different URI and
1136   &SHOULD; be retrieved using a GET method on that resource. This method
1137   exists primarily to allow the output of a POST-activated script to
1138   redirect the user agent to a selected resource. The new URI is not a
1139   substitute reference for the originally requested resource. The 303
1140   response &MUST-NOT; be cached, but the response to the second
1141   (redirected) request might be cacheable.
1142</t>
1143<t>
1144   The different URI &SHOULD; be given by the Location field in the
1145   response. Unless the request method was HEAD, the entity of the
1146   response &SHOULD; contain a short hypertext note with a hyperlink to
1147   the new URI(s).
1148  <list><t>
1149      <x:h>Note:</x:h> Many pre-HTTP/1.1 user agents do not understand the 303
1150      status. When interoperability with such clients is a concern, the
1151      302 status code may be used instead, since most user agents react
1152      to a 302 response as described here for 303.
1153  </t></list>
1154</t>
1155</section>
1156
1157<section title="304 Not Modified" anchor="status.304">
1158  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1159  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1160<t>
1161   If the client has performed a conditional GET request and access is
1162   allowed, but the document has not been modified, the server &SHOULD;
1163   respond with this status code. The 304 response &MUST-NOT; contain a
1164   message-body, and thus is always terminated by the first empty line
1165   after the header fields.
1166</t>
1167<t>
1168   The response &MUST; include the following header fields:
1169  <list style="symbols">
1170    <t>Date, unless its omission is required by [clockless.origin.server.operation]</t>
1171  </list>
1172</t>
1173<t>
1174   If a clockless origin server obeys these rules, and proxies and
1175   clients add their own Date to any response received without one (as
1176   already specified by [RFC 2068], section <xref target="RFC2068" x:sec="14.19" x:fmt="number"/>), caches will operate
1177   correctly.
1178  <list style="symbols">
1179    <t>ETag and/or Content-Location, if the header would have been sent
1180        in a 200 response to the same request</t>
1181    <t>Expires, Cache-Control, and/or Vary, if the field-value might
1182        differ from that sent in any previous response for the same
1183        variant</t>
1184  </list>
1185</t>
1186<t>
1187   If the conditional GET used a strong cache validator (see &caching;),
1188   the response &SHOULD-NOT;  include other entity-headers.
1189   Otherwise (i.e., the conditional GET used a weak validator), the
1190   response &MUST-NOT; include other entity-headers; this prevents
1191   inconsistencies between cached entity-bodies and updated headers.
1192</t>
1193<t>
1194   If a 304 response indicates an entity not currently cached, then the
1195   cache &MUST; disregard the response and repeat the request without the
1196   conditional.
1197</t>
1198<t>
1199   If a cache uses a received 304 response to update a cache entry, the
1200   cache &MUST; update the entry to reflect any new field values given in
1201   the response.
1202</t>
1203</section>
1204
1205<section title="305 Use Proxy" anchor="status.305">
1206  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1207  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1208<t>
1209   The requested resource &MUST; be accessed through the proxy given by
1210   the Location field. The Location field gives the URI of the proxy.
1211   The recipient is expected to repeat this single request via the
1212   proxy. 305 responses &MUST; only be generated by origin servers.
1213  <list><t>
1214      <x:h>Note:</x:h> RFC 2068 was not clear that 305 was intended to redirect a
1215      single request, and to be generated by origin servers only.  Not
1216      observing these limitations has significant security consequences.
1217  </t></list>
1218</t>
1219</section>
1220
1221<section title="306 (Unused)" anchor="status.306">
1222  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1223  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1224<t>
1225   The 306 status code was used in a previous version of the
1226   specification, is no longer used, and the code is reserved.
1227</t>
1228</section>
1229
1230<section title="307 Temporary Redirect" anchor="status.307">
1231  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1232  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1233<t>
1234   The requested resource resides temporarily under a different URI.
1235   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1236   continue to use the Request-URI for future requests.  This response
1237   is only cacheable if indicated by a Cache-Control or Expires header
1238   field.
1239</t>
1240<t>
1241   The temporary URI &SHOULD; be given by the Location field in the
1242   response. Unless the request method was HEAD, the entity of the
1243   response &SHOULD; contain a short hypertext note with a hyperlink to
1244   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1245   understand the 307 status. Therefore, the note &SHOULD; contain the
1246   information necessary for a user to repeat the original request on
1247   the new URI.
1248</t>
1249<t>
1250   If the 307 status code is received in response to a request other
1251   than GET or HEAD, the user agent &MUST-NOT; automatically redirect the
1252   request unless it can be confirmed by the user, since this might
1253   change the conditions under which the request was issued.
1254</t>
1255</section>
1256</section>
1257
1258<section title="Client Error 4xx" anchor="status.4xx">
1259<t>
1260   The 4xx class of status code is intended for cases in which the
1261   client seems to have erred. Except when responding to a HEAD request,
1262   the server &SHOULD; include an entity containing an explanation of the
1263   error situation, and whether it is a temporary or permanent
1264   condition. These status codes are applicable to any request method.
1265   User agents &SHOULD; display any included entity to the user.
1266</t>
1267<t>
1268   If the client is sending data, a server implementation using TCP
1269   &SHOULD; be careful to ensure that the client acknowledges receipt of
1270   the packet(s) containing the response, before the server closes the
1271   input connection. If the client continues sending data to the server
1272   after the close, the server's TCP stack will send a reset packet to
1273   the client, which may erase the client's unacknowledged input buffers
1274   before they can be read and interpreted by the HTTP application.
1275</t>
1276
1277<section title="400 Bad Request" anchor="status.400">
1278  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1279  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1280<t>
1281   The request could not be understood by the server due to malformed
1282   syntax. The client &SHOULD-NOT;  repeat the request without
1283   modifications.
1284</t>
1285</section>
1286
1287<section title="401 Unauthorized" anchor="status.401">
1288  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1289  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1290<t>
1291   The request requires user authentication. The response &MUST; include a
1292   WWW-Authenticate header field (&header-www-authenticate;) containing a challenge
1293   applicable to the requested resource. The client &MAY; repeat the
1294   request with a suitable Authorization header field (&header-authorization;). If
1295   the request already included Authorization credentials, then the 401
1296   response indicates that authorization has been refused for those
1297   credentials. If the 401 response contains the same challenge as the
1298   prior response, and the user agent has already attempted
1299   authentication at least once, then the user &SHOULD; be presented the
1300   entity that was given in the response, since that entity might
1301   include relevant diagnostic information. HTTP access authentication
1302   is explained in "HTTP Authentication: Basic and Digest Access
1303   Authentication" <xref target="RFC2617"/>.
1304</t>
1305</section>
1306
1307<section title="402 Payment Required" anchor="status.402">
1308  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1309  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1310<t>
1311   This code is reserved for future use.
1312</t>
1313</section>
1314
1315<section title="403 Forbidden" anchor="status.403">
1316  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1317  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1318<t>
1319   The server understood the request, but is refusing to fulfill it.
1320   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1321   If the request method was not HEAD and the server wishes to make
1322   public why the request has not been fulfilled, it &SHOULD; describe the
1323   reason for the refusal in the entity.  If the server does not wish to
1324   make this information available to the client, the status code 404
1325   (Not Found) can be used instead.
1326</t>
1327</section>
1328
1329<section title="404 Not Found" anchor="status.404">
1330  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1331  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1332<t>
1333   The server has not found anything matching the Request-URI. No
1334   indication is given of whether the condition is temporary or
1335   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1336   knows, through some internally configurable mechanism, that an old
1337   resource is permanently unavailable and has no forwarding address.
1338   This status code is commonly used when the server does not wish to
1339   reveal exactly why the request has been refused, or when no other
1340   response is applicable.
1341</t>
1342</section>
1343
1344<section title="405 Method Not Allowed" anchor="status.405">
1345  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1346  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1347<t>
1348   The method specified in the Request-Line is not allowed for the
1349   resource identified by the Request-URI. The response &MUST; include an
1350   Allow header containing a list of valid methods for the requested
1351   resource.
1352</t>
1353</section>
1354
1355<section title="406 Not Acceptable" anchor="status.406">
1356  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1357  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1358<t>
1359   The resource identified by the request is only capable of generating
1360   response entities which have content characteristics not acceptable
1361   according to the accept headers sent in the request.
1362</t>
1363<t>
1364   Unless it was a HEAD request, the response &SHOULD; include an entity
1365   containing a list of available entity characteristics and location(s)
1366   from which the user or user agent can choose the one most
1367   appropriate. The entity format is specified by the media type given
1368   in the Content-Type header field. Depending upon the format and the
1369   capabilities of the user agent, selection of the most appropriate
1370   choice &MAY; be performed automatically. However, this specification
1371   does not define any standard for such automatic selection.
1372  <list><t>
1373      <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1374      not acceptable according to the accept headers sent in the
1375      request. In some cases, this may even be preferable to sending a
1376      406 response. User agents are encouraged to inspect the headers of
1377      an incoming response to determine if it is acceptable.
1378  </t></list>
1379</t>
1380<t>
1381   If the response could be unacceptable, a user agent &SHOULD;
1382   temporarily stop receipt of more data and query the user for a
1383   decision on further actions.
1384</t>
1385</section>
1386
1387<section title="407 Proxy Authentication Required" anchor="status.407">
1388  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1389  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1390<t>
1391   This code is similar to 401 (Unauthorized), but indicates that the
1392   client must first authenticate itself with the proxy. The proxy &MUST;
1393   return a Proxy-Authenticate header field (&header-proxy-authenticate;) containing a
1394   challenge applicable to the proxy for the requested resource. The
1395   client &MAY; repeat the request with a suitable Proxy-Authorization
1396   header field (&header-proxy-authorization;). HTTP access authentication is explained
1397   in "HTTP Authentication: Basic and Digest Access Authentication"
1398   <xref target="RFC2617"/>.
1399</t>
1400</section>
1401
1402<section title="408 Request Timeout" anchor="status.408">
1403  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1404  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1405<t>
1406   The client did not produce a request within the time that the server
1407   was prepared to wait. The client &MAY; repeat the request without
1408   modifications at any later time.
1409</t>
1410</section>
1411
1412<section title="409 Conflict" anchor="status.409">
1413  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1414  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1415<t>
1416   The request could not be completed due to a conflict with the current
1417   state of the resource. This code is only allowed in situations where
1418   it is expected that the user might be able to resolve the conflict
1419   and resubmit the request. The response body &SHOULD; include enough
1420   information for the user to recognize the source of the conflict.
1421   Ideally, the response entity would include enough information for the
1422   user or user agent to fix the problem; however, that might not be
1423   possible and is not required.
1424</t>
1425<t>
1426   Conflicts are most likely to occur in response to a PUT request. For
1427   example, if versioning were being used and the entity being PUT
1428   included changes to a resource which conflict with those made by an
1429   earlier (third-party) request, the server might use the 409 response
1430   to indicate that it can't complete the request. In this case, the
1431   response entity would likely contain a list of the differences
1432   between the two versions in a format defined by the response
1433   Content-Type.
1434</t>
1435</section>
1436
1437<section title="410 Gone" anchor="status.410">
1438  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1439  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1440<t>
1441   The requested resource is no longer available at the server and no
1442   forwarding address is known. This condition is expected to be
1443   considered permanent. Clients with link editing capabilities &SHOULD;
1444   delete references to the Request-URI after user approval. If the
1445   server does not know, or has no facility to determine, whether or not
1446   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1447   used instead. This response is cacheable unless indicated otherwise.
1448</t>
1449<t>
1450   The 410 response is primarily intended to assist the task of web
1451   maintenance by notifying the recipient that the resource is
1452   intentionally unavailable and that the server owners desire that
1453   remote links to that resource be removed. Such an event is common for
1454   limited-time, promotional services and for resources belonging to
1455   individuals no longer working at the server's site. It is not
1456   necessary to mark all permanently unavailable resources as "gone" or
1457   to keep the mark for any length of time -- that is left to the
1458   discretion of the server owner.
1459</t>
1460</section>
1461
1462<section title="411 Length Required" anchor="status.411">
1463  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1464  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1465<t>
1466   The server refuses to accept the request without a defined Content-Length.
1467   The client &MAY; repeat the request if it adds a valid
1468   Content-Length header field containing the length of the message-body
1469   in the request message.
1470</t>
1471</section>
1472
1473<section title="412 Precondition Failed" anchor="status.412">
1474  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1475  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1476<t>
1477   The precondition given in one or more of the request-header fields
1478   evaluated to false when it was tested on the server. This response
1479   code allows the client to place preconditions on the current resource
1480   metainformation (header field data) and thus prevent the requested
1481   method from being applied to a resource other than the one intended.
1482</t>
1483</section>
1484
1485<section title="413 Request Entity Too Large" anchor="status.413">
1486  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1487  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1488<t>
1489   The server is refusing to process a request because the request
1490   entity is larger than the server is willing or able to process. The
1491   server &MAY; close the connection to prevent the client from continuing
1492   the request.
1493</t>
1494<t>
1495   If the condition is temporary, the server &SHOULD; include a Retry-After
1496   header field to indicate that it is temporary and after what
1497   time the client &MAY; try again.
1498</t>
1499</section>
1500
1501<section title="414 Request-URI Too Long" anchor="status.414">
1502  <iref primary="true" item="414 Request-URI Too Long (status code)" x:for-anchor=""/>
1503  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long" x:for-anchor=""/>
1504<t>
1505   The server is refusing to service the request because the Request-URI
1506   is longer than the server is willing to interpret. This rare
1507   condition is only likely to occur when a client has improperly
1508   converted a POST request to a GET request with long query
1509   information, when the client has descended into a URI "black hole" of
1510   redirection (e.g., a redirected URI prefix that points to a suffix of
1511   itself), or when the server is under attack by a client attempting to
1512   exploit security holes present in some servers using fixed-length
1513   buffers for reading or manipulating the Request-URI.
1514</t>
1515</section>
1516
1517<section title="415 Unsupported Media Type" anchor="status.415">
1518  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1519  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1520<t>
1521   The server is refusing to service the request because the entity of
1522   the request is in a format not supported by the requested resource
1523   for the requested method.
1524</t>
1525</section>
1526
1527<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1528  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1529  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1530<t>
1531   The request included a Range request-header field (&header-range;) and none of
1532   the range-specifier values in this field overlap the current extent
1533   of the selected resource.
1534</t>
1535</section>
1536
1537<section title="417 Expectation Failed" anchor="status.417">
1538  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1539  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1540<t>
1541   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1542   could not be met by this server, or, if the server is a proxy,
1543   the server has unambiguous evidence that the request could not be met
1544   by the next-hop server.
1545</t>
1546</section>
1547</section>
1548
1549<section title="Server Error 5xx" anchor="status.5xx">
1550<t>
1551   Response status codes beginning with the digit "5" indicate cases in
1552   which the server is aware that it has erred or is incapable of
1553   performing the request. Except when responding to a HEAD request, the
1554   server &SHOULD; include an entity containing an explanation of the
1555   error situation, and whether it is a temporary or permanent
1556   condition. User agents &SHOULD; display any included entity to the
1557   user. These response codes are applicable to any request method.
1558</t>
1559
1560<section title="500 Internal Server Error" anchor="status.500">
1561  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1562  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1563<t>
1564   The server encountered an unexpected condition which prevented it
1565   from fulfilling the request.
1566</t>
1567</section>
1568
1569<section title="501 Not Implemented" anchor="status.501">
1570  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1571  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1572<t>
1573   The server does not support the functionality required to fulfill the
1574   request. This is the appropriate response when the server does not
1575   recognize the request method and is not capable of supporting it for
1576   any resource.
1577</t>
1578</section>
1579
1580<section title="502 Bad Gateway" anchor="status.502">
1581  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1582  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1583<t>
1584   The server, while acting as a gateway or proxy, received an invalid
1585   response from the upstream server it accessed in attempting to
1586   fulfill the request.
1587</t>
1588</section>
1589
1590<section title="503 Service Unavailable" anchor="status.503">
1591  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1592  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1593<t>
1594   The server is currently unable to handle the request due to a
1595   temporary overloading or maintenance of the server. The implication
1596   is that this is a temporary condition which will be alleviated after
1597   some delay. If known, the length of the delay &MAY; be indicated in a
1598   Retry-After header. If no Retry-After is given, the client &SHOULD;
1599   handle the response as it would for a 500 response.
1600  <list><t>
1601      <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1602      server must use it when becoming overloaded. Some servers may wish
1603      to simply refuse the connection.
1604  </t></list>
1605</t>
1606</section>
1607
1608<section title="504 Gateway Timeout" anchor="status.504">
1609  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1610  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1611<t>
1612   The server, while acting as a gateway or proxy, did not receive a
1613   timely response from the upstream server specified by the URI (e.g.
1614   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1615   to access in attempting to complete the request.
1616  <list><t>
1617      <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1618      return 400 or 500 when DNS lookups time out.
1619  </t></list>
1620</t>
1621</section>
1622
1623<section title="505 HTTP Version Not Supported" anchor="status.505">
1624  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1625  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1626<t>
1627   The server does not support, or refuses to support, the HTTP protocol
1628   version that was used in the request message. The server is
1629   indicating that it is unable or unwilling to complete the request
1630   using the same major version as the client, as described in &http-version;,
1631   other than with this error message. The response &SHOULD; contain
1632   an entity describing why that version is not supported and what other
1633   protocols are supported by that server.
1634</t>
1635
1636</section>
1637</section>
1638</section>
1639
1640
1641<section title="Header Field Definitions" anchor="header.fields">
1642<t>
1643   This section defines the syntax and semantics of all standard
1644   HTTP/1.1 header fields. For entity-header fields, both sender and
1645   recipient refer to either the client or the server, depending on who
1646   sends and who receives the entity.
1647</t>
1648
1649<section title="Allow" anchor="header.allow">
1650  <iref primary="true" item="Allow header" x:for-anchor=""/>
1651  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1652<t>
1653      The Allow entity-header field lists the set of methods supported
1654      by the resource identified by the Request-URI. The purpose of this
1655      field is strictly to inform the recipient of valid methods
1656      associated with the resource. An Allow header field &MUST; be
1657      present in a 405 (Method Not Allowed) response.
1658</t>
1659<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
1660       Allow   = "Allow" ":" #Method
1661</artwork></figure>
1662<t>
1663      Example of use:
1664</t>
1665<figure><artwork type="example">
1666       Allow: GET, HEAD, PUT
1667</artwork></figure>
1668<t>
1669      This field cannot prevent a client from trying other methods.
1670      However, the indications given by the Allow header field value
1671      &SHOULD; be followed. The actual set of allowed methods is defined
1672      by the origin server at the time of each request.
1673</t>
1674<t>
1675      The Allow header field &MAY; be provided with a PUT request to
1676      recommend the methods to be supported by the new or modified
1677      resource. The server is not required to support these methods and
1678      &SHOULD; include an Allow header in the response giving the actual
1679      supported methods.
1680</t>
1681<t>
1682      A proxy &MUST-NOT; modify the Allow header field even if it does not
1683      understand all the methods specified, since the user agent might
1684      have other means of communicating with the origin server.
1685</t>
1686</section>
1687
1688<section title="Expect" anchor="header.expect">
1689  <iref primary="true" item="Expect header" x:for-anchor=""/>
1690  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1691<t>
1692   The Expect request-header field is used to indicate that particular
1693   server behaviors are required by the client.
1694</t>
1695<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"/>
1696   Expect       =  "Expect" ":" 1#expectation
1697
1698   expectation  =  "100-continue" | expectation-extension
1699   expectation-extension =  token [ "=" ( token | quoted-string )
1700                            *expect-params ]
1701   expect-params =  ";" token [ "=" ( token | quoted-string ) ]
1702</artwork></figure>
1703<t>
1704   A server that does not understand or is unable to comply with any of
1705   the expectation values in the Expect field of a request &MUST; respond
1706   with appropriate error status. The server &MUST; respond with a 417
1707   (Expectation Failed) status if any of the expectations cannot be met
1708   or, if there are other problems with the request, some other 4xx
1709   status.
1710</t>
1711<t>
1712   This header field is defined with extensible syntax to allow for
1713   future extensions. If a server receives a request containing an
1714   Expect field that includes an expectation-extension that it does not
1715   support, it &MUST; respond with a 417 (Expectation Failed) status.
1716</t>
1717<t>
1718   Comparison of expectation values is case-insensitive for unquoted
1719   tokens (including the 100-continue token), and is case-sensitive for
1720   quoted-string expectation-extensions.
1721</t>
1722<t>
1723   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1724   return a 417 (Expectation Failed) status if it receives a request
1725   with an expectation that it cannot meet. However, the Expect
1726   request-header itself is end-to-end; it &MUST; be forwarded if the
1727   request is forwarded.
1728</t>
1729<t>
1730   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1731   Expect header.
1732</t>
1733<t>
1734   See &use100; for the use of the 100 (continue) status.
1735</t>
1736</section>
1737
1738<section title="From" anchor="header.from">
1739  <iref primary="true" item="From header" x:for-anchor=""/>
1740  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1741<t>
1742   The From request-header field, if given, &SHOULD; contain an Internet
1743   e-mail address for the human user who controls the requesting user
1744   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1745   in RFC 822 <xref target="RFC822"/> as updated by RFC 1123 <xref target="RFC1123"/>:
1746</t>
1747<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
1748    From   = "From" ":" mailbox
1749</artwork></figure>
1750<t>
1751   An example is:
1752</t>
1753<figure><artwork type="example">
1754    From: webmaster@w3.org
1755</artwork></figure>
1756<t>
1757   This header field &MAY; be used for logging purposes and as a means for
1758   identifying the source of invalid or unwanted requests. It &SHOULD-NOT;
1759   be used as an insecure form of access protection. The interpretation
1760   of this field is that the request is being performed on behalf of the
1761   person given, who accepts responsibility for the method performed. In
1762   particular, robot agents &SHOULD; include this header so that the
1763   person responsible for running the robot can be contacted if problems
1764   occur on the receiving end.
1765</t>
1766<t>
1767   The Internet e-mail address in this field &MAY; be separate from the
1768   Internet host which issued the request. For example, when a request
1769   is passed through a proxy the original issuer's address &SHOULD; be
1770   used.
1771</t>
1772<t>
1773   The client &SHOULD-NOT;  send the From header field without the user's
1774   approval, as it might conflict with the user's privacy interests or
1775   their site's security policy. It is strongly recommended that the
1776   user be able to disable, enable, and modify the value of this field
1777   at any time prior to a request.
1778</t>
1779</section>
1780
1781<section title="Location" anchor="header.location">
1782  <iref primary="true" item="Location header" x:for-anchor=""/>
1783  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1784<t>
1785   The Location response-header field is used to redirect the recipient
1786   to a location other than the Request-URI for completion of the
1787   request or identification of a new resource. For 201 (Created)
1788   responses, the Location is that of the new resource which was created
1789   by the request. For 3xx responses, the location &SHOULD; indicate the
1790   server's preferred URI for automatic redirection to the resource. The
1791   field value consists of a single absolute URI.
1792</t>
1793<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
1794    Location       = "Location" ":" absoluteURI
1795</artwork></figure>
1796<t>
1797   An example is:
1798</t>
1799<figure><artwork type="example">
1800    Location: http://www.w3.org/pub/WWW/People.html
1801</artwork></figure>
1802<t>
1803  <list><t>
1804      <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1805      from Location in that the Content-Location identifies the original
1806      location of the entity enclosed in the request. It is therefore
1807      possible for a response to contain header fields for both Location
1808      and Content-Location.
1809  </t></list>
1810</t>
1811</section>
1812
1813<section title="Max-Forwards" anchor="header.max-forwards">
1814  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
1815  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
1816<t>
1817   The Max-Forwards request-header field provides a mechanism with the
1818   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1819   number of proxies or gateways that can forward the request to the
1820   next inbound server. This can be useful when the client is attempting
1821   to trace a request chain which appears to be failing or looping in
1822   mid-chain.
1823</t>
1824<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
1825    Max-Forwards   = "Max-Forwards" ":" 1*DIGIT
1826</artwork></figure>
1827<t>
1828   The Max-Forwards value is a decimal integer indicating the remaining
1829   number of times this request message may be forwarded.
1830</t>
1831<t>
1832   Each proxy or gateway recipient of a TRACE or OPTIONS request
1833   containing a Max-Forwards header field &MUST; check and update its
1834   value prior to forwarding the request. If the received value is zero
1835   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
1836   respond as the final recipient. If the received Max-Forwards value is
1837   greater than zero, then the forwarded message &MUST; contain an updated
1838   Max-Forwards field with a value decremented by one (1).
1839</t>
1840<t>
1841   The Max-Forwards header field &MAY; be ignored for all other methods
1842   defined by this specification and for any extension methods for which
1843   it is not explicitly referred to as part of that method definition.
1844</t>
1845</section>
1846
1847<section title="Referer" anchor="header.referer">
1848  <iref primary="true" item="Referer header" x:for-anchor=""/>
1849  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
1850<t>
1851   The Referer[sic] request-header field allows the client to specify,
1852   for the server's benefit, the address (URI) of the resource from
1853   which the Request-URI was obtained (the "referrer", although the
1854   header field is misspelled.) The Referer request-header allows a
1855   server to generate lists of back-links to resources for interest,
1856   logging, optimized caching, etc. It also allows obsolete or mistyped
1857   links to be traced for maintenance. The Referer field &MUST-NOT; be
1858   sent if the Request-URI was obtained from a source that does not have
1859   its own URI, such as input from the user keyboard.
1860</t>
1861<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
1862    Referer        = "Referer" ":" ( absoluteURI | relativeURI )
1863</artwork></figure>
1864<t>
1865   Example:
1866</t>
1867<figure><artwork type="example">
1868    Referer: http://www.w3.org/hypertext/DataSources/Overview.html
1869</artwork></figure>
1870<t>
1871   If the field value is a relative URI, it &SHOULD; be interpreted
1872   relative to the Request-URI. The URI &MUST-NOT; include a fragment. See
1873   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
1874</t>
1875</section>
1876
1877<section title="Retry-After" anchor="header.retry-after">
1878  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
1879  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
1880<t>
1881   The Retry-After response-header field can be used with a 503 (Service
1882   Unavailable) response to indicate how long the service is expected to
1883   be unavailable to the requesting client. This field &MAY; also be used
1884   with any 3xx (Redirection) response to indicate the minimum time the
1885   user-agent is asked wait before issuing the redirected request. The
1886   value of this field can be either an HTTP-date or an integer number
1887   of seconds (in decimal) after the time of the response.
1888</t>
1889<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
1890    Retry-After  = "Retry-After" ":" ( HTTP-date | delta-seconds )
1891</artwork></figure>
1892<t>
1893   Two examples of its use are
1894</t>
1895<figure><artwork type="example">
1896    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
1897    Retry-After: 120
1898</artwork></figure>
1899<t>
1900   In the latter example, the delay is 2 minutes.
1901</t>
1902</section>
1903
1904<section title="Server" anchor="header.server">
1905  <iref primary="true" item="Server header" x:for-anchor=""/>
1906  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
1907<t>
1908   The Server response-header field contains information about the
1909   software used by the origin server to handle the request. The field
1910   can contain multiple product tokens (<xref target="product.tokens"/>) and comments
1911   identifying the server and any significant subproducts. The product
1912   tokens are listed in order of their significance for identifying the
1913   application.
1914</t>
1915<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
1916    Server         = "Server" ":" 1*( product | comment )
1917</artwork></figure>
1918<t>
1919   Example:
1920</t>
1921<figure><artwork type="example">
1922    Server: CERN/3.0 libwww/2.17
1923</artwork></figure>
1924<t>
1925   If the response is being forwarded through a proxy, the proxy
1926   application &MUST-NOT; modify the Server response-header. Instead, it
1927   &SHOULD; include a Via field (as described in &header-via;).
1928  <list><t>
1929      <x:h>Note:</x:h> Revealing the specific software version of the server might
1930      allow the server machine to become more vulnerable to attacks
1931      against software that is known to contain security holes. Server
1932      implementors are encouraged to make this field a configurable
1933      option.
1934  </t></list>
1935</t>
1936</section>
1937
1938<section title="User-Agent" anchor="header.user-agent">
1939  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
1940  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
1941<t>
1942   The User-Agent request-header field contains information about the
1943   user agent originating the request. This is for statistical purposes,
1944   the tracing of protocol violations, and automated recognition of user
1945   agents for the sake of tailoring responses to avoid particular user
1946   agent limitations. User agents &SHOULD; include this field with
1947   requests. The field can contain multiple product tokens (<xref target="product.tokens"/>)
1948   and comments identifying the agent and any subproducts which form a
1949   significant part of the user agent. By convention, the product tokens
1950   are listed in order of their significance for identifying the
1951   application.
1952</t>
1953<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
1954    User-Agent     = "User-Agent" ":" 1*( product | comment )
1955</artwork></figure>
1956<t>
1957   Example:
1958</t>
1959<figure><artwork type="example">
1960    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1961</artwork></figure>
1962</section>
1963
1964</section>
1965
1966<section title="IANA Considerations" anchor="IANA.considerations">
1967<t>
1968   TBD.
1969</t>
1970</section>
1971
1972<section title="Security Considerations" anchor="security.considerations">
1973<t>
1974   This section is meant to inform application developers, information
1975   providers, and users of the security limitations in HTTP/1.1 as
1976   described by this document. The discussion does not include
1977   definitive solutions to the problems revealed, though it does make
1978   some suggestions for reducing security risks.
1979</t>
1980
1981<section title="Transfer of Sensitive Information" anchor="security.sensitive">
1982<t>
1983   Like any generic data transfer protocol, HTTP cannot regulate the
1984   content of the data that is transferred, nor is there any a priori
1985   method of determining the sensitivity of any particular piece of
1986   information within the context of any given request. Therefore,
1987   applications &SHOULD; supply as much control over this information as
1988   possible to the provider of that information. Four header fields are
1989   worth special mention in this context: Server, Via, Referer and From.
1990</t>
1991<t>
1992   Revealing the specific software version of the server might allow the
1993   server machine to become more vulnerable to attacks against software
1994   that is known to contain security holes. Implementors &SHOULD; make the
1995   Server header field a configurable option.
1996</t>
1997<t>
1998   Proxies which serve as a portal through a network firewall &SHOULD;
1999   take special precautions regarding the transfer of header information
2000   that identifies the hosts behind the firewall. In particular, they
2001   &SHOULD; remove, or replace with sanitized versions, any Via fields
2002   generated behind the firewall.
2003</t>
2004<t>
2005   The Referer header allows reading patterns to be studied and reverse
2006   links drawn. Although it can be very useful, its power can be abused
2007   if user details are not separated from the information contained in
2008   the Referer. Even when the personal information has been removed, the
2009   Referer header might indicate a private document's URI whose
2010   publication would be inappropriate.
2011</t>
2012<t>
2013   The information sent in the From field might conflict with the user's
2014   privacy interests or their site's security policy, and hence it
2015   &SHOULD-NOT;  be transmitted without the user being able to disable,
2016   enable, and modify the contents of the field. The user &MUST; be able
2017   to set the contents of this field within a user preference or
2018   application defaults configuration.
2019</t>
2020<t>
2021   We suggest, though do not require, that a convenient toggle interface
2022   be provided for the user to enable or disable the sending of From and
2023   Referer information.
2024</t>
2025<t>
2026   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2027   fields can sometimes be used to determine that a specific client or
2028   server have a particular security hole which might be exploited.
2029   Unfortunately, this same information is often used for other valuable
2030   purposes for which HTTP currently has no better mechanism.
2031</t>
2032</section>
2033
2034<section title="Encoding Sensitive Information in URI's" anchor="encoding.sensitive.information.in.uris">
2035<t>
2036   Because the source of a link might be private information or might
2037   reveal an otherwise private information source, it is strongly
2038   recommended that the user be able to select whether or not the
2039   Referer field is sent. For example, a browser client could have a
2040   toggle switch for browsing openly/anonymously, which would
2041   respectively enable/disable the sending of Referer and From
2042   information.
2043</t>
2044<t>
2045   Clients &SHOULD-NOT;  include a Referer header field in a (non-secure)
2046   HTTP request if the referring page was transferred with a secure
2047   protocol.
2048</t>
2049<t>
2050   Authors of services which use the HTTP protocol &SHOULD-NOT;  use GET
2051   based forms for the submission of sensitive data, because this will
2052   cause this data to be encoded in the Request-URI. Many existing
2053   servers, proxies, and user agents will log the request URI in some
2054   place where it might be visible to third parties. Servers can use
2055   POST-based form submission instead
2056</t>
2057</section>
2058
2059<section title="Location Headers and Spoofing" anchor="location.spoofing">
2060<t>
2061   If a single server supports multiple organizations that do not trust
2062   one another, then it &MUST; check the values of Location and Content-Location
2063   headers in responses that are generated under control of
2064   said organizations to make sure that they do not attempt to
2065   invalidate resources over which they have no authority.
2066</t>
2067</section>
2068
2069</section>
2070
2071<section title="Acknowledgments" anchor="ack">
2072<t>
2073   Based on an XML translation of RFC 2616 by Julian Reschke.
2074</t>
2075</section>
2076</middle>
2077<back>
2078<references>
2079
2080<reference anchor="Part1">
2081  <front>
2082    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2083 
2084    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2085      <organization abbrev="Day Software">Day Software</organization>
2086      <address>
2087        <email>fielding@gbiv.com</email>
2088      </address>
2089    </author>
2090 
2091    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2092      <organization>One Laptop per Child</organization>
2093      <address>
2094        <email>jg@laptop.org</email>
2095      </address>
2096    </author>
2097   
2098    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2099      <organization abbrev="HP">Hewlett-Packard Company</organization>
2100      <address>
2101        <email>JeffMogul@acm.org</email>
2102      </address>
2103    </author>
2104 
2105    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2106      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2107      <address>
2108        <email>henrikn@microsoft.com</email>
2109      </address>
2110    </author>
2111 
2112    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2113      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2114      <address>
2115        <email>LMM@acm.org</email>
2116      </address>
2117    </author>
2118   
2119    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2120      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2121      <address>
2122        <email>paulle@microsoft.com</email>
2123      </address>
2124    </author>
2125     
2126    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2127      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2128      <address>
2129        <email>timbl@w3.org</email>
2130      </address>
2131    </author>
2132 
2133    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2134  </front>
2135  <seriesInfo name="Internet-Draft" value="draft-fielding-p1-messaging-&ID-VERSION;"/>
2136  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2137</reference>
2138
2139<reference anchor="Part3">
2140  <front>
2141    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2142 
2143    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2144      <organization abbrev="Day Software">Day Software</organization>
2145      <address>
2146        <email>fielding@gbiv.com</email>
2147      </address>
2148    </author>
2149 
2150    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2151      <organization>One Laptop per Child</organization>
2152      <address>
2153        <email>jg@laptop.org</email>
2154      </address>
2155    </author>
2156   
2157    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2158      <organization abbrev="HP">Hewlett-Packard Company</organization>
2159      <address>
2160        <email>JeffMogul@acm.org</email>
2161      </address>
2162    </author>
2163 
2164    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2165      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2166      <address>
2167        <email>henrikn@microsoft.com</email>
2168      </address>
2169    </author>
2170 
2171    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2172      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2173      <address>
2174        <email>LMM@acm.org</email>
2175      </address>
2176    </author>
2177   
2178    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2179      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2180      <address>
2181        <email>paulle@microsoft.com</email>
2182      </address>
2183    </author>
2184     
2185    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2186      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2187      <address>
2188        <email>timbl@w3.org</email>
2189      </address>
2190    </author>
2191 
2192    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2193  </front>
2194  <seriesInfo name="Internet-Draft" value="draft-fielding-p3-payload-&ID-VERSION;"/>
2195  <x:source href="p3-payload.xml" basename="p3-payload"/>
2196</reference>
2197
2198<reference anchor="Part4">
2199  <front>
2200    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2201 
2202    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2203      <organization abbrev="Day Software">Day Software</organization>
2204      <address>
2205        <email>fielding@gbiv.com</email>
2206      </address>
2207    </author>
2208 
2209    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2210      <organization>One Laptop per Child</organization>
2211      <address>
2212        <email>jg@laptop.org</email>
2213      </address>
2214    </author>
2215   
2216    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2217      <organization abbrev="HP">Hewlett-Packard Company</organization>
2218      <address>
2219        <email>JeffMogul@acm.org</email>
2220      </address>
2221    </author>
2222 
2223    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2224      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2225      <address>
2226        <email>henrikn@microsoft.com</email>
2227      </address>
2228    </author>
2229 
2230    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2231      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2232      <address>
2233        <email>LMM@acm.org</email>
2234      </address>
2235    </author>
2236   
2237    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2238      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2239      <address>
2240        <email>paulle@microsoft.com</email>
2241      </address>
2242    </author>
2243     
2244    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2245      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2246      <address>
2247        <email>timbl@w3.org</email>
2248      </address>
2249    </author>
2250 
2251    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2252  </front>
2253  <seriesInfo name="Internet-Draft" value="draft-fielding-p4-conditional-&ID-VERSION;"/>
2254  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2255</reference>
2256
2257<reference anchor="Part5">
2258  <front>
2259    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2260 
2261    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2262      <organization abbrev="Day Software">Day Software</organization>
2263      <address>
2264        <email>fielding@gbiv.com</email>
2265      </address>
2266    </author>
2267 
2268    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2269      <organization>One Laptop per Child</organization>
2270      <address>
2271        <email>jg@laptop.org</email>
2272      </address>
2273    </author>
2274   
2275    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2276      <organization abbrev="HP">Hewlett-Packard Company</organization>
2277      <address>
2278        <email>JeffMogul@acm.org</email>
2279      </address>
2280    </author>
2281 
2282    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2283      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2284      <address>
2285        <email>henrikn@microsoft.com</email>
2286      </address>
2287    </author>
2288 
2289    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2290      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2291      <address>
2292        <email>LMM@acm.org</email>
2293      </address>
2294    </author>
2295   
2296    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2297      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2298      <address>
2299        <email>paulle@microsoft.com</email>
2300      </address>
2301    </author>
2302     
2303    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2304      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2305      <address>
2306        <email>timbl@w3.org</email>
2307      </address>
2308    </author>
2309 
2310    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2311  </front>
2312  <seriesInfo name="Internet-Draft" value="draft-fielding-p5-range-&ID-VERSION;"/>
2313  <x:source href="p5-range.xml" basename="p5-range"/>
2314</reference>
2315
2316<reference anchor="Part6">
2317  <front>
2318    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2319 
2320    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2321      <organization abbrev="Day Software">Day Software</organization>
2322      <address>
2323        <email>fielding@gbiv.com</email>
2324      </address>
2325    </author>
2326 
2327    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2328      <organization>One Laptop per Child</organization>
2329      <address>
2330        <email>jg@laptop.org</email>
2331      </address>
2332    </author>
2333   
2334    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2335      <organization abbrev="HP">Hewlett-Packard Company</organization>
2336      <address>
2337        <email>JeffMogul@acm.org</email>
2338      </address>
2339    </author>
2340 
2341    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2342      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2343      <address>
2344        <email>henrikn@microsoft.com</email>
2345      </address>
2346    </author>
2347 
2348    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2349      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2350      <address>
2351        <email>LMM@acm.org</email>
2352      </address>
2353    </author>
2354   
2355    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2356      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2357      <address>
2358        <email>paulle@microsoft.com</email>
2359      </address>
2360    </author>
2361     
2362    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2363      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2364      <address>
2365        <email>timbl@w3.org</email>
2366      </address>
2367    </author>
2368 
2369    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2370  </front>
2371  <seriesInfo name="Internet-Draft" value="draft-fielding-p6-cache-&ID-VERSION;"/>
2372  <x:source href="p6-cache.xml" basename="p6-cache"/>
2373</reference>
2374
2375<reference anchor="Part7">
2376  <front>
2377    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2378 
2379    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2380      <organization abbrev="Day Software">Day Software</organization>
2381      <address>
2382        <email>fielding@gbiv.com</email>
2383      </address>
2384    </author>
2385 
2386    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2387      <organization>One Laptop per Child</organization>
2388      <address>
2389        <email>jg@laptop.org</email>
2390      </address>
2391    </author>
2392   
2393    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2394      <organization abbrev="HP">Hewlett-Packard Company</organization>
2395      <address>
2396        <email>JeffMogul@acm.org</email>
2397      </address>
2398    </author>
2399 
2400    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2401      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2402      <address>
2403        <email>henrikn@microsoft.com</email>
2404      </address>
2405    </author>
2406 
2407    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2408      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2409      <address>
2410        <email>LMM@acm.org</email>
2411      </address>
2412    </author>
2413   
2414    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2415      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2416      <address>
2417        <email>paulle@microsoft.com</email>
2418      </address>
2419    </author>
2420     
2421    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2422      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2423      <address>
2424        <email>timbl@w3.org</email>
2425      </address>
2426    </author>
2427 
2428    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2429  </front>
2430  <seriesInfo name="Internet-Draft" value="draft-fielding-p7-auth-&ID-VERSION;"/>
2431  <x:source href="p7-auth.xml" basename="p7-auth"/>
2432</reference>
2433
2434<reference anchor="RFC1123">
2435<front>
2436<title>Requirements for Internet Hosts - Application and Support</title>
2437<author initials="R." surname="Braden" fullname="Robert Braden">
2438<organization>University of Southern California (USC), Information Sciences Institute</organization>
2439<address>
2440<postal>
2441<street>4676 Admiralty Way</street>
2442<city>Marina del Rey</city>
2443<region>CA</region>
2444<code>90292-6695</code>
2445<country>US</country></postal>
2446<phone>+1 213 822 1511</phone>
2447<email>Braden@ISI.EDU</email></address></author>
2448<date month="October" year="1989"/></front>
2449<seriesInfo name="STD" value="3"/>
2450<seriesInfo name="RFC" value="1123"/>
2451</reference>
2452
2453<reference anchor="RFC822">
2454<front>
2455<title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
2456<author initials="D.H." surname="Crocker" fullname="David H. Crocker">
2457<organization>University of Delaware, Dept. of Electrical Engineering</organization>
2458<address>
2459<postal>
2460<street/>
2461<city>Newark</city>
2462<region>DE</region>
2463<code>19711</code>
2464<country>US</country></postal>
2465<email>DCrocker@UDel-Relay</email></address></author>
2466<date month="August" day="13" year="1982"/></front>
2467<seriesInfo name="STD" value="11"/>
2468<seriesInfo name="RFC" value="822"/>
2469</reference>
2470
2471<reference anchor="RFC2068">
2472<front>
2473<title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2474<author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2475<organization>University of California, Irvine, Department of Information and Computer Science</organization>
2476<address>
2477<postal>
2478<street/>
2479<city>Irvine</city>
2480<region>CA</region>
2481<code>92717-3425</code>
2482<country>US</country></postal>
2483<facsimile>+1 714 824 4056</facsimile>
2484<email>fielding@ics.uci.edu</email></address></author>
2485<author initials="J." surname="Gettys" fullname="Jim Gettys">
2486<organization>MIT Laboratory for Computer Science</organization>
2487<address>
2488<postal>
2489<street>545 Technology Square</street>
2490<city>Cambridge</city>
2491<region>MA</region>
2492<code>02139</code>
2493<country>US</country></postal>
2494<facsimile>+1 617 258 8682</facsimile>
2495<email>jg@w3.org</email></address></author>
2496<author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2497<organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2498<address>
2499<postal>
2500<street>250 University Avenue</street>
2501<city>Palo Alto</city>
2502<region>CA</region>
2503<code>94301</code>
2504<country>US</country></postal>
2505<email>mogul@wrl.dec.com</email></address></author>
2506<author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2507<organization>MIT Laboratory for Computer Science</organization>
2508<address>
2509<postal>
2510<street>545 Technology Square</street>
2511<city>Cambridge</city>
2512<region>MA</region>
2513<code>02139</code>
2514<country>US</country></postal>
2515<facsimile>+1 617 258 8682</facsimile>
2516<email>frystyk@w3.org</email></address></author>
2517<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2518<organization>MIT Laboratory for Computer Science</organization>
2519<address>
2520<postal>
2521<street>545 Technology Square</street>
2522<city>Cambridge</city>
2523<region>MA</region>
2524<code>02139</code>
2525<country>US</country></postal>
2526<facsimile>+1 617 258 8682</facsimile>
2527<email>timbl@w3.org</email></address></author>
2528<date month="January" year="1997"/>
2529<abstract>
2530<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>
2531<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>
2532<seriesInfo name="RFC" value="2068"/>
2533</reference>
2534
2535<reference anchor="RFC2617">
2536<front>
2537<title abbrev="HTTP Authentication">HTTP Authentication: Basic and Digest Access Authentication</title>
2538<author initials="J." surname="Franks" fullname="John Franks">
2539<organization>Northwestern University, Department of Mathematics</organization>
2540<address>
2541<postal>
2542<street/>
2543<city>Evanston</city>
2544<region>IL</region>
2545<code>60208-2730</code>
2546<country>US</country></postal>
2547<email>john@math.nwu.edu</email></address></author>
2548<author initials="P.M." surname="Hallam-Baker" fullname="Phillip M. Hallam-Baker">
2549<organization>Verisign Inc.</organization>
2550<address>
2551<postal>
2552<street>301 Edgewater Place</street>
2553<street>Suite 210</street>
2554<city>Wakefield</city>
2555<region>MA</region>
2556<code>01880</code>
2557<country>US</country></postal>
2558<email>pbaker@verisign.com</email></address></author>
2559<author initials="J.L." surname="Hostetler" fullname="Jeffery L. Hostetler">
2560<organization>AbiSource, Inc.</organization>
2561<address>
2562<postal>
2563<street>6 Dunlap Court</street>
2564<city>Savoy</city>
2565<region>IL</region>
2566<code>61874</code>
2567<country>US</country></postal>
2568<email>jeff@AbiSource.com</email></address></author>
2569<author initials="S.D." surname="Lawrence" fullname="Scott D. Lawrence">
2570<organization>Agranat Systems, Inc.</organization>
2571<address>
2572<postal>
2573<street>5 Clocktower Place</street>
2574<street>Suite 400</street>
2575<city>Maynard</city>
2576<region>MA</region>
2577<code>01754</code>
2578<country>US</country></postal>
2579<email>lawrence@agranat.com</email></address></author>
2580<author initials="P.J." surname="Leach" fullname="Paul J. Leach">
2581<organization>Microsoft Corporation</organization>
2582<address>
2583<postal>
2584<street>1 Microsoft Way</street>
2585<city>Redmond</city>
2586<region>WA</region>
2587<code>98052</code>
2588<country>US</country></postal>
2589<email>paulle@microsoft.com</email></address></author>
2590<author initials="A." surname="Luotonen" fullname="Ari Luotonen">
2591<organization>Netscape Communications Corporation</organization>
2592<address>
2593<postal>
2594<street>501 East Middlefield Road</street>
2595<city>Mountain View</city>
2596<region>CA</region>
2597<code>94043</code>
2598<country>US</country></postal></address></author>
2599<author initials="L." surname="Stewart" fullname="Lawrence C. Stewart">
2600<organization>Open Market, Inc.</organization>
2601<address>
2602<postal>
2603<street>215 First Street</street>
2604<city>Cambridge</city>
2605<region>MA</region>
2606<code>02142</code>
2607<country>US</country></postal>
2608<email>stewart@OpenMarket.com</email></address></author>
2609<date month="June" year="1999"/>
2610</front>
2611<seriesInfo name="RFC" value="2617"/>
2612</reference>
2613
2614<reference anchor="Luo1998">
2615<front>
2616<title>Tunneling TCP based protocols through Web proxy servers</title>
2617<author initials="A." surname="Luotonen" fullname="A. Luotonen">
2618  <organization/>
2619</author>
2620<date/>
2621</front>
2622<seriesInfo name="" value="Work in Progress"/>
2623</reference>
2624
2625</references>
2626
2627<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2628<t>
2629   Clarified which error code should be used for inbound server failures
2630   (e.g. DNS failures). (<xref target="status.504"/>).
2631</t>
2632<t>
2633   CREATE had a race that required an Etag be sent when a resource is
2634   first created. (<xref target="status.201"/>).
2635</t>
2636<t>
2637   Rewrite of message transmission requirements to make it much harder
2638   for implementors to get it wrong, as the consequences of errors here
2639   can have significant impact on the Internet, and to deal with the
2640   following problems:
2641  <list style="numbers">
2642      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
2643         this was incorrectly placing a requirement on the behavior of
2644         an implementation of a future version of HTTP/1.x</t>
2645
2646      <t>Made it clear that user-agents should retry requests, not
2647         "clients" in general.</t>
2648
2649      <t>Converted requirements for clients to ignore unexpected 100
2650         (Continue) responses, and for proxies to forward 100 responses,
2651         into a general requirement for 1xx responses.</t>
2652
2653      <t>Modified some TCP-specific language, to make it clearer that
2654         non-TCP transports are possible for HTTP.</t>
2655
2656      <t>Require that the origin server &MUST-NOT; wait for the request
2657         body before it sends a required 100 (Continue) response.</t>
2658
2659      <t>Allow, rather than require, a server to omit 100 (Continue) if
2660         it has already seen some of the request body.</t>
2661
2662      <t>Allow servers to defend against denial-of-service attacks and
2663         broken clients.</t>
2664  </list>
2665</t>
2666<t>
2667   This change adds the Expect header and 417 status code.
2668</t>
2669<t>
2670   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
2671   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
2672</t>
2673<t>
2674   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
2675   implemented in previous versions of this specification. See RFC 2068
2676   <xref target="RFC2068"/>.
2677</t>
2678</section>
2679</back>
2680</rfc>
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