source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1742

Last change on this file since 1742 was 1742, checked in by julian.reschke@…, 7 years ago

Move section about introduction of Transfer-Encoding into P1.

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 247.4 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "July">
16  <!ENTITY ID-YEAR "2012">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY Note "<x:h xmlns:x='http://purl.org/net/xml2rfc/ext'>Note:</x:h>">
19  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#response.cacheability' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY payload                "<xref target='Part2' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY media-types            "<xref target='Part2' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY content-codings        "<xref target='Part2' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY content.negotiation    "<xref target='Part2' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY diff-mime              "<xref target='Part2' x:rel='#differences.between.http.and.mime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY representation         "<xref target='Part2' x:rel='#representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-content-encoding    "<xref target='Part2' x:rel='#header.content-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-content-range   "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-content-type    "<xref target='Part2' x:rel='#header.content-type' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY header-date            "<xref target='Part2' x:rel='#header.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY header-expires         "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY header-mime-version    "<xref target='Part2' x:rel='#mime-version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY methods                "<xref target='Part2' x:rel='#methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY OPTIONS                "<xref target='Part2' x:rel='#OPTIONS' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY status-304             "<xref target='Part4' x:rel='#status.304' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY cons-new-header-fields "<xref target='Part2' x:rel='#considerations.for.creating.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52]>
53<?rfc toc="yes" ?>
54<?rfc symrefs="yes" ?>
55<?rfc sortrefs="yes" ?>
56<?rfc compact="yes"?>
57<?rfc subcompact="no" ?>
58<?rfc linkmailto="no" ?>
59<?rfc editing="no" ?>
60<?rfc comments="yes"?>
61<?rfc inline="yes"?>
62<?rfc rfcedstyle="yes"?>
63<?rfc-ext allow-markup-in-artwork="yes" ?>
64<?rfc-ext include-references-in-index="yes" ?>
65<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="proposed"
66     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
67     xmlns:x='http://purl.org/net/xml2rfc/ext'>
68<x:link rel="next" basename="p2-semantics"/>
69<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
70<front>
71
72  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
73
74  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
75    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
76    <address>
77      <postal>
78        <street>345 Park Ave</street>
79        <city>San Jose</city>
80        <region>CA</region>
81        <code>95110</code>
82        <country>USA</country>
83      </postal>
84      <email>fielding@gbiv.com</email>
85      <uri>http://roy.gbiv.com/</uri>
86    </address>
87  </author>
88
89  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
90    <organization abbrev="W3C">World Wide Web Consortium</organization>
91    <address>
92      <postal>
93        <street>W3C / ERCIM</street>
94        <street>2004, rte des Lucioles</street>
95        <city>Sophia-Antipolis</city>
96        <region>AM</region>
97        <code>06902</code>
98        <country>France</country>
99      </postal>
100      <email>ylafon@w3.org</email>
101      <uri>http://www.raubacapeu.net/people/yves/</uri>
102    </address>
103  </author>
104
105  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
106    <organization abbrev="greenbytes">greenbytes GmbH</organization>
107    <address>
108      <postal>
109        <street>Hafenweg 16</street>
110        <city>Muenster</city><region>NW</region><code>48155</code>
111        <country>Germany</country>
112      </postal>
113      <email>julian.reschke@greenbytes.de</email>
114      <uri>http://greenbytes.de/tech/webdav/</uri>
115    </address>
116  </author>
117
118  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
119  <workgroup>HTTPbis Working Group</workgroup>
120
121<abstract>
122<t>
123   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
124   distributed, collaborative, hypertext information systems. HTTP has been in
125   use by the World Wide Web global information initiative since 1990. This
126   document is Part 1 of the seven-part specification that defines the protocol
127   referred to as "HTTP/1.1" and, taken together, obsoletes
128   <xref target="RFC2616" x:fmt="none">RFC 2616</xref> and moves it to historic
129   status, along with its predecessor <xref target="RFC2068" x:fmt="none">RFC
130   2068</xref>.
131</t>
132<t>
133   Part 1 provides an overview of HTTP and its associated terminology, defines
134   the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
135   the generic message syntax and parsing requirements for HTTP message frames,
136   and describes general security concerns for implementations.
137</t>
138<t>
139   This part also obsoletes RFCs <xref target="RFC2145" x:fmt="none">2145</xref>
140   (on HTTP version numbers) and <xref target="RFC2817" x:fmt="none">2817</xref>
141   (on using CONNECT for TLS upgrades) and moves them to historic status.
142</t>
143</abstract>
144
145<note title="Editorial Note (To be removed by RFC Editor)">
146  <t>
147    Discussion of this draft ought to take place on the HTTPBIS working group
148    mailing list (ietf-http-wg@w3.org), which is archived at
149    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
150  </t>
151  <t>
152    The current issues list is at
153    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
154    documents (including fancy diffs) can be found at
155    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
156  </t>
157  <t>
158    The changes in this draft are summarized in <xref target="changes.since.19"/>.
159  </t>
160</note>
161</front>
162<middle>
163<section title="Introduction" anchor="introduction">
164<t>
165   The Hypertext Transfer Protocol (HTTP) is an application-level
166   request/response protocol that uses extensible semantics and MIME-like
167   message payloads for flexible interaction with network-based hypertext
168   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
169   standard <xref target="RFC3986"/> to indicate the target resource
170   (<xref target="target-resource"/>) and relationships between resources.
171   Messages are passed in a format similar to that used by Internet mail
172   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
173   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
174   between HTTP and MIME messages).
175</t>
176<t>
177   HTTP is a generic interface protocol for information systems. It is
178   designed to hide the details of how a service is implemented by presenting
179   a uniform interface to clients that is independent of the types of
180   resources provided. Likewise, servers do not need to be aware of each
181   client's purpose: an HTTP request can be considered in isolation rather
182   than being associated with a specific type of client or a predetermined
183   sequence of application steps. The result is a protocol that can be used
184   effectively in many different contexts and for which implementations can
185   evolve independently over time.
186</t>
187<t>
188   HTTP is also designed for use as an intermediation protocol for translating
189   communication to and from non-HTTP information systems.
190   HTTP proxies and gateways can provide access to alternative information
191   services by translating their diverse protocols into a hypertext
192   format that can be viewed and manipulated by clients in the same way
193   as HTTP services.
194</t>
195<t>
196   One consequence of HTTP flexibility is that the protocol cannot be
197   defined in terms of what occurs behind the interface. Instead, we
198   are limited to defining the syntax of communication, the intent
199   of received communication, and the expected behavior of recipients.
200   If the communication is considered in isolation, then successful
201   actions ought to be reflected in corresponding changes to the
202   observable interface provided by servers. However, since multiple
203   clients might act in parallel and perhaps at cross-purposes, we
204   cannot require that such changes be observable beyond the scope
205   of a single response.
206</t>
207<t>
208   This document is Part 1 of the seven-part specification of HTTP,
209   defining the protocol referred to as "HTTP/1.1", obsoleting
210   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
211   Part 1 describes the architectural elements that are used or
212   referred to in HTTP, defines the "http" and "https" URI schemes,
213   describes overall network operation and connection management,
214   and defines HTTP message framing and forwarding requirements.
215   Our goal is to define all of the mechanisms necessary for HTTP message
216   handling that are independent of message semantics, thereby defining the
217   complete set of requirements for message parsers and
218   message-forwarding intermediaries.
219</t>
220
221<section title="Requirement Notation" anchor="intro.requirements">
222<t>
223   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
224   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
225   document are to be interpreted as described in <xref target="RFC2119"/>.
226</t>
227</section>
228
229<section title="Syntax Notation" anchor="notation">
230<iref primary="true" item="Grammar" subitem="ALPHA"/>
231<iref primary="true" item="Grammar" subitem="CR"/>
232<iref primary="true" item="Grammar" subitem="CRLF"/>
233<iref primary="true" item="Grammar" subitem="CTL"/>
234<iref primary="true" item="Grammar" subitem="DIGIT"/>
235<iref primary="true" item="Grammar" subitem="DQUOTE"/>
236<iref primary="true" item="Grammar" subitem="HEXDIG"/>
237<iref primary="true" item="Grammar" subitem="HTAB"/>
238<iref primary="true" item="Grammar" subitem="LF"/>
239<iref primary="true" item="Grammar" subitem="OCTET"/>
240<iref primary="true" item="Grammar" subitem="SP"/>
241<iref primary="true" item="Grammar" subitem="VCHAR"/>
242<t>
243   This specification uses the Augmented Backus-Naur Form (ABNF) notation
244   of <xref target="RFC5234"/> with the list rule extension defined in
245   <xref target="abnf.extension"/><xref target="collected.abnf"/> shows
246   the collected ABNF with the list rule expanded.
247</t>
248<t anchor="core.rules">
249  <x:anchor-alias value="ALPHA"/>
250  <x:anchor-alias value="CTL"/>
251  <x:anchor-alias value="CR"/>
252  <x:anchor-alias value="CRLF"/>
253  <x:anchor-alias value="DIGIT"/>
254  <x:anchor-alias value="DQUOTE"/>
255  <x:anchor-alias value="HEXDIG"/>
256  <x:anchor-alias value="HTAB"/>
257  <x:anchor-alias value="LF"/>
258  <x:anchor-alias value="OCTET"/>
259  <x:anchor-alias value="SP"/>
260  <x:anchor-alias value="VCHAR"/>
261   The following core rules are included by
262   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
263   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
264   DIGIT (decimal 0-9), DQUOTE (double quote),
265   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
266   OCTET (any 8-bit sequence of data), SP (space), and
267   VCHAR (any visible <xref target="USASCII"/> character).
268</t>
269<t>
270   As a convention, ABNF rule names prefixed with "obs-" denote
271   "obsolete" grammar rules that appear for historical reasons.
272</t>
273</section>
274</section>
275
276<section title="Architecture" anchor="architecture">
277<t>
278   HTTP was created for the World Wide Web architecture
279   and has evolved over time to support the scalability needs of a worldwide
280   hypertext system. Much of that architecture is reflected in the terminology
281   and syntax productions used to define HTTP.
282</t>
283
284<section title="Client/Server Messaging" anchor="operation">
285<iref primary="true" item="client"/>
286<iref primary="true" item="server"/>
287<iref primary="true" item="connection"/>
288<t>
289   HTTP is a stateless request/response protocol that operates by exchanging
290   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
291   transport or session-layer
292   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
293   program that establishes a connection to a server for the purpose of
294   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
295   program that accepts connections in order to service HTTP requests by
296   sending HTTP responses.
297</t>
298<iref primary="true" item="user agent"/>
299<iref primary="true" item="origin server"/>
300<iref primary="true" item="browser"/>
301<iref primary="true" item="spider"/>
302<iref primary="true" item="sender"/>
303<iref primary="true" item="recipient"/>
304<t>
305   Note that the terms client and server refer only to the roles that
306   these programs perform for a particular connection.  The same program
307   might act as a client on some connections and a server on others.  We use
308   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
309   such as a WWW browser, editor, or spider (web-traversing robot), and
310   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
311   authoritative responses to a request.  For general requirements, we use
312   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
313   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
314   message.
315</t>
316<x:note>
317  <t>
318    &Note; The term 'user agent' covers both those situations where
319    there is a user (human) interacting with the software agent (and for which
320    user interface or interactive suggestions might be made, e.g., warning the
321    user or given the user an option in the case of security or privacy
322    options) and also those where the software agent can act autonomously.
323  </t>
324</x:note>
325<t>
326   Most HTTP communication consists of a retrieval request (GET) for
327   a representation of some resource identified by a URI.  In the
328   simplest case, this might be accomplished via a single bidirectional
329   connection (===) between the user agent (UA) and the origin server (O).
330</t>
331<figure><artwork type="drawing">
332         request   &gt;
333    <x:highlight>UA</x:highlight> ======================================= <x:highlight>O</x:highlight>
334                                &lt;   response
335</artwork></figure>
336<iref primary="true" item="message"/>
337<iref primary="true" item="request"/>
338<iref primary="true" item="response"/>
339<t>
340   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
341   message, beginning with a request-line that includes a method, URI, and
342   protocol version (<xref target="request.line"/>),
343   followed by MIME-like header fields containing
344   request modifiers, client information, and representation metadata
345   (<xref target="header.fields"/>),
346   an empty line to indicate the end of the header section, and finally
347   a message body containing the payload body (if any,
348   <xref target="message.body"/>).
349</t>
350<t>
351   A server responds to the client's request by sending one or more HTTP
352   <x:dfn>response</x:dfn>
353   messages, each beginning with a status line that
354   includes the protocol version, a success or error code, and textual
355   reason phrase (<xref target="status.line"/>),
356   possibly followed by MIME-like header fields containing server
357   information, resource metadata, and representation metadata
358   (<xref target="header.fields"/>),
359   an empty line to indicate the end of the header section, and finally
360   a message body containing the payload body (if any,
361   <xref target="message.body"/>).
362</t>
363<t>
364   The following example illustrates a typical message exchange for a
365   GET request on the URI "http://www.example.com/hello.txt":
366</t>
367<figure><preamble>
368client request:
369</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
370GET /hello.txt HTTP/1.1
371User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
372Host: www.example.com
373Accept: */*
374
375</artwork></figure>
376<figure><preamble>
377server response:
378</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
379HTTP/1.1 200 OK
380Date: Mon, 27 Jul 2009 12:28:53 GMT
381Server: Apache
382Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
383ETag: "34aa387-d-1568eb00"
384Accept-Ranges: bytes
385Content-Length: <x:length-of target="exbody"/>
386Vary: Accept-Encoding
387Content-Type: text/plain
388
389<x:span anchor="exbody">Hello World!
390</x:span></artwork></figure>
391</section>
392
393<section title="Connections and Transport Independence" anchor="transport-independence">
394<t>
395   HTTP messaging is independent of the underlying transport or
396   session-layer connection protocol(s).  HTTP only presumes a reliable
397   transport with in-order delivery of requests and the corresponding
398   in-order delivery of responses.  The mapping of HTTP request and
399   response structures onto the data units of the underlying transport
400   protocol is outside the scope of this specification.
401</t>
402<t>
403   The specific connection protocols to be used for an interaction
404   are determined by client configuration and the target URI
405   (<xref target="target-resource"/>).
406   For example, the "http" URI scheme
407   (<xref target="http.uri"/>) indicates a default connection of TCP
408   over IP, with a default TCP port of 80, but the client might be
409   configured to use a proxy via some other connection port or protocol
410   instead of using the defaults.
411</t>
412<t>
413   A connection might be used for multiple HTTP request/response exchanges,
414   as defined in <xref target="persistent.connections"/>.
415</t>
416</section>
417
418<section title="Intermediaries" anchor="intermediaries">
419<iref primary="true" item="intermediary"/>
420<t>
421   HTTP enables the use of intermediaries to satisfy requests through
422   a chain of connections.  There are three common forms of HTTP
423   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
424   a single intermediary might act as an origin server, proxy, gateway,
425   or tunnel, switching behavior based on the nature of each request.
426</t>
427<figure><artwork type="drawing">
428         &gt;             &gt;             &gt;             &gt;
429    <x:highlight>UA</x:highlight> =========== <x:highlight>A</x:highlight> =========== <x:highlight>B</x:highlight> =========== <x:highlight>C</x:highlight> =========== <x:highlight>O</x:highlight>
430               &lt;             &lt;             &lt;             &lt;
431</artwork></figure>
432<t>
433   The figure above shows three intermediaries (A, B, and C) between the
434   user agent and origin server. A request or response message that
435   travels the whole chain will pass through four separate connections.
436   Some HTTP communication options
437   might apply only to the connection with the nearest, non-tunnel
438   neighbor, only to the end-points of the chain, or to all connections
439   along the chain. Although the diagram is linear, each participant might
440   be engaged in multiple, simultaneous communications. For example, B
441   might be receiving requests from many clients other than A, and/or
442   forwarding requests to servers other than C, at the same time that it
443   is handling A's request.
444</t>
445<t>
446<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
447<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
448   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
449   to describe various requirements in relation to the directional flow of a
450   message: all messages flow from upstream to downstream.
451   Likewise, we use the terms inbound and outbound to refer to
452   directions in relation to the request path:
453   "<x:dfn>inbound</x:dfn>" means toward the origin server and
454   "<x:dfn>outbound</x:dfn>" means toward the user agent.
455</t>
456<t><iref primary="true" item="proxy"/>
457   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
458   client, usually via local configuration rules, to receive requests
459   for some type(s) of absolute URI and attempt to satisfy those
460   requests via translation through the HTTP interface.  Some translations
461   are minimal, such as for proxy requests for "http" URIs, whereas
462   other requests might require translation to and from entirely different
463   application-layer protocols. Proxies are often used to group an
464   organization's HTTP requests through a common intermediary for the
465   sake of security, annotation services, or shared caching.
466</t>
467<t>
468<iref primary="true" item="transforming proxy"/>
469<iref primary="true" item="non-transforming proxy"/>
470   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
471   or configured to modify request or response messages in a semantically
472   meaningful way (i.e., modifications, beyond those required by normal
473   HTTP processing, that change the message in a way that would be
474   significant to the original sender or potentially significant to
475   downstream recipients).  For example, a transforming proxy might be
476   acting as a shared annotation server (modifying responses to include
477   references to a local annotation database), a malware filter, a
478   format transcoder, or an intranet-to-Internet privacy filter.  Such
479   transformations are presumed to be desired by the client (or client
480   organization) that selected the proxy and are beyond the scope of
481   this specification.  However, when a proxy is not intended to transform
482   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
483   requirements that preserve HTTP message semantics. See &status-203; and
484   &header-warning; for status and warning codes related to transformations.
485</t>
486<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
487<iref primary="true" item="accelerator"/>
488   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
489   is a receiving agent that acts
490   as a layer above some other server(s) and translates the received
491   requests to the underlying server's protocol.  Gateways are often
492   used to encapsulate legacy or untrusted information services, to
493   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
494   enable partitioning or load-balancing of HTTP services across
495   multiple machines.
496</t>
497<t>
498   A gateway behaves as an origin server on its outbound connection and
499   as a user agent on its inbound connection.
500   All HTTP requirements applicable to an origin server
501   also apply to the outbound communication of a gateway.
502   A gateway communicates with inbound servers using any protocol that
503   it desires, including private extensions to HTTP that are outside
504   the scope of this specification.  However, an HTTP-to-HTTP gateway
505   that wishes to interoperate with third-party HTTP servers &MUST;
506   conform to HTTP user agent requirements on the gateway's inbound
507   connection and &MUST; implement the <x:ref>Connection</x:ref>
508   (<xref target="header.connection"/>) and <x:ref>Via</x:ref>
509   (<xref target="header.via"/>) header fields for both connections.
510</t>
511<t><iref primary="true" item="tunnel"/>
512   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
513   without changing the messages. Once active, a tunnel is not
514   considered a party to the HTTP communication, though the tunnel might
515   have been initiated by an HTTP request. A tunnel ceases to exist when
516   both ends of the relayed connection are closed. Tunnels are used to
517   extend a virtual connection through an intermediary, such as when
518   transport-layer security is used to establish private communication
519   through a shared firewall proxy.
520</t>
521<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
522<iref primary="true" item="captive portal"/>
523   In addition, there might exist network intermediaries that are not
524   considered part of the HTTP communication but nevertheless act as
525   filters or redirecting agents (usually violating HTTP semantics,
526   causing security problems, and otherwise making a mess of things).
527   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
528   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
529   or "<x:dfn>captive portal</x:dfn>",
530   differs from an HTTP proxy because it has not been selected by the client.
531   Instead, the network intermediary redirects outgoing TCP port 80 packets
532   (and occasionally other common port traffic) to an internal HTTP server.
533   Interception proxies are commonly found on public network access points,
534   as a means of enforcing account subscription prior to allowing use of
535   non-local Internet services, and within corporate firewalls to enforce
536   network usage policies.
537   They are indistinguishable from a man-in-the-middle attack.
538</t>
539<t>
540   HTTP is defined as a stateless protocol, meaning that each request message
541   can be understood in isolation.  Many implementations depend on HTTP's
542   stateless design in order to reuse proxied connections or dynamically
543   load balance requests across multiple servers.  Hence, servers &MUST-NOT;
544   assume that two requests on the same connection are from the same user
545   agent unless the connection is secured and specific to that agent.
546   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
547   been known to violate this requirement, resulting in security and
548   interoperability problems.
549</t>
550</section>
551
552<section title="Caches" anchor="caches">
553<iref primary="true" item="cache"/>
554<t>
555   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
556   subsystem that controls its message storage, retrieval, and deletion.
557   A cache stores cacheable responses in order to reduce the response
558   time and network bandwidth consumption on future, equivalent
559   requests. Any client or server &MAY; employ a cache, though a cache
560   cannot be used by a server while it is acting as a tunnel.
561</t>
562<t>
563   The effect of a cache is that the request/response chain is shortened
564   if one of the participants along the chain has a cached response
565   applicable to that request. The following illustrates the resulting
566   chain if B has a cached copy of an earlier response from O (via C)
567   for a request which has not been cached by UA or A.
568</t>
569<figure><artwork type="drawing">
570            &gt;             &gt;
571       <x:highlight>UA</x:highlight> =========== <x:highlight>A</x:highlight> =========== <x:highlight>B</x:highlight> - - - - - - <x:highlight>C</x:highlight> - - - - - - <x:highlight>O</x:highlight>
572                  &lt;             &lt;
573</artwork></figure>
574<t><iref primary="true" item="cacheable"/>
575   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
576   the response message for use in answering subsequent requests.
577   Even when a response is cacheable, there might be additional
578   constraints placed by the client or by the origin server on when
579   that cached response can be used for a particular request. HTTP
580   requirements for cache behavior and cacheable responses are
581   defined in &caching-overview;
582</t>
583<t>
584   There are a wide variety of architectures and configurations
585   of caches and proxies deployed across the World Wide Web and
586   inside large organizations. These systems include national hierarchies
587   of proxy caches to save transoceanic bandwidth, systems that
588   broadcast or multicast cache entries, organizations that distribute
589   subsets of cached data via optical media, and so on.
590</t>
591</section>
592
593<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
594<t>
595   This specification targets conformance criteria according to the role of
596   a participant in HTTP communication.  Hence, HTTP requirements are placed
597   on senders, recipients, clients, servers, user agents, intermediaries,
598   origin servers, proxies, gateways, or caches, depending on what behavior
599   is being constrained by the requirement.
600</t>
601<t>
602   An implementation is considered conformant if it complies with all of the
603   requirements associated with the roles it partakes in HTTP.
604</t>
605<t>
606   Senders &MUST-NOT; generate protocol elements that do not match the grammar
607   defined by the ABNF rules for those protocol elements.
608</t>
609<t>
610   Unless noted otherwise, recipients &MUST; be able to parse all protocol
611   elements matching the ABNF rules defined for them and &MAY; attempt to recover a usable
612   protocol element from an invalid construct.  HTTP does not define
613   specific error handling mechanisms except when they have a direct impact
614   on security, since different applications of the protocol require
615   different error handling strategies.  For example, a Web browser might
616   wish to transparently recover from a response where the <x:ref>Location</x:ref>
617   header field doesn't parse according to the ABNF, whereas a systems control
618   client might consider any form of error recovery to be dangerous.
619</t>
620</section>
621
622<section title="Protocol Versioning" anchor="http.version">
623  <x:anchor-alias value="HTTP-version"/>
624  <x:anchor-alias value="HTTP-name"/>
625<t>
626   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
627   versions of the protocol. This specification defines version "1.1".
628   The protocol version as a whole indicates the sender's conformance
629   with the set of requirements laid out in that version's corresponding
630   specification of HTTP.
631</t>
632<t>
633   The version of an HTTP message is indicated by an HTTP-version field
634   in the first line of the message. HTTP-version is case-sensitive.
635</t>
636<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/>
637  <x:ref>HTTP-version</x:ref>  = <x:ref>HTTP-name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
638  <x:ref>HTTP-name</x:ref>     = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
639</artwork></figure>
640<t>
641   The HTTP version number consists of two decimal digits separated by a "."
642   (period or decimal point).  The first digit ("major version") indicates the
643   HTTP messaging syntax, whereas the second digit ("minor version") indicates
644   the highest minor version to which the sender is
645   conformant and able to understand for future communication.  The minor
646   version advertises the sender's communication capabilities even when the
647   sender is only using a backwards-compatible subset of the protocol,
648   thereby letting the recipient know that more advanced features can
649   be used in response (by servers) or in future requests (by clients).
650</t>
651<t>
652   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
653   <xref target="RFC1945"/> or a recipient whose version is unknown,
654   the HTTP/1.1 message is constructed such that it can be interpreted
655   as a valid HTTP/1.0 message if all of the newer features are ignored.
656   This specification places recipient-version requirements on some
657   new features so that a conformant sender will only use compatible
658   features until it has determined, through configuration or the
659   receipt of a message, that the recipient supports HTTP/1.1.
660</t>
661<t>
662   The interpretation of a header field does not change between minor
663   versions of the same major HTTP version, though the default
664   behavior of a recipient in the absence of such a field can change.
665   Unless specified otherwise, header fields defined in HTTP/1.1 are
666   defined for all versions of HTTP/1.x.  In particular, the <x:ref>Host</x:ref>
667   and <x:ref>Connection</x:ref> header fields ought to be implemented by all
668   HTTP/1.x implementations whether or not they advertise conformance with
669   HTTP/1.1.
670</t>
671<t>
672   New header fields can be defined such that, when they are
673   understood by a recipient, they might override or enhance the
674   interpretation of previously defined header fields.  When an
675   implementation receives an unrecognized header field, the recipient
676   &MUST; ignore that header field for local processing regardless of
677   the message's HTTP version.  An unrecognized header field received
678   by a proxy &MUST; be forwarded downstream unless the header field's
679   field-name is listed in the message's <x:ref>Connection</x:ref> header field
680   (see <xref target="header.connection"/>).
681   These requirements allow HTTP's functionality to be enhanced without
682   requiring prior update of deployed intermediaries.
683</t>
684<t>
685   Intermediaries that process HTTP messages (i.e., all intermediaries
686   other than those acting as tunnels) &MUST; send their own HTTP-version
687   in forwarded messages.  In other words, they &MUST-NOT; blindly
688   forward the first line of an HTTP message without ensuring that the
689   protocol version in that message matches a version to which that
690   intermediary is conformant for both the receiving and
691   sending of messages.  Forwarding an HTTP message without rewriting
692   the HTTP-version might result in communication errors when downstream
693   recipients use the message sender's version to determine what features
694   are safe to use for later communication with that sender.
695</t>
696<t>
697   An HTTP client &SHOULD; send a request version equal to the highest
698   version to which the client is conformant and
699   whose major version is no higher than the highest version supported
700   by the server, if this is known.  An HTTP client &MUST-NOT; send a
701   version to which it is not conformant.
702</t>
703<t>
704   An HTTP client &MAY; send a lower request version if it is known that
705   the server incorrectly implements the HTTP specification, but only
706   after the client has attempted at least one normal request and determined
707   from the response status or header fields (e.g., <x:ref>Server</x:ref>) that
708   the server improperly handles higher request versions.
709</t>
710<t>
711   An HTTP server &SHOULD; send a response version equal to the highest
712   version to which the server is conformant and
713   whose major version is less than or equal to the one received in the
714   request.  An HTTP server &MUST-NOT; send a version to which it is not
715   conformant.  A server &MAY; send a <x:ref>505 (HTTP Version Not
716   Supported)</x:ref> response if it cannot send a response using the
717   major version used in the client's request.
718</t>
719<t>
720   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
721   if it is known or suspected that the client incorrectly implements the
722   HTTP specification and is incapable of correctly processing later
723   version responses, such as when a client fails to parse the version
724   number correctly or when an intermediary is known to blindly forward
725   the HTTP-version even when it doesn't conform to the given minor
726   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
727   performed unless triggered by specific client attributes, such as when
728   one or more of the request header fields (e.g., <x:ref>User-Agent</x:ref>)
729   uniquely match the values sent by a client known to be in error.
730</t>
731<t>
732   The intention of HTTP's versioning design is that the major number
733   will only be incremented if an incompatible message syntax is
734   introduced, and that the minor number will only be incremented when
735   changes made to the protocol have the effect of adding to the message
736   semantics or implying additional capabilities of the sender.  However,
737   the minor version was not incremented for the changes introduced between
738   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
739   is specifically avoiding any such changes to the protocol.
740</t>
741</section>
742
743<section title="Uniform Resource Identifiers" anchor="uri">
744<iref primary="true" item="resource"/>
745<t>
746   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
747   throughout HTTP as the means for identifying resources. URI references
748   are used to target requests, indicate redirects, and define relationships.
749   HTTP does not limit what a resource might be; it merely defines an interface
750   that can be used to interact with a resource via HTTP. More information on
751   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
752</t>
753  <x:anchor-alias value="URI-reference"/>
754  <x:anchor-alias value="absolute-URI"/>
755  <x:anchor-alias value="relative-part"/>
756  <x:anchor-alias value="authority"/>
757  <x:anchor-alias value="path-abempty"/>
758  <x:anchor-alias value="path-absolute"/>
759  <x:anchor-alias value="port"/>
760  <x:anchor-alias value="query"/>
761  <x:anchor-alias value="uri-host"/>
762  <x:anchor-alias value="partial-URI"/>
763<t>
764   This specification adopts the definitions of "URI-reference",
765   "absolute-URI", "relative-part", "port", "host",
766   "path-abempty", "path-absolute", "query", and "authority" from the
767   URI generic syntax <xref target="RFC3986"/>.
768   In addition, we define a partial-URI rule for protocol elements
769   that allow a relative URI but not a fragment.
770</t>
771<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="URI-reference"/><iref primary="true" item="Grammar" subitem="absolute-URI"/><iref primary="true" item="Grammar" subitem="authority"/><iref primary="true" item="Grammar" subitem="path-absolute"/><iref primary="true" item="Grammar" subitem="port"/><iref primary="true" item="Grammar" subitem="query"/><iref primary="true" item="Grammar" subitem="uri-host"/>
772  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
773  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
774  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
775  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
776  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
777  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
778  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
779  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
780  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
781 
782  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
783</artwork></figure>
784<t>
785   Each protocol element in HTTP that allows a URI reference will indicate
786   in its ABNF production whether the element allows any form of reference
787   (URI-reference), only a URI in absolute form (absolute-URI), only the
788   path and optional query components, or some combination of the above.
789   Unless otherwise indicated, URI references are parsed
790   relative to the effective request URI
791   (<xref target="effective.request.uri"/>).
792</t>
793
794<section title="http URI scheme" anchor="http.uri">
795  <x:anchor-alias value="http-URI"/>
796  <iref item="http URI scheme" primary="true"/>
797  <iref item="URI scheme" subitem="http" primary="true"/>
798<t>
799   The "http" URI scheme is hereby defined for the purpose of minting
800   identifiers according to their association with the hierarchical
801   namespace governed by a potential HTTP origin server listening for
802   TCP connections on a given port.
803</t>
804<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
805  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
806</artwork></figure>
807<t>
808   The HTTP origin server is identified by the generic syntax's
809   <x:ref>authority</x:ref> component, which includes a host identifier
810   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
811   The remainder of the URI, consisting of both the hierarchical path
812   component and optional query component, serves as an identifier for
813   a potential resource within that origin server's name space.
814</t>
815<t>
816   If the host identifier is provided as an IP literal or IPv4 address,
817   then the origin server is any listener on the indicated TCP port at
818   that IP address. If host is a registered name, then that name is
819   considered an indirect identifier and the recipient might use a name
820   resolution service, such as DNS, to find the address of a listener
821   for that host.
822   The host &MUST-NOT; be empty; if an "http" URI is received with an
823   empty host, then it &MUST; be rejected as invalid.
824   If the port subcomponent is empty or not given, then TCP port 80 is
825   assumed (the default reserved port for WWW services).
826</t>
827<t>
828   Regardless of the form of host identifier, access to that host is not
829   implied by the mere presence of its name or address. The host might or might
830   not exist and, even when it does exist, might or might not be running an
831   HTTP server or listening to the indicated port. The "http" URI scheme
832   makes use of the delegated nature of Internet names and addresses to
833   establish a naming authority (whatever entity has the ability to place
834   an HTTP server at that Internet name or address) and allows that
835   authority to determine which names are valid and how they might be used.
836</t>
837<t>
838   When an "http" URI is used within a context that calls for access to the
839   indicated resource, a client &MAY; attempt access by resolving
840   the host to an IP address, establishing a TCP connection to that address
841   on the indicated port, and sending an HTTP request message
842   (<xref target="http.message"/>) containing the URI's identifying data
843   (<xref target="message.routing"/>) to the server.
844   If the server responds to that request with a non-interim HTTP response
845   message, as described in &status-codes;, then that response
846   is considered an authoritative answer to the client's request.
847</t>
848<t>
849   Although HTTP is independent of the transport protocol, the "http"
850   scheme is specific to TCP-based services because the name delegation
851   process depends on TCP for establishing authority.
852   An HTTP service based on some other underlying connection protocol
853   would presumably be identified using a different URI scheme, just as
854   the "https" scheme (below) is used for servers that require an SSL/TLS
855   transport layer on a connection. Other protocols might also be used to
856   provide access to "http" identified resources &mdash; it is only the
857   authoritative interface used for mapping the namespace that is
858   specific to TCP.
859</t>
860<t>
861   The URI generic syntax for authority also includes a deprecated
862   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
863   for including user authentication information in the URI.  Some
864   implementations make use of the userinfo component for internal
865   configuration of authentication information, such as within command
866   invocation options, configuration files, or bookmark lists, even
867   though such usage might expose a user identifier or password.
868   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
869   delimiter) when transmitting an "http" URI in a message.  Recipients
870   of HTTP messages that contain a URI reference &SHOULD; parse for the
871   existence of userinfo and treat its presence as an error, likely
872   indicating that the deprecated subcomponent is being used to obscure
873   the authority for the sake of phishing attacks.
874</t>
875</section>
876
877<section title="https URI scheme" anchor="https.uri">
878   <x:anchor-alias value="https-URI"/>
879   <iref item="https URI scheme"/>
880   <iref item="URI scheme" subitem="https"/>
881<t>
882   The "https" URI scheme is hereby defined for the purpose of minting
883   identifiers according to their association with the hierarchical
884   namespace governed by a potential HTTP origin server listening for
885   SSL/TLS-secured connections on a given TCP port.
886</t>
887<t>
888   All of the requirements listed above for the "http" scheme are also
889   requirements for the "https" scheme, except that a default TCP port
890   of 443 is assumed if the port subcomponent is empty or not given,
891   and the TCP connection &MUST; be secured for privacy through the
892   use of strong encryption prior to sending the first HTTP request.
893</t>
894<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
895  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
896</artwork></figure>
897<t>
898   Unlike the "http" scheme, responses to "https" identified requests
899   are never "public" and thus &MUST-NOT; be reused for shared caching.
900   They can, however, be reused in a private cache if the message is
901   cacheable by default in HTTP or specifically indicated as such by
902   the Cache-Control header field (&header-cache-control;).
903</t>
904<t>
905   Resources made available via the "https" scheme have no shared
906   identity with the "http" scheme even if their resource identifiers
907   indicate the same authority (the same host listening to the same
908   TCP port).  They are distinct name spaces and are considered to be
909   distinct origin servers.  However, an extension to HTTP that is
910   defined to apply to entire host domains, such as the Cookie protocol
911   <xref target="RFC6265"/>, can allow information
912   set by one service to impact communication with other services
913   within a matching group of host domains.
914</t>
915<t>
916   The process for authoritative access to an "https" identified
917   resource is defined in <xref target="RFC2818"/>.
918</t>
919</section>
920
921<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
922<t>
923   Since the "http" and "https" schemes conform to the URI generic syntax,
924   such URIs are normalized and compared according to the algorithm defined
925   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
926   described above for each scheme.
927</t>
928<t>
929   If the port is equal to the default port for a scheme, the normal
930   form is to elide the port subcomponent. Likewise, an empty path
931   component is equivalent to an absolute path of "/", so the normal
932   form is to provide a path of "/" instead. The scheme and host
933   are case-insensitive and normally provided in lowercase; all
934   other components are compared in a case-sensitive manner.
935   Characters other than those in the "reserved" set are equivalent
936   to their percent-encoded octets (see <xref target="RFC3986"
937   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
938</t>
939<t>
940   For example, the following three URIs are equivalent:
941</t>
942<figure><artwork type="example">
943   http://example.com:80/~smith/home.html
944   http://EXAMPLE.com/%7Esmith/home.html
945   http://EXAMPLE.com:/%7esmith/home.html
946</artwork></figure>
947</section>
948</section>
949</section>
950
951<section title="Message Format" anchor="http.message">
952<x:anchor-alias value="generic-message"/>
953<x:anchor-alias value="message.types"/>
954<x:anchor-alias value="HTTP-message"/>
955<x:anchor-alias value="start-line"/>
956<iref item="header section"/>
957<iref item="headers"/>
958<iref item="header field"/>
959<t>
960   All HTTP/1.1 messages consist of a start-line followed by a sequence of
961   octets in a format similar to the Internet Message Format
962   <xref target="RFC5322"/>: zero or more header fields (collectively
963   referred to as the "headers" or the "header section"), an empty line
964   indicating the end of the header section, and an optional message body.
965</t>
966<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
967  <x:ref>HTTP-message</x:ref>   = <x:ref>start-line</x:ref>
968                   *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
969                   <x:ref>CRLF</x:ref>
970                   [ <x:ref>message-body</x:ref> ]
971</artwork></figure>
972<t>
973   The normal procedure for parsing an HTTP message is to read the
974   start-line into a structure, read each header field into a hash
975   table by field name until the empty line, and then use the parsed
976   data to determine if a message body is expected.  If a message body
977   has been indicated, then it is read as a stream until an amount
978   of octets equal to the message body length is read or the connection
979   is closed.
980</t>
981<t>
982   Recipients &MUST; parse an HTTP message as a sequence of octets in an
983   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
984   Parsing an HTTP message as a stream of Unicode characters, without regard
985   for the specific encoding, creates security vulnerabilities due to the
986   varying ways that string processing libraries handle invalid multibyte
987   character sequences that contain the octet LF (%x0A).  String-based
988   parsers can only be safely used within protocol elements after the element
989   has been extracted from the message, such as within a header field-value
990   after message parsing has delineated the individual fields.
991</t>
992<t>
993   An HTTP message can be parsed as a stream for incremental processing or
994   forwarding downstream.  However, recipients cannot rely on incremental
995   delivery of partial messages, since some implementations will buffer or
996   delay message forwarding for the sake of network efficiency, security
997   checks, or payload transformations.
998</t>
999
1000<section title="Start Line" anchor="start.line">
1001  <x:anchor-alias value="Start-Line"/>
1002<t>
1003   An HTTP message can either be a request from client to server or a
1004   response from server to client.  Syntactically, the two types of message
1005   differ only in the start-line, which is either a request-line (for requests)
1006   or a status-line (for responses), and in the algorithm for determining
1007   the length of the message body (<xref target="message.body"/>).
1008   In theory, a client could receive requests and a server could receive
1009   responses, distinguishing them by their different start-line formats,
1010   but in practice servers are implemented to only expect a request
1011   (a response is interpreted as an unknown or invalid request method)
1012   and clients are implemented to only expect a response.
1013</t>
1014<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1015  <x:ref>start-line</x:ref>     = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1016</artwork></figure>
1017<t>
1018</t>
1019<t>
1020   Implementations &MUST-NOT; send whitespace between the start-line and
1021   the first header field. The presence of such whitespace in a request
1022   might be an attempt to trick a server into ignoring that field or
1023   processing the line after it as a new request, either of which might
1024   result in a security vulnerability if other implementations within
1025   the request chain interpret the same message differently.
1026   Likewise, the presence of such whitespace in a response might be
1027   ignored by some clients or cause others to cease parsing.
1028</t>
1029
1030<section title="Request Line" anchor="request.line">
1031  <x:anchor-alias value="Request"/>
1032  <x:anchor-alias value="request-line"/>
1033<t>
1034   A request-line begins with a method token, followed by a single
1035   space (SP), the request-target, another single space (SP), the
1036   protocol version, and ending with CRLF.
1037</t>
1038<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1039  <x:ref>request-line</x:ref>   = <x:ref>method</x:ref> <x:ref>SP</x:ref> <x:ref>request-target</x:ref> <x:ref>SP</x:ref> <x:ref>HTTP-version</x:ref> <x:ref>CRLF</x:ref>
1040</artwork></figure>
1041<iref primary="true" item="method"/>
1042<t anchor="method">
1043   The method token indicates the request method to be performed on the
1044   target resource. The request method is case-sensitive.
1045</t>
1046<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1047  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1048</artwork></figure>
1049<t>
1050   The methods defined by this specification can be found in
1051   &methods;, along with information regarding the HTTP method registry
1052   and considerations for defining new methods.
1053</t>
1054<iref item="request-target"/>
1055<t>
1056   The request-target identifies the target resource upon which to apply
1057   the request, as defined in <xref target="request-target"/>.
1058</t>
1059<t>
1060   No whitespace is allowed inside the method, request-target, and
1061   protocol version.  Hence, recipients typically parse the request-line
1062   into its component parts by splitting on the SP characters.
1063</t>
1064<t>
1065   Unfortunately, some user agents fail to properly encode hypertext
1066   references that have embedded whitespace, sending the characters
1067   directly instead of properly percent-encoding the disallowed characters.
1068   Recipients of an invalid request-line &SHOULD; respond with either a
1069   <x:ref>400 (Bad Request)</x:ref> error or a <x:ref>301 (Moved Permanently)</x:ref>
1070   redirect with the request-target properly encoded.  Recipients &SHOULD-NOT;
1071   attempt to autocorrect and then process the request without a redirect,
1072   since the invalid request-line might be deliberately crafted to bypass
1073   security filters along the request chain.
1074</t>
1075<t>
1076   HTTP does not place a pre-defined limit on the length of a request-line.
1077   A server that receives a method longer than any that it implements
1078   &SHOULD; respond with either a <x:ref>405 (Method Not Allowed)</x:ref>, if it is an origin
1079   server, or a <x:ref>501 (Not Implemented)</x:ref> status code.
1080   A server &MUST; be prepared to receive URIs of unbounded length and
1081   respond with the <x:ref>414 (URI Too Long)</x:ref> status code if the received
1082   request-target would be longer than the server wishes to handle
1083   (see &status-414;).
1084</t>
1085<t>
1086   Various ad-hoc limitations on request-line length are found in practice.
1087   It is &RECOMMENDED; that all HTTP senders and recipients support, at a
1088   minimum, request-line lengths of up to 8000 octets.
1089</t>
1090</section>
1091
1092<section title="Status Line" anchor="status.line">
1093  <x:anchor-alias value="response"/>
1094  <x:anchor-alias value="status-line"/>
1095<t>
1096   The first line of a response message is the status-line, consisting
1097   of the protocol version, a space (SP), the status code, another space,
1098   a possibly-empty textual phrase describing the status code, and
1099   ending with CRLF.
1100</t>
1101<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1102  <x:ref>status-line</x:ref> = <x:ref>HTTP-version</x:ref> <x:ref>SP</x:ref> <x:ref>status-code</x:ref> <x:ref>SP</x:ref> <x:ref>reason-phrase</x:ref> <x:ref>CRLF</x:ref>
1103</artwork></figure>
1104
1105<t anchor="status-code">
1106   The status-code element is a 3-digit integer result code of the attempt to
1107   understand and satisfy the request. See &status-codes; for
1108   further information, such as the list of status codes defined by this
1109   specification, the IANA registry, and considerations for new status codes.
1110</t>
1111<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1112  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1113</artwork></figure>
1114
1115<t anchor="reason-phrase">   
1116   The reason-phrase element exists for the sole purpose of providing a
1117   textual description associated with the numeric status code, mostly
1118   out of deference to earlier Internet application protocols that were more
1119   frequently used with interactive text clients. A client &SHOULD; ignore
1120   the reason-phrase content.
1121</t>
1122<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1123  <x:ref>reason-phrase</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1124</artwork></figure>
1125</section>
1126</section>
1127
1128<section title="Header Fields" anchor="header.fields">
1129  <x:anchor-alias value="header-field"/>
1130  <x:anchor-alias value="field-content"/>
1131  <x:anchor-alias value="field-name"/>
1132  <x:anchor-alias value="field-value"/>
1133  <x:anchor-alias value="obs-fold"/>
1134<t>
1135   Each HTTP header field consists of a case-insensitive field name
1136   followed by a colon (":"), optional whitespace, and the field value.
1137</t>
1138<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="header-field"/><iref primary="true" item="Grammar" subitem="field-name"/><iref primary="true" item="Grammar" subitem="field-value"/><iref primary="true" item="Grammar" subitem="field-content"/><iref primary="true" item="Grammar" subitem="obs-fold"/>
1139  <x:ref>header-field</x:ref>   = <x:ref>field-name</x:ref> ":" <x:ref>OWS</x:ref> <x:ref>field-value</x:ref> <x:ref>BWS</x:ref>
1140  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1141  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1142  <x:ref>field-content</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1143  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1144                 ; obsolete line folding
1145                 ; see <xref target="field.parsing"/>
1146</artwork></figure>
1147<t>
1148   The field-name token labels the corresponding field-value as having the
1149   semantics defined by that header field.  For example, the <x:ref>Date</x:ref>
1150   header field is defined in &header-date; as containing the origination
1151   timestamp for the message in which it appears.
1152</t>
1153<t>
1154   HTTP header fields are fully extensible: there is no limit on the
1155   introduction of new field names, each presumably defining new semantics,
1156   or on the number of header fields used in a given message.  Existing
1157   fields are defined in each part of this specification and in many other
1158   specifications outside the standards process.
1159   New header fields can be introduced without changing the protocol version
1160   if their defined semantics allow them to be safely ignored by recipients
1161   that do not recognize them.
1162</t>
1163<t>
1164   New HTTP header fields &SHOULD; be registered with IANA according
1165   to the procedures in &cons-new-header-fields;.
1166   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1167   field-name is listed in the <x:ref>Connection</x:ref> header field
1168   (<xref target="header.connection"/>) or the proxy is specifically
1169   configured to block or otherwise transform such fields.
1170   Unrecognized header fields &SHOULD; be ignored by other recipients.
1171</t>
1172<t>
1173   The order in which header fields with differing field names are
1174   received is not significant. However, it is "good practice" to send
1175   header fields that contain control data first, such as <x:ref>Host</x:ref>
1176   on requests and <x:ref>Date</x:ref> on responses, so that implementations
1177   can decide when not to handle a message as early as possible.  A server
1178   &MUST; wait until the entire header section is received before interpreting
1179   a request message, since later header fields might include conditionals,
1180   authentication credentials, or deliberately misleading duplicate
1181   header fields that would impact request processing.
1182</t>
1183<t>
1184   Multiple header fields with the same field name &MUST-NOT; be
1185   sent in a message unless the entire field value for that
1186   header field is defined as a comma-separated list [i.e., #(values)].
1187   Multiple header fields with the same field name can be combined into
1188   one "field-name: field-value" pair, without changing the semantics of the
1189   message, by appending each subsequent field value to the combined
1190   field value in order, separated by a comma. The order in which
1191   header fields with the same field name are received is therefore
1192   significant to the interpretation of the combined field value;
1193   a proxy &MUST-NOT; change the order of these field values when
1194   forwarding a message.
1195</t>
1196<x:note>
1197  <t>
1198   &Note; The "Set-Cookie" header field as implemented in
1199   practice can occur multiple times, but does not use the list syntax, and
1200   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1201   for details.) Also note that the Set-Cookie2 header field specified in
1202   <xref target="RFC2965"/> does not share this problem.
1203  </t>
1204</x:note>
1205
1206<section title="Whitespace" anchor="whitespace">
1207<t anchor="rule.LWS">
1208   This specification uses three rules to denote the use of linear
1209   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1210   BWS ("bad" whitespace).
1211</t>
1212<t anchor="rule.OWS">
1213   The OWS rule is used where zero or more linear whitespace octets might
1214   appear. OWS &SHOULD; either not be produced or be produced as a single
1215   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1216   be replaced with a single SP or transformed to all SP octets (each
1217   octet other than SP replaced with SP) before interpreting the field value
1218   or forwarding the message downstream.
1219</t>
1220<t anchor="rule.RWS">
1221   RWS is used when at least one linear whitespace octet is required to
1222   separate field tokens. RWS &SHOULD; be produced as a single SP.
1223   Multiple RWS octets that occur within field-content &SHOULD; either
1224   be replaced with a single SP or transformed to all SP octets before
1225   interpreting the field value or forwarding the message downstream.
1226</t>
1227<t anchor="rule.BWS">
1228   BWS is used where the grammar allows optional whitespace for historical
1229   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
1230   recipients &MUST; accept such bad optional whitespace and remove it before
1231   interpreting the field value or forwarding the message downstream.
1232</t>
1233<t anchor="rule.whitespace">
1234  <x:anchor-alias value="BWS"/>
1235  <x:anchor-alias value="OWS"/>
1236  <x:anchor-alias value="RWS"/>
1237</t>
1238<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/>
1239  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1240                 ; "optional" whitespace
1241  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1242                 ; "required" whitespace
1243  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1244                 ; "bad" whitespace
1245</artwork></figure>
1246</section>
1247
1248<section title="Field Parsing" anchor="field.parsing">
1249<t>
1250   No whitespace is allowed between the header field-name and colon.
1251   In the past, differences in the handling of such whitespace have led to
1252   security vulnerabilities in request routing and response handling.
1253   Any received request message that contains whitespace between a header
1254   field-name and colon &MUST; be rejected with a response code of 400
1255   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1256   message before forwarding the message downstream.
1257</t>
1258<t>
1259   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1260   preferred. The field value does not include any leading or trailing white
1261   space: OWS occurring before the first non-whitespace octet of the
1262   field value or after the last non-whitespace octet of the field value
1263   is ignored and &SHOULD; be removed before further processing (as this does
1264   not change the meaning of the header field).
1265</t>
1266<t>
1267   Historically, HTTP header field values could be extended over multiple
1268   lines by preceding each extra line with at least one space or horizontal
1269   tab (obs-fold). This specification deprecates such line
1270   folding except within the message/http media type
1271   (<xref target="internet.media.type.message.http"/>).
1272   HTTP senders &MUST-NOT; produce messages that include line folding
1273   (i.e., that contain any field-value that matches the obs-fold rule) unless
1274   the message is intended for packaging within the message/http media type.
1275   HTTP recipients &SHOULD; accept line folding and replace any embedded
1276   obs-fold whitespace with either a single SP or a matching number of SP
1277   octets (to avoid buffer copying) prior to interpreting the field value or
1278   forwarding the message downstream.
1279</t>
1280<t>
1281   Historically, HTTP has allowed field content with text in the ISO-8859-1
1282   <xref target="ISO-8859-1"/> character encoding and supported other
1283   character sets only through use of <xref target="RFC2047"/> encoding.
1284   In practice, most HTTP header field values use only a subset of the
1285   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1286   header fields &SHOULD; limit their field values to US-ASCII octets.
1287   Recipients &SHOULD; treat other (obs-text) octets in field content as
1288   opaque data.
1289</t>
1290</section>
1291
1292<section title="Field Length" anchor="field.length">
1293<t>
1294   HTTP does not place a pre-defined limit on the length of header fields,
1295   either in isolation or as a set. A server &MUST; be prepared to receive
1296   request header fields of unbounded length and respond with a <x:ref>4xx
1297   (Client Error)</x:ref> status code if the received header field(s) would be
1298   longer than the server wishes to handle.
1299</t>
1300<t>
1301   A client that receives response headers that are longer than it wishes to
1302   handle can only treat it as a server error.
1303</t>
1304<t>
1305   Various ad-hoc limitations on header length are found in practice. It is
1306   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1307   combined header fields have 4000 or more octets.
1308</t>
1309</section>
1310
1311<section title="Field value components" anchor="field.components">
1312<t anchor="rule.token.separators">
1313  <x:anchor-alias value="tchar"/>
1314  <x:anchor-alias value="token"/>
1315  <x:anchor-alias value="special"/>
1316  <x:anchor-alias value="word"/>
1317   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1318   separated by whitespace or special characters. These special characters
1319   &MUST; be in a quoted string to be used within a parameter value (as defined
1320   in <xref target="transfer.codings"/>).
1321</t>
1322<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="word"/><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"/>
1323  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1324
1325  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1326<!--
1327  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1328 -->
1329  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1330                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1331                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1332                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1333
1334  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1335                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1336                 / "]" / "?" / "=" / "{" / "}"
1337</artwork></figure>
1338<t anchor="rule.quoted-string">
1339  <x:anchor-alias value="quoted-string"/>
1340  <x:anchor-alias value="qdtext"/>
1341  <x:anchor-alias value="obs-text"/>
1342   A string of text is parsed as a single word if it is quoted using
1343   double-quote marks.
1344</t>
1345<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/><iref primary="true" item="Grammar" subitem="obs-text"/>
1346  <x:ref>quoted-string</x:ref>  = <x:ref>DQUOTE</x:ref> *( <x:ref>qdtext</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref>
1347  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1348  <x:ref>obs-text</x:ref>       = %x80-FF
1349</artwork></figure>
1350<t anchor="rule.quoted-pair">
1351  <x:anchor-alias value="quoted-pair"/>
1352   The backslash octet ("\") can be used as a single-octet
1353   quoting mechanism within quoted-string constructs:
1354</t>
1355<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1356  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1357</artwork></figure>
1358<t>
1359   Recipients that process the value of the quoted-string &MUST; handle a
1360   quoted-pair as if it were replaced by the octet following the backslash.
1361</t>
1362<t>
1363   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1364   escaping (i.e., other than DQUOTE and the backslash octet).
1365</t>
1366<t anchor="rule.comment">
1367  <x:anchor-alias value="comment"/>
1368  <x:anchor-alias value="ctext"/>
1369   Comments can be included in some HTTP header fields by surrounding
1370   the comment text with parentheses. Comments are only allowed in
1371   fields containing "comment" as part of their field value definition.
1372</t>
1373<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1374  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1375  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1376</artwork></figure>
1377<t anchor="rule.quoted-cpair">
1378  <x:anchor-alias value="quoted-cpair"/>
1379   The backslash octet ("\") can be used as a single-octet
1380   quoting mechanism within comment constructs:
1381</t>
1382<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1383  <x:ref>quoted-cpair</x:ref>   = "\" ( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1384</artwork></figure>
1385<t>
1386   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1387   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1388</t>
1389</section>
1390
1391<section title="ABNF list extension: #rule" anchor="abnf.extension">
1392<t>
1393  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
1394  improve readability in the definitions of some header field values.
1395</t>
1396<t>
1397  A construct "#" is defined, similar to "*", for defining comma-delimited
1398  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
1399  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
1400  comma (",") and optional whitespace (OWS).   
1401</t>
1402<figure><preamble>
1403  Thus,
1404</preamble><artwork type="example">
1405  1#element =&gt; element *( OWS "," OWS element )
1406</artwork></figure>
1407<figure><preamble>
1408  and:
1409</preamble><artwork type="example">
1410  #element =&gt; [ 1#element ]
1411</artwork></figure>
1412<figure><preamble>
1413  and for n &gt;= 1 and m &gt; 1:
1414</preamble><artwork type="example">
1415  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
1416</artwork></figure>
1417<t>
1418  For compatibility with legacy list rules, recipients &SHOULD; accept empty
1419  list elements. In other words, consumers would follow the list productions:
1420</t>
1421<figure><artwork type="example">
1422  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
1423 
1424  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
1425</artwork></figure>
1426<t>
1427  Note that empty elements do not contribute to the count of elements present,
1428  though.
1429</t>
1430<t>
1431  For example, given these ABNF productions:
1432</t>
1433<figure><artwork type="example">
1434  example-list      = 1#example-list-elmt
1435  example-list-elmt = token ; see <xref target="field.components"/> 
1436</artwork></figure>
1437<t>
1438  Then these are valid values for example-list (not including the double
1439  quotes, which are present for delimitation only):
1440</t>
1441<figure><artwork type="example">
1442  "foo,bar"
1443  "foo ,bar,"
1444  "foo , ,bar,charlie   "
1445</artwork></figure>
1446<t>
1447  But these values would be invalid, as at least one non-empty element is
1448  required:
1449</t>
1450<figure><artwork type="example">
1451  ""
1452  ","
1453  ",   ,"
1454</artwork></figure>
1455<t>
1456  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
1457  expanded as explained above.
1458</t>
1459</section>
1460</section>
1461
1462<section title="Message Body" anchor="message.body">
1463  <x:anchor-alias value="message-body"/>
1464<t>
1465   The message body (if any) of an HTTP message is used to carry the
1466   payload body of that request or response.  The message body is
1467   identical to the payload body unless a transfer coding has been
1468   applied, as described in <xref target="header.transfer-encoding"/>.
1469</t>
1470<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1471  <x:ref>message-body</x:ref> = *OCTET
1472</artwork></figure>
1473<t>
1474   The rules for when a message body is allowed in a message differ for
1475   requests and responses.
1476</t>
1477<t>
1478   The presence of a message body in a request is signaled by a
1479   a <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1480   field. Request message framing is independent of method semantics,
1481   even if the method does not define any use for a message body.
1482</t>
1483<t>
1484   The presence of a message body in a response depends on both
1485   the request method to which it is responding and the response
1486   status code (<xref target="status-code"/>).
1487   Responses to the HEAD request method never include a message body
1488   because the associated response header fields (e.g.,
1489   <x:ref>Transfer-Encoding</x:ref>, <x:ref>Content-Length</x:ref>, etc.) only
1490   indicate what their values would have been if the request method had been
1491   GET. <x:ref>2xx (Successful)</x:ref> responses to CONNECT switch to tunnel
1492   mode instead of having a message body.
1493   All <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, and
1494   <x:ref>304 (Not Modified)</x:ref> responses &MUST-NOT; include a message body.
1495   All other responses do include a message body, although the body
1496   &MAY; be of zero length. (See &status-codes; and &status-304;.)
1497</t>
1498
1499<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1500  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1501  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
1502  <x:anchor-alias value="Transfer-Encoding"/>
1503<t>
1504   When one or more transfer codings are applied to a payload body in order
1505   to form the message body, a Transfer-Encoding header field &MUST; be sent
1506   in the message and &MUST; contain the list of corresponding
1507   transfer-coding names in the same order that they were applied.
1508   Transfer codings are defined in <xref target="transfer.codings"/>.
1509</t>
1510<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1511  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1512</artwork></figure>
1513<t>
1514   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1515   MIME, which was designed to enable safe transport of binary data over a
1516   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1517   However, safe transport has a different focus for an 8bit-clean transfer
1518   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1519   accurately delimit a dynamically generated payload and to distinguish
1520   payload encodings that are only applied for transport efficiency or
1521   security from those that are characteristics of the target resource.
1522</t>
1523<t>
1524   The "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1525   &MUST; be implemented by all HTTP/1.1 recipients because it plays a
1526   crucial role in delimiting messages when the payload body size is not
1527   known in advance.
1528   When the "chunked" transfer-coding is used, it &MUST; be the last
1529   transfer-coding applied to form the message body and &MUST-NOT;
1530   be applied more than once in a message body.
1531   If any transfer-coding is applied to a request payload body,
1532   the final transfer-coding applied &MUST; be "chunked".
1533   If any transfer-coding is applied to a response payload body, then either
1534   the final transfer-coding applied &MUST; be "chunked" or
1535   the message &MUST; be terminated by closing the connection.
1536</t>
1537<figure><preamble>
1538   For example,
1539</preamble><artwork type="example">
1540  Transfer-Encoding: gzip, chunked
1541</artwork><postamble>
1542   indicates that the payload body has been compressed using the gzip
1543   coding and then chunked using the chunked coding while forming the
1544   message body.
1545</postamble></figure>
1546<t>
1547   If more than one Transfer-Encoding header field is present in a message,
1548   the multiple field-values &MUST; be combined into one field-value,
1549   according to the algorithm defined in <xref target="header.fields"/>,
1550   before determining the message body length.
1551</t>
1552<t>
1553   Unlike <x:ref>Content-Encoding</x:ref> (&content-codings;),
1554   Transfer-Encoding is a property of the message, not of the payload, and thus
1555   &MAY; be added or removed by any implementation along the request/response
1556   chain. Additional information about the encoding parameters &MAY; be
1557   provided by other header fields not defined by this specification.
1558</t>
1559<t>
1560   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1561   <x:ref>304 (Not Modified)</x:ref> response (&status-304;) to a GET request,
1562   neither of which includes a message body,
1563   to indicate that the origin server would have applied a transfer coding
1564   to the message body if the request had been an unconditional GET.
1565   This indication is not required, however, because any recipient on
1566   the response chain (including the origin server) can remove transfer
1567   codings when they are not needed.
1568</t>
1569<t>
1570   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1571   implementations advertising only HTTP/1.0 support will not understand
1572   how to process a transfer-encoded payload.
1573   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1574   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1575   might be in the form of specific user configuration or by remembering the
1576   version of a prior received response.
1577   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1578   the corresponding request indicates HTTP/1.1 (or later).
1579</t>
1580<t>
1581   A server that receives a request message with a transfer-coding it does
1582   not understand &SHOULD; respond with <x:ref>501 (Not Implemented)</x:ref> and then
1583   close the connection.
1584</t>
1585</section>
1586
1587<section title="Content-Length" anchor="header.content-length">
1588  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1589  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
1590  <x:anchor-alias value="Content-Length"/>
1591<t>
1592   When a message does not have a <x:ref>Transfer-Encoding</x:ref> header field
1593   and the payload body length can be determined prior to being transferred, a
1594   Content-Length header field &SHOULD; be sent to indicate the length of the
1595   payload body that is either present as the message body, for requests
1596   and non-HEAD responses other than <x:ref>304 (Not Modified)</x:ref>, or
1597   would have been present had the request been an unconditional GET.  The
1598   length is expressed as a decimal number of octets.
1599</t>
1600<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1601  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1602</artwork></figure>
1603<t>
1604   An example is
1605</t>
1606<figure><artwork type="example">
1607  Content-Length: 3495
1608</artwork></figure>
1609<t>
1610   In the case of a response to a HEAD request, Content-Length indicates
1611   the size of the payload body (without any potential transfer-coding)
1612   that would have been sent had the request been a GET.
1613   In the case of a <x:ref>304 (Not Modified)</x:ref> response (&status-304;)
1614   to a GET request, Content-Length indicates the size of the payload body (without
1615   any potential transfer-coding) that would have been sent in a <x:ref>200 (OK)</x:ref>
1616   response.
1617</t>
1618<t>
1619   HTTP's use of Content-Length is significantly different from how it is
1620   used in MIME, where it is an optional field used only within the
1621   "message/external-body" media-type.
1622</t>
1623<t>
1624   Any Content-Length field value greater than or equal to zero is valid.
1625   Since there is no predefined limit to the length of an HTTP payload,
1626   recipients &SHOULD; anticipate potentially large decimal numerals and
1627   prevent parsing errors due to integer conversion overflows
1628   (<xref target="attack.protocol.element.size.overflows"/>).
1629</t>
1630<t>
1631   If a message is received that has multiple Content-Length header fields
1632   (<xref target="header.content-length"/>) with field-values consisting
1633   of the same decimal value, or a single Content-Length header field with
1634   a field value containing a list of identical decimal values (e.g.,
1635   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1636   header fields have been generated or combined by an upstream message
1637   processor, then the recipient &MUST; either reject the message as invalid
1638   or replace the duplicated field-values with a single valid Content-Length
1639   field containing that decimal value prior to determining the message body
1640   length.
1641</t>
1642</section>
1643
1644<section title="Message Body Length" anchor="message.body.length">
1645<t>
1646   The length of a message body is determined by one of the following
1647   (in order of precedence):
1648</t>
1649<t>
1650  <list style="numbers">
1651    <x:lt><t>
1652     Any response to a HEAD request and any response with a
1653     <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, or
1654     <x:ref>304 (Not Modified)</x:ref> status code is always
1655     terminated by the first empty line after the header fields, regardless of
1656     the header fields present in the message, and thus cannot contain a
1657     message body.
1658    </t></x:lt>
1659    <x:lt><t>
1660     Any <x:ref>2xx (Successful)</x:ref> response to a CONNECT request implies that the
1661     connection will become a tunnel immediately after the empty line that
1662     concludes the header fields.  A client &MUST; ignore any
1663     <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1664     fields received in such a message.
1665    </t></x:lt>
1666    <x:lt><t>
1667     If a <x:ref>Transfer-Encoding</x:ref> header field is present
1668     and the "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1669     is the final encoding, the message body length is determined by reading
1670     and decoding the chunked data until the transfer-coding indicates the
1671     data is complete.
1672    </t>
1673    <t>
1674     If a <x:ref>Transfer-Encoding</x:ref> header field is present in a
1675     response and the "chunked" transfer-coding is not the final encoding, the
1676     message body length is determined by reading the connection until it is
1677     closed by the server.
1678     If a Transfer-Encoding header field is present in a request and the
1679     "chunked" transfer-coding is not the final encoding, the message body
1680     length cannot be determined reliably; the server &MUST; respond with
1681     the <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1682    </t>
1683    <t>
1684     If a message is received with both a <x:ref>Transfer-Encoding</x:ref>
1685     and a <x:ref>Content-Length</x:ref> header field, the
1686     Transfer-Encoding overrides the Content-Length.
1687     Such a message might indicate an attempt to perform request or response
1688     smuggling (bypass of security-related checks on message routing or content)
1689     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1690     be removed, prior to forwarding the message downstream, or replaced with
1691     the real message body length after the transfer-coding is decoded.
1692    </t></x:lt>
1693    <x:lt><t>
1694     If a message is received without <x:ref>Transfer-Encoding</x:ref> and with
1695     either multiple <x:ref>Content-Length</x:ref> header fields having
1696     differing field-values or a single Content-Length header field having an
1697     invalid value, then the message framing is invalid and &MUST; be treated
1698     as an error to prevent request or response smuggling.
1699     If this is a request message, the server &MUST; respond with
1700     a <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1701     If this is a response message received by a proxy, the proxy
1702     &MUST; discard the received response, send a <x:ref>502 (Bad Gateway)</x:ref>
1703     status code as its downstream response, and then close the connection.
1704     If this is a response message received by a user-agent, it &MUST; be
1705     treated as an error by discarding the message and closing the connection.
1706    </t></x:lt>
1707    <x:lt><t>
1708     If a valid <x:ref>Content-Length</x:ref> header field is present without
1709     <x:ref>Transfer-Encoding</x:ref>, its decimal value defines the
1710     message body length in octets.  If the actual number of octets sent in
1711     the message is less than the indicated Content-Length, the recipient
1712     &MUST; consider the message to be incomplete and treat the connection
1713     as no longer usable.
1714     If the actual number of octets sent in the message is more than the indicated
1715     Content-Length, the recipient &MUST; only process the message body up to the
1716     field value's number of octets; the remainder of the message &MUST; either
1717     be discarded or treated as the next message in a pipeline.  For the sake of
1718     robustness, a user-agent &MAY; attempt to detect and correct such an error
1719     in message framing if it is parsing the response to the last request on
1720     a connection and the connection has been closed by the server.
1721    </t></x:lt>
1722    <x:lt><t>
1723     If this is a request message and none of the above are true, then the
1724     message body length is zero (no message body is present).
1725    </t></x:lt>
1726    <x:lt><t>
1727     Otherwise, this is a response message without a declared message body
1728     length, so the message body length is determined by the number of octets
1729     received prior to the server closing the connection.
1730    </t></x:lt>
1731  </list>
1732</t>
1733<t>
1734   Since there is no way to distinguish a successfully completed,
1735   close-delimited message from a partially-received message interrupted
1736   by network failure, implementations &SHOULD; use encoding or
1737   length-delimited messages whenever possible.  The close-delimiting
1738   feature exists primarily for backwards compatibility with HTTP/1.0.
1739</t>
1740<t>
1741   A server &MAY; reject a request that contains a message body but
1742   not a <x:ref>Content-Length</x:ref> by responding with
1743   <x:ref>411 (Length Required)</x:ref>.
1744</t>
1745<t>
1746   Unless a transfer-coding other than "chunked" has been applied,
1747   a client that sends a request containing a message body &SHOULD;
1748   use a valid <x:ref>Content-Length</x:ref> header field if the message body
1749   length is known in advance, rather than the "chunked" encoding, since some
1750   existing services respond to "chunked" with a <x:ref>411 (Length Required)</x:ref>
1751   status code even though they understand the chunked encoding.  This
1752   is typically because such services are implemented via a gateway that
1753   requires a content-length in advance of being called and the server
1754   is unable or unwilling to buffer the entire request before processing.
1755</t>
1756<t>
1757   A client that sends a request containing a message body &MUST; include a
1758   valid <x:ref>Content-Length</x:ref> header field if it does not know the
1759   server will handle HTTP/1.1 (or later) requests; such knowledge can be in
1760   the form of specific user configuration or by remembering the version of a
1761   prior received response.
1762</t>
1763</section>
1764</section>
1765
1766<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1767<t>
1768   Request messages that are prematurely terminated, possibly due to a
1769   cancelled connection or a server-imposed time-out exception, &MUST;
1770   result in closure of the connection; sending an HTTP/1.1 error response
1771   prior to closing the connection is &OPTIONAL;.
1772</t>
1773<t>
1774   Response messages that are prematurely terminated, usually by closure
1775   of the connection prior to receiving the expected number of octets or by
1776   failure to decode a transfer-encoded message body, &MUST; be recorded
1777   as incomplete.  A response that terminates in the middle of the header
1778   block (before the empty line is received) cannot be assumed to convey the
1779   full semantics of the response and &MUST; be treated as an error.
1780</t>
1781<t>
1782   A message body that uses the chunked transfer encoding is
1783   incomplete if the zero-sized chunk that terminates the encoding has not
1784   been received.  A message that uses a valid <x:ref>Content-Length</x:ref> is
1785   incomplete if the size of the message body received (in octets) is less than
1786   the value given by Content-Length.  A response that has neither chunked
1787   transfer encoding nor Content-Length is terminated by closure of the
1788   connection, and thus is considered complete regardless of the number of
1789   message body octets received, provided that the header block was received
1790   intact.
1791</t>
1792<t>
1793   A user agent &MUST-NOT; render an incomplete response message body as if
1794   it were complete (i.e., some indication needs to be given to the user that an
1795   error occurred).  Cache requirements for incomplete responses are defined
1796   in &cache-incomplete;.
1797</t>
1798<t>
1799   A server &MUST; read the entire request message body or close
1800   the connection after sending its response, since otherwise the
1801   remaining data on a persistent connection would be misinterpreted
1802   as the next request.  Likewise,
1803   a client &MUST; read the entire response message body if it intends
1804   to reuse the same connection for a subsequent request.  Pipelining
1805   multiple requests on a connection is described in <xref target="pipelining"/>.
1806</t>
1807</section>
1808
1809<section title="Message Parsing Robustness" anchor="message.robustness">
1810<t>
1811   Older HTTP/1.0 client implementations might send an extra CRLF
1812   after a POST request as a lame workaround for some early server
1813   applications that failed to read message body content that was
1814   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1815   preface or follow a request with an extra CRLF.  If terminating
1816   the request message body with a line-ending is desired, then the
1817   client &MUST; include the terminating CRLF octets as part of the
1818   message body length.
1819</t>
1820<t>
1821   In the interest of robustness, servers &SHOULD; ignore at least one
1822   empty line received where a request-line is expected. In other words, if
1823   the server is reading the protocol stream at the beginning of a
1824   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1825   Likewise, although the line terminator for the start-line and header
1826   fields is the sequence CRLF, we recommend that recipients recognize a
1827   single LF as a line terminator and ignore any CR.
1828</t>
1829<t>
1830   When a server listening only for HTTP request messages, or processing
1831   what appears from the start-line to be an HTTP request message,
1832   receives a sequence of octets that does not match the HTTP-message
1833   grammar aside from the robustness exceptions listed above, the
1834   server &MUST; respond with an HTTP/1.1 <x:ref>400 (Bad Request)</x:ref> response. 
1835</t>
1836</section>
1837</section>
1838
1839<section title="Transfer Codings" anchor="transfer.codings">
1840  <x:anchor-alias value="transfer-coding"/>
1841  <x:anchor-alias value="transfer-extension"/>
1842<t>
1843   Transfer-coding values are used to indicate an encoding
1844   transformation that has been, can be, or might need to be applied to a
1845   payload body in order to ensure "safe transport" through the network.
1846   This differs from a content coding in that the transfer-coding is a
1847   property of the message rather than a property of the representation
1848   that is being transferred.
1849</t>
1850<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1851  <x:ref>transfer-coding</x:ref>    = "chunked" ; <xref target="chunked.encoding"/>
1852                     / "compress" ; <xref target="compress.coding"/>
1853                     / "deflate" ; <xref target="deflate.coding"/>
1854                     / "gzip" ; <xref target="gzip.coding"/>
1855                     / <x:ref>transfer-extension</x:ref>
1856  <x:ref>transfer-extension</x:ref> = <x:ref>token</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>transfer-parameter</x:ref> )
1857</artwork></figure>
1858<t anchor="rule.parameter">
1859  <x:anchor-alias value="attribute"/>
1860  <x:anchor-alias value="transfer-parameter"/>
1861  <x:anchor-alias value="value"/>
1862   Parameters are in the form of attribute/value pairs.
1863</t>
1864<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/>
1865  <x:ref>transfer-parameter</x:ref> = <x:ref>attribute</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>value</x:ref>
1866  <x:ref>attribute</x:ref>          = <x:ref>token</x:ref>
1867  <x:ref>value</x:ref>              = <x:ref>word</x:ref>
1868</artwork></figure>
1869<t>
1870   All transfer-coding values are case-insensitive.
1871   The HTTP Transfer Coding registry is defined in
1872   <xref target="transfer.coding.registry"/>.
1873   HTTP/1.1 uses transfer-coding values in the <x:ref>TE</x:ref> header field
1874   (<xref target="header.te"/>) and in the <x:ref>Transfer-Encoding</x:ref>
1875   header field (<xref target="header.transfer-encoding"/>).
1876</t>
1877
1878<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1879  <iref item="chunked (Coding Format)"/>
1880  <iref item="Coding Format" subitem="chunked"/>
1881  <x:anchor-alias value="chunk"/>
1882  <x:anchor-alias value="chunked-body"/>
1883  <x:anchor-alias value="chunk-data"/>
1884  <x:anchor-alias value="chunk-ext"/>
1885  <x:anchor-alias value="chunk-ext-name"/>
1886  <x:anchor-alias value="chunk-ext-val"/>
1887  <x:anchor-alias value="chunk-size"/>
1888  <x:anchor-alias value="last-chunk"/>
1889  <x:anchor-alias value="trailer-part"/>
1890  <x:anchor-alias value="quoted-str-nf"/>
1891  <x:anchor-alias value="qdtext-nf"/>
1892<t>
1893   The chunked encoding modifies the body of a message in order to
1894   transfer it as a series of chunks, each with its own size indicator,
1895   followed by an &OPTIONAL; trailer containing header fields. This
1896   allows dynamically produced content to be transferred along with the
1897   information necessary for the recipient to verify that it has
1898   received the full message.
1899</t>
1900<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="chunked-body"/><iref primary="true" item="Grammar" subitem="chunk"/><iref primary="true" item="Grammar" subitem="chunk-size"/><iref primary="true" item="Grammar" subitem="last-chunk"/><iref primary="true" item="Grammar" subitem="chunk-ext"/><iref primary="true" item="Grammar" subitem="chunk-ext-name"/><iref primary="true" item="Grammar" subitem="chunk-ext-val"/><iref primary="true" item="Grammar" subitem="chunk-data"/><iref primary="true" item="Grammar" subitem="trailer-part"/><iref primary="true" item="Grammar" subitem="quoted-str-nf"/><iref primary="true" item="Grammar" subitem="qdtext-nf"/>
1901  <x:ref>chunked-body</x:ref>   = *<x:ref>chunk</x:ref>
1902                   <x:ref>last-chunk</x:ref>
1903                   <x:ref>trailer-part</x:ref>
1904                   <x:ref>CRLF</x:ref>
1905 
1906  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1907                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1908  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1909  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1910 
1911  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1912  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1913  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1914  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1915  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1916 
1917  <x:ref>quoted-str-nf</x:ref>  = <x:ref>DQUOTE</x:ref> *( <x:ref>qdtext-nf</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref>
1918                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1919  <x:ref>qdtext-nf</x:ref>      = <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1920</artwork></figure>
1921<t>
1922   The chunk-size field is a string of hex digits indicating the size of
1923   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1924   zero, followed by the trailer, which is terminated by an empty line.
1925</t>
1926<t>
1927   The trailer allows the sender to include additional HTTP header
1928   fields at the end of the message. The <x:ref>Trailer</x:ref> header field
1929   can be used to indicate which header fields are included in a trailer (see
1930   <xref target="header.trailer"/>).
1931</t>
1932<t>
1933   A server using chunked transfer-coding in a response &MUST-NOT; use the
1934   trailer for any header fields unless at least one of the following is
1935   true:
1936  <list style="numbers">
1937    <t>the request included a <x:ref>TE</x:ref> header field that indicates
1938    "trailers" is acceptable in the transfer-coding of the response, as
1939    described in <xref target="header.te"/>; or,</t>
1940     
1941    <t>the trailer fields consist entirely of optional metadata, and the
1942    recipient could use the message (in a manner acceptable to the server where
1943    the field originated) without receiving it. In other words, the server that
1944    generated the header (often but not always the origin server) is willing to
1945    accept the possibility that the trailer fields might be silently discarded
1946    along the path to the client.</t>
1947  </list>
1948</t>
1949<t>
1950   This requirement prevents an interoperability failure when the
1951   message is being received by an HTTP/1.1 (or later) proxy and
1952   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1953   conformance with the protocol would have necessitated a possibly
1954   infinite buffer on the proxy.
1955</t>
1956<t>
1957   A process for decoding the "chunked" transfer-coding
1958   can be represented in pseudo-code as:
1959</t>
1960<figure><artwork type="code">
1961  length := 0
1962  read chunk-size, chunk-ext (if any) and CRLF
1963  while (chunk-size &gt; 0) {
1964     read chunk-data and CRLF
1965     append chunk-data to decoded-body
1966     length := length + chunk-size
1967     read chunk-size and CRLF
1968  }
1969  read header-field
1970  while (header-field not empty) {
1971     append header-field to existing header fields
1972     read header-field
1973  }
1974  Content-Length := length
1975  Remove "chunked" from Transfer-Encoding
1976</artwork></figure>
1977<t>
1978   All HTTP/1.1 applications &MUST; be able to receive and decode the
1979   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
1980   they do not understand.
1981</t>
1982<t>
1983   Use of chunk-ext extensions by senders is deprecated; they &SHOULD-NOT; be
1984   sent and definition of new chunk-extensions is discouraged.
1985</t>
1986</section>
1987
1988<section title="Compression Codings" anchor="compression.codings">
1989<t>
1990   The codings defined below can be used to compress the payload of a
1991   message.
1992</t>
1993<x:note><t>
1994   &Note; Use of program names for the identification of encoding formats
1995   is not desirable and is discouraged for future encodings. Their
1996   use here is representative of historical practice, not good
1997   design.
1998</t></x:note>
1999<x:note><t>
2000   &Note; For compatibility with previous implementations of HTTP,
2001   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2002   equivalent to "gzip" and "compress" respectively.
2003</t></x:note>
2004
2005<section title="Compress Coding" anchor="compress.coding">
2006<iref item="compress (Coding Format)"/>
2007<iref item="Coding Format" subitem="compress"/>
2008<t>
2009   The "compress" format is produced by the common UNIX file compression
2010   program "compress". This format is an adaptive Lempel-Ziv-Welch
2011   coding (LZW).
2012</t>
2013</section>
2014
2015<section title="Deflate Coding" anchor="deflate.coding">
2016<iref item="deflate (Coding Format)"/>
2017<iref item="Coding Format" subitem="deflate"/>
2018<t>
2019   The "deflate" format is defined as the "deflate" compression mechanism
2020   (described in <xref target="RFC1951"/>) used inside the "zlib"
2021   data format (<xref target="RFC1950"/>).
2022</t>
2023<x:note>
2024  <t>
2025    &Note; Some incorrect implementations send the "deflate"
2026    compressed data without the zlib wrapper.
2027   </t>
2028</x:note>
2029</section>
2030
2031<section title="Gzip Coding" anchor="gzip.coding">
2032<iref item="gzip (Coding Format)"/>
2033<iref item="Coding Format" subitem="gzip"/>
2034<t>
2035   The "gzip" format is produced by the file compression program
2036   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2037   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2038</t>
2039</section>
2040
2041</section>
2042
2043<section title="TE" anchor="header.te">
2044  <iref primary="true" item="TE header field" x:for-anchor=""/>
2045  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
2046  <x:anchor-alias value="TE"/>
2047  <x:anchor-alias value="t-codings"/>
2048  <x:anchor-alias value="te-params"/>
2049  <x:anchor-alias value="te-ext"/>
2050<t>
2051   The "TE" header field indicates what extension transfer-codings
2052   the client is willing to accept in the response, and whether or not it is
2053   willing to accept trailer fields in a chunked transfer-coding.
2054</t>
2055<t>
2056   Its value consists of the keyword "trailers" and/or a comma-separated
2057   list of extension transfer-coding names with optional accept
2058   parameters (as described in <xref target="transfer.codings"/>).
2059</t>
2060<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
2061  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2062  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2063  <x:ref>te-params</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>te-ext</x:ref> )
2064  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
2065</artwork></figure>
2066<t>
2067   The presence of the keyword "trailers" indicates that the client is
2068   willing to accept trailer fields in a chunked transfer-coding, as
2069   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
2070   transfer-coding values even though it does not itself represent a
2071   transfer-coding.
2072</t>
2073<t>
2074   Examples of its use are:
2075</t>
2076<figure><artwork type="example">
2077  TE: deflate
2078  TE:
2079  TE: trailers, deflate;q=0.5
2080</artwork></figure>
2081<t>
2082   The TE header field only applies to the immediate connection.
2083   Therefore, the keyword &MUST; be supplied within a <x:ref>Connection</x:ref>
2084   header field (<xref target="header.connection"/>) whenever TE is present in
2085   an HTTP/1.1 message.
2086</t>
2087<t>
2088   A server tests whether a transfer-coding is acceptable, according to
2089   a TE field, using these rules:
2090  <list style="numbers">
2091    <x:lt>
2092      <t>The "chunked" transfer-coding is always acceptable. If the
2093         keyword "trailers" is listed, the client indicates that it is
2094         willing to accept trailer fields in the chunked response on
2095         behalf of itself and any downstream clients. The implication is
2096         that, if given, the client is stating that either all
2097         downstream clients are willing to accept trailer fields in the
2098         forwarded response, or that it will attempt to buffer the
2099         response on behalf of downstream recipients.
2100      </t><t>
2101         &Note; HTTP/1.1 does not define any means to limit the size of a
2102         chunked response such that a client can be assured of buffering
2103         the entire response.</t>
2104    </x:lt>
2105    <x:lt>
2106      <t>If the transfer-coding being tested is one of the transfer-codings
2107         listed in the TE field, then it is acceptable unless it
2108         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2109         qvalue of 0 means "not acceptable".)</t>
2110    </x:lt>
2111    <x:lt>
2112      <t>If multiple transfer-codings are acceptable, then the
2113         acceptable transfer-coding with the highest non-zero qvalue is
2114         preferred.  The "chunked" transfer-coding always has a qvalue
2115         of 1.</t>
2116    </x:lt>
2117  </list>
2118</t>
2119<t>
2120   If the TE field-value is empty or if no TE field is present, the only
2121   acceptable transfer-coding is "chunked". A message with no transfer-coding is
2122   always acceptable.
2123</t>
2124
2125<section title="Quality Values" anchor="quality.values">
2126  <x:anchor-alias value="qvalue"/>
2127<t>
2128   Both transfer codings (<x:ref>TE</x:ref> request header field,
2129   <xref target="header.te"/>) and content negotiation (&content.negotiation;)
2130   use short "floating point" numbers to indicate the relative importance
2131   ("weight") of various negotiable parameters.  A weight is normalized to a
2132   real number in the range 0 through 1, where 0 is the minimum and 1 the
2133   maximum value. If a parameter has a quality value of 0, then content with
2134   this parameter is "not acceptable" for the client. HTTP/1.1
2135   applications &MUST-NOT; generate more than three digits after the
2136   decimal point. User configuration of these values &SHOULD; also be
2137   limited in this fashion.
2138</t>
2139<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2140  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2141                 / ( "1" [ "." 0*3("0") ] )
2142</artwork></figure>
2143<x:note>
2144  <t>
2145     &Note; "Quality values" is a misnomer, since these values merely represent
2146     relative degradation in desired quality.
2147  </t>
2148</x:note>
2149</section>
2150</section>
2151
2152<section title="Trailer" anchor="header.trailer">
2153  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
2154  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
2155  <x:anchor-alias value="Trailer"/>
2156<t>
2157   The "Trailer" header field indicates that the given set of
2158   header fields is present in the trailer of a message encoded with
2159   chunked transfer-coding.
2160</t>
2161<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2162  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
2163</artwork></figure>
2164<t>
2165   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2166   message using chunked transfer-coding with a non-empty trailer. Doing
2167   so allows the recipient to know which header fields to expect in the
2168   trailer.
2169</t>
2170<t>
2171   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2172   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
2173   trailer fields in a "chunked" transfer-coding.
2174</t>
2175<t>
2176   Message header fields listed in the Trailer header field &MUST-NOT;
2177   include the following header fields:
2178  <list style="symbols">
2179    <t><x:ref>Transfer-Encoding</x:ref></t>
2180    <t><x:ref>Content-Length</x:ref></t>
2181    <t><x:ref>Trailer</x:ref></t>
2182  </list>
2183</t>
2184</section>
2185</section>
2186
2187<section title="Message Routing" anchor="message.routing">
2188<t>
2189   HTTP request message routing is determined by each client based on the
2190   target resource, the client's proxy configuration, and
2191   establishment or reuse of an inbound connection.  The corresponding
2192   response routing follows the same connection chain back to the client.
2193</t>
2194
2195<section title="Identifying a Target Resource" anchor="target-resource">
2196  <iref primary="true" item="target resource"/>
2197  <iref primary="true" item="target URI"/>
2198<t>
2199   HTTP is used in a wide variety of applications, ranging from
2200   general-purpose computers to home appliances.  In some cases,
2201   communication options are hard-coded in a client's configuration.
2202   However, most HTTP clients rely on the same resource identification
2203   mechanism and configuration techniques as general-purpose Web browsers.
2204</t>
2205<t>
2206   HTTP communication is initiated by a user agent for some purpose.
2207   The purpose is a combination of request semantics, which are defined in
2208   <xref target="Part2"/>, and a target resource upon which to apply those
2209   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2210   an identifier for the "target resource", which a user agent would resolve
2211   to its absolute form in order to obtain the "target URI".  The target URI
2212   excludes the reference's fragment identifier component, if any,
2213   since fragment identifiers are reserved for client-side processing
2214   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2215</t>
2216<t>
2217   HTTP intermediaries obtain the request semantics and target URI
2218   from the request-line of an incoming request message.
2219</t>
2220</section>
2221
2222<section title="Connecting Inbound" anchor="connecting.inbound">
2223<t>
2224   Once the target URI is determined, a client needs to decide whether
2225   a network request is necessary to accomplish the desired semantics and,
2226   if so, where that request is to be directed.
2227</t>
2228<t>
2229   If the client has a response cache and the request semantics can be
2230   satisfied by a cache (<xref target="Part6"/>), then the request is
2231   usually directed to the cache first.
2232</t>
2233<t>
2234   If the request is not satisfied by a cache, then a typical client will
2235   check its configuration to determine whether a proxy is to be used to
2236   satisfy the request.  Proxy configuration is implementation-dependent,
2237   but is often based on URI prefix matching, selective authority matching,
2238   or both, and the proxy itself is usually identified by an "http" or
2239   "https" URI.  If a proxy is applicable, the client connects inbound by
2240   establishing (or reusing) a connection to that proxy.
2241</t>
2242<t>
2243   If no proxy is applicable, a typical client will invoke a handler routine,
2244   usually specific to the target URI's scheme, to connect directly
2245   to an authority for the target resource.  How that is accomplished is
2246   dependent on the target URI scheme and defined by its associated
2247   specification, similar to how this specification defines origin server
2248   access for resolution of the "http" (<xref target="http.uri"/>) and
2249   "https" (<xref target="https.uri"/>) schemes.
2250</t>
2251</section>
2252
2253<section title="Request Target" anchor="request-target">
2254<t>
2255   Once an inbound connection is obtained
2256   (<xref target="connection.management"/>),
2257   the client sends an HTTP request message (<xref target="http.message"/>)
2258   with a request-target derived from the target URI.
2259   There are four distinct formats for the request-target, depending on both
2260   the method being requested and whether the request is to a proxy.
2261</t>   
2262<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/><iref primary="true" item="Grammar" subitem="origin-form"/><iref primary="true" item="Grammar" subitem="absolute-form"/><iref primary="true" item="Grammar" subitem="authority-form"/><iref primary="true" item="Grammar" subitem="asterisk-form"/>
2263  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2264                 / <x:ref>absolute-form</x:ref>
2265                 / <x:ref>authority-form</x:ref>
2266                 / <x:ref>asterisk-form</x:ref>
2267
2268  <x:ref>origin-form</x:ref>    = <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]
2269  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2270  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2271  <x:ref>asterisk-form</x:ref>  = "*"
2272</artwork></figure>
2273<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2274   The most common form of request-target is the origin-form.
2275   When making a request directly to an origin server, other than a CONNECT
2276   or server-wide OPTIONS request (as detailed below),
2277   a client &MUST; send only the absolute path and query components of
2278   the target URI as the request-target.
2279   If the target URI's path component is empty, then the client &MUST; send
2280   "/" as the path within the origin-form of request-target.
2281   A <x:ref>Host</x:ref> header field is also sent, as defined in
2282   <xref target="header.host"/>, containing the target URI's
2283   authority component (excluding any userinfo).
2284</t>
2285<t>
2286   For example, a client wishing to retrieve a representation of the resource
2287   identified as
2288</t>
2289<figure><artwork x:indent-with="  " type="example">
2290http://www.example.org/where?q=now
2291</artwork></figure>
2292<t>
2293   directly from the origin server would open (or reuse) a TCP connection
2294   to port 80 of the host "www.example.org" and send the lines:
2295</t>
2296<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2297GET /where?q=now HTTP/1.1
2298Host: www.example.org
2299</artwork></figure>
2300<t>
2301   followed by the remainder of the request message.
2302</t>
2303<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2304   When making a request to a proxy, other than a CONNECT or server-wide
2305   OPTIONS request (as detailed below), a client &MUST; send the target URI
2306   in absolute-form as the request-target.
2307   The proxy is requested to either service that request from a valid cache,
2308   if possible, or make the same request on the client's behalf to either
2309   the next inbound proxy server or directly to the origin server indicated
2310   by the request-target.  Requirements on such "forwarding" of messages are
2311   defined in <xref target="intermediary.forwarding"/>.
2312</t>
2313<t>
2314   An example absolute-form of request-line would be:
2315</t>
2316<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2317GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
2318</artwork></figure>
2319<t>
2320   To allow for transition to the absolute-form for all requests in some
2321   future version of HTTP, HTTP/1.1 servers &MUST; accept the absolute-form
2322   in requests, even though HTTP/1.1 clients will only send them in requests
2323   to proxies.
2324</t>
2325<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2326   The authority-form of request-target is only used for CONNECT requests
2327   (&CONNECT;).  When making a CONNECT request to establish a tunnel through
2328   one or more proxies, a client &MUST; send only the target URI's
2329   authority component (excluding any userinfo) as the request-target.
2330   For example,
2331</t>
2332<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2333CONNECT www.example.com:80 HTTP/1.1
2334</artwork></figure>
2335<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2336   The asterisk-form of request-target is only used for a server-wide
2337   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2338   for the server as a whole, as opposed to a specific named resource of
2339   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2340   For example,
2341</t>
2342<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2343OPTIONS * HTTP/1.1
2344</artwork></figure>
2345<t>
2346   If a proxy receives an OPTIONS request with an absolute-form of
2347   request-target in which the URI has an empty path and no query component,
2348   then the last proxy on the request chain &MUST; send a request-target
2349   of "*" when it forwards the request to the indicated origin server.
2350</t>
2351<figure><preamble>   
2352   For example, the request
2353</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2354OPTIONS http://www.example.org:8001 HTTP/1.1
2355</artwork></figure>
2356<figure><preamble>   
2357  would be forwarded by the final proxy as
2358</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2359OPTIONS * HTTP/1.1
2360Host: www.example.org:8001
2361</artwork>
2362<postamble>
2363   after connecting to port 8001 of host "www.example.org".
2364</postamble>
2365</figure>
2366</section>
2367
2368<section title="Host" anchor="header.host">
2369  <iref primary="true" item="Host header field" x:for-anchor=""/>
2370  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
2371  <x:anchor-alias value="Host"/>
2372<t>
2373   The "Host" header field in a request provides the host and port
2374   information from the target URI, enabling the origin
2375   server to distinguish among resources while servicing requests
2376   for multiple host names on a single IP address.  Since the Host
2377   field-value is critical information for handling a request, it
2378   &SHOULD; be sent as the first header field following the request-line.
2379</t>
2380<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2381  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2382</artwork></figure>
2383<t>
2384   A client &MUST; send a Host header field in all HTTP/1.1 request
2385   messages.  If the target URI includes an authority component, then
2386   the Host field-value &MUST; be identical to that authority component
2387   after excluding any userinfo (<xref target="http.uri"/>).
2388   If the authority component is missing or undefined for the target URI,
2389   then the Host header field &MUST; be sent with an empty field-value.
2390</t>
2391<t>
2392   For example, a GET request to the origin server for
2393   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
2394</t>
2395<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2396GET /pub/WWW/ HTTP/1.1
2397Host: www.example.org
2398</artwork></figure>
2399<t>
2400   The Host header field &MUST; be sent in an HTTP/1.1 request even
2401   if the request-target is in the absolute-form, since this
2402   allows the Host information to be forwarded through ancient HTTP/1.0
2403   proxies that might not have implemented Host.
2404</t>
2405<t>
2406   When an HTTP/1.1 proxy receives a request with an absolute-form of
2407   request-target, the proxy &MUST; ignore the received
2408   Host header field (if any) and instead replace it with the host
2409   information of the request-target.  If the proxy forwards the request,
2410   it &MUST; generate a new Host field-value based on the received
2411   request-target rather than forward the received Host field-value.
2412</t>
2413<t>
2414   Since the Host header field acts as an application-level routing
2415   mechanism, it is a frequent target for malware seeking to poison
2416   a shared cache or redirect a request to an unintended server.
2417   An interception proxy is particularly vulnerable if it relies on
2418   the Host field-value for redirecting requests to internal
2419   servers, or for use as a cache key in a shared cache, without
2420   first verifying that the intercepted connection is targeting a
2421   valid IP address for that host.
2422</t>
2423<t>
2424   A server &MUST; respond with a <x:ref>400 (Bad Request)</x:ref> status code
2425   to any HTTP/1.1 request message that lacks a Host header field and
2426   to any request message that contains more than one Host header field
2427   or a Host header field with an invalid field-value.
2428</t>
2429</section>
2430
2431<section title="Effective Request URI" anchor="effective.request.uri">
2432  <iref primary="true" item="effective request URI"/>
2433<t>
2434   A server that receives an HTTP request message &MUST; reconstruct
2435   the user agent's original target URI, based on the pieces of information
2436   learned from the request-target, <x:ref>Host</x:ref> header field, and
2437   connection context, in order to identify the intended target resource and
2438   properly service the request. The URI derived from this reconstruction
2439   process is referred to as the "effective request URI".
2440</t>
2441<t>
2442   For a user agent, the effective request URI is the target URI.
2443</t>
2444<t>
2445   If the request-target is in absolute-form, then the effective request URI
2446   is the same as the request-target.  Otherwise, the effective request URI
2447   is constructed as follows.
2448</t>
2449<t>
2450   If the request is received over an SSL/TLS-secured TCP connection,
2451   then the effective request URI's scheme is "https"; otherwise, the
2452   scheme is "http".
2453</t>
2454<t>
2455   If the request-target is in authority-form, then the effective
2456   request URI's authority component is the same as the request-target.
2457   Otherwise, if a <x:ref>Host</x:ref> header field is supplied with a
2458   non-empty field-value, then the authority component is the same as the
2459   Host field-value. Otherwise, the authority component is the concatenation of
2460   the default host name configured for the server, a colon (":"), and the
2461   connection's incoming TCP port number in decimal form.
2462</t>
2463<t>
2464   If the request-target is in authority-form or asterisk-form, then the
2465   effective request URI's combined path and query component is empty.
2466   Otherwise, the combined path and query component is the same as the
2467   request-target.
2468</t>
2469<t>
2470   The components of the effective request URI, once determined as above,
2471   can be combined into absolute-URI form by concatenating the scheme,
2472   "://", authority, and combined path and query component.
2473</t>
2474<figure>
2475<preamble>
2476   Example 1: the following message received over an insecure TCP connection
2477</preamble> 
2478<artwork type="example" x:indent-with="  ">
2479GET /pub/WWW/TheProject.html HTTP/1.1
2480Host: www.example.org:8080
2481</artwork>
2482</figure>
2483<figure>
2484<preamble>
2485  has an effective request URI of
2486</preamble>
2487<artwork type="example" x:indent-with="  ">
2488http://www.example.org:8080/pub/WWW/TheProject.html
2489</artwork>
2490</figure>
2491<figure>
2492<preamble>
2493   Example 2: the following message received over an SSL/TLS-secured TCP
2494   connection
2495</preamble> 
2496<artwork type="example" x:indent-with="  ">
2497OPTIONS * HTTP/1.1
2498Host: www.example.org
2499</artwork>
2500</figure>
2501<figure>
2502<preamble>
2503  has an effective request URI of
2504</preamble>
2505<artwork type="example" x:indent-with="  ">
2506https://www.example.org
2507</artwork>
2508</figure>
2509<t>
2510   An origin server that does not allow resources to differ by requested
2511   host &MAY; ignore the <x:ref>Host</x:ref> field-value and instead replace it
2512   with a configured server name when constructing the effective request URI.
2513</t>
2514<t>
2515   Recipients of an HTTP/1.0 request that lacks a <x:ref>Host</x:ref> header
2516   field &MAY; attempt to use heuristics (e.g., examination of the URI path for
2517   something unique to a particular host) in order to guess the
2518   effective request URI's authority component.
2519</t>
2520</section>
2521
2522<section title="Intermediary Forwarding" anchor="intermediary.forwarding">
2523<t>
2524   As described in <xref target="intermediaries"/>, intermediaries can serve
2525   a variety of roles in the processing of HTTP requests and responses.
2526   Some intermediaries are used to improve performance or availability.
2527   Others are used for access control or to filter content.
2528   Since an HTTP stream has characteristics similar to a pipe-and-filter
2529   architecture, there are no inherent limits to the extent an intermediary
2530   can enhance (or interfere) with either direction of the stream.
2531</t>
2532<t>
2533   In order to avoid request loops, a proxy that forwards requests to other
2534   proxies &MUST; be able to recognize and exclude all of its own server
2535   names, including any aliases, local variations, or literal IP addresses.
2536</t>
2537<t>
2538   If a proxy receives a request-target with a host name that is not a
2539   fully qualified domain name, it &MAY; add its domain to the host name
2540   it received when forwarding the request.  A proxy &MUST-NOT; change the
2541   host name if it is a fully qualified domain name.
2542</t>
2543<t>
2544   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" and "query"
2545   parts of the received request-target when forwarding it to the next inbound
2546   server, except as noted above to replace an empty path with "/" or "*".
2547</t>
2548<t>
2549   Intermediaries that forward a message &MUST; implement the
2550   <x:ref>Connection</x:ref> header field as specified in
2551   <xref target="header.connection"/>.
2552</t>
2553
2554<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2555<!--<t>
2556  <cref anchor="TODO-end-to-end" source="jre">
2557    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2558    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2559  </cref>
2560</t>-->
2561<t>
2562   For the purpose of defining the behavior of caches and non-caching
2563   proxies, we divide HTTP header fields into two categories:
2564  <list style="symbols">
2565      <t>End-to-end header fields, which are  transmitted to the ultimate
2566        recipient of a request or response. End-to-end header fields in
2567        responses &MUST; be stored as part of a cache entry and &MUST; be
2568        transmitted in any response formed from a cache entry.</t>
2569
2570      <t>Hop-by-hop header fields, which are meaningful only for a single
2571        transport-level connection, and are not stored by caches or
2572        forwarded by proxies.</t>
2573  </list>
2574</t>
2575<t>
2576   The following HTTP/1.1 header fields are hop-by-hop header fields:
2577  <list style="symbols">
2578      <t><x:ref>Connection</x:ref></t>
2579      <t>Keep-Alive (<xref target="RFC2068" x:fmt="of" x:sec="19.7.1.1"/>)</t>
2580      <t><x:ref>Proxy-Authenticate</x:ref> (&header-proxy-authenticate;)</t>
2581      <t><x:ref>Proxy-Authorization</x:ref> (&header-proxy-authorization;)</t>
2582      <t><x:ref>TE</x:ref></t>
2583      <t><x:ref>Trailer</x:ref></t>
2584      <t><x:ref>Transfer-Encoding</x:ref></t>
2585      <t><x:ref>Upgrade</x:ref></t>
2586  </list>
2587</t>
2588<t>
2589   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2590</t>
2591<t>
2592   Other hop-by-hop header fields &MUST; be listed in a
2593   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>).
2594</t>
2595</section>
2596
2597<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2598<!--<t>
2599  <cref anchor="TODO-non-mod-headers" source="jre">
2600    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2601    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2602  </cref>
2603</t>-->
2604<t>
2605   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2606   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2607   modify an end-to-end header field unless the definition of that header field requires
2608   or specifically allows that.
2609</t>
2610<t>
2611   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2612   request or response, and it &MUST-NOT; add any of these fields if not
2613   already present:
2614  <list style="symbols">
2615    <t>Allow</t>
2616    <t>Content-Location</t>
2617    <t>Content-MD5</t>
2618    <t>ETag</t>
2619    <t>Last-Modified</t>
2620    <t>Server</t>
2621  </list>
2622</t>
2623<t>
2624   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2625   response:
2626  <list style="symbols">
2627    <t><x:ref>Expires</x:ref> (&header-expires;)</t>
2628  </list>
2629</t>
2630<t>
2631   but it &MAY; add any of these fields if not already present. If an
2632   <x:ref>Expires</x:ref> header field is added, it &MUST; be given a
2633   field value identical to that of the <x:ref>Date</x:ref> header field in
2634   that response.
2635</t>
2636<t>
2637   A proxy &MUST-NOT; modify or add any of the following fields in a
2638   message that contains the no-transform cache-control directive, or in
2639   any request:
2640  <list style="symbols">
2641    <t><x:ref>Content-Encoding</x:ref> (&header-content-encoding;)</t>
2642    <t><x:ref>Content-Range</x:ref> (&header-content-range;)</t>
2643    <t><x:ref>Content-Type</x:ref> (&header-content-type;)</t>
2644  </list>
2645</t>
2646<t>
2647   A transforming proxy &MAY; modify or add these fields to a message
2648   that does not include no-transform, but if it does so, it &MUST; add a
2649   Warning 214 (Transformation applied) if one does not already appear
2650   in the message (see &header-warning;).
2651</t>
2652<x:note>
2653  <t>
2654    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2655    cause authentication failures if stronger authentication
2656    mechanisms are introduced in later versions of HTTP. Such
2657    authentication mechanisms &MAY; rely on the values of header fields
2658    not listed here.
2659  </t>
2660</x:note>
2661<t>
2662   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2663   though it &MAY; change the message body through application or removal
2664   of a transfer-coding (<xref target="transfer.codings"/>).
2665</t>
2666</section>
2667
2668</section>
2669
2670<section title="Associating a Response to a Request" anchor="associating.response.to.request">
2671<t>
2672   HTTP does not include a request identifier for associating a given
2673   request message with its corresponding one or more response messages.
2674   Hence, it relies on the order of response arrival to correspond exactly
2675   to the order in which requests are made on the same connection.
2676   More than one response message per request only occurs when one or more
2677   informational responses (<x:ref>1xx</x:ref>, see &status-1xx;) precede a final response
2678   to the same request.
2679</t>
2680<t>
2681   A client that uses persistent connections and sends more than one request
2682   per connection &MUST; maintain a list of outstanding requests in the
2683   order sent on that connection and &MUST; associate each received response
2684   message to the highest ordered request that has not yet received a final
2685   (non-<x:ref>1xx</x:ref>) response.
2686</t>
2687</section>
2688</section>
2689
2690<section title="Connection Management" anchor="connection.management">
2691
2692<section title="Connection" anchor="header.connection">
2693  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2694  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2695  <x:anchor-alias value="Connection"/>
2696  <x:anchor-alias value="connection-option"/>
2697<t>
2698   The "Connection" header field allows the sender to specify
2699   options that are desired only for that particular connection.
2700   Such connection options &MUST; be removed or replaced before the
2701   message can be forwarded downstream by a proxy or gateway.
2702   This mechanism also allows the sender to indicate which HTTP
2703   header fields used in the message are only intended for the
2704   immediate recipient ("hop-by-hop"), as opposed to all recipients
2705   on the chain ("end-to-end"), enabling the message to be
2706   self-descriptive and allowing future connection-specific extensions
2707   to be deployed in HTTP without fear that they will be blindly
2708   forwarded by previously deployed intermediaries.
2709</t>
2710<t>
2711   The Connection header field's value has the following grammar:
2712</t>
2713<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-option"/>
2714  <x:ref>Connection</x:ref>        = 1#<x:ref>connection-option</x:ref>
2715  <x:ref>connection-option</x:ref> = <x:ref>token</x:ref>
2716</artwork></figure>
2717<t>
2718   Connection options are compared case-insensitively.
2719</t>
2720<t>
2721   A proxy or gateway &MUST; parse a received Connection
2722   header field before a message is forwarded and, for each
2723   connection-option in this field, remove any header field(s) from
2724   the message with the same name as the connection-option, and then
2725   remove the Connection header field itself or replace it with the
2726   sender's own connection options for the forwarded message.
2727</t>
2728<t>
2729   A sender &MUST-NOT; include field-names in the Connection header
2730   field-value for fields that are defined as expressing constraints
2731   for all recipients in the request or response chain, such as the
2732   Cache-Control header field (&header-cache-control;).
2733</t>
2734<t>
2735   The connection options do not have to correspond to a header field
2736   present in the message, since a connection-specific header field
2737   might not be needed if there are no parameters associated with that
2738   connection option.  Recipients that trigger certain connection
2739   behavior based on the presence of connection options &MUST; do so
2740   based on the presence of the connection-option rather than only the
2741   presence of the optional header field.  In other words, if the
2742   connection option is received as a header field but not indicated
2743   within the Connection field-value, then the recipient &MUST; ignore
2744   the connection-specific header field because it has likely been
2745   forwarded by an intermediary that is only partially conformant.
2746</t>
2747<t>
2748   When defining new connection options, specifications ought to
2749   carefully consider existing deployed header fields and ensure
2750   that the new connection option does not share the same name as
2751   an unrelated header field that might already be deployed.
2752   Defining a new connection option essentially reserves that potential
2753   field-name for carrying additional information related to the
2754   connection option, since it would be unwise for senders to use
2755   that field-name for anything else.
2756</t>
2757<t>
2758   HTTP/1.1 defines the "close" connection option for the sender to
2759   signal that the connection will be closed after completion of the
2760   response. For example,
2761</t>
2762<figure><artwork type="example">
2763  Connection: close
2764</artwork></figure>
2765<t>
2766   in either the request or the response header fields indicates that
2767   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2768   after the current request/response is complete.
2769</t>
2770<t>
2771   An HTTP/1.1 client that does not support persistent connections &MUST;
2772   include the "close" connection option in every request message.
2773</t>
2774<t>
2775   An HTTP/1.1 server that does not support persistent connections &MUST;
2776   include the "close" connection option in every response message that
2777   does not have a <x:ref>1xx (Informational)</x:ref> status code.
2778</t>
2779</section>
2780
2781<section title="Via" anchor="header.via">
2782  <iref primary="true" item="Via header field" x:for-anchor=""/>
2783  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
2784  <x:anchor-alias value="pseudonym"/>
2785  <x:anchor-alias value="received-by"/>
2786  <x:anchor-alias value="received-protocol"/>
2787  <x:anchor-alias value="Via"/>
2788<t>
2789   The "Via" header field &MUST; be sent by a proxy or gateway to
2790   indicate the intermediate protocols and recipients between the user
2791   agent and the server on requests, and between the origin server and
2792   the client on responses. It is analogous to the "Received" field
2793   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
2794   and is intended to be used for tracking message forwards,
2795   avoiding request loops, and identifying the protocol capabilities of
2796   all senders along the request/response chain.
2797</t>
2798<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/>
2799  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2800                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2801  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2802  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2803  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2804</artwork></figure>
2805<t>
2806   The received-protocol indicates the protocol version of the message
2807   received by the server or client along each segment of the
2808   request/response chain. The received-protocol version is appended to
2809   the Via field value when the message is forwarded so that information
2810   about the protocol capabilities of upstream applications remains
2811   visible to all recipients.
2812</t>
2813<t>
2814   The protocol-name is excluded if and only if it would be "HTTP". The
2815   received-by field is normally the host and optional port number of a
2816   recipient server or client that subsequently forwarded the message.
2817   However, if the real host is considered to be sensitive information,
2818   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2819   be assumed to be the default port of the received-protocol.
2820</t>
2821<t>
2822   Multiple Via field values represent each proxy or gateway that has
2823   forwarded the message. Each recipient &MUST; append its information
2824   such that the end result is ordered according to the sequence of
2825   forwarding applications.
2826</t>
2827<t>
2828   Comments &MAY; be used in the Via header field to identify the software
2829   of each recipient, analogous to the <x:ref>User-Agent</x:ref> and
2830   <x:ref>Server</x:ref> header fields. However, all comments in the Via field
2831   are optional and &MAY; be removed by any recipient prior to forwarding the
2832   message.
2833</t>
2834<t>
2835   For example, a request message could be sent from an HTTP/1.0 user
2836   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2837   forward the request to a public proxy at p.example.net, which completes
2838   the request by forwarding it to the origin server at www.example.com.
2839   The request received by www.example.com would then have the following
2840   Via header field:
2841</t>
2842<figure><artwork type="example">
2843  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2844</artwork></figure>
2845<t>
2846   A proxy or gateway used as a portal through a network firewall
2847   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2848   region unless it is explicitly enabled to do so. If not enabled, the
2849   received-by host of any host behind the firewall &SHOULD; be replaced
2850   by an appropriate pseudonym for that host.
2851</t>
2852<t>
2853   For organizations that have strong privacy requirements for hiding
2854   internal structures, a proxy or gateway &MAY; combine an ordered
2855   subsequence of Via header field entries with identical received-protocol
2856   values into a single such entry. For example,
2857</t>
2858<figure><artwork type="example">
2859  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2860</artwork></figure>
2861<t>
2862  could be collapsed to
2863</t>
2864<figure><artwork type="example">
2865  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2866</artwork></figure>
2867<t>
2868   Senders &SHOULD-NOT; combine multiple entries unless they are all
2869   under the same organizational control and the hosts have already been
2870   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
2871   have different received-protocol values.
2872</t>
2873</section>
2874
2875<section title="Persistent Connections" anchor="persistent.connections">
2876
2877<section title="Purpose" anchor="persistent.purpose">
2878<t>
2879   Prior to persistent connections, a separate TCP connection was
2880   established for each request, increasing the load on HTTP servers
2881   and causing congestion on the Internet. The use of inline images and
2882   other associated data often requires a client to make multiple
2883   requests of the same server in a short amount of time. Analysis of
2884   these performance problems and results from a prototype
2885   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2886   measurements of actual HTTP/1.1 implementations show good
2887   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2888   T/TCP <xref target="Tou1998"/>.
2889</t>
2890<t>
2891   Persistent HTTP connections have a number of advantages:
2892  <list style="symbols">
2893      <t>
2894        By opening and closing fewer TCP connections, CPU time is saved
2895        in routers and hosts (clients, servers, proxies, gateways,
2896        tunnels, or caches), and memory used for TCP protocol control
2897        blocks can be saved in hosts.
2898      </t>
2899      <t>
2900        HTTP requests and responses can be pipelined on a connection.
2901        Pipelining allows a client to make multiple requests without
2902        waiting for each response, allowing a single TCP connection to
2903        be used much more efficiently, with much lower elapsed time.
2904      </t>
2905      <t>
2906        Network congestion is reduced by reducing the number of packets
2907        caused by TCP opens, and by allowing TCP sufficient time to
2908        determine the congestion state of the network.
2909      </t>
2910      <t>
2911        Latency on subsequent requests is reduced since there is no time
2912        spent in TCP's connection opening handshake.
2913      </t>
2914      <t>
2915        HTTP can evolve more gracefully, since errors can be reported
2916        without the penalty of closing the TCP connection. Clients using
2917        future versions of HTTP might optimistically try a new feature,
2918        but if communicating with an older server, retry with old
2919        semantics after an error is reported.
2920      </t>
2921    </list>
2922</t>
2923<t>
2924   HTTP implementations &SHOULD; implement persistent connections.
2925</t>
2926</section>
2927
2928<section title="Overall Operation" anchor="persistent.overall">
2929<t>
2930   A significant difference between HTTP/1.1 and earlier versions of
2931   HTTP is that persistent connections are the default behavior of any
2932   HTTP connection. That is, unless otherwise indicated, the client
2933   &SHOULD; assume that the server will maintain a persistent connection,
2934   even after error responses from the server.
2935</t>
2936<t>
2937   Persistent connections provide a mechanism by which a client and a
2938   server can signal the close of a TCP connection. This signaling takes
2939   place using the <x:ref>Connection</x:ref> header field
2940   (<xref target="header.connection"/>). Once a close has been signaled, the
2941   client &MUST-NOT; send any more requests on that
2942   connection.
2943</t>
2944
2945<section title="Negotiation" anchor="persistent.negotiation">
2946<t>
2947   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2948   maintain a persistent connection unless a <x:ref>Connection</x:ref> header
2949   field including the connection option "close" was sent in the request. If
2950   the server chooses to close the connection immediately after sending the
2951   response, it &SHOULD; send a Connection header field including the
2952   connection option "close".
2953</t>
2954<t>
2955   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2956   decide to keep it open based on whether the response from a server
2957   contains a <x:ref>Connection</x:ref> header field with the connection option
2958   "close". In case the client does not want to maintain a connection for more
2959   than that request, it &SHOULD; send a Connection header field including the
2960   connection option "close".
2961</t>
2962<t>
2963   If either the client or the server sends the "close" option in the
2964   <x:ref>Connection</x:ref> header field, that request becomes the last one
2965   for the connection.
2966</t>
2967<t>
2968   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2969   maintained for HTTP versions less than 1.1 unless it is explicitly
2970   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2971   compatibility with HTTP/1.0 clients.
2972</t>
2973<t>
2974   Each persistent connection applies to only one transport link.
2975</t>
2976<t>
2977   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2978   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2979   for information and discussion of the problems with the Keep-Alive header field
2980   implemented by many HTTP/1.0 clients).
2981</t>
2982<t>
2983   In order to remain persistent, all messages on the connection &MUST;
2984   have a self-defined message length (i.e., one not defined by closure
2985   of the connection), as described in <xref target="message.body"/>.
2986</t>
2987</section>
2988
2989<section title="Pipelining" anchor="pipelining">
2990<t>
2991   A client that supports persistent connections &MAY; "pipeline" its
2992   requests (i.e., send multiple requests without waiting for each
2993   response). A server &MUST; send its responses to those requests in the
2994   same order that the requests were received.
2995</t>
2996<t>
2997   Clients which assume persistent connections and pipeline immediately
2998   after connection establishment &SHOULD; be prepared to retry their
2999   connection if the first pipelined attempt fails. If a client does
3000   such a retry, it &MUST-NOT; pipeline before it knows the connection is
3001   persistent. Clients &MUST; also be prepared to resend their requests if
3002   the server closes the connection before sending all of the
3003   corresponding responses.
3004</t>
3005<t>
3006   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
3007   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
3008   premature termination of the transport connection could lead to
3009   indeterminate results. A client wishing to send a non-idempotent
3010   request &SHOULD; wait to send that request until it has received the
3011   response status line for the previous request.
3012</t>
3013</section>
3014</section>
3015
3016<section title="Practical Considerations" anchor="persistent.practical">
3017<t>
3018   Servers will usually have some time-out value beyond which they will
3019   no longer maintain an inactive connection. Proxy servers might make
3020   this a higher value since it is likely that the client will be making
3021   more connections through the same server. The use of persistent
3022   connections places no requirements on the length (or existence) of
3023   this time-out for either the client or the server.
3024</t>
3025<t>
3026   When a client or server wishes to time-out it &SHOULD; issue a graceful
3027   close on the transport connection. Clients and servers &SHOULD; both
3028   constantly watch for the other side of the transport close, and
3029   respond to it as appropriate. If a client or server does not detect
3030   the other side's close promptly it could cause unnecessary resource
3031   drain on the network.
3032</t>
3033<t>
3034   A client, server, or proxy &MAY; close the transport connection at any
3035   time. For example, a client might have started to send a new request
3036   at the same time that the server has decided to close the "idle"
3037   connection. From the server's point of view, the connection is being
3038   closed while it was idle, but from the client's point of view, a
3039   request is in progress.
3040</t>
3041<t>
3042   Clients (including proxies) &SHOULD; limit the number of simultaneous
3043   connections that they maintain to a given server (including proxies).
3044</t>
3045<t>
3046   Previous revisions of HTTP gave a specific number of connections as a
3047   ceiling, but this was found to be impractical for many applications. As a
3048   result, this specification does not mandate a particular maximum number of
3049   connections, but instead encourages clients to be conservative when opening
3050   multiple connections.
3051</t>
3052<t>
3053   In particular, while using multiple connections avoids the "head-of-line
3054   blocking" problem (whereby a request that takes significant server-side
3055   processing and/or has a large payload can block subsequent requests on the
3056   same connection), each connection used consumes server resources (sometimes
3057   significantly), and furthermore using multiple connections can cause
3058   undesirable side effects in congested networks.
3059</t>
3060<t>
3061   Note that servers might reject traffic that they deem abusive, including an
3062   excessive number of connections from a client.
3063</t>
3064</section>
3065
3066<section title="Retrying Requests" anchor="persistent.retrying.requests">
3067<t>
3068   Senders can close the transport connection at any time. Therefore,
3069   clients, servers, and proxies &MUST; be able to recover
3070   from asynchronous close events. Client software &MAY; reopen the
3071   transport connection and retransmit the aborted sequence of requests
3072   without user interaction so long as the request sequence is
3073   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
3074   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
3075   human operator the choice of retrying the request(s). Confirmation by
3076   user-agent software with semantic understanding of the application
3077   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
3078   be repeated if the second sequence of requests fails.
3079</t>
3080</section>
3081</section>
3082
3083<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
3084
3085<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
3086<t>
3087   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
3088   flow control mechanisms to resolve temporary overloads, rather than
3089   terminating connections with the expectation that clients will retry.
3090   The latter technique can exacerbate network congestion.
3091</t>
3092</section>
3093
3094<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
3095<t>
3096   An HTTP/1.1 (or later) client sending a message body &SHOULD; monitor
3097   the network connection for an error status code while it is transmitting
3098   the request. If the client sees an error status code, it &SHOULD;
3099   immediately cease transmitting the body. If the body is being sent
3100   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
3101   empty trailer &MAY; be used to prematurely mark the end of the message.
3102   If the body was preceded by a Content-Length header field, the client &MUST;
3103   close the connection.
3104</t>
3105</section>
3106
3107<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
3108<t>
3109   The purpose of the <x:ref>100 (Continue)</x:ref> status code (see &status-100;)
3110   is to allow a client that is sending a request message with a request body
3111   to determine if the origin server is willing to accept the request
3112   (based on the request header fields) before the client sends the request
3113   body. In some cases, it might either be inappropriate or highly
3114   inefficient for the client to send the body if the server will reject
3115   the message without looking at the body.
3116</t>
3117<t>
3118   Requirements for HTTP/1.1 clients:
3119  <list style="symbols">
3120    <t>
3121        If a client will wait for a <x:ref>100 (Continue)</x:ref> response before
3122        sending the request body, it &MUST; send an <x:ref>Expect</x:ref> header
3123        field (&header-expect;) with the "100-continue" expectation.
3124    </t>
3125    <t>
3126        A client &MUST-NOT; send an <x:ref>Expect</x:ref> header field with
3127        the "100-continue" expectation if it does not intend to send a request
3128        body.
3129    </t>
3130  </list>
3131</t>
3132<t>
3133   Because of the presence of older implementations, the protocol allows
3134   ambiguous situations in which a client might send "Expect: 100-continue"
3135   without receiving either a <x:ref>417 (Expectation Failed)</x:ref> 
3136   or a <x:ref>100 (Continue)</x:ref> status code. Therefore, when a client sends this
3137   header field to an origin server (possibly via a proxy) from which it
3138   has never seen a <x:ref>100 (Continue)</x:ref> status code, the client &SHOULD-NOT; 
3139   wait for an indefinite period before sending the request body.
3140</t>
3141<t>
3142   Requirements for HTTP/1.1 origin servers:
3143  <list style="symbols">
3144    <t> Upon receiving a request which includes an <x:ref>Expect</x:ref> header
3145        field with the "100-continue" expectation, an origin server &MUST;
3146        either respond with <x:ref>100 (Continue)</x:ref> status code and continue to read
3147        from the input stream, or respond with a final status code. The
3148        origin server &MUST-NOT; wait for the request body before sending
3149        the <x:ref>100 (Continue)</x:ref> response. If it responds with a final status
3150        code, it &MAY; close the transport connection or it &MAY; continue
3151        to read and discard the rest of the request.  It &MUST-NOT;
3152        perform the request method if it returns a final status code.
3153    </t>
3154    <t> An origin server &SHOULD-NOT;  send a <x:ref>100 (Continue)</x:ref> response if
3155        the request message does not include an <x:ref>Expect</x:ref> header
3156        field with the "100-continue" expectation, and &MUST-NOT; send a
3157        <x:ref>100 (Continue)</x:ref> response if such a request comes from an HTTP/1.0
3158        (or earlier) client. There is an exception to this rule: for
3159        compatibility with <xref target="RFC2068"/>, a server &MAY; send a <x:ref>100 (Continue)</x:ref>
3160        status code in response to an HTTP/1.1 PUT or POST request that does
3161        not include an Expect header field with the "100-continue"
3162        expectation. This exception, the purpose of which is
3163        to minimize any client processing delays associated with an
3164        undeclared wait for <x:ref>100 (Continue)</x:ref> status code, applies only to
3165        HTTP/1.1 requests, and not to requests with any other HTTP-version
3166        value.
3167    </t>
3168    <t> An origin server &MAY; omit a <x:ref>100 (Continue)</x:ref> response if it has
3169        already received some or all of the request body for the
3170        corresponding request.
3171    </t>
3172    <t> An origin server that sends a <x:ref>100 (Continue)</x:ref> response &MUST;
3173        ultimately send a final status code, once the request body is
3174        received and processed, unless it terminates the transport
3175        connection prematurely.
3176    </t>
3177    <t> If an origin server receives a request that does not include an
3178        <x:ref>Expect</x:ref> header field with the "100-continue" expectation,
3179        the request includes a request body, and the server responds
3180        with a final status code before reading the entire request body
3181        from the transport connection, then the server &SHOULD-NOT;  close
3182        the transport connection until it has read the entire request,
3183        or until the client closes the connection. Otherwise, the client
3184        might not reliably receive the response message. However, this
3185        requirement ought not be construed as preventing a server from
3186        defending itself against denial-of-service attacks, or from
3187        badly broken client implementations.
3188      </t>
3189    </list>
3190</t>
3191<t>
3192   Requirements for HTTP/1.1 proxies:
3193  <list style="symbols">
3194    <t> If a proxy receives a request that includes an <x:ref>Expect</x:ref>
3195        header field with the "100-continue" expectation, and the proxy
3196        either knows that the next-hop server complies with HTTP/1.1 or
3197        higher, or does not know the HTTP version of the next-hop
3198        server, it &MUST; forward the request, including the Expect header
3199        field.
3200    </t>
3201    <t> If the proxy knows that the version of the next-hop server is
3202        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
3203        respond with a <x:ref>417 (Expectation Failed)</x:ref> status code.
3204    </t>
3205    <t> Proxies &SHOULD; maintain a record of the HTTP version
3206        numbers received from recently-referenced next-hop servers.
3207    </t>
3208    <t> A proxy &MUST-NOT; forward a <x:ref>100 (Continue)</x:ref> response if the
3209        request message was received from an HTTP/1.0 (or earlier)
3210        client and did not include an <x:ref>Expect</x:ref> header field with
3211        the "100-continue" expectation. This requirement overrides the
3212        general rule for forwarding of <x:ref>1xx</x:ref> responses (see &status-1xx;).
3213    </t>
3214  </list>
3215</t>
3216</section>
3217
3218<section title="Closing Connections on Error" anchor="closing.connections.on.error">
3219<t>
3220   If the client is sending data, a server implementation using TCP
3221   &SHOULD; be careful to ensure that the client acknowledges receipt of
3222   the packet(s) containing the response, before the server closes the
3223   input connection. If the client continues sending data to the server
3224   after the close, the server's TCP stack will send a reset packet to
3225   the client, which might erase the client's unacknowledged input buffers
3226   before they can be read and interpreted by the HTTP application.
3227</t>
3228</section>
3229
3230</section>
3231
3232<section title="Upgrade" anchor="header.upgrade">
3233  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3234  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3235  <x:anchor-alias value="Upgrade"/>
3236  <x:anchor-alias value="protocol"/>
3237  <x:anchor-alias value="protocol-name"/>
3238  <x:anchor-alias value="protocol-version"/>
3239<t>
3240   The "Upgrade" header field allows the client to specify what
3241   additional communication protocols it would like to use, if the server
3242   chooses to switch protocols. Servers can use it to indicate what protocols
3243   they are willing to switch to.
3244</t>
3245<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3246  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3247
3248  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3249  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3250  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3251</artwork></figure>
3252<t>
3253   For example,
3254</t>
3255<figure><artwork type="example">
3256  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3257</artwork></figure>
3258<t>
3259   The Upgrade header field is intended to provide a simple mechanism
3260   for transitioning from HTTP/1.1 to some other, incompatible protocol. It
3261   does so by allowing the client to advertise its desire to use another
3262   protocol, such as a later version of HTTP with a higher major version
3263   number, even though the current request has been made using HTTP/1.1.
3264   This eases the difficult transition between incompatible protocols by
3265   allowing the client to initiate a request in the more commonly
3266   supported protocol while indicating to the server that it would like
3267   to use a "better" protocol if available (where "better" is determined
3268   by the server, possibly according to the nature of the request method
3269   or target resource).
3270</t>
3271<t>
3272   The Upgrade header field only applies to switching application-layer
3273   protocols upon the existing transport-layer connection. Upgrade
3274   cannot be used to insist on a protocol change; its acceptance and use
3275   by the server is optional. The capabilities and nature of the
3276   application-layer communication after the protocol change is entirely
3277   dependent upon the new protocol chosen, although the first action
3278   after changing the protocol &MUST; be a response to the initial HTTP
3279   request containing the Upgrade header field.
3280</t>
3281<t>
3282   The Upgrade header field only applies to the immediate connection.
3283   Therefore, the upgrade keyword &MUST; be supplied within a
3284   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
3285   whenever Upgrade is present in an HTTP/1.1 message.
3286</t>
3287<t>
3288   The Upgrade header field cannot be used to indicate a switch to a
3289   protocol on a different connection. For that purpose, it is more
3290   appropriate to use a <x:ref>3xx (Redirection)</x:ref> response (&status-3xx;).
3291</t>
3292<t>
3293   Servers &MUST; include the "Upgrade" header field in <x:ref>101 (Switching
3294   Protocols)</x:ref> responses to indicate which protocol(s) are being switched to,
3295   and &MUST; include it in <x:ref>426 (Upgrade Required)</x:ref> responses to indicate
3296   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3297   response to indicate that they are willing to upgrade to one of the
3298   specified protocols.
3299</t>
3300<t>
3301   This specification only defines the protocol name "HTTP" for use by
3302   the family of Hypertext Transfer Protocols, as defined by the HTTP
3303   version rules of <xref target="http.version"/> and future updates to this
3304   specification. Additional tokens can be registered with IANA using the
3305   registration procedure defined in <xref target="upgrade.token.registry"/>.
3306</t>
3307</section>
3308
3309</section>
3310
3311<section title="IANA Considerations" anchor="IANA.considerations">
3312
3313<section title="Header Field Registration" anchor="header.field.registration">
3314<t>
3315   HTTP header fields are registered within the Message Header Field Registry
3316   <xref target="RFC3864"/> maintained by IANA at
3317   <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/>.
3318</t>
3319<t>
3320   This document defines the following HTTP header fields, so their
3321   associated registry entries shall be updated according to the permanent
3322   registrations below:
3323</t>
3324<?BEGININC p1-messaging.iana-headers ?>
3325<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3326<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3327   <ttcol>Header Field Name</ttcol>
3328   <ttcol>Protocol</ttcol>
3329   <ttcol>Status</ttcol>
3330   <ttcol>Reference</ttcol>
3331
3332   <c>Connection</c>
3333   <c>http</c>
3334   <c>standard</c>
3335   <c>
3336      <xref target="header.connection"/>
3337   </c>
3338   <c>Content-Length</c>
3339   <c>http</c>
3340   <c>standard</c>
3341   <c>
3342      <xref target="header.content-length"/>
3343   </c>
3344   <c>Host</c>
3345   <c>http</c>
3346   <c>standard</c>
3347   <c>
3348      <xref target="header.host"/>
3349   </c>
3350   <c>TE</c>
3351   <c>http</c>
3352   <c>standard</c>
3353   <c>
3354      <xref target="header.te"/>
3355   </c>
3356   <c>Trailer</c>
3357   <c>http</c>
3358   <c>standard</c>
3359   <c>
3360      <xref target="header.trailer"/>
3361   </c>
3362   <c>Transfer-Encoding</c>
3363   <c>http</c>
3364   <c>standard</c>
3365   <c>
3366      <xref target="header.transfer-encoding"/>
3367   </c>
3368   <c>Upgrade</c>
3369   <c>http</c>
3370   <c>standard</c>
3371   <c>
3372      <xref target="header.upgrade"/>
3373   </c>
3374   <c>Via</c>
3375   <c>http</c>
3376   <c>standard</c>
3377   <c>
3378      <xref target="header.via"/>
3379   </c>
3380</texttable>
3381<!--(END)-->
3382<?ENDINC p1-messaging.iana-headers ?>
3383<t>
3384   Furthermore, the header field-name "Close" shall be registered as
3385   "reserved", since using that name as an HTTP header field might
3386   conflict with the "close" connection option of the "<x:ref>Connection</x:ref>"
3387   header field (<xref target="header.connection"/>).
3388</t>
3389<texttable align="left" suppress-title="true">
3390   <ttcol>Header Field Name</ttcol>
3391   <ttcol>Protocol</ttcol>
3392   <ttcol>Status</ttcol>
3393   <ttcol>Reference</ttcol>
3394
3395   <c>Close</c>
3396   <c>http</c>
3397   <c>reserved</c>
3398   <c>
3399      <xref target="header.field.registration"/>
3400   </c>
3401</texttable>
3402<t>
3403   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3404</t>
3405</section>
3406
3407<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3408<t>
3409   IANA maintains the registry of URI Schemes <xref target="RFC4395"/> at
3410   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>.
3411</t>
3412<t>
3413   This document defines the following URI schemes, so their
3414   associated registry entries shall be updated according to the permanent
3415   registrations below:
3416</t>
3417<texttable align="left" suppress-title="true">
3418   <ttcol>URI Scheme</ttcol>
3419   <ttcol>Description</ttcol>
3420   <ttcol>Reference</ttcol>
3421
3422   <c>http</c>
3423   <c>Hypertext Transfer Protocol</c>
3424   <c><xref target="http.uri"/></c>
3425
3426   <c>https</c>
3427   <c>Hypertext Transfer Protocol Secure</c>
3428   <c><xref target="https.uri"/></c>
3429</texttable>
3430</section>
3431
3432<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3433<t>
3434   This document serves as the specification for the Internet media types
3435   "message/http" and "application/http". The following is to be registered with
3436   IANA (see <xref target="RFC4288"/>).
3437</t>
3438<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3439<iref item="Media Type" subitem="message/http" primary="true"/>
3440<iref item="message/http Media Type" primary="true"/>
3441<t>
3442   The message/http type can be used to enclose a single HTTP request or
3443   response message, provided that it obeys the MIME restrictions for all
3444   "message" types regarding line length and encodings.
3445</t>
3446<t>
3447  <list style="hanging" x:indent="12em">
3448    <t hangText="Type name:">
3449      message
3450    </t>
3451    <t hangText="Subtype name:">
3452      http
3453    </t>
3454    <t hangText="Required parameters:">
3455      none
3456    </t>
3457    <t hangText="Optional parameters:">
3458      version, msgtype
3459      <list style="hanging">
3460        <t hangText="version:">
3461          The HTTP-version number of the enclosed message
3462          (e.g., "1.1"). If not present, the version can be
3463          determined from the first line of the body.
3464        </t>
3465        <t hangText="msgtype:">
3466          The message type &mdash; "request" or "response". If not
3467          present, the type can be determined from the first
3468          line of the body.
3469        </t>
3470      </list>
3471    </t>
3472    <t hangText="Encoding considerations:">
3473      only "7bit", "8bit", or "binary" are permitted
3474    </t>
3475    <t hangText="Security considerations:">
3476      none
3477    </t>
3478    <t hangText="Interoperability considerations:">
3479      none
3480    </t>
3481    <t hangText="Published specification:">
3482      This specification (see <xref target="internet.media.type.message.http"/>).
3483    </t>
3484    <t hangText="Applications that use this media type:">
3485    </t>
3486    <t hangText="Additional information:">
3487      <list style="hanging">
3488        <t hangText="Magic number(s):">none</t>
3489        <t hangText="File extension(s):">none</t>
3490        <t hangText="Macintosh file type code(s):">none</t>
3491      </list>
3492    </t>
3493    <t hangText="Person and email address to contact for further information:">
3494      See Authors Section.
3495    </t>
3496    <t hangText="Intended usage:">
3497      COMMON
3498    </t>
3499    <t hangText="Restrictions on usage:">
3500      none
3501    </t>
3502    <t hangText="Author/Change controller:">
3503      IESG
3504    </t>
3505  </list>
3506</t>
3507</section>
3508<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3509<iref item="Media Type" subitem="application/http" primary="true"/>
3510<iref item="application/http Media Type" primary="true"/>
3511<t>
3512   The application/http type can be used to enclose a pipeline of one or more
3513   HTTP request or response messages (not intermixed).
3514</t>
3515<t>
3516  <list style="hanging" x:indent="12em">
3517    <t hangText="Type name:">
3518      application
3519    </t>
3520    <t hangText="Subtype name:">
3521      http
3522    </t>
3523    <t hangText="Required parameters:">
3524      none
3525    </t>
3526    <t hangText="Optional parameters:">
3527      version, msgtype
3528      <list style="hanging">
3529        <t hangText="version:">
3530          The HTTP-version number of the enclosed messages
3531          (e.g., "1.1"). If not present, the version can be
3532          determined from the first line of the body.
3533        </t>
3534        <t hangText="msgtype:">
3535          The message type &mdash; "request" or "response". If not
3536          present, the type can be determined from the first
3537          line of the body.
3538        </t>
3539      </list>
3540    </t>
3541    <t hangText="Encoding considerations:">
3542      HTTP messages enclosed by this type
3543      are in "binary" format; use of an appropriate
3544      Content-Transfer-Encoding is required when
3545      transmitted via E-mail.
3546    </t>
3547    <t hangText="Security considerations:">
3548      none
3549    </t>
3550    <t hangText="Interoperability considerations:">
3551      none
3552    </t>
3553    <t hangText="Published specification:">
3554      This specification (see <xref target="internet.media.type.application.http"/>).
3555    </t>
3556    <t hangText="Applications that use this media type:">
3557    </t>
3558    <t hangText="Additional information:">
3559      <list style="hanging">
3560        <t hangText="Magic number(s):">none</t>
3561        <t hangText="File extension(s):">none</t>
3562        <t hangText="Macintosh file type code(s):">none</t>
3563      </list>
3564    </t>
3565    <t hangText="Person and email address to contact for further information:">
3566      See Authors Section.
3567    </t>
3568    <t hangText="Intended usage:">
3569      COMMON
3570    </t>
3571    <t hangText="Restrictions on usage:">
3572      none
3573    </t>
3574    <t hangText="Author/Change controller:">
3575      IESG
3576    </t>
3577  </list>
3578</t>
3579</section>
3580</section>
3581
3582<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3583<t>
3584   The HTTP Transfer Coding Registry defines the name space for transfer
3585   coding names.
3586</t>
3587<t>
3588   Registrations &MUST; include the following fields:
3589   <list style="symbols">
3590     <t>Name</t>
3591     <t>Description</t>
3592     <t>Pointer to specification text</t>
3593   </list>
3594</t>
3595<t>
3596   Names of transfer codings &MUST-NOT; overlap with names of content codings
3597   (&content-codings;) unless the encoding transformation is identical, as it
3598   is the case for the compression codings defined in
3599   <xref target="compression.codings"/>.
3600</t>
3601<t>
3602   Values to be added to this name space require IETF Review (see
3603   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3604   conform to the purpose of transfer coding defined in this section.
3605</t>
3606<t>
3607   The registry itself is maintained at
3608   <eref target="http://www.iana.org/assignments/http-parameters"/>.
3609</t>
3610</section>
3611
3612<section title="Transfer Coding Registrations" anchor="transfer.coding.registration">
3613<t>
3614   The HTTP Transfer Coding Registry shall be updated with the registrations
3615   below:
3616</t>
3617<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3618   <ttcol>Name</ttcol>
3619   <ttcol>Description</ttcol>
3620   <ttcol>Reference</ttcol>
3621   <c>chunked</c>
3622   <c>Transfer in a series of chunks</c>
3623   <c>
3624      <xref target="chunked.encoding"/>
3625   </c>
3626   <c>compress</c>
3627   <c>UNIX "compress" program method</c>
3628   <c>
3629      <xref target="compress.coding"/>
3630   </c>
3631   <c>deflate</c>
3632   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3633   the "zlib" data format (<xref target="RFC1950"/>)
3634   </c>
3635   <c>
3636      <xref target="deflate.coding"/>
3637   </c>
3638   <c>gzip</c>
3639   <c>Same as GNU zip <xref target="RFC1952"/></c>
3640   <c>
3641      <xref target="gzip.coding"/>
3642   </c>
3643</texttable>
3644</section>
3645
3646<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3647<t>
3648   The HTTP Upgrade Token Registry defines the name space for protocol-name
3649   tokens used to identify protocols in the <x:ref>Upgrade</x:ref> header
3650   field. Each registered protocol name is associated with contact information
3651   and an optional set of specifications that details how the connection
3652   will be processed after it has been upgraded.
3653</t>
3654<t>
3655   Registrations happen on a "First Come First Served" basis (see
3656   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3657   following rules:
3658  <list style="numbers">
3659    <t>A protocol-name token, once registered, stays registered forever.</t>
3660    <t>The registration &MUST; name a responsible party for the
3661       registration.</t>
3662    <t>The registration &MUST; name a point of contact.</t>
3663    <t>The registration &MAY; name a set of specifications associated with
3664       that token. Such specifications need not be publicly available.</t>
3665    <t>The registration &SHOULD; name a set of expected "protocol-version"
3666       tokens associated with that token at the time of registration.</t>
3667    <t>The responsible party &MAY; change the registration at any time.
3668       The IANA will keep a record of all such changes, and make them
3669       available upon request.</t>
3670    <t>The IESG &MAY; reassign responsibility for a protocol token.
3671       This will normally only be used in the case when a
3672       responsible party cannot be contacted.</t>
3673  </list>
3674</t>
3675<t>
3676   This registration procedure for HTTP Upgrade Tokens replaces that
3677   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3678</t>
3679</section>
3680
3681<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3682<t>
3683   The HTTP Upgrade Token Registry shall be updated with the registration
3684   below:
3685</t>
3686<texttable align="left" suppress-title="true">
3687   <ttcol>Value</ttcol>
3688   <ttcol>Description</ttcol>
3689   <ttcol>Expected Version Tokens</ttcol>
3690   <ttcol>Reference</ttcol>
3691
3692   <c>HTTP</c>
3693   <c>Hypertext Transfer Protocol</c>
3694   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3695   <c><xref target="http.version"/></c>
3696</texttable>
3697<t>
3698   The responsible party is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3699</t>
3700</section>
3701
3702</section>
3703
3704<section title="Security Considerations" anchor="security.considerations">
3705<t>
3706   This section is meant to inform application developers, information
3707   providers, and users of the security limitations in HTTP/1.1 as
3708   described by this document. The discussion does not include
3709   definitive solutions to the problems revealed, though it does make
3710   some suggestions for reducing security risks.
3711</t>
3712
3713<section title="Personal Information" anchor="personal.information">
3714<t>
3715   HTTP clients are often privy to large amounts of personal information
3716   (e.g., the user's name, location, mail address, passwords, encryption
3717   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3718   leakage of this information.
3719   We very strongly recommend that a convenient interface be provided
3720   for the user to control dissemination of such information, and that
3721   designers and implementors be particularly careful in this area.
3722   History shows that errors in this area often create serious security
3723   and/or privacy problems and generate highly adverse publicity for the
3724   implementor's company.
3725</t>
3726</section>
3727
3728<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3729<t>
3730   A server is in the position to save personal data about a user's
3731   requests which might identify their reading patterns or subjects of
3732   interest.  In particular, log information gathered at an intermediary
3733   often contains a history of user agent interaction, across a multitude
3734   of sites, that can be traced to individual users.
3735</t>
3736<t>
3737   HTTP log information is confidential in nature; its handling is often
3738   constrained by laws and regulations.  Log information needs to be securely
3739   stored and appropriate guidelines followed for its analysis.
3740   Anonymization of personal information within individual entries helps,
3741   but is generally not sufficient to prevent real log traces from being
3742   re-identified based on correlation with other access characteristics.
3743   As such, access traces that are keyed to a specific client should not
3744   be published even if the key is pseudonymous.
3745</t>
3746<t>
3747   To minimize the risk of theft or accidental publication, log information
3748   should be purged of personally identifiable information, including
3749   user identifiers, IP addresses, and user-provided query parameters,
3750   as soon as that information is no longer necessary to support operational
3751   needs for security, auditing, or fraud control.
3752</t>
3753</section>
3754
3755<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3756<t>
3757   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3758   the documents returned by HTTP requests to be only those that were
3759   intended by the server administrators. If an HTTP server translates
3760   HTTP URIs directly into file system calls, the server &MUST; take
3761   special care not to serve files that were not intended to be
3762   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3763   other operating systems use ".." as a path component to indicate a
3764   directory level above the current one. On such a system, an HTTP
3765   server &MUST; disallow any such construct in the request-target if it
3766   would otherwise allow access to a resource outside those intended to
3767   be accessible via the HTTP server. Similarly, files intended for
3768   reference only internally to the server (such as access control
3769   files, configuration files, and script code) &MUST; be protected from
3770   inappropriate retrieval, since they might contain sensitive
3771   information. Experience has shown that minor bugs in such HTTP server
3772   implementations have turned into security risks.
3773</t>
3774</section>
3775
3776<section title="DNS-related Attacks" anchor="dns.related.attacks">
3777<t>
3778   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3779   generally prone to security attacks based on the deliberate misassociation
3780   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3781   cautious in assuming the validity of an IP number/DNS name association unless
3782   the response is protected by DNSSec (<xref target="RFC4033"/>).
3783</t>
3784</section>
3785
3786<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3787<t>
3788   By their very nature, HTTP intermediaries are men-in-the-middle, and
3789   represent an opportunity for man-in-the-middle attacks. Compromise of
3790   the systems on which the intermediaries run can result in serious security
3791   and privacy problems. Intermediaries have access to security-related
3792   information, personal information about individual users and
3793   organizations, and proprietary information belonging to users and
3794   content providers. A compromised intermediary, or an intermediary
3795   implemented or configured without regard to security and privacy
3796   considerations, might be used in the commission of a wide range of
3797   potential attacks.
3798</t>
3799<t>
3800   Intermediaries that contain a shared cache are especially vulnerable
3801   to cache poisoning attacks.
3802</t>
3803<t>
3804   Implementors need to consider the privacy and security
3805   implications of their design and coding decisions, and of the
3806   configuration options they provide to operators (especially the
3807   default configuration).
3808</t>
3809<t>
3810   Users need to be aware that intermediaries are no more trustworthy than
3811   the people who run them; HTTP itself cannot solve this problem.
3812</t>
3813<t>
3814   The judicious use of cryptography, when appropriate, might suffice to
3815   protect against a broad range of security and privacy attacks. Such
3816   cryptography is beyond the scope of the HTTP/1.1 specification.
3817</t>
3818</section>
3819
3820<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3821<t>
3822   Because HTTP uses mostly textual, character-delimited fields, attackers can
3823   overflow buffers in implementations, and/or perform a Denial of Service
3824   against implementations that accept fields with unlimited lengths.
3825</t>
3826<t>
3827   To promote interoperability, this specification makes specific
3828   recommendations for minimum size limits on request-line
3829   (<xref target="request.line"/>)
3830   and blocks of header fields (<xref target="header.fields"/>). These are
3831   minimum recommendations, chosen to be supportable even by implementations
3832   with limited resources; it is expected that most implementations will
3833   choose substantially higher limits.
3834</t>
3835<t>
3836   This specification also provides a way for servers to reject messages that
3837   have request-targets that are too long (&status-414;) or request entities
3838   that are too large (&status-4xx;).
3839</t>
3840<t>
3841   Other fields (including but not limited to request methods, response status
3842   phrases, header field-names, and body chunks) &SHOULD; be limited by
3843   implementations carefully, so as to not impede interoperability.
3844</t>
3845</section>
3846</section>
3847
3848<section title="Acknowledgments" anchor="acks">
3849<t>
3850   This edition of HTTP builds on the many contributions that went into
3851   <xref target="RFC1945" format="none">RFC 1945</xref>,
3852   <xref target="RFC2068" format="none">RFC 2068</xref>,
3853   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3854   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3855   substantial contributions made by the previous authors, editors, and
3856   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3857   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3858   Paul J. Leach, and Mark Nottingham.
3859   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
3860   acknowledgements from prior revisions.
3861</t>
3862<t>
3863   Since 1999, the following contributors have helped improve the HTTP
3864   specification by reporting bugs, asking smart questions, drafting or
3865   reviewing text, and evaluating open issues:
3866</t>
3867<?BEGININC acks ?>
3868<t>Adam Barth,
3869Adam Roach,
3870Addison Phillips,
3871Adrian Chadd,
3872Adrien W. de Croy,
3873Alan Ford,
3874Alan Ruttenberg,
3875Albert Lunde,
3876Alek Storm,
3877Alex Rousskov,
3878Alexandre Morgaut,
3879Alexey Melnikov,
3880Alisha Smith,
3881Amichai Rothman,
3882Amit Klein,
3883Amos Jeffries,
3884Andreas Maier,
3885Andreas Petersson,
3886Anne van Kesteren,
3887Anthony Bryan,
3888Asbjorn Ulsberg,
3889Balachander Krishnamurthy,
3890Barry Leiba,
3891Ben Laurie,
3892Benjamin Niven-Jenkins,
3893Bil Corry,
3894Bill Burke,
3895Bjoern Hoehrmann,
3896Bob Scheifler,
3897Boris Zbarsky,
3898Brett Slatkin,
3899Brian Kell,
3900Brian McBarron,
3901Brian Pane,
3902Brian Smith,
3903Bryce Nesbitt,
3904Cameron Heavon-Jones,
3905Carl Kugler,
3906Carsten Bormann,
3907Charles Fry,
3908Chris Newman,
3909Cyrus Daboo,
3910Dale Robert Anderson,
3911Dan Winship,
3912Daniel Stenberg,
3913Dave Cridland,
3914Dave Crocker,
3915Dave Kristol,
3916David Booth,
3917David Singer,
3918David W. Morris,
3919Diwakar Shetty,
3920Dmitry Kurochkin,
3921Drummond Reed,
3922Duane Wessels,
3923Edward Lee,
3924Eliot Lear,
3925Eran Hammer-Lahav,
3926Eric D. Williams,
3927Eric J. Bowman,
3928Eric Lawrence,
3929Eric Rescorla,
3930Erik Aronesty,
3931Florian Weimer,
3932Frank Ellermann,
3933Fred Bohle,
3934Geoffrey Sneddon,
3935Gervase Markham,
3936Greg Wilkins,
3937Harald Tveit Alvestrand,
3938Harry Halpin,
3939Helge Hess,
3940Henrik Nordstrom,
3941Henry S. Thompson,
3942Henry Story,
3943Herbert van de Sompel,
3944Howard Melman,
3945Hugo Haas,
3946Ian Hickson,
3947Ingo Struck,
3948J. Ross Nicoll,
3949James H. Manger,
3950James Lacey,
3951James M. Snell,
3952Jamie Lokier,
3953Jan Algermissen,
3954Jeff Hodges (who came up with the term 'effective Request-URI'),
3955Jeff Walden,
3956Jim Luther,
3957Joe D. Williams,
3958Joe Gregorio,
3959Joe Orton,
3960John C. Klensin,
3961John C. Mallery,
3962John Cowan,
3963John Kemp,
3964John Panzer,
3965John Schneider,
3966John Stracke,
3967John Sullivan,
3968Jonas Sicking,
3969Jonathan Billington,
3970Jonathan Moore,
3971Jonathan Rees,
3972Jordi Ros,
3973Joris Dobbelsteen,
3974Josh Cohen,
3975Julien Pierre,
3976Jungshik Shin,
3977Justin Chapweske,
3978Justin Erenkrantz,
3979Justin James,
3980Kalvinder Singh,
3981Karl Dubost,
3982Keith Hoffman,
3983Keith Moore,
3984Koen Holtman,
3985Konstantin Voronkov,
3986Kris Zyp,
3987Lisa Dusseault,
3988Maciej Stachowiak,
3989Marc Schneider,
3990Marc Slemko,
3991Mark Baker,
3992Mark Pauley,
3993Mark Watson,
3994Markus Isomaki,
3995Markus Lanthaler,
3996Martin J. Duerst,
3997Martin Musatov,
3998Martin Nilsson,
3999Martin Thomson,
4000Matt Lynch,
4001Matthew Cox,
4002Max Clark,
4003Michael Burrows,
4004Michael Hausenblas,
4005Mike Amundsen,
4006Mike Belshe,
4007Mike Kelly,
4008Mike Schinkel,
4009Miles Sabin,
4010Murray S. Kucherawy,
4011Mykyta Yevstifeyev,
4012Nathan Rixham,
4013Nicholas Shanks,
4014Nico Williams,
4015Nicolas Alvarez,
4016Nicolas Mailhot,
4017Noah Slater,
4018Pablo Castro,
4019Pat Hayes,
4020Patrick R. McManus,
4021Paul E. Jones,
4022Paul Hoffman,
4023Paul Marquess,
4024Peter Lepeska,
4025Peter Saint-Andre,
4026Peter Watkins,
4027Phil Archer,
4028Phillip Hallam-Baker,
4029Poul-Henning Kamp,
4030Preethi Natarajan,
4031Ray Polk,
4032Reto Bachmann-Gmuer,
4033Richard Cyganiak,
4034Robert Brewer,
4035Robert Collins,
4036Robert O'Callahan,
4037Robert Olofsson,
4038Robert Sayre,
4039Robert Siemer,
4040Robert de Wilde,
4041Roberto Javier Godoy,
4042Roberto Peon,
4043Ronny Widjaja,
4044S. Mike Dierken,
4045Salvatore Loreto,
4046Sam Johnston,
4047Sam Ruby,
4048Scott Lawrence (who maintained the original issues list),
4049Sean B. Palmer,
4050Shane McCarron,
4051Stefan Eissing,
4052Stefan Tilkov,
4053Stefanos Harhalakis,
4054Stephane Bortzmeyer,
4055Stephen Farrell,
4056Stuart Williams,
4057Subbu Allamaraju,
4058Sylvain Hellegouarch,
4059Tapan Divekar,
4060Ted Hardie,
4061Thomas Broyer,
4062Thomas Nordin,
4063Thomas Roessler,
4064Tim Bray,
4065Tim Morgan,
4066Tim Olsen,
4067Tom Zhou,
4068Travis Snoozy,
4069Tyler Close,
4070Vincent Murphy,
4071Wenbo Zhu,
4072Werner Baumann,
4073Wilbur Streett,
4074Wilfredo Sanchez Vega,
4075William A. Rowe Jr.,
4076William Chan,
4077Willy Tarreau,
4078Xiaoshu Wang,
4079Yaron Goland,
4080Yngve Nysaeter Pettersen,
4081Yoav Nir,
4082Yogesh Bang,
4083Yutaka Oiwa,
4084Zed A. Shaw, and
4085Zhong Yu.
4086</t>
4087<?ENDINC acks ?>
4088</section>
4089
4090</middle>
4091<back>
4092
4093<references title="Normative References">
4094
4095<reference anchor="ISO-8859-1">
4096  <front>
4097    <title>
4098     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4099    </title>
4100    <author>
4101      <organization>International Organization for Standardization</organization>
4102    </author>
4103    <date year="1998"/>
4104  </front>
4105  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4106</reference>
4107
4108<reference anchor="Part2">
4109  <front>
4110    <title>HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation</title>
4111    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4112      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4113      <address><email>fielding@gbiv.com</email></address>
4114    </author>
4115    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4116      <organization abbrev="W3C">World Wide Web Consortium</organization>
4117      <address><email>ylafon@w3.org</email></address>
4118    </author>
4119    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4120      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4121      <address><email>julian.reschke@greenbytes.de</email></address>
4122    </author>
4123    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4124  </front>
4125  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4126  <x:source href="p2-semantics.xml" basename="p2-semantics">
4127    <x:defines>1xx (Informational)</x:defines>
4128    <x:defines>1xx</x:defines>
4129    <x:defines>100 (Continue)</x:defines>
4130    <x:defines>101 (Switching Protocols)</x:defines>
4131    <x:defines>2xx (Successful)</x:defines>
4132    <x:defines>2xx</x:defines>
4133    <x:defines>200 (OK)</x:defines>
4134    <x:defines>204 (No Content)</x:defines>
4135    <x:defines>3xx (Redirection)</x:defines>
4136    <x:defines>3xx</x:defines>
4137    <x:defines>301 (Moved Permanently)</x:defines>
4138    <x:defines>4xx (Client Error)</x:defines>
4139    <x:defines>4xx</x:defines>
4140    <x:defines>400 (Bad Request)</x:defines>
4141    <x:defines>405 (Method Not Allowed)</x:defines>
4142    <x:defines>411 (Length Required)</x:defines>
4143    <x:defines>414 (URI Too Long)</x:defines>
4144    <x:defines>417 (Expectation Failed)</x:defines>
4145    <x:defines>426 (Upgrade Required)</x:defines>
4146    <x:defines>501 (Not Implemented)</x:defines>
4147    <x:defines>502 (Bad Gateway)</x:defines>
4148    <x:defines>505 (HTTP Version Not Supported)</x:defines>
4149    <x:defines>Content-Encoding</x:defines>
4150    <x:defines>Content-Type</x:defines>
4151    <x:defines>Date</x:defines>
4152    <x:defines>Expect</x:defines>
4153    <x:defines>Location</x:defines>
4154    <x:defines>Server</x:defines>
4155    <x:defines>User-Agent</x:defines>
4156  </x:source>
4157</reference>
4158
4159<reference anchor="Part4">
4160  <front>
4161    <title>HTTP/1.1, part 4: Conditional Requests</title>
4162    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
4163      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4164      <address><email>fielding@gbiv.com</email></address>
4165    </author>
4166    <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
4167      <organization abbrev="W3C">World Wide Web Consortium</organization>
4168      <address><email>ylafon@w3.org</email></address>
4169    </author>
4170    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
4171      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4172      <address><email>julian.reschke@greenbytes.de</email></address>
4173    </author>
4174    <date month="&ID-MONTH;" year="&ID-YEAR;" />
4175  </front>
4176  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;" />
4177  <x:source basename="p4-conditional" href="p4-conditional.xml">
4178    <x:defines>304 (Not Modified)</x:defines>
4179  </x:source>
4180</reference>
4181
4182<reference anchor="Part5">
4183  <front>
4184    <title>HTTP/1.1, part 5: Range Requests and Partial Responses</title>
4185    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4186      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4187      <address><email>fielding@gbiv.com</email></address>
4188    </author>
4189    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4190      <organization abbrev="W3C">World Wide Web Consortium</organization>
4191      <address><email>ylafon@w3.org</email></address>
4192    </author>
4193    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4194      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4195      <address><email>julian.reschke@greenbytes.de</email></address>
4196    </author>
4197    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4198  </front>
4199  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
4200  <x:source href="p5-range.xml" basename="p5-range">
4201    <x:defines>Content-Range</x:defines>
4202  </x:source>
4203</reference>
4204
4205<reference anchor="Part6">
4206  <front>
4207    <title>HTTP/1.1, part 6: Caching</title>
4208    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4209      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4210      <address><email>fielding@gbiv.com</email></address>
4211    </author>
4212    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4213      <organization abbrev="W3C">World Wide Web Consortium</organization>
4214      <address><email>ylafon@w3.org</email></address>
4215    </author>
4216    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4217      <organization>Rackspace</organization>
4218      <address><email>mnot@mnot.net</email></address>
4219    </author>
4220    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4221      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4222      <address><email>julian.reschke@greenbytes.de</email></address>
4223    </author>
4224    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4225  </front>
4226  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4227  <x:source href="p6-cache.xml" basename="p6-cache">
4228    <x:defines>Expires</x:defines>
4229  </x:source>
4230</reference>
4231
4232<reference anchor="Part7">
4233  <front>
4234    <title>HTTP/1.1, part 7: Authentication</title>
4235    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4236      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4237      <address><email>fielding@gbiv.com</email></address>
4238    </author>
4239    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4240      <organization abbrev="W3C">World Wide Web Consortium</organization>
4241      <address><email>ylafon@w3.org</email></address>
4242    </author>
4243    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4244      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4245      <address><email>julian.reschke@greenbytes.de</email></address>
4246    </author>
4247    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4248  </front>
4249  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
4250  <x:source href="p7-auth.xml" basename="p7-auth">
4251    <x:defines>Proxy-Authenticate</x:defines>
4252    <x:defines>Proxy-Authorization</x:defines>
4253  </x:source>
4254</reference>
4255
4256<reference anchor="RFC5234">
4257  <front>
4258    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4259    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4260      <organization>Brandenburg InternetWorking</organization>
4261      <address>
4262        <email>dcrocker@bbiw.net</email>
4263      </address> 
4264    </author>
4265    <author initials="P." surname="Overell" fullname="Paul Overell">
4266      <organization>THUS plc.</organization>
4267      <address>
4268        <email>paul.overell@thus.net</email>
4269      </address>
4270    </author>
4271    <date month="January" year="2008"/>
4272  </front>
4273  <seriesInfo name="STD" value="68"/>
4274  <seriesInfo name="RFC" value="5234"/>
4275</reference>
4276
4277<reference anchor="RFC2119">
4278  <front>
4279    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4280    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4281      <organization>Harvard University</organization>
4282      <address><email>sob@harvard.edu</email></address>
4283    </author>
4284    <date month="March" year="1997"/>
4285  </front>
4286  <seriesInfo name="BCP" value="14"/>
4287  <seriesInfo name="RFC" value="2119"/>
4288</reference>
4289
4290<reference anchor="RFC3986">
4291 <front>
4292  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4293  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4294    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4295    <address>
4296       <email>timbl@w3.org</email>
4297       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4298    </address>
4299  </author>
4300  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4301    <organization abbrev="Day Software">Day Software</organization>
4302    <address>
4303      <email>fielding@gbiv.com</email>
4304      <uri>http://roy.gbiv.com/</uri>
4305    </address>
4306  </author>
4307  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4308    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4309    <address>
4310      <email>LMM@acm.org</email>
4311      <uri>http://larry.masinter.net/</uri>
4312    </address>
4313  </author>
4314  <date month='January' year='2005'></date>
4315 </front>
4316 <seriesInfo name="STD" value="66"/>
4317 <seriesInfo name="RFC" value="3986"/>
4318</reference>
4319
4320<reference anchor="USASCII">
4321  <front>
4322    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4323    <author>
4324      <organization>American National Standards Institute</organization>
4325    </author>
4326    <date year="1986"/>
4327  </front>
4328  <seriesInfo name="ANSI" value="X3.4"/>
4329</reference>
4330
4331<reference anchor="RFC1950">
4332  <front>
4333    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4334    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4335      <organization>Aladdin Enterprises</organization>
4336      <address><email>ghost@aladdin.com</email></address>
4337    </author>
4338    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4339    <date month="May" year="1996"/>
4340  </front>
4341  <seriesInfo name="RFC" value="1950"/>
4342  <!--<annotation>
4343    RFC 1950 is an Informational RFC, thus it might be less stable than
4344    this specification. On the other hand, this downward reference was
4345    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4346    therefore it is unlikely to cause problems in practice. See also
4347    <xref target="BCP97"/>.
4348  </annotation>-->
4349</reference>
4350
4351<reference anchor="RFC1951">
4352  <front>
4353    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4354    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4355      <organization>Aladdin Enterprises</organization>
4356      <address><email>ghost@aladdin.com</email></address>
4357    </author>
4358    <date month="May" year="1996"/>
4359  </front>
4360  <seriesInfo name="RFC" value="1951"/>
4361  <!--<annotation>
4362    RFC 1951 is an Informational RFC, thus it might be less stable than
4363    this specification. On the other hand, this downward reference was
4364    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4365    therefore it is unlikely to cause problems in practice. See also
4366    <xref target="BCP97"/>.
4367  </annotation>-->
4368</reference>
4369
4370<reference anchor="RFC1952">
4371  <front>
4372    <title>GZIP file format specification version 4.3</title>
4373    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4374      <organization>Aladdin Enterprises</organization>
4375      <address><email>ghost@aladdin.com</email></address>
4376    </author>
4377    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4378      <address><email>gzip@prep.ai.mit.edu</email></address>
4379    </author>
4380    <author initials="M." surname="Adler" fullname="Mark Adler">
4381      <address><email>madler@alumni.caltech.edu</email></address>
4382    </author>
4383    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4384      <address><email>ghost@aladdin.com</email></address>
4385    </author>
4386    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4387      <address><email>randeg@alumni.rpi.edu</email></address>
4388    </author>
4389    <date month="May" year="1996"/>
4390  </front>
4391  <seriesInfo name="RFC" value="1952"/>
4392  <!--<annotation>
4393    RFC 1952 is an Informational RFC, thus it might be less stable than
4394    this specification. On the other hand, this downward reference was
4395    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4396    therefore it is unlikely to cause problems in practice. See also
4397    <xref target="BCP97"/>.
4398  </annotation>-->
4399</reference>
4400
4401</references>
4402
4403<references title="Informative References">
4404
4405<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4406  <front>
4407    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4408    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4409    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4410    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4411    <author initials="H." surname="Lie" fullname="H. Lie"/>
4412    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4413    <date year="1997" month="September"/>
4414  </front>
4415  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4416</reference>
4417
4418<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4419  <front>
4420    <title>Improving HTTP Latency</title>
4421    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4422    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4423    <date year="1995" month="December"/>
4424  </front>
4425  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4426</reference>
4427
4428<reference anchor='RFC1919'>
4429  <front>
4430    <title>Classical versus Transparent IP Proxies</title>
4431    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4432      <address><email>mchatel@pax.eunet.ch</email></address>
4433    </author>
4434    <date year='1996' month='March' />
4435  </front>
4436  <seriesInfo name='RFC' value='1919' />
4437</reference>
4438
4439<reference anchor="RFC1945">
4440  <front>
4441    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4442    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4443      <organization>MIT, Laboratory for Computer Science</organization>
4444      <address><email>timbl@w3.org</email></address>
4445    </author>
4446    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4447      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4448      <address><email>fielding@ics.uci.edu</email></address>
4449    </author>
4450    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4451      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4452      <address><email>frystyk@w3.org</email></address>
4453    </author>
4454    <date month="May" year="1996"/>
4455  </front>
4456  <seriesInfo name="RFC" value="1945"/>
4457</reference>
4458
4459<reference anchor="RFC2045">
4460  <front>
4461    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4462    <author initials="N." surname="Freed" fullname="Ned Freed">
4463      <organization>Innosoft International, Inc.</organization>
4464      <address><email>ned@innosoft.com</email></address>
4465    </author>
4466    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4467      <organization>First Virtual Holdings</organization>
4468      <address><email>nsb@nsb.fv.com</email></address>
4469    </author>
4470    <date month="November" year="1996"/>
4471  </front>
4472  <seriesInfo name="RFC" value="2045"/>
4473</reference>
4474
4475<reference anchor="RFC2047">
4476  <front>
4477    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4478    <author initials="K." surname="Moore" fullname="Keith Moore">
4479      <organization>University of Tennessee</organization>
4480      <address><email>moore@cs.utk.edu</email></address>
4481    </author>
4482    <date month="November" year="1996"/>
4483  </front>
4484  <seriesInfo name="RFC" value="2047"/>
4485</reference>
4486
4487<reference anchor="RFC2068">
4488  <front>
4489    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4490    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4491      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4492      <address><email>fielding@ics.uci.edu</email></address>
4493    </author>
4494    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4495      <organization>MIT Laboratory for Computer Science</organization>
4496      <address><email>jg@w3.org</email></address>
4497    </author>
4498    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4499      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4500      <address><email>mogul@wrl.dec.com</email></address>
4501    </author>
4502    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4503      <organization>MIT Laboratory for Computer Science</organization>
4504      <address><email>frystyk@w3.org</email></address>
4505    </author>
4506    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4507      <organization>MIT Laboratory for Computer Science</organization>
4508      <address><email>timbl@w3.org</email></address>
4509    </author>
4510    <date month="January" year="1997"/>
4511  </front>
4512  <seriesInfo name="RFC" value="2068"/>
4513</reference>
4514
4515<reference anchor="RFC2145">
4516  <front>
4517    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4518    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4519      <organization>Western Research Laboratory</organization>
4520      <address><email>mogul@wrl.dec.com</email></address>
4521    </author>
4522    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4523      <organization>Department of Information and Computer Science</organization>
4524      <address><email>fielding@ics.uci.edu</email></address>
4525    </author>
4526    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4527      <organization>MIT Laboratory for Computer Science</organization>
4528      <address><email>jg@w3.org</email></address>
4529    </author>
4530    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4531      <organization>W3 Consortium</organization>
4532      <address><email>frystyk@w3.org</email></address>
4533    </author>
4534    <date month="May" year="1997"/>
4535  </front>
4536  <seriesInfo name="RFC" value="2145"/>
4537</reference>
4538
4539<reference anchor="RFC2616">
4540  <front>
4541    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4542    <author initials="R." surname="Fielding" fullname="R. Fielding">
4543      <organization>University of California, Irvine</organization>
4544      <address><email>fielding@ics.uci.edu</email></address>
4545    </author>
4546    <author initials="J." surname="Gettys" fullname="J. Gettys">
4547      <organization>W3C</organization>
4548      <address><email>jg@w3.org</email></address>
4549    </author>
4550    <author initials="J." surname="Mogul" fullname="J. Mogul">
4551      <organization>Compaq Computer Corporation</organization>
4552      <address><email>mogul@wrl.dec.com</email></address>
4553    </author>
4554    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4555      <organization>MIT Laboratory for Computer Science</organization>
4556      <address><email>frystyk@w3.org</email></address>
4557    </author>
4558    <author initials="L." surname="Masinter" fullname="L. Masinter">
4559      <organization>Xerox Corporation</organization>
4560      <address><email>masinter@parc.xerox.com</email></address>
4561    </author>
4562    <author initials="P." surname="Leach" fullname="P. Leach">
4563      <organization>Microsoft Corporation</organization>
4564      <address><email>paulle@microsoft.com</email></address>
4565    </author>
4566    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4567      <organization>W3C</organization>
4568      <address><email>timbl@w3.org</email></address>
4569    </author>
4570    <date month="June" year="1999"/>
4571  </front>
4572  <seriesInfo name="RFC" value="2616"/>
4573</reference>
4574
4575<reference anchor='RFC2817'>
4576  <front>
4577    <title>Upgrading to TLS Within HTTP/1.1</title>
4578    <author initials='R.' surname='Khare' fullname='R. Khare'>
4579      <organization>4K Associates / UC Irvine</organization>
4580      <address><email>rohit@4K-associates.com</email></address>
4581    </author>
4582    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4583      <organization>Agranat Systems, Inc.</organization>
4584      <address><email>lawrence@agranat.com</email></address>
4585    </author>
4586    <date year='2000' month='May' />
4587  </front>
4588  <seriesInfo name='RFC' value='2817' />
4589</reference>
4590
4591<reference anchor='RFC2818'>
4592  <front>
4593    <title>HTTP Over TLS</title>
4594    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4595      <organization>RTFM, Inc.</organization>
4596      <address><email>ekr@rtfm.com</email></address>
4597    </author>
4598    <date year='2000' month='May' />
4599  </front>
4600  <seriesInfo name='RFC' value='2818' />
4601</reference>
4602
4603<reference anchor='RFC2965'>
4604  <front>
4605    <title>HTTP State Management Mechanism</title>
4606    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4607      <organization>Bell Laboratories, Lucent Technologies</organization>
4608      <address><email>dmk@bell-labs.com</email></address>
4609    </author>
4610    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4611      <organization>Epinions.com, Inc.</organization>
4612      <address><email>lou@montulli.org</email></address>
4613    </author>
4614    <date year='2000' month='October' />
4615  </front>
4616  <seriesInfo name='RFC' value='2965' />
4617</reference>
4618
4619<reference anchor='RFC3040'>
4620  <front>
4621    <title>Internet Web Replication and Caching Taxonomy</title>
4622    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4623      <organization>Equinix, Inc.</organization>
4624    </author>
4625    <author initials='I.' surname='Melve' fullname='I. Melve'>
4626      <organization>UNINETT</organization>
4627    </author>
4628    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4629      <organization>CacheFlow Inc.</organization>
4630    </author>
4631    <date year='2001' month='January' />
4632  </front>
4633  <seriesInfo name='RFC' value='3040' />
4634</reference>
4635
4636<reference anchor='RFC3864'>
4637  <front>
4638    <title>Registration Procedures for Message Header Fields</title>
4639    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4640      <organization>Nine by Nine</organization>
4641      <address><email>GK-IETF@ninebynine.org</email></address>
4642    </author>
4643    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4644      <organization>BEA Systems</organization>
4645      <address><email>mnot@pobox.com</email></address>
4646    </author>
4647    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4648      <organization>HP Labs</organization>
4649      <address><email>JeffMogul@acm.org</email></address>
4650    </author>
4651    <date year='2004' month='September' />
4652  </front>
4653  <seriesInfo name='BCP' value='90' />
4654  <seriesInfo name='RFC' value='3864' />
4655</reference>
4656
4657<reference anchor='RFC4033'>
4658  <front>
4659    <title>DNS Security Introduction and Requirements</title>
4660    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4661    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4662    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4663    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4664    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4665    <date year='2005' month='March' />
4666  </front>
4667  <seriesInfo name='RFC' value='4033' />
4668</reference>
4669
4670<reference anchor="RFC4288">
4671  <front>
4672    <title>Media Type Specifications and Registration Procedures</title>
4673    <author initials="N." surname="Freed" fullname="N. Freed">
4674      <organization>Sun Microsystems</organization>
4675      <address>
4676        <email>ned.freed@mrochek.com</email>
4677      </address>
4678    </author>
4679    <author initials="J." surname="Klensin" fullname="J. Klensin">
4680      <address>
4681        <email>klensin+ietf@jck.com</email>
4682      </address>
4683    </author>
4684    <date year="2005" month="December"/>
4685  </front>
4686  <seriesInfo name="BCP" value="13"/>
4687  <seriesInfo name="RFC" value="4288"/>
4688</reference>
4689
4690<reference anchor='RFC4395'>
4691  <front>
4692    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4693    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4694      <organization>AT&amp;T Laboratories</organization>
4695      <address>
4696        <email>tony+urireg@maillennium.att.com</email>
4697      </address>
4698    </author>
4699    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4700      <organization>Qualcomm, Inc.</organization>
4701      <address>
4702        <email>hardie@qualcomm.com</email>
4703      </address>
4704    </author>
4705    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4706      <organization>Adobe Systems</organization>
4707      <address>
4708        <email>LMM@acm.org</email>
4709      </address>
4710    </author>
4711    <date year='2006' month='February' />
4712  </front>
4713  <seriesInfo name='BCP' value='115' />
4714  <seriesInfo name='RFC' value='4395' />
4715</reference>
4716
4717<reference anchor='RFC4559'>
4718  <front>
4719    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4720    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4721    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4722    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4723    <date year='2006' month='June' />
4724  </front>
4725  <seriesInfo name='RFC' value='4559' />
4726</reference>
4727
4728<reference anchor='RFC5226'>
4729  <front>
4730    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4731    <author initials='T.' surname='Narten' fullname='T. Narten'>
4732      <organization>IBM</organization>
4733      <address><email>narten@us.ibm.com</email></address>
4734    </author>
4735    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4736      <organization>Google</organization>
4737      <address><email>Harald@Alvestrand.no</email></address>
4738    </author>
4739    <date year='2008' month='May' />
4740  </front>
4741  <seriesInfo name='BCP' value='26' />
4742  <seriesInfo name='RFC' value='5226' />
4743</reference>
4744
4745<reference anchor="RFC5322">
4746  <front>
4747    <title>Internet Message Format</title>
4748    <author initials="P." surname="Resnick" fullname="P. Resnick">
4749      <organization>Qualcomm Incorporated</organization>
4750    </author>
4751    <date year="2008" month="October"/>
4752  </front> 
4753  <seriesInfo name="RFC" value="5322"/>
4754</reference>
4755
4756<reference anchor="RFC6265">
4757  <front>
4758    <title>HTTP State Management Mechanism</title>
4759    <author initials="A." surname="Barth" fullname="Adam Barth">
4760      <organization abbrev="U.C. Berkeley">
4761        University of California, Berkeley
4762      </organization>
4763      <address><email>abarth@eecs.berkeley.edu</email></address>
4764    </author>
4765    <date year="2011" month="April" />
4766  </front>
4767  <seriesInfo name="RFC" value="6265"/>
4768</reference>
4769
4770<!--<reference anchor='BCP97'>
4771  <front>
4772    <title>Handling Normative References to Standards-Track Documents</title>
4773    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4774      <address>
4775        <email>klensin+ietf@jck.com</email>
4776      </address>
4777    </author>
4778    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4779      <organization>MIT</organization>
4780      <address>
4781        <email>hartmans-ietf@mit.edu</email>
4782      </address>
4783    </author>
4784    <date year='2007' month='June' />
4785  </front>
4786  <seriesInfo name='BCP' value='97' />
4787  <seriesInfo name='RFC' value='4897' />
4788</reference>-->
4789
4790<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4791  <front>
4792    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4793    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4794    <date year="2001" month="November"/>
4795  </front>
4796  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4797</reference>
4798
4799<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4800  <front>
4801    <title>Analysis of HTTP Performance Problems</title>
4802    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4803    <date/>
4804  </front>
4805</reference>
4806
4807<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4808  <front>
4809  <title>Analysis of HTTP Performance</title>
4810  <author initials="J." surname="Touch" fullname="Joe Touch">
4811    <organization>USC/Information Sciences Institute</organization>
4812    <address><email>touch@isi.edu</email></address>
4813  </author>
4814  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4815    <organization>USC/Information Sciences Institute</organization>
4816    <address><email>johnh@isi.edu</email></address>
4817  </author>
4818  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4819    <organization>USC/Information Sciences Institute</organization>
4820    <address><email>katia@isi.edu</email></address>
4821  </author>
4822  <date year="1998" month="Aug"/>
4823  </front>
4824  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4825  <annotation>(original report dated Aug. 1996)</annotation>
4826</reference>
4827
4828</references>
4829
4830
4831<section title="HTTP Version History" anchor="compatibility">
4832<t>
4833   HTTP has been in use by the World-Wide Web global information initiative
4834   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4835   was a simple protocol for hypertext data transfer across the Internet
4836   with only a single request method (GET) and no metadata.
4837   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4838   methods and MIME-like messaging that could include metadata about the data
4839   transferred and modifiers on the request/response semantics. However,
4840   HTTP/1.0 did not sufficiently take into consideration the effects of
4841   hierarchical proxies, caching, the need for persistent connections, or
4842   name-based virtual hosts. The proliferation of incompletely-implemented
4843   applications calling themselves "HTTP/1.0" further necessitated a
4844   protocol version change in order for two communicating applications
4845   to determine each other's true capabilities.
4846</t>
4847<t>
4848   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4849   requirements that enable reliable implementations, adding only
4850   those new features that will either be safely ignored by an HTTP/1.0
4851   recipient or only sent when communicating with a party advertising
4852   conformance with HTTP/1.1.
4853</t>
4854<t>
4855   It is beyond the scope of a protocol specification to mandate
4856   conformance with previous versions. HTTP/1.1 was deliberately
4857   designed, however, to make supporting previous versions easy.
4858   We would expect a general-purpose HTTP/1.1 server to understand
4859   any valid request in the format of HTTP/1.0 and respond appropriately
4860   with an HTTP/1.1 message that only uses features understood (or
4861   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4862   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4863</t>
4864<t>
4865   Since HTTP/0.9 did not support header fields in a request,
4866   there is no mechanism for it to support name-based virtual
4867   hosts (selection of resource by inspection of the <x:ref>Host</x:ref> header
4868   field).  Any server that implements name-based virtual hosts
4869   ought to disable support for HTTP/0.9.  Most requests that
4870   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4871   requests wherein a buggy client failed to properly encode
4872   linear whitespace found in a URI reference and placed in
4873   the request-target.
4874</t>
4875
4876<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4877<t>
4878   This section summarizes major differences between versions HTTP/1.0
4879   and HTTP/1.1.
4880</t>
4881
4882<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4883<t>
4884   The requirements that clients and servers support the <x:ref>Host</x:ref>
4885   header field (<xref target="header.host"/>), report an error if it is
4886   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4887   are among the most important changes defined by HTTP/1.1.
4888</t>
4889<t>
4890   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4891   addresses and servers; there was no other established mechanism for
4892   distinguishing the intended server of a request than the IP address
4893   to which that request was directed. The <x:ref>Host</x:ref> header field was
4894   introduced during the development of HTTP/1.1 and, though it was
4895   quickly implemented by most HTTP/1.0 browsers, additional requirements
4896   were placed on all HTTP/1.1 requests in order to ensure complete
4897   adoption.  At the time of this writing, most HTTP-based services
4898   are dependent upon the Host header field for targeting requests.
4899</t>
4900</section>
4901
4902<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4903<t>
4904   In HTTP/1.0, each connection is established by the client prior to the
4905   request and closed by the server after sending the response. However, some
4906   implementations implement the explicitly negotiated ("Keep-Alive") version
4907   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4908   target="RFC2068"/>.
4909</t>
4910<t>
4911   Some clients and servers might wish to be compatible with these previous
4912   approaches to persistent connections, by explicitly negotiating for them
4913   with a "Connection: keep-alive" request header field. However, some
4914   experimental implementations of HTTP/1.0 persistent connections are faulty;
4915   for example, if a HTTP/1.0 proxy server doesn't understand
4916   <x:ref>Connection</x:ref>, it will erroneously forward that header to the
4917   next inbound server, which would result in a hung connection.
4918</t>
4919<t>
4920   One attempted solution was the introduction of a Proxy-Connection header,
4921   targeted specifically at proxies. In practice, this was also unworkable,
4922   because proxies are often deployed in multiple layers, bringing about the
4923   same problem discussed above.
4924</t>
4925<t>
4926   As a result, clients are encouraged not to send the Proxy-Connection header
4927   in any requests.
4928</t>
4929<t>
4930   Clients are also encouraged to consider the use of Connection: keep-alive
4931   in requests carefully; while they can enable persistent connections with
4932   HTTP/1.0 servers, clients using them need will need to monitor the
4933   connection for "hung" requests (which indicate that the client ought stop
4934   sending the header), and this mechanism ought not be used by clients at all
4935   when a proxy is being used.
4936</t>
4937</section>
4938
4939<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
4940<t>
4941   HTTP/1.1 introduces the <x:ref>Transfer-Encoding</x:ref> header field
4942   (<xref target="header.transfer-encoding"/>). Proxies/gateways &MUST; remove
4943   any transfer-coding prior to forwarding a message via a MIME-compliant
4944   protocol.
4945</t>
4946</section>
4947
4948</section>
4949
4950<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4951<t>
4952  Clarify that the string "HTTP" in the HTTP-version ABFN production is case
4953  sensitive. Restrict the version numbers to be single digits due to the fact
4954  that implementations are known to handle multi-digit version numbers
4955  incorrectly.
4956  (<xref target="http.version"/>)
4957</t>
4958<t>
4959  Update use of abs_path production from RFC 1808 to the path-absolute + query
4960  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4961  request method only.
4962  (<xref target="request-target"/>)
4963</t>
4964<t>
4965  Require that invalid whitespace around field-names be rejected.
4966  (<xref target="header.fields"/>)
4967</t>
4968<t>
4969  Rules about implicit linear whitespace between certain grammar productions
4970  have been removed; now whitespace is only allowed where specifically
4971  defined in the ABNF.
4972  (<xref target="whitespace"/>)
4973</t>
4974<t> 
4975  The NUL octet is no longer allowed in comment and quoted-string
4976  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4977  Non-ASCII content in header fields and reason phrase has been obsoleted and
4978  made opaque (the TEXT rule was removed).
4979  (<xref target="field.components"/>)
4980</t>
4981<t>
4982  Empty list elements in list productions have been deprecated.
4983  (<xref target="abnf.extension"/>)
4984</t>
4985<t>
4986  Require recipients to handle bogus <x:ref>Content-Length</x:ref> header
4987  fields as errors.
4988  (<xref target="message.body"/>)
4989</t>
4990<t>
4991  Remove reference to non-existent identity transfer-coding value tokens.
4992  (Sections <xref format="counter" target="message.body"/> and
4993  <xref format="counter" target="transfer.codings"/>)
4994</t>
4995<t>
4996  Clarification that the chunk length does not include the count of the octets
4997  in the chunk header and trailer. Furthermore disallowed line folding
4998  in chunk extensions, and deprecate their use.
4999  (<xref target="chunked.encoding"/>)
5000</t>
5001<t>
5002  Registration of Transfer Codings now requires IETF Review
5003  (<xref target="transfer.coding.registry"/>)
5004</t>
5005<t>
5006  Remove hard limit of two connections per server.
5007  Remove requirement to retry a sequence of requests as long it was idempotent.
5008  Remove requirements about when servers are allowed to close connections
5009  prematurely.
5010  (<xref target="persistent.practical"/>)
5011</t>
5012<t>
5013  Remove requirement to retry requests under certain cirumstances when the
5014  server prematurely closes the connection.
5015  (<xref target="message.transmission.requirements"/>)
5016</t>
5017<t>
5018  Change ABNF productions for header fields to only define the field value.
5019</t>
5020<t>
5021  Clarify exactly when "close" connection options have to be sent.
5022  (<xref target="header.connection"/>)
5023</t>
5024<t>
5025  Define the semantics of the <x:ref>Upgrade</x:ref> header field in responses
5026  other than 101 (this was incorporated from <xref target="RFC2817"/>).
5027  (<xref target="header.upgrade"/>)
5028</t>
5029</section>
5030</section>
5031
5032<?BEGININC p1-messaging.abnf-appendix ?>
5033<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
5034<figure>
5035<artwork type="abnf" name="p1-messaging.parsed-abnf">
5036<x:ref>BWS</x:ref> = OWS
5037
5038<x:ref>Connection</x:ref> = *( "," OWS ) connection-option *( OWS "," [ OWS
5039 connection-option ] )
5040<x:ref>Content-Length</x:ref> = 1*DIGIT
5041
5042<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5043 ]
5044<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
5045<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
5046<x:ref>Host</x:ref> = uri-host [ ":" port ]
5047
5048<x:ref>OWS</x:ref> = *( SP / HTAB )
5049
5050<x:ref>RWS</x:ref> = 1*( SP / HTAB )
5051
5052<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5053<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5054<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5055 transfer-coding ] )
5056
5057<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5058<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
5059
5060<x:ref>Via</x:ref> = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment
5061 ] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS
5062 comment ] ) ] )
5063
5064<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5065<x:ref>absolute-form</x:ref> = absolute-URI
5066<x:ref>asterisk-form</x:ref> = "*"
5067<x:ref>attribute</x:ref> = token
5068<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5069<x:ref>authority-form</x:ref> = authority
5070
5071<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5072<x:ref>chunk-data</x:ref> = 1*OCTET
5073<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5074<x:ref>chunk-ext-name</x:ref> = token
5075<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5076<x:ref>chunk-size</x:ref> = 1*HEXDIG
5077<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
5078<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5079<x:ref>connection-option</x:ref> = token
5080<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5081 / %x2A-5B ; '*'-'['
5082 / %x5D-7E ; ']'-'~'
5083 / obs-text
5084
5085<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5086<x:ref>field-name</x:ref> = token
5087<x:ref>field-value</x:ref> = *( field-content / obs-fold )
5088
5089<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
5090<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5091<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5092
5093<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
5094
5095<x:ref>message-body</x:ref> = *OCTET
5096<x:ref>method</x:ref> = token
5097
5098<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
5099<x:ref>obs-text</x:ref> = %x80-FF
5100<x:ref>origin-form</x:ref> = path-absolute [ "?" query ]
5101
5102<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5103<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5104<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5105<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5106<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
5107<x:ref>protocol-name</x:ref> = token
5108<x:ref>protocol-version</x:ref> = token
5109<x:ref>pseudonym</x:ref> = token
5110
5111<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5112 / %x5D-7E ; ']'-'~'
5113 / obs-text
5114<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
5115 / %x5D-7E ; ']'-'~'
5116 / obs-text
5117<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5118<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5119<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5120<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5121<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5122<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5123
5124<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5125<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5126<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5127<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5128<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
5129<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
5130 asterisk-form
5131
5132<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5133 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5134<x:ref>start-line</x:ref> = request-line / status-line
5135<x:ref>status-code</x:ref> = 3DIGIT
5136<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
5137
5138<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5139<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5140 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5141<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5142<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5143<x:ref>token</x:ref> = 1*tchar
5144<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5145<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5146 transfer-extension
5147<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5148<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5149
5150<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5151
5152<x:ref>value</x:ref> = word
5153
5154<x:ref>word</x:ref> = token / quoted-string
5155</artwork>
5156</figure>
5157<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5158; Connection defined but not used
5159; Content-Length defined but not used
5160; HTTP-message defined but not used
5161; Host defined but not used
5162; TE defined but not used
5163; Trailer defined but not used
5164; Transfer-Encoding defined but not used
5165; URI-reference defined but not used
5166; Upgrade defined but not used
5167; Via defined but not used
5168; chunked-body defined but not used
5169; http-URI defined but not used
5170; https-URI defined but not used
5171; partial-URI defined but not used
5172; special defined but not used
5173</artwork></figure></section>
5174<?ENDINC p1-messaging.abnf-appendix ?>
5175
5176<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5177
5178<section title="Since RFC 2616">
5179<t>
5180  Extracted relevant partitions from <xref target="RFC2616"/>.
5181</t>
5182</section>
5183
5184<section title="Since draft-ietf-httpbis-p1-messaging-00">
5185<t>
5186  Closed issues:
5187  <list style="symbols"> 
5188    <t>
5189      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5190      "HTTP Version should be case sensitive"
5191      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5192    </t>
5193    <t>
5194      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5195      "'unsafe' characters"
5196      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5197    </t>
5198    <t>
5199      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5200      "Chunk Size Definition"
5201      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5202    </t>
5203    <t>
5204      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5205      "Message Length"
5206      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5207    </t>
5208    <t>
5209      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5210      "Media Type Registrations"
5211      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5212    </t>
5213    <t>
5214      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5215      "URI includes query"
5216      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5217    </t>
5218    <t>
5219      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5220      "No close on 1xx responses"
5221      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5222    </t>
5223    <t>
5224      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5225      "Remove 'identity' token references"
5226      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5227    </t>
5228    <t>
5229      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5230      "Import query BNF"
5231    </t>
5232    <t>
5233      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5234      "qdtext BNF"
5235    </t>
5236    <t>
5237      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5238      "Normative and Informative references"
5239    </t>
5240    <t>
5241      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5242      "RFC2606 Compliance"
5243    </t>
5244    <t>
5245      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5246      "RFC977 reference"
5247    </t>
5248    <t>
5249      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5250      "RFC1700 references"
5251    </t>
5252    <t>
5253      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5254      "inconsistency in date format explanation"
5255    </t>
5256    <t>
5257      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5258      "Date reference typo"
5259    </t>
5260    <t>
5261      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5262      "Informative references"
5263    </t>
5264    <t>
5265      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5266      "ISO-8859-1 Reference"
5267    </t>
5268    <t>
5269      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5270      "Normative up-to-date references"
5271    </t>
5272  </list>
5273</t>
5274<t>
5275  Other changes:
5276  <list style="symbols"> 
5277    <t>
5278      Update media type registrations to use RFC4288 template.
5279    </t>
5280    <t>
5281      Use names of RFC4234 core rules DQUOTE and HTAB,
5282      fix broken ABNF for chunk-data
5283      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5284    </t>
5285  </list>
5286</t>
5287</section>
5288
5289<section title="Since draft-ietf-httpbis-p1-messaging-01">
5290<t>
5291  Closed issues:
5292  <list style="symbols"> 
5293    <t>
5294      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5295      "Bodies on GET (and other) requests"
5296    </t>
5297    <t>
5298      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5299      "Updating to RFC4288"
5300    </t>
5301    <t>
5302      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5303      "Status Code and Reason Phrase"
5304    </t>
5305    <t>
5306      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5307      "rel_path not used"
5308    </t>
5309  </list>
5310</t>
5311<t>
5312  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5313  <list style="symbols"> 
5314    <t>
5315      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5316      "trailer-part").
5317    </t>
5318    <t>
5319      Avoid underscore character in rule names ("http_URL" ->
5320      "http-URL", "abs_path" -> "path-absolute").
5321    </t>
5322    <t>
5323      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5324      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5325      have to be updated when switching over to RFC3986.
5326    </t>
5327    <t>
5328      Synchronize core rules with RFC5234.
5329    </t>
5330    <t>
5331      Get rid of prose rules that span multiple lines.
5332    </t>
5333    <t>
5334      Get rid of unused rules LOALPHA and UPALPHA.
5335    </t>
5336    <t>
5337      Move "Product Tokens" section (back) into Part 1, as "token" is used
5338      in the definition of the Upgrade header field.
5339    </t>
5340    <t>
5341      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5342    </t>
5343    <t>
5344      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5345    </t>
5346  </list>
5347</t>
5348</section>
5349
5350<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5351<t>
5352  Closed issues:
5353  <list style="symbols"> 
5354    <t>
5355      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5356      "HTTP-date vs. rfc1123-date"
5357    </t>
5358    <t>
5359      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5360      "WS in quoted-pair"
5361    </t>
5362  </list>
5363</t>
5364<t>
5365  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5366  <list style="symbols"> 
5367    <t>
5368      Reference RFC 3984, and update header field registrations for headers defined
5369      in this document.
5370    </t>
5371  </list>
5372</t>
5373<t>
5374  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5375  <list style="symbols"> 
5376    <t>
5377      Replace string literals when the string really is case-sensitive (HTTP-version).
5378    </t>
5379  </list>
5380</t>
5381</section>
5382
5383<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5384<t>
5385  Closed issues:
5386  <list style="symbols"> 
5387    <t>
5388      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5389      "Connection closing"
5390    </t>
5391    <t>
5392      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5393      "Move registrations and registry information to IANA Considerations"
5394    </t>
5395    <t>
5396      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5397      "need new URL for PAD1995 reference"
5398    </t>
5399    <t>
5400      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5401      "IANA Considerations: update HTTP URI scheme registration"
5402    </t>
5403    <t>
5404      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5405      "Cite HTTPS URI scheme definition"
5406    </t>
5407    <t>
5408      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5409      "List-type headers vs Set-Cookie"
5410    </t>
5411  </list>
5412</t>
5413<t>
5414  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5415  <list style="symbols"> 
5416    <t>
5417      Replace string literals when the string really is case-sensitive (HTTP-Date).
5418    </t>
5419    <t>
5420      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5421    </t>
5422  </list>
5423</t>
5424</section>
5425
5426<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5427<t>
5428  Closed issues:
5429  <list style="symbols"> 
5430    <t>
5431      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5432      "Out-of-date reference for URIs"
5433    </t>
5434    <t>
5435      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5436      "RFC 2822 is updated by RFC 5322"
5437    </t>
5438  </list>
5439</t>
5440<t>
5441  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5442  <list style="symbols"> 
5443    <t>
5444      Use "/" instead of "|" for alternatives.
5445    </t>
5446    <t>
5447      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5448    </t>
5449    <t>
5450      Only reference RFC 5234's core rules.
5451    </t>
5452    <t>
5453      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5454      whitespace ("OWS") and required whitespace ("RWS").
5455    </t>
5456    <t>
5457      Rewrite ABNFs to spell out whitespace rules, factor out
5458      header field value format definitions.
5459    </t>
5460  </list>
5461</t>
5462</section>
5463
5464<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5465<t>
5466  Closed issues:
5467  <list style="symbols"> 
5468    <t>
5469      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5470      "Header LWS"
5471    </t>
5472    <t>
5473      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5474      "Sort 1.3 Terminology"
5475    </t>
5476    <t>
5477      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5478      "RFC2047 encoded words"
5479    </t>
5480    <t>
5481      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5482      "Character Encodings in TEXT"
5483    </t>
5484    <t>
5485      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5486      "Line Folding"
5487    </t>
5488    <t>
5489      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5490      "OPTIONS * and proxies"
5491    </t>
5492    <t>
5493      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5494      "reason-phrase BNF"
5495    </t>
5496    <t>
5497      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5498      "Use of TEXT"
5499    </t>
5500    <t>
5501      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5502      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5503    </t>
5504    <t>
5505      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5506      "RFC822 reference left in discussion of date formats"
5507    </t>
5508  </list>
5509</t>
5510<t>
5511  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5512  <list style="symbols"> 
5513    <t>
5514      Rewrite definition of list rules, deprecate empty list elements.
5515    </t>
5516    <t>
5517      Add appendix containing collected and expanded ABNF.
5518    </t>
5519  </list>
5520</t>
5521<t>
5522  Other changes:
5523  <list style="symbols"> 
5524    <t>
5525      Rewrite introduction; add mostly new Architecture Section.
5526    </t>
5527    <t>
5528      Move definition of quality values from Part 3 into Part 1;
5529      make TE request header field grammar independent of accept-params (defined in Part 3).
5530    </t>
5531  </list>
5532</t>
5533</section>
5534
5535<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5536<t>
5537  Closed issues:
5538  <list style="symbols"> 
5539    <t>
5540      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5541      "base for numeric protocol elements"
5542    </t>
5543    <t>
5544      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5545      "comment ABNF"
5546    </t>
5547  </list>
5548</t>
5549<t>
5550  Partly resolved issues:
5551  <list style="symbols"> 
5552    <t>
5553      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5554      "205 Bodies" (took out language that implied that there might be
5555      methods for which a request body MUST NOT be included)
5556    </t>
5557    <t>
5558      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5559      "editorial improvements around HTTP-date"
5560    </t>
5561  </list>
5562</t>
5563</section>
5564
5565<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5566<t>
5567  Closed issues:
5568  <list style="symbols"> 
5569    <t>
5570      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5571      "Repeating single-value headers"
5572    </t>
5573    <t>
5574      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5575      "increase connection limit"
5576    </t>
5577    <t>
5578      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5579      "IP addresses in URLs"
5580    </t>
5581    <t>
5582      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5583      "take over HTTP Upgrade Token Registry"
5584    </t>
5585    <t>
5586      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5587      "CR and LF in chunk extension values"
5588    </t>
5589    <t>
5590      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5591      "HTTP/0.9 support"
5592    </t>
5593    <t>
5594      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5595      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5596    </t>
5597    <t>
5598      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5599      "move definitions of gzip/deflate/compress to part 1"
5600    </t>
5601    <t>
5602      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5603      "disallow control characters in quoted-pair"
5604    </t>
5605  </list>
5606</t>
5607<t>
5608  Partly resolved issues:
5609  <list style="symbols"> 
5610    <t>
5611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5612      "update IANA requirements wrt Transfer-Coding values" (add the
5613      IANA Considerations subsection)
5614    </t>
5615  </list>
5616</t>
5617</section>
5618
5619<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5620<t>
5621  Closed issues:
5622  <list style="symbols"> 
5623    <t>
5624      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5625      "header parsing, treatment of leading and trailing OWS"
5626    </t>
5627  </list>
5628</t>
5629<t>
5630  Partly resolved issues:
5631  <list style="symbols"> 
5632    <t>
5633      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5634      "Placement of 13.5.1 and 13.5.2"
5635    </t>
5636    <t>
5637      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5638      "use of term "word" when talking about header structure"
5639    </t>
5640  </list>
5641</t>
5642</section>
5643
5644<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5645<t>
5646  Closed issues:
5647  <list style="symbols"> 
5648    <t>
5649      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5650      "Clarification of the term 'deflate'"
5651    </t>
5652    <t>
5653      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5654      "OPTIONS * and proxies"
5655    </t>
5656    <t>
5657      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5658      "MIME-Version not listed in P1, general header fields"
5659    </t>
5660    <t>
5661      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5662      "IANA registry for content/transfer encodings"
5663    </t>
5664    <t>
5665      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5666      "Case-sensitivity of HTTP-date"
5667    </t>
5668    <t>
5669      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5670      "use of term "word" when talking about header structure"
5671    </t>
5672  </list>
5673</t>
5674<t>
5675  Partly resolved issues:
5676  <list style="symbols"> 
5677    <t>
5678      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5679      "Term for the requested resource's URI"
5680    </t>
5681  </list>
5682</t>
5683</section>
5684
5685<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5686<t>
5687  Closed issues:
5688  <list style="symbols">
5689    <t>
5690      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5691      "Connection Closing"
5692    </t>
5693    <t>
5694      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5695      "Delimiting messages with multipart/byteranges"
5696    </t>
5697    <t>
5698      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5699      "Handling multiple Content-Length headers"
5700    </t>
5701    <t>
5702      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5703      "Clarify entity / representation / variant terminology"
5704    </t>
5705    <t>
5706      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5707      "consider removing the 'changes from 2068' sections"
5708    </t>
5709  </list>
5710</t>
5711<t>
5712  Partly resolved issues:
5713  <list style="symbols"> 
5714    <t>
5715      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5716      "HTTP(s) URI scheme definitions"
5717    </t>
5718  </list>
5719</t>
5720</section>
5721
5722<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5723<t>
5724  Closed issues:
5725  <list style="symbols">
5726    <t>
5727      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5728      "Trailer requirements"
5729    </t>
5730    <t>
5731      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5732      "Text about clock requirement for caches belongs in p6"
5733    </t>
5734    <t>
5735      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5736      "effective request URI: handling of missing host in HTTP/1.0"
5737    </t>
5738    <t>
5739      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5740      "confusing Date requirements for clients"
5741    </t>
5742  </list>
5743</t>
5744<t>
5745  Partly resolved issues:
5746  <list style="symbols"> 
5747    <t>
5748      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5749      "Handling multiple Content-Length headers"
5750    </t>
5751  </list>
5752</t>
5753</section>
5754
5755<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5756<t>
5757  Closed issues:
5758  <list style="symbols">
5759    <t>
5760      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5761      "RFC2145 Normative"
5762    </t>
5763    <t>
5764      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5765      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5766    </t>
5767    <t>
5768      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5769      "define 'transparent' proxy"
5770    </t>
5771    <t>
5772      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5773      "Header Classification"
5774    </t>
5775    <t>
5776      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5777      "Is * usable as a request-uri for new methods?"
5778    </t>
5779    <t>
5780      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5781      "Migrate Upgrade details from RFC2817"
5782    </t>
5783    <t>
5784      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5785      "untangle ABNFs for header fields"
5786    </t>
5787    <t>
5788      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5789      "update RFC 2109 reference"
5790    </t>
5791  </list>
5792</t>
5793</section>
5794
5795<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5796<t>
5797  Closed issues:
5798  <list style="symbols">
5799    <t>
5800      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5801      "Allow is not in 13.5.2"
5802    </t>
5803    <t>
5804      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5805      "Handling multiple Content-Length headers"
5806    </t>
5807    <t>
5808      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5809      "untangle ABNFs for header fields"
5810    </t>
5811    <t>
5812      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5813      "Content-Length ABNF broken"
5814    </t>
5815  </list>
5816</t>
5817</section>
5818
5819<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5820<t>
5821  Closed issues:
5822  <list style="symbols">
5823    <t>
5824      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5825      "HTTP-version should be redefined as fixed length pair of DIGIT . DIGIT"
5826    </t>
5827    <t>
5828      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5829      "Recommend minimum sizes for protocol elements"
5830    </t>
5831    <t>
5832      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5833      "Set expectations around buffering"
5834    </t>
5835    <t>
5836      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5837      "Considering messages in isolation"
5838    </t>
5839  </list>
5840</t>
5841</section>
5842
5843<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5844<t>
5845  Closed issues:
5846  <list style="symbols">
5847    <t>
5848      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5849      "DNS Spoofing / DNS Binding advice"
5850    </t>
5851    <t>
5852      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5853      "move RFCs 2145, 2616, 2817 to Historic status"
5854    </t>
5855    <t>
5856      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5857      "\-escaping in quoted strings"
5858    </t>
5859    <t>
5860      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5861      "'Close' should be reserved in the HTTP header field registry"
5862    </t>
5863  </list>
5864</t>
5865</section>
5866
5867<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5868<t>
5869  Closed issues:
5870  <list style="symbols">
5871    <t>
5872      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5873      "Document HTTP's error-handling philosophy"
5874    </t>
5875    <t>
5876      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5877      "Explain header registration"
5878    </t>
5879    <t>
5880      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5881      "Revise Acknowledgements Sections"
5882    </t>
5883    <t>
5884      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5885      "Retrying Requests"
5886    </t>
5887    <t>
5888      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5889      "Closing the connection on server error"
5890    </t>
5891  </list>
5892</t>
5893</section>
5894
5895<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5896<t>
5897  Closed issues:
5898  <list style="symbols">
5899    <t>
5900      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/158"/>:
5901      "Proxy-Connection and Keep-Alive"
5902    </t>
5903    <t>
5904      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/166"/>:
5905      "Clarify 'User Agent'"
5906    </t>
5907    <t>
5908      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/300"/>:
5909      "Define non-final responses"
5910    </t>
5911    <t>
5912      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
5913      "intended maturity level vs normative references"
5914    </t>
5915    <t>
5916      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/324"/>:
5917      "Intermediary rewriting of queries"
5918    </t>
5919  </list>
5920</t>
5921</section>
5922
5923<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5924<t>
5925  Closed issues:
5926  <list style="symbols">
5927    <t>
5928      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
5929      "message-body in CONNECT response"
5930    </t>
5931    <t>
5932      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
5933      "Misplaced text on connection handling in p2"
5934    </t>
5935    <t>
5936      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/335"/>:
5937      "wording of line folding rule"
5938    </t>
5939    <t>
5940      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/343"/>:
5941      "chunk-extensions"
5942    </t>
5943    <t>
5944      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5945      "make IANA policy definitions consistent"
5946    </t>
5947  </list>
5948</t>
5949</section>
5950
5951<section title="Since draft-ietf-httpbis-p1-messaging-19" anchor="changes.since.19">
5952<t>
5953  Closed issues:
5954  <list style="symbols">
5955    <t>
5956      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5957      "make IANA policy definitions consistent"
5958    </t>
5959    <t>
5960      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/359"/>:
5961      "clarify connection header field values are case-insensitive"
5962    </t>
5963    <t>
5964      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/361"/>:
5965      "ABNF requirements for recipients"
5966    </t>
5967  </list>
5968</t>
5969</section>
5970
5971</section>
5972
5973</back>
5974</rfc>
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