source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1496

Last change on this file since 1496 was 1496, checked in by julian.reschke@…, 8 years ago

Note that some recipients are lax in processing the Location header field (see #185)

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File size: 195.2 KB
[29]1<?xml version="1.0" encoding="utf-8"?>
[101]2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
[8]3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
[29]14  <!ENTITY ID-VERSION "latest">
[1481]15  <!ENTITY ID-MONTH "December">
[1099]16  <!ENTITY ID-YEAR "2011">
[1101]17  <!ENTITY mdash "&#8212;">
[1452]18  <!ENTITY architecture               "<xref target='Part1' x:rel='#architecture' xmlns:x=''/>">
[424]19  <!ENTITY notation                   "<xref target='Part1' x:rel='#notation' xmlns:x=''/>">
[1364]20  <!ENTITY acks                       "<xref target='Part1' x:rel='#acks' xmlns:x=''/>">
[31]21  <!ENTITY messaging                  "<xref target='Part1' xmlns:x=''/>">
22  <!ENTITY payload                    "<xref target='Part3' xmlns:x=''/>">
23  <!ENTITY conditional                "<xref target='Part4' xmlns:x=''/>">
24  <!ENTITY range                      "<xref target='Part5' xmlns:x=''/>">
25  <!ENTITY caching                    "<xref target='Part6' xmlns:x=''/>">
26  <!ENTITY auth                       "<xref target='Part7' xmlns:x=''/>">
27  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x=''/>">
[1452]28  <!ENTITY agent-driven-negotiation   "<xref target='Part3' x:rel='#agent-driven.negotiation' xmlns:x=''/>">
[205]29  <!ENTITY notation-abnf              "<xref target='Part1' x:rel='#notation.abnf' xmlns:x=''/>">
30  <!ENTITY basic-rules                "<xref target='Part1' x:rel='#basic.rules' xmlns:x=''/>">
[1396]31  <!ENTITY field-rules                "<xref target='Part1' x:rel='#field.rules' xmlns:x=''/>">
[31]32  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x=''/>">
[823]33  <!ENTITY effective-request-uri      "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x=''/>">
[1309]34  <!ENTITY intermediaries             "<xref target='Part1' x:rel='#intermediaries' xmlns:x=''/>">
[1417]35  <!ENTITY chunked-encoding           "<xref target='Part1' x:rel='#chunked.encoding' xmlns:x=''/>">
[31]36  <!ENTITY http-url                   "<xref target='Part1' x:rel='#http-url' xmlns:x=''/>">
37  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x=''/>">
38  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x=''/>">
39  <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x=''/>">
[1065]40  <!ENTITY request-target             "<xref target='Part1' x:rel='#request-target' xmlns:x=''/>">
[31]41  <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x=''/>">
42  <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x=''/>">
43  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x=''/>">
44  <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x=''/>">
45  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x=''/>">
46  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x=''/>">
47  <!ENTITY header-authorization       "<xref target='Part7' x:rel='#header.authorization' xmlns:x=''/>">
48  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
[1417]49  <!ENTITY header-connection          "<xref target='Part1' x:rel='#header.connection' xmlns:x=''/>">
[31]50  <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x=''/>">
51  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x=''/>">
[1448]52  <!ENTITY header-content-type        "<xref target='Part3' x:rel='#header.content-type' xmlns:x=''/>">
[31]53  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x=''/>">
54  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x=''/>">
[688]55  <!ENTITY header-fields              "<xref target='Part1' x:rel='#header.fields' xmlns:x=''/>">
[31]56  <!ENTITY header-host                "<xref target='Part1' x:rel='' xmlns:x=''/>">
57  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x=''/>">
58  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x=''/>">
59  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x=''/>">
60  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x=''/>">
61  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x=''/>">
62  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
63  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x=''/>">
64  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x=''/>">
65  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x=''/>">
[835]66  <!ENTITY header-upgrade             "<xref target='Part1' x:rel='#header.upgrade' xmlns:x=''/>">
67  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.te' xmlns:x=''/>">
[31]68  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x=''/>">
69  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x=''/>">
70  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
71  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x=''/>">
[1448]72  <!ENTITY media-types                "<xref target='Part3' x:rel='#media.types' xmlns:x=''/>">
[31]73  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x=''/>">
[190]74  <!ENTITY product-tokens             "<xref target='Part1' x:rel='#product.tokens' xmlns:x=''/>">
[263]75  <!ENTITY media-type-message-http    "<xref target='Part1' x:rel='' xmlns:x=''/>">
[700]76  <!ENTITY status-206                 "<xref target='Part5' x:rel='#status.206' xmlns:x=''/>">
77  <!ENTITY status-304                 "<xref target='Part4' x:rel='#status.304' xmlns:x=''/>">
78  <!ENTITY status-401                 "<xref target='Part7' x:rel='#status.401' xmlns:x=''/>">
79  <!ENTITY status-407                 "<xref target='Part7' x:rel='#status.407' xmlns:x=''/>">
80  <!ENTITY status-412                 "<xref target='Part4' x:rel='#status.412' xmlns:x=''/>">
81  <!ENTITY status-416                 "<xref target='Part5' x:rel='#status.416' xmlns:x=''/>">
[1415]82  <!ENTITY p3-header-fields           "<xref target='Part3' x:rel='#header.field.definitions' xmlns:x=''/>">
[838]83  <!ENTITY p4-status-codes            "<xref target='Part4' x:rel='#status.code.definitions' xmlns:x=''/>">
84  <!ENTITY p5-status-codes            "<xref target='Part5' x:rel='#status.code.definitions' xmlns:x=''/>">
85  <!ENTITY p7-status-codes            "<xref target='Part7' x:rel='#status.code.definitions' xmlns:x=''/>">
[1050]86  <!ENTITY p6-heuristic               "<xref target='Part6' x:rel='#heuristic.freshness' xmlns:x=''/>">
[1111]87  <!ENTITY p6-explicit                "<xref target='Part6' x:rel='#calculating.freshness.lifetime' xmlns:x=''/>">
88  <!ENTITY p6-invalid                 "<xref target='Part6' x:rel='#invalidation.after.updates.or.deletions' xmlns:x=''/>">
90<?rfc toc="yes" ?>
[29]91<?rfc symrefs="yes" ?>
92<?rfc sortrefs="yes" ?>
[8]93<?rfc compact="yes"?>
94<?rfc subcompact="no" ?>
95<?rfc linkmailto="no" ?>
96<?rfc editing="no" ?>
[203]97<?rfc comments="yes"?>
98<?rfc inline="yes"?>
[799]99<?rfc rfcedstyle="yes"?>
[8]100<?rfc-ext allow-markup-in-artwork="yes" ?>
101<?rfc-ext include-references-in-index="yes" ?>
[1477]102<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="proposed"
[446]103     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
[286]104     xmlns:x=''
105     xmlns:rdf=''>
[1472]106<x:link rel="prev" basename="p1-messaging"/>
107<x:link rel="next" basename="p3-payload"/>
[120]110  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
[29]112  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]113    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[8]114    <address>
115      <postal>
[1106]116        <street>345 Park Ave</street>
117        <city>San Jose</city>
[8]118        <region>CA</region>
[1106]119        <code>95110</code>
[29]120        <country>USA</country>
[8]121      </postal>
[29]122      <email></email>
123      <uri></uri>
[8]124    </address>
125  </author>
[29]127  <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]128    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
[8]129    <address>
130      <postal>
[29]131        <street>21 Oak Knoll Road</street>
132        <city>Carlisle</city>
[8]133        <region>MA</region>
[29]134        <code>01741</code>
135        <country>USA</country>
[8]136      </postal>
[844]137      <email></email>
138      <uri></uri>
[8]139    </address>
140  </author>
142  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
[29]143    <organization abbrev="HP">Hewlett-Packard Company</organization>
[8]144    <address>
145      <postal>
[29]146        <street>HP Labs, Large Scale Systems Group</street>
147        <street>1501 Page Mill Road, MS 1177</street>
[8]148        <city>Palo Alto</city>
149        <region>CA</region>
[29]150        <code>94304</code>
151        <country>USA</country>
[8]152      </postal>
[29]153      <email></email>
[8]154    </address>
155  </author>
157  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
[29]158    <organization abbrev="Microsoft">Microsoft Corporation</organization>
[8]159    <address>
160      <postal>
[29]161        <street>1 Microsoft Way</street>
162        <city>Redmond</city>
163        <region>WA</region>
164        <code>98052</code>
165        <country>USA</country>
[8]166      </postal>
[29]167      <email></email>
[8]168    </address>
169  </author>
171  <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]172    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[8]173    <address>
174      <postal>
[29]175        <street>345 Park Ave</street>
176        <city>San Jose</city>
[8]177        <region>CA</region>
[29]178        <code>95110</code>
179        <country>USA</country>
[8]180      </postal>
[29]181      <email></email>
182      <uri></uri>
[8]183    </address>
184  </author>
186  <author initials="P." surname="Leach" fullname="Paul J. Leach">
187    <organization abbrev="Microsoft">Microsoft Corporation</organization>
188    <address>
189      <postal>
190        <street>1 Microsoft Way</street>
191        <city>Redmond</city>
192        <region>WA</region>
193        <code>98052</code>
194      </postal>
195      <email></email>
196    </address>
197  </author>
199  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
200    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
201    <address>
202      <postal>
[34]203        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
204        <street>The Stata Center, Building 32</street>
205        <street>32 Vassar Street</street>
[8]206        <city>Cambridge</city>
207        <region>MA</region>
208        <code>02139</code>
[29]209        <country>USA</country>
[8]210      </postal>
211      <email></email>
[34]212      <uri></uri>
[8]213    </address>
214  </author>
[95]216  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
[94]217    <organization abbrev="W3C">World Wide Web Consortium</organization>
218    <address>
219      <postal>
220        <street>W3C / ERCIM</street>
221        <street>2004, rte des Lucioles</street>
222        <city>Sophia-Antipolis</city>
223        <region>AM</region>
224        <code>06902</code>
225        <country>France</country>
226      </postal>
227      <email></email>
228      <uri></uri>
229    </address>
230  </author>
[95]232  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
233    <organization abbrev="greenbytes">greenbytes GmbH</organization>
234    <address>
235      <postal>
236        <street>Hafenweg 16</street>
237        <city>Muenster</city><region>NW</region><code>48155</code>
238        <country>Germany</country>
239      </postal>
[609]240      <phone>+49 251 2807760</phone>
241      <facsimile>+49 251 2807761</facsimile>
242      <email></email>
243      <uri></uri>
[95]244    </address>
245  </author>
[31]247  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
[440]248  <workgroup>HTTPbis Working Group</workgroup>
[1373]252   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
253   distributed, collaborative, hypertext information systems. HTTP has been in
254   use by the World Wide Web global information initiative since 1990. This
255   document is Part 2 of the seven-part specification that defines the protocol
256   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
259   Part 2 defines the semantics of HTTP messages as expressed by request
260   methods, request header fields, response status codes, and response header
261   fields.
265<note title="Editorial Note (To be removed by RFC Editor)">
266  <t>
267    Discussion of this draft should take place on the HTTPBIS working group
[1268]268    mailing list (, which is archived at
269    <eref target=""/>.
270  </t>
271  <t>
272    The current issues list is at
273    <eref target=""/> and related
274    documents (including fancy diffs) can be found at
[324]275    <eref target=""/>.
[36]276  </t>
[153]277  <t>
[1467]278    The changes in this draft are summarized in <xref target="changes.since.17"/>.
[153]279  </t>
283<section title="Introduction" anchor="introduction">
[162]285   This document defines HTTP/1.1 request and response semantics.  Each HTTP
286   message, as defined in &messaging;, is in the form of either a request or
287   a response.  An HTTP server listens on a connection for HTTP requests and
288   responds to each request, in the order received on that connection, with
289   one or more HTTP response messages.  This document defines the commonly
290   agreed upon semantics of the HTTP uniform interface, the intentions defined
291   by each request method, and the various response messages that might be
[965]292   expected as a result of applying that method to the target resource.
[162]295   This document is currently disorganized in order to minimize the changes
296   between drafts and enable reviewers to see the smaller errata changes.
[980]297   A future draft will reorganize the sections to better reflect the content.
[162]298   In particular, the sections will be ordered according to the typical
299   processing of an HTTP request message (after message parsing): resource
[1163]300   mapping, methods, request modifying header fields, response status,
301   status modifying header fields, and resource metadata.  The current mess
302   reflects how widely dispersed these topics and associated requirements
303   had become in <xref target="RFC2616"/>.
[1452]306<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
308   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
309   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
310   document are to be interpreted as described in <xref target="RFC2119"/>.
[1452]313   This document defines conformance criteria for several roles in HTTP
314   communication, including Senders, Recipients, Clients, Servers, User-Agents,
315   Origin Servers, Intermediaries, Proxies and Gateways. See &architecture;
316   for definitions of these terms.
319   An implementation is considered conformant if it complies with all of the
320   requirements associated with its role(s). Note that SHOULD-level requirements
321   are relevant here, unless one of the documented exceptions is applicable.
324   This document also uses ABNF to define valid protocol elements
325   (<xref target="notation"/>). In addition to the prose requirements placed
326   upon them, Senders &MUST-NOT; generate protocol elements that are invalid.
329   Unless noted otherwise, Recipients &MAY; take steps to recover a usable
330   protocol element from an invalid construct. However, HTTP does not define
331   specific error handling mechanisms, except in cases where it has direct
332   impact on security. This is because different uses of the protocol require
333   different error handling strategies; for example, a Web browser may wish to
334   transparently recover from a response where the Location header field
335   doesn't parse according to the ABNF, whereby in a systems control protocol
336   using HTTP, this type of error recovery could lead to dangerous consequences.
[424]340<section title="Syntax Notation" anchor="notation">
[425]341  <x:anchor-alias value="CR"/>
342  <x:anchor-alias value="DIGIT"/>
343  <x:anchor-alias value="LF"/>
[1425]344  <x:anchor-alias value="HTAB"/>
[425]345  <x:anchor-alias value="VCHAR"/>
[1425]346  <x:anchor-alias value="SP"/>
[543]348  This specification uses the ABNF syntax defined in &notation; (which
349  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
350  <xref target="collected.abnf"/> shows the collected ABNF, with the list
351  rule expanded.
[425]354  The following core rules are included by
355  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
356  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
357  DIGIT (decimal 0-9), DQUOTE (double quote),
[1425]358  HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
359  OCTET (any 8-bit sequence of data), SP (space), and
360  VCHAR (any visible US-ASCII character).
363<section title="Core Rules" anchor="core.rules">
[398]364  <x:anchor-alias value="obs-text"/>
[229]365  <x:anchor-alias value="quoted-string"/>
366  <x:anchor-alias value="token"/>
[1494]367  <x:anchor-alias value="BWS"/>
[356]368  <x:anchor-alias value="OWS"/>
369  <x:anchor-alias value="RWS"/>
[1396]371  The core rules below are defined in <xref target="Part1"/>:
373<figure><artwork type="abnf2616">
[1494]374  <x:ref>BWS</x:ref>           = &lt;BWS, defined in &basic-rules;&gt;
[356]375  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &basic-rules;&gt;
376  <x:ref>RWS</x:ref>           = &lt;RWS, defined in &basic-rules;&gt;
[398]377  <x:ref>obs-text</x:ref>      = &lt;obs-text, defined in &basic-rules;&gt;
[1396]378  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &field-rules;&gt;
379  <x:ref>token</x:ref>         = &lt;token, defined in &field-rules;&gt;
383<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
[374]384  <x:anchor-alias value="absolute-URI"/>
[688]385  <x:anchor-alias value="comment"/>
[391]386  <x:anchor-alias value="partial-URI"/>
[229]387  <x:anchor-alias value="product"/>
[785]388  <x:anchor-alias value="URI-reference"/>
[206]390  The ABNF rules below are defined in other parts:
[207]392<figure><!--Part1--><artwork type="abnf2616">
[374]393  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in &uri;&gt;
[688]394  <x:ref>comment</x:ref>       = &lt;comment, defined in &header-fields;&gt;
[391]395  <x:ref>partial-URI</x:ref>   = &lt;partial-URI, defined in &uri;&gt;
[229]396  <x:ref>product</x:ref>       = &lt;product, defined in &product-tokens;&gt;
[785]397  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in &uri;&gt;
[8]403<section title="Method" anchor="method">
[229]404  <x:anchor-alias value="Method"/>
405  <x:anchor-alias value="extension-method"/>
[1161]407   The Method token indicates the request method to be performed on the target
[972]408   resource (&effective-request-uri;). The method is case-sensitive.
[1128]410<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
411  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
414   The list of methods allowed by a resource can be specified in an
[965]415   Allow header field (<xref target="header.allow"/>). The status code of the response
[8]416   always notifies the client whether a method is currently allowed on a
417   resource, since the set of allowed methods can change dynamically. An
[965]418   origin server &SHOULD; respond with the status code 405 (Method Not Allowed)
[8]419   if the method is known by the origin server but not allowed for the
[965]420   resource, and 501 (Not Implemented) if the method is
[8]421   unrecognized or not implemented by the origin server. The methods GET
422   and HEAD &MUST; be supported by all general-purpose servers. All other
423   methods are &OPTIONAL;; however, if the above methods are implemented,
424   they &MUST; be implemented with the same semantics as those specified
425   in <xref target="method.definitions"/>.
[1128]428<section title="Overview of Methods" anchor="overview.of.methods">
430  The methods listed below are defined in <xref target="method.definitions"/>.
432<texttable align="left">
433  <ttcol>Method Name</ttcol><ttcol>Defined in...</ttcol>
435  <c>OPTIONS</c> <c><xref target="OPTIONS"/></c>
436  <c>GET</c> <c><xref target="GET"/></c>
437  <c>HEAD</c> <c><xref target="HEAD"/></c>
438  <c>POST</c> <c><xref target="POST"/></c>
439  <c>PUT</c> <c><xref target="PUT"/></c>
440  <c>DELETE</c> <c><xref target="DELETE"/></c>
441  <c>TRACE</c> <c><xref target="TRACE"/></c>
442  <c>CONNECT</c> <c><xref target="CONNECT"/></c>
[1161]445  Note that this list is not exhaustive &mdash; it does not include request methods defined
[1128]446  in other specifications.
[270]450<section title="Method Registry" anchor="method.registry">
452  The HTTP Method Registry defines the name space for the Method token in the
453  Request line of an HTTP request.
[286]456  Registrations &MUST; include the following fields:
457  <list style="symbols">
458    <t>Method Name (see <xref target="method"/>)</t>
459    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
460    <t>Pointer to specification text</t>
461  </list>
[270]464  Values to be added to this name space are subject to IETF review
[591]465  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
[672]468  The registry itself is maintained at <eref target=""/>.
[1037]471<section title="Considerations for New Methods" anchor="">
473   When it is necessary to express new semantics for a HTTP request that
474   aren't specific to a single application or media type, and currently defined
475   methods are inadequate, it may be appropriate to register a new method.
[1042]478   HTTP methods are generic; that is, they are potentially applicable to any
479   resource, not just one particular media type, "type" of resource, or
480   application. As such, it is preferred that new HTTP methods be registered
481   in a document that isn't specific to a single application, so that this is
482   clear.
[1040]485   Due to the parsing rules defined in &message-body;, definitions of HTTP
486   methods cannot prohibit the presence of a message-body on either the request
487   or the response message (with responses to HEAD requests being the single
488   exception). Definitions of new methods cannot change this rule, but they can
489   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
[1042]492   New method definitions need to indicate whether they are safe (<xref
[1261]493   target="safe.methods"/>), what semantics (if any) the request body has,
494   and whether they are idempotent (<xref target="idempotent.methods"/>).
495   They also need to state whether they can be cached (&caching;); in
496   particular what conditions a cache may store the response, and under what
497   conditions such a stored response may be used to satisfy a subsequent
498   request.
[1416]505<section title="Header Fields" anchor="header.fields">
507   Header fields are key value pairs that can be used to communicate data about
508   the message, its payload, the target resource, or about the connection
509   itself (i.e., control data).  See &header-fields; for a general definition
510   of their syntax.
[1417]513<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
515   New header fields are registered using the procedures described in
516   <xref target="RFC3864"/>.
519   The requirements for header field names are defined in
520   <xref target="RFC3864" x:fmt="of" x:sec="4.1"/>.  Authors of specifications
521   defining new fields are advised to keep the name as short as practical, and
522   not to prefix them with "X-" if they are to be registered (either
523   immediately or in the future).
526   New header field values typically have their syntax defined using ABNF
527   (<xref target="RFC5234"/>), using the extensions defined in &notation-abnf;
528   as necessary, and are usually constrained to the range of ASCII characters.
529   Header fields needing a greater range of characters can use an encoding
530   such as the one defined in <xref target="RFC5987"/>.
533   Because commas (",") are used as a generic delimiter between field-values,
534   they need to be treated with care if they are allowed in the field-value's
535   payload. Typically, components that might contain a comma are protected with
536   double-quotes using the quoted-string ABNF production (&field-rules;).
539   For example, a textual date and a URI (either of which might contain a comma)
540   could be safely carried in field-values like these:
542<figure><artwork type="example">
543  Example-URI-Field: ",foo",
544                     ""
545  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
[1493]548   Note that double quote delimiters almost always are used with the
549   quoted-string production; using a different syntax inside double quotes
550   will likely cause unnecessary confusion.
[1451]553   Many header fields use a format including (case-insensitively) named
554   parameters (for instance, Content-Type, defined in &header-content-type;).
555   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
[1463]556   parameter value enables recipients to use existing parser components. When
557   allowing both forms, the meaning of a parameter value ought to be
558   independent of the syntax used for it (for an example, see the notes on
559   parameter handling for media types in &media-types;).
[1417]562   Authors of specifications defining new header fields are advised to consider
563   documenting:
564  <list style="symbols">
[1446]565    <x:lt>
566      <t>Whether the field is a single value, or whether it can be a list
567      (delimited by commas; see &header-fields;).</t>
[1463]568      <t>If it does not use the list syntax, document how to treat messages
569      where the header field occurs multiple times (a sensible default would
570      be to ignore the header field, but this might not always be the right
571      choice).</t>
572      <t>Note that intermediaries and software libraries might combine
[1458]573      multiple header field instances into a single one, despite the header
574      field not allowing this. A robust format enables recipients to discover
575      these situations (good example: "Content-Type", as the comma can only
576      appear inside quoted strings; bad example: "Location", as a comma can
577      occur inside a URI).</t>
[1446]578    </x:lt>
579    <x:lt><t>Under what conditions the header field can be used; e.g., only in
[1417]580    responses or requests, in all messages, only on responses to a particular
[1446]581    request method.</t></x:lt>
582    <x:lt><t>Whether it is appropriate to list the field-name in the Connection header
583    (i.e., if the header is to be hop-by-hop, see &header-connection;).</t></x:lt>
584    <x:lt><t>Under what conditions intermediaries are allowed to modify the header
585    field's value, insert or delete it.</t></x:lt>
586    <x:lt><t>How the header might interact with caching (see <xref target="Part6"/>).</t></x:lt>
587    <x:lt><t>Whether the header field is useful or allowable in trailers (see
588    &chunked-encoding;).</t></x:lt>
589    <x:lt><t>Whether the header field should be preserved across redirects.</t></x:lt>
[1417]590  </list>
[8]594<section title="Request Header Fields" anchor="request.header.fields">
[229]595  <x:anchor-alias value="request-header"/>
[1163]597   The request header fields allow the client to pass additional
[8]598   information about the request, and about the client itself, to the
599   server. These fields act as request modifiers, with semantics
600   equivalent to the parameters on a programming language method
601   invocation.
[1138]603<texttable align="left">
604  <ttcol>Header Field Name</ttcol>
605  <ttcol>Defined in...</ttcol>
607  <c>Accept</c> <c>&header-accept;</c>
608  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
609  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
610  <c>Accept-Language</c> <c>&header-accept-language;</c>
611  <c>Authorization</c> <c>&header-authorization;</c>
612  <c>Expect</c> <c><xref target="header.expect"/></c>
613  <c>From</c> <c><xref target="header.from"/></c>
614  <c>Host</c> <c>&header-host;</c>
615  <c>If-Match</c> <c>&header-if-match;</c>
616  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
617  <c>If-None-Match</c> <c>&header-if-none-match;</c>
618  <c>If-Range</c> <c>&header-if-range;</c>
619  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
620  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
621  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
622  <c>Range</c> <c>&header-range;</c>
623  <c>Referer</c> <c><xref target="header.referer"/></c>
624  <c>TE</c> <c>&header-te;</c>
625  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
[1416]629<section title="Response Header Fields" anchor="response.header.fields">
630  <x:anchor-alias value="response-header"/>
632   The response header fields allow the server to pass additional
633   information about the response which cannot be placed in the Status-Line.
634   These header fields give information about the server and about
635   further access to the target resource (&effective-request-uri;).
637<texttable align="left">
638  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
640  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
641  <c>Age</c> <c>&header-age;</c>
642  <c>Allow</c> <c><xref target="header.allow"/></c>
[1436]643  <c>Date</c> <c><xref target=""/></c>
[1416]644  <c>ETag</c> <c>&header-etag;</c>
645  <c>Location</c> <c><xref target="header.location"/></c>
646  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
647  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
648  <c>Server</c> <c><xref target="header.server"/></c>
649  <c>Vary</c> <c>&header-vary;</c>
650  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
[8]656<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
[229]657  <x:anchor-alias value="Reason-Phrase"/>
658  <x:anchor-alias value="Status-Code"/>
[426]659  <x:anchor-alias value="extension-code"/>
[1124]661   The Status-Code element is a 3-digit integer result code of the attempt to
662   understand and satisfy the request.
[1124]665   The Reason-Phrase is intended to give a short textual description of the
[1137]666   Status-Code and is intended for a human user. The client does not need
[1124]667   to examine or display the Reason-Phrase.
669<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"/>
[1124]670  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
[1425]671  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
674   HTTP status codes are extensible. HTTP applications are not required
675   to understand the meaning of all registered status codes, though such
676   understanding is obviously desirable. However, applications &MUST;
677   understand the class of any status code, as indicated by the first
678   digit, and treat any unrecognized response as being equivalent to the
679   x00 status code of that class, with the exception that an
680   unrecognized response &MUST-NOT; be cached. For example, if an
681   unrecognized status code of 431 is received by the client, it can
682   safely assume that there was something wrong with its request and
683   treat the response as if it had received a 400 status code. In such
[866]684   cases, user agents &SHOULD; present to the user the representation enclosed
685   with the response, since that representation is likely to include human-readable
[8]686   information which will explain the unusual status.
[1124]689<section title="Overview of Status Codes" anchor="">
[1137]691   The status codes listed below are defined in <xref target=""/>
692   of this specification, &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
693   The reason phrases listed here are only recommendations &mdash; they can be
694   replaced by local equivalents without affecting the protocol.
696<texttable align="left">
697  <ttcol>Status-Code</ttcol>
698  <ttcol>Reason-Phrase</ttcol>
699  <ttcol>Defined in...</ttcol>
701  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
702  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
704  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
705  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
706  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
707  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
708  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
709  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
710  <c>206</c> <c>Partial Content</c> <c>&status-206;</c>
712  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
713  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
714  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
715  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
716  <c>304</c> <c>Not Modified</c> <c>&status-304;</c>
717  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
718  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
720  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
721  <c>401</c> <c>Unauthorized</c> <c>&status-401;</c>
722  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
723  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
724  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
725  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
726  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
727  <c>407</c> <c>Proxy Authentication Required</c> <c>&status-407;</c>
728  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
729  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
730  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
731  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
732  <c>412</c> <c>Precondition Failed</c> <c>&status-412;</c>
[1322]733  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
[1124]734  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
735  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
736  <c>416</c> <c>Requested range not satisfiable</c> <c>&status-416;</c>
737  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
738  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
740  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
741  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
742  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
743  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
744  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
745  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
748   Note that this list is not exhaustive &mdash; it does not include
749   extension status codes defined in other specifications.
[262]753<section title="Status Code Registry" anchor="status.code.registry">
755  The HTTP Status Code Registry defines the name space for the Status-Code
[924]756  token in the Status-Line of an HTTP response.
759  Values to be added to this name space are subject to IETF review
[591]760  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
763  The registry itself is maintained at <eref target=""/>.
[1038]766<section title="Considerations for New Status Codes" anchor="">
768   When it is necessary to express new semantics for a HTTP response that
769   aren't specific to a single application or media type, and currently defined
770   status codes are inadequate, a new status code can be registered.
[1043]773   HTTP status codes are generic; that is, they are potentially applicable to
774   any resource, not just one particular media type, "type" of resource, or
775   application. As such, it is preferred that new HTTP status codes be
776   registered in a document that isn't specific to a single application, so
777   that this is clear.
[1043]780   Definitions of new HTTP status codes typically explain the request
781   conditions that produce a response containing the status code (e.g.,
782   combinations of request headers and/or method(s)), along with any
783   interactions with response headers (e.g., those that are required, those
784   that modify the semantics of the response).
787   New HTTP status codes are required to fall under one of the categories
788   defined in <xref target=""/>. To allow existing parsers to
789   properly handle them, new status codes cannot disallow a response body,
790   although they can mandate a zero-length response body. They can require the
791   presence of one or more particular HTTP response header(s).
794   Likewise, their definitions can specify that caches are allowed to use
[1035]795   heuristics to determine their freshness (see &caching;; by default, it is
[1043]796   not allowed), and can define how to determine the resource which they
[1035]797   carry a representation for (see <xref
798   target="identifying.response.associated.with.representation"/>; by default,
[1038]799   it is anonymous).
[874]807<section title="Representation" anchor="representation">
[866]809   Request and Response messages &MAY; transfer a representation if not otherwise
810   restricted by the request method or response status code. A representation
811   consists of metadata (representation header fields) and data (representation
812   body).  When a complete or partial representation is enclosed in an HTTP message,
813   it is referred to as the payload of the message. HTTP representations
814   are defined in &payload;.
[866]817   A representation body is only present in a message when a message-body is
818   present, as described in &message-body;. The representation body is obtained
[8]819   from the message-body by decoding any Transfer-Encoding that might
820   have been applied to ensure safe and proper transfer of the message.
823<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
[965]825   It is sometimes necessary to determine an identifier for the resource
[695]826   associated with a representation.
829   An HTTP request representation, when present, is always associated with an
830   anonymous (i.e., unidentified) resource.
[972]833   In the common case, an HTTP response is a representation of the target
834   resource (see &effective-request-uri;). However, this is not always the
835   case. To determine the URI of the resource a response is associated with,
836   the following rules are used (with the first applicable one being selected):
838<t><list style="numbers">
839   <t>If the response status code is 200 or 203 and the request method was GET,
[972]840   the response payload is a representation of the target resource.</t>
[924]841   <t>If the response status code is 204, 206, or 304 and the request method was GET
[972]842   or HEAD, the response payload is a partial representation of the target
[1374]843   resource.</t>
[994]844   <t>If the response has a Content-Location header field, and that URI is the same
[965]845   as the effective request URI, the response payload is a representation of the
[972]846   target resource.</t>
[994]847   <t>If the response has a Content-Location header field, and that URI is not the
[965]848   same as the effective request URI, then the response asserts that its
849   payload is a representation of the resource identified by the
850   Content-Location URI. However, such an assertion cannot be trusted unless
851   it can be verified by other means (not defined by HTTP).</t>
[695]852   <t>Otherwise, the response is a representation of an anonymous (i.e.,
853   unidentified) resource.</t>
856  <cref anchor="TODO-req-uri">
[823]857   The comparison function is going to have to be defined somewhere,
[695]858   because we already need to compare URIs for things like cache invalidation.</cref>
[8]865<section title="Method Definitions" anchor="method.definitions">
[1161]867   The set of common request methods for HTTP/1.1 is defined below. Although
[8]868   this set can be expanded, additional methods cannot be assumed to
869   share the same semantics for separately extended clients and servers.
872<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
874<section title="Safe Methods" anchor="safe.methods">
[286]875<iref item="Safe Methods" primary="true"/>
[969]877   Implementors need to be aware that the software represents the user in
878   their interactions over the Internet, and need to allow
[901]879   the user to be aware of any actions they take which might have an
[8]880   unexpected significance to themselves or others.
[708]883   In particular, the convention has been established that the GET, HEAD,
[1161]884   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
885   of taking an action other than retrieval. These request methods ought
886   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
[8]887   This allows user agents to represent other methods, such as POST, PUT
888   and DELETE, in a special way, so that the user is made aware of the
889   fact that a possibly unsafe action is being requested.
892   Naturally, it is not possible to ensure that the server does not
893   generate side-effects as a result of performing a GET request; in
894   fact, some dynamic resources consider that a feature. The important
895   distinction here is that the user did not request the side-effects,
896   so therefore cannot be held accountable for them.
900<section title="Idempotent Methods" anchor="idempotent.methods">
[286]901<iref item="Idempotent Methods" primary="true"/>
[1161]903   Request methods can also have the property of "idempotence" in that,
904   aside from error or expiration issues, the intended effect of multiple
[657]905   identical requests is the same as for a single request.
[1161]906   PUT, DELETE, and all safe request methods are idempotent.
[657]907   It is important to note that idempotence refers only to changes
908   requested by the client: a server is free to change its state due
909   to multiple requests for the purpose of tracking those requests,
910   versioning of results, etc.
915<section title="OPTIONS" anchor="OPTIONS">
[286]916  <rdf:Description>
917    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
918  </rdf:Description>
[8]919  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
920  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
[1161]922   The OPTIONS method requests information about the
[8]923   communication options available on the request/response chain
[1161]924   identified by the effective request URI. This method allows a client to
[8]925   determine the options and/or requirements associated with a resource,
926   or the capabilities of a server, without implying a resource action
927   or initiating a resource retrieval.
[1161]930   Responses to the OPTIONS method are not cacheable.
[874]933   If the OPTIONS request includes a message-body (as indicated by the
[8]934   presence of Content-Length or Transfer-Encoding), then the media type
935   &MUST; be indicated by a Content-Type field. Although this
936   specification does not define any use for such a body, future
937   extensions to HTTP might use the OPTIONS body to make more detailed
[280]938   queries on the server.
[391]941   If the request-target is an asterisk ("*"), the OPTIONS request is
[8]942   intended to apply to the server in general rather than to a specific
943   resource. Since a server's communication options typically depend on
944   the resource, the "*" request is only useful as a "ping" or "no-op"
945   type of method; it does nothing beyond allowing the client to test
946   the capabilities of the server. For example, this can be used to test
947   a proxy for HTTP/1.1 compliance (or lack thereof).
[391]950   If the request-target is not an asterisk, the OPTIONS request applies
[8]951   only to the options that are available when communicating with that
952   resource.
955   A 200 response &SHOULD; include any header fields that indicate
956   optional features implemented by the server and applicable to that
957   resource (e.g., Allow), possibly including extensions not defined by
958   this specification. The response body, if any, &SHOULD; also include
959   information about the communication options. The format for such a
960   body is not defined by this specification, but might be defined by
961   future extensions to HTTP. Content negotiation &MAY; be used to select
962   the appropriate response format. If no response body is included, the
963   response &MUST; include a Content-Length field with a field-value of
964   "0".
[1163]967   The Max-Forwards header field &MAY; be used to target a
[893]968   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
969   If no Max-Forwards field is present in the request, then the forwarded
[8]970   request &MUST-NOT; include a Max-Forwards field.
974<section title="GET" anchor="GET">
[286]975  <rdf:Description>
976    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
977  </rdf:Description>
[8]978  <iref primary="true" item="GET method" x:for-anchor=""/>
979  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
[1161]981   The GET method requests transfer of a current representation of
982   the target resource.
[972]985   If the target resource is a data-producing process, it is the
[866]986   produced data which shall be returned as the representation in the response and not
[730]987   the source text of the process, unless that text happens to be the output of
988   the process.
991   The semantics of the GET method change to a "conditional GET" if the
992   request message includes an If-Modified-Since, If-Unmodified-Since,
993   If-Match, If-None-Match, or If-Range header field. A conditional GET
[1161]994   requests that the representation be transferred only under the
[8]995   circumstances described by the conditional header field(s). The
[1161]996   conditional GET request is intended to reduce unnecessary network
[874]997   usage by allowing cached representations to be refreshed without requiring
[8]998   multiple requests or transferring data already held by the client.
1001   The semantics of the GET method change to a "partial GET" if the
1002   request message includes a Range header field. A partial GET requests
[866]1003   that only part of the representation be transferred, as described in &header-range;.
[1161]1004   The partial GET request is intended to reduce unnecessary
[866]1005   network usage by allowing partially-retrieved representations to be
[8]1006   completed without transferring data already held by the client.
1009   Bodies on GET requests have no defined semantics. Note that sending a body
1010   on a GET request might cause some existing implementations to reject the
1011   request.
[888]1014   The response to a GET request is cacheable and &MAY; be used to satisfy
1015   subsequent GET and HEAD requests (see &caching;).
1018   See <xref target=""/> for security considerations when used for forms.
1022<section title="HEAD" anchor="HEAD">
[286]1023  <rdf:Description>
1024    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1025  </rdf:Description>
[8]1026  <iref primary="true" item="HEAD method" x:for-anchor=""/>
1027  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
1029   The HEAD method is identical to GET except that the server &MUST-NOT;
[867]1030   return a message-body in the response. The metadata contained
[994]1031   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
[8]1032   to the information sent in response to a GET request. This method can
[867]1033   be used for obtaining metadata about the representation implied by the
[866]1034   request without transferring the representation body. This method is
[8]1035   often used for testing hypertext links for validity, accessibility,
1036   and recent modification.
[888]1039   The response to a HEAD request is cacheable and &MAY; be used to satisfy
1040   a subsequent HEAD request; see &caching;. It also &MAY; be used to update a previously cached
1041   representation from that resource; if the new field values
[874]1042   indicate that the cached representation differs from the current representation (as
[1367]1043   would be indicated by a change in Content-Length, ETag
[8]1044   or Last-Modified), then the cache &MUST; treat the cache entry as
1045   stale.
1048   Bodies on HEAD requests have no defined semantics. Note that sending a body
1049   on a HEAD request might cause some existing implementations to reject the
1050   request.
1054<section title="POST" anchor="POST">
1055  <iref primary="true" item="POST method" x:for-anchor=""/>
1056  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
[1161]1058   The POST method requests that the origin server accept the
[972]1059   representation enclosed in the request as data to be processed by the
1060   target resource. POST is designed to allow a uniform method to cover the
1061   following functions:
[8]1062  <list style="symbols">
1063    <t>
1064      Annotation of existing resources;
1065    </t>
1066    <t>
1067        Posting a message to a bulletin board, newsgroup, mailing list,
1068        or similar group of articles;
1069    </t>
1070    <t>
1071        Providing a block of data, such as the result of submitting a
1072        form, to a data-handling process;
1073    </t>
1074    <t>
1075        Extending a database through an append operation.
1076    </t>
1077  </list>
1080   The actual function performed by the POST method is determined by the
[965]1081   server and is usually dependent on the effective request URI.
1084   The action performed by the POST method might not result in a
1085   resource that can be identified by a URI. In this case, either 200
[924]1086   (OK) or 204 (No Content) is the appropriate response status code,
[874]1087   depending on whether or not the response includes a representation that
[8]1088   describes the result.
1091   If a resource has been created on the origin server, the response
[874]1092   &SHOULD; be 201 (Created) and contain a representation which describes the
[8]1093   status of the request and refers to the new resource, and a Location
[994]1094   header field (see <xref target="header.location"/>).
[910]1097   Responses to POST requests are only cacheable when they
1098   include explicit freshness information (see &p6-explicit;). A
[994]1099   cached POST response with a Content-Location header field
[972]1100   (see &header-content-location;) whose value is the effective
[910]1101   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
1104   Note that POST caching is not widely implemented.
[888]1105   However, the 303 (See Other) response can be used to direct the
1106   user agent to retrieve a cacheable resource.
1110<section title="PUT" anchor="PUT">
1111  <iref primary="true" item="PUT method" x:for-anchor=""/>
1112  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
[1161]1114   The PUT method requests that the state of the target resource
[1158]1115   be created or replaced with the state defined by the representation
1116   enclosed in the request message payload.  A successful PUT of a given
1117   representation would suggest that a subsequent GET on that same target
1118   resource will result in an equivalent representation being returned in
1119   a 200 (OK) response.  However, there is no guarantee that such a state
1120   change will be observable, since the target resource might be acted
1121   upon by other user agents in parallel, or might be subject to dynamic
1122   processing by the origin server, before any subsequent GET is received.
1123   A successful response only implies that the user agent's intent was
1124   achieved at the time of its processing by the origin server.
[1158]1127   If the target resource does not have a current representation and
1128   the PUT successfully creates one, then the origin server &MUST; inform
1129   the user agent by sending a 201 (Created) response.  If the target
1130   resource does have a current representation and that representation is
1131   successfully modified in accordance with the state of the enclosed
1132   representation, then either a 200 (OK) or 204 (No Content) response
1133   &SHOULD; be sent to indicate successful completion of the request.
1136   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
1137   as part of the resource state).
[1158]1140   An origin server &SHOULD; verify that the PUT representation is
1141   consistent with any constraints which the server has for the target
1142   resource that cannot or will not be changed by the PUT.  This is
1143   particularly important when the origin server uses internal
1144   configuration information related to the URI in order to set the
1145   values for representation metadata on GET responses.  When a PUT
1146   representation is inconsistent with the target resource, the origin
1147   server &SHOULD; either make them consistent, by transforming the
1148   representation or changing the resource configuration, or respond
[1168]1149   with an appropriate error message containing sufficient information
1150   to explain why the representation is unsuitable.  The 409 (Conflict)
1151   or 415 (Unsupported Media Type) status codes are suggested, with the
1152   latter being specific to constraints on Content-Type values.
[1158]1155   For example, if the target resource is configured to always have a
1156   Content-Type of "text/html" and the representation being PUT has a
1157   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
1158   (a) reconfigure the target resource to reflect the new media type;
1159   (b) transform the PUT representation to a format consistent with that
1160   of the resource before saving it as the new resource state; or,
[1168]1161   (c) reject the request with a 415 response indicating that the target
[1158]1162   resource is limited to "text/html", perhaps including a link to a
1163   different resource that would be a suitable target for the new
1164   representation.
1167   HTTP does not define exactly how a PUT method affects the state
1168   of an origin server beyond what can be expressed by the intent of
1169   the user agent request and the semantics of the origin server response.
1170   It does not define what a resource might be, in any sense of that
1171   word, beyond the interface provided via HTTP.  It does not define
1172   how resource state is "stored", nor how such storage might change
1173   as a result of a change in resource state, nor how the origin server
1174   translates resource state into representations.  Generally speaking,
1175   all implementation details behind the resource interface are
1176   intentionally hidden by the server.
1179   The fundamental difference between the POST and PUT methods is
1180   highlighted by the different intent for the target resource.
1181   The target resource in a POST request is intended to handle the
1182   enclosed representation as a data-accepting process, such as for
1183   a gateway to some other protocol or a document that accepts annotations.
1184   In contrast, the target resource in a PUT request is intended to
1185   take the enclosed representation as a new or replacement value.
1186   Hence, the intent of PUT is idempotent and visible to intermediaries,
1187   even though the exact effect is only known by the origin server.
1190   Proper interpretation of a PUT request presumes that the user agent
1191   knows what target resource is desired.  A service that is intended
1192   to select a proper URI on behalf of the client, after receiving
1193   a state-changing request, &SHOULD; be implemented using the POST
1194   method rather than PUT.  If the origin server will not make the
1195   requested PUT state change to the target resource and instead
1196   wishes to have it applied to a different resource, such as when the
1197   resource has been moved to a different URI, then the origin server
1198   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
[8]1199   then make its own decision regarding whether or not to redirect the
1200   request.
[1158]1203   A PUT request applied to the target resource &MAY; have side-effects
1204   on other resources.  For example, an article might have a URI for
1205   identifying "the current version" (a resource) which is separate
1206   from the URIs identifying each particular version (different
1207   resources that at one point shared the same state as the current version
1208   resource).  A successful PUT request on "the current version" URI might
1209   therefore create a new version resource in addition to changing the
1210   state of the target resource, and might also cause links to be added
1211   between the related resources.
[1158]1214   An origin server &SHOULD; reject any PUT request that contains a
1215   Content-Range header field, since it might be misinterpreted as
1216   partial content (or might be partial content that is being mistakenly
1217   PUT as a full representation).  Partial content updates are
1218   possible by targeting a separately identified resource with state
1219   that overlaps a portion of the larger resource, or by using a
1220   different method that has been specifically defined for partial
1221   updates (for example, the PATCH method defined in
1222   <xref target="RFC5789"/>).
[1158]1225   Responses to the PUT method are not cacheable. If a PUT request passes
1226   through a cache that has one or more stored responses for the effective
1227   request URI, those stored responses will be invalidated (see
1228   &p6-invalid;).
1232<section title="DELETE" anchor="DELETE">
1233  <iref primary="true" item="DELETE method" x:for-anchor=""/>
1234  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
[972]1236   The DELETE method requests that the origin server delete the target
1237   resource. This method &MAY; be overridden by
[823]1238   human intervention (or other means) on the origin server. The client cannot
[8]1239   be guaranteed that the operation has been carried out, even if the
1240   status code returned from the origin server indicates that the action
1241   has been completed successfully. However, the server &SHOULD-NOT; 
1242   indicate success unless, at the time the response is given, it
1243   intends to delete the resource or move it to an inaccessible
1244   location.
1247   A successful response &SHOULD; be 200 (OK) if the response includes an
[874]1248   representation describing the status, 202 (Accepted) if the action has not
[8]1249   yet been enacted, or 204 (No Content) if the action has been enacted
[866]1250   but the response does not include a representation.
1253   Bodies on DELETE requests have no defined semantics. Note that sending a body
1254   on a DELETE request might cause some existing implementations to reject the
1255   request.
[1111]1258   Responses to the DELETE method are not cacheable. If a DELETE request
1259   passes through a cache that has one or more stored responses for the
1260   effective request URI, those stored responses will be invalidated (see
1261   &p6-invalid;).
1265<section title="TRACE" anchor="TRACE">
[286]1266  <rdf:Description>
1267    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1268  </rdf:Description>
[8]1269  <iref primary="true" item="TRACE method" x:for-anchor=""/>
1270  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
[1161]1272   The TRACE method requests a remote, application-layer loop-back
[8]1273   of the request message. The final recipient of the request
1274   &SHOULD; reflect the message received back to the client as the
[874]1275   message-body of a 200 (OK) response. The final recipient is either the
[1173]1276   origin server or the first proxy to receive a Max-Forwards
[866]1277   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
1278   A TRACE request &MUST-NOT; include a message-body.
1281   TRACE allows the client to see what is being received at the other
1282   end of the request chain and use that data for testing or diagnostic
[29]1283   information. The value of the Via header field (&header-via;) is of
[8]1284   particular interest, since it acts as a trace of the request chain.
1285   Use of the Max-Forwards header field allows the client to limit the
1286   length of the request chain, which is useful for testing a chain of
1287   proxies forwarding messages in an infinite loop.
[874]1290   If the request is valid, the response &SHOULD; have a Content-Type of
1291   "message/http" (see &media-type-message-http;) and contain a message-body
1292   that encloses a copy of the entire request message.
[888]1293   Responses to the TRACE method are not cacheable.
1297<section title="CONNECT" anchor="CONNECT">
1298  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
1299  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
[1161]1301   The CONNECT method requests that the proxy establish a tunnel
1302   to the request-target and then restrict its behavior to blind
1303   forwarding of packets until the connection is closed.
[1161]1306   When using CONNECT, the request-target &MUST; use the authority form
1307   (&request-target;); i.e., the request-target consists of only the
1308   host name and port number of the tunnel destination, separated by a colon.
1309   For example,
[1064]1311<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
[1101]1317   Other HTTP mechanisms can be used normally with the CONNECT method &mdash;
[1061]1318   except end-to-end protocol Upgrade requests, since the
1319   tunnel must be established first.
1322   For example, proxy authentication might be used to establish the
1323   authority to create a tunnel:
[1064]1325<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1328Proxy-Authorization: basic aGVsbG86d29ybGQ=
1332   Bodies on CONNECT requests have no defined semantics. Note that sending a body
1333   on a CONNECT request might cause some existing implementations to reject the
1334   request.
1337   Like any other pipelined HTTP/1.1 request, data to be tunnel may be
1338   sent immediately after the blank line. The usual caveats also apply:
1339   data may be discarded if the eventual response is negative, and the
1340   connection may be reset with no response if more than one TCP segment
1341   is outstanding.
1344<section title="Establishing a Tunnel with CONNECT">
1346   Any successful (2xx) response to a CONNECT request indicates that the
1347   proxy has established a connection to the requested host and port,
1348   and has switched to tunneling the current connection to that server
1349   connection.
1352   It may be the case that the proxy itself can only reach the requested
1353   origin server through another proxy.  In this case, the first proxy
1354   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
1355   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
1356   unless it has either a direct or tunnel connection established to the
1357   authority.
1360   An origin server which receives a CONNECT request for itself &MAY;
1361   respond with a 2xx status code to indicate that a connection is
1362   established.
1365   If at any point either one of the peers gets disconnected, any
1366   outstanding data that came from that peer will be passed to the other
1367   one, and after that also the other connection will be terminated by
1368   the proxy. If there is outstanding data to that peer undelivered,
1369   that data will be discarded.
1377<section title="Status Code Definitions" anchor="">
[1435]1379   The first digit of the Status-Code defines the class of response. The
1380   last two digits do not have any categorization role. There are 5
1381   values for the first digit:
1382  <list style="symbols">
1383    <t>
1384      1xx: Informational - Request received, continuing process
1385    </t>
1386    <t>
1387      2xx: Success - The action was successfully received,
1388        understood, and accepted
1389    </t>
1390    <t>
1391      3xx: Redirection - Further action must be taken in order to
1392        complete the request
1393    </t>
1394    <t>
1395      4xx: Client Error - The request contains bad syntax or cannot
1396        be fulfilled
1397    </t>
1398    <t>
1399      5xx: Server Error - The server failed to fulfill an apparently
1400        valid request
1401    </t>
1402  </list>
[867]1405   Each Status-Code is described below, including any metadata required
[579]1406   in the response.
1409<section title="Informational 1xx" anchor="status.1xx">
1411   This class of status code indicates a provisional response,
[994]1412   consisting only of the Status-Line and optional header fields, and is
1413   terminated by an empty line. There are no required header fields for this
[8]1414   class of status code. Since HTTP/1.0 did not define any 1xx status
1415   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1416   except under experimental conditions.
1419   A client &MUST; be prepared to accept one or more 1xx status responses
1420   prior to a regular response, even if the client does not expect a 100
1421   (Continue) status message. Unexpected 1xx status responses &MAY; be
1422   ignored by a user agent.
1425   Proxies &MUST; forward 1xx responses, unless the connection between the
1426   proxy and its client has been closed, or unless the proxy itself
1427   requested the generation of the 1xx response. (For example, if a
1428   proxy adds a "Expect: 100-continue" field when it forwards a request,
1429   then it need not forward the corresponding 100 (Continue)
1430   response(s).)
1433<section title="100 Continue" anchor="status.100">
1434  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1435  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1437   The client &SHOULD; continue with its request. This interim response is
1438   used to inform the client that the initial part of the request has
1439   been received and has not yet been rejected by the server. The client
1440   &SHOULD; continue by sending the remainder of the request or, if the
1441   request has already been completed, ignore this response. The server
1442   &MUST; send a final response after the request has been completed. See
[29]1443   &use100; for detailed discussion of the use and handling of this
[8]1444   status code.
1448<section title="101 Switching Protocols" anchor="status.101">
1449  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1450  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1452   The server understands and is willing to comply with the client's
[29]1453   request, via the Upgrade message header field (&header-upgrade;), for a
[8]1454   change in the application protocol being used on this connection. The
1455   server will switch protocols to those defined by the response's
1456   Upgrade header field immediately after the empty line which
1457   terminates the 101 response.
1460   The protocol &SHOULD; be switched only when it is advantageous to do
1461   so. For example, switching to a newer version of HTTP is advantageous
1462   over older versions, and switching to a real-time, synchronous
1463   protocol might be advantageous when delivering resources that use
1464   such features.
1469<section title="Successful 2xx" anchor="status.2xx">
1471   This class of status code indicates that the client's request was
1472   successfully received, understood, and accepted.
1475<section title="200 OK" anchor="status.200">
1476  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1477  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
[965]1479   The request has succeeded. The payload returned with the response
[8]1480   is dependent on the method used in the request, for example:
1481  <list style="hanging">
1482    <t hangText="GET">
[1288]1483      a representation of the target resource is sent in the response;
[8]1484    </t>
1485    <t hangText="HEAD">
[1288]1486      the same representation as GET, except without the message-body;
[8]1487    </t>
1488    <t hangText="POST">
[874]1489      a representation describing or containing the result of the action;
[8]1490    </t>
1491    <t hangText="TRACE">
[874]1492      a representation containing the request message as received by the
[8]1493      end server.
1494    </t>
1495  </list>
[886]1498   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1499   freshness for 200 responses.
1503<section title="201 Created" anchor="status.201">
1504  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1505  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
[758]1507   The request has been fulfilled and has resulted in a new resource being
[8]1508   created. The newly created resource can be referenced by the URI(s)
[856]1509   returned in the payload of the response, with the most specific URI
[8]1510   for the resource given by a Location header field. The response
[856]1511   &SHOULD; include a payload containing a list of resource
[8]1512   characteristics and location(s) from which the user or user agent can
[856]1513   choose the one most appropriate. The payload format is specified by
[8]1514   the media type given in the Content-Type header field. The origin
1515   server &MUST; create the resource before returning the 201 status code.
1516   If the action cannot be carried out immediately, the server &SHOULD;
1517   respond with 202 (Accepted) response instead.
1520   A 201 response &MAY; contain an ETag response header field indicating
[874]1521   the current value of the entity-tag for the representation of the resource
[856]1522   just created (see &header-etag;).
1526<section title="202 Accepted" anchor="status.202">
1527  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1528  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1530   The request has been accepted for processing, but the processing has
1531   not been completed.  The request might or might not eventually be
1532   acted upon, as it might be disallowed when processing actually takes
1533   place. There is no facility for re-sending a status code from an
1534   asynchronous operation such as this.
1537   The 202 response is intentionally non-committal. Its purpose is to
1538   allow a server to accept a request for some other process (perhaps a
1539   batch-oriented process that is only run once per day) without
1540   requiring that the user agent's connection to the server persist
[866]1541   until the process is completed. The representation returned with this
[8]1542   response &SHOULD; include an indication of the request's current status
1543   and either a pointer to a status monitor or some estimate of when the
1544   user can expect the request to be fulfilled.
1548<section title="203 Non-Authoritative Information" anchor="status.203">
1549  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1550  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
[1309]1552   The representation in the response has been transformed or otherwise
1553   modified by a transforming proxy (&intermediaries;).  Note that the
1554   behaviour of transforming intermediaries is controlled by the no-transform
1555   Cache-Control directive (&header-cache-control;).
[1309]1558   This status code is only appropriate when the response status code would
1559   have been 200 (OK) otherwise. When the status code before transformation
1560   would have been different, the 214 Transformation Applied warn-code
1561   (&header-warning;) is appropriate.
[886]1564   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1565   freshness for 203 responses.
1569<section title="204 No Content" anchor="status.204">
1570  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1571  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
[1257]1573   The 204 (No Content) status code indicates that the server has
1574   successfully fulfilled the request and that there is no additional
1575   content to return in the response payload body.  Metadata in the
1576   response header fields refer to the target resource and its current
1577   representation after the requested action.
[924]1580   For example, if a 204 status code is received in response to a PUT
[1257]1581   request and the response contains an ETag header field, then the PUT
1582   was successful and the ETag field-value contains the entity-tag for
1583   the new representation of that target resource.
[1257]1586   The 204 response allows a server to indicate that the action has been
1587   successfully applied to the target resource while implying that the
1588   user agent &SHOULD-NOT; traverse away from its current "document view"
1589   (if any).  The server assumes that the user agent will provide some
1590   indication of the success to its user, in accord with its own interface,
1591   and apply any new or updated metadata in the response to the active
1592   representation.
[1257]1595   For example, a 204 status code is commonly used with document editing
1596   interfaces corresponding to a "save" action, such that the document
1597   being saved remains available to the user for editing. It is also
1598   frequently used with interfaces that expect automated data transfers
1599   to be prevalent, such as within distributed version control systems.
1602   The 204 response &MUST-NOT; include a message-body, and thus is always
1603   terminated by the first empty line after the header fields.
1607<section title="205 Reset Content" anchor="status.205">
1608  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1609  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1611   The server has fulfilled the request and the user agent &SHOULD; reset
1612   the document view which caused the request to be sent. This response
1613   is primarily intended to allow input for actions to take place via
1614   user input, followed by a clearing of the form in which the input is
[1058]1615   given so that the user can easily initiate another input action.
1618   The message-body included with the response &MUST; be empty. Note that
1619   receivers still need to parse the response according to the algorithm defined
1620   in &message-body;.
1624<section title="206 Partial Content" anchor="status.206">
1625  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1626  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
[700]1627  <rdf:Description>
1628    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part5</redirects-to>
1629  </rdf:Description>
[29]1631   The server has fulfilled the partial GET request for the resource
[874]1632   and the enclosed payload is a partial representation as defined in &status-206;.
[886]1635   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1636   freshness for 206 responses.
1641<section title="Redirection 3xx" anchor="status.3xx">
1643   This class of status code indicates that further action needs to be
[1428]1644   taken by the user agent in order to fulfill the request.  If the required
1645   action involves a subsequent HTTP request, it &MAY; be carried out by the
1646   user agent without interaction with the user if and only if the method used
1647   in the second request is known to be "safe", as defined in
1648   <xref target="safe.methods"/>.
1651   There are several types of redirects:
1652   <list style="numbers">
1653      <x:lt>
1654        <t>
1655          Redirects of the request to another URI, either temporarily or
1656          permanently. The new URI is specified in the Location header field.
1657          In this specification, the status codes 301 (Moved Permanently),
1658          302 (Found), and 307 (Temporary Redirect) fall under this category.
1659        </t>
1660      </x:lt>
1661      <x:lt>
1662        <t>
1663          Redirection to a new location that represents an indirect response to
1664          the request, such as the result of a POST operation to be retrieved
1665          with a subsequent GET request. This is status code 303 (See Other).
1666        </t>
1667      </x:lt>
1668      <x:lt>
1669        <t>
1670          Redirection offering a choice of matching resources for use by
1671          agent-driven content negotiation (&agent-driven-negotiation;). This
1672          is status code 300 (Multiple Choices).
1673        </t>
1674      </x:lt>
1675      <x:lt>
1676        <t>
1677          Other kinds of redirection, such as to a cached result (status code 304
1678          (Not Modified)).
1679        </t>
1680      </x:lt>
1681   </list>
1684  <t>
[1428]1685    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1686    and 302 (Found) were defined for the first type of redirect, and the second
1687    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1688    However it turned out that web forms using POST expected redirects to change
1689    the operation for the subsequent request to retrieval (GET). To address this
1690    use case, HTTP/1.1 introduced the second type of redirect with the status
1691    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1692    As user agents did not change their behavior to maintain backwards
1693    compatibility, the first revision of HTTP/1.1 added yet another status code,
1694    307 (Temporary Redirect), for which the backwards compatibility problems did
1695    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1696    Over 10 years later, most user agents still do method rewriting for
1697    status codes 301 and 302, therefore this specification makes that behavior
1698    compliant in case the original request was POST.
1699  </t>
1702   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1703   "infinite" redirection loops).
1706  <t>
[756]1707    <x:h>Note:</x:h> An earlier version of this specification recommended a
[629]1708    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
[969]1709    Content developers need to be aware that some clients might
[629]1710    implement such a fixed limitation.
[563]1711  </t>
1714<section title="300 Multiple Choices" anchor="status.300">
1715  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1716  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
[1029]1718   The target resource has more than one
[965]1719   representation, each with its own specific location, and agent-driven
[29]1720   negotiation information (&content-negotiation;) is being provided so that
[965]1721   the user (or user agent) can select a preferred representation by
1722   redirecting its request to that location.
[866]1725   Unless it was a HEAD request, the response &SHOULD; include a representation
[965]1726   containing a list of representation metadata and location(s) from
[8]1727   which the user or user agent can choose the one most appropriate. The
[866]1728   data format is specified by the media type given in the Content-Type
[8]1729   header field. Depending upon the format and the capabilities of
1730   the user agent, selection of the most appropriate choice &MAY; be
1731   performed automatically. However, this specification does not define
1732   any standard for such automatic selection.
1735   If the server has a preferred choice of representation, it &SHOULD;
1736   include the specific URI for that representation in the Location
1737   field; user agents &MAY; use the Location field value for automatic
[884]1738   redirection.
[886]1741   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1742   freshness for 300 responses.
1747<section title="301 Moved Permanently" anchor="status.301">
1748  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1749  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
[965]1751   The target resource has been assigned a new permanent URI and any
[8]1752   future references to this resource &SHOULD; use one of the returned
1753   URIs.  Clients with link editing capabilities ought to automatically
[965]1754   re-link references to the effective request URI to one or more of the new
[884]1755   references returned by the server, where possible.
[886]1758   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1759   freshness for 301 responses.
[8]1762   The new permanent URI &SHOULD; be given by the Location field in the
[866]1763   response. Unless the request method was HEAD, the representation of the
[8]1764   response &SHOULD; contain a short hypertext note with a hyperlink to
1765   the new URI(s).
[88]1768   If the 301 status code is received in response to a request method
1769   that is known to be "safe", as defined in <xref target="safe.methods"/>,
[96]1770   then the request &MAY; be automatically redirected by the user agent without
[88]1771   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
[8]1772   request unless it can be confirmed by the user, since this might
1773   change the conditions under which the request was issued.
1776  <t>
[1428]1777    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1778    request method from POST to GET for the subsequent request. If this
1779    behavior is undesired, status code 307 (Temporary Redirect) can be used
1780    instead.
[563]1781  </t>
1785<section title="302 Found" anchor="status.302">
1786  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1787  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
[965]1789   The target resource resides temporarily under a different URI.
[8]1790   Since the redirection might be altered on occasion, the client &SHOULD;
[965]1791   continue to use the effective request URI for future requests.
1794   The temporary URI &SHOULD; be given by the Location field in the
[866]1795   response. Unless the request method was HEAD, the representation of the
[8]1796   response &SHOULD; contain a short hypertext note with a hyperlink to
1797   the new URI(s).
[88]1800   If the 302 status code is received in response to a request method
1801   that is known to be "safe", as defined in <xref target="safe.methods"/>,
[96]1802   then the request &MAY; be automatically redirected by the user agent without
[88]1803   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
[8]1804   request unless it can be confirmed by the user, since this might
1805   change the conditions under which the request was issued.
1808  <t>
[1428]1809    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1810    request method from POST to GET for the subsequent request. If this
1811    behavior is undesired, status code 307 (Temporary Redirect) can be used
1812    instead.
1813    <cref anchor="issue312">but see <eref target=""/></cref>
[563]1814  </t>
1818<section title="303 See Other" anchor="status.303">
1819  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1820  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
[1421]1822   The 303 status code indicates that the server is redirecting the
1823   user agent to a different resource, as indicated by a URI in the
1824   Location header field, that is intended to provide an indirect
1825   response to the original request.  In order to satisfy the original
1826   request, a user agent &SHOULD; perform a retrieval request using the
[1430]1827   Location URI (a GET or HEAD request if using HTTP), which
[1429]1828   may itself be redirected further, and present the eventual result as an
1829   answer to the original request.
[1421]1830   Note that the new URI in the Location header field is not considered
1831   equivalent to the effective request URI.
[1421]1834   This status code is generally applicable to any HTTP method.  It is
[242]1835   primarily used to allow the output of a POST action to redirect
1836   the user agent to a selected resource, since doing so provides the
1837   information corresponding to the POST response in a form that
1838   can be separately identified, bookmarked, and cached independent
1839   of the original request.
1842   A 303 response to a GET request indicates that the requested
1843   resource does not have a representation of its own that can be
1844   transferred by the server over HTTP.  The Location URI indicates a
[965]1845   resource that is descriptive of the target resource, such that the
1846   follow-on representation might be useful to recipients without
1847   implying that it adequately represents the target resource.
[242]1848   Note that answers to the questions of what can be represented, what
1849   representations are adequate, and what might be a useful description
1850   are outside the scope of HTTP and thus entirely determined by the
[602]1851   URI owner(s).
[884]1854   Except for responses to a HEAD request, the representation of a 303
1855   response &SHOULD; contain a short hypertext note with a hyperlink
1856   to the Location URI.
1860<section title="304 Not Modified" anchor="status.304">
1861  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1862  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
[700]1863  <rdf:Description>
1864    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part4</redirects-to>
1865  </rdf:Description>
[45]1867   The response to the request has not been modified since the conditions
[700]1868   indicated by the client's conditional GET request, as defined in &status-304;.
1872<section title="305 Use Proxy" anchor="status.305">
1873  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1874  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
[924]1876   The 305 status code was defined in a previous version of this specification
[235]1877   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1881<section title="306 (Unused)" anchor="status.306">
1882  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1883  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1885   The 306 status code was used in a previous version of the
1886   specification, is no longer used, and the code is reserved.
1890<section title="307 Temporary Redirect" anchor="status.307">
1891  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1892  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
[965]1894   The target resource resides temporarily under a different URI.
[954]1895   Since the redirection can change over time, the client &SHOULD;
[965]1896   continue to use the effective request URI for future requests.
1899   The temporary URI &SHOULD; be given by the Location field in the
[866]1900   response. Unless the request method was HEAD, the representation of the
[8]1901   response &SHOULD; contain a short hypertext note with a hyperlink to
[1030]1902   the new URI(s), since many pre-HTTP/1.1 user agents do not
[924]1903   understand the 307 status code. Therefore, the note &SHOULD; contain the
[8]1904   information necessary for a user to repeat the original request on
1905   the new URI.
[88]1908   If the 307 status code is received in response to a request method
1909   that is known to be "safe", as defined in <xref target="safe.methods"/>,
[96]1910   then the request &MAY; be automatically redirected by the user agent without
[88]1911   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
[8]1912   request unless it can be confirmed by the user, since this might
1913   change the conditions under which the request was issued.
1916  <t>
1917    <x:h>Note:</x:h> This status code is similar to 302 Found, except that
[1475]1918    it does not allow rewriting the request method from POST to GET. This
1919    specification defines no equivalent counterpart for 301 Moved Permanently.
[1474]1920  </t>
1925<section title="Client Error 4xx" anchor="status.4xx">
1927   The 4xx class of status code is intended for cases in which the
1928   client seems to have erred. Except when responding to a HEAD request,
[874]1929   the server &SHOULD; include a representation containing an explanation of the
[8]1930   error situation, and whether it is a temporary or permanent
1931   condition. These status codes are applicable to any request method.
[874]1932   User agents &SHOULD; display any included representation to the user.
1935   If the client is sending data, a server implementation using TCP
1936   &SHOULD; be careful to ensure that the client acknowledges receipt of
1937   the packet(s) containing the response, before the server closes the
1938   input connection. If the client continues sending data to the server
1939   after the close, the server's TCP stack will send a reset packet to
[901]1940   the client, which might erase the client's unacknowledged input buffers
[8]1941   before they can be read and interpreted by the HTTP application.
1944<section title="400 Bad Request" anchor="status.400">
1945  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1946  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
[1345]1948   The server cannot or will not process the request, due to a client error (e.g.,
[1342]1949   malformed syntax).</t>
1952<section title="401 Unauthorized" anchor="status.401">
1953  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1954  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
[700]1955  <rdf:Description>
1956    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part7</redirects-to>
1957  </rdf:Description>
[700]1959   The request requires user authentication (see &status-401;).
1963<section title="402 Payment Required" anchor="status.402">
1964  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1965  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1967   This code is reserved for future use.
1971<section title="403 Forbidden" anchor="status.403">
1972  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1973  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
[1301]1975   The server understood the request, but refuses to authorize it. Providing
1976   different user authentication credentials might be successful, but any
1977   credentials that were provided in the request are insufficient. The request
1978   &SHOULD-NOT; be repeated with the same credentials.
[8]1981   If the request method was not HEAD and the server wishes to make
1982   public why the request has not been fulfilled, it &SHOULD; describe the
[866]1983   reason for the refusal in the representation.  If the server does not wish to
[8]1984   make this information available to the client, the status code 404
[1301]1985   (Not Found) &MAY; be used instead.
1989<section title="404 Not Found" anchor="status.404">
1990  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1991  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
[965]1993   The server has not found anything matching the effective request URI. No
[8]1994   indication is given of whether the condition is temporary or
1995   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1996   knows, through some internally configurable mechanism, that an old
1997   resource is permanently unavailable and has no forwarding address.
1998   This status code is commonly used when the server does not wish to
1999   reveal exactly why the request has been refused, or when no other
2000   response is applicable.
2004<section title="405 Method Not Allowed" anchor="status.405">
2005  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
2006  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
[965]2008   The method specified in the Request-Line is not allowed for the target
[1288]2009   resource. The response &MUST; include an Allow header field containing a
2010   list of valid methods for the requested resource.
2014<section title="406 Not Acceptable" anchor="status.406">
2015  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
2016  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
2018   The resource identified by the request is only capable of generating
[874]2019   response representations which have content characteristics not acceptable
[1335]2020   according to the Accept and Accept-* header fields sent in the request
2021   (see &p3-header-fields;).
[866]2024   Unless it was a HEAD request, the response &SHOULD; include a representation
2025   containing a list of available representation characteristics and location(s)
[8]2026   from which the user or user agent can choose the one most
[866]2027   appropriate. The data format is specified by the media type given
[8]2028   in the Content-Type header field. Depending upon the format and the
2029   capabilities of the user agent, selection of the most appropriate
2030   choice &MAY; be performed automatically. However, this specification
2031   does not define any standard for such automatic selection.
2034  <t>
2035    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
[994]2036    not acceptable according to the accept header fields sent in the
[901]2037    request. In some cases, this might even be preferable to sending a
[994]2038    406 response. User agents are encouraged to inspect the header fields of
[563]2039    an incoming response to determine if it is acceptable.
2040  </t>
2043   If the response could be unacceptable, a user agent &SHOULD;
2044   temporarily stop receipt of more data and query the user for a
2045   decision on further actions.
2049<section title="407 Proxy Authentication Required" anchor="status.407">
2050  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
2051  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
2053   This code is similar to 401 (Unauthorized), but indicates that the
[700]2054   client must first authenticate itself with the proxy (see &status-407;).
2058<section title="408 Request Timeout" anchor="status.408">
2059  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
2060  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
2062   The client did not produce a request within the time that the server
2063   was prepared to wait. The client &MAY; repeat the request without
2064   modifications at any later time.
2068<section title="409 Conflict" anchor="status.409">
2069  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
2070  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
2072   The request could not be completed due to a conflict with the current
2073   state of the resource. This code is only allowed in situations where
2074   it is expected that the user might be able to resolve the conflict
2075   and resubmit the request. The response body &SHOULD; include enough
2076   information for the user to recognize the source of the conflict.
[874]2077   Ideally, the response representation would include enough information for the
[8]2078   user or user agent to fix the problem; however, that might not be
2079   possible and is not required.
2082   Conflicts are most likely to occur in response to a PUT request. For
[866]2083   example, if versioning were being used and the representation being PUT
[8]2084   included changes to a resource which conflict with those made by an
2085   earlier (third-party) request, the server might use the 409 response
2086   to indicate that it can't complete the request. In this case, the
[866]2087   response representation would likely contain a list of the differences
[8]2088   between the two versions in a format defined by the response
2089   Content-Type.
2093<section title="410 Gone" anchor="status.410">
2094  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
2095  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
[965]2097   The target resource is no longer available at the server and no
[8]2098   forwarding address is known. This condition is expected to be
2099   considered permanent. Clients with link editing capabilities &SHOULD;
[965]2100   delete references to the effective request URI after user approval. If the
[8]2101   server does not know, or has no facility to determine, whether or not
2102   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
[884]2103   used instead.
2106   The 410 response is primarily intended to assist the task of web
2107   maintenance by notifying the recipient that the resource is
2108   intentionally unavailable and that the server owners desire that
2109   remote links to that resource be removed. Such an event is common for
2110   limited-time, promotional services and for resources belonging to
2111   individuals no longer working at the server's site. It is not
2112   necessary to mark all permanently unavailable resources as "gone" or
[1101]2113   to keep the mark for any length of time &mdash; that is left to the
[8]2114   discretion of the server owner.
[886]2117   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
2118   for 410 responses.
2123<section title="411 Length Required" anchor="status.411">
2124  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
2125  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
2127   The server refuses to accept the request without a defined Content-Length.
2128   The client &MAY; repeat the request if it adds a valid
2129   Content-Length header field containing the length of the message-body
2130   in the request message.
2134<section title="412 Precondition Failed" anchor="status.412">
2135  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
2136  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
[700]2137  <rdf:Description>
2138    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part4</redirects-to>
2139  </rdf:Description>
[1163]2141   The precondition given in one or more of the header fields
[45]2142   evaluated to false when it was tested on the server, as defined in
[700]2143   &status-412;.
[1322]2147<section title="413 Request Representation Too Large" anchor="status.413">
2148  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
2149  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
2151   The server is refusing to process a request because the request
[874]2152   representation is larger than the server is willing or able to process. The
[8]2153   server &MAY; close the connection to prevent the client from continuing
2154   the request.
2157   If the condition is temporary, the server &SHOULD; include a Retry-After
2158   header field to indicate that it is temporary and after what
2159   time the client &MAY; try again.
[465]2163<section title="414 URI Too Long" anchor="status.414">
2164  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
2165  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
[965]2167   The server is refusing to service the request because the effective request URI
[8]2168   is longer than the server is willing to interpret. This rare
2169   condition is only likely to occur when a client has improperly
2170   converted a POST request to a GET request with long query
2171   information, when the client has descended into a URI "black hole" of
2172   redirection (e.g., a redirected URI prefix that points to a suffix of
2173   itself), or when the server is under attack by a client attempting to
2174   exploit security holes present in some servers using fixed-length
[965]2175   buffers for reading or manipulating the effective request URI.
2179<section title="415 Unsupported Media Type" anchor="status.415">
2180  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
2181  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
[1161]2183   The server is refusing to service the request because the request
2184   payload is in a format not supported by this request method on the
2185   target resource.
2189<section title="416 Requested Range Not Satisfiable" anchor="status.416">
2190  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
2191  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
[700]2192  <rdf:Description>
2193    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part5</redirects-to>
2194  </rdf:Description>
[1163]2196   The request included a Range header field (&header-range;) and none of
[8]2197   the range-specifier values in this field overlap the current extent
[885]2198   of the selected resource. See &status-416;.
2202<section title="417 Expectation Failed" anchor="status.417">
2203  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
2204  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
[1163]2206   The expectation given in an Expect header field (see <xref target="header.expect"/>)
[8]2207   could not be met by this server, or, if the server is a proxy,
2208   the server has unambiguous evidence that the request could not be met
2209   by the next-hop server.
2213<section title="426 Upgrade Required" anchor="status.426">
2214  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
2215  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
2217   The request can not be completed without a prior protocol upgrade. This
2218   response &MUST; include an Upgrade header field (&header-upgrade;)
2219   specifying the required protocols.
2223<artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2224HTTP/1.1 426 Upgrade Required
2225Upgrade: HTTP/2.0
2226Connection: Upgrade
2230   The server &SHOULD; include a message body in the 426 response which
2231   indicates in human readable form the reason for the error and describes any
2232   alternative courses which may be available to the user.
2237<section title="Server Error 5xx" anchor="status.5xx">
2239   Response status codes beginning with the digit "5" indicate cases in
2240   which the server is aware that it has erred or is incapable of
2241   performing the request. Except when responding to a HEAD request, the
[874]2242   server &SHOULD; include a representation containing an explanation of the
[8]2243   error situation, and whether it is a temporary or permanent
[874]2244   condition. User agents &SHOULD; display any included representation to the
[8]2245   user. These response codes are applicable to any request method.
2248<section title="500 Internal Server Error" anchor="status.500">
2249  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
2250  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
2252   The server encountered an unexpected condition which prevented it
2253   from fulfilling the request.
2257<section title="501 Not Implemented" anchor="status.501">
2258  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
2259  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
2261   The server does not support the functionality required to fulfill the
2262   request. This is the appropriate response when the server does not
2263   recognize the request method and is not capable of supporting it for
2264   any resource.
2268<section title="502 Bad Gateway" anchor="status.502">
2269  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
2270  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
2272   The server, while acting as a gateway or proxy, received an invalid
2273   response from the upstream server it accessed in attempting to
2274   fulfill the request.
2278<section title="503 Service Unavailable" anchor="status.503">
2279  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
2280  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
[1486]2282   The server is currently unable to handle the request due to a
2283   temporary overloading or maintenance of the server.
2286   The implication is that this is a temporary condition which will be
2287   alleviated after some delay. If known, the length of the delay &MAY; be
2288   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2289   If no Retry-After is given, the client &SHOULD; handle the response as it
2290   would for a 500 response.
2293  <t>
2294    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
[901]2295    server must use it when becoming overloaded. Some servers might wish
[563]2296    to simply refuse the connection.
2297  </t>
2301<section title="504 Gateway Timeout" anchor="status.504">
2302  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2303  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2305   The server, while acting as a gateway or proxy, did not receive a
[763]2306   timely response from the upstream server specified by the URI (e.g.,
2307   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
[8]2308   to access in attempting to complete the request.
2311  <t>
[757]2312    <x:h>Note</x:h> to implementors: some deployed proxies are known to
[563]2313    return 400 or 500 when DNS lookups time out.
2314  </t>
2318<section title="505 HTTP Version Not Supported" anchor="status.505">
2319  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2320  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
[172]2322   The server does not support, or refuses to support, the protocol
[8]2323   version that was used in the request message. The server is
2324   indicating that it is unable or unwilling to complete the request
[29]2325   using the same major version as the client, as described in &http-version;,
[8]2326   other than with this error message. The response &SHOULD; contain
[874]2327   a representation describing why that version is not supported and what other
[8]2328   protocols are supported by that server.
[1436]2336<section title="Date/Time Formats" anchor="">
2337  <x:anchor-alias value="HTTP-date"/>
2339   HTTP applications have historically allowed three different formats
2340   for date/time stamps. However, the preferred format is a fixed-length subset
2341   of that defined by <xref target="RFC1123"/>:
2343<figure><artwork type="example" x:indent-with="  ">
2344Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2347   The other formats are described here only for compatibility with obsolete
2348   implementations.
2350<figure><artwork type="example" x:indent-with="  ">
2351Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2352Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2355   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2356   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2357   only generate the RFC 1123 format for representing HTTP-date values
2358   in header fields.
2361   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2362   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2363   equal to UTC (Coordinated Universal Time). This is indicated in the
2364   first two formats by the inclusion of "GMT" as the three-letter
2365   abbreviation for time zone, and &MUST; be assumed when reading the
2366   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2367   additional whitespace beyond that specifically included as SP in the
2368   grammar.
2370<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2371  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2373<t anchor="">
2374  <x:anchor-alias value="rfc1123-date"/>
2375  <x:anchor-alias value="time-of-day"/>
2376  <x:anchor-alias value="hour"/>
2377  <x:anchor-alias value="minute"/>
2378  <x:anchor-alias value="second"/>
2379  <x:anchor-alias value="day-name"/>
2380  <x:anchor-alias value="day"/>
2381  <x:anchor-alias value="month"/>
2382  <x:anchor-alias value="year"/>
2383  <x:anchor-alias value="GMT"/>
2384  Preferred format:
2386<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="time-of-day"/><iref primary="true" item="Grammar" subitem="hour"/><iref primary="true" item="Grammar" subitem="minute"/><iref primary="true" item="Grammar" subitem="second"/><iref primary="true" item="Grammar" subitem="day-name"/><iref primary="true" item="Grammar" subitem="day-name-l"/><iref primary="true" item="Grammar" subitem="day"/><iref primary="true" item="Grammar" subitem="month"/><iref primary="true" item="Grammar" subitem="year"/><iref primary="true" item="Grammar" subitem="GMT"/>
2387  <x:ref>rfc1123-date</x:ref> = <x:ref>day-name</x:ref> "," <x:ref>SP</x:ref> date1 <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
2388  ; fixed length subset of the format defined in
2389  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2391  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2392               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2393               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2394               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2395               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2396               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2397               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2399  <x:ref>date1</x:ref>        = <x:ref>day</x:ref> <x:ref>SP</x:ref> <x:ref>month</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
2400               ; e.g., 02 Jun 1982
2402  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2403  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2404               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2405               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2406               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2407               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2408               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2409               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2410               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2411               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2412               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2413               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2414               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2415  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2417  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2419  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2420                 ; 00:00:00 - 23:59:59
2422  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2423  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2424  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2427  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2428  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2429  same as those defined for the RFC 5322 constructs
2430  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2432<t anchor="">
2433  <x:anchor-alias value="obs-date"/>
2434  <x:anchor-alias value="rfc850-date"/>
2435  <x:anchor-alias value="asctime-date"/>
2436  <x:anchor-alias value="date1"/>
2437  <x:anchor-alias value="date2"/>
2438  <x:anchor-alias value="date3"/>
2439  <x:anchor-alias value="rfc1123-date"/>
2440  <x:anchor-alias value="day-name-l"/>
2441  Obsolete formats:
2443<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2444  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2446<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2447  <x:ref>rfc850-date</x:ref>  = <x:ref>day-name-l</x:ref> "," <x:ref>SP</x:ref> <x:ref>date2</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
2448  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2449                 ; day-month-year (e.g., 02-Jun-82)
2451  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2452         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2453         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2454         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2455         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2456         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2457         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2459<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2460  <x:ref>asctime-date</x:ref> = <x:ref>day-name</x:ref> <x:ref>SP</x:ref> <x:ref>date3</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
2461  <x:ref>date3</x:ref>        = <x:ref>month</x:ref> <x:ref>SP</x:ref> ( 2<x:ref>DIGIT</x:ref> / ( <x:ref>SP</x:ref> 1<x:ref>DIGIT</x:ref> ))
2462                 ; month day (e.g., Jun  2)
2465  <t>
2466    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2467    accepting date values that might have been sent by non-HTTP
2468    applications, as is sometimes the case when retrieving or posting
2469    messages via proxies/gateways to SMTP or NNTP.
2470  </t>
2473  <t>
2474    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2475    to their usage within the protocol stream. Clients and servers are
2476    not required to use these formats for user presentation, request
2477    logging, etc.
2478  </t>
[1415]2483<section title="Header Field Definitions" anchor="header.field.definitions">
[117]2485   This section defines the syntax and semantics of HTTP/1.1 header fields
2486   related to request and response semantics.
2489<section title="Allow" anchor="header.allow">
[1120]2490  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2491  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
[229]2492  <x:anchor-alias value="Allow"/>
[1163]2494   The "Allow" header field lists the set of methods advertised as
[1067]2495   supported by the target resource. The purpose of this field is strictly to
[1161]2496   inform the recipient of valid request methods associated with the resource.
[1235]2498<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2499  <x:ref>Allow</x:ref> = #<x:ref>Method</x:ref>
[1067]2502   Example of use:
2504<figure><artwork type="example">
[356]2505  Allow: GET, HEAD, PUT
[1067]2508   The actual set of allowed methods is defined by the origin server at the
2509   time of each request.
[1101]2512   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
[1068]2513   understand all the methods specified in order to handle them according to
2514   the generic message handling rules.
[1436]2518<section title="Date" anchor="">
2519  <iref primary="true" item="Date header field" x:for-anchor=""/>
2520  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
2521  <x:anchor-alias value="Date"/>
2523   The "Date" header field represents the date and time at which
2524   the message was originated, having the same semantics as the Origination
2525   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2526   The field value is an HTTP-date, as defined in <xref target=""/>;
2527   it &MUST; be sent in rfc1123-date format.
2529<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2530  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
2533   An example is
2535<figure><artwork type="example">
2536  Date: Tue, 15 Nov 1994 08:12:31 GMT
2539   Origin servers &MUST; include a Date header field in all responses,
2540   except in these cases:
2541  <list style="numbers">
2542      <t>If the response status code is 100 (Continue) or 101 (Switching
2543         Protocols), the response &MAY; include a Date header field, at
2544         the server's option.</t>
2546      <t>If the response status code conveys a server error, e.g., 500
2547         (Internal Server Error) or 503 (Service Unavailable), and it is
2548         inconvenient or impossible to generate a valid Date.</t>
2550      <t>If the server does not have a clock that can provide a
2551         reasonable approximation of the current time, its responses
2552         &MUST-NOT; include a Date header field.</t>
2553  </list>
2556   A received message that does not have a Date header field &MUST; be
2557   assigned one by the recipient if the message will be cached by that
2558   recipient.
2561   Clients can use the Date header field as well; in order to keep request
2562   messages small, they are advised not to include it when it doesn't convey
2563   any useful information (as it is usually the case for requests that do not
2564   contain a payload).
2567   The HTTP-date sent in a Date header field &SHOULD-NOT; represent a date and
2568   time subsequent to the generation of the message. It &SHOULD; represent
2569   the best available approximation of the date and time of message
2570   generation, unless the implementation has no means of generating a
2571   reasonably accurate date and time. In theory, the date ought to
2572   represent the moment just before the payload is generated. In
2573   practice, the date can be generated at any time during the message
2574   origination without affecting its semantic value.
[8]2578<section title="Expect" anchor="header.expect">
[1120]2579  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2580  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
[229]2581  <x:anchor-alias value="Expect"/>
2582  <x:anchor-alias value="expectation"/>
[1489]2583  <x:anchor-alias value="expect-param"/>
[1494]2584  <x:anchor-alias value="expect-name"/>
2585  <x:anchor-alias value="expect-value"/>
[1163]2587   The "Expect" header field is used to indicate that particular
[8]2588   server behaviors are required by the client.
[1494]2590<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Expect"/><iref primary="true" item="Grammar" subitem="expectation"/><iref primary="true" item="Grammar" subitem="expect-param"/><iref primary="true" item="Grammar" subitem="expect-value"/><iref primary="true" item="Grammar" subitem="expect-name"/>
[1235]2591  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
[1494]2593  <x:ref>expectation</x:ref>  = <x:ref>expect-name</x:ref> [ <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>expect-value</x:ref> ]
2594                             *( <x:ref>OWS</x:ref> ";" [ <x:ref>OWS</x:ref> <x:ref>expect-param</x:ref> ] )
2595  <x:ref>expect-param</x:ref> = <x:ref>expect-name</x:ref> [ <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>expect-value</x:ref> ]
2597  <x:ref>expect-name</x:ref>  = <x:ref>token</x:ref>
2598  <x:ref>expect-value</x:ref> = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
[1494]2601   If all received Expect header field(s) are syntactically valid but contain
2602   an expectation that the recipient does not understand or cannot comply with,
2603   the recipient &MUST; respond with a 417 (Expectation Failed) status code. A
2604   recipient of a syntactically invalid Expectation header field &MUST; respond
2605   with a 4xx status code other than 417.
[1494]2608   The only expectation defined by this specification is:
[1494]2610<t><iref primary="true" item="100-continue (expect value)"/><iref primary="true" item="Expect Values" subitem="100-continue"/>
2611  100-continue
2612   <list>
2613      <t>
2614        The "100-continue" expectation is defined &use100;. It does not support
2615        any expect-params.
2616      </t>
2617   </list>
[1494]2620   Comparison is case-insensitive for names (expect-name), and case-sensitive
2621   for values (expect-value).
[1494]2624   The Expect mechanism is hop-by-hop: the above requirements apply to any
2625   server, including proxies. However, the Expect header field itself is
2626   end-to-end; it &MUST; be forwarded if the request is forwarded.
[1494]2629   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect
2630   header field.
2634<section title="From" anchor="header.from">
[1120]2635  <iref primary="true" item="From header field" x:for-anchor=""/>
2636  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
[229]2637  <x:anchor-alias value="From"/>
2638  <x:anchor-alias value="mailbox"/>
[1163]2640   The "From" header field, if given, &SHOULD; contain an Internet
[8]2641   e-mail address for the human user who controls the requesting user
2642   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
[327]2643   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
[1235]2645<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2646  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
[327]2648  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2651   An example is:
2653<figure><artwork type="example">
[356]2654  From:
2657   This header field &MAY; be used for logging purposes and as a means for
2658   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2659   be used as an insecure form of access protection. The interpretation
2660   of this field is that the request is being performed on behalf of the
2661   person given, who accepts responsibility for the method performed. In
[994]2662   particular, robot agents &SHOULD; include this header field so that the
[8]2663   person responsible for running the robot can be contacted if problems
2664   occur on the receiving end.
2667   The Internet e-mail address in this field &MAY; be separate from the
2668   Internet host which issued the request. For example, when a request
2669   is passed through a proxy the original issuer's address &SHOULD; be
2670   used.
2673   The client &SHOULD-NOT;  send the From header field without the user's
2674   approval, as it might conflict with the user's privacy interests or
2675   their site's security policy. It is strongly recommended that the
2676   user be able to disable, enable, and modify the value of this field
2677   at any time prior to a request.
2681<section title="Location" anchor="header.location">
[1120]2682  <iref primary="true" item="Location header field" x:for-anchor=""/>
2683  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
[229]2684  <x:anchor-alias value="Location"/>
[1163]2686   The "Location" header field is used to identify a newly created
[698]2687   resource, or to redirect the recipient to a different location for
2688   completion of the request.
2691   For 201 (Created) responses, the Location is the URI of the new resource
2692   which was created by the request. For 3xx responses, the location &SHOULD;
2693   indicate the server's preferred URI for automatic redirection to the
2694   resource.
[785]2697   The field value consists of a single URI-reference. When it has the form
2698   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2699   the final value is computed by resolving it against the effective request
2700   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>).
[1235]2702<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2703  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
[1425]2706<preamble>Examples are:</preamble><!--DO NOT DARE changing the vertical spacing below, it's necessary this way for xml2rfc-->
[785]2707<artwork type="example">
2708  Location:
2709</artwork></figure><figure><artwork type="example">  Location: /index.html
2712  <t>
2713    <x:h>Note:</x:h> Some recipients attempt to recover from Location fields
2714    that are not valid URI references. This specification does not mandate or
2715    define such processing, but does allow it (see <xref target="intro.conformance.and.error.handling"/>).
2716  </t>
[785]2719   There are circumstances in which a fragment identifier in a Location URI
[1283]2720   would not be appropriate. For instance, when it appears in a 201 Created
2721   response, where the Location header field specifies the URI for the entire
2722   created resource.
2725  <t>
[785]2726    <x:h>Note:</x:h> This specification does not define precedence rules
[791]2727    for the case where the original URI, as navigated to by the user
[785]2728    agent, and the Location header field value both contain fragment
[1097]2729    identifiers. Thus be aware that including fragment identifiers might
2730    inconvenience anyone relying on the semantics of the original URI's
2731    fragment identifier.
[785]2732  </t>
2735  <t>
[563]2736    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
[866]2737    from Location in that the Content-Location identifies the most specific
2738    resource corresponding to the enclosed representation.
2739    It is therefore possible for a response to contain header fields for
2740    both Location and Content-Location.
[563]2741  </t>
2745<section title="Max-Forwards" anchor="header.max-forwards">
[1120]2746  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2747  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
[229]2748  <x:anchor-alias value="Max-Forwards"/>
[1163]2750   The "Max-Forwards" header field provides a mechanism with the
[698]2751   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2752   methods to limit the number of times that the request is forwarded by
[1173]2753   proxies. This can be useful when the client is attempting to
[698]2754   trace a request which appears to be failing or looping in mid-chain.
[1235]2756<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2757  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2760   The Max-Forwards value is a decimal integer indicating the remaining
[901]2761   number of times this request message can be forwarded.
[1173]2764   Each recipient of a TRACE or OPTIONS request
[8]2765   containing a Max-Forwards header field &MUST; check and update its
2766   value prior to forwarding the request. If the received value is zero
2767   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2768   respond as the final recipient. If the received Max-Forwards value is
2769   greater than zero, then the forwarded message &MUST; contain an updated
2770   Max-Forwards field with a value decremented by one (1).
[1161]2773   The Max-Forwards header field &MAY; be ignored for all other request
2774   methods.
2778<section title="Referer" anchor="header.referer">
[1120]2779  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2780  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
[229]2781  <x:anchor-alias value="Referer"/>
[1163]2783   The "Referer" [sic] header field allows the client to specify the
[965]2784   URI of the resource from which the effective request URI was obtained (the
[698]2785   "referrer", although the header field is misspelled.).
[994]2788   The Referer header field allows servers to generate lists of back-links to
[593]2789   resources for interest, logging, optimized caching, etc. It also allows
2790   obsolete or mistyped links to be traced for maintenance. Some servers use
2791   Referer as a means of controlling where they allow links from (so-called
[969]2792   "deep linking"), but legitimate requests do not always
2793   contain a Referer header field.
[965]2796   If the effective request URI was obtained from a source that does not have its own
[812]2797   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
[593]2798   sent with the value "about:blank", or not be sent at all. Note that this
2799   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
[1235]2801<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2802  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2805   Example:
2807<figure><artwork type="example">
[356]2808  Referer:
2811   If the field value is a relative URI, it &SHOULD; be interpreted
[965]2812   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
[8]2813   <xref target=""/> for security considerations.
2817<section title="Retry-After" anchor="header.retry-after">
[1120]2818  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2819  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
[229]2820  <x:anchor-alias value="Retry-After"/>
[1163]2822   The header "Retry-After" field can be used with a 503 (Service
[8]2823   Unavailable) response to indicate how long the service is expected to
2824   be unavailable to the requesting client. This field &MAY; also be used
2825   with any 3xx (Redirection) response to indicate the minimum time the
[698]2826   user-agent is asked wait before issuing the redirected request.
2829   The value of this field can be either an HTTP-date or an integer number
[8]2830   of seconds (in decimal) after the time of the response.
[1235]2832<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2833  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
[229]2835<t anchor="">
2836  <x:anchor-alias value="delta-seconds"/>
[212]2837   Time spans are non-negative decimal integers, representing time in
2838   seconds.
2840<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
[229]2841  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
[8]2844   Two examples of its use are
2846<figure><artwork type="example">
[356]2847  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2848  Retry-After: 120
2851   In the latter example, the delay is 2 minutes.
2855<section title="Server" anchor="header.server">
[1120]2856  <iref primary="true" item="Server header field" x:for-anchor=""/>
2857  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
[229]2858  <x:anchor-alias value="Server"/>
[1163]2860   The "Server" header field contains information about the
[698]2861   software used by the origin server to handle the request.
2864   The field can contain multiple product tokens (&product-tokens;) and
2865   comments (&header-fields;) identifying the server and any significant
2866   subproducts. The product tokens are listed in order of their significance
2867   for identifying the application.
[1235]2869<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2870  <x:ref>Server</x:ref> = <x:ref>product</x:ref> *( <x:ref>RWS</x:ref> ( <x:ref>product</x:ref> / <x:ref>comment</x:ref> ) )
2873   Example:
2875<figure><artwork type="example">
[356]2876  Server: CERN/3.0 libwww/2.17
2879   If the response is being forwarded through a proxy, the proxy
[1163]2880   application &MUST-NOT; modify the Server header field. Instead, it
[72]2881   &MUST; include a Via field (as described in &header-via;).
2884  <t>
2885    <x:h>Note:</x:h> Revealing the specific software version of the server might
2886    allow the server machine to become more vulnerable to attacks
2887    against software that is known to contain security holes. Server
2888    implementors are encouraged to make this field a configurable
2889    option.
2890  </t>
2894<section title="User-Agent" anchor="header.user-agent">
[1120]2895  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2896  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
[229]2897  <x:anchor-alias value="User-Agent"/>
[1163]2899   The "User-Agent" header field contains information about the user
[1036]2900   agent originating the request. User agents &SHOULD; include this field with
2901   requests.
2904   Typically, it is used for statistical purposes, the tracing of protocol
2905   violations, and tailoring responses to avoid particular user agent
2906   limitations.
2909   The field can contain multiple product tokens (&product-tokens;)
2910   and comments (&header-fields;) identifying the agent and its
2911   significant subproducts. By convention, the product tokens are listed in
2912   order of their significance for identifying the application.
2915   Because this field is usually sent on every request a user agent makes,
2916   implementations are encouraged not to include needlessly fine-grained
2917   detail, and to limit (or even prohibit) the addition of subproducts by third
2918   parties. Overly long and detailed User-Agent field values make requests
2919   larger and can also be used to identify ("fingerprint") the user against
2920   their wishes.
2923   Likewise, implementations are encouraged not to use the product tokens of
2924   other implementations in order to declare compatibility with them, as this
2925   circumvents the purpose of the field. Finally, they are encouraged not to
2926   use comments to identify products; doing so makes the field value more
2927   difficult to parse.
[1235]2929<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2930  <x:ref>User-Agent</x:ref> = <x:ref>product</x:ref> *( <x:ref>RWS</x:ref> ( <x:ref>product</x:ref> / <x:ref>comment</x:ref> ) )
2933   Example:
2935<figure><artwork type="example">
[356]2936  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
[29]2942<section title="IANA Considerations" anchor="IANA.considerations">
2944<section title="Method Registry" anchor="method.registration">
[1161]2946  The registration procedure for HTTP request methods is defined by
[270]2947  <xref target="method.registry"/> of this document.
[969]2950   The HTTP Method Registry shall be created at <eref target=""/>
[818]2951   and be populated with the registrations below:
[682]2953<?BEGININC p2-semantics.iana-methods ?>
[270]2954<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
[288]2955<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
[270]2956   <ttcol>Method</ttcol>
[286]2957   <ttcol>Safe</ttcol>
[270]2958   <ttcol>Reference</ttcol>
2959   <c>CONNECT</c>
[286]2960   <c>no</c>
[270]2961   <c>
2962      <xref target="CONNECT"/>
2963   </c>
2964   <c>DELETE</c>
[286]2965   <c>no</c>
[270]2966   <c>
2967      <xref target="DELETE"/>
2968   </c>
2969   <c>GET</c>
[286]2970   <c>yes</c>
[270]2971   <c>
2972      <xref target="GET"/>
2973   </c>
2974   <c>HEAD</c>
[286]2975   <c>yes</c>
[270]2976   <c>
2977      <xref target="HEAD"/>
2978   </c>
2979   <c>OPTIONS</c>
[286]2980   <c>yes</c>
[270]2981   <c>
2982      <xref target="OPTIONS"/>
2983   </c>
2984   <c>POST</c>
[286]2985   <c>no</c>
[270]2986   <c>
2987      <xref target="POST"/>
2988   </c>
2989   <c>PUT</c>
[286]2990   <c>no</c>
[270]2991   <c>
2992      <xref target="PUT"/>
2993   </c>
2994   <c>TRACE</c>
[286]2995   <c>yes</c>
[270]2996   <c>
2997      <xref target="TRACE"/>
2998   </c>
[682]3001<?ENDINC p2-semantics.iana-methods ?>
[255]3004<section title="Status Code Registry" anchor="status.code.registration">
[1101]3006   The registration procedure for HTTP Status Codes &mdash; previously defined
3007   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
[288]3008   by <xref target="status.code.registry"/> of this document.
3011   The HTTP Status Code Registry located at <eref target=""/>
[969]3012   shall be updated with the registrations below:
[682]3014<?BEGININC p2-semantics.iana-status-codes ?>
[255]3015<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
[288]3016<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
[255]3017   <ttcol>Value</ttcol>
3018   <ttcol>Description</ttcol>
3019   <ttcol>Reference</ttcol>
3020   <c>100</c>
3021   <c>Continue</c>
3022   <c>
3023      <xref target="status.100"/>
3024   </c>
3025   <c>101</c>
3026   <c>Switching Protocols</c>
3027   <c>
3028      <xref target="status.101"/>
3029   </c>
3030   <c>200</c>
3031   <c>OK</c>
3032   <c>
3033      <xref target="status.200"/>
3034   </c>
3035   <c>201</c>
3036   <c>Created</c>
3037   <c>
3038      <xref target="status.201"/>
3039   </c>
3040   <c>202</c>
3041   <c>Accepted</c>
3042   <c>
3043      <xref target="status.202"/>
3044   </c>
3045   <c>203</c>
3046   <c>Non-Authoritative Information</c>
3047   <c>
3048      <xref target="status.203"/>
3049   </c>
3050   <c>204</c>
3051   <c>No Content</c>
3052   <c>
3053      <xref target="status.204"/>
3054   </c>
3055   <c>205</c>
3056   <c>Reset Content</c>
3057   <c>
3058      <xref target="status.205"/>
3059   </c>
3060   <c>300</c>
3061   <c>Multiple Choices</c>
3062   <c>
3063      <xref target="status.300"/>
3064   </c>
3065   <c>301</c>
3066   <c>Moved Permanently</c>
3067   <c>
3068      <xref target="status.301"/>
3069   </c>
3070   <c>302</c>
3071   <c>Found</c>
3072   <c>
3073      <xref target="status.302"/>
3074   </c>
3075   <c>303</c>
3076   <c>See Other</c>
3077   <c>
3078      <xref target="status.303"/>
3079   </c>
3080   <c>305</c>
3081   <c>Use Proxy</c>
3082   <c>
3083      <xref target="status.305"/>
3084   </c>
3085   <c>306</c>
3086   <c>(Unused)</c>
3087   <c>
3088      <xref target="status.306"/>
3089   </c>
3090   <c>307</c>
3091   <c>Temporary Redirect</c>
3092   <c>
3093      <xref target="status.307"/>
3094   </c>
3095   <c>400</c>
3096   <c>Bad Request</c>
3097   <c>
3098      <xref target="status.400"/>
3099   </c>
3100   <c>402</c>
3101   <c>Payment Required</c>
3102   <c>
3103      <xref target="status.402"/>
3104   </c>
3105   <c>403</c>
3106   <c>Forbidden</c>
3107   <c>
3108      <xref target="status.403"/>
3109   </c>
3110   <c>404</c>
3111   <c>Not Found</c>
3112   <c>
3113      <xref target="status.404"/>
3114   </c>
3115   <c>405</c>
3116   <c>Method Not Allowed</c>
3117   <c>
3118      <xref target="status.405"/>
3119   </c>
3120   <c>406</c>
3121   <c>Not Acceptable</c>
3122   <c>
3123      <xref target="status.406"/>
3124   </c>
3125   <c>407</c>
3126   <c>Proxy Authentication Required</c>
3127   <c>
3128      <xref target="status.407"/>
3129   </c>
3130   <c>408</c>
3131   <c>Request Timeout</c>
3132   <c>
3133      <xref target="status.408"/>
3134   </c>
3135   <c>409</c>
3136   <c>Conflict</c>
3137   <c>
3138      <xref target="status.409"/>
3139   </c>
3140   <c>410</c>
3141   <c>Gone</c>
3142   <c>
3143      <xref target="status.410"/>
3144   </c>
3145   <c>411</c>
3146   <c>Length Required</c>
3147   <c>
3148      <xref target="status.411"/>
3149   </c>
3150   <c>413</c>
[1322]3151   <c>Request Representation Too Large</c>
[255]3152   <c>
3153      <xref target="status.413"/>
3154   </c>
3155   <c>414</c>
[465]3156   <c>URI Too Long</c>
[255]3157   <c>
3158      <xref target="status.414"/>
3159   </c>
3160   <c>415</c>
3161   <c>Unsupported Media Type</c>
3162   <c>
3163      <xref target="status.415"/>
3164   </c>
3165   <c>417</c>
3166   <c>Expectation Failed</c>
3167   <c>
3168      <xref target="status.417"/>
3169   </c>
[1071]3170   <c>426</c>
3171   <c>Upgrade Required</c>
3172   <c>
3173      <xref target="status.426"/>
3174   </c>
[255]3175   <c>500</c>
3176   <c>Internal Server Error</c>
3177   <c>
3178      <xref target="status.500"/>
3179   </c>
3180   <c>501</c>
3181   <c>Not Implemented</c>
3182   <c>
3183      <xref target="status.501"/>
3184   </c>
3185   <c>502</c>
3186   <c>Bad Gateway</c>
3187   <c>
3188      <xref target="status.502"/>
3189   </c>
3190   <c>503</c>
3191   <c>Service Unavailable</c>
3192   <c>
3193      <xref target="status.503"/>
3194   </c>
3195   <c>504</c>
3196   <c>Gateway Timeout</c>
3197   <c>
3198      <xref target="status.504"/>
3199   </c>
3200   <c>505</c>
3201   <c>HTTP Version Not Supported</c>
3202   <c>
3203      <xref target="status.505"/>
3204   </c>
[682]3207<?ENDINC p2-semantics.iana-status-codes ?>
[921]3209<section title="Header Field Registration" anchor="header.field.registration">
[969]3211   The Message Header Field Registry located at <eref target=""/> shall be updated
[290]3212   with the permanent registrations below (see <xref target="RFC3864"/>):
[680]3214<?BEGININC p2-semantics.iana-headers ?>
[253]3215<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
[290]3216<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
[253]3217   <ttcol>Header Field Name</ttcol>
3218   <ttcol>Protocol</ttcol>
3219   <ttcol>Status</ttcol>
3220   <ttcol>Reference</ttcol>
[253]3222   <c>Allow</c>
3223   <c>http</c>
3224   <c>standard</c>
3225   <c>
3226      <xref target="header.allow"/>
3227   </c>
[1436]3228   <c>Date</c>
3229   <c>http</c>
3230   <c>standard</c>
3231   <c>
3232      <xref target=""/>
3233   </c>
[253]3234   <c>Expect</c>
3235   <c>http</c>
3236   <c>standard</c>
3237   <c>
3238      <xref target="header.expect"/>
3239   </c>
3240   <c>From</c>
3241   <c>http</c>
3242   <c>standard</c>
3243   <c>
3244      <xref target="header.from"/>
3245   </c>
3246   <c>Location</c>
3247   <c>http</c>
3248   <c>standard</c>
3249   <c>
3250      <xref target="header.location"/>
3251   </c>
3252   <c>Max-Forwards</c>
3253   <c>http</c>
3254   <c>standard</c>
3255   <c>
3256      <xref target="header.max-forwards"/>
3257   </c>
3258   <c>Referer</c>
3259   <c>http</c>
3260   <c>standard</c>
3261   <c>
3262      <xref target="header.referer"/>
3263   </c>
3264   <c>Retry-After</c>
3265   <c>http</c>
3266   <c>standard</c>
3267   <c>
3268      <xref target="header.retry-after"/>
3269   </c>
3270   <c>Server</c>
3271   <c>http</c>
3272   <c>standard</c>
3273   <c>
3274      <xref target="header.server"/>
3275   </c>
3276   <c>User-Agent</c>
3277   <c>http</c>
3278   <c>standard</c>
3279   <c>
3280      <xref target="header.user-agent"/>
3281   </c>
[680]3284<?ENDINC p2-semantics.iana-headers ?>
[290]3286   The change controller is: "IETF ( - Internet Engineering Task Force".
[8]3291<section title="Security Considerations" anchor="security.considerations">
3293   This section is meant to inform application developers, information
3294   providers, and users of the security limitations in HTTP/1.1 as
3295   described by this document. The discussion does not include
3296   definitive solutions to the problems revealed, though it does make
3297   some suggestions for reducing security risks.
3300<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3302   Like any generic data transfer protocol, HTTP cannot regulate the
3303   content of the data that is transferred, nor is there any a priori
3304   method of determining the sensitivity of any particular piece of
3305   information within the context of any given request. Therefore,
3306   applications &SHOULD; supply as much control over this information as
3307   possible to the provider of that information. Four header fields are
3308   worth special mention in this context: Server, Via, Referer and From.
3311   Revealing the specific software version of the server might allow the
3312   server machine to become more vulnerable to attacks against software
3313   that is known to contain security holes. Implementors &SHOULD; make the
3314   Server header field a configurable option.
3317   Proxies which serve as a portal through a network firewall &SHOULD;
3318   take special precautions regarding the transfer of header information
3319   that identifies the hosts behind the firewall. In particular, they
3320   &SHOULD; remove, or replace with sanitized versions, any Via fields
3321   generated behind the firewall.
[994]3324   The Referer header field allows reading patterns to be studied and reverse
[8]3325   links drawn. Although it can be very useful, its power can be abused
3326   if user details are not separated from the information contained in
3327   the Referer. Even when the personal information has been removed, the
[994]3328   Referer header field might indicate a private document's URI whose
[8]3329   publication would be inappropriate.
3332   The information sent in the From field might conflict with the user's
3333   privacy interests or their site's security policy, and hence it
3334   &SHOULD-NOT;  be transmitted without the user being able to disable,
3335   enable, and modify the contents of the field. The user &MUST; be able
3336   to set the contents of this field within a user preference or
3337   application defaults configuration.
3340   We suggest, though do not require, that a convenient toggle interface
3341   be provided for the user to enable or disable the sending of From and
3342   Referer information.
[1036]3345   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3346   target="header.server"/>) header fields can sometimes be used to determine
3347   that a specific client or server have a particular security hole which might
3348   be exploited. Unfortunately, this same information is often used for other
3349   valuable purposes for which HTTP currently has no better mechanism.
3352   Furthermore, the User-Agent header field may contain enough entropy to be
3353   used, possibly in conjunction with other material, to uniquely identify the
3354   user.
[1161]3357   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
[994]3358   that was sent in request header fields within the body of their response.
[666]3359   Clients &SHOULD; be careful with sensitive information, like Cookies,
[1161]3360   Authorization credentials, and other header fields that might be used to
[666]3361   collect data from the client.
[184]3365<section title="Encoding Sensitive Information in URIs" anchor="">
3367   Because the source of a link might be private information or might
3368   reveal an otherwise private information source, it is strongly
3369   recommended that the user be able to select whether or not the
3370   Referer field is sent. For example, a browser client could have a
3371   toggle switch for browsing openly/anonymously, which would
3372   respectively enable/disable the sending of Referer and From
3373   information.
[172]3376   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
[8]3377   HTTP request if the referring page was transferred with a secure
3378   protocol.
[969]3381   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3382   sensitive data because that data will be placed in the request-target. Many
[823]3383   existing servers, proxies, and user agents log or display the request-target
3384   in places where it might be visible to third parties. Such services can
[172]3385   use POST-based form submission instead.
3389<section title="Location Headers and Spoofing" anchor="location.spoofing">
3391   If a single server supports multiple organizations that do not trust
3392   one another, then it &MUST; check the values of Location and Content-Location
[994]3393   header fields in responses that are generated under control of
[8]3394   said organizations to make sure that they do not attempt to
3395   invalidate resources over which they have no authority.
[1061]3399<section title="Security Considerations for CONNECT">
3401   Since tunneled data is opaque to the proxy, there are additional
3402   risks to tunneling to other well-known or reserved ports.
3403   A HTTP client CONNECTing to port 25 could relay spam
3404   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3405   access to a small number of known ports.
[1364]3411<section title="Acknowledgments" anchor="acks">
3413  See &acks;.
[119]3419<references title="Normative References">
[31]3421<reference anchor="Part1">
[119]3422  <front>
3423    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3424    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]3425      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]3426      <address><email></email></address>
3427    </author>
3428    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]3429      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3430      <address><email></email></address>
[119]3431    </author>
3432    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3433      <organization abbrev="HP">Hewlett-Packard Company</organization>
3434      <address><email></email></address>
3435    </author>
3436    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3437      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3438      <address><email></email></address>
3439    </author>
3440    <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]3441      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]3442      <address><email></email></address>
3443    </author>
3444    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3445      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3446      <address><email></email></address>
3447    </author>
3448    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3449      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3450      <address><email></email></address>
3451    </author>
3452    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3453      <organization abbrev="W3C">World Wide Web Consortium</organization>
3454      <address><email></email></address>
3455    </author>
3456    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3457      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3458      <address><email></email></address>
3459    </author>
3460    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3461  </front>
3462  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3463  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3466<reference anchor="Part3">
[119]3467  <front>
3468    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3469    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]3470      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]3471      <address><email></email></address>
3472    </author>
3473    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]3474      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3475      <address><email></email></address>
[119]3476    </author>
3477    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3478      <organization abbrev="HP">Hewlett-Packard Company</organization>
3479      <address><email></email></address>
3480    </author>
3481    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3482      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3483      <address><email></email></address>
3484    </author>
3485    <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]3486      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]3487      <address><email></email></address>
3488    </author>
3489    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3490      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3491      <address><email></email></address>
3492    </author>
3493    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3494      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3495      <address><email></email></address>
3496    </author>
3497    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3498      <organization abbrev="W3C">World Wide Web Consortium</organization>
3499      <address><email></email></address>
3500    </author>
3501    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3502      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3503      <address><email></email></address>
3504    </author>
3505    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3506  </front>
3507  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3508  <x:source href="p3-payload.xml" basename="p3-payload"/>
3511<reference anchor="Part4">
[119]3512  <front>
3513    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3514    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
[1106]3515      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]3516      <address><email></email></address>
3517    </author>
3518    <author initials="J." surname="Gettys" fullname="Jim Gettys">
[844]3519      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3520      <address><email></email></address>
[119]3521    </author>
3522    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3523      <organization abbrev="HP">Hewlett-Packard Company</organization>
3524      <address><email></email></address>
3525    </author>
3526    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3527      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3528      <address><email></email></address>
3529    </author>
3530    <author initials="L." surname="Masinter" fullname="Larry Masinter">
[1106]3531      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
[119]3532      <address><email></email></address>
3533    </author>
3534    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3535      <organization abbrev="Microsoft">Microsoft Corporation</organization>