source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1724

Last change on this file since 1724 was 1724, checked in by julian.reschke@…, 7 years ago

update acks (see #219)

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