source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1833

Last change on this file since 1833 was 1833, checked in by fielding@…, 10 years ago

mark-up some definitions and clarify a heading

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 249.4 KB
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=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "August">
16  <!ENTITY ID-YEAR "2012">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY Note "<x:h xmlns:x=''>Note:</x:h>">
19  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x=''/>">
20  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#response.cacheability' xmlns:x=''/>">
21  <!ENTITY payload                "<xref target='Part2' xmlns:x=''/>">
22  <!ENTITY media-types            "<xref target='Part2' x:rel='#media.types' xmlns:x=''/>">
23  <!ENTITY content-codings        "<xref target='Part2' x:rel='#content.codings' xmlns:x=''/>">
24  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x=''/>">
25  <!ENTITY content.negotiation    "<xref target='Part2' x:rel='#content.negotiation' xmlns:x=''/>">
26  <!ENTITY diff-mime              "<xref target='Part2' x:rel='#differences.between.http.and.mime' xmlns:x=''/>">
27  <!ENTITY representation         "<xref target='Part2' x:rel='#representation' xmlns:x=''/>">
28  <!ENTITY header-allow           "<xref target='Part2' x:rel='#header.allow' xmlns:x=''/>">
29  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
30  <!ENTITY header-content-encoding    "<xref target='Part2' x:rel='#header.content-encoding' xmlns:x=''/>">
31  <!ENTITY header-content-location    "<xref target='Part2' x:rel='#header.content-location' xmlns:x=''/>">
32  <!ENTITY header-content-range   "<xref target='Part5' x:rel='#header.content-range' xmlns:x=''/>">
33  <!ENTITY header-content-type    "<xref target='Part2' x:rel='#header.content-type' xmlns:x=''/>">
34  <!ENTITY header-date            "<xref target='Part2' x:rel='' xmlns:x=''/>">
35  <!ENTITY header-etag            "<xref target='Part4' x:rel='#header.etag' xmlns:x=''/>">
36  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x=''/>">
37  <!ENTITY header-expires         "<xref target='Part6' x:rel='#header.expires' xmlns:x=''/>">
38  <!ENTITY header-last-modified   "<xref target='Part4' x:rel='#header.last-modified' xmlns:x=''/>">
39  <!ENTITY header-mime-version    "<xref target='Part2' x:rel='#mime-version' xmlns:x=''/>">
40  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
41  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x=''/>">
42  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x=''/>">
43  <!ENTITY header-server          "<xref target='Part2' x:rel='#header.server' xmlns:x=''/>">
44  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
45  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x=''/>">
46  <!ENTITY methods                "<xref target='Part2' x:rel='#methods' xmlns:x=''/>">
47  <!ENTITY OPTIONS                "<xref target='Part2' x:rel='#OPTIONS' xmlns:x=''/>">
48  <!ENTITY qvalue                 "<xref target='Part2' x:rel='#quality.values' xmlns:x=''/>">
49  <!ENTITY status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
50  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
51  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
52  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x=''/>">
53  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x=''/>">
54  <!ENTITY status-304             "<xref target='Part4' x:rel='#status.304' xmlns:x=''/>">
55  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x=''/>">
56  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
57  <!ENTITY cons-new-header-fields "<xref target='Part2' x:rel='#considerations.for.creating.header.fields' xmlns:x=''/>">
59<?rfc toc="yes" ?>
60<?rfc symrefs="yes" ?>
61<?rfc sortrefs="yes" ?>
62<?rfc compact="yes"?>
63<?rfc subcompact="no" ?>
64<?rfc linkmailto="no" ?>
65<?rfc editing="no" ?>
66<?rfc comments="yes"?>
67<?rfc inline="yes"?>
68<?rfc rfcedstyle="yes"?>
69<?rfc-ext allow-markup-in-artwork="yes" ?>
70<?rfc-ext include-references-in-index="yes" ?>
71<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="proposed"
72     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
73     xmlns:x=''>
74<x:link rel="next" basename="p2-semantics"/>
75<x:feedback template="{docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
78  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: Message Routing and Syntax"</title>
80  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
81    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
82    <address>
83      <postal>
84        <street>345 Park Ave</street>
85        <city>San Jose</city>
86        <region>CA</region>
87        <code>95110</code>
88        <country>USA</country>
89      </postal>
90      <email></email>
91      <uri></uri>
92    </address>
93  </author>
95  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
96    <organization abbrev="W3C">World Wide Web Consortium</organization>
97    <address>
98      <postal>
99        <street>W3C / ERCIM</street>
100        <street>2004, rte des Lucioles</street>
101        <city>Sophia-Antipolis</city>
102        <region>AM</region>
103        <code>06902</code>
104        <country>France</country>
105      </postal>
106      <email></email>
107      <uri></uri>
108    </address>
109  </author>
111  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
112    <organization abbrev="greenbytes">greenbytes GmbH</organization>
113    <address>
114      <postal>
115        <street>Hafenweg 16</street>
116        <city>Muenster</city><region>NW</region><code>48155</code>
117        <country>Germany</country>
118      </postal>
119      <email></email>
120      <uri></uri>
121    </address>
122  </author>
124  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
125  <workgroup>HTTPbis Working Group</workgroup>
129   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
130   distributed, collaborative, hypertext information systems. HTTP has been in
131   use by the World Wide Web global information initiative since 1990.
132   This document provides an overview of HTTP architecture and its associated
133   terminology, defines the "http" and "https" Uniform Resource Identifier
134   (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements,
135   and describes general security concerns for implementations.
139<note title="Editorial Note (To be removed by RFC Editor)">
140  <t>
141    Discussion of this draft takes place on the HTTPBIS working group
142    mailing list (, which is archived at
143    <eref target=""/>.
144  </t>
145  <t>
146    The current issues list is at
147    <eref target=""/> and related
148    documents (including fancy diffs) can be found at
149    <eref target=""/>.
150  </t>
151  <t>
152    The changes in this draft are summarized in <xref target="changes.since.20"/>.
153  </t>
157<section title="Introduction" anchor="introduction">
159   The Hypertext Transfer Protocol (HTTP) is an application-level
160   request/response protocol that uses extensible semantics and MIME-like
161   message payloads for flexible interaction with network-based hypertext
162   information systems. This document is the first in a series of documents
163   that collectively form the HTTP/1.1 specification:
164   <list style="empty">
165    <t>RFC xxx1: Message Routing and Syntax</t>
166    <t><xref target="Part2" x:fmt="none">RFC xxx2</xref>: Semantics and Payloads</t>
167    <t><xref target="Part4" x:fmt="none">RFC xxx3</xref>: Conditional Requests</t>
168    <t><xref target="Part5" x:fmt="none">RFC xxx4</xref>: Range Requests</t>
169    <t><xref target="Part6" x:fmt="none">RFC xxx5</xref>: Caching</t>
170    <t><xref target="Part7" x:fmt="none">RFC xxx6</xref>: Authentication</t>
171   </list>
174   This HTTP/1.1 specification obsoletes and moves to historic status
175   <xref target="RFC2616" x:fmt="none">RFC 2616</xref>, its predecessor
176   <xref target="RFC2068" x:fmt="none">RFC 2068</xref>,
177   <xref target="RFC2145" x:fmt="none">RFC 2145</xref> (on HTTP versioning),
178   and <xref target="RFC2817" x:fmt="none">RFC 2817</xref> (on using CONNECT
179   for TLS upgrades).
182   HTTP is a generic interface protocol for information systems. It is
183   designed to hide the details of how a service is implemented by presenting
184   a uniform interface to clients that is independent of the types of
185   resources provided. Likewise, servers do not need to be aware of each
186   client's purpose: an HTTP request can be considered in isolation rather
187   than being associated with a specific type of client or a predetermined
188   sequence of application steps. The result is a protocol that can be used
189   effectively in many different contexts and for which implementations can
190   evolve independently over time.
193   HTTP is also designed for use as an intermediation protocol for translating
194   communication to and from non-HTTP information systems.
195   HTTP proxies and gateways can provide access to alternative information
196   services by translating their diverse protocols into a hypertext
197   format that can be viewed and manipulated by clients in the same way
198   as HTTP services.
201   One consequence of HTTP flexibility is that the protocol cannot be
202   defined in terms of what occurs behind the interface. Instead, we
203   are limited to defining the syntax of communication, the intent
204   of received communication, and the expected behavior of recipients.
205   If the communication is considered in isolation, then successful
206   actions ought to be reflected in corresponding changes to the
207   observable interface provided by servers. However, since multiple
208   clients might act in parallel and perhaps at cross-purposes, we
209   cannot require that such changes be observable beyond the scope
210   of a single response.
213   This document describes the architectural elements that are used or
214   referred to in HTTP, defines the "http" and "https" URI schemes,
215   describes overall network operation and connection management,
216   and defines HTTP message framing and forwarding requirements.
217   Our goal is to define all of the mechanisms necessary for HTTP message
218   handling that are independent of message semantics, thereby defining the
219   complete set of requirements for message parsers and
220   message-forwarding intermediaries.
224<section title="Requirement Notation" anchor="intro.requirements">
226   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
227   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
228   document are to be interpreted as described in <xref target="RFC2119"/>.
232<section title="Syntax Notation" anchor="notation">
233<iref primary="true" item="Grammar" subitem="ALPHA"/>
234<iref primary="true" item="Grammar" subitem="CR"/>
235<iref primary="true" item="Grammar" subitem="CRLF"/>
236<iref primary="true" item="Grammar" subitem="CTL"/>
237<iref primary="true" item="Grammar" subitem="DIGIT"/>
238<iref primary="true" item="Grammar" subitem="DQUOTE"/>
239<iref primary="true" item="Grammar" subitem="HEXDIG"/>
240<iref primary="true" item="Grammar" subitem="HTAB"/>
241<iref primary="true" item="Grammar" subitem="LF"/>
242<iref primary="true" item="Grammar" subitem="OCTET"/>
243<iref primary="true" item="Grammar" subitem="SP"/>
244<iref primary="true" item="Grammar" subitem="VCHAR"/>
246   This specification uses the Augmented Backus-Naur Form (ABNF) notation
247   of <xref target="RFC5234"/> with the list rule extension defined in
248   <xref target="abnf.extension"/>.  <xref target="collected.abnf"/> shows
249   the collected ABNF with the list rule expanded.
251<t anchor="core.rules">
252  <x:anchor-alias value="ALPHA"/>
253  <x:anchor-alias value="CTL"/>
254  <x:anchor-alias value="CR"/>
255  <x:anchor-alias value="CRLF"/>
256  <x:anchor-alias value="DIGIT"/>
257  <x:anchor-alias value="DQUOTE"/>
258  <x:anchor-alias value="HEXDIG"/>
259  <x:anchor-alias value="HTAB"/>
260  <x:anchor-alias value="LF"/>
261  <x:anchor-alias value="OCTET"/>
262  <x:anchor-alias value="SP"/>
263  <x:anchor-alias value="VCHAR"/>
264   The following core rules are included by
265   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
266   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
267   DIGIT (decimal 0-9), DQUOTE (double quote),
268   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
269   OCTET (any 8-bit sequence of data), SP (space), and
270   VCHAR (any visible <xref target="USASCII"/> character).
273   As a convention, ABNF rule names prefixed with "obs-" denote
274   "obsolete" grammar rules that appear for historical reasons.
279<section title="Architecture" anchor="architecture">
281   HTTP was created for the World Wide Web architecture
282   and has evolved over time to support the scalability needs of a worldwide
283   hypertext system. Much of that architecture is reflected in the terminology
284   and syntax productions used to define HTTP.
287<section title="Client/Server Messaging" anchor="operation">
288<iref primary="true" item="client"/>
289<iref primary="true" item="server"/>
290<iref primary="true" item="connection"/>
292   HTTP is a stateless request/response protocol that operates by exchanging
293   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
294   transport or session-layer
295   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
296   program that establishes a connection to a server for the purpose of
297   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
298   program that accepts connections in order to service HTTP requests by
299   sending HTTP responses.
301<iref primary="true" item="user agent"/>
302<iref primary="true" item="origin server"/>
303<iref primary="true" item="browser"/>
304<iref primary="true" item="spider"/>
305<iref primary="true" item="sender"/>
306<iref primary="true" item="recipient"/>
308   The terms client and server refer only to the roles that
309   these programs perform for a particular connection.  The same program
310   might act as a client on some connections and a server on others.  We use
311   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
312   such as a WWW browser, editor, or spider (web-traversing robot), and
313   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
314   authoritative responses to a request.  For general requirements, we use
315   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
316   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
317   message.
320   HTTP relies upon the Uniform Resource Identifier (URI)
321   standard <xref target="RFC3986"/> to indicate the target resource
322   (<xref target="target-resource"/>) and relationships between resources.
323   Messages are passed in a format similar to that used by Internet mail
324   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
325   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
326   between HTTP and MIME messages).
329   Most HTTP communication consists of a retrieval request (GET) for
330   a representation of some resource identified by a URI.  In the
331   simplest case, this might be accomplished via a single bidirectional
332   connection (===) between the user agent (UA) and the origin server (O).
334<figure><artwork type="drawing">
335         request   &gt;
336    <x:highlight>UA</x:highlight> ======================================= <x:highlight>O</x:highlight>
337                                &lt;   response
339<iref primary="true" item="message"/>
340<iref primary="true" item="request"/>
341<iref primary="true" item="response"/>
343   A client sends an HTTP request to a server in the form of a <x:dfn>request</x:dfn>
344   message, beginning with a request-line that includes a method, URI, and
345   protocol version (<xref target="request.line"/>),
346   followed by header fields containing
347   request modifiers, client information, and representation metadata
348   (<xref target="header.fields"/>),
349   an empty line to indicate the end of the header section, and finally
350   a message body containing the payload body (if any,
351   <xref target="message.body"/>).
354   A server responds to a client's request by sending one or more HTTP
355   <x:dfn>response</x:dfn>
356   messages, each beginning with a status line that
357   includes the protocol version, a success or error code, and textual
358   reason phrase (<xref target="status.line"/>),
359   possibly followed by header fields containing server
360   information, resource metadata, and representation metadata
361   (<xref target="header.fields"/>),
362   an empty line to indicate the end of the header section, and finally
363   a message body containing the payload body (if any,
364   <xref target="message.body"/>).
367   The following example illustrates a typical message exchange for a
368   GET request on the URI "":
371client request:
372</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
373GET /hello.txt HTTP/1.1
374User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
376Accept-Language: en, mi
380server response:
381</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
382HTTP/1.1 200 OK
383Date: Mon, 27 Jul 2009 12:28:53 GMT
384Server: Apache
385Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
386ETag: "34aa387-d-1568eb00"
387Accept-Ranges: bytes
388Content-Length: <x:length-of target="exbody"/>
389Vary: Accept-Encoding
390Content-Type: text/plain
392<x:span anchor="exbody">Hello World!
396<section title="Implementation Diversity" anchor="implementation-diversity">
398   When considering the design of HTTP, it is easy to fall into a trap of
399   thinking that all user agents are general-purpose browsers and all origin
400   servers are large public websites. That is not the case in practice.
401   Common HTTP user agents include household appliances, stereos, scales,
402   firmware update scripts, command-line programs, mobile apps,
403   and communication devices in a multitude of shapes and sizes.  Likewise,
404   common HTTP origin servers include home automation units, configurable
405   networking components, office machines, autonomous robots, news feeds,
406   traffic cameras, ad selectors, and video delivery platforms.
409   The term "user agent" does not imply that there is a human user directly
410   interacting with the software agent at the time of a request. In many
411   cases, a user agent is installed or configured to run in the background
412   and save its results for later inspection (or save only a subset of those
413   results that might be interesting or erroneous). Spiders, for example, are
414   typically given a start URI and configured to follow certain behavior while
415   crawling the Web as a hypertext graph.
418   The implementation diversity of HTTP means that we cannot assume the
419   user agent can make interactive suggestions to a user or provide adequate
420   warning for security or privacy options.  In the few cases where this
421   specification requires reporting of errors to the user, it is acceptable
422   for such reporting to only be observable in an error console or log file.
423   Likewise, requirements that an automated action be confirmed by the user
424   before proceeding can me met via advance configuration choices,
425   run-time options, or simply not proceeding with the unsafe action.
429<section title="Connections and Transport Independence" anchor="transport-independence">
431   HTTP messaging is independent of the underlying transport or
432   session-layer connection protocol(s).  HTTP only presumes a reliable
433   transport with in-order delivery of requests and the corresponding
434   in-order delivery of responses.  The mapping of HTTP request and
435   response structures onto the data units of the underlying transport
436   protocol is outside the scope of this specification.
439   The specific connection protocols to be used for an interaction
440   are determined by client configuration and the target URI
441   (<xref target="target-resource"/>).
442   For example, the "http" URI scheme
443   (<xref target="http.uri"/>) indicates a default connection of TCP
444   over IP, with a default TCP port of 80, but the client might be
445   configured to use a proxy via some other connection port or protocol
446   instead of using the defaults.
449   A connection might be used for multiple HTTP request/response exchanges,
450   as defined in <xref target="persistent.connections"/>.
454<section title="Intermediaries" anchor="intermediaries">
455<iref primary="true" item="intermediary"/>
457   HTTP enables the use of intermediaries to satisfy requests through
458   a chain of connections.  There are three common forms of HTTP
459   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
460   a single intermediary might act as an origin server, proxy, gateway,
461   or tunnel, switching behavior based on the nature of each request.
463<figure><artwork type="drawing">
464         &gt;             &gt;             &gt;             &gt;
465    <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>
466               &lt;             &lt;             &lt;             &lt;
469   The figure above shows three intermediaries (A, B, and C) between the
470   user agent and origin server. A request or response message that
471   travels the whole chain will pass through four separate connections.
472   Some HTTP communication options
473   might apply only to the connection with the nearest, non-tunnel
474   neighbor, only to the end-points of the chain, or to all connections
475   along the chain. Although the diagram is linear, each participant might
476   be engaged in multiple, simultaneous communications. For example, B
477   might be receiving requests from many clients other than A, and/or
478   forwarding requests to servers other than C, at the same time that it
479   is handling A's request.
482<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
483<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
484   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
485   to describe various requirements in relation to the directional flow of a
486   message: all messages flow from upstream to downstream.
487   Likewise, we use the terms inbound and outbound to refer to
488   directions in relation to the request path:
489   "<x:dfn>inbound</x:dfn>" means toward the origin server and
490   "<x:dfn>outbound</x:dfn>" means toward the user agent.
492<t><iref primary="true" item="proxy"/>
493   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
494   client, usually via local configuration rules, to receive requests
495   for some type(s) of absolute URI and attempt to satisfy those
496   requests via translation through the HTTP interface.  Some translations
497   are minimal, such as for proxy requests for "http" URIs, whereas
498   other requests might require translation to and from entirely different
499   application-layer protocols. Proxies are often used to group an
500   organization's HTTP requests through a common intermediary for the
501   sake of security, annotation services, or shared caching.
504<iref primary="true" item="transforming proxy"/>
505<iref primary="true" item="non-transforming proxy"/>
506   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
507   or configured to modify request or response messages in a semantically
508   meaningful way (i.e., modifications, beyond those required by normal
509   HTTP processing, that change the message in a way that would be
510   significant to the original sender or potentially significant to
511   downstream recipients).  For example, a transforming proxy might be
512   acting as a shared annotation server (modifying responses to include
513   references to a local annotation database), a malware filter, a
514   format transcoder, or an intranet-to-Internet privacy filter.  Such
515   transformations are presumed to be desired by the client (or client
516   organization) that selected the proxy and are beyond the scope of
517   this specification.  However, when a proxy is not intended to transform
518   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
519   requirements that preserve HTTP message semantics. See &status-203; and
520   &header-warning; for status and warning codes related to transformations.
522<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
523<iref primary="true" item="accelerator"/>
524   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
525   is a receiving agent that acts
526   as a layer above some other server(s) and translates the received
527   requests to the underlying server's protocol.  Gateways are often
528   used to encapsulate legacy or untrusted information services, to
529   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
530   enable partitioning or load-balancing of HTTP services across
531   multiple machines.
534   A gateway behaves as an origin server on its outbound connection and
535   as a user agent on its inbound connection.
536   All HTTP requirements applicable to an origin server
537   also apply to the outbound communication of a gateway.
538   A gateway communicates with inbound servers using any protocol that
539   it desires, including private extensions to HTTP that are outside
540   the scope of this specification.  However, an HTTP-to-HTTP gateway
541   that wishes to interoperate with third-party HTTP servers &MUST;
542   conform to HTTP user agent requirements on the gateway's inbound
543   connection and &MUST; implement the <x:ref>Connection</x:ref>
544   (<xref target="header.connection"/>) and <x:ref>Via</x:ref>
545   (<xref target="header.via"/>) header fields for both connections.
547<t><iref primary="true" item="tunnel"/>
548   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
549   without changing the messages. Once active, a tunnel is not
550   considered a party to the HTTP communication, though the tunnel might
551   have been initiated by an HTTP request. A tunnel ceases to exist when
552   both ends of the relayed connection are closed. Tunnels are used to
553   extend a virtual connection through an intermediary, such as when
554   transport-layer security is used to establish confidential communication
555   through a shared firewall proxy.
557<t><iref primary="true" item="interception proxy"/>
558<iref primary="true" item="transparent proxy"/>
559<iref primary="true" item="captive portal"/>
560   The above categories for intermediary only consider those acting as
561   participants in the HTTP communication.  There are also intermediaries
562   that can act on lower layers of the network protocol stack, filtering or
563   redirecting HTTP traffic without the knowledge or permission of message
564   senders. Network intermediaries often introduce security flaws or
565   interoperability problems by violating HTTP semantics.  For example, an
566   "<x:dfn>interception proxy</x:dfn>" <xref target="RFC3040"/> (also commonly
567   known as a "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/> or
568   "<x:dfn>captive portal</x:dfn>")
569   differs from an HTTP proxy because it is not selected by the client.
570   Instead, an interception proxy filters or redirects outgoing TCP port 80
571   packets (and occasionally other common port traffic).
572   Interception proxies are commonly found on public network access points,
573   as a means of enforcing account subscription prior to allowing use of
574   non-local Internet services, and within corporate firewalls to enforce
575   network usage policies.
576   They are indistinguishable from a man-in-the-middle attack.
579   HTTP is defined as a stateless protocol, meaning that each request message
580   can be understood in isolation.  Many implementations depend on HTTP's
581   stateless design in order to reuse proxied connections or dynamically
582   load balance requests across multiple servers.  Hence, servers &MUST-NOT;
583   assume that two requests on the same connection are from the same user
584   agent unless the connection is secured and specific to that agent.
585   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
586   been known to violate this requirement, resulting in security and
587   interoperability problems.
591<section title="Caches" anchor="caches">
592<iref primary="true" item="cache"/>
594   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
595   subsystem that controls its message storage, retrieval, and deletion.
596   A cache stores cacheable responses in order to reduce the response
597   time and network bandwidth consumption on future, equivalent
598   requests. Any client or server &MAY; employ a cache, though a cache
599   cannot be used by a server while it is acting as a tunnel.
602   The effect of a cache is that the request/response chain is shortened
603   if one of the participants along the chain has a cached response
604   applicable to that request. The following illustrates the resulting
605   chain if B has a cached copy of an earlier response from O (via C)
606   for a request which has not been cached by UA or A.
608<figure><artwork type="drawing">
609            &gt;             &gt;
610       <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>
611                  &lt;             &lt;
613<t><iref primary="true" item="cacheable"/>
614   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
615   the response message for use in answering subsequent requests.
616   Even when a response is cacheable, there might be additional
617   constraints placed by the client or by the origin server on when
618   that cached response can be used for a particular request. HTTP
619   requirements for cache behavior and cacheable responses are
620   defined in &caching-overview;. 
623   There are a wide variety of architectures and configurations
624   of caches and proxies deployed across the World Wide Web and
625   inside large organizations. These systems include national hierarchies
626   of proxy caches to save transoceanic bandwidth, systems that
627   broadcast or multicast cache entries, organizations that distribute
628   subsets of cached data via optical media, and so on.
632<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
634   This specification targets conformance criteria according to the role of
635   a participant in HTTP communication.  Hence, HTTP requirements are placed
636   on senders, recipients, clients, servers, user agents, intermediaries,
637   origin servers, proxies, gateways, or caches, depending on what behavior
638   is being constrained by the requirement.
641   The verb "generate" is used instead of "send" where a requirement
642   differentiates between creating a protocol element and merely forwarding a
643   received element downstream.
646   An implementation is considered conformant if it complies with all of the
647   requirements associated with the roles it partakes in HTTP. Note that
648   SHOULD-level requirements are relevant here, unless one of the documented
649   exceptions is applicable.
652   In addition to the prose requirements placed upon them, senders &MUST-NOT;
653   generate protocol elements that do not match the grammar defined by the
654   ABNF rules for those protocol elements that are applicable to the sender's
655   role. If a received protocol element is processed, the recipient &MUST; be
656   able to parse any value that would match the ABNF rules for that protocol
657   element, excluding only those rules not applicable to the recipient's role.
660   Unless noted otherwise, a recipient &MAY; attempt to recover a usable
661   protocol element from an invalid construct.  HTTP does not define
662   specific error handling mechanisms except when they have a direct impact
663   on security, since different applications of the protocol require
664   different error handling strategies.  For example, a Web browser might
665   wish to transparently recover from a response where the
666   <x:ref>Location</x:ref> header field doesn't parse according to the ABNF,
667   whereas a systems control client might consider any form of error recovery
668   to be dangerous.
672<section title="Protocol Versioning" anchor="http.version">
673  <x:anchor-alias value="HTTP-version"/>
674  <x:anchor-alias value="HTTP-name"/>
676   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
677   versions of the protocol. This specification defines version "1.1".
678   The protocol version as a whole indicates the sender's conformance
679   with the set of requirements laid out in that version's corresponding
680   specification of HTTP.
683   The version of an HTTP message is indicated by an HTTP-version field
684   in the first line of the message. HTTP-version is case-sensitive.
686<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/>
687  <x:ref>HTTP-version</x:ref>  = <x:ref>HTTP-name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
688  <x:ref>HTTP-name</x:ref>     = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
691   The HTTP version number consists of two decimal digits separated by a "."
692   (period or decimal point).  The first digit ("major version") indicates the
693   HTTP messaging syntax, whereas the second digit ("minor version") indicates
694   the highest minor version to which the sender is
695   conformant and able to understand for future communication.  The minor
696   version advertises the sender's communication capabilities even when the
697   sender is only using a backwards-compatible subset of the protocol,
698   thereby letting the recipient know that more advanced features can
699   be used in response (by servers) or in future requests (by clients).
702   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
703   <xref target="RFC1945"/> or a recipient whose version is unknown,
704   the HTTP/1.1 message is constructed such that it can be interpreted
705   as a valid HTTP/1.0 message if all of the newer features are ignored.
706   This specification places recipient-version requirements on some
707   new features so that a conformant sender will only use compatible
708   features until it has determined, through configuration or the
709   receipt of a message, that the recipient supports HTTP/1.1.
712   The interpretation of a header field does not change between minor
713   versions of the same major HTTP version, though the default
714   behavior of a recipient in the absence of such a field can change.
715   Unless specified otherwise, header fields defined in HTTP/1.1 are
716   defined for all versions of HTTP/1.x.  In particular, the <x:ref>Host</x:ref>
717   and <x:ref>Connection</x:ref> header fields ought to be implemented by all
718   HTTP/1.x implementations whether or not they advertise conformance with
719   HTTP/1.1.
722   New header fields can be defined such that, when they are
723   understood by a recipient, they might override or enhance the
724   interpretation of previously defined header fields.  When an
725   implementation receives an unrecognized header field, the recipient
726   &MUST; ignore that header field for local processing regardless of
727   the message's HTTP version.  An unrecognized header field received
728   by a proxy &MUST; be forwarded downstream unless the header field's
729   field-name is listed in the message's <x:ref>Connection</x:ref> header field
730   (see <xref target="header.connection"/>).
731   These requirements allow HTTP's functionality to be enhanced without
732   requiring prior update of deployed intermediaries.
735   Intermediaries that process HTTP messages (i.e., all intermediaries
736   other than those acting as tunnels) &MUST; send their own HTTP-version
737   in forwarded messages.  In other words, they &MUST-NOT; blindly
738   forward the first line of an HTTP message without ensuring that the
739   protocol version in that message matches a version to which that
740   intermediary is conformant for both the receiving and
741   sending of messages.  Forwarding an HTTP message without rewriting
742   the HTTP-version might result in communication errors when downstream
743   recipients use the message sender's version to determine what features
744   are safe to use for later communication with that sender.
747   An HTTP client &SHOULD; send a request version equal to the highest
748   version to which the client is conformant and
749   whose major version is no higher than the highest version supported
750   by the server, if this is known.  An HTTP client &MUST-NOT; send a
751   version to which it is not conformant.
754   An HTTP client &MAY; send a lower request version if it is known that
755   the server incorrectly implements the HTTP specification, but only
756   after the client has attempted at least one normal request and determined
757   from the response status or header fields (e.g., <x:ref>Server</x:ref>) that
758   the server improperly handles higher request versions.
761   An HTTP server &SHOULD; send a response version equal to the highest
762   version to which the server is conformant and
763   whose major version is less than or equal to the one received in the
764   request.  An HTTP server &MUST-NOT; send a version to which it is not
765   conformant.  A server &MAY; send a <x:ref>505 (HTTP Version Not
766   Supported)</x:ref> response if it cannot send a response using the
767   major version used in the client's request.
770   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
771   if it is known or suspected that the client incorrectly implements the
772   HTTP specification and is incapable of correctly processing later
773   version responses, such as when a client fails to parse the version
774   number correctly or when an intermediary is known to blindly forward
775   the HTTP-version even when it doesn't conform to the given minor
776   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
777   performed unless triggered by specific client attributes, such as when
778   one or more of the request header fields (e.g., <x:ref>User-Agent</x:ref>)
779   uniquely match the values sent by a client known to be in error.
782   The intention of HTTP's versioning design is that the major number
783   will only be incremented if an incompatible message syntax is
784   introduced, and that the minor number will only be incremented when
785   changes made to the protocol have the effect of adding to the message
786   semantics or implying additional capabilities of the sender.  However,
787   the minor version was not incremented for the changes introduced between
788   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
789   is specifically avoiding any such changes to the protocol.
793<section title="Uniform Resource Identifiers" anchor="uri">
794<iref primary="true" item="resource"/>
796   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
797   throughout HTTP as the means for identifying resources. URI references
798   are used to target requests, indicate redirects, and define relationships.
799   HTTP does not limit what a resource might be; it merely defines an interface
800   that can be used to interact with a resource via HTTP. More information on
801   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
803  <x:anchor-alias value="URI-reference"/>
804  <x:anchor-alias value="absolute-URI"/>
805  <x:anchor-alias value="relative-part"/>
806  <x:anchor-alias value="authority"/>
807  <x:anchor-alias value="path-abempty"/>
808  <x:anchor-alias value="path-absolute"/>
809  <x:anchor-alias value="port"/>
810  <x:anchor-alias value="query"/>
811  <x:anchor-alias value="uri-host"/>
812  <x:anchor-alias value="partial-URI"/>
814   This specification adopts the definitions of "URI-reference",
815   "absolute-URI", "relative-part", "port", "host",
816   "path-abempty", "path-absolute", "query", and "authority" from the
817   URI generic syntax <xref target="RFC3986"/>.
818   In addition, we define a partial-URI rule for protocol elements
819   that allow a relative URI but not a fragment.
821<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="URI-reference"><!--exported production--></iref><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"/><iref primary="true" item="Grammar" subitem="partial-URI"><!--exported production--></iref>
822  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
823  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
824  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
825  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
826  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
827  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
828  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
829  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
830  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
832  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
835   Each protocol element in HTTP that allows a URI reference will indicate
836   in its ABNF production whether the element allows any form of reference
837   (URI-reference), only a URI in absolute form (absolute-URI), only the
838   path and optional query components, or some combination of the above.
839   Unless otherwise indicated, URI references are parsed
840   relative to the effective request URI
841   (<xref target="effective.request.uri"/>).
844<section title="http URI scheme" anchor="http.uri">
845  <x:anchor-alias value="http-URI"/>
846  <iref item="http URI scheme" primary="true"/>
847  <iref item="URI scheme" subitem="http" primary="true"/>
849   The "http" URI scheme is hereby defined for the purpose of minting
850   identifiers according to their association with the hierarchical
851   namespace governed by a potential HTTP origin server listening for
852   TCP connections on a given port.
854<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"><!--terminal production--></iref>
855  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
858   The HTTP origin server is identified by the generic syntax's
859   <x:ref>authority</x:ref> component, which includes a host identifier
860   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
861   The remainder of the URI, consisting of both the hierarchical path
862   component and optional query component, serves as an identifier for
863   a potential resource within that origin server's name space.
866   If the host identifier is provided as an IP literal or IPv4 address,
867   then the origin server is any listener on the indicated TCP port at
868   that IP address. If host is a registered name, then that name is
869   considered an indirect identifier and the recipient might use a name
870   resolution service, such as DNS, to find the address of a listener
871   for that host.
872   The host &MUST-NOT; be empty; if an "http" URI is received with an
873   empty host, then it &MUST; be rejected as invalid.
874   If the port subcomponent is empty or not given, then TCP port 80 is
875   assumed (the default reserved port for WWW services).
878   Regardless of the form of host identifier, access to that host is not
879   implied by the mere presence of its name or address. The host might or might
880   not exist and, even when it does exist, might or might not be running an
881   HTTP server or listening to the indicated port. The "http" URI scheme
882   makes use of the delegated nature of Internet names and addresses to
883   establish a naming authority (whatever entity has the ability to place
884   an HTTP server at that Internet name or address) and allows that
885   authority to determine which names are valid and how they might be used.
888   When an "http" URI is used within a context that calls for access to the
889   indicated resource, a client &MAY; attempt access by resolving
890   the host to an IP address, establishing a TCP connection to that address
891   on the indicated port, and sending an HTTP request message
892   (<xref target="http.message"/>) containing the URI's identifying data
893   (<xref target="message.routing"/>) to the server.
894   If the server responds to that request with a non-interim HTTP response
895   message, as described in &status-codes;, then that response
896   is considered an authoritative answer to the client's request.
899   Although HTTP is independent of the transport protocol, the "http"
900   scheme is specific to TCP-based services because the name delegation
901   process depends on TCP for establishing authority.
902   An HTTP service based on some other underlying connection protocol
903   would presumably be identified using a different URI scheme, just as
904   the "https" scheme (below) is used for servers that require an SSL/TLS
905   transport layer on a connection. Other protocols might also be used to
906   provide access to "http" identified resources &mdash; it is only the
907   authoritative interface used for mapping the namespace that is
908   specific to TCP.
911   The URI generic syntax for authority also includes a deprecated
912   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
913   for including user authentication information in the URI.  Some
914   implementations make use of the userinfo component for internal
915   configuration of authentication information, such as within command
916   invocation options, configuration files, or bookmark lists, even
917   though such usage might expose a user identifier or password.
918   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
919   delimiter) when transmitting an "http" URI in a message.  Recipients
920   of HTTP messages that contain a URI reference &SHOULD; parse for the
921   existence of userinfo and treat its presence as an error, likely
922   indicating that the deprecated subcomponent is being used to obscure
923   the authority for the sake of phishing attacks.
927<section title="https URI scheme" anchor="https.uri">
928   <x:anchor-alias value="https-URI"/>
929   <iref item="https URI scheme"/>
930   <iref item="URI scheme" subitem="https"/>
932   The "https" URI scheme is hereby defined for the purpose of minting
933   identifiers according to their association with the hierarchical
934   namespace governed by a potential HTTP origin server listening for
935   SSL/TLS-secured connections on a given TCP port.
938   All of the requirements listed above for the "http" scheme are also
939   requirements for the "https" scheme, except that a default TCP port
940   of 443 is assumed if the port subcomponent is empty or not given,
941   and the TCP connection &MUST; be secured through the
942   use of strong encryption prior to sending the first HTTP request.
944<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"><!--terminal production--></iref>
945  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
948   Unlike the "http" scheme, responses to "https" identified requests
949   are never "public" and thus &MUST-NOT; be reused for shared caching.
950   They can, however, be reused in a private cache if the message is
951   cacheable by default in HTTP or specifically indicated as such by
952   the Cache-Control header field (&header-cache-control;).
955   Resources made available via the "https" scheme have no shared
956   identity with the "http" scheme even if their resource identifiers
957   indicate the same authority (the same host listening to the same
958   TCP port).  They are distinct name spaces and are considered to be
959   distinct origin servers.  However, an extension to HTTP that is
960   defined to apply to entire host domains, such as the Cookie protocol
961   <xref target="RFC6265"/>, can allow information
962   set by one service to impact communication with other services
963   within a matching group of host domains.
966   The process for authoritative access to an "https" identified
967   resource is defined in <xref target="RFC2818"/>.
971<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
973   Since the "http" and "https" schemes conform to the URI generic syntax,
974   such URIs are normalized and compared according to the algorithm defined
975   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
976   described above for each scheme.
979   If the port is equal to the default port for a scheme, the normal
980   form is to elide the port subcomponent. Likewise, an empty path
981   component is equivalent to an absolute path of "/", so the normal
982   form is to provide a path of "/" instead. The scheme and host
983   are case-insensitive and normally provided in lowercase; all
984   other components are compared in a case-sensitive manner.
985   Characters other than those in the "reserved" set are equivalent
986   to their percent-encoded octets (see <xref target="RFC3986"
987   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
990   For example, the following three URIs are equivalent:
992<figure><artwork type="example">
1001<section title="Message Format" anchor="http.message">
1002<x:anchor-alias value="generic-message"/>
1003<x:anchor-alias value="message.types"/>
1004<x:anchor-alias value="HTTP-message"/>
1005<x:anchor-alias value="start-line"/>
1006<iref item="header section"/>
1007<iref item="headers"/>
1008<iref item="header field"/>
1010   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1011   octets in a format similar to the Internet Message Format
1012   <xref target="RFC5322"/>: zero or more header fields (collectively
1013   referred to as the "headers" or the "header section"), an empty line
1014   indicating the end of the header section, and an optional message body.
1016<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"><!--terminal production--></iref>
1017  <x:ref>HTTP-message</x:ref>   = <x:ref>start-line</x:ref>
1018                   *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1019                   <x:ref>CRLF</x:ref>
1020                   [ <x:ref>message-body</x:ref> ]
1023   The normal procedure for parsing an HTTP message is to read the
1024   start-line into a structure, read each header field into a hash
1025   table by field name until the empty line, and then use the parsed
1026   data to determine if a message body is expected.  If a message body
1027   has been indicated, then it is read as a stream until an amount
1028   of octets equal to the message body length is read or the connection
1029   is closed.
1032   Recipients &MUST; parse an HTTP message as a sequence of octets in an
1033   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1034   Parsing an HTTP message as a stream of Unicode characters, without regard
1035   for the specific encoding, creates security vulnerabilities due to the
1036   varying ways that string processing libraries handle invalid multibyte
1037   character sequences that contain the octet LF (%x0A).  String-based
1038   parsers can only be safely used within protocol elements after the element
1039   has been extracted from the message, such as within a header field-value
1040   after message parsing has delineated the individual fields.
1043   An HTTP message can be parsed as a stream for incremental processing or
1044   forwarding downstream.  However, recipients cannot rely on incremental
1045   delivery of partial messages, since some implementations will buffer or
1046   delay message forwarding for the sake of network efficiency, security
1047   checks, or payload transformations.
1050<section title="Start Line" anchor="start.line">
1051  <x:anchor-alias value="Start-Line"/>
1053   An HTTP message can either be a request from client to server or a
1054   response from server to client.  Syntactically, the two types of message
1055   differ only in the start-line, which is either a request-line (for requests)
1056   or a status-line (for responses), and in the algorithm for determining
1057   the length of the message body (<xref target="message.body"/>).
1058   In theory, a client could receive requests and a server could receive
1059   responses, distinguishing them by their different start-line formats,
1060   but in practice servers are implemented to only expect a request
1061   (a response is interpreted as an unknown or invalid request method)
1062   and clients are implemented to only expect a response.
1064<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1065  <x:ref>start-line</x:ref>     = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1068   Implementations &MUST-NOT; send whitespace between the start-line and
1069   the first header field. The presence of such whitespace in a request
1070   might be an attempt to trick a server into ignoring that field or
1071   processing the line after it as a new request, either of which might
1072   result in a security vulnerability if other implementations within
1073   the request chain interpret the same message differently.
1074   Likewise, the presence of such whitespace in a response might be
1075   ignored by some clients or cause others to cease parsing.
1078<section title="Request Line" anchor="request.line">
1079  <x:anchor-alias value="Request"/>
1080  <x:anchor-alias value="request-line"/>
1082   A request-line begins with a method token, followed by a single
1083   space (SP), the request-target, another single space (SP), the
1084   protocol version, and ending with CRLF.
1086<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1087  <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>
1090   A server &MUST; be able to parse any received message that begins
1091   with a request-line and matches the ABNF rule for HTTP-message.
1093<iref primary="true" item="method"/>
1094<t anchor="method">
1095   The method token indicates the request method to be performed on the
1096   target resource. The request method is case-sensitive.
1098<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1099  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1102   The methods defined by this specification can be found in
1103   &methods;, along with information regarding the HTTP method registry
1104   and considerations for defining new methods.
1106<iref item="request-target"/>
1108   The request-target identifies the target resource upon which to apply
1109   the request, as defined in <xref target="request-target"/>.
1112   No whitespace is allowed inside the method, request-target, and
1113   protocol version.  Hence, recipients typically parse the request-line
1114   into its component parts by splitting on the SP characters.
1117   Unfortunately, some user agents fail to properly encode hypertext
1118   references that have embedded whitespace, sending the characters
1119   directly instead of properly percent-encoding the disallowed characters.
1120   Recipients of an invalid request-line &SHOULD; respond with either a
1121   <x:ref>400 (Bad Request)</x:ref> error or a <x:ref>301 (Moved Permanently)</x:ref>
1122   redirect with the request-target properly encoded.  Recipients &SHOULD-NOT;
1123   attempt to autocorrect and then process the request without a redirect,
1124   since the invalid request-line might be deliberately crafted to bypass
1125   security filters along the request chain.
1128   HTTP does not place a pre-defined limit on the length of a request-line.
1129   A server that receives a method longer than any that it implements
1130   &SHOULD; respond with either a <x:ref>405 (Method Not Allowed)</x:ref>, if it is an origin
1131   server, or a <x:ref>501 (Not Implemented)</x:ref> status code.
1132   A server &MUST; be prepared to receive URIs of unbounded length and
1133   respond with the <x:ref>414 (URI Too Long)</x:ref> status code if the received
1134   request-target would be longer than the server wishes to handle
1135   (see &status-414;).
1138   Various ad-hoc limitations on request-line length are found in practice.
1139   It is &RECOMMENDED; that all HTTP senders and recipients support, at a
1140   minimum, request-line lengths of up to 8000 octets.
1144<section title="Status Line" anchor="status.line">
1145  <x:anchor-alias value="response"/>
1146  <x:anchor-alias value="status-line"/>
1147  <x:anchor-alias value="status-code"/>
1148  <x:anchor-alias value="reason-phrase"/>
1150   The first line of a response message is the status-line, consisting
1151   of the protocol version, a space (SP), the status code, another space,
1152   a possibly-empty textual phrase describing the status code, and
1153   ending with CRLF.
1155<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1156  <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>
1159   A client &MUST; be able to parse any received message that begins
1160   with a status-line and matches the ABNF rule for HTTP-message.
1163   The status-code element is a 3-digit integer code describing the
1164   result of the server's attempt to understand and satisfy the client's
1165   corresponding request. The rest of the response message is to be
1166   interpreted in light of the semantics defined for that status code.
1167   See &status-codes; for information about the semantics of status codes,
1168   including the classes of status code (indicated by the first digit),
1169   the status codes defined by this specification, considerations for the
1170   definition of new status codes, and the IANA registry.
1172<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1173  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1176   The reason-phrase element exists for the sole purpose of providing a
1177   textual description associated with the numeric status code, mostly
1178   out of deference to earlier Internet application protocols that were more
1179   frequently used with interactive text clients. A client &SHOULD; ignore
1180   the reason-phrase content.
1182<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1183  <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> )
1188<section title="Header Fields" anchor="header.fields">
1189  <x:anchor-alias value="header-field"/>
1190  <x:anchor-alias value="field-content"/>
1191  <x:anchor-alias value="field-name"/>
1192  <x:anchor-alias value="field-value"/>
1193  <x:anchor-alias value="obs-fold"/>
1195   Each HTTP header field consists of a case-insensitive field name
1196   followed by a colon (":"), optional whitespace, and the field value.
1198<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"/>
1199  <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>
1200  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1201  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1202  <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> )
1203  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1204                 ; obsolete line folding
1205                 ; see <xref target="field.parsing"/>
1208   The field-name token labels the corresponding field-value as having the
1209   semantics defined by that header field.  For example, the <x:ref>Date</x:ref>
1210   header field is defined in &header-date; as containing the origination
1211   timestamp for the message in which it appears.
1214   HTTP header fields are fully extensible: there is no limit on the
1215   introduction of new field names, each presumably defining new semantics,
1216   or on the number of header fields used in a given message.  Existing
1217   fields are defined in each part of this specification and in many other
1218   specifications outside the standards process.
1219   New header fields can be introduced without changing the protocol version
1220   if their defined semantics allow them to be safely ignored by recipients
1221   that do not recognize them.
1224   New HTTP header fields &SHOULD; be registered with IANA according
1225   to the procedures in &cons-new-header-fields;.
1226   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1227   field-name is listed in the <x:ref>Connection</x:ref> header field
1228   (<xref target="header.connection"/>) or the proxy is specifically
1229   configured to block or otherwise transform such fields.
1230   Unrecognized header fields &SHOULD; be ignored by other recipients.
1233   The order in which header fields with differing field names are
1234   received is not significant. However, it is "good practice" to send
1235   header fields that contain control data first, such as <x:ref>Host</x:ref>
1236   on requests and <x:ref>Date</x:ref> on responses, so that implementations
1237   can decide when not to handle a message as early as possible.  A server
1238   &MUST; wait until the entire header section is received before interpreting
1239   a request message, since later header fields might include conditionals,
1240   authentication credentials, or deliberately misleading duplicate
1241   header fields that would impact request processing.
1244   Multiple header fields with the same field name &MUST-NOT; be
1245   sent in a message unless the entire field value for that
1246   header field is defined as a comma-separated list [i.e., #(values)].
1247   Multiple header fields with the same field name can be combined into
1248   one "field-name: field-value" pair, without changing the semantics of the
1249   message, by appending each subsequent field value to the combined
1250   field value in order, separated by a comma. The order in which
1251   header fields with the same field name are received is therefore
1252   significant to the interpretation of the combined field value;
1253   a proxy &MUST-NOT; change the order of these field values when
1254   forwarding a message.
1257  <t>
1258   &Note; The "Set-Cookie" header field as implemented in
1259   practice can occur multiple times, but does not use the list syntax, and
1260   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1261   for details.) Also note that the Set-Cookie2 header field specified in
1262   <xref target="RFC2965"/> does not share this problem.
1263  </t>
1266<section title="Whitespace" anchor="whitespace">
1267<t anchor="rule.LWS">
1268   This specification uses three rules to denote the use of linear
1269   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1270   BWS ("bad" whitespace).
1272<t anchor="rule.OWS">
1273   The OWS rule is used where zero or more linear whitespace octets might
1274   appear. OWS &SHOULD; either not be produced or be produced as a single
1275   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1276   be replaced with a single SP or transformed to all SP octets (each
1277   octet other than SP replaced with SP) before interpreting the field value
1278   or forwarding the message downstream.
1280<t anchor="rule.RWS">
1281   RWS is used when at least one linear whitespace octet is required to
1282   separate field tokens. RWS &SHOULD; be produced as a single SP.
1283   Multiple RWS octets that occur within field-content &SHOULD; either
1284   be replaced with a single SP or transformed to all SP octets before
1285   interpreting the field value or forwarding the message downstream.
1287<t anchor="rule.BWS">
1288   BWS is used where the grammar allows optional whitespace for historical
1289   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
1290   recipients &MUST; accept such bad optional whitespace and remove it before
1291   interpreting the field value or forwarding the message downstream.
1293<t anchor="rule.whitespace">
1294  <x:anchor-alias value="BWS"/>
1295  <x:anchor-alias value="OWS"/>
1296  <x:anchor-alias value="RWS"/>
1298<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"/>
1299  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1300                 ; "optional" whitespace
1301  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1302                 ; "required" whitespace
1303  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1304                 ; "bad" whitespace
1308<section title="Field Parsing" anchor="field.parsing">
1310   No whitespace is allowed between the header field-name and colon.
1311   In the past, differences in the handling of such whitespace have led to
1312   security vulnerabilities in request routing and response handling.
1313   Any received request message that contains whitespace between a header
1314   field-name and colon &MUST; be rejected with a response code of 400
1315   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1316   message before forwarding the message downstream.
1319   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1320   preferred. The field value does not include any leading or trailing white
1321   space: OWS occurring before the first non-whitespace octet of the
1322   field value or after the last non-whitespace octet of the field value
1323   is ignored and &SHOULD; be removed before further processing (as this does
1324   not change the meaning of the header field).
1327   Historically, HTTP header field values could be extended over multiple
1328   lines by preceding each extra line with at least one space or horizontal
1329   tab (obs-fold). This specification deprecates such line
1330   folding except within the message/http media type
1331   (<xref target=""/>).
1332   HTTP senders &MUST-NOT; produce messages that include line folding
1333   (i.e., that contain any field-value that matches the obs-fold rule) unless
1334   the message is intended for packaging within the message/http media type.
1335   HTTP recipients &SHOULD; accept line folding and replace any embedded
1336   obs-fold whitespace with either a single SP or a matching number of SP
1337   octets (to avoid buffer copying) prior to interpreting the field value or
1338   forwarding the message downstream.
1341   Historically, HTTP has allowed field content with text in the ISO-8859-1
1342   <xref target="ISO-8859-1"/> character encoding and supported other
1343   character sets only through use of <xref target="RFC2047"/> encoding.
1344   In practice, most HTTP header field values use only a subset of the
1345   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1346   header fields &SHOULD; limit their field values to US-ASCII octets.
1347   Recipients &SHOULD; treat other (obs-text) octets in field content as
1348   opaque data.
1352<section title="Field Length" anchor="field.length">
1354   HTTP does not place a pre-defined limit on the length of header fields,
1355   either in isolation or as a set. A server &MUST; be prepared to receive
1356   request header fields of unbounded length and respond with a <x:ref>4xx
1357   (Client Error)</x:ref> status code if the received header field(s) would be
1358   longer than the server wishes to handle.
1361   A client that receives response header fields that are longer than it wishes
1362   to handle can only treat it as a server error.
1365   Various ad-hoc limitations on header field length are found in practice. It
1366   is &RECOMMENDED; that all HTTP senders and recipients support messages whose
1367   combined header fields have 4000 or more octets.
1371<section title="Field value components" anchor="field.components">
1372<t anchor="rule.token.separators">
1373  <x:anchor-alias value="tchar"/>
1374  <x:anchor-alias value="token"/>
1375  <x:anchor-alias value="special"/>
1376  <x:anchor-alias value="word"/>
1377   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1378   separated by whitespace or special characters. These special characters
1379   &MUST; be in a quoted string to be used within a parameter value (as defined
1380   in <xref target="transfer.codings"/>).
1382<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"><!--unused production--></iref>
1383  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1385  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1387  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1388 -->
1389  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1390                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1391                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1392                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1394  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1395                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1396                 / "]" / "?" / "=" / "{" / "}"
1398<t anchor="rule.quoted-string">
1399  <x:anchor-alias value="quoted-string"/>
1400  <x:anchor-alias value="qdtext"/>
1401  <x:anchor-alias value="obs-text"/>
1402   A string of text is parsed as a single word if it is quoted using
1403   double-quote marks.
1405<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"/>
1406  <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>
1407  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1408  <x:ref>obs-text</x:ref>       = %x80-FF
1410<t anchor="rule.quoted-pair">
1411  <x:anchor-alias value="quoted-pair"/>
1412   The backslash octet ("\") can be used as a single-octet
1413   quoting mechanism within quoted-string constructs:
1415<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1416  <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> )
1419   Recipients that process the value of the quoted-string &MUST; handle a
1420   quoted-pair as if it were replaced by the octet following the backslash.
1423   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1424   escaping (i.e., other than DQUOTE and the backslash octet).
1426<t anchor="rule.comment">
1427  <x:anchor-alias value="comment"/>
1428  <x:anchor-alias value="ctext"/>
1429   Comments can be included in some HTTP header fields by surrounding
1430   the comment text with parentheses. Comments are only allowed in
1431   fields containing "comment" as part of their field value definition.
1433<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1434  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1435  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1437<t anchor="rule.quoted-cpair">
1438  <x:anchor-alias value="quoted-cpair"/>
1439   The backslash octet ("\") can be used as a single-octet
1440   quoting mechanism within comment constructs:
1442<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1443  <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> )
1446   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1447   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1453<section title="Message Body" anchor="message.body">
1454  <x:anchor-alias value="message-body"/>
1456   The message body (if any) of an HTTP message is used to carry the
1457   payload body of that request or response.  The message body is
1458   identical to the payload body unless a transfer coding has been
1459   applied, as described in <xref target="header.transfer-encoding"/>.
1461<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1462  <x:ref>message-body</x:ref> = *OCTET
1465   The rules for when a message body is allowed in a message differ for
1466   requests and responses.
1469   The presence of a message body in a request is signaled by a
1470   a <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1471   field. Request message framing is independent of method semantics,
1472   even if the method does not define any use for a message body.
1475   The presence of a message body in a response depends on both
1476   the request method to which it is responding and the response
1477   status code (<xref target="status.line"/>).
1478   Responses to the HEAD request method never include a message body
1479   because the associated response header fields (e.g.,
1480   <x:ref>Transfer-Encoding</x:ref>, <x:ref>Content-Length</x:ref>, etc.) only
1481   indicate what their values would have been if the request method had been
1482   GET. <x:ref>2xx (Successful)</x:ref> responses to CONNECT switch to tunnel
1483   mode instead of having a message body.
1484   All <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, and
1485   <x:ref>304 (Not Modified)</x:ref> responses &MUST-NOT; include a message body.
1486   All other responses do include a message body, although the body
1487   &MAY; be of zero length.
1490<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1491  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1492  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
1493  <x:anchor-alias value="Transfer-Encoding"/>
1495   When one or more transfer codings are applied to a payload body in order
1496   to form the message body, a Transfer-Encoding header field &MUST; be sent
1497   in the message and &MUST; contain the list of corresponding
1498   transfer-coding names in the same order that they were applied.
1499   Transfer codings are defined in <xref target="transfer.codings"/>.
1501<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1502  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1505   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1506   MIME, which was designed to enable safe transport of binary data over a
1507   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1508   However, safe transport has a different focus for an 8bit-clean transfer
1509   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1510   accurately delimit a dynamically generated payload and to distinguish
1511   payload encodings that are only applied for transport efficiency or
1512   security from those that are characteristics of the target resource.
1515   The "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1516   &MUST; be implemented by all HTTP/1.1 recipients because it plays a
1517   crucial role in delimiting messages when the payload body size is not
1518   known in advance.
1519   When the "chunked" transfer-coding is used, it &MUST; be the last
1520   transfer-coding applied to form the message body and &MUST-NOT;
1521   be applied more than once in a message body.
1522   If any transfer-coding is applied to a request payload body,
1523   the final transfer-coding applied &MUST; be "chunked".
1524   If any transfer-coding is applied to a response payload body, then either
1525   the final transfer-coding applied &MUST; be "chunked" or
1526   the message &MUST; be terminated by closing the connection.
1529   For example,
1530</preamble><artwork type="example">
1531  Transfer-Encoding: gzip, chunked
1533   indicates that the payload body has been compressed using the gzip
1534   coding and then chunked using the chunked coding while forming the
1535   message body.
1538   If more than one Transfer-Encoding header field is present in a message,
1539   the multiple field-values &MUST; be combined into one field-value,
1540   according to the algorithm defined in <xref target="header.fields"/>,
1541   before determining the message body length.
1544   Unlike <x:ref>Content-Encoding</x:ref> (&content-codings;),
1545   Transfer-Encoding is a property of the message, not of the payload, and thus
1546   &MAY; be added or removed by any implementation along the request/response
1547   chain. Additional information about the encoding parameters &MAY; be
1548   provided by other header fields not defined by this specification.
1551   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1552   <x:ref>304 (Not Modified)</x:ref> response (&status-304;) to a GET request,
1553   neither of which includes a message body,
1554   to indicate that the origin server would have applied a transfer coding
1555   to the message body if the request had been an unconditional GET.
1556   This indication is not required, however, because any recipient on
1557   the response chain (including the origin server) can remove transfer
1558   codings when they are not needed.
1561   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1562   implementations advertising only HTTP/1.0 support will not understand
1563   how to process a transfer-encoded payload.
1564   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1565   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1566   might be in the form of specific user configuration or by remembering the
1567   version of a prior received response.
1568   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1569   the corresponding request indicates HTTP/1.1 (or later).
1572   A server that receives a request message with a transfer-coding it does
1573   not understand &SHOULD; respond with <x:ref>501 (Not Implemented)</x:ref> and then
1574   close the connection.
1578<section title="Content-Length" anchor="header.content-length">
1579  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1580  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
1581  <x:anchor-alias value="Content-Length"/>
1583   When a message does not have a <x:ref>Transfer-Encoding</x:ref> header field
1584   and the payload body length can be determined prior to being transferred, a
1585   Content-Length header field &SHOULD; be sent to indicate the length of the
1586   payload body that is either present as the message body, for requests
1587   and non-HEAD responses other than <x:ref>304 (Not Modified)</x:ref>, or
1588   would have been present had the request been an unconditional GET.  The
1589   length is expressed as a decimal number of octets.
1591<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1592  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1595   An example is
1597<figure><artwork type="example">
1598  Content-Length: 3495
1601   In the case of a response to a HEAD request, Content-Length indicates
1602   the size of the payload body (without any potential transfer-coding)
1603   that would have been sent had the request been a GET.
1604   In the case of a <x:ref>304 (Not Modified)</x:ref> response (&status-304;)
1605   to a GET request, Content-Length indicates the size of the payload body (without
1606   any potential transfer-coding) that would have been sent in a <x:ref>200 (OK)</x:ref>
1607   response.
1610   Any Content-Length field value greater than or equal to zero is valid.
1611   Since there is no predefined limit to the length of an HTTP payload,
1612   recipients &SHOULD; anticipate potentially large decimal numerals and
1613   prevent parsing errors due to integer conversion overflows
1614   (<xref target="attack.protocol.element.size.overflows"/>).
1617   If a message is received that has multiple Content-Length header fields
1618   with field-values consisting of the same decimal value, or a single
1619   Content-Length header field with a field value containing a list of
1620   identical decimal values (e.g., "Content-Length: 42, 42"), indicating that
1621   duplicate Content-Length header fields have been generated or combined by an
1622   upstream message processor, then the recipient &MUST; either reject the
1623   message as invalid or replace the duplicated field-values with a single
1624   valid Content-Length field containing that decimal value prior to
1625   determining the message body length.
1628  <t>
1629   &Note; HTTP's use of Content-Length for message framing differs
1630   significantly from the same field's use in MIME, where it is an optional
1631   field used only within the "message/external-body" media-type.
1632  </t>
1636<section title="Message Body Length" anchor="message.body.length">
1638   The length of a message body is determined by one of the following
1639   (in order of precedence):
1642  <list style="numbers">
1643    <x:lt><t>
1644     Any response to a HEAD request and any response with a
1645     <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, or
1646     <x:ref>304 (Not Modified)</x:ref> status code is always
1647     terminated by the first empty line after the header fields, regardless of
1648     the header fields present in the message, and thus cannot contain a
1649     message body.
1650    </t></x:lt>
1651    <x:lt><t>
1652     Any <x:ref>2xx (Successful)</x:ref> response to a CONNECT request implies that the
1653     connection will become a tunnel immediately after the empty line that
1654     concludes the header fields.  A client &MUST; ignore any
1655     <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1656     fields received in such a message.
1657    </t></x:lt>
1658    <x:lt><t>
1659     If a <x:ref>Transfer-Encoding</x:ref> header field is present
1660     and the "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1661     is the final encoding, the message body length is determined by reading
1662     and decoding the chunked data until the transfer-coding indicates the
1663     data is complete.
1664    </t>
1665    <t>
1666     If a <x:ref>Transfer-Encoding</x:ref> header field is present in a
1667     response and the "chunked" transfer-coding is not the final encoding, the
1668     message body length is determined by reading the connection until it is
1669     closed by the server.
1670     If a Transfer-Encoding header field is present in a request and the
1671     "chunked" transfer-coding is not the final encoding, the message body
1672     length cannot be determined reliably; the server &MUST; respond with
1673     the <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1674    </t>
1675    <t>
1676     If a message is received with both a <x:ref>Transfer-Encoding</x:ref>
1677     and a <x:ref>Content-Length</x:ref> header field, the
1678     Transfer-Encoding overrides the Content-Length.
1679     Such a message might indicate an attempt to perform request or response
1680     smuggling (bypass of security-related checks on message routing or content)
1681     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1682     be removed, prior to forwarding the message downstream, or replaced with
1683     the real message body length after the transfer-coding is decoded.
1684    </t></x:lt>
1685    <x:lt><t>
1686     If a message is received without <x:ref>Transfer-Encoding</x:ref> and with
1687     either multiple <x:ref>Content-Length</x:ref> header fields having
1688     differing field-values or a single Content-Length header field having an
1689     invalid value, then the message framing is invalid and &MUST; be treated
1690     as an error to prevent request or response smuggling.
1691     If this is a request message, the server &MUST; respond with
1692     a <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1693     If this is a response message received by a proxy, the proxy
1694     &MUST; discard the received response, send a <x:ref>502 (Bad Gateway)</x:ref>
1695     status code as its downstream response, and then close the connection.
1696     If this is a response message received by a user-agent, it &MUST; be
1697     treated as an error by discarding the message and closing the connection.
1698    </t></x:lt>
1699    <x:lt><t>
1700     If a valid <x:ref>Content-Length</x:ref> header field is present without
1701     <x:ref>Transfer-Encoding</x:ref>, its decimal value defines the
1702     message body length in octets.  If the actual number of octets sent in
1703     the message is less than the indicated Content-Length, the recipient
1704     &MUST; consider the message to be incomplete and treat the connection
1705     as no longer usable.
1706     If the actual number of octets sent in the message is more than the indicated
1707     Content-Length, the recipient &MUST; only process the message body up to the
1708     field value's number of octets; the remainder of the message &MUST; either
1709     be discarded or treated as the next message in a pipeline.  For the sake of
1710     robustness, a user-agent &MAY; attempt to detect and correct such an error
1711     in message framing if it is parsing the response to the last request on
1712     a connection and the connection has been closed by the server.
1713    </t></x:lt>
1714    <x:lt><t>
1715     If this is a request message and none of the above are true, then the
1716     message body length is zero (no message body is present).
1717    </t></x:lt>
1718    <x:lt><t>
1719     Otherwise, this is a response message without a declared message body
1720     length, so the message body length is determined by the number of octets
1721     received prior to the server closing the connection.
1722    </t></x:lt>
1723  </list>
1726   Since there is no way to distinguish a successfully completed,
1727   close-delimited message from a partially-received message interrupted
1728   by network failure, implementations &SHOULD; use encoding or
1729   length-delimited messages whenever possible.  The close-delimiting
1730   feature exists primarily for backwards compatibility with HTTP/1.0.
1733   A server &MAY; reject a request that contains a message body but
1734   not a <x:ref>Content-Length</x:ref> by responding with
1735   <x:ref>411 (Length Required)</x:ref>.
1738   Unless a transfer-coding other than "chunked" has been applied,
1739   a client that sends a request containing a message body &SHOULD;
1740   use a valid <x:ref>Content-Length</x:ref> header field if the message body
1741   length is known in advance, rather than the "chunked" encoding, since some
1742   existing services respond to "chunked" with a <x:ref>411 (Length Required)</x:ref>
1743   status code even though they understand the chunked encoding.  This
1744   is typically because such services are implemented via a gateway that
1745   requires a content-length in advance of being called and the server
1746   is unable or unwilling to buffer the entire request before processing.
1749   A client that sends a request containing a message body &MUST; include a
1750   valid <x:ref>Content-Length</x:ref> header field if it does not know the
1751   server will handle HTTP/1.1 (or later) requests; such knowledge can be in
1752   the form of specific user configuration or by remembering the version of a
1753   prior received response.
1758<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1760   Request messages that are prematurely terminated, possibly due to a
1761   canceled connection or a server-imposed time-out exception, &MUST;
1762   result in closure of the connection; sending an HTTP/1.1 error response
1763   prior to closing the connection is &OPTIONAL;.
1766   Response messages that are prematurely terminated, usually by closure
1767   of the connection prior to receiving the expected number of octets or by
1768   failure to decode a transfer-encoded message body, &MUST; be recorded
1769   as incomplete.  A response that terminates in the middle of the header
1770   block (before the empty line is received) cannot be assumed to convey the
1771   full semantics of the response and &MUST; be treated as an error.
1774   A message body that uses the chunked transfer encoding is
1775   incomplete if the zero-sized chunk that terminates the encoding has not
1776   been received.  A message that uses a valid <x:ref>Content-Length</x:ref> is
1777   incomplete if the size of the message body received (in octets) is less than
1778   the value given by Content-Length.  A response that has neither chunked
1779   transfer encoding nor Content-Length is terminated by closure of the
1780   connection, and thus is considered complete regardless of the number of
1781   message body octets received, provided that the header block was received
1782   intact.
1785   A user agent &MUST-NOT; render an incomplete response message body as if
1786   it were complete (i.e., some indication needs to be given to the user that an
1787   error occurred).  Cache requirements for incomplete responses are defined
1788   in &cache-incomplete;.
1791   A server &MUST; read the entire request message body or close
1792   the connection after sending its response, since otherwise the
1793   remaining data on a persistent connection would be misinterpreted
1794   as the next request.  Likewise,
1795   a client &MUST; read the entire response message body if it intends
1796   to reuse the same connection for a subsequent request.  Pipelining
1797   multiple requests on a connection is described in <xref target="pipelining"/>.
1801<section title="Message Parsing Robustness" anchor="message.robustness">
1803   Older HTTP/1.0 client implementations might send an extra CRLF
1804   after a POST request as a lame workaround for some early server
1805   applications that failed to read message body content that was
1806   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1807   preface or follow a request with an extra CRLF.  If terminating
1808   the request message body with a line-ending is desired, then the
1809   client &MUST; include the terminating CRLF octets as part of the
1810   message body length.
1813   In the interest of robustness, servers &SHOULD; ignore at least one
1814   empty line received where a request-line is expected. In other words, if
1815   the server is reading the protocol stream at the beginning of a
1816   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1817   Likewise, although the line terminator for the start-line and header
1818   fields is the sequence CRLF, we recommend that recipients recognize a
1819   single LF as a line terminator and ignore any CR.
1822   When a server listening only for HTTP request messages, or processing
1823   what appears from the start-line to be an HTTP request message,
1824   receives a sequence of octets that does not match the HTTP-message
1825   grammar aside from the robustness exceptions listed above, the
1826   server &MUST; respond with an HTTP/1.1 <x:ref>400 (Bad Request)</x:ref> response. 
1831<section title="Transfer Codings" anchor="transfer.codings">
1832  <x:anchor-alias value="transfer-coding"/>
1833  <x:anchor-alias value="transfer-extension"/>
1835   Transfer-coding values are used to indicate an encoding
1836   transformation that has been, can be, or might need to be applied to a
1837   payload body in order to ensure "safe transport" through the network.
1838   This differs from a content coding in that the transfer-coding is a
1839   property of the message rather than a property of the representation
1840   that is being transferred.
1842<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1843  <x:ref>transfer-coding</x:ref>    = "chunked" ; <xref target="chunked.encoding"/>
1844                     / "compress" ; <xref target="compress.coding"/>
1845                     / "deflate" ; <xref target="deflate.coding"/>
1846                     / "gzip" ; <xref target="gzip.coding"/>
1847                     / <x:ref>transfer-extension</x:ref>
1848  <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> )
1850<t anchor="rule.parameter">
1851  <x:anchor-alias value="attribute"/>
1852  <x:anchor-alias value="transfer-parameter"/>
1853  <x:anchor-alias value="value"/>
1854   Parameters are in the form of attribute/value pairs.
1856<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"/>
1857  <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>
1858  <x:ref>attribute</x:ref>          = <x:ref>token</x:ref>
1859  <x:ref>value</x:ref>              = <x:ref>word</x:ref>
1862   All transfer-coding values are case-insensitive.
1863   The HTTP Transfer Coding registry is defined in
1864   <xref target="transfer.coding.registry"/>.
1865   HTTP/1.1 uses transfer-coding values in the <x:ref>TE</x:ref> header field
1866   (<xref target="header.te"/>) and in the <x:ref>Transfer-Encoding</x:ref>
1867   header field (<xref target="header.transfer-encoding"/>).
1870<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1871  <iref item="chunked (Coding Format)"/>
1872  <iref item="Coding Format" subitem="chunked"/>
1873  <x:anchor-alias value="chunk"/>
1874  <x:anchor-alias value="chunked-body"/>
1875  <x:anchor-alias value="chunk-data"/>
1876  <x:anchor-alias value="chunk-ext"/>
1877  <x:anchor-alias value="chunk-ext-name"/>
1878  <x:anchor-alias value="chunk-ext-val"/>
1879  <x:anchor-alias value="chunk-size"/>
1880  <x:anchor-alias value="last-chunk"/>
1881  <x:anchor-alias value="trailer-part"/>
1882  <x:anchor-alias value="quoted-str-nf"/>
1883  <x:anchor-alias value="qdtext-nf"/>
1885   The chunked encoding modifies the body of a message in order to
1886   transfer it as a series of chunks, each with its own size indicator,
1887   followed by an &OPTIONAL; trailer containing header fields. This
1888   allows dynamically produced content to be transferred along with the
1889   information necessary for the recipient to verify that it has
1890   received the full message.
1892<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="chunked-body"><!--terminal production--></iref><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"/>
1893  <x:ref>chunked-body</x:ref>   = *<x:ref>chunk</x:ref>
1894                   <x:ref>last-chunk</x:ref>
1895                   <x:ref>trailer-part</x:ref>
1896                   <x:ref>CRLF</x:ref>
1898  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1899                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1900  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1901  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1903  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1904  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1905  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1906  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1907  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1909  <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>
1910                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1911  <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>
1914   Chunk extensions within the chucked encoding are deprecated.
1915   Senders &SHOULD-NOT; send chunk-ext.
1916   Definition of new chunk extensions is discouraged.
1919   The chunk-size field is a string of hex digits indicating the size of
1920   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1921   zero, followed by the trailer, which is terminated by an empty line.
1924<section title="Trailer" anchor="header.trailer">
1925  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
1926  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
1927  <x:anchor-alias value="Trailer"/>
1929   A trailer allows the sender to include additional fields at the end of a
1930   chunked message in order to supply metadata that might be dynamically
1931   generated while the message body is sent, such as a message integrity
1932   check, digital signature, or post-processing status.
1933   The trailer &MUST-NOT; contain fields that need to be known before a
1934   recipient processes the body, such as <x:ref>Transfer-Encoding</x:ref>,
1935   <x:ref>Content-Length</x:ref>, and <x:ref>Trailer</x:ref>.
1938   When a message includes a message body encoded with the chunked
1939   transfer-coding and the sender desires to send metadata in the form of
1940   trailer fields at the end of the message, the sender &SHOULD; send a
1941   <x:ref>Trailer</x:ref> header field before the message body to indicate
1942   which fields will be present in the trailers. This allows the recipient
1943   to prepare for receipt of that metadata before it starts processing the body,
1944   which is useful if the message is being streamed and the recipient wishes
1945   to confirm an integrity check on the fly.
1947<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
1948  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
1951   If no <x:ref>Trailer</x:ref> header field is present, the sender of a
1952   chunked message body &SHOULD; send an empty trailer.
1955   A server &MUST; send an empty trailer with the chunked transfer-coding
1956   unless at least one of the following is true:
1957  <list style="numbers">
1958    <t>the request included a <x:ref>TE</x:ref> header field that indicates
1959    "trailers" is acceptable in the transfer-coding of the response, as
1960    described in <xref target="header.te"/>; or,</t>
1962    <t>the trailer fields consist entirely of optional metadata and the
1963    recipient could use the message (in a manner acceptable to the server where
1964    the field originated) without receiving that metadata. In other words,
1965    the server that generated the header field is willing to accept the
1966    possibility that the trailer fields might be silently discarded along
1967    the path to the client.</t>
1968  </list>
1971   The above requirement prevents the need for an infinite buffer when a
1972   message is being received by an HTTP/1.1 (or later) proxy and forwarded to
1973   an HTTP/1.0 recipient.
1977<section title="Decoding chunked" anchor="decoding.chunked">
1979   A process for decoding the "chunked" transfer-coding
1980   can be represented in pseudo-code as:
1982<figure><artwork type="code">
1983  length := 0
1984  read chunk-size, chunk-ext (if any) and CRLF
1985  while (chunk-size &gt; 0) {
1986     read chunk-data and CRLF
1987     append chunk-data to decoded-body
1988     length := length + chunk-size
1989     read chunk-size and CRLF
1990  }
1991  read header-field
1992  while (header-field not empty) {
1993     append header-field to existing header fields
1994     read header-field
1995  }
1996  Content-Length := length
1997  Remove "chunked" from Transfer-Encoding
1998  Remove Trailer from existing header fields
2001   All HTTP/1.1 applications &MUST; be able to receive and decode the
2002   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2003   they do not understand.
2008<section title="Compression Codings" anchor="compression.codings">
2010   The codings defined below can be used to compress the payload of a
2011   message.
2014<section title="Compress Coding" anchor="compress.coding">
2015<iref item="compress (Coding Format)"/>
2016<iref item="Coding Format" subitem="compress"/>
2018   The "compress" format is produced by the common UNIX file compression
2019   program "compress". This format is an adaptive Lempel-Ziv-Welch
2020   coding (LZW). Recipients &SHOULD; consider "x-compress" to be
2021   equivalent to "compress".
2025<section title="Deflate Coding" anchor="deflate.coding">
2026<iref item="deflate (Coding Format)"/>
2027<iref item="Coding Format" subitem="deflate"/>
2029   The "deflate" format is defined as the "deflate" compression mechanism
2030   (described in <xref target="RFC1951"/>) used inside the "zlib"
2031   data format (<xref target="RFC1950"/>).
2034  <t>
2035    &Note; Some incorrect implementations send the "deflate"
2036    compressed data without the zlib wrapper.
2037   </t>
2041<section title="Gzip Coding" anchor="gzip.coding">
2042<iref item="gzip (Coding Format)"/>
2043<iref item="Coding Format" subitem="gzip"/>
2045   The "gzip" format is produced by the file compression program
2046   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2047   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2048   Recipients &SHOULD; consider "x-gzip" to be equivalent to "gzip".
2054<section title="TE" anchor="header.te">
2055  <iref primary="true" item="TE header field" x:for-anchor=""/>
2056  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
2057  <x:anchor-alias value="TE"/>
2058  <x:anchor-alias value="t-codings"/>
2059  <x:anchor-alias value="t-ranking"/>
2060  <x:anchor-alias value="rank"/>
2062   The "TE" header field in a request indicates what transfer-codings,
2063   besides "chunked", the client is willing to accept in response, and
2064   whether or not the client is willing to accept trailer fields in a
2065   chunked transfer-coding.
2068   The TE field-value consists of a comma-separated list of transfer-coding
2069   names, each allowing for optional parameters (as described in
2070   <xref target="transfer.codings"/>), and/or the keyword "trailers".
2071   Clients &MUST-NOT; send the chunked transfer-coding name in TE;
2072   chunked is always acceptable for HTTP/1.1 recipients.
2074<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="t-ranking"/><iref primary="true" item="Grammar" subitem="rank"/>
2075  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2076  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-coding</x:ref> [ <x:ref>t-ranking</x:ref> ] )
2077  <x:ref>t-ranking</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>rank</x:ref>
2078  <x:ref>rank</x:ref>      = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2079             / ( "1" [ "." 0*3("0") ] )
2082   Three examples of TE use are below.
2084<figure><artwork type="example">
2085  TE: deflate
2086  TE:
2087  TE: trailers, deflate;q=0.5
2090   The presence of the keyword "trailers" indicates that the client is
2091   willing to accept trailer fields in a chunked transfer-coding,
2092   as defined in <xref target="chunked.encoding"/>, on behalf of itself and
2093   any downstream clients. For chained requests, this implies that either:
2094   (a) all downstream clients are willing to accept trailer fields in the
2095   forwarded response; or,
2096   (b) the client will attempt to buffer the response on behalf of downstream
2097   recipients.
2098   Note that HTTP/1.1 does not define any means to limit the size of a
2099   chunked response such that a client can be assured of buffering the
2100   entire response.
2103   When multiple transfer-codings are acceptable, the client &MAY; rank the
2104   codings by preference using a "q" parameter (similar to the qvalues
2105   used in content negotiation fields, &qvalue;). The rank value is a real
2106   number in the range 0 through 1, where 0.001 is the least preferred and
2107   1 is the most preferred; a value of 0 means "not acceptable".
2110   If the TE field-value is empty or if no TE field is present, the only
2111   acceptable transfer-coding is "chunked". A message with no transfer-coding
2112   is always acceptable.
2115   Since the TE header field only applies to the immediate connection,
2116   a sender of TE &MUST; also send a "TE" connection option within the
2117   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
2118   in order to prevent the TE field from being forwarded by intermediaries
2119   that do not support its semantics.
2124<section title="Message Routing" anchor="message.routing">
2126   HTTP request message routing is determined by each client based on the
2127   target resource, the client's proxy configuration, and
2128   establishment or reuse of an inbound connection.  The corresponding
2129   response routing follows the same connection chain back to the client.
2132<section title="Identifying a Target Resource" anchor="target-resource">
2133  <iref primary="true" item="target resource"/>
2134  <iref primary="true" item="target URI"/>
2136   HTTP is used in a wide variety of applications, ranging from
2137   general-purpose computers to home appliances.  In some cases,
2138   communication options are hard-coded in a client's configuration.
2139   However, most HTTP clients rely on the same resource identification
2140   mechanism and configuration techniques as general-purpose Web browsers.
2143   HTTP communication is initiated by a user agent for some purpose.
2144   The purpose is a combination of request semantics, which are defined in
2145   <xref target="Part2"/>, and a target resource upon which to apply those
2146   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2147   an identifier for the "<x:dfn>target resource</x:dfn>", which a user agent
2148   would resolve to its absolute form in order to obtain the
2149   "<x:dfn>target URI</x:dfn>".  The target URI
2150   excludes the reference's fragment identifier component, if any,
2151   since fragment identifiers are reserved for client-side processing
2152   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2155   HTTP intermediaries obtain the request semantics and target URI
2156   from the request-line of an incoming request message.
2160<section title="Connecting Inbound" anchor="connecting.inbound">
2162   Once the target URI is determined, a client needs to decide whether
2163   a network request is necessary to accomplish the desired semantics and,
2164   if so, where that request is to be directed.
2167   If the client has a response cache and the request semantics can be
2168   satisfied by a cache (<xref target="Part6"/>), then the request is
2169   usually directed to the cache first.
2172   If the request is not satisfied by a cache, then a typical client will
2173   check its configuration to determine whether a proxy is to be used to
2174   satisfy the request.  Proxy configuration is implementation-dependent,
2175   but is often based on URI prefix matching, selective authority matching,
2176   or both, and the proxy itself is usually identified by an "http" or
2177   "https" URI.  If a proxy is applicable, the client connects inbound by
2178   establishing (or reusing) a connection to that proxy.
2181   If no proxy is applicable, a typical client will invoke a handler routine,
2182   usually specific to the target URI's scheme, to connect directly
2183   to an authority for the target resource.  How that is accomplished is
2184   dependent on the target URI scheme and defined by its associated
2185   specification, similar to how this specification defines origin server
2186   access for resolution of the "http" (<xref target="http.uri"/>) and
2187   "https" (<xref target="https.uri"/>) schemes.
2191<section title="Request Target" anchor="request-target">
2193   Once an inbound connection is obtained
2194   (<xref target=""/>),
2195   the client sends an HTTP request message (<xref target="http.message"/>)
2196   with a request-target derived from the target URI.
2197   There are four distinct formats for the request-target, depending on both
2198   the method being requested and whether the request is to a proxy.
2200<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"/>
2201  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2202                 / <x:ref>absolute-form</x:ref>
2203                 / <x:ref>authority-form</x:ref>
2204                 / <x:ref>asterisk-form</x:ref>
2206  <x:ref>origin-form</x:ref>    = <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]
2207  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2208  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2209  <x:ref>asterisk-form</x:ref>  = "*"
2211<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2212   The most common form of request-target is the origin-form.
2213   When making a request directly to an origin server, other than a CONNECT
2214   or server-wide OPTIONS request (as detailed below),
2215   a client &MUST; send only the absolute path and query components of
2216   the target URI as the request-target.
2217   If the target URI's path component is empty, then the client &MUST; send
2218   "/" as the path within the origin-form of request-target.
2219   A <x:ref>Host</x:ref> header field is also sent, as defined in
2220   <xref target=""/>, containing the target URI's
2221   authority component (excluding any userinfo).
2224   For example, a client wishing to retrieve a representation of the resource
2225   identified as
2227<figure><artwork x:indent-with="  " type="example">
2231   directly from the origin server would open (or reuse) a TCP connection
2232   to port 80 of the host "" and send the lines:
2234<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2235GET /where?q=now HTTP/1.1
2239   followed by the remainder of the request message.
2241<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2242   When making a request to a proxy, other than a CONNECT or server-wide
2243   OPTIONS request (as detailed below), a client &MUST; send the target URI
2244   in absolute-form as the request-target.
2245   The proxy is requested to either service that request from a valid cache,
2246   if possible, or make the same request on the client's behalf to either
2247   the next inbound proxy server or directly to the origin server indicated
2248   by the request-target.  Requirements on such "forwarding" of messages are
2249   defined in <xref target="message.forwarding"/>.
2252   An example absolute-form of request-line would be:
2254<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2255GET HTTP/1.1
2258   To allow for transition to the absolute-form for all requests in some
2259   future version of HTTP, HTTP/1.1 servers &MUST; accept the absolute-form
2260   in requests, even though HTTP/1.1 clients will only send them in requests
2261   to proxies.
2263<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2264   The authority-form of request-target is only used for CONNECT requests
2265   (&CONNECT;).  When making a CONNECT request to establish a tunnel through
2266   one or more proxies, a client &MUST; send only the target URI's
2267   authority component (excluding any userinfo) as the request-target.
2268   For example,
2270<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2273<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2274   The asterisk-form of request-target is only used for a server-wide
2275   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2276   for the server as a whole, as opposed to a specific named resource of
2277   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2278   For example,
2280<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2281OPTIONS * HTTP/1.1
2284   If a proxy receives an OPTIONS request with an absolute-form of
2285   request-target in which the URI has an empty path and no query component,
2286   then the last proxy on the request chain &MUST; send a request-target
2287   of "*" when it forwards the request to the indicated origin server.
2290   For example, the request
2291</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2295  would be forwarded by the final proxy as
2296</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2297OPTIONS * HTTP/1.1
2301   after connecting to port 8001 of host "".
2306<section title="Host" anchor="">
2307  <iref primary="true" item="Host header field" x:for-anchor=""/>
2308  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
2309  <x:anchor-alias value="Host"/>
2311   The "Host" header field in a request provides the host and port
2312   information from the target URI, enabling the origin
2313   server to distinguish among resources while servicing requests
2314   for multiple host names on a single IP address.  Since the Host
2315   field-value is critical information for handling a request, it
2316   &SHOULD; be sent as the first header field following the request-line.
2318<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2319  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2322   A client &MUST; send a Host header field in all HTTP/1.1 request
2323   messages.  If the target URI includes an authority component, then
2324   the Host field-value &MUST; be identical to that authority component
2325   after excluding any userinfo (<xref target="http.uri"/>).
2326   If the authority component is missing or undefined for the target URI,
2327   then the Host header field &MUST; be sent with an empty field-value.
2330   For example, a GET request to the origin server for
2331   &lt;; would begin with:
2333<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2334GET /pub/WWW/ HTTP/1.1
2338   The Host header field &MUST; be sent in an HTTP/1.1 request even
2339   if the request-target is in the absolute-form, since this
2340   allows the Host information to be forwarded through ancient HTTP/1.0
2341   proxies that might not have implemented Host.
2344   When an HTTP/1.1 proxy receives a request with an absolute-form of
2345   request-target, the proxy &MUST; ignore the received
2346   Host header field (if any) and instead replace it with the host
2347   information of the request-target.  If the proxy forwards the request,
2348   it &MUST; generate a new Host field-value based on the received
2349   request-target rather than forward the received Host field-value.
2352   Since the Host header field acts as an application-level routing
2353   mechanism, it is a frequent target for malware seeking to poison
2354   a shared cache or redirect a request to an unintended server.
2355   An interception proxy is particularly vulnerable if it relies on
2356   the Host field-value for redirecting requests to internal
2357   servers, or for use as a cache key in a shared cache, without
2358   first verifying that the intercepted connection is targeting a
2359   valid IP address for that host.
2362   A server &MUST; respond with a <x:ref>400 (Bad Request)</x:ref> status code
2363   to any HTTP/1.1 request message that lacks a Host header field and
2364   to any request message that contains more than one Host header field
2365   or a Host header field with an invalid field-value.
2369<section title="Effective Request URI" anchor="effective.request.uri">
2370  <iref primary="true" item="effective request URI"/>
2372   A server that receives an HTTP request message &MUST; reconstruct
2373   the user agent's original target URI, based on the pieces of information
2374   learned from the request-target, <x:ref>Host</x:ref> header field, and
2375   connection context, in order to identify the intended target resource and
2376   properly service the request. The URI derived from this reconstruction
2377   process is referred to as the "<x:dfn>effective request URI</x:dfn>".
2380   For a user agent, the effective request URI is the target URI.
2383   If the request-target is in absolute-form, then the effective request URI
2384   is the same as the request-target.  Otherwise, the effective request URI
2385   is constructed as follows.
2388   If the request is received over an SSL/TLS-secured TCP connection,
2389   then the effective request URI's scheme is "https"; otherwise, the
2390   scheme is "http".
2393   If the request-target is in authority-form, then the effective
2394   request URI's authority component is the same as the request-target.
2395   Otherwise, if a <x:ref>Host</x:ref> header field is supplied with a
2396   non-empty field-value, then the authority component is the same as the
2397   Host field-value. Otherwise, the authority component is the concatenation of
2398   the default host name configured for the server, a colon (":"), and the
2399   connection's incoming TCP port number in decimal form.
2402   If the request-target is in authority-form or asterisk-form, then the
2403   effective request URI's combined path and query component is empty.
2404   Otherwise, the combined path and query component is the same as the
2405   request-target.
2408   The components of the effective request URI, once determined as above,
2409   can be combined into absolute-URI form by concatenating the scheme,
2410   "://", authority, and combined path and query component.
2414   Example 1: the following message received over an insecure TCP connection
2416<artwork type="example" x:indent-with="  ">
2417GET /pub/WWW/TheProject.html HTTP/1.1
2423  has an effective request URI of
2425<artwork type="example" x:indent-with="  ">
2431   Example 2: the following message received over an SSL/TLS-secured TCP
2432   connection
2434<artwork type="example" x:indent-with="  ">
2435OPTIONS * HTTP/1.1
2441  has an effective request URI of
2443<artwork type="example" x:indent-with="  ">
2448   An origin server that does not allow resources to differ by requested
2449   host &MAY; ignore the <x:ref>Host</x:ref> field-value and instead replace it
2450   with a configured server name when constructing the effective request URI.
2453   Recipients of an HTTP/1.0 request that lacks a <x:ref>Host</x:ref> header
2454   field &MAY; attempt to use heuristics (e.g., examination of the URI path for
2455   something unique to a particular host) in order to guess the
2456   effective request URI's authority component.
2460<section title="Message Forwarding" anchor="message.forwarding">
2462   As described in <xref target="intermediaries"/>, intermediaries can serve
2463   a variety of roles in the processing of HTTP requests and responses.
2464   Some intermediaries are used to improve performance or availability.
2465   Others are used for access control or to filter content.
2466   Since an HTTP stream has characteristics similar to a pipe-and-filter
2467   architecture, there are no inherent limits to the extent an intermediary
2468   can enhance (or interfere) with either direction of the stream.
2471   In order to avoid request loops, a proxy that forwards requests to other
2472   proxies &MUST; be able to recognize and exclude all of its own server
2473   names, including any aliases, local variations, or literal IP addresses.
2476   If a proxy receives a request-target with a host name that is not a
2477   fully qualified domain name, it &MAY; add its own domain to the host name
2478   it received when forwarding the request.  A proxy &MUST-NOT; change the
2479   host name if it is a fully qualified domain name.
2482   A non-transforming proxy &MUST-NOT; modify the "path-absolute" and "query"
2483   parts of the received request-target when forwarding it to the next inbound
2484   server, except as noted above to replace an empty path with "/" or "*".
2487   Intermediaries that forward a message &MUST; implement the
2488   <x:ref>Connection</x:ref> header field as specified in
2489   <xref target="header.connection"/>.
2492<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2494  <cref anchor="TODO-end-to-end" source="jre">
2495    Restored from <eref target=""/>.
2496    See also <eref target=""/>.
2497  </cref>
2500   For the purpose of defining the behavior of caches and non-caching
2501   proxies, we divide HTTP header fields into two categories:
2502  <list style="symbols">
2503      <t>End-to-end header fields, which are  transmitted to the ultimate
2504        recipient of a request or response. End-to-end header fields in
2505        responses &MUST; be stored as part of a cache entry and &MUST; be
2506        transmitted in any response formed from a cache entry.</t>
2508      <t>Hop-by-hop header fields, which are meaningful only for a single
2509        transport-level connection, and are not stored by caches or
2510        forwarded by proxies.</t>
2511  </list>
2514   The following HTTP/1.1 header fields are hop-by-hop header fields:
2515  <list style="symbols">
2516      <t><x:ref>Connection</x:ref></t>
2517      <t>Keep-Alive (<xref target="RFC2068" x:fmt="of" x:sec=""/>)</t>
2518      <t><x:ref>Proxy-Authenticate</x:ref> (&header-proxy-authenticate;)</t>
2519      <t><x:ref>Proxy-Authorization</x:ref> (&header-proxy-authorization;)</t>
2520      <t><x:ref>TE</x:ref></t>
2521      <t><x:ref>Trailer</x:ref></t>
2522      <t><x:ref>Transfer-Encoding</x:ref></t>
2523      <t><x:ref>Upgrade</x:ref></t>
2524  </list>
2527   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2530   Other hop-by-hop header fields &MUST; be listed in a
2531   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>).
2535<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2537  <cref anchor="TODO-non-mod-headers" source="jre">
2538    Restored from <eref target=""/>.
2539    See also <eref target=""/>.
2540  </cref>
2543   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2544   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2545   modify an end-to-end header field unless the definition of that header field requires
2546   or specifically allows that.
2549   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2550   request or response, and it &MUST-NOT; add any of these fields if not
2551   already present:
2552  <list style="symbols">
2553    <t><x:ref>Allow</x:ref> (&header-allow;)</t>
2554    <t><x:ref>Content-Location</x:ref> (&header-content-location;)</t>
2555    <t>Content-MD5 (<xref target="RFC2616" x:fmt="of" x:sec="14.15"/>)</t>
2556    <t><x:ref>ETag</x:ref> (&header-etag;)</t>
2557    <t><x:ref>Last-Modified</x:ref> (&header-last-modified;)</t>
2558    <t><x:ref>Server</x:ref> (&header-server;)</t>
2559  </list>
2562   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2563   response:
2564  <list style="symbols">
2565    <t><x:ref>Expires</x:ref> (&header-expires;)</t>
2566  </list>
2569   but it &MAY; add any of these fields if not already present. If an
2570   <x:ref>Expires</x:ref> header field is added, it &MUST; be given a
2571   field value identical to that of the <x:ref>Date</x:ref> header field in
2572   that response.
2575   A proxy &MUST-NOT; modify or add any of the following fields in a
2576   message that contains the no-transform cache-control directive, or in
2577   any request:
2578  <list style="symbols">
2579    <t><x:ref>Content-Encoding</x:ref> (&header-content-encoding;)</t>
2580    <t><x:ref>Content-Range</x:ref> (&header-content-range;)</t>
2581    <t><x:ref>Content-Type</x:ref> (&header-content-type;)</t>
2582  </list>
2585   A transforming proxy &MAY; modify or add these fields to a message
2586   that does not include no-transform, but if it does so, it &MUST; add a
2587   Warning 214 (Transformation applied) if one does not already appear
2588   in the message (see &header-warning;).
2591  <t>
2592    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2593    cause authentication failures if stronger authentication
2594    mechanisms are introduced in later versions of HTTP. Such
2595    authentication mechanisms &MAY; rely on the values of header fields
2596    not listed here.
2597  </t>
2600   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2601   though it &MAY; change the message body through application or removal
2602   of a transfer-coding (<xref target="transfer.codings"/>).
2608<section title="Associating a Response to a Request" anchor="">
2610   HTTP does not include a request identifier for associating a given
2611   request message with its corresponding one or more response messages.
2612   Hence, it relies on the order of response arrival to correspond exactly
2613   to the order in which requests are made on the same connection.
2614   More than one response message per request only occurs when one or more
2615   informational responses (<x:ref>1xx</x:ref>, see &status-1xx;) precede a final response
2616   to the same request.
2619   A client that uses persistent connections and sends more than one request
2620   per connection &MUST; maintain a list of outstanding requests in the
2621   order sent on that connection and &MUST; associate each received response
2622   message to the highest ordered request that has not yet received a final
2623   (non-<x:ref>1xx</x:ref>) response.
2628<section title="Connection Management" anchor="">
2630<section title="Connection" anchor="header.connection">
2631  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2632  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2633  <x:anchor-alias value="Connection"/>
2634  <x:anchor-alias value="connection-option"/>
2636   The "Connection" header field allows the sender to specify
2637   options that are desired only for that particular connection.
2638   Such connection options &MUST; be removed or replaced before the
2639   message can be forwarded downstream by a proxy or gateway.
2640   This mechanism also allows the sender to indicate which HTTP
2641   header fields used in the message are only intended for the
2642   immediate recipient ("hop-by-hop"), as opposed to all recipients
2643   on the chain ("end-to-end"), enabling the message to be
2644   self-descriptive and allowing future connection-specific extensions
2645   to be deployed in HTTP without fear that they will be blindly
2646   forwarded by previously deployed intermediaries.
2649   The Connection header field's value has the following grammar:
2651<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-option"/>
2652  <x:ref>Connection</x:ref>        = 1#<x:ref>connection-option</x:ref>
2653  <x:ref>connection-option</x:ref> = <x:ref>token</x:ref>
2656   Connection options are compared case-insensitively.
2659   A proxy or gateway &MUST; parse a received Connection
2660   header field before a message is forwarded and, for each
2661   connection-option in this field, remove any header field(s) from
2662   the message with the same name as the connection-option, and then
2663   remove the Connection header field itself or replace it with the
2664   sender's own connection options for the forwarded message.
2667   A sender &MUST-NOT; include field-names in the Connection header
2668   field-value for fields that are defined as expressing constraints
2669   for all recipients in the request or response chain, such as the
2670   Cache-Control header field (&header-cache-control;).
2673   The connection options do not have to correspond to a header field
2674   present in the message, since a connection-specific header field
2675   might not be needed if there are no parameters associated with that
2676   connection option.  Recipients that trigger certain connection
2677   behavior based on the presence of connection options &MUST; do so
2678   based on the presence of the connection-option rather than only the
2679   presence of the optional header field.  In other words, if the
2680   connection option is received as a header field but not indicated
2681   within the Connection field-value, then the recipient &MUST; ignore
2682   the connection-specific header field because it has likely been
2683   forwarded by an intermediary that is only partially conformant.
2686   When defining new connection options, specifications ought to
2687   carefully consider existing deployed header fields and ensure
2688   that the new connection option does not share the same name as
2689   an unrelated header field that might already be deployed.
2690   Defining a new connection option essentially reserves that potential
2691   field-name for carrying additional information related to the
2692   connection option, since it would be unwise for senders to use
2693   that field-name for anything else.
2696   HTTP/1.1 defines the "close" connection option for the sender to
2697   signal that the connection will be closed after completion of the
2698   response. For example,
2700<figure><artwork type="example">
2701  Connection: close
2704   in either the request or the response header fields indicates that
2705   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2706   after the current request/response is complete.
2709   An HTTP/1.1 client that does not support persistent connections &MUST;
2710   include the "close" connection option in every request message.
2713   An HTTP/1.1 server that does not support persistent connections &MUST;
2714   include the "close" connection option in every response message that
2715   does not have a <x:ref>1xx (Informational)</x:ref> status code.
2719<section title="Via" anchor="header.via">
2720  <iref primary="true" item="Via header field" x:for-anchor=""/>
2721  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
2722  <x:anchor-alias value="pseudonym"/>
2723  <x:anchor-alias value="received-by"/>
2724  <x:anchor-alias value="received-protocol"/>
2725  <x:anchor-alias value="Via"/>
2727   The "Via" header field &MUST; be sent by a proxy or gateway to
2728   indicate the intermediate protocols and recipients between the user
2729   agent and the server on requests, and between the origin server and
2730   the client on responses. It is analogous to the "Received" field
2731   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
2732   and is intended to be used for tracking message forwards,
2733   avoiding request loops, and identifying the protocol capabilities of
2734   all senders along the request/response chain.
2736<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"/>
2737  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2738                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2739  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2740  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2741  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2744   The received-protocol indicates the protocol version of the message
2745   received by the server or client along each segment of the
2746   request/response chain. The received-protocol version is appended to
2747   the Via field value when the message is forwarded so that information
2748   about the protocol capabilities of upstream applications remains
2749   visible to all recipients.
2752   The protocol-name is excluded if and only if it would be "HTTP". The
2753   received-by field is normally the host and optional port number of a
2754   recipient server or client that subsequently forwarded the message.
2755   However, if the real host is considered to be sensitive information,
2756   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2757   be assumed to be the default port of the received-protocol.
2760   Multiple Via field values represent each proxy or gateway that has
2761   forwarded the message. Each recipient &MUST; append its information
2762   such that the end result is ordered according to the sequence of
2763   forwarding applications.
2766   Comments &MAY; be used in the Via header field to identify the software
2767   of each recipient, analogous to the <x:ref>User-Agent</x:ref> and
2768   <x:ref>Server</x:ref> header fields. However, all comments in the Via field
2769   are optional and &MAY; be removed by any recipient prior to forwarding the
2770   message.
2773   For example, a request message could be sent from an HTTP/1.0 user
2774   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2775   forward the request to a public proxy at, which completes
2776   the request by forwarding it to the origin server at
2777   The request received by would then have the following
2778   Via header field:
2780<figure><artwork type="example">
2781  Via: 1.0 fred, 1.1 (Apache/1.1)
2784   A proxy or gateway used as a portal through a network firewall
2785   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2786   region unless it is explicitly enabled to do so. If not enabled, the
2787   received-by host of any host behind the firewall &SHOULD; be replaced
2788   by an appropriate pseudonym for that host.
2791   A proxy or gateway &MAY; combine an ordered subsequence of Via header
2792   field entries into a single such entry if the entries have identical
2793   received-protocol values. For example,
2795<figure><artwork type="example">
2796  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2799  could be collapsed to
2801<figure><artwork type="example">
2802  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2805   Senders &SHOULD-NOT; combine multiple entries unless they are all
2806   under the same organizational control and the hosts have already been
2807   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
2808   have different received-protocol values.
2812<section title="Persistent Connections" anchor="persistent.connections">
2814<section title="Purpose" anchor="persistent.purpose">
2816   Prior to persistent connections, a separate TCP connection was
2817   established for each request, increasing the load on HTTP servers
2818   and causing congestion on the Internet. The use of inline images and
2819   other associated data often requires a client to make multiple
2820   requests of the same server in a short amount of time. Analysis of
2821   these performance problems and results from a prototype
2822   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2823   measurements of actual HTTP/1.1 implementations show good
2824   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2825   T/TCP <xref target="Tou1998"/>.
2828   Persistent HTTP connections have a number of advantages:
2829  <list style="symbols">
2830      <t>
2831        By opening and closing fewer TCP connections, CPU time is saved
2832        in routers and hosts (clients, servers, proxies, gateways,
2833        tunnels, or caches), and memory used for TCP protocol control
2834        blocks can be saved in hosts.
2835      </t>
2836      <t>
2837        HTTP requests and responses can be pipelined on a connection.
2838        Pipelining allows a client to make multiple requests without
2839        waiting for each response, allowing a single TCP connection to
2840        be used much more efficiently, with much lower elapsed time.
2841      </t>
2842      <t>
2843        Network congestion is reduced by reducing the number of packets
2844        caused by TCP opens, and by allowing TCP sufficient time to
2845        determine the congestion state of the network.
2846      </t>
2847      <t>
2848        Latency on subsequent requests is reduced since there is no time
2849        spent in TCP's connection opening handshake.
2850      </t>
2851      <t>
2852        HTTP can evolve more gracefully, since errors can be reported
2853        without the penalty of closing the TCP connection. Clients using
2854        future versions of HTTP might optimistically try a new feature,
2855        but if communicating with an older server, retry with old
2856        semantics after an error is reported.
2857      </t>
2858    </list>
2861   HTTP implementations &SHOULD; implement persistent connections.
2865<section title="Overall Operation" anchor="persistent.overall">
2867   A significant difference between HTTP/1.1 and earlier versions of
2868   HTTP is that persistent connections are the default behavior of any
2869   HTTP connection. That is, unless otherwise indicated, the client
2870   &SHOULD; assume that the server will maintain a persistent connection,
2871   even after error responses from the server.
2874   Persistent connections provide a mechanism by which a client and a
2875   server can signal the close of a TCP connection. This signaling takes
2876   place using the <x:ref>Connection</x:ref> header field
2877   (<xref target="header.connection"/>). Once a close has been signaled, the
2878   client &MUST-NOT; send any more requests on that
2879   connection.
2882<section title="Negotiation" anchor="persistent.negotiation">
2884   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2885   maintain a persistent connection unless a <x:ref>Connection</x:ref> header
2886   field including the connection option "close" was sent in the request. If
2887   the server chooses to close the connection immediately after sending the
2888   response, it &SHOULD; send a Connection header field including the
2889   connection option "close".
2892   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2893   decide to keep it open based on whether the response from a server
2894   contains a <x:ref>Connection</x:ref> header field with the connection option
2895   "close". In case the client does not want to maintain a connection for more
2896   than that request, it &SHOULD; send a Connection header field including the
2897   connection option "close".
2900   If either the client or the server sends the "close" option in the
2901   <x:ref>Connection</x:ref> header field, that request becomes the last one
2902   for the connection.
2905   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2906   maintained for HTTP versions less than 1.1 unless it is explicitly
2907   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2908   compatibility with HTTP/1.0 clients.
2911   Each persistent connection applies to only one transport link.
2914   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2915   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2916   for information and discussion of the problems with the Keep-Alive header field
2917   implemented by many HTTP/1.0 clients).
2920   In order to remain persistent, all messages on the connection &MUST;
2921   have a self-defined message length (i.e., one not defined by closure
2922   of the connection), as described in <xref target="message.body"/>.
2926<section title="Pipelining" anchor="pipelining">
2928   A client that supports persistent connections &MAY; "pipeline" its
2929   requests (i.e., send multiple requests without waiting for each
2930   response). A server &MUST; send its responses to those requests in the
2931   same order that the requests were received.
2934   Clients which assume persistent connections and pipeline immediately
2935   after connection establishment &SHOULD; be prepared to retry their
2936   connection if the first pipelined attempt fails. If a client does
2937   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2938   persistent. Clients &MUST; also be prepared to resend their requests if
2939   the server closes the connection before sending all of the
2940   corresponding responses.
2943   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2944   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2945   premature termination of the transport connection could lead to
2946   indeterminate results. A client wishing to send a non-idempotent
2947   request &SHOULD; wait to send that request until it has received the
2948   response status line for the previous request.
2953<section title="Practical Considerations" anchor="persistent.practical">
2955   Servers will usually have some time-out value beyond which they will
2956   no longer maintain an inactive connection. Proxy servers might make
2957   this a higher value since it is likely that the client will be making
2958   more connections through the same server. The use of persistent
2959   connections places no requirements on the length (or existence) of
2960   this time-out for either the client or the server.
2963   When a client or server wishes to time-out it &SHOULD; issue a graceful
2964   close on the transport connection. Clients and servers &SHOULD; both
2965   constantly watch for the other side of the transport close, and
2966   respond to it as appropriate. If a client or server does not detect
2967   the other side's close promptly it could cause unnecessary resource
2968   drain on the network.
2971   A client, server, or proxy &MAY; close the transport connection at any
2972   time. For example, a client might have started to send a new request
2973   at the same time that the server has decided to close the "idle"
2974   connection. From the server's point of view, the connection is being
2975   closed while it was idle, but from the client's point of view, a
2976   request is in progress.
2979   Clients (including proxies) &SHOULD; limit the number of simultaneous
2980   connections that they maintain to a given server (including proxies).
2983   Previous revisions of HTTP gave a specific number of connections as a
2984   ceiling, but this was found to be impractical for many applications. As a
2985   result, this specification does not mandate a particular maximum number of
2986   connections, but instead encourages clients to be conservative when opening
2987   multiple connections.
2990   In particular, while using multiple connections avoids the "head-of-line
2991   blocking" problem (whereby a request that takes significant server-side
2992   processing and/or has a large payload can block subsequent requests on the
2993   same connection), each connection used consumes server resources (sometimes
2994   significantly), and furthermore using multiple connections can cause
2995   undesirable side effects in congested networks.
2998   Note that servers might reject traffic that they deem abusive, including an
2999   excessive number of connections from a client.
3003<section title="Retrying Requests" anchor="persistent.retrying.requests">
3005   Senders can close the transport connection at any time. Therefore,
3006   clients, servers, and proxies &MUST; be able to recover
3007   from asynchronous close events. Client software &MAY; reopen the
3008   transport connection and retransmit the aborted sequence of requests
3009   without user interaction so long as the request sequence is
3010   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
3011   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
3012   human operator the choice of retrying the request(s). Confirmation by
3013   user-agent software with semantic understanding of the application
3014   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
3015   be repeated if the second sequence of requests fails.
3020<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
3022<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
3024   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
3025   flow control mechanisms to resolve temporary overloads, rather than
3026   terminating connections with the expectation that clients will retry.
3027   The latter technique can exacerbate network congestion.
3031<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
3033   An HTTP/1.1 (or later) client sending a message body &SHOULD; monitor
3034   the network connection for an error status code while it is transmitting
3035   the request. If the client sees an error status code, it &SHOULD;
3036   immediately cease transmitting the body. If the body is being sent
3037   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
3038   empty trailer &MAY; be used to prematurely mark the end of the message.
3039   If the body was preceded by a Content-Length header field, the client &MUST;
3040   close the connection.
3044<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
3046   The purpose of the <x:ref>100 (Continue)</x:ref> status code (see &status-100;)
3047   is to allow a client that is sending a request message with a request body
3048   to determine if the origin server is willing to accept the request
3049   (based on the request header fields) before the client sends the request
3050   body. In some cases, it might either be inappropriate or highly
3051   inefficient for the client to send the body if the server will reject
3052   the message without looking at the body.
3055   Requirements for HTTP/1.1 clients:
3056  <list style="symbols">
3057    <t>
3058        If a client will wait for a <x:ref>100 (Continue)</x:ref> response before
3059        sending the request body, it &MUST; send an <x:ref>Expect</x:ref> header
3060        field (&header-expect;) with the "100-continue" expectation.
3061    </t>
3062    <t>
3063        A client &MUST-NOT; send an <x:ref>Expect</x:ref> header field with
3064        the "100-continue" expectation if it does not intend to send a request
3065        body.
3066    </t>
3067  </list>
3070   Because of the presence of older implementations, the protocol allows
3071   ambiguous situations in which a client might send "Expect: 100-continue"
3072   without receiving either a <x:ref>417 (Expectation Failed)</x:ref>
3073   or a <x:ref>100 (Continue)</x:ref> status code. Therefore, when a client sends this
3074   header field to an origin server (possibly via a proxy) from which it
3075   has never seen a <x:ref>100 (Continue)</x:ref> status code, the client &SHOULD-NOT; 
3076   wait for an indefinite period before sending the request body.
3079   Requirements for HTTP/1.1 origin servers:
3080  <list style="symbols">
3081    <t> Upon receiving a request which includes an <x:ref>Expect</x:ref> header
3082        field with the "100-continue" expectation, an origin server &MUST;
3083        either respond with <x:ref>100 (Continue)</x:ref> status code and continue to read
3084        from the input stream, or respond with a final status code. The
3085        origin server &MUST-NOT; wait for the request body before sending
3086        the <x:ref>100 (Continue)</x:ref> response. If it responds with a final status
3087        code, it &MAY; close the transport connection or it &MAY; continue
3088        to read and discard the rest of the request.  It &MUST-NOT;
3089        perform the request method if it returns a final status code.
3090    </t>
3091    <t> An origin server &SHOULD-NOT;  send a <x:ref>100 (Continue)</x:ref> response if
3092        the request message does not include an <x:ref>Expect</x:ref> header
3093        field with the "100-continue" expectation, and &MUST-NOT; send a
3094        <x:ref>100 (Continue)</x:ref> response if such a request comes from an HTTP/1.0
3095        (or earlier) client. There is an exception to this rule: for
3096        compatibility with <xref target="RFC2068"/>, a server &MAY; send a <x:ref>100 (Continue)</x:ref>
3097        status code in response to an HTTP/1.1 PUT or POST request that does
3098        not include an Expect header field with the "100-continue"
3099        expectation. This exception, the purpose of which is
3100        to minimize any client processing delays associated with an
3101        undeclared wait for <x:ref>100 (Continue)</x:ref> status code, applies only to
3102        HTTP/1.1 requests, and not to requests with any other HTTP-version
3103        value.
3104    </t>
3105    <t> An origin server &MAY; omit a <x:ref>100 (Continue)</x:ref> response if it has
3106        already received some or all of the request body for the
3107        corresponding request.
3108    </t>
3109    <t> An origin server that sends a <x:ref>100 (Continue)</x:ref> response &MUST;
3110        ultimately send a final status code, once the request body is
3111        received and processed, unless it terminates the transport
3112        connection prematurely.
3113    </t>
3114    <t> If an origin server receives a request that does not include an
3115        <x:ref>Expect</x:ref> header field with the "100-continue" expectation,
3116        the request includes a request body, and the server responds
3117        with a final status code before reading the entire request body
3118        from the transport connection, then the server &SHOULD-NOT;  close
3119        the transport connection until it has read the entire request,
3120        or until the client closes the connection. Otherwise, the client
3121        might not reliably receive the response message. However, this
3122        requirement ought not be construed as preventing a server from
3123        defending itself against denial-of-service attacks, or from
3124        badly broken client implementations.
3125      </t>
3126    </list>
3129   Requirements for HTTP/1.1 proxies:
3130  <list style="symbols">
3131    <t> If a proxy receives a request that includes an <x:ref>Expect</x:ref>
3132        header field with the "100-continue" expectation, and the proxy
3133        either knows that the next-hop server complies with HTTP/1.1 or
3134        higher, or does not know the HTTP version of the next-hop
3135        server, it &MUST; forward the request, including the Expect header
3136        field.
3137    </t>
3138    <t> If the proxy knows that the version of the next-hop server is
3139        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
3140        respond with a <x:ref>417 (Expectation Failed)</x:ref> status code.
3141    </t>
3142    <t> Proxies &SHOULD; maintain a record of the HTTP version
3143        numbers received from recently-referenced next-hop servers.
3144    </t>
3145    <t> A proxy &MUST-NOT; forward a <x:ref>100 (Continue)</x:ref> response if the
3146        request message was received from an HTTP/1.0 (or earlier)
3147        client and did not include an <x:ref>Expect</x:ref> header field with
3148        the "100-continue" expectation. This requirement overrides the
3149        general rule for forwarding of <x:ref>1xx</x:ref> responses (see &status-1xx;).
3150    </t>
3151  </list>
3155<section title="Closing Connections on Error" anchor="closing.connections.on.error">
3157   If the client is sending data, a server implementation using TCP
3158   &SHOULD; be careful to ensure that the client acknowledges receipt of
3159   the packet(s) containing the response, before the server closes the
3160   input connection. If the client continues sending data to the server
3161   after the close, the server's TCP stack will send a reset packet to
3162   the client, which might erase the client's unacknowledged input buffers
3163   before they can be read and interpreted by the HTTP application.
3169<section title="Upgrade" anchor="header.upgrade">
3170  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3171  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3172  <x:anchor-alias value="Upgrade"/>
3173  <x:anchor-alias value="protocol"/>
3174  <x:anchor-alias value="protocol-name"/>
3175  <x:anchor-alias value="protocol-version"/>
3177   The "Upgrade" header field allows the client to specify what
3178   additional communication protocols it would like to use, if the server
3179   chooses to switch protocols. Servers can use it to indicate what protocols
3180   they are willing to switch to.
3182<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3183  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3185  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3186  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3187  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3190   For example,
3192<figure><artwork type="example">
3193  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3196   The Upgrade header field is intended to provide a simple mechanism
3197   for transitioning from HTTP/1.1 to some other, incompatible protocol. It
3198   does so by allowing the client to advertise its desire to use another
3199   protocol, such as a later version of HTTP with a higher major version
3200   number, even though the current request has been made using HTTP/1.1.
3201   This eases the difficult transition between incompatible protocols by
3202   allowing the client to initiate a request in the more commonly
3203   supported protocol while indicating to the server that it would like
3204   to use a "better" protocol if available (where "better" is determined
3205   by the server, possibly according to the nature of the request method
3206   or target resource).
3209   The Upgrade header field only applies to switching application-layer
3210   protocols upon the existing transport-layer connection. Upgrade
3211   cannot be used to insist on a protocol change; its acceptance and use
3212   by the server is optional. The capabilities and nature of the
3213   application-layer communication after the protocol change is entirely
3214   dependent upon the new protocol chosen, although the first action
3215   after changing the protocol &MUST; be a response to the initial HTTP
3216   request containing the Upgrade header field.
3219   The Upgrade header field only applies to the immediate connection.
3220   Therefore, the upgrade keyword &MUST; be supplied within a
3221   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
3222   whenever Upgrade is present in an HTTP/1.1 message.
3225   The Upgrade header field cannot be used to indicate a switch to a
3226   protocol on a different connection. For that purpose, it is more
3227   appropriate to use a <x:ref>3xx (Redirection)</x:ref> response (&status-3xx;).
3230   Servers &MUST; include the "Upgrade" header field in <x:ref>101 (Switching
3231   Protocols)</x:ref> responses to indicate which protocol(s) are being switched to,
3232   and &MUST; include it in <x:ref>426 (Upgrade Required)</x:ref> responses to indicate
3233   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3234   response to indicate that they are willing to upgrade to one of the
3235   specified protocols.
3238   This specification only defines the protocol name "HTTP" for use by
3239   the family of Hypertext Transfer Protocols, as defined by the HTTP
3240   version rules of <xref target="http.version"/> and future updates to this
3241   specification. Additional tokens can be registered with IANA using the
3242   registration procedure defined in <xref target="upgrade.token.registry"/>.
3248<section title="IANA Considerations" anchor="IANA.considerations">
3250<section title="Header Field Registration" anchor="header.field.registration">
3252   HTTP header fields are registered within the Message Header Field Registry
3253   <xref target="RFC3864"/> maintained by IANA at
3254   <eref target=""/>.
3257   This document defines the following HTTP header fields, so their
3258   associated registry entries shall be updated according to the permanent
3259   registrations below:
3261<?BEGININC p1-messaging.iana-headers ?>
3262<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3263<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3264   <ttcol>Header Field Name</ttcol>
3265   <ttcol>Protocol</ttcol>
3266   <ttcol>Status</ttcol>
3267   <ttcol>Reference</ttcol>
3269   <c>Connection</c>
3270   <c>http</c>
3271   <c>standard</c>
3272   <c>
3273      <xref target="header.connection"/>
3274   </c>
3275   <c>Content-Length</c>
3276   <c>http</c>
3277   <c>standard</c>
3278   <c>
3279      <xref target="header.content-length"/>
3280   </c>
3281   <c>Host</c>
3282   <c>http</c>
3283   <c>standard</c>
3284   <c>
3285      <xref target=""/>
3286   </c>
3287   <c>TE</c>
3288   <c>http</c>
3289   <c>standard</c>
3290   <c>
3291      <xref target="header.te"/>
3292   </c>
3293   <c>Trailer</c>
3294   <c>http</c>
3295   <c>standard</c>
3296   <c>
3297      <xref target="header.trailer"/>
3298   </c>
3299   <c>Transfer-Encoding</c>
3300   <c>http</c>
3301   <c>standard</c>
3302   <c>
3303      <xref target="header.transfer-encoding"/>
3304   </c>
3305   <c>Upgrade</c>
3306   <c>http</c>
3307   <c>standard</c>
3308   <c>
3309      <xref target="header.upgrade"/>
3310   </c>
3311   <c>Via</c>
3312   <c>http</c>
3313   <c>standard</c>
3314   <c>
3315      <xref target="header.via"/>
3316   </c>
3319<?ENDINC p1-messaging.iana-headers ?>
3321   Furthermore, the header field-name "Close" shall be registered as
3322   "reserved", since using that name as an HTTP header field might
3323   conflict with the "close" connection option of the "<x:ref>Connection</x:ref>"
3324   header field (<xref target="header.connection"/>).
3326<texttable align="left" suppress-title="true">
3327   <ttcol>Header Field Name</ttcol>
3328   <ttcol>Protocol</ttcol>
3329   <ttcol>Status</ttcol>
3330   <ttcol>Reference</ttcol>
3332   <c>Close</c>
3333   <c>http</c>
3334   <c>reserved</c>
3335   <c>
3336      <xref target="header.field.registration"/>
3337   </c>
3340   The change controller is: "IETF ( - Internet Engineering Task Force".
3344<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3346   IANA maintains the registry of URI Schemes <xref target="RFC4395"/> at
3347   <eref target=""/>.
3350   This document defines the following URI schemes, so their
3351   associated registry entries shall be updated according to the permanent
3352   registrations below:
3354<texttable align="left" suppress-title="true">
3355   <ttcol>URI Scheme</ttcol>
3356   <ttcol>Description</ttcol>
3357   <ttcol>Reference</ttcol>
3359   <c>http</c>
3360   <c>Hypertext Transfer Protocol</c>
3361   <c><xref target="http.uri"/></c>
3363   <c>https</c>
3364   <c>Hypertext Transfer Protocol Secure</c>
3365   <c><xref target="https.uri"/></c>
3369<section title="Internet Media Type Registrations" anchor="">
3371   This document serves as the specification for the Internet media types
3372   "message/http" and "application/http". The following is to be registered with
3373   IANA (see <xref target="RFC4288"/>).
3375<section title="Internet Media Type message/http" anchor="">
3376<iref item="Media Type" subitem="message/http" primary="true"/>
3377<iref item="message/http Media Type" primary="true"/>
3379   The message/http type can be used to enclose a single HTTP request or
3380   response message, provided that it obeys the MIME restrictions for all
3381   "message" types regarding line length and encodings.
3384  <list style="hanging" x:indent="12em">
3385    <t hangText="Type name:">
3386      message
3387    </t>
3388    <t hangText="Subtype name:">
3389      http
3390    </t>
3391    <t hangText="Required parameters:">
3392      none
3393    </t>
3394    <t hangText="Optional parameters:">
3395      version, msgtype
3396      <list style="hanging">
3397        <t hangText="version:">
3398          The HTTP-version number of the enclosed message
3399          (e.g., "1.1"). If not present, the version can be
3400          determined from the first line of the body.
3401        </t>
3402        <t hangText="msgtype:">
3403          The message type &mdash; "request" or "response". If not
3404          present, the type can be determined from the first
3405          line of the body.
3406        </t>
3407      </list>
3408    </t>
3409    <t hangText="Encoding considerations:">
3410      only "7bit", "8bit", or "binary" are permitted
3411    </t>
3412    <t hangText="Security considerations:">
3413      none
3414    </t>
3415    <t hangText="Interoperability considerations:">
3416      none
3417    </t>
3418    <t hangText="Published specification:">
3419      This specification (see <xref target=""/>).
3420    </t>
3421    <t hangText="Applications that use this media type:">
3422    </t>
3423    <t hangText="Additional information:">
3424      <list style="hanging">
3425        <t hangText="Magic number(s):">none</t>
3426        <t hangText="File extension(s):">none</t>
3427        <t hangText="Macintosh file type code(s):">none</t>
3428      </list>
3429    </t>
3430    <t hangText="Person and email address to contact for further information:">
3431      See Authors Section.
3432    </t>
3433    <t hangText="Intended usage:">
3434      COMMON
3435    </t>
3436    <t hangText="Restrictions on usage:">
3437      none
3438    </t>
3439    <t hangText="Author/Change controller:">
3440      IESG
3441    </t>
3442  </list>
3445<section title="Internet Media Type application/http" anchor="">
3446<iref item="Media Type" subitem="application/http" primary="true"/>
3447<iref item="application/http Media Type" primary="true"/>
3449   The application/http type can be used to enclose a pipeline of one or more
3450   HTTP request or response messages (not intermixed).
3453  <list style="hanging" x:indent="12em">
3454    <t hangText="Type name:">
3455      application
3456    </t>
3457    <t hangText="Subtype name:">
3458      http
3459    </t>
3460    <t hangText="Required parameters:">
3461      none
3462    </t>
3463    <t hangText="Optional parameters:">
3464      version, msgtype
3465      <list style="hanging">
3466        <t hangText="version:">
3467          The HTTP-version number of the enclosed messages
3468          (e.g., "1.1"). If not present, the version can be
3469          determined from the first line of the body.
3470        </t>
3471        <t hangText="msgtype:">
3472          The message type &mdash; "request" or "response". If not
3473          present, the type can be determined from the first
3474          line of the body.
3475        </t>
3476      </list>
3477    </t>
3478    <t hangText="Encoding considerations:">
3479      HTTP messages enclosed by this type
3480      are in "binary" format; use of an appropriate
3481      Content-Transfer-Encoding is required when
3482      transmitted via E-mail.
3483    </t>
3484    <t hangText="Security considerations:">
3485      none
3486    </t>
3487    <t hangText="Interoperability considerations:">
3488      none
3489    </t>
3490    <t hangText="Published specification:">
3491      This specification (see <xref target=""/>).
3492    </t>
3493    <t hangText="Applications that use this media type:">
3494    </t>
3495    <t hangText="Additional information:">
3496      <list style="hanging">
3497        <t hangText="Magic number(s):">none</t>
3498        <t hangText="File extension(s):">none</t>
3499        <t hangText="Macintosh file type code(s):">none</t>
3500      </list>
3501    </t>
3502    <t hangText="Person and email address to contact for further information:">
3503      See Authors Section.
3504    </t>
3505    <t hangText="Intended usage:">
3506      COMMON
3507    </t>
3508    <t hangText="Restrictions on usage:">
3509      none
3510    </t>
3511    <t hangText="Author/Change controller:">
3512      IESG
3513    </t>
3514  </list>
3519<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3521   The HTTP Transfer Coding Registry defines the name space for transfer
3522   coding names.
3525   Registrations &MUST; include the following fields:
3526   <list style="symbols">
3527     <t>Name</t>
3528     <t>Description</t>
3529     <t>Pointer to specification text</t>
3530   </list>
3533   Names of transfer codings &MUST-NOT; overlap with names of content codings
3534   (&content-codings;) unless the encoding transformation is identical, as
3535   is the case for the compression codings defined in
3536   <xref target="compression.codings"/>.
3539   Values to be added to this name space require IETF Review (see
3540   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3541   conform to the purpose of transfer coding defined in this section.
3542   Use of program names for the identification of encoding formats
3543   is not desirable and is discouraged for future encodings.
3546   The registry itself is maintained at
3547   <eref target=""/>.
3551<section title="Transfer Coding Registrations" anchor="transfer.coding.registration">
3553   The HTTP Transfer Coding Registry shall be updated with the registrations
3554   below:
3556<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3557   <ttcol>Name</ttcol>
3558   <ttcol>Description</ttcol>
3559   <ttcol>Reference</ttcol>
3560   <c>chunked</c>
3561   <c>Transfer in a series of chunks</c>
3562   <c>
3563      <xref target="chunked.encoding"/>
3564   </c>
3565   <c>compress</c>
3566   <c>UNIX "compress" program method</c>
3567   <c>
3568      <xref target="compress.coding"/>
3569   </c>
3570   <c>deflate</c>
3571   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3572   the "zlib" data format (<xref target="RFC1950"/>)
3573   </c>
3574   <c>
3575      <xref target="deflate.coding"/>
3576   </c>
3577   <c>gzip</c>
3578   <c>Same as GNU zip <xref target="RFC1952"/></c>
3579   <c>
3580      <xref target="gzip.coding"/>
3581   </c>
3585<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3587   The HTTP Upgrade Token Registry defines the name space for protocol-name
3588   tokens used to identify protocols in the <x:ref>Upgrade</x:ref> header
3589   field. Each registered protocol name is associated with contact information
3590   and an optional set of specifications that details how the connection
3591   will be processed after it has been upgraded.
3594   Registrations happen on a "First Come First Served" basis (see
3595   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3596   following rules:
3597  <list style="numbers">
3598    <t>A protocol-name token, once registered, stays registered forever.</t>
3599    <t>The registration &MUST; name a responsible party for the
3600       registration.</t>
3601    <t>The registration &MUST; name a point of contact.</t>
3602    <t>The registration &MAY; name a set of specifications associated with
3603       that token. Such specifications need not be publicly available.</t>
3604    <t>The registration &SHOULD; name a set of expected "protocol-version"
3605       tokens associated with that token at the time of registration.</t>
3606    <t>The responsible party &MAY; change the registration at any time.
3607       The IANA will keep a record of all such changes, and make them
3608       available upon request.</t>
3609    <t>The IESG &MAY; reassign responsibility for a protocol token.
3610       This will normally only be used in the case when a
3611       responsible party cannot be contacted.</t>
3612  </list>
3615   This registration procedure for HTTP Upgrade Tokens replaces that
3616   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3620<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3622   The HTTP Upgrade Token Registry shall be updated with the registration
3623   below:
3625<texttable align="left" suppress-title="true">
3626   <ttcol>Value</ttcol>
3627   <ttcol>Description</ttcol>
3628   <ttcol>Expected Version Tokens</ttcol>
3629   <ttcol>Reference</ttcol>
3631   <c>HTTP</c>
3632   <c>Hypertext Transfer Protocol</c>
3633   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3634   <c><xref target="http.version"/></c>
3637   The responsible party is: "IETF ( - Internet Engineering Task Force".
3643<section title="Security Considerations" anchor="security.considerations">
3645   This section is meant to inform application developers, information
3646   providers, and users of the security limitations in HTTP/1.1 as
3647   described by this document. The discussion does not include
3648   definitive solutions to the problems revealed, though it does make
3649   some suggestions for reducing security risks.
3652<section title="Personal Information" anchor="personal.information">
3654   HTTP clients are often privy to large amounts of personal information,
3655   including both information provided by the user to interact with resources
3656   (e.g., the user's name, location, mail address, passwords, encryption
3657   keys, etc.) and information about the user's browsing activity over
3658   time (e.g., history, bookmarks, etc.). HTTP implementations need to
3659   prevent unintentional leakage of this information.
3663<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3665   A server is in the position to save personal data about a user's
3666   requests which might identify their reading patterns or subjects of
3667   interest.  In particular, log information gathered at an intermediary
3668   often contains a history of user agent interaction, across a multitude
3669   of sites, that can be traced to individual users.
3672   HTTP log information is confidential in nature; its handling is often
3673   constrained by laws and regulations.  Log information needs to be securely
3674   stored and appropriate guidelines followed for its analysis.
3675   Anonymization of personal information within individual entries helps,
3676   but is generally not sufficient to prevent real log traces from being
3677   re-identified based on correlation with other access characteristics.
3678   As such, access traces that are keyed to a specific client should not
3679   be published even if the key is pseudonymous.
3682   To minimize the risk of theft or accidental publication, log information
3683   should be purged of personally identifiable information, including
3684   user identifiers, IP addresses, and user-provided query parameters,
3685   as soon as that information is no longer necessary to support operational
3686   needs for security, auditing, or fraud control.
3690<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3692   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3693   the documents returned by HTTP requests to be only those that were
3694   intended by the server administrators. If an HTTP server translates
3695   HTTP URIs directly into file system calls, the server &MUST; take
3696   special care not to serve files that were not intended to be
3697   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3698   other operating systems use ".." as a path component to indicate a
3699   directory level above the current one. On such a system, an HTTP
3700   server &MUST; disallow any such construct in the request-target if it
3701   would otherwise allow access to a resource outside those intended to
3702   be accessible via the HTTP server. Similarly, files intended for
3703   reference only internally to the server (such as access control
3704   files, configuration files, and script code) &MUST; be protected from
3705   inappropriate retrieval, since they might contain sensitive
3706   information. Experience has shown that minor bugs in such HTTP server
3707   implementations have turned into security risks.
3711<section title="DNS-related Attacks" anchor="dns.related.attacks">
3713   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3714   generally prone to security attacks based on the deliberate misassociation
3715   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3716   cautious in assuming the validity of an IP number/DNS name association unless
3717   the response is protected by DNSSec (<xref target="RFC4033"/>).
3721<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3723   By their very nature, HTTP intermediaries are men-in-the-middle, and
3724   represent an opportunity for man-in-the-middle attacks. Compromise of
3725   the systems on which the intermediaries run can result in serious security
3726   and privacy problems. Intermediaries have access to security-related
3727   information, personal information about individual users and
3728   organizations, and proprietary information belonging to users and
3729   content providers. A compromised intermediary, or an intermediary
3730   implemented or configured without regard to security and privacy
3731   considerations, might be used in the commission of a wide range of
3732   potential attacks.
3735   Intermediaries that contain a shared cache are especially vulnerable
3736   to cache poisoning attacks.
3739   Implementers need to consider the privacy and security
3740   implications of their design and coding decisions, and of the
3741   configuration options they provide to operators (especially the
3742   default configuration).
3745   Users need to be aware that intermediaries are no more trustworthy than
3746   the people who run them; HTTP itself cannot solve this problem.
3750<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3752   Because HTTP uses mostly textual, character-delimited fields, attackers can
3753   overflow buffers in implementations, and/or perform a Denial of Service
3754   against implementations that accept fields with unlimited lengths.
3757   To promote interoperability, this specification makes specific
3758   recommendations for minimum size limits on request-line
3759   (<xref target="request.line"/>)
3760   and blocks of header fields (<xref target="header.fields"/>). These are
3761   minimum recommendations, chosen to be supportable even by implementations
3762   with limited resources; it is expected that most implementations will
3763   choose substantially higher limits.
3766   This specification also provides a way for servers to reject messages that
3767   have request-targets that are too long (&status-414;) or request entities
3768   that are too large (&status-4xx;).
3771   Other fields (including but not limited to request methods, response status
3772   phrases, header field-names, and body chunks) &SHOULD; be limited by
3773   implementations carefully, so as to not impede interoperability.
3778<section title="Acknowledgments" anchor="acks">
3780   This edition of HTTP builds on the many contributions that went into
3781   <xref target="RFC1945" format="none">RFC 1945</xref>,
3782   <xref target="RFC2068" format="none">RFC 2068</xref>,
3783   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3784   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3785   substantial contributions made by the previous authors, editors, and
3786   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3787   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3788   Paul J. Leach, and Mark Nottingham.
3789   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
3790   acknowledgements from prior revisions.
3793   Since 1999, the following contributors have helped improve the HTTP
3794   specification by reporting bugs, asking smart questions, drafting or
3795   reviewing text, and evaluating open issues:
3797<?BEGININC acks ?>
3798<t>Adam Barth,
3799Adam Roach,
3800Addison Phillips,
3801Adrian Chadd,
3802Adrien W. de Croy,
3803Alan Ford,
3804Alan Ruttenberg,
3805Albert Lunde,
3806Alek Storm,
3807Alex Rousskov,
3808Alexandre Morgaut,
3809Alexey Melnikov,
3810Alisha Smith,
3811Amichai Rothman,
3812Amit Klein,
3813Amos Jeffries,
3814Andreas Maier,
3815Andreas Petersson,
3816Anil Sharma,
3817Anne van Kesteren,
3818Anthony Bryan,
3819Asbjorn Ulsberg,
3820Balachander Krishnamurthy,
3821Barry Leiba,
3822Ben Laurie,
3823Benjamin Niven-Jenkins,
3824Bil Corry,
3825Bill Burke,
3826Bjoern Hoehrmann,
3827Bob Scheifler,
3828Boris Zbarsky,
3829Brett Slatkin,
3830Brian Kell,
3831Brian McBarron,
3832Brian Pane,
3833Brian Smith,
3834Bryce Nesbitt,
3835Cameron Heavon-Jones,
3836Carl Kugler,
3837Carsten Bormann,
3838Charles Fry,
3839Chris Newman,
3840Cyrus Daboo,
3841Dale Robert Anderson,
3842Dan Wing,
3843Dan Winship,
3844Daniel Stenberg,
3845Dave Cridland,
3846Dave Crocker,
3847Dave Kristol,
3848David Booth,
3849David Singer,
3850David W. Morris,
3851Diwakar Shetty,
3852Dmitry Kurochkin,
3853Drummond Reed,
3854Duane Wessels,
3855Edward Lee,
3856Eliot Lear,
3857Eran Hammer-Lahav,
3858Eric D. Williams,
3859Eric J. Bowman,
3860Eric Lawrence,
3861Eric Rescorla,
3862Erik Aronesty,
3863Florian Weimer,
3864Frank Ellermann,
3865Fred Bohle,
3866Gabriel Montenegro,
3867Geoffrey Sneddon,
3868Gervase Markham,
3869Grahame Grieve,
3870Greg Wilkins,
3871Harald Tveit Alvestrand,
3872Harry Halpin,
3873Helge Hess,
3874Henrik Nordstrom,
3875Henry S. Thompson,
3876Henry Story,
3877Herbert van de Sompel,
3878Howard Melman,
3879Hugo Haas,
3880Ian Fette,
3881Ian Hickson,
3882Ido Safruti,
3883Ingo Struck,
3884J. Ross Nicoll,
3885James H. Manger,
3886James Lacey,
3887James M. Snell,
3888Jamie Lokier,
3889Jan Algermissen,
3890Jeff Hodges (who came up with the term 'effective Request-URI'),
3891Jeff Walden,
3892Jim Luther,
3893Joe D. Williams,
3894Joe Gregorio,
3895Joe Orton,
3896John C. Klensin,
3897John C. Mallery,
3898John Cowan,
3899John Kemp,
3900John Panzer,
3901John Schneider,
3902John Stracke,
3903John Sullivan,
3904Jonas Sicking,
3905Jonathan Billington,
3906Jonathan Moore,
3907Jonathan Rees,
3908Jonathan Silvera,
3909Jordi Ros,
3910Joris Dobbelsteen,
3911Josh Cohen,
3912Julien Pierre,
3913Jungshik Shin,
3914Justin Chapweske,
3915Justin Erenkrantz,
3916Justin James,
3917Kalvinder Singh,
3918Karl Dubost,
3919Keith Hoffman,
3920Keith Moore,
3921Koen Holtman,
3922Konstantin Voronkov,
3923Kris Zyp,
3924Lisa Dusseault,
3925Maciej Stachowiak,
3926Marc Schneider,
3927Marc Slemko,
3928Mark Baker,
3929Mark Pauley,
3930Mark Watson,
3931Markus Isomaki,
3932Markus Lanthaler,
3933Martin J. Duerst,
3934Martin Musatov,
3935Martin Nilsson,
3936Martin Thomson,
3937Matt Lynch,
3938Matthew Cox,
3939Max Clark,
3940Michael Burrows,
3941Michael Hausenblas,
3942Mike Amundsen,
3943Mike Belshe,
3944Mike Kelly,
3945Mike Schinkel,
3946Miles Sabin,
3947Murray S. Kucherawy,
3948Mykyta Yevstifeyev,
3949Nathan Rixham,
3950Nicholas Shanks,
3951Nico Williams,
3952Nicolas Alvarez,
3953Nicolas Mailhot,
3954Noah Slater,
3955Pablo Castro,
3956Pat Hayes,
3957Patrick R. McManus,
3958Paul E. Jones,
3959Paul Hoffman,
3960Paul Marquess,
3961Peter Lepeska,
3962Peter Saint-Andre,
3963Peter Watkins,
3964Phil Archer,
3965Philippe Mougin,
3966Phillip Hallam-Baker,
3967Poul-Henning Kamp,
3968Preethi Natarajan,
3969Rajeev Bector,
3970Ray Polk,
3971Reto Bachmann-Gmuer,
3972Richard Cyganiak,
3973Robert Brewer,
3974Robert Collins,
3975Robert O'Callahan,
3976Robert Olofsson,
3977Robert Sayre,
3978Robert Siemer,
3979Robert de Wilde,
3980Roberto Javier Godoy,
3981Roberto Peon,
3982Ronny Widjaja,
3983S. Mike Dierken,
3984Salvatore Loreto,
3985Sam Johnston,
3986Sam Ruby,
3987Scott Lawrence (who maintained the original issues list),
3988Sean B. Palmer,
3989Shane McCarron,
3990Stefan Eissing,
3991Stefan Tilkov,
3992Stefanos Harhalakis,
3993Stephane Bortzmeyer,
3994Stephen Farrell,
3995Stephen Ludin,
3996Stuart Williams,
3997Subbu Allamaraju,
3998Sylvain Hellegouarch,
3999Tapan Divekar,
4000Tatsuya Hayashi,
4001Ted Hardie,
4002Thomas Broyer,
4003Thomas Nordin,
4004Thomas Roessler,
4005Tim Bray,
4006Tim Morgan,
4007Tim Olsen,
4008Tom Zhou,
4009Travis Snoozy,
4010Tyler Close,
4011Vincent Murphy,
4012Wenbo Zhu,
4013Werner Baumann,
4014Wilbur Streett,
4015Wilfredo Sanchez Vega,
4016William A. Rowe Jr.,
4017William Chan,
4018Willy Tarreau,
4019Xiaoshu Wang,
4020Yaron Goland,
4021Yngve Nysaeter Pettersen,
4022Yoav Nir,
4023Yogesh Bang,
4024Yutaka Oiwa,
4025Zed A. Shaw, and
4026Zhong Yu.
4028<?ENDINC acks ?>
4034<references title="Normative References">
4036<reference anchor="Part2">
4037  <front>
4038    <title>HTTP/1.1, part 2: Semantics and Payloads</title>
4039    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4040      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4041      <address><email></email></address>
4042    </author>
4043    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4044      <organization abbrev="W3C">World Wide Web Consortium</organization>
4045      <address><email></email></address>
4046    </author>
4047    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4048      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4049      <address><email></email></address>
4050    </author>
4051    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4052  </front>
4053  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4054  <x:source href="p2-semantics.xml" basename="p2-semantics">
4055    <x:defines>1xx (Informational)</x:defines>
4056    <x:defines>1xx</x:defines>
4057    <x:defines>100 (Continue)</x:defines>
4058    <x:defines>101 (Switching Protocols)</x:defines>
4059    <x:defines>2xx (Successful)</x:defines>
4060    <x:defines>2xx</x:defines>
4061    <x:defines>200 (OK)</x:defines>
4062    <x:defines>204 (No Content)</x:defines>
4063    <x:defines>3xx (Redirection)</x:defines>
4064    <x:defines>3xx</x:defines>
4065    <x:defines>301 (Moved Permanently)</x:defines>
4066    <x:defines>4xx (Client Error)</x:defines>
4067    <x:defines>4xx</x:defines>
4068    <x:defines>400 (Bad Request)</x:defines>
4069    <x:defines>405 (Method Not Allowed)</x:defines>
4070    <x:defines>411 (Length Required)</x:defines>
4071    <x:defines>414 (URI Too Long)</x:defines>
4072    <x:defines>417 (Expectation Failed)</x:defines>
4073    <x:defines>426 (Upgrade Required)</x:defines>
4074    <x:defines>501 (Not Implemented)</x:defines>
4075    <x:defines>502 (Bad Gateway)</x:defines>
4076    <x:defines>505 (HTTP Version Not Supported)</x:defines>
4077    <x:defines>Allow</x:defines>
4078    <x:defines>Content-Encoding</x:defines>
4079    <x:defines>Content-Location</x:defines>
4080    <x:defines>Content-Type</x:defines>
4081    <x:defines>Date</x:defines>
4082    <x:defines>Expect</x:defines>
4083    <x:defines>Location</x:defines>
4084    <x:defines>Server</x:defines>
4085    <x:defines>User-Agent</x:defines>
4086  </x:source>
4089<reference anchor="Part4">
4090  <front>
4091    <title>HTTP/1.1, part 4: Conditional Requests</title>
4092    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
4093      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4094      <address><email></email></address>
4095    </author>
4096    <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
4097      <organization abbrev="W3C">World Wide Web Consortium</organization>
4098      <address><email></email></address>
4099    </author>
4100    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
4101      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4102      <address><email></email></address>
4103    </author>
4104    <date month="&ID-MONTH;" year="&ID-YEAR;" />
4105  </front>
4106  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;" />
4107  <x:source basename="p4-conditional" href="p4-conditional.xml">
4108    <x:defines>304 (Not Modified)</x:defines>
4109    <x:defines>ETag</x:defines>
4110    <x:defines>Last-Modified</x:defines>
4111  </x:source>
4114<reference anchor="Part5">
4115  <front>
4116    <title>HTTP/1.1, part 5: Range Requests</title>
4117    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4118      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4119      <address><email></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></email></address>
4124    </author>
4125    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4126      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4127      <address><email></email></address>
4128    </author>
4129    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4130  </front>
4131  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
4132  <x:source href="p5-range.xml" basename="p5-range">
4133    <x:defines>Content-Range</x:defines>
4134  </x:source>
4137<reference anchor="Part6">
4138  <front>
4139    <title>HTTP/1.1, part 6: Caching</title>
4140    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4141      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4142      <address><email></email></address>
4143    </author>
4144    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4145      <organization abbrev="W3C">World Wide Web Consortium</organization>
4146      <address><email></email></address>
4147    </author>
4148    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4149      <organization>Rackspace</organization>
4150      <address><email></email></address>
4151    </author>
4152    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4153      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4154      <address><email></email></address>
4155    </author>
4156    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4157  </front>
4158  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4159  <x:source href="p6-cache.xml" basename="p6-cache">
4160    <x:defines>Expires</x:defines>
4161  </x:source>
4164<reference anchor="Part7">
4165  <front>
4166    <title>HTTP/1.1, part 7: Authentication</title>
4167    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4168      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4169      <address><email></email></address>
4170    </author>
4171    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4172      <organization abbrev="W3C">World Wide Web Consortium</organization>
4173      <address><email></email></address>
4174    </author>
4175    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4176      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4177      <address><email></email></address>
4178    </author>
4179    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4180  </front>
4181  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
4182  <x:source href="p7-auth.xml" basename="p7-auth">
4183    <x:defines>Proxy-Authenticate</x:defines>
4184    <x:defines>Proxy-Authorization</x:defines>
4185  </x:source>
4188<reference anchor="RFC5234">
4189  <front>
4190    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4191    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4192      <organization>Brandenburg InternetWorking</organization>
4193      <address>
4194        <email></email>
4195      </address> 
4196    </author>
4197    <author initials="P." surname="Overell" fullname="Paul Overell">
4198      <organization>THUS plc.</organization>
4199      <address>
4200        <email></email>
4201      </address>
4202    </author>
4203    <date month="January" year="2008"/>
4204  </front>
4205  <seriesInfo name="STD" value="68"/>
4206  <seriesInfo name="RFC" value="5234"/>
4209<reference anchor="RFC2119">
4210  <front>
4211    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4212    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4213      <organization>Harvard University</organization>
4214      <address><email></email></address>
4215    </author>
4216    <date month="March" year="1997"/>
4217  </front>
4218  <seriesInfo name="BCP" value="14"/>
4219  <seriesInfo name="RFC" value="2119"/>
4222<reference anchor="RFC3986">
4223 <front>
4224  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4225  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4226    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4227    <address>
4228       <email></email>
4229       <uri></uri>
4230    </address>
4231  </author>
4232  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4233    <organization abbrev="Day Software">Day Software</organization>
4234    <address>
4235      <email></email>
4236      <uri></uri>
4237    </address>
4238  </author>
4239  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4240    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4241    <address>
4242      <email></email>
4243      <uri></uri>
4244    </address>
4245  </author>
4246  <date month='January' year='2005'></date>
4247 </front>
4248 <seriesInfo name="STD" value="66"/>
4249 <seriesInfo name="RFC" value="3986"/>
4252<reference anchor="USASCII">
4253  <front>
4254    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4255    <author>
4256      <organization>American National Standards Institute</organization>
4257    </author>
4258    <date year="1986"/>
4259  </front>
4260  <seriesInfo name="ANSI" value="X3.4"/>
4263<reference anchor="RFC1950">
4264  <front>
4265    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4266    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4267      <organization>Aladdin Enterprises</organization>
4268      <address><email></email></address>
4269    </author>
4270    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4271    <date month="May" year="1996"/>
4272  </front>
4273  <seriesInfo name="RFC" value="1950"/>
4274  <!--<annotation>
4275    RFC 1950 is an Informational RFC, thus it might be less stable than
4276    this specification. On the other hand, this downward reference was
4277    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4278    therefore it is unlikely to cause problems in practice. See also
4279    <xref target="BCP97"/>.
4280  </annotation>-->
4283<reference anchor="RFC1951">
4284  <front>
4285    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4286    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4287      <organization>Aladdin Enterprises</organization>
4288      <address><email></email></address>
4289    </author>
4290    <date month="May" year="1996"/>
4291  </front>
4292  <seriesInfo name="RFC" value="1951"/>
4293  <!--<annotation>
4294    RFC 1951 is an Informational RFC, thus it might be less stable than
4295    this specification. On the other hand, this downward reference was
4296    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4297    therefore it is unlikely to cause problems in practice. See also
4298    <xref target="BCP97"/>.
4299  </annotation>-->
4302<reference anchor="RFC1952">
4303  <front>
4304    <title>GZIP file format specification version 4.3</title>
4305    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4306      <organization>Aladdin Enterprises</organization>
4307      <address><email></email></address>
4308    </author>
4309    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4310      <address><email></email></address>
4311    </author>
4312    <author initials="M." surname="Adler" fullname="Mark Adler">
4313      <address><email></email></address>
4314    </author>
4315    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4316      <address><email></email></address>
4317    </author>
4318    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4319      <address><email></email></address>
4320    </author>
4321    <date month="May" year="1996"/>
4322  </front>
4323  <seriesInfo name="RFC" value="1952"/>
4324  <!--<annotation>
4325    RFC 1952 is an Informational RFC, thus it might be less stable than
4326    this specification. On the other hand, this downward reference was
4327    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4328    therefore it is unlikely to cause problems in practice. See also
4329    <xref target="BCP97"/>.
4330  </annotation>-->
4335<references title="Informative References">
4337<reference anchor="ISO-8859-1">
4338  <front>
4339    <title>
4340     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4341    </title>
4342    <author>
4343      <organization>International Organization for Standardization</organization>
4344    </author>
4345    <date year="1998"/>
4346  </front>
4347  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4350<reference anchor="Nie1997" target="">
4351  <front>
4352    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4353    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4354    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4355    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4356    <author initials="H." surname="Lie" fullname="H. Lie"/>
4357    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4358    <date year="1997" month="September"/>
4359  </front>
4360  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4363<reference anchor="Pad1995" target="">
4364  <front>
4365    <title>Improving HTTP Latency</title>
4366    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4367    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4368    <date year="1995" month="December"/>
4369  </front>
4370  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4373<reference anchor='RFC1919'>
4374  <front>
4375    <title>Classical versus Transparent IP Proxies</title>
4376    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4377      <address><email></email></address>
4378    </author>
4379    <date year='1996' month='March' />
4380  </front>
4381  <seriesInfo name='RFC' value='1919' />
4384<reference anchor="RFC1945">
4385  <front>
4386    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4387    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4388      <organization>MIT, Laboratory for Computer Science</organization>
4389      <address><email></email></address>
4390    </author>
4391    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4392      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4393      <address><email></email></address>
4394    </author>
4395    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4396      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4397      <address><email></email></address>
4398    </author>
4399    <date month="May" year="1996"/>
4400  </front>
4401  <seriesInfo name="RFC" value="1945"/>
4404<reference anchor="RFC2045">
4405  <front>
4406    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4407    <author initials="N." surname="Freed" fullname="Ned Freed">
4408      <organization>Innosoft International, Inc.</organization>
4409      <address><email></email></address>
4410    </author>
4411    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4412      <organization>First Virtual Holdings</organization>
4413      <address><email></email></address>
4414    </author>
4415    <date month="November" year="1996"/>
4416  </front>
4417  <seriesInfo name="RFC" value="2045"/>
4420<reference anchor="RFC2047">
4421  <front>
4422    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4423    <author initials="K." surname="Moore" fullname="Keith Moore">
4424      <organization>University of Tennessee</organization>
4425      <address><email></email></address>
4426    </author>
4427    <date month="November" year="1996"/>
4428  </front>
4429  <seriesInfo name="RFC" value="2047"/>
4432<reference anchor="RFC2068">
4433  <front>
4434    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4435    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4436      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4437      <address><email></email></address>
4438    </author>
4439    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4440      <organization>MIT Laboratory for Computer Science</organization>
4441      <address><email></email></address>
4442    </author>
4443    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4444      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4445      <address><email></email></address>
4446    </author>
4447    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4448      <organization>MIT Laboratory for Computer Science</organization>
4449      <address><email></email></address>
4450    </author>
4451    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4452      <organization>MIT Laboratory for Computer Science</organization>
4453      <address><email></email></address>
4454    </author>
4455    <date month="January" year="1997"/>
4456  </front>
4457  <seriesInfo name="RFC" value="2068"/>
4460<reference anchor="RFC2145">
4461  <front>
4462    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4463    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4464      <organization>Western Research Laboratory</organization>
4465      <address><email></email></address>
4466    </author>
4467    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4468      <organization>Department of Information and Computer Science</organization>
4469      <address><email></email></address>
4470    </author>
4471    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4472      <organization>MIT Laboratory for Computer Science</organization>
4473      <address><email></email></address>
4474    </author>
4475    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4476      <organization>W3 Consortium</organization>
4477      <address><email></email></address>
4478    </author>
4479    <date month="May" year="1997"/>
4480  </front>
4481  <seriesInfo name="RFC" value="2145"/>
4484<reference anchor="RFC2616">
4485  <front>
4486    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4487    <author initials="R." surname="Fielding" fullname="R. Fielding">
4488      <organization>University of California, Irvine</organization>
4489      <address><email></email></address>
4490    </author>
4491    <author initials="J." surname="Gettys" fullname="J. Gettys">
4492      <organization>W3C</organization>
4493      <address><email></email></address>
4494    </author>
4495    <author initials="J." surname="Mogul" fullname="J. Mogul">
4496      <organization>Compaq Computer Corporation</organization>
4497      <address><email></email></address>
4498    </author>
4499    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4500      <organization>MIT Laboratory for Computer Science</organization>
4501      <address><email></email></address>
4502    </author>
4503    <author initials="L." surname="Masinter" fullname="L. Masinter">
4504      <organization>Xerox Corporation</organization>
4505      <address><email></email></address>
4506    </author>
4507    <author initials="P." surname="Leach" fullname="P. Leach">
4508      <organization>Microsoft Corporation</organization>
4509      <address><email></email></address>
4510    </author>
4511    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4512      <organization>W3C</organization>
4513      <address><email></email></address>
4514    </author>
4515    <date month="June" year="1999"/>
4516  </front>
4517  <seriesInfo name="RFC" value="2616"/>
4520<reference anchor='RFC2817'>
4521  <front>
4522    <title>Upgrading to TLS Within HTTP/1.1</title>
4523    <author initials='R.' surname='Khare' fullname='R. Khare'>
4524      <organization>4K Associates / UC Irvine</organization>
4525      <address><email></email></address>
4526    </author>
4527    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4528      <organization>Agranat Systems, Inc.</organization>
4529      <address><email></email></address>
4530    </author>
4531    <date year='2000' month='May' />
4532  </front>
4533  <seriesInfo name='RFC' value='2817' />
4536<reference anchor='RFC2818'>
4537  <front>
4538    <title>HTTP Over TLS</title>
4539    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4540      <organization>RTFM, Inc.</organization>
4541      <address><email></email></address>
4542    </author>
4543    <date year='2000' month='May' />
4544  </front>
4545  <seriesInfo name='RFC' value='2818' />
4548<reference anchor='RFC2965'>
4549  <front>
4550    <title>HTTP State Management Mechanism</title>
4551    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4552      <organization>Bell Laboratories, Lucent Technologies</organization>
4553      <address><email></email></address>
4554    </author>
4555    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4556      <organization>, Inc.</organization>
4557      <address><email></email></address>
4558    </author>
4559    <date year='2000' month='October' />
4560  </front>
4561  <seriesInfo name='RFC' value='2965' />
4564<reference anchor='RFC3040'>
4565  <front>
4566    <title>Internet Web Replication and Caching Taxonomy</title>
4567    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4568      <organization>Equinix, Inc.</organization>
4569    </author>
4570    <author initials='I.' surname='Melve' fullname='I. Melve'>
4571      <organization>UNINETT</organization>
4572    </author>
4573    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4574      <organization>CacheFlow Inc.</organization>
4575    </author>
4576    <date year='2001' month='January' />
4577  </front>
4578  <seriesInfo name='RFC' value='3040' />
4581<reference anchor='RFC3864'>
4582  <front>
4583    <title>Registration Procedures for Message Header Fields</title>
4584    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4585      <organization>Nine by Nine</organization>
4586      <address><email></email></address>
4587    </author>
4588    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4589      <organization>BEA Systems</organization>
4590      <address><email></email></address>
4591    </author>
4592    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4593      <organization>HP Labs</organization>
4594      <address><email></email></address>
4595    </author>
4596    <date year='2004' month='September' />
4597  </front>
4598  <seriesInfo name='BCP' value='90' />
4599  <seriesInfo name='RFC' value='3864' />
4602<reference anchor='RFC4033'>
4603  <front>
4604    <title>DNS Security Introduction and Requirements</title>
4605    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4606    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4607    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4608    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4609    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4610    <date year='2005' month='March' />
4611  </front>
4612  <seriesInfo name='RFC' value='4033' />
4615<reference anchor="RFC4288">
4616  <front>
4617    <title>Media Type Specifications and Registration Procedures</title>
4618    <author initials="N." surname="Freed" fullname="N. Freed">
4619      <organization>Sun Microsystems</organization>
4620      <address>
4621        <email></email>
4622      </address>
4623    </author>
4624    <author initials="J." surname="Klensin" fullname="J. Klensin">
4625      <address>
4626        <email></email>
4627      </address>
4628    </author>
4629    <date year="2005" month="December"/>
4630  </front>
4631  <seriesInfo name="BCP" value="13"/>
4632  <seriesInfo name="RFC" value="4288"/>
4635<reference anchor='RFC4395'>
4636  <front>
4637    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4638    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4639      <organization>AT&amp;T Laboratories</organization>
4640      <address>
4641        <email></email>
4642      </address>
4643    </author>
4644    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4645      <organization>Qualcomm, Inc.</organization>
4646      <address>
4647        <email></email>
4648      </address>
4649    </author>
4650    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4651      <organization>Adobe Systems</organization>
4652      <address>
4653        <email></email>
4654      </address>
4655    </author>
4656    <date year='2006' month='February' />
4657  </front>
4658  <seriesInfo name='BCP' value='115' />
4659  <seriesInfo name='RFC' value='4395' />
4662<reference anchor='RFC4559'>
4663  <front>
4664    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4665    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4666    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4667    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4668    <date year='2006' month='June' />
4669  </front>
4670  <seriesInfo name='RFC' value='4559' />
4673<reference anchor='RFC5226'>
4674  <front>
4675    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4676    <author initials='T.' surname='Narten' fullname='T. Narten'>
4677      <organization>IBM</organization>
4678      <address><email></email></address>
4679    </author>
4680    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4681      <organization>Google</organization>
4682      <address><email></email></address>
4683    </author>
4684    <date year='2008' month='May' />
4685  </front>
4686  <seriesInfo name='BCP' value='26' />
4687  <seriesInfo name='RFC' value='5226' />
4690<reference anchor="RFC5322">
4691  <front>
4692    <title>Internet Message Format</title>
4693    <author initials="P." surname="Resnick" fullname="P. Resnick">
4694      <organization>Qualcomm Incorporated</organization>
4695    </author>
4696    <date year="2008" month="October"/>
4697  </front>
4698  <seriesInfo name="RFC" value="5322"/>
4701<reference anchor="RFC6265">
4702  <front>
4703    <title>HTTP State Management Mechanism</title>
4704    <author initials="A." surname="Barth" fullname="Adam Barth">
4705      <organization abbrev="U.C. Berkeley">
4706        University of California, Berkeley
4707      </organization>
4708      <address><email></email></address>
4709    </author>
4710    <date year="2011" month="April" />
4711  </front>
4712  <seriesInfo name="RFC" value="6265"/>
4715<!--<reference anchor='BCP97'>
4716  <front>
4717    <title>Handling Normative References to Standards-Track Documents</title>
4718    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4719      <address>
4720        <email></email>
4721      </address>
4722    </author>
4723    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4724      <organization>MIT</organization>
4725      <address>
4726        <email></email>
4727      </address>
4728    </author>
4729    <date year='2007' month='June' />
4730  </front>
4731  <seriesInfo name='BCP' value='97' />
4732  <seriesInfo name='RFC' value='4897' />
4735<reference anchor="Kri2001" target="">
4736  <front>
4737    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4738    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4739    <date year="2001" month="November"/>
4740  </front>
4741  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4744<reference anchor="Spe" target="">
4745  <front>
4746    <title>Analysis of HTTP Performance Problems</title>
4747    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4748    <date/>
4749  </front>
4752<reference anchor="Tou1998" target="">
4753  <front>
4754  <title>Analysis of HTTP Performance</title>
4755  <author initials="J." surname="Touch" fullname="Joe Touch">
4756    <organization>USC/Information Sciences Institute</organization>
4757    <address><email></email></address>
4758  </author>
4759  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4760    <organization>USC/Information Sciences Institute</organization>
4761    <address><email></email></address>
4762  </author>
4763  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4764    <organization>USC/Information Sciences Institute</organization>
4765    <address><email></email></address>
4766  </author>
4767  <date year="1998" month="Aug"/>
4768  </front>
4769  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4770  <annotation>(original report dated Aug. 1996)</annotation>
4776<section title="HTTP Version History" anchor="compatibility">
4778   HTTP has been in use by the World-Wide Web global information initiative
4779   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4780   was a simple protocol for hypertext data transfer across the Internet
4781   with only a single request method (GET) and no metadata.
4782   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4783   methods and MIME-like messaging that could include metadata about the data
4784   transferred and modifiers on the request/response semantics. However,
4785   HTTP/1.0 did not sufficiently take into consideration the effects of
4786   hierarchical proxies, caching, the need for persistent connections, or
4787   name-based virtual hosts. The proliferation of incompletely-implemented
4788   applications calling themselves "HTTP/1.0" further necessitated a
4789   protocol version change in order for two communicating applications
4790   to determine each other's true capabilities.
4793   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4794   requirements that enable reliable implementations, adding only
4795   those new features that will either be safely ignored by an HTTP/1.0
4796   recipient or only sent when communicating with a party advertising
4797   conformance with HTTP/1.1.
4800   It is beyond the scope of a protocol specification to mandate
4801   conformance with previous versions. HTTP/1.1 was deliberately
4802   designed, however, to make supporting previous versions easy.
4803   We would expect a general-purpose HTTP/1.1 server to understand
4804   any valid request in the format of HTTP/1.0 and respond appropriately
4805   with an HTTP/1.1 message that only uses features understood (or
4806   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4807   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4810   Since HTTP/0.9 did not support header fields in a request,
4811   there is no mechanism for it to support name-based virtual
4812   hosts (selection of resource by inspection of the <x:ref>Host</x:ref> header
4813   field).  Any server that implements name-based virtual hosts
4814   ought to disable support for HTTP/0.9.  Most requests that
4815   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4816   requests wherein a buggy client failed to properly encode
4817   linear whitespace found in a URI reference and placed in
4818   the request-target.
4821<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4823   This section summarizes major differences between versions HTTP/1.0
4824   and HTTP/1.1.
4827<section title="Multi-homed Web Servers" anchor="">
4829   The requirements that clients and servers support the <x:ref>Host</x:ref>
4830   header field (<xref target=""/>), report an error if it is
4831   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4832   are among the most important changes defined by HTTP/1.1.
4835   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4836   addresses and servers; there was no other established mechanism for
4837   distinguishing the intended server of a request than the IP address
4838   to which that request was directed. The <x:ref>Host</x:ref> header field was
4839   introduced during the development of HTTP/1.1 and, though it was
4840   quickly implemented by most HTTP/1.0 browsers, additional requirements
4841   were placed on all HTTP/1.1 requests in order to ensure complete
4842   adoption.  At the time of this writing, most HTTP-based services
4843   are dependent upon the Host header field for targeting requests.
4847<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4849   In HTTP/1.0, each connection is established by the client prior to the
4850   request and closed by the server after sending the response. However, some
4851   implementations implement the explicitly negotiated ("Keep-Alive") version
4852   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4853   target="RFC2068"/>.
4856   Some clients and servers might wish to be compatible with these previous
4857   approaches to persistent connections, by explicitly negotiating for them
4858   with a "Connection: keep-alive" request header field. However, some
4859   experimental implementations of HTTP/1.0 persistent connections are faulty;
4860   for example, if a HTTP/1.0 proxy server doesn't understand
4861   <x:ref>Connection</x:ref>, it will erroneously forward that header field
4862   to the next inbound server, which would result in a hung connection.
4865   One attempted solution was the introduction of a Proxy-Connection header
4866   field, targeted specifically at proxies. In practice, this was also
4867   unworkable, because proxies are often deployed in multiple layers, bringing
4868   about the same problem discussed above.
4871   As a result, clients are encouraged not to send the Proxy-Connection header
4872   field in any requests.
4875   Clients are also encouraged to consider the use of Connection: keep-alive
4876   in requests carefully; while they can enable persistent connections with
4877   HTTP/1.0 servers, clients using them need will need to monitor the
4878   connection for "hung" requests (which indicate that the client ought stop
4879   sending the header field), and this mechanism ought not be used by clients
4880   at all when a proxy is being used.
4884<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
4886   HTTP/1.1 introduces the <x:ref>Transfer-Encoding</x:ref> header field
4887   (<xref target="header.transfer-encoding"/>). Proxies/gateways &MUST; remove
4888   any transfer-coding prior to forwarding a message via a MIME-compliant
4889   protocol.
4895<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4897  Clarify that the string "HTTP" in the HTTP-version ABNF production is case
4898  sensitive. Restrict the version numbers to be single digits due to the fact
4899  that implementations are known to handle multi-digit version numbers
4900  incorrectly.
4901  (<xref target="http.version"/>)
4904  Update use of abs_path production from RFC 1808 to the path-absolute + query
4905  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4906  request method only.
4907  (<xref target="request-target"/>)
4910  Require that invalid whitespace around field-names be rejected.
4911  (<xref target="header.fields"/>)
4914  Rules about implicit linear whitespace between certain grammar productions
4915  have been removed; now whitespace is only allowed where specifically
4916  defined in the ABNF.
4917  (<xref target="whitespace"/>)
4920  The NUL octet is no longer allowed in comment and quoted-string
4921  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4922  Non-ASCII content in header fields and reason phrase has been obsoleted and
4923  made opaque (the TEXT rule was removed).
4924  (<xref target="field.components"/>)
4927  Empty list elements in list productions have been deprecated.
4928  (<xref target="abnf.extension"/>)
4931  Require recipients to handle bogus <x:ref>Content-Length</x:ref> header
4932  fields as errors.
4933  (<xref target="message.body"/>)
4936  Remove reference to non-existent identity transfer-coding value tokens.
4937  (Sections <xref format="counter" target="message.body"/> and
4938  <xref format="counter" target="transfer.codings"/>)
4941  Clarification that the chunk length does not include the count of the octets
4942  in the chunk header and trailer. Furthermore disallowed line folding
4943  in chunk extensions, and deprecate their use.
4944  (<xref target="chunked.encoding"/>)
4947  Registration of Transfer Codings now requires IETF Review
4948  (<xref target="transfer.coding.registry"/>)
4951  Remove hard limit of two connections per server.
4952  Remove requirement to retry a sequence of requests as long it was idempotent.
4953  Remove requirements about when servers are allowed to close connections
4954  prematurely.
4955  (<xref target="persistent.practical"/>)
4958  Remove requirement to retry requests under certain circumstances when the
4959  server prematurely closes the connection.
4960  (<xref target="message.transmission.requirements"/>)
4963  Change ABNF productions for header fields to only define the field value.
4966  Clarify exactly when "close" connection options have to be sent.
4967  (<xref target="header.connection"/>)
4970  Define the semantics of the <x:ref>Upgrade</x:ref> header field in responses
4971  other than 101 (this was incorporated from <xref target="RFC2817"/>).
4972  (<xref target="header.upgrade"/>)
4975  Take over the Upgrade Token Registry, previously defined in
4976  <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
4977  (<xref target="upgrade.token.registry"/>)
4982<section title="ABNF list extension: #rule" anchor="abnf.extension">
4984  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
4985  improve readability in the definitions of some header field values.
4988  A construct "#" is defined, similar to "*", for defining comma-delimited
4989  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
4990  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
4991  comma (",") and optional whitespace (OWS).   
4994  Thus,
4995</preamble><artwork type="example">
4996  1#element =&gt; element *( OWS "," OWS element )
4999  and:
5000</preamble><artwork type="example">
5001  #element =&gt; [ 1#element ]
5004  and for n &gt;= 1 and m &gt; 1:
5005</preamble><artwork type="example">
5006  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
5009  For compatibility with legacy list rules, recipients &SHOULD; accept empty
5010  list elements. In other words, consumers would follow the list productions:
5012<figure><artwork type="example">
5013  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
5015  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
5018  Note that empty elements do not contribute to the count of elements present,
5019  though.
5022  For example, given these ABNF productions:
5024<figure><artwork type="example">
5025  example-list      = 1#example-list-elmt
5026  example-list-elmt = token ; see <xref target="field.components"/>
5029  Then these are valid values for example-list (not including the double
5030  quotes, which are present for delimitation only):
5032<figure><artwork type="example">
5033  "foo,bar"
5034  "foo ,bar,"
5035  "foo , ,bar,charlie   "
5038  But these values would be invalid, as at least one non-empty element is
5039  required:
5041<figure><artwork type="example">
5042  ""
5043  ","
5044  ",   ,"
5047  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
5048  expanded as explained above.
5052<?BEGININC p1-messaging.abnf-appendix ?>
5053<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5055<artwork type="abnf" name="p1-messaging.parsed-abnf">
5056<x:ref>BWS</x:ref> = OWS
5058<x:ref>Connection</x:ref> = *( "," OWS ) connection-option *( OWS "," [ OWS
5059 connection-option ] )
5060<x:ref>Content-Length</x:ref> = 1*DIGIT
5062<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5063 ]
5064<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
5065<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
5066<x:ref>Host</x:ref> = uri-host [ ":" port ]
5068<x:ref>OWS</x:ref> = *( SP / HTAB )
5070<x:ref>RWS</x:ref> = 1*( SP / HTAB )
5072<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5073<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5074<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5075 transfer-coding ] )
5077<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5078<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
5080<x:ref>Via</x:ref> = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment
5081 ] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS
5082 comment ] ) ] )
5084<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5085<x:ref>absolute-form</x:ref> = absolute-URI
5086<x:ref>asterisk-form</x:ref> = "*"
5087<x:ref>attribute</x:ref> = token
5088<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5089<x:ref>authority-form</x:ref> = authority
5091<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5092<x:ref>chunk-data</x:ref> = 1*OCTET
5093<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5094<x:ref>chunk-ext-name</x:ref> = token
5095<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5096<x:ref>chunk-size</x:ref> = 1*HEXDIG
5097<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
5098<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5099<x:ref>connection-option</x:ref> = token
5100<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5101 / %x2A-5B ; '*'-'['
5102 / %x5D-7E ; ']'-'~'
5103 / obs-text
5105<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5106<x:ref>field-name</x:ref> = token
5107<x:ref>field-value</x:ref> = *( field-content / obs-fold )
5109<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
5110<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5111<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5113<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
5115<x:ref>message-body</x:ref> = *OCTET
5116<x:ref>method</x:ref> = token
5118<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
5119<x:ref>obs-text</x:ref> = %x80-FF
5120<x:ref>origin-form</x:ref> = path-absolute [ "?" query ]
5122<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5123<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5124<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5125<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5126<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
5127<x:ref>protocol-name</x:ref> = token
5128<x:ref>protocol-version</x:ref> = token
5129<x:ref>pseudonym</x:ref> = token
5131<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5132 / %x5D-7E ; ']'-'~'
5133 / obs-text
5134<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
5135 / %x5D-7E ; ']'-'~'
5136 / obs-text
5137<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5138<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5139<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5140<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5141<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5143<x:ref>rank</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5144<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5145<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5146<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5147<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5148<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
5149<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
5150 asterisk-form
5152<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5153 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5154<x:ref>start-line</x:ref> = request-line / status-line
5155<x:ref>status-code</x:ref> = 3DIGIT
5156<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
5158<x:ref>t-codings</x:ref> = "trailers" / ( transfer-coding [ t-ranking ] )
5159<x:ref>t-ranking</x:ref> = OWS ";" OWS "q=" rank
5160<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5161 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5162<x:ref>token</x:ref> = 1*tchar
5163<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5164<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5165 transfer-extension
5166<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5167<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5169<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5171<x:ref>value</x:ref> = word
5173<x:ref>word</x:ref> = token / quoted-string
5177<?ENDINC p1-messaging.abnf-appendix ?>
5179<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5181<section title="Since RFC 2616">
5183  Extracted relevant partitions from <xref target="RFC2616"/>.
5187<section title="Since draft-ietf-httpbis-p1-messaging-00">
5189  Closed issues:
5190  <list style="symbols">
5191    <t>
5192      <eref target=""/>:
5193      "HTTP Version should be case sensitive"
5194      (<eref target=""/>)
5195    </t>
5196    <t>
5197      <eref target=""/>:
5198      "'unsafe' characters"
5199      (<eref target=""/>)
5200    </t>
5201    <t>
5202      <eref target=""/>:
5203      "Chunk Size Definition"
5204      (<eref target=""/>)
5205    </t>
5206    <t>
5207      <eref target=""/>:
5208      "Message Length"
5209      (<eref target=""/>)
5210    </t>
5211    <t>
5212      <eref target=""/>:
5213      "Media Type Registrations"
5214      (<eref target=""/>)
5215    </t>
5216    <t>
5217      <eref target=""/>:
5218      "URI includes query"
5219      (<eref target=""/>)
5220    </t>
5221    <t>
5222      <eref target=""/>:
5223      "No close on 1xx responses"
5224      (<eref target=""/>)
5225    </t>
5226    <t>
5227      <eref target=""/>:
5228      "Remove 'identity' token references"
5229      (<eref target=""/>)
5230    </t>
5231    <t>
5232      <eref target=""/>:
5233      "Import query BNF"
5234    </t>
5235    <t>
5236      <eref target=""/>:
5237      "qdtext BNF"
5238    </t>
5239    <t>
5240      <eref target=""/>:
5241      "Normative and Informative references"
5242    </t>
5243    <t>
5244      <eref target=""/>:
5245      "RFC2606 Compliance"
5246    </t>
5247    <t>
5248      <eref target=""/>:
5249      "RFC977 reference"
5250    </t>
5251    <t>
5252      <eref target=""/>:
5253      "RFC1700 references"
5254    </t>
5255    <t>
5256      <eref target=""/>:
5257      "inconsistency in date format explanation"
5258    </t>
5259    <t>
5260      <eref target=""/>:
5261      "Date reference typo"
5262    </t>
5263    <t>
5264      <eref target=""/>:
5265      "Informative references"
5266    </t>
5267    <t>
5268      <eref target=""/>:
5269      "ISO-8859-1 Reference"
5270    </t>
5271    <t>
5272      <eref target=""/>:
5273      "Normative up-to-date references"
5274    </t>
5275  </list>
5278  Other changes:
5279  <list style="symbols">
5280    <t>
5281      Update media type registrations to use RFC4288 template.
5282    </t>
5283    <t>
5284      Use names of RFC4234 core rules DQUOTE and HTAB,
5285      fix broken ABNF for chunk-data
5286      (work in progress on <eref target=""/>)
5287    </t>
5288  </list>
5292<section title="Since draft-ietf-httpbis-p1-messaging-01">
5294  Closed issues:
5295  <list style="symbols">
5296    <t>
5297      <eref target=""/>:
5298      "Bodies on GET (and other) requests"
5299    </t>
5300    <t>
5301      <eref target=""/>:
5302      "Updating to RFC4288"
5303    </t>
5304    <t>
5305      <eref target=""/>:
5306      "Status Code and Reason Phrase"
5307    </t>
5308    <t>
5309      <eref target=""/>:
5310      "rel_path not used"
5311    </t>
5312  </list>
5315  Ongoing work on ABNF conversion (<eref target=""/>):
5316  <list style="symbols">
5317    <t>
5318      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5319      "trailer-part").
5320    </t>
5321    <t>
5322      Avoid underscore character in rule names ("http_URL" ->
5323      "http-URL", "abs_path" -> "path-absolute").
5324    </t>
5325    <t>
5326      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5327      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5328      have to be updated when switching over to RFC3986.
5329    </t>
5330    <t>
5331      Synchronize core rules with RFC5234.
5332    </t>
5333    <t>
5334      Get rid of prose rules that span multiple lines.
5335    </t>
5336    <t>
5337      Get rid of unused rules LOALPHA and UPALPHA.
5338    </t>
5339    <t>
5340      Move "Product Tokens" section (back) into Part 1, as "token" is used
5341      in the definition of the Upgrade header field.
5342    </t>
5343    <t>
5344      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5345    </t>
5346    <t>
5347      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5348    </t>
5349  </list>
5353<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5355  Closed issues:
5356  <list style="symbols">
5357    <t>
5358      <eref target=""/>:
5359      "HTTP-date vs. rfc1123-date"
5360    </t>
5361    <t>
5362      <eref target=""/>:
5363      "WS in quoted-pair"
5364    </t>
5365  </list>
5368  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5369  <list style="symbols">
5370    <t>
5371      Reference RFC 3984, and update header field registrations for header
5372      fields defined in this document.
5373    </t>
5374  </list>
5377  Ongoing work on ABNF conversion (<eref target=""/>):
5378  <list style="symbols">
5379    <t>
5380      Replace string literals when the string really is case-sensitive (HTTP-version).
5381    </t>
5382  </list>
5386<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5388  Closed issues:
5389  <list style="symbols">
5390    <t>
5391      <eref target=""/>:
5392      "Connection closing"
5393    </t>
5394    <t>
5395      <eref target=""/>:
5396      "Move registrations and registry information to IANA Considerations"
5397    </t>
5398    <t>
5399      <eref target=""/>:
5400      "need new URL for PAD1995 reference"
5401    </t>
5402    <t>
5403      <eref target=""/>:
5404      "IANA Considerations: update HTTP URI scheme registration"
5405    </t>
5406    <t>
5407      <eref target=""/>:
5408      "Cite HTTPS URI scheme definition"
5409    </t>
5410    <t>
5411      <eref target=""/>:
5412      "List-type header fields vs Set-Cookie"
5413    </t>
5414  </list>
5417  Ongoing work on ABNF conversion (<eref target=""/>):
5418  <list style="symbols">
5419    <t>
5420      Replace string literals when the string really is case-sensitive (HTTP-Date).
5421    </t>
5422    <t>
5423      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5424    </t>
5425  </list>
5429<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5431  Closed issues:
5432  <list style="symbols">
5433    <t>
5434      <eref target=""/>:
5435      "Out-of-date reference for URIs"
5436    </t>
5437    <t>
5438      <eref target=""/>:
5439      "RFC 2822 is updated by RFC 5322"
5440    </t>
5441  </list>
5444  Ongoing work on ABNF conversion (<eref target=""/>):
5445  <list style="symbols">
5446    <t>
5447      Use "/" instead of "|" for alternatives.
5448    </t>
5449    <t>
5450      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5451    </t>
5452    <t>
5453      Only reference RFC 5234's core rules.
5454    </t>
5455    <t>
5456      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5457      whitespace ("OWS") and required whitespace ("RWS").
5458    </t>
5459    <t>
5460      Rewrite ABNFs to spell out whitespace rules, factor out
5461      header field value format definitions.
5462    </t>
5463  </list>
5467<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5469  Closed issues:
5470  <list style="symbols">
5471    <t>
5472      <eref target=""/>:
5473      "Header LWS"
5474    </t>
5475    <t>
5476      <eref target=""/>:
5477      "Sort 1.3 Terminology"
5478    </t>
5479    <t>
5480      <eref target=""/>:
5481      "RFC2047 encoded words"
5482    </t>
5483    <t>
5484      <eref target=""/>:
5485      "Character Encodings in TEXT"
5486    </t>
5487    <t>
5488      <eref target=""/>:
5489      "Line Folding"
5490    </t>
5491    <t>
5492      <eref target=""/>:
5493      "OPTIONS * and proxies"
5494    </t>
5495    <t>
5496      <eref target=""/>:
5497      "reason-phrase BNF"
5498    </t>
5499    <t>
5500      <eref target=""/>:
5501      "Use of TEXT"
5502    </t>
5503    <t>
5504      <eref target=""/>:
5505      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5506    </t>
5507    <t>
5508      <eref target=""/>:
5509      "RFC822 reference left in discussion of date formats"
5510    </t>
5511  </list>
5514  Final work on ABNF conversion (<eref target=""/>):
5515  <list style="symbols">
5516    <t>
5517      Rewrite definition of list rules, deprecate empty list elements.
5518    </t>
5519    <t>
5520      Add appendix containing collected and expanded ABNF.
5521    </t>
5522  </list>
5525  Other changes:
5526  <list style="symbols">
5527    <t>
5528      Rewrite introduction; add mostly new Architecture Section.
5529    </t>
5530    <t>
5531      Move definition of quality values from Part 3 into Part 1;
5532      make TE request header field grammar independent of accept-params (defined in Part 3).
5533    </t>
5534  </list>
5538<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5540  Closed issues:
5541  <list style="symbols">
5542    <t>
5543      <eref target=""/>:
5544      "base for numeric protocol elements"
5545    </t>
5546    <t>
5547      <eref target=""/>:
5548      "comment ABNF"
5549    </t>
5550  </list>
5553  Partly resolved issues:
5554  <list style="symbols">
5555    <t>
5556      <eref target=""/>:
5557      "205 Bodies" (took out language that implied that there might be
5558      methods for which a request body MUST NOT be included)
5559    </t>
5560    <t>
5561      <eref target=""/>:
5562      "editorial improvements around HTTP-date"
5563    </t>
5564  </list>
5568<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5570  Closed issues:
5571  <list style="symbols">
5572    <t>
5573      <eref target=""/>:
5574      "Repeating single-value header fields"
5575    </t>
5576    <t>
5577      <eref target=""/>:
5578      "increase connection limit"
5579    </t>
5580    <t>
5581      <eref target=""/>:
5582      "IP addresses in URLs"
5583    </t>
5584    <t>
5585      <eref target=""/>:
5586      "take over HTTP Upgrade Token Registry"
5587    </t>
5588    <t>
5589      <eref target=""/>:
5590      "CR and LF in chunk extension values"
5591    </t>
5592    <t>
5593      <eref target=""/>:
5594      "HTTP/0.9 support"
5595    </t>
5596    <t>
5597      <eref target=""/>:
5598      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5599    </t>
5600    <t>
5601      <eref target=""/>:
5602      "move definitions of gzip/deflate/compress to part 1"
5603    </t>
5604    <t>
5605      <eref target=""/>:
5606      "disallow control characters in quoted-pair"
5607    </t>
5608  </list>
5611  Partly resolved issues:
5612  <list style="symbols">
5613    <t>
5614      <eref target=""/>:
5615      "update IANA requirements wrt Transfer-Coding values" (add the
5616      IANA Considerations subsection)
5617    </t>
5618  </list>
5622<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5624  Closed issues:
5625  <list style="symbols">
5626    <t>
5627      <eref target=""/>:
5628      "header parsing, treatment of leading and trailing OWS"
5629    </t>
5630  </list>
5633  Partly resolved issues:
5634  <list style="symbols">
5635    <t>
5636      <eref target=""/>:
5637      "Placement of 13.5.1 and 13.5.2"
5638    </t>
5639    <t>
5640      <eref target=""/>:
5641      "use of term "word" when talking about header field structure"
5642    </t>
5643  </list>
5647<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5649  Closed issues:
5650  <list style="symbols">
5651    <t>
5652      <eref target=""/>:
5653      "Clarification of the term 'deflate'"
5654    </t>
5655    <t>
5656      <eref target=""/>:
5657      "OPTIONS * and proxies"
5658    </t>
5659    <t>
5660      <eref target=""/>:
5661      "MIME-Version not listed in P1, general header fields"
5662    </t>
5663    <t>
5664      <eref target=""/>:
5665      "IANA registry for content/transfer encodings"
5666    </t>
5667    <t>
5668      <eref target=""/>:
5669      "Case-sensitivity of HTTP-date"
5670    </t>
5671    <t>
5672      <eref target=""/>:
5673      "use of term "word" when talking about header field structure"
5674    </t>
5675  </list>
5678  Partly resolved issues:
5679  <list style="symbols">
5680    <t>
5681      <eref target=""/>:
5682      "Term for the requested resource's URI"
5683    </t>
5684  </list>
5688<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5690  Closed issues:
5691  <list style="symbols">
5692    <t>
5693      <eref target=""/>:
5694      "Connection Closing"
5695    </t>
5696    <t>
5697      <eref target=""/>:
5698      "Delimiting messages with multipart/byteranges"
5699    </t>
5700    <t>
5701      <eref target=""/>:
5702      "Handling multiple Content-Length header fields"
5703    </t>
5704    <t>
5705      <eref target=""/>:
5706      "Clarify entity / representation / variant terminology"
5707    </t>
5708    <t>
5709      <eref target=""/>:
5710      "consider removing the 'changes from 2068' sections"
5711    </t>
5712  </list>
5715  Partly resolved issues:
5716  <list style="symbols">
5717    <t>
5718      <eref target=""/>:
5719      "HTTP(s) URI scheme definitions"
5720    </t>
5721  </list>
5725<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5727  Closed issues:
5728  <list style="symbols">
5729    <t>
5730      <eref target=""/>:
5731      "Trailer requirements"
5732    </t>
5733    <t>
5734      <eref target=""/>:
5735      "Text about clock requirement for caches belongs in p6"
5736    </t>
5737    <t>
5738      <eref target=""/>:
5739      "effective request URI: handling of missing host in HTTP/1.0"
5740    </t>
5741    <t>
5742      <eref target=""/>:
5743      "confusing Date requirements for clients"
5744    </t>
5745  </list>
5748  Partly resolved issues:
5749  <list style="symbols">
5750    <t>
5751      <eref target=""/>:
5752      "Handling multiple Content-Length header fields"
5753    </t>
5754  </list>
5758<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5760  Closed issues:
5761  <list style="symbols">
5762    <t>
5763      <eref target=""/>:
5764      "RFC2145 Normative"
5765    </t>
5766    <t>
5767      <eref target=""/>:
5768      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5769    </t>
5770    <t>
5771      <eref target=""/>:
5772      "define 'transparent' proxy"
5773    </t>
5774    <t>
5775      <eref target=""/>:
5776      "Header Field Classification"
5777    </t>
5778    <t>
5779      <eref target=""/>:
5780      "Is * usable as a request-uri for new methods?"
5781    </t>
5782    <t>
5783      <eref target=""/>:
5784      "Migrate Upgrade details from RFC2817"
5785    </t>
5786    <t>
5787      <eref target=""/>:
5788      "untangle ABNFs for header fields"
5789    </t>
5790    <t>
5791      <eref target=""/>:
5792      "update RFC 2109 reference"
5793    </t>
5794  </list>
5798<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5800  Closed issues:
5801  <list style="symbols">
5802    <t>
5803      <eref target=""/>:
5804      "Allow is not in 13.5.2"
5805    </t>
5806    <t>
5807      <eref target=""/>:
5808      "Handling multiple Content-Length header fields"
5809    </t>
5810    <t>
5811      <eref target=""/>:
5812      "untangle ABNFs for header fields"
5813    </t>
5814    <t>
5815      <eref target=""/>:
5816      "Content-Length ABNF broken"
5817    </t>
5818  </list>
5822<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5824  Closed issues:
5825  <list style="symbols">
5826    <t>
5827      <eref target=""/>:
5828      "HTTP-version should be redefined as fixed length pair of DIGIT . DIGIT"
5829    </t>
5830    <t>
5831      <eref target=""/>:
5832      "Recommend minimum sizes for protocol elements"
5833    </t>
5834    <t>
5835      <eref target=""/>:
5836      "Set expectations around buffering"
5837    </t>
5838    <t>
5839      <eref target=""/>:
5840      "Considering messages in isolation"
5841    </t>
5842  </list>
5846<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5848  Closed issues:
5849  <list style="symbols">
5850    <t>
5851      <eref target=""/>:
5852      "DNS Spoofing / DNS Binding advice"
5853    </t>
5854    <t>
5855      <eref target=""/>:
5856      "move RFCs 2145, 2616, 2817 to Historic status"
5857    </t>
5858    <t>
5859      <eref target=""/>:
5860      "\-escaping in quoted strings"
5861    </t>
5862    <t>
5863      <eref target=""/>:
5864      "'Close' should be reserved in the HTTP header field registry"
5865    </t>
5866  </list>
5870<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5872  Closed issues:
5873  <list style="symbols">
5874    <t>
5875      <eref target=""/>:
5876      "Document HTTP's error-handling philosophy"
5877    </t>
5878    <t>
5879      <eref target=""/>:
5880      "Explain header field registration"
5881    </t>
5882    <t>
5883      <eref target=""/>:
5884      "Revise Acknowledgements Sections"
5885    </t>
5886    <t>
5887      <eref target=""/>:
5888      "Retrying Requests"
5889    </t>
5890    <t>
5891      <eref target=""/>:
5892      "Closing the connection on server error"
5893    </t>
5894  </list>
5898<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5900  Closed issues:
5901  <list style="symbols">
5902    <t>
5903      <eref target=""/>:
5904      "Proxy-Connection and Keep-Alive"
5905    </t>
5906    <t>
5907      <eref target=""/>:
5908      "Clarify 'User Agent'"
5909    </t>
5910    <t>
5911      <eref target=""/>:
5912      "Define non-final responses"
5913    </t>
5914    <t>
5915      <eref target=""/>:
5916      "intended maturity level vs normative references"
5917    </t>
5918    <t>
5919      <eref target=""/>:
5920      "Intermediary rewriting of queries"
5921    </t>
5922  </list>
5926<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5928  Closed issues:
5929  <list style="symbols">
5930    <t>
5931      <eref target=""/>:
5932      "message-body in CONNECT response"
5933    </t>
5934    <t>
5935      <eref target=""/>:
5936      "Misplaced text on connection handling in p2"
5937    </t>
5938    <t>
5939      <eref target=""/>:
5940      "wording of line folding rule"
5941    </t>
5942    <t>
5943      <eref target=""/>:
5944      "chunk-extensions"
5945    </t>
5946    <t>
5947      <eref target=""/>:
5948      "make IANA policy definitions consistent"
5949    </t>
5950  </list>
5954<section title="Since draft-ietf-httpbis-p1-messaging-19" anchor="changes.since.19">
5956  Closed issues:
5957  <list style="symbols">
5958    <t>
5959      <eref target=""/>:
5960      "make IANA policy definitions consistent"
5961    </t>
5962    <t>
5963      <eref target=""/>:
5964      "clarify connection header field values are case-insensitive"
5965    </t>
5966    <t>
5967      <eref target=""/>:
5968      "ABNF requirements for recipients"
5969    </t>
5970    <t>
5971      <eref target=""/>:
5972      "note introduction of new IANA registries as normative changes"
5973    </t>
5974    <t>
5975      <eref target=""/>:
5976      "Reference to ISO-8859-1 is informative"
5977    </t>
5978  </list>
5982<section title="Since draft-ietf-httpbis-p1-messaging-20" anchor="changes.since.20">
5984  None yet.
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