source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1768

Last change on this file since 1768 was 1768, checked in by julian.reschke@…, 10 years ago

hyperlink header field definitions (P1)

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  • Property svn:mime-type set to text/xml
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>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 "July">
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 status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
49  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
50  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
51  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x=''/>">
52  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x=''/>">
53  <!ENTITY status-304             "<xref target='Part4' x:rel='#status.304' xmlns:x=''/>">
54  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x=''/>">
55  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
56  <!ENTITY cons-new-header-fields "<xref target='Part2' x:rel='#considerations.for.creating.header.fields' xmlns:x=''/>">
58<?rfc toc="yes" ?>
59<?rfc symrefs="yes" ?>
60<?rfc sortrefs="yes" ?>
61<?rfc compact="yes"?>
62<?rfc subcompact="no" ?>
63<?rfc linkmailto="no" ?>
64<?rfc editing="no" ?>
65<?rfc comments="yes"?>
66<?rfc inline="yes"?>
67<?rfc rfcedstyle="yes"?>
68<?rfc-ext allow-markup-in-artwork="yes" ?>
69<?rfc-ext include-references-in-index="yes" ?>
70<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="proposed"
71     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
72     xmlns:x=''>
73<x:link rel="next" basename="p2-semantics"/>
74<x:feedback template="{docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
77  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
79  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
80    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
81    <address>
82      <postal>
83        <street>345 Park Ave</street>
84        <city>San Jose</city>
85        <region>CA</region>
86        <code>95110</code>
87        <country>USA</country>
88      </postal>
89      <email></email>
90      <uri></uri>
91    </address>
92  </author>
94  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
95    <organization abbrev="W3C">World Wide Web Consortium</organization>
96    <address>
97      <postal>
98        <street>W3C / ERCIM</street>
99        <street>2004, rte des Lucioles</street>
100        <city>Sophia-Antipolis</city>
101        <region>AM</region>
102        <code>06902</code>
103        <country>France</country>
104      </postal>
105      <email></email>
106      <uri></uri>
107    </address>
108  </author>
110  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
111    <organization abbrev="greenbytes">greenbytes GmbH</organization>
112    <address>
113      <postal>
114        <street>Hafenweg 16</street>
115        <city>Muenster</city><region>NW</region><code>48155</code>
116        <country>Germany</country>
117      </postal>
118      <email></email>
119      <uri></uri>
120    </address>
121  </author>
123  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
124  <workgroup>HTTPbis Working Group</workgroup>
128   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
129   distributed, collaborative, hypertext information systems. HTTP has been in
130   use by the World Wide Web global information initiative since 1990. This
131   document is Part 1 of the seven-part specification that defines the protocol
132   referred to as "HTTP/1.1" and, taken together, obsoletes
133   <xref target="RFC2616" x:fmt="none">RFC 2616</xref> and moves it to historic
134   status, along with its predecessor <xref target="RFC2068" x:fmt="none">RFC
135   2068</xref>.
138   Part 1 provides an overview of HTTP and its associated terminology, defines
139   the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
140   the generic message syntax and parsing requirements for HTTP message frames,
141   and describes general security concerns for implementations.
144   This part also obsoletes RFCs <xref target="RFC2145" x:fmt="none">2145</xref>
145   (on HTTP version numbers) and <xref target="RFC2817" x:fmt="none">2817</xref>
146   (on using CONNECT for TLS upgrades) and moves them to historic status.
150<note title="Editorial Note (To be removed by RFC Editor)">
151  <t>
152    Discussion of this draft takes place on the HTTPBIS working group
153    mailing list (, which is archived at
154    <eref target=""/>.
155  </t>
156  <t>
157    The current issues list is at
158    <eref target=""/> and related
159    documents (including fancy diffs) can be found at
160    <eref target=""/>.
161  </t>
162  <t>
163    The changes in this draft are summarized in <xref target="changes.since.19"/>.
164  </t>
168<section title="Introduction" anchor="introduction">
170   The Hypertext Transfer Protocol (HTTP) is an application-level
171   request/response protocol that uses extensible semantics and MIME-like
172   message payloads for flexible interaction with network-based hypertext
173   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
174   standard <xref target="RFC3986"/> to indicate the target resource
175   (<xref target="target-resource"/>) and relationships between resources.
176   Messages are passed in a format similar to that used by Internet mail
177   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
178   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
179   between HTTP and MIME messages).
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 is Part 1 of the seven-part specification of HTTP,
214   defining the protocol referred to as "HTTP/1.1", obsoleting
215   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
216   Part 1 describes the architectural elements that are used or
217   referred to in HTTP, defines the "http" and "https" URI schemes,
218   describes overall network operation and connection management,
219   and defines HTTP message framing and forwarding requirements.
220   Our goal is to define all of the mechanisms necessary for HTTP message
221   handling that are independent of message semantics, thereby defining the
222   complete set of requirements for message parsers and
223   message-forwarding intermediaries.
226<section title="Requirement Notation" anchor="intro.requirements">
228   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
229   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
230   document are to be interpreted as described in <xref target="RFC2119"/>.
234<section title="Syntax Notation" anchor="notation">
235<iref primary="true" item="Grammar" subitem="ALPHA"/>
236<iref primary="true" item="Grammar" subitem="CR"/>
237<iref primary="true" item="Grammar" subitem="CRLF"/>
238<iref primary="true" item="Grammar" subitem="CTL"/>
239<iref primary="true" item="Grammar" subitem="DIGIT"/>
240<iref primary="true" item="Grammar" subitem="DQUOTE"/>
241<iref primary="true" item="Grammar" subitem="HEXDIG"/>
242<iref primary="true" item="Grammar" subitem="HTAB"/>
243<iref primary="true" item="Grammar" subitem="LF"/>
244<iref primary="true" item="Grammar" subitem="OCTET"/>
245<iref primary="true" item="Grammar" subitem="SP"/>
246<iref primary="true" item="Grammar" subitem="VCHAR"/>
248   This specification uses the Augmented Backus-Naur Form (ABNF) notation
249   of <xref target="RFC5234"/> with the list rule extension defined in
250   <xref target="abnf.extension"/>.  <xref target="collected.abnf"/> shows
251   the collected ABNF with the list rule expanded.
253<t anchor="core.rules">
254  <x:anchor-alias value="ALPHA"/>
255  <x:anchor-alias value="CTL"/>
256  <x:anchor-alias value="CR"/>
257  <x:anchor-alias value="CRLF"/>
258  <x:anchor-alias value="DIGIT"/>
259  <x:anchor-alias value="DQUOTE"/>
260  <x:anchor-alias value="HEXDIG"/>
261  <x:anchor-alias value="HTAB"/>
262  <x:anchor-alias value="LF"/>
263  <x:anchor-alias value="OCTET"/>
264  <x:anchor-alias value="SP"/>
265  <x:anchor-alias value="VCHAR"/>
266   The following core rules are included by
267   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
268   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
269   DIGIT (decimal 0-9), DQUOTE (double quote),
270   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
271   OCTET (any 8-bit sequence of data), SP (space), and
272   VCHAR (any visible <xref target="USASCII"/> character).
275   As a convention, ABNF rule names prefixed with "obs-" denote
276   "obsolete" grammar rules that appear for historical reasons.
281<section title="Architecture" anchor="architecture">
283   HTTP was created for the World Wide Web architecture
284   and has evolved over time to support the scalability needs of a worldwide
285   hypertext system. Much of that architecture is reflected in the terminology
286   and syntax productions used to define HTTP.
289<section title="Client/Server Messaging" anchor="operation">
290<iref primary="true" item="client"/>
291<iref primary="true" item="server"/>
292<iref primary="true" item="connection"/>
294   HTTP is a stateless request/response protocol that operates by exchanging
295   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
296   transport or session-layer
297   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
298   program that establishes a connection to a server for the purpose of
299   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
300   program that accepts connections in order to service HTTP requests by
301   sending HTTP responses.
303<iref primary="true" item="user agent"/>
304<iref primary="true" item="origin server"/>
305<iref primary="true" item="browser"/>
306<iref primary="true" item="spider"/>
307<iref primary="true" item="sender"/>
308<iref primary="true" item="recipient"/>
310   The terms client and server refer only to the roles that
311   these programs perform for a particular connection.  The same program
312   might act as a client on some connections and a server on others.  We use
313   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
314   such as a WWW browser, editor, or spider (web-traversing robot), and
315   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
316   authoritative responses to a request.  For general requirements, we use
317   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
318   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
319   message.
322   Most HTTP communication consists of a retrieval request (GET) for
323   a representation of some resource identified by a URI.  In the
324   simplest case, this might be accomplished via a single bidirectional
325   connection (===) between the user agent (UA) and the origin server (O).
327<figure><artwork type="drawing">
328         request   &gt;
329    <x:highlight>UA</x:highlight> ======================================= <x:highlight>O</x:highlight>
330                                &lt;   response
332<iref primary="true" item="message"/>
333<iref primary="true" item="request"/>
334<iref primary="true" item="response"/>
336   A client sends an HTTP request to a server in the form of a <x:dfn>request</x:dfn>
337   message, beginning with a request-line that includes a method, URI, and
338   protocol version (<xref target="request.line"/>),
339   followed by MIME-like header fields containing
340   request modifiers, client information, and representation metadata
341   (<xref target="header.fields"/>),
342   an empty line to indicate the end of the header section, and finally
343   a message body containing the payload body (if any,
344   <xref target="message.body"/>).
347   A server responds to a client's request by sending one or more HTTP
348   <x:dfn>response</x:dfn>
349   messages, each beginning with a status line that
350   includes the protocol version, a success or error code, and textual
351   reason phrase (<xref target="status.line"/>),
352   possibly followed by MIME-like header fields containing server
353   information, resource metadata, and representation metadata
354   (<xref target="header.fields"/>),
355   an empty line to indicate the end of the header section, and finally
356   a message body containing the payload body (if any,
357   <xref target="message.body"/>).
360   The following example illustrates a typical message exchange for a
361   GET request on the URI "":
364client request:
365</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
366GET /hello.txt HTTP/1.1
367User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
369Accept: */*
373server response:
374</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
375HTTP/1.1 200 OK
376Date: Mon, 27 Jul 2009 12:28:53 GMT
377Server: Apache
378Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
379ETag: "34aa387-d-1568eb00"
380Accept-Ranges: bytes
381Content-Length: <x:length-of target="exbody"/>
382Vary: Accept-Encoding
383Content-Type: text/plain
385<x:span anchor="exbody">Hello World!
389<section title="Implementation Diversity" anchor="implementation-diversity">
391   When considering the design of HTTP, it is easy to fall into a trap of
392   thinking that all user agents are general-purpose browsers and all origin
393   servers are large public websites. That is not the case in practice.
394   Common HTTP user agents include household appliances, stereos, scales,
395   software/firmware updaters, command-line programs, mobile apps,
396   and communication devices in a multitude of shapes and sizes.  Likewise,
397   common HTTP origin servers include home automation units, configurable
398   networking components, office machines, autonomous robots, news feeds,
399   traffic cameras, ad selectors, and video delivery platforms.
402   The term "user agent" does not imply that there is a human user directly
403   interacting with the software agent at the time of a request. In many
404   cases, a user agent is installed or configured to run in the background
405   and save its results for later inspection (or save only a subset of those
406   results that might be interesting or erroneous). Spiders, for example, are
407   typically given a start URI and configured to follow certain behavior while
408   crawling the Web as a hypertext graph.
411   The implementation diversity of HTTP means that we cannot assume the
412   user agent can make interactive suggestions to a user or provide adequate
413   warning for security or privacy options.  In the few cases where this
414   specification requires reporting of errors to the user, it is acceptable
415   for such reporting to only be visible in an error console or log file.
416   Likewise, requirements that an automated action be confirmed by the user
417   before proceeding can me met via advance configuration choices,
418   run-time options, or simply not proceeding with the unsafe action.
422<section title="Connections and Transport Independence" anchor="transport-independence">
424   HTTP messaging is independent of the underlying transport or
425   session-layer connection protocol(s).  HTTP only presumes a reliable
426   transport with in-order delivery of requests and the corresponding
427   in-order delivery of responses.  The mapping of HTTP request and
428   response structures onto the data units of the underlying transport
429   protocol is outside the scope of this specification.
432   The specific connection protocols to be used for an interaction
433   are determined by client configuration and the target URI
434   (<xref target="target-resource"/>).
435   For example, the "http" URI scheme
436   (<xref target="http.uri"/>) indicates a default connection of TCP
437   over IP, with a default TCP port of 80, but the client might be
438   configured to use a proxy via some other connection port or protocol
439   instead of using the defaults.
442   A connection might be used for multiple HTTP request/response exchanges,
443   as defined in <xref target="persistent.connections"/>.
447<section title="Intermediaries" anchor="intermediaries">
448<iref primary="true" item="intermediary"/>
450   HTTP enables the use of intermediaries to satisfy requests through
451   a chain of connections.  There are three common forms of HTTP
452   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
453   a single intermediary might act as an origin server, proxy, gateway,
454   or tunnel, switching behavior based on the nature of each request.
456<figure><artwork type="drawing">
457         &gt;             &gt;             &gt;             &gt;
458    <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>
459               &lt;             &lt;             &lt;             &lt;
462   The figure above shows three intermediaries (A, B, and C) between the
463   user agent and origin server. A request or response message that
464   travels the whole chain will pass through four separate connections.
465   Some HTTP communication options
466   might apply only to the connection with the nearest, non-tunnel
467   neighbor, only to the end-points of the chain, or to all connections
468   along the chain. Although the diagram is linear, each participant might
469   be engaged in multiple, simultaneous communications. For example, B
470   might be receiving requests from many clients other than A, and/or
471   forwarding requests to servers other than C, at the same time that it
472   is handling A's request.
475<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
476<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
477   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
478   to describe various requirements in relation to the directional flow of a
479   message: all messages flow from upstream to downstream.
480   Likewise, we use the terms inbound and outbound to refer to
481   directions in relation to the request path:
482   "<x:dfn>inbound</x:dfn>" means toward the origin server and
483   "<x:dfn>outbound</x:dfn>" means toward the user agent.
485<t><iref primary="true" item="proxy"/>
486   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
487   client, usually via local configuration rules, to receive requests
488   for some type(s) of absolute URI and attempt to satisfy those
489   requests via translation through the HTTP interface.  Some translations
490   are minimal, such as for proxy requests for "http" URIs, whereas
491   other requests might require translation to and from entirely different
492   application-layer protocols. Proxies are often used to group an
493   organization's HTTP requests through a common intermediary for the
494   sake of security, annotation services, or shared caching.
497<iref primary="true" item="transforming proxy"/>
498<iref primary="true" item="non-transforming proxy"/>
499   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
500   or configured to modify request or response messages in a semantically
501   meaningful way (i.e., modifications, beyond those required by normal
502   HTTP processing, that change the message in a way that would be
503   significant to the original sender or potentially significant to
504   downstream recipients).  For example, a transforming proxy might be
505   acting as a shared annotation server (modifying responses to include
506   references to a local annotation database), a malware filter, a
507   format transcoder, or an intranet-to-Internet privacy filter.  Such
508   transformations are presumed to be desired by the client (or client
509   organization) that selected the proxy and are beyond the scope of
510   this specification.  However, when a proxy is not intended to transform
511   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
512   requirements that preserve HTTP message semantics. See &status-203; and
513   &header-warning; for status and warning codes related to transformations.
515<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
516<iref primary="true" item="accelerator"/>
517   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
518   is a receiving agent that acts
519   as a layer above some other server(s) and translates the received
520   requests to the underlying server's protocol.  Gateways are often
521   used to encapsulate legacy or untrusted information services, to
522   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
523   enable partitioning or load-balancing of HTTP services across
524   multiple machines.
527   A gateway behaves as an origin server on its outbound connection and
528   as a user agent on its inbound connection.
529   All HTTP requirements applicable to an origin server
530   also apply to the outbound communication of a gateway.
531   A gateway communicates with inbound servers using any protocol that
532   it desires, including private extensions to HTTP that are outside
533   the scope of this specification.  However, an HTTP-to-HTTP gateway
534   that wishes to interoperate with third-party HTTP servers &MUST;
535   conform to HTTP user agent requirements on the gateway's inbound
536   connection and &MUST; implement the <x:ref>Connection</x:ref>
537   (<xref target="header.connection"/>) and <x:ref>Via</x:ref>
538   (<xref target="header.via"/>) header fields for both connections.
540<t><iref primary="true" item="tunnel"/>
541   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
542   without changing the messages. Once active, a tunnel is not
543   considered a party to the HTTP communication, though the tunnel might
544   have been initiated by an HTTP request. A tunnel ceases to exist when
545   both ends of the relayed connection are closed. Tunnels are used to
546   extend a virtual connection through an intermediary, such as when
547   transport-layer security is used to establish private communication
548   through a shared firewall proxy.
550<t><iref primary="true" item="interception proxy"/>
551<iref primary="true" item="transparent proxy"/>
552<iref primary="true" item="captive portal"/>
553   The above categories for intermediary only consider those acting as
554   participants in the HTTP communication.  There are also intermediaries
555   that can act on lower layers of the network protocol stack, filtering or
556   redirecting HTTP traffic without the knowledge or permission of message
557   senders. Network intermediaries often introduce security flaws or
558   interoperability problems by violating HTTP semantics.  For example, an
559   "<x:dfn>interception proxy</x:dfn>" <xref target="RFC3040"/> (also commonly
560   known as a "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/> or
561   "<x:dfn>captive portal</x:dfn>")
562   differs from an HTTP proxy because it is not selected by the client.
563   Instead, an interception proxy filters or redirects outgoing TCP port 80
564   packets (and occasionally other common port traffic).
565   Interception proxies are commonly found on public network access points,
566   as a means of enforcing account subscription prior to allowing use of
567   non-local Internet services, and within corporate firewalls to enforce
568   network usage policies.
569   They are indistinguishable from a man-in-the-middle attack.
572   HTTP is defined as a stateless protocol, meaning that each request message
573   can be understood in isolation.  Many implementations depend on HTTP's
574   stateless design in order to reuse proxied connections or dynamically
575   load balance requests across multiple servers.  Hence, servers &MUST-NOT;
576   assume that two requests on the same connection are from the same user
577   agent unless the connection is secured and specific to that agent.
578   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
579   been known to violate this requirement, resulting in security and
580   interoperability problems.
584<section title="Caches" anchor="caches">
585<iref primary="true" item="cache"/>
587   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
588   subsystem that controls its message storage, retrieval, and deletion.
589   A cache stores cacheable responses in order to reduce the response
590   time and network bandwidth consumption on future, equivalent
591   requests. Any client or server &MAY; employ a cache, though a cache
592   cannot be used by a server while it is acting as a tunnel.
595   The effect of a cache is that the request/response chain is shortened
596   if one of the participants along the chain has a cached response
597   applicable to that request. The following illustrates the resulting
598   chain if B has a cached copy of an earlier response from O (via C)
599   for a request which has not been cached by UA or A.
601<figure><artwork type="drawing">
602            &gt;             &gt;
603       <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>
604                  &lt;             &lt;
606<t><iref primary="true" item="cacheable"/>
607   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
608   the response message for use in answering subsequent requests.
609   Even when a response is cacheable, there might be additional
610   constraints placed by the client or by the origin server on when
611   that cached response can be used for a particular request. HTTP
612   requirements for cache behavior and cacheable responses are
613   defined in &caching-overview;. 
616   There are a wide variety of architectures and configurations
617   of caches and proxies deployed across the World Wide Web and
618   inside large organizations. These systems include national hierarchies
619   of proxy caches to save transoceanic bandwidth, systems that
620   broadcast or multicast cache entries, organizations that distribute
621   subsets of cached data via optical media, and so on.
625<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
627   This specification targets conformance criteria according to the role of
628   a participant in HTTP communication.  Hence, HTTP requirements are placed
629   on senders, recipients, clients, servers, user agents, intermediaries,
630   origin servers, proxies, gateways, or caches, depending on what behavior
631   is being constrained by the requirement. The verb "generate" is used
632   instead of "send" where a requirement differentiates between creating a
633   protocol element and merely forwarding a received element downstream.
636   An implementation is considered conformant if it complies with all of the
637   requirements associated with the roles it partakes in HTTP.
640   A sender &MUST-NOT; generate protocol elements that do not match
641   the grammar defined by the ABNF rules for those protocol elements that
642   are applicable to the sender's role.
643   If a received protocol element is processed, the recipient &MUST; be able
644   to parse any value that would match the ABNF rules for that protocol
645   element, excluding only those rules not applicable to the recipient's role.
648   Unless noted otherwise, a recipient &MAY; attempt to recover a usable
649   protocol element from an invalid construct.  HTTP does not define
650   specific error handling mechanisms except when they have a direct impact
651   on security, since different applications of the protocol require
652   different error handling strategies.  For example, a Web browser might
653   wish to transparently recover from a response where the <x:ref>Location</x:ref>
654   header field doesn't parse according to the ABNF, whereas a systems control
655   client might consider any form of error recovery to be dangerous.
659<section title="Protocol Versioning" anchor="http.version">
660  <x:anchor-alias value="HTTP-version"/>
661  <x:anchor-alias value="HTTP-name"/>
663   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
664   versions of the protocol. This specification defines version "1.1".
665   The protocol version as a whole indicates the sender's conformance
666   with the set of requirements laid out in that version's corresponding
667   specification of HTTP.
670   The version of an HTTP message is indicated by an HTTP-version field
671   in the first line of the message. HTTP-version is case-sensitive.
673<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/>
674  <x:ref>HTTP-version</x:ref>  = <x:ref>HTTP-name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
675  <x:ref>HTTP-name</x:ref>     = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
678   The HTTP version number consists of two decimal digits separated by a "."
679   (period or decimal point).  The first digit ("major version") indicates the
680   HTTP messaging syntax, whereas the second digit ("minor version") indicates
681   the highest minor version to which the sender is
682   conformant and able to understand for future communication.  The minor
683   version advertises the sender's communication capabilities even when the
684   sender is only using a backwards-compatible subset of the protocol,
685   thereby letting the recipient know that more advanced features can
686   be used in response (by servers) or in future requests (by clients).
689   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
690   <xref target="RFC1945"/> or a recipient whose version is unknown,
691   the HTTP/1.1 message is constructed such that it can be interpreted
692   as a valid HTTP/1.0 message if all of the newer features are ignored.
693   This specification places recipient-version requirements on some
694   new features so that a conformant sender will only use compatible
695   features until it has determined, through configuration or the
696   receipt of a message, that the recipient supports HTTP/1.1.
699   The interpretation of a header field does not change between minor
700   versions of the same major HTTP version, though the default
701   behavior of a recipient in the absence of such a field can change.
702   Unless specified otherwise, header fields defined in HTTP/1.1 are
703   defined for all versions of HTTP/1.x.  In particular, the <x:ref>Host</x:ref>
704   and <x:ref>Connection</x:ref> header fields ought to be implemented by all
705   HTTP/1.x implementations whether or not they advertise conformance with
706   HTTP/1.1.
709   New header fields can be defined such that, when they are
710   understood by a recipient, they might override or enhance the
711   interpretation of previously defined header fields.  When an
712   implementation receives an unrecognized header field, the recipient
713   &MUST; ignore that header field for local processing regardless of
714   the message's HTTP version.  An unrecognized header field received
715   by a proxy &MUST; be forwarded downstream unless the header field's
716   field-name is listed in the message's <x:ref>Connection</x:ref> header field
717   (see <xref target="header.connection"/>).
718   These requirements allow HTTP's functionality to be enhanced without
719   requiring prior update of deployed intermediaries.
722   Intermediaries that process HTTP messages (i.e., all intermediaries
723   other than those acting as tunnels) &MUST; send their own HTTP-version
724   in forwarded messages.  In other words, they &MUST-NOT; blindly
725   forward the first line of an HTTP message without ensuring that the
726   protocol version in that message matches a version to which that
727   intermediary is conformant for both the receiving and
728   sending of messages.  Forwarding an HTTP message without rewriting
729   the HTTP-version might result in communication errors when downstream
730   recipients use the message sender's version to determine what features
731   are safe to use for later communication with that sender.
734   An HTTP client &SHOULD; send a request version equal to the highest
735   version to which the client is conformant and
736   whose major version is no higher than the highest version supported
737   by the server, if this is known.  An HTTP client &MUST-NOT; send a
738   version to which it is not conformant.
741   An HTTP client &MAY; send a lower request version if it is known that
742   the server incorrectly implements the HTTP specification, but only
743   after the client has attempted at least one normal request and determined
744   from the response status or header fields (e.g., <x:ref>Server</x:ref>) that
745   the server improperly handles higher request versions.
748   An HTTP server &SHOULD; send a response version equal to the highest
749   version to which the server is conformant and
750   whose major version is less than or equal to the one received in the
751   request.  An HTTP server &MUST-NOT; send a version to which it is not
752   conformant.  A server &MAY; send a <x:ref>505 (HTTP Version Not
753   Supported)</x:ref> response if it cannot send a response using the
754   major version used in the client's request.
757   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
758   if it is known or suspected that the client incorrectly implements the
759   HTTP specification and is incapable of correctly processing later
760   version responses, such as when a client fails to parse the version
761   number correctly or when an intermediary is known to blindly forward
762   the HTTP-version even when it doesn't conform to the given minor
763   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
764   performed unless triggered by specific client attributes, such as when
765   one or more of the request header fields (e.g., <x:ref>User-Agent</x:ref>)
766   uniquely match the values sent by a client known to be in error.
769   The intention of HTTP's versioning design is that the major number
770   will only be incremented if an incompatible message syntax is
771   introduced, and that the minor number will only be incremented when
772   changes made to the protocol have the effect of adding to the message
773   semantics or implying additional capabilities of the sender.  However,
774   the minor version was not incremented for the changes introduced between
775   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
776   is specifically avoiding any such changes to the protocol.
780<section title="Uniform Resource Identifiers" anchor="uri">
781<iref primary="true" item="resource"/>
783   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
784   throughout HTTP as the means for identifying resources. URI references
785   are used to target requests, indicate redirects, and define relationships.
786   HTTP does not limit what a resource might be; it merely defines an interface
787   that can be used to interact with a resource via HTTP. More information on
788   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
790  <x:anchor-alias value="URI-reference"/>
791  <x:anchor-alias value="absolute-URI"/>
792  <x:anchor-alias value="relative-part"/>
793  <x:anchor-alias value="authority"/>
794  <x:anchor-alias value="path-abempty"/>
795  <x:anchor-alias value="path-absolute"/>
796  <x:anchor-alias value="port"/>
797  <x:anchor-alias value="query"/>
798  <x:anchor-alias value="uri-host"/>
799  <x:anchor-alias value="partial-URI"/>
801   This specification adopts the definitions of "URI-reference",
802   "absolute-URI", "relative-part", "port", "host",
803   "path-abempty", "path-absolute", "query", and "authority" from the
804   URI generic syntax <xref target="RFC3986"/>.
805   In addition, we define a partial-URI rule for protocol elements
806   that allow a relative URI but not a fragment.
808<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="URI-reference"/><iref primary="true" item="Grammar" subitem="absolute-URI"/><iref primary="true" item="Grammar" subitem="authority"/><iref primary="true" item="Grammar" subitem="path-absolute"/><iref primary="true" item="Grammar" subitem="port"/><iref primary="true" item="Grammar" subitem="query"/><iref primary="true" item="Grammar" subitem="uri-host"/>
809  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
810  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
811  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
812  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
813  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
814  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
815  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
816  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
817  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
819  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
822   Each protocol element in HTTP that allows a URI reference will indicate
823   in its ABNF production whether the element allows any form of reference
824   (URI-reference), only a URI in absolute form (absolute-URI), only the
825   path and optional query components, or some combination of the above.
826   Unless otherwise indicated, URI references are parsed
827   relative to the effective request URI
828   (<xref target="effective.request.uri"/>).
831<section title="http URI scheme" anchor="http.uri">
832  <x:anchor-alias value="http-URI"/>
833  <iref item="http URI scheme" primary="true"/>
834  <iref item="URI scheme" subitem="http" primary="true"/>
836   The "http" URI scheme is hereby defined for the purpose of minting
837   identifiers according to their association with the hierarchical
838   namespace governed by a potential HTTP origin server listening for
839   TCP connections on a given port.
841<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
842  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
845   The HTTP origin server is identified by the generic syntax's
846   <x:ref>authority</x:ref> component, which includes a host identifier
847   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
848   The remainder of the URI, consisting of both the hierarchical path
849   component and optional query component, serves as an identifier for
850   a potential resource within that origin server's name space.
853   If the host identifier is provided as an IP literal or IPv4 address,
854   then the origin server is any listener on the indicated TCP port at
855   that IP address. If host is a registered name, then that name is
856   considered an indirect identifier and the recipient might use a name
857   resolution service, such as DNS, to find the address of a listener
858   for that host.
859   The host &MUST-NOT; be empty; if an "http" URI is received with an
860   empty host, then it &MUST; be rejected as invalid.
861   If the port subcomponent is empty or not given, then TCP port 80 is
862   assumed (the default reserved port for WWW services).
865   Regardless of the form of host identifier, access to that host is not
866   implied by the mere presence of its name or address. The host might or might
867   not exist and, even when it does exist, might or might not be running an
868   HTTP server or listening to the indicated port. The "http" URI scheme
869   makes use of the delegated nature of Internet names and addresses to
870   establish a naming authority (whatever entity has the ability to place
871   an HTTP server at that Internet name or address) and allows that
872   authority to determine which names are valid and how they might be used.
875   When an "http" URI is used within a context that calls for access to the
876   indicated resource, a client &MAY; attempt access by resolving
877   the host to an IP address, establishing a TCP connection to that address
878   on the indicated port, and sending an HTTP request message
879   (<xref target="http.message"/>) containing the URI's identifying data
880   (<xref target="message.routing"/>) to the server.
881   If the server responds to that request with a non-interim HTTP response
882   message, as described in &status-codes;, then that response
883   is considered an authoritative answer to the client's request.
886   Although HTTP is independent of the transport protocol, the "http"
887   scheme is specific to TCP-based services because the name delegation
888   process depends on TCP for establishing authority.
889   An HTTP service based on some other underlying connection protocol
890   would presumably be identified using a different URI scheme, just as
891   the "https" scheme (below) is used for servers that require an SSL/TLS
892   transport layer on a connection. Other protocols might also be used to
893   provide access to "http" identified resources &mdash; it is only the
894   authoritative interface used for mapping the namespace that is
895   specific to TCP.
898   The URI generic syntax for authority also includes a deprecated
899   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
900   for including user authentication information in the URI.  Some
901   implementations make use of the userinfo component for internal
902   configuration of authentication information, such as within command
903   invocation options, configuration files, or bookmark lists, even
904   though such usage might expose a user identifier or password.
905   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
906   delimiter) when transmitting an "http" URI in a message.  Recipients
907   of HTTP messages that contain a URI reference &SHOULD; parse for the
908   existence of userinfo and treat its presence as an error, likely
909   indicating that the deprecated subcomponent is being used to obscure
910   the authority for the sake of phishing attacks.
914<section title="https URI scheme" anchor="https.uri">
915   <x:anchor-alias value="https-URI"/>
916   <iref item="https URI scheme"/>
917   <iref item="URI scheme" subitem="https"/>
919   The "https" URI scheme is hereby defined for the purpose of minting
920   identifiers according to their association with the hierarchical
921   namespace governed by a potential HTTP origin server listening for
922   SSL/TLS-secured connections on a given TCP port.
925   All of the requirements listed above for the "http" scheme are also
926   requirements for the "https" scheme, except that a default TCP port
927   of 443 is assumed if the port subcomponent is empty or not given,
928   and the TCP connection &MUST; be secured for privacy through the
929   use of strong encryption prior to sending the first HTTP request.
931<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
932  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
935   Unlike the "http" scheme, responses to "https" identified requests
936   are never "public" and thus &MUST-NOT; be reused for shared caching.
937   They can, however, be reused in a private cache if the message is
938   cacheable by default in HTTP or specifically indicated as such by
939   the Cache-Control header field (&header-cache-control;).
942   Resources made available via the "https" scheme have no shared
943   identity with the "http" scheme even if their resource identifiers
944   indicate the same authority (the same host listening to the same
945   TCP port).  They are distinct name spaces and are considered to be
946   distinct origin servers.  However, an extension to HTTP that is
947   defined to apply to entire host domains, such as the Cookie protocol
948   <xref target="RFC6265"/>, can allow information
949   set by one service to impact communication with other services
950   within a matching group of host domains.
953   The process for authoritative access to an "https" identified
954   resource is defined in <xref target="RFC2818"/>.
958<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
960   Since the "http" and "https" schemes conform to the URI generic syntax,
961   such URIs are normalized and compared according to the algorithm defined
962   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
963   described above for each scheme.
966   If the port is equal to the default port for a scheme, the normal
967   form is to elide the port subcomponent. Likewise, an empty path
968   component is equivalent to an absolute path of "/", so the normal
969   form is to provide a path of "/" instead. The scheme and host
970   are case-insensitive and normally provided in lowercase; all
971   other components are compared in a case-sensitive manner.
972   Characters other than those in the "reserved" set are equivalent
973   to their percent-encoded octets (see <xref target="RFC3986"
974   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
977   For example, the following three URIs are equivalent:
979<figure><artwork type="example">
988<section title="Message Format" anchor="http.message">
989<x:anchor-alias value="generic-message"/>
990<x:anchor-alias value="message.types"/>
991<x:anchor-alias value="HTTP-message"/>
992<x:anchor-alias value="start-line"/>
993<iref item="header section"/>
994<iref item="headers"/>
995<iref item="header field"/>
997   All HTTP/1.1 messages consist of a start-line followed by a sequence of
998   octets in a format similar to the Internet Message Format
999   <xref target="RFC5322"/>: zero or more header fields (collectively
1000   referred to as the "headers" or the "header section"), an empty line
1001   indicating the end of the header section, and an optional message body.
1003<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1004  <x:ref>HTTP-message</x:ref>   = <x:ref>start-line</x:ref>
1005                   *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1006                   <x:ref>CRLF</x:ref>
1007                   [ <x:ref>message-body</x:ref> ]
1010   The normal procedure for parsing an HTTP message is to read the
1011   start-line into a structure, read each header field into a hash
1012   table by field name until the empty line, and then use the parsed
1013   data to determine if a message body is expected.  If a message body
1014   has been indicated, then it is read as a stream until an amount
1015   of octets equal to the message body length is read or the connection
1016   is closed.
1019   Recipients &MUST; parse an HTTP message as a sequence of octets in an
1020   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1021   Parsing an HTTP message as a stream of Unicode characters, without regard
1022   for the specific encoding, creates security vulnerabilities due to the
1023   varying ways that string processing libraries handle invalid multibyte
1024   character sequences that contain the octet LF (%x0A).  String-based
1025   parsers can only be safely used within protocol elements after the element
1026   has been extracted from the message, such as within a header field-value
1027   after message parsing has delineated the individual fields.
1030   An HTTP message can be parsed as a stream for incremental processing or
1031   forwarding downstream.  However, recipients cannot rely on incremental
1032   delivery of partial messages, since some implementations will buffer or
1033   delay message forwarding for the sake of network efficiency, security
1034   checks, or payload transformations.
1037<section title="Start Line" anchor="start.line">
1038  <x:anchor-alias value="Start-Line"/>
1040   An HTTP message can either be a request from client to server or a
1041   response from server to client.  Syntactically, the two types of message
1042   differ only in the start-line, which is either a request-line (for requests)
1043   or a status-line (for responses), and in the algorithm for determining
1044   the length of the message body (<xref target="message.body"/>).
1045   In theory, a client could receive requests and a server could receive
1046   responses, distinguishing them by their different start-line formats,
1047   but in practice servers are implemented to only expect a request
1048   (a response is interpreted as an unknown or invalid request method)
1049   and clients are implemented to only expect a response.
1051<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1052  <x:ref>start-line</x:ref>     = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1055   Implementations &MUST-NOT; send whitespace between the start-line and
1056   the first header field. The presence of such whitespace in a request
1057   might be an attempt to trick a server into ignoring that field or
1058   processing the line after it as a new request, either of which might
1059   result in a security vulnerability if other implementations within
1060   the request chain interpret the same message differently.
1061   Likewise, the presence of such whitespace in a response might be
1062   ignored by some clients or cause others to cease parsing.
1065<section title="Request Line" anchor="request.line">
1066  <x:anchor-alias value="Request"/>
1067  <x:anchor-alias value="request-line"/>
1069   A request-line begins with a method token, followed by a single
1070   space (SP), the request-target, another single space (SP), the
1071   protocol version, and ending with CRLF.
1073<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1074  <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>
1077   A server &MUST; be able to parse any received message that begins
1078   with a request-line and matches the ABNF rule for HTTP-message.
1080<iref primary="true" item="method"/>
1081<t anchor="method">
1082   The method token indicates the request method to be performed on the
1083   target resource. The request method is case-sensitive.
1085<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1086  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1089   The methods defined by this specification can be found in
1090   &methods;, along with information regarding the HTTP method registry
1091   and considerations for defining new methods.
1093<iref item="request-target"/>
1095   The request-target identifies the target resource upon which to apply
1096   the request, as defined in <xref target="request-target"/>.
1099   No whitespace is allowed inside the method, request-target, and
1100   protocol version.  Hence, recipients typically parse the request-line
1101   into its component parts by splitting on the SP characters.
1104   Unfortunately, some user agents fail to properly encode hypertext
1105   references that have embedded whitespace, sending the characters
1106   directly instead of properly percent-encoding the disallowed characters.
1107   Recipients of an invalid request-line &SHOULD; respond with either a
1108   <x:ref>400 (Bad Request)</x:ref> error or a <x:ref>301 (Moved Permanently)</x:ref>
1109   redirect with the request-target properly encoded.  Recipients &SHOULD-NOT;
1110   attempt to autocorrect and then process the request without a redirect,
1111   since the invalid request-line might be deliberately crafted to bypass
1112   security filters along the request chain.
1115   HTTP does not place a pre-defined limit on the length of a request-line.
1116   A server that receives a method longer than any that it implements
1117   &SHOULD; respond with either a <x:ref>405 (Method Not Allowed)</x:ref>, if it is an origin
1118   server, or a <x:ref>501 (Not Implemented)</x:ref> status code.
1119   A server &MUST; be prepared to receive URIs of unbounded length and
1120   respond with the <x:ref>414 (URI Too Long)</x:ref> status code if the received
1121   request-target would be longer than the server wishes to handle
1122   (see &status-414;).
1125   Various ad-hoc limitations on request-line length are found in practice.
1126   It is &RECOMMENDED; that all HTTP senders and recipients support, at a
1127   minimum, request-line lengths of up to 8000 octets.
1131<section title="Status Line" anchor="status.line">
1132  <x:anchor-alias value="response"/>
1133  <x:anchor-alias value="status-line"/>
1134  <x:anchor-alias value="status-code"/>
1135  <x:anchor-alias value="reason-phrase"/>
1137   The first line of a response message is the status-line, consisting
1138   of the protocol version, a space (SP), the status code, another space,
1139   a possibly-empty textual phrase describing the status code, and
1140   ending with CRLF.
1142<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1143  <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>
1146   A client &MUST; be able to parse any received message that begins
1147   with a status-line and matches the ABNF rule for HTTP-message.
1150   The status-code element is a 3-digit integer code describing the
1151   result of the server's attempt to understand and satisfy the client's
1152   corresponding request. The rest of the response message is to be
1153   interpreted in light of the semantics defined for that status code.
1154   See &status-codes; for information about the semantics of status codes,
1155   including the classes of status code (indicated by the first digit),
1156   the status codes defined by this specification, considerations for the
1157   definition of new status codes, and the IANA registry.
1159<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1160  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1163   The reason-phrase element exists for the sole purpose of providing a
1164   textual description associated with the numeric status code, mostly
1165   out of deference to earlier Internet application protocols that were more
1166   frequently used with interactive text clients. A client &SHOULD; ignore
1167   the reason-phrase content.
1169<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1170  <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> )
1175<section title="Header Fields" anchor="header.fields">
1176  <x:anchor-alias value="header-field"/>
1177  <x:anchor-alias value="field-content"/>
1178  <x:anchor-alias value="field-name"/>
1179  <x:anchor-alias value="field-value"/>
1180  <x:anchor-alias value="obs-fold"/>
1182   Each HTTP header field consists of a case-insensitive field name
1183   followed by a colon (":"), optional whitespace, and the field value.
1185<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"/>
1186  <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>
1187  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1188  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1189  <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> )
1190  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1191                 ; obsolete line folding
1192                 ; see <xref target="field.parsing"/>
1195   The field-name token labels the corresponding field-value as having the
1196   semantics defined by that header field.  For example, the <x:ref>Date</x:ref>
1197   header field is defined in &header-date; as containing the origination
1198   timestamp for the message in which it appears.
1201   HTTP header fields are fully extensible: there is no limit on the
1202   introduction of new field names, each presumably defining new semantics,
1203   or on the number of header fields used in a given message.  Existing
1204   fields are defined in each part of this specification and in many other
1205   specifications outside the standards process.
1206   New header fields can be introduced without changing the protocol version
1207   if their defined semantics allow them to be safely ignored by recipients
1208   that do not recognize them.
1211   New HTTP header fields &SHOULD; be registered with IANA according
1212   to the procedures in &cons-new-header-fields;.
1213   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1214   field-name is listed in the <x:ref>Connection</x:ref> header field
1215   (<xref target="header.connection"/>) or the proxy is specifically
1216   configured to block or otherwise transform such fields.
1217   Unrecognized header fields &SHOULD; be ignored by other recipients.
1220   The order in which header fields with differing field names are
1221   received is not significant. However, it is "good practice" to send
1222   header fields that contain control data first, such as <x:ref>Host</x:ref>
1223   on requests and <x:ref>Date</x:ref> on responses, so that implementations
1224   can decide when not to handle a message as early as possible.  A server
1225   &MUST; wait until the entire header section is received before interpreting
1226   a request message, since later header fields might include conditionals,
1227   authentication credentials, or deliberately misleading duplicate
1228   header fields that would impact request processing.
1231   Multiple header fields with the same field name &MUST-NOT; be
1232   sent in a message unless the entire field value for that
1233   header field is defined as a comma-separated list [i.e., #(values)].
1234   Multiple header fields with the same field name can be combined into
1235   one "field-name: field-value" pair, without changing the semantics of the
1236   message, by appending each subsequent field value to the combined
1237   field value in order, separated by a comma. The order in which
1238   header fields with the same field name are received is therefore
1239   significant to the interpretation of the combined field value;
1240   a proxy &MUST-NOT; change the order of these field values when
1241   forwarding a message.
1244  <t>
1245   &Note; The "Set-Cookie" header field as implemented in
1246   practice can occur multiple times, but does not use the list syntax, and
1247   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1248   for details.) Also note that the Set-Cookie2 header field specified in
1249   <xref target="RFC2965"/> does not share this problem.
1250  </t>
1253<section title="Whitespace" anchor="whitespace">
1254<t anchor="rule.LWS">
1255   This specification uses three rules to denote the use of linear
1256   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1257   BWS ("bad" whitespace).
1259<t anchor="rule.OWS">
1260   The OWS rule is used where zero or more linear whitespace octets might
1261   appear. OWS &SHOULD; either not be produced or be produced as a single
1262   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1263   be replaced with a single SP or transformed to all SP octets (each
1264   octet other than SP replaced with SP) before interpreting the field value
1265   or forwarding the message downstream.
1267<t anchor="rule.RWS">
1268   RWS is used when at least one linear whitespace octet is required to
1269   separate field tokens. RWS &SHOULD; be produced as a single SP.
1270   Multiple RWS octets that occur within field-content &SHOULD; either
1271   be replaced with a single SP or transformed to all SP octets before
1272   interpreting the field value or forwarding the message downstream.
1274<t anchor="rule.BWS">
1275   BWS is used where the grammar allows optional whitespace for historical
1276   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
1277   recipients &MUST; accept such bad optional whitespace and remove it before
1278   interpreting the field value or forwarding the message downstream.
1280<t anchor="rule.whitespace">
1281  <x:anchor-alias value="BWS"/>
1282  <x:anchor-alias value="OWS"/>
1283  <x:anchor-alias value="RWS"/>
1285<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"/>
1286  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1287                 ; "optional" whitespace
1288  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1289                 ; "required" whitespace
1290  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1291                 ; "bad" whitespace
1295<section title="Field Parsing" anchor="field.parsing">
1297   No whitespace is allowed between the header field-name and colon.
1298   In the past, differences in the handling of such whitespace have led to
1299   security vulnerabilities in request routing and response handling.
1300   Any received request message that contains whitespace between a header
1301   field-name and colon &MUST; be rejected with a response code of 400
1302   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1303   message before forwarding the message downstream.
1306   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1307   preferred. The field value does not include any leading or trailing white
1308   space: OWS occurring before the first non-whitespace octet of the
1309   field value or after the last non-whitespace octet of the field value
1310   is ignored and &SHOULD; be removed before further processing (as this does
1311   not change the meaning of the header field).
1314   Historically, HTTP header field values could be extended over multiple
1315   lines by preceding each extra line with at least one space or horizontal
1316   tab (obs-fold). This specification deprecates such line
1317   folding except within the message/http media type
1318   (<xref target=""/>).
1319   HTTP senders &MUST-NOT; produce messages that include line folding
1320   (i.e., that contain any field-value that matches the obs-fold rule) unless
1321   the message is intended for packaging within the message/http media type.
1322   HTTP recipients &SHOULD; accept line folding and replace any embedded
1323   obs-fold whitespace with either a single SP or a matching number of SP
1324   octets (to avoid buffer copying) prior to interpreting the field value or
1325   forwarding the message downstream.
1328   Historically, HTTP has allowed field content with text in the ISO-8859-1
1329   <xref target="ISO-8859-1"/> character encoding and supported other
1330   character sets only through use of <xref target="RFC2047"/> encoding.
1331   In practice, most HTTP header field values use only a subset of the
1332   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1333   header fields &SHOULD; limit their field values to US-ASCII octets.
1334   Recipients &SHOULD; treat other (obs-text) octets in field content as
1335   opaque data.
1339<section title="Field Length" anchor="field.length">
1341   HTTP does not place a pre-defined limit on the length of header fields,
1342   either in isolation or as a set. A server &MUST; be prepared to receive
1343   request header fields of unbounded length and respond with a <x:ref>4xx
1344   (Client Error)</x:ref> status code if the received header field(s) would be
1345   longer than the server wishes to handle.
1348   A client that receives response headers that are longer than it wishes to
1349   handle can only treat it as a server error.
1352   Various ad-hoc limitations on header length are found in practice. It is
1353   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1354   combined header fields have 4000 or more octets.
1358<section title="Field value components" anchor="field.components">
1359<t anchor="rule.token.separators">
1360  <x:anchor-alias value="tchar"/>
1361  <x:anchor-alias value="token"/>
1362  <x:anchor-alias value="special"/>
1363  <x:anchor-alias value="word"/>
1364   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1365   separated by whitespace or special characters. These special characters
1366   &MUST; be in a quoted string to be used within a parameter value (as defined
1367   in <xref target="transfer.codings"/>).
1369<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"/>
1370  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1372  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1374  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1375 -->
1376  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1377                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1378                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1379                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1381  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1382                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1383                 / "]" / "?" / "=" / "{" / "}"
1385<t anchor="rule.quoted-string">
1386  <x:anchor-alias value="quoted-string"/>
1387  <x:anchor-alias value="qdtext"/>
1388  <x:anchor-alias value="obs-text"/>
1389   A string of text is parsed as a single word if it is quoted using
1390   double-quote marks.
1392<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"/>
1393  <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>
1394  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1395  <x:ref>obs-text</x:ref>       = %x80-FF
1397<t anchor="rule.quoted-pair">
1398  <x:anchor-alias value="quoted-pair"/>
1399   The backslash octet ("\") can be used as a single-octet
1400   quoting mechanism within quoted-string constructs:
1402<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1403  <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> )
1406   Recipients that process the value of the quoted-string &MUST; handle a
1407   quoted-pair as if it were replaced by the octet following the backslash.
1410   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1411   escaping (i.e., other than DQUOTE and the backslash octet).
1413<t anchor="rule.comment">
1414  <x:anchor-alias value="comment"/>
1415  <x:anchor-alias value="ctext"/>
1416   Comments can be included in some HTTP header fields by surrounding
1417   the comment text with parentheses. Comments are only allowed in
1418   fields containing "comment" as part of their field value definition.
1420<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1421  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1422  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1424<t anchor="rule.quoted-cpair">
1425  <x:anchor-alias value="quoted-cpair"/>
1426   The backslash octet ("\") can be used as a single-octet
1427   quoting mechanism within comment constructs:
1429<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1430  <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> )
1433   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1434   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1438<section title="ABNF list extension: #rule" anchor="abnf.extension">
1440  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
1441  improve readability in the definitions of some header field values.
1444  A construct "#" is defined, similar to "*", for defining comma-delimited
1445  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
1446  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
1447  comma (",") and optional whitespace (OWS).   
1450  Thus,
1451</preamble><artwork type="example">
1452  1#element =&gt; element *( OWS "," OWS element )
1455  and:
1456</preamble><artwork type="example">
1457  #element =&gt; [ 1#element ]
1460  and for n &gt;= 1 and m &gt; 1:
1461</preamble><artwork type="example">
1462  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
1465  For compatibility with legacy list rules, recipients &SHOULD; accept empty
1466  list elements. In other words, consumers would follow the list productions:
1468<figure><artwork type="example">
1469  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
1471  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
1474  Note that empty elements do not contribute to the count of elements present,
1475  though.
1478  For example, given these ABNF productions:
1480<figure><artwork type="example">
1481  example-list      = 1#example-list-elmt
1482  example-list-elmt = token ; see <xref target="field.components"/>
1485  Then these are valid values for example-list (not including the double
1486  quotes, which are present for delimitation only):
1488<figure><artwork type="example">
1489  "foo,bar"
1490  "foo ,bar,"
1491  "foo , ,bar,charlie   "
1494  But these values would be invalid, as at least one non-empty element is
1495  required:
1497<figure><artwork type="example">
1498  ""
1499  ","
1500  ",   ,"
1503  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
1504  expanded as explained above.
1509<section title="Message Body" anchor="message.body">
1510  <x:anchor-alias value="message-body"/>
1512   The message body (if any) of an HTTP message is used to carry the
1513   payload body of that request or response.  The message body is
1514   identical to the payload body unless a transfer coding has been
1515   applied, as described in <xref target="header.transfer-encoding"/>.
1517<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1518  <x:ref>message-body</x:ref> = *OCTET
1521   The rules for when a message body is allowed in a message differ for
1522   requests and responses.
1525   The presence of a message body in a request is signaled by a
1526   a <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1527   field. Request message framing is independent of method semantics,
1528   even if the method does not define any use for a message body.
1531   The presence of a message body in a response depends on both
1532   the request method to which it is responding and the response
1533   status code (<xref target="status.line"/>).
1534   Responses to the HEAD request method never include a message body
1535   because the associated response header fields (e.g.,
1536   <x:ref>Transfer-Encoding</x:ref>, <x:ref>Content-Length</x:ref>, etc.) only
1537   indicate what their values would have been if the request method had been
1538   GET. <x:ref>2xx (Successful)</x:ref> responses to CONNECT switch to tunnel
1539   mode instead of having a message body.
1540   All <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, and
1541   <x:ref>304 (Not Modified)</x:ref> responses &MUST-NOT; include a message body.
1542   All other responses do include a message body, although the body
1543   &MAY; be of zero length.
1546<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1547  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1548  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
1549  <x:anchor-alias value="Transfer-Encoding"/>
1551   When one or more transfer codings are applied to a payload body in order
1552   to form the message body, a Transfer-Encoding header field &MUST; be sent
1553   in the message and &MUST; contain the list of corresponding
1554   transfer-coding names in the same order that they were applied.
1555   Transfer codings are defined in <xref target="transfer.codings"/>.
1557<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1558  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1561   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1562   MIME, which was designed to enable safe transport of binary data over a
1563   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1564   However, safe transport has a different focus for an 8bit-clean transfer
1565   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1566   accurately delimit a dynamically generated payload and to distinguish
1567   payload encodings that are only applied for transport efficiency or
1568   security from those that are characteristics of the target resource.
1571   The "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1572   &MUST; be implemented by all HTTP/1.1 recipients because it plays a
1573   crucial role in delimiting messages when the payload body size is not
1574   known in advance.
1575   When the "chunked" transfer-coding is used, it &MUST; be the last
1576   transfer-coding applied to form the message body and &MUST-NOT;
1577   be applied more than once in a message body.
1578   If any transfer-coding is applied to a request payload body,
1579   the final transfer-coding applied &MUST; be "chunked".
1580   If any transfer-coding is applied to a response payload body, then either
1581   the final transfer-coding applied &MUST; be "chunked" or
1582   the message &MUST; be terminated by closing the connection.
1585   For example,
1586</preamble><artwork type="example">
1587  Transfer-Encoding: gzip, chunked
1589   indicates that the payload body has been compressed using the gzip
1590   coding and then chunked using the chunked coding while forming the
1591   message body.
1594   If more than one Transfer-Encoding header field is present in a message,
1595   the multiple field-values &MUST; be combined into one field-value,
1596   according to the algorithm defined in <xref target="header.fields"/>,
1597   before determining the message body length.
1600   Unlike <x:ref>Content-Encoding</x:ref> (&content-codings;),
1601   Transfer-Encoding is a property of the message, not of the payload, and thus
1602   &MAY; be added or removed by any implementation along the request/response
1603   chain. Additional information about the encoding parameters &MAY; be
1604   provided by other header fields not defined by this specification.
1607   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1608   <x:ref>304 (Not Modified)</x:ref> response (&status-304;) to a GET request,
1609   neither of which includes a message body,
1610   to indicate that the origin server would have applied a transfer coding
1611   to the message body if the request had been an unconditional GET.
1612   This indication is not required, however, because any recipient on
1613   the response chain (including the origin server) can remove transfer
1614   codings when they are not needed.
1617   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1618   implementations advertising only HTTP/1.0 support will not understand
1619   how to process a transfer-encoded payload.
1620   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1621   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1622   might be in the form of specific user configuration or by remembering the
1623   version of a prior received response.
1624   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1625   the corresponding request indicates HTTP/1.1 (or later).
1628   A server that receives a request message with a transfer-coding it does
1629   not understand &SHOULD; respond with <x:ref>501 (Not Implemented)</x:ref> and then
1630   close the connection.
1634<section title="Content-Length" anchor="header.content-length">
1635  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1636  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
1637  <x:anchor-alias value="Content-Length"/>
1639   When a message does not have a <x:ref>Transfer-Encoding</x:ref> header field
1640   and the payload body length can be determined prior to being transferred, a
1641   Content-Length header field &SHOULD; be sent to indicate the length of the
1642   payload body that is either present as the message body, for requests
1643   and non-HEAD responses other than <x:ref>304 (Not Modified)</x:ref>, or
1644   would have been present had the request been an unconditional GET.  The
1645   length is expressed as a decimal number of octets.
1647<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1648  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1651   An example is
1653<figure><artwork type="example">
1654  Content-Length: 3495
1657   In the case of a response to a HEAD request, Content-Length indicates
1658   the size of the payload body (without any potential transfer-coding)
1659   that would have been sent had the request been a GET.
1660   In the case of a <x:ref>304 (Not Modified)</x:ref> response (&status-304;)
1661   to a GET request, Content-Length indicates the size of the payload body (without
1662   any potential transfer-coding) that would have been sent in a <x:ref>200 (OK)</x:ref>
1663   response.
1666   Any Content-Length field value greater than or equal to zero is valid.
1667   Since there is no predefined limit to the length of an HTTP payload,
1668   recipients &SHOULD; anticipate potentially large decimal numerals and
1669   prevent parsing errors due to integer conversion overflows
1670   (<xref target="attack.protocol.element.size.overflows"/>).
1673   If a message is received that has multiple Content-Length header fields
1674   with field-values consisting of the same decimal value, or a single
1675   Content-Length header field with a field value containing a list of
1676   identical decimal values (e.g., "Content-Length: 42, 42"), indicating that
1677   duplicate Content-Length header fields have been generated or combined by an
1678   upstream message processor, then the recipient &MUST; either reject the
1679   message as invalid or replace the duplicated field-values with a single
1680   valid Content-Length field containing that decimal value prior to
1681   determining the message body length.
1684  <t>
1685   &Note; HTTP's use of Content-Length for message framing differs
1686   significantly from the same field's use in MIME, where it is an optional
1687   field used only within the "message/external-body" media-type.
1688  </t>
1692<section title="Message Body Length" anchor="message.body.length">
1694   The length of a message body is determined by one of the following
1695   (in order of precedence):
1698  <list style="numbers">
1699    <x:lt><t>
1700     Any response to a HEAD request and any response with a
1701     <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, or
1702     <x:ref>304 (Not Modified)</x:ref> status code is always
1703     terminated by the first empty line after the header fields, regardless of
1704     the header fields present in the message, and thus cannot contain a
1705     message body.
1706    </t></x:lt>
1707    <x:lt><t>
1708     Any <x:ref>2xx (Successful)</x:ref> response to a CONNECT request implies that the
1709     connection will become a tunnel immediately after the empty line that
1710     concludes the header fields.  A client &MUST; ignore any
1711     <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1712     fields received in such a message.
1713    </t></x:lt>
1714    <x:lt><t>
1715     If a <x:ref>Transfer-Encoding</x:ref> header field is present
1716     and the "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1717     is the final encoding, the message body length is determined by reading
1718     and decoding the chunked data until the transfer-coding indicates the
1719     data is complete.
1720    </t>
1721    <t>
1722     If a <x:ref>Transfer-Encoding</x:ref> header field is present in a
1723     response and the "chunked" transfer-coding is not the final encoding, the
1724     message body length is determined by reading the connection until it is
1725     closed by the server.
1726     If a Transfer-Encoding header field is present in a request and the
1727     "chunked" transfer-coding is not the final encoding, the message body
1728     length cannot be determined reliably; the server &MUST; respond with
1729     the <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1730    </t>
1731    <t>
1732     If a message is received with both a <x:ref>Transfer-Encoding</x:ref>
1733     and a <x:ref>Content-Length</x:ref> header field, the
1734     Transfer-Encoding overrides the Content-Length.
1735     Such a message might indicate an attempt to perform request or response
1736     smuggling (bypass of security-related checks on message routing or content)
1737     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1738     be removed, prior to forwarding the message downstream, or replaced with
1739     the real message body length after the transfer-coding is decoded.
1740    </t></x:lt>
1741    <x:lt><t>
1742     If a message is received without <x:ref>Transfer-Encoding</x:ref> and with
1743     either multiple <x:ref>Content-Length</x:ref> header fields having
1744     differing field-values or a single Content-Length header field having an
1745     invalid value, then the message framing is invalid and &MUST; be treated
1746     as an error to prevent request or response smuggling.
1747     If this is a request message, the server &MUST; respond with
1748     a <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1749     If this is a response message received by a proxy, the proxy
1750     &MUST; discard the received response, send a <x:ref>502 (Bad Gateway)</x:ref>
1751     status code as its downstream response, and then close the connection.
1752     If this is a response message received by a user-agent, it &MUST; be
1753     treated as an error by discarding the message and closing the connection.
1754    </t></x:lt>
1755    <x:lt><t>
1756     If a valid <x:ref>Content-Length</x:ref> header field is present without
1757     <x:ref>Transfer-Encoding</x:ref>, its decimal value defines the
1758     message body length in octets.  If the actual number of octets sent in
1759     the message is less than the indicated Content-Length, the recipient
1760     &MUST; consider the message to be incomplete and treat the connection
1761     as no longer usable.
1762     If the actual number of octets sent in the message is more than the indicated
1763     Content-Length, the recipient &MUST; only process the message body up to the
1764     field value's number of octets; the remainder of the message &MUST; either
1765     be discarded or treated as the next message in a pipeline.  For the sake of
1766     robustness, a user-agent &MAY; attempt to detect and correct such an error
1767     in message framing if it is parsing the response to the last request on
1768     a connection and the connection has been closed by the server.
1769    </t></x:lt>
1770    <x:lt><t>
1771     If this is a request message and none of the above are true, then the
1772     message body length is zero (no message body is present).
1773    </t></x:lt>
1774    <x:lt><t>
1775     Otherwise, this is a response message without a declared message body
1776     length, so the message body length is determined by the number of octets
1777     received prior to the server closing the connection.
1778    </t></x:lt>
1779  </list>
1782   Since there is no way to distinguish a successfully completed,
1783   close-delimited message from a partially-received message interrupted
1784   by network failure, implementations &SHOULD; use encoding or
1785   length-delimited messages whenever possible.  The close-delimiting
1786   feature exists primarily for backwards compatibility with HTTP/1.0.
1789   A server &MAY; reject a request that contains a message body but
1790   not a <x:ref>Content-Length</x:ref> by responding with
1791   <x:ref>411 (Length Required)</x:ref>.
1794   Unless a transfer-coding other than "chunked" has been applied,
1795   a client that sends a request containing a message body &SHOULD;
1796   use a valid <x:ref>Content-Length</x:ref> header field if the message body
1797   length is known in advance, rather than the "chunked" encoding, since some
1798   existing services respond to "chunked" with a <x:ref>411 (Length Required)</x:ref>
1799   status code even though they understand the chunked encoding.  This
1800   is typically because such services are implemented via a gateway that
1801   requires a content-length in advance of being called and the server
1802   is unable or unwilling to buffer the entire request before processing.
1805   A client that sends a request containing a message body &MUST; include a
1806   valid <x:ref>Content-Length</x:ref> header field if it does not know the
1807   server will handle HTTP/1.1 (or later) requests; such knowledge can be in
1808   the form of specific user configuration or by remembering the version of a
1809   prior received response.
1814<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1816   Request messages that are prematurely terminated, possibly due to a
1817   cancelled connection or a server-imposed time-out exception, &MUST;
1818   result in closure of the connection; sending an HTTP/1.1 error response
1819   prior to closing the connection is &OPTIONAL;.
1822   Response messages that are prematurely terminated, usually by closure
1823   of the connection prior to receiving the expected number of octets or by
1824   failure to decode a transfer-encoded message body, &MUST; be recorded
1825   as incomplete.  A response that terminates in the middle of the header
1826   block (before the empty line is received) cannot be assumed to convey the
1827   full semantics of the response and &MUST; be treated as an error.
1830   A message body that uses the chunked transfer encoding is
1831   incomplete if the zero-sized chunk that terminates the encoding has not
1832   been received.  A message that uses a valid <x:ref>Content-Length</x:ref> is
1833   incomplete if the size of the message body received (in octets) is less than
1834   the value given by Content-Length.  A response that has neither chunked
1835   transfer encoding nor Content-Length is terminated by closure of the
1836   connection, and thus is considered complete regardless of the number of
1837   message body octets received, provided that the header block was received
1838   intact.
1841   A user agent &MUST-NOT; render an incomplete response message body as if
1842   it were complete (i.e., some indication needs to be given to the user that an
1843   error occurred).  Cache requirements for incomplete responses are defined
1844   in &cache-incomplete;.
1847   A server &MUST; read the entire request message body or close
1848   the connection after sending its response, since otherwise the
1849   remaining data on a persistent connection would be misinterpreted
1850   as the next request.  Likewise,
1851   a client &MUST; read the entire response message body if it intends
1852   to reuse the same connection for a subsequent request.  Pipelining
1853   multiple requests on a connection is described in <xref target="pipelining"/>.
1857<section title="Message Parsing Robustness" anchor="message.robustness">
1859   Older HTTP/1.0 client implementations might send an extra CRLF
1860   after a POST request as a lame workaround for some early server
1861   applications that failed to read message body content that was
1862   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1863   preface or follow a request with an extra CRLF.  If terminating
1864   the request message body with a line-ending is desired, then the
1865   client &MUST; include the terminating CRLF octets as part of the
1866   message body length.
1869   In the interest of robustness, servers &SHOULD; ignore at least one
1870   empty line received where a request-line is expected. In other words, if
1871   the server is reading the protocol stream at the beginning of a
1872   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1873   Likewise, although the line terminator for the start-line and header
1874   fields is the sequence CRLF, we recommend that recipients recognize a
1875   single LF as a line terminator and ignore any CR.
1878   When a server listening only for HTTP request messages, or processing
1879   what appears from the start-line to be an HTTP request message,
1880   receives a sequence of octets that does not match the HTTP-message
1881   grammar aside from the robustness exceptions listed above, the
1882   server &MUST; respond with an HTTP/1.1 <x:ref>400 (Bad Request)</x:ref> response. 
1887<section title="Transfer Codings" anchor="transfer.codings">
1888  <x:anchor-alias value="transfer-coding"/>
1889  <x:anchor-alias value="transfer-extension"/>
1891   Transfer-coding values are used to indicate an encoding
1892   transformation that has been, can be, or might need to be applied to a
1893   payload body in order to ensure "safe transport" through the network.
1894   This differs from a content coding in that the transfer-coding is a
1895   property of the message rather than a property of the representation
1896   that is being transferred.
1898<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1899  <x:ref>transfer-coding</x:ref>    = "chunked" ; <xref target="chunked.encoding"/>
1900                     / "compress" ; <xref target="compress.coding"/>
1901                     / "deflate" ; <xref target="deflate.coding"/>
1902                     / "gzip" ; <xref target="gzip.coding"/>
1903                     / <x:ref>transfer-extension</x:ref>
1904  <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> )
1906<t anchor="rule.parameter">
1907  <x:anchor-alias value="attribute"/>
1908  <x:anchor-alias value="transfer-parameter"/>
1909  <x:anchor-alias value="value"/>
1910   Parameters are in the form of attribute/value pairs.
1912<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"/>
1913  <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>
1914  <x:ref>attribute</x:ref>          = <x:ref>token</x:ref>
1915  <x:ref>value</x:ref>              = <x:ref>word</x:ref>
1918   All transfer-coding values are case-insensitive.
1919   The HTTP Transfer Coding registry is defined in
1920   <xref target="transfer.coding.registry"/>.
1921   HTTP/1.1 uses transfer-coding values in the <x:ref>TE</x:ref> header field
1922   (<xref target="header.te"/>) and in the <x:ref>Transfer-Encoding</x:ref>
1923   header field (<xref target="header.transfer-encoding"/>).
1926<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1927  <iref item="chunked (Coding Format)"/>
1928  <iref item="Coding Format" subitem="chunked"/>
1929  <x:anchor-alias value="chunk"/>
1930  <x:anchor-alias value="chunked-body"/>
1931  <x:anchor-alias value="chunk-data"/>
1932  <x:anchor-alias value="chunk-ext"/>
1933  <x:anchor-alias value="chunk-ext-name"/>
1934  <x:anchor-alias value="chunk-ext-val"/>
1935  <x:anchor-alias value="chunk-size"/>
1936  <x:anchor-alias value="last-chunk"/>
1937  <x:anchor-alias value="trailer-part"/>
1938  <x:anchor-alias value="quoted-str-nf"/>
1939  <x:anchor-alias value="qdtext-nf"/>
1941   The chunked encoding modifies the body of a message in order to
1942   transfer it as a series of chunks, each with its own size indicator,
1943   followed by an &OPTIONAL; trailer containing header fields. This
1944   allows dynamically produced content to be transferred along with the
1945   information necessary for the recipient to verify that it has
1946   received the full message.
1948<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="chunked-body"/><iref primary="true" item="Grammar" subitem="chunk"/><iref primary="true" item="Grammar" subitem="chunk-size"/><iref primary="true" item="Grammar" subitem="last-chunk"/><iref primary="true" item="Grammar" subitem="chunk-ext"/><iref primary="true" item="Grammar" subitem="chunk-ext-name"/><iref primary="true" item="Grammar" subitem="chunk-ext-val"/><iref primary="true" item="Grammar" subitem="chunk-data"/><iref primary="true" item="Grammar" subitem="trailer-part"/><iref primary="true" item="Grammar" subitem="quoted-str-nf"/><iref primary="true" item="Grammar" subitem="qdtext-nf"/>
1949  <x:ref>chunked-body</x:ref>   = *<x:ref>chunk</x:ref>
1950                   <x:ref>last-chunk</x:ref>
1951                   <x:ref>trailer-part</x:ref>
1952                   <x:ref>CRLF</x:ref>
1954  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1955                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1956  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1957  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1959  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1960  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1961  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1962  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1963  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1965  <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>
1966                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1967  <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>
1970   The chunk-size field is a string of hex digits indicating the size of
1971   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1972   zero, followed by the trailer, which is terminated by an empty line.
1975   The trailer allows the sender to include additional HTTP header
1976   fields at the end of the message. The <x:ref>Trailer</x:ref> header field
1977   can be used to indicate which header fields are included in a trailer (see
1978   <xref target="header.trailer"/>).
1981   A server using chunked transfer-coding in a response &MUST-NOT; use the
1982   trailer for any header fields unless at least one of the following is
1983   true:
1984  <list style="numbers">
1985    <t>the request included a <x:ref>TE</x:ref> header field that indicates
1986    "trailers" is acceptable in the transfer-coding of the response, as
1987    described in <xref target="header.te"/>; or,</t>
1989    <t>the trailer fields consist entirely of optional metadata, and the
1990    recipient could use the message (in a manner acceptable to the server where
1991    the field originated) without receiving it. In other words, the server that
1992    generated the header (often but not always the origin server) is willing to
1993    accept the possibility that the trailer fields might be silently discarded
1994    along the path to the client.</t>
1995  </list>
1998   This requirement prevents an interoperability failure when the
1999   message is being received by an HTTP/1.1 (or later) proxy and
2000   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2001   conformance with the protocol would have necessitated a possibly
2002   infinite buffer on the proxy.
2005   A process for decoding the "chunked" transfer-coding
2006   can be represented in pseudo-code as:
2008<figure><artwork type="code">
2009  length := 0
2010  read chunk-size, chunk-ext (if any) and CRLF
2011  while (chunk-size &gt; 0) {
2012     read chunk-data and CRLF
2013     append chunk-data to decoded-body
2014     length := length + chunk-size
2015     read chunk-size and CRLF
2016  }
2017  read header-field
2018  while (header-field not empty) {
2019     append header-field to existing header fields
2020     read header-field
2021  }
2022  Content-Length := length
2023  Remove "chunked" from Transfer-Encoding
2026   All HTTP/1.1 applications &MUST; be able to receive and decode the
2027   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2028   they do not understand.
2031   Use of chunk-ext extensions by senders is deprecated; they &SHOULD-NOT; be
2032   sent and definition of new chunk-extensions is discouraged.
2036<section title="Compression Codings" anchor="compression.codings">
2038   The codings defined below can be used to compress the payload of a
2039   message.
2042   &Note; Use of program names for the identification of encoding formats
2043   is not desirable and is discouraged for future encodings. Their
2044   use here is representative of historical practice, not good
2045   design.
2048   &Note; For compatibility with previous implementations of HTTP,
2049   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2050   equivalent to "gzip" and "compress" respectively.
2053<section title="Compress Coding" anchor="compress.coding">
2054<iref item="compress (Coding Format)"/>
2055<iref item="Coding Format" subitem="compress"/>
2057   The "compress" format is produced by the common UNIX file compression
2058   program "compress". This format is an adaptive Lempel-Ziv-Welch
2059   coding (LZW).
2063<section title="Deflate Coding" anchor="deflate.coding">
2064<iref item="deflate (Coding Format)"/>
2065<iref item="Coding Format" subitem="deflate"/>
2067   The "deflate" format is defined as the "deflate" compression mechanism
2068   (described in <xref target="RFC1951"/>) used inside the "zlib"
2069   data format (<xref target="RFC1950"/>).
2072  <t>
2073    &Note; Some incorrect implementations send the "deflate"
2074    compressed data without the zlib wrapper.
2075   </t>
2079<section title="Gzip Coding" anchor="gzip.coding">
2080<iref item="gzip (Coding Format)"/>
2081<iref item="Coding Format" subitem="gzip"/>
2083   The "gzip" format is produced by the file compression program
2084   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2085   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2091<section title="TE" anchor="header.te">
2092  <iref primary="true" item="TE header field" x:for-anchor=""/>
2093  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
2094  <x:anchor-alias value="TE"/>
2095  <x:anchor-alias value="t-codings"/>
2096  <x:anchor-alias value="te-params"/>
2097  <x:anchor-alias value="te-ext"/>
2099   The "TE" header field indicates what extension transfer-codings
2100   the client is willing to accept in the response, and whether or not it is
2101   willing to accept trailer fields in a chunked transfer-coding.
2104   Its value consists of the keyword "trailers" and/or a comma-separated
2105   list of extension transfer-coding names with optional accept
2106   parameters (as described in <xref target="transfer.codings"/>).
2108<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
2109  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2110  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2111  <x:ref>te-params</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>te-ext</x:ref> )
2112  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
2115   The presence of the keyword "trailers" indicates that the client is
2116   willing to accept trailer fields in a chunked transfer-coding, as
2117   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
2118   transfer-coding values even though it does not itself represent a
2119   transfer-coding.
2122   Examples of its use are:
2124<figure><artwork type="example">
2125  TE: deflate
2126  TE:
2127  TE: trailers, deflate;q=0.5
2130   The TE header field only applies to the immediate connection.
2131   Therefore, the keyword &MUST; be supplied within a <x:ref>Connection</x:ref>
2132   header field (<xref target="header.connection"/>) whenever TE is present in
2133   an HTTP/1.1 message.
2136   A server tests whether a transfer-coding is acceptable, according to
2137   a TE field, using these rules:
2138  <list style="numbers">
2139    <x:lt>
2140      <t>The "chunked" transfer-coding is always acceptable. If the
2141         keyword "trailers" is listed, the client indicates that it is
2142         willing to accept trailer fields in the chunked response on
2143         behalf of itself and any downstream clients. The implication is
2144         that, if given, the client is stating that either all
2145         downstream clients are willing to accept trailer fields in the
2146         forwarded response, or that it will attempt to buffer the
2147         response on behalf of downstream recipients.
2148      </t><t>
2149         &Note; HTTP/1.1 does not define any means to limit the size of a
2150         chunked response such that a client can be assured of buffering
2151         the entire response.</t>
2152    </x:lt>
2153    <x:lt>
2154      <t>If the transfer-coding being tested is one of the transfer-codings
2155         listed in the TE field, then it is acceptable unless it
2156         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2157         qvalue of 0 means "not acceptable".)</t>
2158    </x:lt>
2159    <x:lt>
2160      <t>If multiple transfer-codings are acceptable, then the
2161         acceptable transfer-coding with the highest non-zero qvalue is
2162         preferred.  The "chunked" transfer-coding always has a qvalue
2163         of 1.</t>
2164    </x:lt>
2165  </list>
2168   If the TE field-value is empty or if no TE field is present, the only
2169   acceptable transfer-coding is "chunked". A message with no transfer-coding is
2170   always acceptable.
2173<section title="Quality Values" anchor="quality.values">
2174  <x:anchor-alias value="qvalue"/>
2176   Both transfer codings (<x:ref>TE</x:ref> request header field,
2177   <xref target="header.te"/>) and content negotiation (&content.negotiation;)
2178   use short "floating point" numbers to indicate the relative importance
2179   ("weight") of various negotiable parameters.  A weight is normalized to a
2180   real number in the range 0 through 1, where 0 is the minimum and 1 the
2181   maximum value. If a parameter has a quality value of 0, then content with
2182   this parameter is "not acceptable" for the client. HTTP/1.1
2183   applications &MUST-NOT; generate more than three digits after the
2184   decimal point. User configuration of these values &SHOULD; also be
2185   limited in this fashion.
2187<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2188  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2189                 / ( "1" [ "." 0*3("0") ] )
2192  <t>
2193     &Note; "Quality values" is a misnomer, since these values merely represent
2194     relative degradation in desired quality.
2195  </t>
2200<section title="Trailer" anchor="header.trailer">
2201  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
2202  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
2203  <x:anchor-alias value="Trailer"/>
2205   The "Trailer" header field indicates that the given set of
2206   header fields is present in the trailer of a message encoded with
2207   chunked transfer-coding.
2209<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2210  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
2213   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2214   message using chunked transfer-coding with a non-empty trailer. Doing
2215   so allows the recipient to know which header fields to expect in the
2216   trailer.
2219   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2220   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
2221   trailer fields in a "chunked" transfer-coding.
2224   Message header fields listed in the Trailer header field &MUST-NOT;
2225   include the following header fields:
2226  <list style="symbols">
2227    <t><x:ref>Transfer-Encoding</x:ref></t>
2228    <t><x:ref>Content-Length</x:ref></t>
2229    <t><x:ref>Trailer</x:ref></t>
2230  </list>
2235<section title="Message Routing" anchor="message.routing">
2237   HTTP request message routing is determined by each client based on the
2238   target resource, the client's proxy configuration, and
2239   establishment or reuse of an inbound connection.  The corresponding
2240   response routing follows the same connection chain back to the client.
2243<section title="Identifying a Target Resource" anchor="target-resource">
2244  <iref primary="true" item="target resource"/>
2245  <iref primary="true" item="target URI"/>
2247   HTTP is used in a wide variety of applications, ranging from
2248   general-purpose computers to home appliances.  In some cases,
2249   communication options are hard-coded in a client's configuration.
2250   However, most HTTP clients rely on the same resource identification
2251   mechanism and configuration techniques as general-purpose Web browsers.
2254   HTTP communication is initiated by a user agent for some purpose.
2255   The purpose is a combination of request semantics, which are defined in
2256   <xref target="Part2"/>, and a target resource upon which to apply those
2257   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2258   an identifier for the "target resource", which a user agent would resolve
2259   to its absolute form in order to obtain the "target URI".  The target URI
2260   excludes the reference's fragment identifier component, if any,
2261   since fragment identifiers are reserved for client-side processing
2262   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2265   HTTP intermediaries obtain the request semantics and target URI
2266   from the request-line of an incoming request message.
2270<section title="Connecting Inbound" anchor="connecting.inbound">
2272   Once the target URI is determined, a client needs to decide whether
2273   a network request is necessary to accomplish the desired semantics and,
2274   if so, where that request is to be directed.
2277   If the client has a response cache and the request semantics can be
2278   satisfied by a cache (<xref target="Part6"/>), then the request is
2279   usually directed to the cache first.
2282   If the request is not satisfied by a cache, then a typical client will
2283   check its configuration to determine whether a proxy is to be used to
2284   satisfy the request.  Proxy configuration is implementation-dependent,
2285   but is often based on URI prefix matching, selective authority matching,
2286   or both, and the proxy itself is usually identified by an "http" or
2287   "https" URI.  If a proxy is applicable, the client connects inbound by
2288   establishing (or reusing) a connection to that proxy.
2291   If no proxy is applicable, a typical client will invoke a handler routine,
2292   usually specific to the target URI's scheme, to connect directly
2293   to an authority for the target resource.  How that is accomplished is
2294   dependent on the target URI scheme and defined by its associated
2295   specification, similar to how this specification defines origin server
2296   access for resolution of the "http" (<xref target="http.uri"/>) and
2297   "https" (<xref target="https.uri"/>) schemes.
2301<section title="Request Target" anchor="request-target">
2303   Once an inbound connection is obtained
2304   (<xref target=""/>),
2305   the client sends an HTTP request message (<xref target="http.message"/>)
2306   with a request-target derived from the target URI.
2307   There are four distinct formats for the request-target, depending on both
2308   the method being requested and whether the request is to a proxy.
2310<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"/>
2311  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2312                 / <x:ref>absolute-form</x:ref>
2313                 / <x:ref>authority-form</x:ref>
2314                 / <x:ref>asterisk-form</x:ref>
2316  <x:ref>origin-form</x:ref>    = <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]
2317  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2318  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2319  <x:ref>asterisk-form</x:ref>  = "*"
2321<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2322   The most common form of request-target is the origin-form.
2323   When making a request directly to an origin server, other than a CONNECT
2324   or server-wide OPTIONS request (as detailed below),
2325   a client &MUST; send only the absolute path and query components of
2326   the target URI as the request-target.
2327   If the target URI's path component is empty, then the client &MUST; send
2328   "/" as the path within the origin-form of request-target.
2329   A <x:ref>Host</x:ref> header field is also sent, as defined in
2330   <xref target=""/>, containing the target URI's
2331   authority component (excluding any userinfo).
2334   For example, a client wishing to retrieve a representation of the resource
2335   identified as
2337<figure><artwork x:indent-with="  " type="example">
2341   directly from the origin server would open (or reuse) a TCP connection
2342   to port 80 of the host "" and send the lines:
2344<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2345GET /where?q=now HTTP/1.1
2349   followed by the remainder of the request message.
2351<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2352   When making a request to a proxy, other than a CONNECT or server-wide
2353   OPTIONS request (as detailed below), a client &MUST; send the target URI
2354   in absolute-form as the request-target.
2355   The proxy is requested to either service that request from a valid cache,
2356   if possible, or make the same request on the client's behalf to either
2357   the next inbound proxy server or directly to the origin server indicated
2358   by the request-target.  Requirements on such "forwarding" of messages are
2359   defined in <xref target="intermediary.forwarding"/>.
2362   An example absolute-form of request-line would be:
2364<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2365GET HTTP/1.1
2368   To allow for transition to the absolute-form for all requests in some
2369   future version of HTTP, HTTP/1.1 servers &MUST; accept the absolute-form
2370   in requests, even though HTTP/1.1 clients will only send them in requests
2371   to proxies.
2373<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2374   The authority-form of request-target is only used for CONNECT requests
2375   (&CONNECT;).  When making a CONNECT request to establish a tunnel through
2376   one or more proxies, a client &MUST; send only the target URI's
2377   authority component (excluding any userinfo) as the request-target.
2378   For example,
2380<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2383<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2384   The asterisk-form of request-target is only used for a server-wide
2385   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2386   for the server as a whole, as opposed to a specific named resource of
2387   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2388   For example,
2390<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2391OPTIONS * HTTP/1.1
2394   If a proxy receives an OPTIONS request with an absolute-form of
2395   request-target in which the URI has an empty path and no query component,
2396   then the last proxy on the request chain &MUST; send a request-target
2397   of "*" when it forwards the request to the indicated origin server.
2400   For example, the request
2401</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2405  would be forwarded by the final proxy as
2406</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2407OPTIONS * HTTP/1.1
2411   after connecting to port 8001 of host "".
2416<section title="Host" anchor="">
2417  <iref primary="true" item="Host header field" x:for-anchor=""/>
2418  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
2419  <x:anchor-alias value="Host"/>
2421   The "Host" header field in a request provides the host and port
2422   information from the target URI, enabling the origin
2423   server to distinguish among resources while servicing requests
2424   for multiple host names on a single IP address.  Since the Host
2425   field-value is critical information for handling a request, it
2426   &SHOULD; be sent as the first header field following the request-line.
2428<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2429  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2432   A client &MUST; send a Host header field in all HTTP/1.1 request
2433   messages.  If the target URI includes an authority component, then
2434   the Host field-value &MUST; be identical to that authority component
2435   after excluding any userinfo (<xref target="http.uri"/>).
2436   If the authority component is missing or undefined for the target URI,
2437   then the Host header field &MUST; be sent with an empty field-value.
2440   For example, a GET request to the origin server for
2441   &lt;; would begin with:
2443<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2444GET /pub/WWW/ HTTP/1.1
2448   The Host header field &MUST; be sent in an HTTP/1.1 request even
2449   if the request-target is in the absolute-form, since this
2450   allows the Host information to be forwarded through ancient HTTP/1.0
2451   proxies that might not have implemented Host.
2454   When an HTTP/1.1 proxy receives a request with an absolute-form of
2455   request-target, the proxy &MUST; ignore the received
2456   Host header field (if any) and instead replace it with the host
2457   information of the request-target.  If the proxy forwards the request,
2458   it &MUST; generate a new Host field-value based on the received
2459   request-target rather than forward the received Host field-value.
2462   Since the Host header field acts as an application-level routing
2463   mechanism, it is a frequent target for malware seeking to poison
2464   a shared cache or redirect a request to an unintended server.
2465   An interception proxy is particularly vulnerable if it relies on
2466   the Host field-value for redirecting requests to internal
2467   servers, or for use as a cache key in a shared cache, without
2468   first verifying that the intercepted connection is targeting a
2469   valid IP address for that host.
2472   A server &MUST; respond with a <x:ref>400 (Bad Request)</x:ref> status code
2473   to any HTTP/1.1 request message that lacks a Host header field and
2474   to any request message that contains more than one Host header field
2475   or a Host header field with an invalid field-value.
2479<section title="Effective Request URI" anchor="effective.request.uri">
2480  <iref primary="true" item="effective request URI"/>
2482   A server that receives an HTTP request message &MUST; reconstruct
2483   the user agent's original target URI, based on the pieces of information
2484   learned from the request-target, <x:ref>Host</x:ref> header field, and
2485   connection context, in order to identify the intended target resource and
2486   properly service the request. The URI derived from this reconstruction
2487   process is referred to as the "effective request URI".
2490   For a user agent, the effective request URI is the target URI.
2493   If the request-target is in absolute-form, then the effective request URI
2494   is the same as the request-target.  Otherwise, the effective request URI
2495   is constructed as follows.
2498   If the request is received over an SSL/TLS-secured TCP connection,
2499   then the effective request URI's scheme is "https"; otherwise, the
2500   scheme is "http".
2503   If the request-target is in authority-form, then the effective
2504   request URI's authority component is the same as the request-target.
2505   Otherwise, if a <x:ref>Host</x:ref> header field is supplied with a
2506   non-empty field-value, then the authority component is the same as the
2507   Host field-value. Otherwise, the authority component is the concatenation of
2508   the default host name configured for the server, a colon (":"), and the
2509   connection's incoming TCP port number in decimal form.
2512   If the request-target is in authority-form or asterisk-form, then the
2513   effective request URI's combined path and query component is empty.
2514   Otherwise, the combined path and query component is the same as the
2515   request-target.
2518   The components of the effective request URI, once determined as above,
2519   can be combined into absolute-URI form by concatenating the scheme,
2520   "://", authority, and combined path and query component.
2524   Example 1: the following message received over an insecure TCP connection
2526<artwork type="example" x:indent-with="  ">
2527GET /pub/WWW/TheProject.html HTTP/1.1
2533  has an effective request URI of
2535<artwork type="example" x:indent-with="  ">
2541   Example 2: the following message received over an SSL/TLS-secured TCP
2542   connection
2544<artwork type="example" x:indent-with="  ">
2545OPTIONS * HTTP/1.1
2551  has an effective request URI of
2553<artwork type="example" x:indent-with="  ">
2558   An origin server that does not allow resources to differ by requested
2559   host &MAY; ignore the <x:ref>Host</x:ref> field-value and instead replace it
2560   with a configured server name when constructing the effective request URI.
2563   Recipients of an HTTP/1.0 request that lacks a <x:ref>Host</x:ref> header
2564   field &MAY; attempt to use heuristics (e.g., examination of the URI path for
2565   something unique to a particular host) in order to guess the
2566   effective request URI's authority component.
2570<section title="Intermediary Forwarding" anchor="intermediary.forwarding">
2572   As described in <xref target="intermediaries"/>, intermediaries can serve
2573   a variety of roles in the processing of HTTP requests and responses.
2574   Some intermediaries are used to improve performance or availability.
2575   Others are used for access control or to filter content.
2576   Since an HTTP stream has characteristics similar to a pipe-and-filter
2577   architecture, there are no inherent limits to the extent an intermediary
2578   can enhance (or interfere) with either direction of the stream.
2581   In order to avoid request loops, a proxy that forwards requests to other
2582   proxies &MUST; be able to recognize and exclude all of its own server
2583   names, including any aliases, local variations, or literal IP addresses.
2586   If a proxy receives a request-target with a host name that is not a
2587   fully qualified domain name, it &MAY; add its domain to the host name
2588   it received when forwarding the request.  A proxy &MUST-NOT; change the
2589   host name if it is a fully qualified domain name.
2592   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" and "query"
2593   parts of the received request-target when forwarding it to the next inbound
2594   server, except as noted above to replace an empty path with "/" or "*".
2597   Intermediaries that forward a message &MUST; implement the
2598   <x:ref>Connection</x:ref> header field as specified in
2599   <xref target="header.connection"/>.
2602<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2604  <cref anchor="TODO-end-to-end" source="jre">
2605    Restored from <eref target=""/>.
2606    See also <eref target=""/>.
2607  </cref>
2610   For the purpose of defining the behavior of caches and non-caching
2611   proxies, we divide HTTP header fields into two categories:
2612  <list style="symbols">
2613      <t>End-to-end header fields, which are  transmitted to the ultimate
2614        recipient of a request or response. End-to-end header fields in
2615        responses &MUST; be stored as part of a cache entry and &MUST; be
2616        transmitted in any response formed from a cache entry.</t>
2618      <t>Hop-by-hop header fields, which are meaningful only for a single
2619        transport-level connection, and are not stored by caches or
2620        forwarded by proxies.</t>
2621  </list>
2624   The following HTTP/1.1 header fields are hop-by-hop header fields:
2625  <list style="symbols">
2626      <t><x:ref>Connection</x:ref></t>
2627      <t>Keep-Alive (<xref target="RFC2068" x:fmt="of" x:sec=""/>)</t>
2628      <t><x:ref>Proxy-Authenticate</x:ref> (&header-proxy-authenticate;)</t>
2629      <t><x:ref>Proxy-Authorization</x:ref> (&header-proxy-authorization;)</t>
2630      <t><x:ref>TE</x:ref></t>
2631      <t><x:ref>Trailer</x:ref></t>
2632      <t><x:ref>Transfer-Encoding</x:ref></t>
2633      <t><x:ref>Upgrade</x:ref></t>
2634  </list>
2637   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2640   Other hop-by-hop header fields &MUST; be listed in a
2641   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>).
2645<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2647  <cref anchor="TODO-non-mod-headers" source="jre">
2648    Restored from <eref target=""/>.
2649    See also <eref target=""/>.
2650  </cref>
2653   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2654   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2655   modify an end-to-end header field unless the definition of that header field requires
2656   or specifically allows that.
2659   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2660   request or response, and it &MUST-NOT; add any of these fields if not
2661   already present:
2662  <list style="symbols">
2663    <t><x:ref>Allow</x:ref> (&header-allow;)</t>
2664    <t><x:ref>Content-Location</x:ref> (&header-content-location;)</t>
2665    <t>Content-MD5 (<xref target="RFC2616" x:fmt="of" x:sec="14.15"/>)</t>
2666    <t><x:ref>ETag</x:ref> (&header-etag;)</t>
2667    <t><x:ref>Last-Modified</x:ref> (&header-last-modified;)</t>
2668    <t><x:ref>Server</x:ref> (&header-server;)</t>
2669  </list>
2672   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2673   response:
2674  <list style="symbols">
2675    <t><x:ref>Expires</x:ref> (&header-expires;)</t>
2676  </list>
2679   but it &MAY; add any of these fields if not already present. If an
2680   <x:ref>Expires</x:ref> header field is added, it &MUST; be given a
2681   field value identical to that of the <x:ref>Date</x:ref> header field in
2682   that response.
2685   A proxy &MUST-NOT; modify or add any of the following fields in a
2686   message that contains the no-transform cache-control directive, or in
2687   any request:
2688  <list style="symbols">
2689    <t><x:ref>Content-Encoding</x:ref> (&header-content-encoding;)</t>
2690    <t><x:ref>Content-Range</x:ref> (&header-content-range;)</t>
2691    <t><x:ref>Content-Type</x:ref> (&header-content-type;)</t>
2692  </list>
2695   A transforming proxy &MAY; modify or add these fields to a message
2696   that does not include no-transform, but if it does so, it &MUST; add a
2697   Warning 214 (Transformation applied) if one does not already appear
2698   in the message (see &header-warning;).
2701  <t>
2702    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2703    cause authentication failures if stronger authentication
2704    mechanisms are introduced in later versions of HTTP. Such
2705    authentication mechanisms &MAY; rely on the values of header fields
2706    not listed here.
2707  </t>
2710   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2711   though it &MAY; change the message body through application or removal
2712   of a transfer-coding (<xref target="transfer.codings"/>).
2718<section title="Associating a Response to a Request" anchor="">
2720   HTTP does not include a request identifier for associating a given
2721   request message with its corresponding one or more response messages.
2722   Hence, it relies on the order of response arrival to correspond exactly
2723   to the order in which requests are made on the same connection.
2724   More than one response message per request only occurs when one or more
2725   informational responses (<x:ref>1xx</x:ref>, see &status-1xx;) precede a final response
2726   to the same request.
2729   A client that uses persistent connections and sends more than one request
2730   per connection &MUST; maintain a list of outstanding requests in the
2731   order sent on that connection and &MUST; associate each received response
2732   message to the highest ordered request that has not yet received a final
2733   (non-<x:ref>1xx</x:ref>) response.
2738<section title="Connection Management" anchor="">
2740<section title="Connection" anchor="header.connection">
2741  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2742  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2743  <x:anchor-alias value="Connection"/>
2744  <x:anchor-alias value="connection-option"/>
2746   The "Connection" header field allows the sender to specify
2747   options that are desired only for that particular connection.
2748   Such connection options &MUST; be removed or replaced before the
2749   message can be forwarded downstream by a proxy or gateway.
2750   This mechanism also allows the sender to indicate which HTTP
2751   header fields used in the message are only intended for the
2752   immediate recipient ("hop-by-hop"), as opposed to all recipients
2753   on the chain ("end-to-end"), enabling the message to be
2754   self-descriptive and allowing future connection-specific extensions
2755   to be deployed in HTTP without fear that they will be blindly
2756   forwarded by previously deployed intermediaries.
2759   The Connection header field's value has the following grammar:
2761<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-option"/>
2762  <x:ref>Connection</x:ref>        = 1#<x:ref>connection-option</x:ref>
2763  <x:ref>connection-option</x:ref> = <x:ref>token</x:ref>
2766   Connection options are compared case-insensitively.
2769   A proxy or gateway &MUST; parse a received Connection
2770   header field before a message is forwarded and, for each
2771   connection-option in this field, remove any header field(s) from
2772   the message with the same name as the connection-option, and then
2773   remove the Connection header field itself or replace it with the
2774   sender's own connection options for the forwarded message.
2777   A sender &MUST-NOT; include field-names in the Connection header
2778   field-value for fields that are defined as expressing constraints
2779   for all recipients in the request or response chain, such as the
2780   Cache-Control header field (&header-cache-control;).
2783   The connection options do not have to correspond to a header field
2784   present in the message, since a connection-specific header field
2785   might not be needed if there are no parameters associated with that
2786   connection option.  Recipients that trigger certain connection
2787   behavior based on the presence of connection options &MUST; do so
2788   based on the presence of the connection-option rather than only the
2789   presence of the optional header field.  In other words, if the
2790   connection option is received as a header field but not indicated
2791   within the Connection field-value, then the recipient &MUST; ignore
2792   the connection-specific header field because it has likely been
2793   forwarded by an intermediary that is only partially conformant.
2796   When defining new connection options, specifications ought to
2797   carefully consider existing deployed header fields and ensure
2798   that the new connection option does not share the same name as
2799   an unrelated header field that might already be deployed.
2800   Defining a new connection option essentially reserves that potential
2801   field-name for carrying additional information related to the
2802   connection option, since it would be unwise for senders to use
2803   that field-name for anything else.
2806   HTTP/1.1 defines the "close" connection option for the sender to
2807   signal that the connection will be closed after completion of the
2808   response. For example,
2810<figure><artwork type="example">
2811  Connection: close
2814   in either the request or the response header fields indicates that
2815   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2816   after the current request/response is complete.
2819   An HTTP/1.1 client that does not support persistent connections &MUST;
2820   include the "close" connection option in every request message.
2823   An HTTP/1.1 server that does not support persistent connections &MUST;
2824   include the "close" connection option in every response message that
2825   does not have a <x:ref>1xx (Informational)</x:ref> status code.
2829<section title="Via" anchor="header.via">
2830  <iref primary="true" item="Via header field" x:for-anchor=""/>
2831  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
2832  <x:anchor-alias value="pseudonym"/>
2833  <x:anchor-alias value="received-by"/>
2834  <x:anchor-alias value="received-protocol"/>
2835  <x:anchor-alias value="Via"/>
2837   The "Via" header field &MUST; be sent by a proxy or gateway to
2838   indicate the intermediate protocols and recipients between the user
2839   agent and the server on requests, and between the origin server and
2840   the client on responses. It is analogous to the "Received" field
2841   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
2842   and is intended to be used for tracking message forwards,
2843   avoiding request loops, and identifying the protocol capabilities of
2844   all senders along the request/response chain.
2846<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"/>
2847  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2848                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2849  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2850  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2851  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2854   The received-protocol indicates the protocol version of the message
2855   received by the server or client along each segment of the
2856   request/response chain. The received-protocol version is appended to
2857   the Via field value when the message is forwarded so that information
2858   about the protocol capabilities of upstream applications remains
2859   visible to all recipients.
2862   The protocol-name is excluded if and only if it would be "HTTP". The
2863   received-by field is normally the host and optional port number of a
2864   recipient server or client that subsequently forwarded the message.
2865   However, if the real host is considered to be sensitive information,
2866   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2867   be assumed to be the default port of the received-protocol.
2870   Multiple Via field values represent each proxy or gateway that has
2871   forwarded the message. Each recipient &MUST; append its information
2872   such that the end result is ordered according to the sequence of
2873   forwarding applications.
2876   Comments &MAY; be used in the Via header field to identify the software
2877   of each recipient, analogous to the <x:ref>User-Agent</x:ref> and
2878   <x:ref>Server</x:ref> header fields. However, all comments in the Via field
2879   are optional and &MAY; be removed by any recipient prior to forwarding the
2880   message.
2883   For example, a request message could be sent from an HTTP/1.0 user
2884   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2885   forward the request to a public proxy at, which completes
2886   the request by forwarding it to the origin server at
2887   The request received by would then have the following
2888   Via header field:
2890<figure><artwork type="example">
2891  Via: 1.0 fred, 1.1 (Apache/1.1)
2894   A proxy or gateway used as a portal through a network firewall
2895   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2896   region unless it is explicitly enabled to do so. If not enabled, the
2897   received-by host of any host behind the firewall &SHOULD; be replaced
2898   by an appropriate pseudonym for that host.
2901   For organizations that have strong privacy requirements for hiding
2902   internal structures, a proxy or gateway &MAY; combine an ordered
2903   subsequence of Via header field entries with identical received-protocol
2904   values into a single such entry. For example,
2906<figure><artwork type="example">
2907  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2910  could be collapsed to
2912<figure><artwork type="example">
2913  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2916   Senders &SHOULD-NOT; combine multiple entries unless they are all
2917   under the same organizational control and the hosts have already been
2918   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
2919   have different received-protocol values.
2923<section title="Persistent Connections" anchor="persistent.connections">
2925<section title="Purpose" anchor="persistent.purpose">
2927   Prior to persistent connections, a separate TCP connection was
2928   established for each request, increasing the load on HTTP servers
2929   and causing congestion on the Internet. The use of inline images and
2930   other associated data often requires a client to make multiple
2931   requests of the same server in a short amount of time. Analysis of
2932   these performance problems and results from a prototype
2933   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2934   measurements of actual HTTP/1.1 implementations show good
2935   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2936   T/TCP <xref target="Tou1998"/>.
2939   Persistent HTTP connections have a number of advantages:
2940  <list style="symbols">
2941      <t>
2942        By opening and closing fewer TCP connections, CPU time is saved
2943        in routers and hosts (clients, servers, proxies, gateways,
2944        tunnels, or caches), and memory used for TCP protocol control
2945        blocks can be saved in hosts.
2946      </t>
2947      <t>
2948        HTTP requests and responses can be pipelined on a connection.
2949        Pipelining allows a client to make multiple requests without
2950        waiting for each response, allowing a single TCP connection to
2951        be used much more efficiently, with much lower elapsed time.
2952      </t>
2953      <t>
2954        Network congestion is reduced by reducing the number of packets
2955        caused by TCP opens, and by allowing TCP sufficient time to
2956        determine the congestion state of the network.
2957      </t>
2958      <t>
2959        Latency on subsequent requests is reduced since there is no time
2960        spent in TCP's connection opening handshake.
2961      </t>
2962      <t>
2963        HTTP can evolve more gracefully, since errors can be reported
2964        without the penalty of closing the TCP connection. Clients using
2965        future versions of HTTP might optimistically try a new feature,
2966        but if communicating with an older server, retry with old
2967        semantics after an error is reported.
2968      </t>
2969    </list>
2972   HTTP implementations &SHOULD; implement persistent connections.
2976<section title="Overall Operation" anchor="persistent.overall">
2978   A significant difference between HTTP/1.1 and earlier versions of
2979   HTTP is that persistent connections are the default behavior of any
2980   HTTP connection. That is, unless otherwise indicated, the client
2981   &SHOULD; assume that the server will maintain a persistent connection,
2982   even after error responses from the server.
2985   Persistent connections provide a mechanism by which a client and a
2986   server can signal the close of a TCP connection. This signaling takes
2987   place using the <x:ref>Connection</x:ref> header field
2988   (<xref target="header.connection"/>). Once a close has been signaled, the
2989   client &MUST-NOT; send any more requests on that
2990   connection.
2993<section title="Negotiation" anchor="persistent.negotiation">
2995   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2996   maintain a persistent connection unless a <x:ref>Connection</x:ref> header
2997   field including the connection option "close" was sent in the request. If
2998   the server chooses to close the connection immediately after sending the
2999   response, it &SHOULD; send a Connection header field including the
3000   connection option "close".
3003   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
3004   decide to keep it open based on whether the response from a server
3005   contains a <x:ref>Connection</x:ref> header field with the connection option
3006   "close". In case the client does not want to maintain a connection for more
3007   than that request, it &SHOULD; send a Connection header field including the
3008   connection option "close".
3011   If either the client or the server sends the "close" option in the
3012   <x:ref>Connection</x:ref> header field, that request becomes the last one
3013   for the connection.
3016   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
3017   maintained for HTTP versions less than 1.1 unless it is explicitly
3018   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
3019   compatibility with HTTP/1.0 clients.
3022   Each persistent connection applies to only one transport link.
3025   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
3026   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
3027   for information and discussion of the problems with the Keep-Alive header field
3028   implemented by many HTTP/1.0 clients).
3031   In order to remain persistent, all messages on the connection &MUST;
3032   have a self-defined message length (i.e., one not defined by closure
3033   of the connection), as described in <xref target="message.body"/>.
3037<section title="Pipelining" anchor="pipelining">
3039   A client that supports persistent connections &MAY; "pipeline" its
3040   requests (i.e., send multiple requests without waiting for each
3041   response). A server &MUST; send its responses to those requests in the
3042   same order that the requests were received.
3045   Clients which assume persistent connections and pipeline immediately
3046   after connection establishment &SHOULD; be prepared to retry their
3047   connection if the first pipelined attempt fails. If a client does
3048   such a retry, it &MUST-NOT; pipeline before it knows the connection is
3049   persistent. Clients &MUST; also be prepared to resend their requests if
3050   the server closes the connection before sending all of the
3051   corresponding responses.
3054   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
3055   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
3056   premature termination of the transport connection could lead to
3057   indeterminate results. A client wishing to send a non-idempotent
3058   request &SHOULD; wait to send that request until it has received the
3059   response status line for the previous request.
3064<section title="Practical Considerations" anchor="persistent.practical">
3066   Servers will usually have some time-out value beyond which they will
3067   no longer maintain an inactive connection. Proxy servers might make
3068   this a higher value since it is likely that the client will be making
3069   more connections through the same server. The use of persistent
3070   connections places no requirements on the length (or existence) of
3071   this time-out for either the client or the server.
3074   When a client or server wishes to time-out it &SHOULD; issue a graceful
3075   close on the transport connection. Clients and servers &SHOULD; both
3076   constantly watch for the other side of the transport close, and
3077   respond to it as appropriate. If a client or server does not detect
3078   the other side's close promptly it could cause unnecessary resource
3079   drain on the network.
3082   A client, server, or proxy &MAY; close the transport connection at any
3083   time. For example, a client might have started to send a new request
3084   at the same time that the server has decided to close the "idle"
3085   connection. From the server's point of view, the connection is being
3086   closed while it was idle, but from the client's point of view, a
3087   request is in progress.
3090   Clients (including proxies) &SHOULD; limit the number of simultaneous
3091   connections that they maintain to a given server (including proxies).
3094   Previous revisions of HTTP gave a specific number of connections as a
3095   ceiling, but this was found to be impractical for many applications. As a
3096   result, this specification does not mandate a particular maximum number of
3097   connections, but instead encourages clients to be conservative when opening
3098   multiple connections.
3101   In particular, while using multiple connections avoids the "head-of-line
3102   blocking" problem (whereby a request that takes significant server-side
3103   processing and/or has a large payload can block subsequent requests on the
3104   same connection), each connection used consumes server resources (sometimes
3105   significantly), and furthermore using multiple connections can cause
3106   undesirable side effects in congested networks.
3109   Note that servers might reject traffic that they deem abusive, including an
3110   excessive number of connections from a client.
3114<section title="Retrying Requests" anchor="persistent.retrying.requests">
3116   Senders can close the transport connection at any time. Therefore,
3117   clients, servers, and proxies &MUST; be able to recover
3118   from asynchronous close events. Client software &MAY; reopen the
3119   transport connection and retransmit the aborted sequence of requests
3120   without user interaction so long as the request sequence is
3121   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
3122   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
3123   human operator the choice of retrying the request(s). Confirmation by
3124   user-agent software with semantic understanding of the application
3125   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
3126   be repeated if the second sequence of requests fails.
3131<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
3133<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
3135   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
3136   flow control mechanisms to resolve temporary overloads, rather than
3137   terminating connections with the expectation that clients will retry.
3138   The latter technique can exacerbate network congestion.
3142<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
3144   An HTTP/1.1 (or later) client sending a message body &SHOULD; monitor
3145   the network connection for an error status code while it is transmitting
3146   the request. If the client sees an error status code, it &SHOULD;
3147   immediately cease transmitting the body. If the body is being sent
3148   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
3149   empty trailer &MAY; be used to prematurely mark the end of the message.
3150   If the body was preceded by a Content-Length header field, the client &MUST;
3151   close the connection.
3155<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
3157   The purpose of the <x:ref>100 (Continue)</x:ref> status code (see &status-100;)
3158   is to allow a client that is sending a request message with a request body
3159   to determine if the origin server is willing to accept the request
3160   (based on the request header fields) before the client sends the request
3161   body. In some cases, it might either be inappropriate or highly
3162   inefficient for the client to send the body if the server will reject
3163   the message without looking at the body.
3166   Requirements for HTTP/1.1 clients:
3167  <list style="symbols">
3168    <t>
3169        If a client will wait for a <x:ref>100 (Continue)</x:ref> response before
3170        sending the request body, it &MUST; send an <x:ref>Expect</x:ref> header
3171        field (&header-expect;) with the "100-continue" expectation.
3172    </t>
3173    <t>
3174        A client &MUST-NOT; send an <x:ref>Expect</x:ref> header field with
3175        the "100-continue" expectation if it does not intend to send a request
3176        body.
3177    </t>
3178  </list>
3181   Because of the presence of older implementations, the protocol allows
3182   ambiguous situations in which a client might send "Expect: 100-continue"
3183   without receiving either a <x:ref>417 (Expectation Failed)</x:ref>
3184   or a <x:ref>100 (Continue)</x:ref> status code. Therefore, when a client sends this
3185   header field to an origin server (possibly via a proxy) from which it
3186   has never seen a <x:ref>100 (Continue)</x:ref> status code, the client &SHOULD-NOT; 
3187   wait for an indefinite period before sending the request body.
3190   Requirements for HTTP/1.1 origin servers:
3191  <list style="symbols">
3192    <t> Upon receiving a request which includes an <x:ref>Expect</x:ref> header
3193        field with the "100-continue" expectation, an origin server &MUST;
3194        either respond with <x:ref>100 (Continue)</x:ref> status code and continue to read
3195        from the input stream, or respond with a final status code. The
3196        origin server &MUST-NOT; wait for the request body before sending
3197        the <x:ref>100 (Continue)</x:ref> response. If it responds with a final status
3198        code, it &MAY; close the transport connection or it &MAY; continue
3199        to read and discard the rest of the request.  It &MUST-NOT;
3200        perform the request method if it returns a final status code.
3201    </t>
3202    <t> An origin server &SHOULD-NOT;  send a <x:ref>100 (Continue)</x:ref> response if
3203        the request message does not include an <x:ref>Expect</x:ref> header
3204        field with the "100-continue" expectation, and &MUST-NOT; send a
3205        <x:ref>100 (Continue)</x:ref> response if such a request comes from an HTTP/1.0
3206        (or earlier) client. There is an exception to this rule: for
3207        compatibility with <xref target="RFC2068"/>, a server &MAY; send a <x:ref>100 (Continue)</x:ref>
3208        status code in response to an HTTP/1.1 PUT or POST request that does
3209        not include an Expect header field with the "100-continue"
3210        expectation. This exception, the purpose of which is
3211        to minimize any client processing delays associated with an
3212        undeclared wait for <x:ref>100 (Continue)</x:ref> status code, applies only to
3213        HTTP/1.1 requests, and not to requests with any other HTTP-version
3214        value.
3215    </t>
3216    <t> An origin server &MAY; omit a <x:ref>100 (Continue)</x:ref> response if it has
3217        already received some or all of the request body for the
3218        corresponding request.
3219    </t>
3220    <t> An origin server that sends a <x:ref>100 (Continue)</x:ref> response &MUST;
3221        ultimately send a final status code, once the request body is
3222        received and processed, unless it terminates the transport
3223        connection prematurely.
3224    </t>
3225    <t> If an origin server receives a request that does not include an
3226        <x:ref>Expect</x:ref> header field with the "100-continue" expectation,
3227        the request includes a request body, and the server responds
3228        with a final status code before reading the entire request body
3229        from the transport connection, then the server &SHOULD-NOT;  close
3230        the transport connection until it has read the entire request,
3231        or until the client closes the connection. Otherwise, the client
3232        might not reliably receive the response message. However, this
3233        requirement ought not be construed as preventing a server from
3234        defending itself against denial-of-service attacks, or from
3235        badly broken client implementations.
3236      </t>
3237    </list>
3240   Requirements for HTTP/1.1 proxies:
3241  <list style="symbols">
3242    <t> If a proxy receives a request that includes an <x:ref>Expect</x:ref>
3243        header field with the "100-continue" expectation, and the proxy
3244        either knows that the next-hop server complies with HTTP/1.1 or
3245        higher, or does not know the HTTP version of the next-hop
3246        server, it &MUST; forward the request, including the Expect header
3247        field.
3248    </t>
3249    <t> If the proxy knows that the version of the next-hop server is
3250        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
3251        respond with a <x:ref>417 (Expectation Failed)</x:ref> status code.
3252    </t>
3253    <t> Proxies &SHOULD; maintain a record of the HTTP version
3254        numbers received from recently-referenced next-hop servers.
3255    </t>
3256    <t> A proxy &MUST-NOT; forward a <x:ref>100 (Continue)</x:ref> response if the
3257        request message was received from an HTTP/1.0 (or earlier)
3258        client and did not include an <x:ref>Expect</x:ref> header field with
3259        the "100-continue" expectation. This requirement overrides the
3260        general rule for forwarding of <x:ref>1xx</x:ref> responses (see &status-1xx;).
3261    </t>
3262  </list>
3266<section title="Closing Connections on Error" anchor="closing.connections.on.error">
3268   If the client is sending data, a server implementation using TCP
3269   &SHOULD; be careful to ensure that the client acknowledges receipt of
3270   the packet(s) containing the response, before the server closes the
3271   input connection. If the client continues sending data to the server
3272   after the close, the server's TCP stack will send a reset packet to
3273   the client, which might erase the client's unacknowledged input buffers
3274   before they can be read and interpreted by the HTTP application.
3280<section title="Upgrade" anchor="header.upgrade">
3281  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3282  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3283  <x:anchor-alias value="Upgrade"/>
3284  <x:anchor-alias value="protocol"/>
3285  <x:anchor-alias value="protocol-name"/>
3286  <x:anchor-alias value="protocol-version"/>
3288   The "Upgrade" header field allows the client to specify what
3289   additional communication protocols it would like to use, if the server
3290   chooses to switch protocols. Servers can use it to indicate what protocols
3291   they are willing to switch to.
3293<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3294  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3296  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3297  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3298  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3301   For example,
3303<figure><artwork type="example">
3304  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3307   The Upgrade header field is intended to provide a simple mechanism
3308   for transitioning from HTTP/1.1 to some other, incompatible protocol. It
3309   does so by allowing the client to advertise its desire to use another
3310   protocol, such as a later version of HTTP with a higher major version
3311   number, even though the current request has been made using HTTP/1.1.
3312   This eases the difficult transition between incompatible protocols by
3313   allowing the client to initiate a request in the more commonly
3314   supported protocol while indicating to the server that it would like
3315   to use a "better" protocol if available (where "better" is determined
3316   by the server, possibly according to the nature of the request method
3317   or target resource).
3320   The Upgrade header field only applies to switching application-layer
3321   protocols upon the existing transport-layer connection. Upgrade
3322   cannot be used to insist on a protocol change; its acceptance and use
3323   by the server is optional. The capabilities and nature of the
3324   application-layer communication after the protocol change is entirely
3325   dependent upon the new protocol chosen, although the first action
3326   after changing the protocol &MUST; be a response to the initial HTTP
3327   request containing the Upgrade header field.
3330   The Upgrade header field only applies to the immediate connection.
3331   Therefore, the upgrade keyword &MUST; be supplied within a
3332   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
3333   whenever Upgrade is present in an HTTP/1.1 message.
3336   The Upgrade header field cannot be used to indicate a switch to a
3337   protocol on a different connection. For that purpose, it is more
3338   appropriate to use a <x:ref>3xx (Redirection)</x:ref> response (&status-3xx;).
3341   Servers &MUST; include the "Upgrade" header field in <x:ref>101 (Switching
3342   Protocols)</x:ref> responses to indicate which protocol(s) are being switched to,
3343   and &MUST; include it in <x:ref>426 (Upgrade Required)</x:ref> responses to indicate
3344   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3345   response to indicate that they are willing to upgrade to one of the
3346   specified protocols.
3349   This specification only defines the protocol name "HTTP" for use by
3350   the family of Hypertext Transfer Protocols, as defined by the HTTP
3351   version rules of <xref target="http.version"/> and future updates to this
3352   specification. Additional tokens can be registered with IANA using the
3353   registration procedure defined in <xref target="upgrade.token.registry"/>.
3359<section title="IANA Considerations" anchor="IANA.considerations">
3361<section title="Header Field Registration" anchor="header.field.registration">
3363   HTTP header fields are registered within the Message Header Field Registry
3364   <xref target="RFC3864"/> maintained by IANA at
3365   <eref target=""/>.
3368   This document defines the following HTTP header fields, so their
3369   associated registry entries shall be updated according to the permanent
3370   registrations below:
3372<?BEGININC p1-messaging.iana-headers ?>
3373<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3374<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3375   <ttcol>Header Field Name</ttcol>
3376   <ttcol>Protocol</ttcol>
3377   <ttcol>Status</ttcol>
3378   <ttcol>Reference</ttcol>
3380   <c>Connection</c>
3381   <c>http</c>
3382   <c>standard</c>
3383   <c>
3384      <xref target="header.connection"/>
3385   </c>
3386   <c>Content-Length</c>
3387   <c>http</c>
3388   <c>standard</c>
3389   <c>
3390      <xref target="header.content-length"/>
3391   </c>
3392   <c>Host</c>
3393   <c>http</c>
3394   <c>standard</c>
3395   <c>
3396      <xref target=""/>
3397   </c>
3398   <c>TE</c>
3399   <c>http</c>
3400   <c>standard</c>
3401   <c>
3402      <xref target="header.te"/>
3403   </c>
3404   <c>Trailer</c>
3405   <c>http</c>
3406   <c>standard</c>
3407   <c>
3408      <xref target="header.trailer"/>
3409   </c>
3410   <c>Transfer-Encoding</c>
3411   <c>http</c>
3412   <c>standard</c>
3413   <c>
3414      <xref target="header.transfer-encoding"/>
3415   </c>
3416   <c>Upgrade</c>
3417   <c>http</c>
3418   <c>standard</c>
3419   <c>
3420      <xref target="header.upgrade"/>
3421   </c>
3422   <c>Via</c>
3423   <c>http</c>
3424   <c>standard</c>
3425   <c>
3426      <xref target="header.via"/>
3427   </c>
3430<?ENDINC p1-messaging.iana-headers ?>
3432   Furthermore, the header field-name "Close" shall be registered as
3433   "reserved", since using that name as an HTTP header field might
3434   conflict with the "close" connection option of the "<x:ref>Connection</x:ref>"
3435   header field (<xref target="header.connection"/>).
3437<texttable align="left" suppress-title="true">
3438   <ttcol>Header Field Name</ttcol>
3439   <ttcol>Protocol</ttcol>
3440   <ttcol>Status</ttcol>
3441   <ttcol>Reference</ttcol>
3443   <c>Close</c>
3444   <c>http</c>
3445   <c>reserved</c>
3446   <c>
3447      <xref target="header.field.registration"/>
3448   </c>
3451   The change controller is: "IETF ( - Internet Engineering Task Force".
3455<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3457   IANA maintains the registry of URI Schemes <xref target="RFC4395"/> at
3458   <eref target=""/>.
3461   This document defines the following URI schemes, so their
3462   associated registry entries shall be updated according to the permanent
3463   registrations below:
3465<texttable align="left" suppress-title="true">
3466   <ttcol>URI Scheme</ttcol>
3467   <ttcol>Description</ttcol>
3468   <ttcol>Reference</ttcol>
3470   <c>http</c>
3471   <c>Hypertext Transfer Protocol</c>
3472   <c><xref target="http.uri"/></c>
3474   <c>https</c>
3475   <c>Hypertext Transfer Protocol Secure</c>
3476   <c><xref target="https.uri"/></c>
3480<section title="Internet Media Type Registrations" anchor="">
3482   This document serves as the specification for the Internet media types
3483   "message/http" and "application/http". The following is to be registered with
3484   IANA (see <xref target="RFC4288"/>).
3486<section title="Internet Media Type message/http" anchor="">
3487<iref item="Media Type" subitem="message/http" primary="true"/>
3488<iref item="message/http Media Type" primary="true"/>
3490   The message/http type can be used to enclose a single HTTP request or
3491   response message, provided that it obeys the MIME restrictions for all
3492   "message" types regarding line length and encodings.
3495  <list style="hanging" x:indent="12em">
3496    <t hangText="Type name:">
3497      message
3498    </t>
3499    <t hangText="Subtype name:">
3500      http
3501    </t>
3502    <t hangText="Required parameters:">
3503      none
3504    </t>
3505    <t hangText="Optional parameters:">
3506      version, msgtype
3507      <list style="hanging">
3508        <t hangText="version:">
3509          The HTTP-version number of the enclosed message
3510          (e.g., "1.1"). If not present, the version can be
3511          determined from the first line of the body.
3512        </t>
3513        <t hangText="msgtype:">
3514          The message type &mdash; "request" or "response". If not
3515          present, the type can be determined from the first
3516          line of the body.
3517        </t>
3518      </list>
3519    </t>
3520    <t hangText="Encoding considerations:">
3521      only "7bit", "8bit", or "binary" are permitted
3522    </t>
3523    <t hangText="Security considerations:">
3524      none
3525    </t>
3526    <t hangText="Interoperability considerations:">
3527      none
3528    </t>
3529    <t hangText="Published specification:">
3530      This specification (see <xref target=""/>).
3531    </t>
3532    <t hangText="Applications that use this media type:">
3533    </t>
3534    <t hangText="Additional information:">
3535      <list style="hanging">
3536        <t hangText="Magic number(s):">none</t>
3537        <t hangText="File extension(s):">none</t>
3538        <t hangText="Macintosh file type code(s):">none</t>
3539      </list>
3540    </t>
3541    <t hangText="Person and email address to contact for further information:">
3542      See Authors Section.
3543    </t>
3544    <t hangText="Intended usage:">
3545      COMMON
3546    </t>
3547    <t hangText="Restrictions on usage:">
3548      none
3549    </t>
3550    <t hangText="Author/Change controller:">
3551      IESG
3552    </t>
3553  </list>
3556<section title="Internet Media Type application/http" anchor="">
3557<iref item="Media Type" subitem="application/http" primary="true"/>
3558<iref item="application/http Media Type" primary="true"/>
3560   The application/http type can be used to enclose a pipeline of one or more
3561   HTTP request or response messages (not intermixed).
3564  <list style="hanging" x:indent="12em">
3565    <t hangText="Type name:">
3566      application
3567    </t>
3568    <t hangText="Subtype name:">
3569      http
3570    </t>
3571    <t hangText="Required parameters:">
3572      none
3573    </t>
3574    <t hangText="Optional parameters:">
3575      version, msgtype
3576      <list style="hanging">
3577        <t hangText="version:">
3578          The HTTP-version number of the enclosed messages
3579          (e.g., "1.1"). If not present, the version can be
3580          determined from the first line of the body.
3581        </t>
3582        <t hangText="msgtype:">
3583          The message type &mdash; "request" or "response". If not
3584          present, the type can be determined from the first
3585          line of the body.
3586        </t>
3587      </list>
3588    </t>
3589    <t hangText="Encoding considerations:">
3590      HTTP messages enclosed by this type
3591      are in "binary" format; use of an appropriate
3592      Content-Transfer-Encoding is required when
3593      transmitted via E-mail.
3594    </t>
3595    <t hangText="Security considerations:">
3596      none
3597    </t>
3598    <t hangText="Interoperability considerations:">
3599      none
3600    </t>
3601    <t hangText="Published specification:">
3602      This specification (see <xref target=""/>).
3603    </t>
3604    <t hangText="Applications that use this media type:">
3605    </t>
3606    <t hangText="Additional information:">
3607      <list style="hanging">
3608        <t hangText="Magic number(s):">none</t>
3609        <t hangText="File extension(s):">none</t>
3610        <t hangText="Macintosh file type code(s):">none</t>
3611      </list>
3612    </t>
3613    <t hangText="Person and email address to contact for further information:">
3614      See Authors Section.
3615    </t>
3616    <t hangText="Intended usage:">
3617      COMMON
3618    </t>
3619    <t hangText="Restrictions on usage:">
3620      none
3621    </t>
3622    <t hangText="Author/Change controller:">
3623      IESG
3624    </t>
3625  </list>
3630<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3632   The HTTP Transfer Coding Registry defines the name space for transfer
3633   coding names.
3636   Registrations &MUST; include the following fields:
3637   <list style="symbols">
3638     <t>Name</t>
3639     <t>Description</t>
3640     <t>Pointer to specification text</t>
3641   </list>
3644   Names of transfer codings &MUST-NOT; overlap with names of content codings
3645   (&content-codings;) unless the encoding transformation is identical, as it
3646   is the case for the compression codings defined in
3647   <xref target="compression.codings"/>.
3650   Values to be added to this name space require IETF Review (see
3651   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3652   conform to the purpose of transfer coding defined in this section.
3655   The registry itself is maintained at
3656   <eref target=""/>.
3660<section title="Transfer Coding Registrations" anchor="transfer.coding.registration">
3662   The HTTP Transfer Coding Registry shall be updated with the registrations
3663   below:
3665<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3666   <ttcol>Name</ttcol>
3667   <ttcol>Description</ttcol>
3668   <ttcol>Reference</ttcol>
3669   <c>chunked</c>
3670   <c>Transfer in a series of chunks</c>
3671   <c>
3672      <xref target="chunked.encoding"/>
3673   </c>
3674   <c>compress</c>
3675   <c>UNIX "compress" program method</c>
3676   <c>
3677      <xref target="compress.coding"/>
3678   </c>
3679   <c>deflate</c>
3680   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3681   the "zlib" data format (<xref target="RFC1950"/>)
3682   </c>
3683   <c>
3684      <xref target="deflate.coding"/>
3685   </c>
3686   <c>gzip</c>
3687   <c>Same as GNU zip <xref target="RFC1952"/></c>
3688   <c>
3689      <xref target="gzip.coding"/>
3690   </c>
3694<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3696   The HTTP Upgrade Token Registry defines the name space for protocol-name
3697   tokens used to identify protocols in the <x:ref>Upgrade</x:ref> header
3698   field. Each registered protocol name is associated with contact information
3699   and an optional set of specifications that details how the connection
3700   will be processed after it has been upgraded.
3703   Registrations happen on a "First Come First Served" basis (see
3704   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3705   following rules:
3706  <list style="numbers">
3707    <t>A protocol-name token, once registered, stays registered forever.</t>
3708    <t>The registration &MUST; name a responsible party for the
3709       registration.</t>
3710    <t>The registration &MUST; name a point of contact.</t>
3711    <t>The registration &MAY; name a set of specifications associated with
3712       that token. Such specifications need not be publicly available.</t>
3713    <t>The registration &SHOULD; name a set of expected "protocol-version"
3714       tokens associated with that token at the time of registration.</t>
3715    <t>The responsible party &MAY; change the registration at any time.
3716       The IANA will keep a record of all such changes, and make them
3717       available upon request.</t>
3718    <t>The IESG &MAY; reassign responsibility for a protocol token.
3719       This will normally only be used in the case when a
3720       responsible party cannot be contacted.</t>
3721  </list>
3724   This registration procedure for HTTP Upgrade Tokens replaces that
3725   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3729<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3731   The HTTP Upgrade Token Registry shall be updated with the registration
3732   below:
3734<texttable align="left" suppress-title="true">
3735   <ttcol>Value</ttcol>
3736   <ttcol>Description</ttcol>
3737   <ttcol>Expected Version Tokens</ttcol>
3738   <ttcol>Reference</ttcol>
3740   <c>HTTP</c>
3741   <c>Hypertext Transfer Protocol</c>
3742   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3743   <c><xref target="http.version"/></c>
3746   The responsible party is: "IETF ( - Internet Engineering Task Force".
3752<section title="Security Considerations" anchor="security.considerations">
3754   This section is meant to inform application developers, information
3755   providers, and users of the security limitations in HTTP/1.1 as
3756   described by this document. The discussion does not include
3757   definitive solutions to the problems revealed, though it does make
3758   some suggestions for reducing security risks.
3761<section title="Personal Information" anchor="personal.information">
3763   HTTP clients are often privy to large amounts of personal information
3764   (e.g., the user's name, location, mail address, passwords, encryption
3765   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3766   leakage of this information.
3767   We very strongly recommend that a convenient interface be provided
3768   for the user to control dissemination of such information, and that
3769   designers and implementors be particularly careful in this area.
3770   History shows that errors in this area often create serious security
3771   and/or privacy problems and generate highly adverse publicity for the
3772   implementor's company.
3776<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3778   A server is in the position to save personal data about a user's
3779   requests which might identify their reading patterns or subjects of
3780   interest.  In particular, log information gathered at an intermediary
3781   often contains a history of user agent interaction, across a multitude
3782   of sites, that can be traced to individual users.
3785   HTTP log information is confidential in nature; its handling is often
3786   constrained by laws and regulations.  Log information needs to be securely
3787   stored and appropriate guidelines followed for its analysis.
3788   Anonymization of personal information within individual entries helps,
3789   but is generally not sufficient to prevent real log traces from being
3790   re-identified based on correlation with other access characteristics.
3791   As such, access traces that are keyed to a specific client should not
3792   be published even if the key is pseudonymous.
3795   To minimize the risk of theft or accidental publication, log information
3796   should be purged of personally identifiable information, including
3797   user identifiers, IP addresses, and user-provided query parameters,
3798   as soon as that information is no longer necessary to support operational
3799   needs for security, auditing, or fraud control.
3803<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3805   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3806   the documents returned by HTTP requests to be only those that were
3807   intended by the server administrators. If an HTTP server translates
3808   HTTP URIs directly into file system calls, the server &MUST; take
3809   special care not to serve files that were not intended to be
3810   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3811   other operating systems use ".." as a path component to indicate a
3812   directory level above the current one. On such a system, an HTTP
3813   server &MUST; disallow any such construct in the request-target if it
3814   would otherwise allow access to a resource outside those intended to
3815   be accessible via the HTTP server. Similarly, files intended for
3816   reference only internally to the server (such as access control
3817   files, configuration files, and script code) &MUST; be protected from
3818   inappropriate retrieval, since they might contain sensitive
3819   information. Experience has shown that minor bugs in such HTTP server
3820   implementations have turned into security risks.
3824<section title="DNS-related Attacks" anchor="dns.related.attacks">
3826   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3827   generally prone to security attacks based on the deliberate misassociation
3828   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3829   cautious in assuming the validity of an IP number/DNS name association unless
3830   the response is protected by DNSSec (<xref target="RFC4033"/>).
3834<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3836   By their very nature, HTTP intermediaries are men-in-the-middle, and
3837   represent an opportunity for man-in-the-middle attacks. Compromise of
3838   the systems on which the intermediaries run can result in serious security
3839   and privacy problems. Intermediaries have access to security-related
3840   information, personal information about individual users and
3841   organizations, and proprietary information belonging to users and
3842   content providers. A compromised intermediary, or an intermediary
3843   implemented or configured without regard to security and privacy
3844   considerations, might be used in the commission of a wide range of
3845   potential attacks.
3848   Intermediaries that contain a shared cache are especially vulnerable
3849   to cache poisoning attacks.
3852   Implementors need to consider the privacy and security
3853   implications of their design and coding decisions, and of the
3854   configuration options they provide to operators (especially the
3855   default configuration).
3858   Users need to be aware that intermediaries are no more trustworthy than
3859   the people who run them; HTTP itself cannot solve this problem.
3862   The judicious use of cryptography, when appropriate, might suffice to
3863   protect against a broad range of security and privacy attacks. Such
3864   cryptography is beyond the scope of the HTTP/1.1 specification.
3868<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3870   Because HTTP uses mostly textual, character-delimited fields, attackers can
3871   overflow buffers in implementations, and/or perform a Denial of Service
3872   against implementations that accept fields with unlimited lengths.
3875   To promote interoperability, this specification makes specific
3876   recommendations for minimum size limits on request-line
3877   (<xref target="request.line"/>)
3878   and blocks of header fields (<xref target="header.fields"/>). These are
3879   minimum recommendations, chosen to be supportable even by implementations
3880   with limited resources; it is expected that most implementations will
3881   choose substantially higher limits.
3884   This specification also provides a way for servers to reject messages that
3885   have request-targets that are too long (&status-414;) or request entities
3886   that are too large (&status-4xx;).
3889   Other fields (including but not limited to request methods, response status
3890   phrases, header field-names, and body chunks) &SHOULD; be limited by
3891   implementations carefully, so as to not impede interoperability.
3896<section title="Acknowledgments" anchor="acks">
3898   This edition of HTTP builds on the many contributions that went into
3899   <xref target="RFC1945" format="none">RFC 1945</xref>,
3900   <xref target="RFC2068" format="none">RFC 2068</xref>,
3901   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3902   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3903   substantial contributions made by the previous authors, editors, and
3904   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3905   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3906   Paul J. Leach, and Mark Nottingham.
3907   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
3908   acknowledgements from prior revisions.
3911   Since 1999, the following contributors have helped improve the HTTP
3912   specification by reporting bugs, asking smart questions, drafting or
3913   reviewing text, and evaluating open issues:
3915<?BEGININC acks ?>
3916<t>Adam Barth,
3917Adam Roach,
3918Addison Phillips,
3919Adrian Chadd,
3920Adrien W. de Croy,
3921Alan Ford,
3922Alan Ruttenberg,
3923Albert Lunde,
3924Alek Storm,
3925Alex Rousskov,
3926Alexandre Morgaut,
3927Alexey Melnikov,
3928Alisha Smith,
3929Amichai Rothman,
3930Amit Klein,
3931Amos Jeffries,
3932Andreas Maier,
3933Andreas Petersson,
3934Anne van Kesteren,
3935Anthony Bryan,
3936Asbjorn Ulsberg,
3937Balachander Krishnamurthy,
3938Barry Leiba,
3939Ben Laurie,
3940Benjamin Niven-Jenkins,
3941Bil Corry,
3942Bill Burke,
3943Bjoern Hoehrmann,
3944Bob Scheifler,
3945Boris Zbarsky,
3946Brett Slatkin,
3947Brian Kell,
3948Brian McBarron,
3949Brian Pane,
3950Brian Smith,
3951Bryce Nesbitt,
3952Cameron Heavon-Jones,
3953Carl Kugler,
3954Carsten Bormann,
3955Charles Fry,
3956Chris Newman,
3957Cyrus Daboo,
3958Dale Robert Anderson,
3959Dan Winship,
3960Daniel Stenberg,
3961Dave Cridland,
3962Dave Crocker,
3963Dave Kristol,
3964David Booth,
3965David Singer,
3966David W. Morris,
3967Diwakar Shetty,
3968Dmitry Kurochkin,
3969Drummond Reed,
3970Duane Wessels,
3971Edward Lee,
3972Eliot Lear,
3973Eran Hammer-Lahav,
3974Eric D. Williams,
3975Eric J. Bowman,
3976Eric Lawrence,
3977Eric Rescorla,
3978Erik Aronesty,
3979Florian Weimer,
3980Frank Ellermann,
3981Fred Bohle,
3982Geoffrey Sneddon,
3983Gervase Markham,
3984Greg Wilkins,
3985Harald Tveit Alvestrand,
3986Harry Halpin,
3987Helge Hess,
3988Henrik Nordstrom,
3989Henry S. Thompson,
3990Henry Story,
3991Herbert van de Sompel,
3992Howard Melman,
3993Hugo Haas,
3994Ian Hickson,
3995Ingo Struck,
3996J. Ross Nicoll,
3997James H. Manger,
3998James Lacey,
3999James M. Snell,
4000Jamie Lokier,
4001Jan Algermissen,
4002Jeff Hodges (who came up with the term 'effective Request-URI'),
4003Jeff Walden,
4004Jim Luther,
4005Joe D. Williams,
4006Joe Gregorio,
4007Joe Orton,
4008John C. Klensin,
4009John C. Mallery,
4010John Cowan,
4011John Kemp,
4012John Panzer,
4013John Schneider,
4014John Stracke,
4015John Sullivan,
4016Jonas Sicking,
4017Jonathan Billington,
4018Jonathan Moore,
4019Jonathan Rees,
4020Jordi Ros,
4021Joris Dobbelsteen,
4022Josh Cohen,
4023Julien Pierre,
4024Jungshik Shin,
4025Justin Chapweske,
4026Justin Erenkrantz,
4027Justin James,
4028Kalvinder Singh,
4029Karl Dubost,
4030Keith Hoffman,
4031Keith Moore,
4032Koen Holtman,
4033Konstantin Voronkov,
4034Kris Zyp,
4035Lisa Dusseault,
4036Maciej Stachowiak,
4037Marc Schneider,
4038Marc Slemko,
4039Mark Baker,
4040Mark Pauley,
4041Mark Watson,
4042Markus Isomaki,
4043Markus Lanthaler,
4044Martin J. Duerst,
4045Martin Musatov,
4046Martin Nilsson,
4047Martin Thomson,
4048Matt Lynch,
4049Matthew Cox,
4050Max Clark,
4051Michael Burrows,
4052Michael Hausenblas,
4053Mike Amundsen,
4054Mike Belshe,
4055Mike Kelly,
4056Mike Schinkel,
4057Miles Sabin,
4058Murray S. Kucherawy,
4059Mykyta Yevstifeyev,
4060Nathan Rixham,
4061Nicholas Shanks,
4062Nico Williams,
4063Nicolas Alvarez,
4064Nicolas Mailhot,
4065Noah Slater,
4066Pablo Castro,
4067Pat Hayes,
4068Patrick R. McManus,
4069Paul E. Jones,
4070Paul Hoffman,
4071Paul Marquess,
4072Peter Lepeska,
4073Peter Saint-Andre,
4074Peter Watkins,
4075Phil Archer,
4076Phillip Hallam-Baker,
4077Poul-Henning Kamp,
4078Preethi Natarajan,
4079Ray Polk,
4080Reto Bachmann-Gmuer,
4081Richard Cyganiak,
4082Robert Brewer,
4083Robert Collins,
4084Robert O'Callahan,
4085Robert Olofsson,
4086Robert Sayre,
4087Robert Siemer,
4088Robert de Wilde,
4089Roberto Javier Godoy,
4090Roberto Peon,
4091Ronny Widjaja,
4092S. Mike Dierken,
4093Salvatore Loreto,
4094Sam Johnston,
4095Sam Ruby,
4096Scott Lawrence (who maintained the original issues list),
4097Sean B. Palmer,
4098Shane McCarron,
4099Stefan Eissing,
4100Stefan Tilkov,
4101Stefanos Harhalakis,
4102Stephane Bortzmeyer,
4103Stephen Farrell,
4104Stephen Ludin,
4105Stuart Williams,
4106Subbu Allamaraju,
4107Sylvain Hellegouarch,
4108Tapan Divekar,
4109Ted Hardie,
4110Thomas Broyer,
4111Thomas Nordin,
4112Thomas Roessler,
4113Tim Bray,
4114Tim Morgan,
4115Tim Olsen,
4116Tom Zhou,
4117Travis Snoozy,
4118Tyler Close,
4119Vincent Murphy,
4120Wenbo Zhu,
4121Werner Baumann,
4122Wilbur Streett,
4123Wilfredo Sanchez Vega,
4124William A. Rowe Jr.,
4125William Chan,
4126Willy Tarreau,
4127Xiaoshu Wang,
4128Yaron Goland,
4129Yngve Nysaeter Pettersen,
4130Yoav Nir,
4131Yogesh Bang,
4132Yutaka Oiwa,
4133Zed A. Shaw, and
4134Zhong Yu.
4136<?ENDINC acks ?>
4142<references title="Normative References">
4144<reference anchor="ISO-8859-1">
4145  <front>
4146    <title>
4147     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4148    </title>
4149    <author>
4150      <organization>International Organization for Standardization</organization>
4151    </author>
4152    <date year="1998"/>
4153  </front>
4154  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4157<reference anchor="Part2">
4158  <front>
4159    <title>HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation</title>
4160    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4161      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4162      <address><email></email></address>
4163    </author>
4164    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4165      <organization abbrev="W3C">World Wide Web Consortium</organization>
4166      <address><email></email></address>
4167    </author>
4168    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4169      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4170      <address><email></email></address>
4171    </author>
4172    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4173  </front>
4174  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4175  <x:source href="p2-semantics.xml" basename="p2-semantics">
4176    <x:defines>1xx (Informational)</x:defines>
4177    <x:defines>1xx</x:defines>
4178    <x:defines>100 (Continue)</x:defines>
4179    <x:defines>101 (Switching Protocols)</x:defines>
4180    <x:defines>2xx (Successful)</x:defines>
4181    <x:defines>2xx</x:defines>
4182    <x:defines>200 (OK)</x:defines>
4183    <x:defines>204 (No Content)</x:defines>
4184    <x:defines>3xx (Redirection)</x:defines>
4185    <x:defines>3xx</x:defines>
4186    <x:defines>301 (Moved Permanently)</x:defines>
4187    <x:defines>4xx (Client Error)</x:defines>
4188    <x:defines>4xx</x:defines>
4189    <x:defines>400 (Bad Request)</x:defines>
4190    <x:defines>405 (Method Not Allowed)</x:defines>
4191    <x:defines>411 (Length Required)</x:defines>
4192    <x:defines>414 (URI Too Long)</x:defines>
4193    <x:defines>417 (Expectation Failed)</x:defines>
4194    <x:defines>426 (Upgrade Required)</x:defines>
4195    <x:defines>501 (Not Implemented)</x:defines>
4196    <x:defines>502 (Bad Gateway)</x:defines>
4197    <x:defines>505 (HTTP Version Not Supported)</x:defines>
4198    <x:defines>Allow</x:defines>
4199    <x:defines>Content-Encoding</x:defines>
4200    <x:defines>Content-Location</x:defines>
4201    <x:defines>Content-Type</x:defines>
4202    <x:defines>Date</x:defines>
4203    <x:defines>Expect</x:defines>
4204    <x:defines>Location</x:defines>
4205    <x:defines>Server</x:defines>
4206    <x:defines>User-Agent</x:defines>
4207  </x:source>
4210<reference anchor="Part4">
4211  <front>
4212    <title>HTTP/1.1, part 4: Conditional Requests</title>
4213    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
4214      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4215      <address><email></email></address>
4216    </author>
4217    <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
4218      <organization abbrev="W3C">World Wide Web Consortium</organization>
4219      <address><email></email></address>
4220    </author>
4221    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
4222      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4223      <address><email></email></address>
4224    </author>
4225    <date month="&ID-MONTH;" year="&ID-YEAR;" />
4226  </front>
4227  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;" />
4228  <x:source basename="p4-conditional" href="p4-conditional.xml">
4229    <x:defines>304 (Not Modified)</x:defines>
4230    <x:defines>ETag</x:defines>
4231    <x:defines>Last-Modified</x:defines>
4232  </x:source>
4235<reference anchor="Part5">
4236  <front>
4237    <title>HTTP/1.1, part 5: Range Requests and Partial Responses</title>
4238    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4239      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4240      <address><email></email></address>
4241    </author>
4242    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4243      <organization abbrev="W3C">World Wide Web Consortium</organization>
4244      <address><email></email></address>
4245    </author>
4246    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4247      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4248      <address><email></email></address>
4249    </author>
4250    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4251  </front>
4252  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
4253  <x:source href="p5-range.xml" basename="p5-range">
4254    <x:defines>Content-Range</x:defines>
4255  </x:source>
4258<reference anchor="Part6">
4259  <front>
4260    <title>HTTP/1.1, part 6: Caching</title>
4261    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4262      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4263      <address><email></email></address>
4264    </author>
4265    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4266      <organization abbrev="W3C">World Wide Web Consortium</organization>
4267      <address><email></email></address>
4268    </author>
4269    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4270      <organization>Rackspace</organization>
4271      <address><email></email></address>
4272    </author>
4273    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4274      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4275      <address><email></email></address>
4276    </author>
4277    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4278  </front>
4279  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4280  <x:source href="p6-cache.xml" basename="p6-cache">
4281    <x:defines>Expires</x:defines>
4282  </x:source>
4285<reference anchor="Part7">
4286  <front>
4287    <title>HTTP/1.1, part 7: Authentication</title>
4288    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4289      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4290      <address><email></email></address>
4291    </author>
4292    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4293      <organization abbrev="W3C">World Wide Web Consortium</organization>
4294      <address><email></email></address>
4295    </author>
4296    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4297      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4298      <address><email></email></address>
4299    </author>
4300    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4301  </front>
4302  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
4303  <x:source href="p7-auth.xml" basename="p7-auth">
4304    <x:defines>Proxy-Authenticate</x:defines>
4305    <x:defines>Proxy-Authorization</x:defines>
4306  </x:source>
4309<reference anchor="RFC5234">
4310  <front>
4311    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4312    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4313      <organization>Brandenburg InternetWorking</organization>
4314      <address>
4315        <email></email>
4316      </address> 
4317    </author>
4318    <author initials="P." surname="Overell" fullname="Paul Overell">
4319      <organization>THUS plc.</organization>
4320      <address>
4321        <email></email>
4322      </address>
4323    </author>
4324    <date month="January" year="2008"/>
4325  </front>
4326  <seriesInfo name="STD" value="68"/>
4327  <seriesInfo name="RFC" value="5234"/>
4330<reference anchor="RFC2119">
4331  <front>
4332    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4333    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4334      <organization>Harvard University</organization>
4335      <address><email></email></address>
4336    </author>
4337    <date month="March" year="1997"/>
4338  </front>
4339  <seriesInfo name="BCP" value="14"/>
4340  <seriesInfo name="RFC" value="2119"/>
4343<reference anchor="RFC3986">
4344 <front>
4345  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4346  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4347    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4348    <address>
4349       <email></email>
4350       <uri></uri>
4351    </address>
4352  </author>
4353  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4354    <organization abbrev="Day Software">Day Software</organization>
4355    <address>
4356      <email></email>
4357      <uri></uri>
4358    </address>
4359  </author>
4360  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4361    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4362    <address>
4363      <email></email>
4364      <uri></uri>
4365    </address>
4366  </author>
4367  <date month='January' year='2005'></date>
4368 </front>
4369 <seriesInfo name="STD" value="66"/>
4370 <seriesInfo name="RFC" value="3986"/>
4373<reference anchor="USASCII">
4374  <front>
4375    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4376    <author>
4377      <organization>American National Standards Institute</organization>
4378    </author>
4379    <date year="1986"/>
4380  </front>
4381  <seriesInfo name="ANSI" value="X3.4"/>
4384<reference anchor="RFC1950">
4385  <front>
4386    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4387    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4388      <organization>Aladdin Enterprises</organization>
4389      <address><email></email></address>
4390    </author>
4391    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4392    <date month="May" year="1996"/>
4393  </front>
4394  <seriesInfo name="RFC" value="1950"/>
4395  <!--<annotation>
4396    RFC 1950 is an Informational RFC, thus it might be less stable than
4397    this specification. On the other hand, this downward reference was
4398    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4399    therefore it is unlikely to cause problems in practice. See also
4400    <xref target="BCP97"/>.
4401  </annotation>-->
4404<reference anchor="RFC1951">
4405  <front>
4406    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4407    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4408      <organization>Aladdin Enterprises</organization>
4409      <address><email></email></address>
4410    </author>
4411    <date month="May" year="1996"/>
4412  </front>
4413  <seriesInfo name="RFC" value="1951"/>
4414  <!--<annotation>
4415    RFC 1951 is an Informational RFC, thus it might be less stable than
4416    this specification. On the other hand, this downward reference was
4417    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4418    therefore it is unlikely to cause problems in practice. See also
4419    <xref target="BCP97"/>.
4420  </annotation>-->
4423<reference anchor="RFC1952">
4424  <front>
4425    <title>GZIP file format specification version 4.3</title>
4426    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4427      <organization>Aladdin Enterprises</organization>
4428      <address><email></email></address>
4429    </author>
4430    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4431      <address><email></email></address>
4432    </author>
4433    <author initials="M." surname="Adler" fullname="Mark Adler">
4434      <address><email></email></address>
4435    </author>
4436    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4437      <address><email></email></address>
4438    </author>
4439    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4440      <address><email></email></address>
4441    </author>
4442    <date month="May" year="1996"/>
4443  </front>
4444  <seriesInfo name="RFC" value="1952"/>
4445  <!--<annotation>
4446    RFC 1952 is an Informational RFC, thus it might be less stable than
4447    this specification. On the other hand, this downward reference was
4448    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4449    therefore it is unlikely to cause problems in practice. See also
4450    <xref target="BCP97"/>.
4451  </annotation>-->
4456<references title="Informative References">
4458<reference anchor="Nie1997" target="">
4459  <front>
4460    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4461    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4462    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4463    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4464    <author initials="H." surname="Lie" fullname="H. Lie"/>
4465    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4466    <date year="1997" month="September"/>
4467  </front>
4468  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4471<reference anchor="Pad1995" target="">
4472  <front>
4473    <title>Improving HTTP Latency</title>
4474    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4475    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4476    <date year="1995" month="December"/>
4477  </front>
4478  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4481<reference anchor='RFC1919'>
4482  <front>
4483    <title>Classical versus Transparent IP Proxies</title>
4484    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4485      <address><email></email></address>
4486    </author>
4487    <date year='1996' month='March' />
4488  </front>
4489  <seriesInfo name='RFC' value='1919' />
4492<reference anchor="RFC1945">
4493  <front>
4494    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4495    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4496      <organization>MIT, Laboratory for Computer Science</organization>
4497      <address><email></email></address>
4498    </author>
4499    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4500      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4501      <address><email></email></address>
4502    </author>
4503    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4504      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4505      <address><email></email></address>
4506    </author>
4507    <date month="May" year="1996"/>
4508  </front>
4509  <seriesInfo name="RFC" value="1945"/>
4512<reference anchor="RFC2045">
4513  <front>
4514    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4515    <author initials="N." surname="Freed" fullname="Ned Freed">
4516      <organization>Innosoft International, Inc.</organization>
4517      <address><email></email></address>
4518    </author>
4519    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4520      <organization>First Virtual Holdings</organization>
4521      <address><email></email></address>
4522    </author>
4523    <date month="November" year="1996"/>
4524  </front>
4525  <seriesInfo name="RFC" value="2045"/>
4528<reference anchor="RFC2047">
4529  <front>
4530    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4531    <author initials="K." surname="Moore" fullname="Keith Moore">
4532      <organization>University of Tennessee</organization>
4533      <address><email></email></address>
4534    </author>
4535    <date month="November" year="1996"/>
4536  </front>
4537  <seriesInfo name="RFC" value="2047"/>
4540<reference anchor="RFC2068">
4541  <front>
4542    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4543    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4544      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4545      <address><email></email></address>
4546    </author>
4547    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4548      <organization>MIT Laboratory for Computer Science</organization>
4549      <address><email></email></address>
4550    </author>
4551    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4552      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4553      <address><email></email></address>
4554    </author>
4555    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4556      <organization>MIT Laboratory for Computer Science</organization>
4557      <address><email></email></address>
4558    </author>
4559    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4560      <organization>MIT Laboratory for Computer Science</organization>
4561      <address><email></email></address>
4562    </author>
4563    <date month="January" year="1997"/>
4564  </front>
4565  <seriesInfo name="RFC" value="2068"/>
4568<reference anchor="RFC2145">
4569  <front>
4570    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4571    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4572      <organization>Western Research Laboratory</organization>
4573      <address><email></email></address>
4574    </author>
4575    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4576      <organization>Department of Information and Computer Science</organization>
4577      <address><email></email></address>
4578    </author>
4579    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4580      <organization>MIT Laboratory for Computer Science</organization>
4581      <address><email></email></address>
4582    </author>
4583    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4584      <organization>W3 Consortium</organization>
4585      <address><email></email></address>
4586    </author>
4587    <date month="May" year="1997"/>
4588  </front>
4589  <seriesInfo name="RFC" value="2145"/>
4592<reference anchor="RFC2616">
4593  <front>
4594    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4595    <author initials="R." surname="Fielding" fullname="R. Fielding">
4596      <organization>University of California, Irvine</organization>
4597      <address><email></email></address>
4598    </author>
4599    <author initials="J." surname="Gettys" fullname="J. Gettys">
4600      <organization>W3C</organization>
4601      <address><email></email></address>
4602    </author>
4603    <author initials="J." surname="Mogul" fullname="J. Mogul">
4604      <organization>Compaq Computer Corporation</organization>
4605      <address><email></email></address>
4606    </author>
4607    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4608      <organization>MIT Laboratory for Computer Science</organization>
4609      <address><email></email></address>
4610    </author>
4611    <author initials="L." surname="Masinter" fullname="L. Masinter">
4612      <organization>Xerox Corporation</organization>
4613      <address><email></email></address>
4614    </author>
4615    <author initials="P." surname="Leach" fullname="P. Leach">
4616      <organization>Microsoft Corporation</organization>
4617      <address><email></email></address>
4618    </author>
4619    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4620      <organization>W3C</organization>
4621      <address><email></email></address>
4622    </author>
4623    <date month="June" year="1999"/>
4624  </front>
4625  <seriesInfo name="RFC" value="2616"/>
4628<reference anchor='RFC2817'>
4629  <front>
4630    <title>Upgrading to TLS Within HTTP/1.1</title>
4631    <author initials='R.' surname='Khare' fullname='R. Khare'>
4632      <organization>4K Associates / UC Irvine</organization>
4633      <address><email></email></address>
4634    </author>
4635    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4636      <organization>Agranat Systems, Inc.</organization>
4637      <address><email></email></address>
4638    </author>
4639    <date year='2000' month='May' />
4640  </front>
4641  <seriesInfo name='RFC' value='2817' />
4644<reference anchor='RFC2818'>
4645  <front>
4646    <title>HTTP Over TLS</title>
4647    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4648      <organization>RTFM, Inc.</organization>
4649      <address><email></email></address>
4650    </author>
4651    <date year='2000' month='May' />
4652  </front>
4653  <seriesInfo name='RFC' value='2818' />
4656<reference anchor='RFC2965'>
4657  <front>
4658    <title>HTTP State Management Mechanism</title>
4659    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4660      <organization>Bell Laboratories, Lucent Technologies</organization>
4661      <address><email></email></address>
4662    </author>
4663    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4664      <organization>, Inc.</organization>
4665      <address><email></email></address>
4666    </author>
4667    <date year='2000' month='October' />
4668  </front>
4669  <seriesInfo name='RFC' value='2965' />
4672<reference anchor='RFC3040'>
4673  <front>
4674    <title>Internet Web Replication and Caching Taxonomy</title>
4675    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4676      <organization>Equinix, Inc.</organization>
4677    </author>
4678    <author initials='I.' surname='Melve' fullname='I. Melve'>
4679      <organization>UNINETT</organization>
4680    </author>
4681    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4682      <organization>CacheFlow Inc.</organization>
4683    </author>
4684    <date year='2001' month='January' />
4685  </front>
4686  <seriesInfo name='RFC' value='3040' />
4689<reference anchor='RFC3864'>
4690  <front>
4691    <title>Registration Procedures for Message Header Fields</title>
4692    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4693      <organization>Nine by Nine</organization>
4694      <address><email></email></address>
4695    </author>
4696    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4697      <organization>BEA Systems</organization>
4698      <address><email></email></address>
4699    </author>
4700    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4701      <organization>HP Labs</organization>
4702      <address><email></email></address>
4703    </author>
4704    <date year='2004' month='September' />
4705  </front>
4706  <seriesInfo name='BCP' value='90' />
4707  <seriesInfo name='RFC' value='3864' />
4710<reference anchor='RFC4033'>
4711  <front>
4712    <title>DNS Security Introduction and Requirements</title>
4713    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4714    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4715    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4716    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4717    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4718    <date year='2005' month='March' />
4719  </front>
4720  <seriesInfo name='RFC' value='4033' />
4723<reference anchor="RFC4288">
4724  <front>
4725    <title>Media Type Specifications and Registration Procedures</title>
4726    <author initials="N." surname="Freed" fullname="N. Freed">
4727      <organization>Sun Microsystems</organization>
4728      <address>
4729        <email></email>
4730      </address>
4731    </author>
4732    <author initials="J." surname="Klensin" fullname="J. Klensin">
4733      <address>
4734        <email></email>
4735      </address>
4736    </author>
4737    <date year="2005" month="December"/>
4738  </front>
4739  <seriesInfo name="BCP" value="13"/>
4740  <seriesInfo name="RFC" value="4288"/>
4743<reference anchor='RFC4395'>
4744  <front>
4745    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4746    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4747      <organization>AT&amp;T Laboratories</organization>
4748      <address>
4749        <email></email>
4750      </address>
4751    </author>
4752    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4753      <organization>Qualcomm, Inc.</organization>
4754      <address>
4755        <email></email>
4756      </address>
4757    </author>
4758    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4759      <organization>Adobe Systems</organization>
4760      <address>
4761        <email></email>
4762      </address>
4763    </author>
4764    <date year='2006' month='February' />
4765  </front>
4766  <seriesInfo name='BCP' value='115' />
4767  <seriesInfo name='RFC' value='4395' />
4770<reference anchor='RFC4559'>
4771  <front>
4772    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4773    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4774    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4775    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4776    <date year='2006' month='June' />
4777  </front>
4778  <seriesInfo name='RFC' value='4559' />
4781<reference anchor='RFC5226'>
4782  <front>
4783    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4784    <author initials='T.' surname='Narten' fullname='T. Narten'>
4785      <organization>IBM</organization>
4786      <address><email></email></address>
4787    </author>
4788    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4789      <organization>Google</organization>
4790      <address><email></email></address>
4791    </author>
4792    <date year='2008' month='May' />
4793  </front>
4794  <seriesInfo name='BCP' value='26' />
4795  <seriesInfo name='RFC' value='5226' />
4798<reference anchor="RFC5322">
4799  <front>
4800    <title>Internet Message Format</title>
4801    <author initials="P." surname="Resnick" fullname="P. Resnick">
4802      <organization>Qualcomm Incorporated</organization>
4803    </author>
4804    <date year="2008" month="October"/>
4805  </front>
4806  <seriesInfo name="RFC" value="5322"/>
4809<reference anchor="RFC6265">
4810  <front>
4811    <title>HTTP State Management Mechanism</title>
4812    <author initials="A." surname="Barth" fullname="Adam Barth">
4813      <organization abbrev="U.C. Berkeley">
4814        University of California, Berkeley
4815      </organization>
4816      <address><email></email></address>
4817    </author>
4818    <date year="2011" month="April" />
4819  </front>
4820  <seriesInfo name="RFC" value="6265"/>
4823<!--<reference anchor='BCP97'>
4824  <front>
4825    <title>Handling Normative References to Standards-Track Documents</title>
4826    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4827      <address>
4828        <email></email>
4829      </address>
4830    </author>
4831    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4832      <organization>MIT</organization>
4833      <address>
4834        <email></email>
4835      </address>
4836    </author>
4837    <date year='2007' month='June' />
4838  </front>
4839  <seriesInfo name='BCP' value='97' />
4840  <seriesInfo name='RFC' value='4897' />
4843<reference anchor="Kri2001" target="">
4844  <front>
4845    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4846    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4847    <date year="2001" month="November"/>
4848  </front>
4849  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4852<reference anchor="Spe" target="">
4853  <front>
4854    <title>Analysis of HTTP Performance Problems</title>
4855    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4856    <date/>
4857  </front>
4860<reference anchor="Tou1998" target="">
4861  <front>
4862  <title>Analysis of HTTP Performance</title>
4863  <author initials="J." surname="Touch" fullname="Joe Touch">
4864    <organization>USC/Information Sciences Institute</organization>
4865    <address><email></email></address>
4866  </author>
4867  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4868    <organization>USC/Information Sciences Institute</organization>
4869    <address><email></email></address>
4870  </author>
4871  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4872    <organization>USC/Information Sciences Institute</organization>
4873    <address><email></email></address>
4874  </author>
4875  <date year="1998" month="Aug"/>
4876  </front>
4877  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4878  <annotation>(original report dated Aug. 1996)</annotation>
4884<section title="HTTP Version History" anchor="compatibility">
4886   HTTP has been in use by the World-Wide Web global information initiative
4887   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4888   was a simple protocol for hypertext data transfer across the Internet
4889   with only a single request method (GET) and no metadata.
4890   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4891   methods and MIME-like messaging that could include metadata about the data
4892   transferred and modifiers on the request/response semantics. However,
4893   HTTP/1.0 did not sufficiently take into consideration the effects of
4894   hierarchical proxies, caching, the need for persistent connections, or
4895   name-based virtual hosts. The proliferation of incompletely-implemented
4896   applications calling themselves "HTTP/1.0" further necessitated a
4897   protocol version change in order for two communicating applications
4898   to determine each other's true capabilities.
4901   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4902   requirements that enable reliable implementations, adding only
4903   those new features that will either be safely ignored by an HTTP/1.0
4904   recipient or only sent when communicating with a party advertising
4905   conformance with HTTP/1.1.
4908   It is beyond the scope of a protocol specification to mandate
4909   conformance with previous versions. HTTP/1.1 was deliberately
4910   designed, however, to make supporting previous versions easy.
4911   We would expect a general-purpose HTTP/1.1 server to understand
4912   any valid request in the format of HTTP/1.0 and respond appropriately
4913   with an HTTP/1.1 message that only uses features understood (or
4914   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4915   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4918   Since HTTP/0.9 did not support header fields in a request,
4919   there is no mechanism for it to support name-based virtual
4920   hosts (selection of resource by inspection of the <x:ref>Host</x:ref> header
4921   field).  Any server that implements name-based virtual hosts
4922   ought to disable support for HTTP/0.9.  Most requests that
4923   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4924   requests wherein a buggy client failed to properly encode
4925   linear whitespace found in a URI reference and placed in
4926   the request-target.
4929<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4931   This section summarizes major differences between versions HTTP/1.0
4932   and HTTP/1.1.
4935<section title="Multi-homed Web Servers" anchor="">
4937   The requirements that clients and servers support the <x:ref>Host</x:ref>
4938   header field (<xref target=""/>), report an error if it is
4939   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4940   are among the most important changes defined by HTTP/1.1.
4943   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4944   addresses and servers; there was no other established mechanism for
4945   distinguishing the intended server of a request than the IP address
4946   to which that request was directed. The <x:ref>Host</x:ref> header field was
4947   introduced during the development of HTTP/1.1 and, though it was
4948   quickly implemented by most HTTP/1.0 browsers, additional requirements
4949   were placed on all HTTP/1.1 requests in order to ensure complete
4950   adoption.  At the time of this writing, most HTTP-based services
4951   are dependent upon the Host header field for targeting requests.
4955<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4957   In HTTP/1.0, each connection is established by the client prior to the
4958   request and closed by the server after sending the response. However, some
4959   implementations implement the explicitly negotiated ("Keep-Alive") version
4960   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4961   target="RFC2068"/>.
4964   Some clients and servers might wish to be compatible with these previous
4965   approaches to persistent connections, by explicitly negotiating for them
4966   with a "Connection: keep-alive" request header field. However, some
4967   experimental implementations of HTTP/1.0 persistent connections are faulty;
4968   for example, if a HTTP/1.0 proxy server doesn't understand
4969   <x:ref>Connection</x:ref>, it will erroneously forward that header to the
4970   next inbound server, which would result in a hung connection.
4973   One attempted solution was the introduction of a Proxy-Connection header,
4974   targeted specifically at proxies. In practice, this was also unworkable,
4975   because proxies are often deployed in multiple layers, bringing about the
4976   same problem discussed above.
4979   As a result, clients are encouraged not to send the Proxy-Connection header
4980   in any requests.
4983   Clients are also encouraged to consider the use of Connection: keep-alive
4984   in requests carefully; while they can enable persistent connections with
4985   HTTP/1.0 servers, clients using them need will need to monitor the
4986   connection for "hung" requests (which indicate that the client ought stop
4987   sending the header), and this mechanism ought not be used by clients at all
4988   when a proxy is being used.
4992<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
4994   HTTP/1.1 introduces the <x:ref>Transfer-Encoding</x:ref> header field
4995   (<xref target="header.transfer-encoding"/>). Proxies/gateways &MUST; remove
4996   any transfer-coding prior to forwarding a message via a MIME-compliant
4997   protocol.
5003<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
5005  Clarify that the string "HTTP" in the HTTP-version ABFN production is case
5006  sensitive. Restrict the version numbers to be single digits due to the fact
5007  that implementations are known to handle multi-digit version numbers
5008  incorrectly.
5009  (<xref target="http.version"/>)
5012  Update use of abs_path production from RFC 1808 to the path-absolute + query
5013  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5014  request method only.
5015  (<xref target="request-target"/>)
5018  Require that invalid whitespace around field-names be rejected.
5019  (<xref target="header.fields"/>)
5022  Rules about implicit linear whitespace between certain grammar productions
5023  have been removed; now whitespace is only allowed where specifically
5024  defined in the ABNF.
5025  (<xref target="whitespace"/>)
5028  The NUL octet is no longer allowed in comment and quoted-string
5029  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
5030  Non-ASCII content in header fields and reason phrase has been obsoleted and
5031  made opaque (the TEXT rule was removed).
5032  (<xref target="field.components"/>)
5035  Empty list elements in list productions have been deprecated.
5036  (<xref target="abnf.extension"/>)
5039  Require recipients to handle bogus <x:ref>Content-Length</x:ref> header
5040  fields as errors.
5041  (<xref target="message.body"/>)
5044  Remove reference to non-existent identity transfer-coding value tokens.
5045  (Sections <xref format="counter" target="message.body"/> and
5046  <xref format="counter" target="transfer.codings"/>)
5049  Clarification that the chunk length does not include the count of the octets
5050  in the chunk header and trailer. Furthermore disallowed line folding
5051  in chunk extensions, and deprecate their use.
5052  (<xref target="chunked.encoding"/>)
5055  Registration of Transfer Codings now requires IETF Review
5056  (<xref target="transfer.coding.registry"/>)
5059  Remove hard limit of two connections per server.
5060  Remove requirement to retry a sequence of requests as long it was idempotent.
5061  Remove requirements about when servers are allowed to close connections
5062  prematurely.
5063  (<xref target="persistent.practical"/>)
5066  Remove requirement to retry requests under certain cirumstances when the
5067  server prematurely closes the connection.
5068  (<xref target="message.transmission.requirements"/>)
5071  Change ABNF productions for header fields to only define the field value.
5074  Clarify exactly when "close" connection options have to be sent.
5075  (<xref target="header.connection"/>)
5078  Define the semantics of the <x:ref>Upgrade</x:ref> header field in responses
5079  other than 101 (this was incorporated from <xref target="RFC2817"/>).
5080  (<xref target="header.upgrade"/>)
5083  Take over the Upgrade Token Registry, previously defined in
5084  <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
5085  (<xref target="upgrade.token.registry"/>)
5090<?BEGININC p1-messaging.abnf-appendix ?>
5091<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5093<artwork type="abnf" name="p1-messaging.parsed-abnf">
5094<x:ref>BWS</x:ref> = OWS
5096<x:ref>Connection</x:ref> = *( "," OWS ) connection-option *( OWS "," [ OWS
5097 connection-option ] )
5098<x:ref>Content-Length</x:ref> = 1*DIGIT
5100<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5101 ]
5102<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
5103<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
5104<x:ref>Host</x:ref> = uri-host [ ":" port ]
5106<x:ref>OWS</x:ref> = *( SP / HTAB )
5108<x:ref>RWS</x:ref> = 1*( SP / HTAB )
5110<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5111<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5112<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5113 transfer-coding ] )
5115<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5116<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
5118<x:ref>Via</x:ref> = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment
5119 ] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS
5120 comment ] ) ] )
5122<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5123<x:ref>absolute-form</x:ref> = absolute-URI
5124<x:ref>asterisk-form</x:ref> = "*"
5125<x:ref>attribute</x:ref> = token
5126<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5127<x:ref>authority-form</x:ref> = authority
5129<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5130<x:ref>chunk-data</x:ref> = 1*OCTET
5131<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5132<x:ref>chunk-ext-name</x:ref> = token
5133<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5134<x:ref>chunk-size</x:ref> = 1*HEXDIG
5135<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
5136<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5137<x:ref>connection-option</x:ref> = token
5138<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5139 / %x2A-5B ; '*'-'['
5140 / %x5D-7E ; ']'-'~'
5141 / obs-text
5143<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5144<x:ref>field-name</x:ref> = token
5145<x:ref>field-value</x:ref> = *( field-content / obs-fold )
5147<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
5148<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5149<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5151<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
5153<x:ref>message-body</x:ref> = *OCTET
5154<x:ref>method</x:ref> = token
5156<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
5157<x:ref>obs-text</x:ref> = %x80-FF
5158<x:ref>origin-form</x:ref> = path-absolute [ "?" query ]
5160<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5161<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5162<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5163<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5164<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
5165<x:ref>protocol-name</x:ref> = token
5166<x:ref>protocol-version</x:ref> = token
5167<x:ref>pseudonym</x:ref> = token
5169<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5170 / %x5D-7E ; ']'-'~'
5171 / obs-text
5172<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
5173 / %x5D-7E ; ']'-'~'
5174 / obs-text
5175<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5176<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5177<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5178<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5179<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5180<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5182<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5183<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5184<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5185<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5186<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
5187<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
5188 asterisk-form
5190<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5191 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5192<x:ref>start-line</x:ref> = request-line / status-line
5193<x:ref>status-code</x:ref> = 3DIGIT
5194<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
5196<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5197<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5198 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5199<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5200<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5201<x:ref>token</x:ref> = 1*tchar
5202<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5203<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5204 transfer-extension
5205<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5206<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5208<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5210<x:ref>value</x:ref> = word
5212<x:ref>word</x:ref> = token / quoted-string
5215<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5216; Connection defined but not used
5217; Content-Length defined but not used
5218; HTTP-message defined but not used
5219; Host defined but not used
5220; TE defined but not used
5221; Trailer defined but not used
5222; Transfer-Encoding defined but not used
5223; URI-reference defined but not used
5224; Upgrade defined but not used
5225; Via defined but not used
5226; chunked-body defined but not used
5227; http-URI defined but not used
5228; https-URI defined but not used
5229; partial-URI defined but not used
5230; special defined but not used
5232<?ENDINC p1-messaging.abnf-appendix ?>
5234<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5236<section title="Since RFC 2616">
5238  Extracted relevant partitions from <xref target="RFC2616"/>.
5242<section title="Since draft-ietf-httpbis-p1-messaging-00">
5244  Closed issues:
5245  <list style="symbols">
5246    <t>
5247      <eref target=""/>:
5248      "HTTP Version should be case sensitive"
5249      (<eref target=""/>)
5250    </t>
5251    <t>
5252      <eref target=""/>:
5253      "'unsafe' characters"
5254      (<eref target=""/>)
5255    </t>
5256    <t>
5257      <eref target=""/>:
5258      "Chunk Size Definition"
5259      (<eref target=""/>)
5260    </t>
5261    <t>
5262      <eref target=""/>:
5263      "Message Length"
5264      (<eref target=""/>)
5265    </t>
5266    <t>
5267      <eref target=""/>:
5268      "Media Type Registrations"
5269      (<eref target=""/>)
5270    </t>
5271    <t>
5272      <eref target=""/>:
5273      "URI includes query"
5274      (<eref target=""/>)
5275    </t>
5276    <t>
5277      <eref target=""/>:
5278      "No close on 1xx responses"
5279      (<eref target=""/>)
5280    </t>
5281    <t>
5282      <eref target=""/>:
5283      "Remove 'identity' token references"
5284      (<eref target=""/>)
5285    </t>
5286    <t>
5287      <eref target=""/>:
5288      "Import query BNF"
5289    </t>
5290    <t>
5291      <eref target=""/>:
5292      "qdtext BNF"
5293    </t>
5294    <t>
5295      <eref target=""/>:
5296      "Normative and Informative references"
5297    </t>
5298    <t>
5299      <eref target=""/>:
5300      "RFC2606 Compliance"
5301    </t>
5302    <t>
5303      <eref target=""/>:
5304      "RFC977 reference"
5305    </t>
5306    <t>
5307      <eref target=""/>:
5308      "RFC1700 references"
5309    </t>
5310    <t>
5311      <eref target=""/>:
5312      "inconsistency in date format explanation"
5313    </t>
5314    <t>
5315      <eref target=""/>:
5316      "Date reference typo"
5317    </t>
5318    <t>
5319      <eref target=""/>:
5320      "Informative references"
5321    </t>
5322    <t>
5323      <eref target=""/>:
5324      "ISO-8859-1 Reference"
5325    </t>
5326    <t>
5327      <eref target=""/>:
5328      "Normative up-to-date references"
5329    </t>
5330  </list>
5333  Other changes:
5334  <list style="symbols">
5335    <t>
5336      Update media type registrations to use RFC4288 template.
5337    </t>
5338    <t>
5339      Use names of RFC4234 core rules DQUOTE and HTAB,
5340      fix broken ABNF for chunk-data
5341      (work in progress on <eref target=""/>)
5342    </t>
5343  </list>
5347<section title="Since draft-ietf-httpbis-p1-messaging-01">
5349  Closed issues:
5350  <list style="symbols">
5351    <t>
5352      <eref target=""/>:
5353      "Bodies on GET (and other) requests"
5354    </t>
5355    <t>
5356      <eref target=""/>:
5357      "Updating to RFC4288"
5358    </t>
5359    <t>
5360      <eref target=""/>:
5361      "Status Code and Reason Phrase"
5362    </t>
5363    <t>
5364      <eref target=""/>:
5365      "rel_path not used"
5366    </t>
5367  </list>
5370  Ongoing work on ABNF conversion (<eref target=""/>):
5371  <list style="symbols">
5372    <t>
5373      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5374      "trailer-part").
5375    </t>
5376    <t>
5377      Avoid underscore character in rule names ("http_URL" ->
5378      "http-URL", "abs_path" -> "path-absolute").
5379    </t>
5380    <t>
5381      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5382      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5383      have to be updated when switching over to RFC3986.
5384    </t>
5385    <t>
5386      Synchronize core rules with RFC5234.
5387    </t>
5388    <t>
5389      Get rid of prose rules that span multiple lines.
5390    </t>
5391    <t>
5392      Get rid of unused rules LOALPHA and UPALPHA.
5393    </t>
5394    <t>
5395      Move "Product Tokens" section (back) into Part 1, as "token" is used
5396      in the definition of the Upgrade header field.
5397    </t>
5398    <t>
5399      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5400    </t>
5401    <t>
5402      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5403    </t>
5404  </list>
5408<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5410  Closed issues:
5411  <list style="symbols">
5412    <t>
5413      <eref target=""/>:
5414      "HTTP-date vs. rfc1123-date"
5415    </t>
5416    <t>
5417      <eref target=""/>:
5418      "WS in quoted-pair"
5419    </t>
5420  </list>
5423  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5424  <list style="symbols">
5425    <t>
5426      Reference RFC 3984, and update header field registrations for headers defined
5427      in this document.
5428    </t>
5429  </list>
5432  Ongoing work on ABNF conversion (<eref target=""/>):
5433  <list style="symbols">
5434    <t>
5435      Replace string literals when the string really is case-sensitive (HTTP-version).
5436    </t>
5437  </list>
5441<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5443  Closed issues:
5444  <list style="symbols">
5445    <t>
5446      <eref target=""/>:
5447      "Connection closing"
5448    </t>
5449    <t>
5450      <eref target=""/>:
5451      "Move registrations and registry information to IANA Considerations"
5452    </t>
5453    <t>
5454      <eref target=""/>:
5455      "need new URL for PAD1995 reference"
5456    </t>
5457    <t>
5458      <eref target=""/>:
5459      "IANA Considerations: update HTTP URI scheme registration"
5460    </t>
5461    <t>
5462      <eref target=""/>:
5463      "Cite HTTPS URI scheme definition"
5464    </t>
5465    <t>
5466      <eref target=""/>:
5467      "List-type headers vs Set-Cookie"
5468    </t>
5469  </list>
5472  Ongoing work on ABNF conversion (<eref target=""/>):
5473  <list style="symbols">
5474    <t>
5475      Replace string literals when the string really is case-sensitive (HTTP-Date).
5476    </t>
5477    <t>
5478      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5479    </t>
5480  </list>
5484<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5486  Closed issues:
5487  <list style="symbols">
5488    <t>
5489      <eref target=""/>:
5490      "Out-of-date reference for URIs"
5491    </t>
5492    <t>
5493      <eref target=""/>:
5494      "RFC 2822 is updated by RFC 5322"
5495    </t>
5496  </list>
5499  Ongoing work on ABNF conversion (<eref target=""/>):
5500  <list style="symbols">
5501    <t>
5502      Use "/" instead of "|" for alternatives.
5503    </t>
5504    <t>
5505      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5506    </t>
5507    <t>
5508      Only reference RFC 5234's core rules.
5509    </t>
5510    <t>
5511      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5512      whitespace ("OWS") and required whitespace ("RWS").
5513    </t>
5514    <t>
5515      Rewrite ABNFs to spell out whitespace rules, factor out
5516      header field value format definitions.
5517    </t>
5518  </list>
5522<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5524  Closed issues:
5525  <list style="symbols">
5526    <t>
5527      <eref target=""/>:
5528      "Header LWS"
5529    </t>
5530    <t>
5531      <eref target=""/>:
5532      "Sort 1.3 Terminology"
5533    </t>
5534    <t>
5535      <eref target=""/>:
5536      "RFC2047 encoded words"
5537    </t>
5538    <t>
5539      <eref target=""/>:
5540      "Character Encodings in TEXT"
5541    </t>
5542    <t>
5543      <eref target=""/>:
5544      "Line Folding"
5545    </t>
5546    <t>
5547      <eref target=""/>:
5548      "OPTIONS * and proxies"
5549    </t>
5550    <t>
5551      <eref target=""/>:
5552      "reason-phrase BNF"
5553    </t>
5554    <t>
5555      <eref target=""/>:
5556      "Use of TEXT"
5557    </t>
5558    <t>
5559      <eref target=""/>:
5560      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5561    </t>
5562    <t>
5563      <eref target=""/>:
5564      "RFC822 reference left in discussion of date formats"
5565    </t>
5566  </list>
5569  Final work on ABNF conversion (<eref target=""/>):
5570  <list style="symbols">
5571    <t>
5572      Rewrite definition of list rules, deprecate empty list elements.
5573    </t>
5574    <t>
5575      Add appendix containing collected and expanded ABNF.
5576    </t>
5577  </list>
5580  Other changes:
5581  <list style="symbols">
5582    <t>
5583      Rewrite introduction; add mostly new Architecture Section.
5584    </t>
5585    <t>
5586      Move definition of quality values from Part 3 into Part 1;
5587      make TE request header field grammar independent of accept-params (defined in Part 3).
5588    </t>
5589  </list>
5593<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5595  Closed issues:
5596  <list style="symbols">
5597    <t>
5598      <eref target=""/>:
5599      "base for numeric protocol elements"
5600    </t>
5601    <t>
5602      <eref target=""/>:
5603      "comment ABNF"
5604    </t>
5605  </list>
5608  Partly resolved issues:
5609  <list style="symbols">
5610    <t>
5611      <eref target=""/>:
5612      "205 Bodies" (took out language that implied that there might be
5613      methods for which a request body MUST NOT be included)
5614    </t>
5615    <t>
5616      <eref target=""/>:
5617      "editorial improvements around HTTP-date"
5618    </t>
5619  </list>
5623<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5625  Closed issues:
5626  <list style="symbols">
5627    <t>
5628      <eref target=""/>:
5629      "Repeating single-value headers"
5630    </t>
5631    <t>
5632      <eref target=""/>:
5633      "increase connection limit"
5634    </t>
5635    <t>
5636      <eref target=""/>:
5637      "IP addresses in URLs"
5638    </t>
5639    <t>
5640      <eref target=""/>:
5641      "take over HTTP Upgrade Token Registry"
5642    </t>
5643    <t>
5644      <eref target=""/>:
5645      "CR and LF in chunk extension values"
5646    </t>
5647    <t>
5648      <eref target=""/>:
5649      "HTTP/0.9 support"
5650    </t>
5651    <t>
5652      <eref target=""/>:
5653      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5654    </t>
5655    <t>
5656      <eref target=""/>:
5657      "move definitions of gzip/deflate/compress to part 1"
5658    </t>
5659    <t>
5660      <eref target=""/>:
5661      "disallow control characters in quoted-pair"
5662    </t>
5663  </list>
5666  Partly resolved issues:
5667  <list style="symbols">
5668    <t>
5669      <eref target=""/>:
5670      "update IANA requirements wrt Transfer-Coding values" (add the
5671      IANA Considerations subsection)
5672    </t>
5673  </list>
5677<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5679  Closed issues:
5680  <list style="symbols">
5681    <t>
5682      <eref target=""/>:
5683      "header parsing, treatment of leading and trailing OWS"
5684    </t>
5685  </list>
5688  Partly resolved issues:
5689  <list style="symbols">
5690    <t>
5691      <eref target=""/>:
5692      "Placement of 13.5.1 and 13.5.2"
5693    </t>
5694    <t>
5695      <eref target=""/>:
5696      "use of term "word" when talking about header structure"
5697    </t>
5698  </list>
5702<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5704  Closed issues:
5705  <list style="symbols">
5706    <t>
5707      <eref target=""/>:
5708      "Clarification of the term 'deflate'"
5709    </t>
5710    <t>
5711      <eref target=""/>:
5712      "OPTIONS * and proxies"
5713    </t>
5714    <t>
5715      <eref target=""/>:
5716      "MIME-Version not listed in P1, general header fields"
5717    </t>
5718    <t>
5719      <eref target=""/>:
5720      "IANA registry for content/transfer encodings"
5721    </t>
5722    <t>
5723      <eref target=""/>:
5724      "Case-sensitivity of HTTP-date"
5725    </t>
5726    <t>
5727      <eref target=""/>:
5728      "use of term "word" when talking about header structure"
5729    </t>
5730  </list>
5733  Partly resolved issues:
5734  <list style="symbols">
5735    <t>
5736      <eref target=""/>:
5737      "Term for the requested resource's URI"
5738    </t>
5739  </list>
5743<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5745  Closed issues:
5746  <list style="symbols">
5747    <t>
5748      <eref target=""/>:
5749      "Connection Closing"
5750    </t>
5751    <t>
5752      <eref target=""/>:
5753      "Delimiting messages with multipart/byteranges"
5754    </t>
5755    <t>
5756      <eref target=""/>:
5757      "Handling multiple Content-Length headers"
5758    </t>
5759    <t>
5760      <eref target=""/>:
5761      "Clarify entity / representation / variant terminology"
5762    </t>
5763    <t>
5764      <eref target=""/>:
5765      "consider removing the 'changes from 2068' sections"
5766    </t>
5767  </list>
5770  Partly resolved issues:
5771  <list style="symbols">
5772    <t>
5773      <eref target=""/>:
5774      "HTTP(s) URI scheme definitions"
5775    </t>
5776  </list>
5780<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5782  Closed issues:
5783  <list style="symbols">
5784    <t>
5785      <eref target=""/>:
5786      "Trailer requirements"
5787    </t>
5788    <t>
5789      <eref target=""/>:
5790      "Text about clock requirement for caches belongs in p6"
5791    </t>
5792    <t>
5793      <eref target=""/>:
5794      "effective request URI: handling of missing host in HTTP/1.0"
5795    </t>
5796    <t>
5797      <eref target=""/>:
5798      "confusing Date requirements for clients"
5799    </t>
5800  </list>
5803  Partly resolved issues:
5804  <list style="symbols">
5805    <t>
5806      <eref target=""/>:
5807      "Handling multiple Content-Length headers"
5808    </t>
5809  </list>
5813<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5815  Closed issues:
5816  <list style="symbols">
5817    <t>
5818      <eref target=""/>:
5819      "RFC2145 Normative"
5820    </t>
5821    <t>
5822      <eref target=""/>:
5823      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5824    </t>
5825    <t>
5826      <eref target=""/>:
5827      "define 'transparent' proxy"
5828    </t>
5829    <t>
5830      <eref target=""/>:
5831      "Header Classification"
5832    </t>
5833    <t>
5834      <eref target=""/>:
5835      "Is * usable as a request-uri for new methods?"
5836    </t>
5837    <t>
5838      <eref target=""/>:
5839      "Migrate Upgrade details from RFC2817"
5840    </t>
5841    <t>
5842      <eref target=""/>:
5843      "untangle ABNFs for header fields"
5844    </t>
5845    <t>
5846      <eref target=""/>:
5847      "update RFC 2109 reference"
5848    </t>
5849  </list>
5853<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5855  Closed issues:
5856  <list style="symbols">
5857    <t>
5858      <eref target=""/>:
5859      "Allow is not in 13.5.2"
5860    </t>
5861    <t>
5862      <eref target=""/>:
5863      "Handling multiple Content-Length headers"
5864    </t>
5865    <t>
5866      <eref target=""/>:
5867      "untangle ABNFs for header fields"
5868    </t>
5869    <t>
5870      <eref target=""/>:
5871      "Content-Length ABNF broken"
5872    </t>
5873  </list>
5877<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5879  Closed issues:
5880  <list style="symbols">
5881    <t>
5882      <eref target=""/>:
5883      "HTTP-version should be redefined as fixed length pair of DIGIT . DIGIT"
5884    </t>
5885    <t>
5886      <eref target=""/>:
5887      "Recommend minimum sizes for protocol elements"
5888    </t>
5889    <t>
5890      <eref target=""/>:
5891      "Set expectations around buffering"
5892    </t>
5893    <t>
5894      <eref target=""/>:
5895      "Considering messages in isolation"
5896    </t>
5897  </list>
5901<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5903  Closed issues:
5904  <list style="symbols">
5905    <t>
5906      <eref target=""/>:
5907      "DNS Spoofing / DNS Binding advice"
5908    </t>
5909    <t>
5910      <eref target=""/>:
5911      "move RFCs 2145, 2616, 2817 to Historic status"
5912    </t>
5913    <t>
5914      <eref target=""/>:
5915      "\-escaping in quoted strings"
5916    </t>
5917    <t>
5918      <eref target=""/>:
5919      "'Close' should be reserved in the HTTP header field registry"
5920    </t>
5921  </list>
5925<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5927  Closed issues:
5928  <list style="symbols">
5929    <t>
5930      <eref target=""/>:
5931      "Document HTTP's error-handling philosophy"
5932    </t>
5933    <t>
5934      <eref target=""/>:
5935      "Explain header registration"
5936    </t>
5937    <t>
5938      <eref target=""/>:
5939      "Revise Acknowledgements Sections"
5940    </t>
5941    <t>
5942      <eref target=""/>:
5943      "Retrying Requests"
5944    </t>
5945    <t>
5946      <eref target=""/>:
5947      "Closing the connection on server error"
5948    </t>
5949  </list>
5953<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5955  Closed issues:
5956  <list style="symbols">
5957    <t>
5958      <eref target=""/>:
5959      "Proxy-Connection and Keep-Alive"
5960    </t>
5961    <t>
5962      <eref target=""/>:
5963      "Clarify 'User Agent'"
5964    </t>
5965    <t>
5966      <eref target=""/>:
5967      "Define non-final responses"
5968    </t>
5969    <t>
5970      <eref target=""/>:
5971      "intended maturity level vs normative references"
5972    </t>
5973    <t>
5974      <eref target=""/>:
5975      "Intermediary rewriting of queries"
5976    </t>
5977  </list>
5981<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5983  Closed issues:
5984  <list style="symbols">
5985    <t>
5986      <eref target=""/>:
5987      "message-body in CONNECT response"
5988    </t>
5989    <t>
5990      <eref target=""/>:
5991      "Misplaced text on connection handling in p2"
5992    </t>
5993    <t>
5994      <eref target=""/>:
5995      "wording of line folding rule"
5996    </t>
5997    <t>
5998      <eref target=""/>:
5999      "chunk-extensions"
6000    </t>
6001    <t>
6002      <eref target=""/>:
6003      "make IANA policy definitions consistent"
6004    </t>
6005  </list>
6009<section title="Since draft-ietf-httpbis-p1-messaging-19" anchor="changes.since.19">
6011  Closed issues:
6012  <list style="symbols">
6013    <t>
6014      <eref target=""/>:
6015      "make IANA policy definitions consistent"
6016    </t>
6017    <t>
6018      <eref target=""/>:
6019      "clarify connection header field values are case-insensitive"
6020    </t>
6021    <t>
6022      <eref target=""/>:
6023      "ABNF requirements for recipients"
6024    </t>
6025    <t>
6026      <eref target=""/>:
6027      "note introduction of new IANA registries as normative changes"
6028    </t>
6029  </list>
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