source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1618

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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="Method" anchor="method">
314  <x:anchor-alias value="method"/>
315  <x:anchor-alias value="extension-method"/>
316<t>
317   The method token indicates the request method to be performed on the target
318   resource (&effective-request-uri;). The method is case-sensitive.
319</t>
320<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
321  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
322</artwork></figure>
323<t>
324   The list of methods allowed by a resource can be specified in an
325   Allow header field (<xref target="header.allow"/>). The status code of the response
326   always notifies the client whether a method is currently allowed on a
327   resource, since the set of allowed methods can change dynamically. An
328   origin server &SHOULD; respond with the status code 405 (Method Not Allowed)
329   if the method is known by the origin server but not allowed for the
330   resource, and 501 (Not Implemented) if the method is
331   unrecognized or not implemented by the origin server. The methods GET
332   and HEAD &MUST; be supported by all general-purpose servers. All other
333   methods are &OPTIONAL;; however, if the above methods are implemented,
334   they &MUST; be implemented with the same semantics as those specified
335   in <xref target="method.definitions"/>.
336</t>
337
338<section title="Overview of Methods" anchor="overview.of.methods">
339<t>
340  The methods listed below are defined in <xref target="method.definitions"/>.
341</t>
342<texttable align="left">
343  <ttcol>Method Name</ttcol><ttcol>Defined in...</ttcol>
344 
345  <c>OPTIONS</c> <c><xref target="OPTIONS"/></c>
346  <c>GET</c> <c><xref target="GET"/></c>
347  <c>HEAD</c> <c><xref target="HEAD"/></c>
348  <c>POST</c> <c><xref target="POST"/></c>
349  <c>PUT</c> <c><xref target="PUT"/></c>
350  <c>DELETE</c> <c><xref target="DELETE"/></c>
351  <c>TRACE</c> <c><xref target="TRACE"/></c>
352  <c>CONNECT</c> <c><xref target="CONNECT"/></c>
353</texttable>
354<t>
355  Note that this list is not exhaustive &mdash; it does not include request methods defined
356  in other specifications.
357</t>
358</section>
359
360<section title="Method Registry" anchor="method.registry">
361<t>
362  The HTTP Method Registry defines the name space for the method token in the
363  Request line of an HTTP request.
364</t>
365<t>
366  Registrations &MUST; include the following fields:
367  <list style="symbols">
368    <t>Method Name (see <xref target="method"/>)</t>
369    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
370    <t>Pointer to specification text</t>
371  </list>
372</t>
373<t>
374  Values to be added to this name space require IETF Review
375  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
376</t>
377<t>
378  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
379</t>
380
381<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
382<t>
383   When it is necessary to express new semantics for a HTTP request that
384   aren't specific to a single application or media type, and currently defined
385   methods are inadequate, it may be appropriate to register a new method.
386</t>
387<t>
388   HTTP methods are generic; that is, they are potentially applicable to any
389   resource, not just one particular media type, "type" of resource, or
390   application. As such, it is preferred that new HTTP methods be registered
391   in a document that isn't specific to a single application, so that this is
392   clear.
393</t>
394<t>
395   Due to the parsing rules defined in &message-body;, definitions of HTTP
396   methods cannot prohibit the presence of a message body on either the request
397   or the response message (with responses to HEAD requests being the single
398   exception). Definitions of new methods cannot change this rule, but they can
399   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
400</t>
401<t>
402   New method definitions need to indicate whether they are safe (<xref
403   target="safe.methods"/>), what semantics (if any) the request body has,
404   and whether they are idempotent (<xref target="idempotent.methods"/>).
405   They also need to state whether they can be cached (&caching;); in
406   particular what conditions a cache may store the response, and under what
407   conditions such a stored response may be used to satisfy a subsequent
408   request.
409</t>
410</section>
411
412</section>
413</section>
414
415<section title="Header Fields" anchor="header.fields">
416<t>
417   Header fields are key value pairs that can be used to communicate data about
418   the message, its payload, the target resource, or about the connection
419   itself (i.e., control data).  See &header-fields; for a general definition
420   of their syntax.
421</t>
422
423<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
424<t>
425   New header fields are registered using the procedures described in
426   <xref target="RFC3864"/>.
427</t>
428<t>
429   The requirements for header field names are defined in
430   <xref target="RFC3864" x:fmt="of" x:sec="4.1"/>.  Authors of specifications
431   defining new fields are advised to keep the name as short as practical, and
432   not to prefix them with "X-" if they are to be registered (either
433   immediately or in the future).
434</t>
435<t>
436   New header field values typically have their syntax defined using ABNF
437   (<xref target="RFC5234"/>), using the extension defined in &abnf-extension;
438   as necessary, and are usually constrained to the range of ASCII characters.
439   Header fields needing a greater range of characters can use an encoding
440   such as the one defined in <xref target="RFC5987"/>.
441</t>
442<t>
443   Because commas (",") are used as a generic delimiter between field-values,
444   they need to be treated with care if they are allowed in the field-value's
445   payload. Typically, components that might contain a comma are protected with
446   double-quotes using the quoted-string ABNF production (&field-components;).
447</t>
448<t>
449   For example, a textual date and a URI (either of which might contain a comma)
450   could be safely carried in field-values like these:
451</t>
452<figure><artwork type="example">
453  Example-URI-Field: "http://example.com/a.html,foo",
454                     "http://without-a-comma.example.com/"
455  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
456</artwork></figure>
457<t>
458   Note that double quote delimiters almost always are used with the
459   quoted-string production; using a different syntax inside double quotes
460   will likely cause unnecessary confusion.
461</t>
462<t>
463   Many header fields use a format including (case-insensitively) named
464   parameters (for instance, Content-Type, defined in &header-content-type;).
465   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
466   parameter value enables recipients to use existing parser components. When
467   allowing both forms, the meaning of a parameter value ought to be
468   independent of the syntax used for it (for an example, see the notes on
469   parameter handling for media types in &media-types;).
470</t>
471<t>
472   Authors of specifications defining new header fields are advised to consider
473   documenting:
474  <list style="symbols">
475    <x:lt>
476      <t>Whether the field is a single value, or whether it can be a list
477      (delimited by commas; see &header-fields;).</t>
478      <t>If it does not use the list syntax, document how to treat messages
479      where the header field occurs multiple times (a sensible default would
480      be to ignore the header field, but this might not always be the right
481      choice).</t>
482      <t>Note that intermediaries and software libraries might combine
483      multiple header field instances into a single one, despite the header
484      field not allowing this. A robust format enables recipients to discover
485      these situations (good example: "Content-Type", as the comma can only
486      appear inside quoted strings; bad example: "Location", as a comma can
487      occur inside a URI).</t>
488    </x:lt>
489    <x:lt><t>Under what conditions the header field can be used; e.g., only in
490    responses or requests, in all messages, only on responses to a particular
491    request method.</t></x:lt>
492    <x:lt><t>Whether it is appropriate to list the field-name in the Connection header
493    (i.e., if the header is to be hop-by-hop, see &header-connection;).</t></x:lt>
494    <x:lt><t>Under what conditions intermediaries are allowed to modify the header
495    field's value, insert or delete it.</t></x:lt>
496    <x:lt><t>How the header might interact with caching (see <xref target="Part6"/>).</t></x:lt>
497    <x:lt><t>Whether the header field is useful or allowable in trailers (see
498    &chunked-encoding;).</t></x:lt>
499    <x:lt><t>Whether the header field should be preserved across redirects.</t></x:lt>
500  </list>
501</t>
502</section>
503
504<section title="Request Header Fields" anchor="request.header.fields">
505  <x:anchor-alias value="request-header"/>
506<t>
507   The request header fields allow the client to pass additional
508   information about the request, and about the client itself, to the
509   server. These fields act as request modifiers, with semantics
510   equivalent to the parameters on a programming language method
511   invocation.
512</t>
513<texttable align="left">
514  <ttcol>Header Field Name</ttcol>
515  <ttcol>Defined in...</ttcol>
516
517  <c>Accept</c> <c>&header-accept;</c>
518  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
519  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
520  <c>Accept-Language</c> <c>&header-accept-language;</c>
521  <c>Authorization</c> <c>&header-authorization;</c>
522  <c>Expect</c> <c><xref target="header.expect"/></c>
523  <c>From</c> <c><xref target="header.from"/></c>
524  <c>Host</c> <c>&header-host;</c>
525  <c>If-Match</c> <c>&header-if-match;</c>
526  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
527  <c>If-None-Match</c> <c>&header-if-none-match;</c>
528  <c>If-Range</c> <c>&header-if-range;</c>
529  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
530  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
531  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
532  <c>Range</c> <c>&header-range;</c>
533  <c>Referer</c> <c><xref target="header.referer"/></c>
534  <c>TE</c> <c>&header-te;</c>
535  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
536</texttable>
537</section>
538
539<section title="Response Header Fields" anchor="response.header.fields">
540  <x:anchor-alias value="response-header"/>
541<t>
542   The response header fields allow the server to pass additional
543   information about the response which cannot be placed in the status-line.
544   These header fields give information about the server and about
545   further access to the target resource (&effective-request-uri;).
546</t>
547<texttable align="left">
548  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
549
550  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
551  <c>Age</c> <c>&header-age;</c>
552  <c>Allow</c> <c><xref target="header.allow"/></c>
553  <c>Date</c> <c><xref target="header.date"/></c>
554  <c>ETag</c> <c>&header-etag;</c>
555  <c>Location</c> <c><xref target="header.location"/></c>
556  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
557  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
558  <c>Server</c> <c><xref target="header.server"/></c>
559  <c>Vary</c> <c>&header-vary;</c>
560  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
561</texttable>
562</section>
563
564</section>
565
566<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
567  <x:anchor-alias value="reason-phrase"/>
568  <x:anchor-alias value="status-code"/>
569  <x:anchor-alias value="extension-code"/>
570<t>
571   The status-code element is a 3-digit integer result code of the attempt to
572   understand and satisfy the request.
573</t>
574<t>
575   The reason-phrase is intended to give a short textual description of the
576   status-code and is intended for a human user. The client does not need
577   to examine or display the reason-phrase.
578</t>
579<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"/>
580  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
581  <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> )
582</artwork></figure>
583<t>
584   HTTP status codes are extensible. HTTP applications are not required
585   to understand the meaning of all registered status codes, though such
586   understanding is obviously desirable. However, applications &MUST;
587   understand the class of any status code, as indicated by the first
588   digit, and treat any unrecognized response as being equivalent to the
589   x00 status code of that class, with the exception that an
590   unrecognized response &MUST-NOT; be cached. For example, if an
591   unrecognized status code of 431 is received by the client, it can
592   safely assume that there was something wrong with its request and
593   treat the response as if it had received a 400 status code. In such
594   cases, user agents &SHOULD; present to the user the representation enclosed
595   with the response, since that representation is likely to include human-readable
596   information which will explain the unusual status.
597</t>
598<t>
599   The first digit of the status-code defines the class of response. The
600   last two digits do not have any categorization role. There are 5
601   values for the first digit:
602  <list style="symbols">
603    <t>
604      1xx: Informational - Request received, continuing process
605    </t>
606    <t>
607      2xx: Success - The action was successfully received,
608        understood, and accepted
609    </t>
610    <t>
611      3xx: Redirection - Further action needs to be taken in order to
612        complete the request
613    </t>
614    <t>
615      4xx: Client Error - The request contains bad syntax or cannot
616        be fulfilled
617    </t>
618    <t>
619      5xx: Server Error - The server failed to fulfill an apparently
620        valid request
621    </t>
622  </list>
623</t>
624
625<section title="Overview of Status Codes" anchor="overview.of.status.codes">
626<t> 
627   The status codes listed below are defined in <xref target="status.codes"/>
628   of this specification, &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
629   The reason phrases listed here are only recommendations &mdash; they can be
630   replaced by local equivalents without affecting the protocol.
631</t>
632<texttable align="left">
633  <ttcol>status-code</ttcol>
634  <ttcol>reason-phrase</ttcol>
635  <ttcol>Defined in...</ttcol>
636 
637  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
638  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
639
640  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
641  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
642  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
643  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
644  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
645  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
646  <c>206</c> <c>Partial Content</c> <c anchor="status.206">&status-206;</c>
647
648  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
649  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
650  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
651  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
652  <c>304</c> <c>Not Modified</c> <c anchor="status.304">&status-304;</c>
653  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
654  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
655
656  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
657  <c>401</c> <c>Unauthorized</c> <c anchor="status.401">&status-401;</c>
658  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
659  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
660  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
661  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
662  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
663  <c>407</c> <c>Proxy Authentication Required</c> <c anchor="status.407">&status-407;</c>
664  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
665  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
666  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
667  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
668  <c>412</c> <c>Precondition Failed</c> <c anchor="status.412">&status-412;</c>
669  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
670  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
671  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
672  <c>416</c> <c>Requested range not satisfiable</c> <c anchor="status.416">&status-416;</c>
673  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
674  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
675
676  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
677  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
678  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
679  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
680  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
681  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
682</texttable>
683<t>
684   Note that this list is not exhaustive &mdash; it does not include
685   extension status codes defined in other specifications.
686</t>
687</section>
688
689<section title="Status Code Registry" anchor="status.code.registry">
690<t>
691  The HTTP Status Code Registry defines the name space for the status-code
692  token in the status-line of an HTTP response.
693</t>
694<t>
695  Values to be added to this name space require IETF Review
696  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
697</t>
698<t>
699  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
700</t>
701
702<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
703<t>
704   When it is necessary to express new semantics for a HTTP response that
705   aren't specific to a single application or media type, and currently defined
706   status codes are inadequate, a new status code can be registered.
707</t>
708<t>
709   HTTP status codes are generic; that is, they are potentially applicable to
710   any resource, not just one particular media type, "type" of resource, or
711   application. As such, it is preferred that new HTTP status codes be
712   registered in a document that isn't specific to a single application, so
713   that this is clear.
714</t>
715<t>
716   Definitions of new HTTP status codes typically explain the request
717   conditions that produce a response containing the status code (e.g.,
718   combinations of request headers and/or method(s)), along with any
719   interactions with response headers (e.g., those that are required, those
720   that modify the semantics of the response).
721</t>
722<t>
723   New HTTP status codes are required to fall under one of the categories
724   defined in <xref target="status.codes"/>. To allow existing parsers to
725   properly handle them, new status codes cannot disallow a response body,
726   although they can mandate a zero-length response body. They can require the
727   presence of one or more particular HTTP response header(s).
728</t>
729<t>
730   Likewise, their definitions can specify that caches are allowed to use
731   heuristics to determine their freshness (see &caching;; by default, it is
732   not allowed), and can define how to determine the resource which they
733   carry a representation for (see <xref
734   target="identifying.response.associated.with.representation"/>; by default,
735   it is anonymous).
736</t>
737</section>
738
739</section>
740
741<section title="Status Code Definitions" anchor="status.codes">
742<t>
743   Each status-code is described below, including any metadata required
744   in the response.
745</t>
746<t>
747   For most status codes the response can carry a payload, in which case a
748   Content-Type header field indicates the payload's media type
749   (&header-content-type;).
750</t>
751
752<section title="Informational 1xx" anchor="status.1xx">
753<t>
754   This class of status code indicates a provisional response,
755   consisting only of the status-line and optional header fields, and is
756   terminated by an empty line. There are no required header fields for this
757   class of status code. Since HTTP/1.0 did not define any 1xx status
758   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
759   except under experimental conditions.
760</t>
761<t>
762   A client &MUST; be prepared to accept one or more 1xx status responses
763   prior to a regular response, even if the client does not expect a 100
764   (Continue) status message. Unexpected 1xx status responses &MAY; be
765   ignored by a user agent.
766</t>
767<t>
768   Proxies &MUST; forward 1xx responses, unless the connection between the
769   proxy and its client has been closed, or unless the proxy itself
770   requested the generation of the 1xx response. (For example, if a
771   proxy adds a "Expect: 100-continue" field when it forwards a request,
772   then it need not forward the corresponding 100 (Continue)
773   response(s).)
774</t>
775
776<section title="100 Continue" anchor="status.100">
777  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
778  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
779<t>
780   The client &SHOULD; continue with its request. This interim response is
781   used to inform the client that the initial part of the request has
782   been received and has not yet been rejected by the server. The client
783   &SHOULD; continue by sending the remainder of the request or, if the
784   request has already been completed, ignore this response. The server
785   &MUST; send a final response after the request has been completed. See
786   &use100; for detailed discussion of the use and handling of this
787   status code.
788</t>
789</section>
790
791<section title="101 Switching Protocols" anchor="status.101">
792  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
793  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
794<t>
795   The server understands and is willing to comply with the client's
796   request, via the Upgrade message header field (&header-upgrade;), for a
797   change in the application protocol being used on this connection. The
798   server will switch protocols to those defined by the response's
799   Upgrade header field immediately after the empty line which
800   terminates the 101 response.
801</t>
802<t>
803   The protocol &SHOULD; be switched only when it is advantageous to do
804   so. For example, switching to a newer version of HTTP is advantageous
805   over older versions, and switching to a real-time, synchronous
806   protocol might be advantageous when delivering resources that use
807   such features.
808</t>
809</section>
810</section>
811
812<section title="Successful 2xx" anchor="status.2xx">
813<t>
814   This class of status code indicates that the client's request was
815   successfully received, understood, and accepted.
816</t>
817
818<section title="200 OK" anchor="status.200">
819  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
820  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
821<t>
822   The request has succeeded. The payload returned with the response
823   is dependent on the method used in the request, for example:
824  <list style="hanging">
825    <t hangText="GET">
826      a representation of the target resource is sent in the response;
827    </t>
828    <t hangText="HEAD">
829      the same representation as GET, except without the message body;
830    </t>
831    <t hangText="POST">
832      a representation describing or containing the result of the action;
833    </t>
834    <t hangText="TRACE">
835      a representation containing the request message as received by the
836      end server.
837    </t>
838  </list>
839</t>
840<t>
841   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
842   freshness for 200 responses.
843</t>
844</section>
845
846<section title="201 Created" anchor="status.201">
847  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
848  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
849<t>
850   The request has been fulfilled and has resulted in a new resource being
851   created.
852</t>
853<t>
854   The newly created resource is typically linked to from the response payload,
855   with the most relevant URI also being carried in the Location header field.
856   If the newly created resource's URI is the same as the Effective Request URI,
857   this information can be omitted (e.g., in the case of a response to a PUT
858   request). 
859</t>
860<t>
861   The origin server &MUST; create the resource before returning the 201 status
862   code. If the action cannot be carried out immediately, the server &SHOULD;
863   respond with 202 (Accepted) response instead.
864</t>
865<t>
866   A 201 response &MAY; contain an ETag response header field indicating
867   the current value of the entity-tag for the representation of the resource
868   just created (see &header-etag;).
869</t>
870</section>
871
872<section title="202 Accepted" anchor="status.202">
873  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
874  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
875<t>
876   The request has been accepted for processing, but the processing has
877   not been completed.  The request might or might not eventually be
878   acted upon, as it might be disallowed when processing actually takes
879   place. There is no facility for re-sending a status code from an
880   asynchronous operation such as this.
881</t>
882<t>
883   The 202 response is intentionally non-committal. Its purpose is to
884   allow a server to accept a request for some other process (perhaps a
885   batch-oriented process that is only run once per day) without
886   requiring that the user agent's connection to the server persist
887   until the process is completed. The representation returned with this
888   response &SHOULD; include an indication of the request's current status
889   and either a pointer to a status monitor or some estimate of when the
890   user can expect the request to be fulfilled.
891</t>
892</section>
893
894<section title="203 Non-Authoritative Information" anchor="status.203">
895  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
896  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
897<t>
898   The representation in the response has been transformed or otherwise
899   modified by a transforming proxy (&intermediaries;).  Note that the
900   behavior of transforming intermediaries is controlled by the no-transform
901   Cache-Control directive (&header-cache-control;).
902</t>
903<t>
904   This status code is only appropriate when the response status code would
905   have been 200 (OK) otherwise. When the status code before transformation
906   would have been different, the 214 Transformation Applied warn-code
907   (&header-warning;) is appropriate.
908</t>
909<t>
910   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
911   freshness for 203 responses.
912</t>
913</section>
914
915<section title="204 No Content" anchor="status.204">
916  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
917  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
918<t>
919   The 204 (No Content) status code indicates that the server has
920   successfully fulfilled the request and that there is no additional
921   content to return in the response payload body.  Metadata in the
922   response header fields refer to the target resource and its current
923   representation after the requested action.
924</t>
925<t>
926   For example, if a 204 status code is received in response to a PUT
927   request and the response contains an ETag header field, then the PUT
928   was successful and the ETag field-value contains the entity-tag for
929   the new representation of that target resource.
930</t>
931<t>
932   The 204 response allows a server to indicate that the action has been
933   successfully applied to the target resource while implying that the
934   user agent &SHOULD-NOT; traverse away from its current "document view"
935   (if any).  The server assumes that the user agent will provide some
936   indication of the success to its user, in accord with its own interface,
937   and apply any new or updated metadata in the response to the active
938   representation.
939</t>
940<t>
941   For example, a 204 status code is commonly used with document editing
942   interfaces corresponding to a "save" action, such that the document
943   being saved remains available to the user for editing. It is also
944   frequently used with interfaces that expect automated data transfers
945   to be prevalent, such as within distributed version control systems.
946</t>
947<t>
948   The 204 response &MUST-NOT; include a message body, and thus is always
949   terminated by the first empty line after the header fields.
950</t>
951</section>
952
953<section title="205 Reset Content" anchor="status.205">
954  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
955  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
956<t>
957   The server has fulfilled the request and the user agent &SHOULD; reset
958   the document view which caused the request to be sent. This response
959   is primarily intended to allow input for actions to take place via
960   user input, followed by a clearing of the form in which the input is
961   given so that the user can easily initiate another input action.
962</t>
963<t>   
964   The message body included with the response &MUST; be empty. Note that
965   receivers still need to parse the response according to the algorithm defined
966   in &message-body;.
967</t>
968</section>
969</section>
970
971<section title="Redirection 3xx" anchor="status.3xx">
972<t>
973   This class of status code indicates that further action needs to be
974   taken by the user agent in order to fulfill the request.  If the required
975   action involves a subsequent HTTP request, it &MAY; be carried out by the
976   user agent without interaction with the user if and only if the method used
977   in the second request is known to be "safe", as defined in
978   <xref target="safe.methods"/>.
979</t>
980<t>
981   There are several types of redirects:
982   <list style="numbers">
983      <x:lt>
984        <t>
985          Redirects of the request to another URI, either temporarily or
986          permanently. The new URI is specified in the Location header field.
987          In this specification, the status codes 301 (Moved Permanently),
988          302 (Found), and 307 (Temporary Redirect) fall under this category.
989        </t>
990      </x:lt>
991      <x:lt>
992        <t>
993          Redirection to a new location that represents an indirect response to
994          the request, such as the result of a POST operation to be retrieved
995          with a subsequent GET request. This is status code 303 (See Other).
996        </t>
997      </x:lt>
998      <x:lt>
999        <t>
1000          Redirection offering a choice of matching resources for use by
1001          agent-driven content negotiation (&agent-driven-negotiation;). This
1002          is status code 300 (Multiple Choices).
1003        </t>
1004      </x:lt>
1005      <x:lt>
1006        <t>
1007          Other kinds of redirection, such as to a cached result (status code 304
1008          (Not Modified), see &status-304;).
1009        </t>
1010      </x:lt>
1011   </list>
1012</t>
1013<x:note>
1014  <t>
1015    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1016    and 302 (Found) were defined for the first type of redirect, and the second
1017    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1018    However it turned out that web forms using POST expected redirects to change
1019    the operation for the subsequent request to retrieval (GET). To address this
1020    use case, HTTP/1.1 introduced the second type of redirect with the status
1021    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1022    As user agents did not change their behavior to maintain backwards
1023    compatibility, the first revision of HTTP/1.1 added yet another status code,
1024    307 (Temporary Redirect), for which the backwards compatibility problems did
1025    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1026    Over 10 years later, most user agents still do method rewriting for
1027    status codes 301 and 302, therefore this specification makes that behavior
1028    conformant in case the original request was POST.
1029  </t>
1030</x:note>
1031<t>
1032   A Location header field on a 3xx response indicates that a client &MAY;
1033   automatically redirect to the URI provided; see <xref target="header.location"/>.
1034</t>
1035<t>
1036   Note that for methods not known to be "safe", as defined in <xref target="safe.methods"/>,
1037   automatic redirection needs to done with care, since the redirect might
1038   change the conditions under which the request was issued.
1039</t>
1040<t>
1041   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1042   "infinite" redirection loops).
1043</t>
1044<x:note>
1045  <t>
1046    <x:h>Note:</x:h> An earlier version of this specification recommended a
1047    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1048    Content developers need to be aware that some clients might
1049    implement such a fixed limitation.
1050  </t>
1051</x:note>
1052
1053<section title="300 Multiple Choices" anchor="status.300">
1054  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1055  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1056<t>
1057   The target resource has more than one
1058   representation, each with its own specific location, and agent-driven
1059   negotiation information (&content-negotiation;) is being provided so that
1060   the user (or user agent) can select a preferred representation by
1061   redirecting its request to that location.
1062</t>
1063<t>
1064   Unless it was a HEAD request, the response &SHOULD; include a representation
1065   containing a list of representation metadata and location(s) from
1066   which the user or user agent can choose the one most appropriate. Depending
1067   upon the format and the capabilities of
1068   the user agent, selection of the most appropriate choice &MAY; be
1069   performed automatically. However, this specification does not define
1070   any standard for such automatic selection.
1071</t>
1072<t>
1073   If the server has a preferred choice of representation, it &SHOULD;
1074   include the specific URI for that representation in the Location
1075   field; user agents &MAY; use the Location field value for automatic
1076   redirection.
1077</t>
1078<t>
1079   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1080   freshness for 300 responses.
1081</t>
1082
1083</section>
1084
1085<section title="301 Moved Permanently" anchor="status.301">
1086  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1087  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1088<t>
1089   The target resource has been assigned a new permanent URI and any
1090   future references to this resource &SHOULD; use one of the returned
1091   URIs.  Clients with link editing capabilities ought to automatically
1092   re-link references to the effective request URI to one or more of the new
1093   references returned by the server, where possible.
1094</t>
1095<t>
1096   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1097   freshness for 301 responses.
1098</t>
1099<t>
1100   The new permanent URI &SHOULD; be given by the Location field in the
1101   response. A response payload can contain a short hypertext note with a
1102   hyperlink to the new URI(s).
1103</t>
1104<x:note>
1105  <t>
1106    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1107    request method from POST to GET for the subsequent request. If this
1108    behavior is undesired, status code 307 (Temporary Redirect) can be used
1109    instead.
1110  </t>
1111</x:note>
1112</section>
1113
1114<section title="302 Found" anchor="status.302">
1115  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1116  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1117<t>
1118   The target resource resides temporarily under a different URI.
1119   Since the redirection might be altered on occasion, the client &SHOULD;
1120   continue to use the effective request URI for future requests.
1121</t>
1122<t>
1123   The temporary URI &SHOULD; be given by the Location field in the
1124   response. A response payload can contain a short hypertext note with a
1125   hyperlink to the new URI(s).
1126</t>
1127<x:note>
1128  <t>
1129    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1130    request method from POST to GET for the subsequent request. If this
1131    behavior is undesired, status code 307 (Temporary Redirect) can be used
1132    instead.
1133  </t>
1134</x:note>
1135</section>
1136
1137<section title="303 See Other" anchor="status.303">
1138  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1139  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1140<t>
1141   The 303 status code indicates that the server is redirecting the
1142   user agent to a different resource, as indicated by a URI in the
1143   Location header field, that is intended to provide an indirect
1144   response to the original request.  In order to satisfy the original
1145   request, a user agent &SHOULD; perform a retrieval request using the
1146   Location URI (a GET or HEAD request if using HTTP), which
1147   may itself be redirected further, and present the eventual result as an
1148   answer to the original request.
1149   Note that the new URI in the Location header field is not considered
1150   equivalent to the effective request URI.
1151</t>
1152<t>
1153   This status code is generally applicable to any HTTP method.  It is
1154   primarily used to allow the output of a POST action to redirect
1155   the user agent to a selected resource, since doing so provides the
1156   information corresponding to the POST response in a form that
1157   can be separately identified, bookmarked, and cached independent
1158   of the original request.
1159</t>
1160<t>
1161   A 303 response to a GET request indicates that the requested
1162   resource does not have a representation of its own that can be
1163   transferred by the server over HTTP.  The Location URI indicates a
1164   resource that is descriptive of the target resource, such that the
1165   follow-on representation might be useful to recipients without
1166   implying that it adequately represents the target resource.
1167   Note that answers to the questions of what can be represented, what
1168   representations are adequate, and what might be a useful description
1169   are outside the scope of HTTP and thus entirely determined by the
1170   URI owner(s).
1171</t>
1172<t>
1173   Except for responses to a HEAD request, the representation of a 303
1174   response &SHOULD; contain a short hypertext note with a hyperlink
1175   to the Location URI.
1176</t>
1177</section>
1178
1179<section title="305 Use Proxy" anchor="status.305">
1180  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1181  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1182<t>
1183   The 305 status code was defined in a previous version of this specification
1184   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1185</t>
1186</section>
1187
1188<section title="306 (Unused)" anchor="status.306">
1189  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1190  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1191<t>
1192   The 306 status code was used in a previous version of the
1193   specification, is no longer used, and the code is reserved.
1194</t>
1195</section>
1196
1197<section title="307 Temporary Redirect" anchor="status.307">
1198  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1199  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1200<t>
1201   The target resource resides temporarily under a different URI.
1202   Since the redirection can change over time, the client &SHOULD;
1203   continue to use the effective request URI for future requests.
1204</t>
1205<t>
1206   The temporary URI &SHOULD; be given by the Location field in the
1207   response. A response payload can contain a short hypertext note with a
1208   hyperlink to the new URI(s).
1209</t>
1210<x:note>
1211  <t>
1212    <x:h>Note:</x:h> This status code is similar to 302 Found, except that
1213    it does not allow rewriting the request method from POST to GET. This
1214    specification defines no equivalent counterpart for 301 Moved Permanently
1215    (<xref target="draft-reschke-http-status-308"/>, however, defines the
1216    status code 308 Permanent Redirect for this purpose).
1217  </t>
1218</x:note>
1219</section>
1220</section>
1221
1222<section title="Client Error 4xx" anchor="status.4xx">
1223<t>
1224   The 4xx class of status code is intended for cases in which the
1225   client seems to have erred. Except when responding to a HEAD request,
1226   the server &SHOULD; include a representation containing an explanation of the
1227   error situation, and whether it is a temporary or permanent
1228   condition. These status codes are applicable to any request method.
1229   User agents &SHOULD; display any included representation to the user.
1230</t>
1231
1232<section title="400 Bad Request" anchor="status.400">
1233  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1234  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1235<t>
1236   The server cannot or will not process the request, due to a client error (e.g.,
1237   malformed syntax).
1238</t>
1239</section>
1240
1241<section title="402 Payment Required" anchor="status.402">
1242  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1243  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1244<t>
1245   This code is reserved for future use.
1246</t>
1247</section>
1248
1249<section title="403 Forbidden" anchor="status.403">
1250  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1251  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1252<t>
1253   The server understood the request, but refuses to authorize it. Providing
1254   different user authentication credentials might be successful, but any
1255   credentials that were provided in the request are insufficient. The request
1256   &SHOULD-NOT; be repeated with the same credentials.
1257</t>
1258<t>
1259   If the request method was not HEAD and the server wishes to make
1260   public why the request has not been fulfilled, it &SHOULD; describe the
1261   reason for the refusal in the representation.  If the server does not wish to
1262   make this information available to the client, the status code 404
1263   (Not Found) &MAY; be used instead.
1264</t>
1265</section>
1266
1267<section title="404 Not Found" anchor="status.404">
1268  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1269  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1270<t>
1271   The server has not found anything matching the effective request URI. No
1272   indication is given of whether the condition is temporary or
1273   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1274   knows, through some internally configurable mechanism, that an old
1275   resource is permanently unavailable and has no forwarding address.
1276   This status code is commonly used when the server does not wish to
1277   reveal exactly why the request has been refused, or when no other
1278   response is applicable.
1279</t>
1280</section>
1281
1282<section title="405 Method Not Allowed" anchor="status.405">
1283  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1284  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1285<t>
1286   The method specified in the request-line is not allowed for the target
1287   resource. The response &MUST; include an Allow header field containing a
1288   list of valid methods for the requested resource.
1289</t>
1290</section>
1291
1292<section title="406 Not Acceptable" anchor="status.406">
1293  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1294  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1295<t>
1296   The resource identified by the request is only capable of generating
1297   response representations which have content characteristics not acceptable
1298   according to the Accept and Accept-* header fields sent in the request
1299   (see &p3-header-fields;).
1300</t>
1301<t>
1302   Unless it was a HEAD request, the response &SHOULD; include a representation
1303   containing a list of available representation characteristics and location(s)
1304   from which the user or user agent can choose the one most
1305   appropriate. Depending upon the format and the
1306   capabilities of the user agent, selection of the most appropriate
1307   choice &MAY; be performed automatically. However, this specification
1308   does not define any standard for such automatic selection.
1309</t>
1310<x:note>
1311  <t>
1312    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1313    not acceptable according to the accept header fields sent in the
1314    request. In some cases, this might even be preferable to sending a
1315    406 response. User agents are encouraged to inspect the header fields of
1316    an incoming response to determine if it is acceptable.
1317  </t>
1318</x:note>
1319<t>
1320   If the response could be unacceptable, a user agent &SHOULD;
1321   temporarily stop receipt of more data and query the user for a
1322   decision on further actions.
1323</t>
1324</section>
1325
1326<section title="408 Request Timeout" anchor="status.408">
1327  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1328  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1329<t>
1330   The client did not produce a request within the time that the server
1331   was prepared to wait. The client &MAY; repeat the request without
1332   modifications at any later time.
1333</t>
1334</section>
1335
1336<section title="409 Conflict" anchor="status.409">
1337  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1338  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1339<t>
1340   The request could not be completed due to a conflict with the current
1341   state of the resource. This code is only allowed in situations where
1342   it is expected that the user might be able to resolve the conflict
1343   and resubmit the request. The response body &SHOULD; include enough
1344   information for the user to recognize the source of the conflict.
1345   Ideally, the response representation would include enough information for the
1346   user or user agent to fix the problem; however, that might not be
1347   possible and is not required.
1348</t>
1349<t>
1350   Conflicts are most likely to occur in response to a PUT request. For
1351   example, if versioning were being used and the representation being PUT
1352   included changes to a resource which conflict with those made by an
1353   earlier (third-party) request, the server might use the 409 response
1354   to indicate that it can't complete the request. In this case, the
1355   response representation would likely contain a list of the differences
1356   between the two versions.
1357</t>
1358</section>
1359
1360<section title="410 Gone" anchor="status.410">
1361  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1362  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1363<t>
1364   The target resource is no longer available at the server and no
1365   forwarding address is known. This condition is expected to be
1366   considered permanent. Clients with link editing capabilities &SHOULD;
1367   delete references to the effective request URI after user approval. If the
1368   server does not know, or has no facility to determine, whether or not
1369   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1370   used instead.
1371</t>
1372<t>
1373   The 410 response is primarily intended to assist the task of web
1374   maintenance by notifying the recipient that the resource is
1375   intentionally unavailable and that the server owners desire that
1376   remote links to that resource be removed. Such an event is common for
1377   limited-time, promotional services and for resources belonging to
1378   individuals no longer working at the server's site. It is not
1379   necessary to mark all permanently unavailable resources as "gone" or
1380   to keep the mark for any length of time &mdash; that is left to the
1381   discretion of the server owner.
1382</t>
1383<t>
1384   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
1385   for 410 responses.
1386</t>
1387</section>
1388
1389<section title="411 Length Required" anchor="status.411">
1390  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1391  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1392<t>
1393   The server refuses to accept the request without a defined Content-Length.
1394   The client &MAY; repeat the request if it adds a valid
1395   Content-Length header field containing the length of the message body
1396   in the request message.
1397</t>
1398</section>
1399
1400<section title="413 Request Representation Too Large" anchor="status.413">
1401  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
1402  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
1403<t>
1404   The server is refusing to process a request because the request
1405   representation is larger than the server is willing or able to process. The
1406   server &MAY; close the connection to prevent the client from continuing
1407   the request.
1408</t>
1409<t>
1410   If the condition is temporary, the server &SHOULD; include a Retry-After
1411   header field to indicate that it is temporary and after what
1412   time the client &MAY; try again.
1413</t>
1414</section>
1415
1416<section title="414 URI Too Long" anchor="status.414">
1417  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
1418  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
1419<t>
1420   The server is refusing to service the request because the effective request URI
1421   is longer than the server is willing to interpret. This rare
1422   condition is only likely to occur when a client has improperly
1423   converted a POST request to a GET request with long query
1424   information, when the client has descended into a URI "black hole" of
1425   redirection (e.g., a redirected URI prefix that points to a suffix of
1426   itself), or when the server is under attack by a client attempting to
1427   exploit security holes present in some servers using fixed-length
1428   buffers for reading or manipulating the request-target.
1429</t>
1430</section>
1431
1432<section title="415 Unsupported Media Type" anchor="status.415">
1433  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1434  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1435<t>
1436   The server is refusing to service the request because the request
1437   payload is in a format not supported by this request method on the
1438   target resource.
1439</t>
1440</section>
1441
1442<section title="417 Expectation Failed" anchor="status.417">
1443  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1444  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1445<t>
1446   The expectation given in an Expect header field (see <xref target="header.expect"/>)
1447   could not be met by this server, or, if the server is a proxy,
1448   the server has unambiguous evidence that the request could not be met
1449   by the next-hop server.
1450</t>
1451</section>
1452
1453<section title="426 Upgrade Required" anchor="status.426">
1454  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
1455  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
1456<t>
1457   The request can not be completed without a prior protocol upgrade. This
1458   response &MUST; include an Upgrade header field (&header-upgrade;)
1459   specifying the required protocols.
1460</t>
1461<figure>
1462<preamble>Example:</preamble>
1463<artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
1464HTTP/1.1 426 Upgrade Required
1465Upgrade: HTTP/3.0
1466Connection: Upgrade
1467Content-Length: <x:length-of target="s426body"/>
1468Content-Type: text/plain
1469
1470<x:span anchor="s426body">This service requires use of the HTTP/3.0 protocol.
1471</x:span></artwork></figure>
1472<t>
1473   The server &SHOULD; include a message body in the 426 response which
1474   indicates in human readable form the reason for the error and describes any
1475   alternative courses which may be available to the user.
1476</t>
1477</section>
1478</section>
1479
1480<section title="Server Error 5xx" anchor="status.5xx">
1481<t>
1482   Response status codes beginning with the digit "5" indicate cases in
1483   which the server is aware that it has erred or is incapable of
1484   performing the request. Except when responding to a HEAD request, the
1485   server &SHOULD; include a representation containing an explanation of the
1486   error situation, and whether it is a temporary or permanent
1487   condition. User agents &SHOULD; display any included representation to the
1488   user. These response codes are applicable to any request method.
1489</t>
1490
1491<section title="500 Internal Server Error" anchor="status.500">
1492  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1493  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1494<t>
1495   The server encountered an unexpected condition which prevented it
1496   from fulfilling the request.
1497</t>
1498</section>
1499
1500<section title="501 Not Implemented" anchor="status.501">
1501  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1502  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1503<t>
1504   The server does not support the functionality required to fulfill the
1505   request. This is the appropriate response when the server does not
1506   recognize the request method and is not capable of supporting it for
1507   any resource.
1508</t>
1509</section>
1510
1511<section title="502 Bad Gateway" anchor="status.502">
1512  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1513  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1514<t>
1515   The server, while acting as a gateway or proxy, received an invalid
1516   response from the upstream server it accessed in attempting to
1517   fulfill the request.
1518</t>
1519</section>
1520
1521<section title="503 Service Unavailable" anchor="status.503">
1522  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1523  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1524<t>
1525   The server is currently unable to handle the request due to a
1526   temporary overloading or maintenance of the server.
1527</t>
1528<t>
1529   The implication is that this is a temporary condition which will be
1530   alleviated after some delay. If known, the length of the delay &MAY; be
1531   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
1532   If no Retry-After is given, the client &SHOULD; handle the response as it
1533   would for a 500 response.
1534</t>
1535<x:note>
1536  <t>
1537    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1538    server has to use it when becoming overloaded. Some servers might wish
1539    to simply refuse the connection.
1540  </t>
1541</x:note>
1542</section>
1543
1544<section title="504 Gateway Timeout" anchor="status.504">
1545  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1546  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1547<t>
1548   The server, while acting as a gateway or proxy, did not receive a
1549   timely response from the upstream server specified by the URI (e.g.,
1550   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
1551   to access in attempting to complete the request.
1552</t>
1553<x:note>
1554  <t>
1555    <x:h>Note</x:h> to implementors: some deployed proxies are known to
1556    return 400 or 500 when DNS lookups time out.
1557  </t>
1558</x:note>
1559</section>
1560
1561<section title="505 HTTP Version Not Supported" anchor="status.505">
1562  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1563  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1564<t>
1565   The server does not support, or refuses to support, the protocol
1566   version that was used in the request message. The server is
1567   indicating that it is unable or unwilling to complete the request
1568   using the same major version as the client, as described in &http-version;,
1569   other than with this error message. The response &SHOULD; contain
1570   a representation describing why that version is not supported and what other
1571   protocols are supported by that server.
1572</t>
1573
1574</section>
1575</section>
1576</section>
1577
1578</section>
1579
1580<section title="Representation" anchor="representation">
1581<t>
1582   Request and Response messages &MAY; transfer a representation if not otherwise
1583   restricted by the request method or response status code. A representation
1584   consists of metadata (representation header fields) and data (representation
1585   body).  When a complete or partial representation is enclosed in an HTTP message,
1586   it is referred to as the payload of the message. HTTP representations
1587   are defined in &payload;.
1588</t>
1589<t>
1590   A representation body is only present in a message when a message body is
1591   present, as described in &message-body;. The representation body is obtained
1592   from the message body by decoding any Transfer-Encoding that might
1593   have been applied to ensure safe and proper transfer of the message.
1594</t>
1595
1596<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
1597<t>
1598   It is sometimes necessary to determine an identifier for the resource
1599   associated with a representation.
1600</t>
1601<t>
1602   An HTTP request representation, when present, is always associated with an
1603   anonymous (i.e., unidentified) resource.
1604</t>
1605<t>
1606   In the common case, an HTTP response is a representation of the target
1607   resource (see &effective-request-uri;). However, this is not always the
1608   case. To determine the URI of the resource a response is associated with,
1609   the following rules are used (with the first applicable one being selected):
1610</t>
1611<t><list style="numbers">
1612   <t>If the response status code is 200 or 203 and the request method was GET,
1613   the response payload is a representation of the target resource.</t>
1614   <t>If the response status code is 204, 206, or 304 and the request method was GET
1615   or HEAD, the response payload is a partial representation of the target
1616   resource.</t>
1617   <t>If the response has a Content-Location header field, and that URI is the same
1618   as the effective request URI, the response payload is a representation of the
1619   target resource.</t>
1620   <t>If the response has a Content-Location header field, and that URI is not the
1621   same as the effective request URI, then the response asserts that its
1622   payload is a representation of the resource identified by the
1623   Content-Location URI. However, such an assertion cannot be trusted unless
1624   it can be verified by other means (not defined by HTTP).</t>
1625   <t>Otherwise, the response is a representation of an anonymous (i.e.,
1626   unidentified) resource.</t>
1627</list></t>
1628<t>
1629  <cref anchor="TODO-req-uri">
1630   The comparison function is going to have to be defined somewhere,
1631   because we already need to compare URIs for things like cache invalidation.</cref>
1632</t>
1633</section>
1634
1635</section>
1636
1637
1638<section title="Method Definitions" anchor="method.definitions">
1639<t>
1640   The set of common request methods for HTTP/1.1 is defined below. Although
1641   this set can be expanded, additional methods cannot be assumed to
1642   share the same semantics for separately extended clients and servers.
1643</t>
1644
1645<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
1646
1647<section title="Safe Methods" anchor="safe.methods">
1648<iref item="Safe Methods" primary="true"/>
1649<t>
1650   Implementors need to be aware that the software represents the user in
1651   their interactions over the Internet, and need to allow
1652   the user to be aware of any actions they take which might have an
1653   unexpected significance to themselves or others.
1654</t>
1655<t>
1656   In particular, the convention has been established that the GET, HEAD,
1657   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
1658   of taking an action other than retrieval. These request methods ought
1659   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
1660   This allows user agents to represent other methods, such as POST, PUT
1661   and DELETE, in a special way, so that the user is made aware of the
1662   fact that a possibly unsafe action is being requested.
1663</t>
1664<t>
1665   Naturally, it is not possible to ensure that the server does not
1666   generate side-effects as a result of performing a GET request; in
1667   fact, some dynamic resources consider that a feature. The important
1668   distinction here is that the user did not request the side-effects,
1669   so therefore cannot be held accountable for them.
1670</t>
1671</section>
1672
1673<section title="Idempotent Methods" anchor="idempotent.methods">
1674<iref item="Idempotent Methods" primary="true"/>
1675<t>
1676   Request methods can also have the property of "idempotence" in that,
1677   aside from error or expiration issues, the intended effect of multiple
1678   identical requests is the same as for a single request.
1679   PUT, DELETE, and all safe request methods are idempotent.
1680   It is important to note that idempotence refers only to changes
1681   requested by the client: a server is free to change its state due
1682   to multiple requests for the purpose of tracking those requests,
1683   versioning of results, etc.
1684</t>
1685</section>
1686</section>
1687
1688<section title="OPTIONS" anchor="OPTIONS">
1689  <rdf:Description>
1690    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1691  </rdf:Description>
1692  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
1693  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
1694<t>
1695   The OPTIONS method requests information about the
1696   communication options available on the request/response chain
1697   identified by the effective request URI. This method allows a client to
1698   determine the options and/or requirements associated with a resource,
1699   or the capabilities of a server, without implying a resource action
1700   or initiating a resource retrieval.
1701</t>
1702<t>
1703   Responses to the OPTIONS method are not cacheable.
1704</t>
1705<t>
1706   If the OPTIONS request includes a message body (as indicated by the
1707   presence of Content-Length or Transfer-Encoding), then the media type
1708   &MUST; be indicated by a Content-Type field. Although this
1709   specification does not define any use for such a body, future
1710   extensions to HTTP might use the OPTIONS body to make more detailed
1711   queries on the server.
1712</t>
1713<t>
1714   If the request-target (&request-target;) is an asterisk ("*"),
1715   the OPTIONS request is
1716   intended to apply to the server in general rather than to a specific
1717   resource. Since a server's communication options typically depend on
1718   the resource, the "*" request is only useful as a "ping" or "no-op"
1719   type of method; it does nothing beyond allowing the client to test
1720   the capabilities of the server. For example, this can be used to test
1721   a proxy for HTTP/1.1 conformance (or lack thereof).
1722</t>
1723<t>
1724   If the request-target is not an asterisk, the OPTIONS request applies
1725   only to the options that are available when communicating with that
1726   resource.
1727</t>
1728<t>
1729   A 200 response &SHOULD; include any header fields that indicate
1730   optional features implemented by the server and applicable to that
1731   resource (e.g., Allow), possibly including extensions not defined by
1732   this specification. The response body, if any, &SHOULD; also include
1733   information about the communication options. The format for such a
1734   body is not defined by this specification, but might be defined by
1735   future extensions to HTTP. Content negotiation &MAY; be used to select
1736   the appropriate response format. If no response body is included, the
1737   response &MUST; include a Content-Length field with a field-value of
1738   "0".
1739</t>
1740<t>
1741   The Max-Forwards header field &MAY; be used to target a
1742   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
1743   If no Max-Forwards field is present in the request, then the forwarded
1744   request &MUST-NOT; include a Max-Forwards field.
1745</t>
1746</section>
1747
1748<section title="GET" anchor="GET">
1749  <rdf:Description>
1750    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1751  </rdf:Description>
1752  <iref primary="true" item="GET method" x:for-anchor=""/>
1753  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
1754<t>
1755   The GET method requests transfer of a current representation of
1756   the target resource.
1757</t>
1758<t>   
1759   If the target resource is a data-producing process, it is the
1760   produced data which shall be returned as the representation in the response and not
1761   the source text of the process, unless that text happens to be the output of
1762   the process.
1763</t>
1764<t>
1765   The semantics of the GET method change to a "conditional GET" if the
1766   request message includes an If-Modified-Since, If-Unmodified-Since,
1767   If-Match, If-None-Match, or If-Range header field. A conditional GET
1768   requests that the representation be transferred only under the
1769   circumstances described by the conditional header field(s). The
1770   conditional GET request is intended to reduce unnecessary network
1771   usage by allowing cached representations to be refreshed without requiring
1772   multiple requests or transferring data already held by the client.
1773</t>
1774<t>
1775   The semantics of the GET method change to a "partial GET" if the
1776   request message includes a Range header field. A partial GET requests
1777   that only part of the representation be transferred, as described in &header-range;.
1778   The partial GET request is intended to reduce unnecessary
1779   network usage by allowing partially-retrieved representations to be
1780   completed without transferring data already held by the client.
1781</t>
1782<t>
1783   Bodies on GET requests have no defined semantics. Note that sending a body
1784   on a GET request might cause some existing implementations to reject the
1785   request.
1786</t>
1787<t>
1788   The response to a GET request is cacheable and &MAY; be used to satisfy
1789   subsequent GET and HEAD requests (see &caching;).
1790</t>
1791<t>
1792   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
1793</t>
1794</section>
1795
1796<section title="HEAD" anchor="HEAD">
1797  <rdf:Description>
1798    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1799  </rdf:Description>
1800  <iref primary="true" item="HEAD method" x:for-anchor=""/>
1801  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
1802<t>
1803   The HEAD method is identical to GET except that the server &MUST-NOT;
1804   return a message body in the response. The metadata contained
1805   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
1806   to the information sent in response to a GET request. This method can
1807   be used for obtaining metadata about the representation implied by the
1808   request without transferring the representation body. This method is
1809   often used for testing hypertext links for validity, accessibility,
1810   and recent modification.
1811</t>
1812<t>
1813   The response to a HEAD request is cacheable and &MAY; be used to satisfy
1814   a subsequent HEAD request. It also has potential side effects on
1815   previously stored responses to GET; see &p6-head;.
1816</t>
1817<t>
1818   Bodies on HEAD requests have no defined semantics. Note that sending a body
1819   on a HEAD request might cause some existing implementations to reject the
1820   request.
1821</t>
1822</section>
1823
1824<section title="POST" anchor="POST">
1825  <iref primary="true" item="POST method" x:for-anchor=""/>
1826  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
1827<t>
1828   The POST method requests that the origin server accept the
1829   representation enclosed in the request as data to be processed by the
1830   target resource. POST is designed to allow a uniform method to cover the
1831   following functions:
1832  <list style="symbols">
1833    <t>
1834      Annotation of existing resources;
1835    </t>
1836    <t>
1837        Posting a message to a bulletin board, newsgroup, mailing list,
1838        or similar group of articles;
1839    </t>
1840    <t>
1841        Providing a block of data, such as the result of submitting a
1842        form, to a data-handling process;
1843    </t>
1844    <t>
1845        Extending a database through an append operation.
1846    </t>
1847  </list>
1848</t>
1849<t>
1850   The actual function performed by the POST method is determined by the
1851   server and is usually dependent on the effective request URI.
1852</t>
1853<t>
1854   The action performed by the POST method might not result in a
1855   resource that can be identified by a URI. In this case, either 200
1856   (OK) or 204 (No Content) is the appropriate response status code,
1857   depending on whether or not the response includes a representation that
1858   describes the result.
1859</t>
1860<t>
1861   If a resource has been created on the origin server, the response
1862   &SHOULD; be 201 (Created) and contain a representation which describes the
1863   status of the request and refers to the new resource, and a Location
1864   header field (see <xref target="header.location"/>).
1865</t>
1866<t>
1867   Responses to POST requests are only cacheable when they
1868   include explicit freshness information (see &p6-explicit;). A
1869   cached POST response with a Content-Location header field
1870   (see &header-content-location;) whose value is the effective
1871   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
1872</t>
1873<t>
1874   Note that POST caching is not widely implemented.
1875   However, the 303 (See Other) response can be used to direct the
1876   user agent to retrieve a cacheable representation of the resource.
1877</t>
1878</section>
1879
1880<section title="PUT" anchor="PUT">
1881  <iref primary="true" item="PUT method" x:for-anchor=""/>
1882  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
1883<t>
1884   The PUT method requests that the state of the target resource
1885   be created or replaced with the state defined by the representation
1886   enclosed in the request message payload.  A successful PUT of a given
1887   representation would suggest that a subsequent GET on that same target
1888   resource will result in an equivalent representation being returned in
1889   a 200 (OK) response.  However, there is no guarantee that such a state
1890   change will be observable, since the target resource might be acted
1891   upon by other user agents in parallel, or might be subject to dynamic
1892   processing by the origin server, before any subsequent GET is received.
1893   A successful response only implies that the user agent's intent was
1894   achieved at the time of its processing by the origin server.
1895</t>
1896<t>   
1897   If the target resource does not have a current representation and
1898   the PUT successfully creates one, then the origin server &MUST; inform
1899   the user agent by sending a 201 (Created) response.  If the target
1900   resource does have a current representation and that representation is
1901   successfully modified in accordance with the state of the enclosed
1902   representation, then either a 200 (OK) or 204 (No Content) response
1903   &SHOULD; be sent to indicate successful completion of the request.
1904</t>
1905<t>
1906   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
1907   as part of the resource state).
1908</t>
1909<t>
1910   An origin server &SHOULD; verify that the PUT representation is
1911   consistent with any constraints which the server has for the target
1912   resource that cannot or will not be changed by the PUT.  This is
1913   particularly important when the origin server uses internal
1914   configuration information related to the URI in order to set the
1915   values for representation metadata on GET responses.  When a PUT
1916   representation is inconsistent with the target resource, the origin
1917   server &SHOULD; either make them consistent, by transforming the
1918   representation or changing the resource configuration, or respond
1919   with an appropriate error message containing sufficient information
1920   to explain why the representation is unsuitable.  The 409 (Conflict)
1921   or 415 (Unsupported Media Type) status codes are suggested, with the
1922   latter being specific to constraints on Content-Type values.
1923</t>
1924<t>
1925   For example, if the target resource is configured to always have a
1926   Content-Type of "text/html" and the representation being PUT has a
1927   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
1928   (a) reconfigure the target resource to reflect the new media type;
1929   (b) transform the PUT representation to a format consistent with that
1930   of the resource before saving it as the new resource state; or,
1931   (c) reject the request with a 415 response indicating that the target
1932   resource is limited to "text/html", perhaps including a link to a
1933   different resource that would be a suitable target for the new
1934   representation.
1935</t>
1936<t>
1937   HTTP does not define exactly how a PUT method affects the state
1938   of an origin server beyond what can be expressed by the intent of
1939   the user agent request and the semantics of the origin server response.
1940   It does not define what a resource might be, in any sense of that
1941   word, beyond the interface provided via HTTP.  It does not define
1942   how resource state is "stored", nor how such storage might change
1943   as a result of a change in resource state, nor how the origin server
1944   translates resource state into representations.  Generally speaking,
1945   all implementation details behind the resource interface are
1946   intentionally hidden by the server.
1947</t>
1948<t>
1949   The fundamental difference between the POST and PUT methods is
1950   highlighted by the different intent for the target resource.
1951   The target resource in a POST request is intended to handle the
1952   enclosed representation as a data-accepting process, such as for
1953   a gateway to some other protocol or a document that accepts annotations.
1954   In contrast, the target resource in a PUT request is intended to
1955   take the enclosed representation as a new or replacement value.
1956   Hence, the intent of PUT is idempotent and visible to intermediaries,
1957   even though the exact effect is only known by the origin server.
1958</t>
1959<t>
1960   Proper interpretation of a PUT request presumes that the user agent
1961   knows what target resource is desired.  A service that is intended
1962   to select a proper URI on behalf of the client, after receiving
1963   a state-changing request, &SHOULD; be implemented using the POST
1964   method rather than PUT.  If the origin server will not make the
1965   requested PUT state change to the target resource and instead
1966   wishes to have it applied to a different resource, such as when the
1967   resource has been moved to a different URI, then the origin server
1968   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
1969   then make its own decision regarding whether or not to redirect the
1970   request.
1971</t>
1972<t>
1973   A PUT request applied to the target resource &MAY; have side-effects
1974   on other resources.  For example, an article might have a URI for
1975   identifying "the current version" (a resource) which is separate
1976   from the URIs identifying each particular version (different
1977   resources that at one point shared the same state as the current version
1978   resource).  A successful PUT request on "the current version" URI might
1979   therefore create a new version resource in addition to changing the
1980   state of the target resource, and might also cause links to be added
1981   between the related resources.
1982</t>
1983<t>
1984   An origin server &SHOULD; reject any PUT request that contains a
1985   Content-Range header field, since it might be misinterpreted as
1986   partial content (or might be partial content that is being mistakenly
1987   PUT as a full representation).  Partial content updates are
1988   possible by targeting a separately identified resource with state
1989   that overlaps a portion of the larger resource, or by using a
1990   different method that has been specifically defined for partial
1991   updates (for example, the PATCH method defined in
1992   <xref target="RFC5789"/>).
1993</t>
1994<t>
1995   Responses to the PUT method are not cacheable. If a PUT request passes
1996   through a cache that has one or more stored responses for the effective
1997   request URI, those stored responses will be invalidated (see
1998   &p6-invalid;).
1999</t>
2000</section>
2001
2002<section title="DELETE" anchor="DELETE">
2003  <iref primary="true" item="DELETE method" x:for-anchor=""/>
2004  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
2005<t>
2006   The DELETE method requests that the origin server delete the target
2007   resource. This method &MAY; be overridden by
2008   human intervention (or other means) on the origin server. The client cannot
2009   be guaranteed that the operation has been carried out, even if the
2010   status code returned from the origin server indicates that the action
2011   has been completed successfully. However, the server &SHOULD-NOT; 
2012   indicate success unless, at the time the response is given, it
2013   intends to delete the resource or move it to an inaccessible
2014   location.
2015</t>
2016<t>
2017   A successful response &SHOULD; be 200 (OK) if the response includes an
2018   representation describing the status, 202 (Accepted) if the action has not
2019   yet been enacted, or 204 (No Content) if the action has been enacted
2020   but the response does not include a representation.
2021</t>
2022<t>
2023   Bodies on DELETE requests have no defined semantics. Note that sending a body
2024   on a DELETE request might cause some existing implementations to reject the
2025   request.
2026</t>
2027<t>
2028   Responses to the DELETE method are not cacheable. If a DELETE request
2029   passes through a cache that has one or more stored responses for the
2030   effective request URI, those stored responses will be invalidated (see
2031   &p6-invalid;).
2032</t>
2033</section>
2034
2035<section title="TRACE" anchor="TRACE">
2036  <rdf:Description>
2037    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
2038  </rdf:Description>
2039  <iref primary="true" item="TRACE method" x:for-anchor=""/>
2040  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
2041<t>
2042   The TRACE method requests a remote, application-layer loop-back
2043   of the request message. The final recipient of the request
2044   &SHOULD; reflect the message received back to the client as the
2045   message body of a 200 (OK) response. The final recipient is either the
2046   origin server or the first proxy to receive a Max-Forwards
2047   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
2048   A TRACE request &MUST-NOT; include a message body.
2049</t>
2050<t>
2051   TRACE allows the client to see what is being received at the other
2052   end of the request chain and use that data for testing or diagnostic
2053   information. The value of the Via header field (&header-via;) is of
2054   particular interest, since it acts as a trace of the request chain.
2055   Use of the Max-Forwards header field allows the client to limit the
2056   length of the request chain, which is useful for testing a chain of
2057   proxies forwarding messages in an infinite loop.
2058</t>
2059<t>
2060   If the request is valid, the response &SHOULD; have a Content-Type of
2061   "message/http" (see &media-type-message-http;) and contain a message body
2062   that encloses a copy of the entire request message.
2063   Responses to the TRACE method are not cacheable.
2064</t>
2065</section>
2066
2067<section title="CONNECT" anchor="CONNECT">
2068  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
2069  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
2070<t>
2071   The CONNECT method requests that the proxy establish a tunnel
2072   to the request-target and, if successful, thereafter restrict its behavior
2073   to blind forwarding of packets until the connection is closed.
2074</t>
2075<t>
2076   When using CONNECT, the request-target &MUST; use the authority form
2077   (&request-target;); i.e., the request-target consists of only the
2078   host name and port number of the tunnel destination, separated by a colon.
2079   For example,
2080</t>
2081<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2082CONNECT server.example.com:80 HTTP/1.1
2083Host: server.example.com:80
2084
2085</artwork></figure>
2086<t>
2087   Any successful (2xx) response to a CONNECT request indicates that the
2088   proxy has established a connection to the requested host and port,
2089   and has switched to tunneling the current connection to that server
2090   connection.
2091   The tunneled data from the server begins immediately after the blank line
2092   that concludes the successful response's header block.
2093   A server &SHOULD-NOT; send any Transfer-Encoding or Content-Length
2094   header fields in a successful response.
2095   A client &MUST; ignore any Content-Length or Transfer-Encoding header
2096   fields received in a successful response.
2097</t>
2098<t>
2099   Any response other than a successful response indicates that the tunnel
2100   has not yet been formed and that the connection remains governed by HTTP.
2101</t>
2102<t>
2103   Proxy authentication might be used to establish the
2104   authority to create a tunnel:
2105</t>
2106<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2107CONNECT server.example.com:80 HTTP/1.1
2108Host: server.example.com:80
2109Proxy-Authorization: basic aGVsbG86d29ybGQ=
2110
2111</artwork></figure>
2112<t>
2113   A message body on a CONNECT request has no defined semantics. Sending a
2114   body on a CONNECT request might cause existing implementations to reject
2115   the request.
2116</t>
2117<t>
2118   Similar to a pipelined HTTP/1.1 request, data to be tunneled from client
2119   to server &MAY; be sent immediately after the request (before a response
2120   is received). The usual caveats also apply:
2121   data may be discarded if the eventual response is negative, and the
2122   connection may be reset with no response if more than one TCP segment
2123   is outstanding.
2124</t>
2125<t>
2126   It may be the case that the proxy itself can only reach the requested
2127   origin server through another proxy.  In this case, the first proxy
2128   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
2129   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
2130   unless it has either a direct or tunnel connection established to the
2131   authority.
2132</t>
2133<t>
2134   If at any point either one of the peers gets disconnected, any
2135   outstanding data that came from that peer will be passed to the other
2136   one, and after that also the other connection will be terminated by
2137   the proxy. If there is outstanding data to that peer undelivered,
2138   that data will be discarded.
2139</t>
2140<t>
2141   An origin server which receives a CONNECT request for itself &MAY;
2142   respond with a 2xx status code to indicate that a connection is
2143   established.  However, most origin servers do not implement CONNECT.
2144</t>
2145</section>
2146</section>
2147
2148<section title="Common Protocol Parameters" anchor="common.protocol.parameters">
2149<section title="Date/Time Formats" anchor="http.date">
2150  <x:anchor-alias value="HTTP-date"/>
2151<t>
2152   HTTP applications have historically allowed three different formats
2153   for date/time stamps. However, the preferred format is a fixed-length subset
2154   of that defined by <xref target="RFC1123"/>:
2155</t>
2156<figure><artwork type="example" x:indent-with="  ">
2157Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2158</artwork></figure>
2159<t>
2160   The other formats are described here only for compatibility with obsolete
2161   implementations.
2162</t>
2163<figure><artwork type="example" x:indent-with="  ">
2164Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2165Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2166</artwork></figure>
2167<t>
2168   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2169   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2170   only generate the RFC 1123 format for representing HTTP-date values
2171   in header fields.
2172</t>
2173<t>
2174   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2175   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2176   equal to UTC (Coordinated Universal Time). This is indicated in the
2177   first two formats by the inclusion of "GMT" as the three-letter
2178   abbreviation for time zone, and &MUST; be assumed when reading the
2179   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2180   additional whitespace beyond that specifically included as SP in the
2181   grammar.
2182</t>
2183<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2184  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2185</artwork></figure>
2186<t anchor="preferred.date.format">
2187  <x:anchor-alias value="rfc1123-date"/>
2188  <x:anchor-alias value="time-of-day"/>
2189  <x:anchor-alias value="hour"/>
2190  <x:anchor-alias value="minute"/>
2191  <x:anchor-alias value="second"/>
2192  <x:anchor-alias value="day-name"/>
2193  <x:anchor-alias value="day"/>
2194  <x:anchor-alias value="month"/>
2195  <x:anchor-alias value="year"/>
2196  <x:anchor-alias value="GMT"/>
2197  Preferred format:
2198</t>
2199<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"/>
2200  <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>
2201  ; fixed length subset of the format defined in
2202  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2203 
2204  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2205               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2206               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2207               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2208               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2209               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2210               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2211               
2212  <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>
2213               ; e.g., 02 Jun 1982
2214
2215  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2216  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2217               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2218               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2219               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2220               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2221               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2222               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2223               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2224               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2225               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2226               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2227               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2228  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2229
2230  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2231
2232  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2233                 ; 00:00:00 - 23:59:59
2234                 
2235  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2236  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2237  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2238</artwork></figure>
2239<t>
2240  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2241  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2242  same as those defined for the RFC 5322 constructs
2243  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2244</t>
2245<t anchor="obsolete.date.formats">
2246  <x:anchor-alias value="obs-date"/>
2247  <x:anchor-alias value="rfc850-date"/>
2248  <x:anchor-alias value="asctime-date"/>
2249  <x:anchor-alias value="date1"/>
2250  <x:anchor-alias value="date2"/>
2251  <x:anchor-alias value="date3"/>
2252  <x:anchor-alias value="rfc1123-date"/>
2253  <x:anchor-alias value="day-name-l"/>
2254  Obsolete formats:
2255</t>
2256<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2257  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2258</artwork></figure>
2259<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2260  <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>
2261  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2262                 ; day-month-year (e.g., 02-Jun-82)
2263
2264  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2265         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2266         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2267         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2268         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2269         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2270         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2271</artwork></figure>
2272<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2273  <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>
2274  <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> ))
2275                 ; month day (e.g., Jun  2)
2276</artwork></figure>
2277<x:note>
2278  <t>
2279    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2280    accepting date values that might have been sent by non-HTTP
2281    applications, as is sometimes the case when retrieving or posting
2282    messages via proxies/gateways to SMTP or NNTP.
2283  </t>
2284</x:note>
2285<x:note>
2286  <t>
2287    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2288    to their usage within the protocol stream. Clients and servers are
2289    not required to use these formats for user presentation, request
2290    logging, etc.
2291  </t>
2292</x:note>
2293</section>
2294
2295<section title="Product Tokens" anchor="product.tokens">
2296  <x:anchor-alias value="product"/>
2297  <x:anchor-alias value="product-version"/>
2298<t>
2299   Product tokens are used to allow communicating applications to
2300   identify themselves by software name and version. Most fields using
2301   product tokens also allow sub-products which form a significant part
2302   of the application to be listed, separated by whitespace. By
2303   convention, the products are listed in order of their significance
2304   for identifying the application.
2305</t>
2306<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2307  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2308  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2309</artwork></figure>
2310<t>
2311   Examples:
2312</t>
2313<figure><artwork type="example">
2314  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2315  Server: Apache/0.8.4
2316</artwork></figure>
2317<t>
2318   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2319   used for advertising or other non-essential information. Although any
2320   token octet &MAY; appear in a product-version, this token &SHOULD;
2321   only be used for a version identifier (i.e., successive versions of
2322   the same product &SHOULD; only differ in the product-version portion of
2323   the product value).
2324</t>
2325</section>
2326</section>
2327
2328<section title="Header Field Definitions" anchor="header.field.definitions">
2329<t>
2330   This section defines the syntax and semantics of HTTP/1.1 header fields
2331   related to request and response semantics.
2332</t>
2333
2334<section title="Allow" anchor="header.allow">
2335  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2336  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2337  <x:anchor-alias value="Allow"/>
2338<t>
2339   The "Allow" header field lists the set of methods advertised as
2340   supported by the target resource. The purpose of this field is strictly to
2341   inform the recipient of valid request methods associated with the resource.
2342</t>
2343<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2344  <x:ref>Allow</x:ref> = #<x:ref>method</x:ref>
2345</artwork></figure>
2346<t>
2347   Example of use:
2348</t>
2349<figure><artwork type="example">
2350  Allow: GET, HEAD, PUT
2351</artwork></figure>
2352<t>
2353   The actual set of allowed methods is defined by the origin server at the
2354   time of each request.
2355</t>
2356<t>
2357   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2358   understand all the methods specified in order to handle them according to
2359   the generic message handling rules.
2360</t>
2361</section>
2362
2363<section title="Date" anchor="header.date">
2364  <iref primary="true" item="Date header field" x:for-anchor=""/>
2365  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
2366  <x:anchor-alias value="Date"/>
2367<t>
2368   The "Date" header field represents the date and time at which
2369   the message was originated, having the same semantics as the Origination
2370   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2371   The field value is an HTTP-date, as defined in <xref target="http.date"/>;
2372   it &MUST; be sent in rfc1123-date format.
2373</t>
2374<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2375  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
2376</artwork></figure>
2377<t>
2378   An example is
2379</t>
2380<figure><artwork type="example">
2381  Date: Tue, 15 Nov 1994 08:12:31 GMT
2382</artwork></figure>
2383<t>
2384   Origin servers &MUST; include a Date header field in all responses,
2385   except in these cases:
2386  <list style="numbers">
2387      <t>If the response status code is 100 (Continue) or 101 (Switching
2388         Protocols), the response &MAY; include a Date header field, at
2389         the server's option.</t>
2390
2391      <t>If the response status code conveys a server error, e.g., 500
2392         (Internal Server Error) or 503 (Service Unavailable), and it is
2393         inconvenient or impossible to generate a valid Date.</t>
2394
2395      <t>If the server does not have a clock that can provide a
2396         reasonable approximation of the current time, its responses
2397         &MUST-NOT; include a Date header field.</t>
2398  </list>
2399</t>
2400<t>
2401   A received message that does not have a Date header field &MUST; be
2402   assigned one by the recipient if the message will be cached by that
2403   recipient.
2404</t>
2405<t>
2406   Clients can use the Date header field as well; in order to keep request
2407   messages small, they are advised not to include it when it doesn't convey
2408   any useful information (as is usually the case for requests that do not
2409   contain a payload).
2410</t>
2411<t>
2412   The HTTP-date sent in a Date header field &SHOULD-NOT; represent a date and
2413   time subsequent to the generation of the message. It &SHOULD; represent
2414   the best available approximation of the date and time of message
2415   generation, unless the implementation has no means of generating a
2416   reasonably accurate date and time. In theory, the date ought to
2417   represent the moment just before the payload is generated. In
2418   practice, the date can be generated at any time during the message
2419   origination without affecting its semantic value.
2420</t>
2421</section>
2422
2423<section title="Expect" anchor="header.expect">
2424  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2425  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2426  <x:anchor-alias value="Expect"/>
2427  <x:anchor-alias value="expectation"/>
2428  <x:anchor-alias value="expect-param"/>
2429  <x:anchor-alias value="expect-name"/>
2430  <x:anchor-alias value="expect-value"/>
2431<t>
2432   The "Expect" header field is used to indicate that particular
2433   server behaviors are required by the client.
2434</t>
2435<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"/>
2436  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
2437 
2438  <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> ]
2439                             *( <x:ref>OWS</x:ref> ";" [ <x:ref>OWS</x:ref> <x:ref>expect-param</x:ref> ] )
2440  <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> ]
2441 
2442  <x:ref>expect-name</x:ref>  = <x:ref>token</x:ref>
2443  <x:ref>expect-value</x:ref> = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
2444</artwork></figure>
2445<t>
2446   If all received Expect header field(s) are syntactically valid but contain
2447   an expectation that the recipient does not understand or cannot comply with,
2448   the recipient &MUST; respond with a 417 (Expectation Failed) status code. A
2449   recipient of a syntactically invalid Expectation header field &MUST; respond
2450   with a 4xx status code other than 417.
2451</t>
2452<t>
2453   The only expectation defined by this specification is:
2454</t>
2455<t><iref primary="true" item="100-continue (expect value)"/><iref primary="true" item="Expect Values" subitem="100-continue"/>
2456  100-continue
2457   <list>
2458      <t>
2459        The "100-continue" expectation is defined &use100;. It does not support
2460        any expect-params.
2461      </t>
2462   </list>
2463</t>
2464<t>
2465   Comparison is case-insensitive for names (expect-name), and case-sensitive
2466   for values (expect-value).
2467</t>
2468<t>
2469   The Expect mechanism is hop-by-hop: the above requirements apply to any
2470   server, including proxies. However, the Expect header field itself is
2471   end-to-end; it &MUST; be forwarded if the request is forwarded.
2472</t>
2473<t>
2474   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect
2475   header field.
2476</t>
2477</section>
2478
2479<section title="From" anchor="header.from">
2480  <iref primary="true" item="From header field" x:for-anchor=""/>
2481  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2482  <x:anchor-alias value="From"/>
2483  <x:anchor-alias value="mailbox"/>
2484<t>
2485   The "From" header field, if given, &SHOULD; contain an Internet
2486   e-mail address for the human user who controls the requesting user
2487   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2488   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2489</t>
2490<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2491  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
2492 
2493  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2494</artwork></figure>
2495<t>
2496   An example is:
2497</t>
2498<figure><artwork type="example">
2499  From: webmaster@example.org
2500</artwork></figure>
2501<t>
2502   This header field &MAY; be used for logging purposes and as a means for
2503   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2504   be used as an insecure form of access protection. The interpretation
2505   of this field is that the request is being performed on behalf of the
2506   person given, who accepts responsibility for the method performed. In
2507   particular, robot agents &SHOULD; include this header field so that the
2508   person responsible for running the robot can be contacted if problems
2509   occur on the receiving end.
2510</t>
2511<t>
2512   The Internet e-mail address in this field &MAY; be separate from the
2513   Internet host which issued the request. For example, when a request
2514   is passed through a proxy the original issuer's address &SHOULD; be
2515   used.
2516</t>
2517<t>
2518   The client &SHOULD-NOT;  send the From header field without the user's
2519   approval, as it might conflict with the user's privacy interests or
2520   their site's security policy. It is strongly recommended that the
2521   user be able to disable, enable, and modify the value of this field
2522   at any time prior to a request.
2523</t>
2524</section>
2525
2526<section title="Location" anchor="header.location">
2527  <iref primary="true" item="Location header field" x:for-anchor=""/>
2528  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2529  <x:anchor-alias value="Location"/>
2530<t>
2531   The "Location" header field &MAY; be sent in responses to refer to
2532   a specific resource in accordance with the semantics of the status
2533   code.
2534</t>
2535<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2536  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2537</artwork></figure>
2538<t>
2539   For 201 (Created) responses, the Location is the URI of the new resource
2540   which was created by the request. For 3xx responses, the location &SHOULD;
2541   indicate the server's preferred URI for automatic redirection to the
2542   resource.
2543</t>
2544<t>
2545   The field value consists of a single URI-reference. When it has the form
2546   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2547   the final value is computed by resolving it against the effective request
2548   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>). If the original URI, as
2549   navigated to by the user agent, did contain a fragment identifier, and the
2550   final value does not, then the original URI's fragment identifier is added
2551   to the final value.
2552</t>
2553<figure>
2554<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-->
2555<artwork type="example">
2556  Location: /pub/WWW/People.html#tim
2557</artwork>
2558<postamble>would result in a final value of "http://www.example.org/pub/WWW/People.html#tim"</postamble>
2559</figure>
2560<figure>
2561<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-->
2562<artwork type="example">
2563  Location: http://www.example.net/index.html
2564</artwork>
2565<postamble>would result in a final value of "http://www.example.net/index.html#larry", preserving the original fragment identifier.</postamble>
2566</figure>
2567<x:note>
2568  <t>
2569    <x:h>Note:</x:h> Some recipients attempt to recover from Location fields
2570    that are not valid URI references. This specification does not mandate or
2571    define such processing, but does allow it (see <xref target="intro.conformance.and.error.handling"/>).
2572  </t>
2573</x:note>
2574<t>
2575   There are circumstances in which a fragment identifier in a Location URI
2576   would not be appropriate. For instance, when it appears in a 201 Created
2577   response, where the Location header field specifies the URI for the entire
2578   created resource.
2579</t>
2580<x:note>
2581  <t>
2582    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2583    from Location in that the Content-Location identifies the most specific
2584    resource corresponding to the enclosed representation.
2585    It is therefore possible for a response to contain header fields for
2586    both Location and Content-Location.
2587  </t>
2588</x:note>
2589</section>
2590
2591<section title="Max-Forwards" anchor="header.max-forwards">
2592  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2593  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2594  <x:anchor-alias value="Max-Forwards"/>
2595<t>
2596   The "Max-Forwards" header field provides a mechanism with the
2597   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2598   methods to limit the number of times that the request is forwarded by
2599   proxies. This can be useful when the client is attempting to
2600   trace a request which appears to be failing or looping mid-chain.
2601</t>
2602<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2603  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2604</artwork></figure>
2605<t>
2606   The Max-Forwards value is a decimal integer indicating the remaining
2607   number of times this request message can be forwarded.
2608</t>
2609<t>
2610   Each recipient of a TRACE or OPTIONS request
2611   containing a Max-Forwards header field &MUST; check and update its
2612   value prior to forwarding the request. If the received value is zero
2613   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2614   respond as the final recipient. If the received Max-Forwards value is
2615   greater than zero, then the forwarded message &MUST; contain an updated
2616   Max-Forwards field with a value decremented by one (1).
2617</t>
2618<t>
2619   The Max-Forwards header field &MAY; be ignored for all other request
2620   methods.
2621</t>
2622</section>
2623
2624<section title="Referer" anchor="header.referer">
2625  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2626  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2627  <x:anchor-alias value="Referer"/>
2628<t>
2629   The "Referer" [sic] header field allows the client to specify the
2630   URI of the resource from which the target URI was obtained (the
2631   "referrer", although the header field is misspelled.).
2632</t>
2633<t>
2634   The Referer header field allows servers to generate lists of back-links to
2635   resources for interest, logging, optimized caching, etc. It also allows
2636   obsolete or mistyped links to be traced for maintenance. Some servers use
2637   Referer as a means of controlling where they allow links from (so-called
2638   "deep linking"), but legitimate requests do not always
2639   contain a Referer header field.
2640</t>
2641<t>
2642   If the target URI was obtained from a source that does not have its own
2643   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2644   sent with the value "about:blank", or not be sent at all. Note that this
2645   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2646</t>
2647<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2648  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2649</artwork></figure>
2650<t>
2651   Example:
2652</t>
2653<figure><artwork type="example">
2654  Referer: http://www.example.org/hypertext/Overview.html
2655</artwork></figure>
2656<t>
2657   If the field value is a relative URI, it &SHOULD; be interpreted
2658   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2659   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2660</t>
2661</section>
2662
2663<section title="Retry-After" anchor="header.retry-after">
2664  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2665  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2666  <x:anchor-alias value="Retry-After"/>
2667<t>
2668   The header "Retry-After" field can be used with a 503 (Service
2669   Unavailable) response to indicate how long the service is expected to
2670   be unavailable to the requesting client. This field &MAY; also be used
2671   with any 3xx (Redirection) response to indicate the minimum time the
2672   user-agent is asked to wait before issuing the redirected request.
2673</t>
2674<t>
2675   The value of this field can be either an HTTP-date or an integer number
2676   of seconds (in decimal) after the time of the response.
2677</t>
2678<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2679  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2680</artwork></figure>
2681<t anchor="rule.delta-seconds">
2682  <x:anchor-alias value="delta-seconds"/>
2683   Time spans are non-negative decimal integers, representing time in
2684   seconds.
2685</t>
2686<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2687  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2688</artwork></figure>
2689<t>
2690   Two examples of its use are
2691</t>
2692<figure><artwork type="example">
2693  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2694  Retry-After: 120
2695</artwork></figure>
2696<t>
2697   In the latter example, the delay is 2 minutes.
2698</t>
2699</section>
2700
2701<section title="Server" anchor="header.server">
2702  <iref primary="true" item="Server header field" x:for-anchor=""/>
2703  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2704  <x:anchor-alias value="Server"/>
2705<t>
2706   The "Server" header field contains information about the
2707   software used by the origin server to handle the request.
2708</t>
2709<t>
2710   The field can contain multiple
2711   product tokens (<xref target="product.tokens"/>) and
2712   comments (&header-fields;) identifying the server and any significant
2713   subproducts. The product tokens are listed in order of their significance
2714   for identifying the application.
2715</t>
2716<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2717  <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> ) )
2718</artwork></figure>
2719<t>
2720   Example:
2721</t>
2722<figure><artwork type="example">
2723  Server: CERN/3.0 libwww/2.17
2724</artwork></figure>
2725<t>
2726   If the response is being forwarded through a proxy, the proxy
2727   application &MUST-NOT; modify the Server header field. Instead, it
2728   &MUST; include a Via field (as described in &header-via;).
2729</t>
2730<x:note>
2731  <t>
2732    <x:h>Note:</x:h> Revealing the specific software version of the server might
2733    allow the server machine to become more vulnerable to attacks
2734    against software that is known to contain security holes. Server
2735    implementors are encouraged to make this field a configurable
2736    option.
2737  </t>
2738</x:note>
2739</section>
2740
2741<section title="User-Agent" anchor="header.user-agent">
2742  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2743  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2744  <x:anchor-alias value="User-Agent"/>
2745<t>
2746   The "User-Agent" header field contains information about the user
2747   agent originating the request. User agents &SHOULD; include this field with
2748   requests.
2749</t>
2750<t>
2751   Typically, it is used for statistical purposes, the tracing of protocol
2752   violations, and tailoring responses to avoid particular user agent
2753   limitations.
2754</t>
2755<t>
2756   The field can contain multiple
2757   product tokens (<xref target="product.tokens"/>)
2758   and comments (&header-fields;) identifying the agent and its
2759   significant subproducts. By convention, the product tokens are listed in
2760   order of their significance for identifying the application.
2761</t>
2762<t>
2763   Because this field is usually sent on every request a user agent makes,
2764   implementations are encouraged not to include needlessly fine-grained
2765   detail, and to limit (or even prohibit) the addition of subproducts by third
2766   parties. Overly long and detailed User-Agent field values make requests
2767   larger and can also be used to identify ("fingerprint") the user against
2768   their wishes.
2769</t>
2770<t>
2771   Likewise, implementations are encouraged not to use the product tokens of
2772   other implementations in order to declare compatibility with them, as this
2773   circumvents the purpose of the field. Finally, they are encouraged not to
2774   use comments to identify products; doing so makes the field value more
2775   difficult to parse.
2776</t>
2777<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2778  <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> ) )
2779</artwork></figure>
2780<t>
2781   Example:
2782</t>
2783<figure><artwork type="example">
2784  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2785</artwork></figure>
2786</section>
2787
2788</section>
2789
2790<section title="IANA Considerations" anchor="IANA.considerations">
2791
2792<section title="Method Registry" anchor="method.registration">
2793<t>
2794  The registration procedure for HTTP request methods is defined by
2795  <xref target="method.registry"/> of this document.
2796</t>
2797<t>
2798   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2799   and be populated with the registrations below:
2800</t>
2801<?BEGININC p2-semantics.iana-methods ?>
2802<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2803<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2804   <ttcol>Method</ttcol>
2805   <ttcol>Safe</ttcol>
2806   <ttcol>Reference</ttcol>
2807   <c>CONNECT</c>
2808   <c>no</c>
2809   <c>
2810      <xref target="CONNECT"/>
2811   </c>
2812   <c>DELETE</c>
2813   <c>no</c>
2814   <c>
2815      <xref target="DELETE"/>
2816   </c>
2817   <c>GET</c>
2818   <c>yes</c>
2819   <c>
2820      <xref target="GET"/>
2821   </c>
2822   <c>HEAD</c>
2823   <c>yes</c>
2824   <c>
2825      <xref target="HEAD"/>
2826   </c>
2827   <c>OPTIONS</c>
2828   <c>yes</c>
2829   <c>
2830      <xref target="OPTIONS"/>
2831   </c>
2832   <c>POST</c>
2833   <c>no</c>
2834   <c>
2835      <xref target="POST"/>
2836   </c>
2837   <c>PUT</c>
2838   <c>no</c>
2839   <c>
2840      <xref target="PUT"/>
2841   </c>
2842   <c>TRACE</c>
2843   <c>yes</c>
2844   <c>
2845      <xref target="TRACE"/>
2846   </c>
2847</texttable>
2848<!--(END)-->
2849<?ENDINC p2-semantics.iana-methods ?>
2850</section>
2851
2852<section title="Status Code Registry" anchor="status.code.registration">
2853<t>
2854   The registration procedure for HTTP Status Codes &mdash; previously defined
2855   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2856   by <xref target="status.code.registry"/> of this document.
2857</t>
2858<t>
2859   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2860   shall be updated with the registrations below:
2861</t>
2862<?BEGININC p2-semantics.iana-status-codes ?>
2863<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2864<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2865   <ttcol>Value</ttcol>
2866   <ttcol>Description</ttcol>
2867   <ttcol>Reference</ttcol>
2868   <c>100</c>
2869   <c>Continue</c>
2870   <c>
2871      <xref target="status.100"/>
2872   </c>
2873   <c>101</c>
2874   <c>Switching Protocols</c>
2875   <c>
2876      <xref target="status.101"/>
2877   </c>
2878   <c>200</c>
2879   <c>OK</c>
2880   <c>
2881      <xref target="status.200"/>
2882   </c>
2883   <c>201</c>
2884   <c>Created</c>
2885   <c>
2886      <xref target="status.201"/>
2887   </c>
2888   <c>202</c>
2889   <c>Accepted</c>
2890   <c>
2891      <xref target="status.202"/>
2892   </c>
2893   <c>203</c>
2894   <c>Non-Authoritative Information</c>
2895   <c>
2896      <xref target="status.203"/>
2897   </c>
2898   <c>204</c>
2899   <c>No Content</c>
2900   <c>
2901      <xref target="status.204"/>
2902   </c>
2903   <c>205</c>
2904   <c>Reset Content</c>
2905   <c>
2906      <xref target="status.205"/>
2907   </c>
2908   <c>300</c>
2909   <c>Multiple Choices</c>
2910   <c>
2911      <xref target="status.300"/>
2912   </c>
2913   <c>301</c>
2914   <c>Moved Permanently</c>
2915   <c>
2916      <xref target="status.301"/>
2917   </c>
2918   <c>302</c>
2919   <c>Found</c>
2920   <c>
2921      <xref target="status.302"/>
2922   </c>
2923   <c>303</c>
2924   <c>See Other</c>
2925   <c>
2926      <xref target="status.303"/>
2927   </c>
2928   <c>305</c>
2929   <c>Use Proxy</c>
2930   <c>
2931      <xref target="status.305"/>
2932   </c>
2933   <c>306</c>
2934   <c>(Unused)</c>
2935   <c>
2936      <xref target="status.306"/>
2937   </c>
2938   <c>307</c>
2939   <c>Temporary Redirect</c>
2940   <c>
2941      <xref target="status.307"/>
2942   </c>
2943   <c>400</c>
2944   <c>Bad Request</c>
2945   <c>
2946      <xref target="status.400"/>
2947   </c>
2948   <c>402</c>
2949   <c>Payment Required</c>
2950   <c>
2951      <xref target="status.402"/>
2952   </c>
2953   <c>403</c>
2954   <c>Forbidden</c>
2955   <c>
2956      <xref target="status.403"/>
2957   </c>
2958   <c>404</c>
2959   <c>Not Found</c>
2960   <c>
2961      <xref target="status.404"/>
2962   </c>
2963   <c>405</c>
2964   <c>Method Not Allowed</c>
2965   <c>
2966      <xref target="status.405"/>
2967   </c>
2968   <c>406</c>
2969   <c>Not Acceptable</c>
2970   <c>
2971      <xref target="status.406"/>
2972   </c>
2973   <c>408</c>
2974   <c>Request Timeout</c>
2975   <c>
2976      <xref target="status.408"/>
2977   </c>
2978   <c>409</c>
2979   <c>Conflict</c>
2980   <c>
2981      <xref target="status.409"/>
2982   </c>
2983   <c>410</c>
2984   <c>Gone</c>
2985   <c>
2986      <xref target="status.410"/>
2987   </c>
2988   <c>411</c>
2989   <c>Length Required</c>
2990   <c>
2991      <xref target="status.411"/>
2992   </c>
2993   <c>413</c>
2994   <c>Request Representation Too Large</c>
2995   <c>
2996      <xref target="status.413"/>
2997   </c>
2998   <c>414</c>
2999   <c>URI Too Long</c>
3000   <c>
3001      <xref target="status.414"/>
3002   </c>
3003   <c>415</c>
3004   <c>Unsupported Media Type</c>
3005   <c>
3006      <xref target="status.415"/>
3007   </c>
3008   <c>417</c>
3009   <c>Expectation Failed</c>
3010   <c>
3011      <xref target="status.417"/>
3012   </c>
3013   <c>426</c>
3014   <c>Upgrade Required</c>
3015   <c>
3016      <xref target="status.426"/>
3017   </c>
3018   <c>500</c>
3019   <c>Internal Server Error</c>
3020   <c>
3021      <xref target="status.500"/>
3022   </c>
3023   <c>501</c>
3024   <c>Not Implemented</c>
3025   <c>
3026      <xref target="status.501"/>
3027   </c>
3028   <c>502</c>
3029   <c>Bad Gateway</c>
3030   <c>
3031      <xref target="status.502"/>
3032   </c>
3033   <c>503</c>
3034   <c>Service Unavailable</c>
3035   <c>
3036      <xref target="status.503"/>
3037   </c>
3038   <c>504</c>
3039   <c>Gateway Timeout</c>
3040   <c>
3041      <xref target="status.504"/>
3042   </c>
3043   <c>505</c>
3044   <c>HTTP Version Not Supported</c>
3045   <c>
3046      <xref target="status.505"/>
3047   </c>
3048</texttable>
3049<!--(END)-->
3050<?ENDINC p2-semantics.iana-status-codes ?>
3051</section>
3052<section title="Header Field Registration" anchor="header.field.registration">
3053<t>
3054   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3055   with the permanent registrations below (see <xref target="RFC3864"/>):
3056</t>
3057<?BEGININC p2-semantics.iana-headers ?>
3058<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3059<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3060   <ttcol>Header Field Name</ttcol>
3061   <ttcol>Protocol</ttcol>
3062   <ttcol>Status</ttcol>
3063   <ttcol>Reference</ttcol>
3064
3065   <c>Allow</c>
3066   <c>http</c>
3067   <c>standard</c>
3068   <c>
3069      <xref target="header.allow"/>
3070   </c>
3071   <c>Date</c>
3072   <c>http</c>
3073   <c>standard</c>
3074   <c>
3075      <xref target="header.date"/>
3076   </c>
3077   <c>Expect</c>
3078   <c>http</c>
3079   <c>standard</c>
3080   <c>
3081      <xref target="header.expect"/>
3082   </c>
3083   <c>From</c>
3084   <c>http</c>
3085   <c>standard</c>
3086   <c>
3087      <xref target="header.from"/>
3088   </c>
3089   <c>Location</c>
3090   <c>http</c>
3091   <c>standard</c>
3092   <c>
3093      <xref target="header.location"/>
3094   </c>
3095   <c>Max-Forwards</c>
3096   <c>http</c>
3097   <c>standard</c>
3098   <c>
3099      <xref target="header.max-forwards"/>
3100   </c>
3101   <c>Referer</c>
3102   <c>http</c>
3103   <c>standard</c>
3104   <c>
3105      <xref target="header.referer"/>
3106   </c>
3107   <c>Retry-After</c>
3108   <c>http</c>
3109   <c>standard</c>
3110   <c>
3111      <xref target="header.retry-after"/>
3112   </c>
3113   <c>Server</c>
3114   <c>http</c>
3115   <c>standard</c>
3116   <c>
3117      <xref target="header.server"/>
3118   </c>
3119   <c>User-Agent</c>
3120   <c>http</c>
3121   <c>standard</c>
3122   <c>
3123      <xref target="header.user-agent"/>
3124   </c>
3125</texttable>
3126<!--(END)-->
3127<?ENDINC p2-semantics.iana-headers ?>
3128<t>
3129   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3130</t>
3131</section>
3132</section>
3133
3134<section title="Security Considerations" anchor="security.considerations">
3135<t>
3136   This section is meant to inform application developers, information
3137   providers, and users of the security limitations in HTTP/1.1 as
3138   described by this document. The discussion does not include
3139   definitive solutions to the problems revealed, though it does make
3140   some suggestions for reducing security risks.
3141</t>
3142
3143<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3144<t>
3145   Like any generic data transfer protocol, HTTP cannot regulate the
3146   content of the data that is transferred, nor is there any a priori
3147   method of determining the sensitivity of any particular piece of
3148   information within the context of any given request. Therefore,
3149   applications &SHOULD; supply as much control over this information as
3150   possible to the provider of that information. Four header fields are
3151   worth special mention in this context: Server, Via, Referer and From.
3152</t>
3153<t>
3154   Revealing the specific software version of the server might allow the
3155   server machine to become more vulnerable to attacks against software
3156   that is known to contain security holes. Implementors &SHOULD; make the
3157   Server header field a configurable option.
3158</t>
3159<t>
3160   Proxies which serve as a portal through a network firewall &SHOULD;
3161   take special precautions regarding the transfer of header information
3162   that identifies the hosts behind the firewall. In particular, they
3163   &SHOULD; remove, or replace with sanitized versions, any Via fields
3164   generated behind the firewall.
3165</t>
3166<t>
3167   The Referer header field allows reading patterns to be studied and reverse
3168   links drawn. Although it can be very useful, its power can be abused
3169   if user details are not separated from the information contained in
3170   the Referer. Even when the personal information has been removed, the
3171   Referer header field might indicate a private document's URI whose
3172   publication would be inappropriate.
3173</t>
3174<t>
3175   The information sent in the From field might conflict with the user's
3176   privacy interests or their site's security policy, and hence it
3177   &SHOULD-NOT;  be transmitted without the user being able to disable,
3178   enable, and modify the contents of the field. The user &MUST; be able
3179   to set the contents of this field within a user preference or
3180   application defaults configuration.
3181</t>
3182<t>
3183   We suggest, though do not require, that a convenient toggle interface
3184   be provided for the user to enable or disable the sending of From and
3185   Referer information.
3186</t>
3187<t>
3188   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3189   target="header.server"/>) header fields can sometimes be used to determine
3190   that a specific client or server has a particular security hole which might
3191   be exploited. Unfortunately, this same information is often used for other
3192   valuable purposes for which HTTP currently has no better mechanism.
3193</t>
3194<t>
3195   Furthermore, the User-Agent header field may contain enough entropy to be
3196   used, possibly in conjunction with other material, to uniquely identify the
3197   user.
3198</t>
3199<t>
3200   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3201   that was sent in request header fields within the body of their response.
3202   Clients &SHOULD; be careful with sensitive information, like Cookies,
3203   Authorization credentials, and other header fields that might be used to
3204   collect data from the client.
3205</t> 
3206</section>
3207
3208<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3209<t>
3210   Because the source of a link might be private information or might
3211   reveal an otherwise private information source, it is strongly
3212   recommended that the user be able to select whether or not the
3213   Referer field is sent. For example, a browser client could have a
3214   toggle switch for browsing openly/anonymously, which would
3215   respectively enable/disable the sending of Referer and From
3216   information.
3217</t>
3218<t>
3219   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3220   HTTP request if the referring page was transferred with a secure
3221   protocol.
3222</t>
3223<t>
3224   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3225   sensitive data because that data will be placed in the request-target. Many
3226   existing servers, proxies, and user agents log or display the request-target
3227   in places where it might be visible to third parties. Such services can
3228   use POST-based form submission instead.
3229</t>
3230</section>
3231
3232<section title="Location Header Fields: Spoofing and Information Leakage" anchor="location.spoofing-leakage">
3233<t>
3234   If a single server supports multiple organizations that do not trust
3235   one another, then it &MUST; check the values of Location and Content-Location
3236   header fields in responses that are generated under control of
3237   said organizations to make sure that they do not attempt to
3238   invalidate resources over which they have no authority.
3239</t>
3240<t>
3241   Furthermore, appending the fragment identifier from one URI to another
3242   one obtained from a Location header field might leak confidential
3243   information to the target server &mdash; although the fragment identifier is
3244   not transmitted in the final request, it might be visible to the user agent
3245   through other means, such as scripting.
3246</t>
3247</section>
3248
3249<section title="Security Considerations for CONNECT">
3250<t>
3251   Since tunneled data is opaque to the proxy, there are additional
3252   risks to tunneling to other well-known or reserved ports.
3253   A HTTP client CONNECTing to port 25 could relay spam
3254   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3255   access to a small number of known ports.
3256</t>
3257</section>
3258
3259</section>
3260
3261<section title="Acknowledgments" anchor="acks">
3262<t>
3263  See &acks;.
3264</t>
3265</section>
3266</middle>
3267<back>
3268
3269<references title="Normative References">
3270
3271<reference anchor="Part1">
3272  <front>
3273    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3274    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3275      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3276      <address><email>fielding@gbiv.com</email></address>
3277    </author>
3278    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3279      <organization abbrev="W3C">World Wide Web Consortium</organization>
3280      <address><email>ylafon@w3.org</email></address>
3281    </author>
3282    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3283      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3284      <address><email>julian.reschke@greenbytes.de</email></address>
3285    </author>
3286    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3287  </front>
3288  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3289  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3290</reference>
3291
3292<reference anchor="Part3">
3293  <front>
3294    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3295    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3296      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3297      <address><email>fielding@gbiv.com</email></address>
3298    </author>
3299    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3300      <organization abbrev="W3C">World Wide Web Consortium</organization>
3301      <address><email>ylafon@w3.org</email></address>
3302    </author>
3303    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3304      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3305      <address><email>julian.reschke@greenbytes.de</email></address>
3306    </author>
3307    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3308  </front>
3309  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3310  <x:source href="p3-payload.xml" basename="p3-payload"/>
3311</reference>
3312
3313<reference anchor="Part4">
3314  <front>
3315    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3316    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3317      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3318      <address><email>fielding@gbiv.com</email></address>
3319    </author>
3320    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3321      <organization abbrev="W3C">World Wide Web Consortium</organization>
3322      <address><email>ylafon@w3.org</email></address>
3323    </author>
3324    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3325      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3326      <address><email>julian.reschke@greenbytes.de</email></address>
3327    </author>
3328    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3329  </front>
3330  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3331  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3332</reference>
3333
3334<reference anchor="Part5">
3335  <front>
3336    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3337    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3338      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3339      <address><email>fielding@gbiv.com</email></address>
3340    </author>
3341    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3342      <organization abbrev="W3C">World Wide Web Consortium</organization>
3343      <address><email>ylafon@w3.org</email></address>
3344    </author>
3345    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3346      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3347      <address><email>julian.reschke@greenbytes.de</email></address>
3348    </author>
3349    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3350  </front>
3351  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3352  <x:source href="p5-range.xml" basename="p5-range"/>
3353</reference>
3354
3355<reference anchor="Part6">
3356  <front>
3357    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3358    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3359      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3360      <address><email>fielding@gbiv.com</email></address>
3361    </author>
3362    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3363      <organization abbrev="W3C">World Wide Web Consortium</organization>
3364      <address><email>ylafon@w3.org</email></address>
3365    </author>
3366    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3367      <organization>Rackspace</organization>
3368      <address><email>mnot@mnot.net</email></address>
3369    </author>
3370    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3371      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3372      <address><email>julian.reschke@greenbytes.de</email></address>
3373    </author>
3374    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3375  </front>
3376  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3377  <x:source href="p6-cache.xml" basename="p6-cache"/>
3378</reference>
3379
3380<reference anchor="Part7">
3381  <front>
3382    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3383    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3384      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3385      <address><email>fielding@gbiv.com</email></address>
3386    </author>
3387    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3388      <organization abbrev="W3C">World Wide Web Consortium</organization>
3389      <address><email>ylafon@w3.org</email></address>
3390    </author>
3391    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3392      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3393      <address><email>julian.reschke@greenbytes.de</email></address>
3394    </author>
3395    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3396  </front>
3397  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3398  <x:source href="p7-auth.xml" basename="p7-auth"/>
3399</reference>
3400
3401<reference anchor="RFC2119">
3402  <front>
3403    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3404    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3405      <organization>Harvard University</organization>
3406      <address><email>sob@harvard.edu</email></address>
3407    </author>
3408    <date month="March" year="1997"/>
3409  </front>
3410  <seriesInfo name="BCP" value="14"/>
3411  <seriesInfo name="RFC" value="2119"/>
3412</reference>
3413
3414<reference anchor="RFC3986">
3415 <front>
3416  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3417  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3418    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3419    <address>
3420       <email>timbl@w3.org</email>
3421       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3422    </address>
3423  </author>
3424  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3425    <organization abbrev="Day Software">Day Software</organization>
3426    <address>
3427      <email>fielding@gbiv.com</email>
3428      <uri>http://roy.gbiv.com/</uri>
3429    </address>
3430  </author>
3431  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3432    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3433    <address>
3434      <email>LMM@acm.org</email>
3435      <uri>http://larry.masinter.net/</uri>
3436    </address>
3437  </author>
3438  <date month='January' year='2005'></date>
3439 </front>
3440 <seriesInfo name="STD" value="66"/>
3441 <seriesInfo name="RFC" value="3986"/>
3442</reference>
3443
3444<reference anchor="RFC5234">
3445  <front>
3446    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3447    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3448      <organization>Brandenburg InternetWorking</organization>
3449      <address>
3450        <email>dcrocker@bbiw.net</email>
3451      </address> 
3452    </author>
3453    <author initials="P." surname="Overell" fullname="Paul Overell">
3454      <organization>THUS plc.</organization>
3455      <address>
3456        <email>paul.overell@thus.net</email>
3457      </address>
3458    </author>
3459    <date month="January" year="2008"/>
3460  </front>
3461  <seriesInfo name="STD" value="68"/>
3462  <seriesInfo name="RFC" value="5234"/>
3463</reference>
3464
3465</references>
3466
3467<references title="Informative References">
3468
3469<reference anchor="RFC1123">
3470  <front>
3471    <title>Requirements for Internet Hosts - Application and Support</title>
3472    <author initials="R." surname="Braden" fullname="Robert Braden">
3473      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3474      <address><email>Braden@ISI.EDU</email></address>
3475    </author>
3476    <date month="October" year="1989"/>
3477  </front>
3478  <seriesInfo name="STD" value="3"/>
3479  <seriesInfo name="RFC" value="1123"/>
3480</reference>
3481
3482<reference anchor="RFC1945">
3483  <front>
3484    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3485    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3486      <organization>MIT, Laboratory for Computer Science</organization>
3487      <address><email>timbl@w3.org</email></address>
3488    </author>
3489    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3490      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3491      <address><email>fielding@ics.uci.edu</email></address>
3492    </author>
3493    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3494      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3495      <address><email>frystyk@w3.org</email></address>
3496    </author>
3497    <date month="May" year="1996"/>
3498  </front>
3499  <seriesInfo name="RFC" value="1945"/>
3500</reference>
3501
3502<reference anchor="RFC2068">
3503  <front>
3504    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3505    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3506      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3507      <address><email>fielding@ics.uci.edu</email></address>
3508    </author>
3509    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3510      <organization>MIT Laboratory for Computer Science</organization>
3511      <address><email>jg@w3.org</email></address>
3512    </author>
3513    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3514      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3515      <address><email>mogul@wrl.dec.com</email></address>
3516    </author>
3517    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3518      <organization>MIT Laboratory for Computer Science</organization>
3519      <address><email>frystyk@w3.org</email></address>
3520    </author>
3521    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3522      <organization>MIT Laboratory for Computer Science</organization>
3523      <address><email>timbl@w3.org</email></address>
3524    </author>
3525    <date month="January" year="1997"/>
3526  </front>
3527  <seriesInfo name="RFC" value="2068"/>
3528</reference>
3529
3530<reference anchor="RFC2616">
3531  <front>
3532    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3533    <author initials="R." surname="Fielding" fullname="R. Fielding">
3534      <organization>University of California, Irvine</organization>
3535      <address><email>fielding@ics.uci.edu</email></address>
3536    </author>
3537    <author initials="J." surname="Gettys" fullname="J. Gettys">
3538      <organization>W3C</organization>
3539      <address><email>jg@w3.org</email></address>
3540    </author>
3541    <author initials="J." surname="Mogul" fullname="J. Mogul">
3542      <organization>Compaq Computer Corporation</organization>
3543      <address><email>mogul@wrl.dec.com</email></address>
3544    </author>
3545    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3546      <organization>MIT Laboratory for Computer Science</organization>
3547      <address><email>frystyk@w3.org</email></address>
3548    </author>
3549    <author initials="L." surname="Masinter" fullname="L. Masinter">
3550      <organization>Xerox Corporation</organization>
3551      <address><email>masinter@parc.xerox.com</email></address>
3552    </author>
3553    <author initials="P." surname="Leach" fullname="P. Leach">
3554      <organization>Microsoft Corporation</organization>
3555      <address><email>paulle@microsoft.com</email></address>
3556    </author>
3557    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3558      <organization>W3C</organization>
3559      <address><email>timbl@w3.org</email></address>
3560    </author>
3561    <date month="June" year="1999"/>
3562  </front>
3563  <seriesInfo name="RFC" value="2616"/>
3564</reference>
3565
3566<reference anchor='RFC2817'>
3567  <front>
3568    <title>Upgrading to TLS Within HTTP/1.1</title>
3569    <author initials='R.' surname='Khare' fullname='R. Khare'>
3570      <organization>4K Associates / UC Irvine</organization>
3571      <address><email>rohit@4K-associates.com</email></address>
3572    </author>
3573    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3574      <organization>Agranat Systems, Inc.</organization>
3575      <address><email>lawrence@agranat.com</email></address>
3576    </author>
3577    <date year='2000' month='May' />
3578  </front>
3579  <seriesInfo name='RFC' value='2817' />
3580</reference>
3581
3582<reference anchor='RFC3864'>
3583  <front>
3584    <title>Registration Procedures for Message Header Fields</title>
3585    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3586      <organization>Nine by Nine</organization>
3587      <address><email>GK-IETF@ninebynine.org</email></address>
3588    </author>
3589    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3590      <organization>BEA Systems</organization>
3591      <address><email>mnot@pobox.com</email></address>
3592    </author>
3593    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3594      <organization>HP Labs</organization>
3595      <address><email>JeffMogul@acm.org</email></address>
3596    </author>
3597    <date year='2004' month='September' />
3598  </front>
3599  <seriesInfo name='BCP' value='90' />
3600  <seriesInfo name='RFC' value='3864' />
3601</reference>
3602
3603<reference anchor='RFC5226'>
3604  <front>
3605    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3606    <author initials='T.' surname='Narten' fullname='T. Narten'>
3607      <organization>IBM</organization>
3608      <address><email>narten@us.ibm.com</email></address>
3609    </author>
3610    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3611      <organization>Google</organization>
3612      <address><email>Harald@Alvestrand.no</email></address>
3613    </author>
3614    <date year='2008' month='May' />
3615  </front>
3616  <seriesInfo name='BCP' value='26' />
3617  <seriesInfo name='RFC' value='5226' />
3618</reference>
3619
3620<reference anchor="RFC5322">
3621  <front>
3622    <title>Internet Message Format</title>
3623    <author initials="P." surname="Resnick" fullname="P. Resnick">
3624      <organization>Qualcomm Incorporated</organization>
3625    </author>
3626    <date year="2008" month="October"/>
3627  </front> 
3628  <seriesInfo name="RFC" value="5322"/>
3629</reference>
3630
3631<reference anchor='RFC5789'>
3632  <front>
3633    <title>PATCH Method for HTTP</title>
3634    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3635      <organization>Linden Lab</organization>
3636    </author>
3637    <author initials='J.' surname='Snell' fullname='J. Snell' />
3638    <date year='2010' month='March' />
3639  </front>
3640  <seriesInfo name='RFC' value='5789' />
3641</reference>
3642
3643<reference anchor="RFC5987">
3644        <front>
3645    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3646    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3647      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3648      <address>
3649        <postal>
3650          <street>Hafenweg 16</street>
3651          <city>Muenster</city><region>NW</region><code>48155</code>
3652          <country>Germany</country>
3653        </postal>
3654        <email>julian.reschke@greenbytes.de</email>     
3655        <uri>http://greenbytes.de/tech/webdav/</uri>   
3656      </address>
3657    </author>
3658    <date month="August" year="2010"/>
3659  </front>
3660  <seriesInfo name="RFC" value="5987"/>
3661</reference>
3662
3663<reference anchor="draft-reschke-http-status-308">
3664        <front>
3665    <title abbrev="HTTP Status Code 308">The Hypertext Transfer Protocol (HTTP) Status Code 308 (Permanent Redirect)</title>
3666    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3667      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3668      <address>
3669        <email>julian.reschke@greenbytes.de</email>     
3670      </address>
3671    </author>
3672    <date month="March" year="2012"/>
3673  </front>
3674  <seriesInfo name="Internet-Draft" value="draft-reschke-http-status-308-07"/>
3675</reference>
3676
3677</references>
3678
3679<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3680<t>
3681  This document takes over the Status Code Registry, previously defined
3682  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3683  (<xref target="status.code.registry"/>)
3684</t>
3685<t>
3686  Broadened the definition of 203 (Non-Authoritative Information) to include
3687  cases of payload transformations as well.
3688  (<xref target="status.203"/>)
3689</t>
3690<t>
3691  Status codes 301, 302, and 307: removed the normative requirements on both
3692  response payloads and user interaction.
3693  (<xref target="status.3xx"/>)
3694</t>
3695<t>
3696  Failed to consider that there are many other request methods that are safe
3697  to automatically redirect, and further that the user agent is able to make
3698  that determination based on the request method semantics.
3699  Furthermore, allow user agents to rewrite the method from POST to GET
3700  for status codes 301 and 302.
3701  (Sections <xref format="counter" target="status.301"/>,
3702  <xref format="counter" target="status.302"/> and
3703  <xref format="counter" target="status.307"/>)
3704</t>
3705<t>
3706  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3707  It used to indicate that the target resource needs to be accessed through the
3708  proxy given by the Location field. The Location field gave the URI of the
3709  proxy. The recipient was expected to repeat this single request via the proxy.
3710  (<xref target="status.305"/>)
3711</t>
3712<t>
3713  Define status 426 (Upgrade Required) (this was incorporated from
3714  <xref target="RFC2817"/>).
3715  (<xref target="status.426"/>)
3716</t>
3717<t>
3718  Clarify definition of POST.
3719  (<xref target="POST"/>)
3720</t>
3721<t>
3722  Remove requirement to handle all Content-* header fields; ban use of
3723  Content-Range with PUT.
3724  (<xref target="PUT"/>)
3725</t>
3726<t>
3727  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3728  (<xref target="CONNECT"/>)
3729</t>
3730<t>
3731  Change ABNF productions for header fields to only define the field value.
3732  (<xref target="header.field.definitions"/>)
3733</t>
3734<t>
3735  Reclassify "Allow" as response header field, removing the option to
3736  specify it in a PUT request.
3737  Relax the server requirement on the contents of the Allow header field and
3738  remove requirement on clients to always trust the header field value.
3739  (<xref target="header.allow"/>)
3740</t>
3741<t>
3742  The ABNF for the Expect header field has been both fixed (allowing parameters
3743  for value-less expectations as well) and simplified (allowing trailing
3744  semicolons after "100-continue" when they were invalid before).
3745  (<xref target="header.expect"/>)
3746</t>
3747<t>
3748  Correct syntax of Location header field to allow URI references (including
3749  relative references and fragments), as referred symbol "absoluteURI" wasn't
3750  what was expected, and add some clarifications as to when use of fragments
3751  would not be appropriate.
3752  (<xref target="header.location"/>)
3753</t>
3754<t>
3755  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
3756  extension methods could have used it as well).
3757  (<xref target="header.max-forwards"/>)
3758</t>
3759<t>
3760  Allow Referer field value of "about:blank" as alternative to not specifying it.
3761  (<xref target="header.referer"/>)
3762</t>
3763<t>
3764  In the description of the Server header field, the Via field
3765  was described as a SHOULD. The requirement was and is stated
3766  correctly in the description of the Via header field in &header-via;.
3767  (<xref target="header.server"/>)
3768</t>
3769</section>
3770
3771<?BEGININC p2-semantics.abnf-appendix ?>
3772<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
3773<figure>
3774<artwork type="abnf" name="p2-semantics.parsed-abnf">
3775<x:ref>Allow</x:ref> = [ ( "," / method ) *( OWS "," [ OWS method ] ) ]
3776
3777<x:ref>BWS</x:ref> = &lt;BWS, defined in [Part1], Section 3.2.1&gt;
3778
3779<x:ref>Date</x:ref> = HTTP-date
3780
3781<x:ref>Expect</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
3782
3783<x:ref>From</x:ref> = mailbox
3784
3785<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
3786
3787<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
3788
3789<x:ref>Location</x:ref> = URI-reference
3790
3791<x:ref>Max-Forwards</x:ref> = 1*DIGIT
3792
3793<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 3.2.1&gt;
3794
3795<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 3.2.1&gt;
3796<x:ref>Referer</x:ref> = absolute-URI / partial-URI
3797<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
3798
3799<x:ref>Server</x:ref> = product *( RWS ( product / comment ) )
3800
3801<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
3802<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
3803
3804<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
3805<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
3806
3807<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2.4&gt;
3808
3809<x:ref>date1</x:ref> = day SP month SP year
3810<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
3811<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
3812<x:ref>day</x:ref> = 2DIGIT
3813<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
3814 / %x54.75.65 ; Tue
3815 / %x57.65.64 ; Wed
3816 / %x54.68.75 ; Thu
3817 / %x46.72.69 ; Fri
3818 / %x53.61.74 ; Sat
3819 / %x53.75.6E ; Sun
3820<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
3821 / %x54.75.65.73.64.61.79 ; Tuesday
3822 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
3823 / %x54.68.75.72.73.64.61.79 ; Thursday
3824 / %x46.72.69.64.61.79 ; Friday
3825 / %x53.61.74.75.72.64.61.79 ; Saturday
3826 / %x53.75.6E.64.61.79 ; Sunday
3827<x:ref>delta-seconds</x:ref> = 1*DIGIT
3828
3829<x:ref>expect-name</x:ref> = token
3830<x:ref>expect-param</x:ref> = expect-name [ BWS "=" BWS expect-value ]
3831<x:ref>expect-value</x:ref> = token / quoted-string
3832<x:ref>expectation</x:ref> = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
3833 OWS expect-param ] )
3834
3835<x:ref>hour</x:ref> = 2DIGIT
3836
3837<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
3838<x:ref>method</x:ref> = token
3839<x:ref>minute</x:ref> = 2DIGIT
3840<x:ref>month</x:ref> = %x4A.61.6E ; Jan
3841 / %x46.65.62 ; Feb
3842 / %x4D.61.72 ; Mar
3843 / %x41.70.72 ; Apr
3844 / %x4D.61.79 ; May
3845 / %x4A.75.6E ; Jun
3846 / %x4A.75.6C ; Jul
3847 / %x41.75.67 ; Aug
3848 / %x53.65.70 ; Sep
3849 / %x4F.63.74 ; Oct
3850 / %x4E.6F.76 ; Nov
3851 / %x44.65.63 ; Dec
3852
3853<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
3854<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 3.2.4&gt;
3855
3856<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
3857<x:ref>product</x:ref> = token [ "/" product-version ]
3858<x:ref>product-version</x:ref> = token
3859
3860<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.4&gt;
3861
3862<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
3863<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
3864<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
3865
3866<x:ref>second</x:ref> = 2DIGIT
3867<x:ref>status-code</x:ref> = 3DIGIT
3868
3869<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
3870<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.4&gt;
3871
3872<x:ref>year</x:ref> = 4DIGIT
3873</artwork>
3874</figure>
3875<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
3876; Allow defined but not used
3877; Date defined but not used
3878; Expect defined but not used
3879; From defined but not used
3880; Location defined but not used
3881; Max-Forwards defined but not used
3882; Referer defined but not used
3883; Retry-After defined but not used
3884; Server defined but not used
3885; User-Agent defined but not used
3886; reason-phrase defined but not used
3887; status-code defined but not used
3888</artwork></figure></section>
3889<?ENDINC p2-semantics.abnf-appendix ?>
3890
3891<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
3892
3893<section title="Since RFC 2616">
3894<t>
3895  Extracted relevant partitions from <xref target="RFC2616"/>.
3896</t>
3897</section>
3898
3899<section title="Since draft-ietf-httpbis-p2-semantics-00">
3900<t>
3901  Closed issues:
3902  <list style="symbols"> 
3903    <t>
3904      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
3905      "Via is a MUST"
3906      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
3907    </t>
3908    <t>
3909      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
3910      "Fragments allowed in Location"
3911      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
3912    </t>
3913    <t>
3914      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
3915      "Safe Methods vs Redirection"
3916      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
3917    </t>
3918    <t>
3919      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
3920      "Revise description of the POST method"
3921      (<eref target="http://purl.org/NET/http-errata#post"/>)
3922    </t>
3923    <t>
3924      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
3925      "Normative and Informative references"
3926    </t>
3927    <t>
3928      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
3929      "RFC2606 Compliance"
3930    </t>
3931    <t>
3932      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
3933      "Informative references"
3934    </t>
3935    <t>
3936      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
3937      "Redundant cross-references"
3938    </t>
3939  </list>
3940</t>
3941<t>
3942  Other changes:
3943  <list style="symbols"> 
3944    <t>
3945      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
3946    </t>
3947  </list>
3948</t>
3949</section>
3950
3951<section title="Since draft-ietf-httpbis-p2-semantics-01">
3952<t>
3953  Closed issues:
3954  <list style="symbols"> 
3955    <t>
3956      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
3957      "PUT side effects"
3958    </t>
3959    <t>
3960      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
3961      "Duplicate Host header requirements"
3962    </t>
3963  </list>
3964</t>
3965<t>
3966  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3967  <list style="symbols"> 
3968    <t>
3969      Move "Product Tokens" section (back) into Part 1, as "token" is used
3970      in the definition of the Upgrade header field.
3971    </t>
3972    <t>
3973      Add explicit references to BNF syntax and rules imported from other parts of the specification.
3974    </t>
3975    <t>
3976      Copy definition of delta-seconds from Part6 instead of referencing it.
3977    </t>
3978  </list>
3979</t>
3980</section>
3981
3982<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
3983<t>
3984  Closed issues:
3985  <list style="symbols"> 
3986    <t>
3987      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
3988      "Requiring Allow in 405 responses"
3989    </t>
3990    <t>
3991      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
3992      "Status Code Registry"
3993    </t>
3994    <t>
3995      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
3996      "Redirection vs. Location"
3997    </t>
3998    <t>
3999      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
4000      "Cacheability of 303 response"
4001    </t>
4002    <t>
4003      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
4004      "305 Use Proxy"
4005    </t>
4006    <t>
4007      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
4008      "Classification for Allow header"
4009    </t>
4010    <t>
4011      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4012      "PUT - 'store under' vs 'store at'"
4013    </t>
4014  </list>
4015</t>
4016<t>
4017  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4018  <list style="symbols"> 
4019    <t>
4020      Reference RFC 3984, and update header field registrations for headers defined
4021      in this document.
4022    </t>
4023  </list>
4024</t>
4025<t>
4026  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4027  <list style="symbols"> 
4028    <t>
4029      Replace string literals when the string really is case-sensitive (method).
4030    </t>
4031  </list>
4032</t>
4033</section>
4034
4035<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
4036<t>
4037  Closed issues:
4038  <list style="symbols"> 
4039    <t>
4040      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
4041      "OPTIONS request bodies"
4042    </t>
4043    <t>
4044      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
4045      "Description of CONNECT should refer to RFC2817"
4046    </t>
4047    <t>
4048      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
4049      "Location Content-Location reference request/response mixup"
4050    </t>
4051  </list>
4052</t>
4053<t>
4054  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
4055  <list style="symbols"> 
4056    <t>
4057      Added initial proposal for registration process, plus initial
4058      content (non-HTTP/1.1 methods to be added by a separate specification).
4059    </t>
4060  </list>
4061</t>
4062</section>
4063
4064<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
4065<t>
4066  Closed issues:
4067  <list style="symbols"> 
4068    <t>
4069      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4070      "Content-*"
4071    </t>
4072    <t>
4073      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4074      "RFC 2822 is updated by RFC 5322"
4075    </t>
4076  </list>
4077</t>
4078<t>
4079  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4080  <list style="symbols"> 
4081    <t>
4082      Use "/" instead of "|" for alternatives.
4083    </t>
4084    <t>
4085      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4086      whitespace ("OWS") and required whitespace ("RWS").
4087    </t>
4088    <t>
4089      Rewrite ABNFs to spell out whitespace rules, factor out
4090      header field value format definitions.
4091    </t>
4092  </list>
4093</t>
4094</section>
4095
4096<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
4097<t>
4098  Closed issues:
4099  <list style="symbols"> 
4100    <t>
4101      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4102      "reason-phrase BNF"
4103    </t>
4104  </list>
4105</t>
4106<t>
4107  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4108  <list style="symbols"> 
4109    <t>
4110      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4111    </t>
4112  </list>
4113</t>
4114</section>
4115
4116<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4117<t>
4118  Closed issues:
4119  <list style="symbols"> 
4120    <t>
4121      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4122      "Clarify when Referer is sent"
4123    </t>
4124    <t>
4125      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4126      "status codes vs methods"
4127    </t>
4128    <t>
4129      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4130      "Do not require "updates" relation for specs that register status codes or method names"
4131    </t>
4132  </list>
4133</t>
4134</section>
4135
4136<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4137<t>
4138  Closed issues:
4139  <list style="symbols"> 
4140    <t>
4141      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4142      "Idempotency"
4143    </t>
4144    <t>
4145      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4146      "TRACE security considerations"
4147    </t>
4148    <t>
4149      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4150      "Clarify rules for determining what entities a response carries"
4151    </t>
4152    <t>
4153      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4154      "update note citing RFC 1945 and 2068"
4155    </t>
4156    <t>
4157      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4158      "update note about redirect limit"
4159    </t>
4160    <t>
4161      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4162      "Location header ABNF should use 'URI'"
4163    </t>
4164    <t>
4165      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4166      "fragments in Location vs status 303"
4167    </t>
4168    <t>
4169      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4170      "move IANA registrations for optional status codes"
4171    </t>
4172  </list>
4173</t>
4174<t>
4175  Partly resolved issues:
4176  <list style="symbols"> 
4177    <t>
4178      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4179      "Are OPTIONS and TRACE safe?"
4180    </t>
4181  </list>
4182</t>
4183</section>
4184
4185<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4186<t>
4187  Closed issues:
4188  <list style="symbols"> 
4189    <t>
4190      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4191      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4192      status codes when fixing this previously)
4193    </t>
4194  </list>
4195</t>
4196</section>
4197
4198<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4199<t>
4200  Closed issues:
4201  <list style="symbols"> 
4202    <t>
4203      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4204      "Fragment combination / precedence during redirects"
4205    </t>
4206  </list>
4207</t>
4208<t>
4209  Partly resolved issues:
4210  <list style="symbols"> 
4211    <t>
4212      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4213      "Location header payload handling"
4214    </t>
4215    <t>
4216      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4217      "Term for the requested resource's URI"
4218    </t>
4219  </list>
4220</t>
4221</section>
4222
4223<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4224<t>
4225  Closed issues:
4226  <list style="symbols"> 
4227    <t>
4228      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4229      "Clarify 'Requested Variant'"
4230    </t>
4231    <t>
4232      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4233      "Clarify entity / representation / variant terminology"
4234    </t>
4235    <t>
4236      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4237      "Methods and Caching"
4238    </t>
4239    <t>
4240      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4241      "OPTIONS vs Max-Forwards"
4242    </t>
4243    <t>
4244      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4245      "Status codes and caching"
4246    </t>
4247    <t>
4248      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4249      "consider removing the 'changes from 2068' sections"
4250    </t>
4251  </list>
4252</t>
4253</section>
4254
4255<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4256<t>
4257  Closed issues:
4258  <list style="symbols"> 
4259    <t>
4260      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4261      "Considerations for new status codes"
4262    </t>
4263    <t>
4264      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4265      "Considerations for new methods"
4266    </t>
4267    <t>
4268      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4269      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4270    </t>
4271  </list>
4272</t>
4273</section>
4274
4275<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4276<t>
4277  Closed issues:
4278  <list style="symbols"> 
4279    <t>
4280      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4281      "Fragment combination / precedence during redirects" (added warning
4282      about having a fragid on the redirect may cause inconvenience in
4283      some cases)
4284    </t>
4285    <t>
4286      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4287      "Content-* vs. PUT"
4288    </t>
4289    <t>
4290      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4291      "205 Bodies"
4292    </t>
4293    <t>
4294      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4295      "Understanding Content-* on non-PUT requests"
4296    </t>
4297    <t>
4298      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4299      "Content-*"
4300    </t>
4301    <t>
4302      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4303      "Header type defaulting"
4304    </t>
4305    <t>
4306      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4307      "PUT - 'store under' vs 'store at'"
4308    </t>
4309    <t>
4310      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4311      "duplicate ABNF for reason-phrase"
4312    </t>
4313    <t>
4314      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4315      "Note special status of Content-* prefix in header registration procedures"
4316    </t>
4317    <t>
4318      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4319      "Max-Forwards vs extension methods"
4320    </t>
4321    <t>
4322      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4323      "What is the value space of HTTP status codes?" (actually fixed in
4324      draft-ietf-httpbis-p2-semantics-11)
4325    </t>
4326    <t>
4327      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4328      "Header Classification"
4329    </t>
4330    <t>
4331      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4332      "PUT side effect: invalidation or just stale?"
4333    </t>
4334    <t>
4335      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4336      "proxies not supporting certain methods"
4337    </t>
4338    <t>
4339      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4340      "Migrate CONNECT from RFC2817 to p2"
4341    </t>
4342    <t>
4343      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4344      "Migrate Upgrade details from RFC2817"
4345    </t>
4346    <t>
4347      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4348      "clarify PUT semantics'"
4349    </t>
4350    <t>
4351      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4352      "duplicate ABNF for 'Method'"
4353    </t>
4354    <t>
4355      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4356      "untangle ABNFs for header fields"
4357    </t>
4358  </list>
4359</t>
4360</section>
4361
4362<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4363<t>
4364  Closed issues:
4365  <list style="symbols"> 
4366    <t>
4367      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4368      "untangle ABNFs for header fields"
4369    </t>
4370    <t>
4371      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4372      "message body in CONNECT request"
4373    </t>
4374  </list>
4375</t>
4376</section>
4377
4378<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4379<t>
4380  Closed issues:
4381  <list style="symbols"> 
4382    <t>
4383      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4384      "Clarify status code for rate limiting"
4385    </t>
4386    <t>
4387      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4388      "clarify 403 forbidden"
4389    </t>
4390    <t>
4391      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4392      "Clarify 203 Non-Authoritative Information"
4393    </t>
4394    <t>
4395      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4396      "update default reason phrase for 413"
4397    </t>
4398  </list>
4399</t>
4400</section>
4401
4402<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4403<t>
4404  Closed issues:
4405  <list style="symbols"> 
4406    <t>
4407      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4408      "Strength of requirements on Accept re: 406"
4409    </t>
4410    <t>
4411      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4412      "400 response isn't generic"
4413    </t>
4414  </list>
4415</t>
4416</section>
4417
4418<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4419<t>
4420  Closed issues:
4421  <list style="symbols"> 
4422    <t>
4423      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4424      "Redirects and non-GET methods"
4425    </t>
4426    <t>
4427      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
4428      "Document HTTP's error-handling philosophy"
4429    </t>
4430    <t>
4431      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4432      "Considerations for new headers"
4433    </t>
4434    <t>
4435      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4436      "clarify 303 redirect on HEAD"
4437    </t>
4438  </list>
4439</t>
4440</section>
4441
4442<section title="Since draft-ietf-httpbis-p2-semantics-17" anchor="changes.since.17">
4443<t>
4444  Closed issues:
4445  <list style="symbols"> 
4446    <t>
4447      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4448      "Location header payload handling"
4449    </t>
4450    <t>
4451      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4452      "Clarify status code for rate limiting" (change backed out because
4453      a new status code is being defined for this purpose)
4454    </t>
4455    <t>
4456      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4457      "should there be a permanent variant of 307"
4458    </t>
4459    <t>
4460      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/325"/>:
4461      "When are Location's semantics triggered?"
4462    </t>
4463    <t>
4464      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/327"/>:
4465      "'expect' grammar missing OWS"
4466    </t>
4467    <t>
4468      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/329"/>:
4469      "header field considerations: quoted-string vs use of double quotes"
4470    </t>
4471  </list>
4472</t>
4473</section>
4474
4475<section title="Since draft-ietf-httpbis-p2-semantics-18" anchor="changes.since.18">
4476<t>
4477  Closed issues:
4478  <list style="symbols"> 
4479    <t>
4480      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/227"/>:
4481      "Combining HEAD responses"
4482    </t>
4483    <t>
4484      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/238"/>:
4485      "Requirements for user intervention during redirects"
4486    </t>
4487    <t>
4488      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
4489      "message-body in CONNECT response"
4490    </t>
4491    <t>
4492      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/295"/>:
4493      "Applying original fragment to 'plain' redirected URI"
4494    </t>
4495    <t>
4496      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
4497      "Misplaced text on connection handling in p2"
4498    </t>
4499    <t>
4500      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/331"/>:
4501      "clarify that 201 doesn't require Location header fields"
4502    </t>
4503    <t>
4504      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/332"/>:
4505      "relax requirements on hypertext in 3/4/5xx error responses"
4506    </t>
4507    <t>
4508      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/333"/>:
4509      "example for 426 response should have a payload"
4510    </t>
4511    <t>
4512      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/336"/>:
4513      "drop indirection entries for status codes"
4514    </t>
4515  </list>
4516</t>
4517</section>
4518
4519<section title="Since draft-ietf-httpbis-p2-semantics-19" anchor="changes.since.19">
4520<t>
4521  Closed issues:
4522  <list style="symbols"> 
4523    <t>
4524      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4525      "should there be a permanent variant of 307"
4526    </t>
4527  </list>
4528</t>
4529</section>
4530
4531</section>
4532
4533</back>
4534</rfc>
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