source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1619

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "March">
16  <!ENTITY ID-YEAR "2012">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY architecture               "<xref target='Part1' x:rel='#architecture' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY notation                   "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY acks                       "<xref target='Part1' x:rel='#acks' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY payload                    "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY conditional                "<xref target='Part4' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY range                      "<xref target='Part5' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY caching                    "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY auth                       "<xref target='Part7' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY agent-driven-negotiation   "<xref target='Part3' x:rel='#agent-driven.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY abnf-extension             "<xref target='Part1' x:rel='#abnf.extension' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY whitespace                 "<xref target='Part1' x:rel='#whitespace' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY field-components           "<xref target='Part1' x:rel='#field.components' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY effective-request-uri      "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY intermediaries             "<xref target='Part1' x:rel='#intermediaries' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY chunked-encoding           "<xref target='Part1' x:rel='#chunked.encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY http-url                   "<xref target='Part1' x:rel='#http-url' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY request-target             "<xref target='Part1' x:rel='#request-target' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY header-authorization       "<xref target='Part7' x:rel='#header.authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY header-connection          "<xref target='Part1' x:rel='#header.connection' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY header-content-type        "<xref target='Part3' x:rel='#header.content-type' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY header-fields              "<xref target='Part1' x:rel='#header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56  <!ENTITY header-host                "<xref target='Part1' x:rel='#header.host' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
57  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
58  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
59  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
60  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
61  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
62  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
63  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
64  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
65  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
66  <!ENTITY header-upgrade             "<xref target='Part1' x:rel='#header.upgrade' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
67  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.te' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
68  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
69  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
70  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
71  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
72  <!ENTITY media-types                "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
73  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
74  <!ENTITY media-type-message-http    "<xref target='Part1' x:rel='#internet.media.type.message.http' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
75  <!ENTITY status-206                 "<xref target='Part5' x:rel='#status.206' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
76  <!ENTITY status-304                 "<xref target='Part4' x:rel='#status.304' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
77  <!ENTITY status-401                 "<xref target='Part7' x:rel='#status.401' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
78  <!ENTITY status-407                 "<xref target='Part7' x:rel='#status.407' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
79  <!ENTITY status-412                 "<xref target='Part4' x:rel='#status.412' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
80  <!ENTITY status-416                 "<xref target='Part5' x:rel='#status.416' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
81  <!ENTITY p3-header-fields           "<xref target='Part3' x:rel='#header.field.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
82  <!ENTITY p4-status-codes            "<xref target='Part4' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
83  <!ENTITY p5-status-codes            "<xref target='Part5' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
84  <!ENTITY p7-status-codes            "<xref target='Part7' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
85  <!ENTITY p6-heuristic               "<xref target='Part6' x:rel='#heuristic.freshness' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
86  <!ENTITY p6-explicit                "<xref target='Part6' x:rel='#calculating.freshness.lifetime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
87  <!ENTITY p6-invalid                 "<xref target='Part6' x:rel='#invalidation.after.updates.or.deletions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
88  <!ENTITY p6-head                 "<xref target='Part6' x:rel='#head.effects' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
89]>
90<?rfc toc="yes" ?>
91<?rfc symrefs="yes" ?>
92<?rfc sortrefs="yes" ?>
93<?rfc compact="yes"?>
94<?rfc subcompact="no" ?>
95<?rfc linkmailto="no" ?>
96<?rfc editing="no" ?>
97<?rfc comments="yes"?>
98<?rfc inline="yes"?>
99<?rfc rfcedstyle="yes"?>
100<?rfc-ext allow-markup-in-artwork="yes" ?>
101<?rfc-ext include-references-in-index="yes" ?>
102<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="proposed"
103     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
104     xmlns:x='http://purl.org/net/xml2rfc/ext'
105     xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'>
106<x:link rel="prev" basename="p1-messaging"/>
107<x:link rel="next" basename="p3-payload"/>
108<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
109<front>
110
111  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
112
113  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
114    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
115    <address>
116      <postal>
117        <street>345 Park Ave</street>
118        <city>San Jose</city>
119        <region>CA</region>
120        <code>95110</code>
121        <country>USA</country>
122      </postal>
123      <email>fielding@gbiv.com</email>
124      <uri>http://roy.gbiv.com/</uri>
125    </address>
126  </author>
127
128  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
129    <organization abbrev="W3C">World Wide Web Consortium</organization>
130    <address>
131      <postal>
132        <street>W3C / ERCIM</street>
133        <street>2004, rte des Lucioles</street>
134        <city>Sophia-Antipolis</city>
135        <region>AM</region>
136        <code>06902</code>
137        <country>France</country>
138      </postal>
139      <email>ylafon@w3.org</email>
140      <uri>http://www.raubacapeu.net/people/yves/</uri>
141    </address>
142  </author>
143
144  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
145    <organization abbrev="greenbytes">greenbytes GmbH</organization>
146    <address>
147      <postal>
148        <street>Hafenweg 16</street>
149        <city>Muenster</city><region>NW</region><code>48155</code>
150        <country>Germany</country>
151      </postal>
152      <phone>+49 251 2807760</phone>
153      <facsimile>+49 251 2807761</facsimile>
154      <email>julian.reschke@greenbytes.de</email>
155      <uri>http://greenbytes.de/tech/webdav/</uri>
156    </address>
157  </author>
158
159  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
160  <workgroup>HTTPbis Working Group</workgroup>
161
162<abstract>
163<t>
164   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
165   distributed, collaborative, hypertext information systems. HTTP has been in
166   use by the World Wide Web global information initiative since 1990. This
167   document is Part 2 of the seven-part specification that defines the protocol
168   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
169</t>
170<t>
171   Part 2 defines the semantics of HTTP messages as expressed by request
172   methods, request header fields, response status codes, and response header
173   fields.
174</t>
175</abstract>
176
177<note title="Editorial Note (To be removed by RFC Editor)">
178  <t>
179    Discussion of this draft should take place on the HTTPBIS working group
180    mailing list (ietf-http-wg@w3.org), which is archived at
181    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
182  </t>
183  <t>
184    The current issues list is at
185    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
186    documents (including fancy diffs) can be found at
187    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
188  </t>
189  <t>
190    The changes in this draft are summarized in <xref target="changes.since.19"/>.
191  </t>
192</note>
193</front>
194<middle>
195<section title="Introduction" anchor="introduction">
196<t>
197   This document defines HTTP/1.1 request and response semantics.  Each HTTP
198   message, as defined in &messaging;, is in the form of either a request or
199   a response.  An HTTP server listens on a connection for HTTP requests and
200   responds to each request, in the order received on that connection, with
201   one or more HTTP response messages.  This document defines the commonly
202   agreed upon semantics of the HTTP uniform interface, the intentions defined
203   by each request method, and the various response messages that might be
204   expected as a result of applying that method to the target resource.
205</t>
206<t>
207   This document is currently disorganized in order to minimize the changes
208   between drafts and enable reviewers to see the smaller errata changes.
209   A future draft will reorganize the sections to better reflect the content.
210   In particular, the sections will be ordered according to the typical
211   processing of an HTTP request message (after message parsing): resource
212   mapping, methods, request modifying header fields, response status,
213   status modifying header fields, and resource metadata.  The current mess
214   reflects how widely dispersed these topics and associated requirements
215   had become in <xref target="RFC2616"/>.
216</t>
217
218<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
219<t>
220   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
221   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
222   document are to be interpreted as described in <xref target="RFC2119"/>.
223</t>
224<t>
225   This document defines conformance criteria for several roles in HTTP
226   communication, including Senders, Recipients, Clients, Servers, User-Agents,
227   Origin Servers, Intermediaries, Proxies and Gateways. See &architecture;
228   for definitions of these terms.
229</t>
230<t>
231   An implementation is considered conformant if it complies with all of the
232   requirements associated with its role(s). Note that SHOULD-level requirements
233   are relevant here, unless one of the documented exceptions is applicable.
234</t>
235<t>
236   This document also uses ABNF to define valid protocol elements
237   (<xref target="notation"/>). In addition to the prose requirements placed
238   upon them, Senders &MUST-NOT; generate protocol elements that are invalid.
239</t>
240<t>
241   Unless noted otherwise, Recipients &MAY; take steps to recover a usable
242   protocol element from an invalid construct. However, HTTP does not define
243   specific error handling mechanisms, except in cases where it has direct
244   impact on security. This is because different uses of the protocol require
245   different error handling strategies; for example, a Web browser may wish to
246   transparently recover from a response where the Location header field
247   doesn't parse according to the ABNF, whereby in a systems control protocol
248   using HTTP, this type of error recovery could lead to dangerous consequences.
249</t>
250</section>
251
252<section title="Syntax Notation" anchor="notation">
253  <x:anchor-alias value="CR"/>
254  <x:anchor-alias value="DIGIT"/>
255  <x:anchor-alias value="LF"/>
256  <x:anchor-alias value="HTAB"/>
257  <x:anchor-alias value="VCHAR"/>
258  <x:anchor-alias value="SP"/>
259<t>
260   This specification uses the Augmented Backus-Naur Form (ABNF) notation
261   of <xref target="RFC5234"/> with the list rule extension defined in
262   &notation;<xref target="collected.abnf"/> shows the collected ABNF
263   with the list rule expanded.
264</t>
265<t>
266  The following core rules are included by
267  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
268  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
269  DIGIT (decimal 0-9), DQUOTE (double quote),
270  HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
271  OCTET (any 8-bit sequence of data), SP (space), and
272  VCHAR (any visible US-ASCII character).
273</t>
274
275<section title="Core Rules" anchor="core.rules">
276  <x:anchor-alias value="obs-text"/>
277  <x:anchor-alias value="quoted-string"/>
278  <x:anchor-alias value="token"/>
279  <x:anchor-alias value="BWS"/>
280  <x:anchor-alias value="OWS"/>
281  <x:anchor-alias value="RWS"/>
282<t>
283  The core rules below are defined in <xref target="Part1"/>:
284</t>
285<figure><artwork type="abnf2616">
286  <x:ref>BWS</x:ref>           = &lt;BWS, defined in &whitespace;&gt;
287  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &whitespace;&gt;
288  <x:ref>RWS</x:ref>           = &lt;RWS, defined in &whitespace;&gt;
289  <x:ref>obs-text</x:ref>      = &lt;obs-text, defined in &field-components;&gt;
290  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &field-components;&gt;
291  <x:ref>token</x:ref>         = &lt;token, defined in &field-components;&gt;
292</artwork></figure>
293</section>
294
295<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
296  <x:anchor-alias value="absolute-URI"/>
297  <x:anchor-alias value="comment"/>
298  <x:anchor-alias value="partial-URI"/>
299  <x:anchor-alias value="URI-reference"/>
300<t>
301  The ABNF rules below are defined in other parts:
302</t>
303<figure><!--Part1--><artwork type="abnf2616">
304  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in &uri;&gt;
305  <x:ref>comment</x:ref>       = &lt;comment, defined in &field-components;&gt;
306  <x:ref>partial-URI</x:ref>   = &lt;partial-URI, defined in &uri;&gt;
307  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in &uri;&gt;
308</artwork></figure>
309</section>
310</section>
311</section>
312
313<section title="Methods" anchor="methods">
314  <x:anchor-alias value="method"/>
315<t>
316   The method token indicates the request method to be performed on the target
317   resource (&effective-request-uri;). The method is case-sensitive.
318</t>
319<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
320  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
321</artwork></figure>
322<t>
323   The list of methods allowed by a resource can be specified in an
324   Allow header field (<xref target="header.allow"/>). The status code of the response
325   always notifies the client whether a method is currently allowed on a
326   resource, since the set of allowed methods can change dynamically. An
327   origin server &SHOULD; respond with the status code 405 (Method Not Allowed)
328   if the method is known by the origin server but not allowed for the
329   resource, and 501 (Not Implemented) if the method is
330   unrecognized or not implemented by the origin server. The methods GET
331   and HEAD &MUST; be supported by all general-purpose servers. All other
332   methods are &OPTIONAL;; however, if the above methods are implemented,
333   they &MUST; be implemented with the same semantics as those specified
334   in <xref target="method.definitions"/>.
335</t>
336
337<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
338
339<section title="Safe Methods" anchor="safe.methods">
340<iref item="Safe Methods" primary="true"/>
341<t>
342   Implementors need to be aware that the software represents the user in
343   their interactions over the Internet, and need to allow
344   the user to be aware of any actions they take which might have an
345   unexpected significance to themselves or others.
346</t>
347<t>
348   In particular, the convention has been established that the GET, HEAD,
349   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
350   of taking an action other than retrieval. These request methods ought
351   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
352   This allows user agents to represent other methods, such as POST, PUT
353   and DELETE, in a special way, so that the user is made aware of the
354   fact that a possibly unsafe action is being requested.
355</t>
356<t>
357   Naturally, it is not possible to ensure that the server does not
358   generate side-effects as a result of performing a GET request; in
359   fact, some dynamic resources consider that a feature. The important
360   distinction here is that the user did not request the side-effects,
361   so therefore cannot be held accountable for them.
362</t>
363</section>
364
365<section title="Idempotent Methods" anchor="idempotent.methods">
366<iref item="Idempotent Methods" primary="true"/>
367<t>
368   Request methods can also have the property of "idempotence" in that,
369   aside from error or expiration issues, the intended effect of multiple
370   identical requests is the same as for a single request.
371   PUT, DELETE, and all safe request methods are idempotent.
372   It is important to note that idempotence refers only to changes
373   requested by the client: a server is free to change its state due
374   to multiple requests for the purpose of tracking those requests,
375   versioning of results, etc.
376</t>
377</section>
378</section>
379
380<section title="Method Registry" anchor="method.registry">
381<t>
382  The HTTP Method Registry defines the name space for the method token in the
383  Request line of an HTTP request.
384</t>
385<t>
386  Registrations &MUST; include the following fields:
387  <list style="symbols">
388    <t>Method Name (see <xref target="methods"/>)</t>
389    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
390    <t>Pointer to specification text</t>
391  </list>
392</t>
393<t>
394  Values to be added to this name space require IETF Review
395  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
396</t>
397<t>
398  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
399</t>
400
401<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
402<t>
403   When it is necessary to express new semantics for a HTTP request that
404   aren't specific to a single application or media type, and currently defined
405   methods are inadequate, it may be appropriate to register a new method.
406</t>
407<t>
408   HTTP methods are generic; that is, they are potentially applicable to any
409   resource, not just one particular media type, "type" of resource, or
410   application. As such, it is preferred that new HTTP methods be registered
411   in a document that isn't specific to a single application, so that this is
412   clear.
413</t>
414<t>
415   Due to the parsing rules defined in &message-body;, definitions of HTTP
416   methods cannot prohibit the presence of a message body on either the request
417   or the response message (with responses to HEAD requests being the single
418   exception). Definitions of new methods cannot change this rule, but they can
419   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
420</t>
421<t>
422   New method definitions need to indicate whether they are safe (<xref
423   target="safe.methods"/>), what semantics (if any) the request body has,
424   and whether they are idempotent (<xref target="idempotent.methods"/>).
425   They also need to state whether they can be cached (&caching;); in
426   particular what conditions a cache may store the response, and under what
427   conditions such a stored response may be used to satisfy a subsequent
428   request.
429</t>
430</section>
431</section>
432
433<section title="Method Definitions" anchor="method.definitions">
434
435<section title="OPTIONS" anchor="OPTIONS">
436  <rdf:Description>
437    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
438  </rdf:Description>
439  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
440  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
441<t>
442   The OPTIONS method requests information about the
443   communication options available on the request/response chain
444   identified by the effective request URI. This method allows a client to
445   determine the options and/or requirements associated with a resource,
446   or the capabilities of a server, without implying a resource action
447   or initiating a resource retrieval.
448</t>
449<t>
450   Responses to the OPTIONS method are not cacheable.
451</t>
452<t>
453   If the OPTIONS request includes a message body (as indicated by the
454   presence of Content-Length or Transfer-Encoding), then the media type
455   &MUST; be indicated by a Content-Type field. Although this
456   specification does not define any use for such a body, future
457   extensions to HTTP might use the OPTIONS body to make more detailed
458   queries on the server.
459</t>
460<t>
461   If the request-target (&request-target;) is an asterisk ("*"),
462   the OPTIONS request is
463   intended to apply to the server in general rather than to a specific
464   resource. Since a server's communication options typically depend on
465   the resource, the "*" request is only useful as a "ping" or "no-op"
466   type of method; it does nothing beyond allowing the client to test
467   the capabilities of the server. For example, this can be used to test
468   a proxy for HTTP/1.1 conformance (or lack thereof).
469</t>
470<t>
471   If the request-target is not an asterisk, the OPTIONS request applies
472   only to the options that are available when communicating with that
473   resource.
474</t>
475<t>
476   A 200 response &SHOULD; include any header fields that indicate
477   optional features implemented by the server and applicable to that
478   resource (e.g., Allow), possibly including extensions not defined by
479   this specification. The response body, if any, &SHOULD; also include
480   information about the communication options. The format for such a
481   body is not defined by this specification, but might be defined by
482   future extensions to HTTP. Content negotiation &MAY; be used to select
483   the appropriate response format. If no response body is included, the
484   response &MUST; include a Content-Length field with a field-value of
485   "0".
486</t>
487<t>
488   The Max-Forwards header field &MAY; be used to target a
489   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
490   If no Max-Forwards field is present in the request, then the forwarded
491   request &MUST-NOT; include a Max-Forwards field.
492</t>
493</section>
494
495<section title="GET" anchor="GET">
496  <rdf:Description>
497    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
498  </rdf:Description>
499  <iref primary="true" item="GET method" x:for-anchor=""/>
500  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
501<t>
502   The GET method requests transfer of a current representation of
503   the target resource.
504</t>
505<t>   
506   If the target resource is a data-producing process, it is the
507   produced data which shall be returned as the representation in the response and not
508   the source text of the process, unless that text happens to be the output of
509   the process.
510</t>
511<t>
512   The semantics of the GET method change to a "conditional GET" if the
513   request message includes an If-Modified-Since, If-Unmodified-Since,
514   If-Match, If-None-Match, or If-Range header field. A conditional GET
515   requests that the representation be transferred only under the
516   circumstances described by the conditional header field(s). The
517   conditional GET request is intended to reduce unnecessary network
518   usage by allowing cached representations to be refreshed without requiring
519   multiple requests or transferring data already held by the client.
520</t>
521<t>
522   The semantics of the GET method change to a "partial GET" if the
523   request message includes a Range header field. A partial GET requests
524   that only part of the representation be transferred, as described in &header-range;.
525   The partial GET request is intended to reduce unnecessary
526   network usage by allowing partially-retrieved representations to be
527   completed without transferring data already held by the client.
528</t>
529<t>
530   Bodies on GET requests have no defined semantics. Note that sending a body
531   on a GET request might cause some existing implementations to reject the
532   request.
533</t>
534<t>
535   The response to a GET request is cacheable and &MAY; be used to satisfy
536   subsequent GET and HEAD requests (see &caching;).
537</t>
538<t>
539   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
540</t>
541</section>
542
543<section title="HEAD" anchor="HEAD">
544  <rdf:Description>
545    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
546  </rdf:Description>
547  <iref primary="true" item="HEAD method" x:for-anchor=""/>
548  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
549<t>
550   The HEAD method is identical to GET except that the server &MUST-NOT;
551   return a message body in the response. The metadata contained
552   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
553   to the information sent in response to a GET request. This method can
554   be used for obtaining metadata about the representation implied by the
555   request without transferring the representation body. This method is
556   often used for testing hypertext links for validity, accessibility,
557   and recent modification.
558</t>
559<t>
560   The response to a HEAD request is cacheable and &MAY; be used to satisfy
561   a subsequent HEAD request. It also has potential side effects on
562   previously stored responses to GET; see &p6-head;.
563</t>
564<t>
565   Bodies on HEAD requests have no defined semantics. Note that sending a body
566   on a HEAD request might cause some existing implementations to reject the
567   request.
568</t>
569</section>
570
571<section title="POST" anchor="POST">
572  <iref primary="true" item="POST method" x:for-anchor=""/>
573  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
574<t>
575   The POST method requests that the origin server accept the
576   representation enclosed in the request as data to be processed by the
577   target resource. POST is designed to allow a uniform method to cover the
578   following functions:
579  <list style="symbols">
580    <t>
581      Annotation of existing resources;
582    </t>
583    <t>
584        Posting a message to a bulletin board, newsgroup, mailing list,
585        or similar group of articles;
586    </t>
587    <t>
588        Providing a block of data, such as the result of submitting a
589        form, to a data-handling process;
590    </t>
591    <t>
592        Extending a database through an append operation.
593    </t>
594  </list>
595</t>
596<t>
597   The actual function performed by the POST method is determined by the
598   server and is usually dependent on the effective request URI.
599</t>
600<t>
601   The action performed by the POST method might not result in a
602   resource that can be identified by a URI. In this case, either 200
603   (OK) or 204 (No Content) is the appropriate response status code,
604   depending on whether or not the response includes a representation that
605   describes the result.
606</t>
607<t>
608   If a resource has been created on the origin server, the response
609   &SHOULD; be 201 (Created) and contain a representation which describes the
610   status of the request and refers to the new resource, and a Location
611   header field (see <xref target="header.location"/>).
612</t>
613<t>
614   Responses to POST requests are only cacheable when they
615   include explicit freshness information (see &p6-explicit;). A
616   cached POST response with a Content-Location header field
617   (see &header-content-location;) whose value is the effective
618   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
619</t>
620<t>
621   Note that POST caching is not widely implemented.
622   However, the 303 (See Other) response can be used to direct the
623   user agent to retrieve a cacheable representation of the resource.
624</t>
625</section>
626
627<section title="PUT" anchor="PUT">
628  <iref primary="true" item="PUT method" x:for-anchor=""/>
629  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
630<t>
631   The PUT method requests that the state of the target resource
632   be created or replaced with the state defined by the representation
633   enclosed in the request message payload.  A successful PUT of a given
634   representation would suggest that a subsequent GET on that same target
635   resource will result in an equivalent representation being returned in
636   a 200 (OK) response.  However, there is no guarantee that such a state
637   change will be observable, since the target resource might be acted
638   upon by other user agents in parallel, or might be subject to dynamic
639   processing by the origin server, before any subsequent GET is received.
640   A successful response only implies that the user agent's intent was
641   achieved at the time of its processing by the origin server.
642</t>
643<t>   
644   If the target resource does not have a current representation and
645   the PUT successfully creates one, then the origin server &MUST; inform
646   the user agent by sending a 201 (Created) response.  If the target
647   resource does have a current representation and that representation is
648   successfully modified in accordance with the state of the enclosed
649   representation, then either a 200 (OK) or 204 (No Content) response
650   &SHOULD; be sent to indicate successful completion of the request.
651</t>
652<t>
653   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
654   as part of the resource state).
655</t>
656<t>
657   An origin server &SHOULD; verify that the PUT representation is
658   consistent with any constraints which the server has for the target
659   resource that cannot or will not be changed by the PUT.  This is
660   particularly important when the origin server uses internal
661   configuration information related to the URI in order to set the
662   values for representation metadata on GET responses.  When a PUT
663   representation is inconsistent with the target resource, the origin
664   server &SHOULD; either make them consistent, by transforming the
665   representation or changing the resource configuration, or respond
666   with an appropriate error message containing sufficient information
667   to explain why the representation is unsuitable.  The 409 (Conflict)
668   or 415 (Unsupported Media Type) status codes are suggested, with the
669   latter being specific to constraints on Content-Type values.
670</t>
671<t>
672   For example, if the target resource is configured to always have a
673   Content-Type of "text/html" and the representation being PUT has a
674   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
675   (a) reconfigure the target resource to reflect the new media type;
676   (b) transform the PUT representation to a format consistent with that
677   of the resource before saving it as the new resource state; or,
678   (c) reject the request with a 415 response indicating that the target
679   resource is limited to "text/html", perhaps including a link to a
680   different resource that would be a suitable target for the new
681   representation.
682</t>
683<t>
684   HTTP does not define exactly how a PUT method affects the state
685   of an origin server beyond what can be expressed by the intent of
686   the user agent request and the semantics of the origin server response.
687   It does not define what a resource might be, in any sense of that
688   word, beyond the interface provided via HTTP.  It does not define
689   how resource state is "stored", nor how such storage might change
690   as a result of a change in resource state, nor how the origin server
691   translates resource state into representations.  Generally speaking,
692   all implementation details behind the resource interface are
693   intentionally hidden by the server.
694</t>
695<t>
696   The fundamental difference between the POST and PUT methods is
697   highlighted by the different intent for the target resource.
698   The target resource in a POST request is intended to handle the
699   enclosed representation as a data-accepting process, such as for
700   a gateway to some other protocol or a document that accepts annotations.
701   In contrast, the target resource in a PUT request is intended to
702   take the enclosed representation as a new or replacement value.
703   Hence, the intent of PUT is idempotent and visible to intermediaries,
704   even though the exact effect is only known by the origin server.
705</t>
706<t>
707   Proper interpretation of a PUT request presumes that the user agent
708   knows what target resource is desired.  A service that is intended
709   to select a proper URI on behalf of the client, after receiving
710   a state-changing request, &SHOULD; be implemented using the POST
711   method rather than PUT.  If the origin server will not make the
712   requested PUT state change to the target resource and instead
713   wishes to have it applied to a different resource, such as when the
714   resource has been moved to a different URI, then the origin server
715   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
716   then make its own decision regarding whether or not to redirect the
717   request.
718</t>
719<t>
720   A PUT request applied to the target resource &MAY; have side-effects
721   on other resources.  For example, an article might have a URI for
722   identifying "the current version" (a resource) which is separate
723   from the URIs identifying each particular version (different
724   resources that at one point shared the same state as the current version
725   resource).  A successful PUT request on "the current version" URI might
726   therefore create a new version resource in addition to changing the
727   state of the target resource, and might also cause links to be added
728   between the related resources.
729</t>
730<t>
731   An origin server &SHOULD; reject any PUT request that contains a
732   Content-Range header field, since it might be misinterpreted as
733   partial content (or might be partial content that is being mistakenly
734   PUT as a full representation).  Partial content updates are
735   possible by targeting a separately identified resource with state
736   that overlaps a portion of the larger resource, or by using a
737   different method that has been specifically defined for partial
738   updates (for example, the PATCH method defined in
739   <xref target="RFC5789"/>).
740</t>
741<t>
742   Responses to the PUT method are not cacheable. If a PUT request passes
743   through a cache that has one or more stored responses for the effective
744   request URI, those stored responses will be invalidated (see
745   &p6-invalid;).
746</t>
747</section>
748
749<section title="DELETE" anchor="DELETE">
750  <iref primary="true" item="DELETE method" x:for-anchor=""/>
751  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
752<t>
753   The DELETE method requests that the origin server delete the target
754   resource. This method &MAY; be overridden by
755   human intervention (or other means) on the origin server. The client cannot
756   be guaranteed that the operation has been carried out, even if the
757   status code returned from the origin server indicates that the action
758   has been completed successfully. However, the server &SHOULD-NOT; 
759   indicate success unless, at the time the response is given, it
760   intends to delete the resource or move it to an inaccessible
761   location.
762</t>
763<t>
764   A successful response &SHOULD; be 200 (OK) if the response includes an
765   representation describing the status, 202 (Accepted) if the action has not
766   yet been enacted, or 204 (No Content) if the action has been enacted
767   but the response does not include a representation.
768</t>
769<t>
770   Bodies on DELETE requests have no defined semantics. Note that sending a body
771   on a DELETE request might cause some existing implementations to reject the
772   request.
773</t>
774<t>
775   Responses to the DELETE method are not cacheable. If a DELETE request
776   passes through a cache that has one or more stored responses for the
777   effective request URI, those stored responses will be invalidated (see
778   &p6-invalid;).
779</t>
780</section>
781
782<section title="TRACE" anchor="TRACE">
783  <rdf:Description>
784    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
785  </rdf:Description>
786  <iref primary="true" item="TRACE method" x:for-anchor=""/>
787  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
788<t>
789   The TRACE method requests a remote, application-layer loop-back
790   of the request message. The final recipient of the request
791   &SHOULD; reflect the message received back to the client as the
792   message body of a 200 (OK) response. The final recipient is either the
793   origin server or the first proxy to receive a Max-Forwards
794   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
795   A TRACE request &MUST-NOT; include a message body.
796</t>
797<t>
798   TRACE allows the client to see what is being received at the other
799   end of the request chain and use that data for testing or diagnostic
800   information. The value of the Via header field (&header-via;) is of
801   particular interest, since it acts as a trace of the request chain.
802   Use of the Max-Forwards header field allows the client to limit the
803   length of the request chain, which is useful for testing a chain of
804   proxies forwarding messages in an infinite loop.
805</t>
806<t>
807   If the request is valid, the response &SHOULD; have a Content-Type of
808   "message/http" (see &media-type-message-http;) and contain a message body
809   that encloses a copy of the entire request message.
810   Responses to the TRACE method are not cacheable.
811</t>
812</section>
813
814<section title="CONNECT" anchor="CONNECT">
815  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
816  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
817<t>
818   The CONNECT method requests that the proxy establish a tunnel
819   to the request-target and, if successful, thereafter restrict its behavior
820   to blind forwarding of packets until the connection is closed.
821</t>
822<t>
823   When using CONNECT, the request-target &MUST; use the authority form
824   (&request-target;); i.e., the request-target consists of only the
825   host name and port number of the tunnel destination, separated by a colon.
826   For example,
827</t>
828<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
829CONNECT server.example.com:80 HTTP/1.1
830Host: server.example.com:80
831
832</artwork></figure>
833<t>
834   Any successful (2xx) response to a CONNECT request indicates that the
835   proxy has established a connection to the requested host and port,
836   and has switched to tunneling the current connection to that server
837   connection.
838   The tunneled data from the server begins immediately after the blank line
839   that concludes the successful response's header block.
840   A server &SHOULD-NOT; send any Transfer-Encoding or Content-Length
841   header fields in a successful response.
842   A client &MUST; ignore any Content-Length or Transfer-Encoding header
843   fields received in a successful response.
844</t>
845<t>
846   Any response other than a successful response indicates that the tunnel
847   has not yet been formed and that the connection remains governed by HTTP.
848</t>
849<t>
850   Proxy authentication might be used to establish the
851   authority to create a tunnel:
852</t>
853<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
854CONNECT server.example.com:80 HTTP/1.1
855Host: server.example.com:80
856Proxy-Authorization: basic aGVsbG86d29ybGQ=
857
858</artwork></figure>
859<t>
860   A message body on a CONNECT request has no defined semantics. Sending a
861   body on a CONNECT request might cause existing implementations to reject
862   the request.
863</t>
864<t>
865   Similar to a pipelined HTTP/1.1 request, data to be tunneled from client
866   to server &MAY; be sent immediately after the request (before a response
867   is received). The usual caveats also apply:
868   data may be discarded if the eventual response is negative, and the
869   connection may be reset with no response if more than one TCP segment
870   is outstanding.
871</t>
872<t>
873   It may be the case that the proxy itself can only reach the requested
874   origin server through another proxy.  In this case, the first proxy
875   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
876   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
877   unless it has either a direct or tunnel connection established to the
878   authority.
879</t>
880<t>
881   If at any point either one of the peers gets disconnected, any
882   outstanding data that came from that peer will be passed to the other
883   one, and after that also the other connection will be terminated by
884   the proxy. If there is outstanding data to that peer undelivered,
885   that data will be discarded.
886</t>
887<t>
888   An origin server which receives a CONNECT request for itself &MAY;
889   respond with a 2xx status code to indicate that a connection is
890   established.  However, most origin servers do not implement CONNECT.
891</t>
892</section>
893</section>
894
895</section>
896
897<section title="Header Fields" anchor="header.fields">
898<t>
899   Header fields are key value pairs that can be used to communicate data about
900   the message, its payload, the target resource, or about the connection
901   itself (i.e., control data).  See &header-fields; for a general definition
902   of their syntax.
903</t>
904
905<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
906<t>
907   New header fields are registered using the procedures described in
908   <xref target="RFC3864"/>.
909</t>
910<t>
911   The requirements for header field names are defined in
912   <xref target="RFC3864" x:fmt="of" x:sec="4.1"/>.  Authors of specifications
913   defining new fields are advised to keep the name as short as practical, and
914   not to prefix them with "X-" if they are to be registered (either
915   immediately or in the future).
916</t>
917<t>
918   New header field values typically have their syntax defined using ABNF
919   (<xref target="RFC5234"/>), using the extension defined in &abnf-extension;
920   as necessary, and are usually constrained to the range of ASCII characters.
921   Header fields needing a greater range of characters can use an encoding
922   such as the one defined in <xref target="RFC5987"/>.
923</t>
924<t>
925   Because commas (",") are used as a generic delimiter between field-values,
926   they need to be treated with care if they are allowed in the field-value's
927   payload. Typically, components that might contain a comma are protected with
928   double-quotes using the quoted-string ABNF production (&field-components;).
929</t>
930<t>
931   For example, a textual date and a URI (either of which might contain a comma)
932   could be safely carried in field-values like these:
933</t>
934<figure><artwork type="example">
935  Example-URI-Field: "http://example.com/a.html,foo",
936                     "http://without-a-comma.example.com/"
937  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
938</artwork></figure>
939<t>
940   Note that double quote delimiters almost always are used with the
941   quoted-string production; using a different syntax inside double quotes
942   will likely cause unnecessary confusion.
943</t>
944<t>
945   Many header fields use a format including (case-insensitively) named
946   parameters (for instance, Content-Type, defined in &header-content-type;).
947   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
948   parameter value enables recipients to use existing parser components. When
949   allowing both forms, the meaning of a parameter value ought to be
950   independent of the syntax used for it (for an example, see the notes on
951   parameter handling for media types in &media-types;).
952</t>
953<t>
954   Authors of specifications defining new header fields are advised to consider
955   documenting:
956  <list style="symbols">
957    <x:lt>
958      <t>Whether the field is a single value, or whether it can be a list
959      (delimited by commas; see &header-fields;).</t>
960      <t>If it does not use the list syntax, document how to treat messages
961      where the header field occurs multiple times (a sensible default would
962      be to ignore the header field, but this might not always be the right
963      choice).</t>
964      <t>Note that intermediaries and software libraries might combine
965      multiple header field instances into a single one, despite the header
966      field not allowing this. A robust format enables recipients to discover
967      these situations (good example: "Content-Type", as the comma can only
968      appear inside quoted strings; bad example: "Location", as a comma can
969      occur inside a URI).</t>
970    </x:lt>
971    <x:lt><t>Under what conditions the header field can be used; e.g., only in
972    responses or requests, in all messages, only on responses to a particular
973    request method.</t></x:lt>
974    <x:lt><t>Whether it is appropriate to list the field-name in the Connection header
975    (i.e., if the header is to be hop-by-hop, see &header-connection;).</t></x:lt>
976    <x:lt><t>Under what conditions intermediaries are allowed to modify the header
977    field's value, insert or delete it.</t></x:lt>
978    <x:lt><t>How the header might interact with caching (see <xref target="Part6"/>).</t></x:lt>
979    <x:lt><t>Whether the header field is useful or allowable in trailers (see
980    &chunked-encoding;).</t></x:lt>
981    <x:lt><t>Whether the header field should be preserved across redirects.</t></x:lt>
982  </list>
983</t>
984</section>
985
986<section title="Request Header Fields" anchor="request.header.fields">
987  <x:anchor-alias value="request-header"/>
988<t>
989   The request header fields allow the client to pass additional
990   information about the request, and about the client itself, to the
991   server. These fields act as request modifiers, with semantics
992   equivalent to the parameters on a programming language method
993   invocation.
994</t>
995<texttable align="left">
996  <ttcol>Header Field Name</ttcol>
997  <ttcol>Defined in...</ttcol>
998
999  <c>Accept</c> <c>&header-accept;</c>
1000  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
1001  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
1002  <c>Accept-Language</c> <c>&header-accept-language;</c>
1003  <c>Authorization</c> <c>&header-authorization;</c>
1004  <c>Expect</c> <c><xref target="header.expect"/></c>
1005  <c>From</c> <c><xref target="header.from"/></c>
1006  <c>Host</c> <c>&header-host;</c>
1007  <c>If-Match</c> <c>&header-if-match;</c>
1008  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
1009  <c>If-None-Match</c> <c>&header-if-none-match;</c>
1010  <c>If-Range</c> <c>&header-if-range;</c>
1011  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
1012  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
1013  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
1014  <c>Range</c> <c>&header-range;</c>
1015  <c>Referer</c> <c><xref target="header.referer"/></c>
1016  <c>TE</c> <c>&header-te;</c>
1017  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
1018</texttable>
1019</section>
1020
1021<section title="Response Header Fields" anchor="response.header.fields">
1022  <x:anchor-alias value="response-header"/>
1023<t>
1024   The response header fields allow the server to pass additional
1025   information about the response which cannot be placed in the status-line.
1026   These header fields give information about the server and about
1027   further access to the target resource (&effective-request-uri;).
1028</t>
1029<texttable align="left">
1030  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
1031
1032  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
1033  <c>Age</c> <c>&header-age;</c>
1034  <c>Allow</c> <c><xref target="header.allow"/></c>
1035  <c>Date</c> <c><xref target="header.date"/></c>
1036  <c>ETag</c> <c>&header-etag;</c>
1037  <c>Location</c> <c><xref target="header.location"/></c>
1038  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
1039  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
1040  <c>Server</c> <c><xref target="header.server"/></c>
1041  <c>Vary</c> <c>&header-vary;</c>
1042  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
1043</texttable>
1044</section>
1045
1046</section>
1047
1048<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1049  <x:anchor-alias value="reason-phrase"/>
1050  <x:anchor-alias value="status-code"/>
1051  <x:anchor-alias value="extension-code"/>
1052<t>
1053   The status-code element is a 3-digit integer result code of the attempt to
1054   understand and satisfy the request.
1055</t>
1056<t>
1057   The reason-phrase is intended to give a short textual description of the
1058   status-code and is intended for a human user. The client does not need
1059   to examine or display the reason-phrase.
1060</t>
1061<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"/>
1062  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1063  <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> )
1064</artwork></figure>
1065<t>
1066   HTTP status codes are extensible. HTTP applications are not required
1067   to understand the meaning of all registered status codes, though such
1068   understanding is obviously desirable. However, applications &MUST;
1069   understand the class of any status code, as indicated by the first
1070   digit, and treat any unrecognized response as being equivalent to the
1071   x00 status code of that class, with the exception that an
1072   unrecognized response &MUST-NOT; be cached. For example, if an
1073   unrecognized status code of 431 is received by the client, it can
1074   safely assume that there was something wrong with its request and
1075   treat the response as if it had received a 400 status code. In such
1076   cases, user agents &SHOULD; present to the user the representation enclosed
1077   with the response, since that representation is likely to include human-readable
1078   information which will explain the unusual status.
1079</t>
1080<t>
1081   The first digit of the status-code defines the class of response. The
1082   last two digits do not have any categorization role. There are 5
1083   values for the first digit:
1084  <list style="symbols">
1085    <t>
1086      1xx: Informational - Request received, continuing process
1087    </t>
1088    <t>
1089      2xx: Success - The action was successfully received,
1090        understood, and accepted
1091    </t>
1092    <t>
1093      3xx: Redirection - Further action needs to be taken in order to
1094        complete the request
1095    </t>
1096    <t>
1097      4xx: Client Error - The request contains bad syntax or cannot
1098        be fulfilled
1099    </t>
1100    <t>
1101      5xx: Server Error - The server failed to fulfill an apparently
1102        valid request
1103    </t>
1104  </list>
1105</t>
1106
1107<section title="Overview of Status Codes" anchor="overview.of.status.codes">
1108<t> 
1109   The status codes listed below are defined in <xref target="status.codes"/>
1110   of this specification, &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
1111   The reason phrases listed here are only recommendations &mdash; they can be
1112   replaced by local equivalents without affecting the protocol.
1113</t>
1114<texttable align="left">
1115  <ttcol>status-code</ttcol>
1116  <ttcol>reason-phrase</ttcol>
1117  <ttcol>Defined in...</ttcol>
1118 
1119  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
1120  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
1121
1122  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
1123  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
1124  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
1125  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
1126  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
1127  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
1128  <c>206</c> <c>Partial Content</c> <c anchor="status.206">&status-206;</c>
1129
1130  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
1131  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
1132  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
1133  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
1134  <c>304</c> <c>Not Modified</c> <c anchor="status.304">&status-304;</c>
1135  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
1136  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
1137
1138  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
1139  <c>401</c> <c>Unauthorized</c> <c anchor="status.401">&status-401;</c>
1140  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
1141  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
1142  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
1143  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
1144  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
1145  <c>407</c> <c>Proxy Authentication Required</c> <c anchor="status.407">&status-407;</c>
1146  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
1147  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
1148  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
1149  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
1150  <c>412</c> <c>Precondition Failed</c> <c anchor="status.412">&status-412;</c>
1151  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
1152  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
1153  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
1154  <c>416</c> <c>Requested range not satisfiable</c> <c anchor="status.416">&status-416;</c>
1155  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
1156  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
1157
1158  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
1159  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
1160  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
1161  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
1162  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
1163  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
1164</texttable>
1165<t>
1166   Note that this list is not exhaustive &mdash; it does not include
1167   extension status codes defined in other specifications.
1168</t>
1169</section>
1170
1171<section title="Status Code Registry" anchor="status.code.registry">
1172<t>
1173  The HTTP Status Code Registry defines the name space for the status-code
1174  token in the status-line of an HTTP response.
1175</t>
1176<t>
1177  Values to be added to this name space require IETF Review
1178  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
1179</t>
1180<t>
1181  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
1182</t>
1183
1184<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
1185<t>
1186   When it is necessary to express new semantics for a HTTP response that
1187   aren't specific to a single application or media type, and currently defined
1188   status codes are inadequate, a new status code can be registered.
1189</t>
1190<t>
1191   HTTP status codes are generic; that is, they are potentially applicable to
1192   any resource, not just one particular media type, "type" of resource, or
1193   application. As such, it is preferred that new HTTP status codes be
1194   registered in a document that isn't specific to a single application, so
1195   that this is clear.
1196</t>
1197<t>
1198   Definitions of new HTTP status codes typically explain the request
1199   conditions that produce a response containing the status code (e.g.,
1200   combinations of request headers and/or method(s)), along with any
1201   interactions with response headers (e.g., those that are required, those
1202   that modify the semantics of the response).
1203</t>
1204<t>
1205   New HTTP status codes are required to fall under one of the categories
1206   defined in <xref target="status.codes"/>. To allow existing parsers to
1207   properly handle them, new status codes cannot disallow a response body,
1208   although they can mandate a zero-length response body. They can require the
1209   presence of one or more particular HTTP response header(s).
1210</t>
1211<t>
1212   Likewise, their definitions can specify that caches are allowed to use
1213   heuristics to determine their freshness (see &caching;; by default, it is
1214   not allowed), and can define how to determine the resource which they
1215   carry a representation for (see <xref
1216   target="identifying.response.associated.with.representation"/>; by default,
1217   it is anonymous).
1218</t>
1219</section>
1220
1221</section>
1222
1223<section title="Status Code Definitions" anchor="status.codes">
1224<t>
1225   Each status-code is described below, including any metadata required
1226   in the response.
1227</t>
1228<t>
1229   For most status codes the response can carry a payload, in which case a
1230   Content-Type header field indicates the payload's media type
1231   (&header-content-type;).
1232</t>
1233
1234<section title="Informational 1xx" anchor="status.1xx">
1235<t>
1236   This class of status code indicates a provisional response,
1237   consisting only of the status-line and optional header fields, and is
1238   terminated by an empty line. There are no required header fields for this
1239   class of status code. Since HTTP/1.0 did not define any 1xx status
1240   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1241   except under experimental conditions.
1242</t>
1243<t>
1244   A client &MUST; be prepared to accept one or more 1xx status responses
1245   prior to a regular response, even if the client does not expect a 100
1246   (Continue) status message. Unexpected 1xx status responses &MAY; be
1247   ignored by a user agent.
1248</t>
1249<t>
1250   Proxies &MUST; forward 1xx responses, unless the connection between the
1251   proxy and its client has been closed, or unless the proxy itself
1252   requested the generation of the 1xx response. (For example, if a
1253   proxy adds a "Expect: 100-continue" field when it forwards a request,
1254   then it need not forward the corresponding 100 (Continue)
1255   response(s).)
1256</t>
1257
1258<section title="100 Continue" anchor="status.100">
1259  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1260  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1261<t>
1262   The client &SHOULD; continue with its request. This interim response is
1263   used to inform the client that the initial part of the request has
1264   been received and has not yet been rejected by the server. The client
1265   &SHOULD; continue by sending the remainder of the request or, if the
1266   request has already been completed, ignore this response. The server
1267   &MUST; send a final response after the request has been completed. See
1268   &use100; for detailed discussion of the use and handling of this
1269   status code.
1270</t>
1271</section>
1272
1273<section title="101 Switching Protocols" anchor="status.101">
1274  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1275  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1276<t>
1277   The server understands and is willing to comply with the client's
1278   request, via the Upgrade message header field (&header-upgrade;), for a
1279   change in the application protocol being used on this connection. The
1280   server will switch protocols to those defined by the response's
1281   Upgrade header field immediately after the empty line which
1282   terminates the 101 response.
1283</t>
1284<t>
1285   The protocol &SHOULD; be switched only when it is advantageous to do
1286   so. For example, switching to a newer version of HTTP is advantageous
1287   over older versions, and switching to a real-time, synchronous
1288   protocol might be advantageous when delivering resources that use
1289   such features.
1290</t>
1291</section>
1292</section>
1293
1294<section title="Successful 2xx" anchor="status.2xx">
1295<t>
1296   This class of status code indicates that the client's request was
1297   successfully received, understood, and accepted.
1298</t>
1299
1300<section title="200 OK" anchor="status.200">
1301  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1302  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1303<t>
1304   The request has succeeded. The payload returned with the response
1305   is dependent on the method used in the request, for example:
1306  <list style="hanging">
1307    <t hangText="GET">
1308      a representation of the target resource is sent in the response;
1309    </t>
1310    <t hangText="HEAD">
1311      the same representation as GET, except without the message body;
1312    </t>
1313    <t hangText="POST">
1314      a representation describing or containing the result of the action;
1315    </t>
1316    <t hangText="TRACE">
1317      a representation containing the request message as received by the
1318      end server.
1319    </t>
1320  </list>
1321</t>
1322<t>
1323   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1324   freshness for 200 responses.
1325</t>
1326</section>
1327
1328<section title="201 Created" anchor="status.201">
1329  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1330  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1331<t>
1332   The request has been fulfilled and has resulted in a new resource being
1333   created.
1334</t>
1335<t>
1336   The newly created resource is typically linked to from the response payload,
1337   with the most relevant URI also being carried in the Location header field.
1338   If the newly created resource's URI is the same as the Effective Request URI,
1339   this information can be omitted (e.g., in the case of a response to a PUT
1340   request). 
1341</t>
1342<t>
1343   The origin server &MUST; create the resource before returning the 201 status
1344   code. If the action cannot be carried out immediately, the server &SHOULD;
1345   respond with 202 (Accepted) response instead.
1346</t>
1347<t>
1348   A 201 response &MAY; contain an ETag response header field indicating
1349   the current value of the entity-tag for the representation of the resource
1350   just created (see &header-etag;).
1351</t>
1352</section>
1353
1354<section title="202 Accepted" anchor="status.202">
1355  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1356  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1357<t>
1358   The request has been accepted for processing, but the processing has
1359   not been completed.  The request might or might not eventually be
1360   acted upon, as it might be disallowed when processing actually takes
1361   place. There is no facility for re-sending a status code from an
1362   asynchronous operation such as this.
1363</t>
1364<t>
1365   The 202 response is intentionally non-committal. Its purpose is to
1366   allow a server to accept a request for some other process (perhaps a
1367   batch-oriented process that is only run once per day) without
1368   requiring that the user agent's connection to the server persist
1369   until the process is completed. The representation returned with this
1370   response &SHOULD; include an indication of the request's current status
1371   and either a pointer to a status monitor or some estimate of when the
1372   user can expect the request to be fulfilled.
1373</t>
1374</section>
1375
1376<section title="203 Non-Authoritative Information" anchor="status.203">
1377  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1378  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1379<t>
1380   The representation in the response has been transformed or otherwise
1381   modified by a transforming proxy (&intermediaries;).  Note that the
1382   behavior of transforming intermediaries is controlled by the no-transform
1383   Cache-Control directive (&header-cache-control;).
1384</t>
1385<t>
1386   This status code is only appropriate when the response status code would
1387   have been 200 (OK) otherwise. When the status code before transformation
1388   would have been different, the 214 Transformation Applied warn-code
1389   (&header-warning;) is appropriate.
1390</t>
1391<t>
1392   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1393   freshness for 203 responses.
1394</t>
1395</section>
1396
1397<section title="204 No Content" anchor="status.204">
1398  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1399  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1400<t>
1401   The 204 (No Content) status code indicates that the server has
1402   successfully fulfilled the request and that there is no additional
1403   content to return in the response payload body.  Metadata in the
1404   response header fields refer to the target resource and its current
1405   representation after the requested action.
1406</t>
1407<t>
1408   For example, if a 204 status code is received in response to a PUT
1409   request and the response contains an ETag header field, then the PUT
1410   was successful and the ETag field-value contains the entity-tag for
1411   the new representation of that target resource.
1412</t>
1413<t>
1414   The 204 response allows a server to indicate that the action has been
1415   successfully applied to the target resource while implying that the
1416   user agent &SHOULD-NOT; traverse away from its current "document view"
1417   (if any).  The server assumes that the user agent will provide some
1418   indication of the success to its user, in accord with its own interface,
1419   and apply any new or updated metadata in the response to the active
1420   representation.
1421</t>
1422<t>
1423   For example, a 204 status code is commonly used with document editing
1424   interfaces corresponding to a "save" action, such that the document
1425   being saved remains available to the user for editing. It is also
1426   frequently used with interfaces that expect automated data transfers
1427   to be prevalent, such as within distributed version control systems.
1428</t>
1429<t>
1430   The 204 response &MUST-NOT; include a message body, and thus is always
1431   terminated by the first empty line after the header fields.
1432</t>
1433</section>
1434
1435<section title="205 Reset Content" anchor="status.205">
1436  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1437  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1438<t>
1439   The server has fulfilled the request and the user agent &SHOULD; reset
1440   the document view which caused the request to be sent. This response
1441   is primarily intended to allow input for actions to take place via
1442   user input, followed by a clearing of the form in which the input is
1443   given so that the user can easily initiate another input action.
1444</t>
1445<t>   
1446   The message body included with the response &MUST; be empty. Note that
1447   receivers still need to parse the response according to the algorithm defined
1448   in &message-body;.
1449</t>
1450</section>
1451</section>
1452
1453<section title="Redirection 3xx" anchor="status.3xx">
1454<t>
1455   This class of status code indicates that further action needs to be
1456   taken by the user agent in order to fulfill the request.  If the required
1457   action involves a subsequent HTTP request, it &MAY; be carried out by the
1458   user agent without interaction with the user if and only if the method used
1459   in the second request is known to be "safe", as defined in
1460   <xref target="safe.methods"/>.
1461</t>
1462<t>
1463   There are several types of redirects:
1464   <list style="numbers">
1465      <x:lt>
1466        <t>
1467          Redirects of the request to another URI, either temporarily or
1468          permanently. The new URI is specified in the Location header field.
1469          In this specification, the status codes 301 (Moved Permanently),
1470          302 (Found), and 307 (Temporary Redirect) fall under this category.
1471        </t>
1472      </x:lt>
1473      <x:lt>
1474        <t>
1475          Redirection to a new location that represents an indirect response to
1476          the request, such as the result of a POST operation to be retrieved
1477          with a subsequent GET request. This is status code 303 (See Other).
1478        </t>
1479      </x:lt>
1480      <x:lt>
1481        <t>
1482          Redirection offering a choice of matching resources for use by
1483          agent-driven content negotiation (&agent-driven-negotiation;). This
1484          is status code 300 (Multiple Choices).
1485        </t>
1486      </x:lt>
1487      <x:lt>
1488        <t>
1489          Other kinds of redirection, such as to a cached result (status code 304
1490          (Not Modified), see &status-304;).
1491        </t>
1492      </x:lt>
1493   </list>
1494</t>
1495<x:note>
1496  <t>
1497    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1498    and 302 (Found) were defined for the first type of redirect, and the second
1499    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1500    However it turned out that web forms using POST expected redirects to change
1501    the operation for the subsequent request to retrieval (GET). To address this
1502    use case, HTTP/1.1 introduced the second type of redirect with the status
1503    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1504    As user agents did not change their behavior to maintain backwards
1505    compatibility, the first revision of HTTP/1.1 added yet another status code,
1506    307 (Temporary Redirect), for which the backwards compatibility problems did
1507    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1508    Over 10 years later, most user agents still do method rewriting for
1509    status codes 301 and 302, therefore this specification makes that behavior
1510    conformant in case the original request was POST.
1511  </t>
1512</x:note>
1513<t>
1514   A Location header field on a 3xx response indicates that a client &MAY;
1515   automatically redirect to the URI provided; see <xref target="header.location"/>.
1516</t>
1517<t>
1518   Note that for methods not known to be "safe", as defined in <xref target="safe.methods"/>,
1519   automatic redirection needs to done with care, since the redirect might
1520   change the conditions under which the request was issued.
1521</t>
1522<t>
1523   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1524   "infinite" redirection loops).
1525</t>
1526<x:note>
1527  <t>
1528    <x:h>Note:</x:h> An earlier version of this specification recommended a
1529    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1530    Content developers need to be aware that some clients might
1531    implement such a fixed limitation.
1532  </t>
1533</x:note>
1534
1535<section title="300 Multiple Choices" anchor="status.300">
1536  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1537  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1538<t>
1539   The target resource has more than one
1540   representation, each with its own specific location, and agent-driven
1541   negotiation information (&content-negotiation;) is being provided so that
1542   the user (or user agent) can select a preferred representation by
1543   redirecting its request to that location.
1544</t>
1545<t>
1546   Unless it was a HEAD request, the response &SHOULD; include a representation
1547   containing a list of representation metadata and location(s) from
1548   which the user or user agent can choose the one most appropriate. Depending
1549   upon the format and the capabilities of
1550   the user agent, selection of the most appropriate choice &MAY; be
1551   performed automatically. However, this specification does not define
1552   any standard for such automatic selection.
1553</t>
1554<t>
1555   If the server has a preferred choice of representation, it &SHOULD;
1556   include the specific URI for that representation in the Location
1557   field; user agents &MAY; use the Location field value for automatic
1558   redirection.
1559</t>
1560<t>
1561   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1562   freshness for 300 responses.
1563</t>
1564
1565</section>
1566
1567<section title="301 Moved Permanently" anchor="status.301">
1568  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1569  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1570<t>
1571   The target resource has been assigned a new permanent URI and any
1572   future references to this resource &SHOULD; use one of the returned
1573   URIs.  Clients with link editing capabilities ought to automatically
1574   re-link references to the effective request URI to one or more of the new
1575   references returned by the server, where possible.
1576</t>
1577<t>
1578   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1579   freshness for 301 responses.
1580</t>
1581<t>
1582   The new permanent URI &SHOULD; be given by the Location field in the
1583   response. A response payload can contain a short hypertext note with a
1584   hyperlink to the new URI(s).
1585</t>
1586<x:note>
1587  <t>
1588    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1589    request method from POST to GET for the subsequent request. If this
1590    behavior is undesired, status code 307 (Temporary Redirect) can be used
1591    instead.
1592  </t>
1593</x:note>
1594</section>
1595
1596<section title="302 Found" anchor="status.302">
1597  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1598  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1599<t>
1600   The target resource resides temporarily under a different URI.
1601   Since the redirection might be altered on occasion, the client &SHOULD;
1602   continue to use the effective request URI for future requests.
1603</t>
1604<t>
1605   The temporary URI &SHOULD; be given by the Location field in the
1606   response. A response payload can contain a short hypertext note with a
1607   hyperlink to the new URI(s).
1608</t>
1609<x:note>
1610  <t>
1611    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1612    request method from POST to GET for the subsequent request. If this
1613    behavior is undesired, status code 307 (Temporary Redirect) can be used
1614    instead.
1615  </t>
1616</x:note>
1617</section>
1618
1619<section title="303 See Other" anchor="status.303">
1620  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1621  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1622<t>
1623   The 303 status code indicates that the server is redirecting the
1624   user agent to a different resource, as indicated by a URI in the
1625   Location header field, that is intended to provide an indirect
1626   response to the original request.  In order to satisfy the original
1627   request, a user agent &SHOULD; perform a retrieval request using the
1628   Location URI (a GET or HEAD request if using HTTP), which
1629   may itself be redirected further, and present the eventual result as an
1630   answer to the original request.
1631   Note that the new URI in the Location header field is not considered
1632   equivalent to the effective request URI.
1633</t>
1634<t>
1635   This status code is generally applicable to any HTTP method.  It is
1636   primarily used to allow the output of a POST action to redirect
1637   the user agent to a selected resource, since doing so provides the
1638   information corresponding to the POST response in a form that
1639   can be separately identified, bookmarked, and cached independent
1640   of the original request.
1641</t>
1642<t>
1643   A 303 response to a GET request indicates that the requested
1644   resource does not have a representation of its own that can be
1645   transferred by the server over HTTP.  The Location URI indicates a
1646   resource that is descriptive of the target resource, such that the
1647   follow-on representation might be useful to recipients without
1648   implying that it adequately represents the target resource.
1649   Note that answers to the questions of what can be represented, what
1650   representations are adequate, and what might be a useful description
1651   are outside the scope of HTTP and thus entirely determined by the
1652   URI owner(s).
1653</t>
1654<t>
1655   Except for responses to a HEAD request, the representation of a 303
1656   response &SHOULD; contain a short hypertext note with a hyperlink
1657   to the Location URI.
1658</t>
1659</section>
1660
1661<section title="305 Use Proxy" anchor="status.305">
1662  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1663  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1664<t>
1665   The 305 status code was defined in a previous version of this specification
1666   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1667</t>
1668</section>
1669
1670<section title="306 (Unused)" anchor="status.306">
1671  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1672  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1673<t>
1674   The 306 status code was used in a previous version of the
1675   specification, is no longer used, and the code is reserved.
1676</t>
1677</section>
1678
1679<section title="307 Temporary Redirect" anchor="status.307">
1680  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1681  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1682<t>
1683   The target resource resides temporarily under a different URI.
1684   Since the redirection can change over time, the client &SHOULD;
1685   continue to use the effective request URI for future requests.
1686</t>
1687<t>
1688   The temporary URI &SHOULD; be given by the Location field in the
1689   response. A response payload can contain a short hypertext note with a
1690   hyperlink to the new URI(s).
1691</t>
1692<x:note>
1693  <t>
1694    <x:h>Note:</x:h> This status code is similar to 302 Found, except that
1695    it does not allow rewriting the request method from POST to GET. This
1696    specification defines no equivalent counterpart for 301 Moved Permanently
1697    (<xref target="draft-reschke-http-status-308"/>, however, defines the
1698    status code 308 Permanent Redirect for this purpose).
1699  </t>
1700</x:note>
1701</section>
1702</section>
1703
1704<section title="Client Error 4xx" anchor="status.4xx">
1705<t>
1706   The 4xx class of status code is intended for cases in which the
1707   client seems to have erred. Except when responding to a HEAD request,
1708   the server &SHOULD; include a representation containing an explanation of the
1709   error situation, and whether it is a temporary or permanent
1710   condition. These status codes are applicable to any request method.
1711   User agents &SHOULD; display any included representation to the user.
1712</t>
1713
1714<section title="400 Bad Request" anchor="status.400">
1715  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1716  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1717<t>
1718   The server cannot or will not process the request, due to a client error (e.g.,
1719   malformed syntax).
1720</t>
1721</section>
1722
1723<section title="402 Payment Required" anchor="status.402">
1724  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1725  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1726<t>
1727   This code is reserved for future use.
1728</t>
1729</section>
1730
1731<section title="403 Forbidden" anchor="status.403">
1732  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1733  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1734<t>
1735   The server understood the request, but refuses to authorize it. Providing
1736   different user authentication credentials might be successful, but any
1737   credentials that were provided in the request are insufficient. The request
1738   &SHOULD-NOT; be repeated with the same credentials.
1739</t>
1740<t>
1741   If the request method was not HEAD and the server wishes to make
1742   public why the request has not been fulfilled, it &SHOULD; describe the
1743   reason for the refusal in the representation.  If the server does not wish to
1744   make this information available to the client, the status code 404
1745   (Not Found) &MAY; be used instead.
1746</t>
1747</section>
1748
1749<section title="404 Not Found" anchor="status.404">
1750  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1751  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1752<t>
1753   The server has not found anything matching the effective request URI. No
1754   indication is given of whether the condition is temporary or
1755   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1756   knows, through some internally configurable mechanism, that an old
1757   resource is permanently unavailable and has no forwarding address.
1758   This status code is commonly used when the server does not wish to
1759   reveal exactly why the request has been refused, or when no other
1760   response is applicable.
1761</t>
1762</section>
1763
1764<section title="405 Method Not Allowed" anchor="status.405">
1765  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1766  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1767<t>
1768   The method specified in the request-line is not allowed for the target
1769   resource. The response &MUST; include an Allow header field containing a
1770   list of valid methods for the requested resource.
1771</t>
1772</section>
1773
1774<section title="406 Not Acceptable" anchor="status.406">
1775  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1776  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1777<t>
1778   The resource identified by the request is only capable of generating
1779   response representations which have content characteristics not acceptable
1780   according to the Accept and Accept-* header fields sent in the request
1781   (see &p3-header-fields;).
1782</t>
1783<t>
1784   Unless it was a HEAD request, the response &SHOULD; include a representation
1785   containing a list of available representation characteristics and location(s)
1786   from which the user or user agent can choose the one most
1787   appropriate. Depending upon the format and the
1788   capabilities of the user agent, selection of the most appropriate
1789   choice &MAY; be performed automatically. However, this specification
1790   does not define any standard for such automatic selection.
1791</t>
1792<x:note>
1793  <t>
1794    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1795    not acceptable according to the accept header fields sent in the
1796    request. In some cases, this might even be preferable to sending a
1797    406 response. User agents are encouraged to inspect the header fields of
1798    an incoming response to determine if it is acceptable.
1799  </t>
1800</x:note>
1801<t>
1802   If the response could be unacceptable, a user agent &SHOULD;
1803   temporarily stop receipt of more data and query the user for a
1804   decision on further actions.
1805</t>
1806</section>
1807
1808<section title="408 Request Timeout" anchor="status.408">
1809  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1810  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1811<t>
1812   The client did not produce a request within the time that the server
1813   was prepared to wait. The client &MAY; repeat the request without
1814   modifications at any later time.
1815</t>
1816</section>
1817
1818<section title="409 Conflict" anchor="status.409">
1819  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1820  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1821<t>
1822   The request could not be completed due to a conflict with the current
1823   state of the resource. This code is only allowed in situations where
1824   it is expected that the user might be able to resolve the conflict
1825   and resubmit the request. The response body &SHOULD; include enough
1826   information for the user to recognize the source of the conflict.
1827   Ideally, the response representation would include enough information for the
1828   user or user agent to fix the problem; however, that might not be
1829   possible and is not required.
1830</t>
1831<t>
1832   Conflicts are most likely to occur in response to a PUT request. For
1833   example, if versioning were being used and the representation being PUT
1834   included changes to a resource which conflict with those made by an
1835   earlier (third-party) request, the server might use the 409 response
1836   to indicate that it can't complete the request. In this case, the
1837   response representation would likely contain a list of the differences
1838   between the two versions.
1839</t>
1840</section>
1841
1842<section title="410 Gone" anchor="status.410">
1843  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1844  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1845<t>
1846   The target resource is no longer available at the server and no
1847   forwarding address is known. This condition is expected to be
1848   considered permanent. Clients with link editing capabilities &SHOULD;
1849   delete references to the effective request URI after user approval. If the
1850   server does not know, or has no facility to determine, whether or not
1851   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1852   used instead.
1853</t>
1854<t>
1855   The 410 response is primarily intended to assist the task of web
1856   maintenance by notifying the recipient that the resource is
1857   intentionally unavailable and that the server owners desire that
1858   remote links to that resource be removed. Such an event is common for
1859   limited-time, promotional services and for resources belonging to
1860   individuals no longer working at the server's site. It is not
1861   necessary to mark all permanently unavailable resources as "gone" or
1862   to keep the mark for any length of time &mdash; that is left to the
1863   discretion of the server owner.
1864</t>
1865<t>
1866   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
1867   for 410 responses.
1868</t>
1869</section>
1870
1871<section title="411 Length Required" anchor="status.411">
1872  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1873  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1874<t>
1875   The server refuses to accept the request without a defined Content-Length.
1876   The client &MAY; repeat the request if it adds a valid
1877   Content-Length header field containing the length of the message body
1878   in the request message.
1879</t>
1880</section>
1881
1882<section title="413 Request Representation Too Large" anchor="status.413">
1883  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
1884  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
1885<t>
1886   The server is refusing to process a request because the request
1887   representation is larger than the server is willing or able to process. The
1888   server &MAY; close the connection to prevent the client from continuing
1889   the request.
1890</t>
1891<t>
1892   If the condition is temporary, the server &SHOULD; include a Retry-After
1893   header field to indicate that it is temporary and after what
1894   time the client &MAY; try again.
1895</t>
1896</section>
1897
1898<section title="414 URI Too Long" anchor="status.414">
1899  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
1900  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
1901<t>
1902   The server is refusing to service the request because the effective request URI
1903   is longer than the server is willing to interpret. This rare
1904   condition is only likely to occur when a client has improperly
1905   converted a POST request to a GET request with long query
1906   information, when the client has descended into a URI "black hole" of
1907   redirection (e.g., a redirected URI prefix that points to a suffix of
1908   itself), or when the server is under attack by a client attempting to
1909   exploit security holes present in some servers using fixed-length
1910   buffers for reading or manipulating the request-target.
1911</t>
1912</section>
1913
1914<section title="415 Unsupported Media Type" anchor="status.415">
1915  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1916  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1917<t>
1918   The server is refusing to service the request because the request
1919   payload is in a format not supported by this request method on the
1920   target resource.
1921</t>
1922</section>
1923
1924<section title="417 Expectation Failed" anchor="status.417">
1925  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1926  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1927<t>
1928   The expectation given in an Expect header field (see <xref target="header.expect"/>)
1929   could not be met by this server, or, if the server is a proxy,
1930   the server has unambiguous evidence that the request could not be met
1931   by the next-hop server.
1932</t>
1933</section>
1934
1935<section title="426 Upgrade Required" anchor="status.426">
1936  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
1937  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
1938<t>
1939   The request can not be completed without a prior protocol upgrade. This
1940   response &MUST; include an Upgrade header field (&header-upgrade;)
1941   specifying the required protocols.
1942</t>
1943<figure>
1944<preamble>Example:</preamble>
1945<artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
1946HTTP/1.1 426 Upgrade Required
1947Upgrade: HTTP/3.0
1948Connection: Upgrade
1949Content-Length: <x:length-of target="s426body"/>
1950Content-Type: text/plain
1951
1952<x:span anchor="s426body">This service requires use of the HTTP/3.0 protocol.
1953</x:span></artwork></figure>
1954<t>
1955   The server &SHOULD; include a message body in the 426 response which
1956   indicates in human readable form the reason for the error and describes any
1957   alternative courses which may be available to the user.
1958</t>
1959</section>
1960</section>
1961
1962<section title="Server Error 5xx" anchor="status.5xx">
1963<t>
1964   Response status codes beginning with the digit "5" indicate cases in
1965   which the server is aware that it has erred or is incapable of
1966   performing the request. Except when responding to a HEAD request, the
1967   server &SHOULD; include a representation containing an explanation of the
1968   error situation, and whether it is a temporary or permanent
1969   condition. User agents &SHOULD; display any included representation to the
1970   user. These response codes are applicable to any request method.
1971</t>
1972
1973<section title="500 Internal Server Error" anchor="status.500">
1974  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1975  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1976<t>
1977   The server encountered an unexpected condition which prevented it
1978   from fulfilling the request.
1979</t>
1980</section>
1981
1982<section title="501 Not Implemented" anchor="status.501">
1983  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1984  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1985<t>
1986   The server does not support the functionality required to fulfill the
1987   request. This is the appropriate response when the server does not
1988   recognize the request method and is not capable of supporting it for
1989   any resource.
1990</t>
1991</section>
1992
1993<section title="502 Bad Gateway" anchor="status.502">
1994  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1995  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1996<t>
1997   The server, while acting as a gateway or proxy, received an invalid
1998   response from the upstream server it accessed in attempting to
1999   fulfill the request.
2000</t>
2001</section>
2002
2003<section title="503 Service Unavailable" anchor="status.503">
2004  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
2005  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
2006<t>
2007   The server is currently unable to handle the request due to a
2008   temporary overloading or maintenance of the server.
2009</t>
2010<t>
2011   The implication is that this is a temporary condition which will be
2012   alleviated after some delay. If known, the length of the delay &MAY; be
2013   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2014   If no Retry-After is given, the client &SHOULD; handle the response as it
2015   would for a 500 response.
2016</t>
2017<x:note>
2018  <t>
2019    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
2020    server has to use it when becoming overloaded. Some servers might wish
2021    to simply refuse the connection.
2022  </t>
2023</x:note>
2024</section>
2025
2026<section title="504 Gateway Timeout" anchor="status.504">
2027  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2028  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2029<t>
2030   The server, while acting as a gateway or proxy, did not receive a
2031   timely response from the upstream server specified by the URI (e.g.,
2032   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2033   to access in attempting to complete the request.
2034</t>
2035<x:note>
2036  <t>
2037    <x:h>Note</x:h> to implementors: some deployed proxies are known to
2038    return 400 or 500 when DNS lookups time out.
2039  </t>
2040</x:note>
2041</section>
2042
2043<section title="505 HTTP Version Not Supported" anchor="status.505">
2044  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2045  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
2046<t>
2047   The server does not support, or refuses to support, the protocol
2048   version that was used in the request message. The server is
2049   indicating that it is unable or unwilling to complete the request
2050   using the same major version as the client, as described in &http-version;,
2051   other than with this error message. The response &SHOULD; contain
2052   a representation describing why that version is not supported and what other
2053   protocols are supported by that server.
2054</t>
2055
2056</section>
2057</section>
2058</section>
2059
2060</section>
2061
2062<section title="Representation" anchor="representation">
2063<t>
2064   Request and Response messages &MAY; transfer a representation if not otherwise
2065   restricted by the request method or response status code. A representation
2066   consists of metadata (representation header fields) and data (representation
2067   body).  When a complete or partial representation is enclosed in an HTTP message,
2068   it is referred to as the payload of the message. HTTP representations
2069   are defined in &payload;.
2070</t>
2071<t>
2072   A representation body is only present in a message when a message body is
2073   present, as described in &message-body;. The representation body is obtained
2074   from the message body by decoding any Transfer-Encoding that might
2075   have been applied to ensure safe and proper transfer of the message.
2076</t>
2077
2078<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
2079<t>
2080   It is sometimes necessary to determine an identifier for the resource
2081   associated with a representation.
2082</t>
2083<t>
2084   An HTTP request representation, when present, is always associated with an
2085   anonymous (i.e., unidentified) resource.
2086</t>
2087<t>
2088   In the common case, an HTTP response is a representation of the target
2089   resource (see &effective-request-uri;). However, this is not always the
2090   case. To determine the URI of the resource a response is associated with,
2091   the following rules are used (with the first applicable one being selected):
2092</t>
2093<t><list style="numbers">
2094   <t>If the response status code is 200 or 203 and the request method was GET,
2095   the response payload is a representation of the target resource.</t>
2096   <t>If the response status code is 204, 206, or 304 and the request method was GET
2097   or HEAD, the response payload is a partial representation of the target
2098   resource.</t>
2099   <t>If the response has a Content-Location header field, and that URI is the same
2100   as the effective request URI, the response payload is a representation of the
2101   target resource.</t>
2102   <t>If the response has a Content-Location header field, and that URI is not the
2103   same as the effective request URI, then the response asserts that its
2104   payload is a representation of the resource identified by the
2105   Content-Location URI. However, such an assertion cannot be trusted unless
2106   it can be verified by other means (not defined by HTTP).</t>
2107   <t>Otherwise, the response is a representation of an anonymous (i.e.,
2108   unidentified) resource.</t>
2109</list></t>
2110<t>
2111  <cref anchor="TODO-req-uri">
2112   The comparison function is going to have to be defined somewhere,
2113   because we already need to compare URIs for things like cache invalidation.</cref>
2114</t>
2115</section>
2116
2117</section>
2118
2119
2120<section title="Common Protocol Parameters" anchor="common.protocol.parameters">
2121<section title="Date/Time Formats" anchor="http.date">
2122  <x:anchor-alias value="HTTP-date"/>
2123<t>
2124   HTTP applications have historically allowed three different formats
2125   for date/time stamps. However, the preferred format is a fixed-length subset
2126   of that defined by <xref target="RFC1123"/>:
2127</t>
2128<figure><artwork type="example" x:indent-with="  ">
2129Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2130</artwork></figure>
2131<t>
2132   The other formats are described here only for compatibility with obsolete
2133   implementations.
2134</t>
2135<figure><artwork type="example" x:indent-with="  ">
2136Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2137Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2138</artwork></figure>
2139<t>
2140   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2141   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2142   only generate the RFC 1123 format for representing HTTP-date values
2143   in header fields.
2144</t>
2145<t>
2146   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2147   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2148   equal to UTC (Coordinated Universal Time). This is indicated in the
2149   first two formats by the inclusion of "GMT" as the three-letter
2150   abbreviation for time zone, and &MUST; be assumed when reading the
2151   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2152   additional whitespace beyond that specifically included as SP in the
2153   grammar.
2154</t>
2155<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2156  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2157</artwork></figure>
2158<t anchor="preferred.date.format">
2159  <x:anchor-alias value="rfc1123-date"/>
2160  <x:anchor-alias value="time-of-day"/>
2161  <x:anchor-alias value="hour"/>
2162  <x:anchor-alias value="minute"/>
2163  <x:anchor-alias value="second"/>
2164  <x:anchor-alias value="day-name"/>
2165  <x:anchor-alias value="day"/>
2166  <x:anchor-alias value="month"/>
2167  <x:anchor-alias value="year"/>
2168  <x:anchor-alias value="GMT"/>
2169  Preferred format:
2170</t>
2171<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"/>
2172  <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>
2173  ; fixed length subset of the format defined in
2174  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2175 
2176  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2177               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2178               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2179               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2180               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2181               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2182               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2183               
2184  <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>
2185               ; e.g., 02 Jun 1982
2186
2187  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2188  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2189               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2190               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2191               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2192               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2193               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2194               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2195               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2196               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2197               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2198               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2199               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2200  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2201
2202  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2203
2204  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2205                 ; 00:00:00 - 23:59:59
2206                 
2207  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2208  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2209  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2210</artwork></figure>
2211<t>
2212  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2213  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2214  same as those defined for the RFC 5322 constructs
2215  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2216</t>
2217<t anchor="obsolete.date.formats">
2218  <x:anchor-alias value="obs-date"/>
2219  <x:anchor-alias value="rfc850-date"/>
2220  <x:anchor-alias value="asctime-date"/>
2221  <x:anchor-alias value="date1"/>
2222  <x:anchor-alias value="date2"/>
2223  <x:anchor-alias value="date3"/>
2224  <x:anchor-alias value="rfc1123-date"/>
2225  <x:anchor-alias value="day-name-l"/>
2226  Obsolete formats:
2227</t>
2228<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2229  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2230</artwork></figure>
2231<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2232  <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>
2233  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2234                 ; day-month-year (e.g., 02-Jun-82)
2235
2236  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2237         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2238         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2239         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2240         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2241         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2242         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2243</artwork></figure>
2244<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2245  <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>
2246  <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> ))
2247                 ; month day (e.g., Jun  2)
2248</artwork></figure>
2249<x:note>
2250  <t>
2251    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2252    accepting date values that might have been sent by non-HTTP
2253    applications, as is sometimes the case when retrieving or posting
2254    messages via proxies/gateways to SMTP or NNTP.
2255  </t>
2256</x:note>
2257<x:note>
2258  <t>
2259    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2260    to their usage within the protocol stream. Clients and servers are
2261    not required to use these formats for user presentation, request
2262    logging, etc.
2263  </t>
2264</x:note>
2265</section>
2266
2267<section title="Product Tokens" anchor="product.tokens">
2268  <x:anchor-alias value="product"/>
2269  <x:anchor-alias value="product-version"/>
2270<t>
2271   Product tokens are used to allow communicating applications to
2272   identify themselves by software name and version. Most fields using
2273   product tokens also allow sub-products which form a significant part
2274   of the application to be listed, separated by whitespace. By
2275   convention, the products are listed in order of their significance
2276   for identifying the application.
2277</t>
2278<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2279  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2280  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2281</artwork></figure>
2282<t>
2283   Examples:
2284</t>
2285<figure><artwork type="example">
2286  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2287  Server: Apache/0.8.4
2288</artwork></figure>
2289<t>
2290   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2291   used for advertising or other non-essential information. Although any
2292   token octet &MAY; appear in a product-version, this token &SHOULD;
2293   only be used for a version identifier (i.e., successive versions of
2294   the same product &SHOULD; only differ in the product-version portion of
2295   the product value).
2296</t>
2297</section>
2298</section>
2299
2300<section title="Header Field Definitions" anchor="header.field.definitions">
2301<t>
2302   This section defines the syntax and semantics of HTTP/1.1 header fields
2303   related to request and response semantics.
2304</t>
2305
2306<section title="Allow" anchor="header.allow">
2307  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2308  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2309  <x:anchor-alias value="Allow"/>
2310<t>
2311   The "Allow" header field lists the set of methods advertised as
2312   supported by the target resource. The purpose of this field is strictly to
2313   inform the recipient of valid request methods associated with the resource.
2314</t>
2315<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2316  <x:ref>Allow</x:ref> = #<x:ref>method</x:ref>
2317</artwork></figure>
2318<t>
2319   Example of use:
2320</t>
2321<figure><artwork type="example">
2322  Allow: GET, HEAD, PUT
2323</artwork></figure>
2324<t>
2325   The actual set of allowed methods is defined by the origin server at the
2326   time of each request.
2327</t>
2328<t>
2329   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2330   understand all the methods specified in order to handle them according to
2331   the generic message handling rules.
2332</t>
2333</section>
2334
2335<section title="Date" anchor="header.date">
2336  <iref primary="true" item="Date header field" x:for-anchor=""/>
2337  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
2338  <x:anchor-alias value="Date"/>
2339<t>
2340   The "Date" header field represents the date and time at which
2341   the message was originated, having the same semantics as the Origination
2342   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2343   The field value is an HTTP-date, as defined in <xref target="http.date"/>;
2344   it &MUST; be sent in rfc1123-date format.
2345</t>
2346<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2347  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
2348</artwork></figure>
2349<t>
2350   An example is
2351</t>
2352<figure><artwork type="example">
2353  Date: Tue, 15 Nov 1994 08:12:31 GMT
2354</artwork></figure>
2355<t>
2356   Origin servers &MUST; include a Date header field in all responses,
2357   except in these cases:
2358  <list style="numbers">
2359      <t>If the response status code is 100 (Continue) or 101 (Switching
2360         Protocols), the response &MAY; include a Date header field, at
2361         the server's option.</t>
2362
2363      <t>If the response status code conveys a server error, e.g., 500
2364         (Internal Server Error) or 503 (Service Unavailable), and it is
2365         inconvenient or impossible to generate a valid Date.</t>
2366
2367      <t>If the server does not have a clock that can provide a
2368         reasonable approximation of the current time, its responses
2369         &MUST-NOT; include a Date header field.</t>
2370  </list>
2371</t>
2372<t>
2373   A received message that does not have a Date header field &MUST; be
2374   assigned one by the recipient if the message will be cached by that
2375   recipient.
2376</t>
2377<t>
2378   Clients can use the Date header field as well; in order to keep request
2379   messages small, they are advised not to include it when it doesn't convey
2380   any useful information (as is usually the case for requests that do not
2381   contain a payload).
2382</t>
2383<t>
2384   The HTTP-date sent in a Date header field &SHOULD-NOT; represent a date and
2385   time subsequent to the generation of the message. It &SHOULD; represent
2386   the best available approximation of the date and time of message
2387   generation, unless the implementation has no means of generating a
2388   reasonably accurate date and time. In theory, the date ought to
2389   represent the moment just before the payload is generated. In
2390   practice, the date can be generated at any time during the message
2391   origination without affecting its semantic value.
2392</t>
2393</section>
2394
2395<section title="Expect" anchor="header.expect">
2396  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2397  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2398  <x:anchor-alias value="Expect"/>
2399  <x:anchor-alias value="expectation"/>
2400  <x:anchor-alias value="expect-param"/>
2401  <x:anchor-alias value="expect-name"/>
2402  <x:anchor-alias value="expect-value"/>
2403<t>
2404   The "Expect" header field is used to indicate that particular
2405   server behaviors are required by the client.
2406</t>
2407<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"/>
2408  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
2409 
2410  <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> ]
2411                             *( <x:ref>OWS</x:ref> ";" [ <x:ref>OWS</x:ref> <x:ref>expect-param</x:ref> ] )
2412  <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> ]
2413 
2414  <x:ref>expect-name</x:ref>  = <x:ref>token</x:ref>
2415  <x:ref>expect-value</x:ref> = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
2416</artwork></figure>
2417<t>
2418   If all received Expect header field(s) are syntactically valid but contain
2419   an expectation that the recipient does not understand or cannot comply with,
2420   the recipient &MUST; respond with a 417 (Expectation Failed) status code. A
2421   recipient of a syntactically invalid Expectation header field &MUST; respond
2422   with a 4xx status code other than 417.
2423</t>
2424<t>
2425   The only expectation defined by this specification is:
2426</t>
2427<t><iref primary="true" item="100-continue (expect value)"/><iref primary="true" item="Expect Values" subitem="100-continue"/>
2428  100-continue
2429   <list>
2430      <t>
2431        The "100-continue" expectation is defined &use100;. It does not support
2432        any expect-params.
2433      </t>
2434   </list>
2435</t>
2436<t>
2437   Comparison is case-insensitive for names (expect-name), and case-sensitive
2438   for values (expect-value).
2439</t>
2440<t>
2441   The Expect mechanism is hop-by-hop: the above requirements apply to any
2442   server, including proxies. However, the Expect header field itself is
2443   end-to-end; it &MUST; be forwarded if the request is forwarded.
2444</t>
2445<t>
2446   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect
2447   header field.
2448</t>
2449</section>
2450
2451<section title="From" anchor="header.from">
2452  <iref primary="true" item="From header field" x:for-anchor=""/>
2453  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2454  <x:anchor-alias value="From"/>
2455  <x:anchor-alias value="mailbox"/>
2456<t>
2457   The "From" header field, if given, &SHOULD; contain an Internet
2458   e-mail address for the human user who controls the requesting user
2459   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2460   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2461</t>
2462<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2463  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
2464 
2465  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2466</artwork></figure>
2467<t>
2468   An example is:
2469</t>
2470<figure><artwork type="example">
2471  From: webmaster@example.org
2472</artwork></figure>
2473<t>
2474   This header field &MAY; be used for logging purposes and as a means for
2475   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2476   be used as an insecure form of access protection. The interpretation
2477   of this field is that the request is being performed on behalf of the
2478   person given, who accepts responsibility for the method performed. In
2479   particular, robot agents &SHOULD; include this header field so that the
2480   person responsible for running the robot can be contacted if problems
2481   occur on the receiving end.
2482</t>
2483<t>
2484   The Internet e-mail address in this field &MAY; be separate from the
2485   Internet host which issued the request. For example, when a request
2486   is passed through a proxy the original issuer's address &SHOULD; be
2487   used.
2488</t>
2489<t>
2490   The client &SHOULD-NOT;  send the From header field without the user's
2491   approval, as it might conflict with the user's privacy interests or
2492   their site's security policy. It is strongly recommended that the
2493   user be able to disable, enable, and modify the value of this field
2494   at any time prior to a request.
2495</t>
2496</section>
2497
2498<section title="Location" anchor="header.location">
2499  <iref primary="true" item="Location header field" x:for-anchor=""/>
2500  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2501  <x:anchor-alias value="Location"/>
2502<t>
2503   The "Location" header field &MAY; be sent in responses to refer to
2504   a specific resource in accordance with the semantics of the status
2505   code.
2506</t>
2507<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2508  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2509</artwork></figure>
2510<t>
2511   For 201 (Created) responses, the Location is the URI of the new resource
2512   which was created by the request. For 3xx responses, the location &SHOULD;
2513   indicate the server's preferred URI for automatic redirection to the
2514   resource.
2515</t>
2516<t>
2517   The field value consists of a single URI-reference. When it has the form
2518   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2519   the final value is computed by resolving it against the effective request
2520   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>). If the original URI, as
2521   navigated to by the user agent, did contain a fragment identifier, and the
2522   final value does not, then the original URI's fragment identifier is added
2523   to the final value.
2524</t>
2525<figure>
2526<preamble>For example, the original URI "http://www.example.org/~tim", combined with a field value given as:</preamble><!--DO NOT DARE changing the vertical spacing below, it's necessary this way for xml2rfc-->
2527<artwork type="example">
2528  Location: /pub/WWW/People.html#tim
2529</artwork>
2530<postamble>would result in a final value of "http://www.example.org/pub/WWW/People.html#tim"</postamble>
2531</figure>
2532<figure>
2533<preamble>An original URI "http://www.example.org/index.html#larry", combined with a field value given as:</preamble><!--DO NOT DARE changing the vertical spacing below, it's necessary this way for xml2rfc-->
2534<artwork type="example">
2535  Location: http://www.example.net/index.html
2536</artwork>
2537<postamble>would result in a final value of "http://www.example.net/index.html#larry", preserving the original fragment identifier.</postamble>
2538</figure>
2539<x:note>
2540  <t>
2541    <x:h>Note:</x:h> Some recipients attempt to recover from Location fields
2542    that are not valid URI references. This specification does not mandate or
2543    define such processing, but does allow it (see <xref target="intro.conformance.and.error.handling"/>).
2544  </t>
2545</x:note>
2546<t>
2547   There are circumstances in which a fragment identifier in a Location URI
2548   would not be appropriate. For instance, when it appears in a 201 Created
2549   response, where the Location header field specifies the URI for the entire
2550   created resource.
2551</t>
2552<x:note>
2553  <t>
2554    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2555    from Location in that the Content-Location identifies the most specific
2556    resource corresponding to the enclosed representation.
2557    It is therefore possible for a response to contain header fields for
2558    both Location and Content-Location.
2559  </t>
2560</x:note>
2561</section>
2562
2563<section title="Max-Forwards" anchor="header.max-forwards">
2564  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2565  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2566  <x:anchor-alias value="Max-Forwards"/>
2567<t>
2568   The "Max-Forwards" header field provides a mechanism with the
2569   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2570   methods to limit the number of times that the request is forwarded by
2571   proxies. This can be useful when the client is attempting to
2572   trace a request which appears to be failing or looping mid-chain.
2573</t>
2574<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2575  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2576</artwork></figure>
2577<t>
2578   The Max-Forwards value is a decimal integer indicating the remaining
2579   number of times this request message can be forwarded.
2580</t>
2581<t>
2582   Each recipient of a TRACE or OPTIONS request
2583   containing a Max-Forwards header field &MUST; check and update its
2584   value prior to forwarding the request. If the received value is zero
2585   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2586   respond as the final recipient. If the received Max-Forwards value is
2587   greater than zero, then the forwarded message &MUST; contain an updated
2588   Max-Forwards field with a value decremented by one (1).
2589</t>
2590<t>
2591   The Max-Forwards header field &MAY; be ignored for all other request
2592   methods.
2593</t>
2594</section>
2595
2596<section title="Referer" anchor="header.referer">
2597  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2598  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2599  <x:anchor-alias value="Referer"/>
2600<t>
2601   The "Referer" [sic] header field allows the client to specify the
2602   URI of the resource from which the target URI was obtained (the
2603   "referrer", although the header field is misspelled.).
2604</t>
2605<t>
2606   The Referer header field allows servers to generate lists of back-links to
2607   resources for interest, logging, optimized caching, etc. It also allows
2608   obsolete or mistyped links to be traced for maintenance. Some servers use
2609   Referer as a means of controlling where they allow links from (so-called
2610   "deep linking"), but legitimate requests do not always
2611   contain a Referer header field.
2612</t>
2613<t>
2614   If the target URI was obtained from a source that does not have its own
2615   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2616   sent with the value "about:blank", or not be sent at all. Note that this
2617   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2618</t>
2619<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2620  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2621</artwork></figure>
2622<t>
2623   Example:
2624</t>
2625<figure><artwork type="example">
2626  Referer: http://www.example.org/hypertext/Overview.html
2627</artwork></figure>
2628<t>
2629   If the field value is a relative URI, it &SHOULD; be interpreted
2630   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2631   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2632</t>
2633</section>
2634
2635<section title="Retry-After" anchor="header.retry-after">
2636  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2637  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2638  <x:anchor-alias value="Retry-After"/>
2639<t>
2640   The header "Retry-After" field can be used with a 503 (Service
2641   Unavailable) response to indicate how long the service is expected to
2642   be unavailable to the requesting client. This field &MAY; also be used
2643   with any 3xx (Redirection) response to indicate the minimum time the
2644   user-agent is asked to wait before issuing the redirected request.
2645</t>
2646<t>
2647   The value of this field can be either an HTTP-date or an integer number
2648   of seconds (in decimal) after the time of the response.
2649</t>
2650<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2651  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2652</artwork></figure>
2653<t anchor="rule.delta-seconds">
2654  <x:anchor-alias value="delta-seconds"/>
2655   Time spans are non-negative decimal integers, representing time in
2656   seconds.
2657</t>
2658<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2659  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2660</artwork></figure>
2661<t>
2662   Two examples of its use are
2663</t>
2664<figure><artwork type="example">
2665  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2666  Retry-After: 120
2667</artwork></figure>
2668<t>
2669   In the latter example, the delay is 2 minutes.
2670</t>
2671</section>
2672
2673<section title="Server" anchor="header.server">
2674  <iref primary="true" item="Server header field" x:for-anchor=""/>
2675  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2676  <x:anchor-alias value="Server"/>
2677<t>
2678   The "Server" header field contains information about the
2679   software used by the origin server to handle the request.
2680</t>
2681<t>
2682   The field can contain multiple
2683   product tokens (<xref target="product.tokens"/>) and
2684   comments (&header-fields;) identifying the server and any significant
2685   subproducts. The product tokens are listed in order of their significance
2686   for identifying the application.
2687</t>
2688<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2689  <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> ) )
2690</artwork></figure>
2691<t>
2692   Example:
2693</t>
2694<figure><artwork type="example">
2695  Server: CERN/3.0 libwww/2.17
2696</artwork></figure>
2697<t>
2698   If the response is being forwarded through a proxy, the proxy
2699   application &MUST-NOT; modify the Server header field. Instead, it
2700   &MUST; include a Via field (as described in &header-via;).
2701</t>
2702<x:note>
2703  <t>
2704    <x:h>Note:</x:h> Revealing the specific software version of the server might
2705    allow the server machine to become more vulnerable to attacks
2706    against software that is known to contain security holes. Server
2707    implementors are encouraged to make this field a configurable
2708    option.
2709  </t>
2710</x:note>
2711</section>
2712
2713<section title="User-Agent" anchor="header.user-agent">
2714  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2715  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2716  <x:anchor-alias value="User-Agent"/>
2717<t>
2718   The "User-Agent" header field contains information about the user
2719   agent originating the request. User agents &SHOULD; include this field with
2720   requests.
2721</t>
2722<t>
2723   Typically, it is used for statistical purposes, the tracing of protocol
2724   violations, and tailoring responses to avoid particular user agent
2725   limitations.
2726</t>
2727<t>
2728   The field can contain multiple
2729   product tokens (<xref target="product.tokens"/>)
2730   and comments (&header-fields;) identifying the agent and its
2731   significant subproducts. By convention, the product tokens are listed in
2732   order of their significance for identifying the application.
2733</t>
2734<t>
2735   Because this field is usually sent on every request a user agent makes,
2736   implementations are encouraged not to include needlessly fine-grained
2737   detail, and to limit (or even prohibit) the addition of subproducts by third
2738   parties. Overly long and detailed User-Agent field values make requests
2739   larger and can also be used to identify ("fingerprint") the user against
2740   their wishes.
2741</t>
2742<t>
2743   Likewise, implementations are encouraged not to use the product tokens of
2744   other implementations in order to declare compatibility with them, as this
2745   circumvents the purpose of the field. Finally, they are encouraged not to
2746   use comments to identify products; doing so makes the field value more
2747   difficult to parse.
2748</t>
2749<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2750  <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> ) )
2751</artwork></figure>
2752<t>
2753   Example:
2754</t>
2755<figure><artwork type="example">
2756  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2757</artwork></figure>
2758</section>
2759
2760</section>
2761
2762<section title="IANA Considerations" anchor="IANA.considerations">
2763
2764<section title="Method Registry" anchor="method.registration">
2765<t>
2766  The registration procedure for HTTP request methods is defined by
2767  <xref target="method.registry"/> of this document.
2768</t>
2769<t>
2770   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2771   and be populated with the registrations below:
2772</t>
2773<?BEGININC p2-semantics.iana-methods ?>
2774<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2775<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2776   <ttcol>Method</ttcol>
2777   <ttcol>Safe</ttcol>
2778   <ttcol>Reference</ttcol>
2779   <c>CONNECT</c>
2780   <c>no</c>
2781   <c>
2782      <xref target="CONNECT"/>
2783   </c>
2784   <c>DELETE</c>
2785   <c>no</c>
2786   <c>
2787      <xref target="DELETE"/>
2788   </c>
2789   <c>GET</c>
2790   <c>yes</c>
2791   <c>
2792      <xref target="GET"/>
2793   </c>
2794   <c>HEAD</c>
2795   <c>yes</c>
2796   <c>
2797      <xref target="HEAD"/>
2798   </c>
2799   <c>OPTIONS</c>
2800   <c>yes</c>
2801   <c>
2802      <xref target="OPTIONS"/>
2803   </c>
2804   <c>POST</c>
2805   <c>no</c>
2806   <c>
2807      <xref target="POST"/>
2808   </c>
2809   <c>PUT</c>
2810   <c>no</c>
2811   <c>
2812      <xref target="PUT"/>
2813   </c>
2814   <c>TRACE</c>
2815   <c>yes</c>
2816   <c>
2817      <xref target="TRACE"/>
2818   </c>
2819</texttable>
2820<!--(END)-->
2821<?ENDINC p2-semantics.iana-methods ?>
2822</section>
2823
2824<section title="Status Code Registry" anchor="status.code.registration">
2825<t>
2826   The registration procedure for HTTP Status Codes &mdash; previously defined
2827   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2828   by <xref target="status.code.registry"/> of this document.
2829</t>
2830<t>
2831   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2832   shall be updated with the registrations below:
2833</t>
2834<?BEGININC p2-semantics.iana-status-codes ?>
2835<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2836<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2837   <ttcol>Value</ttcol>
2838   <ttcol>Description</ttcol>
2839   <ttcol>Reference</ttcol>
2840   <c>100</c>
2841   <c>Continue</c>
2842   <c>
2843      <xref target="status.100"/>
2844   </c>
2845   <c>101</c>
2846   <c>Switching Protocols</c>
2847   <c>
2848      <xref target="status.101"/>
2849   </c>
2850   <c>200</c>
2851   <c>OK</c>
2852   <c>
2853      <xref target="status.200"/>
2854   </c>
2855   <c>201</c>
2856   <c>Created</c>
2857   <c>
2858      <xref target="status.201"/>
2859   </c>
2860   <c>202</c>
2861   <c>Accepted</c>
2862   <c>
2863      <xref target="status.202"/>
2864   </c>
2865   <c>203</c>
2866   <c>Non-Authoritative Information</c>
2867   <c>
2868      <xref target="status.203"/>
2869   </c>
2870   <c>204</c>
2871   <c>No Content</c>
2872   <c>
2873      <xref target="status.204"/>
2874   </c>
2875   <c>205</c>
2876   <c>Reset Content</c>
2877   <c>
2878      <xref target="status.205"/>
2879   </c>
2880   <c>300</c>
2881   <c>Multiple Choices</c>
2882   <c>
2883      <xref target="status.300"/>
2884   </c>
2885   <c>301</c>
2886   <c>Moved Permanently</c>
2887   <c>
2888      <xref target="status.301"/>
2889   </c>
2890   <c>302</c>
2891   <c>Found</c>
2892   <c>
2893      <xref target="status.302"/>
2894   </c>
2895   <c>303</c>
2896   <c>See Other</c>
2897   <c>
2898      <xref target="status.303"/>
2899   </c>
2900   <c>305</c>
2901   <c>Use Proxy</c>
2902   <c>
2903      <xref target="status.305"/>
2904   </c>
2905   <c>306</c>
2906   <c>(Unused)</c>
2907   <c>
2908      <xref target="status.306"/>
2909   </c>
2910   <c>307</c>
2911   <c>Temporary Redirect</c>
2912   <c>
2913      <xref target="status.307"/>
2914   </c>
2915   <c>400</c>
2916   <c>Bad Request</c>
2917   <c>
2918      <xref target="status.400"/>
2919   </c>
2920   <c>402</c>
2921   <c>Payment Required</c>
2922   <c>
2923      <xref target="status.402"/>
2924   </c>
2925   <c>403</c>
2926   <c>Forbidden</c>
2927   <c>
2928      <xref target="status.403"/>
2929   </c>
2930   <c>404</c>
2931   <c>Not Found</c>
2932   <c>
2933      <xref target="status.404"/>
2934   </c>
2935   <c>405</c>
2936   <c>Method Not Allowed</c>
2937   <c>
2938      <xref target="status.405"/>
2939   </c>
2940   <c>406</c>
2941   <c>Not Acceptable</c>
2942   <c>
2943      <xref target="status.406"/>
2944   </c>
2945   <c>408</c>
2946   <c>Request Timeout</c>
2947   <c>
2948      <xref target="status.408"/>
2949   </c>
2950   <c>409</c>
2951   <c>Conflict</c>
2952   <c>
2953      <xref target="status.409"/>
2954   </c>
2955   <c>410</c>
2956   <c>Gone</c>
2957   <c>
2958      <xref target="status.410"/>
2959   </c>
2960   <c>411</c>
2961   <c>Length Required</c>
2962   <c>
2963      <xref target="status.411"/>
2964   </c>
2965   <c>413</c>
2966   <c>Request Representation Too Large</c>
2967   <c>
2968      <xref target="status.413"/>
2969   </c>
2970   <c>414</c>
2971   <c>URI Too Long</c>
2972   <c>
2973      <xref target="status.414"/>
2974   </c>
2975   <c>415</c>
2976   <c>Unsupported Media Type</c>
2977   <c>
2978      <xref target="status.415"/>
2979   </c>
2980   <c>417</c>
2981   <c>Expectation Failed</c>
2982   <c>
2983      <xref target="status.417"/>
2984   </c>
2985   <c>426</c>
2986   <c>Upgrade Required</c>
2987   <c>
2988      <xref target="status.426"/>
2989   </c>
2990   <c>500</c>
2991   <c>Internal Server Error</c>
2992   <c>
2993      <xref target="status.500"/>
2994   </c>
2995   <c>501</c>
2996   <c>Not Implemented</c>
2997   <c>
2998      <xref target="status.501"/>
2999   </c>
3000   <c>502</c>
3001   <c>Bad Gateway</c>
3002   <c>
3003      <xref target="status.502"/>
3004   </c>
3005   <c>503</c>
3006   <c>Service Unavailable</c>
3007   <c>
3008      <xref target="status.503"/>
3009   </c>
3010   <c>504</c>
3011   <c>Gateway Timeout</c>
3012   <c>
3013      <xref target="status.504"/>
3014   </c>
3015   <c>505</c>
3016   <c>HTTP Version Not Supported</c>
3017   <c>
3018      <xref target="status.505"/>
3019   </c>
3020</texttable>
3021<!--(END)-->
3022<?ENDINC p2-semantics.iana-status-codes ?>
3023</section>
3024<section title="Header Field Registration" anchor="header.field.registration">
3025<t>
3026   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3027   with the permanent registrations below (see <xref target="RFC3864"/>):
3028</t>
3029<?BEGININC p2-semantics.iana-headers ?>
3030<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3031<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3032   <ttcol>Header Field Name</ttcol>
3033   <ttcol>Protocol</ttcol>
3034   <ttcol>Status</ttcol>
3035   <ttcol>Reference</ttcol>
3036
3037   <c>Allow</c>
3038   <c>http</c>
3039   <c>standard</c>
3040   <c>
3041      <xref target="header.allow"/>
3042   </c>
3043   <c>Date</c>
3044   <c>http</c>
3045   <c>standard</c>
3046   <c>
3047      <xref target="header.date"/>
3048   </c>
3049   <c>Expect</c>
3050   <c>http</c>
3051   <c>standard</c>
3052   <c>
3053      <xref target="header.expect"/>
3054   </c>
3055   <c>From</c>
3056   <c>http</c>
3057   <c>standard</c>
3058   <c>
3059      <xref target="header.from"/>
3060   </c>
3061   <c>Location</c>
3062   <c>http</c>
3063   <c>standard</c>
3064   <c>
3065      <xref target="header.location"/>
3066   </c>
3067   <c>Max-Forwards</c>
3068   <c>http</c>
3069   <c>standard</c>
3070   <c>
3071      <xref target="header.max-forwards"/>
3072   </c>
3073   <c>Referer</c>
3074   <c>http</c>
3075   <c>standard</c>
3076   <c>
3077      <xref target="header.referer"/>
3078   </c>
3079   <c>Retry-After</c>
3080   <c>http</c>
3081   <c>standard</c>
3082   <c>
3083      <xref target="header.retry-after"/>
3084   </c>
3085   <c>Server</c>
3086   <c>http</c>
3087   <c>standard</c>
3088   <c>
3089      <xref target="header.server"/>
3090   </c>
3091   <c>User-Agent</c>
3092   <c>http</c>
3093   <c>standard</c>
3094   <c>
3095      <xref target="header.user-agent"/>
3096   </c>
3097</texttable>
3098<!--(END)-->
3099<?ENDINC p2-semantics.iana-headers ?>
3100<t>
3101   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3102</t>
3103</section>
3104</section>
3105
3106<section title="Security Considerations" anchor="security.considerations">
3107<t>
3108   This section is meant to inform application developers, information
3109   providers, and users of the security limitations in HTTP/1.1 as
3110   described by this document. The discussion does not include
3111   definitive solutions to the problems revealed, though it does make
3112   some suggestions for reducing security risks.
3113</t>
3114
3115<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3116<t>
3117   Like any generic data transfer protocol, HTTP cannot regulate the
3118   content of the data that is transferred, nor is there any a priori
3119   method of determining the sensitivity of any particular piece of
3120   information within the context of any given request. Therefore,
3121   applications &SHOULD; supply as much control over this information as
3122   possible to the provider of that information. Four header fields are
3123   worth special mention in this context: Server, Via, Referer and From.
3124</t>
3125<t>
3126   Revealing the specific software version of the server might allow the
3127   server machine to become more vulnerable to attacks against software
3128   that is known to contain security holes. Implementors &SHOULD; make the
3129   Server header field a configurable option.
3130</t>
3131<t>
3132   Proxies which serve as a portal through a network firewall &SHOULD;
3133   take special precautions regarding the transfer of header information
3134   that identifies the hosts behind the firewall. In particular, they
3135   &SHOULD; remove, or replace with sanitized versions, any Via fields
3136   generated behind the firewall.
3137</t>
3138<t>
3139   The Referer header field allows reading patterns to be studied and reverse
3140   links drawn. Although it can be very useful, its power can be abused
3141   if user details are not separated from the information contained in
3142   the Referer. Even when the personal information has been removed, the
3143   Referer header field might indicate a private document's URI whose
3144   publication would be inappropriate.
3145</t>
3146<t>
3147   The information sent in the From field might conflict with the user's
3148   privacy interests or their site's security policy, and hence it
3149   &SHOULD-NOT;  be transmitted without the user being able to disable,
3150   enable, and modify the contents of the field. The user &MUST; be able
3151   to set the contents of this field within a user preference or
3152   application defaults configuration.
3153</t>
3154<t>
3155   We suggest, though do not require, that a convenient toggle interface
3156   be provided for the user to enable or disable the sending of From and
3157   Referer information.
3158</t>
3159<t>
3160   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3161   target="header.server"/>) header fields can sometimes be used to determine
3162   that a specific client or server has a particular security hole which might
3163   be exploited. Unfortunately, this same information is often used for other
3164   valuable purposes for which HTTP currently has no better mechanism.
3165</t>
3166<t>
3167   Furthermore, the User-Agent header field may contain enough entropy to be
3168   used, possibly in conjunction with other material, to uniquely identify the
3169   user.
3170</t>
3171<t>
3172   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3173   that was sent in request header fields within the body of their response.
3174   Clients &SHOULD; be careful with sensitive information, like Cookies,
3175   Authorization credentials, and other header fields that might be used to
3176   collect data from the client.
3177</t> 
3178</section>
3179
3180<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3181<t>
3182   Because the source of a link might be private information or might
3183   reveal an otherwise private information source, it is strongly
3184   recommended that the user be able to select whether or not the
3185   Referer field is sent. For example, a browser client could have a
3186   toggle switch for browsing openly/anonymously, which would
3187   respectively enable/disable the sending of Referer and From
3188   information.
3189</t>
3190<t>
3191   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3192   HTTP request if the referring page was transferred with a secure
3193   protocol.
3194</t>
3195<t>
3196   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3197   sensitive data because that data will be placed in the request-target. Many
3198   existing servers, proxies, and user agents log or display the request-target
3199   in places where it might be visible to third parties. Such services can
3200   use POST-based form submission instead.
3201</t>
3202</section>
3203
3204<section title="Location Header Fields: Spoofing and Information Leakage" anchor="location.spoofing-leakage">
3205<t>
3206   If a single server supports multiple organizations that do not trust
3207   one another, then it &MUST; check the values of Location and Content-Location
3208   header fields in responses that are generated under control of
3209   said organizations to make sure that they do not attempt to
3210   invalidate resources over which they have no authority.
3211</t>
3212<t>
3213   Furthermore, appending the fragment identifier from one URI to another
3214   one obtained from a Location header field might leak confidential
3215   information to the target server &mdash; although the fragment identifier is
3216   not transmitted in the final request, it might be visible to the user agent
3217   through other means, such as scripting.
3218</t>
3219</section>
3220
3221<section title="Security Considerations for CONNECT">
3222<t>
3223   Since tunneled data is opaque to the proxy, there are additional
3224   risks to tunneling to other well-known or reserved ports.
3225   A HTTP client CONNECTing to port 25 could relay spam
3226   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3227   access to a small number of known ports.
3228</t>
3229</section>
3230
3231</section>
3232
3233<section title="Acknowledgments" anchor="acks">
3234<t>
3235  See &acks;.
3236</t>
3237</section>
3238</middle>
3239<back>
3240
3241<references title="Normative References">
3242
3243<reference anchor="Part1">
3244  <front>
3245    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3246    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3247      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3248      <address><email>fielding@gbiv.com</email></address>
3249    </author>
3250    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3251      <organization abbrev="W3C">World Wide Web Consortium</organization>
3252      <address><email>ylafon@w3.org</email></address>
3253    </author>
3254    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3255      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3256      <address><email>julian.reschke@greenbytes.de</email></address>
3257    </author>
3258    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3259  </front>
3260  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3261  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3262</reference>
3263
3264<reference anchor="Part3">
3265  <front>
3266    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3267    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3268      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3269      <address><email>fielding@gbiv.com</email></address>
3270    </author>
3271    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3272      <organization abbrev="W3C">World Wide Web Consortium</organization>
3273      <address><email>ylafon@w3.org</email></address>
3274    </author>
3275    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3276      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3277      <address><email>julian.reschke@greenbytes.de</email></address>
3278    </author>
3279    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3280  </front>
3281  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3282  <x:source href="p3-payload.xml" basename="p3-payload"/>
3283</reference>
3284
3285<reference anchor="Part4">
3286  <front>
3287    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3288    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3289      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3290      <address><email>fielding@gbiv.com</email></address>
3291    </author>
3292    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3293      <organization abbrev="W3C">World Wide Web Consortium</organization>
3294      <address><email>ylafon@w3.org</email></address>
3295    </author>
3296    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3297      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3298      <address><email>julian.reschke@greenbytes.de</email></address>
3299    </author>
3300    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3301  </front>
3302  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3303  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3304</reference>
3305
3306<reference anchor="Part5">
3307  <front>
3308    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3309    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3310      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3311      <address><email>fielding@gbiv.com</email></address>
3312    </author>
3313    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3314      <organization abbrev="W3C">World Wide Web Consortium</organization>
3315      <address><email>ylafon@w3.org</email></address>
3316    </author>
3317    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3318      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3319      <address><email>julian.reschke@greenbytes.de</email></address>
3320    </author>
3321    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3322  </front>
3323  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3324  <x:source href="p5-range.xml" basename="p5-range"/>
3325</reference>
3326
3327<reference anchor="Part6">
3328  <front>
3329    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3330    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3331      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3332      <address><email>fielding@gbiv.com</email></address>
3333    </author>
3334    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3335      <organization abbrev="W3C">World Wide Web Consortium</organization>
3336      <address><email>ylafon@w3.org</email></address>
3337    </author>
3338    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3339      <organization>Rackspace</organization>
3340      <address><email>mnot@mnot.net</email></address>
3341    </author>
3342    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3343      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3344      <address><email>julian.reschke@greenbytes.de</email></address>
3345    </author>
3346    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3347  </front>
3348  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3349  <x:source href="p6-cache.xml" basename="p6-cache"/>
3350</reference>
3351
3352<reference anchor="Part7">
3353  <front>
3354    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3355    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3356      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3357      <address><email>fielding@gbiv.com</email></address>
3358    </author>
3359    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3360      <organization abbrev="W3C">World Wide Web Consortium</organization>
3361      <address><email>ylafon@w3.org</email></address>
3362    </author>
3363    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3364      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3365      <address><email>julian.reschke@greenbytes.de</email></address>
3366    </author>
3367    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3368  </front>
3369  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3370  <x:source href="p7-auth.xml" basename="p7-auth"/>
3371</reference>
3372
3373<reference anchor="RFC2119">
3374  <front>
3375    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3376    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3377      <organization>Harvard University</organization>
3378      <address><email>sob@harvard.edu</email></address>
3379    </author>
3380    <date month="March" year="1997"/>
3381  </front>
3382  <seriesInfo name="BCP" value="14"/>
3383  <seriesInfo name="RFC" value="2119"/>
3384</reference>
3385
3386<reference anchor="RFC3986">
3387 <front>
3388  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3389  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3390    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3391    <address>
3392       <email>timbl@w3.org</email>
3393       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3394    </address>
3395  </author>
3396  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3397    <organization abbrev="Day Software">Day Software</organization>
3398    <address>
3399      <email>fielding@gbiv.com</email>
3400      <uri>http://roy.gbiv.com/</uri>
3401    </address>
3402  </author>
3403  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3404    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3405    <address>
3406      <email>LMM@acm.org</email>
3407      <uri>http://larry.masinter.net/</uri>
3408    </address>
3409  </author>
3410  <date month='January' year='2005'></date>
3411 </front>
3412 <seriesInfo name="STD" value="66"/>
3413 <seriesInfo name="RFC" value="3986"/>
3414</reference>
3415
3416<reference anchor="RFC5234">
3417  <front>
3418    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3419    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3420      <organization>Brandenburg InternetWorking</organization>
3421      <address>
3422        <email>dcrocker@bbiw.net</email>
3423      </address> 
3424    </author>
3425    <author initials="P." surname="Overell" fullname="Paul Overell">
3426      <organization>THUS plc.</organization>
3427      <address>
3428        <email>paul.overell@thus.net</email>
3429      </address>
3430    </author>
3431    <date month="January" year="2008"/>
3432  </front>
3433  <seriesInfo name="STD" value="68"/>
3434  <seriesInfo name="RFC" value="5234"/>
3435</reference>
3436
3437</references>
3438
3439<references title="Informative References">
3440
3441<reference anchor="RFC1123">
3442  <front>
3443    <title>Requirements for Internet Hosts - Application and Support</title>
3444    <author initials="R." surname="Braden" fullname="Robert Braden">
3445      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3446      <address><email>Braden@ISI.EDU</email></address>
3447    </author>
3448    <date month="October" year="1989"/>
3449  </front>
3450  <seriesInfo name="STD" value="3"/>
3451  <seriesInfo name="RFC" value="1123"/>
3452</reference>
3453
3454<reference anchor="RFC1945">
3455  <front>
3456    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3457    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3458      <organization>MIT, Laboratory for Computer Science</organization>
3459      <address><email>timbl@w3.org</email></address>
3460    </author>
3461    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3462      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3463      <address><email>fielding@ics.uci.edu</email></address>
3464    </author>
3465    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3466      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3467      <address><email>frystyk@w3.org</email></address>
3468    </author>
3469    <date month="May" year="1996"/>
3470  </front>
3471  <seriesInfo name="RFC" value="1945"/>
3472</reference>
3473
3474<reference anchor="RFC2068">
3475  <front>
3476    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3477    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3478      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3479      <address><email>fielding@ics.uci.edu</email></address>
3480    </author>
3481    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3482      <organization>MIT Laboratory for Computer Science</organization>
3483      <address><email>jg@w3.org</email></address>
3484    </author>
3485    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3486      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3487      <address><email>mogul@wrl.dec.com</email></address>
3488    </author>
3489    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3490      <organization>MIT Laboratory for Computer Science</organization>
3491      <address><email>frystyk@w3.org</email></address>
3492    </author>
3493    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3494      <organization>MIT Laboratory for Computer Science</organization>
3495      <address><email>timbl@w3.org</email></address>
3496    </author>
3497    <date month="January" year="1997"/>
3498  </front>
3499  <seriesInfo name="RFC" value="2068"/>
3500</reference>
3501
3502<reference anchor="RFC2616">
3503  <front>
3504    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3505    <author initials="R." surname="Fielding" fullname="R. Fielding">
3506      <organization>University of California, Irvine</organization>
3507      <address><email>fielding@ics.uci.edu</email></address>
3508    </author>
3509    <author initials="J." surname="Gettys" fullname="J. Gettys">
3510      <organization>W3C</organization>
3511      <address><email>jg@w3.org</email></address>
3512    </author>
3513    <author initials="J." surname="Mogul" fullname="J. Mogul">
3514      <organization>Compaq Computer Corporation</organization>
3515      <address><email>mogul@wrl.dec.com</email></address>
3516    </author>
3517    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3518      <organization>MIT Laboratory for Computer Science</organization>
3519      <address><email>frystyk@w3.org</email></address>
3520    </author>
3521    <author initials="L." surname="Masinter" fullname="L. Masinter">
3522      <organization>Xerox Corporation</organization>
3523      <address><email>masinter@parc.xerox.com</email></address>
3524    </author>
3525    <author initials="P." surname="Leach" fullname="P. Leach">
3526      <organization>Microsoft Corporation</organization>
3527      <address><email>paulle@microsoft.com</email></address>
3528    </author>
3529    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3530      <organization>W3C</organization>
3531      <address><email>timbl@w3.org</email></address>
3532    </author>
3533    <date month="June" year="1999"/>
3534  </front>
3535  <seriesInfo name="RFC" value="2616"/>
3536</reference>
3537
3538<reference anchor='RFC2817'>
3539  <front>
3540    <title>Upgrading to TLS Within HTTP/1.1</title>
3541    <author initials='R.' surname='Khare' fullname='R. Khare'>
3542      <organization>4K Associates / UC Irvine</organization>
3543      <address><email>rohit@4K-associates.com</email></address>
3544    </author>
3545    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3546      <organization>Agranat Systems, Inc.</organization>
3547      <address><email>lawrence@agranat.com</email></address>
3548    </author>
3549    <date year='2000' month='May' />
3550  </front>
3551  <seriesInfo name='RFC' value='2817' />
3552</reference>
3553
3554<reference anchor='RFC3864'>
3555  <front>
3556    <title>Registration Procedures for Message Header Fields</title>
3557    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3558      <organization>Nine by Nine</organization>
3559      <address><email>GK-IETF@ninebynine.org</email></address>
3560    </author>
3561    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3562      <organization>BEA Systems</organization>
3563      <address><email>mnot@pobox.com</email></address>
3564    </author>
3565    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3566      <organization>HP Labs</organization>
3567      <address><email>JeffMogul@acm.org</email></address>
3568    </author>
3569    <date year='2004' month='September' />
3570  </front>
3571  <seriesInfo name='BCP' value='90' />
3572  <seriesInfo name='RFC' value='3864' />
3573</reference>
3574
3575<reference anchor='RFC5226'>
3576  <front>
3577    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3578    <author initials='T.' surname='Narten' fullname='T. Narten'>
3579      <organization>IBM</organization>
3580      <address><email>narten@us.ibm.com</email></address>
3581    </author>
3582    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3583      <organization>Google</organization>
3584      <address><email>Harald@Alvestrand.no</email></address>
3585    </author>
3586    <date year='2008' month='May' />
3587  </front>
3588  <seriesInfo name='BCP' value='26' />
3589  <seriesInfo name='RFC' value='5226' />
3590</reference>
3591
3592<reference anchor="RFC5322">
3593  <front>
3594    <title>Internet Message Format</title>
3595    <author initials="P." surname="Resnick" fullname="P. Resnick">
3596      <organization>Qualcomm Incorporated</organization>
3597    </author>
3598    <date year="2008" month="October"/>
3599  </front> 
3600  <seriesInfo name="RFC" value="5322"/>
3601</reference>
3602
3603<reference anchor='RFC5789'>
3604  <front>
3605    <title>PATCH Method for HTTP</title>
3606    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3607      <organization>Linden Lab</organization>
3608    </author>
3609    <author initials='J.' surname='Snell' fullname='J. Snell' />
3610    <date year='2010' month='March' />
3611  </front>
3612  <seriesInfo name='RFC' value='5789' />
3613</reference>
3614
3615<reference anchor="RFC5987">
3616        <front>
3617    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3618    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3619      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3620      <address>
3621        <postal>
3622          <street>Hafenweg 16</street>
3623          <city>Muenster</city><region>NW</region><code>48155</code>
3624          <country>Germany</country>
3625        </postal>
3626        <email>julian.reschke@greenbytes.de</email>     
3627        <uri>http://greenbytes.de/tech/webdav/</uri>   
3628      </address>
3629    </author>
3630    <date month="August" year="2010"/>
3631  </front>
3632  <seriesInfo name="RFC" value="5987"/>
3633</reference>
3634
3635<reference anchor="draft-reschke-http-status-308">
3636        <front>
3637    <title abbrev="HTTP Status Code 308">The Hypertext Transfer Protocol (HTTP) Status Code 308 (Permanent Redirect)</title>
3638    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3639      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3640      <address>
3641        <email>julian.reschke@greenbytes.de</email>     
3642      </address>
3643    </author>
3644    <date month="March" year="2012"/>
3645  </front>
3646  <seriesInfo name="Internet-Draft" value="draft-reschke-http-status-308-07"/>
3647</reference>
3648
3649</references>
3650
3651<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3652<t>
3653  Clarify definition of POST.
3654  (<xref target="POST"/>)
3655</t>
3656<t>
3657  Remove requirement to handle all Content-* header fields; ban use of
3658  Content-Range with PUT.
3659  (<xref target="PUT"/>)
3660</t>
3661<t>
3662  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3663  (<xref target="CONNECT"/>)
3664</t>
3665<t>
3666  This document takes over the Status Code Registry, previously defined
3667  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3668  (<xref target="status.code.registry"/>)
3669</t>
3670<t>
3671  Broadened the definition of 203 (Non-Authoritative Information) to include
3672  cases of payload transformations as well.
3673  (<xref target="status.203"/>)
3674</t>
3675<t>
3676  Status codes 301, 302, and 307: removed the normative requirements on both
3677  response payloads and user interaction.
3678  (<xref target="status.3xx"/>)
3679</t>
3680<t>
3681  Failed to consider that there are many other request methods that are safe
3682  to automatically redirect, and further that the user agent is able to make
3683  that determination based on the request method semantics.
3684  Furthermore, allow user agents to rewrite the method from POST to GET
3685  for status codes 301 and 302.
3686  (Sections <xref format="counter" target="status.301"/>,
3687  <xref format="counter" target="status.302"/> and
3688  <xref format="counter" target="status.307"/>)
3689</t>
3690<t>
3691  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3692  It used to indicate that the target resource needs to be accessed through the
3693  proxy given by the Location field. The Location field gave the URI of the
3694  proxy. The recipient was expected to repeat this single request via the proxy.
3695  (<xref target="status.305"/>)
3696</t>
3697<t>
3698  Define status 426 (Upgrade Required) (this was incorporated from
3699  <xref target="RFC2817"/>).
3700  (<xref target="status.426"/>)
3701</t>
3702<t>
3703  Change ABNF productions for header fields to only define the field value.
3704  (<xref target="header.field.definitions"/>)
3705</t>
3706<t>
3707  Reclassify "Allow" as response header field, removing the option to
3708  specify it in a PUT request.
3709  Relax the server requirement on the contents of the Allow header field and
3710  remove requirement on clients to always trust the header field value.
3711  (<xref target="header.allow"/>)
3712</t>
3713<t>
3714  The ABNF for the Expect header field has been both fixed (allowing parameters
3715  for value-less expectations as well) and simplified (allowing trailing
3716  semicolons after "100-continue" when they were invalid before).
3717  (<xref target="header.expect"/>)
3718</t>
3719<t>
3720  Correct syntax of Location header field to allow URI references (including
3721  relative references and fragments), as referred symbol "absoluteURI" wasn't
3722  what was expected, and add some clarifications as to when use of fragments
3723  would not be appropriate.
3724  (<xref target="header.location"/>)
3725</t>
3726<t>
3727  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
3728  extension methods could have used it as well).
3729  (<xref target="header.max-forwards"/>)
3730</t>
3731<t>
3732  Allow Referer field value of "about:blank" as alternative to not specifying it.
3733  (<xref target="header.referer"/>)
3734</t>
3735<t>
3736  In the description of the Server header field, the Via field
3737  was described as a SHOULD. The requirement was and is stated
3738  correctly in the description of the Via header field in &header-via;.
3739  (<xref target="header.server"/>)
3740</t>
3741</section>
3742
3743<?BEGININC p2-semantics.abnf-appendix ?>
3744<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
3745<figure>
3746<artwork type="abnf" name="p2-semantics.parsed-abnf">
3747<x:ref>Allow</x:ref> = [ ( "," / method ) *( OWS "," [ OWS method ] ) ]
3748
3749<x:ref>BWS</x:ref> = &lt;BWS, defined in [Part1], Section 3.2.1&gt;
3750
3751<x:ref>Date</x:ref> = HTTP-date
3752
3753<x:ref>Expect</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
3754
3755<x:ref>From</x:ref> = mailbox
3756
3757<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
3758
3759<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
3760
3761<x:ref>Location</x:ref> = URI-reference
3762
3763<x:ref>Max-Forwards</x:ref> = 1*DIGIT
3764
3765<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 3.2.1&gt;
3766
3767<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 3.2.1&gt;
3768<x:ref>Referer</x:ref> = absolute-URI / partial-URI
3769<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
3770
3771<x:ref>Server</x:ref> = product *( RWS ( product / comment ) )
3772
3773<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
3774<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
3775
3776<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
3777<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
3778
3779<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2.4&gt;
3780
3781<x:ref>date1</x:ref> = day SP month SP year
3782<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
3783<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
3784<x:ref>day</x:ref> = 2DIGIT
3785<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
3786 / %x54.75.65 ; Tue
3787 / %x57.65.64 ; Wed
3788 / %x54.68.75 ; Thu
3789 / %x46.72.69 ; Fri
3790 / %x53.61.74 ; Sat
3791 / %x53.75.6E ; Sun
3792<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
3793 / %x54.75.65.73.64.61.79 ; Tuesday
3794 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
3795 / %x54.68.75.72.73.64.61.79 ; Thursday
3796 / %x46.72.69.64.61.79 ; Friday
3797 / %x53.61.74.75.72.64.61.79 ; Saturday
3798 / %x53.75.6E.64.61.79 ; Sunday
3799<x:ref>delta-seconds</x:ref> = 1*DIGIT
3800
3801<x:ref>expect-name</x:ref> = token
3802<x:ref>expect-param</x:ref> = expect-name [ BWS "=" BWS expect-value ]
3803<x:ref>expect-value</x:ref> = token / quoted-string
3804<x:ref>expectation</x:ref> = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
3805 OWS expect-param ] )
3806
3807<x:ref>hour</x:ref> = 2DIGIT
3808
3809<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
3810<x:ref>method</x:ref> = token
3811<x:ref>minute</x:ref> = 2DIGIT
3812<x:ref>month</x:ref> = %x4A.61.6E ; Jan
3813 / %x46.65.62 ; Feb
3814 / %x4D.61.72 ; Mar
3815 / %x41.70.72 ; Apr
3816 / %x4D.61.79 ; May
3817 / %x4A.75.6E ; Jun
3818 / %x4A.75.6C ; Jul
3819 / %x41.75.67 ; Aug
3820 / %x53.65.70 ; Sep
3821 / %x4F.63.74 ; Oct
3822 / %x4E.6F.76 ; Nov
3823 / %x44.65.63 ; Dec
3824
3825<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
3826<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 3.2.4&gt;
3827
3828<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
3829<x:ref>product</x:ref> = token [ "/" product-version ]
3830<x:ref>product-version</x:ref> = token
3831
3832<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.4&gt;
3833
3834<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
3835<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
3836<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
3837
3838<x:ref>second</x:ref> = 2DIGIT
3839<x:ref>status-code</x:ref> = 3DIGIT
3840
3841<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
3842<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.4&gt;
3843
3844<x:ref>year</x:ref> = 4DIGIT
3845</artwork>
3846</figure>
3847<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
3848; Allow defined but not used
3849; Date defined but not used
3850; Expect defined but not used
3851; From defined but not used
3852; Location defined but not used
3853; Max-Forwards defined but not used
3854; Referer defined but not used
3855; Retry-After defined but not used
3856; Server defined but not used
3857; User-Agent defined but not used
3858; reason-phrase defined but not used
3859; status-code defined but not used
3860</artwork></figure></section>
3861<?ENDINC p2-semantics.abnf-appendix ?>
3862
3863<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
3864
3865<section title="Since RFC 2616">
3866<t>
3867  Extracted relevant partitions from <xref target="RFC2616"/>.
3868</t>
3869</section>
3870
3871<section title="Since draft-ietf-httpbis-p2-semantics-00">
3872<t>
3873  Closed issues:
3874  <list style="symbols"> 
3875    <t>
3876      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
3877      "Via is a MUST"
3878      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
3879    </t>
3880    <t>
3881      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
3882      "Fragments allowed in Location"
3883      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
3884    </t>
3885    <t>
3886      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
3887      "Safe Methods vs Redirection"
3888      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
3889    </t>
3890    <t>
3891      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
3892      "Revise description of the POST method"
3893      (<eref target="http://purl.org/NET/http-errata#post"/>)
3894    </t>
3895    <t>
3896      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
3897      "Normative and Informative references"
3898    </t>
3899    <t>
3900      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
3901      "RFC2606 Compliance"
3902    </t>
3903    <t>
3904      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
3905      "Informative references"
3906    </t>
3907    <t>
3908      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
3909      "Redundant cross-references"
3910    </t>
3911  </list>
3912</t>
3913<t>
3914  Other changes:
3915  <list style="symbols"> 
3916    <t>
3917      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
3918    </t>
3919  </list>
3920</t>
3921</section>
3922
3923<section title="Since draft-ietf-httpbis-p2-semantics-01">
3924<t>
3925  Closed issues:
3926  <list style="symbols"> 
3927    <t>
3928      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
3929      "PUT side effects"
3930    </t>
3931    <t>
3932      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
3933      "Duplicate Host header requirements"
3934    </t>
3935  </list>
3936</t>
3937<t>
3938  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3939  <list style="symbols"> 
3940    <t>
3941      Move "Product Tokens" section (back) into Part 1, as "token" is used
3942      in the definition of the Upgrade header field.
3943    </t>
3944    <t>
3945      Add explicit references to BNF syntax and rules imported from other parts of the specification.
3946    </t>
3947    <t>
3948      Copy definition of delta-seconds from Part6 instead of referencing it.
3949    </t>
3950  </list>
3951</t>
3952</section>
3953
3954<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
3955<t>
3956  Closed issues:
3957  <list style="symbols"> 
3958    <t>
3959      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
3960      "Requiring Allow in 405 responses"
3961    </t>
3962    <t>
3963      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
3964      "Status Code Registry"
3965    </t>
3966    <t>
3967      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
3968      "Redirection vs. Location"
3969    </t>
3970    <t>
3971      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
3972      "Cacheability of 303 response"
3973    </t>
3974    <t>
3975      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
3976      "305 Use Proxy"
3977    </t>
3978    <t>
3979      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
3980      "Classification for Allow header"
3981    </t>
3982    <t>
3983      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
3984      "PUT - 'store under' vs 'store at'"
3985    </t>
3986  </list>
3987</t>
3988<t>
3989  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
3990  <list style="symbols"> 
3991    <t>
3992      Reference RFC 3984, and update header field registrations for headers defined
3993      in this document.
3994    </t>
3995  </list>
3996</t>
3997<t>
3998  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3999  <list style="symbols"> 
4000    <t>
4001      Replace string literals when the string really is case-sensitive (method).
4002    </t>
4003  </list>
4004</t>
4005</section>
4006
4007<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
4008<t>
4009  Closed issues:
4010  <list style="symbols"> 
4011    <t>
4012      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
4013      "OPTIONS request bodies"
4014    </t>
4015    <t>
4016      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
4017      "Description of CONNECT should refer to RFC2817"
4018    </t>
4019    <t>
4020      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
4021      "Location Content-Location reference request/response mixup"
4022    </t>
4023  </list>
4024</t>
4025<t>
4026  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
4027  <list style="symbols"> 
4028    <t>
4029      Added initial proposal for registration process, plus initial
4030      content (non-HTTP/1.1 methods to be added by a separate specification).
4031    </t>
4032  </list>
4033</t>
4034</section>
4035
4036<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
4037<t>
4038  Closed issues:
4039  <list style="symbols"> 
4040    <t>
4041      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4042      "Content-*"
4043    </t>
4044    <t>
4045      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4046      "RFC 2822 is updated by RFC 5322"
4047    </t>
4048  </list>
4049</t>
4050<t>
4051  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4052  <list style="symbols"> 
4053    <t>
4054      Use "/" instead of "|" for alternatives.
4055    </t>
4056    <t>
4057      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4058      whitespace ("OWS") and required whitespace ("RWS").
4059    </t>
4060    <t>
4061      Rewrite ABNFs to spell out whitespace rules, factor out
4062      header field value format definitions.
4063    </t>
4064  </list>
4065</t>
4066</section>
4067
4068<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
4069<t>
4070  Closed issues:
4071  <list style="symbols"> 
4072    <t>
4073      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4074      "reason-phrase BNF"
4075    </t>
4076  </list>
4077</t>
4078<t>
4079  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4080  <list style="symbols"> 
4081    <t>
4082      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4083    </t>
4084  </list>
4085</t>
4086</section>
4087
4088<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4089<t>
4090  Closed issues:
4091  <list style="symbols"> 
4092    <t>
4093      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4094      "Clarify when Referer is sent"
4095    </t>
4096    <t>
4097      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4098      "status codes vs methods"
4099    </t>
4100    <t>
4101      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4102      "Do not require "updates" relation for specs that register status codes or method names"
4103    </t>
4104  </list>
4105</t>
4106</section>
4107
4108<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4109<t>
4110  Closed issues:
4111  <list style="symbols"> 
4112    <t>
4113      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4114      "Idempotency"
4115    </t>
4116    <t>
4117      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4118      "TRACE security considerations"
4119    </t>
4120    <t>
4121      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4122      "Clarify rules for determining what entities a response carries"
4123    </t>
4124    <t>
4125      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4126      "update note citing RFC 1945 and 2068"
4127    </t>
4128    <t>
4129      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4130      "update note about redirect limit"
4131    </t>
4132    <t>
4133      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4134      "Location header ABNF should use 'URI'"
4135    </t>
4136    <t>
4137      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4138      "fragments in Location vs status 303"
4139    </t>
4140    <t>
4141      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4142      "move IANA registrations for optional status codes"
4143    </t>
4144  </list>
4145</t>
4146<t>
4147  Partly resolved issues:
4148  <list style="symbols"> 
4149    <t>
4150      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4151      "Are OPTIONS and TRACE safe?"
4152    </t>
4153  </list>
4154</t>
4155</section>
4156
4157<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4158<t>
4159  Closed issues:
4160  <list style="symbols"> 
4161    <t>
4162      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4163      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4164      status codes when fixing this previously)
4165    </t>
4166  </list>
4167</t>
4168</section>
4169
4170<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4171<t>
4172  Closed issues:
4173  <list style="symbols"> 
4174    <t>
4175      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4176      "Fragment combination / precedence during redirects"
4177    </t>
4178  </list>
4179</t>
4180<t>
4181  Partly resolved issues:
4182  <list style="symbols"> 
4183    <t>
4184      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4185      "Location header payload handling"
4186    </t>
4187    <t>
4188      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4189      "Term for the requested resource's URI"
4190    </t>
4191  </list>
4192</t>
4193</section>
4194
4195<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4196<t>
4197  Closed issues:
4198  <list style="symbols"> 
4199    <t>
4200      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4201      "Clarify 'Requested Variant'"
4202    </t>
4203    <t>
4204      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4205      "Clarify entity / representation / variant terminology"
4206    </t>
4207    <t>
4208      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4209      "Methods and Caching"
4210    </t>
4211    <t>
4212      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4213      "OPTIONS vs Max-Forwards"
4214    </t>
4215    <t>
4216      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4217      "Status codes and caching"
4218    </t>
4219    <t>
4220      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4221      "consider removing the 'changes from 2068' sections"
4222    </t>
4223  </list>
4224</t>
4225</section>
4226
4227<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4228<t>
4229  Closed issues:
4230  <list style="symbols"> 
4231    <t>
4232      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4233      "Considerations for new status codes"
4234    </t>
4235    <t>
4236      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4237      "Considerations for new methods"
4238    </t>
4239    <t>
4240      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4241      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4242    </t>
4243  </list>
4244</t>
4245</section>
4246
4247<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4248<t>
4249  Closed issues:
4250  <list style="symbols"> 
4251    <t>
4252      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4253      "Fragment combination / precedence during redirects" (added warning
4254      about having a fragid on the redirect may cause inconvenience in
4255      some cases)
4256    </t>
4257    <t>
4258      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4259      "Content-* vs. PUT"
4260    </t>
4261    <t>
4262      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4263      "205 Bodies"
4264    </t>
4265    <t>
4266      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4267      "Understanding Content-* on non-PUT requests"
4268    </t>
4269    <t>
4270      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4271      "Content-*"
4272    </t>
4273    <t>
4274      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4275      "Header type defaulting"
4276    </t>
4277    <t>
4278      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4279      "PUT - 'store under' vs 'store at'"
4280    </t>
4281    <t>
4282      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4283      "duplicate ABNF for reason-phrase"
4284    </t>
4285    <t>
4286      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4287      "Note special status of Content-* prefix in header registration procedures"
4288    </t>
4289    <t>
4290      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4291      "Max-Forwards vs extension methods"
4292    </t>
4293    <t>
4294      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4295      "What is the value space of HTTP status codes?" (actually fixed in
4296      draft-ietf-httpbis-p2-semantics-11)
4297    </t>
4298    <t>
4299      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4300      "Header Classification"
4301    </t>
4302    <t>
4303      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4304      "PUT side effect: invalidation or just stale?"
4305    </t>
4306    <t>
4307      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4308      "proxies not supporting certain methods"
4309    </t>
4310    <t>
4311      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4312      "Migrate CONNECT from RFC2817 to p2"
4313    </t>
4314    <t>
4315      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4316      "Migrate Upgrade details from RFC2817"
4317    </t>
4318    <t>
4319      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4320      "clarify PUT semantics'"
4321    </t>
4322    <t>
4323      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4324      "duplicate ABNF for 'Method'"
4325    </t>
4326    <t>
4327      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4328      "untangle ABNFs for header fields"
4329    </t>
4330  </list>
4331</t>
4332</section>
4333
4334<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4335<t>
4336  Closed issues:
4337  <list style="symbols"> 
4338    <t>
4339      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4340      "untangle ABNFs for header fields"
4341    </t>
4342    <t>
4343      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4344      "message body in CONNECT request"
4345    </t>
4346  </list>
4347</t>
4348</section>
4349
4350<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4351<t>
4352  Closed issues:
4353  <list style="symbols"> 
4354    <t>
4355      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4356      "Clarify status code for rate limiting"
4357    </t>
4358    <t>
4359      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4360      "clarify 403 forbidden"
4361    </t>
4362    <t>
4363      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4364      "Clarify 203 Non-Authoritative Information"
4365    </t>
4366    <t>
4367      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4368      "update default reason phrase for 413"
4369    </t>
4370  </list>
4371</t>
4372</section>
4373
4374<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4375<t>
4376  Closed issues:
4377  <list style="symbols"> 
4378    <t>
4379      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4380      "Strength of requirements on Accept re: 406"
4381    </t>
4382    <t>
4383      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4384      "400 response isn't generic"
4385    </t>
4386  </list>
4387</t>
4388</section>
4389
4390<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4391<t>
4392  Closed issues:
4393  <list style="symbols"> 
4394    <t>
4395      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4396      "Redirects and non-GET methods"
4397    </t>
4398    <t>
4399      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
4400      "Document HTTP's error-handling philosophy"
4401    </t>
4402    <t>
4403      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4404      "Considerations for new headers"
4405    </t>
4406    <t>
4407      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4408      "clarify 303 redirect on HEAD"
4409    </t>
4410  </list>
4411</t>
4412</section>
4413
4414<section title="Since draft-ietf-httpbis-p2-semantics-17" anchor="changes.since.17">
4415<t>
4416  Closed issues:
4417  <list style="symbols"> 
4418    <t>
4419      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4420      "Location header payload handling"
4421    </t>
4422    <t>
4423      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4424      "Clarify status code for rate limiting" (change backed out because
4425      a new status code is being defined for this purpose)
4426    </t>
4427    <t>
4428      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4429      "should there be a permanent variant of 307"
4430    </t>
4431    <t>
4432      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/325"/>:
4433      "When are Location's semantics triggered?"
4434    </t>
4435    <t>
4436      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/327"/>:
4437      "'expect' grammar missing OWS"
4438    </t>
4439    <t>
4440      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/329"/>:
4441      "header field considerations: quoted-string vs use of double quotes"
4442    </t>
4443  </list>
4444</t>
4445</section>
4446
4447<section title="Since draft-ietf-httpbis-p2-semantics-18" anchor="changes.since.18">
4448<t>
4449  Closed issues:
4450  <list style="symbols"> 
4451    <t>
4452      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/227"/>:
4453      "Combining HEAD responses"
4454    </t>
4455    <t>
4456      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/238"/>:
4457      "Requirements for user intervention during redirects"
4458    </t>
4459    <t>
4460      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
4461      "message-body in CONNECT response"
4462    </t>
4463    <t>
4464      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/295"/>:
4465      "Applying original fragment to 'plain' redirected URI"
4466    </t>
4467    <t>
4468      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
4469      "Misplaced text on connection handling in p2"
4470    </t>
4471    <t>
4472      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/331"/>:
4473      "clarify that 201 doesn't require Location header fields"
4474    </t>
4475    <t>
4476      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/332"/>:
4477      "relax requirements on hypertext in 3/4/5xx error responses"
4478    </t>
4479    <t>
4480      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/333"/>:
4481      "example for 426 response should have a payload"
4482    </t>
4483    <t>
4484      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/336"/>:
4485      "drop indirection entries for status codes"
4486    </t>
4487  </list>
4488</t>
4489</section>
4490
4491<section title="Since draft-ietf-httpbis-p2-semantics-19" anchor="changes.since.19">
4492<t>
4493  Closed issues:
4494  <list style="symbols"> 
4495    <t>
4496      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4497      "should there be a permanent variant of 307"
4498    </t>
4499  </list>
4500</t>
4501</section>
4502
4503</section>
4504
4505</back>
4506</rfc>
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