source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1589

Last change on this file since 1589 was 1589, checked in by fielding@…, 8 years ago

user agents always parse relative to the original URI, not the effective URI

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 239.6 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "March">
16  <!ENTITY ID-YEAR "2012">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#response.cacheability' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY diff-mime              "<xref target='Part3' x:rel='#differences.between.http.and.mime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY representation         "<xref target='Part3' x:rel='#representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-date            "<xref target='Part2' x:rel='#header.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-mime-version    "<xref target='Part3' x:rel='#mime-version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY OPTIONS                "<xref target='Part2' x:rel='#OPTIONS' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-code-reasonphr  "<xref target='Part2' x:rel='#status.code.and.reason.phrase' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY cons-new-header-fields "<xref target='Part2' x:rel='#considerations.for.creating.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45]>
46<?rfc toc="yes" ?>
47<?rfc symrefs="yes" ?>
48<?rfc sortrefs="yes" ?>
49<?rfc compact="yes"?>
50<?rfc subcompact="no" ?>
51<?rfc linkmailto="no" ?>
52<?rfc editing="no" ?>
53<?rfc comments="yes"?>
54<?rfc inline="yes"?>
55<?rfc rfcedstyle="yes"?>
56<?rfc-ext allow-markup-in-artwork="yes" ?>
57<?rfc-ext include-references-in-index="yes" ?>
58<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="proposed"
59     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
60     xmlns:x='http://purl.org/net/xml2rfc/ext'>
61<x:link rel="next" basename="p2-semantics"/>
62<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
63<front>
64
65  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
66
67  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
68    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
69    <address>
70      <postal>
71        <street>345 Park Ave</street>
72        <city>San Jose</city>
73        <region>CA</region>
74        <code>95110</code>
75        <country>USA</country>
76      </postal>
77      <email>fielding@gbiv.com</email>
78      <uri>http://roy.gbiv.com/</uri>
79    </address>
80  </author>
81
82  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
83    <organization abbrev="W3C">World Wide Web Consortium</organization>
84    <address>
85      <postal>
86        <street>W3C / ERCIM</street>
87        <street>2004, rte des Lucioles</street>
88        <city>Sophia-Antipolis</city>
89        <region>AM</region>
90        <code>06902</code>
91        <country>France</country>
92      </postal>
93      <email>ylafon@w3.org</email>
94      <uri>http://www.raubacapeu.net/people/yves/</uri>
95    </address>
96  </author>
97
98  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
99    <organization abbrev="greenbytes">greenbytes GmbH</organization>
100    <address>
101      <postal>
102        <street>Hafenweg 16</street>
103        <city>Muenster</city><region>NW</region><code>48155</code>
104        <country>Germany</country>
105      </postal>
106      <phone>+49 251 2807760</phone>
107      <facsimile>+49 251 2807761</facsimile>
108      <email>julian.reschke@greenbytes.de</email>
109      <uri>http://greenbytes.de/tech/webdav/</uri>
110    </address>
111  </author>
112
113  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
114  <workgroup>HTTPbis Working Group</workgroup>
115
116<abstract>
117<t>
118   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
119   distributed, collaborative, hypertext information systems. HTTP has been in
120   use by the World Wide Web global information initiative since 1990. This
121   document is Part 1 of the seven-part specification that defines the protocol
122   referred to as "HTTP/1.1" and, taken together, obsoletes
123   <xref target="RFC2616" x:fmt="none">RFC 2616</xref> and moves it to historic
124   status, along with its predecessor <xref target="RFC2068" x:fmt="none">RFC
125   2068</xref>.
126</t>
127<t>
128   Part 1 provides an overview of HTTP and its associated terminology, defines
129   the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
130   the generic message syntax and parsing requirements for HTTP message frames,
131   and describes general security concerns for implementations.
132</t>
133<t>
134   This part also obsoletes RFCs <xref target="RFC2145" x:fmt="none">2145</xref>
135   (on HTTP version numbers) and <xref target="RFC2817" x:fmt="none">2817</xref>
136   (on using CONNECT for TLS upgrades) and moves them to historic status.
137</t>
138</abstract>
139
140<note title="Editorial Note (To be removed by RFC Editor)">
141  <t>
142    Discussion of this draft should take place on the HTTPBIS working group
143    mailing list (ietf-http-wg@w3.org), which is archived at
144    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
145  </t>
146  <t>
147    The current issues list is at
148    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
149    documents (including fancy diffs) can be found at
150    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
151  </t>
152  <t>
153    The changes in this draft are summarized in <xref target="changes.since.18"/>.
154  </t>
155</note>
156</front>
157<middle>
158<section title="Introduction" anchor="introduction">
159<t>
160   The Hypertext Transfer Protocol (HTTP) is an application-level
161   request/response protocol that uses extensible semantics and MIME-like
162   message payloads for flexible interaction with network-based hypertext
163   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
164   standard <xref target="RFC3986"/> to indicate the target resource and
165   relationships between resources.
166   Messages are passed in a format similar to that used by Internet mail
167   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
168   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
169   between HTTP and MIME messages).
170</t>
171<t>
172   HTTP is a generic interface protocol for information systems. It is
173   designed to hide the details of how a service is implemented by presenting
174   a uniform interface to clients that is independent of the types of
175   resources provided. Likewise, servers do not need to be aware of each
176   client's purpose: an HTTP request can be considered in isolation rather
177   than being associated with a specific type of client or a predetermined
178   sequence of application steps. The result is a protocol that can be used
179   effectively in many different contexts and for which implementations can
180   evolve independently over time.
181</t>
182<t>
183   HTTP is also designed for use as an intermediation protocol for translating
184   communication to and from non-HTTP information systems.
185   HTTP proxies and gateways can provide access to alternative information
186   services by translating their diverse protocols into a hypertext
187   format that can be viewed and manipulated by clients in the same way
188   as HTTP services.
189</t>
190<t>
191   One consequence of HTTP flexibility is that the protocol cannot be
192   defined in terms of what occurs behind the interface. Instead, we
193   are limited to defining the syntax of communication, the intent
194   of received communication, and the expected behavior of recipients.
195   If the communication is considered in isolation, then successful
196   actions ought to be reflected in corresponding changes to the
197   observable interface provided by servers. However, since multiple
198   clients might act in parallel and perhaps at cross-purposes, we
199   cannot require that such changes be observable beyond the scope
200   of a single response.
201</t>
202<t>
203   This document is Part 1 of the seven-part specification of HTTP,
204   defining the protocol referred to as "HTTP/1.1", obsoleting
205   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
206   Part 1 describes the architectural elements that are used or
207   referred to in HTTP, defines the "http" and "https" URI schemes,
208   describes overall network operation and connection management,
209   and defines HTTP message framing and forwarding requirements.
210   Our goal is to define all of the mechanisms necessary for HTTP message
211   handling that are independent of message semantics, thereby defining the
212   complete set of requirements for message parsers and
213   message-forwarding intermediaries.
214</t>
215
216<section title="Requirement Notation" anchor="intro.requirements">
217<t>
218   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
219   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
220   document are to be interpreted as described in <xref target="RFC2119"/>.
221</t>
222</section>
223
224<section title="Syntax Notation" anchor="notation">
225<iref primary="true" item="Grammar" subitem="ALPHA"/>
226<iref primary="true" item="Grammar" subitem="CR"/>
227<iref primary="true" item="Grammar" subitem="CRLF"/>
228<iref primary="true" item="Grammar" subitem="CTL"/>
229<iref primary="true" item="Grammar" subitem="DIGIT"/>
230<iref primary="true" item="Grammar" subitem="DQUOTE"/>
231<iref primary="true" item="Grammar" subitem="HEXDIG"/>
232<iref primary="true" item="Grammar" subitem="HTAB"/>
233<iref primary="true" item="Grammar" subitem="LF"/>
234<iref primary="true" item="Grammar" subitem="OCTET"/>
235<iref primary="true" item="Grammar" subitem="SP"/>
236<iref primary="true" item="Grammar" subitem="VCHAR"/>
237<t>
238   This specification uses the Augmented Backus-Naur Form (ABNF) notation
239   of <xref target="RFC5234"/> with the list rule extension defined in
240   <xref target="abnf.extension"/><xref target="collected.abnf"/> shows
241   the collected ABNF with the list rule expanded.
242</t>
243<t anchor="core.rules">
244  <x:anchor-alias value="ALPHA"/>
245  <x:anchor-alias value="CTL"/>
246  <x:anchor-alias value="CR"/>
247  <x:anchor-alias value="CRLF"/>
248  <x:anchor-alias value="DIGIT"/>
249  <x:anchor-alias value="DQUOTE"/>
250  <x:anchor-alias value="HEXDIG"/>
251  <x:anchor-alias value="HTAB"/>
252  <x:anchor-alias value="LF"/>
253  <x:anchor-alias value="OCTET"/>
254  <x:anchor-alias value="SP"/>
255  <x:anchor-alias value="VCHAR"/>
256   The following core rules are included by
257   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
258   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
259   DIGIT (decimal 0-9), DQUOTE (double quote),
260   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
261   OCTET (any 8-bit sequence of data), SP (space), and
262   VCHAR (any visible <xref target="USASCII"/> character).
263</t>
264<t>
265   As a convention, ABNF rule names prefixed with "obs-" denote
266   "obsolete" grammar rules that appear for historical reasons.
267</t>
268</section>
269</section>
270
271<section title="Architecture" anchor="architecture">
272<t>
273   HTTP was created for the World Wide Web architecture
274   and has evolved over time to support the scalability needs of a worldwide
275   hypertext system. Much of that architecture is reflected in the terminology
276   and syntax productions used to define HTTP.
277</t>
278
279<section title="Client/Server Messaging" anchor="operation">
280<iref primary="true" item="client"/>
281<iref primary="true" item="server"/>
282<iref primary="true" item="connection"/>
283<t>
284   HTTP is a stateless request/response protocol that operates by exchanging
285   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
286   transport or session-layer
287   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
288   program that establishes a connection to a server for the purpose of
289   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
290   program that accepts connections in order to service HTTP requests by
291   sending HTTP responses.
292</t>
293<iref primary="true" item="user agent"/>
294<iref primary="true" item="origin server"/>
295<iref primary="true" item="browser"/>
296<iref primary="true" item="spider"/>
297<iref primary="true" item="sender"/>
298<iref primary="true" item="recipient"/>
299<t>
300   Note that the terms client and server refer only to the roles that
301   these programs perform for a particular connection.  The same program
302   might act as a client on some connections and a server on others.  We use
303   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
304   such as a WWW browser, editor, or spider (web-traversing robot), and
305   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
306   authoritative responses to a request.  For general requirements, we use
307   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
308   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
309   message.
310</t>
311<x:note>
312  <t>
313    <x:h>Note:</x:h> The term 'user agent' covers both those situations where
314    there is a user (human) interacting with the software agent (and for which
315    user interface or interactive suggestions might be made, e.g., warning the
316    user or given the user an option in the case of security or privacy
317    options) and also those where the software agent may act autonomously.
318  </t>
319</x:note>
320<t>
321   Most HTTP communication consists of a retrieval request (GET) for
322   a representation of some resource identified by a URI.  In the
323   simplest case, this might be accomplished via a single bidirectional
324   connection (===) between the user agent (UA) and the origin server (O).
325</t>
326<figure><artwork type="drawing">
327         request   &gt;
328    UA ======================================= O
329                                &lt;   response
330</artwork></figure>
331<iref primary="true" item="message"/>
332<iref primary="true" item="request"/>
333<iref primary="true" item="response"/>
334<t>
335   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
336   message, beginning with a request-line that includes a method, URI, and
337   protocol version (<xref target="request.line"/>),
338   followed by MIME-like header fields containing
339   request modifiers, client information, and representation metadata
340   (<xref target="header.fields"/>),
341   an empty line to indicate the end of the header section, and finally
342   a message body containing the payload body (if any,
343   <xref target="message.body"/>).
344</t>
345<t>
346   A server responds to the client's request by sending one or more HTTP
347   <x:dfn>response</x:dfn>
348   messages, each beginning with a status line that
349   includes the protocol version, a success or error code, and textual
350   reason phrase (<xref target="status.line"/>),
351   possibly followed by MIME-like header fields containing server
352   information, resource metadata, and representation metadata
353   (<xref target="header.fields"/>),
354   an empty line to indicate the end of the header section, and finally
355   a message body containing the payload body (if any,
356   <xref target="message.body"/>).
357</t>
358<t>
359   The following example illustrates a typical message exchange for a
360   GET request on the URI "http://www.example.com/hello.txt":
361</t>
362<figure><preamble>
363client request:
364</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
365GET /hello.txt HTTP/1.1
366User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
367Host: www.example.com
368Accept: */*
369
370</artwork></figure>
371<figure><preamble>
372server response:
373</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
374HTTP/1.1 200 OK
375Date: Mon, 27 Jul 2009 12:28:53 GMT
376Server: Apache
377Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
378ETag: "34aa387-d-1568eb00"
379Accept-Ranges: bytes
380Content-Length: <x:length-of target="exbody"/>
381Vary: Accept-Encoding
382Content-Type: text/plain
383
384<x:span anchor="exbody">Hello World!
385</x:span></artwork></figure>
386</section>
387
388<section title="Connections and Transport Independence" anchor="transport-independence">
389<t>
390   HTTP messaging is independent of the underlying transport or
391   session-layer connection protocol(s).  HTTP only presumes a reliable
392   transport with in-order delivery of requests and the corresponding
393   in-order delivery of responses.  The mapping of HTTP request and
394   response structures onto the data units of the underlying transport
395   protocol is outside the scope of this specification.
396</t>
397<t>
398   The specific connection protocols to be used for an interaction
399   are determined by client configuration and the target resource's URI.
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       UA =========== A =========== B - - - - - - C - - - - - - O
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 request's target URI (<xref target="target-resource"/>),
783   if known by the recipient, or the effective request URI
784   (<xref target="effective.request.uri"/>).
785</t>
786
787<section title="http URI scheme" anchor="http.uri">
788  <x:anchor-alias value="http-URI"/>
789  <iref item="http URI scheme" primary="true"/>
790  <iref item="URI scheme" subitem="http" primary="true"/>
791<t>
792   The "http" URI scheme is hereby defined for the purpose of minting
793   identifiers according to their association with the hierarchical
794   namespace governed by a potential HTTP origin server listening for
795   TCP connections on a given port.
796</t>
797<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
798  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
799</artwork></figure>
800<t>
801   The HTTP origin server is identified by the generic syntax's
802   <x:ref>authority</x:ref> component, which includes a host identifier
803   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
804   The remainder of the URI, consisting of both the hierarchical path
805   component and optional query component, serves as an identifier for
806   a potential resource within that origin server's name space.
807</t>
808<t>
809   If the host identifier is provided as an IP literal or IPv4 address,
810   then the origin server is any listener on the indicated TCP port at
811   that IP address. If host is a registered name, then that name is
812   considered an indirect identifier and the recipient might use a name
813   resolution service, such as DNS, to find the address of a listener
814   for that host.
815   The host &MUST-NOT; be empty; if an "http" URI is received with an
816   empty host, then it &MUST; be rejected as invalid.
817   If the port subcomponent is empty or not given, then TCP port 80 is
818   assumed (the default reserved port for WWW services).
819</t>
820<t>
821   Regardless of the form of host identifier, access to that host is not
822   implied by the mere presence of its name or address. The host might or might
823   not exist and, even when it does exist, might or might not be running an
824   HTTP server or listening to the indicated port. The "http" URI scheme
825   makes use of the delegated nature of Internet names and addresses to
826   establish a naming authority (whatever entity has the ability to place
827   an HTTP server at that Internet name or address) and allows that
828   authority to determine which names are valid and how they might be used.
829</t>
830<t>
831   When an "http" URI is used within a context that calls for access to the
832   indicated resource, a client &MAY; attempt access by resolving
833   the host to an IP address, establishing a TCP connection to that address
834   on the indicated port, and sending an HTTP request message
835   (<xref target="http.message"/>) containing the URI's identifying data
836   (<xref target="message.routing"/>) to the server.
837   If the server responds to that request with a non-interim HTTP response
838   message, as described in &status-code-reasonphr;, then that response
839   is considered an authoritative answer to the client's request.
840</t>
841<t>
842   Although HTTP is independent of the transport protocol, the "http"
843   scheme is specific to TCP-based services because the name delegation
844   process depends on TCP for establishing authority.
845   An HTTP service based on some other underlying connection protocol
846   would presumably be identified using a different URI scheme, just as
847   the "https" scheme (below) is used for servers that require an SSL/TLS
848   transport layer on a connection. Other protocols might also be used to
849   provide access to "http" identified resources &mdash; it is only the
850   authoritative interface used for mapping the namespace that is
851   specific to TCP.
852</t>
853<t>
854   The URI generic syntax for authority also includes a deprecated
855   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
856   for including user authentication information in the URI.  Some
857   implementations make use of the userinfo component for internal
858   configuration of authentication information, such as within command
859   invocation options, configuration files, or bookmark lists, even
860   though such usage might expose a user identifier or password.
861   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
862   delimiter) when transmitting an "http" URI in a message.  Recipients
863   of HTTP messages that contain a URI reference &SHOULD; parse for the
864   existence of userinfo and treat its presence as an error, likely
865   indicating that the deprecated subcomponent is being used to obscure
866   the authority for the sake of phishing attacks.
867</t>
868</section>
869
870<section title="https URI scheme" anchor="https.uri">
871   <x:anchor-alias value="https-URI"/>
872   <iref item="https URI scheme"/>
873   <iref item="URI scheme" subitem="https"/>
874<t>
875   The "https" URI scheme is hereby defined for the purpose of minting
876   identifiers according to their association with the hierarchical
877   namespace governed by a potential HTTP origin server listening for
878   SSL/TLS-secured connections on a given TCP port.
879</t>
880<t>
881   All of the requirements listed above for the "http" scheme are also
882   requirements for the "https" scheme, except that a default TCP port
883   of 443 is assumed if the port subcomponent is empty or not given,
884   and the TCP connection &MUST; be secured for privacy through the
885   use of strong encryption prior to sending the first HTTP request.
886</t>
887<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
888  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
889</artwork></figure>
890<t>
891   Unlike the "http" scheme, responses to "https" identified requests
892   are never "public" and thus &MUST-NOT; be reused for shared caching.
893   They can, however, be reused in a private cache if the message is
894   cacheable by default in HTTP or specifically indicated as such by
895   the Cache-Control header field (&header-cache-control;).
896</t>
897<t>
898   Resources made available via the "https" scheme have no shared
899   identity with the "http" scheme even if their resource identifiers
900   indicate the same authority (the same host listening to the same
901   TCP port).  They are distinct name spaces and are considered to be
902   distinct origin servers.  However, an extension to HTTP that is
903   defined to apply to entire host domains, such as the Cookie protocol
904   <xref target="RFC6265"/>, can allow information
905   set by one service to impact communication with other services
906   within a matching group of host domains.
907</t>
908<t>
909   The process for authoritative access to an "https" identified
910   resource is defined in <xref target="RFC2818"/>.
911</t>
912</section>
913
914<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
915<t>
916   Since the "http" and "https" schemes conform to the URI generic syntax,
917   such URIs are normalized and compared according to the algorithm defined
918   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
919   described above for each scheme.
920</t>
921<t>
922   If the port is equal to the default port for a scheme, the normal
923   form is to elide the port subcomponent. Likewise, an empty path
924   component is equivalent to an absolute path of "/", so the normal
925   form is to provide a path of "/" instead. The scheme and host
926   are case-insensitive and normally provided in lowercase; all
927   other components are compared in a case-sensitive manner.
928   Characters other than those in the "reserved" set are equivalent
929   to their percent-encoded octets (see <xref target="RFC3986"
930   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
931</t>
932<t>
933   For example, the following three URIs are equivalent:
934</t>
935<figure><artwork type="example">
936   http://example.com:80/~smith/home.html
937   http://EXAMPLE.com/%7Esmith/home.html
938   http://EXAMPLE.com:/%7esmith/home.html
939</artwork></figure>
940</section>
941</section>
942</section>
943
944<section title="Message Format" anchor="http.message">
945<x:anchor-alias value="generic-message"/>
946<x:anchor-alias value="message.types"/>
947<x:anchor-alias value="HTTP-message"/>
948<x:anchor-alias value="start-line"/>
949<iref item="header section"/>
950<iref item="headers"/>
951<iref item="header field"/>
952<t>
953   All HTTP/1.1 messages consist of a start-line followed by a sequence of
954   octets in a format similar to the Internet Message Format
955   <xref target="RFC5322"/>: zero or more header fields (collectively
956   referred to as the "headers" or the "header section"), an empty line
957   indicating the end of the header section, and an optional message body.
958</t>
959<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
960  <x:ref>HTTP-message</x:ref>   = <x:ref>start-line</x:ref>
961                   *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
962                   <x:ref>CRLF</x:ref>
963                   [ <x:ref>message-body</x:ref> ]
964</artwork></figure>
965<t>
966   The normal procedure for parsing an HTTP message is to read the
967   start-line into a structure, read each header field into a hash
968   table by field name until the empty line, and then use the parsed
969   data to determine if a message body is expected.  If a message body
970   has been indicated, then it is read as a stream until an amount
971   of octets equal to the message body length is read or the connection
972   is closed.
973</t>
974<t>
975   Recipients &MUST; parse an HTTP message as a sequence of octets in an
976   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
977   Parsing an HTTP message as a stream of Unicode characters, without regard
978   for the specific encoding, creates security vulnerabilities due to the
979   varying ways that string processing libraries handle invalid multibyte
980   character sequences that contain the octet LF (%x0A).  String-based
981   parsers can only be safely used within protocol elements after the element
982   has been extracted from the message, such as within a header field-value
983   after message parsing has delineated the individual fields.
984</t>
985<t>
986   An HTTP message can be parsed as a stream for incremental processing or
987   forwarding downstream.  However, recipients cannot rely on incremental
988   delivery of partial messages, since some implementations will buffer or
989   delay message forwarding for the sake of network efficiency, security
990   checks, or payload transformations.
991</t>
992
993<section title="Start Line" anchor="start.line">
994  <x:anchor-alias value="Start-Line"/>
995<t>
996   An HTTP message can either be a request from client to server or a
997   response from server to client.  Syntactically, the two types of message
998   differ only in the start-line, which is either a request-line (for requests)
999   or a status-line (for responses), and in the algorithm for determining
1000   the length of the message body (<xref target="message.body"/>).
1001   In theory, a client could receive requests and a server could receive
1002   responses, distinguishing them by their different start-line formats,
1003   but in practice servers are implemented to only expect a request
1004   (a response is interpreted as an unknown or invalid request method)
1005   and clients are implemented to only expect a response.
1006</t>
1007<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1008  <x:ref>start-line</x:ref>     = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1009</artwork></figure>
1010<t>
1011</t>
1012<t>
1013   Implementations &MUST-NOT; send whitespace between the start-line and
1014   the first header field. The presence of such whitespace in a request
1015   might be an attempt to trick a server into ignoring that field or
1016   processing the line after it as a new request, either of which might
1017   result in a security vulnerability if other implementations within
1018   the request chain interpret the same message differently.
1019   Likewise, the presence of such whitespace in a response might be
1020   ignored by some clients or cause others to cease parsing.
1021</t>
1022
1023<section title="Request Line" anchor="request.line">
1024  <x:anchor-alias value="Request"/>
1025  <x:anchor-alias value="request-line"/>
1026<t>
1027   A request-line begins with a method token, followed by a single
1028   space (SP), the request-target, another single space (SP), the
1029   protocol version, and ending with CRLF.
1030</t>
1031<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1032  <x:ref>request-line</x:ref>   = <x:ref>method</x:ref> <x:ref>SP</x:ref> <x:ref>request-target</x:ref> <x:ref>SP</x:ref> <x:ref>HTTP-version</x:ref> <x:ref>CRLF</x:ref>
1033</artwork></figure>
1034<iref primary="true" item="method"/>
1035<t anchor="method">
1036   The method token indicates the request method to be performed on the
1037   target resource. The request method is case-sensitive.
1038</t>
1039<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1040  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1041</artwork></figure>
1042<t>
1043   The methods defined by this specification can be found in
1044   &method;, along with information regarding the HTTP method registry
1045   and considerations for defining new methods.
1046</t>
1047<iref item="request-target"/>
1048<t>
1049   The request-target identifies the target resource upon which to apply
1050   the request, as defined in <xref target="request-target"/>.
1051</t>
1052<t>
1053   No whitespace is allowed inside the method, request-target, and
1054   protocol version.  Hence, recipients typically parse the request-line
1055   into its component parts by splitting on the SP characters.
1056</t>
1057<t>
1058   Unfortunately, some user agents fail to properly encode hypertext
1059   references that have embedded whitespace, sending the characters
1060   directly instead of properly percent-encoding the disallowed characters.
1061   Recipients of an invalid request-line &SHOULD; respond with either a
1062   400 (Bad Request) error or a 301 (Moved Permanently) redirect with the
1063   request-target properly encoded.  Recipients &SHOULD-NOT; attempt to
1064   autocorrect and then process the request without a redirect, since the
1065   invalid request-line might be deliberately crafted to bypass
1066   security filters along the request chain.
1067</t>
1068<t>
1069   HTTP does not place a pre-defined limit on the length of a request-line.
1070   A server that receives a method longer than any that it implements
1071   &SHOULD; respond with either a 404 (Not Allowed), if it is an origin
1072   server, or a 501 (Not Implemented) status code.
1073   A server &MUST; be prepared to receive URIs of unbounded length and
1074   respond with the 414 (URI Too Long) status code if the received
1075   request-target would be longer than the server wishes to handle
1076   (see &status-414;).
1077</t>
1078<t>
1079   Various ad-hoc limitations on request-line length are found in practice.
1080   It is &RECOMMENDED; that all HTTP senders and recipients support, at a
1081   minimum, request-line lengths of up to 8000 octets.
1082</t>
1083</section>
1084
1085<section title="Status Line" anchor="status.line">
1086  <x:anchor-alias value="response"/>
1087  <x:anchor-alias value="status-line"/>
1088<t>
1089   The first line of a response message is the status-line, consisting
1090   of the protocol version, a space (SP), the status code, another space,
1091   a possibly-empty textual phrase describing the status code, and
1092   ending with CRLF.
1093</t>
1094<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1095  <x:ref>status-line</x:ref> = <x:ref>HTTP-version</x:ref> <x:ref>SP</x:ref> <x:ref>status-code</x:ref> <x:ref>SP</x:ref> <x:ref>reason-phrase</x:ref> <x:ref>CRLF</x:ref>
1096</artwork></figure>
1097
1098<t anchor="status-code">
1099   The status-code element is a 3-digit integer result code of the attempt to
1100   understand and satisfy the request. See &status-code-reasonphr; for
1101   further information, such as the list of status codes defined by this
1102   specification, the IANA registry, and considerations for new status codes.
1103</t>
1104<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1105  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1106</artwork></figure>
1107
1108<t anchor="reason-phrase">   
1109   The reason-phrase element exists for the sole purpose of providing a
1110   textual description associated with the numeric status code, mostly
1111   out of deference to earlier Internet application protocols that were more
1112   frequently used with interactive text clients. A client &SHOULD; ignore
1113   the reason-phrase content.
1114</t>
1115<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1116  <x:ref>reason-phrase</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1117</artwork></figure>
1118</section>
1119</section>
1120
1121<section title="Header Fields" anchor="header.fields">
1122  <x:anchor-alias value="header-field"/>
1123  <x:anchor-alias value="field-content"/>
1124  <x:anchor-alias value="field-name"/>
1125  <x:anchor-alias value="field-value"/>
1126  <x:anchor-alias value="obs-fold"/>
1127<t>
1128   Each HTTP header field consists of a case-insensitive field name
1129   followed by a colon (":"), optional whitespace, and the field value.
1130</t>
1131<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="header-field"/><iref primary="true" item="Grammar" subitem="field-name"/><iref primary="true" item="Grammar" subitem="field-value"/><iref primary="true" item="Grammar" subitem="field-content"/><iref primary="true" item="Grammar" subitem="obs-fold"/>
1132  <x:ref>header-field</x:ref>   = <x:ref>field-name</x:ref> ":" <x:ref>OWS</x:ref> <x:ref>field-value</x:ref> <x:ref>BWS</x:ref>
1133  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1134  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1135  <x:ref>field-content</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1136  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1137                 ; obsolete line folding
1138                 ; see <xref target="field.parsing"/>
1139</artwork></figure>
1140<t>
1141   The field-name token labels the corresponding field-value as having the
1142   semantics defined by that header field.  For example, the Date header field
1143   is defined in &header-date; as containing the origination
1144   timestamp for the message in which it appears.
1145</t>
1146<t>
1147   HTTP header fields are fully extensible: there is no limit on the
1148   introduction of new field names, each presumably defining new semantics,
1149   or on the number of header fields used in a given message.  Existing
1150   fields are defined in each part of this specification and in many other
1151   specifications outside the standards process.
1152   New header fields can be introduced without changing the protocol version
1153   if their defined semantics allow them to be safely ignored by recipients
1154   that do not recognize them.
1155</t>
1156<t>
1157   New HTTP header fields &SHOULD; be registered with IANA according
1158   to the procedures in &cons-new-header-fields;.
1159   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1160   field-name is listed in the Connection header field
1161   (<xref target="header.connection"/>) or the proxy is specifically
1162   configured to block or otherwise transform such fields.
1163   Unrecognized header fields &SHOULD; be ignored by other recipients.
1164</t>
1165<t>
1166   The order in which header fields with differing field names are
1167   received is not significant. However, it is "good practice" to send
1168   header fields that contain control data first, such as Host on
1169   requests and Date on responses, so that implementations can decide
1170   when not to handle a message as early as possible.  A server &MUST;
1171   wait until the entire header section is received before interpreting
1172   a request message, since later header fields might include conditionals,
1173   authentication credentials, or deliberately misleading duplicate
1174   header fields that would impact request processing.
1175</t>
1176<t>
1177   Multiple header fields with the same field name &MUST-NOT; be
1178   sent in a message unless the entire field value for that
1179   header field is defined as a comma-separated list [i.e., #(values)].
1180   Multiple header fields with the same field name can be combined into
1181   one "field-name: field-value" pair, without changing the semantics of the
1182   message, by appending each subsequent field value to the combined
1183   field value in order, separated by a comma. The order in which
1184   header fields with the same field name are received is therefore
1185   significant to the interpretation of the combined field value;
1186   a proxy &MUST-NOT; change the order of these field values when
1187   forwarding a message.
1188</t>
1189<x:note>
1190  <t>
1191   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1192   practice can occur multiple times, but does not use the list syntax, and
1193   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1194   for details.) Also note that the Set-Cookie2 header field specified in
1195   <xref target="RFC2965"/> does not share this problem.
1196  </t>
1197</x:note>
1198
1199<section title="Whitespace" anchor="whitespace">
1200<t anchor="rule.LWS">
1201   This specification uses three rules to denote the use of linear
1202   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1203   BWS ("bad" whitespace).
1204</t>
1205<t anchor="rule.OWS">
1206   The OWS rule is used where zero or more linear whitespace octets might
1207   appear. OWS &SHOULD; either not be produced or be produced as a single
1208   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1209   be replaced with a single SP or transformed to all SP octets (each
1210   octet other than SP replaced with SP) before interpreting the field value
1211   or forwarding the message downstream.
1212</t>
1213<t anchor="rule.RWS">
1214   RWS is used when at least one linear whitespace octet is required to
1215   separate field tokens. RWS &SHOULD; be produced as a single SP.
1216   Multiple RWS octets that occur within field-content &SHOULD; either
1217   be replaced with a single SP or transformed to all SP octets before
1218   interpreting the field value or forwarding the message downstream.
1219</t>
1220<t anchor="rule.BWS">
1221   BWS is used where the grammar allows optional whitespace for historical
1222   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
1223   recipients &MUST; accept such bad optional whitespace and remove it before
1224   interpreting the field value or forwarding the message downstream.
1225</t>
1226<t anchor="rule.whitespace">
1227  <x:anchor-alias value="BWS"/>
1228  <x:anchor-alias value="OWS"/>
1229  <x:anchor-alias value="RWS"/>
1230</t>
1231<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/>
1232  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1233                 ; "optional" whitespace
1234  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1235                 ; "required" whitespace
1236  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1237                 ; "bad" whitespace
1238</artwork></figure>
1239</section>
1240
1241<section title="Field Parsing" anchor="field.parsing">
1242<t>
1243   No whitespace is allowed between the header field-name and colon.
1244   In the past, differences in the handling of such whitespace have led to
1245   security vulnerabilities in request routing and response handling.
1246   Any received request message that contains whitespace between a header
1247   field-name and colon &MUST; be rejected with a response code of 400
1248   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1249   message before forwarding the message downstream.
1250</t>
1251<t>
1252   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1253   preferred. The field value does not include any leading or trailing white
1254   space: OWS occurring before the first non-whitespace octet of the
1255   field value or after the last non-whitespace octet of the field value
1256   is ignored and &SHOULD; be removed before further processing (as this does
1257   not change the meaning of the header field).
1258</t>
1259<t>
1260   Historically, HTTP header field values could be extended over multiple
1261   lines by preceding each extra line with at least one space or horizontal
1262   tab (obs-fold). This specification deprecates such line
1263   folding except within the message/http media type
1264   (<xref target="internet.media.type.message.http"/>).
1265   HTTP senders &MUST-NOT; produce messages that include line folding
1266   (i.e., that contain any field-value that matches the obs-fold rule) unless
1267   the message is intended for packaging within the message/http media type.
1268   HTTP recipients &SHOULD; accept line folding and replace any embedded
1269   obs-fold whitespace with either a single SP or a matching number of SP
1270   octets (to avoid buffer copying) prior to interpreting the field value or
1271   forwarding the message downstream.
1272</t>
1273<t>
1274   Historically, HTTP has allowed field content with text in the ISO-8859-1
1275   <xref target="ISO-8859-1"/> character encoding and supported other
1276   character sets only through use of <xref target="RFC2047"/> encoding.
1277   In practice, most HTTP header field values use only a subset of the
1278   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1279   header fields &SHOULD; limit their field values to US-ASCII octets.
1280   Recipients &SHOULD; treat other (obs-text) octets in field content as
1281   opaque data.
1282</t>
1283</section>
1284
1285<section title="Field Length" anchor="field.length">
1286<t>
1287   HTTP does not place a pre-defined limit on the length of header fields,
1288   either in isolation or as a set. A server &MUST; be prepared to receive
1289   request header fields of unbounded length and respond with a 4xx status
1290   code if the received header field(s) would be longer than the server wishes
1291   to handle.
1292</t>
1293<t>
1294   A client that receives response headers that are longer than it wishes to
1295   handle can only treat it as a server error.
1296</t>
1297<t>
1298   Various ad-hoc limitations on header length are found in practice. It is
1299   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1300   combined header fields have 4000 or more octets.
1301</t>
1302</section>
1303
1304<section title="Field value components" anchor="field.components">
1305<t anchor="rule.token.separators">
1306  <x:anchor-alias value="tchar"/>
1307  <x:anchor-alias value="token"/>
1308  <x:anchor-alias value="special"/>
1309  <x:anchor-alias value="word"/>
1310   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1311   separated by whitespace or special characters. These special characters
1312   &MUST; be in a quoted string to be used within a parameter value (as defined
1313   in <xref target="transfer.codings"/>).
1314</t>
1315<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="word"/><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"/>
1316  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1317
1318  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1319<!--
1320  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1321 -->
1322  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1323                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1324                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1325                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1326
1327  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1328                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1329                 / "]" / "?" / "=" / "{" / "}"
1330</artwork></figure>
1331<t anchor="rule.quoted-string">
1332  <x:anchor-alias value="quoted-string"/>
1333  <x:anchor-alias value="qdtext"/>
1334  <x:anchor-alias value="obs-text"/>
1335   A string of text is parsed as a single word if it is quoted using
1336   double-quote marks.
1337</t>
1338<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/><iref primary="true" item="Grammar" subitem="obs-text"/>
1339  <x:ref>quoted-string</x:ref>  = <x:ref>DQUOTE</x:ref> *( <x:ref>qdtext</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref>
1340  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1341  <x:ref>obs-text</x:ref>       = %x80-FF
1342</artwork></figure>
1343<t anchor="rule.quoted-pair">
1344  <x:anchor-alias value="quoted-pair"/>
1345   The backslash octet ("\") can be used as a single-octet
1346   quoting mechanism within quoted-string constructs:
1347</t>
1348<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1349  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1350</artwork></figure>
1351<t>
1352   Recipients that process the value of the quoted-string &MUST; handle a
1353   quoted-pair as if it were replaced by the octet following the backslash.
1354</t>
1355<t>
1356   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1357   escaping (i.e., other than DQUOTE and the backslash octet).
1358</t>
1359<t anchor="rule.comment">
1360  <x:anchor-alias value="comment"/>
1361  <x:anchor-alias value="ctext"/>
1362   Comments can be included in some HTTP header fields by surrounding
1363   the comment text with parentheses. Comments are only allowed in
1364   fields containing "comment" as part of their field value definition.
1365</t>
1366<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1367  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1368  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1369</artwork></figure>
1370<t anchor="rule.quoted-cpair">
1371  <x:anchor-alias value="quoted-cpair"/>
1372   The backslash octet ("\") can be used as a single-octet
1373   quoting mechanism within comment constructs:
1374</t>
1375<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1376  <x:ref>quoted-cpair</x:ref>   = "\" ( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1377</artwork></figure>
1378<t>
1379   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1380   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1381</t>
1382</section>
1383
1384<section title="ABNF list extension: #rule" anchor="abnf.extension">
1385<t>
1386  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
1387  improve readability in the definitions of some header field values.
1388</t>
1389<t>
1390  A construct "#" is defined, similar to "*", for defining comma-delimited
1391  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
1392  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
1393  comma (",") and optional whitespace (OWS).   
1394</t>
1395<figure><preamble>
1396  Thus,
1397</preamble><artwork type="example">
1398  1#element =&gt; element *( OWS "," OWS element )
1399</artwork></figure>
1400<figure><preamble>
1401  and:
1402</preamble><artwork type="example">
1403  #element =&gt; [ 1#element ]
1404</artwork></figure>
1405<figure><preamble>
1406  and for n &gt;= 1 and m &gt; 1:
1407</preamble><artwork type="example">
1408  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
1409</artwork></figure>
1410<t>
1411  For compatibility with legacy list rules, recipients &SHOULD; accept empty
1412  list elements. In other words, consumers would follow the list productions:
1413</t>
1414<figure><artwork type="example">
1415  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
1416 
1417  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
1418</artwork></figure>
1419<t>
1420  Note that empty elements do not contribute to the count of elements present,
1421  though.
1422</t>
1423<t>
1424  For example, given these ABNF productions:
1425</t>
1426<figure><artwork type="example">
1427  example-list      = 1#example-list-elmt
1428  example-list-elmt = token ; see <xref target="field.components"/> 
1429</artwork></figure>
1430<t>
1431  Then these are valid values for example-list (not including the double
1432  quotes, which are present for delimitation only):
1433</t>
1434<figure><artwork type="example">
1435  "foo,bar"
1436  "foo ,bar,"
1437  "foo , ,bar,charlie   "
1438</artwork></figure>
1439<t>
1440  But these values would be invalid, as at least one non-empty element is
1441  required:
1442</t>
1443<figure><artwork type="example">
1444  ""
1445  ","
1446  ",   ,"
1447</artwork></figure>
1448<t>
1449  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
1450  expanded as explained above.
1451</t>
1452</section>
1453</section>
1454
1455<section title="Message Body" anchor="message.body">
1456  <x:anchor-alias value="message-body"/>
1457<t>
1458   The message body (if any) of an HTTP message is used to carry the
1459   payload body of that request or response.  The message body is
1460   identical to the payload body unless a transfer coding has been
1461   applied, as described in <xref target="header.transfer-encoding"/>.
1462</t>
1463<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1464  <x:ref>message-body</x:ref> = *OCTET
1465</artwork></figure>
1466<t>
1467   The rules for when a message body is allowed in a message differ for
1468   requests and responses.
1469</t>
1470<t>
1471   The presence of a message body in a request is signaled by a
1472   a Content-Length or Transfer-Encoding header field.
1473   Request message framing is independent of method semantics,
1474   even if the method does not define any use for a message body.
1475</t>
1476<t>
1477   The presence of a message body in a response depends on both
1478   the request method to which it is responding and the response
1479   status code (<xref target="status-code"/>).
1480   Responses to the HEAD request method never include a message body
1481   because the associated response header fields (e.g., Transfer-Encoding,
1482   Content-Length, etc.) only indicate what their values would have been
1483   if the request method had been GET.
1484   Successful (2xx) responses to CONNECT switch to tunnel mode instead of
1485   having a message body.
1486   All 1xx (Informational), 204 (No Content), and 304 (Not Modified)
1487   responses &MUST-NOT; include a message body.
1488   All other responses do include a message body, although the body
1489   &MAY; be of zero length.
1490</t>
1491
1492<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1493  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1494  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
1495  <x:anchor-alias value="Transfer-Encoding"/>
1496<t>
1497   When one or more transfer codings are applied to a payload body in order
1498   to form the message body, a Transfer-Encoding header field &MUST; be sent
1499   in the message and &MUST; contain the list of corresponding
1500   transfer-coding names in the same order that they were applied.
1501   Transfer codings are defined in <xref target="transfer.codings"/>.
1502</t>
1503<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1504  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1505</artwork></figure>
1506<t>
1507   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1508   MIME, which was designed to enable safe transport of binary data over a
1509   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1510   However, safe transport has a different focus for an 8bit-clean transfer
1511   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1512   accurately delimit a dynamically generated payload and to distinguish
1513   payload encodings that are only applied for transport efficiency or
1514   security from those that are characteristics of the target resource.
1515</t>
1516<t>
1517   The "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1518   &MUST; be implemented by all HTTP/1.1 recipients because it plays a
1519   crucial role in delimiting messages when the payload body size is not
1520   known in advance.
1521   When the "chunked" transfer-coding is used, it &MUST; be the last
1522   transfer-coding applied to form the message body and &MUST-NOT;
1523   be applied more than once in a message body.
1524   If any transfer-coding is applied to a request payload body,
1525   the final transfer-coding applied &MUST; be "chunked".
1526   If any transfer-coding is applied to a response payload body, then either
1527   the final transfer-coding applied &MUST; be "chunked" or
1528   the message &MUST; be terminated by closing the connection.
1529</t>
1530<figure><preamble>
1531   For example,
1532</preamble><artwork type="example">
1533  Transfer-Encoding: gzip, chunked
1534</artwork><postamble>
1535   indicates that the payload body has been compressed using the gzip
1536   coding and then chunked using the chunked coding while forming the
1537   message body.
1538</postamble></figure>
1539<t>
1540   If more than one Transfer-Encoding header field is present in a message,
1541   the multiple field-values &MUST; be combined into one field-value,
1542   according to the algorithm defined in <xref target="header.fields"/>,
1543   before determining the message body length.
1544</t>
1545<t>
1546   Unlike Content-Encoding (&content-codings;), Transfer-Encoding is a
1547   property of the message, not of the payload, and thus &MAY; be added or
1548   removed by any implementation along the request/response chain.
1549   Additional information about the encoding parameters &MAY; be provided
1550   by other header fields not defined by this specification.
1551</t>
1552<t>
1553   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1554   304 response to a GET request, neither of which includes a message body,
1555   to indicate that the origin server would have applied a transfer coding
1556   to the message body if the request had been an unconditional GET.
1557   This indication is not required, however, because any recipient on
1558   the response chain (including the origin server) can remove transfer
1559   codings when they are not needed.
1560</t>
1561<t>
1562   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1563   implementations advertising only HTTP/1.0 support will not understand
1564   how to process a transfer-encoded payload.
1565   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1566   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1567   might be in the form of specific user configuration or by remembering the
1568   version of a prior received response.
1569   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1570   the corresponding request indicates HTTP/1.1 (or later).
1571</t>
1572<t>
1573   A server that receives a request message with a transfer-coding it does
1574   not understand &SHOULD; respond with 501 (Not Implemented) and then
1575   close the connection.
1576</t>
1577</section>
1578
1579<section title="Content-Length" anchor="header.content-length">
1580  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1581  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
1582  <x:anchor-alias value="Content-Length"/>
1583<t>
1584   When a message does not have a Transfer-Encoding header field and the
1585   payload body length can be determined prior to being transferred, a
1586   Content-Length header field &SHOULD; be sent to indicate the length of the
1587   payload body that is either present as the message body, for requests
1588   and non-HEAD responses other than 304, or would have been present had
1589   the request been an unconditional GET.  The length is expressed as a
1590   decimal number of octets.
1591</t>
1592<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1593  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1594</artwork></figure>
1595<t>
1596   An example is
1597</t>
1598<figure><artwork type="example">
1599  Content-Length: 3495
1600</artwork></figure>
1601<t>
1602   In the case of a response to a HEAD request, Content-Length indicates
1603   the size of the payload body (without any potential transfer-coding)
1604   that would have been sent had the request been a GET.
1605   In the case of a 304 (Not Modified) response to a GET request,
1606   Content-Length indicates the size of the payload body (without
1607   any potential transfer-coding) that would have been sent in a 200 (OK)
1608   response.
1609</t>
1610<t>
1611   HTTP's use of Content-Length is significantly different from how it is
1612   used in MIME, where it is an optional field used only within the
1613   "message/external-body" media-type.
1614</t>
1615<t>
1616   Any Content-Length field value greater than or equal to zero is valid.
1617   Since there is no predefined limit to the length of an HTTP payload,
1618   recipients &SHOULD; anticipate potentially large decimal numerals and
1619   prevent parsing errors due to integer conversion overflows
1620   (<xref target="attack.protocol.element.size.overflows"/>).
1621</t>
1622<t>
1623   If a message is received that has multiple Content-Length header fields
1624   (<xref target="header.content-length"/>) with field-values consisting
1625   of the same decimal value, or a single Content-Length header field with
1626   a field value containing a list of identical decimal values (e.g.,
1627   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1628   header fields have been generated or combined by an upstream message
1629   processor, then the recipient &MUST; either reject the message as invalid
1630   or replace the duplicated field-values with a single valid Content-Length
1631   field containing that decimal value prior to determining the message body
1632   length.
1633</t>
1634</section>
1635
1636<section title="Message Body Length" anchor="message.body.length">
1637<t>
1638   The length of a message body is determined by one of the following
1639   (in order of precedence):
1640</t>
1641<t>
1642  <list style="numbers">
1643    <x:lt><t>
1644     Any response to a HEAD request and any response with a status
1645     code of 100-199, 204, or 304 is always terminated by the first
1646     empty line after the header fields, regardless of the header
1647     fields present in the message, and thus cannot contain a message body.
1648    </t></x:lt>
1649    <x:lt><t>
1650     Any successful (2xx) response to a CONNECT request implies that the
1651     connection will become a tunnel immediately after the empty line that
1652     concludes the header fields.  A client &MUST; ignore any Content-Length
1653     or Transfer-Encoding header fields received in such a message.
1654    </t></x:lt>
1655    <x:lt><t>
1656     If a Transfer-Encoding header field is present
1657     and the "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1658     is the final encoding, the message body length is determined by reading
1659     and decoding the chunked data until the transfer-coding indicates the
1660     data is complete.
1661    </t>
1662    <t>
1663     If a Transfer-Encoding header field is present in a response and the
1664     "chunked" transfer-coding is not the final encoding, the message body
1665     length is determined by reading the connection until it is closed by
1666     the server.
1667     If a Transfer-Encoding header field is present in a request and the
1668     "chunked" transfer-coding is not the final encoding, the message body
1669     length cannot be determined reliably; the server &MUST; respond with
1670     the 400 (Bad Request) status code and then close the connection.
1671    </t>
1672    <t>
1673     If a message is received with both a Transfer-Encoding header field
1674     and a Content-Length header field, the Transfer-Encoding overrides
1675     the Content-Length.
1676     Such a message might indicate an attempt to perform request or response
1677     smuggling (bypass of security-related checks on message routing or content)
1678     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1679     be removed, prior to forwarding the message downstream, or replaced with
1680     the real message body length after the transfer-coding is decoded.
1681    </t></x:lt>
1682    <x:lt><t>
1683     If a message is received without Transfer-Encoding and with either
1684     multiple Content-Length header fields having differing field-values or
1685     a single Content-Length header field having an invalid value, then the
1686     message framing is invalid and &MUST; be treated as an error to
1687     prevent request or response smuggling.
1688     If this is a request message, the server &MUST; respond with
1689     a 400 (Bad Request) status code and then close the connection.
1690     If this is a response message received by a proxy, the proxy
1691     &MUST; discard the received response, send a 502 (Bad Gateway)
1692     status code as its downstream response, and then close the connection.
1693     If this is a response message received by a user-agent, it &MUST; be
1694     treated as an error by discarding the message and closing the connection.
1695    </t></x:lt>
1696    <x:lt><t>
1697     If a valid Content-Length header field
1698     is present without Transfer-Encoding, its decimal value defines the
1699     message body length in octets.  If the actual number of octets sent in
1700     the message is less than the indicated Content-Length, the recipient
1701     &MUST; consider the message to be incomplete and treat the connection
1702     as no longer usable.
1703     If the actual number of octets sent in the message is more than the indicated
1704     Content-Length, the recipient &MUST; only process the message body up to the
1705     field value's number of octets; the remainder of the message &MUST; either
1706     be discarded or treated as the next message in a pipeline.  For the sake of
1707     robustness, a user-agent &MAY; attempt to detect and correct such an error
1708     in message framing if it is parsing the response to the last request on
1709     a connection and the connection has been closed by the server.
1710    </t></x:lt>
1711    <x:lt><t>
1712     If this is a request message and none of the above are true, then the
1713     message body length is zero (no message body is present).
1714    </t></x:lt>
1715    <x:lt><t>
1716     Otherwise, this is a response message without a declared message body
1717     length, so the message body length is determined by the number of octets
1718     received prior to the server closing the connection.
1719    </t></x:lt>
1720  </list>
1721</t>
1722<t>
1723   Since there is no way to distinguish a successfully completed,
1724   close-delimited message from a partially-received message interrupted
1725   by network failure, implementations &SHOULD; use encoding or
1726   length-delimited messages whenever possible.  The close-delimiting
1727   feature exists primarily for backwards compatibility with HTTP/1.0.
1728</t>
1729<t>
1730   A server &MAY; reject a request that contains a message body but
1731   not a Content-Length by responding with 411 (Length Required).
1732</t>
1733<t>
1734   Unless a transfer-coding other than "chunked" has been applied,
1735   a client that sends a request containing a message body &SHOULD;
1736   use a valid Content-Length header field if the message body length
1737   is known in advance, rather than the "chunked" encoding, since some
1738   existing services respond to "chunked" with a 411 (Length Required)
1739   status code even though they understand the chunked encoding.  This
1740   is typically because such services are implemented via a gateway that
1741   requires a content-length in advance of being called and the server
1742   is unable or unwilling to buffer the entire request before processing.
1743</t>
1744<t>
1745   A client that sends a request containing a message body &MUST; include a
1746   valid Content-Length header field if it does not know the server will
1747   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1748   of specific user configuration or by remembering the version of a prior
1749   received response.
1750</t>
1751</section>
1752</section>
1753
1754<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1755<t>
1756   Request messages that are prematurely terminated, possibly due to a
1757   cancelled connection or a server-imposed time-out exception, &MUST;
1758   result in closure of the connection; sending an HTTP/1.1 error response
1759   prior to closing the connection is &OPTIONAL;.
1760</t>
1761<t>
1762   Response messages that are prematurely terminated, usually by closure
1763   of the connection prior to receiving the expected number of octets or by
1764   failure to decode a transfer-encoded message body, &MUST; be recorded
1765   as incomplete.  A response that terminates in the middle of the header
1766   block (before the empty line is received) cannot be assumed to convey the
1767   full semantics of the response and &MUST; be treated as an error.
1768</t>
1769<t>
1770   A message body that uses the chunked transfer encoding is
1771   incomplete if the zero-sized chunk that terminates the encoding has not
1772   been received.  A message that uses a valid Content-Length is incomplete
1773   if the size of the message body received (in octets) is less than the
1774   value given by Content-Length.  A response that has neither chunked
1775   transfer encoding nor Content-Length is terminated by closure of the
1776   connection, and thus is considered complete regardless of the number of
1777   message body octets received, provided that the header block was received
1778   intact.
1779</t>
1780<t>
1781   A user agent &MUST-NOT; render an incomplete response message body as if
1782   it were complete (i.e., some indication must be given to the user that an
1783   error occurred).  Cache requirements for incomplete responses are defined
1784   in &cache-incomplete;.
1785</t>
1786<t>
1787   A server &MUST; read the entire request message body or close
1788   the connection after sending its response, since otherwise the
1789   remaining data on a persistent connection would be misinterpreted
1790   as the next request.  Likewise,
1791   a client &MUST; read the entire response message body if it intends
1792   to reuse the same connection for a subsequent request.  Pipelining
1793   multiple requests on a connection is described in <xref target="pipelining"/>.
1794</t>
1795</section>
1796
1797<section title="Message Parsing Robustness" anchor="message.robustness">
1798<t>
1799   Older HTTP/1.0 client implementations might send an extra CRLF
1800   after a POST request as a lame workaround for some early server
1801   applications that failed to read message body content that was
1802   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1803   preface or follow a request with an extra CRLF.  If terminating
1804   the request message body with a line-ending is desired, then the
1805   client &MUST; include the terminating CRLF octets as part of the
1806   message body length.
1807</t>
1808<t>
1809   In the interest of robustness, servers &SHOULD; ignore at least one
1810   empty line received where a request-line is expected. In other words, if
1811   the server is reading the protocol stream at the beginning of a
1812   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1813   Likewise, although the line terminator for the start-line and header
1814   fields is the sequence CRLF, we recommend that recipients recognize a
1815   single LF as a line terminator and ignore any CR.
1816</t>
1817<t>
1818   When a server listening only for HTTP request messages, or processing
1819   what appears from the start-line to be an HTTP request message,
1820   receives a sequence of octets that does not match the HTTP-message
1821   grammar aside from the robustness exceptions listed above, the
1822   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1823</t>
1824</section>
1825</section>
1826
1827<section title="Transfer Codings" anchor="transfer.codings">
1828  <x:anchor-alias value="transfer-coding"/>
1829  <x:anchor-alias value="transfer-extension"/>
1830<t>
1831   Transfer-coding values are used to indicate an encoding
1832   transformation that has been, can be, or might need to be applied to a
1833   payload body in order to ensure "safe transport" through the network.
1834   This differs from a content coding in that the transfer-coding is a
1835   property of the message rather than a property of the representation
1836   that is being transferred.
1837</t>
1838<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1839  <x:ref>transfer-coding</x:ref>    = "chunked" ; <xref target="chunked.encoding"/>
1840                     / "compress" ; <xref target="compress.coding"/>
1841                     / "deflate" ; <xref target="deflate.coding"/>
1842                     / "gzip" ; <xref target="gzip.coding"/>
1843                     / <x:ref>transfer-extension</x:ref>
1844  <x:ref>transfer-extension</x:ref> = <x:ref>token</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>transfer-parameter</x:ref> )
1845</artwork></figure>
1846<t anchor="rule.parameter">
1847  <x:anchor-alias value="attribute"/>
1848  <x:anchor-alias value="transfer-parameter"/>
1849  <x:anchor-alias value="value"/>
1850   Parameters are in the form of attribute/value pairs.
1851</t>
1852<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/>
1853  <x:ref>transfer-parameter</x:ref> = <x:ref>attribute</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>value</x:ref>
1854  <x:ref>attribute</x:ref>          = <x:ref>token</x:ref>
1855  <x:ref>value</x:ref>              = <x:ref>word</x:ref>
1856</artwork></figure>
1857<t>
1858   All transfer-coding values are case-insensitive.
1859   The HTTP Transfer Coding registry is defined in
1860   <xref target="transfer.coding.registry"/>.
1861   HTTP/1.1 uses transfer-coding values in the TE header field
1862   (<xref target="header.te"/>) and in the Transfer-Encoding header field
1863   (<xref target="header.transfer-encoding"/>).
1864</t>
1865
1866<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1867  <iref item="chunked (Coding Format)"/>
1868  <iref item="Coding Format" subitem="chunked"/>
1869  <x:anchor-alias value="chunk"/>
1870  <x:anchor-alias value="chunked-body"/>
1871  <x:anchor-alias value="chunk-data"/>
1872  <x:anchor-alias value="chunk-ext"/>
1873  <x:anchor-alias value="chunk-ext-name"/>
1874  <x:anchor-alias value="chunk-ext-val"/>
1875  <x:anchor-alias value="chunk-size"/>
1876  <x:anchor-alias value="last-chunk"/>
1877  <x:anchor-alias value="trailer-part"/>
1878  <x:anchor-alias value="quoted-str-nf"/>
1879  <x:anchor-alias value="qdtext-nf"/>
1880<t>
1881   The chunked encoding modifies the body of a message in order to
1882   transfer it as a series of chunks, each with its own size indicator,
1883   followed by an &OPTIONAL; trailer containing header fields. This
1884   allows dynamically produced content to be transferred along with the
1885   information necessary for the recipient to verify that it has
1886   received the full message.
1887</t>
1888<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="chunked-body"/><iref primary="true" item="Grammar" subitem="chunk"/><iref primary="true" item="Grammar" subitem="chunk-size"/><iref primary="true" item="Grammar" subitem="last-chunk"/><iref primary="true" item="Grammar" subitem="chunk-ext"/><iref primary="true" item="Grammar" subitem="chunk-ext-name"/><iref primary="true" item="Grammar" subitem="chunk-ext-val"/><iref primary="true" item="Grammar" subitem="chunk-data"/><iref primary="true" item="Grammar" subitem="trailer-part"/><iref primary="true" item="Grammar" subitem="quoted-str-nf"/><iref primary="true" item="Grammar" subitem="qdtext-nf"/>
1889  <x:ref>chunked-body</x:ref>   = *<x:ref>chunk</x:ref>
1890                   <x:ref>last-chunk</x:ref>
1891                   <x:ref>trailer-part</x:ref>
1892                   <x:ref>CRLF</x:ref>
1893 
1894  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1895                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1896  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1897  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1898 
1899  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1900  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1901  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1902  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1903  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1904 
1905  <x:ref>quoted-str-nf</x:ref>  = <x:ref>DQUOTE</x:ref> *( <x:ref>qdtext-nf</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref>
1906                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1907  <x:ref>qdtext-nf</x:ref>      = <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1908</artwork></figure>
1909<t>
1910   The chunk-size field is a string of hex digits indicating the size of
1911   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1912   zero, followed by the trailer, which is terminated by an empty line.
1913</t>
1914<t>
1915   The trailer allows the sender to include additional HTTP header
1916   fields at the end of the message. The Trailer header field can be
1917   used to indicate which header fields are included in a trailer (see
1918   <xref target="header.trailer"/>).
1919</t>
1920<t>
1921   A server using chunked transfer-coding in a response &MUST-NOT; use the
1922   trailer for any header fields unless at least one of the following is
1923   true:
1924  <list style="numbers">
1925    <t>the request included a TE header field that indicates "trailers" is
1926     acceptable in the transfer-coding of the  response, as described in
1927     <xref target="header.te"/>; or,</t>
1928     
1929    <t>the trailer fields consist entirely of optional metadata, and the
1930    recipient could use the message (in a manner acceptable to the server where
1931    the field originated) without receiving it. In other words, the server that
1932    generated the header (often but not always the origin server) is willing to
1933    accept the possibility that the trailer fields might be silently discarded
1934    along the path to the client.</t>
1935  </list>
1936</t>
1937<t>
1938   This requirement prevents an interoperability failure when the
1939   message is being received by an HTTP/1.1 (or later) proxy and
1940   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1941   conformance with the protocol would have necessitated a possibly
1942   infinite buffer on the proxy.
1943</t>
1944<t>
1945   A process for decoding the "chunked" transfer-coding
1946   can be represented in pseudo-code as:
1947</t>
1948<figure><artwork type="code">
1949  length := 0
1950  read chunk-size, chunk-ext (if any) and CRLF
1951  while (chunk-size &gt; 0) {
1952     read chunk-data and CRLF
1953     append chunk-data to decoded-body
1954     length := length + chunk-size
1955     read chunk-size and CRLF
1956  }
1957  read header-field
1958  while (header-field not empty) {
1959     append header-field to existing header fields
1960     read header-field
1961  }
1962  Content-Length := length
1963  Remove "chunked" from Transfer-Encoding
1964</artwork></figure>
1965<t>
1966   All HTTP/1.1 applications &MUST; be able to receive and decode the
1967   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
1968   they do not understand.
1969</t>
1970<t>
1971   Use of chunk-ext extensions by senders is deprecated; they &SHOULD-NOT; be
1972   sent and definition of new chunk-extensions is discouraged.
1973</t>
1974</section>
1975
1976<section title="Compression Codings" anchor="compression.codings">
1977<t>
1978   The codings defined below can be used to compress the payload of a
1979   message.
1980</t>
1981<x:note><t>
1982   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
1983   is not desirable and is discouraged for future encodings. Their
1984   use here is representative of historical practice, not good
1985   design.
1986</t></x:note>
1987<x:note><t>
1988   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
1989   applications &SHOULD; consider "x-gzip" and "x-compress" to be
1990   equivalent to "gzip" and "compress" respectively.
1991</t></x:note>
1992
1993<section title="Compress Coding" anchor="compress.coding">
1994<iref item="compress (Coding Format)"/>
1995<iref item="Coding Format" subitem="compress"/>
1996<t>
1997   The "compress" format is produced by the common UNIX file compression
1998   program "compress". This format is an adaptive Lempel-Ziv-Welch
1999   coding (LZW).
2000</t>
2001</section>
2002
2003<section title="Deflate Coding" anchor="deflate.coding">
2004<iref item="deflate (Coding Format)"/>
2005<iref item="Coding Format" subitem="deflate"/>
2006<t>
2007   The "deflate" format is defined as the "deflate" compression mechanism
2008   (described in <xref target="RFC1951"/>) used inside the "zlib"
2009   data format (<xref target="RFC1950"/>).
2010</t>
2011<x:note>
2012  <t>
2013    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2014    compressed data without the zlib wrapper.
2015   </t>
2016</x:note>
2017</section>
2018
2019<section title="Gzip Coding" anchor="gzip.coding">
2020<iref item="gzip (Coding Format)"/>
2021<iref item="Coding Format" subitem="gzip"/>
2022<t>
2023   The "gzip" format is produced by the file compression program
2024   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2025   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2026</t>
2027</section>
2028
2029</section>
2030
2031<section title="TE" anchor="header.te">
2032  <iref primary="true" item="TE header field" x:for-anchor=""/>
2033  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
2034  <x:anchor-alias value="TE"/>
2035  <x:anchor-alias value="t-codings"/>
2036  <x:anchor-alias value="te-params"/>
2037  <x:anchor-alias value="te-ext"/>
2038<t>
2039   The "TE" header field indicates what extension transfer-codings
2040   the client is willing to accept in the response, and whether or not it is
2041   willing to accept trailer fields in a chunked transfer-coding.
2042</t>
2043<t>
2044   Its value consists of the keyword "trailers" and/or a comma-separated
2045   list of extension transfer-coding names with optional accept
2046   parameters (as described in <xref target="transfer.codings"/>).
2047</t>
2048<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
2049  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2050  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2051  <x:ref>te-params</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>te-ext</x:ref> )
2052  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
2053</artwork></figure>
2054<t>
2055   The presence of the keyword "trailers" indicates that the client is
2056   willing to accept trailer fields in a chunked transfer-coding, as
2057   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
2058   transfer-coding values even though it does not itself represent a
2059   transfer-coding.
2060</t>
2061<t>
2062   Examples of its use are:
2063</t>
2064<figure><artwork type="example">
2065  TE: deflate
2066  TE:
2067  TE: trailers, deflate;q=0.5
2068</artwork></figure>
2069<t>
2070   The TE header field only applies to the immediate connection.
2071   Therefore, the keyword &MUST; be supplied within a Connection header
2072   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2073</t>
2074<t>
2075   A server tests whether a transfer-coding is acceptable, according to
2076   a TE field, using these rules:
2077  <list style="numbers">
2078    <x:lt>
2079      <t>The "chunked" transfer-coding is always acceptable. If the
2080         keyword "trailers" is listed, the client indicates that it is
2081         willing to accept trailer fields in the chunked response on
2082         behalf of itself and any downstream clients. The implication is
2083         that, if given, the client is stating that either all
2084         downstream clients are willing to accept trailer fields in the
2085         forwarded response, or that it will attempt to buffer the
2086         response on behalf of downstream recipients.
2087      </t><t>
2088         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2089         chunked response such that a client can be assured of buffering
2090         the entire response.</t>
2091    </x:lt>
2092    <x:lt>
2093      <t>If the transfer-coding being tested is one of the transfer-codings
2094         listed in the TE field, then it is acceptable unless it
2095         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2096         qvalue of 0 means "not acceptable".)</t>
2097    </x:lt>
2098    <x:lt>
2099      <t>If multiple transfer-codings are acceptable, then the
2100         acceptable transfer-coding with the highest non-zero qvalue is
2101         preferred.  The "chunked" transfer-coding always has a qvalue
2102         of 1.</t>
2103    </x:lt>
2104  </list>
2105</t>
2106<t>
2107   If the TE field-value is empty or if no TE field is present, the only
2108   acceptable transfer-coding is "chunked". A message with no transfer-coding is
2109   always acceptable.
2110</t>
2111
2112<section title="Quality Values" anchor="quality.values">
2113  <x:anchor-alias value="qvalue"/>
2114<t>
2115   Both transfer codings (TE request header field, <xref target="header.te"/>)
2116   and content negotiation (&content.negotiation;) use short "floating point"
2117   numbers to indicate the relative importance ("weight") of various
2118   negotiable parameters.  A weight is normalized to a real number in
2119   the range 0 through 1, where 0 is the minimum and 1 the maximum
2120   value. If a parameter has a quality value of 0, then content with
2121   this parameter is "not acceptable" for the client. HTTP/1.1
2122   applications &MUST-NOT; generate more than three digits after the
2123   decimal point. User configuration of these values &SHOULD; also be
2124   limited in this fashion.
2125</t>
2126<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2127  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2128                 / ( "1" [ "." 0*3("0") ] )
2129</artwork></figure>
2130<x:note>
2131  <t>
2132     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2133     relative degradation in desired quality.
2134  </t>
2135</x:note>
2136</section>
2137</section>
2138
2139<section title="Trailer" anchor="header.trailer">
2140  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
2141  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
2142  <x:anchor-alias value="Trailer"/>
2143<t>
2144   The "Trailer" header field indicates that the given set of
2145   header fields is present in the trailer of a message encoded with
2146   chunked transfer-coding.
2147</t>
2148<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2149  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
2150</artwork></figure>
2151<t>
2152   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2153   message using chunked transfer-coding with a non-empty trailer. Doing
2154   so allows the recipient to know which header fields to expect in the
2155   trailer.
2156</t>
2157<t>
2158   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2159   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
2160   trailer fields in a "chunked" transfer-coding.
2161</t>
2162<t>
2163   Message header fields listed in the Trailer header field &MUST-NOT;
2164   include the following header fields:
2165  <list style="symbols">
2166    <t>Transfer-Encoding</t>
2167    <t>Content-Length</t>
2168    <t>Trailer</t>
2169  </list>
2170</t>
2171</section>
2172</section>
2173
2174<section title="Message Routing" anchor="message.routing">
2175<t>
2176   HTTP request message routing is determined by each client based on the
2177   target resource, the client's proxy configuration, and
2178   establishment or reuse of an inbound connection.  The corresponding
2179   response routing follows the same connection chain back to the client.
2180</t>
2181
2182<section title="Identifying a Target Resource" anchor="target-resource">
2183  <iref primary="true" item="target resource"/>
2184  <iref primary="true" item="target URI"/>
2185<t>
2186   HTTP is used in a wide variety of applications, ranging from
2187   general-purpose computers to home appliances.  In some cases,
2188   communication options are hard-coded in a client's configuration.
2189   However, most HTTP clients rely on the same resource identification
2190   mechanism and configuration techniques as general-purpose Web browsers.
2191</t>
2192<t>
2193   HTTP communication is initiated by a user agent for some purpose.
2194   The purpose is a combination of request semantics, which are defined in
2195   <xref target="Part2"/>, and a target resource upon which to apply those
2196   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2197   an identifier for the "target resource", which a user agent would resolve
2198   to its absolute form in order to obtain the "target URI".  The target URI
2199   excludes the reference's fragment identifier component, if any,
2200   since fragment identifiers are reserved for client-side processing
2201   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2202</t>
2203<t>
2204   HTTP intermediaries obtain the request semantics and target URI
2205   from the request-line of an incoming request message.
2206</t>
2207</section>
2208
2209<section title="Connecting Inbound" anchor="connecting.inbound">
2210<t>
2211   Once the target URI is determined, a client needs to decide whether
2212   a network request is necessary to accomplish the desired semantics and,
2213   if so, where that request is to be directed.
2214</t>
2215<t>
2216   If the client has a response cache and the request semantics can be
2217   satisfied by a cache (<xref target="Part6"/>), then the request is
2218   usually directed to the cache first.
2219</t>
2220<t>
2221   If the request is not satisfied by a cache, then a typical client will
2222   check its configuration to determine whether a proxy is to be used to
2223   satisfy the request.  Proxy configuration is implementation-dependent,
2224   but is often based on URI prefix matching, selective authority matching,
2225   or both, and the proxy itself is usually identified by an "http" or
2226   "https" URI.  If a proxy is applicable, the client connects inbound by
2227   establishing (or reusing) a connection to that proxy.
2228</t>
2229<t>
2230   If no proxy is applicable, a typical client will invoke a handler routine,
2231   usually specific to the target URI's scheme, to connect directly
2232   to an authority for the target resource.  How that is accomplished is
2233   dependent on the target URI scheme and defined by its associated
2234   specification, similar to how this specification defines origin server
2235   access for resolution of the "http" (<xref target="http.uri"/>) and
2236   "https" (<xref target="https.uri"/>) schemes.
2237</t>
2238</section>
2239
2240<section title="Request Target" anchor="request-target">
2241<t>
2242   Once an inbound connection is obtained
2243   (<xref target="connection.management"/>),
2244   the client sends an HTTP request message (<xref target="http.message"/>)
2245   with a request-target derived from the target URI.
2246   There are four distinct formats for the request-target, depending on both
2247   the method being requested and whether the request is to a proxy.
2248</t>   
2249<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/><iref primary="true" item="Grammar" subitem="origin-form"/><iref primary="true" item="Grammar" subitem="absolute-form"/><iref primary="true" item="Grammar" subitem="authority-form"/><iref primary="true" item="Grammar" subitem="asterisk-form"/>
2250  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2251                 / <x:ref>absolute-form</x:ref>
2252                 / <x:ref>authority-form</x:ref>
2253                 / <x:ref>asterisk-form</x:ref>
2254
2255  <x:ref>origin-form</x:ref>    = <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]
2256  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2257  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2258  <x:ref>asterisk-form</x:ref>  = "*"
2259</artwork></figure>
2260<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2261   The most common form of request-target is the origin-form.
2262   When making a request directly to an origin server, other than a CONNECT
2263   or server-wide OPTIONS request (as detailed below),
2264   a client &MUST; send only the absolute path and query components of
2265   the target URI as the request-target.
2266   If the target URI's path component is empty, then the client &MUST; send
2267   "/" as the path within the origin-form of request-target.
2268   A Host header field is also sent, as defined in
2269   <xref target="header.host"/>, containing the target URI's
2270   authority component (excluding any userinfo).
2271</t>
2272<t>
2273   For example, a client wishing to retrieve a representation of the resource
2274   identified as
2275</t>
2276<figure><artwork x:indent-with="  ">
2277http://www.example.org/where?q=now
2278</artwork></figure>
2279<t>
2280   directly from the origin server would open (or reuse) a TCP connection
2281   to port 80 of the host "www.example.org" and send the lines:
2282</t>
2283<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2284GET /where?q=now HTTP/1.1
2285Host: www.example.org
2286</artwork></figure>
2287<t>
2288   followed by the remainder of the request message.
2289</t>
2290<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2291   When making a request to a proxy, other than a CONNECT or server-wide
2292   OPTIONS request (as detailed below), a client &MUST; send the target URI
2293   in absolute-form as the request-target.
2294   The proxy is requested to either service that request from a valid cache,
2295   if possible, or make the same request on the client's behalf to either
2296   the next inbound proxy server or directly to the origin server indicated
2297   by the request-target.  Requirements on such "forwarding" of messages are
2298   defined in <xref target="intermediary.forwarding"/>.
2299</t>
2300<t>
2301   An example absolute-form of request-line would be:
2302</t>
2303<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2304GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
2305</artwork></figure>
2306<t>
2307   To allow for transition to the absolute-form for all requests in some
2308   future version of HTTP, HTTP/1.1 servers &MUST; accept the absolute-form
2309   in requests, even though HTTP/1.1 clients will only send them in requests
2310   to proxies.
2311</t>
2312<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2313   The authority-form of request-target is only used for CONNECT requests
2314   (&CONNECT;).  When making a CONNECT request to establish a tunnel through
2315   one or more proxies, a client &MUST; send only the target URI's
2316   authority component (excluding any userinfo) as the request-target.
2317   For example,
2318</t>
2319<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2320CONNECT www.example.com:80 HTTP/1.1
2321</artwork></figure>
2322<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2323   The asterisk-form of request-target is only used for a server-wide
2324   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2325   for the server as a whole, as opposed to a specific named resource of
2326   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2327   For example,
2328</t>
2329<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2330OPTIONS * HTTP/1.1
2331</artwork></figure>
2332<t>
2333   If a proxy receives an OPTIONS request with an absolute-form of
2334   request-target in which the URI has an empty path and no query component,
2335   then the last proxy on the request chain &MUST; send a request-target
2336   of "*" when it forwards the request to the indicated origin server.
2337</t>
2338<figure><preamble>   
2339   For example, the request
2340</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2341OPTIONS http://www.example.org:8001 HTTP/1.1
2342</artwork></figure>
2343<figure><preamble>   
2344  would be forwarded by the final proxy as
2345</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2346OPTIONS * HTTP/1.1
2347Host: www.example.org:8001
2348</artwork>
2349<postamble>
2350   after connecting to port 8001 of host "www.example.org".
2351</postamble>
2352</figure>
2353</section>
2354
2355<section title="Host" anchor="header.host">
2356  <iref primary="true" item="Host header field" x:for-anchor=""/>
2357  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
2358  <x:anchor-alias value="Host"/>
2359<t>
2360   The "Host" header field in a request provides the host and port
2361   information from the target URI, enabling the origin
2362   server to distinguish among resources while servicing requests
2363   for multiple host names on a single IP address.  Since the Host
2364   field-value is critical information for handling a request, it
2365   &SHOULD; be sent as the first header field following the request-line.
2366</t>
2367<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2368  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2369</artwork></figure>
2370<t>
2371   A client &MUST; send a Host header field in all HTTP/1.1 request
2372   messages.  If the target URI includes an authority component, then
2373   the Host field-value &MUST; be identical to that authority component
2374   after excluding any userinfo (<xref target="http.uri"/>).
2375   If the authority component is missing or undefined for the target URI,
2376   then the Host header field &MUST; be sent with an empty field-value.
2377</t>
2378<t>
2379   For example, a GET request to the origin server for
2380   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
2381</t>
2382<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2383GET /pub/WWW/ HTTP/1.1
2384Host: www.example.org
2385</artwork></figure>
2386<t>
2387   The Host header field &MUST; be sent in an HTTP/1.1 request even
2388   if the request-target is in the absolute-form, since this
2389   allows the Host information to be forwarded through ancient HTTP/1.0
2390   proxies that might not have implemented Host.
2391</t>
2392<t>
2393   When an HTTP/1.1 proxy receives a request with an absolute-form of
2394   request-target, the proxy &MUST; ignore the received
2395   Host header field (if any) and instead replace it with the host
2396   information of the request-target.  If the proxy forwards the request,
2397   it &MUST; generate a new Host field-value based on the received
2398   request-target rather than forward the received Host field-value.
2399</t>
2400<t>
2401   Since the Host header field acts as an application-level routing
2402   mechanism, it is a frequent target for malware seeking to poison
2403   a shared cache or redirect a request to an unintended server.
2404   An interception proxy is particularly vulnerable if it relies on
2405   the Host field-value for redirecting requests to internal
2406   servers, or for use as a cache key in a shared cache, without
2407   first verifying that the intercepted connection is targeting a
2408   valid IP address for that host.
2409</t>
2410<t>
2411   A server &MUST; respond with a 400 (Bad Request) status code to
2412   any HTTP/1.1 request message that lacks a Host header field and
2413   to any request message that contains more than one Host header field
2414   or a Host header field with an invalid field-value.
2415</t>
2416</section>
2417
2418<section title="Effective Request URI" anchor="effective.request.uri">
2419  <iref primary="true" item="effective request URI"/>
2420<t>
2421   A server that receives an HTTP request message &MUST; reconstruct
2422   the user agent's original target URI, based on the pieces of information
2423   learned from the request-target, Host, and connection context, in order
2424   to identify the intended target resource and properly service the request.
2425   The URI derived from this reconstruction process is referred to as the
2426   "effective request URI".
2427</t>
2428<t>
2429   If the request-target is in absolute-form, then the effective request URI
2430   is the same as the request-target.  Otherwise, the effective request URI
2431   is constructed as follows.
2432</t>
2433<t>
2434   If the request is received over an SSL/TLS-secured TCP connection,
2435   then the effective request URI's scheme is "https"; otherwise, the
2436   scheme is "http".
2437</t>
2438<t>
2439   If the request-target is in authority-form, then the effective
2440   request URI's authority component is the same as the request-target.
2441   Otherwise, if a Host header field is supplied with a non-empty field-value,
2442   then the authority component is the same as the Host field-value.
2443   Otherwise, the authority component is the concatenation of the default
2444   hostname configured for the server, a colon (":"), and the connection's
2445   incoming TCP port number in decimal form.
2446</t>
2447<t>
2448   If the request-target is in authority-form or asterisk-form, then the
2449   effective request URI's combined path and query component is empty.
2450   Otherwise, the combined path and query component is the same as the
2451   request-target.
2452</t>
2453<t>
2454   The components of the effective request URI, once determined as above,
2455   can be combined into absolute-URI form by concatenating the scheme,
2456   "://", authority, and combined path and query component.
2457</t>
2458<figure>
2459<preamble>
2460   Example 1: the following message received over an insecure TCP connection
2461</preamble> 
2462<artwork type="example" x:indent-with="  ">
2463GET /pub/WWW/TheProject.html HTTP/1.1
2464Host: www.example.org:8080
2465</artwork>
2466</figure>
2467<figure>
2468<preamble>
2469  has an effective request URI of
2470</preamble>
2471<artwork type="example" x:indent-with="  ">
2472http://www.example.org:8080/pub/WWW/TheProject.html
2473</artwork>
2474</figure>
2475<figure>
2476<preamble>
2477   Example 2: the following message received over an SSL/TLS-secured TCP
2478   connection
2479</preamble> 
2480<artwork type="example" x:indent-with="  ">
2481OPTIONS * HTTP/1.1
2482Host: www.example.org
2483</artwork>
2484</figure>
2485<figure>
2486<preamble>
2487  has an effective request URI of
2488</preamble>
2489<artwork type="example" x:indent-with="  ">
2490https://www.example.org
2491</artwork>
2492</figure>
2493<t>
2494   An origin server that does not allow resources to differ by requested
2495   host &MAY; ignore the Host field-value and instead replace it with a
2496   configured server name when constructing the effective request URI.
2497</t>
2498<t>
2499   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
2500   attempt to use heuristics (e.g., examination of the URI path for
2501   something unique to a particular host) in order to guess the
2502   effective request URI's authority component.
2503</t>
2504</section>
2505
2506<section title="Intermediary Forwarding" anchor="intermediary.forwarding">
2507<t>
2508   As described in <xref target="intermediaries"/>, intermediaries can serve
2509   a variety of roles in the processing of HTTP requests and responses.
2510   Some intermediaries are used to improve performance or availability.
2511   Others are used for access control or to filter content.
2512   Since an HTTP stream has characteristics similar to a pipe-and-filter
2513   architecture, there are no inherent limits to the extent an intermediary
2514   can enhance (or interfere) with either direction of the stream.
2515</t>
2516<t>
2517   In order to avoid request loops, a proxy that forwards requests to other
2518   proxies &MUST; be able to recognize and exclude all of its own server
2519   names, including any aliases, local variations, or literal IP addresses.
2520</t>
2521<t>
2522   If a proxy receives a request-target with a host name that is not a
2523   fully qualified domain name, it &MAY; add its domain to the host name
2524   it received when forwarding the request.  A proxy &MUST-NOT; change the
2525   host name if it is a fully qualified domain name.
2526</t>
2527<t>
2528   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" and "query"
2529   parts of the received request-target when forwarding it to the next inbound
2530   server, except as noted above to replace an empty path with "/" or "*".
2531</t>
2532<t>
2533   Intermediaries that forward a message &MUST; implement the
2534   Connection header field as specified in <xref target="header.connection"/>.
2535</t>
2536
2537<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2538<!--<t>
2539  <cref anchor="TODO-end-to-end" source="jre">
2540    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2541    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2542  </cref>
2543</t>-->
2544<t>
2545   For the purpose of defining the behavior of caches and non-caching
2546   proxies, we divide HTTP header fields into two categories:
2547  <list style="symbols">
2548      <t>End-to-end header fields, which are  transmitted to the ultimate
2549        recipient of a request or response. End-to-end header fields in
2550        responses &MUST; be stored as part of a cache entry and &MUST; be
2551        transmitted in any response formed from a cache entry.</t>
2552
2553      <t>Hop-by-hop header fields, which are meaningful only for a single
2554        transport-level connection, and are not stored by caches or
2555        forwarded by proxies.</t>
2556  </list>
2557</t>
2558<t>
2559   The following HTTP/1.1 header fields are hop-by-hop header fields:
2560  <list style="symbols">
2561      <t>Connection</t>
2562      <t>Keep-Alive</t>
2563      <t>Proxy-Authenticate</t>
2564      <t>Proxy-Authorization</t>
2565      <t>TE</t>
2566      <t>Trailer</t>
2567      <t>Transfer-Encoding</t>
2568      <t>Upgrade</t>
2569  </list>
2570</t>
2571<t>
2572   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2573</t>
2574<t>
2575   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2576   (<xref target="header.connection"/>).
2577</t>
2578</section>
2579
2580<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2581<!--<t>
2582  <cref anchor="TODO-non-mod-headers" source="jre">
2583    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2584    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2585  </cref>
2586</t>-->
2587<t>
2588   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2589   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2590   modify an end-to-end header field unless the definition of that header field requires
2591   or specifically allows that.
2592</t>
2593<t>
2594   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2595   request or response, and it &MUST-NOT; add any of these fields if not
2596   already present:
2597  <list style="symbols">
2598    <t>Allow</t>
2599    <t>Content-Location</t>
2600    <t>Content-MD5</t>
2601    <t>ETag</t>
2602    <t>Last-Modified</t>
2603    <t>Server</t>
2604  </list>
2605</t>
2606<t>
2607   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2608   response:
2609  <list style="symbols">
2610    <t>Expires</t>
2611  </list>
2612</t>
2613<t>
2614   but it &MAY; add any of these fields if not already present. If an
2615   Expires header field is added, it &MUST; be given a field-value identical to
2616   that of the Date header field in that response.
2617</t>
2618<t>
2619   A proxy &MUST-NOT; modify or add any of the following fields in a
2620   message that contains the no-transform cache-control directive, or in
2621   any request:
2622  <list style="symbols">
2623    <t>Content-Encoding</t>
2624    <t>Content-Range</t>
2625    <t>Content-Type</t>
2626  </list>
2627</t>
2628<t>
2629   A transforming proxy &MAY; modify or add these fields to a message
2630   that does not include no-transform, but if it does so, it &MUST; add a
2631   Warning 214 (Transformation applied) if one does not already appear
2632   in the message (see &header-warning;).
2633</t>
2634<x:note>
2635  <t>
2636    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2637    cause authentication failures if stronger authentication
2638    mechanisms are introduced in later versions of HTTP. Such
2639    authentication mechanisms &MAY; rely on the values of header fields
2640    not listed here.
2641  </t>
2642</x:note>
2643<t>
2644   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2645   though it &MAY; change the message body through application or removal
2646   of a transfer-coding (<xref target="transfer.codings"/>).
2647</t>
2648</section>
2649
2650</section>
2651
2652<section title="Associating a Response to a Request" anchor="associating.response.to.request">
2653<t>
2654   HTTP does not include a request identifier for associating a given
2655   request message with its corresponding one or more response messages.
2656   Hence, it relies on the order of response arrival to correspond exactly
2657   to the order in which requests are made on the same connection.
2658   More than one response message per request only occurs when one or more
2659   informational responses (1xx, see &status-1xx;) precede a final response
2660   to the same request.
2661</t>
2662<t>
2663   A client that uses persistent connections and sends more than one request
2664   per connection &MUST; maintain a list of outstanding requests in the
2665   order sent on that connection and &MUST; associate each received response
2666   message to the highest ordered request that has not yet received a final
2667   (non-1xx) response.
2668</t>
2669</section>
2670</section>
2671
2672<section title="Connection Management" anchor="connection.management">
2673
2674<section title="Connection" anchor="header.connection">
2675  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2676  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2677  <x:anchor-alias value="Connection"/>
2678  <x:anchor-alias value="connection-token"/>
2679<t>
2680   The "Connection" header field allows the sender to specify
2681   options that are desired only for that particular connection.
2682   Such connection options &MUST; be removed or replaced before the
2683   message can be forwarded downstream by a proxy or gateway.
2684   This mechanism also allows the sender to indicate which HTTP
2685   header fields used in the message are only intended for the
2686   immediate recipient ("hop-by-hop"), as opposed to all recipients
2687   on the chain ("end-to-end"), enabling the message to be
2688   self-descriptive and allowing future connection-specific extensions
2689   to be deployed in HTTP without fear that they will be blindly
2690   forwarded by previously deployed intermediaries.
2691</t>
2692<t>
2693   The Connection header field's value has the following grammar:
2694</t>
2695<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2696  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
2697  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2698</artwork></figure>
2699<t>
2700   A proxy or gateway &MUST; parse a received Connection
2701   header field before a message is forwarded and, for each
2702   connection-token in this field, remove any header field(s) from
2703   the message with the same name as the connection-token, and then
2704   remove the Connection header field itself or replace it with the
2705   sender's own connection options for the forwarded message.
2706</t>
2707<t>
2708   A sender &MUST-NOT; include field-names in the Connection header
2709   field-value for fields that are defined as expressing constraints
2710   for all recipients in the request or response chain, such as the
2711   Cache-Control header field (&header-cache-control;).
2712</t>
2713<t>
2714   The connection options do not have to correspond to a header field
2715   present in the message, since a connection-specific header field
2716   might not be needed if there are no parameters associated with that
2717   connection option.  Recipients that trigger certain connection
2718   behavior based on the presence of connection options &MUST; do so
2719   based on the presence of the connection-token rather than only the
2720   presence of the optional header field.  In other words, if the
2721   connection option is received as a header field but not indicated
2722   within the Connection field-value, then the recipient &MUST; ignore
2723   the connection-specific header field because it has likely been
2724   forwarded by an intermediary that is only partially conformant.
2725</t>
2726<t>
2727   When defining new connection options, specifications ought to
2728   carefully consider existing deployed header fields and ensure
2729   that the new connection-token does not share the same name as
2730   an unrelated header field that might already be deployed.
2731   Defining a new connection-token essentially reserves that potential
2732   field-name for carrying additional information related to the
2733   connection option, since it would be unwise for senders to use
2734   that field-name for anything else.
2735</t>
2736<t>
2737   HTTP/1.1 defines the "close" connection option for the sender to
2738   signal that the connection will be closed after completion of the
2739   response. For example,
2740</t>
2741<figure><artwork type="example">
2742  Connection: close
2743</artwork></figure>
2744<t>
2745   in either the request or the response header fields indicates that
2746   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2747   after the current request/response is complete.
2748</t>
2749<t>
2750   An HTTP/1.1 client that does not support persistent connections &MUST;
2751   include the "close" connection option in every request message.
2752</t>
2753<t>
2754   An HTTP/1.1 server that does not support persistent connections &MUST;
2755   include the "close" connection option in every response message that
2756   does not have a 1xx (Informational) status code.
2757</t>
2758</section>
2759
2760<section title="Via" anchor="header.via">
2761  <iref primary="true" item="Via header field" x:for-anchor=""/>
2762  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
2763  <x:anchor-alias value="pseudonym"/>
2764  <x:anchor-alias value="received-by"/>
2765  <x:anchor-alias value="received-protocol"/>
2766  <x:anchor-alias value="Via"/>
2767<t>
2768   The "Via" header field &MUST; be sent by a proxy or gateway to
2769   indicate the intermediate protocols and recipients between the user
2770   agent and the server on requests, and between the origin server and
2771   the client on responses. It is analogous to the "Received" field
2772   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
2773   and is intended to be used for tracking message forwards,
2774   avoiding request loops, and identifying the protocol capabilities of
2775   all senders along the request/response chain.
2776</t>
2777<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"/>
2778  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2779                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2780  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2781  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2782  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2783</artwork></figure>
2784<t>
2785   The received-protocol indicates the protocol version of the message
2786   received by the server or client along each segment of the
2787   request/response chain. The received-protocol version is appended to
2788   the Via field value when the message is forwarded so that information
2789   about the protocol capabilities of upstream applications remains
2790   visible to all recipients.
2791</t>
2792<t>
2793   The protocol-name is excluded if and only if it would be "HTTP". The
2794   received-by field is normally the host and optional port number of a
2795   recipient server or client that subsequently forwarded the message.
2796   However, if the real host is considered to be sensitive information,
2797   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2798   be assumed to be the default port of the received-protocol.
2799</t>
2800<t>
2801   Multiple Via field values represent each proxy or gateway that has
2802   forwarded the message. Each recipient &MUST; append its information
2803   such that the end result is ordered according to the sequence of
2804   forwarding applications.
2805</t>
2806<t>
2807   Comments &MAY; be used in the Via header field to identify the software
2808   of each recipient, analogous to the User-Agent and Server header fields.
2809   However, all comments in the Via field are optional and &MAY; be removed
2810   by any recipient prior to forwarding the message.
2811</t>
2812<t>
2813   For example, a request message could be sent from an HTTP/1.0 user
2814   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2815   forward the request to a public proxy at p.example.net, which completes
2816   the request by forwarding it to the origin server at www.example.com.
2817   The request received by www.example.com would then have the following
2818   Via header field:
2819</t>
2820<figure><artwork type="example">
2821  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2822</artwork></figure>
2823<t>
2824   A proxy or gateway used as a portal through a network firewall
2825   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2826   region unless it is explicitly enabled to do so. If not enabled, the
2827   received-by host of any host behind the firewall &SHOULD; be replaced
2828   by an appropriate pseudonym for that host.
2829</t>
2830<t>
2831   For organizations that have strong privacy requirements for hiding
2832   internal structures, a proxy or gateway &MAY; combine an ordered
2833   subsequence of Via header field entries with identical received-protocol
2834   values into a single such entry. For example,
2835</t>
2836<figure><artwork type="example">
2837  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2838</artwork></figure>
2839<t>
2840  could be collapsed to
2841</t>
2842<figure><artwork type="example">
2843  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2844</artwork></figure>
2845<t>
2846   Senders &SHOULD-NOT; combine multiple entries unless they are all
2847   under the same organizational control and the hosts have already been
2848   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
2849   have different received-protocol values.
2850</t>
2851</section>
2852
2853<section title="Persistent Connections" anchor="persistent.connections">
2854
2855<section title="Purpose" anchor="persistent.purpose">
2856<t>
2857   Prior to persistent connections, a separate TCP connection was
2858   established for each request, increasing the load on HTTP servers
2859   and causing congestion on the Internet. The use of inline images and
2860   other associated data often requires a client to make multiple
2861   requests of the same server in a short amount of time. Analysis of
2862   these performance problems and results from a prototype
2863   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2864   measurements of actual HTTP/1.1 implementations show good
2865   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2866   T/TCP <xref target="Tou1998"/>.
2867</t>
2868<t>
2869   Persistent HTTP connections have a number of advantages:
2870  <list style="symbols">
2871      <t>
2872        By opening and closing fewer TCP connections, CPU time is saved
2873        in routers and hosts (clients, servers, proxies, gateways,
2874        tunnels, or caches), and memory used for TCP protocol control
2875        blocks can be saved in hosts.
2876      </t>
2877      <t>
2878        HTTP requests and responses can be pipelined on a connection.
2879        Pipelining allows a client to make multiple requests without
2880        waiting for each response, allowing a single TCP connection to
2881        be used much more efficiently, with much lower elapsed time.
2882      </t>
2883      <t>
2884        Network congestion is reduced by reducing the number of packets
2885        caused by TCP opens, and by allowing TCP sufficient time to
2886        determine the congestion state of the network.
2887      </t>
2888      <t>
2889        Latency on subsequent requests is reduced since there is no time
2890        spent in TCP's connection opening handshake.
2891      </t>
2892      <t>
2893        HTTP can evolve more gracefully, since errors can be reported
2894        without the penalty of closing the TCP connection. Clients using
2895        future versions of HTTP might optimistically try a new feature,
2896        but if communicating with an older server, retry with old
2897        semantics after an error is reported.
2898      </t>
2899    </list>
2900</t>
2901<t>
2902   HTTP implementations &SHOULD; implement persistent connections.
2903</t>
2904</section>
2905
2906<section title="Overall Operation" anchor="persistent.overall">
2907<t>
2908   A significant difference between HTTP/1.1 and earlier versions of
2909   HTTP is that persistent connections are the default behavior of any
2910   HTTP connection. That is, unless otherwise indicated, the client
2911   &SHOULD; assume that the server will maintain a persistent connection,
2912   even after error responses from the server.
2913</t>
2914<t>
2915   Persistent connections provide a mechanism by which a client and a
2916   server can signal the close of a TCP connection. This signaling takes
2917   place using the Connection header field (<xref target="header.connection"/>). Once a close
2918   has been signaled, the client &MUST-NOT; send any more requests on that
2919   connection.
2920</t>
2921
2922<section title="Negotiation" anchor="persistent.negotiation">
2923<t>
2924   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2925   maintain a persistent connection unless a Connection header field including
2926   the connection-token "close" was sent in the request. If the server
2927   chooses to close the connection immediately after sending the
2928   response, it &SHOULD; send a Connection header field including the
2929   connection-token "close".
2930</t>
2931<t>
2932   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2933   decide to keep it open based on whether the response from a server
2934   contains a Connection header field with the connection-token close. In case
2935   the client does not want to maintain a connection for more than that
2936   request, it &SHOULD; send a Connection header field including the
2937   connection-token close.
2938</t>
2939<t>
2940   If either the client or the server sends the close token in the
2941   Connection header field, that request becomes the last one for the
2942   connection.
2943</t>
2944<t>
2945   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2946   maintained for HTTP versions less than 1.1 unless it is explicitly
2947   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2948   compatibility with HTTP/1.0 clients.
2949</t>
2950<t>
2951   Each persistent connection applies to only one transport link.
2952</t>
2953<t>
2954   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2955   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2956   for information and discussion of the problems with the Keep-Alive header field
2957   implemented by many HTTP/1.0 clients).
2958</t>
2959<t>
2960   In order to remain persistent, all messages on the connection &MUST;
2961   have a self-defined message length (i.e., one not defined by closure
2962   of the connection), as described in <xref target="message.body"/>.
2963</t>
2964</section>
2965
2966<section title="Pipelining" anchor="pipelining">
2967<t>
2968   A client that supports persistent connections &MAY; "pipeline" its
2969   requests (i.e., send multiple requests without waiting for each
2970   response). A server &MUST; send its responses to those requests in the
2971   same order that the requests were received.
2972</t>
2973<t>
2974   Clients which assume persistent connections and pipeline immediately
2975   after connection establishment &SHOULD; be prepared to retry their
2976   connection if the first pipelined attempt fails. If a client does
2977   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2978   persistent. Clients &MUST; also be prepared to resend their requests if
2979   the server closes the connection before sending all of the
2980   corresponding responses.
2981</t>
2982<t>
2983   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2984   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2985   premature termination of the transport connection could lead to
2986   indeterminate results. A client wishing to send a non-idempotent
2987   request &SHOULD; wait to send that request until it has received the
2988   response status line for the previous request.
2989</t>
2990</section>
2991</section>
2992
2993<section title="Practical Considerations" anchor="persistent.practical">
2994<t>
2995   Servers will usually have some time-out value beyond which they will
2996   no longer maintain an inactive connection. Proxy servers might make
2997   this a higher value since it is likely that the client will be making
2998   more connections through the same server. The use of persistent
2999   connections places no requirements on the length (or existence) of
3000   this time-out for either the client or the server.
3001</t>
3002<t>
3003   When a client or server wishes to time-out it &SHOULD; issue a graceful
3004   close on the transport connection. Clients and servers &SHOULD; both
3005   constantly watch for the other side of the transport close, and
3006   respond to it as appropriate. If a client or server does not detect
3007   the other side's close promptly it could cause unnecessary resource
3008   drain on the network.
3009</t>
3010<t>
3011   A client, server, or proxy &MAY; close the transport connection at any
3012   time. For example, a client might have started to send a new request
3013   at the same time that the server has decided to close the "idle"
3014   connection. From the server's point of view, the connection is being
3015   closed while it was idle, but from the client's point of view, a
3016   request is in progress.
3017</t>
3018<t>
3019   Clients (including proxies) &SHOULD; limit the number of simultaneous
3020   connections that they maintain to a given server (including proxies).
3021</t>
3022<t>
3023   Previous revisions of HTTP gave a specific number of connections as a
3024   ceiling, but this was found to be impractical for many applications. As a
3025   result, this specification does not mandate a particular maximum number of
3026   connections, but instead encourages clients to be conservative when opening
3027   multiple connections.
3028</t>
3029<t>
3030   In particular, while using multiple connections avoids the "head-of-line
3031   blocking" problem (whereby a request that takes significant server-side
3032   processing and/or has a large payload can block subsequent requests on the
3033   same connection), each connection used consumes server resources (sometimes
3034   significantly), and furthermore using multiple connections can cause
3035   undesirable side effects in congested networks.
3036</t>
3037<t>
3038   Note that servers might reject traffic that they deem abusive, including an
3039   excessive number of connections from a client.
3040</t>
3041</section>
3042
3043<section title="Retrying Requests" anchor="persistent.retrying.requests">
3044<t>
3045   Senders can close the transport connection at any time. Therefore,
3046   clients, servers, and proxies &MUST; be able to recover
3047   from asynchronous close events. Client software &MAY; reopen the
3048   transport connection and retransmit the aborted sequence of requests
3049   without user interaction so long as the request sequence is
3050   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
3051   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
3052   human operator the choice of retrying the request(s). Confirmation by
3053   user-agent software with semantic understanding of the application
3054   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
3055   be repeated if the second sequence of requests fails.
3056</t>
3057</section>
3058</section>
3059
3060<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
3061
3062<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
3063<t>
3064   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
3065   flow control mechanisms to resolve temporary overloads, rather than
3066   terminating connections with the expectation that clients will retry.
3067   The latter technique can exacerbate network congestion.
3068</t>
3069</section>
3070
3071<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
3072<t>
3073   An HTTP/1.1 (or later) client sending a message body &SHOULD; monitor
3074   the network connection for an error status code while it is transmitting
3075   the request. If the client sees an error status code, it &SHOULD;
3076   immediately cease transmitting the body. If the body is being sent
3077   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
3078   empty trailer &MAY; be used to prematurely mark the end of the message.
3079   If the body was preceded by a Content-Length header field, the client &MUST;
3080   close the connection.
3081</t>
3082</section>
3083
3084<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
3085<t>
3086   The purpose of the 100 (Continue) status code (see &status-100;) is to
3087   allow a client that is sending a request message with a request body
3088   to determine if the origin server is willing to accept the request
3089   (based on the request header fields) before the client sends the request
3090   body. In some cases, it might either be inappropriate or highly
3091   inefficient for the client to send the body if the server will reject
3092   the message without looking at the body.
3093</t>
3094<t>
3095   Requirements for HTTP/1.1 clients:
3096  <list style="symbols">
3097    <t>
3098        If a client will wait for a 100 (Continue) response before
3099        sending the request body, it &MUST; send an Expect header
3100        field (&header-expect;) with the "100-continue" expectation.
3101    </t>
3102    <t>
3103        A client &MUST-NOT; send an Expect header field (&header-expect;)
3104        with the "100-continue" expectation if it does not intend
3105        to send a request body.
3106    </t>
3107  </list>
3108</t>
3109<t>
3110   Because of the presence of older implementations, the protocol allows
3111   ambiguous situations in which a client might send "Expect: 100-continue"
3112   without receiving either a 417 (Expectation Failed)
3113   or a 100 (Continue) status code. Therefore, when a client sends this
3114   header field to an origin server (possibly via a proxy) from which it
3115   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
3116   wait for an indefinite period before sending the request body.
3117</t>
3118<t>
3119   Requirements for HTTP/1.1 origin servers:
3120  <list style="symbols">
3121    <t> Upon receiving a request which includes an Expect header
3122        field with the "100-continue" expectation, an origin server &MUST;
3123        either respond with 100 (Continue) status code and continue to read
3124        from the input stream, or respond with a final status code. The
3125        origin server &MUST-NOT; wait for the request body before sending
3126        the 100 (Continue) response. If it responds with a final status
3127        code, it &MAY; close the transport connection or it &MAY; continue
3128        to read and discard the rest of the request.  It &MUST-NOT;
3129        perform the request method if it returns a final status code.
3130    </t>
3131    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
3132        the request message does not include an Expect header
3133        field with the "100-continue" expectation, and &MUST-NOT; send a
3134        100 (Continue) response if such a request comes from an HTTP/1.0
3135        (or earlier) client. There is an exception to this rule: for
3136        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
3137        status code in response to an HTTP/1.1 PUT or POST request that does
3138        not include an Expect header field with the "100-continue"
3139        expectation. This exception, the purpose of which is
3140        to minimize any client processing delays associated with an
3141        undeclared wait for 100 (Continue) status code, applies only to
3142        HTTP/1.1 requests, and not to requests with any other HTTP-version
3143        value.
3144    </t>
3145    <t> An origin server &MAY; omit a 100 (Continue) response if it has
3146        already received some or all of the request body for the
3147        corresponding request.
3148    </t>
3149    <t> An origin server that sends a 100 (Continue) response &MUST;
3150        ultimately send a final status code, once the request body is
3151        received and processed, unless it terminates the transport
3152        connection prematurely.
3153    </t>
3154    <t> If an origin server receives a request that does not include an
3155        Expect header field with the "100-continue" expectation,
3156        the request includes a request body, and the server responds
3157        with a final status code before reading the entire request body
3158        from the transport connection, then the server &SHOULD-NOT;  close
3159        the transport connection until it has read the entire request,
3160        or until the client closes the connection. Otherwise, the client
3161        might not reliably receive the response message. However, this
3162        requirement ought not be construed as preventing a server from
3163        defending itself against denial-of-service attacks, or from
3164        badly broken client implementations.
3165      </t>
3166    </list>
3167</t>
3168<t>
3169   Requirements for HTTP/1.1 proxies:
3170  <list style="symbols">
3171    <t> If a proxy receives a request that includes an Expect header
3172        field with the "100-continue" expectation, and the proxy
3173        either knows that the next-hop server complies with HTTP/1.1 or
3174        higher, or does not know the HTTP version of the next-hop
3175        server, it &MUST; forward the request, including the Expect header
3176        field.
3177    </t>
3178    <t> If the proxy knows that the version of the next-hop server is
3179        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
3180        respond with a 417 (Expectation Failed) status code.
3181    </t>
3182    <t> Proxies &SHOULD; maintain a record of the HTTP version
3183        numbers received from recently-referenced next-hop servers.
3184    </t>
3185    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
3186        request message was received from an HTTP/1.0 (or earlier)
3187        client and did not include an Expect header field with
3188        the "100-continue" expectation. This requirement overrides the
3189        general rule for forwarding of 1xx responses (see &status-1xx;).
3190    </t>
3191  </list>
3192</t>
3193</section>
3194
3195<section title="Closing Connections on Error" anchor="closing.connections.on.error">
3196<t>
3197   If the client is sending data, a server implementation using TCP
3198   &SHOULD; be careful to ensure that the client acknowledges receipt of
3199   the packet(s) containing the response, before the server closes the
3200   input connection. If the client continues sending data to the server
3201   after the close, the server's TCP stack will send a reset packet to
3202   the client, which might erase the client's unacknowledged input buffers
3203   before they can be read and interpreted by the HTTP application.
3204</t>
3205</section>
3206
3207</section>
3208
3209<section title="Upgrade" anchor="header.upgrade">
3210  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3211  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3212  <x:anchor-alias value="Upgrade"/>
3213  <x:anchor-alias value="protocol"/>
3214  <x:anchor-alias value="protocol-name"/>
3215  <x:anchor-alias value="protocol-version"/>
3216<t>
3217   The "Upgrade" header field allows the client to specify what
3218   additional communication protocols it would like to use, if the server
3219   chooses to switch protocols. Servers can use it to indicate what protocols
3220   they are willing to switch to.
3221</t>
3222<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3223  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3224
3225  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3226  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3227  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3228</artwork></figure>
3229<t>
3230   For example,
3231</t>
3232<figure><artwork type="example">
3233  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3234</artwork></figure>
3235<t>
3236   The Upgrade header field is intended to provide a simple mechanism
3237   for transitioning from HTTP/1.1 to some other, incompatible protocol. It
3238   does so by allowing the client to advertise its desire to use another
3239   protocol, such as a later version of HTTP with a higher major version
3240   number, even though the current request has been made using HTTP/1.1.
3241   This eases the difficult transition between incompatible protocols by
3242   allowing the client to initiate a request in the more commonly
3243   supported protocol while indicating to the server that it would like
3244   to use a "better" protocol if available (where "better" is determined
3245   by the server, possibly according to the nature of the request method
3246   or target resource).
3247</t>
3248<t>
3249   The Upgrade header field only applies to switching application-layer
3250   protocols upon the existing transport-layer connection. Upgrade
3251   cannot be used to insist on a protocol change; its acceptance and use
3252   by the server is optional. The capabilities and nature of the
3253   application-layer communication after the protocol change is entirely
3254   dependent upon the new protocol chosen, although the first action
3255   after changing the protocol &MUST; be a response to the initial HTTP
3256   request containing the Upgrade header field.
3257</t>
3258<t>
3259   The Upgrade header field only applies to the immediate connection.
3260   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3261   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3262   HTTP/1.1 message.
3263</t>
3264<t>
3265   The Upgrade header field cannot be used to indicate a switch to a
3266   protocol on a different connection. For that purpose, it is more
3267   appropriate to use a 3xx redirection response (&status-3xx;).
3268</t>
3269<t>
3270   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3271   Protocols) responses to indicate which protocol(s) are being switched to,
3272   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3273   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3274   response to indicate that they are willing to upgrade to one of the
3275   specified protocols.
3276</t>
3277<t>
3278   This specification only defines the protocol name "HTTP" for use by
3279   the family of Hypertext Transfer Protocols, as defined by the HTTP
3280   version rules of <xref target="http.version"/> and future updates to this
3281   specification. Additional tokens can be registered with IANA using the
3282   registration procedure defined in <xref target="upgrade.token.registry"/>.
3283</t>
3284</section>
3285
3286</section>
3287
3288<section title="IANA Considerations" anchor="IANA.considerations">
3289
3290<section title="Header Field Registration" anchor="header.field.registration">
3291<t>
3292   HTTP header fields are registered within the Message Header Field Registry
3293   <xref target="RFC3864"/> maintained by IANA at
3294   <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/>.
3295</t>
3296<t>
3297   This document defines the following HTTP header fields, so their
3298   associated registry entries shall be updated according to the permanent
3299   registrations below:
3300</t>
3301<?BEGININC p1-messaging.iana-headers ?>
3302<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3303<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3304   <ttcol>Header Field Name</ttcol>
3305   <ttcol>Protocol</ttcol>
3306   <ttcol>Status</ttcol>
3307   <ttcol>Reference</ttcol>
3308
3309   <c>Connection</c>
3310   <c>http</c>
3311   <c>standard</c>
3312   <c>
3313      <xref target="header.connection"/>
3314   </c>
3315   <c>Content-Length</c>
3316   <c>http</c>
3317   <c>standard</c>
3318   <c>
3319      <xref target="header.content-length"/>
3320   </c>
3321   <c>Host</c>
3322   <c>http</c>
3323   <c>standard</c>
3324   <c>
3325      <xref target="header.host"/>
3326   </c>
3327   <c>TE</c>
3328   <c>http</c>
3329   <c>standard</c>
3330   <c>
3331      <xref target="header.te"/>
3332   </c>
3333   <c>Trailer</c>
3334   <c>http</c>
3335   <c>standard</c>
3336   <c>
3337      <xref target="header.trailer"/>
3338   </c>
3339   <c>Transfer-Encoding</c>
3340   <c>http</c>
3341   <c>standard</c>
3342   <c>
3343      <xref target="header.transfer-encoding"/>
3344   </c>
3345   <c>Upgrade</c>
3346   <c>http</c>
3347   <c>standard</c>
3348   <c>
3349      <xref target="header.upgrade"/>
3350   </c>
3351   <c>Via</c>
3352   <c>http</c>
3353   <c>standard</c>
3354   <c>
3355      <xref target="header.via"/>
3356   </c>
3357</texttable>
3358<!--(END)-->
3359<?ENDINC p1-messaging.iana-headers ?>
3360<t>
3361   Furthermore, the header field-name "Close" shall be registered as
3362   "reserved", since using that name as an HTTP header field might
3363   conflict with the "close" connection option of the "Connection"
3364   header field (<xref target="header.connection"/>).
3365</t>
3366<texttable align="left" suppress-title="true">
3367   <ttcol>Header Field Name</ttcol>
3368   <ttcol>Protocol</ttcol>
3369   <ttcol>Status</ttcol>
3370   <ttcol>Reference</ttcol>
3371
3372   <c>Close</c>
3373   <c>http</c>
3374   <c>reserved</c>
3375   <c>
3376      <xref target="header.field.registration"/>
3377   </c>
3378</texttable>
3379<t>
3380   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3381</t>
3382</section>
3383
3384<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3385<t>
3386   IANA maintains the registry of URI Schemes <xref target="RFC4395"/> at
3387   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>.
3388</t>
3389<t>
3390   This document defines the following URI schemes, so their
3391   associated registry entries shall be updated according to the permanent
3392   registrations below:
3393</t>
3394<texttable align="left" suppress-title="true">
3395   <ttcol>URI Scheme</ttcol>
3396   <ttcol>Description</ttcol>
3397   <ttcol>Reference</ttcol>
3398
3399   <c>http</c>
3400   <c>Hypertext Transfer Protocol</c>
3401   <c><xref target="http.uri"/></c>
3402
3403   <c>https</c>
3404   <c>Hypertext Transfer Protocol Secure</c>
3405   <c><xref target="https.uri"/></c>
3406</texttable>
3407</section>
3408
3409<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3410<t>
3411   This document serves as the specification for the Internet media types
3412   "message/http" and "application/http". The following is to be registered with
3413   IANA (see <xref target="RFC4288"/>).
3414</t>
3415<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3416<iref item="Media Type" subitem="message/http" primary="true"/>
3417<iref item="message/http Media Type" primary="true"/>
3418<t>
3419   The message/http type can be used to enclose a single HTTP request or
3420   response message, provided that it obeys the MIME restrictions for all
3421   "message" types regarding line length and encodings.
3422</t>
3423<t>
3424  <list style="hanging" x:indent="12em">
3425    <t hangText="Type name:">
3426      message
3427    </t>
3428    <t hangText="Subtype name:">
3429      http
3430    </t>
3431    <t hangText="Required parameters:">
3432      none
3433    </t>
3434    <t hangText="Optional parameters:">
3435      version, msgtype
3436      <list style="hanging">
3437        <t hangText="version:">
3438          The HTTP-version number of the enclosed message
3439          (e.g., "1.1"). If not present, the version can be
3440          determined from the first line of the body.
3441        </t>
3442        <t hangText="msgtype:">
3443          The message type &mdash; "request" or "response". If not
3444          present, the type can be determined from the first
3445          line of the body.
3446        </t>
3447      </list>
3448    </t>
3449    <t hangText="Encoding considerations:">
3450      only "7bit", "8bit", or "binary" are permitted
3451    </t>
3452    <t hangText="Security considerations:">
3453      none
3454    </t>
3455    <t hangText="Interoperability considerations:">
3456      none
3457    </t>
3458    <t hangText="Published specification:">
3459      This specification (see <xref target="internet.media.type.message.http"/>).
3460    </t>
3461    <t hangText="Applications that use this media type:">
3462    </t>
3463    <t hangText="Additional information:">
3464      <list style="hanging">
3465        <t hangText="Magic number(s):">none</t>
3466        <t hangText="File extension(s):">none</t>
3467        <t hangText="Macintosh file type code(s):">none</t>
3468      </list>
3469    </t>
3470    <t hangText="Person and email address to contact for further information:">
3471      See Authors Section.
3472    </t>
3473    <t hangText="Intended usage:">
3474      COMMON
3475    </t>
3476    <t hangText="Restrictions on usage:">
3477      none
3478    </t>
3479    <t hangText="Author/Change controller:">
3480      IESG
3481    </t>
3482  </list>
3483</t>
3484</section>
3485<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3486<iref item="Media Type" subitem="application/http" primary="true"/>
3487<iref item="application/http Media Type" primary="true"/>
3488<t>
3489   The application/http type can be used to enclose a pipeline of one or more
3490   HTTP request or response messages (not intermixed).
3491</t>
3492<t>
3493  <list style="hanging" x:indent="12em">
3494    <t hangText="Type name:">
3495      application
3496    </t>
3497    <t hangText="Subtype name:">
3498      http
3499    </t>
3500    <t hangText="Required parameters:">
3501      none
3502    </t>
3503    <t hangText="Optional parameters:">
3504      version, msgtype
3505      <list style="hanging">
3506        <t hangText="version:">
3507          The HTTP-version number of the enclosed messages
3508          (e.g., "1.1"). If not present, the version can be
3509          determined from the first line of the body.
3510        </t>
3511        <t hangText="msgtype:">
3512          The message type &mdash; "request" or "response". If not
3513          present, the type can be determined from the first
3514          line of the body.
3515        </t>
3516      </list>
3517    </t>
3518    <t hangText="Encoding considerations:">
3519      HTTP messages enclosed by this type
3520      are in "binary" format; use of an appropriate
3521      Content-Transfer-Encoding is required when
3522      transmitted via E-mail.
3523    </t>
3524    <t hangText="Security considerations:">
3525      none
3526    </t>
3527    <t hangText="Interoperability considerations:">
3528      none
3529    </t>
3530    <t hangText="Published specification:">
3531      This specification (see <xref target="internet.media.type.application.http"/>).
3532    </t>
3533    <t hangText="Applications that use this media type:">
3534    </t>
3535    <t hangText="Additional information:">
3536      <list style="hanging">
3537        <t hangText="Magic number(s):">none</t>
3538        <t hangText="File extension(s):">none</t>
3539        <t hangText="Macintosh file type code(s):">none</t>
3540      </list>
3541    </t>
3542    <t hangText="Person and email address to contact for further information:">
3543      See Authors Section.
3544    </t>
3545    <t hangText="Intended usage:">
3546      COMMON
3547    </t>
3548    <t hangText="Restrictions on usage:">
3549      none
3550    </t>
3551    <t hangText="Author/Change controller:">
3552      IESG
3553    </t>
3554  </list>
3555</t>
3556</section>
3557</section>
3558
3559<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3560<t>
3561   The HTTP Transfer Coding Registry defines the name space for transfer
3562   coding names.
3563</t>
3564<t>
3565   Registrations &MUST; include the following fields:
3566   <list style="symbols">
3567     <t>Name</t>
3568     <t>Description</t>
3569     <t>Pointer to specification text</t>
3570   </list>
3571</t>
3572<t>
3573   Names of transfer codings &MUST-NOT; overlap with names of content codings
3574   (&content-codings;) unless the encoding transformation is identical, as it
3575   is the case for the compression codings defined in
3576   <xref target="compression.codings"/>.
3577</t>
3578<t>
3579   Values to be added to this name space require IETF Review (see
3580   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3581   conform to the purpose of transfer coding defined in this section.
3582</t>
3583<t>
3584   The registry itself is maintained at
3585   <eref target="http://www.iana.org/assignments/http-parameters"/>.
3586</t>
3587</section>
3588
3589<section title="Transfer Coding Registrations" anchor="transfer.coding.registration">
3590<t>
3591   The HTTP Transfer Coding Registry shall be updated with the registrations
3592   below:
3593</t>
3594<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3595   <ttcol>Name</ttcol>
3596   <ttcol>Description</ttcol>
3597   <ttcol>Reference</ttcol>
3598   <c>chunked</c>
3599   <c>Transfer in a series of chunks</c>
3600   <c>
3601      <xref target="chunked.encoding"/>
3602   </c>
3603   <c>compress</c>
3604   <c>UNIX "compress" program method</c>
3605   <c>
3606      <xref target="compress.coding"/>
3607   </c>
3608   <c>deflate</c>
3609   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3610   the "zlib" data format (<xref target="RFC1950"/>)
3611   </c>
3612   <c>
3613      <xref target="deflate.coding"/>
3614   </c>
3615   <c>gzip</c>
3616   <c>Same as GNU zip <xref target="RFC1952"/></c>
3617   <c>
3618      <xref target="gzip.coding"/>
3619   </c>
3620</texttable>
3621</section>
3622
3623<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3624<t>
3625   The HTTP Upgrade Token Registry defines the name space for protocol-name
3626   tokens used to identify protocols in the Upgrade header field.
3627   Each registered protocol-name is associated with contact information and
3628   an optional set of specifications that details how the connection
3629   will be processed after it has been upgraded.
3630</t>
3631<t>
3632   Registrations require IETF Review (see
3633   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3634   following rules:
3635  <list style="numbers">
3636    <t>A protocol-name token, once registered, stays registered forever.</t>
3637    <t>The registration &MUST; name a responsible party for the
3638       registration.</t>
3639    <t>The registration &MUST; name a point of contact.</t>
3640    <t>The registration &MAY; name a set of specifications associated with
3641       that token. Such specifications need not be publicly available.</t>
3642    <t>The registration &SHOULD; name a set of expected "protocol-version"
3643       tokens associated with that token at the time of registration.</t>
3644    <t>The responsible party &MAY; change the registration at any time.
3645       The IANA will keep a record of all such changes, and make them
3646       available upon request.</t>
3647    <t>The IESG &MAY; reassign responsibility for a protocol token.
3648       This will normally only be used in the case when a
3649       responsible party cannot be contacted.</t>
3650  </list>
3651</t>
3652<t>
3653   This registration procedure for HTTP Upgrade Tokens replaces that
3654   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3655</t>
3656</section>
3657
3658<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3659<t>
3660   The HTTP Upgrade Token Registry shall be updated with the registration
3661   below:
3662</t>
3663<texttable align="left" suppress-title="true">
3664   <ttcol>Value</ttcol>
3665   <ttcol>Description</ttcol>
3666   <ttcol>Expected Version Tokens</ttcol>
3667   <ttcol>Reference</ttcol>
3668
3669   <c>HTTP</c>
3670   <c>Hypertext Transfer Protocol</c>
3671   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3672   <c><xref target="http.version"/></c>
3673</texttable>
3674<t>
3675   The responsible party is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3676</t>
3677</section>
3678
3679</section>
3680
3681<section title="Security Considerations" anchor="security.considerations">
3682<t>
3683   This section is meant to inform application developers, information
3684   providers, and users of the security limitations in HTTP/1.1 as
3685   described by this document. The discussion does not include
3686   definitive solutions to the problems revealed, though it does make
3687   some suggestions for reducing security risks.
3688</t>
3689
3690<section title="Personal Information" anchor="personal.information">
3691<t>
3692   HTTP clients are often privy to large amounts of personal information
3693   (e.g., the user's name, location, mail address, passwords, encryption
3694   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3695   leakage of this information.
3696   We very strongly recommend that a convenient interface be provided
3697   for the user to control dissemination of such information, and that
3698   designers and implementors be particularly careful in this area.
3699   History shows that errors in this area often create serious security
3700   and/or privacy problems and generate highly adverse publicity for the
3701   implementor's company.
3702</t>
3703</section>
3704
3705<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3706<t>
3707   A server is in the position to save personal data about a user's
3708   requests which might identify their reading patterns or subjects of
3709   interest.  In particular, log information gathered at an intermediary
3710   often contains a history of user agent interaction, across a multitude
3711   of sites, that can be traced to individual users.
3712</t>
3713<t>
3714   HTTP log information is confidential in nature; its handling is often
3715   constrained by laws and regulations.  Log information needs to be securely
3716   stored and appropriate guidelines followed for its analysis.
3717   Anonymization of personal information within individual entries helps,
3718   but is generally not sufficient to prevent real log traces from being
3719   re-identified based on correlation with other access characteristics.
3720   As such, access traces that are keyed to a specific client should not
3721   be published even if the key is pseudonymous.
3722</t>
3723<t>
3724   To minimize the risk of theft or accidental publication, log information
3725   should be purged of personally identifiable information, including
3726   user identifiers, IP addresses, and user-provided query parameters,
3727   as soon as that information is no longer necessary to support operational
3728   needs for security, auditing, or fraud control.
3729</t>
3730</section>
3731
3732<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3733<t>
3734   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3735   the documents returned by HTTP requests to be only those that were
3736   intended by the server administrators. If an HTTP server translates
3737   HTTP URIs directly into file system calls, the server &MUST; take
3738   special care not to serve files that were not intended to be
3739   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3740   other operating systems use ".." as a path component to indicate a
3741   directory level above the current one. On such a system, an HTTP
3742   server &MUST; disallow any such construct in the request-target if it
3743   would otherwise allow access to a resource outside those intended to
3744   be accessible via the HTTP server. Similarly, files intended for
3745   reference only internally to the server (such as access control
3746   files, configuration files, and script code) &MUST; be protected from
3747   inappropriate retrieval, since they might contain sensitive
3748   information. Experience has shown that minor bugs in such HTTP server
3749   implementations have turned into security risks.
3750</t>
3751</section>
3752
3753<section title="DNS-related Attacks" anchor="dns.related.attacks">
3754<t>
3755   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3756   generally prone to security attacks based on the deliberate misassociation
3757   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3758   cautious in assuming the validity of an IP number/DNS name association unless
3759   the response is protected by DNSSec (<xref target="RFC4033"/>).
3760</t>
3761</section>
3762
3763<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3764<t>
3765   By their very nature, HTTP intermediaries are men-in-the-middle, and
3766   represent an opportunity for man-in-the-middle attacks. Compromise of
3767   the systems on which the intermediaries run can result in serious security
3768   and privacy problems. Intermediaries have access to security-related
3769   information, personal information about individual users and
3770   organizations, and proprietary information belonging to users and
3771   content providers. A compromised intermediary, or an intermediary
3772   implemented or configured without regard to security and privacy
3773   considerations, might be used in the commission of a wide range of
3774   potential attacks.
3775</t>
3776<t>
3777   Intermediaries that contain a shared cache are especially vulnerable
3778   to cache poisoning attacks.
3779</t>
3780<t>
3781   Implementors need to consider the privacy and security
3782   implications of their design and coding decisions, and of the
3783   configuration options they provide to operators (especially the
3784   default configuration).
3785</t>
3786<t>
3787   Users need to be aware that intermediaries are no more trustworthy than
3788   the people who run them; HTTP itself cannot solve this problem.
3789</t>
3790<t>
3791   The judicious use of cryptography, when appropriate, might suffice to
3792   protect against a broad range of security and privacy attacks. Such
3793   cryptography is beyond the scope of the HTTP/1.1 specification.
3794</t>
3795</section>
3796
3797<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3798<t>
3799   Because HTTP uses mostly textual, character-delimited fields, attackers can
3800   overflow buffers in implementations, and/or perform a Denial of Service
3801   against implementations that accept fields with unlimited lengths.
3802</t>
3803<t>
3804   To promote interoperability, this specification makes specific
3805   recommendations for minimum size limits on request-line
3806   (<xref target="request.line"/>)
3807   and blocks of header fields (<xref target="header.fields"/>). These are
3808   minimum recommendations, chosen to be supportable even by implementations
3809   with limited resources; it is expected that most implementations will
3810   choose substantially higher limits.
3811</t>
3812<t>
3813   This specification also provides a way for servers to reject messages that
3814   have request-targets that are too long (&status-414;) or request entities
3815   that are too large (&status-4xx;).
3816</t>
3817<t>
3818   Other fields (including but not limited to request methods, response status
3819   phrases, header field-names, and body chunks) &SHOULD; be limited by
3820   implementations carefully, so as to not impede interoperability.
3821</t>
3822</section>
3823</section>
3824
3825<section title="Acknowledgments" anchor="acks">
3826<t>
3827   This edition of HTTP builds on the many contributions that went into
3828   <xref target="RFC1945" format="none">RFC 1945</xref>,
3829   <xref target="RFC2068" format="none">RFC 2068</xref>,
3830   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3831   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3832   substantial contributions made by the previous authors, editors, and
3833   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3834   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3835   Paul J. Leach, and Mark Nottingham.
3836   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
3837   acknowledgements from prior revisions.
3838</t>
3839<t>
3840   Since 1999, the following contributors have helped improve the HTTP
3841   specification by reporting bugs, asking smart questions, drafting or
3842   reviewing text, and evaluating open issues:
3843</t>
3844<?BEGININC acks ?>
3845<t>Adam Barth,
3846Adam Roach,
3847Addison Phillips,
3848Adrian Chadd,
3849Adrien de Croy,
3850Alan Ford,
3851Alan Ruttenberg,
3852Albert Lunde,
3853Alex Rousskov,
3854Alexey Melnikov,
3855Alisha Smith,
3856Amichai Rothman,
3857Amit Klein,
3858Amos Jeffries,
3859Andreas Maier,
3860Andreas Petersson,
3861Anne van Kesteren,
3862Anthony Bryan,
3863Asbjorn Ulsberg,
3864Balachander Krishnamurthy,
3865Barry Leiba,
3866Ben Laurie,
3867Benjamin Niven-Jenkins,
3868Bil Corry,
3869Bill Burke,
3870Bjoern Hoehrmann,
3871Bob Scheifler,
3872Boris Zbarsky,
3873Brett Slatkin,
3874Brian Kell,
3875Brian McBarron,
3876Brian Pane,
3877Brian Smith,
3878Bryce Nesbitt,
3879Cameron Heavon-Jones,
3880Carl Kugler,
3881Carsten Bormann,
3882Charles Fry,
3883Chris Newman,
3884Cyrus Daboo,
3885Dale Robert Anderson,
3886Dan Winship,
3887Daniel Stenberg,
3888Dave Cridland,
3889Dave Crocker,
3890Dave Kristol,
3891David Booth,
3892David Singer,
3893David W. Morris,
3894Diwakar Shetty,
3895Dmitry Kurochkin,
3896Drummond Reed,
3897Duane Wessels,
3898Edward Lee,
3899Eliot Lear,
3900Eran Hammer-Lahav,
3901Eric D. Williams,
3902Eric J. Bowman,
3903Eric Lawrence,
3904Eric Rescorla,
3905Erik Aronesty,
3906Florian Weimer,
3907Frank Ellermann,
3908Fred Bohle,
3909Geoffrey Sneddon,
3910Gervase Markham,
3911Greg Wilkins,
3912Harald Tveit Alvestrand,
3913Harry Halpin,
3914Helge Hess,
3915Henrik Nordstrom,
3916Henry S. Thompson,
3917Henry Story,
3918Herbert van de Sompel,
3919Howard Melman,
3920Hugo Haas,
3921Ian Hickson,
3922Ingo Struck,
3923J. Ross Nicoll,
3924James H. Manger,
3925James Lacey,
3926James M. Snell,
3927Jamie Lokier,
3928Jan Algermissen,
3929Jeff Hodges (for coming up with the term 'effective Request-URI'),
3930Jeff Walden,
3931Jim Luther,
3932Joe D. Williams,
3933Joe Gregorio,
3934Joe Orton,
3935John C. Klensin,
3936John C. Mallery,
3937John Cowan,
3938John Kemp,
3939John Panzer,
3940John Schneider,
3941John Stracke,
3942Jonas Sicking,
3943Jonathan Billington,
3944Jonathan Moore,
3945Jonathan Rees,
3946Jordi Ros,
3947Joris Dobbelsteen,
3948Josh Cohen,
3949Julien Pierre,
3950Jungshik Shin,
3951Justin Chapweske,
3952Justin Erenkrantz,
3953Justin James,
3954Kalvinder Singh,
3955Karl Dubost,
3956Keith Hoffman,
3957Keith Moore,
3958Koen Holtman,
3959Konstantin Voronkov,
3960Kris Zyp,
3961Lisa Dusseault,
3962Maciej Stachowiak,
3963Marc Schneider,
3964Marc Slemko,
3965Mark Baker,
3966Mark Pauley,
3967Markus Lanthaler,
3968Martin J. Duerst,
3969Martin Thomson,
3970Matt Lynch,
3971Matthew Cox,
3972Max Clark,
3973Michael Burrows,
3974Michael Hausenblas,
3975Mike Amundsen,
3976Mike Belshe,
3977Mike Kelly,
3978Mike Schinkel,
3979Miles Sabin,
3980Mykyta Yevstifeyev,
3981Nathan Rixham,
3982Nicholas Shanks,
3983Nico Williams,
3984Nicolas Alvarez,
3985Nicolas Mailhot,
3986Noah Slater,
3987Pablo Castro,
3988Pat Hayes,
3989Patrick R. McManus,
3990Paul E. Jones,
3991Paul Hoffman,
3992Paul Marquess,
3993Peter Saint-Andre,
3994Peter Watkins,
3995Phil Archer,
3996Phillip Hallam-Baker,
3997Poul-Henning Kamp,
3998Preethi Natarajan,
3999Ray Polk,
4000Reto Bachmann-Gmuer,
4001Richard Cyganiak,
4002Robert Brewer,
4003Robert Collins,
4004Robert O'Callahan,
4005Robert Olofsson,
4006Robert Sayre,
4007Robert Siemer,
4008Robert de Wilde,
4009Roberto Javier Godoy,
4010Ronny Widjaja,
4011S. Mike Dierken,
4012Salvatore Loreto,
4013Sam Johnston,
4014Sam Ruby,
4015Scott Lawrence (for maintaining the original issues list),
4016Sean B. Palmer,
4017Shane McCarron,
4018Stefan Eissing,
4019Stefan Tilkov,
4020Stefanos Harhalakis,
4021Stephane Bortzmeyer,
4022Stephen Farrell,
4023Stuart Williams,
4024Subbu Allamaraju,
4025Sylvain Hellegouarch,
4026Tapan Divekar,
4027Ted Hardie,
4028Thomas Broyer,
4029Thomas Nordin,
4030Thomas Roessler,
4031Tim Morgan,
4032Tim Olsen,
4033Travis Snoozy,
4034Tyler Close,
4035Vincent Murphy,
4036Wenbo Zhu,
4037Werner Baumann,
4038Wilbur Streett,
4039Wilfredo Sanchez Vega,
4040William A. Rowe Jr.,
4041William Chan,
4042Willy Tarreau,
4043Xiaoshu Wang,
4044Yaron Goland,
4045Yngve Nysaeter Pettersen,
4046Yogesh Bang,
4047Yutaka Oiwa,
4048Zed A. Shaw, and
4049Zhong Yu.
4050</t>
4051<?ENDINC acks ?>
4052</section>
4053
4054</middle>
4055<back>
4056
4057<references title="Normative References">
4058
4059<reference anchor="ISO-8859-1">
4060  <front>
4061    <title>
4062     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4063    </title>
4064    <author>
4065      <organization>International Organization for Standardization</organization>
4066    </author>
4067    <date year="1998"/>
4068  </front>
4069  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4070</reference>
4071
4072<reference anchor="Part2">
4073  <front>
4074    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4075    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4076      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4077      <address><email>fielding@gbiv.com</email></address>
4078    </author>
4079    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4080      <organization abbrev="W3C">World Wide Web Consortium</organization>
4081      <address><email>ylafon@w3.org</email></address>
4082    </author>
4083    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4084      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4085      <address><email>julian.reschke@greenbytes.de</email></address>
4086    </author>
4087    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4088  </front>
4089  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4090  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4091</reference>
4092
4093<reference anchor="Part3">
4094  <front>
4095    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4096    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4097      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4098      <address><email>fielding@gbiv.com</email></address>
4099    </author>
4100    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4101      <organization abbrev="W3C">World Wide Web Consortium</organization>
4102      <address><email>ylafon@w3.org</email></address>
4103    </author>
4104    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4105      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4106      <address><email>julian.reschke@greenbytes.de</email></address>
4107    </author>
4108    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4109  </front>
4110  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4111  <x:source href="p3-payload.xml" basename="p3-payload"/>
4112</reference>
4113
4114<reference anchor="Part6">
4115  <front>
4116    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4117    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4118      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4119      <address><email>fielding@gbiv.com</email></address>
4120    </author>
4121    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4122      <organization abbrev="W3C">World Wide Web Consortium</organization>
4123      <address><email>ylafon@w3.org</email></address>
4124    </author>
4125    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4126      <organization>Rackspace</organization>
4127      <address><email>mnot@mnot.net</email></address>
4128    </author>
4129    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4130      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4131      <address><email>julian.reschke@greenbytes.de</email></address>
4132    </author>
4133    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4134  </front>
4135  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4136  <x:source href="p6-cache.xml" basename="p6-cache"/>
4137</reference>
4138
4139<reference anchor="RFC5234">
4140  <front>
4141    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4142    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4143      <organization>Brandenburg InternetWorking</organization>
4144      <address>
4145        <email>dcrocker@bbiw.net</email>
4146      </address> 
4147    </author>
4148    <author initials="P." surname="Overell" fullname="Paul Overell">
4149      <organization>THUS plc.</organization>
4150      <address>
4151        <email>paul.overell@thus.net</email>
4152      </address>
4153    </author>
4154    <date month="January" year="2008"/>
4155  </front>
4156  <seriesInfo name="STD" value="68"/>
4157  <seriesInfo name="RFC" value="5234"/>
4158</reference>
4159
4160<reference anchor="RFC2119">
4161  <front>
4162    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4163    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4164      <organization>Harvard University</organization>
4165      <address><email>sob@harvard.edu</email></address>
4166    </author>
4167    <date month="March" year="1997"/>
4168  </front>
4169  <seriesInfo name="BCP" value="14"/>
4170  <seriesInfo name="RFC" value="2119"/>
4171</reference>
4172
4173<reference anchor="RFC3986">
4174 <front>
4175  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4176  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4177    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4178    <address>
4179       <email>timbl@w3.org</email>
4180       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4181    </address>
4182  </author>
4183  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4184    <organization abbrev="Day Software">Day Software</organization>
4185    <address>
4186      <email>fielding@gbiv.com</email>
4187      <uri>http://roy.gbiv.com/</uri>
4188    </address>
4189  </author>
4190  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4191    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4192    <address>
4193      <email>LMM@acm.org</email>
4194      <uri>http://larry.masinter.net/</uri>
4195    </address>
4196  </author>
4197  <date month='January' year='2005'></date>
4198 </front>
4199 <seriesInfo name="STD" value="66"/>
4200 <seriesInfo name="RFC" value="3986"/>
4201</reference>
4202
4203<reference anchor="USASCII">
4204  <front>
4205    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4206    <author>
4207      <organization>American National Standards Institute</organization>
4208    </author>
4209    <date year="1986"/>
4210  </front>
4211  <seriesInfo name="ANSI" value="X3.4"/>
4212</reference>
4213
4214<reference anchor="RFC1950">
4215  <front>
4216    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4217    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4218      <organization>Aladdin Enterprises</organization>
4219      <address><email>ghost@aladdin.com</email></address>
4220    </author>
4221    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4222    <date month="May" year="1996"/>
4223  </front>
4224  <seriesInfo name="RFC" value="1950"/>
4225  <!--<annotation>
4226    RFC 1950 is an Informational RFC, thus it might be less stable than
4227    this specification. On the other hand, this downward reference was
4228    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4229    therefore it is unlikely to cause problems in practice. See also
4230    <xref target="BCP97"/>.
4231  </annotation>-->
4232</reference>
4233
4234<reference anchor="RFC1951">
4235  <front>
4236    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4237    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4238      <organization>Aladdin Enterprises</organization>
4239      <address><email>ghost@aladdin.com</email></address>
4240    </author>
4241    <date month="May" year="1996"/>
4242  </front>
4243  <seriesInfo name="RFC" value="1951"/>
4244  <!--<annotation>
4245    RFC 1951 is an Informational RFC, thus it might be less stable than
4246    this specification. On the other hand, this downward reference was
4247    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4248    therefore it is unlikely to cause problems in practice. See also
4249    <xref target="BCP97"/>.
4250  </annotation>-->
4251</reference>
4252
4253<reference anchor="RFC1952">
4254  <front>
4255    <title>GZIP file format specification version 4.3</title>
4256    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4257      <organization>Aladdin Enterprises</organization>
4258      <address><email>ghost@aladdin.com</email></address>
4259    </author>
4260    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4261      <address><email>gzip@prep.ai.mit.edu</email></address>
4262    </author>
4263    <author initials="M." surname="Adler" fullname="Mark Adler">
4264      <address><email>madler@alumni.caltech.edu</email></address>
4265    </author>
4266    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4267      <address><email>ghost@aladdin.com</email></address>
4268    </author>
4269    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4270      <address><email>randeg@alumni.rpi.edu</email></address>
4271    </author>
4272    <date month="May" year="1996"/>
4273  </front>
4274  <seriesInfo name="RFC" value="1952"/>
4275  <!--<annotation>
4276    RFC 1952 is an Informational RFC, thus it might be less stable than
4277    this specification. On the other hand, this downward reference was
4278    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4279    therefore it is unlikely to cause problems in practice. See also
4280    <xref target="BCP97"/>.
4281  </annotation>-->
4282</reference>
4283
4284</references>
4285
4286<references title="Informative References">
4287
4288<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4289  <front>
4290    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4291    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4292    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4293    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4294    <author initials="H." surname="Lie" fullname="H. Lie"/>
4295    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4296    <date year="1997" month="September"/>
4297  </front>
4298  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4299</reference>
4300
4301<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4302  <front>
4303    <title>Improving HTTP Latency</title>
4304    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4305    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4306    <date year="1995" month="December"/>
4307  </front>
4308  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4309</reference>
4310
4311<reference anchor='RFC1919'>
4312  <front>
4313    <title>Classical versus Transparent IP Proxies</title>
4314    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4315      <address><email>mchatel@pax.eunet.ch</email></address>
4316    </author>
4317    <date year='1996' month='March' />
4318  </front>
4319  <seriesInfo name='RFC' value='1919' />
4320</reference>
4321
4322<reference anchor="RFC1945">
4323  <front>
4324    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4325    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4326      <organization>MIT, Laboratory for Computer Science</organization>
4327      <address><email>timbl@w3.org</email></address>
4328    </author>
4329    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4330      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4331      <address><email>fielding@ics.uci.edu</email></address>
4332    </author>
4333    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4334      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4335      <address><email>frystyk@w3.org</email></address>
4336    </author>
4337    <date month="May" year="1996"/>
4338  </front>
4339  <seriesInfo name="RFC" value="1945"/>
4340</reference>
4341
4342<reference anchor="RFC2045">
4343  <front>
4344    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4345    <author initials="N." surname="Freed" fullname="Ned Freed">
4346      <organization>Innosoft International, Inc.</organization>
4347      <address><email>ned@innosoft.com</email></address>
4348    </author>
4349    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4350      <organization>First Virtual Holdings</organization>
4351      <address><email>nsb@nsb.fv.com</email></address>
4352    </author>
4353    <date month="November" year="1996"/>
4354  </front>
4355  <seriesInfo name="RFC" value="2045"/>
4356</reference>
4357
4358<reference anchor="RFC2047">
4359  <front>
4360    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4361    <author initials="K." surname="Moore" fullname="Keith Moore">
4362      <organization>University of Tennessee</organization>
4363      <address><email>moore@cs.utk.edu</email></address>
4364    </author>
4365    <date month="November" year="1996"/>
4366  </front>
4367  <seriesInfo name="RFC" value="2047"/>
4368</reference>
4369
4370<reference anchor="RFC2068">
4371  <front>
4372    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4373    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4374      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4375      <address><email>fielding@ics.uci.edu</email></address>
4376    </author>
4377    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4378      <organization>MIT Laboratory for Computer Science</organization>
4379      <address><email>jg@w3.org</email></address>
4380    </author>
4381    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4382      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4383      <address><email>mogul@wrl.dec.com</email></address>
4384    </author>
4385    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4386      <organization>MIT Laboratory for Computer Science</organization>
4387      <address><email>frystyk@w3.org</email></address>
4388    </author>
4389    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4390      <organization>MIT Laboratory for Computer Science</organization>
4391      <address><email>timbl@w3.org</email></address>
4392    </author>
4393    <date month="January" year="1997"/>
4394  </front>
4395  <seriesInfo name="RFC" value="2068"/>
4396</reference>
4397
4398<reference anchor="RFC2145">
4399  <front>
4400    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4401    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4402      <organization>Western Research Laboratory</organization>
4403      <address><email>mogul@wrl.dec.com</email></address>
4404    </author>
4405    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4406      <organization>Department of Information and Computer Science</organization>
4407      <address><email>fielding@ics.uci.edu</email></address>
4408    </author>
4409    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4410      <organization>MIT Laboratory for Computer Science</organization>
4411      <address><email>jg@w3.org</email></address>
4412    </author>
4413    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4414      <organization>W3 Consortium</organization>
4415      <address><email>frystyk@w3.org</email></address>
4416    </author>
4417    <date month="May" year="1997"/>
4418  </front>
4419  <seriesInfo name="RFC" value="2145"/>
4420</reference>
4421
4422<reference anchor="RFC2616">
4423  <front>
4424    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4425    <author initials="R." surname="Fielding" fullname="R. Fielding">
4426      <organization>University of California, Irvine</organization>
4427      <address><email>fielding@ics.uci.edu</email></address>
4428    </author>
4429    <author initials="J." surname="Gettys" fullname="J. Gettys">
4430      <organization>W3C</organization>
4431      <address><email>jg@w3.org</email></address>
4432    </author>
4433    <author initials="J." surname="Mogul" fullname="J. Mogul">
4434      <organization>Compaq Computer Corporation</organization>
4435      <address><email>mogul@wrl.dec.com</email></address>
4436    </author>
4437    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4438      <organization>MIT Laboratory for Computer Science</organization>
4439      <address><email>frystyk@w3.org</email></address>
4440    </author>
4441    <author initials="L." surname="Masinter" fullname="L. Masinter">
4442      <organization>Xerox Corporation</organization>
4443      <address><email>masinter@parc.xerox.com</email></address>
4444    </author>
4445    <author initials="P." surname="Leach" fullname="P. Leach">
4446      <organization>Microsoft Corporation</organization>
4447      <address><email>paulle@microsoft.com</email></address>
4448    </author>
4449    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4450      <organization>W3C</organization>
4451      <address><email>timbl@w3.org</email></address>
4452    </author>
4453    <date month="June" year="1999"/>
4454  </front>
4455  <seriesInfo name="RFC" value="2616"/>
4456</reference>
4457
4458<reference anchor='RFC2817'>
4459  <front>
4460    <title>Upgrading to TLS Within HTTP/1.1</title>
4461    <author initials='R.' surname='Khare' fullname='R. Khare'>
4462      <organization>4K Associates / UC Irvine</organization>
4463      <address><email>rohit@4K-associates.com</email></address>
4464    </author>
4465    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4466      <organization>Agranat Systems, Inc.</organization>
4467      <address><email>lawrence@agranat.com</email></address>
4468    </author>
4469    <date year='2000' month='May' />
4470  </front>
4471  <seriesInfo name='RFC' value='2817' />
4472</reference>
4473
4474<reference anchor='RFC2818'>
4475  <front>
4476    <title>HTTP Over TLS</title>
4477    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4478      <organization>RTFM, Inc.</organization>
4479      <address><email>ekr@rtfm.com</email></address>
4480    </author>
4481    <date year='2000' month='May' />
4482  </front>
4483  <seriesInfo name='RFC' value='2818' />
4484</reference>
4485
4486<reference anchor='RFC2965'>
4487  <front>
4488    <title>HTTP State Management Mechanism</title>
4489    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4490      <organization>Bell Laboratories, Lucent Technologies</organization>
4491      <address><email>dmk@bell-labs.com</email></address>
4492    </author>
4493    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4494      <organization>Epinions.com, Inc.</organization>
4495      <address><email>lou@montulli.org</email></address>
4496    </author>
4497    <date year='2000' month='October' />
4498  </front>
4499  <seriesInfo name='RFC' value='2965' />
4500</reference>
4501
4502<reference anchor='RFC3040'>
4503  <front>
4504    <title>Internet Web Replication and Caching Taxonomy</title>
4505    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4506      <organization>Equinix, Inc.</organization>
4507    </author>
4508    <author initials='I.' surname='Melve' fullname='I. Melve'>
4509      <organization>UNINETT</organization>
4510    </author>
4511    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4512      <organization>CacheFlow Inc.</organization>
4513    </author>
4514    <date year='2001' month='January' />
4515  </front>
4516  <seriesInfo name='RFC' value='3040' />
4517</reference>
4518
4519<reference anchor='RFC3864'>
4520  <front>
4521    <title>Registration Procedures for Message Header Fields</title>
4522    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4523      <organization>Nine by Nine</organization>
4524      <address><email>GK-IETF@ninebynine.org</email></address>
4525    </author>
4526    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4527      <organization>BEA Systems</organization>
4528      <address><email>mnot@pobox.com</email></address>
4529    </author>
4530    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4531      <organization>HP Labs</organization>
4532      <address><email>JeffMogul@acm.org</email></address>
4533    </author>
4534    <date year='2004' month='September' />
4535  </front>
4536  <seriesInfo name='BCP' value='90' />
4537  <seriesInfo name='RFC' value='3864' />
4538</reference>
4539
4540<reference anchor='RFC4033'>
4541  <front>
4542    <title>DNS Security Introduction and Requirements</title>
4543    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4544    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4545    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4546    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4547    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4548    <date year='2005' month='March' />
4549  </front>
4550  <seriesInfo name='RFC' value='4033' />
4551</reference>
4552
4553<reference anchor="RFC4288">
4554  <front>
4555    <title>Media Type Specifications and Registration Procedures</title>
4556    <author initials="N." surname="Freed" fullname="N. Freed">
4557      <organization>Sun Microsystems</organization>
4558      <address>
4559        <email>ned.freed@mrochek.com</email>
4560      </address>
4561    </author>
4562    <author initials="J." surname="Klensin" fullname="J. Klensin">
4563      <address>
4564        <email>klensin+ietf@jck.com</email>
4565      </address>
4566    </author>
4567    <date year="2005" month="December"/>
4568  </front>
4569  <seriesInfo name="BCP" value="13"/>
4570  <seriesInfo name="RFC" value="4288"/>
4571</reference>
4572
4573<reference anchor='RFC4395'>
4574  <front>
4575    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4576    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4577      <organization>AT&amp;T Laboratories</organization>
4578      <address>
4579        <email>tony+urireg@maillennium.att.com</email>
4580      </address>
4581    </author>
4582    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4583      <organization>Qualcomm, Inc.</organization>
4584      <address>
4585        <email>hardie@qualcomm.com</email>
4586      </address>
4587    </author>
4588    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4589      <organization>Adobe Systems</organization>
4590      <address>
4591        <email>LMM@acm.org</email>
4592      </address>
4593    </author>
4594    <date year='2006' month='February' />
4595  </front>
4596  <seriesInfo name='BCP' value='115' />
4597  <seriesInfo name='RFC' value='4395' />
4598</reference>
4599
4600<reference anchor='RFC4559'>
4601  <front>
4602    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4603    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4604    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4605    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4606    <date year='2006' month='June' />
4607  </front>
4608  <seriesInfo name='RFC' value='4559' />
4609</reference>
4610
4611<reference anchor='RFC5226'>
4612  <front>
4613    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4614    <author initials='T.' surname='Narten' fullname='T. Narten'>
4615      <organization>IBM</organization>
4616      <address><email>narten@us.ibm.com</email></address>
4617    </author>
4618    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4619      <organization>Google</organization>
4620      <address><email>Harald@Alvestrand.no</email></address>
4621    </author>
4622    <date year='2008' month='May' />
4623  </front>
4624  <seriesInfo name='BCP' value='26' />
4625  <seriesInfo name='RFC' value='5226' />
4626</reference>
4627
4628<reference anchor="RFC5322">
4629  <front>
4630    <title>Internet Message Format</title>
4631    <author initials="P." surname="Resnick" fullname="P. Resnick">
4632      <organization>Qualcomm Incorporated</organization>
4633    </author>
4634    <date year="2008" month="October"/>
4635  </front> 
4636  <seriesInfo name="RFC" value="5322"/>
4637</reference>
4638
4639<reference anchor="RFC6265">
4640  <front>
4641    <title>HTTP State Management Mechanism</title>
4642    <author initials="A." surname="Barth" fullname="Adam Barth">
4643      <organization abbrev="U.C. Berkeley">
4644        University of California, Berkeley
4645      </organization>
4646      <address><email>abarth@eecs.berkeley.edu</email></address>
4647    </author>
4648    <date year="2011" month="April" />
4649  </front>
4650  <seriesInfo name="RFC" value="6265"/>
4651</reference>
4652
4653<!--<reference anchor='BCP97'>
4654  <front>
4655    <title>Handling Normative References to Standards-Track Documents</title>
4656    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4657      <address>
4658        <email>klensin+ietf@jck.com</email>
4659      </address>
4660    </author>
4661    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4662      <organization>MIT</organization>
4663      <address>
4664        <email>hartmans-ietf@mit.edu</email>
4665      </address>
4666    </author>
4667    <date year='2007' month='June' />
4668  </front>
4669  <seriesInfo name='BCP' value='97' />
4670  <seriesInfo name='RFC' value='4897' />
4671</reference>-->
4672
4673<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4674  <front>
4675    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4676    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4677    <date year="2001" month="November"/>
4678  </front>
4679  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4680</reference>
4681
4682<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4683  <front>
4684    <title>Analysis of HTTP Performance Problems</title>
4685    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4686    <date/>
4687  </front>
4688</reference>
4689
4690<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4691  <front>
4692  <title>Analysis of HTTP Performance</title>
4693  <author initials="J." surname="Touch" fullname="Joe Touch">
4694    <organization>USC/Information Sciences Institute</organization>
4695    <address><email>touch@isi.edu</email></address>
4696  </author>
4697  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4698    <organization>USC/Information Sciences Institute</organization>
4699    <address><email>johnh@isi.edu</email></address>
4700  </author>
4701  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4702    <organization>USC/Information Sciences Institute</organization>
4703    <address><email>katia@isi.edu</email></address>
4704  </author>
4705  <date year="1998" month="Aug"/>
4706  </front>
4707  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4708  <annotation>(original report dated Aug. 1996)</annotation>
4709</reference>
4710
4711</references>
4712
4713
4714<section title="HTTP Version History" anchor="compatibility">
4715<t>
4716   HTTP has been in use by the World-Wide Web global information initiative
4717   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4718   was a simple protocol for hypertext data transfer across the Internet
4719   with only a single request method (GET) and no metadata.
4720   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4721   methods and MIME-like messaging that could include metadata about the data
4722   transferred and modifiers on the request/response semantics. However,
4723   HTTP/1.0 did not sufficiently take into consideration the effects of
4724   hierarchical proxies, caching, the need for persistent connections, or
4725   name-based virtual hosts. The proliferation of incompletely-implemented
4726   applications calling themselves "HTTP/1.0" further necessitated a
4727   protocol version change in order for two communicating applications
4728   to determine each other's true capabilities.
4729</t>
4730<t>
4731   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4732   requirements that enable reliable implementations, adding only
4733   those new features that will either be safely ignored by an HTTP/1.0
4734   recipient or only sent when communicating with a party advertising
4735   conformance with HTTP/1.1.
4736</t>
4737<t>
4738   It is beyond the scope of a protocol specification to mandate
4739   conformance with previous versions. HTTP/1.1 was deliberately
4740   designed, however, to make supporting previous versions easy.
4741   We would expect a general-purpose HTTP/1.1 server to understand
4742   any valid request in the format of HTTP/1.0 and respond appropriately
4743   with an HTTP/1.1 message that only uses features understood (or
4744   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4745   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4746</t>
4747<t>
4748   Since HTTP/0.9 did not support header fields in a request,
4749   there is no mechanism for it to support name-based virtual
4750   hosts (selection of resource by inspection of the Host header
4751   field).  Any server that implements name-based virtual hosts
4752   ought to disable support for HTTP/0.9.  Most requests that
4753   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4754   requests wherein a buggy client failed to properly encode
4755   linear whitespace found in a URI reference and placed in
4756   the request-target.
4757</t>
4758
4759<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4760<t>
4761   This section summarizes major differences between versions HTTP/1.0
4762   and HTTP/1.1.
4763</t>
4764
4765<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4766<t>
4767   The requirements that clients and servers support the Host header
4768   field (<xref target="header.host"/>), report an error if it is
4769   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4770   are among the most important changes defined by HTTP/1.1.
4771</t>
4772<t>
4773   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4774   addresses and servers; there was no other established mechanism for
4775   distinguishing the intended server of a request than the IP address
4776   to which that request was directed. The Host header field was
4777   introduced during the development of HTTP/1.1 and, though it was
4778   quickly implemented by most HTTP/1.0 browsers, additional requirements
4779   were placed on all HTTP/1.1 requests in order to ensure complete
4780   adoption.  At the time of this writing, most HTTP-based services
4781   are dependent upon the Host header field for targeting requests.
4782</t>
4783</section>
4784
4785<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4786<t>
4787   In HTTP/1.0, each connection is established by the client prior to the
4788   request and closed by the server after sending the response. However, some
4789   implementations implement the explicitly negotiated ("Keep-Alive") version
4790   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4791   target="RFC2068"/>.
4792</t>
4793<t>
4794   Some clients and servers might wish to be compatible with these previous
4795   approaches to persistent connections, by explicitly negotiating for them
4796   with a "Connection: keep-alive" request header field. However, some
4797   experimental implementations of HTTP/1.0 persistent connections are faulty;
4798   for example, if a HTTP/1.0 proxy server doesn't understand Connection, it
4799   will erroneously forward that header to the next inbound server, which
4800   would result in a hung connection.
4801</t>
4802<t>
4803   One attempted solution was the introduction of a Proxy-Connection header,
4804   targeted specifically at proxies. In practice, this was also unworkable,
4805   because proxies are often deployed in multiple layers, bringing about the
4806   same problem discussed above.
4807</t>
4808<t>
4809   As a result, clients are encouraged not to send the Proxy-Connection header
4810   in any requests.
4811</t>
4812<t>
4813   Clients are also encouraged to consider the use of Connection: keep-alive
4814   in requests carefully; while they can enable persistent connections with
4815   HTTP/1.0 servers, clients using them need will need to monitor the
4816   connection for "hung" requests (which indicate that the client ought stop
4817   sending the header), and this mechanism ought not be used by clients at all
4818   when a proxy is being used.
4819</t>
4820</section>
4821</section>
4822
4823<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4824<t>
4825  Clarify that the string "HTTP" in the HTTP-version ABFN production is case
4826  sensitive. Restrict the version numbers to be single digits due to the fact
4827  that implementations are known to handle multi-digit version numbers
4828  incorrectly.
4829  (<xref target="http.version"/>)
4830</t>
4831<t>
4832  Update use of abs_path production from RFC 1808 to the path-absolute + query
4833  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4834  request method only.
4835  (<xref target="request-target"/>)
4836</t>
4837<t>
4838  Require that invalid whitespace around field-names be rejected.
4839  (<xref target="header.fields"/>)
4840</t>
4841<t>
4842  Rules about implicit linear whitespace between certain grammar productions
4843  have been removed; now whitespace is only allowed where specifically
4844  defined in the ABNF.
4845  (<xref target="whitespace"/>)
4846</t>
4847<t> 
4848  The NUL octet is no longer allowed in comment and quoted-string
4849  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4850  Non-ASCII content in header fields and reason phrase has been obsoleted and
4851  made opaque (the TEXT rule was removed).
4852  (<xref target="field.components"/>)
4853</t>
4854<t>
4855  Empty list elements in list productions have been deprecated.
4856  (<xref target="abnf.extension"/>)
4857</t>
4858<t>
4859  Require recipients to handle bogus Content-Length header fields as errors.
4860  (<xref target="message.body"/>)
4861</t>
4862<t>
4863  Remove reference to non-existent identity transfer-coding value tokens.
4864  (Sections <xref format="counter" target="message.body"/> and
4865  <xref format="counter" target="transfer.codings"/>)
4866</t>
4867<t>
4868  Clarification that the chunk length does not include the count of the octets
4869  in the chunk header and trailer. Furthermore disallowed line folding
4870  in chunk extensions, and deprecate their use.
4871  (<xref target="chunked.encoding"/>)
4872</t>
4873<t>
4874  Registration of Transfer Codings now requires IETF Review
4875  (<xref target="transfer.coding.registry"/>)
4876</t>
4877<t>
4878  Remove hard limit of two connections per server.
4879  Remove requirement to retry a sequence of requests as long it was idempotent.
4880  Remove requirements about when servers are allowed to close connections
4881  prematurely.
4882  (<xref target="persistent.practical"/>)
4883</t>
4884<t>
4885  Remove requirement to retry requests under certain cirumstances when the
4886  server prematurely closes the connection.
4887  (<xref target="message.transmission.requirements"/>)
4888</t>
4889<t>
4890  Change ABNF productions for header fields to only define the field value.
4891</t>
4892<t>
4893  Clarify exactly when close connection options must be sent.
4894  (<xref target="header.connection"/>)
4895</t>
4896<t>
4897  Define the semantics of the "Upgrade" header field in responses other than
4898  101 (this was incorporated from <xref target="RFC2817"/>).
4899  (<xref target="header.upgrade"/>)
4900</t>
4901</section>
4902
4903<section title="Changes from RFC 2817" anchor="changes.from.rfc.2817">
4904<t>
4905  Registration of Upgrade tokens now requires IETF Review
4906  (<xref target="upgrade.token.registry"/>)
4907</t>
4908</section>
4909</section>
4910
4911<?BEGININC p1-messaging.abnf-appendix ?>
4912<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4913<figure>
4914<artwork type="abnf" name="p1-messaging.parsed-abnf">
4915<x:ref>BWS</x:ref> = OWS
4916
4917<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4918 connection-token ] )
4919<x:ref>Content-Length</x:ref> = 1*DIGIT
4920
4921<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4922 ]
4923<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
4924<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
4925<x:ref>Host</x:ref> = uri-host [ ":" port ]
4926
4927<x:ref>OWS</x:ref> = *( SP / HTAB )
4928
4929<x:ref>RWS</x:ref> = 1*( SP / HTAB )
4930
4931<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4932<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4933<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4934 transfer-coding ] )
4935
4936<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4937<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
4938
4939<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
4940 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
4941 )
4942
4943<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4944<x:ref>absolute-form</x:ref> = absolute-URI
4945<x:ref>asterisk-form</x:ref> = "*"
4946<x:ref>attribute</x:ref> = token
4947<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4948<x:ref>authority-form</x:ref> = authority
4949
4950<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
4951<x:ref>chunk-data</x:ref> = 1*OCTET
4952<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
4953<x:ref>chunk-ext-name</x:ref> = token
4954<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4955<x:ref>chunk-size</x:ref> = 1*HEXDIG
4956<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
4957<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4958<x:ref>connection-token</x:ref> = token
4959<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4960 / %x2A-5B ; '*'-'['
4961 / %x5D-7E ; ']'-'~'
4962 / obs-text
4963
4964<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4965<x:ref>field-name</x:ref> = token
4966<x:ref>field-value</x:ref> = *( field-content / obs-fold )
4967
4968<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
4969<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4970<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4971
4972<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
4973
4974<x:ref>message-body</x:ref> = *OCTET
4975<x:ref>method</x:ref> = token
4976
4977<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
4978<x:ref>obs-text</x:ref> = %x80-FF
4979<x:ref>origin-form</x:ref> = path-absolute [ "?" query ]
4980
4981<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4982<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4983<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4984<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4985<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
4986<x:ref>protocol-name</x:ref> = token
4987<x:ref>protocol-version</x:ref> = token
4988<x:ref>pseudonym</x:ref> = token
4989
4990<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4991 / %x5D-7E ; ']'-'~'
4992 / obs-text
4993<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
4994 / %x5D-7E ; ']'-'~'
4995 / obs-text
4996<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4997<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
4998<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
4999<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5000<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5001<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5002
5003<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5004<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5005<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5006<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5007<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
5008<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
5009 asterisk-form
5010
5011<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5012 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5013<x:ref>start-line</x:ref> = request-line / status-line
5014<x:ref>status-code</x:ref> = 3DIGIT
5015<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
5016
5017<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5018<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5019 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5020<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5021<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5022<x:ref>token</x:ref> = 1*tchar
5023<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5024<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5025 transfer-extension
5026<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5027<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5028
5029<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5030
5031<x:ref>value</x:ref> = word
5032
5033<x:ref>word</x:ref> = token / quoted-string
5034</artwork>
5035</figure>
5036<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5037; Connection defined but not used
5038; Content-Length defined but not used
5039; HTTP-message defined but not used
5040; Host defined but not used
5041; TE defined but not used
5042; Trailer defined but not used
5043; Transfer-Encoding defined but not used
5044; URI-reference defined but not used
5045; Upgrade defined but not used
5046; Via defined but not used
5047; chunked-body defined but not used
5048; http-URI defined but not used
5049; https-URI defined but not used
5050; partial-URI defined but not used
5051; special defined but not used
5052</artwork></figure></section>
5053<?ENDINC p1-messaging.abnf-appendix ?>
5054
5055<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5056
5057<section title="Since RFC 2616">
5058<t>
5059  Extracted relevant partitions from <xref target="RFC2616"/>.
5060</t>
5061</section>
5062
5063<section title="Since draft-ietf-httpbis-p1-messaging-00">
5064<t>
5065  Closed issues:
5066  <list style="symbols"> 
5067    <t>
5068      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5069      "HTTP Version should be case sensitive"
5070      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5071    </t>
5072    <t>
5073      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5074      "'unsafe' characters"
5075      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5076    </t>
5077    <t>
5078      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5079      "Chunk Size Definition"
5080      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5081    </t>
5082    <t>
5083      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5084      "Message Length"
5085      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5086    </t>
5087    <t>
5088      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5089      "Media Type Registrations"
5090      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5091    </t>
5092    <t>
5093      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5094      "URI includes query"
5095      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5096    </t>
5097    <t>
5098      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5099      "No close on 1xx responses"
5100      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5101    </t>
5102    <t>
5103      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5104      "Remove 'identity' token references"
5105      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5106    </t>
5107    <t>
5108      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5109      "Import query BNF"
5110    </t>
5111    <t>
5112      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5113      "qdtext BNF"
5114    </t>
5115    <t>
5116      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5117      "Normative and Informative references"
5118    </t>
5119    <t>
5120      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5121      "RFC2606 Compliance"
5122    </t>
5123    <t>
5124      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5125      "RFC977 reference"
5126    </t>
5127    <t>
5128      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5129      "RFC1700 references"
5130    </t>
5131    <t>
5132      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5133      "inconsistency in date format explanation"
5134    </t>
5135    <t>
5136      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5137      "Date reference typo"
5138    </t>
5139    <t>
5140      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5141      "Informative references"
5142    </t>
5143    <t>
5144      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5145      "ISO-8859-1 Reference"
5146    </t>
5147    <t>
5148      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5149      "Normative up-to-date references"
5150    </t>
5151  </list>
5152</t>
5153<t>
5154  Other changes:
5155  <list style="symbols"> 
5156    <t>
5157      Update media type registrations to use RFC4288 template.
5158    </t>
5159    <t>
5160      Use names of RFC4234 core rules DQUOTE and HTAB,
5161      fix broken ABNF for chunk-data
5162      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5163    </t>
5164  </list>
5165</t>
5166</section>
5167
5168<section title="Since draft-ietf-httpbis-p1-messaging-01">
5169<t>
5170  Closed issues:
5171  <list style="symbols"> 
5172    <t>
5173      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5174      "Bodies on GET (and other) requests"
5175    </t>
5176    <t>
5177      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5178      "Updating to RFC4288"
5179    </t>
5180    <t>
5181      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5182      "Status Code and Reason Phrase"
5183    </t>
5184    <t>
5185      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5186      "rel_path not used"
5187    </t>
5188  </list>
5189</t>
5190<t>
5191  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5192  <list style="symbols"> 
5193    <t>
5194      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5195      "trailer-part").
5196    </t>
5197    <t>
5198      Avoid underscore character in rule names ("http_URL" ->
5199      "http-URL", "abs_path" -> "path-absolute").
5200    </t>
5201    <t>
5202      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5203      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5204      have to be updated when switching over to RFC3986.
5205    </t>
5206    <t>
5207      Synchronize core rules with RFC5234.
5208    </t>
5209    <t>
5210      Get rid of prose rules that span multiple lines.
5211    </t>
5212    <t>
5213      Get rid of unused rules LOALPHA and UPALPHA.
5214    </t>
5215    <t>
5216      Move "Product Tokens" section (back) into Part 1, as "token" is used
5217      in the definition of the Upgrade header field.
5218    </t>
5219    <t>
5220      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5221    </t>
5222    <t>
5223      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5224    </t>
5225  </list>
5226</t>
5227</section>
5228
5229<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5230<t>
5231  Closed issues:
5232  <list style="symbols"> 
5233    <t>
5234      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5235      "HTTP-date vs. rfc1123-date"
5236    </t>
5237    <t>
5238      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5239      "WS in quoted-pair"
5240    </t>
5241  </list>
5242</t>
5243<t>
5244  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5245  <list style="symbols"> 
5246    <t>
5247      Reference RFC 3984, and update header field registrations for headers defined
5248      in this document.
5249    </t>
5250  </list>
5251</t>
5252<t>
5253  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5254  <list style="symbols"> 
5255    <t>
5256      Replace string literals when the string really is case-sensitive (HTTP-version).
5257    </t>
5258  </list>
5259</t>
5260</section>
5261
5262<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5263<t>
5264  Closed issues:
5265  <list style="symbols"> 
5266    <t>
5267      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5268      "Connection closing"
5269    </t>
5270    <t>
5271      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5272      "Move registrations and registry information to IANA Considerations"
5273    </t>
5274    <t>
5275      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5276      "need new URL for PAD1995 reference"
5277    </t>
5278    <t>
5279      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5280      "IANA Considerations: update HTTP URI scheme registration"
5281    </t>
5282    <t>
5283      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5284      "Cite HTTPS URI scheme definition"
5285    </t>
5286    <t>
5287      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5288      "List-type headers vs Set-Cookie"
5289    </t>
5290  </list>
5291</t>
5292<t>
5293  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5294  <list style="symbols"> 
5295    <t>
5296      Replace string literals when the string really is case-sensitive (HTTP-Date).
5297    </t>
5298    <t>
5299      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5300    </t>
5301  </list>
5302</t>
5303</section>
5304
5305<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5306<t>
5307  Closed issues:
5308  <list style="symbols"> 
5309    <t>
5310      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5311      "Out-of-date reference for URIs"
5312    </t>
5313    <t>
5314      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5315      "RFC 2822 is updated by RFC 5322"
5316    </t>
5317  </list>
5318</t>
5319<t>
5320  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5321  <list style="symbols"> 
5322    <t>
5323      Use "/" instead of "|" for alternatives.
5324    </t>
5325    <t>
5326      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5327    </t>
5328    <t>
5329      Only reference RFC 5234's core rules.
5330    </t>
5331    <t>
5332      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5333      whitespace ("OWS") and required whitespace ("RWS").
5334    </t>
5335    <t>
5336      Rewrite ABNFs to spell out whitespace rules, factor out
5337      header field value format definitions.
5338    </t>
5339  </list>
5340</t>
5341</section>
5342
5343<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5344<t>
5345  Closed issues:
5346  <list style="symbols"> 
5347    <t>
5348      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5349      "Header LWS"
5350    </t>
5351    <t>
5352      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5353      "Sort 1.3 Terminology"
5354    </t>
5355    <t>
5356      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5357      "RFC2047 encoded words"
5358    </t>
5359    <t>
5360      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5361      "Character Encodings in TEXT"
5362    </t>
5363    <t>
5364      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5365      "Line Folding"
5366    </t>
5367    <t>
5368      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5369      "OPTIONS * and proxies"
5370    </t>
5371    <t>
5372      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5373      "reason-phrase BNF"
5374    </t>
5375    <t>
5376      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5377      "Use of TEXT"
5378    </t>
5379    <t>
5380      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5381      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5382    </t>
5383    <t>
5384      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5385      "RFC822 reference left in discussion of date formats"
5386    </t>
5387  </list>
5388</t>
5389<t>
5390  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5391  <list style="symbols"> 
5392    <t>
5393      Rewrite definition of list rules, deprecate empty list elements.
5394    </t>
5395    <t>
5396      Add appendix containing collected and expanded ABNF.
5397    </t>
5398  </list>
5399</t>
5400<t>
5401  Other changes:
5402  <list style="symbols"> 
5403    <t>
5404      Rewrite introduction; add mostly new Architecture Section.
5405    </t>
5406    <t>
5407      Move definition of quality values from Part 3 into Part 1;
5408      make TE request header field grammar independent of accept-params (defined in Part 3).
5409    </t>
5410  </list>
5411</t>
5412</section>
5413
5414<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5415<t>
5416  Closed issues:
5417  <list style="symbols"> 
5418    <t>
5419      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5420      "base for numeric protocol elements"
5421    </t>
5422    <t>
5423      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5424      "comment ABNF"
5425    </t>
5426  </list>
5427</t>
5428<t>
5429  Partly resolved issues:
5430  <list style="symbols"> 
5431    <t>
5432      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5433      "205 Bodies" (took out language that implied that there might be
5434      methods for which a request body MUST NOT be included)
5435    </t>
5436    <t>
5437      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5438      "editorial improvements around HTTP-date"
5439    </t>
5440  </list>
5441</t>
5442</section>
5443
5444<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5445<t>
5446  Closed issues:
5447  <list style="symbols"> 
5448    <t>
5449      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5450      "Repeating single-value headers"
5451    </t>
5452    <t>
5453      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5454      "increase connection limit"
5455    </t>
5456    <t>
5457      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5458      "IP addresses in URLs"
5459    </t>
5460    <t>
5461      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5462      "take over HTTP Upgrade Token Registry"
5463    </t>
5464    <t>
5465      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5466      "CR and LF in chunk extension values"
5467    </t>
5468    <t>
5469      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5470      "HTTP/0.9 support"
5471    </t>
5472    <t>
5473      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5474      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5475    </t>
5476    <t>
5477      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5478      "move definitions of gzip/deflate/compress to part 1"
5479    </t>
5480    <t>
5481      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5482      "disallow control characters in quoted-pair"
5483    </t>
5484  </list>
5485</t>
5486<t>
5487  Partly resolved issues:
5488  <list style="symbols"> 
5489    <t>
5490      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5491      "update IANA requirements wrt Transfer-Coding values" (add the
5492      IANA Considerations subsection)
5493    </t>
5494  </list>
5495</t>
5496</section>
5497
5498<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5499<t>
5500  Closed issues:
5501  <list style="symbols"> 
5502    <t>
5503      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5504      "header parsing, treatment of leading and trailing OWS"
5505    </t>
5506  </list>
5507</t>
5508<t>
5509  Partly resolved issues:
5510  <list style="symbols"> 
5511    <t>
5512      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5513      "Placement of 13.5.1 and 13.5.2"
5514    </t>
5515    <t>
5516      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5517      "use of term "word" when talking about header structure"
5518    </t>
5519  </list>
5520</t>
5521</section>
5522
5523<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5524<t>
5525  Closed issues:
5526  <list style="symbols"> 
5527    <t>
5528      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5529      "Clarification of the term 'deflate'"
5530    </t>
5531    <t>
5532      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5533      "OPTIONS * and proxies"
5534    </t>
5535    <t>
5536      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5537      "MIME-Version not listed in P1, general header fields"
5538    </t>
5539    <t>
5540      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5541      "IANA registry for content/transfer encodings"
5542    </t>
5543    <t>
5544      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5545      "Case-sensitivity of HTTP-date"
5546    </t>
5547    <t>
5548      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5549      "use of term "word" when talking about header structure"
5550    </t>
5551  </list>
5552</t>
5553<t>
5554  Partly resolved issues:
5555  <list style="symbols"> 
5556    <t>
5557      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5558      "Term for the requested resource's URI"
5559    </t>
5560  </list>
5561</t>
5562</section>
5563
5564<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5565<t>
5566  Closed issues:
5567  <list style="symbols">
5568    <t>
5569      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5570      "Connection Closing"
5571    </t>
5572    <t>
5573      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5574      "Delimiting messages with multipart/byteranges"
5575    </t>
5576    <t>
5577      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5578      "Handling multiple Content-Length headers"
5579    </t>
5580    <t>
5581      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5582      "Clarify entity / representation / variant terminology"
5583    </t>
5584    <t>
5585      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5586      "consider removing the 'changes from 2068' sections"
5587    </t>
5588  </list>
5589</t>
5590<t>
5591  Partly resolved issues:
5592  <list style="symbols"> 
5593    <t>
5594      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5595      "HTTP(s) URI scheme definitions"
5596    </t>
5597  </list>
5598</t>
5599</section>
5600
5601<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5602<t>
5603  Closed issues:
5604  <list style="symbols">
5605    <t>
5606      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5607      "Trailer requirements"
5608    </t>
5609    <t>
5610      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5611      "Text about clock requirement for caches belongs in p6"
5612    </t>
5613    <t>
5614      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5615      "effective request URI: handling of missing host in HTTP/1.0"
5616    </t>
5617    <t>
5618      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5619      "confusing Date requirements for clients"
5620    </t>
5621  </list>
5622</t>
5623<t>
5624  Partly resolved issues:
5625  <list style="symbols"> 
5626    <t>
5627      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5628      "Handling multiple Content-Length headers"
5629    </t>
5630  </list>
5631</t>
5632</section>
5633
5634<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5635<t>
5636  Closed issues:
5637  <list style="symbols">
5638    <t>
5639      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5640      "RFC2145 Normative"
5641    </t>
5642    <t>
5643      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5644      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5645    </t>
5646    <t>
5647      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5648      "define 'transparent' proxy"
5649    </t>
5650    <t>
5651      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5652      "Header Classification"
5653    </t>
5654    <t>
5655      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5656      "Is * usable as a request-uri for new methods?"
5657    </t>
5658    <t>
5659      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5660      "Migrate Upgrade details from RFC2817"
5661    </t>
5662    <t>
5663      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5664      "untangle ABNFs for header fields"
5665    </t>
5666    <t>
5667      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5668      "update RFC 2109 reference"
5669    </t>
5670  </list>
5671</t>
5672</section>
5673
5674<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5675<t>
5676  Closed issues:
5677  <list style="symbols">
5678    <t>
5679      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5680      "Allow is not in 13.5.2"
5681    </t>
5682    <t>
5683      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5684      "Handling multiple Content-Length headers"
5685    </t>
5686    <t>
5687      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5688      "untangle ABNFs for header fields"
5689    </t>
5690    <t>
5691      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5692      "Content-Length ABNF broken"
5693    </t>
5694  </list>
5695</t>
5696</section>
5697
5698<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5699<t>
5700  Closed issues:
5701  <list style="symbols">
5702    <t>
5703      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5704      "HTTP-version should be redefined as fixed length pair of DIGIT . DIGIT"
5705    </t>
5706    <t>
5707      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5708      "Recommend minimum sizes for protocol elements"
5709    </t>
5710    <t>
5711      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5712      "Set expectations around buffering"
5713    </t>
5714    <t>
5715      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5716      "Considering messages in isolation"
5717    </t>
5718  </list>
5719</t>
5720</section>
5721
5722<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5723<t>
5724  Closed issues:
5725  <list style="symbols">
5726    <t>
5727      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5728      "DNS Spoofing / DNS Binding advice"
5729    </t>
5730    <t>
5731      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5732      "move RFCs 2145, 2616, 2817 to Historic status"
5733    </t>
5734    <t>
5735      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5736      "\-escaping in quoted strings"
5737    </t>
5738    <t>
5739      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5740      "'Close' should be reserved in the HTTP header field registry"
5741    </t>
5742  </list>
5743</t>
5744</section>
5745
5746<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5747<t>
5748  Closed issues:
5749  <list style="symbols">
5750    <t>
5751      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5752      "Document HTTP's error-handling philosophy"
5753    </t>
5754    <t>
5755      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5756      "Explain header registration"
5757    </t>
5758    <t>
5759      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5760      "Revise Acknowledgements Sections"
5761    </t>
5762    <t>
5763      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5764      "Retrying Requests"
5765    </t>
5766    <t>
5767      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5768      "Closing the connection on server error"
5769    </t>
5770  </list>
5771</t>
5772</section>
5773
5774<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5775<t>
5776  Closed issues:
5777  <list style="symbols">
5778    <t>
5779      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/166"/>:
5780      "Clarify 'User Agent'"
5781    </t>
5782    <t>
5783      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/300"/>:
5784      "Define non-final responses"
5785    </t>
5786    <t>
5787      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
5788      "intended maturity level vs normative references"
5789    </t>
5790    <t>
5791      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/324"/>:
5792      "Intermediary rewriting of queries"
5793    </t>
5794    <t>
5795      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/158"/>:
5796      "Proxy-Connection and Keep-Alive"
5797    </t>
5798  </list>
5799</t>
5800</section>
5801
5802<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5803<t>
5804  Closed issues:
5805  <list style="symbols">
5806    <t>
5807      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
5808      "message-body in CONNECT response"
5809    </t>
5810    <t>
5811      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
5812      "Misplaced text on connection handling in p2"
5813    </t>
5814    <t>
5815      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/335"/>:
5816      "wording of line folding rule"
5817    </t>
5818    <t>
5819      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/343"/>:
5820      "chunk-extensions"
5821    </t>
5822    <t>
5823      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/346"/>:
5824      "make IANA policy definitions consistent"
5825    </t>
5826  </list>
5827</t>
5828</section>
5829
5830</section>
5831
5832</back>
5833</rfc>
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