source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1616

Last change on this file since 1616 was 1616, checked in by julian.reschke@…, 8 years ago

mark artwork as example (not even editorial)

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  • Property svn:mime-type set to text/xml
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "March">
16  <!ENTITY ID-YEAR "2012">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#response.cacheability' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY diff-mime              "<xref target='Part3' x:rel='#differences.between.http.and.mime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY representation         "<xref target='Part3' x:rel='#representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-date            "<xref target='Part2' x:rel='#header.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-mime-version    "<xref target='Part3' x:rel='#mime-version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY OPTIONS                "<xref target='Part2' x:rel='#OPTIONS' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-code-reasonphr  "<xref target='Part2' x:rel='#status.code.and.reason.phrase' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY cons-new-header-fields "<xref target='Part2' x:rel='#considerations.for.creating.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45]>
46<?rfc toc="yes" ?>
47<?rfc symrefs="yes" ?>
48<?rfc sortrefs="yes" ?>
49<?rfc compact="yes"?>
50<?rfc subcompact="no" ?>
51<?rfc linkmailto="no" ?>
52<?rfc editing="no" ?>
53<?rfc comments="yes"?>
54<?rfc inline="yes"?>
55<?rfc rfcedstyle="yes"?>
56<?rfc-ext allow-markup-in-artwork="yes" ?>
57<?rfc-ext include-references-in-index="yes" ?>
58<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="proposed"
59     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
60     xmlns:x='http://purl.org/net/xml2rfc/ext'>
61<x:link rel="next" basename="p2-semantics"/>
62<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
63<front>
64
65  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
66
67  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
68    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
69    <address>
70      <postal>
71        <street>345 Park Ave</street>
72        <city>San Jose</city>
73        <region>CA</region>
74        <code>95110</code>
75        <country>USA</country>
76      </postal>
77      <email>fielding@gbiv.com</email>
78      <uri>http://roy.gbiv.com/</uri>
79    </address>
80  </author>
81
82  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
83    <organization abbrev="W3C">World Wide Web Consortium</organization>
84    <address>
85      <postal>
86        <street>W3C / ERCIM</street>
87        <street>2004, rte des Lucioles</street>
88        <city>Sophia-Antipolis</city>
89        <region>AM</region>
90        <code>06902</code>
91        <country>France</country>
92      </postal>
93      <email>ylafon@w3.org</email>
94      <uri>http://www.raubacapeu.net/people/yves/</uri>
95    </address>
96  </author>
97
98  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
99    <organization abbrev="greenbytes">greenbytes GmbH</organization>
100    <address>
101      <postal>
102        <street>Hafenweg 16</street>
103        <city>Muenster</city><region>NW</region><code>48155</code>
104        <country>Germany</country>
105      </postal>
106      <phone>+49 251 2807760</phone>
107      <facsimile>+49 251 2807761</facsimile>
108      <email>julian.reschke@greenbytes.de</email>
109      <uri>http://greenbytes.de/tech/webdav/</uri>
110    </address>
111  </author>
112
113  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
114  <workgroup>HTTPbis Working Group</workgroup>
115
116<abstract>
117<t>
118   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
119   distributed, collaborative, hypertext information systems. HTTP has been in
120   use by the World Wide Web global information initiative since 1990. This
121   document is Part 1 of the seven-part specification that defines the protocol
122   referred to as "HTTP/1.1" and, taken together, obsoletes
123   <xref target="RFC2616" x:fmt="none">RFC 2616</xref> and moves it to historic
124   status, along with its predecessor <xref target="RFC2068" x:fmt="none">RFC
125   2068</xref>.
126</t>
127<t>
128   Part 1 provides an overview of HTTP and its associated terminology, defines
129   the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
130   the generic message syntax and parsing requirements for HTTP message frames,
131   and describes general security concerns for implementations.
132</t>
133<t>
134   This part also obsoletes RFCs <xref target="RFC2145" x:fmt="none">2145</xref>
135   (on HTTP version numbers) and <xref target="RFC2817" x:fmt="none">2817</xref>
136   (on using CONNECT for TLS upgrades) and moves them to historic status.
137</t>
138</abstract>
139
140<note title="Editorial Note (To be removed by RFC Editor)">
141  <t>
142    Discussion of this draft should take place on the HTTPBIS working group
143    mailing list (ietf-http-wg@w3.org), which is archived at
144    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
145  </t>
146  <t>
147    The current issues list is at
148    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
149    documents (including fancy diffs) can be found at
150    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
151  </t>
152  <t>
153    The changes in this draft are summarized in <xref target="changes.since.19"/>.
154  </t>
155</note>
156</front>
157<middle>
158<section title="Introduction" anchor="introduction">
159<t>
160   The Hypertext Transfer Protocol (HTTP) is an application-level
161   request/response protocol that uses extensible semantics and MIME-like
162   message payloads for flexible interaction with network-based hypertext
163   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
164   standard <xref target="RFC3986"/> to indicate the target resource
165   (<xref target="target-resource"/>) and relationships between resources.
166   Messages are passed in a format similar to that used by Internet mail
167   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
168   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
169   between HTTP and MIME messages).
170</t>
171<t>
172   HTTP is a generic interface protocol for information systems. It is
173   designed to hide the details of how a service is implemented by presenting
174   a uniform interface to clients that is independent of the types of
175   resources provided. Likewise, servers do not need to be aware of each
176   client's purpose: an HTTP request can be considered in isolation rather
177   than being associated with a specific type of client or a predetermined
178   sequence of application steps. The result is a protocol that can be used
179   effectively in many different contexts and for which implementations can
180   evolve independently over time.
181</t>
182<t>
183   HTTP is also designed for use as an intermediation protocol for translating
184   communication to and from non-HTTP information systems.
185   HTTP proxies and gateways can provide access to alternative information
186   services by translating their diverse protocols into a hypertext
187   format that can be viewed and manipulated by clients in the same way
188   as HTTP services.
189</t>
190<t>
191   One consequence of HTTP flexibility is that the protocol cannot be
192   defined in terms of what occurs behind the interface. Instead, we
193   are limited to defining the syntax of communication, the intent
194   of received communication, and the expected behavior of recipients.
195   If the communication is considered in isolation, then successful
196   actions ought to be reflected in corresponding changes to the
197   observable interface provided by servers. However, since multiple
198   clients might act in parallel and perhaps at cross-purposes, we
199   cannot require that such changes be observable beyond the scope
200   of a single response.
201</t>
202<t>
203   This document is Part 1 of the seven-part specification of HTTP,
204   defining the protocol referred to as "HTTP/1.1", obsoleting
205   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
206   Part 1 describes the architectural elements that are used or
207   referred to in HTTP, defines the "http" and "https" URI schemes,
208   describes overall network operation and connection management,
209   and defines HTTP message framing and forwarding requirements.
210   Our goal is to define all of the mechanisms necessary for HTTP message
211   handling that are independent of message semantics, thereby defining the
212   complete set of requirements for message parsers and
213   message-forwarding intermediaries.
214</t>
215
216<section title="Requirement Notation" anchor="intro.requirements">
217<t>
218   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
219   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
220   document are to be interpreted as described in <xref target="RFC2119"/>.
221</t>
222</section>
223
224<section title="Syntax Notation" anchor="notation">
225<iref primary="true" item="Grammar" subitem="ALPHA"/>
226<iref primary="true" item="Grammar" subitem="CR"/>
227<iref primary="true" item="Grammar" subitem="CRLF"/>
228<iref primary="true" item="Grammar" subitem="CTL"/>
229<iref primary="true" item="Grammar" subitem="DIGIT"/>
230<iref primary="true" item="Grammar" subitem="DQUOTE"/>
231<iref primary="true" item="Grammar" subitem="HEXDIG"/>
232<iref primary="true" item="Grammar" subitem="HTAB"/>
233<iref primary="true" item="Grammar" subitem="LF"/>
234<iref primary="true" item="Grammar" subitem="OCTET"/>
235<iref primary="true" item="Grammar" subitem="SP"/>
236<iref primary="true" item="Grammar" subitem="VCHAR"/>
237<t>
238   This specification uses the Augmented Backus-Naur Form (ABNF) notation
239   of <xref target="RFC5234"/> with the list rule extension defined in
240   <xref target="abnf.extension"/><xref target="collected.abnf"/> shows
241   the collected ABNF with the list rule expanded.
242</t>
243<t anchor="core.rules">
244  <x:anchor-alias value="ALPHA"/>
245  <x:anchor-alias value="CTL"/>
246  <x:anchor-alias value="CR"/>
247  <x:anchor-alias value="CRLF"/>
248  <x:anchor-alias value="DIGIT"/>
249  <x:anchor-alias value="DQUOTE"/>
250  <x:anchor-alias value="HEXDIG"/>
251  <x:anchor-alias value="HTAB"/>
252  <x:anchor-alias value="LF"/>
253  <x:anchor-alias value="OCTET"/>
254  <x:anchor-alias value="SP"/>
255  <x:anchor-alias value="VCHAR"/>
256   The following core rules are included by
257   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
258   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
259   DIGIT (decimal 0-9), DQUOTE (double quote),
260   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
261   OCTET (any 8-bit sequence of data), SP (space), and
262   VCHAR (any visible <xref target="USASCII"/> character).
263</t>
264<t>
265   As a convention, ABNF rule names prefixed with "obs-" denote
266   "obsolete" grammar rules that appear for historical reasons.
267</t>
268</section>
269</section>
270
271<section title="Architecture" anchor="architecture">
272<t>
273   HTTP was created for the World Wide Web architecture
274   and has evolved over time to support the scalability needs of a worldwide
275   hypertext system. Much of that architecture is reflected in the terminology
276   and syntax productions used to define HTTP.
277</t>
278
279<section title="Client/Server Messaging" anchor="operation">
280<iref primary="true" item="client"/>
281<iref primary="true" item="server"/>
282<iref primary="true" item="connection"/>
283<t>
284   HTTP is a stateless request/response protocol that operates by exchanging
285   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
286   transport or session-layer
287   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
288   program that establishes a connection to a server for the purpose of
289   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
290   program that accepts connections in order to service HTTP requests by
291   sending HTTP responses.
292</t>
293<iref primary="true" item="user agent"/>
294<iref primary="true" item="origin server"/>
295<iref primary="true" item="browser"/>
296<iref primary="true" item="spider"/>
297<iref primary="true" item="sender"/>
298<iref primary="true" item="recipient"/>
299<t>
300   Note that the terms client and server refer only to the roles that
301   these programs perform for a particular connection.  The same program
302   might act as a client on some connections and a server on others.  We use
303   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
304   such as a WWW browser, editor, or spider (web-traversing robot), and
305   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
306   authoritative responses to a request.  For general requirements, we use
307   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
308   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
309   message.
310</t>
311<x:note>
312  <t>
313    <x:h>Note:</x:h> The term 'user agent' covers both those situations where
314    there is a user (human) interacting with the software agent (and for which
315    user interface or interactive suggestions might be made, e.g., warning the
316    user or given the user an option in the case of security or privacy
317    options) and also those where the software agent may act autonomously.
318  </t>
319</x:note>
320<t>
321   Most HTTP communication consists of a retrieval request (GET) for
322   a representation of some resource identified by a URI.  In the
323   simplest case, this might be accomplished via a single bidirectional
324   connection (===) between the user agent (UA) and the origin server (O).
325</t>
326<figure><artwork type="drawing">
327         request   &gt;
328    UA ======================================= O
329                                &lt;   response
330</artwork></figure>
331<iref primary="true" item="message"/>
332<iref primary="true" item="request"/>
333<iref primary="true" item="response"/>
334<t>
335   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
336   message, beginning with a request-line that includes a method, URI, and
337   protocol version (<xref target="request.line"/>),
338   followed by MIME-like header fields containing
339   request modifiers, client information, and representation metadata
340   (<xref target="header.fields"/>),
341   an empty line to indicate the end of the header section, and finally
342   a message body containing the payload body (if any,
343   <xref target="message.body"/>).
344</t>
345<t>
346   A server responds to the client's request by sending one or more HTTP
347   <x:dfn>response</x:dfn>
348   messages, each beginning with a status line that
349   includes the protocol version, a success or error code, and textual
350   reason phrase (<xref target="status.line"/>),
351   possibly followed by MIME-like header fields containing server
352   information, resource metadata, and representation metadata
353   (<xref target="header.fields"/>),
354   an empty line to indicate the end of the header section, and finally
355   a message body containing the payload body (if any,
356   <xref target="message.body"/>).
357</t>
358<t>
359   The following example illustrates a typical message exchange for a
360   GET request on the URI "http://www.example.com/hello.txt":
361</t>
362<figure><preamble>
363client request:
364</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
365GET /hello.txt HTTP/1.1
366User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
367Host: www.example.com
368Accept: */*
369
370</artwork></figure>
371<figure><preamble>
372server response:
373</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
374HTTP/1.1 200 OK
375Date: Mon, 27 Jul 2009 12:28:53 GMT
376Server: Apache
377Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
378ETag: "34aa387-d-1568eb00"
379Accept-Ranges: bytes
380Content-Length: <x:length-of target="exbody"/>
381Vary: Accept-Encoding
382Content-Type: text/plain
383
384<x:span anchor="exbody">Hello World!
385</x:span></artwork></figure>
386</section>
387
388<section title="Connections and Transport Independence" anchor="transport-independence">
389<t>
390   HTTP messaging is independent of the underlying transport or
391   session-layer connection protocol(s).  HTTP only presumes a reliable
392   transport with in-order delivery of requests and the corresponding
393   in-order delivery of responses.  The mapping of HTTP request and
394   response structures onto the data units of the underlying transport
395   protocol is outside the scope of this specification.
396</t>
397<t>
398   The specific connection protocols to be used for an interaction
399   are determined by client configuration and the target URI
400   (<xref target="target-resource"/>).
401   For example, the "http" URI scheme
402   (<xref target="http.uri"/>) indicates a default connection of TCP
403   over IP, with a default TCP port of 80, but the client might be
404   configured to use a proxy via some other connection port or protocol
405   instead of using the defaults.
406</t>
407<t>
408   A connection might be used for multiple HTTP request/response exchanges,
409   as defined in <xref target="persistent.connections"/>.
410</t>
411</section>
412
413<section title="Intermediaries" anchor="intermediaries">
414<iref primary="true" item="intermediary"/>
415<t>
416   HTTP enables the use of intermediaries to satisfy requests through
417   a chain of connections.  There are three common forms of HTTP
418   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
419   a single intermediary might act as an origin server, proxy, gateway,
420   or tunnel, switching behavior based on the nature of each request.
421</t>
422<figure><artwork type="drawing">
423         &gt;             &gt;             &gt;             &gt;
424    <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>
425               &lt;             &lt;             &lt;             &lt;
426</artwork></figure>
427<t>
428   The figure above shows three intermediaries (A, B, and C) between the
429   user agent and origin server. A request or response message that
430   travels the whole chain will pass through four separate connections.
431   Some HTTP communication options
432   might apply only to the connection with the nearest, non-tunnel
433   neighbor, only to the end-points of the chain, or to all connections
434   along the chain. Although the diagram is linear, each participant might
435   be engaged in multiple, simultaneous communications. For example, B
436   might be receiving requests from many clients other than A, and/or
437   forwarding requests to servers other than C, at the same time that it
438   is handling A's request.
439</t>
440<t>
441<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
442<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
443   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
444   to describe various requirements in relation to the directional flow of a
445   message: all messages flow from upstream to downstream.
446   Likewise, we use the terms inbound and outbound to refer to
447   directions in relation to the request path:
448   "<x:dfn>inbound</x:dfn>" means toward the origin server and
449   "<x:dfn>outbound</x:dfn>" means toward the user agent.
450</t>
451<t><iref primary="true" item="proxy"/>
452   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
453   client, usually via local configuration rules, to receive requests
454   for some type(s) of absolute URI and attempt to satisfy those
455   requests via translation through the HTTP interface.  Some translations
456   are minimal, such as for proxy requests for "http" URIs, whereas
457   other requests might require translation to and from entirely different
458   application-layer protocols. Proxies are often used to group an
459   organization's HTTP requests through a common intermediary for the
460   sake of security, annotation services, or shared caching.
461</t>
462<t>
463<iref primary="true" item="transforming proxy"/>
464<iref primary="true" item="non-transforming proxy"/>
465   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
466   or configured to modify request or response messages in a semantically
467   meaningful way (i.e., modifications, beyond those required by normal
468   HTTP processing, that change the message in a way that would be
469   significant to the original sender or potentially significant to
470   downstream recipients).  For example, a transforming proxy might be
471   acting as a shared annotation server (modifying responses to include
472   references to a local annotation database), a malware filter, a
473   format transcoder, or an intranet-to-Internet privacy filter.  Such
474   transformations are presumed to be desired by the client (or client
475   organization) that selected the proxy and are beyond the scope of
476   this specification.  However, when a proxy is not intended to transform
477   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
478   requirements that preserve HTTP message semantics. See &status-203; and
479   &header-warning; for status and warning codes related to transformations.
480</t>
481<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
482<iref primary="true" item="accelerator"/>
483   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
484   is a receiving agent that acts
485   as a layer above some other server(s) and translates the received
486   requests to the underlying server's protocol.  Gateways are often
487   used to encapsulate legacy or untrusted information services, to
488   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
489   enable partitioning or load-balancing of HTTP services across
490   multiple machines.
491</t>
492<t>
493   A gateway behaves as an origin server on its outbound connection and
494   as a user agent on its inbound connection.
495   All HTTP requirements applicable to an origin server
496   also apply to the outbound communication of a gateway.
497   A gateway communicates with inbound servers using any protocol that
498   it desires, including private extensions to HTTP that are outside
499   the scope of this specification.  However, an HTTP-to-HTTP gateway
500   that wishes to interoperate with third-party HTTP servers &MUST;
501   conform to HTTP user agent requirements on the gateway's inbound
502   connection and &MUST; implement the Connection
503   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
504   header fields for both connections.
505</t>
506<t><iref primary="true" item="tunnel"/>
507   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
508   without changing the messages. Once active, a tunnel is not
509   considered a party to the HTTP communication, though the tunnel might
510   have been initiated by an HTTP request. A tunnel ceases to exist when
511   both ends of the relayed connection are closed. Tunnels are used to
512   extend a virtual connection through an intermediary, such as when
513   transport-layer security is used to establish private communication
514   through a shared firewall proxy.
515</t>
516<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
517<iref primary="true" item="captive portal"/>
518   In addition, there may exist network intermediaries that are not
519   considered part of the HTTP communication but nevertheless act as
520   filters or redirecting agents (usually violating HTTP semantics,
521   causing security problems, and otherwise making a mess of things).
522   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
523   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
524   or "<x:dfn>captive portal</x:dfn>",
525   differs from an HTTP proxy because it has not been selected by the client.
526   Instead, the network intermediary redirects outgoing TCP port 80 packets
527   (and occasionally other common port traffic) to an internal HTTP server.
528   Interception proxies are commonly found on public network access points,
529   as a means of enforcing account subscription prior to allowing use of
530   non-local Internet services, and within corporate firewalls to enforce
531   network usage policies.
532   They are indistinguishable from a man-in-the-middle attack.
533</t>
534<t>
535   HTTP is defined as a stateless protocol, meaning that each request message
536   can be understood in isolation.  Many implementations depend on HTTP's
537   stateless design in order to reuse proxied connections or dynamically
538   load balance requests across multiple servers.  Hence, servers &MUST-NOT;
539   assume that two requests on the same connection are from the same user
540   agent unless the connection is secured and specific to that agent.
541   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
542   been known to violate this requirement, resulting in security and
543   interoperability problems.
544</t>
545</section>
546
547<section title="Caches" anchor="caches">
548<iref primary="true" item="cache"/>
549<t>
550   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
551   subsystem that controls its message storage, retrieval, and deletion.
552   A cache stores cacheable responses in order to reduce the response
553   time and network bandwidth consumption on future, equivalent
554   requests. Any client or server &MAY; employ a cache, though a cache
555   cannot be used by a server while it is acting as a tunnel.
556</t>
557<t>
558   The effect of a cache is that the request/response chain is shortened
559   if one of the participants along the chain has a cached response
560   applicable to that request. The following illustrates the resulting
561   chain if B has a cached copy of an earlier response from O (via C)
562   for a request which has not been cached by UA or A.
563</t>
564<figure><artwork type="drawing">
565            &gt;             &gt;
566       UA =========== A =========== B - - - - - - C - - - - - - O
567                  &lt;             &lt;
568</artwork></figure>
569<t><iref primary="true" item="cacheable"/>
570   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
571   the response message for use in answering subsequent requests.
572   Even when a response is cacheable, there might be additional
573   constraints placed by the client or by the origin server on when
574   that cached response can be used for a particular request. HTTP
575   requirements for cache behavior and cacheable responses are
576   defined in &caching-overview;
577</t>
578<t>
579   There are a wide variety of architectures and configurations
580   of caches and proxies deployed across the World Wide Web and
581   inside large organizations. These systems include national hierarchies
582   of proxy caches to save transoceanic bandwidth, systems that
583   broadcast or multicast cache entries, organizations that distribute
584   subsets of cached data via optical media, and so on.
585</t>
586</section>
587
588<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
589<t>
590   This specification targets conformance criteria according to the role of
591   a participant in HTTP communication.  Hence, HTTP requirements are placed
592   on senders, recipients, clients, servers, user agents, intermediaries,
593   origin servers, proxies, gateways, or caches, depending on what behavior
594   is being constrained by the requirement.
595</t>
596<t>
597   An implementation is considered conformant if it complies with all of the
598   requirements associated with the roles it partakes in HTTP.
599</t>
600<t>
601   Senders &MUST-NOT; generate protocol elements that do not match the grammar
602   defined by the ABNF rules for those protocol elements.
603</t>
604<t>
605   Unless otherwise noted, recipients &MAY; attempt to recover a usable
606   protocol element from an invalid construct.  HTTP does not define
607   specific error handling mechanisms except when they have a direct impact
608   on security, since different applications of the protocol require
609   different error handling strategies.  For example, a Web browser might
610   wish to transparently recover from a response where the Location header
611   field doesn't parse according to the ABNF, whereas a systems control
612   client might consider any form of error recovery to be dangerous.
613</t>
614</section>
615
616<section title="Protocol Versioning" anchor="http.version">
617  <x:anchor-alias value="HTTP-version"/>
618  <x:anchor-alias value="HTTP-name"/>
619<t>
620   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
621   versions of the protocol. This specification defines version "1.1".
622   The protocol version as a whole indicates the sender's conformance
623   with the set of requirements laid out in that version's corresponding
624   specification of HTTP.
625</t>
626<t>
627   The version of an HTTP message is indicated by an HTTP-version field
628   in the first line of the message. HTTP-version is case-sensitive.
629</t>
630<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/>
631  <x:ref>HTTP-version</x:ref>  = <x:ref>HTTP-name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
632  <x:ref>HTTP-name</x:ref>     = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
633</artwork></figure>
634<t>
635   The HTTP version number consists of two decimal digits separated by a "."
636   (period or decimal point).  The first digit ("major version") indicates the
637   HTTP messaging syntax, whereas the second digit ("minor version") indicates
638   the highest minor version to which the sender is
639   conformant and able to understand for future communication.  The minor
640   version advertises the sender's communication capabilities even when the
641   sender is only using a backwards-compatible subset of the protocol,
642   thereby letting the recipient know that more advanced features can
643   be used in response (by servers) or in future requests (by clients).
644</t>
645<t>
646   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
647   <xref target="RFC1945"/> or a recipient whose version is unknown,
648   the HTTP/1.1 message is constructed such that it can be interpreted
649   as a valid HTTP/1.0 message if all of the newer features are ignored.
650   This specification places recipient-version requirements on some
651   new features so that a conformant sender will only use compatible
652   features until it has determined, through configuration or the
653   receipt of a message, that the recipient supports HTTP/1.1.
654</t>
655<t>
656   The interpretation of a header field does not change between minor
657   versions of the same major HTTP version, though the default
658   behavior of a recipient in the absence of such a field can change.
659   Unless specified otherwise, header fields defined in HTTP/1.1 are
660   defined for all versions of HTTP/1.x.  In particular, the Host and
661   Connection header fields ought to be implemented by all HTTP/1.x
662   implementations whether or not they advertise conformance with HTTP/1.1.
663</t>
664<t>
665   New header fields can be defined such that, when they are
666   understood by a recipient, they might override or enhance the
667   interpretation of previously defined header fields.  When an
668   implementation receives an unrecognized header field, the recipient
669   &MUST; ignore that header field for local processing regardless of
670   the message's HTTP version.  An unrecognized header field received
671   by a proxy &MUST; be forwarded downstream unless the header field's
672   field-name is listed in the message's Connection header-field
673   (see <xref target="header.connection"/>).
674   These requirements allow HTTP's functionality to be enhanced without
675   requiring prior update of deployed intermediaries.
676</t>
677<t>
678   Intermediaries that process HTTP messages (i.e., all intermediaries
679   other than those acting as tunnels) &MUST; send their own HTTP-version
680   in forwarded messages.  In other words, they &MUST-NOT; blindly
681   forward the first line of an HTTP message without ensuring that the
682   protocol version in that message matches a version to which that
683   intermediary is conformant for both the receiving and
684   sending of messages.  Forwarding an HTTP message without rewriting
685   the HTTP-version might result in communication errors when downstream
686   recipients use the message sender's version to determine what features
687   are safe to use for later communication with that sender.
688</t>
689<t>
690   An HTTP client &SHOULD; send a request version equal to the highest
691   version to which the client is conformant and
692   whose major version is no higher than the highest version supported
693   by the server, if this is known.  An HTTP client &MUST-NOT; send a
694   version to which it is not conformant.
695</t>
696<t>
697   An HTTP client &MAY; send a lower request version if it is known that
698   the server incorrectly implements the HTTP specification, but only
699   after the client has attempted at least one normal request and determined
700   from the response status or header fields (e.g., Server) that the
701   server improperly handles higher request versions.
702</t>
703<t>
704   An HTTP server &SHOULD; send a response version equal to the highest
705   version to which the server is conformant and
706   whose major version is less than or equal to the one received in the
707   request.  An HTTP server &MUST-NOT; send a version to which it is not
708   conformant.  A server &MAY; send a 505 (HTTP
709   Version Not Supported) response if it cannot send a response using the
710   major version used in the client's request.
711</t>
712<t>
713   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
714   if it is known or suspected that the client incorrectly implements the
715   HTTP specification and is incapable of correctly processing later
716   version responses, such as when a client fails to parse the version
717   number correctly or when an intermediary is known to blindly forward
718   the HTTP-version even when it doesn't conform to the given minor
719   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
720   performed unless triggered by specific client attributes, such as when
721   one or more of the request header fields (e.g., User-Agent) uniquely
722   match the values sent by a client known to be in error.
723</t>
724<t>
725   The intention of HTTP's versioning design is that the major number
726   will only be incremented if an incompatible message syntax is
727   introduced, and that the minor number will only be incremented when
728   changes made to the protocol have the effect of adding to the message
729   semantics or implying additional capabilities of the sender.  However,
730   the minor version was not incremented for the changes introduced between
731   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
732   is specifically avoiding any such changes to the protocol.
733</t>
734</section>
735
736<section title="Uniform Resource Identifiers" anchor="uri">
737<iref primary="true" item="resource"/>
738<t>
739   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
740   throughout HTTP as the means for identifying resources. URI references
741   are used to target requests, indicate redirects, and define relationships.
742   HTTP does not limit what a resource might be; it merely defines an interface
743   that can be used to interact with a resource via HTTP. More information on
744   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
745</t>
746  <x:anchor-alias value="URI-reference"/>
747  <x:anchor-alias value="absolute-URI"/>
748  <x:anchor-alias value="relative-part"/>
749  <x:anchor-alias value="authority"/>
750  <x:anchor-alias value="path-abempty"/>
751  <x:anchor-alias value="path-absolute"/>
752  <x:anchor-alias value="port"/>
753  <x:anchor-alias value="query"/>
754  <x:anchor-alias value="uri-host"/>
755  <x:anchor-alias value="partial-URI"/>
756<t>
757   This specification adopts the definitions of "URI-reference",
758   "absolute-URI", "relative-part", "port", "host",
759   "path-abempty", "path-absolute", "query", and "authority" from the
760   URI generic syntax <xref target="RFC3986"/>.
761   In addition, we define a partial-URI rule for protocol elements
762   that allow a relative URI but not a fragment.
763</t>
764<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"/>
765  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
766  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
767  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
768  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
769  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
770  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
771  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
772  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
773  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
774 
775  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
776</artwork></figure>
777<t>
778   Each protocol element in HTTP that allows a URI reference will indicate
779   in its ABNF production whether the element allows any form of reference
780   (URI-reference), only a URI in absolute form (absolute-URI), only the
781   path and optional query components, or some combination of the above.
782   Unless otherwise indicated, URI references are parsed
783   relative to the effective request URI
784   (<xref target="effective.request.uri"/>).
785</t>
786
787<section title="http URI scheme" anchor="http.uri">
788  <x:anchor-alias value="http-URI"/>
789  <iref item="http URI scheme" primary="true"/>
790  <iref item="URI scheme" subitem="http" primary="true"/>
791<t>
792   The "http" URI scheme is hereby defined for the purpose of minting
793   identifiers according to their association with the hierarchical
794   namespace governed by a potential HTTP origin server listening for
795   TCP connections on a given port.
796</t>
797<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
798  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
799</artwork></figure>
800<t>
801   The HTTP origin server is identified by the generic syntax's
802   <x:ref>authority</x:ref> component, which includes a host identifier
803   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
804   The remainder of the URI, consisting of both the hierarchical path
805   component and optional query component, serves as an identifier for
806   a potential resource within that origin server's name space.
807</t>
808<t>
809   If the host identifier is provided as an IP literal or IPv4 address,
810   then the origin server is any listener on the indicated TCP port at
811   that IP address. If host is a registered name, then that name is
812   considered an indirect identifier and the recipient might use a name
813   resolution service, such as DNS, to find the address of a listener
814   for that host.
815   The host &MUST-NOT; be empty; if an "http" URI is received with an
816   empty host, then it &MUST; be rejected as invalid.
817   If the port subcomponent is empty or not given, then TCP port 80 is
818   assumed (the default reserved port for WWW services).
819</t>
820<t>
821   Regardless of the form of host identifier, access to that host is not
822   implied by the mere presence of its name or address. The host might or might
823   not exist and, even when it does exist, might or might not be running an
824   HTTP server or listening to the indicated port. The "http" URI scheme
825   makes use of the delegated nature of Internet names and addresses to
826   establish a naming authority (whatever entity has the ability to place
827   an HTTP server at that Internet name or address) and allows that
828   authority to determine which names are valid and how they might be used.
829</t>
830<t>
831   When an "http" URI is used within a context that calls for access to the
832   indicated resource, a client &MAY; attempt access by resolving
833   the host to an IP address, establishing a TCP connection to that address
834   on the indicated port, and sending an HTTP request message
835   (<xref target="http.message"/>) containing the URI's identifying data
836   (<xref target="message.routing"/>) to the server.
837   If the server responds to that request with a non-interim HTTP response
838   message, as described in &status-code-reasonphr;, then that response
839   is considered an authoritative answer to the client's request.
840</t>
841<t>
842   Although HTTP is independent of the transport protocol, the "http"
843   scheme is specific to TCP-based services because the name delegation
844   process depends on TCP for establishing authority.
845   An HTTP service based on some other underlying connection protocol
846   would presumably be identified using a different URI scheme, just as
847   the "https" scheme (below) is used for servers that require an SSL/TLS
848   transport layer on a connection. Other protocols might also be used to
849   provide access to "http" identified resources &mdash; it is only the
850   authoritative interface used for mapping the namespace that is
851   specific to TCP.
852</t>
853<t>
854   The URI generic syntax for authority also includes a deprecated
855   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
856   for including user authentication information in the URI.  Some
857   implementations make use of the userinfo component for internal
858   configuration of authentication information, such as within command
859   invocation options, configuration files, or bookmark lists, even
860   though such usage might expose a user identifier or password.
861   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
862   delimiter) when transmitting an "http" URI in a message.  Recipients
863   of HTTP messages that contain a URI reference &SHOULD; parse for the
864   existence of userinfo and treat its presence as an error, likely
865   indicating that the deprecated subcomponent is being used to obscure
866   the authority for the sake of phishing attacks.
867</t>
868</section>
869
870<section title="https URI scheme" anchor="https.uri">
871   <x:anchor-alias value="https-URI"/>
872   <iref item="https URI scheme"/>
873   <iref item="URI scheme" subitem="https"/>
874<t>
875   The "https" URI scheme is hereby defined for the purpose of minting
876   identifiers according to their association with the hierarchical
877   namespace governed by a potential HTTP origin server listening for
878   SSL/TLS-secured connections on a given TCP port.
879</t>
880<t>
881   All of the requirements listed above for the "http" scheme are also
882   requirements for the "https" scheme, except that a default TCP port
883   of 443 is assumed if the port subcomponent is empty or not given,
884   and the TCP connection &MUST; be secured for privacy through the
885   use of strong encryption prior to sending the first HTTP request.
886</t>
887<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
888  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
889</artwork></figure>
890<t>
891   Unlike the "http" scheme, responses to "https" identified requests
892   are never "public" and thus &MUST-NOT; be reused for shared caching.
893   They can, however, be reused in a private cache if the message is
894   cacheable by default in HTTP or specifically indicated as such by
895   the Cache-Control header field (&header-cache-control;).
896</t>
897<t>
898   Resources made available via the "https" scheme have no shared
899   identity with the "http" scheme even if their resource identifiers
900   indicate the same authority (the same host listening to the same
901   TCP port).  They are distinct name spaces and are considered to be
902   distinct origin servers.  However, an extension to HTTP that is
903   defined to apply to entire host domains, such as the Cookie protocol
904   <xref target="RFC6265"/>, can allow information
905   set by one service to impact communication with other services
906   within a matching group of host domains.
907</t>
908<t>
909   The process for authoritative access to an "https" identified
910   resource is defined in <xref target="RFC2818"/>.
911</t>
912</section>
913
914<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
915<t>
916   Since the "http" and "https" schemes conform to the URI generic syntax,
917   such URIs are normalized and compared according to the algorithm defined
918   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
919   described above for each scheme.
920</t>
921<t>
922   If the port is equal to the default port for a scheme, the normal
923   form is to elide the port subcomponent. Likewise, an empty path
924   component is equivalent to an absolute path of "/", so the normal
925   form is to provide a path of "/" instead. The scheme and host
926   are case-insensitive and normally provided in lowercase; all
927   other components are compared in a case-sensitive manner.
928   Characters other than those in the "reserved" set are equivalent
929   to their percent-encoded octets (see <xref target="RFC3986"
930   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
931</t>
932<t>
933   For example, the following three URIs are equivalent:
934</t>
935<figure><artwork type="example">
936   http://example.com:80/~smith/home.html
937   http://EXAMPLE.com/%7Esmith/home.html
938   http://EXAMPLE.com:/%7esmith/home.html
939</artwork></figure>
940</section>
941</section>
942</section>
943
944<section title="Message Format" anchor="http.message">
945<x:anchor-alias value="generic-message"/>
946<x:anchor-alias value="message.types"/>
947<x:anchor-alias value="HTTP-message"/>
948<x:anchor-alias value="start-line"/>
949<iref item="header section"/>
950<iref item="headers"/>
951<iref item="header field"/>
952<t>
953   All HTTP/1.1 messages consist of a start-line followed by a sequence of
954   octets in a format similar to the Internet Message Format
955   <xref target="RFC5322"/>: zero or more header fields (collectively
956   referred to as the "headers" or the "header section"), an empty line
957   indicating the end of the header section, and an optional message body.
958</t>
959<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
960  <x:ref>HTTP-message</x:ref>   = <x:ref>start-line</x:ref>
961                   *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
962                   <x:ref>CRLF</x:ref>
963                   [ <x:ref>message-body</x:ref> ]
964</artwork></figure>
965<t>
966   The normal procedure for parsing an HTTP message is to read the
967   start-line into a structure, read each header field into a hash
968   table by field name until the empty line, and then use the parsed
969   data to determine if a message body is expected.  If a message body
970   has been indicated, then it is read as a stream until an amount
971   of octets equal to the message body length is read or the connection
972   is closed.
973</t>
974<t>
975   Recipients &MUST; parse an HTTP message as a sequence of octets in an
976   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
977   Parsing an HTTP message as a stream of Unicode characters, without regard
978   for the specific encoding, creates security vulnerabilities due to the
979   varying ways that string processing libraries handle invalid multibyte
980   character sequences that contain the octet LF (%x0A).  String-based
981   parsers can only be safely used within protocol elements after the element
982   has been extracted from the message, such as within a header field-value
983   after message parsing has delineated the individual fields.
984</t>
985<t>
986   An HTTP message can be parsed as a stream for incremental processing or
987   forwarding downstream.  However, recipients cannot rely on incremental
988   delivery of partial messages, since some implementations will buffer or
989   delay message forwarding for the sake of network efficiency, security
990   checks, or payload transformations.
991</t>
992
993<section title="Start Line" anchor="start.line">
994  <x:anchor-alias value="Start-Line"/>
995<t>
996   An HTTP message can either be a request from client to server or a
997   response from server to client.  Syntactically, the two types of message
998   differ only in the start-line, which is either a request-line (for requests)
999   or a status-line (for responses), and in the algorithm for determining
1000   the length of the message body (<xref target="message.body"/>).
1001   In theory, a client could receive requests and a server could receive
1002   responses, distinguishing them by their different start-line formats,
1003   but in practice servers are implemented to only expect a request
1004   (a response is interpreted as an unknown or invalid request method)
1005   and clients are implemented to only expect a response.
1006</t>
1007<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1008  <x:ref>start-line</x:ref>     = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1009</artwork></figure>
1010<t>
1011</t>
1012<t>
1013   Implementations &MUST-NOT; send whitespace between the start-line and
1014   the first header field. The presence of such whitespace in a request
1015   might be an attempt to trick a server into ignoring that field or
1016   processing the line after it as a new request, either of which might
1017   result in a security vulnerability if other implementations within
1018   the request chain interpret the same message differently.
1019   Likewise, the presence of such whitespace in a response might be
1020   ignored by some clients or cause others to cease parsing.
1021</t>
1022
1023<section title="Request Line" anchor="request.line">
1024  <x:anchor-alias value="Request"/>
1025  <x:anchor-alias value="request-line"/>
1026<t>
1027   A request-line begins with a method token, followed by a single
1028   space (SP), the request-target, another single space (SP), the
1029   protocol version, and ending with CRLF.
1030</t>
1031<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1032  <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>
1033</artwork></figure>
1034<iref primary="true" item="method"/>
1035<t anchor="method">
1036   The method token indicates the request method to be performed on the
1037   target resource. The request method is case-sensitive.
1038</t>
1039<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1040  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1041</artwork></figure>
1042<t>
1043   The methods defined by this specification can be found in
1044   &method;, along with information regarding the HTTP method registry
1045   and considerations for defining new methods.
1046</t>
1047<iref item="request-target"/>
1048<t>
1049   The request-target identifies the target resource upon which to apply
1050   the request, as defined in <xref target="request-target"/>.
1051</t>
1052<t>
1053   No whitespace is allowed inside the method, request-target, and
1054   protocol version.  Hence, recipients typically parse the request-line
1055   into its component parts by splitting on the SP characters.
1056</t>
1057<t>
1058   Unfortunately, some user agents fail to properly encode hypertext
1059   references that have embedded whitespace, sending the characters
1060   directly instead of properly percent-encoding the disallowed characters.
1061   Recipients of an invalid request-line &SHOULD; respond with either a
1062   400 (Bad Request) error or a 301 (Moved Permanently) redirect with the
1063   request-target properly encoded.  Recipients &SHOULD-NOT; attempt to
1064   autocorrect and then process the request without a redirect, since the
1065   invalid request-line might be deliberately crafted to bypass
1066   security filters along the request chain.
1067</t>
1068<t>
1069   HTTP does not place a pre-defined limit on the length of a request-line.
1070   A server that receives a method longer than any that it implements
1071   &SHOULD; respond with either a 405 (Not Allowed), if it is an origin
1072   server, or a 501 (Not Implemented) status code.
1073   A server &MUST; be prepared to receive URIs of unbounded length and
1074   respond with the 414 (URI Too Long) status code if the received
1075   request-target would be longer than the server wishes to handle
1076   (see &status-414;).
1077</t>
1078<t>
1079   Various ad-hoc limitations on request-line length are found in practice.
1080   It is &RECOMMENDED; that all HTTP senders and recipients support, at a
1081   minimum, request-line lengths of up to 8000 octets.
1082</t>
1083</section>
1084
1085<section title="Status Line" anchor="status.line">
1086  <x:anchor-alias value="response"/>
1087  <x:anchor-alias value="status-line"/>
1088<t>
1089   The first line of a response message is the status-line, consisting
1090   of the protocol version, a space (SP), the status code, another space,
1091   a possibly-empty textual phrase describing the status code, and
1092   ending with CRLF.
1093</t>
1094<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1095  <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>
1096</artwork></figure>
1097
1098<t anchor="status-code">
1099   The status-code element is a 3-digit integer result code of the attempt to
1100   understand and satisfy the request. See &status-code-reasonphr; for
1101   further information, such as the list of status codes defined by this
1102   specification, the IANA registry, and considerations for new status codes.
1103</t>
1104<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1105  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1106</artwork></figure>
1107
1108<t anchor="reason-phrase">   
1109   The reason-phrase element exists for the sole purpose of providing a
1110   textual description associated with the numeric status code, mostly
1111   out of deference to earlier Internet application protocols that were more
1112   frequently used with interactive text clients. A client &SHOULD; ignore
1113   the reason-phrase content.
1114</t>
1115<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1116  <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> )
1117</artwork></figure>
1118</section>
1119</section>
1120
1121<section title="Header Fields" anchor="header.fields">
1122  <x:anchor-alias value="header-field"/>
1123  <x:anchor-alias value="field-content"/>
1124  <x:anchor-alias value="field-name"/>
1125  <x:anchor-alias value="field-value"/>
1126  <x:anchor-alias value="obs-fold"/>
1127<t>
1128   Each HTTP header field consists of a case-insensitive field name
1129   followed by a colon (":"), optional whitespace, and the field value.
1130</t>
1131<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"/>
1132  <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>
1133  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1134  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1135  <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> )
1136  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1137                 ; obsolete line folding
1138                 ; see <xref target="field.parsing"/>
1139</artwork></figure>
1140<t>
1141   The field-name token labels the corresponding field-value as having the
1142   semantics defined by that header field.  For example, the Date header field
1143   is defined in &header-date; as containing the origination
1144   timestamp for the message in which it appears.
1145</t>
1146<t>
1147   HTTP header fields are fully extensible: there is no limit on the
1148   introduction of new field names, each presumably defining new semantics,
1149   or on the number of header fields used in a given message.  Existing
1150   fields are defined in each part of this specification and in many other
1151   specifications outside the standards process.
1152   New header fields can be introduced without changing the protocol version
1153   if their defined semantics allow them to be safely ignored by recipients
1154   that do not recognize them.
1155</t>
1156<t>
1157   New HTTP header fields &SHOULD; be registered with IANA according
1158   to the procedures in &cons-new-header-fields;.
1159   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1160   field-name is listed in the Connection header field
1161   (<xref target="header.connection"/>) or the proxy is specifically
1162   configured to block or otherwise transform such fields.
1163   Unrecognized header fields &SHOULD; be ignored by other recipients.
1164</t>
1165<t>
1166   The order in which header fields with differing field names are
1167   received is not significant. However, it is "good practice" to send
1168   header fields that contain control data first, such as Host on
1169   requests and Date on responses, so that implementations can decide
1170   when not to handle a message as early as possible.  A server &MUST;
1171   wait until the entire header section is received before interpreting
1172   a request message, since later header fields might include conditionals,
1173   authentication credentials, or deliberately misleading duplicate
1174   header fields that would impact request processing.
1175</t>
1176<t>
1177   Multiple header fields with the same field name &MUST-NOT; be
1178   sent in a message unless the entire field value for that
1179   header field is defined as a comma-separated list [i.e., #(values)].
1180   Multiple header fields with the same field name can be combined into
1181   one "field-name: field-value" pair, without changing the semantics of the
1182   message, by appending each subsequent field value to the combined
1183   field value in order, separated by a comma. The order in which
1184   header fields with the same field name are received is therefore
1185   significant to the interpretation of the combined field value;
1186   a proxy &MUST-NOT; change the order of these field values when
1187   forwarding a message.
1188</t>
1189<x:note>
1190  <t>
1191   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1192   practice can occur multiple times, but does not use the list syntax, and
1193   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1194   for details.) Also note that the Set-Cookie2 header field specified in
1195   <xref target="RFC2965"/> does not share this problem.
1196  </t>
1197</x:note>
1198
1199<section title="Whitespace" anchor="whitespace">
1200<t anchor="rule.LWS">
1201   This specification uses three rules to denote the use of linear
1202   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1203   BWS ("bad" whitespace).
1204</t>
1205<t anchor="rule.OWS">
1206   The OWS rule is used where zero or more linear whitespace octets might
1207   appear. OWS &SHOULD; either not be produced or be produced as a single
1208   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1209   be replaced with a single SP or transformed to all SP octets (each
1210   octet other than SP replaced with SP) before interpreting the field value
1211   or forwarding the message downstream.
1212</t>
1213<t anchor="rule.RWS">
1214   RWS is used when at least one linear whitespace octet is required to
1215   separate field tokens. RWS &SHOULD; be produced as a single SP.
1216   Multiple RWS octets that occur within field-content &SHOULD; either
1217   be replaced with a single SP or transformed to all SP octets before
1218   interpreting the field value or forwarding the message downstream.
1219</t>
1220<t anchor="rule.BWS">
1221   BWS is used where the grammar allows optional whitespace for historical
1222   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
1223   recipients &MUST; accept such bad optional whitespace and remove it before
1224   interpreting the field value or forwarding the message downstream.
1225</t>
1226<t anchor="rule.whitespace">
1227  <x:anchor-alias value="BWS"/>
1228  <x:anchor-alias value="OWS"/>
1229  <x:anchor-alias value="RWS"/>
1230</t>
1231<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"/>
1232  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1233                 ; "optional" whitespace
1234  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1235                 ; "required" whitespace
1236  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1237                 ; "bad" whitespace
1238</artwork></figure>
1239</section>
1240
1241<section title="Field Parsing" anchor="field.parsing">
1242<t>
1243   No whitespace is allowed between the header field-name and colon.
1244   In the past, differences in the handling of such whitespace have led to
1245   security vulnerabilities in request routing and response handling.
1246   Any received request message that contains whitespace between a header
1247   field-name and colon &MUST; be rejected with a response code of 400
1248   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1249   message before forwarding the message downstream.
1250</t>
1251<t>
1252   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1253   preferred. The field value does not include any leading or trailing white
1254   space: OWS occurring before the first non-whitespace octet of the
1255   field value or after the last non-whitespace octet of the field value
1256   is ignored and &SHOULD; be removed before further processing (as this does
1257   not change the meaning of the header field).
1258</t>
1259<t>
1260   Historically, HTTP header field values could be extended over multiple
1261   lines by preceding each extra line with at least one space or horizontal
1262   tab (obs-fold). This specification deprecates such line
1263   folding except within the message/http media type
1264   (<xref target="internet.media.type.message.http"/>).
1265   HTTP senders &MUST-NOT; produce messages that include line folding
1266   (i.e., that contain any field-value that matches the obs-fold rule) unless
1267   the message is intended for packaging within the message/http media type.
1268   HTTP recipients &SHOULD; accept line folding and replace any embedded
1269   obs-fold whitespace with either a single SP or a matching number of SP
1270   octets (to avoid buffer copying) prior to interpreting the field value or
1271   forwarding the message downstream.
1272</t>
1273<t>
1274   Historically, HTTP has allowed field content with text in the ISO-8859-1
1275   <xref target="ISO-8859-1"/> character encoding and supported other
1276   character sets only through use of <xref target="RFC2047"/> encoding.
1277   In practice, most HTTP header field values use only a subset of the
1278   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1279   header fields &SHOULD; limit their field values to US-ASCII octets.
1280   Recipients &SHOULD; treat other (obs-text) octets in field content as
1281   opaque data.
1282</t>
1283</section>
1284
1285<section title="Field Length" anchor="field.length">
1286<t>
1287   HTTP does not place a pre-defined limit on the length of header fields,
1288   either in isolation or as a set. A server &MUST; be prepared to receive
1289   request header fields of unbounded length and respond with a 4xx status
1290   code if the received header field(s) would be longer than the server wishes
1291   to handle.
1292</t>
1293<t>
1294   A client that receives response headers that are longer than it wishes to
1295   handle can only treat it as a server error.
1296</t>
1297<t>
1298   Various ad-hoc limitations on header length are found in practice. It is
1299   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1300   combined header fields have 4000 or more octets.
1301</t>
1302</section>
1303
1304<section title="Field value components" anchor="field.components">
1305<t anchor="rule.token.separators">
1306  <x:anchor-alias value="tchar"/>
1307  <x:anchor-alias value="token"/>
1308  <x:anchor-alias value="special"/>
1309  <x:anchor-alias value="word"/>
1310   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1311   separated by whitespace or special characters. These special characters
1312   &MUST; be in a quoted string to be used within a parameter value (as defined
1313   in <xref target="transfer.codings"/>).
1314</t>
1315<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"/>
1316  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1317
1318  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1319<!--
1320  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1321 -->
1322  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1323                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1324                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1325                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1326
1327  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1328                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1329                 / "]" / "?" / "=" / "{" / "}"
1330</artwork></figure>
1331<t anchor="rule.quoted-string">
1332  <x:anchor-alias value="quoted-string"/>
1333  <x:anchor-alias value="qdtext"/>
1334  <x:anchor-alias value="obs-text"/>
1335   A string of text is parsed as a single word if it is quoted using
1336   double-quote marks.
1337</t>
1338<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"/>
1339  <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>
1340  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1341  <x:ref>obs-text</x:ref>       = %x80-FF
1342</artwork></figure>
1343<t anchor="rule.quoted-pair">
1344  <x:anchor-alias value="quoted-pair"/>
1345   The backslash octet ("\") can be used as a single-octet
1346   quoting mechanism within quoted-string constructs:
1347</t>
1348<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1349  <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> )
1350</artwork></figure>
1351<t>
1352   Recipients that process the value of the quoted-string &MUST; handle a
1353   quoted-pair as if it were replaced by the octet following the backslash.
1354</t>
1355<t>
1356   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1357   escaping (i.e., other than DQUOTE and the backslash octet).
1358</t>
1359<t anchor="rule.comment">
1360  <x:anchor-alias value="comment"/>
1361  <x:anchor-alias value="ctext"/>
1362   Comments can be included in some HTTP header fields by surrounding
1363   the comment text with parentheses. Comments are only allowed in
1364   fields containing "comment" as part of their field value definition.
1365</t>
1366<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1367  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1368  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1369</artwork></figure>
1370<t anchor="rule.quoted-cpair">
1371  <x:anchor-alias value="quoted-cpair"/>
1372   The backslash octet ("\") can be used as a single-octet
1373   quoting mechanism within comment constructs:
1374</t>
1375<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1376  <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> )
1377</artwork></figure>
1378<t>
1379   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1380   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1381</t>
1382</section>
1383
1384<section title="ABNF list extension: #rule" anchor="abnf.extension">
1385<t>
1386  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
1387  improve readability in the definitions of some header field values.
1388</t>
1389<t>
1390  A construct "#" is defined, similar to "*", for defining comma-delimited
1391  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
1392  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
1393  comma (",") and optional whitespace (OWS).   
1394</t>
1395<figure><preamble>
1396  Thus,
1397</preamble><artwork type="example">
1398  1#element =&gt; element *( OWS "," OWS element )
1399</artwork></figure>
1400<figure><preamble>
1401  and:
1402</preamble><artwork type="example">
1403  #element =&gt; [ 1#element ]
1404</artwork></figure>
1405<figure><preamble>
1406  and for n &gt;= 1 and m &gt; 1:
1407</preamble><artwork type="example">
1408  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
1409</artwork></figure>
1410<t>
1411  For compatibility with legacy list rules, recipients &SHOULD; accept empty
1412  list elements. In other words, consumers would follow the list productions:
1413</t>
1414<figure><artwork type="example">
1415  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
1416 
1417  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
1418</artwork></figure>
1419<t>
1420  Note that empty elements do not contribute to the count of elements present,
1421  though.
1422</t>
1423<t>
1424  For example, given these ABNF productions:
1425</t>
1426<figure><artwork type="example">
1427  example-list      = 1#example-list-elmt
1428  example-list-elmt = token ; see <xref target="field.components"/> 
1429</artwork></figure>
1430<t>
1431  Then these are valid values for example-list (not including the double
1432  quotes, which are present for delimitation only):
1433</t>
1434<figure><artwork type="example">
1435  "foo,bar"
1436  "foo ,bar,"
1437  "foo , ,bar,charlie   "
1438</artwork></figure>
1439<t>
1440  But these values would be invalid, as at least one non-empty element is
1441  required:
1442</t>
1443<figure><artwork type="example">
1444  ""
1445  ","
1446  ",   ,"
1447</artwork></figure>
1448<t>
1449  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
1450  expanded as explained above.
1451</t>
1452</section>
1453</section>
1454
1455<section title="Message Body" anchor="message.body">
1456  <x:anchor-alias value="message-body"/>
1457<t>
1458   The message body (if any) of an HTTP message is used to carry the
1459   payload body of that request or response.  The message body is
1460   identical to the payload body unless a transfer coding has been
1461   applied, as described in <xref target="header.transfer-encoding"/>.
1462</t>
1463<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1464  <x:ref>message-body</x:ref> = *OCTET
1465</artwork></figure>
1466<t>
1467   The rules for when a message body is allowed in a message differ for
1468   requests and responses.
1469</t>
1470<t>
1471   The presence of a message body in a request is signaled by a
1472   a Content-Length or Transfer-Encoding header field.
1473   Request message framing is independent of method semantics,
1474   even if the method does not define any use for a message body.
1475</t>
1476<t>
1477   The presence of a message body in a response depends on both
1478   the request method to which it is responding and the response
1479   status code (<xref target="status-code"/>).
1480   Responses to the HEAD request method never include a message body
1481   because the associated response header fields (e.g., Transfer-Encoding,
1482   Content-Length, etc.) only indicate what their values would have been
1483   if the request method had been GET.
1484   Successful (2xx) responses to CONNECT switch to tunnel mode instead of
1485   having a message body.
1486   All 1xx (Informational), 204 (No Content), and 304 (Not Modified)
1487   responses &MUST-NOT; include a message body.
1488   All other responses do include a message body, although the body
1489   &MAY; be of zero length.
1490</t>
1491
1492<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1493  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1494  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
1495  <x:anchor-alias value="Transfer-Encoding"/>
1496<t>
1497   When one or more transfer codings are applied to a payload body in order
1498   to form the message body, a Transfer-Encoding header field &MUST; be sent
1499   in the message and &MUST; contain the list of corresponding
1500   transfer-coding names in the same order that they were applied.
1501   Transfer codings are defined in <xref target="transfer.codings"/>.
1502</t>
1503<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1504  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1505</artwork></figure>
1506<t>
1507   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1508   MIME, which was designed to enable safe transport of binary data over a
1509   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1510   However, safe transport has a different focus for an 8bit-clean transfer
1511   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1512   accurately delimit a dynamically generated payload and to distinguish
1513   payload encodings that are only applied for transport efficiency or
1514   security from those that are characteristics of the target resource.
1515</t>
1516<t>
1517   The "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1518   &MUST; be implemented by all HTTP/1.1 recipients because it plays a
1519   crucial role in delimiting messages when the payload body size is not
1520   known in advance.
1521   When the "chunked" transfer-coding is used, it &MUST; be the last
1522   transfer-coding applied to form the message body and &MUST-NOT;
1523   be applied more than once in a message body.
1524   If any transfer-coding is applied to a request payload body,
1525   the final transfer-coding applied &MUST; be "chunked".
1526   If any transfer-coding is applied to a response payload body, then either
1527   the final transfer-coding applied &MUST; be "chunked" or
1528   the message &MUST; be terminated by closing the connection.
1529</t>
1530<figure><preamble>
1531   For example,
1532</preamble><artwork type="example">
1533  Transfer-Encoding: gzip, chunked
1534</artwork><postamble>
1535   indicates that the payload body has been compressed using the gzip
1536   coding and then chunked using the chunked coding while forming the
1537   message body.
1538</postamble></figure>
1539<t>
1540   If more than one Transfer-Encoding header field is present in a message,
1541   the multiple field-values &MUST; be combined into one field-value,
1542   according to the algorithm defined in <xref target="header.fields"/>,
1543   before determining the message body length.
1544</t>
1545<t>
1546   Unlike Content-Encoding (&content-codings;), Transfer-Encoding is a
1547   property of the message, not of the payload, and thus &MAY; be added or
1548   removed by any implementation along the request/response chain.
1549   Additional information about the encoding parameters &MAY; be provided
1550   by other header fields not defined by this specification.
1551</t>
1552<t>
1553   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1554   304 response to a GET request, neither of which includes a message body,
1555   to indicate that the origin server would have applied a transfer coding
1556   to the message body if the request had been an unconditional GET.
1557   This indication is not required, however, because any recipient on
1558   the response chain (including the origin server) can remove transfer
1559   codings when they are not needed.
1560</t>
1561<t>
1562   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1563   implementations advertising only HTTP/1.0 support will not understand
1564   how to process a transfer-encoded payload.
1565   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1566   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1567   might be in the form of specific user configuration or by remembering the
1568   version of a prior received response.
1569   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1570   the corresponding request indicates HTTP/1.1 (or later).
1571</t>
1572<t>
1573   A server that receives a request message with a transfer-coding it does
1574   not understand &SHOULD; respond with 501 (Not Implemented) and then
1575   close the connection.
1576</t>
1577</section>
1578
1579<section title="Content-Length" anchor="header.content-length">
1580  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1581  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
1582  <x:anchor-alias value="Content-Length"/>
1583<t>
1584   When a message does not have a Transfer-Encoding header field and the
1585   payload body length can be determined prior to being transferred, a
1586   Content-Length header field &SHOULD; be sent to indicate the length of the
1587   payload body that is either present as the message body, for requests
1588   and non-HEAD responses other than 304, or would have been present had
1589   the request been an unconditional GET.  The length is expressed as a
1590   decimal number of octets.
1591</t>
1592<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1593  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1594</artwork></figure>
1595<t>
1596   An example is
1597</t>
1598<figure><artwork type="example">
1599  Content-Length: 3495
1600</artwork></figure>
1601<t>
1602   In the case of a response to a HEAD request, Content-Length indicates
1603   the size of the payload body (without any potential transfer-coding)
1604   that would have been sent had the request been a GET.
1605   In the case of a 304 (Not Modified) response to a GET request,
1606   Content-Length indicates the size of the payload body (without
1607   any potential transfer-coding) that would have been sent in a 200 (OK)
1608   response.
1609</t>
1610<t>
1611   HTTP's use of Content-Length is significantly different from how it is
1612   used in MIME, where it is an optional field used only within the
1613   "message/external-body" media-type.
1614</t>
1615<t>
1616   Any Content-Length field value greater than or equal to zero is valid.
1617   Since there is no predefined limit to the length of an HTTP payload,
1618   recipients &SHOULD; anticipate potentially large decimal numerals and
1619   prevent parsing errors due to integer conversion overflows
1620   (<xref target="attack.protocol.element.size.overflows"/>).
1621</t>
1622<t>
1623   If a message is received that has multiple Content-Length header fields
1624   (<xref target="header.content-length"/>) with field-values consisting
1625   of the same decimal value, or a single Content-Length header field with
1626   a field value containing a list of identical decimal values (e.g.,
1627   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1628   header fields have been generated or combined by an upstream message
1629   processor, then the recipient &MUST; either reject the message as invalid
1630   or replace the duplicated field-values with a single valid Content-Length
1631   field containing that decimal value prior to determining the message body
1632   length.
1633</t>
1634</section>
1635
1636<section title="Message Body Length" anchor="message.body.length">
1637<t>
1638   The length of a message body is determined by one of the following
1639   (in order of precedence):
1640</t>
1641<t>
1642  <list style="numbers">
1643    <x:lt><t>
1644     Any response to a HEAD request and any response with a status
1645     code of 100-199, 204, or 304 is always terminated by the first
1646     empty line after the header fields, regardless of the header
1647     fields present in the message, and thus cannot contain a message body.
1648    </t></x:lt>
1649    <x:lt><t>
1650     Any successful (2xx) response to a CONNECT request implies that the
1651     connection will become a tunnel immediately after the empty line that
1652     concludes the header fields.  A client &MUST; ignore any Content-Length
1653     or Transfer-Encoding header fields received in such a message.
1654    </t></x:lt>
1655    <x:lt><t>
1656     If a Transfer-Encoding header field is present
1657     and the "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1658     is the final encoding, the message body length is determined by reading
1659     and decoding the chunked data until the transfer-coding indicates the
1660     data is complete.
1661    </t>
1662    <t>
1663     If a Transfer-Encoding header field is present in a response and the
1664     "chunked" transfer-coding is not the final encoding, the message body
1665     length is determined by reading the connection until it is closed by
1666     the server.
1667     If a Transfer-Encoding header field is present in a request and the
1668     "chunked" transfer-coding is not the final encoding, the message body
1669     length cannot be determined reliably; the server &MUST; respond with
1670     the 400 (Bad Request) status code and then close the connection.
1671    </t>
1672    <t>
1673     If a message is received with both a Transfer-Encoding header field
1674     and a Content-Length header field, the Transfer-Encoding overrides
1675     the Content-Length.
1676     Such a message might indicate an attempt to perform request or response
1677     smuggling (bypass of security-related checks on message routing or content)
1678     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1679     be removed, prior to forwarding the message downstream, or replaced with
1680     the real message body length after the transfer-coding is decoded.
1681    </t></x:lt>
1682    <x:lt><t>
1683     If a message is received without Transfer-Encoding and with either
1684     multiple Content-Length header fields having differing field-values or
1685     a single Content-Length header field having an invalid value, then the
1686     message framing is invalid and &MUST; be treated as an error to
1687     prevent request or response smuggling.
1688     If this is a request message, the server &MUST; respond with
1689     a 400 (Bad Request) status code and then close the connection.
1690     If this is a response message received by a proxy, the proxy
1691     &MUST; discard the received response, send a 502 (Bad Gateway)
1692     status code as its downstream response, and then close the connection.
1693     If this is a response message received by a user-agent, it &MUST; be
1694     treated as an error by discarding the message and closing the connection.
1695    </t></x:lt>
1696    <x:lt><t>
1697     If a valid Content-Length header field
1698     is present without Transfer-Encoding, its decimal value defines the
1699     message body length in octets.  If the actual number of octets sent in
1700     the message is less than the indicated Content-Length, the recipient
1701     &MUST; consider the message to be incomplete and treat the connection
1702     as no longer usable.
1703     If the actual number of octets sent in the message is more than the indicated
1704     Content-Length, the recipient &MUST; only process the message body up to the
1705     field value's number of octets; the remainder of the message &MUST; either
1706     be discarded or treated as the next message in a pipeline.  For the sake of
1707     robustness, a user-agent &MAY; attempt to detect and correct such an error
1708     in message framing if it is parsing the response to the last request on
1709     a connection and the connection has been closed by the server.
1710    </t></x:lt>
1711    <x:lt><t>
1712     If this is a request message and none of the above are true, then the
1713     message body length is zero (no message body is present).
1714    </t></x:lt>
1715    <x:lt><t>
1716     Otherwise, this is a response message without a declared message body
1717     length, so the message body length is determined by the number of octets
1718     received prior to the server closing the connection.
1719    </t></x:lt>
1720  </list>
1721</t>
1722<t>
1723   Since there is no way to distinguish a successfully completed,
1724   close-delimited message from a partially-received message interrupted
1725   by network failure, implementations &SHOULD; use encoding or
1726   length-delimited messages whenever possible.  The close-delimiting
1727   feature exists primarily for backwards compatibility with HTTP/1.0.
1728</t>
1729<t>
1730   A server &MAY; reject a request that contains a message body but
1731   not a Content-Length by responding with 411 (Length Required).
1732</t>
1733<t>
1734   Unless a transfer-coding other than "chunked" has been applied,
1735   a client that sends a request containing a message body &SHOULD;
1736   use a valid Content-Length header field if the message body length
1737   is known in advance, rather than the "chunked" encoding, since some
1738   existing services respond to "chunked" with a 411 (Length Required)
1739   status code even though they understand the chunked encoding.  This
1740   is typically because such services are implemented via a gateway that
1741   requires a content-length in advance of being called and the server
1742   is unable or unwilling to buffer the entire request before processing.
1743</t>
1744<t>
1745   A client that sends a request containing a message body &MUST; include a
1746   valid Content-Length header field if it does not know the server will
1747   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1748   of specific user configuration or by remembering the version of a prior
1749   received response.
1750</t>
1751</section>
1752</section>
1753
1754<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1755<t>
1756   Request messages that are prematurely terminated, possibly due to a
1757   cancelled connection or a server-imposed time-out exception, &MUST;
1758   result in closure of the connection; sending an HTTP/1.1 error response
1759   prior to closing the connection is &OPTIONAL;.
1760</t>
1761<t>
1762   Response messages that are prematurely terminated, usually by closure
1763   of the connection prior to receiving the expected number of octets or by
1764   failure to decode a transfer-encoded message body, &MUST; be recorded
1765   as incomplete.  A response that terminates in the middle of the header
1766   block (before the empty line is received) cannot be assumed to convey the
1767   full semantics of the response and &MUST; be treated as an error.
1768</t>
1769<t>
1770   A message body that uses the chunked transfer encoding is
1771   incomplete if the zero-sized chunk that terminates the encoding has not
1772   been received.  A message that uses a valid Content-Length is incomplete
1773   if the size of the message body received (in octets) is less than the
1774   value given by Content-Length.  A response that has neither chunked
1775   transfer encoding nor Content-Length is terminated by closure of the
1776   connection, and thus is considered complete regardless of the number of
1777   message body octets received, provided that the header block was received
1778   intact.
1779</t>
1780<t>
1781   A user agent &MUST-NOT; render an incomplete response message body as if
1782   it were complete (i.e., some indication needs to be given to the user that an
1783   error occurred).  Cache requirements for incomplete responses are defined
1784   in &cache-incomplete;.
1785</t>
1786<t>
1787   A server &MUST; read the entire request message body or close
1788   the connection after sending its response, since otherwise the
1789   remaining data on a persistent connection would be misinterpreted
1790   as the next request.  Likewise,
1791   a client &MUST; read the entire response message body if it intends
1792   to reuse the same connection for a subsequent request.  Pipelining
1793   multiple requests on a connection is described in <xref target="pipelining"/>.
1794</t>
1795</section>
1796
1797<section title="Message Parsing Robustness" anchor="message.robustness">
1798<t>
1799   Older HTTP/1.0 client implementations might send an extra CRLF
1800   after a POST request as a lame workaround for some early server
1801   applications that failed to read message body content that was
1802   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1803   preface or follow a request with an extra CRLF.  If terminating
1804   the request message body with a line-ending is desired, then the
1805   client &MUST; include the terminating CRLF octets as part of the
1806   message body length.
1807</t>
1808<t>
1809   In the interest of robustness, servers &SHOULD; ignore at least one
1810   empty line received where a request-line is expected. In other words, if
1811   the server is reading the protocol stream at the beginning of a
1812   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1813   Likewise, although the line terminator for the start-line and header
1814   fields is the sequence CRLF, we recommend that recipients recognize a
1815   single LF as a line terminator and ignore any CR.
1816</t>
1817<t>
1818   When a server listening only for HTTP request messages, or processing
1819   what appears from the start-line to be an HTTP request message,
1820   receives a sequence of octets that does not match the HTTP-message
1821   grammar aside from the robustness exceptions listed above, the
1822   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1823</t>
1824</section>
1825</section>
1826
1827<section title="Transfer Codings" anchor="transfer.codings">
1828  <x:anchor-alias value="transfer-coding"/>
1829  <x:anchor-alias value="transfer-extension"/>
1830<t>
1831   Transfer-coding values are used to indicate an encoding
1832   transformation that has been, can be, or might need to be applied to a
1833   payload body in order to ensure "safe transport" through the network.
1834   This differs from a content coding in that the transfer-coding is a
1835   property of the message rather than a property of the representation
1836   that is being transferred.
1837</t>
1838<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1839  <x:ref>transfer-coding</x:ref>    = "chunked" ; <xref target="chunked.encoding"/>
1840                     / "compress" ; <xref target="compress.coding"/>
1841                     / "deflate" ; <xref target="deflate.coding"/>
1842                     / "gzip" ; <xref target="gzip.coding"/>
1843                     / <x:ref>transfer-extension</x:ref>
1844  <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> )
1845</artwork></figure>
1846<t anchor="rule.parameter">
1847  <x:anchor-alias value="attribute"/>
1848  <x:anchor-alias value="transfer-parameter"/>
1849  <x:anchor-alias value="value"/>
1850   Parameters are in the form of attribute/value pairs.
1851</t>
1852<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"/>
1853  <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>
1854  <x:ref>attribute</x:ref>          = <x:ref>token</x:ref>
1855  <x:ref>value</x:ref>              = <x:ref>word</x:ref>
1856</artwork></figure>
1857<t>
1858   All transfer-coding values are case-insensitive.
1859   The HTTP Transfer Coding registry is defined in
1860   <xref target="transfer.coding.registry"/>.
1861   HTTP/1.1 uses transfer-coding values in the TE header field
1862   (<xref target="header.te"/>) and in the Transfer-Encoding header field
1863   (<xref target="header.transfer-encoding"/>).
1864</t>
1865
1866<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1867  <iref item="chunked (Coding Format)"/>
1868  <iref item="Coding Format" subitem="chunked"/>
1869  <x:anchor-alias value="chunk"/>
1870  <x:anchor-alias value="chunked-body"/>
1871  <x:anchor-alias value="chunk-data"/>
1872  <x:anchor-alias value="chunk-ext"/>
1873  <x:anchor-alias value="chunk-ext-name"/>
1874  <x:anchor-alias value="chunk-ext-val"/>
1875  <x:anchor-alias value="chunk-size"/>
1876  <x:anchor-alias value="last-chunk"/>
1877  <x:anchor-alias value="trailer-part"/>
1878  <x:anchor-alias value="quoted-str-nf"/>
1879  <x:anchor-alias value="qdtext-nf"/>
1880<t>
1881   The chunked encoding modifies the body of a message in order to
1882   transfer it as a series of chunks, each with its own size indicator,
1883   followed by an &OPTIONAL; trailer containing header fields. This
1884   allows dynamically produced content to be transferred along with the
1885   information necessary for the recipient to verify that it has
1886   received the full message.
1887</t>
1888<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"/>
1889  <x:ref>chunked-body</x:ref>   = *<x:ref>chunk</x:ref>
1890                   <x:ref>last-chunk</x:ref>
1891                   <x:ref>trailer-part</x:ref>
1892                   <x:ref>CRLF</x:ref>
1893 
1894  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1895                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1896  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1897  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1898 
1899  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1900  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1901  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1902  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1903  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1904 
1905  <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>
1906                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1907  <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>
1908</artwork></figure>
1909<t>
1910   The chunk-size field is a string of hex digits indicating the size of
1911   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1912   zero, followed by the trailer, which is terminated by an empty line.
1913</t>
1914<t>
1915   The trailer allows the sender to include additional HTTP header
1916   fields at the end of the message. The Trailer header field can be
1917   used to indicate which header fields are included in a trailer (see
1918   <xref target="header.trailer"/>).
1919</t>
1920<t>
1921   A server using chunked transfer-coding in a response &MUST-NOT; use the
1922   trailer for any header fields unless at least one of the following is
1923   true:
1924  <list style="numbers">
1925    <t>the request included a TE header field that indicates "trailers" is
1926     acceptable in the transfer-coding of the  response, as described in
1927     <xref target="header.te"/>; or,</t>
1928     
1929    <t>the trailer fields consist entirely of optional metadata, and the
1930    recipient could use the message (in a manner acceptable to the server where
1931    the field originated) without receiving it. In other words, the server that
1932    generated the header (often but not always the origin server) is willing to
1933    accept the possibility that the trailer fields might be silently discarded
1934    along the path to the client.</t>
1935  </list>
1936</t>
1937<t>
1938   This requirement prevents an interoperability failure when the
1939   message is being received by an HTTP/1.1 (or later) proxy and
1940   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1941   conformance with the protocol would have necessitated a possibly
1942   infinite buffer on the proxy.
1943</t>
1944<t>
1945   A process for decoding the "chunked" transfer-coding
1946   can be represented in pseudo-code as:
1947</t>
1948<figure><artwork type="code">
1949  length := 0
1950  read chunk-size, chunk-ext (if any) and CRLF
1951  while (chunk-size &gt; 0) {
1952     read chunk-data and CRLF
1953     append chunk-data to decoded-body
1954     length := length + chunk-size
1955     read chunk-size and CRLF
1956  }
1957  read header-field
1958  while (header-field not empty) {
1959     append header-field to existing header fields
1960     read header-field
1961  }
1962  Content-Length := length
1963  Remove "chunked" from Transfer-Encoding
1964</artwork></figure>
1965<t>
1966   All HTTP/1.1 applications &MUST; be able to receive and decode the
1967   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
1968   they do not understand.
1969</t>
1970<t>
1971   Use of chunk-ext extensions by senders is deprecated; they &SHOULD-NOT; be
1972   sent and definition of new chunk-extensions is discouraged.
1973</t>
1974</section>
1975
1976<section title="Compression Codings" anchor="compression.codings">
1977<t>
1978   The codings defined below can be used to compress the payload of a
1979   message.
1980</t>
1981<x:note><t>
1982   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
1983   is not desirable and is discouraged for future encodings. Their
1984   use here is representative of historical practice, not good
1985   design.
1986</t></x:note>
1987<x:note><t>
1988   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
1989   applications &SHOULD; consider "x-gzip" and "x-compress" to be
1990   equivalent to "gzip" and "compress" respectively.
1991</t></x:note>
1992
1993<section title="Compress Coding" anchor="compress.coding">
1994<iref item="compress (Coding Format)"/>
1995<iref item="Coding Format" subitem="compress"/>
1996<t>
1997   The "compress" format is produced by the common UNIX file compression
1998   program "compress". This format is an adaptive Lempel-Ziv-Welch
1999   coding (LZW).
2000</t>
2001</section>
2002
2003<section title="Deflate Coding" anchor="deflate.coding">
2004<iref item="deflate (Coding Format)"/>
2005<iref item="Coding Format" subitem="deflate"/>
2006<t>
2007   The "deflate" format is defined as the "deflate" compression mechanism
2008   (described in <xref target="RFC1951"/>) used inside the "zlib"
2009   data format (<xref target="RFC1950"/>).
2010</t>
2011<x:note>
2012  <t>
2013    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2014    compressed data without the zlib wrapper.
2015   </t>
2016</x:note>
2017</section>
2018
2019<section title="Gzip Coding" anchor="gzip.coding">
2020<iref item="gzip (Coding Format)"/>
2021<iref item="Coding Format" subitem="gzip"/>
2022<t>
2023   The "gzip" format is produced by the file compression program
2024   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2025   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2026</t>
2027</section>
2028
2029</section>
2030
2031<section title="TE" anchor="header.te">
2032  <iref primary="true" item="TE header field" x:for-anchor=""/>
2033  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
2034  <x:anchor-alias value="TE"/>
2035  <x:anchor-alias value="t-codings"/>
2036  <x:anchor-alias value="te-params"/>
2037  <x:anchor-alias value="te-ext"/>
2038<t>
2039   The "TE" header field indicates what extension transfer-codings
2040   the client is willing to accept in the response, and whether or not it is
2041   willing to accept trailer fields in a chunked transfer-coding.
2042</t>
2043<t>
2044   Its value consists of the keyword "trailers" and/or a comma-separated
2045   list of extension transfer-coding names with optional accept
2046   parameters (as described in <xref target="transfer.codings"/>).
2047</t>
2048<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"/>
2049  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2050  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2051  <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> )
2052  <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> ]
2053</artwork></figure>
2054<t>
2055   The presence of the keyword "trailers" indicates that the client is
2056   willing to accept trailer fields in a chunked transfer-coding, as
2057   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
2058   transfer-coding values even though it does not itself represent a
2059   transfer-coding.
2060</t>
2061<t>
2062   Examples of its use are:
2063</t>
2064<figure><artwork type="example">
2065  TE: deflate
2066  TE:
2067  TE: trailers, deflate;q=0.5
2068</artwork></figure>
2069<t>
2070   The TE header field only applies to the immediate connection.
2071   Therefore, the keyword &MUST; be supplied within a Connection header
2072   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2073</t>
2074<t>
2075   A server tests whether a transfer-coding is acceptable, according to
2076   a TE field, using these rules:
2077  <list style="numbers">
2078    <x:lt>
2079      <t>The "chunked" transfer-coding is always acceptable. If the
2080         keyword "trailers" is listed, the client indicates that it is
2081         willing to accept trailer fields in the chunked response on
2082         behalf of itself and any downstream clients. The implication is
2083         that, if given, the client is stating that either all
2084         downstream clients are willing to accept trailer fields in the
2085         forwarded response, or that it will attempt to buffer the
2086         response on behalf of downstream recipients.
2087      </t><t>
2088         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2089         chunked response such that a client can be assured of buffering
2090         the entire response.</t>
2091    </x:lt>
2092    <x:lt>
2093      <t>If the transfer-coding being tested is one of the transfer-codings
2094         listed in the TE field, then it is acceptable unless it
2095         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2096         qvalue of 0 means "not acceptable".)</t>
2097    </x:lt>
2098    <x:lt>
2099      <t>If multiple transfer-codings are acceptable, then the
2100         acceptable transfer-coding with the highest non-zero qvalue is
2101         preferred.  The "chunked" transfer-coding always has a qvalue
2102         of 1.</t>
2103    </x:lt>
2104  </list>
2105</t>
2106<t>
2107   If the TE field-value is empty or if no TE field is present, the only
2108   acceptable transfer-coding is "chunked". A message with no transfer-coding is
2109   always acceptable.
2110</t>
2111
2112<section title="Quality Values" anchor="quality.values">
2113  <x:anchor-alias value="qvalue"/>
2114<t>
2115   Both transfer codings (TE request header field, <xref target="header.te"/>)
2116   and content negotiation (&content.negotiation;) use short "floating point"
2117   numbers to indicate the relative importance ("weight") of various
2118   negotiable parameters.  A weight is normalized to a real number in
2119   the range 0 through 1, where 0 is the minimum and 1 the maximum
2120   value. If a parameter has a quality value of 0, then content with
2121   this parameter is "not acceptable" for the client. HTTP/1.1
2122   applications &MUST-NOT; generate more than three digits after the
2123   decimal point. User configuration of these values &SHOULD; also be
2124   limited in this fashion.
2125</t>
2126<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2127  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2128                 / ( "1" [ "." 0*3("0") ] )
2129</artwork></figure>
2130<x:note>
2131  <t>
2132     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2133     relative degradation in desired quality.
2134  </t>
2135</x:note>
2136</section>
2137</section>
2138
2139<section title="Trailer" anchor="header.trailer">
2140  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
2141  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
2142  <x:anchor-alias value="Trailer"/>
2143<t>
2144   The "Trailer" header field indicates that the given set of
2145   header fields is present in the trailer of a message encoded with
2146   chunked transfer-coding.
2147</t>
2148<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2149  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
2150</artwork></figure>
2151<t>
2152   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2153   message using chunked transfer-coding with a non-empty trailer. Doing
2154   so allows the recipient to know which header fields to expect in the
2155   trailer.
2156</t>
2157<t>
2158   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2159   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
2160   trailer fields in a "chunked" transfer-coding.
2161</t>
2162<t>
2163   Message header fields listed in the Trailer header field &MUST-NOT;
2164   include the following header fields:
2165  <list style="symbols">
2166    <t>Transfer-Encoding</t>
2167    <t>Content-Length</t>
2168    <t>Trailer</t>
2169  </list>
2170</t>
2171</section>
2172</section>
2173
2174<section title="Message Routing" anchor="message.routing">
2175<t>
2176   HTTP request message routing is determined by each client based on the
2177   target resource, the client's proxy configuration, and
2178   establishment or reuse of an inbound connection.  The corresponding
2179   response routing follows the same connection chain back to the client.
2180</t>
2181
2182<section title="Identifying a Target Resource" anchor="target-resource">
2183  <iref primary="true" item="target resource"/>
2184  <iref primary="true" item="target URI"/>
2185<t>
2186   HTTP is used in a wide variety of applications, ranging from
2187   general-purpose computers to home appliances.  In some cases,
2188   communication options are hard-coded in a client's configuration.
2189   However, most HTTP clients rely on the same resource identification
2190   mechanism and configuration techniques as general-purpose Web browsers.
2191</t>
2192<t>
2193   HTTP communication is initiated by a user agent for some purpose.
2194   The purpose is a combination of request semantics, which are defined in
2195   <xref target="Part2"/>, and a target resource upon which to apply those
2196   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2197   an identifier for the "target resource", which a user agent would resolve
2198   to its absolute form in order to obtain the "target URI".  The target URI
2199   excludes the reference's fragment identifier component, if any,
2200   since fragment identifiers are reserved for client-side processing
2201   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2202</t>
2203<t>
2204   HTTP intermediaries obtain the request semantics and target URI
2205   from the request-line of an incoming request message.
2206</t>
2207</section>
2208
2209<section title="Connecting Inbound" anchor="connecting.inbound">
2210<t>
2211   Once the target URI is determined, a client needs to decide whether
2212   a network request is necessary to accomplish the desired semantics and,
2213   if so, where that request is to be directed.
2214</t>
2215<t>
2216   If the client has a response cache and the request semantics can be
2217   satisfied by a cache (<xref target="Part6"/>), then the request is
2218   usually directed to the cache first.
2219</t>
2220<t>
2221   If the request is not satisfied by a cache, then a typical client will
2222   check its configuration to determine whether a proxy is to be used to
2223   satisfy the request.  Proxy configuration is implementation-dependent,
2224   but is often based on URI prefix matching, selective authority matching,
2225   or both, and the proxy itself is usually identified by an "http" or
2226   "https" URI.  If a proxy is applicable, the client connects inbound by
2227   establishing (or reusing) a connection to that proxy.
2228</t>
2229<t>
2230   If no proxy is applicable, a typical client will invoke a handler routine,
2231   usually specific to the target URI's scheme, to connect directly
2232   to an authority for the target resource.  How that is accomplished is
2233   dependent on the target URI scheme and defined by its associated
2234   specification, similar to how this specification defines origin server
2235   access for resolution of the "http" (<xref target="http.uri"/>) and
2236   "https" (<xref target="https.uri"/>) schemes.
2237</t>
2238</section>
2239
2240<section title="Request Target" anchor="request-target">
2241<t>
2242   Once an inbound connection is obtained
2243   (<xref target="connection.management"/>),
2244   the client sends an HTTP request message (<xref target="http.message"/>)
2245   with a request-target derived from the target URI.
2246   There are four distinct formats for the request-target, depending on both
2247   the method being requested and whether the request is to a proxy.
2248</t>   
2249<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"/>
2250  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2251                 / <x:ref>absolute-form</x:ref>
2252                 / <x:ref>authority-form</x:ref>
2253                 / <x:ref>asterisk-form</x:ref>
2254
2255  <x:ref>origin-form</x:ref>    = <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]
2256  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2257  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2258  <x:ref>asterisk-form</x:ref>  = "*"
2259</artwork></figure>
2260<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2261   The most common form of request-target is the origin-form.
2262   When making a request directly to an origin server, other than a CONNECT
2263   or server-wide OPTIONS request (as detailed below),
2264   a client &MUST; send only the absolute path and query components of
2265   the target URI as the request-target.
2266   If the target URI's path component is empty, then the client &MUST; send
2267   "/" as the path within the origin-form of request-target.
2268   A Host header field is also sent, as defined in
2269   <xref target="header.host"/>, containing the target URI's
2270   authority component (excluding any userinfo).
2271</t>
2272<t>
2273   For example, a client wishing to retrieve a representation of the resource
2274   identified as
2275</t>
2276<figure><artwork x:indent-with="  " type="example">
2277http://www.example.org/where?q=now
2278</artwork></figure>
2279<t>
2280   directly from the origin server would open (or reuse) a TCP connection
2281   to port 80 of the host "www.example.org" and send the lines:
2282</t>
2283<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2284GET /where?q=now HTTP/1.1
2285Host: www.example.org
2286</artwork></figure>
2287<t>
2288   followed by the remainder of the request message.
2289</t>
2290<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2291   When making a request to a proxy, other than a CONNECT or server-wide
2292   OPTIONS request (as detailed below), a client &MUST; send the target URI
2293   in absolute-form as the request-target.
2294   The proxy is requested to either service that request from a valid cache,
2295   if possible, or make the same request on the client's behalf to either
2296   the next inbound proxy server or directly to the origin server indicated
2297   by the request-target.  Requirements on such "forwarding" of messages are
2298   defined in <xref target="intermediary.forwarding"/>.
2299</t>
2300<t>
2301   An example absolute-form of request-line would be:
2302</t>
2303<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2304GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
2305</artwork></figure>
2306<t>
2307   To allow for transition to the absolute-form for all requests in some
2308   future version of HTTP, HTTP/1.1 servers &MUST; accept the absolute-form
2309   in requests, even though HTTP/1.1 clients will only send them in requests
2310   to proxies.
2311</t>
2312<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2313   The authority-form of request-target is only used for CONNECT requests
2314   (&CONNECT;).  When making a CONNECT request to establish a tunnel through
2315   one or more proxies, a client &MUST; send only the target URI's
2316   authority component (excluding any userinfo) as the request-target.
2317   For example,
2318</t>
2319<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2320CONNECT www.example.com:80 HTTP/1.1
2321</artwork></figure>
2322<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2323   The asterisk-form of request-target is only used for a server-wide
2324   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2325   for the server as a whole, as opposed to a specific named resource of
2326   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2327   For example,
2328</t>
2329<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2330OPTIONS * HTTP/1.1
2331</artwork></figure>
2332<t>
2333   If a proxy receives an OPTIONS request with an absolute-form of
2334   request-target in which the URI has an empty path and no query component,
2335   then the last proxy on the request chain &MUST; send a request-target
2336   of "*" when it forwards the request to the indicated origin server.
2337</t>
2338<figure><preamble>   
2339   For example, the request
2340</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2341OPTIONS http://www.example.org:8001 HTTP/1.1
2342</artwork></figure>
2343<figure><preamble>   
2344  would be forwarded by the final proxy as
2345</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2346OPTIONS * HTTP/1.1
2347Host: www.example.org:8001
2348</artwork>
2349<postamble>
2350   after connecting to port 8001 of host "www.example.org".
2351</postamble>
2352</figure>
2353</section>
2354
2355<section title="Host" anchor="header.host">
2356  <iref primary="true" item="Host header field" x:for-anchor=""/>
2357  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
2358  <x:anchor-alias value="Host"/>
2359<t>
2360   The "Host" header field in a request provides the host and port
2361   information from the target URI, enabling the origin
2362   server to distinguish among resources while servicing requests
2363   for multiple host names on a single IP address.  Since the Host
2364   field-value is critical information for handling a request, it
2365   &SHOULD; be sent as the first header field following the request-line.
2366</t>
2367<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2368  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2369</artwork></figure>
2370<t>
2371   A client &MUST; send a Host header field in all HTTP/1.1 request
2372   messages.  If the target URI includes an authority component, then
2373   the Host field-value &MUST; be identical to that authority component
2374   after excluding any userinfo (<xref target="http.uri"/>).
2375   If the authority component is missing or undefined for the target URI,
2376   then the Host header field &MUST; be sent with an empty field-value.
2377</t>
2378<t>
2379   For example, a GET request to the origin server for
2380   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
2381</t>
2382<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2383GET /pub/WWW/ HTTP/1.1
2384Host: www.example.org
2385</artwork></figure>
2386<t>
2387   The Host header field &MUST; be sent in an HTTP/1.1 request even
2388   if the request-target is in the absolute-form, since this
2389   allows the Host information to be forwarded through ancient HTTP/1.0
2390   proxies that might not have implemented Host.
2391</t>
2392<t>
2393   When an HTTP/1.1 proxy receives a request with an absolute-form of
2394   request-target, the proxy &MUST; ignore the received
2395   Host header field (if any) and instead replace it with the host
2396   information of the request-target.  If the proxy forwards the request,
2397   it &MUST; generate a new Host field-value based on the received
2398   request-target rather than forward the received Host field-value.
2399</t>
2400<t>
2401   Since the Host header field acts as an application-level routing
2402   mechanism, it is a frequent target for malware seeking to poison
2403   a shared cache or redirect a request to an unintended server.
2404   An interception proxy is particularly vulnerable if it relies on
2405   the Host field-value for redirecting requests to internal
2406   servers, or for use as a cache key in a shared cache, without
2407   first verifying that the intercepted connection is targeting a
2408   valid IP address for that host.
2409</t>
2410<t>
2411   A server &MUST; respond with a 400 (Bad Request) status code to
2412   any HTTP/1.1 request message that lacks a Host header field and
2413   to any request message that contains more than one Host header field
2414   or a Host header field with an invalid field-value.
2415</t>
2416</section>
2417
2418<section title="Effective Request URI" anchor="effective.request.uri">
2419  <iref primary="true" item="effective request URI"/>
2420<t>
2421   A server that receives an HTTP request message &MUST; reconstruct
2422   the user agent's original target URI, based on the pieces of information
2423   learned from the request-target, Host, and connection context, in order
2424   to identify the intended target resource and properly service the request.
2425   The URI derived from this reconstruction process is referred to as the
2426   "effective request URI".
2427</t>
2428<t>
2429   For a user agent, the effective request URI is the target URI.
2430</t>
2431<t>
2432   If the request-target is in absolute-form, then the effective request URI
2433   is the same as the request-target.  Otherwise, the effective request URI
2434   is constructed as follows.
2435</t>
2436<t>
2437   If the request is received over an SSL/TLS-secured TCP connection,
2438   then the effective request URI's scheme is "https"; otherwise, the
2439   scheme is "http".
2440</t>
2441<t>
2442   If the request-target is in authority-form, then the effective
2443   request URI's authority component is the same as the request-target.
2444   Otherwise, if a Host header field is supplied with a non-empty field-value,
2445   then the authority component is the same as the Host field-value.
2446   Otherwise, the authority component is the concatenation of the default
2447   hostname configured for the server, a colon (":"), and the connection's
2448   incoming TCP port number in decimal form.
2449</t>
2450<t>
2451   If the request-target is in authority-form or asterisk-form, then the
2452   effective request URI's combined path and query component is empty.
2453   Otherwise, the combined path and query component is the same as the
2454   request-target.
2455</t>
2456<t>
2457   The components of the effective request URI, once determined as above,
2458   can be combined into absolute-URI form by concatenating the scheme,
2459   "://", authority, and combined path and query component.
2460</t>
2461<figure>
2462<preamble>
2463   Example 1: the following message received over an insecure TCP connection
2464</preamble> 
2465<artwork type="example" x:indent-with="  ">
2466GET /pub/WWW/TheProject.html HTTP/1.1
2467Host: www.example.org:8080
2468</artwork>
2469</figure>
2470<figure>
2471<preamble>
2472  has an effective request URI of
2473</preamble>
2474<artwork type="example" x:indent-with="  ">
2475http://www.example.org:8080/pub/WWW/TheProject.html
2476</artwork>
2477</figure>
2478<figure>
2479<preamble>
2480   Example 2: the following message received over an SSL/TLS-secured TCP
2481   connection
2482</preamble> 
2483<artwork type="example" x:indent-with="  ">
2484OPTIONS * HTTP/1.1
2485Host: www.example.org
2486</artwork>
2487</figure>
2488<figure>
2489<preamble>
2490  has an effective request URI of
2491</preamble>
2492<artwork type="example" x:indent-with="  ">
2493https://www.example.org
2494</artwork>
2495</figure>
2496<t>
2497   An origin server that does not allow resources to differ by requested
2498   host &MAY; ignore the Host field-value and instead replace it with a
2499   configured server name when constructing the effective request URI.
2500</t>
2501<t>
2502   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
2503   attempt to use heuristics (e.g., examination of the URI path for
2504   something unique to a particular host) in order to guess the
2505   effective request URI's authority component.
2506</t>
2507</section>
2508
2509<section title="Intermediary Forwarding" anchor="intermediary.forwarding">
2510<t>
2511   As described in <xref target="intermediaries"/>, intermediaries can serve
2512   a variety of roles in the processing of HTTP requests and responses.
2513   Some intermediaries are used to improve performance or availability.
2514   Others are used for access control or to filter content.
2515   Since an HTTP stream has characteristics similar to a pipe-and-filter
2516   architecture, there are no inherent limits to the extent an intermediary
2517   can enhance (or interfere) with either direction of the stream.
2518</t>
2519<t>
2520   In order to avoid request loops, a proxy that forwards requests to other
2521   proxies &MUST; be able to recognize and exclude all of its own server
2522   names, including any aliases, local variations, or literal IP addresses.
2523</t>
2524<t>
2525   If a proxy receives a request-target with a host name that is not a
2526   fully qualified domain name, it &MAY; add its domain to the host name
2527   it received when forwarding the request.  A proxy &MUST-NOT; change the
2528   host name if it is a fully qualified domain name.
2529</t>
2530<t>
2531   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" and "query"
2532   parts of the received request-target when forwarding it to the next inbound
2533   server, except as noted above to replace an empty path with "/" or "*".
2534</t>
2535<t>
2536   Intermediaries that forward a message &MUST; implement the
2537   Connection header field as specified in <xref target="header.connection"/>.
2538</t>
2539
2540<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2541<!--<t>
2542  <cref anchor="TODO-end-to-end" source="jre">
2543    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2544    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2545  </cref>
2546</t>-->
2547<t>
2548   For the purpose of defining the behavior of caches and non-caching
2549   proxies, we divide HTTP header fields into two categories:
2550  <list style="symbols">
2551      <t>End-to-end header fields, which are  transmitted to the ultimate
2552        recipient of a request or response. End-to-end header fields in
2553        responses &MUST; be stored as part of a cache entry and &MUST; be
2554        transmitted in any response formed from a cache entry.</t>
2555
2556      <t>Hop-by-hop header fields, which are meaningful only for a single
2557        transport-level connection, and are not stored by caches or
2558        forwarded by proxies.</t>
2559  </list>
2560</t>
2561<t>
2562   The following HTTP/1.1 header fields are hop-by-hop header fields:
2563  <list style="symbols">
2564      <t>Connection</t>
2565      <t>Keep-Alive</t>
2566      <t>Proxy-Authenticate</t>
2567      <t>Proxy-Authorization</t>
2568      <t>TE</t>
2569      <t>Trailer</t>
2570      <t>Transfer-Encoding</t>
2571      <t>Upgrade</t>
2572  </list>
2573</t>
2574<t>
2575   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2576</t>
2577<t>
2578   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2579   (<xref target="header.connection"/>).
2580</t>
2581</section>
2582
2583<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2584<!--<t>
2585  <cref anchor="TODO-non-mod-headers" source="jre">
2586    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2587    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2588  </cref>
2589</t>-->
2590<t>
2591   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2592   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2593   modify an end-to-end header field unless the definition of that header field requires
2594   or specifically allows that.
2595</t>
2596<t>
2597   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2598   request or response, and it &MUST-NOT; add any of these fields if not
2599   already present:
2600  <list style="symbols">
2601    <t>Allow</t>
2602    <t>Content-Location</t>
2603    <t>Content-MD5</t>
2604    <t>ETag</t>
2605    <t>Last-Modified</t>
2606    <t>Server</t>
2607  </list>
2608</t>
2609<t>
2610   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2611   response:
2612  <list style="symbols">
2613    <t>Expires</t>
2614  </list>
2615</t>
2616<t>
2617   but it &MAY; add any of these fields if not already present. If an
2618   Expires header field is added, it &MUST; be given a field-value identical to
2619   that of the Date header field in that response.
2620</t>
2621<t>
2622   A proxy &MUST-NOT; modify or add any of the following fields in a
2623   message that contains the no-transform cache-control directive, or in
2624   any request:
2625  <list style="symbols">
2626    <t>Content-Encoding</t>
2627    <t>Content-Range</t>
2628    <t>Content-Type</t>
2629  </list>
2630</t>
2631<t>
2632   A transforming proxy &MAY; modify or add these fields to a message
2633   that does not include no-transform, but if it does so, it &MUST; add a
2634   Warning 214 (Transformation applied) if one does not already appear
2635   in the message (see &header-warning;).
2636</t>
2637<x:note>
2638  <t>
2639    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2640    cause authentication failures if stronger authentication
2641    mechanisms are introduced in later versions of HTTP. Such
2642    authentication mechanisms &MAY; rely on the values of header fields
2643    not listed here.
2644  </t>
2645</x:note>
2646<t>
2647   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2648   though it &MAY; change the message body through application or removal
2649   of a transfer-coding (<xref target="transfer.codings"/>).
2650</t>
2651</section>
2652
2653</section>
2654
2655<section title="Associating a Response to a Request" anchor="associating.response.to.request">
2656<t>
2657   HTTP does not include a request identifier for associating a given
2658   request message with its corresponding one or more response messages.
2659   Hence, it relies on the order of response arrival to correspond exactly
2660   to the order in which requests are made on the same connection.
2661   More than one response message per request only occurs when one or more
2662   informational responses (1xx, see &status-1xx;) precede a final response
2663   to the same request.
2664</t>
2665<t>
2666   A client that uses persistent connections and sends more than one request
2667   per connection &MUST; maintain a list of outstanding requests in the
2668   order sent on that connection and &MUST; associate each received response
2669   message to the highest ordered request that has not yet received a final
2670   (non-1xx) response.
2671</t>
2672</section>
2673</section>
2674
2675<section title="Connection Management" anchor="connection.management">
2676
2677<section title="Connection" anchor="header.connection">
2678  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2679  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2680  <x:anchor-alias value="Connection"/>
2681  <x:anchor-alias value="connection-token"/>
2682<t>
2683   The "Connection" header field allows the sender to specify
2684   options that are desired only for that particular connection.
2685   Such connection options &MUST; be removed or replaced before the
2686   message can be forwarded downstream by a proxy or gateway.
2687   This mechanism also allows the sender to indicate which HTTP
2688   header fields used in the message are only intended for the
2689   immediate recipient ("hop-by-hop"), as opposed to all recipients
2690   on the chain ("end-to-end"), enabling the message to be
2691   self-descriptive and allowing future connection-specific extensions
2692   to be deployed in HTTP without fear that they will be blindly
2693   forwarded by previously deployed intermediaries.
2694</t>
2695<t>
2696   The Connection header field's value has the following grammar:
2697</t>
2698<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2699  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
2700  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2701</artwork></figure>
2702<t>
2703   A proxy or gateway &MUST; parse a received Connection
2704   header field before a message is forwarded and, for each
2705   connection-token in this field, remove any header field(s) from
2706   the message with the same name as the connection-token, and then
2707   remove the Connection header field itself or replace it with the
2708   sender's own connection options for the forwarded message.
2709</t>
2710<t>
2711   A sender &MUST-NOT; include field-names in the Connection header
2712   field-value for fields that are defined as expressing constraints
2713   for all recipients in the request or response chain, such as the
2714   Cache-Control header field (&header-cache-control;).
2715</t>
2716<t>
2717   The connection options do not have to correspond to a header field
2718   present in the message, since a connection-specific header field
2719   might not be needed if there are no parameters associated with that
2720   connection option.  Recipients that trigger certain connection
2721   behavior based on the presence of connection options &MUST; do so
2722   based on the presence of the connection-token rather than only the
2723   presence of the optional header field.  In other words, if the
2724   connection option is received as a header field but not indicated
2725   within the Connection field-value, then the recipient &MUST; ignore
2726   the connection-specific header field because it has likely been
2727   forwarded by an intermediary that is only partially conformant.
2728</t>
2729<t>
2730   When defining new connection options, specifications ought to
2731   carefully consider existing deployed header fields and ensure
2732   that the new connection-token does not share the same name as
2733   an unrelated header field that might already be deployed.
2734   Defining a new connection-token essentially reserves that potential
2735   field-name for carrying additional information related to the
2736   connection option, since it would be unwise for senders to use
2737   that field-name for anything else.
2738</t>
2739<t>
2740   HTTP/1.1 defines the "close" connection option for the sender to
2741   signal that the connection will be closed after completion of the
2742   response. For example,
2743</t>
2744<figure><artwork type="example">
2745  Connection: close
2746</artwork></figure>
2747<t>
2748   in either the request or the response header fields indicates that
2749   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2750   after the current request/response is complete.
2751</t>
2752<t>
2753   An HTTP/1.1 client that does not support persistent connections &MUST;
2754   include the "close" connection option in every request message.
2755</t>
2756<t>
2757   An HTTP/1.1 server that does not support persistent connections &MUST;
2758   include the "close" connection option in every response message that
2759   does not have a 1xx (Informational) status code.
2760</t>
2761</section>
2762
2763<section title="Via" anchor="header.via">
2764  <iref primary="true" item="Via header field" x:for-anchor=""/>
2765  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
2766  <x:anchor-alias value="pseudonym"/>
2767  <x:anchor-alias value="received-by"/>
2768  <x:anchor-alias value="received-protocol"/>
2769  <x:anchor-alias value="Via"/>
2770<t>
2771   The "Via" header field &MUST; be sent by a proxy or gateway to
2772   indicate the intermediate protocols and recipients between the user
2773   agent and the server on requests, and between the origin server and
2774   the client on responses. It is analogous to the "Received" field
2775   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
2776   and is intended to be used for tracking message forwards,
2777   avoiding request loops, and identifying the protocol capabilities of
2778   all senders along the request/response chain.
2779</t>
2780<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"/>
2781  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2782                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2783  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2784  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2785  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2786</artwork></figure>
2787<t>
2788   The received-protocol indicates the protocol version of the message
2789   received by the server or client along each segment of the
2790   request/response chain. The received-protocol version is appended to
2791   the Via field value when the message is forwarded so that information
2792   about the protocol capabilities of upstream applications remains
2793   visible to all recipients.
2794</t>
2795<t>
2796   The protocol-name is excluded if and only if it would be "HTTP". The
2797   received-by field is normally the host and optional port number of a
2798   recipient server or client that subsequently forwarded the message.
2799   However, if the real host is considered to be sensitive information,
2800   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2801   be assumed to be the default port of the received-protocol.
2802</t>
2803<t>
2804   Multiple Via field values represent each proxy or gateway that has
2805   forwarded the message. Each recipient &MUST; append its information
2806   such that the end result is ordered according to the sequence of
2807   forwarding applications.
2808</t>
2809<t>
2810   Comments &MAY; be used in the Via header field to identify the software
2811   of each recipient, analogous to the User-Agent and Server header fields.
2812   However, all comments in the Via field are optional and &MAY; be removed
2813   by any recipient prior to forwarding the message.
2814</t>
2815<t>
2816   For example, a request message could be sent from an HTTP/1.0 user
2817   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2818   forward the request to a public proxy at p.example.net, which completes
2819   the request by forwarding it to the origin server at www.example.com.
2820   The request received by www.example.com would then have the following
2821   Via header field:
2822</t>
2823<figure><artwork type="example">
2824  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2825</artwork></figure>
2826<t>
2827   A proxy or gateway used as a portal through a network firewall
2828   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2829   region unless it is explicitly enabled to do so. If not enabled, the
2830   received-by host of any host behind the firewall &SHOULD; be replaced
2831   by an appropriate pseudonym for that host.
2832</t>
2833<t>
2834   For organizations that have strong privacy requirements for hiding
2835   internal structures, a proxy or gateway &MAY; combine an ordered
2836   subsequence of Via header field entries with identical received-protocol
2837   values into a single such entry. For example,
2838</t>
2839<figure><artwork type="example">
2840  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2841</artwork></figure>
2842<t>
2843  could be collapsed to
2844</t>
2845<figure><artwork type="example">
2846  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2847</artwork></figure>
2848<t>
2849   Senders &SHOULD-NOT; combine multiple entries unless they are all
2850   under the same organizational control and the hosts have already been
2851   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
2852   have different received-protocol values.
2853</t>
2854</section>
2855
2856<section title="Persistent Connections" anchor="persistent.connections">
2857
2858<section title="Purpose" anchor="persistent.purpose">
2859<t>
2860   Prior to persistent connections, a separate TCP connection was
2861   established for each request, increasing the load on HTTP servers
2862   and causing congestion on the Internet. The use of inline images and
2863   other associated data often requires a client to make multiple
2864   requests of the same server in a short amount of time. Analysis of
2865   these performance problems and results from a prototype
2866   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2867   measurements of actual HTTP/1.1 implementations show good
2868   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2869   T/TCP <xref target="Tou1998"/>.
2870</t>
2871<t>
2872   Persistent HTTP connections have a number of advantages:
2873  <list style="symbols">
2874      <t>
2875        By opening and closing fewer TCP connections, CPU time is saved
2876        in routers and hosts (clients, servers, proxies, gateways,
2877        tunnels, or caches), and memory used for TCP protocol control
2878        blocks can be saved in hosts.
2879      </t>
2880      <t>
2881        HTTP requests and responses can be pipelined on a connection.
2882        Pipelining allows a client to make multiple requests without
2883        waiting for each response, allowing a single TCP connection to
2884        be used much more efficiently, with much lower elapsed time.
2885      </t>
2886      <t>
2887        Network congestion is reduced by reducing the number of packets
2888        caused by TCP opens, and by allowing TCP sufficient time to
2889        determine the congestion state of the network.
2890      </t>
2891      <t>
2892        Latency on subsequent requests is reduced since there is no time
2893        spent in TCP's connection opening handshake.
2894      </t>
2895      <t>
2896        HTTP can evolve more gracefully, since errors can be reported
2897        without the penalty of closing the TCP connection. Clients using
2898        future versions of HTTP might optimistically try a new feature,
2899        but if communicating with an older server, retry with old
2900        semantics after an error is reported.
2901      </t>
2902    </list>
2903</t>
2904<t>
2905   HTTP implementations &SHOULD; implement persistent connections.
2906</t>
2907</section>
2908
2909<section title="Overall Operation" anchor="persistent.overall">
2910<t>
2911   A significant difference between HTTP/1.1 and earlier versions of
2912   HTTP is that persistent connections are the default behavior of any
2913   HTTP connection. That is, unless otherwise indicated, the client
2914   &SHOULD; assume that the server will maintain a persistent connection,
2915   even after error responses from the server.
2916</t>
2917<t>
2918   Persistent connections provide a mechanism by which a client and a
2919   server can signal the close of a TCP connection. This signaling takes
2920   place using the Connection header field (<xref target="header.connection"/>). Once a close
2921   has been signaled, the client &MUST-NOT; send any more requests on that
2922   connection.
2923</t>
2924
2925<section title="Negotiation" anchor="persistent.negotiation">
2926<t>
2927   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2928   maintain a persistent connection unless a Connection header field including
2929   the connection-token "close" was sent in the request. If the server
2930   chooses to close the connection immediately after sending the
2931   response, it &SHOULD; send a Connection header field including the
2932   connection-token "close".
2933</t>
2934<t>
2935   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2936   decide to keep it open based on whether the response from a server
2937   contains a Connection header field with the connection-token close. In case
2938   the client does not want to maintain a connection for more than that
2939   request, it &SHOULD; send a Connection header field including the
2940   connection-token close.
2941</t>
2942<t>
2943   If either the client or the server sends the close token in the
2944   Connection header field, that request becomes the last one for the
2945   connection.
2946</t>
2947<t>
2948   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2949   maintained for HTTP versions less than 1.1 unless it is explicitly
2950   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2951   compatibility with HTTP/1.0 clients.
2952</t>
2953<t>
2954   Each persistent connection applies to only one transport link.
2955</t>
2956<t>
2957   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2958   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2959   for information and discussion of the problems with the Keep-Alive header field
2960   implemented by many HTTP/1.0 clients).
2961</t>
2962<t>
2963   In order to remain persistent, all messages on the connection &MUST;
2964   have a self-defined message length (i.e., one not defined by closure
2965   of the connection), as described in <xref target="message.body"/>.
2966</t>
2967</section>
2968
2969<section title="Pipelining" anchor="pipelining">
2970<t>
2971   A client that supports persistent connections &MAY; "pipeline" its
2972   requests (i.e., send multiple requests without waiting for each
2973   response). A server &MUST; send its responses to those requests in the
2974   same order that the requests were received.
2975</t>
2976<t>
2977   Clients which assume persistent connections and pipeline immediately
2978   after connection establishment &SHOULD; be prepared to retry their
2979   connection if the first pipelined attempt fails. If a client does
2980   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2981   persistent. Clients &MUST; also be prepared to resend their requests if
2982   the server closes the connection before sending all of the
2983   corresponding responses.
2984</t>
2985<t>
2986   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2987   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2988   premature termination of the transport connection could lead to
2989   indeterminate results. A client wishing to send a non-idempotent
2990   request &SHOULD; wait to send that request until it has received the
2991   response status line for the previous request.
2992</t>
2993</section>
2994</section>
2995
2996<section title="Practical Considerations" anchor="persistent.practical">
2997<t>
2998   Servers will usually have some time-out value beyond which they will
2999   no longer maintain an inactive connection. Proxy servers might make
3000   this a higher value since it is likely that the client will be making
3001   more connections through the same server. The use of persistent
3002   connections places no requirements on the length (or existence) of
3003   this time-out for either the client or the server.
3004</t>
3005<t>
3006   When a client or server wishes to time-out it &SHOULD; issue a graceful
3007   close on the transport connection. Clients and servers &SHOULD; both
3008   constantly watch for the other side of the transport close, and
3009   respond to it as appropriate. If a client or server does not detect
3010   the other side's close promptly it could cause unnecessary resource
3011   drain on the network.
3012</t>
3013<t>
3014   A client, server, or proxy &MAY; close the transport connection at any
3015   time. For example, a client might have started to send a new request
3016   at the same time that the server has decided to close the "idle"
3017   connection. From the server's point of view, the connection is being
3018   closed while it was idle, but from the client's point of view, a
3019   request is in progress.
3020</t>
3021<t>
3022   Clients (including proxies) &SHOULD; limit the number of simultaneous
3023   connections that they maintain to a given server (including proxies).
3024</t>
3025<t>
3026   Previous revisions of HTTP gave a specific number of connections as a
3027   ceiling, but this was found to be impractical for many applications. As a
3028   result, this specification does not mandate a particular maximum number of
3029   connections, but instead encourages clients to be conservative when opening
3030   multiple connections.
3031</t>
3032<t>
3033   In particular, while using multiple connections avoids the "head-of-line
3034   blocking" problem (whereby a request that takes significant server-side
3035   processing and/or has a large payload can block subsequent requests on the
3036   same connection), each connection used consumes server resources (sometimes
3037   significantly), and furthermore using multiple connections can cause
3038   undesirable side effects in congested networks.
3039</t>
3040<t>
3041   Note that servers might reject traffic that they deem abusive, including an
3042   excessive number of connections from a client.
3043</t>
3044</section>
3045
3046<section title="Retrying Requests" anchor="persistent.retrying.requests">
3047<t>
3048   Senders can close the transport connection at any time. Therefore,
3049   clients, servers, and proxies &MUST; be able to recover
3050   from asynchronous close events. Client software &MAY; reopen the
3051   transport connection and retransmit the aborted sequence of requests
3052   without user interaction so long as the request sequence is
3053   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
3054   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
3055   human operator the choice of retrying the request(s). Confirmation by
3056   user-agent software with semantic understanding of the application
3057   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
3058   be repeated if the second sequence of requests fails.
3059</t>
3060</section>
3061</section>
3062
3063<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
3064
3065<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
3066<t>
3067   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
3068   flow control mechanisms to resolve temporary overloads, rather than
3069   terminating connections with the expectation that clients will retry.
3070   The latter technique can exacerbate network congestion.
3071</t>
3072</section>
3073
3074<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
3075<t>
3076   An HTTP/1.1 (or later) client sending a message body &SHOULD; monitor
3077   the network connection for an error status code while it is transmitting
3078   the request. If the client sees an error status code, it &SHOULD;
3079   immediately cease transmitting the body. If the body is being sent
3080   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
3081   empty trailer &MAY; be used to prematurely mark the end of the message.
3082   If the body was preceded by a Content-Length header field, the client &MUST;
3083   close the connection.
3084</t>
3085</section>
3086
3087<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
3088<t>
3089   The purpose of the 100 (Continue) status code (see &status-100;) is to
3090   allow a client that is sending a request message with a request body
3091   to determine if the origin server is willing to accept the request
3092   (based on the request header fields) before the client sends the request
3093   body. In some cases, it might either be inappropriate or highly
3094   inefficient for the client to send the body if the server will reject
3095   the message without looking at the body.
3096</t>
3097<t>
3098   Requirements for HTTP/1.1 clients:
3099  <list style="symbols">
3100    <t>
3101        If a client will wait for a 100 (Continue) response before
3102        sending the request body, it &MUST; send an Expect header
3103        field (&header-expect;) with the "100-continue" expectation.
3104    </t>
3105    <t>
3106        A client &MUST-NOT; send an Expect header field (&header-expect;)
3107        with the "100-continue" expectation if it does not intend
3108        to send a request body.
3109    </t>
3110  </list>
3111</t>
3112<t>
3113   Because of the presence of older implementations, the protocol allows
3114   ambiguous situations in which a client might send "Expect: 100-continue"
3115   without receiving either a 417 (Expectation Failed)
3116   or a 100 (Continue) status code. Therefore, when a client sends this
3117   header field to an origin server (possibly via a proxy) from which it
3118   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
3119   wait for an indefinite period before sending the request body.
3120</t>
3121<t>
3122   Requirements for HTTP/1.1 origin servers:
3123  <list style="symbols">
3124    <t> Upon receiving a request which includes an Expect header
3125        field with the "100-continue" expectation, an origin server &MUST;
3126        either respond with 100 (Continue) status code and continue to read
3127        from the input stream, or respond with a final status code. The
3128        origin server &MUST-NOT; wait for the request body before sending
3129        the 100 (Continue) response. If it responds with a final status
3130        code, it &MAY; close the transport connection or it &MAY; continue
3131        to read and discard the rest of the request.  It &MUST-NOT;
3132        perform the request method if it returns a final status code.
3133    </t>
3134    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
3135        the request message does not include an Expect header
3136        field with the "100-continue" expectation, and &MUST-NOT; send a
3137        100 (Continue) response if such a request comes from an HTTP/1.0
3138        (or earlier) client. There is an exception to this rule: for
3139        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
3140        status code in response to an HTTP/1.1 PUT or POST request that does
3141        not include an Expect header field with the "100-continue"
3142        expectation. This exception, the purpose of which is
3143        to minimize any client processing delays associated with an
3144        undeclared wait for 100 (Continue) status code, applies only to
3145        HTTP/1.1 requests, and not to requests with any other HTTP-version
3146        value.
3147    </t>
3148    <t> An origin server &MAY; omit a 100 (Continue) response if it has
3149        already received some or all of the request body for the
3150        corresponding request.
3151    </t>
3152    <t> An origin server that sends a 100 (Continue) response &MUST;
3153        ultimately send a final status code, once the request body is
3154        received and processed, unless it terminates the transport
3155        connection prematurely.
3156    </t>
3157    <t> If an origin server receives a request that does not include an
3158        Expect header field with the "100-continue" expectation,
3159        the request includes a request body, and the server responds
3160        with a final status code before reading the entire request body
3161        from the transport connection, then the server &SHOULD-NOT;  close
3162        the transport connection until it has read the entire request,
3163        or until the client closes the connection. Otherwise, the client
3164        might not reliably receive the response message. However, this
3165        requirement ought not be construed as preventing a server from
3166        defending itself against denial-of-service attacks, or from
3167        badly broken client implementations.
3168      </t>
3169    </list>
3170</t>
3171<t>
3172   Requirements for HTTP/1.1 proxies:
3173  <list style="symbols">
3174    <t> If a proxy receives a request that includes an Expect header
3175        field with the "100-continue" expectation, and the proxy
3176        either knows that the next-hop server complies with HTTP/1.1 or
3177        higher, or does not know the HTTP version of the next-hop
3178        server, it &MUST; forward the request, including the Expect header
3179        field.
3180    </t>
3181    <t> If the proxy knows that the version of the next-hop server is
3182        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
3183        respond with a 417 (Expectation Failed) status code.
3184    </t>
3185    <t> Proxies &SHOULD; maintain a record of the HTTP version
3186        numbers received from recently-referenced next-hop servers.
3187    </t>
3188    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
3189        request message was received from an HTTP/1.0 (or earlier)
3190        client and did not include an Expect header field with
3191        the "100-continue" expectation. This requirement overrides the
3192        general rule for forwarding of 1xx responses (see &status-1xx;).
3193    </t>
3194  </list>
3195</t>
3196</section>
3197
3198<section title="Closing Connections on Error" anchor="closing.connections.on.error">
3199<t>
3200   If the client is sending data, a server implementation using TCP
3201   &SHOULD; be careful to ensure that the client acknowledges receipt of
3202   the packet(s) containing the response, before the server closes the
3203   input connection. If the client continues sending data to the server
3204   after the close, the server's TCP stack will send a reset packet to
3205   the client, which might erase the client's unacknowledged input buffers
3206   before they can be read and interpreted by the HTTP application.
3207</t>
3208</section>
3209
3210</section>
3211
3212<section title="Upgrade" anchor="header.upgrade">
3213  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3214  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3215  <x:anchor-alias value="Upgrade"/>
3216  <x:anchor-alias value="protocol"/>
3217  <x:anchor-alias value="protocol-name"/>
3218  <x:anchor-alias value="protocol-version"/>
3219<t>
3220   The "Upgrade" header field allows the client to specify what
3221   additional communication protocols it would like to use, if the server
3222   chooses to switch protocols. Servers can use it to indicate what protocols
3223   they are willing to switch to.
3224</t>
3225<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3226  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3227
3228  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3229  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3230  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3231</artwork></figure>
3232<t>
3233   For example,
3234</t>
3235<figure><artwork type="example">
3236  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3237</artwork></figure>
3238<t>
3239   The Upgrade header field is intended to provide a simple mechanism
3240   for transitioning from HTTP/1.1 to some other, incompatible protocol. It
3241   does so by allowing the client to advertise its desire to use another
3242   protocol, such as a later version of HTTP with a higher major version
3243   number, even though the current request has been made using HTTP/1.1.
3244   This eases the difficult transition between incompatible protocols by
3245   allowing the client to initiate a request in the more commonly
3246   supported protocol while indicating to the server that it would like
3247   to use a "better" protocol if available (where "better" is determined
3248   by the server, possibly according to the nature of the request method
3249   or target resource).
3250</t>
3251<t>
3252   The Upgrade header field only applies to switching application-layer
3253   protocols upon the existing transport-layer connection. Upgrade
3254   cannot be used to insist on a protocol change; its acceptance and use
3255   by the server is optional. The capabilities and nature of the
3256   application-layer communication after the protocol change is entirely
3257   dependent upon the new protocol chosen, although the first action
3258   after changing the protocol &MUST; be a response to the initial HTTP
3259   request containing the Upgrade header field.
3260</t>
3261<t>
3262   The Upgrade header field only applies to the immediate connection.
3263   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3264   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3265   HTTP/1.1 message.
3266</t>
3267<t>
3268   The Upgrade header field cannot be used to indicate a switch to a
3269   protocol on a different connection. For that purpose, it is more
3270   appropriate to use a 3xx redirection response (&status-3xx;).
3271</t>
3272<t>
3273   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3274   Protocols) responses to indicate which protocol(s) are being switched to,
3275   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3276   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3277   response to indicate that they are willing to upgrade to one of the
3278   specified protocols.
3279</t>
3280<t>
3281   This specification only defines the protocol name "HTTP" for use by
3282   the family of Hypertext Transfer Protocols, as defined by the HTTP
3283   version rules of <xref target="http.version"/> and future updates to this
3284   specification. Additional tokens can be registered with IANA using the
3285   registration procedure defined in <xref target="upgrade.token.registry"/>.
3286</t>
3287</section>
3288
3289</section>
3290
3291<section title="IANA Considerations" anchor="IANA.considerations">
3292
3293<section title="Header Field Registration" anchor="header.field.registration">
3294<t>
3295   HTTP header fields are registered within the Message Header Field Registry
3296   <xref target="RFC3864"/> maintained by IANA at
3297   <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/>.
3298</t>
3299<t>
3300   This document defines the following HTTP header fields, so their
3301   associated registry entries shall be updated according to the permanent
3302   registrations below:
3303</t>
3304<?BEGININC p1-messaging.iana-headers ?>
3305<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3306<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3307   <ttcol>Header Field Name</ttcol>
3308   <ttcol>Protocol</ttcol>
3309   <ttcol>Status</ttcol>
3310   <ttcol>Reference</ttcol>
3311
3312   <c>Connection</c>
3313   <c>http</c>
3314   <c>standard</c>
3315   <c>
3316      <xref target="header.connection"/>
3317   </c>
3318   <c>Content-Length</c>
3319   <c>http</c>
3320   <c>standard</c>
3321   <c>
3322      <xref target="header.content-length"/>
3323   </c>
3324   <c>Host</c>
3325   <c>http</c>
3326   <c>standard</c>
3327   <c>
3328      <xref target="header.host"/>
3329   </c>
3330   <c>TE</c>
3331   <c>http</c>
3332   <c>standard</c>
3333   <c>
3334      <xref target="header.te"/>
3335   </c>
3336   <c>Trailer</c>
3337   <c>http</c>
3338   <c>standard</c>
3339   <c>
3340      <xref target="header.trailer"/>
3341   </c>
3342   <c>Transfer-Encoding</c>
3343   <c>http</c>
3344   <c>standard</c>
3345   <c>
3346      <xref target="header.transfer-encoding"/>
3347   </c>
3348   <c>Upgrade</c>
3349   <c>http</c>
3350   <c>standard</c>
3351   <c>
3352      <xref target="header.upgrade"/>
3353   </c>
3354   <c>Via</c>
3355   <c>http</c>
3356   <c>standard</c>
3357   <c>
3358      <xref target="header.via"/>
3359   </c>
3360</texttable>
3361<!--(END)-->
3362<?ENDINC p1-messaging.iana-headers ?>
3363<t>
3364   Furthermore, the header field-name "Close" shall be registered as
3365   "reserved", since using that name as an HTTP header field might
3366   conflict with the "close" connection option of the "Connection"
3367   header field (<xref target="header.connection"/>).
3368</t>
3369<texttable align="left" suppress-title="true">
3370   <ttcol>Header Field Name</ttcol>
3371   <ttcol>Protocol</ttcol>
3372   <ttcol>Status</ttcol>
3373   <ttcol>Reference</ttcol>
3374
3375   <c>Close</c>
3376   <c>http</c>
3377   <c>reserved</c>
3378   <c>
3379      <xref target="header.field.registration"/>
3380   </c>
3381</texttable>
3382<t>
3383   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3384</t>
3385</section>
3386
3387<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3388<t>
3389   IANA maintains the registry of URI Schemes <xref target="RFC4395"/> at
3390   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>.
3391</t>
3392<t>
3393   This document defines the following URI schemes, so their
3394   associated registry entries shall be updated according to the permanent
3395   registrations below:
3396</t>
3397<texttable align="left" suppress-title="true">
3398   <ttcol>URI Scheme</ttcol>
3399   <ttcol>Description</ttcol>
3400   <ttcol>Reference</ttcol>
3401
3402   <c>http</c>
3403   <c>Hypertext Transfer Protocol</c>
3404   <c><xref target="http.uri"/></c>
3405
3406   <c>https</c>
3407   <c>Hypertext Transfer Protocol Secure</c>
3408   <c><xref target="https.uri"/></c>
3409</texttable>
3410</section>
3411
3412<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3413<t>
3414   This document serves as the specification for the Internet media types
3415   "message/http" and "application/http". The following is to be registered with
3416   IANA (see <xref target="RFC4288"/>).
3417</t>
3418<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3419<iref item="Media Type" subitem="message/http" primary="true"/>
3420<iref item="message/http Media Type" primary="true"/>
3421<t>
3422   The message/http type can be used to enclose a single HTTP request or
3423   response message, provided that it obeys the MIME restrictions for all
3424   "message" types regarding line length and encodings.
3425</t>
3426<t>
3427  <list style="hanging" x:indent="12em">
3428    <t hangText="Type name:">
3429      message
3430    </t>
3431    <t hangText="Subtype name:">
3432      http
3433    </t>
3434    <t hangText="Required parameters:">
3435      none
3436    </t>
3437    <t hangText="Optional parameters:">
3438      version, msgtype
3439      <list style="hanging">
3440        <t hangText="version:">
3441          The HTTP-version number of the enclosed message
3442          (e.g., "1.1"). If not present, the version can be
3443          determined from the first line of the body.
3444        </t>
3445        <t hangText="msgtype:">
3446          The message type &mdash; "request" or "response". If not
3447          present, the type can be determined from the first
3448          line of the body.
3449        </t>
3450      </list>
3451    </t>
3452    <t hangText="Encoding considerations:">
3453      only "7bit", "8bit", or "binary" are permitted
3454    </t>
3455    <t hangText="Security considerations:">
3456      none
3457    </t>
3458    <t hangText="Interoperability considerations:">
3459      none
3460    </t>
3461    <t hangText="Published specification:">
3462      This specification (see <xref target="internet.media.type.message.http"/>).
3463    </t>
3464    <t hangText="Applications that use this media type:">
3465    </t>
3466    <t hangText="Additional information:">
3467      <list style="hanging">
3468        <t hangText="Magic number(s):">none</t>
3469        <t hangText="File extension(s):">none</t>
3470        <t hangText="Macintosh file type code(s):">none</t>
3471      </list>
3472    </t>
3473    <t hangText="Person and email address to contact for further information:">
3474      See Authors Section.
3475    </t>
3476    <t hangText="Intended usage:">
3477      COMMON
3478    </t>
3479    <t hangText="Restrictions on usage:">
3480      none
3481    </t>
3482    <t hangText="Author/Change controller:">
3483      IESG
3484    </t>
3485  </list>
3486</t>
3487</section>
3488<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3489<iref item="Media Type" subitem="application/http" primary="true"/>
3490<iref item="application/http Media Type" primary="true"/>
3491<t>
3492   The application/http type can be used to enclose a pipeline of one or more
3493   HTTP request or response messages (not intermixed).
3494</t>
3495<t>
3496  <list style="hanging" x:indent="12em">
3497    <t hangText="Type name:">
3498      application
3499    </t>
3500    <t hangText="Subtype name:">
3501      http
3502    </t>
3503    <t hangText="Required parameters:">
3504      none
3505    </t>
3506    <t hangText="Optional parameters:">
3507      version, msgtype
3508      <list style="hanging">
3509        <t hangText="version:">
3510          The HTTP-version number of the enclosed messages
3511          (e.g., "1.1"). If not present, the version can be
3512          determined from the first line of the body.
3513        </t>
3514        <t hangText="msgtype:">
3515          The message type &mdash; "request" or "response". If not
3516          present, the type can be determined from the first
3517          line of the body.
3518        </t>
3519      </list>
3520    </t>
3521    <t hangText="Encoding considerations:">
3522      HTTP messages enclosed by this type
3523      are in "binary" format; use of an appropriate
3524      Content-Transfer-Encoding is required when
3525      transmitted via E-mail.
3526    </t>
3527    <t hangText="Security considerations:">
3528      none
3529    </t>
3530    <t hangText="Interoperability considerations:">
3531      none
3532    </t>
3533    <t hangText="Published specification:">
3534      This specification (see <xref target="internet.media.type.application.http"/>).
3535    </t>
3536    <t hangText="Applications that use this media type:">
3537    </t>
3538    <t hangText="Additional information:">
3539      <list style="hanging">
3540        <t hangText="Magic number(s):">none</t>
3541        <t hangText="File extension(s):">none</t>
3542        <t hangText="Macintosh file type code(s):">none</t>
3543      </list>
3544    </t>
3545    <t hangText="Person and email address to contact for further information:">
3546      See Authors Section.
3547    </t>
3548    <t hangText="Intended usage:">
3549      COMMON
3550    </t>
3551    <t hangText="Restrictions on usage:">
3552      none
3553    </t>
3554    <t hangText="Author/Change controller:">
3555      IESG
3556    </t>
3557  </list>
3558</t>
3559</section>
3560</section>
3561
3562<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3563<t>
3564   The HTTP Transfer Coding Registry defines the name space for transfer
3565   coding names.
3566</t>
3567<t>
3568   Registrations &MUST; include the following fields:
3569   <list style="symbols">
3570     <t>Name</t>
3571     <t>Description</t>
3572     <t>Pointer to specification text</t>
3573   </list>
3574</t>
3575<t>
3576   Names of transfer codings &MUST-NOT; overlap with names of content codings
3577   (&content-codings;) unless the encoding transformation is identical, as it
3578   is the case for the compression codings defined in
3579   <xref target="compression.codings"/>.
3580</t>
3581<t>
3582   Values to be added to this name space require IETF Review (see
3583   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3584   conform to the purpose of transfer coding defined in this section.
3585</t>
3586<t>
3587   The registry itself is maintained at
3588   <eref target="http://www.iana.org/assignments/http-parameters"/>.
3589</t>
3590</section>
3591
3592<section title="Transfer Coding Registrations" anchor="transfer.coding.registration">
3593<t>
3594   The HTTP Transfer Coding Registry shall be updated with the registrations
3595   below:
3596</t>
3597<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3598   <ttcol>Name</ttcol>
3599   <ttcol>Description</ttcol>
3600   <ttcol>Reference</ttcol>
3601   <c>chunked</c>
3602   <c>Transfer in a series of chunks</c>
3603   <c>
3604      <xref target="chunked.encoding"/>
3605   </c>
3606   <c>compress</c>
3607   <c>UNIX "compress" program method</c>
3608   <c>
3609      <xref target="compress.coding"/>
3610   </c>
3611   <c>deflate</c>
3612   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3613   the "zlib" data format (<xref target="RFC1950"/>)
3614   </c>
3615   <c>
3616      <xref target="deflate.coding"/>
3617   </c>
3618   <c>gzip</c>
3619   <c>Same as GNU zip <xref target="RFC1952"/></c>
3620   <c>
3621      <xref target="gzip.coding"/>
3622   </c>
3623</texttable>
3624</section>
3625
3626<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3627<t>
3628   The HTTP Upgrade Token Registry defines the name space for protocol-name
3629   tokens used to identify protocols in the Upgrade header field.
3630   Each registered protocol-name is associated with contact information and
3631   an optional set of specifications that details how the connection
3632   will be processed after it has been upgraded.
3633</t>
3634<t>
3635   Registrations require IETF Review (see
3636   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3637   following rules:
3638  <list style="numbers">
3639    <t>A protocol-name token, once registered, stays registered forever.</t>
3640    <t>The registration &MUST; name a responsible party for the
3641       registration.</t>
3642    <t>The registration &MUST; name a point of contact.</t>
3643    <t>The registration &MAY; name a set of specifications associated with
3644       that token. Such specifications need not be publicly available.</t>
3645    <t>The registration &SHOULD; name a set of expected "protocol-version"
3646       tokens associated with that token at the time of registration.</t>
3647    <t>The responsible party &MAY; change the registration at any time.
3648       The IANA will keep a record of all such changes, and make them
3649       available upon request.</t>
3650    <t>The IESG &MAY; reassign responsibility for a protocol token.
3651       This will normally only be used in the case when a
3652       responsible party cannot be contacted.</t>
3653  </list>
3654</t>
3655<t>
3656   This registration procedure for HTTP Upgrade Tokens replaces that
3657   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3658</t>
3659</section>
3660
3661<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3662<t>
3663   The HTTP Upgrade Token Registry shall be updated with the registration
3664   below:
3665</t>
3666<texttable align="left" suppress-title="true">
3667   <ttcol>Value</ttcol>
3668   <ttcol>Description</ttcol>
3669   <ttcol>Expected Version Tokens</ttcol>
3670   <ttcol>Reference</ttcol>
3671
3672   <c>HTTP</c>
3673   <c>Hypertext Transfer Protocol</c>
3674   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3675   <c><xref target="http.version"/></c>
3676</texttable>
3677<t>
3678   The responsible party is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3679</t>
3680</section>
3681
3682</section>
3683
3684<section title="Security Considerations" anchor="security.considerations">
3685<t>
3686   This section is meant to inform application developers, information
3687   providers, and users of the security limitations in HTTP/1.1 as
3688   described by this document. The discussion does not include
3689   definitive solutions to the problems revealed, though it does make
3690   some suggestions for reducing security risks.
3691</t>
3692
3693<section title="Personal Information" anchor="personal.information">
3694<t>
3695   HTTP clients are often privy to large amounts of personal information
3696   (e.g., the user's name, location, mail address, passwords, encryption
3697   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3698   leakage of this information.
3699   We very strongly recommend that a convenient interface be provided
3700   for the user to control dissemination of such information, and that
3701   designers and implementors be particularly careful in this area.
3702   History shows that errors in this area often create serious security
3703   and/or privacy problems and generate highly adverse publicity for the
3704   implementor's company.
3705</t>
3706</section>
3707
3708<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3709<t>
3710   A server is in the position to save personal data about a user's
3711   requests which might identify their reading patterns or subjects of
3712   interest.  In particular, log information gathered at an intermediary
3713   often contains a history of user agent interaction, across a multitude
3714   of sites, that can be traced to individual users.
3715</t>
3716<t>
3717   HTTP log information is confidential in nature; its handling is often
3718   constrained by laws and regulations.  Log information needs to be securely
3719   stored and appropriate guidelines followed for its analysis.
3720   Anonymization of personal information within individual entries helps,
3721   but is generally not sufficient to prevent real log traces from being
3722   re-identified based on correlation with other access characteristics.
3723   As such, access traces that are keyed to a specific client should not
3724   be published even if the key is pseudonymous.
3725</t>
3726<t>
3727   To minimize the risk of theft or accidental publication, log information
3728   should be purged of personally identifiable information, including
3729   user identifiers, IP addresses, and user-provided query parameters,
3730   as soon as that information is no longer necessary to support operational
3731   needs for security, auditing, or fraud control.
3732</t>
3733</section>
3734
3735<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3736<t>
3737   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3738   the documents returned by HTTP requests to be only those that were
3739   intended by the server administrators. If an HTTP server translates
3740   HTTP URIs directly into file system calls, the server &MUST; take
3741   special care not to serve files that were not intended to be
3742   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3743   other operating systems use ".." as a path component to indicate a
3744   directory level above the current one. On such a system, an HTTP
3745   server &MUST; disallow any such construct in the request-target if it
3746   would otherwise allow access to a resource outside those intended to
3747   be accessible via the HTTP server. Similarly, files intended for
3748   reference only internally to the server (such as access control
3749   files, configuration files, and script code) &MUST; be protected from
3750   inappropriate retrieval, since they might contain sensitive
3751   information. Experience has shown that minor bugs in such HTTP server
3752   implementations have turned into security risks.
3753</t>
3754</section>
3755
3756<section title="DNS-related Attacks" anchor="dns.related.attacks">
3757<t>
3758   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3759   generally prone to security attacks based on the deliberate misassociation
3760   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3761   cautious in assuming the validity of an IP number/DNS name association unless
3762   the response is protected by DNSSec (<xref target="RFC4033"/>).
3763</t>
3764</section>
3765
3766<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3767<t>
3768   By their very nature, HTTP intermediaries are men-in-the-middle, and
3769   represent an opportunity for man-in-the-middle attacks. Compromise of
3770   the systems on which the intermediaries run can result in serious security
3771   and privacy problems. Intermediaries have access to security-related
3772   information, personal information about individual users and
3773   organizations, and proprietary information belonging to users and
3774   content providers. A compromised intermediary, or an intermediary
3775   implemented or configured without regard to security and privacy
3776   considerations, might be used in the commission of a wide range of
3777   potential attacks.
3778</t>
3779<t>
3780   Intermediaries that contain a shared cache are especially vulnerable
3781   to cache poisoning attacks.
3782</t>
3783<t>
3784   Implementors need to consider the privacy and security
3785   implications of their design and coding decisions, and of the
3786   configuration options they provide to operators (especially the
3787   default configuration).
3788</t>
3789<t>
3790   Users need to be aware that intermediaries are no more trustworthy than
3791   the people who run them; HTTP itself cannot solve this problem.
3792</t>
3793<t>
3794   The judicious use of cryptography, when appropriate, might suffice to
3795   protect against a broad range of security and privacy attacks. Such
3796   cryptography is beyond the scope of the HTTP/1.1 specification.
3797</t>
3798</section>
3799
3800<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3801<t>
3802   Because HTTP uses mostly textual, character-delimited fields, attackers can
3803   overflow buffers in implementations, and/or perform a Denial of Service
3804   against implementations that accept fields with unlimited lengths.
3805</t>
3806<t>
3807   To promote interoperability, this specification makes specific
3808   recommendations for minimum size limits on request-line
3809   (<xref target="request.line"/>)
3810   and blocks of header fields (<xref target="header.fields"/>). These are
3811   minimum recommendations, chosen to be supportable even by implementations
3812   with limited resources; it is expected that most implementations will
3813   choose substantially higher limits.
3814</t>
3815<t>
3816   This specification also provides a way for servers to reject messages that
3817   have request-targets that are too long (&status-414;) or request entities
3818   that are too large (&status-4xx;).
3819</t>
3820<t>
3821   Other fields (including but not limited to request methods, response status
3822   phrases, header field-names, and body chunks) &SHOULD; be limited by
3823   implementations carefully, so as to not impede interoperability.
3824</t>
3825</section>
3826</section>
3827
3828<section title="Acknowledgments" anchor="acks">
3829<t>
3830   This edition of HTTP builds on the many contributions that went into
3831   <xref target="RFC1945" format="none">RFC 1945</xref>,
3832   <xref target="RFC2068" format="none">RFC 2068</xref>,
3833   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3834   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3835   substantial contributions made by the previous authors, editors, and
3836   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3837   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3838   Paul J. Leach, and Mark Nottingham.
3839   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
3840   acknowledgements from prior revisions.
3841</t>
3842<t>
3843   Since 1999, the following contributors have helped improve the HTTP
3844   specification by reporting bugs, asking smart questions, drafting or
3845   reviewing text, and evaluating open issues:
3846</t>
3847<?BEGININC acks ?>
3848<t>Adam Barth,
3849Adam Roach,
3850Addison Phillips,
3851Adrian Chadd,
3852Adrien W. de Croy,
3853Alan Ford,
3854Alan Ruttenberg,
3855Albert Lunde,
3856Alex Rousskov,
3857Alexey Melnikov,
3858Alisha Smith,
3859Amichai Rothman,
3860Amit Klein,
3861Amos Jeffries,
3862Andreas Maier,
3863Andreas Petersson,
3864Anne van Kesteren,
3865Anthony Bryan,
3866Asbjorn Ulsberg,
3867Balachander Krishnamurthy,
3868Barry Leiba,
3869Ben Laurie,
3870Benjamin Niven-Jenkins,
3871Bil Corry,
3872Bill Burke,
3873Bjoern Hoehrmann,
3874Bob Scheifler,
3875Boris Zbarsky,
3876Brett Slatkin,
3877Brian Kell,
3878Brian McBarron,
3879Brian Pane,
3880Brian Smith,
3881Bryce Nesbitt,
3882Cameron Heavon-Jones,
3883Carl Kugler,
3884Carsten Bormann,
3885Charles Fry,
3886Chris Newman,
3887Cyrus Daboo,
3888Dale Robert Anderson,
3889Dan Winship,
3890Daniel Stenberg,
3891Dave Cridland,
3892Dave Crocker,
3893Dave Kristol,
3894David Booth,
3895David Singer,
3896David W. Morris,
3897Diwakar Shetty,
3898Dmitry Kurochkin,
3899Drummond Reed,
3900Duane Wessels,
3901Edward Lee,
3902Eliot Lear,
3903Eran Hammer-Lahav,
3904Eric D. Williams,
3905Eric J. Bowman,
3906Eric Lawrence,
3907Eric Rescorla,
3908Erik Aronesty,
3909Florian Weimer,
3910Frank Ellermann,
3911Fred Bohle,
3912Geoffrey Sneddon,
3913Gervase Markham,
3914Greg Wilkins,
3915Harald Tveit Alvestrand,
3916Harry Halpin,
3917Helge Hess,
3918Henrik Nordstrom,
3919Henry S. Thompson,
3920Henry Story,
3921Herbert van de Sompel,
3922Howard Melman,
3923Hugo Haas,
3924Ian Hickson,
3925Ingo Struck,
3926J. Ross Nicoll,
3927James H. Manger,
3928James Lacey,
3929James M. Snell,
3930Jamie Lokier,
3931Jan Algermissen,
3932Jeff Hodges (for coming up with the term 'effective Request-URI'),
3933Jeff Walden,
3934Jim Luther,
3935Joe D. Williams,
3936Joe Gregorio,
3937Joe Orton,
3938John C. Klensin,
3939John C. Mallery,
3940John Cowan,
3941John Kemp,
3942John Panzer,
3943John Schneider,
3944John Stracke,
3945Jonas Sicking,
3946Jonathan Billington,
3947Jonathan Moore,
3948Jonathan Rees,
3949Jordi Ros,
3950Joris Dobbelsteen,
3951Josh Cohen,
3952Julien Pierre,
3953Jungshik Shin,
3954Justin Chapweske,
3955Justin Erenkrantz,
3956Justin James,
3957Kalvinder Singh,
3958Karl Dubost,
3959Keith Hoffman,
3960Keith Moore,
3961Koen Holtman,
3962Konstantin Voronkov,
3963Kris Zyp,
3964Lisa Dusseault,
3965Maciej Stachowiak,
3966Marc Schneider,
3967Marc Slemko,
3968Mark Baker,
3969Mark Pauley,
3970Markus Lanthaler,
3971Martin J. Duerst,
3972Martin Thomson,
3973Matt Lynch,
3974Matthew Cox,
3975Max Clark,
3976Michael Burrows,
3977Michael Hausenblas,
3978Mike Amundsen,
3979Mike Belshe,
3980Mike Kelly,
3981Mike Schinkel,
3982Miles Sabin,
3983Mykyta Yevstifeyev,
3984Nathan Rixham,
3985Nicholas Shanks,
3986Nico Williams,
3987Nicolas Alvarez,
3988Nicolas Mailhot,
3989Noah Slater,
3990Pablo Castro,
3991Pat Hayes,
3992Patrick R. McManus,
3993Paul E. Jones,
3994Paul Hoffman,
3995Paul Marquess,
3996Peter Saint-Andre,
3997Peter Watkins,
3998Phil Archer,
3999Phillip Hallam-Baker,
4000Poul-Henning Kamp,
4001Preethi Natarajan,
4002Ray Polk,
4003Reto Bachmann-Gmuer,
4004Richard Cyganiak,
4005Robert Brewer,
4006Robert Collins,
4007Robert O'Callahan,
4008Robert Olofsson,
4009Robert Sayre,
4010Robert Siemer,
4011Robert de Wilde,
4012Roberto Javier Godoy,
4013Ronny Widjaja,
4014S. Mike Dierken,
4015Salvatore Loreto,
4016Sam Johnston,
4017Sam Ruby,
4018Scott Lawrence (for maintaining the original issues list),
4019Sean B. Palmer,
4020Shane McCarron,
4021Stefan Eissing,
4022Stefan Tilkov,
4023Stefanos Harhalakis,
4024Stephane Bortzmeyer,
4025Stephen Farrell,
4026Stuart Williams,
4027Subbu Allamaraju,
4028Sylvain Hellegouarch,
4029Tapan Divekar,
4030Ted Hardie,
4031Thomas Broyer,
4032Thomas Nordin,
4033Thomas Roessler,
4034Tim Morgan,
4035Tim Olsen,
4036Travis Snoozy,
4037Tyler Close,
4038Vincent Murphy,
4039Wenbo Zhu,
4040Werner Baumann,
4041Wilbur Streett,
4042Wilfredo Sanchez Vega,
4043William A. Rowe Jr.,
4044William Chan,
4045Willy Tarreau,
4046Xiaoshu Wang,
4047Yaron Goland,
4048Yngve Nysaeter Pettersen,
4049Yogesh Bang,
4050Yutaka Oiwa,
4051Zed A. Shaw, and
4052Zhong Yu.
4053</t>
4054<?ENDINC acks ?>
4055</section>
4056
4057</middle>
4058<back>
4059
4060<references title="Normative References">
4061
4062<reference anchor="ISO-8859-1">
4063  <front>
4064    <title>
4065     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4066    </title>
4067    <author>
4068      <organization>International Organization for Standardization</organization>
4069    </author>
4070    <date year="1998"/>
4071  </front>
4072  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4073</reference>
4074
4075<reference anchor="Part2">
4076  <front>
4077    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4078    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4079      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4080      <address><email>fielding@gbiv.com</email></address>
4081    </author>
4082    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4083      <organization abbrev="W3C">World Wide Web Consortium</organization>
4084      <address><email>ylafon@w3.org</email></address>
4085    </author>
4086    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4087      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4088      <address><email>julian.reschke@greenbytes.de</email></address>
4089    </author>
4090    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4091  </front>
4092  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4093  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4094</reference>
4095
4096<reference anchor="Part3">
4097  <front>
4098    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4099    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4100      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4101      <address><email>fielding@gbiv.com</email></address>
4102    </author>
4103    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4104      <organization abbrev="W3C">World Wide Web Consortium</organization>
4105      <address><email>ylafon@w3.org</email></address>
4106    </author>
4107    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4108      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4109      <address><email>julian.reschke@greenbytes.de</email></address>
4110    </author>
4111    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4112  </front>
4113  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4114  <x:source href="p3-payload.xml" basename="p3-payload"/>
4115</reference>
4116
4117<reference anchor="Part6">
4118  <front>
4119    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4120    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4121      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4122      <address><email>fielding@gbiv.com</email></address>
4123    </author>
4124    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4125      <organization abbrev="W3C">World Wide Web Consortium</organization>
4126      <address><email>ylafon@w3.org</email></address>
4127    </author>
4128    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4129      <organization>Rackspace</organization>
4130      <address><email>mnot@mnot.net</email></address>
4131    </author>
4132    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4133      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4134      <address><email>julian.reschke@greenbytes.de</email></address>
4135    </author>
4136    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4137  </front>
4138  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4139  <x:source href="p6-cache.xml" basename="p6-cache"/>
4140</reference>
4141
4142<reference anchor="RFC5234">
4143  <front>
4144    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4145    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4146      <organization>Brandenburg InternetWorking</organization>
4147      <address>
4148        <email>dcrocker@bbiw.net</email>
4149      </address> 
4150    </author>
4151    <author initials="P." surname="Overell" fullname="Paul Overell">
4152      <organization>THUS plc.</organization>
4153      <address>
4154        <email>paul.overell@thus.net</email>
4155      </address>
4156    </author>
4157    <date month="January" year="2008"/>
4158  </front>
4159  <seriesInfo name="STD" value="68"/>
4160  <seriesInfo name="RFC" value="5234"/>
4161</reference>
4162
4163<reference anchor="RFC2119">
4164  <front>
4165    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4166    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4167      <organization>Harvard University</organization>
4168      <address><email>sob@harvard.edu</email></address>
4169    </author>
4170    <date month="March" year="1997"/>
4171  </front>
4172  <seriesInfo name="BCP" value="14"/>
4173  <seriesInfo name="RFC" value="2119"/>
4174</reference>
4175
4176<reference anchor="RFC3986">
4177 <front>
4178  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4179  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4180    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4181    <address>
4182       <email>timbl@w3.org</email>
4183       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4184    </address>
4185  </author>
4186  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4187    <organization abbrev="Day Software">Day Software</organization>
4188    <address>
4189      <email>fielding@gbiv.com</email>
4190      <uri>http://roy.gbiv.com/</uri>
4191    </address>
4192  </author>
4193  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4194    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4195    <address>
4196      <email>LMM@acm.org</email>
4197      <uri>http://larry.masinter.net/</uri>
4198    </address>
4199  </author>
4200  <date month='January' year='2005'></date>
4201 </front>
4202 <seriesInfo name="STD" value="66"/>
4203 <seriesInfo name="RFC" value="3986"/>
4204</reference>
4205
4206<reference anchor="USASCII">
4207  <front>
4208    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4209    <author>
4210      <organization>American National Standards Institute</organization>
4211    </author>
4212    <date year="1986"/>
4213  </front>
4214  <seriesInfo name="ANSI" value="X3.4"/>
4215</reference>
4216
4217<reference anchor="RFC1950">
4218  <front>
4219    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4220    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4221      <organization>Aladdin Enterprises</organization>
4222      <address><email>ghost@aladdin.com</email></address>
4223    </author>
4224    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4225    <date month="May" year="1996"/>
4226  </front>
4227  <seriesInfo name="RFC" value="1950"/>
4228  <!--<annotation>
4229    RFC 1950 is an Informational RFC, thus it might be less stable than
4230    this specification. On the other hand, this downward reference was
4231    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4232    therefore it is unlikely to cause problems in practice. See also
4233    <xref target="BCP97"/>.
4234  </annotation>-->
4235</reference>
4236
4237<reference anchor="RFC1951">
4238  <front>
4239    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4240    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4241      <organization>Aladdin Enterprises</organization>
4242      <address><email>ghost@aladdin.com</email></address>
4243    </author>
4244    <date month="May" year="1996"/>
4245  </front>
4246  <seriesInfo name="RFC" value="1951"/>
4247  <!--<annotation>
4248    RFC 1951 is an Informational RFC, thus it might be less stable than
4249    this specification. On the other hand, this downward reference was
4250    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4251    therefore it is unlikely to cause problems in practice. See also
4252    <xref target="BCP97"/>.
4253  </annotation>-->
4254</reference>
4255
4256<reference anchor="RFC1952">
4257  <front>
4258    <title>GZIP file format specification version 4.3</title>
4259    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4260      <organization>Aladdin Enterprises</organization>
4261      <address><email>ghost@aladdin.com</email></address>
4262    </author>
4263    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4264      <address><email>gzip@prep.ai.mit.edu</email></address>
4265    </author>
4266    <author initials="M." surname="Adler" fullname="Mark Adler">
4267      <address><email>madler@alumni.caltech.edu</email></address>
4268    </author>
4269    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4270      <address><email>ghost@aladdin.com</email></address>
4271    </author>
4272    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4273      <address><email>randeg@alumni.rpi.edu</email></address>
4274    </author>
4275    <date month="May" year="1996"/>
4276  </front>
4277  <seriesInfo name="RFC" value="1952"/>
4278  <!--<annotation>
4279    RFC 1952 is an Informational RFC, thus it might be less stable than
4280    this specification. On the other hand, this downward reference was
4281    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4282    therefore it is unlikely to cause problems in practice. See also
4283    <xref target="BCP97"/>.
4284  </annotation>-->
4285</reference>
4286
4287</references>
4288
4289<references title="Informative References">
4290
4291<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4292  <front>
4293    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4294    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4295    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4296    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4297    <author initials="H." surname="Lie" fullname="H. Lie"/>
4298    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4299    <date year="1997" month="September"/>
4300  </front>
4301  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4302</reference>
4303
4304<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4305  <front>
4306    <title>Improving HTTP Latency</title>
4307    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4308    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4309    <date year="1995" month="December"/>
4310  </front>
4311  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4312</reference>
4313
4314<reference anchor='RFC1919'>
4315  <front>
4316    <title>Classical versus Transparent IP Proxies</title>
4317    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4318      <address><email>mchatel@pax.eunet.ch</email></address>
4319    </author>
4320    <date year='1996' month='March' />
4321  </front>
4322  <seriesInfo name='RFC' value='1919' />
4323</reference>
4324
4325<reference anchor="RFC1945">
4326  <front>
4327    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4328    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4329      <organization>MIT, Laboratory for Computer Science</organization>
4330      <address><email>timbl@w3.org</email></address>
4331    </author>
4332    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4333      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4334      <address><email>fielding@ics.uci.edu</email></address>
4335    </author>
4336    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4337      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4338      <address><email>frystyk@w3.org</email></address>
4339    </author>
4340    <date month="May" year="1996"/>
4341  </front>
4342  <seriesInfo name="RFC" value="1945"/>
4343</reference>
4344
4345<reference anchor="RFC2045">
4346  <front>
4347    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4348    <author initials="N." surname="Freed" fullname="Ned Freed">
4349      <organization>Innosoft International, Inc.</organization>
4350      <address><email>ned@innosoft.com</email></address>
4351    </author>
4352    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4353      <organization>First Virtual Holdings</organization>
4354      <address><email>nsb@nsb.fv.com</email></address>
4355    </author>
4356    <date month="November" year="1996"/>
4357  </front>
4358  <seriesInfo name="RFC" value="2045"/>
4359</reference>
4360
4361<reference anchor="RFC2047">
4362  <front>
4363    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4364    <author initials="K." surname="Moore" fullname="Keith Moore">
4365      <organization>University of Tennessee</organization>
4366      <address><email>moore@cs.utk.edu</email></address>
4367    </author>
4368    <date month="November" year="1996"/>
4369  </front>
4370  <seriesInfo name="RFC" value="2047"/>
4371</reference>
4372
4373<reference anchor="RFC2068">
4374  <front>
4375    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4376    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4377      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4378      <address><email>fielding@ics.uci.edu</email></address>
4379    </author>
4380    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4381      <organization>MIT Laboratory for Computer Science</organization>
4382      <address><email>jg@w3.org</email></address>
4383    </author>
4384    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4385      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4386      <address><email>mogul@wrl.dec.com</email></address>
4387    </author>
4388    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4389      <organization>MIT Laboratory for Computer Science</organization>
4390      <address><email>frystyk@w3.org</email></address>
4391    </author>
4392    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4393      <organization>MIT Laboratory for Computer Science</organization>
4394      <address><email>timbl@w3.org</email></address>
4395    </author>
4396    <date month="January" year="1997"/>
4397  </front>
4398  <seriesInfo name="RFC" value="2068"/>
4399</reference>
4400
4401<reference anchor="RFC2145">
4402  <front>
4403    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4404    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4405      <organization>Western Research Laboratory</organization>
4406      <address><email>mogul@wrl.dec.com</email></address>
4407    </author>
4408    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4409      <organization>Department of Information and Computer Science</organization>
4410      <address><email>fielding@ics.uci.edu</email></address>
4411    </author>
4412    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4413      <organization>MIT Laboratory for Computer Science</organization>
4414      <address><email>jg@w3.org</email></address>
4415    </author>
4416    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4417      <organization>W3 Consortium</organization>
4418      <address><email>frystyk@w3.org</email></address>
4419    </author>
4420    <date month="May" year="1997"/>
4421  </front>
4422  <seriesInfo name="RFC" value="2145"/>
4423</reference>
4424
4425<reference anchor="RFC2616">
4426  <front>
4427    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4428    <author initials="R." surname="Fielding" fullname="R. Fielding">
4429      <organization>University of California, Irvine</organization>
4430      <address><email>fielding@ics.uci.edu</email></address>
4431    </author>
4432    <author initials="J." surname="Gettys" fullname="J. Gettys">
4433      <organization>W3C</organization>
4434      <address><email>jg@w3.org</email></address>
4435    </author>
4436    <author initials="J." surname="Mogul" fullname="J. Mogul">
4437      <organization>Compaq Computer Corporation</organization>
4438      <address><email>mogul@wrl.dec.com</email></address>
4439    </author>
4440    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4441      <organization>MIT Laboratory for Computer Science</organization>
4442      <address><email>frystyk@w3.org</email></address>
4443    </author>
4444    <author initials="L." surname="Masinter" fullname="L. Masinter">
4445      <organization>Xerox Corporation</organization>
4446      <address><email>masinter@parc.xerox.com</email></address>
4447    </author>
4448    <author initials="P." surname="Leach" fullname="P. Leach">
4449      <organization>Microsoft Corporation</organization>
4450      <address><email>paulle@microsoft.com</email></address>
4451    </author>
4452    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4453      <organization>W3C</organization>
4454      <address><email>timbl@w3.org</email></address>
4455    </author>
4456    <date month="June" year="1999"/>
4457  </front>
4458  <seriesInfo name="RFC" value="2616"/>
4459</reference>
4460
4461<reference anchor='RFC2817'>
4462  <front>
4463    <title>Upgrading to TLS Within HTTP/1.1</title>
4464    <author initials='R.' surname='Khare' fullname='R. Khare'>
4465      <organization>4K Associates / UC Irvine</organization>
4466      <address><email>rohit@4K-associates.com</email></address>
4467    </author>
4468    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4469      <organization>Agranat Systems, Inc.</organization>
4470      <address><email>lawrence@agranat.com</email></address>
4471    </author>
4472    <date year='2000' month='May' />
4473  </front>
4474  <seriesInfo name='RFC' value='2817' />
4475</reference>
4476
4477<reference anchor='RFC2818'>
4478  <front>
4479    <title>HTTP Over TLS</title>
4480    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4481      <organization>RTFM, Inc.</organization>
4482      <address><email>ekr@rtfm.com</email></address>
4483    </author>
4484    <date year='2000' month='May' />
4485  </front>
4486  <seriesInfo name='RFC' value='2818' />
4487</reference>
4488
4489<reference anchor='RFC2965'>
4490  <front>
4491    <title>HTTP State Management Mechanism</title>
4492    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4493      <organization>Bell Laboratories, Lucent Technologies</organization>
4494      <address><email>dmk@bell-labs.com</email></address>
4495    </author>
4496    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4497      <organization>Epinions.com, Inc.</organization>
4498      <address><email>lou@montulli.org</email></address>
4499    </author>
4500    <date year='2000' month='October' />
4501  </front>
4502  <seriesInfo name='RFC' value='2965' />
4503</reference>
4504
4505<reference anchor='RFC3040'>
4506  <front>
4507    <title>Internet Web Replication and Caching Taxonomy</title>
4508    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4509      <organization>Equinix, Inc.</organization>
4510    </author>
4511    <author initials='I.' surname='Melve' fullname='I. Melve'>
4512      <organization>UNINETT</organization>
4513    </author>
4514    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4515      <organization>CacheFlow Inc.</organization>
4516    </author>
4517    <date year='2001' month='January' />
4518  </front>
4519  <seriesInfo name='RFC' value='3040' />
4520</reference>
4521
4522<reference anchor='RFC3864'>
4523  <front>
4524    <title>Registration Procedures for Message Header Fields</title>
4525    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4526      <organization>Nine by Nine</organization>
4527      <address><email>GK-IETF@ninebynine.org</email></address>
4528    </author>
4529    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4530      <organization>BEA Systems</organization>
4531      <address><email>mnot@pobox.com</email></address>
4532    </author>
4533    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4534      <organization>HP Labs</organization>
4535      <address><email>JeffMogul@acm.org</email></address>
4536    </author>
4537    <date year='2004' month='September' />
4538  </front>
4539  <seriesInfo name='BCP' value='90' />
4540  <seriesInfo name='RFC' value='3864' />
4541</reference>
4542
4543<reference anchor='RFC4033'>
4544  <front>
4545    <title>DNS Security Introduction and Requirements</title>
4546    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4547    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4548    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4549    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4550    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4551    <date year='2005' month='March' />
4552  </front>
4553  <seriesInfo name='RFC' value='4033' />
4554</reference>
4555
4556<reference anchor="RFC4288">
4557  <front>
4558    <title>Media Type Specifications and Registration Procedures</title>
4559    <author initials="N." surname="Freed" fullname="N. Freed">
4560      <organization>Sun Microsystems</organization>
4561      <address>
4562        <email>ned.freed@mrochek.com</email>
4563      </address>
4564    </author>
4565    <author initials="J." surname="Klensin" fullname="J. Klensin">
4566      <address>
4567        <email>klensin+ietf@jck.com</email>
4568      </address>
4569    </author>
4570    <date year="2005" month="December"/>
4571  </front>
4572  <seriesInfo name="BCP" value="13"/>
4573  <seriesInfo name="RFC" value="4288"/>
4574</reference>
4575
4576<reference anchor='RFC4395'>
4577  <front>
4578    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4579    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4580      <organization>AT&amp;T Laboratories</organization>
4581      <address>
4582        <email>tony+urireg@maillennium.att.com</email>
4583      </address>
4584    </author>
4585    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4586      <organization>Qualcomm, Inc.</organization>
4587      <address>
4588        <email>hardie@qualcomm.com</email>
4589      </address>
4590    </author>
4591    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4592      <organization>Adobe Systems</organization>
4593      <address>
4594        <email>LMM@acm.org</email>
4595      </address>
4596    </author>
4597    <date year='2006' month='February' />
4598  </front>
4599  <seriesInfo name='BCP' value='115' />
4600  <seriesInfo name='RFC' value='4395' />
4601</reference>
4602
4603<reference anchor='RFC4559'>
4604  <front>
4605    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4606    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4607    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4608    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4609    <date year='2006' month='June' />
4610  </front>
4611  <seriesInfo name='RFC' value='4559' />
4612</reference>
4613
4614<reference anchor='RFC5226'>
4615  <front>
4616    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4617    <author initials='T.' surname='Narten' fullname='T. Narten'>
4618      <organization>IBM</organization>
4619      <address><email>narten@us.ibm.com</email></address>
4620    </author>
4621    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4622      <organization>Google</organization>
4623      <address><email>Harald@Alvestrand.no</email></address>
4624    </author>
4625    <date year='2008' month='May' />
4626  </front>
4627  <seriesInfo name='BCP' value='26' />
4628  <seriesInfo name='RFC' value='5226' />
4629</reference>
4630
4631<reference anchor="RFC5322">
4632  <front>
4633    <title>Internet Message Format</title>
4634    <author initials="P." surname="Resnick" fullname="P. Resnick">
4635      <organization>Qualcomm Incorporated</organization>
4636    </author>
4637    <date year="2008" month="October"/>
4638  </front> 
4639  <seriesInfo name="RFC" value="5322"/>
4640</reference>
4641
4642<reference anchor="RFC6265">
4643  <front>
4644    <title>HTTP State Management Mechanism</title>
4645    <author initials="A." surname="Barth" fullname="Adam Barth">
4646      <organization abbrev="U.C. Berkeley">
4647        University of California, Berkeley
4648      </organization>
4649      <address><email>abarth@eecs.berkeley.edu</email></address>
4650    </author>
4651    <date year="2011" month="April" />
4652  </front>
4653  <seriesInfo name="RFC" value="6265"/>
4654</reference>
4655
4656<!--<reference anchor='BCP97'>
4657  <front>
4658    <title>Handling Normative References to Standards-Track Documents</title>
4659    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4660      <address>
4661        <email>klensin+ietf@jck.com</email>
4662      </address>
4663    </author>
4664    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4665      <organization>MIT</organization>
4666      <address>
4667        <email>hartmans-ietf@mit.edu</email>
4668      </address>
4669    </author>
4670    <date year='2007' month='June' />
4671  </front>
4672  <seriesInfo name='BCP' value='97' />
4673  <seriesInfo name='RFC' value='4897' />
4674</reference>-->
4675
4676<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4677  <front>
4678    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4679    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4680    <date year="2001" month="November"/>
4681  </front>
4682  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4683</reference>
4684
4685<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4686  <front>
4687    <title>Analysis of HTTP Performance Problems</title>
4688    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4689    <date/>
4690  </front>
4691</reference>
4692
4693<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4694  <front>
4695  <title>Analysis of HTTP Performance</title>
4696  <author initials="J." surname="Touch" fullname="Joe Touch">
4697    <organization>USC/Information Sciences Institute</organization>
4698    <address><email>touch@isi.edu</email></address>
4699  </author>
4700  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4701    <organization>USC/Information Sciences Institute</organization>
4702    <address><email>johnh@isi.edu</email></address>
4703  </author>
4704  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4705    <organization>USC/Information Sciences Institute</organization>
4706    <address><email>katia@isi.edu</email></address>
4707  </author>
4708  <date year="1998" month="Aug"/>
4709  </front>
4710  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4711  <annotation>(original report dated Aug. 1996)</annotation>
4712</reference>
4713
4714</references>
4715
4716
4717<section title="HTTP Version History" anchor="compatibility">
4718<t>
4719   HTTP has been in use by the World-Wide Web global information initiative
4720   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4721   was a simple protocol for hypertext data transfer across the Internet
4722   with only a single request method (GET) and no metadata.
4723   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4724   methods and MIME-like messaging that could include metadata about the data
4725   transferred and modifiers on the request/response semantics. However,
4726   HTTP/1.0 did not sufficiently take into consideration the effects of
4727   hierarchical proxies, caching, the need for persistent connections, or
4728   name-based virtual hosts. The proliferation of incompletely-implemented
4729   applications calling themselves "HTTP/1.0" further necessitated a
4730   protocol version change in order for two communicating applications
4731   to determine each other's true capabilities.
4732</t>
4733<t>
4734   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4735   requirements that enable reliable implementations, adding only
4736   those new features that will either be safely ignored by an HTTP/1.0
4737   recipient or only sent when communicating with a party advertising
4738   conformance with HTTP/1.1.
4739</t>
4740<t>
4741   It is beyond the scope of a protocol specification to mandate
4742   conformance with previous versions. HTTP/1.1 was deliberately
4743   designed, however, to make supporting previous versions easy.
4744   We would expect a general-purpose HTTP/1.1 server to understand
4745   any valid request in the format of HTTP/1.0 and respond appropriately
4746   with an HTTP/1.1 message that only uses features understood (or
4747   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4748   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4749</t>
4750<t>
4751   Since HTTP/0.9 did not support header fields in a request,
4752   there is no mechanism for it to support name-based virtual
4753   hosts (selection of resource by inspection of the Host header
4754   field).  Any server that implements name-based virtual hosts
4755   ought to disable support for HTTP/0.9.  Most requests that
4756   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4757   requests wherein a buggy client failed to properly encode
4758   linear whitespace found in a URI reference and placed in
4759   the request-target.
4760</t>
4761
4762<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4763<t>
4764   This section summarizes major differences between versions HTTP/1.0
4765   and HTTP/1.1.
4766</t>
4767
4768<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4769<t>
4770   The requirements that clients and servers support the Host header
4771   field (<xref target="header.host"/>), report an error if it is
4772   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4773   are among the most important changes defined by HTTP/1.1.
4774</t>
4775<t>
4776   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4777   addresses and servers; there was no other established mechanism for
4778   distinguishing the intended server of a request than the IP address
4779   to which that request was directed. The Host header field was
4780   introduced during the development of HTTP/1.1 and, though it was
4781   quickly implemented by most HTTP/1.0 browsers, additional requirements
4782   were placed on all HTTP/1.1 requests in order to ensure complete
4783   adoption.  At the time of this writing, most HTTP-based services
4784   are dependent upon the Host header field for targeting requests.
4785</t>
4786</section>
4787
4788<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4789<t>
4790   In HTTP/1.0, each connection is established by the client prior to the
4791   request and closed by the server after sending the response. However, some
4792   implementations implement the explicitly negotiated ("Keep-Alive") version
4793   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4794   target="RFC2068"/>.
4795</t>
4796<t>
4797   Some clients and servers might wish to be compatible with these previous
4798   approaches to persistent connections, by explicitly negotiating for them
4799   with a "Connection: keep-alive" request header field. However, some
4800   experimental implementations of HTTP/1.0 persistent connections are faulty;
4801   for example, if a HTTP/1.0 proxy server doesn't understand Connection, it
4802   will erroneously forward that header to the next inbound server, which
4803   would result in a hung connection.
4804</t>
4805<t>
4806   One attempted solution was the introduction of a Proxy-Connection header,
4807   targeted specifically at proxies. In practice, this was also unworkable,
4808   because proxies are often deployed in multiple layers, bringing about the
4809   same problem discussed above.
4810</t>
4811<t>
4812   As a result, clients are encouraged not to send the Proxy-Connection header
4813   in any requests.
4814</t>
4815<t>
4816   Clients are also encouraged to consider the use of Connection: keep-alive
4817   in requests carefully; while they can enable persistent connections with
4818   HTTP/1.0 servers, clients using them need will need to monitor the
4819   connection for "hung" requests (which indicate that the client ought stop
4820   sending the header), and this mechanism ought not be used by clients at all
4821   when a proxy is being used.
4822</t>
4823</section>
4824</section>
4825
4826<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4827<t>
4828  Clarify that the string "HTTP" in the HTTP-version ABFN production is case
4829  sensitive. Restrict the version numbers to be single digits due to the fact
4830  that implementations are known to handle multi-digit version numbers
4831  incorrectly.
4832  (<xref target="http.version"/>)
4833</t>
4834<t>
4835  Update use of abs_path production from RFC 1808 to the path-absolute + query
4836  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4837  request method only.
4838  (<xref target="request-target"/>)
4839</t>
4840<t>
4841  Require that invalid whitespace around field-names be rejected.
4842  (<xref target="header.fields"/>)
4843</t>
4844<t>
4845  Rules about implicit linear whitespace between certain grammar productions
4846  have been removed; now whitespace is only allowed where specifically
4847  defined in the ABNF.
4848  (<xref target="whitespace"/>)
4849</t>
4850<t> 
4851  The NUL octet is no longer allowed in comment and quoted-string
4852  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4853  Non-ASCII content in header fields and reason phrase has been obsoleted and
4854  made opaque (the TEXT rule was removed).
4855  (<xref target="field.components"/>)
4856</t>
4857<t>
4858  Empty list elements in list productions have been deprecated.
4859  (<xref target="abnf.extension"/>)
4860</t>
4861<t>
4862  Require recipients to handle bogus Content-Length header fields as errors.
4863  (<xref target="message.body"/>)
4864</t>
4865<t>
4866  Remove reference to non-existent identity transfer-coding value tokens.
4867  (Sections <xref format="counter" target="message.body"/> and
4868  <xref format="counter" target="transfer.codings"/>)
4869</t>
4870<t>
4871  Clarification that the chunk length does not include the count of the octets
4872  in the chunk header and trailer. Furthermore disallowed line folding
4873  in chunk extensions, and deprecate their use.
4874  (<xref target="chunked.encoding"/>)
4875</t>
4876<t>
4877  Registration of Transfer Codings now requires IETF Review
4878  (<xref target="transfer.coding.registry"/>)
4879</t>
4880<t>
4881  Remove hard limit of two connections per server.
4882  Remove requirement to retry a sequence of requests as long it was idempotent.
4883  Remove requirements about when servers are allowed to close connections
4884  prematurely.
4885  (<xref target="persistent.practical"/>)
4886</t>
4887<t>
4888  Remove requirement to retry requests under certain cirumstances when the
4889  server prematurely closes the connection.
4890  (<xref target="message.transmission.requirements"/>)
4891</t>
4892<t>
4893  Change ABNF productions for header fields to only define the field value.
4894</t>
4895<t>
4896  Clarify exactly when close connection options have to be sent.
4897  (<xref target="header.connection"/>)
4898</t>
4899<t>
4900  Define the semantics of the "Upgrade" header field in responses other than
4901  101 (this was incorporated from <xref target="RFC2817"/>).
4902  (<xref target="header.upgrade"/>)
4903</t>
4904</section>
4905
4906<section title="Changes from RFC 2817" anchor="changes.from.rfc.2817">
4907<t>
4908  Registration of Upgrade tokens now requires IETF Review
4909  (<xref target="upgrade.token.registry"/>)
4910</t>
4911</section>
4912</section>
4913
4914<?BEGININC p1-messaging.abnf-appendix ?>
4915<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4916<figure>
4917<artwork type="abnf" name="p1-messaging.parsed-abnf">
4918<x:ref>BWS</x:ref> = OWS
4919
4920<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4921 connection-token ] )
4922<x:ref>Content-Length</x:ref> = 1*DIGIT
4923
4924<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4925 ]
4926<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
4927<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
4928<x:ref>Host</x:ref> = uri-host [ ":" port ]
4929
4930<x:ref>OWS</x:ref> = *( SP / HTAB )
4931
4932<x:ref>RWS</x:ref> = 1*( SP / HTAB )
4933
4934<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4935<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4936<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4937 transfer-coding ] )
4938
4939<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4940<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
4941
4942<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
4943 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
4944 )
4945
4946<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4947<x:ref>absolute-form</x:ref> = absolute-URI
4948<x:ref>asterisk-form</x:ref> = "*"
4949<x:ref>attribute</x:ref> = token
4950<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4951<x:ref>authority-form</x:ref> = authority
4952
4953<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
4954<x:ref>chunk-data</x:ref> = 1*OCTET
4955<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
4956<x:ref>chunk-ext-name</x:ref> = token
4957<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4958<x:ref>chunk-size</x:ref> = 1*HEXDIG
4959<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
4960<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4961<x:ref>connection-token</x:ref> = token
4962<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4963 / %x2A-5B ; '*'-'['
4964 / %x5D-7E ; ']'-'~'
4965 / obs-text
4966
4967<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4968<x:ref>field-name</x:ref> = token
4969<x:ref>field-value</x:ref> = *( field-content / obs-fold )
4970
4971<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
4972<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4973<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4974
4975<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
4976
4977<x:ref>message-body</x:ref> = *OCTET
4978<x:ref>method</x:ref> = token
4979
4980<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
4981<x:ref>obs-text</x:ref> = %x80-FF
4982<x:ref>origin-form</x:ref> = path-absolute [ "?" query ]
4983
4984<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4985<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4986<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4987<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4988<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
4989<x:ref>protocol-name</x:ref> = token
4990<x:ref>protocol-version</x:ref> = token
4991<x:ref>pseudonym</x:ref> = token
4992
4993<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4994 / %x5D-7E ; ']'-'~'
4995 / obs-text
4996<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
4997 / %x5D-7E ; ']'-'~'
4998 / obs-text
4999<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5000<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5001<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5002<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5003<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5004<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5005
5006<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5007<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5008<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5009<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5010<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
5011<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
5012 asterisk-form
5013
5014<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5015 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5016<x:ref>start-line</x:ref> = request-line / status-line
5017<x:ref>status-code</x:ref> = 3DIGIT
5018<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
5019
5020<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5021<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5022 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5023<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5024<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5025<x:ref>token</x:ref> = 1*tchar
5026<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5027<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5028 transfer-extension
5029<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5030<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5031
5032<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5033
5034<x:ref>value</x:ref> = word
5035
5036<x:ref>word</x:ref> = token / quoted-string
5037</artwork>
5038</figure>
5039<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5040; Connection defined but not used
5041; Content-Length defined but not used
5042; HTTP-message defined but not used
5043; Host defined but not used
5044; TE defined but not used
5045; Trailer defined but not used
5046; Transfer-Encoding defined but not used
5047; URI-reference defined but not used
5048; Upgrade defined but not used
5049; Via defined but not used
5050; chunked-body defined but not used
5051; http-URI defined but not used
5052; https-URI defined but not used
5053; partial-URI defined but not used
5054; special defined but not used
5055</artwork></figure></section>
5056<?ENDINC p1-messaging.abnf-appendix ?>
5057
5058<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5059
5060<section title="Since RFC 2616">
5061<t>
5062  Extracted relevant partitions from <xref target="RFC2616"/>.
5063</t>
5064</section>
5065
5066<section title="Since draft-ietf-httpbis-p1-messaging-00">
5067<t>
5068  Closed issues:
5069  <list style="symbols"> 
5070    <t>
5071      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5072      "HTTP Version should be case sensitive"
5073      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5074    </t>
5075    <t>
5076      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5077      "'unsafe' characters"
5078      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5079    </t>
5080    <t>
5081      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5082      "Chunk Size Definition"
5083      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5084    </t>
5085    <t>
5086      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5087      "Message Length"
5088      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5089    </t>
5090    <t>
5091      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5092      "Media Type Registrations"
5093      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5094    </t>
5095    <t>
5096      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5097      "URI includes query"
5098      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5099    </t>
5100    <t>
5101      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5102      "No close on 1xx responses"
5103      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5104    </t>
5105    <t>
5106      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5107      "Remove 'identity' token references"
5108      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5109    </t>
5110    <t>
5111      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5112      "Import query BNF"
5113    </t>
5114    <t>
5115      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5116      "qdtext BNF"
5117    </t>
5118    <t>
5119      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5120      "Normative and Informative references"
5121    </t>
5122    <t>
5123      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5124      "RFC2606 Compliance"
5125    </t>
5126    <t>
5127      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5128      "RFC977 reference"
5129    </t>
5130    <t>
5131      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5132      "RFC1700 references"
5133    </t>
5134    <t>
5135      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5136      "inconsistency in date format explanation"
5137    </t>
5138    <t>
5139      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5140      "Date reference typo"
5141    </t>
5142    <t>
5143      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5144      "Informative references"
5145    </t>
5146    <t>
5147      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5148      "ISO-8859-1 Reference"
5149    </t>
5150    <t>
5151      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5152      "Normative up-to-date references"
5153    </t>
5154  </list>
5155</t>
5156<t>
5157  Other changes:
5158  <list style="symbols"> 
5159    <t>
5160      Update media type registrations to use RFC4288 template.
5161    </t>
5162    <t>
5163      Use names of RFC4234 core rules DQUOTE and HTAB,
5164      fix broken ABNF for chunk-data
5165      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5166    </t>
5167  </list>
5168</t>
5169</section>
5170
5171<section title="Since draft-ietf-httpbis-p1-messaging-01">
5172<t>
5173  Closed issues:
5174  <list style="symbols"> 
5175    <t>
5176      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5177      "Bodies on GET (and other) requests"
5178    </t>
5179    <t>
5180      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5181      "Updating to RFC4288"
5182    </t>
5183    <t>
5184      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5185      "Status Code and Reason Phrase"
5186    </t>
5187    <t>
5188      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5189      "rel_path not used"
5190    </t>
5191  </list>
5192</t>
5193<t>
5194  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5195  <list style="symbols"> 
5196    <t>
5197      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5198      "trailer-part").
5199    </t>
5200    <t>
5201      Avoid underscore character in rule names ("http_URL" ->
5202      "http-URL", "abs_path" -> "path-absolute").
5203    </t>
5204    <t>
5205      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5206      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5207      have to be updated when switching over to RFC3986.
5208    </t>
5209    <t>
5210      Synchronize core rules with RFC5234.
5211    </t>
5212    <t>
5213      Get rid of prose rules that span multiple lines.
5214    </t>
5215    <t>
5216      Get rid of unused rules LOALPHA and UPALPHA.
5217    </t>
5218    <t>
5219      Move "Product Tokens" section (back) into Part 1, as "token" is used
5220      in the definition of the Upgrade header field.
5221    </t>
5222    <t>
5223      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5224    </t>
5225    <t>
5226      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5227    </t>
5228  </list>
5229</t>
5230</section>
5231
5232<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5233<t>
5234  Closed issues:
5235  <list style="symbols"> 
5236    <t>
5237      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5238      "HTTP-date vs. rfc1123-date"
5239    </t>
5240    <t>
5241      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5242      "WS in quoted-pair"
5243    </t>
5244  </list>
5245</t>
5246<t>
5247  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5248  <list style="symbols"> 
5249    <t>
5250      Reference RFC 3984, and update header field registrations for headers defined
5251      in this document.
5252    </t>
5253  </list>
5254</t>
5255<t>
5256  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5257  <list style="symbols"> 
5258    <t>
5259      Replace string literals when the string really is case-sensitive (HTTP-version).
5260    </t>
5261  </list>
5262</t>
5263</section>
5264
5265<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5266<t>
5267  Closed issues:
5268  <list style="symbols"> 
5269    <t>
5270      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5271      "Connection closing"
5272    </t>
5273    <t>
5274      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5275      "Move registrations and registry information to IANA Considerations"
5276    </t>
5277    <t>
5278      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5279      "need new URL for PAD1995 reference"
5280    </t>
5281    <t>
5282      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5283      "IANA Considerations: update HTTP URI scheme registration"
5284    </t>
5285    <t>
5286      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5287      "Cite HTTPS URI scheme definition"
5288    </t>
5289    <t>
5290      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5291      "List-type headers vs Set-Cookie"
5292    </t>
5293  </list>
5294</t>
5295<t>
5296  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5297  <list style="symbols"> 
5298    <t>
5299      Replace string literals when the string really is case-sensitive (HTTP-Date).
5300    </t>
5301    <t>
5302      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5303    </t>
5304  </list>
5305</t>
5306</section>
5307
5308<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5309<t>
5310  Closed issues:
5311  <list style="symbols"> 
5312    <t>
5313      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5314      "Out-of-date reference for URIs"
5315    </t>
5316    <t>
5317      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5318      "RFC 2822 is updated by RFC 5322"
5319    </t>
5320  </list>
5321</t>
5322<t>
5323  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5324  <list style="symbols"> 
5325    <t>
5326      Use "/" instead of "|" for alternatives.
5327    </t>
5328    <t>
5329      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5330    </t>
5331    <t>
5332      Only reference RFC 5234's core rules.
5333    </t>
5334    <t>
5335      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5336      whitespace ("OWS") and required whitespace ("RWS").
5337    </t>
5338    <t>
5339      Rewrite ABNFs to spell out whitespace rules, factor out
5340      header field value format definitions.
5341    </t>
5342  </list>
5343</t>
5344</section>
5345
5346<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5347<t>
5348  Closed issues:
5349  <list style="symbols"> 
5350    <t>
5351      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5352      "Header LWS"
5353    </t>
5354    <t>
5355      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5356      "Sort 1.3 Terminology"
5357    </t>
5358    <t>
5359      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5360      "RFC2047 encoded words"
5361    </t>
5362    <t>
5363      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5364      "Character Encodings in TEXT"
5365    </t>
5366    <t>
5367      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5368      "Line Folding"
5369    </t>
5370    <t>
5371      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5372      "OPTIONS * and proxies"
5373    </t>
5374    <t>
5375      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5376      "reason-phrase BNF"
5377    </t>
5378    <t>
5379      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5380      "Use of TEXT"
5381    </t>
5382    <t>
5383      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5384      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5385    </t>
5386    <t>
5387      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5388      "RFC822 reference left in discussion of date formats"
5389    </t>
5390  </list>
5391</t>
5392<t>
5393  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5394  <list style="symbols"> 
5395    <t>
5396      Rewrite definition of list rules, deprecate empty list elements.
5397    </t>
5398    <t>
5399      Add appendix containing collected and expanded ABNF.
5400    </t>
5401  </list>
5402</t>
5403<t>
5404  Other changes:
5405  <list style="symbols"> 
5406    <t>
5407      Rewrite introduction; add mostly new Architecture Section.
5408    </t>
5409    <t>
5410      Move definition of quality values from Part 3 into Part 1;
5411      make TE request header field grammar independent of accept-params (defined in Part 3).
5412    </t>
5413  </list>
5414</t>
5415</section>
5416
5417<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5418<t>
5419  Closed issues:
5420  <list style="symbols"> 
5421    <t>
5422      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5423      "base for numeric protocol elements"
5424    </t>
5425    <t>
5426      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5427      "comment ABNF"
5428    </t>
5429  </list>
5430</t>
5431<t>
5432  Partly resolved issues:
5433  <list style="symbols"> 
5434    <t>
5435      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5436      "205 Bodies" (took out language that implied that there might be
5437      methods for which a request body MUST NOT be included)
5438    </t>
5439    <t>
5440      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5441      "editorial improvements around HTTP-date"
5442    </t>
5443  </list>
5444</t>
5445</section>
5446
5447<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5448<t>
5449  Closed issues:
5450  <list style="symbols"> 
5451    <t>
5452      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5453      "Repeating single-value headers"
5454    </t>
5455    <t>
5456      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5457      "increase connection limit"
5458    </t>
5459    <t>
5460      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5461      "IP addresses in URLs"
5462    </t>
5463    <t>
5464      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5465      "take over HTTP Upgrade Token Registry"
5466    </t>
5467    <t>
5468      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5469      "CR and LF in chunk extension values"
5470    </t>
5471    <t>
5472      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5473      "HTTP/0.9 support"
5474    </t>
5475    <t>
5476      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5477      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5478    </t>
5479    <t>
5480      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5481      "move definitions of gzip/deflate/compress to part 1"
5482    </t>
5483    <t>
5484      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5485      "disallow control characters in quoted-pair"
5486    </t>
5487  </list>
5488</t>
5489<t>
5490  Partly resolved issues:
5491  <list style="symbols"> 
5492    <t>
5493      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5494      "update IANA requirements wrt Transfer-Coding values" (add the
5495      IANA Considerations subsection)
5496    </t>
5497  </list>
5498</t>
5499</section>
5500
5501<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5502<t>
5503  Closed issues:
5504  <list style="symbols"> 
5505    <t>
5506      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5507      "header parsing, treatment of leading and trailing OWS"
5508    </t>
5509  </list>
5510</t>
5511<t>
5512  Partly resolved issues:
5513  <list style="symbols"> 
5514    <t>
5515      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5516      "Placement of 13.5.1 and 13.5.2"
5517    </t>
5518    <t>
5519      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5520      "use of term "word" when talking about header structure"
5521    </t>
5522  </list>
5523</t>
5524</section>
5525
5526<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5527<t>
5528  Closed issues:
5529  <list style="symbols"> 
5530    <t>
5531      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5532      "Clarification of the term 'deflate'"
5533    </t>
5534    <t>
5535      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5536      "OPTIONS * and proxies"
5537    </t>
5538    <t>
5539      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5540      "MIME-Version not listed in P1, general header fields"
5541    </t>
5542    <t>
5543      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5544      "IANA registry for content/transfer encodings"
5545    </t>
5546    <t>
5547      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5548      "Case-sensitivity of HTTP-date"
5549    </t>
5550    <t>
5551      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5552      "use of term "word" when talking about header structure"
5553    </t>
5554  </list>
5555</t>
5556<t>
5557  Partly resolved issues:
5558  <list style="symbols"> 
5559    <t>
5560      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5561      "Term for the requested resource's URI"
5562    </t>
5563  </list>
5564</t>
5565</section>
5566
5567<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5568<t>
5569  Closed issues:
5570  <list style="symbols">
5571    <t>
5572      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5573      "Connection Closing"
5574    </t>
5575    <t>
5576      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5577      "Delimiting messages with multipart/byteranges"
5578    </t>
5579    <t>
5580      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5581      "Handling multiple Content-Length headers"
5582    </t>
5583    <t>
5584      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5585      "Clarify entity / representation / variant terminology"
5586    </t>
5587    <t>
5588      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5589      "consider removing the 'changes from 2068' sections"
5590    </t>
5591  </list>
5592</t>
5593<t>
5594  Partly resolved issues:
5595  <list style="symbols"> 
5596    <t>
5597      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5598      "HTTP(s) URI scheme definitions"
5599    </t>
5600  </list>
5601</t>
5602</section>
5603
5604<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5605<t>
5606  Closed issues:
5607  <list style="symbols">
5608    <t>
5609      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5610      "Trailer requirements"
5611    </t>
5612    <t>
5613      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5614      "Text about clock requirement for caches belongs in p6"
5615    </t>
5616    <t>
5617      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5618      "effective request URI: handling of missing host in HTTP/1.0"
5619    </t>
5620    <t>
5621      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5622      "confusing Date requirements for clients"
5623    </t>
5624  </list>
5625</t>
5626<t>
5627  Partly resolved issues:
5628  <list style="symbols"> 
5629    <t>
5630      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5631      "Handling multiple Content-Length headers"
5632    </t>
5633  </list>
5634</t>
5635</section>
5636
5637<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5638<t>
5639  Closed issues:
5640  <list style="symbols">
5641    <t>
5642      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5643      "RFC2145 Normative"
5644    </t>
5645    <t>
5646      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5647      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5648    </t>
5649    <t>
5650      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5651      "define 'transparent' proxy"
5652    </t>
5653    <t>
5654      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5655      "Header Classification"
5656    </t>
5657    <t>
5658      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5659      "Is * usable as a request-uri for new methods?"
5660    </t>
5661    <t>
5662      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5663      "Migrate Upgrade details from RFC2817"
5664    </t>
5665    <t>
5666      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5667      "untangle ABNFs for header fields"
5668    </t>
5669    <t>
5670      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5671      "update RFC 2109 reference"
5672    </t>
5673  </list>
5674</t>
5675</section>
5676
5677<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5678<t>
5679  Closed issues:
5680  <list style="symbols">
5681    <t>
5682      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5683      "Allow is not in 13.5.2"
5684    </t>
5685    <t>
5686      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5687      "Handling multiple Content-Length headers"
5688    </t>
5689    <t>
5690      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5691      "untangle ABNFs for header fields"
5692    </t>
5693    <t>
5694      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5695      "Content-Length ABNF broken"
5696    </t>
5697  </list>
5698</t>
5699</section>
5700
5701<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5702<t>
5703  Closed issues:
5704  <list style="symbols">
5705    <t>
5706      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5707      "HTTP-version should be redefined as fixed length pair of DIGIT . DIGIT"
5708    </t>
5709    <t>
5710      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5711      "Recommend minimum sizes for protocol elements"
5712    </t>
5713    <t>
5714      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5715      "Set expectations around buffering"
5716    </t>
5717    <t>
5718      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5719      "Considering messages in isolation"
5720    </t>
5721  </list>
5722</t>
5723</section>
5724
5725<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5726<t>
5727  Closed issues:
5728  <list style="symbols">
5729    <t>
5730      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5731      "DNS Spoofing / DNS Binding advice"
5732    </t>
5733    <t>
5734      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5735      "move RFCs 2145, 2616, 2817 to Historic status"
5736    </t>
5737    <t>
5738      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5739      "\-escaping in quoted strings"
5740    </t>
5741    <t>
5742      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5743      "'Close' should be reserved in the HTTP header field registry"
5744    </t>
5745  </list>
5746</t>
5747</section>
5748
5749<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5750<t>
5751  Closed issues:
5752  <list style="symbols">
5753    <t>
5754      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5755      "Document HTTP's error-handling philosophy"
5756    </t>
5757    <t>
5758      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5759      "Explain header registration"
5760    </t>
5761    <t>
5762      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5763      "Revise Acknowledgements Sections"
5764    </t>
5765    <t>
5766      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5767      "Retrying Requests"
5768    </t>
5769    <t>
5770      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5771      "Closing the connection on server error"
5772    </t>
5773  </list>
5774</t>
5775</section>
5776
5777<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5778<t>
5779  Closed issues:
5780  <list style="symbols">
5781    <t>
5782      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/158"/>:
5783      "Proxy-Connection and Keep-Alive"
5784    </t>
5785    <t>
5786      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/166"/>:
5787      "Clarify 'User Agent'"
5788    </t>
5789    <t>
5790      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/300"/>:
5791      "Define non-final responses"
5792    </t>
5793    <t>
5794      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
5795      "intended maturity level vs normative references"
5796    </t>
5797    <t>
5798      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/324"/>:
5799      "Intermediary rewriting of queries"
5800    </t>
5801  </list>
5802</t>
5803</section>
5804
5805<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5806<t>
5807  Closed issues:
5808  <list style="symbols">
5809    <t>
5810      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
5811      "message-body in CONNECT response"
5812    </t>
5813    <t>
5814      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
5815      "Misplaced text on connection handling in p2"
5816    </t>
5817    <t>
5818      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/335"/>:
5819      "wording of line folding rule"
5820    </t>
5821    <t>
5822      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/343"/>:
5823      "chunk-extensions"
5824    </t>
5825    <t>
5826      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5827      "make IANA policy definitions consistent"
5828    </t>
5829  </list>
5830</t>
5831</section>
5832
5833<section title="Since draft-ietf-httpbis-p1-messaging-19" anchor="changes.since.19">
5834<t>
5835  None yet.
5836</t>
5837</section>
5838
5839</section>
5840
5841</back>
5842</rfc>
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