source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1640

Last change on this file since 1640 was 1640, checked in by julian.reschke@…, 7 years ago

Step 2 of p2/p3-merge (see #351)

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 197.8 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="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
256<t>
257   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
258   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
259   document are to be interpreted as described in <xref target="RFC2119"/>.
260</t>
261<t>
262   This document defines conformance criteria for several roles in HTTP
263   communication, including Senders, Recipients, Clients, Servers, User-Agents,
264   Origin Servers, Intermediaries, Proxies and Gateways. See &architecture;
265   for definitions of these terms.
266</t>
267<t>
268   An implementation is considered conformant if it complies with all of the
269   requirements associated with its role(s). Note that SHOULD-level requirements
270   are relevant here, unless one of the documented exceptions is applicable.
271</t>
272<t>
273   This document also uses ABNF to define valid protocol elements
274   (<xref target="notation"/>). In addition to the prose requirements placed
275   upon them, Senders &MUST-NOT; generate protocol elements that are invalid.
276</t>
277<t>
278   Unless noted otherwise, Recipients &MAY; take steps to recover a usable
279   protocol element from an invalid construct. However, HTTP does not define
280   specific error handling mechanisms, except in cases where it has direct
281   impact on security. This is because different uses of the protocol require
282   different error handling strategies; for example, a Web browser may wish to
283   transparently recover from a response where the Location header field
284   doesn't parse according to the ABNF, whereby in a systems control protocol
285   using HTTP, this type of error recovery could lead to dangerous consequences.
286</t>
287</section>
288
289<section title="Syntax Notation" anchor="notation">
290  <x:anchor-alias value="CR"/>
291  <x:anchor-alias value="DIGIT"/>
292  <x:anchor-alias value="LF"/>
293  <x:anchor-alias value="HTAB"/>
294  <x:anchor-alias value="VCHAR"/>
295  <x:anchor-alias value="SP"/>
296<t>
297   This specification uses the Augmented Backus-Naur Form (ABNF) notation
298   of <xref target="RFC5234"/> with the list rule extension defined in
299   &notation;<xref target="collected.abnf"/> shows the collected ABNF
300   with the list rule expanded.
301</t>
302<t>
303  The following core rules are included by
304  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
305  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
306  DIGIT (decimal 0-9), DQUOTE (double quote),
307  HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
308  OCTET (any 8-bit sequence of data), SP (space), and
309  VCHAR (any visible US-ASCII character).
310</t>
311
312<section title="Core Rules" anchor="core.rules">
313  <x:anchor-alias value="obs-text"/>
314  <x:anchor-alias value="quoted-string"/>
315  <x:anchor-alias value="token"/>
316  <x:anchor-alias value="BWS"/>
317  <x:anchor-alias value="OWS"/>
318  <x:anchor-alias value="RWS"/>
319<t>
320  The core rules below are defined in <xref target="Part1"/>:
321</t>
322<figure><artwork type="abnf2616">
323  <x:ref>BWS</x:ref>           = &lt;BWS, defined in &whitespace;&gt;
324  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &whitespace;&gt;
325  <x:ref>RWS</x:ref>           = &lt;RWS, defined in &whitespace;&gt;
326  <x:ref>obs-text</x:ref>      = &lt;obs-text, defined in &field-components;&gt;
327  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &field-components;&gt;
328  <x:ref>token</x:ref>         = &lt;token, defined in &field-components;&gt;
329</artwork></figure>
330</section>
331
332<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
333  <x:anchor-alias value="absolute-URI"/>
334  <x:anchor-alias value="comment"/>
335  <x:anchor-alias value="partial-URI"/>
336  <x:anchor-alias value="URI-reference"/>
337<t>
338  The ABNF rules below are defined in other parts:
339</t>
340<figure><!--Part1--><artwork type="abnf2616">
341  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in &uri;&gt;
342  <x:ref>comment</x:ref>       = &lt;comment, defined in &field-components;&gt;
343  <x:ref>partial-URI</x:ref>   = &lt;partial-URI, defined in &uri;&gt;
344  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in &uri;&gt;
345</artwork></figure>
346</section>
347</section>
348</section>
349
350<section title="Methods" anchor="methods">
351  <x:anchor-alias value="method"/>
352<t>
353   The method token indicates the request method to be performed on the target
354   resource (&effective-request-uri;). The method is case-sensitive.
355</t>
356<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
357  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
358</artwork></figure>
359<t>
360   The list of methods allowed by a resource can be specified in an
361   Allow header field (<xref target="header.allow"/>). The status code of the response
362   always notifies the client whether a method is currently allowed on a
363   resource, since the set of allowed methods can change dynamically. An
364   origin server &SHOULD; respond with the status code 405 (Method Not Allowed)
365   if the method is known by the origin server but not allowed for the
366   resource, and 501 (Not Implemented) if the method is
367   unrecognized or not implemented by the origin server. The methods GET
368   and HEAD &MUST; be supported by all general-purpose servers. All other
369   methods are &OPTIONAL;; however, if the above methods are implemented,
370   they &MUST; be implemented with the same semantics as those specified
371   in <xref target="method.definitions"/>.
372</t>
373
374<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
375
376<section title="Safe Methods" anchor="safe.methods">
377<iref item="Safe Methods" primary="true"/>
378<t>
379   Implementors need to be aware that the software represents the user in
380   their interactions over the Internet, and need to allow
381   the user to be aware of any actions they take which might have an
382   unexpected significance to themselves or others.
383</t>
384<t>
385   In particular, the convention has been established that the GET, HEAD,
386   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
387   of taking an action other than retrieval. These request methods ought
388   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
389   This allows user agents to represent other methods, such as POST, PUT
390   and DELETE, in a special way, so that the user is made aware of the
391   fact that a possibly unsafe action is being requested.
392</t>
393<t>
394   Naturally, it is not possible to ensure that the server does not
395   generate side-effects as a result of performing a GET request; in
396   fact, some dynamic resources consider that a feature. The important
397   distinction here is that the user did not request the side-effects,
398   so therefore cannot be held accountable for them.
399</t>
400</section>
401
402<section title="Idempotent Methods" anchor="idempotent.methods">
403<iref item="Idempotent Methods" primary="true"/>
404<t>
405   Request methods can also have the property of "idempotence" in that,
406   aside from error or expiration issues, the intended effect of multiple
407   identical requests is the same as for a single request.
408   PUT, DELETE, and all safe request methods are idempotent.
409   It is important to note that idempotence refers only to changes
410   requested by the client: a server is free to change its state due
411   to multiple requests for the purpose of tracking those requests,
412   versioning of results, etc.
413</t>
414</section>
415</section>
416
417<section title="Method Registry" anchor="method.registry">
418<t>
419  The HTTP Method Registry defines the name space for the method token in the
420  Request line of an HTTP request.
421</t>
422<t>
423  Registrations &MUST; include the following fields:
424  <list style="symbols">
425    <t>Method Name (see <xref target="methods"/>)</t>
426    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
427    <t>Pointer to specification text</t>
428  </list>
429</t>
430<t>
431  Values to be added to this name space require IETF Review
432  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
433</t>
434<t>
435  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
436</t>
437
438<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
439<t>
440   When it is necessary to express new semantics for a HTTP request that
441   aren't specific to a single application or media type, and currently defined
442   methods are inadequate, it may be appropriate to register a new method.
443</t>
444<t>
445   HTTP methods are generic; that is, they are potentially applicable to any
446   resource, not just one particular media type, "type" of resource, or
447   application. As such, it is preferred that new HTTP methods be registered
448   in a document that isn't specific to a single application, so that this is
449   clear.
450</t>
451<t>
452   Due to the parsing rules defined in &message-body;, definitions of HTTP
453   methods cannot prohibit the presence of a message body on either the request
454   or the response message (with responses to HEAD requests being the single
455   exception). Definitions of new methods cannot change this rule, but they can
456   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
457</t>
458<t>
459   New method definitions need to indicate whether they are safe (<xref
460   target="safe.methods"/>), what semantics (if any) the request body has,
461   and whether they are idempotent (<xref target="idempotent.methods"/>).
462   They also need to state whether they can be cached (&caching;); in
463   particular what conditions a cache may store the response, and under what
464   conditions such a stored response may be used to satisfy a subsequent
465   request.
466</t>
467</section>
468</section>
469
470<section title="Method Definitions" anchor="method.definitions">
471
472<section title="OPTIONS" anchor="OPTIONS">
473  <rdf:Description>
474    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
475  </rdf:Description>
476  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
477  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
478<t>
479   The OPTIONS method requests information about the
480   communication options available on the request/response chain
481   identified by the effective request URI. This method allows a client to
482   determine the options and/or requirements associated with a resource,
483   or the capabilities of a server, without implying a resource action
484   or initiating a resource retrieval.
485</t>
486<t>
487   Responses to the OPTIONS method are not cacheable.
488</t>
489<t>
490   If the OPTIONS request includes a message body (as indicated by the
491   presence of Content-Length or Transfer-Encoding), then the media type
492   &MUST; be indicated by a Content-Type field. Although this
493   specification does not define any use for such a body, future
494   extensions to HTTP might use the OPTIONS body to make more detailed
495   queries on the server.
496</t>
497<t>
498   If the request-target (&request-target;) is an asterisk ("*"),
499   the OPTIONS request is
500   intended to apply to the server in general rather than to a specific
501   resource. Since a server's communication options typically depend on
502   the resource, the "*" request is only useful as a "ping" or "no-op"
503   type of method; it does nothing beyond allowing the client to test
504   the capabilities of the server. For example, this can be used to test
505   a proxy for HTTP/1.1 conformance (or lack thereof).
506</t>
507<t>
508   If the request-target is not an asterisk, the OPTIONS request applies
509   only to the options that are available when communicating with that
510   resource.
511</t>
512<t>
513   A 200 response &SHOULD; include any header fields that indicate
514   optional features implemented by the server and applicable to that
515   resource (e.g., Allow), possibly including extensions not defined by
516   this specification. The response body, if any, &SHOULD; also include
517   information about the communication options. The format for such a
518   body is not defined by this specification, but might be defined by
519   future extensions to HTTP. Content negotiation &MAY; be used to select
520   the appropriate response format. If no response body is included, the
521   response &MUST; include a Content-Length field with a field-value of
522   "0".
523</t>
524<t>
525   The Max-Forwards header field &MAY; be used to target a
526   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
527   If no Max-Forwards field is present in the request, then the forwarded
528   request &MUST-NOT; include a Max-Forwards field.
529</t>
530</section>
531
532<section title="GET" anchor="GET">
533  <rdf:Description>
534    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
535  </rdf:Description>
536  <iref primary="true" item="GET method" x:for-anchor=""/>
537  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
538<t>
539   The GET method requests transfer of a current representation of
540   the target resource.
541</t>
542<t>   
543   If the target resource is a data-producing process, it is the
544   produced data which shall be returned as the representation in the response and not
545   the source text of the process, unless that text happens to be the output of
546   the process.
547</t>
548<t>
549   The semantics of the GET method change to a "conditional GET" if the
550   request message includes an If-Modified-Since, If-Unmodified-Since,
551   If-Match, If-None-Match, or If-Range header field. A conditional GET
552   requests that the representation be transferred only under the
553   circumstances described by the conditional header field(s). The
554   conditional GET request is intended to reduce unnecessary network
555   usage by allowing cached representations to be refreshed without requiring
556   multiple requests or transferring data already held by the client.
557</t>
558<t>
559   The semantics of the GET method change to a "partial GET" if the
560   request message includes a Range header field. A partial GET requests
561   that only part of the representation be transferred, as described in &header-range;.
562   The partial GET request is intended to reduce unnecessary
563   network usage by allowing partially-retrieved representations to be
564   completed without transferring data already held by the client.
565</t>
566<t>
567   Bodies on GET requests have no defined semantics. Note that sending a body
568   on a GET request might cause some existing implementations to reject the
569   request.
570</t>
571<t>
572   The response to a GET request is cacheable and &MAY; be used to satisfy
573   subsequent GET and HEAD requests (see &caching;).
574</t>
575<t>
576   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
577</t>
578</section>
579
580<section title="HEAD" anchor="HEAD">
581  <rdf:Description>
582    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
583  </rdf:Description>
584  <iref primary="true" item="HEAD method" x:for-anchor=""/>
585  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
586<t>
587   The HEAD method is identical to GET except that the server &MUST-NOT;
588   return a message body in the response. The metadata contained
589   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
590   to the information sent in response to a GET request. This method can
591   be used for obtaining metadata about the representation implied by the
592   request without transferring the representation body. This method is
593   often used for testing hypertext links for validity, accessibility,
594   and recent modification.
595</t>
596<t>
597   The response to a HEAD request is cacheable and &MAY; be used to satisfy
598   a subsequent HEAD request. It also has potential side effects on
599   previously stored responses to GET; see &p6-head;.
600</t>
601<t>
602   Bodies on HEAD requests have no defined semantics. Note that sending a body
603   on a HEAD request might cause some existing implementations to reject the
604   request.
605</t>
606</section>
607
608<section title="POST" anchor="POST">
609  <iref primary="true" item="POST method" x:for-anchor=""/>
610  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
611<t>
612   The POST method requests that the origin server accept the
613   representation enclosed in the request as data to be processed by the
614   target resource. POST is designed to allow a uniform method to cover the
615   following functions:
616  <list style="symbols">
617    <t>
618      Annotation of existing resources;
619    </t>
620    <t>
621        Posting a message to a bulletin board, newsgroup, mailing list,
622        or similar group of articles;
623    </t>
624    <t>
625        Providing a block of data, such as the result of submitting a
626        form, to a data-handling process;
627    </t>
628    <t>
629        Extending a database through an append operation.
630    </t>
631  </list>
632</t>
633<t>
634   The actual function performed by the POST method is determined by the
635   server and is usually dependent on the effective request URI.
636</t>
637<t>
638   The action performed by the POST method might not result in a
639   resource that can be identified by a URI. In this case, either 200
640   (OK) or 204 (No Content) is the appropriate response status code,
641   depending on whether or not the response includes a representation that
642   describes the result.
643</t>
644<t>
645   If a resource has been created on the origin server, the response
646   &SHOULD; be 201 (Created) and contain a representation which describes the
647   status of the request and refers to the new resource, and a Location
648   header field (see <xref target="header.location"/>).
649</t>
650<t>
651   Responses to POST requests are only cacheable when they
652   include explicit freshness information (see &p6-explicit;). A
653   cached POST response with a Content-Location header field
654   (see &header-content-location;) whose value is the effective
655   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
656</t>
657<t>
658   Note that POST caching is not widely implemented.
659   However, the 303 (See Other) response can be used to direct the
660   user agent to retrieve a cacheable representation of the resource.
661</t>
662</section>
663
664<section title="PUT" anchor="PUT">
665  <iref primary="true" item="PUT method" x:for-anchor=""/>
666  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
667<t>
668   The PUT method requests that the state of the target resource
669   be created or replaced with the state defined by the representation
670   enclosed in the request message payload.  A successful PUT of a given
671   representation would suggest that a subsequent GET on that same target
672   resource will result in an equivalent representation being returned in
673   a 200 (OK) response.  However, there is no guarantee that such a state
674   change will be observable, since the target resource might be acted
675   upon by other user agents in parallel, or might be subject to dynamic
676   processing by the origin server, before any subsequent GET is received.
677   A successful response only implies that the user agent's intent was
678   achieved at the time of its processing by the origin server.
679</t>
680<t>   
681   If the target resource does not have a current representation and
682   the PUT successfully creates one, then the origin server &MUST; inform
683   the user agent by sending a 201 (Created) response.  If the target
684   resource does have a current representation and that representation is
685   successfully modified in accordance with the state of the enclosed
686   representation, then either a 200 (OK) or 204 (No Content) response
687   &SHOULD; be sent to indicate successful completion of the request.
688</t>
689<t>
690   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
691   as part of the resource state).
692</t>
693<t>
694   An origin server &SHOULD; verify that the PUT representation is
695   consistent with any constraints which the server has for the target
696   resource that cannot or will not be changed by the PUT.  This is
697   particularly important when the origin server uses internal
698   configuration information related to the URI in order to set the
699   values for representation metadata on GET responses.  When a PUT
700   representation is inconsistent with the target resource, the origin
701   server &SHOULD; either make them consistent, by transforming the
702   representation or changing the resource configuration, or respond
703   with an appropriate error message containing sufficient information
704   to explain why the representation is unsuitable.  The 409 (Conflict)
705   or 415 (Unsupported Media Type) status codes are suggested, with the
706   latter being specific to constraints on Content-Type values.
707</t>
708<t>
709   For example, if the target resource is configured to always have a
710   Content-Type of "text/html" and the representation being PUT has a
711   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
712   (a) reconfigure the target resource to reflect the new media type;
713   (b) transform the PUT representation to a format consistent with that
714   of the resource before saving it as the new resource state; or,
715   (c) reject the request with a 415 response indicating that the target
716   resource is limited to "text/html", perhaps including a link to a
717   different resource that would be a suitable target for the new
718   representation.
719</t>
720<t>
721   HTTP does not define exactly how a PUT method affects the state
722   of an origin server beyond what can be expressed by the intent of
723   the user agent request and the semantics of the origin server response.
724   It does not define what a resource might be, in any sense of that
725   word, beyond the interface provided via HTTP.  It does not define
726   how resource state is "stored", nor how such storage might change
727   as a result of a change in resource state, nor how the origin server
728   translates resource state into representations.  Generally speaking,
729   all implementation details behind the resource interface are
730   intentionally hidden by the server.
731</t>
732<t>
733   The fundamental difference between the POST and PUT methods is
734   highlighted by the different intent for the target resource.
735   The target resource in a POST request is intended to handle the
736   enclosed representation as a data-accepting process, such as for
737   a gateway to some other protocol or a document that accepts annotations.
738   In contrast, the target resource in a PUT request is intended to
739   take the enclosed representation as a new or replacement value.
740   Hence, the intent of PUT is idempotent and visible to intermediaries,
741   even though the exact effect is only known by the origin server.
742</t>
743<t>
744   Proper interpretation of a PUT request presumes that the user agent
745   knows what target resource is desired.  A service that is intended
746   to select a proper URI on behalf of the client, after receiving
747   a state-changing request, &SHOULD; be implemented using the POST
748   method rather than PUT.  If the origin server will not make the
749   requested PUT state change to the target resource and instead
750   wishes to have it applied to a different resource, such as when the
751   resource has been moved to a different URI, then the origin server
752   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
753   then make its own decision regarding whether or not to redirect the
754   request.
755</t>
756<t>
757   A PUT request applied to the target resource &MAY; have side-effects
758   on other resources.  For example, an article might have a URI for
759   identifying "the current version" (a resource) which is separate
760   from the URIs identifying each particular version (different
761   resources that at one point shared the same state as the current version
762   resource).  A successful PUT request on "the current version" URI might
763   therefore create a new version resource in addition to changing the
764   state of the target resource, and might also cause links to be added
765   between the related resources.
766</t>
767<t>
768   An origin server &SHOULD; reject any PUT request that contains a
769   Content-Range header field, since it might be misinterpreted as
770   partial content (or might be partial content that is being mistakenly
771   PUT as a full representation).  Partial content updates are
772   possible by targeting a separately identified resource with state
773   that overlaps a portion of the larger resource, or by using a
774   different method that has been specifically defined for partial
775   updates (for example, the PATCH method defined in
776   <xref target="RFC5789"/>).
777</t>
778<t>
779   Responses to the PUT method are not cacheable. If a PUT request passes
780   through a cache that has one or more stored responses for the effective
781   request URI, those stored responses will be invalidated (see
782   &p6-invalid;).
783</t>
784</section>
785
786<section title="DELETE" anchor="DELETE">
787  <iref primary="true" item="DELETE method" x:for-anchor=""/>
788  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
789<t>
790   The DELETE method requests that the origin server delete the target
791   resource. This method &MAY; be overridden by
792   human intervention (or other means) on the origin server. The client cannot
793   be guaranteed that the operation has been carried out, even if the
794   status code returned from the origin server indicates that the action
795   has been completed successfully. However, the server &SHOULD-NOT; 
796   indicate success unless, at the time the response is given, it
797   intends to delete the resource or move it to an inaccessible
798   location.
799</t>
800<t>
801   A successful response &SHOULD; be 200 (OK) if the response includes an
802   representation describing the status, 202 (Accepted) if the action has not
803   yet been enacted, or 204 (No Content) if the action has been enacted
804   but the response does not include a representation.
805</t>
806<t>
807   Bodies on DELETE requests have no defined semantics. Note that sending a body
808   on a DELETE request might cause some existing implementations to reject the
809   request.
810</t>
811<t>
812   Responses to the DELETE method are not cacheable. If a DELETE request
813   passes through a cache that has one or more stored responses for the
814   effective request URI, those stored responses will be invalidated (see
815   &p6-invalid;).
816</t>
817</section>
818
819<section title="TRACE" anchor="TRACE">
820  <rdf:Description>
821    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
822  </rdf:Description>
823  <iref primary="true" item="TRACE method" x:for-anchor=""/>
824  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
825<t>
826   The TRACE method requests a remote, application-layer loop-back
827   of the request message. The final recipient of the request
828   &SHOULD; reflect the message received back to the client as the
829   message body of a 200 (OK) response. The final recipient is either the
830   origin server or the first proxy to receive a Max-Forwards
831   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
832   A TRACE request &MUST-NOT; include a message body.
833</t>
834<t>
835   TRACE allows the client to see what is being received at the other
836   end of the request chain and use that data for testing or diagnostic
837   information. The value of the Via header field (&header-via;) is of
838   particular interest, since it acts as a trace of the request chain.
839   Use of the Max-Forwards header field allows the client to limit the
840   length of the request chain, which is useful for testing a chain of
841   proxies forwarding messages in an infinite loop.
842</t>
843<t>
844   If the request is valid, the response &SHOULD; have a Content-Type of
845   "message/http" (see &media-type-message-http;) and contain a message body
846   that encloses a copy of the entire request message.
847   Responses to the TRACE method are not cacheable.
848</t>
849</section>
850
851<section title="CONNECT" anchor="CONNECT">
852  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
853  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
854<t>
855   The CONNECT method requests that the proxy establish a tunnel
856   to the request-target and, if successful, thereafter restrict its behavior
857   to blind forwarding of packets until the connection is closed.
858</t>
859<t>
860   When using CONNECT, the request-target &MUST; use the authority form
861   (&request-target;); i.e., the request-target consists of only the
862   host name and port number of the tunnel destination, separated by a colon.
863   For example,
864</t>
865<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
866CONNECT server.example.com:80 HTTP/1.1
867Host: server.example.com:80
868
869</artwork></figure>
870<t>
871   Any successful (2xx) response to a CONNECT request indicates that the
872   proxy has established a connection to the requested host and port,
873   and has switched to tunneling the current connection to that server
874   connection.
875   The tunneled data from the server begins immediately after the blank line
876   that concludes the successful response's header block.
877   A server &SHOULD-NOT; send any Transfer-Encoding or Content-Length
878   header fields in a successful response.
879   A client &MUST; ignore any Content-Length or Transfer-Encoding header
880   fields received in a successful response.
881</t>
882<t>
883   Any response other than a successful response indicates that the tunnel
884   has not yet been formed and that the connection remains governed by HTTP.
885</t>
886<t>
887   Proxy authentication might be used to establish the
888   authority to create a tunnel:
889</t>
890<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
891CONNECT server.example.com:80 HTTP/1.1
892Host: server.example.com:80
893Proxy-Authorization: basic aGVsbG86d29ybGQ=
894
895</artwork></figure>
896<t>
897   A message body on a CONNECT request has no defined semantics. Sending a
898   body on a CONNECT request might cause existing implementations to reject
899   the request.
900</t>
901<t>
902   Similar to a pipelined HTTP/1.1 request, data to be tunneled from client
903   to server &MAY; be sent immediately after the request (before a response
904   is received). The usual caveats also apply:
905   data may be discarded if the eventual response is negative, and the
906   connection may be reset with no response if more than one TCP segment
907   is outstanding.
908</t>
909<t>
910   It may be the case that the proxy itself can only reach the requested
911   origin server through another proxy.  In this case, the first proxy
912   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
913   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
914   unless it has either a direct or tunnel connection established to the
915   authority.
916</t>
917<t>
918   If at any point either one of the peers gets disconnected, any
919   outstanding data that came from that peer will be passed to the other
920   one, and after that also the other connection will be terminated by
921   the proxy. If there is outstanding data to that peer undelivered,
922   that data will be discarded.
923</t>
924<t>
925   An origin server which receives a CONNECT request for itself &MAY;
926   respond with a 2xx status code to indicate that a connection is
927   established.  However, most origin servers do not implement CONNECT.
928</t>
929</section>
930</section>
931
932</section>
933
934<section title="Header Fields" anchor="header.fields">
935<t>
936   Header fields are key value pairs that can be used to communicate data about
937   the message, its payload, the target resource, or about the connection
938   itself (i.e., control data).  See &header-fields; for a general definition
939   of their syntax.
940</t>
941
942<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
943<t>
944   New header fields are registered using the procedures described in
945   <xref target="RFC3864"/>.
946</t>
947<t>
948   The requirements for header field names are defined in
949   <xref target="RFC3864" x:fmt="of" x:sec="4.1"/>.  Authors of specifications
950   defining new fields are advised to keep the name as short as practical, and
951   not to prefix them with "X-" if they are to be registered (either
952   immediately or in the future).
953</t>
954<t>
955   New header field values typically have their syntax defined using ABNF
956   (<xref target="RFC5234"/>), using the extension defined in &abnf-extension;
957   as necessary, and are usually constrained to the range of ASCII characters.
958   Header fields needing a greater range of characters can use an encoding
959   such as the one defined in <xref target="RFC5987"/>.
960</t>
961<t>
962   Because commas (",") are used as a generic delimiter between field-values,
963   they need to be treated with care if they are allowed in the field-value's
964   payload. Typically, components that might contain a comma are protected with
965   double-quotes using the quoted-string ABNF production (&field-components;).
966</t>
967<t>
968   For example, a textual date and a URI (either of which might contain a comma)
969   could be safely carried in field-values like these:
970</t>
971<figure><artwork type="example">
972  Example-URI-Field: "http://example.com/a.html,foo",
973                     "http://without-a-comma.example.com/"
974  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
975</artwork></figure>
976<t>
977   Note that double quote delimiters almost always are used with the
978   quoted-string production; using a different syntax inside double quotes
979   will likely cause unnecessary confusion.
980</t>
981<t>
982   Many header fields use a format including (case-insensitively) named
983   parameters (for instance, Content-Type, defined in &header-content-type;).
984   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
985   parameter value enables recipients to use existing parser components. When
986   allowing both forms, the meaning of a parameter value ought to be
987   independent of the syntax used for it (for an example, see the notes on
988   parameter handling for media types in &media-types;).
989</t>
990<t>
991   Authors of specifications defining new header fields are advised to consider
992   documenting:
993  <list style="symbols">
994    <x:lt>
995      <t>Whether the field is a single value, or whether it can be a list
996      (delimited by commas; see &header-fields;).</t>
997      <t>If it does not use the list syntax, document how to treat messages
998      where the header field occurs multiple times (a sensible default would
999      be to ignore the header field, but this might not always be the right
1000      choice).</t>
1001      <t>Note that intermediaries and software libraries might combine
1002      multiple header field instances into a single one, despite the header
1003      field not allowing this. A robust format enables recipients to discover
1004      these situations (good example: "Content-Type", as the comma can only
1005      appear inside quoted strings; bad example: "Location", as a comma can
1006      occur inside a URI).</t>
1007    </x:lt>
1008    <x:lt><t>Under what conditions the header field can be used; e.g., only in
1009    responses or requests, in all messages, only on responses to a particular
1010    request method.</t></x:lt>
1011    <x:lt><t>Whether it is appropriate to list the field-name in the Connection header
1012    (i.e., if the header is to be hop-by-hop, see &header-connection;).</t></x:lt>
1013    <x:lt><t>Under what conditions intermediaries are allowed to modify the header
1014    field's value, insert or delete it.</t></x:lt>
1015    <x:lt><t>How the header might interact with caching (see <xref target="Part6"/>).</t></x:lt>
1016    <x:lt><t>Whether the header field is useful or allowable in trailers (see
1017    &chunked-encoding;).</t></x:lt>
1018    <x:lt><t>Whether the header field should be preserved across redirects.</t></x:lt>
1019  </list>
1020</t>
1021</section>
1022
1023<section title="Request Header Fields" anchor="request.header.fields">
1024  <x:anchor-alias value="request-header"/>
1025<t>
1026   The request header fields allow the client to pass additional
1027   information about the request, and about the client itself, to the
1028   server. These fields act as request modifiers, with semantics
1029   equivalent to the parameters on a programming language method
1030   invocation.
1031</t>
1032<texttable align="left">
1033  <ttcol>Header Field Name</ttcol>
1034  <ttcol>Defined in...</ttcol>
1035
1036  <c>Accept</c> <c>&header-accept;</c>
1037  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
1038  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
1039  <c>Accept-Language</c> <c>&header-accept-language;</c>
1040  <c>Authorization</c> <c>&header-authorization;</c>
1041  <c>Expect</c> <c><xref target="header.expect"/></c>
1042  <c>From</c> <c><xref target="header.from"/></c>
1043  <c>Host</c> <c>&header-host;</c>
1044  <c>If-Match</c> <c>&header-if-match;</c>
1045  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
1046  <c>If-None-Match</c> <c>&header-if-none-match;</c>
1047  <c>If-Range</c> <c>&header-if-range;</c>
1048  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
1049  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
1050  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
1051  <c>Range</c> <c>&header-range;</c>
1052  <c>Referer</c> <c><xref target="header.referer"/></c>
1053  <c>TE</c> <c>&header-te;</c>
1054  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
1055</texttable>
1056</section>
1057
1058<section title="Response Header Fields" anchor="response.header.fields">
1059  <x:anchor-alias value="response-header"/>
1060<t>
1061   The response header fields allow the server to pass additional
1062   information about the response which cannot be placed in the status-line.
1063   These header fields give information about the server and about
1064   further access to the target resource (&effective-request-uri;).
1065</t>
1066<texttable align="left">
1067  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
1068
1069  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
1070  <c>Age</c> <c>&header-age;</c>
1071  <c>Allow</c> <c><xref target="header.allow"/></c>
1072  <c>Date</c> <c><xref target="header.date"/></c>
1073  <c>ETag</c> <c>&header-etag;</c>
1074  <c>Location</c> <c><xref target="header.location"/></c>
1075  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
1076  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
1077  <c>Server</c> <c><xref target="header.server"/></c>
1078  <c>Vary</c> <c>&header-vary;</c>
1079  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
1080</texttable>
1081</section>
1082
1083</section>
1084
1085<section title="Status Codes" anchor="status.codes">
1086<t>
1087   The status-code element is a 3-digit integer result code of the attempt to
1088   understand and satisfy the request.
1089</t>
1090<t>
1091   HTTP status codes are extensible. HTTP applications are not required
1092   to understand the meaning of all registered status codes, though such
1093   understanding is obviously desirable. However, applications &MUST;
1094   understand the class of any status code, as indicated by the first
1095   digit, and treat any unrecognized response as being equivalent to the
1096   x00 status code of that class, with the exception that an
1097   unrecognized response &MUST-NOT; be cached. For example, if an
1098   unrecognized status code of 431 is received by the client, it can
1099   safely assume that there was something wrong with its request and
1100   treat the response as if it had received a 400 status code. In such
1101   cases, user agents &SHOULD; present to the user the representation enclosed
1102   with the response, since that representation is likely to include human-readable
1103   information which will explain the unusual status.
1104</t>
1105<t>
1106   The first digit of the status-code defines the class of response. The
1107   last two digits do not have any categorization role. There are 5
1108   values for the first digit:
1109  <list style="symbols">
1110    <t>
1111      1xx: Informational - Request received, continuing process
1112    </t>
1113    <t>
1114      2xx: Success - The action was successfully received,
1115        understood, and accepted
1116    </t>
1117    <t>
1118      3xx: Redirection - Further action needs to be taken in order to
1119        complete the request
1120    </t>
1121    <t>
1122      4xx: Client Error - The request contains bad syntax or cannot
1123        be fulfilled
1124    </t>
1125    <t>
1126      5xx: Server Error - The server failed to fulfill an apparently
1127        valid request
1128    </t>
1129  </list>
1130</t>
1131<t>
1132   For most status codes the response can carry a payload, in which case a
1133   Content-Type header field indicates the payload's media type
1134   (&header-content-type;).
1135</t>
1136
1137<section title="Overview of Status Codes" anchor="overview.of.status.codes">
1138<t> 
1139   The status codes listed below are defined in this specification,
1140   &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
1141   The reason phrases listed here are only recommendations &mdash; they can be
1142   replaced by local equivalents without affecting the protocol.
1143</t>
1144<texttable align="left">
1145  <ttcol>status-code</ttcol>
1146  <ttcol>reason-phrase</ttcol>
1147  <ttcol>Defined in...</ttcol>
1148 
1149  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
1150  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
1151
1152  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
1153  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
1154  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
1155  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
1156  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
1157  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
1158  <c>206</c> <c>Partial Content</c> <c anchor="status.206">&status-206;</c>
1159
1160  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
1161  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
1162  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
1163  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
1164  <c>304</c> <c>Not Modified</c> <c anchor="status.304">&status-304;</c>
1165  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
1166  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
1167
1168  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
1169  <c>401</c> <c>Unauthorized</c> <c anchor="status.401">&status-401;</c>
1170  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
1171  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
1172  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
1173  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
1174  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
1175  <c>407</c> <c>Proxy Authentication Required</c> <c anchor="status.407">&status-407;</c>
1176  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
1177  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
1178  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
1179  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
1180  <c>412</c> <c>Precondition Failed</c> <c anchor="status.412">&status-412;</c>
1181  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
1182  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
1183  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
1184  <c>416</c> <c>Requested range not satisfiable</c> <c anchor="status.416">&status-416;</c>
1185  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
1186  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
1187
1188  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
1189  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
1190  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
1191  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
1192  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
1193  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
1194</texttable>
1195<t>
1196   Note that this list is not exhaustive &mdash; it does not include
1197   extension status codes defined in other specifications.
1198</t>
1199</section>
1200
1201<section title="Status Code Registry" anchor="status.code.registry">
1202<t>
1203  The HTTP Status Code Registry defines the name space for the status-code
1204  token in the status-line of an HTTP response.
1205</t>
1206<t>
1207  Values to be added to this name space require IETF Review
1208  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
1209</t>
1210<t>
1211  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
1212</t>
1213
1214<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
1215<t>
1216   When it is necessary to express new semantics for a HTTP response that
1217   aren't specific to a single application or media type, and currently defined
1218   status codes are inadequate, a new status code can be registered.
1219</t>
1220<t>
1221   HTTP status codes are generic; that is, they are potentially applicable to
1222   any resource, not just one particular media type, "type" of resource, or
1223   application. As such, it is preferred that new HTTP status codes be
1224   registered in a document that isn't specific to a single application, so
1225   that this is clear.
1226</t>
1227<t>
1228   Definitions of new HTTP status codes typically explain the request
1229   conditions that produce a response containing the status code (e.g.,
1230   combinations of request headers and/or method(s)), along with any
1231   interactions with response headers (e.g., those that are required, those
1232   that modify the semantics of the response).
1233</t>
1234<t>
1235   New HTTP status codes are required to fall under one of the categories
1236   defined in <xref target="status.codes"/>. To allow existing parsers to
1237   properly handle them, new status codes cannot disallow a response body,
1238   although they can mandate a zero-length response body. They can require the
1239   presence of one or more particular HTTP response header(s).
1240</t>
1241<t>
1242   Likewise, their definitions can specify that caches are allowed to use
1243   heuristics to determine their freshness (see &caching;; by default, it is
1244   not allowed), and can define how to determine the resource which they
1245   carry a representation for (see <xref
1246   target="identifying.response.associated.with.representation"/>; by default,
1247   it is anonymous).
1248</t>
1249</section>
1250
1251</section>
1252
1253<section title="Informational 1xx" anchor="status.1xx">
1254<t>
1255   This class of status code indicates a provisional response,
1256   consisting only of the status-line and optional header fields, and is
1257   terminated by an empty line. There are no required header fields for this
1258   class of status code. Since HTTP/1.0 did not define any 1xx status
1259   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1260   except under experimental conditions.
1261</t>
1262<t>
1263   A client &MUST; be prepared to accept one or more 1xx status responses
1264   prior to a regular response, even if the client does not expect a 100
1265   (Continue) status message. Unexpected 1xx status responses &MAY; be
1266   ignored by a user agent.
1267</t>
1268<t>
1269   Proxies &MUST; forward 1xx responses, unless the connection between the
1270   proxy and its client has been closed, or unless the proxy itself
1271   requested the generation of the 1xx response. (For example, if a
1272   proxy adds a "Expect: 100-continue" field when it forwards a request,
1273   then it need not forward the corresponding 100 (Continue)
1274   response(s).)
1275</t>
1276
1277<section title="100 Continue" anchor="status.100">
1278  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1279  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1280<t>
1281   The client &SHOULD; continue with its request. This interim response is
1282   used to inform the client that the initial part of the request has
1283   been received and has not yet been rejected by the server. The client
1284   &SHOULD; continue by sending the remainder of the request or, if the
1285   request has already been completed, ignore this response. The server
1286   &MUST; send a final response after the request has been completed. See
1287   &use100; for detailed discussion of the use and handling of this
1288   status code.
1289</t>
1290</section>
1291
1292<section title="101 Switching Protocols" anchor="status.101">
1293  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1294  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1295<t>
1296   The server understands and is willing to comply with the client's
1297   request, via the Upgrade message header field (&header-upgrade;), for a
1298   change in the application protocol being used on this connection. The
1299   server will switch protocols to those defined by the response's
1300   Upgrade header field immediately after the empty line which
1301   terminates the 101 response.
1302</t>
1303<t>
1304   The protocol &SHOULD; be switched only when it is advantageous to do
1305   so. For example, switching to a newer version of HTTP is advantageous
1306   over older versions, and switching to a real-time, synchronous
1307   protocol might be advantageous when delivering resources that use
1308   such features.
1309</t>
1310</section>
1311</section>
1312
1313<section title="Successful 2xx" anchor="status.2xx">
1314<t>
1315   This class of status code indicates that the client's request was
1316   successfully received, understood, and accepted.
1317</t>
1318
1319<section title="200 OK" anchor="status.200">
1320  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1321  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1322<t>
1323   The request has succeeded. The payload returned with the response
1324   is dependent on the method used in the request, for example:
1325  <list style="hanging">
1326    <t hangText="GET">
1327      a representation of the target resource is sent in the response;
1328    </t>
1329    <t hangText="HEAD">
1330      the same representation as GET, except without the message body;
1331    </t>
1332    <t hangText="POST">
1333      a representation describing or containing the result of the action;
1334    </t>
1335    <t hangText="TRACE">
1336      a representation containing the request message as received by the
1337      end server.
1338    </t>
1339  </list>
1340</t>
1341<t>
1342   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1343   freshness for 200 responses.
1344</t>
1345</section>
1346
1347<section title="201 Created" anchor="status.201">
1348  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1349  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1350<t>
1351   The request has been fulfilled and has resulted in a new resource being
1352   created.
1353</t>
1354<t>
1355   The newly created resource is typically linked to from the response payload,
1356   with the most relevant URI also being carried in the Location header field.
1357   If the newly created resource's URI is the same as the Effective Request URI,
1358   this information can be omitted (e.g., in the case of a response to a PUT
1359   request). 
1360</t>
1361<t>
1362   The origin server &MUST; create the resource before returning the 201 status
1363   code. If the action cannot be carried out immediately, the server &SHOULD;
1364   respond with 202 (Accepted) response instead.
1365</t>
1366<t>
1367   A 201 response &MAY; contain an ETag response header field indicating
1368   the current value of the entity-tag for the representation of the resource
1369   just created (see &header-etag;).
1370</t>
1371</section>
1372
1373<section title="202 Accepted" anchor="status.202">
1374  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1375  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1376<t>
1377   The request has been accepted for processing, but the processing has
1378   not been completed.  The request might or might not eventually be
1379   acted upon, as it might be disallowed when processing actually takes
1380   place. There is no facility for re-sending a status code from an
1381   asynchronous operation such as this.
1382</t>
1383<t>
1384   The 202 response is intentionally non-committal. Its purpose is to
1385   allow a server to accept a request for some other process (perhaps a
1386   batch-oriented process that is only run once per day) without
1387   requiring that the user agent's connection to the server persist
1388   until the process is completed. The representation returned with this
1389   response &SHOULD; include an indication of the request's current status
1390   and either a pointer to a status monitor or some estimate of when the
1391   user can expect the request to be fulfilled.
1392</t>
1393</section>
1394
1395<section title="203 Non-Authoritative Information" anchor="status.203">
1396  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1397  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1398<t>
1399   The representation in the response has been transformed or otherwise
1400   modified by a transforming proxy (&intermediaries;).  Note that the
1401   behavior of transforming intermediaries is controlled by the no-transform
1402   Cache-Control directive (&header-cache-control;).
1403</t>
1404<t>
1405   This status code is only appropriate when the response status code would
1406   have been 200 (OK) otherwise. When the status code before transformation
1407   would have been different, the 214 Transformation Applied warn-code
1408   (&header-warning;) is appropriate.
1409</t>
1410<t>
1411   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1412   freshness for 203 responses.
1413</t>
1414</section>
1415
1416<section title="204 No Content" anchor="status.204">
1417  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1418  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1419<t>
1420   The 204 (No Content) status code indicates that the server has
1421   successfully fulfilled the request and that there is no additional
1422   content to return in the response payload body.  Metadata in the
1423   response header fields refer to the target resource and its current
1424   representation after the requested action.
1425</t>
1426<t>
1427   For example, if a 204 status code is received in response to a PUT
1428   request and the response contains an ETag header field, then the PUT
1429   was successful and the ETag field-value contains the entity-tag for
1430   the new representation of that target resource.
1431</t>
1432<t>
1433   The 204 response allows a server to indicate that the action has been
1434   successfully applied to the target resource while implying that the
1435   user agent &SHOULD-NOT; traverse away from its current "document view"
1436   (if any).  The server assumes that the user agent will provide some
1437   indication of the success to its user, in accord with its own interface,
1438   and apply any new or updated metadata in the response to the active
1439   representation.
1440</t>
1441<t>
1442   For example, a 204 status code is commonly used with document editing
1443   interfaces corresponding to a "save" action, such that the document
1444   being saved remains available to the user for editing. It is also
1445   frequently used with interfaces that expect automated data transfers
1446   to be prevalent, such as within distributed version control systems.
1447</t>
1448<t>
1449   The 204 response &MUST-NOT; include a message body, and thus is always
1450   terminated by the first empty line after the header fields.
1451</t>
1452</section>
1453
1454<section title="205 Reset Content" anchor="status.205">
1455  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1456  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1457<t>
1458   The server has fulfilled the request and the user agent &SHOULD; reset
1459   the document view which caused the request to be sent. This response
1460   is primarily intended to allow input for actions to take place via
1461   user input, followed by a clearing of the form in which the input is
1462   given so that the user can easily initiate another input action.
1463</t>
1464<t>   
1465   The message body included with the response &MUST; be empty. Note that
1466   receivers still need to parse the response according to the algorithm defined
1467   in &message-body;.
1468</t>
1469</section>
1470</section>
1471
1472<section title="Redirection 3xx" anchor="status.3xx">
1473<t>
1474   This class of status code indicates that further action needs to be
1475   taken by the user agent in order to fulfill the request.  If the required
1476   action involves a subsequent HTTP request, it &MAY; be carried out by the
1477   user agent without interaction with the user if and only if the method used
1478   in the second request is known to be "safe", as defined in
1479   <xref target="safe.methods"/>.
1480</t>
1481<t>
1482   There are several types of redirects:
1483   <list style="numbers">
1484      <x:lt>
1485        <t>
1486          Redirects of the request to another URI, either temporarily or
1487          permanently. The new URI is specified in the Location header field.
1488          In this specification, the status codes 301 (Moved Permanently),
1489          302 (Found), and 307 (Temporary Redirect) fall under this category.
1490        </t>
1491      </x:lt>
1492      <x:lt>
1493        <t>
1494          Redirection to a new location that represents an indirect response to
1495          the request, such as the result of a POST operation to be retrieved
1496          with a subsequent GET request. This is status code 303 (See Other).
1497        </t>
1498      </x:lt>
1499      <x:lt>
1500        <t>
1501          Redirection offering a choice of matching resources for use by
1502          agent-driven content negotiation (&agent-driven-negotiation;). This
1503          is status code 300 (Multiple Choices).
1504        </t>
1505      </x:lt>
1506      <x:lt>
1507        <t>
1508          Other kinds of redirection, such as to a cached result (status code 304
1509          (Not Modified), see &status-304;).
1510        </t>
1511      </x:lt>
1512   </list>
1513</t>
1514<x:note>
1515  <t>
1516    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1517    and 302 (Found) were defined for the first type of redirect, and the second
1518    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1519    However it turned out that web forms using POST expected redirects to change
1520    the operation for the subsequent request to retrieval (GET). To address this
1521    use case, HTTP/1.1 introduced the second type of redirect with the status
1522    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1523    As user agents did not change their behavior to maintain backwards
1524    compatibility, the first revision of HTTP/1.1 added yet another status code,
1525    307 (Temporary Redirect), for which the backwards compatibility problems did
1526    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1527    Over 10 years later, most user agents still do method rewriting for
1528    status codes 301 and 302, therefore this specification makes that behavior
1529    conformant in case the original request was POST.
1530  </t>
1531</x:note>
1532<t>
1533   A Location header field on a 3xx response indicates that a client &MAY;
1534   automatically redirect to the URI provided; see <xref target="header.location"/>.
1535</t>
1536<t>
1537   Note that for methods not known to be "safe", as defined in <xref target="safe.methods"/>,
1538   automatic redirection needs to done with care, since the redirect might
1539   change the conditions under which the request was issued.
1540</t>
1541<t>
1542   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1543   "infinite" redirection loops).
1544</t>
1545<x:note>
1546  <t>
1547    <x:h>Note:</x:h> An earlier version of this specification recommended a
1548    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1549    Content developers need to be aware that some clients might
1550    implement such a fixed limitation.
1551  </t>
1552</x:note>
1553
1554<section title="300 Multiple Choices" anchor="status.300">
1555  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1556  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1557<t>
1558   The target resource has more than one
1559   representation, each with its own specific location, and agent-driven
1560   negotiation information (&content-negotiation;) is being provided so that
1561   the user (or user agent) can select a preferred representation by
1562   redirecting its request to that location.
1563</t>
1564<t>
1565   Unless it was a HEAD request, the response &SHOULD; include a representation
1566   containing a list of representation metadata and location(s) from
1567   which the user or user agent can choose the one most appropriate. Depending
1568   upon the format and the capabilities of
1569   the user agent, selection of the most appropriate choice &MAY; be
1570   performed automatically. However, this specification does not define
1571   any standard for such automatic selection.
1572</t>
1573<t>
1574   If the server has a preferred choice of representation, it &SHOULD;
1575   include the specific URI for that representation in the Location
1576   field; user agents &MAY; use the Location field value for automatic
1577   redirection.
1578</t>
1579<t>
1580   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1581   freshness for 300 responses.
1582</t>
1583
1584</section>
1585
1586<section title="301 Moved Permanently" anchor="status.301">
1587  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1588  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1589<t>
1590   The target resource has been assigned a new permanent URI and any
1591   future references to this resource &SHOULD; use one of the returned
1592   URIs.  Clients with link editing capabilities ought to automatically
1593   re-link references to the effective request URI to one or more of the new
1594   references returned by the server, where possible.
1595</t>
1596<t>
1597   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1598   freshness for 301 responses.
1599</t>
1600<t>
1601   The new permanent URI &SHOULD; be given by the Location field in the
1602   response. A response payload can contain a short hypertext note with a
1603   hyperlink to the new URI(s).
1604</t>
1605<x:note>
1606  <t>
1607    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1608    request method from POST to GET for the subsequent request. If this
1609    behavior is undesired, status code 307 (Temporary Redirect) can be used
1610    instead.
1611  </t>
1612</x:note>
1613</section>
1614
1615<section title="302 Found" anchor="status.302">
1616  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1617  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1618<t>
1619   The target resource resides temporarily under a different URI.
1620   Since the redirection might be altered on occasion, the client &SHOULD;
1621   continue to use the effective request URI for future requests.
1622</t>
1623<t>
1624   The temporary URI &SHOULD; be given by the Location field in the
1625   response. A response payload can contain a short hypertext note with a
1626   hyperlink to the new URI(s).
1627</t>
1628<x:note>
1629  <t>
1630    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1631    request method from POST to GET for the subsequent request. If this
1632    behavior is undesired, status code 307 (Temporary Redirect) can be used
1633    instead.
1634  </t>
1635</x:note>
1636</section>
1637
1638<section title="303 See Other" anchor="status.303">
1639  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1640  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1641<t>
1642   The 303 status code indicates that the server is redirecting the
1643   user agent to a different resource, as indicated by a URI in the
1644   Location header field, that is intended to provide an indirect
1645   response to the original request.  In order to satisfy the original
1646   request, a user agent &SHOULD; perform a retrieval request using the
1647   Location URI (a GET or HEAD request if using HTTP), which
1648   may itself be redirected further, and present the eventual result as an
1649   answer to the original request.
1650   Note that the new URI in the Location header field is not considered
1651   equivalent to the effective request URI.
1652</t>
1653<t>
1654   This status code is generally applicable to any HTTP method.  It is
1655   primarily used to allow the output of a POST action to redirect
1656   the user agent to a selected resource, since doing so provides the
1657   information corresponding to the POST response in a form that
1658   can be separately identified, bookmarked, and cached independent
1659   of the original request.
1660</t>
1661<t>
1662   A 303 response to a GET request indicates that the requested
1663   resource does not have a representation of its own that can be
1664   transferred by the server over HTTP.  The Location URI indicates a
1665   resource that is descriptive of the target resource, such that the
1666   follow-on representation might be useful to recipients without
1667   implying that it adequately represents the target resource.
1668   Note that answers to the questions of what can be represented, what
1669   representations are adequate, and what might be a useful description
1670   are outside the scope of HTTP and thus entirely determined by the
1671   URI owner(s).
1672</t>
1673<t>
1674   Except for responses to a HEAD request, the representation of a 303
1675   response &SHOULD; contain a short hypertext note with a hyperlink
1676   to the Location URI.
1677</t>
1678</section>
1679
1680<section title="305 Use Proxy" anchor="status.305">
1681  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1682  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1683<t>
1684   The 305 status code was defined in a previous version of this specification
1685   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1686</t>
1687</section>
1688
1689<section title="306 (Unused)" anchor="status.306">
1690  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1691  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1692<t>
1693   The 306 status code was used in a previous version of the
1694   specification, is no longer used, and the code is reserved.
1695</t>
1696</section>
1697
1698<section title="307 Temporary Redirect" anchor="status.307">
1699  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1700  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1701<t>
1702   The target resource resides temporarily under a different URI.
1703   Since the redirection can change over time, the client &SHOULD;
1704   continue to use the effective request URI for future requests.
1705</t>
1706<t>
1707   The temporary URI &SHOULD; be given by the Location field in the
1708   response. A response payload can contain a short hypertext note with a
1709   hyperlink to the new URI(s).
1710</t>
1711<x:note>
1712  <t>
1713    <x:h>Note:</x:h> This status code is similar to 302 Found, except that
1714    it does not allow rewriting the request method from POST to GET. This
1715    specification defines no equivalent counterpart for 301 Moved Permanently
1716    (<xref target="draft-reschke-http-status-308"/>, however, defines the
1717    status code 308 Permanent Redirect for this purpose).
1718  </t>
1719</x:note>
1720</section>
1721</section>
1722
1723<section title="Client Error 4xx" anchor="status.4xx">
1724<t>
1725   The 4xx class of status code is intended for cases in which the
1726   client seems to have erred. Except when responding to a HEAD request,
1727   the server &SHOULD; include a representation containing an explanation of the
1728   error situation, and whether it is a temporary or permanent
1729   condition. These status codes are applicable to any request method.
1730   User agents &SHOULD; display any included representation to the user.
1731</t>
1732
1733<section title="400 Bad Request" anchor="status.400">
1734  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1735  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1736<t>
1737   The server cannot or will not process the request, due to a client error (e.g.,
1738   malformed syntax).
1739</t>
1740</section>
1741
1742<section title="402 Payment Required" anchor="status.402">
1743  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1744  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1745<t>
1746   This code is reserved for future use.
1747</t>
1748</section>
1749
1750<section title="403 Forbidden" anchor="status.403">
1751  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1752  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1753<t>
1754   The server understood the request, but refuses to authorize it. Providing
1755   different user authentication credentials might be successful, but any
1756   credentials that were provided in the request are insufficient. The request
1757   &SHOULD-NOT; be repeated with the same credentials.
1758</t>
1759<t>
1760   If the request method was not HEAD and the server wishes to make
1761   public why the request has not been fulfilled, it &SHOULD; describe the
1762   reason for the refusal in the representation.  If the server does not wish to
1763   make this information available to the client, the status code 404
1764   (Not Found) &MAY; be used instead.
1765</t>
1766</section>
1767
1768<section title="404 Not Found" anchor="status.404">
1769  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1770  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1771<t>
1772   The server has not found anything matching the effective request URI. No
1773   indication is given of whether the condition is temporary or
1774   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1775   knows, through some internally configurable mechanism, that an old
1776   resource is permanently unavailable and has no forwarding address.
1777   This status code is commonly used when the server does not wish to
1778   reveal exactly why the request has been refused, or when no other
1779   response is applicable.
1780</t>
1781</section>
1782
1783<section title="405 Method Not Allowed" anchor="status.405">
1784  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1785  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1786<t>
1787   The method specified in the request-line is not allowed for the target
1788   resource. The response &MUST; include an Allow header field containing a
1789   list of valid methods for the requested resource.
1790</t>
1791</section>
1792
1793<section title="406 Not Acceptable" anchor="status.406">
1794  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1795  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1796<t>
1797   The resource identified by the request is only capable of generating
1798   response representations which have content characteristics not acceptable
1799   according to the Accept and Accept-* header fields sent in the request
1800   (see &p3-header-fields;).
1801</t>
1802<t>
1803   Unless it was a HEAD request, the response &SHOULD; include a representation
1804   containing a list of available representation characteristics and location(s)
1805   from which the user or user agent can choose the one most
1806   appropriate. Depending upon the format and the
1807   capabilities of the user agent, selection of the most appropriate
1808   choice &MAY; be performed automatically. However, this specification
1809   does not define any standard for such automatic selection.
1810</t>
1811<x:note>
1812  <t>
1813    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1814    not acceptable according to the accept header fields sent in the
1815    request. In some cases, this might even be preferable to sending a
1816    406 response. User agents are encouraged to inspect the header fields of
1817    an incoming response to determine if it is acceptable.
1818  </t>
1819</x:note>
1820<t>
1821   If the response could be unacceptable, a user agent &SHOULD;
1822   temporarily stop receipt of more data and query the user for a
1823   decision on further actions.
1824</t>
1825</section>
1826
1827<section title="408 Request Timeout" anchor="status.408">
1828  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1829  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1830<t>
1831   The client did not produce a request within the time that the server
1832   was prepared to wait. The client &MAY; repeat the request without
1833   modifications at any later time.
1834</t>
1835</section>
1836
1837<section title="409 Conflict" anchor="status.409">
1838  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1839  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1840<t>
1841   The request could not be completed due to a conflict with the current
1842   state of the resource. This code is only allowed in situations where
1843   it is expected that the user might be able to resolve the conflict
1844   and resubmit the request. The response body &SHOULD; include enough
1845   information for the user to recognize the source of the conflict.
1846   Ideally, the response representation would include enough information for the
1847   user or user agent to fix the problem; however, that might not be
1848   possible and is not required.
1849</t>
1850<t>
1851   Conflicts are most likely to occur in response to a PUT request. For
1852   example, if versioning were being used and the representation being PUT
1853   included changes to a resource which conflict with those made by an
1854   earlier (third-party) request, the server might use the 409 response
1855   to indicate that it can't complete the request. In this case, the
1856   response representation would likely contain a list of the differences
1857   between the two versions.
1858</t>
1859</section>
1860
1861<section title="410 Gone" anchor="status.410">
1862  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1863  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1864<t>
1865   The target resource is no longer available at the server and no
1866   forwarding address is known. This condition is expected to be
1867   considered permanent. Clients with link editing capabilities &SHOULD;
1868   delete references to the effective request URI after user approval. If the
1869   server does not know, or has no facility to determine, whether or not
1870   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1871   used instead.
1872</t>
1873<t>
1874   The 410 response is primarily intended to assist the task of web
1875   maintenance by notifying the recipient that the resource is
1876   intentionally unavailable and that the server owners desire that
1877   remote links to that resource be removed. Such an event is common for
1878   limited-time, promotional services and for resources belonging to
1879   individuals no longer working at the server's site. It is not
1880   necessary to mark all permanently unavailable resources as "gone" or
1881   to keep the mark for any length of time &mdash; that is left to the
1882   discretion of the server owner.
1883</t>
1884<t>
1885   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
1886   for 410 responses.
1887</t>
1888</section>
1889
1890<section title="411 Length Required" anchor="status.411">
1891  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1892  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1893<t>
1894   The server refuses to accept the request without a defined Content-Length.
1895   The client &MAY; repeat the request if it adds a valid
1896   Content-Length header field containing the length of the message body
1897   in the request message.
1898</t>
1899</section>
1900
1901<section title="413 Request Representation Too Large" anchor="status.413">
1902  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
1903  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
1904<t>
1905   The server is refusing to process a request because the request
1906   representation is larger than the server is willing or able to process. The
1907   server &MAY; close the connection to prevent the client from continuing
1908   the request.
1909</t>
1910<t>
1911   If the condition is temporary, the server &SHOULD; include a Retry-After
1912   header field to indicate that it is temporary and after what
1913   time the client &MAY; try again.
1914</t>
1915</section>
1916
1917<section title="414 URI Too Long" anchor="status.414">
1918  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
1919  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
1920<t>
1921   The server is refusing to service the request because the effective request URI
1922   is longer than the server is willing to interpret. This rare
1923   condition is only likely to occur when a client has improperly
1924   converted a POST request to a GET request with long query
1925   information, when the client has descended into a URI "black hole" of
1926   redirection (e.g., a redirected URI prefix that points to a suffix of
1927   itself), or when the server is under attack by a client attempting to
1928   exploit security holes present in some servers using fixed-length
1929   buffers for reading or manipulating the request-target.
1930</t>
1931</section>
1932
1933<section title="415 Unsupported Media Type" anchor="status.415">
1934  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1935  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1936<t>
1937   The server is refusing to service the request because the request
1938   payload is in a format not supported by this request method on the
1939   target resource.
1940</t>
1941</section>
1942
1943<section title="417 Expectation Failed" anchor="status.417">
1944  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1945  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1946<t>
1947   The expectation given in an Expect header field (see <xref target="header.expect"/>)
1948   could not be met by this server, or, if the server is a proxy,
1949   the server has unambiguous evidence that the request could not be met
1950   by the next-hop server.
1951</t>
1952</section>
1953
1954<section title="426 Upgrade Required" anchor="status.426">
1955  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
1956  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
1957<t>
1958   The request can not be completed without a prior protocol upgrade. This
1959   response &MUST; include an Upgrade header field (&header-upgrade;)
1960   specifying the required protocols.
1961</t>
1962<figure>
1963<preamble>Example:</preamble>
1964<artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
1965HTTP/1.1 426 Upgrade Required
1966Upgrade: HTTP/3.0
1967Connection: Upgrade
1968Content-Length: <x:length-of target="s426body"/>
1969Content-Type: text/plain
1970
1971<x:span anchor="s426body">This service requires use of the HTTP/3.0 protocol.
1972</x:span></artwork></figure>
1973<t>
1974   The server &SHOULD; include a message body in the 426 response which
1975   indicates in human readable form the reason for the error and describes any
1976   alternative courses which may be available to the user.
1977</t>
1978</section>
1979</section>
1980
1981<section title="Server Error 5xx" anchor="status.5xx">
1982<t>
1983   Response status codes beginning with the digit "5" indicate cases in
1984   which the server is aware that it has erred or is incapable of
1985   performing the request. Except when responding to a HEAD request, the
1986   server &SHOULD; include a representation containing an explanation of the
1987   error situation, and whether it is a temporary or permanent
1988   condition. User agents &SHOULD; display any included representation to the
1989   user. These response codes are applicable to any request method.
1990</t>
1991
1992<section title="500 Internal Server Error" anchor="status.500">
1993  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1994  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1995<t>
1996   The server encountered an unexpected condition which prevented it
1997   from fulfilling the request.
1998</t>
1999</section>
2000
2001<section title="501 Not Implemented" anchor="status.501">
2002  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
2003  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
2004<t>
2005   The server does not support the functionality required to fulfill the
2006   request. This is the appropriate response when the server does not
2007   recognize the request method and is not capable of supporting it for
2008   any resource.
2009</t>
2010</section>
2011
2012<section title="502 Bad Gateway" anchor="status.502">
2013  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
2014  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
2015<t>
2016   The server, while acting as a gateway or proxy, received an invalid
2017   response from the upstream server it accessed in attempting to
2018   fulfill the request.
2019</t>
2020</section>
2021
2022<section title="503 Service Unavailable" anchor="status.503">
2023  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
2024  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
2025<t>
2026   The server is currently unable to handle the request due to a
2027   temporary overloading or maintenance of the server.
2028</t>
2029<t>
2030   The implication is that this is a temporary condition which will be
2031   alleviated after some delay. If known, the length of the delay &MAY; be
2032   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2033   If no Retry-After is given, the client &SHOULD; handle the response as it
2034   would for a 500 response.
2035</t>
2036<x:note>
2037  <t>
2038    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
2039    server has to use it when becoming overloaded. Some servers might wish
2040    to simply refuse the connection.
2041  </t>
2042</x:note>
2043</section>
2044
2045<section title="504 Gateway Timeout" anchor="status.504">
2046  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2047  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2048<t>
2049   The server, while acting as a gateway or proxy, did not receive a
2050   timely response from the upstream server specified by the URI (e.g.,
2051   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2052   to access in attempting to complete the request.
2053</t>
2054<x:note>
2055  <t>
2056    <x:h>Note</x:h> to implementors: some deployed proxies are known to
2057    return 400 or 500 when DNS lookups time out.
2058  </t>
2059</x:note>
2060</section>
2061
2062<section title="505 HTTP Version Not Supported" anchor="status.505">
2063  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2064  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
2065<t>
2066   The server does not support, or refuses to support, the protocol
2067   version that was used in the request message. The server is
2068   indicating that it is unable or unwilling to complete the request
2069   using the same major version as the client, as described in &http-version;,
2070   other than with this error message. The response &SHOULD; contain
2071   a representation describing why that version is not supported and what other
2072   protocols are supported by that server.
2073</t>
2074
2075</section>
2076</section>
2077
2078</section>
2079
2080<section title="Representation" anchor="representation">
2081<t>
2082   Request and Response messages &MAY; transfer a representation if not otherwise
2083   restricted by the request method or response status code. A representation
2084   consists of metadata (representation header fields) and data (representation
2085   body).  When a complete or partial representation is enclosed in an HTTP message,
2086   it is referred to as the payload of the message. HTTP representations
2087   are defined in &payload;.
2088</t>
2089<t>
2090   A representation body is only present in a message when a message body is
2091   present, as described in &message-body;. The representation body is obtained
2092   from the message body by decoding any Transfer-Encoding that might
2093   have been applied to ensure safe and proper transfer of the message.
2094</t>
2095
2096<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
2097<t>
2098   It is sometimes necessary to determine an identifier for the resource
2099   associated with a representation.
2100</t>
2101<t>
2102   An HTTP request representation, when present, is always associated with an
2103   anonymous (i.e., unidentified) resource.
2104</t>
2105<t>
2106   In the common case, an HTTP response is a representation of the target
2107   resource (see &effective-request-uri;). However, this is not always the
2108   case. To determine the URI of the resource a response is associated with,
2109   the following rules are used (with the first applicable one being selected):
2110</t>
2111<t><list style="numbers">
2112   <t>If the response status code is 200 or 203 and the request method was GET,
2113   the response payload is a representation of the target resource.</t>
2114   <t>If the response status code is 204, 206, or 304 and the request method was GET
2115   or HEAD, the response payload is a partial representation of the target
2116   resource.</t>
2117   <t>If the response has a Content-Location header field, and that URI is the same
2118   as the effective request URI, the response payload is a representation of the
2119   target resource.</t>
2120   <t>If the response has a Content-Location header field, and that URI is not the
2121   same as the effective request URI, then the response asserts that its
2122   payload is a representation of the resource identified by the
2123   Content-Location URI. However, such an assertion cannot be trusted unless
2124   it can be verified by other means (not defined by HTTP).</t>
2125   <t>Otherwise, the response is a representation of an anonymous (i.e.,
2126   unidentified) resource.</t>
2127</list></t>
2128<t>
2129  <cref anchor="TODO-req-uri">
2130   The comparison function is going to have to be defined somewhere,
2131   because we already need to compare URIs for things like cache invalidation.</cref>
2132</t>
2133</section>
2134
2135</section>
2136
2137
2138<section title="Common Protocol Parameters" anchor="common.protocol.parameters">
2139<section title="Date/Time Formats" anchor="http.date">
2140  <x:anchor-alias value="HTTP-date"/>
2141<t>
2142   HTTP applications have historically allowed three different formats
2143   for date/time stamps. However, the preferred format is a fixed-length subset
2144   of that defined by <xref target="RFC1123"/>:
2145</t>
2146<figure><artwork type="example" x:indent-with="  ">
2147Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2148</artwork></figure>
2149<t>
2150   The other formats are described here only for compatibility with obsolete
2151   implementations.
2152</t>
2153<figure><artwork type="example" x:indent-with="  ">
2154Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2155Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2156</artwork></figure>
2157<t>
2158   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2159   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2160   only generate the RFC 1123 format for representing HTTP-date values
2161   in header fields.
2162</t>
2163<t>
2164   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2165   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2166   equal to UTC (Coordinated Universal Time). This is indicated in the
2167   first two formats by the inclusion of "GMT" as the three-letter
2168   abbreviation for time zone, and &MUST; be assumed when reading the
2169   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2170   additional whitespace beyond that specifically included as SP in the
2171   grammar.
2172</t>
2173<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2174  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2175</artwork></figure>
2176<t anchor="preferred.date.format">
2177  <x:anchor-alias value="rfc1123-date"/>
2178  <x:anchor-alias value="time-of-day"/>
2179  <x:anchor-alias value="hour"/>
2180  <x:anchor-alias value="minute"/>
2181  <x:anchor-alias value="second"/>
2182  <x:anchor-alias value="day-name"/>
2183  <x:anchor-alias value="day"/>
2184  <x:anchor-alias value="month"/>
2185  <x:anchor-alias value="year"/>
2186  <x:anchor-alias value="GMT"/>
2187  Preferred format:
2188</t>
2189<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"/>
2190  <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>
2191  ; fixed length subset of the format defined in
2192  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2193 
2194  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2195               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2196               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2197               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2198               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2199               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2200               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2201               
2202  <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>
2203               ; e.g., 02 Jun 1982
2204
2205  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2206  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2207               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2208               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2209               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2210               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2211               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2212               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2213               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2214               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2215               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2216               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2217               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2218  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2219
2220  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2221
2222  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2223                 ; 00:00:00 - 23:59:59
2224                 
2225  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2226  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2227  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2228</artwork></figure>
2229<t>
2230  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2231  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2232  same as those defined for the RFC 5322 constructs
2233  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2234</t>
2235<t anchor="obsolete.date.formats">
2236  <x:anchor-alias value="obs-date"/>
2237  <x:anchor-alias value="rfc850-date"/>
2238  <x:anchor-alias value="asctime-date"/>
2239  <x:anchor-alias value="date1"/>
2240  <x:anchor-alias value="date2"/>
2241  <x:anchor-alias value="date3"/>
2242  <x:anchor-alias value="rfc1123-date"/>
2243  <x:anchor-alias value="day-name-l"/>
2244  Obsolete formats:
2245</t>
2246<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2247  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2248</artwork></figure>
2249<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2250  <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>
2251  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2252                 ; day-month-year (e.g., 02-Jun-82)
2253
2254  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2255         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2256         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2257         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2258         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2259         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2260         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2261</artwork></figure>
2262<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2263  <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>
2264  <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> ))
2265                 ; month day (e.g., Jun  2)
2266</artwork></figure>
2267<x:note>
2268  <t>
2269    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2270    accepting date values that might have been sent by non-HTTP
2271    applications, as is sometimes the case when retrieving or posting
2272    messages via proxies/gateways to SMTP or NNTP.
2273  </t>
2274</x:note>
2275<x:note>
2276  <t>
2277    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2278    to their usage within the protocol stream. Clients and servers are
2279    not required to use these formats for user presentation, request
2280    logging, etc.
2281  </t>
2282</x:note>
2283</section>
2284
2285<section title="Product Tokens" anchor="product.tokens">
2286  <x:anchor-alias value="product"/>
2287  <x:anchor-alias value="product-version"/>
2288<t>
2289   Product tokens are used to allow communicating applications to
2290   identify themselves by software name and version. Most fields using
2291   product tokens also allow sub-products which form a significant part
2292   of the application to be listed, separated by whitespace. By
2293   convention, the products are listed in order of their significance
2294   for identifying the application.
2295</t>
2296<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2297  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2298  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2299</artwork></figure>
2300<t>
2301   Examples:
2302</t>
2303<figure><artwork type="example">
2304  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2305  Server: Apache/0.8.4
2306</artwork></figure>
2307<t>
2308   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2309   used for advertising or other non-essential information. Although any
2310   token octet &MAY; appear in a product-version, this token &SHOULD;
2311   only be used for a version identifier (i.e., successive versions of
2312   the same product &SHOULD; only differ in the product-version portion of
2313   the product value).
2314</t>
2315</section>
2316</section>
2317
2318<section title="Header Field Definitions" anchor="header.field.definitions">
2319<t>
2320   This section defines the syntax and semantics of HTTP/1.1 header fields
2321   related to request and response semantics.
2322</t>
2323
2324<section title="Allow" anchor="header.allow">
2325  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2326  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2327  <x:anchor-alias value="Allow"/>
2328<t>
2329   The "Allow" header field lists the set of methods advertised as
2330   supported by the target resource. The purpose of this field is strictly to
2331   inform the recipient of valid request methods associated with the resource.
2332</t>
2333<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2334  <x:ref>Allow</x:ref> = #<x:ref>method</x:ref>
2335</artwork></figure>
2336<t>
2337   Example of use:
2338</t>
2339<figure><artwork type="example">
2340  Allow: GET, HEAD, PUT
2341</artwork></figure>
2342<t>
2343   The actual set of allowed methods is defined by the origin server at the
2344   time of each request.
2345</t>
2346<t>
2347   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2348   understand all the methods specified in order to handle them according to
2349   the generic message handling rules.
2350</t>
2351</section>
2352
2353<section title="Date" anchor="header.date">
2354  <iref primary="true" item="Date header field" x:for-anchor=""/>
2355  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
2356  <x:anchor-alias value="Date"/>
2357<t>
2358   The "Date" header field represents the date and time at which
2359   the message was originated, having the same semantics as the Origination
2360   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2361   The field value is an HTTP-date, as defined in <xref target="http.date"/>;
2362   it &MUST; be sent in rfc1123-date format.
2363</t>
2364<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2365  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
2366</artwork></figure>
2367<t>
2368   An example is
2369</t>
2370<figure><artwork type="example">
2371  Date: Tue, 15 Nov 1994 08:12:31 GMT
2372</artwork></figure>
2373<t>
2374   Origin servers &MUST; include a Date header field in all responses,
2375   except in these cases:
2376  <list style="numbers">
2377      <t>If the response status code is 100 (Continue) or 101 (Switching
2378         Protocols), the response &MAY; include a Date header field, at
2379         the server's option.</t>
2380
2381      <t>If the response status code conveys a server error, e.g., 500
2382         (Internal Server Error) or 503 (Service Unavailable), and it is
2383         inconvenient or impossible to generate a valid Date.</t>
2384
2385      <t>If the server does not have a clock that can provide a
2386         reasonable approximation of the current time, its responses
2387         &MUST-NOT; include a Date header field.</t>
2388  </list>
2389</t>
2390<t>
2391   A received message that does not have a Date header field &MUST; be
2392   assigned one by the recipient if the message will be cached by that
2393   recipient.
2394</t>
2395<t>
2396   Clients can use the Date header field as well; in order to keep request
2397   messages small, they are advised not to include it when it doesn't convey
2398   any useful information (as is usually the case for requests that do not
2399   contain a payload).
2400</t>
2401<t>
2402   The HTTP-date sent in a Date header field &SHOULD-NOT; represent a date and
2403   time subsequent to the generation of the message. It &SHOULD; represent
2404   the best available approximation of the date and time of message
2405   generation, unless the implementation has no means of generating a
2406   reasonably accurate date and time. In theory, the date ought to
2407   represent the moment just before the payload is generated. In
2408   practice, the date can be generated at any time during the message
2409   origination without affecting its semantic value.
2410</t>
2411</section>
2412
2413<section title="Expect" anchor="header.expect">
2414  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2415  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2416  <x:anchor-alias value="Expect"/>
2417  <x:anchor-alias value="expectation"/>
2418  <x:anchor-alias value="expect-param"/>
2419  <x:anchor-alias value="expect-name"/>
2420  <x:anchor-alias value="expect-value"/>
2421<t>
2422   The "Expect" header field is used to indicate that particular
2423   server behaviors are required by the client.
2424</t>
2425<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"/>
2426  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
2427 
2428  <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> ]
2429                             *( <x:ref>OWS</x:ref> ";" [ <x:ref>OWS</x:ref> <x:ref>expect-param</x:ref> ] )
2430  <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> ]
2431 
2432  <x:ref>expect-name</x:ref>  = <x:ref>token</x:ref>
2433  <x:ref>expect-value</x:ref> = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
2434</artwork></figure>
2435<t>
2436   If all received Expect header field(s) are syntactically valid but contain
2437   an expectation that the recipient does not understand or cannot comply with,
2438   the recipient &MUST; respond with a 417 (Expectation Failed) status code. A
2439   recipient of a syntactically invalid Expectation header field &MUST; respond
2440   with a 4xx status code other than 417.
2441</t>
2442<t>
2443   The only expectation defined by this specification is:
2444</t>
2445<t><iref primary="true" item="100-continue (expect value)"/><iref primary="true" item="Expect Values" subitem="100-continue"/>
2446  100-continue
2447   <list>
2448      <t>
2449        The "100-continue" expectation is defined &use100;. It does not support
2450        any expect-params.
2451      </t>
2452   </list>
2453</t>
2454<t>
2455   Comparison is case-insensitive for names (expect-name), and case-sensitive
2456   for values (expect-value).
2457</t>
2458<t>
2459   The Expect mechanism is hop-by-hop: the above requirements apply to any
2460   server, including proxies. However, the Expect header field itself is
2461   end-to-end; it &MUST; be forwarded if the request is forwarded.
2462</t>
2463<t>
2464   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect
2465   header field.
2466</t>
2467</section>
2468
2469<section title="From" anchor="header.from">
2470  <iref primary="true" item="From header field" x:for-anchor=""/>
2471  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2472  <x:anchor-alias value="From"/>
2473  <x:anchor-alias value="mailbox"/>
2474<t>
2475   The "From" header field, if given, &SHOULD; contain an Internet
2476   e-mail address for the human user who controls the requesting user
2477   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2478   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2479</t>
2480<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2481  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
2482 
2483  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2484</artwork></figure>
2485<t>
2486   An example is:
2487</t>
2488<figure><artwork type="example">
2489  From: webmaster@example.org
2490</artwork></figure>
2491<t>
2492   This header field &MAY; be used for logging purposes and as a means for
2493   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2494   be used as an insecure form of access protection. The interpretation
2495   of this field is that the request is being performed on behalf of the
2496   person given, who accepts responsibility for the method performed. In
2497   particular, robot agents &SHOULD; include this header field so that the
2498   person responsible for running the robot can be contacted if problems
2499   occur on the receiving end.
2500</t>
2501<t>
2502   The Internet e-mail address in this field &MAY; be separate from the
2503   Internet host which issued the request. For example, when a request
2504   is passed through a proxy the original issuer's address &SHOULD; be
2505   used.
2506</t>
2507<t>
2508   The client &SHOULD-NOT;  send the From header field without the user's
2509   approval, as it might conflict with the user's privacy interests or
2510   their site's security policy. It is strongly recommended that the
2511   user be able to disable, enable, and modify the value of this field
2512   at any time prior to a request.
2513</t>
2514</section>
2515
2516<section title="Location" anchor="header.location">
2517  <iref primary="true" item="Location header field" x:for-anchor=""/>
2518  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2519  <x:anchor-alias value="Location"/>
2520<t>
2521   The "Location" header field &MAY; be sent in responses to refer to
2522   a specific resource in accordance with the semantics of the status
2523   code.
2524</t>
2525<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2526  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2527</artwork></figure>
2528<t>
2529   For 201 (Created) responses, the Location is the URI of the new resource
2530   which was created by the request. For 3xx responses, the location &SHOULD;
2531   indicate the server's preferred URI for automatic redirection to the
2532   resource.
2533</t>
2534<t>
2535   The field value consists of a single URI-reference. When it has the form
2536   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2537   the final value is computed by resolving it against the effective request
2538   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>). If the original URI, as
2539   navigated to by the user agent, did contain a fragment identifier, and the
2540   final value does not, then the original URI's fragment identifier is added
2541   to the final value.
2542</t>
2543<figure>
2544<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-->
2545<artwork type="example">
2546  Location: /pub/WWW/People.html#tim
2547</artwork>
2548<postamble>would result in a final value of "http://www.example.org/pub/WWW/People.html#tim"</postamble>
2549</figure>
2550<figure>
2551<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-->
2552<artwork type="example">
2553  Location: http://www.example.net/index.html
2554</artwork>
2555<postamble>would result in a final value of "http://www.example.net/index.html#larry", preserving the original fragment identifier.</postamble>
2556</figure>
2557<x:note>
2558  <t>
2559    <x:h>Note:</x:h> Some recipients attempt to recover from Location fields
2560    that are not valid URI references. This specification does not mandate or
2561    define such processing, but does allow it (see <xref target="intro.conformance.and.error.handling"/>).
2562  </t>
2563</x:note>
2564<t>
2565   There are circumstances in which a fragment identifier in a Location URI
2566   would not be appropriate. For instance, when it appears in a 201 Created
2567   response, where the Location header field specifies the URI for the entire
2568   created resource.
2569</t>
2570<x:note>
2571  <t>
2572    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2573    from Location in that the Content-Location identifies the most specific
2574    resource corresponding to the enclosed representation.
2575    It is therefore possible for a response to contain header fields for
2576    both Location and Content-Location.
2577  </t>
2578</x:note>
2579</section>
2580
2581<section title="Max-Forwards" anchor="header.max-forwards">
2582  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2583  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2584  <x:anchor-alias value="Max-Forwards"/>
2585<t>
2586   The "Max-Forwards" header field provides a mechanism with the
2587   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2588   methods to limit the number of times that the request is forwarded by
2589   proxies. This can be useful when the client is attempting to
2590   trace a request which appears to be failing or looping mid-chain.
2591</t>
2592<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2593  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2594</artwork></figure>
2595<t>
2596   The Max-Forwards value is a decimal integer indicating the remaining
2597   number of times this request message can be forwarded.
2598</t>
2599<t>
2600   Each recipient of a TRACE or OPTIONS request
2601   containing a Max-Forwards header field &MUST; check and update its
2602   value prior to forwarding the request. If the received value is zero
2603   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2604   respond as the final recipient. If the received Max-Forwards value is
2605   greater than zero, then the forwarded message &MUST; contain an updated
2606   Max-Forwards field with a value decremented by one (1).
2607</t>
2608<t>
2609   The Max-Forwards header field &MAY; be ignored for all other request
2610   methods.
2611</t>
2612</section>
2613
2614<section title="Referer" anchor="header.referer">
2615  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2616  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2617  <x:anchor-alias value="Referer"/>
2618<t>
2619   The "Referer" [sic] header field allows the client to specify the
2620   URI of the resource from which the target URI was obtained (the
2621   "referrer", although the header field is misspelled.).
2622</t>
2623<t>
2624   The Referer header field allows servers to generate lists of back-links to
2625   resources for interest, logging, optimized caching, etc. It also allows
2626   obsolete or mistyped links to be traced for maintenance. Some servers use
2627   Referer as a means of controlling where they allow links from (so-called
2628   "deep linking"), but legitimate requests do not always
2629   contain a Referer header field.
2630</t>
2631<t>
2632   If the target URI was obtained from a source that does not have its own
2633   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2634   sent with the value "about:blank", or not be sent at all. Note that this
2635   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2636</t>
2637<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2638  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2639</artwork></figure>
2640<t>
2641   Example:
2642</t>
2643<figure><artwork type="example">
2644  Referer: http://www.example.org/hypertext/Overview.html
2645</artwork></figure>
2646<t>
2647   If the field value is a relative URI, it &SHOULD; be interpreted
2648   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2649   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2650</t>
2651</section>
2652
2653<section title="Retry-After" anchor="header.retry-after">
2654  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2655  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2656  <x:anchor-alias value="Retry-After"/>
2657<t>
2658   The header "Retry-After" field can be used with a 503 (Service
2659   Unavailable) response to indicate how long the service is expected to
2660   be unavailable to the requesting client. This field &MAY; also be used
2661   with any 3xx (Redirection) response to indicate the minimum time the
2662   user-agent is asked to wait before issuing the redirected request.
2663</t>
2664<t>
2665   The value of this field can be either an HTTP-date or an integer number
2666   of seconds (in decimal) after the time of the response.
2667</t>
2668<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2669  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2670</artwork></figure>
2671<t anchor="rule.delta-seconds">
2672  <x:anchor-alias value="delta-seconds"/>
2673   Time spans are non-negative decimal integers, representing time in
2674   seconds.
2675</t>
2676<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2677  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2678</artwork></figure>
2679<t>
2680   Two examples of its use are
2681</t>
2682<figure><artwork type="example">
2683  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2684  Retry-After: 120
2685</artwork></figure>
2686<t>
2687   In the latter example, the delay is 2 minutes.
2688</t>
2689</section>
2690
2691<section title="Server" anchor="header.server">
2692  <iref primary="true" item="Server header field" x:for-anchor=""/>
2693  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2694  <x:anchor-alias value="Server"/>
2695<t>
2696   The "Server" header field contains information about the
2697   software used by the origin server to handle the request.
2698</t>
2699<t>
2700   The field can contain multiple
2701   product tokens (<xref target="product.tokens"/>) and
2702   comments (&header-fields;) identifying the server and any significant
2703   subproducts. The product tokens are listed in order of their significance
2704   for identifying the application.
2705</t>
2706<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2707  <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> ) )
2708</artwork></figure>
2709<t>
2710   Example:
2711</t>
2712<figure><artwork type="example">
2713  Server: CERN/3.0 libwww/2.17
2714</artwork></figure>
2715<t>
2716   If the response is being forwarded through a proxy, the proxy
2717   application &MUST-NOT; modify the Server header field. Instead, it
2718   &MUST; include a Via field (as described in &header-via;).
2719</t>
2720<x:note>
2721  <t>
2722    <x:h>Note:</x:h> Revealing the specific software version of the server might
2723    allow the server machine to become more vulnerable to attacks
2724    against software that is known to contain security holes. Server
2725    implementors are encouraged to make this field a configurable
2726    option.
2727  </t>
2728</x:note>
2729</section>
2730
2731<section title="User-Agent" anchor="header.user-agent">
2732  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2733  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2734  <x:anchor-alias value="User-Agent"/>
2735<t>
2736   The "User-Agent" header field contains information about the user
2737   agent originating the request. User agents &SHOULD; include this field with
2738   requests.
2739</t>
2740<t>
2741   Typically, it is used for statistical purposes, the tracing of protocol
2742   violations, and tailoring responses to avoid particular user agent
2743   limitations.
2744</t>
2745<t>
2746   The field can contain multiple
2747   product tokens (<xref target="product.tokens"/>)
2748   and comments (&header-fields;) identifying the agent and its
2749   significant subproducts. By convention, the product tokens are listed in
2750   order of their significance for identifying the application.
2751</t>
2752<t>
2753   Because this field is usually sent on every request a user agent makes,
2754   implementations are encouraged not to include needlessly fine-grained
2755   detail, and to limit (or even prohibit) the addition of subproducts by third
2756   parties. Overly long and detailed User-Agent field values make requests
2757   larger and can also be used to identify ("fingerprint") the user against
2758   their wishes.
2759</t>
2760<t>
2761   Likewise, implementations are encouraged not to use the product tokens of
2762   other implementations in order to declare compatibility with them, as this
2763   circumvents the purpose of the field. Finally, they are encouraged not to
2764   use comments to identify products; doing so makes the field value more
2765   difficult to parse.
2766</t>
2767<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2768  <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> ) )
2769</artwork></figure>
2770<t>
2771   Example:
2772</t>
2773<figure><artwork type="example">
2774  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2775</artwork></figure>
2776</section>
2777
2778</section>
2779
2780<section title="IANA Considerations" anchor="IANA.considerations">
2781
2782<section title="Method Registry" anchor="method.registration">
2783<t>
2784  The registration procedure for HTTP request methods is defined by
2785  <xref target="method.registry"/> of this document.
2786</t>
2787<t>
2788   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2789   and be populated with the registrations below:
2790</t>
2791<?BEGININC p2-semantics.iana-methods ?>
2792<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2793<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2794   <ttcol>Method</ttcol>
2795   <ttcol>Safe</ttcol>
2796   <ttcol>Reference</ttcol>
2797   <c>CONNECT</c>
2798   <c>no</c>
2799   <c>
2800      <xref target="CONNECT"/>
2801   </c>
2802   <c>DELETE</c>
2803   <c>no</c>
2804   <c>
2805      <xref target="DELETE"/>
2806   </c>
2807   <c>GET</c>
2808   <c>yes</c>
2809   <c>
2810      <xref target="GET"/>
2811   </c>
2812   <c>HEAD</c>
2813   <c>yes</c>
2814   <c>
2815      <xref target="HEAD"/>
2816   </c>
2817   <c>OPTIONS</c>
2818   <c>yes</c>
2819   <c>
2820      <xref target="OPTIONS"/>
2821   </c>
2822   <c>POST</c>
2823   <c>no</c>
2824   <c>
2825      <xref target="POST"/>
2826   </c>
2827   <c>PUT</c>
2828   <c>no</c>
2829   <c>
2830      <xref target="PUT"/>
2831   </c>
2832   <c>TRACE</c>
2833   <c>yes</c>
2834   <c>
2835      <xref target="TRACE"/>
2836   </c>
2837</texttable>
2838<!--(END)-->
2839<?ENDINC p2-semantics.iana-methods ?>
2840</section>
2841
2842<section title="Status Code Registry" anchor="status.code.registration">
2843<t>
2844   The registration procedure for HTTP Status Codes &mdash; previously defined
2845   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2846   by <xref target="status.code.registry"/> of this document.
2847</t>
2848<t>
2849   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2850   shall be updated with the registrations below:
2851</t>
2852<?BEGININC p2-semantics.iana-status-codes ?>
2853<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2854<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2855   <ttcol>Value</ttcol>
2856   <ttcol>Description</ttcol>
2857   <ttcol>Reference</ttcol>
2858   <c>100</c>
2859   <c>Continue</c>
2860   <c>
2861      <xref target="status.100"/>
2862   </c>
2863   <c>101</c>
2864   <c>Switching Protocols</c>
2865   <c>
2866      <xref target="status.101"/>
2867   </c>
2868   <c>200</c>
2869   <c>OK</c>
2870   <c>
2871      <xref target="status.200"/>
2872   </c>
2873   <c>201</c>
2874   <c>Created</c>
2875   <c>
2876      <xref target="status.201"/>
2877   </c>
2878   <c>202</c>
2879   <c>Accepted</c>
2880   <c>
2881      <xref target="status.202"/>
2882   </c>
2883   <c>203</c>
2884   <c>Non-Authoritative Information</c>
2885   <c>
2886      <xref target="status.203"/>
2887   </c>
2888   <c>204</c>
2889   <c>No Content</c>
2890   <c>
2891      <xref target="status.204"/>
2892   </c>
2893   <c>205</c>
2894   <c>Reset Content</c>
2895   <c>
2896      <xref target="status.205"/>
2897   </c>
2898   <c>300</c>
2899   <c>Multiple Choices</c>
2900   <c>
2901      <xref target="status.300"/>
2902   </c>
2903   <c>301</c>
2904   <c>Moved Permanently</c>
2905   <c>
2906      <xref target="status.301"/>
2907   </c>
2908   <c>302</c>
2909   <c>Found</c>
2910   <c>
2911      <xref target="status.302"/>
2912   </c>
2913   <c>303</c>
2914   <c>See Other</c>
2915   <c>
2916      <xref target="status.303"/>
2917   </c>
2918   <c>305</c>
2919   <c>Use Proxy</c>
2920   <c>
2921      <xref target="status.305"/>
2922   </c>
2923   <c>306</c>
2924   <c>(Unused)</c>
2925   <c>
2926      <xref target="status.306"/>
2927   </c>
2928   <c>307</c>
2929   <c>Temporary Redirect</c>
2930   <c>
2931      <xref target="status.307"/>
2932   </c>
2933   <c>400</c>
2934   <c>Bad Request</c>
2935   <c>
2936      <xref target="status.400"/>
2937   </c>
2938   <c>402</c>
2939   <c>Payment Required</c>
2940   <c>
2941      <xref target="status.402"/>
2942   </c>
2943   <c>403</c>
2944   <c>Forbidden</c>
2945   <c>
2946      <xref target="status.403"/>
2947   </c>
2948   <c>404</c>
2949   <c>Not Found</c>
2950   <c>
2951      <xref target="status.404"/>
2952   </c>
2953   <c>405</c>
2954   <c>Method Not Allowed</c>
2955   <c>
2956      <xref target="status.405"/>
2957   </c>
2958   <c>406</c>
2959   <c>Not Acceptable</c>
2960   <c>
2961      <xref target="status.406"/>
2962   </c>
2963   <c>408</c>
2964   <c>Request Timeout</c>
2965   <c>
2966      <xref target="status.408"/>
2967   </c>
2968   <c>409</c>
2969   <c>Conflict</c>
2970   <c>
2971      <xref target="status.409"/>
2972   </c>
2973   <c>410</c>
2974   <c>Gone</c>
2975   <c>
2976      <xref target="status.410"/>
2977   </c>
2978   <c>411</c>
2979   <c>Length Required</c>
2980   <c>
2981      <xref target="status.411"/>
2982   </c>
2983   <c>413</c>
2984   <c>Request Representation Too Large</c>
2985   <c>
2986      <xref target="status.413"/>
2987   </c>
2988   <c>414</c>
2989   <c>URI Too Long</c>
2990   <c>
2991      <xref target="status.414"/>
2992   </c>
2993   <c>415</c>
2994   <c>Unsupported Media Type</c>
2995   <c>
2996      <xref target="status.415"/>
2997   </c>
2998   <c>417</c>
2999   <c>Expectation Failed</c>
3000   <c>
3001      <xref target="status.417"/>
3002   </c>
3003   <c>426</c>
3004   <c>Upgrade Required</c>
3005   <c>
3006      <xref target="status.426"/>
3007   </c>
3008   <c>500</c>
3009   <c>Internal Server Error</c>
3010   <c>
3011      <xref target="status.500"/>
3012   </c>
3013   <c>501</c>
3014   <c>Not Implemented</c>
3015   <c>
3016      <xref target="status.501"/>
3017   </c>
3018   <c>502</c>
3019   <c>Bad Gateway</c>
3020   <c>
3021      <xref target="status.502"/>
3022   </c>
3023   <c>503</c>
3024   <c>Service Unavailable</c>
3025   <c>
3026      <xref target="status.503"/>
3027   </c>
3028   <c>504</c>
3029   <c>Gateway Timeout</c>
3030   <c>
3031      <xref target="status.504"/>
3032   </c>
3033   <c>505</c>
3034   <c>HTTP Version Not Supported</c>
3035   <c>
3036      <xref target="status.505"/>
3037   </c>
3038</texttable>
3039<!--(END)-->
3040<?ENDINC p2-semantics.iana-status-codes ?>
3041</section>
3042<section title="Header Field Registration" anchor="header.field.registration">
3043<t>
3044   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3045   with the permanent registrations below (see <xref target="RFC3864"/>):
3046</t>
3047<?BEGININC p2-semantics.iana-headers ?>
3048<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3049<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3050   <ttcol>Header Field Name</ttcol>
3051   <ttcol>Protocol</ttcol>
3052   <ttcol>Status</ttcol>
3053   <ttcol>Reference</ttcol>
3054
3055   <c>Allow</c>
3056   <c>http</c>
3057   <c>standard</c>
3058   <c>
3059      <xref target="header.allow"/>
3060   </c>
3061   <c>Date</c>
3062   <c>http</c>
3063   <c>standard</c>
3064   <c>
3065      <xref target="header.date"/>
3066   </c>
3067   <c>Expect</c>
3068   <c>http</c>
3069   <c>standard</c>
3070   <c>
3071      <xref target="header.expect"/>
3072   </c>
3073   <c>From</c>
3074   <c>http</c>
3075   <c>standard</c>
3076   <c>
3077      <xref target="header.from"/>
3078   </c>
3079   <c>Location</c>
3080   <c>http</c>
3081   <c>standard</c>
3082   <c>
3083      <xref target="header.location"/>
3084   </c>
3085   <c>Max-Forwards</c>
3086   <c>http</c>
3087   <c>standard</c>
3088   <c>
3089      <xref target="header.max-forwards"/>
3090   </c>
3091   <c>Referer</c>
3092   <c>http</c>
3093   <c>standard</c>
3094   <c>
3095      <xref target="header.referer"/>
3096   </c>
3097   <c>Retry-After</c>
3098   <c>http</c>
3099   <c>standard</c>
3100   <c>
3101      <xref target="header.retry-after"/>
3102   </c>
3103   <c>Server</c>
3104   <c>http</c>
3105   <c>standard</c>
3106   <c>
3107      <xref target="header.server"/>
3108   </c>
3109   <c>User-Agent</c>
3110   <c>http</c>
3111   <c>standard</c>
3112   <c>
3113      <xref target="header.user-agent"/>
3114   </c>
3115</texttable>
3116<!--(END)-->
3117<?ENDINC p2-semantics.iana-headers ?>
3118<t>
3119   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3120</t>
3121</section>
3122</section>
3123
3124<section title="Security Considerations" anchor="security.considerations">
3125<t>
3126   This section is meant to inform application developers, information
3127   providers, and users of the security limitations in HTTP/1.1 as
3128   described by this document. The discussion does not include
3129   definitive solutions to the problems revealed, though it does make
3130   some suggestions for reducing security risks.
3131</t>
3132
3133<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3134<t>
3135   Like any generic data transfer protocol, HTTP cannot regulate the
3136   content of the data that is transferred, nor is there any a priori
3137   method of determining the sensitivity of any particular piece of
3138   information within the context of any given request. Therefore,
3139   applications &SHOULD; supply as much control over this information as
3140   possible to the provider of that information. Four header fields are
3141   worth special mention in this context: Server, Via, Referer and From.
3142</t>
3143<t>
3144   Revealing the specific software version of the server might allow the
3145   server machine to become more vulnerable to attacks against software
3146   that is known to contain security holes. Implementors &SHOULD; make the
3147   Server header field a configurable option.
3148</t>
3149<t>
3150   Proxies which serve as a portal through a network firewall &SHOULD;
3151   take special precautions regarding the transfer of header information
3152   that identifies the hosts behind the firewall. In particular, they
3153   &SHOULD; remove, or replace with sanitized versions, any Via fields
3154   generated behind the firewall.
3155</t>
3156<t>
3157   The Referer header field allows reading patterns to be studied and reverse
3158   links drawn. Although it can be very useful, its power can be abused
3159   if user details are not separated from the information contained in
3160   the Referer. Even when the personal information has been removed, the
3161   Referer header field might indicate a private document's URI whose
3162   publication would be inappropriate.
3163</t>
3164<t>
3165   The information sent in the From field might conflict with the user's
3166   privacy interests or their site's security policy, and hence it
3167   &SHOULD-NOT;  be transmitted without the user being able to disable,
3168   enable, and modify the contents of the field. The user &MUST; be able
3169   to set the contents of this field within a user preference or
3170   application defaults configuration.
3171</t>
3172<t>
3173   We suggest, though do not require, that a convenient toggle interface
3174   be provided for the user to enable or disable the sending of From and
3175   Referer information.
3176</t>
3177<t>
3178   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3179   target="header.server"/>) header fields can sometimes be used to determine
3180   that a specific client or server has a particular security hole which might
3181   be exploited. Unfortunately, this same information is often used for other
3182   valuable purposes for which HTTP currently has no better mechanism.
3183</t>
3184<t>
3185   Furthermore, the User-Agent header field may contain enough entropy to be
3186   used, possibly in conjunction with other material, to uniquely identify the
3187   user.
3188</t>
3189<t>
3190   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3191   that was sent in request header fields within the body of their response.
3192   Clients &SHOULD; be careful with sensitive information, like Cookies,
3193   Authorization credentials, and other header fields that might be used to
3194   collect data from the client.
3195</t> 
3196</section>
3197
3198<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3199<t>
3200   Because the source of a link might be private information or might
3201   reveal an otherwise private information source, it is strongly
3202   recommended that the user be able to select whether or not the
3203   Referer field is sent. For example, a browser client could have a
3204   toggle switch for browsing openly/anonymously, which would
3205   respectively enable/disable the sending of Referer and From
3206   information.
3207</t>
3208<t>
3209   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3210   HTTP request if the referring page was transferred with a secure
3211   protocol.
3212</t>
3213<t>
3214   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3215   sensitive data because that data will be placed in the request-target. Many
3216   existing servers, proxies, and user agents log or display the request-target
3217   in places where it might be visible to third parties. Such services can
3218   use POST-based form submission instead.
3219</t>
3220</section>
3221
3222<section title="Location Header Fields: Spoofing and Information Leakage" anchor="location.spoofing-leakage">
3223<t>
3224   If a single server supports multiple organizations that do not trust
3225   one another, then it &MUST; check the values of Location and Content-Location
3226   header fields in responses that are generated under control of
3227   said organizations to make sure that they do not attempt to
3228   invalidate resources over which they have no authority.
3229</t>
3230<t>
3231   Furthermore, appending the fragment identifier from one URI to another
3232   one obtained from a Location header field might leak confidential
3233   information to the target server &mdash; although the fragment identifier is
3234   not transmitted in the final request, it might be visible to the user agent
3235   through other means, such as scripting.
3236</t>
3237</section>
3238
3239<section title="Security Considerations for CONNECT">
3240<t>
3241   Since tunneled data is opaque to the proxy, there are additional
3242   risks to tunneling to other well-known or reserved ports.
3243   A HTTP client CONNECTing to port 25 could relay spam
3244   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3245   access to a small number of known ports.
3246</t>
3247</section>
3248
3249</section>
3250
3251<section title="Acknowledgments" anchor="acks">
3252<t>
3253  See &acks;.
3254</t>
3255</section>
3256</middle>
3257<back>
3258
3259<references title="Normative References">
3260
3261<reference anchor="Part1">
3262  <front>
3263    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3264    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3265      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3266      <address><email>fielding@gbiv.com</email></address>
3267    </author>
3268    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3269      <organization abbrev="W3C">World Wide Web Consortium</organization>
3270      <address><email>ylafon@w3.org</email></address>
3271    </author>
3272    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3273      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3274      <address><email>julian.reschke@greenbytes.de</email></address>
3275    </author>
3276    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3277  </front>
3278  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3279  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3280</reference>
3281
3282<reference anchor="Part3">
3283  <front>
3284    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3285    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3286      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3287      <address><email>fielding@gbiv.com</email></address>
3288    </author>
3289    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3290      <organization abbrev="W3C">World Wide Web Consortium</organization>
3291      <address><email>ylafon@w3.org</email></address>
3292    </author>
3293    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3294      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3295      <address><email>julian.reschke@greenbytes.de</email></address>
3296    </author>
3297    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3298  </front>
3299  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3300  <x:source href="p3-payload.xml" basename="p3-payload"/>
3301</reference>
3302
3303<reference anchor="Part4">
3304  <front>
3305    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3306    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3307      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3308      <address><email>fielding@gbiv.com</email></address>
3309    </author>
3310    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3311      <organization abbrev="W3C">World Wide Web Consortium</organization>
3312      <address><email>ylafon@w3.org</email></address>
3313    </author>
3314    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3315      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3316      <address><email>julian.reschke@greenbytes.de</email></address>
3317    </author>
3318    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3319  </front>
3320  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3321  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3322</reference>
3323
3324<reference anchor="Part5">
3325  <front>
3326    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3327    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3328      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3329      <address><email>fielding@gbiv.com</email></address>
3330    </author>
3331    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3332      <organization abbrev="W3C">World Wide Web Consortium</organization>
3333      <address><email>ylafon@w3.org</email></address>
3334    </author>
3335    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3336      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3337      <address><email>julian.reschke@greenbytes.de</email></address>
3338    </author>
3339    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3340  </front>
3341  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3342  <x:source href="p5-range.xml" basename="p5-range"/>
3343</reference>
3344
3345<reference anchor="Part6">
3346  <front>
3347    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3348    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3349      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3350      <address><email>fielding@gbiv.com</email></address>
3351    </author>
3352    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3353      <organization abbrev="W3C">World Wide Web Consortium</organization>
3354      <address><email>ylafon@w3.org</email></address>
3355    </author>
3356    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3357      <organization>Rackspace</organization>
3358      <address><email>mnot@mnot.net</email></address>
3359    </author>
3360    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3361      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3362      <address><email>julian.reschke@greenbytes.de</email></address>
3363    </author>
3364    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3365  </front>
3366  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3367  <x:source href="p6-cache.xml" basename="p6-cache"/>
3368</reference>
3369
3370<reference anchor="Part7">
3371  <front>
3372    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3373    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3374      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3375      <address><email>fielding@gbiv.com</email></address>
3376    </author>
3377    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3378      <organization abbrev="W3C">World Wide Web Consortium</organization>
3379      <address><email>ylafon@w3.org</email></address>
3380    </author>
3381    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3382      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3383      <address><email>julian.reschke@greenbytes.de</email></address>
3384    </author>
3385    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3386  </front>
3387  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3388  <x:source href="p7-auth.xml" basename="p7-auth"/>
3389</reference>
3390
3391<reference anchor="RFC1950">
3392  <front>
3393    <title>ZLIB Compressed Data Format Specification version 3.3</title>
3394    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
3395      <organization>Aladdin Enterprises</organization>
3396      <address><email>ghost@aladdin.com</email></address>
3397    </author>
3398    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
3399    <date month="May" year="1996"/>
3400  </front>
3401  <seriesInfo name="RFC" value="1950"/>
3402  <!--<annotation>
3403    RFC 1950 is an Informational RFC, thus it might be less stable than
3404    this specification. On the other hand, this downward reference was
3405    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
3406    therefore it is unlikely to cause problems in practice. See also
3407    <xref target="BCP97"/>.
3408  </annotation>-->
3409</reference>
3410
3411<reference anchor="RFC1951">
3412  <front>
3413    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
3414    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
3415      <organization>Aladdin Enterprises</organization>
3416      <address><email>ghost@aladdin.com</email></address>
3417    </author>
3418    <date month="May" year="1996"/>
3419  </front>
3420  <seriesInfo name="RFC" value="1951"/>
3421  <!--<annotation>
3422    RFC 1951 is an Informational RFC, thus it might be less stable than
3423    this specification. On the other hand, this downward reference was
3424    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
3425    therefore it is unlikely to cause problems in practice. See also
3426    <xref target="BCP97"/>.
3427  </annotation>-->
3428</reference>
3429
3430<reference anchor="RFC1952">
3431  <front>
3432    <title>GZIP file format specification version 4.3</title>
3433    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
3434      <organization>Aladdin Enterprises</organization>
3435      <address><email>ghost@aladdin.com</email></address>
3436    </author>
3437    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
3438      <address><email>gzip@prep.ai.mit.edu</email></address>
3439    </author>
3440    <author initials="M." surname="Adler" fullname="Mark Adler">
3441      <address><email>madler@alumni.caltech.edu</email></address>
3442    </author>
3443    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
3444      <address><email>ghost@aladdin.com</email></address>
3445    </author>
3446    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
3447      <address><email>randeg@alumni.rpi.edu</email></address>
3448    </author>
3449    <date month="May" year="1996"/>
3450  </front>
3451  <seriesInfo name="RFC" value="1952"/>
3452  <!--<annotation>
3453    RFC 1952 is an Informational RFC, thus it might be less stable than
3454    this specification. On the other hand, this downward reference was
3455    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
3456    therefore it is unlikely to cause problems in practice. See also
3457    <xref target="BCP97"/>.
3458  </annotation>-->
3459</reference>
3460
3461<reference anchor="RFC2045">
3462  <front>
3463    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3464    <author initials="N." surname="Freed" fullname="Ned Freed">
3465      <organization>Innosoft International, Inc.</organization>
3466      <address><email>ned@innosoft.com</email></address>
3467    </author>
3468    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3469      <organization>First Virtual Holdings</organization>
3470      <address><email>nsb@nsb.fv.com</email></address>
3471    </author>
3472    <date month="November" year="1996"/>
3473  </front>
3474  <seriesInfo name="RFC" value="2045"/>
3475</reference>
3476
3477<reference anchor="RFC2046">
3478  <front>
3479    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
3480    <author initials="N." surname="Freed" fullname="Ned Freed">
3481      <organization>Innosoft International, Inc.</organization>
3482      <address><email>ned@innosoft.com</email></address>
3483    </author>
3484    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3485      <organization>First Virtual Holdings</organization>
3486      <address><email>nsb@nsb.fv.com</email></address>
3487    </author>
3488    <date month="November" year="1996"/>
3489  </front>
3490  <seriesInfo name="RFC" value="2046"/>
3491</reference>
3492
3493<reference anchor="RFC2119">
3494  <front>
3495    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3496    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3497      <organization>Harvard University</organization>
3498      <address><email>sob@harvard.edu</email></address>
3499    </author>
3500    <date month="March" year="1997"/>
3501  </front>
3502  <seriesInfo name="BCP" value="14"/>
3503  <seriesInfo name="RFC" value="2119"/>
3504</reference>
3505
3506<reference anchor="RFC3986">
3507 <front>
3508  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3509  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3510    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3511    <address>
3512       <email>timbl@w3.org</email>
3513       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3514    </address>
3515  </author>
3516  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3517    <organization abbrev="Day Software">Day Software</organization>
3518    <address>
3519      <email>fielding@gbiv.com</email>
3520      <uri>http://roy.gbiv.com/</uri>
3521    </address>
3522  </author>
3523  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3524    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3525    <address>
3526      <email>LMM@acm.org</email>
3527      <uri>http://larry.masinter.net/</uri>
3528    </address>
3529  </author>
3530  <date month='January' year='2005'></date>
3531 </front>
3532 <seriesInfo name="STD" value="66"/>
3533 <seriesInfo name="RFC" value="3986"/>
3534</reference>
3535
3536<reference anchor='RFC4647'>
3537  <front>
3538    <title>Matching of Language Tags</title>
3539    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
3540      <organization>Yahoo! Inc.</organization>
3541      <address><email>addison@inter-locale.com</email></address>
3542    </author>
3543    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
3544      <organization>Google</organization>
3545      <address><email>mark.davis@macchiato.com</email></address>
3546    </author>
3547    <date year='2006' month='September' />
3548  </front>
3549  <seriesInfo name='BCP' value='47' />
3550  <seriesInfo name='RFC' value='4647' />
3551</reference>
3552
3553<reference anchor="RFC5234">
3554  <front>
3555    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3556    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3557      <organization>Brandenburg InternetWorking</organization>
3558      <address>
3559        <email>dcrocker@bbiw.net</email>
3560      </address> 
3561    </author>
3562    <author initials="P." surname="Overell" fullname="Paul Overell">
3563      <organization>THUS plc.</organization>
3564      <address>
3565        <email>paul.overell@thus.net</email>
3566      </address>
3567    </author>
3568    <date month="January" year="2008"/>
3569  </front>
3570  <seriesInfo name="STD" value="68"/>
3571  <seriesInfo name="RFC" value="5234"/>
3572</reference>
3573
3574<reference anchor='RFC5646'>
3575  <front>
3576    <title>Tags for Identifying Languages</title>
3577    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
3578      <organization>Lab126</organization>
3579      <address><email>addison@inter-locale.com</email></address>
3580    </author>
3581    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
3582      <organization>Google</organization>
3583      <address><email>mark.davis@google.com</email></address>
3584    </author>
3585    <date month='September' year='2009' />
3586  </front>
3587  <seriesInfo name='BCP' value='47' />
3588  <seriesInfo name='RFC' value='5646' />
3589</reference>
3590
3591</references>
3592
3593<references title="Informative References">
3594
3595<reference anchor="RFC1123">
3596  <front>
3597    <title>Requirements for Internet Hosts - Application and Support</title>
3598    <author initials="R." surname="Braden" fullname="Robert Braden">
3599      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3600      <address><email>Braden@ISI.EDU</email></address>
3601    </author>
3602    <date month="October" year="1989"/>
3603  </front>
3604  <seriesInfo name="STD" value="3"/>
3605  <seriesInfo name="RFC" value="1123"/>
3606</reference>
3607
3608<reference anchor="RFC1945">
3609  <front>
3610    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3611    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3612      <organization>MIT, Laboratory for Computer Science</organization>
3613      <address><email>timbl@w3.org</email></address>
3614    </author>
3615    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3616      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3617      <address><email>fielding@ics.uci.edu</email></address>
3618    </author>
3619    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3620      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3621      <address><email>frystyk@w3.org</email></address>
3622    </author>
3623    <date month="May" year="1996"/>
3624  </front>
3625  <seriesInfo name="RFC" value="1945"/>
3626</reference>
3627
3628<reference anchor="RFC2049">
3629  <front>
3630    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
3631    <author initials="N." surname="Freed" fullname="Ned Freed">
3632      <organization>Innosoft International, Inc.</organization>
3633      <address><email>ned@innosoft.com</email></address>
3634    </author>
3635    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3636      <organization>First Virtual Holdings</organization>
3637      <address><email>nsb@nsb.fv.com</email></address>
3638    </author>
3639    <date month="November" year="1996"/>
3640  </front>
3641  <seriesInfo name="RFC" value="2049"/>
3642</reference>
3643
3644<reference anchor="RFC2068">
3645  <front>
3646    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3647    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3648      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3649      <address><email>fielding@ics.uci.edu</email></address>
3650    </author>
3651    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3652      <organization>MIT Laboratory for Computer Science</organization>
3653      <address><email>jg@w3.org</email></address>
3654    </author>
3655    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3656      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3657      <address><email>mogul@wrl.dec.com</email></address>
3658    </author>
3659    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3660      <organization>MIT Laboratory for Computer Science</organization>
3661      <address><email>frystyk@w3.org</email></address>
3662    </author>
3663    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3664      <organization>MIT Laboratory for Computer Science</organization>
3665      <address><email>timbl@w3.org</email></address>
3666    </author>
3667    <date month="January" year="1997"/>
3668  </front>
3669  <seriesInfo name="RFC" value="2068"/>
3670</reference>
3671
3672<reference anchor="RFC2076">
3673  <front>
3674    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
3675    <author initials="J." surname="Palme" fullname="Jacob Palme">
3676      <organization>Stockholm University/KTH</organization>
3677      <address><email>jpalme@dsv.su.se</email></address>
3678    </author>
3679    <date month="February" year="1997"/>
3680  </front>
3681  <seriesInfo name="RFC" value="2076"/>
3682</reference>
3683
3684<reference anchor="RFC2277">
3685  <front>
3686    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
3687    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
3688      <organization>UNINETT</organization>
3689      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
3690    </author>
3691    <date month="January" year="1998"/>
3692  </front>
3693  <seriesInfo name="BCP" value="18"/>
3694  <seriesInfo name="RFC" value="2277"/>
3695</reference>
3696
3697<reference anchor='RFC2295'>
3698  <front>
3699    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
3700    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
3701      <organization>Technische Universiteit Eindhoven</organization>
3702      <address>
3703        <email>koen@win.tue.nl</email>
3704      </address>
3705    </author>
3706    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
3707      <organization>Hewlett-Packard Company</organization>
3708      <address>
3709        <email>mutz@hpl.hp.com</email>
3710      </address>
3711    </author>
3712    <date year='1998' month='March'/>
3713  </front>
3714  <seriesInfo name='RFC' value='2295'/>
3715</reference>
3716
3717<reference anchor="RFC2388">
3718  <front>
3719    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
3720    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3721      <organization>Xerox Palo Alto Research Center</organization>
3722      <address><email>masinter@parc.xerox.com</email></address>
3723    </author>
3724    <date year="1998" month="August"/>
3725  </front>
3726  <seriesInfo name="RFC" value="2388"/>
3727</reference>
3728
3729<reference anchor="RFC2557">
3730  <front>
3731    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
3732    <author initials="F." surname="Palme" fullname="Jacob Palme">
3733      <organization>Stockholm University and KTH</organization>
3734      <address><email>jpalme@dsv.su.se</email></address>
3735    </author>
3736    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
3737      <organization>Microsoft Corporation</organization>
3738      <address><email>alexhop@microsoft.com</email></address>
3739    </author>
3740    <author initials="N." surname="Shelness" fullname="Nick Shelness">
3741      <organization>Lotus Development Corporation</organization>
3742      <address><email>Shelness@lotus.com</email></address>
3743    </author>
3744    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
3745      <address><email>stef@nma.com</email></address>
3746    </author>
3747    <date year="1999" month="March"/>
3748  </front>
3749  <seriesInfo name="RFC" value="2557"/>
3750</reference>
3751
3752<reference anchor="RFC2616">
3753  <front>
3754    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3755    <author initials="R." surname="Fielding" fullname="R. Fielding">
3756      <organization>University of California, Irvine</organization>
3757      <address><email>fielding@ics.uci.edu</email></address>
3758    </author>
3759    <author initials="J." surname="Gettys" fullname="J. Gettys">
3760      <organization>W3C</organization>
3761      <address><email>jg@w3.org</email></address>
3762    </author>
3763    <author initials="J." surname="Mogul" fullname="J. Mogul">
3764      <organization>Compaq Computer Corporation</organization>
3765      <address><email>mogul@wrl.dec.com</email></address>
3766    </author>
3767    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3768      <organization>MIT Laboratory for Computer Science</organization>
3769      <address><email>frystyk@w3.org</email></address>
3770    </author>
3771    <author initials="L." surname="Masinter" fullname="L. Masinter">
3772      <organization>Xerox Corporation</organization>
3773      <address><email>masinter@parc.xerox.com</email></address>
3774    </author>
3775    <author initials="P." surname="Leach" fullname="P. Leach">
3776      <organization>Microsoft Corporation</organization>
3777      <address><email>paulle@microsoft.com</email></address>
3778    </author>
3779    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3780      <organization>W3C</organization>
3781      <address><email>timbl@w3.org</email></address>
3782    </author>
3783    <date month="June" year="1999"/>
3784  </front>
3785  <seriesInfo name="RFC" value="2616"/>
3786</reference>
3787
3788<reference anchor='RFC2817'>
3789  <front>
3790    <title>Upgrading to TLS Within HTTP/1.1</title>
3791    <author initials='R.' surname='Khare' fullname='R. Khare'>
3792      <organization>4K Associates / UC Irvine</organization>
3793      <address><email>rohit@4K-associates.com</email></address>
3794    </author>
3795    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3796      <organization>Agranat Systems, Inc.</organization>
3797      <address><email>lawrence@agranat.com</email></address>
3798    </author>
3799    <date year='2000' month='May' />
3800  </front>
3801  <seriesInfo name='RFC' value='2817' />
3802</reference>
3803
3804<reference anchor="RFC3629">
3805  <front>
3806    <title>UTF-8, a transformation format of ISO 10646</title>
3807    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
3808      <organization>Alis Technologies</organization>
3809      <address><email>fyergeau@alis.com</email></address>
3810    </author>
3811    <date month="November" year="2003"/>
3812  </front>
3813  <seriesInfo name="STD" value="63"/>
3814  <seriesInfo name="RFC" value="3629"/>
3815</reference>
3816
3817<reference anchor='RFC3864'>
3818  <front>
3819    <title>Registration Procedures for Message Header Fields</title>
3820    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3821      <organization>Nine by Nine</organization>
3822      <address><email>GK-IETF@ninebynine.org</email></address>
3823    </author>
3824    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3825      <organization>BEA Systems</organization>
3826      <address><email>mnot@pobox.com</email></address>
3827    </author>
3828    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3829      <organization>HP Labs</organization>
3830      <address><email>JeffMogul@acm.org</email></address>
3831    </author>
3832    <date year='2004' month='September' />
3833  </front>
3834  <seriesInfo name='BCP' value='90' />
3835  <seriesInfo name='RFC' value='3864' />
3836</reference>
3837
3838<reference anchor="RFC4288">
3839  <front>
3840    <title>Media Type Specifications and Registration Procedures</title>
3841    <author initials="N." surname="Freed" fullname="N. Freed">
3842      <organization>Sun Microsystems</organization>
3843      <address>
3844        <email>ned.freed@mrochek.com</email>
3845      </address>
3846    </author>
3847    <author initials="J." surname="Klensin" fullname="J. Klensin">
3848      <address>
3849        <email>klensin+ietf@jck.com</email>
3850      </address>
3851    </author>
3852    <date year="2005" month="December"/>
3853  </front>
3854  <seriesInfo name="BCP" value="13"/>
3855  <seriesInfo name="RFC" value="4288"/>
3856</reference>
3857
3858<reference anchor='RFC5226'>
3859  <front>
3860    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3861    <author initials='T.' surname='Narten' fullname='T. Narten'>
3862      <organization>IBM</organization>
3863      <address><email>narten@us.ibm.com</email></address>
3864    </author>
3865    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3866      <organization>Google</organization>
3867      <address><email>Harald@Alvestrand.no</email></address>
3868    </author>
3869    <date year='2008' month='May' />
3870  </front>
3871  <seriesInfo name='BCP' value='26' />
3872  <seriesInfo name='RFC' value='5226' />
3873</reference>
3874
3875<reference anchor="RFC5322">
3876  <front>
3877    <title>Internet Message Format</title>
3878    <author initials="P." surname="Resnick" fullname="P. Resnick">
3879      <organization>Qualcomm Incorporated</organization>
3880    </author>
3881    <date year="2008" month="October"/>
3882  </front> 
3883  <seriesInfo name="RFC" value="5322"/>
3884</reference>
3885
3886<reference anchor='RFC5789'>
3887  <front>
3888    <title>PATCH Method for HTTP</title>
3889    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3890      <organization>Linden Lab</organization>
3891    </author>
3892    <author initials='J.' surname='Snell' fullname='J. Snell' />
3893    <date year='2010' month='March' />
3894  </front>
3895  <seriesInfo name='RFC' value='5789' />
3896</reference>
3897
3898<reference anchor="RFC5987">
3899        <front>
3900    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3901    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3902      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3903      <address>
3904        <postal>
3905          <street>Hafenweg 16</street>
3906          <city>Muenster</city><region>NW</region><code>48155</code>
3907          <country>Germany</country>
3908        </postal>
3909        <email>julian.reschke@greenbytes.de</email>     
3910        <uri>http://greenbytes.de/tech/webdav/</uri>   
3911      </address>
3912    </author>
3913    <date month="August" year="2010"/>
3914  </front>
3915  <seriesInfo name="RFC" value="5987"/>
3916</reference>
3917
3918<reference anchor="RFC6151">
3919  <front>
3920    <title>Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms</title>
3921    <author initials="S." surname="Turner" fullname="S. Turner"/>
3922    <author initials="L." surname="Chen" fullname="L. Chen"/>
3923    <date year="2011" month="March" />
3924  </front>
3925  <seriesInfo name="RFC" value="6151" />
3926</reference>
3927
3928<reference anchor="RFC6266">
3929  <front>
3930    <title abbrev="Content-Disposition in HTTP">Use of the Content-Disposition Header Field
3931    in the Hypertext Transfer Protocol (HTTP)</title>
3932    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3933      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3934      <address>
3935        <email>julian.reschke@greenbytes.de</email>
3936      </address>
3937    </author>
3938    <date month="June" year="2011"/>
3939  </front>
3940  <seriesInfo name='RFC' value='6266' />
3941</reference>
3942
3943<reference anchor="draft-reschke-http-status-308">
3944        <front>
3945    <title abbrev="HTTP Status Code 308">The Hypertext Transfer Protocol (HTTP) Status Code 308 (Permanent Redirect)</title>
3946    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3947      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3948      <address>
3949        <email>julian.reschke@greenbytes.de</email>     
3950      </address>
3951    </author>
3952    <date month="March" year="2012"/>
3953  </front>
3954  <seriesInfo name="Internet-Draft" value="draft-reschke-http-status-308-07"/>
3955</reference>
3956
3957</references>
3958
3959<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3960<t>
3961  Clarify definition of POST.
3962  (<xref target="POST"/>)
3963</t>
3964<t>
3965  Remove requirement to handle all Content-* header fields; ban use of
3966  Content-Range with PUT.
3967  (<xref target="PUT"/>)
3968</t>
3969<t>
3970  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3971  (<xref target="CONNECT"/>)
3972</t>
3973<t>
3974  This document takes over the Status Code Registry, previously defined
3975  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3976  (<xref target="status.code.registry"/>)
3977</t>
3978<t>
3979  Broadened the definition of 203 (Non-Authoritative Information) to include
3980  cases of payload transformations as well.
3981  (<xref target="status.203"/>)
3982</t>
3983<t>
3984  Status codes 301, 302, and 307: removed the normative requirements on both
3985  response payloads and user interaction.
3986  (<xref target="status.3xx"/>)
3987</t>
3988<t>
3989  Failed to consider that there are many other request methods that are safe
3990  to automatically redirect, and further that the user agent is able to make
3991  that determination based on the request method semantics.
3992  Furthermore, allow user agents to rewrite the method from POST to GET
3993  for status codes 301 and 302.
3994  (Sections <xref format="counter" target="status.301"/>,
3995  <xref format="counter" target="status.302"/> and
3996  <xref format="counter" target="status.307"/>)
3997</t>
3998<t>
3999  Deprecate 305 Use Proxy status code, because user agents did not implement it.
4000  It used to indicate that the target resource needs to be accessed through the
4001  proxy given by the Location field. The Location field gave the URI of the
4002  proxy. The recipient was expected to repeat this single request via the proxy.
4003  (<xref target="status.305"/>)
4004</t>
4005<t>
4006  Define status 426 (Upgrade Required) (this was incorporated from
4007  <xref target="RFC2817"/>).
4008  (<xref target="status.426"/>)
4009</t>
4010<t>
4011  Change ABNF productions for header fields to only define the field value.
4012  (<xref target="header.field.definitions"/>)
4013</t>
4014<t>
4015  Reclassify "Allow" as response header field, removing the option to
4016  specify it in a PUT request.
4017  Relax the server requirement on the contents of the Allow header field and
4018  remove requirement on clients to always trust the header field value.
4019  (<xref target="header.allow"/>)
4020</t>
4021<t>
4022  The ABNF for the Expect header field has been both fixed (allowing parameters
4023  for value-less expectations as well) and simplified (allowing trailing
4024  semicolons after "100-continue" when they were invalid before).
4025  (<xref target="header.expect"/>)
4026</t>
4027<t>
4028  Correct syntax of Location header field to allow URI references (including
4029  relative references and fragments), as referred symbol "absoluteURI" wasn't
4030  what was expected, and add some clarifications as to when use of fragments
4031  would not be appropriate.
4032  (<xref target="header.location"/>)
4033</t>
4034<t>
4035  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
4036  extension methods could have used it as well).
4037  (<xref target="header.max-forwards"/>)
4038</t>
4039<t>
4040  Allow Referer field value of "about:blank" as alternative to not specifying it.
4041  (<xref target="header.referer"/>)
4042</t>
4043<t>
4044  In the description of the Server header field, the Via field
4045  was described as a SHOULD. The requirement was and is stated
4046  correctly in the description of the Via header field in &header-via;.
4047  (<xref target="header.server"/>)
4048</t>
4049</section>
4050
4051<?BEGININC p2-semantics.abnf-appendix ?>
4052<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4053<figure>
4054<artwork type="abnf" name="p2-semantics.parsed-abnf">
4055<x:ref>Allow</x:ref> = [ ( "," / method ) *( OWS "," [ OWS method ] ) ]
4056
4057<x:ref>BWS</x:ref> = &lt;BWS, defined in [Part1], Section 3.2.1&gt;
4058
4059<x:ref>Date</x:ref> = HTTP-date
4060
4061<x:ref>Expect</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
4062
4063<x:ref>From</x:ref> = mailbox
4064
4065<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4066
4067<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4068
4069<x:ref>Location</x:ref> = URI-reference
4070
4071<x:ref>Max-Forwards</x:ref> = 1*DIGIT
4072
4073<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 3.2.1&gt;
4074
4075<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 3.2.1&gt;
4076<x:ref>Referer</x:ref> = absolute-URI / partial-URI
4077<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
4078
4079<x:ref>Server</x:ref> = product *( RWS ( product / comment ) )
4080
4081<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
4082<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
4083
4084<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
4085<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4086
4087<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2.4&gt;
4088
4089<x:ref>date1</x:ref> = day SP month SP year
4090<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4091<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4092<x:ref>day</x:ref> = 2DIGIT
4093<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4094 / %x54.75.65 ; Tue
4095 / %x57.65.64 ; Wed
4096 / %x54.68.75 ; Thu
4097 / %x46.72.69 ; Fri
4098 / %x53.61.74 ; Sat
4099 / %x53.75.6E ; Sun
4100<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4101 / %x54.75.65.73.64.61.79 ; Tuesday
4102 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4103 / %x54.68.75.72.73.64.61.79 ; Thursday
4104 / %x46.72.69.64.61.79 ; Friday
4105 / %x53.61.74.75.72.64.61.79 ; Saturday
4106 / %x53.75.6E.64.61.79 ; Sunday
4107<x:ref>delta-seconds</x:ref> = 1*DIGIT
4108
4109<x:ref>expect-name</x:ref> = token
4110<x:ref>expect-param</x:ref> = expect-name [ BWS "=" BWS expect-value ]
4111<x:ref>expect-value</x:ref> = token / quoted-string
4112<x:ref>expectation</x:ref> = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
4113 OWS expect-param ] )
4114
4115<x:ref>hour</x:ref> = 2DIGIT
4116
4117<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
4118<x:ref>method</x:ref> = token
4119<x:ref>minute</x:ref> = 2DIGIT
4120<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4121 / %x46.65.62 ; Feb
4122 / %x4D.61.72 ; Mar
4123 / %x41.70.72 ; Apr
4124 / %x4D.61.79 ; May
4125 / %x4A.75.6E ; Jun
4126 / %x4A.75.6C ; Jul
4127 / %x41.75.67 ; Aug
4128 / %x53.65.70 ; Sep
4129 / %x4F.63.74 ; Oct
4130 / %x4E.6F.76 ; Nov
4131 / %x44.65.63 ; Dec
4132
4133<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4134<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 3.2.4&gt;
4135
4136<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
4137<x:ref>product</x:ref> = token [ "/" product-version ]
4138<x:ref>product-version</x:ref> = token
4139
4140<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.4&gt;
4141
4142<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4143<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4144
4145<x:ref>second</x:ref> = 2DIGIT
4146
4147<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4148<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.4&gt;
4149
4150<x:ref>year</x:ref> = 4DIGIT
4151</artwork>
4152</figure>
4153<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4154; Allow defined but not used
4155; Date defined but not used
4156; Expect defined but not used
4157; From defined but not used
4158; Location defined but not used
4159; Max-Forwards defined but not used
4160; Referer defined but not used
4161; Retry-After defined but not used
4162; Server defined but not used
4163; User-Agent defined but not used
4164; obs-text defined but not used
4165</artwork></figure></section>
4166<?ENDINC p2-semantics.abnf-appendix ?>
4167
4168<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4169
4170<section title="Since RFC 2616">
4171<t>
4172  Extracted relevant partitions from <xref target="RFC2616"/>.
4173</t>
4174</section>
4175
4176<section title="Since draft-ietf-httpbis-p2-semantics-00">
4177<t>
4178  Closed issues:
4179  <list style="symbols"> 
4180    <t>
4181      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
4182      "Via is a MUST"
4183      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
4184    </t>
4185    <t>
4186      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
4187      "Fragments allowed in Location"
4188      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
4189    </t>
4190    <t>
4191      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4192      "Safe Methods vs Redirection"
4193      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
4194    </t>
4195    <t>
4196      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
4197      "Revise description of the POST method"
4198      (<eref target="http://purl.org/NET/http-errata#post"/>)
4199    </t>
4200    <t>
4201      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4202      "Normative and Informative references"
4203    </t>
4204    <t>
4205      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4206      "RFC2606 Compliance"
4207    </t>
4208    <t>
4209      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4210      "Informative references"
4211    </t>
4212    <t>
4213      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
4214      "Redundant cross-references"
4215    </t>
4216  </list>
4217</t>
4218<t>
4219  Other changes:
4220  <list style="symbols"> 
4221    <t>
4222      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
4223    </t>
4224  </list>
4225</t>
4226</section>
4227
4228<section title="Since draft-ietf-httpbis-p2-semantics-01">
4229<t>
4230  Closed issues:
4231  <list style="symbols"> 
4232    <t>
4233      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
4234      "PUT side effects"
4235    </t>
4236    <t>
4237      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
4238      "Duplicate Host header requirements"
4239    </t>
4240  </list>
4241</t>
4242<t>
4243  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4244  <list style="symbols"> 
4245    <t>
4246      Move "Product Tokens" section (back) into Part 1, as "token" is used
4247      in the definition of the Upgrade header field.
4248    </t>
4249    <t>
4250      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4251    </t>
4252    <t>
4253      Copy definition of delta-seconds from Part6 instead of referencing it.
4254    </t>
4255  </list>
4256</t>
4257</section>
4258
4259<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
4260<t>
4261  Closed issues:
4262  <list style="symbols"> 
4263    <t>
4264      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
4265      "Requiring Allow in 405 responses"
4266    </t>
4267    <t>
4268      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
4269      "Status Code Registry"
4270    </t>
4271    <t>
4272      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
4273      "Redirection vs. Location"
4274    </t>
4275    <t>
4276      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
4277      "Cacheability of 303 response"
4278    </t>
4279    <t>
4280      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
4281      "305 Use Proxy"
4282    </t>
4283    <t>
4284      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
4285      "Classification for Allow header"
4286    </t>
4287    <t>
4288      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4289      "PUT - 'store under' vs 'store at'"
4290    </t>
4291  </list>
4292</t>
4293<t>
4294  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4295  <list style="symbols"> 
4296    <t>
4297      Reference RFC 3984, and update header field registrations for headers defined
4298      in this document.
4299    </t>
4300  </list>
4301</t>
4302<t>
4303  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4304  <list style="symbols"> 
4305    <t>
4306      Replace string literals when the string really is case-sensitive (method).
4307    </t>
4308  </list>
4309</t>
4310</section>
4311
4312<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
4313<t>
4314  Closed issues:
4315  <list style="symbols"> 
4316    <t>
4317      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
4318      "OPTIONS request bodies"
4319    </t>
4320    <t>
4321      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
4322      "Description of CONNECT should refer to RFC2817"
4323    </t>
4324    <t>
4325      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
4326      "Location Content-Location reference request/response mixup"
4327    </t>
4328  </list>
4329</t>
4330<t>
4331  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
4332  <list style="symbols"> 
4333    <t>
4334      Added initial proposal for registration process, plus initial
4335      content (non-HTTP/1.1 methods to be added by a separate specification).
4336    </t>
4337  </list>
4338</t>
4339</section>
4340
4341<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
4342<t>
4343  Closed issues:
4344  <list style="symbols"> 
4345    <t>
4346      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4347      "Content-*"
4348    </t>
4349    <t>
4350      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4351      "RFC 2822 is updated by RFC 5322"
4352    </t>
4353  </list>
4354</t>
4355<t>
4356  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4357  <list style="symbols"> 
4358    <t>
4359      Use "/" instead of "|" for alternatives.
4360    </t>
4361    <t>
4362      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4363      whitespace ("OWS") and required whitespace ("RWS").
4364    </t>
4365    <t>
4366      Rewrite ABNFs to spell out whitespace rules, factor out
4367      header field value format definitions.
4368    </t>
4369  </list>
4370</t>
4371</section>
4372
4373<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
4374<t>
4375  Closed issues:
4376  <list style="symbols"> 
4377    <t>
4378      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4379      "reason-phrase BNF"
4380    </t>
4381  </list>
4382</t>
4383<t>
4384  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4385  <list style="symbols"> 
4386    <t>
4387      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4388    </t>
4389  </list>
4390</t>
4391</section>
4392
4393<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4394<t>
4395  Closed issues:
4396  <list style="symbols"> 
4397    <t>
4398      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4399      "Clarify when Referer is sent"
4400    </t>
4401    <t>
4402      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4403      "status codes vs methods"
4404    </t>
4405    <t>
4406      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4407      "Do not require "updates" relation for specs that register status codes or method names"
4408    </t>
4409  </list>
4410</t>
4411</section>
4412
4413<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4414<t>
4415  Closed issues:
4416  <list style="symbols"> 
4417    <t>
4418      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4419      "Idempotency"
4420    </t>
4421    <t>
4422      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4423      "TRACE security considerations"
4424    </t>
4425    <t>
4426      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4427      "Clarify rules for determining what entities a response carries"
4428    </t>
4429    <t>
4430      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4431      "update note citing RFC 1945 and 2068"
4432    </t>
4433    <t>
4434      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4435      "update note about redirect limit"
4436    </t>
4437    <t>
4438      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4439      "Location header ABNF should use 'URI'"
4440    </t>
4441    <t>
4442      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4443      "fragments in Location vs status 303"
4444    </t>
4445    <t>
4446      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4447      "move IANA registrations for optional status codes"
4448    </t>
4449  </list>
4450</t>
4451<t>
4452  Partly resolved issues:
4453  <list style="symbols"> 
4454    <t>
4455      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4456      "Are OPTIONS and TRACE safe?"
4457    </t>
4458  </list>
4459</t>
4460</section>
4461
4462<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4463<t>
4464  Closed issues:
4465  <list style="symbols"> 
4466    <t>
4467      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4468      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4469      status codes when fixing this previously)
4470    </t>
4471  </list>
4472</t>
4473</section>
4474
4475<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4476<t>
4477  Closed issues:
4478  <list style="symbols"> 
4479    <t>
4480      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4481      "Fragment combination / precedence during redirects"
4482    </t>
4483  </list>
4484</t>
4485<t>
4486  Partly resolved issues:
4487  <list style="symbols"> 
4488    <t>
4489      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4490      "Location header payload handling"
4491    </t>
4492    <t>
4493      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4494      "Term for the requested resource's URI"
4495    </t>
4496  </list>
4497</t>
4498</section>
4499
4500<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4501<t>
4502  Closed issues:
4503  <list style="symbols"> 
4504    <t>
4505      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4506      "Clarify 'Requested Variant'"
4507    </t>
4508    <t>
4509      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4510      "Clarify entity / representation / variant terminology"
4511    </t>
4512    <t>
4513      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4514      "Methods and Caching"
4515    </t>
4516    <t>
4517      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4518      "OPTIONS vs Max-Forwards"
4519    </t>
4520    <t>
4521      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4522      "Status codes and caching"
4523    </t>
4524    <t>
4525      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4526      "consider removing the 'changes from 2068' sections"
4527    </t>
4528  </list>
4529</t>
4530</section>
4531
4532<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4533<t>
4534  Closed issues:
4535  <list style="symbols"> 
4536    <t>
4537      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4538      "Considerations for new status codes"
4539    </t>
4540    <t>
4541      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4542      "Considerations for new methods"
4543    </t>
4544    <t>
4545      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4546      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4547    </t>
4548  </list>
4549</t>
4550</section>
4551
4552<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4553<t>
4554  Closed issues:
4555  <list style="symbols"> 
4556    <t>
4557      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4558      "Fragment combination / precedence during redirects" (added warning
4559      about having a fragid on the redirect may cause inconvenience in
4560      some cases)
4561    </t>
4562    <t>
4563      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4564      "Content-* vs. PUT"
4565    </t>
4566    <t>
4567      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4568      "205 Bodies"
4569    </t>
4570    <t>
4571      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4572      "Understanding Content-* on non-PUT requests"
4573    </t>
4574    <t>
4575      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4576      "Content-*"
4577    </t>
4578    <t>
4579      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4580      "Header type defaulting"
4581    </t>
4582    <t>
4583      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4584      "PUT - 'store under' vs 'store at'"
4585    </t>
4586    <t>
4587      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4588      "duplicate ABNF for reason-phrase"
4589    </t>
4590    <t>
4591      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4592      "Note special status of Content-* prefix in header registration procedures"
4593    </t>
4594    <t>
4595      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4596      "Max-Forwards vs extension methods"
4597    </t>
4598    <t>
4599      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4600      "What is the value space of HTTP status codes?" (actually fixed in
4601      draft-ietf-httpbis-p2-semantics-11)
4602    </t>
4603    <t>
4604      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4605      "Header Classification"
4606    </t>
4607    <t>
4608      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4609      "PUT side effect: invalidation or just stale?"
4610    </t>
4611    <t>
4612      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4613      "proxies not supporting certain methods"
4614    </t>
4615    <t>
4616      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4617      "Migrate CONNECT from RFC2817 to p2"
4618    </t>
4619    <t>
4620      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4621      "Migrate Upgrade details from RFC2817"
4622    </t>
4623    <t>
4624      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4625      "clarify PUT semantics'"
4626    </t>
4627    <t>
4628      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4629      "duplicate ABNF for 'Method'"
4630    </t>
4631    <t>
4632      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4633      "untangle ABNFs for header fields"
4634    </t>
4635  </list>
4636</t>
4637</section>
4638
4639<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4640<t>
4641  Closed issues:
4642  <list style="symbols"> 
4643    <t>
4644      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4645      "untangle ABNFs for header fields"
4646    </t>
4647    <t>
4648      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4649      "message body in CONNECT request"
4650    </t>
4651  </list>
4652</t>
4653</section>
4654
4655<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4656<t>
4657  Closed issues:
4658  <list style="symbols"> 
4659    <t>
4660      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4661      "Clarify status code for rate limiting"
4662    </t>
4663    <t>
4664      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4665      "clarify 403 forbidden"
4666    </t>
4667    <t>
4668      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4669      "Clarify 203 Non-Authoritative Information"
4670    </t>
4671    <t>
4672      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4673      "update default reason phrase for 413"
4674    </t>
4675  </list>
4676</t>
4677</section>
4678
4679<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4680<t>
4681  Closed issues:
4682  <list style="symbols"> 
4683    <t>
4684      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4685      "Strength of requirements on Accept re: 406"
4686    </t>
4687    <t>
4688      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4689      "400 response isn't generic"
4690    </t>
4691  </list>
4692</t>
4693</section>
4694
4695<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4696<t>
4697  Closed issues:
4698  <list style="symbols"> 
4699    <t>
4700      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4701      "Redirects and non-GET methods"
4702    </t>
4703    <t>
4704      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
4705      "Document HTTP's error-handling philosophy"
4706    </t>
4707    <t>
4708      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4709      "Considerations for new headers"
4710    </t>
4711    <t>
4712      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4713      "clarify 303 redirect on HEAD"
4714    </t>
4715  </list>
4716</t>
4717</section>
4718
4719<section title="Since draft-ietf-httpbis-p2-semantics-17" anchor="changes.since.17">
4720<t>
4721  Closed issues:
4722  <list style="symbols"> 
4723    <t>
4724      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4725      "Location header payload handling"
4726    </t>
4727    <t>
4728      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4729      "Clarify status code for rate limiting" (change backed out because
4730      a new status code is being defined for this purpose)
4731    </t>
4732    <t>
4733      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4734      "should there be a permanent variant of 307"
4735    </t>
4736    <t>
4737      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/325"/>:
4738      "When are Location's semantics triggered?"
4739    </t>
4740    <t>
4741      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/327"/>:
4742      "'expect' grammar missing OWS"
4743    </t>
4744    <t>
4745      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/329"/>:
4746      "header field considerations: quoted-string vs use of double quotes"
4747    </t>
4748  </list>
4749</t>
4750</section>
4751
4752<section title="Since draft-ietf-httpbis-p2-semantics-18" anchor="changes.since.18">
4753<t>
4754  Closed issues:
4755  <list style="symbols"> 
4756    <t>
4757      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/227"/>:
4758      "Combining HEAD responses"
4759    </t>
4760    <t>
4761      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/238"/>:
4762      "Requirements for user intervention during redirects"
4763    </t>
4764    <t>
4765      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
4766      "message-body in CONNECT response"
4767    </t>
4768    <t>
4769      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/295"/>:
4770      "Applying original fragment to 'plain' redirected URI"
4771    </t>
4772    <t>
4773      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
4774      "Misplaced text on connection handling in p2"
4775    </t>
4776    <t>
4777      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/331"/>:
4778      "clarify that 201 doesn't require Location header fields"
4779    </t>
4780    <t>
4781      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/332"/>:
4782      "relax requirements on hypertext in 3/4/5xx error responses"
4783    </t>
4784    <t>
4785      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/333"/>:
4786      "example for 426 response should have a payload"
4787    </t>
4788    <t>
4789      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/336"/>:
4790      "drop indirection entries for status codes"
4791    </t>
4792  </list>
4793</t>
4794</section>
4795
4796<section title="Since draft-ietf-httpbis-p2-semantics-19" anchor="changes.since.19">
4797<t>
4798  Closed issues:
4799  <list style="symbols"> 
4800    <t>
4801      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4802      "should there be a permanent variant of 307"
4803    </t>
4804  </list>
4805</t>
4806</section>
4807
4808</section>
4809
4810</back>
4811</rfc>
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