source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1673

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