source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1642

Last change on this file since 1642 was 1642, checked in by julian.reschke@…, 8 years ago

Step 4 of p2/p3-merge (see #351)

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 199.0 KB
Line 
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  <!ENTITY architecture               "<xref target='Part1' x:rel='#architecture' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
90  <!ENTITY notation                   "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
91  <!ENTITY abnf-extension             "<xref target='Part1' x:rel='#abnf.extension' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
92  <!ENTITY acks                       "<xref target='Part1' x:rel='#acks' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
93  <!ENTITY whitespace                 "<xref target='Part1' x:rel='#whitespace' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
94  <!ENTITY field-components           "<xref target='Part1' x:rel='#field.components' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
95  <!ENTITY caching-neg-resp           "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
96  <!ENTITY header-transfer-encoding   "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
97  <!ENTITY header-content-length      "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
98  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
99  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
100  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
101  <!ENTITY header-last-modified       "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
102  <!ENTITY header-user-agent          "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
103  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
104  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
105  <!ENTITY multipart-byteranges       "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
106  <!ENTITY http-date                  "<xref target='Part2' x:rel='#http.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
107  <!ENTITY qvalue                     "<xref target='Part1' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
108  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
109  <!ENTITY effective-request-uri      "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
110  <!ENTITY compression-codings        "<xref target='Part1' x:rel='#compression.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
111  <!ENTITY transfer-codings           "<xref target='Part1' x:rel='#transfer.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
112  <!ENTITY compress-coding            "<xref target='Part1' x:rel='#compress.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
113  <!ENTITY deflate-coding             "<xref target='Part1' x:rel='#deflate.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
114  <!ENTITY gzip-coding                "<xref target='Part1' x:rel='#gzip.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
115  <!ENTITY response-representation    "<xref target='Part2' x:rel='#identifying.response.associated.with.representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
116]>
117<?rfc toc="yes" ?>
118<?rfc symrefs="yes" ?>
119<?rfc sortrefs="yes" ?>
120<?rfc compact="yes"?>
121<?rfc subcompact="no" ?>
122<?rfc linkmailto="no" ?>
123<?rfc editing="no" ?>
124<?rfc comments="yes"?>
125<?rfc inline="yes"?>
126<?rfc rfcedstyle="yes"?>
127<?rfc-ext allow-markup-in-artwork="yes" ?>
128<?rfc-ext include-references-in-index="yes" ?>
129<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="proposed"
130     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
131     xmlns:x='http://purl.org/net/xml2rfc/ext'
132     xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'>
133<x:link rel="prev" basename="p1-messaging"/>
134<x:link rel="next" basename="p3-payload"/>
135<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
136<front>
137
138  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation</title>
139
140  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
141    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
142    <address>
143      <postal>
144        <street>345 Park Ave</street>
145        <city>San Jose</city>
146        <region>CA</region>
147        <code>95110</code>
148        <country>USA</country>
149      </postal>
150      <email>fielding@gbiv.com</email>
151      <uri>http://roy.gbiv.com/</uri>
152    </address>
153  </author>
154
155  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
156    <organization abbrev="W3C">World Wide Web Consortium</organization>
157    <address>
158      <postal>
159        <street>W3C / ERCIM</street>
160        <street>2004, rte des Lucioles</street>
161        <city>Sophia-Antipolis</city>
162        <region>AM</region>
163        <code>06902</code>
164        <country>France</country>
165      </postal>
166      <email>ylafon@w3.org</email>
167      <uri>http://www.raubacapeu.net/people/yves/</uri>
168    </address>
169  </author>
170
171  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
172    <organization abbrev="greenbytes">greenbytes GmbH</organization>
173    <address>
174      <postal>
175        <street>Hafenweg 16</street>
176        <city>Muenster</city><region>NW</region><code>48155</code>
177        <country>Germany</country>
178      </postal>
179      <phone>+49 251 2807760</phone>
180      <facsimile>+49 251 2807761</facsimile>
181      <email>julian.reschke@greenbytes.de</email>
182      <uri>http://greenbytes.de/tech/webdav/</uri>
183    </address>
184  </author>
185
186  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
187  <workgroup>HTTPbis Working Group</workgroup>
188
189<abstract>
190<t>
191   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
192   distributed, collaborative, hypertext information systems. HTTP has been in
193   use by the World Wide Web global information initiative since 1990. This
194   document is Part 2 of the seven-part specification that defines the protocol
195   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
196</t>
197<t>
198   Part 2 defines the semantics of HTTP messages as expressed by request
199   methods, request header fields, response status codes, and response header
200   fields. Furthermore, it defines HTTP message content, metadata, and content
201   negotiation.
202   <cref>#351</cref>
203</t>
204</abstract>
205
206<note title="Editorial Note (To be removed by RFC Editor)">
207  <t>
208    Discussion of this draft should take place on the HTTPBIS working group
209    mailing list (ietf-http-wg@w3.org), which is archived at
210    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
211  </t>
212  <t>
213    The current issues list is at
214    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
215    documents (including fancy diffs) can be found at
216    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
217  </t>
218  <t>
219    The changes in this draft are summarized in <xref target="changes.since.19"/>.
220  </t>
221</note>
222</front>
223<middle>
224<section title="Introduction" anchor="introduction">
225<t>
226   This document defines HTTP/1.1 request and response semantics.  Each HTTP
227   message, as defined in &messaging;, is in the form of either a request or
228   a response.  An HTTP server listens on a connection for HTTP requests and
229   responds to each request, in the order received on that connection, with
230   one or more HTTP response messages.  This document defines the commonly
231   agreed upon semantics of the HTTP uniform interface, the intentions defined
232   by each request method, and the various response messages that might be
233   expected as a result of applying that method to the target resource.
234</t>
235<t>
236   Furthermore, it defines HTTP/1.1 message payloads (a.k.a., content), the
237   associated metadata header fields that define how the payload is intended
238   to be interpreted by a recipient, the request header fields that
239   might influence content selection, and the various selection algorithms
240   that are collectively referred to as HTTP content negotiation.
241   <cref>#351</cref>
242</t>
243<t>
244   This document is currently disorganized in order to minimize the changes
245   between drafts and enable reviewers to see the smaller errata changes.
246   A future draft will reorganize the sections to better reflect the content.
247   In particular, the sections will be ordered according to the typical
248   processing of an HTTP request message (after message parsing): resource
249   mapping, methods, request modifying header fields, response status,
250   status modifying header fields, and resource metadata.  The current mess
251   reflects how widely dispersed these topics and associated requirements
252   had become in <xref target="RFC2616"/>.
253</t>
254
255<section title="Terminology" anchor="terminology">
256<t>
257   This specification uses a number of terms to refer to the roles
258   played by participants in, and objects of, the HTTP communication.
259</t>
260<t>
261  <iref item="content negotiation"/>
262  <x:dfn>content negotiation</x:dfn>
263  <list>
264    <t>
265      The mechanism for selecting the appropriate representation when
266      servicing a request. The representation in any response
267      can be negotiated (including error responses).
268    </t>
269  </list>
270</t>
271<t>
272  <iref primary="true" item="selected representation"/>
273  <x:dfn>selected representation</x:dfn>
274  <list>
275    <t>
276      The current representation of the target resource that would have been
277      selected in a successful response if the same request had used the
278      method GET and excluded any conditional request header fields.
279    </t>
280  </list>
281</t>
282</section>
283
284<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
285<t>
286   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
287   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
288   document are to be interpreted as described in <xref target="RFC2119"/>.
289</t>
290<t>
291   This document defines conformance criteria for several roles in HTTP
292   communication, including Senders, Recipients, Clients, Servers, User-Agents,
293   Origin Servers, Intermediaries, Proxies and Gateways. See &architecture;
294   for definitions of these terms.
295</t>
296<t>
297   An implementation is considered conformant if it complies with all of the
298   requirements associated with its role(s). Note that SHOULD-level requirements
299   are relevant here, unless one of the documented exceptions is applicable.
300</t>
301<t>
302   This document also uses ABNF to define valid protocol elements
303   (<xref target="notation"/>). In addition to the prose requirements placed
304   upon them, Senders &MUST-NOT; generate protocol elements that are invalid.
305</t>
306<t>
307   Unless noted otherwise, Recipients &MAY; take steps to recover a usable
308   protocol element from an invalid construct. However, HTTP does not define
309   specific error handling mechanisms, except in cases where it has direct
310   impact on security. This is because different uses of the protocol require
311   different error handling strategies; for example, a Web browser may wish to
312   transparently recover from a response where the Location header field
313   doesn't parse according to the ABNF, whereby in a systems control protocol
314   using HTTP, this type of error recovery could lead to dangerous consequences.
315</t>
316</section>
317
318<section title="Syntax Notation" anchor="notation">
319  <x:anchor-alias value="ALPHA"/>
320  <x:anchor-alias value="CR"/>
321  <x:anchor-alias value="DIGIT"/>
322  <x:anchor-alias value="LF"/>
323  <x:anchor-alias value="OCTET"/>
324  <x:anchor-alias value="SP"/>
325  <x:anchor-alias value="VCHAR"/>
326<t>
327   This specification uses the Augmented Backus-Naur Form (ABNF) notation
328   of <xref target="RFC5234"/> with the list rule extension defined in
329   &notation;<xref target="collected.abnf"/> shows the collected ABNF
330   with the list rule expanded.
331</t>
332<t>
333  The following core rules are included by
334  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
335  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
336  DIGIT (decimal 0-9), DQUOTE (double quote),
337  HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
338  OCTET (any 8-bit sequence of data), SP (space), and
339  VCHAR (any visible US-ASCII character).
340</t>
341
342<section title="Core Rules" anchor="core.rules">
343  <x:anchor-alias value="obs-text"/>
344  <x:anchor-alias value="quoted-string"/>
345  <x:anchor-alias value="token"/>
346  <x:anchor-alias value="word"/>
347  <x:anchor-alias value="BWS"/>
348  <x:anchor-alias value="OWS"/>
349  <x:anchor-alias value="RWS"/>
350<t>
351  The core rules below are defined in <xref target="Part1"/>:
352</t>
353<figure><artwork type="abnf2616">
354  <x:ref>BWS</x:ref>           = &lt;BWS, defined in &whitespace;&gt;
355  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &whitespace;&gt;
356  <x:ref>RWS</x:ref>           = &lt;RWS, defined in &whitespace;&gt;
357  <x:ref>obs-text</x:ref>      = &lt;obs-text, defined in &field-components;&gt;
358  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &field-components;&gt;
359  <x:ref>token</x:ref>         = &lt;token, defined in &field-components;&gt;
360  <x:ref>word</x:ref>          = &lt;word, defined in &field-components;&gt;
361</artwork></figure>
362</section>
363
364<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
365  <x:anchor-alias value="absolute-URI"/>
366  <x:anchor-alias value="comment"/>
367  <x:anchor-alias value="partial-URI"/>
368  <x:anchor-alias value="qvalue"/>
369  <x:anchor-alias value="URI-reference"/>
370<t>
371  The ABNF rules below are defined in other parts:
372</t>
373<figure><!--Part1--><artwork type="abnf2616">
374  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in &uri;&gt;
375  <x:ref>comment</x:ref>       = &lt;comment, defined in &field-components;&gt;
376  <x:ref>partial-URI</x:ref>   = &lt;partial-URI, defined in &uri;&gt;
377  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in &uri;&gt;
378</artwork></figure>
379</section>
380</section>
381</section>
382
383<section title="Methods" anchor="methods">
384  <x:anchor-alias value="method"/>
385<t>
386   The method token indicates the request method to be performed on the target
387   resource (&effective-request-uri;). The method is case-sensitive.
388</t>
389<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
390  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
391</artwork></figure>
392<t>
393   The list of methods allowed by a resource can be specified in an
394   Allow header field (<xref target="header.allow"/>). The status code of the response
395   always notifies the client whether a method is currently allowed on a
396   resource, since the set of allowed methods can change dynamically. An
397   origin server &SHOULD; respond with the status code 405 (Method Not Allowed)
398   if the method is known by the origin server but not allowed for the
399   resource, and 501 (Not Implemented) if the method is
400   unrecognized or not implemented by the origin server. The methods GET
401   and HEAD &MUST; be supported by all general-purpose servers. All other
402   methods are &OPTIONAL;; however, if the above methods are implemented,
403   they &MUST; be implemented with the same semantics as those specified
404   in <xref target="method.definitions"/>.
405</t>
406
407<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
408
409<section title="Safe Methods" anchor="safe.methods">
410<iref item="Safe Methods" primary="true"/>
411<t>
412   Implementors need to be aware that the software represents the user in
413   their interactions over the Internet, and need to allow
414   the user to be aware of any actions they take which might have an
415   unexpected significance to themselves or others.
416</t>
417<t>
418   In particular, the convention has been established that the GET, HEAD,
419   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
420   of taking an action other than retrieval. These request methods ought
421   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
422   This allows user agents to represent other methods, such as POST, PUT
423   and DELETE, in a special way, so that the user is made aware of the
424   fact that a possibly unsafe action is being requested.
425</t>
426<t>
427   Naturally, it is not possible to ensure that the server does not
428   generate side-effects as a result of performing a GET request; in
429   fact, some dynamic resources consider that a feature. The important
430   distinction here is that the user did not request the side-effects,
431   so therefore cannot be held accountable for them.
432</t>
433</section>
434
435<section title="Idempotent Methods" anchor="idempotent.methods">
436<iref item="Idempotent Methods" primary="true"/>
437<t>
438   Request methods can also have the property of "idempotence" in that,
439   aside from error or expiration issues, the intended effect of multiple
440   identical requests is the same as for a single request.
441   PUT, DELETE, and all safe request methods are idempotent.
442   It is important to note that idempotence refers only to changes
443   requested by the client: a server is free to change its state due
444   to multiple requests for the purpose of tracking those requests,
445   versioning of results, etc.
446</t>
447</section>
448</section>
449
450<section title="Method Registry" anchor="method.registry">
451<t>
452  The HTTP Method Registry defines the name space for the method token in the
453  Request line of an HTTP request.
454</t>
455<t>
456  Registrations &MUST; include the following fields:
457  <list style="symbols">
458    <t>Method Name (see <xref target="methods"/>)</t>
459    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
460    <t>Pointer to specification text</t>
461  </list>
462</t>
463<t>
464  Values to be added to this name space require IETF Review
465  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
466</t>
467<t>
468  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
469</t>
470
471<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
472<t>
473   When it is necessary to express new semantics for a HTTP request that
474   aren't specific to a single application or media type, and currently defined
475   methods are inadequate, it may be appropriate to register a new method.
476</t>
477<t>
478   HTTP methods are generic; that is, they are potentially applicable to any
479   resource, not just one particular media type, "type" of resource, or
480   application. As such, it is preferred that new HTTP methods be registered
481   in a document that isn't specific to a single application, so that this is
482   clear.
483</t>
484<t>
485   Due to the parsing rules defined in &message-body;, definitions of HTTP
486   methods cannot prohibit the presence of a message body on either the request
487   or the response message (with responses to HEAD requests being the single
488   exception). Definitions of new methods cannot change this rule, but they can
489   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
490</t>
491<t>
492   New method definitions need to indicate whether they are safe (<xref
493   target="safe.methods"/>), what semantics (if any) the request body has,
494   and whether they are idempotent (<xref target="idempotent.methods"/>).
495   They also need to state whether they can be cached (&caching;); in
496   particular what conditions a cache may store the response, and under what
497   conditions such a stored response may be used to satisfy a subsequent
498   request.
499</t>
500</section>
501</section>
502
503<section title="Method Definitions" anchor="method.definitions">
504
505<section title="OPTIONS" anchor="OPTIONS">
506  <rdf:Description>
507    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
508  </rdf:Description>
509  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
510  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
511<t>
512   The OPTIONS method requests information about the
513   communication options available on the request/response chain
514   identified by the effective request URI. This method allows a client to
515   determine the options and/or requirements associated with a resource,
516   or the capabilities of a server, without implying a resource action
517   or initiating a resource retrieval.
518</t>
519<t>
520   Responses to the OPTIONS method are not cacheable.
521</t>
522<t>
523   If the OPTIONS request includes a message body (as indicated by the
524   presence of Content-Length or Transfer-Encoding), then the media type
525   &MUST; be indicated by a Content-Type field. Although this
526   specification does not define any use for such a body, future
527   extensions to HTTP might use the OPTIONS body to make more detailed
528   queries on the server.
529</t>
530<t>
531   If the request-target (&request-target;) is an asterisk ("*"),
532   the OPTIONS request is
533   intended to apply to the server in general rather than to a specific
534   resource. Since a server's communication options typically depend on
535   the resource, the "*" request is only useful as a "ping" or "no-op"
536   type of method; it does nothing beyond allowing the client to test
537   the capabilities of the server. For example, this can be used to test
538   a proxy for HTTP/1.1 conformance (or lack thereof).
539</t>
540<t>
541   If the request-target is not an asterisk, the OPTIONS request applies
542   only to the options that are available when communicating with that
543   resource.
544</t>
545<t>
546   A 200 response &SHOULD; include any header fields that indicate
547   optional features implemented by the server and applicable to that
548   resource (e.g., Allow), possibly including extensions not defined by
549   this specification. The response body, if any, &SHOULD; also include
550   information about the communication options. The format for such a
551   body is not defined by this specification, but might be defined by
552   future extensions to HTTP. Content negotiation &MAY; be used to select
553   the appropriate response format. If no response body is included, the
554   response &MUST; include a Content-Length field with a field-value of
555   "0".
556</t>
557<t>
558   The Max-Forwards header field &MAY; be used to target a
559   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
560   If no Max-Forwards field is present in the request, then the forwarded
561   request &MUST-NOT; include a Max-Forwards field.
562</t>
563</section>
564
565<section title="GET" anchor="GET">
566  <rdf:Description>
567    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
568  </rdf:Description>
569  <iref primary="true" item="GET method" x:for-anchor=""/>
570  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
571<t>
572   The GET method requests transfer of a current representation of
573   the target resource.
574</t>
575<t>   
576   If the target resource is a data-producing process, it is the
577   produced data which shall be returned as the representation in the response and not
578   the source text of the process, unless that text happens to be the output of
579   the process.
580</t>
581<t>
582   The semantics of the GET method change to a "conditional GET" if the
583   request message includes an If-Modified-Since, If-Unmodified-Since,
584   If-Match, If-None-Match, or If-Range header field. A conditional GET
585   requests that the representation be transferred only under the
586   circumstances described by the conditional header field(s). The
587   conditional GET request is intended to reduce unnecessary network
588   usage by allowing cached representations to be refreshed without requiring
589   multiple requests or transferring data already held by the client.
590</t>
591<t>
592   The semantics of the GET method change to a "partial GET" if the
593   request message includes a Range header field. A partial GET requests
594   that only part of the representation be transferred, as described in &header-range;.
595   The partial GET request is intended to reduce unnecessary
596   network usage by allowing partially-retrieved representations to be
597   completed without transferring data already held by the client.
598</t>
599<t>
600   Bodies on GET requests have no defined semantics. Note that sending a body
601   on a GET request might cause some existing implementations to reject the
602   request.
603</t>
604<t>
605   The response to a GET request is cacheable and &MAY; be used to satisfy
606   subsequent GET and HEAD requests (see &caching;).
607</t>
608<t>
609   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
610</t>
611</section>
612
613<section title="HEAD" anchor="HEAD">
614  <rdf:Description>
615    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
616  </rdf:Description>
617  <iref primary="true" item="HEAD method" x:for-anchor=""/>
618  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
619<t>
620   The HEAD method is identical to GET except that the server &MUST-NOT;
621   return a message body in the response. The metadata contained
622   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
623   to the information sent in response to a GET request. This method can
624   be used for obtaining metadata about the representation implied by the
625   request without transferring the representation body. This method is
626   often used for testing hypertext links for validity, accessibility,
627   and recent modification.
628</t>
629<t>
630   The response to a HEAD request is cacheable and &MAY; be used to satisfy
631   a subsequent HEAD request. It also has potential side effects on
632   previously stored responses to GET; see &p6-head;.
633</t>
634<t>
635   Bodies on HEAD requests have no defined semantics. Note that sending a body
636   on a HEAD request might cause some existing implementations to reject the
637   request.
638</t>
639</section>
640
641<section title="POST" anchor="POST">
642  <iref primary="true" item="POST method" x:for-anchor=""/>
643  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
644<t>
645   The POST method requests that the origin server accept the
646   representation enclosed in the request as data to be processed by the
647   target resource. POST is designed to allow a uniform method to cover the
648   following functions:
649  <list style="symbols">
650    <t>
651      Annotation of existing resources;
652    </t>
653    <t>
654        Posting a message to a bulletin board, newsgroup, mailing list,
655        or similar group of articles;
656    </t>
657    <t>
658        Providing a block of data, such as the result of submitting a
659        form, to a data-handling process;
660    </t>
661    <t>
662        Extending a database through an append operation.
663    </t>
664  </list>
665</t>
666<t>
667   The actual function performed by the POST method is determined by the
668   server and is usually dependent on the effective request URI.
669</t>
670<t>
671   The action performed by the POST method might not result in a
672   resource that can be identified by a URI. In this case, either 200
673   (OK) or 204 (No Content) is the appropriate response status code,
674   depending on whether or not the response includes a representation that
675   describes the result.
676</t>
677<t>
678   If a resource has been created on the origin server, the response
679   &SHOULD; be 201 (Created) and contain a representation which describes the
680   status of the request and refers to the new resource, and a Location
681   header field (see <xref target="header.location"/>).
682</t>
683<t>
684   Responses to POST requests are only cacheable when they
685   include explicit freshness information (see &p6-explicit;). A
686   cached POST response with a Content-Location header field
687   (see &header-content-location;) whose value is the effective
688   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
689</t>
690<t>
691   Note that POST caching is not widely implemented.
692   However, the 303 (See Other) response can be used to direct the
693   user agent to retrieve a cacheable representation of the resource.
694</t>
695</section>
696
697<section title="PUT" anchor="PUT">
698  <iref primary="true" item="PUT method" x:for-anchor=""/>
699  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
700<t>
701   The PUT method requests that the state of the target resource
702   be created or replaced with the state defined by the representation
703   enclosed in the request message payload.  A successful PUT of a given
704   representation would suggest that a subsequent GET on that same target
705   resource will result in an equivalent representation being returned in
706   a 200 (OK) response.  However, there is no guarantee that such a state
707   change will be observable, since the target resource might be acted
708   upon by other user agents in parallel, or might be subject to dynamic
709   processing by the origin server, before any subsequent GET is received.
710   A successful response only implies that the user agent's intent was
711   achieved at the time of its processing by the origin server.
712</t>
713<t>   
714   If the target resource does not have a current representation and
715   the PUT successfully creates one, then the origin server &MUST; inform
716   the user agent by sending a 201 (Created) response.  If the target
717   resource does have a current representation and that representation is
718   successfully modified in accordance with the state of the enclosed
719   representation, then either a 200 (OK) or 204 (No Content) response
720   &SHOULD; be sent to indicate successful completion of the request.
721</t>
722<t>
723   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
724   as part of the resource state).
725</t>
726<t>
727   An origin server &SHOULD; verify that the PUT representation is
728   consistent with any constraints which the server has for the target
729   resource that cannot or will not be changed by the PUT.  This is
730   particularly important when the origin server uses internal
731   configuration information related to the URI in order to set the
732   values for representation metadata on GET responses.  When a PUT
733   representation is inconsistent with the target resource, the origin
734   server &SHOULD; either make them consistent, by transforming the
735   representation or changing the resource configuration, or respond
736   with an appropriate error message containing sufficient information
737   to explain why the representation is unsuitable.  The 409 (Conflict)
738   or 415 (Unsupported Media Type) status codes are suggested, with the
739   latter being specific to constraints on Content-Type values.
740</t>
741<t>
742   For example, if the target resource is configured to always have a
743   Content-Type of "text/html" and the representation being PUT has a
744   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
745   (a) reconfigure the target resource to reflect the new media type;
746   (b) transform the PUT representation to a format consistent with that
747   of the resource before saving it as the new resource state; or,
748   (c) reject the request with a 415 response indicating that the target
749   resource is limited to "text/html", perhaps including a link to a
750   different resource that would be a suitable target for the new
751   representation.
752</t>
753<t>
754   HTTP does not define exactly how a PUT method affects the state
755   of an origin server beyond what can be expressed by the intent of
756   the user agent request and the semantics of the origin server response.
757   It does not define what a resource might be, in any sense of that
758   word, beyond the interface provided via HTTP.  It does not define
759   how resource state is "stored", nor how such storage might change
760   as a result of a change in resource state, nor how the origin server
761   translates resource state into representations.  Generally speaking,
762   all implementation details behind the resource interface are
763   intentionally hidden by the server.
764</t>
765<t>
766   The fundamental difference between the POST and PUT methods is
767   highlighted by the different intent for the target resource.
768   The target resource in a POST request is intended to handle the
769   enclosed representation as a data-accepting process, such as for
770   a gateway to some other protocol or a document that accepts annotations.
771   In contrast, the target resource in a PUT request is intended to
772   take the enclosed representation as a new or replacement value.
773   Hence, the intent of PUT is idempotent and visible to intermediaries,
774   even though the exact effect is only known by the origin server.
775</t>
776<t>
777   Proper interpretation of a PUT request presumes that the user agent
778   knows what target resource is desired.  A service that is intended
779   to select a proper URI on behalf of the client, after receiving
780   a state-changing request, &SHOULD; be implemented using the POST
781   method rather than PUT.  If the origin server will not make the
782   requested PUT state change to the target resource and instead
783   wishes to have it applied to a different resource, such as when the
784   resource has been moved to a different URI, then the origin server
785   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
786   then make its own decision regarding whether or not to redirect the
787   request.
788</t>
789<t>
790   A PUT request applied to the target resource &MAY; have side-effects
791   on other resources.  For example, an article might have a URI for
792   identifying "the current version" (a resource) which is separate
793   from the URIs identifying each particular version (different
794   resources that at one point shared the same state as the current version
795   resource).  A successful PUT request on "the current version" URI might
796   therefore create a new version resource in addition to changing the
797   state of the target resource, and might also cause links to be added
798   between the related resources.
799</t>
800<t>
801   An origin server &SHOULD; reject any PUT request that contains a
802   Content-Range header field, since it might be misinterpreted as
803   partial content (or might be partial content that is being mistakenly
804   PUT as a full representation).  Partial content updates are
805   possible by targeting a separately identified resource with state
806   that overlaps a portion of the larger resource, or by using a
807   different method that has been specifically defined for partial
808   updates (for example, the PATCH method defined in
809   <xref target="RFC5789"/>).
810</t>
811<t>
812   Responses to the PUT method are not cacheable. If a PUT request passes
813   through a cache that has one or more stored responses for the effective
814   request URI, those stored responses will be invalidated (see
815   &p6-invalid;).
816</t>
817</section>
818
819<section title="DELETE" anchor="DELETE">
820  <iref primary="true" item="DELETE method" x:for-anchor=""/>
821  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
822<t>
823   The DELETE method requests that the origin server delete the target
824   resource. This method &MAY; be overridden by
825   human intervention (or other means) on the origin server. The client cannot
826   be guaranteed that the operation has been carried out, even if the
827   status code returned from the origin server indicates that the action
828   has been completed successfully. However, the server &SHOULD-NOT; 
829   indicate success unless, at the time the response is given, it
830   intends to delete the resource or move it to an inaccessible
831   location.
832</t>
833<t>
834   A successful response &SHOULD; be 200 (OK) if the response includes an
835   representation describing the status, 202 (Accepted) if the action has not
836   yet been enacted, or 204 (No Content) if the action has been enacted
837   but the response does not include a representation.
838</t>
839<t>
840   Bodies on DELETE requests have no defined semantics. Note that sending a body
841   on a DELETE request might cause some existing implementations to reject the
842   request.
843</t>
844<t>
845   Responses to the DELETE method are not cacheable. If a DELETE request
846   passes through a cache that has one or more stored responses for the
847   effective request URI, those stored responses will be invalidated (see
848   &p6-invalid;).
849</t>
850</section>
851
852<section title="TRACE" anchor="TRACE">
853  <rdf:Description>
854    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
855  </rdf:Description>
856  <iref primary="true" item="TRACE method" x:for-anchor=""/>
857  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
858<t>
859   The TRACE method requests a remote, application-layer loop-back
860   of the request message. The final recipient of the request
861   &SHOULD; reflect the message received back to the client as the
862   message body of a 200 (OK) response. The final recipient is either the
863   origin server or the first proxy to receive a Max-Forwards
864   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
865   A TRACE request &MUST-NOT; include a message body.
866</t>
867<t>
868   TRACE allows the client to see what is being received at the other
869   end of the request chain and use that data for testing or diagnostic
870   information. The value of the Via header field (&header-via;) is of
871   particular interest, since it acts as a trace of the request chain.
872   Use of the Max-Forwards header field allows the client to limit the
873   length of the request chain, which is useful for testing a chain of
874   proxies forwarding messages in an infinite loop.
875</t>
876<t>
877   If the request is valid, the response &SHOULD; have a Content-Type of
878   "message/http" (see &media-type-message-http;) and contain a message body
879   that encloses a copy of the entire request message.
880   Responses to the TRACE method are not cacheable.
881</t>
882</section>
883
884<section title="CONNECT" anchor="CONNECT">
885  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
886  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
887<t>
888   The CONNECT method requests that the proxy establish a tunnel
889   to the request-target and, if successful, thereafter restrict its behavior
890   to blind forwarding of packets until the connection is closed.
891</t>
892<t>
893   When using CONNECT, the request-target &MUST; use the authority form
894   (&request-target;); i.e., the request-target consists of only the
895   host name and port number of the tunnel destination, separated by a colon.
896   For example,
897</t>
898<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
899CONNECT server.example.com:80 HTTP/1.1
900Host: server.example.com:80
901
902</artwork></figure>
903<t>
904   Any successful (2xx) response to a CONNECT request indicates that the
905   proxy has established a connection to the requested host and port,
906   and has switched to tunneling the current connection to that server
907   connection.
908   The tunneled data from the server begins immediately after the blank line
909   that concludes the successful response's header block.
910   A server &SHOULD-NOT; send any Transfer-Encoding or Content-Length
911   header fields in a successful response.
912   A client &MUST; ignore any Content-Length or Transfer-Encoding header
913   fields received in a successful response.
914</t>
915<t>
916   Any response other than a successful response indicates that the tunnel
917   has not yet been formed and that the connection remains governed by HTTP.
918</t>
919<t>
920   Proxy authentication might be used to establish the
921   authority to create a tunnel:
922</t>
923<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
924CONNECT server.example.com:80 HTTP/1.1
925Host: server.example.com:80
926Proxy-Authorization: basic aGVsbG86d29ybGQ=
927
928</artwork></figure>
929<t>
930   A message body on a CONNECT request has no defined semantics. Sending a
931   body on a CONNECT request might cause existing implementations to reject
932   the request.
933</t>
934<t>
935   Similar to a pipelined HTTP/1.1 request, data to be tunneled from client
936   to server &MAY; be sent immediately after the request (before a response
937   is received). The usual caveats also apply:
938   data may be discarded if the eventual response is negative, and the
939   connection may be reset with no response if more than one TCP segment
940   is outstanding.
941</t>
942<t>
943   It may be the case that the proxy itself can only reach the requested
944   origin server through another proxy.  In this case, the first proxy
945   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
946   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
947   unless it has either a direct or tunnel connection established to the
948   authority.
949</t>
950<t>
951   If at any point either one of the peers gets disconnected, any
952   outstanding data that came from that peer will be passed to the other
953   one, and after that also the other connection will be terminated by
954   the proxy. If there is outstanding data to that peer undelivered,
955   that data will be discarded.
956</t>
957<t>
958   An origin server which receives a CONNECT request for itself &MAY;
959   respond with a 2xx status code to indicate that a connection is
960   established.  However, most origin servers do not implement CONNECT.
961</t>
962</section>
963</section>
964
965</section>
966
967<section title="Header Fields" anchor="header.fields">
968<t>
969   Header fields are key value pairs that can be used to communicate data about
970   the message, its payload, the target resource, or about the connection
971   itself (i.e., control data).  See &header-fields; for a general definition
972   of their syntax.
973</t>
974
975<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
976<t>
977   New header fields are registered using the procedures described in
978   <xref target="RFC3864"/>.
979</t>
980<t>
981   The requirements for header field names are defined in
982   <xref target="RFC3864" x:fmt="of" x:sec="4.1"/>.  Authors of specifications
983   defining new fields are advised to keep the name as short as practical, and
984   not to prefix them with "X-" if they are to be registered (either
985   immediately or in the future).
986</t>
987<t>
988   New header field values typically have their syntax defined using ABNF
989   (<xref target="RFC5234"/>), using the extension defined in &abnf-extension;
990   as necessary, and are usually constrained to the range of ASCII characters.
991   Header fields needing a greater range of characters can use an encoding
992   such as the one defined in <xref target="RFC5987"/>.
993</t>
994<t>
995   Because commas (",") are used as a generic delimiter between field-values,
996   they need to be treated with care if they are allowed in the field-value's
997   payload. Typically, components that might contain a comma are protected with
998   double-quotes using the quoted-string ABNF production (&field-components;).
999</t>
1000<t>
1001   For example, a textual date and a URI (either of which might contain a comma)
1002   could be safely carried in field-values like these:
1003</t>
1004<figure><artwork type="example">
1005  Example-URI-Field: "http://example.com/a.html,foo",
1006                     "http://without-a-comma.example.com/"
1007  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
1008</artwork></figure>
1009<t>
1010   Note that double quote delimiters almost always are used with the
1011   quoted-string production; using a different syntax inside double quotes
1012   will likely cause unnecessary confusion.
1013</t>
1014<t>
1015   Many header fields use a format including (case-insensitively) named
1016   parameters (for instance, Content-Type, defined in &header-content-type;).
1017   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
1018   parameter value enables recipients to use existing parser components. When
1019   allowing both forms, the meaning of a parameter value ought to be
1020   independent of the syntax used for it (for an example, see the notes on
1021   parameter handling for media types in &media-types;).
1022</t>
1023<t>
1024   Authors of specifications defining new header fields are advised to consider
1025   documenting:
1026  <list style="symbols">
1027    <x:lt>
1028      <t>Whether the field is a single value, or whether it can be a list
1029      (delimited by commas; see &header-fields;).</t>
1030      <t>If it does not use the list syntax, document how to treat messages
1031      where the header field occurs multiple times (a sensible default would
1032      be to ignore the header field, but this might not always be the right
1033      choice).</t>
1034      <t>Note that intermediaries and software libraries might combine
1035      multiple header field instances into a single one, despite the header
1036      field not allowing this. A robust format enables recipients to discover
1037      these situations (good example: "Content-Type", as the comma can only
1038      appear inside quoted strings; bad example: "Location", as a comma can
1039      occur inside a URI).</t>
1040    </x:lt>
1041    <x:lt><t>Under what conditions the header field can be used; e.g., only in
1042    responses or requests, in all messages, only on responses to a particular
1043    request method.</t></x:lt>
1044    <x:lt><t>Whether it is appropriate to list the field-name in the Connection header
1045    (i.e., if the header is to be hop-by-hop, see &header-connection;).</t></x:lt>
1046    <x:lt><t>Under what conditions intermediaries are allowed to modify the header
1047    field's value, insert or delete it.</t></x:lt>
1048    <x:lt><t>How the header might interact with caching (see <xref target="Part6"/>).</t></x:lt>
1049    <x:lt><t>Whether the header field is useful or allowable in trailers (see
1050    &chunked-encoding;).</t></x:lt>
1051    <x:lt><t>Whether the header field should be preserved across redirects.</t></x:lt>
1052  </list>
1053</t>
1054</section>
1055
1056<section title="Request Header Fields" anchor="request.header.fields">
1057  <x:anchor-alias value="request-header"/>
1058<t>
1059   The request header fields allow the client to pass additional
1060   information about the request, and about the client itself, to the
1061   server. These fields act as request modifiers, with semantics
1062   equivalent to the parameters on a programming language method
1063   invocation.
1064</t>
1065<texttable align="left">
1066  <ttcol>Header Field Name</ttcol>
1067  <ttcol>Defined in...</ttcol>
1068
1069  <c>Accept</c> <c>&header-accept;</c>
1070  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
1071  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
1072  <c>Accept-Language</c> <c>&header-accept-language;</c>
1073  <c>Authorization</c> <c>&header-authorization;</c>
1074  <c>Expect</c> <c><xref target="header.expect"/></c>
1075  <c>From</c> <c><xref target="header.from"/></c>
1076  <c>Host</c> <c>&header-host;</c>
1077  <c>If-Match</c> <c>&header-if-match;</c>
1078  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
1079  <c>If-None-Match</c> <c>&header-if-none-match;</c>
1080  <c>If-Range</c> <c>&header-if-range;</c>
1081  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
1082  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
1083  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
1084  <c>Range</c> <c>&header-range;</c>
1085  <c>Referer</c> <c><xref target="header.referer"/></c>
1086  <c>TE</c> <c>&header-te;</c>
1087  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
1088</texttable>
1089</section>
1090
1091<section title="Response Header Fields" anchor="response.header.fields">
1092  <x:anchor-alias value="response-header"/>
1093<t>
1094   The response header fields allow the server to pass additional
1095   information about the response which cannot be placed in the status-line.
1096   These header fields give information about the server and about
1097   further access to the target resource (&effective-request-uri;).
1098</t>
1099<texttable align="left">
1100  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
1101
1102  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
1103  <c>Age</c> <c>&header-age;</c>
1104  <c>Allow</c> <c><xref target="header.allow"/></c>
1105  <c>Date</c> <c><xref target="header.date"/></c>
1106  <c>ETag</c> <c>&header-etag;</c>
1107  <c>Location</c> <c><xref target="header.location"/></c>
1108  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
1109  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
1110  <c>Server</c> <c><xref target="header.server"/></c>
1111  <c>Vary</c> <c>&header-vary;</c>
1112  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
1113</texttable>
1114</section>
1115
1116</section>
1117
1118<section title="Status Codes" anchor="status.codes">
1119<t>
1120   The status-code element is a 3-digit integer result code of the attempt to
1121   understand and satisfy the request.
1122</t>
1123<t>
1124   HTTP status codes are extensible. HTTP applications are not required
1125   to understand the meaning of all registered status codes, though such
1126   understanding is obviously desirable. However, applications &MUST;
1127   understand the class of any status code, as indicated by the first
1128   digit, and treat any unrecognized response as being equivalent to the
1129   x00 status code of that class, with the exception that an
1130   unrecognized response &MUST-NOT; be cached. For example, if an
1131   unrecognized status code of 431 is received by the client, it can
1132   safely assume that there was something wrong with its request and
1133   treat the response as if it had received a 400 status code. In such
1134   cases, user agents &SHOULD; present to the user the representation enclosed
1135   with the response, since that representation is likely to include human-readable
1136   information which will explain the unusual status.
1137</t>
1138<t>
1139   The first digit of the status-code defines the class of response. The
1140   last two digits do not have any categorization role. There are 5
1141   values for the first digit:
1142  <list style="symbols">
1143    <t>
1144      1xx: Informational - Request received, continuing process
1145    </t>
1146    <t>
1147      2xx: Success - The action was successfully received,
1148        understood, and accepted
1149    </t>
1150    <t>
1151      3xx: Redirection - Further action needs to be taken in order to
1152        complete the request
1153    </t>
1154    <t>
1155      4xx: Client Error - The request contains bad syntax or cannot
1156        be fulfilled
1157    </t>
1158    <t>
1159      5xx: Server Error - The server failed to fulfill an apparently
1160        valid request
1161    </t>
1162  </list>
1163</t>
1164<t>
1165   For most status codes the response can carry a payload, in which case a
1166   Content-Type header field indicates the payload's media type
1167   (&header-content-type;).
1168</t>
1169
1170<section title="Overview of Status Codes" anchor="overview.of.status.codes">
1171<t> 
1172   The status codes listed below are defined in this specification,
1173   &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
1174   The reason phrases listed here are only recommendations &mdash; they can be
1175   replaced by local equivalents without affecting the protocol.
1176</t>
1177<texttable align="left">
1178  <ttcol>status-code</ttcol>
1179  <ttcol>reason-phrase</ttcol>
1180  <ttcol>Defined in...</ttcol>
1181 
1182  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
1183  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
1184
1185  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
1186  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
1187  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
1188  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
1189  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
1190  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
1191  <c>206</c> <c>Partial Content</c> <c anchor="status.206">&status-206;</c>
1192
1193  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
1194  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
1195  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
1196  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
1197  <c>304</c> <c>Not Modified</c> <c anchor="status.304">&status-304;</c>
1198  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
1199  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
1200
1201  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
1202  <c>401</c> <c>Unauthorized</c> <c anchor="status.401">&status-401;</c>
1203  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
1204  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
1205  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
1206  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
1207  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
1208  <c>407</c> <c>Proxy Authentication Required</c> <c anchor="status.407">&status-407;</c>
1209  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
1210  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
1211  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
1212  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
1213  <c>412</c> <c>Precondition Failed</c> <c anchor="status.412">&status-412;</c>
1214  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
1215  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
1216  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
1217  <c>416</c> <c>Requested range not satisfiable</c> <c anchor="status.416">&status-416;</c>
1218  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
1219  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
1220
1221  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
1222  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
1223  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
1224  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
1225  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
1226  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
1227</texttable>
1228<t>
1229   Note that this list is not exhaustive &mdash; it does not include
1230   extension status codes defined in other specifications.
1231</t>
1232</section>
1233
1234<section title="Status Code Registry" anchor="status.code.registry">
1235<t>
1236  The HTTP Status Code Registry defines the name space for the status-code
1237  token in the status-line of an HTTP response.
1238</t>
1239<t>
1240  Values to be added to this name space require IETF Review
1241  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
1242</t>
1243<t>
1244  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
1245</t>
1246
1247<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
1248<t>
1249   When it is necessary to express new semantics for a HTTP response that
1250   aren't specific to a single application or media type, and currently defined
1251   status codes are inadequate, a new status code can be registered.
1252</t>
1253<t>
1254   HTTP status codes are generic; that is, they are potentially applicable to
1255   any resource, not just one particular media type, "type" of resource, or
1256   application. As such, it is preferred that new HTTP status codes be
1257   registered in a document that isn't specific to a single application, so
1258   that this is clear.
1259</t>
1260<t>
1261   Definitions of new HTTP status codes typically explain the request
1262   conditions that produce a response containing the status code (e.g.,
1263   combinations of request headers and/or method(s)), along with any
1264   interactions with response headers (e.g., those that are required, those
1265   that modify the semantics of the response).
1266</t>
1267<t>
1268   New HTTP status codes are required to fall under one of the categories
1269   defined in <xref target="status.codes"/>. To allow existing parsers to
1270   properly handle them, new status codes cannot disallow a response body,
1271   although they can mandate a zero-length response body. They can require the
1272   presence of one or more particular HTTP response header(s).
1273</t>
1274<t>
1275   Likewise, their definitions can specify that caches are allowed to use
1276   heuristics to determine their freshness (see &caching;; by default, it is
1277   not allowed), and can define how to determine the resource which they
1278   carry a representation for (see <xref
1279   target="identifying.response.associated.with.representation"/>; by default,
1280   it is anonymous).
1281</t>
1282</section>
1283
1284</section>
1285
1286<section title="Informational 1xx" anchor="status.1xx">
1287<t>
1288   This class of status code indicates a provisional response,
1289   consisting only of the status-line and optional header fields, and is
1290   terminated by an empty line. There are no required header fields for this
1291   class of status code. Since HTTP/1.0 did not define any 1xx status
1292   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1293   except under experimental conditions.
1294</t>
1295<t>
1296   A client &MUST; be prepared to accept one or more 1xx status responses
1297   prior to a regular response, even if the client does not expect a 100
1298   (Continue) status message. Unexpected 1xx status responses &MAY; be
1299   ignored by a user agent.
1300</t>
1301<t>
1302   Proxies &MUST; forward 1xx responses, unless the connection between the
1303   proxy and its client has been closed, or unless the proxy itself
1304   requested the generation of the 1xx response. (For example, if a
1305   proxy adds a "Expect: 100-continue" field when it forwards a request,
1306   then it need not forward the corresponding 100 (Continue)
1307   response(s).)
1308</t>
1309
1310<section title="100 Continue" anchor="status.100">
1311  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1312  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1313<t>
1314   The client &SHOULD; continue with its request. This interim response is
1315   used to inform the client that the initial part of the request has
1316   been received and has not yet been rejected by the server. The client
1317   &SHOULD; continue by sending the remainder of the request or, if the
1318   request has already been completed, ignore this response. The server
1319   &MUST; send a final response after the request has been completed. See
1320   &use100; for detailed discussion of the use and handling of this
1321   status code.
1322</t>
1323</section>
1324
1325<section title="101 Switching Protocols" anchor="status.101">
1326  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1327  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1328<t>
1329   The server understands and is willing to comply with the client's
1330   request, via the Upgrade message header field (&header-upgrade;), for a
1331   change in the application protocol being used on this connection. The
1332   server will switch protocols to those defined by the response's
1333   Upgrade header field immediately after the empty line which
1334   terminates the 101 response.
1335</t>
1336<t>
1337   The protocol &SHOULD; be switched only when it is advantageous to do
1338   so. For example, switching to a newer version of HTTP is advantageous
1339   over older versions, and switching to a real-time, synchronous
1340   protocol might be advantageous when delivering resources that use
1341   such features.
1342</t>
1343</section>
1344</section>
1345
1346<section title="Successful 2xx" anchor="status.2xx">
1347<t>
1348   This class of status code indicates that the client's request was
1349   successfully received, understood, and accepted.
1350</t>
1351
1352<section title="200 OK" anchor="status.200">
1353  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1354  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1355<t>
1356   The request has succeeded. The payload returned with the response
1357   is dependent on the method used in the request, for example:
1358  <list style="hanging">
1359    <t hangText="GET">
1360      a representation of the target resource is sent in the response;
1361    </t>
1362    <t hangText="HEAD">
1363      the same representation as GET, except without the message body;
1364    </t>
1365    <t hangText="POST">
1366      a representation describing or containing the result of the action;
1367    </t>
1368    <t hangText="TRACE">
1369      a representation containing the request message as received by the
1370      end server.
1371    </t>
1372  </list>
1373</t>
1374<t>
1375   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1376   freshness for 200 responses.
1377</t>
1378</section>
1379
1380<section title="201 Created" anchor="status.201">
1381  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1382  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1383<t>
1384   The request has been fulfilled and has resulted in a new resource being
1385   created.
1386</t>
1387<t>
1388   The newly created resource is typically linked to from the response payload,
1389   with the most relevant URI also being carried in the Location header field.
1390   If the newly created resource's URI is the same as the Effective Request URI,
1391   this information can be omitted (e.g., in the case of a response to a PUT
1392   request). 
1393</t>
1394<t>
1395   The origin server &MUST; create the resource before returning the 201 status
1396   code. If the action cannot be carried out immediately, the server &SHOULD;
1397   respond with 202 (Accepted) response instead.
1398</t>
1399<t>
1400   A 201 response &MAY; contain an ETag response header field indicating
1401   the current value of the entity-tag for the representation of the resource
1402   just created (see &header-etag;).
1403</t>
1404</section>
1405
1406<section title="202 Accepted" anchor="status.202">
1407  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1408  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1409<t>
1410   The request has been accepted for processing, but the processing has
1411   not been completed.  The request might or might not eventually be
1412   acted upon, as it might be disallowed when processing actually takes
1413   place. There is no facility for re-sending a status code from an
1414   asynchronous operation such as this.
1415</t>
1416<t>
1417   The 202 response is intentionally non-committal. Its purpose is to
1418   allow a server to accept a request for some other process (perhaps a
1419   batch-oriented process that is only run once per day) without
1420   requiring that the user agent's connection to the server persist
1421   until the process is completed. The representation returned with this
1422   response &SHOULD; include an indication of the request's current status
1423   and either a pointer to a status monitor or some estimate of when the
1424   user can expect the request to be fulfilled.
1425</t>
1426</section>
1427
1428<section title="203 Non-Authoritative Information" anchor="status.203">
1429  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1430  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1431<t>
1432   The representation in the response has been transformed or otherwise
1433   modified by a transforming proxy (&intermediaries;).  Note that the
1434   behavior of transforming intermediaries is controlled by the no-transform
1435   Cache-Control directive (&header-cache-control;).
1436</t>
1437<t>
1438   This status code is only appropriate when the response status code would
1439   have been 200 (OK) otherwise. When the status code before transformation
1440   would have been different, the 214 Transformation Applied warn-code
1441   (&header-warning;) is appropriate.
1442</t>
1443<t>
1444   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1445   freshness for 203 responses.
1446</t>
1447</section>
1448
1449<section title="204 No Content" anchor="status.204">
1450  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1451  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1452<t>
1453   The 204 (No Content) status code indicates that the server has
1454   successfully fulfilled the request and that there is no additional
1455   content to return in the response payload body.  Metadata in the
1456   response header fields refer to the target resource and its current
1457   representation after the requested action.
1458</t>
1459<t>
1460   For example, if a 204 status code is received in response to a PUT
1461   request and the response contains an ETag header field, then the PUT
1462   was successful and the ETag field-value contains the entity-tag for
1463   the new representation of that target resource.
1464</t>
1465<t>
1466   The 204 response allows a server to indicate that the action has been
1467   successfully applied to the target resource while implying that the
1468   user agent &SHOULD-NOT; traverse away from its current "document view"
1469   (if any).  The server assumes that the user agent will provide some
1470   indication of the success to its user, in accord with its own interface,
1471   and apply any new or updated metadata in the response to the active
1472   representation.
1473</t>
1474<t>
1475   For example, a 204 status code is commonly used with document editing
1476   interfaces corresponding to a "save" action, such that the document
1477   being saved remains available to the user for editing. It is also
1478   frequently used with interfaces that expect automated data transfers
1479   to be prevalent, such as within distributed version control systems.
1480</t>
1481<t>
1482   The 204 response &MUST-NOT; include a message body, and thus is always
1483   terminated by the first empty line after the header fields.
1484</t>
1485</section>
1486
1487<section title="205 Reset Content" anchor="status.205">
1488  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1489  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1490<t>
1491   The server has fulfilled the request and the user agent &SHOULD; reset
1492   the document view which caused the request to be sent. This response
1493   is primarily intended to allow input for actions to take place via
1494   user input, followed by a clearing of the form in which the input is
1495   given so that the user can easily initiate another input action.
1496</t>
1497<t>   
1498   The message body included with the response &MUST; be empty. Note that
1499   receivers still need to parse the response according to the algorithm defined
1500   in &message-body;.
1501</t>
1502</section>
1503</section>
1504
1505<section title="Redirection 3xx" anchor="status.3xx">
1506<t>
1507   This class of status code indicates that further action needs to be
1508   taken by the user agent in order to fulfill the request.  If the required
1509   action involves a subsequent HTTP request, it &MAY; be carried out by the
1510   user agent without interaction with the user if and only if the method used
1511   in the second request is known to be "safe", as defined in
1512   <xref target="safe.methods"/>.
1513</t>
1514<t>
1515   There are several types of redirects:
1516   <list style="numbers">
1517      <x:lt>
1518        <t>
1519          Redirects of the request to another URI, either temporarily or
1520          permanently. The new URI is specified in the Location header field.
1521          In this specification, the status codes 301 (Moved Permanently),
1522          302 (Found), and 307 (Temporary Redirect) fall under this category.
1523        </t>
1524      </x:lt>
1525      <x:lt>
1526        <t>
1527          Redirection to a new location that represents an indirect response to
1528          the request, such as the result of a POST operation to be retrieved
1529          with a subsequent GET request. This is status code 303 (See Other).
1530        </t>
1531      </x:lt>
1532      <x:lt>
1533        <t>
1534          Redirection offering a choice of matching resources for use by
1535          agent-driven content negotiation (&agent-driven-negotiation;). This
1536          is status code 300 (Multiple Choices).
1537        </t>
1538      </x:lt>
1539      <x:lt>
1540        <t>
1541          Other kinds of redirection, such as to a cached result (status code 304
1542          (Not Modified), see &status-304;).
1543        </t>
1544      </x:lt>
1545   </list>
1546</t>
1547<x:note>
1548  <t>
1549    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1550    and 302 (Found) were defined for the first type of redirect, and the second
1551    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1552    However it turned out that web forms using POST expected redirects to change
1553    the operation for the subsequent request to retrieval (GET). To address this
1554    use case, HTTP/1.1 introduced the second type of redirect with the status
1555    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1556    As user agents did not change their behavior to maintain backwards
1557    compatibility, the first revision of HTTP/1.1 added yet another status code,
1558    307 (Temporary Redirect), for which the backwards compatibility problems did
1559    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1560    Over 10 years later, most user agents still do method rewriting for
1561    status codes 301 and 302, therefore this specification makes that behavior
1562    conformant in case the original request was POST.
1563  </t>
1564</x:note>
1565<t>
1566   A Location header field on a 3xx response indicates that a client &MAY;
1567   automatically redirect to the URI provided; see <xref target="header.location"/>.
1568</t>
1569<t>
1570   Note that for methods not known to be "safe", as defined in <xref target="safe.methods"/>,
1571   automatic redirection needs to done with care, since the redirect might
1572   change the conditions under which the request was issued.
1573</t>
1574<t>
1575   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1576   "infinite" redirection loops).
1577</t>
1578<x:note>
1579  <t>
1580    <x:h>Note:</x:h> An earlier version of this specification recommended a
1581    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1582    Content developers need to be aware that some clients might
1583    implement such a fixed limitation.
1584  </t>
1585</x:note>
1586
1587<section title="300 Multiple Choices" anchor="status.300">
1588  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1589  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1590<t>
1591   The target resource has more than one
1592   representation, each with its own specific location, and agent-driven
1593   negotiation information (&content-negotiation;) is being provided so that
1594   the user (or user agent) can select a preferred representation by
1595   redirecting its request to that location.
1596</t>
1597<t>
1598   Unless it was a HEAD request, the response &SHOULD; include a representation
1599   containing a list of representation metadata and location(s) from
1600   which the user or user agent can choose the one most appropriate. Depending
1601   upon the format and the capabilities of
1602   the user agent, selection of the most appropriate choice &MAY; be
1603   performed automatically. However, this specification does not define
1604   any standard for such automatic selection.
1605</t>
1606<t>
1607   If the server has a preferred choice of representation, it &SHOULD;
1608   include the specific URI for that representation in the Location
1609   field; user agents &MAY; use the Location field value for automatic
1610   redirection.
1611</t>
1612<t>
1613   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1614   freshness for 300 responses.
1615</t>
1616
1617</section>
1618
1619<section title="301 Moved Permanently" anchor="status.301">
1620  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1621  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1622<t>
1623   The target resource has been assigned a new permanent URI and any
1624   future references to this resource &SHOULD; use one of the returned
1625   URIs.  Clients with link editing capabilities ought to automatically
1626   re-link references to the effective request URI to one or more of the new
1627   references returned by the server, where possible.
1628</t>
1629<t>
1630   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1631   freshness for 301 responses.
1632</t>
1633<t>
1634   The new permanent URI &SHOULD; be given by the Location field in the
1635   response. A response payload can contain a short hypertext note with a
1636   hyperlink to the new URI(s).
1637</t>
1638<x:note>
1639  <t>
1640    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1641    request method from POST to GET for the subsequent request. If this
1642    behavior is undesired, status code 307 (Temporary Redirect) can be used
1643    instead.
1644  </t>
1645</x:note>
1646</section>
1647
1648<section title="302 Found" anchor="status.302">
1649  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1650  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1651<t>
1652   The target resource resides temporarily under a different URI.
1653   Since the redirection might be altered on occasion, the client &SHOULD;
1654   continue to use the effective request URI for future requests.
1655</t>
1656<t>
1657   The temporary URI &SHOULD; be given by the Location field in the
1658   response. A response payload can contain a short hypertext note with a
1659   hyperlink to the new URI(s).
1660</t>
1661<x:note>
1662  <t>
1663    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1664    request method from POST to GET for the subsequent request. If this
1665    behavior is undesired, status code 307 (Temporary Redirect) can be used
1666    instead.
1667  </t>
1668</x:note>
1669</section>
1670
1671<section title="303 See Other" anchor="status.303">
1672  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1673  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1674<t>
1675   The 303 status code indicates that the server is redirecting the
1676   user agent to a different resource, as indicated by a URI in the
1677   Location header field, that is intended to provide an indirect
1678   response to the original request.  In order to satisfy the original
1679   request, a user agent &SHOULD; perform a retrieval request using the
1680   Location URI (a GET or HEAD request if using HTTP), which
1681   may itself be redirected further, and present the eventual result as an
1682   answer to the original request.
1683   Note that the new URI in the Location header field is not considered
1684   equivalent to the effective request URI.
1685</t>
1686<t>
1687   This status code is generally applicable to any HTTP method.  It is
1688   primarily used to allow the output of a POST action to redirect
1689   the user agent to a selected resource, since doing so provides the
1690   information corresponding to the POST response in a form that
1691   can be separately identified, bookmarked, and cached independent
1692   of the original request.
1693</t>
1694<t>
1695   A 303 response to a GET request indicates that the requested
1696   resource does not have a representation of its own that can be
1697   transferred by the server over HTTP.  The Location URI indicates a
1698   resource that is descriptive of the target resource, such that the
1699   follow-on representation might be useful to recipients without
1700   implying that it adequately represents the target resource.
1701   Note that answers to the questions of what can be represented, what
1702   representations are adequate, and what might be a useful description
1703   are outside the scope of HTTP and thus entirely determined by the
1704   URI owner(s).
1705</t>
1706<t>
1707   Except for responses to a HEAD request, the representation of a 303
1708   response &SHOULD; contain a short hypertext note with a hyperlink
1709   to the Location URI.
1710</t>
1711</section>
1712
1713<section title="305 Use Proxy" anchor="status.305">
1714  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1715  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1716<t>
1717   The 305 status code was defined in a previous version of this specification
1718   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1719</t>
1720</section>
1721
1722<section title="306 (Unused)" anchor="status.306">
1723  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1724  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1725<t>
1726   The 306 status code was used in a previous version of the
1727   specification, is no longer used, and the code is reserved.
1728</t>
1729</section>
1730
1731<section title="307 Temporary Redirect" anchor="status.307">
1732  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1733  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1734<t>
1735   The target resource resides temporarily under a different URI.
1736   Since the redirection can change over time, the client &SHOULD;
1737   continue to use the effective request URI for future requests.
1738</t>
1739<t>
1740   The temporary URI &SHOULD; be given by the Location field in the
1741   response. A response payload can contain a short hypertext note with a
1742   hyperlink to the new URI(s).
1743</t>
1744<x:note>
1745  <t>
1746    <x:h>Note:</x:h> This status code is similar to 302 Found, except that
1747    it does not allow rewriting the request method from POST to GET. This
1748    specification defines no equivalent counterpart for 301 Moved Permanently
1749    (<xref target="draft-reschke-http-status-308"/>, however, defines the
1750    status code 308 Permanent Redirect for this purpose).
1751  </t>
1752</x:note>
1753</section>
1754</section>
1755
1756<section title="Client Error 4xx" anchor="status.4xx">
1757<t>
1758   The 4xx class of status code is intended for cases in which the
1759   client seems to have erred. Except when responding to a HEAD request,
1760   the server &SHOULD; include a representation containing an explanation of the
1761   error situation, and whether it is a temporary or permanent
1762   condition. These status codes are applicable to any request method.
1763   User agents &SHOULD; display any included representation to the user.
1764</t>
1765
1766<section title="400 Bad Request" anchor="status.400">
1767  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1768  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1769<t>
1770   The server cannot or will not process the request, due to a client error (e.g.,
1771   malformed syntax).
1772</t>
1773</section>
1774
1775<section title="402 Payment Required" anchor="status.402">
1776  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1777  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1778<t>
1779   This code is reserved for future use.
1780</t>
1781</section>
1782
1783<section title="403 Forbidden" anchor="status.403">
1784  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1785  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1786<t>
1787   The server understood the request, but refuses to authorize it. Providing
1788   different user authentication credentials might be successful, but any
1789   credentials that were provided in the request are insufficient. The request
1790   &SHOULD-NOT; be repeated with the same credentials.
1791</t>
1792<t>
1793   If the request method was not HEAD and the server wishes to make
1794   public why the request has not been fulfilled, it &SHOULD; describe the
1795   reason for the refusal in the representation.  If the server does not wish to
1796   make this information available to the client, the status code 404
1797   (Not Found) &MAY; be used instead.
1798</t>
1799</section>
1800
1801<section title="404 Not Found" anchor="status.404">
1802  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1803  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1804<t>
1805   The server has not found anything matching the effective request URI. No
1806   indication is given of whether the condition is temporary or
1807   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1808   knows, through some internally configurable mechanism, that an old
1809   resource is permanently unavailable and has no forwarding address.
1810   This status code is commonly used when the server does not wish to
1811   reveal exactly why the request has been refused, or when no other
1812   response is applicable.
1813</t>
1814</section>
1815
1816<section title="405 Method Not Allowed" anchor="status.405">
1817  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1818  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1819<t>
1820   The method specified in the request-line is not allowed for the target
1821   resource. The response &MUST; include an Allow header field containing a
1822   list of valid methods for the requested resource.
1823</t>
1824</section>
1825
1826<section title="406 Not Acceptable" anchor="status.406">
1827  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1828  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1829<t>
1830   The resource identified by the request is only capable of generating
1831   response representations which have content characteristics not acceptable
1832   according to the Accept and Accept-* header fields sent in the request
1833   (see &p3-header-fields;).
1834</t>
1835<t>
1836   Unless it was a HEAD request, the response &SHOULD; include a representation
1837   containing a list of available representation characteristics and location(s)
1838   from which the user or user agent can choose the one most
1839   appropriate. Depending upon the format and the
1840   capabilities of the user agent, selection of the most appropriate
1841   choice &MAY; be performed automatically. However, this specification
1842   does not define any standard for such automatic selection.
1843</t>
1844<x:note>
1845  <t>
1846    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1847    not acceptable according to the accept header fields sent in the
1848    request. In some cases, this might even be preferable to sending a
1849    406 response. User agents are encouraged to inspect the header fields of
1850    an incoming response to determine if it is acceptable.
1851  </t>
1852</x:note>
1853<t>
1854   If the response could be unacceptable, a user agent &SHOULD;
1855   temporarily stop receipt of more data and query the user for a
1856   decision on further actions.
1857</t>
1858</section>
1859
1860<section title="408 Request Timeout" anchor="status.408">
1861  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1862  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1863<t>
1864   The client did not produce a request within the time that the server
1865   was prepared to wait. The client &MAY; repeat the request without
1866   modifications at any later time.
1867</t>
1868</section>
1869
1870<section title="409 Conflict" anchor="status.409">
1871  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1872  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1873<t>
1874   The request could not be completed due to a conflict with the current
1875   state of the resource. This code is only allowed in situations where
1876   it is expected that the user might be able to resolve the conflict
1877   and resubmit the request. The response body &SHOULD; include enough
1878   information for the user to recognize the source of the conflict.
1879   Ideally, the response representation would include enough information for the
1880   user or user agent to fix the problem; however, that might not be
1881   possible and is not required.
1882</t>
1883<t>
1884   Conflicts are most likely to occur in response to a PUT request. For
1885   example, if versioning were being used and the representation being PUT
1886   included changes to a resource which conflict with those made by an
1887   earlier (third-party) request, the server might use the 409 response
1888   to indicate that it can't complete the request. In this case, the
1889   response representation would likely contain a list of the differences
1890   between the two versions.
1891</t>
1892</section>
1893
1894<section title="410 Gone" anchor="status.410">
1895  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1896  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1897<t>
1898   The target resource is no longer available at the server and no
1899   forwarding address is known. This condition is expected to be
1900   considered permanent. Clients with link editing capabilities &SHOULD;
1901   delete references to the effective request URI after user approval. If the
1902   server does not know, or has no facility to determine, whether or not
1903   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1904   used instead.
1905</t>
1906<t>
1907   The 410 response is primarily intended to assist the task of web
1908   maintenance by notifying the recipient that the resource is
1909   intentionally unavailable and that the server owners desire that
1910   remote links to that resource be removed. Such an event is common for
1911   limited-time, promotional services and for resources belonging to
1912   individuals no longer working at the server's site. It is not
1913   necessary to mark all permanently unavailable resources as "gone" or
1914   to keep the mark for any length of time &mdash; that is left to the
1915   discretion of the server owner.
1916</t>
1917<t>
1918   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
1919   for 410 responses.
1920</t>
1921</section>
1922
1923<section title="411 Length Required" anchor="status.411">
1924  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1925  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1926<t>
1927   The server refuses to accept the request without a defined Content-Length.
1928   The client &MAY; repeat the request if it adds a valid
1929   Content-Length header field containing the length of the message body
1930   in the request message.
1931</t>
1932</section>
1933
1934<section title="413 Request Representation Too Large" anchor="status.413">
1935  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
1936  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
1937<t>
1938   The server is refusing to process a request because the request
1939   representation is larger than the server is willing or able to process. The
1940   server &MAY; close the connection to prevent the client from continuing
1941   the request.
1942</t>
1943<t>
1944   If the condition is temporary, the server &SHOULD; include a Retry-After
1945   header field to indicate that it is temporary and after what
1946   time the client &MAY; try again.
1947</t>
1948</section>
1949
1950<section title="414 URI Too Long" anchor="status.414">
1951  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
1952  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
1953<t>
1954   The server is refusing to service the request because the effective request URI
1955   is longer than the server is willing to interpret. This rare
1956   condition is only likely to occur when a client has improperly
1957   converted a POST request to a GET request with long query
1958   information, when the client has descended into a URI "black hole" of
1959   redirection (e.g., a redirected URI prefix that points to a suffix of
1960   itself), or when the server is under attack by a client attempting to
1961   exploit security holes present in some servers using fixed-length
1962   buffers for reading or manipulating the request-target.
1963</t>
1964</section>
1965
1966<section title="415 Unsupported Media Type" anchor="status.415">
1967  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1968  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1969<t>
1970   The server is refusing to service the request because the request
1971   payload is in a format not supported by this request method on the
1972   target resource.
1973</t>
1974</section>
1975
1976<section title="417 Expectation Failed" anchor="status.417">
1977  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1978  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1979<t>
1980   The expectation given in an Expect header field (see <xref target="header.expect"/>)
1981   could not be met by this server, or, if the server is a proxy,
1982   the server has unambiguous evidence that the request could not be met
1983   by the next-hop server.
1984</t>
1985</section>
1986
1987<section title="426 Upgrade Required" anchor="status.426">
1988  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
1989  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
1990<t>
1991   The request can not be completed without a prior protocol upgrade. This
1992   response &MUST; include an Upgrade header field (&header-upgrade;)
1993   specifying the required protocols.
1994</t>
1995<figure>
1996<preamble>Example:</preamble>
1997<artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
1998HTTP/1.1 426 Upgrade Required
1999Upgrade: HTTP/3.0
2000Connection: Upgrade
2001Content-Length: <x:length-of target="s426body"/>
2002Content-Type: text/plain
2003
2004<x:span anchor="s426body">This service requires use of the HTTP/3.0 protocol.
2005</x:span></artwork></figure>
2006<t>
2007   The server &SHOULD; include a message body in the 426 response which
2008   indicates in human readable form the reason for the error and describes any
2009   alternative courses which may be available to the user.
2010</t>
2011</section>
2012</section>
2013
2014<section title="Server Error 5xx" anchor="status.5xx">
2015<t>
2016   Response status codes beginning with the digit "5" indicate cases in
2017   which the server is aware that it has erred or is incapable of
2018   performing the request. Except when responding to a HEAD request, the
2019   server &SHOULD; include a representation containing an explanation of the
2020   error situation, and whether it is a temporary or permanent
2021   condition. User agents &SHOULD; display any included representation to the
2022   user. These response codes are applicable to any request method.
2023</t>
2024
2025<section title="500 Internal Server Error" anchor="status.500">
2026  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
2027  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
2028<t>
2029   The server encountered an unexpected condition which prevented it
2030   from fulfilling the request.
2031</t>
2032</section>
2033
2034<section title="501 Not Implemented" anchor="status.501">
2035  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
2036  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
2037<t>
2038   The server does not support the functionality required to fulfill the
2039   request. This is the appropriate response when the server does not
2040   recognize the request method and is not capable of supporting it for
2041   any resource.
2042</t>
2043</section>
2044
2045<section title="502 Bad Gateway" anchor="status.502">
2046  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
2047  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
2048<t>
2049   The server, while acting as a gateway or proxy, received an invalid
2050   response from the upstream server it accessed in attempting to
2051   fulfill the request.
2052</t>
2053</section>
2054
2055<section title="503 Service Unavailable" anchor="status.503">
2056  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
2057  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
2058<t>
2059   The server is currently unable to handle the request due to a
2060   temporary overloading or maintenance of the server.
2061</t>
2062<t>
2063   The implication is that this is a temporary condition which will be
2064   alleviated after some delay. If known, the length of the delay &MAY; be
2065   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2066   If no Retry-After is given, the client &SHOULD; handle the response as it
2067   would for a 500 response.
2068</t>
2069<x:note>
2070  <t>
2071    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
2072    server has to use it when becoming overloaded. Some servers might wish
2073    to simply refuse the connection.
2074  </t>
2075</x:note>
2076</section>
2077
2078<section title="504 Gateway Timeout" anchor="status.504">
2079  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2080  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2081<t>
2082   The server, while acting as a gateway or proxy, did not receive a
2083   timely response from the upstream server specified by the URI (e.g.,
2084   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2085   to access in attempting to complete the request.
2086</t>
2087<x:note>
2088  <t>
2089    <x:h>Note</x:h> to implementors: some deployed proxies are known to
2090    return 400 or 500 when DNS lookups time out.
2091  </t>
2092</x:note>
2093</section>
2094
2095<section title="505 HTTP Version Not Supported" anchor="status.505">
2096  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2097  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
2098<t>
2099   The server does not support, or refuses to support, the protocol
2100   version that was used in the request message. The server is
2101   indicating that it is unable or unwilling to complete the request
2102   using the same major version as the client, as described in &http-version;,
2103   other than with this error message. The response &SHOULD; contain
2104   a representation describing why that version is not supported and what other
2105   protocols are supported by that server.
2106</t>
2107
2108</section>
2109</section>
2110
2111</section>
2112
2113<section title="Representation" anchor="representation">
2114<t>
2115   Request and Response messages &MAY; transfer a representation if not otherwise
2116   restricted by the request method or response status code. A representation
2117   consists of metadata (representation header fields) and data (representation
2118   body).  When a complete or partial representation is enclosed in an HTTP message,
2119   it is referred to as the payload of the message. HTTP representations
2120   are defined in &payload;.
2121</t>
2122<t>
2123   A representation body is only present in a message when a message body is
2124   present, as described in &message-body;. The representation body is obtained
2125   from the message body by decoding any Transfer-Encoding that might
2126   have been applied to ensure safe and proper transfer of the message.
2127</t>
2128
2129<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
2130<t>
2131   It is sometimes necessary to determine an identifier for the resource
2132   associated with a representation.
2133</t>
2134<t>
2135   An HTTP request representation, when present, is always associated with an
2136   anonymous (i.e., unidentified) resource.
2137</t>
2138<t>
2139   In the common case, an HTTP response is a representation of the target
2140   resource (see &effective-request-uri;). However, this is not always the
2141   case. To determine the URI of the resource a response is associated with,
2142   the following rules are used (with the first applicable one being selected):
2143</t>
2144<t><list style="numbers">
2145   <t>If the response status code is 200 or 203 and the request method was GET,
2146   the response payload is a representation of the target resource.</t>
2147   <t>If the response status code is 204, 206, or 304 and the request method was GET
2148   or HEAD, the response payload is a partial representation of the target
2149   resource.</t>
2150   <t>If the response has a Content-Location header field, and that URI is the same
2151   as the effective request URI, the response payload is a representation of the
2152   target resource.</t>
2153   <t>If the response has a Content-Location header field, and that URI is not the
2154   same as the effective request URI, then the response asserts that its
2155   payload is a representation of the resource identified by the
2156   Content-Location URI. However, such an assertion cannot be trusted unless
2157   it can be verified by other means (not defined by HTTP).</t>
2158   <t>Otherwise, the response is a representation of an anonymous (i.e.,
2159   unidentified) resource.</t>
2160</list></t>
2161<t>
2162  <cref anchor="TODO-req-uri">
2163   The comparison function is going to have to be defined somewhere,
2164   because we already need to compare URIs for things like cache invalidation.</cref>
2165</t>
2166</section>
2167
2168</section>
2169
2170
2171<section title="Common Protocol Parameters" anchor="common.protocol.parameters">
2172<section title="Date/Time Formats" anchor="http.date">
2173  <x:anchor-alias value="HTTP-date"/>
2174<t>
2175   HTTP applications have historically allowed three different formats
2176   for date/time stamps. However, the preferred format is a fixed-length subset
2177   of that defined by <xref target="RFC1123"/>:
2178</t>
2179<figure><artwork type="example" x:indent-with="  ">
2180Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2181</artwork></figure>
2182<t>
2183   The other formats are described here only for compatibility with obsolete
2184   implementations.
2185</t>
2186<figure><artwork type="example" x:indent-with="  ">
2187Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2188Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2189</artwork></figure>
2190<t>
2191   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2192   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2193   only generate the RFC 1123 format for representing HTTP-date values
2194   in header fields.
2195</t>
2196<t>
2197   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2198   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2199   equal to UTC (Coordinated Universal Time). This is indicated in the
2200   first two formats by the inclusion of "GMT" as the three-letter
2201   abbreviation for time zone, and &MUST; be assumed when reading the
2202   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2203   additional whitespace beyond that specifically included as SP in the
2204   grammar.
2205</t>
2206<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2207  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2208</artwork></figure>
2209<t anchor="preferred.date.format">
2210  <x:anchor-alias value="rfc1123-date"/>
2211  <x:anchor-alias value="time-of-day"/>
2212  <x:anchor-alias value="hour"/>
2213  <x:anchor-alias value="minute"/>
2214  <x:anchor-alias value="second"/>
2215  <x:anchor-alias value="day-name"/>
2216  <x:anchor-alias value="day"/>
2217  <x:anchor-alias value="month"/>
2218  <x:anchor-alias value="year"/>
2219  <x:anchor-alias value="GMT"/>
2220  Preferred format:
2221</t>
2222<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"/>
2223  <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>
2224  ; fixed length subset of the format defined in
2225  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2226 
2227  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2228               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2229               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2230               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2231               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2232               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2233               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2234               
2235  <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>
2236               ; e.g., 02 Jun 1982
2237
2238  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2239  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2240               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2241               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2242               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2243               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2244               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2245               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2246               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2247               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2248               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2249               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2250               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2251  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2252
2253  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2254
2255  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2256                 ; 00:00:00 - 23:59:59
2257                 
2258  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2259  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2260  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2261</artwork></figure>
2262<t>
2263  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2264  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2265  same as those defined for the RFC 5322 constructs
2266  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2267</t>
2268<t anchor="obsolete.date.formats">
2269  <x:anchor-alias value="obs-date"/>
2270  <x:anchor-alias value="rfc850-date"/>
2271  <x:anchor-alias value="asctime-date"/>
2272  <x:anchor-alias value="date1"/>
2273  <x:anchor-alias value="date2"/>
2274  <x:anchor-alias value="date3"/>
2275  <x:anchor-alias value="rfc1123-date"/>
2276  <x:anchor-alias value="day-name-l"/>
2277  Obsolete formats:
2278</t>
2279<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2280  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2281</artwork></figure>
2282<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2283  <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>
2284  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2285                 ; day-month-year (e.g., 02-Jun-82)
2286
2287  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2288         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2289         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2290         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2291         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2292         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2293         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2294</artwork></figure>
2295<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2296  <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>
2297  <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> ))
2298                 ; month day (e.g., Jun  2)
2299</artwork></figure>
2300<x:note>
2301  <t>
2302    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2303    accepting date values that might have been sent by non-HTTP
2304    applications, as is sometimes the case when retrieving or posting
2305    messages via proxies/gateways to SMTP or NNTP.
2306  </t>
2307</x:note>
2308<x:note>
2309  <t>
2310    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2311    to their usage within the protocol stream. Clients and servers are
2312    not required to use these formats for user presentation, request
2313    logging, etc.
2314  </t>
2315</x:note>
2316</section>
2317
2318<section title="Product Tokens" anchor="product.tokens">
2319  <x:anchor-alias value="product"/>
2320  <x:anchor-alias value="product-version"/>
2321<t>
2322   Product tokens are used to allow communicating applications to
2323   identify themselves by software name and version. Most fields using
2324   product tokens also allow sub-products which form a significant part
2325   of the application to be listed, separated by whitespace. By
2326   convention, the products are listed in order of their significance
2327   for identifying the application.
2328</t>
2329<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2330  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2331  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2332</artwork></figure>
2333<t>
2334   Examples:
2335</t>
2336<figure><artwork type="example">
2337  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2338  Server: Apache/0.8.4
2339</artwork></figure>
2340<t>
2341   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2342   used for advertising or other non-essential information. Although any
2343   token octet &MAY; appear in a product-version, this token &SHOULD;
2344   only be used for a version identifier (i.e., successive versions of
2345   the same product &SHOULD; only differ in the product-version portion of
2346   the product value).
2347</t>
2348</section>
2349</section>
2350
2351<section title="Header Field Definitions" anchor="header.field.definitions">
2352<t>
2353   This section defines the syntax and semantics of HTTP/1.1 header fields
2354   related to request and response semantics.
2355</t>
2356
2357<section title="Allow" anchor="header.allow">
2358  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2359  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2360  <x:anchor-alias value="Allow"/>
2361<t>
2362   The "Allow" header field lists the set of methods advertised as
2363   supported by the target resource. The purpose of this field is strictly to
2364   inform the recipient of valid request methods associated with the resource.
2365</t>
2366<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2367  <x:ref>Allow</x:ref> = #<x:ref>method</x:ref>
2368</artwork></figure>
2369<t>
2370   Example of use:
2371</t>
2372<figure><artwork type="example">
2373  Allow: GET, HEAD, PUT
2374</artwork></figure>
2375<t>
2376   The actual set of allowed methods is defined by the origin server at the
2377   time of each request.
2378</t>
2379<t>
2380   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2381   understand all the methods specified in order to handle them according to
2382   the generic message handling rules.
2383</t>
2384</section>
2385
2386<section title="Date" anchor="header.date">
2387  <iref primary="true" item="Date header field" x:for-anchor=""/>
2388  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
2389  <x:anchor-alias value="Date"/>
2390<t>
2391   The "Date" header field represents the date and time at which
2392   the message was originated, having the same semantics as the Origination
2393   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2394   The field value is an HTTP-date, as defined in <xref target="http.date"/>;
2395   it &MUST; be sent in rfc1123-date format.
2396</t>
2397<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2398  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
2399</artwork></figure>
2400<t>
2401   An example is
2402</t>
2403<figure><artwork type="example">
2404  Date: Tue, 15 Nov 1994 08:12:31 GMT
2405</artwork></figure>
2406<t>
2407   Origin servers &MUST; include a Date header field in all responses,
2408   except in these cases:
2409  <list style="numbers">
2410      <t>If the response status code is 100 (Continue) or 101 (Switching
2411         Protocols), the response &MAY; include a Date header field, at
2412         the server's option.</t>
2413
2414      <t>If the response status code conveys a server error, e.g., 500
2415         (Internal Server Error) or 503 (Service Unavailable), and it is
2416         inconvenient or impossible to generate a valid Date.</t>
2417
2418      <t>If the server does not have a clock that can provide a
2419         reasonable approximation of the current time, its responses
2420         &MUST-NOT; include a Date header field.</t>
2421  </list>
2422</t>
2423<t>
2424   A received message that does not have a Date header field &MUST; be
2425   assigned one by the recipient if the message will be cached by that
2426   recipient.
2427</t>
2428<t>
2429   Clients can use the Date header field as well; in order to keep request
2430   messages small, they are advised not to include it when it doesn't convey
2431   any useful information (as is usually the case for requests that do not
2432   contain a payload).
2433</t>
2434<t>
2435   The HTTP-date sent in a Date header field &SHOULD-NOT; represent a date and
2436   time subsequent to the generation of the message. It &SHOULD; represent
2437   the best available approximation of the date and time of message
2438   generation, unless the implementation has no means of generating a
2439   reasonably accurate date and time. In theory, the date ought to
2440   represent the moment just before the payload is generated. In
2441   practice, the date can be generated at any time during the message
2442   origination without affecting its semantic value.
2443</t>
2444</section>
2445
2446<section title="Expect" anchor="header.expect">
2447  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2448  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2449  <x:anchor-alias value="Expect"/>
2450  <x:anchor-alias value="expectation"/>
2451  <x:anchor-alias value="expect-param"/>
2452  <x:anchor-alias value="expect-name"/>
2453  <x:anchor-alias value="expect-value"/>
2454<t>
2455   The "Expect" header field is used to indicate that particular
2456   server behaviors are required by the client.
2457</t>
2458<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"/>
2459  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
2460 
2461  <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> ]
2462                             *( <x:ref>OWS</x:ref> ";" [ <x:ref>OWS</x:ref> <x:ref>expect-param</x:ref> ] )
2463  <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> ]
2464 
2465  <x:ref>expect-name</x:ref>  = <x:ref>token</x:ref>
2466  <x:ref>expect-value</x:ref> = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
2467</artwork></figure>
2468<t>
2469   If all received Expect header field(s) are syntactically valid but contain
2470   an expectation that the recipient does not understand or cannot comply with,
2471   the recipient &MUST; respond with a 417 (Expectation Failed) status code. A
2472   recipient of a syntactically invalid Expectation header field &MUST; respond
2473   with a 4xx status code other than 417.
2474</t>
2475<t>
2476   The only expectation defined by this specification is:
2477</t>
2478<t><iref primary="true" item="100-continue (expect value)"/><iref primary="true" item="Expect Values" subitem="100-continue"/>
2479  100-continue
2480   <list>
2481      <t>
2482        The "100-continue" expectation is defined &use100;. It does not support
2483        any expect-params.
2484      </t>
2485   </list>
2486</t>
2487<t>
2488   Comparison is case-insensitive for names (expect-name), and case-sensitive
2489   for values (expect-value).
2490</t>
2491<t>
2492   The Expect mechanism is hop-by-hop: the above requirements apply to any
2493   server, including proxies. However, the Expect header field itself is
2494   end-to-end; it &MUST; be forwarded if the request is forwarded.
2495</t>
2496<t>
2497   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect
2498   header field.
2499</t>
2500</section>
2501
2502<section title="From" anchor="header.from">
2503  <iref primary="true" item="From header field" x:for-anchor=""/>
2504  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2505  <x:anchor-alias value="From"/>
2506  <x:anchor-alias value="mailbox"/>
2507<t>
2508   The "From" header field, if given, &SHOULD; contain an Internet
2509   e-mail address for the human user who controls the requesting user
2510   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2511   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2512</t>
2513<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2514  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
2515 
2516  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2517</artwork></figure>
2518<t>
2519   An example is:
2520</t>
2521<figure><artwork type="example">
2522  From: webmaster@example.org
2523</artwork></figure>
2524<t>
2525   This header field &MAY; be used for logging purposes and as a means for
2526   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2527   be used as an insecure form of access protection. The interpretation
2528   of this field is that the request is being performed on behalf of the
2529   person given, who accepts responsibility for the method performed. In
2530   particular, robot agents &SHOULD; include this header field so that the
2531   person responsible for running the robot can be contacted if problems
2532   occur on the receiving end.
2533</t>
2534<t>
2535   The Internet e-mail address in this field &MAY; be separate from the
2536   Internet host which issued the request. For example, when a request
2537   is passed through a proxy the original issuer's address &SHOULD; be
2538   used.
2539</t>
2540<t>
2541   The client &SHOULD-NOT;  send the From header field without the user's
2542   approval, as it might conflict with the user's privacy interests or
2543   their site's security policy. It is strongly recommended that the
2544   user be able to disable, enable, and modify the value of this field
2545   at any time prior to a request.
2546</t>
2547</section>
2548
2549<section title="Location" anchor="header.location">
2550  <iref primary="true" item="Location header field" x:for-anchor=""/>
2551  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2552  <x:anchor-alias value="Location"/>
2553<t>
2554   The "Location" header field &MAY; be sent in responses to refer to
2555   a specific resource in accordance with the semantics of the status
2556   code.
2557</t>
2558<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2559  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2560</artwork></figure>
2561<t>
2562   For 201 (Created) responses, the Location is the URI of the new resource
2563   which was created by the request. For 3xx responses, the location &SHOULD;
2564   indicate the server's preferred URI for automatic redirection to the
2565   resource.
2566</t>
2567<t>
2568   The field value consists of a single URI-reference. When it has the form
2569   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2570   the final value is computed by resolving it against the effective request
2571   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>). If the original URI, as
2572   navigated to by the user agent, did contain a fragment identifier, and the
2573   final value does not, then the original URI's fragment identifier is added
2574   to the final value.
2575</t>
2576<figure>
2577<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-->
2578<artwork type="example">
2579  Location: /pub/WWW/People.html#tim
2580</artwork>
2581<postamble>would result in a final value of "http://www.example.org/pub/WWW/People.html#tim"</postamble>
2582</figure>
2583<figure>
2584<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-->
2585<artwork type="example">
2586  Location: http://www.example.net/index.html
2587</artwork>
2588<postamble>would result in a final value of "http://www.example.net/index.html#larry", preserving the original fragment identifier.</postamble>
2589</figure>
2590<x:note>
2591  <t>
2592    <x:h>Note:</x:h> Some recipients attempt to recover from Location fields
2593    that are not valid URI references. This specification does not mandate or
2594    define such processing, but does allow it (see <xref target="intro.conformance.and.error.handling"/>).
2595  </t>
2596</x:note>
2597<t>
2598   There are circumstances in which a fragment identifier in a Location URI
2599   would not be appropriate. For instance, when it appears in a 201 Created
2600   response, where the Location header field specifies the URI for the entire
2601   created resource.
2602</t>
2603<x:note>
2604  <t>
2605    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2606    from Location in that the Content-Location identifies the most specific
2607    resource corresponding to the enclosed representation.
2608    It is therefore possible for a response to contain header fields for
2609    both Location and Content-Location.
2610  </t>
2611</x:note>
2612</section>
2613
2614<section title="Max-Forwards" anchor="header.max-forwards">
2615  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2616  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2617  <x:anchor-alias value="Max-Forwards"/>
2618<t>
2619   The "Max-Forwards" header field provides a mechanism with the
2620   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2621   methods to limit the number of times that the request is forwarded by
2622   proxies. This can be useful when the client is attempting to
2623   trace a request which appears to be failing or looping mid-chain.
2624</t>
2625<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2626  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2627</artwork></figure>
2628<t>
2629   The Max-Forwards value is a decimal integer indicating the remaining
2630   number of times this request message can be forwarded.
2631</t>
2632<t>
2633   Each recipient of a TRACE or OPTIONS request
2634   containing a Max-Forwards header field &MUST; check and update its
2635   value prior to forwarding the request. If the received value is zero
2636   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2637   respond as the final recipient. If the received Max-Forwards value is
2638   greater than zero, then the forwarded message &MUST; contain an updated
2639   Max-Forwards field with a value decremented by one (1).
2640</t>
2641<t>
2642   The Max-Forwards header field &MAY; be ignored for all other request
2643   methods.
2644</t>
2645</section>
2646
2647<section title="Referer" anchor="header.referer">
2648  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2649  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2650  <x:anchor-alias value="Referer"/>
2651<t>
2652   The "Referer" [sic] header field allows the client to specify the
2653   URI of the resource from which the target URI was obtained (the
2654   "referrer", although the header field is misspelled.).
2655</t>
2656<t>
2657   The Referer header field allows servers to generate lists of back-links to
2658   resources for interest, logging, optimized caching, etc. It also allows
2659   obsolete or mistyped links to be traced for maintenance. Some servers use
2660   Referer as a means of controlling where they allow links from (so-called
2661   "deep linking"), but legitimate requests do not always
2662   contain a Referer header field.
2663</t>
2664<t>
2665   If the target URI was obtained from a source that does not have its own
2666   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2667   sent with the value "about:blank", or not be sent at all. Note that this
2668   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2669</t>
2670<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2671  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2672</artwork></figure>
2673<t>
2674   Example:
2675</t>
2676<figure><artwork type="example">
2677  Referer: http://www.example.org/hypertext/Overview.html
2678</artwork></figure>
2679<t>
2680   If the field value is a relative URI, it &SHOULD; be interpreted
2681   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2682   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2683</t>
2684</section>
2685
2686<section title="Retry-After" anchor="header.retry-after">
2687  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2688  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2689  <x:anchor-alias value="Retry-After"/>
2690<t>
2691   The header "Retry-After" field can be used with a 503 (Service
2692   Unavailable) response to indicate how long the service is expected to
2693   be unavailable to the requesting client. This field &MAY; also be used
2694   with any 3xx (Redirection) response to indicate the minimum time the
2695   user-agent is asked to wait before issuing the redirected request.
2696</t>
2697<t>
2698   The value of this field can be either an HTTP-date or an integer number
2699   of seconds (in decimal) after the time of the response.
2700</t>
2701<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2702  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2703</artwork></figure>
2704<t anchor="rule.delta-seconds">
2705  <x:anchor-alias value="delta-seconds"/>
2706   Time spans are non-negative decimal integers, representing time in
2707   seconds.
2708</t>
2709<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2710  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2711</artwork></figure>
2712<t>
2713   Two examples of its use are
2714</t>
2715<figure><artwork type="example">
2716  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2717  Retry-After: 120
2718</artwork></figure>
2719<t>
2720   In the latter example, the delay is 2 minutes.
2721</t>
2722</section>
2723
2724<section title="Server" anchor="header.server">
2725  <iref primary="true" item="Server header field" x:for-anchor=""/>
2726  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2727  <x:anchor-alias value="Server"/>
2728<t>
2729   The "Server" header field contains information about the
2730   software used by the origin server to handle the request.
2731</t>
2732<t>
2733   The field can contain multiple
2734   product tokens (<xref target="product.tokens"/>) and
2735   comments (&header-fields;) identifying the server and any significant
2736   subproducts. The product tokens are listed in order of their significance
2737   for identifying the application.
2738</t>
2739<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2740  <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> ) )
2741</artwork></figure>
2742<t>
2743   Example:
2744</t>
2745<figure><artwork type="example">
2746  Server: CERN/3.0 libwww/2.17
2747</artwork></figure>
2748<t>
2749   If the response is being forwarded through a proxy, the proxy
2750   application &MUST-NOT; modify the Server header field. Instead, it
2751   &MUST; include a Via field (as described in &header-via;).
2752</t>
2753<x:note>
2754  <t>
2755    <x:h>Note:</x:h> Revealing the specific software version of the server might
2756    allow the server machine to become more vulnerable to attacks
2757    against software that is known to contain security holes. Server
2758    implementors are encouraged to make this field a configurable
2759    option.
2760  </t>
2761</x:note>
2762</section>
2763
2764<section title="User-Agent" anchor="header.user-agent">
2765  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2766  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2767  <x:anchor-alias value="User-Agent"/>
2768<t>
2769   The "User-Agent" header field contains information about the user
2770   agent originating the request. User agents &SHOULD; include this field with
2771   requests.
2772</t>
2773<t>
2774   Typically, it is used for statistical purposes, the tracing of protocol
2775   violations, and tailoring responses to avoid particular user agent
2776   limitations.
2777</t>
2778<t>
2779   The field can contain multiple
2780   product tokens (<xref target="product.tokens"/>)
2781   and comments (&header-fields;) identifying the agent and its
2782   significant subproducts. By convention, the product tokens are listed in
2783   order of their significance for identifying the application.
2784</t>
2785<t>
2786   Because this field is usually sent on every request a user agent makes,
2787   implementations are encouraged not to include needlessly fine-grained
2788   detail, and to limit (or even prohibit) the addition of subproducts by third
2789   parties. Overly long and detailed User-Agent field values make requests
2790   larger and can also be used to identify ("fingerprint") the user against
2791   their wishes.
2792</t>
2793<t>
2794   Likewise, implementations are encouraged not to use the product tokens of
2795   other implementations in order to declare compatibility with them, as this
2796   circumvents the purpose of the field. Finally, they are encouraged not to
2797   use comments to identify products; doing so makes the field value more
2798   difficult to parse.
2799</t>
2800<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2801  <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> ) )
2802</artwork></figure>
2803<t>
2804   Example:
2805</t>
2806<figure><artwork type="example">
2807  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2808</artwork></figure>
2809</section>
2810
2811</section>
2812
2813<section title="IANA Considerations" anchor="IANA.considerations">
2814
2815<section title="Method Registry" anchor="method.registration">
2816<t>
2817  The registration procedure for HTTP request methods is defined by
2818  <xref target="method.registry"/> of this document.
2819</t>
2820<t>
2821   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2822   and be populated with the registrations below:
2823</t>
2824<?BEGININC p2-semantics.iana-methods ?>
2825<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2826<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2827   <ttcol>Method</ttcol>
2828   <ttcol>Safe</ttcol>
2829   <ttcol>Reference</ttcol>
2830   <c>CONNECT</c>
2831   <c>no</c>
2832   <c>
2833      <xref target="CONNECT"/>
2834   </c>
2835   <c>DELETE</c>
2836   <c>no</c>
2837   <c>
2838      <xref target="DELETE"/>
2839   </c>
2840   <c>GET</c>
2841   <c>yes</c>
2842   <c>
2843      <xref target="GET"/>
2844   </c>
2845   <c>HEAD</c>
2846   <c>yes</c>
2847   <c>
2848      <xref target="HEAD"/>
2849   </c>
2850   <c>OPTIONS</c>
2851   <c>yes</c>
2852   <c>
2853      <xref target="OPTIONS"/>
2854   </c>
2855   <c>POST</c>
2856   <c>no</c>
2857   <c>
2858      <xref target="POST"/>
2859   </c>
2860   <c>PUT</c>
2861   <c>no</c>
2862   <c>
2863      <xref target="PUT"/>
2864   </c>
2865   <c>TRACE</c>
2866   <c>yes</c>
2867   <c>
2868      <xref target="TRACE"/>
2869   </c>
2870</texttable>
2871<!--(END)-->
2872<?ENDINC p2-semantics.iana-methods ?>
2873</section>
2874
2875<section title="Status Code Registry" anchor="status.code.registration">
2876<t>
2877   The registration procedure for HTTP Status Codes &mdash; previously defined
2878   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2879   by <xref target="status.code.registry"/> of this document.
2880</t>
2881<t>
2882   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2883   shall be updated with the registrations below:
2884</t>
2885<?BEGININC p2-semantics.iana-status-codes ?>
2886<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2887<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2888   <ttcol>Value</ttcol>
2889   <ttcol>Description</ttcol>
2890   <ttcol>Reference</ttcol>
2891   <c>100</c>
2892   <c>Continue</c>
2893   <c>
2894      <xref target="status.100"/>
2895   </c>
2896   <c>101</c>
2897   <c>Switching Protocols</c>
2898   <c>
2899      <xref target="status.101"/>
2900   </c>
2901   <c>200</c>
2902   <c>OK</c>
2903   <c>
2904      <xref target="status.200"/>
2905   </c>
2906   <c>201</c>
2907   <c>Created</c>
2908   <c>
2909      <xref target="status.201"/>
2910   </c>
2911   <c>202</c>
2912   <c>Accepted</c>
2913   <c>
2914      <xref target="status.202"/>
2915   </c>
2916   <c>203</c>
2917   <c>Non-Authoritative Information</c>
2918   <c>
2919      <xref target="status.203"/>
2920   </c>
2921   <c>204</c>
2922   <c>No Content</c>
2923   <c>
2924      <xref target="status.204"/>
2925   </c>
2926   <c>205</c>
2927   <c>Reset Content</c>
2928   <c>
2929      <xref target="status.205"/>
2930   </c>
2931   <c>300</c>
2932   <c>Multiple Choices</c>
2933   <c>
2934      <xref target="status.300"/>
2935   </c>
2936   <c>301</c>
2937   <c>Moved Permanently</c>
2938   <c>
2939      <xref target="status.301"/>
2940   </c>
2941   <c>302</c>
2942   <c>Found</c>
2943   <c>
2944      <xref target="status.302"/>
2945   </c>
2946   <c>303</c>
2947   <c>See Other</c>
2948   <c>
2949      <xref target="status.303"/>
2950   </c>
2951   <c>305</c>
2952   <c>Use Proxy</c>
2953   <c>
2954      <xref target="status.305"/>
2955   </c>
2956   <c>306</c>
2957   <c>(Unused)</c>
2958   <c>
2959      <xref target="status.306"/>
2960   </c>
2961   <c>307</c>
2962   <c>Temporary Redirect</c>
2963   <c>
2964      <xref target="status.307"/>
2965   </c>
2966   <c>400</c>
2967   <c>Bad Request</c>
2968   <c>
2969      <xref target="status.400"/>
2970   </c>
2971   <c>402</c>
2972   <c>Payment Required</c>
2973   <c>
2974      <xref target="status.402"/>
2975   </c>
2976   <c>403</c>
2977   <c>Forbidden</c>
2978   <c>
2979      <xref target="status.403"/>
2980   </c>
2981   <c>404</c>
2982   <c>Not Found</c>
2983   <c>
2984      <xref target="status.404"/>
2985   </c>
2986   <c>405</c>
2987   <c>Method Not Allowed</c>
2988   <c>
2989      <xref target="status.405"/>
2990   </c>
2991   <c>406</c>
2992   <c>Not Acceptable</c>
2993   <c>
2994      <xref target="status.406"/>
2995   </c>
2996   <c>408</c>
2997   <c>Request Timeout</c>
2998   <c>
2999      <xref target="status.408"/>
3000   </c>
3001   <c>409</c>
3002   <c>Conflict</c>
3003   <c>
3004      <xref target="status.409"/>
3005   </c>
3006   <c>410</c>
3007   <c>Gone</c>
3008   <c>
3009      <xref target="status.410"/>
3010   </c>
3011   <c>411</c>
3012   <c>Length Required</c>
3013   <c>
3014      <xref target="status.411"/>
3015   </c>
3016   <c>413</c>
3017   <c>Request Representation Too Large</c>
3018   <c>
3019      <xref target="status.413"/>
3020   </c>
3021   <c>414</c>
3022   <c>URI Too Long</c>
3023   <c>
3024      <xref target="status.414"/>
3025   </c>
3026   <c>415</c>
3027   <c>Unsupported Media Type</c>
3028   <c>
3029      <xref target="status.415"/>
3030   </c>
3031   <c>417</c>
3032   <c>Expectation Failed</c>
3033   <c>
3034      <xref target="status.417"/>
3035   </c>
3036   <c>426</c>
3037   <c>Upgrade Required</c>
3038   <c>
3039      <xref target="status.426"/>
3040   </c>
3041   <c>500</c>
3042   <c>Internal Server Error</c>
3043   <c>
3044      <xref target="status.500"/>
3045   </c>
3046   <c>501</c>
3047   <c>Not Implemented</c>
3048   <c>
3049      <xref target="status.501"/>
3050   </c>
3051   <c>502</c>
3052   <c>Bad Gateway</c>
3053   <c>
3054      <xref target="status.502"/>
3055   </c>
3056   <c>503</c>
3057   <c>Service Unavailable</c>
3058   <c>
3059      <xref target="status.503"/>
3060   </c>
3061   <c>504</c>
3062   <c>Gateway Timeout</c>
3063   <c>
3064      <xref target="status.504"/>
3065   </c>
3066   <c>505</c>
3067   <c>HTTP Version Not Supported</c>
3068   <c>
3069      <xref target="status.505"/>
3070   </c>
3071</texttable>
3072<!--(END)-->
3073<?ENDINC p2-semantics.iana-status-codes ?>
3074</section>
3075<section title="Header Field Registration" anchor="header.field.registration">
3076<t>
3077   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3078   with the permanent registrations below (see <xref target="RFC3864"/>):
3079</t>
3080<?BEGININC p2-semantics.iana-headers ?>
3081<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3082<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3083   <ttcol>Header Field Name</ttcol>
3084   <ttcol>Protocol</ttcol>
3085   <ttcol>Status</ttcol>
3086   <ttcol>Reference</ttcol>
3087
3088   <c>Allow</c>
3089   <c>http</c>
3090   <c>standard</c>
3091   <c>
3092      <xref target="header.allow"/>
3093   </c>
3094   <c>Date</c>
3095   <c>http</c>
3096   <c>standard</c>
3097   <c>
3098      <xref target="header.date"/>
3099   </c>
3100   <c>Expect</c>
3101   <c>http</c>
3102   <c>standard</c>
3103   <c>
3104      <xref target="header.expect"/>
3105   </c>
3106   <c>From</c>
3107   <c>http</c>
3108   <c>standard</c>
3109   <c>
3110      <xref target="header.from"/>
3111   </c>
3112   <c>Location</c>
3113   <c>http</c>
3114   <c>standard</c>
3115   <c>
3116      <xref target="header.location"/>
3117   </c>
3118   <c>Max-Forwards</c>
3119   <c>http</c>
3120   <c>standard</c>
3121   <c>
3122      <xref target="header.max-forwards"/>
3123   </c>
3124   <c>Referer</c>
3125   <c>http</c>
3126   <c>standard</c>
3127   <c>
3128      <xref target="header.referer"/>
3129   </c>
3130   <c>Retry-After</c>
3131   <c>http</c>
3132   <c>standard</c>
3133   <c>
3134      <xref target="header.retry-after"/>
3135   </c>
3136   <c>Server</c>
3137   <c>http</c>
3138   <c>standard</c>
3139   <c>
3140      <xref target="header.server"/>
3141   </c>
3142   <c>User-Agent</c>
3143   <c>http</c>
3144   <c>standard</c>
3145   <c>
3146      <xref target="header.user-agent"/>
3147   </c>
3148</texttable>
3149<!--(END)-->
3150<?ENDINC p2-semantics.iana-headers ?>
3151<t>
3152   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3153</t>
3154</section>
3155</section>
3156
3157<section title="Security Considerations" anchor="security.considerations">
3158<t>
3159   This section is meant to inform application developers, information
3160   providers, and users of the security limitations in HTTP/1.1 as
3161   described by this document. The discussion does not include
3162   definitive solutions to the problems revealed, though it does make
3163   some suggestions for reducing security risks.
3164</t>
3165
3166<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3167<t>
3168   Like any generic data transfer protocol, HTTP cannot regulate the
3169   content of the data that is transferred, nor is there any a priori
3170   method of determining the sensitivity of any particular piece of
3171   information within the context of any given request. Therefore,
3172   applications &SHOULD; supply as much control over this information as
3173   possible to the provider of that information. Four header fields are
3174   worth special mention in this context: Server, Via, Referer and From.
3175</t>
3176<t>
3177   Revealing the specific software version of the server might allow the
3178   server machine to become more vulnerable to attacks against software
3179   that is known to contain security holes. Implementors &SHOULD; make the
3180   Server header field a configurable option.
3181</t>
3182<t>
3183   Proxies which serve as a portal through a network firewall &SHOULD;
3184   take special precautions regarding the transfer of header information
3185   that identifies the hosts behind the firewall. In particular, they
3186   &SHOULD; remove, or replace with sanitized versions, any Via fields
3187   generated behind the firewall.
3188</t>
3189<t>
3190   The Referer header field allows reading patterns to be studied and reverse
3191   links drawn. Although it can be very useful, its power can be abused
3192   if user details are not separated from the information contained in
3193   the Referer. Even when the personal information has been removed, the
3194   Referer header field might indicate a private document's URI whose
3195   publication would be inappropriate.
3196</t>
3197<t>
3198   The information sent in the From field might conflict with the user's
3199   privacy interests or their site's security policy, and hence it
3200   &SHOULD-NOT;  be transmitted without the user being able to disable,
3201   enable, and modify the contents of the field. The user &MUST; be able
3202   to set the contents of this field within a user preference or
3203   application defaults configuration.
3204</t>
3205<t>
3206   We suggest, though do not require, that a convenient toggle interface
3207   be provided for the user to enable or disable the sending of From and
3208   Referer information.
3209</t>
3210<t>
3211   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3212   target="header.server"/>) header fields can sometimes be used to determine
3213   that a specific client or server has a particular security hole which might
3214   be exploited. Unfortunately, this same information is often used for other
3215   valuable purposes for which HTTP currently has no better mechanism.
3216</t>
3217<t>
3218   Furthermore, the User-Agent header field may contain enough entropy to be
3219   used, possibly in conjunction with other material, to uniquely identify the
3220   user.
3221</t>
3222<t>
3223   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3224   that was sent in request header fields within the body of their response.
3225   Clients &SHOULD; be careful with sensitive information, like Cookies,
3226   Authorization credentials, and other header fields that might be used to
3227   collect data from the client.
3228</t> 
3229</section>
3230
3231<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3232<t>
3233   Because the source of a link might be private information or might
3234   reveal an otherwise private information source, it is strongly
3235   recommended that the user be able to select whether or not the
3236   Referer field is sent. For example, a browser client could have a
3237   toggle switch for browsing openly/anonymously, which would
3238   respectively enable/disable the sending of Referer and From
3239   information.
3240</t>
3241<t>
3242   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3243   HTTP request if the referring page was transferred with a secure
3244   protocol.
3245</t>
3246<t>
3247   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3248   sensitive data because that data will be placed in the request-target. Many
3249   existing servers, proxies, and user agents log or display the request-target
3250   in places where it might be visible to third parties. Such services can
3251   use POST-based form submission instead.
3252</t>
3253</section>
3254
3255<section title="Location Header Fields: Spoofing and Information Leakage" anchor="location.spoofing-leakage">
3256<t>
3257   If a single server supports multiple organizations that do not trust
3258   one another, then it &MUST; check the values of Location and Content-Location
3259   header fields in responses that are generated under control of
3260   said organizations to make sure that they do not attempt to
3261   invalidate resources over which they have no authority.
3262</t>
3263<t>
3264   Furthermore, appending the fragment identifier from one URI to another
3265   one obtained from a Location header field might leak confidential
3266   information to the target server &mdash; although the fragment identifier is
3267   not transmitted in the final request, it might be visible to the user agent
3268   through other means, such as scripting.
3269</t>
3270</section>
3271
3272<section title="Security Considerations for CONNECT">
3273<t>
3274   Since tunneled data is opaque to the proxy, there are additional
3275   risks to tunneling to other well-known or reserved ports.
3276   A HTTP client CONNECTing to port 25 could relay spam
3277   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3278   access to a small number of known ports.
3279</t>
3280</section>
3281
3282</section>
3283
3284<section title="Acknowledgments" anchor="acks">
3285<t>
3286  See &acks;.
3287</t>
3288</section>
3289</middle>
3290<back>
3291
3292<references title="Normative References">
3293
3294<reference anchor="Part1">
3295  <front>
3296    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3297    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3298      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3299      <address><email>fielding@gbiv.com</email></address>
3300    </author>
3301    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3302      <organization abbrev="W3C">World Wide Web Consortium</organization>
3303      <address><email>ylafon@w3.org</email></address>
3304    </author>
3305    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3306      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3307      <address><email>julian.reschke@greenbytes.de</email></address>
3308    </author>
3309    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3310  </front>
3311  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3312  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3313</reference>
3314
3315<reference anchor="Part3">
3316  <front>
3317    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3318    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3319      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3320      <address><email>fielding@gbiv.com</email></address>
3321    </author>
3322    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3323      <organization abbrev="W3C">World Wide Web Consortium</organization>
3324      <address><email>ylafon@w3.org</email></address>
3325    </author>
3326    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3327      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3328      <address><email>julian.reschke@greenbytes.de</email></address>
3329    </author>
3330    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3331  </front>
3332  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3333  <x:source href="p3-payload.xml" basename="p3-payload"/>
3334</reference>
3335
3336<reference anchor="Part4">
3337  <front>
3338    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3339    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3340      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3341      <address><email>fielding@gbiv.com</email></address>
3342    </author>
3343    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3344      <organization abbrev="W3C">World Wide Web Consortium</organization>
3345      <address><email>ylafon@w3.org</email></address>
3346    </author>
3347    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3348      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3349      <address><email>julian.reschke@greenbytes.de</email></address>
3350    </author>
3351    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3352  </front>
3353  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3354  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3355</reference>
3356
3357<reference anchor="Part5">
3358  <front>
3359    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3360    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3361      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3362      <address><email>fielding@gbiv.com</email></address>
3363    </author>
3364    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3365      <organization abbrev="W3C">World Wide Web Consortium</organization>
3366      <address><email>ylafon@w3.org</email></address>
3367    </author>
3368    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3369      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3370      <address><email>julian.reschke@greenbytes.de</email></address>
3371    </author>
3372    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3373  </front>
3374  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3375  <x:source href="p5-range.xml" basename="p5-range"/>
3376</reference>
3377
3378<reference anchor="Part6">
3379  <front>
3380    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3381    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3382      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3383      <address><email>fielding@gbiv.com</email></address>
3384    </author>
3385    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3386      <organization abbrev="W3C">World Wide Web Consortium</organization>
3387      <address><email>ylafon@w3.org</email></address>
3388    </author>
3389    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3390      <organization>Rackspace</organization>
3391      <address><email>mnot@mnot.net</email></address>
3392    </author>
3393    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3394      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3395      <address><email>julian.reschke@greenbytes.de</email></address>
3396    </author>
3397    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3398  </front>
3399  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3400  <x:source href="p6-cache.xml" basename="p6-cache"/>
3401</reference>
3402
3403<reference anchor="Part7">
3404  <front>
3405    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3406    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3407      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3408      <address><email>fielding@gbiv.com</email></address>
3409    </author>
3410    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3411      <organization abbrev="W3C">World Wide Web Consortium</organization>
3412      <address><email>ylafon@w3.org</email></address>
3413    </author>
3414    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3415      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3416      <address><email>julian.reschke@greenbytes.de</email></address>
3417    </author>
3418    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3419  </front>
3420  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3421  <x:source href="p7-auth.xml" basename="p7-auth"/>
3422</reference>
3423
3424<reference anchor="RFC1950">
3425  <front>
3426    <title>ZLIB Compressed Data Format Specification version 3.3</title>
3427    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
3428      <organization>Aladdin Enterprises</organization>
3429      <address><email>ghost@aladdin.com</email></address>
3430    </author>
3431    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
3432    <date month="May" year="1996"/>
3433  </front>
3434  <seriesInfo name="RFC" value="1950"/>
3435  <!--<annotation>
3436    RFC 1950 is an Informational RFC, thus it might be less stable than
3437    this specification. On the other hand, this downward reference was
3438    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
3439    therefore it is unlikely to cause problems in practice. See also
3440    <xref target="BCP97"/>.
3441  </annotation>-->
3442</reference>
3443
3444<reference anchor="RFC1951">
3445  <front>
3446    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
3447    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
3448      <organization>Aladdin Enterprises</organization>
3449      <address><email>ghost@aladdin.com</email></address>
3450    </author>
3451    <date month="May" year="1996"/>
3452  </front>
3453  <seriesInfo name="RFC" value="1951"/>
3454  <!--<annotation>
3455    RFC 1951 is an Informational RFC, thus it might be less stable than
3456    this specification. On the other hand, this downward reference was
3457    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
3458    therefore it is unlikely to cause problems in practice. See also
3459    <xref target="BCP97"/>.
3460  </annotation>-->
3461</reference>
3462
3463<reference anchor="RFC1952">
3464  <front>
3465    <title>GZIP file format specification version 4.3</title>
3466    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
3467      <organization>Aladdin Enterprises</organization>
3468      <address><email>ghost@aladdin.com</email></address>
3469    </author>
3470    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
3471      <address><email>gzip@prep.ai.mit.edu</email></address>
3472    </author>
3473    <author initials="M." surname="Adler" fullname="Mark Adler">
3474      <address><email>madler@alumni.caltech.edu</email></address>
3475    </author>
3476    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
3477      <address><email>ghost@aladdin.com</email></address>
3478    </author>
3479    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
3480      <address><email>randeg@alumni.rpi.edu</email></address>
3481    </author>
3482    <date month="May" year="1996"/>
3483  </front>
3484  <seriesInfo name="RFC" value="1952"/>
3485  <!--<annotation>
3486    RFC 1952 is an Informational RFC, thus it might be less stable than
3487    this specification. On the other hand, this downward reference was
3488    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
3489    therefore it is unlikely to cause problems in practice. See also
3490    <xref target="BCP97"/>.
3491  </annotation>-->
3492</reference>
3493
3494<reference anchor="RFC2045">
3495  <front>
3496    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3497    <author initials="N." surname="Freed" fullname="Ned Freed">
3498      <organization>Innosoft International, Inc.</organization>
3499      <address><email>ned@innosoft.com</email></address>
3500    </author>
3501    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3502      <organization>First Virtual Holdings</organization>
3503      <address><email>nsb@nsb.fv.com</email></address>
3504    </author>
3505    <date month="November" year="1996"/>
3506  </front>
3507  <seriesInfo name="RFC" value="2045"/>
3508</reference>
3509
3510<reference anchor="RFC2046">
3511  <front>
3512    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
3513    <author initials="N." surname="Freed" fullname="Ned Freed">
3514      <organization>Innosoft International, Inc.</organization>
3515      <address><email>ned@innosoft.com</email></address>
3516    </author>
3517    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3518      <organization>First Virtual Holdings</organization>
3519      <address><email>nsb@nsb.fv.com</email></address>
3520    </author>
3521    <date month="November" year="1996"/>
3522  </front>
3523  <seriesInfo name="RFC" value="2046"/>
3524</reference>
3525
3526<reference anchor="RFC2119">
3527  <front>
3528    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3529    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3530      <organization>Harvard University</organization>
3531      <address><email>sob@harvard.edu</email></address>
3532    </author>
3533    <date month="March" year="1997"/>
3534  </front>
3535  <seriesInfo name="BCP" value="14"/>
3536  <seriesInfo name="RFC" value="2119"/>
3537</reference>
3538
3539<reference anchor="RFC3986">
3540 <front>
3541  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3542  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3543    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3544    <address>
3545       <email>timbl@w3.org</email>
3546       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3547    </address>
3548  </author>
3549  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3550    <organization abbrev="Day Software">Day Software</organization>
3551    <address>
3552      <email>fielding@gbiv.com</email>
3553      <uri>http://roy.gbiv.com/</uri>
3554    </address>
3555  </author>
3556  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3557    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3558    <address>
3559      <email>LMM@acm.org</email>
3560      <uri>http://larry.masinter.net/</uri>
3561    </address>
3562  </author>
3563  <date month='January' year='2005'></date>
3564 </front>
3565 <seriesInfo name="STD" value="66"/>
3566 <seriesInfo name="RFC" value="3986"/>
3567</reference>
3568
3569<reference anchor='RFC4647'>
3570  <front>
3571    <title>Matching of Language Tags</title>
3572    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
3573      <organization>Yahoo! Inc.</organization>
3574      <address><email>addison@inter-locale.com</email></address>
3575    </author>
3576    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
3577      <organization>Google</organization>
3578      <address><email>mark.davis@macchiato.com</email></address>
3579    </author>
3580    <date year='2006' month='September' />
3581  </front>
3582  <seriesInfo name='BCP' value='47' />
3583  <seriesInfo name='RFC' value='4647' />
3584</reference>
3585
3586<reference anchor="RFC5234">
3587  <front>
3588    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3589    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3590      <organization>Brandenburg InternetWorking</organization>
3591      <address>
3592        <email>dcrocker@bbiw.net</email>
3593      </address> 
3594    </author>
3595    <author initials="P." surname="Overell" fullname="Paul Overell">
3596      <organization>THUS plc.</organization>
3597      <address>
3598        <email>paul.overell@thus.net</email>
3599      </address>
3600    </author>
3601    <date month="January" year="2008"/>
3602  </front>
3603  <seriesInfo name="STD" value="68"/>
3604  <seriesInfo name="RFC" value="5234"/>
3605</reference>
3606
3607<reference anchor='RFC5646'>
3608  <front>
3609    <title>Tags for Identifying Languages</title>
3610    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
3611      <organization>Lab126</organization>
3612      <address><email>addison@inter-locale.com</email></address>
3613    </author>
3614    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
3615      <organization>Google</organization>
3616      <address><email>mark.davis@google.com</email></address>
3617    </author>
3618    <date month='September' year='2009' />
3619  </front>
3620  <seriesInfo name='BCP' value='47' />
3621  <seriesInfo name='RFC' value='5646' />
3622</reference>
3623
3624</references>
3625
3626<references title="Informative References">
3627
3628<reference anchor="RFC1123">
3629  <front>
3630    <title>Requirements for Internet Hosts - Application and Support</title>
3631    <author initials="R." surname="Braden" fullname="Robert Braden">
3632      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3633      <address><email>Braden@ISI.EDU</email></address>
3634    </author>
3635    <date month="October" year="1989"/>
3636  </front>
3637  <seriesInfo name="STD" value="3"/>
3638  <seriesInfo name="RFC" value="1123"/>
3639</reference>
3640
3641<reference anchor="RFC1945">
3642  <front>
3643    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3644    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3645      <organization>MIT, Laboratory for Computer Science</organization>
3646      <address><email>timbl@w3.org</email></address>
3647    </author>
3648    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3649      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3650      <address><email>fielding@ics.uci.edu</email></address>
3651    </author>
3652    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3653      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3654      <address><email>frystyk@w3.org</email></address>
3655    </author>
3656    <date month="May" year="1996"/>
3657  </front>
3658  <seriesInfo name="RFC" value="1945"/>
3659</reference>
3660
3661<reference anchor="RFC2049">
3662  <front>
3663    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
3664    <author initials="N." surname="Freed" fullname="Ned Freed">
3665      <organization>Innosoft International, Inc.</organization>
3666      <address><email>ned@innosoft.com</email></address>
3667    </author>
3668    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3669      <organization>First Virtual Holdings</organization>
3670      <address><email>nsb@nsb.fv.com</email></address>
3671    </author>
3672    <date month="November" year="1996"/>
3673  </front>
3674  <seriesInfo name="RFC" value="2049"/>
3675</reference>
3676
3677<reference anchor="RFC2068">
3678  <front>
3679    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3680    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3681      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3682      <address><email>fielding@ics.uci.edu</email></address>
3683    </author>
3684    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3685      <organization>MIT Laboratory for Computer Science</organization>
3686      <address><email>jg@w3.org</email></address>
3687    </author>
3688    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3689      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3690      <address><email>mogul@wrl.dec.com</email></address>
3691    </author>
3692    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3693      <organization>MIT Laboratory for Computer Science</organization>
3694      <address><email>frystyk@w3.org</email></address>
3695    </author>
3696    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3697      <organization>MIT Laboratory for Computer Science</organization>
3698      <address><email>timbl@w3.org</email></address>
3699    </author>
3700    <date month="January" year="1997"/>
3701  </front>
3702  <seriesInfo name="RFC" value="2068"/>
3703</reference>
3704
3705<reference anchor="RFC2076">
3706  <front>
3707    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
3708    <author initials="J." surname="Palme" fullname="Jacob Palme">
3709      <organization>Stockholm University/KTH</organization>
3710      <address><email>jpalme@dsv.su.se</email></address>
3711    </author>
3712    <date month="February" year="1997"/>
3713  </front>
3714  <seriesInfo name="RFC" value="2076"/>
3715</reference>
3716
3717<reference anchor="RFC2277">
3718  <front>
3719    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
3720    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
3721      <organization>UNINETT</organization>
3722      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
3723    </author>
3724    <date month="January" year="1998"/>
3725  </front>
3726  <seriesInfo name="BCP" value="18"/>
3727  <seriesInfo name="RFC" value="2277"/>
3728</reference>
3729
3730<reference anchor='RFC2295'>
3731  <front>
3732    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
3733    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
3734      <organization>Technische Universiteit Eindhoven</organization>
3735      <address>
3736        <email>koen@win.tue.nl</email>
3737      </address>
3738    </author>
3739    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
3740      <organization>Hewlett-Packard Company</organization>
3741      <address>
3742        <email>mutz@hpl.hp.com</email>
3743      </address>
3744    </author>
3745    <date year='1998' month='March'/>
3746  </front>
3747  <seriesInfo name='RFC' value='2295'/>
3748</reference>
3749
3750<reference anchor="RFC2388">
3751  <front>
3752    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
3753    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3754      <organization>Xerox Palo Alto Research Center</organization>
3755      <address><email>masinter@parc.xerox.com</email></address>
3756    </author>
3757    <date year="1998" month="August"/>
3758  </front>
3759  <seriesInfo name="RFC" value="2388"/>
3760</reference>
3761
3762<reference anchor="RFC2557">
3763  <front>
3764    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
3765    <author initials="F." surname="Palme" fullname="Jacob Palme">
3766      <organization>Stockholm University and KTH</organization>
3767      <address><email>jpalme@dsv.su.se</email></address>
3768    </author>
3769    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
3770      <organization>Microsoft Corporation</organization>
3771      <address><email>alexhop@microsoft.com</email></address>
3772    </author>
3773    <author initials="N." surname="Shelness" fullname="Nick Shelness">
3774      <organization>Lotus Development Corporation</organization>
3775      <address><email>Shelness@lotus.com</email></address>
3776    </author>
3777    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
3778      <address><email>stef@nma.com</email></address>
3779    </author>
3780    <date year="1999" month="March"/>
3781  </front>
3782  <seriesInfo name="RFC" value="2557"/>
3783</reference>
3784
3785<reference anchor="RFC2616">
3786  <front>
3787    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3788    <author initials="R." surname="Fielding" fullname="R. Fielding">
3789      <organization>University of California, Irvine</organization>
3790      <address><email>fielding@ics.uci.edu</email></address>
3791    </author>
3792    <author initials="J." surname="Gettys" fullname="J. Gettys">
3793      <organization>W3C</organization>
3794      <address><email>jg@w3.org</email></address>
3795    </author>
3796    <author initials="J." surname="Mogul" fullname="J. Mogul">
3797      <organization>Compaq Computer Corporation</organization>
3798      <address><email>mogul@wrl.dec.com</email></address>
3799    </author>
3800    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3801      <organization>MIT Laboratory for Computer Science</organization>
3802      <address><email>frystyk@w3.org</email></address>
3803    </author>
3804    <author initials="L." surname="Masinter" fullname="L. Masinter">
3805      <organization>Xerox Corporation</organization>
3806      <address><email>masinter@parc.xerox.com</email></address>
3807    </author>
3808    <author initials="P." surname="Leach" fullname="P. Leach">
3809      <organization>Microsoft Corporation</organization>
3810      <address><email>paulle@microsoft.com</email></address>
3811    </author>
3812    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3813      <organization>W3C</organization>
3814      <address><email>timbl@w3.org</email></address>
3815    </author>
3816    <date month="June" year="1999"/>
3817  </front>
3818  <seriesInfo name="RFC" value="2616"/>
3819</reference>
3820
3821<reference anchor='RFC2817'>
3822  <front>
3823    <title>Upgrading to TLS Within HTTP/1.1</title>
3824    <author initials='R.' surname='Khare' fullname='R. Khare'>
3825      <organization>4K Associates / UC Irvine</organization>
3826      <address><email>rohit@4K-associates.com</email></address>
3827    </author>
3828    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3829      <organization>Agranat Systems, Inc.</organization>
3830      <address><email>lawrence@agranat.com</email></address>
3831    </author>
3832    <date year='2000' month='May' />
3833  </front>
3834  <seriesInfo name='RFC' value='2817' />
3835</reference>
3836
3837<reference anchor="RFC3629">
3838  <front>
3839    <title>UTF-8, a transformation format of ISO 10646</title>
3840    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
3841      <organization>Alis Technologies</organization>
3842      <address><email>fyergeau@alis.com</email></address>
3843    </author>
3844    <date month="November" year="2003"/>
3845  </front>
3846  <seriesInfo name="STD" value="63"/>
3847  <seriesInfo name="RFC" value="3629"/>
3848</reference>
3849
3850<reference anchor='RFC3864'>
3851  <front>
3852    <title>Registration Procedures for Message Header Fields</title>
3853    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3854      <organization>Nine by Nine</organization>
3855      <address><email>GK-IETF@ninebynine.org</email></address>
3856    </author>
3857    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3858      <organization>BEA Systems</organization>
3859      <address><email>mnot@pobox.com</email></address>
3860    </author>
3861    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3862      <organization>HP Labs</organization>
3863      <address><email>JeffMogul@acm.org</email></address>
3864    </author>
3865    <date year='2004' month='September' />
3866  </front>
3867  <seriesInfo name='BCP' value='90' />
3868  <seriesInfo name='RFC' value='3864' />
3869</reference>
3870
3871<reference anchor="RFC4288">
3872  <front>
3873    <title>Media Type Specifications and Registration Procedures</title>
3874    <author initials="N." surname="Freed" fullname="N. Freed">
3875      <organization>Sun Microsystems</organization>
3876      <address>
3877        <email>ned.freed@mrochek.com</email>
3878      </address>
3879    </author>
3880    <author initials="J." surname="Klensin" fullname="J. Klensin">
3881      <address>
3882        <email>klensin+ietf@jck.com</email>
3883      </address>
3884    </author>
3885    <date year="2005" month="December"/>
3886  </front>
3887  <seriesInfo name="BCP" value="13"/>
3888  <seriesInfo name="RFC" value="4288"/>
3889</reference>
3890
3891<reference anchor='RFC5226'>
3892  <front>
3893    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3894    <author initials='T.' surname='Narten' fullname='T. Narten'>
3895      <organization>IBM</organization>
3896      <address><email>narten@us.ibm.com</email></address>
3897    </author>
3898    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3899      <organization>Google</organization>
3900      <address><email>Harald@Alvestrand.no</email></address>
3901    </author>
3902    <date year='2008' month='May' />
3903  </front>
3904  <seriesInfo name='BCP' value='26' />
3905  <seriesInfo name='RFC' value='5226' />
3906</reference>
3907
3908<reference anchor="RFC5322">
3909  <front>
3910    <title>Internet Message Format</title>
3911    <author initials="P." surname="Resnick" fullname="P. Resnick">
3912      <organization>Qualcomm Incorporated</organization>
3913    </author>
3914    <date year="2008" month="October"/>
3915  </front> 
3916  <seriesInfo name="RFC" value="5322"/>
3917</reference>
3918
3919<reference anchor='RFC5789'>
3920  <front>
3921    <title>PATCH Method for HTTP</title>
3922    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3923      <organization>Linden Lab</organization>
3924    </author>
3925    <author initials='J.' surname='Snell' fullname='J. Snell' />
3926    <date year='2010' month='March' />
3927  </front>
3928  <seriesInfo name='RFC' value='5789' />
3929</reference>
3930
3931<reference anchor="RFC5987">
3932        <front>
3933    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3934    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3935      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3936      <address>
3937        <postal>
3938          <street>Hafenweg 16</street>
3939          <city>Muenster</city><region>NW</region><code>48155</code>
3940          <country>Germany</country>
3941        </postal>
3942        <email>julian.reschke@greenbytes.de</email>     
3943        <uri>http://greenbytes.de/tech/webdav/</uri>   
3944      </address>
3945    </author>
3946    <date month="August" year="2010"/>
3947  </front>
3948  <seriesInfo name="RFC" value="5987"/>
3949</reference>
3950
3951<reference anchor="RFC6151">
3952  <front>
3953    <title>Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms</title>
3954    <author initials="S." surname="Turner" fullname="S. Turner"/>
3955    <author initials="L." surname="Chen" fullname="L. Chen"/>
3956    <date year="2011" month="March" />
3957  </front>
3958  <seriesInfo name="RFC" value="6151" />
3959</reference>
3960
3961<reference anchor="RFC6266">
3962  <front>
3963    <title abbrev="Content-Disposition in HTTP">Use of the Content-Disposition Header Field
3964    in the Hypertext Transfer Protocol (HTTP)</title>
3965    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3966      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3967      <address>
3968        <email>julian.reschke@greenbytes.de</email>
3969      </address>
3970    </author>
3971    <date month="June" year="2011"/>
3972  </front>
3973  <seriesInfo name='RFC' value='6266' />
3974</reference>
3975
3976<reference anchor="draft-reschke-http-status-308">
3977        <front>
3978    <title abbrev="HTTP Status Code 308">The Hypertext Transfer Protocol (HTTP) Status Code 308 (Permanent Redirect)</title>
3979    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3980      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3981      <address>
3982        <email>julian.reschke@greenbytes.de</email>     
3983      </address>
3984    </author>
3985    <date month="March" year="2012"/>
3986  </front>
3987  <seriesInfo name="Internet-Draft" value="draft-reschke-http-status-308-07"/>
3988</reference>
3989
3990</references>
3991
3992<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3993<t>
3994  Clarify definition of POST.
3995  (<xref target="POST"/>)
3996</t>
3997<t>
3998  Remove requirement to handle all Content-* header fields; ban use of
3999  Content-Range with PUT.
4000  (<xref target="PUT"/>)
4001</t>
4002<t>
4003  Take over definition of CONNECT method from <xref target="RFC2817"/>.
4004  (<xref target="CONNECT"/>)
4005</t>
4006<t>
4007  This document takes over the Status Code Registry, previously defined
4008  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
4009  (<xref target="status.code.registry"/>)
4010</t>
4011<t>
4012  Broadened the definition of 203 (Non-Authoritative Information) to include
4013  cases of payload transformations as well.
4014  (<xref target="status.203"/>)
4015</t>
4016<t>
4017  Status codes 301, 302, and 307: removed the normative requirements on both
4018  response payloads and user interaction.
4019  (<xref target="status.3xx"/>)
4020</t>
4021<t>
4022  Failed to consider that there are many other request methods that are safe
4023  to automatically redirect, and further that the user agent is able to make
4024  that determination based on the request method semantics.
4025  Furthermore, allow user agents to rewrite the method from POST to GET
4026  for status codes 301 and 302.
4027  (Sections <xref format="counter" target="status.301"/>,
4028  <xref format="counter" target="status.302"/> and
4029  <xref format="counter" target="status.307"/>)
4030</t>
4031<t>
4032  Deprecate 305 Use Proxy status code, because user agents did not implement it.
4033  It used to indicate that the target resource needs to be accessed through the
4034  proxy given by the Location field. The Location field gave the URI of the
4035  proxy. The recipient was expected to repeat this single request via the proxy.
4036  (<xref target="status.305"/>)
4037</t>
4038<t>
4039  Define status 426 (Upgrade Required) (this was incorporated from
4040  <xref target="RFC2817"/>).
4041  (<xref target="status.426"/>)
4042</t>
4043<t>
4044  Change ABNF productions for header fields to only define the field value.
4045  (<xref target="header.field.definitions"/>)
4046</t>
4047<t>
4048  Reclassify "Allow" as response header field, removing the option to
4049  specify it in a PUT request.
4050  Relax the server requirement on the contents of the Allow header field and
4051  remove requirement on clients to always trust the header field value.
4052  (<xref target="header.allow"/>)
4053</t>
4054<t>
4055  The ABNF for the Expect header field has been both fixed (allowing parameters
4056  for value-less expectations as well) and simplified (allowing trailing
4057  semicolons after "100-continue" when they were invalid before).
4058  (<xref target="header.expect"/>)
4059</t>
4060<t>
4061  Correct syntax of Location header field to allow URI references (including
4062  relative references and fragments), as referred symbol "absoluteURI" wasn't
4063  what was expected, and add some clarifications as to when use of fragments
4064  would not be appropriate.
4065  (<xref target="header.location"/>)
4066</t>
4067<t>
4068  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
4069  extension methods could have used it as well).
4070  (<xref target="header.max-forwards"/>)
4071</t>
4072<t>
4073  Allow Referer field value of "about:blank" as alternative to not specifying it.
4074  (<xref target="header.referer"/>)
4075</t>
4076<t>
4077  In the description of the Server header field, the Via field
4078  was described as a SHOULD. The requirement was and is stated
4079  correctly in the description of the Via header field in &header-via;.
4080  (<xref target="header.server"/>)
4081</t>
4082</section>
4083
4084<?BEGININC p2-semantics.abnf-appendix ?>
4085<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4086<figure>
4087<artwork type="abnf" name="p2-semantics.parsed-abnf">
4088<x:ref>Allow</x:ref> = [ ( "," / method ) *( OWS "," [ OWS method ] ) ]
4089
4090<x:ref>BWS</x:ref> = &lt;BWS, defined in [Part1], Section 3.2.1&gt;
4091
4092<x:ref>Date</x:ref> = HTTP-date
4093
4094<x:ref>Expect</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
4095
4096<x:ref>From</x:ref> = mailbox
4097
4098<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4099
4100<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4101
4102<x:ref>Location</x:ref> = URI-reference
4103
4104<x:ref>Max-Forwards</x:ref> = 1*DIGIT
4105
4106<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 3.2.1&gt;
4107
4108<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 3.2.1&gt;
4109<x:ref>Referer</x:ref> = absolute-URI / partial-URI
4110<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
4111
4112<x:ref>Server</x:ref> = product *( RWS ( product / comment ) )
4113
4114<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
4115<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
4116
4117<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
4118<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4119
4120<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2.4&gt;
4121
4122<x:ref>date1</x:ref> = day SP month SP year
4123<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4124<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4125<x:ref>day</x:ref> = 2DIGIT
4126<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4127 / %x54.75.65 ; Tue
4128 / %x57.65.64 ; Wed
4129 / %x54.68.75 ; Thu
4130 / %x46.72.69 ; Fri
4131 / %x53.61.74 ; Sat
4132 / %x53.75.6E ; Sun
4133<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4134 / %x54.75.65.73.64.61.79 ; Tuesday
4135 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4136 / %x54.68.75.72.73.64.61.79 ; Thursday
4137 / %x46.72.69.64.61.79 ; Friday
4138 / %x53.61.74.75.72.64.61.79 ; Saturday
4139 / %x53.75.6E.64.61.79 ; Sunday
4140<x:ref>delta-seconds</x:ref> = 1*DIGIT
4141
4142<x:ref>expect-name</x:ref> = token
4143<x:ref>expect-param</x:ref> = expect-name [ BWS "=" BWS expect-value ]
4144<x:ref>expect-value</x:ref> = token / quoted-string
4145<x:ref>expectation</x:ref> = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
4146 OWS expect-param ] )
4147
4148<x:ref>hour</x:ref> = 2DIGIT
4149
4150<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
4151<x:ref>method</x:ref> = token
4152<x:ref>minute</x:ref> = 2DIGIT
4153<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4154 / %x46.65.62 ; Feb
4155 / %x4D.61.72 ; Mar
4156 / %x41.70.72 ; Apr
4157 / %x4D.61.79 ; May
4158 / %x4A.75.6E ; Jun
4159 / %x4A.75.6C ; Jul
4160 / %x41.75.67 ; Aug
4161 / %x53.65.70 ; Sep
4162 / %x4F.63.74 ; Oct
4163 / %x4E.6F.76 ; Nov
4164 / %x44.65.63 ; Dec
4165
4166<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4167<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 3.2.4&gt;
4168
4169<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
4170<x:ref>product</x:ref> = token [ "/" product-version ]
4171<x:ref>product-version</x:ref> = token
4172
4173<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.4&gt;
4174
4175<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4176<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4177
4178<x:ref>second</x:ref> = 2DIGIT
4179
4180<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4181<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.4&gt;
4182
4183word = &lt;word, defined in [Part1], Section 3.2.4&gt;
4184
4185<x:ref>year</x:ref> = 4DIGIT
4186</artwork>
4187</figure>
4188<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4189; Allow defined but not used
4190; Date defined but not used
4191; Expect defined but not used
4192; From defined but not used
4193; Location defined but not used
4194; Max-Forwards defined but not used
4195; Referer defined but not used
4196; Retry-After defined but not used
4197; Server defined but not used
4198; User-Agent defined but not used
4199; obs-text defined but not used
4200; word defined but not used
4201</artwork></figure></section>
4202<?ENDINC p2-semantics.abnf-appendix ?>
4203
4204<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4205
4206<section title="Since RFC 2616">
4207<t>
4208  Extracted relevant partitions from <xref target="RFC2616"/>.
4209</t>
4210</section>
4211
4212<section title="Since draft-ietf-httpbis-p2-semantics-00">
4213<t>
4214  Closed issues:
4215  <list style="symbols"> 
4216    <t>
4217      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
4218      "Via is a MUST"
4219      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
4220    </t>
4221    <t>
4222      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
4223      "Fragments allowed in Location"
4224      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
4225    </t>
4226    <t>
4227      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4228      "Safe Methods vs Redirection"
4229      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
4230    </t>
4231    <t>
4232      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
4233      "Revise description of the POST method"
4234      (<eref target="http://purl.org/NET/http-errata#post"/>)
4235    </t>
4236    <t>
4237      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4238      "Normative and Informative references"
4239    </t>
4240    <t>
4241      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4242      "RFC2606 Compliance"
4243    </t>
4244    <t>
4245      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4246      "Informative references"
4247    </t>
4248    <t>
4249      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
4250      "Redundant cross-references"
4251    </t>
4252  </list>
4253</t>
4254<t>
4255  Other changes:
4256  <list style="symbols"> 
4257    <t>
4258      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
4259    </t>
4260  </list>
4261</t>
4262</section>
4263
4264<section title="Since draft-ietf-httpbis-p2-semantics-01">
4265<t>
4266  Closed issues:
4267  <list style="symbols"> 
4268    <t>
4269      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
4270      "PUT side effects"
4271    </t>
4272    <t>
4273      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
4274      "Duplicate Host header requirements"
4275    </t>
4276  </list>
4277</t>
4278<t>
4279  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4280  <list style="symbols"> 
4281    <t>
4282      Move "Product Tokens" section (back) into Part 1, as "token" is used
4283      in the definition of the Upgrade header field.
4284    </t>
4285    <t>
4286      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4287    </t>
4288    <t>
4289      Copy definition of delta-seconds from Part6 instead of referencing it.
4290    </t>
4291  </list>
4292</t>
4293</section>
4294
4295<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
4296<t>
4297  Closed issues:
4298  <list style="symbols"> 
4299    <t>
4300      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
4301      "Requiring Allow in 405 responses"
4302    </t>
4303    <t>
4304      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
4305      "Status Code Registry"
4306    </t>
4307    <t>
4308      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
4309      "Redirection vs. Location"
4310    </t>
4311    <t>
4312      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
4313      "Cacheability of 303 response"
4314    </t>
4315    <t>
4316      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
4317      "305 Use Proxy"
4318    </t>
4319    <t>
4320      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
4321      "Classification for Allow header"
4322    </t>
4323    <t>
4324      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4325      "PUT - 'store under' vs 'store at'"
4326    </t>
4327  </list>
4328</t>
4329<t>
4330  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4331  <list style="symbols"> 
4332    <t>
4333      Reference RFC 3984, and update header field registrations for headers defined
4334      in this document.
4335    </t>
4336  </list>
4337</t>
4338<t>
4339  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4340  <list style="symbols"> 
4341    <t>
4342      Replace string literals when the string really is case-sensitive (method).
4343    </t>
4344  </list>
4345</t>
4346</section>
4347
4348<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
4349<t>
4350  Closed issues:
4351  <list style="symbols"> 
4352    <t>
4353      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
4354      "OPTIONS request bodies"
4355    </t>
4356    <t>
4357      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
4358      "Description of CONNECT should refer to RFC2817"
4359    </t>
4360    <t>
4361      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
4362      "Location Content-Location reference request/response mixup"
4363    </t>
4364  </list>
4365</t>
4366<t>
4367  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
4368  <list style="symbols"> 
4369    <t>
4370      Added initial proposal for registration process, plus initial
4371      content (non-HTTP/1.1 methods to be added by a separate specification).
4372    </t>
4373  </list>
4374</t>
4375</section>
4376
4377<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
4378<t>
4379  Closed issues:
4380  <list style="symbols"> 
4381    <t>
4382      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4383      "Content-*"
4384    </t>
4385    <t>
4386      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4387      "RFC 2822 is updated by RFC 5322"
4388    </t>
4389  </list>
4390</t>
4391<t>
4392  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4393  <list style="symbols"> 
4394    <t>
4395      Use "/" instead of "|" for alternatives.
4396    </t>
4397    <t>
4398      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4399      whitespace ("OWS") and required whitespace ("RWS").
4400    </t>
4401    <t>
4402      Rewrite ABNFs to spell out whitespace rules, factor out
4403      header field value format definitions.
4404    </t>
4405  </list>
4406</t>
4407</section>
4408
4409<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
4410<t>
4411  Closed issues:
4412  <list style="symbols"> 
4413    <t>
4414      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4415      "reason-phrase BNF"
4416    </t>
4417  </list>
4418</t>
4419<t>
4420  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4421  <list style="symbols"> 
4422    <t>
4423      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4424    </t>
4425  </list>
4426</t>
4427</section>
4428
4429<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4430<t>
4431  Closed issues:
4432  <list style="symbols"> 
4433    <t>
4434      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4435      "Clarify when Referer is sent"
4436    </t>
4437    <t>
4438      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4439      "status codes vs methods"
4440    </t>
4441    <t>
4442      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4443      "Do not require "updates" relation for specs that register status codes or method names"
4444    </t>
4445  </list>
4446</t>
4447</section>
4448
4449<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4450<t>
4451  Closed issues:
4452  <list style="symbols"> 
4453    <t>
4454      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4455      "Idempotency"
4456    </t>
4457    <t>
4458      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4459      "TRACE security considerations"
4460    </t>
4461    <t>
4462      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4463      "Clarify rules for determining what entities a response carries"
4464    </t>
4465    <t>
4466      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4467      "update note citing RFC 1945 and 2068"
4468    </t>
4469    <t>
4470      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4471      "update note about redirect limit"
4472    </t>
4473    <t>
4474      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4475      "Location header ABNF should use 'URI'"
4476    </t>
4477    <t>
4478      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4479      "fragments in Location vs status 303"
4480    </t>
4481    <t>
4482      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4483      "move IANA registrations for optional status codes"
4484    </t>
4485  </list>
4486</t>
4487<t>
4488  Partly resolved issues:
4489  <list style="symbols"> 
4490    <t>
4491      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4492      "Are OPTIONS and TRACE safe?"
4493    </t>
4494  </list>
4495</t>
4496</section>
4497
4498<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4499<t>
4500  Closed issues:
4501  <list style="symbols"> 
4502    <t>
4503      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4504      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4505      status codes when fixing this previously)
4506    </t>
4507  </list>
4508</t>
4509</section>
4510
4511<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4512<t>
4513  Closed issues:
4514  <list style="symbols"> 
4515    <t>
4516      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4517      "Fragment combination / precedence during redirects"
4518    </t>
4519  </list>
4520</t>
4521<t>
4522  Partly resolved issues:
4523  <list style="symbols"> 
4524    <t>
4525      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4526      "Location header payload handling"
4527    </t>
4528    <t>
4529      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4530      "Term for the requested resource's URI"
4531    </t>
4532  </list>
4533</t>
4534</section>
4535
4536<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4537<t>
4538  Closed issues:
4539  <list style="symbols"> 
4540    <t>
4541      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4542      "Clarify 'Requested Variant'"
4543    </t>
4544    <t>
4545      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4546      "Clarify entity / representation / variant terminology"
4547    </t>
4548    <t>
4549      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4550      "Methods and Caching"
4551    </t>
4552    <t>
4553      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4554      "OPTIONS vs Max-Forwards"
4555    </t>
4556    <t>
4557      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4558      "Status codes and caching"
4559    </t>
4560    <t>
4561      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4562      "consider removing the 'changes from 2068' sections"
4563    </t>
4564  </list>
4565</t>
4566</section>
4567
4568<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4569<t>
4570  Closed issues:
4571  <list style="symbols"> 
4572    <t>
4573      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4574      "Considerations for new status codes"
4575    </t>
4576    <t>
4577      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4578      "Considerations for new methods"
4579    </t>
4580    <t>
4581      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4582      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4583    </t>
4584  </list>
4585</t>
4586</section>
4587
4588<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4589<t>
4590  Closed issues:
4591  <list style="symbols"> 
4592    <t>
4593      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4594      "Fragment combination / precedence during redirects" (added warning
4595      about having a fragid on the redirect may cause inconvenience in
4596      some cases)
4597    </t>
4598    <t>
4599      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4600      "Content-* vs. PUT"
4601    </t>
4602    <t>
4603      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4604      "205 Bodies"
4605    </t>
4606    <t>
4607      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4608      "Understanding Content-* on non-PUT requests"
4609    </t>
4610    <t>
4611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4612      "Content-*"
4613    </t>
4614    <t>
4615      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4616      "Header type defaulting"
4617    </t>
4618    <t>
4619      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4620      "PUT - 'store under' vs 'store at'"
4621    </t>
4622    <t>
4623      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4624      "duplicate ABNF for reason-phrase"
4625    </t>
4626    <t>
4627      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4628      "Note special status of Content-* prefix in header registration procedures"
4629    </t>
4630    <t>
4631      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4632      "Max-Forwards vs extension methods"
4633    </t>
4634    <t>
4635      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4636      "What is the value space of HTTP status codes?" (actually fixed in
4637      draft-ietf-httpbis-p2-semantics-11)
4638    </t>
4639    <t>
4640      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4641      "Header Classification"
4642    </t>
4643    <t>
4644      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4645      "PUT side effect: invalidation or just stale?"
4646    </t>
4647    <t>
4648      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4649      "proxies not supporting certain methods"
4650    </t>
4651    <t>
4652      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4653      "Migrate CONNECT from RFC2817 to p2"
4654    </t>
4655    <t>
4656      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4657      "Migrate Upgrade details from RFC2817"
4658    </t>
4659    <t>
4660      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4661      "clarify PUT semantics'"
4662    </t>
4663    <t>
4664      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4665      "duplicate ABNF for 'Method'"
4666    </t>
4667    <t>
4668      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4669      "untangle ABNFs for header fields"
4670    </t>
4671  </list>
4672</t>
4673</section>
4674
4675<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4676<t>
4677  Closed issues:
4678  <list style="symbols"> 
4679    <t>
4680      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4681      "untangle ABNFs for header fields"
4682    </t>
4683    <t>
4684      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4685      "message body in CONNECT request"
4686    </t>
4687  </list>
4688</t>
4689</section>
4690
4691<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4692<t>
4693  Closed issues:
4694  <list style="symbols"> 
4695    <t>
4696      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4697      "Clarify status code for rate limiting"
4698    </t>
4699    <t>
4700      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4701      "clarify 403 forbidden"
4702    </t>
4703    <t>
4704      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4705      "Clarify 203 Non-Authoritative Information"
4706    </t>
4707    <t>
4708      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4709      "update default reason phrase for 413"
4710    </t>
4711  </list>
4712</t>
4713</section>
4714
4715<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4716<t>
4717  Closed issues:
4718  <list style="symbols"> 
4719    <t>
4720      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4721      "Strength of requirements on Accept re: 406"
4722    </t>
4723    <t>
4724      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4725      "400 response isn't generic"
4726    </t>
4727  </list>
4728</t>
4729</section>
4730
4731<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4732<t>
4733  Closed issues:
4734  <list style="symbols"> 
4735    <t>
4736      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4737      "Redirects and non-GET methods"
4738    </t>
4739    <t>
4740      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
4741      "Document HTTP's error-handling philosophy"
4742    </t>
4743    <t>
4744      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4745      "Considerations for new headers"
4746    </t>
4747    <t>
4748      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4749      "clarify 303 redirect on HEAD"
4750    </t>
4751  </list>
4752</t>
4753</section>
4754
4755<section title="Since draft-ietf-httpbis-p2-semantics-17" anchor="changes.since.17">
4756<t>
4757  Closed issues:
4758  <list style="symbols"> 
4759    <t>
4760      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4761      "Location header payload handling"
4762    </t>
4763    <t>
4764      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4765      "Clarify status code for rate limiting" (change backed out because
4766      a new status code is being defined for this purpose)
4767    </t>
4768    <t>
4769      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4770      "should there be a permanent variant of 307"
4771    </t>
4772    <t>
4773      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/325"/>:
4774      "When are Location's semantics triggered?"
4775    </t>
4776    <t>
4777      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/327"/>:
4778      "'expect' grammar missing OWS"
4779    </t>
4780    <t>
4781      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/329"/>:
4782      "header field considerations: quoted-string vs use of double quotes"
4783    </t>
4784  </list>
4785</t>
4786</section>
4787
4788<section title="Since draft-ietf-httpbis-p2-semantics-18" anchor="changes.since.18">
4789<t>
4790  Closed issues:
4791  <list style="symbols"> 
4792    <t>
4793      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/227"/>:
4794      "Combining HEAD responses"
4795    </t>
4796    <t>
4797      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/238"/>:
4798      "Requirements for user intervention during redirects"
4799    </t>
4800    <t>
4801      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
4802      "message-body in CONNECT response"
4803    </t>
4804    <t>
4805      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/295"/>:
4806      "Applying original fragment to 'plain' redirected URI"
4807    </t>
4808    <t>
4809      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
4810      "Misplaced text on connection handling in p2"
4811    </t>
4812    <t>
4813      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/331"/>:
4814      "clarify that 201 doesn't require Location header fields"
4815    </t>
4816    <t>
4817      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/332"/>:
4818      "relax requirements on hypertext in 3/4/5xx error responses"
4819    </t>
4820    <t>
4821      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/333"/>:
4822      "example for 426 response should have a payload"
4823    </t>
4824    <t>
4825      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/336"/>:
4826      "drop indirection entries for status codes"
4827    </t>
4828  </list>
4829</t>
4830</section>
4831
4832<section title="Since draft-ietf-httpbis-p2-semantics-19" anchor="changes.since.19">
4833<t>
4834  Closed issues:
4835  <list style="symbols"> 
4836    <t>
4837      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4838      "should there be a permanent variant of 307"
4839    </t>
4840  </list>
4841</t>
4842</section>
4843
4844</section>
4845
4846</back>
4847</rfc>
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